JPH01122966A - Production of carbon material - Google Patents

Abstract

PURPOSE:To obtain a carbon material having excellent surface precision, heat resistance, etc., by mixing a carbonaceous material and a thermosetting resin giving the 2nd glassy carbonaceous material after carbonization at a specific ratio, dispersing the mixture in a solvent containing a surfactant, spray-drying the dispersion and compression molding in cold and hot state. CONSTITUTION:(A) The 1st carbonaceous material selected from powdery or granular graphite and carbon black and (B) a thermosetting resin (e.g., phenolic resin) forming a glassy 2nd carbonaceous material after carbonization are prepared beforehand. The component A and the component B are mixed with each other at a ratio to give a carbonized product containing 5-50vol.% of the component A and having a spherical region of the component B accounting for 3-10 times the area of the component A and the non-spherical region filling the circumference of the spherical region. The mixture is dispersed in a solvent containing a surfactant, granulated by spray-drying and pressed in cold and hot state to obtain a carbon material suitable as a base for magnetic disk for high-density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a carbon material suitable for a magnetic disk substrate used in a magnetic disk for high-density recording.

[Prior Art] In recent years, with the rapid progress of magnetic disk devices and the increase in the recording density of magnetic disks as magnetic recording media, the following
As shown in (2) to (3), there is a demand for improved characteristics of magnetic disk substrates.

■First of all, in order to increase the recording density of magnetic disks, the surface quality of the substrate must have excellent surface precision and few defects.■In order to improve the tracking ability of the magnetic head, the surface of the magnetic disk substrate must be smooth. (1) It has a surface shape with small pitch waviness that would deteriorate the surface flatness and no minute protrusions, and (2) has chemical properties that allow for good surface treatment as a substrate on which a magnetic medium is supported. With,
It is non-magnetic; ■ It has excellent corrosion resistance and weather resistance, as well as high strength and hardness; ■ It has good flying characteristics and improves C3s (contact, start, stop) resistance. It is required to be lightweight.

Under these circumstances, instead of conventional aluminum alloy magnetic disk substrates, ceramics coated with glass or glass plates have recently been developed as magnetic disk substrates for high-density recording. These substrates have excellent heat resistance and corrosion resistance, high rigidity, and excellent surface precision can be obtained by surface polishing, so that high-density recording is possible.

However, these materials have the disadvantage of being susceptible to brittle fracture. Therefore, reliability is low because it is easily damaged by rotation, impact, damage, heat shock, etc.

Although it is possible to form a stabilizing layer at grain boundaries to improve fracture toughness, this method cannot sufficiently prevent brittle fracture.

Furthermore, since ceramic materials have a high specific gravity, they place a greater load on the disk drive drive system than aluminum alloy substrates, making it difficult to downsize the drive device.

On the other hand, carbon materials have a small specific gravity of 1.5 to 2.0, a small coefficient of thermal expansion, and excellent thermal stability. Therefore, it is expected that carbon materials will be put into practical use as magnetic disk substrates for high-density recording instead of the aforementioned aluminum alloys or ceramic materials.

Furthermore, among these carbon materials, vitreous carbon has the characteristic of being dense and difficult for gas to pass through.

On the other hand, a vitreous carbon/carbon composite material in which graphite is dispersed in vitreous carbon is used as a separator material for fuel cells and the like. This composite material is made by adding graphite powder to a thermosetting resin, but it is easy to dissipate moisture and volatile components during drying, curing, and carbonization in the post-process. It can be fired at a high temperature increase rate of C/hour.Furthermore, the fracture toughness is improved by adding graphite powder.

Conventionally, such carbon materials are produced by extruding a flux made by kneading artificial graphite powder and thermosetting resin powder with a thermosetting resin liquid and a thickener, and then forming it into a plate shape in a rolling process.
It is manufactured by cutting out a disc shape, drying it, hardening it, and firing it.

[Problems to be solved by the invention] However, although conventional vitreous carbon can obtain excellent surface precision by surface polishing, it is a carbon material that is prone to brittle fracture and has poor resistance to crack propagation. Therefore, like ceramic materials, vitreous carbon is easily damaged by impact and has a problem of low reliability.

On the other hand, although the fracture toughness of vitreous carbon/carbon composites has been improved by adding graphite powder,
Even in carbon composite materials, in addition to the presence of closed pores of 1 μm or more inside, it also contains large graphite particles with a particle size of 30 μm or more, so surface polishing creates the excellent surface necessary for high-density recording. Therefore, in order to improve the surface precision, it is necessary to reduce the particle size of the carbon powder added, so artificial graphite powder or carbon black powder with a particle size of 1 μm or less is used. need to be used.

