JP2640278B2 - Magnetic recording media - Google Patents

Description

The present invention relates to an improvement in a magnetic recording medium comprising a non-magnetic support, a magnetic layer and a back layer.

(Prior Art) In general, as a magnetic recording medium for audio, video, computer (disk, memory tape), etc., a magnetic layer in which a ferromagnetic powder is dispersed in a binder (a binder) is formed on a non-magnetic support. Is used.

In recent years, these magnetic recording media have been required to have high-density recording, and by increasing the size of ferromagnetic powder, alloy powder, filling, and ultra-smoothness of the magnetic recording medium, the signal / noise has been increased and the noise has been reduced. Has been achieved. However, in high-density recording, the charging characteristics, head cleaning characteristics, running durability characteristics, and recording and reproducing head wear characteristics must be good.
Furthermore, it is required that recording and reproduction signals / noise (dropout) caused by foreign matter such as dust on a magnetic recording medium be small. For this purpose, as a raw material of the magnetic recording medium, a filler called a carbon black or an abrasive having a Mohs hardness of 8 or more is used. Specifically, USP 3630910, USP 3833412, USP 4614685
And U.S. Pat. No. 4,539,257 and JP-A-59-193533.

As a method other than the magnetic recording medium raw material, there is a technique relating to burnishing of a magnetic recording medium. For example,
58-46768, JP-A-56-90429, JP-B-58-46767 and JP-B-63-259830.

Even with the above technology, it was extremely difficult to adjust running durability characteristics, head wear characteristics, head cleaning characteristics, and the like. Also, reduction of dropout was insufficient.

Specifically, ultra-smoothing of a magnetic recording medium increases the friction coefficient and deteriorates running durability characteristics. For this purpose, carbon black or an abrasive having a Mohs' hardness of 6 or more is used as a raw material of the magnetic recording medium to ensure running durability and durability, but head wear increases. Also, if the amount of the abrasive added to the raw material is reduced to adjust the head wear, the head cleaning characteristics deteriorate. Therefore, it is extremely difficult to adjust these in a well-balanced manner.

In addition to the above, even if there are proposals such as Japanese Patent Publication No. 58-46768, Japanese Patent Publication No. 56-90429, Japanese Patent Publication No. 58-46767, and Japanese Patent Publication No. 63-259830, running durability characteristics and head wear characteristics ,
It was extremely difficult to adjust all of the head cleaning characteristics and the dropout characteristics in a well-balanced manner.

Conventionally, in order to improve the electromagnetic conversion characteristics, ferromagnetic powder has been oriented in the longitudinal direction within the coating surface so that it can be laid down in the longitudinal direction as much as possible. Although such a method certainly increases the output and improves the squareness ratio (Br / Bm), it can sufficiently improve the running durability such as dropout (DO) and still image durability (still life). Did not. The cause of the dropout may be due to the binder, but often due to the ferromagnetic powder. Therefore, the present inventors examined the effect of the ferromagnetic powder on the friction coefficient and the dropout, and found that the relationship between the positions of the ferromagnetic powder present in the magnetic layer greatly affected the friction coefficient and the occurrence of dropout. all right. As a result of measuring the position of the ferromagnetic powder using a high-speed electron beam diffraction method to solve such a problem, there is a strong correlation between dropout and durability of the still image, and there is also close contact with head contamination and head wear. It was found that not only the relationship but also that the magnetic layer surface was brought into contact with and slid with a specific metal to obtain an extremely excellent magnetic recording medium, leading to the present invention.

(Object of the Invention) It is an object of the present invention to solve the drawbacks of the prior art and to provide a magnetic recording medium in which all of the running durability characteristics, head wear characteristics, head cleaning characteristics, and dropout characteristics are adjusted in a well-balanced manner.

(Constitution of the Invention) The object of the present invention is to provide a ferromagnetic powder, a binder,
In a magnetic recording medium provided on a non-magnetic support having a magnetic layer containing an additive, the surface of the magnetic layer is contacted and slid with a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more, and is subjected to high-speed reflection electron diffraction. This can be achieved by a magnetic recording medium characterized by having a magnetic layer in which the ratio of the number of diffraction points from the ferromagnetic powder on the surface of the magnetic layer and the ratio of N (220) / N (113) are 1.65 or more.

Further, in the magnetic recording medium, the magnetic layer surface is contacted with a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more, the ratio of the number of diffraction points of the magnetic layer before sliding,
That is, it can be achieved by a magnetic recording medium characterized in that the ratio of N (220) / N (113) is less than 1.65.

