JP7388470B2 - Magnetic recording media, magnetic recording/reproducing devices, and magnetic recording media cartridges - Google Patents

Description

The present disclosure relates to a magnetic recording medium, a magnetic recording/reproducing device using the same, and a magnetic recording medium cartridge.

Tape-shaped magnetic recording media are widely used for storing electronic data. For example, Patent Document 1 describes smoothing the surface of a magnetic layer in order to improve the electromagnetic conversion characteristics of a magnetic recording medium. Further, this document describes adding a lubricant to the magnetic layer in order to suppress friction caused by contact between the magnetic recording medium and the head.

Japanese Patent Application Publication No. 2006-65953

Incidentally, such tape-shaped magnetic recording media are required to be able to stably record or reproduce information during recording or reproduction.

Therefore, a magnetic recording medium that can exhibit good running performance during use is desired.

A magnetic recording medium according to an embodiment of the present disclosure is a tape-shaped magnetic recording medium, and includes a base, an underlayer provided on the base, and a magnetic layer provided on the underlayer. . The substrate contains polyester as a main component. The average thickness of the base layer is 0.9 μm or less. The underlayer and magnetic layer contain a lubricant. The magnetic layer has a surface provided with a large number of holes, and the arithmetic mean roughness Ra of the surface is 2.5 nm or less. The entire BET specific surface area of the magnetic recording medium in a dry state with the lubricant removed is 3.5 m ² /g or more. The squareness ratio of the magnetic recording medium in the vertical direction is 65% or more. The average thickness of the magnetic layer is 90 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less.

A magnetic recording and reproducing apparatus as an embodiment of the present disclosure includes a feeding device capable of sequentially feeding out the magnetic recording medium (by rotating a wound body of the magnetic recording medium), and a magnetic recording medium fed out from the feeding device. A winding device capable of winding up a magnetic recording medium and a device capable of writing information to and reading information from a magnetic recording medium while in contact with the magnetic recording medium traveling from a feeding device to a winding device. It is equipped with a magnetic head that can perform

In the magnetic recording medium and magnetic recording/reproducing device as an embodiment of the present disclosure, the underlayer is relatively thin, so not only the material cost is reduced, but also an increase in the amount of winding per cartridge is expected. In addition, since the entire BET specific surface area of the magnetic recording medium is 3.5 m ² /g or more, lubricant can be stably supplied to the surface of the magnetic recording medium even if the underlayer is made thin. .

1 is a cross-sectional view of a magnetic recording medium according to an embodiment of the present disclosure. 2 is a schematic explanatory diagram showing the layout of data bands and servo bands in the magnetic recording medium shown in FIG. 1. FIG. FIG. 2B is a schematic explanatory diagram showing an enlarged view of the data band shown in FIG. 2A. 2 is a cross-sectional view schematically showing the cross-sectional structure of ε iron oxide particles contained in the magnetic layer shown in FIG. 1. FIG. 2 is a schematic diagram of a recording/reproducing apparatus using the magnetic recording medium shown in FIG. 1. FIG. FIG. 7 is a cross-sectional view schematically showing a cross-sectional structure of epsilon iron oxide particles as a modified example. FIG. 7 is a cross-sectional view of a magnetic recording medium as another modification. It is a schematic diagram showing a tensile test machine. It is a schematic diagram explaining the measuring method of a dynamic friction coefficient.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the explanation will be given in the following order.
1. One embodiment 1-1. Configuration of magnetic recording medium 1-2. Manufacturing method of magnetic recording medium 1-3. Configuration of recording/reproducing device 1-4. Effect 2. Variant

<1. One embodiment>
[1-1 Configuration of magnetic recording medium 10]
FIG. 1 shows an example of a cross-sectional configuration of a magnetic recording medium 10 according to an embodiment of the present disclosure. As shown in FIG. 1, the magnetic recording medium 10 has a laminated structure in which a plurality of layers are laminated. Specifically, the magnetic recording medium 10 includes a long tape-shaped base 11, a base layer 12 provided on one main surface 11A of the base 11, and a magnetic layer provided on the base layer 12. 13, and a back layer 14 provided on the other main surface 11B of the base 11. The surface 13S of the magnetic layer 13 becomes the surface on which the magnetic head comes into contact and travels. Note that the base layer 12 and the back layer 14 are provided as necessary, and may be omitted. Note that the average thickness of the magnetic recording medium 10 is preferably 5.6 μm or less, for example. Further, the Young's modulus of the magnetic recording medium 10 is preferably 7.78 GPa or less, for example.

The Young's modulus of the magnetic recording medium 10 is measured using, for example, a tensile tester. For example, as shown in FIG. 7, the tensile tester includes a main body part 81, a movable part 82 that can move up and down in the vertical direction with respect to the main body part 81, a gripping jig 83 attached to the main body part 81, and a movable part 82. A gripping jig 84 attached to the portion 82 is provided. The gripping jig 83 and the gripping jig 84 are jigs for gripping the ends of the measurement sample 10S cut out from the magnetic recording medium 10, respectively. As the tensile tester, for example, "AG-100D" manufactured by Shimadzu Corporation can be used.

When it is desired to measure the Young's modulus in the longitudinal direction of the magnetic recording medium 10 using the tensile tester shown in FIG. 7, first, the magnetic recording medium 10 is cut to a length of 180 mm to prepare a measurement sample 10S. Next, a gripping jig 83 and a gripping jig 84 capable of fixing the measurement sample 10S over the entire width (for example, 1/2 inch) are attached to the main body part 81 and movable part 82 of the tensile tester, respectively, and then Both longitudinal ends of the measurement sample 10S are fixed by the jig 83 and the gripping jig 84, respectively. At this time, the interval between the gripping jig 83 and the gripping jig 84 is set to 100 mm. Thereafter, the distance between the gripping jigs 83 and 84 is widened in the longitudinal direction of the measurement sample 10S at a pulling speed of 0.1 mm/min to apply stress to the measurement sample 10S. Based on the change in stress and the amount of elongation at this time, Young's modulus can be calculated using the following formula.
E={(ΔN/S)/(ΔX/L)}×10 ⁶ [N/m ² ]
however,
ΔN: Change in stress [N]
S: Cross-sectional area of measurement sample 10S [mm ² ]
ΔX: Amount of elongation [mm]
L: Interval between gripping jigs [mm]
The stress range is from 0.5N to 1.0N, and the change in stress (ΔN) and the amount of elongation (ΔX) at this time are used for calculation.

The magnetic recording medium 10 has a long tape shape, and travels along its longitudinal direction during recording and reproducing operations. It is preferable that the magnetic recording medium 10 is used in a recording/reproducing apparatus that includes a ring-type head as a recording head, for example.

(Base 11)
The base 11 is a nonmagnetic support that supports the underlayer 12 and the magnetic layer 13. The base 11 is in the form of a long film. The upper limit of the average thickness of the base body 11 is preferably 4.2 μm or less, more preferably 4.0 μm or less. When the upper limit of the average thickness of the base body 11 is 4.2 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to a general magnetic recording medium. The lower limit of the average thickness of the base body 11 is preferably 3 μm or more, more preferably 3.2 μm or more. When the lower limit of the average thickness of the base body 11 is 3 μm or more, a decrease in strength of the base body 11 can be suppressed.

The average thickness of the base 11 is determined as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to produce a sample. Subsequently, the layers of the sample other than the substrate 11, that is, the underlayer 12, the magnetic layer 13, and the back layer 14, are removed using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a laser hologage (LGH-110C) manufactured by Mitutoyo as a measuring device, the thickness of the base 11, which is a sample, is measured at five or more positions, and the measured values are simply averaged ( (arithmetic mean) to calculate the average thickness of the base body 11. Note that the measurement position is randomly selected from the sample.

The base body 11 contains, for example, polyester as a main component. In addition to polyesters, the base 11 may contain at least one of polyolefins, cellulose derivatives, vinyl resins, and other polymer resins. When the base body 11 contains two or more of the above materials, the two or more materials may be mixed, copolymerized, or laminated.

Examples of the polyesters contained in the base 11 include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), and PEB. (polyethylene-p-oxybenzoate) and polyethylene bisphenoxycarboxylate.

The polyolefins contained in the base body 11 include, for example, at least one of PE (polyethylene) and PP (polypropylene). The cellulose derivative includes, for example, at least one of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate). The vinyl resin includes, for example, at least one of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

Other polymeric resins contained in the base 11 include, for example, PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), and PAI (polyamideimide). ), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, e.g. Zylon (registered trademark)), polyether, PEK (polyetherketone), polyether ester, PES (polyether sulfone), PEI ( (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

(Magnetic layer 13)
The magnetic layer 13 is a recording layer for recording signals. The magnetic layer 13 includes, for example, magnetic powder, a binder, and a lubricant. The magnetic layer 13 may further contain additives such as conductive particles, abrasives, and rust preventives, if necessary.

The magnetic layer 13 has a surface 13S provided with a large number of holes 13A. Lubricant is stored in these many holes 13A. Preferably, the large number of holes 13A extend perpendicularly to the surface of the magnetic layer 13. This is because the ability to supply lubricant to the surface 13S of the magnetic layer 13 can be improved. Note that a portion of the large number of holes 13A may extend in the vertical direction.

The arithmetic mean roughness Ra of the surface 13S of the magnetic layer 13 is 2.5 nm or less, preferably 2.2 nm or less, and more preferably 1.9 nm or less. When the arithmetic mean roughness Ra is 2.5 nm or less, excellent electromagnetic conversion characteristics can be obtained. The lower limit of the arithmetic mean roughness Ra of the surface 13S of the magnetic layer 13 is preferably 0.8 nm or more, more preferably 1.0 nm or more. When the lower limit of the arithmetic mean roughness Ra of the surface 13S of the magnetic layer 13 is 0.8 nm or more, it is possible to suppress a decrease in runnability due to an increase in friction.

The arithmetic mean roughness Ra of the surface 13S is determined as follows. First, the surface of the magnetic layer 13 is observed using an AFM (Atomic Force Microscope) to obtain an AFM image of 40 μm×40 μm. The AFM is Nano Scope IIIa D3100 manufactured by Digital Instruments, the cantilever is made of silicon single crystal, and the tapping frequency is tuned to 200 Hz to 400 Hz for measurement. As the cantilever, for example, "SPM probe NCH normal type PointProbe L (cantilever length) = 125 um" manufactured by Nano World can be used. Next, the AFM image is divided into 512×512 (=262,144) measurement points, and the height Z(i) (i: measurement point number, i=1 to 262,144) is measured at each measurement point. Simply average (arithmetic mean) the height Z(i) of each measured point and calculate the average height (average surface) Zave(=(Z(1)+Z(2)+...+Z(262,144))/ 262,144). Next, the deviation Z"(i) (=|Z(i)-Zave|) from the average center line at each measurement point is calculated, and the arithmetic mean roughness Ra [nm] (=(Z"(1)+Z "(2)+...+Z" (262,144))/262,144) is calculated. At this time, image processing is performed using flatten order 2 and planefit order 3 XY filtering processing as data.

The lower limit of the entire BET specific surface area of the magnetic recording medium 10 in a dry state with the lubricant removed is 3.5 m ² /g or more, preferably 4.0 m ² /g or more, more preferably 4.5 m ^{2 /} g. g or more, and even more preferably 5.0 m ² /g or more. If the lower limit of the BET specific surface area is 3.5 m ² /g or more, even after repeated recording or reproduction (that is, even after repeatedly running the magnetic head in contact with the surface of the magnetic recording medium 10) , it is possible to suppress a decrease in the amount of lubricant supplied between the surface of the magnetic layer 13 and the magnetic head. Therefore, an increase in the coefficient of dynamic friction can be suppressed.

The upper limit of the total BET specific surface area of the magnetic recording medium 10 in a dry state with the lubricant removed is preferably 7.0 m ² /g or less, more preferably 6.0 m ² /g or less, and even more preferably 5.0 m 2 /g or less. .5 m ² /g or less. When the upper limit of the BET specific surface area is 7.0 m ² /g or less, the lubricant can be sufficiently supplied without being depleted even after many runs. Therefore, an increase in the coefficient of dynamic friction can be suppressed.

The magnetic recording medium 10 in a state in which the lubricant has been removed and dried is a magnetic recording medium in which the magnetic recording medium 10 is immersed in hexane at room temperature for 24 hours, then taken out from the hexane and air-dried. Refers to medium 10.

The overall average pore diameter of the magnetic recording medium 10 determined by the BJH method is 6 nm or more and 12 nm or less, preferably 7 nm or more and 10 nm or less, and more preferably 7.5 nm or more and 10 nm or less. When the average pore diameter is 6 nm or more and 12 nm or less, the effect of suppressing the increase in the coefficient of dynamic friction described above can be further improved.

The BET specific surface area and pore distribution (pore volume, pore diameter at maximum pore volume during desorption) are determined as follows. First, the magnetic recording medium 10, which is about 10% larger than the area of 0.1265 m ² , is immersed in hexane (an amount that is sufficient for immersing the tape, for example, 150 mL) for 24 hours, then air-dried, and the area is 0.1265 m ² . (For example, cut off 50 cm from both ends of the dried tape to prepare a tape width x 10 m.) A measurement sample is prepared by cutting it into a size of 10 m. Next, the pore distribution (pore volume and average pore diameter) is determined by the BJH method using a specific surface area/pore distribution measuring device. The measuring device and measurement conditions are shown below. In this way, the average diameter of the pores is determined.
Measurement environment: Room temperature Measuring device: Micromeritics 3FLEX
Measured adsorbate: _N2 gas measurement pressure range (P/P0): 0 to 0.995
Regarding the measured pressure range, the pressure is varied according to the table below. The pressure values in the table below are relative pressures P/P0. In the table below, for example, in step 1, the pressure is changed from a starting pressure of 0.000 to an ultimate pressure of 0.010, changing by 0.001 per 10 seconds. Once the pressure reaches the ultimate pressure, the next step of pressure change is performed. The same applies to steps 2 to 10. However, in each step, if the pressure has not reached equilibrium, the device waits for the pressure to reach equilibrium before moving on to the next step.

