JP5043586B2 - Magnetic recording medium and method for manufacturing the same - 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 to a recording / reproducing apparatus and an approach to a recording medium.

  The approach to 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 to the recording 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, or plates, sufficient capacity can be achieved unless the gaps in the magnetic layer are reduced to increase the filling properties of the magnetic layer. Can not. To increase the capacity, it is necessary to simultaneously orient the magnetic powder. Furthermore, in order to adapt to the use of the MR head described above, it is necessary to reduce the roughness of the magnetic layer surface and make it smooth. Therefore, various methods for drying a magnetic coating film that becomes a magnetic layer by removing the solvent and methods for aligning magnetic powder have been proposed (for example, Patent Documents 1 to 7). In Patent Documents 1 to 3, as a method for highly orienting magnetic powder, a magnetic field orientation is obtained by combining a permanent magnet capable of obtaining a high magnetic field at a relatively low cost and a solenoid coil capable of obtaining a magnetic field in a certain direction. Is disclosed. Patent Documents 4 to 7 disclose drying methods for reducing the roughness of the magnetic layer surface and smoothing it.

  Specifically, in Patent Document 1, a magnetic field (first magnetic field) having an intensity of 1800 Oe (1.8 kOe) or more is applied before starting the drying process on the magnetic coating film, and then the magnetic coating film is applied. A drying and orientation method is disclosed in which a magnetic field (second magnetic field) having an intensity of 400 Oe (0.4 kOe) or more is applied while a drying process is performed on. The coercive force of the magnetic powder contained in the magnetic coating film is about 600 Oe.

  In the orientation / drying method described in Patent Document 2, first, a magnetic powder is oriented by applying a high strength magnetic field to a magnetic coating film with a high magnetic field coil, and then a low strength magnetic field is applied to the magnetic coating with a low magnetic field coil. It is applied to the film to prevent the magnetic powder from returning and to dry the magnetic coating film. A low strength magnetic field gives a magnetic field strength of 20% or less of the maximum magnetic field strength. The intensity of the high intensity magnetic field is 5 to 10 kOe, and the intensity of the low intensity magnetic field is 50 to 1000 Oe.

  Regarding the orientation / drying method described in Patent Document 3, similarly to the method described in Patent Document 1, the first magnetic field orientation is performed by the first magnetic field generating means before starting the drying of the magnetic coating material by the drying apparatus, and then The second magnetic field orientation is performed by the second magnetic field generating means in the drying apparatus. The average magnetic field strength generated by the second magnetic field generating means is 1/3 or less of the maximum magnetic field strength by the first magnetic field generating means. The coercive force of the magnetic powder contained in the magnetic coating film is, for example, 520 Oe.

  Patent Document 4 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 5 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.

  In an example of the method for manufacturing a magnetic recording medium disclosed in Patent Document 6, the boiling point of the solvent contained in the magnetic paint is 130 ° C. or less. 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 7 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 7 discloses that the drying rate in the constant rate drying process is 1 to 20 kg / m ² · hr during the drying process.

As described above, all of the manufacturing apparatuses and manufacturing methods disclosed in Patent Documents 4 to 7 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 62-175931 A JP-A-6-20273 JP-A-7-134825 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 is sufficiently high, the magnetic powder cannot be highly oriented, and the smoothness becomes insufficient.

  In the method described in Patent Document 1, the first magnetic field is formed outside the drying unit, and the second magnetic field is formed inside the drying unit. Before entering the magnetic field, the magnetic field intensity to which the magnetic coating film is exposed becomes a value close to zero. Therefore, when the particle size of the magnetic powder is small and the coercive force is high, so-called return orientation is likely to occur after magnetization by the first magnetic field. Moreover, once the return orientation occurs, it is difficult to achieve good orientation again by the magnetization by the second magnetic field.

  Also in the method described in Patent Document 2, since the high magnetic field orientation is performed before the drying step and the drying is performed while performing the low magnetic field orientation, so-called return orientation is easily generated after the magnetization by the high strength magnetic field. In magnetization, it is difficult to reorientate magnetic powder that has been reorientated again.

  Also in the method described in Patent Document 3, since the first magnetic field generating means is provided outside the drying apparatus and the second magnetic field orientation means is provided in the drying means, the magnetic coating film is the first magnetic field. Between passing through the generating means and entering the second magnetic field orientation means, the magnetic field strength to which the magnetic coating film is exposed becomes a value close to zero. Therefore, when the particle size of the magnetic powder is small and the coercive force is high, so-called return orientation is likely to occur after magnetization by the first magnetic field orientation means. In addition, with the magnetization by the second magnetic field orientation means, it is difficult to properly orient the magnetic powder that has been oriented back again.

  As a method for obtaining high orientation, it is conceivable to arrange the magnetic field generating means so that the magnetic field is continuously applied to the magnetic coating film immediately after the coating is applied until the applied magnetic coating is completely dried. However, the equipment becomes very expensive and is not realistic.

  In view of the above situation, the present invention provides a method of manufacturing a magnetic recording medium capable of forming a magnetic layer having high orientation, filling properties, and smoothness.

