JPH0573898A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium having an excellent preservable property, high output and C/N characteristic and excellent durability. CONSTITUTION:This magnetic recording medium is constituted by providing a magnetic layer contg. ferromagnetic metallic powder, binder and polishing agent on a nonmagnetic base and contains aluminum in the surface of the above-mentioned ferromagnetic metallic powder. The content thereof is 2 to 5wt.% of the above-mentioned ferromagnetic metallic powder. The crystallite size of the oxide film of the ferromagnetic metallic powder is 15 to 50Angstrom and the above-mentioned polishing agent contains a polishing agent at 10 to 20 pts.wt. per 100 pts.wt. ferromagnetic metallic powder. In addition, the above- mentioned magnetic layer contains a rust preventive agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, a magnetic recording medium comprising a non-magnetic support and a magnetic layer. In particular, it relates to a magnetic recording medium containing a ferromagnetic metal powder in the magnetic layer.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as magnetic tapes, video tapes, floppy disks and the like. The magnetic recording medium is basically formed by laminating a magnetic layer in which ferromagnetic powder is dispersed in a binder on a non-magnetic support.

A magnetic recording medium is required to have a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. Particularly, with the recent widespread use of 8-mm video tape recorders and the like, video tapes are required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability. In recent years, in order to improve the electromagnetic conversion characteristics of magnetic recording media, ferromagnetic metal powders exhibiting excellent magnetic characteristics (for example, coercive force) have been used as ferromagnetic powders. The ferromagnetic metal powder is composed of a ferromagnetic metal such as iron, cobalt and nickel, or an alloy powder thereof, and by using this, a magnetic recording medium having good electromagnetic conversion characteristics can be obtained.

As for the ferromagnetic powder, it is generally considered that the electromagnetic conversion characteristics of the magnetic recording medium can be improved by using a finely powdered ferromagnetic powder. However, the hardness of ferromagnetic metal powder is γ-
Magnetic recording medium manufactured using a ferromagnetic metal powder according to a conventional method, since the content of the ferromagnetic metal powder is lower than that of a different metal containing .gamma.-iron oxide ferromagnetic powder containing different metals such as iron oxide ferromagnetic powder and cobalt. The magnetic layer (1) tends to have a lower hardness than the magnetic layer produced by using the γ-iron oxide ferromagnetic powder or the different metal / γ-iron oxide ferromagnetic powder. Therefore, the magnetic layer of the magnetic recording medium using the ferromagnetic metal powder is easily damaged by coming into contact with the magnetic head or the like during running. In such a damaged magnetic layer, the electromagnetic conversion characteristics are deteriorated, so that the purpose of using the ferromagnetic metal powder is not achieved.

Therefore, when a ferromagnetic metal powder is used, usually, a large amount of an abrasive is added to the magnetic layer to form a portion having high hardness in the magnetic layer, and the magnetic layer and the running system such as a magnetic head are used. A method of preventing damage to the magnetic layer due to contact with a member is adopted. That is, if the content of the abrasive is high,
The fact that the portion of the magnetic layer having high hardness is increased makes it less susceptible to damage to the magnetic layer.

However, in reality, when a large amount of abrasive is mixed to such an extent that the magnetic layer using the ferromagnetic metal powder exhibits good strength, it is necessary to reduce the content of the ferromagnetic metal powder as a result. Come on. Therefore, there is a problem in that the obtained magnetic recording medium does not easily exhibit sufficient electromagnetic conversion characteristics despite the use of the ferromagnetic metal powder.

As described above, the main factors for improving the electromagnetic conversion characteristics are:
Since it is a ferromagnetic metal powder, the polishing agent does not directly contribute to the improvement of electromagnetic conversion characteristics. Therefore, in a magnetic recording medium such as an 8 mm video tape which is required to exhibit particularly high electromagnetic conversion characteristics, the electromagnetic conversion characteristics accompanying a decrease in the compounding ratio of the ferromagnetic metal powder due to the addition of a large amount of abrasives. Is especially problematic.

On the other hand, it is known that a small amount of aluminum is added in the production of a ferromagnetic metal powder for the purpose of preventing sintering of particles during heat reduction (for example, Japanese Examined Patent Publication 59).
No. 19163), however, nothing is known about how the obtained ferromagnetic metal powder functions in the magnetic layer. So while showing good running durability,
For the purpose of providing a magnetic recording medium in which the characteristics of a ferromagnetic metal powder having excellent magnetic characteristics are sufficiently exhibited.
In a magnetic recording medium comprising a non-magnetic support and a magnetic layer in which a ferromagnetic metal fine powder and an abrasive are dispersed in a binder provided on the support, the ferromagnetic metal fine powder is converted to a metal. 1 to 6% by weight of aluminum component,
A magnetic recording medium has been proposed, characterized in that the abrasive for the magnetic layer is mainly composed of one selected from α-alumina, chromium oxide, silicon carbide and silicon nitride (Japanese Patent Laid-Open No. 63-103424). Publication.).

This proposal has demonstrated excellent effects such as abrasion resistance, output reduction, and C / N ratio with an 8 mm video tape, but if such a technique is applied as it is to a video tape for broadcasting. It was not possible to meet the required characteristics in terms of durability, output, storage stability. Therefore, as a result of analyzing the factors that affect the durability, output, and storability, the amount of alumina as the sintering inhibitor of the ferromagnetic metal powder, the thickness of the oxide film of the ferromagnetic metal powder, the amount of the abrasive and the rust prevention It was found that the presence or absence of the agent had a great influence, and the present invention was completed.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having excellent storage stability, high output and C / N characteristics, and excellent durability.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having a magnetic layer containing a ferromagnetic metal powder, a binder and an abrasive on a non-magnetic support, wherein the surface of the ferromagnetic metal powder is provided. Aluminum is included, the content thereof is 2 to 5% by weight with respect to the ferromagnetic metal powder, the crystallite size of the oxide film of the ferromagnetic metal powder is 15 to 50Å, and the magnetic layer is the ferromagnetic metal. 10 to 100 parts by weight of powder
It can be achieved by a magnetic recording medium characterized by containing ˜20 parts by weight of an abrasive and the magnetic layer containing an anticorrosive agent.

