JPH01235021A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and traveling durability by incorporating at least a vinyl monomer which can be polymerized by radiation irradiation into the magnetic layer of the uppermost layer and incorporating the vinyl monomer into the magnetic layers except the uppermost layer at the ratio lower than in the uppermost layer or incorporating no vinyl monomer therein, then subjecting the magnetic layers to the radiation irradiation. CONSTITUTION:The vinyl monomer which can be crosslinked or polymerized by the radiation irradiation is incorporated into the magnetic layer of the uppermost layer. The content of the vinyl monomer is specified to the ratio lower in the lower layer of the magnetic layers than in the uppermost layer or the vinyl monomer may not be incorporated into the lower layer. The magnetic layers are crosslinked or polymerized by the radiation irradiation. The magnetic layers having the excellent adhesiveness, electromagnetic conversion characteristics, durability, etc., are thereby obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a magnetic recording medium having multiple magnetic layers.

In particular, the present invention relates to a magnetic recording medium containing a ferromagnetic alloy powder in a magnetic layer that has improved electromagnetic characteristics, head wear, and durability.

[Prior art]

Conventionally, magnetic recording media such as video tapes and audio tapes have been widely used in which a magnetic layer containing ferromagnetic iron oxide powder, ferromagnetic metal powder, etc. dispersed in a binder is coated on a non-magnetic support. There is. In particular, ferromagnetic metal powder has coercive force (
Hc) and is suitable for high-density recording.

In recent years, along with the increasing recording density of magnetic recording media,
Demand for high-quality image and sound quality is becoming higher and higher.
It has become necessary to improve electromagnetic conversion characteristics, especially to increase C/N (carrier-to-noise ratio) and lower 8N (bias noise).

In addition, the magnetic recording media currently widely used for -a are:
As a binder, there is a method of using thermoplastic resins such as vinyl chloride-vinyl acetate resin, vinyl chloride, vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, acrylonitrile butadiene resin, alone or in combination. This method has the disadvantage that the abrasion resistance of the magnetic layer is poor and the running path of the magnetic tape is contaminated.

Also known are methods of using thermosetting resins such as melamine resins and urea resins, or methods of adding crosslinking binders such as isocyanate compounds and compounds having epoxy rings to the thermoplastic resins through chemical reactions. There is. However, when using the above-mentioned crosslinking binder, 1) there is a problem in the storage stability of the dispersion liquid in which fii particles are dispersed, and it is difficult to maintain the uniformity of the physical properties of the magnetic coating liquid and, by extension, the homogeneity of the magnetic recording medium. 2) A heat treatment step is essential for curing the coating film after application and drying, and it takes a long time.

In order to prevent these drawbacks, acrylic ester oligomers and monomers are used as binders, and after drying, they are cured by radiation irradiation [ff Methods for manufacturing magnetic recording media are disclosed in Japanese Patent Publication No. 47-12423 and Japanese Patent Application Laid-open No. 47-1363.
No. 9, JP-A-47-15104, JP-A-50-774
It is disclosed in various publications such as No. 33 and Japanese Unexamined Patent Publication No. 56-25231.

However, the manufacturing method disclosed in the above patent publication is highly advanced! A magnetic recording medium with magnetic conversion characteristics and durability could not be obtained.

[Problem to be solved by the invention]

In recent years, there has been a demand for higher image quality in magnetic recording media.

This requires closer contact between the magnetic layer surface and the video head and audio head.
It is important to improve the surface smoothness of the magnetic recording medium and to further dramatically improve the dispersibility of the ferromagnetic fine powder. The smoother the surface of the unidirectional layer, the greater the friction in the running system inside the video tape recorder.
As running tension increases, magnetic recording media are required to have increasingly severe running durability. For this reason,
Conventional manufacturing methods for magnetic recording media have not yielded magnetic recording media that have the smoothness of the surface of the magnetic layer, the dispersibility of the ferromagnetic fine powder, and the running durability.

