JP4544641B2 - Magnetic recording medium and manufacturing method thereof - Google Patents

Description

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

  Examples of the magnetic recording medium include a magnetic tape, a magnetic disk, and a magnetic card. One of the uses of magnetic tape is various uses such as audio, video, and computer. As for data backup tapes for computers, magnetic tapes with a recording capacity of several hundred GB per magnetic tape have been commercialized as the capacity of hard disks to be backed up increases. However, as the capacity of hard disks is further increased, it is inevitable that a large capacity backup tape exceeding 1 TB is required. Therefore, it is indispensable to increase the capacity of magnetic tape.

  Methods for increasing the capacity include an approach from a recording / reproducing apparatus and an approach from a recording medium.

  The approach from the recording / reproducing apparatus is, for example, shortening the wavelength of the recording signal or narrowing the track pitch. In this case, since the leakage magnetic flux from the magnetic tape becomes small, an MR head that can obtain a high output even with a very small magnetic flux is often used as the reproducing head.

  The approach from the medium is to make the magnetic powder finer and to improve the magnetic properties of the magnetic powder.

  Conventionally, magnetic powders used in data backup tapes for computers include magnetic powders used in audio tapes and home video tapes (eg, ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, chromium oxide). The same magnetic powder as that of the magnetic powder) was used. At present, it is proposed to use a needle-like ferromagnetic iron-based metal powder having a particle size of about 25 nm to 65 nm.

  Since the acicular magnetic powder exhibits magnetic characteristics due to its shape magnetic anisotropy, the coercive force (Hc) tends to decrease and the short wavelength recording characteristics tend to decrease when the particle diameter decreases. However, regarding plate-like or granular hexagonal Ba-ferrite magnetic powder, iron nitride magnetic powder, etc. (fine particle magnetic powder) that exhibit magnetic properties due to magnetocrystalline anisotropy even when the particle diameter is as small as about 5 nm to 30 nm. Has been proposed for use as a material for magnetic recording media.

  However, even when using any of the above-mentioned magnetic powders such as needles, granules, and plates, sufficient capacity cannot be realized unless the gaps in the magnetic layer are reduced to increase the filling property of the magnetic layer. . At the same time, in order to adapt to the use of the MR head, which is an approach from the above-described recording / reproducing apparatus, it is necessary to reduce the roughness of the surface of the magnetic layer and make it smooth. Therefore, as an approach from manufacturing technology, various methods for drying a magnetic coating film that becomes a magnetic layer by removing a solvent have been proposed (for example, Patent Documents 1 to 4).

  Patent Document 1 discloses a magnetic recording medium manufacturing apparatus including a plurality of alignment devices each including an alignment magnet and a dryer. In this manufacturing apparatus, the wind speed and temperature of the warm air supplied from each dryer can be controlled for each orientation apparatus. And in this manufacturing apparatus, the wind speed of the warm air supplied from several orientation apparatus is set so that it may increase sequentially along the advancing direction of a nonmagnetic support body.

  Patent Document 2 discloses a drying apparatus including two or more drying zones. In this drying apparatus, the low-temperature drying zone is disposed at the most upstream, and the high-temperature drying zone is disposed downstream from the low-temperature drying zone. The low-temperature drying zone is equipped with a low-temperature gas blowing nozzle that allows low-temperature and low-humidity gas to be blown out. In the high-temperature drying zone, gas that is hotter than the gas blown from the low-temperature gas blowing nozzle can be blown out. A hot gas blowing nozzle is arranged.

  Patent Document 3 discloses an example of a method for manufacturing a magnetic recording medium. In this manufacturing method, the boiling point of the solvent contained in the magnetic paint is 130 ° C. or lower. And in the drying process including the constant rate drying process and the decreasing rate drying process, the ambient temperature after the decreasing rate drying process is set to 40 ° C. to 80 ° C. In the same document, the atmospheric temperature in the constant rate drying process is usually higher than that in the rate decreasing drying process. Therefore, in the method of manufacturing a magnetic recording medium described in the same document, although there is a moment when the drying speed (amount of solvent removed per unit time) becomes constant, aggressive constant rate drying is not performed. In the constant rate drying process, the drying speed is constant, whereas in the decreasing rate drying process, the drying speed decreases with the decrease of the solvent in the coating film.

Patent Document 4 discloses a magnetic recording medium and a manufacturing method thereof. The amount of residual solvent contained in the magnetic layer of this magnetic recording medium is 5 mg / m ² . Patent Document 4 discloses that the drying rate in the constant rate drying process is 1 to 20 kg / m ² · hr during the drying process. At this drying speed, the constant rate drying period is 0.1 seconds or less. However, constant rate drying cannot be performed positively in such a short time.

As described above, all of the manufacturing apparatus and the manufacturing method disclosed in Patent Documents 1 to 4 have shifted to the decreasing rate drying process without going through a relatively long constant rate drying process. The reason is that if the constant rate drying process is lengthened, there are disadvantages such as an increase in the size of drying equipment and orientation equipment, and a reduction in production speed.
JP-A-10-124866 Japanese Patent Laid-Open No. 2004-19958 Japanese Patent Laid-Open No. 63-42030 JP-A-4-229415

  However, in the methods described in these documents, the filling rate of the magnetic powder in the magnetic layer cannot be made sufficiently high, and the smoothness becomes insufficient.

  In view of the above situation, the present invention provides a magnetic recording medium having a high filling rate of magnetic powder in a magnetic layer and high smoothness, and a method for manufacturing the same.

The method for producing a magnetic recording medium of the present invention is a method for producing a magnetic recording medium in which a magnetic layer is disposed on one main surface side of a nonmagnetic support,
On one main surface of the nonmagnetic support, a nonmagnetic paint containing a nonmagnetic powder, a second binder resin, and a second solvent, a magnetic paint containing a magnetic powder, a first binder resin, and a first solvent are provided. A non-magnetic coating film and a magnetic coating film are formed in this order by wet-on-wetting, and a drying process for removing the first solvent and the second solvent from the magnetic coating film and the non-magnetic coating material is performed for a predetermined period. However, the magnetic powder contained in the magnetic coating film is magnetically oriented in a predetermined direction, including a magnetic layer forming step,
In the magnetic layer formation step, the drying treatment is
A preheating process of heating the magnetic coating until the increase in surface temperature of the magnetic coating stops and reaches a substantially constant temperature;
A constant rate drying process that is performed after the preheating process, and the surface temperature of the magnetic coating film is maintained at the substantially constant temperature;
The surface temperature of the magnetic coating film, which is performed after the constant rate drying process, is higher than that when the constant rate drying process is performed, and comprises a reduced rate drying process for solidifying the magnetic coating film,
Heat per unit time supplied to the magnetic coating film in the decreasing rate drying process is more than that in the constant rate drying process,
By the drying process performed in the magnetic layer forming step, the second solvent contained in the nonmagnetic coating film is removed, and the nonmagnetic coating film becomes a nonmagnetic layer,
The total thickness of the magnetic coating film and the non-magnetic coating film before the drying treatment is 0.3 μm to 24 μm,
The constant rate drying period in which the constant rate drying process is performed is 0.2 seconds or more,
The first solvent consists of one solvent or two or more solvents having different boiling points,
The second solvent consists of one kind of solvent, or consists of two or more kinds of solvents having different boiling points,
The difference ( tb− Ts) between the boiling point tb of the solvent having the lowest boiling point among the solvents contained in the first solvent and the second solvent and the surface temperature Ts of the magnetic coating film during the constant rate drying period is 1 to 50 ° C.
Another method of manufacturing the magnetic recording medium of the present invention is a method of manufacturing a magnetic recording medium in which a magnetic layer is disposed on one main surface side of a nonmagnetic support,
A method of manufacturing a magnetic recording medium in which a magnetic layer is disposed on one main surface side of a nonmagnetic support,
A magnetic coating containing magnetic powder, a first binder resin, and a first solvent is applied to one main surface of the nonmagnetic support to form a magnetic coating, and the first solvent is removed from the magnetic coating. A magnetic layer forming step of magnetically orienting the magnetic powder contained in the magnetic coating film in a predetermined direction while performing a drying treatment to be removed for a predetermined period,
In the magnetic layer forming step, the drying treatment is performed after a preheating process of heating the magnetic coating film until an increase in the surface temperature of the magnetic coating film stops and reaches a substantially constant temperature. The constant rate drying process in which the surface temperature of the magnetic coating film is maintained at the substantially constant temperature, and the surface temperature of the magnetic coating film that is performed after the constant rate drying process is performing the constant rate drying process. It is higher than that, and consists of a reduced rate drying process that solidifies the magnetic coating film,
Heat per unit time supplied to the magnetic coating film in the decreasing rate drying process is more than that in the constant rate drying process,
The thickness of the magnetic coating film before the drying treatment is 0.3 μm to 24 μm,
The constant rate drying period in which the constant rate drying process is performed is 0.2 seconds or more,
The first solvent is composed of one kind of solvent or two or more kinds of solvents having different boiling points, the boiling point T _{b of the} solvent having the lowest boiling point among the solvents contained in the first solvent, and the constant rate The difference (T _b −T _s ) from the surface temperature T _s of the magnetic coating film during the drying period is 1 ° C. to 50 ° C.