The magnetic recording medium of the present invention is achieved by defining the following four factors. The surface of the ferromagnetic metal powder contains Al in an amount of 2 to 5% by weight. The crystallite size of the oxide film of ferromagnetic metal powder is set to 15 to 5
Control to 0Å. The magnetic layer contains at least a rust preventive agent. 10 to 10 parts by weight of abrasive powder for 100 parts by weight of ferromagnetic metal powder
Contains 20 parts by weight.

That is, by adding Al more than the ferromagnetic metal powder alone, the hardness is increased, and if the durability is the same without using the factor of, the amount of the polishing agent is reduced and the ferromagnetic metal powder is reduced. It is possible to improve the filling degree and thus the output. Also, if the filling degree is the same as the ferromagnetic metal powder of the magnetic recording medium created without using the same factor,
The durability can be improved because the amount of the abrasive added can be increased.

Further, the output can be improved by reducing the thickness of the oxide film as described above. The deterioration of the storage stability due to the reduction of the thickness of the oxide film can be made compatible with the output and the storage stability by using at least one rust preventive agent. Further, in order to improve the durability, the amount of the abrasive is increased by the above, and the decrease of the filling degree due to the increase of the amount of the abrasive is covered by the above-mentioned output improvement.

In other words, the factors (1) and (2) have a positive effect on the output and the filling degree of the ferromagnetic metal powder, but on the contrary, they have a negative effect on the storage stability and durability. By defining the above, it was possible to correct this negative effect, compensate for the mutually contradictory characteristics, and improve the characteristics. In the present invention, the amount of Al on the surface of the ferromagnetic metal powder is 2 to the ferromagnetic powder.
Any means may be included so that the content is 5% by weight. Here, the weight% of Al means the weight% of metal equivalent to Al. That is, the existence form and existence composition of Al on the surface of the ferromagnetic metal powder are arbitrary, but it is sufficient that at least it can be a forming factor of the oxide film on the surface. Generally, the Al
Exists in the oxide film as a composition form of oxide, but the composition is also arbitrary. The oxide film can contain an element other than Al.

The abundance of Al in the oxide film is 1 atom% or more, preferably 5 atom% or more in terms of metal. Further, in the present invention, the crystallite size of the oxide film of the ferromagnetic metal powder is 15 to 100Å, preferably 20 to 4
It is preferable to control to 0Å. A conventionally known method can be appropriately applied to the means for forming the oxide film. For example, a compound containing at least Al as a metal component in a metal oxide of a ferromagnetic metal powder raw material, such as iron oxyhydroxide, cobalt hydroxide, or α-Fe ₂ O ₃ (for example, sulfuric acid called a sintering inhibitor). It is possible to form an oxide film containing at least Al on the metal surface by depositing (salt, nitrate, etc.), reducing this, and then oxidizing it.

The reduction conditions in this case include a method of treating at 300 to 600 ° C. for 30 minutes to 24 hours in a dry hydrogen gas atmosphere. The oxidation treatment condition may be gas phase oxidation or liquid phase oxidation, and various oxidation conditions can be selected. By appropriately adjusting the oxygen partial pressure, temperature, etc. The range can be controlled, and any oxidation treatment other than the usual slow oxidation treatment can be performed.

The gradual oxidation treatment conditions include, for example, oxidizing dried and dehydrated air and dry nitrogen in a container from a ratio of 1:20 to 1: 0 at 25 to 60 ° C. for 2 to 24 hours. Be done. Further, as the liquid phase oxidation treatment condition,
It may be mentioned that air is blown in the organic solvent to gradually oxidize, and in this case, a method of heating when evaporating the solvent may be mentioned.

Further, if desired, after the gas phase oxidation, heat treatment can be carried out in an oxygen-containing gas at 25 to 60 ° C. or higher for a desired time, usually 30 minutes or longer. Further, ozone oxidation, plasma oxidation treatment, etc. can also be used. Examples of metal elements other than Al that can form the oxide film include Si, Ti, and B.
These are used in the form of a salt or a compound like Al, and the adhesion to the metal oxide is carried out by, for example, mixing the metal oxide in a suspension thereof, washing with water, drying, and heat dehydration treatment. Is mentioned.

As the rust preventive agent which is the above-mentioned factor, known antioxidants, rust preventives and the like can be mentioned. It is preferable that the rust preventive agent has a function of improving dispersibility in addition to the main rust preventive function. The rust preventive agent may be in any form as long as it exists in the magnetic layer, but it is preferable to use a ferromagnetic metal powder coated on its surface with the rust preventive agent.

Examples of the coating method include a method of suspending a ferromagnetic metal powder in an organic solvent, adding a rust preventive agent with stirring, and then drying. The amount of the rust preventive agent coated is 0.1 to 1 with respect to 100 parts by weight of the ferromagnetic metal powder.
The amount is 00 parts by weight, preferably 0.5 to 5 parts by weight. The rust preventive agent used in the present invention, that is, as the antioxidant, phosphoric acid, phosphoric acid monoester, phosphoric acid diester such as dilauryl phosphate, phosphonic acid, benzotriazole, tetraazaindene, sulfamide, guanidine, nucleic acid, pyridine, Examples include metal chelating agents such as amine, hydroquinone and EDTA, naphthenic acid, alkenyl succinic acid and the like.

Preferred rust preventives include compounds represented by the following general formula. In the present invention, it is particularly preferable to use the following organophosphorus compound having a function of preventing rust and a function of enhancing the dispersibility of the ferromagnetic metal powder. (1) (RO) _n PO (OM) _3-n (2) (RO) _n P (OM) _3-n (3) (R) _n P (OM) _3-n (4) RPO (OM) _{2 In} each formula, R represents a substituted or unsubstituted alkyl group having 6 to 40 carbon atoms, an aralkyl group, an alkylphenyl group, an alkylphenylalkylene oxide group, an alkenyl group, or an aryl group, and M is a hydrogen atom. , Alkali metal or -N
(R ¹ ) ₄ is represented, R ¹ is an alkyl group having 1 to 20 carbon atoms, and n is 1 or 2.

