JPH09100466A - Abradant composition for producing magnetic recording medium substrate and production of magnetic recording medium substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an abradant composition capable of providing low surface roughness required for densification of a magnetic recording medium and abrading a substrate at a much higher speed, having a specific viscosity, containing water, an abradant and a specific abrasion promoter. SOLUTION: This abradant composition for producing a magnetic recording medium carbon substrate comprises (A) 50-99.8wt.% based on the composition of water, (B) 0.05-30wt.% of an alumina abradant (one having 0.001-6μm average particle diameter and <=15μm maximum particle diameter) and (C) 0.05-20wt.% of an abrasion promoter composed of a compound (e.g. aluminum nitrate, aluminum sulfate or magnesium sulfate) forming an oxidative ion in the abradant composition and has 5-200cPs viscosity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasive composition used for producing a magnetic recording medium substrate and a method for producing a magnetic recording medium substrate, and more particularly to a low surface required for high density magnetic recording medium. The present invention relates to an abrasive composition for producing a magnetic recording medium substrate and a method for producing a substrate for a magnetic recording medium, which can give roughness to the substrate and polish the substrate at a higher speed.

[0002]

2. Description of the Related Art In recent years, as a substrate for a magnetic recording medium represented by a substrate for a hard disk (HD), an aluminum substrate and a glass substrate which have been generally used in the past, and an impact resistant substrate are used. There is a carbon substrate made of glassy carbon or the like, which has been attracting attention for the purpose of improving its properties, reducing the weight by reducing the thickness, and reducing the power consumption of the motor by reducing the weight.

In manufacturing these magnetic recording medium substrates, in order to obtain the flatness / surface roughness required for the final product,
After a lapping process for polishing the surface and a chamfering process for chamfering by grinding the outer peripheral surface and the inner peripheral surface, a polishing process for final polishing is performed.

Further, these magnetic recording medium substrates are required to have a surface with low surface roughness and high precision as the density of the magnetic recording medium increases, and in particular, a carbon substrate is polished. It has been required to develop an excellent polishing method in the lapping process and the polishing process to provide a carbon substrate having the above performance.

In response to such a request, for example, Japanese Patent Laid-Open No. 6-
In Japanese Patent No. 339853, a carbon substrate is
In a mirror finishing polishing method of a carbon substrate, which is subjected to mirror finish polishing using alumina abrasive grains and a polishing aid, a polishing method using aluminum nitrate, aluminum chloride or the like as the polishing aid has been proposed.

The carbon substrate obtained by using the above polishing method has a low surface roughness to some extent. However, when a carbon substrate is polished using the above-mentioned polishing method, a satisfactory polishing rate has not been obtained yet, and the productivity of the carbon substrate is not sufficient.

Therefore, an object of the present invention is to provide an abrasive composition for producing a magnetic recording medium substrate, which gives the substrate a low surface roughness necessary for increasing the density of the magnetic recording medium and further polishes the substrate at a higher speed. An object of the present invention is to provide a method for manufacturing an object and a substrate for a magnetic recording medium.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have used a specific compound as a polishing accelerator in an abrasive composition for producing a magnetic recording medium substrate, and have a viscosity of the abrasive composition. It has been found that the surface roughness of the substrate can be lowered and the polishing rate can be improved by setting the value to a specific range.

The present invention has been made based on the above findings, and in an abrasive composition for producing a magnetic recording medium substrate, which contains water, an abrasive and a polishing accelerator, the abrasive composition serves as the polishing accelerator. Among these, there is provided an abrasive composition for producing a magnetic recording medium substrate, wherein a compound that forms an oxidizing ion is used and the viscosity of the abrasive composition is 5 to 200 cps.

The present invention also provides a method for producing a magnetic recording medium substrate, which comprises a polishing step using an abrasive composition for producing a magnetic recording medium substrate containing water, an abrasive and a polishing accelerator. Provided is a method for producing a substrate for a magnetic recording medium, wherein a compound that forms an oxidizing ion in the abrasive composition is used as an accelerator, and the viscosity of the abrasive composition is 5 to 200 cps. It is a thing.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION First, the abrasive composition for producing a magnetic recording medium substrate of the present invention (hereinafter simply referred to as "abrasive composition")
Sometimes)) will be described in detail.

