JPS618730A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled recording medium without generation of clogging in a head and having excellent durability, etc. by forming a topcoat layer contg. a fine-particle pigment having less than specified particle diameter, an antioxidant, and >=1 kind among three components of a monomer, an oligomer, and a polymer on the surface of a magnetic layer on a nonmagnetic substrate. CONSTITUTION:The fine powder of silica or Al2O3 having <200Angstrom mean particle diameter and an antioxidant, especially an antioxidant having a radiation-curing (metha)acrylate group, are simultaneously incorporated into a binder contg. >=1 kind among a monomer, an oligomer, and a polymer to obtain a paint, which is used to form a topcoat layer on a magnetic layer. A lubricant can be preferably incorporated into the topcoat layer. Ferromagnetic alloy powder having >=48m<2>/g specific surface by the BET method is incorporated into a resinous binder to form the magnetic layer having >=1,000Oe coercive force and <=0.08mum surface roughness. The magnetic recording medium having excellent traveling stability, etc. is thus obtained.

Description

[Detailed description of the invention] One skin, four water! The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium that is less likely to clog or drop out and has excellent running stability and durability.

(b) Conventional waves and their problems Currently, magnetic recording media are widely used in the fields of audio, video, computers, magnetic disks, etc., and as a result, the amount of information recorded on magnetic recording media has increased. is increasing year by year, and 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.

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.

Also, in coating-type magnetic recording layers, a top coat layer is provided to protect the magnetic layer, but conventional top coat layers have the disadvantage of being easily peeled off.

In order to improve these drawbacks, the inventors of the present invention have conducted extensive research and found that in a magnetic recording medium in which a magnetic recording layer is provided on a non-magnetic base material, It is proposed in the heading that by providing a top coat layer of a specific component, an excellent magnetic recording medium with improved runnability, durability, etc., which were considered to be the drawbacks mentioned above, can be obtained (Japanese Patent Application No. 1983). -1525
No. 8.

(Japanese Patent Application No. 15259/1982), the inventors of the present invention have conducted further research and found that since the conventional top coat layer does not contain fine particle pigments, the top coat itself does not have a cleaning effect on the head. Therefore, it was discovered that the above-mentioned drawback of easy peeling was found, and the above-mentioned drawback was improved when the top coat layer contained at least one of monomers, oligomers, and polymers, a fine particle pigment of a specific particle size, and an antioxidant. The inventors have discovered that an excellent magnetic recording medium with less clogging, level down, and dropout can be obtained, and have arrived at the present invention.

That is, the present invention provides a magnetic recording medium in which a magnetic recording layer is provided on a non-magnetic base material, in which a top coat layer on the surface of the magnetic recording layer comprises at least one of monomers, oligomers, and polymers, a fine particle pigment, and an antioxidant. The present invention relates to a magnetic recording medium characterized in that the fine particle pigment has an average particle diameter of less than 200.

When a top coat layer is provided on the magnetic recording layer, the friction effect can be improved in the case of a coated magnetic layer, and dust removal and durability can be improved, and the top coat layer can be provided on the ferromagnetic thin film. With this method, a magnetic recording medium with excellent rust prevention, corrosion resistance, durability, and running stability can be obtained.However, as magnetic recording media with a top coat layer are used repeatedly, the top coat layer may wear off on the head. Things stick and accumulate. As a result, clogging, level down, and dropouts are more likely to occur. This tendency is remarkable in those that do not contain fine particle pigments. By containing the fine particle pigment, the fine particle pigment acts as an abrasive, scrapes off the deposits on the head, and has a cleaning effect on the head, thereby eliminating clogging and level drop.

Therefore, dropout can be reduced. Furthermore, when it contains an antioxidant and at least one of monomers, oligomers, and polymers, the antioxidant improves the adsorption of the top coat layer to the magnetic layer, reducing peeling and abrasion of the top coat. Also monomer,
By at least one of oligomers and polymers,
The adhesive force of the antioxidant to the magnetic layer becomes uniform, which improves electromagnetic conversion characteristics and envelope, eliminates minute unevenness, and further reduces abrasion.

In addition, runnability becomes stable under temperature and humidity conditions, especially under high temperature and high humidity conditions, head adhesion and top coat abrasion are reduced, and changes in friction are also stabilized.

As fine particle pigments, ZrO2, Cr203, A120
3, Y203, CeO2,, Fe304.