It is preferable that the magnetic layer 13 has a plurality of servo bands SB and a plurality of data bands DB in advance, as shown in FIG. 2A, for example. FIG. 2A is a schematic explanatory diagram showing the layout of the data band DB and servo band SB in the magnetic recording medium 10, and shows the layout in a plane perpendicular to the stacking direction in the magnetic recording medium 10 having a stacked structure. As shown in FIG. 2A, the plurality of servo bands SB are provided at equal intervals in the width direction of the magnetic recording medium 10. The width direction of the magnetic recording medium 10 is a direction perpendicular to both the longitudinal direction of the magnetic recording medium 10 and the stacking direction of the magnetic recording medium 10. A data band DB is provided between adjacent servo bands SB in the width direction. A servo signal for tracking control of the magnetic head is written in advance in the servo band SB. User data is recorded in the data band DB.

The upper limit of the ratio R _S (=(S _SB /S)×100) of the total area S _SB of the servo band SB to the area S of the surface 13S of the magnetic layer 13 is preferably 4 from the viewpoint of ensuring a high recording capacity. .0% or less, more preferably 3.0% or less, even more preferably 2.0% or less. On the other hand, the lower limit of the ratio R _S of the total area S SB of the servo band SB to the area S of the surface of the magnetic layer ₁₃ is preferably 0.8% or more from the viewpoint of ensuring 5 or more servo tracks.

The ratio R _S of the total area S _SB of the servo band SB to the area S of the surface of the magnetic layer 13 is, for example, when the magnetic recording medium 10 is prepared using a ferricolloid developer (Sigma Car Q, manufactured by Sigma High Chemical Co., Ltd.). It can be measured by developing the magnetic recording medium 10 using an optical microscope and then observing the developed magnetic recording medium 10 using an optical microscope. The servo band width W _SB and the number of servo bands SB are measured from an image observed with an optical microscope. Next, the ratio R _S is determined from the following formula.
Ratio R _S [%] = (((servo band width W _SB )×(number of servo bands))/(width of magnetic recording medium 10))×100

The number of servo bands SB is preferably 5 or more, more preferably 5+4n (where n is a positive integer) or more. When the number of servo bands SB is 5 or more, it is possible to suppress the influence on servo signals due to dimensional changes in the width direction of the magnetic recording medium 10, and to ensure stable recording and reproducing characteristics with less off-track.

The upper limit value of the servo bandwidth W _SB is preferably 95 μm or less, more preferably 60 μm or less, and even more preferably 30 μm or less, from the viewpoint of ensuring high recording capacity. The lower limit of the servo band width W _SB is preferably 10 μm or more from the viewpoint of manufacturing the recording head. The width of the servo band width _WSB is determined as follows. First, the magnetic recording medium 10 is developed using a ferricolloid developer (Sigma Car Q, manufactured by Sigma High Chemical Co., Ltd.). Next, by observing the developed magnetic recording medium 10 with an optical microscope, the width of the servo band width _WSB can be measured.

The magnetic layer 13 is configured to be able to form a plurality of data tracks Tk in the data band DB, as shown in FIG. 2B. In this case, the upper limit value of the data track width W _Tk is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less, from the viewpoint of ensuring a high recording capacity. The lower limit of the data track width W _Tk is preferably 0.02 μm or more from the viewpoint of magnetic particle size.

From the viewpoint of ensuring high recording capacity, the magnetic layer 13 is capable of recording data such that the minimum value of the distance L between magnetization reversals is preferably 48 nm or less, more preferably 44 nm or less, and even more preferably 40 nm or less. It is configured. The lower limit of the minimum value of the distance L between magnetization reversals is considered from the viewpoint of the magnetic particle size.

The upper limit of the average thickness of the magnetic layer 13 is preferably 90 nm or less, particularly preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. If the upper limit of the average thickness of the magnetic layer 13 is 90 nm or less, self-demagnetization loss, thickness loss, etc. can be reduced when a ring-type head is used as the recording head, so that the electromagnetic conversion characteristics can be improved. can.

The lower limit of the average thickness of the magnetic layer 13 is preferably 35 nm or more. When the upper limit of the average thickness of the magnetic layer 13 is 35 nm or more, when an MR type head is used as a reproducing head, output can be ensured and electromagnetic conversion characteristics can be improved.

The average thickness of the magnetic layer 13 is determined as follows. First, a carbon film is formed on the surface 13S of the magnetic layer 13 and the surface 14S of the back layer 14 of the magnetic recording medium 10 by a vapor deposition method, and then a tungsten thin film is formed on the carbon film covering the surface 13S of the magnetic layer 13 by a vapor deposition method. Form further. These carbon films and tungsten films protect the sample during the thinning process described later.

Next, the magnetic recording medium 10 is processed into a thin section by the FIB (Focused Ion Beam) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as a protective film as a pretreatment for observing a TEM image of a cross section, which will be described later. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. That is, by thinning, a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10 is formed. The cross section of the obtained thinned sample is observed using a transmission electron microscope (TEM) under the following conditions to obtain a TEM image. Note that the magnification and acceleration voltage may be adjusted as appropriate depending on the type of device.
Equipment: TEM (H9000NAR manufactured by Hitachi)
Acceleration voltage: 300kV
Magnification: 100,000x

Next, the thickness of the magnetic layer 13 is measured at at least ten positions in the longitudinal direction of the magnetic recording medium 10 using the obtained TEM image. The average value obtained by simply averaging (arithmetic average) the obtained measured values is defined as the average thickness of the magnetic layer 13. Note that the measurement position shall be selected at random from the test piece.

(Magnetic powder)
The magnetic powder includes, for example, powder of nanoparticles containing ε iron oxide (hereinafter referred to as "ε iron oxide particles"). Epsilon iron oxide particles can obtain high coercive force even in fine particles. The epsilon iron oxide contained in the epsilon iron oxide particles is preferably crystallized preferentially in the thickness direction (perpendicular direction) of the magnetic recording medium 10.

FIG. 3 is a cross-sectional view schematically showing an example of the cross-sectional structure of the ε iron oxide particles 20 included in the magnetic layer 13. As shown in FIG. 3, the ε iron oxide particles 20 have a spherical shape or a substantially spherical shape, or a cubic shape or a substantially cubic shape. Since the ε iron oxide particles 20 have the above-described shape, when the ε iron oxide particles 20 are used as the magnetic particles, the magnetic The contact area between particles in the thickness direction of the recording medium 10 can be reduced, and aggregation of particles can be suppressed. Therefore, it is possible to improve the dispersibility of the magnetic powder and obtain a better SNR (Signal-to-Noise Ratio).

The ε iron oxide particles 20 may have, for example, a core-shell structure. Specifically, the ε iron oxide particles 20 include a core portion 21 and a two-layer shell portion 22 provided around the core portion 21, as shown in FIG. The two-layer shell portion 22 includes a first shell portion 22a provided on the core portion 21 and a second shell portion 22b provided on the first shell portion 22a.

The core portion 21 of the ε iron oxide particles 20 contains ε iron oxide. The ε-iron oxide contained in the core portion 21 preferably has ε-Fe ₂ O ₃ crystal as its main phase, and more preferably consists of single-phase ε-Fe ₂ O ₃ .

The first shell portion 22a covers at least a portion of the periphery of the core portion 21. Specifically, the first shell portion 22a may partially cover the periphery of the core portion 21, or may cover the entire periphery of the core portion 21. From the viewpoint of ensuring sufficient exchange coupling between the core part 21 and the first shell part 22a and improving magnetic properties, it is preferable that the entire surface of the core part 21 be covered.

The first shell portion 22a is a so-called soft magnetic layer, and includes a soft magnetic material such as α-Fe, Ni-Fe alloy, or Fe-Si-Al alloy. α-Fe may be obtained by reducing ε iron oxide contained in the core portion 21.

The second shell portion 22b is an oxide film serving as an oxidation prevention layer. The second shell portion 22b contains alpha iron oxide, aluminum oxide, or silicon oxide. The α iron oxide contains, for example, at least one kind of iron oxide among Fe ₃ O ₄ , Fe ₂ O ₃ and FeO. When the first shell portion 22a includes α-Fe (soft magnetic material), α-iron oxide may be obtained by oxidizing α-Fe contained in the first shell portion 22a.

Since the ε iron oxide particles 20 have the first shell portion 22a as described above, the ε iron oxide particles (core shell The coercive force Hc of the particle) 20 as a whole can be adjusted to a coercive force Hc suitable for recording. Further, since the ε iron oxide particles 20 have the second shell portion 22b as described above, the ε iron oxide particles 20 are exposed to air during the manufacturing process of the magnetic recording medium 10 and before that process, and the particle surface It is possible to suppress the deterioration of the properties of the ε iron oxide particles 20 due to the occurrence of rust or the like. Therefore, by covering the first shell portion 22a with the second shell portion 22b, deterioration of the characteristics of the magnetic recording medium 10 can be suppressed.

The average particle size (average maximum particle size) of the magnetic powder is preferably 25 nm or less, more preferably 8 nm or more and 22 nm or less, and even more preferably 12 nm or more and 22 nm or less. In the magnetic recording medium 10, an area whose size is 1/2 of the recording wavelength becomes an actual magnetized area. Therefore, by setting the average particle size of the magnetic powder to less than half the shortest recording wavelength, a good S/N ratio can be obtained. Therefore, when the average particle size of the magnetic powder is 22 nm or less, good electromagnetic properties can be achieved in a high recording density magnetic recording medium 10 (for example, a magnetic recording medium 10 configured to be able to record signals at the shortest recording wavelength of 50 nm or less). Conversion characteristics (eg SNR) can be obtained. On the other hand, when the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

The average aspect ratio of the magnetic powder is preferably 1 or more and 3.0 or less, more preferably 1 or more and 2.8 or less, and even more preferably 1 or more and 1.8 or less. When the average aspect ratio of the magnetic powder is within the range of 1 or more and 3.0 or less, agglomeration of the magnetic powder can be suppressed, and when the magnetic powder is vertically aligned in the process of forming the magnetic layer 13, the magnetic powder It is possible to suppress the resistance added to the Therefore, the vertical orientation of the magnetic powder can be improved.

The average particle size and average aspect ratio of the above magnetic powder are determined as follows. First, the magnetic recording medium 10 to be measured is processed into a thin section by the FIB (Focused Ion Beam) method or the like. The thinning is performed along the length direction (longitudinal direction) of the magnetic tape. That is, by this thinning, a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10 is formed. The obtained thin sample was examined using a transmission electron microscope (Hitachi High Technologies H-9500) at an accelerating voltage of 200 kV and a total magnification of 500,000 times, so that the entire magnetic layer 13 was included in the thickness direction of the magnetic layer 13. Observe the cross section and take a TEM photograph. Next, 50 particles are randomly selected from the taken TEM photograph, and the long axis length DL and short axis length DS of each particle are measured. Here, the long axis length DL means the maximum distance between two parallel lines drawn from any angle so as to be in contact with the contour of each particle (so-called maximum Feret diameter). On the other hand, the short axis length DS means the maximum length of the particle in the direction perpendicular to the long axis length DL of the particle.

Subsequently, the average long axis length DLave is determined by simply averaging (arithmetic mean) the long axis lengths DL of the 50 measured particles. The average major axis length DLave thus determined is defined as the average particle size of the magnetic powder. Further, the average short axis length DSave is obtained by simply averaging (arithmetic mean) the short axis lengths DS of the 50 measured particles. Then, the average aspect ratio (DLave/DSave) of the particles is determined from the average major axis length DLave and the average minor axis length DSave.

The average particle volume of the magnetic powder is preferably 5500 nm ³ or less, more preferably 270 nm ³ or more and 5500 nm ³ or less, even more preferably 900 nm ³ or more and 5500 nm ³ or less. When the average particle volume of the magnetic powder is 5500 nm ³ or less, the same effect as when the average particle size of the magnetic powder is 22 nm or less can be obtained. On the other hand, when the average particle volume of the magnetic powder is 270 nm ³ or more, the same effect as when the average particle size of the magnetic powder is 8 nm or more can be obtained.

When the ε iron oxide particles 20 have a spherical or nearly spherical shape, the average particle volume of the magnetic powder is determined as follows. First, the average major axis length DLave is determined in the same manner as the method for calculating the average particle size of the magnetic powder described above. Next, the average volume V of the magnetic powder is determined using the following formula.
V=(π/6)×(DLave) ³

(binder)
As the binder, a resin having a structure obtained by imparting a crosslinking reaction to a polyurethane resin, a vinyl chloride resin, or the like is preferable. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium 10. The resin to be blended is not particularly limited as long as it is a resin commonly used in the coating type magnetic recording medium 10.

For example, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-chlorinated Vinyl-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-chloride Vinyl copolymers, methacrylic acid ester-ethylene copolymers, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymers, acrylonitrile-butadiene copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose dichloromethane) acetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyester resin, amino resin, synthetic rubber, and the like.

Further, examples of thermosetting resins or reactive resins include phenol resins, epoxy resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, urea formaldehyde resins, and the like.

In addition, polar functional groups such as -SO ₃ M, -OSO ₃ M, -COOM, and P=O(OM) ₂ are introduced into each of the above-mentioned binders for the purpose of improving the dispersibility of the magnetic powder. You can leave it there. Here, M in the above chemical formula is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

Further, examples of the polar functional group include side chain types having terminal groups of -NR1R2 and -NR1R2R3 ⁺ X ^- , and main chain types having >NR1R2 ⁺ X ^- . Here, R1, R2, and R3 in the above formula are hydrogen atoms or hydrocarbon groups, and ^X- is a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. Further, examples of the polar functional group include -OH, -SH, -CN, and epoxy group.

