JP6561190B2 - Magnetic tape and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnetic tape and a manufacturing method thereof.

  There are two types of magnetic recording media, tape-shaped and disk-shaped. For data storage applications such as data backup, tape-shaped magnetic recording media, ie magnetic tape, are mainly used. As for the layer structure of the magnetic tape, as described in paragraphs 0035 and 0038 of Patent Document 1, for example, a nonmagnetic layer (a nonmagnetic underlayer is disclosed in Patent Document 1) is provided between the nonmagnetic support and the magnetic layer. (Hereinafter referred to as “multi-layer configuration”) is currently mainstream.

  Recording and / or reproduction of a signal on the magnetic tape is usually performed by causing the magnetic tape to run in the drive and bringing the magnetic tape surface (magnetic layer surface) into contact with (sliding) the magnetic head. Here, by reducing the size of the particles constituting the ferromagnetic powder contained in the magnetic layer, it is possible to reduce noise when reproducing the signal recorded on the magnetic tape, and as a result, electromagnetic conversion characteristics (SNR). ; Signal-to-Noise ratio) can be improved. In this regard, for example, in paragraph 0024 of Patent Document 1, from the viewpoint of noise reduction, the average plate surface diameter of the ferromagnetic hexagonal ferrite powder (described in Patent Document 1 as hexagonal ferrite magnetic powder) is shown. It is described that the thickness is 30 nm or less.

JP 2012-38367 A

  Examples of the ferromagnetic powder used in the magnetic layer include various ferromagnetic powders such as ferromagnetic hexagonal ferrite powder and ferromagnetic metal powder. Among these, the ferromagnetic hexagonal ferrite powder is said to be a preferable ferromagnetic powder because it can exhibit good magnetic properties even when the particle size is reduced.

  On the other hand, magnetic tapes used for data storage are currently stored in a low-temperature and low-humidity environment such as a data center where temperature and humidity are controlled (for example, in an environment with a temperature of 10 to 15 ° C. and a relative humidity of about 10 to 20%). There are many cases. However, from the viewpoint of reducing the air conditioning cost for temperature and humidity management, it is desirable that the temperature and humidity management of the storage environment can be relaxed or made unnecessary.

  In view of the above, the present inventors have reduced the particle size of the ferromagnetic hexagonal ferrite powder in order to increase the SNR in the magnetic tape having a multilayer structure having a nonmagnetic layer between the nonmagnetic support and the magnetic layer. (Hereinafter referred to as “particulate”), and consideration was given to reducing or eliminating the temperature and humidity control conditions during storage of magnetic tape. As a result, the magnetic tape having a multilayer structure including the ferromagnetic hexagonal ferrite powder finely divided to increase the SNR in the magnetic layer is in an environment in which temperature and humidity management is eased or unnecessary (hereinafter referred to as “high temperature and high humidity environment”). It has become clear that an unprecedented phenomenon that the coefficient of friction increases when the vehicle is driven in the drive after storage in (1)). The high temperature and high humidity environment is, for example, an environment having a temperature of 30 ° C. or higher and a relative humidity of 50% or higher. It is desirable to suppress the increase in the friction coefficient because it causes a decrease in running characteristics such as running stability and running durability of the magnetic tape.

  As described above, in conventional magnetic tapes having a multi-layer structure, the electromagnetic conversion characteristics (SNR) are improved, and the friction coefficient in running in a drive after storage in a high temperature and high humidity environment (hereinafter simply referred to as “friction after storage”). It is also difficult to achieve both suppression of increase in the coefficient.

  Accordingly, an object of the present invention is to provide a magnetic tape having a multi-layer structure that can exhibit excellent electromagnetic conversion characteristics and that suppresses an increase in the coefficient of friction after storage in a high-temperature and high-humidity environment.

One embodiment of the present invention provides:
A magnetic tape having a nonmagnetic layer comprising a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer comprising a ferromagnetic powder and a binder on the nonmagnetic layer,
Containing at least a fatty acid ester in the magnetic layer;
The ferromagnetic powder is a ferromagnetic hexagonal ferrite powder,
The ferromagnetic hexagonal ferrite powder has a crystallite volume determined by X-ray diffraction analysis in the range of 1000 to 2400 nm ³ and a crystallite size D _{x (107)} determined from the diffraction peak of the (107) plane and transmission. the ratio of the magnetization easy axis particle size _{D TEM} obtained by the type electron _{microscope, D x (107) / D} TEM, it is but 1.1 or more,
Formula 1 in the longitudinal direction of the magnetic tape 1:
ΔSFD = SFD _{25 ° C.} −SFD _{−190 ° C.} Formula 1
The magnetic tape whose ΔSFD calculated by is in the range of 0.50 to 1.60,
About.

In Formula 1, SFD _{25 ° C.} is a switching field distribution (SFD) measured in the longitudinal direction of the magnetic tape in an environment of temperature 25 ° C., and SFD _{−190 ° C.} is in an environment of temperature −190 ° C. It is reversal magnetic field distribution SFD measured in a magnetic tape longitudinal direction. The longitudinal direction SFD of the magnetic tape can be obtained by a known magnetic property measuring device such as a vibrating sample magnetometer. The same applies to the SFD measurement of the ferromagnetic powder described later. Moreover, the temperature at the time of SFD measurement can be adjusted with the setting of a measuring apparatus.

The shape of the particles constituting the ferromagnetic hexagonal ferrite powder was obtained by photographing the powder taken out from the magnetic layer with a transmission electron microscope at a photographing magnification of 100,000, and printing it on a photographic paper so that the total magnification was 500,000 times. In the particle photograph obtained in this way, the contour of the particle (primary particle) is traced and specified by a digitizer. Extraction of the ferromagnetic hexagonal ferrite powder from the magnetic layer can be performed by, for example, the method described in Examples below, but any method that can extract the powder from the magnetic layer may be used. The method is not limited. The primary particles are independent particles without aggregation. Imaging with a transmission electron microscope is performed by a direct method using a transmission electron microscope at an acceleration voltage of 300 kV. Observation and measurement of a transmission electron microscope in Examples described later were performed using Hitachi transmission electron microscope H-9000 type and Carl Zeiss image analysis software KS-400.
With respect to the shape of the particles constituting the ferromagnetic hexagonal ferrite powder, “plate shape” refers to a shape having two plate surfaces facing each other. On the other hand, among such particle shapes having no plate surface, a shape having a distinction between a major axis and a minor axis is an “elliptical shape”. The long axis is determined as an axis (straight line) that can take the longest particle. On the other hand, the short axis is determined as the axis having the longest length when the particle length is taken with a straight line orthogonal to the long axis. A shape in which the major axis and the minor axis are not distinguished, that is, a shape in which the major axis length = the minor axis length is “spherical”. A shape whose major axis and minor axis cannot be specified from the shape is hereinafter referred to as an indeterminate shape.

The easy magnetization axis direction particle size D _TEM is a size measured for primary particles, for plate-like particles, the plate thickness of the primary particles, for elliptical particles, the short axis length of the primary particles, spherical particles Is the diameter of the primary particle. These particle sizes are primary particle sizes in the c-axis direction, which is the direction of the easy axis of magnetization of the ferromagnetic hexagonal ferrite powder particles.
Photographing with the transmission electron microscope for specifying the above-described particle shape is performed without subjecting the powder to be photographed to orientation processing. On the other hand, at the time of photographing with a transmission electron microscope for _DTEM measurement, after subjecting the photographing target powder to orientation treatment in the horizontal direction (direction parallel to the horizontal plane), The particle photograph is taken with a transmission electron microscope. The magnetic force, size, etc. of the magnet used for the orientation treatment are not limited. An example of the alignment treatment will be described later in Examples. By applying the orientation treatment in the horizontal direction, the magnetization easy axis direction of the particles constituting the ferromagnetic hexagonal ferrite powder is oriented in the direction parallel to the sample stage in the transmission electron microscope. The easy magnetization axis direction (c-axis direction) particle size can be obtained. It should be noted that the description regarding angles such as horizontal and parallel includes the range of errors allowed in the technical field to which the present invention belongs. For example, it means that the angle is within the range of strict angle ± 10 °, and the error from the strict angle is preferably 5 ° or less, and more preferably 3 ° or less. The easy magnetization axis direction particle size D _TEM is obtained by tracing the contours of 500 particles randomly extracted in the photographed particle photograph as described above, and using image analysis software (for example, Carl Zeiss image analysis software KS-400). ) Is the arithmetic average of the particle sizes obtained. The plate thickness means the shortest distance between two plate surfaces. In addition, the particle size D _TEM is equivalent to a circle equivalent diameter for particles having a shape other than plate, ellipse, and sphere (indefinite shape). The equivalent circle diameter refers to the diameter of a circle having the same area as the area within the contour traced in the particle photograph.

