JP5292349B2 - Magnetic recording medium manufacturing apparatus and magnetic recording medium manufacturing method - Google Patents

Description

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

  Currently, the magnetic layer is becoming thinner as the density of magnetic recording on the magnetic recording medium is increased. When the magnetic layer becomes thin, the unevenness of the surface of the support is easily reflected on the surface of the magnetic layer, so that the smoothness of the surface of the magnetic layer is likely to be impaired. If the smoothness of the surface of the magnetic layer is impaired, the electromagnetic conversion characteristics deteriorate. Therefore, by forming a nonmagnetic layer on the support and forming the magnetic layer on this nonmagnetic layer, the smoothness of the surface of the magnetic layer A manufacturing method for ensuring the above has been proposed. The magnetic layer is formed by performing orientation while the magnetic coating layer is in a wet state, and drying and curing. The orientation is a process for making the direction of the magnetic particles contained in the magnetic coating layer constant by exposing the magnetic coating layer to a magnetic field.

  As a method for producing such a magnetic recording medium, a nonmagnetic coating solution is applied to a support to form a nonmagnetic layer, and then a magnetic coating solution containing a magnetic material is applied on the undried nonmagnetic layer. There is known a wet-on-wet manufacturing method in which a nonmagnetic layer and a magnetic layer are applied and cured.

  In the wet-on-wet manufacturing method, since the magnetic coating layer is formed on the undried nonmagnetic layer, there is a concern that the interface between both layers is likely to be disturbed, resulting in deterioration of electromagnetic conversion characteristics. In recent years, with the increase in recording density of magnetic recording media, it has been demanded that the magnetic layer be formed thinner. However, when the magnetic layer is made thinner, the interface between the nonmagnetic layer and the magnetic layer is disturbed. The effect on the electromagnetic conversion characteristics becomes more prominent.

  Accordingly, a wet-on-dry manufacturing method in which a nonmagnetic coating solution applied to a support is dried and a magnetic layer is formed on the dried nonmagnetic layer has been reviewed. In the wet-on-dry method, fluid disturbance does not occur between the nonmagnetic layer and the magnetic layer, so even when the magnetic layer is thinned, the interface between both layers can be made uniform, and high recording is possible. Suitable for high density magnetic recording media.

  As a method for manufacturing a wet-on-dry magnetic recording medium, for example, those described in Patent Documents 1 to 6 below are known.

JP 2006-331575 A JP 2006-209882 A JP 2006-209822 A JP 2002-367159 A JP 2003-340348 A JP 2001-84584 A

  However, in the wet-on-dry method, since the dried nonmagnetic layer contains a fine porous portion, the solvent in the magnetic coating solution applied on the nonmagnetic layer must penetrate into the nonmagnetic layer. Due to this, drying of the magnetic coating layer is accelerated. And if drying of a magnetic coating liquid advances too much before performing an orientation, orientation failure will arise and an electromagnetic conversion characteristic will deteriorate.

  In the above-mentioned Patent Document 1, it is possible to suppress the occurrence of turbulence at the interface between the nonmagnetic layer and the magnetic layer by setting the time from the application of the magnetic coating solution to the orientation to 0.05 seconds or less. Although described, since the distance between the coating portion and the orientation portion of the magnetic coating solution is too short, restrictions on the layout of the apparatus and the conveyance speed of the support are increased.

  In the above-mentioned Patent Document 2, it is described that after applying a nonmagnetic coating solution and performing a drying treatment, the magnetic coating solution is applied while maintaining the film state of the nonmagnetic layer after the drying treatment. The organic solvent contained in the magnetic coating layer penetrates too much into the nonmagnetic layer, and the magnetic coating layer dries quickly.

  Patent Document 3 describes that a solvent layer is formed on a nonmagnetic layer and a magnetic layer is formed on the solvent layer. However, the number of steps for forming the solvent layer increases. Moreover, the interface is roughened by the solvent contained in the solvent layer penetrating into the nonmagnetic layer.

  Patent Document 4 describes that the magnetic coating solution contains more than 50% by weight of an organic solvent having a boiling point of 120 ° C. or higher, but the organic solvent used in the magnetic coating solution is limited.

  Patent Document 5 describes that after applying a coating solution on an object to be coated, a solvent is applied and the applied coating solution is diluted. However, the applied coating solution can be reused. It is not possible to avoid a decrease in productivity.

  In Patent Document 6, after a nonmagnetic layer is formed, a backcoat layer coating solution is applied to the surface of the support opposite to the nonmagnetic coating layer, and the backcoat layer coating solution is in a wet state. Although it is described that the magnetic coating solution is applied and dried at a certain time to delay the drying of the magnetic coating solution, both sides of the support are in a wet state during the manufacturing process. It will increase.

  In the present invention, when a magnetic layer is formed on a nonmagnetic layer, the magnetic coating solution solvent penetrates into the dried nonmagnetic layer, resulting in poor alignment of the magnetic layer and deterioration of electromagnetic conversion characteristics. Provided are a method for manufacturing a magnetic recording medium, an apparatus for manufacturing a magnetic recording medium, and a magnetic recording medium.

  In the case of forming a magnetic coating layer on a dried non-magnetic layer by a wet-on-dry manufacturing method, the present inventor dried the magnetic coating layer before performing orientation on the magnetic coating layer. It was found that solvent penetration into the nonmagnetic layer was the main factor rather than evaporation. Then, the present inventors have found that the support can be cooled to prevent the solvent of the magnetic layer from penetrating into the nonmagnetic layer, and poor orientation can be improved.

The present invention is an apparatus for manufacturing a magnetic recording medium, comprising: a non-magnetic layer formed on a support in a belt-like support; and a magnetic layer formed on the non-magnetic layer,
A non-magnetic coating liquid coating unit for coating a non-magnetic coating liquid on the substrate to be conveyed and forming a non-magnetic coating layer;
A first drying unit for drying the nonmagnetic coating layer formed in the nonmagnetic coating solution coating unit to form the nonmagnetic layer;
Applying a magnetic coating solution containing a magnetic material on the non-magnetic layer formed in the first drying unit, and forming a magnetic coating layer;
An orientation part for orienting magnetic particles contained in the magnetic coating layer formed in the magnetic coating liquid coating part;
And a cooling means for adjusting the temperature of the support that is disposed and transported between the first drying section and the orientation section.

