JPS59172153A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease considerably light transmittance in a magnetic part without giving any adverse influence on the filling density, etc. of magnetic powder by incorporating carbon black having >=3wt% volatile component in the back coating layer on the rear of a base in a tape of a VHS system. CONSTITUTION:A back coating layer contg. a filler consisting of carbon black having >=3wt% volatile component and zinc oxide powder having <=0.3mu average particle size is provided on the rear of a base having a magnetic layer on the main surface. The carbon black contg. >=4wt% volatile component consisting essentially of an oxygen-contg. group such as a carboxylic group, quinone group, phenol group or lactone group is used. Zinc oxide powder having <=0.3mu average particle size is further used in combination therewith to provide fine and smooth ruggedness in the surface condition of the coating layer, by which the wear resistance is prevented and the chip-off of said layer by sliding contact with the guide of a VTR is prevented. The back coating layer is formed by applying a coating prepd. by mixing and dispersing a filler composed of carbon black and zinc oxide powder in a binder on the rear of the base formed preliminarily with the magnetic layer on the main surface to 0.3-3.0mu thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium in which a back coat layer is provided on the back surface of a base having a magnetic layer on the main surface, and particularly to a VH
The purpose of the present invention is to provide a videotape suitable for three types of cassette type VTR.

In a VH3 type cassette VTR, the magnetic tape end is detected based on the difference in light transmittance between the transparent leader tape section and the magnetic tape section, so it is desirable that the magnetic tape section be made as opaque as possible. Conventionally, the above requirements have been met by including a colorant (opacifying agent) such as carbon blank in the magnetic layer. However, the inclusion of such a colorant in the magnetic layer is not desirable from the viewpoint of magnetic properties, since increasing the amount will affect the packing density of the magnetic powder.

From the above point of view, the inventors conducted various studies in order to make the magnetic tape part opaque by providing a back coat layer on the back surface of a base having a magnetic layer on the main surface and incorporating a carbon blank into this back coat layer. As a result, the volatile components were 3
It has been found that using a carbon blank of more than 10% by weight makes it possible to make the magnetic tape part opaque without adversely affecting the magnetic properties. It was also found that there is a risk that surface scratches and powder dropouts may occur, and that the detached materials may be transferred to the surface of the magnetic layer during tape winding, resulting in a decrease in magnetic properties.

Therefore, we attempted to add other fillers to improve the durability of the bank coat layer together with the above-mentioned carbon blank containing 3% by weight or more of volatile components, but in this case, depending on the type of other fillers, the There was a fear that the surface condition of the coating layer would become too rough and this surface condition would be transferred to the magnetic layer at the same time as the tape was wound, thereby greatly deteriorating the video characteristics. In addition, a back coat layer that does not have such concerns and can give good results in terms of running stability has poor abrasion resistance and is easily damaged by sliding contact with a VTR guide, etc. Scratching occurs, and the peeled off material from the coating is transferred to the magnetic layer that is in contact with the tape, which may adversely affect the video characteristics.

In view of the above, this invention has been made by intensively studying the material of the filler to be used in combination with a carbon blank containing a volatile component of 3% by weight or more, and has found that zinc oxide powder having a specific shape and a specific particle size is extremely suitable. Something was known and done. That is, the present invention provides a bank coat containing a filler consisting of a carbon blank having a volatile component of 3% by weight or more and a zinc oxide powder having an average particle size of 0.3μ or less on the back side of a base having a magnetic layer on the main surface. The present invention relates to a magnetic recording medium characterized by providing a layer.

According to this invention, the light transmittance of the magnetic part can be significantly reduced without adversely affecting the packing density of the magnetic powder by using a carbon blank containing volatile components of 3% by weight or more in the back coat layer on the back of the base. was completed, VH3
In addition, it is possible to provide a videotape that is extremely suitable for a cassette-type VTR, and also to provide a videotape that has a bank coat layer that has excellent durability and does not show any deterioration in magnetic properties due to the lack of durability as described above. can.

The above-mentioned improvement in durability is based on the combined use of zinc oxide powder with an average particle size of 0.3μ or less, but the back coat layer using such zinc oxide powder has a surface state with extremely fine irregularities. This greatly contributes to improving video characteristics. Furthermore, by providing this type of back coat layer, running stability in a VTR is improved and wow and flutter during running is significantly reduced.

The carbon blank used in this invention contains 3% by weight of volatile components mainly composed of oxygen-containing groups such as carboxyl groups, quinone groups, phenol groups, and lactone groups.
As mentioned above, the content is preferably 4% by weight or more.

This type of carbon blank has particularly excellent dispersibility with the binder, so it makes the surface condition of the bank coat layer suitable, and also contributes greatly to opacity, improving video characteristics, light transmittance, durability, and running stability. All of these improvements will give good results.

Commercially available carbon blanks include Cabot Blank Pearl L and Black Pearl 130.
0, Mitsubishi #2400B3 Mitsubishi #2200B manufactured by Mitsubishi Chemical Corporation
, Mitsubishi #1000, Mitsubishi MA-100, Mitsubishi MA-8,
Columbian Carbon Nippon Co., Ltd. Royal Spectra, Neo Spectra AG, Raven 5250. Examples include 1255 and 1040.

In this invention, the zinc oxide powder used in combination with carbon black can be either a zinc oxide powder produced by a conventional dry method or a zinc oxide powder produced by a wet method.
Those having an average particle diameter of 0.3 μm or less are preferably used.