The method for manufacturing a magnetic recording medium of the present invention is a method for manufacturing a magnetic recording medium in which a magnetic layer is disposed on one main surface side of a nonmagnetic support, and the method is provided on one main surface side of the nonmagnetic support. Applying a magnetic coating material containing magnetic powder, a first binder resin and a first solvent to form a magnetic coating film, and performing a drying process for removing the first solvent from the magnetic coating film for a predetermined period, Including a magnetic layer forming step of magnetically orienting magnetic powder contained in the magnetic coating film in a predetermined direction. In the magnetic layer forming step, the drying treatment is substantially constant with the increase in the surface temperature of the magnetic coating film stopped. A preheating process for heating the magnetic coating film until the temperature reaches a constant temperature, a constant rate drying process that is performed after the preheating process to keep the surface temperature of the magnetic coating film substantially constant, and a preheating process that is performed after the constant rate drying process. The surface temperature of the magnetic coating film is the constant rate drying process. The constant rate drying period during which the constant rate drying process is performed is 0.2 seconds or more, and includes a reduced rate drying process that solidifies the magnetic coating film. Orientation is performed after the preheating process is started, using the first orientation means and the second orientation means in this order, while the magnetic field strength in the first orientation means reaches the second orientation means from the place where the magnetic field strength is the highest. The minimum value of the magnetic field strength to which the magnetic coating film is exposed is W _1min , the maximum value of the magnetic field strength to which the magnetic coating film is exposed in the second orientation means is W _2max , and the magnetic coating film is in the second orientation means. when the W _2min the minimum value of the magnetic field strength exposed is, these values _{(W 2max -W 1min) / W} 2max ≦ 0.9, _{and, (W 2max -W 2min) /} W 2max ≦ 0. The relationship 5 is satisfied.

  The present invention can provide a method for producing a magnetic recording medium capable of forming a magnetic layer with high orientation, high filling, and high smoothness.

  As a result of repeated studies on conditions for drying treatment and magnetic field orientation performed after application of the magnetic coating material, the present inventors selected conditions that could not be conventionally assumed for drying treatment, and It was found that a magnetic layer having high orientation, high filling, and high smoothness can be obtained by starting the magnetic field orientation treatment after the start and performing the magnetic field orientation treatment under predetermined conditions. Before describing an example of a method for manufacturing a magnetic recording medium according to 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. 7, 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 nonmagnetic 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 from the outside to the coating film. In the drying process in the method of manufacturing the conventional magnetic recording medium shown in FIG. 7, since the solvent removal (drying) 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, this manufacturing method is advantageous for improving the efficiency of production and reducing the cost, but is insufficient for further high orientation, high packing, and smoothing of the magnetic powder in the magnetic layer constituting the magnetic recording medium. Met.

  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 process). 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 process, 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 magnetic coating film approaches the temperature of the atmosphere in the dryer (decreasing drying process).

  In this way, if there is a constant rate drying process during the drying process, it is possible to suppress the occurrence of violent flow due to boiling or the generation of bubbles in the fluid magnetic coating film containing the first solvent. Is done. In addition, if a constant rate drying process is positively provided during the drying process, the period during which the solvent content of the magnetic coating film decreases at a substantially constant rate becomes longer. For this reason, the number of voids that can be generated in the magnetic coating film with the removal of the magnetic solvent is reduced, and 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.

  The constant rate drying period is 0.2 seconds or more. When the constant rate drying period is 0.2 seconds or more, it is possible to suppress the occurrence of intense convection in the coating film during drying, and therefore, a magnetic layer having high filling property and high surface smoothness is formed with high productivity. it can. 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.

  Next, an example of a conventional method of manufacturing a magnetic recording medium will be described with reference to FIGS. 8A and 8B. FIG. 8A is a conceptual diagram for explaining an example of a conventional method of manufacturing a magnetic recording medium, and FIG. 8B is a graph showing a change in magnetic field strength in the dryer shown in FIG. 8A.

  As shown in FIG. 8A, first, in the coating zone A ′, a magnetic coating 81 containing magnetic powder is applied to one main surface side of the belt-like nonmagnetic support 71 to form a magnetic coating film. Next, the strip-shaped laminate t1 including the nonmagnetic support 71 and the magnetic coating film is passed between the orientation means (first orientation means) provided with a pair of permanent magnets to perform the orientation treatment. The laminate t1 that has passed through the first orientation means is conveyed into the dryer 61. The conveying means is constituted by, for example, a plurality of guide rolls 51 and the like.

  In the dryer 61, a plurality of hot air supply units 111, an exhaust unit 21 for exhausting hot air containing solvent vapor, and second orientation means 31b are arranged. The second orientation unit 31 b includes a plurality of solenoid coils 311. The plurality of hot air supply units 111 includes a hot air supply unit 11a disposed on the upstream side of the second orientation unit 31b, a hot air supply unit 11b disposed between the solenoid coils 311 adjacent to each other in the traveling direction of the stacked body t1, and And a hot air supply unit 11c disposed on the downstream side of the second orientation means 31b. Here, the “upstream side” refers to the side close to the application zone A ′ in the direction in which the laminate T is conveyed, and the “downstream side” refers to the side far from the application zone A ′.

  In an example of a conventional method for manufacturing a magnetic recording medium as shown in FIG. 8A, a pair of permanent magnets 31a is provided in consideration of the workability of application by the coater 41 and the disposition of the hot air supply unit. The orientation means (first orientation means) is disposed between the coating zone A ′ and the dryer 61. Moreover, in order to ensure the air volume by the hot air supply part 11b, the space | interval of the solenoid coil 311 adjacent to the advancing direction of the laminated body t1 is designed comparatively large. Therefore, as shown in FIG. 8B, the magnetic field strength to which the magnetic coating film is exposed decreases to near zero after the laminate t1 passes through the first orientation means 31a and enters the second orientation means 31b. is doing. Further, since the interval between the solenoid coils 311 adjacent to each other in the traveling direction of the laminated body t1 is large, the difference between the maximum value and the minimum value of the magnetic field strength to which the magnetic coating film is exposed in the magnetic field orientation using the second orientation means 31b. Is extremely large. Therefore, it has been difficult to obtain a coating film having a high degree of filling with a highly oriented magnetic powder.