  In the present invention and the present specification, the powder means an aggregate of a plurality of particles. The number of crystallites contained in the particle is one or more, and may be one or two or more. Preferably, the number of crystallites contained in one particle (primary particle) is one. The aggregate of a plurality of particles is not limited to an embodiment in which the particles constituting the assembly are in direct contact with each other, and an embodiment in which a binder, an additive, or the like described later is interposed between the particles is also included. The In the following, the term particle may be used to denote powder.

In X-ray diffraction analysis of ferromagnetic hexagonal ferrite powder, a test piece (usually recovered in a powder state) obtained by scraping a part or all of a magnetic layer from a magnetic tape with an arbitrary peeling means such as a blade. Shall be used. The test piece may contain components other than the ferromagnetic hexagonal ferrite powder, but even if such a component is contained, it is possible to detect a diffraction peak peculiar to the hexagonal ferrite. The amount of the sample piece used for the X-ray diffraction analysis is, for example, 0.001 to 1 g, but may be any amount that can obtain diffraction peaks on the (110) plane and the (107) plane of hexagonal ferrite described later.
The X-ray diffraction analysis is performed under the following conditions using a powder X-ray diffraction measurement device (for example, RINT2500 manufactured by Rigaku Corporation).
Use Cu source (Output 55kV, 280mA)
Scan condition: The range of 10 to 70 degrees is 0.05 degrees / step, 3 degrees / min.
In the X-ray diffraction spectrum obtained under the above conditions, the crystallite size of each diffraction plane is calculated from the diffraction line widths (half widths) of the (110) plane and (107) plane of hexagonal ferrite using the Scherrer equation. calculate. The Scherrer equation is the following equation.
<Scherrer formula>
Crystallite size (Å) = K × λ / (β × cos θ)
K: Scherrer constant λ: wavelength of X-ray tube used [使用]
β: diffraction line width (half-value width) [radian]
θ: Diffraction angle 2θ / θ [radian]
Using the Scherrer equation, the crystallite size D _{x (110)} obtained from the diffraction peak on the (110) plane and the crystallite size D _{x (107)} obtained from the diffraction peak on the (107) plane are calculated. In the Scherrer equation, the crystallite size is calculated in units of Å, so a value obtained by converting the calculated value into the unit nm is adopted. 1Å = 0.1 nm.

Among the diffractive surfaces, the (107) plane is located near the easy magnetization axis direction (c-axis direction). Therefore, the crystallite size D _{x (107)} obtained from the diffraction peak of the (107) plane is a crystal in the easy axis direction (c-axis direction) obtained by X-ray diffraction analysis of the crystallite of the ferromagnetic hexagonal ferrite powder. Can be considered a child size. That is, it can be regarded as the thickness of the crystallite obtained by X-ray diffraction analysis when the shape is plate-like, the short axis length when it is elliptical, and the diameter when it is spherical.
The (110) plane is located in a direction orthogonal to the easy axis direction. Therefore, the crystallite size D _{x (110)} obtained from the diffraction peak of the (110) plane is the plate diameter of the crystallite obtained by X-ray diffraction analysis when the shape is plate-like, or when the shape is elliptical. In the case of a long axis length or a spherical shape, it can be regarded as a diameter.
For the plate shape, the crystallite shape is regarded as a regular hexagonal column, and the crystallite volume obtained by X-ray diffraction analysis is based on the formula for the regular hexagonal column volume,
Crystallite volume (nm ³ ) = (3√3 × D _{x (110)} ² × D _{x (107)} ) / 8
I will ask.
On the other hand, for ellipsoids and spheres, the crystallite volume determined by X-ray diffraction analysis is based on the calculation formula for the volume of the ellipsoid and sphere.
Crystallite volume (nm ³ ) = (πD _{x (110)} ² × D _{x (107)} ) / 6
I will ask.
For irregular shapes, as well as elliptical and spherical shapes,
Crystallite volume (nm ³ ) = (πD _{x (110)} ² × D _{x (107)} ) / 6
Suppose that the crystallite volume calculated | required by X-ray diffraction analysis is calculated | required.

With regard to ΔSFD described above and various values obtained by easy magnetization axis direction particle size D _TEM and X-ray diffraction analysis obtained by observation with a transmission electron microscope, the present inventors have conducted intensive studies and newly added the following points. As a result, the magnetic tape according to one embodiment of the present invention was completed. However, the following includes inferences by the present inventors. The present invention is not limited to such inference.

As a ferromagnetic powder, a magnetic tape containing a ferromagnetic hexagonal ferrite powder having a crystallite volume in the range of 1000 to 2400 nm ^{3 in} a magnetic layer can exhibit good electromagnetic conversion characteristics (SNR). This is presumed to be because noise can be reduced as described above.

Furthermore, regarding the increase in the coefficient of friction after storage in a high-temperature and high-humidity environment, the present inventor believes that it is difficult to supply the lubricant from the nonmagnetic layer to the magnetic layer by storing in such an environment. Are thinking. This point will be further explained. In a magnetic tape having a multilayer structure having a nonmagnetic layer between a nonmagnetic support and a magnetic layer, the nonmagnetic layer functions as a tank for supplying a lubricant to the magnetic layer. It is said that you can. However, the present inventors consider that the storage in a high temperature and high humidity environment makes it difficult for the lubricant to be supplied (difficult to migrate) from the nonmagnetic layer to the magnetic layer, although the reason is not clear. Since the lubricant can exert the effect of reducing the coefficient of friction by being present in the magnetic layer, insufficient supply of the lubricant from the nonmagnetic layer to the magnetic layer may be caused after storage in a high temperature and high humidity environment. The present inventors presume that the cause of the increase in the friction coefficient.
In view of this, the present inventors considered that the decrease in the amount of fatty acid ester supplied from the nonmagnetic layer to the magnetic layer due to storage in a high-temperature and high-humidity environment can be compensated by promoting the supply of fatty acid ester from the inside of the magnetic layer to the surface of the magnetic layer. Repeated examination. The reason for focusing on fatty acid esters among various lubricants is that fatty acid esters are said to be components that can contribute to the reduction of the friction coefficient by forming a liquid film on the surface of the magnetic layer. This point will be further described later. As a result of intensive studies, the present inventors have reached D _{x (107)} / D _TEM and ΔSFD within the ranges described above. Hereinafter, this point will be further described.

Regarding the ratio of the above-mentioned D _{x (107)} to the easy magnetization axial particle size D _TEM obtained by observation with a transmission electron microscope, D _{x (107)} / D _TEM , the present inventors I guess.
The present inventors consider that D _{x (107)} becomes a smaller value as the crystal structure of hexagonal ferrite is more strained. On the other hand, it is considered that the influence of the distortion of the crystal structure does not appear in the _DTEM that is the size measured by the transmission electron microscope, that is, the physical size. Therefore, the inventors speculate that the greater the ratio of D _{x (107)} to D _TEM , the less the strain in the hexagonal ferrite crystal structure. The present inventors consider that the ferromagnetic hexagonal ferrite powder with less strain in the crystal structure is less likely to adsorb the fatty acid ester as D _{x (107)} / D _TEM shows a value of 1.1 or more. This makes it possible to form a fatty acid ester liquid film on the surface of the magnetic layer without inhibiting the fatty acid ester from moving from the inside of the magnetic layer to the surface of the magnetic layer. The present inventors speculate that it contributes to the suppression of the increase in the coefficient of friction after storage.

