JPH03278312A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve traveling durability and wearing resistance of a back coating layer and a magnetic layer by incorporating carbon black of <=30nm particle size and >=300ml/100g DBP oil absorption and a lubricant into the back coating layer. CONSTITUTION:The carbon black having <=30nm particle size and >=300ml/100g DBP oil absorption has extremely high holding effect for a lubricant and allows the lubricant to ooze out from the back coating layer very slowly, little by little, for a long time. This increases the lubricating property and durability of the medium. Moreover, transfer of a rugged pattern of the back coating layer surface to a magnetic layer is prevented, and thereby, the obtd. magnetic recording medium has excellent traveling durability and wearing resistance of the back coating layer and the magnetic layer. It is more effective to preliminarily subject the carbon black to adsorption treatment with the lubricant, and thereby, the lubricant is enough adsorbed to the carbon black. Thus, lubricating property and durability can be further improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium in which the back layer has excellent lubricating properties, running properties, and wear resistance. It is.

[Conventional technology]

In recent years, magnetic recording media are required to have higher recording density and higher performance. The characteristics required of magnetic recording media for high-density recording and high performance include increasing the degree of filling of ferromagnetic powder, increasing coercive force, and satisfying short wavelength recording and digital recording.

Further, as performance increases, the transport speed of the magnetic recording medium in the recording/reproducing deck is required to be, for example, 5 m/min or more. Therefore, the total length of the magnetic recording medium in the longitudinal direction increases, and in order to shorten the unwinding time, the magnetic recording medium is rewound at a speed ten times or more higher than the normal transport speed. Since a magnetic recording medium with a length of approximately 60 minutes is rewound in about 1 minute, the speed is 60 times the normal transport speed. Furthermore, when the sheet is rewound in about 30 seconds, the speed becomes 120 times the normal conveyance speed.

While higher performance and higher recording density are required, magnetic recording media are also required to have characteristics that can withstand increasingly harsh conditions. Such durability is required for both the magnetic layer and the back layer, but improving the durability of the back layer is particularly important.

Conventionally, measures to improve durability have been taken such as strengthening the coating film, reducing the coefficient of friction, preventing abrasion, and reducing surface electrical resistance.

However, the above-mentioned conventional countermeasure techniques are insufficient to solve the various problems that occur during high-speed conveyance, and are not satisfactory. Therefore, we need technologies to strengthen the coating film of magnetic recording media, reduce the coefficient of friction, and prevent scratching so that they can be satisfied even during high-speed conveyance, or to improve the performance of the other side, such as the traveling guide system or the cassette container for magnetic recording media. It has been desired to develop a technology to prevent scratching, an improvement in the electromagnetic conversion characteristics of magnetic recording media, and in particular a technology to prevent an increase in the number of dropouts.

In particular, conventional means for preventing magnetic recording media from being scratched as described above are still insufficient, and dropouts still occur due to scratches during running. In addition, the conventional method for preventing dust from adhering to magnetic recording media is to add a conductive substance such as carbon black to the back layer to increase the conductivity of the medium (lower the surface electrical resistance) and release the charged charges. However, these measures alone are not sufficient to prevent static electricity, and if the amount of filler such as carbon black is increased to further increase conductivity, it not only worsens the running properties of the tape but also , the strength of the coating film on the back layer decreases, and recording and
There are problems such as loss of reproduction characteristics. The latter problem also occurs when abrasives are added to improve running stability.

Therefore, in order to improve durability, reduce the number of dropouts, and improve surface electrical resistance, we created a magnetic layer with ferromagnetic powder dispersed in a binder on a non-magnetic support, and carbon black in a binder on the back side of the magnetic layer. A magnetic recording medium having a back layer dispersed in
A magnetic recording medium has been proposed which is characterized by having an oil content of 1100 n and an amount of DBP (dibutyl phthalate) supplied of 140 g or more per 100 g of acetic black (Japanese Patent Application Laid-open No. 187417/1983).

