JPH06215366A - Disk substrate and its production - Google Patents

Abstract

PURPOSE:To obtain a disk substrate excellent in corrosion, weather and shock resistance by using a glassy carbon composite material with fine selective ruggedness formed on the surface. CONSTITUTION:A glassy carbon composite material with fine selective ruggedness formed on the surface is used. The roughness of the ruggedness is regulated to about 10-100Angstrom . The composite material has such high strength that cracking and chipping are hardly occurred when it is subjected to working of inner and outer circumferences and chamfering at the time of working a substrate and the objective disk substrate having high rigidity and satisfactory surface smoothness is obtd. This substrate is nonmagnetic and has satisfactory corrosion and weather resistance and high shock resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk substrate used as a recording medium and a manufacturing method thereof.

[0002]

2. Description of the Related Art Recently, the importance of a magnetic disk device as an external storage device of a computer system has been increasing, and its recording density has been remarkably improved. In such a drive system of the magnetic disk device, when the magnetic disk is rotating at a high speed and at a constant speed, the magnetic head is in a floating state separated from the magnetic disk, and when the magnetic disk is stopped, the magnetic head and the magnetic disk are separated from each other. Contact CSS (Co
The ntact start and stop method is adopted. In such a CSS system, it is necessary to reduce the flying height in order to improve the recording / reproducing characteristics. This object is achieved by improving the surface smoothness of the magnetic disk.

However, if the surface smoothness of the magnetic disk is increased, the magnetic head is likely to be attracted to the magnetic disk, and the surface is likely to be damaged at the time of start-up. By the way, conventionally, an Al substrate plated with Ni—P is mirror-finished by polishing with free abrasive grains, and then has a predetermined roughness by polishing with a polishing tape or free abrasive grains. Techniques such as finishing the surface, or etching the glass substrate with an etching agent such as hydrogen fluoride to finish the surface having a predetermined roughness are known.

However, each of the above techniques has a problem that the cost is high. Moreover, there is a problem that it is difficult to control when finishing a surface having a predetermined roughness, poor reproducibility, and it is difficult to mass-produce a surface having uniform characteristics. Further, with respect to the Al substrate, there is a problem that the rigidity becomes insufficient when the thickness becomes thin.
That is, if the rigidity is insufficient, the substrate waviness will not be able to be flattened during mirror surface processing, and when a wavy substrate is used for a disk, uneven rotation will occur and the flying height of the magnetic head will be small. It causes inconvenience that you can not
Further, there is a disadvantage that the disk is deformed when chucking the spindle. Also, the disc manufacturing is A
A method of forming a magnetic film on a substrate made of l by a thin film forming means such as sparring is generally used, but in this case, the substrate temperature is several hundreds of degrees Celsius, so heat resistance is required. However, A
The l-made substrate has a problem of insufficient heat resistance, and as a result, the substrate is thermally deformed. Furthermore, it is known that the coercive force of the magnetic film increases when the substrate is heated after film formation, and from this viewpoint, heat treatment may be performed, and therefore heat resistance is further required. Also, there is a problem with the Al substrate.

By the way, glass such as crystallized glass and tempered glass is rich in rigidity and heat resistance. In addition, although glass is excellent in surface smoothness and hardness required for a substrate, it has a drawback that it is vulnerable to breakage (impact) and that water is likely to be adsorbed on the surface. In addition, in order to obtain a high-performance magnetic film at the time of sputtering for forming a magnetic film, it is necessary to increase the degree of vacuum. However, decompression (vacuum) causes water to seep out from the inside of the glass, making it difficult to increase the degree of vacuum. There is also. Furthermore, when heating the substrate, an infrared heater is often used, but infrared rays penetrate the substrate, the heating efficiency of the substrate is poor, and dust is likely to be attached due to static electricity due to the high specific resistance of the substrate, It also causes an increase in error rate.

