JPS59165237A - Production of coating composition for magnetic film - Google Patents

Abstract

PURPOSE:To obtain a coated film which is extremely slippery and has an excellent electric characteristic by applying high shearing stress to a kneaded material then decreasing gradually the shearing stress in the stage of obtaining a magnetic coating. CONSTITUTION:70g powder of polivinyl butyral and 700g magnetic powder are charged into a kneader, and are mixed for about 15min. 250g cyclohexanone is gradually added to the mixture and the mixture is kneaded for about 4hr while about 50kg/cm<2> shearing stress is applied thereon. The shearing stress increases once to about 150kg/cm<2> on account of a change in the viscosity of the mixture, etc. but attains finally about 100kg/cm<2> value even if the condition for kneading is the same. While the kneading is continued, 520g cyclohexanone is added by taking about 5hr and the kneaded material is gradually dissolved to decrease gradually the shearing stress. The magnetic disc produced by such method is further dipped in a freon soln. of perfluoroalkyl ether, whereby the coating is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for producing a coating composition for magnetic films such as magnetic disks.

[Prior art]

Traditionally, magnetic disks are manufactured by coating a substrate with a paint made by dispersing ferromagnetic particles in a polymeric binder solution.
This is done through processes such as thermosetting and processing. Generally, magnetic powder particles in a coating film are randomly aggregated and exist as aggregates of non-uniform size. Therefore, as a high-density disk, it was not fully satisfactory in terms of electrical defects and surface smoothness. This point was improved in 1983.
Although this method was described in Japanese Patent No. 25406, it was still insufficient in terms of surface smoothness, especially for magnetic disks with ultra-high recording densities of 15,000 BP I or higher.

[Object of the Invention] The present invention has been made in view of the above, and an object of the present invention is to provide a method for producing a coating composition for a magnetic film that has excellent electrical properties.

[Summary of the invention]

The magnetic recording material depends on the quality of the magnetic paint used to form the magnetic film. In other words, it was discovered that when obtaining a magnetic paint, a very smooth coating film with excellent electrical properties can be obtained by applying the present invention, in which a high scratch stress is applied to the cross-wire material and then the scratch stress is gradually reduced. did.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on examples.

Example 1 70 g of polyvinyl butyral powder and 700 g of magnetic powder were put into a kneader mixer and mixed for about 15 minutes. Next, 250 g of cyclohexanone was gradually added, and kneader cross-crossing was carried out for about 4 hours while applying a shear stress of about 50 kg/cm 2 . During this time, even if the kneader crosstalk conditions remain the same, the stress will be approximately 50% due to changes in the viscosity of the mixture, etc.
To? / cm2, but eventually it will be about 100
The value will be KSI/crn2. Therefore, while the kneader crosstalk continued as it was, cyclohexanone 52
By adding 0 g over a period of about 5 hours, the kneaded material is gradually dissolved and the strain stress is gradually reduced. Next, 760 g of this mixture was poured into a 3-ton ball mill pot, 200 g of cyclohexanone was added, and the mixture was kneaded in a ball mill for 5 days to disperse the magnetic powder. Next, 600 g of a cyclohexanone solution of 120 g of phenol resin and epoxy resin, 500 g of isophorone,
Add 170 g of dioxane to prepare a paint for magnetic disks. Next, this paint was applied to an aluminum disk whose surface had been cleaned in advance to a film thickness of 0.6 to 0.8 μm.
It was oriented and baked at 220C for 2 hours. After the coating film was baked, the surface roughness of the magnetic disk was R820, 02 μm.
Conventional magnetic disk ()j, = 0.10 to 0.15 μm
) was much better. This magnetic disk is further polished to a film thickness of 0.5 to 0.7 μm.

The surface was processed to Ra=0.0 iμm. Coating was carried out by further immersing the magnetic disk manufactured by the above method in a perfluoroalkyl ether solution. The floating characteristics of the magnetic disk manufactured by the above process were investigated by mounting a vinyl sensor on the magnetic head. As a result, the floating characteristics have been significantly improved compared to conventional magnetic disks (see figure). Also, in terms of electrical characteristics, the S/N ratio has improved by about 25 inches compared to the conventional model.

This is because the magnetic powder particles in the coating film are individually dispersed.

Examples 2 to 6 A mixture having the composition shown in Table 1 was kneaded under the same conditions as in Example 1,
Furthermore, the solvents in Table 22 and Table 3 were added, followed by the compositions in Table 4,
A coating composition was produced in the same manner as in Example 1. All of them showed excellent effects similar to those described above. Alumina is added as a filler and has the effect of increasing the strength of the coating film. Note that the numbers in the table indicate parts by weight.

Table 1 (first step) Table 2 (2nd step) Table 3 (3rd step) Table 4 (4th step)

[Brief explanation of the drawing]

The figure is a diagram showing the floating characteristics of a magnetic disk as a result of implementing an embodiment of the present invention.

Claims (1)

[Claims] 1. 100 parts by weight of magnetic powder, 44 at least one polymer selected from the group consisting of polyvinyl butyral, polyvinyl formal, and polyvinyl acetate.
parts by weight, 0.1 to 15 parts by weight of filler and 20 to 60 parts by weight of solvent
A mixture consisting of parts by weight is subjected to abrasion stress of 10 to 400 Kf.
The first step is kneading by applying a force of /cm2, and the second step is gradually reducing the rubbing stress in the first step while gradually adding 40 to 440 parts by weight of the solvent to the kneaded product.The total amount of solvent is 3rd step of adding and kneading a solvent to make 120 to 500 parts by weight, 20 to 70 parts by weight of epoxy resin;
A fourth step of adding 20 to 70 parts by weight of phenolic resin and a suitable amount of solvent to obtain a paint with the required viscosity, and further kneading.
1. A method for producing a coating composition for a magnetic film, comprising the steps of: 2. The method for producing a coating composition for a magnetic film according to claim 1, characterized in that a rubbing stress of 10 to 400 Kf/crn2 is applied using a kneader. 3. The method for producing a coating composition for a magnetic film according to claim 1 or 2, wherein the shear stress is 20 to 300 Ky/cm". 4. In the fourth step, further polyurethane 2 to A method for producing a coating composition for a magnetic film according to any one of claims 1 to 3, in which 30 parts by weight is added and kneaded. 5. Claims 1 to 3, wherein the polymer is polyvinyl butyral. 6. The method for producing a coating composition for a magnetic film according to any one of Claims 4 to 6. The method for producing a coating composition for a magnetic film according to any one of Claims 1 to 5, wherein the filler is alumina. Method: 7. The method for producing a coating composition for a magnetic film according to any one of claims 1 to 5, wherein in the first step, the composition is kneaded without adding a filler.