In the magnetic recording medium of the present invention, a magnetic layer containing a ferromagnetic powder, a binder and additives (carbon black, abrasives, lubricants, etc.) is provided on a non-magnetic support. It has a basic structure in which the layer is provided on a nonmagnetic support opposite to the magnetic layer.

In this magnetic recording medium, the ratio of diffraction points from ferromagnetic powder by high-speed reflection electron beam diffraction, that is, N (220) / N (11
The fact that the ratio of 3) is 1.65 or less is considered to indicate that the needle-like crystals of the ferromagnetic powder on the surface of the magnetic layer are oriented more perpendicularly to the surface of the magnetic layer. Is considered to be advantageous for the coefficient of friction because the extreme points of the needle-like crystals are exposed on the surface, and that the binder component effectively exerts a binding effect.

The present inventors have intensively studied a magnetic recording medium having more excellent head wear characteristics, head cleaning characteristics, and dropout characteristics while maintaining running durability characteristics and signal / noise characteristics.

As a result, a ferromagnetic powder, a magnetic layer containing a binder, carbon black, an abrasive and a lubricant are provided on a non-magnetic support, and a back layer containing a binder and carbon black is provided on the non-magnetic support opposite to the magnetic layer. In the magnetic recording medium provided above, the entire surface of the magnetic layer is contacted with a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more,
The magnetic layer is slid, and the ratio of the number of diffraction points from the ferromagnetic powder on the surface of the magnetic layer by high-speed reflection electron diffraction of the magnetic layer, that is, N
It has been found that by setting the ratio of (220) / N (113) from a magnetic layer having a ratio of less than 1.65 to 1.65 or more, a magnetic recording medium having excellent head wear characteristics, head cleaning characteristics, and dropout characteristics can be obtained. Also, the ratio of the diffraction points, ie, N
The ratio of (220) / N (113) is desirably set to 1.70 or more.

The reason why a magnetic recording medium having excellent running durability characteristics and signal / noise characteristics and excellent head wear characteristics and head cleaning characteristics even when the ratio of the diffraction points is 1.65 or more is obtained is as follows: Mohs hardness of 6 or more. When the magnetic layer is contacted and slid with carbon steel alloys and cemented carbides of the above, needle-like crystals of ferromagnetic powder in which poles oriented vertically on the surface of the magnetic layer are excessively exposed on the surface Is worn out, and the height of the exposed extreme points is averaged. The dropout characteristics are considered to be due to the fact that dust and protrusions on the surface of the magnetic layer are removed by a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more, and that the magnetic layer has a cutting effect. I have.

The reason for using carbon steel alloys and cemented carbides in the present invention is that with conventional ceramic blades or glass blades of alumina oxide, silicon, zirnium, etc., only the edges are cut, and the surface is smooth, so there is no grinding effect, The hard alloy has fine irregularities on the surface, and is considered to be used not only for cutting at the edge but also for cutting the surface of the magnetic layer on the surface. This effect is strong, and the ferromagnetic powder present on the surface of the magnetic layer is also scraped off, and it is considered that the effect of the present invention can be obtained.

On the other hand, it is considered that the wear of the ferromagnetic powder is promoted by the mutual wear powder of the carbon steel alloy due to the cohesive wear of the ferromagnetic powder and the carbon steel.

As the metal material to be contact-slid as described above, a carbon steel alloy having a Mohs hardness of 6 or more and a cemented carbide are used, and stainless steel, tungsten carbide (WC containing WC), titanium carbide (TiC) and the like are effective. The shape may be plate-like or rod-like according to the tape width, but is preferably plate-like.

As for the contact sliding conditions, the number of times is preferably 1 to 10 times, the temperature is preferably 5 to 60 ° C., the humidity is preferably 30 to 90% RH, and the contact area is 5 mm.
-The tape width is preferably equal to or less than the tape width (the contact point may be plural).

The contact incident angle is not particularly limited, but is preferably 20 to 170
゜. The pre-contact tension is preferably 10 to 300 g / tape width. The pushing amount into the tape is preferably 1 to 30 mm from the position where the tape and the metal material come into contact for the first time. The sliding speed is preferably from 10 to 400 m / min. Also, between the sliding section outlet and the reel and hub around which the tape is wound,
It is preferable to perform surface contact cleaning with a tissue and a cloth.

The processing step may be performed after the calendering step with the calendering processing, after the coating without the calendering processing, before and after slitting, before and after winding, or before and after assembling in a cassette.

