JPH01304174A - Polishing fluid and method of polishing hard disc base plate - Google Patents

Abstract

PURPOSE:To accomplish a high surface roughness of a polishing fluid comprising a dispersion of a polishing agent consisting mainly of sintered abrasive grains in a solvent by incorporating a small amount of crushed abrasive grains having a diameter larger than that of the sintered grains and preferably PVA as anti- settling agent into the fluid. CONSTITUTION:A polishing fluid is obtained by dispersing a polishing agent consisting of, e.g., 100 pts.wt. sintered abrasive grains having a grain diameter of about 6mum and 1-30 pts.wt. crushed alumina grains having a grain diameter of about 10mum in an aqueous solvent, the ratio of the polishing agent to water being about 1:2, and incorporating 0.3-3wt.%, based on the total polishing fluid, PVA as ante-setting agent into the dispersion. For example, a suede-type nonwoven polishing fabric is used with this polishing fluid to polish a hard disc under conditions of, e.g., a rotational speed of an upper surface plate of 60r.p.m., a processing pressure of 50kg/cm<2>, and a polishing fluid feed rate of 100m1/min.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a polishing liquid used when polishing the surface of a substrate for a hard disk such as a magnetic disk, and further relates to a polishing liquid for use in hard disks using the polishing liquid. The present invention relates to a method for polishing a substrate.

[Summary of the Invention] The present invention provides a polishing liquid in which an abrasive mainly composed of sintered abrasive grains is dispersed in a solvent, and by adding a predetermined amount of crushed abrasive grains to the sintered abrasive grains, a large surface The purpose of this invention is to provide a polishing liquid that provides a high level of roughness.

Further, the present invention provides a method of polishing the surface of a ceramic substrate for a hard disk using a polishing liquid in which an abrasive material consisting of the above-mentioned sintered abrasive grains and crushed abrasive grains is dispersed in a solvent.
The objective is to obtain the surface roughness required for hard disk substrates.

[Prior Art] For example, disk-shaped magnetic disks that can be randomly accessed are widely used as storage media for computers and the like. Magnetic disks whose substrates are made of hard materials such as ceramic plates, glass plates, or A1 alloys whose surfaces are alumite-treated have come to be used.

The above-mentioned magnetic disk is one in which, for example, a magnetic layer involved in recording and reproduction, a protective film layer that protects the magnetic layer, a lubricant layer that improves running properties, etc. are sequentially laminated on a hard disk substrate or the like. It rotates at high speed in the circumferential direction to record and reproduce information on a large number of concentric tracks.

Incidentally, in such a magnetic disk, it is necessary that the surface of the hard disk substrate before the magnetic layer is formed has fine irregularities. That is, the above-mentioned fine irregularities greatly contribute to the running performance, durability, and output of the magnetic disk, and also contribute to improving the adhesion of the magnetic layer coated on the substrate.

An example of a method for forming these fine irregularities is polishing, which is a type of polishing. In the above-mentioned borishing process, slurry-like abrasive grains made by mixing an abrasive material with water or oil, etc., and liquefying it, that is, a polishing liquid, is supplied between a surface plate with a flat surface and a workpiece, and the machining pressure is This is a processing method that transfers the flatness of the surface plate by removing the necessary amount of machining allowance from the workpiece with an abrasive cutting edge using the rotational movement of the surface plate while adding

[Problem to be solved by the invention]

By the way, the grinder +91 used in the boring process of the hard disk surface has a diameter of, for example, 0.
Sintered abrasive grains made by sintering fine alumina oxide grains of about 2 to 0.3 microns are used as an abrasive, and water or oil,
A slurry made by mixing a dispersant, a surfactant, etc. is used.

