Method of manufacturing disk-shaped glass substrate, method of manufacturing circular ring-shaped glass plate, method of manufacturing glass substrate for magnetic disk, disk-shaped glass substrate, circular ring-shaped glass substrate, and glass substrate for magnetic disk

Abstract

To provide a method of manufacturing a disk-shaped glass substrate, a method of manufacturing a circular ring-shaped glass substrate, a method of manufacturing a glass substrate for a magnetic disk, a disk-shaped glass substrate, a circular ring-shaped glass substrate, and a glass substrate for a magnetic disk by irradiating an end surface of the disk-shaped glass substrate with laser light to smooth the end surface and form the chamfered surface without deteriorating the roundness of the end surface of the disk-shaped glass substrate.SOLUTION: A method of manufacturing a disk-shaped glass substrate includes: preparing a disk-shaped glass substrate 1 having main surfaces 11a and 11b and an outer peripheral end surface 12; and irradiating laser light L from a laser irradiation device 30 along the outer peripheral end surface 12 of the disk-shaped glass substrate 1 for more than one revolution.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a disk-shaped glass substrate, a method for manufacturing a circular glass substrate, and a method for manufacturing a glass substrate for a magnetic disk, which include processing a shape using laser light, and to a disk-shaped glass substrate, a circular glass substrate, and a glass substrate for a magnetic disk. [Background technology]

[0002] Nowadays, hard disk drives for recording data are used in personal computers, notebook personal computers, DVD (Digital Versatile Disc) recording devices, cloud computing data centers, etc. Hard disk drives use magnetic disks in which a magnetic layer is provided on a circular non-magnetic glass substrate for magnetic disks.

[0003] Conventionally, in such a manufacturing method of a glass substrate for a magnetic disk, a technique is known in which an annular glass substrate is cut from a raw glass plate, and the inner peripheral end face and the outer peripheral end face of the annular glass substrate are irradiated with a laser beam to smooth the inner peripheral end face and the outer peripheral end face and form a chamfered surface (Patent Document 1). Specifically, the inner peripheral end face and the outer peripheral end face of the annular glass substrate are irradiated with a laser beam to heat the inner peripheral end face and the outer peripheral end face to a temperature equal to or higher than the softening point of the glass, thereby melting the inner peripheral end face and the outer peripheral end face. As a result, the inner peripheral end face and the outer peripheral end face are smoothed, and a chamfered surface is formed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-150546 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above technique, when the laser light is irradiated once along each of the inner peripheral end face and the outer peripheral end face of the annular glass substrate, the inner peripheral end face and the outer peripheral end face are smoothed and a chamfered surface is formed, but the roundness of the inner peripheral end face and / or the outer peripheral end face of the annular glass substrate may deteriorate (become large). Furthermore, when an annular glass substrate with deteriorated roundness at the inner peripheral end face and / or the outer peripheral end face is used as a glass substrate for a magnetic disk, it is considered that the air flow may be disturbed during high-speed rotation, causing fluttering.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to provide a technology for smoothing the end face and forming a chamfered surface by irradiating laser light to the end face of a disk-shaped glass substrate or annular glass substrate without deteriorating the roundness of the end face of the disk-shaped glass substrate or annular glass substrate. [Means for solving the problem]

[0007] According to a first aspect of the present invention, there is provided a method for producing a disk-shaped glass substrate, comprising the steps of: Preparing a disk-shaped raw glass plate having a main surface and an outer peripheral end surface; and irradiating the outer peripheral end face of the disk-shaped raw glass plate with laser light for more than one revolution.

[0008] In the manufacturing method of a disk-shaped glass substrate according to the first aspect of the present invention, an overlapping irradiation distance along the outer peripheral edge face from a position where the laser light irradiation starts to a position where the laser light irradiation ends may be equal to or greater than a circumferential length of the outer peripheral edge face of a spot diameter of the laser light on the outer peripheral edge face.

[0009] In the method for producing a disk-shaped glass substrate according to the first aspect of the present invention, the outer circumferential end face after irradiation with the laser light may have a circularity of 15 μm or less.

[0010] In the method for manufacturing a disk-shaped glass substrate according to the first aspect of the present invention, the depth of a recess in the outer peripheral end face radially inward from a position where the laser light irradiation started after the laser light irradiation is terminated may be 15 μm or less.

[0011] In the method for producing a disk-shaped glass substrate according to the first aspect of the present invention, the disk-shaped glass substrate may be a ring-shaped glass substrate having a circular hole in the center.

[0012] According to a second aspect of the present invention, there is provided a method for producing a glass substrate for a magnetic disk, comprising at least polishing a main surface of a disk-shaped glass substrate produced by the method for producing a disk-shaped glass substrate according to the first aspect of the present invention.

