JP2010027123A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium which has an excellent electromagnetic conversion characteristic. <P>SOLUTION: The perpendicular magnetic recording medium is provided with, sequentially on a non-magnetic support: a soft magnetic layer including a soft magnetic powder and a binder; and a magnetic layer including a ferromagnetic powder and a binder, and is provided with a non-magnetic layer including a non-magnetic powder and a binder between the non-magnetic support and the soft magnetic layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium, and more particularly to a coating type magnetic recording medium excellent in high density recording.

  In general, magnetic recording is mainly performed using a magnetization in the in-plane direction of a recording medium. However, in the method using the in-plane magnetization, it is difficult to obtain a recording density higher than a certain level because the demagnetizing field in the recording medium increases when attempting to increase the recording density.

  In order to exceed the limit of the recording density, a perpendicular magnetic recording method using magnetization in a direction perpendicular to the surface of the recording medium has been proposed in recent years. This perpendicular magnetic recording system has a characteristic that a demagnetizing field in a recording medium is reduced at a high recording density, and can be said to be a recording system suitable for a high recording density. In particular, recently, a coated film type perpendicular magnetic recording medium has attracted attention from the viewpoint of practicality such as cost advantage and durability of the coating type.

  In general, in order to efficiently generate a magnetic flux leakage from the medium surface, a soft magnetic layer having a high magnetic permeability and a low coercive force is formed between a magnetic layer vertically aligned with a nonmagnetic support. It is known as disclosed in Patent Documents 1 to 3.

  For example, in Patent Document 1, a low coercive force layer having a coercive force of 15.9 kA / m (200 Oe) or less, which is measured in the longitudinal direction, including magnetic powder and a binder on a nonmagnetic support, and magnetic powder and a binder In this order, the magnetic layer for signal recording containing 5 to 50 nm is composed of iron or a transition element mainly composed of iron and nitrogen as essential constituent elements. And an essentially spherical or elliptical iron nitride-based magnetic powder having an average particle diameter of 1 to 2 and an average axial ratio of 1 to 2, and are substantially perpendicularly oriented and measured in a direction perpendicular to the magnetic layer surface. The magnetic force is 79.6 to 318.4 kA / m (1000 to 4000 Oe), the square shape measured in the vertical direction is in the range of 0.6 to 0.9 after demagnetizing correction, and the magnetic layer thickness is 300 nm or less. Magnetic recording medium characterized by It has been disclosed.

In Patent Document 2, a magnetic recording medium in which a soft magnetic layer and a ferromagnetic layer adjacent to the soft magnetic layer are formed on the nonmagnetic support so as to be the uppermost layer, the ferromagnetic layer is made strong with a binder resin. When the thickness of the ferromagnetic layer is X μm and the sum of the maximum height SR _p and the maximum depth SR _v (P−V) of the magnetic layer is Y μm. A magnetic recording medium characterized by 0.1 ≦ X + Y ≦ 0.4 is disclosed.

  In Patent Document 3, in a magnetic recording medium in which a magnetic layer comprising at least two layers of a low coercive force layer and a quasi-perpendicularly oriented magnetic layer provided adjacent thereto is formed on a nonmagnetic support. The low coercive force layer is mainly composed of a magnetic powder having an average particle size of 200 mm or less, a Curie temperature of 180 ° C. or less, and a coercive force of 1.59 kA / m (20 Oe) or less, and a binder resin. The quasi-perpendicularly oriented magnetic layer mainly comprises a ferromagnetic powder and a binder resin, and the ferromagnetic powder has a magnetic axis oriented in a quasi-perpendicular direction with respect to the surface of the nonmagnetic support. A magnetic recording medium is disclosed which is a powder and has a quasi-vertically oriented magnetic layer having a thickness of 0.5 μm or less.

JP 2004-335019 A JP 7-78332 A JP-A-5-325174

  However, in these conventional techniques, the characteristics of the magnetic powder of the uppermost magnetic layer and the relationship between the thickness of the magnetic layer and the roughness shape are characterized to improve electromagnetic conversion characteristics. (Patent Documents 1 and 2), the soft magnetic powder of the low coercive force layer (soft magnetic layer) is characterized, and the surface property of the upper magnetic layer is deteriorated due to the orientation and aggregation of the lower magnetic powder during vertical orientation. Although it is a preventive measure, its effect was not sufficient.

  It is an object of the present invention to provide a perpendicular magnetic recording medium that solves the above-mentioned drawbacks of the prior art and has excellent electromagnetic conversion characteristics.

  As a result of intensive studies on the configuration of the coating type perpendicular recording medium, the present inventors have found that if the coating type perpendicular recording medium has the following configuration, a perpendicular magnetic recording medium having good electromagnetic conversion characteristics can be obtained. It came to make this invention.