The ratio of the number of diffraction points from the ferromagnetic powder on the surface of the magnetic layer by high-speed reflection electron diffraction of the magnetic layer of the present invention, that is, N (22
As described above, the ratio of 0) / N (113) to 1.65 or more can be obtained by sliding with a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more under the above conditions. The ratio of N (220) / N (113) in the layer should be less than 1.65.

The ratio of the number of diffraction points from the ferromagnetic powder on the surface of the magnetic layer by high-speed electron diffraction of the magnetic layer, that is, the ratio of N (220) / N (113) can define the plane orientation of the needle-like crystals on the surface of the magnetic layer. ,
It is considered that the fact that this ratio is less than 1.65 indicates that the needle-like crystals on the surface of the magnetic layer stand more perpendicularly to the surface of the magnetic layer. N (220) refers to the surface on the long axis side of the acicular ferromagnetic fine powder, and N (113) refers to the surface on the short axis side.

Therefore, the fact that the value of N (220) is large means that there are many long-axis surfaces of the acicular ferromagnetic fine powder on the surface of the magnetic layer, and the ferromagnetic powder is in-plane with respect to the plane of the magnetic layer. Means that many are oriented. Also N (11
The fact that the value of 3) is large means that there are many short-axis-side surfaces of the acicular ferromagnetic fine powder on the surface of the magnetic layer, and the ferromagnetic powder is oriented in a direction perpendicular to the plane of the magnetic layer. Means that. N (220) N (113) =
1.65 is one inflection point. If the value is larger than 1.65, it indicates that there are many N (220) planes, indicating that the face is oriented in the in-plane direction, that is, lying, and if the value is smaller than 1.65, N (22).
0) The plane is small, indicating that the ferromagnetic powder is vertically oriented, that is, standing. When the acicular ferromagnetic powder is lying, the squareness ratio is increased, and the output is improved.
However, the bond with the binder is weak and the strength is not so high.
On the other hand, if the needle-like ferromagnetic powder is standing, the squareness ratio is low and the output is difficult to be obtained, but the binding with the binder is strong and the strength is increased. In this way, N
By using a magnetic recording medium having a magnetic layer with (220) / N (113) of less than 1.65, the magnetic layer surface is brought into contact with and slid with a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more, so that N
(220) / N (113) should be 1.65 or more. N (22
The reason why 0) / N (113) is 1.65 or more is not clear, but it is considered that the above-mentioned value may be obtained by cutting or extracting the ferromagnetic powder standing on the surface of the magnetic layer. .

The magnetic recording medium having a magnetic layer in which N (220) / N (113) is less than 1.65 can be manufactured as follows.

Immediately after the dispersion of the ferromagnetic powder is applied to a support such as polyethylene terephthalate, the operation of orienting the ferromagnetic powder in the longitudinal direction by a permanent magnet is performed. At this time, a solenoid magnet may be used as the magnet. Orientation operation may be performed by using a permanent magnet and a solenoid magnet together, or by applying a dry air at 20 ° C. to 130 ° C. to the support immediately after the ferromagnetic powder dispersion is applied. The strength of the magnetic field is 700-400
0 Gauss is preferred. The transport speed of the support is 10 to 1000 m / m
in is preferred. By such an orientation operation, the ratio of the number of diffraction points from the ferromagnetic powder by the high-speed reflection electron beam diffraction on the surface of the magnetic layer, that is, the ratio of N (220) / N (113) changes. The ratio increases as the orientation increases and the orientation decreases. The residence time of the orientation is preferably 5 seconds or less.

Further, the ratio of N (220) / N (113) is Y, and the squareness ratio SQ is X
When Y is 1.65 or less, X is preferably 0.8 to 1.0 Y = 6.24165X−3.7922 ± 0.1837, that is, −3.9759 <Y−6.24165X <−3.6085.

As the ferromagnetic powder used in the present invention, γ-Fe ₂ O ₃ , C
o-containing (deposition, denaturation, doping) γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co
Containing (deposition, modified, _{doped) Fe 3 O 4, FeO X} , containing Co of (wearing the, modified, doped) FeO _{X (X} = 1.33~1.50) can be used.

The particle size of these ferromagnetic powders is about 0.005 to 1 micron in length, and the ratio of shaft length / shaft width is about 1/1 to 50/1. The specific surface area of these ferromagnetic powders is 1 m ² / g to 70 m
It is about ² / g. The water content of these ferromagnetic powders is 0.2 to
2.0 wt%. The content of the coating solution when these ferromagnetic powders are used is 0.00 to 2.00 wt%. The surfaces of these ferromagnetic powders may be impregnated with a dispersant, a lubricant, an antistatic agent and the like described below in a solvent prior to dispersion and adsorbed thereon for each purpose.