[0013] According to a third aspect of the present invention, there is provided a method for producing an annular glass substrate, comprising the steps of: preparing an annular glass plate having a main surface and an outer peripheral end surface and an inner peripheral end surface which are concentric with each other; and irradiating the inner peripheral end face of the annular glass plate with laser light for more than one revolution.

[0014] In the method for manufacturing an annular glass substrate according to the third aspect of the present invention, an overlapping irradiation distance along the inner edge face from a position where irradiation of the laser light starts to a position where irradiation of the laser light ends may be equal to or greater than a circumferential length of the spot diameter of the laser light on the inner edge face in the circumferential direction of the inner edge face.

[0015] In the method for manufacturing an annular glass substrate according to the third aspect of the present invention, the inner circumferential edge surface after irradiation with the laser light may have a circularity of 15 μm or less.

[0016] According to a fourth aspect of the present invention, there is provided a method for manufacturing a glass substrate for a magnetic disk, comprising at least polishing a main surface of the annular glass substrate manufactured by the method for manufacturing an annular glass substrate according to the third aspect of the present invention.

[0017] According to a fifth aspect of the present invention, there is provided a disk-shaped glass substrate, A main surface and an outer peripheral end surface, There is provided a disk-shaped glass substrate, wherein the outer peripheral end surface has at least two regions with different roughnesses in the circumferential direction of the outer peripheral end surface.

[0018] In the disk-shaped glass substrate according to the fifth aspect of the present invention, the at least two regions having different roughnesses may include a low roughness region and a high roughness region, In the circumferential direction of the outer circumferential end face, a length of the low roughness region may be shorter than a length of the high roughness region.

[0019] In the disk-shaped glass substrate according to the fifth aspect of the present invention, the outer peripheral edge face may have a roundness of 15 μm or less.

[0020] According to a sixth aspect of the present invention, there is provided a glass substrate for a magnetic disk, which uses the disk-shaped glass substrate according to the fifth aspect of the present invention.

[0021] According to a seventh aspect of the present invention, there is provided an annular glass substrate, a main surface and an outer peripheral end surface and an inner peripheral end surface that are concentric with each other; There is provided an annular glass substrate, wherein the inner peripheral end surface has at least two regions with different roughnesses in the circumferential direction of the inner peripheral end surface.

[0022] In the ring-shaped glass substrate according to the seventh aspect of the present invention, the at least two regions having different roughness may include a low roughness region and a high roughness region, In the circumferential direction of the inner circumferential end face, a length of the low roughness region may be shorter than a length of the high roughness region.

[0023] In the ring-shaped glass substrate according to the seventh aspect of the present invention, the inner peripheral edge face may have a circularity of 15 μm or less.

[0024] According to an eighth aspect of the present invention, there is provided a glass substrate for a magnetic disk, which uses the annular glass substrate according to the seventh aspect of the present invention. Effect of the Invention

[0025] According to the present invention, it is possible to provide a technique for smoothing an end face and forming a chamfered surface without deteriorating the roundness of the end face of a disk-shaped glass substrate or annular glass substrate. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1A is a perspective view showing an example of a glass substrate manufactured by the manufacturing method of this embodiment, FIG. 1B is a diagram showing an example of the cross-sectional shape of an outer peripheral end face of a glass substrate manufactured by the manufacturing method of this embodiment, and FIG. 1C is a diagram showing an example of the cross-sectional shape of an inner peripheral end face of a glass substrate manufactured by the manufacturing method of this embodiment. [Diagram 2] 1A and 1B are diagrams illustrating an example of a rotation device and a laser irradiation device for performing end face treatment included in the manufacturing method of the present embodiment. [Diagram 3] FIG. 1A is a diagram showing a state where irradiation of the outer peripheral edge face of the glass substrate with laser light has started in an edge treatment using laser light included in the manufacturing method of this embodiment; FIG. 1B is a diagram showing a state where irradiation of the outer peripheral edge face of the glass substrate with laser light has progressed; and FIG. 1C is a diagram showing the state of the outer peripheral edge face of the glass substrate when irradiation of the outer peripheral edge face of the glass substrate with laser light has been completed in one revolution. [Figure 4] 11A and 11B are diagrams showing a state in which the laser light is irradiated along the outer peripheral edge face of the glass substrate for more than one revolution in edge face treatment using the laser light included in the manufacturing method of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] First, a disk-shaped glass substrate manufactured by the manufacturing method of this embodiment will be described with reference to FIGS. 1(a) to 1(c).

[0028] 1(a), the glass substrate 1 is a thin glass substrate having a disk shape. A circular hole concentric with the outer periphery is formed in the center of the disk-shaped glass substrate 1. In other words, the glass substrate 1 can be said to have an annular shape.

