JPS628330A - magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersiblity of carbon black and polishing agent and to improve an electromagnetic conversion characteristic and running durability by subjecting a pigment and binder to powder mixing and dispersing. CONSTITUTION:The pigment and binder subjected to powder mixing are used. A polyurethane resin, etc. are used for the binder. A higher fatty acid such as lecithin is usable as the dispersant. alpha-Alumina, etc. are used for the polishing agent. The carbon black having preferably 100-30mmu size of primary particles is added to the mixture. A Henschel mixer is optimum as a powder mixing and dispersing machine. The dispersiblity of the carbon black and polishing agent is improved by such constitution, by which the electromagnetic conversion characteristic and running durability are improved.

Description

[Detailed description of the invention] Industrial applications The present invention relates to audio tapes and video tapes.

The present invention relates to a magnetic recording medium that can be used for magnetic cards, magnetic disks, etc.

BACKGROUND OF THE INVENTION In recent years, efforts have been made to improve the dispersibility of magnetic paints, particularly in video tapes, in order to improve their electromagnetic conversion characteristics (actual running characteristics). Attempts have been made to make magnetic powder into finer particles and to use binders with hydrophilic groups introduced, but the dispersion of pigments such as carbon black and abrasives has not yet reached a satisfactory state.

Regarding carbon black, a carbon black surface-treated with a radical-generating metal has been proposed in Japanese Patent Application No. 58-139793, but it has the problem that it must be used in combination with a radiation-curable resin.

Regarding dispersion of an abrasive, dry mixing of a dispersant and an abrasive is proposed in Japanese Patent Application No. 58-139067.

However, the adhesion with the binder component has not been improved, and there have been drawbacks such as powder falling and increased noise.

Problems to be Solved by the Invention Conventionally, carbon black was considered to be an antistatic agent, but now its function as a solid lubricant is becoming more important. On the other hand, abrasives are indispensable due to the problem of the interface between the magnetic recording medium and the magnetic head. From the above viewpoint, in a magnetic recording medium to which both carbon black and abrasive are added, improvement in their dispersibility leads to improvement in electromagnetic conversion characteristics and running durability.

In the conventional examples, improvement in the dispersibility of both carbon black and abrasive was not clarified. In view of the above problems, the present invention improves the dispersibility of carbon black and abrasive, and improves electromagnetic conversion characteristics and running durability. The present invention provides a magnetic recording medium with improved properties.

Means for Solving the Problems In order to solve the above problems, the magnetic recording medium of the present invention comprises:
Pigment and binder are mixed and dispersed in powder.

Function The present invention improves electromagnetic conversion characteristics and running durability by improving the dispersibility of carbon black and abrasive with the above configuration.

Example Iron oxide is used as the magnetic powder used in the present invention.

CO-containing iron oxide or metallic iron, Fe-Go, Fe-
Ni, Co-Ni, Fe-Ni-Cr, F
e-Go-B, Fe-Go-Or-B
etc. As the binder, polyurethane resin, vinyl chloride resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, polyester resin, butyral resin, and phenoxy resin are used. As a dispersing agent, lecithin or higher fatty acids such as oleic acid, palmitic acid, etc. can be used. As an abrasive, α
-Alumina, α-Fa205. Chromium oxide etc. are used. As carbon black, both channel carbon and furnace carbon are used, and the size of the missing particles is 5oOmμ to 10mμ, preferably 1oOmμ to 30mμ.
A substance with a size of μ is added. As the powder mixing and dispersing machine, a shell mixer is most suitable, but a high speed mixer, a vibration mill, a high speed stone mill, etc. may also be used.

Various kneaders are used in conjunction with the cross-dispersion of magnetic paint. For example, three roll mill, agitator mill, John mill, ball mill, pebble mill, sand grinder, high speed impeller dispersing machine.

Disper Attritor, Homomitsu Klein Flow.

A double planetary mixer, a pressure kneader, two ultrasonic dispersers, a Koball mill, etc. are used alone or in combination.

(Example 1) 1 part by weight of ferromagnetic Co-coated iron oxide oleic acid 10 parts by weight of polyurethane resin containing thorium sulfonate group The above composition was kneaded in a pressure kneader for 1 hour, and then MI
CK-) Luene-MIBK (2:2:1) 200 parts by weight were added and dispersed with a sand grinder for 1 hour.

