JPS60217526A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which decreases curling and drop-out by forming a back coat layer coated with a mixture composed of a lubricating agent sensitive with and curable by radiations and a resin sensitive with and curable by radiations on the rear of a substrate on which a magnetic recording layer is provided. CONSTITUTION:The back coat layer contg. 0.1-50pts.wt. the lubricating agent curable by radiations such as ester of a fatty acid of 7-30C having >=1 polymerizable unsatd. double bonds and alcohol of 1-30C, olefin-modified silicone oil, (meth)acrylic compd. having a molecular chain exhibiting lubricity, etc. together with 100pts.wt. the resin sensitive with and curable by radiations is provided on the rear of the non-magnetic substrate on the front of which the magnetic layer is formed. The magnetic recording medium having the back coat layer and the thin ferromagnetic layer on the inside and which prevents curling prevents drop-out, is highly resistant to wear, is of the coating type having no tack between the magnetic layer and the back coat layer and can be quickly cured by irradiation of electron rays is thus obtd.

Description

[Detailed description of the invention] Industrial applications The present invention relates to magnetic recording media.

Specifically, by backcoating a thin film type magnetic recording medium in which a ferromagnetic thin film is formed on a support or a coated and removable magnetic recording medium in which a coating film is formed on a support, the coefficient of friction is reduced. The present invention relates to a magnetic recording medium that reduces curling with a ferromagnetic thin film layer on the inside, making it possible to reduce dropouts.

BACKGROUND OF THE INVENTION At present, magnetic recording media are widely used in the fields of magnetic tapes for audio and video, magnetic disks for computers, word processors, and the like. Along with this, the number of information layers recorded on the magnetic recording medium is increasing year by year, and the recording medium is increasingly required to have a high recording density. However, when forming ferromagnetic 1IyA using methods such as electroplating, chemical plating, vacuum evaporation, sputtering, and ion blating, the ferromagnetic thin film formed is 100% metal, alloy, or oxide thereof. In addition, it can have high recording density. However, when a ferromagnetic layer is formed by the above method, the surface condition of the support strongly influences the surface condition of the ferromagnetic thin film.

It is desirable that the surface of the magnetic surface be smoother to reduce spacing loss with the magnetic head and reduce dropout. Also, the support for the meng is required to be smoother. However, if the support is smooth, it will stick to guide rollers or support pins when it is run as a magnetic tape, magnetic disk, or the like.

In view of these circumstances, the present inventors have proposed a magnetic recording medium equipped with a back layer that improves the various drawbacks of conventional magnetic recording media and exhibits extremely effective effects. . For example, a mixture of a thermoplastic resin typified by vinyl chloride-vinyl acetate copolymer, polyurethane, and an incyanate compound, or a mixture of this and nitrocellulose added thereto, is used as a binder, and non-magnetic powder is added thereto. By forming it as a dispersed layer, (1) it reduces the coefficient of friction on the back surface, (2) it reduces curling with the magnetic surface on the inside, and (3) it reduces the cinching phenomenon (loosening of the winding during sudden stops). ) and (4) prevention of adhesion between the magnetic surface and the back surface.

These technologies basically have a ferromagnetic thin film layer on one side of the support and a back layer on the other side, and the back layer consists of dispersing non-magnetic powder in a binder mainly composed of thermosetting resin. It can be said that it was mixed. In magnetic recording media having such a back layer, another problem has been recognized as compared to one without a back layer, and that is jitter. Jitter is a phenomenon in which screen shakes occur due to minute phase fluctuations. This jitter seems to be related to the smoothness of tape running.

OBJECT OF THE INVENTION Accordingly, an object of the present invention is to provide a novel magnetic recording medium. Another object of the present invention is to provide a magnetic recording medium that has low frictional resistance, can reduce curling with the magnetic recording layer inside, and can reduce dropouts.

The purpose of these developments is to provide a magnetic recording medium comprising a magnetic recording layer on one side of a support, coat the other side with a mixture of a radiation-sensitive curable lubricant and a radiation-sensitive curable resin, This is achieved by a magnetic recording medium characterized by having a back layer fixed by radiation.

Structure and Effects of the Invention The radiation-sensitive curable resin used in the present invention is a resin having one or more unsaturated double bonds in its molecular chain, which is cured by crosslinking or polymerization after generating radicals when irradiated with radiation. It is a resin containing. It is known that some polymeric substances disintegrate when irradiated with radiation, while others cause intermolecular crosslinking. Examples of the latter include polyethylene and polypropylene.

Polystyrene, polyacrylate, polyacrylamide, polyvinyl chloride, polyester.

Examples include polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrylolein, and such crosslinked polymers are used in the back coat layer.

Furthermore, the radiation-sensitive curable resin used in the present invention can also be prepared by radiation-sensitizing a thermoplastic resin, which is preferable from the viewpoint of curing speed and the like. A specific example of radiation-sensitive modification is acrylic acid, which exhibits an unsaturated double bond that is radically polymerizable.

Groups that can be crosslinked or polymerized and dried by radiation irradiation, such as acrylic double bonds such as methacrylic acid or their ester compounds, allylic double bonds such as diallyl phthalate, and unsaturated bonds such as maleic acid and maleic acid derivatives. It is introduced into the molecule. Other unsaturated double bonds that can be crosslinked and polymerized by radiation irradiation can be used.

Specifically, for example, there are the following.