The ferromagnetic powder contained in the magnetic layer is preferably a cobalt-containing iron oxide, and the iron oxide replaces divalent iron with trivalent iron by 1 to 3.
It is known that a magnetic recording medium excellent in running durability and signal / noise can be obtained by containing 15% by weight. If the amount of divalent iron, such as acicular iron oxide, which is ferromagnetic powder, is less than 1% by weight of trivalent iron, it is disadvantageous for S / N, and if it contains more than 15% by weight, ferromagnetic powder and binder (Binder)
Is inferior in running durability, which is not preferable.

As the binder used for the magnetic layer and the back layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

The thermoplastic resin has a softening temperature of 150 ° C. or less, an average molecular weight of 10,000 to 300,000, and a degree of polymerization of about 50 to 2,000.For example, vinyl chloride vinyl acetate copolymer, vinyl chloride polymer, vinylidene chloride vinylidene chloride Polymer, vinyl acrylonitrile copolymer, acrylate acrylonitrile copolymer, acrylate vinylidene chloride copolymer, acrylate styrene copolymer,
Methacrylate acrylonitrile copolymer, methacrylate vinylidene chloride copolymer, methacrylate styrene copolymer, urethane elastomer,
Nylon-silicone resin, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, Cellulose propionate, nitrocellulose, ethylcellulose, methylcellulose, propylcellulose, methylethylcellulose, carboxymethylcellulose, acetylcellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, various types of synthesis Rubber-based 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 after application, and the molecular weight becomes infinite due to reactions such as condensation and addition by heating after application and drying. Among these resins, those which do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic-based reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin Mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol /
High molecular weight diol / triphenylmethane triisocyanate mixture, polyamine resin, polyimine resin and mixtures thereof.

These thermoplastic resins, thermosetting resins, and reactive resins have a carboxylic acid, a sulfinic acid, a sulfenic acid, a sulfonic acid, a phosphoric acid, a sulfuric acid, a sulfuric acid, a phosphon, a phosphine, a boric acid, a boric acid ester group as a functional group other than the main functional group. Acid groups such as acid ester groups, phosphoric ester groups, and alkyl ester groups thereof (these acidic groups may be in the form of Na salt, etc.), amino acids; aminosulfonic acids, sulfuric acid or phosphoric esters of amino alcohol, alkyl betaine type, etc. An amphoteric group of
Amino group, imino group, imide group, amide group, epoxy group, etc. It usually contains one or more hydroxyl groups, alkosyl groups, thiol groups, halogen groups, silyl groups, and siloxane groups, and each functional group is a resin. 1 x 10 ^-6 equivalents per g-1
It is preferred to contain × 10 ^-2 equivalents.

These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the ferromagnetic powder and the binder in the magnetic layer is in the range of 5 to 300 parts by weight of the binder per 100 parts by weight of the ferromagnetic powder. The mixing ratio of the fine powder in the back layer and the binder is 100 by weight.
The binder is used in an amount of 30 to 300 parts by weight based on parts by weight. Additives include dispersants, lubricants, abrasives, antistatic agents, antioxidants, solvents and the like.

As the polyisocyanate used in the present invention, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate Isocyanates such as isophorone diisocyanate, products of said isocyanates and polyalcohols, and 2 to 15 formed by condensation of isocyanates.
It is possible to use monomeric polyisocyanates and the like.
The average molecular weight of these polyisocyanates is 100 to 200
00 is preferred. 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-110N, Takenate D-200, Takenate D-202, Takenate 300S, Takenate 500 (manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidule T-80,
Sumijur 44S, Sumijur PF, Sumijur L,
Sumidule N, Death Module L, Death Module I
L, death module N, death module HL, death module T65, death module 15, death module R, death module RF, death module SL, death module Z427
3 (manufactured by Sumitomo Bayer), etc. These can be used alone or in combination of two or more utilizing the difference in curing reactivity. Also, for the purpose of accelerating the curing reaction, a hydroxyl group (butanediol, hexanediol, polyurethane having a molecular weight of 1,000 to 10,000, water, etc.), an amino group (monomethylamine, dimethylamine,
Trimethylamine) or a metal oxide catalyst. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanates are preferably used in an amount of 5 to 40% by weight of the total amount of the binder.