In the present invention, the combination of phenylphosphonic acid represented by (4) and the phosphoric acid ester represented by (1) is most suitable, and the compounding ratio of phenylphosphonic acid to phosphoric acid ester is 1 to 1 by weight. It is in the range of 10:10 to 1, preferably 1 to 5: 5-1. The amount of these rust preventives used is 0.1 to 1 with respect to 100 parts by weight of the ferromagnetic metal powder.
It is selected from the range of 0 parts by weight, preferably 0.5 to 7 parts by weight.

In the present invention, the above-mentioned abrasive is contained in the magnetic layer in an amount of 10 to 20% by weight, preferably 10 to 15% by weight, based on the ferromagnetic metal powder. The abrasive contains Al atoms. It is preferable to use the material of the composition containing. That is, when the material is used as the polishing agent, a particular effect can be expected in improving durability, but the details of the mechanism are unknown, but the surface of the polishing agent and the ferromagnetic metal powder is It is considered that the affinity with existing Al atoms is increased, and as a result, large durability can be achieved with a small amount.

The abrasive preferably has a Mohs hardness of 9 or more, and specifically, α-Al ₂ O ₃ is particularly preferable. Hereinafter, the matters relating to the respective factors (1) to (3) of the present invention described above will be mainly described, and other matters that can be appropriately selected will be described. The ferromagnetic metal powder used in the present invention is not particularly limited in its base material, and may be an alloy or a metal simple substance, particularly one containing iron, cobalt or nickel. Its specific surface area (S _BET )
Is 40 m ² / g or more, preferably 50 m ² / g or more, and the coercive force is preferably 1000 to 3000 Oe, more preferably 1550 Oe or more. Also, Bm is 250
0 gauss or more, preferably 2800 gauss or more, and the saturation magnetization (σ _S ) is preferably 100 to 200.

The crystallite size of the metal component portion of the ferromagnetic metal powder excluding the oxide film is preferably 100 to 220Å, more preferably 140 to 200Å. If it is less than 100Å, it is not preferable because of poor dispersibility, and 220Å
A larger value is not preferable because the C / N is poor. The shape of the ferromagnetic metal powder is not particularly limited, but normally needle-shaped, granular, dice-shaped, rice granular and plate-shaped particles are used.

As an example of this ferromagnetic metal powder, the metal content in the ferromagnetic metal powder is 60% by weight or more, and 70% by weight or more of the metal content is at least one kind of ferromagnetic metal or alloy (eg, Fe, Co, Ni, Fe-Co, F
e-Ni, Co-Ni, Co-Ni-Fe), and other components (eg, Al, Si, S, Sc) within the range of 40% by weight or less, more preferably 20% by weight or less of the metal content. , T
i, V, Cr, Mn, Cu, Zn, Y, Mo, Rh, P
d, Ag, Sn, Sb, Te, Ba, Ta, W, Re,
Au, Hg, Pb, Bi, La, Ce, Pr, Nd,
Examples of the alloy include B, P), iron nitride, and iron carbide. Further, the ferromagnetic metal powder contains a small amount of water, hydroxide or oxide, alkali metal element (Na,
K, etc.), an alkaline earth metal element (Mg, Ca, Sr), or the like.

The following are typical methods for producing these ferromagnetic metal powders. (A) Method of reducing complex organic acid salt (mainly oxalate) with reducing gas such as hydrogen (b) Method of reducing iron oxide with reducing gas such as hydrogen to obtain Fe or Fe-Co particles (C) A method of thermally decomposing a metal carbonyl compound (d) An aqueous solution of a ferromagnetic metal, sodium borohydride,
A method of reducing by adding a reducing agent such as hypophosphite or hydrazine (e) A method of electrolytically depositing a ferromagnetic metal powder using a mercury cathode and then separating it from mercury (f) An inert metal at low pressure Method of Obtaining Fine Powder by Evaporating in Gas The above method can be appropriately applied to form the ferromagnetic metal powder having an oxide film of the present invention, but the method of (b) is preferable as described above. In addition, in the present invention, an ordinary ferromagnetic metal powder other than the ferromagnetic metal powder of the present invention is used.
It can be used together in the range of 0% by weight or less.

The abrasive for the magnetic layer or the back layer used in the present invention is used to improve the durability of the magnetic tape and the head cleaning effect of the VTR, and is generally a material having an abrasive action or a polishing action. -Alumina, γ
-Alumina, α-γ-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main component:
Corundum and magnetite), garnet, silica stone, silicon nitride,
Boron Nitride, Molybdenum Carbide, Boron Carbide, Tungsten Carbide, Titanium Carbide, Tripoly, Diatomite, Dolomite, etc., which are mainly used in combination of up to 4 types of Mohs hardness of 6 or more. An average particle size of 0.005 to 5 μm is used,
It is particularly preferably 0.01 to 2 μm. In the case of the back layer, 0.01 to 5 parts by weight is preferably used with respect to 100 parts by weight of the resin.

As the powdery lubricant used in the magnetic layer or back layer of the present invention, graphite, molybdenum disulfide, boric acid nitride, graphite fluoride, calcium carbonate, barium sulfate, silicon oxide, titanium oxide, zinc oxide, Inorganic fine powder such as tin oxide and tungsten disulfide, acrylic styrene resin fine powder, benzoguanamine resin fine powder, melamine resin fine powder, polyolefin resin fine powder, polyester resin fine powder, polyamide resin fine powder, polyimide Resin fine powder, resin fine powder such as polyfluorinated ethylene resin fine powder, and the like.

