JPS60223025A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which is free from a decrease in the electromagnetic conversion characteristic, has small friction and obviates chipping by forming a top coat layer having 20-200Angstrom surface roughness Rmax to the surface of the thin ferromagnetic film of the magnetic recording medium which is provided with the thin ferromagnetic film on a non-magnetic substrate material. CONSTITUTION:The magnetic recording medium which has excellent rust preventiveness, corrosion resistance, durability and running stability and is free from clogging is obtd. when the top coat layer is provided on the thin ferromagnetic film. The magnetic recording layer which lesses the decrease in the electromagnetic conversion characteristic, has a good envelope, a substantially low noise level and low friction and decreases chipping is obtd. by forming the top coat layer having 20-200Angstrom surface roughness. A method of applying the top coat on the magnetic substrate, passing the substrate through a drying furnace and curing the coating by electron rays or UV rays is adopted to obtain 20- 200Angstrom surface roughness.

Description

[Detailed Description of the Invention] This invention relates to magnetic recording media and, in particular, magnetic recording in which a magnetic recording layer is an excellent ferromagnetic thin film that does not deteriorate running stability, durability, or electromagnetic change characteristics. It's about the medium.

Currently, magnetic recording media are being widely used in fields such as audio, video, computers, and magnetic disks, 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 deposition, and ion blating do not contain a binder, so the magnetic recording layer is damaged due to friction when sliding in contact with a magnetic head. were likely to be scraped off or destroyed.

Furthermore, 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 the 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.
Magnetic record.

It is said that lubricant can be constantly supplied to the surface of the recording layer, and that it has excellent effects on the durability of the magnetic recording layer (extent of scratches and peeling) and changes in the coefficient of dynamic friction.
In this method, in which the ferromagnetic thin film is not provided with a top coat layer and only the back coat layer contains a lubricant, the level of friction between the magnetic thin film and the magnetic head is still high, resulting in poor running, and corrosion resistance. However, the antirust effect was still not sufficient.

Ha. In order to improve these shortcomings, the inventors of the present invention have conducted extensive research and found that in magnetic recording media in which a ferromagnetic thin film is provided on a non-magnetic base material, a top coat layer of a specific component is formed on the surface of the thin film. It is proposed in the heading that an excellent magnetic recording medium with improved runnability, durability, etc., which were considered to be disadvantageous as described above, can be obtained by providing a
(Japanese Patent Application No. 59-15259) 9 As a result of further research by the present inventors, the surface roughness of the top coat layer was reduced to Rmax.
The inventors have arrived at the present invention by discovering that a magnetic recording medium with no deterioration in mold retention, low friction, and no abrasion can be obtained when the thickness is 20 to 2008.

That is, the present invention provides a magnetic recording medium in which a ferromagnetic thin film is provided on a non-magnetic base material, in which the surface roughness of the top coat layer on the surface of the ferromagnetic thin film is 20 to 2008 in terms of R+++a. The present invention relates to a characteristic magnetic recording medium.

When a top coat layer is provided on the ferromagnetic thin film.

Excellent rust prevention, corrosion resistance, durability, and running stability.

However, a magnetic recording medium without clogging can be obtained.

Surface roughness of top coat layer (TAYLOR-HOBSO
Rrnax value in pre-step method manufactured by N company, Tallis company, cutoff 0.17+nm, needle pressure 2 mg, needle Q, IX
2.5. " (hereinafter the same applies) is set to 20 to 200A, in addition to the above characteristics, there is less deterioration in mold retention, a good envelope, a sufficiently low noise level, low friction, and less scraping. You can get something.

When the surface roughness exceeds 2008, there is a reduction in mold retention (-2 dB) and the output is reduced. If the surface roughness is less than 20A, the surface roughness will be good and the friction will be high, making it easy to scrape.

In order to obtain a surface roughness of 20 to 200A, the following method can be adopted.

1. Apply a top coat, pass through a drying oven, and cure with electron beam or ultraviolet rays.

゛2. A top coat is applied and cured with electron beam or ultraviolet light without passing through a drying oven.

