JPH0647495B2 - Carbon material and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbon material suitable for a magnetic disk substrate used for a magnetic disk for high density recording and a method for producing the carbon material.

[Prior Art] In recent years, due to the breakthrough of a magnetic disk device and the increase in recording density of a magnetic disk as a magnetic recording medium, it is desired to improve the characteristics of a magnetic disk substrate as described below. .

First, in order to increase the recording density of a magnetic disk, the surface property of the substrate is excellent in surface accuracy, there are few defects, and the magnetic disk substrate has a surface smoothness and It has a surface with no minute protrusions that have minute pitch waviness that deteriorates the surface flatness, and has a chemical property with good surface treatability as a substrate on which a magnetic medium is carried. It is magnetic, has excellent corrosion resistance and weather resistance, has high strength and hardness, and has good levitation characteristics, and is lightweight to improve CSS (contact, start, stop) resistance. Is required.

By the way, conventionally, an aluminum alloy has been used for a magnetic disk substrate. However, due to the presence of an intermetallic compound, this aluminum alloy substrate has a center-portion average roughness R (a) even if its surface is sufficiently polished. However, the surface accuracy of 0.02 μm or less cannot be obtained, and the intermetallic compound of 10 to 20 μm becomes recesses and protrusions. For this reason, waviness at a fine pitch and head hit occur, and the above-mentioned requirements or requirements as a magnetic disk substrate for high-density magnetic recording cannot be satisfied.

Therefore, conventionally, the following measures (A) to (C) have been considered. In other words, (A) to make the aluminum alloy base material of the substrate highly purified, (B) to form an alumite coating on the surface of the aluminum alloy substrate to improve polishing workability and abrasion resistance, (C) aluminum alloy substrate For example, a plating film of Ni-P or the like may be formed on the surface to improve polishing workability.

However, each of the above methods has the following problems. First, it is extremely difficult in the manufacturing process to further refine the aluminum alloy base material as in (A). Further, a high-purity aluminum alloy is difficult to handle in terms of corrosion resistance and cleanliness.

Further, even if the aluminum alloy base material is highly purified, the hardness and rigidity of the metal material are limited, and the workability for improving shape accuracy such as flatness and smoothness is poor.

Further, in (B), the aluminum itself of the substrate serves as a material to form an alumite film, so that the intermetallic compound is likely to be incorporated into the alumite film and cause a defect.

Furthermore, a thin film magnetic medium (γ-Fe ₂ O
_In the heat treatment step for forming ( ₃ ), cracks and deformation of the substrate are likely to occur because the difference in the coefficient of thermal expansion between the substrate and the coating is large.

Furthermore, when a plating film is formed as in (C), there is a problem in that it is easily charged by heat treatment.

Therefore, recently, as a magnetic disk substrate for high density recording,
Glass-coated ceramics or glass plates have been developed. Since these substrates have excellent heat resistance and corrosion resistance, and have high rigidity and excellent surface roughness obtained by surface polishing, high density recording is possible.

However, these materials have the drawback of being prone to brittle fracture. For this reason, it is easily damaged by rotation, impact, damage, heat shock, etc., so that the reliability is low.

Although a means of increasing the fracture toughness by forming a stabilizing layer at the grain boundaries can be considered, brittle fracture cannot be sufficiently prevented.

Further, since the ceramics-based material has a high specific gravity, a larger load is applied to the disk drive system as compared with the aluminum alloy substrate, and it is difficult to downsize the drive device.

On the other hand, the carbon material has a small specific gravity of 1.5 to 2.0, a small thermal expansion coefficient, and excellent thermal stability. Therefore, it is expected that a carbon material will be put to practical use as a magnetic disk substrate for high density recording in place of the above-mentioned aluminum alloy or ceramic material.

[Problems to be Solved by the Invention] However, although conventional glassy carbon can locally obtain excellent surface accuracy by surface polishing, in reality, minute recesses are formed on the surface during the manufacturing process. Is difficult to prevent. In other words, it is impossible to avoid the generation of closed pores due to dissipated moisture and volatile components in the process of molding the thermosetting resin, then drying it, curing it, and carbonizing it at high temperature. Minute recesses are formed.

Moreover, in order to obtain a dense structure, for example, 1000 ° C.
It is necessary to perform heat treatment in the temperature range up to 1 ° C./hour at a heating rate of 1 ° C./hour or less. Therefore, since the yield is extremely low, the cost is high and it is difficult to industrialize and put into practical use.