The above composition was mixed and dispersed for 10 minutes using a Henschel mixer. After adding a dispersion mixture of carbon black, α-Fe205, and vinyl chloride resin to the magnetic powder dispersion while stirring at high speed with a dispersion, it was further mixed with a sand grinder.
It was dispersed over time to make a magnetic paint. Next, 1 part by weight of pentyl stearate, 1 part by weight of stearic acid, and Coronate L (
Add 4 parts by weight of polyisocyanate (manufactured by Nippon Polyurethane Co., Ltd.) and mix with a disper for 3 minutes at 3000 rpm.
The mixture was stirred and filtered through a 1 μm filter to obtain a coating solution.

14 μtn thick (D) Coated on ethylene terephthalate film, oriented, dried, mirror-finished, and then cured.

Furthermore, a back coat layer containing carbon blank as a main component was provided on the polyethylene terephthalate on the side opposite to the magnetic layer to obtain a magnetic tape.

(Comparative Example 1) In Example 1, the α-Fe20s t carbon blank and the mixed dispersion of the hinyl chloride-hinyl acetate-vinyl alcohol copolymer were mixed into MXK-) luene-MIBK (2
A magnetic tape was obtained in the same manner except that 40 parts by weight (2:1) was added and mixed and dispersed in a ball mill for 72 hours.

In addition, MEK-)luene-MIB used for dispersing magnetic powder
K (2:2:1) was 180 parts by weight, and the solid content concentration of the paint was constant.

(Example 2) Ferromagnetic alloy powder (Fe-Ni-0r) lecithin
1 part by weight polyurethane resin
After kneading 12 parts by weight of the above composition for 30 minutes in a continuous kneader, 250 parts by weight of MEK-)luene-MIBK (2:2:1) was added and dispersed in an attritor for 1 hour.

α-Alumina (average particle size 0.2 μm) 7 parts by weight Carbon black (Cabot Furnace Black xC-
72) 2 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer (manufactured by UCC, vMcH) s parts by weight The above composition was mixed and dispersed for 16 minutes using a Henschel mixer. While stirring the dispersion of magnetic material at high speed with a dispersion machine, remove carbon blank and α-alumina.

After the dispersion mixture of vinyl chloride resin was added, the mixture was further dispersed for 1 hour using a cobal mill to obtain a magnetic paint. Next, 1 part by weight of butyl stearate, 1 part by weight of myristic acid, and 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Co., Ltd., polyisocyanate) were added, and the mixture was heated at 30°C for 30 minutes using a disper.
The mixture was stirred at o rpm and filtered through a 1 μm filter to obtain a coating solution.

10 μm thick (7) Ho IJ x Coated on ethylene terephthalate film, oriented, dried, mirror-finished, and then cured.

Furthermore, a back coat layer containing carbon blank as a main component was provided on the polyethylene terephthalate on the side opposite to the magnetic layer to obtain a magnetic tape.

(Comparative Example 2) In Example 2, α-Albas, carbon black,
Mixed dispersion of vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer was prepared by
(2:2:1) 50 parts by weight was added and milled in a ball mill.
A magnetic tape was obtained in the same manner except that the mixture was mixed and dispersed for 2 hours. Note that MEK-)luene-MIBK (2:2:1) used for dispersing the magnetic powder was 200 parts by weight, and the solid content concentration of the paint was constant.

Each of the obtained magnetic tapes was cut into A-inch pieces, wound into a cassette half, and the C/N at 5 MHz was measured.

The video tape for C/N measurement was a VHS video tape recorder (Matsushita Electric Industrial Co., Ltd. NY-AAOO), and in the case of an alloy magnetic material, the recording/reproducing head was changed to a Sendust alloy. Standard tapes include National Video Tape, Super HG120 (NV-Tl2O,...), Matsushita Electric Industrial (
The C/N was set as OdB.

Durability is measured when the tape is placed in an environment of 40℃ and 80% RH2.
The condition of the 00 bus was observed after it was run.

The surface roughness was measured using Talysurf manufactured by Rank Taylor Hobson and expressed as Ra. Ra means the arithmetic mean of the deviation of υ from the center line of surface roughness. The surface roughness is smaller than that of the previous model, and the noise is also lower, resulting in a 1 dB improvement in C/N. As for durability, in the comparative example, powder falling off and dropouts increased after about 100 to 120 passes. In addition, the pigment in the present invention includes solid lubricants,
It was effective for all organic, inorganic, and metal pigments used as antistatic agents and abrasives.

From the above, it is clear that the present invention is effective in terms of surface roughness, C/N, and durability.

Claims (1)

[Claims] A magnetic recording medium characterized by using a powder-mixed pigment and a binder.