JPS63255815A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an S/N preferably, C/N characteristic, electric chargeability and drop-outs by using polyurethane consisting of specific components as a binder for a magnetic layer, fine carbon powder of a specific oil absorption for a back layer and a specific amt. of fine carbon powder for the magnetic layer. CONSTITUTION:The polyurethane consisting of polyester polyol essentially consisting of at least one kind selected from diol having an amino group or amide group, dicarboxylic acid having the amino group or amide group and hydroxycarboxylic acid having the amino group and amide group and diisocyalate is used as the binder of the magnetic recording layer. The fine carbon powder having >=150ml/100g oil absorption is used for the back layer and the fine carbon powder is used for the magnetic layer at <=5wt.% (including zero) of the weight of the fine ferromagnetic powder. The magnetic recording medium which is improved in the antistatic performance, is prevented of an increase in the number of drop-outs and is improved in the S/N and C/N is thereby obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] 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-characteristics and C/N characteristics, is less likely to be charged, has little dropout, and is highly reliable. The present invention relates to an excellent magnetic recording medium.

[Prior art and problems]

Conventionally, in magnetic recording media, in order to improve the running stability during high-speed rewinding and to prevent the support of the magnetic recording medium from being scraped, the back layer is placed on the side of the support opposite to the side on which the magnetic layer is provided. It is located on the surface of the 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 electrical 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
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. Due to a decrease in S/N
This leads to deterioration of electromagnetic conversion characteristics such as characteristics and dropout, 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 S/N 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 problems]

As a result of various studies, the present inventors found that diols having an amino group or an amide group, dicarboxylic acids having an amino group or an amide group, and hydroxycarboxylic acids having an amino group or an amide group can be used as binders for the magnetic recording layer. A polyurethane consisting of a polyester polyol and diisocyanate containing at least one selected from the following as an essential component is used, a carbon-based fine powder with an oil absorption of 150 m12/100 g or more is used for the back layer, and a ferromagnetic fine powder is used for the magnetic layer. By using 5% by weight or less (including zero) of carbon-based fine powder, the problems of the prior art were solved and the object of the present invention was achieved.

The present invention will be explained in detail below.

The polyurethane used as a binder for the magnetic layer in the present invention is at least one selected from diols having an amino group or an amide group, dicarboxylic acids having an amino group or an amide group, and hydroxycarboxylic acids having an amino group or an amide group. It is a polyurethane consisting of a polyester polyol and diisocyanate whose essential components are polyester polyol and diisocyanate. Here, the amino group is a primary amino group (-Nl2)
, represents a secondary group or an aromatic group, and when there are two or more R1s, these may be the same or different, and two R1s may be linked to each other to form a ring.Alkyl group) or an aromatic group, and when there are two R2s, they may be the same or different;
2 may be connected to each other to form a ring.

As the diol, dicarboxylic acid and hydroxycarboxylic acid having an amino group or amide group, compounds represented by the following general formulas (I) to (V) are preferred.

In the formula, X and Y are each independently -OH or -Coo
R3 represents a hydrogen atom, an aliphatic group (e.g. an alkyl group), or an aromatic group, R4 represents a hydrogen atom or an aliphatic group, and n and m each independently represent an integer of 0 to 4. .

The polyester polyol used in the present invention is a polycondensation product of a dihydric alcohol and a dibasic acid, which has at least the above-mentioned amino group or amide group and contains one selected from diols, dicarboxylic acids, and hydroxycarboxylic acids as an essential component. It is. As the dihydric alcohol and dibasic acid that can be used in combination with the diol, dicarboxylic acid and hydroxycarboxylic acid having an amino group or amide group, compounds commonly used in polyester polyols can be used. For example, dihydric alcohols include ethylene glycol, propylene glycol, butanediol, and 1,6-hexanediol.

Examples of dibasic acids include adipic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, and terephthalic acid.

In addition, the diisocyanates used to form polyurethane by reacting with the above polyester polyol include 1, for example, 2,4-tolylene diisocyanate, 2
．． 6-tolylene diisocyanate, 1゜3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 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,
Examples include hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and the like.

In the present invention, the polyurethane having a quaternary ammonium salt as an amino group is produced by converting the amino group in the polymer into 4 after producing the polyester polyol or producing the polyurethane.
It can be obtained by grading.

