JPS59116922A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To make the surface roughness of a backing layer negligible and to make best use of the resilience of a radiation sensitive resin by dispersing a surfactant as a filler in a binder contg. said resin. dispersing a pigment therein according to need and curing the same thereby forming the backing layer. CONSTITUTION:A radiation sensitive resin contains >=2 pieces of such unsatd. double bonds which generate radicals by radiations and produce a crosslinked structure, in a molecular chain. The production of such structure is also possible by the radiation sensitive modification of a thermoplastic resin which is acrylic double bonds, etc. such as acrylic acid, methacrylic acid or their ester compd. exhibiting unsatd. double bonds having radical polymerizability. The surfactant as a filler has no effect of preventing the electrification of the backing layer unless it is contained at about 1pt.wt. or above by the weight of the resin, and if it is contained at >=20pts.wt., exudation on the surfaces arises and is undesirable. A pigment is adequately added according to need to suppress the exudation of the surfactant in the backing layer and the transfer thereof to the magnetic layer on a storage at high humidity.

Description

Detailed Description of the Invention The present invention relates to a magnetic recording medium, and more particularly to a thin film magnetic recording medium in which a ferromagnetic thin film is formed on a support by electroplating, chemical plating, vacuum evaporation, sputtering, ion blating, etc. By using a surfactant such as carbon black or graphite in the back layer of the media, the surface roughness of the back layer can be ignored and the flexibility of the resin in the bank layer can be fully utilized. The present invention relates to an improved magnetic recording medium.

Magnetic tape is now widely used in audio, video, and computer applications. Along with this, the amount of information recorded on media has increased year by year, and media are increasingly required to have high recording density.

In current recording methods using magnetic heads, the spacing loss between the tape and the head is 546 T [dB] (d
:Tape-head distance (recording wavelength). As can be seen from this equation, in short wavelength recording with high recording density, the rate of output reduction due to d2 and spacing is significantly larger than that in long wavelength recording. Therefore, even if a small foreign object is on the tape surface, it will be detected as a dropout.

Possible causes of dropouts include magnetic powder falling off from the surface of the magnetic tape deposited film due to deterioration of the paint film due to repeated stress, the base being scraped off during running, or static electricity caused by dust, etc. Examples include those that stick to the base surface and then transfer to the deposited film surface. To prevent these problems, for example, for the latter cause, a paint made by mixing carbon black or graphite with an organic binder is applied to the support surface (bank surface) opposite to the magnetic surface of the magnetic tape to strengthen the base. l
Methods have been devised to reduce the amount of scratches on the scale base. Through these processes, the tendency for dropouts to increase due to repeated driving can be suppressed. However, this level is not perfect, and there is a need to further reduce dropouts. The applicant has conducted a detailed investigation into the cause of this phenomenon and has published the results in Japanese Patent Application No. 54362/1983. Usually thermoset resins are used as binders. In that case, after the backing layer is applied, the tape is wound up and subjected to a heat curing treatment. However, at the time when the coating is finished, the trench hardening reaction has not started in the bank layer, and the coating film is weak. Hacked coatings containing carbon black, graphite, or other inorganic fillers tend to transfer to the magnetic layer surface on the opposite side with which they are in contact, resulting in dropouts and I found out that it was the cause of the head clogging. It is thought that a similar phenomenon of scalloping may occur even in thermoplastic resins. By providing a backing layer, it is possible to suppress an increase in dropouts due to repeated running, but this is the reason why dropouts are not so low when the number of runs is small.

In order to eliminate the above-mentioned problems in the back layer forming process, radiation-sensitive resin (resin that can be cured by irradiation with radiation) is used.
After forming a back layer with a paint mixed with carbon black or graphite or other inorganic fillers as a binder, it is irradiated with radiation from an active energy ray source and subjected to a curing treatment, or the surface is coated as is. After the treatment, a curing treatment is performed to create three-dimensional crosslinking in the back layer, creating a strong coating film, and then winding up the tape, which reduces dropouts caused by the causes mentioned above. be. According to this method, the tape is wound up after the crosslinking reaction of the coating film has finished.
Even if the back layer comes into close contact with the magnetic layer by winding, no transition from the back layer to the magnetic layer occurs.