  The magnetic recording medium of the present invention is manufactured using the above-described method for manufacturing a magnetic recording medium of the present invention.

  In the present invention, in the magnetic layer formation step, the surface temperature of the magnetic coating film is substantially constant for 0.2 seconds or more, and constant rate drying is performed. Therefore, the filling rate of the magnetic powder is high and the surface smoothness is high. Can form an excellent magnetic layer. Therefore, according to the present invention, it is possible to provide a magnetic recording medium with higher capacity and higher output, and a method for manufacturing the same.

  As a result of repeated examinations of conditions for drying treatment and magnetic field orientation performed after application of the magnetic paint, the present inventors selected magnetic powder by selecting conditions that could not be conventionally assumed for drying treatment. The present inventors have found that a magnetic layer having excellent filling properties and surface smoothness can be obtained. Before describing an example of the method for manufacturing a magnetic recording medium of the present invention, first, a drying process in a conventional method for manufacturing a magnetic recording medium will be described with reference to FIG.

  In FIG. 4, a curve formed by a solid line indicates a change in the content of the solvent in the coating film, and a curve formed by a dotted line indicates a change in the temperature of the coating film surface.

When a drying process is started in a dryer for a magnetic coating film formed by applying a magnetic paint on one main surface side of a non-magnetic support, as shown in FIG. , Rising until reaching a temperature at which the solvent begins to evaporate rapidly (preheating period). There is little decrease in the solvent content in the coating film during this preheating period. After this period, the evaporation of the solvent becomes serious. In the conventional example, hot air having a relatively high temperature and a relatively high wind speed is supplied to the coating film. For this reason, the amount of heat received by the coating from the surroundings is overwhelmingly greater than the latent heat of evaporation taken away from the coating by evaporation of the solvent from the coating. Therefore, the solvent is evaporated in a very short time. The surface temperature Ts of the coating film increases rapidly, and the solvent content of the coating film decreases rapidly. Over time, the solvent in the coating film is almost gone, the coating film is fixed, and the surface temperature Ts of the coating film approaches the atmospheric temperature in the dryer (decreasing drying period). “Fixed” means that the easy axis of magnetization returns and is not oriented.

  Conventionally, the magnetic field orientation for aligning the easy axis of magnetization of the magnetic powder contained in the coating film has been performed after the end of the application and before the end of the decreasing rate drying period. Magnetic field orientation is performed by applying a magnetic field to the coating film from the outside. In the drying process in the conventional method of manufacturing a magnetic recording medium shown in FIG. 4, since the removal (drying) of the solvent is completed in a relatively short time, the coating speed can be increased, the dryer length can be shortened, and the magnetic field can be reduced. The equipment required for orientation is small. Therefore, the conventional method of manufacturing a magnetic recording medium that performs such a drying process has the advantages that the production efficiency is good and the capital investment is small. However, while this production method is advantageous for high production efficiency and cost reduction, it is insufficient for further increasing the filling rate and smoothing of the magnetic powder in the magnetic layer constituting the magnetic recording medium.

  On the other hand, in the method for manufacturing a magnetic recording medium of this embodiment, the magnetic layer is obtained through a drying process in which the temperature control as shown in FIG. 1 is performed on the surface temperature Ts of the magnetic coating film. The magnetic recording medium manufacturing method of the present embodiment is not limited to a single-layer structure magnetic recording medium in which a magnetic layer is directly provided on a nonmagnetic support, but also magnetically via a nonmagnetic layer on a nonmagnetic support. The present invention is also applied to a magnetic recording medium having a multilayer structure provided with layers.

As shown in FIG. 1, in the magnetic recording medium manufacturing method of the present embodiment, as in the case of the conventional manufacturing method, first, the temperature of the surface of the magnetic coating film is rapidly increased by the first solvent in the magnetic coating film. To a temperature at which it begins to evaporate (preheating period). Thereafter, the surface temperature Ts of the magnetic coating film is kept substantially constant for 0.2 seconds or longer (constant rate drying period). During the constant rate drying period, the balance between the latent heat of evaporation taken from the magnetic coating film by the evaporation of the first solvent from the magnetic coating film and the amount of heat received from the surroundings by the magnetic coating film is almost balanced. Therefore, the surface temperature Ts of the magnetic coating film is kept substantially constant. During this time, the solvent content of the magnetic coating film decreases at a substantially constant rate. Thereafter, when almost no first solvent is present in the magnetic coating film, the coating film is fixed, and the surface temperature Ts of the first coating film approaches the temperature of the atmosphere in the dryer (decreasing drying period).

Thus, when a constant rate drying period of 0.2 seconds or more is provided during the drying process, intense flow accompanying boiling or the like occurs in the fluid magnetic coating film containing the first solvent, or bubbles are generated. It is suppressed. In addition, by actively providing a constant rate drying period during the drying process, the period during which the solvent content of the magnetic coating film decreases at a substantially constant rate becomes longer, and accordingly, the magnetic coating film is removed along with the removal of the first solvent. There are fewer voids that can be generated. Therefore, the magnetic powder can be more densely filled in the magnetic layer. Furthermore, since the smoothness of the surface of the magnetic layer obtained is also improved, the output of the magnetic recording medium is improved.

  When the thickness of the coating film (hereinafter also referred to as “wet thickness”) is dried, it becomes 1/3 to 1/8 before drying. When the magnetic recording medium has a single-layer structure in which a magnetic layer is directly disposed on a nonmagnetic support, the thickness of the magnetic layer (hereinafter also referred to as “dry thickness”) is preferably 0.1 μm to 3 μm. Preferably it is 0.5 micrometer-2 micrometers. Therefore, the magnetic coating is preferably applied so that the wet thickness is preferably 0.3 μm to 24 μm, more preferably 1.5 μm to 16 μm. When the magnetic recording medium has a multilayer structure in which a magnetic layer is provided on a nonmagnetic support via a nonmagnetic layer, the total thickness of the magnetic layer and the nonmagnetic layer is preferably 0.1 μm to 3 μm, More preferably, it is 0.5 μm to 2.0 μm. Therefore, when a magnetic coating film is formed on a nonmagnetic coating film (which becomes a nonmagnetic layer after drying) by wet-on-wet, the thickness of the magnetic coating film and the thickness of the nonmagnetic coating film The total sum is preferably 0.3 μm to 24 μm, more preferably 1.5 μm to 16 μm. In this case, the thickness of the magnetic coating film is preferably 0.03 μm to 1.6 μm, more preferably 0.1 μm to 0.8 μm, and the thickness of the nonmagnetic coating film is preferably 0.27 μm to 22 μm. .4 μm, more preferably 1.4 μm to 15.2 μm.

  The constant rate drying period needs to be 0.2 seconds or more. Similarly, when the magnetic coating film is formed wet-on-wet on the non-magnetic coating film, the constant rate drying period needs to be 0.2 seconds or more. If the constant rate drying period is too short (in other words, if the solvent removal rate is too fast), intense convection occurs or bubbles are generated in the magnetic coating film during drying. For this reason, the filling property of the magnetic powder and the smoothness of the magnetic layer in the obtained magnetic layer are impaired.

  Although there is no restriction | limiting in particular about the upper limit of a constant rate drying period, when too long, productivity will fall remarkably. Moreover, since fixing takes time, many orientation magnets are needed, and installation costs. Therefore, the upper limit of the constant rate drying period is preferably 10 seconds or less. Further, from the viewpoint of further enhancing the filling property, smoothness, and orientation, the constant rate drying period is more preferably 1 second or longer and 10 seconds or shorter.

The surface temperature Ts of the magnetic coating film during the constant rate drying period varies depending on the boiling point of the first solvent contained in the magnetic coating film. The first solvent is composed of one kind of solvent or two or more kinds of solvents having different boiling points, and the boiling point T _{b of the} solvent having the lowest boiling point among the one or more kinds of solvents contained in the first solvent is The surface temperature Ts and the difference (T _b −T _s ) of the magnetic coating film are preferably 1 ° C. to 50 ° C. Specifically, since the surface temperature Ts of the magnetic coating film during the constant rate drying period is preferably 30 ° C. to 80 ° C., the T _b is 1 ° C. to 50 ° C. higher than any temperature in this temperature range. high the Most preferred. By selecting such a solvent, it becomes easy to control the constant rate drying period.

  A conventionally known method can be used to control the surface temperature Ts of the magnetic coating film during constant rate drying. Basically, the latent heat of evaporation taken away from the magnetic coating film by evaporation of the first solvent from the magnetic coating film and the amount of heat received from the surroundings by the magnetic coating film may be substantially balanced. Specifically, a dryer or the like may be used as the heating unit, and the temperature and speed of the hot air, the distance between the magnetic coating film and the heating unit, and the like may be adjusted as appropriate. A far infrared heater may be used as the heating means. These heating means may be used alone or in combination.

  There is no restriction | limiting in particular also about the method of discharging | emitting the evaporated 1st solvent out of drying process atmosphere, What is necessary is just to perform using a conventionally well-known method. For example, it may be discharged out of the atmosphere in a vapor state, or may be once condensed by a condensing means and then discharged out of the atmosphere.

