JPS5914127A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance abrasion resistance, antistatic characteristics, etc. of the back coat layer of a video tape, etc., by forming the back coat layer contg. fillers including 2 kinds of carbon black having ultrafine particle size and coarser particle size each having particle diameter in a specified range. CONSTITUTION:A video tape or the like is prepared by forming a back coat layer contg. a mixture of 30-90wt% carbon black having 10-35nm particle diameter and 70-10wt% carbon black having 40-150nm particle diameter by <=90wt% of the total weight of fillers, and the fillers including at least one of BaSO4, CaCO3, ZnO, etc. besides carbon black by 30-80wt% of the total weight of the fillers and a binder. As a result, antistaticness and resistance to irregular winding is enhanced, and a tape or the like enhanced in abrasion resistance of the back coat layer, and improved in traveling and video characteristics is obtained.

Description

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

In magnetic tapes used for reel-to-reel VTRs, on the back of the base which has a magnetic layer on the main surface,
A back coat layer is provided in which a filler containing carphone black is dispersed and bonded to a binder, which prevents the tape from charging and winding irregularly, and also improves the abrasion resistance of the back side of the tape (prevents scratching of the back side). I'm letting you do it.

However, in order to obtain good conductivity, conventional carphone black has been selected to use particles as fine as possible and have a very large specific surface area, resulting in poor abrasion resistance of the back coat layer and difficulty in sliding with the VTR guide nut. When the tape is wound, the backcoat layer is easily scratched, and when the tape is wound, the coating film is transferred to the opposing magnetic layer, which may adversely affect the video characteristics.

As a result of intensive studies from the above viewpoint, the inventors found that carbon black with a specific particle size distribution provides good results in terms of not only antistatic properties and prevention of irregular winding, but also the abrasion resistance of the back coat layer. This led to the completion of this invention.

That is, in the present invention, 30 to 90% by weight of particles with a particle size of 10 to 35 mμ and 70 to 10% by weight of particles with a particle size of 40 to 150 mμ are applied to the back surface of a base having a magnetic layer on the main surface.
The present invention relates to a magnetic recording medium characterized in that it is provided with a back coat layer containing a filler containing carbon black.

The carbon black used in this invention mainly has a very small particle size in the range of 10 to 35 mμ, as shown in the above, and a particle size larger than that shown in the above. That is, the particle size is 40
~150 mμ or 10 to 70% by weight of the total particle size distribution.By having such a particle size distribution, it is possible to prevent static electricity and prevent irregular winding, and improve the abrasion resistance of the back coat layer. It's a big improvement.

Here, if the ratio of particles with large particle sizes is less than 10% by weight, the effect of improving abrasion resistance will not be sufficient, and if it exceeds 70% by weight, the coating film properties will be impaired and the video characteristics will be adversely affected. I'm afraid.

A commercially available carphone black that satisfies the particle size distribution of the present invention is Conductex-97 manufactured by Columbian Carphone Japan Co., Ltd.
5, Same 900, Same 950, etc., but carbon blacks satisfying these particle size distributions may be mixed and used.

In this invention, other fillers may be used in combination with the above-mentioned carbon black, if necessary. Other suitable fillers generally have an average particle size of 0.05
Examples include barium sulfate, calcium carbonate, zinc oxide, etc. with a particle size of ~2 μm, and titanium oxides with particle sizes similar to those described above are also suitable.

If these other fillers are used in combination, the abrasion resistance will be further improved. In addition, relatively soft fillers such as barium sulfate, calcium carbonate, and zinc oxide will reduce VTR due to the abrasiveness of the back coat layer. Damage to sliding contact parts such as guides can be suppressed.

The total amount of carbon black and other fillers is preferably about 30 to 80% by weight of the total amount of the binder, and the amount of fillers other than carbon black is as follows: The amount may be 90% by weight or less, preferably 40 to 80% by weight, in the total amount with carphone black, that is, in the total filler.

In this invention, there are no particular restrictions on the binder that binds carbon black and other fillers.
Adhesion to the base, abrasion resistance, etc. - Examples include vinyl acetate copolymer resin.