Further, the present invention is a method for producing a magnetic recording medium, comprising a strip-shaped support, a nonmagnetic layer formed on the support, and a magnetic layer formed on the nonmagnetic layer,
A non-magnetic coating solution coating step of coating a non-magnetic coating solution on the substrate to be conveyed and forming a non-magnetic coating layer;
A first drying step of drying the nonmagnetic coating layer formed in the nonmagnetic coating liquid coating step to form the nonmagnetic layer;
Applying a magnetic coating solution containing a magnetic material on the non-magnetic layer formed in the first drying step to form a magnetic coating layer; and
An orientation step of orienting magnetic particles contained in the magnetic coating layer formed in the magnetic coating liquid coating step ;
And a cooling step of adjusting the temperature of the support before the start of the alignment step after the nonmagnetic coating solution coating step.

  According to the present invention, when forming a magnetic layer on a dried nonmagnetic layer, the magnetic coating solution solvent penetrates into the nonmagnetic layer, resulting in poor alignment of the magnetic layer and electromagnetic conversion characteristics. It is possible to provide a method of manufacturing a magnetic recording medium, a magnetic recording medium manufacturing apparatus, and a magnetic recording medium that can suppress deterioration.

It is a cross-sectional schematic diagram which shows the magnetic tape manufactured. It is a figure which shows the manufacturing apparatus of a magnetic tape. It is a figure which shows the modification of the manufacturing apparatus of a magnetic tape. It is a figure which shows the modification of the manufacturing apparatus of a magnetic tape.

  In the following, a procedure for manufacturing a magnetic tape as an example of a magnetic recording medium and a configuration of a manufacturing apparatus used therefor will be described.

FIG. 1 is a diagram schematically showing a cross section of a magnetic tape to be manufactured.
In the manufactured magnetic tape MT, a nonmagnetic layer 1 and a magnetic layer 2 are laminated on a support B.

FIG. 2 is a diagram showing a magnetic tape manufacturing apparatus. The manufacturing apparatus 10 includes a feed roll 11 around which a long belt-like support B is wound, and a support in which a nonmagnetic layer and a magnetic layer are sequentially formed. The magnetic tape is manufactured while the support B fed from the feed roll 11 is transported along the transport path.

  The manufacturing apparatus 10 includes, in order from the upstream side in the transport direction of the support B to be transported, the nonmagnetic coating liquid coating unit 12, the first drying unit 13, the magnetic coating liquid coating unit 14, and the orientation and drying of the magnetic layer. And an orientation portion 20 for performing the following. In addition, a guide roller 6 that supports the opposite side of the recording surface (the surface on which the magnetic layer and the nonmagnetic layer are provided) of the support B to be transported is appropriately provided in the transport path of the support B.

  The nonmagnetic coating liquid coating unit 12 coats a coating liquid containing nonmagnetic particles on the upper surface of the support B to form a nonmagnetic coating layer.

  The first drying unit 13 dries the nonmagnetic coating layer formed by the nonmagnetic coating liquid coating unit 12. The nonmagnetic coating layer is solidified by drying and becomes a nonmagnetic layer.

  The magnetic coating solution application unit 14 applies a coating solution containing magnetic particles on the nonmagnetic layer to form a magnetic coating layer. The magnetic coating layer is conveyed downstream in a wet state.

  The orientation unit 20 orients the magnetic particles contained in the wet magnetic coating layer and dries the magnetic coating layer.

  The orientation unit 20 has a space in which the support B on which the magnetic coating layer is formed is conveyed. A permanent magnet magnetic circuit in which a plurality of permanent magnets 25 that generate a magnetic field are arranged along the transport path is formed in the orientation unit 20. The permanent magnets 25 are arranged in pairs so as to sandwich the transport path, and a plurality of the pairs are arranged at intervals along the transport path. The paired permanent magnets 25 are arranged so that the magnetic poles of the portions facing each other are different. At this time, the direction of the magnetic field generated between the pair of permanent magnets 25 is perpendicular to the surface of the support B to be transported. In the present embodiment, a permanent magnet magnetic circuit is used as the orientation portion, but a solenoid coil may be used, or these may be used in combination. In this embodiment, a vertical magnetic field is generated in the orientation device to vertically align the magnetic coating layer. However, a magnetic field (longitudinal magnetic field) in the transport direction of the support is generated to longitudinally align the magnetic coating layer. It doesn't matter if you let them.

  The orientation portion 20 is provided with an air supply hole 24a and an exhaust hole 24b. The air supply holes 24 a introduce high-temperature dry air into the orientation unit 20. The introduced drying air passes through the gaps between the permanent magnets 25 arranged in the transport direction, and dries the magnetic coating layer of the support transported in the orientation unit 20. The exhaust hole 24b exhausts the dry air in the orientation unit 20 to the outside.

  Thus, in the orientation unit 20, the magnetic coating layer formed on the support B is exposed to the magnetic field of the permanent magnet 25, so that the magnetic particles contained in the magnetic coating layer move according to the direction of the magnetic field, Orientation of the magnetic particles is performed. Moreover, in the orientation part 20, the magnetic coating layer is dried by the drying air.

  The support B on which the magnetic layer and the nonmagnetic layer are formed is taken up by a take-up roll 19 and sent to the next process such as a calendar process (not shown), and then cut to a desired tape width. Complete.

  The manufacturing apparatus 10 sets the support B to 18 ° C. or less after the end of the nonmagnetic coating liquid coating process and before the start of the alignment process. In this configuration example, the manufacturing apparatus 10 includes a cooling unit 30 disposed between the first drying unit 13 and the orientation unit 20.

  The cooling unit 30 blows air to cool the support B being conveyed in the conveyance section Pc from the carry-out port of the first drying unit to the carry-in port of the orientation unit. The air may be blown on the surface of the support B on which the nonmagnetic coating liquid is applied, or on the opposite surface.

  Air is dry air of 10 ° C. or higher and 23 ° C. or lower. If air can cool a support body, not only dry air but other inert gas and gas can be used. In addition, although the one where the temperature which cools the support body B is low has the effect which suppresses penetration of a solvent, in order to prevent the support body B and the dew condensation of the manufacturing apparatus 10, it is necessary to lower the dew point of an application part, and productivity is high. It will go down. For this reason, air is preferably 10 ° C. or higher.

  According to this configuration example, after the magnetic coating solution is applied and before the orientation, the support B is cooled by the cooling unit 30 so that the solvent contained in the magnetic coating solution applied on the nonmagnetic layer is transferred to the nonmagnetic layer. It is possible to suppress permeation and to prevent the magnetic coating layer from drying quickly before orientation. Therefore, it is possible to suppress alignment failure and deterioration of electromagnetic conversion characteristics.

FIG. 3 is a diagram illustrating a modification of the manufacturing apparatus.
In this example, in the conveyance section Pc, on the downstream side of the coating liquid magnetic layer coating liquid coating unit 14 and on the upstream side of the orientation unit 20, the cooling roller 32 that functions as a cooling unit and the control for adjusting the temperature of the cooling roller 32 are performed. The part 34 is arranged.

