JPH01173418A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve S/N and C/N by using polyurethane as a binder of a magnetic layer, fine powder of a carbon system as a back layer and fine powder of the carbon system as the magnetic layer. CONSTITUTION:The polyurethane consisting of the chain extender selected from the group consisting of diol, diamine and hydroxyamine compds. having amino groups and amide groups as well as polyol and diisocyanate is used as the binder of the magnetic layer and the fine powder of the carbon system having >=150ml/100g oil absorption is used for the back layer; in addition, the fine powder of the carbon system of <=5% of the weight of the fine ferromagnetic powder is used for the magnetic layer. The magnetic recording medium which has the excellent S/N characteristic and C/N characteristic, substantially prevents electrostatic charge, has less drop-outs and has the excellent reliability is thereby obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium that has excellent S/N characteristics and C/N characteristics, is less likely to be charged, has less dropout, and is reliable. The present invention relates to a magnetic recording medium with excellent properties.

[Prior art and its problems] Conventionally, in magnetic recording media, a magnetic layer was provided on the support for the purpose of improving running stability during high-speed rewinding and preventing the support from being scraped. A back layer is provided on the surface opposite to the surface. A conductive substance such as carbon black is added to this back layer to prevent an increase in the number of dropouts. This increases the conductivity of the recording medium (lowers the surface electrical resistance) and releases the charged charges, thereby preventing dust and the like from adhering to the magnetic recording medium and preventing an increase in the number of dropouts. However, such means alone are not sufficient to prevent static electricity, and there are limits to preventing an increase in the number of dropouts.

In order to improve this problem, a method has been proposed in which a large amount of conductive material such as carbon black is added to the magnetic layer to improve conductivity and prevent charging (for example, JP-A-58-133
No. 626, No. 58-158032, No. 59-1935
Publication No. 33, etc.).

However, if the amount of filler such as carbon black is increased in order to increase conductivity, the dispersibility of the magnetic liquid will deteriorate, the surface properties of the magnetic layer will deteriorate, and the content of magnetic material in the coating film will deteriorate. As a result, electromagnetic conversion characteristics such as S/N characteristics and dropouts are deteriorated due to a decrease in the signal-to-noise ratio and dropouts, and a satisfactory result has not been obtained.

Therefore, with the combination of conventional techniques, a magnetic recording medium that prevents dropout and increase in dropout, has excellent S/N characteristics, and has an excellent antistatic effect cannot be obtained.

Therefore, a first object of the present invention is to provide a novel binder for a magnetic layer, thereby providing a magnetic recording medium with excellent antistatic properties. The second object is to provide a magnetic recording medium with improved dropout of the magnetic layer. The third object is to provide a magnetic recording medium with an excellent SZN ratio. The fourth object is to provide a magnetic recording medium with good sensitivity. The fifth object is to provide a magnetic recording medium with little output drop and good durability.

[Means for Solving the Problems] As a result of various studies, the present inventors have found that a binder for the magnetic recording layer is selected from the group consisting of diols, diamines, and hydroxyamine compounds having an amino group or an amide group. Using polyurethane made of a chain extender, polyol, and diisocyanate, the back layer has an oil absorption of 150 mIL/
By using 100 g or more of carbon-based fine powder and using 5% by weight or less (including zero) of carbon-based fine powder in the magnetic layer based on the ferromagnetic fine powder, the problems of the conventional technology were solved, and the present invention The purpose of the invention was achieved.

[Structure of the Invention] The present invention provides a magnetic recording medium in which a magnetic layer containing ferromagnetic fine powder and a binder is provided on one surface of a support, and a back layer containing carbon-based powder is provided on the other surface. (A) As a binder for the magnetic layer, a chain extender selected from the group consisting of diols, diamines, and hydroxyamine compounds having an amino group or an amide group, and a polyurethane made of a polyol and a diisocyanate are used; (B) The back layer has an oil absorption of 150mJ! /100g or more of carbon-based fine powder, and (C) using carbon-based fine powder of 5% by weight or less (including zero) based on the ferromagnetic fine powder in the magnetic layer. It's in the medium.

[Detailed description of the invention] The present invention will be explained in detail below.

