JPH09100465A - 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, containing water, an abradant and a specific abrasion promoter. SOLUTION: This abradant composition for producing a magnetic recording medium carbon substrate comprises (A) 40-99.4wt.% 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) 0.5-30wt.% of an abrasion promoter composed of (C1 ) an oxidizing group-containing aluminum salt such as aluminum nitrate and (C2) an oxidizing group-containing magnesium salt such as magnesium nitrate in the weight ratio of the component C1 /C2 of 1/10 to 10/1.

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, in the above polishing method, an aluminum salt of an oxidizing group is used alone as a polishing aid, and when a carbon substrate is polished using an abrasive composition containing the polishing aid, it still remains. The actual situation is that a satisfactory polishing rate has not been obtained and the productivity of the carbon substrate is not sufficient.

Further, the above publication does not describe the use of two kinds of compounds in combination as a polishing aid.

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

[0009]

Means for Solving the Problems As a result of intensive studies, the inventors of the present invention have found that the surface roughness of a substrate can be improved by using a combination of specific compounds as a polishing accelerator in an abrasive composition for producing a magnetic recording medium substrate. It was found that the polishing rate can be reduced and the polishing rate can be improved.

The present invention has been made based on the above findings, and in an abrasive composition for producing a magnetic recording medium substrate containing water, an abrasive and a polishing accelerator, an oxidizing group is used as the polishing accelerator. It is intended to provide an abrasive composition for producing a magnetic recording medium substrate, which comprises using an aluminum salt containing and a magnesium salt containing an oxidizing group.

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, which comprises using an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group as an accelerator.

[0012]

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 abrasive 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 variously selected according to the required quality of the product, etc., but the average particle size as 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.

Further, the maximum particle size of the above-mentioned abrasive 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 25% 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. If the content is more than 30% by weight, the surface roughness of the substrate may increase. 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.

Thus, in the abrasive composition of the present invention, an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group are used as the polishing accelerator.
As the oxidizable group, any oxidizable group may be used in the invention without any particular limitation. Preferred oxidizing groups are those whose aluminum salt and its magnesium salt are water-soluble. Examples of such a preferable oxidizing group include a nitric acid group, a sulfuric acid group, a sulfite group, a persulfate group, a hydrochloric acid group, a perchloric acid group, a phosphoric acid group, a phosphorous acid group, a hypophosphorous acid group, and pyrophosphoric acid. Groups, carbonic acid groups and the like. As the aluminum salt containing an oxidizing group, for example, aluminum nitrate, aluminum sulfate, aluminum phosphate, aluminum carbonate or the like can be used. As the magnesium salt containing an oxidizing group, for example, magnesium nitrate, magnesium sulfate, magnesium phosphate, magnesium carbonate or the like can be used.

As described above, the present invention is characterized in that a combination of an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group is used as a polishing accelerator. Specifically,
Examples include aluminum nitrate and magnesium nitrate, aluminum sulfate and magnesium nitrate, aluminum sulfate and magnesium sulfate, aluminum phosphate and magnesium nitrate, and the like.

The above-mentioned aluminum salt containing an oxidizable group and the above-mentioned magnesium salt containing an oxidizable group are contained in the abrasive composition of the present invention in a total amount of preferably 0.5 to 30% by weight, more preferably 1 to 20% by weight. It is contained by weight%. If the content is less than 0.5% by weight, the effect of the chemical components is low,
There is a possibility that the surface roughness of the substrate will be high and the polishing rate will be low. If it exceeds 30% by weight, the effect of the chemical components will become too large, and there will be a possibility that the surface defects of the substrate will increase.

The weight ratio (former / latter) of the content of the aluminum salt containing the oxidizing group and the content of the magnesium salt containing the oxidizing group in the abrasive composition of the present invention is preferably 1/10. 10/1, more preferably 1/5
It is 5/1. If the weight ratio of the above contents is less than 1/10, the number of surface defects on the substrate may increase, resulting in 10/1.
If it exceeds, the surface roughness of the substrate may increase.

