JP3335262B2 - Magnetic recording medium substrate and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium substrate and a method of manufacturing the same, and more particularly, to a magnetic recording medium substrate useful for a recording device in a computer or a data processor and a method of manufacturing the same. Things.

[0002]

2. Description of the Related Art As is well known, as a substrate material for a magnetic recording medium such as a magnetic disk, an aluminum (Al) alloy, which is a non-magnetic material, is frequently used. Nickel-phosphorus (Ni) on a substrate made of
-P) layer is formed, and a chromium (Cr) layer, a cobalt (Co) alloy layer, and a carbon (C) protective film are sequentially formed thereon by sputtering.

In recent years, in order to improve the recording capacity, a glass substrate having a smoother surface and a Cr layer, a Co alloy layer and a C protective film sequentially formed by sputtering has been known. In recent years, a recording medium using a glassy carbon made of a phenol-formaldehyde resin as a raw material and forming a magnetic thin film in the same manner as described above has also appeared.

As described above, in particular, a magnetic recording / reproducing apparatus of recent years is desired to have a large recording capacity. Therefore, further miniaturization and weight reduction of the apparatus are required. A recording medium substrate cannot satisfy such market demands, and therefore, development of a new magnetic recording medium substrate has been desired.

[0005]

That is, the above Al-Mg
The alloy substrate has a high specific gravity (about 2.6) and a thickness of 1
mm or less, it is impossible to reduce the size and weight of the substrate and the recording apparatus, and the thickness using the glass substrate can be reduced to 1 mm or less. However, the specific gravity is as large as about 2.5, which is insufficient for reducing the size and weight.

Further, Japanese Patent Application Laid-Open No. 3-52116 discloses that a phenol-formaldehyde resin is press-molded, then carbonized and fired to obtain a glassy carbon substrate. At 10
Although a relatively light-weight magnetic recording medium having a specific gravity of 1.85 is obtained by the method of re-baking by applying a pressure of at least 00 atm to the substrate, the process is complicated, and a pressure of at least 1000 atm at 2,000 ° C or more Not only is the cost increased due to the application of pressure, but also the substrate using this phenol-formaldehyde has the disadvantage that pores, ie, surface defects, are present on the substrate surface even though it is reduced.

In particular, when the thickness of the magnetic layer on the substrate is 0.1 μm
In the following thin-film magnetic disks, since the surface state of the substrate is reflected on the surface of the magnetic layer, pores (surface defects) such as pinholes on the substrate surface cause bit errors in magnetic recording.

In the method described in Japanese Patent Publication No. 3-11005, polyacrylonitrile glassy carbon, bitch glassy carbon, lignin glassy carbon, phenolic resinous glassy carbon, furan resinous glassy carbon are disclosed. And a disk substrate using an alkyd resin-based glassy carbon, an unsaturated polyester-based glassy carbon, and a xylene resin-based glassy carbon.
5, the surface defect consisting of pores of 2 μm or more on the surface is 5 to 5 per disk-shaped substrate with a diameter of 130 mm.
There are more than 10 and it is not suitable as a substrate for a magnetic recording medium.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object the purpose of being lightweight, capable of being thinned, having excellent mechanical strength, having a smooth and dense surface, and having pores. An object of the present invention is to provide a magnetic recording medium substrate which can be manufactured and provided at low cost without surface defects and a method for manufacturing the same.

[0010] The structure of the magnetic recording medium employed in the present invention to solve the above-mentioned problem is characterized in that it is mainly composed of glassy carbon produced using a polycarbodiimide resin as a raw material. The configuration of the method is
The method is characterized in that a polycarbodiimide resin or a composition mainly composed of a polycarbodiimide resin is molded into an appropriate shape, and then the molded product is carbonized into glassy carbon, and then processed into a substrate for a magnetic recording medium. is there.

Hereinafter, the present invention will be described in detail.

The above-mentioned polycarbodiimide resin itself is known or can be produced in the same manner as known ones. US Pat. No. 2,941,95
No. 6, JP-B-47-33279; Or
g. Chem. , 28 , 2069-2075 (196
3) Chemical Review 198l, vo
l. 8l. No. For example, it can be easily produced by a condensation reaction involving the removal of carbon dioxide from an organic diisocyanate in the presence of a carbodiimidization catalyst.

The organic diisocyanate used in the production of the polycarbodiimide resin may be any of aliphatic, alicyclic, aromatic, and aromatic-aliphatic types. Used alone or
Two or more kinds may be used in combination.

Specifically, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate,
Mixture of tolylene diisocyanate and 2,6-tolylene diisocyanate, crude tolylene diisocyanate, xylene diisocyanate, m-phenyl diisocyanate, naphthylene-1,5-diisocyanate, 4,4,4
-Bipiphenylene diisocyanate, 3,3, -dimethoxy-4,4, -biphenyl diisocyanate, or a mixture thereof can be exemplified as the organic diisocyanate.

