JPS61273722A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic transducing characteristic and light transmittance of the titled medium by providing a magnetic layer on one surface of a carrier and furnishing a layer contg. specified carbon black on the other surface. CONSTITUTION:A back-coat layer contg. contg. carbon black is provided on the surface of a carrier opposite to the surface on which a magnetic layer is formed. Carbon black having about 2.0-8.5pH and >=about 90 tinting strength by the ASTM method is used as the carbon black to be incorporated into the back-coat layer. About 25-400pts.wt. carbon black is preferably incorporated into 100pts.wt. binder to form the back-coat layer. Besides, the mean particle diameter of the carbon black is controlled to about 0.01-0.05mum. Consequently, the electromagnetic trasducing characteristic is improved and the light transmittance is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape.

[Prior art and its problems]

Conventionally, from the viewpoint of achieving high-density recording, finely divided magnetic powder has been used for magnetic recording media.

However, when the magnetic powder is made into fine particles, the light transmittance of the magnetic layer containing the fine magnetic powder increases, which has the disadvantage of causing problems in the operation of the magnetic recording/reproducing device. That is,
For example, in a home video tape recorder, etc., a transparent leader tape section at the end of a magnetic tape, which is a magnetic recording medium, is detected. In other words, when light passes through this leader tape section, it is detected that the end of the magnetic tape has been reached. Although there is a tape end detection mechanism that senses and stops the running of the magnetic tape, if the light transmittance increases in areas other than the leader tape section, the tape end detection mechanism is likely to malfunction.

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

However, if a large amount of carbon black is added to the magnetic paint for forming the magnetic layer, the dispersibility of the magnetic powder becomes poor, resulting in a decrease in electromagnetic conversion characteristics.

Therefore, in order to avoid adding a large amount of carbon black to the magnetic layer and to reduce the light transmittance in the magnetic layer component, a carbon black-containing layer, a so-called back coat layer, is added to the opposite side of the support from the magnetic layer component side. It is proposed that a

However, in order to provide this back coat layer, from the viewpoint of productivity, it is necessary to prepare a paint containing a large amount of carbon black in advance, and then sequentially apply this pre-made carbon black-containing paint to the support. However, this carbon black-containing paint must be applied before curing can begin. However, with conventional products, the time it takes for this curing to begin, that is, the pot life of the carbon black-containing paint, is short, resulting in a correspondingly low productivity. If you try to make it longer, it has the disadvantage that the light transmittance increases.

[Disclosure of the invention]

The inventor of the present invention received a revelation that the contradictory drawbacks of light transmittance and productivity of the so-called back coat layer may be caused by the carbon black used, and continued research on various carbon blacks. As a result, if a carbon black with a pH value of about 2.0 to 8.5 and a tinting strength of about 90 or more according to the ASTM method is used as the carbon black contained in the so-called back coat layer, the paint containing this carbon black can be used. The pot life is long, so the productivity of the magnetic recording medium is improved accordingly, and the light transmittance of this carbon black-containing layer portion is low, which prevents the tape end detection mechanism of the magnetic recording and reproducing device from malfunctioning. I discovered that.

In other words, if the pH value of carbon black contained in the so-called back coat layer is approximately 2.0 to 8.5, the pot life of the paint containing this carbon black will be long, and the carbon The dispersibility of black is good, and it has become possible to provide a so-called back coat layer with low light transmittance with good productivity.

If the pH value is too large (over 8.5), the reaction with the curing agent will be accelerated and the pot life will be too short; on the other hand, if the pH value is too small (less than 2), the dispersion The carbon black remains aggregated, and the light transmittance of the entire backcoat layer is no longer small.

In addition, it is not sufficient to use carbon black with a pH value of about 2.0 to 8.5. In other words, carbon black with such characteristics must be used in a large amount to form a so-called back coat. The coloring power of carbon black (according to ASTM method) must be approximately 90 or higher, since the light transmittance of the layer may not be reduced, which may reduce dispersibility and shorten pot life. This was also discovered.

