Glass plate and method for manufacturing glass substrate for magnetic disk

Abstract

The invention relates to a glass plate and a method for manufacturing a glass substrate for a magnetic disk. In order to suppress strain (retardation value) in the main surface of a disc-shaped glass plate during shape processing of the end surface of the disc-shaped glass plate by a laser, the disc-shaped glass plate is suspended from a base, and while the glass plate is suspended, the glass plate is heated in a non-contact manner, and the end surface of the disc-shaped glass plate is shaped. And processing the end surface into a target shape while irradiating the end surface of the glass plate with laser light and moving the laser light relative to the end surface in the circumferential direction of the disc-shaped glass plate.

Description

[0001] This application is a divisional application. The Chinese national application number of the original application is 202080042072.6, the application date is June 29, 2020, and the name of the invention is “Method for manufacturing glass plate and method for manufacturing magnetic disk”. Technical Field

[0002] The present invention relates to a method for manufacturing a glass plate including subjecting an end surface of a disk-shaped glass plate to a shape processing, and a method for manufacturing a magnetic disk using the method for manufacturing a glass plate. Background Art

[0003] A hard disk device for data recording uses a magnetic disk having a magnetic layer provided on a disk-shaped nonmagnetic glass substrate for a magnetic disk.

[0004] When manufacturing a glass substrate for a magnetic disk, the end surface of a disk-shaped glass blank plate, which is the basis of the final product, i.e., the glass substrate for a magnetic disk, is preferably smoothed in order to prevent fine particles from adhering to the main surface and adversely affecting the performance of the magnetic disk. In addition, from the perspective of assembling the magnetic disk into the HDD device with good accuracy, it is further preferred to unify the end surface of the glass plate into a target shape so that it is suitable for the grip of a jig that grips the outer peripheral end surface of the glass substrate when a magnetic film is formed on the main surface of the glass substrate.

[0005] As a method for making the end face of a glass plate have a target shape, a method of chamfering the edge of a glass plate using a laser is known. For example, while the entire glass member as the glass plate is maintained at a predetermined temperature higher than room temperature, the glass plate is irradiated with a laser in such a manner that the irradiation point moves along the corner of the glass member, thereby heating at least a portion of the corner to a higher temperature than other portions to soften it and perform chamfering (Patent Document 1).

[0006] When performing the chamfering process, the glass member is usually placed on a predetermined support and fixed to the support, and after heating, the corner of the glass member is irradiated with laser light.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 2612332 Summary of the invention

[0010] Problems to be solved by the invention

[0011] However, if the above-mentioned existing method is used for processing, it is known that the substrate after processing will have a large residual strain. The cause was investigated and it was found that heat was scattered from the heated glass component to the supporting platform of the glass component through these contact portions, so the glass component could not be heated uniformly in essence. As a result, the temperature history during processing varies according to the position in the plane of the main surface of the glass component, and the difference between the maximum and minimum values ​​of the strain (delay value) in the main surface of the glass component, i.e., the strain distribution (strain deviation), becomes larger. If the strain distribution is large, the glass component may be easily bent or cracked in various processes such as the processing process of the glass component thereafter.

[0012] Therefore, an object of the present invention is to provide a method for manufacturing a glass plate and a method for manufacturing a magnetic disk, wherein, when a glass plate is manufactured by shaping the end surface of a disk-shaped glass plate by laser irradiation, the distribution of in-plane strain (delay value) within the main surface of the glass plate can be suppressed.

[0013] Means for solving problems

[0014] One embodiment of the present invention is a method for manufacturing a glass plate, which includes performing a shape processing on an end surface of a disk-shaped glass plate. The manufacturing method includes:

[0015] The step of suspending the disk-shaped glass sheet from the base; and

[0016] The step of heating the glass plate in a non-contact manner while irradiating the end face of the glass plate with a laser while keeping the glass plate suspended, moving the laser relative to the end face in the circumferential direction of the disc-shaped glass plate, and processing the end face into a target shape.

[0017] One embodiment of the present invention is also a method for manufacturing a glass plate, which includes performing a shape processing on the end surface of a disk-shaped glass plate. The manufacturing method includes:

[0018] The step of arranging the glass plate in a disk shape in such a manner that the glass plate does not contact the base; and

[0019] The step of heating the glass plate disposed in the atmosphere in a non-contact manner and irradiating the end face of the glass plate with a laser so that the laser moves relative to the end face in the circumferential direction of the disc-shaped glass plate and the end face is processed into a target shape.

[0020] The glass plate is preferably heated in a non-contact manner so that the temperature difference within the main surface is 50° C. or less.

[0021] In the step of processing the end surface into a target shape, it is preferable to set the irradiation conditions of the laser beam so as to form a chamfered surface on the end surface.

[0022] At this time, it is preferable to set the above conditions so that a ratio C / Th of a length C of the chamfered surface along the radial direction of the main surface to a thickness Th of the glass sheet is 0.1 to 0.7.

[0023] The arithmetic mean roughness Ra of the end surface formed by the laser is preferably 0.02 μm or less.

[0024] It is preferable that the ratio W2 / D of the length W2 of the laser beam irradiated onto the end surface in the circumferential direction to the diameter D of the glass plate is 0.03 to 0.2.

[0025] Preferably, the cross-sectional intensity distribution of the laser irradiated onto the end face is single-mode, the width of the laser beam at the irradiation position in the end face in the thickness direction of the glass plate is set to W1 [mm], the thickness of the glass plate is set to Th [mm], and the power density of the laser is set to Pd, W1>Th, Pd×Th is 0.8~3.5 [W / mm].

[0026] It is preferable that the power density Pd be set so that the diameter of the glass plate formed by the irradiation with the laser beam becomes larger than the diameter of the glass plate before the irradiation with the laser beam.

[0027] The moving speed of the laser beam along the end surface is preferably 0.7 to 140 [mm / sec].

[0028] The Young's modulus of the glass plate is preferably 70 [GPa] or more.

[0029] The linear expansion coefficient of the glass plate is preferably 100×10 -7 [1 / K] or less.

[0030] The glass plate preferably has a thickness Th of 0.7 mm or less.

[0031] The method for manufacturing the glass plate preferably includes the step of grinding or polishing the main surface of the glass plate whose end surface is processed into a target shape.

[0032] After the end surface is processed into a target shape and before the main surface is ground or polished, the end surface is not polished, or even if the end surface is polished, the machining allowance due to the polishing of the end surface is 5 μm or less.

[0033] 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 above-mentioned method for producing a glass plate.

[0034] Effects of the Invention

[0035] According to the above-mentioned glass plate manufacturing method and magnetic disk manufacturing method, when manufacturing a glass plate by shaping the end surface of a disk-shaped glass plate by laser irradiation, the distribution of in-plane strain (retardation value) in the main surface of the glass plate can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a diagram for explaining irradiation with laser light in a method for producing a glass plate according to one embodiment.

[0037] Figure 2 This is a diagram for explaining an example of the shape of a beam at an irradiation position of a laser beam.

[0038] Figure 3 This is a diagram for explaining the light beam and light intensity distribution at the irradiation position of the laser beam.

[0039] Figure 4 This is a diagram for explaining the shape of the end surface after shape processing using laser.