(1) Vinyl chloride copolymer vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Vinyl chloride-vinyl alcohol copolymer, vinyl chloride-
These include vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer. Examples include Carbide's VROI-1°VYNQ, VYEGX, and VERR.

Furthermore, examples of vinyl chloride-based copolymers include carboxyl group-containing vinyl chloride-vinyl carboxylate co-brittle polymers, where (A>vinyl chloride).

There is a copolymer consisting of (B) carboxylic acid vinyl ester, (C) unsaturated carboxylic acid, and (D) unsaturated carboxylic acid anhydride and having an average polymerization fi of 100 to 400, which gives favorable results. In the production of the copolymer, specific examples of monomers to be copolymerized with vinyl chloride (A) include:
As the carboxylic acid vinyl ester (B), vinyl acetate,
Examples include vinyl propionate, vinyl versatate (trade name of Shell Co.), and vinyl acetate is preferred. Unsaturated carboxylic acids (C) include maleic acid, itaconic acid,
Examples include fumaric acid, acrylic acid, methacrylic acid, and maleic acid is preferred.

In the copolymer, vinyl chloride (A> is 5 of the sum of vinyl chloride (A) and carboxylic acid vinyl ester (B))
0 to 80% by weight. That is, vinyl chloride (A
If the amount exceeds 80% by weight based on the above sum, the viscosity of the solution increases due to mixing with the magnetic powder, so it is necessary to lower the viscosity of the paint when applying the magnetic paint to the substrate, and a large amount of solvent must be used. I will have to. On the other hand, vinyl chloride (A
If the amount of > is less than 50% by weight based on the above sum, the strength of the coating film surface will be weak, and the coating film may peel or block, which is not preferable. Furthermore, the copolymer contains vinyl chloride (
The amount of unsaturated carboxylic acid (C) is 1 to 5 parts by weight per 100 parts by weight of A) and carboxylic acid vinyl ester (B).

That is, if it is less than 1 part by weight, the reactivity with the thermosetting resin is weak, while if it exceeds 5 parts by weight, the reactivity with the thermosetting resin is rapid and the pot life of the paint is short, making it difficult to put it into practical use.

Moreover, the reason why the average degree of polymerization of the copolymer is set to 100 to 400 is that when it is mixed with a radiation-sensitive curable resin to be described later and applied to a substrate as a magnetic paint, the average degree of polymerization is 100 to 400.
If it is less than 00, the coating surface is weak and it is not practical, and if it is less than 4
If it exceeds 0.00, the viscosity of the paint becomes high, making it difficult to apply a highly concentrated solution. In addition, it is particularly preferable that the copolymer has an average degree of polymerization of 200 to 400 in view of the properties of the coated surface, the coating material, etc.

The above-mentioned vinyl chloride copolymer is produced by the method described later.
Radiation sensitivity modification is performed by introducing acrylic double bonds, maleic acid double bonds, and allylic double bonds.

(2) Saturated polyester resin Saturated polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid, and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1°2-propylene glycol,
Dipropylene glyconyl, 1,3-butanediol, 1
, 71-butanediol, 1,6-hexanediol,
Saturated polyester resins obtained by reaction with polyhydric alcohols such as pentaerythritol, sorbitol, neopentyl glycol, and 1,4-cyclohexane dimetatool, or resins obtained by modifying these polyester resins to 803 Na, etc. (e.g. Vylon 538) etc. These are also subjected to radiation sensitivity modification using the method described later.

(3) A polyester compound containing a radiation-curable unsaturated double bond in the unsaturated polyester resin molecular chain. For example, an ester bond between a polybasic acid and a polyhydric alcohol described as a thermoplastic resin in item (2).
Examples include unsaturated polyester resins, prepolymers, and oligomers containing radiation-curable unsaturated double bonds in which a portion of the polybasic acid is an unsaturated polybasic acid such as maleic acid or fumaric acid. I can do it.

Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in Section (2), and examples of the radiation-curable unsaturated double bond include maleic acid,
Mention may be made of fumaric acid.

The radiation-curable unsaturated polyester resin is produced by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohol components, and then producing a 180 to 200 After dehydration or dealcoholization reaction in a nitrogen atmosphere, the temperature is raised to 240-280°C, and a polyester resin can be obtained by condensation reaction under reduced pressure of 0.5-111II11-1. The content of maleic acid, yafmaric acid, etc. is 1 to 40 mol% in the acid component, preferably 10 to 3 mol%, due to crosslinking during production, radiation curability, etc.
It is 0 mol%.

(4) Polyvinyl alcohol resin There are polyvinyl alcohol, butyral resin, acetal resin, formal resin, etc., and copolymers of these components. These resins are also subjected to radiation sensitivity modification of the hydroxyl groups contained therein by a method described later.

(5) Epoxy resin 1. Epoxy resin produced by the reaction of phenoxy resin bisphenol A with epichlorohydrin or methylepichlorohydrin (for example, Epikote 152.154.828.1001 manufactured by Shell Chemical Co., Ltd.).
16o4.1007, DEN 43 manufactured by Dow Chemical Company
1. DER732, DER511, DER331, Evicron 400° Evicron 800 manufactured by Dainippon Ink and Chemicals, etc., phenoxy resin of Union Carbide Co., Ltd., which is a high polymerization degree resin of the above epoxy (for example, PKH
A, PKHC, PKH)-1, etc.) Copolymers of brominated bisphenol A and Ebichlor [drift, e.g. Ebichlor 145, 152, 153 manufactured by Dainippon Ink and Chemicals Co., Ltd.
．． 1120) etc. These resins are also subjected to radiation sensitivity modification using the epoxy groups contained therein.

