JPH08279148A - Tape-shaped magnetic recording medium - Google Patents

Abstract

PURPOSE: To prevent the powder dislodgment onto a magnetic layer surface and the clogging of a magnetic head and the magnetic layer surface by specifying the volume of the magnetic parts projecting form the vertex of the max. projecting parts of a nonmagnetic base to a value larger than 0 and below 100μm<3> per 0.03mm. CONSTITUTION: The absence of head stains and decreased drop-outs are resulted with the magnetic recording medium 1 which is below 100μm<3> , particularly below 50μm<3> and more particularly <=50μm<3> per 0.03mm in the volume of the projecting parts 2 of the magnetic layer and/or the magnetic recording medium which is <=100pieces/mm in the number of cracks at the edges of the magnetic layer. Friction resistance is large and the traveling property is poor with the magnetic recording media which have no projecting parts of the magnetic layer at all. Further, some media are damaged at the edges of the nonmagnetic base 4 and the flawing of guide flanges by some media is resulted. Both of the head stains and the drop-outs are many with the recording media which are >=100μm<3> in the volume per 0.03mm of the projecting parts of the magnetic layer and are over 100pieces/mm in the number of cracks of the magnetic layer 3.

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, particularly a tape-shaped magnetic recording medium in which a magnetic layer is coated on a non-magnetic support and slitted in the longitudinal direction, and more specifically a thick single-layer magnetic layer. The present invention relates to a magnetic recording medium for a high-definition VTR that has a high density recording / reproducing of a digital signal.

[0002]

2. Description of the Related Art Generally, as a magnetic recording medium, a magnetic recording medium in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support is used. In particular, tape-shaped magnetic recording media include ferromagnetic powder as a binder,
A magnetic coating solution is prepared by mixing and dispersing with an additive and an organic solvent, and after coating this magnetic coating solution on a non-magnetic support,
It is manufactured by drying to make a wide magnetic recording medium (original) and cutting it to a required width such as 8 mm, 1/2 inch, 1 inch using a slitter device. The cutting method is, for example, as shown in FIG. 3, a magnetic recording medium raw material 11 is cut into a desired width by a slitter 10 constituted by a large number of upper blades 12 and lower blades 13 facing each other, and the obtained tape shape is obtained. The magnetic recording medium 1 is wound around the pancake 15 via the guide roller 14.

In the slit cross section of the magnetic recording medium obtained by the above-mentioned cutting, the magnetic layer 3 usually protrudes from the apex of the maximum convex portion of the nonmagnetic support 4 as shown in FIG.
As shown in FIG. 2, the magnetic layer 3 has a shape having many cracks 7 at the edge portion. In a high-definition magnetic recording medium having a thick single-layer magnetic layer, which is suitable for recording / reproducing a long-wavelength digital signal, the shape of this slit cross section, that is, the protrusion of the magnetic layer or the occurrence of cracks in the edge portion is particularly remarkable. is there.

[0004]

However, in the magnetic recording medium having the above-mentioned slit cross-sectional shape, the magnetic layer having a protruding or cracked edge portion is used for a long period of time and is scraped off by a damaged guide flange, so that the magnetic layer There is a problem that powder is dropped onto the surface and clogging between the magnetic head and the surface of the magnetic layer occurs, resulting in frequent occurrence of dropouts and the like. As a means for solving this problem, Japanese Patent Application Laid-Open No. 3-248324 describes that the nonmagnetic support is projected in the slit cross section to prevent the magnetic layer from being scraped. However, this magnetic recording medium has a drawback that the non-magnetic support is damaged by the knife effect of the damaged guide flange, and the protruding non-magnetic support further damages the guide flange. The present invention solves the above problems, by improving the sharpness of the edge of the magnetic layer, the frequency of powder falling onto the magnetic layer surface and clogging between the magnetic head and the magnetic layer surface is reduced, As a result, it is an object of the present invention to provide a magnetic recording medium having extremely few dropouts.

[0005]

The inventors of the present invention have found that the smaller the magnetic layer portion (hereinafter also referred to as the magnetic layer protruding portion) protruding from the maximum convex portion of the nonmagnetic support in the slit cross section, or the magnetic layer. It was found that as the number of cracks in the edge portion of the magnetic disk decreases, the abrasion of the magnetic layer due to the damaged flange decreases, and the present invention has been completed based on this finding. That is, the first aspect of the present invention is to provide a magnetic recording medium obtained by providing a magnetic layer on one surface of a non-magnetic support and slitting it in the longitudinal direction. The volume of the magnetic layer portion projecting from the apex of the maximum convex portion of the non-magnetic support divided into broken lines (hereinafter also referred to as dividing lines) is 0 per 0.03 mm.
It is a tape-shaped magnetic recording medium characterized by being larger than 100 μm ³ . A second aspect of the present invention is a magnetic recording medium obtained by providing a magnetic layer on one surface of a non-magnetic support and slitting it in the longitudinal direction, wherein the number of cracks in the edge portion of the magnetic layer is 0 to 100 / mm. A tape-shaped magnetic recording medium characterized by the above.

The first aspect of the present invention will be described in detail with reference to FIG. 1. A magnetic layer 3 (and a back layer 5 on the other surface as necessary) is provided on one surface of the non-magnetic support 4 in the longitudinal direction. A magnetic recording medium 1 obtained by slitting, which is divided into a line (dividing line) 6 perpendicularly drawn from the apex of the non-magnetic support maximum convex portion of the slit cross section and protruding from the non-magnetic support maximum convex portion. The volume of the formed magnetic layer portion (magnetic layer protruding portion) 2 is 0.03.
It is characterized by being greater than 0 and less than 100 μm ³ , preferably 50 μm ³ or less per mm.

