JP5031474B2 - 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 of magnetic tape include an approach from a recording / reproducing apparatus and an approach from a recording medium.

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

  The approach from the 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, and plates, sufficient capacity cannot be realized unless the gaps in the magnetic layer are reduced to increase the filling property of the magnetic layer. . At the same time, in order to adapt to the use of the MR head, which is the approach from the recording / reproducing apparatus described above, it is necessary to reduce the roughness of the surface of the magnetic layer and make it smooth. Therefore, various approaches for improving the drying process of the magnetic coating film for removing the solvent to form the magnetic layer have been proposed as approaches from the manufacturing technology (see, for example, Patent Documents 1 to 4).

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

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

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

Patent Document 4 discloses a magnetic recording medium and a manufacturing method thereof. In this magnetic recording medium, head contamination and DO (dropout) are improved by setting the amount of residual solvent contained in the magnetic layer to 5 mg / m ² or less. Further, in Patent Document 4, in order to realize the residual solvent amount of 5 mg / m ² or less, the drying rate in the constant rate drying process is 1 to 20 kg / m ² · hr during the drying process. It is disclosed. However, it is not disclosed that in the constant rate drying process, the air flow for drying the magnetic coating film is caused to flow from the other main surface side where the magnetic coating film of the nonmagnetic support is not formed.

As described above, in the manufacturing apparatus and the manufacturing method disclosed in Patent Documents 1 to 4, the opposite of the non-magnetic support on the side where the magnetic coating film is provided in the period before the decreasing rate drying period. It is not disclosed that a drying process is performed by supplying heat from the side, and after a relatively short constant rate drying process, the process proceeds to a decreasing rate drying process. The reason is that if the amount of heat is supplied from the opposite side of the non-magnetic support on which the magnetic coating film is provided or if the constant rate drying process is lengthened, the drying equipment and the orientation equipment become larger, the production speed decreases, etc. This is because there is a disadvantage.
JP-A-10-124866 Japanese Patent Laid-Open No. 2004-19958 Japanese Patent Laid-Open No. 63-42030 JP-A-4-229415

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

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

  The method for 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 paint containing magnetic powder, a first binder resin, and a first solvent to form a magnetic coating film, and performing a drying process to remove the first solvent from the magnetic coating film. In the magnetic layer forming step, the drying treatment is performed after a preheating process for heating the magnetic coating film until the surface temperature of the magnetic coating film stops rising and reaches a substantially constant temperature, and after the preheating process. The constant temperature drying process in which the surface temperature of the magnetic coating film is maintained at a substantially constant temperature, and the surface temperature of the magnetic coating film that is performed after the constant rate drying process is higher than the surface temperature in the constant rate drying process. Until the magnetic coating is heated and solidified. In the preheating process and the constant rate drying process, the air flow for drying the magnetic coating film is caused to flow from the other main surface side of the nonmagnetic support on which the magnetic coating film is not formed. To do.

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

  In the present invention, in the preheating process and the constant rate drying process, the air flow for drying the magnetic coating film is flowed from the main surface side where the magnetic coating film of the nonmagnetic support is not formed. A magnetic layer having excellent surface smoothness can be formed. Therefore, according to the present invention, it is possible to provide a magnetic recording medium with higher capacity and higher output, and a method for manufacturing the same.

  As a result of repeated studies on the conditions of the drying process performed after the application of the magnetic paint, the present inventors have selected the conditions that could not be conventionally assumed for the drying process, so It has been found that a magnetic layer having excellent smoothness can be obtained. Before describing the method for manufacturing a magnetic recording medium of the present invention, first, the drying process in the method for manufacturing a conventional magnetic recording medium will be described with reference to FIG.

  In FIG. 4, the curve consisting of a solid line shows the change (solvent content curve) of the solvent content (hereinafter also referred to as “solvent content”) in the coating film, and the curve consisting of a dotted line is the paint curve. The change in the surface temperature of the film (coating temperature curve) is shown.

  When a drying process is started in a dryer for a magnetic coating film formed by applying a magnetic paint on one main surface side of a non-magnetic support, as shown in FIG. The temperature rises to a temperature at which the amount of solvent evaporation increases 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 conventional drying equipment, hot air having a relatively high temperature and a relatively high wind speed is supplied to the coating film from the side of the nonmagnetic support on which the magnetic coating film is formed. Therefore, the amount of heat supplied from the surroundings to the coating film is overwhelmingly larger than the latent heat of evaporation taken away from the coating film as the solvent evaporates from the coating film. Therefore, the solvent is evaporated in a very short time. That is, the surface temperature Ts of the coating film rises rapidly, and the solvent content of the coating film decreases sharply after almost no constant-rate drying period (described later) in which the surface temperature of the coating film is kept substantially constant. . Over time, the solvent in the coating film almost disappears, the coating film is solidified, and the surface temperature Ts of the coating film approaches the atmospheric temperature in the dryer (decreasing drying period). “Solidification” means that the easy axis of magnetization returns and is not oriented.

  In the magnetic layer forming step, when magnetically orienting the magnetic powder contained in the magnetic coating film in a predetermined direction while performing a drying process, conventionally, it is performed between the end of the application and before the end of the reduced rate drying period. It was. Magnetic field orientation is performed by applying a magnetic field to the coating film from the outside. In the drying process in the conventional method for producing a magnetic recording medium shown in FIG. 4, which hardly passes through a constant rate drying period (described later) and supplies hot air from the side on which the magnetic coating film of the nonmagnetic support is formed, Since removal (drying) of the solvent is completed in a relatively short time, the coating speed can be increased, the dryer length can be shortened, and the equipment required for magnetic field orientation can be reduced. Therefore, the conventional method of manufacturing a magnetic recording medium that performs such a drying process has the advantages of high production efficiency and less capital investment. However, while this conventional manufacturing method is advantageous for high production efficiency and cost reduction, it is insufficient for further increasing the filling rate and smoothing of the magnetic powder in the magnetic layer constituting the magnetic recording medium. .

