WO2005009681A1

WO2005009681A1 - Process for mirror-finishing edge of recording media disk raw plate

Info

Publication number: WO2005009681A1
Application number: PCT/US2004/020003
Authority: WO
Inventors: Michihiro Yamahara
Original assignee: 3M Innovative Properties Company
Priority date: 2003-07-04
Filing date: 2004-06-22
Publication date: 2005-02-03
Also published as: CN1816420A; TW200505627A; JP2005022047A; KR20060030892A

Abstract

A method for providing a mirror-finish on the edge of a recording-media-disk raw plate is disclosed, by which a pit of the edge of the recording-media-disk raw plate is removed in a short time with simple procedure and low cost. Also disclosed is a process for mirror-finishing the edge of a recording-media-disk raw plate comprising: grinding the edge of the recording-media-disk raw plate made of ceramic plate with an abrasive grain-containing resin brush (2, 2’), without using free abrasive grains.

Description

PROCESS FOR MIRROR-FINISHING EDGE OF RECORDING MEDIA DISK RAW PLATE

TECHNICAL FIELD The present invention relates to a process for mirror-finishing the edge of a recording-media-disk raw plate, and particularly to a process for mirror-finishing the edge of a recording-media-disk raw plate which is punched out from ceramic plate, without using free abrasive grains.

BACKGROUND Conventionally, disk materials have been widely used as substrates for information recording media such as hard disks for personal computers and acoustic media, for example, compact disks and mini disks. In recent years, there have been ever-increasing demands for ceramic plates which are capable of recording information with high density, and attention has been focused on the development of processing technology thereof. Disk substrates for information recording media are typically formed in the following manners. Ceramic plate is first punched out with a ceramic cutter to form a recording-media-disk raw plate and the edge is then chamfered. In general, a chamfering process is performed by grinding and shaping the edge of the disk raw plate into trapezoid in cross-section with a diamond wheel. Because the diamond wheel is much harder than ceramic, a number of pits are created on the ground plate face during the grinding and shaping processes. Fine particles derived from grounding-wastes and grinding adjuvant enter the pits as foreign matter, and are ejected therefrom during the subsequent processes, causing contamination on the substrate surface. A finishing process, therefore, is performed for the edge of the disk raw plate so as to remove the pits. [0010] SUMMARY The present invention is intended for solving the above-mentioned conventional problems and there is provided a process for mirror-finishing the edge of a recording- media-disk raw plate, by which a pit of the edge of the recording-media-disk raw plate is removed in a short time with simple procedure and low cost. The present invention provides a process for mirror-finishing the edge of a recording-media-disk raw plate comprising: grinding the edge of the recording-media-disk raw plate made of ceramic plate with an abrasive grain-containing resin brush, without using free abrasive grains, by which the above-mentioned object is achieved. The process for mirror-finishing the edge of a recording-media-disk raw plate of the present invention, for example comprises: (1) grinding the edge of the recording-media-disk raw plate made of ceramic plate to shape; and (2) grinding the edge of the disk raw plate with an abrasive grain-containing resin brush, without using free abrasive grains. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic cross-sectional view that shows the shape of the edge of a recording-media-disk raw plate that is ground and shaped by using a diamond wheel. FIG. 2 is a schematic cross-sectional view that shows one embodiment of a process for mirror-finishing the edge of a recording-media-disk raw plate. FIG. 3 is a perspective view that shows one example of a wheel-like resin brush in which two kinds of resin brushes are combined.

[REFERENCE NUMERALS] a ... upper side of trapezoid

Theta ... inclination angle on two ends of trapezoid 1 ... stack of recording-media-disk raw plates