However, unless a large amount of carbon black, graphite, etc. is incorporated into the resin, there will be no effect on charging. Therefore, the surface roughness of the bank layer becomes a problem, and the output of the magnetic layer decreases.

In order to solve these drawbacks, the present invention uses surfactants instead of carbon blanks, graphite, etc., and takes antistatic measures, so that the surface roughness of the bank layer can be ignored. Since the flexibility of the resin can be fully utilized, this has the advantage of increasing output.

The radiation-sensitive resin used in the present invention is one that contains two or more unsaturated double bonds in its molecular chain so that radicals are generated by the radiation vessel 1 to form a crosslinked structure, and this is also a thermoplastic resin. It is also possible to make the radiation sensitive to radiation.

Specific examples of radiation-sensitive modification include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which exhibit an unsaturated double bond that has Lovecal polymerizability, and allylic double bonds such as diallylphthale-1. This method involves introducing into the molecule a group that can be crosslinked or polymerized and dried by radiation irradiation, such as a double bond or an unsaturated bond such as maleic acid or a maleic acid derivative.

Other unsaturated double bonds that can be crosslinked and polymerized by radiation irradiation can be used.

Thermoplastic resins that can be modified into radiation-sensitive resins are shown below.

(a) Vinyl chloride copolymer vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer Polymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, such as UCC's VROH+ VYN
C.

Examples include VYEGX and UCC's VERR.

An acrylic double bond, a maleic acid double bond, and an allylic double bond are introduced into the above copolymer by a method described later to effect radiation sensitivity modification.

(b) Saturated polyester resins Saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid and ethylene glycol, diethylene glycol/l/l, di-IJ serine, trimethylolpropane.

By ester bonding with polyhydric alcohols such as 12-propylene glycol, 1.3-phthanediol, dipropylene glycol, 14-butanediol, 16-hexanediol, pentaerythritol, nrubitol, glycerin, neopentyl glycol, 14-cyclohexane dimetatool. The resulting saturated polyester resin or a resin obtained by modifying these polyester resins with S Oa Na or the like (Pylon 53S). Radiation sensitivity degeneration is performed using the methods described below.

(C) Unsaturated polyester resin A polyester compound containing a radiation-curable unsaturated double bond in its molecular chain, for example, consisting of an ester bond between a polybasic acid and a polyhydric alcohol as described as the thermoplastic resin in item (b). Examples include unsaturated polyester resins, prepolymers, and oligomers containing radiation-curable unsaturated double bonds in which part of the polybasic acid is maleic acid in saturated polyester resins.

Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in Section (ah), and examples of the radiation-curable unsaturated double bond include maleic acid, fumaric acid, etc. .

The radiation-curable unsaturated polyester resin is manufactured by a conventional method by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohol components, that is, in the presence of a catalyst.
After dehydration or dealcoholization under a nitrogen atmosphere at ~200℃, the temperature is raised to 240~280℃ and 0.5~1■Hg
A polyester resin can be obtained by a condensation reaction under reduced pressure. The content of maleic acid, fumaric acid, etc. in the acid component is 1 to 40 mol, preferably 10 to 30 mol, in view of crosslinking during production, radiation curability, etc.

(d) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components. The hydroxyl groups contained in these resins are subjected to radiation sensitization modification by a method described later.

(e) Ester resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, epichlorohydrin, and methyl epichlorohydrin - manufactured by Ciel Chemical (Epicoat 152, 154° 828.1001.10
'04,1007) Made by Dow Chemical (DEN 431
, DER732, DKR511゜DER331), manufactured by Dainippon Ink (Ebikuron-400゜Ebikuron-8o
o), Furthermore, phenoxy resin (PKHA, pKHc, PKHH manufactured by UCC, which is a high polymerization degree resin of the above epoxy), a copolymer of brominated hisphenol A and epichlorohydrin, and a copolymer of brominated hisphenol A and epichlorohydrin, manufactured by Dainippon Ink and Chemicals (Evicron 145, 15)
2,153°1120) etc.