[0006]

DISCLOSURE OF THE INVENTION Under such circumstances, carbon, particularly glassy carbon, has begun to attract attention as a material completely different from the above-mentioned aluminum alloy and glass. That is, glassy carbon generally has a three-dimensional network structure, and is obtained by firing and carbonizing a cured product of a thermosetting resin having an insoluble / infusible property in an inert atmosphere. And
This material has excellent gas impermeability, high hardness, and has an isotropic structure. Furthermore, in addition to characteristics such as light weight, heat resistance, high electrical conductivity, corrosion resistance, high thermal conductivity, and high lubricity,
Since it is homogeneous and does not generate carbon powder even when used for sliding parts, it is expected to be widely used in various fields including the electronics industry, nuclear power industry and space industry.

From this point of view, the applicant of the present invention has also proposed using glassy carbon as a substrate of a hard disk. That is, cracks and chips are unlikely to occur during inner / outer peripheral processing and chamfer processing during substrate processing, and high strength from the viewpoint of reliability during handling during texture formation and thin film formation, magnetic head It is necessary to reduce the waviness of the substrate from the followability of the substrate, the rigidity of the substrate material is high, the surface smoothness of the substrate is good for high recording density, non-magnetic, corrosion resistance, weather resistance Good hardness, high impact resistance, high reliability from the viewpoint of manufacturing reliability and CSS characteristics (durability), to improve CSS characteristics and reduce spindle load of hard disk drive In addition, we paid attention to the fact that the substrate is lightweight and the specific resistance of the substrate material is small in order to prevent the adhesion of dust etc. due to static electricity, and glassy carbon was used as the substrate of the hard disk It is the has been proposed to use.

By the way, it has been gradually understood that it is not simply that glassy carbon is used. That is, it has been found that it is important to have a predetermined surface roughness in order to improve the attraction to the magnetic head and enhance the durability. The present invention has been proposed in order to achieve such an object, and the present invention is characterized in that it is composed of a glassy carbon composite material and has minute selective irregularities formed on its surface. A disk substrate that can be used is proposed.

Further, the glassy carbon composite material in which at least one kind of particles selected from the group consisting of metal oxide particles, metal carbide particles, metal nitride particles and metal boride particles is dispersed is selectively etched. The present invention proposes a method of manufacturing a disk substrate, which is characterized by the above. In the present invention, the selective unevenness is formed by reactive sputter etching using an oxidizing gas such as O ₂ or CO ₂ ,
It is formed by etching the carbon portion by heat treatment in an oxidizing gas atmosphere. That is, the selective unevenness has a smooth surface formed by polishing the surface of the composite material, but only the carbon portion is selectively removed by, for example, oxidizing the surface of the composite material, and as a result, only a part of the fine particles remains as a protrusion. Means that a predetermined unevenness is formed by.

The roughness of such selective unevenness is about 1 or less.
It is preferably 0 to 100Å. Note that the selective unevenness having such characteristics is achieved by selecting the sputtering conditions and heat treatment conditions. For example, as the sputtering conditions, the time is about 1 to 20 minutes, the temperature is room temperature to about 300 ° C.,
The gas pressure is about 1 to 20 milliTorr, and the heat treatment conditions are a time of about 30 to 120 minutes and a temperature of about 300 to.
It is preferable to select 600 ° C.

The glassy carbon composite material contains glassy carbon as a main component, and metal oxide fine particles such as alumina fine particles, titanium oxide fine particles and silicon oxide fine particles,
Examples thereof include those in which at least one kind of fine particles selected from the group of metal carbide fine particles such as titanium carbide fine particles, metal nitride fine particles such as boron nitride, and metal boride fine particles are dispersed. The fine particles are not limited to one type,
Two or more kinds of particles may be used, and not only particles having a single dispersity but also a plurality of kinds having different particle diameters may be used.

The fine particles used in the glassy carbon composite material preferably have a particle size of about 10 μm or less, preferably about 2 μm or less, and more preferably about 1 μm or less, particularly preferably 0.1
You may make it use the thing below micrometer. As a method for producing such fine particles, there are a gas evaporation method, a plasma evaporation method, a gas phase chemical reaction method, etc. as a method utilizing a gas phase reaction, and a precipitation method, a melt spray heat method as a method utilizing a liquid phase reaction. It is possible to use a method of pulverization / classification from a method of producing ultrafine particles such as a decomposition method.