2 ... wheel-like resin brush

DETAILED DESCRIPTION In the present invention, a recording-media-disk raw plate refers to a disk material which is used as a disk substrate for information recording media on and from which electronic information may be written and read, such as a hard-disk ceramic substrate and a silicon wafer substrate. In the case of using glass as the recording-media-disk raw plate, a material thereof may be amorphous glass or crystalline glass. The thickness of the disk raw plate, when used as hard disks, is typically 0.4 to 1.4 mm, and more typically, 0.6 to 0.8 mm. When ceramic plate is processed into a disk substrate for an information recording medium, the ceramic plate is typically punched out in toroidal shape with a ceramic cutter. Next, the edge of the punched-out disk raw plate is ground and shaped, typically into trapezoid in cross-section with a diamond wheel for cutting the corners of the edge off. FIG. 1 is a schematic cross-sectional view that shows the shape of the edge of an example embodiment recording-media-disk raw plate that is ground and shaped by using a diamond wheel. In the case when the thickness of the disk raw plate is 0.6 mm, the upper side "a" of the trapezoid has a length of about 300 um, and the inclination angle "theta" on the both ends is about 45°. When a fragile material such as ceramic is ground to shape with using a diamond wheel, pits are formed all through the ground surface. The edge of the disk raw plate ground and shaped into trapezoid in cross-section, there are pits having a diameter of 20 to 50 um all through the ground surface. The pits are often filled with foreign matter such as grinding-wastes, and the foreign matter is ejected therefrom during the subsequent processes to cause contamination on the substrate surface. In recent years, particularly, higher density has been required in the recording media, and contamination on the substrate surface should be eliminated to the utmost. Accordingly, the pits present at the edge of the recording-media-disk raw plate should be removed. According to one aspect of the present disclosure, the pits are removed by mirror- finishing the edge of a disk raw plate which has been ground to shape into trapezoid in cross-section. Specifically, the edge of the disk raw plate is ground with an abrasive grain- containing resin brush without using free abrasive grains, such as those in a slurry. Grains that break free from the resin brush are not considered as the free abrasive grains. It should also be noted that the edge of the disk raw plate comprises both of the external edge and the internal edge of the disk raw plate. The abrasive grain-containing resin brush refers to a brush, filament parts or bristle parts of which, offering the friction function, is made of a resin containing abrasive grains. The filament (or bristle) refers to a long-shaped member having a small cross section which is bendable. Examples of grain-containing resin brushes are discussed below. The filament parts generally have an aspect ratio of at least 1 , and more generally at least 5, more typically at least 10, and most typically at least 20. This aspect ratio is defined as a value of a length divided by average width. The filament parts may have desirable arbitrary length or width, and a shape of its cross section may be, for example, a circle, ellipse, square, triangle, rectangle, polygon, or complex ellipse (such as triellipse and quadrellipse). The filament parts, therefore, can have various areas in cross section. The filament parts, for example, may have arched or wavy curves, patterns thereon, and may have tapers from the bottom to the top. The diameter of the filament parts generally may be in a range of 0.01 to 100 mm, and are more generaly 0.05 to 50 mm, and typically 0.1 to 25 mm, more typically 0.2 to 10 mm, and most typically 0.25 to 5 mm. The length of the filament, that is, trim's length may be in a range of 1 to 1000 mm, typically 2 to 100 mm, preferably 3 to 75 mm, more preferably 4 to 50 mm, and most preferably 5 to 50 mm. The resin composing the filament parts preferably has flexibility. This is because the filament parts are able to follow irregularities at the edge of the recording-media-disk raw plate to conduct grinding uniformly. This resin preferably has appropriate self- disintegration ability. This is because the resin wears during use and brings fresh abrasive grains into contact with the object to be ground constantly, which promotes efficient grinding. The resin may be thermoplastic polymer or thermoplastic elastomer. The shore D durometer hardness at room temperature of the resin is typically at least about 30, which is a value determined by ASTM D790, more typically from about 30 to about 90. Examples of thermoplastic polymer include polycarbonate, polyether imide, polyester, polyethylene, polysulfone, polystyrene, polybutylene, acrylonitrile butadiene styrene block copolymer, polypropylene, acetal polymer, polyurethane, polyamide, and combinations thereof. Examples of thermoplastic elastomer include segmented polyester thermoplastic elastomer, segmented polyurethane thermoplastic elastomer, segmented polyamide thermoplastic elastomer, combinations of thermoplastic elastomer and thermoplastic polymer, and ionomer thermoplastic elastomer. Preferable thermoplastic polymer and thermoplastic elastomer as the above- mentioned resin are further detailed, for example, in line 7 from the bottom on page 45 to line 6 on page 50 of Japanese Patent Kohyo Publication No. 2001-502185, which is incorporated by reference herein. Examples of the abrasive grains include grains of molten aluminum oxide, heat- treated molten aluminum oxide, ceramic aluminum oxide, heat-treated aluminum oxide, silicon carbide, titanium diboride, aluminum zirconia, diamond, boron carbide, ceria, cubic boron nitride, garnet, and combinations of these grains. The abrasive grains generally have a grain size in a range of about 0.1 to 1500 um. The grain size is typically from about 1 to 1300 um, and more typically from 50 to 500 um. As shown in TABLE 1, for example, the grain size of the abrasive grains can be appropriately adjusted in accordance with uses and desirable functions of the abrasive grain-containing resin brush.

