JP2632197C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial applications)   The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer.
And a magnetic recording medium having two magnetic layers. (Prior art and its problems)   In recent years, with the development of magnetic recording, the demand for high image quality and high sound quality is increasing more and more.
Electromagnetic conversion characteristics have been improved, and in particular ferromagnetic powders have been made finer and more dense,
The noise near the carrier is reduced and the C / N is increased by smoothing the air tape surface.
Is required. At the same time, the coefficient of friction is reduced by smoothing the surface.
Therefore, it is necessary to further improve running performance and durability. In addition, the magnetic recording medium
The body is consumed in large quantities, and it is consumed in large quantities as media
It is required that the cost can be reduced. Multilayering is one such technique. So
This is appropriate because the upper layer has characteristics for high image quality and the lower layer has characteristics for high sound quality.
This is because a ferromagnetic powder can be used. In addition, appropriate layering depends on the layer.
It also has the feature that it can be manufactured at low cost because quality can be used. Currently electromagnetic transducer
To improve the surface properties of the magnetic layer surface and improve the ferromagnetic properties of the ferromagnetic powder in the magnetic layer.
It is known to increase the filling rate.   To increase the packing ratio of ferromagnetic powder in the magnetic layer, a binder other than ferromagnetic powder must be used.
And reducing the solid content ratio of lubricants, antistatic agents, abrasives, etc. And dispersing the ferromagnetic powder at an advanced level
A method to increase the retraction rate is conceivable. However, in the former case,
The physical properties of the adhesive tape, especially the adhesion strength and tensile strength of the coating film, decrease, and the coefficient of friction and
The surface electric resistance is increased, and the running durability is greatly deteriorated. In the latter case,
The dispersing process takes a very long time, and the inherent properties of ferromagnetic powder, especially needle-shaped
There are problems such as destruction of noise and deterioration of noise level.
It could not be a step.   Therefore, JP-A-58-200425 aims at improving electromagnetic conversion characteristics such as sensitivity,
High-sensitivity, high-density magnetic
In order to obtain a pneumatic recording medium, the second layer (upper layer) is
Contains certain lubricants, antistatic agents and abrasives, but does not particularly affect durable running characteristics.
The first layer (lower layer) was proposed not to contain the above additives. As a result, S
/ N, head wear and still showed good results, but the tape was edged
When sliding, the edge of the first magnetic layer was found to be easily damaged.
The line durability was found to be insufficient.   On the other hand, when the magnetic head and the medium contact and slide, the damage and wear of the magnetic head are reduced.
On the surface of the magnetic recording medium for the purpose of further improving the durability of the magnetic recording medium.
Do not contain or reduce the amount of inorganic oxide fine particles such as
It is known from JP-A-58-9215 that the layer contains fine particles of an inorganic oxide such as alumina.
Have been. This is because the presence of alumina on the surface improves durability but is exposed on the surface
Problems such as scratching, chipping and accelerated wear of the magnetic head
It is said that. However, in this case, since the second layer (upper layer) has a small amount of abrasive,
Although the wear was small, the still durability was remarkably inferior.   Accordingly, the present invention provides an audio recording system which is insufficient in the prior art due to tape edge damage.
Magnetic recording with improved level-down and still durability as well as improved S / N
The purpose is to provide a recording medium.   Further, the present invention is easy and inexpensive to manufacture, and simultaneously improves electromagnetic conversion characteristics and running durability.
It is an object of the present invention to provide a magnetic recording medium. (Means for solving the problem)   The present invention provides a method comprising the steps of: providing, on a surface on a non-magnetic support, a ferromagnetic powder and a binder, respectively.
In a magnetic recording medium comprising a magnetic layer and a second magnetic layer provided in this order,
The layer contains 1 to 15 wt% of an α-alumina abrasive based on the ferromagnetic powder in the magnetic layer.
One magnetic layer contains 5 to 50 wt. Of abrasive having Mohs hardness of less than 8 with respect to the ferromagnetic powder in the magnetic layer.
%, And the first magnetic layer contains more abrasive than the second magnetic layer.
Magnetic recording medium. That is, in the present invention, a high-hardness grinding
Α-alumina as an abrasive is 1 to 15% by weight, preferably 3 to 11% by weight based on the ferromagnetic powder.
%, The running property and durability are maintained, and the first magnetic layer (lower layer) has Mohs hardness.