The present inventors have developed conventional techniques such as a method using a thermoplastic resin or a thermosetting resin, a method of adding a crosslinkable binder by the above-mentioned chemical reaction, and a method of using a hardenable binder by radiation crosslinking. The present invention was achieved as a result of intensive research to improve the drawbacks. Therefore, the objects of the present invention are to provide properties that could not be achieved with conventional magnetic recording media, namely: 1) excellent electromagnetic conversion properties, 2) excellent dispersibility of ferromagnetic fine powder, and 3) storage of magnetic coating liquid. The object of the present invention is to provide a magnetic recording medium that has good stability and uniform performance, 4) has excellent running durability, and 5) does not require a heat treatment step for curing the coating film.

[Means to solve the problem]

The above problems can be solved by the method described below. That is, the present invention provides a magnetic recording medium having a plurality of magnetic layers formed by dispersing ferromagnetic powder in a compound that can be crosslinked or polymerized by radiation irradiation on a nonmagnetic support.
The uppermost magnetic layer contains at least a vinyl monomer that can be polymerized by radiation irradiation, the magnetic layers other than the uppermost layer contain less or no vinyl monomer than the uppermost layer, and the magnetic layer is irradiated with radiation. A magnetic recording medium characterized by:

In the present invention, the thickness of the uppermost magnetic layer is preferably 2 μm or less, and particularly the uppermost layer has an average long-sleeved grain length of less than 0.3 μm and a crystallite size of 30 μm as measured by X-ray diffraction.
The lower layer uses magnetic powder with a crystallite size larger than that of the upper layer, and the dry thickness of the top layer is 2.0.
So-called wet-on-wet method (sequential multilayer coating method or simultaneous multilayer coating method) to create a thin layer of μm or less
It is preferable that the magnetic layer is provided by multilayer coating.

The present inventors have found that a magnetic layer with excellent electromagnetic conversion characteristics and durability can be obtained by containing a vinyl monomer that can be crosslinked or polymerized by radiation in a magnetic layer and crosslinking or polymerizing it by irradiation with radiation. Shrinkage occurs during the polymerization process,
Adhesion with the support will be poor, but by making the magnetic layer into multiple layers as described above and reducing or eliminating the content of the vinyl monomer in the lower magnetic layer, the adhesion, electromagnetic conversion characteristics, and durability can be improved. A magnetic layer with excellent properties etc. could be formed.

The present invention will be explained in detail below.

The vinyl monomer that can be crosslinked or polymerized by radiation irradiation used in the magnetic layer (especially the upper layer) in the present invention is a compound having one or more carbon-carbon unsaturated bonds in the molecule, and includes (meth)acrylic esters, Examples include (meth)acrylamides, allyl compounds, vinyl ethers, vinyl esters, vinyl heterocyclic compounds, N-ruvinyl compounds, styrenes, acrylic acid, methacrylic acid, crotonic acids, itaconic acids, and olefins. It will be done. Among these, preferred are the following compounds containing two or more methacryloyl groups. Specifically, polyethylene glycol (meth)acrylates such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and penta Erythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentayrythritol hexa(meth)acrylate, tris(β-(meth)acryloyloxyethyl)isocyanurate, bis(β-
(meth)acryloyloxyethyl)isocyanurate,
or polyisosoameric (2,4-tolylene diisocyanate, 2.6-)lylene diisonanate, 1
, 3-xylylene diisocyanate, 1.4-xylylene diisocyanate, 1.5-knuck diisocyanate, m-phenyl diisocyanate, p-phenyl diisocyanate, 3,3-dimethylphenylene diisocyanate, 4.4 -diphenylmethane diisocyanate, 3,3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpropane), and hydroxy (meth)acrylate compound (2- Examples include reactive compounds with hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc.), and poly(meth)acrylates having two or more functional groups. These monomers may be used alone or in combination of two or more.