When the volume of the magnetic layer protrusion 2 per 0.03 mm is 100 μm ³ or more, the abrasion is remarkable, and the powder of the magnetic layer is more likely to fall off. As a result, the running path of the magnetic recording medium and the surface of the magnetic layer are contaminated. Clogging occurs between the magnetic layer and the magnetic head. These stains and clogging cause dropout and the like as described above. Further, when the volume of the magnetic layer projecting portion 2 is 0, that is, when the magnetic layer does not project, the magnetic layer will not be scraped and powder will fall off, but there is a problem that friction resistance becomes large and running property deteriorates. It is not preferable because it may occur, the non-magnetic support 4 may be damaged, or the guide flange may be further damaged. Further, the second aspect of the present invention will be described in detail with reference to FIG. 2, which is characterized in that the number of cracks 7 at the edge portion of the magnetic layer 3 is 0 to 100 / mm.

[0008]

In the first aspect of the present invention, since the volume of the protruding magnetic layer portion 2 is as small as less than 100 μm ³ per 0.03 mm, contact with the guide flange is small and abrasion of the magnetic layer is small. In addition, since the volume of the protruding magnetic layer portion 2 is larger than 0, the lubricant and the abrasive contained in the magnetic layer act to keep the running property good. In the second aspect of the present invention, the number of cracks 7 which adversely affects the strength of the edge portion of the magnetic layer is 0.
Since it is as small as 100 pieces / mm, the edge portion has excellent strength.

As a method for realizing the slit cross section of the magnetic recording medium of the present invention, the slit speed, the meshing depth, the upper blade (male blade) and the lower blade (female blade) are used in cutting using the above-mentioned slitting device. The peripheral speed ratio (upper blade peripheral speed / lower blade peripheral speed), the continuous use time of the slit blade, and the curing agent ratio in the binder composition of the magnetic layer are adjusted. The slit speed is preferably high, but specifically, the range of 200 to 800 m / min is suitable, preferably 300 to 600 m / min, and more preferably 400.
~ 500 m / min. The meshing depth is preferably deep, but specifically, the range of 0.1 to 0.8 mm is suitable, preferably 0.25 to 0.7 mm, and more preferably 0.4 to 0.5 mm. . As the peripheral speed ratio of the upper blade and the lower blade, specifically, the range of 0 to 10 is appropriate,
It is preferably 0.5 to 8, more preferably 3 to 6.
It is preferable that the ratio of the curing agent in the binder composition of the magnetic layer is large, specifically 10 to 40 wt% in the magnetic layer.
% Is appropriate, preferably 15 to 35 wt%,
More preferably, it is 20 to 30 wt%. In particular, in order to keep the number of cracks in a preferable range, it is effective to adjust the engagement depth of the blade. The factor affecting the number of cracks is brittleness of the magnetic layer, and if the amount of the curing agent is excessively increased, the magnetic layer becomes brittle and the number of cracks tends to increase.

The constituents of the magnetic recording medium of the present invention will be described in more detail below. The magnetic recording medium of the present invention comprises a non-magnetic support, a magnetic layer provided on the support, and a back coat layer (also simply referred to as a back layer) provided on the side opposite to the magnetic layer as necessary. The magnetic layer is composed of ferromagnetic fine powder and, if necessary, powdery components such as carbon black, abrasives and powdery lubricant, and a binder in which these powdery components are dispersed. It is the same as the magnetic layer except that a non-magnetic powder is used instead of the powder. The binder is composed of a resin component and a curing agent that is blended if necessary.

First, the non-magnetic support of the magnetic recording medium of the present invention will be described. The non-magnetic support used in the present invention is not particularly limited, but the thickness is preferably about 5 to 10 μm, particularly about 6 to 9 μm, and the Young's modulus in the width direction is 100.
It is preferably 0 Kg / mm ² or more, and particularly preferably 1200 Kg / mm ² or more. The Young's modulus in the longitudinal direction is 400 to 12
00 Kg / mm ² , preferably 450 to 1000 Kg /
The range is mm ² .

In order to obtain the physical properties of the magnetic layer of the present invention, the binder resin composition of the magnetic layer, the additive composition and their blending amounts are controlled, and further calendering conditions for surface smoothing the magnetic layer are set. Control is important.

Materials include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride, polycarbonate, polyimide and polyamide. , Plastics such as polysulfone can be used, but polyethylene terephthalate, polyethylene naphthalate, polyamide and polyimide are preferable, and polyethylene naphthalate (PEN) is particularly preferable. 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 prior to coating. With respect to these supports, for example, the specification of West German Patent 3338854A and JP-A-59-1169.
26, U.S. Pat. No. 4,388,368; Yukio Mitsuishi, "Fiber and Industry", Vol. 31, p50-55, 1975.
It is listed in the year. The center line average surface roughness of these supports is 0.001 to 0.5 μm (cut-off value of 0.
25 mm) is preferred.

The polyethylene naphthalate used in the present invention includes ethylene-2,6-naphthalenedicarboxylate homopolymers, copolymers containing 70% by weight or more of ethylene-2,6-naphthalenedicarboxylate repeating units, A mixture of these and other polymers (however,
The PEN component accounts for 70% by weight or more), and the polyester composition essentially does not lose the properties of PEN. This PEN is a film-forming polymer.

