JPS59124029A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a superior magnetic recording medium free from curl, having a low coefft. of friction, and causing hardly drop-out while preventing after- cure by forming a protective film contg. a radiation-curing resin having unsatd. double bonds and a thermoplastic resin on the surface of a ferromagnetic thin film. CONSTITUTION:A coating liq. is prepd. by adding a lubricant to a soln. of a mixture of a radiation-curing resin having unsatd. double bonds such as acrylic modified urethane elastomer with a thermoplastic resin such as a vinyl chloride- vinyl acetate-vinyl alcohol copolymer. The coating liq. is applied to the surface of a ferromagnetic thin film formed on a support, and the solvent is evaporated by drying with hot air and an infrared lamp. The resulting film is cured by irradiating electron beams or the like in an inert gaseous atmosphere to form a protective film. Thus, a magnetic recording medium having a protective film with superior wear resistance is obtd. at a high curing reaction rate without causing sticking due to aftercure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film magnetic recording medium with excellent wear resistance.

Electroplating, chemical plating, vacuum deposition, sputtering,
Thin-film magnetic recording media, in which a ferromagnetic thin film is formed on a support by ion blating, etc., can reduce the thickness of the magnetic layer by an order of magnitude compared to conventional coating-type magnetic recording media, making it easier to record video signals. Although it is ideal for high-density recording, ferromagnetic thin films are extremely hard and wear out the magnetic head.
It also has the disadvantage of being subject to heavy wear. Therefore, it is practically necessary to form some kind of protective film on the surface, and a thermosetting protective film using a peroxide and an ultraviolet curing protective film using a photosensitizer have been proposed. However, in these products, curing reaction catalysts, photosensitizers, etc. are added, and although the resin as a protective film is cured, these additives may impede running properties or may interfere with the curing process (even after being wound into a roll). After-cure (occurs) causes adhesion to the back side of the base, and in extreme cases can even damage the surface of the protective film.

The effect is particularly severe under high temperature and high humidity conditions.

Furthermore, the curing reaction rate is slow, which is disadvantageous for high-speed application of protective film coatings.

Therefore, it is an object of the present invention to solve the above-mentioned problems in conventional ferromagnetic thin film magnetic recording media provided with a protective film. The present invention achieves the intended purpose by providing an excellent protective film for this type of magnetic recording medium, and the protective film is cured with radiation such as an electron beam (5).
(hereinafter referred to as radiation sensitive) unsaturated double bond-containing resin,
It is characterized by containing a thermoplastic resin. - Since the protective film of the present invention is cured by radiation such as electron beams, the use of conventional catalysts and additives is unnecessary, the above-mentioned problems are solved, and the wear resistance required for the protective film is improved. The effects of running stability and oxidation resistance of the magnetic thin film are exhibited. Moreover, in the present invention, the radiation-sensitive unsaturated double bond-containing resin is polymerized into a three-dimensional network structure by radical generation by radiation such as electron beams, and the polymerization process is instantaneous. Provides a smooth surface with a simple process without an after-cure process.

The inventor attempted to construct a protective film for a ferromagnetic thin film using only a radiation-sensitive resin, but the protective film became hard.
It was found that the hardness increased, the curl of the magnetic recording medium became more severe, and the electromagnetic properties deteriorated at high frequencies. Therefore, the present invention was able to provide a magnetic recording medium that does not have this problem and is far superior to the prior art by using a radiation-sensitive resin and a thermosetting resin in combination.

In such a combination, radiation-sensitive resin increases the hardness of the protective film through curing and makes it rigid, whereas thermoplastic resin softens such hardness and rigidity and imparts appropriate flexibility. The two types of resins work well together to reduce friction and prevent curling of the magnetic recording medium, and protect the magnetic head and magnetic film, improve running properties, and prevent curling. Output in the short wavelength range and video S/
N improves.

In order to satisfy the properties shown below, the mixing ratio of the thermoplastic resin and the radiation-sensitive resin or elastomer is particularly preferably 2:8 rather than 8:2.

In addition, in order for the thermoplastic A resin to impart excessive flexibility to the magnetic coating film, its molecular weight should be 5000 or more, preferably 8000.
The above is necessary for the molecular weight effect.