In the present invention, in addition to the above-mentioned vinyl monomer, other compounds crosslinkable or polymerizable by radiation in the magnetic layer include (A) polyvinyl chloride containing one or more i-groups and one or more carbon-carbon unsaturated bonds in the molecule; Type Compound (B) Urethane compounds each containing one or more polar groups and one or more carbon-carbon unsaturated bonds in the molecule can be used in appropriate combinations.

In the present invention, the total amount of the vinyl monomer and compound (A) and/or compound (B) used in each layer is 50% by weight or less, particularly 15 to
Preferably it is 40% by weight. However, as described above, in the present invention, the content of the vinyl monomer in the lower layer of the magnetic layer is lower than that in the uppermost layer, and the lower layer does not need to contain the vinyl monomer.

The polyvinyl chloride compound (A) containing one or more polar groups and one or more carbon-carbon unsaturated bonds in the molecule used in the present invention includes COJ, OH,
SOJ, SO2 gate, POIM□, OPO, M2 group (M
is a vinyl chloride polymer, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl propionate copolymer, and a carbon-carbon unsaturated bond. It is a copolymer such as a vinylidene chloride-vinyl acetate copolymer. Preferred polar groups are CO□H, SO, and M groups, and more preferred are Co and )l groups. The content of these polar groups is 10-1 per gram of polymer.
It is preferably about 7 to 10-' equivalents, more preferably 10-6 to 10-' equivalents, and most preferably 10-S to 5 Xl0-' equivalents. If it is outside this range, the dispersibility of the ferromagnetic fine powder will be poor and the electromagnetic conversion characteristics will also be significantly reduced. The average content of carbon-carbon unsaturated bonds is 1 to 20 per molecule, preferably 2.
0 molecular weight which is ~15 is 3,000 to 50.00
0 preferably 8,000 to 30,000. Outside this range, curing properties may be poor or durability may be poor.

These compounds are based on polyvinyl chloride polymers such as vinyl chloride-vinyl acetate copolymers,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate copolymer Polymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinylidene chloride-vinyl acetate-
Maleic acid copolymer, vinylidene chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-acrylic acid copolymer, vinyl chloride-vinyl acetate=
Vinyl chloride copolymers such as acrylic acid-vinyl alcohol copolymers, and these copolymers may be used after being saponified.

The carbon-carbon unsaturated bond can be introduced by modifying a part of the hydroxyl group or carboxyl group of these copolymers, or a part of the hydroxyl group generated by saponification. For example, a compound having an epoxy ring and a carbon-carbon unsaturated bond, such as glycidyl acrylate, may be reacted with a part of the hydroxyl group of the base polymer, or a part of the hydroxyl group or carboxyl group of the copolymer may be reacted with a polyfunctional isonolone. (e.g., 2.4-)lylene diisocyanate, 2-1., 2.6-)lylene diisocyanate, 1
．． 3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3-dimethylphenylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3,3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triad addition of trimethylolpropane, etc.) to remove the remaining NGO group. Active hydrogen compounds having a (meth)acryloyl group (hereinafter acryloyl group and methacryloyl group are collectively referred to as (meth)acryloyl group), such as (
Hydroxyalkyl (meth)acrylates such as meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, (meth)
Acrylamide, N-methylol (meth)acrylamide, etc.).

Furthermore, examples of methods for introducing polar groups include the following methods. A part of the hydroxyl group or carboxyl group of the above-mentioned pace copolymer,
Alternatively, a part of the hydroxyl group generated by saponification is reacted with one NGO group of a polyfunctional isocyanate, and the remaining NGO group is converted into CQ, H group, SO, lJ, 0P03
? It can be obtained by reacting a hydroxyl compound containing a lZ group or the like. It is also possible to introduce the polar group simultaneously with the introduction of the carbon-carbon unsaturated bond. Alternatively, a compound having both a polar group and a carbon-carbon unsaturated bond may be used. The method of introducing these groups is not limited to the above-mentioned method. Synthesis examples of these resins are given in JP-A Nos. 61-89207, 61-106605, and 5
It is disclosed in No. 7-40744, No. 59-8126, etc.

