JPS59172151A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To give a surface roughness of necessary minimum to secure a video characteristic to and also to impprove the wear resistance of a magnetic recording medium by installing a back coat layer containing spherical zinc oxide powder having a specific mean grain size to the back of the base. CONSTITUTION:A back coat layer containing 60-99wt% of spherical zinc oxide powder having a mean grain size of <=0.15mu and 1-40wt% of zinc oxide powder having a mean grain size of 0.16-1.5mu, is installed to the back of a base, to the main surface of which a magnetic layer is formed. The zinc oxide powder of <=0.15mu is manufactured after a wet method, has a spherical shape and small diameter, and well disperse into various kinds of binders in the back coat layer. Moreover, the powder is relatively soft, being about 4 in Mohs' hardness. The zinc oxide powder of 0.16-1.5mu can prevent occurrence of worn out of the magnetic recording medium using this zinc oxide powder when the medium is contacted with and slid on a VTR guide, etc. Therefore, the magnetic recording medium using these zinc oxide powders can secure the running stability and video characteristic and, at the same time, can have a back coat layer which is excellent in resistance to wear. The back coat layer is formed by applying a coating material which is prepared by mixing and dispersing the zinc oxide powders into a binder to the back of a base, to the main surface of which a magnetic layer is formed in advance. The applying thickness of the powders is usually set at 0.5-30mu.

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 surface of a hese having a magnetic layer on its main surface.

A high-sensitivity videotape is known in which the output in the high frequency range is greatly improved by using a smooth surface and improving the surface properties of the magnetic layer formed thereon. However, although this type of tape has the above-mentioned good video characteristics, there is a problem in that the back surface of the base is too smooth, resulting in a significant loss of running stability during recording and reproduction using a cartridge-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 base, which has a smooth surface. There was a concern that the state would transfer to the opposing magnetic layer at the same time as the tape was wound, thereby significantly degrading 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.

Therefore, through subsequent research, the inventors conducted extensive research to find fillers that could be included in the bank coat layer to provide the minimum surface roughness necessary to ensure video characteristics while also improving abrasion resistance. As a result of investigation, we found that a mixed system of a specific filler with a very small particle size and a similar material with a relatively large particle size is extremely suitable, and we have developed this invention. It's arrived.

That is, this invention provides 60 to 99% by weight of spherical zinc oxide powder with an average particle size of 0.15 μm or less and an average particle size of 0.16 to 1.5 on the back surface of a base having a magnetic layer on the main surface.
The present invention relates to a magnetic recording medium such as a videotape, characterized in that it is provided with a back coat layer containing 1 to 40% by weight of μ zinc oxide powder.

The above average particle diameter used in this invention is 0.15
Zinc oxide powder with a size of less than μ is different from zinc oxide powder produced by the conventional dry method, and is produced by the wet method, as shown in the electron micrographs in Figures 1 and 2.
While the zinc oxide powder produced by the conventional dry method (Fig. 2) is angular granular, the zinc oxide powder produced by the wet method of this invention (Fig. 1) is spherical and has a small particle size. , it is well dispersed in various binders in the back coat layer. It also has the property of being relatively soft with a Mohs hardness of about 4.

The inventors focused on the above-mentioned properties and tried using only fillers with a spherical shape and a very small average particle size of 0.15μ or less, and found that the backing formed It has been found that the surface of the coating layer has very fine irregularities, which gives good results in both running stability and video characteristics of the cassette tape. However, the use of only particles having such a particle size has the disadvantage that they easily become scratched when sliding in contact with a VTR guide or the like.

Average particle size used in this invention: 0.16 to 1.5
μ zinc oxide powder is intended to avoid the above-mentioned drawbacks, and zinc oxide powder with a relatively large particle size is used in an amount of 1 to 40% by weight, preferably 3 to 20% by weight. , those with an average particle diameter of 0.15μ or less are included in the total 6
By using 0 to 99% by weight, preferably 80 to 97% by weight, in addition to ensuring running stability and video characteristics,
It has been found that good results can also be obtained in the abrasion resistance of the back coat layer.

The combined amount of the filler containing the zinc oxide powder having the above-mentioned combination of particle sizes and the carbon blank described below is preferably about 30 to 80% by weight of the total mold amount with the binder of the back coat layer. If this amount is too small, running stability and abrasion resistance during the above-mentioned effects will be impaired, and if it 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 the zinc oxide powder, and any binder that has excellent adhesion to the base, wear resistance, etc. can be used. For example, cellulose resin,
Examples include polyurethane resins, polyester resins, polyisocyanates, and vinyl chloride-vinyl acetate copolymer resins.

