JPH047013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a magnetic disk substrate, particularly a thin film type magnetic disk substrate.

(Prior Art) Recently, so-called thin-film magnetic disks, in which a magnetic thin film is formed on a substrate by plating or sputtering and used as a recording layer, have attracted attention because of their high recording density. There are two types of substrates commonly used for this type of disk: those with extremely smooth surfaces, and those with so-called texture processing, in which various fine linear grooves are formed on the entire surface in the circumferential direction. There is.

As is well known, recording and reproducing on a magnetic disk is performed with the head floating about 0.1 to 0.5 .mu.m above the disk surface. This flying height (gap) has a large effect on the recording and reproducing characteristics, and if the disk surface has undulations or irregularities, the flying height may become uneven depending on the location of the disk, or the effective flying height may increase. As a result, problems arise in which modulation occurs in the reproduced output or the recording density deteriorates. In the case of a thin-film magnetic disk, most of the unevenness and waviness on the disk surface are caused by the unevenness and waviness on the surface of the disk substrate. Therefore, in the past, disk substrates were mirror-polished to obtain a smooth surface, and the materials used were those with excellent abrasiveness, such as NiP hard thick film plated on Al, or Al surfaces. Anodized aluminum, glass, ceramics, etc. are used. Furthermore, in order to reduce the contact area between the disk and the head and to smooth the friction between the disk surface and the head, the substrate made of the above material is finished to a mirror surface, and then polished in the circumferential direction using abrasive paper or an abrasive agent of appropriate roughness. Texture treatment is applied to form countless linear grooves.

On the other hand, the above-mentioned substrate materials are expensive, and polishing them to a mirror surface increases the cost, so rough polishing is required.
An inexpensive disk substrate has been proposed in which a heat-resistant polymer such as polyimide is coated on a non-magnetic substrate such as Al. The role of this heat-resistant polymer film is to prevent corrosion due to electrochemical interaction between the magnetic film formed thereon and a non-magnetic substrate such as Al, and to obtain a smooth surface. Further, the reason why a heat-resistant polymer material is used is that the substrate temperature rises in the process of manufacturing the magnetic film, and furthermore, it is reliable because it shows little change over time when used for a long time.
The present invention relates to a method of manufacturing this magnetic disk substrate.

In addition, the applicant has proposed a method for forming a synthetic resin film having a stoichiometric composition by first evaporating two or more monomers in a vacuum processing chamber and polymerizing them on a substrate. The monomer is vapor-deposited onto the substrate by raising the temperature of the substrate indoors to a temperature higher than the higher of the evaporation temperatures of these monomers and the temperature of the inner wall of the vacuum chamber to higher than the temperature of the substrate. Method (omnidirectional simultaneous vapor deposition polymerization method)
(Japanese Patent Application Laid-Open No. 61-261322 and Patent Application No. 1983-
206764).

(Problems to be Solved by the Invention) Spin coating and spraying have been proposed as methods for applying a heat-resistant polymer material to a non-magnetic substrate such as Al, but spin coating Disadvantages include that the coating film is thicker on the outer circumferential side than on the outer edge, and that it is not possible to coat both sides of the substrate at the same time.Also, with the spray method, the coating thickness on the surface of the disk substrate is uneven. The drawbacks are that it is easy to use and that the film thickness cannot be controlled in practice. Furthermore, neither method allows coating onto a textured substrate while leaving the texture intact. Therefore, when a magnetic disk is manufactured using a disk substrate coated with a heat-resistant polymer material using a conventional coating method, there are problems such as modulation of the playback output and differences in the playback output between disks. However, since it was not possible to create a textured state, there was a problem that the coefficient of friction increased. That is, it has been almost impossible to control the unevenness of the surface of the disk substrate.

The present invention solves the above-mentioned drawbacks in forming a heat-resistant polymer material on the surface of a non-magnetic substrate, and provides a method for producing a disk substrate with a smooth surface even if the surface of the non-magnetic substrate is rough-finished. The purpose is to propose the following.

(Means for Solving the Problems) The present invention solves the above problems by using the omnidirectional simultaneous vapor deposition polymerization method previously proposed by the applicant. A magnetic disk substrate having a heat-resistant organic polymer film on the surface of the substrate is placed in a vacuum container with a heated inner wall, in which two or more monomers are evaporated, and the evaporated components are transferred to the heated non-magnetic substrate in the vacuum container. It was manufactured using a vapor deposition polymerization method that polymerizes on the surface.