As described above, the abrasive composition of the present invention contains water, the abrasive and the polishing accelerator as essential components.
Hereinafter, these components will be described.

Examples of the above-mentioned abrasives used in the abrasive composition of the present invention include alumina-based abrasives containing aluminum oxide (Al ₂ O ₃ ) as a main component and silica-based abrasives. The alumina-based abrasives, depending on the difference in particle size and properties thereof, include, for example, pulverized alumina-based abrasives, hexagonal plate-shaped alumina-based abrasives, calcined alumina-based abrasives, and the like. Various selections can be made according to quality and the like. Further, as the silica-based abrasive, Nal is used.
co company Nalco 2360 colloidal silica,
Ludox manufactured by Dow Corning can be used. Of these, the use of alumina-based abrasives is preferable because the polishing rate is high, and it is particularly preferable to use hexagonal plate-shaped alumina-based abrasives and calcined alumina-based abrasives because defects on the substrate surface can be reduced.

The particle size of the above-mentioned abrasive can be selected variously according to the required quality of the product, etc., but the average particle size in a general range is preferably. It is 0.001 to 6 μm, and more preferably 0.01 to 3 μm. When the average particle diameter is within the above range, it is easy to process the surface roughness of the substrate to be small without slowing the polishing rate, which is preferable.

The maximum particle size of the above-mentioned abrasives can be variously selected according to the required quality of the product, etc., but the maximum particle size in a general range is preferably 15 μm or less, and more preferably. Is 6 μm or less. When the maximum particle size is 15 μm or less, it is possible to process the substrate so that surface defects are reduced, which is preferable.

The above-mentioned abrasive is used by dispersing it in the abrasive composition of the present invention. The content of the abrasive in the abrasive composition of the present invention can be variously selected according to the viscosity of the abrasive composition, the required quality of the product, and the like.
As a general range, the content is preferably 0.05 to 3
It is 0% by weight, more preferably 0.5 to 20% by weight. If the content is less than 0.05% by weight, the polishing pad and the substrate may come into direct contact with each other, causing scratches on the substrate. There is

The above abrasive is contained in the abrasive composition of the present invention in an amount of 0.05 to 30% by weight, the average particle diameter is 0.001 to 6 μm, and the maximum particle diameter is 15 μm.
It is particularly preferably m or less.

In the abrasive composition of the present invention, a compound that forms an oxidizing ion in the abrasive composition is used as the polishing accelerator.

The oxidizing ion in the compound forming an oxidizing ion in the above-mentioned abrasive composition can be used in the present invention without particular limitation as long as it has some oxidizing action. Preferred oxidizing ions are those in which the above-mentioned compound forming an oxidizing ion is water-soluble. Examples of such preferable oxidizing ions include:
Examples thereof include nitrate ion, sulfate ion, chlorine ion, perchlorate ion, phosphate ion, carbonate ion and the like.
As the compound that forms the above-mentioned oxidizing ions, for example, aluminum nitrate, magnesium sulfate, aluminum sulfate, calcium sulfate and the like can be used, and aluminum nitrate and magnesium sulfate are particularly preferable.

The above-mentioned compound forming an oxidizing ion is
In the abrasive composition of the present invention, preferably 0.05 to 20.
%, More preferably 0.1 to 20% by weight, and most preferably 0.5 to 10% by weight. When the content is in the above range, a high polishing rate can be obtained and a low surface roughness of the substrate can be obtained, which is preferable.

The viscosity of the abrasive composition of the present invention is 5
˜200 cps, preferably 10-100 cps. When the above viscosity is less than 5 cps and 200 cp
When it exceeds s, the fluidity is not in the proper range, the polishing rate is lowered, and the surface roughness of the substrate is increased.

