JPH0734256B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape.

[Prior art and its problems]

From the standpoint of achieving high density recording, finely divided magnetic powder has been used for the magnetic recording medium.

However, when the magnetic powder is made into fine particles, there is a drawback that the light transmittance of the magnetic layer containing the fine magnetic particles becomes large, which causes a problem in the operation of the magnetic recording / reproducing apparatus. That is,
For example, in a video tape recorder for home use, it is detected that the transparent leader tape portion at the end of the magnetic tape, which is a magnetic recording medium, is detected, that is, when the light passes through the leader tape portion, the end of the magnetic tape is reached. When the magnetic tape is sensed and the running of the magnetic tape is stopped, a tape end detecting mechanism is provided. However, if the light transmittance becomes large even in a portion other than the leader tape portion, the tape end detecting mechanism is likely to malfunction. .

Therefore, in order to prevent such a malfunction of the tape edge detection mechanism, a large amount of carbon black is added to the magnetic layer to reduce the light transmittance of the magnetic layer.

However, when a large amount of carbon black is added to the magnetic coating material for forming the magnetic layer, the dispersibility of the magnetic powder is deteriorated and the electromagnetic conversion characteristics are deteriorated.

Therefore, in order not to add a large amount of carbon black to the magnetic layer and to reduce the light transmittance in the magnetic layer constituting portion, a carbon black containing layer, a so-called back coat layer, is formed on the surface of the support opposite to the magnetic layer constituting side. Is proposed.

However, in order to provide this back coat layer, from the viewpoint of productivity, a paint containing a large amount of carbon black is prepared in advance, and the pre-made carbon black containing paint is applied to the support in order. However, this carbon black-containing paint must be applied by the time curing begins. However, in the conventional one, the time until the curing starts, that is, the pot life of the carbon black-containing paint is short and the productivity is low, and conversely, the productivity is improved, that is, the pot life of the carbon black-containing paint is increased. Then, there is a drawback that the light transmittance becomes large.

[Disclosure of Invention]

The present inventor was informed that the contradictory defects of the light transmittance and productivity of the back coat layer might be caused by the carbon black used, and continued research on various carbon blacks. As a result, if the carbon black to be contained in the so-called back coat layer has a PH value of about 2.0 to 8.5 and a coloring power according to the ASTM method of about 90 or more, the pot life of the paint containing this carbon black is long and It has been found that the productivity of the magnetic recording medium is improved by that much, and the light transmittance of the carbon black containing layer portion is low, so that the tape end detection mechanism of the magnetic recording / reproducing apparatus does not malfunction.

That is, when a carbon black having a PH value of about 2.0 to 8.5 to be contained in the so-called back coat layer is used, the pot life of the paint containing the carbon black is long, and the dispersibility of the carbon black in the paint is good. That is, a back coat layer having a so-called small light transmittance can be provided with good productivity. Incidentally, PH
If the value is more than 8.5 and too large, the pot life becomes too short due to the reaction with the curing agent, and conversely, if the PH value is too small (less than 2), the dispersibility decreases and the carbon The black remains aggregated, and the light transmittance of the entire back coat layer is not small.

Further, it is not sufficient to use only carbon black having a PH value of about 2.0 to 8.5, that is, if a large amount of carbon black is not used in the carbon black having such characteristics, the light transmittance of the so-called back coat layer is In some cases, the carbon black may not become small, and the dispersibility may be reduced and the pot life may be shortened. Therefore, it was also clarified that the coloring power of the carbon black (by the ASTM method) must be about 90 or more. .

Then, as the carbon black to be contained in the back coat layer, those satisfying the above characteristics may be used, and more preferably, the content of the carbon black is 100 parts by weight of the binder for forming the back coat layer. To about 25 to 400 parts by weight is preferable. The average particle size of carbon black is about 0.01.
A back coat layer having a thickness of about 0.05 μm constitutes a more preferable back coat layer.

The so-called back coat layer containing the carbon black having the above-mentioned characteristics preferably has a thickness of about 0.3 to 4 μm.