Fe2O3, ZrSiO4, 5b2o, 5n02, T
Examples include i02.

The particle size of these fine particle pigments is less than 200A, more preferably 150A or less. The particle size of the fine particle pigment is 20
If it exceeds 0 A, the spacing loss becomes large, the output fluctuation becomes large, and the non-uniformity of the fine particle pigment in the top coat layer becomes noticeable, causing image unevenness and distortion, which affects the image.

For example, in the case of S i 02, these fine particle pigments are: ■Ultrafine particle colloidal solution of silicic anhydride (Snowtex, water-based, methanol silica sol, Ichisan Kagaku) ■Ultrafine anhydrous silica produced by combustion of purified silicon tetrachloride (Standard product 100A) (Aerosil, Nippon Aerosil Co., Ltd.), etc.

Further, the ultrafine particle colloidal solution of (1) above, ultrafine aluminum oxide produced by the same vapor phase method as in (2), titanium oxide, and the above-mentioned fine particle pigment may be used.

The antioxidant used in the top coat layer of the present invention may be any antioxidant as long as it prevents metal oxidation.
Common antioxidants are used such as: These are 1
) phenolic antioxidant, 2) amine antioxidant,
3) Phosphorous 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, 1. 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, 2,4-dihydroxybenzophenone, and 2,4.5-dihydroxybenzophenone.
Examples include methacrylate and acrylate types such as trihydroxybutylobenone and hydroquinone.

2) Examples of amine antioxidants include phenyl-β-naphthylamine, 〆-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 the R of the phosphoric acid ester moiety contains an alkyl group, an alkylphenyl group, other chloroethylene, propylene oxide, and the R as 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 include NH4 type, methacrylate type, and acrylate type. Specifically, phosphite esters such as triphenyl phosphite, triotadecyl phosphite, tridecyl phosphite, 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.

Examples include nonylphenyl hydroxy methacrylate phosphate, acrylate types thereof, phenyl phosphate, other alcohols, phenyl phosphates such as nonylphenyl, and phosphoric acid esters such as vanadium acidic phosphate 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)", from the viewpoint of suppressing back-type transfer to the ferromagnetic thin film, 4-Tertiary butyl catechol methacrylate (acrylate), dimethylaminoethyl methacrylate (acrylate), ethyl hydroxy methacrylate (acrylate) phosphate, cetyl hydroxy phosphate methacrylate (acryladra, stearyl methacrylate (acrylate) phosphate), and phenyl types of the above. 2,2'thio-bis(4-methyl-6-tert-butyl-phenol) methacrylate (acrylate)
etc. are preferred. The phosphoric acid ester can be produced by known methods, 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. and prevention of dropouts,
In addition to the characteristic effects such as reducing the difference in output depending on the inner and outer diameters when wound into a roll, it can also have processing effects such as being able to be manufactured online.

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, snolic acid, lylunic 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.

Silicones are those made by modifying fatty acids.

A partially fluorine-modified material is 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: CH3CH2=
CHCOOR, CH2=C-C00RCH2=CH-C
H2GOOR1 CH2= CHCON HCH20COR.

CH20COCH=CH2, RC○0CH=CH,2.

RCOOCH, 2-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 23 or less, and these are fluorine-substituted It is also possible to do this. As a fluorine substituted substance, CnF2nH-1CnF, +r++I (CH2)m
(However, m=1 to 5), R CnF2n++S○2 NCH2CH2-1CnF2
n+1CH2CH2NHCH2CH2-1CnF2n-
10-OQ -COOCH2CH2- and the like.

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

As the polymer used in the top coat layer of the present invention, thermoplastic, thermosetting, or reactive resins conventionally used for magnetic recording media, or mixtures thereof, are used, but the strength of the resulting coating film, etc. A radiation-curing type resin is preferred, particularly a radiation-curing type resin.

As a thermoplastic resin, the softening temperature is 150°C or less.

Those with an average molecular weight of 10,000 to 200,000 and a degree of polymerization of about 200 to 2,000, such as vinyl chloride-vinyl acetate copolymers (including those with carboxylic acid introduced), vinyl chloride-vinyl acetate- Vinyl alcohol copolymers (including those with carboxylic acid introduced), vinyl chloride-
Vinylidene chloride copolymer, vinyl chloride-acryoni 1
~Ryl copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer
.

Polymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, urethane elastomer, nylon-silicon resin, nitro Cellulose-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 copolymer, amino resin,
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. Also, 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, and melamine resin.

Alkyd stool fat, silicone resin, acrylic reactive resin,
Epoxy-polyamide resins, nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycol/ High molecular weight diol/triphenylmethane triisocyanate mixtures, 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-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 various 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 is (A) having two or more unsaturated double bonds that are curable by radiation.

A plastic-like compound with a molecular weight of 5,000 to 100,000, (B) having one or more unsaturated double bonds that are curable by radiation, or having no radiation curability, and a molecular weight of 3,000 to 100,000. and (C) an unsaturated double bond that is curable by radiation.
A compound having a molecular weight of 200 to 3,000,
(A) 20-70% by weight, (B) 20-80% by weight, (
C) A combination used in a proportion of 10 to 40% by weight.

The radiation-curable monomers, radiation-curable oligomers, and radiation-curable polymers used in the top coat layer of the present invention include acrylic acid, methacrylic acid, which has an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability; Alternatively, groups that can be crosslinked or polymerized and dried by radiation irradiation, such as acrylic double bonds such as those in ester compounds, allylic double bonds such as diallyl phthalate, and unsaturated bonds such as maleic acid and maleic acid derivatives, can be added to the molecule. Examples include polymers, oligomers, and polymers contained or introduced therein.

Compounds with a molecular weight of less than 2,000 are used as radiation-curable monomers, and compounds with molecular weights of 2°000 to 1 as oligomers are used.
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,
Examples include 6-hexane glycol diacrylate, but particularly preferred are N-vinylpyrrolidone,
Pentaerythritol tetraacrylate (methacrylate), pentaerythritol triacrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate (Aronix M-7100, M-540)
0,5500, 5700, etc., Toagosei), acrylic modified products of Tuboran 4040) in urethane elastomers, or those into which functional groups such as C0OH are introduced, acrylates (methacrylates) of phenol ethylene oxide adducts, the following general An acrylic group (methacrylic group) or ε-
caprolactone - a compound with an acrylic group, where m=1. Compounds where a=2 and b=4 (hereinafter).

special pentaerythritol metal shrinkage material A), rn=1
, a compound where a = 3, b = 3 (hereinafter referred to as special pentaerythritol condensate B), a compound where m = 1, a = 5, b = o (hereinafter referred to as special pentaerythritol condensate C), m = 2 , a = 5, b = o (hereinafter referred to as special pentaerythritol condensate), and special acrylates represented by the following general formula.

(1) (CH2=CHCOO(Jl) 3-CCH
,ON (special acrylate A) (2) (CI2 =CHC00CH) 3 CCH
2CHa (special acrylate B) (3) (CHz=CHCOnOC3H,;)n 0C
HJ) 3 CCH2CI (3 (Special Acrylate D) (Special Acrylate E) CH, CH2COOCH=CH.

(Special acrylate F) (7) CH2C00CH= C
H.

(Special acrylate G) (8)C8,=CHC0O-(CH,CH20)4-C
OCH=CH2 (Special Acrylate H) (Special Acrylate E) (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.

By using at least one organic binder among these monomers, oligomers, and polymers, the top coat layer is reinforced, the breaking strength of the paint film is increased, the paint film is strengthened, the top coat is less likely to wear off, and it can withstand high temperatures. Stable running performance under high humidity conditions. Therefore, a magnetic recording medium with less dropout, less head adhesion, less top coat abrasion, and stable friction changes can be obtained. Further, when a radiation-curable binder is 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.

In the top coat layer, the above-mentioned fine particle pigment has a molecular weight of 15°000~
It contains 1,000,000 pieces/100P2, preferably 20,000 to aoo, oo.

piece/100P2. Since the antioxidant is within the electrically acceptable range up to a top coat film thickness of 450A, the antioxidant is applied to a thickness of 450A. When the top coat film thickness is less than 5A, the amount of antioxidant decreases, the adhesion to the magnetic recording layer becomes weaker, and abrasion occurs, which tends to cause clogging, level down, and dropout, especially in the case of ferromagnetic thin films. The rust prevention effect is weakened, corrosion occurs, the film is severely damaged, and the output of electromagnetic conversion characteristics is reduced.

Organic binder of the above monomer, oligomer, or polymer: antioxidant = 10:90 to 90:10, preferably 1
0:90 to 70:30 (by weight), and the lubricant is 0.5 to 300 parts by weight per 100 parts by weight of the organic binder and ten antioxidants.