The PEN film used in the present invention can be produced by biaxially orienting an unstretched film. Biaxial orientation is, for example, PE in sequential biaxial orientation.
A temperature higher than the glass transition temperature of N, preferably 3 to 1
The first stage is stretched at a temperature higher by 0 ° C., and then the second stage is stretched at the same temperature range as the first stage stretching temperature or 10 ° C. higher. The stretching ratio is at least 2 in the uniaxial direction, more preferably 2.5 or more, and the area ratio is preferably 6 times or more, more preferably 8 times or more. The heat treatment (heat setting) is preferably carried out under tension at a temperature of 170 ° C. or higher, more preferably 190 ° C. or higher. The upper limit of the heat treatment temperature depends on the treatment time, but it goes without saying that the film has a stable shape. The heat treatment time is preferably several seconds to several tens of seconds, more preferably 3 to 30 seconds. Then, 1.05 in the vertical direction under the conditions of (temperature lower than glass transition temperature by 10 ° C.) to (temperature lower than melting temperature by 40 ° C.).
˜2.5 times, 1.05 to 2.5 times in the transverse direction, and re-heat treatment is performed in the range of (temperature lower than glass transition temperature by 50 ° C.) to (temperature lower than melting temperature by 10 ° C.). Is preferred.

The ferromagnetic powder used in the magnetic layer of the present invention is
Although not particularly limited, when a ferromagnetic metal powder containing iron, cobalt or nickel is used, the effect is remarkable, and α-Fe, Co, Ni, Fe-Co alloy, Fe-C are used.
o-Ni alloy, Fe-Co-Ni-P alloy, Fe-Co
Ferromagnetic metal fine powders such as -Ni-B alloy, Fe-Ni-Zn alloy, Ni-Co alloy, and Co-Ni-Fe alloy are preferable.

The shape of these ferromagnetic metal powders is not particularly limited, and needle-shaped particles, granular particles, dice-shaped particles, rice particles, and plate-shaped particles are usually used. In the case of needles, the particle size is 0.05 to 0.5 μm, preferably 0.05 to 0.5 μm.
The major axis length is 0.3 μm, particularly preferably 0.10 to 0.25 μm, and the major axis length / minor axis length is 2/1 to 25/1, preferably 3/1 to 15/1, and particularly preferably 4 / 1-12 /
1, and in the case of a plate, the plate diameter is 0.02 to 0.20.
μm, preferably 0.03 to 0.10 μm, particularly preferably 0.04 to 0.07 μm, and the plate diameter / plate thickness is 1/1.
˜30 / 1, preferably 2/1 to 10/1, particularly preferably 2.5 to 7/1.

The specific surface area (specific surface area S _BET ) of these ferromagnetic metal powders is 47 to 80 m ² / g, more preferably 53 to 70 m ² / g, and the coercive force (Hc) is 125.
0 to 2500 Oe, saturation magnetization (σ _S ) is 100 to 18
It is 0 emu / g, preferably 110 to 150 emu / g. Water content is 0.1 to 2.0% by weight, pH is 3-1
1 (5 g ferromagnetic powder / 100 g water) is preferred. The surface of these ferromagnetic metal powders is impregnated with a rust preventive agent, a surface treatment agent, a dispersant, a lubricant, an antistatic agent, etc., which will be described later, in a solvent for each purpose and is adsorbed. May be.

As the ferromagnetic metal powder, the metal content is 60% by weight or more, and 70% by weight or more of the metal content is at least one type of ferromagnetic metal powder or alloy (eg Fe, Fe--Co, Fe-Co-Ni, Co, N
i, Fe-Ni, Co-Ni, Co-Ni-Fe), and other components (eg, Al, Si, S, 40% by weight or less, more preferably 20% by weight or less) of the metal content. S
c, Ti, V, Cr, Mn, Cu, Zn, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
d, B, P) may be included in the alloy, iron nitride, iron carbide, and the like. In particular, in order to supplement the strength of metallic iron among these, it is desirable to provide Al, Si, or Cr individually or in a mixture on the surface layer. Further, the ferromagnetic metal powder contains a small amount of a hydroxide or oxide, an alkali metal element (Na,
K, etc.), an alkaline earth metal element (Mg, Ca, Sr), or the like. The method for producing these ferromagnetic metal powders is already known, and the ferromagnetic metal powder, which is a typical example of the ferromagnetic metal powder used in the present invention, can also be produced according to these known methods.

In particular, in the present invention, the following method can be mentioned as an example of the method for producing the ferromagnetic alloy powder used as the ferromagnetic powder. (A) Method of reducing complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen: (b) Reduction of iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles Method: (c) Method for thermally decomposing a metal carbonyl compound: (d) Sodium borohydride in an aqueous solution of a ferromagnetic metal,
Method of reducing by adding reducing agent such as hypophosphite or hydrazine: (e) Method of electrolytically depositing ferromagnetic metal powder using mercury cathode and then separating from mercury: (f) Metal at low pressure To obtain a fine powder by evaporation in an inert gas:

As the ferromagnetic powder used in the present invention, plate-shaped hexagonal barium ferrite can also be used. Barium ferrite has a particle size of about 0.001 to 1 micron and a thickness of 1/2 to 1/20 of the diameter. The specific gravity of barium ferrite is 4-6 g / cc, a specific surface area is 1m ² / g~70m ² / g. Also, if desired,
FeO _x (X = 1.33 to 1.50), Co-containing FeO
_X , etc. can also be used. As the non-magnetic powder that can be used in the back layer provided according to the need of the present invention,
For example, there are various powders as disclosed in JP-A-59-110038. That is, carbon black, graphite, tungsten disulfide, boron nitride,
Examples thereof include silicon dioxide, calcium carbonate, aluminum oxide, iron oxide, titanium dioxide, magnesium oxide, zinc oxide, calcium oxide, lithopone, talc and stannic oxide.