Examples of the dispersant used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, linolenic acid, and stearolic acid. Ten~
50 fatty acids (R ₁ COOH, R ₁ is an alkyl group having 9 to 49 carbon atoms), alkali metals (Li, Na, K, NH ₄ ⁺
Etc.) or alkaline earth metals (Mg, Ca, Ba etc.), Cu, Pb
Metal soaps, fatty acid amides of the above fatty acids; lecithin, etc., as well as higher alcohols having 4 or more carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol) and their sulfates and phosphates , Amine compounds and the like can also be used. In addition, polyalkylene oxides and their sulfates, phosphates, amine compounds and the like, sulfosuccinic acid, sulfonesuccinate and the like can also be used.
It is also possible to introduce Si and F substituents into these compounds because they change the compatibility and properties with the binder. One or more of these dispersants are usually used, and one kind of the dispersant is added in an amount of 0.005 to 20 parts by weight based on 100 parts by weight of the binder. Regarding the method of using these dispersants, the dispersants may be applied to the surface of the ferromagnetic powder or non-magnetic powder in advance, or may be added during dispersion.

In addition, as a compound preferable as a dispersant, a surfactant such as a carboxylic acid or a phosphoric ester, or a fluorine-based surfactant Florard FC95, FC129, FC430, or FC431 can be used.

Lubricants and antioxidants used in the magnetic layer and the back layer of the present invention include molybdenum disulfide, boron nitride, graphite fluoride, calcium carbonate, barium sulfate, silicon oxide,
Inorganic fine powders such as titanium oxide, zinc oxide, 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, polyfluorinated ethylene resin fine powder Sodium resin fine powder, silicon oil, fatty acid modified silicone oil, graphite, fluorine alcohol, polyolefin (polyethylene wax, etc.), polyglycol (polyethylene oxide) Wax, etc.), tetrafluoroethylene oxide wax, polytetrafluoroglycol, perfluorofatty acid, perfluorofatty acid ester, perfluoroalkyl sulfate, perfluoroalkyl phosphate, alkyl phosphate, polyphenyl ether,
One or two of monobasic fatty acids having 10 to 50 carbon atoms and monohydric or dihydric alcohols having 3 to 50 carbon atoms, trihydric alcohols, tetrahydric alcohols, and hexahydric alcohols Fatty acid esters composed of the above, fatty acid esters composed of monobasic fatty acids having 10 or more carbon atoms and monohydric to hexahydric alcohols having a total of 11 to 50 carbon atoms in total with the carbon atoms of the fatty acids, etc. Organic compound lubricants can be used. In addition, fatty acids having 8 to 50 carbon atoms, fatty acid amides, and aliphatic alcohols 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 phosphate, octyl palmitate, ethyl stearate, butyl stearate, octyl stearate, amyl stearate, anhydrosorbitan monostearate, anhydrosorbitan tetrastearate, anhydrosorbitan ethylene oxide monostearate, oleyl oleate, oleyl alcohol ,
Lauryl alcohol, etc., can be used alone or in combination. As the lubricant used in the present invention, so-called lubricating oil additives can be used alone or in combination, and antioxidants (such as alkylphenols) and rust inhibitors (such as naphthenic acid, alkenyl succinic acid, and dilauryl phosphate) can be used. ), Oily agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.).

As the antistatic agent used in the present invention, graphite, carbon black, carbon black graft polymer,
Conductive powders such as tin oxide-antimony oxide, tin oxide, titanium oxide-tin oxide-antimony oxide; natural surfactants such as saponin; alkylene oxide-based, glycerin-based;
Nonionic surfactants such as glycidol, polyhydric alcohols, polyhydric alcohol esters, and alkylphenol EO adducts; higher alkylamines, cyclic amines, hydantoin derivatives, amidoamines, esteramides, quaternary ammonium salts, pyridine and other heterocycles Surfactants, such as phosphoniums, phosphoniums or sulfoniums;
Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, and phosphate group; amino acids; amphoteric surfactants such as aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and alkyl betaine type Agents and the like are used. These surfactants may be added alone or as a mixture. Also, these surfactants may be 1mg / m ² ~550mg / m ² overcoat on the surface of the magnetic recording medium. The amount of these surfactants used in the magnetic recording medium is 0.01 to 100 parts by weight of the ferromagnetic powder.
~ 10 parts by weight. These are used as antistatic agents, but are sometimes applied for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and application aids.

