JPH0687292B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and particularly to a ferromagnetic material having a hexagonal plate shape and having an easy axis of magnetization in a direction perpendicular to the plate surface. The present invention relates to a magnetic recording medium provided with a magnetic layer formed by dispersing the above in a binder to improve its output and running durability.

The magnetic recording medium according to the present invention is suitable for use in, for example, magnetic tapes, magnetic disks, magnetic cards, floppy disks and the like.

[Prior art]

Conventionally, γ-Fe ₂ O has been used as a magnetic recording medium on a non-magnetic support.
Magnetic recording media provided with a magnetic layer in which fine powders of ferromagnetic substances such as acicular crystals of Cr ₃ , CrO ₂ and the like are dispersed in a binder are widely used. Further, more recently, recording media have been required to have larger recording capacities and smaller recording sizes. Therefore, "improvement of recording density of magnetic recording media" has become an important issue in this technical field. In order to obtain a recording medium suitable for high-density recording as described above using conventional acicular ferromagnetic fine powder, the maximum size of acicular fine powder is sufficiently smaller than the recording wavelength or recording bit length. Must be
Currently, the acicular ferromagnetic powder has a particle size of 0.3 μm.
The shortest recording wavelength is about 1 μm. In order to obtain a magnetic recording medium capable of higher density recording in the future, it is necessary to further reduce the size of the acicular ferromagnetic powder. However, in such small needle-shaped magnetic powder, the thickness is extremely thin, 100 Å or less, and the volume of the particle is also 10 ^-17 cm ³ or less, which is extremely small, and the magnetic properties deteriorate due to thermal agitation and surface effects. However, there is a problem that sufficient orientation cannot be obtained even when a magnetic field is applied to the magnetic coating film.

In order to solve such a problem in recent years, for example, Japanese Patent Laid-Open No.
As described in JP-A-6525 and JP-A-58-6526, a magnetic recording medium using a hexagonal ferrite having a flat plate shape and an easy axis of magnetization in a direction perpendicular to the plate surface has been developed as a ferromagnetic material. It was The average particle size of these ferromagnetic powders is
It has become possible to reduce the thickness to 0.05 μm or less, and high density recording has become possible using this ferromagnetic fine powder.

[Problems to be solved by the invention]

By using the hexagonal ferrite ferromagnetic powder in this way, it is possible to make the ferromagnetic fine powder finer and more highly packed, so that it is possible to improve the output and C / N of the magnetic recording medium. . On the other hand, however, it has been extremely difficult to maintain the durability of the magnetic layer as the ferromagnetic fine powder is made finer. In order to solve such a problem, conventionally, for example, an isophorone-based curing agent is used to strengthen the magnetic layer and reduce noise (JP-A-60-55516), and the active hydrogen equivalent of the binder is specified. To improve the S / N (Japanese Patent No. 60-70518), CBA as a binder component,
Polyurethane resin and NBR are mixed and used together to improve the dispersibility of various components of the magnetic layer (No. 60-193127), and an abrasive is added under specific conditions (No. 61-94222), Graphitized carbon was added to improve re-output (see
61-139926), improving the durability of the magnetic layer formed by emulsifying the binder (the same as 61-210517), and reducing the μ value of the added graphite to improve the durability of the magnetic layer. (U.S. Pat. No. 6,214,128), a radiation-sensitive binder is used to improve the efficiency of the manufacturing process.
-233414 gazette), the particle size of the abrasive is reduced (61-2737).
No. 35), and the binder is 10 to 30% by weight.
And the specific surface area is 70 to 120 m ² / g (62-).
Various measures such as 38531 gazette) have been proposed. But,
These measures include, for example, a thermocycle durability test on a floppy disk [low temperature (5 ° C) and high temperature (60 ° C)].
In a continuous running durability test under an environment in which is recycled for 24 hours], sufficient results have not yet been obtained.

[Means and Actions for Solving Problems]

In view of the problems in the above-described conventional technology, the present inventors have
As a result of earnest studies on a magnetic recording medium using such extremely finely divided hexagonal ferrite, a flat hexagonal ferromagnetic material having a specific surface area and a flat plate having a specific plate ratio and a specific surface area have been obtained. Hexagonal ferromagnetic material and an abrasive having a specific average particle size are used together in a specific ratio to form a magnetic layer, and the surface roughness (Ra) of the magnetic layer is set to a specific range. The inventors of the present invention have found that the output of the magnetic layer can be further improved and the running durability of the magnetic recording medium can be remarkably improved.