The resins that can be used in the present invention are not limited to these synthetic examples.

Urethane compound (B) containing one or more polar groups and one or more carbon-carbon unsaturated bonds in the molecule used in the present invention
The main chain skeleton is polyester, polyether,
Any of polyester ether, polycaprolactone, polycarbonate, etc. may be used. The most commonly used is polyester. Specific examples of dibasic acids used in these are palmic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanoic acid, maleic acid, fumaric acid, itaconic acid, trimethyladipic acid, hexahydro Phthalic acid, tetrahydrophthalic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, etc. can be used. Examples of dihydric alcohols include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 2,2-dimethylpropane-1,3 -Diol, 2,2-diethylpropane-
1,3-diol, fuclohexane-1,3-diol, cyclohexane-1,4-diol, cyclohexane-1,4-dimetatool, cyclohexane-1,3-dimetatool, 2,2-bis(4-hydroxyethoxy-
cyclohexyl)propane, 2,2-bis(4-hydroxyethoxy-phenyl)propane, 2,2-bis(4
-hydroxyethoxyethoxy-phenyl)propane, etc. can be used. It is also possible to use a lactone-based polyester skeleton made of T-butyrolactone, δ-valerolactone, ε-caprolactone, or the like. In addition, as polycarbonate type, 1,6-hexanediol,
1.8-octanediol, 1. Carbonic esters such as lO-decanediol can be used. As an isocyanate that forms a urethane bond, 2.4-)
lylene diisocyanate, 2.6-1-lylene diisocyanate, 1.3-xylylene diisocyanate, 1,
4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3-dimethylphenylene diisonanate, 4,4-diphenylmethane diisonanate, 3,3-dimethyl-4,4-diphthalate Polyvalent isocyanates such as enylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and tolylene diisocyanate triadduct of trimethylolpropane can be used. Further, a part of the dibasic acid and dihydric alcohol may be replaced with trivalent or higher acid and alcohol. Polar groups include CO□H, SO3, SO,
M, POJz, OPO3M2 groups (M is hydrogen, alkali metal, ammonium) and carbon-carbon unsaturated bonds may be present at the ends or side chains of the polyurethane.

The preferred type of polar group is CO□)lSsos
It is h. Further, a preferable carbon-carbon unsaturated bond is an acryloyl group. Methods for introducing these groups include 1) using a trivalent or higher acid or a dibasic acid containing a polar group instead of the above dibasic acid, 2) adding a polar group to urethane having an isocyanate group at the end. It can be obtained by reacting an active hydrogen compound containing one or more (meth)acryloyl groups and one or more 085 groups. Synthesis examples of these compounds include JP-A-59-17
No. 4660, No. 59-223712, No. 60-353
No. 22, No. 60-119626, No. 60-12076
No. 5, No. 61-77134, No. 61-222028, etc.

Compounds that can be used in the present invention are not limited to these disclosed examples.

The preferred amount of polar groups in the urethane compound used in the present invention is preferably 10-7 to 10-' equivalent per gram of polymer, more preferably lo-6 to 10
-4 equivalents, most preferably 10-5 to 5 x 10-
s equivalent. Molecular weight: 1,000 to 100.0
00, preferably from 2,000 to 50,000, particularly preferably from 3,000 to 30,000. If the amount of polar groups is out of this range, the dispersibility of the ferromagnetic fine powder will be poor, leading to a decrease in electric conduction conversion characteristics and deterioration of durability. The average content of carbon-carbon unsaturated bonds is 1.5 to 10 per molecule, preferably 2 to 10.
It is 8.

If the molecular weight is less than 1000, the magnetic layer of the obtained magnetic recording medium will be too strong, causing problems such as cracking when bent, and curling of the magnetic 8μ recording medium due to curing shrinkage after irradiation with radiation. Cheap. On the other hand, the molecular weight is 1
If it exceeds 00,000, the solubility of the urethane (meth)acrylate in the solvent tends to be poor, which not only makes it inconvenient to handle, but also makes it difficult to handle. This is not desirable.