*: Preferable range The abrasive grains are contained in the filament parts in an amount so that the ratio by weight of the abrasive grains to the resin is 0.25 to 1, preferably 0.4 to 0.8. The amount of the abrasive grains under the ratio by weight of 0.25 is so small that it takes too much time to finish, while the amount of the abrasive grains over the ratio by weight of 1 is so large with respect to the resin that the brush becomes lower in strength and becomes short in service life. Generally, the abrasive grains are scattered so as to form substantially well- dispersed distribution; however, this is not required. Also, while most of the abrasive grains are completely embedded in the resin, this does not mean to exclude the possibility that the grains are partly exposed to the outside of the resin surface. It is preferable that an abrasive grain-containing resin brush employed in the present invention is a shape which has a disk-like hub part and plural filament (or bristle) parts which are extended from the periphery of the hub part in the radial direction. This is because the external edge and the internal edge of a disk raw plate are easily able to be ground with using the periphery of the disk-like resin brush. Additionally, a plurality of disk-like resin brushes may be stacked coaxially to make a wider brush. The abrasive grain-containing resin brush can be prepared from a plastic resin containing abrasive grains by monolithic (or one-piece) molding, thereby obtaining a tough resin brush in lower costs. That is, by first, resin is heated over the melting point at which the resin flows; next, abrasive grains are dispersed into the resin to provide slurry; then, the resin slurry is introduced to a metal mold comprising a chamber in a predetermined shape; the resin slurry is flown into the chamber of the metal mold to form a shape of a resin brush; and the resin is solidified by cooling to take the shaped resin brush out of the metal mold. The resulting abrasive grain-containing resin brush comprises the hub part and the filament parts which are monolithically molded, and has no variation in shape among individuals, and is superior in toughness and durability. Commercial examples of such an abrasive grain-containing resin brush include "3M BRISTLE DISK (trade name)" available from Minnesota Mining and Manufacturing Company and "3M RADIAL BRISTLE MARGARET DISK (trade name)" available from Sumitomo 3M Inc. In the procedure of grinding, a load is applied to the filament parts of the abrasive grain-containing resin brush so as to contact with and rub against the edge of the disk raw plate, that is, the internal edge and/or the external edge. The grinding conditions may appropriately be adjusted depending on the required level of finishing, and selection of the particular conditions is within application of ordinary skill by one skilled in the art. In general, the peripheral speed of the resin brush is adjusted in the range of about 1000 to 3000 m/min relative to the edge of the disk raw plate. The plunge is in the range of about 0.5 to 2.0 mm. The grinding time is in the range of about 5 to 60 seconds. Proper sheets of the abrasive grain-containing resin brush may be stacked for using. In the case when the abrasive grain-containing resin brush is disk-like, plural brushes can be coaxially stacked, and be used as a wheel-like multi-element brush. Such a wheel-like brush is convenient for finishing all together the edges of the plural disk raw plates which have been stacked and fixed. FIG. 2 is a schematic cross-sectional view that shows one embodiment of a process for mirror-finishing the edge of a recording-media-disk raw plate. Plural disk raw plates are coaxially stacked to form a stack 1 and fixed on an axis. The stack 1 is connected to a motor 3 via the axis and is rotated. The disk-like abrasive grain-containing resin brushes are coaxially stacked so as to make wheel-like brushes 2 and 2', which are fixed adjacent to the stack 1 of the disk raw plates. The wheel-like brushes 2 and 2' are also connected to motors 4 and 4' via an axis and are rotated. The wheel-like brushes 2 and 2' are allowed to move along a rail 5 and to contact with the external edge of the stack 1 of the disk raw plates with a plunge of 0.5 to 2.0 mm. The internal edge of the disk raw plates may be mirror-finished by using the abrasive grain-containing resin brush with the size adjusted to the diameter of a central hole of the disk raw plates. Also, the internal edge and the external edge of the disk raw plates may be mirror-finished by conducting so-called centerless grinding. Slurries containing free abrasive grains does not need to be used in a grinding process of the present invention. The grinding process, therefore, reduce waste water and accordingly treatment costs involved with such water. Further, the present invention does not need a process of removing free abrasive grains after grinding. Since the abrasive grains are contained in the resin brush, the change of kinds of the resin brushes is sufficient for changing kinds of the abrasive grains. That is, the selection of the abrasive grains depending on the condition of a ground surface, such that the grinding with the abrasive grains having a large grain size is performed for a rough ground surface in the initial stage of the grinding process while the grinding with the abrasive grains having a small grain size is performed for a fine ground surface in the later stage of the grinding process, can be made simply and continually by changing kinds of the resin brushes from the resin brush for rough finishing to the resin brush for fine finishing. As a result, the grinding time can be drastically shortened while maintaining the level of the finishing on the ground surface. In a conventional grinding process employing free abrasive grains, it should be noted that the abrasive grains are attached to a disk raw plate to flow thereon and accordingly the disk raw plate need to be once washed for changing kinds of the abrasive grains. The change of kinds of the abrasive grains, therefore, is not practical in the grinding process, and typically the same kind of the abrasive grains is used throughout the grinding process. Consequently, the abrasive grains for a grade of medium finishing or fine finishing are used from the initial stage of grinding, leading to inferior efficiency of grinding and a comparatively long grinding time. The kind or type of the resin brush(es) may be changed by replacing the resin brush in a grinding device. Otherwise, in the case when plural resin brushes are coaxially stacked so as to make a wheel-like brush, regions of different kinds of the resin brushes may be prepared therein. Thus, the kinds of the resin brush(es) can be simply changed by moving the disk raw plate along the wheel of the resin brush. FIG. 3 is a perspective view that shows one example of a wheel-like resin brush in which two kinds of resin brushes are combined. There are provided a region 6 in which a first resin brush is coaxially stacked and a region 7 in which a second resin brush is coaxially stacked. The width 1] of the the first resin brush region is not necessarily equal to the width 1₂ of the second resin brush region, and the width lj and the width 1₂ may be appropriately changed.