<6> mm cellulose derivatives of various molecular weights are also effective as thermoplastic components. Among them, the most effective are nitrified cotton, cellulose acetobutyrate, ethyl cellulose, and butyl cellulose.

Acetylcellulose and the like are preferred. These are also subjected to radiation sensitivity modification by utilizing the hydroxyl groups in the resin by a method described later.

(7) Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyether ester resins,
Polyvinylpyrrolidone resins and their derivatives (eg, vinylpyrrolidone-ethylene copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, hydroxyl group-containing acrylic or methacrylic resins, etc. can also be used.

Other usable binder components include monomers such as acrylic acid, methacrylic acid, acrylamide, and methacrylamide. Various polyesters are used as binders with double bonds.

Polyols, polyurethanes, etc. can be modified with acrylic compounds having dim bonds. By blending a polyhydric alcohol and a polycarboxylic acid as necessary, products with various molecular weights can be produced.

In addition, the above content describes only a part of the radiation-sensitive curable resin according to the present invention.

Further, in addition to the radiation-sensitive curable resin, a non-radiation-sensitive curable resin may be blended in an amount of not more than % by weight based on the sum of both. Examples of such non-radiation-sensitive curable resins include the above-mentioned polymers before radiation-sensitive modification used in the production of radiation-sensitive curable resins.

Further, by blending a thermoplastic elastomer or a prepolymer with the radiation-sensitive modified thermoplastic resin, an even tougher coating film can be obtained.

In addition, it is even more effective if these elastomers or prepolymers are similarly modified to be radiation-sensitive curable.

Examples of elastomers or prepolymers that can be used in the present invention include the following.

(1) Polyurethane elastomers and prepolymers and telomers Polyurethane elastomers are particularly effective in terms of abrasion resistance and adhesion to polyethylene terephthalate films.

Examples of such urethane compounds include 2.4-t-lylene diisocyanate, 2.6
-Drylene diisocyanate, 1゜3-xylylene diisocyanate, 1,4-xylylene diisocyanate 1-
11.5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3',3''-dimethyl-4,4'-diphenylmethane diisocyanate, 4.4'-diphenylmethane diisocyanate, 3.3'-dimethylbiphenylene diisocyanate, 4. Various polyvalent isocyanates such as 4'-biphenylene diisocyanate, hexamethylene diisocyanate, isotumelon diisocyanate, dicyclohexylmethane diisocyanate, Desmodur N, etc. and linear saturated polyesters (e.g., ethylene glycol, diethylene glycol, glycerin, Polyhydric alcohols such as methylolpropane, 1,4-butanediol, 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexanedimethanol, phthalic anhydride, isophthalic acid, Polycondensates with saturated polybasic acids such as terephthalic acid, maleic acid, succinic acid, and adipic acid), linear saturated polyethers (polyethylene glycol,
Polyurethane elastomers, prepolymers, telomers, etc. made of polycondensates of various polyesters such as polypropylene glycol, polydetramethylene glycol, etc.), caprolactam, hydroxyl-containing acrylic esters, and hydroxyl-containing methacrylic esters are effective.

These elastomers may be combined as they are with the various radiation-sensitive modified thermoplastic resins.

Furthermore, it is very effective to modify the polyurethane elastomer to be radiation sensitive by reacting it with a monomer having an acrylic double bond or allylic double bond that reacts with the isocyanate group or hydroxyl group at the end of the polyurethane elastomer. .

(2) Acrylonitrile-butadiene copolymer elastomer An acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as polyBD liquid resin manufactured by Sinclair Vetrochemical Co., Ltd., or an elastomer such as Hiker 1432J manufactured by Nippon Zeon Co., Ltd. In particular, it is suitable as a 2-stomer component in which the double bonds in butadiene generate radicals by radiation to cause crosslinking and polymerization.

(3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group such as PolyBD Liquid Resin R-15 manufactured by Sinclair Vetrochemical Co., Ltd. is particularly suitable in terms of compatibility with thermoplastic resins. Since the R-15 polymer has a hydroxyl group at the end of the molecule, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the end of the molecule, making it more advantageous as a binder.

Yota, polybutadiene cyclized product (manufactured by Japan Synthetic Rubber Co., Ltd. C
BR-M 901) also exhibits excellent performance when combined with thermoplastic resin. In particular, cyclized polybutadiene has excellent properties as a binder, as the efficiency of crosslinking polymerization through group 01 lines is high due to the radicals of the unsaturated bonds that polybutadiene originally has.

Other thermoplastic elastomers and other suitable prepolymer systems include styrene-butadiene rubber, chloride rubber, acrylic rubber, isoprene rubber and its cyclized product (CIR701 manufactured by Japan Synthetic Rubber Co., Ltd.), epoxy-modified rubber, internal Elastomers such as plasticized saturated linear polyester (Vylon #300 manufactured by Toyobo Co., Ltd.) can also be used effectively by undergoing radiation-sensitive modification treatment.

The radiation-sensitive curable lubricant used in the present invention is a compound (hereinafter referred to as a lubricant) that has an unsaturated bond that is sensitive to radiation and a molecular chain that exhibits lubricity. , C7-30 fatty acid having at least one polymerizable unsaturated double bond, C7
-30 unsaturated fatty acids and alcohols having 1 to 30 carbon atoms, olefin-modified silicone oils.

