JPH06349049A - Carbon substrate and recording medium - Google Patents

Abstract

PURPOSE:To provide the recording medium having the low flying height of a head and excellent CSS durability by providing the surface of a carbon substrate having surface roughness of a prescribed value with a recording film. CONSTITUTION:Glassy carbon is produced by executing a first treatment at about 1000 to 1400 deg.C in an inert atmosphere, then executing a second treatment to make heat treatment at about 1500 to 2000 deg.C under about >=1000atm. The magnetic recording medium is produced by using such carbon. The magnetic recording medium which has high bending strength, is substantially free from cracking and chipping in the production stage for magnetic disks, is as light as 1.6 to 1.8 density, has small intrinsic resistivity, high corrosion resistance and weatherability and high hardness and is nonmagnetic is thereby obtd. The carbon substrate having a trough-shaped surface is formed and the surface roughness of about 40 to 100Angstrom center line average height and about 1 to 6 Rp/Ra with the center line height as Rp is obtd. by a texturing technique using a polishing tape and free abrasive grains. The recording medium having the low flying height of the head and the excellent CSS durability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium using carbon such as glassy carbon as a substrate.

[0002]

BACKGROUND OF THE INVENTION Currently, aluminum alloys are mainly used as a material for hard disk substrates, and Ni-P of about 10 μm is formed on the surface of the aluminum alloy.
Plated ones are used. However,
The aluminum alloy substrate has a problem that its rigidity becomes insufficient when the thickness becomes thin. In other words, if the rigidity is insufficient, the substrate will be wavy during mirror surface processing and cannot be flattened. Therefore, when a wavy substrate is used as a disk, uneven rotation will occur and the flying height of the magnetic head will be small. There is an inconvenience that it cannot be done, and further, there is an inconvenience that the disk is deformed when chucking the spindle.

Further, a disk is generally manufactured by forming a magnetic film on a substrate by a thin film forming means such as sparring. At this time, since the substrate temperature is several hundreds of degrees, heat resistance is required. To be done. However, the substrate made mainly of an aluminum alloy 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. From this viewpoint, heat treatment may be carried out, and therefore heat resistance is further required. For this reason, carbon, particularly glassy carbon, has begun to attract attention as a material completely different from aluminum alloys. The applicant of the present application has also proposed to utilize glassy carbon as a substrate for a hard disk (Japanese Patent Laid-Open No. 60-33333).

[0005]

DISCLOSURE OF THE INVENTION The present inventor pays attention to the items required for a hard disk substrate, that is, cracks and chips are less likely to occur during inner / outer peripheral processing and chamfer processing during substrate processing, and texture formation and thin film formation. In order to achieve high recording density, it is necessary to reduce the waviness of the substrate due to the followability of the magnetic head because of the high strength in terms of reliability during handling during formation, and the high rigidity of the substrate material. The surface smoothness of the substrate is good,
There are no microscopic defects, the substrate is non-magnetic in order to improve the characteristics of the magnetic film, it has good corrosion resistance and weather resistance, it has excellent impact resistance, reliability during manufacturing, and CSS characteristics. From the standpoint of (durability), it has a high hardness, the CSS characteristics are improved, and the spindle load of the hard disk drive is reduced. The board is lightweight. Focusing on the fact that the specific resistance is small, a magnetic recording medium using glassy carbon as a hard disk substrate has been proposed, and this magnetic recording medium has been praised by various parties.

That is, for example, a curing step of curing a thermosetting resin and a carbonizing and firing step of heating and carbonizing the resin material obtained by this curing step are provided, and the carbonizing and firing step is performed under an inert atmosphere. At about 1000-14
A first treatment step of heat treatment at 00 ° C., an inert atmosphere,
And about 1500 at a pressure of about 1000 atm or more.
A method for producing glassy carbon, which comprises a second treatment step of heat treatment at ˜2000 ° C., or a thermosetting resin capable of containing about 20% by weight or more of water in the state of an initial condensate before curing. And a carbonization and firing step of heating and carbonizing the resin material obtained by this curing step, wherein the carbonization and firing step is a heat treatment at about 1000 to 1400 ° C. in an inert atmosphere. According to the method for producing glassy carbon, which has a treatment step of 1 and a second treatment step of performing heat treatment at about 1500 to 2000 ° C. under an inert atmosphere and a pressure of about 1000 atm or more, for example, bending strength is 24kgf / mm ² have the above properties, in particular flexural strength has a 24kgf / mm ² or more characteristics, and characteristics of glass such pore size of pores is 0.1μm or less Carbon is obtained, the magnetic recording medium produced using such a glassy carbon was excellent as compared with those of the past.