  The total concentration of the remaining components excluding the first solvent (hereinafter also referred to as “solvent exclusion component”) among all the components of the magnetic coating used for forming the magnetic coating film is preferably 10 to 50 wt%, and 20 -35 wt% is more preferable. This is because if the concentration of the solvent-excluded component in the magnetic coating is too low, the viscosity is too small and the dispersibility of the solvent-excluded component decreases, and the uniformity of the magnetic coating film decreases. On the other hand, if the concentration of the solvent-excluded component in the magnetic coating is too high, the viscosity becomes too high and the applicability of the magnetic coating decreases. Therefore, the content of the first solvent in the paint is preferably 50 to 90 wt%, more preferably 65 to 80 wt%.

  The first solvent contained in the magnetic paint is not particularly limited as long as it is a solvent contained in a conventionally known paint for forming a magnetic layer. For example, methyl ethyl ketone (boiling point 80 ° C.), cyclohexanone (boiling point 156 ° C.), methyl isobutyl Ketone solvents such as ketone (boiling point 116 ° C.), ether solvents such as tetrahydrofuran (boiling point 66 ° C.) and dioxane (boiling point 101 ° C.), acetate esters such as ethyl acetate (boiling point 77 ° C.) and butyl acetate (boiling point 127 ° C.) System solvents, toluene (boiling point 111 ° C.) and the like. These may be used alone or in combination of two or more. Of these, cyclohexanone, methyl ethyl ketone, tetrahydrofuran, toluene, and the like are preferable from the viewpoints of solubility in the first binder resin, dispersibility in the magnetic powder, evaporation rate, and cost.

  As described above, when the magnetic recording medium has a single layer structure, the thickness of the magnetic coating film is preferably 0.3 μm to 24 μm, and more preferably 1.5 μm to 16 μm. When the magnetic recording medium has a multilayer structure, the thickness of the magnetic coating film is preferably 0.03 μm to 1.6 μm, and more preferably 0.1 μm to 0.8 μm. These ranges are preferred because if the thickness of the magnetic coating film is too thin, it becomes difficult to form a uniform magnetic coating film, and the formation of the magnetic coating film itself becomes difficult. Moreover, if the thickness of the magnetic coating film is too thick (that is, if the thickness of the magnetic layer is too thick), the electromagnetic conversion characteristics are lowered or the cost is increased.

  The magnetic field orientation performed in parallel with the drying process can be performed by a conventionally known method according to the type of the magnetic recording medium. Specifically, for the magnetic field orientation, for example, a permanent magnet or a solenoid coil that generates a magnetic field may be used alone or in combination.

  For example, in a production line for producing a long magnetic tape, a region where a magnetic paint is applied to one main surface side of a nonmagnetic support is defined as an application zone. A region where the drying treatment is performed on the magnetic coating film formed in the coating zone is defined as a drying zone. In the drying zone, preheating, constant rate drying, and reduced rate drying are performed in this order on the magnetic coating film. In this case, a permanent magnet is disposed between the application zone and the drying zone, and a plurality of solenoid coils are disposed in the drying zone. In the drying zone, it is preferable to perform magnetic field orientation using a solenoid coil on the magnetic coating film to complete the magnetic field orientation. This is because the magnetic field orientation can be performed efficiently and reliably. Magnetic field orientation using a solenoid coil may be performed on the pre-heated magnetic coating film. However, since the orientation equipment becomes too large and takes up space and costs increase, it is not always necessary to perform magnetic field orientation on the pre-heated magnetic coating film.

  When most of the solvent in the magnetic coating film is removed by constant rate drying, it is preferable that magnetic field orientation using a solenoid coil be performed on the magnetic coating film at least until immediately before the reduced rate drying is started. This is because if the magnetic coating film during solvent removal is released from the magnetic field, the orientation of the easy magnetization axis aligned in one direction may be impaired.

  The strength of the external magnetic field applied by the permanent magnet is preferably 5 kOe to 15 kOe. The strength of the external magnetic field applied by the solenoid coil is preferably 1.5 kOe to 10 kOe.

  Next, an example of the method for manufacturing a magnetic recording medium of the present invention will be described more specifically with reference to FIG.

  First, in the coating zone A, a magnetic coating 8 containing magnetic powder is applied to one main surface side of the belt-like nonmagnetic support 7 to form a magnetic coating film. Next, the belt-like laminate T including the nonmagnetic support 7 and the magnetic coating film is passed through a repulsive magnetic field formed between the pair of permanent magnets 9. Next, it is carried into the drying zone B.

  The magnetic paint is applied by a conventionally known method such as a gravure coating method or a die coating method. The conveying means is composed of, for example, a plurality of guide rolls 5 and the like.

  In the drying zone B, a plurality of hot air supply units 1, a heater 4, an exhaust unit 2 that exhausts hot air containing solvent vapor, and a plurality of solenoid coils 3 are arranged. For example, the plurality of solenoid coils 3 are arranged at substantially equal intervals along the traveling direction of the production line. The hot air supply unit 1 is, for example, a dryer capable of blowing hot air. The number, position, and the like of the hot air supply unit 1 and the exhaust unit 2 are appropriately determined in consideration of the coating speed, the drying zone length, and the like.

The plurality of hot air supply units 1 include a first hot air supply / exit unit 1 a disposed upstream of all the solenoid coils 3, a second hot air supply unit 1 b disposed between the solenoid coils 3, and all the solenoid coils 3. 3rd hot-air supply part 1c arrange | positioned rather than the downstream. Here, “upstream side” refers to the side close to the application zone A in the direction in which the laminate T is conveyed, and “downstream side” refers to the side far from the application zone B.

  The laminated body T carried into the drying zone B is first preheated by hot air blown out from the plurality of first hot air supply units 1a. It is preferable that the temperature of the hot air supplied from the first hot air supply unit 1a is relatively low and the wind speed is relatively slow. The preferred temperature and the preferred wind speed vary depending on the thickness of the magnetic coating film, the type of solvent contained in the magnetic coating film (solvent composition), the coating speed of the magnetic paint, etc., but the temperature is usually preferably 35 to 90 ° C. Is preferably 0.5 to 15 m / sec. This is because if the temperature of the hot air is too low and / or if the wind speed of the hot air is too slow, preheating is not sufficiently performed and the start of constant rate drying is also delayed. In addition, if the temperature of the hot air is too high and / or the speed of the hot air is too high, the surface temperature Ts of the magnetic coating film during constant rate drying becomes too high, and the constant rate drying period can be controlled within a preferable range. Because it becomes difficult.

  As for the distance of the 1st hot air supply part 1a and the laminated body T, 1 cm-100 cm are preferable. If the distance is too short, the hot air will hit the magnetic coating film too much, causing uneven drying or uneven drying inside the magnetic coating film. In addition, if the distance is too long, the hot air cannot sufficiently reach the surface of the magnetic coating film, and drying cannot be performed sufficiently.

  The heater 4 is, for example, a far infrared heater. In the far infrared heater, the area of the heating element is much larger than that of the dryer, and a large area can be uniformly heated at a time. The heater 4 is not necessarily required. However, if the heater 4 is provided, the magnetic coating film constituting the laminated body T can be preheated more uniformly, which is preferable.

  Next, the preheated laminated body T is heated by the hot air supplied from the second hot air supply unit 1b so that the surface temperature Ts of the magnetic coating film is kept substantially constant for 0.2 seconds or more. The “substantially constant” includes not only strictly constant but also substantially constant, and includes, for example, a range of ± 1 ° C.

  The constant rate drying period during which the surface temperature Ts of the magnetic coating film is kept substantially constant can be controlled by the temperature of the hot air, the wind speed, and the like. The said constant rate drying period needs to be 0.2 second or more. If the constant rate drying period is too short (in other words, if the solvent removal rate is too fast), intense convection occurs or bubbles are generated in the magnetic coating film during drying. Therefore, the filling property and smoothness of the magnetic layer are impaired. The upper limit of the constant rate drying period is not particularly limited, but if it is too long, not only does the effect of providing the constant rate drying period reach saturation, but the productivity is significantly reduced or the equipment is enlarged and the production cost is increased. . Therefore, the upper limit of the constant rate drying period is preferably 10 seconds or less. From the viewpoint of improving not only the filling property and smoothness but also the orientation, it is more preferable that the constant rate drying period is 1 second or more and 10 seconds or less.

  The surface temperature Ts of the magnetic coating film during constant rate drying varies depending on the thickness of the magnetic coating film, the solvent composition in the magnetic coating film, and the coating speed of the magnetic paint, but is preferably 30 ° C. to 80 ° C., 40 ° C. It is more preferable that it is -70 degreeC. This is because the constant rate drying period can be controlled within a preferable range by controlling the surface temperature Ts of the coating film within these ranges.

  The preferred temperature and the preferred wind speed of the hot air supplied from the second hot air supply unit 1b vary depending on the thickness of the magnetic coating film, the solvent composition in the magnetic coating film, the coating speed of the magnetic paint, etc., but the temperature is 40-100. ° C is preferred, and the wind speed is preferably 0.5 to 15 m / sec. This is because if the temperature of the hot air is too low and / or the speed of the hot air is too slow, the constant rate drying period becomes too long and the production efficiency decreases. If the hot air temperature is too high and / or the hot air speed is too high, the constant rate drying period will be too short, the filling rate of the magnetic powder in the magnetic layer will be low, and the smoothness of the magnetic layer surface will deteriorate. Because it does.