  Further, the inventors of the present invention have an influence on the migration amount of the fatty acid ester from the inside of the magnetic layer to the magnetic layer surface with respect to the migration of the fatty acid ester to the surface of the magnetic layer. I guess. Specifically, the present inventors have found that the more the hexagonal ferrite powder in the magnetic layer is aligned in the longitudinal direction, the easier the fatty acid ester migrates from the inside of the magnetic layer to the surface of the magnetic layer, and the ferromagnetic hexagonal ferrite powder in the longitudinal direction. It is thought that the fatty acid ester is prevented from migrating from the inside of the magnetic layer to the surface of the magnetic layer as the arrangement of is random. In this regard, according to the study by the present inventors, the ΔSFD increases as the arrangement of the ferromagnetic hexagonal ferrite powder in the longitudinal direction of the magnetic tape becomes random, and the ferromagnetic hexagonal ferrite powder increases in the longitudinal direction of the magnetic tape. The ΔSFD tended to be smaller as the lines were aligned. Therefore, the inventors of the present invention decrease the amount of fatty acid ester transferred from the inside of the magnetic layer to the surface of the magnetic layer as the ΔSFD increases, and increase the amount of transfer of the fatty acid ester from the inside of the magnetic layer to the surface of the magnetic layer as the ΔSFD decreases. I think so. Then, the present inventors supply a fatty acid ester in an amount sufficient to suppress an increase in the coefficient of friction after storage to the magnetic layer surface from the inside of the magnetic layer in the magnetic layer having the above ΔSFD in the range of 0.50 to 1.60. It is presumed that ferromagnetic hexagonal ferrite powder exists in a state where it can be produced. The present inventors believe that this also contributes to the formation of a fatty acid ester liquid film on the surface of the magnetic layer, which is sufficient to suppress an increase in the coefficient of friction after storage in a high temperature and high humidity environment.

  As described above, the present inventors compensate for the decrease in the supply amount of fatty acid ester from the nonmagnetic layer to the magnetic layer due to storage in a high temperature and high humidity environment by promoting the supply of fatty acid ester from the inside of the magnetic layer to the surface of the magnetic layer. Therefore, it is considered that an increase in the coefficient of friction after storage in a high-temperature and high-humidity environment can be suppressed. However, the above is an inference by the present inventors and does not limit the present invention.

In one embodiment, D _{x (107)} / D _TEM of the ferromagnetic hexagonal ferrite powder is in the range of 1.1 to 1.5.

^3. The magnetic tape according to claim 1, wherein a crystallite volume obtained by X-ray diffraction analysis of the ferromagnetic hexagonal ferrite powder is in a range of 1000 to 1500 nm ³ .

  In one embodiment, the ΔSFD is in the range of 0.50 to 1.00.

A further aspect of the present invention is a method for producing the above magnetic tape,
Preparing a magnetic layer forming composition;
Applying the prepared composition for forming a magnetic layer onto a nonmagnetic layer formed on a nonmagnetic support;
Forming a magnetic layer via
The step of preparing the composition for forming a magnetic layer includes
A first step of obtaining a dispersion by dispersing the ferromagnetic hexagonal ferrite powder, the binder and the solvent in the presence of the first dispersed beads;
A second stage of dispersing the dispersion obtained in the first stage in the presence of a second dispersed bead having a smaller bead diameter and density than the first dispersed beads;
Manufacturing method including,
About. If the dispersion containing the ferromagnetic hexagonal ferrite powder is dispersed through the two-stage dispersion treatment as described above, it is possible to suppress the occurrence of distortion in the crystal structure of the ferromagnetic hexagonal ferrite powder. The inventors speculate. More specifically, by using beads having a smaller bead diameter and density than the first dispersed beads as the second dispersed beads, the energy applied to the particles of the ferromagnetic hexagonal ferrite powder in the dispersion treatment is reduced. The present inventors consider that it contributes to suppression of this. However, this is merely a guess and does not limit the present invention. Moreover, the magnetic tape concerning 1 aspect of this invention is not limited to what is manufactured by the said manufacturing method.

  In one embodiment, the second stage is performed on a mass basis in the presence of the second dispersed beads in an amount greater than 10 times the ferromagnetic hexagonal ferrite powder.

  In one embodiment, the bead diameter of the second dispersed beads is 1/100 or less of the bead diameter of the first dispersed beads.

  In one aspect, the bead diameter of the second dispersed beads is in the range of 80-1000 nm.

In one aspect, the density of the second dispersed beads is no greater than 3.7 g / cm ³ .

  In one aspect, the second dispersed bead is a diamond bead.

In one aspect, the first step comprises the following formula 2:
ΔSFD _powder = SFD _{powder 100 ° C.} −SFD _{powder 25 ° C.} Equation 2
A step of obtaining a dispersion by dispersing a ferromagnetic hexagonal ferrite powder having a ΔSFD _powder calculated in the range of 0.05 to 1.90, a binder and a solvent in the presence of the first dispersion beads. It is. In Equation 2, SFD _powder 100 ° _C. is a reversal magnetic field distribution SFD of the ferromagnetic hexagonal ferrite powder measured in an environment at a temperature of 100 ° C., and SFD powder 25 ° _C. is a ferromagnetic material measured in an environment at a temperature of 25 ° C. It is a reversal magnetic field distribution SFD of hexagonal ferrite powder.

  According to one aspect of the present invention, a magnetic tape that can exhibit excellent electromagnetic conversion characteristics, and that suppresses an increase in friction coefficient when running in a drive after being stored in a high-temperature and high-humidity environment, And a method for producing such a magnetic tape.

[Magnetic tape]
A magnetic tape according to one embodiment of the present invention has a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and has a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer. A magnetic tape comprising a fatty acid ester at least in a magnetic layer, wherein the ferromagnetic powder is a ferromagnetic hexagonal ferrite powder, and the ferromagnetic hexagonal ferrite powder has a crystallite volume of 1000 determined by X-ray diffraction analysis. Is in the range of ˜2400 nm ³ and the above D _{x (107)} / D _TEM is 1.1 or more, and ΔSFD calculated by the above formula 1 in the longitudinal direction of the magnetic tape is 0.50 to 1.60. A magnetic tape that is in range.
Hereinafter, the magnetic tape will be described in more detail. Unless otherwise specified, the magnetic characteristics without a specified measurement temperature are values measured in an environment at a temperature of 25 ° C.

<Crystal volume determined by X-ray diffraction analysis>
Method for measuring crystallite volume (hereinafter also referred to as “V _XRD ”) obtained by X-ray diffraction analysis (XRD; X-ray diffraction) of ferromagnetic hexagonal ferrite powder contained in the magnetic layer of the magnetic tape. Is as described above. The present inventors believe that the V _XRD of the ferromagnetic hexagonal ferrite powder contained in the magnetic layer being 2400 nm ³ or less contributes to an improvement in SNR due to noise reduction. Further, as a result of the study by the present inventors, it was confirmed that V _XRD of 1000 nm ³ or more also contributes to obtaining a good SNR. Accordingly, the V _XRD of the ferromagnetic hexagonal ferrite powder contained in the magnetic layer of the magnetic tape is in the range of 1000 to 2400 nm ³ . From the viewpoint of further improvement of the _{SNR, V XRD} is preferably in the range of 1000 - 2000 nm ^3, more preferably in the range of 1000～1700Nm ^3, more preferably in the range of 1000～1500Nm ³ . V _XRD can be adjusted by the size of the ferromagnetic hexagonal ferrite powder used in the composition for forming a magnetic layer, the dispersion conditions when preparing the composition for forming a magnetic layer, and the like. V _XRD tends to decrease as the dispersion condition is strengthened.

< _{Dx (107)} / D _TEM >
The measuring method of _{Dx (107)} and _DTEM is as described above. The Dx ₍₁₀₇₎ / D _TEM of the ferromagnetic hexagonal ferrite powder contained in the magnetic layer of the magnetic tape is 1.1 or more. If D _{x (107)} / D _TEM is 1.1 or more, this contributes to suppressing an increase in the coefficient of friction when the magnetic tape is stored in a high-temperature and high-humidity environment and then driven in a drive. The inventors are thinking. The inference by the present inventors regarding this point is as described above. D _{x (107)} / D _TEM is preferably 1.1 or more, more preferably 1.2 or more, and further preferably 1.3 or more. Further, D _{x (107)} / D _TEM is, for example, 1.1 or more and 1.5 or less, but as described above, D _{x (107)} / D _TEM is larger as the distortion in the crystal structure of hexagonal ferrite is smaller. Since it becomes a value and is considered preferable, it may exceed 1.5. For example, D _{x (107)} / D _TEM may be 1.1 or more and 1.7 or less, or 1.1 or more and 1.6 or less.