It was true that the durability of the back layer was improved, the surface electrical resistance was improved, and there was a tendency for dropouts to decrease.
The particle size is too large in view of the recent trend toward high-density recording.
The surface tended to be rough, and the unevenness of the back layer was easily reflected on the magnetic layer. It has also been proposed to use carbon black and fatty acids in the back layer (Japanese Patent Application Laid-Open No. 63-441
Publication No. 3, Publication No. 63-144417, Publication No. 63-14
4418 Publication), the lubricant retention ability of the carbon blacks described in these publications is low, the lubricant tends to concentrate more than necessary on the surface of the backing layer, and impurities that come out with the lubricant precipitate, resulting in short-term problems. During running, there were problems such as the heads becoming dirty, and during long-term running, there was a problem that lubricant gradually became insufficient.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a magnetic recording medium with excellent running durability and abrasion resistance of the back layer and magnetic layer.

[Means to solve the problem]

The object of the present invention is to provide a magnetic layer in which ferromagnetic powder is dispersed in a binder on one side of a non-magnetic support, and a back layer in which inorganic powder mainly composed of carbon black is dispersed in a binder on the other side. In the provided magnetic recording medium, the back layer has a particle size of 30 nm or less and a DBP oil absorption of 300 ml! /
This is achieved by a magnetic recording medium characterized by containing 100 g or more of carbon black and a lubricant.

The carbon black used in the back layer of the present invention (hereinafter simply referred to as the carbon black of the present invention) has a carbon black of 300%
ml/100g or more] BP oil supply amount refers to dibutyl phthalate oil supply amount, and 300 m of dibutyl phthalate per 100g of carbon black.
It refers to carbon black that has the ability to adsorb 1JJ or more. That is, in the present invention, the DBP oil supply amount is 300
By using carbon black, which has an extremely high lubricant retention capacity of mN/1008 or more, the lubricant is dispensed more slowly and over a longer period of time than the back layer, increasing lubricity and durability. In addition, since the carbon black particle size is as small as 30 nm or less, unevenness on the surface of the back layer is not transferred to the magnetic layer. Furthermore, in the present invention,
By adsorbing the carbon black of the present invention with a lubricant in advance, the lubricant is efficiently and sufficiently adsorbed to the carbon black, and the carbon black has excellent lubricant retention and dispensing effects. Lubrication properties and durability properties are improved.

The carbon black of the present invention has a particle size of 30 nm or less and has a DB
P oil supply amount is 300 mlf/100g or more. 30
If the particle size is larger than nm, the surface properties of the back layer will deteriorate, and the unevenness of the back layer will be easily transferred to the magnetic layer. In addition, the amount of carbon black per unit area increases as the particle size becomes smaller,
Accordingly, the amount of lubricant retained increases.

A large value means that the material tends to have an agglomerated structure, has high porosity, and has a high ability to retain lubricant. Examples of such carbon blacks include acetylene black, which is known as hollow carbon black, Ketchien Black [EC, and Ketchien Black E].
C-DJ600 or the like is used.

The back layer of the present invention is applicable not only to a so-called coating type magnetic recording medium having a magnetic layer made of the above-mentioned ferromagnetic powder and a binder, but also to a metal thin film type in which a ferromagnetic metal thin film is provided on a nonmagnetic support by a vapor deposition method or the like. It can also be applied to back layers of magnetic recording media.

The method of coexisting the carbon black of the present invention and the lubricant in the back layer is not particularly limited. Examples include a method in which the carbon black is added together with the carbon black of the present invention at the time of preparing the back layer paint, and a method in which both are used in combination.

Examples of lubricants used in combination with the carbon black of the present invention include silicone oil fluorinated alcohol, polyolefin (polyethylene wax, etc.), polyglycol (
polyethylene oxide wax, etc.), alkyl phosphoric acid ester, polyphenyl ether, monobasic fatty acid with 10 to 22 carbon atoms, monovalent alcohol or divalent alcohol with 3 to 12 carbon atoms, trivalent alcohol, tetravalent alcohol Fatty acid esters consisting of any one or two or more hexahydric alcohols, monobasic fatty acids having 10 or more carbon atoms, and monobasic fatty acids having a total number of carbon atoms of 11 to 28 carbon atoms. Fatty acid esters made of alcohols having a valence to hexavalence can be used. Furthermore, fatty acids or fatty acid amides and aliphatic alcohols having 8 to 22 carbon atoms can also be used.