On the other hand, radiation-sensitive resins or elastomers are elastomers or preforms of elastomers that are obtained by crosslinking or polymerizing with radiation as a single substance and have excellent rubber elasticity, flexibility, and adhesion to polyester substrates as synthetic rubbers. Refers to polymers, oligomers, and telomers. As will be described later, this nidistomer is subjected to radiation-sensitivity modification to generate radicals and a crosslinked structure when exposed to radiation. Further, in order to use it as a coating for forming a protective film, this resin or nidistomer must be soluble in a solvent.

It is also desired that the thermoplastic resin and the radiation-sensitive elastomer or its prepolymer, oligomer, or telomer have good compatibility.

3-1 Examples of thermoplastic resins that are effective in the present invention include the following synthetic resins for coatings.

(I) 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, vinyl chloride-vinyl acetate-terminated QH side chain alkyl group copolymer, such as UCC VROH, VYN
C.

VYMClVYEC-X, VYMS-X, etc., UCC company V
ERR et al.

(II) Saturated polyester resin phthalic acid, isophthalic acid, terephthalic acid, maleic acid,
Saturated polybasic acids such as maleic acid derivatives, co-phosphoric acid, adividic acid, and sebacic acid, ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,2 propylene glycol, 1,3 butanediol, diethylene glycol, 1 .4 butanediol, 1.
Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 6-hexanediol, pentaerythritol, sorbitol, chrycerin, neopentyl glycol, and 1,4-cyclohexane dimetatool, or these polyester resins modified with 5Q3Na etc. A resin having an average molecular weight of 5000 or more is particularly desirable. (Pylon V530 manufactured by Toyobo Co., Ltd.) (Ill) Polyvinyl alcohol, polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components are also good.

(IV) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A and epichlorohydrin or methylepichlorohydrin, such as Shell Chemical (Epicor) 152,154°82-8.1001.100
7), Dow chemicals (DEN431, DER752
, DER511, DER331), Dainippon Ink (
Epicron 400. Epiclon aOO), the above-mentioned epoxy high polymerization resin 7:r-/# resin (PKHA, PKHC, PKHH) manufactured by UCC, and brominated bisphenol A and epichlorohydrin copolymer such as Dainippon Ink ( Epicron 145.152, 153.1
120) etc. are also effective.

(v) Cellulose cotton conductor Cellulose derivatives of various molecular weights are also effective as the thermoplastic component of the present invention. Among them, the most effective are nitrified cotton, cellulose acetoptylate,
Ethyl cellulose, butyl cellulose, acetyl cellulose, etc. are suitable.

The geothermal plastics include thermoplastic rigid polyurethane resins, polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacecool resins, and hydroxyl group-containing resins. Acrylic resins containing at least one type of acrylic ester and methacrylic ester as a polymerization component are also effective for the purpose of the present invention.

3-2 On the other hand, the radiation-sensitive resin or prepolymer to be combined with the thermoplastic resin is as follows.

(I) Polyurethane elastomers and prepolymers and telomers Examples of such urethane compounds include, as isocyanates, 2.4-) luene diisocyanate, 2.6
- Toluene diisocyanate, 1.3-xylene diisocyanate, 1.4-xylene diisocyanate, 1
．． 5-naphthalene diisocyanate, m-phenyl diisocyanate, P-phenyl diisocyanate,
3,3+-dimethyl-4,41-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate), 3,3'-dimethylbiphenylene diisocyanate, 4,4'-biphenylene diisocyanate, hexamethylene diisocyanate, infron diisocyanate, Dicyclohexylmethane diisocyanate, various polyhydric incyanates such as Desmodur L1 and Desmodur N, linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1.4-methanediol, 1.6-hexanediol, pentaerylene glycol, etc.) Slit, sorbitol, neopentyl glycol, polyhydric alcohols such as 1,4-chlorohexanedimethanol, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid,
(by condensation polymerization with a saturated polybase such as sebacic acid)
, polyurethane consisting of condensation products with various polyesters such as linear saturated polyethers (polyethylene glycol, polypyrene glycol, polytetraethylene glycol), caprolactam, hydroxyl-containing acrylic esters, hydroxyl-containing methacrylic esters, etc. Elastomers, prepolymers, and telomers are effective.

