JPS61911A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve runnability and durability by providing a top cost layer having specific components on the surface of a thin ferromagnetic film formed on a non-magnetic base material. CONSTITUTION:The top coat layer contg. radiation-curing monomer or oligomer having <=2,000 number average mol.wt., radiation-curing oligomer having >=2,000 number average mol.wt., antioxidant and lubricating agent is formed on the surface of the thin ferromagnetic film provided on the non-magnetic base material. More specifically, said additives are diluted with a solvent and the soln. is thinly coated on the thin ferromagnetic metallic film and is cured. The top coat layer is thereby reinforced, by which chipping and sticking are eliminated and friction is made low. The durability in high-temp. traveling and the effect of rust prevention are improved and the friction resistance on the surface of the magnetic layer is decreased.

Description

[Detailed Description of the Invention] L-IF 1 [Year I-] This invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium whose magnetic recording layer is a ferromagnetic thin film with excellent running stability and durability. .

4 points Magnetic recording media are now widely used in the fields of audio, video, computers, magnetic disks, etc., and the amount of information recorded on magnetic recording media is increasing year by year. As a result, magnetic recording media are increasingly required to have higher recording densities.

Non-binder type magnetic recording media, which are easier to make thinner than coating-type magnetic recording media and have higher saturation magnetization, that is, magnetic recording media made of ferromagnetic thin films, have problems with corrosion, impact, and friction strength, and are difficult to record magnetic signals. Friction or destruction may occur due to high-speed relative movement with the magnetic head during the reproducing and erasing processes. In other words, magnetic recording media on which a ferromagnetic thin film is formed by methods such as electroplating, electroless plating, sputtering, vacuum evaporation, and ion blating do not contain a binder, so when they come in contact with a magnetic head, they are magnetic due to friction. The recording layer was likely to be scraped off or destroyed.

Further, the surface of a magnetic recording medium made of a ferromagnetic thin film is easily corroded, and as corrosion progresses, practical characteristics such as head touch and wear resistance deteriorate, and electromagnetic conversion characteristics are also adversely affected.

Therefore, a method of applying lubricant on the surface of the magnetic metal thin film (
(Japanese Patent Publication No. 39-25246), however, in such a method, the lubricant is wiped off by a magnetic head, etc., and the lubricating effect is not permanent. The effect was not as expected.

In addition, as a means of continuously supplying a lubricating effect to the magnetic recording layer, a lubricating layer (back coat layer) containing a liquid or semi-solid lubricant and an organic binder as main components is provided on the opposite surface of the magnetic recording layer. A method (Japanese Patent Publication No. 57-29769) has also been proposed, in which the lubricant oozing on the back side of the magnetic recording layer is transferred to the magnetic recording layer when it is rolled into a roll.
This method can constantly supply lubricant to the surface of the magnetic recording layer, and is said to have excellent effects on the durability of the magnetic recording layer (extent of scratches and peeling) and changes in the coefficient of dynamic friction. If a ferromagnetic thin film is not provided with a top coat layer and a lubricant is contained only in the back coat layer, the level of friction between the magnetic thin film and the magnetic head is still high, resulting in poor running, and corrosion resistance and rust prevention. The effects were still not satisfactory.

(zs) No. 11 Zhang 7 - Method for Solving In order to improve these drawbacks, the inventors of the present invention, as a result of intensive research, found that in a magnetic recording medium in which a ferromagnetic thin film is provided on a non-magnetic base material, the thin film surface It has been discovered that by providing a 1-tube coat layer of a specific component on top of the magnetic recording medium, an excellent magnetic recording medium with improved running properties, durability, etc., which were considered to be the drawbacks mentioned above, can be obtained.