  On the other hand, in the drying process in the method for producing a magnetic recording medium of the present invention, in the preheating period and the constant rate drying period before the decreasing rate drying period, from the main surface side where the magnetic coating film of the nonmagnetic support is not formed. Drying is performed by flowing a drying air stream. In other words, the preheating process of heating the magnetic coating film until the surface temperature rise of the magnetic coating film stops and reaches a substantially constant temperature, and the surface temperature of the magnetic coating film that is performed after the preheating process is maintained at a substantially constant temperature. In the constant rate drying process, the airflow for drying flows from the main surface side where the magnetic coating film of the nonmagnetic support is not formed. As a result, even when the solvent is evaporated in a very short time, the air flow for drying is not directly blown onto the magnetic coating film, so the filling rate of the magnetic powder is high and the surface smoothness is high. An excellent magnetic layer can be formed.

  Here, the preheating period refers to a period during which a preheating process for heating the magnetic coating film is performed until the increase in the surface temperature of the magnetic coating film stops and reaches a substantially constant temperature. The constant rate drying period refers to a period during which a constant rate drying process is performed after the preheating process and the surface temperature of the magnetic coating film is maintained at a substantially constant temperature. This is called the drying temperature. Also, the rate-of-decreasing drying period is a period for performing the rate-decreasing drying process that is performed after the constant-rate drying process and heating and solidifying the magnetic coating until the surface temperature of the magnetic coating becomes higher than the surface temperature in the constant-rate drying process Say.

  If the airflow for drying is flowed from the main surface side where the magnetic coating film of the nonmagnetic support is not formed in the period prior to the decreasing rate drying period, the magnetic paint without airflow such as far-infrared irradiation is used. The amount of heat supplied to the surface may be supplied from any main surface side of the non-magnetic support. However, when hot air is used as a drying air flow for simplification of the drying equipment, the surface of the magnetic coating film is supplied. The supply of heat is also performed from the main surface side where the magnetic coating film of the nonmagnetic support is not formed.

  The method for producing a magnetic recording medium according to the present invention includes a magnetic recording medium having a single layer structure in which a magnetic layer is directly provided on a nonmagnetic support, and a magnetic layer via a nonmagnetic layer on the nonmagnetic support. The present invention is also applied to a magnetic recording medium having a multi-layer structure provided with. In the method for producing a magnetic recording medium of the present invention, in the magnetic layer forming step, magnetic field orientation that aligns the easy axis of magnetization of the magnetic powder may be performed while performing a drying process, but it may not be performed.

  FIG. 1 is a conceptual diagram showing the relationship between the surface temperature of a coating film and the solvent content in the coating film in an example of the method for producing a magnetic recording medium of the present invention. In FIG. 1, the curve composed of a solid line indicates a change in the solvent content (solvent content curve) in the coating film, and the curve composed of a dotted line indicates a change in the surface temperature of the coating film (coating temperature curve). ing. 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 evaporated by the solvent in the magnetic coating film. The temperature rises to the temperature at which it begins to begin (preheating period) Thereafter, the surface temperature Ts of the magnetic coating film is kept substantially constant for a predetermined period (constant rate drying period). During the constant rate drying period, the balance between the latent heat of evaporation taken from the magnetic coating film by the evaporation of the 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 solvent is present in the magnetic coating film, the coating film is solidified, and the surface temperature Ts of the magnetic coating film approaches the temperature of the atmosphere in the dryer (decreasing drying period).

  As described above, when a constant rate drying period is provided during the drying process, it is possible to suppress the occurrence of intense flow accompanying boiling or the like and the generation of bubbles in the fluid magnetic coating film containing the solvent. . In addition, by actively providing a constant rate drying period during the drying process, the period during which the solvent content of the magnetic coating film decreases at a substantially constant rate is lengthened, and therefore, in the magnetic coating film as the solvent is removed. There are fewer voids that can be generated. Therefore, the magnetic powder can be more densely filled in the magnetic layer. Furthermore, since the smoothness of the surface of the magnetic layer obtained is also improved, the output of the magnetic recording medium is improved.

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

  The constant rate drying period is preferably 0.2 seconds or more. Similarly, when the magnetic coating film is formed on the non-magnetic coating film by the wet-on-wet coating method, the constant rate drying period is preferably 0.2 seconds or more. If the constant rate drying period is too short (in other words, if the removal rate of the solvent is too fast), violent convection is likely to occur in the magnetic coating film being dried, or bubbles are likely to be generated. This is because the magnetic powder filling property and the smoothness of the magnetic layer in the obtained magnetic layer tend to be impaired.

  The upper limit of the constant rate drying period is not particularly limited, but if it is too long, the productivity will be significantly reduced, and it will take time to solidify the coating film. And the equipment is expensive. Therefore, the upper limit of the constant rate drying period is preferably 10 seconds or less. Further, from the viewpoint of further enhancing the filling property, smoothness, and orientation, the constant rate drying period is more preferably 1 second or longer and 10 seconds or shorter.