(lubricant)
The lubricant contained in the magnetic layer 13 contains, for example, fatty acids and fatty acid esters. The fatty acid contained in the lubricant preferably contains at least one of a compound represented by the following general formula <1> and a compound represented by the general formula <2>, for example. Further, the fatty acid ester contained in the lubricant preferably contains at least one of a compound represented by the following general formula <3> and a compound represented by the general formula <4>. The lubricant contains two types of compounds, the compound represented by the general formula <1> and the compound represented by the general formula <3>, so that the compound represented by the general formula <2> and the compound represented by the general formula <3> are obtained. By including two types of the compound represented by the general formula <1> and the compound represented by the general formula <4>, the compound represented by the general formula <2> and the compound represented by the general formula <4> By including two types of compounds represented by general formula <1>, by including three types of compounds represented by general formula <2>, and by including three types of compounds represented by general formula <3>, the general By including three types of compounds represented by formula <1>, the compound represented by general formula <2>, and the compound represented by general formula <4>, the compound represented by general formula <1>, the compound represented by general formula <3>> and the compound represented by general formula <4>, the compound represented by general formula <2>, the compound represented by general formula <3>, and the compound represented by general formula <4> are included. or a compound represented by general formula <1>, a compound represented by general formula <2>, a compound represented by general formula <3>, and a compound represented by general formula <4>. By including the four types of compounds, it is possible to suppress an increase in the coefficient of dynamic friction due to repeated recording or reproduction in the magnetic recording medium 10. As a result, the running performance of the magnetic recording medium 10 can be further improved.
CH ₃ (CH ₂ ) _n COOH…<1>
(However, in the general formula <1>, n is an integer selected from the range of 14 to 22.)
CH ₃ (CH ₂ ) _p COO(CH ₂ ) _q CH ₃ …<2>
(However, in the general formula <2>, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 2 to 5.)
CH ₃ (CH ₂ ) _n CH=CH (CH ₂ ) _m COOH…<3>
(However, in the general formula <3>, n+m is an integer selected from the range of 12 to 20.)
CH ₃ (CH ₂ ) _p COO-(CH ₂ ) _q CH(CH ₃ ) ₂ …<4>
(However, in the general formula <4>, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 1 to 3.)

(Additive)
The magnetic layer 13 contains aluminum oxide (α, β or γ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide ( It may further contain rutile type or anatase type titanium oxide).

(base layer 12)
Underlayer 12 is a nonmagnetic layer containing nonmagnetic powder and a binder. The base layer 12 may further contain at least one additive selected from a lubricant, conductive particles, a hardening agent, a rust preventive, and the like, if necessary. Further, the base layer 12 may have a multilayer structure in which a plurality of layers are stacked. The average thickness of the base layer 12 is preferably 0.5 μm or more and 0.9 μm or less, more preferably 0.6 μm or more and 0.7 μm or less. By reducing the average thickness of the underlayer 12 to 0.9 μm or less, the Young's modulus of the entire magnetic recording medium 10 is more effectively reduced than when the base 11 is made thinner. Therefore, the tension on the magnetic recording medium 10 can be easily controlled. Further, by setting the average thickness of the base layer 12 to 0.5 μm or more, the adhesive force between the base body 11 and the base layer 12 is ensured. Moreover, variations in the thickness of the underlayer 12 can be suppressed, and the roughness of the surface 13S of the magnetic layer 13 can be prevented from increasing.

Note that the average thickness of the base layer 12 is determined, for example, as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to produce a sample. Subsequently, with respect to the sample magnetic recording medium 10, the underlayer 12 and the magnetic layer 13 are peeled off from the base 11. Next, using a laser hologage (LGH-110C) manufactured by Mitutoyo as a measuring device, the thickness of the laminate of the base layer 12 and magnetic layer 13 peeled off from the base 11 is measured at five or more positions. do. Thereafter, the measured values are simply averaged (arithmetic averaged) to calculate the average thickness of the laminate of the underlayer 12 and the magnetic layer 13. Note that the measurement position is randomly selected from the sample. Finally, the average thickness of the underlayer 12 is determined by subtracting the average thickness of the magnetic layer 13 measured using the TEM as described above from the average thickness of the laminate.

The base layer 12 may have pores, that is, the base layer 12 may be provided with a large number of pores. The pores in the underlayer 12 may be formed, for example, by forming pores (pores 13A) in the magnetic layer 13, and in particular, the pores in the underlayer 12 may be formed by forming pores (pores 13A) in the magnetic layer 13. It can be formed by pressing the protrusion of the magnetic layer against the surface of the magnetic layer. That is, by forming a recess corresponding to the shape of the protrusion on the surface 13S of the magnetic layer 13, pores can be formed in the magnetic layer 13 and the underlayer 12, respectively. Further, pores may be formed as the solvent evaporates during the drying process of the coating material for forming the magnetic layer. In addition, when the magnetic layer forming paint is applied to the surface of the underlayer 12 to form the magnetic layer 13, the solvent in the magnetic layer forming paint may cause the underlayer 12 formed when the lower layer is applied and dried. It can penetrate into the underlying layer 12 through the pores. Thereafter, when the solvent that has permeated into the underlayer 12 evaporates in the drying process of the magnetic layer 13, the solvent that has permeated into the underlayer 12 moves from the underlayer 12 to the surface 13S of the magnetic layer 13, causing fine particles. Holes may also be formed. The pores formed in this manner may, for example, communicate the magnetic layer 13 and the underlayer 12. The average diameter of the pores can be adjusted by changing the solid content or type of solvent of the magnetic layer-forming paint and/or the drying conditions of the magnetic layer-forming paint. By forming pores in both the magnetic layer 13 and the underlayer 12, a particularly suitable amount of lubricant appears on the magnetic layer side surface for good running stability, and reduces dynamic friction caused by repeated recording or reproduction. It is possible to further suppress an increase in the coefficient.

From the viewpoint of suppressing a decrease in the coefficient of dynamic friction after repeated recording or reproduction, it is preferable that the holes in the underlayer 12 and the holes 13A in the magnetic layer 13 are connected. Here, the connection between the holes in the underlayer 12 and the holes 13A in the magnetic layer 13 means that some of the many holes in the underlayer 12 and many holes in the magnetic layer 13 are connected to each other. This includes a state in which some of 13A are connected.

From the viewpoint of improving the supply of lubricant to the surface 13S of the magnetic layer 13, it is preferable that the large number of holes include holes extending perpendicularly to the surface 13S of the magnetic layer 13. . In addition, from the viewpoint of improving the supply of lubricant to the surface 13S of the magnetic layer 13, the holes in the underlayer 12 extending perpendicularly to the surface 13S of the magnetic layer 13 and the surface of the magnetic layer 13 It is preferable that the hole 13A of the magnetic layer 13 extending perpendicularly to the hole 13S is connected to the hole 13S.

(Non-magnetic powder of base layer 12)
The non-magnetic powder includes, for example, at least one of inorganic particle powder and organic particle powder. Further, the non-magnetic powder may include carbon powder such as carbon black. Note that one type of non-magnetic powder may be used alone, or two or more types of non-magnetic powder may be used in combination. Inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Examples of the shape of the non-magnetic powder include various shapes such as acicular, spherical, cubic, and plate-like, but are not limited thereto.

(Binder for base layer 12)
The binder in the underlayer 12 is the same as that in the magnetic layer 13 described above.

(Back layer 14)
The back layer 14 contains, for example, a binder and nonmagnetic powder. The back layer 14 may further contain at least one additive selected from a lubricant, a curing agent, an antistatic agent, and the like, if necessary. The binder and nonmagnetic powder in the back layer 14 are the same as the binder and nonmagnetic powder in the base layer 12 described above.

The average particle size of the nonmagnetic powder in the back layer 14 is preferably 10 nm or more and 150 nm or less, more preferably 15 nm or more and 110 nm or less. The average particle size of the non-magnetic powder in the back layer 14 is determined in the same manner as the average particle size of the magnetic powder in the magnetic layer 13 described above. The non-magnetic powder may include one having two or more particle size distributions.

The upper limit of the average thickness of the back layer 14 is preferably 0.6 μm or less, particularly preferably 0.5 μm or less. If the upper limit of the average thickness of the back layer 14 is 0.6 μm or less, even if the average thickness of the magnetic recording medium 10 is 5.6 μm or less, the thickness of the underlayer 12 and the base 11 can be kept thick. , it is possible to maintain running stability of the magnetic recording medium 10 within the recording/reproducing apparatus. The lower limit of the average thickness of the back layer 14 is not particularly limited, but is, for example, 0.2 μm or more, particularly preferably 0.3 μm or more.

The average thickness of the back layer 14 is determined as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to produce a sample. Next, using a laser hologage (LGH-110C) manufactured by Mitutoyo as a measuring device, the thickness of the sample magnetic recording medium 10 is measured at five or more points, and the measured values are simply averaged ( (arithmetic mean) to calculate the average thickness t _T [μm] of the magnetic recording medium 10. Note that the measurement position is randomly selected from the sample. Subsequently, the back layer 14 is removed from the sample magnetic recording medium 10 using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. After that, the thickness of the sample from which the back layer 14 has been removed from the magnetic recording medium 10 is measured again using the above laser hologage at five or more points, and the measured values are simply averaged (arithmetically averaged). The average thickness t _B [μm] of the magnetic recording medium 10 from which . Note that the measurement position is randomly selected from the sample. Finally, the average thickness t _b [μm] of the back layer 14 is determined from the following formula.
t _b [μm] = t _T [μm] - t _B [μm]

As shown in FIG. 1, the back layer 14 has a surface provided with a large number of protrusions 14A. The large number of protrusions 14A are for forming a large number of holes 13A on the surface 13S of the magnetic layer 13 when the magnetic recording medium 10 is rolled up. The large number of holes 13A are formed by, for example, a large number of nonmagnetic particles protruding from the surface of the back layer 14.

(Average thickness of magnetic recording medium 10)
The upper limit of the average thickness (average total thickness) of the magnetic recording medium 10 is preferably 5.6 μm or less, more preferably 5.2 μm or less, particularly preferably 4.8 μm or less, and even more preferably 4.4 μm or less. . When the average thickness of the magnetic recording medium 10 is 5.6 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to a general magnetic recording medium. The lower limit of the average thickness of the magnetic recording medium 10 is not particularly limited, but is, for example, 3.5 μm or more.

The average thickness tT of the magnetic recording medium 10 is determined as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to produce a sample. Next, the thickness of the sample is measured at five or more positions using a Mitutoyo Laser Hologage (LGH-110C) as a measuring device, and the measured values are simply averaged (arithmetic mean). Calculate the value tT [μm]. Note that the measurement position is randomly selected from the sample.

(Coercive force Hc)
The upper limit of the coercive force Hc in the longitudinal direction of the magnetic recording medium 10 is preferably 2000 Oe or less, more preferably 1900 Oe or less, even more preferably 1800 Oe or less. When the coercive force Hc2 in the longitudinal direction is 2000 Oe or less, the magnetization responds sensitively to the perpendicular magnetic field from the recording head, so that a good recording pattern can be formed.

The lower limit of the coercive force Hc measured in the longitudinal direction of the magnetic recording medium 10 is preferably 1000 Oe or more. When the lower limit of the coercive force Hc in the longitudinal direction is 1000 Oe or more, demagnetization due to magnetic flux leakage from the recording head can be suppressed.

The above coercive force Hc is determined as follows. A measurement sample is prepared by stacking three magnetic recording media 10 and adhering them with double-sided tape, and then punching them out with a punch of φ6.39 mm. At this time, marking is performed using any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium can be recognized. Then, using a vibrating sample magnetometer (VSM), an MH loop of a measurement sample (the entire magnetic recording medium 10) corresponding to the longitudinal direction of the magnetic recording medium 10 (travel direction of the magnetic recording medium 10) is performed. Measure. Next, the coating film (base layer 12, magnetic layer 13, back layer 14, etc.) is wiped off using acetone, ethanol, or the like, leaving only the base 11. Then, three of the obtained substrates 11 are stacked and adhered with double-sided tape, and then punched with a punch of φ6.39 mm to obtain a background correction sample (hereinafter simply referred to as a correction sample). Thereafter, the MH loop of the correction sample (substrate 11) corresponding to the longitudinal direction of the substrate 11 (the running direction of the magnetic recording medium 10) is measured using the VSM.

In the measurement of the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (substrate 11), for example, a sensitive vibrating sample magnetometer manufactured by Toei Kogyo ``VSM-P7- 15 type" is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, and average number of MHs: 20.

After obtaining the two MH loops, background correction is performed by subtracting the MH loop of the correction sample (substrate 11) from the MH loop of the measurement sample (the entire magnetic recording medium 10). , the MH loop after background correction is obtained. The measurement and analysis program attached to the "VSMP7-15" is used to calculate this background correction.

The coercive force Hc is determined from the obtained MH loop after background correction. Note that this calculation uses the measurement and analysis program attached to the "VSM-P7-15 type". Note that all of the above MH loop measurements are performed at 25°C. Further, it is assumed that "demagnetizing field correction" is not performed when measuring the MH loop in the longitudinal direction of the magnetic recording medium 10.

(Square ratio)
The squareness ratio S1 in the vertical direction (thickness direction) of the magnetic recording medium 10 is, for example, 65% or more, preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, particularly preferably 85%. That's all. When the squareness ratio S1 is 65% or more, the vertical orientation of the magnetic powder becomes sufficiently high, so that a more excellent SNR can be obtained.