The polycarbodiimide resin used in the present invention has the following formula: -RN = C = N- (wherein R represents an organic diisocyanate residue)
And a homopolymer or a copolymer comprising at least one type of repeating unit represented by the formula:

As R in the above formula which is an organic diisocyanate residue, an aromatic diisocyanate residue is particularly preferable (here, the organic diisocyanate residue is a group obtained by removing two isocyanate groups (NCO) from an organic diisocyanate molecule). The rest). Specific examples of such a polycarbodiimide resin include the following.

Embedded image

In the above formulas, n is 10 to 10 and 0.
00, preferably in the range of 50 to 5,000, and the terminal of the polycarbodiimide resin may be sealed with monoisocyanate or the like, thus sealing the terminal of the polycarbodiimide. Examples of the monoisocyanate for controlling the molecular weight thereof include phenyl isocyanate, (ortho, meta, para) -tolyl isocyanate, dimethylphenyl isocyanate, cyclohexyl isocyanate, and methyl isocyanate.

The above-mentioned polycarbodiimide resin can be obtained as a solution or as a powder precipitated from the solution. The polycarbodiimide resin thus obtained is, in the case of a polycarbodiimide resin obtained in a liquid form,
In the case of a polycarbodiimide resin obtained as it is or by distilling off the solvent, or in the case of a polycarbodiimide resin obtained as a powder, it may be used as it is or after dissolving it in a solvent to form a liquid.

In the present invention, first, for example, a plate-shaped or disk-shaped molded product is formed from the above-mentioned polycarbodiimide resin or polycarbodiimide resin solution. The method for molding this molded product can be generally used in such a step, and is not particularly limited. Examples thereof include injection molding, compression molding, casting molding, vacuum molding, and extrusion molding. Can be mentioned.

Next, by heating the molded product molded as described above and carbonizing the polycarbodiimide resin, a desired plate-shaped or disk-shaped glassy carbon molded product can be obtained. . This carbonization step can be performed under an inert atmosphere such as in a vacuum or in a nitrogen gas, and the final firing temperature at that time is preferably 1000 ° C.
３3000 ° C.

The rate of temperature rise to the final firing temperature in the carbonization step is preferably 2 ° C./hour or less, and if the final firing temperature is reached too early, the porosity becomes 0.02% or more. It is not preferable because pores having a size of 0.1 μm or more are generated on the surface.

The glassy carbon molded product obtained in this way is lightweight, can be formed into a thin film, has excellent mechanical strength, is extremely smooth and dense, and is measured for physical properties. ~ 0.019%, bulk density is 1.
It was found to be 51 to 1.70 g / cm ^3, which is an extremely excellent material for a substrate for a magnetic recording medium, having no pores of 0.1 μm or more on the surface.

As a result of having the above-mentioned excellent physical properties, the glassy carbon is processed into a disk having an adjusted outer diameter and inner diameter, and, if necessary, adsorption between a magnetic head floating surface and a magnetic recording medium surface. The magnetic recording medium substrate of the present invention obtained by performing texture processing on the surface of the magnetic recording medium to prevent the phenomenon not only can increase the recording density, but also enables the weight of the recording medium to be reduced. Allows the recording device drive motor to be downsized,
It is possible to reduce the size and weight of the recording device. Further, since the manufacturing method of the present invention is relatively simple, the cost of manufacturing the recording medium can be reduced.

Further, the substrate for a magnetic recording medium of the present invention includes:
Since there are no pores (surface defects) of 0.1 μm or more on the surface, a bit error of magnetic recording does not occur even when a thin film magnetic disk is used.

[0025]

EXAMPLES The present invention will be further described below with reference to examples.

Examples 1 to 6 Mixture of 2,4-tolylene diisocyanate / 2,6-tolylene diisocyanate (80:20) [TDI] 5
4 g was reacted in 500 ml of tetrachloroethylene together with 0.12 g of a carbodiimidation catalyst (1-phenyl-3-methylphospholene oxide) at 120 ° C. for 5 hours to obtain a polycarbodiimide solution.

The reaction solution was passed through a glass Petri dish, dried at 60 ° C. for 20 hours and at 120 ° C. for 20 hours, and then heated to 200 ° C. at a rate of 1 ° C./hour to obtain a cured plate. The temperature of the obtained cured plate was increased to 1500 ° C. at a rate of 2 ° C./hour.

The carbon plate thus obtained was subjected to inner and outer diameter processing and processing for equalizing the plate pressure, and then to both-side simultaneous grinding and simultaneous double-side polishing using diamond abrasive grains. The substrate for a magnetic recording medium shown in FIG.

[Table 1]

[0029] Thereafter, the surface roughness was measured with a surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.), and the bulk density and the presence of pores (0.1 μm or more) on the surface were examined by an optical microscope.
In addition, Shore hardness and porosity were also measured. The results are shown in Table 2 below.
Shown in Note that “surface defect” in Table 2 represents the number of pores of 0.1 μm or more on the surface of one substrate.

[Table 2]

On the above-mentioned substrate, a Cr film was formed as a first film, a Co—NiCr alloy film was formed as a second film, and a C film was formed as a protective film by sputtering to obtain a magnetic recording medium. As a result, as shown in Table 3 below, it was found that the composition had good characteristics.