In the abrasive composition of the present invention, for example, a predetermined amount of an abrasive, a predetermined amount of an aluminum salt containing an oxidizing group, and a predetermined amount of a magnesium salt containing an oxidizing group are individually added to water (pure water). It can be prepared by dispersing and dissolving in water, mixing these, adding other components described below as needed, and adding water with stirring until a predetermined amount is reached.

The water used in the abrasive composition of the present invention preferably has a content of 40 to 99.
It is used so as to be 4% by weight, more preferably 65 to 99% by weight. If the content of water is less than 40% by weight, the dispersibility of the abrasive may be lowered and the surface roughness of the substrate may be increased. If it exceeds 99% by weight, a high polishing rate may not be obtained. There is a fear.

Further, in the abrasive composition of the present invention,
In addition to the above components, other components may be added as necessary. Examples of such components include a thickener, a dispersant for abrasives, and a dispersant for abrasives (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 polishing composition of the present invention can be used in any stage of the polishing process as long as it is a polishing process for manufacturing a substrate of 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-sided polishing machine 2 shown in FIGS. 1 and 2 will be described. In the double-sided polishing machine 2, a lower surface plate 4 rotating 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 surface plate 9 and the lower surface plate 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 described. 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 [JIS A (JISK-6301)] of the polishing pad attached to the surface plate of the double-sided polishing machine is preferably 40 to 100, more preferably 60 to 100. The lower platen rotation speed of the double-sided polishing machine depends on the polishing machine size. For example, 9B manufactured by SPEED FAM
If it is a mold double-side polishing machine, preferably 10-100 rpm
And more preferably 20 to 60 rpm. The flow rate of the abrasive composition depends on the size of the polishing machine, but is preferably 5 to 300 cc / min, and more preferably 10 to 150 cc / min for a 9B type double-side polishing machine manufactured by SPEEDFAM. is there.

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.

[0036]

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 3 and Comparative Examples 1 to 7 Abrasive compositions were prepared by dispersing the polishing accelerators and abrasives shown in Table 1 in water, mixing and stirring. Using this abrasive composition, a diameter of 2.5 lapped with SiC abrasive grains having a particle diameter of 75 μm by a double-side polishing machine shown in FIGS. 1 and 2.
An inch carbon substrate was polished. At this time, the double-side polishing machine was used under the following set conditions.

<Setting conditions of 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 Hardness of polishing pad; 90 Lower surface plate 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 polishing rate was determined by dividing the difference by the processing time (30 minutes). <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)

[0041]

[Table 1]

From the results of Table 1, the following can be seen. Examples 1 to 2 using a combination of an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group as a polishing accelerator when hexagonal plate alumina was used as an abrasive
When polishing is performed using the magnetic recording medium substrate-manufacturing abrasive composition, the surface roughness of the obtained substrate is such that an aluminum salt containing an oxidizing group or a magnesium salt containing an oxidizing group is used alone as a polishing accelerator. The polishing rate is further improved while being about the same as when it was (Comparative Examples 1 to 5). In the case where calcined alumina was used as the abrasive (Example 3
Also in Comparative Examples 6 to 7), the same results as in the case of using the hexagonal plate-shaped alumina are obtained.

[0043]

As described above in detail, the abrasive composition for producing a magnetic recording medium substrate of the present invention comprises a combination of an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group as a polishing accelerator. By using it, it is possible to provide the magnetic recording medium substrate with a low surface roughness necessary for increasing the density of the magnetic recording medium, and to polish the substrate 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, which comprises water, an abrasive and a polishing accelerator, wherein the polishing accelerator is an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group. An abrasive composition for producing a magnetic recording medium substrate, comprising: 2. The abrasive is an alumina abrasive.
The abrasive composition according to claim 1. 3. The abrasive composition contains an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group in a total amount of 0.5 to 30% by weight, and contains the oxidizing group. The weight ratio (former / latter) of the content of the aluminum salt and the content of the magnesium salt containing the oxidizing group is 1/1.
The abrasive composition according to claim 1 or 2, which is 0 to 10/1. 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 aluminum salt containing an oxidizing group is aluminum nitrate, and the magnesium salt containing an oxidizing group is magnesium nitrate. 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: A method for producing a substrate for a magnetic recording medium, which comprises using an aluminum salt containing an oxidizing group and a magnesium salt containing an oxidizing group. 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.