Further, glassy carbon is a material that causes brittle fracture among carbon materials, has low resistance to crack propagation, and is susceptible to damage as with ceramic materials, and thus has a problem of low reliability. .

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 a thermosetting resin to which graphite powder is added. However, it is easy to dissipate water and volatile components at the time of drying, curing and carbonization in the subsequent steps. The firing can be performed at a high temperature rising rate of / hour. Further, the addition of graphite powder improves fracture toughness.

However, even in this glassy carbon / carbon composite material, in addition to the presence of closed pores of 1 μm or more inside,
Since large graphite particles having a particle size of 30 μm or more are contained, it is impossible to obtain the excellent surface accuracy required for high density recording by surface polishing.

The present invention has been made in view of such problems,
Equipped with various properties (light weight, high strength, low thermal expansion coefficient, etc.) necessary for a magnetic disk substrate for high density recording,
An object of the present invention is to provide a carbon material having excellent surface accuracy after surface polishing and a method for producing the carbon material.

[Means for Solving Problems] The carbon material according to the present invention is obtained by carbonizing and firing at least one first carbonaceous material selected from powdery or lumpy graphite and carbon black, and a thermosetting resin. Formed glassy second carbonaceous material, the first carbonaceous material is contained in an amount of 5 to 50% by volume, the second carbonaceous material has a spherical region, and the spherical region And a non-spherical region filling the periphery of the non-spherical region, wherein the spherical region has an area ratio of 3 to 10 times that of the first carbonaceous material and the non-spherical region.

The method for producing a carbon material according to the present invention is a method in which at least one carbonaceous material selected from powdery or lumpy graphite and carbon black is mixed with a thermosetting resin that becomes vitreous carbon after carbonization, and a preliminary 2050 to 260 after molding
It is characterized by isotropically applying a pressure of 1000 to 3000 atm at a temperature of 0 ° C.

[Operation] According to the present invention, graphite or carbon black is mixed with a thermosetting resin that becomes vitreous carbon after carbonization and firing.
Pre-baking is performed at 00 to 1500 ° C. Then, the pre-fired product isotropically at a temperature of 2050 to 2600 ° C.
This is baked by applying a pressure of 00 to 3000 atm.

The structure of the obtained carbon material is composed of spherical vitreous carbon (second carbonaceous material) around which powdery or massive graphite and / or carbon black (first carbonaceous material) and non-spherical vitreous carbon material. (Second carbonaceous material). In the carbon material according to the present invention, the content of the first monolith is 5 by volume ratio.
To 50%, and the spherical vitreous carbon region has an area ratio of 3 to 10 times that of the first carbonaceous and non-spherical regions, so that the bulk specific gravity is 1.70 or more and the density is high.
The closed porosity is 6% or less, the number of residual pores is extremely small, and the bending strength is 1000 kgf / cm ² or more.

By carrying out the carbonization and calcination treatment at a high temperature and a high pressure as described above, the closed pores existing therein disappear, and a high-density and high-strength carbon material can be obtained. Therefore, a carbon material having an excellent surface accuracy can be obtained by surface polishing, and in a magnetic disk using this carbon material, the magnetic head can be stably floated and stable recording characteristics can be obtained. In addition, since there are no protrusions or recesses that cause defects in the magnetic thin film on the surface of the substrate, the magnetic characteristics are stable, and since it is lightweight, the load on the drive system is small.

Further, the carbon material according to the present invention has sufficient mechanical strength in manufacturing processes such as machining and polishing, and during high speed rotation used as a magnetic disk. As described above, when the carbon material according to the present invention is applied to a magnetic disk substrate, this substrate has necessary and sufficient characteristics as a substrate used for a high density recording magnetic disk.

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

Examples of the thermosetting resin that turns into vitreous carbon after carbonization and firing include granular phenolic resins, furan-based resins, xylene-based resins, melamine-based resins, and aniline-based resins having a particle size of 5 to 40 μm after carbonization and firing. Powdered one,
There are water-based or oil-based liquids such as resole and novolac type phenol formaldehyde type resins, furan type resins, xylene type resins, melamine type resins, and aniline type resins.

Further, as the first carbonaceous material, there are graphite such as artificial graphite, natural graphite, and quiche graphite, and carbon black, and one or more kinds selected from this graphite and carbon black are used. . The first carbonaceous material is in the form of powder, particles, or lumps (flakes, etc.).