(n) Acrylonitrile-butadiene copolymer elastomer Elastomers such as the acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD liquid range manufactured by Sinclair Petrochemical Co., Ltd., or Hiker 1432J manufactured by Nippon Zeon Co., Ltd. The double bond in butadiene is suitable as an elastomer component for crosslinking and polymerization by generating radicals with electron beams.

In addition, those with terminal hydroxyl groups can be radioactive by adding an acrylic unsaturated double bond via diisocyanate, etc.
This is effective in further increasing sensitivity.

(II[) Polybutadiene Elastomer 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 plastics. R-15
Since the prepolymer 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 even more advantageous as a binder.

In addition, polybutadiene cyclized products Nippon Synthetic Rubber CB, R-
M 9101 also exhibits excellent performance in combination with thermoplastics. In particular, cyclized polybutadiene has high efficiency in crosslinking polymerization by radiation using radicals of unsaturated bonds inherent in polybutadiene, and has excellent properties as a binder.

Suitable geothermal plastic elastomers and prepolymers are chlorinated rubber, acrylic rubber, isoprene rubber, and their cyclized products (ClR70 manufactured by Nippon Synthetic Rubber Co., Ltd.).
Elastomers such as 1), epoxy-modified rubber, internally plasticized saturated linear polyester (Toyobo Vylon +3OO), etc. are also effective in the present invention when subjected to the radiation-sensitive modification treatment described below.

3-3 Specific examples of the electrosensitive modification described above include acrylic acid having an unsaturated double bond with radical polymerizability;
Molecules with groups that can be crosslinked or polymerized 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 to be introduced inside.

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

A more specific method of radiation sensitivity modification is to react one molecule of the above thermoplastic resin or its prepolymer having one or more hydroxyl groups in the molecule with one or more molecules of isocyanate groups of a polyisocyanate compound, and then react the isocyanate groups of one or more molecules of a polyisocyanate compound. A reaction product with one or more molecules of a monomer having a group that reacts with a group and one or more molecules of a monomer having an unsaturated double bond having radiation curability, for example, linear polycaprolactone pcP-2ooo (manufactured by Chisso Corporation) with toluene added to one hydroxyl group. Examples include resins having two or more acrylic double bonds at the terminals obtained by reacting one molecule of diisocyanate and then one molecule of 2-hydroxyethyl methacrylate, or prepolymers, oligomers, and telomers thereof.

In addition, the polyisocyanate compounds used in this N include 2,4-toluene diincyanate, 2,6-
Toluene diisocyanate, 1.3-xylene diisocyanate, 1.4-xylene diisocyanate, m-
phenylene diisocyanate), P-phenylene diisocyanate, hexamethylene diisocyanate, inphorone diisocyanate, desmodur L, fsmodur IL (manufactured by Bayer AG, West Germany), and the like.

Monomers having a group that reacts with an incyanate group and a radiation-curable unsaturated double bond include 2-hydroxyethyl ester of acrylic acid or methacrylic acid, 2-hydroxyethyl ester of acrylic acid or methacrylic acid;
Esters with a hydroxyl group such as hydroxypropyl ester and 2-hydroxyoctyl ester Monomers that have an active hydrogen that reacts with isocyanate groups and contain an acrylic double bond such as niacrylamide, methacrylamide, N-methylol acrylamide, etc. Furthermore, allyl alcohol, maleic acid polyhydric alcohol ester compounds, mono- or diglycerides of long-chain fatty acids having unsaturated double bonds, and other unsaturated double bonds having active hydrogen that reacts with incyanate groups and having radiation curability. Also included are monomers containing.

6-4 When using a solvent in the present invention, acetone,
Ketones such as methyl ethyl ketone, methyl imbutyl ketone, and cyclohexanone, incyanates such as methanol, ethanol, impropatol, butanol, alcohols that cannot be used in heat curing, and substances with ether bonds such as tetrahydrofuran and dioxane dimethyl formamide , vinylpyrrolidone, nitropropane, etc., and diluted aromatic hydrocarbons or solvents such as toluene, xylene, etc. are used.

As substrates used for coating, polyethylene terephthalate films, which are currently widely used as substrates for magnetic recording media, and polyimide films, polyamide-imide films, etc., are used for applications that require further heat resistance, and in particular polyester In the case of thin film, axial stretching or biaxial stretching is often applied.

