JPH0312366B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium such as a magnetic tape, which has a coating film having conductivity and lubricity on the back side of a substrate having a magnetic metal vapor deposited film. A magnetic recording medium having a magnetic metal vapor-deposited film is generally produced by moving a substrate such as a polyester film onto a rotating can via rollers, and then applying the film to the rotating can under vacuum.
It is manufactured by heating and vapor-depositing highly magnetic metals such as Co and Ni. However, with this method, the base film is easily charged due to the influence of secondary electrons from the evaporation source, and the film elongates due to thermal expansion, causing slips due to the speed difference between the rotating can and the traveling film, which causes charging. When such electrostatic charges occur, the running film tends to stick to the rotating can, which inevitably causes vertical wrinkles in the film, and when a magnetic metal vapor deposited film is formed on this film, the output fluctuates significantly. There were drawbacks that were increasing rapidly. As a result of intensive studies in view of the above circumstances, the inventors formed a coating film containing a specific carbon black and a fatty acid on one side of a substrate such as a polyester film, and each time a coating film containing a specific carbon black and a fatty acid was deposited on the other side. Since the coating film has excellent conductivity and lubricity, it effectively suppresses charging due to the influence of secondary electrons during vacuum deposition and slippage caused by film elongation. This led to the realization that a magnetic recording medium with small output fluctuations could be obtained, leading to the completion of this invention. That is, in this invention, 20 to 80% of the total amount of binder resin is applied to the back surface of the substrate having the magnetic metal vapor-deposited film.
% by weight of carbon black and a saturated fatty acid having 12 to 18 carbon atoms in a proportion of 0.1 to 5.0 parts by weight per 100 parts by weight of the carbon black. This relates to recording media. By the way, in general magnetic tapes, in order to improve the winding characteristics or running performance of the tape, a coating film containing carbon black or carbon black and fatty acid esters, fatty acid metal salts, etc. is provided on the back side of the base material having the magnetic layer. This is already known.
However, when such a known coating film is applied to the present invention, it may not be possible to effectively prevent the occurrence of vertical wrinkles during vacuum deposition, or the strength of the coating may be weakened, making it impossible to obtain the desired effect. . The reason for this is that sufficient antistatic effect cannot be obtained with carbon black alone, fatty acid ester has a low boiling point and evaporates during vacuum evaporation, so there is almost no effect when used in combination with carbon black, and fatty acid metal salts do not exhibit their original properties. In order to exhibit the lubricating function, at least 5% by weight or more, usually about 10% by weight, of carbon black is required. In this case, the strength of the coating film or the adhesion to the substrate surface will be significantly reduced, and the rotation during vacuum deposition will be reduced. This is because the coating film may partially fall off due to sliding contact when running on the can, or it may easily fall off over time during recording and reproduction. On the other hand, in the coating film according to the present invention,
Saturated fatty acids with 12 to 18 carbon atoms, which are used in combination with carbon black, have a relatively high boiling point and exhibit a good lubricating function in small amounts of less than 5% by weight of carbon black, so they do not volatilize during vacuum deposition and reduce the strength of the coating. It does not cause problems such as deterioration of adhesion or decrease in adhesive strength, and its excellent lubricity and carbon black's conductive function have a remarkable effect on preventing static electricity during vacuum deposition, and greatly contribute to reducing output fluctuations. It is something. As the carbon black in this invention,
Those having an average particle diameter of 5 μm or less are suitable, and any of the various commercially available particles can be used. Specific examples of commercially available products include KETSUCHEN BLACK EC manufactured by Lion Akzo, BLACK PEARL L manufactured by CABOT, and SEAST manufactured by Tokai Electrode.
5H, Asahi Carbon Co., Ltd.'s product name HS-500, Mitsubishi Kasei Co., Ltd.'s product name H-600, etc. Furthermore, examples of saturated fatty acids having 12 to 18 carbon atoms used in combination with carbon black include lauric acid, palmitic acid, and stearic acid. The thickness of the coating film containing carbon black and saturated fatty acids having 12 to 18 carbon atoms is generally about 0.05 to 5 μm. As a binder resin used to form such a coating film on a substrate, it is generally preferable to use a binder resin that has low adhesion to the magnetic metal vapor deposited film. Of course, the adhesiveness may be lowered by using other additives in combination. Specifically, cellulose resin, polyvinyl chloride resin, polyvinyl butyral resin, polymethyl methacrylate resin, acrylonitrile-butadiene-styrene copolymer resin,
Examples include polystyrene resin, vinyl chloride-vinyl acetate copolymer resin, and polyurethane resin. The proportion of carbon black is preferably 20 to 80% by weight, preferably 40 to 60% by weight, based on the total amount of carbon black and the binder resin, and saturated fatty acids having 12 to 18 carbon atoms are per 100 parts by weight
The amount is preferably 0.1 to 5.0 parts by weight, preferably 0.5 to 3 parts by weight. Next, examples of this invention will be described. In the following, parts shall mean parts by weight. Example 60 parts of VYHH (product name manufactured by UCC; vinyl chloride-vinyl acetate copolymer resin) and KETSUCHEN BLACK were applied to one side of a 10μ thick polyester base film.
A paint consisting of 40 parts of EC (carbon black), 1 part of palmitic acid, 150 parts of methyl isobutyl ketone, and 150 parts of toluene was applied to a dry thickness of 0.5 μm. Next, while running the can at a speed of 10 m/min so that the coated surface is in contact with the rotating can in the vacuum system, a magnetic material with a Co/Ni weight ratio of 8/2 and a coercive force of 500 oersteds is applied. A metal vapor deposition film of 0.1μ is applied to the other side of the above base film.
Formed thickly. Then, the magnetic tape of the present invention was obtained by cutting it into 1/2 inch width pieces. Comparative Example 1 A magnetic tape was produced in the same manner as in Example except that palmitic acid in the paint component was not used. Comparative Example 2 A magnetic tape was produced in the same manner as in Example, except that one part of n-butyl stearate was used instead of palmitic acid in the paint component. Comparative Example 3 A magnetic tape was produced in the same manner as in Example except that 1 part of zinc stearate was used instead of palmitic acid in the paint component. Comparative Example 4 A magnetic tape was produced in the same manner as in Example except that 1 part of oleic acid was used instead of palmitic acid in the paint component. The magnetic tapes of the above examples and comparative examples were loaded into a videotape recorder VT-8000 (manufactured by Hitachi) and the output fluctuations after running 300 times at 40°C and 80%RH were as follows. It was as shown in the table below. In addition, before performing vacuum deposition, the surface electrical resistance and friction coefficient of the coating surface of the polyester base film on which each coating was formed was investigated.
The results are also listed in the table below. The surface electrical resistance is determined by suspending a test film with a tension of 50 g between a pair of electrodes spaced apart by 1 cm, and examining the resistance value when a voltage of 500 V is applied. was measured by the rotating drum method.

[Table] As is clear from the above table, it can be seen that the magnetic tape of the present invention has a significantly small output fluctuation.

Claims (1)

[Claims] 1. Carbon black in a proportion of 20 to 80% by weight based on the total amount of the binder resin and a proportion of 0.1 to 5.0 parts by weight based on 100 parts by weight of this carbon black on the back surface of the substrate having a magnetic metal vapor deposited film. number of carbons in
A magnetic recording medium characterized by being provided with a coating film containing 12 to 18 saturated fatty acids.