As the resin component of the binder used in the magnetic layer and back layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, ultraviolet curable resins, A visible light curable resin or a mixture thereof is used.

The thermoplastic resin has a softening temperature of 150 ° C.
Hereinafter, those having a number average molecular weight of 10,000 to 300,000 and a degree of polymerization of about 50 to 2,000, more preferably 2
It is about 0 to 600, and for example, vinyl chloride vinyl acetate copolymer, vinyl chloride polymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl vinylidene chloride copolymer, vinyl acrylonitrile copolymer, acrylic ester acrylonitrile. Copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon -Silicon-based resin, nitrocellulose-polyamide resin, polyvinyl chloride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (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 Resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber type thermoplastic resins, and mixtures thereof are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating solution,
By heating and humidifying after drying, the molecular weight becomes infinite due to reactions such as condensation and addition. 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 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 (PO) as functional groups in addition to the main functional groups. (OM) (OM)), phosphonic acid, sulfuric acid (OSO ₃ M) and acidic groups such as ester groups (M is H, alkali metal, alkaline earth metal, hydrocarbon group), amino acids, amino sulfone Acids, sulfuric acid or phosphoric acid esters of amino alcohols, amphoteric groups such as alkyl betaine type, amino groups, imino groups,
Imido group, amide group, etc., hydroxyl group, alkoxyl group,
Thiol group, alkylthio group, halogen group (F, Cl,
Br, I), a silyl group, a siloxane group, an epoxy group, an isocyanato group, a cyano group, a nitrile group, an oxo group, an acryl group, and a phosphine group are usually contained in one type or more and 6 types or less,
Each functional group is 1 × 10 ⁻⁶ equivalent to 1 × 1 per 1 g of resin.
It is preferable to contain 0 ^-2 equivalent.

As the curing agent, a polyisocyanate compound is usually used. Examples of the polyisocyanate compound used in the magnetic layer and / or the back layer of the present invention include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, Isocyanates such as isophorone diisocyanate, triphenylmethane triisocyanate, and isophorone diisocyanate, products of the isocyanates and polyalcohols, and polyisocyanates of 2 to 10 mer produced by condensation of the isocyanates, or triisocyanates It is possible to use, for example, a product of polyurethane and polyurethane having a terminal functional group of isocyanate. The average molecular weight of these polyisocyanates is 100 to 20.
000 is preferable. Commercially available trade names of these polyisocyanate compounds are Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL (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, Sumidule 44S, Sumidule PF, Sumidule 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 Z4273 (Sumitomo Bayer), etc. It can be used in combination of two or more utilizing the difference of. For the purpose of accelerating the curing reaction, hydroxyl groups (butanediol, hexanediol, molecular weight of 1000-100
A compound having an amino group (monomethylamine, dimethylamine, trimethylamine, etc.) or a metal oxide catalyst can also be used in combination. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanates have a total amount of binder resin and polyisocyanate of 10 in both the magnetic layer and the back layer.
It is preferable to use 2 to 70 parts by weight per 0 parts by weight, and more preferably 5 to 50 parts by weight. Examples thereof are JP-A-60-131622 and JP-A-61-161.
No. 74138, etc.

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 10 by weight.
The binder is used in the range of 5 to 300 parts by weight based on 0 parts by weight. The mixing ratio of the powder of the back layer and the binder is 8 to 400 parts by weight of the binder based on 100 parts by weight of the powder. As additives, carbon black,
Abrasives, lubricants, dispersants / dispersion aids, antifungal agents, antistatic agents, antioxidants, solvents and the like are added.

As the carbon black used in the magnetic layer and the back layer of the present invention, a furnace for rubber, a thermal for rubber, a black for color, an acetylene black and the like can be used. These carbon blacks are used for the purpose of preventing electrification of the tape, light-shielding agent, friction coefficient adjusting agent, and improving durability. Specific examples of these carbon black abbreviations in the United States are SAF, ISAF, IISAF, T,
HAF, SPF, FF, FEF, HMF, GPF, APF, SRF, MPF
, ECF, SCF, CF, FT, MT, HCC, HCF, MCF, LFF
, RCF, etc., and those classified in ASTM standard D-1765-82a of the United States can be used. The average particle size of these carbon blacks used in the present invention is from 5 to
1000nm (electron microscope), nitrogen adsorption method specific surface area 1-80
0 m ² / g, pH 4-11 (JIS K-6221-1982 method),
Dibutyl phthalate (DBP) Oil absorption is 10 to 800 mL
(ML) / 100g (JIS standard K-6221-1982 method). The size of the carbon black used in the present invention is
Carbon black of 5 to 100 nm is used for the purpose of lowering the surface electric resistance of the coating film, and 50% when controlling the strength of the coating film.
~ 1000 nm carbon black can be used.
In addition, for the purpose of controlling the surface roughness of the coating film, finer carbon black (less than 100 nm) is used for smoothing to reduce spacing loss. (100 nm or more) is used.
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 later, or may be grafted with a resin before use. 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. Hollow carbon black can also be used as the special carbon black.