  That is, in a perpendicular magnetic recording medium in which a soft magnetic layer containing soft magnetic powder and a binder and a magnetic layer containing ferromagnetic powder and a binder are provided in this order on the nonmagnetic support, the nonmagnetic support is provided. A nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the body and the soft magnetic layer.

  The ratio of the nonmagnetic powder contained in the soft magnetic layer is 5 parts by weight or less with respect to the soft magnetic powder.

  The powder contained in the soft magnetic layer is substantially only soft magnetic powder.

  In a perpendicular magnetic recording medium in which a soft magnetic layer containing soft magnetic powder and a binder and a magnetic layer containing ferromagnetic powder and a binder are provided in this order on a nonmagnetic support, the nonmagnetic support and By providing a nonmagnetic layer containing a nonmagnetic powder and a binder between the soft magnetic layer, material components other than the soft magnetic powder and the binder that are conventionally blended in the soft magnetic layer are removed from the soft magnetic layer. Since it can be excluded and included in the nonmagnetic layer, it is possible to prevent magnetization disturbance in soft magnetism. Further, by providing the nonmagnetic layer, the surface protrusions of the nonmagnetic support can be concealed. With these effects, a perpendicular magnetic recording medium having good electromagnetic conversion characteristics can be obtained.

  The perpendicular magnetic recording medium of the present invention can be obtained by forming at least a nonmagnetic layer, a soft magnetic layer, and a magnetic layer in this order on one main surface of a nonmagnetic support and drying them. When used as a magnetic disk, a similar layer can be formed on the other main surface. When used as a magnetic tape, a back layer containing carbon black can be formed on the other main surface.

  The formation of each of the above layers can be performed by a conventionally known coating method such as gravure coating, roll coating, blade coating or extrusion coating. The soft magnetic layer is formed on the nonmagnetic layer by a wet-on-dry method in which the nonmagnetic layer is applied and dried by a conventionally known method, and then the soft magnetic layer is formed thereon. Alternatively, using a multilayer extrusion die, a non-magnetic layer and a soft magnetic layer can be discharged almost simultaneously onto a non-magnetic support by a wet-on-wet method that forms a non-magnetic layer and a soft magnetic layer. Also good. As a method for forming a magnetic layer on a soft magnetic layer, a wet-on method is used in which a soft magnetic coating and a magnetic coating are ejected almost simultaneously onto a nonmagnetic layer using a multilayer extrusion die. It may be formed by a wet method, or may be applied by a wet-on-dry method after coating, drying, and smoothing the soft magnetic layer. However, when the soft magnetic layer is coated, dried, and smoothed and then applied by a wet-on-dry method, the interface between the magnetic layer and the soft magnetic layer becomes smooth, and a magnetic layer having no variation in thickness is obtained. Therefore, noise is reduced and electromagnetic conversion characteristics are improved, which is more preferable.

  Hereinafter, the components of the present invention will be described in detail.

<Nonmagnetic layer>
The thickness of the nonmagnetic layer is preferably 0.2 μm or more and less than 1.5 μm, and more preferably 0.9 μm or less. This range is preferred if the thickness is less than 0.2 μm, the effect of concealing the surface protrusions of the nonmagnetic support and the effect of improving the durability are reduced, and if it exceeds 1.5 μm, the total thickness of the magnetic tape is increased. This is because the recording capacity per tape roll becomes small.

  Nonmagnetic powders used for the nonmagnetic layer include titanium oxide, iron oxide, and aluminum oxide. Iron oxide alone or a mixed system of iron oxide and aluminum oxide is preferably used. The particle shape of the non-magnetic powder may be spherical, plate-like, needle-like, or spindle-like, but in the case of needle-like or spindle-like, the major axis length is usually 50 to 200 nm and the minor axis length is 5 to 100 nm. Is preferred. In the case of a granular shape, a particle size of 5 to 200 nm, more preferably 5 to 100 nm is used.

  Furthermore, it is preferable to add carbon black having a particle size of 0.01 to 0.1 μm for the purpose of improving conductivity. In order to apply the undercoat layer smoothly and with little thickness unevenness, it is particularly preferable to use nonmagnetic powder and carbon black having a sharp particle size distribution. Instead of carbon black, plate-like ITO (indium and tin composite oxide) powder having an average particle diameter of 10 to 100 nm may be used.

  In order to control the temperature / humidity expansion coefficient, elastic modulus, and magnetic layer smoothness of the magnetic recording medium, a nonmagnetic plate-like powder having an average particle diameter of 10 to 100 nm may be added. As the nonmagnetic plate-like powder, rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used.

