Method for manufacturing glass plate and method for manufacturing magnetic disk
When a laser beam is used to perform shape processing on an edge surface of a disk-shaped glass plate, in order to suppress strain (retardation values) in the main surface of the glass plate, the disk-shaped glass plate is floated above a base, and the edge surface of the glass plate is processed into a target shape by irradiating the edge surface with the laser beam while contactlessly heating the glass plate in a state where the glass plate is floated, and moving the laser beam relative to the edge surface in the circumferential direction of the disk-shaped glass plate.
1 . A method for manufacturing a glass plate including processing for performing shape processing on an edge surface of a disk-shaped glass plate, the method comprising:
floating the disk-shaped glass plate above a base in a state where the disk-shaped glass plate is not supported by a support tool;
preheating the disk-shaped glass plate by contactlessly heating an entirety of the disk-shaped glass plate uniformly in a state where the disk-shaped glass plate is floated, the preheating being performed such that an in-plane temperature difference in a middle circumferential portion of at least one of a pair of main surfaces of the disk-shaped glass plate is 50° C. or less, the middle circumferential portion being a portion located 25% or more away from an inner circumferential end of the at least one of the pair of main surfaces and from an outer circumferential end of the at least one of the pair of main surfaces; and
processing the edge surface of the disk-shaped glass plate into a target shape by softening and/or melting the edge surface, the softening and/or melting being performed by irradiating with a laser beam the edge surface of the disk-shaped glass plate that has been preheated in the state where the disk-shaped glass plate is floated, and by rotating the disk-shaped glass plate to move the laser beam relative to the edge surface in a circumferential direction of the disk-shaped glass plate,
the preheating in the state where the disk-shaped glass plate is floated being performed and completed, prior to the processing of the edge surface of the disk-shaped glass plate, and the in-plane temperature difference in the middle circumferential portion being kept 50° C. or less during the processing of the edge surface, such that a difference of a maximum retardation value and a minimum retardation value among retardation values of twelve measurement points in the at least one of the pair of main surfaces of the disk-shaped glass plate is 30 nm or less, the twelve measurement points including four points on a circumference that are located away from each other at 90 degrees at each of three radial positions that are located radially outward away from the inner circumferential end by 25%, 50%, and 75% in the at least one of the pair of main surfaces of which the inner circumferential end is set to be 0% and of which the outer circumferential end is set to be 100%.
2 . The method for manufacturing a glass plate according to claim 1 ,
wherein, in the processing the edge surface into the target shape, irradiation conditions of the laser beam are set so as to form a chamfered surface on the edge surface.
3 . The method for manufacturing a glass plate according to claim 2 ,
wherein the conditions are set such that a ratio C/Th of a length C of the chamfered surface extending in a radial direction of a main surface of the disk-shaped glass plate, relative to a thickness Th of the disk-shaped glass plate is in a range of 0.1 to 0.7.
4 . The method for manufacturing a glass plate according to claim 1 ,
wherein an arithmetic average roughness Ra of the edge surface formed by the laser beam is 0.02 μm or less.
5 . The method for manufacturing a glass plate according to claim 1 ,
wherein a ratio W2/D of a length W2 in the circumferential direction of luminous flux of the laser beam with which the edge surface is irradiated, relative to a diameter D of the disk-shaped glass plate before being irradiated with the laser beam is in a range of 0.03 to 0.2.
6 . The method for manufacturing a glass plate according to claim 1 ,
wherein a cross-sectional intensity distribution of the laser beam with which the edge surface is irradiated is a single mode, and W1>Th holds true and Pd×Th is in a range of 0.8 to 3.5 (W/mm) where a width of luminous flux of the laser beam in a thickness direction of the disk-shaped glass plate at an irradiation position of the edge surface is W1 (mm), a thickness of the disk-shaped glass plate is Th (mm), and a power density of the laser beam is Pd.
7 . The method for manufacturing a glass plate according to claim 6 ,
wherein the power density Pd is set such that a diameter of the disk-shaped glass plate formed through irradiation with the laser beam is larger than a diameter of the disk-shaped glass plate before being irradiated with the laser beam.
8 . The method for manufacturing a glass plate according to claim 1 ,
wherein a moving speed at which the laser beam relatively moves along the edge surface is in a range of 0.7 to 140 (mm/s).
9 . The method for manufacturing a glass plate according to claim 1 ,
wherein the disk-shaped glass plate has a Young's modulus of 70 (GPa) or more.
10 . The method for manufacturing a glass plate according to claim 1 ,
wherein the disk-shaped glass plate has a coefficient of linear thermal expansion of 100×10 −7 (1/K) or less.
11 . The method for manufacturing a glass plate according to claim 1 ,
wherein the disk-shaped glass plate has a thickness Th of 0.7 mm or less.
12 . The method for manufacturing a glass plate according to claim 1 , further comprising
grinding or polishing a main surface of the disk-shaped glass plate in which the edge surface has been processed into the target shape,
wherein no edge surface is polished after the edge surface has been processed into the target shape and before the main surface is ground or polished.
13 . A method for manufacturing a magnetic disk,
wherein a magnetic film is formed on a main surface of the disk-shaped glass plate manufactured using the method for manufacturing a glass plate according to claim 1 .
14 . The method for manufacturing a glass plate according to claim 1 , further comprising
grinding or polishing a main surface of the disk-shaped glass plate in which the edge surface has been processed into the target shape, and
polishing the edge surface after the edge surface has been processed into the target shape and before the main surface is ground or polished, the polishing of the edge surface being performed such that an amount of machining allowance for polishing the edge surface is 5 μm or less.
15 . A method for manufacturing a glass plate including processing for performing shape processing on an edge surface of a disk-shaped glass plate, the method comprising:
disposing the disk-shaped glass plate, a support tool, and a base such that the disk-shaped glass plate does not come into contact with the support tool and the base;
preheating the disk-shaped glass plate by heating an entirety of the disk-shaped glass plate uniformly in a state where the disk-shaped glass plate is not in contact with the support tool and the base, the preheating being performed such that an in-plane temperature difference in a middle circumferential portion of at least one of a pair of main surfaces of the disk-shaped glass plate is 50° C. or less, the middle circumferential portion being a portion located 25% or more away from an inner circumferential end of the at least one of the pair of main surfaces and from an outer circumferential end of the at least one of the pair of main surfaces; and
processing the edge surface of the disk-shaped glass plate into a target shape by softening and/or melting the edge surface, the softening and/or melting being performed by irradiating with a laser beam the edge surface in a state where the disk-shaped glass plate has been preheated and is not in contact with the base and the support tool, and by rotating the disk-shaped glass plate to move the laser beam relative to the edge surface in a circumferential direction of the disk-shaped glass plate,
the preheating in the state where the disk-shaped glass plate is not in contact with the support tool and the base being performed and completed, prior to the processing of the edge surface of the disk-shaped glass plate, and the in-plane temperature difference in the middle circumferential portion being kept 50° C. or less during the processing of the edge surface, such that a difference of a maximum retardation value and a minimum retardation value among retardation values of twelve measurement points in the at least one of the pair of main surfaces of the disk-shaped glass plate is 30 nm or less, the twelve measurement points including four points on a circumference that are located away from each other at 90 degrees at each of three radial positions that are located radially outward away from the inner circumferential end by 25%, 50%, and 75% in the at least one of the pair of main surfaces of which the inner circumferential end is set to be 0% and of which the outer circumferential end is set to be 100%.