That is, the glassy carbon obtained as described above has improved mechanical strength such as a bending strength of 24 kgf / mm ² or more, and there is almost no cracking or chipping which is a concern in the magnetic disk manufacturing process. Also, the elastic modulus is about 250
The surface roughness is 0 Kgf / mm ² or more, there is no problem of waviness, and the surface smoothness (center line average roughness Ra) after mirror polishing can be up to about 1.0 nm. Almost no defects (open holes, crystal grain boundaries, etc.) are recognized, the density is 1.6 to 1.8, which is lightweight, the specific resistance is small, and the corrosion resistance and weather resistance are good. High hardness and non-magnetic. From the above, this glassy carbon had extremely preferable characteristics as a substrate of a recording medium.

By the way, when a recording medium is formed by using glassy carbon having such excellent characteristics, recording / recording is performed by the surface profile of a substrate made of glassy carbon.
It has been found that there is a large difference in reproduction characteristics. Therefore, research and development for forming a desired surface profile have been earnestly pursued, and, for example, treatment by high temperature heat treatment in an oxidizing atmosphere or chemical etching has been attempted.
However, these methods have poor reproducibility, and development of new technology is required.

[0009] From the above, attention has been paid to the texture technique used in the case of the aluminum substrate. However, even if the texture technique in the case of an aluminum substrate using a polishing tape or loose abrasive grains is applied to a carbon substrate, a preferable one was not obtained. That is, it was not possible to obtain a head having a low flying height and excellent CSS durability.

As a result of earnestly researching such problems, the surface of an aluminum substrate by a texture technique using a polishing tape or loose abrasive grains and a carbon substrate by a texture technique using a polishing tape or loose abrasive grains. The surface of the carbon substrate, which is completely different from the surface of the carbon substrate obtained by the texturing technique using the polishing tape or the loose abrasive grains, has a valley-shaped one as shown in FIG. As shown in FIG. 2, the surface of the aluminum substrate formed by the texture technique using particles has a mountain-like shape, and such a difference in surface profile cannot be handled by the technical idea of the aluminum substrate. Was understood.

As a result of earnestly promoting further research based on such knowledge, Ra and Rp / R
a (however, Ra is center line average roughness, Rp is center line height)
It has been found that when the values of and are within a predetermined range, the head flying height is low and the CSS durability is excellent. The present invention has been achieved in this way, Ra is about 40 ~ 100 Å, Rp / Ra (however,
Ra is the center line average roughness, Rp is the center line height) and is about 1 to 6
The present invention provides a carbon substrate characterized by

Ra is about 40 to 100Å, Rp / Ra
Is more preferably about 2.5-5. Further, the present invention provides a carbon substrate characterized in that Ra is about 10 to 40Å and Rp / Ra (where Ra is the centerline average roughness and Rp is the centerline height) is about 4 to 15. .

It is more preferable that Ra is about 25 to 40Å and Rp / Ra is about 5 to 10. Also, Ra is about 4
Recording comprising a carbon film having a recording film thickness of 0 to 100Å, Rp / Ra (where Ra is the center line average roughness, and Rp is the center line height) of about 1 to 6 and a recording film is provided on the carbon substrate. It provides a medium.

Ra is about 40 to 100Å, Rp / Ra
Is more preferably about 2.5-5. Further, a recording film is provided on a carbon substrate having Ra of about 10 to 40Å and Rp / Ra (where Ra is the center line average roughness and Rp is the center line height) of about 4 to 15. The present invention provides a recording medium characterized by:

It is more preferable that Ra is about 25 to 40Å and Rp / Ra is about 5 to 10. And, the carbon substrate of the surface profile as described above is obtained by a texture technique using a polishing tape or free abrasive grains. This is the type of polishing tape, the type of free abrasive grains, the polishing time, and the time of polishing. This is achieved by adjusting various factors such as pressure.

Incidentally, Ra is about 40 to 100Å, Rp /
In order to obtain a carbon substrate having Ra of about 1 to 6, tape type # 4000 flat type manufactured by Nippon Micro Coating Co., tape feeding speed 400 mm / min, processing pressure 0.8 k
g / cm ² , tape oscillating 460 reciprocations / minute, roller rubber hardness 60 degrees, work rotation speed 50 rpm, processing time 40 seconds,
It may be carried out under the conditions such as a JS602 3 wt% polishing liquid manufactured by Johnson.