Specific examples of these organic compound lubricants include ethyl caprylate, ptinoppecaprylate, octinoperaurate,
Lauric acid, ptinopelauric acid, octinobemyristate, etinopemiristate, butyl myristate, octyl myristate, ethyl palmitate, ptynobe palmitate, octyl palmitate, stearate, ethinobestearate, butinopestearate, amyl octinobestearate, anhydrosorbitan Tristearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, anhydrosorbitan tetrastearate, oleyl alcohol, lauryl alcohol, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid and amides thereof etc.

Particularly preferred among these lubricants are fatty acids, and the amount of these lubricants present when forming the back layer is 0 to 100 parts by weight of the carbon black of the present invention.
．． 01 to 10 parts by weight, preferably 0.1 to 2 parts by weight.

It is preferable from the above-mentioned viewpoint that these lubricants are adsorbed onto carbon black in advance. The method of adsorption is, for example, by taking 30 parts by weight of carbon black and adding 150 to 30 parts by weight of an organic solvent such as methyl ethyl ketone or cyclohexanone.
0.00 parts by weight, further add 0.003 to 3 parts by weight of a lubricant, and stir and adsorb for 5 hours to 3 days.

There are no particular limitations on the ferromagnetic powder used in the magnetic layer of the coated magnetic recording medium of the present invention. ferromagnetic alloy powder, r
In addition to Fez○3, Fe50<, and Co metamorphosed iron oxide, metamorphosed barium ferrite and metamorphosed strontium ferrite can be mentioned.

An example of a ferromagnetic alloy powder is a ferromagnetic alloy powder in which the metal content is 75% by weight or more, and the metal content is 80% by weight.
The above is at least one ferromagnetic metal or alloy (e.g., Fe, Co, Ni, Fe-Co, Fe-Ni, Co-
N15Co-Fe-N+, etc., and other components (e.g., AI, S], 5SSc, Ti
, V, Cr.

Mn5Cu, Zn5Y, Mo, Rh, PdSAg.

5nSSb%B, Ba5Ta, W, Re, Au.

Hg, Pb, PSLa, Ce5PrSNdSTe.

Bi, etc.). Further, the self-ferromagnetic metal component may contain a small amount of water, hydroxide, or oxide.

Specific ferromagnetic powders include r-FezO3, Co-containing rFe2O3, Fe+04, Co-containing Fe5.
0<, r-FeOx, Co-containing T-FeOx (X
=1.33~1.50), Cr0z and Co-N1-P
Known ferromagnetic powders include alloys, Co-N1-Fe-B alloys, Fe-Ni-Zn alloys, Ni-Co alloys, and Co-Ni-Fe alloys.

Methods for producing these ferromagnetic powders are already known, and ferromagnetic alloy powder, which is a typical example of the ferromagnetic powder used in the present invention, can also be produced according to these known methods.

That is, as an example of a method for producing ferromagnetic alloy powder, the following method can be mentioned.

(a) A method of reducing complex organic acid salts (mainly sulfuric acid salts) with a reducing gas such as hydrogen: (b) A method of reducing iron oxide with a reducing gas such as hydrogen to produce Fe or Fe-Co particles. Method for obtaining: (C) Method for thermally decomposing a metal carbonyl compound: (d)
A method of reducing an aqueous solution of a ferromagnetic metal by adding a reducing agent such as boron hydride, hypophosphite, or hydrazine: (e) Ferromagnetic metal powder was electrolytically deposited using a mercury cathode. Method for subsequent separation from mercury: (f) Method for obtaining a fine powder by evaporating the metal in an inert gas at low pressure: The preferred particle size of these ferromagnetic powders is about 0, former to 1
In micron length, the ratio of axial length/narrow width is 1/1 to 50/
It is about 1. Further, the preferable specific surface area of these ferromagnetic powders is about 1 m'/g to 60 m'7g.

When using ferromagnetic powder, its shape is not particularly limited, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used.

The specific surface @(5RET) of this ferromagnetic alloy powder is 4
It is preferably 0 m1/g or more, and furthermore, 45rn
It is particularly preferable to use a material of 1/g or more.