[EXAMPLES] The present invention is further illustrated by the following examples and is not restricted thereto.

Example 1 A toroidal glass plate having a thickness of 2 mm, a diameter of 63.5 mm, and a central hole diameter of 20 mm was prepared as a recording-media-disk raw plate. The edge of this disk raw plate was ground and shaped into trapezoid as shown in FIG. 1 by using a JIS#500 diamond grinding wheel having a diameter of 63.5 mm and a hole diameter of 20 mm, the wheel being available under the trade name "MED 500" from Mitsubishi Materials K.K. The length of the upper side "a" of the trapezoid was about 400 um, and the inclination angle "theta" on both of the ends was about 45°. Pits were formed all through the upper face and the right and left slanting faces of the edge of the disk raw plate. A JIS#120 (average grain size of 120 um) aluminum oxide abrasive grain- containing resin brush having an external diameter of 50 mm and a shore D hardness of 95, the brush being available under the trade name "3M RADIAL BRISTLE MARGARET DISK" from Sumitomo 3M Inc. was coaxially stacked by five sheets. Next, a JIS#400 aluminum oxide abrasive grain-containing resin brush having an outside diameter of 50 mm and a shore D hardness of 95, the brush being available under the trade name "3M RADIAL BRISTLE MARGARET DISK" from Sumitomo 3M Inc. was coaxially stacked thereon by five discs. As a result, a wheel-like resin brush as shown in FIG. 3 in which two kinds of abrasive grain-containing resin brushes are combined was obtained. First, the wheel-like resin brush and the disk raw plate were rotated in opposite directions to each other, and the external edge of the disk raw plate was allowed to contact with the region of the JIS#120 aluminum oxide abrasive grain-containing resin brush with applying a load. The grinding conditions were: the wheel-like resin brush had a peripheral speed of 1600 m/min; the disk raw plate had a peripheral speed of 46 RPM; the plunge was 1 mm; and the grinding time was 20 seconds. Next, the external edge of the disk raw plate was allowed to contact with the region of the JIS#400 (average grain size of 30 um) aluminum oxide abrasive grain-containing resin brush with applying a load. The grinding conditions were: the wheel-like resin brush had a peripheral speed of 1600 m/min; the disk raw plate had a peripheral speed of 46 RPM; the entering was 1 mm; and the grinding time was 20 seconds. After grinding, the ground face was visually observed under a laser microscope, and a pit removal rate was calculated. The results are shown in Table 2.

Example 2 The external edge of the disk raw plate was mirror-finished in the same manner as

Example 1 except that a grinding time of 40 seconds in a range of the JIS#400 aluminum oxide abrasive grain-containing resin brush, was employed. A pit removal rate of the ground face were calculated in the same manner as Example 1. The results are shown in Table 2.