These carbon blacks are preferably used in the magnetic layer in an amount of 0.1 to 30 parts by weight per 100 parts by weight of the ferromagnetic powder, and in the case of the back layer, the resin 1 is used.
It is desirable to use 20 to 400 parts by weight with respect to 00 parts by weight. 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 1972). Examples of these carbon blacks are U.S. Pat. Nos. 4,539,257, 4,614,685, and JP-A-61-924.
24, JP-A-61-99927 and the like.

The abrasive used for the magnetic layer and the back layer of the present invention is used to improve the durability of the magnetic recording medium and the head cleaning effect of the VTR, and is generally a material having an abrasive action or a polishing action. , Α-alumina,
γ-alumina, α, γ-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main components: corundum and magnetite), garnet, silica stone, nitriding Silicon, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, quartz, tripoly, diatomaceous earth, dolomite, etc., mainly having a Mohs hardness of 6 or more, more preferably a Mohs hardness of 8 or more up to 1 to 4 kinds. Used in combination. These abrasives have an average particle size of 0.005 to 5 microns and are used.
It is particularly preferably 0.01 to 2 microns. In the case of the magnetic layer, these abrasives are added in the range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. Further, in the case of the back layer, 0.
It is preferably used in an amount of 01 to 5 parts by weight. Specific examples thereof include AKP1 and AKP1 manufactured by Sumitomo Chemical Co., Ltd.
5, AKP20, AKP30, AKP50, AKP8
0, Hit50, Hit100 and the like. These are described in Japanese Patent Publication No. 52-28642.

As the powdery lubricant used in the magnetic layer and the back layer of the present invention, graphite, molybdenum disulfide, boron 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 There are fine resin powders such as fine resin powders and fine polyfluorinated ethylene resin powders.

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, fluoroalcohol,
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 perfluoroalkylbenzene sulfonic acid ester and perfluoroalkyl phosphoric acid ester, alkyl sulfuric acid ester, alkyl sulfonic acid ester, alkyl phosphonic acid triester, alkyl phosphonic acid monoester, alkyl phosphonic acid diester, alkyl phosphoric acid Organic acids and organic acid ester compounds such as esters and succinic acid esters, nitrogen-containing sulfur (hetero) ring compounds such as triazaindolizine, tetraazaindene, benzotriazole, benzodiazole, EDTA, etc. Composed of 40 monobasic fatty acids and one or more monohydric alcohols or dihydric alcohols having 2 to 40 carbon atoms, trihydric alcohols, tetrahydric alcohols and hexahydric alcohols Fatty acid esters Fatty acid esters consisting of monobasic fatty acids having 10 or more carbon atoms and monovalent to hexavalent alcohols having 11 to 70 carbon atoms in total with the carbon number of the fatty acids, fatty acids having 8 to 40 carbon atoms, or Fatty acid amides, fatty acid alkylamides, and fatty alcohols can also be used.

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 alkylamide, butoxyethyl stearate,
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 antioxidants (alkylphenol, benzotriazine, tetraazaindene, sulfamide) known as rust preventives are used. , Metal chelators such as guanidine, nucleic acid, pyridine, amine, hydroquinone, and EDTA), rust suppressants (naphthenic acid, alkenylsuccinic acid, phosphoric acid, dilauryl phosphate, etc.), oiliness agents (rapeseed oil, lauryl alcohol, etc.) , Extreme pressure agents (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.), detergent dispersants, viscosity index improvers, pour point depressants, foam depressants and the like. These lubricants have an amount of 0.
It is added in the range of 01 to 30 parts by weight.

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 and stearolic acid. , Fatty acids having 2 to 40 carbon atoms such as behenic acid, maleic acid and phthalic acid (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, etc.) or alkaline earth metal (Mg, Ca, Ba, etc.), metal soap (copper oleate) composed of NH ₄ ⁺ , Cu, Pb, etc., fatty acid amide; lecithin (soybean oil lecithin), etc. Is used. In addition to these, higher alcohols having 4 to 40 carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol) and their sulfuric acid esters, sulfonic acids, phenylsulfonic acids, alkylsulfonic acids, sulfonic acid esters, phosphoric acid monoesters, phosphoric acid diesters , Phosphoric acid triester, alkylphosphonic acid, phenylphosphonic acid, amine compounds and the like can also be used. Further, polyethylene glycol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid metal salt, sulfosuccinic acid ester and the like can also be used. These dispersants are usually used in one or more kinds, and one kind of the dispersant is 0.005 with respect to 100 parts by weight of the binder.
Is added in the range of ˜20 parts by weight. 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. Such materials are disclosed, for example, in JP-B-39-28369, JP-B-44-17945, JP-B-48-15001, US Pat. No. 3,387,993, and JP-A-347002.
No. 1 specification and the like.

The antifungal agent used in the present invention is 2- (4
-Thiazolyl) -benzimidazole, N- (fluorodichloromethylthio) -phthalimide, 10,10'-
Oxybisphenoxysarcin, 2,4,5,6-tetrachloroisophthalonitrile, P-tolyljodomethylsulfone, triiodoallyl alcohol, dihydroacetate, mercury phenyloleate, bis (tributyltin) oxide, salicylani There are rides.