In the method for manufacturing a magnetic recording medium of the present invention, the magnetic field orientation is performed using the first orientation means 3a and the second orientation means 3b in this order after the start of the preheating process (see FIG. 2A). The minimum value of the magnetic field strength to which the magnetic coating film is exposed during the period from the point where the magnetic field strength in the first orientation means 3a is the largest to the inside of the second orientation means 3b is defined as W _1min . maximum value W _2max of the magnetic field strength magnetic layer is exposed in a unit 3b, and the minimum value of the magnetic coating film in the second alignment means 3b are exposed when the W _2min, these values (W _2max - _{W 1min) / W 2max ≦ 0.9} , and, to satisfy the relation _{(W 2max -W 2min) / W} 2max ≦ 0.5 ( see FIG. 2B).

As described above, the pre-heat treatment is started and the magnetic field orientation is started in a state where the fluidity of the paint is improved, and the first (W _2max −W _1min ) / W _2max ≦ 0.9 is satisfied. The orientation means 3a is placed in the dryer 6 and the first orientation means 3a and the second orientation means 3b are placed in contact with each other (see FIG. 2A) or as close as possible to each other (see FIG. 6A). . This significantly reduces the magnetic field strength to which the magnetic coating film is exposed after the magnetic coating film passes through the portion having the highest magnetic field strength in the first orientation means 3a and enters the second orientation means 3b. Therefore, so-called return orientation can be effectively suppressed. Furthermore, placing (W _2max -W _2min) / W as relationship _2max ≦ 0.5 is satisfied, for example, it makes good contact with the plurality of solenoid coils 301 constituting the second alignment means 3b. Thereby, since the fluctuation | variation of the magnetic field intensity which the magnetic coating film is applied by the 2nd orientation means 3b can be suppressed, the said return orientation can be suppressed until it becomes a magnetic layer by fixing a magnetic coating film. Therefore, as shown in the results in Examples described later, it is possible to form a magnetic layer with high filling, high surface smoothness, and highly oriented magnetic powder.

  The magnetic field strength applied by the first orientation means 3a and exposed to the magnetic coating film is preferably 398 kA / m to 1194 kA / m (5 kOe to 15 kOe), and the magnetic field strength applied by the second orientation means and exposed to the magnetic coating film is 119 kA / m to 796 kA / m (1.5 kOe to 10 kOe) is preferable. When the magnetic field strength applied by the first orientation means 3a is within the above range, the magnetic powder is highly oriented and a magnetic layer having high smoothness is obtained by suppressing magnetic aggregation in the magnetic coating film. be able to. When the magnetic field strength applied by the second orientation means 3b is within the above range, it is possible to effectively prevent disorder of orientation due to the return orientation of the magnetic powder highly oriented by the first orientation means. Further, when the magnetic field strength applied by the second orientation means 3b is 30% or more and less than 100% of the magnetic field strength applied by the first orientation means 3a, the magnetic powder can be oriented inexpensively and efficiently, preferable.

  Examples of the first orientation means 3a include at least one of orientation means including a plurality of permanent magnets and orientation means including a plurality of solenoid coils, but a high-intensity magnetic field can be obtained at a relatively low cost. Thus, an orientation means (repulsive magnet) that makes the same pole of the permanent magnet face each other is preferable. The second orientation means 3b includes at least one of orientation means including a plurality of permanent magnets and orientation means including a plurality of solenoid coils. A magnetic field having a relatively constant magnetic field strength has a constant length. The orientation means having a plurality of solenoid coils obtained in (1) is preferable.

  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 the magnetic layer 13 is disposed directly on the nonmagnetic support 11 as shown in FIG. 3, the thickness of the magnetic layer 13 (hereinafter also referred to as “dry thickness”). Is preferably 0.1 μm to 3 μm, more preferably 0.5 μm to 2 μm. 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 structure in which the magnetic layer 13 is provided on the nonmagnetic support 11 via the nonmagnetic layer 12 as shown in FIG. 4, the sum of the thickness of the magnetic layer and the thickness of the nonmagnetic layer is provided. Is preferably 0.1 μm to 3 μm, more preferably 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 surface temperature Ts of the magnetic coating film during the constant rate drying process varies depending on the boiling point of the solvent (hereinafter also referred to as “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 T _s and the difference (T _b −T _s ) of the magnetic coating film are preferably 1 ° C. to 50 ° C. Specifically, since the surface temperature T _s of the magnetic coating film during the constant rate drying process is preferably 30 ° C. to 80 ° C., the T _b is 1 ° C. to 50 ° C. higher than any temperature in this temperature range. A lower temperature is preferable. 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 T _s of the magnetic coating film during the constant rate drying process. 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. When the concentration of the solvent-excluded component in the magnetic coating is within the above range, the dispersibility of the solvent-excluded component in the magnetic coating is good, and a more uniform magnetic coating film can be formed.