The bank coat layer in this invention is formed by applying a coating material in which zinc oxide powder is mixed and dispersed in the binder described above to a thickness of usually 0.5 to 3.0 μm on the back surface of a base on which a magnetic layer has been previously formed on the main surface. However, this back coat layer may contain carbon black as part of the filler or a suitable lubricant, if necessary.

Carbon black colors (makes the back of the magnetic layer opaque)
This gives good results in detecting the edge of a magnetic tape in a VH3 type cassette VTR, but the amount used is up to 60% by weight of the total amount of filler (usually 3 to 4%).
0% by weight). It is desirable to use a carbon blank that has excellent dispersibility in the binder, such as Blank Pearl L manufactured by Cabot Corporation.

The IvJ lubricant reduces the coefficient of friction of the backcoat layer, improves 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. 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 provide a magnetic recording medium that can satisfy both running stability and video characteristics, and has a back coat layer that has excellent abrasion resistance.

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

Example I CO-containing acicular magnetic iron oxide powder 250 parts Carbon black 12" granular α-iron oxide
10 Nitrified cotton
22〃Polyurethane resin
19 Trifunctional low molecular weight isocyanate 7
Compound Cyclohexanone 340//Toluene 340/l n-butyl stearate 3 Myristic acid
3. A magnetic paint having the above composition was applied onto a 14 μm thick polyester film with good surface smoothness to a dry thickness of 5 μm, and after drying, surface treatment was performed.

A backcoat layer paint having the composition shown below was applied to the back of the obtained magnetic tape so that the dry thickness was 1μ, and after drying, surface treatment was performed, and the tape was cut to a predetermined width to make a videotape. Ta.

240 parts of zinc oxide powder with an average particle size of 0.1 μm Zinc oxide powder with an average particle size of 0.3 μm 30~Carbon Black (Black Pearl manufactured by Cabot Co., Ltd. 30)
Volatile component 5% by weight) Cellulose resin (nitrified cotton) 100 Polyurethane resin 70 Trifunctional low molecular weight isocyanate 30 To compound n-butyl stearate 3 Myristic acid 2 Cyclohexanone 750 Toluene
750〃Example 2 As a filler for the bank coat layer, instead of zinc oxide powder with an average particle size of 0 to 0.1 μ, an average particle size of 0.05 μ was used.
Example 1 except that 240 parts of zinc oxide powder with an average particle diameter of 0.6μ was used instead of 240 parts of zinc oxide powder with an average particle diameter of 0.3μ, and 30 parts of zinc oxide powder with an average particle diameter of 0.6μ
I made a videotape in exactly the same way.

Example 3 As a filler for the back coat layer, an average particle size of 0.1 μ
The amount of zinc oxide powder used was changed from 240 parts to 270 parts, and 30 parts of zinc oxide powder with an average particle size of 0.4 μ was used instead of the zinc oxide powder with an average particle size of 0.3 μ, respectively.
A videotape was produced in exactly the same manner as in Example 1, except that the carbon blank was omitted.

Comparative Example 1 Example 1 except that 30 parts of zinc oxide powder with an average particle size of 0.1 μm was used as the filler for the back coat layer instead of the zinc oxide powder with an average particle size of 0.3 μm. I made a videotape in exactly the same way.

Surface roughness, abrasion resistance (decrease in video S/N ratio), color S/N ratio as video characteristics, and running stability of the back coat layer of each of the video tapes of Examples 1 to 3 and Comparative Example 1 The results of examining (wow and flutter) were as shown in the following table.

In addition, each characteristic test was conducted by the following method.

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

<Abrasion resistance> Using a VH3 system + 7) VTR, a practical running test was repeated 10 times on a sample tape recording a 50% gray signal in an atmosphere of 40'C and 80RH, and a video S/
The amount of decrease in the video S/N ratio after running with respect to the N ratio was measured.

<Color S/N ratio> Using a VH3 system VTR, record a single color chroma signal from a color video noise measuring device on a sample tape11, play it back, measure the AM noise component, and calculate the color S/N ratio. The values are shown relative to the reference tape.

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

As is clear from the table above, the videotape of this invention is
It can be seen that the back coat layer has excellent abrasion resistance and satisfies both color S/N ratio and running stability.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph (20,000 times) of the zinc oxide powder used in this invention, and FIG. 2 is an electron micrograph (20,000 times) of the conventionally used zinc oxide powder. Patent applicant Hitachi Maxell Co., Ltd. Agent: Haru Takaoka [-・-■1- ・・-1
−・”: □,゛2j

Claims (1)

[Claims] 1. On the back side of the base that has a magnetic layer on the main surface, 60 to 99% by weight of zinc oxide powder that is spherical and has an average particle size of 0.15 μ or less, and zinc oxide that has an average particle size of 0.16 to 1.5 μ A magnetic recording medium characterized by being provided with a back coat layer containing 1 to 40% by weight of powder.