[0040] Figure 5 (a) to (c) are diagrams for explaining the difference in end face shape due to the difference in laser irradiation conditions. DETAILED DESCRIPTION

[0041] Figure 1 This is a diagram for explaining irradiation with laser light in a method for producing a glass plate according to one embodiment. Figure 2 This is a diagram for explaining an example of the shape of a beam at an irradiation position of a laser beam. Figure 3 This is a diagram for explaining the light beam and light intensity distribution at the irradiation position of the laser beam. Figure 4 This is a diagram for explaining the shape of the end surface after shape processing using laser.

[0042] The glass plate shaped by the manufacturing method of the glass plate of the present embodiment is a disc shape, formed into a shape with a circular hole at the center of the disc shape to form an inner peripheral end that is concentric with the outer peripheral end. In other words, the glass plate of the present embodiment is a ring-shaped glass plate. In addition to the ring shape, the disc shape of the glass plate of the present embodiment can also be a disc shape without the above-mentioned circular hole. As an example of a glass plate shaped by the manufacturing method of the glass plate of the present embodiment, it is not limited to a glass substrate for a magnetic disk, and a glass partition for HDD or other products (including intermediates before processing) can be cited.

[0043] In order to produce a glass plate with a unified end face in a target shape from the glass plate, or to prevent the connection portion between the end face and the main surface of the glass plate from becoming an angular edge, the glass plate is subjected to shape processing to form a chamfer at the connection portion between the main surface and the end face of the glass plate.

[0044] In particular, when manufacturing a disk-shaped glass substrate for a magnetic disk having a circular hole, it is desirable to unify the shape of the end face of the disk-shaped glass plate, which is the basis of the final product, i.e., the glass substrate for the magnetic disk, into a target shape in order to assemble the magnetic disk into an HDD device with good accuracy and to firmly hold the end face of the glass substrate by a fixture when forming a magnetic film on the main surface of the glass substrate. In addition, in order to prevent fine particles from adhering to the main surface and adversely affecting the performance of the magnetic disk, it is desirable to make the surface of the end face where particles are easily generated smooth. For this reason, in the present embodiment, a laser is used for shape processing for chamfering.

[0045] Specifically, if Figure 1 As shown, a glass plate 10 in the shape of a disk with a circular hole 16 has a main surface 12 and an end surface 14. Figure 1 In the example shown, the outer peripheral end surface is the end surface 14 that is shaped by the laser L, but the inner peripheral end surface along the circular hole 16 may also be the object of the laser shaping. At least one of the inner peripheral end surface and the outer peripheral end surface may be the object of the laser shaping.

[0046] In this embodiment, the glass plate 10 is placed in a horizontal state, and in this state, the end face 14 is irradiated with laser light, and the end face 14 is processed into a target shape while the laser light L is relatively moved relative to the end face 14 in the circumferential direction of the glass plate 10 in a disk shape. Alternatively, the main surface 12 of the glass plate 10 may be placed in a vertical state, and in this state, the end face 14 is irradiated with laser light L, and the end face 14 is processed into a target shape. There is no particular limitation on the arrangement direction of the glass plate 10. The laser light L is irradiated onto the end face 14, for example, from the normal direction of the end face 14. As for the laser light L, the laser light L emitted from the laser light source 20 described later is made parallel light by passing through an optical system 22 including a collimator, etc., and then the laser light L is converged by a converging lens 24, and the expanded laser light L is irradiated onto the end face 14.

[0047] On the other hand, the glass plate 10 is rotated at a constant speed with the center position of the glass plate 10 as the rotation center. In this way, the laser light L and the end surface 14 are moved relative to each other in the circumferential direction of the disc-shaped glass plate 10, and the laser light L is irradiated to the entire circumference of the end surface 14 of the glass plate 10. Instead of rotating the glass plate 10, the irradiation position of the laser light L may be moved along the end surface 14, as long as the laser light L and the end surface 14 are moved relative to each other.

[0048] Here, the irradiation of the laser L to the end face 14 may be performed from the normal direction of the position of the irradiated end face 14, or may be tilted from the normal direction. For example, it may be tilted at an angle of 45 degrees or less from the normal direction. In addition to the completely normal direction (tilt angle 0 degrees), the normal direction also includes a range within which the tilt angle relative to the normal direction is within 10 degrees as an allowable range.

[0049] In the shaping process using the laser light L, the glass plate 10 is preheated to a high temperature, and then the laser light L and the end surface 14 are moved relative to each other in the circumferential direction of the disc-shaped glass plate 10. At this time, in order to irradiate the entire circumference of the end surface 14 of the glass plate 10 with the laser light L, the glass plate 10 is usually mounted and fixed on a support table, or the glass plate 10 is clamped and fixed by a support device. However, since the heat of the glass plate 10 reaching a high temperature is dissipated from the support table or the support device, the glass plate 10 cannot be heated uniformly in essence. As a result, the temperature history in the main surface 12 of the glass plate 10 is different, and the glass plate 10 is prone to strain distribution.

[0050] Specifically, if the conventional shape processing using the laser L is described, in order to irradiate the laser L to the entire thickness direction of the glass plate 10 at the end surface 14 near the irradiation position of the laser L of the glass plate 10, the size of the support table or the support tool or the contact position with the main surface is adjusted. In other words, in order to expose the outer peripheral end surface and / or the inner peripheral end surface of the glass plate 10 to the outside over the entire circumference of the glass plate 10, the size of the support table or the support tool or the contact position with the main surface 12 of the glass plate 10 is adjusted. At this time, the contact position on the main surface 12 of the glass plate 10 that contacts the support table or the support tool is a region on the main surface 12 that is more than a predetermined distance inside from the outer peripheral end surface and more than a predetermined distance outside from the inner peripheral end surface. In other words, the above-mentioned contact position can be said to be a portion other than the outermost peripheral portion and the innermost peripheral portion on the main surface 12 of the glass plate 10 (also referred to as a mid-peripheral portion).

[0051] Taking into account the positional deviation when the glass plate 10 is placed on a support table or a support device, the above-mentioned predetermined distance can be set to, for example, 5 mm or more. Assuming that the predetermined distance is set to 5 mm, the mid-circumference portion is an area on the main surface 12 that is 5 mm or more away from the outer peripheral end surface and 5 mm or more away from the inner peripheral end surface.

[0052] After the glass plate 10 is placed on a support or a support tool, the laser light L is usually irradiated onto the end surface 14 of the glass plate 10 while continuing to heat the glass plate 10. However, conventionally, part of the heat of the heated glass plate 10 is dissipated through the support or the support tool, so that the main surface 12 of the glass plate 10 cannot be heated substantially uniformly, resulting in temperature distribution. As a result, the temperature history varies depending on the position within the main surface 12 of the glass plate 10, so that abnormal strain is generated in the mid-circumference portion of the glass plate 10, and strain distribution is easily generated.