There are compounds that have a molecular chain exhibiting lubricity and an acrylic, methacrylic, or allylic double bond in one molecule.

Melting point -1 having at least one polymerizable unsaturated double bond
As fatty acids at 6 to 81°C, undecylenic acid (M, P
, 24.5°C), oleic acid (M.

P, 14℃), elaidic acid (M, P', 51℃)
゛.

Linoleic acid (M, P, -, 9°C), linoleic acid (M.

P, -11°C), erucic acid (M, P, 34°C).

Brassidic acid (M, P, 65°C), etc. In addition to soybean oil, linseed oil, tung oil, etc., ethyl linoleate.

Examples include isopropyl linoleate and butyl linoleate. Examples of olefin-modified silicone oils include F-412, 413, 414, and 41 manufactured by Shin-Etsu Silicone Co., Ltd.
5,,4'16. X-22-903゜X-47-300
, PSB-154, X-62-719, (RCOO)n
si (CI-12>4-n.

(RCOO)nSi(CH2):+-n. etc.

CH2CH20F3 For compounds in which a molecular chain exhibiting slipperiness and an acrylic, methacrylic, or allylic double bond are present in the molecule, the acrylic, methacrylic, or allylic double bond in the compound is: ○ 1 CH2= CH-C-0-1 H3 CI-12=C-C-1CH2= CH-CI-12-
0-CH2=CH-CONH-1 is desirable. Further, the formula of the substrate 1 of the above compound is CH3 CH2=CHCOOR, CH=C-COOR, if R is a linear or branched hydrocarbon group.

CH2=CI-1-CI-1200OR.

CH2=CHC0NHCHHz 0COR.

CH2=C(CH3)CONHCH20COR1CH2
0COCH=CH2CHOCOR, etc. C1-120COR as R is Cn H2n, n= Cn to127y Cn l
-12th-1 etc.

Furthermore, there are phosphoric acid esters, which have the structure R+ -0-P-0-R3 2 , where R+, R2 and R3 are C7-C3o linear alkyl or alkenyl groups, allyl alcohol, and hydroxyl group-containing acrylic esters. or NC7-C3o linear alkyl or alkenyl group, allyl alcohol, hydroxyl group-containing acrylic ester, which has a hydroxyl group-containing methacrylic ester as an essential component;
It can be any combination of a hydroxyl group-containing methacrylic ester and a hydroxyl group.

Furthermore, when R contains fluorine, the basic structural formula of the compound is CH3 CH2=CHC00R(CH2=C-C00Rf).

CH2=CI-1-CH2COORf.

C13 CH2=C-CH3CO-ORf.

Cl2 = Cz = Chh CH20CO'Rf, CH3 CR2=C-CI-12CI-120CORf.

Cl-12=CHC0NHCH20CORf, CH2'
0COCH=CH2 CHOCORf etc., and CH200OR as Rf
f is Cn F27L++, Cn F2. sn (C
H2) m (however, m=1 to 5)°, Cn F 27L++ 8 02 N CR2C1-1
2CIl F2n, +1 The lubricant is blended in an amount of 0.1 to 50 parts by weight, preferably 1 to 20 parts by weight, per 100 parts by weight of the radiation-sensitive curable resin. That is, if the amount is less than 0.1 part by weight, the effect of reducing frictional resistance will be insufficient, while if it exceeds 50 parts by weight, the dispersibility will decrease.

In this way, non-magnetic powder is blended into the back layer made of the composition comprising the radiation-sensitive curable resin and the lubricant, if necessary.

The non-magnetic powder blended into the back layer is one of the pigments or fillers known in the art.
One or more species are selected. These powders are added to adjust the surface unevenness and to enhance the reinforcing effect of the backing layer. The irregularities on the surface of the backing layer are largely involved in the above-mentioned scintching phenomenon, and the scintching phenomenon can be improved by providing appropriate irregularities. Also, the unevenness of the back layer affects the running properties of the tape.

It also affects the adhesion between the magnetic film and the back layer.

If the unevenness of the back layer becomes too rough, output fluctuations are likely to occur. It is necessary to select an appropriate back layer surface roughness for a specific combination of materials in order to reduce the cinching phenomenon and not cause output fluctuations. The particle size of the non-magnetic powder, the dispersion state of the contained particles, etc. determine the unevenness of the back layer.

As mentioned above, these non-magnetic powders play an important role in toughening the back layer and reducing wear of the back layer. In order to enhance the enhancement effect, hard powder such as abrasive powder may be used at least partially as the non-magnetic powder. Additionally, conductive powder may be included to provide an antistatic effect. Examples of non-magnetic powders that can be used include (1) conductive powders such as carbon black and graphite, (2) Si 02 , T! 02, AJ2
20a, Cr 2.03.

Si C, Ce 02 , Ca Coal, zinc oxide, goethite, α-1”e203. Inorganic fillers such as talc, kaolin, Ca5O3, boron nitride, graphite fluoride, molybdenum disulfide, etc. (1) and ( A combination of 2) is also used.A typical example is CaCo
3. carbon black, etc. The amount of the non-magnetic powder used is expressed in terms of weight, and for (1), the amount of binder 10 is expressed in terms of weight.
20 to 100 parts to 0 parts, preferably 20 to 150 parts
parts, and for (2) it is 10 to 300 parts, preferably 200 to 250 parts. That is, if the amount of non-magnetic powder used exceeds the above value, the back layer becomes brittle and
On the contrary, the disadvantage is that the number of dropouts increases.