However, fine powder carbon materials such as carbon black cause secondary aggregation when mixed with thermosetting resins, making it difficult to uniformly disperse them. Such secondary aggregation causes uneven polishing when the surface is polished after carbonization firing.

In order to improve the dispersibility of the finely divided carbon material, a solvent and a surfactant are added to a low-viscosity thermosetting resin to form a slurry.
Next, a method may be considered in which this is poured into a mold and then dried, but this method has the disadvantage that the drying process after molding requires a long time.

Furthermore, in this method, the rate of occurrence of defects such as cracks and blisters increases due to the dissipation of a large amount of volatile matter, and the yield decreases, resulting in an increase in manufacturing costs.

Alternatively, carbon powder and thermosetting resin powder can be mixed in a ball mill or the like and molded by hot pressing, but carbon powder is flat and slippery, and is a fine powder that makes it difficult to handle. The sex is extremely bad.

The present invention has been made in view of such problems, and includes:
It is possible to manufacture a carbon material that has various properties (light weight, high strength, low coefficient of thermal expansion, etc.) required as a substrate for magnetic disks for high-density recording, and by uniformly dispersing graphite or carbon black, uneven polishing can be avoided. It is an object of the present invention to provide a method for manufacturing a carbon material that can prevent the occurrence of cracks and blisters, shorten the molding and drying steps, and further prevent the occurrence of cracks and blisters.

[Means for Solving the Problems] The carbon material produced by the method of the present invention contains at least one selected from powdery or lumpy graphite and carbon black.
a first carbonaceous material and a glassy second carbonaceous material formed by carbonizing and firing a thermosetting resin, and after carbonizing and firing, the first carbonaceous material has a volume ratio of 5 to 5. 50%, the second carbonaceous material has a spherical region and a non-spherical region filling the periphery of the spherical region, and the spherical region has an area ratio that is larger than that of the first carbonaceous material and the non-spherical region. It is 3 to 10 times that of

Such carbon material is manufactured as follows. First, at least one type of carbonaceous material selected from powdery or lumpy graphite and carbon black, and a thermosetting resin that becomes glassy carbon after carbonization firing are mixed in a solvent containing an anionic surfactant or the like. to form a low-viscosity slurry.

Next, dry granulation is performed using a spray dryer, and the obtained granulated particles are preformed by cold and hot pressing using a mold. Thereafter, for example, after pre-firing this pre-formed body at a temperature of 1000 to 1500°C, the pre-fired product is isotropically
This is fired by applying a pressure of 0.000 to 3000 atm.

[Function] In the present invention, the first carbonaceous material and the thermosetting resin are
It is dispersed in a solvent to form a low-viscosity slurry, dried and granulated using a spray dryer, and then cold and hot press-molded.

In this case, since an anionic surfactant is added to the solvent, the raw materials are very well dispersed in the solvent.

Further, since the particles granulated by spray drying are spherical and have a particle size of 50 to 100 μm, they can be easily filled into a mold and have good pressability.

Furthermore, since the steps of mixing, molding, drying and curing of the thermosetting resin, which conventionally required a long time, can be performed in a short time, manufacturing costs can be reduced.

The structure of the carbon material obtained in this way is such that powdery or lumpy graphite and/or carbon black (first carbon material) is surrounded by spherical vitreous carbon (second carbon material), and non-spherical The vitreous carbon (second carbonaceous material) is uniformly dispersed in the vitreous carbon (second carbonaceous material). The carbon material produced by the method of the present invention has a content of the first carbonaceous material in a volume ratio of 5 to 5.
0%, and since the area ratio of the spherical vitreous carbon region is 3 to 10 times that of the first carbonaceous and non-spherical region, the bulk specific gravity is 1.70 or more, which is high density, and the closed With a porosity of 2% or less, there are very few remaining pores, and the fine carbon filler is evenly distributed, so the bending strength is 1.
It is high at over 500 kgf/cot.

By carrying out the above-mentioned carbonization firing treatment at high temperature and high pressure, the existing closed pores are eliminated, and a high-density and high-strength carbon material is obtained. Therefore, a carbon material with excellent surface precision can be obtained by surface polishing, and in a magnetic disk using this carbon material, the magnetic head can fly stably and stable recording characteristics can be obtained. In addition, since there are no protrusions or depressions on the substrate surface that can cause defects in the magnetic thin film, the magnetic properties are stable, and although the substrate is lightweight, there is little load on the drive system.

Furthermore, this carbon material has sufficient mechanical strength during manufacturing processes such as machining and polishing, and during high speed rotation when used as a magnetic disk. Therefore, when this carbon material is applied to a magnetic disk substrate, this substrate has necessary and sufficient characteristics as a substrate used in a high-density recording magnetic disk.