[0029] The glass substrate 1 is used, for example, as a substrate for a magnetic disk. The size of the glass substrate 1 is not limited, but is, for example, a size suitable for a magnetic disk having a nominal diameter of 2.5 inches or more (for example, 2.5 inches, 3.5 inches, 5 inches, etc.). In the case of a glass substrate for a magnetic disk having a nominal diameter of 2.5 inches, for example, the outer diameter (diameter) is 55 to 70 mm, the diameter of the center hole (diameter) is 20 mm, and the plate thickness is 0.3 to 0.8 mm. In the case of a glass substrate for a magnetic disk having a nominal diameter of 3.5 inches, for example, the outer diameter is 85 to 100 mm, the diameter of the center hole is 25 mm, and the plate thickness is 0.3 to 0.8 mm.

[0030] The glass substrate 1 has a pair of opposing main surfaces 11a, 11b, an outer peripheral end face 12, and an inner peripheral end face 13 that defines a central hole. The main surface 11a is an annular surface having two concentric circles as its outer and inner edges. The main surface 11b has the same shape as the main surface 11a and is concentric with it. The outer peripheral end face 12 is a surface that connects the outer edge of the main surface 11a to the outer edge of the main surface 11b. The inner peripheral end face 13 is a surface that connects the inner edge of the main surface 11a to the inner edge of the main surface 11b.

[0031] 1(b), the connection portions between the outer peripheral end face 12 and the main surfaces 11a, 11b are each rounded. In other words, the corners formed by the outer peripheral end face 12 and the main surfaces 11a, 11b are each chamfered. As a result, the outer peripheral end face 12 is smoothly curved such that the central portion in the thickness direction of the glass substrate 1 protrudes toward the outside in the radial direction of the glass substrate 1.

[0032] 1(c), the connection portions between the inner peripheral end face 13 and the main surfaces 11a, 11b are each rounded. In other words, the corners formed by the inner peripheral end face 13 and the main surfaces 11a, 11b are each chamfered. As a result, the inner peripheral end face 13 is smoothly curved such that the central portion in the thickness direction of the glass substrate 1 protrudes toward the inside in the radial direction of the glass substrate 1.

[0033] When a magnetic disk is manufactured using the glass substrate 1, at least the main surfaces 11a and 11b are polished, and then magnetic layers are formed on the main surfaces 11a and 11b. If necessary, the main surfaces 11a and 11b may be ground before the polishing.

[0034] Here, in order to reliably hold the outer peripheral end face 12 and the inner peripheral end face 13 of the glass substrate 1 with a jig when forming a magnetic layer on the main surfaces 11a and 11b of the glass substrate 1, it is desirable that the outer peripheral end face 12 and the inner peripheral end face 13 of the glass substrate 1 are aligned to a target shape. Also, in order to accurately incorporate the magnetic disk into an HDD device, it is desirable that the outer peripheral end face 12 and the inner peripheral end face 13 of the glass substrate 1 are aligned to a target shape. Furthermore, in order to prevent fine particles from adhering to the main surfaces and adversely affecting the performance of the magnetic disk, it is desirable that the outer peripheral end face 12 and the inner peripheral end face 13, where particles are likely to be generated, are smooth.

[0035] Therefore, in this embodiment, in order to process the outer peripheral end face 12 into the cross-sectional shape shown in FIG. 1(b) and the inner peripheral end face 13 into the cross-sectional shape shown in FIG. 1(c), end face processing is performed on the glass substrate 1 using laser light.

[0036] Next, a process for separating the disk-shaped glass substrate and a process for treating the edge surface using a laser beam, which are included in the manufacturing method of this embodiment, will be described.

[0037] The process of separating the disk-shaped glass substrate is a process of separating the glass substrate 1 having a disk shape from a sheet-shaped glass plate. Here, as the glass plate, aluminosilicate glass, soda-lime glass, borosilicate glass, etc. can be used. In particular, amorphous aluminosilicate glass can be suitably used in that it can be chemically strengthened as necessary and can produce a glass substrate for a magnetic disk excellent in the flatness of the main surface of the substrate and the strength of the substrate. Such a glass plate may be produced, for example, by using a float method or an overflow downdraw method, or may be produced by press-molding a lump of glass using a mold. As a method of separating the glass substrate 1 having a disk shape from the glass plate, a method of cutting by making a cut line using a well-known scriber, or a method of irradiating a glass plate with a laser beam to form a circular defect and separating the glass plate along the circular defect can be used. After the glass substrate 1 is separated from the sheet-like glass plate, and before edge treatment, the outer peripheral edge face 12 is preferably approximately perpendicular to the main surfaces 11a, 11b, and the inner peripheral edge face 13 is also preferably approximately perpendicular to the main surfaces 11a, 11b. The glass substrate 1 separated from the sheet-like glass plate is an example of a "disk-shaped raw glass plate" and an "annular raw glass plate".