That is, the present invention is a magnetic layer comprising a non-magnetic support, a hexagonal tabular plate, and a fine powder of a ferromagnetic material having an easy axis of magnetization in a direction perpendicular to the flat plate surface dispersed in a binder. In the magnetic recording medium provided with, the ferromagnetic material has a plate-like ratio of 3 to 5, a specific surface area of 50 to 70 m ² / g, and the magnetic layer has a Mohs hardness of not less than and an average particle size of Is 0.4 to 0/8
An abrasive having a thickness of μm is contained in a proportion of 7 to 15% by weight with respect to the ferromagnetic material, and the surface roughness (Ra) of the magnetic layer has a cutoff of 0.
The magnetic recording medium is characterized by having a 25 mm center line average roughness of 0.01 to 0.03 μm.

The present invention will be described in detail below.

The magnetic recording medium of the present invention basically comprises a non-magnetic support and a magnetic layer provided thereon.

Examples of the non-magnetic support in the present invention include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefin resins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and vinyl resins such as polyvinyl chloride. , Polycarbonate resin, polyamide resin, polyimide resin, polyamideimide resin, polysulfone resin, polysulfone resin, polyethersulfone resin, and various plastics or plastic composition films, plates, aluminum copper, stainless steel, zinc There are plate-like bodies such as metal materials such as, glass porcelain, ceramics such as pottery, and composites of the above materials. The shape of these supports may be preliminarily formed into a desired shape, or may be formed, for example, by cutting after forming the magnetic layer and the back layer described later. These supports may be previously subjected to various pretreatments such as corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, metal vapor deposition treatment and alkali treatment.

The magnetic layer provided on this support is basically in the form of a hexagonal plate, and is a ferromagnetic powder having an easy axis of magnetization in a direction perpendicular to the plate surface, a Mohs hardness of 6 or more, and an average particle size of
It consists of an abrasive of 0.4 to 0.8 μm and a binder for bonding them to form a layer.

The ferromagnetic material is a hexagonal plate-like ferromagnetic material having an easy axis of magnetization in the direction perpendicular to the plate surface, and for example, hexagonal ferrite powder, that is, barium ferrite, strontium ferrite, lead ferrite, calcium ferrite or cobalt thereof. Substitutes and the like, and particularly preferable are cobalt substitutes of barium ferrite and cobalt substitutes of strontium ferrite. Generally, the plate diameter (average particle size) of a hexagonal tabular ferromagnetic material is about 0.01 to about 0.10 μm, and the plate thickness (average thickness) is about 0.00.
It is about 5 to about 5 μm, but in the present invention, the plate-like ratio {= (particle diameter) / (thickness)} is 3 to 5 and the specific surface area is 50 to
70 m ² / g is used. If the specific surface area is less than 50 m ² / g, it is not possible to expect a sufficient output increase in the magnetic layer, and 70 m ² / g
When it exceeds the above range, it becomes difficult to disperse the ferromagnetic fine powder, and the durability of the magnetic layer cannot be in the optimum state. As a method for producing the hexagonal tabular ferromagnetic material, any known coprecipitation-heating reaction method, hydrothermal synthesis method, molten salt method, glass crystallization method and the like can be used. The specific surface area of ferromagnetic fine powder is BE
Measured by the T method. For example, using Cantersorb (manufactured by Canterchrome, USA), dehydration in a nitrogen gas atmosphere at a temperature of 250 ° C. for 30 minutes, and then using the BET one-point method (partial pressure: 0.3
It can be measured at 0).

On the other hand, the abrasive is an abrasive having a Mohs hardness of 6 or more and an average particle size of 0.4 to 0.8 μm.
Silicon carbide, chromium oxide, corundum, artificial corundum,
Diamond, artificial diamond, garnet, emery (main component: corundum + magnetite) are used. These abrasives have a Mohs hardness of 6 or more and an average particle size of
The size of 0.4 to 0.8 μm is effective. These abrasives are used in a ratio of 7 to 15 parts by weight based on 100 parts by weight of the ferromagnetic material. If it is less than this, sufficient durability cannot be obtained, and if it is too much, the filling degree of the ferromagnetic material in the magnetic layer decreases,
Not enough output. For each purpose, the surface of these ferromagnetic powders may be impregnated with a dispersant, a lubricant, an antistatic agent, etc., which will be described later, prior to dispersion and adsorbed.

