JPS6059529A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent running stability and wear resistance of a back coating layer and having a particularly good video characteristic by providing the back coating layer contg. specific alkaline BaSO4 powder and alpha-Fe2O3 powder on the rear of a base having a magnetic layer on the main plane. CONSTITUTION:BaSO4 powder which is the dry powder prepd. by charging, for example, neutral BaSO4 powder manufactured by various methods into an aq. NaOH soln. and mixing the same then rinsing thoroughly the powder and of which the pH when said dry powder is dispersed into water is in a 7.5-10pH range is dispersed together with alpha-Fe2O3 powder having <=0.2mu average grain size into a resin binder soln. An additive such as carbon black is added thereto for preventing electrification, etc. thereby preparing a coating liquid. Such coating liquid is coated on the rear of a base provided with a magnetic layer and is dried, by which a back coating layer is formed. The magnetic tape which has good running stability, has excellent wear resistance of the back coating layer, obviates the wear of a tape guide and has a good color SN ratio is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic tape or other magnetic recording medium comprising a support having a magnetic layer on its main surface and a back coat layer provided on the back surface.

For magnetic tapes in which a magnetic layer is placed on the main surface of a support such as a polyester film, an appropriate filler is added to the back surface of the support in order to improve running stability and prevent static electricity. A back coat layer is provided. Barium sulfate powder has been proposed as one of the fillers to be included in such a backcoat layer, as it gives very good results in terms of various properties such as running stability and magnetic properties, but even with this, barium sulfate powder has not yet been proposed. Although the abrasion resistance of the back coat layer was sufficient, it was apparent that the abrasion resistance of the back coat layer was sufficient.

As a result of intensive studies to avoid the above-mentioned drawbacks, the inventors found that among barium sulfate powders, when this powder is poured into water and stirred and dispersed, the pH of the liquid becomes 7.5 or more. It has been discovered that when an alkaline material is used together with α-Fe*Os powder, the abrasion resistance of the back coat layer is significantly improved, and this invention was made possible.

That is, in this invention, barium sulfate powder with a pH of 7.5 to 10 is coated with α-Fa on the back surface of a support having a magnetic layer on the main surface.
The present invention relates to a magnetic recording medium characterized in that a back coat layer containing mes powder is provided.

The alkaline barium sulfate powder used in this invention can be obtained by, for example, adding neutral barium sulfate powder produced by various methods into an alkaline aqueous solution such as sodium hydroxide, and then washing thoroughly with water. be able to.

Alternatively, alkaline barium sulfate powder can also be obtained by obtaining barium sulfate powder according to the following reaction formula: BaS+NagS04→BaSO4+Nam5 and then thoroughly washing it with water. In other words, the sodium sulfide produced as a by-product in the above reaction formula decomposes in the subsequent water washing process to produce sodium hydroxide, so unless this sodium hydroxide is specifically neutralized, it will adhere to the barium sulfate powder and form the powder. is alkaline.

The reason why the pH of the alkaline barium sulfate powder is set to 7.5 to 10 in this invention is that if the pH becomes lower than 7.5, the effect of improving the abrasion resistance of the back coat layer will not be sufficiently obtained. This is because if the pH is greater than 10, there is a risk that the binder in the backcoat layer may lose its dispersibility in the binder and be altered in quality. In view of this, the most desirable pH range is 7.9 to 9.5.

Furthermore, it is said that the average particle size of the barium sulfate powder is preferably 2μ or less, but this is because if the particle size is larger than this, the surface properties of the magnetic layer on the main surface of the support will be adversely affected in the rolled state. This is also because the dispersibility of the backcoat layer in the binder decreases, making it difficult to fully demonstrate its original function.

We recommend using alkaline barium sulfate powder with binder 10.
It is generally good to set the base part to 40 to 400 with respect to the 0-heavy electric part, and if it is too small, the original function such as improving running stability will not be fully demonstrated, and if it is too large, the layer strength will decrease, which is not preferable. .

Further, it is desirable that the average particle diameter of the α-Fe101 powder used in combination in this invention is set to 0.2μ or less. The reason for this is that if the particle size is larger than this, it will adversely affect the surface properties of the magnetic layer on the main surface of the support in the rolled state, resulting in deterioration of video characteristics and making it difficult to fully demonstrate its original function. , α-Fe 20g has stricter particle size restrictions than the alkaline barium sulfate powder mentioned above.
This is because the larger particle size of the powder has a greater effect on the surface properties of the magnetic layer than the above-mentioned barium sulfate powder. It is best to set the amount in the range of 1 to 50% with respect to the total foot of the foot, and if it is too low, sufficient running stability will not be obtained.
Also, if the amount is too large, it may damage the opposing tape guide, etc., which is undesirable. In general, the formation of the back coat layer in this invention involves adding the above-mentioned alkaline barium sulfate powder and α-Fat's to an organic solvent together with a binder. A paint is prepared by mixing and adding various known additives as necessary, such as adding carbon black to reduce light transmittance and chargeability. It is done by applying it to the back of the body.