The resin and non-magnetic powder are sufficiently mixed and dispersed in various devices such as a ball mill, a sand grind mill, a roll mill, an I&speed impeller disperser, a homogenizer, and an ultrasonic separation machine to obtain a back layer paint. This back layer paint is applied onto the nonmagnetic material by a conventional method. This coating film has a thickness of 0.1 to 3 μm on a dry basis, preferably 0.2 μm.
~2 μm.

In the present invention, when a solvent is used, acetone is used.

Methyl ethyl ketone, methyl isobutyl ketone.

Ketones such as cyclohexanone, alcohols that cannot be used with isocyanate thermosetting binders such as methanol, ethanol, isopropanol, butanol, ethers such as tetrahydrofuran and dioxane,
Dimethylformamide.

Diluents or solvents such as solvents such as vinylpyrrolidone and nitropropane, and aromatic hydrocarbons such as toluene and xylene are used.

The substrate to be coated is polyethylene terephthalate film, which is currently widely used as a magnetic recording medium, and for applications that require further heat resistance, polyimide film, polyamide-imide film, etc. are used, especially polyester film. In many cases, thin material bases are subjected to uniaxial or biaxial stretching treatment.

Regarding the binder for radiation-sensitive hardening type magnetic recording media according to the present invention, various antistatic agents, 9 dispersants, abrasives, etc. commonly used in the application are added in addition to the additives of the invention according to the application. It is also effective to do so.

As the active energy ray used for crosslinking the magnetic coating film in the present invention, an electron beam using an electron beam accelerator as a ray source is advantageous for the reasons described below.

However, there are other sources such as gamma rays and S
r Beta rays with a 9° source, X with an X-ray generator as a source
Lines etc. can also be used.

As an irradiation source, electron beam accelerators are recommended for the following reasons: absorption dose control, self-shielding of ionizing radiation for introduction into manufacturing process lines, ease of connection with sequence control of process line equipment, etc. is advantageous. Various types of electron beam accelerators have been put into practical use, including the Kotscroft type, bumpgraph type, commutative transformer type, iron-core insulated transformer type, and linear accelerator type, mainly due to differences in the method of generating high voltage 4Q. . However, when magnetic recording media are used for general purposes, most have a thin magnetic film thickness of 10 microns or less, and the high acceleration voltage of 1000 kV or more normally used in the above-mentioned accelerator is unnecessary. An electron beam accelerator with a low acceleration voltage of 0 OkV or less is sufficient. Although the cost of the system itself is lower in low acceleration voltage accelerators,
Moreover, it is even more advantageous in terms of equipment costs for shielding ionizing radiation.

Next, Table 1 shows the advantages of shielding equipment costs.

(Left below) Table 1 Accelerating voltage and shielding thickness Accelerating voltage kV Shielding Shielding thickness (clll) 150
Lead 0.5 20'O Lead 2 300 Lead 3 500 Concrete 85 750 Concrete 115 1.000 Concrete 125 2.000 Concrete 1 to 175 3.000 Concrete 190 [Radiation Utilization Research Bulletin Canned Page 8 (Atomic Energy Association of Japan) (quoted from August 11979)] As shown in Table 1, in an electron accelerator of 300 kV or less,
By using a lead plate (maximum 3 cm) as a shielding material to cover the entire acceleration tube surrounding the part to be irradiated with the electron beam, it is possible to sufficiently block the accelerating X-rays. For this reason, there is no need to separately provide an expensive electron beam irradiation chamber, and the system itself can be incorporated into a ceramic recording medium manufacturing line. It becomes possible to perform one curing process online.

A concrete example of such a system is the US Energy
Low voltage type electron beam accelerator (electrocurtain system) manufactured by Science Inc. (ESI)
, 810 companies' electron beam accelerators (broad beam systems)
A self-shielded scanning low-voltage electron beam accelerator manufactured by Polymer Physics, West Germany is suitable. 150
When the above-mentioned binder and coating film are cured using a low voltage accelerator of This is undesirable because it increases the adhesion of film shedding and, in video applications, the same adhesion to rotating cylinders. On the other hand, at an absorbed dose of 0.5 to 5 M rad, polymerization and crosslinking by electron beam are appropriate;
The back layer coating has an appropriate balance between flexibility and rigidity, and the wear resistance between the back layer heads is improved, and there is no head adhesion or cylinder adhesion, resulting in an excellent magnetic recording medium.

In addition, during radiation crosslinking, it is important to irradiate the recording medium with radiation in a stream of inert gas such as nitrogen gas or helium gas. is extremely porous, so irradiating it with radiation in the air will cause the radicals generated in the polymer to undergo an effective crosslinking reaction due to the effects of ozone, etc. generated by the radiation. impede work.

The effect is that not only the surface of the magnetic layer is porous, but also the inside of the coating film is affected by the inhibition of crosslinking by the binder. Therefore, the atmosphere in the area where the active energy rays are irradiated should have an oxygen concentration of at most 1%, preferably 3. OOOp
It is important to maintain an inert gas atmosphere of nitrogen, helium, carbon dioxide, etc. below pm.

In the present invention, the recording layer formed on one surface of the support may be a coated film or a ferromagnetic thin film. First, as a coated film, a magnetic paint made by dispersing magnetic powder with a thermosetting resin or an electron beam-sensitive curable resin is used to obtain a thickness of 0.5 to 20 μm, preferably 0.5 to 10 μm, after drying. It is coated in a similar manner and cured under heating or irradiation with radiation.