  The distance between the second hot air supply unit 1b and the laminate T is preferably 1 cm to 100 cm. If the distance is too short, the hot air will hit the magnetic coating film too much, causing uneven drying or uneven drying inside the magnetic coating film. In addition, if the distance is too long, the hot air cannot sufficiently reach the surface of the magnetic coating film, and drying cannot be performed sufficiently.

  Next, the laminated body T that has passed under the second hot air supply unit 1b is further heated by the hot air blown out from the third hot air supply unit 1c. It is preferable that the temperature of the hot air supplied by the third hot air supply unit 1c is relatively high and the wind speed is relatively fast. By supplying more heat to the magnetic coating film than during constant rate drying, the first solvent remaining in the magnetic coating film is removed as much as possible in a relatively short time, thereby shortening the rate of drying period. Because. Thereby, the enlargement of the installation accompanying performing constant rate drying for a predetermined period can be suppressed. In addition, the amount of the final residual solvent in the magnetic coating film can be reduced, and the running durability of the magnetic layer can be improved. Here, the final residual solvent amount in the magnetic coating film is the residual amount of the trace solvent that could not be removed even after the drying treatment.

  The preferred temperature of the hot air supplied from the third hot air supply unit 1c, the preferred wind speed varies depending on the thickness of the magnetic coating film, the type of solvent contained in the magnetic coating film (solvent composition), the coating speed of the magnetic paint, etc. In general, the temperature is preferably 60 to 120 ° C. and the wind speed is preferably 0.5 to 30 m / sec so that more heat can be supplied to the magnetic coating film than during constant rate drying. This is because if the hot air temperature is too low and / or the hot air velocity is too slow, the amount of the final residual solvent in the magnetic coating film increases and the running durability of the magnetic layer decreases. In addition, if the temperature of the hot air is too high and / or the wind speed of the hot air is too high, the nonmagnetic support may be thermally deformed.

  The distance between the third hot air supply unit 1c and the laminate T is preferably 1 cm to 100 cm. If the distance is too short, the hot air will hit the magnetic coating film too much, causing uneven drying or uneven drying inside the magnetic coating film. In addition, if the distance is too long, the hot air cannot sufficiently reach the surface of the magnetic coating film, and drying cannot be performed sufficiently.

If necessary, the manufacturing line, further downstream from the third hot air supply unit 1c, and provided with a heating means such as a dryer or far infrared heater, if less final residual traces of solvent in the magnetic layer, the magnetic The durability of the layer can be improved.

  In the example described with reference to FIG. 2, the hot air supply direction is orthogonal to the traveling direction of the stacked body T, but the hot air supply direction is not limited to this example. In order to control the constant temperature drying period within a preferable range, for example, the hot air supply unit 1 may be tilted so that the hot air supplied from the hot air supply unit 1 flows from the downstream side to the upstream side. Moreover, the constant temperature drying period can also be adjusted to a desired range by setting the position and the number of the exhaust parts 2 appropriately.

  Further, the temperature and the wind speed of the hot air supplied from the first hot air supply unit 1a, the second hot air supply unit 1b, and the third hot air supply unit 1c are not necessarily different from each other, for example, they are the same. May be. However, for example, the hot air supplied from the first hot air supply unit 1a, the hot air supplied from the second hot air supply unit 1b, and the third hot air supply unit 1c are secured while securing a constant rate drying period of 2 seconds or more. If the temperature and the wind speed are the same, the zone length of the drying zone is increased, and further, the equipment necessary for performing magnetic field orientation is increased. Therefore, it is preferable that the amount of heat supplied by the heating means such as the hot air supply unit is larger in the order of the first hot air supply unit 1a, the second hot air supply unit 1b, and the third hot air supply unit 1c.

  The method for manufacturing a single-layer magnetic recording medium in which the magnetic layer is disposed directly on one main surface of the nonmagnetic support has been described above as an example. A magnetic recording medium having a multilayer structure in which a magnetic layer is disposed via a nonmagnetic layer can be manufactured in the same manner.

  Next, an example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium of the present invention will be described. As shown in FIG. 3, a magnetic recording medium 10 manufactured by an example of a method for manufacturing the magnetic recording medium has a nonmagnetic layer 12 and a magnetic layer 13 in this order on one main surface of the nonmagnetic support 11. Has been placed. A back coat layer 14 is disposed on the other main surface of the nonmagnetic support 11. However, the nonmagnetic layer 12 and the backcoat layer 14 are not necessarily required and may or may not be present.

  In the present application, the magnetic characteristics of the ferromagnetic powder are values measured with a sample vibration type magnetometer when an external magnetic field 1273.3 kA / m (16 kOe) is applied.

  In the present application, the average particle diameter is measured by measuring the maximum diameter of 100 particles (major axis diameter for needle-like powder and plate diameter for plate-like powder) from a photograph taken with a transmission electron microscope (TEM). A value obtained by averaging these values (number average particle diameter.

<Non-magnetic support>
The thickness of the nonmagnetic support 11 varies depending on the use of the magnetic recording medium, but is usually 2 μm to 8 μm, more preferably 2.5 μm to 6 μm. This is because if the thickness of the nonmagnetic support 11 is too thin, it is difficult to form a magnetic coating film or a nonmagnetic coating film formed using a nonmagnetic paint, and the strength of the magnetic recording medium is reduced. Further, if the thickness of the nonmagnetic support 11 is too thick, the total thickness of the magnetic recording medium is increased. For example, in the case of a magnetic tape, the recording capacity per roll is reduced.

The Young's modulus in the longitudinal direction of the nonmagnetic support 11 is preferably 6 GPa (612 kg / mm ² ) or more, and more preferably 8 GPa (816 kg / mm ² ) or more. This is because if the Young's modulus is too small, the running of the magnetic tape becomes unstable. In the magnetic tape on which information is recorded by the helical scan method, the Young's modulus in the longitudinal direction (MD) / Young's modulus in the width direction (TD) is preferably 0.60 to 0.80, and 0.65. It is more preferable that it is -0.75. If (MD's Young's modulus / TD's Young's modulus) is too small or too large, the mechanism is currently unknown, but the output variation (flatness) between the entry side and the exit side of the track of the magnetic head. ) Becomes larger. The flatness is minimized when (Young's modulus of MD / Young's modulus of TD) is around 0.70. For magnetic tape on which information is recorded by the linear recording method, the reason is not clear, but if (MD Young's modulus / TD Young's modulus) is 0.70 to 1.30, the flatness can be kept small. It is possible and preferable. Examples of the nonmagnetic support 11 that satisfies these characteristics include a biaxially stretched aromatic polyamide base film and a biaxially stretched aromatic polyimide film.

<Nonmagnetic layer>
As will be described later, in order to reduce the thickness loss or increase the resolution when information is recorded at a short wavelength, the thickness of the magnetic layer 13 is preferably less than 0.2 μm. When the thickness of the magnetic layer 13 is less than 0.2 μm, in order to ensure the durability of the magnetic layer 13 and to apply the magnetic paint with good uniformity in the formation process, the magnetic layer 13 and the magnetic layer 13 are magnetically coupled. A nonmagnetic layer 12 is preferably provided between the layer 13 and the layer 13. The nonmagnetic layer 12 includes, for example, a nonmagnetic powder and a second binder resin. As the second binder resin included in the nonmagnetic layer 12, for example, a binder resin similar to the first binder resin constituting the magnetic layer 13 is used.

  The thickness of the nonmagnetic layer 12 is preferably 0.2 μm or more and 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 0.5 μm or less. If the thickness of the nonmagnetic layer 12 is too thin, the unevenness of the surface of the nonmagnetic support also affects the magnetic layer 13, and the effect of reducing the uneven thickness of the magnetic layer 13 by providing the nonmagnetic layer 12 is durable. This is because the effect of securing the property is reduced. Further, if the thickness of the nonmagnetic layer 12 is too thick, the total thickness of the magnetic tape becomes too thick and the recording capacity per magnetic tape roll becomes small. In addition, the unevenness | corrugation of the surface of a nonmagnetic support body is quite large compared with the level of the smoothness of a magnetic layer.

  Non-magnetic powder components include carbon black, titanium oxide, iron oxide, aluminum oxide and the like. Usually, carbon black is used alone, or carbon black and titanium oxide, iron oxide, aluminum oxide, etc. It is used by mixing with other nonmagnetic powders. In order to form a smooth nonmagnetic layer 12 by forming a coating film with less thickness unevenness, it is preferable to use a nonmagnetic powder having a sharp particle size distribution. The average particle diameter of the nonmagnetic powder is preferably, for example, 10 nm to 1000 nm, and more preferably 10 nm to 500 nm, from the viewpoints of uniformity, surface smoothness, rigidity, and conductivity of the nonmagnetic layer 12. .