Examples of such materials include "Microbial disaster and prevention technology", 1972 engineering book, "Chemistry and industry" 32,
904 (1979) and the like. As the antistatic agent other than carbon black used in the present invention, conductive powder such as graphite, modified graphite, carbon black graft polymer, tin oxide-antimony oxide, tin oxide, titanium oxide-tin oxide-antimony oxide; saponin, etc. Natural surfactants; alkylene oxide-based, glycerin-based, glycidol-based, polyhydric alcohols, polyhydric alcohol esters, nonionic surfactants such as alkylphenol EO adducts; higher alkylamines, cyclic amines, hydantoin derivatives, amidoamines, ester amides , Quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium, and other cationic surfactants; carboxylic acids, sulfonic acids, phosphonic acids,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, phosphonic acid esters, phosphoric acid ester groups; amino acids; aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, amphoteric surfactants such as alkyl betaine type Is 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 parts by weight per 100 parts by weight of the ferromagnetic powder. The amount used in the back layer is 0.01 to 3 per 100 parts by weight of the binder.
0 parts by weight. These are used as antistatic agents, but sometimes for other purposes, such as dispersion,
It may be applied as an improvement of magnetic properties, an improvement of lubricity, a coating aid, a wetting agent, a curing accelerator, or a dispersion accelerator.

The magnetic layer can be formed according to a usual method. For example, the ferromagnetic powder and the resin component and magnetic layer forming components such as an abrasive and a curing agent which are optionally blended are kneaded and dispersed with a solvent to prepare a magnetic coating, and the magnetic coating is applied to a non-magnetic support. It is possible to use the method of applying to. As the organic solvent used in the dispersion, kneading, and coating of the present invention, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran in any ratio; 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,
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde, hexane and the like can be used. These solvents are usually used in two or more kinds at an arbitrary ratio. In addition, a trace amount of impurities (polymer of the solvent itself, water,
Raw material components, etc.) may be included. These solvents are used in an amount of 100 to 20,000 parts by weight based on 100 parts by weight of the total solid content of the magnetic layer forming coating material, the back layer forming coating material and the undercoat liquid. The solid content of the magnetic layer-forming coating material is preferably 10 to 4
0% by weight. The solid content of the back layer coating material is preferably 5 to 20% by weight. An aqueous solvent (water, alcohol, acetone, etc.) can be used instead of the organic solvent.

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 preparing the magnetic layer-forming coating material and the back layer-forming coating material, a conventional kneading machine such as a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, and a zegbari (Sz
egvari), attritor, high speed impeller, disperser, high speed stone mill, high speed impact mill, disperser,
Kneader, high speed mixer, ribbon blender, cokneader, intensive mixer, tumbler, blender,
Dispersers, homogenizers, single-screw extruders, twin-screw extruders, ultrasonic dispersers, and the like can be used. Usually, a plurality of these dispersing / kneading machines are provided for the dispersing / kneading, and the treatment is continuously performed. For details of the technique regarding kneading and dispersion, see T.W. C. PATTON (TC Patton) "Paint Flow and Pigment
Dispersion "(Paint Flow and Pigment Dispersion), published in 1964 by John Wiley & Sons (John Willie & Sons) and Shinichi Tanaka," Industrial Materials, "Vol. 25, 37 (1977), and other references cited in the book. There is. As an auxiliary material for the dispersion and kneading, in order to efficiently carry out the dispersion and kneading, a steel ball having a diameter equivalent to a sphere of 10 cmφ to 0.05 mmφ
Steel beads, ceramic beads, glass beads, organic polymer beads can be used. Also, these materials are not limited to spherical shapes. Also, US Pat. No. 2,581,414
No. 2855156 and the like. 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 or 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
Prepared 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, bar coat, extrusion coat, spin coat, etc. can be used, and other methods are also possible. For a detailed explanation, see "Coating Industry" published by Asakura Shoten, pp. 253-277 (Showa 4
6.3.20. Issued).

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 multilayer coating, sequential multilayer coating and the like may be performed. These are disclosed, for example, in JP-A-57-123532 and JP-B-62-37451.

By such a method, about 1 to about 1 is formed on the support.
If necessary, the magnetic coating material applied to a thickness of about 200 μm may be dried in a multi-stage manner at 20 ° C. to 130 ° C. immediately after the ferromagnetic powder in the layer is dried at about 500 to 5000 G in a desired direction (vertical, longitudinal, width, random, oblique, etc.). ), That is, after the magnetic field orientation treatment, the formed magnetic layer is treated with
Dry to a thickness of 30 μm. The transport speed of the support at this time is usually 10 m / min to 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 0.1 to 40 mg. / (1/2 inch) / m ²
And

After drying in this way, the coating layer is subjected to calendering treatment if necessary. For calendar processing, for example, a super calendar roll or the like is used. By performing the calendering process, voids generated by removal of the solvent during drying are reduced and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained.

In the calendering step, when a curing agent is used as a binder-forming component, 90% by weight or more of the curing agent contained in the magnetic layer is usually contained in the magnetic layer in an unreacted state. Therefore, at least 50% by weight (particularly preferably 8%) of the curing agent is subjected to a curing treatment.
It is desirable to carry out the subsequent treatment after the reaction of 0% by weight or more). The curing treatment includes a heat curing treatment and an electron beam curing treatment, and any method can be used in the present invention. The unreacted curing agent contained in the magnetic layer calendered by this curing reaction reacts with a resin component such as a vinyl chloride copolymer and a polyurethane resin to form a three-dimensional network crosslinked structure. To do. The heat treatment process itself is already known, and the heat treatment can be performed according to these methods also in the present invention. For example, the heat treatment is usually performed by setting the heating time to 40 ° C. or higher (preferably within the range of 50 to 80 ° C.) and the heating time to usually 20 hours or longer (preferably 24 hours to 7 days). Further, the process itself of the curing treatment by electron beam irradiation is already known, and the curing treatment can be carried out according to these methods also in the present invention.