For the radiation-curable protective film of the present invention, it is effective to use various antistatic agents, lubricants, dispersants, coating film strength reinforcing additives, etc. that are commonly used in the application as appropriate depending on the application.

Lubricants used in combination with the electron beam curable resin include CnH2n+3COOI ((n-14 to 22) higher fatty acids, CnH2n+108 (n = 14 to 22) higher fatty alcohols, esters of the above fatty acids and aliphatic alcohols, Acid amides etc. are effective.

In addition, silicone oligomers, fatty acid-modified silicone oils, fluorine oils, fluorinated polyesters (Dupont
, Krytowax, Validax, Monte Edison's Huonpurin), etc. are effective.

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

However, there are also γ-rays using Co60 as a source, Br
β-rays using a ray source of 90 mm, X-rays using an X-ray generator as a ray source, etc. are also used.

As an irradiation source, electron beam accelerators are used for the reasons of controlling the absorbed dose, self-closing ionizing radiation for introduction into the manufacturing process line, and ease of connection for sequence control with various process line equipment. is advantageous.

Conventionally, various types of electron beam accelerators have been put into practical use, such as the Kotscroft type, the bump graph type, the shared transformer type, the iron-core insulated transformer type, and the linear accelerator type, depending mainly on the method of obtaining high voltage.

Regarding the characteristics of the electron beam used when curing the protective film, in terms of penetrating power, it is convenient to use an electron beam accelerator with an accelerating voltage of 100 to 750 KV and irradiate at an absorbed dose of 0.1 to 5 megaland. It is.

In particular, in the case of magnetic tape, the coating thickness to be cured is small, so the low-m
An H-type electron beam accelerator (electrocurtain system) or the like is extremely advantageous for introduction into a tape coating processing line, for continuous secondary X-rays inside the accelerator, etc.

Of course, a van de Graaff accelerator, which has been widely used as an electron beam accelerator, may also be used.

In addition, during electron beam curing, it is important to irradiate the protective coating with an electron beam in an inert gas stream such as N gas or He gas; , inhibits radicals generated in the polymer due to the influence of 02, etc. generated by electron beam irradiation from effectively working on the crosslinking reaction. The effect is particularly noticeable on the surface of the magnetic protective layer. Therefore, the surrounding atmosphere of the part to be irradiated with radiation is N H
e, 1 It is important to maintain an inert gas atmosphere such as C02.

Next, the present invention will be specifically explained with reference to Examples.

Example: Synthesis example of radiation-sensitive paint a) Synthesis of acrylic modified urethane elastomer (
Electrosensitive elastomer) 250 parts of diphenylmethane diisocyanate (MDI)-based urethane prepolymer with terminal incyanate (Nipporan 4040 manufactured by Nippon Polyurethane), 32.5 parts of 2-hydroxyethyl methacrylate (HEMA), 0.07 part of hydroquine, Put 0,009 parts of tin octylate into a reaction can, heat and dissolve at 80°C, then add 43.5 parts of tolylene diisocyanate dropwise while cooling so that the temperature inside the reaction can becomes 80-90°C. The reaction is allowed to proceed until the NC0 reaction rate reaches 95% or more.

b) Synthesis of acrylic modified polyether-based urethane-terminated elastomer (electrosensitive elastomer) Polyether P'l'G-500 manufactured by Nippon Polyurethane Co., Ltd.
250 parts, 2HHMA 32.5 parts, hydroquinone 0,
007 parts of tin octylate and 0.009 parts of tin octylate were placed in a reaction can, heated and dissolved at 80°C, and then 43.5 parts of TDI was added dropwise while cooling the reaction can so that the temperature within the can became 80 to 90°C.
After the dropwise addition was completed, the reaction was allowed to proceed at 80° C. until the NCO reaction rate reached 95% or more.