Further, in order to obtain a carbon substrate having Ra of about 10 to 40Å and Rp / Ra of about 4 to 15, tape type # 4000 flat type manufactured by Nippon Micro Coating Co., tape feeding speed 400 mm / min, Processing pressure 0.8k
g / cm ² , tape oscillating 460 reciprocations / minute, roller rubber hardness 60 degrees, workpiece rotation speed 50 rpm, processing time 10 seconds,
It may be carried out under the conditions such as a JS602 3 wt% polishing liquid manufactured by Johnson.

Needless to say, if the other factors are changed, the above conditions will be changed accordingly. Hereinafter, the present invention will be described in detail. The carbon substrate used in the present invention, particularly a substrate made of glassy carbon, includes a curing step of curing a thermosetting resin and a carbonizing and firing step of heating and carbonizing the resin material obtained by this curing step. In the method for producing glassy carbon, the carbonizing and firing step is performed under an inert atmosphere at about 1000-1.
A first treatment step of heat treatment at 400 ° C., an inert atmosphere, and a pressure of about 1000 atm or more for about 15
It is obtained by a method for producing glassy carbon, which comprises a second treatment step of heat treatment at 00 to 2000 ° C.

A preferable thermosetting resin 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. Resin is 2
When the low boiling point substance is trapped in the resin (or in the cured product), the low boiling point substance is accumulated even if the low boiling point substance is confined in the resin (or the cured product) by making it hydrophilic enough to contain 0% by weight or more of water. It will never happen. In order to completely disperse and dissolve the low boiling point substance in the resin,
A resin composition that can contain water by weight or more 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 (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 has been found that a water-soluble capacity exceeding 10 is sufficient.

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.

Further, a filler can be added in carrying out the present invention. As the filler, various carbon materials including the above-mentioned thermosetting resin, for example, polyacrylonitrile-based carbon material, cellulose-based carbon material, rayon-based carbon material, pitch-based carbon material, lignin-based carbon material, phenol resin-based carbon material, furan In addition to resin-based carbon materials, epoxy resin-based carbon materials, alkyd resin-based carbon materials, unsaturated polyester-based carbon materials, and xylene resin-based carbon materials, there are various types of graphite, carbon black, and the like.

Then, the thermosetting resin, the filler and the like as described above are put into a mold having a predetermined shape according to the intended use before curing, and a curing step such as heating is performed to obtain a predetermined shape. A resin material is obtained. In the carbonization and firing step of heating and carbonizing the resin material having a predetermined shape obtained in this manner, about 1000 in an inert atmosphere.
˜1400 ° C., then about 1500-2 at a pressure of about 1000 atm or more in an inert atmosphere.
Heat treatment at 000 ° C.

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.

Here, the inert atmosphere in the pretreatment step (first treatment step) is an atmosphere which does not contain oxygen and which is usually composed of at least one gas selected from the group consisting of helium, argon, nitrogen and the like. Or, it means a reduced pressure or vacuum state. Further, the temperature in the pretreatment step is required to be about 1000 to 1400 ° C, more preferably about 1100 to 1300 ° C. In this case, the carbonization firing time may be appropriately selected depending on the type and shape of the resin material and the firing temperature.

If the pretreatment firing temperature is too low, that is, lower than 1000 ° C., sufficient carbonization has not yet been reached in the pretreatment process stage, and the pores have not become sufficiently small. or,
Hydrogen and oxygen remaining in the material are not sufficiently removed in the pretreatment process, and if pressure heat treatment is performed with residual hydrogen and oxygen present, the release of hydrogen and oxygen is suppressed, and The above reaction may be caused, the carbon-carbon bond may be broken, and the strength may be reduced. Therefore, the target characteristics are not reached even after the subsequent pressure heat treatment step.

On the contrary, when the pretreatment firing temperature exceeds 1400 ° C. and is too high, pores are scarcely found and the structure is very dense, but graphitization is progressing, and after-treatment is performed. Even if the pressure heat treatment is performed, the strength becomes insufficient. For this reason, chipping or the like is likely to occur even with a slight impact during the manufacturing process of the recording medium. The inert atmosphere in the pressure heat treatment step which is the post-treatment step (second treatment step) is usually at least one gas atmosphere selected from the group consisting of argon, nitrogen and the like. The temperature in the pressure heat treatment step needs to be about 1500 to 2000 ° C. 1
If the temperature is too low below 500 ° C, the expected effect cannot be obtained. On the other hand, at a temperature higher than 2000 ° C. and too high, graphitization proceeds and the density becomes high, but the mechanical strength decreases. For this reason, chipping or the like is likely to occur even with a slight impact during the manufacturing process of the recording medium.