The back coat layer in this invention is a coating material in which a filler containing carphone black is mixed and dispersed in the binder described above, and is coated on the back side of a base on which a magnetic layer has been previously formed on the main surface. Although this layer is formed by coating it to a thickness of , this layer may contain various additives such as a suitable lubricant as necessary.

The lubricant reduces the friction coefficient of the bank coat layer, improves its durability, and 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. Specifically, fatty acids, fatty acid esters, liquid paraff,
Examples include inn. The additive content is 5 parts by weight or less (usually 0.01 to 5 parts by weight) based on 100 parts by weight of the total amount of filler.
It is better to

As described above, according to the present invention, it is possible to provide a magnetic recording medium that not only prevents charging and winding irregularities, but also has a back coat layer with extremely high wear resistance.

In the following, embodiments of the present invention will be explained. In the following, parts shall mean parts by weight.

Example I CO-containing acicular magnetic iron oxide powder 250 parts Granular α-iron oxide 20 parts Carbon black 12 parts Nitrified cotton
22 parts polyurethane resin 19 parts trifunctional low molecular weight isocyanate compound 7 parts cyclohexanone 340 parts toluene
340 parts 11-butyl stearate
3 parts liquid paraffin
A magnetic coating composition consisting of 2 parts myristic acid and 2 parts was applied onto a polyester base film having a good surface smoothness with a thickness of 20 microns to a dry thickness of 6 microns, dried, and then subjected to surface treatment.

On the back of the obtained magnetic tape, paint for Harakko-1 having the composition shown below was applied to a dry thickness of 3 μm. After drying, surface treatment was performed, and the tape was cut into a specified IJ size and I made a tape.

Carbon black (powder with average particle size of 26,771μ)
(300 parts 70% by weight, 30% by weight powder with average particle size 64mm)
100 parts polyurethane resin
70 parts trifunctional low molecular weight isocyanate-1 compound
30 parts liquid paraffin
3 parts Cyclohexanone 750 parts Toluene 750 parts Comparative Example 1 Ketjenblack EC manufactured by Lion Akzo Co., Ltd. was used as carbon black to be included in the Betsu i Dacoat paint.
A videotape was made in exactly the same manner as in Example 1, except that 300 parts of (average particle size: 30 mμ) were used.

Example 2 120 parts of the carbon black shown in Example 1 and an average particle size of 0 were used as fillers to be included in the back coat paint.
．． A videotape was made in the same manner as in Example 1, except that 180 parts of 51 L of barium sulfate was used.

Comparative Example 2 Ketjenblack EC shown in Comparative Example 1 was used as carbon black to be included in the paint for Barafco-1.
A videotape was made in the same manner as in Example 2, except that 0 copies were used.

Example 3 120 parts of the carbon black shown in Example 1 and an average particle size of 0 were used as fillers to be included in the paint for puncture coating.
．． A videotape was made in the same manner as in Example 1, except that 180 parts of 2μ calcium carbonate was used.

Comparative Example 3 Ketjenblack EC shown in Comparative Example 1 was used as carbon black to be included in the back coat paint.
A videotape was made in the same manner as in Example 3, except that a portion of the sample was used.

The abrasion resistance of the back coat layer of each of the video tapes of Examples 1 to 3 and Comparative Examples 1 to 3 was evaluated by the following θ1 test, and the results were as shown in the table below.

<Abrasion resistance> A sample tape with a width of 2 5.4 mm wound on a reel was
Load it into a 1 inch helical VTR (type C) and
After 00 repeated running tests, the number of scratches that occurred on the back surface of the tape was counted, and the abrasion resistance was evaluated based on the number of scratches.

As is clear from the above table, it can be seen that the video tape of the present invention has an extremely excellent abrasion resistance of the back coat layer.

Claims (1)

[Claims] (1) Carphone black consisting of 30 to 90% by weight of particles with a particle size of 10 to 35 mμ and 70 to 10% by weight of particles with a particle size of 40 to 150 mμ is applied to the back of the base having a magnetic layer on the main surface. 1. A magnetic recording medium comprising a back coat layer containing a filler.