JPH0656651B2 - Magnetic disk - Google Patents

Description

The present invention relates to a magnetic recording medium, and more particularly to a magnetic disk. The magnetic disk according to the present invention is characterized by having improved properties capable of meeting the demand for higher recording density. Here, the “magnetic disk” is, as generally recognized in this technical field, for example, a hard disk, a floppy disk, or the like,
For example, metal such as aluminum, glass, plastic,
It refers to a rotary magnetic recording medium in which a magnetic coating film is formed on various other substrates.

As is well known, various magnetic recording media for magnetic disk devices, which are composed of a magnetic material powder and a resin binder composition, have been proposed in this technical field.
Such a recording medium is generally prepared by dispersing a magnetic material powder such as γ-Fe ₂ O ₃ in a resin binder composition, applying the resulting dispersion to the disk surface of a magnetic disk, and It is prepared by baking and curing the formed magnetic coating film according to a conventional method. However, the properties of such known recording media cannot keep up with the recent trend of increasing the capacity and increasing the recording density of magnetic disk devices. That is, the conventional recording medium has been required as the disk and bed approach and the contact start / stop (CSS) system is adopted.
Good dispersion of magnetic powder, coating strength (CSS resistance
Properties, wear resistance, damage resistance, corrosion resistance, etc.) and other properties cannot be satisfied. Especially C-resistant
It is a problem to improve the SS property and to reduce the suction force of the head (which means the extent to which the head adheres to the recording medium, and when this is large, the medium is crushed), but in order to solve these problems, A method has also been proposed in which a lubricant is applied to the surface of a disk recording medium to impregnate it with the medium. However, this conventional lubricant-impregnated recording medium has a drawback that it is susceptible to oxidation.

The present invention provides an improved magnetic recording medium, especially a magnetic disk, which overcomes the drawbacks unavoidable in the conventional magnetic recording medium as described above, through the use of the improved magnetic film-forming coating composition. Has an aim.

For this purpose, according to the present invention, there is provided a magnetic disk having a magnetic film on a substrate, wherein the magnetic film comprises (A) a magnetic material powder and (B) 5 to 40% by weight of the magnetic material powder. Carbon powder, and (C) (1) 3 with respect to 100 parts by weight of the magnetic material powder.
5 to 95 parts by weight of a self-crosslinking thermosetting acrylic resin having an N-methylolamide group or an N-alkoxymethylamide group as a reactive functional group, and (2) 1 to 30 parts by weight of the acrylic resin % Of a butyral resin or a formal resin as a binder component.

According to the present invention, a resin binder for a magnetic recording medium type is prepared by further adding carbon powder and butyral resin or formal resin to a mixture of thermosetting acrylic resin and epoxy resin, phenol resin, melamine resin and the like. The composition can be prepared.

Carbon powder is effective for improving CSS resistance and abrasion resistance, among the coating film strength, and butyral resin or formal resin is methyl ethyl ketone (ME).
It is effective for improving resistance to solvent such as K), flexibility, and impregnation property of lubricant. Therefore, the recording medium obtained is a recording medium suitable as a high-density medium characterized by having particularly low frictional resistance and being not damaged by the head. This recording medium is not only excellent in corrosion resistance, but also excellent in dispersibility of magnetic powder and has good recording characteristics and high orientation.

According to the present invention, a self-crosslinking (that is, self-curing) type thermosetting acrylic resin having an N-methylolamide group or an N-alkoxymethylamide group as a reactive functional group is added to 100 parts by weight of magnetic material powder. It is preferably used in an amount of 35 to 95 parts by weight. Such an acrylic resin is composed of, for example, acrylamide, styrene, acrylic acid ester, methacrylic acid ester, acrylonitrile, and the like. Such resins are commonly used, for example, Duraclon "SE-5377" and SE.
-5437 (both manufactured by Mitsubishi Rayon Co., Ltd.) and the like are commercially available.

Usually, a phenol resin, an epoxy resin, a melamine resin or the like can be used together with the acrylic resin. Such a resin can be arbitrarily selected from a wide range of resins commonly used in this technical field, and
The type and amount can be arbitrarily selected according to the desired purpose. However, it is advantageous that such a resin is soluble in an alcohol solvent in consideration of production of a recording medium.

As an example of such a resin, Smirask PC-25
(Otoyu Bakelite Phenolic Resin), Epicoat # 1001 (Ciel Epoxy Resin), and the like.

The magnetic material powder that can be used in the present invention is
It contains magnetic powder capable of satisfying the performance required for a magnetic recording medium, for example, acicular fine particles such as γ-Fe ₂ O ₃ and Fe ₃ O ₄ .