[0038] Next, edge treatment using laser light is performed individually on the outer peripheral edge surface 12 and / or the inner peripheral edge surface 13 of the glass substrate 1 separated from the sheet-like glass plate. In the edge treatment, as shown in Fig. 2, the outer peripheral edge surface 12 and / or the inner peripheral edge surface 13 are irradiated with laser light L from a laser irradiation device 30 while rotating the glass substrate 1 at a constant speed by a rotation device 20. Note that only one of the edge treatment on the outer peripheral edge surface 12 and the edge treatment on the inner peripheral edge surface 13 may be performed. Furthermore, when both are performed, either one may be performed first, or they may be performed simultaneously.

[0039] The rotating device 20 includes a mounting table 21 on which the glass substrate 1 is placed, a rotating shaft 22 connected to the mounting table 21, a rotating motor 23 connected to the rotating shaft 22 and rotating the rotating shaft 22, and a support table 24 supporting the rotating motor 23. The rotating motor 23 rotates the rotating shaft 22 at a constant speed, whereby the mounting table 21 connected to the rotating shaft 22 rotates at a constant speed. The constant speed rotation of the mounting table 21 also rotates the glass substrate 1 placed on the mounting table 21 at a constant speed. The glass substrate 1 is placed on the mounting table 21 such that the center position of the glass substrate 1 approximately coincides with the rotation center position of the rotating shaft 22.

[0040] The laser irradiation device 30 includes a laser light source, an optical system, a focusing lens, etc., and irradiates a part of the outer peripheral end face 12 and a part of the inner peripheral end face 13 with laser light L in order to soften the part of the outer peripheral end face 12 and the part of the inner peripheral end face 13. The type of laser light L is not particularly limited as long as the irradiated parts are softened, but for example, a CO2 laser is preferably used. The oscillation form of the laser light L is not particularly limited, and may be any of continuous wave light (CW light), pulsed wave light, and modulated light of continuous wave light.

[0041] When the laser light L is irradiated to the outer peripheral end face 12, it is preferable to irradiate from the normal direction of the outer peripheral end face 12 as shown by the solid line in FIG. 2, but the range of the inclination angle with respect to the normal direction within 20 degrees is also included in the allowable range. When the laser light L is irradiated to the inner peripheral end face 13, it is preferable to irradiate from the normal direction of the inner peripheral end face 13 by irradiating the laser light L from above the central hole of the glass substrate 1 to a mirror 25 arranged inside the central hole of the glass substrate 1 as shown by the dotted line in FIG. 2, and reflecting the laser light L by the mirror 25. When the laser light is irradiated to the inner peripheral end face 13, the range of the inclination angle with respect to the normal direction within 20 degrees is also included in the allowable range. It is preferable that the spot diameter of the laser light L on the outer peripheral end face 12 is larger in the circumferential direction of the outer peripheral end face 12 than in the thickness direction of the glass substrate 1. In this case, the energy of the laser light L can be efficiently used for chamfering the corners on the main surface 11a side and the corners on the main surface 11b side. The width of the spot diameter in the circumferential direction of the outer peripheral end face 12 is preferably 2 mm or more. The width of the spot diameter in the thickness direction of the glass substrate 1 is preferably larger than the plate thickness of the glass substrate 1, and is preferably 1 mm or more. The corners on the main surface 11a side and the main surface 11b side can be evenly chamfered by irradiating the laser light L so that the luminous flux of the laser light L evenly protrudes on both sides in the thickness direction of the glass substrate 1. If the width of the spot diameter in the thickness direction of the glass substrate 1 is less than 1 mm, it may be difficult to adjust the optical system of the laser irradiation device 30. The spot diameter of the laser light L on the inner peripheral end face 13 is also the same as the spot diameter of the laser light L on the outer peripheral end face 12.

[0042] In this way, by irradiating the outer peripheral end face 12 with the laser beam L to heat it, the outer peripheral end face 12 can be softened and processed into a curved surface protruding radially outward, for example, as shown in Fig. 1(b). Similarly, by irradiating the inner peripheral end face 13 with the laser beam L to heat it, the inner peripheral end face 13 can be softened and processed into a curved surface protruding radially inward, for example, as shown in Fig. 1(c).

[0043] Next, the manner in which the laser light L is irradiated along the outer peripheral end face 12 will be described using the outer peripheral end face 12 as an example. First, the rotation device 20 starts rotating the glass substrate 1. In this embodiment, as shown in FIG. 3(a), the rotation device 20 rotates the glass substrate 1 counterclockwise. Then, when the rotation speed of the glass substrate 1 becomes constant, the irradiation of the laser light L onto the outer peripheral end face 12 is started. Here, as shown in FIG. 3(a), the center position of the irradiation spot when the irradiation of the laser light L onto the outer peripheral end face 12 is started is set as the irradiation start position SP. Then, the laser light L is irradiated onto the outer peripheral end face 12 while rotating the glass substrate 1 at a constant speed counterclockwise by the rotation device 20. For example, when the glass substrate 1 is rotated 180 degrees counterclockwise, the laser light L is irradiated clockwise along a region of half the circumference from the irradiation start position SP to the current irradiation position on the outer peripheral end face 12 as shown in FIG. 3(b). In other words, by rotating the glass substrate 1 by 180 degrees, the irradiation start position SP of the laser light L on the outer peripheral end face 12 moves half a circumference in the counterclockwise direction. Then, by rotating the glass substrate 1 by another 180 degrees, the laser light L is irradiated onto the entire area of ​​one circumference of the outer peripheral end face 12. In other words, by rotating the glass substrate 1 by 360 degrees counterclockwise by the rotation device 20, the irradiation start position SP of the laser light L on the outer peripheral end face 12 moves one circumference in the counterclockwise direction.