As the carbon black used in the present invention, furnace black for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific examples of abbreviations of these carbon blacks in the United States include SAF, ISAF, I
ISAF, T, HAF, SPF, FF, FEF, HMF, GPF, APF, SRF, M
PF, ECF, SCF, CF, FT, MT, HCC, HCF, MCF, LFF, RCF
And those classified into D-1765-82a of the US ASTM standard can be used. The average particle size of these carbon blacks used in the present invention is 5 to 10
00 nm (electron microscope), nitrogen adsorption method specific surface area 1-1500 m ² /
g and pH are 2 to 13 (JIS standard K-6221-1982 method), and dibutyl phthalate (DBP) oil absorption is 5 to 2000 ml / 100 g (JIS standard K-6221-1982 method). The content of these carbon blacks used in the present invention is 0.00 to 20% by weight.
The size of the carbon black used in the present invention is, for the purpose of lowering the surface electric resistance of the coating film, 5 to 100 nm of carbon black, and 50 to 50% when controlling the strength of the coating film.
Uses 1000nm carbon black. In order to control the surface roughness of the coating film, a finer carbon black (100 nm) is used for smoothing to reduce spacing loss.
In the following, coarse carbon black (50 nm or more) is used for the purpose of roughening and lowering the friction coefficient. As described above, the type and the amount of carbon black to be used are properly used depending on the purpose required for the magnetic recording medium.

Further, these carbon blacks may be surface-treated with a dispersant described below or the like, or may be used after being grafted with a resin. Further, a carbon black produced by treating the furnace at a temperature of 2000 ° C. or higher at a temperature of 2000 ° C. or more and partially graphitizing the surface can also be used. Also, hollow carbon black can be used as a special carbon black.

These carbon blacks are ferromagnetic powders for magnetic layers
It is desirable to use 0.1 to 20 parts by weight based on 100 parts by weight. Physical properties of carbon black and carbon black that can be used in the present invention are, for example, "Carbon Black Handbook",
Edited by Carbon Black Association (issued in 1971).

As the abrasive for the magnetic layer and the back layer used in the present invention, a material having a polishing action or polishing action generally used, α-alumina, γ-alumina, α-γ-alumina,
Fused alumina, carbon silicon, chromium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main component: corundum and magnetite), garnet, silica, silicon nitride, boron nitride, molybdenum carbide, carbonized Boron, tungsten carbide, titanium carbide,
Quartz, tripoly, diatomaceous earth, dolomite, and the like, and materials having a Mohs' hardness of 6 or more, more preferably 8 or more, are used in combination of 1 to 4 kinds. These abrasives have an average particle size of 0.005 to 5 μm, and particularly preferably 0.01 to 2 μm. These abrasives are used in an amount of 0.01 to 2 parts per 100 parts by weight of the binder.
It is added in the range of 0 parts by weight.

Dispersion of the present invention, kneading, as the organic solvent used in the application, acetone, methyl ethyl ketone in any ratio,
Ketones such as methyl isobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran: alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol and methyl cyclohexanol; methyl acetate, ethyl acetate,
Esters such as butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate and glycol monoethyl ether; ethers such as diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether and dioxane; (aromatic hydrocarbons); methylene chloride And chlorinated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, and N, N-dimethylformaldehyde and hexane.

The method of dispersion and kneading is not particularly limited, and the order of addition of each component can be appropriately set. For the preparation of the magnetic paint and the back layer paint, a conventional kneading machine, for example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, a Tsegbari (Sz
egvari), attritor, high-speed impeller, disperser, high-speed stone mill, high-speed impact mill, disper, kneader, high-speed mixer, ribbon blender, co-kneader, intensive mixer, tumbler, blender, disperser, homogenizer, single screw extruder , A twin screw extruder, an ultrasonic disperser, and the like. For details of the kneading and dispersing technology, see “Paint Fl” by TCPATTON (TC Patton).
ow and Pigment Dispersion ", 1964 John Wile
It is described in y & Sons, Inc. (John Wiley and Sons), Shinichi Tanaka, “Industrial Materials”, Vol. 25, 37 (1977), and in the references cited in the book. Combined solution sending and application. It is also described in specifications such as U.S. Patent 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 according to the method described in the above-mentioned book or the cited document of the book.

The formation of the magnetic layer is performed by dissolving in an organic solvent any combination of the above compositions and the like, and coating and drying the coating solution on a support. When used as a tape, the thickness of the support is 2.5 to 1
The thickness is about 00 μm, preferably about 3 to 70 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. As materials, polyethylene terephthalate, polyesters such as polyethylene terephthalate, polypropylene, polyolefins such as polyethylene, cellulose triacetate, cellulose derivatives such as cellulose diacetate,
In addition to vinyl resins such as polyvinyl chloride and polyvinylidene 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, German Patent 3338854A, JP-A-59-116926, U.S. Pat.
No. 8, Yukio Mitsuishi, Textile and Industry, vol. 31, p. 50-55, 1975.