According to the present invention, carbon powder having an average particle diameter of 2000 μm or less is preferably added to the magnetic material powder in an amount of 5 to 5.
It is advantageous to use 40% by weight. Such carbon powder can be appropriately selected and used from commercial products, and examples thereof include RAVEN 7000 and 8000 manufactured by Columbia Carbon Co., USA, and CONDUCTEX93.
0 and 950 (both are trade names) can be listed.

According to the invention, it is advantageous to use the butyral or formal resin in an amount of 1 to 30% by weight, based on the acrylic resin. These resins can be used alone or in combination according to the desired purpose, and in any case, the characteristics of the obtained magnetic recording medium are not deteriorated. Examples of the butyral resin include S-lex BX-1, BX-L, BMS, BLS (all manufactured by Sekisui Chemical Co., Ltd.), and the like.
As formal resin, Denka formal 20,30
And 100 (both are manufactured by Denki Kagaku Kogyo Co., Ltd.) and the like.

When a magnetic recording medium is produced using the coating composition according to the present invention, since the dispersibility of the magnetic powder is excellent as described above, the kneading time required for preparing the coating composition for forming a coating film Can be shortened, and excessive and complicated kneading operations which are inevitable in the conventional method can be eliminated. This means in other words that it is possible to prevent the coercive force of the magnetic material from decreasing.

Application of the coating composition can be carried out according to conventional film-forming techniques, for example using spin coating, roll coating, dip coating, and the like. Subsequent processing can also be carried out according to the method conventionally used conventionally in this technical field.

Subsequently, the present invention will be described in more detail with reference to the following examples.

Example The following components (excluding silicone oil KF-69) were blended in the proportions indicated, kneaded in a ball mill for 24 hours, and after addition of silicone oil KF-69:
The kneading was continued for another 20 hours. The coating composition thus obtained had the magnetic powder uniformly dispersed therein.

The resulting coating composition was applied onto an aluminum disc for a magnetic disk according to the spin coating method, and baked and cured at a temperature of 220 ° C. for 30 minutes. After the tape was polished, the surface of the polished surface was coated with the following lubricant under the coating conditions described below, and baked at a temperature of 220 ° C. for 30 minutes.

Lubricants: KRYTOX, DuPont fluorinated alkyl polyether (high temperature liquid lubricant).

Lubricant coating conditions: coating liquid concentration = 1% solution, coating rotation speed = 500 rpm. (Spin coating) The magnetic recording medium thus obtained was subjected to the following evaluation test. Incidentally, in this evaluation test, JP-A-55-29
The strength test method described in Japanese Patent No. 67 and the magnetic disk evaluation method described in Japanese Patent Application Laid-Open No. 56-3437 were referred to.

In the same manner as above, various magnetic recording media were prepared by variously changing the addition amounts of carbon powder and butyral resin, and subjected to the following evaluation tests.

Evaluation test I Low speed / high load dragging CSS with respect to the amount of carbon powder added
Evaluation of Dependency of Number of Times and Head Adsorption Force: The following conditions were applied to evaluate the above dependency on the amount of carbon powder added.

Measurement of the number of times of low-speed high-load dragging CSS (acceleration test): Set the magnetic disk under test in the magnetic disk drive and
It was rotated at a speed of 00 rpm. In order to perform the test in an accelerated manner, a load of 100 g was applied to the head slider holding the head (load of 8 g). Under such pressurizing condition, contact start / stop (C
(SS) was repeated, and the number of times (CSS number) until a change in sliding noise, dust amount and color tone was visually observed on the surface of the magnetic film of the disk was measured. The number of CSS is
Aim to achieve at least about 20 times.

Measurement of head attraction force (g): When the magnetic disk under test is set in the magnetic disk device and the head is left on the magnetic disk under pressure for 24 hours, the saturation of the attraction force acting between the two (head attraction force, measurement (Read as g from the scale of the tension gauge of the device) was measured. The measurement was performed on 50 heads and the average value was obtained. It should be noted that about 20 g of the suction force of the head is a standard for achievement.

The obtained results are plotted and graphed in FIG. 1 attached. As can be seen from this graph, the number of dragging CSSs (times) increases as the amount of carbon added (% to the magnetic powder) increases (see curve I),
In contrast to this, the head adsorption force (g) gradually decreased (see curve II). Here, when the curve I exhibits a sharp rise, the curve II drops sharply, and thereafter, both are almost constant (CSS number: about 50 times, head adsorption force) after the carbon addition amount exceeds 10%. : About 8 g), and it can be seen that the amount of CSS starts to decrease at a carbon addition amount of 40%, although the head adsorption force is almost unchanged.