When the amount of the organic binder of the present invention is less than this,
A uniform adsorption force of the antioxidant to the magnetic layer cannot be obtained, and scraping occurs, making clogging, level reduction, and dropout more likely to occur.

Furthermore, by adding carbon black, dropout prevention measures are more effective. At this time, carbon/fine particle pigment = 1/9 to 8/2, preferably 1/9 to 515
It is.

The thickness of the top coat layer is preferably 5 to 8,000. If it is too thick, it may cause a decrease in mold retention or cause scratching. Also, if it is too thin, clogging will occur. In the case of a ferromagnetic thin film, it is preferably 450A or less. 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 top coat layer is formed thereon, 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 preferable range is 5
-450A, and 10-300A is more preferable.

On the other hand, the magnetic layer of the present invention can be applied to either a coating type consisting of a coating film containing 1 ferromagnetic particles and a binder, or a metal thin film type consisting of a ferromagnetic metal thin film. 304, Co-doped 2'Fe2O3, cO-doped Fe 203
F B'304 solid solution-Co-based compound coated type 2'-F
e203, Co-based compound coated Kun-Fe3Oe
(2' Also includes an intermediate oxidation state with Fe2O3. Co-based compounds here include cobalt oxide, cobalt hydroxide, cobalt ferrite, cobalt ion adsorbates, etc., which utilize the magnetic anisotropy of cobalt to improve coercive force. )
, or iron, cobalt, nickel and other ferromagnetic metals, or Fe-Co, Fe-Ni, Co-Ni, Fe-
Rh% Fe-Cu, Fe-Au-Co-Cu,
C.

-Au, Go -Y-Co-La, Co-Pr
, Co-Gd, Go-8m, Co-Pt,
NiCu, Fe-Co-Nd, Mn
Bi, Mn-8b, Mn-Al, Fe-Go
Examples include magnetic alloys such as -Cr and Go-Ni-Cr, and ferrite-based magnetic materials such as Ba ferrite and Sr ferrite.

Conventionally, as a ferromagnetic powder, for example, 7y)'e203
, does it contain CO? r-F e203, F e304, G
.

Containing Fe5o4, C'02, etc. were often used,
The magnetic properties of these ferromagnetic powders, such as coercive force and maximum residual magnetic flux density, are insufficient for high-sensitivity, high-density recording.
It is not very suitable for signals with a short recording wavelength of about 1)-m or less or for magnetic recording with a narrow track width.

As requirements for magnetic recording media become more stringent, ferromagnetic powders with properties suitable for high-density recording have been developed and proposed. Such magnetic powders include Fe, C01
Metals or alloys such as Fe-Co, Fe-Co-Ni, Co-Ni, and A1. There are alloys with Cr, Si, etc. A magnetic recording layer using such an alloy powder must have a high coercive force and a high residual magnetic flux density for the purpose of high-density recording, and various manufacturing methods or alloys are used to make the magnetic powder meet these standards. Preferably, the composition is selected.

The inventors manufactured magnetic recording media using various alloy powders, and the specific surface area measured by the BET method was 48 m2/g.
In the above, the coercive force of the magnetic layer is 10,000e or more, and the surface roughness of the magnetic layer is [R20 (average value of 20 times) at a cutoff of 0° and 17 mm when measured by Talystep described below.
It has been found that a magnetic recording medium with a sufficiently low noise level and suitable for high-density, short-wavelength recording can be obtained when the value (hereinafter the same applies) is 0.08/- or less. When the top coat layer of the present invention is combined with the top coat layer of the present invention, the effect of reducing the cinching phenomenon (loosening of the winding during rapid stop), dropout, and friction is produced. As plastic films such as phthalate, polyimide, and polyamide tend to be thinner, with a thickness of approximately 11 μm or less, the tightness of the tape is becoming increasingly tight, which can lead to roughness of the back surface, especially when there is a back coat. is transferred to the magnetic surface, causing a decrease in output. However, the above-mentioned combination of the magnetic recording layer and top coat layer is preferable because such problems can be alleviated. In addition,
Ferromagnetic substances whose main component is ferromagnetic metal have high electrical resistance and are prone to dropouts, so countermeasures against static electricity are required. problems can be solved, which is extremely convenient.