However, the above-mentioned hard disk substrate requires a surface roughness of a certain value (for example, center line average roughness Ra = about 35 people) from the viewpoint of durability and output, but commercially available sintered abrasives It is extremely difficult to satisfy this value with grains (polishing liquid). That is, since the sintered abrasive grains are agglomerates of fine alumina oxide grains, their strength is not very strong, and the abrasive grains break during polishing, resulting in a small particle size actually involved in the processing. Therefore, the surface roughness required for a hard disk substrate cannot be obtained using only the sintered abrasive grains.

Therefore, it is possible to increase the surface roughness by increasing the particle size of the sintered abrasive grains, but as shown in Figure 3, the surface roughness increases to some extent in proportion to the abrasive grain size. However, as mentioned above, since the grain size actually involved in processing becomes small, there is a limit to the surface roughness. This is particularly noticeable in ceramic substrates or glass plates whose surfaces are made of hard oxides, or A2 alloy substrates subjected to alumite treatment. For this reason, conventionally, in order to obtain the necessary surface roughness for the hard disk substrate, texturing processing or the like is further performed on the surface of the substrate. therefore,
Polishing the surface of a hard disk substrate requires two steps, which increases costs.

On the other hand, as the particle size of the sintered abrasive grains increases, the abrasive grains tend to settle during polishing. For this reason, when polishing both sides of the surface of a hard disk substrate, the particle size of the sintered abrasive grains supplied to both sides of the substrate varies, which causes variations in the surface roughness. The centerline average roughness of the lower surface of the hard disk substrate is about 1.5 to 2 times the centerline average roughness of the upper surface. As a result, the resulting magnetic disks suffer from spacing loss and other differences in performance, making it impossible to provide highly reliable magnetic disks.

Therefore, the present invention has been proposed in view of the above-mentioned conventional problems, and an object of the present invention is to provide a polishing liquid that can provide a high surface roughness. Another object of the present invention is to provide a polishing method that prevents sedimentation of abrasive grains.

A further object of the present invention is to provide a method for polishing a hard disk substrate that provides the surface roughness required for the hard disk substrate.

Another object of the present invention is to provide a method for polishing a hard disk substrate to make the surface roughness of both surfaces of the substrate uniform.

[Means to solve the problem]

The inventors of the present invention have conducted research over a long period of time to achieve the above-mentioned objective, and have found that crushing abrasive grains with a diameter larger than that of sintered abrasive grains are effective in obtaining a large surface roughness. The present invention was completed based on the knowledge that polyvinyl alcohol is effective in preventing sedimentation.

That is, the polishing liquid of the present invention is a polishing liquid in which an abrasive mainly composed of sintered abrasive grains is dispersed in a solvent, and in which 1 to 30 parts by weight of crushed abrasive is added to 100 parts by weight of the sintered abrasive grains. It is characterized by the addition of grains.

Furthermore, the polishing liquid of the present invention is characterized in that the particle size of the crushed abrasive grains is larger than the particle size of the sintered abrasive grains.

Furthermore, the polishing liquid of the present invention is characterized in that polyvinyl alcohol, which is an anti-settling agent, is added to the polishing liquid.

Further, in the method for polishing a hard disk substrate of the present invention, when polishing the surface of a ceramic substrate for a hard disk, an abrasive material consisting of 100 parts by weight of sintered abrasive grains and 1 to 30 parts by weight of crushed abrasive grains is dispersed in a solvent. This method is characterized by using a highly refined Ig solution.

Further, in the method for polishing a hard disk substrate of the present invention, when polishing both sides of the surface of a ceramic substrate for a hard disk, an abrasive consisting of 100 parts by weight of sintered abrasive grains and 1 to 30 parts by weight of crushed abrasive grains and an anti-settling agent are used. This method is characterized by the use of a polishing liquid in which a certain polyvinyl alcohol is dispersed in a solvent.

The above-mentioned crushing abrasive grains are obtained by pulverizing an alumina abrasive material or a silicon carbide abrasive material using a pulverizer, etc., and then grading the particles.
Unlike sintered abrasive grains, which are agglomerates of fine grains, abrasive grains are so-called single grains. Therefore, the above-mentioned crushing abrasive grains are strong and there is no risk of the particles breaking even when subjected to polishing.