<Soft magnetic layer>
High magnetic permeability fine particles (soft magnetic powder) can be dispersed and coated in a binder to form a soft magnetic layer. The relative magnetic permeability of the soft magnetic layer is preferably 20 or more, more preferably 50 or more, from the viewpoint of stabilizing the recording magnetization. From the viewpoint of overwriting failure, the coercive force of the soft magnetic layer is preferably 11.9 kA / m (150 Oe) or less, more preferably 7.96 kA / m (100 Oe) or less, and further 3.98 kA / m (50 Oe) or less. preferable. The thickness of the soft magnetic layer is preferably in the range of 0.001 to 1 μm, more preferably in the range of 0.003 to 0.5 μm, and still more preferably in the range of 0.005 to 0.2 μm. This range is preferable because if it is less than 0.001 μm, the effect as the keeper layer may be difficult to be exhibited, and if it exceeds 1 μm, it may cause overwriting failure.

The soft magnetic powder is not particularly limited as long as it satisfies the above conditions. Ferrite soft magnetic powders such as magnetite, γ-Fe ₂ O ₃ , Mn—Zn ferrite, and Ni—Zn ferrite, Fe, Ni , Co, and soft magnetic powders of these alloys are preferably used.

These soft magnetic powder of acicular, granular, plate-like, but may be any, in order to reduce the H _c granular is preferred. In addition to predetermined atoms, these powders include Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, It may contain atoms such as Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb.

The specific surface area of these soft magnetic powders is preferably 10 to 100 m ² / g, more preferably 40 to 70 m ² / g in terms of SBET. If it is out of the range of 10 to 100 m ² / g, it is difficult to obtain good surface properties. Average particle size is 0.01 to 1 μm, bulk density is 0.4 to 1.5, adsorption moisture is 0.1% to 2%, DBP oil absorption is 5 to 100 ml / 100 g, PH is 3 or more 10 or less is preferable.

Further, it is preferable that surface treatment of the particle surface of the soft magnetic powder with _{Al 2 O 3, SiO 2,} TiO 2, ZrO 2, SnO 2, Sb 2 O 3, ZnO. In particular, Al ₂ O 3, SiO ₂ , TiO ₂ , and ZrO ₂ are preferable for dispersibility, but Al ₂ O ₃ , SiO ₂ , and ZrO ₂ are more preferable.

  As the binder used for the soft magnetic layer, the same binder as that used for the magnetic layer and the nonmagnetic layer can be used. The content of the binder is preferably 7 to 50 parts by mass, and more preferably 10 to 35 parts by mass with respect to 100 parts by mass of the soft magnetic powder.

  The soft magnetic layer may contain nonmagnetic powders such as carbon black and solid lubricant as needed in order to impart conductivity and surface lubricity to the ferromagnetic layer. As such carbon black and solid lubricant, those similar to those contained in the magnetic layer can be used. The soft magnetic layer may contain nonmagnetic powders such as iron oxide and aluminum oxide other than carbon black and solid lubricant. By containing such a nonmagnetic powder, the adhesion between the soft magnetic layer and the magnetic layer can be improved.

  The nonmagnetic powder contained in the soft magnetic layer is preferably 5 parts by weight or less with respect to the soft magnetic powder. This range is preferable because if it exceeds 5 parts by weight, noise may increase due to disturbance of magnetization in the soft magnetic layer. From the viewpoint of improving the electromagnetic conversion characteristics of the magnetic layer, it is preferable that the soft magnetic layer does not contain the nonmagnetic powder as described above in addition to the soft magnetic powder and the binder.

  The soft magnetic layer may contain a lubricant. As the lubricant, a lubricant similar to the lubricant used for the magnetic layer and the nonmagnetic layer can be used.

  In forming the soft magnetic layer, the soft magnetic coating is applied on the nonmagnetic layer by wet-on-dry or wet-on-wet methods. After coating, the magnetic field may be oriented in the longitudinal direction before drying. The magnetic field orientation can be performed by a conventionally known method, and a repulsive magnetic field in which permanent magnets having the same polarity are opposed to each other, or a solenoid coil can be used. The orientation magnetic field strength is preferably an external magnetic field that is at least three times the coercivity of the soft magnetic powder used.

  As a method for forming a magnetic layer on a soft magnetic layer, a wet-on method is used in which a soft magnetic coating and a magnetic coating are ejected almost simultaneously onto a nonmagnetic layer using a multilayer extrusion die. It may be formed by a wet method, or may be applied by a wet-on-dry method after coating, drying, and smoothing the soft magnetic layer. However, when the soft magnetic layer is coated, dried, and smoothed and then applied by a wet-on-dry method, the interface between the magnetic layer and the soft magnetic layer becomes smooth, and a magnetic layer having no variation in thickness is obtained. Therefore, noise is reduced and electromagnetic conversion characteristics are improved, which is more preferable. As the smoothing process, a calendar process is preferable.

  As a calendering roll, a combination of a heat-resistant plastic roll such as epoxy, polyester, nylon, polyimide, polyamide, and polyimideamide (may be kneaded with carbon, metal or other inorganic compound) and a metal roll ( It can also be treated with a combination of 3 to 7 stages) or metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and the linear pressure is preferably 196 kN / m (200 kg / cm) or higher, more preferably 294 kN / m (300 kg / cm) or higher, The speed is in the range of 20 to 700 m / min. By performing the calendering treatment, the porosity of the nonmagnetic layer and the soft magnetic layer can be controlled, and the penetration of the solvent contained in the magnetic paint when forming the magnetic layer can be controlled. A uniform and smooth magnetic layer can be formed.