Specific examples of the fine particles include, for example, various polishing abrasive grains (SiC type, alumina type, silica type) manufactured by Fujimi Abrasives Co., Ltd., and aluminum oxide ultrafine particles (aluminum) manufactured by Nippon Aerosil Co., Ltd. Oxide C,
Fine particles (particle diameter of about 0.02 μm, δ-alumina) converted to α-alumina by flash firing method (particle diameter of about 0.09 μm), fine particles of titanium oxide of Sumitomo Cement Co., Ltd. (particle diameter of about 0.01-0. 03 μm, anatase) and the like.

It is preferable that the fine particles are dispersed and contained in a ratio of fine particles / glassy carbon (volume ratio) of 0.001 to 0.2, preferably about 0.05 to 0.1. . The glassy carbon used in the glassy carbon composite material is a glassy carbon obtained by carbonizing a thermosetting resin, or a glass obtained by carbonizing a resin modified so as to be thermoset by copolymerization or cocondensation. Shaped carbon can be used.

A preferable thermosetting resin in the present invention is one which can contain 20% by weight or more of water in the state of an initial condensate before curing. Here, the "initial condensate" means a resin before curing, which may contain a considerable amount of raw material monomers, but refers to a resin composition having a high viscosity due to addition and / or condensation reaction to some extent. . A characteristic of the thermosetting resin composition is that a low boiling point substance such as condensed water does not accumulate during curing, that is, the initial condensate having a high viscosity before the thermosetting resin is cured. By making the resin hydrophilic enough to contain 20% by weight or more of water in the above state, even if the low-boiling substance is trapped in the resin (or in the cured product), The accumulation of things will not occur.
In order to completely disperse and dissolve the low-boiling substance in the resin, a resin composition that can contain 30% by weight or more of water is desirable.

At what viscosity of the thermosetting resin composition, if the water-solubility of the resin composition exceeds 20% by weight, almost no pores will be formed after curing and carbonization. It depends on the type of raw material resin, the degree of polymerization, the blending ratio, etc., but according to the results of the research conducted by the present inventor,
20% by weight in a viscosity state of 8000 cps / 20 ° C
It is sufficient if it has a water-soluble capacity that exceeds.

The initial condensate of the thermosetting resin in the present invention can be appropriately designed depending on the type of raw material resin, blending ratio, control of polymerization degree, modification and the like. Examples of the thermosetting resin used in the present invention include phenol resin, epoxy resin, unsaturated polyester resin, ester resin,
Furan resin, urea resin, melamine resin, alkyd resin, xylene resin and the like can be mentioned, and these resins are used as they are, or by blending or modifying them. Resins based on modified phenol-furan resins are preferred, for example JP-A-60-17120.
No. 8, JP-A-60-171209, JP-A-6
The thermosetting resins disclosed in JP-A No. 0-171210 and JP-A No. 60-171121 are mentioned. As those that can be modified into a thermosetting resin, the above-mentioned phenolic resins, thermosetting resins such as furan resin, or asphalt, materials having a naturally high carbonization yield such as pitches, lignin, cellulose, Examples thereof include hydrophilic substances having a relatively high carbonization yield, such as tragacanth gum, gum arabic, humic acid, and various sugars.

Then, the thermosetting resin and the fine particles as described above are put into a mold having a desired predetermined shape before curing, and a resin material having a predetermined shape is obtained by a curing step such as heating. . In the carbonization and firing step of heating and carbonizing the resin material having a predetermined shape thus obtained,
It is preferable to perform heat treatment at about 1000 to 1400 ° C. in an inert atmosphere, and then perform heat treatment at about 1500 to 2000 ° C. under a pressure of about 1000 atmospheres or more in an inert atmosphere.