The proportion of the crushed abrasive grains is preferably 1 to 30 parts by weight based on 100 parts by weight of the sintered abrasive grains. That is, if the amount of the above-mentioned crushing abrasive grains is 1 part by weight or less, the amount of the crushing abrasive grains added is insufficient for polishing a hard disk substrate that requires a large surface roughness, and the desired surface roughness cannot be obtained. I can't. On the other hand, even if 30 parts by weight or more of the crushing abrasive grains are added, the surface roughness of the substrate will not increase compared to the amount added, so it is meaningless to add more than this amount.

Further, the particle size of the crushing abrasive grains is preferably larger than the particle size of the sintered abrasive grains, and further preferably, the particle size (count) is smaller. That is, if the particle size of the crushed abrasive grains is the same as or smaller than the particle size of the sintered abrasive grains, a large surface roughness cannot be obtained. When performing polishing,
The grain size and grain size may be appropriately selected depending on the surface roughness required for the workpiece.

Examples of such crushing abrasive grains include alumina-based crushing abrasive grains such as Hi-Lamp, White Hi-Lamp, and Takamijin manufactured by Kosho Kogyo Co., Ltd., and silicon carbide-based crushing abrasive grains such as Black, also manufactured by Kosho Kogyo Co., Ltd. - Examples include high lap, green high lap, etc. The above high lap is
It is a fused alumina abrasive with dark brown crystals containing a small amount of titanium, silica, etc. It has the highest toughness and is the most widely used abrasive. White Hi-Lap is an extremely pure fused alumina abrasive with white crystals, which is harder than A abrasive (JIS R6210-1958) but slightly brittle. Takamijin is a milky-white abrasive with good grain shape made by firing alumina oxide at a high temperature of 1300°C or higher and then pulverizing it into fine particles.It is softer than fused alumina abrasives and has an average particle size of 2.5 microns. It is the smallest particle in The Blank Hi-Lap is a black crystalline abrasive that is harder but more brittle than a fused alumina abrasive, and is suitable for polishing nonmetals such as stone, glass, and ceramics. In addition, Green Hi-Lap is an extremely pure silicon carbide abrasive with green crystals, and is a C abrasive (JIS
R6210-1958) is an abrasive with less hardness than brittleness and good thermal conductivity.

The above-mentioned polyvinyl alcohol (PVA) completely dissolves and disperses in the polishing liquid, and prevents the abrasive from settling without impairing the performance of the polishing liquid or adversely affecting the polishing equipment. . Therefore, it is particularly suitable for polishing the surface of a hard disk substrate that requires a high surface roughness.

That is, in order to obtain a large surface roughness, the particle size of the crushed abrasive grains is made larger than the particle size of the sintered abrasive grains, so the crushed abrasive grains in particular tend to settle toward the lower surface plate. Therefore, if polyvinyl alcohol, which is an antisedimentation agent, is added to the polishing liquid, the abrasive grains are prevented from settling, thereby eliminating the difference in surface roughness between the two surfaces of the substrate. Also,
Since the above-mentioned polyvinyl alcohol is inexpensive, it is possible to supply an inexpensive polishing liquid that is satisfactory in terms of cost.

In addition to the above-mentioned polyvinyl alcohol, for example, a water-soluble polymeric agent can also be used as the anti-settling agent.

On the other hand, examples of the solvent include water or oil, a separating agent, a surfactant, and the like. In addition, a dispersant and a surfactant may be used appropriately as necessary.

Furthermore, a commercially available polishing liquid in which an abrasive material mainly composed of the sintered abrasive grains is dispersed in a solvent is used. This is to make use of the characteristics required as a polishing liquid and to improve the suspension of the crushed abrasive grains added.