The polyurethane used as the binder for the magnetic layer in the present invention is a polyurethane comprising a chain extender selected from the group consisting of diols, diamines and hydroxyamine compounds having amino groups or amide groups, a polyol, and a diisocyanate. Here, the amino group represents a primary amino group (-NH2), a secondary amino group (-NHR'), a tertiary amino group, or an aromatic group, and when there is one or more R1, these are the same. and may be different, and when two R1s are linked to each other to form a ring and represent an aliphatic group (e.g., an alkyl group) or an aromatic group, and there are two R2s, they may be the same. may also be different, or two R2s may be linked to each other to form a ring.

Examples of the chain extender having an amino group or an amide group include compounds represented by the following general formulas (I) to (■).

General formula (I) Hard.

X (CH2)n N (CH2)-Y-Formula (I
I) General formula (IV) R'/ General formula (Vl) X(OH□)n CH2N (:R2(CH2).Y
General formula (■) X(CH2). 0H (CH2). Y [In the formula, X and Y each independently represent -OH or R3 is a hydrogen atom, an aliphatic group (e.g., an alkyl group)
, or an aromatic group, R4 and R5 represent a hydrogen atom or an aliphatic group, and n, m and 1 each independently represent an integer of 0 to 8. ) In particular, those having an amino group or an amide group in the side chain are preferable from the viewpoint of dispersibility, and more preferably one having an amino group or an amide group in the main chain.
An amino group or an amide group is bonded through 5 carbon atoms.

The polyols used in the present invention are various polyols known per se, such as polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, and polybutadiene polyols.

In addition, examples of the diisocyanate used to form polyurethane by reacting with the above polyol include 2
．． 4-1-lylene diisocyanate, 2.6-1-lylene diisocyanate, 1°3-xylylene diisocyanate, 1,4-xylylene diisocyanate 1-. 1,5-
Naphthalene diisocyanate, m-phenylene diisocyanate, P-phenylene diisocyanate, 3,3-dimethylphenylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3,3-dimethyl-4,4
-Diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and the like.

In the present invention, a polyurethane having a quaternary ammonium salt as an amino group can be obtained by quaternizing the amino group in the polymer after producing the polyurethane.

Furthermore, in the present invention, ordinary polyurethane can be used together with the above-mentioned polyurethane having an amino group or an amide group.

The polyurethane used in the present invention has an amino group or an amide group in a proportion of 10-
It is preferable to contain 6 to 10 −3 equivalents/g. The molecular weight is preferably about 10,000 to 200,000, more preferably 20,000 to 150,000. More preferably, it is 30,000 to 100,000.

Although the above polyurethane may be used alone as a binder, it is more preferable to use it in combination with a vinyl chloride copolymer since this improves the dispersibility of the ferromagnetic fine powder. Examples of the vinyl chloride copolymer used in combination include vinyl chloride-
Vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid-
Vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinylidene chloride-vinyl acetate-maleic acid copolymer, vinylidene chloride-propionic acid Oxidation of vinyl chloride-based polymers such as vinyl-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-acrylic acid copolymer, vinyl chloride-vinyl acetate-acrylic acid-vinyl alcohol copolymer, and these copolymers. Examples include those that have been made.

The vinyl chloride polymer may have a polar group such as a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, or a hydroxyl group.

Furthermore, polar groups (-tl:OOM, -503M, -0P0
3M, -0M, etc., where M is a hydrogen atom, sodium,
or potassium), or by introducing these polar groups into the polyurethane having an amino group or amide group according to the present invention is also effective and preferred.

When the polyurethane having an amino group or amide group according to the present invention and the vinyl chloride copolymer are used together, the weight ratio of vinyl chloride copolymer/total polyurethane is 100/20 to 100/20.
100/200 is preferred.

The details of the carbon-based fine powder such as carbon black used in the back layer will be described later, but its dibutyl phthalate (
DBP) Oil absorption amount is 150ml/100g or more. However, carbon black having a DBP oil absorption of less than 150 mu/100 g may be used in combination. Further, a carbon-based fine powder such as carbon black can be used for the magnetic layer, and the oil absorption amount of the carbon-based fine powder used for this magnetic layer is not particularly limited, but it is preferably 150 mj27100 g or more.

Further, the amount of carbon-based fine powder used in the magnetic layer needs to be as small as 5 parts by weight or less (including zero) per 100 parts by weight of ferromagnetic fine powder.

There are no particular limitations on the ferromagnetic fine powder used in the magnetic layer of the magnetic recording medium of the present invention. Ferromagnetic metal fine powder, ferromagnetic alloy fine powder, r-Fe203, Fe, 0. t, (:o
In addition to modified iron oxide, modified barium ferrite, modified strontium ferrite, etc. can be mentioned.