  As the second solvent contained in the nonmagnetic paint for forming the nonmagnetic layer 12, for example, the same solvent as the first solvent contained in the magnetic paint may be used. Similarly to the first solvent, the second solvent is composed of one kind of solvent or two or more kinds of solvents having different boiling points. The difference (tb−Ts) between the boiling point tb of the solvent having the lowest boiling point among the solvents contained in the first solvent and the second solvent and the surface temperature Ts of the magnetic coating film during the constant rate drying period is 1 It is preferable in it being 50 degreeC or more. By selecting such a solvent, the constant rate drying period can be easily controlled.

  The solvent exclusion component concentration (total concentration of other components excluding the second solvent) in the nonmagnetic paint is preferably 10 to 50% by weight, and more preferably 20 to 35% by weight. This is because if the solvent-excluded component in the nonmagnetic coating is too low, the viscosity is too small and the dispersibility of the nonmagnetic powder decreases, and the interface between the magnetic coating and the nonmagnetic coating becomes uneven. On the other hand, if the solvent-excluded component concentration in the nonmagnetic paint is too high, the viscosity becomes too high and the applicability of the nonmagnetic paint decreases. Therefore, the content of the second solvent in the nonmagnetic paint is preferably 50 to 90% by weight, and more preferably 65 to 80% by weight.

<Surface treatment agent>
The nonmagnetic powder contained in the nonmagnetic layer 12 and the magnetic powder and nonmagnetic powder contained in the magnetic layer 13 are preferably subjected to a surface treatment in order to improve dispersibility. As the surface treatment agent used for this surface treatment, a phosphoric acid surface treatment agent, a carboxylic acid surface treatment agent, an amine surface treatment agent, a chelating agent, various silane coupling agents and the like are suitable.

Examples of the phosphoric acid-based surface treatment agent include alkyl phosphates such as monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, and diethyl phosphate, and aromatic phosphates such as phenylphosphonic acid and monooctylphenylphosphonic acid. It is done. Commercially available products include “GARFAC RS410” manufactured by Toho Chemical, “JP-502”, “JP-504” manufactured by Johoku Chemical Industry,
“JP-508” or the like can be used.

  Examples of the carboxylic acid-based surface treatment agent include benzoic acid, phthalic acid, tetracarboxyl naphthalene, dicarboxyl naphthalene, and fatty acids having 12 to 22 carbon atoms.

  Examples of the amine-based surface treatment agent include aliphatic amines having 8 to 22 carbon atoms, aromatic amines, alkanolamines, and alkoxyalkylamines.

  Examples of chelating agents include 1,10-phenanthroline, EDTA (ethylenediaminetetraacetic acid), dimethylglyoxime, acetylacetone, glycine, dithiazone, nitrilotriacetic acid and the like.

  As the usage-amount of a surface treating agent, it is preferable in it being 0.5-5 weight part with respect to 100 weight part of magnetic powder. The molecular weight of the surface treatment agent is preferably 1000 or less, and more preferably 500 or less. These surface treatment agents are preferably blended before kneading, during kneading, after kneading, before dispersion in the solvent, or during dispersion in the solvent, each component of the nonmagnetic paint and each component of the magnetic paint.

<Magnetic layer>
The thickness of the magnetic layer 13 is preferably 0.1 μm to 3 μm, more preferably 0.5 μm to 2 μm, when it is directly formed on the nonmagnetic support 11. When formed on the nonmagnetic support 11 via the nonmagnetic layer 12, the thickness of the magnetic layer 13 is preferably 0.01 μm or more and less than 0.2 μm, and more preferably 0.03 or more and 0.1 μm or less. These ranges are preferred because if the thickness is too small, the output obtained is small and it is difficult to form the uniform magnetic layer 13. Further, if the thickness is too thick, the resolution characteristic for short wavelength recording is deteriorated.

  The magnetic powder contained in the magnetic layer 13 is preferably a ferromagnetic iron metal magnetic powder, an iron nitride magnetic powder, a plate-shaped hexagonal Ba-ferrite magnetic powder, or the like.

The average particle size of the ferromagnetic iron-based metal magnetic powder is preferably 10 nm to 60 nm, and more preferably 15 nm to 45 nm. This is because if the average particle size is too small, the coercive force (Hc) decreases or the surface energy of the particles increases, making it difficult to disperse in the magnetic paint. If the average particle size is too large, particle noise based on the particle size increases.
Because.

The coercive force of the ferromagnetic iron-based metal magnetic powder is preferably 160 to 320 kA / m (2010 to 4020 Oe), and more preferably 200 to 300 kA / m (2515 to 3770 Oe). Saturation magnetization is preferably to be ^{60~200A · m 2 / Kg (60~200emu} / g), more preferably a ^{80~180A · m 2 / Kg (80~180emu} / g).

One of the indices indicating the orientation of the magnetic powder of the magnetic recording medium is a square (Br / Bs), and (Br / Bs) is preferably 0.8 or more, and 0.84 or more. More preferred. Bs is a saturation magnetic flux density , and Br is a residual magnetic flux density .

BET specific surface area of the ferromagnetic iron-based metal magnetic powder is preferably at least 35m ² / g, more preferably at least ^{40m 2 / g, 50m 2 /} g or more is even more preferred. Although there is no restriction | limiting in particular about the upper limit of a BET specific surface area, Usually, it is 100 m < ² > / g or less.

  The ferromagnetic iron-based metal magnetic powder may contain transition metals such as Mn, Zn, Ni, Cu, and Co as metal elements constituting the magnetic powder. Among them, it is preferable that Co or Ni is contained, and among these, Co is particularly preferable in that the saturation magnetization can be most improved.

  The content of the transition metal element is preferably 5 to 50 and more preferably 10 to 30 with respect to the Fe content 100 in the magnetic powder in terms of atomic ratio.

  In addition to the above transition metal elements, ferromagnetic iron-based metal magnetic powders include yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium as other metal elements constituting the magnetic powder. In addition, at least one rare earth element selected from terbium and the like may be further contained. Among these, when at least one selected from cerium, neodymium and samarium, terbium and yttrium is contained, a high coercive force (Hc) is obtained, which is preferable. In terms of atomic ratio, the rare earth element content is preferably 0.2 to 20, more preferably 0.3 to 15 with respect to the Fe content 100 in the alloy, 0.5 More preferably, it is 10-10.

  Known iron nitride magnetic powders can be used. The shape of the iron nitride magnetic powder may be a spherical shape or an indefinite shape such as a cubic shape in addition to the needle shape.

The coercive force of the iron nitride magnetic powder is preferably 160 to 320 kA / m (2010 to 4020 Oe), and more preferably 200 to 300 kA / m (2515 to 3770 Oe). Saturation magnetization of the iron nitride magnetic powder, preferably as a ^{60~200A · m 2 / Kg (60~200emu} / g), preferably more When it is ^{80~180A · m 2 / Kg (80~180emu} / g) .

The average particle size of the iron nitride magnetic powder is preferably 5 to 20 nm, and more preferably 10 to 17 nm. This is because if the average particle size is too small, the coercive force decreases or the surface energy of the particles increases, making it difficult to disperse in the magnetic paint. Moreover, if the average particle size is too large, particle noise based on the particle size increases. Further, BET specific surface area of the iron nitride magnetic powder is preferably at least 35m ² / g, more preferably at least 40 m ² / g, and still more preferably, more than 50 m ² / g. Although there is no restriction | limiting in particular about the upper limit of the said BET specific surface area, Usually, it is preferable in it being 100 m < ² > / g or less.

  The ferromagnetic iron-based metal magnetic powder and / or the iron nitride magnetic powder may be surface-treated with Al, Si, P, Y, Zr or an oxide thereof. This is for improving the corrosion resistance and dispersibility and controlling the coercive force.

The coercive force of the hexagonal Ba-ferrite magnetic powder is preferably 120 to 320 kA / m, and the saturation magnetization is preferably 40 to 60 A · m ² / kg (40 to 60 emu / g). Moreover, the average particle diameter (length of the longest part of the plate surface, plate diameter) of the hexagonal Ba-ferrite magnetic powder is preferably 10 nm to 30 nm, more preferably 10 nm to 25 nm, and more preferably 10 nm to 20 nm. Is more preferable. This is because if the average particle size is too small, the surface energy of the particles increases, so that dispersion in the magnetic paint becomes difficult, and if it is too large, particle noise based on the size of the particles increases. The plate ratio (plate diameter / plate thickness) is preferably less than 3, more preferably 2 or less. The BET specific surface area of the hexagonal Ba-ferrite magnetic powder is preferably 1 to 100 m ² / g.

  The product of the residual magnetic flux density in the tape longitudinal direction of the magnetic layer 13 and the magnetic layer thickness is preferably 0.0018 to 0.05 μTm, more preferably 0.0036 to 0.05 μTm, and 0.004 to 0. More preferably, it is 0.05 μTm. This is because if the product of the residual magnetic flux density and the thickness of the magnetic layer 13 is too small, the reproduction output by the MR head becomes small, and if it is too large, the reproduction output by the MR head tends to be distorted. The magnetic recording medium having the magnetic layer 13 having the product in this range can perform short wavelength recording. In addition, the reproduction output when reproduced by the MR head is large, the distortion of the reproduction output is small, and the output-to-noise ratio can be increased, which is preferable.