As a binder for forming the magnetic layer by combining the above components to form a magnetic layer, there are conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof.

The thermoplastic resin has a softening temperature of 150 ° C. or lower, an average molecular weight of about 10,000 to about 300,000, and a degree of polymerization of about 50 to 2,000. Specific resins include, for example, vinyl chloride-
Vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer , Methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, vinylidene chloride-acrylonitrile copolymer, budien-acrylonitrile copolymer, styrene-butadiene copolymer , Polyamide resin, polyvinyl butyral resin, cellulose derivative (cellulose acetate, cellulose diacetate, cellulose triacetate cellulose propionate,
(Nitrocellulose etc.), urethane elastomer, nylon-silicon copolymer, nitrocellulose / polyamide resin, polyvinyl fluoride resin, polyester resin, chlorovinyl ether-acrylic acid ester copolymer, amino resin, heat of various synthetic rubbers There are plastic resins and mixtures thereof.

A thermosetting resin or a reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, and by heating after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, polyurethane resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose-melamine resin, high molecular weight polyester resin / isocyanate prepolymer There are mixtures, methacrylate polymer / diisocyanate mixtures, urea-formaldehyde resins, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate mixtures, polyamine resins and mixtures thereof.

These thermoplastic resins, thermosetting resins, and reactive resins include, in addition to the main functional groups, carboxylic acid groups, sulfinic acid groups, sulfonic acid groups, phosphoric acid groups, sulfuric acid ester groups, phosphoric acid ester groups, and other acidic groups as functional groups, Amino acids, aminosulfonic acids, sulfuric acid of amino alcohols, phosphoric acid esters, amphoteric groups such as alkylbetaine type, amino groups, imino groups, imide groups, amide groups, etc., and also hydroxyl groups, alkoxyl groups, thiol groups, halogen groups, Usually 1 silyl group and siloxane group
Includes at least 6 species, each functional group is 1 per 1g of resin
It is preferable to contain x10 ^-6 eq / g to ^{1x10 -2} eq / g.

As the binder of the present invention, the above synthetic resins may be used alone or in combination. In the magnetic layer, the mixing ratio of the ferromagnetic fine powder and the binder is determined by the ferromagnetic fine powder.
It is used in an amount within the range of 5 to 300 parts by weight of binder with respect to 100 parts by weight.

In addition to this, it is desirable to use a polyisocyanate curing agent together with the above-mentioned binder. As the curing agent, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-o-toluidine diisocyanate, isophorone diisocyanate,
Various isocyanates such as triphenylmethane triisocyanate, reaction products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available products of these polyisocyanates include "Coronate L", "Coronate HL", and "Coronate 20".
"30", "Coronate 2031", "Millionate MR", "Millionate MTL" (these are trade names of Nippon Polyurethane Industry Co., Ltd.), "Takenate D-102", "Takenate D-110N", "Takenate D" -200 ", Takenate D-20
2 "(these are the product names: Takeda Pharmaceutical Co., Ltd.),
"Dismodule L", "Dismodule IL",
Examples include polyfunctional isocyanates such as "Dismodur N" and "Dismodur HL" (each of which is a product of Sumitomo Bayer Co., Ltd.), or urethane prepolymers having isocyanate groups at both ends. These may be used alone or in combination of two or more by utilizing the difference in curing reactivity. It is desirable that these compounds are polyfunctional. For the purpose of accelerating the curing reaction,
A compound having a hydroxyl group, an amino group, etc. can also be used in combination. The amount of these curing agents used is 100
It is used in a proportion of 5 to 40 parts by weight per part by weight.

In the coating liquid prepared for forming the magnetic layer, in addition to the above-mentioned ferromagnetic fine powder, binder and abrasive, for various purposes such as lubricant, dispersant, antistatic agent and rust preventive agent. Additives can be added.