Furthermore, in the present invention, ordinary polyurethane can be used in combination with the polyurethane having an amino group or amide group.

The polyurethane used in the present invention has an amino group or an amide group of 104 as a proportion of the total amount of the polyurethane polymer.
It is preferable to contain up to 10 −3 equivalents/g. The molecular weight is preferably about 10,000 to 200,000, more preferably 20,000 to 150,000.

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-vinyl propionate -vinyl alcohol copolymer,
Examples include vinyl chloride copolymers such as vinyl chloride-vinyl acetate-acrylic acid copolymer, vinyl chloride-vinyl acetate-acrylic acid-vinyl alcohol copolymer, and oxidized copolymers of these.

Among vinyl chloride copolymers, vinyl chloride copolymers with polar groups such as carboxylic acid groups or salts thereof, sulfonic acid groups or salts thereof, phosphoric acid groups or salts thereof, amino groups, and hydroxyl groups have improved dispersibility. It is particularly preferred because of its excellent effects.

Furthermore, polar groups (-COOM, -5o, M, -0PO3
It is also effective to use it in combination with a polyurethane having a hydrogen atom, sodium, or potassium, or by introducing these polar groups into the polyurethane having an amino group or an amide group according to the present invention. There is a preferable option.

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 is 150mA/100g or more. However, carbon black having a DBP oil absorption of 150 m Q /100 g or less 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 + afl/100 g or more. 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. In addition to ferromagnetic metal fine powder, ferromagnetic alloy fine powder, y-Fe, O, Fe, 04, and CO modified iron oxides, modified barium ferrite and modified strontium ferrite can be used.

As an example of a ferromagnetic alloy powder, the metal content in the ferromagnetic fine powder 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, Go, Ni, Fe-Co, Fe-Ni, C
o-Ni, Co-N1-Fe), and the metal content is 2
Other components (e.g., Ajl, S
i, S, Sc, Ti, 'V, Cr, Mn,
Cu, Zn, Y, Mo, Rh, Pd, Ag,
, Sn, Sb, Te, Ba, Ta, W, Re,
Au, Hg, Pb, Bi, La, Ce.

Mention may be made of alloys which may contain Pr, Nd, B, P). In addition, if the above ferromagnetic metal is mixed with a small amount of water,
It may also contain a hydroxide or an oxide.

Particularly preferred ferromagnetic fine powders are γ-Fe, 03, CO gold-containing γ-Fe20. , 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 Fe-Co 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 (S BET) of this ferromagnetic alloy powder is 30r
It is preferably rF/g or more, more preferably 40 rrf/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 polyester polyol containing the above-mentioned amino group or amide group 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 made of the polyester polyol 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 acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic ester Styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin, polyvinyl fluoride, chloride Vinylidene acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer , polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof.

Examples of these resins include Japanese Patent Publication No. 37-6877, Japanese Patent Publication No. 39-12528, Japanese Patent Publication No. 39-19282, Japanese Patent Publication No. 40-5349, Japanese Patent Publication No. 40-20907, Japanese Patent Publication No. 41-9463, and Japanese Patent Publication No. 41-9463. 41-14059, Special Publication No. 41-16985, Special Publication No. 6428, Special Publication No. 11621, Special Publication No. 11621, Special Publication No. 11621, Special Publication No. 43-4623, Special Publication No. 15206, Special Publication No. 43-15206, Special Publication No. 2889, Special Publication No. 1973, Special Publication No. -17947, Special Publication No. 44-18232, Special Publication No. 14020, Special Publication No. 45-14500,
Special Publication No. 47-18573, Special Publication No. 47-22063, Special Publication No. 47-22064, Special Publication No. 47-22068
No., Special Publication No. 47-22069, Special Publication No. 47-2207
No. 0, Special Publication No. 47-27886, Japanese Patent Publication No. 133-1983
521, JP 58-137133, JP 58-16
6533, JP-A-58-222433, JP-A-59-5
It is described in publications such as 8642.

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 reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and Mixture of diisocyanate prepolymers.

Mixtures of polyester polyols (excluding polyester polyols having amino or amide groups according to the invention) and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate, polyamine resins and A mixture of these, etc.