[0044] Here, when the irradiation of the laser light L is terminated at the point where the laser light L is irradiated to an area of ​​one circumference of the outer peripheral end face 12, the roundness of the outer peripheral end face 12 may deteriorate (become larger). The inventors have searched for the cause of the deterioration of the roundness of the outer peripheral end face 12, and have found that, as shown in FIG. 3(c), the irradiation start position SP of the laser light L on the outer peripheral end face 12 and its vicinity may be slightly recessed radially inward relative to other areas on the outer peripheral end face 12 to an extent that cannot be recognized by the naked eye. The reason for the slight recession is not necessarily clear, but one of the factors is presumed to be that the heating is insufficient at the irradiation start position SP of the laser light L, and the amount of protrusion radially outward at the irradiation start position SP and its vicinity is smaller than that of other areas. When the glass substrate 1 is used as a substrate for a magnetic disk and the magnetic disk rotates at high speed, the slight recession on the outer peripheral end face 12 of the glass substrate 1 may disturb the flow of air and cause fluttering.

[0045] Therefore, in this embodiment, as shown in FIG. 4, the glass substrate 1 is rotated counterclockwise more than 360 degrees, and the laser light L is irradiated so as to go over one revolution along the outer peripheral end surface 12. In other words, after the movement of the irradiation start position SP of the laser light L on the outer peripheral end surface 12 exceeds one revolution, the irradiation of the laser light L is terminated, and the rotation of the glass substrate 1 by the rotating device 20 is terminated. In other words, the irradiation end position EP, which is the center position of the irradiation spot when the irradiation of the laser light L on the outer peripheral end surface 12 is terminated, is on the area of ​​the outer peripheral end surface 12 that has already been irradiated with the laser light L. As a result, at least the irradiation start position SP is irradiated with the laser light L twice. As a result, the heating shortage at the irradiation start position SP is compensated for, and the amount of protrusion in the radial outward direction at the irradiation start position SP and its vicinity can be made larger than the amount of irradiation with the laser light L once. And the depth of the recess formed at the irradiation start position SP and its vicinity can be made small. In this embodiment, the depth of the recess at the outer peripheral end surface 12 means the depth of the recess in the radial direction of the glass substrate 1. That is, the depth of the recess is equal to the difference between the radius of the reference circle (perfect circle) that is the design target of the outer peripheral end face 12 and the distance from the center of the reference circle to the part of the recess that is closest to the center of the reference circle. The roundness of the outer peripheral end face 12 is defined as the difference between the radii of the inscribed circle and the circumscribed circle of the contour line of the outer peripheral end face 12. The contour line of the outer peripheral end face 12 can be obtained by arranging a plate-shaped probe that is longer than the thickness of the glass substrate 1 so as to face the outer peripheral end face 12 in the thickness direction of the glass substrate 1 and rotating the glass substrate 1 in the circumferential direction. The roundness of the outer peripheral end face 12 can be measured, for example, by a roundness measuring device. Here, the roundness of the outer peripheral end face 12 excluding the above-mentioned recessed portion is sufficiently smaller than the depth of the recess formed at the irradiation start position SP and its vicinity. Therefore, based on the definition of circularity, the depth of the recess formed at the irradiation start position SP and its vicinity essentially represents the circularity of the outer peripheral end face 12, and by reducing the depth of the recess, the circularity of the outer peripheral end face 12 can be made even smaller.By irradiating the laser light L over one revolution along the outer peripheral end face 12, the depth of the recess at the irradiation start position SP of the laser light L and its vicinity is preferably 15 μm or less, and the circularity of the outer peripheral end face 12 is preferably 15 μm or less. In addition, the distance d from the irradiation start position SP to the irradiation end position EP, which is the distance over which the laser light L is irradiated in an overlapping manner along the outer peripheral end face 12, is preferably equal to or greater than the width of the spot diameter of the laser light L on the outer peripheral end face 12 in the circumferential direction of the outer peripheral end face 12.