5 to 50% by weight, preferably 15 to 50% by weight of an abrasive having a degree of less than 8 with respect to the ferromagnetic powder
This prevents tape edge damage while maintaining the surface properties of the lower layer.   The amount of the α-alumina abrasive in the second layer is 1% by weight or less based on the ferromagnetic powder, or
Abrasives other than lumina are not preferred because of poor polishing ability and reduced durability. Also 15
If the content is more than wt%, the head wear will be too large, and the electromagnetic conversion characteristics in the high range will be inferior.
No. If the amount of the abrasive in the first layer is less than 5 wt%, the damage of the tape edge is not improved.
If it is not more than 50 wt%, the magnetic properties of the first layer deteriorate and the electromagnetic conversion characteristics in the low frequency range
Is undesirably reduced. When the Mohs hardness of the first layer abrasive is 8 or more, the surface property is poor.
It is not preferable because it deteriorates.   Α-alumina is used as the upper layer abrasive used in the present invention. Among them
When the average particle diameter is 0.6 μm or less, the surface property of the magnetic layer becomes smooth, which is preferable.
New   Examples of α-alumina products are Sumitomo Chemical Co., Ltd.AKP20, 30, 50, 100, HIT-20,
50, 100, and Showa Light Metal's UA-5200, UA-5300, UA-5205, and UA-5305.   Using other abrasives with Mohs hardness of 8 or more together with α-alumina
Is also good.   Titanium oxide, tin oxide, red iron oxide, etc. are used as the lower layer abrasive. Above polishing
Among the materials, bengara with an average particle diameter of 0.6 μm or less, and even 0.1 μm or less
The surface property of the functional layer is improved, which is preferable.   Further, the present invention provides a thin layer in which the uppermost layer has a thickness of 2.0 μm or less, particularly 1.0 μm or less. It is preferable to provide a magnetic layer by multi-layer coating using a wet-on-wet method.
[Functions and Effects of the Invention]   The abrasive contained in the upper layer of the multi-layered magnetic layer is formed of a magnetic head or a guide port.
It is necessary to have a small amount of durability in order to slide with the tool. Too much abrasive
As a result, the degree of filling of the ferromagnetic powder decreases, and therefore, the S / N ratio decreases. Also increase durability
It is necessary to use a hard abrasive for this purpose.
When used, the calender moldability is reduced due to hardness. More granular abrasive
Surface properties are reduced due to use.   On the other hand, in the lower magnetic layer, use a relatively soft abrasive
The tape edge damage has been solved by increasing the edge strength.
If the amount is small, the polishing ability at the tape edge cannot be secured, and if it is too large, particulate matter
The presence of a large amount lowers the surface properties of the lower layer, which in turn degrades the surface properties of the upper layer.
Affect. A hard abrasive can be applied to the lower magnetic layer to prevent tape edge damage.
Even if a small amount (smaller than a soft abrasive) is used, calender moldability is poor.
A smooth surface cannot be obtained. Therefore, the abrasive of the present invention having a hardness and an amount is assembled in the upper layer and the lower layer.
By using them together, there is no tape edge damage to the lower magnetic layer and the
A magnetic recording medium with improved surface properties can be obtained.   As the ferromagnetic fine powder used in the present invention, γ-Fe_TwoO_Three, Co-containing (deposition, metamorphosis,
Dope) γ-Fe_TwoO_Three, Fe_ThreeO_Four, Co-containing (deposition, denaturation, doping) Fe_ThreeO_Four, FeO_x, C
o Containing (deposition, denaturation, doping) FeO_x(X = 1.33 to 1.50), CrO_TwoAnd Rn, Te, Sb, Sr,
Fe, Ti, V, Mn, Cr_TwoO_ThreeCrO containing at least one of the following_Two, Fe, Co, Ni, Fe-Co alloy
, Fe-Ni alloy, Fe-Co-Ni alloy, Co-Ni-P alloy, Co-Ni-Fe-B gold, Fe-Ni-Z
n alloy, Ni-Co alloy, Co-Ni-Fe alloy, Fe-N alloy, Fe-Co-Cr alloy, Mn-Bi alloy
Known ferromagnetic powders such as gold can be used.   The particle size of these ferromagnetic powders is about 0.005 to 1 micron, and the axial length / axial width
Is about 1/1 to 50/1. Further, the specific surface area (S_BE
T) Is 1m^Two/ g ~ 70m^Two/ g. The water content of these ferromagnetic powders is 0.2 to 2.