C) Synthesis of acrylic modified polybutadiene elastomer (electrosensitive elastomer) Low molecular weight terminal hydroxyl group polybutadiene polyBD liquid resin R-15 manufactured by Sinclair Petrochemical Co., Ltd. 250 parts, 28 parts, MAI 2.5 parts, Hydroxy/Nia 0.00
Add 7 parts and 0.009 parts of tin octylate to the entire reaction vessel.8
After heating and dissolving at 0°C, 43.5 parts of 'r DI was added dropwise while cooling so that the temperature inside the reaction vessel was 80 to 90°C.
After the dropwise addition was completed, the reaction was allowed to proceed at 80° C. until the NCO reaction rate reached 95% or more.

d) Synthesis of polycaprolactam-based acrylic modified polyol PCP-0200 (polycaprolactone manufactured by Chisso Corporation) 250 parts, 2-hydroxyethyl methacrylate 12
22 parts, 0024 parts of hydroquinone, 0 tin octylate
Pour 063 parts into a reaction can, heat and melt at 80°C, and TD1
165. The second part is added dropwise while being cooled so that the temperature inside the reaction vessel becomes 80 to 90°C, and after the completion of dropping, the reaction is allowed to occur at 80°C until the NC0 reaction rate reaches 95% or more.

The molecular weight of this resin is 1140.

e) Synthesis example of unsaturated polyester BBC resin: 166 parts of dimethyl sepatate, 12.2 parts of dimethyl adipate,
648 parts of dimethyl maleate, 76 parts of neobentyl glycol, 74 parts of 1,6-hexanediol, and 10 parts of tetra-n-butyl titanate were charged into a reaction vessel and N2
240-260℃ after demethanol reaction at 180℃ in air flow
By raising the temperature to
A resin close to an internally plasticized elastomer was obtained.

Example 1 A cobalt/nickel (atomic ratio 8/2) alloy ingot was prepared, and a long ferromagnetic thin film was formed on a polyethylene terephthalate base by vacuum evaporation. The vapor deposition was carried out by electron beam heating, using the so-called oblique vapor deposition method at a central incidence angle of 70°. 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@-3 Pa, and oxygen gas was introduced into the chamber until the pressure reached 6.3.times.10@-2 Pa 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 coercive force of approximately 100
0 Qe, and the residual magnetic flux Br was about so o o Gs, which is favorable as a magnetic recording medium.

On the other hand, a blend having the following composition selected from the above resins was prepared.

MEK of this resin composition/) Luene (1/1) 0, 3
A solution prepared by adding 3 wt % of monostearic acid to the wt % solution was prepared and applied onto the above-mentioned ferromagnetic thin film using a gravure coating method. After coating, the solvent was dried with hot air and infrared rays, and the surface was smoothed. Using an electrocurtain type electron beam accelerator manufactured by Energy Sciences, the acceleration voltage was 150 KV, the electrode current was iomA, and the total irradiation amount was 5 M.
The coating film was cured by irradiation with an electron beam under N 2 gas atmosphere under rad conditions.

The obtained tape was cut into 1-inch width to obtain a videotape consisting of a ferromagnetic thin film (Sample A) Comparative Example 1 Next, the vinyl chloride and pirul alcohol copolymer used in Example 1 had electron beam sensitivity. Acrylic double bond introduction was introduced.

Acrylic double bond-introduced vinyl chloride, vinyl alcohol copolymer 50 parts by weight Acrylic double bond-introduced polyether urethane elastomer (b),
50 parts by weight Lubricant (Grade fatty acid modified silicone oil) 3 parts by weight 2) The acrylic double bond-introduced vinyl chloride vinyl alcohol copolymer used in the above was synthesized according to the following procedure.

Note 1) The vinyl chloride vinyl alcohol copolymer used as the raw material in Example 1 and Comparative Example 1 was produced by the following synthesis method.

1) Production method of vinyl chloride vinyl alcohol copolymer (vinyl chloride group/vinyl acetate group) ratio is 75725,
A vinyl chloride-vinyl acetate copolymer with an average degree of polymerization n = 400 is used as a raw material, and this is suspended in a mixed dispersion medium of MIBK (a solvent such as methyl isobutyl ketone and water).
By mechanical dispersion using a stirrer, etc., a cloudy substance similar to a slurry of swollen resin is created.

Next, sodium sodium methylate is added as a catalyst, and the temperature is maintained at around 80°C to saponify the acetyl groups of vinyl acetate to hydroxyl groups.

In addition, you may use a stabilizer to prevent acid removal or a suspending agent to ensure uniform suspension.

Next, acetic acid and catalyst generated from the released acetyl groups are removed by washing the saponified slurry with water.
Increases resin stability. In this case, a decoloring step for removing chlorine ions, etc. may be added, depending on necessity, in order to erase the coloration during saponification.