As an example of a ferromagnetic alloy powder, the metal content in the ferromagnetic fine powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one type of ferromagnetic metal. , Go, Ni, Fe-Go, Fe-Ni, Go
-Ni, Go-Ni-Fe), and the metal content is 20
Other components (e.g., A fl , S
i, S, Sc, Ti, V, Cr, Mn, C
u, Zn%Y, Mo, Rh, Pd, Ag, S
n, Sb, Te, Ba, Ta, W, Re%A
u, Hg, Pb, Bi, La, (:e, Pr, Nd%B
, P). Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide.

Particularly preferred ferromagnetic fine powders include r-Fe203 and CO gold-containing r-Fe203. These are barium ferrite, Fe (metal magnetic powder), and ferromagnetic alloy powder.

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

That is, examples of the method for producing ferromagnetic alloy powder include the following method.

(a) Method of reducing complex organic acid salts (mainly oxalates) with a reducing gas such as hydrogen: (b) Obtaining Fe or Fe1l:o particles by reducing iron oxide with a reducing gas such as hydrogen Method: (C) Method of thermally decomposing a metal carbonyl compound: (d) Method of reducing an aqueous solution of a ferromagnetic metal by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine: (e) Method for electrolytically depositing ferromagnetic metal powder using a mercury cathode and then separating it from mercury: (f) Method for obtaining fine powder by evaporating the metal in a low-pressure inert gas: When using ferromagnetic alloy powder Although there is no particular restriction on the shape, needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used.

The specific surface area (SBET) of this ferromagnetic alloy powder is 30rr
f/g or more, more preferably 40 m2/g or more, particularly preferably 45 m2/g or more.

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

In the magnetic layer according to the present invention, a polyurethane made of a chain extender containing an amino group or an amide group as described above and a vinyl chloride copolymer resin used together with the polyurethane are used as a binder.

Furthermore, a known binder can be used in combination with these in the magnetic layer. Further, although a known binder is used for the back layer, it is particularly preferable to use the above-mentioned polyurethane comprising a chain extender containing an amino group or an amide group of the present invention. Examples of the binder used in combination or in the present invention include conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof.

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 1.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acetate ester acrylotrile copolymer, acrylic acid ester vinylidene chloride copolymer, 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 tree layer, nitrocellulose-polyamide resin, polyfluoride Vinyl, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene Butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

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, epoxy resin, polyurethane curable resin, urea resin, melamine resin,
Alkyd resin, silicone resin, acrylic reactive resin,
Epoxy-polyamide resins, nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and isocyanate bripolymers, mixtures of methacrylate copolymers and diisocyanate bripolymers, polyester polyols (with the exception of polyesters having amino or amide groups according to the invention) (excluding polyols) and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and mixtures thereof.

These binders may be used alone or in combination;
Additives are added to stupidity. The mixing ratio of the ferromagnetic fine powder and the binder in the magnetic layer is in the range of 5 to 300 parts by weight based on 100 parts by weight of the ferromagnetic fine powder. The mixing ratio of powder and binder for the back layer is 1 part powder by weight.
The binder is used in an amount of 5 to 400 parts by weight per 00 parts by weight.

As additives, dispersants, lubricants, abrasives, etc. are added.

These thermoplastic resins, thermosetting resins, and reactive resins are
In addition to the main functional groups, acidic groups such as carboxylic acid, sulfinic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric ester group: amino acids, amino sulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, alkyl betaines Amphoteric groups such as type; usually contains one or more types of amphoteric groups such as amino groups, imino groups, imido groups, amide groups, or hydroxyl groups, alkoxyl groups, thiol groups, silyl groups, and siloxane groups, each functional group per gram of resin. per lXl0-6~
It is preferable to include I x 10-2 eq.

Polyisocyanate can be used for the magnetic recording layer. Examples of polyisocyanates include isocyanates such as tolylene diisocyanate, 4,4°-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, 0-toluidine diisocyanate, inphorone diisocyanate, and triphenylmethane triisocyanate. Examples include products of isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates. Commercially available trade names of these polyisocyanates include Coronate L1, Coronate HL, Coronate 2030, Coronate 2031, and Millionate MR.
, Millionate MTL (manufactured by Nippon Polyurethane), Takenate D-102, Takenate D-11ON, Takenate D-200, Takenate D-202 (Takeda Pharmaceutical Company)
manufactured by), Sumidur N75 (manufactured by Resident Bayer Urethane)
, Parnock D-750, Parnock D-802 (manufactured by Dainippon Ink & Chemicals), Desmodule L, Desmodule IL, Desmodule N, Desmodule HL (
These can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity. Further, for the purpose of accelerating the curing reaction, a compound having a hydroxyl group or an amino group can also be used in combination. It is desirable that these polyisocyanate compounds contain three or more isocyanate groups/molecule.