  The surface temperature Ts of the magnetic coating film during the constant rate drying period varies depending on the boiling point of the 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 composed of two or more kinds of solvents having different boiling points, and the surface temperature Ts of the magnetic coating film during the constant rate drying period is the solvent contained in the first solvent. The temperature is set to be lower than the boiling point Tb of the solvent having the lowest boiling point, and the difference between Tb and Ts (Tb−Ts) is preferably 1 ° C. to 50 ° C. Specifically, since the surface temperature Ts of the magnetic coating film during the constant rate drying period is preferably 30 ° C. to 80 ° C., the Tb is 1 ° C. to 50 ° C. higher than any temperature in the Ts temperature range. A higher 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 Ts of the magnetic coating film during the constant rate drying period. 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. However, in the method for manufacturing a magnetic recording medium according to the present embodiment, the drying airflow is made to flow from the main surface side where the magnetic coating film of the nonmagnetic support is not formed, regardless of what means is used as the heat supply means. There is a need.

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

  The first solvent contained in the magnetic paint is not particularly limited as long as it is a solvent contained in a conventionally known magnetic layer forming paint. For example, methyl ethyl ketone (boiling point 80 ° C.), cyclohexanone (boiling point 156 ° C.), methyl isobutyl ketone Ketone solvents such as (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.) Examples thereof include a solvent and toluene (boiling point 111 ° C.). These may be used alone or in combination of two or more. Among these, cyclohexanone, methyl ethyl ketone, tetrahydrofuran, or toluene is preferable from the viewpoints of solubility in a binder resin (hereinafter also referred to as “first binder resin”) contained in the magnetic coating material, dispersibility in magnetic powder, evaporation rate, and cost. preferable.

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

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

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

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

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

  Next, an example of the method for manufacturing a magnetic recording medium of the present invention will be described more specifically with reference to FIG. FIG. 2 is a conceptual diagram showing an example of the magnetic layer forming process of the present invention.

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

  The magnetic paint is applied by a conventionally known method such as a gravure coating method or a die coating method. The conveying means for the nonmagnetic support 7 and the laminate T is composed of, for example, a plurality of guide rolls 4 and the like.

  In the drying zone B, a plurality of hot air supply units (lower first hot air supply unit 1a2, lower second hot air supply unit 1b2, lower third hot air supply unit 1c2, upper third hot air supply unit 1c1), solvent An exhaust part (upper first exhaust part 2a1, upper second exhaust part 2b1, upper third exhaust part 2c1, lower third exhaust part 2c2) for exhausting hot air containing steam, and a plurality of solenoid coils 3 are arranged. ing. For example, the plurality of solenoid coils 3 are arranged at substantially equal intervals along the traveling direction of the production line. The hot air supply unit is, for example, a dryer capable of blowing hot air. The number and positions of the hot air supply units and the exhaust units are appropriately determined in consideration of the coating speed, the drying zone length, and the like.

  The hot air supply unit includes a lower first hot air supply unit 1a2 disposed upstream of all the solenoid coils 3, and a lower second hot air supply unit 1b2 disposed between the solenoid coils 3. A lower third hot air supply unit 1c2 and an upper third hot air supply unit 1c1 disposed downstream of the solenoid coil 3. 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.

  The laminated body T carried into the drying zone B is first blown out from a plurality of lower first hot air supply units 1a2 provided on the main surface side opposite to the side on which the magnetic coating film of the laminated body T is formed. Preheated by hot air (preheating process). Since the lower first hot air supply unit 1a2 is provided on the main surface side opposite to the side on which the magnetic coating film of the laminate T is formed, the hot air is not directly blown onto the magnetic coating film and is dried. It is possible to form a magnetic layer in which unevenness does not occur and drying inside the magnetic coating film does not become uneven, the filling rate of the magnetic powder is high, and the surface smoothness is excellent. It is preferable that the temperature of the hot air supplied from the lower first hot air supply unit 1a2 is relatively low and the wind speed is also relatively low. The preferred temperature and preferred wind speed vary depending on the thickness of the magnetic coating film, the type of solvent contained in the magnetic coating film (solvent composition), the transport speed of the laminate T, etc., but the temperature is usually preferably 35 ° C to 90 ° C. The wind speed is preferably 0.5 m / second to 15 m / second. This is because when the temperature of the hot air is too low and / or when the wind speed of the hot air is too slow, the preheating is not sufficiently performed and the start of the constant rate drying process is also delayed. In addition, when the temperature of the hot air is too high and / or when the wind speed of the hot air is too high, the surface temperature Ts of the magnetic coating film during the constant rate drying process becomes too high, and the constant rate drying period is within a preferable range. This is because it becomes difficult to control.

  The distance between the lower first hot air supply unit 1a2 and the laminate T is preferably 1 cm to 100 cm. This is because if the distance is within the above range, drying can be performed satisfactorily.

  A heater (not shown) may be used instead of the lower first hot air supply unit 1a2. For example, a far infrared heater can be used as the heater. In the far infrared heater, the area of the heating element is much larger than that of the dryer, and a large area can be uniformly heated at a time. When the heater is used, the heater is not necessarily disposed on the main surface side opposite to the side on which the magnetic coating film of the laminate T is formed, but on the main surface side on which the magnetic coating film of the laminate T is formed. There may be. Further, in the stage of the preheating process, since the evaporation of the solvent is slight, it is not always necessary to flow a drying airflow when preheating using a heater. It is necessary to flow from the main surface side opposite to the side on which the magnetic coating film is formed. Moreover, a heating means may be provided inside the guide roll 4 and the guide roll 4 may be used as a heating roll.

