JPS5841422A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with superior antistatic properties and lubricity by laying a coated film contg. graphite powder and a modified silicone lubricant on the rear side of a substrate. CONSTITUTION:Graphite powder having <=10mum average particle size and a modified silicone lubricant which is liq. or semisolid at ordinary temp. are coated onto the rear side of a substrate having a magnetic layer with a resin binder. The modified silicone lubricant is prepared by modification with an org. group contg. no fluorine atom, and it is silicone modified with polyether, alcohol, alkyl or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic tape, in which a coating film having electrical conductivity and lubricating properties is provided on the back surface of a substrate having a magnetic layer.

Conventionally, attempts have been made to provide a coating film containing graphite powder and fluorine-containing silicone oil on the back side of a base film such as a polyester film having a magnetic layer, mainly from the viewpoint of improving the winding characteristics or running stability of a magnetic tape. However, it was still not satisfactory in terms of the reduction in output fluctuations at the end of the day.

It is also possible to run a substrate, such as a polyester film in particular, over a rotating can via rollers, and apply Co to this under vacuum.
In a magnetic recording medium having a magnetic metal vapor deposited film made by heating and vapor depositing a highly magnetic metal such as Ni, even if the conventional back coating film is provided, the output fluctuation will not be reduced due to the following peculiar phenomenon. showed little effect.

In other words, in this type of magnetic recording medium, 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 slippage due to the speed difference between the rotating can and the traveling film. This can cause electrical charging, and when such electrical charging occurs, the running film tries 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, There is a problem that the output fluctuation increases significantly, but even if the conventional back coating film containing graphite powder and fluorine-containing silicone oil is provided to solve this problem, the silicone oil will not volatilize during vacuum deposition. As a result, a sufficient antistatic effect could not be obtained, and as a result, it was not possible to significantly reduce output fluctuations.

As a result of intensive studies in view of the above circumstances, the inventors formed a coating film containing graphite powder and a silicone lubricant modified with a fluorine atom-free organic group on one surface of a substrate such as a polyester film. However, in each case, a magnetic metal vapor deposition film was provided on the other side, and since the above-mentioned specific lubricant has a better affinity with the binder resin and graphite than the silicone oil mentioned above, Due to the synergistic effect of its good lubrication function and the conductive and lubricating functions of graphite powder, it is effective against charging due to the influence of secondary electrons during vacuum deposition and due to slip caused by film elongation. We found that this greatly contributes to reducing fluctuations in output.

Also, if the back coating film with the above structure is distorted, the magnetic layer may be -L.
The magnetic metal vapor deposited film as described above is provided, but the number is not limited to γ-Fe2O3 powder, co-containing 1-Fe 203
Even when a general magnetic layer is provided, which is made by binding magnetic powder such as powder, ferromagnetic metal such as α-Fe powder, or alloy powder with a binder resin, its good lubricity makes it difficult to record and reproduce data. It was also found that running stability was significantly improved, and from this point of view, it was also possible to reduce output fluctuations.

As described above, the gist of the magnetic recording medium of the present invention is that a coating film containing graphite powder and a silicone lubricant modified with a fluorine atom-free valve organic group is provided on the back surface of a substrate having a magnetic layer. According to this, it is possible to provide a magnetic recording medium with significantly improved output fluctuation.

The graphite powder used in this invention preferably has an average particle size of 10 μm or less. This type of powder has both a lubricating function and a conductive function, and has inferior binding properties during coating compared to carbon black, or has been modified with a fluorine-free organic group used in conjunction with carbon black. It is held relatively stably in the binder resin by the silicone-based lubricant.

The silicone lubricant used in this invention is liquid or semi-solid at room temperature and is modified with a fluorine-free organic group, and the modified group includes fatty acids, polyethers, etc. that do not contain fluorine atoms in their molecules. /lz, alcohol, alkyl groups, etc., as long as they have excellent affinity with the binder resin or graphite powder.