Examples of these resins include Japanese Patent Publication No. 39-8103, Japanese Patent Publication No. 9779-1979, Japanese Patent Publication No. 7192-1971, and Japanese Patent Publication No. 41-7192.
No. 1-8016, Special Publication No. 14275, Special Publication No. 41-1427, Special Publication No. 14275
2-13179, Special Publication No. 43-12081, Special Publication No. 44-28023, Special Publication No. 45-14501, Special Publication No. 45-24902, Special Publication No. 46-13103, Special Publication No. 47-22065, Special Publication No. 1972 -22066,
Special Publication No. 47-22067, Special Publication No. 47-22072, Special Publication No. 47-22073, Special Publication No. 47-28045
No., Special Publication No. 47-28048, Special Publication No. 47-2892
No. 2, etc.

These binders may be used alone or in combination;
Other additives may be added. 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 powder: 10:1 by weight
The binder is used in an amount of 5 to 400 parts by weight based on 0 parts by weight.

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 acidic groups such as carboxylic acid, sulfinic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, and phosphoric ester group; amino acids, amino sulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and alkyl betaines. Amphoteric groups such as amino groups, imino groups, imido groups, amido groups, etc., or hydroxyl groups, alkoxyl groups, thiol groups, halogen groups, silyl groups, siloxane groups, etc. The functional group is I per gram of resin.
It is preferable to include X 10-'eq to I X 10-'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, 〇-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate. , products of the isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates. Commercially available trade names of these polyisocyanates include Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL (manufactured by Nippon Polyurethane Co., Ltd.), Takenate D-102, Takenate D-11ON, Takenate D-200, Takenate Kano 202 (manufactured by Takeda Pharmaceutical Co., Ltd.), Desmodule L, Desmodule IL, Desmodule N, Desmodule HL (manufactured by Sumitomo Bayer)
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 compounds be polyfunctional.

As mentioned above, the back layer according to the present invention has a DBP oil absorption amount (JIS standard) [-8221-1982 method] of 150 m.
A carbon-based fine powder (for example, carbon black, etc.) with a weight of Q /100g or more 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. A specific example of the abbreviation of these carbon blacks in the United States is SAF.
, l5AF, ll5AF, T, )IAF, SPF,
FF, FEF, H to F, GPF, APF, S
RF, MPF, ECF.

SCF, CF, FT, MT, HCC, HCF,
There are MCF, LFF, RCF, etc., and the US AST
Those classified as D-1765-82a of the M standard can be used. The average particle size of these carbon blacks used in the present invention is 10 to 1000 millimicrons (electron micrometer), and the specific surface area by nitrogen adsorption method is 1 to 80 millimicrons.
0i/g, p)l is 6 to 11 (-62 to JIS standard
21-1982 Act). The size of the carbon black used in the present invention is 10 to 100 millimicrons for the purpose of lowering the surface electrical resistance of the coating film, and carbon black of 50 to 1000 millimicrons to control the strength of the coating film. I use it. In addition, in order to control the surface roughness of the coating film, finer particles of carbon black (1
Coarse particles of carbon black (50 millimicrons or less) are used to roughen the surface and lower the coefficient of friction. 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.

Carbon black that can be used in the present invention is, for example, "Carbon Black Handbook", edited by Carbon Black Association (1971).
(published in 2013) can be used as a reference.

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 to 5.
Micron size is used, particularly preferably 0
．． 05-5 microns.

These abrasives contain 0.00 parts by weight per 100 parts by weight of the binder.
It is added in an amount of 1 to 20 parts by weight. Regarding these, Japanese Patent Publication No. 49-39402, Japanese Patent Publication No. 52-28642, U.S. Patent No. 3,687,725, U.S. Patent No. 3,007
, 807, U.S. Pat. No. 3,041,196, U.S. Pat. No. 3,293,066, U.S. Pat.
．． No. 190, British Patent No. 1,145,349, West German Patent No. 853,211, etc.