When the particle size of the powdery or lumpy first carbonaceous material is large, it becomes a starting point of crack generation in the molded product. Therefore, it is preferable to use a particle size of 1 μm or less at the maximum.

After mixing the raw materials, the powdery or lumpy first carbonaceous material is dispersed around a thermosetting resin such as granular phenolformaldehyde resin, and after carbonization and firing, the first carbonaceous material is formed at the interface with the spherical glassy carbon. The presence of one carbonaceous region forms a three-dimensional continuum structure.

The first carbonaceous material dispersed around the spherical vitreous carbon prevents the propagation of cracks generated from the vitreous carbon region,
It has the effect of increasing toughness in terms of tissue. Therefore, the impact resistance of the molded product is improved, and the frequency of occurrence of cracks is significantly reduced during the manufacturing process such as polishing or during the use of the magnetic disk.

Further, the first carbonaceous material is added so that the volume ratio after carbonization and calcination becomes 5 to 50%. If the added amount is less than 5% by volume, the above-mentioned toughness improving effect cannot be obtained and the impact resistance becomes extremely low. On the contrary, if the addition amount exceeds 50%, the continuity of the vitreous carbon structure is lost, the mechanical strength is lowered, and the surface accuracy after surface polishing is lowered. Therefore, the addition amount of the first carbonaceous material is set to 5 to 50% by volume.

Furthermore, the proportion of the spherical glassy carbon is such that the spherical glassy carbon is 3 to 5 times the powdery or lumpy first carbonaceous and non-spherical glassy carbon in terms of area ratio after firing. Select and mix each raw material. The area ratio indicates the area ratio of the spherical vitreous carbon to the first carbonaceous material and the non-spherical carbonaceous material per unit area.

If the proportion of the spherical glassy carbon is larger than this, the rigidity of the molded body increases, but brittle fracture is likely to occur, resulting in a material having low mechanical strength.

If the proportion of the spherical glassy carbon is smaller than this, the number of fine pores that do not disappear even by the HIP treatment increases, the mechanical strength of the molded body decreases, and the surface accuracy of the molded body decreases. Therefore, a carbon material suitable for a magnetic disk substrate cannot be obtained.

Thus, the proportion of spherical vitreous carbon is also related to the volume ratio of the powdery or lumpy carbonaceous material used in the raw material, therefore, in the initial raw material blending, the blending ratio and particles of each raw material to be used It is necessary to select the diameter sufficiently.

Next, a method of manufacturing the carbon material having such a structure will be described. First, the first carbonaceous material and a granular or liquid thermosetting resin are mixed in a predetermined amount, an organic thickener and an antifoaming agent are added, and then a high shearing force kneader such as a pressure kneader equipped with a vacuum exhaust device is kneaded. It is kneaded by a machine and preformed into a predetermined shape.

In addition, in the spherical and liquid thermosetting resin (second carbonaceous material) and the powdery or granular first carbonaceous material described above, an organic binder and a solvent, and if necessary, an organic dispersant and It is also possible to add a foaming agent or a wetting agent, mix with a hot mill or the like to obtain a high-viscosity slurry, form a green sheet (baking precursor) having a desired thickness by a doctor blade method, and then perform preforming. .

Further, to the spherical thermosetting resin, liquid thermosetting resin and powdery or lumpy carbon, an organic binder, a solvent and an organic dispersant are added, and a slurry mixed with a pot mill or the like is sprayed with a spray dryer or the like. Dry granulation may be performed, and the resulting mixed granulated particles may be preformed into a desired shape.

Then, after heating the preformed body to a temperature of 700 to 1500 ° C. to pre-fire it ,. 2050 to 2600 ° C
An isotropic pressure of 1000 to 3000 atm is applied in the temperature range. As a result, a dense structure in which closed pores inside the material disappear is obtained.

If the temperature range to which isotropic pressure is applied is lower than this, even if the number of closed pores decreases, the effect is essentially weak to temperature.Therefore, there is a difference between when pressure is applied and when pressure is not applied. There is almost no difference in the effect of reducing pores. On the contrary, when pressure is applied, dehydrogenation reaction in the material is suppressed, and the tissue tends not to shrink into trees. Further, when the pressure treatment is performed in this relatively low temperature range, the closed pores are not completely eliminated, and the closed pores between the air entrapped in the molded product and the matrix and the filler are hardly reduced.

