Method for manufacturing glass plate, method for manufacturing glass substrate for magnetic disk, method for manufacturing magnetic disk, and device for processing glass plate

Abstract

The manufacturing method of the glass plate includes irradiating the inner peripheral end surface of the glass plate with a circular ring shape with a laser beam. When the inner peripheral end surface is irradiated with the laser beam, the laser beam is condensed by a condenser lens to become diffuse light, and the diffuse light is irradiated to the inner peripheral end surface from a direction inclined with respect to the main surface of the glass plate.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a glass plate including irradiating the inner peripheral end surface of a ring-shaped glass plate with laser light, a method for manufacturing a glass substrate for a magnetic disk using the method for manufacturing a glass plate, a method for manufacturing a magnetic disk, and a glass plate processing device. Background Art

[0002] A hard disk drive (HDD) device for data recording uses a magnetic disk in which a magnetic layer is provided on a ring-shaped non-magnetic magnetic disk glass substrate.

[0003] When manufacturing a glass substrate for a magnetic disk, the end surface of the annular glass plate constituting the blank plate of the glass substrate for a magnetic disk as a final product is preferably smoothed to prevent fine particles from adhering to the main surface and adversely affecting the magnetic disk performance. In addition, from the perspective of assembling the magnetic disk into the HDD device with high precision, it is preferred to unify the end surface of the glass plate into a target shape so that it is suitable for holding by a fixture that holds the outer peripheral end surface of the glass substrate when a magnetic film is formed on the main surface of the glass substrate.

[0004] As a method for making the end face of a ring-shaped glass plate into a target shape, a method of chamfering the edge of a glass plate using a laser is known. For example, a technology is known that can use a laser to easily and at low cost smooth the inner and outer peripheral end faces of a glass substrate for an information recording medium (Patent Document 1).

[0005] Specifically, when chamfering the inner end surface, a reflector is arranged in the inner hole of the annular glass plate, laser is irradiated toward the reflector from above the main surface of the glass plate, and reflected light of the laser reflected by the reflector is irradiated to the inner end surface.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2002-150546 Summary of the invention

[0009] Problems to be solved by the invention

[0010] However, when the inner peripheral end faces of multiple glass plates are irradiated with laser light using the above-mentioned technology, in order to prevent the glass plates from colliding with the reflector, for example, each time the glass plates are replaced, the reflector needs to be withdrawn from the inner hole or moved to the inner hole of the next glass plate to be processed. In this case, a moving mechanism for moving the reflector is required, and the movement of the reflector also takes time. On the other hand, when the glass plates are moved without moving the reflector, the moving path also becomes complicated. Therefore, the device structure of the laser irradiation device using the reflector becomes complicated, and the productivity is deteriorated.

[0011] Therefore, the object of the present invention is to provide a method for manufacturing a glass plate, a method for manufacturing a glass substrate for a magnetic disk, and a method for manufacturing a magnetic disk, wherein when a glass plate is manufactured by irradiating the inner circumferential end surface of a ring-shaped glass plate with a laser, the laser irradiation can be performed by a simplified device structure.

[0012] Means for solving problems

[0013] One embodiment of the present invention relates to a method for manufacturing a glass plate, including a process of irradiating a laser beam along an inner peripheral end surface corresponding to an inner hole of a ring-shaped glass plate.

[0014] In the above process, when the inner peripheral end face is irradiated with the laser light, the laser light is condensed by a condenser lens to become diffused light, and the diffused light is irradiated to the inner peripheral end face from a direction inclined with respect to the main surface of the glass plate.

[0015] Preferably, through the above treatment, corners between the main surfaces on both sides of the glass plate and the inner peripheral end surface are chamfered.

[0016] The inclination angle of the central axis of the laser beam with respect to the main surface is preferably 20 degrees or less.

[0017] The diffusion angle of the laser light is preferably 20 degrees or less.

[0018] Preferably, through the above treatment, the corners between the main surfaces on both sides of the glass plate and the inner peripheral end surface are chamfered;

[0019] The cross-sectional shape of the inner peripheral end surface whose corner is chamfered is line-symmetrical with respect to a center line passing through the center in the thickness direction of the glass plate and parallel to the main surface.

[0020] The position where the laser light is focused by the focusing lens is preferably located above a plane including the main surface radially outward of a position of the inner peripheral end surface that faces an irradiation position of the laser light on the inner peripheral end surface with the center of the inner hole interposed therebetween.

[0021] The glass plate is preferably a glass substrate serving as a master plate of a glass substrate for a magnetic disk.

[0022] After the irradiation with the laser beam, it is preferred that the main surface of the glass plate be ground or polished without performing a polishing process on the inner peripheral end surface.

[0023] Another aspect of the present invention is a method for producing a glass substrate for a magnetic disk. The method for producing a glass substrate for a magnetic disk is characterized in that after producing a glass plate by the above-mentioned method for producing a glass plate, a main surface of the glass plate is ground or polished to produce the glass substrate for a magnetic disk.