Thermosetting resins and radiation-sensitive curable resins used as binders in such magnetic paints include:
Commonly known items are used. Examples include those in which polyurethane 1-Las 1 hemer, prepolymer, telomer, isocyanate compound, etc. are blended with each of the polymers before modification or the resin after radiation-sensitive modification, and thermosetting resins.

Further, as the radiation-sensitive curable resin, there are the ones mentioned above, and the coating method and curing method are also as described above.

When the present invention uses a solvent, acetone is used.

Methyl ethyl ketone, methyl isobutyl ketone.

Ketones such as cyclohexanone, alcohols that cannot be used with isocyanate thermosetting binders such as methanol, ethanol, isopropanol, butanol, ethers such as tetrahydrofuran and dioxane,
Dimethylformamide.

Diluents or solvents such as solvents such as vinylpyrrolidone and nitropropane, and aromatic hydrocarbons such as toluene and xylene are used.

The magnetic powder used in the present invention is γ-Ft203
, Fe304. Co-doped 7-Fe2O3° CO-doped 7-Fe203-Fe3O4 solid solution.

Cr 02 , co-based compound coated type 7”-Fe203
゜CO-based compound coated type 1”e 304 (T-Fe
Also includes intermediate oxidation states with 203. Also, here CO
The system compounds are cobalt oxide and cobalt hydroxide.

A case is shown in which the magnetic anisotropy of cobalt, such as cobalt ferrite and cobalt ion adsorbates, is utilized in the coercive direction. ), and magnetic powders whose main component is a ferromagnetic metal element such as Go, Fe-Co, Fe-Co-N, Co-Ni, etc. It can be produced by a wet reduction method using a reducing agent such as Na1-14, by a dry reduction method using hydrogen gas after treating the iron oxide surface with a Si compound, or by vacuum evaporation in a low-pressure argon gas stream. Examples include methods. Also, single crystal barium f≧
Fine powder can also be used.

The above-mentioned magnetic fine powder may be in an acicular or granular form, and is selected depending on the intended use as a magnetic recording medium. For example, in the case of a needle-like shape, the average long axis is 0.1 to 1 μm, and the average short axis is 0.02 to 0.1 μm.
Those at the foot of the mountain are preferable, and in the case of granular forms, those with an average particle size of 0.01 to 0.5 μm are preferable.

In the case of a ferroelastic thin film, the magnetic layer is deposited by preparing a cobalt/nickel (atomic ratio 8/2) alloy ingot, and forming a long ferromagnetic thin film on a support by vacuum deposition. do. The vapor deposition is performed by electron beam heating, and a so-called oblique vapor deposition method with a central incidence angle of 70' is employed.

A cylindrical can is used to cool the base film, and the cooling temperature is maintained at 5°C. The vacuum chamber is evacuated to 3'x10-3 Pa, and oxygen gas is introduced into it until the pressure reaches 6.3x10-2 Pa for vapor deposition. The film thickness is adjusted to about 80 OA by adjusting the power applied to the electronic mirror and the driving speed of the support film.

The ferromagnetic thin film thus obtained has a coercivity of about 10
000e1 magnetic flux density IBr is 8000G, and a suitable magnetic recording medium can be obtained.

Examples and comparative examples of the present invention are shown below. The characteristics were measured or evaluated as follows.

(A) Coefficient of friction Wrap the magnetic tape around a polished aluminum cylinder with a diameter of 4Il1m at an angle of 180 degrees with the back surface inside, run at 2 cm7 sec, and measure the tension on the sending side and winding side. Then, I calculated it.

(B) Scinching phenomenon Using a commercially available VH3 type VTR, after fast forwarding the entire length of the tape, fast reversing was performed, stopping when 50 m remained, and fast reversing was roughly performed to the end. Thereafter, the winding state of the tape was visually observed. The case where there was no gap between the tape layers and the winding condition was good was rated O, and the case where a gap occurred between the tape layers was rated X.

(C) Abrasion of the back layer Using a commercially available VH8 type VTR, it was run 50 times at a temperature of 40° C. and a relative humidity of 80%, and then dirt inside the cassette case was observed.

The case where there is dirt is marked as X, the case where there is no dirt is marked as O, and the case in between is marked as △.

([)] The magnetic layer and back layer were wound up on an adhesive VHS reel and left in an environment at 60° C. for 5 days, and the adhesion status was visually evaluated.

O indicates no adhesion, and X indicates adhesion.
And so.

(E) Jitter Using a VH8 type VTR, the test was run 100 times at a temperature of 40° C. and a relative humidity of 80%, and screen shake was visually observed. The case where there is no screen wobbling is set as 0, and the case where there is screen shake is set as X.゛(F) A magnetic tape cut into 5 mm x 50 mm curls was placed on a smooth glass plate, and the case with no curl was set as O, the case with curl was set as X, and the case with large curl was set as xX.

(G) Surface roughness Determined by the 20-point average method from a chart obtained using Talystep (manufactured by TAYLOR-HOBSON).

Prior to Examples, resin synthesis examples will be shown.