  The content of the first solvent in the magnetic coating used for forming the magnetic coating film is preferably 50 to 90 wt%, more preferably 65 to 80 wt%, because the magnetic coating can be satisfactorily applied.

  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. When the thickness of the magnetic coating film is within these ranges, a more uniform magnetic coating film can be formed.

  Next, an example of the method for manufacturing the magnetic recording medium of the present invention will be described more specifically with reference to FIGS. 2A and 2B. FIG. 2A is a conceptual diagram illustrating an example of a method for manufacturing a magnetic recording medium according to the present invention, and FIG. 2B is a graph showing changes in magnetic field strength in a dryer described later.

  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. The magnetic paint is applied by a conventionally known method such as a gravure coating method or a die coating method.

  Next, the belt-like laminate T <b> 1 including the nonmagnetic support 7 and the magnetic coating film is conveyed into the dryer 6. The conveying means is composed of, for example, a plurality of guide rolls 5 and the like.

  In the dryer 6, a plurality of hot air supply units 1, an exhaust unit 2 for exhausting hot air containing solvent vapor, a first alignment unit 3a, and a second alignment unit 3b are arranged. The first orientation means 3a is, for example, an orientation means having a pair of permanent magnets, and the second orientation means 3b is an orientation means having a plurality of solenoid coils 301. The plurality of hot air supply units 1 are disposed on the upstream side of the first alignment unit 3a and the second alignment unit 3b, and the first hot air supply unit 1a is disposed on the downstream side of the first alignment unit 3a. 2 hot-air supply part 1b and 3rd hot-air supply part 1c are included. Here, the “upstream side” refers to the side close to the application zone A in the direction in which the laminate T1 is conveyed, and the “downstream side” refers to the side far from the application zone A.

  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 laminated body T1 that has entered the drying chamber 6 is preheated by the first hot air supply unit 1a disposed on the upstream side of the first orientation means 3a. It is preferable that the temperature and wind speed of the hot air supplied from the first hot air supply unit 1a are relatively low and the wind speed is relatively slow. The temperature is preferably 35 to 90 ° C. and the wind speed is preferably 0.5 to 15 m / sec, although it varies depending on the wind speed of hot air, the thickness of the coating film, the solvent composition in the coating film, the coating speed, and the like. When the temperature and the wind speed of the hot air are within the above ranges, preheating can be sufficiently performed, the preferable range of the constant rate drying period can be easily controlled, and the production facility can be prevented from becoming too large.

  The distance between the outlet of the first hot air supply unit 1a and the coating film is preferably 1 to 100 cm. When the distance is 1 to 100 cm, the preheating process can be sufficiently performed, and the occurrence of uneven drying caused by excessive hot air hitting the coating film can be suppressed.

  If the preheating process is completed on the upstream side of the first orientation means 3a, it is preferable because the subsequent constant rate drying period can be easily controlled within a preferable range.

Is next to the laminate T1 preheated, for example, maintained by hot air supplied from the second hot air supply unit 1b, for example, 0.2 seconds to 10 seconds, the surface temperature Ts of the magnetic coating film is substantially constant To be heated. The “substantially constant” includes not only strictly constant but also substantially constant, and includes a case where the temperature is within a range of ± 1 ° C.

  The hot air blown from the second hot air supply unit 1b flows from the downstream side to the upstream side through the cylindrical internal space formed by the plurality of solenoid coils 301, and is arranged upstream of the second orientation means 3b. The exhaust part 2 is exhausted. The constant rate drying period can be controlled by, for example, the temperature and wind speed of hot air supplied from the second hot air supply unit 1b.

  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. If the temperature and the wind speed of the hot air are within the above ranges, a highly filled and highly smooth magnetic layer can be formed with high productivity.

  The distance between the outlet of the second hot air supply unit 1b and the coating film is preferably 1 to 100 cm. When the distance is 1 to 100 cm, constant rate drying can be sufficiently performed, and generation of uneven drying caused by excessive hot air hitting the coating film can be suppressed.

  The surface temperature Ts of the magnetic coating film during the constant rate drying process 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. It is more preferable that it is C-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.

  When the constant rate drying process is completed in the magnetic field formed by the second orientation means 3b, it is preferable because the return orientation does not occur.

  Next, the laminated body T1 that has passed under the second hot air supply unit 1b is further heated by the hot air blown 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 when performing constant rate drying, the solvent remaining in the magnetic coating film can be removed as much as possible in a relatively short time to shorten the drying rate. is there. 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 is supplied to the magnetic coating film than during the constant rate drying process. If the temperature and the wind speed of the hot air are within the above ranges, a magnetic layer with high filling, high smoothness, and a small amount of the final residual solvent can be formed.

  The distance between the third hot air supply unit 1c and the laminate T1 is preferably 1 cm to 100 cm. When the distance is 1 to 100 cm, the reduction drying process can be sufficiently performed, and the occurrence of uneven drying caused by excessive hot air hitting the coating film can be suppressed.

  If necessary, a heating means such as a dryer or a far-infrared heater may be provided further downstream of the third hot air supply unit 1c in the production line to remove a trace amount of the residual solvent in the magnetic coating film. The durability of the layer can be improved.

  In the example described with reference to FIG. 2A, the hot air supply direction is orthogonal to the traveling direction of the stacked body T1, 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 more smoothly 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 ensuring the constant rate drying period for a predetermined time or more. If the temperature and wind speed are the same for the hot air, the length of the dryer becomes longer, and further, the equipment necessary for performing magnetic field orientation also becomes larger. Therefore, it is preferable that the amount of heat supplied by the heating means such as the hot air supply unit increases 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.

