JPH0684163A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To ensure good durability and excellent over-write characteristic by setting thickness of a magnetic layer to 1mum or lower and containing porous carbon particles having the predetermined characteristics in the predetermined amount. CONSTITUTION:A magnetic recording medium has a supporting material having conductivity and a magnetic layer where magnetic powder is dispered into a resin of combining agent. Thickness of the magnetic layer is set to 1mum or lower and Porous carbon particles in the average grain size of 20 to 40mn are added in the 3 to 10wt.% to resin of combining agent. The supporting material is characterized in 10<6> to 10<8>OMEGA/square and the magnetic powder should be the hexagonal ferrite magnetic powder having the average grain size in the range of 0.01 to 0.1mum. Thereby, a magnetic recording medium having excellent durability and over-write characteristic can be obtained without resulting in remarkable deterioration of the reproduced output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium coated with a magnetic layer, and more particularly to a magnetic recording medium excellent in overwrite characteristics.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been used for audio,
It is widely used as a medium for recording a large amount of information in various fields such as video and computer. In particular,
A magnetic recording medium in which a magnetic coating material in which magnetic powder is dispersed in a binder resin is applied on a support is superior in manufacturing cost and productivity to a magnetic recording medium using a vacuum technique such as vapor deposition. Since then, it is on the market in large numbers. by the way,
In recent years, along with the increase in the amount of information to be handled, it has been required to increase the recording capacity of magnetic recording media.

As a method of increasing the recording capacity,
There is a method of forming a magnetic recording medium that can obtain high output and improving the linear recording density by narrowing the gap of the magnetic head. According to this, the recording capacity per unit area of the magnetic recording medium can be improved.

[0004]

By the way, when the head gap of the magnetic head is narrowed as described above, there is a drawback that the overwrite characteristic of the magnetic recording medium is deteriorated. This is because the past information recorded in the deep portion of the magnetic layer cannot be rewritten by new writing to the magnetic recording medium, and is remarkable when the magnetic layer is thicker than the head gap. Is.

Therefore, it is conceivable to thin the magnetic layer to the same extent as the head gap of the magnetic head, but if the magnetic layer is simply thinned, there is a problem that the durability is significantly reduced.

The present invention has been made in view of the above technical problems, and an object thereof is to provide a magnetic recording medium excellent in overwrite characteristics without lowering reproduction output and durability. is there.

[0007]

A magnetic recording medium of the present invention is a magnetic recording medium provided with a support having conductivity and a magnetic layer in which magnetic powder is dispersed in a binder resin,
The thickness of the magnetic layer is less than 1 micron and the average particle size is 20-40
3 to 10 nm of porous carbon particles to binder resin
It is characterized by being added by weight.

In the present invention, the support is particularly preferably 10 ⁶ ~
10 ⁸ It is characterized by being Ω / □. Further, the present invention is characterized in that the magnetic powder is a hexagonal ferrite magnetic powder having an average particle size in the range of 0.01 to 0.1 micron.

[0009]

The magnetic recording medium of the present invention has a magnetic layer of 1 micron or less as described above. Therefore, even if the head gap of the magnetic head is narrowed to about 0.6 μm, by keeping the thickness of the magnetic layer to 1 μm or less, no information remains and excellent overwrite characteristics can be secured. The thickness of the magnetic layer is particularly preferably set in the range of 0.3 to 0.7 μm, whereby excellent overwrite characteristics can be secured without causing a significant decrease in durability.

By the way, if the magnetic layer is simply thinned, the durability of the magnetic layer is lowered. However, according to the present invention, 3 to 10 parts by weight of porous carbon is added to the binder resin in the magnetic layer. There is. By adding a predetermined amount of porous carbon to the magnetic layer in this way, the magnetic layer itself can have high durability without significantly reducing the reproduction output, and the durability is reduced due to thinning. Can be suppressed. Porous carbon has a stronger cohesive force than other additives, and when a large amount of porous carbon is added, it causes a decrease in reproduction output and also an increase in noise due to a decrease in dispersion of magnetic powder due to an increase in viscosity of the magnetic paint. May invite you. On the other hand, if the amount of the porous carbon added is small, the strength of the binder resin does not increase and the durability of the magnetic layer cannot be improved.