Reference Example

Example of Japanese Patent Kokai Publication No. 2001-246536 The edge of the same type of recording-media-disk raw plate as used in Example 1 was ground and shaped into trapezoid in the same manner as Example 1. Plural sheets of these plates were stacked and fixed to a rotary axis. The following grinding wheels were prepared: a JIS#600 (average grain size of 15 um) aluminum oxide grinding wheel having a diameter of 160 mm, a density of 1.8 g/cm , and a shore D hardness of 90, the wheel being available under the trade name "DLO WHEEL" from Sumitomo 3M Inc. and a JIS#10000 cerium oxide grinding wheel having a diameter of 160 mm, a density of 2.0 g/cm³, and a shore D hardness of 95, the wheel being available under the trade name "DLO WHEEL" from Sumitomo 3M Inc. A groove having a shape corresponding to the shape of the edge of the disk raw plate was provided on each of the grinding wheels by using a dresser. First, the edge of the disk raw plate was ground by using the JIS#600 aluminum oxide grinding wheel. The grinding process was as follows: the JIS#600 aluminum oxide grinding wheel and the disk raw plate were rotated in opposite directions to each other, and a load was applied so as to allow the edges of them to contact with each other. The grinding conditions were: the grinding wheel had a peripheral speed of 2000 m/min; the disk raw plate had a peripheral speed of 46 RPM; the load was 2 to 5 kg, and the grinding time was 10 seconds. Next, the JIS#600 aluminum oxide grinding wheel was replaced with the

JIS#10000 (average grain size of 0.3 um) cerium oxide grinding wheel, and the same process was performed for grinding the edge of the disk raw plate. The grinding conditions were: the wheel had a peripheral speed of 2000 m min; the load was 2 to 5 kg; the disk raw plate had a peripheral speed of 46 RPM; and the grinding time was 20 seconds. A pit removal rate of the ground face were calculated in the same manner as Example 1. The results are shown in Table 2.

Comparative Example The edge of the same type of recording-media-disk raw plate as used in Example 1 was ground and shaped into trapezoid in the same manner as Example 1. Plural sheets of these plates were stacked and fixed to a rotary axis. The edge of the disk raw plate was ground with a grinding brush. The grinding process was as follows: the grinding brush and the disk raw plate were rotated in opposite directions to each other, and the edge of the disk raw plate and the brush were allowed to contact with each other while supplying a water slurry containing 10 to 20 % of cerium oxide as a grinding assistant at a rate of 10 liter/min. The grinding conditions were: a peripheral speed of 1000 m/min of the grinding brush, an entering of 5 mm, a peripheral speed of 46 RPM of the disk raw plate, and a grinding time of 1800 seconds. A pit removal rate of the ground face was calculated in the same manner as

Example 1. The results are shown in Table 2.

^a: Ratio by weight of abrasive grains to resin ^bb:: RReemmoovvaall rraattee ooff llaarrggee ppiittss hhaavviinngg aa ddiiaammeetteer of 10 um or more ^c: Removal rate of small pits having a diameter of 10 um or less According to a process for mirror- finishing the edge of a recording-media-disk raw plate of the present invention, a pit of the edge of the recording-media-disk raw plate is removed in a short time with simple procedure and low cost.

Claims

CLAIMS: 1. A process for mirror-finishing the edge of a recording-media-disk raw plate comprising; grinding the edge of the recording-media-disk raw plate made of ceramic plate with an abrasive grain-containing resin brush, without using free abrasive grains. 2. The process according to claim 1, wherein the abrasive grain-containing resin brush comprises a disk-like hub part and plural filament parts which are extended from the periphery of the hub part in radius directions, and wherein the filament parts are made of a plastic resin containing abrasive particles. 3. The process according to claim 1 or 2, wherein the abrasive grain- containing resin brush is prepared from a plastic resin containing abrasive grains by monolithic molding. 4. The process according to any one of claims 1 to 3, wherein the abrasive grains and the resin are in the ratio by weight of from 0.25 to 1. 5. The process according to any one of claims 1 to 4, wherein grinding the edge of the disk raw plate with an abrasive grain-containing resin brush further comprises: grinding with an abrasive grain-containing resin brush for rough finishing; and grinding with an abrasive grain-containing resin brush for medium finishing or for fine finishing. 6. The process according to any one of claims 1 to 5, further including: grinding the edge of the recording-media-disc raw plate to shape, prior to grinding the edge of the disk raw plate with an abrasive grain-containing resin brush.