As mentioned above, in the case where only the lubricant is applied onto the surface of the ferromagnetic thin film, or where the lubricant contained in the Barafco-1 layer is applied to the thin film by back-side transfer, the lubricant is not applied. If the lubricant cannot be supplied continuously, or even if the lubricant can be supplied continuously, if the lubricant in the backcoat layer is transferred to a ferromagnetic thin film without a top coat, for example, the deposited film will be free of oxygen introduction. In the case of (oxygen-free metal film, Japanese Patent Publication No. 57-29769), 1. However, if oxygen is introduced using the currently commonly used vapor deposition method (oxygen-containing metal film), the film will become unstable, resulting in decreased output, clogging, and poor image quality. Or the frictional resistance is still large and insufficient, and sometimes the film comes off or breaks, especially when measuring steel, the film penetrates through and comes off.
It has been found that the drawback of clogging, which is a major problem, cannot be overcome, and that none of these methods can provide satisfactory rust prevention and corrosion resistance. The following (A), (B), (
C) and (D), i.e. (A) number average molecular weight 2,00
0 or less radiation-curable oligomer or monomer, (
B) Radiation-curable type with a number average molecular weight of 2,000 or more, (C
) By providing a top coat layer containing an antioxidant and CD) a lubricant, the monomers and oligomers have a reinforcing effect, resulting in less abrasion and excellent rust prevention, corrosion resistance, durability, and running stability. The inventors have discovered that a magnetic recording medium can be obtained, and have arrived at the present invention.

That is, the present invention provides a magnetic recording medium in which a ferromagnetic thin film is provided on a nonmagnetic base material, and the following (A) is provided on the surface -E of the ferromagnetic thin film.
), (B), (C) and (D), that is, (A) a radiation-curable oligomer with a number average molecular weight of 12,000 or less, or (B) a radiation-curable oligomer with a number average molecular weight of 2.000 or more The present invention relates to a magnetic recording medium characterized by being provided with a top coat layer containing (C) an antioxidant and (D) a lubricant.

The ferromagnetic metals or ferromagnetic alloys used in the ferromagnetic thin film of the present invention include iron, cobalt, nickel and other ferromagnetic metals, Fc-Co, Fe-Ni, Co-
Nt, Fe-Rh, Fe-Co, Fe-Au
, Co-Cu, Co-Δu, co-Y, Co-La
, Co-Pr, Co-Gd, Co-
Sm, Co-Pt, N+-Cu,
F e -G O-N (1, Mn-B i, Mn-
3b, magnetic alloys such as Mn-AI.

The ferromagnetic thin film is made of a non-magnetic substrate, i.e. a polyester film,
The above metal or alloy can be applied directly or through a non-magnetic thin film layer to a known substrate such as a plastic film such as a polyamide film, a metal plate such as an aluminum plate or a stainless steel plate, or an inorganic plate such as a glass plate. It can be formed by vacuum evaporation, sputtering, ion blating, plating, or other methods.

The ferromagnetic thin film of the present invention can be manufactured by any of the above-mentioned methods, but a vacuum of 5.0 x 10-6 Torr as described in Example 5 of the Japanese Patent Publication No. 57-29769 can be used. Among them, the method (1) in which the width direction is inclined at 50 degrees with respect to the evaporation source is compared to the method (1) in which the direction of vapor deposition is inclined in the longitudinal direction (90 degrees to 30 degrees), which is currently generally performed. (2) is preferably used, which is not inclined in the width direction and is vapor-deposited at ~I x 10-4 Torr while introducing 02 or 02 and Ar as an atmosphere.

The vapor deposited film produced by method (1) above is completely metallic (except for the surface that is naturally oxidized after being taken out into the air), whereas the film produced by method (2) has a trace amount of oxygen gas. In the case where a metal or alloy is deposited in a vacuum where . The presence of this oxide is favorable for magnetic recording media, especially when there is a large amount of oxide at the interface with the base and on the surface opposite to the base.
It has been found that good characteristics can be obtained in the present invention7
Ta. 2. Also, as a method for introducing oxygen into a ferromagnetic metal thin film, in addition to the above-mentioned vapor deposition in the presence of oxygen, a film deposited by vacuum vapor deposition in the absence of oxygen may be deposited in an atmosphere of, for example, 90° C. and 20% RH. It is also possible to forcibly oxidize the base and make the surface opposite to the base oxide only.

As mentioned above, the oxygen content of a ferromagnetic thin film containing oxygen is as follows: If the magnetic recording layer consists of only a ferromagnetic thin film and does not have a top coat layer, even if the back coat layer contains a lubricant. However, the vapor deposited film produced by the currently used vapor deposition method contains oxygen, and has a high friction level, lacks running stability, and is inferior in durability. Although this is superior in terms of corrosion resistance, coercive force, and electromagnetic conversion characteristics compared to vapor-deposited films that do not contain oxygen, the frictional resistance with magnetic heads, etc. is still large and insufficient, and the running stability and durability are Practical level characteristics cannot be obtained at this point. Then, the lubricant in the backcoat layer transfers to the deposited film and damages the film, resulting in unstable output, resulting in decreased output, clogging, no images, or unstable friction level. At 1 o'clock, the membrane comes off or breaks. Particularly when measuring steel, the film penetrates through and comes off, causing clogging, which poses a problem. Therefore, it is not possible to obtain a satisfactory magnetic recording medium by simply incorporating a lubricant into the back coat layer, and by applying only a lubricant to the topcoat 1-PI, only a temporary reduction in friction can be obtained, which prevents rusty,
Since corrosion resistance and durability are also significantly inferior, as a technical means to solve these problems, the present invention provides a specific top coat layer.