The preferred composition ratio of the compound (A) and compound CB) is 20 to 90 parts by weight, 780 to 10 parts by weight, particularly preferably 30 to 80 parts/70 to 20 parts by weight. If the ratio of the compound represented by (A) is less than this ratio or the ratio of the compound represented by (B) is less than this ratio, durability cannot be obtained. Further, the amount of the vinyl monomer added is preferably 50 parts by weight or less, particularly preferably 15 to 40 parts by weight, based on the total parts by weight of the compounds represented by (A) and (B).

There are no particular restrictions on the ferromagnetic powder used in the magnetic layer of the present invention, and ferromagnetic iron oxide powders such as γ-Fe2O3, Fezes, or intermediate iron oxides thereof, such as FeO, (1,33<x≦1.5), may be used. , Co-Fed, (1,33< x
≦1.5), cobalt-containing ferromagnetic iron oxide, ferromagnetic metal powder, etc. can be used.

In this case, the fine ferromagnetic powder in the uppermost layer and the fine ferromagnetic powder in the lower layer may be the same or different.

In the present invention, the ferromagnetic fine powder used particularly in the uppermost layer is Co-Fe0 (1,
Cobalt-containing ferromagnetic iron oxide expressed by 33 The thickness of the uppermost layer in the present invention is preferably 2 μm or less, particularly 1 μm or less. The coercive force of the fine ferromagnetic powder in the uppermost layer is preferably 600 Oersteds to 5000 Oersteds.

The thickness of the magnetic layers other than the top layer is preferably 0.5 μm or more. If the thickness is less than about 0.5 μm, the uppermost layer is likely to be affected by the surface roughness of the heath, and the electromagnetic conversion characteristics may deteriorate.

Organic solvents used for dispersion and application of magnetic coating liquid include acetone, methyl ethyl ketone, methyl isobutyl getone,
Ketones such as cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether; ethyl ether, glycol dimethyl ether, glycol monoethyl ether,
Ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride,
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, and dichlorobenzene can be selected and used.

Furthermore, additives such as lubricants, abrasives, dispersants, antistatic agents, and rust preventives may be added to the magnetic coating liquid of the present invention. Saturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, fluorine compounds, etc. may be added when preparing the magnetic coating liquid, or after drying or irradiation. Dissolved in a solvent or applied directly to the surface of the magnetic layer, or
May be sprayed.

Materials for the support to which the magnetic coating liquid is applied include polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; polycarbonate, polyimide, polyamideimide, etc. In addition to plastics, non-magnetic metals such as aluminum, copper, tin, zinc, or non-magnetic alloys containing these, and plastics on which metals such as aluminum are vapor-deposited can also be used.

In addition, the forms of non-magnetic supports include films, tapes, sheets,
It may be a disk, card, drum, etc., and various materials are selected and sized as necessary depending on the form.

The thickness of the non-magnetic support is 5 to 100 μm, preferably 5 to 100 μm.
It is 80 μm.

In addition, the support of the present invention is used for the purpose of preventing static electricity, preventing transfer, preventing wow and flutter, improving the strength of magnetic recording media, and making the back surface matte. A so-called back coat may also be provided.

The coating method of the present invention uses a so-called wet-on-wet coating method in which a lower layer coating solution and an upper layer coating solution are applied in a wet state in a superimposed manner, and a sequential coating method or simultaneous multilayer coating method can be used to achieve favorable effects. is obtained.

As the wet-on-wet coating method, it is possible to use the coating methods shown in Japanese Patent Application Laid-open Nos. 61-139929 and 62-212933.

Note that when the coating thickness of the top layer is 1 μm, it is difficult to obtain the desired thickness unless a wet-on-wet method is used.