Resin synthesis example (a) Hinyl chloride/vinyl acetate/vinyl alcohol 93/2
Copolymer 100 with a composition of 15% by weight and a molecular weight of 18,000
After heating and dissolving 238 parts of toluene and 95 parts of hexanone, the temperature was raised to 80°C, 7.5 parts of the following TDI adduct was added, further 0.002 parts of tin octylate and 0.002 parts of hydroquinone were added, and the mixture was heated to 82°C. The reaction is carried out in a N2 gas stream until the reaction rate of isocyanate (NCO) reaches 90% or more. After the reaction is completed, cool and methyl ethyl ketone 238
Add 1 part to dilute. The obtained resin composition is designated as <a>. Note that the molecular weight of this resin is 19,200.

Synthesis of TDI adduct 348 parts of tolylene diisocyanate (TDj) was heated to 80°C in a flask for 14 days in a N2 stream, and then 260 parts of 2-hydroxyethyl methacrylate (2-IEMA), 0.07 part of tin octylate, Hydroquinone 0.05
The mixture was added dropwise while controlling the cooling so that the temperature inside the reaction vessel was 80 to 85°C, and after the addition was completed, the mixture was stirred at 80°C for 3 hours to complete the reaction. After the reaction is complete, take it out, cool it down,
A white base-like TDI 21-I EMA adduct was obtained.

Resin synthesis example (b) 100 parts of butyral resin (a copolymer with a composition of 42/20155% by weight of butyral groups/acetal groups/vinyl alcohol groups and a molecular weight of 33,800) was mixed with 20'O parts of toluene and 200 parts of methyl isobutyl ketone. After heating and melting, 80
℃, added 128 parts of the same TDI adduct as in resin synthesis example (a'), further added 0.026 parts of tin octylate and 0.002 parts of hydroquinone, and at 80°C in N2 gas stream the NC0 reaction rate was 90% or more. Let them react until it happens.

After the reaction was completed, it was cooled and 238 parts of methyl ethyl ketone was added.
The diluted product is called (b). Note that the molecular weight of this resin is 42,000.

Resin synthesis example (c) Saturated polyester resin (Dynamite Nobel @L-
411) Isophorone diisocyanate synthesized according to resin synthesis example (a) by heating and dissolving 100 parts in 116 parts of toluene and 116 parts of methyl ethyl ketone and heating to 80°C.
Add 2.84 parts of adduct, further add 0.006 part of tin octylate, and 0.006 part of hydroquinone, and react at 80° C. in a N2 gas stream until the NCO reaction rate reaches 90% or more.

The resulting resin composition is referred to as (C). The molecular weight of this resin is 20,600.

Resin synthesis example (d) 291.2 parts of dimethyl terephthalate, 291.2 parts of dimethyl isophthalate, 64.8 parts of dimethyl maleate, 251.2 parts of ethylene glycol, 364.8 parts of 1,4-butanediol, 1, 81.2 parts of 3-butanediol and 4.0 parts of tetra-n-butyl titanate were charged into a reaction vessel, and after a demethanol reaction at 180°C in a N2 gas stream, the temperature was raised to 240-260°C and 0.5-1+nm 1 liter. A linear unsaturated polyester resin with a molecular fi of 8000 was obtained by the pressure condensation reaction.

Resin synthesis example (e) 20 parts of glycidyl methacrylate, 30 parts of butyl acrylate, 37.5 parts of toluene, and 37.5 parts of methyl isobutyl ketone were placed in a reaction vessel and heated to 80°C, and 60 parts of glycidyl methacrylate, 90 parts of butyl acrylate, 6 parts of benzoyl peroxide, 112.5 parts of toluene and 112.5 parts of methyl isobutyl ketone were added dropwise to 80
Reaction was carried out at ~90°C for 4 hours, 125 parts of Doriethanolamine and 0.5 part of hydroquinone were added and dissolved, and 40 parts of acrylic acid was added dropwise, followed by reaction at the same temperature until the acid value reached 5 or less. The resulting resin composition is referred to as (e). The molecular weight of this resin is 150,000.

Resin Synthesis Example (f) 10 parts of 2-hydroxyethyl methacrylate, 40 parts of butyl acrylate, 37.5 parts of toluene and 37.5 parts of methyl isobutyl ketone were placed in a reaction vessel, and after heating to 80°C,
30 parts of 2-hydroxyethyl methacrylate, 120 parts of butyl acrylate, and 8 parts of benzoyl peroxide as a polymerization initiator were dissolved in 112.5 parts of toluene and 112.5 parts of methyl isobutyl ketone.
℃ for 4 hours, and 330 parts of the main reactant was added with TDI-- synthesized according to the TDI adduct in Resin Synthesis Example (a).
Added 44 parts of acrylic alcohol adduct, 0.012 parts of tin octylate, and 0 parts of high i-quinone.
．． The reaction was carried out at 80° C. in the presence of 12 parts of 0.012 parts until the NGO reaction rate was 90% or more. The obtained resin composition is designated as (f).

The molecular weight of this resin is 15,000.

Resin Synthesis Example (9) 250 parts of Adeka Polyether P-1000 (polyether manufactured by Jimika Co., Ltd.), 3 parts of 2-hydroxyethyl, and 0.017 parts of tin octylate were placed in a reaction vessel, and after heating and dissolving at 80°C, 87.0 parts of TDI was added at a temperature of 80 to 90°C in the reaction vessel.
The solution is added dropwise while cooling so that the reaction rate is 80° C. After the completion of the dropwise addition, the reaction is allowed to proceed until the NGO reaction rate reaches 95% or more. The obtained resin composition is ((1>). The molecular weight of this resin is 1610.