The binder used above is not particularly limited, and
4M paulownia resin, polyurethane resin, vinyl chloride-vinyl acetate copolymer, polyester resin BK.

Any conventionally used material such as acrylonitrile-butadiene copolymer can be used.

As described above, the present invention is characterized in that alkaline barium sulfate powder and α-Fag's powder are used together as a filler in the back coat layer, which makes the back coat layer resistant to wear. A magnetic recording medium with excellent properties can be provided.

Next, examples of this invention will be described. In addition, in the following, "part" means a heavy part. Also.

The barium sulfate powders with pH 9, 4 and 8.0 used in the following examples were manufactured by the following method. b.

<Production of alkaline barium sulfate powder> Average particle size 0.
1 μIII, 1.000 parts of barium sulfate powder with pH 7 was dissolved in 1 mol/11 sodium hydroxide aqueous solution 210,009
After thoroughly stirring and dispersing the mixture, the mixture was aged for about 1 hour. Thereafter, the mixture was thoroughly washed with water, filtered, and dried to obtain barium sulfate powders with pHs of 9.4 and 8.0.

Example 1 Co-containing magnetic iron oxide powder 250 parts Carbon black 13.75 parts Granular α-iron oxide (particle size 1.0 μIII), 13 parts Cr
5OI powder (particle size 1.0μmm) 2 parts Ajs+Os
Powder 5 parts Zinc stearate 1.25 parts Nitrified cotton 22.6 parts Polyurethane resin 20.1 parts Trifunctional isocyanate compound 7.5 parts Cyclohexanone 340 parts Toluene 340 parts n-butyl stearate 3 parts [listic acid 6.25 parts A magnetic paint having the above composition was applied onto a polyester base film with a thickness of 14 μm to a dry thickness of 5 μm, and after drying, surface treatment was performed to form a magnetic layer.0 The back side of the obtained magnetic tape A back coat paint having the following composition was applied to the surface to a dry thickness of 1 μm, dried, and then cut into a predetermined width to make a videotape. Carbon black (particle size 43 μfi) 50 parts Nitrified cotton 135 parts Polyurethane resin 94s Trifunctional low molecular weight isocyanate 40 parts n-butyl stearate 5 parts Myristic acid 10 parts Cyclohexanone 1,000 parts Toluene 1,000 parts Example 2 Example 1 except that barium sulfate powder with a pH of 8.0 was used on the back side of the magnetic tape obtained in the same manner as in Example 1.
A similar backcoat paint was applied to the tape to a dry thickness of about 1 micron, and after drying, it was cut to the specified width to make a videotape.

Comparative Example 1 PH9,
A back coat paint having the same composition as in Example 1, except that barium sulfate with a pH of 7.0 was used in the same weight instead of barium sulfate in Example 4, was applied to a dry thickness of 1 μm, dried, and then coated with the specified coating material. I cut it into strips and made a videotape.

Comparative Example 2 Example 1 was applied to the back of a magnetic tape obtained in the same manner as Comparative Example 1.
Among the compositions of back coat paints in
A back coat paint having the same composition as Comparative Example 1 except that 50 parts of Os was not added was used to a dry thickness of 1 μm.
The material was coated to form tin, dried, and then cut to a specified width to make video tapes.

The video tapes of the various Examples and Comparative Examples described above were characterized by light glare and resistance, surface roughness of the back coat layer, video characteristics (color S/N ratio), abrasion resistance of the back coat layer, running stability, and tape guide performance. The results of examining the abrasion properties are shown in the table below. In addition, the % negative characteristic is measured and evaluated as follows. Using a VH8 system VTR (video tape recorder),
The sample tape was irradiated with light having a wavelength of 9,0001, and its transmittance was measured.

<Surface Roughness> The center line average roughness (Ra) of the sample tape was measured using a stylus type surface roughness meter.

<Color SN ratio> Using a VH8 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 8N ratio, and calculate the relative value with the reference tape. It was shown in

<Abrasion resistance and tape guide wear> VH8 system V
Using TR, a practical running test of a sample tape with a 50% gray signal recorded was repeated 100 times, and video SN was recorded before running.
The decrease in video S/N ratio after driving was measured.

At the same time, the state of wear of the tape guide of the VTR and the tape guide of the cassette was visually determined.

<Running Stability> Using a VH8 type VTR, run the sample tape 1000 times, then observe the deformation of the tape. If no tape deformation is observed, the tape is good; if only a little is observed, the tape is considered poor. Cases where the deformation was significant were evaluated as poor.

As is clear from the results in the above table, the videotape of the present invention, that is, alkaline BJLSO4 and α-Fo2s
Example 1 and Example 2 in which il was used in combination with Comparative Example 1 in which neutral conventional BaSO4 and α-ii"52os were used in combination
In terms of running stability and abrasion resistance of the back coat layer,
It can be seen that both are excellent.

Applicant: Hitachi Maxell, Ltd. Representative Atsushi Nagai (11)

Claims (1)

[Claims] (1) PH7 on the back side of the support having the main surface KvB layer,
1. A magnetic recording medium comprising a back coat layer containing 5 to 10 barium sulfate powder or α-Fe Os powder.