JPH0679376B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium excellent in running property, surface electrical resistance and scratch resistance.

[Prior Art] Conventionally, as a magnetic recording medium such as a video tape, an audio tape, a memory tape, and a magnetic disk, a magnetic layer in which ferromagnetic fine powder is dispersed in a binder is provided on one surface of a non-magnetic support, Those having a back layer on the surface are widely used.

Various measures have been taken to improve the running characteristics of such magnetic recording media. For example, the friction coefficient (μ value) is reduced to improve the running property, or the surface electric resistance is reduced to accumulate static electricity. In order to prevent the formation of carbon black, to provide head cleaning properties and to improve running properties, abrasives such as α-alumina (α-Al ₂ O ₃ ) and chromium oxide (Cr ₂ O ₃ ) Have been attempted to be included.

[Problems to be solved by the invention]

However, even by such means, the coefficient of friction,
It is not possible to satisfy all of the dropout reduction, scratch resistance, running durability, etc., and the development of means that can satisfy all of these is desired.

[Means for solving problems]

The present inventors have conducted various studies on the above additives in order to obtain a magnetic recording medium having excellent characteristics as described above, and as a result, by using α-alumina and carbon black, which have a specific average particle size relationship, in the magnetic layer. The present invention was achieved by succeeding in obtaining a magnetic recording medium excellent in various characteristics.

That is, the present invention provides a magnetic recording medium having a magnetic layer having ferromagnetic fine powder dispersed in a binder on one surface of a non-magnetic support and a non-magnetic back layer on the other surface of the non-magnetic support. Further, α-alumina and carbon black are contained in 2 to 7 parts by weight of α-alumina and 2 to 7 parts by weight of carbon black with respect to 100 parts by weight of the ferromagnetic fine powder, and the average particle size of α-alumina is 0.01. .About.0.4 μm, and the average particle size of carbon black is 1/1 / the average particle size of α-alumina.
It is a magnetic recording medium characterized by being doubled.

The average particle size of α-alumina is 0.01 μm to 0.4.
It is preferably about μm.

Hereinafter, the present invention will be described in detail.

The ferromagnetic fine powder used in the present invention includes γ-Fe ₂ O ₃ ,
Co-containing γ-Fe ₂ O ₃ , FeOx (1.33 <x ≦ 1.5), Co-containing F
Ferromagnetic iron oxides such as eOx (1.33 <x ≦ 1.5), chromium dioxide, and ferromagnetic alloy powders that are conventionally used for coating type magnetic recording media are all used.

As the binder used in the magnetic layer and the back layer of the present invention, conventionally used thermoplastic resins, thermosetting resins,
A reactive resin or a mixture of these is used.

The thermoplastic resin has a softening temperature of 150 ° C. or lower, an average molecular weight of 10,000 to 300,000, and a degree of polymerization of about 50 to 2000. Acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester Styrene copolymer, urethane elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyvinyl alcohol, vinylidene acrylonitrile copolymer,
Butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, 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 in the coating liquid state.
The molecular weight is 200,000 or less, and by heating after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. 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 isocyanate prepolymer. Polymer mixture, methacrylate copolymer and diisocyanate prepolymer mixture, polyester polyol and polyisocyanate mixture, urea formaldehyde resin, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate mixture, polyamine resin and the like And the like.

The α-alumina used in the magnetic layer of the present invention preferably has an average particle size of 0.01 μm to 0.4 μm, and more preferably 0.04 μm to 0.2 μm.
AKP20 (0.4μm or less), AKP30 (0.3μm or less), AKP50 (0.2μm), AKP80 (0.15μm), Hit50
(0.2 μm) and Hit100 (0.06 μm) (trade names, all manufactured by Sumitomo Chemical Co., Ltd.). Among them, especially AKP80, Hit5
0 and Hit100 are preferable.

As the carbon black used in the present invention together with the α-alumina, those having an average particle size of 1 to 1/2 times the average particle size of α-alumina are used.

If the combination of the average particle diameters of both is out of the above range, preferable improvements in various properties cannot be obtained. For example, when the average particle size of carbon black is larger than the average particle size of α-alumina, the surface property is improved, the μ value is decreased, the occurrence of dropout is reduced, but the scratch resistance is deteriorated, The average particle size of carbon black is 1/2 of the average particle size of α-alumina
If it is smaller, μ value and scratch resistance are improved,
The surface property becomes poor and the occurrence of dropout increases.

The addition amount of the above additive is the ferromagnetic fine powder in the magnetic layer.
2 to 7 parts by weight of α-alumina and 2 to 7 parts by weight of carbon black are used per 100 parts by weight. Commercially available carbon black is used, for example, Conductex SC
(Colombian), 0.02μm, HS100 (Electrochemical industry)
0.05 μm, BS200 (Cabot) 0.01 μm, BP800 (Cabot) 0.02 μm, Asahi # 80 to Asahi # 35 (Asahi Carbon), etc.

The thickness of the magnetic layer is 10 times or more the average particle size of the α-alumina, preferably 2 μm to 6.5 μm.