By such treatment, the glassy carbon becomes
It is substantially non-porous, more packing, and the micropores present inside the material are smaller in size and densified. Moreover, since the pressure heat treatment step was set to 2000 ° C. or less, graphitization of glassy carbon was suppressed, the density was high, and the mechanical strength (bending strength) was greatly improved to 24 kg / mm ² or more,
The cracks and chips during substrate processing are drastically reduced, and the reliability of handling when forming a thin film is improved.

The present invention will be described in more detail below with reference to examples.

[0021]

【Example】

Example 1 500 parts by weight of furfuryl alcohol and 92
% Paraformaldehyde (480 parts by weight) was stirred and dissolved at 80 ° C., and a mixed solution of 520 parts by weight of phenol, 8.8 parts by weight of sodium hydroxide and 45 parts by weight of water was added dropwise with stirring. After completion of the dropping, reaction was carried out at 80 ° C. for 3 hours.
After this, 80 parts by weight of phenol, sodium hydroxide 8.
A mixture of 8 parts by weight and 45 parts by weight of water was further added dropwise,
The reaction was carried out at 80 ° C for 4.53 hours. After cooling to 30 ° C., the mixture was neutralized with 70% aqueous paratoluenesulfonic acid solution. The neutralized product was dehydrated under reduced pressure to remove 150 parts by weight of water, and 500 parts by weight of furfuryl alcohol was added and mixed.

1% by weight of alumina fine particles having an average primary particle diameter of 2 μm and 1% by weight of alumina fine particles having an average primary particle diameter of 0.02 μm were added to this thermosetting resin initial condensate, and the mixture was thoroughly mixed with a sand mill. Dispersed and mixed. Then, this was molded, cured with acid, and then carbonized at 1300 ° C. to produce a glassy carbon / alumina composite material having a disk shape with a diameter of 2.5 inches.

After this, precision machining of the inner and outer circumferences and chamfering was performed, and a double-sided sanding machine (9
It was attached to a carrier of a B type double-sided polishing machine) and subjected to a lapping and polishing process. The center line average surface roughness Ra after the final polishing step was 50Å. Next, the substrate made of glassy carbon / alumina composite material with Ra of 50 Å was placed in an oven at 500 ° C.
It heat-processed over time and performed selective etching. The center line average surface roughness Ra by this selective etching is 82.
It was Å.

Then, the substrate thus obtained, which is made of a glassy carbon composite material having fine selective irregularities formed on the surface thereof, is washed and dried, and then a Cr film having a thickness of 100 nm is formed on the surface. A CoCrTa magnetic film having a thickness of 60 nm and a carbon protective film having a thickness of 25 Å were successively provided in order by a sputtering means. After this, a perfluoropolyether-based lubricant (Fomblin AM20 from Montedison Co.
01) was applied by a spin coating method to a thickness of 40Å.

Example 2 1% by weight of silicon carbide fine particles having an average primary particle diameter of 1 μm and 1% by weight of silicon carbide fine particles having an average primary particle diameter of 0.02 μm were added to the thermosetting resin initial condensate obtained in Example 1. A glassy carbon / silicon carbide composite material was obtained in the same manner as in Example 1 except that 1% by weight was added.

Thereafter, this glassy carbon / silicon carbide composite material is used in the same manner as in Example 1, and the center line average surface roughness Ra is 78Å by the same selective etching.
A magnetic disk was obtained in the same manner as above. Example 3 1% by weight of silicon nitride fine particles having an average primary particle diameter of 1 μm was added to the thermosetting resin initial condensate obtained in Example 1.
Silicon carbide fine particles having an average primary particle diameter of 0.02 μm were added in a proportion of 1% by weight, and a glassy carbon / silicon nitride / silicon carbide composite material was obtained in the same manner as in Example 1.