  When the rise in the surface temperature of the magnetic coating film stops and reaches a substantially constant temperature, the preheating process ends. Next, the preheated laminate T is predetermined by hot air supplied from the lower second hot air supply unit 1b2 provided on the main surface side opposite to the side on which the magnetic coating film of the laminate T is formed. During this period, the surface temperature Ts of the magnetic coating film is heated so as to be kept substantially constant (constant rate drying process). The “substantially constant” includes not only the case where it is strictly constant, but also the case where it fluctuates within a range of ± 1 ° C. with respect to the surface temperature Ts at the end of the preheating process. Even in the constant rate drying process, the lower second hot air supply unit 1b2 is provided on the main surface side opposite to the side on which the magnetic coating film of the laminate T is formed, like the lower first hot air supply unit 1a2. As a result, hot air is not directly blown onto the magnetic coating film, causing uneven drying, non-uniform drying inside the magnetic coating film, high filling rate of magnetic powder, and smoothness of the surface. Can form an excellent magnetic layer.

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

  The surface temperature Ts of the magnetic coating film during 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.

  The preferred temperature and preferred wind speed of the hot air supplied from the lower second hot air supply unit 1b2 depend on the thickness of the magnetic coating film, the solvent composition in the magnetic coating film, the transport speed of the laminate T, etc., but the temperature is The temperature is preferably 40 ° C to 100 ° C, and the wind speed is preferably 0.5 m / sec to 15 m / sec. This is because if the temperature of the hot air is too low and / or the speed of the hot air is too slow, the constant rate drying period becomes too long and the production efficiency decreases. If the hot air temperature is too high and / or the hot air speed is too high, the constant rate drying period will be too short, the filling rate of the magnetic powder in the magnetic layer will be low, and the smoothness of the magnetic layer surface will deteriorate. Because it does.

  The distance between the lower second hot air supply part 1b2 and the laminate T is preferably 1 cm to 100 cm. This is because if the distance is within the above range, drying can be performed satisfactorily.

  Next, the laminated body T that has passed over the lower second hot air supply unit 1b2 is further heated by the hot air blown from the upper third hot air supply unit 1c1 and the lower third hot air supply unit 1c2. Thereby, the constant rate drying process is completed, and the decreasing rate drying process is started. In the decreasing rate drying process, the third hot air supply unit may be provided on the side of the laminate T on which the magnetic coating film is formed, on the opposite side, or on both sides as shown in FIG. It may be provided. The magnetic coating film of the laminate T that has been transported in the vicinity of the third hot air supply units 1c1 and 1c2 has already passed the constant rate drying period, and enters the decreasing rate drying period to solidify the coating film to form a magnetic layer. Therefore, even if hot air is blown directly onto the magnetic coating film, the filling property and smoothness of the magnetic layer are not impaired. It is preferable that the temperature of the hot air supplied by the third hot air supply units 1c1 and 1c2 is relatively high and the wind speed is relatively fast. By supplying more heat to the magnetic coating film than in the constant rate drying process, the first solvent remaining in the magnetic coating film is removed as much as possible in a relatively short time, thereby shortening the rate-of-decreasing drying period. It is to do. Thereby, the enlargement of the equipment accompanying performing a constant rate drying process for a predetermined period can be controlled. 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 and preferred wind speed of the hot air supplied from the third hot air supply units 1c1, 1c2 are the thickness of the magnetic coating film, the type of solvent contained in the magnetic coating film (solvent composition), the transport speed of the laminate T, etc. The temperature is preferably 60 ° C. to 120 ° C. and the wind speed is 0.5 m / sec to 30 m / sec so that more heat can be supplied to the magnetic coating film than during the constant rate drying process. preferable. This is because if the hot air temperature is too low and / or the hot air velocity is too slow, the amount of the final residual solvent in the magnetic coating film increases and the running durability of the magnetic layer decreases. In addition, if the temperature of the hot air is too high and / or the wind speed of the hot air is too high, the nonmagnetic support may be thermally deformed.

  The distance between the third hot air supply parts 1c1, 1c2 and the laminate T is preferably 1 cm to 100 cm. This is because the final residual solvent amount can be reduced if the distance is within the above range.

  If necessary, heating means such as a dryer or a far-infrared heater may be provided further downstream of the third hot air supply units 1c1 and 1c2 in the production line to remove a trace amount of the final residual solvent in the magnetic coating film. The durability of the magnetic layer can be further improved.

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

  Moreover, the temperature and wind speed of the hot air supplied from the lower first hot air supply unit 1a2, the lower second hot air supply unit 1b2, and the third hot air supply units 1c1, 1c2 do not necessarily have to be different from each other. For example, both may be the same. However, for example, the hot air supplied from the lower first hot air supply unit 1a2, the hot air supplied from the lower second hot air supply unit 1b2, and the third hot air supply while securing the constant rate drying period of 2 seconds or more If the temperature and wind speed are the same for the hot air supplied from the sections 1c1 and 1c2, the zone length of the drying zone B 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 is larger in the order of the lower first hot air supply unit 1a2, the lower second hot air supply unit 1b2, and the third hot air supply units 1c1 and 1c2.

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

  Next, an example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium of the present invention will be described with reference to the drawings. FIG. 3 is a partial cross-sectional view showing an example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium of the present invention. In FIG. 3, the magnetic recording medium 10 has a nonmagnetic layer 12 and a magnetic layer 13 arranged in this order on one main surface of a nonmagnetic support 11. 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 be provided as necessary.

  In this specification, the magnetic properties of the ferromagnetic powder are values measured by a sample vibration type magnetometer when an external magnetic field 1273.3 kA / m (16 kOe) is applied.