As the organic compound type lubricant, silicone oil (dialkyl polysiloxane, dialkoxy polysiloxane, phenyl polysiloxane, fluoroalkyl polysiloxane (KF96, KF69 manufactured by Shin-Etsu Chemical Co., Ltd.) is used.
Etc.)), fatty acid modified silicone oil, fluorinated alcohol,
Polyolefin (polyethylene wax, polypropylene, etc.), polyglycol (ethylene glycol, polyethylene oxide wax, etc.), tetrafluoroethylene oxide wax, polytetrafluoroglycol, perfluoroalkyl ether, perfluoro fatty acid, perfluoro fatty acid ester, perfluoroalkyl sulfate ester , Perfluoroalkyl sulfonate,
Compounds in which fluorine or silicon is introduced, such as perfluoroalkylbenzenesulfonic acid ester and perfluoroalkylphosphoric acid ester; alkyl sulfate, alkylsulfonic acid ester, alkylphosphonic acid triester, alkylphosphonic acid monoester, alkylphosphonic acid diester, alkylphosphoric acid Organic acids and organic acid ester compounds such as esters and succinates; nitrogen / sulfur-containing heterocyclic compounds such as triazaindolizine, tetraazaindene, benzotriazole, benzotriazine, benzodiazole and EDTA; carbon Any one or more of monobasic fatty acids having 10 to 40 carbon atoms and monohydric alcohols or dihydric alcohols having 2 to 40 carbon atoms, trihydric alcohols, tetrahydric alcohols, and hexahydric alcohols Consists of Fatty acid esters, fatty acid esters composed of monobasic fatty acids having 10 or more carbon atoms and monohydric to hexavalent alcohols having 11 to 70 carbon atoms in total with the carbon number of the fatty acids, and 8 carbon atoms It is also possible to use fatty acids or fatty acid amides, fatty acid amides, fatty acid alkylamides, and aliphatic alcohols of -40.

Specific examples of these compounds include butyl caprylate, octyl caprylate, ethyl laurate, butyl laurate, octyl laurate, ethyl myristate, butyl myristate, octyl myristate, 2-ethylhexyl myristate, Ethyl palmitate, butyl palmitate, octyl palmitate, 2-ethylhexyl palmitate, ethyl stearate, butyl stearate, isobutyl stearate, octyl stearate, 2-ethylhexyl stearate, amyl stearate, isoamyl stearate, 2 stearate.
Ethyl pentyl, 2-hexyldecyl stearate, isotridecyl stearate, stearic acid amide, stearic acid alkyl amide, butoxyethyl ateariate,
Anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, anhydrosorbitan tetrastearate, oleyl oleate, oleyl alcohol, lauryl alcohol, montan wax, carnauba wax, etc. alone or in combination. Can be used.

As the lubricant used in the present invention, so-called lubricating oil additives can be used alone or in combination, and oiliness agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (dibenzyl sulfide, tricresyl) are used. Phosphates, tributyl phosphite, etc.), detergent dispersants, viscosity index improvers, pour point depressants, foam stop agents and the like. These lubricants are added in the range of 0.01 to 30 parts by weight with respect to 100 parts by weight of the binder.

The dispersant and dispersion aid used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid. , Fatty acids such as behenic acid, maleic acid and phthalic acid having 2 to 40 carbon atoms (R ₁ COOH, R ₁ is alkyl group having ₁ to 39 carbon atoms, phenyl group, aralkyl group), alkali metal of the above fatty acids (Li, Na, K) or NH ₄ ⁺ or the like or alkaline earth metal (Mg, Ca, Ba or the like), Cu, P
Metal soaps such as b (copper oleate), fatty acid amides; lecithin (soybean oil lecithin) and the like are used. In addition to these, higher alcohols having 4 to 40 carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol) and their sulfates, amine compounds and the like can also be used. Also, polyethylene glycol,
Polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid metal salt, sulfosuccinic acid ester, the above-mentioned rust preventive and the like may also be included. When these dispersants are used in the magnetic layer, the amount is in the range of 0.005 to 20 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the binder. When it is used for the back layer, it is 0.005 per 100 parts by weight of the binder.
To 20 parts by weight, preferably 0.01 to 5 parts by weight.

As for the method of using these dispersants, not only the ferromagnetic powder but also the surface of the non-magnetic powder may be pre-deposited as described above, or may be added during the dispersion. Such a compound is disclosed, for example, in Japanese Patent Publication No. 39-28369, Japanese Patent Publication No. 44-17945, Japanese Patent Publication No. 44-18221, Japanese Patent Publication No. 48-7441, Japanese Patent Publication No. 48-15001, Japanese Patent Publication No. 48-15002, JP-B-48-16363, JP-B-49-39402, US Pat. No. 3,387,993,
No. 3470021 and the like.

As the antifungal agent used in the present invention, 2-
(4-thiazolyl) -benzimidazole, N- (fluorodichloromethylthio) -phthalimide, 10,1
0'-oxybisphenoxarcin, 2,4,5,6-
Examples include tetrachloroisophthalonitrile, p-tolyldiiodomethyl sulfone, triiodoallyl alcohol, dihydroacetate, mercury phenyloleate, bis (tributyltin oxide), and salicylanilide. Such a thing is shown, for example, in "Microbial Hazard and Prevention Technology", 1972 Engineering Book, "Chemistry and Industry" 32,904 (1979) and the like.

The carbon black used in the magnetic layer and back layer of the present invention is a furnace for rubber, a thermal for rubber,
Color black, acetylene black, etc. can be used. These carbon blacks are used for the purpose of antistatic agent, light shielding agent, friction coefficient adjusting agent and improving durability of the tape. Specific examples of carbon black abbreviations in the US are SAF, ISAF, and IISA.
F, T, HAF, SPF, FF, FEF, HMF, GP
F, APF, SRF, MPF, ECF, SCF, CF,
FT, MT, HCC, HCF, MCF, LFF, RCF
Etc., American ASTM standard D-1765-82a
You can use those that are classified into. The average particle size of these carbon blacks used in the present invention is 5 to 1000 mμ (electron microscope), the nitrogen adsorption method specific surface area is 1 to 800 m ² / g, and the pH is 4 to 11 (JIS standard K-6221-1982 method). ), Dibutyl phthalate (DBP) oil absorption is 10 to 800 ml / 100 g (JI
S standard K-6221-1982 method). The size of the carbon black used in the present invention is 5 to 100 mμ for the purpose of lowering the surface electric resistance of the coating film, and 50 to 10 when controlling the strength of the coating film.
A carbon black of 00 mμ is used. Further, for the purpose of controlling the surface roughness of the coating film, finer carbon black (100
Coarse particles of carbon black (100 mμ or more) are used for the purpose of roughening the surface roughness (less than mμ) to lower the friction coefficient. As described above, the kind and the amount of carbon black added are properly selected according to the purpose required for the magnetic recording medium. Further, these carbon blacks may be surface-treated with a dispersant described later or may be grafted with a resin before use. Also, the temperature of the furnace when producing carbon black is set to 2000 ° C.
It is also possible to use a material which has been treated as described above and whose part of the surface has been graphitized. Hollow carbon black can also be used as the special carbon black.

