JPS6055889B2 - magnetic disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic disk, and an object thereof is to provide a magnetic disk having a magnetic layer with low light transmittance and excellent conductivity.

In general, a magnetic disk has a disk-shaped substrate with a magnetic layer formed on both or one side, and is rotated at high speed while a magnetic head is brought into sliding contact with the disk for recording and reproduction.It is used by being stored in a jacket in a magnetic disk cartridge, etc. When doing so, the timing of the start of a track is detected by light that passes through an index hole drilled at a predetermined position on the magnetic disk in correspondence with an index window provided in the jacket.

For this reason, if the optical transmittance of a magnetic disk is high, light will pass through even in areas where there are no index holes, leading to the possibility that the track start timing will be detected incorrectly, causing errors due to timing errors and other problems. .

In addition, if the magnetic layer of a magnetic disk has poor conductivity and high electrical resistance, it is likely to be charged with electricity, and static electricity may be generated between the magnetic disk and the jacket or between the magnetic disk and the magnetic head during recording and reproduction, causing errors. or may generate noise. In order to solve this problem, a method is generally adopted in which carbon black is included in the magnetic layer, but although this method lowers the light transmittance and improves the conductivity, it is not sufficient, and the film properties and resistance are lowered. There are drawbacks in terms of solvent properties, and carbon black cannot be incorporated into the magnetic layer with a high degree of filling, so the output cannot be increased. The present invention was developed based on various studies in view of the current situation.By incorporating graphite fine particles into the magnetic layer of a magnetic disk, the light transmittance can be sufficiently reduced, and the electrical resistance can also be sufficiently reduced. This was done based on the discovery that by incorporating fine graphite particles at a high filling degree, output could be increased and film properties and solvent resistance would also be improved.

It is not necessarily clear why graphite fine particles can exhibit such an effect compared to carbon black, but carbon black is a very small spherical particle with an average particle size of 0.015 to 0.3μ, whereas Graphite fine particles are relatively large particles with an average particle size of 0.5 to 50μ and are flat in shape, so they have a large shielding effect on light that is about to pass through, and the graphite fine particles are connected to each other in a structured arrangement. It is thought that the structure is easy to form, and as a result, the light transmittance is sufficiently reduced and the electrical resistance is also sufficiently reduced. Furthermore, since carbon black has a porous structure, it absorbs the binder component in the magnetic layer, and therefore becomes bulky and cannot be contained in the magnetic layer with a high packing degree, resulting in poor coating properties, whereas graphite fine particles Because it has a porous structure and high crystallinity, it increases the degree of filling in the magnetic layer and improves the film properties, making it possible to increase the output.
It is believed that both light transmittance and electrical resistance can be further reduced. In addition, since fine graphite particles have excellent lubricity, the magnetic disk according to the present invention has improved durability and running performance. If the graphite fine particles used in this invention have an average particle size of less than 0.5μ, the light shielding effect will be poor, and if it is more than 5μ, the surface of the magnetic layer will become rough, making it impossible to improve the output. It is preferable to use one having a diameter of 0.5 to 1.0 μm, more preferably one in the range of 0.5 to 1.0 μm.

In addition, if the content of graphite fine particles is too small, the surface electrical resistance will increase, and if it is too large, the strength of the coating will decrease and problems will arise in durability, so it is preferably in the range of 3 to 15% by weight.
More preferably, the amount is in the range of 7 to 1%. Specific examples of such graphite fine particles include CSSP (scaly graphite manufactured by Nippon Graphite Industries Co., Ltd.) and AUP earthy graphite manufactured by Tamoto Graphite Industries Co., Ltd.). Graphite fine particles can be incorporated into the magnetic layer by a conventional method, and a magnetic paint is prepared by adding a predetermined proportion of graphite fine particles to a mixture of magnetic powder, a binder, and an organic solvent-based or aqueous dispersion medium. This may be applied to the surface of a substrate such as a polyester film by a conventional means and dried.

Next, embodiments of the invention will be described.

Example 1. A magnetic paint consisting of this composition was prepared and applied to a thickness of 75 mm.
It is coated on a μ polyester base film and dried to form magnetic layers with various layer thicknesses. +l? Shichisho 17e) Pu m plow Y] 100 small bolts J? Fufu - I made a thin disc using eight pieces of firewood.

Example 2. In the composition of the magnetic paint in Example 1, AUP (earthy graphite manufactured by Nippon Graphite Industries Co., Ltd., average particle size 0) was used instead of CSSP.
．． A magnetic disk was produced in the same manner as in Example 1 except that the same amount of 7p) was used.

Example 3. In the composition of the magnetic paint in Example 1,
In addition to CSSP, ACP (scaly graphite manufactured by Nippon Graphite Industries Co., Ltd.,
A magnetic disk was produced in the same manner as in Example 1, except that the same amount of particles with an average particle size of 10 μm was used.

Comparative example 1. A magnetic disk was produced in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of Diablack G (carbon blank manufactured by Mitsubishi Kasei Corporation, average particle diameter 43 mμ) was used in place of CSSP.

Comparative example 2. A magnetic disk was prepared in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of Mitsubishi #2300 (carbon black manufactured by Mitsubishi Kasei Corporation, average particle size 15 rr) was used instead of CSSP. Ivy.

Comparative example 3. In the composition of the magnetic paint in Example 1, Asahi Thermal (carbon black manufactured by Asahi Carbon Co., Ltd.) was used instead of CSSP.
A magnetic disk was produced in the same manner as in Example 1 except that particles with an average particle size of 90 nm and 1 μm were used.

ANS■, X3B8/76
-74, the light transmittance was measured.

Figure 1 shows the measurement results in graph form, with graph A representing Example 1, graph B representing Example 2, graph C representing Example 3, graph D representing Comparative Example 1, and graph E representing Comparative Example 2. Graph F shows Comparative Example 3. As is clear from this graph, the magnetic layer according to the present invention (Example 1,
2) has a much lower light transmittance at any magnetic layer thickness than those containing carbon black in the magnetic layer (Comparative Examples 1 to 3), and from this, the material according to the present invention has a light shielding effect. It can be seen that the light transmittance can be much lower than that using conventional carbon black. In addition, regarding a large number of magnetic disks with different magnetic layer thicknesses obtained in each example and each comparative example, JIS, C624
O, 9.4. The surface electrical resistance was measured according to 1.

Figure 2 shows the measurement results in graphs; graph A is Example 1, graph B is Example 2, graph C is Example 3, graph D is Comparative Example 1, graph E is Comparative Example 2, Graph F shows Comparative Example 3. As is clear from this graph, the magnetic layer according to the present invention was obtained by containing fine graphite particles having an average particle size of 0.7 to 1.0 μm (Examples 1 and 2).
) has a much smaller surface electrical resistance at any magnetic layer thickness than those containing carbon black in the magnetic layer (Comparative Examples 1 to 3), and from this, the material according to the present invention has excellent conductivity and is superior to conventional It can be seen that the surface electrical resistance can be made much smaller than that using carbon black. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the thickness of the magnetic layer of a magnetic disk and light transmittance, and FIG. 2 is a diagram showing the relationship between the thickness of the magnetic layer of the magnetic disk and surface electrical resistance.

Claims (1)

[Claims] 1. A magnetic disk characterized by containing graphite fine particles in a magnetic layer.