[0024] Still another aspect of the present invention is a method for producing a magnetic disk, characterized in that a magnetic film is formed on a main surface of a glass plate produced by the method for producing a glass substrate for a magnetic disk.

[0025] Still another aspect of the present invention is a glass plate processing apparatus that performs a laser irradiation process along an inner peripheral end surface that corresponds to an inner hole of a ring-shaped glass plate.

[0026] In the above process, when the inner peripheral end face is irradiated with the laser light, the laser light is condensed by a condenser lens to become diffused light, and the diffused light is irradiated to the inner peripheral end face from a direction inclined with respect to the main surface of the glass plate.

[0027] It is preferable that the processing is performed so that corners between the main surfaces on both sides of the glass plate and the inner peripheral end surface are chamfered.

[0028] Effects of the Invention

[0029] According to the above-mentioned glass plate manufacturing method, magnetic disk glass substrate manufacturing method, magnetic disk manufacturing method and glass plate processing device, in a device for manufacturing a glass plate by irradiating the inner circumferential end surface of a ring-shaped glass plate with laser, laser irradiation can be performed with a simplified device structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 (a) is a perspective view of an example of a glass plate manufactured by the method for manufacturing a glass plate according to one embodiment, Figure 1 (b) is a diagram showing an example of the cross-sectional shape of the end face of the glass plate after the chamfered surface is formed. Figure 1 (c) is a diagram showing an example of the cross-sectional shape of the end surface of the glass plate before the chamfered surface is formed.

[0031] Figure 2 This is a diagram for explaining irradiation with laser light performed in a method for producing a glass plate according to one embodiment.

[0032] Figure 3This is a diagram for explaining irradiation with laser light performed in a method for producing a glass plate according to one embodiment.

[0033] Figure 4 The diagram is for explaining irradiation with laser light performed in a method for manufacturing a glass plate using diffused light. DETAILED DESCRIPTION

[0034] Hereinafter, a method for manufacturing a glass plate, a glass plate processing apparatus, a method for manufacturing a magnetic disk glass substrate, and a method for manufacturing a magnetic disk according to an embodiment will be described in detail.

[0035] The glass plate manufactured by the manufacturing method of the glass plate of one embodiment is used as a glass substrate for a magnetic disk, for example, because the end surface of the annular glass plate is chamfered. Figure 1 (a) is a perspective view of an example of a ring-shaped glass plate manufactured by a method for manufacturing a glass plate according to an embodiment. The ring-shaped glass plate is a glass plate having a circular outer circumference. In addition, the ring-shaped glass plate has an inner hole that is concentric with the circle and has an inner circumference. In addition, the ring-shaped glass plate has a pair of main surfaces.

[0036] Figure 1 The glass plate 1 shown in (a) can be used as a glass substrate for a magnetic disk. When the glass plate 1 is used as a glass substrate for a magnetic disk, the size of the magnetic disk glass substrate is not limited, for example, the size of the magnetic disk glass substrate with a nominal diameter of 2.5 inches or 3.5 inches. In the case of a magnetic disk glass substrate with a nominal diameter of 2.5 inches, the outer diameter (diameter) is 55 to 70 mm, for example, the outer diameter is 65 mm or 67 mm, the inner hole diameter (diameter) is 20 mm, and the plate thickness is 0.3 to 1.3 mm. In the case of a magnetic disk glass substrate with a nominal diameter of 3.5 inches, the outer diameter is 85 to 100 mm, for example, the outer diameter is 95 mm, 96 mm or 97 mm, the inner hole diameter is 25 mm, and the plate thickness is 0.3 to 1.3 mm.

[0037] Figure 1 In the glass plate 1 shown in (a), the corner between the end face (inner peripheral end face and / or outer peripheral end face) and the main surface is chamfered by the shape processing of the end face to form a chamfered surface (or chamfered portion). It should be noted that in the present invention, as described below, even if the chamfered area, i.e., the chamfered portion, is not a flat surface, the chamfered portion is also referred to as a chamfered surface. Figure 1 (b) is a diagram showing an example of the cross-sectional shape of the entire end surface with chamfered corners according to the present invention. The end surface with two chamfered corners has two chamfered surfaces 5. The cross-sectional shape is the shape of the glass plate 1 passing through the center of the annular shape of the glass plate 1 and along the radial direction and the plate thickness direction. Figure 1As shown in (b), the cross-sectional shape of the chamfered surface 5 is a curved surface shape consisting of a smooth curve convex outward in the surface of the glass plate. Figure 1 As shown in the example shown in (b), the chamfered surfaces 5 connected to the two main surfaces and the side wall surface 6 between the two chamfered surfaces 5 can form a curved surface as a whole. Figure 1 In other examples of the cross-sectional shape shown in (b), the chamfered surfaces connected to the two main surfaces can be formed by two curved shapes, and the side wall surface between the two chamfered surfaces can be formed by a straight line shape orthogonal to the main surface or a curved curve shape other than the chamfered surface. The chamfer length in the radial direction of the glass plate 1 after the chamfering process is defined as the difference between the radius of the most protruding position of the end surface in the radial direction and the radius of the position where the main surface starts to tilt toward the end surface, and can be, for example, 30 to 200 μm.