Further, as the ferromagnetic powder used in the present invention, plate-shaped hexagonal barium ferrite can also be used. The preferred particle size of barium ferrite is about 0001 to 1 micron in diameter with a thickness of 1/2 to 1/20 of the diameter. Preferably, the specific gravity of barium ferrite is 4-6 g/cc
The specific surface area is 1 m''/g to 60 m'/g.

The surface of these ferromagnetic powders may be impregnated with a dispersant, a lubricant, an antistatic agent, etc., which will be described later, in a solvent prior to dispersion for each purpose, and may be adsorbed thereon.

The coercive force of the tape using these ferromagnetic powders is 300
~2CC100e is preferred.

As the binder that can be used in the back layer and magnetic layer according to the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 300,000, and a degree of polymerization of about 50 to 2.
00 [1 or so, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile) IJ copolymer, acrylic acid ester vinylidene chloride copolymer Polymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer,
Methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicon based mBFE, nitrocellulose-polyamide resin, polyhuccavinyl, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer , polyamide N resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.)
, styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amine resin, various synthetic rubber-based thermoplastic resins, and mixtures thereof.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin,
Melamine resins, alkyd resins, silicone resins, acrylic reactive resins, epoxy-polyamide resins, nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and incyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, polyesters These include mixtures of polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate, polyamine resins, polyimine resins, and mixtures thereof.

These binders may be used alone or in combination;
Other additives may be added. The mixing ratio of the ferromagnetic powder and the binder in the magnetic layer is in the range of 5 to 300 parts by weight per 100 parts by weight of the ferromagnetic powder. The mixing ratio of the powder and binder for the back layer is in the range of 5 to 400 parts by weight based on 100 parts by weight of the powder.

Additives include dispersants, lubricants, abrasives, and the like.

These thermoplastic resins, thermosetting resins, and reactive resins are
In addition to the main functional groups, functional groups include carboxylic acid, sulfinic acid, sulfenic acid, sulfonic acid, sulfuric acid, phosphonic acid,
Acidic groups such as phosphinic acid, boric acid, sulfuric acid ester groups, phosphoric ester groups, and alkyl ester groups thereof (these acidic groups may be in the form of Na salts, etc.); amino acids, aminosulfonic acids, sulfuric acid of amino alcohols or phosphoric acid esters, amphoteric groups such as alkyl betaine types; amino groups, imino groups, imido groups, amide groups, epoxy groups, etc., or hydroxyl groups, alkoxyl groups, thiol groups, halogen groups,
Usually contains one to six types of silyl groups and siloxane groups,
Each functional group is lXl0-'eQ~lX per gram of resin.
It is preferable to include l0-2eQ.

Examples of the polyisocyanate used as the fluorine component of the binder resin or the crosslinking agent of the resin used in the present invention include tolylene diisocyanate), Il, II
Isocyanates such as '-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, O-)luidine diisocyanate, inphorone diisocyanate, triphenylmethane triisocyanate, inphorone diisocyanate, and the incyanate. Products of polyalcohols and polyisocyanates, and polyisocyanates produced by condensation of isocyanates can be used. The commercially available product names of these polyisocyanates include Coronate (1) HL
, Coronate 2030, Coronate) 2031, Millionate MR.

Millionate MTL (made by Japanese polyurethane),
Takenate D-102, Takenate D-1]ON.

Takenate D-200, Takenate D-202 (manufactured by Takeda Pharmaceutical ■), Desmodule Upper 1 Desmodule IL, f
There are products such as Smodor N1 Desmodinyl HL (manufactured by Sumitomo Bayer), and these can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity.

In the back layer according to the present invention, conventional carbon black may be used in combination with the carbon black of the present invention described above. Conventional carbon blacks that can be used in combination include furnace blacks for rubber, blacks for rubber manope colors, and the like. In addition to the carbon black used in the back layer of the present invention described above, the following conventional carbon blacks and acetylene blacks can be used for the magnetic layer.

Examples of abbreviations for carbon black in the United States are SAP, 15AF, 15AF ST 5H.
All'', SPF 5FFSFEF, HMF 5G
PF, APF 5SRF SMPF.