As a method of applying pressure, a method of applying hydraulic pressure or other mechanical force from the outside into a closed container to directly or indirectly apply pressure to the material being processed can be used. By this method, the atmospheric pressure in the closed container can be increased to 1000 atmospheric pressure or higher, and this pressure can be used to apply an isotropic pressure to the internal sample. Such treatment can be carried out by a hot isostatic press.

Good results can be obtained when the pressure in the pressure heat treatment step is 1000 atm or higher, particularly about 1500 atm or higher, regardless of the type of the thermosetting resin composition. The glassy carbon thus obtained has a large mechanical strength and has a surface smoothness of R after mirror polishing.
It is possible for a to be up to about 1.0 nm, and minute defects (opening, grain boundaries, etc.) are hardly recognized on the material surface. or,
It also has the properties of glassy carbon itself, that is, low specific resistance, good corrosion resistance and weather resistance, light weight, high hardness, and non-magnetic properties.

The glassy carbon substrate as described above is first subjected to finish polishing. This final polishing can be obtained by mirror finishing using a polishing liquid such as loose abrasive grains by a double-sided lapping device in which polishing cloths are attached to upper and lower surface plates. The surface profile of the glassy carbon after this finish polishing has a surface roughness Ra of about 5 to 10Å.

After that, mechanical texture processing is performed using the polishing tape and the loose abrasive grains. As shown in FIG. 3, this texture processing is performed by pressing the polishing tape 3 against the substrate 1 rotating at a constant speed by the contact roller 2 with a predetermined processing pressure. At this time, the contact roller 2 is swung if necessary. During processing, the polishing tape 3 is fed at a constant speed and a polishing liquid is supplied.
When using free abrasive grains, the polishing tape is a buff tape,
A polishing liquid containing loose abrasive grains is used as the polishing liquid.

Then, a magnetic recording medium according to the present invention is obtained by providing a film such as a Cr underlayer film or a CoNiCr magnetic film on the carbon substrate obtained as described above. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0033]

Example: Furfuryl alcohol 500 parts by weight, 92%
480 parts by weight of paraformaldehyde and 30 parts by weight of water are dissolved by stirring at 75 ° C, and phenol 52 is added under stirring.
0 parts by weight, sodium hydroxide 8.8 parts by weight and water 45
Part by weight of the mixed solution was added dropwise. After the dropping was completed, the reaction was carried out at 75 ° C for 3 hours. Then, a mixed solution of 80 parts by weight of phenol, 8.8 parts by weight of sodium hydroxide and 45 parts by weight of water was further added dropwise and reacted at 75 ° C. for 4.5 hours. 30 ° C
After cooling to 60%, it was neutralized with a 60% aqueous paratoluenesulfonic acid solution. The neutralized product was dehydrated under reduced pressure to remove 170 parts by weight of water, and 500 parts by weight of furfuryl alcohol was added and mixed. The viscosity of the obtained resin is 370 at 20 ° C.
It was cps. The water content of the resin was measured and found to be 39% by weight.

To 100 parts by weight of this thermosetting resin, 3.5 parts by weight of a mixed solution of 70 parts by weight of paratoluenesulfonic acid, 20 parts by weight of water and 10 parts by weight of cellosolve was added, and after sufficiently stirring, the thickness was increased. It was poured into a 5 mm mold and degassed under reduced pressure. Next, it was heat-cured at 50 ° C. for 3 hours and further at 80 ° C. for 2 days. The obtained resin cured product is put into an organic firing furnace (made by Chugai Furnace Industry Co., Ltd.), heated in a nitrogen atmosphere to 700 ° C. at a heating rate of 2 to 5 ° C./hour, and further in a vacuum of about 0.5 mTorr. 1200 ℃ at a heating rate of 5 to 20 ℃ / hour
The mixture was heated and calcined up to, held at this temperature for 2 hours, and then cooled.

Next, the glassy carbon obtained in the pretreatment step was inserted into a sample chamber of a hot isostatic pressing (HIP) apparatus, and pressurized with argon gas at a temperature rising rate of 500 ° C./hour. The mixture was heated to 1500 ° C., kept at 1500 ° C. and 2000 atm for 1 hour, and then cooled. The density of the obtained glassy carbon was 1.65 g / cm ³ , and the fracture surface was clearly glassy.