The squareness ratio S1 is determined as follows. A measurement sample is prepared by stacking three magnetic recording media 10 and adhering them with double-sided tape, and then punching them out with a punch of φ6.39 mm. At this time, marking is performed using any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium can be recognized. Then, using a vibrating sample magnetometer (VSM), an MH loop of a measurement sample (the entire magnetic recording medium 10) corresponding to the longitudinal direction of the magnetic recording medium 10 (travel direction of the magnetic recording medium 10) is performed. Measure. Next, the coating film (base layer 12, magnetic layer 13, back layer 14, etc.) is wiped off using acetone, ethanol, or the like, leaving only the base 11. Then, three of the obtained substrates 11 are stacked and adhered with double-sided tape, and then punched with a punch of φ6.39 mm to obtain a background correction sample (hereinafter simply referred to as a correction sample). Thereafter, the MH loop of the correction sample (substrate 11) corresponding to the longitudinal direction of the substrate 11 (the running direction of the magnetic recording medium 10) is measured using the VSM.

In the measurement of the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (substrate 11), for example, a sensitive vibrating sample magnetometer manufactured by Toei Kogyo ``VSM-P7- 15 type" is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, and average number of MHs: 20.

After obtaining the two MH loops, background correction is performed by subtracting the MH loop of the correction sample (substrate 11) from the MH loop of the measurement sample (the entire magnetic recording medium 10). , the MH loop after background correction is obtained. The measurement and analysis program attached to the "VSMP7-15" is used to calculate this background correction.

The obtained saturation magnetization Ms (emu) and residual magnetization Mr (emu) of the MH loop after background correction are substituted into the following formula to calculate the squareness ratio S1 (%).
Squareness ratio S1 (%) = (Mr/Ms) x 100
Note that all of the above MH loop measurements are performed at 25°C. Further, it is assumed that "demagnetizing field correction" is not performed when measuring the MH loop in the direction perpendicular to the magnetic recording medium 10.

The squareness ratio S2 of the magnetic recording medium 10 in the longitudinal direction (running direction) is preferably 35% or less, more preferably 30% or less, even more preferably 25% or less, particularly preferably 20% or less, and most preferably 15%. It is as follows. When the squareness ratio S2 is 35% or less, the vertical orientation of the magnetic powder becomes sufficiently high, so that a more excellent SNR can be obtained.

The squareness ratio S2 is determined in the same manner as the squareness ratio S1, except that the MH loop is measured in the longitudinal direction (running direction) of the magnetic recording medium 10 and the substrate 11.

(activation volume Vact)
The activation volume Vact is preferably 8000 nm ³ or less, more preferably 6000 nm ³ or less, even more preferably 5000 nm ³ or less, particularly preferably 4000 nm ³ or less, most preferably 3000 nm ^{3 or} less. When the activation volume Vact is 8000 nm ³ or less, the magnetic powder is well dispersed, so the bit reversal region can be made steep, and the leakage magnetic field from the recording head can reduce the magnetization recorded in adjacent tracks. Signal deterioration can be suppressed. Therefore, better SNR is obtained.

The above activation volume Vact is determined by the following formula derived by Street & Woolley.
Vact (nm ³ )=kB×T×Χirr/(μ0×Ms×S)
(However, kB: Boltzmann constant (1.38×10 ^-23 J/K), T: temperature (K), Χirr: irreversible magnetic susceptibility, μ0: magnetic permeability of vacuum, S: magnetorheological coefficient, Ms: saturation Magnetization (emu/cm ³ ))

The irreversible magnetic susceptibility Χirr, the saturation magnetization Ms, and the magnetorheological coefficient S substituted into the above equation are obtained as follows using VSM. The measurement sample used for VSM is prepared by punching out three magnetic recording media 10 stacked with double-sided tape with a punch of φ6.39 mm. At this time, marking is performed using any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium 10 can be recognized. Note that the measurement direction by VSM is the thickness direction (vertical direction) of the magnetic recording medium 10. Further, it is assumed that the measurement by VSM is performed at 25° C. on a measurement sample cut out from the elongated magnetic recording medium 10. Further, when measuring the MH loop in the thickness direction (perpendicular direction) of the magnetic recording medium 10, "demagnetizing field correction" is not performed. Furthermore, in the measurement of the M-H loop of the measurement sample (the entire magnetic recording medium 10) and the M-H loop of the correction sample (substrate 11), a high-sensitivity vibrating sample magnetometer "VSM" manufactured by Toei Kogyo Co., Ltd. -P7-15 type” is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, and average number of MHs: 20.

(irreversible magnetic susceptibility Χirr)
The irreversible magnetic susceptibility Χirr is defined as the slope of the residual magnetization curve (DCD curve) near the residual magnetic force Hr. First, a magnetic field of -1193 kA/m (15 kOe) is applied to the entire magnetic recording medium 10, and the magnetic field is returned to zero to create a residual magnetization state. Thereafter, a magnetic field of about 15.9 kA/m (200 Oe) is applied in the opposite direction to return the magnet to zero and measure the amount of residual magnetization. Thereafter, a magnetic field that is 15.9 kA/m larger than the previously applied magnetic field is applied and the measurement is repeated to return to zero, and the amount of residual magnetization is plotted against the applied magnetic field to measure the DCD curve. From the obtained DCD curve, the point at which the amount of magnetization becomes zero is defined as the residual magnetic force Hr, and the DCD curve is further differentiated to determine the slope of the DCD curve in each magnetic field. In the slope of this DCD curve, the slope near the residual magnetic force Hr is Χirr.

(Saturation magnetization Ms)
First, an MH loop after background correction is obtained in the same manner as the method for measuring the coercive force Hc described above. Next, Ms (emu/cm ³ ) is calculated from the value of the obtained saturation magnetization Ms (emu) of the MH loop and the volume (cm ³ ) of the magnetic layer 13 in the measurement sample. Note that the volume of the magnetic layer 13 is determined by multiplying the area of the measurement sample by the average thickness of the magnetic layer 13. The method for calculating the average thickness of the magnetic layer 13 necessary for calculating the volume of the magnetic layer 13 is as described above.

(Magneto-rheological coefficient S)
First, a magnetic field of -1193 kA/m (15 kOe) is applied to the entire magnetic recording medium 10 (measurement sample) to return the magnetic field to zero and create a residual magnetization state. Thereafter, a magnetic field equivalent to the value of the residual magnetic force Hr obtained from the DCD curve is applied in the opposite direction. The amount of magnetization is continuously measured at regular time intervals for 1000 seconds while a magnetic field is applied. The magnetorheological coefficient S is calculated by comparing the thus obtained relationship between the time t and the amount of magnetization M(t) with the following formula.
M(t)=M0+S×ln(t)
(However, M(t): amount of magnetization at time t, M0: amount of initial magnetization, S: magnetorheological coefficient, ln(t): natural logarithm of time)

(Friction coefficient ratio (μ _B /μ _A ))
The magnetic recording medium 10 preferably has a dynamic friction coefficient μ _A between the surface 13S of the magnetic layer 13 of the magnetic recording medium 10 and the magnetic head when a tension of 0.4 N is applied in the longitudinal direction of the magnetic recording medium 10. , the friction coefficient ratio (μ _{B /} μ _A ) is 1.0 or more and 2.0 or less, more preferably 1.0 or more and 1.8 or less, and even more preferably 1.0 or more and 1.6 or less. When the friction coefficient ratio (μ _B /μ _A ) is within the above numerical range, it is possible to reduce changes in the dynamic friction coefficient due to tension fluctuations during running, and thus the running of the magnetic recording medium 10 can be stabilized. .

The dynamic friction coefficient μA and the dynamic friction coefficient μB for calculating the friction coefficient ratio (μB/μA) are obtained as follows. First, as shown in FIG. 8, a 1/2 inch wide magnetic recording medium 10 is placed on two 1 inch diameter cylindrical guide rolls 91 and 92 which are spaced apart from each other and arranged in parallel. Place it so that the surfaces 13S of the two are in contact with each other. The two guide rolls 91 and 92 are fixed in position with respect to each other.

Next, the surface 13S of the magnetic layer 13 of the magnetic recording medium 10 is brought into contact with the head block (for recording and reproduction) 93 mounted on the LTO5 drive, and the included angle θ1 [°] = 5.6°. One end of the magnetic recording medium 10 is gripped by a gripping jig 94 and connected to a movable strain gauge 95. A weight 96 is suspended from the other end of the magnetic recording medium 10, and a tension T0 of 0.4N is applied. Give. Note that the head block 93 is fixed at a position where the embrace angle θ1 [°] is 5.6°. Thereby, the positional relationship between the guide rolls 91, 92 and the head block 93 is also fixed.

Next, by the movable strain gauge 95, the magnetic recording medium 10 is slid 60 mm toward the movable strain gauge 95 with respect to the head block 93 at a speed of 10 mm/s. The output value (voltage) of the movable strain gauge 95 during this sliding is converted into T[N] based on a linear relationship between the output value and the load (described later) that has been obtained in advance. Obtain T[N] 13 times from the start of the 60 mm slide to the stop of the slide, and simply average the 11 T[N] excluding the first and last two times. Thus, T _ave [N] is obtained.
Then, calculate the dynamic friction coefficient _μA using the following formula.

The above linear relationship is obtained as follows. That is, the output value (voltage) of the movable strain gauge 95 is obtained for each case where a load of 0.4 N is applied to the movable strain gauge 95 and when a load of 1.5 N is applied to the movable strain gauge 95. A linear relationship between the output value and the load is obtained from the two obtained output values and the two loads. Using this linear relationship, as described above, the output value (voltage) from the movable strain gauge 95 during sliding is converted into T[N].

The dynamic friction coefficient μ _B is measured in the same manner as the dynamic friction coefficient μ _A , except that the tension T ₀ [N] applied to the other end is 1.2N.
A friction coefficient ratio (μ _B /μ _A ) is calculated from the dynamic friction coefficient μ _A and the dynamic friction coefficient μ _B measured as described above.

If the kinetic friction coefficient between the surface 13S of the magnetic layer 13 and the magnetic head is μC when the tension applied to the magnetic recording medium 10 is 0.6N, then the kinetic friction coefficient μC(5) at the fifth time from the start of the run and the start of the run. The friction coefficient ratio (μC(1000)/μC(5)) to the 1000th dynamic friction coefficient μC(1000) is preferably 1.0 or more and 2.0 or less, more preferably 1.2 or more and 1.8 or less. It is. When the friction coefficient ratio (μC(1000)/μC(5)) is 1.0 or more and 2.0 or less, changes in the dynamic friction coefficient due to multiple runs can be reduced, thereby stabilizing the running of the magnetic recording medium 10. be able to. Here, it is assumed that a drive compatible with the magnetic recording medium 10 is used as the magnetic head.

(Friction coefficient ratio (μ _C(1000) / μ _C(5) ))
The dynamic friction coefficient μC(5) and the dynamic friction coefficient μC(1000) for calculating the friction coefficient ratio (μC(1000)/μC(5)) are obtained as follows.

Preferably, the magnetic recording medium 10 has a dynamic friction coefficient μ _{C( 5)} and the dynamic friction coefficient μ _C(1000) at the 1000th reciprocation when the magnetic head is reciprocated 1000 times (μ _{C (1000)} / μ _{C (5)} ) is 1.0 to 2. .0, more preferably 1.0 to 1.8, even more preferably 1.0 to 1.6. By having the friction coefficient ratio (μ _{C (1000)} / μ _{C (5)} ) within the above numerical range, changes in the dynamic friction coefficient due to multiple runs can be reduced, so that the running of the magnetic recording medium 10 is stabilized. can be done.

The dynamic friction coefficient μ C( _{5) and the dynamic friction coefficient μ C (1000)} for calculating the friction coefficient ratio (μ _C(1000) /μ _C(5) ) are obtained as follows.
The magnetic recording medium 10 was moved to the movable strain gauge 71 in the same manner as the method for measuring the coefficient of dynamic friction _μA , except that the tension T ₀ [N] applied to the other end of the magnetic recording medium 10 was set to 0.6N. Connect with. Then, the magnetic recording medium 10 is slid 60 mm toward the movable strain gauge with respect to the head block 74 at 10 mm/s (outward path) and 60 mm away from the movable strain gauge (return path). This reciprocating motion is repeated 1000 times. Among these 1000 reciprocating movements, the output value (voltage) of the strain gauge was obtained 13 times between the start of the 60 mm sliding movement on the 5th outward movement and the stop of the sliding movement, and the dynamic friction coefficient μ _A It is converted to T[N] based on the linear relationship between the output value and the load determined in (described later). T _ave [N] is obtained by simply averaging the 11 times excluding the first and last two times. The dynamic friction coefficient μ _C(5) is determined by the following formula.
Further, the dynamic friction coefficient μ _{C (1000)} is obtained in the same manner as the dynamic friction coefficient μ _{C (5)} except that the 1000th outbound measurement is performed.
The friction coefficient ratio μ _{C ( 1000} ) / μ C (5 _{) is calculated from the dynamic friction coefficient μ C (5) and the dynamic friction coefficient μ C (1000 )} measured as described above.

[1-2 Method for manufacturing magnetic recording medium 10]
Next, a method for manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a paint for forming a base layer is prepared by kneading and dispersing non-magnetic powder, a binder, a lubricant, etc. in a solvent. Next, a paint for forming a magnetic layer is prepared by kneading and dispersing magnetic powder, a binder, a lubricant, etc. in a solvent. Next, a paint for forming a back layer is prepared by kneading and dispersing a binder, nonmagnetic powder, etc. in a solvent. For preparing the paint for forming the magnetic layer, the paint for forming the base layer, and the paint for forming the back layer, the following solvents, dispersing devices, and kneading devices can be used, for example.

Examples of solvents used in the above paint preparation include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohol solvents such as methanol, ethanol, and propanol, methyl acetate, ethyl acetate, butyl acetate, and propyl acetate. , ester solvents such as ethyl lactate and ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, methylene chloride, ethylene chloride, Examples include halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform, and chlorobenzene. These may be used alone or in an appropriate mixture.

