JPS595429A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic tape good in dispersibility of carbon black, and superior in traveling stability and video characteristics, by forming a backing layer contg. as a filler, carbon black contg. a specified amt. of volatile component or more on the backside of a base having a magnetic layer. CONSTITUTION:Carbon black contg. >=3wt% volatile component consisting mainly of oxygen-contg. groups, such as carboxyl, quinone, or phenol groups, e.g., ''Black Pearl L'' made by Cabot Ltd., etc., is contained by 10-100wt% of all the fillers including other additives, such as CaCO3 and BaSO4, in the backing layer contg. 30-80wt% binder of the total weight of the binder and the total additives. This backing layer is formed on the backside of the support reverse to the magnetic layer. As a result, a magnetic tape thus obtained satisfies both requirements of traveling stability and video characteristics, and it is capable of detecting the end of the tape even when the magnetic layer is not made opaque, and suitable for use in a VHS type VTR or the like.

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 base having a magnetic layer on its main surface.

High-sensitivity video tapes are known in which the output in the high frequency range is greatly improved by using a base with 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, the back surface of the base is too smooth, so there is a problem in that running stability is significantly impaired during recording and reproduction using 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 base, which has a smooth surface. There was a concern that the state would be transferred to the opposing magnetic layer when the tape was wound, and that this would greatly deteriorate the video characteristics.

Therefore, through subsequent research, the inventors conducted extensive research into fillers that could provide the minimum surface roughness necessary to ensure video characteristics as a filler to be included in the back coat layer. It was discovered that black is extremely suitable, and this invention was developed.

That is, the present invention provides a bank coat layer containing carbon black containing volatile components of 2% or more by weight as part or all of the filler on the back side of a base having a magnetic layer on the main surface. This invention relates to magnetic recording media such as video tapes.

The above carbon black used in this invention is
It contains at least 3% by weight, preferably at least 4% by weight, of volatile components mainly composed of oxygen-containing groups such as carboxyl groups, quinone groups, phenol groups, and lactone groups. Wetting when kneading with binder 2
The dispersion effect is promoted well and the dispersibility in the binder is improved, and as a result, the surface condition of the back coat layer formed has very fine irregularities, which improves the running stability of the cassette tape. Gives good results with video characteristics.

In addition, the back coat layer containing carbon black has the effect of reducing the light transmittance of the entire magnetic tape due to the coloring function (opacity) of carbon black.
This gives good results in detecting the tape end in a VH8 type cassette type VTR. In other words, the detection of the tape edge in the above method is performed based on the difference in light transmittance between the transparent leader tape section and the magnetic tape section, so conventionally the magnetic layer is colored with carbon black or the like (to make it opaque).
The above-mentioned difference in light transmittance was increased by adding an agent, but in this case there was a problem in that the surface properties of the magnetic layer and the filling rate of the magnetic powder were significantly impaired. However, by making the bank coat layer opaque, the magnetic layer does not have to be made opaque or strictly necessary, so there is no fear of the above-mentioned problems occurring.

The average particle diameter of carbon black, which brings about these various effects, is generally 5.5% from the viewpoint of making the surface condition of the back coat layer appropriate and reducing the light transmittance.
It is preferable that the thickness is 0μ or less.

Specific examples of commercially available carbon blacks include Cabot's Black Pearl, Black Pearl 1300, Mitsubishi F2400B1 Mitsubishi +, manufactured by Mitsubishi Kasei, etc.
2200B, Mitsubishi #1000, Mitsubishi MA-100, Mitsubishi MA-8, Columbian Carbon Nihon Sha Royal Spectra, Neo Spectra AG, Rabe 75250.
Examples include 1255 and 1040.

In this invention, other fillers may be used in combination with the carbon black, if necessary. Other fillers have an average particle size of 0.1 μm or less, preferably 0.1 μm or less, so as not to impair the characteristics of carphone black.
．． Calcium carbonate, barium sulfate, titanium oxide, etc. with a thickness of about 0.05 to 0.08 μm are preferable. When using carbon black alone, the durability of the back coat layer tends to be slightly inferior, but
This durability can be improved by using fillers with the above properties.