The _DTEM can be adjusted by the size of the ferromagnetic hexagonal ferrite powder used in the magnetic layer forming composition, the dispersion conditions when preparing the magnetic layer forming composition, and the like. Enough to enhance the dispersion _{conditions, D TEM} tends to decrease.

On the other hand, the present inventors consider that D _{x (107)} becomes smaller due to the influence of the distortion of the crystal structure of hexagonal ferrite as described above. Therefore, in order to adjust D _{x (107)} , it is preferable to control the dispersion conditions during preparation of the magnetic layer forming composition so as to suppress the generation of strain. This point will be further described later. In addition, D _{x (107)} and D _{x (110)} should be adjusted according to the size of the ferromagnetic hexagonal ferrite powder used in the magnetic layer forming composition, the dispersion conditions when preparing the magnetic layer forming composition, and the like. Can do. For example, D _{x (107)} and D _{x (110)} tend to decrease as the dispersion time increases.

Respect the described _{D TEM, D x (107)} , D x (110) _{above, D TEM may, D x (107) / unless D TEM} is equal to or greater than 1.1, the number is not limited in particular . As long as D _{x (107)} becomes D _{x (107)} / D _TEM 1.1 or more and V _XRD calculated using this value and D _{x (110)} is within the above-mentioned range, The numerical value is not particularly limited. The value of D _{x (110)} is not particularly limited as long as V _XRD calculated using this value and D _{x (107)} falls within the above-described range. As an example, for example, D _TEM has a range of 1.0 to 10.0 nm, D _{x ( 107)} has a range of 1.0 to 15.0 nm, and D _{x (110)} has a range of 10.0 to 30.0 nm. it can. However, as described above, it is not limited to these ranges.

<ΔSFD calculated by Formula 1>
ΔSFD calculated by Equation 1 in the longitudinal direction of the magnetic tape is in the range of 0.50 to 1.60. It is considered that ΔSFD being 1.60 or less contributes to the formation of a fatty acid ester liquid film on the surface of the magnetic layer that is sufficient to suppress an increase in the friction coefficient. Moreover, it is guessed that it is contributed to friction coefficient raise suppression that said (DELTA) SFD is 0.50 or more. This is because the smaller the ΔSFD value, the more fatty acid ester is formed on the surface of the magnetic layer, but the presence of an excessive amount of fatty acid ester may also cause an increase in the coefficient of friction. . From this point, the ΔSFD is 0.50 or more. The ΔSFD is preferably 1.55 or less, more preferably 1.50 or less, still more preferably 1.40 or less, from the viewpoint of further suppressing an increase in the friction coefficient. It is more preferably 20 or less, even more preferably 1.00 or less, and even more preferably 0.90 or less. Further, from the same viewpoint, the ΔSFD is preferably 0.55 or more, more preferably 0.60 or more, and further preferably 0.70 or more. In a preferred embodiment, ΔSFD is in the range of 0.50 to 1.40, and in a more preferred embodiment, ΔSFD is in the range of 0.50 to 1.00.

ΔSFD is a value indicating the temperature dependence of the reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape. The smaller the value, the smaller the change in SFD due to temperature, and the larger the value, the greater the change in SFD due to temperature. Means. The present inventors have found that the above-mentioned magnetic tape has a high temperature and high humidity environment that ΔSFD calculated by Equation 1 showing the difference between SFD _{25 ° C.} and SFD _{−190 ° C.} is in the range of 0.50 to 1.60. The present inventors consider that it contributes to suppressing an increase in the coefficient of friction when the vehicle is stored in the drive after being stored below. The inference by the present inventors regarding this point is as described above. According to the study by the present inventors, ΔSFD calculated by Equation 1 can be controlled by the magnetic tape preparation method, and the following tendencies were mainly observed:
(A) The value decreases with increasing dispersibility of the ferromagnetic powder in the magnetic layer;
(B) The value decreases as the ferromagnetic powder having a smaller temperature dependence of SFD is used;
(C) The value decreases as the ferromagnetic powder is aligned in the longitudinal direction of the magnetic layer (as the orientation in the longitudinal direction increases), and the value increases as the orientation in the longitudinal direction decreases.

  For example, with respect to (A), strengthening of dispersion conditions (elongation of dispersion time, reduction in diameter and increase of the diameter of dispersion beads used for dispersion, etc.), use of a dispersant, and the like can be mentioned. As the dispersant, known dispersants, commercially available dispersants and the like can be used without any limitation.

On the other hand, with regard to (B), for example, as an example, the SFD of the ferromagnetic powder calculated by the following formula 2 and measured in an environment at a temperature of 100 ° C. and SFD measured in an environment at a temperature of 25 ° C. A ferromagnetic _powder having a difference ΔSFD _powder of preferably 0.05 to 1.90, more preferably 0.05 to 1.80, and still more preferably 0.50 to 1.80 is used. it can. However, even if out of the above range, ΔSFD calculated by Equation 1 of the magnetic tape can be controlled to a range of 0.50 or more by other control.
ΔSFD _powder = SFD _{powder 100 ° C.} −SFD _{powder 25 ° C.} Equation 2
(In Formula 2, SFD _powder 100 ° _C. is a reversal magnetic field distribution SFD of a ferromagnetic powder measured in an environment at a temperature of 100 ° C., and SFD powder 25 ° _C. is a ferromagnetic powder measured in an environment at a temperature of 25 ° C. (Reversed magnetic field distribution SFD.)

  With respect to (C), a method of making the orientation treatment of the magnetic layer a vertical orientation or a method of making the orientation non-orientation without performing the orientation treatment can be employed.

  Therefore, for example, by controlling one of the above means (A) to (C) or arbitrarily combining two or more thereof, ΔSFD calculated by Equation 1 is in the range of 0.50 to 1.60. Tape can be obtained.

<Lubricant>
In general, fatty acids and fatty acid derivatives such as fatty acid esters and fatty acid amides are widely used as lubricants in magnetic tapes. With respect to the lubricant, the lubricant is generally roughly classified into a fluid lubricant and a boundary lubricant. Fatty acid esters are said to be components that can function as fluid lubricants, whereas fatty acids and fatty acid amides are said to be components that can function as boundary lubricants. The fluid lubricant is considered to be a lubricant that itself forms a liquid film on the surface of the magnetic layer and can reduce friction by the flow of the liquid film. On the other hand, the boundary lubricant is considered to be a lubricant that can lower the contact friction by adsorbing to the surface of a powder (for example, ferromagnetic powder) and forming a strong lubricant film. Thus, fatty acid esters are considered to be different in action as a lubricant from fatty acids and fatty acid amides. And as described in detail above, the present inventors have formed a liquid film on the surface of the magnetic layer that is sufficient to suppress an increase in the coefficient of friction after storage in a high-temperature and high-humidity environment. It is inferred that D _{x (107)} / D _TEM and ΔSFD are within the ranges described above.

  Examples of fatty acid esters include esters such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, elaidic acid, such as butyl myristate, butyl palmitate, Butyl stearate (butyl stearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate Amyl stearate, butoxyethyl stearate, and the like. The amount of the fatty acid ester is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the ferromagnetic hexagonal ferrite powder, as the content in the composition for forming a magnetic layer. Part. In addition, when adding 2 or more types of different fatty acid ester to the composition for magnetic layer formation, content shall mean those total content. In the present invention and the present specification, the same applies to the contents of other components unless otherwise specified. Moreover, a nonmagnetic layer can be formed using the composition containing fatty acid ester as a composition for nonmagnetic layer formation, and it is preferable to form in that way. The fatty acid ester content in the composition for forming a nonmagnetic layer is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. The lubricant such as fatty acid ester contained in the composition for forming a nonmagnetic layer can move from the nonmagnetic layer to the magnetic layer during or after the production of the magnetic tape. The amount of lubricant contained and the amount of lubricant contained in the nonmagnetic layer of the magnetic tape are not necessarily the same. As for the magnetic layer, since the lubricant can be transferred from the nonmagnetic layer to the magnetic layer, the amount of lubricant contained in the magnetic layer forming composition and the amount of lubricant contained in the magnetic layer of the magnetic tape Are not necessarily the same.