<Magnetic layer>
The thickness of the magnetic layer is 300 nm or less, particularly preferably 10 to 300 nm, more preferably 20 to 300 nm, and most preferably 30 to 250 nm. In the case of perpendicular recording, the influence of recording demagnetization due to the magnetic layer thickness is less than in the case of longitudinal recording, but the easy magnetization axis is substantially perpendicular and the easy magnetization axis is dispersed to some extent. For this reason, if it exceeds 300 nm, it tends to be affected by recording demagnetization. If it is less than 10 nm, it is difficult to obtain a uniform magnetic layer, and the reproduction output becomes small.

  In the present invention, the average particle size of the magnetic powder is extremely fine with 5 to 50 nm coupled with the unique shape as described above. Surface smoothness is obtained.

  In the case of a magnetic tape, the coercive force in the perpendicular direction of the magnetic layer is 79.6 to 318.4 kA / m (1000 to 4000 Oe), preferably 119.4 to 318.4 kA / m (1500 to 4000 Oe). . If it is less than 79.6 kA / m, even in perpendicular recording, it becomes susceptible to recording demagnetization due to the demagnetizing field caused by dispersion in the magnetic layer of the easy magnetization axis, and exceeds 318.4 kA / m 2. As a result, recording with a magnetic head becomes difficult.

Further, the perpendicular square (B _r / B _m ) of this magnetic layer is 0.6 to 0.9 after demagnetizing field correction, particularly preferably 0.65 to 0.9, and substantially It has an easy axis in the direction perpendicular to the axis.

  Furthermore, the product of the saturation magnetic flux density and the thickness in the vertical direction is 0.001 to 0.1 μTm, preferably 0.0015 to 0.08 μTm. If it is less than 0.001 μTm, the reproduction output is small, and if it exceeds 0.1 μTm, even if it is perpendicular recording, it tends to be difficult to obtain a high output in the intended short wavelength region.

The average surface roughness _{R a} of the magnetic layer is a 1.0～3.2Nm, the center value of the unevenness of the magnetic layer P0, when the maximum projection height was set to P 1, (P1-P0) is 10 When P20 is the 20th convex amount at 30 nm, if (P1-P20) is 5 nm or less, the contact with the magnetic head is improved and a high reproduction output is obtained.

  The magnetic layer preferably contains conventionally known carbon black for the purpose of improving conductivity and surface lubricity. As this carbon black, acetylene black, furnace black, thermal black, etc. can be used. The average particle diameter is preferably 5 to 200 nm, more preferably 10 to 100 nm. When the thickness is less than 5 nm, it is difficult to disperse the carbon black. When the thickness exceeds 200 nm, it is necessary to include a large amount of carbon black. In either case, the surface becomes rough, which tends to cause a decrease in output.

  The content of carbon black is preferably 0.2 to 5% by weight and more preferably 0.5 to 4% by weight with respect to the magnetic powder. If it is less than 0.2% by weight, the effect is small, and if it exceeds 5% by weight, the surface of the magnetic layer tends to be rough.

  The magnetic layer preferably contains an iron nitride magnetic powder, a Co magnetic powder, or a barium ferrite magnetic powder as a ferromagnetic powder. Since these magnetic powders have magnetocrystalline anisotropy, the rotational smoothness of the magnetic powder is small just by aligning the easy axis of magnetization in the vertical direction during orientation, so the surface smoothness of the magnetic layer does not deteriorate and high density recording A magnetic layer having excellent surface smoothness suitable for the above can be obtained. These strong powders are suitable for high density recording because they have high coercive force and high saturation magnetization.

  The ferromagnetic powder preferably has a particle diameter (plate diameter) of 5 to 50 nm and an axial ratio (plate ratio) of 1 to 2. In particular, when iron nitride magnetic powder and Co magnetic powder are used as the ferromagnetic powder, the particles are fine and have a small anisotropy, so that the content of the ferromagnetic powder can be increased and the orientation treatment is performed. A decrease in the surface properties of the ferromagnetic layer due to the rotational motion of the ferromagnetic powder can be suppressed.

  The magnetic layer preferably contains 40 to 90% by weight of the ferromagnetic powder. Since the ferromagnetic powder has a granular shape, a ferromagnetic layer having a high magnetic powder content can be formed.

<Binder>
As binders used in the magnetic layer, soft magnetic layer, and nonmagnetic layer, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol A polyurethane resin, at least one selected from a copolymer resin, a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and a cellulose resin such as nitrocellulose; And a combination of these.

  Among these resins, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination.

  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.