In the present invention, the magnetic recording medium thus prepared is cut into a desired shape under ordinary conditions by using an ordinary cutting machine such as a slitter, and then wound on a plastic or metal reel. In the present invention, the surface of the magnetic layer thus formed, or the surface of the magnetic layer and the surface of the back layer are magnetic recording media (magnetic layer, back layer, edge end surface, base surface) immediately before or before winding. May be burnished with a polishing tape. These are disclosed, for example, in JP-A-63-259830.
It is disclosed in Japanese Patent Publication No.

In the wiping treatment of the magnetic recording medium, the surface layer of the magnetic recording medium is made of a non-woven fabric or the like for the purpose of removing dirt on the surface of the magnetic recording medium and excess lubricant, and the magnetic layer surface, the back layer surface, the edge end surface and the back side base. This is done by wiping the surface. Examples of such wiping materials include various types of Vilene made by Japan Vilene and Toraysee made by Toray, Kuraray WRP series made by Exaine and Kuraray, and non-woven fabric made of nylon, non-woven fabric made of polyester, non-woven fabric made of rayon, non-woven fabric made of acrylonitrile, A blended non-woven fabric or the like can also be used. In addition, tissue paper, Kimwipe, etc. can also be used. These are described in, for example, JP-A-1-201824. By this wiping treatment, the deposits and organic substances on the magnetic layer and / or the back layer are completely removed, and the frequency of dropout or clogging is reduced.

These production methods include powder pretreatment / surface treatment, kneading / dispersion, coating / orientation / drying, calendar treatment, curing treatment (heat treatment, radiation (EB) treatment), cutting, burnishing treatment, and wiping. It is desirable to carry out the treatment and winding steps continuously. See also
The method shown in Japanese Patent No. 3181 is considered to be a basic and important technique in this field. However, the order of processing is not limited to the above order.

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.

Although the present invention describes the magnetic recording medium of the first invention and the magnetic recording medium of the second invention as separate inventions, the configuration of the first invention and the second invention. It goes without saying that a magnetic recording medium having the above structure also belongs to the category of the present invention.

[0051]

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 and comparative examples are parts by weight.

[Example 1] [I] of the following magnetic coating composition
Was placed in a kneader and sufficiently kneaded, then [II] was additionally charged and sufficiently kneaded, and [III] was added and mixed and dispersed before coating to prepare a magnetic coating material. After adjusting the viscosity of the obtained magnetic coating, polyethylene naphthalate (Young's modulus in MD direction 800 Kg / mm ² , TD
Direction Young's modulus of 750 Kg / mm ² ) and dry film thickness of 3μ
It was applied so that it would be m.

Magnetic coating composition [I] Ferromagnetic metal powder 100 parts (Fe metal powder containing 22 atom% of Co and 10 atom% of Al with respect to Fe, major axis length: 0.08 μm, specific surface area ( S _BET ): 57 m ² / g) Phosphate ester (phenylphosphonic acid) 2 parts Vinyl chloride copolymer resin 9.5 parts (Nippon Zeon Co., Ltd .: MR110) Polyurethane resin (Toyobo Co., Ltd .: UR8600) 5 parts 2 ethylhexyl palmitate 0.6 parts Cyclohexanone 60 parts Methyl ethyl ketone 80 parts [II] Dispersion 1 Carbon black 1 part (Mitsubishi Kasei: # 3250B) Polyurethane resin (Toyobo: UR8600) 1 part Methyl ethyl ketone 10 parts Dispersion 2 Polishing material 13 parts (by Sumitomo chemical Co., Ltd.: HIT55 [α-Al ₂ O _3] vinyl chloride copolymer resin, 1 part (Nippon Zeon (strain Made: MR110) Cyclohexanone 60 parts Methyl ethyl ketone 40 parts [III] Polyisocyanate 4 parts (Nippon Polyurethane Co .: Coronate 3040) Stearic acid amide 0.5 parts Palmitic acid 0.5 parts Butoxyethyl stearate 0.5 parts Methyl ethyl ketone 50 parts Toluene 30 parts The non-magnetic support coated with this magnetic coating is subjected to magnetic field orientation treatment and drying in a state where the magnetic coating is not dried, and then the back layer coating composition [I] below is coated with the same [II] immediately before coating. Was added to the back surface of the support coated with the magnetic paint so that the dry thickness was 0.6 μm.

Back layer coating composition [I] Carbon black 97 parts (Cabot Co .: BP800) Carbon black 3 parts (Cancarb Co .: MTCI) α-Al ₂ O ₃ 0.1 part (Sumitomo Chemical Co., Ltd.) : HIT55) 2-ethylhexyl stearate 0.5 part Copper oleate 0.1 part Vinyl chloride copolymer resin 50 parts (Nippon Zeon Co., Ltd .: MR110) Polyurethane resin 40 parts (Toyobo Co., Ltd .: UR8300) Cyclohexanone 200 parts Methyl ethyl ketone 300 parts [II] Polyisocyanate 20 parts (Nippon Polyurethane Co., Ltd .: Coronate 3040) Methyl ethyl ketone 3500 parts Toluene 200 parts Silicone compound 0.1 parts (Shin-Etsu Chemical Co., Ltd .: KF69) Temperature 90
℃, linear pressure 350Kg / cm, speed 200m / min 5
This was repeated to prepare a laminate composed of a non-magnetic support, a magnetic layer and a back layer.

