JPS5928238A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide satisfactory stability in traveling and satisfactory video characteristics and to improve the adhesive strength of a back coat layer to its base, by forming the back coat layer contg. barium sulfate of 0.01-0.1mum average grain size on the rear side of the base having a magnetic layer on the principal side. CONSTITUTION:Barium sulfate is well dispersible in a binder incorporated in a back coat layer, and barium sulfae of <=0.1mum small average grain size can be easily manufactued. A back coat layer contg. the barium sulfate has very fine surface unevenness and produces a favorable effect on the stability of a cassette tape in traveling and video characteristics. When the grain size is <0.01mum, it is difficult to form the fine surface unevenness, so the preferred grain size is >=0.01mum. Since barium sulfate with about 3 Mohs' hardness is relatively soft, it does not damage the guide of a cassette VTR, etc., and the back coat layer has high adhesive strength to its base and does not cause stripping during use.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the back coat layer of a magnetic recording medium such as a video tape, which is formed by providing a back coat layer on the back side of a base having a magnetic layer on its surface.

A high-sensitivity videotape is known that uses a surface-smooth base to improve the surface properties of the magnetic layer formed thereon, thereby greatly improving the output in the high-frequency range. Although these types of tapes have the above-mentioned good video properties, the back surface of the base is too smooth, which causes a problem in that the running stability is significantly impaired during recording and reproduction on a cassette type VTR or the like.

In order to solve the above problem, the inventors attempted to roughen the surface by providing a back coat layer containing various fillers on the back surface of the surface-smooth base. There was a concern that the surface state would transfer to the opposing magnetic layer during tape winding and that this would greatly degrade video characteristics.

In addition, the fL back coat layer, which eliminates such concerns and also gives good results in running stability, has poor adhesion between it and the back surface of the base, and gradually peels off during use, resulting in insufficient performance. There was a problem that the performance could not be achieved.

Therefore, through subsequent research, the inventors determined that the filler to be included in the backcoat layer provides the minimum surface roughness necessary to ensure video properties, while significantly impairing the adhesion to the base surface. As a result of intensive research into materials with no concerns, we found that barium sulfate with an average particle diameter of 0.1 μm or less is extremely suitable, leading to the creation of this invention.

That is, the present invention provides a magnetic recording medium such as a videotape, characterized in that a back coat layer containing barium sulfate with an average particle size of 0.01 to 0.1 μm is provided on the back side of a base having a magnetic layer in raw blood. This is related to.

The above-mentioned barium sulfate used in the present invention is one that is easily manufactured and available, and has a small particle size of 0.1 μin or less on average, and is well dispersed in various binders in the back coat layer. Therefore, the surface condition of the back coat layer formed using this material has very fine irregularities, which gives good results to both the running stability of the cassette tape and the video characteristics. However, if it is smaller than 0.017Lm, it becomes difficult to form fine irregularities on the surface of the back coat layer.
01 μm or more is preferable. In addition, this type of barium sulfate has a Mohs hardness of about 3 and is relatively soft, so there is no risk of damaging the guides of cassette VTRs, and moreover, the back coat formed using such barium sulfate The layer has good adhesion to the base and does not cause problems with peeling off during use.

The content of barium sulfate should normally be 30 to 80% by weight in the total amount of the back coat layer together with the binder.If this amount is too small, running stability will be impaired during the above effect. If the amount is too large, the coating film properties may be impaired and the video properties may be adversely affected.

There are no particular restrictions on the binder for binding barium sulfate, and any binder with excellent adhesiveness to the base, abrasion resistance, etc. can be used. Examples include cellulose resins, polyurethane resins, polyester resins, polyisocyanates, vinyl chloride-vinyl acetate copolymer resins, and the like.

The back coat layer in this invention is formed by applying a coating material in which barium sulfate is mixed and dispersed in the binder described above to a thickness of usually 0.3 to 3.0 μm on the back surface of a base on which a magnetic layer has been previously formed around the circumference. formed by. This back coat layer G may contain an appropriate lubricant as required.

The lubricant reduces the coefficient of friction of the backcoat layer to improve durability, and also provides good results in preventing filler powder from falling off. Any material that is solid (semi-solid) or liquid at room temperature can be used as long as it is soluble in organic solvents.

Specific examples include fatty acids, fatty acid esters, liquid paraffin, and the like. The amount added may be 5 parts by weight or less (usually 0.01 to 5 parts by weight) based on 100 parts by weight of the total filler.

As described above, according to the present invention, it is possible to provide a magnetic recording medium that can satisfy both running stability and video characteristics, and also has poor adhesiveness between the back coat I@ and the base. .

Next, embodiments of this invention will be described. In the following, "gun" means parts by weight.

Example CO-containing acicular magnetic iron oxide powder 250 carbon black 12 granular α
-Iron oxide 10 nitrified cotton
22 polyurethane resins 19 trifunctional low molecular weight r-socyanate compounds 7 cyclohexanone 340 toluene
3406vS stearic acid n
-Butyl 3-item liquid paraffin
2 cities myristic acid
A magnetic paint having the above composition was applied onto a 14 μm thick polyester base film with a long surface flatness to a dry thickness of 5 μm, dried, and then surface treated.

A back coat material having the composition shown below was applied to the back of the obtained magnetic tape so that the dry thickness was 0.8 μm, and after drying, surface treatment was performed, and the tape was cut into a predetermined width. I made a videotape.

Barium sulfate 300 nitrified cotton 100 polyurethane resin 70 trifunctional low-molecular-weight incyanate compound 30 n-butyl stearate 3 liquid paraffin 3 myristin vR2 cyclohexanone 750 toluene 750 copies Back of the above videotape The surface roughness of the coating layer, color S/N ratio as a video characteristic, running stability, and adhesion of the back coating layer to the base film were investigated using the barium sulfate particle size as a parameter.The results are shown in the table below. It was as shown.

In the table, Comparative Example 1 is the result of a videotape produced in the same manner as the Example except that no back coat layer is provided, and Comparative Example 2 is the result of a videotape produced in the same manner as in the Example except that the back coat layer is not provided. Comparative Example 3 is a videotape produced in the same manner as in Example except that calcium carbonate with a particle size of 0.07 μm was used instead of barium sulfate. The result is.

Moreover, each characteristic test was conducted by the following method.

Surface Roughness> The center line average roughness @a) was measured using a stylus blood suction roughness meter.

Color S/N ratio〉 Using a VH8 system VTLT, record and playback the Isshiki Roma signal of the color video noise measuring device on the sample tape ζ.
The color S/N ratio was calculated by measuring the M noise component and expressed as a relative value with respect to the standard tape.

Running Stability> ■H5H5 System Using TR, audio signals were recorded and reproduced on the sample tape, and wow and flutter was measured.

<Adhesiveness> Adhere cellophane tape to the back coat layer surface, and peel it once (7). Judging with the naked eye the state of peeling of the back coat j-, if no peeling is observed, ○, slightly observed. Cases were evaluated as △, and cases where peeling was significant were evaluated as ×.

Patent applicant Makoto Ishiita, Director of the Agency of Industrial Science and Technology - Patent applicant Atsushi Nagai, Representative of Hitachi Maxell Co., Ltd. Designated representative: Director of the Osaka Institute of Industrial Science and Technology, Agency of Industrial Science and Technology 8 Fuji
Male (9) 195-

Claims (1)

[Claims] (1) A magnetic recording medium characterized in that a back coat layer containing barium sulfate with an average particle diameter of 0.01 to OIIIm is provided on the back side of a base having a magnetic layer on its surface.