[0046] Similarly to the outer peripheral end face 12, the inner peripheral end face 13 is irradiated with the laser light L so as to go around the inner peripheral end face 13 more than once, so that the amount of radial inward protrusion at the irradiation start position and its vicinity can be made larger than that in the case of irradiating the laser light L once. The depth of the recess formed at the irradiation start position and its vicinity can be made smaller. In this embodiment, the depth of the recess on the inner peripheral end face 13 means the depth of the recess in the radial direction of the glass substrate 1. That is, the depth of the recess is equal to the difference between the radius of the reference circle (perfect circle) that is the design target of the inner peripheral end face 13 and the distance from the center of the reference circle to the part of the recess that is farthest from the center of the reference circle. The roundness of the inner peripheral end face 13 is defined as the difference between the radii of the inscribed circle and the circumscribed circle of the contour line of the inner peripheral end face 13. The contour line of the inner peripheral end face 13 can be obtained by arranging a plate-shaped probe longer than the thickness of the glass substrate 1 so as to face the inner peripheral end face 13 in the thickness direction of the glass substrate 1, and rotating the glass substrate 1 in the circumferential direction. The roundness of the inner peripheral end face 13 can also be measured by a roundness measuring device, similar to the roundness of the outer peripheral end face 12. Here, the roundness of the inner peripheral end face 13 excluding the above-mentioned recessed portion is sufficiently smaller than the depth of the recess formed at the irradiation start position and its vicinity. Therefore, according to the definition of roundness, the depth of the recess formed at the irradiation start position and its vicinity substantially represents the roundness of the inner peripheral end face 13, and the roundness of the inner peripheral end face 13 can be made smaller by reducing the depth of the recess. In the inner peripheral end face 13, the depth of the recess at the irradiation start position of the laser light L and its vicinity is preferably 15 μm or less, and the roundness of the inner peripheral end face 13 is preferably 15 μm or less. In addition, it is preferable that the distance from the irradiation start position to the irradiation end position, which is the distance over which the laser light L is overlappingly irradiated along the inner end face 13, is greater than or equal to the circumferential width of the spot diameter of the laser light L on the inner end face 13.

[0047] In the manufacturing method of this embodiment, a main surface grinding process, a main surface polishing process, or the like may be performed after the end face processing using the above-mentioned laser light.

[0048] In the main surface grinding process, a double-sided grinding machine equipped with a planetary gear mechanism is used to perform grinding on the main surfaces 11a and 11b of the glass substrate 1. The removal amount by grinding is, for example, about several μm to 100 μm. The double-sided grinding machine has an upper surface plate and a lower surface plate, and the glass substrate 1 is sandwiched between the upper surface plate and the lower surface plate. The glass substrate 1 and each surface plate are moved relatively to each other to grind the main surfaces 11a and 11b. The surface plate may be one on which a fixed abrasive grinding sheet having abrasive grains such as diamond fixed with resin is attached. The main surface grinding process may be omitted.

[0049] In the main surface polishing process, the main surfaces 11a and 11b are polished. The removal amount by polishing is, for example, about 0.1 μm to 50 μm. The purpose of the main surface polishing is to remove scratches and distortions remaining on the main surfaces 11a and 11b due to the previous process, to reduce waviness, microwaviness, and roughness, and to make the main surfaces 11a and 11b mirror-finished. For the main surface polishing, a polishing liquid containing, as free abrasive grains, for example, cerium oxide abrasive grains, zirconia abrasive grains (particle size: about 0.5 to 2 μm at D50), or silica abrasive grains (particle size: about 10 to 100 nm at D50) is used. The main surface polishing process may be performed in two or more stages.

[0050] According to the manufacturing method according to the above-mentioned aspect of the present invention, the outer peripheral end face 12 and the inner peripheral end face 13 can be smoothed by irradiating the outer peripheral end face 12 and the inner peripheral end face 13 with the laser light L. In addition, since the connection portion between the outer peripheral end face 12 and the main surfaces 11a, 11b is chamfered, the outer peripheral end face 12 can be processed into a smoothly curved shape such that the central portion in the thickness direction of the glass substrate 1 protrudes toward the radially outer side of the glass substrate 1. In addition, since the connection portion between the inner peripheral end face 13 and the main surfaces 11a, 11b is chamfered, the inner peripheral end face 13 can be processed into a smoothly curved shape such that the central portion in the thickness direction of the glass substrate 1 protrudes toward the radially inner side of the glass substrate 1.

[0051] According to the manufacturing method according to the above-mentioned aspect of the present invention, the laser light L is irradiated along the outer peripheral end face 12 and the inner peripheral end face 13 of the glass substrate 1 so as to extend more than one revolution. This makes it possible to increase the amount of radially outward protrusion at the irradiation start position on the outer peripheral end face 12 and its vicinity compared to the case where the laser light L is irradiated once. Similarly, it makes it possible to increase the amount of radially inward protrusion at the irradiation start position on the inner peripheral end face 13 and its vicinity compared to the case where the laser light L is irradiated once. As a result, it is possible to make the circularity of the outer peripheral end face 12 and the inner peripheral end face 13 smaller compared to the case where the laser light L is irradiated only one revolution along the outer peripheral end face 12 and the inner peripheral end face 13.