According to the studies by the present inventors, when the average particle diameter of carbon added to the magnetic layer is larger than 40 nm, it becomes difficult to increase the strength of the binder resin.
If it is less than 20 nm, the cohesive force of carbon is extremely strong, which rather reduces the conductive effect and hinders the dispersion of the paint. Therefore, by setting the average particle size of the carbon added to the magnetic layer to be within the range of 20 to 40 nm, more excellent strength can be obtained.

The characteristic of the present invention is that
That is, the magnetic layer is made conductive by the addition of carbon as described above, and the support is made conductive. With such a configuration, even if high-resistance magnetic powder such as Ba-ferrite is used as the magnetic powder,
Sufficient conductivity can be ensured without impairing the electromagnetic conversion characteristics, and thus deterioration of durability can be suppressed. And the resistance of the support is 10 ⁶ ~ 10 ⁸ It is particularly preferable to set to about Ω / □.

As such a support, it is possible to use a support such as a polyethylene terephthalate film on which a conductive layer is provided, or a support composed of a metal film or the like.

The magnetic powder usable in the magnetic recording medium of the present invention includes γ-Fe ₂ O ₃ and Co-coated γ-Fe.
₂ O ₃ , metal powder, hexagonal ferrite, etc. can be used. Among them, hexagonal ferrite powder is the most preferable magnetic powder in the present invention because it is most suitable for high density recording.

As the hexagonal ferrite, M-type and W-type hexagonal ferrite powders can be used. In addition,
63-139017, JP-A-63-144118, the hexagonal ferrite powder, etc. in which the spinel type ferrite is coated on the surface of the plate-shaped hexagonal ferrite is
It is a preferable material for the present invention because a temporary change in coercive force (Hc) with respect to a temperature change, that is, a temperature change (ΔHc) is small. And as a magnetic powder, it is most suitable for high-density magnetic recording.
It is preferable to use magnetic powder having a coercive force.

The binder resin used in the present invention includes:
It is possible to use various known ones that have been conventionally used, for example, polyurethane resin, polyester resin, polycarbonate resin, polyacrylic resin, epoxy resin, phenol resin, vinyl chloride resin, Examples thereof include vinyl acetate-based resins, and mixtures or copolymers thereof.

As the lubricant, a fatty acid ester synthesized from a fatty acid such as lauric acid, palmitic acid, stearic acid and a monohydric alcohol is preferable. For example, butyl stearate, butoxyethyl stearate, oleyl stearate, butyl laurate. Examples include rate, butoxyethyl palmylate and the like.

As the polishing agent, for example, TiO ₂ , Cr ₂
Mohs hardness of O ₃ , Al ₂ O ₃ , SiC, ZrO ₂ etc.
0.5 to more than 6 inorganic powders per 100 parts by weight of magnetic powder
It is recommended to add about 10 parts by weight.

[0019]

The present invention will be described in detail below with reference to specific examples. (Specific Example 1) [Conducting layer paint component] Acetylene black 48.1 parts by weight Polyurethane 45.3 〃 Polyester 6.6 〃 Methyl ethyl ketone 200 〃 Cyclohexanone 300 〃 [Magnetic paint component] Co-Ti substituted Ba-ferrite magnetic powder 100 parts by weight ( Average particle size 0.08 micron, coercive force (Hc) 700 Oe) Al ₂ O ₃ powder (average particle size 0.3 micron) 10〃 polyurethane resin 12〃 (average molecular weight 45000) nitrocellulose 3〃 phosphoric ester 3〃 myristic acid 1〃 Stearic acid 3 〃 Stearic acid n-butyl 1 〃 Methyl ethyl ketone 80 〃 Cyclohexane 80 〃 Toluene 80 〃 First of all, the conductive layer paint components described above are thoroughly mixed to prepare a conductive layer paint, and an isocyanate compound is used as a curing agent.
10.4 parts by weight was added and stirred.