3. When applying the top coat, apply the top coat while keeping it highly viscous.

4. In the steps 1 and 2 above, the material is calendered in an uncured state (with or without passing through a drying oven), and then cured with an electron beam or ultraviolet rays.

5. In step 4 above, the material is passed through a drying oven or not), then semi-cured under slightly low dose conditions (0,01~2 Mrad), then calendered, and then electron beam or ultraviolet curing is performed.

6. In steps 1 to 5 above, a calendering step may be added as the final step.

The ferromagnetic metal or ferromagnetic alloy used in the ferromagnetic thin film of the present invention includes iron, cobalt, nickel and other ferromagnetic metals, or Fe-Go, Fe-Ni, Co.
-N i, Fe-Rh, Fe-Cu, Fe-
Au, Co-Cu, Co-Au, Go-Y, Co-La
, Co-Pr, Co-Gd, Co-8m, Co-Pt,
N1-Cu, Fa-Co-Nd, Mn-B1. Mn-
8b, magnetic alloys such as Mn-Al.

The ferromagnetic thin film is made of a non-magnetic substrate, i.e. a polyester film,
The above-mentioned metal or alloy is deposited directly or through a non-magnetic thin film layer on 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 vapor deposition, 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 the ferromagnetic thin film of the present invention may be manufactured using a vacuum of 5.0XIO''6 Torr as described in Example 5 of Japanese Patent Publication No. 57-29769. Among them, the method (1) in which the width direction is inclined at an angle of 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. , which is not inclined in the width direction, and which is vapor-deposited at ~1×10-Torr while introducing 02 or 0□ and Ar as the atmosphere (2) is preferably used.

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 invention.

In addition to the method of introducing oxygen into the ferromagnetic metal thin film, in addition to the above-mentioned method of vapor deposition in the presence of oxygen, the method of introducing oxygen into the ferromagnetic metal thin film is to deposit the film by vacuum vapor deposition in the absence of oxygen in an atmosphere such as 90° C. and 20% RH. It is also possible to perform forced oxidation and make the base and the opposite surface only oxide.

The oxygen content of the ferromagnetic thin film containing oxygen is O・×1
00 is 3-60%.

Magnetic metals As mentioned above, if the magnetic recording layer is made of only a ferromagnetic thin film and does not have a top coat layer, the friction level will be high and the running stability will be poor, even if the back coat layer contains a lubricant. Also, the durability is poor, and the vapor deposited film without a top coat layer contains oxygen, but this is compared to the vapor deposited film that does not contain oxygen. Although it has excellent corrosion resistance, coercive force, electromagnetic conversion characteristics, etc., the frictional resistance with magnetic heads etc. is still large and insufficient, making it impossible to achieve practical level characteristics in terms of running stability and durability. . 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. , sometimes 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 top coat layer, only a temporary reduction in friction can be obtained.
Since rust prevention, corrosion resistance, and durability are also significantly inferior, as a technical means to solve these problems, the present invention provides a top coat layer with a thickness of 200 mm or less.

Although the components of the top coat layer of the present invention are not particularly limited,
It can contain lubricants, antioxidants, organic binders, and the like.

As the lubricant, 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

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 (RCOO)
H and R are alkyl groups having 11 or more carbon atoms), and fatty acid esters include fatty acid esters consisting of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms; A fatty acid ester or the like is used, which is composed of a monobasic fatty acid having 17 or more monobasic fatty acids 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. The alcohol used is one made of higher alcohol, and the fluorine used is one obtained by electrolytic substitution, telomerization, oligomerization, etc.

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 double bond in their molecules, such as acrylic esters, methacrylic esters, vinyl acetate esters, acrylic amide compounds, and vinyl alcohol esters. , methyl vinyl alcohol ester, allyl alcohol ester, glyceride, etc. These lubricants are represented by the structural formula: CH3 CH2=CHC0OR, CH2=C-C00RCH2:
CH-CH2C0OR, CH2=CHC0NHCH20COR, CH20COR
RCOOC=CH2, RCOOCH2-CH=CH2
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 12 or more and 2
3 or less, and these can also be fluorine-substituted products. As a fluorine substituted product, Cn F 2n+1-1Cn F 2n<+ (CH2
) n+ - (however, m=1 to 5), R CnF2n+lSO2NC82CH2-1, etc.