Radiation sensitivity modification is performed using the epoxy groups contained in these resins.

(f) Cellulose derivatives Cellulose derivatives of various molecular weights are still effective as thermoplastic components. Among these, particularly effective ones are nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, acetyl cellulose, etc., and radiation sensitivity modification is carried out by utilizing the hydroxyl groups in the resin by the method described later.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacecool resins, Acrylic resins containing at least one type of acrylic ester and methacrylic ester containing hydroxyl groups as mold synthesis components are also effective.

Furthermore, by blending a thermoplastic nidistomer or prepolymer with the radiation-sensitive modified thermoplastic resin,
An even tougher coating film can be obtained. Furthermore, as discussed below, these elastomers or pre-J'J
Mothers are also more effective if modified to be radiosensitive. Listed below are elastomers or prepolymers that can be combined with the radiation-sensitive resin.

(g) Polyurethane elastomers, prepolymers, and telomers Polyurethane elastomers are particularly effective in terms of good abrasion resistance and good adhesion to PET films.

Examples of such urethane compounds include 2,4-)luenediiso7ane-l-,2,
6-Toluene diisocyanate, 13-xylene diisocyanate, 14-xylene diisocyanate, 15-
Naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate 1. 331
~Dimethyl-44'-diphenylmethane diisocyanate, 4.4. '-diphenylmethanecyinoaanate,
33'-7 methylbiphenylene diisocyanate, 4.
Various polyvalent isocyanates such as 4'-biphenylene diisocyanate, hexamethylene diisocyanate, influorone diisocyanate, dicyclohexylmethane diiso/anate Desmodur L and Desmodur N, and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin.

Trimethylolpropane, 14-butanediol.

16-hexanediol, pentaerythritol.

Sorbitol, neopentyl y-/l/,
1.4=Condensation polymerization of a polyhydric alcohol such as cyclohexane dimetatool with a saturated polybasic acid such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid), line Polyurethane elastomers, prepolymers, and zolomers are made of condensation products of various polyesters such as saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic esters, and hydroxyl-containing methacrylic esters. It is valid.

These elastomers may be combined as they are with various radiation-sensitive thermoplastics, but elastomers may also have an acrylic double bond or allylic double bond that reacts with the terminal incyanate group or hydroxyl group of the urethane distomer. Modification to radiosensitivity by reacting with monomers is very effective.

(h) Acrylonitrile-butadiene copolymer elastomer "Acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD Liquid Resin manufactured by Thomas Sinclair Petrochemical Co., Ltd., or Hiker 14'32J manufactured by Nippon Kaon Co., Ltd. Nidistomer is particularly suitable as an elastomer component in which the double bonds in the tsukudiene generate radicals by radiation and are crosslinked and polymerized.

(1) Holiftazoene Elas l-A prepolymer having a low molecular weight terminal hydroxyl group such as PolyBD Liquid Resin R-15 manufactured by Sinclair Petrochemical Co., Ltd. is particularly suitable from the viewpoint of compatibility with thermoplastic cleavage. R
Since the -15 prepolymer has a hydroxyl group at the end of the molecule, it is possible to increase radiation sensitivity by adding an acrylic unsaturated double bond to the end of the molecule.
It is even more advantageous as a binder.

7-1 Polybutadiene cyclized product Japan Synthetic Rubber cB
R-M90] also exhibits excellent performance when combined with a thermoplastic resin. In particular, cyclized polybutadiene has good crosslinking polymerization efficiency due to the radiation inherent in polybutadiene, and has excellent properties as a binder.

Suitable low thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber and its cyclized product (Nippon Synthetic Rubber Co., Ltd. 0 engineering R70), epoxy modified rubber, internal Plasticized saturated linear polyester (Toyobo Vylon-A 300) and other nidistomers can also be effectively used by subjecting them to the radiation-sensitizing modification treatment described below.