  In addition, in this specification, the average particle diameter is 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). It is a value (number average particle diameter) obtained by actual measurement and averaging these values.

<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 coating material, and the strength of the magnetic recording medium is reduced. Further, if the thickness of the nonmagnetic support 11 is too thick, the total thickness of the magnetic recording medium is increased. For example, in the case of a magnetic tape, the recording capacity per roll is reduced.

The Young's modulus in the longitudinal direction of the nonmagnetic support 11 is preferably 6 GPa (612 kg / mm ² ) or more, and more preferably 8 GPa (816 kg / mm ² ) or more. This is because if the Young's modulus is too small, the running of the magnetic tape becomes unstable. In the magnetic tape on which information is recorded by the helical scan method, the Young's modulus in the longitudinal direction (MD) / Young's modulus in the width direction (TD) is preferably 0.60 to 0.80, and 0.65. It is more preferable that it is -0.75. If (MD's Young's modulus / TD's Young's modulus) is too small or too large, the mechanism is currently unknown, but the output variation (flatness) between the entry side and the exit side of the track of the magnetic head. ) Becomes larger. The flatness is minimized when (Young's modulus of MD / Young's modulus of TD) is around 0.70. For magnetic tape on which information is recorded by the linear recording method, the reason is not clear, but if (MD Young's modulus / TD Young's modulus) is 0.70 to 1.30, the flatness can be kept small. 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 less than 0.2 μm. When the thickness of the magnetic layer 13 is less than 0.2 μm, in order to ensure the durability of the magnetic layer 13 and to apply the magnetic paint with good uniformity in the formation process, the magnetic layer 13 and the magnetic layer 13 are magnetically coupled. A nonmagnetic layer 12 is preferably provided between the layer 13 and the layer 13. The nonmagnetic layer 12 includes, for example, nonmagnetic powder and a binder resin. As the binder resin contained in the nonmagnetic layer 12 (hereinafter also referred to as “second binder resin”), for example, a binder resin similar to the first binder resin constituting the magnetic layer 13 is used.

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

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

  As a solvent contained in the nonmagnetic paint for forming the nonmagnetic layer 12 (hereinafter also referred to as “second solvent”), 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, but the surface temperature Ts of the magnetic coating film during the constant rate drying period described above is: The temperature is set to be lower than 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 difference (tb−Ts) between the tb and the Ts is 1 ° C. or more and 50 ° C. The following is preferable. By selecting such a solvent, the constant rate drying period can be easily controlled.

  The content of the solvent exclusion component (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 content of the solvent-exclusion component in the non-magnetic coating is too small, the viscosity is too small and the dispersibility of the non-magnetic powder decreases, and the interface between the magnetic coating and the non-magnetic coating becomes uneven. . On the other hand, if the content of the solvent-exclusion component in the nonmagnetic paint is too large, 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. As commercial products, “GARFAC RS410” manufactured by Toho Chemical Co., Ltd., “JP-502”, “JP-504”, “JP-508” manufactured by Johoku Chemical Industry Co., Ltd., and the like can be used.

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

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

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

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

<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, more preferably 0.03 μm or more and 0.1 μm or less. These ranges are preferred because if the thickness is too small, the output obtained is small and it is difficult to form the uniform magnetic layer 13. Further, if the thickness is too thick, the resolution characteristic for short wavelength recording is deteriorated.

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

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

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.

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

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

  A well-known thing can be used for an iron nitride magnetic powder. The shape of the iron nitride magnetic powder may be a spherical shape or an indefinite shape such as a cubic shape in addition to the needle shape.

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

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

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

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

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

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

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

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

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

  The content of the first binder resin contained in the magnetic coating for forming the magnetic layer is preferably 7 to 50 parts by weight, and 10 to 35 parts by weight, with respect to 100 parts by weight of the magnetic powder. And more preferred. When the first 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. It is preferable.

  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 to crosslink. It is preferable that a thermosetting crosslinking agent 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 film is formed by a wet-on-wet coating method on a nonmagnetic coating film formed by coating a nonmagnetic coating material on a nonmagnetic support, a nonmagnetic coating film is used. Part of the polyisocyanate therein is diffusely supplied to the magnetic coating film. Therefore, even if the magnetic paint does not contain polyisocyanate, crosslinking is performed to some extent in the magnetic coating film.

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

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

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

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

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

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

  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 the fatty acid ester 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 Various ester compounds such as oleate, butyl stearate, sec-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 2-hexyldecyl stearate, Examples include butyl palmitate, 2-ethylhexyl myristate, oleyl oleate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, diethylene glycol dipalmitate, etc. Door can be.

  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 the reduction effect of a friction coefficient will become small as content of 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 ester contained in the magnetic layer 13 may be the same as the fatty acid ester contained in the nonmagnetic layer 12.

<Back coat layer>
A back coat layer 14 is preferably provided on the main surface of the nonmagnetic support 11 opposite to the main 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. If the thickness of the backcoat layer 14 is too thin, the effect of improving the running performance is insufficient, and if the thickness is too thick, the total thickness of the magnetic tape is increased and the recording capacity per magnetic tape is reduced. is there.

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

  The average particle size of the small particle size carbon black is preferably 5 nm or more and less than 200 nm, and more preferably 10 to 100 nm. If the average particle size is too small, it is difficult to disperse the carbon black in the paint, and if the average particle size is too large, a large amount of carbon black is required. Therefore, if the average particle diameter is too small or too large, the surface of the backcoat layer becomes rough, and there is a risk of causing back-off (embossing) to the magnetic layer, which is not preferable.

  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 14.