  The magnetic layer may contain a fatty acid and / or a fatty acid amide. Examples of the fatty acid include the above-mentioned various fatty acids, stearic acid, myristic acid, and palmitic acid are preferable, and stearic acid is more preferable. The fatty acid may be contained in the magnetic layer in the form of a salt such as a metal salt. Examples of fatty acid amides include the amides of various fatty acids described above, such as lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, and the like. Regarding fatty acid and fatty acid derivatives (esters, amides, etc.), the fatty acid-derived site of the fatty acid derivative preferably has the same or similar structure as the fatty acid used in combination. For example, as an example, when stearic acid is used as the fatty acid, it is preferable to use stearic acid ester and / or stearic acid amide.

  The amount of the fatty acid is, for example, 0.1 to 10.0 parts by mass, preferably 1.0 to 7.0 parts per 100.0 parts by mass of the ferromagnetic hexagonal ferrite powder as the content in the composition for forming a magnetic layer. Part by mass. Moreover, the fatty acid amide content in the composition for forming a magnetic layer is, for example, 0.1 to 3.0 parts by mass, preferably 0.1 to 1. parts by mass per 100.0 parts by mass of the ferromagnetic hexagonal ferrite powder. 0 parts by mass.

  On the other hand, the fatty acid content in the composition for forming a nonmagnetic layer is, for example, 1.0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. It is. The fatty acid amide content in the composition for forming a nonmagnetic layer is, for example, 0.1 to 3.0 parts by weight, preferably 0.1 to 1.0 parts by weight, per 100.0 parts by weight of the nonmagnetic powder. Part.

<Magnetic layer>
Next, the magnetic layer will be described in more detail.

(Ferromagnetic hexagonal ferrite powder)
The ferromagnetic hexagonal ferrite powder V _XRD and D _{x (107)} / D _TEM are as described above. The hexagonal ferrite composing the ferromagnetic hexagonal ferrite powder can be barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, a mixed crystal of two or more of these. For example, magnetoplumbite type (M type) barium ferrite and strontium ferrite, magnetoplumbite type ferrite whose particle surface is coated with spinel, and composite magnetoplumbite type barium partially containing a spinel phase. Examples thereof include ferrite and strontium ferrite.

The ferromagnetic hexagonal ferrite powder (raw material powder) used in the composition for forming a magnetic layer may have an activation volume, which is one of particle size indexes, in the range of, for example, 800 to 4000 nm ³ . The activation volume is a value determined by the method shown in the examples described later. For details of the ferromagnetic hexagonal ferrite powder, paragraphs 0134 to 0136 of JP2011-216149A can also be referred to, for example. In one embodiment, it is also preferable to use a ferromagnetic hexagonal ferrite powder having the above-mentioned ΔSFD _powder in the range described above as the raw material powder.

In one embodiment, the average particle size of the ferromagnetic hexagonal ferrite powder contained in the magnetic layer can be in the range of 8-50 nm, preferably in the range of 8-30 nm. The average particle size of the ferromagnetic hexagonal ferrite powder is measured by tracing the outline of the particle (primary particle) as described above in the particle photograph taken for specifying the particle shape described above. To do. The particle size here is the plate diameter for plate-like particles, the long axis length for elliptical particles, the diameter for spherical particles, and the equivalent circle diameter for indeterminate shapes. The equivalent circle diameter is as described above. And let the arithmetic mean of the particle size of 500 particles obtained about 500 particles extracted at random be an average particle size. The average particle size is a value obtained by observation with a transmission electron microscope without subjecting the powder to be imaged to orientation treatment, and therefore does not necessarily match the above-mentioned _DTEM value.
In addition, unless otherwise indicated, let the average particle size regarding the various powder as described in this invention and this specification be the value measured by the said method.

  The content (filling ratio) of the ferromagnetic powder (ferromagnetic hexagonal ferrite powder) in the magnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%. A high filling factor is preferable from the viewpoint of improving the recording density.

(Binder, curing agent)
The magnetic tape includes a binder in the magnetic layer together with the ferromagnetic hexagonal ferrite powder. As binder, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl butyral A single or a plurality of resins can be used in combination such as a polyvinyl alkyl resin such as the above. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin. These resins can also be used as a binder in the nonmagnetic layer and the backcoat layer described later. JP, 2010-24113, A paragraphs 0028-0031 can be referred to for the above binder. Moreover, a hardening | curing agent can also be used with resin which can be used as the said binder. A polyisocyanate is suitable as the curing agent. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the composition for forming a magnetic layer, and preferably 50.0 to 80.0 masses from the viewpoint of improving the coating film strength. It can be added and used in parts.

(Additive)
The magnetic layer includes at least a fatty acid ester as an additive, and may further include a fatty acid and / or a fatty acid amide as described above. Furthermore, additives other than these lubricants can be added as necessary. Examples of the additive include a nonmagnetic filler, a dispersant / dispersion aid, an antifungal agent, an antistatic agent, an antioxidant, and carbon black. The nonmagnetic filler is synonymous with nonmagnetic powder. As the nonmagnetic filler, a nonmagnetic filler that can function as an abrasive, a nonmagnetic filler that can function as a protrusion forming agent that forms protrusions that protrude moderately on the surface of the magnetic layer (for example, nonmagnetic colloidal particles, etc.) Is mentioned. As a preferred example of nonmagnetic colloidal particles, silica colloidal particles (colloidal silica) can be exemplified. The colloidal particles in the present invention and the present specification are added at least 1 g per 100 mL of at least one organic solvent of methyl ethyl ketone, cyclohexanone, toluene or ethyl acetate, or a mixed solvent containing two or more of the above solvents in an arbitrary mixing ratio. In this case, the particles that can be dispersed without being settled to give a colloidal dispersion. For colloidal particles, the average particle size is a value determined by the method described in paragraph 0015 of JP2011-048878A as an average particle size measurement method. On the other hand, examples of the dispersant include known dispersants such as a carboxy group-containing compound and a nitrogen-containing compound. For example, the nitrogen-containing compound may be any of a primary amine represented by NH ₂ R, a secondary amine represented by NHR ₂ , and a tertiary amine represented by NR ₃ . In the above, R represents an arbitrary structure constituting the nitrogen-containing compound, and a plurality of R may be the same or different. The nitrogen-containing compound may be a compound (polymer) having a plurality of repeating structures in the molecule. The present inventors consider that the nitrogen-containing part of the nitrogen-containing compound functions as an adsorbing part to the particle surface of the ferromagnetic hexagonal ferrite powder is the reason why the nitrogen-containing compound can act as a dispersant. . Examples of the carboxy group-containing compound include fatty acids such as oleic acid. Regarding the carboxy group-containing compound, the present inventors consider that the carboxy group functions as an adsorbing part on the particle surface of the ferromagnetic hexagonal ferrite powder, and that the carboxy group-containing compound can function as a dispersant. Yes. It is also preferable to use a carboxy group-containing compound and a nitrogen-containing compound in combination.
As the additive, commercially available products can be appropriately selected and used according to desired properties.

  The magnetic layer described above is provided on the nonmagnetic support via the nonmagnetic layer. Details of the nonmagnetic layer and the nonmagnetic support will be described later.

<Nonmagnetic layer>
The magnetic tape has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder used for the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. The details can be referred to paragraphs 0146 to 0150 of JP2011-216149A. JP, 2010-24113, A paragraphs 0040-0041 can also be referred to about carbon black which can be used for a nonmagnetic layer. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%.

  For other details such as binders and additives for the nonmagnetic layer, known techniques relating to the nonmagnetic layer can be applied. For example, with respect to the amount and type of the binder and the amount and type of the additive, known techniques relating to the magnetic layer can also be applied.

  The nonmagnetic layer in the present invention and the present specification includes a substantially nonmagnetic layer containing a small amount of ferromagnetic powder together with the nonmagnetic powder, for example, as impurities or intentionally. . Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. And a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably has no residual magnetic flux density and coercive force.