Preferred specific examples of these radiation-curing lubricants include:
Examples include stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate), glycerin methacrylate (acrylate), glycol methacrylate-1 (acrylate), silicone methacrylate (acrylate), and the like.

Any antioxidant may be used as long as it prevents the oxidation of metals, but the following common antioxidants are used. These are l) phenolic antioxidants, 2)
Amine antioxidant, 3) Phosphorus antioxidant, 4) Sulfur antioxidant, 5) Organic acid, alcohol, ester antioxidant, 6) Quinone antioxidant, 7) Inorganic acid, inorganic salt They are roughly divided into structural types such as antioxidants.

Specific examples of the above-mentioned 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.

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 and acrylate types such as 2,4-dihydroxybenzophenone, 2,4.5-trihydroxybutyrophenone, and hydroquinone.

2) Examples of amine antioxidants include phenyl-β-naphthylamine, 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 and acrylate 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 R in the phosphoric acid ester moiety contains an alkyl group, an alkylbuenyl group, and other ethylene oxide and propylene oxide. as C
is preferably 1-26, more preferably 1-22. Phosphate ster includes mono-, di-, and tri-components, and may contain many mono- or di-components.
Tri-type ones may be cut. Phosphate esters also include NH4 type, methacrylate type, and acrylate type. Specifically, phosphite esters such as triphenyl phosphite, triotadecyl phosphite, tridecylphosbuite, and trilauryl trithiophosphite, hexamethylphosphoric triamide, butyl phosphate, cetyl phosphate, butoxyethyl phosphate, 2-ethylhexyl phosphate, β-chloroethyl phosphate, butoxyethyl phosphate diethylamine salt, di(2-ethylhexyl) phosphate, ethylene glycol acid phosphate, (2-hydroxyethyl)
Methacrylate phosphate, butyl hydroxy methacrylate phosphate, capryl hydroxy methacrylate phosphate, myristyl hydroxy methacrylate phosphate, stearyl hydroxy methacrylate phosphate, cetyl hydroxy methacrylate phosphate, butylphenyl hydroxy methacrylate phosphate, amyl phenyl hydroxy methacrylate phosphate, nonylphenyl hydroxymethacrylate phosphates and their acrylate types, phenyl phosphates, other alcohols, and phenyl phosphates such as nonylphenyl;
Examples include phosphoric acid esters such as vanadium acidic phosphoric acid esters.

4) Sulfur-based antioxidants include dilauryl thiodipropionate, distearyl thiodipropionate, laurylstearyl thiodipropionate, simiristyl thiodipropionate, distearyl β, β'-thiodibutyrate, 2 -mercaptobenzimidazole, dilauryl sulfide, 4,4'-thio-bis(3-methyl-6-tert-butyl-phenol), 2,2'-thio-bis(4-methyl-6-tert-butyl-phenol), Examples include radiation-curing types such as methacrylates such as (butylphenol) and acrylates. 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, such as monoglycol salicylate methacrylate (acrylate), 4 - tert-butylcatechol methacrylate (acrylate), dimethylaminoethyl methacrylate (acrylate), ethyl hydroxy methacrylate (acrylate) phosphate, cetyl hydroxyphosphate methacrylate (
acrylate), stearyl methacrylate (acrylate) phosphate, and the phenyl types of those listed above, 2,2'thio-bis(4-methyl-6-tert-butyl-phenol) methacrylate (acrylate), and the like are preferred. The phosphoric acid ester can be produced by any known method, including the method described in Japanese Patent Publication No. 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. 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. .

The organic binder that can be used in the top coat layer of the present invention includes polymers, monomers, and oligomers.