As mentioned above, the back layer according to the present invention has a DBP oil absorption of 150 rnf (according to JIS standard -8221-1982 method).
1.7100 g or more of carbon-based fine powder (eg, carbon black, etc.) is used.

Examples of the carbon black used include furnace black for rubber, thermal black for rubber, and black for color. Further, in the magnetic layer, a small amount of carbon-based fine powder (for example, carbon black, etc.) can be used, such as 5 parts by weight or less (including zero) per 100 parts by weight of ferromagnetic fine powder. Specific examples of the abbreviations of these carbon blacks in the United States are SAF, 15AF, 115AF, and T.
, to ■F, 5Pli, FF, FEF%HMF, G
PF, APF, 5RFJPF, EGF, SCF, (:
F, FT, MT, HCC%HCF, MeF, LFF,
RCF, etc., and D-17 of the American A57M standard.
Those classified as 65-82a can be used. The average particle size of these carbon blacks used in the present invention is 10 to 1000 millimicrons (electron microscope), and the specific area by nitrogen adsorption method is 1 to 800 rn2/g, p
)( is 6 to 11 (JIS standard -6221-1982
law). The size of the carbon black used in the present invention is 10 to 1
Carbon black of 0.00 mm is used, and carbon black of 50 to 1000 mm is used when controlling the strength of the coating film. In addition, for the purpose of controlling the surface roughness of the coating film, finer particles of carbon black (100 millimicrons or less) are used for smoothing to reduce spacing loss, and coarser particles of carbon are used for the purpose of roughening the surface and lowering the coefficient of friction. Use black (50 mm or more).

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. Also,
These carbon blacks may be used after being surface-treated with a dispersant described below or grafted with a resin. In addition, the temperature of the furnace when producing carbon black was set to 20
It is also possible to use a material whose surface is partially graphitized by treatment at 00° C. or higher. Moreover, hollow carbon black can also be used as a special carbon black. For carbon black that can be used in the present invention, for example, "Carbon Black Handbook 1," edited by the Carbon Black Association (published in 1972) can be referred to.

An abrasive can be used for the back layer and the magnetic recording 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 components: corundum and magnetite), garnet, silica, silicon nitride, boron nitride, molybdenum carbide, Boron carbide, tungsten carbide, titanium carbide, tripoly, diatomaceous earth, dolomite, etc., which mainly have a Mohs hardness of 6 or more, are used in combinations of one to four types. These abrasives have an average particle size of 0.01~
A size of 5 microns is used, particularly preferably 0.05 to 5 microns. These abrasives are added in an amount of 0.001 to 50 parts by weight based on 100 parts by weight of the binder.

A lubricant can be used in the back layer and magnetic recording layer according to the present invention. Lubricants used in the present invention include silicone oil, graphite, molybdenum disulfide, boron nitride, graphite fluoride, fluorinated alcohol, polyolefin (polyethylene wax, etc.), polyglycol (polyethylene oxide wax, etc.), alkyl phosphoric acid Ester, polyphenyl ether, tungsten disulfide, monobasic fatty acid with 10 to 20 carbon atoms and 3 to 12 carbon atoms
Fatty acid esters consisting of one or more of m alcohols, dihydric alcohols, trihydric alcohols, tetrahydric alcohols, and hexahydric alcohols;
Fatty acid esters consisting of a monobasic fatty acid having 10 or more carbon atoms and a monovalent to hexavalent alcohol having a total of 11 to 28 carbon atoms 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 butyl caprylate, octyl caprylate, ethyl laurate, butyl laurate, octyl laurate, ethyl myristate, butyl myristate,
Octyl myristate, ethyl palmitate, butyl palmitate, octyl palmitate, ethyl stearate, butyl stearate, octyl stearate, amyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tri Examples include stearate, anhydrosorbitan tetrastearate, oleyl oleate, oleyl alcohol, and lauryl alcohol. In addition, so-called lubricating oil additives can be used alone as the lubricant used in the present invention, and antioxidants (alkylphenols, etc.), rust inhibitors (
naphthenic acid, alkenylsuccinic acid, dilauryl phosphate, etc.), oily agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.), detergent and dispersant, viscosity These include index improvers, pour point depressants, antifoam agents, etc.

