JPH0319609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, particularly a magnetic disk, and an object of the present invention is to reduce light transmittance.

In a floppy disk, a magnetic disk is housed in a jacket, and during use, the track start timing is determined by light that passes through an index hole that is drilled at a predetermined position on the magnetic disk in correspondence with the index window on the jacket side. is being detected. Therefore, if the light transmittance of the magnetic disk itself is high, light will pass through even where there is no index hole, causing the track start timing to be detected incorrectly and errors due to timing failures to occur. The light transmittance of the disk needs to be as small as possible.

In addition, in video magnetic tape cartridges, a transparent leader tape is connected to the end of the magnetic tape, and the light from the light detection lamp is transmitted only through the leader tape portion and is detected by the tape end sensor. Since the edge of the magnetic tape is to be detected, it is necessary to reduce the light transmittance of the magnetic tape itself as much as possible.

Therefore, conventionally, in magnetic recording media such as magnetic disks and magnetic tapes, carbon black or the like is mixed into the magnetic layer in order to reduce the surface electrical resistance.
Efforts are being made to reduce the light transmittance. However, when a large amount of colored pigment such as carbon black is added to a magnetic paint, the magnetic properties decrease in proportion to the amount added, so there is a problem in that the light transmittance cannot be sufficiently reduced. Furthermore, in order to increase the density, it is necessary to make the magnetic layer thinner, but the conventional method results in too high a light transmittance, so there is a limit to how thin the magnetic paint can be applied.

The present invention focuses on this fact and provides magnetic recording media such as magnetic disks and magnetic tapes having magnetic layers on both sides or one side of a base film.
A metal evaporated film is attached to both sides or one side of the base film, and the light transmittance is kept as low as possible by this metal evaporated film, and conductive substances such as carbon black added to the magnetic layer are also used to prevent static electricity. It is possible to prevent deterioration of magnetic properties by changing the amount of the magnetic layer, and also to freely select the thickness of the magnetic layer.

Metal vapor deposition films include aluminum, zinc, tin, lead,
A metal such as copper or silver is formed on the surface of the base film by a known vacuum deposition method. The total thickness of this metal vapor deposited film is 0.01μ or more when it is formed on both sides of the base film to exhibit the necessary and sufficient light shielding effect, but it is preferably 0.01 to 0.2μ.
within the range of This is because if the film thickness is too small, the light transmittance cannot be suppressed to a sufficiently low level, whereas if it is too large, the adhesive force will decrease, which is not preferable.

Next, examples of the present invention will be described.

Example: On both sides of a polyester base film 1 with a thickness of 75 μm, aluminum vapor deposited films 2 were formed to a thickness of 0.05 μm by vacuum evaporation method, and the surfaces of both vapor deposited films 2 were coated with a magnetic paint having the following composition to increase the layer thickness. A large number of magnetic sheets having various magnetic layers 3 were made, and a disk shape was punched out from each magnetic sheet to produce a large number of magnetic disks with magnetic layers 3 having different thicknesses.

Composition of magnetic paint γ-Fe ₂ O ₃ magnetic powder 68 parts by weight Carbon black 6 parts by weight VAGH (manufactured by UCC, USA, vinyl chloride-vinyl acetate-vinyl alcohol copolymer) 26 parts by weight N1432J (manufactured by Nippon Zeon Co., Ltd., acrylonitrile) -butadiene copolymer) 5 parts by weight Coronate L (manufactured by Nippon Polyurethane Co., Ltd., polyisocyanate) 2 parts by weight Methyl isobutyl ketone 75 parts by weight Toluene 75 parts by weight Example 2 In the composition of the magnetic paint in Example 1, no carbon black was used. A magnetic disk was produced in the same manner as in Example 1 except that no additive was added.

Comparative Example 1 A magnetic disk was manufactured in the same manner as in Example 1 except that the aluminum vapor deposited film was removed.

Comparative Example 2 A magnetic disk was produced in the same manner as in Example 1, except that the aluminum vapor deposited film was removed from Example 1, and carbon black was removed from the composition of the magnetic paint.

The light transmittance of a large number of magnetic disks having different magnetic layer thicknesses obtained in each of these Examples and Comparative Examples was measured using a light transmittance meter with a light source of 900 nm. The measurement results are shown in FIG.

As is clear from FIG. 2, the products according to the present invention (Example 1,
2), due to the excellent light shielding effect of the aluminum vapor deposited film, compared to Comparative Example 1, which does not have such a metal vapor deposited film.
It was confirmed that the light transmittance was much lower than that of No. 2, regardless of the presence or absence of carbon black in the magnetic layer.

In the present invention, the base film 1 may have a cross-sectional structure in which the metal vapor deposited film 2 is formed only on one side and the magnetic layer 3 is directly coated on the other side.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a magnetic disk which is one of the magnetic recording media according to the present invention, and Figure 2 is the thickness of the magnetic layer in each magnetic disk of Examples 1 and 2 and Comparative Examples 1 and 2 according to the present invention. FIG. DESCRIPTION OF SYMBOLS 1...Base film, 2...Metal vapor deposition film, 3...Magnetic layer.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on both sides or one side of a base film, characterized in that a 0.01 to 0.2 μ thick metal vapor deposition film such as aluminum is attached to both sides or one side of the base film.