[0052] Example 1 In order to confirm the effect of the end surface treatment using the laser light included in the manufacturing method of this embodiment, the laser light L was irradiated along the outer peripheral end surface 12 of the annular glass substrate 1 while changing the overlap irradiation distance (the distance d from the irradiation start position SP to the irradiation end position EP), and then the roundness of the outer peripheral end surface 12 was measured. The glass substrate 1 used was an annular glass substrate having an outer diameter of 97 mm, an inner diameter of 25 mm, and a thickness of 0.6 mm. A CO2 laser was used as the laser light L, and the power of the laser light L was 50 W and the spot diameter was 2 mm. The rotation speed of the glass substrate 1 (relative speed at the irradiation position) was 20 mm / s. The roundness of the outer peripheral end surface 12 was then measured by a roundness measuring device. The results are shown in Table 1 below.

[0053] [Table 1]

[0054] Example 2 In order to confirm the effect of edge treatment using laser light, which is included in the manufacturing method of this embodiment, laser light L was irradiated along the inner peripheral edge 13 of the annular glass substrate 1 while changing the overlap irradiation distance, and then the roundness of the inner peripheral edge 13 was measured. The glass substrate 1, laser light L, irradiation conditions of the laser light L, and rotation speed of the glass substrate 1 were the same as in Example 1. The roundness of the inner peripheral edge 13 was measured using the same roundness measuring device as in Example 1. The results are shown in Table 2 below.

[0055] [Table 2]

[0056] From the results shown in Table 1 above, it can be seen that the circularity of the outer peripheral end face 12 is smaller when the laser light L is irradiated more than once along the outer peripheral end face 12 (conditions 2 to 6) than when the laser light L is irradiated only once along the outer peripheral end face 12 (condition 1). It can also be seen that the circularity of the outer peripheral end face 12 decreases as the overlapping irradiation distance of the laser light L increases. Furthermore, in the outer peripheral end face 12, the region where the laser light L was irradiated overlappingly had a lower arithmetic mean roughness Ra than the region where the laser light L was irradiated only once. Furthermore, in the circumferential direction of the outer peripheral end face 12, the length of the region where the arithmetic mean roughness Ra was low was shorter than the length of the region where the arithmetic mean roughness Ra was high.

[0057] From the results shown in Table 2 above, it can be seen that the circularity of the inner peripheral end face 13 is smaller when the laser light L is irradiated more than once along the inner peripheral end face 13 (conditions 8 to 12) than when the laser light L is irradiated only once along the inner peripheral end face 13 (condition 7). It can also be seen that the circularity of the inner peripheral end face 13 decreases as the overlapping irradiation distance of the laser light L increases. Also, in the inner peripheral end face 13, the area irradiated with the laser light L in an overlapping manner had a lower arithmetic mean roughness Ra than the area irradiated only once. Also, in the circumferential direction of the inner peripheral end face 13, the length of the area with a low arithmetic mean roughness Ra was shorter than the length of the area with a high arithmetic mean roughness Ra.

[0058] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the claims. Modifications of the above embodiment will be described below.

[0059] In the above embodiment, the rotation direction of the glass substrate 1 by the rotation device 20 is counterclockwise, but the rotation direction of the glass substrate 1 by the rotation device 20 may be clockwise. In this case, the laser light L is irradiated counterclockwise along the outer peripheral end face 12 and the inner peripheral end face 13. In addition, in the above embodiment, the irradiation of the laser light L is started when the rotation speed of the glass substrate 1 becomes constant, but this is not limited thereto, and the irradiation of the laser light L may be started simultaneously with the start of the rotation of the glass substrate 1, or the irradiation of the laser light L may be started before the rotation speed of the glass substrate 1 becomes constant.

[0060] In the above embodiment, the glass substrate 1 is rotated by the rotation device 20 while the laser light L is irradiated from the fixed laser irradiation device 30, but this is not limited thereto. For example, an optical system such as a micromirror device provided in the laser irradiation device 30 may be driven to continuously deflect the light beam, so that the laser light L may be irradiated while moving in the circumferential direction toward the outer peripheral end face 12 and the inner peripheral end face 13 of the glass substrate 1 fixed to the mounting table.

[0061] In the above embodiment, the irradiation of the laser light L onto the outer peripheral end face 12 and the irradiation of the laser light L onto the inner peripheral end face 12 are performed separately using the same laser irradiation device 30, but the irradiation of the inner peripheral end face 13 may be performed after the irradiation of the outer peripheral end face 12 is completed, or the irradiation of the outer peripheral end face 12 may be performed after the irradiation of the inner peripheral end face 13 is completed. Alternatively, the outer peripheral end face 12 and the inner peripheral end face 13 may be simultaneously processed by simultaneously irradiating the outer peripheral end face 12 and the inner peripheral end face 13 with different laser light L from different laser irradiation devices 30.