Resin synthesis example (h) 250 parts of NIAX polyol PCP-0200 (Polycaprolactone manufactured by Chisso Corporation), 122.2 parts of 2-hydroxyethyl methacrylate, 0.024 parts of hydroquinone, and 0.033 parts of tin octylate were placed in a reaction can. 80℃
After heating and dissolving, 1163.6 parts of TD is added dropwise while cooling when the temperature inside the reactor reaches 80 to 90°C, and after the dropwise addition is completed, the reaction is allowed to occur at 80°C until the NCO conversion rate reaches 95% or more. The obtained resin composition is referred to as (h).

The molecular weight of this resin is 1140.

Resin synthesis example (+) After heating and dissolving 200 parts of Epicote 828 (epoxy resin manufactured by Shell) in 25 parts of toluene and 25 parts of methyl ethyl ketone, 27 parts of N,N-dimethylbenzylamine and 14 parts of hydroquinone were added, and the temperature was raised to 80°C. 69 parts of acrylic acid was added dropwise and reacted at 80°C until the acid value reached 5 or less. The obtained resin composition is designated as (i). The molecular weight of this resin is 5
It is 00.

Example 1 A cobalt/nickel (atomic ratio 8/2) alloy ingot was prepared, and a long ferromagnetic llll5 was formed on a polyethylene terephthalate base by vacuum evaporation. Vapor deposition was performed by electron beam heating, and a so-called oblique vapor deposition method with a central incidence angle of 70' was adopted. A cylindrical can was used to cool the base film, and the cooling temperature was maintained at 5°C. The vacuum chamber was evacuated to 3.times.10'lJa, and oxygen gas was introduced into it until the pressure reached 6.3.times.10.sup.-2pa for vapor deposition. By adjusting the power given to the electron gun and the driving speed of the base film, the film thickness was made to be approximately 800 mm.

The ferromagnetic thin film thus obtained has a coercivity of approximately 100
0 person, 3r was approximately 8000G, and a suitable magnetic recording medium was obtained.

On the other hand, prepare the resin composition (a) ((1) in which 3 wt% of stearyl acrylate is added to the MEK/toluene (1/1) 0.3 wt% solution, and apply this to the opposite side of the ferromagnetic thin film. It was coated using the 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 ESI, an acceleration voltage of 150 Kev and an electrode current of 20 mA were applied. N under the condition of total irradiation ffi10 Mrad
The coating film was cured by irradiation with an electron beam in a two-gas atmosphere.

The obtained tape was cut into 1/2 inch width to obtain a videotape consisting of a ferromagnetic thin film (Sample A). The crosslinking of the back coat film by this method is thought to be due to both the radicalization of the acrylic double synthesis and the radical (de)ICI formation generated in the vinyl chloride/vinyl acetate resin molecular chain, but it is not clear. It is thought that it is working.

Example 2 A back layer made of the resin composition (C) and (11) was formed on the same ferromagnetic thin film as used in Example 1 to obtain a videotape (Samples B and C). Similarly, the concentration of the solution was Q, 3 wt%, and 3 wt% of trifluoroechel acrylate was added.The conditions for curing by electron beam were also the same as in Example 1.

Comparative Example 1 Phenoxy resin (PKHH) manufactured by Union Carbide was mixed with 0.3 wt% of MEK/cyclohexanone (3,/1).
It dissolves well as a solution, and immediately before application, the solid content concentration is 7.
5%) was added and dissolved in an amount of 2 Qwt% based on the solid content of PKHH, gravure coated on the back layer of the same ferromagnetic layer film used in Example 1, dried by heating, and then dried and cured using an infrared lamp.

This was slit into 1/2 inch pieces to obtain a videotape (Sample D).

Comparative Example 2 Ultraviolet curing epoxy resin Azoka Ultraset (B'6
136J) to MEK/)-Lucon (1/1) Q, 3w
t% as a solution, and further dissolve the catalyst solution PS-33.
was added in an amount of 3 wt % based on the solid content of B6136J, and gravure coating was performed on the same ferromagnetic thin film back layer as used in Example 1. After heating and drying, the coating film formed was cured using an ultraviolet curing system having one each of 2 kW and 3 kW ultraviolet lamps. This was cut into 1/2 inch pieces to obtain a videotape (Sample E).

When the above characteristics were measured for these samples A, B, C, D, and E, the results shown in Table 2 were obtained.

Comparing the results of the Examples with these cases, it can be seen that each property is excellent and that a ferromagnetic thin film type magnetic recording medium provided with an electron beam hardened back layer can be put to practical use.

In the embodiments of the present invention, a so-called vapor deposition method is used to form a ferromagnetic thin film, but it is clear that sputtering, ion blasting, and other dry or wet thin film forming methods are also included as necessary from the spirit of the present invention. It is.

(Margin below) A B C magnetic layer and back layer Adhesiveness OOO Karl OOO back coat []E None >0.9 0.6~0,80.6~0.8Δ △　O X XX XX

Claims (2)

[Claims] (1) In a magnetic recording medium comprising a magnetic recording layer on one side of a support, a mixture of a radiation-sensitive curable lubricant and a radiation-sensitive curable resin is applied to the other side and cured by radiation. A magnetic recording medium characterized by comprising a back layer consisting of: (2) The magnetic recording medium according to claim 1, wherein the amount of the radiation-curable lubricant is 0.1 to 50 parts by weight per 100 parts by weight of the radiation-sensitive curable resin.