0 wt%. The water content of the coating solution when using these ferromagnetic powders is 0.00 to 2.0.
0 wt%. The surface of these ferromagnetic powders is coated with a dispersant, lubricant, Impregnate and adsorb inhibitors in a solvent prior to dispersion for each purpose.
You may. These ferromagnetic powders contain Sr, Pb, Mn, Ni, Cd, Cr, Al,
It is preferable to include heavy metals such as Si, Ti, Cu, and Zn. Alumina is added to these ferromagnetic powders.
Etc. may be applied and melted.   The ferromagnetic powder used in the present invention includes plate-like hexagonal barium ferrite.
Can also be used. Barium ferrite particle size is about 0.001 to 1 micron diameter
And the thickness is 1/2 to 1/20 of the diameter. The specific gravity of barium ferrite is 4-6 g / cc,
Specific surface area is 1m^Two/ g ~ 70m^Two/ g. The surface of these ferromagnetic powders will be described later.
Powders, lubricants, antistatic agents, etc. should be included in the solvent prior to dispersion for each purpose.
It may be immersed and adsorbed.   As the binder used in the magnetic layer of the present invention, a conventionally known thermoplastic resin, heat
Curable resins, reactive resins, and mixtures thereof are used.   The thermoplastic resin has a softening temperature of 150 ° C or less and an average molecular weight of 10,000 to 300,000.
Having a degree of polymerization of about 50 to 2000, for example, vinyl chloride vinyl acetate copolymer,
Vinyl chloride copolymer, vinyl chloride vinylidene chloride copolymer, vinyl acryloyl chloride
Nitrile copolymer, acrylate acrylonitrile copolymer, acrylic acid
Ester vinylidene chloride copolymer, acrylate styrene copolymer, meta
Acrylate acrylonitrile copolymer, methacrylate vinyl chloride
Den copolymer, methacrylate styrene copolymer, urethane elastomer,
Nylon-silicone resin, nitrocellulose-polyamide resin, polyhookabi
Nyl, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile
Copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulo
Acetate butyrate, cellulose diacetate, cellulose triacetate
, Cellulose propionate, nitrocellulose, ethylcellulose, methyl
Cellulose, propylcellulose, methylethylcellulose, carboxymethyl
Cellulose, acetylcellulose, etc.), styrene butadiene copolymer, polyether
Stell resin, chlorovinyl ether acrylate copolymer, amino resin,
Various synthetic rubber-based thermoplastic resins and mixtures thereof are used.   As a thermosetting resin or a reactive resin, it has a molecular weight of 200,000 or less in the state of a coating liquid. Yes, by heating after coating and drying, the molecular weight is reduced by reactions such as condensation and addition.
It will be infinite. In addition, among these resins, during the time until the resin is thermally decomposed
Those that do not soften or melt are preferred. Specifically, for example, phenol resin, pheno
Xy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin,
Alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin
Fat, nitrocellulose melamine resin, high molecular weight polyester resin and isocyanate
Mixture of toprepolymer, methacrylate copolymer and diisocyanate prepolymer
Mixture of polyester, polyester polyol and polyisocyanate, urea
Formaldehyde resin, low molecular weight glycol / high molecular weight diol / triphenyl
Mixture of methane triisocyanate, polyamine resin, polyimine resin and the same
And mixtures thereof.   These binders may be used alone or in combination.
It is. The mixing ratio of the ferromagnetic powder and the binder in the magnetic layer is 100 wt.
The binder is used in an amount of 5 to 300 parts by weight per part. If necessary, set a back layer.
In the case of glowing, the mixing ratio of the fine powder in the back layer and the binder is 100 parts by weight of the fine powder by weight.
The binder is used in the range of 30 to 300 parts by weight. Additives include dispersants, lubricants,
Abrasives, antistatic agents, antioxidants, solvents and the like are added.   These thermoplastic resins, thermosetting resins, and reactive resins are used in addition to the main functional groups.
Carboxylic acid, sulfinic acid, sulfenic acid, sulfonic acid, phosphoric acid, sulfuric acid as functional groups
, Phosphon, phosphine, boric acid, sulfate group, phosphate group,
Acidic groups such as alkyl ester groups (these acidic groups may be in the form of Na salts, etc.),
Amino acids; aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols
, An amphoteric group such as an alkyl betaine type, an amino group, an imino group, an imide group, an amide
Group, epoxy group, etc., also a hydroxyl group, an alkoxyl group, a thiol group, a halogen group,
Usually contains at least one silyl group and at least six siloxane groups, and each functional group is 1 g of resin.