These lubricants are preferably added in an amount of 0.05 to 20 parts by weight per 100 parts by weight of the binder.

A dispersant can be used in the back layer and magnetic recording layer. Dispersants used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid,
Fatty acids having 10 to 22 carbon atoms (R7C0OH, R' is an alkyl group having 9 to 21 carbon atoms) such as lylunic acid and stearolic acid, alkali metals (Li, Na,
K, etc.) or alkaline earth metals (Mg, Ca, B, etc.)
a), Cu.

Metal soaps made of salts such as PB; lecithin, etc. are used. In addition, higher alcohols having 4 or more carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol), and their sulfuric esters, phosphoric esters, etc. can also be used. The stiff dispersant is binder 1
It is added in an amount of 0.005 to 20 parts by weight per 00 parts by weight. These dispersants may be used by depositing them on the surface of the ferromagnetic fine powder or nonmagnetic fine powder in advance, or by adding them during dispersion.

An antistatic agent can be used in the back layer and the magnetic recording layer. Antistatic agents used in the present invention include conductive powders such as graphite, carbon black, and carbon black graft polymers; natural surfactants such as saponins; alkylene oxides, glycerin, glycidol, polyhydric alcohols, and polyhydric alcohol esters. , nonionic surfactants such as alkinophenol EO adducts: higher alkyl amino acids, cyclic amines, hydantoin derivatives, amidoamines, ester amides, quaternary ammonium salts, lysine and other heterocycles, phosphoniums or sulfoniums, etc. Cationic surfactant: Anionic surfactant containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric ester group; Amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, alkyl betaine type Amphoteric surfactants such as

These surfactants may be added alone or in combination. The amount of these surfactants used is 0.01 to 10 parts by weight per 100 parts by weight of the ferromagnetic fine powder. These are used as antistatic agents, but are sometimes used for other purposes, such as dispersion, improving magnetic properties, improving lubricity,
It may also be applied as a coating aid.

Organic solvents used for dispersing, kneading, and coating carbon-based fine powder in the back layer and ferromagnetic fine powder in the magnetic recording layer may include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. in any ratio.
Ketones such as isophorone and tetrahydrofuran; alcohols such as methanol, ethanol, propatool, butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol; methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, acetic acid Ester types such as glycol monoethyl ether, glycol ether types such as tetrahydrofuran, glycol dimethyl ether, glycol nomoethyl ether, and dioxane:
Tar-based (aromatic hydrocarbons) such as benzene, toluene, xylene, cresol, chlorobenzene, and styrene:
Chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene, N,N-dimethylformamide, hexane, and the like can be used.

The magnetic recording layer and the back layer are formed by arbitrarily combining the above compositions, etc., dissolving them in an organic solvent, coating them as a coating solution on a support, and drying them. There are no particular restrictions on the support used. When used as a tape, the thickness of the support is about 2.5 to 100 microns, preferably about 3 to 70 microns. In the case of a disk or card shape, the thickness is about 0.5 to 10 mm. Materials include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride, and plastics such as polycarbonate, polyamide, and polysulfone. In addition, metals such as aluminum and copper,
Ceramics such as glass can also be used. These supports are subjected to corona discharge treatment, plasma treatment,
Undercoat treatment, heat treatment, dust removal treatment, metal vapor deposition treatment, and alkali treatment may be performed.

There are no particular restrictions on the method of kneading the ferromagnetic fine powder, etc., and the order of addition of each component can be set as appropriate. For the preparation of magnetic paints, the usual kneading machines are used, such as two-roll mills, three-roll mills, ball mills, pebble mills, thoron mills, sand grinders, Szegvari attritors, high-speed impellers, grainers, high-speed stone mills, high-speed Thrust mill, disper, kneader
1 High speed mixer, ribbon blender, coneater, intensive mixer, tumbler, blender, disperser, homogenizer, single screw extruder,
A two-wheel screw extruder, an ultrasonic dispersion machine, etc. can be used.

Methods for applying the above magnetic recording layer and back layer onto the support include air doctor coating, blade coating,
Air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, etc. can be used. Other methods are also possible.The order in which the magnetic recording layer and back layer are coated is not particularly limited, and they may be coated separately or may be coated simultaneously.