(Function) When the inner wall of the vacuum container is heated and two or more types of monomers, such as pyromellitic dianhydride and 4,4'-diaminodiphenyl ether, are evaporated in the vacuum container, the evaporated components are absorbed into the vacuum container. is vapor-deposited and polymerized on the surface of the heated non-magnetic substrate, forming a heat-resistant organic polymer film of polyimide. This effect is almost the same as the vapor deposition polymerization method previously proposed by the applicant, but the following unique effect is observed in the vapor deposition process, and the present invention utilizes this unique effect. The company began manufacturing magnetic disk substrates using the same technology. That is, the evaporated components of each monomer are evaporated and polymerized on the surface of the non-magnetic substrate to form a heat-resistant organic polymer film, but the thickness of the deposited polymer film is small compared to the average roughness of the surface of the non-magnetic substrate. In some cases, the surface roughness of the polymer film is almost the same as the surface roughness of the substrate, and as the film thickness increases, the surface roughness of the polymer film gradually becomes smoother. When the polymer film was formed to a thickness approximately twice the average surface roughness of the substrate, the surface roughness was found to be reduced to approximately 1/2 of the roughness of the substrate surface.

Therefore, in order to form a polymer film with a smooth surface using an inexpensive substrate such as a roughly polished Al substrate, it is sufficient to increase the thickness of the deposited polymer film. When attempting to obtain a textured state even after the formation of heat-resistant organic polymers using a substrate, the thickness of the deposited film may be reduced. Moreover, the polymer film can be formed on both sides of the substrate at the same time, and the entire surface of the polymer can be smoothed, resulting in good productivity, no modulation of the reproduction output, and even when processing a large number of substrates, it is possible to control the film thickness. This can be easily controlled by controlling the evaporation of the monomer.

(Example) The apparatus used to carry out the present invention is as shown in the first diagram, and a heater 3 is provided around the outer periphery of a vacuum container 2 equipped with a vacuum exhaust port 1 to heat the inner wall of the vacuum container 2. Monomer gas introduction nozzles 8a and 8b are introduced into the vacuum container 2 from a plurality of externally provided monomer evaporation sources 4a and 4b through pipes 7 each equipped with a valve 5 and a heater 6. . By independently controlling each heater 9a, 9b using a heater for heating each evaporation source 4a, 4b, the temperature of each evaporation source 4a, 4b can be arbitrarily controlled. Reference numeral 10 indicates non-magnetic substrates such as aluminum, ceramics, glass, etc., and a plurality of non-magnetic substrates such as aluminum, ceramics, glass, etc. are attached to a shaft-shaped jig 11 through a mounting hole formed in the center of each substrate 10, and the vacuum vessel 2 is attached.
The substrate was placed inside the substrate and heated from the surrounding area using a heater 12 for heating the substrate. 13 is a main valve.

A magnetic disk substrate was manufactured in the following manner using the apparatus described above.

Example 1 One evaporation source 4a is filled with pyromellitic dianhydride as a raw material monomer, and the other evaporation source 4b is filled with pyromellitic dianhydride as a raw material monomer.
4,4'-diaminodiphenyl ether is charged as a raw material monomer. Thereafter, the main valve 13 is opened to exhaust the inside of the vacuum container 2 and each evaporation source 4a, 4b to 1×10 ⁻⁵ Torr or less. Next, the evaporation source 4a,
The valves 5, 5 of the pipes 7, 7 of 4b are closed, and the heater 3 and the substrate heating heater 12 are operated so that the inner wall of the vacuum container 2 is at 180°C and the substrate 10 is at 180°C, and the pyromellitic dianhydride is heated. 170℃, 4,
The heaters 9a and 9b of the evaporation sources 4a and 4b are controlled and operated so that the temperature of 4'-diaminodiphenyl ether is 160°C. After that, valve 5,
5 is opened, monomer gas is introduced from monomer gas introduction nozzles 8a and 8b, and the evaporated components are vapor-deposited and polymerized on the substrate 10. The base 10 has a surface roughness of 0.1μ
A non-magnetic substrate made of Al and having a diameter of 5.25 inches was used in a roughly polished state. Since the substrate 10 was heated to 180° C., the evaporated components of the monomers did not precipitate alone on the substrate surface, but only polymerized products of each monomer precipitated in a layered manner. The deposition rate was 1050〓/min.
The obtained layered polymer was a heat-resistant organic polymer made of polyimide, and was extremely heat-resistant, with a polymerization reduction rate of less than 10% when the temperature was raised to 400°C. The relationship between the thickness of the polyimide deposited film and its surface roughness is as shown by curve A in FIG. The surface becomes smooth, and the film thickness is reduced to 0.2 μm, that is, 2 times the surface roughness of the substrate 10.
When the film was doubled, the roughness of the film surface was approximately half that of 0.05 μm, and when 1.0 μm was deposited, the surface roughness was 0.008 μm, which was sufficiently smooth for a magnetic disk substrate.