1 × 10 per^-6eq ~ 1 × 10^-2It is preferable to include eq.   As the polyisocyanate used in the present invention, tolylene diisocyanate,
4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate
G, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o -Toluidine diisocyanate, isophorone diisocyanate,
Isocyanates such as tantriisocyanate;
Product with alcohol or dimer to 15-mer formed by condensation of isocyanates
And the like. These polyisocyanates
Preferably, the average molecular weight is from 100 to 20,000. These polyisocyanates
The commercially available trade names of Coronate L, Coronate HL, Coronate 20
30, Coronate 2031, Millionate MR, Millionate MTL (Nippon Polyurethanes Co., Ltd.)
Takenate D-102, Takenate D-110N, Takenate D-200, Takenate D-2
02, Takenate 300S, Takenate 500 (manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T-80,
Midule 44S, Sumidule PF, Sumidule L, Sumidule N, Desmoji
Module L, death module IL, death module N, death module HL, death module
Module T65, death module 15, death module R, death module RF, desmo
Joule SL, Death Module Z4273 (Sumitomo Bayer), etc.
Or by combining two or more using the difference in curing reactivity
Can be used. Also, for the purpose of accelerating the curing reaction, a hydroxyl group (butanediol
Toluene, hexanediol, polyurethane having a molecular weight of 1,000 to 10,000, water, etc.), amino
Compounds having a group (monomethylamine, dimethylamine, trimethylamine, etc.)
Alternatively, a metal oxide catalyst can be used in combination. Having these hydroxyl or amino groups
Preferably, the compound is polyfunctional. These polyisocyanates are binders
It is preferable to use 5 to 40% by weight of the total amount.   The lubricant and antioxidant used in the magnetic layer of the present invention include molybdenum disulfide.
, Tikka boron, Hooker graphite, Calcium carbonate, Barium sulfate, Keiso oxide, Oxidation
Inorganic fine powder such as titanium, zinc oxide, tin oxide, tungsten disulfide, acrylic
Lene-based resin fine powder, benzoguanamine-based resin fine powder, melamine-based resin fine powder,
Fine powder of polyolefin resin, fine powder of polyester resin, fine powder of polyamide resin
Fine resin powder such as polyimide resin fine powder and polyhooker ethylene resin fine powder
, Silicone oil, fatty acid modified silicone oil, graphite, fluorine alcohol
Polyolefin (polyethylene wax, etc.), polyglycol (polyethylene)
Oxide wax, etc.), tetrafluoroethylene oxide wax, polyteto Lafluoroglycol, perfluorofatty acid, perfluorofatty acid ester,
-Fluoroalkyl sulfate, perfluoroalkyl phosphate, alkyl
Ruphosphate ester, polyphenyl ether, monobasic fatty acids having 10 to 20 carbon atoms and carbon
Number 3 to 12 monohydric alcohol or dihydric alcohol, trihydric alcohol,
Consisting of one or more of tetrahydric alcohol and hexahydric alcohol
Fatty acid esters, monobasic fatty acids having 10 or more carbon atoms and
Fatty acid esters composed of mono- to hexa-hydric alcohols having a total of 11 to 28 carbon atoms
Organic compound lubricants, such as the like, can be used. Also, fatty acids having 8 to 22 carbon atoms or fatty acids
Amides and aliphatic alcohols can also be used. Specific examples of these organic compound lubricants
Butyl caprylate, octyl caprylate, ethyl laurate, lauri
Butyl phosphate, octyl laurate, ethyl myristate, butyl myristate,
Octyl myristate, ethyl palmitate, butyl palmitate, palmitin
Octyl acid, ethyl stearate, butyl stearate, octyl stearate
, Amyl stearate, anhydrosorbitan monostearate, anhydroso
Rubitan distearate, anhydrosorbitan tristearate, anhydro
Sorbitan tetrastearate, anhydrosorbitan ethylene oxide monos
Tearate, oleyl oleate, oleyl alcohol, lauryl alcohol, etc.
Available alone or in combination. Also as a lubricant used in the present invention
Can use so-called lubricating oil additives alone or in combination.