In the present invention, it is preferable to irradiate radiation after applying a magnetic paint and performing calender treatment, but it is also possible to perform calender treatment after irradiation. Alternatively, it is also possible to irradiate one more time.

The radiation irradiated to the magnetic layer of the present invention includes electron beam, γ
Although rays, β rays, ultraviolet rays, etc. can be used, electron beams are preferable. As the electron beam accelerator, a scanning method, double scanning method, curtain beam method, broad beam curtain method, etc. can be adopted. The electron beam has an accelerating voltage of 100 to 500 kV, preferably 150 to 300 kV, and an absorbed dose of 1 to 20 M.
rad, preferably 3 to 15 Mrad. When the accelerating voltage is less than 100 kV, the amount of energy transmitted is insufficient, and when it exceeds 500 kV, the energy efficiency used for polymerization decreases, making it uneconomical. As absorbed dose, I Mra
If it is less than d, the curing reaction is insufficient and the strength of the magnetic layer cannot be obtained.
If it exceeds 20 Mrad, the energy efficiency used for curing decreases, the object to be irradiated generates heat, and especially the plastic support deforms, which is not preferable.

The present invention will be explained in more detail below using Examples and Comparative Examples. In the following Examples and Comparative Examples, all "parts" indicate "parts by weight."

Example 1 A magnetic coating liquid having the following composition was mixed and dispersed in a ball mill for 50 hours. Yusei coating M (A) Co-FeOx 100 parts (x=1
．． 45, coercive force 9500e, average major axis particle length 0.20μ
m, crystallite size 1250 people BET specific surface area 50 bo/g) 10 parts vinyl chloride copolymer acrylate (acid value I3,
Molecular weight 20,000, average acryloyl group content 2.8
) molecule) Urethane acrylate 5 parts (acid value 10
, molecule 1 tlO,000, average acryloyl group content 3
trimethylolpropane triacrylate 5 parts stearic acid 1 part butyl stearate 2 parts oleic acid
1 part Cr2Ch (average particle size 0.3
μm) 5 parts carbon black
1 part methyl ethyl ketone 24
0 parts cyclohexanone 80 parts Magnetic coating liquid (B) Co-FeOx 100 parts (x =
1.45, coercive force 8800e, crystallite size 300 people,
BET specific surface area 35rrf/g) Binder composition 12 parts vinyl chloride copolymer acrylate (acid value 13, molecular weight 20,000, average acryloyl group content 2.8 pieces/molecule) urethane acrylate 8 parts (acid value 1
0, molecular weight 10,000, average acryloyl group content 3
(7 molecules) Trimethylolpropane tri 2 parts acrylate stearic acid 1 part butyl stearate 2 parts carbon black
2 parts methyl ethyl ketone
240 parts cyclohexanone 8
0 parts magnetic coating liquid (C) Magnetic coating liquid (D) which is the same as magnetic coating liquid (B) except that trimethylolpropane triacrylate is removed. The composition ratio is the same as that of the magnetic coating liquid (A) except that the binder used in the magnetic coating liquid (B) is used.

Magnetic coating liquid (E) Urethane prepolymer (Nippon Polyurethane Co., Ltd. +12) was used instead of urethane acrylate in magnetic coating liquid (C).
Same as magnetic coating liquid (C) except that 304) was used.

After dispersion, the surface roughness (Ra) is 0.008 at a thickness of 15 μm.
Each of the magnetic coating liquids described above was applied alone or in a multilayer structure (wet-on-wet coating method is used in the case of multilayers) to a polyethylene terephthalate support of ttm, and after orientation with a cobalt magnet, the solvent was dried (MAX 10
After 0'C), calendering was performed.

Next, it was irradiated with an electron beam at an accelerating voltage of 200 kV to an absorbed dose of 5 Mrad, and then sliced into 1/2 inch width.
Video magnetic tape samples Nos. 1 to 8 were obtained. The components and effects are summarized in Table 1.