<Back coat layer>
The magnetic tape may have a backcoat layer containing a nonmagnetic powder and a binder on the side of the nonmagnetic support opposite to the side having the magnetic layer and the nonmagnetic layer. The back coat layer preferably contains one or both of carbon black and inorganic powder. For the binder contained in the backcoat layer and various additives that can optionally be contained, known techniques relating to the formulation of the magnetic layer and / or the nonmagnetic layer can be applied.

<Non-magnetic support>
Next, the nonmagnetic support will be described. Examples of the nonmagnetic support include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like.

<Thickness of nonmagnetic support, magnetic layer, nonmagnetic layer, and backcoat layer>
Regarding the thickness of the nonmagnetic support and each layer in the magnetic tape, the thickness of the nonmagnetic support is, for example, 3.0 to 80.0 μm, preferably 3.0 to 50.0 μm, and more preferably. Is in the range of 3.0-10.0 μm.

  The thickness of the magnetic layer can be optimized by the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used. The thickness of the magnetic layer is generally 10 nm to 100 nm, preferably 20 to 90 nm, more preferably 30 to 70 nm from the viewpoint of high density recording. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

  The thickness of the nonmagnetic layer is, for example, 50 nm or more, preferably 70 nm or more, and more preferably 100 nm or more. On the other hand, the thickness of the nonmagnetic layer is preferably 800 nm or less, and more preferably 500 nm or less.

  The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably in the range of 0.1 to 0.7 μm.

  The thickness of each layer of the magnetic tape and the nonmagnetic support can be determined by a known film thickness measurement method. As an example, for example, after a cross section in the thickness direction of the magnetic tape is exposed by a known method such as an ion beam or a microtome, the exposed cross section is observed with a scanning electron microscope. Various thicknesses can be obtained as an arithmetic average of thicknesses obtained at one location in the thickness direction in cross-sectional observation, or at two or more locations randomly extracted, for example, at two locations. Alternatively, the thickness of each layer may be obtained as a design thickness calculated from manufacturing conditions.

<Manufacturing process>
(Preparation of each layer forming composition)
The step of preparing a composition for forming a magnetic layer, a nonmagnetic layer, or a backcoat layer usually includes at least a kneading step, a dispersing step, and a mixing step provided before and after these steps. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powders, binders, nonmagnetic powders, various additives and solvents used for the preparation of each layer forming composition may be added at the beginning or middle of any step. As a solvent, 1 type, or 2 or more types of the various solvents normally used for manufacture of a coating type magnetic tape can be used. JP, 2011-216149, A paragraph 0153 can be referred to for a solvent. In addition, individual raw materials may be added in two or more steps. For example, the binder may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In the manufacturing process of the magnetic tape, a conventional known manufacturing technique can be used as a part of the process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. A well-known thing can be used for a disperser.

Regarding the dispersion treatment of the magnetic layer forming composition, as described above, it is possible to suppress the occurrence of distortion in the crystal structure of the ferromagnetic hexagonal ferrite powder by dispersing through the two-stage dispersion treatment. The present inventors have inferred. A preferable manufacturing method from this point is a manufacturing method of the magnetic tape,
Preparing a magnetic layer forming composition;
Applying the prepared magnetic layer forming composition onto a nonmagnetic layer formed on a nonmagnetic support;
Forming a magnetic layer via
The step of preparing the composition for forming a magnetic layer includes:
A first step of obtaining a dispersion by dispersing the ferromagnetic hexagonal ferrite powder, the binder and the solvent in the presence of the first dispersed beads;
A second stage of dispersing the dispersion obtained in the first stage in the presence of a second dispersed bead having a smaller bead diameter and density than the first dispersed beads;
Manufacturing method including,
It is.

  It is preferable to break up coarse agglomerates of ferromagnetic hexagonal ferrite powder in the first stage and perform the second stage as a subsequent dispersion. In order to increase the dispersibility of the ferromagnetic hexagonal ferrite powder, the first and second steps described above should be performed as a dispersion treatment prior to mixing the ferromagnetic hexagonal ferrite powder with other powder components. Is preferred. For example, when forming a magnetic layer containing the above-mentioned non-magnetic filler (abrasive, projection forming agent), before mixing with the non-magnetic filler, ferromagnetic hexagonal ferrite powder, binder, solvent and optionally added. As the dispersion treatment of the liquid containing the additive (magnetic liquid), it is preferable to perform the first stage and the second stage.

The bead diameter of the second dispersed beads is preferably 1/100 or less, more preferably 1/500 or less of the bead diameter of the first dispersed beads. The bead diameter of the second dispersed beads is, for example, 1 / 10,000 or more of the bead diameter of the first dispersed beads, but is not limited to this range. For example, the bead diameter of the second dispersed beads is preferably in the range of 80 to 1000 nm. On the other hand, the bead diameter of the first dispersed beads can be in the range of 0.2 to 1.0 mm, for example.
In the present invention and the present specification, the bead diameter is a value measured by a method similar to the method for measuring the average particle size of the powder described above.

The second stage is preferably performed under the condition that the second dispersed beads are present in an amount of 10 times or more of the ferromagnetic hexagonal ferrite powder on a mass basis, and in an amount of 10 to 30 times. More preferably, it is carried out under existing conditions.
On the other hand, the amount of the first dispersed beads in the first stage is also preferably in the above range.

The second dispersed beads are beads having a lower density than the first dispersed beads. Here, the density is obtained by dividing the mass (unit: g) of the dispersed beads by the volume (unit: cm ³ ). The measurement is performed by the Archimedes method. The density of the second dispersed beads is preferably 3.7 g / cm ³ , more preferably 3.5 g / cm ³ or less. Preferred second dispersed beads in terms of density include diamond beads, silicon carbide beads, silicon nitride beads, and the like. Preferred second dispersed beads in terms of density and hardness include diamond beads. Can do.
On the other hand, the first dispersion beads, preferably density is 3.7 g / cm ³ greater than the dispersion beads, density is 3.8 g / cm ³ or more dispersing beads more preferably, 4.0 g / cm ³ or more dispersion More preferred are beads. The density of the first dispersed beads is, for example, 7.0 g / cm ³ or less, but may be more than 7.0 g / cm ³ . As the first dispersed beads, zirconia beads, alumina beads or the like are preferably used, and zirconia beads are more preferably used.

The longer the dispersion time, for example, the longer the dispersion time in the second stage, the smaller V _XRD and D _{x (107)} tend to be. Further, the longer the dispersion time, the smaller the ΔSFD tends to be. The dispersion time is not particularly limited, and may be set according to the type of disperser used.

(Coating process)
The magnetic layer can be formed by applying the magnetic layer forming composition in layers or sequentially with the nonmagnetic layer forming composition. The backcoat layer can be formed by applying the backcoat layer to the side opposite to the side of the nonmagnetic support having the magnetic layer and the nonmagnetic layer (or these layers will be provided later). JP, 2010-231843, A paragraph 0066 can be referred to for the details of application for formation of each layer.

(Other processes)
JP, 2010-231843, A paragraphs 0067-0070 can be referred to for other various processes for magnetic tape manufacture.

  The magnetic tape described above can be run in a drive with a low coefficient of friction even after being stored in a high temperature and high humidity environment.

  Hereinafter, the present invention will be described based on examples. However, this invention is not limited to the aspect shown in the Example. In addition, unless otherwise indicated, the display of "part" described below and "%" shows "mass part" and "mass%".

The following activation volume is a value measured and calculated using a powder in the same powder lot as the ferromagnetic hexagonal ferrite powder used in the magnetic layer forming composition. The measurement is performed using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a magnetic field sweep speed of 3 minutes and 30 minutes of the coercive force Hc measurement section, and the relationship between Hc and activation volume V due to the following thermal fluctuations. The activation volume was calculated from the formula. The measurement was performed in an environment of 23 ° C. ± 1 ° C.
Hc = 2Ku / Ms {1-[(KuT / kV) ln (At / 0.693)] 1/2}
[In the above formula, Ku: anisotropy constant, Ms: saturation magnetization, k: Boltzmann constant, T: absolute temperature, V: activation volume, A: spin precession frequency, t: magnetic field inversion time]

The weight average molecular weight described below is a value in terms of polystyrene measured by gel permeation chromatography (GPC) under the following measurement conditions.
GPC device: HLC-8120 (manufactured by Tosoh Corporation):
Column: TSK gel Multipore HXL-M (Tosoh, 7.8 mm ID (inner diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

  The specific surface area is a value obtained by a nitrogen adsorption method (also called a BET (Brunauer-Emmett-Teller) one-point method), and is a value measured for primary particles. Below, the specific surface area calculated | required by this method is described as a BET specific surface area.