[0053] Furthermore, according to the inventor's research, the strain of the glass plate 10 caused by contact with the support table or the support device is generated with a certain degree of expansion in the mid-circumference part regardless of the size of the specified distance from the above-mentioned end surface 14. Therefore, in the radial direction of the main surface 12 of the glass plate 10, when the inner circumference end is set to 0% and the outer circumference end is set to 100%, it can be seen that the mid-circumference part that is about 25% or more away from the inner circumference end and the outer circumference end can be detected. Therefore, when evaluating the strain distribution, for example, the strain can be evaluated by measuring the strain at any plurality of positions of the mid-circumference part that are 25%, 50%, and 75% away from the inner circumference end of the glass plate 10 in the radial direction. Regarding these three radial measurement positions, for example, when a circular ring-shaped glass with an outer diameter of 95mm and an inner diameter of 25mm is used as a glass plate, the distances from the inner circumference end are 8.75mm, 17.5mm, and 26.25mm, respectively (the distances from the center are 21.25mm, 30mm, and 38.75mm, respectively).

[0054] On the other hand, in this embodiment, if Figure 1 As shown, by suspending the glass plate 10 from the mounting surface 18 of the base so that the glass plate 10 and the mounting surface 18 are in a non-contact state, the glass plate 10 is then heated by a method that does not contact the glass plate 10 while the end face of the glass plate 10 is irradiated with laser light L. The heating device is not shown in the figure. The non-contact heating of the glass plate 10 can be performed, for example, by utilizing heat radiation from a heater or the like or by heating in a heat transfer furnace. Alternatively, the entire glass plate 10 is heated using a heating laser different from the laser light L. The irradiation spot diameter of the heating laser is not particularly limited, but is preferably 3 / 4 or more of the diameter (outer diameter) of the glass plate 10 because it is easy to improve the heating efficiency. In addition, the heating laser can be made to scan the entire surface of the main surface 12 of the glass plate 10, or multiple lasers can be used. As the heating laser, for example, a CO2 laser can be used. The light of the CO2 laser is usually absorbed by glass by more than 99%, so the glass plate can be effectively heated.

[0055] Thus, heat does not flow out of the glass sheet 10 through the contact portion with the support table or the supporting device, so it is easy to uniformly heat the glass sheet 10. As a result, the thermal history of the mid-circumference portion of the glass sheet 10 is easy to be uniform, so the generation of abnormal strain in the mid-circumference portion can be suppressed.

[0056] In this way, when the end face of the glass plate 10 is irradiated with the laser light L, the glass plate 10 is suspended from the mounting surface 18 so that the glass plate 10 is not in contact with the mounting surface 18, and the glass plate 10 is heated by a method that does not contact the glass plate 10 while the end face of the glass plate 10 is irradiated with the laser light L. At this time, the laser light L is relatively moved in the circumferential direction of the disk-shaped glass plate 10 with respect to the end face 14. Thus, the end face 14 can be processed into a target shape.

[0057] The glass plate 10 can be suspended by applying a suspension force or an attraction force to the glass plate 10 using a known technique such as ultrasound, gas pressure, or electrostatic force. The suspension amount H is not particularly limited as long as it is stable, and can be, for example, 0.1 mm or more, more preferably 0.5 to 5 mm. This suspension can suppress the outflow of heat from the support platform or the support device.

[0058] For example, in the case of ultrasound, the density of the gas caused by standing waves is used, or further the acoustic radiation pressure is used. If the vibrator and the reflector serving as the sound source are arranged in parallel to form a standing wave sound field, a levitation force is generated due to the density difference at the position of the standing wave node where the air pressure decreases, and the object can be floated at this position. However, since the levitation force is small, it is preferable to use the levitation force generated by the acoustic radiation pressure. For the acoustic radiation pressure, if the object is placed in parallel on a vibration plate in a bending vibration mode or a longitudinal vibration mode, the acoustic radiation pressure acts on the bottom surface of the object that blocks the propagation of the sound wave, thereby generating a levitation force. The amount of suspension caused by this levitation force can be, for example, more than 0.1 mm, and more preferably 0.5 to 5 mm. This suspension can suppress outflow through a support table or a supporting device.

[0059] In addition, by arranging the ultrasonic generating surface facing the main surface 12 of the glass plate 10, a compressed thin air film is formed on the surface of the ultrasonic generating surface, thereby forming a repulsive force that separates the ultrasonic generating surface from the glass plate 10, so that the glass plate 10 is in a state of not contacting the ultrasonic generating surface. On the other hand, the negative pressure formed by sucking air from the ultrasonic generating surface is used as an attractive force, so that the glass plate 10 can be fixed in a state of being separated from the ultrasonic generating surface, that is, the glass plate 10 can be clamped in a non-contact state. Therefore, by rotating the ultrasonic generating surface, the rotation of the glass plate 10 can be easily controlled. Depending on the situation, it is also possible to fix (clamp) the glass plate 10 to the ultrasonic generating surface in a non-contact state with respect to the base using only ultrasonic waves without using an attractive force.

[0060] In this case, it is preferable to perform ultrasonic control to keep the floating amount constant so that the floating amount does not change during processing.

[0061] When utilizing the pressure of the gas, a non-contact chuck utilizing the Bernoulli effect may be used. For example, a cylindrical chamber is provided above the base and facing the base, a high-speed swirling flow (vortex) is generated in the chamber, and the negative pressure generated at the center of the swirling flow and the positive pressure generated by the exhaust gas flowing out of the cylindrical chamber to the outside are used to attract the target object, so that the target object can be suspended from the base. When utilizing the pressure of the gas, since the force for fixing the glass plate 10 without contact is relatively strong, the rotation of the glass plate 10 can be easily controlled by rotating the base together with the chuck. In addition, the target object may be charged and suspended by electrostatic force. This suspension method may be used alone, or any two or more of the above-mentioned ultrasonic waves, gas pressure, electrostatic force, etc. may be used in combination.

[0062] In this way, the disk-shaped glass plate 10 is suspended from the base, and while the glass plate 10 is suspended, the glass plate 10 is heated in a non-contact manner, while the end surface of the glass plate 10 is irradiated with laser light L, so that the laser light L is relatively moved in the circumferential direction of the glass plate 10 relative to the end surface 14, and the end surface 14 is processed into a target shape. By irradiating the glass plate 10 with laser light L, the shape of the end surface 14 of the glass plate 10 can be made uniform without deviating from the target shape, a chamfered surface can be formed, and further, the deviation of the strain (retardation value) in the plane of the main surface 12 of the glass plate 10 can be suppressed, that is, the strain distribution can be suppressed. For example, the difference between the maximum and minimum values ​​of the retardation value in the mid-circumference of the surface of the glass plate 10 subjected to shape processing by irradiation of the laser L exceeds 30 nm when the glass plate 10 is heated in a state of being placed on the mounting surface 18 of the base and subjected to shape processing by irradiation of the laser L. On the other hand, when the glass plate 10 is heated in a state of being suspended from the mounting surface 18 of the present embodiment and subjected to shape processing by irradiation of the laser L, the above-mentioned difference in the retardation value of the glass plate 10 can be made 30 nm or less, preferably 20 nm or less. In addition, the surface of the end face 14 can be made smooth. The above-mentioned difference in the retardation value in the mid-circumference of the surface of the glass plate 10 is more preferably 10 nm or less, and further preferably 5 nm or less. If the above-mentioned difference in the retardation value is large, the glass plate may be warped or cracked during the heating process in the subsequent process. In particular, when the glass plate is finally used as a glass substrate for a magnetic disk, it is heated to a high temperature in the subsequent film forming process of the magnetic film on the substrate surface, so it is important to reduce the above-mentioned difference in the retardation value.