  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 14 is magnetic, the backcoat layer is usually nonmagnetic.

  In this specification, using a general-purpose three-dimensional surface structure analyzer “New View 5000” manufactured by ZYGO, the surface roughness of 10 fields of view is measured by scanning white light interferometry, and the average value is averaged. The surface roughness Ra is used. 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 coefficient of friction and improve the running performance of the magnetic head, it is preferable to use a cellulose resin and a polyurethane resin in combination as the binder resin. The content of the binder resin is usually preferably 40 to 150 parts by weight, more preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight based on 100 parts by weight of the total powder contained in the backcoat layer 14. More preferably, it is part by weight and even more preferably 70 to 110 parts by weight. This is because if the amount is too small, the strength of the backcoat layer 14 becomes insufficient, and if the amount is too large, the friction coefficient tends to increase. When the total powder weight contained in the back coat layer is 100 parts by weight, the binder resin preferably contains 30 to 70 parts by weight of a cellulose-based resin and 20 to 50 parts by weight of a polyurethane-based resin. The coating material for forming the backcoat layer 14 preferably contains a crosslinking agent in order to cure the binder resin. As a crosslinking agent, a polyisocyanate compound etc. are mentioned, for example.

  The crosslinking agent contained in the coating material for forming the backcoat layer 14 is the same as the crosslinking agent contained in the magnetic coating material for forming the magnetic layer and the nonmagnetic coating material for forming the nonmagnetic layer, for example. Good. The content of the crosslinking agent is usually preferably 10 to 50 parts by weight, more preferably 10 to 35 parts by weight, and even more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder resin. . This is because if the amount is too small, the strength of the backcoat layer 14 becomes weak, and if the amount is too large, the dynamic friction coefficient against SUS (stainless steel) increases.

<Organic solvent>
As the second solvent contained in the nonmagnetic paint for forming the nonmagnetic layer and the solvent contained in the paint for forming the backcoat layer, the same solvent as the first solvent contained in the magnetic paint for forming the magnetic layer may be used. . Further, the content of the solvent-exclusion component in the non-magnetic coating material for forming the non-magnetic layer and the content of the solvent-exclusion component in the coating material for forming the back coat layer are 10 to 50 weights for the same reason as in the case of the magnetic coating material. % Is preferable, and 20 to 35% by weight is more preferable. Therefore, the content of the second solvent contained in the nonmagnetic paint is preferably 50 to 90% by weight, more preferably 65 to 80% by weight, and the content of the solvent contained in the paint for forming the backcoat layer is also 50%. -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.

Example 1
<Preparation of coating material for nonmagnetic layer formation>
The following components A, B, and C were prepared as blending components for the nonmagnetic layer-forming coating material. First, component A was kneaded with a batch kneader. Next, the B component was added to the kneaded A component and stirred, and then subjected to a dispersion treatment for 60 minutes (residence time) using a sand mill. Furthermore, the C component was added to the mixture of the A component and the B component, and the mixture was stirred and filtered to obtain a nonmagnetic coating material for forming a nonmagnetic layer.
(1) Component A acicular iron oxide (average particle size: 0.11 μm) 68 parts by weight Carbon black (average particle size: 0.025 μm) 20 parts by weight Granular alumina powder (average particle size: 0.4 μm) 12 parts by weight Methyl acid phosphate 1 part by weight Vinyl chloride-hydroxypropyl acrylate copolymer resin 9 parts by weight (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 5 parts by weight (Glass transition temperature: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Tetrahydrofuran 13 parts by weight Cyclohexanone 63 parts by weight Methyl ethyl ketone 137 parts by weight (2) B component butyl stearate 2 parts by weight Cyclohexanone 50 parts by weight Toluene 50 parts by weight (3) C component Polyisocyanate 6 parts by weight Cyclohexanone 9 parts by weight Toluene 9 parts by weight

<Preparation of coating material for magnetic layer formation>
The following a component, b component, and c component were prepared as a compounding component of the magnetic layer forming paint. First, the component a was kneaded with a batch kneader. Next, the b component was added to the kneaded a component and diluted with stirring to obtain an undispersed paint. Subsequently, the undispersed paint was subjected to a dispersion treatment for 90 minutes (residence time) using a nanomill (manufactured by Asada Tekko). Furthermore, the c component was added to the mixture of the a component and the b component, stirred, and filtered to obtain a magnetic coating material for forming the magnetic layer.
(1) Component a Ferromagnetic iron-based metal magnetic powder 100 parts by weight (Al—Y—Fe—Co) [σs: 120 Am ^{2 /} kg (120 emu / g), Hc: 176.3 kA / m (2215 Oe), average particle Diameter: 45 nm, true density ρ: 5.7 g / cm ³ ]
Vinyl chloride-hydroxypropyl acrylate copolymer resin 17 parts by weight Polyester polyurethane resin 6 parts by weight Granular alumina powder (average particle size: 0.2 μm) 10 parts by weight Methyl acid phosphate 4 parts by weight Methyl ethyl ketone 35 parts by weight Cyclohexanone 110 parts by weight Toluene 110 Parts by weight (2) component b palmitic acid amide 1 part by weight butyl stearate 1 part by weight cyclohexanone 30 parts by weight toluene 30 parts by weight (3) component c polyisocyanate 6 parts by weight methyl ethyl ketone 2 parts by weight cyclohexanone 8 parts by weight toluene 8 parts by weight

  Next, the magnetic layer forming process of this embodiment will be described with reference to FIG. FIG. 5 is a conceptual diagram showing the magnetic layer forming process of this embodiment. In FIG. 5, the same parts as those of FIG.