[Example 1]
The formulation of each layer forming composition is shown below.

<Prescription of composition for forming magnetic layer>
(Magnetic liquid)
Ferromagnetic hexagonal ferrite powder A (M-type barium ferrite, ΔSFD _powder : see Table 1, activation volume: see Table 1): 100.0 parts oleic acid: 2.0 parts vinyl chloride copolymer (MR manufactured by Nippon Zeon Co., Ltd.) -104): 10.0 parts SO ₃ Na group-containing polyurethane resin: 4.0 parts (weight average molecular weight 70000, SO ₃ Na group: 0.07 meq / g)
Amine-based polymer (DISPERBYK-102 manufactured by Big Chemie): 6.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (Abrasive liquid)
α-alumina (BET specific surface area 19 m ² / g): 6.0 parts SO ₃ Na group-containing polyurethane resin (weight average molecular weight 70000, SO ₃ Na groups: 0.1 meq / g): 0.6 parts 2,3- Dihydroxynaphthalene: 0.6 parts Cyclohexanone: 23.0 parts (projection forming agent solution)
Colloidal silica (average particle size 120 nm): 2.0 parts methyl ethyl ketone: 8.0 parts (lubricant / curing agent liquid)
Stearic acid: 3.0 parts Stearic acid amide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Japan Polyurethane Coronate (registered trademark) L): 3 .0 part

<Prescription of composition for forming nonmagnetic layer>
Non-magnetic inorganic powder α iron oxide (average particle size 10 nm, BET specific surface area 75 m ^{2 /} g): 100.0 parts carbon black (average particle size: 20 nm): 25.0 parts SO ₃ Na group-containing polyurethane resin (weight average) Molecular weight 70000, SO ₃ Na group content 0.2 meq / g): 18.0 parts Stearic acid: 1.0 parts Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

<Prescription of composition for forming backcoat layer>
Nonmagnetic inorganic powder: α-iron oxide (average particle size: 0.15 μm, BET specific surface area 52 m ^{2 /} g): 80.0 parts carbon black (average particle size: 20 nm): 20.0 parts vinyl chloride copolymer: 13.0 parts sulfonate group-containing polyurethane resin: 6.0 parts phenylphosphonic acid: 3.0 parts cyclohexanone: 155.0 parts methyl ethyl ketone: 155.0 parts stearic acid: 3.0 parts butyl stearate: 3.0 parts Polyisocyanate: 5.0 parts Cyclohexanone: 200.0 parts

<Preparation of magnetic layer forming composition>
A composition for forming a magnetic layer was prepared by the following method.
The various components of the magnetic liquid are dispersed for 24 hours using a zirconia bead (first dispersed beads, density 6.0 g / cm ³ ) having a bead diameter of 0.5 mmΦ by a batch type vertical sand mill, and then, 0.5 μφ. Dispersion A was prepared by filtering using a filter having an average pore size of 5 μm (first stage). The zirconia beads were used in an amount 10 times that of the ferromagnetic hexagonal barium ferrite powder on a mass basis.
After that, Dispersion A was dispersed for 1 hour using diamond beads (second dispersion beads, density 3.5 g / cm ³ ) with a bead diameter of 500 nmΦ by a batch type vertical sand mill, and the diamond beads were centrifuged using a centrifuge. A dispersion liquid (dispersion liquid B) was prepared (second stage). The following magnetic liquid is dispersion B thus obtained. The diamond beads were used in an amount 10 times that of the ferromagnetic hexagonal barium ferrite powder on a mass basis.
For the abrasive liquid, various components of the above-mentioned abrasive liquid are mixed and put into a horizontal bead mill disperser together with zirconia beads having a bead diameter of 0.3 mmΦ, and the bead volume / (abrasive liquid volume + bead volume) becomes 80%. Then, the bead mill dispersion treatment was performed for 120 minutes, the treated liquid was taken out, and the ultrasonic dispersion filtration treatment was performed using a flow type ultrasonic dispersion filtration apparatus. Thus, an abrasive liquid was prepared.
The prepared magnetic liquid and abrasive liquid, and the above-mentioned protrusion-forming agent liquid and lubricant / curing agent liquid are introduced into a dissolver stirrer, and stirred for 30 minutes at a peripheral speed of 10 m / sec. After three passes at 7.5 kg / min, the composition for forming a magnetic layer was prepared by filtering through a filter having a pore diameter of 1 μm.

<Preparation of nonmagnetic layer forming composition>
Various components of the above composition for forming a nonmagnetic layer are dispersed for 24 hours using a zirconia bead having a bead diameter of 0.1 mm by a batch type vertical sand mill, and then using a filter having an average pore diameter of 0.5 μm. The composition for nonmagnetic layer formation was prepared by filtering.

<Preparation of composition for forming backcoat layer>
Among the various components of the composition for forming a back coat layer, components excluding lubricant (stearic acid and butyl stearate), polyisocyanate and 200.0 parts of cyclohexanone were kneaded and diluted with an open kneader, and then dispersed in a horizontal bead mill. Using a zirconia bead with a bead diameter of 1 mmΦ by a machine, the bead filling rate was 80% by volume, the rotor tip peripheral speed was 10 m / sec. Thereafter, the above-mentioned remaining components were added and stirred with a dissolver, and the resulting dispersion was filtered using a filter having an average pore size of 1 μm to prepare a composition for forming a backcoat layer.

<Preparation of magnetic tape>
On the surface of a support made of polyethylene naphthalate having a thickness of 5.0 μm, the nonmagnetic layer-forming composition prepared above was applied and dried so that the thickness after drying was 100 nm. The magnetic layer forming composition prepared above was applied so that the thickness was 70 nm. While this composition for forming a magnetic layer was in an undried state, it was dried by applying a vertical alignment treatment in which a magnetic field having a magnetic field strength of 0.3 T was applied in a direction perpendicular to the coated surface. Thereafter, the backcoat layer-forming composition prepared above was applied to the opposite surface of the support so that the thickness after drying was 0.4 μm and dried. The obtained tape is calendered (surface smoothing treatment) at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a roll surface temperature of 100 ° C. with a calendar composed only of a metal roll, and then in an environment with an atmospheric temperature of 70 ° C. Heat treatment was performed for 36 hours. After the heat treatment, it was slit to a width of 1/2 inch (0.0127 meter) to obtain a magnetic tape.

[Examples 2 to 5, Comparative Examples 1 to 6]
In the magnetic liquid preparation, a ferromagnetic hexagonal barium ferrite powder (M-type barium ferrite) having the activation volume and ΔSFD _powder shown in Table 1 was used, and the second stage was performed under the conditions shown in Table 1 in the dispersion treatment of the magnetic liquid. A magnetic tape was produced in the same manner as in Example 1 except that the above was performed.

<Measurement method, evaluation method>
1. Observation of the shape of the ferromagnetic hexagonal ferrite powder, average particle size Examples, tape samples obtained by cutting out a part of the magnetic tape of the comparative example were immersed in ethanol after removing the backcoat layer using acetone, Sonic dispersed. Since the magnetic hexagonal ferrite powder was separated from the magnetic layer by swelling the magnetic layer with ethanol, the separated ferromagnetic hexagonal ferrite powder was recovered by filtration. Here, when the non-magnetic filler is also recovered together with the ferromagnetic hexagonal ferrite powder, the ferromagnetic hexagonal ferrite powder may be separated from the non-magnetic filler using a magnet.
The back coat layer can also be removed with a solvent other than acetone. The magnetic layer can be swollen by a solvent other than ethanol to separate the ferromagnetic hexagonal ferrite powder.
1 mg of the recovered ferromagnetic hexagonal ferrite powder (photographing target powder) was put into 5 ml of pure water and subjected to ultrasonic dispersion (28 kHz, 10 minutes) to prepare a dispersion. 5 μL of the prepared dispersion was dropped onto a grid mesh (mesh sample dish) and allowed to dry naturally (no alignment treatment). The powder to be photographed was introduced into a transmission electron microscope together with the grid mesh, photographed with a transmission electron microscope, a particle photograph was obtained, and the shape was observed. As a result, it was confirmed that the ferromagnetic hexagonal ferrite powders used in the examples and comparative examples had a plate shape.
Furthermore, when the average particle size (average plate diameter) was calculated | required by the method described previously using the image | photographed particle | grain photograph, it was the range of 10-30 nm in both the Example and the comparative example.