Phenol, etc.), rust inhibitors (naphthenic acid, alkenyl succinic acid, dilauryl sulfide)
Oily agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (gibe
Ndyl sulfide, tricresyl phosphate, tributyl phosphite, etc.)
, Detergents / dispersants, viscosity index improvers, pour point depressants, foaming agents and the like. These jun
The lubricant is added in the range of 0.05 to 20 parts by weight based on 100 parts by weight of the binder.   Carbon black used in the present invention is furnace for rubber, thermal for rubber,
Color black, acetylene black and the like can be used. These carbon
Specific examples of black abbreviations in the United States include SAF, ISAF, IISAF, T, HAF, and S.
PF, FF, FEF, HMF, GPF, APF, SRF, MPF, ECF, SCF, CF, FT, MT, HCC, HCF, MC
F, LFF, RCF, etc. and are classified under D-1765-82a of the US ASTM standard. Can be used. These carbon bras used in the present invention
The average particle size of the pack is 5 to 1000 millimicrons (electron microscope), compared with the nitrogen adsorption method.
Surface area is 1-1500m^Two/ g, PH is 2-13 (JIS standard K-6221-1982 method), dibutylphthalate
Plate (DBP) oil absorption is 5-2000ml / 100g (JIS standard K-6221-1982 method). The present invention
The water content of these carbon blacks used in the above is 0.00 to 20% by weight. Departure
The size of the car phone black used for lightening is intended to reduce the surface electrical resistance of the coating film.
5 to 100 millimicron carbon black and control the strength of the coating film.
When using 50-1000 millimicron carbon black. Table of coating film
Finer grain for smoothing to reduce spacing loss for the purpose of controlling surface roughness
To reduce the friction coefficient by roughening carbon black (100 mm or less)
Uses coarse and coarse carbon black (over 50 millimicrons). Like this
The type and amount of carbon black to be used depend on the purpose required for the magnetic recording medium.
Be killed.   These carbon blacks may be surface-treated with a dispersing agent,
It may be used after grafting with a fat. Also, when producing carbon black,
Furnace temperature of 2000 ° C or higher and part of the surface graphitized can be used.
Wear. Also, use hollow carbon black as a special carbon black.
Can also be.   In the case of a magnetic layer, these carbon blacks are used in an amount of 0 to 100 parts by weight of the ferromagnetic fine powder.
It is desirable to use from 1 to 20 parts by weight. Carbon black and carbon black that can be used in the present invention
The physical property values of carbon black and carbon black
You can refer to the Talk Association, (issued in 1971).   The dispersants used in the present invention include caprylic acid, capric acid, lauric acid,
Listic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidin
Fatty acids having 10 to 26 carbon atoms, such as acids, linoleic acid, linolenic acid, and stearolic acid
(R₁COOH, R₁Is an alkyl group having 9 to 25 carbon atoms),
Li metal (Li, Na, K, NH_Four ⁺Etc.) or alkaline earth metals (Mg, Ca, B
a), metal soaps composed of Cu, Pb, etc., fatty acid amides of the above fatty acids; lecithin
Etc. are used. In addition, higher alcohols having 4 or more carbon atoms (butanol, Butyl alcohol, myristyl alcohol, stearyl alcohol) and these
Sulfuric acid esters, phosphoric acid esters, amine compounds and the like can also be used. Also poly
Alkylene oxides and their sulfates, phosphates and amine compounds
And sulfosuccinic acid, sulfosuccinate and the like can also be used. These compounds
Introduce Si and F substituents to change the compatibility and properties with the binder.
Both are possible. These dispersants are usually used in one or more types, and one type of dispersant
Is added in the range of 0.005 to 20 parts by weight based on 100 parts by weight of the binder. This
These dispersants can be used by pre-adhering them to the surface of ferromagnetic or non-magnetic fine powder.
And may be added during dispersion.   Other preferred compounds as the dispersant include carboxylic acids and phosphate esters.
Surfactants such as Fluorosurfactants FC95, FC-129, FC
430 and FC431 can be used.   The organic solvent used in the dispersion, kneading and coating of the present invention may be used in any ratio.