A ceramic substrate is used as the hard disk substrate. Note that the ceramic substrate includes a ceramic plate and a glass plate made of a single ceramic whose surface to be polished is an oxide.

An alumite-treated A42 alloy plate or the like is used.

[Function] According to the polishing liquid of the present invention, since a predetermined amount of crushing abrasive grains are added to the abrasive material mainly composed of sintered abrasive grains, the abrasive grains are not crushed during polishing. This ensures the abrasive grain size and provides a large surface roughness. Further, by making the particle size of the crushed abrasive grains larger than the particle size of the sintered abrasive grains, a large surface roughness can also be obtained. Furthermore, by adding polyvinyl alcohol to these abrasives, sedimentation of the abrasive grains is prevented.

When the surface of a ceramic substrate for a hard disk is polished using such a polishing liquid, a large surface roughness required for the hard disk substrate can be obtained, and the surface roughness on both sides of the substrate can be made uniform.

〔Example〕

The present invention will be described below based on specific examples.

First, a polishing apparatus for polishing a hard disk substrate using a polishing liquid according to the present invention will be described.

As shown in Fig. 1, the polishing device described above mainly consists of a lower surface plate (2) and an upper surface plate (3) that are arranged to sandwich the hard disk substrate (1) from above and below. . The lower surface plate (2) and the upper surface plate (3) are disk-shaped and have a flat surface that contacts the hard disk substrate (1), and are configured to rotate in opposite directions. Among the surface plates, the upper surface plate (3) is movable up and down and is adapted to apply a predetermined processing pressure to the hard disk substrate (1). Also, the lower surface plate (
A carrier (4) for holding the hard disk substrate (1) is disposed between the hard disk substrate (1) and the hard disk substrate (1). The carrier (4) is configured to rotate while revolving in the same direction as the lower surface plate (2) by a sun gear and an internal gear (both not shown) provided in the main body of the device. Furthermore, polishing pads, that is, nonwoven fabrics (5) and (6), are attached to the lower surface plate (2) and the upper surface plate (3), respectively, and these nonwoven fabrics (5) and (6) are attached to the polishing liquid. and comes into contact with the hard disk substrate (1).

The upper surface plate (3) and the nonwoven fabric (6) attached to the upper surface plate (3) have polishing liquid supply holes (3a) for supplying the polishing UWX to the hard disk substrate (1). .

(6a) are drilled, and these supply holes (3a), (6a
) is supplied with Boricinda liquid.

To polish a hard disk substrate using the polishing device described above, first, the hard disk substrate (1) is placed on the carrier (
4) holds a plurality of hard disk substrates, lowers the upper surface plate (3), and sandwiches the hard disk substrate (1) between the upper surface plate (3) and the lower surface plate (2); 3), a predetermined processing pressure is applied to the hard disk substrate (1). Next, while rotating the lower surface plate (2), upper surface plate (3), and carrier (4), the polishing process is performed while supplying the polishing liquid through the polishing liquid supply holes (3a) and (6a). give

According to this, both surfaces of the hard disk substrate (1) are simultaneously scraped off by the cutting edge of the abrasive material due to the relative rotational movement between the upper and lower surface plates (3), (2) and the carrier (4). .

Next, the grinding zero according to the present invention? & was prepared under the following conditions,
The surface of a ceramic substrate for a hard disk was polished using the above-mentioned polishing device. In other words, alumina crushing abrasive grains with a grain size of 6μ1 and grain size 2500 were added to an abrasive material mainly consisting of sintered abrasive grains with a grain size of 6μ1. Alumina crushing abrasive grains with a diameter of 10 μ2 and a grain size of No. 1500 were added for each of the sintered abrasive grains.
．． Polishing liquids were prepared by adding 3%, 5%, and 10.15% by weight of each abrasive and mixing them at a ratio of 1:2 (abrasive and water) using water as a solvent. In this example, a commercially available polishing liquid was used.