Such binding agents, as a 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 ₁ R ₂ , —N ⁺ R ₃ R ₄ R ₅ [in these formulas, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ represents hydrogen or a hydrocarbon group], and those having an epoxy group are preferably used.

This is because the use of such a binder improves the dispersibility of the magnetic powder and the like. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  These binders are usually used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of the magnetic powder, soft magnetic powder and nonmagnetic powder. In particular, when a vinyl chloride resin and a polyurethane resin are used in combination, it is preferable to use 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin.

  Moreover, it is preferable to use together with these binders, the thermosetting crosslinking agent couple | bonded with the functional group etc. which are contained in a binder, and bridge | crosslinks.

  Examples of such crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates such as are preferably used.

  These crosslinking agents are usually used in a proportion of 1 to 50 parts by weight with respect to 100 parts by weight of the binder. More preferably, it is 15 to 35 parts by weight.

  Further, a radiation curable resin may be used instead of the thermosetting crosslinking agent as described above. As the radiation curable resin, an acrylic monomer or an acrylic oligomer is used. The radiation curable resin preferably has two or more double bonds in the molecule and has a weight average molecular weight of 50 to 300 per double bond. When a radiation curable resin is used for the undercoat layer, the ratio of the radiation curable resin contained in the undercoat layer is preferably 5 to 30 wt% with respect to the total amount of the binder and the radiation curable resin.

<Organic solvent>
In the present invention, examples of organic solvents used in the production of magnetic paints, soft magnetic paints, and nonmagnetic paints include ketone solvents such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, acetic acid, and the like. Examples thereof include acetate solvents such as ethyl and butyl acetate, and glycol solvents such as ethylene glycol, propylene glycol, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether. These organic solvents are used alone or in combination, and are used in a mixture with toluene or the like.

  In the present invention, abrasives, lubricants, and dispersants can be used as additives used in the production of magnetic paints, soft magnetic paints, and nonmagnetic paints.

<Abrasive etc.>
As abrasives to be included in the magnetic layer and nonmagnetic layer, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide Those having a Mohs hardness of 6 or more, such as titanium oxide, silicon dioxide, and boron nitride, can be used alone or in combination. The particle size of these abrasives is usually preferably 10 to 200 nm as an average particle size.

  In addition, conventionally known carbon black may be added to the magnetic paint and non-magnetic paint for the purpose of improving conductivity and surface lubricity, if necessary. As carbon black, acetylene black, furnace black, thermal black, and the like can be used. Those having an average particle diameter of 10 to 100 nm are preferred. This range is preferable because when the average particle size is less than 10 nm, it is difficult to disperse carbon black. When the average particle size exceeds 100 nm, it is necessary to add a large amount of carbon black. Because it becomes. If necessary, two or more carbon blacks having different average particle diameters may be used.

<Lubricant>
For magnetic paints, soft magnetic paints and non-magnetic paints, 0.5 to 5% by weight of fatty acid, 0.2 to 3% by weight of fatty acid ester, 0.5%, based on the total powder contained in the paint. It is preferable to contain ˜5.0% by weight of fatty acid amide. The addition of the fatty acid in the above range is preferable because if the amount is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5% by weight, the toughness may be lost.

  It is preferable to add an ester of fatty acid within the above range. If the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3% by weight, the amount transferred to the magnetic layer is too large. This is because side effects such as sticking may occur. The addition of the fatty acid amide within the above range is preferable when the amount is less than 0.5% by weight, and direct contact at the head / magnetic layer interface occurs and the effect of preventing seizure is small. This is because defects such as the above may occur. As the fatty acid, 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. These 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.

  As the fatty acid ester, the fatty acid ester is preferably used. As the fatty acid amide, a fatty acid amide having 10 or more carbon atoms such as palmitic acid and stearic acid can be used.

<Dispersant>
A dispersant can be used to satisfactorily disperse additives such as magnetic powder, soft magnetic powder, abrasive and carbon black. Examples of such a dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearic acid, and the like. 18 fatty acids [RCOOH (R is an alkyl group or alkenyl group having 11 to 17 carbon atoms)], a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, a compound containing fluorine of the fatty acid ester, Fatty acid amide, polyalkylene oxide alkyl phosphate ester, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonate, phosphoric acid Various conventionally known dispersants such as salts and copper phthalocyanine And either can be used. These may be used alone or in combination. In any layer, the dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  In the present invention, together with the magnetic powder and binder described above, an organic solvent and the additive component described above are used to produce a magnetic paint by dispersion treatment according to the above method. According to a conventional method, a magnetic recording medium is produced by coating on a nonmagnetic support, drying, forming a magnetic layer, and passing through a required processing step.

  Here, the thickness of the magnetic layer is preferably in the range of 10 to 150 nm, more preferably in the range of 20 to 100 nm, and most preferably in the range of 30 to 70 nm. This range is preferable because if the output is less than 10 nm, it is difficult to apply a uniform magnetic layer, and if it exceeds 150 nm, the resolution of the short wavelength signal may deteriorate. . In order to further improve the short wavelength recording characteristics, the thickness of the magnetic layer is more preferably 20 to 100 nm, and most preferably 30 to 70 nm.