Thereafter, this glassy carbon / silicon nitride / silicon carbide composite material was used to carry out the same procedure as in Example 1,
The same selective etching was performed to obtain a center line average surface roughness Ra of 78 Å, and the same procedure was performed thereafter to obtain a magnetic disk. [Example 4] A 2.5 inch diameter disk substrate made of the glassy carbon / silicon carbide composite material obtained in Example 2 was used with a sputtering apparatus SPF430H manufactured by Anelva and Ar: O ₂ = 1. 1: 1 (molecular weight ratio) mixed gas was introduced as a reactive gas, and sputter etching (selective etching) was performed in an atmosphere of 10 milliTorr.
A magnetic disk having a center line average surface roughness Ra of 70Å was obtained, and thereafter the same procedure as in Example 2 was carried out to obtain a magnetic disk.

Example 5 1% by weight of silicon carbide fine particles having an average primary particle diameter of 1 μm and 1% by weight of silicon carbide fine particles having an average primary particle diameter of 0.02 μm were added to the thermosetting resin initial condensate obtained in Example 1. A glassy carbon / silicon carbide composite material was obtained in the same manner as in Example 1 except that 1% by weight was added.

Then, the glassy carbon / silicon carbide composite material was used to form a disk substrate having a diameter of 2.5 inches, and then a hot isostatic press (HIP) device was used to perform processing at 2000 ° C., 2000. It was kept at atmospheric pressure for 0.5 hour and subjected to HIP treatment. The thus obtained disk substrate was selectively etched in the same manner as in Example 1 to obtain a film having a centerline average surface roughness Ra of 69Å. Thereafter, the same procedure was performed to obtain a magnetic disk.

[Comparative Example 1] A 2.5 inch diameter disk substrate made of the glassy carbon / silicon carbide composite material obtained in Example 1 was replaced with an alumina-based polishing tape of No. 6000 instead of being selectively etched. A texture was applied to obtain a substrate having a center line average surface roughness Ra of 85Å.

The substrate thus obtained was washed and dried, and then a 100 nm thick Cr film, 60 n
An m-thick CoCrTa magnetic film and a 25Å-thick carbon protective film were successively provided in this order by sputtering means. Then, a perfluoropolyether lubricant (Fomblin AM2001 manufactured by Montedison Co., Ltd.) was applied to the surface by spin coating at a rate of 4Å.
A thick coating was applied to obtain a magnetic disk.

[Characteristics] The magnetic disks obtained in the above examples were heat-treated at 100 ° C. for 1 hour and then subjected to a glide high test and a CSS durability test. The results are shown in Table 1 below. Table-1 Glide high test CSS test Example 1 0.075 μm cleared 50000 times Example 2 0.075 μm cleared 60000 times Example 3 0.075 μm cleared 55000 times Example 4 0.075 μm Clear 65000 times Example 5 Clear 0.075 μm Clear 63000 times Comparative Example 1-1 Life at 12,000 times * Life is judged by whether the friction coefficient exceeds 0.6.

[0033]

[Effect] A recording medium with high durability can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuro Aoki 2606, Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Co., Ltd.Institute of Information Science (72) Inventor Kazuo Maki, 2606, Akabane, Kaiga-cho, Haga-gun, Tochigi Company Information Science Laboratory

Claims (6)

[Claims] 1. A disk substrate comprising a glassy carbon composite material and having minute selective irregularities formed on the surface thereof. 2. Roughness of the fine selective unevenness is about 10
The disk substrate according to claim 1, wherein the disk substrate has a thickness of about 100Å. 3. The glassy carbon composite material comprises glassy carbon in which at least one kind of particles selected from the group consisting of metal oxide particles, metal carbide particles, metal nitride particles and metal boride particles is dispersed. The disk substrate according to claim 1, which is a thing. 4. The disk substrate according to claim 3, wherein the fine particles have a particle size of about 10 μm or less. 5. The disk substrate according to claim 3, wherein the volume ratio of fine particles / glassy carbon is about 0.001 to 0.2. 6. Metal oxide fine particles, metal carbide fine particles,
A method for producing a disk substrate, which comprises selectively etching a glassy carbon composite material in which at least one kind of fine particles selected from the group of fine particles of metal nitride and fine particles of metal boride are dispersed.