JPS59172123A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To realize a magnetic recording medium which is excellent in electric conductivity and, at the same time, whose magnetic layer has good surface smoothness and electromagnetic conversion characteristic by mixing carbon black having a specific surface area and absorbed oil quantity into magnetic layer forming materials. CONSTITUTION:Carbon black having <=500m<2>/g of specific surface area measured after BET method and 100-200ml/100g of oil absorption and containing <=3wt% of volatile matter, is mixed into a magnetic layer. When the specific surface is larger than 500m<2>/ g, the electric resistance of the carbon black becomes smaller, but its dispersibility in magnetic coating material becomes worse and the surface smoothness of the magnetic layer also becomes worse, resuting in inferior electromagnetic conversion characteristic. When the oil absorption becomes <=100ml/100g, the carbon black can be dispersed easily, but the electric resistance goes to higher. On the contrary, when the absorbed oil quantity attains to >=200ml/100g, the dispersibility becomes worse and the surface smoothness of the magnetic layer is lowered. When the volatile matter is more in quantity, the carbon black adapts itself to binders and the dispersibility becomes better, but it is better to use carbon black containing less amount of volatile matter to lower the electric resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and its purpose is to provide a magnetic recording medium that has excellent conductivity, a magnetic layer with good surface smoothness, and excellent electromagnetic conversion characteristics. .

The magnetic layer of a magnetic recording medium is usually made by applying magnetic powder together with a binder onto a substrate such as a polyester film, and carbon black is generally included in the magnetic layer from the viewpoint of coloring the magnetic layer or preventing static electricity. There is.

However, conventional carbon blanks have relatively poor dispersibility in the magnetic layer, and if you try to sufficiently reduce the surface electrical resistance by incorporating carbon black into the magnetic layer, at least approximately It is necessary to contain 7% by weight or more, and it is usually 1% by weight based on the magnetic powder.
Because it contains a large amount of carbon black (0 to 20% by weight), the surface smoothness of the magnetic layer deteriorates, sensitivity also decreases, and sufficiently good electromagnetic conversion characteristics cannot be obtained. When powder is used, the dispersibility of the metal magnetic powder decreases due to the influence of such carbon black, making it difficult to sufficiently improve electromagnetic conversion characteristics.

Under these circumstances, the inventors conducted various studies on carbon black to be included in the magnetic layer, and found that BE
When a carbon blank containing fine particles with a specific surface area of 500%/g or less according to the T method, an oil absorption of 100 to 200 m7!7100g, and a volatile component of 3% by weight or less is included in the magnetic layer, a small amount of addition can be achieved. The inventors have discovered that it is possible to sufficiently reduce the surface electrical resistance and to improve the surface smoothness of the magnetic layer, thereby sufficiently improving the electromagnetic conversion characteristics, leading to the present invention.

The carbon blank used in the present invention must have a specific surface area of 5[)'0rrr/g or less according to the BET method, an oil absorption of 100 to 200 mn/100 g, and contain volatile components of 3% by weight or less. Preferably, BET
When the specific surface area determined by the method is larger than 500 nr/g, it becomes easier to form a so-called striated array structure and the electrical resistance becomes low, but on the other hand, the dispersibility in the magnetic paint becomes poor and the surface smoothness of the magnetic layer becomes poor, which is not good. It is not possible to obtain suitable electromagnetic conversion characteristics. In addition, the amount of oil supplied is the amount of dibutyl phthalate, and if this amount of oil absorption is smaller than Loom//100g, dispersion becomes easier, but it becomes difficult to form a struttle arrangement structure, which increases the electrical resistance, and 200m1//
If it is larger than 100 g, it is easy to form a striated structure (on the other hand, the dispersibility in the magnetic paint becomes poor, and the surface smoothness of the magnetic layer deteriorates.Furthermore, volatile components include carboxyl groups, quinone groups, etc. on the surface of the carbon blank, This is caused by oxygen-containing groups such as phenol groups and lactone groups. In order to lower the resistance, it is better to have fewer compounds attached to the surface, so it is preferable to use a volatile component of 3% by weight or less.Such carbon black is used, for example, as carbon black for rubber kneading. Specific examples include carbon black manufactured by Mitsubishi Kasei.If the amount used is less than 1% by weight based on the magnetic powder, the desired effect will not be obtained, and if it exceeds 6% by weight. Since the surface smoothness of the magnetic layer deteriorates and the electromagnetic conversion characteristics deteriorate, it is preferable to use it in an amount of 1 to 6 times the magnetic powder.

Incorporation of such carbon black into the magnetic layer can be carried out according to a conventional method. For example, a carbon blank is added together with magnetic powder into an organic solvent solution in which a binder resin is dissolved, and the carbon black is sufficiently dispersed using a ball mill or the like. A magnetic paint may be prepared, applied to the surface of a substrate such as polyester, and dried.