The preferred range of coercive force in the magnetic recording layer is 100
0 to 20,000e, and if the magnetic head exceeds this range, the magnetic head will become saturated during recording, and demagnetization will become difficult. The larger the specific surface area of magnetic powder, the more likely it is to improve the S/N ratio.
It has been found that if the specific surface area is too large, the dispersion of the magnetic powder into the binder becomes poor and the effect tends to be saturated. On the other hand, the surface roughness of the magnetic recording layer affects the recording sensitivity, and when the surface roughness is small, the recording sensitivity at short wavelengths increases. Ferromagnetic alloys that can satisfy the above characteristics include C01FeCo, Fe-Go-Ni, Co
-Ni, etc., and Cr.

A1. A fine powder to which Si or the like is added is used. These are fine powders obtained by wet reduction of metal salts with a reducing agent such as BH4, fine powders obtained by coating the surface of iron oxide with an St compound and then dry reduction in H2 gas, or fine powders obtained by evaporating alloys in low-pressure argon. It is a fine powder or the like, has an axial ratio of 1:5 to 1:10, has a residual magnetic flux density Br of 2000 to 3000 Gauss, and satisfies the above conditions of coercive force and specific surface area.

The alloy magnetic powder can be made into a magnetic paint using various binders, but thermosetting resin binders and radiation curing binders are generally preferred, and other additives such as dispersants, lubricants, and antistatic agents are also used. It can be used according to conventional methods. Since magnetic powder with a BET specific surface area of 48 m2/g or more is used, there is a problem with monodispersibility, so it is preferable to use a surfactant, an organic titanium coupling agent, a silane coupling agent, etc. as a dispersant. As a binder, vinyl chloride/vinyl acetate/vinyl alcohol copolymer,
A binder consisting of a polyurethane prepolymer and a polyisocyanate, a binder further containing nitrocellulose, and other known thermosetting binders,
Alternatively, a radiation-curable binder containing an acrylic double bond, a maleic double bond, or the like that is sensitive to ionization energy as a resin group can be used.

According to a conventional method, the alloy magnetic powder is mixed with a binder, a prescribed solvent, and various additives to form a magnetic coating, which is applied to a substrate such as a polyester base and cured by heat or radiation to form a magnetic film. Then, calendar processing is further performed.

It is more preferable to use a radiation-curable binder because it allows continuous curing during production and eliminates the above-mentioned back-type transfer, thereby preventing dropouts. On top of that,
Radiation curing can be done online, which helps save energy and reduce the number of people involved in manufacturing, leading to lower costs.

In terms of characteristics, in addition to dropouts caused by tight winding during thermosetting, differences in pressure at the inner and outer diameters when wound into a roll can cause output differences depending on the distance in the length direction of the magnetic tape. It disappears.

Base thickness is 11. It becomes thinner than μm, and the hardness of the metal magnetic powder? -Since it is smaller than magnetic oxides such as Fe203, the surface hardness of the magnetic layer is small and it is easily affected by winding tightness, but this effect can be removed with a radiation-curable back coat layer, and the inner and outer diameters This is particularly preferable because it can eliminate output differences and dropout differences.

The ferromagnetic metal or ferromagnetic alloy used in the ferromagnetic thin film of the present invention includes iron, cobalt, nickel, other ferromagnetic metals, Fe-Co, Fe-Ni, Go-N
i, Fe-Rh, Fe-Cu.

Fe-Au, Co-Cu, Go-Au, Co-Y, Go
-La, C'o-Pr, Co-Gd, Co-8m, C
o-Pt, Ni-Cu, Fe-Co-N
d, Mn-B i, Mn-8b, Mn-Al, F
Examples include magnetic alloys such as e-Co-Cr and Co-Ni-Cr.

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 manufactured by the above-mentioned method can be used. (1) in which the width direction is inclined at 50 degrees with respect to the evaporation source in a vacuum, which is currently generally practiced, is that the direction of vapor deposition is inclined in the longitudinal direction (90 degrees to 30 degrees). ) and the width direction; is not inclined, and the atmosphere is 02 or 02 and Ar.
(2) is preferably used, which is vapor-deposited at ~I x 10 = Tor r while introducing.

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 so that the surface opposite to the base contains only oxide.

The oxygen content of the ferromagnetic thin film containing oxygen is (0/magnetic metal)×100, which is 3 to 60%.