  The cooling roller 32 has a substantially cylindrical shape, and is in contact with the support B on which the circumferential surface is conveyed. The temperature of the cooling roller 32 is adjusted by the control unit 34 so that at least the circumferential surface is 10 ° C. or higher and 23 ° C. or lower.

  According to this configuration example, the support B can be set to 18 ° C. or less after the nonmagnetic coating liquid coating process of the nonmagnetic coating liquid coating unit 13 is completed and before the alignment process of the alignment unit 20 is started.

FIG. 4 is a diagram illustrating a modification of the manufacturing apparatus.
In this example, the transport section Pc is provided with a control unit 38 that adjusts the temperature of at least one of the coating head that discharges the magnetic coating liquid of the coating liquid magnetic layer coating liquid coating unit 14 and the magnetic coating liquid. The controller 38 adjusts the temperature of at least one of the coating head and the magnetic coating solution to 10 ° C. or more and 23 ° C. or less.

  In the above configuration, the magnetic coating layer was dried in the orientation unit 20 simultaneously with the orientation of the magnetic particles contained in the magnetic coating layer. However, a second drying unit (not shown) for drying the magnetic coating layer may be provided after orientation in the orientation unit 20. Also in this case, by providing the cooling means as in the above example between the first drying unit 13 and the orientation unit 20, the support is placed at 18 ° C. after the nonmagnetic coating liquid coating step and before the orientation step. It can be as follows.

  Next, the support, the nonmagnetic coating solution for the nonmagnetic coating layer, and the magnetic coating solution for the magnetic coating layer will be described.

  The configuration of the nonmagnetic material contained in the nonmagnetic coating solution of the nonmagnetic coating layer is not limited, but usually consists of at least a resin, preferably a powder, for example, an inorganic powder or an organic powder dispersed in the resin Is mentioned. The inorganic powder is usually preferably a nonmagnetic powder, but a magnetic powder may be used as long as this layer is substantially nonmagnetic.

  The nonmagnetic powder can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Examples of inorganic compounds include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and nitridation with an α conversion rate of 90% or more. Silicon, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. are used alone or in combination. The

The surface of the nonmagnetic powder is subjected to surface treatment, and Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, and Y ₂ O ₃ are preferably present. Especially preferred dispersibility is a _{Al 2 O 3, SiO 2,} TiO 2, ZrO 2, more preferably from _{Al 2 O 3, SiO 2,} ZrO 2. These may be used in combination or may be used alone. In addition, a co-precipitated surface treatment layer may be used depending on the purpose, and a method of treating the surface layer with silica after first making alumina present, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

The nonmagnetic powder is used in a range of 20 to 0.1 by weight and 10 to 0.2 by volume with respect to the binder. Japanese Patent Application Laid-Open Nos. 59-142541, 61-214127, and 63-140420 stipulate that the nonmagnetic coating layer contains SnO ₂ . These use iron oxide or BaFe in the magnetic coating layer and have a specific gravity smaller than SnO ₂ , but they are both undercoat formulations of the magnetic coating layer, and their thickness is much thinner than that of the magnetic coating layer. This is an invention different from the present invention.

  The magnetic particles used in the magnetic layer are not particularly limited, but include ferromagnetic metal powder containing α-Fe as a main component, γ-FeOx (x = 1.33 to 1.5), and Co-modified. γ-FeOx (x = 1.33 to 1.5), ferromagnetic alloy fine powder mainly composed of Fe, Ni or Co (75% or more), hexagonal ferrite powder such as barium ferrite and strontium ferrite, iron nitride For example, known ferromagnetic powders can be used. In addition to predetermined atoms, these ferromagnetic powders include Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Atoms such as Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B may be included. These ferromagnetic fine powders may be treated in advance with a dispersant, lubricant, surfactant, antistatic agent or the like, which will be described later. Specifically, JP-B Nos. 44-14090, 45-18372, 47-22062, 47-22513, 46-28466, 46-38755, 47-4286, 47 -12222, 47-17284, 47-18509, 47-18573, 39-10307, 48-39639, U.S. Patent Nos. 3026215, 3031341, 3100194, 324205 No. 3,33889014 and the like.

  Among the ferromagnetic powders, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of the ferromagnetic alloy fine powder can be used, and the following method can be mention | raise | lifted. Method of reducing complex organic acid salt (mainly oxalate) with reducing gas such as hydrogen, method of reducing iron oxide with reducing gas such as hydrogen to obtain Fe or Fe-Co particles, metal carbonyl compound A method of thermal decomposition, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite, or hydrazine to an aqueous solution of a ferromagnetic metal, and evaporating the metal in a low-pressure inert gas to form a fine powder. How to get. The ferromagnetic alloy powder obtained in this manner is a known slow oxidation treatment, that is, a method of drying after immersing in an organic solvent, and after immersing in an organic solvent, an oxygen-containing gas is fed to form an oxide film on the surface and then dried. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

If the ferromagnetic metal powder and the ferromagnetic alloy powder of the magnetic coating layer are expressed by a specific surface area by the BET method, it is 25 to 80 m ² / g, preferably 35 to 60 m ² / g. If it is 25 or less, the noise becomes high, and if it is 80 or more, it is difficult to obtain surface properties. The crystallite size of the ferromagnetic metal powder and the ferromagnetic alloy powder is 450 to 100 angstrom, preferably 350 to 150 angstrom. The saturation magnetization σs of the iron oxide magnetic powder is 50 emu / g or more, preferably 70 emu / g or more, and in the case of a ferromagnetic metal fine powder, 100 emu / g or more is preferred.

  The r1500 of the ferromagnetic metal powder and the ferromagnetic alloy powder is preferably 1.5 or less. More preferably, r1500 is 1.0 or less. r1500 indicates the percentage of the amount of magnetization that remains without being reversed when a magnetic field of 1500 Oe is applied in the opposite direction after saturation magnetization of the magnetic recording medium. The moisture content of the ferromagnetic metal powder and the ferromagnetic alloy powder is preferably 0.01 to 2%. It is preferable to optimize the moisture content of the ferromagnetic metal powder and the ferromagnetic alloy powder depending on the type of the binder. The tap density of γ iron oxide is preferably 0.5 g / cc or more, and more preferably 0.8 g / cc or more.