Seton, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone,
Ketones such as sophorone and tetrahydrofuran; methanol, ethanol, propa
Knol, butanol, isobutyl alcohol, isopropyl alcohol, methyl
Alcohols such as cyclohexanol; methyl acetate, ethyl acetate, butyl acetate
, Isobutyl acetate, isopropyl acetate, ethyl lactate, glycol monoethyl acetate
Ester such as ether; diethyl ether, tetrahydrofuran, glycol
Ethers such as dimethyl ether, glycol monoethyl ether and dioxane
System: benzene, toluene, xylene, cresol, chlorobenzene, styrene
Any tar system (aromatic hydrocarbon); methylene chloride, ethylene chloride,
Salts such as carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene
Hydrogenated hydrocarbons, N, N-dimethylformamide, hexane and the like can be used.   The method of kneading is not particularly limited, and the order of addition of each component is appropriately set.
Can be. For the preparation of the magnetic paint and the back layer paint, a usual kneading machine, for example,
Roll mill, triple roll mill, ball mill, pebble mill, tron mill, sand
Grinder, Sgegvari, Attritor, High-speed impeller, Disperser,
High-speed stone mill, high-speed impact mill, disperser, kneader, high-speed mixer, Bon blender, co-kneader, intensive mixer, tumbler, blender
, Disperser, homogenizer, single screw extruder, twin screw
-An extruder, an ultrasonic disperser or the like can be used. Kneading and dispersing
For details of the technology, see "Paint Flow and Pigme" by T.C.PATTON.
nt Dispersion ”(Paint Flow and Pigment Dispersion
1964 Published by John Wiley & Sons (John Wiley and Sons)
It is described in the book "Industrial Materials", Vol.
For kneading, these kneading and dispersing machines are appropriately combined for sending and coating. Also
And U.S. Pat. Nos. 2,581,414 and 2,855,156. Departure
Even in the case of clarification, the method described in the above book and the cited reference of the book, etc. shall be mixed.
By kneading and dispersing, a magnetic paint and a back layer paint can be prepared.   The magnetic layer is formed by dissolving in an organic solvent any combination of the above compositions and the like,
And apply and dry on a support. When used as a tape, the thickness of the support 2
The size is about 0.5 to 100 microns, preferably about 3 to 70 microns. Disc or
Has a thickness of about 0.03 to 10 mm in the case of a card, and has a cylindrical shape in the case of a drum.
You can also. The material is polyethylene terephthalate, polyethylene naphtha
Polyesters such as polyesters, polypropylene and polyethylene
Derived celluloses, cellulose triacetate, cellulose diacetate, etc.
Resins, polyvinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate
Aluminum, copper, etc. in addition to plastics such as
Ceramics such as metal and glass can also be used. These supports are pre-coated
And corona discharge treatment, plasma treatment, undercoat treatment, heat treatment, dust removal treatment, metal deposition
Treatment and alkali treatment may be performed. For these supports, for example, West
No. 3338854A, JP-A-59-116926, U.S. Pat.No. 4,388,368;
Industry, Vol. 31, p. 50-55, 1975.   As a method for applying the magnetic layer and the back layer on the support, air
Turcoat, blade coat, air knife coat, squeeze coat, impregnation coat
, Reverse roll coat, transfer roll coat, gravure coat, kiss
Coat, cast coat, spray coat, bar coat, spin coat, etc. are used And other methods are possible.
The details are described in pp. 253-277 (Showa 46.3.20, issued in 1962).
You. In particular, in the case of the present invention, the coating solution for the lower layer and the coating solution for the upper layer are layered in a wet state and coated.
A so-called wet-on-wet coating method of fabricing is preferable.   As a wet-on-wet method, a coating method described in JP-A-61-139929 is used.
Can be used.   In addition, such as the method of dispersing the ferromagnetic powder and the binder and the method of coating the support,
Details are described in JP-A-54-46011 and JP-A-54-21805.   According to such a method, the magnetic layer applied on the support may have a strong magnetic
Immediately after drying, the powder is treated to orient in the desired direction while drying, and then formed.
The magnetic layer is dried. The transport speed of the support at this time is usually from 10 m / min to 1000 m / min.
The drying temperature is controlled between 20 ° C and 130 ° C. Also, if necessary, the surface is smooth
The magnetic recording medium of the present invention is manufactured by subjecting the magnetic recording medium to processing or cutting into a desired shape.
I do. These manufacturing methods include filler surface treatment, kneading / dispersing, coating, heat treatment,
Rendering, irradiation (EB) treatment, surface polishing treatment, and cutting process can be performed continuously.
preferable. Further, the steps can be divided into several steps as required.   In these processes, temperature and humidity are controlled.