  In the present invention, the magnetic layer is preferably formed via an undercoat layer. Further, a topcoat layer (the uppermost nonmagnetic layer) may be provided on the magnetic layer as necessary for the purpose of protecting the magnetic layer. Further, the above magnetic layer may be formed on both sides of the nonmagnetic support in order to increase the capacity of the magnetic recording medium. On the other hand, when the magnetic layer is formed only on one side of the nonmagnetic support, it is usually preferable to form the backcoat layer on the back side.

<Non-magnetic support>
Although the thickness of a nonmagnetic support body changes with uses, a 1.5-11 micrometers thing is normally used. The thickness of the nonmagnetic support is more preferably 2 to 7 μm. The non-magnetic support having a thickness in this range is used when the thickness is less than 1.5 μm because it becomes difficult to form a film and the tape strength decreases. When the thickness exceeds 11 μm, the total thickness of the tape is increased. This is because the recording capacity per tape roll is reduced.

The longitudinal Young's modulus of the nonmagnetic support, preferably 5.8GPa (590kg / mm ²⁾ or more, 7.1GPa (720kg / mm ²⁾ or more is more preferable. The reason why the Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 5.8 GPa or more is that the tape running becomes unstable when the Young's modulus in the longitudinal direction is less than 5.8 GPa.

  In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction is preferably in the range of 0.6 to 0.8, and more preferably in the range of 0.65 to 0.75. The Young's modulus in the longitudinal direction / Young's modulus in the width direction is good when the range is less than 0.6 or more than 0.8. The mechanism is currently unknown, but from the entrance side of the magnetic head track. This is because the output variation (flatness) between the output sides increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.7.

  In the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.7 to 1.3, although the reason is not clear.

  The temperature expansion coefficient in the width direction of the nonmagnetic support is preferably −10 to 10 × 10 −6, and the humidity expansion coefficient is preferably 0 to 10 × 10 −6. The reason why this range is preferred is that if it is outside this range, off-track occurs due to changes in temperature and humidity, and the error rate increases.

  Examples of the nonmagnetic support satisfying the above-described characteristics include biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, and aromatic polyimide film.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the part in an Example and a comparative example is a weight part. Moreover, the average particle diameter in an Example and a comparative example is a number average particle diameter.

<1. Non-magnetic paint component>
(1.1) Non-magnetic paint component 1
Acicular iron oxide 80 parts Carbon black 17 parts Granular alumina powder 3 parts Vinyl chloride-hydroxypropyl acrylate copolymer 9 parts (containing -SO3 Na group: 0.7 x 10-4 equivalent / g)
Polyester polyurethane resin 7 parts Glass transition temperature: 40 ° C., contained —SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g
Phenylphosphonic acid 1 part Toluene 64 parts Cyclohexanone 60 parts Methyl ethyl ketone 58 parts (1.2) Non-magnetic paint component 2
Myristic acid 2.0 parts Butyl stearate 1.5 parts Cyclohexanone 50 parts Toluene 50 parts (1.3) Non-magnetic paint component 3
Polyisocyanate 7 parts Cyclohexanone 10 parts Toluene 10 parts <2. Soft magnetic paint component>
(2.1) Soft magnetic paint component 1
Magnetite 100 parts Vinyl chloride-hydroxypropyl acrylate copolymer 18 parts Polyester polyurethane resin 4.8 parts Phenylphosphonic acid 2.7 parts Toluene 88 parts Cyclohexanone 82 parts Methyl ethyl ketone 19 parts (2.2) Soft magnetic paint component 2
Cyclohexanone 66 parts Toluene 66 parts (2.3) Soft magnetic paint component 3
Butyl stearate 1.0 part Polyisocyanate 3.6 parts Cyclohexanone 21 parts Toluene 21 parts <3. Magnetic paint component>
(3.1) Kneading process component Magnetic powder (YN-Fe) 100 parts Y / Fe: 5.3 at%,
N / Fe: 10.8at%
σs: 135.2 A · m2 / kg
Hc: 226.9 kA / m
Average particle diameter: 20 nm, axial ratio: 1.1
Vinyl chloride copolymer 23.2 parts MR-555 manufactured by Nippon Zeon Co., Ltd.
Polyester polyurethane resin 6.4 parts contained-SO ₃ Na group: 1.0 × 10 −4 equivalent / g
Phenylphosphonic acid 6 parts Toluene 132 parts Cyclohexanone 124 parts Methyl ethyl ketone 7.4 parts (3.2) Dilution process components Toluene 175 parts Cyclohexanone 175 parts (3.3) Compounding process components Polyisocyanate 4.6 parts Toluene 6.5 parts Cyclohexanone 6.5 parts In the above non-magnetic paint component (1.1) after kneading non-magnetic paint component 1 with a batch kneader, (1.2) adding non-magnetic paint component 2 and stirring, and then holding time in a sand mill Was dispersed for 60 minutes, (1.3) nonmagnetic paint component 3 was added to this, and the mixture was stirred and filtered to obtain a nonmagnetic paint.

