JPS5914123A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a tape for use in VTR or the like having superior traveling characteristics and superior abrasion resistance, etc., by forming a layer contg. a mixture of smaller particles of BaSO4 or CaSO4 having specified average particle diameter or less, and larger particles in a specified range of average particle diameter mixed in a specified ratio on the backside of a base having a magnetic layer formed. CONSTITUTION:On the backside of the base reverse to the magnetic layer a back coat layer is formed contg. a mixture of 60-99wt% BaSO4 or CaSO4 having <=90nm average particle diameter, and 1-40wt% BaSO4 or CaSO4 having 0.1-1mum average particle diameter, by 30-80wt% of the total weight of this mixture and a binder. As a result, the obtained tape is improved in video characteristics and traveling stability, and enhanced in abrasion resistance, too.

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 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 76-layer 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, making it difficult to use a cassette type V T.
There is a problem in that running stability is significantly impaired during recording and reproduction using R and 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 when the tape was wound, thereby thickening (degrading) the video characteristics.

In addition, the Unabacco-1 layer, which eliminates such concerns and gives good results in terms of running stability, has poor abrasion resistance and is susceptible to damage to the backcoat layer due to sliding contact with the V T'R guide, etc. Scratching easily occurs, and the separated coating material transfers to the magnetic layer that is in contact with the tape winding, which may also have an adverse effect on the video characteristics.

Therefore, through subsequent research, the inventors determined that Barafco-1 was the middle layer? As a filler that should be included, we have carefully researched the filler that provides the minimum necessary surface roughness to ensure video characteristics and improves wear resistance.As a result, we have selected a specific filler whose particle size has been made extremely small. It was discovered that a mixture of the same material with a relatively large particle size is extremely suitable, and this invention was made based on this knowledge.

That is, this invention provides 60 to 99% by weight of barium sulfate and/or calcium carbonate with an average particle diameter of 0.09μ or less, and barium sulfate and/or calcium carbonate with an average particle diameter of 01 to 1μ on the back side of a base having a magnetic layer on the soil surface. The present invention relates to a magnetic recording medium characterized in that it is provided with a back coat layer containing 1 to 40M% and 4M% of calcium carbonate.

The above-mentioned barium sulfate and calcium carbonate used in this invention both disperse well in various binders in the back coat layer, and even those having a small particle size of 0.09μ or less on average can be easily manufactured and obtained. Furthermore, it has the property of being relatively soft with a Mohs hardness of about 3.

Focusing on the above-mentioned properties, the inventors initially used as a filler only barium sulfate or calcium carbonate, which had a very small average particle size of 0.09μ or less. As a result, we found that the surface condition of the back coat layer formed was very finely uneven, which gave good results for both the running stability and video characteristics of the cassette tape. However, with such a particle size, the abrasion resistance of the formed backcoat layer was insufficient, and there was a drawback that it easily became scratched during sliding contact, which is a guide for VTRs.

The barium sulfate or calcium carbonate having an average particle size of 01 to 1μ used in this invention is intended to avoid the above-mentioned drawbacks, and at least one type of barium sulfate or calcium carbonate having a relatively large particle size is used in this invention. 1 to 40% by weight, preferably 3 to 20% by weight of the total, and particles with an average particle size of 0.09μ or less are used for 60% of the total.
It has been found that by using ~99% by weight, preferably 80 to 97% by weight, good results can be obtained not only in ensuring running stability and video characteristics but also in the abrasion resistance of the back coat layer. .

The total amount of the filler containing barium sulfate or calcium carbonate having the combination of the above particle sizes and the carbon black described below is usually about 30 to 80% by weight of the total amount of the binder in the back coat layer. If this amount is too small, the running stability and abrasion resistance during the above-mentioned effect 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 barium sulfate or calcium carbonate, and any binder with excellent adhesion to the base, abrasion resistance, etc. can be used. Examples include fiber cord resin, polyurethane resin, polyester resin, polyisocyanate, and vinyl chloride-vinyl acetate copolymer resin.