[0038] In the case of a glass substrate for a magnetic disk, after grinding and / or polishing the main surface of the glass plate 1 as necessary, a magnetic film is formed on the main surface of the glass plate 1 to produce a magnetic disk.

[0039] Figure 1 (c) is a diagram showing an example of the cross-sectional shape of the inner peripheral end face 7 of a glass plate (hereinafter also referred to as a glass blank) before the chamfered surface is formed. By irradiating the inner peripheral end face 7 with a laser beam described later, the corner of the boundary between the main surface of the glass blank and the inner peripheral end face 7 is heated to a temperature above the softening point and partially melted, for example Figure 1 (b) is a curved surface, thereby performing chamfering. The inner peripheral end surface 7 of the glass blank before the chamfering is formed is a surface substantially perpendicular to the main surface of the glass blank. The outer peripheral end surface also has a surface substantially perpendicular to the main surface of the glass blank like the inner peripheral end surface 7. By irradiating such a surface with a laser described later, the corner between the main surface and the inner peripheral end surface 7 can be chamfered, for example, Figure 1 (b) shows the chamfered surface 5. It should be noted that, Figure 1 The cross-sectional shape of the inner peripheral end face 7 shown in (c) is an example and is not limited to a shape that is substantially orthogonal to the main surface. It may also be a shape with slightly rounded corners or a shape that is inclined relative to the main surface. However, if the cross-sectional shape of the inner peripheral end face 7 is linearly symmetrical with respect to a center line that passes through the center of the thickness in the thickness direction of the glass blank plate and is parallel to the main surface before the chamfered surface 5 is formed (described later), then the cross-sectional shape of the inner peripheral end face after laser irradiation, that is, the inner peripheral end face after the chamfered surface 5 is formed, is also likely to be linearly symmetrical, which is preferred.

[0040] Figure 2 and Figure 31 is a diagram for explaining the irradiation of laser light in a method for manufacturing a glass plate 1 according to an embodiment. By irradiating with laser light L, a chamfered surface 5 can be formed on the inner peripheral end surface 7, and the surface roughness of the inner peripheral end surface 7 or the chamfered surface 5 can be reduced. The surface roughness of the inner peripheral end surface (chamfered surface 5 and / or side wall surface 6) after irradiation with laser light L is 50 nm or less in terms of arithmetic mean roughness Ra (JIS B0601 2001) and / or 500 nm or less in terms of maximum height Rz (JIS B0601 2001). The surface roughness can be measured, for example, by a laser microscope.

[0041] like Figure 2 and Figure 3 As shown in FIG. 1 , when the laser light L is irradiated onto the inner peripheral end surface 7 along the inner hole 3 of the annular glass plate (i.e., the annular glass blank plate 2) before laser irradiation, the laser light L is irradiated onto the inner peripheral end surface 7 in such a manner that the laser light L moves relative to the inner peripheral end surface 7 along the circumferential direction of the glass blank plate 2. In other words, at this time, the laser light L is changed from the focused light L1 to the diffused light L2 by passing through the focusing position 12 of the focusing lens 10, and the diffused light L2 is irradiated onto the inner peripheral end surface 7 from a direction inclined with respect to the main surface of the glass blank plate 2. That is, at Figure 2 , Figure 3 In the embodiment shown, the laser light L is condensed by the condenser lens 10 to become the diffused light L2, and the diffused light L2 is irradiated to the inner peripheral end surface 7 from a direction inclined relative to the main surface. Irradiating the diffused light L2 from a direction inclined relative to the main surface means irradiating the diffused light L2 with the central axis of the light beam inclined relative to the main surface. Figure 2 , Figure 3 In the embodiment shown, laser light L focused by focusing lens 10 passes through focusing position (focus) 12 and becomes diffused light L2, and then irradiates inner peripheral end surface 7. It is noted that the laser light L may be focused and diffused at least in the thickness direction of the glass blank.

[0042] The light beam of the diffused light L2 is small near the focusing position 12. If the light beam is large, the portion of the glass blank plate 2 that faces the irradiation position 14 of the laser light L on the inner peripheral end face 7 with the center of the annular glass blank plate 2 sandwiched therebetween becomes an obstacle to the optical path, causing light to be scattered, or even if the light passes through the facing portion, the light intensity of the transmitted light is reduced, making it difficult to form the chamfered surface 5, or it is impossible to ensure light intensity to the extent that the cross-sectional shape of the inner peripheral end face becomes a line-symmetrical shape.