Then, with # 500 to # 8000 abrasive grains
Mirror-polished, and the surface pore condition and pore diameter of the polished surface are determined by
Observed with a microscope. Pore size is 0.05-0.01 μm
The following are problems that may cause problems (opening and grain boundaries).
Etc.) did not exist. The surface smoothness is Ra 1.0
nm, which was extremely good. In addition, the material
Bending strength measured according to JIS standard R1601
As a result, bending strength is 29.8 kg / mm²Met. Bullet
The sex rate is 2500 kgf / mm ²Met.

The substrate made of glassy carbon thus obtained was subjected to finish polishing under the conditions shown in Table 1 below, and then subjected to texture treatment under the conditions shown in Table 2 below. did. Table-1 Polishing equipment; Double-sided lapping equipment made by Speedfam DSL
-9B Abrasive cloth; Surfing 018-3 Processing pressure; 150 g / cm ² Processing time; 10 minutes, 30 minutes Abrasive; Snowtex ZL: water = 1: 9 pH 2-10 Table-2 tape; Nippon Micro Coating Co. # 4000 flat type Tape feed speed; 400 mm / min Processing pressure; 0.8 kg / cm ² Tape swing; 460 reciprocations / minute Roller rubber hardness; 60 degrees Workpiece rotation speed; 50 rpm Processing time; 10-60 seconds Polishing liquid; made by Johnson JS602 3 wt% polishing liquid Then, a Cr film, a CoNiCr magnetic film, and a carbon film are provided on the glassy carbon substrate that has been subjected to the texture treatment as described above, and the magnetic properties of the glassy carbon-Cr film-CoNiCr film-Carbon film structure are provided. A recording medium was obtained.

Since the CSS test and the 2 μGHT test of the magnetic recording medium constructed as described above were performed,
It is shown in Table 3 together with the surface profile of the glassy carbon substrate by the texture treatment. Table-3 Tape type Processing time Ra Rp / Rp CSS count 2 μGHT Comparative example 1 Flat type 4 40 seconds 18 Å 4.8 0 (adsorption) OK Comparative example 2 Flat type 4 40 seconds 21 Å 4.8 0 (adsorption) OK Comparative example 3 Flat type 1 20 seconds 24 Å 4.6 1023 OK Comparative example 4 Flat type 3 60 seconds 116 Å 2.3 1652 NG Comparative example 5 Flat type 2 60 seconds 121 Å 2.2 498 NG Present invention 1 Flat type 2 10 seconds 30 Å 6 150,000 times or more OK Present invention 2 Flat type 2 40 seconds 41 Å 4.3 50,000 times or more OK Present invention 3 Flat type 2 40 seconds 59 Å 3.5 20,000 times OK Present invention 4 Flat type 2 40 seconds 70 Å 3.1 30,000 times or more OK Present invention 5 Flat type 3 40 seconds 72 Å 2.7 30,000 times or more OK Present invention 6 Flat type 2 40 seconds 73 Å 3 0 30,000 times or more OK Present invention 7 Flat type 2 40 seconds 74Å 3.2 30,000 times or more OK Present invention 8 Flat type 2 40 seconds 98 Å 2.7 40,000 times or more OK * Ra, Rp are surface roughness testers Measured with TENCOR P2 (needle curvature radius 0.6 μmR, measurement length 250 μm, no cutoff) * CSS count is 70% at a radius of 18 mm
An AlTiC (4μ ") head is used and the head load is 6
In g, the motor on time at 3600 rpm is 8 seconds, the motor off time is 8 seconds, and the number of times when the friction coefficient becomes smaller than 0.6 is displayed.

[0039]

[Effect] A head having a low flying height and excellent CSS durability can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a surface of a carbon substrate by a texture technique using a polishing tape and loose abrasive grains.

FIG. 2 is a schematic cross-sectional view of the surface of an aluminum substrate by a texture technique using a polishing tape and loose abrasive grains.

FIG. 3 is an explanatory diagram of texture processing.

Claims (4)

[Claims] 1. Ra is about 40 to 100Å, Rp / Ra
(However, Ra is a center line average roughness, Rp is a center line height) is about 1-6, The carbon substrate characterized by the above-mentioned. 2. Ra is about 10 to 40Å and Rp / Ra (where Ra is the centerline average roughness and Rp is the centerline height) is about 4
The carbon substrate is characterized in that 3. Ra is about 40 to 100Å, Rp / Ra
A recording medium, wherein a recording film is provided on a carbon substrate having a center line average roughness of Ra and a center line height of Rp of about 1 to 6. 4. Ra is about 10 to 40Å and Rp / Ra (where Ra is the center line average roughness and Rp is the center line height) is about 4.
A recording medium having a recording film provided on a carbon substrate having a size of .about.15.