[0063] According to one embodiment, in the preheating of the glass plate 10 before the shaping process using the laser L, the glass plate is preferably heated by a non-contact method so that the temperature difference of the mid-circumference portion within the plane of the main surface 12 is 50° C. or less. Thereby, the shape of the chamfered surface can be formed uniformly on the circumference, and the above-mentioned difference in retardation value can be reduced. It is more preferable to heat by a non-contact method so that the above-mentioned temperature difference is 20° C. or less.

[0064] In order to make the end face 14 have a target shape by irradiation with the laser light L, the following irradiation conditions can be mentioned.

[0065] The cross-sectional intensity distribution of the laser light L irradiated to the end face 14 is preferably single-mode. That is, the cross-sectional intensity distribution of the laser light L is Gaussian distribution. The width of the beam of the laser light L at the irradiation position in the end face 14 in the thickness direction of the glass plate 10 is calculated as follows: Figure 2 As shown in the figure, W1[mm] is set, and the thickness of the glass plate 10 is set as Figure 1 , 3 The power density of laser L is set to Pd [W / mm 2 ], in the irradiation of the laser L, the conditions of W1>Th and Pd×Th being 0.8~3.5 [W / mm] are used. Here, the beam of laser L is irradiated in a manner that exceeds both sides of the thickness direction of the glass plate 10. In addition, by making the width of the laser L exceeding both sides of the end surface 14 the same, the glass plate 10 can be chamfered evenly on both sides in the thickness direction, and the shapes of the two chamfered surfaces 14c can be made the same. The power density Pd is the value obtained by dividing the total power P [W] of the laser L by the area of ​​the beam of the portion irradiated by the laser L. The beam of laser L forms an ellipse with a short axis radius of W1 / 2 and a long axis radius of W2 / 2 (refer to Figure 2 ), the power density Pd is specified as 4×P / W1 / W2 / π[W / mm 2 ](π is the ratio of a circle to a circle).

[0066] Here, as an example of laser L, CO2 laser is used, but as long as the oscillation wavelength is absorbed by glass, it is not limited to CO2 laser. For example, CO laser (oscillation wavelength ~ 5μm or oscillation wavelength ~ 10.6μm), Er-YAG laser (oscillation wavelength ~ 2.94μm), etc. can be cited. When using CO2 laser, the wavelength is preferably above 3μm. In addition, it is more preferable to make the wavelength below 11μm. If the wavelength is shorter than 3μm, it is difficult for glass to absorb laser L, and sometimes it is impossible to fully heat the end face 14 of the glass plate 10. In addition, if the wavelength is longer than 11μm, it is sometimes difficult to obtain a laser device. It should be noted that there is no particular limitation on the oscillation form of the laser light source 20, and it can be any of continuous oscillation light (CW light), pulsed oscillation light, and modulated light of continuous oscillation light. However, in the case of pulsed oscillation light and modulated light of continuous oscillation light, when the relative movement speed of the laser L is fast, the shape of the chamfered surface 14c may be uneven in the moving direction. In this case, the frequency of oscillation and modulation is preferably 1 kHz or more, more preferably 5 kHz or more, and even more preferably 10 kHz or more.

[0067] The width W1 of the beam and the length W2 described later can be set by using, for example, two cylindrical lenses to adjust the irradiation position of the laser L on the glass plate 10. In addition, the width W1 can be obtained by a beam profiler, and the length W2 can be obtained from the beam shape obtained by the beam profiler and the diameter D of the glass plate.

[0068] By making the width W1 of the laser L larger than the thickness Th of the glass plate 10, the laser L can be fully irradiated to the side ends of the main surface 12 side of the end face 14 (both sides in the thickness direction), and a part of the glass plate 10 can be softened and melted by heat, thereby forming a chamfered surface.

[0069] If the ratio Th / W1 of the width W1 of the laser L to the thickness Th of the glass plate 10 is too large (that is, Th / W1 is too close to 1), the heating of the edge portion of the glass plate 10 is weakened due to the influence of the steep gradient range of the laser intensity distribution, while the heating of the center portion of the thickness direction of the end face 14 of the glass plate 10 is strengthened. Therefore, it is easy to form a spherical end face described later, which is not preferred. In addition, if Th / W1 is too small, the heating of the end face 14 by the laser L becomes too small, and it is sometimes difficult to form the chamfered surface 14c. From the above point of view, Th / W1 is preferably in the range of 0.3 to 0.9.

[0070] On the other hand, when the power density Pd of the laser L is too low, the end face 14 is not heated sufficiently and the chamfered surface is not formed. On the other hand, when the power density Pd is too high, the end face 14 is rounded into a spherical shape by heat, and the thickness of the spherical shape in the thickness direction is greater than the thickness Th of the glass plate 10.

[0071] Therefore, the irradiation conditions are preferably W1>Th, Pd×Th=0.8 to 3.5 [W / mm]. Pd×Th is preferably 3.0 [W / mm] or less, more preferably 1.0 to 2.8 [W / mm], and even more preferably 1.2 to 2.3 [W / mm].

[0072] Since Pd×Th=0.8~3.5[W / mm], when the thickness Th of the glass plate 10 becomes thinner and the irradiation condition deviates from Pd×Th=0.8~3.5[W / mm], it means that the power density Pd can be increased. By increasing the power density Pd, the reduction in the irradiation area of ​​the glass plate 10 caused by the laser L can be compensated by the power density Pd, and the chamfered surface 14c can be formed.

[0073] It should be noted that in order to simultaneously form chamfered surfaces of the same shape on both sides of the glass plate 10 in the thickness direction, it is preferred to align the center position of the beam of laser L in the width direction with the center position of the glass plate 10 in the thickness direction of the glass plate 10 .

[0074] By using such conditions, the shape of the end face 14 of the glass plate 10 can be unified into the target shape without deviating from the target shape, and the chamfered surface 14 c can be formed. In addition, the surface of the end face 14 can be made smooth.

[0075] As described above, the chamfered surface 14c can be formed by limiting the range of the value of Pd×Th, but by controlling the value of Pd×Th and the value of the moving speed and irradiating the end surface 14 with the laser L, the chamfered surface 14c can be effectively formed on the end surface 14 of the glass plate 10. In addition, by controlling the value of Pd×Th and the value of the moving speed in more detail, not only the chamfered surface 14c but also the surface perpendicular to the main surface 12 of the glass plate 10, that is, the side wall surface 14t can be formed. As a result, the shape of the end surface 14 can be made uniform without deviation from the target shape. In addition, the surface of the end surface 14 can be made smooth. In this case, the end surface 14 of the glass plate 10 before the chamfered surface 14c is formed has a surface perpendicular to the main surface 12 at least in the center portion in the thickness direction of the glass plate 10. By irradiating the end face 14 of the glass plate 10 with laser light L, the edge portions on both sides of the end face 14 of the glass plate 10 in the thickness direction (the boundary portions between the main surface 12 and the end face 14), for example, the corner portions bent at right angles, are softened and / or melted, and the edge portions of the end face 14 are chamfered into a shape with an arc. At the same time, a surface (side wall surface 14t) perpendicular to the main surface 12 sandwiched by the chamfered surfaces on both sides in the thickness direction of the glass plate 10 can be formed on the chamfered end face 14. In particular, the end face 14 preferably includes a surface (side wall surface 14t) perpendicular to the main surface 12 and having a length of not less than 1 / 10 of the thickness Th, and a chamfered surface 14c. The length T (see Figure 4 ) is more preferably greater than one fifth of the thickness Th.