In the case of the magnetic layer, these carbon blacks are preferably used in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the ferromagnetic powder. Further, in the case of the back layer, it is desirable to use 20 to 400 parts by weight with respect to 100 parts by weight of the resin described later. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook", edited by Carbon Black Association (published in 1969). Examples of these carbon blacks are shown in US Pat.
39257, U.S. Pat. No. 4,614,685, JP-A-61.
-92424 and JP-A 61-99927.

Antistatic agents other than carbon black used in the present invention include graphite, modified graphite,
Conductive powder such as carbon black graft polymer, tin oxide-antimony oxide, tin oxide, titanium oxide-tin oxide-antimony oxide, natural surfactant such as saponin, alkylene oxide type, glycerin type, glycidol type, polyhydric alcohol , Polyhydric alcohol esters, nonionic surfactants such as alkylphenol EO adducts; higher alkylamines, cyclic amines, hydantoin derivatives,
Cationic surfactants such as amidoamines, ester amides, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids, phosphonic acids, phosphoric acids, sulfuric acid esters, phosphonic acid esters, phosphoric acid esters Anionic surfactant containing an acidic group such as; amino acids; aminosulfonic acids,
Sulfuric acid or phosphoric acid esters of amino alcohol, and amphoteric surfactants such as alkyl betaine type are used. These surfactants may be added alone or as a mixture.
The amount of these surfactants used in the magnetic recording medium is 0.01 to 10 per 100 parts by weight of the ferromagnetic metal powder.
Parts by weight. The amount of binder used in the back layer is 1
It is 0.01 to 30 parts by weight per 00 parts by weight. These are used as antistatic agents, but sometimes they are used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, coating aid, curing accelerator and dispersion accelerator. ..

As the binder used in the magnetic layer of the present invention or the back layer optionally provided, a conventionally known thermoplastic resin, thermosetting resin, reactive resin, electron beam curable resin, ultraviolet curable resin, visible Light curable resins and mixtures of these are used. The thermoplastic resin has a softening temperature of 150 ° C. or lower and an average molecular weight of 10,000 to 300.
000, the degree of polymerization is about 50 to 2000, more preferably about 200 to 600. For example, vinyl chloride vinyl acetate copolymer, vinyl chloride copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, chloride Vinyl vinyl alcohol copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic ester acrylonitrile copolymer, acrylic ester vinylidene chloride copolymer, acrylic ester styrene copolymer, methacrylic ester Acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyvinyl alcohol, vinylidene chloride acrylo Tolyl copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, ethyl cellulose, methyl cellulose, propyl cellulose, methyl ethyl cellulose, (Carboxymethyl cellulose, acetyl cellulose, etc.), styrene-butadiene copolymer, polyester resin, polycarbonate resin, chlorovinyl ether acrylate copolymer, amino resin, various synthetic rubber thermoplastic resins, and mixtures thereof are used. ..

The thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating solution.
By heating and humidifying after drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Among these resins, those that do not soften or melt before the resin thermally decomposes are preferable. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane resin, polyester resin, polyurethane polycarbonate resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin (electron beam curing resin), epoxy-polyamide Resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol / high molecular weight Examples include diol / triphenylmethane triisocyanate mixtures, polyamine resins, polyimine resins, and mixtures thereof.

These thermoplastic resins, thermosetting resins, and reactive resins have carboxylic acid (COOM), sulfinic acid, sulfenic acid, sulfonic acid (SO ₃ M), phosphoric acid (OPO) as functional groups in addition to the main functional groups. (OM) ₂ ), phosphonic acid (PO (OM) ₂ ), sulfuric acid (OSO ₃ M) and acidic groups such as ester groups thereof (M is H, alkaline metal, alkaline earth metal, hydrocarbon group), Amino acids; aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, amphoteric groups such as alkylbetaine type, amino groups, imino groups, imide groups, amide groups, etc., and hydroxyl groups,
Alkoxyl group, thiol group, alkylthio group, halogen group (F, Cl, Br, I), silyl group, siloxane group, epoxy group, isocyanato group, cyano group, nitrile group, oxo group, acryl group, phosphine group are usually 1 Includes 1 to 6 species, each functional group is 1 x 1 per 1g of resin
It is preferable to contain 0 ⁻⁶ eq to 1 × 10 ⁻² eq.

These binders may be used alone or in combination, and additives may be added. The mixing ratio of the ferromagnetic metal powder and the binder in the magnetic layer is 5 to 300 parts by weight, preferably 10 to 100 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder. The mixing ratio of the fine powder and the binder in the back layer is 10 by weight.
The binder is used in an amount of 8 to 400 parts by weight, preferably 20 to 150 parts by weight, based on 0 part by weight. As the additive, the above-mentioned dispersant, lubricant, abrasive, antistatic agent, antioxidant, solvent and the like can be added.