[0043] In this embodiment, by intentionally using the diffused light L2 after passing through the focusing position 12, it is possible to reduce the light beam near the portion (position A described later) that is likely to become an obstacle of the glass blank plate 2. As a result, the laser light L is easy to avoid the portion that is likely to become an obstacle of the glass blank plate 2. Therefore, the inclination angle of the diffused light L2 with respect to the main surface of the glass blank plate 2 can be reduced.

[0044] Furthermore, by reducing the inclination angle with respect to the main surface of the glass blank plate 2 and irradiating the diffuse light L2, the temperature of the corners on both sides of the thickness direction of the inner peripheral end surface 7 at the focusing position 12 is approximately close to the same temperature during irradiation. Therefore, it is easy to make the cross-sectional shape of the inner peripheral end surface a line-symmetrical shape and a target shape. That is, the cross-sectional shape of the inner peripheral end surface can be made line-symmetrical with respect to the center line passing through the center of the thickness direction of the glass plate 1 and parallel to the main surface.

[0045] Here, the line-symmetric shape means that when the contour line of the cross-sectional shape is folded back with respect to the center line passing through the middle of the glass plate 1 in the thickness direction and parallel to the main surface, the maximum deviation of the contour lines of the end surfaces at each position in the thickness direction in the direction parallel to the main surface is 30 [μm] or less. The maximum deviation is more preferably 20 [μm] or less. If the maximum deviation is greater than 30 [μm], the posture of the glass plate 1 is unstable when the inner hole 3 is maintained in a film forming device for forming a magnetic film or the like that functions as a magnetic disk, and an accident of breaking or falling of the glass plate 1 is likely to occur. In addition, with respect to the cross-sectional shape of the inner peripheral end surface of the glass blank plate 2, the line-symmetric shape means that the above-mentioned maximum deviation is 30 [μm] or less when the glass blank plate 2 is used instead of the glass plate 1.

[0046] It should be noted that, in order to prevent the portion 20 of the irradiation position 14 of the inner peripheral end surface 7 sandwiching the center of the inner hole 3 from becoming an obstacle to the optical path, the focusing position 12 is preferably set in an area centered above the position of the inner peripheral end surface 7 sandwiching the center of the inner hole 3 and the irradiation position 14 of the diffuse light L2 on the inner peripheral end surface 7 (hereinafter also referred to as "position A"). The focusing position 12 can take into account the specifications of the laser L (inclination angle θ, diffusion angle Various adjustments are made to the thickness of the glass blank plate 2 and the diameter of the inner hole 3, etc. In addition, the focusing position 12 is preferably set above the plane including the main surface which is located radially outward from the position A. In this way, the effect of fully expanding the beam area (spot diameter) of the diffused light L2 at the irradiation position 14 can also be obtained. In other words, the focusing position 12 is preferably separated from the above-mentioned position A in the radial direction outward by a distance greater than 0 mm when viewed from above. The distance is more preferably 10 mm or more, and further preferably 20 mm or more. Regarding the distance, the upper limit does not need to be particularly set, and in order to avoid the enlargement of the device, it can be set to 300 mm or less, for example. It should be noted that in this specification, viewing from above refers to viewing from a direction perpendicular to the main surface of the glass plate.

[0047] The laser light L can be emitted from a laser oscillator (not shown). In order to move the laser light L (diffused light L2) relative to the inner peripheral end surface 7 in the circumferential direction of the glass blank 2, for example, a method can be used in which the center of the annular shape of the glass blank 2 is aligned with the rotation center of a turntable (not shown) and fixed, and the glass blank 2 is rotated. For example, the laser light L can be irradiated to the inner peripheral end surface 7 of the glass blank 2 rotating with the turntable, so that the laser light is scanned along the inner peripheral end surface 7 of the glass blank 2. The relative movement speed between the laser light L and the inner peripheral end surface 7 of the glass blank 2 can be, for example, 0.7 to 100 [mm / sec].

[0048] As the laser L, for example, a CO2 laser can be used. The wavelength of the CO2 laser is preferably 3 μm or more. It should be noted that the laser L may be a laser other than the CO2 laser, such as a CO laser (oscillation wavelength of about 5 μm or about 10.6 μm), an Er-YAG laser (oscillation wavelength of about 2.94 μm), etc., as long as the oscillation wavelength is absorbed by glass.

[0049] The size and shape of the beam (irradiation spot) of the laser light L at the irradiation position on the inner peripheral end surface 7 may be, for example, a circle with a diameter of 1 to 10 mm, or an ellipse with an area equivalent thereto. The size and shape of the irradiation spot may be appropriately selected according to the thickness of the glass blank plate 2 to be chamfered, but in order to make the cross-sectional shape of the inner peripheral end surface 7 linearly symmetrical, it is preferably a size larger than the thickness of the glass blank plate 2 in the thickness direction.