The above facts indicate that the number of drag CSS can be increased and the head attracting force can be reduced by increasing the carbon addition amount, and particularly when the carbon addition amount is 5 to 40% with respect to the magnetic powder. Since it is possible to simultaneously achieve improvement in CSS resistance and reduction in head suction force, it is clearly stated that such a range is an optimum practical range for CSS media.

Evaluation Test II Evaluation of Dependence of Adhesion of Coating Film on Addition Amount of Carbon Powder: The following evaluation tests were conducted to evaluate whether the adhesion of the coating film changes with the addition amount of carbon powder.
After subjecting the test magnetic recording medium to a usual 6φ bending test, the degree of peeling of the coating film was observed by rubbing the bending portion with gauze, and evaluated by a 5-point method: 5 points: coating film No peeling 4 points: No peeling (only scratches) 3 points: Slightly peeling 2 points: Almost peeling 1 point: Peeling off with a very small amount 0 point: Completely peeling FIG. 2 is attached. This graph shows that the adhesion of the coating film gradually decreased after the amount of carbon powder added exceeded 20%. The adhesion strength evaluation when the amount of carbon powder added was 40% was 3 points, which was acceptable for the magnetic recording medium.

Evaluation test III Low-speed high-load drag CS with respect to butyral resin addition amount
Evaluation of Dependence on S Number of Times and Solvent Resistance: The following conditions were applied to evaluate the above dependency on the amount of butyral resin added. Measurement of low-speed high-load drag drag CSS times (times) (acceleration test): Load = 100 g (head load 8 g) Disk rotation speed = 400 rpm Measurement of solvent resistance Solvent used = wire rod impregnated with MEK (methyl ethyl ketone) MEK The coating film (film thickness 1 μ) is rubbed and the number of rubbing until the substrate is exposed is recorded. Solvent resistance (especially M resistance)
Use this number of rubbing (times) as a means to evaluate EK).

The results obtained are as shown in the attached FIG.
In the figure, curve I shows the number of low speed and high load dragging CSS, and curve II shows the number of rubbing which is an evaluation standard of solvent resistance.

From FIG. 3, it can be seen that the number of dragging CSSs and the solvent resistance increase as the amount of butyral resin added (% with respect to the acrylic resin) increases. However, the solvent resistance began to show a drop after the addition amount of butyral resin reached 30%. In addition, when the formal resin was used instead of the butyral resin (alone or as a mixture with the butyral resin), the same result as above could be obtained.

Evaluation Test IV Evaluation of Dependence of Impregnation of Lubricant on Addition Amount of Butyral Resin: CRYTOX (above) was used as a lubricant, and the degree of the impregnation depends on the addition amount of butyral resin (% to acrylic resin). Was tested to see if it changed.
That is, the coating concentration (%) of Krytox that can be impregnated each time was evaluated by changing the addition amount of butyral resin.
When applying Krytox, 400 r.p.
A disk speed of m. was applied. The obtained results are as shown in the attached FIG.

From FIG. 4, it can be seen that as the addition amount of butyral resin increases, the impregnated amount of Krytox also increases, and becomes constant when the former reaches 10%. Also in this test, when a formal resin and a butyral resin / formal resin mixture were used in place of the butyral resin, the results substantially matching the curve of FIG. 4 were obtained.

[Brief description of drawings]

Figure 1 shows the amount of carbon powder added and low speed / high load drag C
A graph showing the relationship between the number of SSs and the head adsorption force. Fig. 2 is a graph showing the relationship between the amount of carbon powder added and the adhesion of the coating film. Fig. 3 is a butyral resin addition amount and low speed high load drag. FIG. 4 is a graph showing the relationship between the number of CSSs and solvent resistance, and FIG. 4 is a graph showing the relationship between the amount of butyral resin added and the concentration of the lubricant coating liquid.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaomi Naito 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Ryuichi Suzuki, 1015, Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture Fujitsu Limited ( 72) Inventor Mitsuru Nagai 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Limited (56) References JP-B 44-17946 (JP, B1) JP-B 46-13103 (JP, B1) JP-B Sho 51-25112 (JP, B2)

Claims (1)

[Claims] 1. A magnetic disk having a magnetic film on a substrate, wherein the magnetic film comprises (A) a magnetic material powder and (B) 5 to 40% by weight of the magnetic material powder. (C) (1) 3 with respect to 100 parts by weight of the magnetic material powder
5 to 95 parts by weight of a self-crosslinking thermosetting acrylic resin having an N-methylolamide group or an N-alkoxymethylamide group as a reactive functional group, and (2) 1 to 30 parts by weight of the acrylic resin % Of a butyral resin or a formal resin as a binder component.