[Example] Examples of the present invention will be specifically described below.

Thermosetting resins that become glassy carbon after carbonization and firing include granular phenol resins, furan resins, xylene resins, melamine resins, and aniline resins that have a particle size of 5 to 40 μm after carbonization and firing. There are powdered ones and aqueous or oily liquid ones such as resol and novolac type phenol formaldehyde resins, furan resins, xylene resins, melamine resins, and aniline resins.

Further, as the first carbon material, there are graphite such as artificial graphite, natural graphite, and quiche graphite, and carbon black, and one or more types selected from these graphite and carbon black are used. . This first carbonaceous material is in the form of powder, grains, or lumps (scale-like, etc.).

If the particle size of the powdery or lumpy first carbonaceous material is large, it will become a starting point for cracks in the molded product, so it is preferable to use particles with a maximum particle size of 1 μm or less.

After mixing each raw material, this powdery or lumpy first carbon material is dispersed around the thermosetting resin such as granular phenol formaldehyde resin, and after carbonization firing, the first carbonaceous material is dispersed at the interface with the spherical vitreous carbon. One carbonaceous region is present, forming a three-dimensional continuum structure.

The first carbonaceous material dispersed around the spherical vitreous carbon blocks the propagation of cracks generated from the vitreous carbon region,
Tissue-wise, it has the effect of increasing toughness. This licking improves the impact resistance of the molded product, and significantly reduces the frequency of cracks occurring during manufacturing processes such as polishing or during use of the magnetic disk.

Further, the first carbonaceous substance is added in a volume ratio of 5 to 50% after carbonization and firing. If the amount added is 5% by volume without grooves, the above-mentioned effect of improving toughness cannot be obtained, and impact resistance becomes extremely low. On the other hand, if the amount added exceeds 50% by volume, the continuity of the vitreous carbon structure is lost, and not only the mechanical strength decreases, but also the surface precision after surface polishing decreases.

Therefore, the amount of the first carbonaceous substance added is 5 to 50% by volume.

Furthermore, the proportion of the spherical vitreous carbon is such that the area ratio after firing is 3 to 10 times that of the granular or lump-like first carbon and non-spherical vitreous carbon.
Select and mix each raw material.

If the proportion of spherical vitreous carbon is larger than this, the molded body will have a high rigidity, but will be susceptible to brittle fracture, resulting in a material with low mechanical strength.

If the proportion of spherical vitreous carbon is smaller than this, there will be many fine pores that do not disappear even with HIP treatment, which will reduce the mechanical strength of the molded product and reduce the surface precision of the molded product. , a carbon material suitable for a magnetic disk substrate cannot be obtained.

In this way, the proportion of spherical vitreous carbon is also related to the volume ratio of powdery or lumpy carbon used as raw materials, so when blending the initial raw materials, the proportion of each raw material used and the particles It is necessary to select the diameter sufficiently.

Next, a method for manufacturing the carbon material configured as described above will be explained.

First, a predetermined amount of the first carbonaceous material and a granular or liquid thermosetting resin are blended, added to a solvent together with a surfactant and an organic binder, and mixed with a high-speed stirrer such as a homomixer to obtain a low viscosity. slurry.

As the surfactant, anionic surfactants such as alkylbenzene sulfonate, alkylnaphthalene sulfonate, alkyl sulfosuccinate, and naphthalene sulfonate formalin condensate are used. The organic binder is added to improve granulation properties, and starch, polyvinyl alcohol, etc., which are generally used for granulation of ceramic raw materials, are used. Water and hydroalcohol are used as solvents.

The slurry adjusted to an appropriate viscosity is dried and granulated using a spray dryer such as a rotating disk type or a pressure nozzle type.

The degree of dryness and particle system of the granulated particles can be adjusted by conditions such as the viscosity of the slurry, the temperature at the inlet and outlet of the slurry, the rotation speed of the disk, and the ejection pressure. By selecting appropriate conditions, it is possible to obtain granulated particles having a particle size of 50 to 100 μm, in which the surface of spherical thermosetting resin powder is coated with a uniform mixture of fine carbon powder and thermosetting resin.

After filling the granulated particles into a mold, in the case of cold processing,
00~1500 Kgf/co! In the case of hot working, press forming is performed at a temperature of 120 to 300° C. and a surface pressure of about 10 to 50 Kgf/cot. Since the granulated particles have good slipperiness and are dry, the amount of stirring components generated especially during hot pressing is extremely small, and the press workability is good, and the incidence of defects is also extremely low.