[0050] The average power density of the beam at the irradiation position of the laser light L is, for example, 1 to 30 [W / mm 2 The average power density is the total power [W] of the laser L divided by the area [mm2] of the beam on the surface including the portion of the inner peripheral end surface 7 irradiated by the laser L. 2] (that is, when a part of the light beam overflows from the inner peripheral end surface 7, the area of ​​the overflowing part is also included). The total power of the laser light L may be, for example, 10 to 300 [W].

[0051] When the diffused light L2 is irradiated onto the inner peripheral end surface 7, it is preferred that the laser light L be irradiated so that the central axis of the light beam of the diffused light L2 passes above the center of the annular shape of the glass blank plate 2 (a position above the glass blank plate 2 on the central axis of the glass blank plate 2 perpendicular to the main surface). By doing so, the incident angle of the laser light L onto the inner peripheral end surface 7 becomes close to vertical, so that the energy loss due to the reflection of the laser light L can be suppressed to a minimum, thereby effectively forming the chamfered surface 5.

[0052] In addition, it is preferable to heat the glass blank plate 2 before and / or during the irradiation of the laser light L. By doing so, it is possible to reduce the residual strain generated near the inner peripheral end surface after the chamfering process by the laser light L. As a heating method, for example, a heater is arranged around the glass blank plate 2 to increase the temperature of the entire glass blank plate 2. As the heater, for example, an infrared heater such as a halogen lamp heater, a carbon heater, or a sheathed heater can be used.

[0053] By irradiating the inner peripheral end surface 7 with the diffused light L2 of the laser light L that has passed through the focusing position 12, it is not necessary to arrange a reflecting mirror in the inner hole 3 as in the prior art. Therefore, the conveying paths of the glass blank 2 and the glass plate 1 are not restricted, and the device configuration can be simplified.

[0054] Figure 4 This is a diagram for explaining irradiation with laser light performed in a method for manufacturing a glass plate 1 using a method different from the present invention. Figure 4 This is an example of irradiating the inner peripheral end face 7 with the convergent light L1. As the convergent light L1 moves away from the irradiation position 14 of the inner peripheral end face 7, the light beam spreads more, so that the opposing portion 20 of the glass blank plate 2 opposing the irradiation position 14 of the laser light L on the inner peripheral end face 7 becomes an obstacle, and part of the light is scattered, or even if the light is transmitted, the intensity of the transmitted light is reduced, making it difficult to form the chamfered surface 5, or it is impossible to ensure the light intensity to the extent that the cross-sectional shape of the inner peripheral end face becomes a line-symmetrical shape.

[0055] The inclination angle θ of the central axis of the light beam of the diffused light L2 (laser light) relative to the main surface (see Figure 3), as described above, in order to make the cross-sectional shape of the inner peripheral end face a line-symmetrical shape, the inclination angle θ is preferably small, specifically, preferably 20 degrees or less, more preferably 15 degrees or less, and even more preferably 10 degrees or less. In addition, it is preferred that the diffused light L2 is irradiated only from one main surface side of the glass blank 2 from a direction inclined relative to the main surface. In this case, the glass blank 2 can be firmly fixed from the other main surface side opposite to the one main surface, and the positional deviation of the glass blank 2 can be suppressed. As a result, precise shape control can be performed, so it is easy to make the inner peripheral end face the above-mentioned line-symmetrical shape throughout the entire inner peripheral end face. In addition, the device configuration can be greatly simplified. The minimum value of the inclination angle θ is not particularly limited, for example, it is preferably 1 degree or more. If the inclination angle θ is less than 1 degree, it may be difficult to adjust the optical system during mass production.

[0056] In addition, the diffusion angle of the laser light L (Refer to Figure 4 . Indicating the narrowing or widening angle of the light beam when focusing or diffusing), from the perspective of easily reducing the above-mentioned tilt angle θ, it is preferably less than 20 degrees, more preferably less than 10 degrees, and further preferably less than 5 degrees in full angle. In addition, the diffusion angle The smaller the angle, the easier it is to position the laser oscillator and / or optical system components such as lenses farther from the glass blank 2 to be processed. This has the advantage of increasing the degree of freedom in designing auxiliary devices such as loading / unloading the glass blank 2 in the laser irradiation device. The minimum value of is not particularly limited, but is preferably 0.5 degrees or more in full angle. If it is less than 0.5 degrees, the device may become larger.

[0057] The manufacturing method of the glass blank plate 2 to be irradiated with the laser light L is not particularly limited, and the glass blank plate 2 may be manufactured by, for example, a float process, a down-draw process, or a press process. A plurality of disc-shaped glass plates having inner holes may be taken out from a wide sheet-shaped glass plate manufactured by a float process or a down-draw process. The method of taking out the disc-shaped glass plate from the wide sheet-shaped glass plate may be performed by cutting with a known marker, or by irradiating the glass plate with laser light to form a circular defect and cut into a ring shape.