[0076] According to one embodiment, the vertical surface (side wall surface 14t) formed together with the chamfered surface 14c by irradiation of the laser L is different from the surface vertical to the main surface 12 of the end surface 14 before the chamfered surface 14c is formed by irradiation of the laser L, and is a newly formed surface, and the surface roughness Rz and the arithmetic mean roughness Ra are reduced by irradiation of the laser L. In addition, the distance in the radial direction from the center position of the disk-shaped glass plate 10 to the vertical surface (side wall surface 14t) becomes larger.

[0077] It should be noted that the surface perpendicular to the main surface 12 (side wall surface 14 t ) refers to a surface within a permissible range of 90 degrees±2 degrees relative to the main surface 12 .

[0078] Hereinafter, a method for manufacturing a glass plate including the shape processing of the above-mentioned glass plate 10 will be described using a method for manufacturing a glass substrate for a magnetic disk.

[0079] and Figure 1 Similarly to the glass plate 10 shown, the glass substrate for magnetic disk is also a glass substrate of a thin plate in the shape of a disk with a circular hole. There is no limitation on the size of the glass substrate for magnetic disk, and the glass substrate for magnetic disk is, for example, a size of a glass substrate for magnetic disk with a nominal diameter of 2.5 inches or 3.5 inches. In the case of a glass substrate for magnetic disk with a nominal diameter of 3.5 inches, for example, the outer diameter (nominal value) is 95 mm to 97 mm. In the case of a glass substrate for magnetic disk with a nominal diameter of 2.5 inches, for example, the outer diameter (nominal value) is 65 mm to 67 mm. The thickness of the glass substrate for magnetic disk is, for example, 0.20 mm to 0.65 mm, preferably 0.30 mm to 0.65 mm, and preferably 0.30 mm to 0.53 mm. A magnetic layer is formed on the main surface of the glass substrate to produce a magnetic disk.

[0080] The glass substrate has Figure 4 The glass plate 10 has the same end face shape as the outer peripheral end of the glass plate 10 shown. The glass plate 10 includes: a pair of main surfaces 12, 12; a side wall surface 14t formed on the end face 14 of the outer peripheral end; and chamfered surfaces 14c, 14c between the side wall surface 14t and the main surfaces 12, 12. Similar to the end face 14 of the outer peripheral end, the end face of the inner peripheral end also includes: a side wall surface not shown; and a chamfered surface not shown between the side wall surface and the main surfaces 12, 12. This shape is the target shape in the shape processing of the end face 14 using the laser L. The target shape is described below.

[0081] The side wall surface 14t is a surface extending in a direction substantially perpendicular to the main surface 12. Substantially perpendicular means that the inclination angle of the side wall surface 14t relative to the main surface 12 is in the range of 88 to 92 degrees. The chamfered surface 14c is smoothly connected to the main surface 12 and extends toward the side wall surface 14t. The chamfered surface 14c forms a curved shape protruding outward and is smoothly connected to the side wall surface 14t. Therefore, Figure 4 The length C [mm] of the chamfered surface 14 c along the radial direction of the main surface 12 is the length of a portion inclined with respect to the main surface 12 at an inclination angle in the range of more than 2 degrees and less than 88 degrees.

[0082] The curved shape of the chamfered surface 14 c when cut along the radial direction and the thickness direction of the main surface 12 is a shape in which the inclination angle of the chamfered surface 14 c with respect to the main surface 12 continuously increases as it goes radially outward.

[0083] When manufacturing such a glass substrate, for example, a glass blank slightly larger than the size of the glass plate 10 can be cut out from a prefabricated large glass plate using a laser.

[0084] The large flat glass before cutting out the glass blank is, for example, a glass plate of a certain thickness produced by a float process or a down-draw process. Alternatively, it may be a glass plate obtained by pressing a glass block using a mold. The thickness of the glass plate is thicker than the target thickness when it becomes the final product, i.e., the glass substrate for a magnetic disk, by a processing allowance for grinding and polishing, for example, a few μm to several hundred μm thick.

[0085] It should be noted that, in addition to the method of cutting the glass blank using a laser, the following method can also be used as in the prior art: a cut line is formed on the glass plate using a scriber, and a crack is generated along the cut line by heating, etc., and then the glass blank is cut. Alternatively, the glass blank can be cut by wet etching using an etching solution such as hydrofluoric acid.

[0086] When a glass blank is cut from a large flat glass by laser, a solid-state laser such as a YAG laser or an Nd:YAG laser is used as the laser. Therefore, the wavelength of the laser is, for example, in the range of 1030 nm to 1070 nm. In this case, the laser is, for example, a pulsed laser with a pulse width of 10×10 -12 The light energy of the laser can be appropriately adjusted according to the pulse width and the repetition frequency of the pulse width. By irradiating the laser, defects can be intermittently formed at discrete positions along the boundary line to be cut.

[0087] Thereafter, the outer part of the defective glass sheet, which is separated from the inner part by the boundary line, is heated higher than the inner part, or the outer part is heated to separate the outer part from the inner part of the glass sheet.

[0088] Alternatively, other types of lasers may be continuously irradiated along the above-mentioned boundary line, so that defects formed discretely along the boundary line to be cut are continuous in a linear shape by laser irradiation. For example, as another type of laser, a CO2 laser may be used. By this laser, linear defects may be formed to connect defects formed intermittently. In this case, as required, the outer part of the outer part and the inner part bounded by the above-mentioned boundary line may be heated higher than the inner part, or the outer part may be heated, thereby separating the outer part and the inner part of the glass plate. In this way, a circular plate-shaped glass blank can be cut from the flat glass. The surface roughness Rz of the end face of the circular plate-shaped glass blank thus formed is, for example, 1 to 10 μm, and the arithmetic mean roughness Ra is, for example, 0.1 to 1 μm.

[0089] In order to make concentric circular holes in the cut disc-shaped glass blank, circular holes are made by laser irradiation and a scriber, or by etching, as in the above method. The glass blank with circular holes becomes a glass blank plate when manufacturing a glass substrate for a magnetic disk.

[0090] In order to obtain Figure 1 The end faces 14 (end faces at the outer circumferential end and end faces at the inner circumferential end) of the disk-shaped glass plate 10 shown in the figure are formed with chamfered faces 14c, and are processed by laser light L. In the processing by laser light L, as described above, the glass plate 10 (glass blank) is suspended from the mounting surface 18 by a known technique, and the end face 14 of the glass plate 10 (glass blank) heated in the suspended state is irradiated with laser light L (for example, from the normal direction of the end face 14), and the end face 14 and the laser light L are relatively moved in the circumferential direction of the disk-shaped glass plate 10, and the shape of the end face 14 is processed into a target shape. The laser light L is preferably a laser light having a single-mode cross-sectional intensity distribution, and as the irradiation conditions of the laser light L, it is preferable that the width W1>thickness Th, and Pd×Th is 0.8 to 3.5 [W / mm 2 ]. Thus, the shape of the end surface 14 of the glass plate 10 can be made uniform without deviation from the target shape, and a chamfered surface can be formed.