On this substrate 10 on which polyimide was deposited with a thickness of 1.0 μm, a Cr film of 1000% and 70% Co-20 was applied by sputtering.
A magnetic disk was fabricated by successively depositing 650% Ni-10%Cr alloy film and 400% C film. The magnetic properties of this disk are Brδ=530Gμm, Hc=800
At Oe, S・R=0.85, the same characteristics as the conventional NiP-plated Al substrate were obtained. This means that no harmful gases are emitted from the polyimide film during sputtering. When we evaluated the recording and playback characteristics of this magnetic disk, we found that it had a playback output of 1.25MHz,
Characteristics of (Eop) = 1.8 mV, resolution 91%, and modulation = ±4.5% were obtained. The levitation of the head was also stable. Moreover, the difference in reproduction output between the front and back sides was less than ±5%. Furthermore, magnetic disks were prepared under exactly the same conditions for five substrates prepared at the same time, and the magnetic properties and recording/reproducing properties were measured, and the difference was found to be less than ±7%.

The film thickness distribution of the polyimide film on the substrate 10 was also measured, and the distribution among the five substrates and within the plane of one substrate was both 5% or less. In order to form a polyimide film with better heat resistance on the substrate 10, it is preferable to close the valves 5 and 5 of the evaporation sources 4a and 4b to stop the evaporation polymerization, and then perform heat treatment at 250°C for 10 minutes. In that case, the polymerization reduction will be 5% or less.

Example 2 A heat-resistant organic polymer film of polyimide was formed in the same manner as in Example 1, using an aluminum substrate mirror-polished and textured to an average roughness of 0.08 μm as the non-magnetic substrate 10. .
When the unevenness of the texture was measured by changing the thickness of the deposited polyimide film, the results were as shown by curve B in FIG. 3. As can be seen from this result, even when a 0.05 μm polyimide film is formed, the texture of the substrate 10 itself is almost maintained on this surface. A magnetic disk was fabricated by successively sputtering Cr, CoNiCr, and C films on the textured disk substrate on which the 0.05 μm polyimide film was formed in the same manner as in Example 1. When this disk was subjected to a CSS test, which is a wear resistance test, the friction coefficient after 10,000 CSS tests was 0.32.
No occurrence of head crush was observed. For comparison, textures are not processed.
NiP plated Al substrate (commercially available conventional substrate)
A magnetic disk was made by continuously sputtering Cr, CoNiCr, and C films on top of the disk, and after 10,000 CSS tests, the friction coefficient was 1.8, and wear marks caused by the head were observed. The above results show that when a polyimide film is formed on a textured substrate by the method of the present invention, a polyimide overcoat can be formed without damaging the textured state of the substrate.

In addition, as a heat-resistant organic polymer film, polyamide,
The method of the present invention can be similarly applied to polyurea and the like.

(Effects of the Invention) As described above, in the present invention, two or more types of monomers are evaporated in a vacuum container whose inner wall is heated, and the evaporated components are transferred to the surface of the heated nonmagnetic substrate in the vacuum container. Since a magnetic disk substrate having a heat-resistant organic polymer film is manufactured by polymerizing with It is possible to create a smooth magnetic disk substrate using a roughly polished substrate, or to create a magnetic disk substrate overcoated with a heat-resistant organic polymer film using a textured substrate without impairing the texture state. Moreover, since the polymer film can be simultaneously formed on the inner surface of the substrate, it is easy to mass-produce, and the thickness of the formed polymer film is uniform, allowing for modulation of the reproduction output as a magnetic disk. Moreover, even if the film is produced in large quantities, the film thickness can be easily controlled and formed uniformly, so that the recording and reproducing characteristics can be made uniform.

[Brief explanation of drawings]

Figure 1 shows one of the devices used to carry out the method of the present invention.
FIG. 2 is a diagram showing the relationship between the thickness of a deposited polyimide film and its surface roughness, and FIG. 3 is a diagram showing the relationship between the thickness of a deposited polyimide film and texture roughness. 2... Vacuum container, 3, 9a, 9b, 12... Heater, 4a, 4b... Evaporation source, 10... Nonmagnetic substrate.

Claims (1)

[Claims] 1. A magnetic disk substrate having a heat-resistant organic polymer film on the surface of a non-magnetic substrate such as aluminum, ceramics, glass, etc. is placed in a vacuum container whose inner wall is heated, and two or more types of monomers are evaporated therein. A method for producing a magnetic disk substrate, characterized in that the evaporated component is produced by a vapor deposition polymerization method in which the evaporated component is polymerized on the heated surface of the non-magnetic substrate in the vacuum container. 2. The method of manufacturing a magnetic disk substrate according to claim 1, wherein the nonmagnetic substrate has fine linear grooves formed all over its surface.