The distance between the first alignment means 3a and the second alignment means 3b in the traveling direction of the stacked body T1 is not particularly limited as long as the relationship of (W _2max −W _1min ) / W _2max ≦ 0.9 is satisfied. However, the first aligning means 3a and the second aligning means 3b are arranged so as to be in contact with each other or as close as possible to each other so that the difference (W _2max −W _1min ) is as small as possible. Preferably. Further, the value of the difference (W _2max −W _1min ) may be a positive number or a negative number.

Second alignment means 3b for example, if a plurality of solenoid coils 301, the distance between the solenoid coil 301 adjacent to each other in the traveling direction of the laminate T1 _{is, (W 2max -W 2min) /} W 2max ≦ 0 As long as the relationship of .5 is satisfied, there is no particular limitation. However, as the difference between the second alignment means 3b in a magnetic field strength W _2max and W _2min magnetic coating film is exposed (W _2max -W _2min) becomes as small as possible, when the distance is short as possible preferred.

  FIG. 5A is a conceptual diagram for explaining another example of the method for producing a magnetic recording medium of the present invention, and FIG. 5B is a graph showing changes in magnetic field strength in the dryer described in FIG. 5A.

In the method of manufacturing the magnetic recording medium shown in FIG. 5A, a plurality of second hot air supply units 1b are used, and the second hot air supply unit 1b is interposed between the solenoid coils 301 adjacent to each other along the traveling direction of the multilayer body T1. Has been placed. Except for the above, the manufacturing method of the magnetic recording medium shown in FIG. 5A is the same as the manufacturing method of the magnetic recording medium shown in FIG. 2A. In this case, the spacing between the solenoid coil 301 adjacent along the traveling direction of the laminate T1 is, is greater than that in the example described with reference to FIGS. 2A and _{2B, (W 2max -W 2min)} / W 2max The value of increases. However, this example is preferable in terms of easier control of the constant rate drying period than the example described using FIG. 2A.

  FIG. 6A is a conceptual diagram illustrating still another example of the method for manufacturing a magnetic recording medium of the present invention, and FIG. 6B is a graph showing changes in magnetic field strength in the dryer 6 shown in FIG. 6A. It is.

In the method of manufacturing the magnetic recording medium shown in FIG. 6A, the first orientation means 3a and the second orientation means 3b are in mutual relation within the range where the relationship of (W _2max −W _1min ) / W _2max ≦ 0.9 is satisfied. The example is the same as that described with reference to FIG.

  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. 4, the magnetic recording medium 10 manufactured by an example of the manufacturing method of the magnetic recording medium has a nonmagnetic layer 12 and a magnetic layer 13 on one main surface of the nonmagnetic support 11. Arranged in order. 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). These values are average 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.

Longitudinal Young's modulus of the nonmagnetic support 11, since the running of the magnetic tape is stabilized, preferable to be 6GPa (612kg / mm ²⁾ or more, and more preferably 8GPa (816kg / mm ²⁾ or more. In a magnetic tape on which information is recorded by the helical scan method, (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. When (MD Young's modulus / TD Young's modulus) is 0.60 to 0.80, the mechanism is currently unknown, but the output variation between the entry side and the exit side of the track of the magnetic head. (Flatness) decreases. 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. Possible and preferred. 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 0.1 μm or less. When the thickness of the magnetic layer 13 is 0.1 μm or less, 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 nonmagnetic support 11 and the magnetic layer 13 A nonmagnetic layer 12 is preferably provided between the layer 13 and the layer 13. The nonmagnetic layer 12 includes, for example, nonmagnetic powder and a binder resin (second binder resin). For the second binder resin contained in the nonmagnetic layer 12, for example, a binder resin similar to the binder resin (first binder resin) constituting the magnetic layer 13 is used.

  The thickness of the nonmagnetic layer is preferably 0.2 μm or more and 1.0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less. When the thickness of the nonmagnetic layer is 0.2 μm or more and 1.0 μm or less, the effect of reducing the thickness unevenness of the magnetic layer 13 by providing the nonmagnetic layer 12 is sufficiently exerted, and the durability of the magnetic layer 13 is improved. Higher recording capacity (per magnetic tape roll) can be secured. 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.

The nonmagnetic layer has a particle diameter of 10 nm to 100 nm (more preferably 10 nm to 10 nm) for the purpose of improving the uniformity of the film thickness of the nonmagnetic layer 12, improving the surface smoothness, controlling the rigidity, and controlling the dimensional stability. 49 nm) non-magnetic plate-like particles are preferably contained. Examples of the components of the nonmagnetic plate-like particles include rare earth elements such as aluminum oxide and cerium, oxides such as zirconium oxide, silicon oxide, titanium oxide, manganese oxide, and iron oxide, or composite oxides of indium and tin. It is done.

  In order to improve the conductivity of the nonmagnetic layer, a plate-like carbon powder such as graphite having an average particle size of 10 to 100 nm, a plate-like ITO (indium-tin composite oxide) powder having an average particle size of 10 to 100 nm, etc. May be added as a non-magnetic plate-like powder. The nonmagnetic layer preferably contains 15 to 95% by weight of plate-like ITO powder out of the total weight of all inorganic powders in the nonmagnetic layer.