As the kneading device used for preparing the above-mentioned paint, for example, a continuous twin-screw kneader, a continuous twin-screw kneader capable of diluting in multiple stages, a kneader, a pressure kneader, a roll kneader, etc. can be used. , but is not particularly limited to these devices. In addition, examples of dispersion equipment used in the above-mentioned paint preparation include roll mills, ball mills, horizontal sand mills, vertical sand mills, spike mills, pin mills, tower mills, pearl mills (for example, "DCP Mill" manufactured by Eirich, etc.), homogenizers, super Although a dispersion device such as a sonic dispersion machine can be used, the present invention is not particularly limited to these devices.

Next, the base layer 12 is formed by applying a base layer forming paint to one main surface 11A of the base 11 and drying it. Subsequently, the magnetic layer 13 is formed on the base layer 12 by applying a magnetic layer forming paint onto the base layer 12 and drying it. Note that during drying, it is preferable to orient the magnetic powder in the thickness direction of the substrate 11 using a magnetic field, for example, using a solenoid coil. Further, during drying, the magnetic powder may be magnetically oriented in the running direction (longitudinal direction) of the base 11 using, for example, a solenoid coil, and then the magnetic powder may be oriented in the thickness direction of the base 11. By performing such a magnetic field orientation treatment, the degree of vertical orientation (that is, the squareness ratio S1) of the magnetic powder can be improved. After forming the magnetic layer 13, a back layer forming paint is applied to the other main surface 11B of the base 11 and dried to form the back layer 14. As a result, a magnetic recording medium 10 is obtained.

The squareness ratios S1 and S2 are, for example, the intensity of the magnetic field applied to the coating film of the coating material for forming the magnetic layer, the concentration of solid content in the coating material for forming the magnetic layer, the drying conditions of the coating film of the coating material for forming the magnetic layer (drying The desired value is set by adjusting the temperature and drying time). The strength of the magnetic field applied to the coating film is preferably at least twice the coercive force of the magnetic powder. In order to further increase the squareness ratio S1 (that is, to further lower the squareness ratio S2), it is preferable to improve the state of dispersion of the magnetic powder in the coating material for forming the magnetic layer. In order to further increase the squareness ratio S1, it is also effective to magnetize the magnetic powder before the magnetic layer forming paint enters the orientation device for orienting the magnetic powder in a magnetic field. Note that the above methods for adjusting the squareness ratios S1 and S2 may be used alone or in combination of two or more.

Thereafter, the obtained magnetic recording medium 10 is calendered to smooth the surface 13S of the magnetic layer 13. Next, the calendered magnetic recording medium 10 is wound up into a roll, and the magnetic recording medium 10 is heated in this state to make the many protrusions 14A on the surface of the back layer 14 magnetic. It is transferred onto the surface 13S of the layer 13. As a result, a large number of holes 13A are formed on the surface 13S of the magnetic layer 13.

The temperature of the heat treatment is preferably 50°C or higher and 80°C or lower. When the temperature of the heat treatment is 50° C. or higher, good transferability can be obtained. On the other hand, if the temperature of the heat treatment is 80° C. or higher, the number of pores becomes too large, and there is a risk that there will be too much lubricant on the surface 13S of the magnetic layer 13. Here, the temperature of the heat treatment is the temperature of the atmosphere in which the magnetic recording medium 10 is held.

The heat treatment time is preferably 15 hours or more and 40 hours or less. When the heat treatment time is 15 hours or more, good transferability can be obtained. On the other hand, when the heat treatment time is 40 hours or less, it is possible to suppress a decrease in productivity.

Finally, the magnetic recording medium 10 is cut into a predetermined width (for example, 1/2 inch width). Through the above steps, the desired magnetic recording medium 10 can be obtained.

In the above manufacturing method, by transferring a large number of protrusions 14A provided on the surface 14S of the back layer 14 to the surface 13S of the magnetic layer 13, pores (pores 13A) are formed on the surface of the magnetic layer 13. However, the method of forming pores is not limited to this. For example, pores may be formed on the surface 13S of the magnetic layer 13 by adjusting the type of solvent contained in the magnetic layer forming paint and/or adjusting the drying conditions of the magnetic layer forming paint. Furthermore, for example, in the process of drying the solvent of the paint for forming a magnetic layer, pores may be formed due to the uneven distribution of the solids and solvent contained in the paint for forming the magnetic layer. In addition, during the process of applying the magnetic layer forming paint, the solvent contained in the magnetic layer forming paint is also absorbed into the underlying layer 12 through the pores of the underlying layer 12 formed when the lower layer is applied and dried. It can be done. As the solvent moves from the underlayer 12 through the magnetic layer 13 in the drying process after the coating, pores that communicate the magnetic layer 13 and the underlayer 12 may be formed.

[1-3 Configuration of recording/reproducing device 30]
Next, with reference to FIG. 4, the configuration of the recording/reproducing apparatus 30 that records information on the above-described magnetic recording medium 10 and reproduces information from the above-described magnetic recording medium 10 will be described.

The recording/reproducing device 30 has a configuration that can adjust the tension applied to the magnetic recording medium 10 in the longitudinal direction. Further, the recording/reproducing device 30 has a configuration in which a magnetic recording medium cartridge 10A can be loaded therein. Here, for ease of explanation, a case will be described in which the recording/reproducing apparatus 30 has a configuration in which one magnetic recording medium cartridge 10A can be loaded. However, in the present disclosure, the recording/reproducing device 30 may have a configuration in which a plurality of magnetic recording medium cartridges 10A can be loaded.

The recording/reproducing device 30 is connected to information processing devices such as a server 41 and a personal computer (hereinafter referred to as "PC") 42 via a network 43, for example, and magnetically records data supplied from these information processing devices. It is configured to be recordable on the medium cartridge 10A.

As shown in FIG. 4, the recording/reproducing device 30 includes a spindle 31, a reel 32, a drive device 33, a drive device 34, a plurality of guide rollers 35, a head unit 36, and a communication interface (hereinafter referred to as I). /F) 37 and a control device 38.

The spindle 31 is configured such that the magnetic recording medium cartridge 10A can be attached thereto. The magnetic recording medium cartridge 10A complies with the LTO (Linear Tape Open) standard, and rotatably accommodates a single reel 10C on which the magnetic recording medium 10 is wound in a cartridge case 10B. A V-shaped servo pattern is recorded in advance on the magnetic recording medium 10 as a servo signal. The reel 32 is configured to be able to fix the leading end of the magnetic recording medium 10 pulled out from the magnetic recording medium cartridge 10A.

The drive device 33 is a device that rotates the spindle 31. The drive device 34 is a device that rotates the reel 32. When recording or reproducing data on the magnetic recording medium 10, the drive device 33 and the drive device 34 rotate the spindle 31 and the reel 32, respectively, thereby causing the magnetic recording medium 10 to travel. The guide roller 35 is a roller for guiding the running of the magnetic recording medium 10.

The head unit 36 includes a plurality of recording heads for recording data signals on the magnetic recording medium 10 , a plurality of reproducing heads for reproducing data signals recorded on the magnetic recording medium 10 , and a plurality of reproducing heads for reproducing data signals recorded on the magnetic recording medium 10 . and a plurality of servo heads for reproducing recorded servo signals. For example, a ring-type head can be used as the recording head, and a magnetoresistive magnetic head, for example, can be used as the reproducing head, but the types of the recording head and the reproducing head are not limited to these.

The I/F 37 is for communicating with information processing devices such as the server 41 and the PC 42, and is connected to the network 43.

The control device 38 controls the entire recording/reproducing device 30 . For example, the control device 38 records data signals supplied from the information processing devices, such as the server 41 and the PC 42, on the magnetic recording medium 10 using the head unit 36. Further, in response to requests from information processing devices such as the server 41 and the PC 42, the control device 38 reproduces data signals recorded on the magnetic recording medium 10 using the head unit 36, and supplies the reproduced data signals to the information processing devices.

[1-4 Effect]
As described above, the magnetic recording medium 10 of the present embodiment is a tape-shaped member in which the base body 11, the underlayer 12, and the magnetic layer 13 are laminated, and each of the following structural requirements (1) to (8) is provided. It was designed to satisfy the following.
(1) The base 11 contains polyester as a main component.
(2) The average thickness of the base layer 12 is 0.9 μm or less.
(3) Underlayer 12 and magnetic layer 13 contain a lubricant.
(4) The magnetic layer 13 has a surface 13S provided with a large number of holes 13A, and the arithmetic mean roughness Ra of the surface 13S is 2.5 nm or less.
(5) The entire BET specific surface area of the magnetic recording medium 10 in a dry state with the lubricant removed is 3.5 m ² /g or more.
(6) The squareness ratio of the magnetic recording medium 10 in the vertical direction is 65% or more.
(7) The average thickness of the magnetic layer 13 is 90 nm or less.
(8) The average thickness of the magnetic recording medium 10 is 5.6 μm or less.

By having such a configuration, the magnetic recording medium 10 of the present embodiment can suppress an increase in the coefficient of dynamic friction after repeatedly recording or reproducing, even if the overall thickness is small. Furthermore, since the underlayer 12 is relatively thin, it is possible to reduce material costs and increase the amount of winding of the magnetic recording medium 10 that can be loaded into one magnetic recording medium cartridge 10A. Furthermore, since the thickness of the underlayer 12 is reduced relative to the thickness of the base 11, the Young's modulus of the entire magnetic recording medium 10 can be reduced. Since the Young's modulus of the base layer 12 containing non-magnetic powder and a binder is higher than that of the substrate 11 mainly composed of polyester, even if the thickness of the magnetic recording medium 10 remains unchanged, the Young's modulus of the substrate 11 is By reducing the thickness of the underlayer 12 relative to the thickness, the base 11 becomes more dominant as a factor determining the Young's modulus of the magnetic recording medium 10. Since the overall Young's modulus of the magnetic recording medium 10 can be reduced, when the magnetic recording medium 10 is run while applying tension along the longitudinal direction to the magnetic recording medium 10, the magnetic recording medium 10 is The responsiveness of deformation is improved. Therefore, when recording or reproducing in the recording/reproducing device 30, the running stability of the magnetic recording medium 10 can be improved.

<2. Modified example>
(Modification 1)
In the embodiment described above, the epsilon iron oxide particles 20 (FIG. 3) having the shell part 22 having a two-layer structure have been described as an example, but the magnetic recording medium of the present technology can be , the ε iron oxide particles 20A having a single-layer shell portion 23 may be included. The shell portion 23 in the ε iron oxide particle 20A has, for example, the same configuration as the first shell portion 22a. However, from the viewpoint of suppressing characteristic deterioration, the ε iron oxide particles 20 having the two-layer shell portion 22 described in the above embodiment are preferable to the ε iron oxide particles 20A of Modification 1.

(Modification 2)
In the magnetic recording medium 10 of the above-described embodiment, the epsilon iron oxide particles 20 having a core-shell structure have been described as an example, but the epsilon iron oxide particles may contain an additive instead of the core-shell structure, or It has a core-shell structure and may contain additives. In this case, part of the Fe in the ε iron oxide particles is replaced by the additive. When the epsilon iron oxide particles contain an additive, the coercive force Hc of the epsilon iron oxide particles as a whole can be adjusted to a coercive force Hc suitable for recording, so that ease of recording can be improved. The additive is a metal element other than iron, preferably a trivalent metal element, more preferably at least one of Al (aluminum), Ga (gallium) and In (indium), even more preferably Al and Ga. At least one of them.

Specifically, ε-iron oxide containing additives is a ε-Fe ₂ -xMxO ₃ crystal (where M is a metal element other than iron, preferably a trivalent metal element, more preferably Al, Ga, and In). At least one of them, and even more preferably at least one of Al and Ga. x is, for example, 0<x<1.

(Modification 3)
The magnetic powder of the present disclosure may include powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles") instead of powder of ε iron oxide particles. The hexagonal ferrite particles have, for example, a hexagonal plate shape or a substantially hexagonal plate shape. The hexagonal ferrite preferably contains at least one of Ba (barium), Sr (strontium), Pb (lead), and Ca (calcium), more preferably at least one of Ba and Sr. The hexagonal ferrite may specifically be, for example, barium ferrite or strontium ferrite. Barium ferrite may further contain at least one of Sr, Pb, and Ca in addition to Ba. Strontium ferrite may further contain at least one of Ba, Pb, and Ca in addition to Sr.

More specifically, hexagonal ferrite has an average composition represented by the general formula MFe ₁₂ O ₁₉ . However, M is, for example, at least one metal selected from Ba, Sr, Pb, and Ca, preferably at least one metal selected from Ba and Sr. M may be a combination of Ba and one or more metals selected from the group consisting of Sr, Pb, and Ca. Furthermore, M may be a combination of Sr and one or more metals selected from the group consisting of Ba, Pb, and Ca. In the above general formula, a part of Fe may be substituted with another metal element.

When the magnetic powder includes a powder of hexagonal ferrite particles, the average particle size of the magnetic powder is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. The average particle size of the magnetic powder is preferably 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. Further, the average particle size of the magnetic powder is, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. Therefore, the average particle size of the magnetic powder containing hexagonal ferrite particle powder can be, for example, 10 nm or more and 50 nm or less, 10 nm or more and 40 nm or less, 12 nm or more and 30 nm or less, 12 nm or more and 25 nm or less, or 15 nm or more and 22 nm or less. When the average particle size of the magnetic powder is equal to or less than the above upper limit (e.g., 50 nm or less, particularly 30 nm or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in the high recording density magnetic recording medium 10. I can do it. When the average particle size of the magnetic powder is at least the above lower limit (for example, at least 10 nm, preferably at least 12 nm), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) are obtained. be able to.

When the magnetic powder includes powder of hexagonal ferrite particles, the average aspect ratio of the magnetic powder is preferably 1 or more and 3.5 or less, more preferably 1 or more and 3.1 or less, or 1.5 or more and 3.0 or less. Even more preferably, it is 1.8 or more and 2.8 or less. By having the average aspect ratio of the magnetic powder within the above numerical range, agglomeration of the magnetic powder can be suppressed, and furthermore, when the magnetic powder is vertically aligned in the process of forming the magnetic layer 13, the resistance applied to the magnetic powder can be suppressed. can be suppressed. This can lead to improved vertical alignment of the magnetic powder.