ECF, CF, FTS MT S HCCS
There are MCF, LFF, RCF, etc.
Those classified as D-1765-82a of the American A37M standard can be used. The carbon black used in the back layer or magnetic layer in the present invention has an average particle size of 10 to 101,000 nm.
(liquid microscopy), nitrogen adsorption method specific surface area is 1 to 800
m'/gSpH is 6 to 11 (-6221- according to JIS standard)
1982 method), DBF oil supply amount is 10 to 400 ml/
You can choose from 100g (JIS standard 6221-1982 method). The size of carbon black is 10 to 1 in order to lower the surface electrical resistance of the back layer or magnetic layer coating film.
100 N of carbon black can be used in combination or independently with 50 to 11000 N of carbon black when controlling the strength of each coating film. Further, in order to control the surface roughness of each coating film, fine particles of carbon black (50 nm or more) can be used for smoothing to reduce spacing loss. In this way, the type and amount of carbon black to be added can be selected depending on the purpose required for the magnetic recording medium.

Further, these carbon blacks may be surface-treated with a dispersant described below or grafted with a resin before use. Further, it is also possible to use carbon black whose surface is partially graphitized by treating the furnace at a temperature of 2000° C. or higher when producing carbon black.

Moreover, hollow carbon black can also be used as a special carbon black. When these carbon blacks are added to the magnetic layer, it is desirable to use them in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder. Carbon black that can be used in the present invention is, for example, “
You can refer to "Carbon Black Handbook", edited by Carbon Black Association (published in 1972).

The amount of carbon black other than the carbon black of the present invention that can be used in combination in the back layer of the present invention is in the range of 10 to 90 parts by weight based on 100 parts by weight of the carbon black of the present invention.

An abrasive can be used for the back layer and the magnetic layer. The abrasive used in the present invention is a commonly used material with an abrasive or polishing effect, such as fused alumina,
α-alumina, silicon carbide, chromium oxide, cerium oxide,
Corundum, artificial diamond, α-iron oxide, garnet, emery (main ingredients: corundum and magnetite), garnet, sandstone, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, quartz, tripoli, Diatomaceous earth, dolomite, etc., mainly materials with a Mohs hardness of 6 or more, preferably 8 or more, are used.
These abrasives, which are used in combination of up to four types, have an average particle size of 0.005 to 5 microns, particularly preferably 0.01 to 2 microns. These abrasives are added in an amount of 0.1 to 20 parts by weight based on 0 parts by weight of the binder 1().

A dispersant can be used in the back layer and the magnetic layer. Dispersants used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, stearolic acid, etc. 10-22
fatty acids (R, C0OH, R, is an alkyl group having 9 to 21 carbon atoms), alkali metals (Li, N
a, K, etc.) or alkaline earth metals (Mg.

(Ca, Ba, etc.) or metal soaps consisting of NH, Φ, Cu, Pb, etc.; fatty acid amides of the above fatty acids; lecithin, etc. are used. In addition, higher alcohols with 4 or more carbon atoms (butanol, octyl alcohol, myristyl alcohol)
C
However, polyalkylene oxides and their sulfuric acid esters and phosphoric acid esters can also be used. These dispersants are added in an amount of 0.005 to 20 parts by weight per 100 parts by weight of the binder. These dispersants O may be used by depositing them on the surface of the ferromagnetic powder or nonmagnetic powder in advance, or by adding them during dispersion. Such items are, for example, Special Publication No. 39-28369, Special Publication No. 17945-1973.
No., Special Publication No. 48-15001, U.S. Patent No. 338799
No. 3, No. 3470021, etc.

An antistatic agent can be used in the back layer and magnetic layer. Examples of antistatic agents used in the present invention include conductive powders such as graphite and carbon black graft polymers; natural surfactants such as saponin; alkylene oxide types, glycerin types, glycidol types, polyhydric alcohols, and polyhydric alcohol esters. , alkylphenol E○
Nonionic surfactants such as adducts; cationic surfactants such as higher alkylamines, cyclic amines, hydantoin derivatives, amidoamines, ester amides, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums ; Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphoric ester group; Amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, alkyl betaine type, etc Amphoteric surfactants and the like are used.