Zinc oxide powder with an average particle size of 0.3μ or less is well dispersed in various binders in the back coat layer, and has a Mohs hardness of about 4, which is appropriate. The back coat layer formed using this method has a very fine surface with smooth irregularities and has excellent abrasion resistance, and does not easily become scratched even when it comes into sliding contact with a VTR guide, etc. There is almost no deterioration in video characteristics caused by this. Furthermore, since it has a suitable hardness, there is no risk of damaging the guide of the cassette type VTR.

In the present invention, the amount of the filler consisting of the above-mentioned zinc oxide powder and the above-mentioned carbon blank is preferably such that it usually accounts for 30 to 80% by weight of the total amount of the mold together with the binder. The proportion of carbon black in the composition is preferably 1 to 60% by weight, preferably 3 to 40% by weight.

There are no particular restrictions on the binder for dispersing and binding the filler made of zinc oxide powder and carbon black, and any binder that has excellent adhesion to the base, abrasion resistance, etc. can be used. Examples include cellulose resin, polyurethane resin, polyester resin, polyisocyanate, and vinyl chloride-vinyl acetate copolymer resin.

The back coat layer in the present invention is a paint in which a filler consisting of carbon black and zinc oxide powder 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 it is formed by coating to a thickness of 3.0 μm, this layer may contain an appropriate additive such as a lubricant, if necessary.

The lubricant reduces the coefficient of friction of the backcoat layer to further 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 an organic solvent. Specific examples include fatty acids, fatty acid esters, liquid paraffin, and the like. The amount added is preferably 5 parts by weight or less (usually 0.1 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 form a back coat layer with low light transmittance and good durability, and to provide a magnetic recording medium that satisfies video characteristics and ground running stability. .

Next, embodiments of this invention will be described. In the following, parts shall mean parts by weight.

Example Co-containing acicular magnetic iron oxide powder 250 parts Carbon black 12" granular α-iron oxide
1o Nitrified cotton
22〃Polyurethane resin
19 Trifunctional low molecular weight isocyanate 7
〃Compound cyclohexanone 34o//Toluene 34o〃n-butyl stearate 3〃Myristic acid
3.0 A magnetic paint having the above composition was applied onto a 14 μm thick polyester base film with good surface ratio i properties to a dry thickness of 5 μm, dried, and then surface treated.

A hackcoat paint having the composition shown below was applied to the back of the obtained magnetic tape so that the dry thickness was 1 μm, and after drying, the tape was cut into a predetermined width to make a videotape.

Carbon black (Cabosoto 30 parts black pearl, volatile component 5% by weight) Zinc oxide powder 270〃Nitrified cotton
100 Polyurethane resin 70 Trifunctional low molecular weight isocyanate 30 Mono-compound n-butyl stearate 3 Myristic acid 2 Cyclohexanone
750〃Toluene
750〃Light transmittance of the magnetic part of the above video tape, durability of the back coat layer (video S/N ratio reduction rate), surface roughness, color S/N ratio as video characteristics and running stability (wow and flutter) was investigated using the particle size of the zinc oxide powder as a parameter, and the results were as shown in the following table.

In the table, Comparative Example 1 is the result of a videotape produced in the same manner as in the Example except that the particle size of the zinc oxide powder was outside the range of the present invention, and Comparative Example 2 is the result of a videotape produced in the same manner as in the Example except that the particle size of the zinc oxide powder was changed to a value outside the range of the present invention. The results of a videotape produced in the same manner as in Example except that calcium carbonate with a particle size of 0.07 μm were used. Comparative Example 3 differs from the results in Comparative Example 3 in which the carbon blank was changed from Cabo Soto's Black Pearl to Tokai Carbon's Gist 5H (volatile components, 1.
These are the results of a videotape produced in the same manner as in Example except that the concentration was changed to 8% by weight). Moreover, each characteristic test was conducted by the following method.

Light transmittance> Using the optical tape terminal detection part of a VH3 type VTR, we measured the voltage that occurs at the phototransistor when there is a magnetic tape in the optical path, and the voltage that occurs at the phototransistor when no magnetic tape is present. The ratio is expressed as a percentage.

<Durability> Using a VH3 type VTR, a practical running test was performed on a sample tape recording a 50% gray signal in an atmosphere of 40°C and 80RH 100 times, and the video S/N ratio before running was compared with that after running. The amount of decrease in video S/N ratio was measured.

<Surface roughness> Center line average roughness (Ra) was measured using a stylus type surface roughness meter.

<Color S/N ratio> Using a VH3 system VTR, record and play back the one-color chroma signal of a color video noise measuring device on the sample tape, measure the AM noise component, calculate the color S/N ratio, and measure the color S/N ratio. Shown as a relative value to the tape.

<Running Stability> Using a VH3 type VTR, audio signals were recorded and reproduced on a sample tape, and wow and flutter was measured.

3 As is clear from the above table, the videotape of this invention:
It can be seen that the light transmittance is low, the back coat layer has excellent durability, and both the color S/N ratio and running stability are satisfied.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. Carbon black with a volatile component of 3% by weight or more and an average particle size of 0.3 is placed on the back of the base which has a magnetic layer on the main surface.
A magnetic recording medium characterized by being provided with a back coat layer containing a filler made of zinc oxide powder with a particle size of less than μ.