Patent Application
20080020679
A silicate glass plate formed by float process was processed into a doughnut-type circular glass plate (a circular glass plate having a circular hole at its center) from which a glass substrate having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 0.635 mm would be obtained. The inner and outer peripheral edge surfaces were ground by diamond abrasive particles, and the upper and lower surfaces of the glass plate were lapped by alumina abrasive particles.
Then, the inner and outer peripheral edge surfaces were chamfered with a chamfer width of 0.15 mm and a chamfer angle of 45°.
After the inner and outer peripheral edge surfaces were processed, mirror finish processing was carried out on the edge surfaces by brush polishing using the cerium oxide slurry as a polishing compound and using a brush as a polishing tool. The processing amount was 30 μm by the removed amount in the radius direction.
Then, upper and bottom principal planes were polished by a double side polisher using a cerium oxide slurry (cerium oxide average particle size: about 1.1 μm) as a polishing compound and using a urethane pad as a polishing tool. The processing amount was 35 μm in total in the direction of the thickness between the upper and lower principal planes.
Further, the upper and lower principal planes were polished by a double side polisher using, as a polishing compound, cerium oxide (average particle size: about 0.2 μm) having an average particle size smaller than that of the above cerium oxide and using a urethane pad as a polishing tool. The processing amount was 1.6 μm in total in the direction of the thickness between the upper and lower principal planes.
The principal plane of the circular glass plate thus prepared was observed by an atomic force microscope manufacture by Veeco Instruments and as a result, the surface roughness Ra was 0.48 nm.
Further, a slurry of the present invention were prepared as follows.
COMPOL-80 manufactured by FUJIMI INCORPORATED was diluted with distilled water to prepare 2 kg of a slurry liquid containing water and colloidal silica at a solid content concentration of 24 mass %.
Further, 200 g of polyoxypropylene diamine (tradename: polyetheramine D230) manufactured by BASF, having a weight average molecular weight of 230, was added to 1.8 kg of distilled water, followed by stirring to prepare a polyetheramine aqueous solution. The content of the polyetheramine in this aqueous solution is 10 mass %.
The above prepared slurry liquid and aqueous solution were mixed to prepare a slurry (dispersion). The pH of the slurry was 10.9.
The principal plane of the above circular glass plate with Ra of 0.48 nm was polished by using a polishing pad made of a polyurethane foam having a pad hardness of 55.5, a Shore A hardness of 53.5°, a compressibility of 1.9% and a density of 0.24 g/cm3 as a polishing tool and using the above slurry as a polishing compound, under a polishing pressure of 14.7 kPa at a carrier circumferential speed of 14 m/min for 20 minutes. As a result, a glass substrate having Ra on the principal plane of 0.129 nm was obtained. The removed amount was 0.18 μm.
Before measurement of Ra, the following cleaning was carried out. That is, cleaning by pure water shower, scrub cleaning with PVA (poly-vinyl alcohol) sponge and water, scrub cleaning with PVA (poly-vinyl alcohol) sponge and an alkali detergent, scrub cleaning with PVA (poly-vinyl alcohol) sponge and water, and cleaning by pure water shower were sequentially carried out, and then air blowing was carried out.
An aqueous solution to be mixed with the slurry liquid was prepared as follows. Namely, 120 g of a polyetheramine was added to 1.88 kg of distilled water, followed by stirring to prepare a polyetheramine aqueous solution. The content of the polyetheramine in this aqueous solution is 6 mass %. The polyetheramine aqueous solution was mixed with 2 kg of the same slurry liquid as in Example 1 to prepare a slurry having a pH of 10.8.
Polishing was carried out for 20 minutes in the same manner as in Example 1 except that the above slurry was used as a slurry to obtain a glass substrate with Ra on the principal plane of 0.130 nm. The removed amount was 0.18 μm.
An aqueous solution to be mixed with the slurry liquid was prepared as follows. Namely, 40 g of a polyetheramine was added to 1.96 kg of distilled water, followed by stirring to prepare a polyetheramine aqueous solution. The content of the polyetheramine in this aqueous solution is 2 mass %. The polyetheramine aqueous solution was mixed with 2 L of the same slurry liquid as in Example 1 to prepare a slurry having a pH of 10.6.
Polishing was carried out for 20 minutes in the same manner as in Example 1 except that the above slurry was used as a slurry to obtain a glass substrate with Ra on the principal plane of 0.146 nm. The removed amount was 0.19 μm.
Polishing was carried out in the same manner as in Example 1 except that double side polishing was carried out by using a polishing pad made of a polyurethane foam having a pad density of 40.6, a Shore A hardness of 79°, a compressibility of 0.5% and a density of 0.54 g/cm3 as a polishing tool, under a polishing pressure of 12 kPa, at a carrier circumferential speed of 40 m/min for a polishing time of 50 minutes. As a result, a glass substrate with Ra on the principal plane of 0.125 nm and a degree of roll-off of 15.2 nm was obtained. The removed amount was 0.90 μm. The degree of roll-off was measured by using NV200 manufactured by Zygo Co., Ltd.
Further, with respect to 19 very small defects present on the principal plane of the glass substrate thus obtained, the shape and the components of the defects were analyzed by SEM-EDX and as a result, non of them were convex defects by masking.
The above COMPOL-80 was diluted with distilled water to prepare a slurry having a solid content concentration of 12 mass %. Polishing was carried out in the same manner as in Example 1 except that the above slurry was used as a slurry to obtain a glass substrate with Ra on the principal plane of 0.176 nm. The removed amount was 0.37 μm.
Polishing was carried out in the same manner as in Example 4 except that one prepared by diluting the above COMPOL-80 with distilled water to have a solid content concentration of 12 mass % was used as a slurry and that polishing was carried out for 45 minutes, to obtain a glass substrate with Ra on the principal plane of 0.132 nm and a degree of roll-off of 112.3 nm. The removed amount was 0.90 μm.
It is considered that Ra was so small as the same level as in Example 4 because polishing was carried out for a long time of 50 minutes by using a soft polishing pad having a pad density of 40.6.
Whereas, polishing was carried out under the similar conditions as in Comparative Example 2 except that the slurry in Comparative Example 2 was used, and with respect to five very small defects present on the principal plane of the obtained glass substrate, the shape and the components of the defects were analyzed in the same manner as in Example 4 and as a result, three of them were convex defects by masking.
The present invention is applicable to production of a glass substrate for a magnetic disk.
The entire disclosures of Japanese Patent Application No. 2006-195396 filed on Jul. 18, 2006 and Japanese Patent Application No. 2006-262514 filed on Sep. 27, 2006 including specifications, claims, drawing and summaries are incorporated herein by reference in their entireties.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-195396 | Jul 2006 | JP | national |
| 2006-262514 | Sep 2006 | JP | national |