As the lubricant, various silicone oils such as dialkyl polysiloxane, dialkoxy polysiloxane, monoalkyl monoalkoxy polysiloxane, phenyl polysiloxane, fluoroalkyl polysiloxane, saturated or unsaturated higher fatty acid, fatty acid ester, higher fatty acid amide , Inorganic fine powders such as higher alcohols and graphite, molybdenum disulfide, tungsten disulfide, boron nitride, graphite fluoride, polyethylene, polypropylene,
Polyethylene vinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene, α-olefin polymer, unsaturated aliphatic hydrocarbon that is liquid at room temperature (compound in which n-olefin double bond is bonded to terminal carbon, carbon Number of atoms: about 20), fatty acid ester consisting of monobasic fatty acid having 12 to 20 carbon atoms and monohydric alcohol having 3 to 12 carbon atoms, fluorocarbon, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate ester, poly Examples include phenyl ether, fatty acid, fatty acid ester, and fatty alcohol. These lubricants are added in an amount of 0.2 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic material.

As the dispersant, caprylic acid, capric acid, lauric acid,
Fatty acids having 10 to 22 carbon atoms such as myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and stearolic acid, alkali metals of these fatty acids, or alkaline earth metals, copper, Examples include metal soaps using lead and the like, amides of the above fatty acids, polyalkylene oxide alkyl phosphates, lecithin, trialkyl polyolefin oxyquaternary ammonium salts, higher alcohols, sulfates of these alcohols, phosphates and the like. These dispersants may be used alone or as a mixture. This dispersant is used in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic material.

Graphite, carbon black,
Powder of conductive material such as carbon black graphite polymer, natural surfactant such as saponin, alkylene oxide-based, glycerin-based, glycidol-based, polyhydric alcohol-based, nonionic surfactant such as polyhydric alcohol ester, higher alkylamine, Cyclic amines, hydantoin derivatives, amidoamines, ester amides, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acid, sulfate ester groups,
Examples include anionic surfactants such as acidic groups such as phosphate groups, amino acids, aminosulfonic acids, sulfates or phosphates of amino alcohols, and amphoteric surfactants such as alkylbetaine type. These surfactants may be used alone or as a mixture. These antistatic agents are used in an amount of 0.2 to 20 parts by weight of conductive fine powder and 0.1 to 10 parts by weight of surfactant per 100 parts by weight of ferromagnetic powder. In addition to its purpose, the above antistatic agent may act as a dispersion, an improvement in magnetic properties, an improvement in lubricity, and a coating aid.

The above-mentioned various additives are added to the coating liquid for forming the magnetic layer, and depending on the type of the additive, after the magnetic layer is dried, it is applied as a solution or dispersion with an organic solvent or as it is on the surface of the magnetic layer. Alternatively, it is sprayed.

As described above, the coating liquid for forming the magnetic layer basically selects each of the above components, and a predetermined amount of the desired binder and other soluble components in a solvent capable of dissolving the selected binder. It is prepared by dissolving, adding a ferromagnetic powder to the solution, stirring, and uniformly dispersing this. Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran, such as alcohol solvents such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol, such as acetic acid. Methyl, ethyl acetate, butyl acetate, isobutyl acetate,
Ester solvents such as isopropyl acetate, ethyl acetate, ethyl lactate, glycol monoethyl ether acetate and ethylene glycol monoacetate, for example ether solvents such as ether, glycol dimethyl ether, glycol monomethyl ether, tetrahydrofuran and dioxane, for example benzene, toluene, xylene. , Cresol, chlorobenzene, aromatic hydrocarbon solvents such as styrene, for example, halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N, N- There are dimethylformamide, hexane and the like, which can be appropriately selected depending on the selected binder, or two or more kinds can be used in combination. These organic solvents are selected so that the components to be dissolved can be completely dissolved, and in the case of a mixed solvent, the respective quantitative ratios are appropriately determined together with the selection of the solvents.
Further, these solvents must not deteriorate the characteristics of the ferromagnetic fine powder which is the main component of the magnetic layer.

In kneading, the ferromagnetic fine powder and the above-mentioned components are all charged into the kneading machine at the same time or individually. For example, there is a method in which ferromagnetic fine powder is added to a solvent containing a dispersant and kneading is continued for a predetermined time to prepare a coating liquid.

For dissolving and dispersing various components in an organic solvent, for example, a two-roll mill, a three-roll mill, a ball mill, a bevel mill, a tron mill, a sand grinder, a seg barrier tryter,
High Speed Impeller Disperser, High Speed Stone Mill, High Speed Impact Mill, Disperser, Kneader, High Speed Mixer, Ribbon Blender, Cokneader, Intensive Mixer, Tumbler, Blender, Disperser, Homogenizer,
Various kneaders such as an ultrasonic disperser are used. And the technique of kneading and dispersion is as described in "Flow of Paint and Dispersion of Pigment" by Tee, C. and Patton (Published in 1975).
Two or more magnetic layers may be simultaneously coated by the multilayer simultaneous coating method.