A method for providing a top coat layer containing at least one of monomers, oligomers, and polymers, fine particle pigments, antioxidants, lubricants, etc. on the surface of the magnetic recording layer is to dilute the additives with a solvent and coat them on the surface of the magnetic layer. There are methods such as thin coating, vaporization of the additive in the air, inert gas, or vacuum and applying the vapor to the surface of the magnetic layer, and methods of mixing and coating with a binder. can do.

In addition, when using radiation-curing additives in the magnetic layer and top coat layer of the present invention, the active energy rays used for crosslinking include electron beams using a radiation accelerator as a radiation source, Co
60 as a radiation source, β-rays as a 5r90 radiation source, X-rays or ultraviolet rays as a radiation source in 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 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 contains an organic binder and the like.

As described above, in the present invention, the top coat layer on the magnetic recording layer contains at least one of monomers, oligomers, and polymers, a fine particle pigment (less than 20 OA), and an antioxidant. In addition to the excellent rust prevention, corrosion resistance, durability, and running stability that can be achieved by providing a top coat layer, the adsorption power of the antioxidant to the magnetic layer can be enhanced by the above-mentioned monomers and oligomers. , the polymer makes it more uniform, the shape retention and envelope are better, there is less abrasion caused by minute unevenness, a strong top coat layer is formed, there is no damage to the film, and the runnability is stable under high temperature and humidity. This results in excellent effects such as less head adhesion, less top coat abrasion, and more stable changes in friction.

E) Utilization of H 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 one of the most important characteristics. It is very useful as it can be used as a videotape, computer tape, or video floppy.

In recent years, the present invention is applicable to video cassette tapes, which have seen remarkable technological progress and whose marketability is likely to expand, master tapes for video tape contact transfer printing, and 8mm video cassette tapes and video floppies, whose markets are expected to expand. By using a magnetic recording layer provided with at least one of monomers, oligomers, and polymers, fine particle pigments (less than 20 OA), and a top coat layer containing an antioxidant, a high-performance magnetic recording layer with extremely good electromagnetic characteristics and physical property reliability is used. A high performance tape can be obtained, and it can be said that the magnetic recording medium of the present invention is highly useful and excellent.

(8) Examples of the present invention are shown below. It should be understood that the present invention is not limited to these Examples.

Example (1) Member and star Mukaho 1 Injection type Parts by weight Cobalt-coated needle-shaped -F e 203 120 parts (major axis 0.4 tons,
Single shaft 0.05P, He 6000 e) Carbon black 5 parts (Mitsubishi carbon black for antistatic use M A-600) Al2O3 powder (
0,5,-powder) 2 parts powder (soybean oil refined lecithin) 3 parts solvent (MEK/toluene 501
50) Mix 100 parts of the above composition in a ball mill for 3 hours to better wet the acicular magnetic iron oxide with the dispersant.

Next, 10 parts of acrylic double bond-introduced saturated polyester resin (in terms of solid content) Io parts of acrylic double bond-introduced salt-vinyl acetate copolymer (in terms of solid content) 10 parts of acrylic double bond-introduced polyether urethane elastomer (in terms of solid content) Type conversion) Solvent (MEK/
A mixture of 200 parts of toluene 5 (1150), a lubricant (higher fatty acid modified silicone oil) and 3 parts of a binder is thoroughly mixed and dissolved. This was put into the ball mill that had been subjected to the magnetic powder treatment and mixed and dispersed again for 42 hours.

The magnetic paint obtained in this way was applied onto a polyester film of No. 15, oriented on a permanent magnet (1600 gauss), the solvent was dried with an infrared lamp or hot air, and after surface smoothing treatment, ESI Acceleration voltage 150K using electrocurtain type electron beam accelerator manufactured by
eV, electrode current 20 mA, total irradiation dose 5 Mr.
The coating film was cured by irradiation with an electron beam under N2 atmosphere under these conditions.

Ton” 1 fake mail Weight part Fe
-Go-Ni alloy powder 100 (Hc=1
2000e, major axis 0.4 part m, minor axis 0°O5Pm, BE
T specific surface 8252 m2/g) Vinyl chloride/vinyl acetate/vinyl alcohol copolymer (UCC Co., USA)
! VAGH) I 5 Polyvinyl butyral resin 10 Acrylic double bond introduced urethane 10 Methyl ethyl ketone/toluene (
50150) 250 to polyester film 3
．． It was coated to a thickness of 5P, and subjected to electron beam curing and calendering.