The viscosity of the abrasive composition of the present invention can be adjusted by using a commonly used thickener. Examples of such thickeners include inorganic colloidal compounds and cellulose compounds. Further, as the thickener, a commercially available product can be used. Examples of such commercial products include, for example, CATALOID-AD.
(Catalyst Chemical Co., Ltd.), Nr2000S (Pete)
r Walter) and the like.

The above-mentioned thickener is contained in an amount such that the viscosity of the abrasive composition of the present invention falls within the above range. Although the amount depends on the type of the thickener, it is generally preferable that the abrasive composition of the present invention contains 0.05 to 3% by weight,
It is more preferable that the content is 0.5 to 2% by weight. When the content is in the above range, a higher polishing rate can be obtained, which is preferable.

The abrasive composition of the present invention is preferably a predetermined amount of an abrasive, a predetermined amount of a compound that forms an oxidizing ion, and an amount of a thickener that makes the viscosity of the abrasive composition within the above range. And are individually dispersed and dissolved in water (pure water), these are mixed, and if necessary, other components described below are added, and then water is added with stirring until a predetermined amount is reached. It can be prepared.

Water used in the abrasive composition of the present invention preferably has a content in the composition of 50 to 99.
It is used so as to be 85% by weight, more preferably 65 to 99% by weight. If the content of water is less than 50% by weight, the dispersibility of the abrasive may be lowered and the surface roughness of the substrate may be increased. If it exceeds 99.85% by weight, a high polishing rate may be obtained. There is a fear that you will not be able to.

In the abrasive composition of the present invention,
In addition to the above components, other components may be added as necessary. Examples of such a component include a dispersant for abrasives and a dispersant for materials to be polished (shavings). These components are preferably contained in the abrasive composition of the present invention in an amount of 0.5 to 10% by weight.

The abrasive composition of the present invention can be used in any stage of the polishing process as long as it is a polishing process for producing a substrate for a magnetic recording medium. For example, it can be used in the above-mentioned lapping process and polishing process. It is particularly preferably used in the polishing step. When a carbon substrate is obtained using the abrasive composition of the present invention, the lapping step may be performed before or after the step of firing the disc-shaped cured resin to obtain the carbon substrate (fired carbonization step). It can be performed (hereinafter, the step of performing lapping before the firing carbonization step is referred to as a “pre-firing lapping step”, and the step of lapping after the firing carbonization step is referred to as a “post-firing lapping step”).

The magnetic recording medium substrate to be polished using the abrasive composition of the present invention may be magnetic or non-magnetic, but generally a non-magnetic one is used. To be As such a magnetic recording medium substrate, a carbon substrate, a glass substrate made of tempered glass or crystallized glass, an aluminum substrate made of an aluminum alloy or the like, a titanium substrate made of titanium or a titanium alloy, a ceramics substrate, a resin or a composite material is used. In particular, a carbon substrate, for example, a carbon substrate obtained by firing a disk-shaped cured resin obtained by core-removing a resin cured between a pair of glass plates of amorphous carbon, or a HIP method is used. The obtained carbon substrate or the like is used, but is not limited thereto.

Next, a preferred method for producing a magnetic recording medium substrate having a polishing method using the abrasive composition of the present invention will be described with reference to FIGS. 1 and 2 by taking a polishing step of a carbon substrate as an example. . Here, FIG. 1 is a schematic front view showing a double-sided polishing machine used in a polishing step in manufacturing a carbon substrate for a magnetic recording medium, with a lower platen omitted, and FIG. 2 is a line XX in FIG. It is a perspective view.

The double-side polishing machine 2 shown in FIGS. 1 and 2 will be described. In the double-side polishing machine 2, a lower surface plate 4 which rotates in the direction of arrow A is provided on a base 3, and a polishing pad 5 is provided on the upper surface thereof. Is installed.