  Examples of the binder resin (first binder resin) contained in the magnetic layer 13 or the binder resin (second binder resin) contained in the nonmagnetic layer 12 include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol. Selected from the group consisting of copolymer resins, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resins, vinyl chloride-vinyl acetate-maleic anhydride copolymer resins, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resins, and cellulosic resins. A combination of at least one kind and a polyurethane resin may be mentioned. Examples of the cellulose resin include nitrocellulose resin.

  Among these, a combination of a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin is preferable. Examples of the polyurethane resin include polyester polyurethane resin, polyether polyurethane resin, polyether polyester polyurethane resin, polycarbonate polyurethane resin, polyester polycarbonate polyurethane resin, and the like.

As the polyurethane resin, as the functional _{group, -COOH, -SO 3 M, -OSO} 3 M, -P = O (OM) 3, -O-P = O (OM) 2 [ In these formulas, M Represents a hydrogen atom, an alkali metal base or an amine salt], —OH, —NR′R ″, —N + R ′ ″ R ″ ″ R ′ ″ ″ [in these formulas, R ′, R ″, R ′ ″, R ″ ″, R ′ ″ ″ represent hydrogen or a hydrocarbon group], or a polyurethane resin made of a polymer having an epoxy group can also be used. When such a polyurethane resin is used, the dispersibility of the powder such as magnetic powder in the magnetic paint is improved.

When two or more kinds of binder resins are used in combination, it is preferable that the polarities of the functional groups are matched, and it is particularly preferable that each of the two kinds of binder resins has a —SO ₃ M group.

  In the magnetic coating material for forming the magnetic layer, the first binder resin is preferably contained in an amount of 7 to 50 parts by weight and more preferably 10 to 35 parts by weight with respect to 100 parts by weight of the magnetic powder. When the binder resin includes a vinyl chloride resin and a polyurethane resin, 5 to 30 parts by weight of the vinyl chloride resin and 2 to 20 parts by weight of the polyurethane resin are included with respect to 100 parts by weight of the magnetic powder. And preferred.

  About content of 2nd binder resin contained in the nonmagnetic coating material for nonmagnetic layer formation, it is preferable in it being 10-55 weight part with respect to 100 weight part of nonmagnetic powder, and it is 15-40 weight part. And more preferred.

  In the magnetic coating material for forming the magnetic layer or the nonmagnetic coating material for forming the nonmagnetic layer, the first binder resin or the second binder resin is combined with the functional group of the first binder resin or the second binder resin. It is preferable that a thermosetting cross-linking agent to be cross-linked is further contained. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products obtained by reacting these isocyanates with a compound having a plurality of hydroxyl groups such as trimethylolpropane, or condensation of the above isocyanates. Various polyisocyanates such as products are preferred. These crosslinking agents are preferably used in an amount of 1 to 30 parts by weight, more preferably 5 to 20 parts by weight, based on 100 parts by weight of the first binder resin or the second binder resin. However, when a magnetic coating is formed wet-on-wet on a nonmagnetic coating formed by applying a nonmagnetic coating on a nonmagnetic support, Part of the polyisocyanate is diffusely supplied to the magnetic coating film. Therefore, even if the magnetic paint does not contain polyisocyanate, crosslinking is performed to some extent in the magnetic coating film.

  The magnetic layer 13 may contain nonmagnetic powder in addition to magnetic powder. Nonmagnetic powders include abrasives and carbon black. When carbon black is included, the conductivity of the magnetic layer 13 is improved.

  As abrasives, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride Etc., mainly having a Mohs hardness of 6 or more. These may be used alone or in combination of two or more.

  The average particle diameter of the abrasive is preferably 10 nm to 250 nm when the thickness of the magnetic layer 13 is as thin as 0.01 to 0.2 μm. When the thickness of the magnetic layer 13 is thicker than 0.2 μm, the average particle diameter of the abrasive is preferably 50 to 1000 nm. The content of the abrasive is preferably 5 to 20 parts by weight and more preferably 8 to 18 parts by weight with respect to 100 parts by weight of the magnetic powder.

  Examples of carbon black include acetylene black, furnace black, and thermal black.

  The average particle size of carbon black is preferably 10 nm to 100 nm. If the average particle size is too small, it is difficult to disperse the carbon black, and if the average particle size is too large, a large amount of carbon black is required. Therefore, if the average particle size is too small or too large, the surface of the magnetic layer 13 becomes rough, which may reduce the output, which is not preferable. The content of carbon black is preferably 0.2 to 5 parts by weight and more preferably 0.5 to 4 parts by weight with respect to 100 parts by weight of the magnetic powder.

<Lubricant>
The nonmagnetic layer 12 preferably further contains a fatty acid and a fatty acid ester as a lubricant. This is because if the nonmagnetic layer 12 contains a predetermined amount of each of these, the friction coefficient with the head of the magnetic tape becomes small. In the nonmagnetic paint, 0.5 to 5.0 parts by weight of fatty acid and 0.2 to 3.0 parts by weight of fatty acid ester are blended with 100 parts by weight of the nonmagnetic powder contained in the nonmagnetic layer 12. It is preferable. This is because if the amount of the fatty acid is less than 0.5 parts by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5.0 parts by weight, the nonmagnetic layer 12 may be plasticized and the toughness may be lost. . Further, if the amount of the fatty acid ester is less than 0.2 parts by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0 parts by weight, the amount transferred to the magnetic layer 13 is too large. This is because there is a risk of causing side effects such as sticking.

  It is preferable to use a fatty acid having 10 or more carbon atoms. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid, and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

  Examples of fatty acid esters include a mixture of butyl stearate and butyl palmitate, dipropylene glycol monobutyl ether acylated with stearic acid, hexamethylene diol acylated with myristic acid to give a diol, glycerin oleate Various ester compounds such as butyl stearate, sec-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 2-hexyldecyl stearate, butyl Examples include palmitate, 2-ethylhexyl myristate, oleyl oleate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, diethylene glycol dipalmitate, and the like. wear.

  The magnetic layer 13 may also contain the fatty acid. In this case, since the fatty acid is transferred between the nonmagnetic layer 12 and the magnetic layer 13, the amount of fatty acid in the magnetic coating is determined based on the fatty acid content contained in the magnetic layer 13 and the fatty acid contained in the nonmagnetic layer 12. When the total amount of all the powders (magnetic powder and nonmagnetic powder) contained in the magnetic layer 13 and the nonmagnetic powder contained in the nonmagnetic layer 12 is 100 parts by weight, 0.0 part by weight is preferable. In addition, when a fatty acid is mix | blended with a nonmagnetic coating material, the fatty acid does not necessarily need to be mix | blended with the magnetic coating material.

  The magnetic layer 13 may contain both a fatty acid amide and a fatty acid ester as a lubricant. This is because the friction coefficient with respect to the head of the tape when the tape is running becomes small. The blending amount in these magnetic coating materials is preferably 0.5 to 3.0 parts by weight of fatty acid amide and 0.2 to 3.0 parts by weight of fatty acid ester with respect to 100 parts by weight of magnetic powder. This is because if the content of the fatty acid amide is less than 0.5 parts by weight, the effect of preventing seizure caused by the mutual contact between the head and the magnetic layer 13 is reduced. Moreover, it is because there exists a possibility that fatty acid amide may bleed out when content of fatty acid amide exceeds 3.0 weight part. Moreover, it is because a friction coefficient reduction effect will become small as content of the ester of a fatty acid is less than 0.2 weight part. Further, if the content of the fatty acid ester exceeds 3.0 parts by weight, side effects such as sticking of the magnetic layer 13 to the head may occur. The lubricant for the magnetic layer 13 and the lubricant for the nonmagnetic layer 12 can move relative to each other.

  Examples of fatty acid amides include fatty acid amides having 10 or more carbon atoms such as palmitic acid and stearic acid. The fatty acid esters contained in the magnetic layer 13 may be the same as the fatty acid esters listed above.

<Back coat layer>
A back coat layer 14 is preferably provided on the surface of the nonmagnetic support 11 opposite to the surface on which the magnetic layer 13 is formed for the purpose of improving running performance. The thickness of the backcoat layer 14 is preferably 0.2 to 0.8 μm. This is because if the thickness of the backcoat layer is too thin, the effect of improving running performance is insufficient, and if the thickness is too thick, the total thickness of the magnetic tape is increased, and the recording capacity per magnetic tape roll is reduced.

  The back coat layer 14 includes, for example, carbon black (CB). Examples of carbon black (CB) include acetylene black, furnace black, and thermal black. Usually, small particle size carbon black and large particle size carbon black having relatively different particle sizes are used in combination. It is preferable to use a combination of a small particle size carbon black and a large particle size carbon black because the effect of improving running performance is increased. The large particle size carbon black is preferably contained in an amount of 5 to 15 parts by weight with respect to 100 parts by weight of the small particle size carbon black.

  The average particle size of the small particle size carbon black is preferably 5 nm or more and less than 200 nm, and more preferably 10 to 100 nm. If the average particle size is too small, it is difficult to disperse the carbon black in the paint, and if the average particle size is too large, a large amount of carbon black is required. Therefore, if the number average particle size is too small or too large, the surface of the backcoat layer becomes rough, and there is a risk of causing back-off (embossing) to the magnetic layer.