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,
A monobasic fatty acid with 10 to 20 carbon atoms and one or two of monohydric alcohol, dihydric alcohol, trihydric alcohol, tetrahydric alcohol, or hexahydric alcohol with 3 to 12 carbon atoms. Fatty acid esters consisting of the above, fatty acid esters consisting of a monobasic fatty acid having 10 or more carbon atoms, and a monohydric to hexavalent alcohol having a total carbon number of 11 to 28 carbon atoms, etc. 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, and palmitate. Butyl acid, octyl palmitate, ethyl stearate, butyl stearate, octyl stearate, amyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, anhydrosorbitan tetrastearate , oleyl oleate, oleyl alcohol, lauryl alcohol, etc. In addition, so-called lubricating oil additives can be used alone as the lubricant used in the present invention, such as antioxidants (alkylphenol, etc.), rust inhibitors (naphthenic acid, alkenylsuccinic acid, dilauryl phosphate, etc.), oil-based agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.), detergents and dispersants, viscosity index improvers, pour point depressants, foam stoppers, etc. be. These lubricants are preferably added in an amount of 0.05 to 20 parts by weight per 100 parts by weight of the binder. Regarding these, please refer to Special Publication No. 43-23889, Special Publication No. 43-23889,
4-18221, JP 48-24041, JP 48-18482, JP 47-28043, JP 57-56132, U.S. Patent No. 3,423,233, U.S. Patent No. 3,470,021 , U.S. Patent No. 3,492
, 235, U.S. Patent No. 3,497,411, U.S. Patent No. 3,523,086, U.S. Patent No. 3,625,760, U.S. Patent No. 3,630,772, U.S. Patent No. 3,634
, 253, U.S. Patent No. 3,642,539, U.S. Patent No. 3,687,725, U.S. Patent No. 4,135.031, “IBM Technical Disclosure
e Bulletin (IBM Technical Disclosure Bulletin)” VOl, 9. N (17
, p779 (December 1966);”ELEKTRO
NIK” (Electronic) 1961, No. 12
゜P2S5; Chemistry Handbook, Applied Edition, p954-967.
It is described in a publication published by Maruzen Co., Ltd. in 1980.

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 such as lyrinnic acid and stearolic acid (RCOOHlRl is an alkyl group having 9 to 21 carbon atoms), alkali metals (LL, Na,
K, etc.) or alkaline earth metals (Mg, Ca, B, etc.)
a), metal soaps made of Cu, Pb, etc.; 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. These dispersants are added in an amount of o, oos to 20 parts by weight based on 100 parts by weight of the binder. How to use these dispersants:
It may be applied to the surface of the ferromagnetic fine powder or nonmagnetic fine powder in advance, or it may be added during dispersion. Such items are, for example, Special Publication No. 39-28369, Special Publication No. 1973-1
No. 7945, Special Publication No. 18221, Special Publication No. 18221, Special Publication No. 1822-
No. 15001, Japanese Patent Publication No. 49-39402, U.S. Patent No. 3
, No. 387,993, No. 3.470.021, etc.

An antistatic agent can be used in the back layer and magnetic recording layer. The antistatic agents used in the present invention include conductive powders such as graphite, carbon black, and carbon black graft polymers; natural surfactants such as saponin; alkylene oxide-based, glycerin-based, glycidol-based,
Nonionic surfactants such as polyhydric alcohols, polyhydric alcohol esters, and alkylphenol EO adducts; higher alkyl amino acids, cyclic amines, hydantoin derivatives, amidoamines, ester amides, quaternary ammonium salts,
Cationic surfactants such as pyridine and other heterocycles, phosphoniums or sulfoniums; Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; Amino acids, amino sulfones Acids, sulfuric acid or MA acid esters of amino alcohols, surface surfactants such as alkyl betaine type, etc. are used. Some examples of surfactant compounds that can be used as antistatic agents include U.S. Pat.
2,676.122, 2.676.924, 2,676.975, 691,566, 2
．． No. 727,860, No. 2,730,498, No. 2,
No. 742,379, No. 2.739,891, No. 3.0
No. 68,101, No. 3,158,484, No. 3.20
No. 1,253, No. 3,210,191, No. 3,294
, No. 540, No. 3.415,649, No. 3,441,
No. 413, No. 3,442,654, No. 3.475, 1
No. 74, No. 3,545,974, West German Patent Publication (OL
S) No. 1.942,665, British Patent No. 1,077.31
No. 7, No. 1,198,450, etc., "Synthesis of Surfactants and Their Applications" by Ryohei Oda et al. (Maki Shoten 1972 edition); Surface Active Agents J (Interscience) by A.W. Publication Co., Ltd. (1985 edition); T. P. Sisley, Encyclopedia of Surf-Active Agents, Volume 2 J (Chemical Publications Co., Ltd., 1964 edition); Surfactant Handbook, Sixth Edition (Industrial Book) Co., Ltd., December 20, 1968); written by Hideo Marumo, Antistatic Agents, J Koshobo (1968), etc.