Example 2 As in Example 1, a magnetic coating liquid with the following composition was mixed with a ball mill for 50 minutes.
Lost for 0 hours due to crosstalk.

Magnetic coating liquid (H) The magnetic coating liquid (A) had the same composition ratio as magnetic chamber a (A) except that the magnetic particles were changed as follows.

Metallic powder (coercive force 15600e, average major axis particle length 0.15 um crystallite size 180, BET specific surface area 56rrt/g) 100 parts ((1) In the Eff coating liquid (C), the composition ratio was the same as that of the magnetic coating liquid ((1)) except that the magnetic particles were changed as follows.

Metal (optional powder (coercive force 13000e, crystallite size 260, BET specific surface value 38rrf/g) 1
00 parts Magnetic coating liquid (J) The composition ratio was the same as that of the magnetic coating liquid (C) except that the magnetic particles in the magnetic coating liquid (C) were changed as follows.

100 parts of Co-FeOx (x=1
．． 45, coercive force 13000e, crystallite size 280 people,
BET specific surface area 45 bi/g) Magnetic coating liquid (K) The composition ratio is the same as that of magnetic coating liquid (H) except that the binder in magnetic coating liquid (H) is changed to the binder of magnetic coating liquid (B). .

Magnetic coating liquid (L) The composition ratio is the same as that of the magnetic coating liquid (H) except that the binder in magnetic chamber 1 (H) is changed to that of the magnetic coating liquid (C).

Surface roughness (Ra) 0.006μ at a thickness of 10μm after dispersion
Each of the above magnetic coating liquids was applied singly or in a multilayer (wet-on-wet method) to a polyethylene terephthalate support of 500 m, oriented using a cobalt magnet, and then the solvent was dried (?IAX110'C) and then calendered. I gave it. Next, the tape was irradiated with an electron beam at an accelerating voltage of 200 kV to give an absorbed dose of 7 Mrad, and then slit into a width of 8 mm to obtain video magnetic tape samples Nα9 to Nα13. The components and effects are summarized in Table 2.

Evaluation method VS (clB) Relative value when 8M1lz video sensitivity C-4 tape measured with amorphous hend is expressed as OdB.

C/N (dB) Noise level at a distance of 0.1 MHz from 8 MHz and 8
Relative value when ratio with MHz sensitivity, sample Nα7 (Example 1) and sample tJn14 (Example 2) are set to OdB.

Still life (minutes) The time until the painter's S/N drops by 6 dB when playing back in still mode.

Number of clogging free commercially available VHS video tape recorders (NV-8200 manufactured by Kenko Denki Sangyo Co., Ltd.) and 8II 1m video recorders (
Fujix-8) was run at a normal running speed, and the number of times until clogging occurred was investigated.

Adhesion Strength A part of the magnetic tape slit into 1/2 inch medium and 8n+Il width is attached to a glass plate with double-sided adhesive tape, and the peel strength is measured when one end of the magnetic tape is pulled in the same direction as the other end. The measurement temperature and humidity conditions are 2350% l? It is H.

[Effects of the Invention] The magnetic recording media (samples kl~3.5.9-11) having the binder combination of the present invention have good magnetic conversion properties (
VS, C/N), and it can be seen that the adhesion strength is high and the running durability (still life, clogging) is excellent.

Representative patent attorney (8107) Kiyotaka Sasaki (3 idiots) +’c　　　　Procedural amendment document December 2, 1986

Claims (1)

[Claims] (1) In a magnetic recording medium having a plurality of magnetic layers on a nonmagnetic support, in which fine ferromagnetic powder is dispersed in a compound that can be crosslinked or polymerized by radiation irradiation, at least the uppermost magnetic layer is irradiated. 1. A magnetic recording medium comprising a vinyl monomer polymerizable by a magnetic recording medium, wherein magnetic layers other than the uppermost layer contain less or no vinyl monomer than the uppermost layer, and the magnetic layers are irradiated with radiation.