[0062] In the above embodiment, the glass substrate 1 has an annular shape with a circular hole formed in the center, but the circular hole does not have to be formed in the center. In this case, the glass substrate 1 has only an outer peripheral end surface 12, and the end surface treatment using the laser light is performed only on the outer peripheral end surface 12.

[0063] The glass substrate 1 manufactured by the manufacturing method of the above embodiment is used as a glass substrate for a magnetic disk, but is not limited to this and can be used for any purpose.

[0064] In the above embodiment, the edge surface treatment using the laser light is performed on the edge surface of the disk-shaped glass substrate 1, but the present invention is not limited to this and can also be applied to the edge surface of a disk-shaped metal plate. [Explanation of symbols]

[0065] 1 Glass substrate 11a, 11b Main surface 12 Outer edge 13 Inner periphery end face 20 Rotating device 21 Placement table 22 Rotating shaft 23 Rotational Motor 24 Support stand 30 Laser irradiation device L Laser light SP irradiation start position EP irradiation end position

Claims

1. A method for manufacturing a disk-shaped glass substrate, comprising the steps of: Preparing a disk-shaped raw glass plate having a main surface and an outer peripheral end surface; irradiating the outer peripheral edge surface of the disk-shaped glass substrate with laser light for more than one revolution.

2. 2. The method for manufacturing a disk-shaped glass substrate according to claim 1, wherein an overlapping irradiation distance along the outer peripheral edge surface from a position where the laser light irradiation starts to a position where the laser light irradiation ends is equal to or greater than a length of a spot diameter of the laser light on the outer peripheral edge surface in a circumferential direction of the outer peripheral edge surface.

3. 3. The method for producing a disk-shaped glass substrate according to claim 1, wherein the outer peripheral edge surface after irradiation with the laser beam has a circularity of 15 μm or less.

4. 4. The method for manufacturing a disk-shaped glass substrate according to claim 1, wherein a depth of a recess in a radial direction inward from a start position of the laser beam irradiation is 15 μm or less on the outer peripheral end face after the laser beam irradiation is terminated.

5. 5. The method for producing a disk-shaped glass substrate according to claim 1, wherein the disk-shaped glass substrate is a circular glass substrate having a circular hole in a center portion thereof.

6. A method for producing a glass substrate for a magnetic disk, comprising at least polishing a main surface of a disk-shaped glass substrate produced by the method according to any one of claims 1 to 5.

7. A method for manufacturing an annular glass substrate, comprising the steps of: preparing an annular glass plate having a main surface and an outer peripheral end surface and an inner peripheral end surface which are concentric with each other; irradiating the inner peripheral edge surface of the annular glass plate with laser light so as to travel more than one revolution around the inner peripheral edge surface of the annular glass plate.

8. 8. The method for manufacturing an annular glass substrate as described in claim 7, wherein an overlapping irradiation distance along the inner edge surface from a start position of irradiation of the laser light to a stop position of irradiation of the laser light is equal to or greater than a circumferential length of the spot diameter of the laser light on the inner edge surface in the circumferential direction of the inner edge surface.

9. 9. The method for producing an annular glass substrate according to claim 7, wherein the inner peripheral edge surface after irradiation with the laser light has a circularity of 15 μm or less.

10. A method for producing a glass substrate for a magnetic disk, comprising at least polishing a main surface of the annular glass substrate produced by the production method according to any one of claims 7 to 9.

11. A disk-shaped glass substrate, A main surface and an outer peripheral end surface, The outer peripheral edge surface of the disk-shaped glass substrate has at least two regions with different roughnesses in a circumferential direction of the outer peripheral edge surface.

12. The at least two regions of different roughness include a low roughness region and a high roughness region, The disk-shaped glass substrate according to claim 11 , wherein a length of the low roughness region is shorter than a length of the high roughness region in a circumferential direction of the outer peripheral end face.

13. 13. The disk-shaped glass substrate according to claim 11, wherein the outer peripheral edge face has a roundness of 15 μm or less.

14. A glass substrate for a magnetic disk, comprising the disk-shaped glass substrate according to any one of claims 11 to 13.

15. A circular glass substrate, a main surface and an outer peripheral end surface and an inner peripheral end surface that are concentric with each other; The inner peripheral edge surface of the annular glass substrate has at least two regions with different roughnesses in a circumferential direction of the inner peripheral edge surface.

16. The at least two regions of different roughness include a low roughness region and a high roughness region, The annular glass substrate according to claim 15 , wherein a length of the low roughness region in a circumferential direction of the inner peripheral end face is shorter than a length of the high roughness region.

17. 17. The annular glass substrate according to claim 15, wherein the inner peripheral edge face has a circularity of 15 μm or less.

18. A glass substrate for magnetic disks, comprising the annular glass substrate according to any one of claims 15 to 17.

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