The coating solution for forming the magnetic layer, which has been subjected to the dispersion treatment, includes, for example, an air doctor coat, a blade cord, an air knife coat,
Squeeze coat, impregnation coat, reverse roll coat,
It is coated on the support by various coating methods such as transfer roll coating, gravure coating, cast coating and spray coating. The thickness of the magnetic layer to be applied is such that the dry thickness is within the range of about 0.5 to 12 μm. In the case of multiple layers, the total thickness is within the above range. Also, this dry thickness depends on the shape of the magnetic recording medium, the application,
Determined by standards, etc.

The magnetic layer coated on the support by the above-mentioned various methods is usually subjected to a magnetic field orientation treatment during the drying to orient the ferromagnetic fine particles in the magnetic layer, and then the drying is completed.

Techniques such as coating of the coating liquid for forming the magnetic layer, magnetic field orientation treatment, and drying are conventionally known, and can be appropriately used or applied for the present invention. In particular, in the present invention, it has been found that a magnetic recording medium having a smooth surface and excellent wear resistance can be obtained by subjecting the magnetic recording medium to surface lubrication treatment. This surface lubrication treatment is performed by a smoothing treatment before drying or a calendering treatment after drying. As a result, when the surface roughness Ra of the magnetic layer is cut off at 0.25 mm and the center line average roughness is 0.01 to 0.03 μm, the running durability is remarkably improved. If the surface roughness Ra is too low, sticking to the magnetic head in the magnetic recording device is likely to occur, and if it is too high, output reduction is likely to occur, both of which are not preferable.

Further, in the case of a coated material, particularly a tape-shaped body (magnetic tape) having a plastic film as a support, it is desirable that a back layer having a desired composition is formed on the back surface thereof. The components of the coating liquid for forming the back layer are exemplified as the components of the coating liquid for forming the magnetic layer, and there are the binders, organic solvents, or inorganic substance-based lubricants described in detail, which may be appropriately selected and configured. it can. The inorganic substance-based lubricant is a fine powder, and its average particle size is 0.8 μm or less,
Particularly preferably, it is 0.4 μm or less. The mixing ratio of the binder and the inorganic substance-based lubricant in the back layer is 1: 0.1 to 1: 4.
It is a ratio within the range of (weight ratio). Then, as in the case of forming the magnetic layer, fine powder of an inorganic substance as a lubricant is uniformly dispersed in an organic solvent of a binder to obtain a back layer forming coating liquid. Then, this coating liquid is applied to the back surface of the support on which the magnetic layer is or is to be formed, and dried to form a back layer. The coating layer in the magnetic recording medium should be as thin as possible in order to increase the recording density per unit of the magnetic recording medium. Therefore, the thickness of the back layer is preferably about 0.3 to 1.5 μm. The preparation, coating and drying of these back layer forming coating liquids are the same as those for the magnetic layer. At this time, the practitioner may appropriately determine whether the support is provided with the magnetic layer or the back layer first. In any case, those skilled in the art can use or apply the conventional techniques to apply the magnetic layer of the present invention. The recording medium can be easily manufactured.

〔Example〕

Hereinafter, the present invention will be described specifically and in detail based on Examples and Comparative Examples. The measurement results of the samples in each example will be collectively described at the end. All "parts" in each example are parts by weight.

Example 1 A coating liquid for forming a magnetic layer was prepared as follows.

Preparation of coating liquid for forming magnetic layer Each component having the following composition was treated with a sand glider for 60 minutes to be thoroughly mixed and dispersed.

Composition-Ferromagnetic fine powder: Co-substituted Ba ferrite (specific surface area: 60 m ² / g, average particle size: 0.04 μm, plate ratio: 4) ...
… 300 parts ・ Binder: Vinyl chloride vinyl acetate copolymer resin “VMCH”
(Product name: Union Carbide Co., Ltd.) 30 parts Lecithin 1.2 parts Graphite fine powder (average particle size: 30 μm) 6 parts Abrasive: Chromium oxide (Mohs hardness: 8-9, average particles) Diameter:
0.5 μm) ...... 30 parts ・ Methyl ethyl ketone ・ ・ ・ 36 parts ・ Toluene 36 parts Furthermore, each component of the following composition was added and treated for 60 minutes to thoroughly mix and disperse.