These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

Organic solvents used in dispersing, kneading, and coating powders such as carbon black in the back layer and ferromagnetic powders in the magnetic layer include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, etc. in any ratio. Ketones; alcohols such as methanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol; methinoacetate, ethinoacetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethinoacetate, glycol monoacetate (F) Ester system such as ethyl ether; diethyl ether glycol dimethyl ether,
Ethers such as glycol monoethyl ether, dioxane, and tetrahydrofuran; Aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, and styrene; Methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and Chlorinated hydrocarbons such as chlorobenzene, N.

N-dimethylformaldehyde, hexane, etc. can be used.

To form the magnetic layer and the back layer, the above compositions are arbitrarily combined and dissolved in an organic solvent, and a coating solution is coated on the support and dried. There are no particular restrictions on the support used. When used as a tape, the thickness of the support is 2.5
~IQ[)- level, preferably around 3-70 degrees.

If it is in the form of a disk or card, the thickness is 0.5-10
It's just a struggle. Materials include polyesters such as polyethylene terephthalate and polyethylene naclate, polyolefins such as polypropylene and polyethylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, and polyamide. In addition to plastics such as polysulfone, metals such as aluminum and copper, and ceramics such as glass can also be used. Prior to coating, these supports were subjected to corona discharge treatment,
Plasma treatment, undercoat treatment, heat treatment, dust removal treatment, metal vapor deposition treatment, and alkali treatment may be performed. Regarding these supports, for example, West German Patent No. 3338854A, Japanese Unexamined Patent Application Publication No. 1987-1], 6926, and U.S. Patent No. 438836
No. 8; Yukio Mitsuishi, “Textiles and Industry” Volume 31, p50
~55. Described in 1975, etc.

There are no particular restrictions on the kneading method for preparing the back layer-forming paint and the magnetic layer-forming paint, and the order of addition of each component can be set as appropriate.

The kneading method may be a conventional kneading machine, such as a two-roll mill, a three-roll mill, a ball mill, or a pebble mill.
Trominobe Sand Grinder, Szegbari (Sze
gvar i), 7 triter, high speed impeller, dispersion machine, high speed stone minobe high speed impact minobe disper, Nigu, high speed mixer ribbon blender, co kneader, intensive mixer, tumbler, blender, disperser, homogenizer, single screw push ratio An extruder, a twin-screw extruder, an ultrasonic dispersion machine, and the like can be used. For details on crosstalk dispersion techniques, see T. C. PATTON (Cheese, P. P.)
“Pa1nt F]ow and Pigment D
ispersion (paint flow and
Pigment Disversion”) 1964 John
Published by Wiley & 5ons (John Wiley)
``Industrial Materials'' by Shin Tanaka, Volume 25, Volume 37
(1977) and others. It is also described in specifications such as US Pat. No. 2,581,414 and US Pat. No. 2,855,156. In the present invention, a magnetic coating material and a back layer coating material can be prepared by carrying out crosstalk dispersion according to the method described in the above-mentioned documents.

Methods for coating the magnetic layer and back layer on the support include air doctor coating, plate coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, clavia coating, kiss coating, cast coating, and spray coating. Coatings, barcodes, spin codes, etc. can be used, and other methods are also possible, and detailed explanations of these can be found in "Coating Ef", pages 253 to 277 (1977) published by Asakura Shoten.
, 3. 20. Publication).

There are no particular restrictions on the order of coating solutions for the magnetic and hack layers. They may be applied separately or simultaneously.

By such a method, the magnetic layer coated on the support is immediately subjected to a treatment to orient the ferromagnetic powder in the layer in a desired direction while drying, if necessary, and then the formed magnetic layer is dried. The transport speed of the support at this time is usually 10
m/min to 800 m/min, and the drying temperature is 20 m/min.
It is controlled at ℃~120℃. Further, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing and cutting it into a desired shape, if necessary. These are, for example,
-23625 Publication, Special Publication No. 39-28368,
It is shown in US Pat. No. 3,473,960, etc. Furthermore, the method disclosed in Japanese Patent Publication No. 41-13181 is considered to be a basic and important technique in this field.

Furthermore, the same method as above is applied to drying the applied hack layer, and it may be dried at the same time as the magnetic layer.