As the polymer, thermoplastic, thermosetting, or reactive resins, which are conventionally used for magnetic recording media, and mixtures thereof are used; A mold resin is preferred.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 20.
0 to 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 acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid 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, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, 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 as thermosetting resins or reactive resins that have a molecular weight of 200,000 or less in the coating liquid state. By heating after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins,
It is preferable that the resin does not soften or melt before it is thermally decomposed. Specifically, examples include phenol resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, epoxy-polyamide resins, nitrocellulose melamine resins, high molecular weight polyester resins, and isocyanate resins. Mixtures of polymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/high molecular weight diols/
A mixture of triphenylmethane triisocyanate, a polyamine resin, and a mixture 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-vinyl alcohol copolymers. Vinyl alcohol copolymers (including those with carboxylic acid introduced), or acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymers (
(including those into which carboxylic acid has been introduced) and urethane acrylate; for radiation curing resins, in addition to the above-mentioned preferred combinations,
Acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, allylic double bonds such as diallyl phthalate, maleic acid, maleic acid derivatives, etc., which exhibit radically polymerizable unsaturated double bonds. It is possible to use a thermoplastic resin containing or introducing into its molecule a group that can be crosslinked or polymerized and dried by radiation irradiation, such as an unsaturated bond. Other usable binder components include monomers such as acrylic acid, methacrylic acid, and acrylamide. Binders with double bonds include five types of polyesters, polyols,
Polyurethane and the like can also be modified with a compound having an acrylic double bond. 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.

More preferred are (A) those having two or more unsaturated double bonds that are curable by radiation and having a molecular weight of 5,000 to i;
oo, ooo plastic-like compound, (B) having one or more unsaturated double bonds that are curable by radiation,
Or non-radiation curable, molecular weight 3,000-10
0,000, and (C) a compound with a molecular weight of 200 to 3,000 having one or more unsaturated double bonds that is curable by radiation, (A) 20 to 70% by weight, (B ) 20-80% by weight, (C') 10-40% by weight.

The radiation-curable monomer, radiation-curable oligomer, and radiation-curable polymer include:

Acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which have unsaturated double bonds that are sensitive to ionization energy and exhibit radical polymerizability; allylic double bonds such as diallyl phthalate; Monomers, oligomers, polymers, etc. containing or introducing into the molecule groups that can be crosslinked or polymerized and dried by radiation irradiation, such as unsaturated bonds such as maleic acid and maleic acid derivatives, can be used.

The radiation-curable monomer is a compound with a molecular weight of less than 2.000, and the oligomer is a compound with a molecular weight of 2.000 to 1.
Ten thousand things are used. These are styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1,6-hexane glycol diacrylate, 1
, 6-hexane glycol dimethacrylate, etc., but particularly preferred are N-vinylpyrrolidone, pentaerythritol tetraacrylate (methacrylate), pentaerythritol triacrylate (
methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate (Aloex M-7100, M-54
00, 5500, 5700, etc., Toagosei), acrylic modified products of Tuborane 4040) in urethane elastomers, or those into which functional groups such as C0OH have been introduced, acrylates (methacrylates) of phenol ethylene oxide adducts, the following general An acrylic group (methacrylic group) or ε in the pentaerythritol fused ring represented by the formula
- caprolactone In the formula, m=1. Compound where a=2, b=4 (hereinafter referred to as special pentaerythritol condensate A)
, m=1, a=3. Compound where b=3 (hereinafter referred to as special pentaerythritol condensate B), m=1, a=6, b
= o compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, b = o compound (hereinafter referred to as special pentaerythritol condensate C), and special acrylate represented by the following general formula etc.

(1)(C)+2=CHC00CH2)3-CCH20
1 ((special acrylate A) (2), (CH7=C)l COOCH2) 3 CC
II 2CH3 (Special Acrylate B) (3) (C112= cllco −+ QCs 1
16)n-QC)12)3CCI(2CH3
(Special acrylate D) (Special acrylate E) (Special acrylate F) (7) CI, C00CH= C) 12° (Special acrylate G) (8) C11,= CHCOO-(CH, CIl□0
)4 C0C) I=C112 (Special acrylate H) (Special acrylate I) (Special acrylate J) A Niacrylic acid, X: Polyhydric alcohol, Y: Polybasic acid,
(Special Acrylate K) In addition, radiation-curable oligomers include polyfunctional oligoester acrylates represented by the general formula below, acrylic modified urethane elastomers, or those into which functional groups such as C0OH are introduced. Can be mentioned.