[Table 3]

Example 7 Methylene diphenyl diisocyanate [MDI] 50 g
In 880 ml of tetrahydrofuran with 0.12 g of a carbodiimidation catalyst (1-phenyl-3-methylphospholene oxide) at 68 ° C. for 15 hours,
A polycarbodiimide solution was obtained.

The reaction solution was passed through a glass Petri dish, dried at 40 ° C. for 20 hours and at 120 ° C. for 40 hours, and then heated to 200 ° C. at a rate of 1 ° C./hour to obtain a cured plate.
The obtained cured plate was heated at 2000 ° C. at a heating rate of 2 ° C./hour.
Temperature.

The carbon plate thus obtained was machined in the same manner as the carbon plate of Example 2 to prepare a substrate for a magnetic recording medium, and a magnetic recording medium was obtained in the same manner as in Example 2. , Physical properties and recording / reproducing physical properties were evaluated. The results are shown in Tables 4 and 5 below.

Example 8 54 g of diphenyl ether diisocyanate was added to 850 ml of tetrahydrofuran in a carbodiimidization catalyst (1).
-Phenyl-3-methylphospholene oxide) 0.
The mixture was reacted at 68 ° C. for 15 hours together with 12 g to obtain a polycarbodiimide solution.

The reaction solution was passed through a glass Petri dish, dried at 40 ° C. for 20 hours and at 120 ° C. for 30 hours, and then heated to 200 ° C. at a rate of 1 ° C./hour to obtain a cured plate.
The obtained cured plate was heated at a rate of 2 ° C./hour to 1800 ° C.
Temperature.

The carbon plate thus obtained was machined in the same manner as the carbon plate of Example 2 to prepare a substrate for a magnetic recording medium, and the physical properties were measured and recorded in the same manner as in Example 2. The recycled physical properties were evaluated. The results are shown in Tables 4 and 5 below.
Shown in

Example 9 The cured plate obtained in Example 1 was heated at a rate of 1 ° C./hour for 1 hour.
The temperature was raised to 500 ° C., and the carbon plate thus obtained was machined in the same manner as in Example 2 to prepare a substrate for a magnetic recording medium, and physical properties were measured and measured in the same manner as in Example 2. The recording / reproducing physical properties were evaluated. The results are shown in Tables 4 and 5 below.

[Table 4]

[Table 5]

Comparative Example 1 Using a phenol formaldehyde resin, a substrate for a magnetic recording medium was prepared in the same manner as in Example 2, and the physical properties were measured and the recording / reproducing physical properties were evaluated in the same manner. The results are shown in Tables 6 and 7 below.

Comparative Example 2 P-toluenesulfonic acid was added to furfuryl alcohol at a concentration of 0.1%.
4 parts by weight were added and mixed, a magnetic recording medium substrate was prepared in the same manner as in Example 2, and the physical properties were measured and the recording / reproducing physical properties were evaluated in the same manner. The results are shown in Tables 6 and 7 below.

Comparative Example 3 The cured plate obtained in Example 1 was heated at a rate of 5 ° C./hour at a rate of 1
The temperature was raised to 500 ° C., and the carbon plate thus obtained was machined in the same manner as in Example 2 to prepare a substrate for a magnetic recording medium, and physical properties were measured and measured in the same manner as in Example 2. The recording / reproducing physical properties were evaluated. The results are shown in Tables 6 and 7 below.

[Table 6]

[Table 7]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-347276 (JP, A) JP-A-3-247504 (JP, A) JP-A-2-152167 (JP, A) JP-A-62-167 234232 (JP, A) JP-A-64-72322 (JP, A) JP-A-3-52116 (JP, A) JP-B-3-11005 (JP, B2) (58) Fields investigated (Int. ⁷ , DB name) G11B 5/73

Claims (7)

(57) [Claims] 1. A substrate for a magnetic recording medium, comprising a glassy carbon produced using a polycarbodiimide resin as a raw material. 2. A bulk density of 1.51 g / cm ^{3 to} 1.7.
0 g / cm ^3, a substrate for a magnetic recording medium according to claim 1 porosity of from 0 to 0.019%. 3. The substrate for a magnetic recording medium according to claim 1, wherein pores of 0.1 μm or more do not exist on the surface. 4. A magnetic recording method comprising: molding a polycarbodiimide resin or a composition mainly composed of a polycarbodiimide resin into an appropriate shape; carbonizing the molded product; and processing the resultant into a substrate for a magnetic recording medium. A method for manufacturing a medium substrate. 5. The method for producing a substrate for a magnetic recording medium according to claim 4, wherein the carbonization of the molded product is performed in a vacuum or in an inert atmosphere. 6. The carbonization of the molded product is carried out at 1000 ° C. to 300 ° C.
The method for producing a substrate for a magnetic recording medium according to claim 5, which is performed in a temperature range of 0 ° C. 7. The method for producing a substrate for a magnetic recording medium according to claim 6, wherein the carbonization of the molded product is performed at a heating rate of 2 ° C./hour or less.