It is known that some macromolecules disintegrate when exposed to radiation and others that cause cross-linking between molecules. Are there polyethylene or polypropylene that cause cross-linking between molecules? Polystyrene, polyacrylic ester, polyacrylamide, polyvinyl chloride.

These include polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. If such a crosslinked polymer is used, the crosslinking reaction will occur even without the above-mentioned modification, so it can be used as it is as a bank coat resin for radiation crosslinking.

Furthermore, according to this method, even solvent-free resins that require the use of solvents can be cured in a short time, so such qt4 resins can also be used for back coats.

The surfactant as an antistatic agent used in the present invention is
As anionic types, carboxylates, sulfuric acid derivatives, phosphoric acid derivatives, pentaalkylpolyphosphate-hexaalkyltetrapolyphosphate.

These include dialkylphosphonic acids and sulfonic acids. Examples of the trench cation type include amines, quaternary ammonium salts, imidasolines, amine oxidized ethylene adducts, and quaternary phytic acids.

Nonionic types include polyhydric alcohols, polyhydric fluoric esters, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, amide ethylene oxide adducts, amine oxide ethylene adducts, amides, and the like.

As an amphoteric type, it is alkaline with carboxylic acids, sulfonic acids, metal salts, alkyl betaines, etc.

If the amount of surfactant is less than 1 part by weight relative to the resin (τ), there will be no antistatic effect on the back layer, and if it is more than 20 parts by weight, it will bleed onto the surface, which is undesirable.

By adding an acrylic double bond to the end of the lubricant, CH2-CHCo
OR, CB2=CHC0NHCH2000R(Blic
, B2. , -1CnH2n-1CnH2n-1, etc.), it improves dispersibility and lubricity, and the acrylic double bond generates radicals by radiation treatment, and the radicals generated in the binder component. It reacts with other materials to form a strong bond, resulting in even better surface properties and improved electromagnetic properties.

In addition, 5i02. TiO2, AL203CI'2
03. SiC, CeO2, CaCO2, zinc oxide, goethite + &F C2C3+ talc, kaolin, CaS
O4, 1 element on the nitriding side, Teflon powder, graphite fluoride, molyphane disulfide, zirconia, Ca5i02. asbestos,
Titanium white, white carbon, chrome yellow,
Oil yellow, oil blue, and oil letto are added as appropriate.

Furthermore, it is not always necessary to use one type of surfactant and pigment, but two or three types may be mixed.

The active energy ray used for crosslinking the back coat of the present invention is an electron beam using a radiation accelerator as a source.
'R-rays using Co60 as a radiation source, 6-rays using 5r90 as a radiation source, and X-ray generators! Chi-rays as a source, ultraviolet irradiation, etc. are used.

In particular, as an illuminating radiation source, it is advantageous to use radiation in a radiation heater from the viewpoint of controlling the absorbed dose, introducing it into the manufacturing process line, and blocking ionizing radiation.

The radiation characteristics used when curing the back layer are as follows:
From the perspective of penetrating power, a radiation accelerator with an accelerating voltage of 100 to 750 KV, preferably 150 to 300 KV is used to reduce the absorbed dose to 0.
It is convenient to irradiate to between 5 and 20 Megalands.

When curing the back layer of the present invention, a low-dose type radiation accelerator (Electro Curtain System) manufactured by 11 Energy Sciences Inc. in the US and an accelerator manufactured by RP Co., Ltd. are introduced into the tape coating processing line, and two inside the accelerator are used. This is extremely advantageous for shielding secondary X-rays.

Of course, a van de Graaf type accelerator, which has been widely used as a radiation accelerating material, may also be used.

However, when performing radiation crosslinking, it is important to irradiate the backing layer with radiation in an inert gas stream such as N2 gas or He gas, and irradiating the back layer with radiation in the air will cause radiation irradiation during crosslinking of the binder component. This is extremely disadvantageous because the radicals generated in the g+) mer due to the influence of 03 etc. generated by the above are inhibited from working advantageously in the crosslinking reaction.