[0091] In addition, in order to irradiate the laser light L onto the end face 14 of the glass plate 10 before chamfering, which has a surface perpendicular to the main surface 12 at least in the center in the thickness direction, so as to soften and / or melt the edge of the end face 14 of the glass plate 10, chamfer the edge of the end face 14 into a rounded shape, and further, in order to form a surface perpendicular to the main surface of the glass plate 10 (side wall surface 14t) on the end face 14 after chamfering, the value of Pd×Th and the value of the moving speed are controlled, and the end face 14 is irradiated with the laser light L. As a result, the shape of the end face 14 of the glass plate 10 can be made uniform without deviation from the target shape, and the surface perpendicular to the main surface 12 (side wall surface 14t) and the chamfered surface 14c can be formed.

[0092] Figure 5 (a) to (c) are diagrams for explaining differences in the shape of the end face 14 due to differences in the irradiation conditions of the laser light L. Figure 5 In (a) to (c), the thickness Th in the irradiation conditions is fixed to 0.7 mm, the width W1 is fixed to 1.0 mm, Th / W1 is fixed to 0.7, and the length W2 is fixed to 10 mm, the moving speed at the irradiation position is fixed to 2 mm / sec, and the power density Pd is changed to change Pd×Th, and an example of the shape of the end face 14 at this time is shown. It should be noted that as the glass plate before processing, a glass plate with a glass transition temperature Tg of 500°C, a diameter of 95 mm, and an end face 14 perpendicular to the main surface 12 is used. The surface roughness Rz of the end face 14 is 5 μm, and the arithmetic mean roughness Ra is 0.5 μm. The laser L is irradiated to the outer peripheral end face of the glass blank plate.

[0093] Figure 5 (a) shows a state where the laser light L is not irradiated, that is, Pd = 0 [W / mm 2 ] for example. Figure 5 (b) shows that Pd = 1.9 [W / mm 2 ] under the irradiation condition, Figure 5 (c) shows that Pd = 4.0 [W / mm 2 ] is the shape of the end face 14 under the irradiation conditions.

[0094] Figure 5 The end face 14 shown in (c) is spherical in shape, and the outer diameter of the glass plate 10 is reduced. Accordingly, the length of the glass plate 10 in the thickness direction is longer than the thickness of the glass plate 10 (the length between the main surfaces), which is an unpreferred shape for a glass substrate having a certain thickness.

[0095] Therefore, regarding the irradiation conditions using the laser light L, it is preferable to set the irradiation conditions so that the side wall surface 14t substantially perpendicular to the main surface 12 and the chamfered surface 14c connecting the ends of both sides of the side wall surface 14t and the end of the main surface 12 are formed on the end surface 14. In order not to reduce the outer diameter of the glass plate 10 or to prevent the length of the thickness direction of the spherical shape from being longer than the thickness of the glass plate 10 (the length between the main surfaces), the power density Pd is preferably set in the range of 1.2 [W / mm 2 ]~3.0[W / mm 2 ].

[0096] According to one embodiment, as the target shape of the end face 14, the irradiation condition Pd×Th is preferably set in such a way that the ratio C / Th of the length C of the chamfered surface 14c along the radial direction of the main surface 12 to the thickness Th is 0.1 to 0.7. By making C / Th 0.1 to 0.7, the function of the chamfered surface 14c having no corners at the connection portion between the end face 14 and the main surface 12 can be exerted. In addition, when C / Th is less than 0.1, the formation of the chamfered surface 14c is insufficient, and the edge may be easily defective in the subsequent film forming process, etc. In addition, when C / Th exceeds 0.7, the data recording area on the main surface 12 may be reduced. Therefore, by adjusting Pd×Th in the range of 1.2 to 2.3 [W / mm], C / Th can be adjusted. C / Th is more preferably 0.25 to 0.5.

[0097] According to one embodiment, as the target shape of the end face 14, the irradiation conditions are preferably set so that the ratio T / Th of the length T [mm] of the side wall surface 14t along the thickness direction to the thickness Th is 0.1 to 0.8. When T / Th is less than 0.1, the side wall surface 14t is not formed sufficiently, and it is difficult to measure the outer diameter or inner diameter of the glass plate 10, so that measurement deviation may occur and production management may be difficult. In addition, when C / Th exceeds 0.8, the chamfered surface 14c is not formed sufficiently, and the edge may be easily damaged in the subsequent film forming process.

[0098] According to one embodiment, the arithmetic mean roughness Ra (JIS B0601: 2001) of the end face 14 (chamfered surface 14c, side wall surface 14t) formed by the laser L is preferably 0.02 μm or less. Furthermore, the surface roughness Rz (JIS B0601: 2001) is preferably 0.3 μm or less, 0.2 μm or less, more preferably 0.02 μm or less. The surface roughness Rz and the arithmetic mean roughness Ra can be measured, for example, using a laser optical microscope. By irradiating the end face 14 with the laser L under the above-mentioned irradiation conditions, the chamfered surface 14c and the side wall surface 14t can be smoothed.

[0099] In addition, if Figure 1 As shown in FIG. 1 , when the irradiation position of the laser light L is relatively moved along the circumferential direction of the disk-shaped glass plate 10 to perform the shape processing, it is preferable to effectively use the laser light L to heat the end face 14 in the following manner, that is, to increase the length W2 of the disk-shaped glass plate 10 in the circumferential direction to a certain extent (see FIG. Figure 2 ), slowly increase the temperature of the end face 14 caused by heating with the laser L, and reach the maximum temperature at the center point in the circumferential direction of the irradiation position. In this way, the moving speed at the irradiation position of the laser L can be increased, so the processing time can be shortened. According to one embodiment, the ratio W2 / D of the length W2 of the laser beam L irradiated to the end face 14 in the circumferential direction of the disk shape of the glass plate 10 to the diameter D of the glass plate 10 is preferably 0.03 to 0.2. When W2 / D is less than 0.03, the length W2 becomes relatively short, so it is not possible to fully achieve a slow increase in the temperature of the end face 14. When W2 / D exceeds 0.2, the length W2 becomes relatively long. Therefore, in this case, the position where the laser L irradiates the glass plate 10 (the position in the irradiation direction of the laser L) will change significantly due to the curvature of the glass plate 10. As a result, the beam expands, and it is difficult to effectively heat in the circumferential direction. According to one embodiment, Figure 2 As shown, the beam of laser light L irradiated onto the end surface 14 is preferably elliptical.

[0100] It should be noted that if the power density Pd of the end surface 14 is gradually increased by irradiation with the laser L, the shape of the end surface 14 becomes rounded, and the diameter D of the glass plate 10 increases by several tens to several hundreds of μm. If the power density Pd is further increased, the range of the rounding becomes wider, and the length in the thickness direction becomes wider to form a spherical shape, thereby reducing the diameter D of the glass plate 10. That is, the diameter D of the glass plate 10 after shape processing changes according to the magnitude of the power density Pd. Figure 5 The example shown in (c) is an example in which the power density Pd increases excessively, the end surface 14 becomes spherical due to excessive heating, and the diameter of the glass plate 10 becomes short. Figure 5 The outer diameter of the glass plate 10 shown in (c) is smaller than the target diameter of the glass plate 10, which is not preferable. In addition, due to excessive heating of the end surface 14, the spherical shape is easily deviated, and the diameter of the glass plate 10 cannot be made uniform, which is not preferable. Therefore, it is preferable to set the power density Pd so that the diameter of the glass plate 10 formed by irradiation of the laser L is larger than the diameter of the glass plate 10 before irradiation of the laser L.