Note that the average particle size and average aspect ratio of the magnetic powder containing the hexagonal ferrite particle powder are determined as follows. First, the magnetic recording medium 10 to be measured is processed into a thin section by the FIB (Focused Ion Beam) method or the like. The thinning is performed along the length direction (longitudinal direction) of the magnetic tape. The obtained thin sample was examined using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies) at an accelerating voltage of 200 kV and a total magnification of 500,000 times so that the entire recording layer was included in the thickness direction of the recording layer. Perform cross-sectional observation. Next, from the taken TEM photograph, 50 particles with their side faces facing the observation surface are selected, and the maximum plate thickness DA of each particle is measured. The maximum plate thicknesses DA obtained in this manner are simply averaged (arithmetic mean) to obtain the average maximum plate thickness DAave. Subsequently, the plate diameter DB of each magnetic powder is measured. Here, the plate diameter DB means the maximum distance (so-called maximum Feret diameter) among the distances between two parallel lines drawn from any angle so as to be in contact with the contour of the magnetic powder. Subsequently, the average plate diameter DBave is obtained by simply averaging (arithmetic mean) the measured plate diameters DB. Then, the average aspect ratio (DBave/DAave) of the particles is determined from the average maximum plate thickness DAave and the average plate diameter DBave.

When the magnetic powder includes powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 5900 nm ³ or less, more preferably 500 nm ³ or more and 3400 nm ³ or less, and even more preferably 1000 nm ³ or more and 2500 nm ^{3 or} less. When the average particle volume of the magnetic powder is 5900 nm ³ or less, the same effect as when the average particle size of the magnetic powder is 30 nm or less can be obtained. On the other hand, when the average particle volume of the magnetic powder is 500 nm ³ or more, the same effect as when the average particle size of the magnetic powder is 12 nm or more can be obtained.

Note that the average particle volume of the magnetic powder is determined as follows. First, the average maximum plate thickness DAave and the average plate diameter DBave are determined by the method for calculating the average particle size of magnetic powder described above. Next, the average volume V of the ε iron oxide particles is determined using the following formula.
V=3√3/8×DAave×DBave×DBave ²

According to a particularly preferred embodiment of the present technology, the magnetic powder may be barium ferrite magnetic powder or strontium ferrite magnetic powder, more preferably barium ferrite magnetic powder. Barium ferrite magnetic powder includes magnetic particles of iron oxide having barium ferrite as a main phase (hereinafter referred to as "barium ferrite particles"). Barium ferrite magnetic powder has high reliability in data recording, with its coercive force not decreasing even in high-temperature and humid environments. From this point of view, barium ferrite magnetic powder is preferable as the magnetic powder.

The average particle size of the barium ferrite magnetic powder is 50 nm or less, more preferably 10 nm or more and 40 nm or less, and even more preferably 12 nm or more and 25 nm or less.

When the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness tm [nm] of the magnetic layer 13 is preferably 35 nm≦tm≦100 nm, particularly preferably 80 nm or less. Further, the coercive force Hc measured in the thickness direction (vertical direction) of the magnetic recording medium 10 is preferably 160 kA/m or more and 280 kA/m or less, more preferably 165 kA/m or more and 275 kA/m or less, and even more preferably 170 kA/m or less. m or more and 270 kA/m or less.

(Modification 4)
The magnetic powder may include powder of nanoparticles containing Co-containing spinel ferrite (hereinafter referred to as "cobalt ferrite particles") instead of powder of ε iron oxide particles. It is preferable that the cobalt ferrite particles have uniaxial anisotropy. The cobalt ferrite particles have, for example, a cubic or nearly cubic shape. The Co-containing spinel ferrite may further contain at least one of Ni, Mn, Al, Cu, and Zn in addition to Co.

Co-containing spinel ferrite has, for example, an average composition represented by the following formula.
C _x M _y Fe ₂ O _Z
(However, in formula (1), M is, for example, at least one metal selected from Ni, Mn, Al, Cu, and Zn. x is within the range of 0.4≦x≦1.0. y is a value within the range of 0≦y≦0.3.However, x and y satisfy the relationship (x+y)≦1.0.z is within the range of 3≦z≦4 is the value. Part of Fe may be substituted with another metal element.)

When the magnetic powder includes powder of cobalt ferrite particles, the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm or more and 23 nm or less. When the average particle size of the magnetic powder is 25 nm or less, good electromagnetic conversion characteristics (for example, SNR) can be obtained in the high recording density magnetic recording medium 10. On the other hand, when the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained. When the magnetic powder includes powder of cobalt ferrite particles, the average aspect ratio of the magnetic powder is the same as in the above embodiment. Further, the average particle size and average aspect ratio of the magnetic powder are also determined in the same manner as the calculation method of the above-mentioned embodiment.

The average particle volume of the magnetic powder is preferably 15,000 nm ³ or less, more preferably 1,000 nm ³ or more and 12,000 nm ³ or less. When the average particle volume of the magnetic powder is 15,000 nm ³ or less, the same effect as when the average particle size of the magnetic powder is 25 nm or less can be obtained. On the other hand, when the average particle volume of the magnetic powder is 1000 nm ³ or more, the same effect as when the average particle size of the magnetic powder is 10 nm or more can be obtained. The average particle volume of the magnetic powder is determined by the method of calculating the average particle volume of the magnetic powder in the above-mentioned embodiment (the method of calculating the average particle volume when the ε iron oxide particles have a cubic or almost cubic shape). ).

The coercive force Hc of the cobalt ferrite magnetic powder is preferably 2,500 Oe or more, more preferably 2,600 Oe or more and 3,500 Oe or less.

(Modification 5)
The magnetic recording medium 10 may further include a barrier layer 15 provided on at least one surface of the base 11, as shown in FIG. 6, for example. The barrier layer 15 is a layer for suppressing dimensional changes in the base 11 depending on the environment. For example, one example of the cause of the dimensional change is the hygroscopicity of the base 11, and by providing the barrier layer 15, the speed at which moisture enters the base 11 can be reduced. Barrier layer 15 includes, for example, metal or metal oxide. The metals mentioned here include, for example, Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, and Ba. , Pt, Au, and Ta. As the metal oxide, for example, a metal oxide containing one or more of the above metals can be used. More specifically, for example, at least one of Al ₂ O ₃ , CuO, CoO, SiO ₂ , Cr ₂ O ₃ , TiO ₂ , Ta ₂ O ₅ and ZrO ₂ can be used. Further, the barrier layer 15 may include diamond-like carbon (DLC), diamond, or the like.

The average thickness of the barrier layer 15 is preferably 20 nm or more and 1000 nm or less, more preferably 50 nm or more and 1000 nm or less. The average thickness of the barrier layer 15 is determined in the same manner as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is adjusted as appropriate depending on the thickness of the barrier layer 15.

(Modification 6)
In the above embodiment, a large number of holes 13A are formed on the surface 13S of the magnetic layer 13 by transferring a large number of protrusions 14A provided on the surface of the back layer 14 to the surface 13S of the magnetic layer 13. Although the method for forming the large number of holes 13A has been described, the method for forming the large number of holes 13A is not limited to this. For example, a large number of holes 13A may be formed on the surface 13S of the magnetic layer 13 by adjusting the type of solvent contained in the magnetic layer forming paint and the drying conditions of the magnetic layer forming paint.

(Modification 7)
The magnetic recording medium 10 according to the embodiment described above may be used in a library device. In this case, the library device may include a plurality of recording and reproducing devices 30 in the above-described embodiment.

EXAMPLES Hereinafter, the present disclosure will be specifically described with reference to Examples, but the present disclosure is not limited to these Examples.

In the following Examples and Comparative Examples, squareness ratio S1 in the vertical direction, squareness ratio S2 in the longitudinal direction, pore distribution (pore volume, pore diameter at maximum pore volume during desorption), BET specific surface area, average aspect ratio. , the average particle size of the magnetic powder, the average particle volume of the magnetic powder, the average thickness of the magnetic layer, the average thickness of the base layer, the average thickness of the back layer, the average thickness of the substrate, and the arithmetic mean roughness of the surface of the magnetic layer are: This is a value determined by the measurement method described in the above-mentioned embodiment.

[Example 1]
A magnetic recording medium as Example 1 was obtained as follows.

<Preparation process of paint for forming magnetic layer>
A paint for forming a magnetic layer was prepared as follows. First, a first composition having the following composition was kneaded using an extruder. Next, the kneaded first composition and the second composition having the following composition were added to a stirring tank equipped with a disperser for preliminary mixing. Subsequently, the mixture was further mixed in a sand mill and filtered to prepare a coating material for forming a magnetic layer.

(First composition)
Each component and weight in the first composition are as follows.
・Barium ferrite (BaFe ₁₂ O ₁₉ ) particle powder (hexagonal plate shape, average aspect ratio 2.8, average particle volume 1950 nm ³ ): 100 parts by mass ・Vinyl chloride resin (cyclohexanone solution 30% by mass): 42 parts by mass (Including solvent)
(Polymerization degree 300, Mn=10000, OSO ₃ K=0.07 mmol/g as a polar group,
Contains secondary OH=0.3 mmol/g. )
- Aluminum oxide powder: 5 parts by mass (α-Al ₂ O ₃ , average particle size 0.1 μm)
・Carbon black (manufactured by Tokai Carbon Co., Ltd., product name: SEAST TA): 2 parts by mass

(Second composition)
The components and weights of the second composition are as follows.
・Vinyl chloride resin: 3 parts by mass (including solution)
(Resin solution: resin content 30% by mass, cyclohexanone 70% by mass)
・n-Butyl stearate: 2 parts by mass ・Methyl ethyl ketone: 121.3 parts by mass ・Toluene: 121.3 parts by mass ・Cyclohexanone: 60.7 parts by mass

4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation) as a curing agent and 2 parts by mass of stearic acid as a lubricant fatty acid were added to the magnetic layer forming paint prepared as described above. Added.

<Preparation process of paint for base layer formation>
A paint for forming a base layer was prepared as follows. First, a third composition having the following composition was kneaded using an extruder. Next, the kneaded third composition and the fourth composition having the following composition were added to a stirring tank equipped with a disper for preliminary mixing. Subsequently, the mixture was further mixed in a sand mill and filtered to prepare a paint for forming a base layer.

(Third composition)
Each component and weight in the third composition are as follows.
・Acicular iron oxide powder (α-Fe ₂ O ₃ , average major axis length 0.15 μm): 100 parts by mass ・Vinyl chloride resin: 60.6 parts by mass (including solution)
(Resin solution: resin content 30% by mass, cyclohexanone 70% by mass)
・Carbon black (average particle size 20 nm): 10 parts by mass

(Fourth composition)
Each component and weight in the fourth composition are as follows.
・Polyurethane resin UR8200 (manufactured by Toyobo): 18.5 parts by mass ・n-butyl stearate: 2 parts by mass ・Methyl ethyl ketone: 108.2 parts by mass ・Toluene: 108.2 parts by mass ・Cyclohexanone: 18.5 parts by mass

4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation) as a curing agent and 2 parts by mass of stearic acid as a lubricant fatty acid were added to the base layer forming paint prepared as described above. Added.

<Preparation process of paint for forming back layer>
A paint for forming a back layer was prepared as follows. A paint for forming a back layer was prepared by mixing the following raw materials in a stirring tank equipped with a disperser and filtering the mixture.
・Small particle size carbon black powder (average particle size (D50) 20 nm): 90 parts by mass ・Large particle size carbon black powder (average particle size (D50) 270 nm): 10 parts by weight ・Polyester polyurethane (Tosoh Corporation) Company manufactured, product name: N-2304): 100 parts by mass / Methyl ethyl ketone: 500 parts by mass / Toluene: 400 parts by mass / Cyclohexanone: 100 parts by mass

<Coating process>
Using the magnetic layer-forming paint and the base layer-forming paint prepared as described above, the average thickness was applied to one main surface of a long polyester film with an average thickness of 4.0 μm, which is a non-magnetic support, after calendering. An underlayer having a thickness of 0.6 μm and a magnetic layer having an average thickness of 80 nm were formed as follows. First, a base layer-forming paint was applied on one main surface of the polyester film and dried to form a base layer. Next, a magnetic layer-forming paint was applied onto the underlayer and dried to form a magnetic layer. In addition, when drying the paint for forming the magnetic layer, the magnetic powder was magnetically oriented in the thickness direction of the film using a solenoid coil. In addition, the drying conditions (drying temperature and drying time) of the paint for forming the magnetic layer were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium are shown in Table 1 below. set to the value. Subsequently, a back layer forming coating material was applied onto the other main surface of the polyester film, dried, and calendered to form a back layer having an average thickness of 0.3 μm. A magnetic recording medium was thus obtained.

<Calendar process and transfer process>
Subsequently, a calender treatment was performed to smooth the surface of the magnetic layer. Next, the magnetic recording medium with the smoothed surface of the magnetic layer was wound up into a roll, and the magnetic recording medium in that state was subjected to a heat treatment at 60° C. for 10 hours. After rewinding the magnetic recording medium into a roll so that the end located on the inner circumferential side is located on the outer circumferential side, the magnetic recording medium is heated in that state at 60°C for 10 hours. The process was repeated. As a result, many protrusions on the surface of the back layer were transferred to the surface of the magnetic layer, and many holes were formed on the surface of the magnetic layer.

<Cutting process>
The magnetic recording medium obtained as described above was cut into 1/2 inch (12.65 mm) width pieces. As a result, the desired elongated magnetic recording medium (average thickness 5.6 μm) was obtained. The BET specific surface area of the obtained magnetic recording medium after removing the lubricant and drying it was 4 m ² /g.

[Example 2]
A magnetic recording medium as Example 2 was obtained in the same manner as in Example 1 except that the average thickness of the underlayer was 0.8 μm.