The carbon black to be contained in the back coat layer may be one that satisfies the above-mentioned properties, but it is more desirable that the carbon black content be higher than the binder 100 for constituting the back coat layer. Preferably, the proportion is about 25 to 400 parts by weight.

Further, the average particle size of carbon black is about 0.01 to 0.0
A back coat layer having a thickness of about 5 μm is also more preferable.

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

[Example 1] A predetermined magnetic paint was applied to the front side of the base film as a support, and a coloring strength (ASTM
100 parts by weight of carbon black with an average particle size of 24 square meters, 40 parts by weight of nitrocellulose, 30 parts by weight of polyurethane resin, 2 parts by weight of silicone oil,
After thoroughly mixing and dispersing 450 parts by weight of a mixed solvent of equal amounts of methyl ethyl ketone, toluene and methyl isobutyl ketone in a sand mill, 30 parts by weight of a polyisocyanate curing agent was added and mixed to make a so-called back coat layer paint. is applied to a predetermined thickness, and through predetermined steps, a magnetic recording medium such as a magnetic tape is obtained, in which a magnetic layer is formed on the front side and a so-called back coat layer containing carbon black is formed on the back side.

[Example 2] A magnetic recording medium is obtained in the same manner as in Example 1 using carbon black having a pH value of 6 and a tinting power of 120 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 using carbon black having a pH value of 8 and a tinting power of 140 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 using carbon black with PHHI 35 and tinting power of 100 as the carbon black contained in the back coat layer.

[Comparative Example 2] A magnetic recording medium is obtained in the same manner as in Example 1 using carbon black containing PHHO20 and tinting power of 100 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 using carbon black with PHHO20 and tinting power of 80 as the carbon black contained in the back coat layer.

〔Characteristic〕

Regarding the magnetic recording media such as magnetic tapes obtained on each side, its electromagnetic conversion characteristics, light (wavelength 8000-9000λ)
) When examining the transmittance and pot life (time until gelation starts) of the paint for backcoat layer composition, the results are shown in the table.

Table 1 Bomb black has a 21 value of about 2.0 to 8.5 and a tinting strength (according to ASTM method) of about 90.
With the above properties, it is possible to obtain a magnetic recording medium that has good electromagnetic conversion characteristics, low light transmittance, and does not cause malfunction of the tape end detection mechanism using an optical sensor.
Furthermore, since the paint for forming the backcoat layer has a long pot life, it is possible to make a large amount of paint at once in advance, which increases productivity.

On the other hand, if the valence 21 of the carbon black contained in the back coat layer is too low, the electromagnetic conversion characteristics will be poor, and only a magnetic recording medium with relatively high light transmittance will be obtained; If the valence of 21 is too high, the electromagnetic conversion characteristics will not be as good, the light transmittance will be high, and the pot life of the paint for forming the back coat layer will be short compared to that of the present invention. It's bad.

Furthermore, when carbon black with low tinting power is used, as can be seen from Comparative Example 3, the light transmittance increases rapidly.

〔effect〕

The present invention uses carbon black that is contained in a so-called back coat layer that is coated on the other side of a support having a magnetic layer coated on one side, and has a valence of 21 of about 2.0 to 8.5 and a coloring power of ( The electromagnetic conversion characteristics of the magnetic recording medium are good because the magnetic recording medium (according to ASTM method) is approximately 90 or higher, and the light transmittance is low, preventing malfunctions in magnetic recording and reproducing devices equipped with a tape end detection mechanism using an optical sensor. Furthermore, since the pot life of the paint used to make up the magnetic recording medium is long, a large amount of paint can be prepared in advance at one time, providing a magnetic recording medium with high productivity. can do.

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Claims (1)

[Claims] A magnetic layer is provided on one side of the support, and a pH value of approximately 2 is provided on the other side.
．． 1. A magnetic recording medium comprising a layer containing carbon black having a tinting strength of about 90 or more according to the ASTM method.