The properties of the vinyl chloride-vinyl alcohol copolymer obtained by the saponification method 1 described above were as follows.

Vinyl chloride group 87% Vinyl acetate group 06% or less Vinyl alcohol group 126% Polymerization degree 36
0 Note 2) Above vinyl chloride-vinyl alcohol copolymer 7
50 parts of toluene, 1250 parts of cyclohexanone, and 500 parts of cyclohexanone were placed in a 51A flask and dissolved in a heating bath, and the temperature was raised to 80°C. 614 parts of ditolylene diisocyanate-hydroxyethyl methacrylate adduct were added, and further, 12 g of tin octylate, 12 g of tin octylate, and 0.5 g of hydroquinone were added. 012 copies added 8
The reaction is allowed to proceed at 0° C. in a N2 stream until the NCO reaction rate reaches 90% or more. After the reaction is complete, remove methyl ethyl ketone 1.
Add 250 parts to dilute.

) Preparation of 2-hydroxyethyl methacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) After heating 348 parts of tolylene diisocyanate to 80°C in a fourth flask in a N2 stream, 2-hexane 260 parts of ethylene methacrylate, tin octylate O.07
10.05 parts of hydroquino at a temperature of 80% in the reaction vessel.
After completion of the dropwise addition, the mixture was stirred at 80'C for 3 hours while cooling was controlled to reach ~85°C to complete the reaction. After the reaction is complete, take it out and cool it, then add 2HH of TDI in the form of a white paste.
Obtained an MA.

It was manufactured under the same conditions as in Example 1.

When dropout, steel durability time, friction coefficient, curl, and electromagnetic properties were evaluated, the results shown in Table 1 were obtained.

In Table 1, the dropout is VH8 manufactured by Matsushita Denko Sangyo.
This is the number of dropouts per minute when a so-called 3-step wave is recorded and played back using . The still durability time is the time it takes for the playback screen to become fully (visible) when playing stills using the same deck and signal. In this case, the main cause is considered to be deterioration and clogging of the magnetic layer. However, such a phenomenon did not occur for more than 30 minutes in all three samples.

The friction coefficient μ is a calculated value using Euler's equation from the tension before and after the stainless steel pin. Curl is determined visually.

As described above, according to the present invention, a magnetic recording medium can be provided that has a strong surface that is free from curling, has a small friction coefficient, little dropout, and has a long steel time.

Example 2 Saturated polyester resin 20 parts by weight (L-411 manufactured by Dynamite Nobel) Acrylic double bond-introduced polyprolactam urethane prepolymer (d)
80 parts by weight of solvent (MEK/TOL
so/so) Lubricant (higher fatty acid modified silicone oil)
10 parts by weight Example 3 Phenoxy resin (PKHH manufactured by Union Carbide) 40 parts by weight Acrylic double bond-introduced polybutadiene elastomer TC) 60
Parts by weight Example 4 Epoxy resin (Shell Chemical Epicoat 152) 50]
Part ii Polybutadiene elastomer acrylic modified product (c
) 50 parts by weight Packaging was carried out under the same conditions as in Example 1.

Similar to Example 1, these examples also have excellent magnetic characteristics and electromagnetic characteristics.

UV curing epoxy resin Azoka Ultraset B613
80 parts by weight of 6J and 20 parts by weight of vinyl chloride vinyl alcohol copolymer (degree of polymerization 6oo) were added to MEK/) luene (1
/1) dissolved well as a 0.3 wt% solution, and further added catalyst solution gPS-33 to 3 wt% of B6136J solid content.
Gravure coating was carried out on the same ferromagnetic thin film as used in Example 1.

After heating and drying, the coating film formed was cured using an ultraviolet curing system having one each of 2KW and 3KW ultraviolet lamps. This was cut to -inch width to obtain a videotape.

Table 6 Comparative Example 2 shows that the desired results cannot be obtained even when a UV-cured epoxy resin is used as a protective film.

Agent's name: Motohiro Kurauchi

Claims (1)

[Claims] t. A ferromagnetic thin film is formed on a support, and a protective film containing a radiation-curable resin having an unsaturated double bond and a thermoplastic resin is formed on the surface of the ferromagnetic thin film. Features of magnetic recording media. 2. The magnetic recording medium according to item 1 above, wherein the protective film contains a compound having slipperiness.