  The average particle size of the large particle size carbon black is preferably 200 to 400 nm.

  The total amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight and more preferably 70 to 95 parts by weight of the total powder weight contained in the back coat layer.

  The average surface roughness Ra of the backcoat layer 14 is preferably 3 to 8 nm, and more preferably 4 to 7 nm. Since the magnetic signal recorded on the magnetic layer 13 may be disturbed if the backcoat layer is magnetic, the backcoat layer is usually nonmagnetic.

  In addition, in this application, the surface roughness of 10 visual fields is measured by a scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO, and the average value is defined as the average surface roughness (Ra). Yes. In the measurement, a 50 × objective lens was used and the measurement was performed at 2 × zoom. Therefore, the magnification is 100 times. The measurement visual field is 72 μm × 54 μm.

  The back coat layer preferably contains, for example, iron oxide for the purpose of improving the strength. The average particle diameter of iron oxide is preferably 100 to 600 nm, and more preferably 200 to 500 nm. The content of iron oxide is preferably 2 to 40% by weight of the total powder weight, and more preferably 5 to 30% by weight. Further, it is preferable that 0.5 to 5% by weight of alumina having an average particle diameter of 100 to 600 nm is added in the total powder weight because the strength of the backcoat layer is further improved.

  The backcoat layer 14 includes a binder resin, but the binder resin in the backcoat layer 14 may be the same as the binder resin included in the magnetic layer 13 and the nonmagnetic layer 12 described above. However, in order to reduce the friction coefficient and improve the running performance of the magnetic head, it is preferable to use a cellulose resin and a polyurethane resin in combination. The binder resin content is usually preferably 40 to 150 parts by weight, more preferably 50 to 120 parts by weight, and more preferably 60 to 110 parts by weight with respect to 100 parts by weight of the total powder contained in the backcoat layer. Parts are more preferable, and 70 to 110 parts by weight are even more preferable. This is because if the amount is too small, the strength of the backcoat layer 14 becomes insufficient, and if the amount is too large, the friction coefficient tends to increase. When the total powder weight contained in the back coat layer is 100 parts by weight, the binder resin preferably contains 30 to 70 parts by weight of a cellulose-based resin and 20 to 50 parts by weight of a polyurethane-based resin. The coating material for forming the backcoat layer 14 preferably contains a crosslinking agent in order to cure the binder resin. As a crosslinking agent, a polyisocyanate compound etc. are mentioned, for example.

  The cross-linking agent contained in the paint for forming the backcoat layer 14 is the same as the cross-linking agent contained in the magnetic paint for forming the magnetic layer 13 and the non-magnetic paint for forming the nonmagnetic layer 12 described above, for example. It's okay. The content of the crosslinking agent is usually preferably 10 to 50 parts by weight, more preferably 10 to 35 parts by weight, and even more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder resin. . This is because if the amount is too small, the strength of the backcoat layer 14 becomes weak, and if the amount is too large, the dynamic friction coefficient against SUS (stainless steel) increases.

<Organic solvent>
If the second solvent contained in the nonmagnetic paint for forming the nonmagnetic layer 12 and the solvent contained in the paint for forming the backcoat layer 14 are those of the first solvent contained in the magnetic paint for forming the magnetic layer 13. Good. In addition, the solvent exclusion component concentration in the nonmagnetic paint used for forming the nonmagnetic layer and the solvent exclusion component concentration of the paint for forming the backcoat layer 14 are 10 to 50 wt% for the same reason as in the case of the magnetic paint. Preferably, 20 to 35 wt% is more preferable. Therefore, the content of the second solvent contained in the nonmagnetic paint is preferably 50 to 90 wt%, more preferably 65 to 80 wt%, and the content of the solvent contained in the paint for forming the backcoat layer 14 is also 50 to 90 wt%. 90 wt% is preferable, and 65-80 wt% is more preferable.

  EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

<Nonmagnetic coating for nonmagnetic layer formation>
(1) Component A acicular iron oxide (average particle size: 0.11 μm) 68 parts by weight Carbon black (average particle size: 0.025 μm) 20 parts by weight Granular alumina powder (average particle size: 0.4 μm) 12 parts by weight Methyl acid phosphate 1 part by weight Vinyl chloride-hydroxypropyl acrylate copolymer resin 9 parts by weight (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 5 parts by weight (Glass transition temperature: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Tetrahydrofuran 13 parts by weight Cyclohexanone 63 parts by weight Methyl ethyl ketone 137 parts by weight (2) B component butyl stearate 2 parts by weight Cyclohexanone 50 parts by weight Toluene 50 parts by weight (3) C component Polyisocyanate 6 parts by weight Cyclohexanone 9 parts by weight Toluene 9 parts by weight

<Magnetic coating for magnetic layer formation>
(1) Component a Ferromagnetic iron-based metal magnetic powder 100 parts by weight (Al—Y—Fe—Co) [σs: 120 Am2 / kg (120 emu / g)
Hc: 176.3 kA / m (2215 Oe) average particle diameter: 45 nm, true density ρ: 5.7 g / cc]
Vinyl chloride-hydroxypropyl acrylate copolymer resin 17 parts by weight Polyester polyurethane resin 6 parts by weight Granular alumina powder (average particle size: 0.2 μm) 10 parts by weight Methyl acid phosphate 4 parts by weight Methyl ethyl ketone 35 parts by weight Cyclohexanone 110 parts by weight Toluene 110 Parts by weight (2) component b palmitic acid amide 1 part by weight butyl stearate 1 part by weight cyclohexanone 30 parts by weight toluene 30 parts by weight (3) component c polyisocyanate 6 parts by weight methyl ethyl ketone 2 parts by weight cyclohexanone 8 parts by weight toluene 8 parts by weight

  Of the coating components for forming the nonmagnetic layer, the component A was kneaded with a batch kneader. The B component was added to the kneaded A component and stirred, and then dispersed for 60 minutes (residence time) using a sand mill. Furthermore, the C component was added to the mixture of the A component and the B component, and the mixture was stirred and filtered to obtain a nonmagnetic coating material for forming a nonmagnetic layer.

  On the other hand, the component a was kneaded with a batch kneader. Next, the b component was added to the k component kneaded and diluted with stirring to obtain an undispersed paint. Subsequently, the undispersed paint was subjected to a dispersion treatment for 90 minutes (residence time) using a nanomill (manufactured by Asada Tekko). Furthermore, the c component was added to the mixture of the a component and the b component, stirred, and filtered to obtain a magnetic coating material for forming the magnetic layer.

  The nonmagnetic coating material for forming the nonmagnetic layer was applied onto a nonmagnetic support composed of a polyethylene naphthalate film having a thickness of 8 μm using an extrusion coater to form a nonmagnetic coating film. Next, a magnetic coating film was formed on the non-magnetic coating film by applying a magnetic coating for forming a magnetic layer wet-on-wet using an extrusion coater.

  The thickness of the non-magnetic coating film is 4.5 μm so that the thickness after drying and calendering (ie, the thickness of the non-magnetic layer) is 0.9 μm, and the thickness of the magnetic coating film is after drying and calendering. The thickness (that is, the thickness of the magnetic layer) was set to 0.3 μm so as to be 0.08 μm. The coating speed of the magnetic coating for forming the magnetic layer was 150 m / min.

  Subsequently, the laminated body in which the nonmagnetic coating film and the magnetic coating film were formed in this order on the nonmagnetic support was passed between NN opposing magnets (398 kA / m). Thereafter, magnetic field orientation was performed while removing the solvent contained in the nonmagnetic coating film and the magnetic coating film in the manner shown in FIG.

  In this embodiment, the heater 4 in FIG. 2 is not used. Five solenoid coils (398 kA / m, 5 units) were used to perform magnetic field orientation. Table 1 shows the drying conditions such as the temperature of the hot air, the wind speed, and the distance between the hot air supply unit and the magnetic coating film.

<Components of paint for forming backcoat layer>
Carbon black (average particle diameter 25 nm) 80 parts Carbon black (average particle diameter 350 nm) 10 parts Particulate iron oxide (average particle diameter 50 nm) 10 parts by weight Nitrocellulose 45 parts by weight Polyurethane resin 30 parts by weight Cyclohexanone 260 parts by weight Toluene 260 Parts by weight methyl ethyl ketone 525 parts by weight polyisocyanate 15 parts by weight

  All the components other than the polyisocyanate among the components of the paint for forming the backcoat layer were dispersed and mixed in a sand mill, and then the polyisocyanate was added thereto. The obtained mixture was filtered to obtain a paint for forming a backcoat layer. This paint was applied to the surface opposite to the surface on the magnetic layer side of the nonmagnetic support and dried.

  The magnetic sheet thus obtained was mirror-finished (calendar treatment) under the conditions of a temperature of 100 ° C. and a linear pressure of 196 kN / m using a seven-stage calendar made of a metal roll. Next, a magnetic tape for evaluation was produced by aging at 60 ° C. for 48 hours while the magnetic sheet was wound around the core.