When using gamma iron oxide, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, more preferably 5 to 10%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 2 to 8%. The pH of the ferromagnetic metal powder and the ferromagnetic alloy powder is preferably optimized depending on the combination with the binder used. The range of the pH of the ferromagnetic metal powder and the ferromagnetic alloy powder is 4 to 12, preferably 6 to 10. The ferromagnetic metal powder and the ferromagnetic alloy powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof if necessary. The amount thereof is 0.1 to 10% with respect to the ferromagnetic metal powder and the ferromagnetic alloy powder. When the surface treatment is performed, the adsorption of a lubricant such as a fatty acid is preferably 100 mg / m ² or less. Ferromagnetic metal powders and ferromagnetic alloy powders may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr.

  Further, it is preferable that the number of pores of the ferromagnetic metal powder and the ferromagnetic alloy powder is small, and the value is 20% by volume or less, more preferably 5% by volume or less. The shape of the ferromagnetic metal powder and the ferromagnetic alloy powder may be any of a needle shape, a granular shape, a rice granular shape, and a plate shape as long as the above-described characteristics regarding the particle size are satisfied. In order to achieve SFD 0.6 or less of the ferromagnetic metal powder and the ferromagnetic alloy powder, it is necessary to reduce the distribution of the coercive force (holding force) Hc of the ferromagnetic metal powder and the ferromagnetic alloy powder. For this purpose, there are methods such as improving the particle size distribution of goethite, preventing sintering of γ-hematite, and slowing the deposition rate of cobalt for cobalt-modified iron oxide.

  Examples of the hexagonal ferrite powder include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and substitutions thereof such as Co. More specifically, magnetoplumbite type barium ferrite and strontium ferrite, magnetoplumbite type ferrite whose particle surface is coated with spinel, magnetoplumbite type barium ferrite and strontium ferrite partially containing a spinel phase, etc. Is mentioned. In addition to predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg , Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb may be included. In general, elements such as Co—Zn, Co—Ti, Co—Ti—Zr, Co—Ti—Zn, Ni—Ti—Zn, Nb—Zn—Co, Sb—Zn—Co, and Nb—Zn are added. You can use things. Some raw materials and production methods contain specific impurities. Other preferable atoms and the content thereof are the same as those of the ferromagnetic metal powder.

The average plate diameter of the hexagonal ferrite powder is 10 nm to 40 nm, preferably 10 nm to 30 nm, and more preferably 15 nm to 25 nm.
The average plate ratio [arithmetic average of (plate diameter / plate thickness)] is 1-15, and preferably 1-7.
When the average plate ratio is 1 to 15, sufficient orientation can be obtained while maintaining high filling properties in the magnetic layer, and noise increase due to stacking between particles can be suppressed. The specific surface area (SBET) by the BET method within the above particle size range is preferably 40 m ² / g or more, more preferably 40 to 200 m ² / g, and 60 to 100 m ² / g. Most preferred.

  The distribution of the particle plate diameter and plate thickness of the hexagonal ferrite powder is generally preferably as narrow as possible. Quantifying the particle plate diameter and plate thickness can be compared by randomly measuring 50 0 particles from the particle T E M photo. In many cases, the distribution of the particle plate diameter and plate thickness is not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0. 1 to 1. 0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improvement process. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

  The coercive force (Hc) of the hexagonal ferrite powder can be in the range of 143.3 to 318.5 kA / m (1800 to 4000 Oe), preferably 159.2 to 238.9 kA / m (2000 to 3000 Oe). ). More preferably, it is 191.0-214.9 kA / m (2200-2800 Oe). The coercive force (Hc) can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions, and the like.

The saturation magnetization (σs) of the hexagonal ferrite powder is 30 to 80 A · m ² / kg (emu / g). Higher saturation magnetization (σs) is preferable, but tends to be smaller as the particle size becomes smaller. In order to improve the saturation magnetization (σ s), it is well known to combine spinel ferrite with magnetoplumbite ferrite and to select the type and amount of elements contained. It is also possible to use W-type hexagonal ferrite. When the magnetic material is dispersed, the surface of the magnetic material particles is also treated with a material suitable for the dispersion medium and the polymer. As the surface treatment agent, inorganic compounds and organic compounds are used. Typical examples of the main compound include oxides or hydroxides such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The addition amount is 0.1 to 10% by mass with respect to the mass of the magnetic substance. The pH of the magnetic material is also important for dispersion. Usually, about 4 to 12 has optimum values depending on the dispersion medium and polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects the dispersion. Although there is an optimum value depending on the dispersion medium and the polymer, 0.01 to 2.0% is usually selected.

The hexagonal ferrite powder is manufactured by mixing (1) barium oxide / iron oxide / metal oxide replacing iron and boron oxide as a glass forming substance so as to have a desired ferrite composition, and then melting and quenching. A glass crystallization method for obtaining barium ferrite crystal powder by washing and pulverizing after re-heating treatment, and (2) neutralizing barium ferrite composition metal salt solution with alkali to produce by-products Hydrothermal reaction method in which barium ferrite crystal powder is obtained by liquid phase heating at 100 ° C or higher after removal of water, followed by washing, drying and pulverization, (3) neutralizing barium ferrite composition metal salt solution with alkali, by-product There is a coprecipitation method in which the product is removed, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder, but the present invention does not select a production method. The hexagonal ferrite powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as required. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid is 100 mg / m ² or less. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they do not particularly affect the characteristics.

  As the binder used for the nonmagnetic coating layer and the magnetic coating layer, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000. Examples of such include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a structural unit, polyurethane resins, and various rubber resins. Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyester resins. And a mixture of an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like.

  These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. Moreover, it is also possible to use well-known electron beam curable resin for a nonmagnetic coating layer or a magnetic coating layer. These examples and their production methods are described in detail in JP-A No. 62-256219. The above resins can be used alone or in combination, but preferably at least one selected from the group of vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer. A combination of a seed and a polyurethane resin, or a combination of these with a polyisocyanate can be mentioned.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all the binders shown here, COOM, SO ₃ M, OSO ₃ M, P═O (OM) ₂ , O—P═O are required to obtain better dispersibility and durability. (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), OH, NR ² , N ⁺ R ³ , R is a hydrocarbon group), at least one selected from an epoxy group, SH, CN, and the like It is preferable to use those obtained by introducing the above polar groups by copolymerization or addition reaction. The amount of such a polar group is 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  Specific examples of the binder include Union Carbide Corporation: VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC, PKFE, Nisshin Chemical Industry Manufactured by: MPR-TA, MPR-TA5, MPR-TAL, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, manufactured by Denki Kagaku: 1000W, DX80, DX81, DX82, DX83, manufactured by Nippon Zeon : MR110, MR100, 400X110A, manufactured by Nippon Polyurethane Co., Ltd .: Nipponporan N2301, N2302, N2304, manufactured by Dainippon Ink Co., Ltd .: Pandex T-5105, T-R3080, T-5201, Vernock D-400, D-210-80, Crisbon 6109, 7209, Oriental Manufactured by: Byron UR8200, UR8300, RV530, RV280, manufactured by Dainichi Seika Co., Ltd .: Daifueramine 4020, 5020, 5100, 5300, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Co., Ltd .: MX5004, manufactured by Sanyo Chemical Co., Ltd .: Samprene SP-150, Asahi Kasei Co., Ltd .: Saran F310, F210 and the like.