By such a method, the magnetic layer coated on the support is immediately subjected to a treatment to orient the magnetic powder in the layer without drying, if necessary, and then the formed magnetic layer is dried. The conveyance speed of the support at this time is usually 10 m/min to 800 m/min.
m/min and the drying temperature is controlled between 20°C and 120°C. Further, the magnetic recording medium of the present invention is manufactured by performing surface smoothing processing or cutting into a desired shape if necessary.

Further, the same method as above is applied to drying the coated back layer, and the coated back layer may be dried at the same time as the magnetic recording layer.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Note that "parts" in Examples and Comparative Examples indicate "parts by weight."

The polyurethane of the present invention used in this example was synthesized as follows. That is, the polyols shown in Table 1,
Using a diisocyanate and a chain extender having an amino group or an amide group, the conventional method (r Synthetic Polymer Vol. 1v, 309
Polyurethane was synthesized according to the following article (see page 369, Breakfast Shoten, June 15, 1970). The results are shown in Table 1.

Example 1 A magnetic paint having the composition shown below was prepared and coated on a polyethylene terephthalate nonmagnetic support having a thickness of 10 μm so that the thickness of the magnetic layer after drying was 3.0 μm.

Magnetic paint composition: 100 parts of Go-containing y-Fe203 powder (Co: 2 wt% relative to iron oxide, specific surface area [S-bet]: 45rn"/g) 10 parts of vinyl chloride/vinyl acetate/maleic anhydride copolymer ( Made by Nippon Zeon ■: 400X 100A) Polyurethane [I co 9 parts polyisocyanate
5 parts (made by Nippon Polyurethane: Coronate L)
) Oleic acid 1 part Butyl stearate 2 parts Carbon black 2 parts (Average particle size: 20111μ
, Oil absorption: 170mI! , 7100g) α-Alumina 10 parts Methyl ethyl ketone
After kneading and preparing 300 parts of a backing solution of the following composition in a ball mill, 10 parts of Coronate 3041 (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed and dispersed uniformly, the viscosity was adjusted, and a polyester support opposite to the magnetic layer was added. It was applied to the body surface to a thickness of 2 μm and dried.

Carbon black 90 parts (average particle size: 20 mμ, oil absorption: 160+nJZ/loOg) Carbon black 30 parts (Leben MTP:
(manufactured by Colombia) (Average particle size: 250 mμ, oil absorption + 50 mL/l00 g) 30 parts of polyurethane resin, Tuboran N-2304,
(Manufactured by Nippon Polyurethane Co., Ltd.) Phenoxy resin
5 parts (PKHH, manufactured by Union Carbide) Saran resin (manufactured by Dow Chemical) 25 parts stearic acid 5 parts methyl ethyl ketone
800 parts cyclohexane
The non-magnetic support coated with 200 parts of magnetic paint was subjected to magnetic field orientation treatment while the magnetic paint was not dry, and after drying, calender treatment was performed, and each part was slit into 2-inch widths. produced a videotape.

Regarding the obtained sample No. 1, the charging voltage, C/N value, and number of dropouts of the magnetic layer were measured by the following methods, and the results are shown in Table 2.

(Magnetic layer charging voltage) Using a charging voltage measuring device, the charging voltage was measured while the actual machine was running.

(C/N value) Using a spectrum analyzer, set the reference tape to sample N.
o, 5 (OdB), and the C/N value (dB) for a carrier of 8 MHz was compared and measured.

(Number of dropouts) The number of dropouts is shown after 250 passes are repeated. Dropout is 1 on the dropout counter.
, sx The number of cases in which the reproduction output level was reduced by 16 dB or more in a period of 10-6 seconds or more was 7 minutes.

[Example 2] The following composition was placed in a co-kneader and thoroughly kneaded, and then the product was placed in a ball mill and thoroughly kneaded.
5 (trade name of polyisocyanate compound manufactured by Bayer)
A magnetic paint was prepared by adding 5 parts of the solid content and uniformly mixing and dispersing the mixture.

