JPS6171415A - Coating type vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a coating type vertical magnetic recording medium for which barium ferrite magnetic powder having excellent orientation and surface characteristic is used by adding a specific amt. of fatty acid to the magnetic powder. CONSTITUTION:A fatty acid is added to the magnetic powder in the range of weight %+ or -10% calculated by the equation. The coating type vertical magnetic recording medium which realizes simultaneously the high orientation and high surface characteristic and for which the barium ferrite magnetic powder is used is thus obtd. In the equation, S: the BET specific surface area of the magnetic powder, M: the molecular weight of the fatty acid, a: the monomolecular sectional area for each one molecule of the fatty acid, N: Avogadro's number. The N: Avogadro's number = 6.022X10<23> with respect to the barium ferrite magnetic powder.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to magnetic tapes, floppy disks, etc. used in audio equipment, video equipment, computers, etc.
The present invention relates to a coated perpendicular magnetic recording medium that uses barium ferrite as magnetic powder in magnetic carts and the like.

(Conventional structure and its problems) Recent magnetic recording media used in audio equipment, video equipment, computers, etc. are required to have higher density and higher performance.In particular, floppy disks are required to have higher recording density. There is fierce competition for this. Therefore, barium ferrite magnetic powder, which has emerged as the ideal material for coating-type magnetic recording media, is used. ゛In the medium, the axis of easy magnetization (perpendicular to the plate surface, crystallographically
Various efforts have been made to orient the base film (axis) perpendicularly to the plane of the base film. Conventional know-how regarding this method can be divided into three parts: know-how on manufacturing barium ferrite magnetic powder, know-how on dispersing the obtained magnetic powder to make excellent paint, and know-how on coating process. There is. However, from the perspective of manufacturing coating media, it is important to make paints.

We have no choice but to accumulate know-how on the coating process, and therefore we have conducted a lot of research in this regard. One of the important findings obtained there is that higher fatty acids are extremely involved in the orientation of barium ferrite, and that the optimum amount of fatty acids is well-supported both experimentally and theoretically. There is a discovery that there is.

It is widely known that fatty acids are originally excellent dispersants for iron oxide magnetic powder, but when considering the optimal amount, we rely on empirical knowledge, but in reality, many samples We had no choice but to adjust and define it in a practical manner. Also, typical fatty acids include:

Syristic acid and stearic acid are solid powders at room temperature, and if added in excess, they will stand out on the surface of the magnetic layer, significantly impairing the surface properties of the coating film and deteriorating its magnetic properties. Met.

On the other hand, even if the amount was less than the optimum amount, it could not achieve sufficient effect as a dispersant.

Therefore, even if the particle size, surface area, surface roughness, etc. of the magnetic powder change, if we can calculate the optimal amount of fatty acids and obtain a calculation formula that closely matches the experimental data, we can use it as a coating know-how. Needless to say, this is one of the most important things.

(Object of the Invention) The object of the present invention is to provide a calculation formula for calculating the above-mentioned optimum amount of fatty acids, and thereby to create a coated perpendicular magnetic recording medium using barium ferrite magnetic powder that has excellent orientation and surface properties. It is about providing.

(Structure of the Invention) The present invention provides high orientation and high surface properties by adding fatty acids to magnetic powder in the range of weight % ± 10% calculated by the formula described in the claims section. It is composed of a coated perpendicular magnetic recording medium using barium ferrite magnetic powder that simultaneously achieves the following.

In considering the optimum amount of fatty acids, it has been found that barium ferrite magnetic powder is easily adsorbed and surface-modified by fatty acids, especially linear saturated higher fatty acids such as myristic acid and stearic acid.

Therefore, C, M, C0 (Critical
We will proceed with the discussion by introducing the concept of Micelle Concentration (critical micelle concentration). First, Table 1 summarizes the specifications of the magnetic powder and myristic acid used in the experiment.

Table 1: Next, what weight percent of fatty acids is the CMC amount in barium ferrite magnetic powder?

The CMC amount is easily calculated as follows without explanation.

Here, S: B, E, T, specific surface area (actual value, unit Bo/g)
M: Molecular weight of fatty acid a: Single molecule cross-sectional area per molecule of fatty acid (unit d) N: Avogadro's number (6,022X10") As is clear from the above formula, the CMC amount is B, E, T, specific surface area S It can be seen that more fatty acids are required for magnetic powder with a smaller particle size in proportion to .

(Explanation of Examples) Examples are given below to demonstrate the validity of the above-mentioned CMC concept and that the calculated CMC values match well with actual experimental values. A coating-type perpendicular magnetic recording medium with excellent properties will be described in detail.

First, in order to perform preliminary dispersion, the following materials were placed together with balls in a ball mill container and kneaded for 15 hours.

Barium ferrite magnetic powder ・・・・・・・・・ 10
0 parts Mixed solvent (MEK, toluene, cyclohexanone total) 250 parts Myristic acid ... Each part shown in Figure 1 Carbon black ......
・・・・・・・・・ 5 parts (manufactured by Cavonet Co., Ltd. 1 product number VUL
CAN XC-72) Lecithin ・・・・・・
・・・・・・・・・・・・・・・・・・・・・ 3rd part Next, salt-vinyl acetate copolymer resin (as solid content) as a binder for dispersion in the method... 15 parts (manufactured by UCC, product number VAG) I) were added and kneaded continuously for 70 hours.