  The binder is used in the range of 5 to 50% by weight, preferably in the range of 10 to 30% by weight, based on the ferromagnetic powder. It is preferable to use a combination of 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin, and 2 to 20% by weight of polyisocyanate.

When a polyurethane resin is used, the glass transition temperature is preferably −50 to 100 ° C., the elongation at break is 100 to 2000%, the stress at break is 0.05 to 10 kg / cm ² , and the yield point is preferably 0.05 to 10 kg / cm ² . The magnetic recording medium consists of two layers. Therefore, the amount of the binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, the molecular weight of each resin forming the magnetic coating layer, the polar group amount, or the above-mentioned Of course, it is possible to change the physical characteristics of the resin between the non-magnetic coating layer and the magnetic coating layer as required.

  Examples of the polyisocyanate include tolylene diisocyanate, 4-4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-tolui diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and the like. Isocyanates, products of these isocyanates and polyalcohols, polyisocyanates produced by condensation of isocyanates, and the like can be used. Commercially available product names of these isocyanates include: Nippon Polyurethanes: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical: Takenate D-102, Takenate D- 110N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer Co., Ltd .: Death Module L, Death Module IL, Death Module N, Death Module HL, etc., which can be used alone or by utilizing the difference in curing reactivity. One or a combination of two or more can be used for both the nonmagnetic coating layer and the magnetic coating layer.

Carbon black used for the magnetic coating layer may be rubber furnace, rubber thermal, color black, acetylene black, or the like. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle diameter is 5 m to 300 m μm, pH is 2 to 10, moisture content is 0.1 to 10%, tap density is 0.1 to 1 g / cc is preferred. Specific examples of carbon black include: Cabot Corporation: BLACKPEARLS 2000, 1300, 1000, 900, 800, 700, VULCAN XC-72, Asahi Carbon Corporation: # 80, # 60, # 55, # 50, # 35 Manufactured by Mitsubishi Chemical Industries, Ltd .: # 2400B, # 2300, # 900, # 1000, # 30, # 40, # 10B, manufactured by Conlongbia Carbon Co .: CONDUCTEX SC, RAVEN 150, 50, 40, 15 and the like. Carbon black may be surface-treated with a dispersant or the like, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Carbon black may be dispersed with a binder in advance before being added to the magnetic coating. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% with respect to the ferromagnetic powder. Carbon black functions to prevent the magnetic coating layer from being charged, reduce the coefficient of friction, impart light-shielding properties, and improve film strength. These differ depending on the carbon black used. Therefore, the type, amount, and combination of carbon black is changed between the non-magnetic coating layer and the magnetic coating layer, and it is properly used according to the purpose based on the above-mentioned various characteristics such as particle size, oil absorption, conductivity, and pH. Of course it is possible. For example, it is possible to prevent charging by using highly conductive carbon black for the nonmagnetic layer and to reduce the friction coefficient by using carbon black having a large particle size for the magnetic coating layer. For the carbon black that can be used in the magnetic coating layer, for example, “Carbon Black Handbook” (edited by Carbon Black Association) can be referred to.

As an abrasive used in the magnetic coating layer, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide having an α conversion ratio of 90% or more Known materials having a Mohs hardness of 6 or more, such as titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Further, a composite of these abrasives (a product obtained by surface-treating an abrasive with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect is not affected if the main component is 90% or more. The particle size of these abrasives is preferably from 0.01 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may broaden the particle size distribution and have the same effect. You can also. The tap density is preferably 0.3 to ² g / cc, the moisture content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is 1 to 30 m ² / g. The shape of the abrasive may be acicular, spherical, or cubic, but those having a corner in a part of the shape are preferable because of high polishing properties.

Specific examples of abrasives include: Sumitomo Chemical Co., Ltd .: AKP-20, AKP-30, AKP-50, HIT-50, Nippon Chemical Industry Co., Ltd .: G5, G7, S-1, and Toda Kogyo Co., Ltd .: 100ED, 140ED and the like. Of course, it is possible to change the type, amount, and combination of the abrasive depending on the purpose, depending on the nonmagnetic coating layer and the magnetic coating layer. These abrasives may be added to the magnetic paint after being dispersed with a binder in advance. As for the abrasive | polishing agent which exists in the surface of the magnetic coating layer of a magnetic recording medium, and its end surface, 5 pieces / 100 micrometers ² or more are preferable.

  As the additive, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like are used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, fluorinated graphite, silicone oil, silicone with polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate ester And alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof, polyphenyl ethers, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds and branched) And these metal salts (Li, Na, K, Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (It does not matter whether it contains an unsaturated bond or it may be branched), carbon number 1 -22 alkoxy alcohols, monobasic fatty acids having 10 to 24 carbon atoms (which may contain unsaturated bonds or branched) and monovalent, divalent, trivalent, and tetravalent carbon atoms having 2 to 12 carbon atoms. Mono-fatty acid ester, di-fatty acid ester, tri-fatty acid ester, alkylene oxide polymer comprising any one of monovalent, pentavalent and hexavalent alcohols (which may contain an unsaturated bond or may be branched) Monoalkyl ether fatty acid esters, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used. Specific examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, myristic Examples include octyl acid, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, and lauryl alcohol.

  In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, alkyl Amphoteric surfactants such as bedine type can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

  The type and amount of the lubricant and the surfactant can be properly used in the nonmagnetic coating layer and the magnetic coating layer as necessary. For example, in the non-magnetic coating layer and magnetic coating layer, fatty acids with different melting points are used to control bleeding to the surface, and esters with different boiling points and polarities are used to control bleeding to the surface. By doing so, it is conceivable to improve the stability of coating and increase the amount of lubricant added to the non-magnetic layer to improve the lubricating effect, and is not limited to the examples shown here.