The top coat layer of the present invention contains a radiation-curable oligomer or monomer with a number average molecular weight of 2.000 or less, a radiation-curable oligomer with a number average molecular weight of 2,000 or more, an antioxidant, and a lubricant.

Number-average molecules used in the top coat layer of the present invention - Figure 2
,000 or less, dipentaerythritol-based acrylates [e.g. DPHA, D
PCA-20, 30, 40, 60, 120 (trade name) manufactured by Nippon Kayaku Co., Ltd.] and vinyl group- or acrylic group-containing monomers [e.g. Aronix M-150, 15, 2, 20
5,210°215.233.240.315.325
(trade name) manufactured by Toagosei Co., Ltd.].

Number average molecular weight 2 used in the top coat layer of the present invention,
Examples of radiation-curable oligomers of 000 or less include acrylic acid, methacrylic acid, or acrylic double bonds such as ester compounds thereof, which have unsaturated double bonds that are sensitive to ionization energy and exhibit radical polymerization, and diallyl. Oligomers containing or introducing into the oligomer molecule groups that can be crosslinked or polymerized and dried by radiation irradiation, such as allylic double bonds such as phthalate and unsaturated bonds such as maleic acid and maleic acid derivatives, can be used.

These radiation-curable oligomers include polyfunctional oligoesters represented by the following general formulas, acrylates (Aronix M-6100, 7100, 8100, etc., Toagosei Chemical Industry Co., Ltd.), urethane elastomers, and Tuboran 4040). Examples include acrylic modified products and those into which functional groups such as COOH are introduced.

(In the formula, R,,R2: alkyl group, n: integer) As the radiation-curable oligomer with a number average molecular weight of 2,000 or more used in the top coat layer of the present invention, Epicoat 100
4.1001.828 acrylate, urethane acrylate oligomer produced as described below, etc. are used.

1) Synthesis of radiation-curable adduct body TDI (1 mol) and 2HE at 80°C under N2 atmosphere
One mole of A is reacted to synthesize a 2HEA adduct of TDI.

2) Synthesis of urethane oligomer 1 mol of propylene glycol is reacted with 2 mol of TDI at 40°C, and polycaprolactone polyol (Plaxel-2000, manufactured by Daicel,
(molecular weight: 2000) are reacted at 50°C in a methyl ethyl ketone solvent.

3) Urethane acrylate oligomer (molecule: Itt
1 mole of the urethane ossigomer of Synthesis 2) of 5000 was reacted with 2 moles of the radiation-curable adduct of 1) at 50° C. for 48 hours.

By using radiation-curable monomers and oligomers with a molecular weight of 2,000 or less, they have good adhesion to the ferromagnetic thin film and have low friction, so they do not stop at high temperatures and can run at high temperatures. has good durability. However, if this product alone is used, the coating film may shrink so much that it may cause curling or cracking, and the coating film is hard, which may cause scratching or adhesion.

On the other hand, by using a radiation-curable urethane oligomer with a number average molecular weight of 2,000 or more, it has good adhesion to the ferromagnetic thin film, the top coat layer is reinforced by the oligomer, and the breaking strength of the coating film is increased. The film is strengthened, and the paint film becomes softer and more elastic, with improved scratch resistance, no scratching or adhesion, and less shrinkage of the paint film.

However, this alone has high friction and tends to stop at high temperatures.

By using both a radiation-curable monomer or oligomer with a number average molecular weight of 2,000 or less and a radiation-curable oligomer with a number average molecular weight of 2,000 or more, there is no scratching, no adhesion, low friction, and durability in high-temperature running. It is possible to obtain a magnetic recording medium having uniform characteristics in the length direction, with good hardening, little dropout, and no curling during curing when wound into a roll.