  The coating zone A has the same configuration as the coating zone A in FIG. 2 except that two extrusion coaters are continuously arranged.

  The hot air supply unit in the drying zone B includes a first hot air supply unit including an upper first hot air supply unit 1a1 and a lower first hot air supply unit 1a2, and an upper second hot air supply unit 1b1 and a lower second hot air supply unit 1b2. And a third hot air supply unit including an upper third hot air supply unit 1c1 and a lower third hot air supply unit 1c2. The exhaust part of the drying zone B includes a first exhaust part including an upper first exhaust part 2a1 and a lower first exhaust part 2a2, and an upper second exhaust part 2b1 and a lower second exhaust part 2b2. 2 exhaust parts, and a third exhaust part having an upper third exhaust part 2c1 and a lower third exhaust part 2c2.

  First, in the coating zone A, the nonmagnetic coating material 8a for forming the nonmagnetic layer is applied onto a nonmagnetic support 7 made of a polyethylene naphthalate film having a thickness of 8 μm by using an extrusion type coater. A coating film was formed. Next, the magnetic coating film 8b for forming the magnetic layer was coated on the nonmagnetic coating film by a wet-on-wet coating method using an extrusion coater to form a magnetic coating film.

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

  Next, the laminated body T in which the nonmagnetic coating film and the magnetic coating film are formed in this order on the nonmagnetic support 7 is made of a permanent magnet 9 (external magnetic field: 398 kA / m) whose N pole and N pole face each other. Passed between. Thereafter, in the drying zone B shown in FIG. 5, magnetic field orientation was performed while removing the solvent contained in the nonmagnetic coating film and the magnetic coating film.

  In this embodiment, five solenoid coils 3 (external magnetic field: 398 kA / m) were used to perform magnetic field orientation. The third hot air supply unit uses two of the upper third hot air supply unit 1c1 and the lower third hot air supply unit 1c2, the temperature of the hot air is 100 ° C., the wind speed is 40 m / sec, and the distance from the laminate T Table 1 shows drying conditions such as the temperature of the hot air, the wind speed, and the distance between the hot air supply unit and the laminate T. Note that “upper” in the “position” column of the hot air supply unit in Table 1 does not use the hot air supply unit on the side opposite to the magnetic layer side of the nonmagnetic support 7 and uses the hot air supply unit on the magnetic layer side. "Lower side" indicates that the hot air supply part on the magnetic layer side of the nonmagnetic support 7 is not used, and only the hot air supply part on the opposite side to the magnetic layer side is used.

  The temperature and wind speed of each of the first hot air supply unit and the second hot air supply unit become substantially constant (constant drying temperature) when the surface temperature of the magnetic coating film stops increasing, and the constant rate After maintaining the drying temperature for a predetermined time, the surface temperature of the magnetic coating film was adjusted to be higher than the constant drying temperature so that the nonmagnetic coating film and the magnetic coating film were solidified.

<Preparation of paint for forming backcoat layer>
The following components were prepared as blending components for the backcoat layer-forming paint.
Carbon black (average particle size: 25 nm) 80 parts by weight Carbon black (average particle size: 350 nm) 10 parts by weight Granular iron oxide (average particle size: 50 nm) 10 parts by weight Nitrocellulose 45 parts by weight Polyurethane resin 30 parts by weight Cyclohexanone 260 parts by weight Parts Toluene 260 parts by weight Methyl ethyl ketone 525 parts by weight Polyisocyanate 15 parts by weight

  Next, all the components other than the polyisocyanate among the components of the coating material for forming the backcoat layer were dispersed and mixed in a sand mill, and then the polyisocyanate was added thereto. Subsequently, 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 to obtain a magnetic sheet.

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

(Examples 2 and 3, Comparative Examples 1 and 2)
As shown in Table 1, magnetic tapes for evaluation of Examples 2 and 3 and Comparative Examples 1 and 2 were produced in the same manner as Example 1 except that the drying conditions were different.

  The evaluation magnetic tapes obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated as follows, and the results are shown in Table 1.

<Constant rate drying period>
Infrared sensors (fiber type infrared radiation thermometer “FTZ6 type” manufactured by Japan Sensor Co., Ltd.) were arranged in the drying zone B at intervals of 20 cm, and the surface temperature Ts of the magnetic layer was measured. If the temperature difference is within 2 ° C. no matter how the surface temperatures Ts of the respective magnetic layers obtained from the three continuously arranged sensors are combined, it is determined that constant rate drying is being performed. The drying time was measured. The average value of the surface temperature Ts of the magnetic layer during constant rate drying is shown in Table 1 as the constant rate drying temperature.

<Surface roughness of magnetic layer>
As described above, the surface roughness of 10 fields of the surface of the magnetic layer is measured by a scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer “New View 5000” manufactured by ZYGO, and the average value thereof. Was the average surface 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 was 72 μm × 54 μm.

<Magnetic properties>
After applying an external magnetic field of 0.8 MA / m (10 kOe) to the magnetic tape, the square magnet (Br / Bs) and the saturation magnetization 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 resin-sealing the magnetic tape, 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 shortest distance between any five points on the boundary line and the outline of the magnetic layer was measured, 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 volume filling degree (Vol%) of the magnetic powder was determined from the following formula (2) using Bs, σs (emu / g) and the true density ρ (g / cm ³ ) of the magnetic powder.