  As shown in Table 1, magnetic sheets for evaluation of Examples 2 to 7 and Comparative Examples 1 and 2 were produced in the same manner as Example 1 except that the drying conditions were different.

  Evaluation of the obtained magnetic sheet for evaluation was performed as follows. The results are shown in Table 1.

<Constant drying period>
Infrared sensors (fiber type infrared radiation thermometer (FTZ6 type, manufactured by Japan Sensor Co., Ltd.)) were placed in the drying zone at intervals of 20 cm, and the surface temperature Ts of the magnetic layer was measured. If the temperature difference is within 2 ° C. no matter how the surface temperatures Ts of the respective magnetic layers obtained from the three continuously arranged sensors are combined, it is determined that constant rate drying is being performed. The drying period was measured.

<Surface roughness of magnetic layer>
Using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO, the surface roughness of 10 points was measured by scanning white light interferometry, and the average value was defined as the average roughness Rz. In the measurement, a 50 × objective lens was used and the measurement was performed at 2 × zoom. Therefore, the magnification is 100 times. The measurement visual field is 72 μm × 54 μm.

<Magnetic properties>
After applying an external magnetic field of 0.8 MA / m (10 kOe) to the magnetic sheet, the square shape (Br / Bs) and the saturation magnetization amount Mst (memu / cm ² ) per unit area of the magnetic layer were measured. For these measurements, a sample vibration type magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd. was used.

<Volume filling degree>
After sealing the magnetic tape with resin, a cross section in the thickness direction of the magnetic tape was cut out in the longitudinal direction of the tape using a focused ion beam processing apparatus. Next, a photograph of the cross section (BSE image, magnification: 100,000 times) was taken using a scanning electron microscope (SEM). Photographing was performed for 10 fields of view so as not to include overlapping portions. Next, in each photograph, a boundary line was drawn on the interface between the magnetic layer and the nonmagnetic layer, and a line was also drawn on the outer shape of the magnetic layer facing the boundary line. The line width was 0.5 mm.

  Next, for each photograph, the distance between the boundary line and the corresponding line was measured at five locations, and the average value was measured as the thickness t (μm) of the magnetic layer. Then, the saturation magnetic flux density Bs (G) was obtained by the following equation (1) using Mst and the thickness t (μm) of the magnetic layer. Further, the filling degree (Vol%) of the magnetic powder was obtained from the following equation (2) using Bs, σs (emu / g) and the true density ρ (g / cc) of the magnetic powder.

Bs = 4π × Mst / t (1)
Filling degree (Vol%) = Bs / (4π · σs · ρ) × 100 (2)

  As shown in Table 1, for the magnetic tapes of Examples 1 to 6, the volume filling property of the magnetic powder is higher than that of Comparative Examples 1 and 2 in which the constant rate drying time is less than 0.2 seconds, and the magnetic tape is magnetic. It was confirmed that the smoothness of the layer was excellent. About the orientation (square shape) of the magnetic powder of the magnetic tape of Examples 1-6, it was 0.8 or more and was equivalent to that of the comparative example. If the constant rate drying period is 0.2 seconds or more and less than 10 seconds, not only the smoothness of the magnetic layer and the filling property of the magnetic powder, but also the orientation (square shape) of the magnetic powder is superior to the comparative example. It was confirmed that a magnetic recording medium could be provided.

  As mentioned above, although an example of the manufacturing method of the magnetic recording medium of this invention was demonstrated, this example applies the coating material which contains powder with binder resin on a support body, and dries, and forms the process of forming a functional layer. It can also be applied to other product fields including.

  Since the present invention can form a magnetic layer having a high filling ratio of magnetic powder and excellent surface smoothness, the present invention is useful as a method for producing a magnetic recording medium capable of increasing the capacity and outputting high power. is there.

The conceptual diagram which showed the change of the temperature of the coating-film surface in the example of the manufacturing method of the magnetic recording medium of this invention, and the change of the solvent content in a coating-film The conceptual diagram which showed the mode of the drying process in an example of the manufacturing method of the magnetic recording medium of this invention Partial sectional view of an example of the magnetic recording medium of the present invention Schematic diagram showing changes in coating surface temperature and solvent content in the coating film in an example of a conventional method of manufacturing a magnetic recording medium

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hot air supply part 1a 1st hot air supply part 1b 2nd hot air supply part 1c 3rd hot air supply part 2 Exhaust part 3 Solenoid coil (orientation magnet)
4 Heater 5 Guide Roll T Laminate 10 Magnetic Recording Medium

Claims (8)

A method of manufacturing a magnetic recording medium in which a magnetic layer is disposed on one main surface side of a nonmagnetic support,
On one main surface of the nonmagnetic support, a nonmagnetic paint containing a nonmagnetic powder, a second binder resin, and a second solvent, a magnetic paint containing a magnetic powder, a first binder resin, and a first solvent are provided. A non-magnetic coating film and a magnetic coating film are formed in this order by wet-on-wetting, and a drying process for removing the first solvent and the second solvent from the magnetic coating film and the non-magnetic coating material is performed for a predetermined period. However, the magnetic powder contained in the magnetic coating film is magnetically oriented in a predetermined direction, including a magnetic layer forming step,
In the magnetic layer formation step, the drying treatment is
A preheating process of heating the magnetic coating until the increase in surface temperature of the magnetic coating stops and reaches a substantially constant temperature;
A constant rate drying process that is performed after the preheating process, and the surface temperature of the magnetic coating film is maintained at the substantially constant temperature;
The surface temperature of the magnetic coating film, which is performed after the constant rate drying process, is higher than that when the constant rate drying process is performed, and comprises a reduced rate drying process for solidifying the magnetic coating film,
Heat per unit time supplied to the magnetic coating film in the decreasing rate drying process is more than that in the constant rate drying process,
By the drying process performed in the magnetic layer forming step, the second solvent contained in the nonmagnetic coating film is removed, and the nonmagnetic coating film becomes a nonmagnetic layer,
The total thickness of the magnetic coating film and the non-magnetic coating film before the drying treatment is 0.3 μm to 24 μm,
The constant rate drying period in which the constant rate drying process is performed is 0.2 seconds or more,
The first solvent consists of one solvent or two or more solvents having different boiling points,
The second solvent consists of one kind of solvent, or consists of two or more kinds of solvents having different boiling points,
The difference ( tb− Ts) between the boiling point tb of the solvent having the lowest boiling point among the solvents contained in the first solvent and the second solvent and the surface temperature Ts of the magnetic coating film during the constant rate drying period is The manufacturing method of a magnetic-recording medium which is 1 to 50 degreeC.   A method of manufacturing a magnetic recording medium in which a magnetic layer is disposed on one main surface side of a nonmagnetic support,
  A magnetic coating containing magnetic powder, a first binder resin, and a first solvent is applied to one main surface of the nonmagnetic support to form a magnetic coating, and the first solvent is removed from the magnetic coating. A magnetic layer forming step of magnetically orienting the magnetic powder contained in the magnetic coating film in a predetermined direction while performing a drying treatment to be removed for a predetermined period,
  In the magnetic layer forming step, the drying treatment is performed after a preheating process of heating the magnetic coating film until an increase in the surface temperature of the magnetic coating film stops and reaches a substantially constant temperature. The constant rate drying process in which the surface temperature of the magnetic coating film is maintained at the substantially constant temperature, and the surface temperature of the magnetic coating film that is performed after the constant rate drying process is performing the constant rate drying process. It is higher than that, and consists of a reduced rate drying process that solidifies the magnetic coating film,
  Heat per unit time supplied to the magnetic coating film in the decreasing rate drying process is more than that in the constant rate drying process,
  The thickness of the magnetic coating film before the drying treatment is 0.3 μm to 24 μm,
The constant rate drying period in which the constant rate drying process is performed is 0.2 seconds or more,
  The first solvent is composed of one kind of solvent or two or more kinds of solvents having different boiling points, and the boiling point T of the solvent having the lowest boiling point among the solvents contained in the first solvent. _b And the surface temperature T of the magnetic coating film during the constant rate drying period _s Difference from (T _b -T _s ) Is 1 ° C to 50 ° C. The constant rate drying period, method of manufacturing a magnetic recording medium according to claim 1 or 2 or less 10 seconds. The constant rate drying period, method of manufacturing a magnetic recording medium according to a second claim 1 or 2 which is 10 seconds. 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein a surface temperature of the magnetic coating film is 30 ° C. to 80 ° C. during the constant rate drying period. The magnetic powder comprises a ferromagnetic iron-based metal magnetic powder, the average particle diameter of the ferromagnetic iron-based metal magnetic powder manufacturing method of a magnetic recording medium according to claim 1 or 2 which is 10 to 60 nm. The magnetic powder includes magnetic iron nitride powder, the average particle diameter of the magnetic iron nitride powder method for manufacturing a magnetic recording medium according to claim 1 or 2 which is 5 nm to 20 nm. The magnetic powder includes a hexagonal Ba- ferrite magnetic powder, a manufacturing method of a magnetic recording medium according to claim 1 or 2 average particle diameter of the hexagonal Ba- ferrite magnetic powder is 10 nm to 30 nm.

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