2. The direction of the easy magnetization axis particle size D _TEM obtained by transmission electron microscopy
Above 1. 1 mg of the ferromagnetic hexagonal ferrite powder recovered in (1) was put into 5 ml of pure water and subjected to ultrasonic dispersion (28 kHz, 10 minutes) to prepare a dispersion. 5 μL of the prepared dispersion was dropped onto a grid mesh (mesh-shaped sample plate) in which magnets (the magnetic force of each magnet was 1.5 T) on both sides (left and right) and dried naturally. In this way, the imaging target powder was subjected to an orientation treatment in the horizontal direction. The imaging target powder subjected to this orientation treatment was introduced into the transmission electron microscope together with the grid mesh, and D _TEM (average plate thickness) was determined by the method described above.

3. Crystallite volume V _XRD determined by X-ray diffraction analysis
The magnetic layer of the magnetic tapes of Examples and Comparative Examples was scraped off with a blade to obtain a test piece (powder state) for X-ray diffraction analysis.
Using about 0.03 g of the test piece, X-ray diffraction analysis was performed under the conditions described above. RINT2500 manufactured by Rigaku Corporation was used as the powder X-ray diffraction measurement apparatus. From the analysis results, D _{x (107)} and D _{x (110)} were calculated by the method described above. V _XRD was calculated from D _{x (107)} and D _{x (110)} using the previously described calculation formula.

4). ΔSFD _{powder of} ferromagnetic hexagonal ferrite _powder
The ΔSFD _powder defined by the above-mentioned formula 2 of the ferromagnetic hexagonal ferrite powder was measured with an applied magnetic field of 796 kA / m (10 kOe) using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

5). Measurement of ΔSFD in the longitudinal direction of the magnetic tape ΔSFD defined by the above-mentioned formula 1 in the longitudinal direction of the magnetic tape is measured with an applied magnetic field of 796 kA / m (10 kOe) using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). did.

6). Electromagnetic conversion characteristics (SNR)
In an environment of 23 ° C. ± 1 ° C., the recording head (MIG (Metal-in-Gap), gap length 0.15 μm, saturation magnetic flux density 1.8 T) and reproducing GMR for the magnetic tapes of Examples and Comparative Examples A (Giant Magnetoresistive) head (reproduction track width 1 μm) was attached to a loop tester to record a signal having a linear recording density of 200 kfci, and then SNR was measured. Table 1 shows the SNRs of the examples and the comparative examples as relative values in which the SNR of the comparative example 4 is 0 dB. If the SNR is +1.0 dB or more, preferably +1.5 dB or more, it can be evaluated that it has performance capable of meeting future severe needs accompanying high-density recording.

7). Measurement of Friction Coefficient after Storage under High Temperature and High Humidity Environment The magnetic tapes of Examples and Comparative Examples were each wound around a reel and stored in an environment of 60 ° C. and 90% relative humidity for 1 week. When the magnetic tape after storage was brought into contact with a SUS (Steel Use Stainless) 420 member at a temperature of 23 ° C. and a relative humidity of 50%, a running speed of 14 mm / sec. The 10th pass friction coefficient was measured by repeatedly running 10 passes. The measurement results are shown in Table 1. When the friction coefficient exceeded 0.80 during repeated running (> 0.80), the surface of the magnetic layer and the SUS420 member adhered to each other and could not be run thereafter. Such a comparative example is described as “> 0.80 (attached)” in Table 1.

  The above measurement results and evaluation results are shown in Table 1.

  From the results shown in Table 1, the magnetic tape of the example (magnetic tape having a multilayer structure) exhibits excellent electromagnetic conversion characteristics, and an increase in the coefficient of friction after storage in a high temperature and high humidity environment is suppressed. I can confirm that.

  The present invention is useful in the technical field of high-density magnetic recording media such as backup tapes.

Claims (11)

A nonmagnetic layer comprising a nonmagnetic powder and a binder on a nonmagnetic support;
A magnetic layer containing ferromagnetic powder and a binder on the nonmagnetic layer;
A magnetic tape having a backcoat layer containing a nonmagnetic powder and a binder on a side opposite to the side having the magnetic layer and the nonmagnetic layer of the nonmagnetic support,
Including at least a fatty acid ester in the magnetic layer;
The ferromagnetic powder is a ferromagnetic hexagonal ferrite powder,
The ferromagnetic hexagonal ferrite powder has a crystallite volume determined by X-ray diffraction analysis in the range of 1000 to 2400 nm ³ , and a crystallite size D _{x (107)} determined from the diffraction peak of the (107) plane and transmission. the ratio of the magnetization easy axis particle size _{D TEM} obtained by the type electron _{microscope, D x (107) / D} TEM, it is but 1.1 or more,
A magnetic tape in which ΔSFD calculated by the following formula 1 in the longitudinal direction of the magnetic tape is in the range of 0.50 to 1.60, and the thickness of the backcoat layer is 0.9 μm or less;
ΔSFD = SFD _{25 ° C.} −SFD _{−190 ° C.} Formula 1
In Equation 1, SFD _{25 ° C.} is a reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape under an environment of 25 ° C., and SFD _{−190 ° C.} is in the longitudinal direction of the magnetic tape under an environment of temperature −190 ° C. It is a switching field distribution SFD to be measured. The magnetic tape according to claim 1, wherein D _{x (107)} / D _TEM of the ferromagnetic hexagonal ferrite powder is in a range of 1.1 to 1.5. The magnetic tape according to claim 1, wherein a crystallite volume obtained by X-ray diffraction analysis of the ferromagnetic hexagonal ferrite powder is in a range of 1000 to 1500 nm ³ . The magnetic tape according to claim 1, wherein the ΔSFD is in a range of 0.50 to 1.00. It is a manufacturing method of the magnetic tape of any one of Claims 1-4,
Preparing a magnetic layer forming composition;
Applying the prepared composition for forming a magnetic layer onto a nonmagnetic layer formed on a nonmagnetic support;
Forming a magnetic layer via
The step of preparing the magnetic layer forming composition comprises:
A first step of obtaining a dispersion by dispersing the ferromagnetic hexagonal ferrite powder, the binder and the solvent in the presence of the first dispersed beads;
A second stage in which the dispersion obtained in the first stage is subjected to a dispersion treatment in the presence of second dispersed beads having a smaller bead diameter and density than the first dispersed beads;
The said manufacturing method including. The manufacturing method according to claim 5, wherein the second step is performed on a mass basis in the presence of the second dispersed beads in an amount of 10 times or more of the ferromagnetic hexagonal ferrite powder. The manufacturing method according to claim 5 or 6, wherein a bead diameter of the second dispersed beads is 1/100 or less of a bead diameter of the first dispersed beads. The manufacturing method according to any one of claims 5 to 7, wherein a bead diameter of the second dispersed beads is in a range of 80 to 1000 nm. The density of said 2nd dispersion | distribution bead is 3.7 g / cm < ³ > or less, The manufacturing method of any one of Claims 5-8. The manufacturing method according to claim 5, wherein the second dispersed beads are diamond beads. In the first step, a ferromagnetic hexagonal ferrite powder having a ΔSFD _powder calculated by the following formula 2 in the range of 0.05 to 1.90, a binder and a solvent are added in the presence of the first dispersed beads. The production method according to any one of claims 5 to 10, which is a step of obtaining a dispersion by performing a dispersion treatment;
ΔSFD _powder = SFD _{powder 100 ° C.} −SFD _{powder 25 ° C.} Equation 2
In Equation 2, SFD _powder 100 ° _C. is a reversal magnetic field distribution SFD of the ferromagnetic hexagonal ferrite powder measured in an environment at a temperature of 100 ° C., and SFD powder 25 ° _C. is a ferromagnetic material measured in an environment at a temperature of 25 ° C. It is a reversal magnetic field distribution SFD of hexagonal ferrite powder.