On the other hand, an alumite-treated A1 alloy substrate was used as the ceramic substrate, and a total of 10 alumite-treated substrates were polished by holding them on five 9-inch carriers. The polishing conditions were as follows: Suede type non-woven fabric was used, the rotation speed of the upper surface plate was 60 rpm, and the processing pressure was 5.
A polishing liquid having the above composition was supplied at 100 mf/min at 0 g/cJ, and polishing was performed for 7 minutes.

The results are shown in FIG. In FIG. 2, the horizontal axis indicates the amount of crushing abrasive grains added (% by weight), and the vertical axis indicates the centerline surface roughness (in terms of surface roughness) of the substrate surface. Further, in the figure, the solid line indicates the center line average roughness of the substrate surface using a polishing liquid to which crushing abrasive grains with a particle size of 10 μm are added, and the broken line represents crushing abrasive grains with a particle size of 6 μm.

As can be seen from Figure 2, when the particle size of the crushed abrasive grains is the same as the particle size of the sintered abrasive grains (i.e., indicated by the broken line in Figure 2), the ratio of addition of the crushed abrasive grains Regardless, the surface roughness was constant, and the surface roughness required for a hard disk substrate (about 35 people) could not be obtained. On the other hand, if the particle size of the crushed abrasive grains is larger than that of the sintered abrasive grains (in other words, as shown by the solid line in Figure 2), even if only 1% by weight of the crushed abrasive grains are added, a large surface Roughness is obtained, 3-5% by weight
By adding the crushing abrasive grains, the surface roughness required for the hard disk substrate was obtained. Also, as can be seen from Figure 2,
Even if the amount of the crushing abrasive grains added is further increased, the surface roughness cannot be improved compared to the amount added, so the amount of the crushing abrasive grains added is 100 parts by weight of the sintered abrasive grains as described above. It is preferable to use 1 to 30 parts by weight.

Therefore, the research of the present invention [? According to [, the surface roughness required for a hard disk substrate can be easily obtained by simply adding a predetermined amount of inexpensive crushing abrasive grains to a commercially available polishing liquid. Therefore, since the purpose of the grinding process is achieved in one step, the conventional texturing process can be omitted and the manufacturing process can be simplified.

In addition, in this example, a polishing liquid to which polyvinyl alcohol, which is an anti-sinking agent, was added was prepared under the following conditions, and the polishing liquid was used to polish the surface of a ceramic substrate for a hard disk using the above-mentioned polishing apparatus. did.

In other words, an abrasive material mainly composed of sintered abrasive grains with a particle size of 6μ,
Alumina crushing abrasive grains with a particle size of 10μ1 and a particle size of No. 1500 were added to the sintered abrasive grains in an amount of 5% by weight, and polyvinyl alcohol was added in an amount of 0.3% by weight based on the entire polishing liquid.
, 0.5, 1.0°, and 3.0% by weight, respectively, and mixed at a ratio of 1:2 (abrasive material and water) using water as a solvent to prepare polishing liquids.

On the other hand, the ceramic substrate was anodized like the previous one! Using alloy substrates, a total of five 5.25-inch alumite-treated substrates were polished by holding them on five 9-inch carriers. The polishing conditions were as follows: suede type non-woven fabric was used, the rotation speed of the upper surface plate was 5 Orpm, the processing pressure was 50 g/cJ, and the polishing liquid with the above composition was supplied at 100 d/min for 5 minutes. was applied.

The results are shown in Table 1. In Table 1, Ra indicates the center line average roughness of the substrate surface on the upper surface plate side, and Rb indicates the center line average roughness of the substrate surface on the lower surface plate side.

Table 1 As can be seen from Table 1 above, when polishing is performed using a polishing liquid containing 0.3% or 0.5% by weight of polyvinyl alcohol, the surface roughness of both surfaces of the substrate Variations were observed. That is, 0.3% by weight, 0.
This is believed to be because the addition amount of polyvinyl alcohol of 5% by weight does not completely prevent sedimentation of the abrasive grains.