As shown in FIG. 2, on the upper side of the lower platen 4, a sun gear 6 rotating in the central arrow B direction and an internal gear 7 rotating in the outer peripheral side arrow C direction mesh with each other to revolve. A plurality of planetary gear-shaped carriers 8 that rotate while being rotated are provided, and the carbon substrate 1, which is a workpiece, is set in the plurality of holes of each carrier 8. Further, as shown in FIG. 1, an upper surface plate 9 is provided above the lower surface plate 4 and the carrier 8, and a polishing pad (not shown) is attached to the lower surface thereof. The upper surface plate 9 is an air cylinder 1
It is rotatably attached to the tip of the output rod of No. 0 through the bracket 11 and can be moved up and down by the air cylinder 10. At the time of lowering, it is on the base 3 side.
It engages with the groove of the rotor 12 which rotates in the direction of arrow D, and rotates in the same direction.

Between the upper platen 9 and the lower platen 4,
The slurry composition of the present invention is supplied by a slurry supply pipe (not shown). Then, by lowering the upper platen 9 by the air cylinder 10, the carbon substrate that moves integrally with the carrier 8 is sandwiched between the lower platen 4 and the upper platen 9 and polished.

The method for producing a carbon substrate having a polishing step using the above-mentioned double-sided polishing machine will be further explained. The carbon substrate fired by the usual method is fired to obtain the flatness and surface roughness required for the final product. It is subjected to a post-wrapping process. Next, the carbon substrate is subjected to chamfer processing for chamfering the inner peripheral surface and the outer peripheral surface thereof. After that, it was subjected to a polishing process using a double-sided polishing machine,
A final product with a defined surface roughness is obtained.

The conditions for polishing the carbon substrate using the above double-sided polishing machine depend on the type of carbon substrate, the required quality of the final product, the polishing material, etc., but the general conditions are as follows. That is, the processing pressure is preferably 10
To 2000 g / cm ² , more preferably 30 to 3
It is 00 g / cm ² . The processing time is preferably from 2 to 120 minutes, and more preferably from 2 to 30 minutes. The hardness of the polishing pad mounted on the surface plate of the double-sided polishing machine [according to JIS A (JISK-6301)] is preferably 40 to 100, more preferably 60 to 1
00. The lower platen rotation speed of the double-sided polishing machine depends on the size of the polishing machine, but is preferably 10 to 10 for a 9B type double-side polishing machine manufactured by SPEED FAM.
It is 0 rpm, and more preferably 20 to 60 rpm. The flow rate of the abrasive composition depends on the size of the polishing machine. For example, a 9B type double side polishing machine manufactured by SPEED FAM is preferably 5 to 300 cc / min, more preferably 10 to 150 cc / min. It is min.

The preferred method for producing a magnetic recording medium substrate having a polishing step using the abrasive composition of the present invention has been described above. However, the production method is not limited to the above-mentioned embodiment, and for example, the carbon substrate described above is used. It can be applied to substrates other than the above, and can be similarly applied to the lapping step.

Further, in the present invention, a grindstone of an abrasive material is mounted on the surface plate of the double-sided polishing machine instead of the polishing pad,
The substrate may be polished while pouring an aqueous solution of the polishing accelerator having a predetermined concentration between the platens. It is particularly preferable to use such a polishing method in the lapping step and the polishing step.

[0037]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Examples 1 to 5 and Comparative Examples 1 to 4 The polishing accelerators and abrasives shown in Table 1 and, if necessary, a thickener are dispersed in water and stirred to have the viscosity shown in Table 1. An abrasive composition was prepared. Using this abrasive composition, a particle size of 75 μm was obtained by a double-side polishing machine shown in FIGS. 1 and 2.
A 2.5 inch diameter carbon substrate lapped with the above SiC abrasive grains was polished. At this time, the double-side polishing machine was used under the following set conditions.

<Setting conditions for double-sided polishing machine> Double-sided polishing machine used: SPEED FAM 9B type double-sided polishing machine Processing pressure: 150 g / cm ² Processing time: 30 minutes Polishing pad hardness: 90 Lower platen rotation speed: 40 rpm Polishing Material composition flow rate: 50 cc / min

The polishing rate of the carbon substrate and the surface roughness Ra of the carbon substrate after polishing were measured by the following measuring methods. Table 1 shows the results.