[Examples 3 to 5]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (perpendicular direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Magnetic recording media as Examples 3 to 5 were obtained in the same manner as above.

[Example 6]
The average thickness of the base layer was 0.9 μm, the average thickness of the back layer was 0.4 μm, and the average thickness of the base was 4.2 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 4.5 m ² /g. Except for these, a magnetic recording medium as Example 6 was obtained in the same manner as in Example 1 above.

[Example 7]
The average thickness of the base layer was 0.7 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 5.0 m ² /g. Except for these, a magnetic recording medium as Example 7 was obtained in the same manner as in Example 1 above.

[Example 8]
In the process of preparing the paint for forming the magnetic layer, strontium ferrite particle powder (hexagonal plate shape, average aspect ratio 3.0, average particle size 21.3 nm, particle volume 2000 nm ³ ) was used as the magnetic powder. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 8 was obtained in the same manner as in Example 1 above.

[Example 9]
In the process of preparing the paint for forming the magnetic layer, powder of ε iron oxide particles (spherical, average aspect ratio 1.1, average particle size 16 nm, particle volume 2150 nm ³ ) was used as the magnetic powder. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 9 was obtained in the same manner as in Example 1 above.

[Example 10]
In the process of preparing the paint for forming the magnetic layer, cobalt ferrite powder (cubic shape, average aspect ratio 1.7, average particle size 18.5 nm, particle volume 2200 nm ³ ) was used as magnetic powder. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 10 was obtained in the same manner as in Example 1 above.

[Example 11]
The average thickness of the base layer was 0.9 μm, the average thickness of the back layer was 0.4 μm, and the average thickness of the base was 4.2 μm. In addition, the amount of small particle size carbon black powder (average particle size (D50) 20 nm) in the back layer forming paint was set to 80 parts by mass, and the large particle size carbon black powder (average particle size (D50) 270 nm) was set at 20 parts by mass. In addition, the heating conditions were adjusted in the transfer step, and the pore volume was set to 0.023 cm ³ /g, and the pore diameter of the maximum pore volume at the time of desorption was set to 9 nm. Furthermore, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 11 was obtained in the same manner as in Example 1 above.

[Example 12]
The average thickness of the base layer was 0.9 μm, the average thickness of the back layer was 0.4 μm, and the average thickness of the base was 4.2 μm. In addition, the heating conditions were adjusted in the transfer process, and the pore diameter of the maximum pore volume at the time of desorption was set to 10 nm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 12 was obtained in the same manner as in Example 1 above.

[Example 13]
The average thickness of the back layer was 0.5 μm, and the average thickness of the substrate was 3.6 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 13 was obtained in the same manner as in Example 1 above.

[Example 14]
When forming the back layer forming paint, 70 parts by mass of small particle size carbon black powder (average particle size (D50) 50 nm) was used instead of small particle size carbon black powder (average particle size (D50) 20 nm). and the amount of large particle size carbon black powder (average particle size (D50) 270 nm) was 30 parts by mass. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 6.0 m ² /g. Except for these, a magnetic recording medium as Example 16 was obtained in the same manner as in Example 1 above. Note that the pore diameter of the maximum pore volume at the time of desorption was 12 nm.

[Example 15]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 17 was obtained in the same manner as in Example 1 above.

[Example 16]
The average thickness of the base layer was 0.9 μm, the average thickness of the back layer was 0.4 μm, and the average thickness of the base was 4.2 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 18 was obtained in the same manner as in Example 1 above. Note that the BET specific surface area was 3.9 m ² /g.

[Example 17]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 19 was obtained in the same manner as in Example 1 above. Note that the BET specific surface area was 3.8 m ² /g.

[Example 18]
Except that in the preparation process of the paint for forming the magnetic layer, powder of hexagonal plate-shaped barium ferrite particles having an average aspect ratio of 2.5, an average particle size of 19.0 nm, and an average particle volume of ¹⁶⁰⁰ nm was used as the magnetic powder. A magnetic recording medium as Example 20 was obtained in the same manner as in Example 1 above. Note that the pore diameter of the maximum pore volume at the time of desorption was 7 nm.

[Example 19]
Except that in the preparation process of ^the paint for forming the magnetic layer, powder of hexagonal plate-shaped barium ferrite particles having an average aspect ratio of 2.3, an average particle size of 17.0 nm, and an average particle volume of 1300 nm was used as the magnetic powder. A magnetic recording medium as Example 21 was obtained in the same manner as in Example 1 above. Note that the pore diameter of the maximum pore volume at the time of desorption was 6 nm.

[Example 20]
The average thickness of the magnetic layer was 60 nm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 22 was obtained in the same manner as in Example 1 above. Note that the BET specific surface area was 3.9 m ² /g.

[Example 21]
The average thickness of the magnetic layer was 40 nm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, a magnetic recording medium as Example 23 was obtained in the same manner as in Example 1 above. Note that the BET specific surface area was 3.8 m ² /g.

[Example 22]
In the process of preparing the paint for forming the magnetic layer, a powder of hexagonal plate-shaped barium ferrite particles having an average particle size of 23.0 nm and an average particle volume of 2500 nm ³ was used as the magnetic powder. Further, the average thickness of the base layer was 0.5 μm. Except for these, a magnetic recording medium as Example 24 was obtained in the same manner as in Example 1 above.

[Example 23]
In the preparation process of the paint for forming the magnetic layer, the same procedure as in Example 1 was performed, except that a powder of hexagonal plate-shaped barium ferrite particles with an average particle size of 23.0 nm and an average particle volume of 2500 nm ³ was used as the magnetic powder. A magnetic recording medium as Example 25 was obtained in the same manner.

[Example 24]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 3.5 m ² /g. Except for these, a magnetic recording medium as Example 26 was obtained in the same manner as in Example 1 above.

[Comparative example 1]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 3.0 m ² /g. Except for these, a magnetic recording medium as Comparative Example 1 was obtained in the same manner as in Example 1 above.

[Comparative example 2]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Further, the average thickness of the base layer was 1.2 μm. Except for these, a magnetic recording medium as Comparative Example 2 was obtained in the same manner as in Example 1 above.

[Comparative example 3]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Further, the average thickness of the base layer was 1.2 μm. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 2.0 m ² /g. Except for these, a magnetic recording medium as Comparative Example 3 was obtained in the same manner as in Example 1 above.

[Comparative example 4]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 2.0 m ² /g. Except for these, a magnetic recording medium as Comparative Example 4 was obtained in the same manner as in Example 1 above.

[Comparative example 5]
In forming the back layer forming paint, 80 parts by mass of small particle size carbon black powder (average particle size (D50) 50 nm) was used instead of small particle size carbon black powder (average particle size (D50) 20 nm). and the amount of large particle size carbon black powder (average particle size (D50) 270 nm) was 20 parts by mass. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Furthermore, the heating conditions in the transfer process were adjusted to have a pore volume of 0.018 cm ³ /g and a BET specific surface area of 3.0 m ² /g. Except for these, a magnetic recording medium as Comparative Example 5 was obtained in the same manner as in Example 1 above.

[Comparative example 6]
In forming the back layer forming paint, 90 parts by mass of small particle size carbon black powder (average particle size (D50) 50 nm) was used instead of small particle size carbon black powder (average particle size (D50) 20 nm). was blended. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Further, the heating conditions in the transfer step were adjusted to have a pore volume of 0.015 cm ³ /g and a BET specific surface area of 2.5 m ² /g. Except for these, a magnetic recording medium as Comparative Example 6 was obtained in the same manner as in Example 1 above.

[Comparative Example 7]
In forming the back layer forming paint, 100 parts by mass of small particle size carbon black powder (average particle size (D50) 20 nm) is blended, and large particle size carbon black powder (average particle size (D50) 270 nm) was set to 0 parts by mass. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Furthermore, the heating conditions were adjusted in the transfer step, so that the pore volume was 0.015 cm ³ /g, the pore diameter of the maximum pore volume during desorption was 5 nm, and the BET specific surface area was 2.0 m ² /g. Except for these, a magnetic recording medium as Comparative Example 7 was obtained in the same manner as in Example 1 above.

[Comparative example 8]
In forming the back layer forming paint, 100 parts by mass of small particle size carbon black powder (average particle size (D50) 20 nm) is blended, and large particle size carbon black powder (average particle size (D50) 270 nm) was set to 0 parts by mass. Further, the average thickness of the base layer was 0.5 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Further, the heating conditions were adjusted in the transfer step, so that the pore volume was 0.015 cm ³ /g, the pore diameter of the maximum pore volume during desorption was 5 nm, and the BET specific surface area was 2.0 m ² /g. Except for these, a magnetic recording medium as Comparative Example 7 was obtained in the same manner as in Example 1 above.

[Comparative Example 9]
The average thickness of the base layer was 1.0 μm, and the average thickness of the back layer was 0.5 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 3.8 m ² /g. Except for these, a magnetic recording medium as Comparative Example 9 was obtained in the same manner as in Example 1 above.

[Comparative Example 10]
The average thickness of the base layer was 1.4 μm. In addition, in the coating process, the drying conditions were adjusted, and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 3. Furthermore, the heating conditions in the transfer process were adjusted to give a BET specific surface area of 3.5 m ² /g. Except for these, a magnetic recording medium as Comparative Example 10 was obtained in the same manner as in Example 1 above.

[Comparative Examples 11 and 12]
In the coating process, the drying conditions were adjusted and the squareness ratio S1 in the thickness direction (vertical direction) and the squareness ratio S2 in the longitudinal direction of the magnetic recording medium were set to the values shown in Table 1. Except for these, magnetic recording media as Comparative Examples 11 and 12 were obtained in the same manner as in Example 1 above.

[evaluation]
Regarding the magnetic recording media of Examples 1 to 26 and Comparative Examples 1 to 10 obtained as described above, the above-mentioned friction coefficient ratio (μ _B /μ _A ) and friction coefficient ratio (μ _{C (1000)} / μ _C In addition to ₍₅₎ ), the following evaluations were performed.

(SNR)
The SNR (electromagnetic conversion characteristics) of the magnetic recording medium was measured in a 25°C environment using a 1/2-inch tape transport device (manufactured by Mountain Engineering II, MTS Transport) equipped with a recording/playback head and a recording/playback amplifier. . A ring head with a gap length of 0.2 μm was used as the recording head, and a GMR head with a distance between shields of 0.1 μm was used as the read head. The relative speed was 6 m/s, the recording clock frequency was 160 MHz, and the recording track width was 2.0 μm. Further, the SNR was calculated based on the method described in the following literature. The results are shown in Tables 1 and 3 as relative values assuming that the SNR of Example 1 is 1 dB.
Y. Okazaki: "An Error Rate Emulation System.", IEEE Trans. Man., 31, pp.3093-3095(1995)

Table 2 summarizes the configuration and evaluation results of the magnetic recording media in each Example and each Comparative Example.

As shown in Table 2, in Examples 1 to 24, the entire BET specific surface area of the magnetic recording medium in a dry state with the lubricant removed is 3.5 m ² /g or more, so repeated recording or reproduction is not possible. Even after this, the lubricant was stably supplied to the interface between the magnetic recording medium and the magnetic head, and an increase in the friction coefficient ratio could be suppressed. On the other hand, in Comparative Examples 1, 3 to 8, the entire BET specific surface area of the magnetic recording medium in a dry state with the lubricant removed is less than 3.5 m ² /g, so after repeated recording or reproduction, An increase in the friction coefficient ratio was observed.

Furthermore, in Comparative Examples 2, 9, and 10, although the entire BET specific surface area of the magnetic recording medium after removing the lubricant and drying it was 3.5 m ² /g or more, the average thickness of the underlayer was 0.5 m 2 /g or more. Since it exceeded 9 μm, the Young's modulus was high, and an increase in the friction coefficient ratio was also observed after repeated recording or reproduction.

Further, in Examples 1 to 24, the squareness ratio S1 in the perpendicular direction (thickness direction) of the magnetic recording medium is 65% or more, so that a good SNR is obtained. On the other hand, in Comparative Examples 11 and 12, since the squareness ratio S1 in the vertical direction (thickness direction) of the magnetic recording medium was less than 65%, deterioration of the SNR was observed.

Although the present disclosure has been specifically described above with reference to the embodiments and modifications thereof, the present disclosure is not limited to the above embodiments, etc., and various modifications are possible.

For example, the configurations, methods, processes, shapes, materials, numerical values, etc. mentioned in the above-mentioned embodiments and modifications thereof are merely examples, and the configurations, methods, processes, shapes, materials, numerical values, etc. that differ from these as necessary. etc. may also be used. Specifically, the magnetic recording medium of the present disclosure may include components other than the base, underlayer, magnetic layer, back layer, and barrier layer. Further, the chemical formulas of compounds, etc. are representative ones, and as long as they are general names of the same compound, they are not limited to the stated valency, etc.

Further, the configurations, methods, processes, shapes, materials, numerical values, etc. of the above-described embodiments and their modifications can be combined with each other without departing from the gist of the present disclosure.

Furthermore, in the numerical ranges described in stages in this specification, the upper limit or lower limit of the numerical range of one stage may be replaced with the upper limit or lower limit of the numerical range of another stage. The materials exemplified in this specification can be used alone or in combination of two or more, unless otherwise specified.