  All or part of the additives may be added in any step of magnetic coating production, for example, when mixed with ferromagnetic powder before the kneading step, in the kneading step with ferromagnetic powder, binder and solvent. When adding, when adding at a dispersion | distribution process, when adding after dispersion | distribution, when adding just before application | coating, etc., there exists. Examples of lubricant products include: NAF-102, NAA-415, NAA-312, NAA-160, NAA-180, NAA-174, NAA-175, NAA-222, NAA-34, NAA, manufactured by NOF Corporation. -35, NAA-171, NAA-122, NAA-142, NAA-160, NAA-173K, castor hardened fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, Naimine L- 201, Nymene L-202, Nymene S-202, Nonion E-208, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-210, Nonion HS-206, Nonion L- 2, Nonion S-2, Nonion S-4, Nonion O-2, Nonion LP 20R, Nonion PP-40R, Nonion SP-60R, Nonion OP-80R, Nonion OP-85R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monoguri MB, Nonion DS-60, Anon BF, Anon LG , Butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Chemical Co., Inc .: oleic acid, manufactured by Takemoto Yushi Co., Ltd .: FAL-205, FAL-123, manufactured by Shin Nippon Chemical Co., Ltd .: ND Chemical-made: TA-3, KF-96, KF-96L, KF-96H, KF410, KF420, KF965, KF54, KF50, KF56, KF-907, KF-851, X-22-819, X-22 822, KF-905, KF-700, KF-393, KF-8 7, KF-860, KF-865, X-22-980, KF-101, KF-102, KF-103, X-22-3710, X-22-3715, KF-910, KF-3935, Lion Armor Company: Armide P, Armide C, Armor slip CP, Lion Oil & Fats: Duomin TDO, Nisshin Oil: BA-41G, Sanyo Chemical: Profan 2012E, New Pole PE61, Ionette MS-400, Ionet MO -200, Ionette DL-200, Ionet DS-300, Ionet DS-1000, Ionet DO-200, and the like.

  The organic solvent is an arbitrary ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol. , Esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, cresol, chlorobenzene , Aromatic hydrocarbons such as, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydride Emissions, chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, those hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. If necessary, the type and amount of the organic solvent may be changed between the magnetic coating layer and the nonmagnetic coating layer. The solubility parameter of the magnetic coating layer improves the surface properties by using a highly volatile solvent for the nonmagnetic coating layer, and improves the coating stability by using a solvent with high surface tension (cyclohexanone, dioxane, etc.) for the magnetic coating layer. Examples include increasing the filling degree using a high solvent, but are not limited to these examples.

  The thickness structure of the magnetic recording medium is that the support is 1 to 100 μm, preferably 5 to 20 μm, the thickness of the nonmagnetic layer is 0.5 to 10 μm, preferably 1 to 5 μm, and the thickness of the magnetic layer is 0.05 μm to 1.0 μm. Hereinafter, it is preferably 0.05 μm or more and 0.6 μm or less, more preferably 0.05 μm or more and 0.3 μm or less. The total thickness of the magnetic layer and the nonmagnetic layer is used in the range of 1/100 to 2 times the thickness of the support.

  A nonmagnetic coating layer for improving adhesion may be provided between the support and the nonmagnetic layer. The thickness of the nonmagnetic coating layer is 0.01 to 2 μm, preferably 0.05 to 0.5 μm.

  A backcoat layer may be provided on the side of the support opposite to the side on which the magnetic layer is formed. The back coat layer has a thickness of 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known nonmagnetic coating layers and backcoat layers can be used.

Supports such as polyethylene terephthalate, biaxially stretched polyethylene terephthalate, polyethylene naphthalate, and other polyesters, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide, etc. Can be used. These supports may be subjected in advance to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment and the like. It is necessary to use a support having a center line average surface roughness of 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less. In addition, these supports preferably have not only a small centerline average surface roughness but also no coarse protrusions of 1 μm or more. The surface roughness shape is freely controlled by the size and amount of filler added to the support as required. Examples of these fillers include organic fine powders such as acrylic, in addition to oxides and carbonates such as Ca, Si, and Ti. The F-5 value in the tape running direction of the support is preferably 5 to 50 kg / mm ² , the F-5 value in the tape width direction is preferably 3 to 30 kg / mm ² , and the F-5 value in the tape longitudinal direction is Generally, it is higher than the F-5 value in the tape width direction, but this is not the case when it is necessary to increase the strength in the width direction.

The heat shrinkage rate of the support is 100 ° C. for 30 minutes in the tape running direction and the width direction, preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferably 1%. Hereinafter, it is more preferably 0.5% or less. The breaking strength in both directions 5 to 100 kg / mm ^2, the elastic modulus is preferably from 100 to 2,000 kg / mm ^2.

  The process for producing a magnetic coating material (coating liquid containing a magnetic material) for a magnetic recording medium comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes as necessary. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent may be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

  Conventionally known manufacturing techniques can be used as a part of the process. In the kneading process, a material having a strong kneading force such as a continuous kneader or a pressure kneader is used, so that a high residual magnetization density (Br ) Can be obtained. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, 30% or more of the total binder is preferable) and 100 parts of the ferromagnetic powder are kneaded in the range of 15 to 500 parts. It is processed. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274.

  A conventionally known manufacturing technique can be used for a coating apparatus used in a manufacturing apparatus for a magnetic recording medium having a sequential multilayer structure. For example, a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in the coating of a magnetic paint, can be mentioned.

  In order to prevent a decrease in electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the ferromagnetic powder, the inside of the coating head can be formed by a method as disclosed in Japanese Patent Application Laid-Open Nos. 62-95174 and 1-2236968. It is desirable to apply shear to the coating solution. Further, the viscosity of the magnetic coating material preferably satisfies the numerical range disclosed in JP-A-3-8471.

  As a magnet that generates a magnetic field for orientation, either a solenoid coil or a permanent magnet may be used as long as it generates a magnetic field of 1000 G or more, but the direction of the magnetic field does not change as much as possible before and after the orientation equipment. It is preferable to design to. Furthermore, it is preferable to provide an appropriate drying step in advance before orientation so that the orientation after drying is the highest.

  A heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyimide amide or the like is used as the calendering roll for performing the surface smoothing treatment of the magnetic recording medium. Moreover, it can also process with metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more, and the velocity is in the range of 20 m / min to 700 m / min.

The friction coefficient with respect to SUS420J of the magnetic layer of the manufactured magnetic recording medium and its opposite surface is preferably 0.5 or less, more preferably 0.3 or less, the surface resistivity is preferably 10 ⁻⁵ to 10 ⁻¹² ohm / sq, magnetic The elastic modulus at 0.5% elongation of the layer is preferably 100 to 2000 Kg / mm ^{2 in} both the running direction and the width direction, the breaking strength is preferably 1 to 30 Kg / cm ² , and the elastic modulus of the magnetic recording medium is the running direction and longitudinal direction. The direction is preferably 100-1500 Kg / mm ² , the residual spread is preferably 0.5% or less, and the heat shrinkage rate at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less, most preferably Preferably it is 0.1% or less.