3 Magnetism 1) A polyester film with a thickness of 12 Pm was moved along the circumferential surface of a cylindrical cooling can, and 02+Ar (volume ratio 1:
l) at a rate of 800 cc per minute and the degree of vacuum was set to 1. OX
In a chamber with 10=Tor r, Co8O-
An alloy consisting of Ni20 is melted and the incident angle is 90° to 30°.
Co-N with a film thickness of 0.15Pm was deposited obliquely only on the 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. He
= 10000 e. The average amount of oxygen in the film was 40% at an atomic ratio of Co to Ni (0/CoN i) x 100.

A polyester film with a thickness of 127 m was moved along the surface of a cylindrical cooling can, and the degree of vacuum was set to 5, OX.
In a chamber set to 10-6T, o r r,
Sacrifice IJL! - Vapor deposition was carried out in the same manner as in case -. Film thickness is 0°1
5Pm and consists essentially of G o -N i.

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. Hc
= 9000 e. The average amount of oxygen in the film was 45% in atomic ratio to Co and Ni.

53 A 12 μm thick polyester film was moved along the curve of a cylindrical cooling can in the same manner as m[, except that the oxidation step with oxygen was omitted, and the degree of vacuum was set to 5. OXI 0-6
Deposition was carried out in the same manner as on W in a chamber set to Torr. The film thickness is 0.45Pm and is essentially Go-Ni.
It was more than that. He”9500e.

(2) Formation of top coat layer O Top coat composition Top coat 1 parts by weight dimethylaminoethyl methacrylate-ho, 5 colloidal Si
O2 particle size 150A 0.01 pentatrithritol tetraacrylate molecular weight 352 0.2 stearic acid 0.1KMEK
100 Top coat composition 2 Part by weight Monoglycol salicylate acrylate 0.3 ■ Manufacturing method Nocolloida/L
/TiO2100A 0.04 Pentatritrithritol tetraacrylate molecular weight 352 0. I N-vinylpyrrolidone Molecular weight 111 0.1 Fluorine (electrolytic method) 0.2 MEK/Toluene (1/1) 100 Topcoat 3 Methacryloxyethyl phosphate 1. OCr
203 (vapor phase method similar to ■, 180A) 0.01
Acrylic modified PVC monoacetate vinyl alcohol copolymer (
Contains maleic acid) Molecular weight: 20,000 0.2 Trimethylolpropane triacrylate Molecular weight: 296
0.2 myristate myristylate 0.1 behenic acid 0.2 stearic acid acrylate 0.1 cyclohexanone 100s JiiJLL Dimethylaminoethyl methacrylate, pentaerythritol tetraacrylate, and stearic acid in top coat composition 1 to 0.5: 0° 2: Q, IK,
The film thickness was adjusted by changing K. Coated on the magnetic layers 1, 2 and 3 respectively, 150 KeV, 8 mA,
4 Mrad.

Irradiation was performed in N2 gas. The amount of 5i02 was determined by electron microscopy.
00,000 pieces/100. It was J-m2. The relationship between this film thickness and output is shown in FIG. In the figure, A indicates the magnetic layer 1, and A indicates the magnetic layer 2.3.

From FIG. 1, it can be seen that for magnetic layer 1, the output decreases within 3.5 dB when the thickness is 800^ or less, and for magnetic layer 2.
As for No. 3, it was found that those with a film thickness of 450 8 or less were good with an output drop of 3.5 dB or less. Those below 5A had poor adsorption properties and were prone to falling off from the coating film, making them unusable.

Large spot ■λ Top coat composition 2 was applied on top of magnetic layer 1, heated and dried, and heated to 150 KeV, 10 mA, 5 M rad, N2
Irradiation was performed in gas. The film thickness was 70A. As a comparative example, top coat composition 2 excluding the binder (ratio 2) was adopted, and the characteristics of these magnetic recording media were
Shown in the table.

Table 1 In Table 1, TC abrasion indicates top coat abrasion, and DO indicates dropout.

At 0°C, top coat with binder (Real 2, T i
There were no problems with both the top coat containing 800,000/100)-2 O2 in the top coat layer and the top coat without binder (Ratio 2), but when running at a high temperature of 40°C and 80%, Example 2 Compared to Comparative Example 2, head adhesion and
No more clogging and fewer dropouts. Steel properties are also further improved.