Furthermore, as a binder and abrasive for next dispersion, polyurethane resin (as a solid substance)...15 parts (manufactured by Nippon Polyurethane Co., Ltd., product number N-2304) abrasive (
α-A et al.03)・・・・・・・・・・・・・・・
・・・・・・ 3 parts were used as a hardening agent in magnetic paint.
6 parts of Coronate L (trade name: manufactured by Nippon Polyurethane Co., Ltd.) was added, and filtered through a filter with an average pore size of 3 μm to a thickness of 7.
After coating and drying on a 7 μm polyethylene terephthalate film and calendering at 80°C.

A magnetic layer with a thickness of 4 μm was obtained by heat treatment at 60° C. for 20 hours. Thereafter, it was punched and polished to obtain a 3.5-inch single-sided coated floppy disk. Incidentally, all parts in the middle part of the examples are parts by weight.

For the samples with the above myristic acid moieties varied, the X-ray rocking dispersion angle (Δθ5°), which indicates the degree of geometrical vertical orientation of the hexagonal plate-shaped barium ferrite magnetic powder, and the magnetic vertical orientation described below. The p value, which indicates the degree, and the glossiness, which indicates the surface smoothness, were measured.

(i) Measurement of rocking dispersion angle (-〇,.) Ba ferrite (00g
)(n) Measurement of p value Vibrating sample magnetometer (manufactured by Toei Kogyo, product number VSMP-Is)
Maximum applied magnetic field 5KOe M- in both vertical and horizontal directions with a certain number of sample films stacked
Draw an H curve and calculate the p value as follows without demagnetizing field correction.

p value - r(1)/Br(/) (Or; residual magnetic flux density, (1), (1) vertical and horizontal force, respectively) The results thus obtained are shown in FIG.

Also, -〇. The correlation coefficient between the value and the p value is -0,961, indicating an extremely high negative correlation.

From the graph in Figure 1, the number of parts of myristic acid added is:
40 for 4 parts. . It can be seen that both the p value (1 in Figure 1) and the p value (2 in Figure 1) are sufficient. These four parts almost match the value obtained from the above-mentioned equation derived from the CMC concept. That is, when calculated by substituting the data in Table 1 into the formula for calculating the amount of CMC (expressed as wt%), it is calculated as follows: = 3.79% by weight (approximately 4 parts)
becomes.

(City) Measurement of Glossiness The value indicated by the glossmeter (product number VG-10, manufactured by Nippon Heavy Industries, Ltd., Inc./Reflection angle of 45 degrees) is taken as the glossiness.

The results of the glossiness are shown in FIG. With calendering (4 in Figure 2) and without calendering (3 in Figure 2), the added parts of silistic acid that gave the highest gloss were 3 parts and 5 parts, respectively, and the average was 4 parts. It has become. Furthermore, in the calendered sample, the gloss level significantly decreases as the number of parts added (more than 5 parts) increases, so it is clear that although excess myristic acid does not reduce the orientation, it deteriorates the surface properties of the magnetic layer.

From the above results, a model with a relative orientation is estimated, and an idea for the optimal amount of fatty acids is derived.

That is, in barium ferrite magnetic powder that has not been surface-modified with an organic material, if fatty acids are present during preliminary dispersion, most of the fatty acids are adsorbed to the magnetic powder and form something similar to a monomolecular micelle structure.

It has already been found through another analysis that it is not adsorbed by the carbon black that coexists at this time. In the case of CMCMC, therefore, as the amount of fatty acids (which can be considered as a dispersant for magnetic powders) increases, the dispersibility of many magnetic powders becomes better, the geometrical orientation becomes better, and therefore the magnetic orientation also becomes better. In the case of CMCMC, it is thought that excess fatty acids that do not form a micellar structure are present in the coating film, and are embossed onto the surface by calendering, impairing the surface properties. Therefore,
In order to improve the orientation and at the same time not impair the surface properties, the amount of silistic acid added before and after CMCMC is desirable, and the allowable range is ±10 parts before and after the amount of CMC, based on other experimental data. did.

This CMC concept is fully effective in the case of linear saturated higher fats (preferably those with a molecular formula of 14 to 18 carbon atoms), such as myristic acid used in this experiment. It turned out to be.

(Effect of the invention) As is clear from the above explanation, adding fatty acids useful as excellent dispersants in CMC-calculated amounts provides the best orientation and surface properties, and this amount is the optimal amount of added fatty acids. The effect and significance of the present invention is significant in that this fact has been experimentally and theoretically supported.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the measurement results of P value, and FIG. 2 is a graph showing the measurement results of glossiness. 1...-〇. , 2... p value, 3... Glossiness without calendering, 4... Glossiness with calendering. Patent applicant: Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] (1) Weight% of magnetic powder calculated by the following formula ±10%
A coated perpendicular magnetic recording medium characterized in that a fatty acid is added within the range of . (S・M)/(a・N)×100 (wt%) S: BET specific surface area of magnetic powder M: Molecular weight of fatty acid a: Single molecule cross-sectional area per molecule of fatty acid N: Avogadro's number (2) The coated perpendicular magnetic recording medium according to claim (1), wherein the fatty acid is a monobasic linear saturated higher fatty acid.