As described above, the magnetic recording medium as an embodiment of the present disclosure can exhibit good running performance during use.
Note that the effects of the present disclosure are not limited to these, and may be any effects described in this specification. Further, the present technology can have the following configuration.
(1)
A tape-shaped magnetic recording medium,
A base body;
a base layer provided on the base;
a magnetic layer provided on the underlayer;
The base body contains polyester as a main component,
The average thickness of the base layer is 0.9 μm or less,
The underlayer and the magnetic layer contain a lubricant,
The magnetic layer has a surface provided with a large number of holes, and the arithmetic mean roughness Ra of the surface is 2.5 nm or less,
The entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 3.5 m ² /g or more,
The squareness ratio of the magnetic recording medium in the vertical direction is 65% or more,
The average thickness of the magnetic layer is 90 nm or less,
The average thickness of the magnetic recording medium is 5.6 μm or less.Magnetic recording medium.
(2)
The magnetic recording medium according to (1) above, wherein the magnetic recording medium has a Young's modulus of 7.78 GPa or less.
(3)
The magnetic recording medium according to (1) or (2) above, wherein the average thickness of the base is 4.2 μm or less.
(4)
further comprising a back layer provided on the opposite side of the base layer to the base layer,
The magnetic recording medium according to any one of (1) to (3) above, wherein the back layer has an average thickness of 0.3 μm or more and 0.5 μm or less.
(5)
The magnetic recording medium according to any one of (1) to (4) above, wherein the underlayer has an average thickness of 0.5 μm or more.
(6)
The magnetic recording medium according to any one of (1) to (5) above, wherein the overall average pore diameter of the magnetic recording medium determined by the BJH method is 6 nm or more and 12 nm or less.
(7)
Dynamic friction coefficient μA between the surface and the magnetic head when the tension applied to the magnetic recording medium is 0.4N, and the surface and the magnetic head when the tension applied to the magnetic recording medium is 1.2N. The magnetic recording medium according to any one of (1) to (6) above, wherein the friction coefficient ratio μB/μA between the dynamic friction coefficient μB and the friction coefficient μB is 1.0 or more and 1.8 or less.
(8)
When the tension applied to the magnetic recording medium is 0.6 N, the coefficient of kinetic friction μC(5) between the surface and the magnetic head at the fifth time after the start of running of the magnetic recording medium and the force applied to the magnetic recording medium When the tension is 0.6 N, the friction coefficient ratio μC(1000)/μC(5 ) is 1.2 or more and 1.8 or less. The magnetic recording medium according to any one of (1) to (7) above.
(9)
The magnetic layer includes magnetic powder,
The magnetic recording medium according to any one of (1) to (8) above, wherein the magnetic powder has an average aspect ratio of 1.1 or more and 3.0 or less.
(10)
The magnetic layer includes magnetic powder,
The magnetic powder includes hexagonal ferrite containing at least one of Ba (barium) and Sr (strontium), ε iron oxide, or Co (cobalt) containing spinel ferrite. The magnetic recording medium according to any one of the above.
(11)
The magnetic layer includes magnetic powder,
The magnetic recording medium according to any one of (1) to (10) above, wherein the magnetic powder has an average particle size of 25 nm or less.
(12)
The magnetic recording medium according to any one of (1) to (11) above, wherein the lubricant contains at least one compound represented by the following general formulas <1> to <4>, respectively. .
CH ₃ (CH ₂ ) _n COOH…<1>
(However, in the general formula <1>, n is an integer selected from the range of 14 to 22.)
CH ₃ (CH ₂ ) _p COO(CH ₂ ) _q CH ₃ …<2>
(However, in the general formula <2>, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 2 to 5.)
CH ₃ (CH ₂ ) _n CH=CH (CH ₂ ) _m COOH…<3>
(However, in the general formula <3>, n+m is an integer selected from the range of 12 to 20.)
CH ₃ (CH ₂ ) _p COO-(CH ₂ ) _q CH(CH ₃ ) ₂ …<4>
(However, in the general formula <4>, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 1 to 3.)
(13)
The base layer has a large number of holes,
The magnetic recording medium according to any one of (1) to (12) above, wherein the hole in the magnetic layer and the hole in the underlayer are connected.
(14)
The magnetic recording medium according to any one of (1) to (13) above, wherein the surface of the magnetic layer has an arithmetic mean roughness Ra of 0.8 nm or more.
(15)
The magnetic recording medium according to any one of (1) to (14) above, wherein the entire BET specific surface area of the magnetic recording medium in a state where the lubricant is removed and dried is 4.0 m ² /g or more. .
(16)
The magnetic recording medium according to any one of (1) to (15) above, wherein the entire BET specific surface area of the magnetic recording medium in a state where the lubricant is removed and dried is 4.5 m ² /g or more. .
(17)
The magnetic recording medium according to any one of (1) to (16) above, wherein the entire BET specific surface area of the magnetic recording medium in a state where the lubricant is removed and dried is 5.0 m ² /g or more. .
(18)
The magnetic recording medium according to any one of (1) to (17) above, wherein the entire BET specific surface area of the magnetic recording medium in a state in which the lubricant is removed and dried is 7.0 m ² /g or less. .
(19)
The magnetic recording medium according to any one of (1) to (18) above, wherein the entire BET specific surface area of the magnetic recording medium in a state where the lubricant is removed and dried is 6.0 m ² /g or less. .
(20)
The magnetic recording medium according to any one of (1) to (19) above, wherein the magnetic recording medium has a total BET specific surface area of 5.5 m ² /g or less in a state in which the lubricant has been removed and it has been dried. .
(21)
a feeding section capable of sequentially feeding out tape-shaped magnetic recording media;
a winding unit capable of winding up the magnetic recording medium fed out from the feeding unit;
a magnetic head capable of writing information to and reading information from the magnetic recording medium while being in contact with the magnetic recording medium traveling from the sending section to the winding section; ,
The magnetic recording medium is
A base body;
a base layer provided on the base;
a magnetic layer provided on the underlayer;
The base body contains polyester as a main component,
The average thickness of the base layer is 0.9 μm or less,
The underlayer and the magnetic layer contain a lubricant,
The magnetic layer has a surface provided with a large number of holes, and the arithmetic mean roughness Ra of the surface is 2.5 nm or less,
The entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 3.5 m ² /g or more,
The squareness ratio of the magnetic recording medium in the vertical direction is 65% or more,
The average thickness of the magnetic layer is 90 nm or less,
The average thickness of the magnetic recording medium is 5.6 μm or less. A magnetic recording and reproducing device.
(22)
The magnetic recording and reproducing apparatus according to (21) above, which has a configuration in which tension applied in the longitudinal direction of the magnetic recording medium can be adjusted.
(23)
The tape-shaped magnetic recording medium according to any one of (1) to (22) above;
A magnetic recording medium cartridge comprising: a casing that accommodates the magnetic recording medium.

DESCRIPTION OF SYMBOLS 10...Magnetic recording medium, 11...Substrate, 11A, 11B...Main surface, 12...Underlayer, 13...Magnetic layer, 14...Back layer, 20, 20A...ε iron oxide particles, 21...Core part, 22...Shell part , 22a... first shell part, 22b... second shell part, 30... recording/reproducing device, 31... spindle, 32... reel, 33, 34... drive device, 35... guide roller, 36... head unit, 37... communication interface , 38...control device, 41...server, 42...personal computer, 43...network.

Claims (28)

A tape-shaped magnetic recording medium,
A base body;
a base layer provided on the base;
a magnetic layer provided on the underlayer;
The base body contains polyester as a main component,
The average thickness of the base layer is 0.9 μm or less,
The magnetic recording medium includes a lubricant,
The magnetic layer has a surface provided with a large number of holes, and the arithmetic mean roughness Ra of the surface is 2.5 nm or less,
The entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 3.5 m ² /g or more,
The squareness ratio in the longitudinal direction of the magnetic recording medium is 35% or less,
The average thickness of the magnetic layer is 90 nm or less,
The average thickness of the magnetic recording medium is 5.6 μm or less,
The magnetic layer includes magnetic powder, and the magnetic powder has an average particle volume of 1950 nm ³ or less. A magnetic recording medium. The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic recording medium is 5.2 μm or less. The magnetic recording medium according to claim 1 or 2, wherein the data track width of the magnetic layer is 1500 nm or less. The magnetic recording medium according to any one of claims 1 to 3, wherein the average thickness of the magnetic layer is 70 nm or less. The magnetic recording medium according to any one of claims 1 to 4, wherein the magnetic recording medium has a Young's modulus of 7.78 GPa or less. The magnetic recording medium according to any one of claims 1 to 5, wherein the average thickness of the base is 4.2 μm or less. further comprising a back layer provided on the opposite side of the base layer to the base layer,
The magnetic recording medium according to any one of claims 1 to 6, wherein the average thickness of the back layer is 0.3 μm or more and 0.5 μm or less. The magnetic recording medium according to any one of claims 1 to 7, wherein the average thickness of the underlayer is 0.5 μm or more. The magnetic recording medium according to any one of claims 1 to 8, wherein the overall average pore diameter of the magnetic recording medium determined by the BJH method is 6 nm or more and 12 nm or less. Dynamic friction coefficient μA between the surface and the magnetic head when the tension applied to the magnetic recording medium is 0.4N, and the surface and the magnetic head when the tension applied to the magnetic recording medium is 1.2N. The magnetic recording medium according to any one of claims 1 to 9, wherein a friction coefficient ratio μB/μA between the dynamic friction coefficient μB and the dynamic friction coefficient μB is 1.0 or more and 1.8 or less. When the tension applied to the magnetic recording medium is 0.6 N, the coefficient of kinetic friction μC(5) between the surface and the magnetic head at the fifth time after the start of running of the magnetic recording medium and the force applied to the magnetic recording medium When the tension is 0.6 N, the friction coefficient ratio μC(1000)/μC(5 ) is 1.2 or more and 1.8 or less. The magnetic recording medium according to any one of claims 1 to 10. The magnetic recording medium according to any one of claims 1 to 11, wherein the average aspect ratio of the magnetic powder is 1.1 or more and 3.0 or less. The magnetic powder includes hexagonal ferrite containing at least one of Ba (barium) and Sr (strontium), ε iron oxide, or Co (cobalt) containing spinel ferrite. The magnetic recording medium according to item 1. The magnetic recording medium according to any one of claims 1 to 13, wherein the average particle size of the magnetic powder is 25 nm or less. The magnetic recording medium according to any one of claims 1 to 14, wherein the lubricant contains at least one compound represented by the following general formulas <1> to <4>.
CH ₃ (CH ₂ ) _n COOH…<1>
(However, in the general formula <1>, n is an integer selected from the range of 14 to 22.)
CH ₃ (CH ₂ ) _p COO(CH ₂ ) _q CH ₃ …<2>
(However, in the general formula <2>, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 2 to 5.)
CH ₃ (CH ₂ ) _n CH=CH (CH ₂ ) _m COOH…<3>
(However, in the general formula <3>, n+m is an integer selected from the range of 12 to 20.)
CH ₃ (CH ₂ ) _p COO-(CH ₂ ) _q CH(CH ₃ ) ₂ …<4>
(However, in the general formula <4>, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 1 to 3.) The base layer has a large number of holes,
The magnetic recording medium according to any one of claims 1 to 15, wherein a hole in the magnetic layer and a hole in the underlayer are connected. The magnetic recording medium according to any one of claims 1 to 16, wherein the surface of the magnetic layer has an arithmetic mean roughness Ra of 0.8 nm or more. The magnetic recording medium according to any one of claims 1 to 17, wherein the entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 4.0 m ² /g or more. The magnetic recording medium according to any one of claims 1 to 18, wherein the entire BET specific surface area of the magnetic recording medium in a state where the lubricant has been removed and dried is 4.5 m ² /g or more. The magnetic recording medium according to any one of claims 1 to 19, wherein the entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 5.0 m ² /g or more. The magnetic recording medium according to any one of claims 1 to 20, wherein the entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 7.0 m ² /g or less. The magnetic recording medium according to any one of claims 1 to 21, wherein the entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 6.0 m ² /g or less. The magnetic recording medium according to any one of claims 1 to 22, wherein the entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 5.5 m ² /g or less. The magnetic recording medium according to any one of claims 1 to 23, wherein the average particle volume of the magnetic powder is 1600 nm ³ or less. The magnetic recording medium according to any one of claims 1 to 23, wherein the average particle volume of the magnetic powder is 1300 nm ³ or less. a feeding section capable of sequentially feeding out tape-shaped magnetic recording media;
a winding unit capable of winding up the magnetic recording medium fed out from the feeding unit;
a magnetic head capable of writing information to and reading information from the magnetic recording medium while being in contact with the magnetic recording medium traveling from the sending section to the winding section; ,
The magnetic recording medium is
A base body;
a base layer provided on the base;
a magnetic layer provided on the underlayer;
The base body contains polyester as a main component,
The average thickness of the base layer is 0.9 μm or less,
The magnetic recording medium includes a lubricant,
The magnetic layer has a surface provided with a large number of holes, and the arithmetic mean roughness Ra of the surface is 2.5 nm or less,
The entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 3.5 m ² /g or more,
The squareness ratio in the longitudinal direction of the magnetic recording medium is 35% or less,
The average thickness of the magnetic layer is 90 nm or less,
The average thickness of the magnetic recording medium is 5.6 μm or less,
The magnetic layer includes magnetic powder, and the average particle volume of the magnetic powder is 1950 nm ³ or less. A magnetic recording/reproducing device. The magnetic recording and reproducing apparatus according to claim 26, having a configuration that allows adjustment of tension applied in the longitudinal direction of the magnetic recording medium. a tape-shaped magnetic recording medium;
a casing that accommodates the magnetic recording medium;
The magnetic recording medium is
A base body;
a base layer provided on the base;
a magnetic layer provided on the underlayer;
The base body contains polyester as a main component,
The average thickness of the base layer is 0.9 μm or less,
The magnetic recording medium includes a lubricant,
The magnetic layer has a surface provided with a large number of holes, and the arithmetic mean roughness Ra of the surface is 2.5 nm or less,
The entire BET specific surface area of the magnetic recording medium in a state in which the lubricant has been removed and dried is 3.5 m ² /g or more,
The squareness ratio in the longitudinal direction of the magnetic recording medium is 35% or less,
The average thickness of the magnetic layer is 90 nm or less,
The average thickness of the magnetic recording medium is 5.6 μm or less,
The magnetic layer includes magnetic powder, and the average particle volume of the magnetic powder is 1950 nm ³ or less. A magnetic recording medium cartridge.