〔Effect of the invention〕

The carbon black of the present invention is 300 ml/1.00
Since it has a DBP oil supply amount of more than 30g and the particle size is less than 30nm, it has an extremely high lubricant retention ability and dispenses lubricant more slowly than the back layer over a long period of time, increasing lubricity and durability. At the same time, since the unevenness on the surface of the back layer is prevented from being transferred to the magnetic layer, it is possible to provide a magnetic recording medium with excellent running durability and abrasion resistance of the back layer and the magnetic layer. Furthermore, by adsorbing the carbon black of the present invention with a lubricant in advance, the lubricant is efficiently and sufficiently adsorbed to the carbon black, and the lubricant retention effect and dispensing effect of the carbon black are excellent. , -Layer lubrication properties and durability properties are improved.

〔Example〕

The present invention will be explained in more detail below using Examples. Those skilled in the art will readily understand that the components, proportions, order of operations, etc. shown herein are subject to change without departing from the spirit of the invention.

Therefore, the invention should not be limited to the examples below. In addition, parts in Examples and Comparative Examples indicate parts by weight.

Examples 1 to 5 and Comparative Examples 1 to 3 The magnetic layer is as follows, and is common to both Examples and Comparative Examples.

A part of the following composition was placed in a ball mill and thoroughly kneaded, and the remaining part was placed in a ball mill and thoroughly kneaded to obtain Desmodur L-75 (trade name of polyisone anate manufactured by Bayer).
A magnetic paint was prepared by adding 15 parts.

Magnetic paint composition Uniformly mixed and dispersed lecithin 1 part oleic acid 1 part octyl laurate 1 part lauric acid
1 part butyl acetate
300 parts methyl ethyl ketone 300 parts After adjusting the viscosity of this magnetic paint, it was applied to the surface of a polyethylene terephthalate substrate, oriented, dried, and calendered to prepare a sample.

Back layer: After cross-mixing the back liquid of the following composition with a ball mill,
Add 5 parts of Coronate 2061 (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.), mix and disperse uniformly, adjust the viscosity, and add 1.5 parts of Coronate 2061 (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.) to the polyester substrate side opposite to the magnetic layer.
It was applied to a thickness of ρ and dried.

Carbon black (see Table 1) Saran resin (manufactured by Dow Chemical Company) 15 parts Lubricant (see Table 1)
(See table) This tape was polished to a mirror finish using a calendar and then slit into 2-inch-wide pieces to create samples.

However, in the case of Comparative Example 3, the above methyl ethyl ketone 70
Since the viscosity was too low with 0 parts and 10 parts of cyclohexanone, 600 parts of methyl ethyl ketone + 40 parts of cyclohexanone was used.
I made it to 0 copies.

Further, the order of species of the carbon blacks listed in Table 1 and their properties are as shown in the table below.

In addition, the carbon blacks of Examples 1 to 4 and Comparative Examples 1 to 3 were lubricant-free, and all lubricants were added at the time of kneading adjustment. For ENBLACK E and C, stearic acid was added to 0.0% per 100 parts of carbon before ball mill kneading adjustment. For 93750B, a lubricant-free product was used, and the adsorption treated Ketchen Black E, C1, and 93750B were used during kneading adjustment.
DOB and 0.3 parts of stearic acid were added.

The samples thus obtained were evaluated in the following tests, and the results are shown in Table 1.

- Winding condition: The winding condition after one run was visually judged.

・Magnetic surface scratches: Judged visually on the magnetic surface after one run.

- Increased number of dropouts: The number of dropouts is the number of dropouts that have lowered the playback output level by 16dB or more in a period of 15 The difference was defined as the increase in the number of dropouts.

As shown in Table 1, in Examples 1 to 4 in which at least the carbon black of the present invention was used, the winding condition, magnetic surface scratches, and increased number of dropouts were all different from that of the carbon black other than the present invention. It can be seen that this shows a remarkable improvement compared to Comparative Examples 1 to 3 used.

Claims (2)

[Claims] (1) A magnetic layer with ferromagnetic powder dispersed in a binder on one side of a non-magnetic support, and a back layer with inorganic powder mainly composed of carbon black dispersed in a binder on the other side. In the recording medium, the back layer has a particle size of 30 nm.
A magnetic recording medium comprising carbon black and a lubricant having a DBP oil absorption of 300 ml/100 g or more. (2) The magnetic recording medium according to claim 1, wherein the carbon black is adsorbed using the lubricant.