The molecular weight of the radiation-curable oligomer having a number average molecular weight of 2,000 or more used in the present invention is preferably 2,000 to 10,000 or less. If the molecular weight exceeds 10,000, solubility in a solvent decreases and uneven coating tends to occur.

And when radiation-curable monomers and oligomers are used,
Continuous processing is possible in manufacturing the top coat layer, and processing can be performed online, which is useful for energy saving and cost reduction. These compounds can be used alone or in the form of mixtures.

As the antioxidant used in the present invention, ordinary antioxidants are used, and these include l) phenolic antioxidant, 2) amine antioxidant, 3) phosphorus antioxidant, 4
) sulfur-based antioxidants, 5) organic acid, alcohol, and ester-based antioxidants, 6) quinone-based antioxidants, and 7) inorganic acids and inorganic salt-based antioxidants.

Specific examples of the above various antioxidants include: 1) As a phenolic antioxidant, 2.6-di-tert-butyl-P
-cresol, 2,6-di-tert-butyl-phenol,
2,4-di-methyl-6-tert-butyl-phenol, butylhydroxyanisole, 2,2'-methylenebis(
4-methyl-6-tert-butylphenol), 4.4'-
Butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), tetrakis[methylene-3(3,5
-di-tert-butyl-4-hydroxyphenyl)propionate comethane, l, I.

3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, dibutylhydroxytoluene,
Examples include propyl gallate, guaiac butter, and nordihydroguaiaretic acid. Radiation-curing types include monoglycol salicylate, 2,5-di-tert-butylhydroquinone,
Examples include methacrylate, acrylate, and vinyl types such as 2,4-dihydroxybenzophenone, 2,4.5-trihydroxybutyrophenone, and hydroquinone.

2) Examples of amine antioxidants include phenyl-β-naphthylamine, d-naphthylamine, N,N'-di-butyl-P-phenylenediamine, phenothiazine, N
, N'-diphenyl-p-phenylenediamine, alkanolamines, phospholipids, and the like. Among amine-based materials, radiation-curable materials such as dimethylaminoethyl methacrylate, acrylate, and vinyl types can be cited as radiation-curable materials.

3) As the phosphorus antioxidant, a radiation curing type or a non-radiation curing type is used, and the R of the phosphoric acid ester moiety contains an alkyl group, an alkylphenyl group, and other ethylene oxide and propylene oxide. C
is preferably 1-26, more preferably 1-22. The phosphoric acid esters include mono-, di-, and tri-type phosphoric acid esters, and may have a large mono- or di-component content, and tri-type phosphoric acid esters may be cut. Phosphate esters also include methacrylate-1, acrylate, and vinyl types. Specifically, phosphite esters such as triphenyl phosphite, triotadecyl phosphite, tridecyl phosphite, 1-dilauryl 1-helithiophosphite, hexamethylphosphoric triamide, butyl phosphate, cetyl phosphate, butoxyethyl Phosphate, 2-ethylhexylphosphate-1-1β-chloroethylphosphate, B1~
Diethyl phosphate diethylamine salt, di(2-ethylhexyl) phosphate, ethylene glycol acid phosphate, methacryloxyethyl bosphate, bis(methacryloxyethyl) phosphate-I~, and their acrylate types, phenyl phosphate,
Examples include other alcohols and phosphoric acid esters such as phenyl phosphates such as nonylphenyl.

4) Examples of sulfur-based antioxidants include dilaurylthiodipropione-1-, distearylthiodipropionate, laurylstearylthiodipropionone-1-, cimilistylthiodipropionate, distearyl β, and β. '-thiodibutyrate, '2-mercap[benzimidazole, dilauryl sulfide, 4,4'-thio-bis(3-methyl-6-tert-butyl-phenol), 2,2
Examples include methacrylates such as '-thio-bis(4-methyl-6-tert-butylphenol), acrylates, and radiation-curing types such as vinyl types. Moreover, these may contain ethylene oxide and propylene oxide.

5) Examples of organic acid, alcohol, and ester antioxidants include sorbitol, glycerin, propylene glycol,
Examples include adipic acid, citric acid, ascorbic acid, etc.
These radiation-curing types may also be used.

6) Examples of quinone antioxidants include hydroquinone and tocopherol, among which radiation-curing types may be used.

7) Phosphoric acid is a typical example of the inorganic acid and inorganic salt antioxidant.