(In the formula, R,, R2: alkyl group, n: integer) By using an organic binder, the adhesion with the ferromagnetic thin film is good, the top coat layer is reinforced by the binder, the breaking strength of the coating film is increased, and The film is strengthened, there is less top coat abrasion, and durability at high temperatures is improved.

Therefore, it is possible to obtain a magnetic recording medium that has uniform characteristics in the length direction, with little dropout, and no curling during curing when wound into a roll. If there is no binder, there will be a stoppage at high temperatures, severe scratching, and adhesion. In addition, when using a radiation-curable binder, continuous processing is possible in manufacturing the top coat layer, and processing can be performed online, resulting in energy savings and
Helps reduce costs.

A method for providing a top coat layer containing a lubricant on the surface of a ferromagnetic thin film includes diluting the additive with a solvent and coating it thinly on the ferromagnetic metal thin film, or diluting the additive with a solvent, or applying the additive in the air, in an inert gas, Alternatively, there are methods such as vaporizing it in a vacuum and applying the vapor to the surface of a ferromagnetic metal, and methods of mixing and applying it together with a binder, which can be applied.

When using a radiation-curable additive in the top coat layer of the present invention, the active energy rays used for crosslinking include electron beams using a radiation accelerator, t-rays using Co60 as a source, and 5r90. Beta-rays used as a radiation source, X-rays or ultraviolet rays used as a radiation source from an X-ray generator, 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 back coat layer is not necessary in the present invention, it is preferable if there is a back coat layer because running properties will be more stable.

Delicious. The back coat layer contains commonly used inorganic pigments, lubricants, organic binders, and the like.

As described above, in the present invention, the surface roughness of the top coat layer on the ferromagnetic thin film is set to Rmax of 20 to 200A.
In addition to (1) excellent rust prevention, corrosion resistance, durability, and running stability, and (2) no clogging, provided by the top coat layer, Furthermore, (3) no deterioration of electromagnetic conversion characteristics, (4) good envelope, (5) sufficiently low noise level, (6) low coefficient of friction, and (7) little abrasion. It has excellent effects.

Part 1 The magnetic recording medium of the present invention can be used as an audio tape, a video tape, a computer tape, an endless tape, a magnetic disk, etc. Among them, the magnetic recording medium of the present invention can be used as a video tape, a computer tape, etc. in which dropout is one of the most important characteristics. It can be used as a tape and is very useful.

In recent years, the surface of 20 to 200 of the present invention is 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 a magnetic recording layer made of a thin metal film with a rough top coat layer, it is possible to obtain a high-performance tape with extremely good electromagnetic conversion characteristics and reliable physical properties.
It can be said that the magnetic recording medium of the present invention is highly useful and excellent.

Part 1 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) Thickness 12. -m polyester film was moved along the curve of the cylindrical cooling can, and 02+Ar (volume ratio 1
:1) is flowed at a speed of 800cc per minute and the degree of vacuum is 1.0X.
In a chamber at IO-'Torr, Co 80,
An alloy made of Ni2O is melted and the incident angle is 90° to 30°.
The film thickness is 0.15. ”m of Co-N
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. H
e” 10000 e, the average amount of oxygen in the film is CO and N
The atomic ratio (0/CoN i X 100) to i was 40%.

Strong AjJO [1 A polyester film with a thickness of 12 Pm was moved along the surface of a cylindrical cooling can, and the degree of vacuum was set to 5.0XlO-
In a chamber at sTorr, the E gland'-
It was deposited in the same way as in the case of . The film has a thickness of 0°15 Pm and is substantially made of Co--Ni.

This tape was forcibly oxidized in an atmosphere of 90° C. and 20% RH, so that only oxide was formed on the surface opposite to the base. H.C.
=90008. The average amount of oxygen in the film was 45% in atomic ratio to Co and Ni.