Example 1 A carbon black having a predetermined magnetic coating on the front surface side of the base film as a support and a PH value of 3 on the back surface side, a coloring power (according to the ASTM method) of 100, and an average particle diameter of 24 mμ. (Cabot's Black Pearls2) 100 parts by weight, nitrocellulose 40 parts by weight, polyurethane resin 30 parts by weight, silicone oil 2 parts by weight, methyl ethyl ketone, toluene and methyl isobutyl ketone equivalent weight 450 parts by weight are thoroughly mixed and dispersed in a sand mill. After that, 30 parts by weight of a polyisocyanate curing agent is added to and mixed with this to form a coating for a so-called back coat layer, the coating is applied in a predetermined manner, and a magnetic layer is formed on the front surface side and a back surface side is subjected to predetermined steps. To obtain a magnetic recording medium such as a magnetic tape on which a so-called back coat layer containing carbon black is formed.

Example 2 A magnetic recording medium is obtained in the same manner as in Example 1, except that a carbon black having a PH value of 6 and a coloring power of 120 (Raven C manufactured by Colombian Carbon) is used as the carbon black contained in the back coat layer.

Example 3 A magnetic recording medium is obtained in the same manner as in Example 1, except that a carbon black having a PH value of 8 and a coloring power of 140 (# 45 manufactured by Mitsubishi Kasei) is used as the carbon black contained in the back coat layer.

Comparative Example 1 A magnetic recording medium is obtained in the same manner as in Example 1, except that the carbon black contained in the back coat layer has a PH value of 1.5 and a coloring power of 100.

Comparative Example 2 A magnetic recording medium is obtained in the same manner as in Example 1 except that a carbon black having a PH value of 9.0 and a coloring power of 100 (ELFTEX8 manufactured by Cabot Corporation) is used as the carbon black contained in the back coat layer.

Comparative Example 3 A magnetic recording medium is obtained in the same manner as in Example 1 except that a carbon black having a PH value of 9.0 and a coloring power of 80 (ELFTEX12 manufactured by Cabot Corporation) is used as the carbon black contained in the back coat layer.

〔Characteristic〕

For the magnetic recording medium such as the magnetic tape obtained in each of the above examples, the electromagnetic conversion characteristics, light (wavelength 8000 to 9000Å) transmittance, and pot life (time until gelation start) of the coating material for the back coat layer were examined. , As shown in the table.

According to this, if the carbon black contained in the back coat layer has a PH value of about 2.0 to 8.5 and a coloring power (according to the ASTM method) of about 90 or more, good electromagnetic conversion characteristics can be obtained. In addition, a magnetic recording medium having a small light transmittance that does not cause a malfunction in the tape end detection mechanism by the optical sensor can be obtained. Furthermore, since the pot life of the coating material for the back coat layer is long, a large amount of it can be used at a time in advance. It can be seen that the paint can be made and the productivity is improved.

On the other hand, when the PH value of the carbon black to be contained in the back coat layer is too small, the electromagnetic conversion characteristics are not good, and only a magnetic recording medium having a relatively large light transmittance can be obtained. If the value is too large, the electromagnetic conversion characteristics are not so good and the light transmittance is large,
Further, the pot life of the coating composition for the back coat layer is short, which is worse than that of the present invention.

Further, when carbon black having a low tinting strength is used, as can be seen from Comparative Example 3, the light transmittance sharply increases.

〔effect〕

The present invention has a PH value of about 2.0 to 8.5 and a coloring power (according to the ASTM method) as a carbon black contained in a so-called back coat layer which is exposed on the other surface of the support having the magnetic layer on one surface. Since we used more than 90, the electromagnetic conversion characteristics of the magnetic recording medium are good, and the light transmittance is small so that no malfunction will occur in the magnetic recording and reproducing device equipped with the tape end detection mechanism by the optical sensor. Furthermore, since the pot life of the coating material for forming such a magnetic recording medium is long, a large amount of coating material can be prepared and stored in advance at one time, and a magnetic recording medium having such high productivity can be provided.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Ogino 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa Nihon Victor Co., Ltd.

Claims (1)

[Claims] 1. A magnetic layer on one side of a support and another side of the support.
A magnetic recording medium comprising a layer containing carbon black having a PH value of about 2.0 to 8.5 and a coloring power of about 90 or more according to the ASTM method.