Among the above-mentioned antioxidants, radiation-curable ones having an acrylic double bond in the molecule 1, such as monoglycol salicylate methacrylate (acrylate), from the viewpoint of suppressing back-type transfer to the ferromagnetic film, 4-Tertiary butyl catechol methacrylate (acrylate), dimethylaminoethyl methacrylate (acrylate), ethyl hydroxy methacrylate (acrylate) phosphate, cetyl hydroxy phosphate methacrylate (acrylate), stearyl methacrylate (acrylate) phosphate-1-1 and the above Of these, phenyl type ones, 2,2'thio-bis(4-methyl-6-tert-butyl-phenol) methacrylate (acrylate), etc. are preferred. The phosphoric acid ester can be produced by any known method, including the method described in JP-A-57-44223. Radiation-curable antioxidants can be cured online into ferromagnetic thin films, so there is no deterioration in surface properties due to back mold transfer due to curling during thermal curing, and therefore no reduction in output. The thickness of the 1-tube coat of the ferromagnetic thin film is preferably 800A or less, and if it is thicker than this, the shape retention will deteriorate. If it is too thick, the surface roughness of the ferromagnetic thin film is less than 100%, so the antioxidant layer thereon increases in thickness and is scraped. This was discovered for the first time in the present invention. In addition to characteristic effects such as preventing dropouts and reducing the difference in output depending on the inner and outer diameter when wound into a roll, it can also have processing effects such as being able to be manufactured online. .

As the lubricant used in the present invention, silicone oil, fluorine oil, fatty acid, fatty acid ester, paraffin, liquid paraffin, surfactant, etc. can be used as the lubricant conventionally used in this type of magnetic recording medium. It is preferable to use/or a fatty acid ester.

Fatty acids include caprylic acid, capric acid, lauric acid,
myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linuric acid,
Fatty acids with 12 or more carbon atoms such as stearolic acid (RC00
HlR is an alkyl group having 11 or more carbon atoms), and fatty acid esters include fatty acid esters consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 3 to 12 carbon atoms, and 17 carbon atoms. Fatty acid esters are used, which are composed of at least one monobasic fatty acid and a monohydric alcohol having 21 to 23 carbon atoms in total.

As the silicone, those made of fatty acid-modified silicones and those partially fluorine-modified are used. As the alcohol fluorine, those obtained by electrolytic substitution, telomerization, oligomerization, etc. are used.

Among the lubricants, radiation-curable ones are also advantageously used. These are used to suppress back-type transfer to the ferromagnetic thin film.
It has the advantages of preventing dropouts, reducing the difference in output depending on the inner and outer diameters when wound into a roll, and being able to be manufactured online.

Radiation-curable lubricants include compounds that have a molecular chain exhibiting lubricity and an acrylic or vinyl double bond in the molecular chain, such as acrylic esters, methacrylic esters, vinyl acetate esters, and acrylic amide-based lubricants. compounds, allyl alcohol esters, glycerides, etc.
The structural formulas of these lubricants are as follows.

CH3 (:l, 112 “CHCOOR. CH2 =C-
COOR, C I-1 0 C O R CH20COR r<, C O O C H 2 - C H = C
H2, etc., where R is a straight chain or branched saturated or unsaturated hydrocarbon group, and the number of carbon atoms is 7 or more, preferably 1.
The number is 2 or more and 23 or less, and these can also be substituted with fluorine. As a fluorine substituted product, CnFZnt+-1Cn Fzn+1 (CH2)+n
-((D, L/, m=1~5), R Cr1Fzn1 S 02 N CH2CH2
-, Cn FZn+l CH2CH2N HCH2CH
2-1CnF, 7n-10-◎-COOCH2CH2-
etc.

Preferred specific examples of these radiation-curing lubricants include:
(meth)acryloxyethyl stearate, stearyl (meth)acrylate, methacrylate of glycerin (
acrylate), glycol methacrylate (acrylate), silicone methacrylate (acrylate), vinyl stearate, vinyl myristate, and the like.

In the top coat layer of the present invention, polymers can also be used in addition to the additives mentioned above. These polymers have conventionally been thermoplastic, thermosetting, or reactive resins used for magnetic recording media, or mixtures thereof, but from the viewpoint of the strength of the resulting coating film, curable types, especially radiation-curable ones, have been used. A mold resin is preferred.

As a thermoplastic resin, the softening temperature is 150°C or less, the average molecular weight is 10,000 to 200,000, and the degree of polymerization is about 20.
0 = about 2,000, such as vinyl chloride-vinyl acetate copolymers (including those with carboxylic acid introduced),
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
(including those with carboxylic acid introduced), vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin, Polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer.

Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate-1-, cellulose diacetate, cellulose 1-helacetate, cellulose propionate, cellulose 21-0, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether - Acrylic acid ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. or.

Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin, and isothiaphor 1. - mixtures of prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate, polyamine resins, and mixtures thereof.

Among these, preferred are cellulose resins (nitrified cotton, etc.), vinyl chloride-vinyl acetate-vinyl alcohol copolymers, thermosetting resins consisting of a combination of urethane (using a curing agent), or vinyl chloride-vinyl acetate. - Consists of a radiation-curable resin consisting of a vinyl alcohol copolymer (including those with carboxylic acid introduced) or an acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer (including those with carboxylic acid introduced) and urethane acrylate. For radiation-curable resins, in addition to the above-mentioned preferred combinations, acrylic double bonds such as acrylic acid, methacrylic acid, or ester compounds thereof, which exhibit radically polymerizable unsaturated double bonds, are used. , resins containing or introducing groups that can be crosslinked or polymerized and dried by radiation irradiation, such as allylic double bonds such as diallyl phthalate, and unsaturated bonds such as maleic acid and maleic acid derivatives, into the molecules of thermoplastic resins. Can be used. Other usable polymer components include acrylic acid, methacrylic acid, acrylamide, etc. in the form of monomers.

As polymers having double bonds, various polyesters, polyols, polyurethanes, etc. can be modified with compounds having acrylic double bonds.

Furthermore, by blending a polyhydric alcohol and a polyhydric carboxylic acid as necessary, products with various molecular weights can be produced. The above-mentioned radiation-sensitive resins are some of them, and these can also be used in combination. Even more preferable is (
A) A plastic-like compound with a molecular weight of 5.000 to ioo', ooo that has two or more unsaturated double bonds that are curable by radiation; (B) A plastic-like compound that has two or more unsaturated double bonds that are curable by radiation. (C) A rubber-like compound having one or more unsaturated double bonds or having no radiation curability and having a molecular weight of 3,000 to IOQ, 000, and (C) a molecular weight 200 having one or more unsaturated double bonds that are curable by radiation. ~3,00
0 compound, (A) 20 to 70% by weight, (B) 20 to
This is a combination in which (C) is used in a proportion of 80% by weight and 10 to 40% by weight. As a result, the breaking strength of the coating film is increased, the coating film is strengthened, there is less abrasion, and there is no transfer of inorganic filler powder to the magnetic layer, so there is less dropout.
A magnetic recording medium can be obtained which has uniform characteristics in the length direction and is free from curling during curing when wound into a roll.

A radiation-curable monomer or oligomer with a number average molecular weight of 2,000 or less, a number average molecular weight of 2,
Methods for providing a top coat layer containing a radiation-curable oligomer of 000 or more, an antioxidant, and a lubricant include diluting the additive with a solvent and coating it thinly on a ferromagnetic metal thin film, or exposing the additive to the atmosphere. There are various methods that can be used, such as vaporizing the metal in a medium, an inert gas, or a vacuum, and applying the vapor to the surface of the ferromagnetic metal. At this time, radiation-curable monomers, oligomers, antioxidants, and lubricants may be mixed and applied to cure, or radiation-curable monomers, oligomers, and antioxidants are first applied, and after curing,
The lubricant can be applied or vapor-deposited on the coating film to form a coating film or a vapor-deposited film. The additive can be applied using a solvent. Further, the vapor deposition of the additive can be performed by depositing the additive in the atmosphere, in an inert gas,
Alternatively, it is vaporized in a vacuum and the vapor is applied to the surface of the substance on which the film is to be formed.

When the additive is vapor-deposited, the surface of the film becomes uniform and a good output waveform can be obtained.

The ratio of radiation-curable monomer, oligomer, antioxidant, and lubricant used in the top coat layer of the present invention is radiation-curable compound:antioxidant = 10:90 to 90:10;
Preferably 30 nia 0 to 70:30 (by weight), lubricant is radiation curable monomer, oligomer 10 antioxidant 100
The amount is 0.5 to 30 parts by weight.