In addition, the above-mentioned magnetic paint components have the average particle size.
3.3 parts by weight of 40 nm porous carbon was added to 100 parts by weight of the binder resin, mixed well, and dispersed for 1 hour using a sand grinder to prepare a magnetic coating material for the magnetic layer. After adding 3 parts by weight of an isocyanate compound as a curing agent to such a magnetic paint and kneading the mixture, a die coater having two nozzles was used so that the film thickness after drying of the conductive layer paint would be 0.3 μm. After adjusting the thickness of the magnetic paint to 0.8 microns after drying,
Simultaneous coating was performed on a 75-micron-thick polyethylene terephthalate film, dried, and calendered to smooth the surface. The polyester film on the opposite side was coated in the same manner, dried, and calendered to obtain a magnetic recording medium. The conductive layer at this time was 2 × 10 ⁶ The resistance value was Ω / □. (Specific Examples 2 to 3) A magnetic recording medium was prepared in the same manner as in Specific Example 1 except that the amount of porous carbon added to the binder resin was changed as shown in Table 1. (Specific Example 4) The average particle size of the porous carbon is 30 nm.
A magnetic recording medium was prepared in the same manner as in Example 1 except that the above recording medium was used. Comparative Examples 1 to 4 Magnetic recording media were prepared in the same manner as in Example 1 except that the amount of porous carbon added to the binder resin was changed as shown in Table 1. (Comparative Example 5) A magnetic recording medium was prepared in the same manner as in Example 1 except that the magnetic coating material was directly applied onto the polyethylene terephthalate film. (Comparative Example 6) A magnetic recording medium was prepared in the same manner as in Example 1 except that the magnetic recording medium was formed so that the thickness of the magnetic layer was 2.0 μm.

The magnetic recording media of the above-mentioned specific examples and comparative examples were punched out into a 3.5-inch size disk, a metal center core was installed in the central portion, and they were rotatably housed in a jacket to form a 3.5-inch floppy disk. did. Table 1 shows the results of examining various characteristics of the 3.5-inch floppy disk manufactured in this manner.

[0022]

[Table 1]

The evaluation items in Table 1 are obtained as follows. The reproduction output was evaluated by the optimum output current at a recording density of 35KFRPI using a ferrite head with a gap length of 0.6 microns and a track width of 120 microns. The rotation speed was 300 rpm, and the track was 79 tracks, which is the innermost circumference.

The durability is that the temperature is 5 ° C. and the humidity is 10 in a 24-hour cycle.
% Environment and a cycle environment where the temperature is 60 ° C and the humidity is 90%.
With the output of 70% lower than the initial output, or when surface damage is observed by visual inspection,
The result is shown in (10,000 passes).

For the overwrite characteristics, the above-mentioned magnetic head was used, the rotation speed was 300 rpm, and the track was 40 tracks. And 10.4kF for the signal written in 2.6kFRPI
Overwriting was performed with RPI, and the ratio of the first written 2.6 kFRPI signal to the residual 2.6 kFRPI signal after overwriting was taken as the overwrite characteristic.

As can be seen from Table 1, according to the floppy disk of the present specific example, even if the magnetic layer is a thin film having a thickness of 1 micron or less, the overwrite property is excellent and the durability is high. It can be seen that it is also possible to secure.

[0027]

As described above in detail, according to the present invention, a magnetic recording medium excellent in durability and overwrite characteristics can be obtained without causing a significant reduction in reproduction output.

Claims (3)

[Claims] 1. A magnetic recording medium comprising a conductive support and a magnetic layer comprising magnetic powder dispersed in a binder resin, wherein the magnetic layer has a thickness of 1 μm or less and an average particle diameter. A magnetic recording medium characterized in that 3 to 10 parts by weight of porous carbon particles having a particle size of 20 to 40 nm are added to the binder resin. 2. The support according to claim 1, is 10 ⁶ ~ 10 ⁸ Ω
A magnetic recording medium characterized by being / □. 3. The magnetic powder according to claim 1 has an average particle size of 0.
A magnetic recording medium characterized by being hexagonal ferrite magnetic powder in the range of 01 to 0.1 micron.