<Polishing Speed> The difference between the substrate thickness before polishing and the substrate thickness after polishing was determined, and the value was divided by the processing time (30 minutes) to determine the polishing rate. <Surface Roughness Ra> The surface roughness was measured with a stylus surface roughness meter (TENCOR P2) under the following conditions. Stylus diameter: 0.6 μm (needle curvature radius), Stylus pressing pressure: 7 mg, measurement length: 250 μm
× 8 places, trace speed; 2.5 μm / sec, cutoff; 1.25 μm (low pass filter)

[0042]

[Table 1]

From the results shown in Table 1, the following can be seen. When hexagonal plate-shaped alumina is used as an abrasive, a compound that forms oxidizing ions in the abrasive composition is used as a polishing accelerator, and the viscosity of the abrasive composition is 5 to 200 cps.
When polishing is performed using the abrasive composition for producing a magnetic recording medium substrate of Examples 1 to 3, the surface roughness of the obtained substrate is such that the viscosity of the abrasive composition is not within the above range. The polishing rate is further improved while being about the same as when polishing with a material (Comparative Examples 1 and 2). Also,
When using calcined alumina as an abrasive (Examples 4 to 5)
Also, in Comparative Examples 3 to 4), the same results as in the case of using the hexagonal plate alumina are obtained.

[0044]

As described above in detail, the abrasive composition for producing a magnetic recording medium substrate of the present invention uses a compound that forms an oxidizing ion in the abrasive composition as a polishing accelerator.
By setting the viscosity of the abrasive composition to 5 to 200 cps, the magnetic recording medium substrate can be provided with a low surface roughness necessary for increasing the density of the magnetic recording medium, and the substrate can be polished at a higher speed. .

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a double-sided polishing machine used in a polishing step of a carbon substrate with a lower platen omitted.

FIG. 2 is a view of the double-side polishing machine of FIG. 1 taken along the line XX.

[Explanation of symbols]

 1 Carbon substrate 2 Double-sided polishing machine 4 Lower surface plate 9 Upper surface plate

Claims (8)

[Claims] 1. An abrasive composition for producing a magnetic recording medium substrate containing water, an abrasive and a polishing accelerator, wherein a compound that forms an oxidizing ion in the abrasive composition is used as the polishing accelerator. And the viscosity of the abrasive composition is 5 to 20
An abrasive composition for producing a magnetic recording medium substrate, which is 0 cps. 2. The abrasive is an alumina abrasive.
The abrasive composition according to claim 1. 3. The abrasive composition according to claim 1, wherein the oxidizing ion-forming compound is contained in the abrasive composition in an amount of 0.05 to 20% by weight. 4. The abrasive composition according to claim 1, wherein
The content of the abrasive is 0.5 to 30% by weight, and the average particle diameter of the abrasive is 0.1.
001 to 6 μm, and the maximum particle size of the abrasive is 15
The abrasive composition according to any one of claims 1 to 3, having a size of not more than μm. 5. The abrasive composition according to claim 1, wherein the compound that forms the oxidizing ion is aluminum nitrate, aluminum sulfate or magnesium sulfate. 6. A method for producing a magnetic recording medium substrate having a polishing step using an abrasive composition for producing a magnetic recording medium substrate containing water, an abrasive and a polishing accelerator, wherein the polishing accelerator is used as the polishing accelerator. A compound which forms an oxidizing ion in the abrasive composition is used, and the viscosity of the abrasive composition is 5 to 2
A method of manufacturing a substrate for a magnetic recording medium, wherein the substrate is 00 cps. 7. The abrasive is an alumina abrasive,
A method of manufacturing a magnetic recording medium substrate according to claim 6. 8. The method for manufacturing a magnetic recording medium substrate according to claim 6, wherein the substrate is a carbon substrate.