[0058] A glass plate processing device according to one embodiment is configured to perform the above-mentioned glass plate manufacturing method. The glass plate processing device includes a laser irradiation device. The laser irradiation device includes a laser oscillator and an optical system component. The optical system component includes a lens including a focusing lens 10, etc. In addition, the glass plate processing device may include a holding portion for holding a glass blank plate by fixing or placing the glass blank plate, and a rotating mechanism for rotating the holding portion. In addition, the glass plate processing device may include a rotating table in which the functions of the holding portion and the rotating mechanism are integrated.

[0059] When manufacturing a glass substrate for a magnetic disk from the glass plate 1 on which the chamfered surface 5 is formed, various treatments described below are performed so that the glass substrate has characteristics suitable for a magnetic disk as a final product.

[0060] The glass plate 1 is subjected to grinding and polishing treatment on the main surface.

[0061] In the grinding and polishing process, grinding and / or polishing are performed on the glass plate 1. When both are performed, polishing is performed after grinding.

[0062] In the grinding process, a pair of main surfaces of the glass plate 1 are ground using a double-sided grinding device equipped with a planetary gear mechanism. Specifically, the outer peripheral end surface of the glass plate 1 is held in a holding hole of a holding member (grinding carrier) provided in the double-sided grinding device, while the main surfaces on both sides of the glass plate 1 are ground. The double-sided grinding device has a pair of upper and lower fixed plates (an upper fixed plate and a lower fixed plate), and the glass plate 1 is clamped between the upper fixed plate and the lower fixed plate. Afterwards, one or both of the upper fixed plate or the lower fixed plate are moved, and the glass plate 1 and each fixed plate are moved relative to each other while supplying a cooling liquid, thereby grinding the two main surfaces of the glass plate 1. For example, a fixed abrasive made of diamond particles fixed with a resin can be formed into a sheet-shaped grinding member and mounted on the fixed plate for grinding.

[0063] Next, the first grinding is performed on the pair of main surfaces of the ground glass plate 1. Specifically, the main surfaces on both sides of the glass plate 1 are ground while the outer peripheral end surface of the glass plate 1 is held in the holding hole of the grinding carrier provided in the double-side grinding device. The purpose of the first grinding is to remove the flaws or deformations remaining on the main surfaces after the grinding process, or to adjust the minute surface irregularities (microscopic waviness, roughness).

[0064] In the first grinding process, a double-sided grinding device having the same structure as the double-sided grinding device used in the above-mentioned grinding process based on fixed abrasives is used to grind the glass plate 1 while applying grinding slurry. In the first grinding process, a grinding slurry containing free abrasives is used. As the free abrasives used in the first grinding, abrasives such as cerium oxide or zirconium oxide are used. The double-sided grinding device also clamps the glass plate 1 between a pair of upper and lower fixed plates in the same manner as the double-sided grinding device. A grinding pad (such as a resin polisher) that is a flat plate in an overall annular shape is installed on the upper surface of the lower fixed plate and the bottom surface of the upper fixed plate. Thereafter, one or both of the upper fixed plate or the lower fixed plate are moved, thereby causing the glass plate 1 to move relative to each fixed plate, thereby grinding the two main surfaces of the glass plate 1. The size of the grinding abrasive is preferably in the range of 0.5 to 3 μm in terms of average particle size (D50).

[0065] After the first grinding, the glass plate 1 may be chemically strengthened. In this case, a mixed molten solution of potassium nitrate and sodium nitrate is used as a chemical strengthening solution, and the glass plate 1 is immersed in the chemical strengthening solution. Thus, a compressive stress layer can be formed on the surface of the glass plate 1 by ion exchange.

[0066] Next, the glass plate 1 is subjected to a second grinding. The purpose of the second grinding treatment is to mirror-grind the main surface. In the second grinding, a double-sided grinding device having the same structure as the double-sided grinding device used in the first grinding is also used. Specifically, while the outer peripheral end surface of the glass plate 1 is held in the holding hole of the grinding carrier provided in the double-sided grinding device, the main surfaces on both sides of the glass plate 1 are ground. In the second grinding treatment, the type and particle size of the free abrasive particles are different from those in the first grinding treatment, and the hardness of the resin polisher is different. The hardness of the resin polisher is preferably smaller than that in the first grinding treatment. For example, a grinding liquid containing colloidal silica as free abrasive particles is supplied between the grinding pad of the double-sided grinding device and the main surface of the glass plate 1, and the main surface of the glass plate 1 is ground. The size of the grinding abrasive particles used in the second grinding is preferably within the range of 5 to 50 nm in terms of the average particle size (d50). The roughness of the pair of main surfaces of the glass plate 1 after the second grinding is preferably 0.2 nm or less in terms of the arithmetic mean roughness Ra (JIS B0601 2001). The surface roughness can be measured by, for example, AFM.

[0067] Whether to perform chemical strengthening treatment can be appropriately selected by considering glass composition and necessity. In addition to the first grinding treatment and the second grinding treatment, other grinding treatments can be further applied, and one grinding treatment can also be used to complete the grinding treatment of two main surfaces. In addition, the order of the above-mentioned treatments can be appropriately changed.