It goes without saying that the binder resin is not limited to those shown in the examples below, and a wide variety of resins known in the art can be used. For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride resin, cellulose resin, acrylic resin, synthetic rubber resin, urethane resin1. Polyester resins, epoxy resins, phenol resins, amino resins, and the like can be used alone or in combination.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 500 parts by weight VAGH
(Manufactured by U, C, C, USA, 60 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Vandesox T-520525 (Tsurethane elastomer manufactured by Dainippon Ink) Desmodur L (Polyisocyanate manufactured by Bayer 15) Compound) Carbon blank (particle size 1915μ, specific surface by BET method, product 110bo/
g, oil supply amount 110 m 7! /100g, volatile components 1.7% by weight, PH8.2) Methyl isobutyl ketone 350〃Cyclohexanone 350Toluene
350〃Put each component of the above composition except for the polyisocyanate compound in a ball mill, mix and disperse for 488 hours, then add the polyisocyanate compound, and then add 1
After mixing and dispersing for a period of time, the mixture was taken out and used as a magnetic paint. This magnetic paint was applied to a 15μ thick polyester film to a dry thickness of 5μ, oriented in a 3000 oersted DC magnetic field, heated and dried, surface treated, cut to a predetermined width, and then used to tape a video tape. I made it.

Example 2 In the composition of the magnetic paint in Example 1, the particle size was 19
μ, specific surface area by BET method 110rrr/g, oil supply amount 110ml/100g, volatile component 1.7% by weight,
Particle size 40μ instead of carbon blank with pH 8.2
, specific surface area 47 po/g, oil supply amount 187 m by BET side
j! A videotape was made in the same manner as in Example 1, except that the same amount of carbon black having a composition of 1.1% by weight, a volatile content of 1.1% by weight, and a pH of 7.3 was used.

Comparative Example 1 In the composition of the magnetic paint in Example 1, the particle size was 19
μ, BET specific surface area 110rrr/g, oil supply amount 110ml! / 100g, volatile components 1.7% by weight
, instead of carbon black with pH 8.2, Ketjen black EC (carbon black manufactured by Ketjen Carbon Co., Ltd., particle size 20-30 μ, specific surface area 10 by BET method) was used.
00rJ/g, oil supply amount 340 m ft /100g,
A videotape was made in the same manner as in Example 1, except that the same amount of volatile components (0.8% by weight, pH 9.5) was used.

Comparative Example 2 In the composition of the magnetic paint in Example 1, the particle size was 19
μ, specific surface area 110r+f/g by BET method.

Oil supply amount 110 m ft /100g, volatile component 1.7
% by weight, in place of carbon black with pH 8.2, Leben 200 (manufactured by Columbia Carbon Co., Ltd., carbon black, particle size 19μ, specific surface area 180M/
A videotape was made in the same manner as in Example 1, except that the same amount of P)(6,0> was used), the amount of oil supplied was 67 ml/100 g, the volatile component was 2.6% by weight, and the same amount of P)(6,0> was used.

Comparative Example 3 In the composition of the magnetic paint in Example 1, the particle size was 19
μ, BET specific surface area 110 i/g, oil supply amount 11
0ml! /100g, volatile components 1.7% by weight, P
Instead of H8.2 carbon black, use Mogalishi Cabosoto carbon blank, particle size 24μ, BET
Specific surface area 138 I/g, oil supply amount 60 m I! /
A videotape was made in the same manner as in Example 1, except that the same amount of 100 g, volatile components 5.0% by weight, PH 3.0) was used.

Comparative Example 4 A videotape was made in the same manner as in Example 1 except that the composition of the magnetic paint in Example 1 was omitted.

The surface electrical resistance, surface smoothness, and sensitivity of the videotapes obtained in each Example and each Comparative Example were measured.

Surface smoothness was measured using a stylus roughness meter, with a stylus speed of 0.06.
The surface roughness C, L, ^) of the magnetic layer was measured under the conditions of cm/sec and a cutoff of 0.08 m, and the surface smoothness was calculated using the relative value calculated according to the following formula based on that of Example 1. I decided whether it was good or bad.

The table below shows the results.

As is clear from the above table, the videotapes obtained in Examples 1 and 2 have lower surface electrical resistance, better surface smoothness, and higher sensitivity than the videotapes obtained in Comparative Examples 1 to 4. This indicates that the magnetic recording medium obtained by the present invention has excellent conductivity, good surface smoothness of the magnetic layer, and excellent electromagnetic conversion characteristics.

Claims (1)

[Claims] 1. Specific surface area by BET method is 500rrr/g or less,
and the oil absorption amount is 100 to 200m#/100g and 3
A magnetic recording medium characterized in that a magnetic layer contains a carbon blank containing volatile components of less than % by weight.