On the other hand, when polishing was performed using a polishing liquid containing 1.0% by weight of polyvinyl alcohol, there was no variation in surface roughness on both sides of the substrate, and almost the same surface roughness was obtained on both sides. . Furthermore, even when the amount of polyvinyl alcohol added was 3.0% by weight, the same surface roughness values were obtained on both sides of the substrate.

Therefore, it can be said that the above-mentioned polyvinyl alcohol is effective in preventing sedimentation of abrasive grains. Therefore, by adding this polyvinyl alcohol to the polishing liquid, the surface roughness on both sides of the substrate can be made uniform, and a highly reliable hard disk substrate can be provided.

〔Effect of the invention〕

As is clear from the above explanation, according to the polishing liquid of the present invention, a predetermined amount of crushed abrasive grains is added to the abrasive material mainly composed of sintered abrasive grains, so that the crushed abrasive grains are added during polishing. The particle size is maintained without shattering, resulting in a large surface roughness. Further, since the particle size of the crushed small grains is made larger than the particle size of the sintered abrasive grains, a large surface roughness is also achieved.

Furthermore, according to the polishing T2 liquid of the present invention, since polyvinyl alcohol is added to the polishing liquid, sedimentation of the abrasive grains can be prevented.

On the other hand, according to the method of polishing a hard disk substrate of the present invention, polishing is performed using a polishing liquid to which crushing abrasive grains are added, so that the surface roughness required for the hard disk substrate can be easily obtained. Furthermore, according to the method for polishing a hard disk substrate of the present invention, since polyvinyl alcohol, which is an anti-settling agent, is added to the polishing liquid to which crushing abrasive grains have been added, sedimentation of the abrasive grains is prevented. The surface roughness on both sides of the substrate becomes uniform.

Thereby, there is no variation in output as a magnetic disk, and it is possible to provide a highly reliable hard disk substrate.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view showing an example of the polishing apparatus used in the present invention, and Figure 2 shows the amount of crushed abrasive grains added when polishing is performed using the polishing liquid to which the present invention is applied. FIG. 3 is a characteristic diagram showing the relationship between surface roughness, and FIG. 3 is a characteristic diagram showing the relationship between abrasive grain size and surface roughness. 1... Hard disk substrate 2... Lower surface plate 3... Upper surface plate 4... Carrier 5. 6... Nonwoven fabric patent applicant Sony Corporation representative Patent attorney Akira Koike (and two others) - ○ Tsuyano m￥6a@c review! h-';: @ Yano

Claims (5)

[Claims] (1) In a polishing liquid in which an abrasive mainly composed of sintered abrasive grains is dispersed in a solvent, 1 to 30 parts by weight of crushing abrasive grains are added to 100 parts by weight of the sintered abrasive grains. A polishing liquid characterized by: (2) The polishing liquid according to claim (1), wherein the particle size of the crushed abrasive grains is larger than the particle size of the sintered abrasive grains. (3) The polishing liquid according to claim (1) or (2), further comprising polyvinyl alcohol as an anti-settling agent. (4) When polishing the surface of a ceramic substrate for a hard disk, use 100 parts by weight of sintered abrasive grains and 1 to 30 parts by weight of crushed abrasive grains.
1. A method for polishing a hard disk substrate, comprising using a polishing liquid in which an abrasive material consisting of parts by weight is dispersed in a solvent. (5) When polishing both sides of the surface of a ceramic substrate for a hard disk, 100 parts by weight of sintered abrasive grains and 1 to 10 parts of crushed abrasive grains are used.
1. A method for polishing a hard disk substrate, comprising using a polishing liquid in which an abrasive comprising 30 parts by weight and polyvinyl alcohol as an anti-settling agent are dispersed in a solvent.