If the amount of the radiation-curable monomer or oligomer is less than this, there will be no adsorption force with the ferromagnetic thin film, making it easier to scrape. If the amount of antioxidant is less than this, the rust prevention effect will be weakened, corrosion of the ferromagnetic thin film will occur, the film will be seriously damaged, and the output in terms of electromagnetic conversion characteristics will be reduced.

The thickness of the layer is preferably 10 to 800. If it is too thick, the retention of the mold will be reduced or it will become uneven. Also, if there are too many books, clogging will occur.

Since the surface roughness of a ferromagnetic thin film without a top coat is preferably 100A or less, it has been found that when a layer of 1 to 100 Å is formed on J2, if it is too thick, scratches may occur. If the amount is too small, the adsorption of the top coat layer will be too weak, and it is expected that clogging will occur. This was discovered for the first time in the present invention. A particularly preferred range is 10-3008.

In addition, the active energy rays used for crosslinking the radiation-curing additive used in the top coat layer of the present invention include electron beams using a radiation accelerator as a radiation source, and 1-
rays, β-rays using 5r90 as a radiation source, anti-rays using an X-ray generator as a radiation source, ultraviolet rays, etc. are used.

In particular, as an irradiation source, it is advantageous to use radiation using a radiation heater from the viewpoints of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation.

Although a backcoat layer is not necessary in the present invention.

A back coat layer is preferable because it further stabilizes running properties. The back coat layer contains commonly used inorganic pigments, lubricants,
It consists of an organic binder.

In the present invention, the top coat layer contains the radiation-curable monomer or oligomer having a number average molecular weight of 2,000 or less, or a number average molecular weight of 2,000 or less! Containing radiation-curable oligomers with f2,000 or higher strengthens the top coat layer, prevents abrasion (= J-free, low friction, and good durability during high-temperature running, and contains antioxidants) According to
It has a remarkable rust-preventing effect, and the inclusion of a lubricant has the effect of reducing the frictional resistance on the surface of the magnetic layer.

A magnetic recording medium with excellent running stability and durability and reduced dropout can be obtained.

(E) - Moxibustion cut $! l-Jfi-* IT The magnetic recording medium of the present invention can be used as audio tape, video tape, computer tape, endless tape, magnetic disk, magnetic camera, etc. Among them, dropout is the three most important characteristics. Some video tapes can be used as computer tapes and are very useful.

In recent years, the specific 1-tub coat layer of the present invention can be applied to high bias HiFi audio cassette tapes, video cassette tapes, master tapes for videotape contact transfer printing, etc., which have undergone remarkable technological progress and marketability has expanded. By using the provided magnetic recording layer consisting of a metal thin film, a high-performance tape having extremely good electromagnetic conversion characteristics and physical property reliability can be obtained, and the magnetic recording medium of the present invention is highly useful and excellent. It can be said that there is.

Examples of the present invention are shown below. Note that it should be understood that the present invention is not limited to this example.

Example 1 (1) A polyester film with a thickness of 12) -m was moved along the surface of a cylindrical cooling can, and 02→-Δr (volume ratio l:1) ) at a rate of 800 cc per minute and the degree of vacuum was set to 1.
In a chamber at 0x10-'Torr, Co8
0, an alloy consisting of Ni2O is melted and the incident angle is 90° ~ 3
Co-N with a film thickness of 0.15 Pm is obliquely deposited only on the 0° part.
An i-0 thin film was formed. A large amount of oxygen was unevenly distributed at the interface with the base and on the surface opposite to the base. Furthermore, the surface opposite to the base was covered almost exclusively with oxide. Il-
1c = 10000° The average amount of oxygen in the film is the atomic ratio of Co and Ni (OX1
00) was 40%.

Co Ni - Strong Ikkun “January” λ l! A polyester film of 7 x 127 y, m was moved along the surface of the cylindrical cooling can, and the vacuum was heated to 9 degrees.
Deposition was carried out in the same manner as for ferromagnetic a3Upl in a chamber set to OXI 01 Torr. Film thickness is 0°1!
5. +Am and consists essentially of Co-Ni.

This tape was forcibly oxidized in an atmosphere of 90° C. and 20% RH, and the surface opposite to the base was left with an oxide. Hc
= 9000 e. The average amount of oxygen in the film was 45% in atomic ratio to Co and Ni.