The thickness of the back layer is preferably 0.1 μm to 2.5 μm.

The magnetic layer of the present invention may further contain other additives such as a dispersant and a lubricant, if necessary.

Further, in the back layer in the present invention, a lubricant, a dispersant,
Additives such as antistatic agents and abrasives can be added. Of these, the fatty acid ester is preferably added in an amount of 0.3 to 3 parts by weight (based on 100 parts of the ferromagnetic fine powder). The fatty acid ester preferably has 11 to 25 carbon atoms.

The organic solvent used in the present invention when dispersing, kneading and coating the above components, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, a ketone system such as tetrahydrofuran at any ratio; methanol, ethanol, propanol, Alcohols such as butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol; methyl acetate,
Ester type such as ethyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate monoethyl ether; ether type such as diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether, dioxane; benzene, toluene, xylene, Tar-based compounds (aromatic hydrocarbons) such as cresol, chlorobenzene and styrene; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde , Hexane, etc. can be used.

As the material of the support used in the present invention, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose derivatives such as cellulose diacetate, vinyl resins such as polyvinyl chloride, polycarbonate, Examples include plastics such as polyamide and polysulfone.

The magnetic recording medium of the present invention is obtained by coating the above components on the above-mentioned support, orienting the magnetic field while drying, and after drying, if necessary, surface treatment such as calendering may be performed. Good.

The back layer may be provided before or after the magnetic layer is provided, and the additives as described above are dispersed and kneaded in the organic solvent together with the binder, and then dried.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

Example 1 The following composition was put into a ball mill and sufficiently kneaded, and then 23 parts of Desmodur-75 (trade name of polyisocyanate compound manufactured by Bayer Co.) was added and uniformly mixed and dispersed to prepare a magnetic paint.

Co-containing γ-Fe ₂ O ₂ powder 300 parts (nitrogen adsorption specific surface area 30 m ² / g) (powder Hc = 700 Oe) 300 parts Vinyl chloride-vinyl acetate compound (VMCH, Union Carbide Co.) 38 parts Nipporan N2304 (Japan Polyurethane) 15 parts Carbon black 8 (Average particle size: Table 1) α-Al ₂ O ₃ 18 parts (Average particle size: Table 1) Oleic acid 3 parts Octyl laurate 3 parts Lauric acid 1.5 parts Butyl acetate 600 parts Methyl ethyl ketone 300 parts This magnetic coating material was adjusted in viscosity and then coated, oriented and dried on the surface of a polyethylene terephthalate substrate to form a magnetic layer.

Next, after kneading and adjusting the back liquid of the following composition with a ball mill, 20 parts of Coronate 3040 (polyisocyanate manufactured by Nippon Polyurethane Company) was added and uniformly mixed and dispersed, and then 2.0 μ thick on the polyester substrate surface opposite to the magnetic layer. And then dried to form a back layer.

Carbon black (HS-100, average particle size 50mμ) 10
0 parts Nipporan-2304 (manufactured by Nippon Polyurethane) 60 parts Vinyl chloride-vinyl acetate compound 40 parts Methyl ethyl ketone 700 parts Butyl acetate 300 parts After mirror-reflecting these tapes with a calender, slit them into 1 inch width to No. 1 to No. The sample of .6 was created.

Table 1 shows the results obtained by performing a specific test as described below on these samples.

(Number of drop outs) Deck using Shiba Soku dropout counter
We examined the number of dropouts of 5 × 10 ^-6 seconds per minute after running 100 passes.

(Scratch on the magnetic layer) For scratches on the magnetic layer, a level of scratches (visual observation) on the magnetic layer after applying a load of 100 g for 5 minutes in the still image of the deck and no scratches ○, streak The one containing
The one with cutting scratches was marked with x.

(VTR Running Tension) Using the VTR, the tape running tension (T ₁ ) at the cylinder inlet side and the tape running tension (T ₂ ) at the cylinder outlet side were observed to find T ₂ / T ₁ . The tape used was a 50-pass running product.

[Effects of the Invention] As is clear from the results of Table 1, it is best that the fillers used in the magnetic layer are similar, and the average diameter of carbon black is smaller than the average particle diameter of α-alumina. 1
It turns out that it is preferable to be ˜1 / 2 times. An increase in the average particle size of carbon black is not preferable because the effect of α-alumina is not exhibited.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hideaki Furusagi 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd. (56) Reference JP-A-61-229233 (JP, A) 62-26630 (JP, A) JP-A-54-97403 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording medium having a non-magnetic backing layer on one surface of a non-magnetic support and a non-magnetic back layer on the other surface of the non-magnetic support. Further, α-alumina and carbon black are added to the ferromagnetic fine powder.
2 to 7 parts by weight of α-alumina and 2 to 7 parts by weight of carbon black per 100 parts by weight, the average particle size of α-alumina is 0.01 to 0.4 μm, and the average particle size of carbon black is A magnetic recording medium characterized by having an average particle diameter of 1 to 1/2 times that of α-alumina.