JPS6032887B2 - magnetic recording medium - Google Patents

Description

[Detailed description of the invention] The present invention relates to magnetic recording media.

Generally, a magnetic recording medium is a substrate made of a polymeric material such as a polyester base coated with a magnetic paint, which is a mixture of magnetic powder and a binder made of a polymeric material.

By the way, the base itself and the binder are insulators, and
The magnetic powder used is a metal oxide with relatively high electrical resistance, such as rFe203, chromium oxide, and cobalt-doped e203, so the electrical resistance of the finished magnetic recording medium is high, which causes static electricity to build up. However, this caused dirt and dust to be absorbed. Therefore, anionic, cationic, nonionic, and amphoteric surfactants have traditionally been used as antistatic agents. It was added and applied to the substrate.

The conventional approach to preventing charging of magnetic recording media has been to lower the electrical resistance of the magnetic recording media in order to regularly discharge the static electricity that has been charged.

In other words, the only way to prevent static electricity was to lower the electrical resistance of the material itself. For this reason, it was not possible to achieve a sufficiently satisfactory antistatic effect, but the inventor of the present invention revised the conventional concept of preventing static electricity - reducing electrical resistance, and realized that the point is that the static electricity that has been charged should be eliminated quickly. Rather than focusing on the idea of electrical resistance, we considered how to quickly reduce static electricity itself. As a result, when using vinyl chloride-vinyl acetate copolymer plasticized with polyurethane resin as a binder, the amount of polyurethane resin is 4% relative to the total amount of binder.
% by weight or less, and further uses an alkyl ether type surfactant and coats a magnetic paint, which is a mixture of these and magnetic powder, on the substrate. We have previously discovered that the size of the particle size becomes significantly smaller.

As a result of further research, the inventors of the present invention found that when a sorpitan ester type surfactant is used together with the above-mentioned alkyl ether type surfactant, the magnetic orientation is improved more than when the alkyl ether type is used alone.

Furthermore, it has been found that the effect of reducing half-life does not change even if the ratio of these active agents is varied within a certain range, keeping the total amount of both active agents constant. Furthermore, since these activators are not acidic, they do not cause rust on the head even under high temperature conditions. This is because head rust occurs when a part of the alkyl ether type surfactant is replaced with a phosphate ester type surfactant to improve orientation without increasing the half-life. This is advantageous compared to the possibility that the substance is strongly acidic. However, since the addition of alkyl ether type and sorbitan ester type surfactants is carried out by simply mixing and kneading the magnetic powder and binder, the strength between the binders deteriorates to some extent, and friction with the magnetic head occurs. Peeling powder from the magnetic film is generated and adheres to the head.

Therefore, the present invention uses magnetic powder whose surface is covered in advance with an alkyl ether type and sorbitan ester type (sorbitan fatty acid ester, polyoxy fatty acid ester) surfactant, thereby greatly increasing the half-life without reducing the strength between the binders. At the same time, it eliminates the problem of head adhesion.
Furthermore, it improves orientation, prevents rust, and provides an excellent magnetic medium.

The reason why the polyurethane resin is used in an amount of 4% by weight or less based on the total amount of the binder is that a synergistic half-life reduction effect with the surfactant can be achieved within this range.

Beyond this range, the half-life increases rapidly. The present invention will be specifically described below with reference to Examples.

Example 1 rFe203 10 parts by weight of an alkyl ether type surfactant (Ne of Nippon Nyukazai ■)
1.8 Sorbitan ester type surfactant (Silver S-80 from Matsumoto Pharmaceutical ■)
1.2 Water 1000
After mixing well and adsorbing the surfactant on the surface of the magnetic powder, it was heated and dried.

The ferromagnetic powder subjected to antistatic treatment in this way is
'21 rFe203 10 parts by weight 10 parts by weight Thermoplastic polyurethane resin 4.5 〃 12 〃 (Goodrich Esten 5701) Vinyl chloride-pinyl acetate copolymer 25.5 〃 18 〃 Binder and It was dispersed with a solvent using a dispersion machine, and the magnetic paint was applied to a polyester base.