[0068] In this way, after manufacturing a glass plate 1 having a chamfered surface 5 formed on the end face by irradiating the end face with the above-mentioned laser L (diffused light L2), the main surface of the glass plate 1 is ground or polished, thereby manufacturing a glass substrate for a magnetic disk that meets the conditions required for a glass substrate for a magnetic disk.

[0069] Thereafter, a magnetic disk is manufactured by forming at least a magnetic film on the main surface of the magnetic disk glass substrate.

[0070] Note that after the chamfered surface 5 is formed by irradiating the end surface with the laser light L (diffused light L2 ), end surface grinding of grinding the end surface (inner peripheral end surface and / or outer peripheral end surface) of the glass plate 1 may be performed.

[0071] Even when such end surface grinding is performed, the arithmetic mean roughness Ra of the end surface of the glass plate 1 having the chamfered surface 5 formed by irradiation with the laser light L can be made less than 50 nm and / or Rz can be made less than 500 nm, so the time required for end surface grinding can be shortened.

[0072] The end face grinding can be performed using a grinding brush method in which free abrasive particles are supplied to the end face while grinding with a grinding brush. However, in order to improve production efficiency, it is preferred to grind or polish the main surface of the glass plate 1 without performing end face grinding. That is, it is preferred to maintain the surface roughness of the end face of the glass plate 1 at the surface roughness of the end face obtained by irradiation with the laser L, and grind or polish the main surface of the glass plate 1 in this state. It should be noted that since the surface roughness of the end face formed by irradiation with the laser L performed in this embodiment is small, the formation of the chamfered surface 5 can sometimes be said to serve as end face grinding. In this case, the above-mentioned end face grinding refers to additional end face grinding other than the end face grinding performed simultaneously in the formation of the chamfered surface 5.

[0073] It should be noted that the additional end face grinding is preferably carried out before the first grinding. If the additional end face grinding is carried out after the first grinding, the main surface after grinding may be flawed sometimes. In addition, the additional end face grinding may be carried out before or after the grinding process of the main surface.

[0074] As the glass material of the glass plate 1 and the glass blank plate 2 serving as the mother plate thereof, amorphous glass such as aluminosilicate glass, soda-lime glass, borosilicate glass, etc. can be used. In particular, from the perspective of being able to produce a magnetic disk glass substrate having excellent flatness of the main surface and substrate strength, the glass material is preferably amorphous glass. In addition, in order to withstand heating during the formation of the magnetic film, the glass transition temperature Tg of the glass plate 1 and the glass blank plate 2 is preferably 450 to 850°C.

[0075] (Experimental Example 1)

[0076] When the irradiation conditions of the laser light L onto the inner peripheral end surface of the annular glass blank plate were variously changed, it was confirmed by simulation whether the light beam was blocked by the glass blank plate.

[0077] (Simulation conditions)

[0078] The shape of the circular glass blank plate is: outer diameter 97mm, inner diameter 25mm, thickness 1mm, and the cross section of the inner peripheral end surface is the same as above. Figure 1 The cross-sectional shape shown in (c) is the same shape

[0079] · Adjust the laser's tilt angle θ and diffusion angle The irradiation spot diameter (diameter), irradiation method (convergent light or diffuse light), and distance from irradiation position 14 to focusing position 12 (distance when viewed from above) were changed in various ways as shown in Table 1, assuming that the inner peripheral end surface of the above-mentioned glass blank plate was irradiated. It should be noted that, in order to simplify the calculation, the irradiation spot diameter was set to the maximum length of the cross section of the light beam in the plate thickness direction of the glass plate at the irradiation position of the inner peripheral end surface (that is, not the length obtained by the cross section perpendicular to the central axis of the laser L inclined at an angle θ). In addition, the center of the irradiation spot diameter coincides with the center of the plate thickness of the inner peripheral end surface.

[0080] Evaluation results: Even if the light beam is small, the case where the glass blank is blocked is recorded as BAD (i.e. Figure 4 The case of no occlusion is recorded as GOOD (i.e. Figure 3 situation).

[0081] [Table 1]

[0082]

[0083] As can be seen from Table 1, even in a case where the light beam is blocked under the conventional condition of using convergent light, laser irradiation can be performed without blocking the light beam by using diffused light.

[0084] When the distance from the irradiation position to the focusing position is greater than 25 mm, the position of the focal point in a plan view is located radially outward from the inner diameter end of the glass blank. That is, it is located radially outward from the above-mentioned "position A". In this case, it is easy to position optical system components such as a laser oscillator and / or a lens relatively far from the glass blank as a processing object. As a result, for example, the degree of freedom in designing an auxiliary device for loading / unloading a glass blank in a laser irradiation device is increased, which is preferred.