As a method of applying the magnetic layer and the back layer on the support, 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, bar coat, etc. can be used, and other methods are also possible. Is described in detail in “Coating Engineering” published by Asakura Shoten, pages 253 to 277 (published in 1963).

According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting in a desired direction while immediately drying the ferromagnetic powder in the layer, if necessary, and then the formed magnetic layer is dried. The transport speed of the support at this time is usually 10
m / min ~ 1000m / min, drying temperature 20 ℃ ~ 130 ℃
Is controlled by If necessary, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing process or cutting into a desired shape. As a cleaning process, there is a surface contact cleaning using a tissue, a cloth, and a grindstone. These may be independent steps or may be associated with the cutting and assembling steps. As the tissue and the cloth, a nonwoven fabric and a microfiber cloth (for example, Toraysee Toraysee) are preferable. These manufacturing methods include filler surface treatment, kneading,
It is preferable that the steps of dispersion, coating, heat treatment, calendering, EB treatment, surface polishing treatment, and cutting are continuously performed. Further, the steps can be divided into several steps as required.

In these steps, the temperature and humidity are controlled, and the temperature is 10 ° C. to 130 ° C., and the humidity is 5 mg / m
³ is a ~20mg / m ^3. These are described, for example, in JP-B-40-2362.
No. 5, JP-B-39-28368, U.S. Pat.
No., etc. Also, Japanese Patent Publication No. 41-13181
The method disclosed in the publication is considered to be a basic and important technique in this field.

〔The invention's effect〕

In the present invention, the magnetic layer surface is contact-slid with the magnetic layer surface with a carbon steel alloy or carbide metal having a Knoop hardness of 6 or more,
The ratio of the number of diffraction points from the ferromagnetic powder on the surface of the magnetic layer by high-speed reflection electron diffraction of the magnetic layer, ie, N (220) / N (1
13) By setting the ratio to 1.65 or more, head wear is reduced, and head dirt, dropout, and static image durability can be improved.

Although the reason for obtaining the effect of the present invention is not clear, N (220) corresponds to the acicular side surface of the ferromagnetic powder, and N (113) corresponds to the acicular end surface of the ferromagnetic powder. Equivalent to.
Therefore, the fact that N (220) / N (113) is 1.65 or more indicates that the ratio of the ferromagnetic powder standing on the surface of the magnetic layer is small and the ratio of the ferromagnetic powder in the lying state is high.

That is, the present invention is a method in which the ferromagnetic powder is in a state of standing on the surface of the magnetic layer and is dropped by sliding with the magnetic head to cause a dropout, or is present as a protrusion and wears the magnetic head. Can be preliminarily cut or extracted by sliding in contact with a carbon steel alloy or a super steel alloy, resulting in an increase in the value of N (220) / N (113), thereby causing dropout and head contamination. It seems that there is little head wear. In the present invention, the ferromagnetic powder in the inside of the magnetic layer is often in a standing state, has a strong adhesive force with the binder, and has good durability.

It is not always clear about the events that occur in the contact sliding of carbon steel and cemented carbide, but between carbon steel and cemented carbide with ferromagnetic powder on the surface of the magnetic recording medium, carbon steel Abrasion powder of carbon steel due to abrasive particles in the magnetic layer, and mutual abrasion powder due to cohesive wear of carbon steel and ferromagnetic powder, wear the ferromagnetic powder in the vertical direction on the surface of the spontaneous layer. Conceivable. Further, in the cemented carbide, the ferromagnetic powder in the vertical direction on the surface of the magnetic layer is cut due to the machinability of particles such as tungsten carbide, and the wear is further promoted by the cut powder. As a result, it is considered that the poles of the ferromagnetic powder in the direction perpendicular to the surface of the magnetic layer are worn or the ferromagnetic powder particles themselves are removed, and the N (220) / N (113) ratio is increased.

Conventional ceramic blades and glass blades made of alumina oxide, silicon, zirconium, etc. have a smooth surface and have no effect other than shaving with an edge, so that a large difference in effect is expected.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.
It is easily understood by those skilled in the art that the components, ratios, operation orders, and the like shown here can be changed without departing from the spirit of the present invention.

Therefore, the present invention should not be limited to the following examples. In the examples, “parts” indicates “parts by weight”.

(Example 1) [I] of the following magnetic layer composition was kneaded sufficiently in a kneader, and [II] was additionally added and kneaded sufficiently.
I] was added and mixed and dispersed to prepare a magnetic paint.