The measurement results of various characteristics were as shown in the table. Example
2 rFe203 10 parts by weight Alkyl ether type surfactant 2 (actinol RIOO from Matsumoto Pharmaceutical ■) Polyoxyethylene sorbitan ester 1'' (T-80 from Matsumoto Pharmaceutical ■) M old K IOOO
The mixture was thoroughly mixed, surface treated, and dried.

The magnetic powder treated in this way was prepared by adding: '11 '21 rFe203 10 parts by weight Thermoplastic polyurethane resin 4.5 〃 12
(Esten 5701) Vinyl chloride-vinyl acetate copolymer 25.5 and 18 Magnetic paints were made with two types of compositions, and magnetic recording media were manufactured.

The measurement results are shown in the table below. Comparative Example 1 For comparison, a magnetic paint was produced by direct mixing without pre-treating the magnetic powder.

Untreated ferromagnetic powder 01 '2' rFe203 10 parts by weight 10 parts by weight Alkyl ether type activator 18 〃 1.8 〃 (Neucoilolo) Sorbitan ester type activator 12 〃 1.2 〃 (Silva S-80 ) Thermoplastic polyurethane resin 4.5 12 (Esten 5701) Vinyl chloride-vinyl acetate copolymer 22.5 18 were kneaded to make a magnetic paint, which was applied to the base.

Characteristics are shown in the table below. This comparative example is compared to Example 1.

Comparative example 2 ○) ■ rFe203 10 parts by weight 10 parts by weight Alkyl ether type surfactant 2〃2〃 (Actinol RIOO) Polyoxyethylene sorbitan 1〃1〃 Ester (T-80) Thermoplastic polyurethane resin 4.5〃 12 〃 (Esten 5701) Vinyl chloride-vinyl acetate copolymer 22.5 〃 18 〃 Two compositions were kneaded to produce a magnetic paint, and this was applied as a base.

The various characteristics were as shown in the table below. Table note: Head adhesion is determined by visually evaluating the adhesion of exfoliated powder from the magnetic coating film to the head using a 5-point method.As can be seen from this table, the magnetic recording medium of the present invention has a higher Although the electrical resistance is almost the same and the half-life is similar,
It can be seen that both the head adhesion and the degree of orientation are improved, and it is excellent both mechanically and electrically.

Example 3 In Example 1, alkyl ether type 1. Beni weight part, sorbitan ester type 1. Instead of using a surfactant in a proportion of 1 part by weight, the total amount of both was 3 parts by weight, and the ratio of both was varied.

The formulation with the binder followed the recipe (2) of Example 1. The results of half-life measurements are shown in FIG. 1 with an x. At the same time, the results using 100 parts by weight of magnetic powder without pretreatment, 3.0 parts by weight of total surfactant, parts by weight of polyurethane (Esten 5701) IZ, and 18 parts by weight of salt-vinyl acetate copolymer are shown in Figure 1. o
It was shown in As can be seen from the figure, the effect remains unchanged even if approximately 50% of the alkyl ether type is replaced with the sorbitan ester type. It also has a slightly shorter half-life than the additive type. It is important from the viewpoint of orientation and head adhesion that the half-life remains unchanged upon substitution. That is, in this example, alkyl ether type 3. When using a weight part of 1, the adhesion to the head is poor and the orientation is poor, but these can be improved by substitution. Note that sorbitan ester type surfactants do not have corrosive properties against heads, unlike strongly acidic surfactants such as phosphate ester type surfactants (which have similar effects). It is also advantageous in that respect.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the effect of surfactants on half-life. Figure 1

Claims (1)

[Claims] 1 Vinyl chloride-vinyl acetate copolymer plasticized with polyurethane resin in an amount of 40% by weight or less based on the total amount of the binder, and an alkyl ether type and sorbitan ester type surfactant (sorbitan ester type is included in the total amount of the surfactant). A magnetic recording medium is a magnetic recording medium formed by coating a substrate with a magnetic coating material, which is prepared by kneading magnetic powder, the surface of which has been previously covered with 50% or less.