The residual solvent contained in the magnetic layer of the manufactured magnetic recording medium is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the magnetic layer is contained in the nonmagnetic layer. Less than the solvent is preferred. The porosity of the magnetic layer and the nonmagnetic layer is preferably 30% by volume or less, more preferably 10% by volume or less. The porosity of the magnetic layer is preferably larger than the porosity of the nonmagnetic layer. However, in the opposite case, there is no problem as long as the porosity of the nonmagnetic layer is 20% or less.

(Example)
In order to investigate the relationship between the temperature of the support during production, the thickness of the magnetic layer, and the electromagnetic conversion characteristics, the inventor performed the following measurements.

  In this measurement, the manufacturing apparatus 10 shown in FIG. 2 was used, and the squareness ratio of the magnetic tape was measured when the thickness of the magnetic layer formed in the magnetic coating liquid application part and the temperature of the support B were changed. As a method for measuring the thickness, the cross section of the dried magnetic tape was observed with an SEM, and the thickness of each of the magnetic layer and the nonmagnetic layer was determined.

  The temperature of the support B was the average value of the temperatures measured immediately after application of the magnetic layer coating solution application part 14 and at the carry-in port of the orientation part 20. As a method for measuring the average temperature, the temperature of the support was measured using an explosion-proof infrared temperature sensor (IRt / c IS manufactured by EDDOX).

  The squareness ratio of the magnetic tape was measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer VSM manufactured by Toei Kogyo Co., Ltd.

  In Example 1, the cooling unit 30 sprayed 15 ° C. dry air on the support B to adjust the temperature of the support to 13 ° C.

  In Example 2, 20 degreeC dry air was sprayed on the support body B by the cooling unit 30, and the temperature of the support body was adjusted to 18 degreeC.

  In Comparative Example 1, the magnetic layer coating solution was applied without cooling in the cooling unit 30 and then dried, and then the orientation unit 20 performed orientation. The temperature of the support was 23 ° C.

  In Examples 1 and 2 and Comparative Example 1, the squareness ratio was measured at each of the magnetic layer thicknesses of 50 nm, 70 nm, and 100 nm.

  The following nonmagnetic coating solution was used. In the following description, “parts” indicates parts by mass.

Iron oxide powder (average major axis length: 80 nm) 80 parts Carbon black (average particle size: 25 nm) 20 parts Electron beam curable vinyl chloride copolymer resin 10 parts Electron beam curable polyurethane resin 5 parts Phenylphosphonic acid 2 parts Methyl ethyl ketone 130 Parts cyclohexanone 100 parts stearic acid 1 part butyl stearate 1.5 parts

  The following magnetic coating solutions were used.

Hexagonal barium ferrite powder 100 parts Hc: 2000 Oe (160 kA / m)
Average plate diameter: 20nm
Average plate ratio: 3
BET specific surface area: 80 m ² / g
σs: 50 emu / g (50 A · m ² / kg)
Sulfonic acid group-containing polyurethane resin 18 parts Diamond powder (average particle diameter: 50 nm) 1 part Silicon carbide powder (average particle diameter: 30 nm) 1 part Cyclohexanone 150 parts Methyl ethyl ketone 150 parts Butyl stearate 2 parts Stearic acid 1 part

  About each of the said magnetic coating liquid and a nonmagnetic coating liquid, after kneading each component for 60 minutes with an open kneader, it disperse | distributed for 600 minutes with the sand mill. 6 parts of a trifunctional low molecular weight polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane) was added to each of the obtained dispersions, and 300 parts of methyl ethyl ketone and 150 parts of cyclohexanone were further added to the magnetic coating liquid. Further, after stirring and mixing for 20 minutes, the mixture was filtered using a filter having an average pore size of 1 μm to prepare a magnetic paint and a non-magnetic paint. The solid content concentration of the obtained magnetic layer coating material was 14.7% by mass. Further, the surface roughness Ra on the magnetic layer application side is 1.4 nm and the surface roughness on the back layer application side so that the thickness after drying the coating for the nonmagnetic layer is 1.5 μm. After coating on a PEN support with Ra of 2.0 nm and drying at 100 ° C., an electron beam with an acceleration voltage of 100 kV and an irradiation dose of 5 Mrad was irradiated. On the nonmagnetic layer thus obtained, the magnetic coating solution was applied wet-on-dry so that the thickness after drying was 50 nm, 70 nm, and 100 nm, and dried at 100 ° C.

  The measurement results are shown in Table 1. Table 1 shows the squareness ratio of the magnetic tape when the temperature of the support (° C.) and the thickness of the magnetic layer (nm) in Examples 1 and 2 and Comparative Example 1 were changed.

When the temperature of the support was 13 ° C., it was found that when the thickness of the magnetic layer was 50 to 100 nm, the squareness ratio was 0.70 or more, and the orientation was performed well.
When the temperature of the support was 18 ° C., it was found that when the thickness of the magnetic layer was 70 to 100 nm, the squareness ratio was 0.70 or more, and the orientation was good. Further, when the thickness of the magnetic layer was 50 nm, the squareness ratio was 0.69, and although it did not reach saturation, it was found that the orientation was sufficiently performed. As a result, it was found that good alignment was performed at 50 nm (thickness after drying) up to 18 ° C.
When the temperature of the support was 23 ° C., the squareness ratio was 0.69 or more when the thickness of the magnetic layer was 100 nm, but when the thickness of the magnetic layer was 50 to 70 nm, the squareness ratio was Was 0.67 or less, indicating that the orientation was poor and the electromagnetic conversion characteristics deteriorated.

  The cooling means of the present invention includes various means for cooling the support to 10 ° C. or higher and 23 ° C. or lower.