  Instead of the plate-like ITO particles, a powdery carbon material may be used. The powdery carbon material may contain carbon black as necessary. Carbon black preferably has a particle size of 10 nm to 100 nm.

  The nonmagnetic layer may contain oxide particles such as iron oxide and aluminum oxide. The average particle diameter of the oxide particles is preferably 10 nm to 100 nm.

  As the binder resin contained in the nonmagnetic layer, for example, the same binder resin as that contained in the magnetic layer is used.

  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 process described above 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 concentration of the solvent-excluded component in the nonmagnetic coating is too low, the viscosity is too small and the dispersibility of the nonmagnetic powder is lowered, thereby making the interface between the magnetic coating and the nonmagnetic coating 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.

  The amount of the surface treatment agent used is preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the magnetic powder or 100 parts by weight of the nonmagnetic 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 preferable because a sufficiently large output can be obtained, the formation of the homogeneous magnetic layer 13 can be easily performed, and the resolution characteristic for short wavelength recording, which is caused when the thickness is too thick, is achieved. This is because the decrease can be suppressed.

  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 these powders is preferably 60 nm or less.

The average particle size of the ferromagnetic iron-based metal magnetic powder is more preferably 10 nm to 60 nm, and more preferably 15 nm to 45 nm. When the average particle size is 10 nm to 60 nm, a sufficiently large coercive force (Hc) can be obtained, dispersion in a magnetic coating can be performed well, and particle noise caused by the average particle size being too large Can be suppressed, which is preferable.
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 (Bs) 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 the saturation magnetization amount, and Br is the residual magnetization amount.

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.

  In terms of atomic ratio, 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 addition to the transition metal elements described above, 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, and more preferably 0.5 to 15 with respect to the Fe content 100 in the alloy. 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 such that a sufficiently large coercive force can be obtained, dispersion in the magnetic coating can be performed well, and particle noise caused by the size of the average particle size. Is small, 5-20 nm is preferable and 10-17 nm is more preferable.

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.

  Ferromagnetic iron-based metal magnetic powder and / or iron nitride magnetic powder is surface treated with Al, Si, P, Y, Zr or their oxides to improve corrosion resistance, improve dispersibility, and control coercive force. May be.

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 longitudinal direction of the magnetic layer 13 and the thickness of the magnetic layer enables short wavelength recording, a large reproduction output when reproduced by an MR head, a small distortion of the reproduction output, and output versus noise. In order to increase the ratio, it is preferably 0.0018 to 0.05 μTm, more preferably 0.0036 to 0.05 μTm, and even more preferably 0.004 to 0.05 μTm.

  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, vinyl chloride-vinyl. Selected from the group consisting of alcohol copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymers, and cellulosic resins. And a combination of at least one selected from polyurethane and polyurethane. Examples of the cellulose resin include nitrocellulose resin.

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

As the polyurethane, as a functional _{group, -COOH, -SO 3 M, -OSO} 3 M, -P = O (OM) 3, in -O-P = O (OM) 2 [ these equations, M is 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 '''''represents hydrogen or a hydrocarbon group], or a polyurethane made of a polymer having an epoxy group can also be used. If such polyurethane is used, the dispersibility of the powder such as magnetic powder in the magnetic coating material 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.

  The content of the second binder resin contained in the nonmagnetic paint for forming the nonmagnetic layer is preferably 10 to 55 parts by weight with respect to 100 parts by weight of the nonmagnetic powder, and 15 to 40 parts by weight. 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 the carbon black is 10 nm to from the viewpoint of improving dispersibility, improving the smoothness of the surface of the magnetic layer 13, and suppressing output reduction caused by the rough surface of the magnetic layer 13. 100 nm is preferable. 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. 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. The non-magnetic paint exhibits a sufficient friction coefficient reduction effect, ensures high toughness of the non-magnetic layer 1, and suppresses the amount of fatty acid ester transferred to the magnetic layer 13 to adhere the magnetic tape and the head. From the viewpoint of preventing the occurrence of side effects such as sticking, 0.5 to 5.0 parts by weight of fatty acid and 0.2 to 3 of fatty acid ester with respect to 100 parts by weight of nonmagnetic powder contained in nonmagnetic layer 12 0.0 part by weight is preferably blended.

  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. Yes.

  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 from the viewpoint of obtaining a high running performance improvement effect and increasing the recording capacity per magnetic tape roll.

  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 carbon black having a small particle size is 5 nm or more and 200 nm from the viewpoint of obtaining a highly smooth back coat layer by suppressing dispersibility in the paint and increasing the amount of carbon black added. Is preferably less than 10 and more preferably 10 to 100 nm.

  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 content of the binder resin is preferably 40 to 150 parts by weight with respect to 100 parts by weight of the total powder contained in the backcoat layer from the viewpoint of forming the backcoat layer 14 having high strength and a low friction coefficient. More preferred is 50 to 120 parts by weight, still more preferred is 60 to 110 parts by weight, and even more preferred is 70 to 110 parts by weight. 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 cross-linking agent is preferably 10 to 50 parts by weight with respect to 100 parts by weight of the binder resin from the viewpoint of forming the backcoat layer 14 having high strength and a small dynamic friction coefficient with respect to SUS (stainless steel). 10 to 35 parts by weight is more preferable, and 10 to 30 parts by weight is even more preferable.

<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. In addition, the average particle diameter in an Example and a comparative example shows a number average particle diameter.