・ SO ₃ Na group-containing polyester polyurethane (Molecular weight: 70,0
00, polar group 150 eq / 10 ⁶ g) ...... 20 parts ・ Methyl ethyl ketone ・ ・ ・ 250 parts ・ Toluene ・ ・ ・ 250 parts Then, the following components were further added and treated for 30 minutes to thoroughly mix and disperse.

・ Polyisocyanate "Coronate 3041" (trade name: manufactured by Nippon Polyurethane Industry Co., Ltd.) ...... 25 parts ・ Butyl stearate …… 4 parts ・ Oleic acid …… 4 parts ・ Toluene …… 270 parts Magnetic layer prepared as above A coating solution for forming was applied to both sides of a discharge-treated polyethylene terephthalate film having a thickness of 75 μm as a support by a gravure roll and subjected to a magnetic field orientation treatment using a cobalt magnet, and then a temperature of 60
It was dried by passing it through an atmosphere of ° C for 60 seconds, and calendered to form a magnetic layer having a thickness of 3 µm. The surface roughness Ra (cutoff 0.25 mm center line average roughness, the same applies hereinafter) of this magnetic layer was 0.02 μm. Using this magnetic film 3.
I made a 5 inch floppy disk. This is designated as Sample 1.

Example 2 A ferromagnetic layer was formed in the same manner as in Example 1 except that the ferromagnetic fine powder of the composition of the coating liquid for forming a magnetic layer in Example 1 was replaced with the following. . The surface roughness Ra of this magnetic layer was 0.02 μm.

Ferromagnetic material used: Co-substituted Ba ferrite (specific surface area: 67 m ² / g, average particle size: 0.04 μm, plate ratio: 5) Using this magnetic film, a 3.5-inch floppy disk was prepared. This is designated as Sample 2.

Example 3 A magnetic layer was formed in the same manner as in Example 1 except that the ferromagnetic fine powder of the composition of the magnetic layer-forming coating liquid in Example 1 was replaced with the following. . The surface roughness Ra of this magnetic layer was 0.02 μm.

Ferromagnetic material used: Co-substituted Ba ferrite (specific surface area: 50 m ² / g, average particle size: 0.04 μm, plate ratio: 3) Using this magnetic film, a 3.5-inch floppy disk was prepared. This is designated as Sample 3.

Comparative Example 1 A ferromagnetic layer was formed in the same manner as in Example 1 except that the ferromagnetic fine powder of the composition of the coating liquid for forming a magnetic layer in Example 1 was replaced with the following. . The surface roughness Ra of this magnetic layer was 0.02 μm.

Ferromagnetic material used: Co-substituted Ba ferrite (specific surface area: 35 m ² / g, average particle diameter: 0.06 μm, plate ratio: 3) Using this magnetic film, a 3.5-inch type floppy disk was prepared. This is designated as Comparative Sample 1.

Comparative Example 2 A ferromagnetic layer was formed in the same manner as in Example 1 except that the ferromagnetic fine powder of the composition of the coating liquid for forming a magnetic layer in Example 1 was replaced with the following. . The surface roughness Ra of this magnetic layer was 0.02 μm.

Ferromagnetic material used: Co-substituted Ba ferrite (specific surface area: 80 m ² / g, average particle size: 0.06 μm, plate ratio: 6) Using this magnetic film, a 3.5-inch floppy disk was prepared. This is designated as Comparative Sample 2.

Example 4 The surface roughness Ra of the magnetic layer in Example 1 was set to 0.03 μm,
Others were the same as in Example 1.

A 3.5-inch floppy disk was created using this magnetic film. This is designated as Sample 4.

Example 5 The surface roughness Ra of the magnetic layer in Example 1 was set to 0.01 μm,
Others were the same as in Example 1.

A 3.5-inch floppy disk was created using this magnetic film. This is designated as Sample 5.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the abrasive and the addition amount of the composition of the coating liquid for forming a magnetic layer in Example 1 were changed to the following, and a magnetic layer was similarly formed. It was The surface roughness Ra of this magnetic layer was 0.01 μm.

Abrasive used: Chromium oxide (average particle size: 0.05 μm)
5 parts A 3.5 inch floppy disk was prepared using this magnetic film. This is designated as Comparative Sample 3.