(2) Formation of top coat layer O Top coat composition Top coat 1 Parts by weight 2.6 Ditert-butyl P-cresol 0.8 Pentalythritol tetraacrylate Molecular weight 352 0.8 Stearic acid 0.2 Butyl myristate 0 .05 MEK/cyclohexanone (1/1) 100 top coat 2 parts by weight Monoglycol salicylate acrylate 1N-vinylpyrrolidone molecular weight 111 0.3 Methacrylic acid modified myristic acid 0.3 Methacrylate of myristyl alcohol 1. OMEK/Toluene (1/1) 100 Topcoat 3 Methacryloxyethyl phosphate 0.5 Special acrylate D molecular weight 534 0.2 Stearic acid 0.5 Stearic acid-modified silicone 0.5 Toluene 100 Topcoat 4 a, dimethylaminoethyl Methacrylate IN-Vinylpyrrolidone 2 MEK/Toluene (1/1) 100 Coat this on the ferromagnetic thin film (1), accelerate voltage 150
Irradiation was performed in KeV, electrode current 10 mA, 5 Mr ad, and N2 gas. On top of that, behenic acid 0.3 MEK 100 t, Yushosu top coat composition, after application, pass through a drying oven.
The sample was calendered in a semi-dry state, and irradiated with an electron beam at an acceleration voltage of 150 KeV, an electrode current of 6 mA, and 3 Mrad.

■Acceleration voltage 150KeV, electrode current 1mA, 0°5M
Electron beam irradiation was performed at rad, then calendering, and finally electron beam irradiation was performed at 3 Mrad.

■Acceleration voltage 150KeV, electrode current 2mA, IMr
Electron beam irradiation was performed in ad, and then the same process as in step 2 was repeated.

■Acceleration voltage 150KeV, electrode current 4mA, 2Mrad
Electron beam irradiation was performed in Step 1, and then the same process as in Step 2 was repeated.

(2) Electron beam irradiation was performed at 3 M r a d, and no calendering was performed.

(2) 2,6 di-tert-butyl p-cresol was removed from top coat composition 1, and 2 parts by weight of pentaerythritol tetraacrylate was added.

(2) MEK/cyclohexanone in top coat composition 1 was replaced with MEK only (MEK boiling point 80°C, cyclohexanone boiling point 155°C). Table 1 shows the results of the various treatments described above for top coat composition 1 with a calendar temperature of 70° C. and a pressure of 10 kg/cm 2°. Note that the top coat film thickness was 100A.

1-■ Calendar condition pressure 5-100kg/
cm2 and temperature between 50 and 110℃ under various conditions, the surface roughness of the Rmax 10A one was too good, and nakiing occurred at a friction of 0.50 at room temperature. The coat was scratched. Also, during mold holding measurements, high friction caused scraping, making measurements impossible.

(2) By using only MEK, under the conditions (2) and (2), drying was too fast and unevenness occurred.

As shown in Table 1 and above, it can be seen that those having a surface roughness of 20 to 200 have good properties such as mold retention. Furthermore, when we investigated the relationship between surface roughness within 200A, we found that 20~is
It was found that the value to o was -1,'5 dB, which was even more preferable.

Next, Topcoat 2 and 3.4 were treated under the same conditions as 1-■, and the results are shown in Table 2.

Table 2 In Table 2, when the surface roughness was within 200A, good results were obtained in both friction and mold retention, and there was no scraping of the top coat.

The molecular weights of the oligomers and polymers of the present invention are determined by the number average molecular weight determined by the following measuring method.

*Measurement of average molecular weight of binder by GPC
El Permeation Chromatogr
aphy) 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, calculate the average molecular weight in terms of polystyrene.

There are molecules with molecular weight Mi in a given high molecular weight substance.
If there are i pieces, the number average molecular weight Mn=ΣN i M i can be expressed.

ΣNi Also, methods for measuring the various properties mentioned above 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.

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

3. Surface roughness TAYLOR-H, Rmax value measured by Talystep manufactured by 0BSON, cutoff 0° 17mm,
Needle pressure 2mg, needle 0. IX2.5F was used.

Agent Akitoshi Ogiri Agent Akiko Ogiri

Claims (2)

[Claims] (1) A magnetic recording medium comprising a ferromagnetic thin film provided on a non-magnetic base material, characterized in that a top coat layer on the surface of the ferromagnetic thin film has a surface roughness of 20 to 2008 in terms of Rmax. recoding media. (2) The magnetic recording medium according to claim 1, wherein a surface roughness of 20 to 200 A at Rmax is achieved by electron beam or UV radiation.