Example 1
<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 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 A · m ² / 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 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 that had been subjected to the dispersion treatment, and these were stirred, and the resultant was 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 stirred 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 that had been subjected to the dispersion treatment and stirred, and the resultant was filtered to obtain a magnetic paint for forming a magnetic layer.

  The nonmagnetic coating material for forming the nonmagnetic layer was applied on 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 such 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 the thickness after drying and calendering ( That is, the thickness of the magnetic layer was set to 0.08 μm. The coating speed of the magnetic coating for forming the magnetic layer was 150 m / min.

Next, the laminated body in which the nonmagnetic coating film and the magnetic coating film are formed in this order on the nonmagnetic support, and the solvent contained in the nonmagnetic coating film and the magnetic coating film in the manner shown in FIG. 2A. The magnetic field orientation was performed while removing. Specifically, first, the preheating process is started by the first hot air supply unit 1a, and then, in the orientation means including the NN opposing magnet which is an example of the first orientation means (W _1max : 7 kOe (557 kA / m) ). Subsequently, the constant rate drying process and the decreasing rate drying process were performed in this order by the second hot air supply unit 1b and the third hot air supply unit 1c while performing magnetic field alignment by the second alignment unit. The conveying speed of the laminate by the conveying means was 150 m / min. At this time, W _1min was set to 3 kOe by adjusting the distance between the first alignment means and the second alignment means.

In this embodiment, as shown in FIG. 2, an orientation means (W _2max : 3 kOe (239 kA / m)) provided with four solenoid coils was used as the second orientation means. 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, an evaluation magnetic tape was produced by aging at 60 ° C. for 48 hours in a state where the magnetic sheet was wound around the core.

(Example 2)
A magnetic tape for evaluation of Example 2 was produced in the same manner as in Example 1 except that the distance between the first orientation means and the second orientation means was adjusted to set W _1min to 0.9 kOe.

(Example 3)
An evaluation magnetic tape of Example 3 was produced in the same manner as in Example 1 except that the distance between the first orientation means and the second orientation means was adjusted to set W _1min to 0.3 kOe.

Example 4
A magnetic tape for evaluation of Example 4 was produced in the same manner as in Example 1 except that the drying / orientation apparatus shown in FIG. 5A was used.

(Example 5)
Using the drying / orientation apparatus shown in FIG. 5A, the conditions of the first to third hot air supply units were set as described in Table 1, and the constant rate drying period was set to 0.2 seconds. Similarly, an evaluation magnetic tape of Example 5 was prepared.

(Example 6)
Using the drying / orientation apparatus shown in FIG. 2A, the conditions of the first to third hot air supply units were set as shown in Table 1, and the constant rate drying period was set to 10 seconds. Thus, a magnetic tape for evaluation of Example 5 was prepared.

[Comparative Example 1]
A magnetic tape for evaluation of Comparative Example 1 was produced in the same manner as in Example 1 except that the drying process by the second hot air supply unit 1b was not performed and the constant rate drying period was 0.1 second.

[Comparative Example 2]
A magnetic tape for evaluation of Comparative Example 2 was produced in the same manner as in Example 1 except that the drying process by the first hot air supply unit 1a was not performed.

[Comparative Example 3]
The drying process using the first hot air supply unit 1a is not performed, the conditions of the second and third hot air supply units are changed to the conditions described in Table 1, and the constant rate drying period is 0.1 seconds. In the same manner as in Example 1, a magnetic tape for evaluation of Comparative Example 3 was produced.

[Comparative Example 4]
Using the conventional manufacturing apparatus shown in FIG. 8A, the drying process using the first hot air supply unit 11a is not performed, and the conditions of the second and third hot air supply units 11b and 11c are changed to the conditions described in Table 1. Then, the constant rate drying period was set to 0.1 second, and the distance between the first alignment means 31a and the second alignment means 31b was adjusted to set W _1min to 0.02 kOe. Thus, a magnetic tape for evaluation of Comparative Example 4 was produced.

[Comparative Example 5]
A magnetic tape for evaluation of Comparative Example 5 was produced in the same manner as in Example 1 except that the distance between the first orientation means and the second orientation means was adjusted to set W _1min to 0.15 kOe.

[Comparative Example 6]
Respect solenoid coil constituting the second alignment means, by adjusting the solenoid coil distance between adjacent in the traveling direction of the magnetic sheet, except that the W _2min and 0.9kOe in the same manner as in Example 1, Comparative Example 6 magnetic tapes for evaluation were prepared.

[Comparative Example 7]
A magnetic tape for evaluation of Comparative Example 7 was produced in the same manner as in Example 1 except that the conventional manufacturing apparatus shown in FIG. 7A was used.

Evaluation of the obtained magnetic sheet for evaluation was performed as follows. The results are shown in Table 1. Incidentally, in Table _{1, W 1max, W 1min,} W 2max, W 2min is properly adjusted and the distance between the first alignment means and the second alignment means, and positions of the solenoid coils of the second alignment means In the apparatus, a gauss meter (manufactured by FW BELL, Model 4048) is passed through a path through which a laminate in which a nonmagnetic coating film and a magnetic coating film are formed in this order on a nonmagnetic support is passed in advance. Was obtained by measuring the magnetic field strength in the apparatus while running at a constant speed.