These surfactants may be added alone or in combination, and 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.

Sometimes they are also used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

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 systems such as glycol monoethyl ether; glycol ether systems such as diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl 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-dimethylformaldehyde, 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,
In addition to cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride, plastics such as polycarbonate, polyamide, and polysulfone, metals such as aluminum and copper, and ceramics such as glass can also be used. Prior to coating, these supports may be subjected to corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, dust removal treatment, metal vapor deposition treatment, and alkali treatment. Regarding these supports, for example, West German Patent No. 3338854A, Japanese Patent Application Laid-Open No. 59-116926
No., U.S. Pat. No. 4,388,368; Yukio Mitsuishi, "Fibers and Industry J31, pp.50-55, 1975.

There is no particular restriction on the method of cross-conducting the ferromagnetic fine powder, etc., and the order of addition of each component can be set as appropriate. For the preparation of magnetic paints, conventional mixing machines are used, such as two-roll mills, three-roll mills, ball mills, pebble mills, thoron mills, sand grinders, Szegvari attritors, high-speed impellers, dispersing machines, high-speed stone mills, high-speed impact mills. Mill, Disper, Kneader 1
High speed mixers, ribbon blenders, co-kneaders, intensive mixers, tumblers, blenders, dispersers, homogenizers, axle screw extruders, twin screw extruders, ultrasonic dispersers, and the like can be used. For details on the technology related to crosstalk dispersion, please refer to T.
Written by C. PATTON (Chee C. PATTON) “Pa
1nt Flow and Pigment Disp
Paint Flow and Pigment Dispersion (1964 John Wi
ley & 5ons (published by John Wiley & Sons) and Nobu Tanaka, "Industrial Materials Jl 25 Volume 3.
7 (1977), etc. 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 paint can also be prepared by carrying out crosstalk dispersion according to the method described in the above-mentioned literature.

Methods for coating the magnetic recording layer and back layer on 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, and other methods are also possible. "Coating Engineering" 2
It is described in detail on pages 53 to 277 (published on March 20, 1971). There is no particular restriction on the order of coating the magnetic recording layer and the back layer, and they may be coated separately or 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 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 1 minute to 800 m
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 subjecting it to surface smoothing processing and cutting it into a desired shape, if necessary. These include, for example, Japanese Patent Publication No. 40-23625, Japanese Patent Publication No. 39-28368, and U.S. Patent No. 34
No. 73960, etc. Furthermore, the method disclosed in Japanese Patent Publication No. 41-13181 is considered to be a basic and important technique in this field.

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. In addition, "1 part" in Examples and Comparative Examples indicates "part by weight."

The polyurethane of the present invention used in this example was synthesized as follows. That is, using a polyester polyol synthesized by polycondensation of an amino group- or amide group-containing compound, a diol, and a dicarboxylic acid, a diisocyanate, and a chain extender shown in Table 1, according to a conventional method ("synthetic polymer,
OV, pp. 309-369, Breakfast Shoten, June 15, 1972), polyurethane was synthesized. 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: Ferromagnetic metal powder (Fe) l
oo part (specific surface area (S-bet): 45 m/g) polyurethane (1) 12
Part oleic acid 1
1 part Butyl stearate 2 parts Methyl ethyl ketone 300 parts The back solution of the following composition was mixed with a ball mill, and then 10 parts of Coronate 2061 (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed and dispersed uniformly.
Adjust the viscosity and add 2μ on the opposite side of the polyester base from the magnetic layer.
It was applied to a thickness of m and dried.

Saran resin (manufactured by Dow Chemical) 25 parts stearic acid
5 parts methyl ethyl ketone 800 parts cyclohexane
A non-magnetic support coated with 200 parts of magnetic paint is subjected to a magnetic field alignment treatment while the magnetic paint is still wet, and after drying, calender treatment is performed, and the material is slit into 172-inch widths to form a VH5 type video tape. was manufactured.