Therefore, in order to substantially completely eliminate the closed pores in the molded body, it is necessary to apply an isotropic pressure of 1,000 to 30,000 atm at a high temperature of 2050 to 2,600 ° C. This can be done with a hot isostatic press (HIP).

In this way, when a high pressure isotropically applied to the preform at a high temperature, the temperature range in which the interplanar spacing d in the C-axis direction sharply decreases in the process of graphitizing the carbon structure, in other words, the crystal lattice Isotropic pressure is applied in the temperature range where the hexagonal steel planes in the inside are rearranged and exhibit pseudofluidity, whereby the closed pores disappear.

By the above HIP treatment, in the fine structure of the molded body,
The pores that existed before the HIP treatment disappeared completely. Further, between the peripheral portion of the spherical glassy carbon produced by carbonization and firing of the thermosetting spherical resin particles and each spherical glassy carbon, powdery or scaly carbon such as graphite and / or carbon black and liquid carbon are formed. It is densely filled with non-spherical glassy carbon produced by carbonization and firing of a thermosetting resin.

By surface-polishing the thus obtained high-density carbon material, it is possible to obtain a high-density recording magnetic disk substrate having excellent surface accuracy, light weight, and small thermal expansion coefficient.

Generally, a carbon material is easily oxidized and depleted in an oxidizing atmosphere at a high temperature. Therefore, when this is used as a magnetic disk substrate, when the medium film is formed by reactive sputtering or the like, and during the oxidation treatment, the substrate is oxidatively depleted, and the surface accuracy of the substrate decreases, It may be deformed. However, it has been found that the onset temperature for oxidative wear of the molded body produced by the method of the present invention is extremely high, and therefore there is no need for the above-mentioned oxidative wear in the temperature range during the formation of the medium layer.

Further, the carbon material has extremely high resistance to alkali and corrosion resistance. Further, the carbon molding produced according to the present invention exhibits excellent acid resistance even in acid treatment at a pH of about 2, and thus has sufficient stability against most chemical treatments.

If it is necessary to further improve the mechanical strength of the high-density carbon material for magnetic disk substrates, a carbon fiber reinforced molded product is sandwiched between the carbon materials during molding to form a laminated molded product. Obtained, subsequently cured and pre-baked, then at a temperature of 2050 ° C to 2600 ° C for 10
By performing an HIP process by applying an isotropic pressure of 00 to 2000 atm, it is possible to obtain a high-strength magnetic disk substrate reinforced with carbon fibers.

Next, the results of manufacturing the carbon materials according to the examples of the present invention and measuring various characteristics thereof will be described. Average particle size is 20μ
Phenol formaldehyde resin with an average particle size of 0.
A graphite powder having a particle size of 1 μm or less is contained in a ratio shown in the “graphite blending amount” column in Table 1 below in the glassy carbon formed of a thermosetting resin by carbonization and the carbonaceous material of graphite. It was blended as described below. In addition, Example 1,
In Nos. 2 and 3, the amount of graphite blended is within the range specified in the present invention, and in Comparative Examples 1 and 2, the amount is out of the range. Further, in the table, the ratio of the spherical region is obtained for a unit area of 100 mm square from a 400-times micrograph.

Next, this raw material was kneaded with a phenol resin solution and molded into a disk shape. After this was dried at 100 ° C. for 12 hours, the temperature range from 150 ° C. to 800 ° C. was raised at a heating rate of 15 ° C./hour and pre-baked. Using a hot isostatic press (HIP), the molded body after pre-baking was subjected to 2000
Under atmospheric pressure, the temperature was raised to 2600 ° C. at a temperature rising rate of 650 ° C./hour, and carbonization treatment was performed. The physical properties of the obtained molded product before and after HIP treatment are also shown in Table 1 above.

Next, the surface of the molded body of Example 2 was polished by a precision lap polishing machine to obtain a disk substrate having a thickness of 1.3 mm and a diameter of 145 mm. Table 2 below shows measured values of various characteristics of the magnetic disk substrate, together with the characteristics of the conventional example (commercially available aluminum substrate).

As is clear from Table 1, in consideration of the strength of the molded body after firing (after HIP treatment), it is necessary to set the blending amount of the graphite powder in the carbonaceous material to 5 to 50%. If the amount of graphite powder is less than 5%, the effect of preventing the propagation of cracks by the graphite powder cannot be obtained, and if it is more than 50%, cracks easily occur between the graphite matrix and the vitreous carbon. , The mechanical strength is reduced.