[0085] (Experimental Example 2)

[0086] The inner peripheral end surface of the glass blank plate was actually chamfered using conditions 10, 12, and 14 in Table 1. The shape of the annular glass blank plate was the same as that of Experimental Example 1 except that the thickness was changed to 0.7 mm. Amorphous aluminosilicate glass with a glass transition point of about 500°C was used as the material of the glass blank plate. CO2 laser was used as the laser L. The entire main surface of the glass blank plate 2 was heated using an infrared heater before irradiation with the laser L. Other conditions and methods for irradiation were appropriately adjusted with reference to the above-mentioned embodiment so that the inner peripheral end surface after chamfering had the same shape as that of the glass blank plate. Figure 1 (b) Same cross-sectional shape.

[0087] As a result, under any condition, the inner peripheral end surface of the obtained glass plate has Figure 1 (b) The same cross-sectional shape is formed with a chamfered surface. In addition, the surface roughness of these inner peripheral end faces is less than 50 nm in terms of arithmetic average roughness Ra (measured using a laser microscope). In addition, the shape is linearly symmetrical with respect to a center line passing through the center of the thickness direction of the glass plate and parallel to the above-mentioned main surface.

[0088] The above describes in detail the method for manufacturing a glass plate, the method for manufacturing a glass substrate for a magnetic disk, the method for manufacturing a magnetic disk, and the glass plate processing device of the present invention, but the present invention is not limited to the above-mentioned embodiments, and various improvements and changes can be made without departing from the scope of the present invention.

[0089] Explanation of symbols

[0090] 1 Glass Pane

[0091] 2 Glass blanks

[0092] 3 inner hole

[0093] 5 Chamfered faces

[0094] 6 Side wall

[0095] 7 Inner peripheral end face

[0096] 10 Condenser lens

[0097] 12 Spotlight Position

[0098] 14 Irradiation position

[0099] 20 Opposing part

Claims

1. A method for manufacturing a glass plate, comprising irradiating a glass plate with a laser beam along an inner peripheral end surface of a glass plate having an inner hole corresponding to the inner hole, wherein: In the process, when the laser is irradiated to the inner peripheral end surface, the laser is condensed by a condenser lens to become diffused light, and the diffused light is irradiated to the inner peripheral end surface from a direction inclined with respect to the main surface of the glass plate. The position where the laser light is focused by the focusing lens is located above a plane including the main surface and radially outward from a position of the inner peripheral end surface that faces an irradiation position of the laser light on the inner peripheral end surface with the center of the inner hole interposed therebetween.

2. The method for manufacturing a glass plate according to claim 1, wherein: The central axis of the laser light has an inclination angle of 20 degrees or less with respect to the main surface.

3. The method for manufacturing a glass plate according to claim 1, wherein: The diffusion angle of the laser light is less than 20 degrees.

4. The method for manufacturing a glass plate according to claim 2, wherein: The diffusion angle of the laser light is less than 20 degrees.

5. The method for producing a glass plate according to any one of claims 1 to 4, wherein: By the treatment, the corners between the main surfaces and the inner peripheral end surfaces on both sides of the glass plate are chamfered. The cross-sectional shape of the inner peripheral end surface whose corner is chamfered is line-symmetrical with respect to a center line passing through the center in the thickness direction of the glass plate and parallel to the main surface.

6. The method for producing a glass plate according to any one of claims 1 to 4, wherein: The glass plate is a glass substrate serving as a master plate of a glass substrate for a magnetic disk.

7. The method for producing a glass plate according to any one of claims 1 to 4, wherein: After the irradiation with the laser beam, the main surface of the glass plate is ground or polished without performing a polishing process on the inner peripheral end surface.

8. The method for manufacturing a glass plate according to claim 5, wherein: After the irradiation with the laser beam, the main surface of the glass plate is ground or polished without performing a polishing process on the inner peripheral end surface.

9. A method for manufacturing a glass substrate for a magnetic disk, characterized in that: The magnetic disk glass substrate is manufactured by grinding or polishing the main surface of the glass plate after manufacturing a glass plate by the manufacturing method of a glass plate according to any one of claims 1 to 6.

10. A method for manufacturing a magnetic disk, characterized in that: A magnetic film is formed on the main surface of the glass plate manufactured by the method for manufacturing a magnetic disk glass substrate according to claim 9 .

11. A glass plate processing device for irradiating a glass plate with an inner hole with a laser beam along an inner peripheral end surface corresponding to the inner hole of the glass plate, characterized in that: In the process, when the laser is irradiated to the inner peripheral end surface, the laser is condensed by a condenser lens to become diffused light, and the diffused light is irradiated to the inner peripheral end surface from a direction inclined with respect to the main surface of the glass plate. The position where the laser light is focused by the focusing lens is located above a plane including the main surface and radially outward from a position of the inner peripheral end surface that faces an irradiation position of the laser light on the inner peripheral end surface with the center of the inner hole interposed therebetween.

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