[0101] The moving speed of the laser L along the end face 14 is preferably 0.7 to 140 mm / sec. Here, the moving speed refers to the relative moving speed with respect to the end face 14. From the perspective of processing efficiency, the shape processing using the laser L is preferably completed when the laser L rotates around the glass plate 10 once. Here, in the case where the moving speed exceeds 140 mm / sec, it is difficult to grasp the timing of completing the shape processing, and it may be difficult to make the starting point and end point of the shape processing consistent. In addition, if the moving speed is lower than 0.7 mm / sec, the shape of the end face 14 will change due to a slight change in Pd×Th, so it is difficult to control the shape of the end face 14. For example, even if a shape having Figure 4 The side wall surface 14t and the chamfered surface 14c shown in FIG. 1 are shaped in the same manner as shown in FIG. 1 , but if Pd×Th is increased by only a small amount, the end surface 14 will be overheated and easily become Figure 5 From these aspects, the moving speed is preferably 0.7 to 140 mm / sec.

[0102] It should be noted that the moving speed is more preferably 20 to 140 mm / second. If the moving speed is 20 mm / second or more, the shape change of the end face 14 relative to the change of Pd×Th is relatively stable, and the productivity is improved by shortening the processing time. Therefore, the moving speed is more preferably 20 to 100 mm / second.

[0103] It should be noted that, in order to promote the formation of chamfers by the laser light L, it is preferable to set the temperature of the glass plate 10 to a temperature higher than room temperature when the chamfering shape processing is performed by the laser light L. In this case, it is preferably Tg-50°C or less (Tg is the glass transition temperature of the glass plate 10). In addition, the temperature of the glass plate 10 when the chamfering shape processing is performed is more preferably in the range of 150 to 400°C. If the temperature of the glass plate 10 is lower than 150°C, the formation of the chamfered surface 14c may not be sufficiently obtained. If the temperature of the glass plate 10 is higher than 400°C, the glass plate 10 may be deformed and it may be difficult to irradiate the end surface 14 with the laser light L. As a method of heating the glass plate 10, for example, the glass plate 10 may be heated before the chamfering process is performed, or the glass plate 10 may be heated while the chamfering process is performed. However, when the glass plate 10 is heated while the chamfering is performed by irradiation of the laser light L, it is difficult to control the temperature due to the multiplier effect of the heating caused by the laser light L, so the deviation of the shape of the end surface 14 may become large. Therefore, when the glass plate 10 is heated, it is preferable to heat the glass plate 10 before chamfering by irradiation with the laser light L. In this case, it is preferable to appropriately keep the glass plate 10 warm during chamfering.

[0104] The glass plate 10 having the end surface 14 shaped in this way is also shaped by the laser light L at the end surface of the inner peripheral end, and then various treatments are performed on the glass plate 10 so as to have characteristics suitable for the final product.

[0105] For example, the end surface 14 after shape processing is subjected to end surface grinding. Through the above-mentioned shape processing, the surface roughness of the chamfered surface 14c and the side wall surface 14t can be reduced, so the processing allowance in the end surface grinding process can be reduced compared with the case where the chamfered surface 14c is processed using a shaped grindstone as in the prior art, which can improve production costs and production efficiency. In one embodiment, end surface grinding can be completely omitted.

[0106] When a magnetic disk glass substrate is produced from the glass plate 10 , the main surface 12 of the glass plate 10 is subsequently subjected to grinding and polishing treatment using the glass plate 10 as an intermediate glass plate before becoming a magnetic disk glass substrate.

[0107] In the grinding / polishing process, the glass plate 10 is polished after being ground.

[0108] In the grinding process, the main surface 12 of the glass plate 10 is ground using a double-sided grinding device equipped with a planetary gear mechanism. Specifically, the main surfaces 12 on both sides of the glass plate 10 are ground while the end surface 14 of the outer peripheral end of the glass plate 10 is held in the holding hole of the holding member provided in the double-sided grinding device. The double-sided grinding device has a pair of upper and lower platens (an upper platen and a lower platen), and the glass plate 10 is clamped between the upper platen and the lower platen. And, while either or both of the upper platen or the lower platen is moved and a coolant is supplied, the glass plate 10 and each platen are relatively moved, thereby grinding the two main surfaces 12 of the glass plate 10.

[0109] For example, a grinding process can be performed by forming a grinding member having fixed abrasive grains in which diamonds are fixed with resin into a sheet shape and attaching the formed grinding member to a fixed plate.

[0110] Next, the first grinding is performed on the main surface 12 of the ground glass plate 10. Specifically, the main surfaces 12 on both sides of the glass plate 10 are ground while the end surface 14 of the outer peripheral end of the glass plate 10 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 scratches or strains remaining on the main surface 12 after the grinding process, or to adjust the minute surface unevenness (micro waviness, roughness).

[0111] 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 using fixed abrasives is used to grind the glass plate 10 while providing 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 10 between an upper and lower pair of fixed plates in the same manner as the double-sided grinding device. A grinding pad (such as a resin polishing material) having a flat plate in the shape of an annular ring as a whole is installed on the upper surface of the lower fixed plate and the bottom surface of the upper fixed plate. In addition, by moving either the upper fixed plate or the lower fixed plate or both of them, the glass plate 10 and each fixed plate are relatively moved, thereby grinding the two main surfaces 12 of the glass plate 10. The size of the grinding abrasive is preferably in the range of 0.5 to 3 μm in terms of average particle size (D50).

[0112] After the first grinding, the glass plate 10 may be chemically strengthened. In this case, a mixed molten solution of potassium nitrate and sodium sulfate is used as a chemical strengthening solution, and the glass plate 10 is immersed in the chemical strengthening solution. Thus, a compressive stress layer can be formed on the surface of the glass plate 10 by ion exchange.

[0113] Next, the glass plate 10 is subjected to a second grinding. The purpose of the second grinding process is to mirror-grind the main surface 12. 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 end surface 14 of the outer peripheral end of the glass plate 10 is held in the holding hole of the grinding carrier provided in the double-sided grinding device, the main surfaces 12 on both sides of the glass plate 10 are ground. In the second grinding process, the type and particle size of the free abrasive particles are different from those in the first grinding process, and the hardness of the resin polishing material is different. The hardness of the resin polishing material is preferably lower than that in the first grinding process. For example, a grinding liquid containing colloidal silica as a free abrasive particle is supplied between the grinding pad of the double-sided grinding device and the main surface 12 of the glass plate 10, and the main surface 12 of the glass plate 10 is ground. The size of the grinding abrasive particles used in the second grinding is preferably in the range of 5 to 50 nm in terms of average particle size (d50).

[0114] It should be noted that whether chemical strengthening treatment is needed can be appropriately selected by considering the glass composition and necessity. In addition to the first grinding treatment and the second grinding treatment, other grinding treatments can be further added, and the grinding treatment of the two main surfaces 12 can also be completed by one grinding treatment. In addition, the order of the above-mentioned treatments can be appropriately changed.