Regarding the obtained sample No. 1, the charging voltage of the magnetic layer, the C value, and the number of dropouts 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 value) Using a spectrum analyzer, the reference tape was set as sample Nα5 (OdB), and the C value (dB) for a carrier of 8 MHz was comparatively measured.

(Number of dropouts) The number of dropouts after repeated running of 250 passes is shown. Dropout is 1 on the dropout counter.
, the number of times in which the reproduction output level was reduced by 16 dB or more in a period of 5 x 10-'see or more was displayed.

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 mixed, and then desmodule L-7
5 (trade name of polyisocyanate compound manufactured by Bayer)
20 parts were added and uniformly mixed and dispersed to prepare a magnetic paint.

Polyurethane (II)
10 parts lecithin
1 part myristic acid 3
Part ethyl stearate 3 parts Lauric acid 3 parts Butyl acetate 400 parts Methyl ethyl ketone 200 parts After adjusting the viscosity of this magnetic paint, it was applied to the surface of a polyethylene terephthalate substrate to a thickness of 5 μm, oriented, and dried.

Samples were prepared by calendaring.

Carbon black (average particle size 30 mμ) was added to this sample.
A sample of sample number 2 was prepared by applying and drying the backing liquid in the same manner as in Example 1 except that 120 parts of oil was used (oil supply amount: 180 mN/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 A sample No. 3 was prepared in the same manner as in Example 1, except that 10 parts of vinyl chloride-vinyl acetate copolymer and 20 parts of polyurethane CI[I] were used.

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

Example 4 As magnetic paint, 10 parts of urethane resin (rV), 5 parts of urethane resin TIM-3003 (Kochu Kasei), and carbon black (average particle size 3011μ, oil supply amount 180d/
Sample 4 was prepared in the same manner as in Example 2 except that 5 parts (100 g) were used.

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

Comparative Example 1 Sample No. 5 was prepared in the same manner as in Example 1 except that Tuboran N-2304 (manufactured by Nippon Polyurethane) was used as the polyurethane resin instead of polyurethane (I) as the magnetic paint.
I created a sample.

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

Comparative example 2' Average particle diameter 20 mμ, oil supply amount 120ra Q /100g
10 parts of carbon black in the magnetic layer and 12 parts in the back layer.
A sample with sample number was prepared in the same manner as in Example 2 except that 0 copy was used.

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

The smaller the absolute value of the charged voltage of the magnetic layer, the better; the larger the positive C/N value, the better; and the smaller the number of dropouts, the better. As is clear from the results in Table 2,
Sample No. 5 (Comparative Example 1) does not use nitrogen-containing polyurethane having an amino group or an amide group as a binder for the magnetic layer, and the charging voltage and number of dropouts are very poor. Sample No. 6 (Comparative Example 2) uses nitrogen-containing polyurethane having an amino group or an amide group as the magnetic layer binder, but the amount of carbon black used in the magnetic layer is as high as 10% by weight, and the amount of carbon black in the back layer is 10% by weight. Black oil absorption is 120rafl/100g
Although the charging voltage was small, the C value and the number of dropouts were very poor. On the other hand, sample number 1 of the present invention
Samples No. 4 to 4 were excellent in charging voltage, C/N value, and number of dropouts.

〔Effect of the invention〕

According to the present invention, a magnetic recording medium with excellent antistatic properties, an increase in the number of dropouts, and an excellent S/N ratio and C/N ratio was obtained.

Procedural amendment March Yu Day, 1986

Claims (3)

[Claims] (1) In 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) the magnetic layer A polyester polyol and diisocyanate, each of which has at least one essential component selected from diols having an amino group or an amide group, dicarboxylic acids having an amino group or an amide group, and hydroxycarboxylic acids having an amino group or an amide group as a binder. (B) carbon-based fine powder with an oil absorption of 150 ml/100 g or more is used in the back layer, and (C) the magnetic layer contains 5% by weight or less (even zero) of the ferromagnetic fine powder. A magnetic recording medium characterized by using carbon-based fine powder (including). (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 100/2.
00. The magnetic recording medium according to claim (1), wherein the magnetic recording medium is 00. (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.