Magnetic layer composition [I] Co-containing γ-Fe_TwoO_ThreePowder (nitrogen adsorption specific surface area 45m^Two/ g, Fe
= 4 tam% powder Hc750Oe) 300 parts Vinyl chloride resin (MR110, manufactured by Nippon Zeon) 25 parts Polyurethane resin (UR8600, manufactured by Toyobo) 20 parts Carbon black (Mitsubishi 950B, average particle size manufactured by Mitsubishi Kasei)
Size 10nm) 12 parts abrasive γ-Al_TwoO_Three(UA5600, Showa Denko KK) 15 parts Oleic acid 3 parts Cyclohexanone 150 parts [II] butyl acetate 850 parts tertbutyl stearate 3 parts [III] Polyisocyanate (Coronate 3040, Bayer)
20 parts Stearic acid 3 parts Methyl ethyl ketone 100 parts 18μm non-magnetic support after viscosity adjustment of this magnetic paint
With a dry film thickness of 5.0 μm on polyethylene terephthalate
Apply, apply magnetic field with 3000 gauss magnet and dry
Subsequently, a magnetic layer was formed by calendaring. Continued,
On the opposite side of the non-magnetic support provided with the magnetic layer,
The product was kneaded and dispersed with [I] in a ball mill, and [II] was added.
Mix and stir to adjust the back solution and apply it to a dry thickness of 2.0 μm.
Cloth was provided to provide a back layer.

Back composition carbon black (cancarb MTCI nitrogen adsorption specific surface area 10
m ² / g Average particle size 250 nm, manufactured by Kancarb Ltd. 30 parts Carbon black (Mitsubishi 3250B nitrogen adsorption specific surface area 160 m ² / g
Average particle size 30 nm, manufactured by Mitsubishi Kasei Co., Ltd. 70 parts Polyurethane polycarbonate (FJ2, manufactured by Dainichi Seika)
(FJ2, manufactured by Dainichi Seika) 30 parts Phenoxy resin (PKHH, manufactured by Union Carbide) 20 parts Methyl ethyl ketone 700 parts Cyclohexanone 300 parts [II] Polyisocyanate (Coronate 3040, manufactured by Nippon Polyurethane) 10 parts Lubricant (silicone) , KF69, manufactured by Shin-Etsu Chemical Co., Ltd.) 0.1 part Lubricant (oleic acid) 1 part Methyl ethyl ketone 100 parts After this, a 1-inch wide slit was made to make a videotape, and contact sliding was performed under the conditions described in Table 1. The number of contacts was one, the number of contact points was two, the incident angle of contact was 45 degrees, the amount of pushing into the tape was 7 mm from the position where the tape and metal material first contacted, and the sliding speed was 300 m / min. Created. Table 2 shows the properties of the obtained tape.

(Evaluation method) Head wear characteristics Under humidification conditions (25 ° C 70% RH), Sony BVH218
Make 20 passes repeatedly with 0 VTR to determine the amount of VTR head wear.

Head Smear When obtaining the wear amount, the state of head smear is observed and the head cleaning characteristics are evaluated.

Dropout quantity At room temperature (25 ℃ 70% RH), Sony BVH2000 VTR
At the same time, recording and playback were performed simultaneously, and the dropout every minute was measured for 60 minutes with a Shibasoku dropout counter.

Still image durability characteristics The evaluation of running durability characteristics was performed at room temperature (25 ° C and 70% RH) in the Sony BVH2000 VTR still image mode.
The additional weight of 200g was applied, and the time until the video output reached -16dB was measured.

As is clear from the experimental examples in Table 2, the magnetic recording medium of the present invention is a magnetic recording medium contacted and slid with a carbon steel alloy stainless steel having a Mohs hardness of 6 or more and a cemented carbide tungsten carbide. Although it has a Mohs hardness of 6 or more, it exhibits superior performance in head abrasion, head cleaning characteristics, and dropout characteristics while maintaining running durability characteristics, as compared to a sapphire or the like which is a crystal of aluminum oxide.

Claims (2)

(57) [Claims] 1. A magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder and an additive provided on a non-magnetic support,
By contacting and sliding the surface of the magnetic layer with a carbon steel alloy or a cemented carbide having a Knoop hardness of 6 or more, the ratio of the number of diffraction points from the ferromagnetic powder by high-speed reflection electron diffraction N (220) / N ( 113) has a magnetic layer having a value of 1.65 or more. 2. The magnetic layer according to claim 1, wherein N (220) / N (113) of the magnetic layer before contacting and sliding with the carbon steel alloy or cemented carbide is less than 1.65. The magnetic recording medium according to the above.