The present specification discloses the following contents.
(1) An apparatus for manufacturing a magnetic recording medium, comprising: a non-magnetic layer formed on the support on a belt-like support; and a magnetic layer formed on the non-magnetic layer,
A non-magnetic coating liquid coating unit for coating a non-magnetic coating liquid on the substrate to be conveyed and forming a non-magnetic coating layer;
A first drying unit for drying the nonmagnetic coating layer formed in the nonmagnetic coating solution coating unit to form the nonmagnetic layer;
Applying a magnetic coating solution containing a magnetic material on the non-magnetic layer formed in the first drying unit, and forming a magnetic coating layer;
An orientation part for orienting magnetic particles contained in the magnetic coating layer formed in the magnetic coating liquid coating part;
And a cooling unit arranged between the first drying unit and the orientation unit to cool the support being conveyed.
(2) The manufacturing apparatus according to (1),
The said cooling means is a manufacturing apparatus which sprays the air of 10 degreeC or more and 23 degrees C or less to the said support body.
(3) The manufacturing apparatus according to (1),
The said cooling means is a manufacturing apparatus which is the conveyance roll which contact | abutted to the said support body and was adjusted to 10 degreeC or more and 23 degrees C or less.
(4) The manufacturing apparatus according to (1),
The said cooling means is a manufacturing apparatus which adjusts at least one among the coating head which discharges the said magnetic coating liquid in the said magnetic coating liquid application part, and the said magnetic coating liquid to 10 degreeC or more and 23 degrees C or less.
(5) The manufacturing apparatus according to any one of (1) to (4),
The manufacturing apparatus which has a 2nd drying part which dries the said magnetic application layer after the orientation in the said orientation part.
(6) A method for producing a magnetic recording medium, comprising: a non-magnetic layer formed on the support on a belt-like support; and a magnetic layer formed on the non-magnetic layer,
A non-magnetic coating solution coating step of coating a non-magnetic coating solution on the substrate to be conveyed and forming a non-magnetic coating layer;
A first drying step of drying the nonmagnetic coating layer formed in the nonmagnetic coating liquid coating unit to form the nonmagnetic layer;
Applying a magnetic coating solution containing a magnetic material on the non-magnetic layer formed in the first drying unit, and forming a magnetic coating layer; and
An orientation step of orienting magnetic particles contained in the magnetic coating layer formed in the magnetic coating liquid coating portion;
And a cooling step in which the support is set to 18 ° C. or less after the nonmagnetic coating liquid coating step and before the alignment step.
(7) The manufacturing method according to (6),
In the cooling step, the support is cooled by spraying air at 10 ° C. or higher and 23 ° C. or lower.
(8) The manufacturing method according to (7),
A production method wherein the air is dry air.
(9) The manufacturing method according to (7),
In the cooling step, a manufacturing method in which a cooling roll adjusted to 10 ° C. or higher and 23 ° C. or lower is brought into contact with the support and cooled.
(10) The manufacturing method according to (7),
In the cooling step, at least one of a coating head for discharging the magnetic coating solution onto the support and the magnetic coating solution is adjusted to 10 ° C. or more and 23 ° C. or less.
(11) The production method according to any one of (6) to (10),
The manufacturing method which has the 2nd drying process which dries the said magnetic application layer after the orientation in the said orientation part.
(12) A magnetic recording medium obtained by the manufacturing method according to any one of (6) to (11).

12 Non-magnetic coating solution application unit 14 Magnetic coating solution application unit 20 Orientation unit 30 Cooling unit

Claims (16)

An apparatus for manufacturing a magnetic recording medium, comprising: a non-magnetic layer formed on a support in a belt-like support; and a magnetic layer formed on the non-magnetic layer,
A non-magnetic coating liquid coating unit for coating a non-magnetic coating liquid on the substrate to be conveyed and forming a non-magnetic coating layer;
A first drying unit for drying the nonmagnetic coating layer formed in the nonmagnetic coating solution coating unit to form the nonmagnetic layer;
Applying a magnetic coating solution containing a magnetic material on the non-magnetic layer formed in the first drying unit, and forming a magnetic coating layer;
An orientation part for orienting magnetic particles contained in the magnetic coating layer formed in the magnetic coating liquid coating part;
And a cooling device for adjusting the temperature of the support that is disposed and conveyed between the first drying unit and the orientation unit.   The manufacturing apparatus according to claim 1,
  The said cooling means is a manufacturing apparatus which cools the said support body to 18 degrees C or less. The manufacturing apparatus according to claim 1 or 2 ,
The said cooling means is a manufacturing apparatus which sprays the air of 10 degreeC or more and 23 degrees C or less to the said support body. The manufacturing apparatus according to claim 1 or 2 ,
The said cooling means is a manufacturing apparatus which is the conveyance roll which contact | abutted to the said support body and was adjusted to 10 degreeC or more and 23 degrees C or less.   The manufacturing apparatus according to claim 3 or 4,
  The said cooling means is a manufacturing apparatus provided in the surface opposite to the surface in which the said nonmagnetic layer of the said support body was formed. The manufacturing apparatus according to claim 1 or 2 ,
The said cooling means is a manufacturing apparatus which adjusts at least one among the coating head which discharges the said magnetic coating liquid in the said magnetic coating liquid application part, and the said magnetic coating liquid to 10 degreeC or more and 23 degrees C or less. The manufacturing apparatus according to any one of claims 1 to 6 ,
The manufacturing apparatus which has a 2nd drying part which dries the said magnetic application layer after the orientation in the said orientation part. A method for producing a magnetic recording medium, comprising: a non-magnetic layer formed on the support on a belt-like support; and a magnetic layer formed on the non-magnetic layer,
A non-magnetic coating solution coating step of coating a non-magnetic coating solution on the substrate to be conveyed and forming a non-magnetic coating layer;
A first drying step of drying the nonmagnetic coating layer formed in the nonmagnetic coating liquid coating step to form the nonmagnetic layer;
Applying a magnetic coating solution containing a magnetic material on the non-magnetic layer formed in the first drying step to form a magnetic coating layer; and
An orientation step of orienting magnetic particles contained in the magnetic coating layer formed in the magnetic coating liquid coating step ;
And a cooling step of adjusting the temperature of the support before the start of the alignment step after the nonmagnetic coating solution coating step.   It is a manufacturing method of Claim 8, Comprising:
  The said cooling process is a manufacturing method which cools the said support body to 18 degrees C or less. It is a manufacturing method of Claim 8 or 9 , Comprising:
In the cooling step, the support is cooled by spraying air at 10 ° C. or higher and 23 ° C. or lower. It is a manufacturing method of Claim 10 , Comprising:
A production method wherein the air is dry air.   It is a manufacturing method of Claim 10 or 11,
  The manufacturing method which blows the said air on the surface opposite to the surface in which the said nonmagnetic layer of the said support body was formed. It is a manufacturing method of Claim 8 or 9 , Comprising:
In the cooling step, a manufacturing method in which a cooling roll adjusted to 10 ° C. or higher and 23 ° C. or lower is brought into contact with the support and cooled. It is a manufacturing method of Claim 13 , Comprising:
The manufacturing method which makes the said conveyance roll contact | abut on the surface opposite to the surface in which the said nonmagnetic layer of the said support body was formed. It is a manufacturing method of Claim 8 or 9 , Comprising:
In the cooling step, at least one of a coating head for discharging the magnetic coating solution onto the support and the magnetic coating solution is adjusted to 10 ° C. or more and 23 ° C. or less. The manufacturing method according to any one of claims 8 to 15 ,
The manufacturing method which has a 2nd drying process which dries the said magnetic application layer after the orientation in the said orientation process .

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