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

  As shown in Table 1, for the magnetic tapes of Examples 1 to 3, only the hot air supply part on the side opposite to the magnetic layer side of the nonmagnetic support was used as the first hot air supply part and the second hot air supply part. Therefore, compared with Comparative Examples 1 and 2 using only the hot air supply part on the magnetic layer side of the nonmagnetic support as the hot air supply part, the volume filling property of the magnetic powder is high and the smoothness of the magnetic layer is excellent. It was confirmed that About the orientation (square shape) of the magnetic powder of the magnetic tape of Examples 1-3, it was 0.85 or more and was superior to that of Comparative Examples 1 and 2. In addition, it was confirmed that when the constant rate drying period was 0.2 seconds or more and less than 10 seconds, a magnetic tape having excellent magnetic layer smoothness and magnetic powder filling properties could be provided.

  As mentioned above, although an example of the manufacturing method of the magnetic recording medium of this invention was demonstrated, this example is the process of apply | coating and drying the coating material which contains powder with binder resin, and forming a functional layer It can be applied to other product fields including

  The present invention is useful as a method for producing a magnetic recording medium having a larger capacity and higher output because it can form a magnetic layer having a high filling rate of magnetic powder and excellent surface smoothness.

It is the conceptual diagram which showed the relationship between the surface temperature of the coating film in the example of the manufacturing method of the magnetic recording medium of this invention, and the solvent content in a coating film. It is the conceptual diagram which showed an example of the magnetic layer formation process of this invention. It is a fragmentary sectional view which shows an example of the magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium of this invention. It is the conceptual diagram which showed the relationship between the surface temperature of the coating film and the solvent content in a coating film in an example of the manufacturing method of the conventional magnetic recording medium. It is the conceptual diagram which showed the magnetic layer formation process of the Example.

Explanation of symbols

1a1 Upper first hot air supply unit 1a2 Lower first hot air supply unit 1b1 Upper second hot air supply unit 1b2 Lower second hot air supply unit 1c1 Upper third hot air supply unit 1c2 Lower third hot air supply unit 2a1 Upper first exhaust Part 2a2 Lower first exhaust part 2b1 Upper second exhaust part 2b2 Lower second exhaust part 2c1 Upper third exhaust part 2c2 Lower third exhaust part 3 Solenoid coil 4 Guide roll T Laminate 10 Magnetic recording medium

Claims (16)

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. Including a magnetic layer forming step of performing a drying treatment to remove,
In the magnetic layer forming step, the drying treatment is performed after a preheating process of heating the magnetic coating film until an increase in the surface temperature of the magnetic coating film stops and reaches a substantially constant temperature. The constant rate drying process in which the surface temperature of the magnetic coating film is maintained at a substantially constant temperature, and the surface temperature of the magnetic coating film that is performed after the constant rate drying process is higher than the surface temperature in the constant rate drying process. It consists of a reduced rate drying process that heats and solidifies the magnetic coating,
Wherein the preheating process and the constant rate drying process, and the flow from the other main surface side of the drying air stream the magnetic layer of the nonmagnetic support is not formed of the magnetic coating film,
The method for producing a magnetic recording medium according to claim 1, wherein the airflow for drying the magnetic coating film in the decreasing rate drying process is higher than the temperature of the airflow for drying in the constant rate drying process .   The method of manufacturing a magnetic recording medium according to claim 1, wherein in the magnetic layer forming step, the magnetic powder contained in the magnetic coating film is magnetically oriented in a predetermined direction while performing the drying treatment. The first solvent consists of one solvent or two or more solvents having different boiling points,
2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the surface temperature of the magnetic coating film in the constant rate drying process is lower than the boiling point of the solvent having the lowest boiling point among the solvents contained in the first solvent. Method.   The method of manufacturing a magnetic recording medium according to claim 1, wherein the drying airflow is hot air.   The method for manufacturing a magnetic recording medium according to claim 1, wherein a constant-rate drying period in which the constant-rate drying process is performed is 0.2 seconds to 10 seconds.   The method for manufacturing a magnetic recording medium according to claim 1, wherein a constant rate drying period in which the constant rate drying process is performed is 1 second to 10 seconds.   The method for producing a magnetic recording medium according to claim 1, wherein a surface temperature of the magnetic coating film in the constant rate drying process is 30 ° C. to 80 ° C.   The difference between the surface temperature of the magnetic coating film in the constant rate drying process and the boiling point of the solvent having the lowest boiling point among the solvents contained in the first solvent is 1 ° C to 50 ° C. Manufacturing method of magnetic recording medium.   The method of manufacturing a magnetic recording medium according to claim 1, wherein a 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 treatment 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 10, 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 first solvent and the second solvent are composed of one kind of solvent or two or more kinds of solvents having different boiling points,
The surface temperature of the magnetic coating film in the constant rate drying process is a temperature lower than the boiling point of the solvent having the lowest boiling point among the solvents contained in the first solvent and the second solvent. A method of manufacturing a magnetic recording medium.   The difference between the surface temperature of the magnetic coating film in the constant rate drying process and the boiling point of the solvent having the lowest boiling point among the solvents contained in the first solvent and the second solvent is 1 ° C to 50 ° C. The method for producing a magnetic recording medium according to claim 12.   The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic powder includes a ferromagnetic iron-based metal magnetic powder, and the ferromagnetic iron-based metal magnetic powder has an average particle diameter of 10 nm to 60 nm.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic powder includes iron nitride magnetic powder, and the iron nitride magnetic powder has an average particle diameter of 5 nm to 20 nm.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic powder includes hexagonal Ba-ferrite magnetic powder, and the hexagonal Ba-ferrite magnetic powder has an average particle diameter of 10 nm to 30 nm.

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