By the HIP treatment at 2600 ° C. and 2000 atm, the bulk specific gravity of each of the molded articles of Examples 1 to 3 increased to 1.8 to 1.9, and the pores significantly decreased. When the surface characteristics after polishing are compared with those of a commercially available aluminum substrate, Examples 1 to 3 are more accurate by one digit or more in surface roughness and strain characteristics.

Next, the influence of the firing treatment conditions will be described. The raw materials were mixed in the mixing ratio of Example 2 described above, molded in the same manner as described above, and then heated to a temperature of 1100 ° C. and pre-baked. Then, firing treatment was performed under each treatment condition shown in Table 3 below.

The physical properties of the sample before and after the treatment and the measured values of various properties as a magnetic disk substrate after polishing the surface of the sample with a precision lapping polishing machine are shown in Tables 4 and 5 below.

However, in Table 5, the parallelism indicates the flatness in the diametrical direction of the substrate, the concentricity indicates either the center point of the outer circumference circle or the center point of the inner circumference circle of the substrate, TIR indicates the whole waviness of the substrate, and ACC indicates The state of micro defects on the substrate surface is shown. The surface roughness (average roughness Ra) indicates the smoothness of the substrate surface.

In Table 4, comparing the results of the HIP treatments under the treatment conditions a to d, the density could not be increased even when pressure was applied at the temperature of 2000 ° C. (treatment condition a). The variety is low.

On the other hand, at a temperature of 2300 to 2600 ° C. (treatment conditions b, c, d), the pores are reduced by applying pressure, and the density is remarkably increased, so that the characteristics after surface polishing are excellent.

In the case of the processing condition e, the heat treatment was performed at 2600 ° C. under atmospheric pressure, and the surface roughness was extremely poor. In the case of the processing condition f, the material was heated to 2300 ° C. under uniaxial pressure, but in the case of this processing, the anisotropy increases with crystallization and the material shrinks greatly in one direction, so that cracks occur inside. Porosity increases significantly.

Therefore, even if the surface is polished, it is not possible to obtain a surface accuracy that can be practically used as a magnetic disk substrate.

As described above, it was confirmed that pressurization under the isotropic pressure at a temperature of 2300 to 2600 ° C. is effective for increasing the density of the vitreous carbon structure.

Next, the magnetic disk substrate of Example 1 and Example 2 described above.
The results of investigating the recording characteristics of a magnetic disk manufactured by using the magnetic disk substrate manufactured under the processing conditions c and d with the compounding amount of 5 will be described. First, α-Fe ₂ O ₃ (thickness: 0.20 μm) was deposited on each substrate by a reactive sputtering method using Fe containing Co as a target. Next, this α-Fe ₂ O ₃ is heated to 330 ° C. in a hydrogen atmosphere to reduce it to Fe ₂ O ₃ , and is further oxidized in air at 330 ° C. to be converted into a γ-Fe ₂ O ₃ magnetic film. Then, a high density magnetic disk was created.

When the head of the obtained magnetic disk was floated with a flying height of 0.2 μm, the head and the magnetic disk did not collide with each other, and stable driving was possible.
Further, when the signal error was confirmed for each magnetic head, it was confirmed that the signal error was remarkably reduced as compared with the above-mentioned comparative example.

EFFECTS OF THE INVENTION According to the present invention, a high-strength carbon material having excellent surface accuracy, light weight, small thermal expansion coefficient, and excellent heat resistance and corrosion resistance can be obtained. It is suitable as a substrate. Further, according to the present invention, a carbon material having such excellent properties can be rapidly manufactured.

Claims (2)

[Claims] 1. At least one first carbonaceous material selected from powdery or lumpy graphite and carbon black, and a glassy second material formed by carbonizing and firing a thermosetting resin.
And the first carbonaceous material is contained in an amount of 5 to 50% by volume, and the second carbonaceous material has a spherical region,
With a non-spherical region filling the periphery of this spherical region,
The spherical region has an area ratio of the first carbonaceous material and the non-spherical region 3
To 10 times the carbon material. 2. At least one carbonaceous material selected from powdery or lumpy graphite and carbon black and a thermosetting resin which becomes vitreous carbon after carbonization and firing are mixed and preformed, and then 2050 to 2050. 1000 at a temperature of 2600 ° C
A method for producing a carbon material, which comprises isotropically applying a pressure of ˜3000 atm.