The back coat layer in this invention is formed by applying a coating material in which the barium sulfate or calcium carbonate is mixed and dispersed in the above binder to a thickness of usually 0.3 to 30 μm on the back surface of a base on which a magnetic layer has been previously formed on the main surface. However, if necessary, this layer may contain additives such as carbon black as a filler and a suitable lubricant.

Carbon black colors (makes the back of the magnetic layer opaque)
(Thus, it gives good results in detecting the magnetic tape edge in a VH8 type cassette VTR, but the amount used is up to 60% by weight of the total amount of filler (usually 10% by weight).
~40% by weight). It is desirable to use carbon black, which has particularly good dispersibility in binders, such as Black Pearl manufactured by Capot.

The lubricant reduces the coefficient of friction of the backcoat layer to improve its durability, and also provides good results in preventing the filler from falling off. As long as it is soluble in an organic solvent, any solid (semi-solid) or liquid can be used.Specifically, fatty acid fatty acid esters, liquid paraffin, etc. can be used.The amount added is based on the total amount of filler. 5 parts by weight or less (usually 0.01 to 5 parts by weight) per 100 parts by weight.

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 this invention will be described. In the following, ``To'' means parts by weight.

Example I Go-containing acicular magnetic iron oxide powder 250 parts Carbon black 12 parts Granular α-iron oxide 10 pieces S nitrified cotton
22 polyurethane resins 19 trifunctional low molecular weight incyanate compounds 7 cyclohexanone 340 toluene
340 n-butyl stearate 3 liquid paraffin
2 cities 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 was applied to the back of the obtained magnetic tape so that the dry thickness was 08P, and after drying, surface treatment was performed and video tapes were made by cutting into the specified size 1. Ta.

Barium sulfate with an average particle size of 0.05 μm 180 Barium sulfate with an average particle size of 02 μm 30 parts Carbon black (Black Pearl, manufactured by Kyaboto Co., Ltd., volatile content 5% by weight) 90 parts Fiber fiber packaging system (resinized cotton) 100 S polyurethane resin
70+S trifunctional low molecular weight incyanate compound 30 gas n-butyl stearate
3 parts S Myristic Saka 2 parts liquid paraffin 3 parts cyclohexanone 750 parts toluene
Example 2 As a filler for the back coat layer, 180 parts of calcium carbonate with an average particle diameter of 007μ was used instead of barium sulfate with an average particle diameter of 005μ, and barium sulfate with an average particle diameter of 0.2μ was replaced with 180 parts of calcium carbonate with an average particle diameter of 015μ. 30 parts of calcium carbonate,
A videotape was made in the same manner as in Example 1 except that each was used separately.

Example 3 Example 1 and all (
I made a videotape in the same way.

Comparative Example 1 As a filler for the bank coat layer, calcium carbonate 210 with an average particle diameter of 0.07μ was used instead of barium sulfate with an average particle diameter of 005μ and barium sulfate with an average particle diameter of 02μ.
The videotape was played in the same manner as in Example 1, except that the capital was used.

The surface roughness of the back coat layer of each of the video tapes of Examples 1 to 3 and Comparative Example 1, abrasion resistance (video S/Ny reduction amount), color S/N ratio and running stability (wow and flutter) as video characteristics. ) The results of the investigation were as shown in the following table. In the table, Comparative Example 2 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> Center line average roughness (Ra) was measured using a stylus type surface roughness meter.

Abrasion Resistance> Vl (Using an S-type VTR, a practical running test of a sample tape with a 50% gray signal recorded in an atmosphere of 40°C and 780% RH was repeated 100 times, and the video S/N before running was
The amount of decrease in the video S/N ratio after running with respect to the ratio was measured.

<Color SIN ratio> V) Using an IS 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, determine the color SIN ratio, and compare it with the standard tape. Shown as a value.

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

As is clear from the table above, the videotape of this invention is
The back coat layer has excellent abrasion resistance and is colored SLN.
It can be seen that both the ratio and running stability can be improved.

Claims (1)

[Claims] (1) On the soil surface (on the back side of the base having a magnetic layer, 60 to 99% by weight of barium sulfate and/or calcium carbonate with an average particle size of 0.09μ or less and an average particle size of 01 to
IP barium sulfate and/or real calcium 1~
A magnetic recording medium comprising a back coat layer containing 40 M%.