  Apart from this, (2.1) soft magnetic paint component 1 is previously mixed at high speed in the components of the above-mentioned soft magnetic paint, the mixed powder is kneaded with a continuous biaxial kneader, and (2.2 ) Add soft magnetic paint component 2 and dilute in at least two stages using a continuous twin-screw kneader and disperse in a sand mill with a residence time of 45 minutes. (2.3) Add soft magnetic paint component 3 to this After stirring and filtering, a soft magnetic paint was obtained.

  Further, separately from the above components of the magnetic paint, the kneading step component (3.1) is previously mixed at high speed, and the mixed powder is kneaded with a continuous biaxial kneader, and further (3.2 ) Dilution process components are added and diluted in at least two stages using a continuous twin-screw kneader. The mixture is dispersed in a sand mill with a residence time of 45 minutes, and then the (3.3) formulation process components are added and stirred. -After filtration, a magnetic paint was used.

  Using an extrusion type coater on a 5 μm thick polyethylene terephthalate support so that the thickness after drying and calendering becomes 0.9 μm and 0.2 μm, respectively. Simultaneous multilayer coating was performed in the order of the magnetic layer and the soft magnetic layer. After drying, it is smoothed with a seven-stage calendar composed of only metal rolls at a processing temperature of 100 ° C. and a linear pressure of 196 kN / m (200 kg / cm), and the sheet is wound on the core to 60 ° C. Aged for 48 hours. After aging, the above-mentioned magnetic paint is sequentially applied onto the soft magnetic layer so that the thickness after drying is 0.05 μm, and while the magnetic layer is still in a wet state, it passes through a magnetic field strength of 5 KG and is perpendicular. Orientation treatment was performed and dried. After drying, the calendar process was performed to obtain a magnetic sheet.

<4. Paint component for back coat layer>
Carbon black (average particle size: 25 nm) 87 parts Carbon black (average particle size: 350 nm) 10 parts Granular alumina powder (average particle size: 80 nm) 3 parts Nitrocellulose 45 parts Polyurethane resin (containing -SO ₃ Na group) 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl ethyl ketone 525 parts The above coating composition for the backcoat layer was dispersed in a sand mill for a residence time of 45 minutes, then 15 parts of polyisocyanate was added to adjust the coating material for the backcoat layer, and filtration was performed. The magnetic sheet was coated on the opposite surface of the magnetic layer so that the thickness after drying and calendering was 0.5 μm and dried.

  The magnetic sheet thus obtained is smoothed under a condition of a processing temperature of 100 ° C. and a linear pressure of 200 kg / cm (196 kN / m) with a seven-stage calendar made of a metal roll, and the magnetic sheet is wound around a core. Was aged at 60 ° C. for 48 hours to obtain a magnetic sheet for evaluation with a back layer of Example 1.

  After applying and drying the non-magnetic paint on the non-magnetic support and performing the calendar process, the soft magnetic paint is sequentially applied, the calendar process is performed, and the magnetic paint is sequentially applied on the soft magnetic layer, A magnetic sheet for evaluation with a back layer of Example 2 was obtained in the same manner as Example 1.

  Example 1 Except that a nonmagnetic coating material was applied and dried on a nonmagnetic support and calendered, followed by aging, and then simultaneous coating of a soft magnetic coating material and a magnetic coating material on the nonmagnetic layer. The magnetic sheet for evaluation with a back layer of Example 3 was obtained in the same manner.

  A magnetic sheet for evaluation with a back layer of Example 4 was obtained in the same manner as in Example 1 except that a nonmagnetic coating material, a soft magnetic coating material, and a magnetic coating material were simultaneously coated on a nonmagnetic support in three layers.

  (2.1) A magnetic sheet for evaluation with a back layer of Example 5 was obtained in the same manner as in Example 1 except that 3 parts of carbon black was added to the soft magnetic coating component 1.

  (2.1) A magnetic sheet for evaluation with a back layer of Example 6 was obtained in the same manner as in Example 1, except that 5 parts of carbon black was added to the soft magnetic paint component 1.

  (2.1) A magnetic sheet for evaluation with a back layer of Example 7 was obtained in the same manner as in Example 1 except that 6 parts of carbon black was added to the soft magnetic paint component 1.

  Except that the same amount of barium ferrite magnetic powder (coercive force: 144.1 kA / m, saturation magnetization: 38.8 Am2 / kg, average major axis diameter: 22 nm, plate ratio: 1) was used as the magnetic powder. A magnetic sheet for evaluation with a back layer of Example 8 was obtained in the same manner as Example 1.