The proportion of carbon black in the total filler is generally 10 to 100% by weight, and the proportion of carbon black in the back coat layer is usually 30% by weight in the total mold amount with the binder.
~80% by weight. If the filler type is too small, the running stability will not be improved, and if it is too large, the coating properties will deteriorate and the video properties will likely be adversely affected.

There are no particular restrictions on the binder used to bind the filler as described above, and any binder that has excellent adhesiveness to the base, abrasion resistance, etc. can be used. For example, cellulose resin,
Examples include polyurethane resins, polyester resins, polyisocyanates, vinyl chloride-vinyl acetate copolymer resins, and the like.

The back coat layer in this invention is a coating material in which carbon black and other fillers are mixed and dispersed in the above-mentioned binder and coated on the back surface of a base on which a magnetic layer has been previously formed on the main surface, to a thickness of usually 0.3 to 3.0 μm. Although this layer is formed by applying it to the surface, 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 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, 11N fatty acid esters, and liquid paraffin. The amount added is preferably 5 parts by weight or less (usually 0.01 to 5 parts by weight) based on the total weight parts of the 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 is suitable for a VH5 type cassette type VTR.

Next, embodiments of the invention will be described. In the following, the terms "part" and "part" refer to heavy parts.

Example 1 CO-containing acicular magnetic iron oxide powder 250 parts Granular α-iron oxide 10 parts Nitrified cotton
21 parts polyurethane resin
18 parts trifunctional low molecular weight incyanate compound 7 parts cyclohexanone 340 parts toluene 340 parts n-butyl stearate 3 parts liquid paraffin
2-part myristic acid
Two parts of the magnetic paint having the above composition were applied onto a 14 μm thick polyester base film with good surface smoothness to a dry thickness of 5 μm, dried, and then surface treated.

A back coat paint having the composition shown below is applied to the back of the obtained magnetic tape so that the dry thickness is 0.8 μm. After drying, surface treatment is performed, and the video tape is cut into a predetermined width. I made it.

Carbon black (Cabot 300 parts Black Pearl, volatile components 5% by weight) Cellulose resin 100 parts Polyurethane resin 70 parts Trifunctional low molecular weight inanate compound 30 parts n-butyl stearate 3 parts Myristic acid
2 parts liquid paraffin
3 parts Cyclohexanone 750 parts Toluene 750 parts Comparative Example 1 Instead of Black Pearl-L (carbon black), M
A videotape was made in the same manner as in Example 1, except that A-600 (carbon black manufactured by Mitsubishi Kasei Corporation, volatile component: 1.0% by weight) was used.

Example 2 The number of parts used of Black Pearl-L (carbon black) was 90 parts, and other fillers had an average particle diameter of 0.07.
Example 1 except that 210 parts of μ calcium carbonate was used.
I made a videotape in the same way.

Comparative Example 2 Instead of Black Pearl-L (carbon black), M
A videotape was made in the same manner as in Example 2, except that A-600 (listed above) was used.

The results of examining the surface roughness of the back coat layer, color S/N ratio as video characteristics, and running stability of each of the video tapes of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in the following table. It was as expected.

In the table, Comparative Example 3 is the result of a videotape produced in the same manner as Example 1 except that no back coat layer was provided. Moreover, each characteristic test was conducted by the following method.

<Surface Roughness> The center line average roughness (Ra) was measured using a stylus type surface roughness tester.

<Color S/N ratio> Using a VH5 system VTR, record and play back the one-color chroma signal of the color video noise measuring device on the sample tape, measure the AM noise component, calculate the color S common ratio, and compare it with the standard tape. Shown as relative values.

Running Stability> Using a VH5 type VTR, audio signals were recorded and reproduced on the sample tape, and wow and flutter was measured.

As is clear from the above table, the videotape of the present invention can satisfy both running stability and video characteristics. Further, since this type of tape has a low light transmittance, good results were obtained in detecting the tape end in a VH5 type cassette type VTR.

Claims (1)

[Claims] (1) Triple t% on the back side of the base which has a magnetic layer on the main surface.
A magnetic recording medium comprising a back coat layer containing carbon black containing the above volatile components as part or all of a filler.