Is represented by the amount of water in the air, 5 mg / m^Three~ 20mg / m^ThreeIt is. These are, for example,
Japanese Patent Publication No. 40-23625, Japanese Patent Publication No. 39-28368, U.S. Pat.No. 3,473,960, etc.
It is squeezed. The method described in Japanese Patent Publication No. 41-13181 is not applicable to this field.
It is considered to be a fundamental and important technology.   Hereinafter, the present invention will be described more specifically with reference to examples. Components, proportions,
The operation order and the like can be changed without departing from the spirit of the present invention.
This is easily understood by those involved in the industry.   Therefore, the present invention should not be limited to the following examples. Incidentally, the parts in the embodiment
Indicates parts by weight.   Hereinafter, the present invention will be described with reference to examples. Formula 1 (for lower layer)   Co-γ-FeOx (x = 1.45, coercive force = 650 Oersted, S_BET 28m^Two/ g) 100 copies   Abrasives Table 1   Vinyl chloride vinyl acetate copolymer (containing 6% of carboxyl groups,   Polymerization degree 420) 20 parts   5 parts of polyester polyurethane   6.7 parts of polyisocyanate (Coronate L)   Stearic acid (industrial) 2 parts   Butyl stearate (industrial) 1 copy   Methyl ethyl ketone / cyclohexanone 200 parts = 8/2 Formula 2 (for upper layer)   Co-γ-FeOx (x = 1.45, coercive force = 700 Oersted, S_BET 35m^Two/ g) 100 copies   Non-magnetic inorganic powder shown in Table 1   Vinyl chloride vinyl acetate copolymer (containing 6% of carboxyl groups,   Polymerization degree 420) 20 parts   5 parts of polyester polyurethane   6.7 parts of polyisocyanate (Coronate L)   Stearic acid (industrial) 3 parts   Butyl stearate (industrial) 2 parts   Methyl ethyl ketone / cyclohexanone appropriate amount   The above composition was sufficiently mixed and dispersed to form a 14 μm thick polyethylene as a magnetic coating solution.
Coat the dry layer so that the upper layer has a dry thickness of 0.6μ and the lower layer has a thickness of 3.2μ on the lentephthalate support.
The cloth was dried, smoothed after drying, and slit to a width of 1/2 inch.   The obtained sample No. The performances of Nos. 1 to 27 were evaluated, and the results are shown in Table 1.   The sample No. 3, 8, 12, 13, 14, 18, and 21 to 27 samples
Other samples were used as comparative samples, and other samples were used as samples of the present invention. Measuring method   Head wear: Cylinder before and after running for 100 hours with VTR (Matsushita NV-G21)               The height of the head from the surface was measured, and the amount of wear was calculated.   Still characteristics: 50% white video signal is recorded and reproduced in still mode.               Record the playback RF output level with a recorder, and the signal level is reduced by half.               Was measured.   YS / N: Use a Shibasoku noise meter (925R),               Pull No. 26 was used, and the difference in S / N ratio was determined. High pass filter 10K               The noise level was measured at 4.2 Hz with a low-pass filter of 4.2 MHz. use               The VTR is Matsushita NV-8200.   CS / N: High pass filter using Shibasoku noise meter (925R)               -10KHz, low-pass filter 500KHzAM. Ie               S / N was measured for amplitude modulation. VTR is Matsushita NV-8               200 was used. Sample No.26 was compared as a reference (0dB)               .   Audio level down: 10 dB below the specified input level over the entire length of the sample               A 1kHz sine wave signal was recorded with a specified bias. Its playback output level               The maximum value of output fluctuation is read from the recording paper               , Expressed in dB.

Claims (1)

A magnetic recording medium comprising a first magnetic layer and a second magnetic layer each containing a ferromagnetic powder and a binder provided on a surface of a non-magnetic support in this order, wherein the second magnetic layer is The first magnetic layer contains 1 to 15% by weight of an α-alumina abrasive based on the ferromagnetic powder in the magnetic layer, and the first magnetic layer contains 5 to 50% by weight of an abrasive having a Mohs hardness of less than 8 based on the ferromagnetic powder in the magnetic layer. And a magnetic recording medium, wherein the first magnetic layer contains more abrasive per ferromagnetic powder than the second magnetic layer.