  Except for using the same amount of Co-based magnetic powder (coercivity: 127.0 kA / m, saturation magnetization: 110.0 Am2 / kg, average particle size: 20 nm, plate ratio: 1.1) as the magnetic powder, A magnetic sheet for evaluation with a back layer of Example 9 was obtained in the same manner as Example 1.

Comparative Example (Comparative Example 1)
A magnetic sheet for evaluation with a back layer of Comparative Example 1 was obtained in the same manner as in Example 1 except that the nonmagnetic layer was not provided.
(Comparative Example 2)
(2.1) A magnetic sheet for evaluation with a back layer of Comparative Example 2 was obtained in the same manner as Comparative Example 1, except that 3 parts of carbon black was added to the soft magnetic coating component 1.
(Comparative Example 3)
(2.1) A magnetic sheet for evaluation with a back layer of Comparative Example 3 was obtained in the same manner as Comparative Example 1 except that 6 parts of carbon black was added to the soft magnetic coating component 1.

<Surface roughness of magnetic layer>
Scan Length was measured at 5 um by scanning white light interferometry with a general-purpose three-dimensional surface structure analyzer “NewView 5000” manufactured by ZYGO. Measurement field of view is 54.2 um x 72.2 um
The center line average roughness of the magnetic layer was determined as _Ra .

<Electromagnetic conversion characteristics>
For evaluation of the electromagnetic conversion characteristics, a drum tester equipped with an electromagnetic induction head (track width: 25 μm, gap length: 0.23 μm) and an MR head (gap length: 0.17 μm) was used. A magnetic tape having a length of about 60 cm was wound around the rotating drum of this drum tester, a signal was recorded with an induction head, and a signal was reproduced with an MR head. Both heads are installed at different locations with respect to the rotating drum, and tracking can be adjusted by operating both heads in the vertical direction. For the output of data signals and noise, the function generator writes a rectangular wave signal with a wavelength of 0.1 μm on the magnetic tape for evaluation of the reproduction output in the short wavelength region, and reads the output when reproducing with the MR head into the spectrum analyzer. Measured with The carrier value of 0.4 μm was set as the medium output C. Further, when a rectangular wave of 0.4 μm was written, an integral value obtained by subtracting the output and system noise from the spectral component corresponding to the recording wavelength of 0.4 μm or more was used as the noise value N. Furthermore, the ratio of the two was taken as C / N, and C, N, and C / N were all obtained with respect to the value of the tape of Comparative Example 1 as a reference.

<Surface electrical resistance>
Prepare a sample with a width of 12.65 mm and a length of 150 mm from the longitudinal direction of the magnetic sheet, and place two electrode rods (a quadrant with a 10 mm radius in cross section) at a distance equal to the width of the sample. Was placed so that its length was perpendicular to the electrode and the measurement surface was in contact with the electrode. Next, a load was applied to both ends of the sample so that the tension was 5 N / mm ^2, and the electrical resistance (Ω / sq) between both electrodes was measured.

  Table 1 shows the evaluation results.

  As can be seen from Table 1, in Examples 1 to 9 according to the present invention, since the nonmagnetic layer is 0.9 μm, it is not affected by the surface protrusions of the nonmagnetic support. It can be seen that Ra is small and output (C) is large.

  Moreover, compared with Examples 3 and 4, Example 1 and 2 have clearly smaller noise because of smoothing the interface between the soft magnetic layer and the magnetic layer by sequentially applying the magnetic layer.

  From Examples 1, 5, 6, and 7, it is clear that the smaller the content of nonmagnetic powder in the soft magnetic layer, the smaller the noise.

  Further, since Comparative Examples 1 to 3 that do not satisfy the claims do not have a nonmagnetic layer, Ra of the magnetic layer is increased due to the influence of the surface protrusions of the nonmagnetic support. As a result, the spacing loss increases and the output (C) decreases, resulting in a low C / N. In addition, since Comparative Example 1 does not contain carbon black, C / N is relatively good, but the electrical resistance is large, and problems such as sticking due to charging and adhesion of dust occur.

Claims (4)

  In a perpendicular magnetic recording medium in which a soft magnetic layer containing soft magnetic powder and a binder and a magnetic layer containing ferromagnetic powder and a binder are provided in this order on a nonmagnetic support, the nonmagnetic support and A perpendicular magnetic recording medium, wherein a nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the soft magnetic layer.   The perpendicular magnetic recording medium according to claim 1, wherein a ratio of the nonmagnetic powder contained in the soft magnetic layer is 5 parts by weight or less with respect to the soft magnetic powder.   2. The perpendicular magnetic recording medium according to claim 1, wherein the powder contained in the soft magnetic layer is substantially only soft magnetic powder.   4. The perpendicular magnetic recording medium according to claim 1, wherein the magnetic layer is provided after the soft magnetic layer is formed by applying, drying and smoothing a soft magnetic paint.