Horisagi Gokui Pancreas l A polyester film with a thickness of 12 m was moved along the circumferential surface of a cylindrical cooling can in the same manner as in the case of Betsei 1, except that the oxidation process using oxygen was omitted, and the vacuum level was 5. OX
, in a chamber set to 1O-6 Torr, oni 1'lJ
Vapor deposition was carried out in the same manner as in the case of L Sato. Membrane J is 0.15 noA
m and consisted essentially of Co-N+. H
c=9500e.

(2) Formation of top coat layer O top coat composition! R Aronix M-81001 Urethane acrylate molecular weight 3000 1 Stearic acid 0.1 Toluene
100 Topco 11 Abdomen Acrylic Oxyethyl Phosphate 1-170 Nix M
-81001 Urethane acrylate molecule R50001 Palmitic acid 0. IMEK/toluene (1/1) 1000 top coat - 1, top coat layer 1 was applied by applying top coat composition 1 as it was on the ferromagnetic thin films (1) and (3), and applying an accelerating voltage of 15
0. As a result of irradiation in N2 gas at KeV, electrode current 6 mA, 3 Mrad, a film thickness of 50 A was obtained.

2. Top coat layer 2 is ferromagnetic thin film (1) and ('2)
Jl:, top coat composition 2 is applied, acceleration voltage IFj
Irradiation was performed in OKeV, electrode current 6 mA, 3 Mrad, and N2 gas. The film thickness was 300A.

Top Coat 1 This is a coating in which the radiation-curable oligomer is removed from the composition of Top Coat 1-1, and the amount of antioxidant is increased by the amount removed.

In addition, the radiation-curable oligomer was removed from the composition of the top coat 2, and the amount of antioxidant was increased by the amount removed.

The characteristics of these magnetic recording media and comparative examples are shown in the following table.

The results in the previous table are discussed below.

1. The runnability of 60% at 40° C. can be improved by adding radiation-curable oligomers. Regarding the friction on the magnetic surface side, the initial friction does not change regardless of the presence or absence of the radiation-curable compound, but in the case without the radiation-curable oligomer (comparative example), it stops after about 2 to 3 times and becomes 0.70 or more, and the friction measurement becomes impossible.

2. It can be seen that the steel properties do not deteriorate even when a radiation-curable oligomer is added compared to when only a radiation-curable phosphate ester is used.

3. Regarding rust, it did not occur after one week of storage, indicating that it has a rust-preventing effect (the simple one without top coat is 3)
Rust occurs within days).

The method for measuring the L-characteristics will be described below.

1. Still characteristics Record at 5 MHz and measure the still characteristics of the playback output. 10 minutes or more is considered an OK level.

2o Magnetic surface side friction measurement Wrap the magnetic tape so that the magnetic surface is on the cylinder side, apply a load of 20 g to one end surface, and rotate the cylinder 9
Friction is measured by reading the change in tension when rotated by 0°.

3. S/N when recording and playing back at an output center frequency of 5 MHz
Indicates a ratio (relative value). The VHS VTR will be modified to be able to measure up to 5 MHz.

4. Rust Store in an environment of 50° C. and 90% RH for one week.

The molecular weight of the oligomer of the present invention is determined by the number average molecular weight determined by the following measuring method.

*Average molecular weight measurement using APC GPC (Gel Perrnt!al: ion
Chromatography is a method in which molecules in a sample are separated based on their size in a mobile phase, and liquid chromatography is performed by filling a column with a porous gel that acts as a molecular sieve.

To calculate the average molecular weight, use polystyrene of known molecular weight as a standard sample and create a calibration curve from its elution time. From this, the average molecule m in terms of polystyrene is calculated.

! j, if there are Ni molecules with a molecular weight Mi in the obtained high molecular weight substance, the number average molecular weight Mn==ΣN i M i can be expressed.

ΣNi

Claims (4)

[Claims] (1) In a magnetic recording medium in which a ferromagnetic thin film is provided on a nonmagnetic base material, the following (A), (B),
A magnetic recording medium comprising a top coat layer containing (C) and (D). (A) Radiation-curable oligomer or monomer with a number average molecular weight of 2,000 or less (B) Radiation-curable oligomer with a number average molecular weight of 2,000 or more (C) Antioxidant (D) Lubricant (2) The magnetic recording medium according to claim 1, wherein the radiation-curable oligomer is a polyfunctional oligoester acrylate. (3) The magnetic recording medium according to claim 1 or 2, wherein the antioxidant contains a radiation-curable antioxidant. (4) The magnetic recording medium according to claim 1, 2, or 3, wherein the lubricant includes a radiation-curable lubricant.