Comparative Example 4 A magnetic layer was formed in the same manner as in Example 1 except that the polishing agent of the composition of the coating liquid for forming a magnetic layer in Example 1 was changed to the following one. The surface roughness Ra of this magnetic layer was 0.05 μm.

Abrasive used: Chromium oxide (average particle size: 1.5 μm) Using this magnetic film, a 3.5-inch floppy disk was prepared. This is designated as Comparative Sample 4.

Comparative Example 5 A magnetic layer was formed in the same manner as in Example 1 except that the abrasive and its addition amount of the composition of the coating liquid for forming a magnetic layer in Example 1 were changed to the following. The surface roughness Ra of this magnetic layer was 0.01 μm.

Abrasive used: Chromium oxide (average particle size: 0.5 μm)
5 parts A 3.5 inch floppy disk was prepared using this magnetic film. This is designated as Comparative Sample 5.

Comparative Example 6 A magnetic layer was formed in the same manner as in Example 1 except that the abrasive and the addition amount of the composition of the coating liquid for forming a magnetic layer in Example 1 were changed as follows. The surface roughness Ra of this magnetic layer was 0.09 μm.

Abrasive used: Chromium oxide (average particle size: 0.5 μm)
60 parts A 3.5 inch floppy disk was made using this magnetic film. This is designated as Comparative Sample 6.

Floppy disk drive "FD-1135-D" (trade name: NEC Corporation) is used for each sample created in each of the above examples.
Then, a thermocycle was carried out for 24 hours under the environmental conditions of a temperature of 5 ° C./relative humidity of 10% to a temperature of 60 ° C./relative humidity of 30%, and a running durability test of each sample floppy disk was carried out.

As a result, the results shown in FIG. 1 and Table 1 were obtained.

As shown in FIG. 1 and Table 1, when the specific surface area of the ferromagnetic material is 70 m ² / g or less (Samples 1 to 5), sufficient durability (25 million pass OK) is secured. At 70 m ² / g or more (Comparative sample 2), the durability was suddenly deteriorated. Further, the reproduction output increases in proportion to the specific surface area, and falls below 90% at 50 m ² / g or less (Comparative Sample 1), and each sample within the scope of the present invention ensures both durability and reproduction output. ing.

Further, as shown in Table 1, when the average particle size of the abrasive is smaller than the range of the present invention (less than 0.4 μm) (Comparative sample 3), or when the addition amount is small (less than 7% by weight) ( In comparison sample 3), sufficient durability is not ensured, and conversely, when the average particle size is made larger than the range of the present invention (comparison sample 4) or the addition amount is increased (comparison sample 6), surface properties are improved. It was found that the output was damaged and sufficient output could not be obtained.

〔The invention's effect〕

According to the present invention, the specific surface area of the hexagonal ferrite that is a ferromagnetic material is 50 to 70 m ² / g, and the average particle size of the abrasive is 0.4.
~ 0.8μm, by adjusting the addition amount in the range of 7-15% by weight, it is possible to achieve both excellent durability and reproduction output, and by setting the average roughness to 0.01-0.03μm, durability and reproduction output. Both of these are ensured, and thus the present invention, which can remarkably improve the characteristics of the magnetic recording medium, is an extremely excellent invention in the art.

[Brief description of drawings]

FIG. 1 shows the specific surface area (unit: m ² · g) of each sample measured on the samples obtained in Examples and Comparative Examples of the present invention.
FIG. 3 is a diagram showing a relationship between durability (unit: × 10 ⁴ passes) and 2F output (unit:%) with respect to ( ^-1 ).

Claims (1)

[Claims] 1. A hexagonal tabular plate is formed on a non-magnetic support,
In a magnetic recording medium provided with a magnetic layer in which a fine powder of a ferromagnetic material having an easy axis of magnetization in a direction perpendicular to the flat plate surface is dispersed in a binder, the plate ratio of the ferromagnetic material is 3
5, the specific surface area is 50 to 70 m ² / g, and the magnetic layer contains an abrasive having a Mohs hardness of 6 or more and an average particle diameter of 0.4 to 0.8 μm in an amount of 7 to 15% by weight relative to the ferromagnetic material. %, And the surface roughness (Ra) of the magnetic layer has a cutoff of 0.25 mm.
A magnetic recording medium having a center line average roughness of 0.01 to 0.03 μm.