As the polyisocyanate used in the magnetic layer and / or back layer of the present invention, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o- Isocyanates such as toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and isophorone diisocyanate, products of the isocyanates with polyalcohols, and 2-1 produced by condensation of isocyanates
It is possible to use a 0-mer polyisocyanate, or a product of polyisocyanate and polyurethane in which the terminal functional group is isocyanate. The average molecular weight of these polyisocyanates is preferably 100 to 20,000. Commercially available trade names of these polyisocyanates are Coronate L and Coronate H.
L, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL (manufactured by Nippon Polyurethane Co., Ltd.), Takenate D-102, Takenate D-1.
10N, Takenate D-200, Takenate D-20
2, Takenate 300S, Takenate 500 (manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidule T-80, Sumidule 44
S, Sumidule PF, Sumidule L, Sumidule N, Death Module L, Death Module IL, Death Module N, Death Module HL, Death Module T6
5, death module 15, death module R, death module RF, death module SL, death module Z4
273 (manufactured by Sumitomo Bayer Co., Ltd.) and the like, and these can be used alone or in combination of two or more utilizing the difference in curing reactivity. For the purpose of accelerating the curing reaction, compounds or metal oxides having a hydroxyl group (butanediol, hexanediol, polyurethane having a molecular weight of 1,000 to 10,000, water, etc.) and an amino group (monomethylamine, dimethylamine, trimethylamine, etc.) A catalyst or a catalyst such as iron acetylacetate can also be used in combination. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanates are preferably used in both the magnetic layer and the back layer in an amount of 2 to 70 parts by weight, more preferably 5 to 50 parts by weight, per 100 parts by weight of the total amount of the binder resin and the polyisocyanate. Examples of these are disclosed in JP-A-60-131622.
And Japanese Patent Laid-Open No. 61-74138.

In the present invention, the organic solvent used for dispersion, kneading and coating for preparing the magnetic coating material and the back layer coating material may be acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, in any ratio. Ketones such as isophorone and tetrahydrofuran; methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol,
Alcohol such as methylcyclohexanol; ester such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate monoethyl ether; diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether, dioxane Ether-based compounds such as benzene, toluene, xylene, cresol, chlorobenzene, styrene and other tar-based compounds (aromatic hydrocarbons); methylene chloride, ethylene chloride, carbon tetrachloride,
Chloroform, ethylene chlorhydrin, chlorinated hydrocarbons such as dichlorobenzene, N, N-dimethylformaldehyde, hexane and the like can be used. Further, these solvents are usually used in two or more kinds at an arbitrary ratio. Also, trace amounts of impurities (polymerization products of the solvent itself,
Water, raw material components, etc.).

These solvents are used as the total solid content of the magnetic coating material or the back layer coating material, and the undercoating liquid for the undercoating layer which will be described later.
It is used in 100 to 20000 parts by weight with respect to 0 parts by weight. The preferable solid content ratio of the magnetic paint is 10 to 40% by weight.
Is. Further, the preferable solid content ratio of the back layer coating material is
It is 5 to 20% by weight. An aqueous solvent (water, alcohol, acetone, etc.) can be used instead of the organic solvent.

The magnetic layer is formed by coating, drying and orienting on a support as a magnetic coating liquid prepared by arbitrarily combining the above compositions. When used as a tape, the thickness of the support is about 2.5 to 100 μm, preferably about 4 to 10 μm. In the case of a disk or card, the thickness is about 0.03 to 10 mm, and in the case of a drum, it can be used in a cylindrical shape. Materials include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride, polycarbonate, polyimide. In addition to plastics such as polyamide and polysulfone, metals such as aluminum and copper and ceramics such as glass can be used. Among these materials, PET and PE
N and aramid are particularly preferred. These supports are subjected to corona discharge treatment, plasma treatment, undercoat treatment,
Heat treatment, dust removal treatment, metal vapor deposition treatment, or alkali treatment may be performed. Regarding these supports, for example, West German Patent 3338854A, JP-A-59-116926, JP-A-61-129731, and US Pat. No. 4,388,368.
Issue: Yukio Mitsuishi, "Fiber and Industry", Vol. 31, p50-55,
It is described in 1975 and the like. In the case of a video tape or the like, the Young's modulus (F5 value) of these supports can be selected from ² to 30 kg / mm ² in both the width direction and the length direction depending on the purpose. Further, it is preferable that at least one surface of the support has a surface roughness (Ra) of 15 nm or less.

The method of dispersion and kneading is not particularly limited, and the order of addition of each component (resin, powder, lubricant, solvent, etc.),
The addition position during dispersion / kneading, the dispersion temperature (0 to 80 ° C.) and the like can be set appropriately. For the preparation of magnetic paints and back layer paints, conventional kneading machines such as a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, and a Segegvar (Szegvar).
i), attritor, high speed impeller, disperser, high speed stone mill, high speed impact mill, disper, kneader,
A high speed mixer, a ribbon blender, a cokneader, an intensive mixer, a tumbler, a blender, a disperser, a homogenizer, a single screw extruder, a twin screw extruder, an ultrasonic disperser, or the like can be used. Usually, these dispersions are
It is equipped with multiple kneaders and performs continuous processing. For details of the technique regarding kneading and dispersion, see T.W. C. CATTON by T.C. Patton "Paint Flow and Pigment Dispersio
n "(Paint Flow and Pigment Dispersion), published by John Wiley & Sons in 1964 (John Willie and Sons), Shinichi Tanaka," Industrial Materials, "Vol. 25, 37 (1977), and other references cited in the book. There is. As an auxiliary material for dispersion and kneading, in order to efficiently carry out the dispersion and kneading, 10c in a sphere equivalent system
Steel balls, steel beads, ceramic beads, glass beads, and organic polymer beads having a diameter of mφ to 0.05 mmφ can be used. Also, these materials are not limited to spherical shapes. It is also described in the specifications such as US Pat. Nos. 2,581,414 and 2,855,156. Also in the present invention, the magnetic coating material and the back layer coating material can be prepared by kneading and dispersing in accordance with the method described in the above-mentioned book and the references cited in the book.

As a method for applying the above-mentioned magnetic coating material and back layer coating material on a support, the viscosity of the coating liquid is 1 to 2
Adjusted to 0000 centistokes (25 ° C), air doctor coat, blade coat, air knife coat,
Squeeze coat, impregnation coat, reverse roll coat,
Transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, rod coat, forward rotation roll coat, curtain coat, extrusion coat, bar coat, etc. can be used, and other methods are also possible. It is described in detail in "Coating Industry", pages 253 to 277 (published by Showa 46. 3.20.), Published by Asakura Shoten. The coating order of these coating liquids can be arbitrarily selected, and corona discharge treatment or the like may be performed before the coating of the desired liquid to improve the adhesion to the undercoat layer or the support. When it is desired to form the magnetic layer or the back layer in multiple layers, simultaneous multi-layer coating, sequential multi-layer coating or the like may be performed. These are disclosed, for example, in JP-A-57-12.
3532, JP-B-62-37451, JP-A-59-142741, JP-A-59-16523.
It is shown in the specification and the like of Japanese Patent Publication No. 9.