Therefore, the atmosphere of the area to be irradiated with active energy rays is
Especially N2 + Hθ with a maximum oxygen concentration of 1%.

It is important to maintain an atmosphere of an inert gas such as CO2.

In the case of ultraviolet irradiation, add 1 to
Contains a photopolymerization sensitizer of 10% by weight.

In the case of ultraviolet rays, the influence of inert gas is less than that of electron beams, so irradiation in the atmosphere is possible.

If the amount of pigment is too large, the coating film will become brittle. Therefore, 200 parts by weight or less is appropriate.

Furthermore, magnetic tapes that should be provided with such a back layer include audio tape, video tape, computer tape, and endless tape. It is quite effective to use it for tape.

As a method for depositing the magnetic layer, for example, a cobalt/nickel (atomic ratio 8/2) alloy ingot is prepared, and a long ferromagnetic thin film is formed on a polyethylene terephthalate base by vacuum deposition.

The vapor deposition is performed by electron beam heating, and a so-called oblique vapor deposition method with a central incident angle of 70° is employed. A cylindrical can is used to cool the base film, and the cooling temperature is maintained at 5°C. Evacuate the vacuum chamber to 3X10”Pa and add oxygen gas to it at a pressure of 6
．． Vapor deposition is performed by introducing the electron beam until it reaches 3×10 ”, Pa. The film thickness is adjusted to about 800 A by adjusting the power given to the electron gun and the driving speed of the base film.

The ferromagnetic thin film thus obtained has a coercive force of approximately 100
00e, B, and r are about 8000G, which is advantageous as a magnetic recording medium.

On the other hand, M E K / of the resin compositions (a) and (g)
) Luene (1/1) 3wt% in 0.3'wt% solution
of stearic acid is prepared, and this is applied onto the ferromagnetic thin film using a gravure coating method. After coating, the solvent was dried using hot air and an infrared lamp, and the surface was smoothed. Using an electrocurtain type electron beam accelerator manufactured by Energy Sciences, N2 was applied at an acceleration voltage of 150 KV, an electrode current of 20 mA, and a total irradiation dose of 10 Mrad.
The coating film is cured by irradiating it with an electron beam under a gas atmosphere.

A videotape consisting of a film is obtained (sample A). The cross-linking of the protective film by this method involves both cross-linking due to radicalization of acrylic double bonds and cross-linking due to radicals generated in vinyl chloride vinyl acetate resin molecular chains (which is thought to be due to de-HCI conversion, but is not obvious). It is thought that it is working.

On the other hand, it is also effective to use a lubricant in the back layer depending on the purpose as described above.

Examples of photosensitizers include benzoin, benzoin methyl ether, and benzoin ethyl ether.

Penzoin inglobil ether9. J, anthraquino A compounds such as methylben, benzyl diacetyl: 7-enyl ketone compounds such as acetophenone and benzophenone, sulfide compounds such as diphenyl disulfide and tetramethylthiuram sulfide, nis-chloromethylnaphthalene, anthracene and hexachlorobutadiene, pentachlorobutane Examples include halogenated hydrocarbons such as gen. The photopolymerization sensitizer is desirably in a range of 01 to 10% based on the solid content of the resin.

Examples will be described below.

[Example 1] Acrylic modified polyurethane elastomer (g)
40 parts quaternary ammonium salt
7 parts mixed solvent Goo part The above mixture was dispersed in a ball mill for 5 hours, and the back side of the polyester film on which the magnetic surface was formed was coated with a dry thickness of 0.
The bank layer was coated at a ratio of 1/L4 and cured by irradiating the bank layer with an electron beam using an electrocurtain type electron beam accelerator at an acceleration voltage of 150 KV, an electrode current of IQmA, and an absorbed dose of 5 Mracl in N2 gas. take,]
The video was cut into //2' video rl, and the sensitivity (4 MHz) was measured using a VHS deck.