Next, this preformed body is heated to a temperature of 1,000 to 1,500°C for pre-baking, and then heated to a temperature of 2,050 to 2,600°C.
It is fired by applying an isotropic pressure of 1,000 to 3,000 atmospheres in a temperature range of . As a result, a dense structure in which closed pores inside the material have disappeared can be obtained.

By the hot isostatic pressing (1-I I P') treatment described above, the pores that existed before the HIP treatment completely disappear in the microstructure of the molded article. In addition, powdery or scale-like carbon such as graphite and/or carbon black is present in the periphery of the spherical vitreous carbon produced by carbonization firing of thermosetting spherical resin particles and between each spherical vitreous carbon. It is densely packed in a uniformly dispersed state in non-spherical vitreous carbon produced by carbonizing and firing a liquid thermosetting resin.

By surface polishing the high-density carbon material obtained in this way, it is possible to obtain a magnetic disk substrate for high-density recording with excellent surface precision, light weight, and a small coefficient of thermal expansion. Phenol-formaldehyde resin powder and carbon black powder having an average particle size of 0.01 μm or less are combined by carbonization firing to form vitreous carbon formed from a thermosetting resin and carbonaceous material consisting of carbon black. %.

This formulation was added to water along with 2 parts by weight of polyvinyl alcohol, 50 parts by weight of a water-soluble phenolic resin liquid, and 1 part by weight of a sodium sialsulfosuccinate surfactant, and the viscosity was adjusted to 100 cps. Then, these were stirred for about 1 hour using a homomixer to obtain a slurry. The obtained slurry was heated at a disc rotation speed of 5000 rpm and a slurry supply amount of 20 fl 1 hour.
It was dried using a rotating disk spray dryer set at an inlet temperature of 200° C. to obtain granulated particles with an average particle size of 100 μm. The obtained granulated particles were filled into a mold, heated to 180°C, and subjected to hot press molding by applying a surface pressure of 10 Kgf/era for 20 minutes. Preliminary firing was carried out by raising the temperature at a heating rate of /hour.

This pre-fired product was heated to 200% using a hot isostatic presser.
The carbonization process was carried out by raising the temperature to 2,600° C. at a rate of 650° C./hour under 0 atmospheric pressure to obtain a disc-shaped compact having a thickness of 2II11 and a diameter of 90 mm.

Round λL 1 part by weight of a sodium sialsulfosuccinate surfactant and a water-soluble phenol resin liquid with a viscosity of 200 cps were added to the above mixture to obtain a slurry with a viscosity of 500 cps. This slurry was poured into a frame mold, dried and hardened, and then pre-baked by heating in a temperature range of 150 to 1000°C at a heating rate of 2°C/hour.Next, Example 1
Same as , HIP treated, thickness is 2 rhymes, diameter is 90m +
A disc-shaped molded product of a was obtained.

L1 Mackerel The above-mentioned mixture was immediately hot press-molded using a mold in the same manner as in Example 1 without being made into a slurry, and after pre-baking, HI
P treated, thickness is 2 mm, diameter is 90111! A disk-shaped molded body with a rating of + was obtained.

For each method of Example 1 and Comparative Example 1.2, the number of days required for production, the yield due to cracks during firing, and the condition of the surface polished by a precision lap polishing machine were investigated. Table 1 below shows the results.

In Example 1 of Table 1, the process is simpler than Comparative Examples 1 and 2, so it can be manufactured in a short time, the yield is high, and the carbon filler is uniformly dispersed, so the surface After polishing, there was no waviness due to uneven polishing, and excellent surface precision was obtained.

[Effects of the Invention] According to the present invention, a high-strength carbon material with excellent surface precision, light weight, low coefficient of thermal expansion, and excellent heat resistance and corrosion resistance can be obtained, and is suitable as a substrate for high-density recording magnetic disks. Carbon material can be obtained. Further, according to the present invention, a carbon material having such excellent properties can be rapidly produced.

Claims (3)

[Claims] (1) At least one type of first carbonaceous material selected from powdery or lumpy graphite and carbon black, and a thermosetting resin that becomes a glassy second carbonaceous material after carbonization firing,
After carbonization firing, the first carbonaceous substance has a volume ratio of 5 to 50
%, and the second carbonaceous spherical region is blended so that the area ratio is 3 to 10 times that of the non-spherical region filling the periphery of this spherical region and the first carbonaceous material, These raw materials are dispersed in a solvent containing a surfactant to form a low-viscosity slurry, which is then dried and granulated using a spray dryer, followed by cold and hot press molding. Production method. (2) The method for producing a carbon material according to claim 1, wherein the surfactant is an anionic surfactant. (3) The method for producing a carbon material according to claim 1 or 2, wherein the viscosity of the slurry is 1000 cps or less.