100 parts of CO-containing r-Fe203 powder (
relative to iron oxide: o: 3 wt%;, relative to Fe3+: 3 wt%;) (Specific surface area (SRET): 40 rrf/g) Vinyl chloride/vinyl acetate/maleic anhydride copolymer 10 parts (VMCH
, manufactured by Union Carbide Co.) Polyurethane [■
9 part lecithin
1 part myristic acid 3 parts ethyl stearate 3 parts lauric acid 3 parts butyl acetate
200 parts chromium oxide
10 parts Methyl ethyl ketone 200 parts After adjusting the viscosity of this magnetic paint, it was applied to the surface of a polyethylene terephthalate support to a thickness of 5 μm, oriented, dried, and calendered to prepare a sample.

Carbon black (average particle size 30 mμ) was added to this sample.
, oil absorption amount 180mji! Sample No. 12 was prepared by applying and drying the backing liquid in the same manner as in Example 1, except that 120 parts of the sample was used (120 parts/100 g), followed by calendering and slitting.

The same test as in Example 1 was conducted and the results are shown in Table 2.

[Example 3] Vinyl chloride/vinyl acetate/maleic anhydride copolymer 10
parts and polyurethane [119 parts, 10 parts of vinyl chloride-vinyl acetate copolymer, polyurethane [[[]1
Sample No. 1 was prepared in the same manner as in Example 1 except that 5 parts were used.
3 samples were created.

The same test as in Example 1 was conducted and the results are shown in Table 2.

[Example 4] As a magnetic paint, 10 parts of urethane resin [rV] and urethane resin TIM-3 were used instead of 119 parts of polyurethane.
Using 5 parts of 03 (Sanyo Chemical), carbon black (average particle size 30 mμ, oil absorption 180 mu 7100 g) 5
Sample No. 4 was prepared in the same manner as in Example 2, except that the sample No. 4 was used in the same manner as in Example 2.

The same test as in Example 1 was conducted and the results are shown in Table 2.

[Comparative Example 1] Sample N was prepared in the same manner as in Example 1, except that Tuboran N-2304 (manufactured by Nippon Polyurethane) was used as a polyurethane resin instead of the urethane resin [I] as the magnetic paint.
o, 5 samples were created.

The same test as in Example 1 was conducted and the results are shown in Table 2.

[Comparative example 2 Average particle size 20mμ, oil absorption 120mu/Zo.

10 parts of carbon black in the magnetic layer and 1 part in the back layer.
Sample No. 1 was prepared in the same manner as in Example 2 except that 20 parts were used.
6 samples were created.

The same test as in Example 1 was conducted and the results are shown in Table 2.

Below, it is better for the margin magnetic layer electrostatic voltage to have a smaller absolute value, for the C/N value to be positive and larger, and for the number of dropouts to be smaller. As is clear from the results in Table 2, sample No. 085 (Comparative Example 1) does not use nitrogen-containing polyurethane having an amino group or amide group as a binder in the magnetic layer, and the charging voltage and dropout number is very poor. Sample No. 6 (Comparative Example 2)
In this case, a nitrogen-containing polyurethane having an amino group or an amide group is used as a binder for the magnetic layer, but the amount of carbon black used in the magnetic layer is as high as 10% by weight, and the oil absorption amount of carbon black in the pack layer is 120 mu/100 g. Although it was small and had a good charging voltage, its C/N value and number of dropouts were very poor. In contrast, sample N01 of the present invention
Samples 1 to 4 were excellent in charging voltage, C/N value, and number of dropouts.

[Effects of the Invention] The magnetic recording medium of the present invention has excellent antistatic properties, prevents an increase in the number of dropouts, and has excellent S/N ratio and C/N ratio. It is.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer containing fine ferromagnetic powder and a binder is provided on one surface of a support and a back layer containing carbon-based powder is provided on the other surface, (A) a binder for the magnetic layer; (B) A polyurethane consisting of a polyol and a diisocyanate and a chain extender selected from the group consisting of diols, diamines, and hydroxyamine compounds having an amino group or an amide group is used as the back layer, and (B) the back layer has an oil absorption amount of 150 ml/ A magnetic recording medium characterized by using 100 g or more of carbon-based fine powder, and (C) using 5% by weight or less (including zero) of carbon-based fine powder in the magnetic layer based on the ferromagnetic fine powder. . 2. As a binder for the magnetic layer, a vinyl chloride copolymer is used together with the polyurethane, and the weight ratio of vinyl chloride copolymer/total polyurethane is 100/20 to 100/
200. The magnetic recording medium according to claim 1, characterized in that the magnetic recording medium is 200 mm. 3. The magnetic recording medium according to claim 1, wherein the ferromagnetic fine powder has a specific surface area of 30 m^2/g or more.