By such a method, about 1 to about 1 is formed on the support.
If necessary, the magnetic liquid applied in a thickness of about 200 μm may dry the ferromagnetic powder in the layer immediately in multiple stages at 20 to 130 ° C. in a desired direction (vertical, longitudinal, width, random, oblique, etc.) at about 500 to 5000 gauss. 2), the formed magnetic layer is dried to a thickness of 0.1 to 30 μm. The transport speed of the support at this time is usually 10 m / min.
It is performed at 900 m / min, the drying temperature is controlled at 20 ° C. to 130 ° C. in a plurality of drying zones, and the residual solvent amount of the coating film is set to 0.1 to 40 mg / m ² . The surface of the magnetic layer or back layer may be subjected to a surface smoothing treatment if necessary so that the center line average surface roughness (Ra) of the magnetic layer or back layer is 0.001 to 0.3 μm (cutoff 0.25 mm). 5 nm
The Young's modulus of the magnetic layer is 1200 Kg / mm ² or more, and the magnetic recording medium of the present invention is manufactured by cutting into a desired shape. These manufacturing methods include the steps of pretreatment / surface treatment of powder, kneading / dispersion, coating / orientation / drying, smoothing treatment, heat treatment, radiation (EB) treatment, surface polishing treatment, cutting and winding. It is desirable to do it. They are,
For example, Japanese Patent Publication No. 40-23625 and Japanese Patent Publication No. 39-39
28368, Japanese Patent Publication No. 47-38802, British Patent No. 1191424, Japanese Patent Publication No. 48-11336, Japanese Patent Publication No. 49-53631, Japanese Patent Publication No. 50-1.
12005, JP-A-51-77303, JP-B-52-17404, JP-A-60-70532.
No. 2, JP-A-2-265672, US Pat. No. 3
No. 473960, etc. Further, the method described in Japanese Patent Publication No. 41-13181 is considered to be a basic and important technique in this field.

The magnetic recording medium thus prepared is cut and then wound on a desired plastic or metal reel.
It is desirable to burnish and / or clean the magnetic recording medium (magnetic layer, back layer, edge surface, base surface) immediately before or before winding. The burnish concretely scratches the magnetic recording medium with a hard material such as a sapphire blade, a razor blade, a super hard material blade, a diamond blade, and a ceramics blade to smooth the protrusions on the surface of the magnetic recording medium. The Mohs hardness of these materials is preferably 8 or more, but there is no particular limitation as long as the protrusions can be removed. The shape of these materials does not have to be a blade in particular, and a shape such as a square shape, a round shape, or a wheel (these materials may be provided around a rotating cylindrical shape) can also be used. Further, in cleaning the magnetic recording medium, the surface layer of the magnetic recording medium is wiped with a non-woven fabric or the like for the magnetic layer surface, the back layer surface, the edge end surface, and the back side base surface for the purpose of removing dirt and excess lubricant on the surface of the magnetic recording medium. By doing. Examples of such wiping materials include various types of Vileen made by Japan Vilene and Toray's Toray, Exeine, product name Kimwipe, various polishing tapes made by Fuji Photo Film, and non-woven fabric made of nylon, non-woven fabric made of polyester, rayon. Non-woven fabric,
Tissue paper such as acrylonitrile non-woven fabric and blended non-woven fabric can be used. These are, for example, Japanese Patent Publication No. 4
6-39309, JP-B-58-46768, JP-A-56-90429, JP-B-58-46.
No. 767, JP-A-63-259830, JP-A-1-201824 and the like.

Ferromagnetic powder or non-magnetic powder used in the present invention, binder, additive (lubricant, dispersant, antistatic agent, surface treatment agent, carbon black, abrasive, light-shielding agent,
An antioxidant, an antifungal agent, etc.), a solvent and a support (which may have an undercoat layer, a back layer, a back undercoat) or a method for producing a magnetic recording medium are described in JP-B-56-26890. You can also refer to what you have.

[0053]

EXAMPLES The present invention will be described more specifically below with reference to examples. It is easily understood by those skilled in the art that the components, ratios, operation sequences, etc. shown here can be changed without departing from the spirit of the present invention. Therefore, the present invention should not be limited to the examples below. The parts in the examples are parts by weight.

[Example 1] [I] of the following magnetic layer composition was put in a kneader and sufficiently kneaded, then [II] was added, and after mixing and dispersing, III was added and dispersed to prepare a magnetic coating solution. Magnetic layer composition [I] a. Ferromagnetic metal powder (composition: 96 wt% Fe, 4 wt% Al) 100 parts (Hc: 1600 Oe, S _BET : 55 m ² / g, σ _S : 130 emu / g) b. Phenylphosphonic acid 3 parts c. Phosphate ester (GAF RE610) 1 part d. Vinyl chloride resin (Nippon Zeon Co., Ltd., MR110) 8 parts e. Polyurethane resin (Toyobo Co., Ltd., UR8600) 4 parts f. Polyurethane resin (Toyobo Co., Ltd., Byron 200) 1 part g. Methyl ethyl ketone 8 parts h. Lubricant: tridecyl stearate 0.3 parts i. Cyclohexanone 40 parts where a is 4% by weight of Al based on the ferromagnetic metal powder.
Is formed, the crystallite size of the oxide film is 30Å, and the crystallite size of the metal portion of the ferromagnetic metal powder is 200Å. The ferromagnetic metal powder a is
The surface was coated with the rust preventives b and c as a pretreatment agent.

The components d, e, f and g were used as a mixture. [II]: Dispersion having the following composition Abrasive: α-alumina 12 parts (average particle size; 0.6 μm: manufactured by Reynolds) Carbon black (Mitsubishi Kasei Co., Ltd. # 3250) 2 parts Polyurethane resin (Toyobo Co., Ltd. ), UR8300) 2 parts Methyl ethyl ketone 20 parts III Polyisocyanate (Nippon Polyurethane Co., Ltd., C3040) 4 parts Lubricant: stearic acid dibutylamide 0.3 parts Lubricant: 2-ethylhexyl myristate 0.3 parts Lubricant: myristin Acid / palmitic acid (1/1) 0.2 part Lubricant: oleic acid 0.5 part The above polyisocyanate and a lubricant component were mixed.