This laminate was heated at 60 ° C. for 24 hours to cure the polyisocyanate compound contained in the laminate, and then slit into a 1/2 inch width under the following slit conditions. Slit speed 400 m / min Engagement depth 0.5 mm Peripheral speed ratio 1.05 After slitting, polishing tape (Fuji Photo Film Co., Ltd .:
The surface of the magnetic layer is subjected to burnishing treatment with K10000) and then a wiping material (WRP736 manufactured by Kuraray Co., Ltd.).
Was wiped off to prepare a 1/2 inch video tape.

[Example 2] A magnetic coating composition was prepared in the same manner as in Example 1 except that the magnetic coating composition [III] was changed to the following composition. [III] Polyisocyanate 4.5 parts (Nippon Polyurethane Company: Coronate 3040) Stearic acid amide 0.5 part Palmitic acid 0.5 part Butoxyethyl stearate 0.5 part Methyl ethyl ketone 50 parts Toluene 30 parts

[Example 3] A magnetic coating composition was prepared in the same manner as in Example 1 except that the slit composition was changed to the following composition. Slit speed 500m / min Engagement depth 0.7mm Peripheral speed ratio 1.05

Comparative Example 1 A magnetic coating composition was prepared in the same manner as in Example 1 except that the magnetic coating composition [III] was changed to the following composition. [III] Polyisocyanate 2 parts (Nippon Polyurethane Co .: Coronate 3040) Stearic acid amide 0.5 part Palmitic acid 0.5 part Butoxyethyl stearate 0.5 part Methyl ethyl ketone 50 parts Toluene 30 parts

Comparative Example 2 A magnetic coating composition was prepared in the same manner as in Example 1 except that the slit composition was changed to the following composition. Slit speed 200m / min Engagement depth 0.05mm Peripheral speed ratio 1.00

Comparative Example 3 A magnetic coating composition was prepared in the same manner as in Example 1, except that the slit composition was changed to the following composition. Slit speed 400m / min Engagement depth 0.9mm Peripheral speed ratio 1.05

[Evaluation Method] Volume of magnetic layer protruding portion: Magnetic layer protruding portion was image-processed with image processing software SALT-IV using a 100 × objective lens with a monochrome scanning laser microscope 1LM21 manufactured by Lasertec Corporation. Was calculated.

Number of cracks: The edge portion of the slit magnetic layer was observed at 400 times with a differential interference microscope, and the number of cracks per 1 mm of the edge portion was measured.

Guide stain: 90 using a D3 type video tape recorder (D350 manufactured by Matsushita Electric Industrial Co., Ltd.)
1 minute length tape in a temperature and humidity atmosphere of 23 ℃ 70% RH
The guide was continuously run 00 times, and the dirt on each guide in the VTR was visually observed. Dirty guide: No dirt is seen. △: Dirt was partially seen. ×: Dirt was seen on the entire surface.

Dropout: Using the above VTR, an initial value, the tape after repeated running was run, and the number of output drops of 5 μsec-8 dB or more was measured by a dropout counter. Table 1 shows the evaluation results of the magnetic recording media obtained in the above Examples and Comparative Examples.

[0065]

[Table 1]

[0066]

As is apparent from the examples of Table 1, the magnetic recording medium of the present invention has a volume of the magnetic layer protrusion of 0.03.
Less than 100 μm ³ per mm, especially 50 μm ³ or less, and / or the number of cracks at the edge portion of the magnetic layer is 1
Those having a number of 00 / mm or less had no head stains and few dropouts. On the other hand, those without any magnetic layer protrusion had a large frictional resistance and poor runnability, and there were also those in which the edge portion of the non-magnetic support was damaged and those in which the guide flange was scratched. . Further, when the volume of the protruding portion of the magnetic layer per 0.03 mm was 100 μm ³ or more, or the number of cracks at the edge portion of the magnetic layer exceeded 100 / mm, both head contamination and dropout were large.

[Brief description of drawings]

FIG. 1 is a diagram showing the shape of a magnetic layer protrusion of a magnetic recording medium of the present invention.

FIG. 2 is a diagram showing an edge portion of a magnetic layer of a magnetic recording medium of the present invention.

FIG. 3 is a diagram showing a slitter for cutting the magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Magnetic layer protrusion 3 Magnetic layer 4 Nonmagnetic support 5 Back coat layer 6 Dividing line 7 Crack 8 Guide flange 9 Tape running direction 10 Slitter 11 Magnetic recording medium original 12 Slitter upper blade 13 Slitter lower blade 14 Guide roller 15 pancake

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

Claims (2)

[Claims] 1. A magnetic recording medium obtained by providing a magnetic layer on one surface of a non-magnetic support and slitting it in the longitudinal direction, wherein a line drawn in the vertical direction from the apex of the largest protrusion of the non-magnetic support in the slit cross section. The volume of the magnetic layer portion projecting from the apex of the largest convex portion of the non-magnetic support divided into
A tape-shaped magnetic recording medium, characterized in that it is greater than 0 and less than 100 μm ³ per m. 2. A magnetic recording medium obtained by providing a magnetic layer on one surface of a non-magnetic support and slitting in the longitudinal direction, wherein the number of cracks at the edge portion of the magnetic layer is 0 to 100 /
A tape-shaped magnetic recording medium having a size of mm.