[Comparative Example 1] In Example 1, S was used instead of the quaternary ammonium salt]
, 02100 parts by weight were added.

As shown in Table 1, it can be seen that when the bank layer is made of a radiation-sensitive resin and a surfactant, there is an amplifier in sensitivity. It can be seen that the influence of the bank layer is significantly different.

[Example 2] Acrylic modified polyester (η・1 fat) 00
Phosphate ester derivatives that are more addictive than alcohol
2 parts mixed solvent 600 parts 0
2. Coating A [Example 3] Vinyl chloride, acid-acetate vinyl alcohol copolymer 60 parts Acrylic modified polyurethane elastomer 40 parts 3rd
grade amine 1 fat mixed solvent
600 copies Table 2 In 01μ coating Example 3, there was no problem when stored for a short period of 1 to 2 days under high temperature and high humidity, but if it was stored for more than 3 days, the surfactant in the bank layer would seep into the bank layer and adhesive would appear. I didn't like it when I came. When Pigment 5i02 was added, the adhesion was suppressed and there was only a slight decrease in output. Therefore,
It is effective to add pigments if necessary. This is shown in Example 4.

[Example 4] In contrast to Example 3, 5i02 20M Amount Part 1/A Application Table 3 Out of 5 grades, 1 is the best.

[Example 5] In contrast to Example 4, the above composition containing 03 parts of benzoin ethyl ether was irradiated with ultraviolet rays. The coating thickness was set to 17.

Table 4 Furthermore, as the amount of pigment increases, the electromagnetic conversion patent application also decreases by -1.
It was found that when the amount exceeds 200 parts by weight, the coating film becomes brittle. When the amount was within 200 parts by weight, the sensitivity was +Q, 46F or higher, which was good.

However, if necessary, it is also effective to add a moisturizer or the like to take advantage of the lubricating effect.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. That's true.

Patent Applicant Tokyo Denki Kagaku Kogyo Co., Ltd. Representative Sono Fukujibe Yumiso Moe Ne MJE Letter Interview with the Commissioner of the Japan Patent Office Mr. Kazuo 1. Indication of the case ■Kun 1957 Patent Application No. 225676 2. Name of the invention Magnetic recording Medium 3, Relationship with the case of the person making the amendment Patent applicant 4, Iseda Voluntary 8, Contents of the amendment I> The following after “It has become required” on page 2, line 19 of the specification: Add text.

``The types include video tape, computer tape, high performance audio tape, multiplexed code tape, magnetic disk, and floppy disk.

There are magnetic recording media such as magnetic cards. 2) "Coating film" on page 3, line 11 of the specification is corrected to "metal thin film."

3) "Magnetic powder falling off" on page 3, line 12 of the specification is corrected to "thin film scraping".

4) "Acidic acid vinegar" in the second line of page 25 of the specification is corrected to "acetic acid."

11

Claims (1)

[Claims] 1. In a magnetic recording medium in which a ferromagnetic thin film layer is provided on one side of a support and a back layer is provided on the other side, the back layer is used as a filler in a binder containing a radiation-sensitive resin. A magnetic recording medium characterized by being formed by dispersing and curing a surfactant and, if necessary, a pigment. 2. Pigment is 5iOz, Ti0z, A1203.0
r203+5IC9CeO2, CaCO3, zinc oxide,
Gusai), JFe203. Talc, kaolin, C
aS O4. Boron nitride, Teflon powder, graphite fluoride, molybdenum disulfide, zirconia, Ca5iO□, asbestos, white titanium, white carbon. The magnetic recording medium according to claim 1, which is chrome yellow, oil yellow, oil blue, or oil red. 3. The magnetic recording medium according to claim 1 or 2, wherein the radiation is an electron beam. 4. Further 1 to 10% by weight of radiation curing paint in the binder
3. A magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium contains a photopolymerizable sensitizer and a back layer is formed by irradiation with ultraviolet rays.