Methyl ethyl ketone 200 parts After adjusting the viscosity of this magnetic coating liquid, dry coating thickness 2.0 on polyethylene naphthalate of 7 μm non-magnetic support.
of the composition [I] is continuously applied to the surface side of a non-magnetic support provided with a magnetic layer by continuously applying a magnetic layer in a magnetic field oriented in a coating direction of 3000 Gauss with a facing magnet of 3000 gauss. Knead with a kneader machine, add [II] in the middle to perform additional kneading and dispersion, and immediately before coating (within 1 hour) II
After providing a coating liquid having a thickness of 0.4 μm prepared by adding I, the magnetic layer was continuously subjected to metal roll calendering treatment at 100 ° C. three times (treatment speed 200 m / min) and slitted into 0.5 inch. After that, the magnetic layer was surface-treated with a diamond rotary blade, and cleaned with Toraysee to prepare a tape.

Back layer composition [I] Carbon black (Cabot Corp., BP800) 100 parts Carbon black (Cancarb Co., Thermax) 5 parts Nitrocellulose (Daicel Corp.) 10 parts Phenoxy resin (UCC) Made, PKHH) 10 parts Polyurethane resin (Nippon Polyurethane, N2301) 25 parts Polyester resin (Toyobo, Byron 500) 10 parts Dispersant (copper oleate) 0.1 parts Lubricant: Phosphate ester (GAF RE610) 2 parts Methyl ethyl ketone 300 parts [II] Carbonate resin (Dainichiseika, FJ2) 5 parts Abrasive (Sumitomo Chemical Co., Ltd., Hit100) 0.3 parts Barium sulphate (Sakai Kagaku, BF1) 0.1 parts Lubricant: dibutyl stearate Amide 0.7 parts Disperse 4 components of the above carbonate resin to lubricant To.

Lubricant: 2-ethylhexyl myristate 0.7 parts III Polyisocyanate (C3040, Nippon Polyurethane Co., Ltd.) 15 parts Methyl ethyl ketone 700 parts This tape was wound 250 m in an M2 format cassette.

[Examples 2 to 4, Comparative Examples 1 to 6] Example 1
A tape was prepared in the same manner as in Example 1 except that the factors listed in Table 1 of the ferromagnetic metal powder of No. 1 were changed. In Comparative Example 6, a tape was prepared in the same manner as in Example 1 except that the abrasive α-alumina of Example 1 was changed to 5 parts.

The crystallite size of the ferromagnetic metal powder and the oxide film was determined as follows. 1 g of the ferromagnetic metal powder is weighed in a nitrogen stream and crushed in a mortar. This ferromagnetic metal powder is uniformly packed in a glass plate and measured with an X-ray diffractometer. The diffraction angles of (220) of 85 to 88 degrees and (110) of 39 to 42 degrees and the half width were obtained, and the crystallite size of the ferromagnetic metal powder was obtained. Regarding the crystallite size of the oxide film, the crystallite size was determined by determining the diffraction angle (25 to 50 degrees) and half width of iron oxide.

Further, the specific surface area S of the ferromagnetic metal powder
_BET was determined by the nitrogen adsorption method. The characteristics of the obtained sample were evaluated as follows, and the results are also shown in Table 1. Characteristic evaluation Preservability RF output = tape was stored at 40 ° C., 90% RH for 1 week, and the level of deterioration was measured by VTR of M2 as compared with the tape (Example 1) stored at room temperature.

Head stain = tape at 40 ° C., 90% RH
Was stored for 1 week and the head stain after 50 passes of M2VTR was evaluated by a three-point method. 3 points: no stain, 2 points: stain, 1 point: remarkable stain

[0063]

[Table 1]

As is clear from the above table, the present invention is excellent in both storage RF output and durability and is superior to the comparative examples. In Comparative Example 1, the amount of Al in the oxide film of the ferromagnetic metal powder is larger than that of the present invention, and the crystallite size is larger. In Comparative Example 2, the amount of Al in the oxide film of the ferromagnetic metal powder is larger than that of the present invention. This is the case when the crystallite size is small and the crystallite size is large.
Comparative Examples 3 and 5 are cases where Al of the oxide film was replaced with Si, and the amount and crystallite size were the same as in the case of Al, and Comparative Example 4 was the same as Comparative Example 3 and crystallized. This is an example of increasing the child size. In Comparative Example 5, the rust preventive agent was omitted. Comparative Example 6 is an example in which the amount of the abrasive is reduced in Example 1, and the durability is poor. It can be seen that these Comparative Examples 1 to 6 cannot achieve good balance between storage RF output and durability.

[0065]

INDUSTRIAL APPLICABILITY The present invention can be manufactured by optimally mixing a ferromagnetic metal powder having a thin oxide film and a known general material, that is, an abrasive, a rust preventive, etc., and stored under severe conditions. Since high output can be maintained and running durability can be ensured without reducing output even afterward, an excellent magnetic recording medium can be provided at low cost.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuji Nishida 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (3)

[Claims] 1. A magnetic recording medium in which a magnetic layer containing a ferromagnetic metal powder, a binder and an abrasive is provided on a non-magnetic support, wherein the surface of the ferromagnetic metal powder contains aluminum and the content thereof is the strong one. 2 to 5% by weight with respect to the magnetic metal powder, and the crystallite size of the oxide film of the ferromagnetic metal powder is 15
˜50Å, and the magnetic layer is the ferromagnetic metal powder 10
A magnetic recording medium comprising 10 to 20 parts by weight of an abrasive with respect to 0 parts by weight, and the magnetic layer containing an anticorrosive agent. 2. The magnetic recording medium according to claim 1, wherein both the abrasive and the metal on the surface of the ferromagnetic metal powder are made of a material containing Al atoms. 3. The magnetic recording medium according to claim 1, wherein the rust preventive agent comprises phenylphosphonic acid and a phosphoric acid ester.