As a commercially available silicone-based lubricant, the fatty acid-modified silicone is manufactured by Shin-Etsu Silicone Co., Ltd. under the trade name TA-93.
0 as a polyether-modified silicone, Toshiba Silicone Co., Ltd. product names 5H-3746, 3749, etc., as alcohol-modified silicones, Silicone Co., Ltd. product names 5F-8427, 8428, etc., as alkyl-modified silicones. Product name 5) 1-230 manufactured by Shi Silicone Co., Ltd.
, BX16-811.5F-8416, etc.

The thickness of the coating film containing graphite powder and the silicone lubricant 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 layer, especially the magnetic metal vapor deposited film. Of course, the resin may also have the adhesive properties lowered by other additives.

Specific examples of the binder resin include cellulose resin, polyvinyl chloride resin, polyvinyl butyral resin, polymethyl methacrylate resin, acrylonitrile-butadiene-styrene copolymer resin, polystyrene resin, vinyl chloride-vinyl acetate copolymer resin, Examples include polyurethane resin.

Graphite powder accounts for 20% of the total amount with the binder resin above.
The amount of the silicone lubricant modified with a fluorine-free organic group is preferably 0.1 to 20 parts by weight per 100 parts by weight of graphite powder. The amount is preferably 0.5 to 5 parts by weight.

Next, examples of this invention will be described. In the following, parts shall mean parts by weight.

Example 1 On one side of a 10μ thick polyester base film, V
YHH (trade name manufactured by U, C, C; vinyl chloride-vinyl acetate copolymer resin) 60 parts, graphite powder 40 parts, TA
1 part of -930 (silicone modified with the aforementioned fatty acid), 150 parts of methyl isobutyl ketone, and 15 parts of toluene.
A paint consisting of 0 parts was applied so that the dry thickness was 0.5 μm. Next, while running a rotating can in the vacuum system at a speed of 10 m/min so as to make contact with the coating surface, the Co/Ni weight ratio was 8/2 and the coercive force was 50.
A magnetic metal vapor-deposited film of 0.0 In Rusted was formed on the other side of the base film to a thickness of 0.1 μm. Then, 1/2
The magnetic tape of the present invention was obtained by cutting into inch pieces.

Example 2 Instead of fatty acid-modified silicone in the paint component, sH-
A magnetic tape was produced in the same manner as in Example 1, except that 1 part of .,3746 (the above-mentioned polyether-modified silicone) was used.

Example 3 Instead of fatty acid-modified silicone in the paint component, 5F-
A magnetic tape was produced in the same manner as in Example 1, except that 1 part of 8428 (alcohol-modified silicone described above) was used.

Example 4 Instead of fatty acid-modified silicone in the paint component, BX1
A magnetic tape was produced in the same manner as in Example 1, except that 1 part of 6-811 (the alkyl-modified silicone described above) was used.

Comparative Example Instead of fatty acid-modified silicone in the paint component, FS-
A magnetic tape was produced in the same manner as in the actual implementation except that one part of 1265 (trade name, manufactured by Toshi Silicone Co., Ltd.; fluorine-containing silicone oil) was used.

Each of the magnetic tapes of the above examples and comparative examples was loaded into a video tape recorder VT-8000 (manufactured by Hitachi), and
The results of examining the output fluctuations after running 300 times at °C and 180% RH were as shown in the table below.

Furthermore, 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 were examined, and the results are also listed in the following table. The surface electrical resistance is determined by hanging the test film under a tension of 50 g between a pair of electrodes spaced apart by 50 g.
The resistance value was investigated when a voltage of 0.0 cm was applied, and the friction coefficient was measured by the rotating drum method.

As is clear from the above table, it can be seen that the magnetic tape of the present invention exhibits significantly small output fluctuations during recording and reproduction.

Patent applicant: Hitachi Maxell, Ltd. Agent Patent Attorney Wataru Ne Wataru Moto Kunio 1.,' 11 death ··.

Claims (1)

[Claims] (1) A magnetic recording medium characterized in that a coating film containing graphite powder and a silicone lubricant modified with a fluorine atom-free organic group is provided on the back surface of a substrate having a magnetic layer.