Daiarashiso 1 Top coat composition 3 was applied on the magnetic layer 2, dried by heating, and irradiated at 150 KeV, 8 mA, 4 Mrad, in N2 gas. The film thickness was 1,508 mm. As comparative examples, top coat composition 3 without the binder (ratio 3) and without top coat (ratio 3') were listed. Table 2 shows the characteristics of these magnetic recording media.

DO Nitro Tube Out At 20℃, there is no difference between the top coat with binder (Real 3) and the top coat without binder (Ratio 3), but 4
When running at a high temperature of 0°C and 580%, Example 3 had less head adhesion, clogging, level reduction, and
There is no top coat abrasion, there are fewer dropouts, and the running performance at high temperatures is improved. The one without top coat (ratio 3') is unfavorable in terms of head adhesion, clogging, level reduction, top coat scraping, dropout, and high-temperature running properties.

Top coat composition 2 was applied onto the magnetic layer 3, heated and dried, and irradiated at 150 KeV, 8 mA, 4 Mrad in N2 gas. The film thickness was 70A.

5 pieces of salmon Top coat composition 2 is applied on top of magnetic layer 4.

The same treatment as in Example 4 was performed. The film thickness was 70A.

Example 4 Top coat composition 3 was applied on top of the magnetic layer 5.
The same treatment was applied. The film thickness was 1,508 mm.

As a comparative example, top coat composition 2 of Example 4 except that the binder was removed (ratio 4) was used. Table 3 shows the characteristics of these magnetic recording media.

As you can see from Table 3, the one with binder (actual 4.5
．． 6) No head adhesion, no clogging, no level down,
There are also fewer top coat scratches and dropouts.

In this way, by adding a binder, antioxidant (rust preventive agent), and particulate inorganic pigment, stability at high temperature running is ensured, and a self-cleaning effect appears, preventing head adhesion, clogging, and leveling. Down and top coats are no longer wrinkled.

When 1508 and 0.01 parts by weight of carbon black were added to Example 4.6, the dropout decreased from 100 to 5.
The number decreased from 0 pieces/min to 100 pieces/min to 40 pieces/min. It can be seen that the addition of carbon black has an effect.

The method for measuring the above characteristics is as follows.

(2) Clogging The VH8 was modified and set to conditions where clogging was likely to occur, and measurements were taken at various temperatures and humidity.

2. Modify the dropout VH3, set it to conditions where dropouts are likely to occur, record a single 5 MHz signal under various conditions such as temperature and humidity, and when played back, the signal will be lower than the average playback level. Count the number of samples for which the time for which the drop is 18 dB or more is 15 P seconds or more per minute for 10 samples,
Take the average.

3. Head adhesion and top coat chipping V HS was modified and the deck in the above conditions was run a certain number of times at various temperatures and humidity, and head adhesion and top coat chipping were observed using microscopic photographs.

4. Estimating the average particle size of the fine particle pigment contained in the top coat layer using a scanning electron microscope, an acceleration voltage of 0.5, ~20 KeV, and a magnification of 10,000 to 100,000 times, using the average particle size and number a, Count 10 points in a field of view of 100P2. In this case, the particles may be agglomerated, so if the variation is large, measure the primary particle diameter.

51 Count 10 points in the field of view of 100P2 and correct them for each 100P2.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of the relationship between top coat film thickness and output in various magnetic layers.

Claims (5)

[Claims] (1) In a magnetic recording medium in which a magnetic recording layer is provided on a non-magnetic base material, the top coat layer on the surface of the magnetic recording layer contains at least one of monomers, oligomers, and polymers, a fine particle pigment, and an antioxidant. A magnetic recording medium, characterized in that the fine particle pigment has an average particle diameter of less than 200 Å. (2) The magnetic recording medium according to claim 1, wherein the antioxidant is radiation-curable. (3) The magnetic recording medium according to claim 1 or 2, wherein the top coat layer contains a lubricant. (4) The magnetic recording layer is made of a resin binder in which ferromagnetic alloy powder having a specific surface area of 48 m^2/g or more is dispersed by the BET method, and the coercive force of the magnetic layer is 1000 O.
The magnetic recording medium according to claim 1, 2, or 3, wherein the surface roughness of the magnetic layer is 0.08 μm or less. (5) The magnetic recording medium according to claim 1, 2, or 3, wherein the magnetic recording layer is made of a ferromagnetic thin film.