<Constant drying period>
Infrared sensors (fiber type infrared radiation thermometer (FTZ6 type, manufactured by Japan Sensor Co., Ltd.)) were placed in the dryer at intervals of 20 cm, and the surface temperature Ts of the magnetic layer was measured by each infrared sensor. 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 evaluation magnetic tapes of Comparative Examples 1 to 4 having a constant rate drying period shorter than 0.2 seconds, (W _2max −W _1min ) / W _2max ≦ 0.9 and ( W _2max -W _2min) / W be _2max ≦ 0.5 relationships have been met, smoothness, orientation, than that of the at least one magnetic tape for evaluation of examples 1 to 6 of the filling property Inferior. About the magnetic tape for evaluation of Comparative Examples 4-7 in which at least one of the two relational expressions is not satisfied, the orientation is inferior to that of the magnetic tape for evaluation of Examples 1-6. On the other hand, for the magnetic tapes for evaluation of Examples 1 to 6, the smoothness of the magnetic coating film is high (the roughness is small), the orientation of the magnetic powder is excellent (the square shape is large), and magnetic High powder filling (high volume filling).

  Since the present invention can form a magnetic layer with a high filling ratio of magnetic powder, excellent surface smoothness and good orientation of magnetic powder, the present invention is capable of increasing the capacity and enabling high output. This is useful as a method for manufacturing a recording medium.

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 1 is a conceptual diagram illustrating an example of a method for manufacturing a magnetic recording medium according to the present invention. The graph which showed the change of the magnetic field intensity in the dryer shown in FIG. 2A Partial sectional view of an example of the magnetic recording medium of the present invention Partial sectional view of another example of the magnetic recording medium of the present invention Schematic diagram illustrating another example of a method for manufacturing a magnetic recording medium of the present invention The graph which showed the change of the magnetic field intensity in the dryer shown to FIG. 5A Schematic diagram illustrating still another example of the method of manufacturing a magnetic recording medium of the present invention The graph which showed the change of the magnetic field intensity in the dryer shown to FIG. 6A 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 Conceptual diagram illustrating an example of a conventional method of manufacturing a magnetic recording medium The graph which showed the change of the magnetic field intensity in the dryer shown to FIG. 7A

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 3a 1st orientation means 3b 2nd orientation means 5 Guide roll T1 laminated body 10 Magnetic recording medium

Claims (9)

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. A constant rate drying process in which the surface temperature of the magnetic coating film is kept substantially constant, and a surface temperature of the magnetic coating film that is performed after the constant rate drying process is higher than that during the constant rate drying process. Consisting of a reduced rate drying process that solidifies the magnetic coating,
The constant rate drying period in which the constant rate drying process is performed is 0.2 seconds or more,
The magnetic field orientation is performed using the first orientation means and the second orientation means in this order after the start of the preheating process.
The first orientation means has a larger maximum magnetic field strength than the second orientation means,
The second orientation means is at least one of orientation means including a plurality of permanent magnets and orientation means including a plurality of solenoid coils,
After passing through the preheating process in which the magnetic coating film is heated by hot air blown from a hot air supply unit disposed upstream of the first orientation means and the second orientation means, the first orientation means was used. Magnetic field orientation is performed,
The constant rate drying process in which the magnetic coating film is heated by hot air blown from a hot air supply unit disposed on the downstream side of the first orientation means ends within a magnetic field formed by the second orientation means. And
W _{1min is} the minimum value of the magnetic field strength to which the magnetic coating film is exposed while reaching the second alignment means from the portion having the highest magnetic field strength in the first alignment means, and the magnetic coating film in the second alignment means. W the maximum value of the magnetic field strength exposed is _2max, the minimum value of the magnetic field strength magnetic layer is exposed in the second alignment means is taken as W _2min, these values (W _2max -W _1min) / W _2max ≦ 0.9, and method of manufacturing a magnetic recording medium characterized by satisfying the relation _{(W 2max -W 2min) / W} 2max ≦ 0.5.   The method for producing a magnetic recording medium according to claim 1, wherein the magnetic powder has an average particle size of 60 nm or less.   The method of manufacturing a magnetic recording medium according to claim 1, wherein the constant rate drying period is 10 seconds or less.   2. 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 process. The first solvent consists of one solvent or two or more solvents having different boiling points,
The difference between the boiling point of the solvent having the lowest boiling point among the solvents contained in the first solvent and the surface temperature of the magnetic coating film during the constant rate drying process is 1 ° C to 50 ° C. A method for producing the magnetic recording medium according to claim.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the thickness of the magnetic coating film before the drying treatment is 0.3 μm to 24 μm. Before applying the magnetic paint,
A step of applying a nonmagnetic coating material containing a nonmagnetic powder, a second binder resin, and a second solvent to the one main surface side of the nonmagnetic support to form a nonmagnetic coating film;
The magnetic recording according to claim 1, wherein the second solvent contained in the nonmagnetic coating film is removed by the drying process performed in the magnetic layer forming step, and the nonmagnetic coating film becomes a nonmagnetic layer. A method for manufacturing a medium. The magnetic property according to claim 7 , wherein the sum of the thickness of the magnetic coating film before the drying treatment and the thickness of the nonmagnetic coating film before the drying treatment are 0.3 μm to 24 μm. A method for manufacturing a recording medium. The second solvent consists of one kind of solvent, or consists of two or more kinds of solvents having different boiling points,
The difference between the boiling point of the solvent having the lowest boiling point among the solvents contained in the first solvent and the second solvent and the surface temperature of the magnetic coating film during the constant rate drying process is 1 ° C to 50 ° C. A method for manufacturing a magnetic recording medium according to claim 5 .

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