[0115] By polishing the main surface 12 of the glass plate 10 in this manner, a magnetic disk glass substrate satisfying the conditions required for the magnetic disk glass plate 10 can be obtained.

[0116] Thereafter, at least a magnetic layer is formed on the glass plate 10 produced by polishing the main surface 12 , thereby producing a magnetic disk.

[0117] Thus, in the manufacturing method of the glass plate 10, the main surface 12 of the glass plate 10 after the shape processing is ground or polished. In this case, after the shape processing of the end face 14 and before the grinding or polishing of the main surface 12, the end face 14 is not polished, or even if the end face 14 is polished, the processing allowance due to the grinding of the end face 14 can be made less than 5μm. Therefore, the change in the outer diameter of the glass plate 10 can be made less than 10μm. This is because the chamfered surface 14c and the side wall surface 14t with small surface unevenness can be formed by the laser L.

[0118] In recent years, due to big data analysis and other factors, the demand for increasing the storage capacity of hard disk drives has become increasingly strong. Therefore, research is being conducted to increase the number of disks that can be mounted on a hard disk drive. When increasing the number of disks assembled in a hard disk drive to increase the storage capacity, the thickness of the disk glass substrate, which accounts for most of the disk thickness, needs to be reduced within the limited space in the disk drive.

[0119] Here, if the thickness of the glass substrate for the disk is reduced, the rigidity of the glass substrate is reduced, and large vibrations are likely to occur, and the vibrations are difficult to calm down. If the amplitude of the vibration of the glass substrate is large, the contact with adjacent disks increases, and the top disk of a plurality of disks arranged at a certain interval may sometimes contact the top surface of the disk storage container of the hard disk drive. In such contact, a part of the disk may be damaged and particles may be generated.

[0120] Therefore, it is not preferred that the rigidity of the glass substrate for magnetic disk is low. From this aspect, regarding the glass plate 10 used in the above-mentioned shape processing, according to one embodiment, the Young's modulus of the glass plate 10 is preferably 70 [GPa] or more, more preferably 80 [GPa] or more, and further preferably 90 [GPa] or more.

[0121] When the glass plate 10 is used as a material for a glass substrate for a magnetic disk, the thickness Th of the glass plate 10 is preferably 0.7 mm or less, more preferably 0.6 mm or less. The smaller the thickness Th, the more the number of magnetic disks mounted in the hard disk drive can be increased.

[0122] The composition of the glass plate 10 is not limited, but is preferably the following composition.

[0123] (Glass 1)

[0124] SiO2 56~80 mol%,

[0125] Li2O 1~10 mol%,

[0126] B2O3 0~4 mol%,

[0127] The total content of MgO and CaO (MgO+CaO) is 9 to 40 mol%.

[0128] The specific gravity of glass 1 is 2.75 g / cm 3 Hereinafter, the glass transition temperature Tg is 650° C. or higher.

[0129] (Glass 2)

[0130] SiO2 56~80 mol%,

[0131] Li2O 1~10 mol%,

[0132] B2O3 0~4 mol%,

[0133] The total content of MgO and CaO (MgO+CaO) is 4-40 mol%.

[0134] The molar ratio of the total content of SiO2 and ZrO2 to the content of Al2O3 ((SiO2+ZrO2) / Al2O3) is 2 to 13.

[0135] The specific gravity of glass 2 is 2.50 g / cm 3 The glass transition temperature Tg is 500°C or higher, and the specific elastic modulus at 20°C is 30 GPa·cm 3 / g or above.

[0136] (Glass 3)

[0137] An amorphous oxide glass containing, expressed in mole %,:

[0138] SiO2 56~65%,

[0139] Al2O3 5~20%,

[0140] B2O3 0~4%,

[0141] MgO 3~28%,

[0142] Li2O 1~10%,

[0143] contain:

[0144] The total content of SiO2 and Al2O3 (SiO2+Al2O3) is 65-80%,

[0145] The total content of MgO and CaO (MgO+CaO) is 11-30%,

[0146] The total content of MgO, CaO, SrO and BaO (MgO+CaO+SrO+BaO) is 12-30%,

[0147] The sum of MgO content, 0.7×CaO content, Li2O content, TiO2 content and ZrO2 content (MgO+0.7CaO+Li2O+TiO2+ZrO2) is more than 16%,

[0148] The sum of 5×Li2O content, 3×Na2O content, 3×K2O content, 2×B2O3 content, MgO content, 2×CaO content, 3×SrO content and BaO content (5Li2O+3Na2O+3K2O+2B2O3+MgO+2CaO+3SrO+BaO) 32-58%,

[0149] The sum of SiO2 content, Al2O3 content, B2O3 content, P2O5 content, 1.5×Na2O content, 1.5×K2O content, 2×SrO content, 3×BaO content and ZnO content (SiO2+Al2O3+B2O3+P2O5+1.5Na2O+1.5K2O+2SrO+3BaO+ZnO) is less than 86%, and

[0150] The sum of SiO2 content, Al2O3 content, B2O3 content, P2O5 content, Na2O content, K2O content, CaO content, 2×SrO content and 3×BaO content (SiO2+Al2O3+B2O3+P2O5+Na2O+K2O+CaO+2SrO+3BaO) is less than 92%,

[0151] The molar ratio of CaO content to MgO content (CaO / MgO) is 2.5 or less,

[0152] The molar ratio of Na2O content to Li2O content (Na2O / Li2O) is 5 or less,

[0153] The molar ratio of Li2O content to the total content of MgO and CaO (Li2O / (MgO+CaO)) is 0.03 to 0.4.

[0154] The molar ratio of SiO2 content to the total content of Li2O, Na2O and K2O (SiO2 / (Li2O+Na2O+K2O)) is 4 to 22,

[0155] The molar ratio of the total content of SiO2 and ZrO2 to Al2O3 ((SiO2+ZrO2) / Al2O3) is 2 to 10.

[0156] The molar ratio of the total content of TiO2 and Al2O3 to the total content of MgO and CaO ((TiO2+Al2O3) / (MgO+CaO)) is 0.35 to 2,

[0157] The molar ratio of the total content of MgO and CaO to the total content of MgO, CaO, SrO and BaO ((MgO+CaO) / (MgO+CaO+SrO+BaO)) is 0.7 to 1,

[0158] The molar ratio of BaO content to the total content of MgO, CaO, SrO and BaO (BaO / (MgO+CaO+SrO+BaO)) is 0.1 or less,

[0159] The molar ratio of the P2O5 content to the total content of B2O3, SiO2, Al2O3 and P2O5 (P2O5 / (B2O3+SiO2+Al2O3+P2O5)) is 0.005 or less,

[0160] The glass transition temperature is 670°C or higher and the Young's modulus is 90 GPa or higher.

[0161] The specific gravity is below 2.75,

[0162] The average linear expansion coefficient at 100-300°C is 40×10 -7 ~70×10 -7 / ℃ range.

[0163] According to one embodiment, the glass plate 10 is preferably composed of glass having a glass transition temperature Tg of 500°C or more, and more preferably a glass transition temperature Tg of 650°C or more. The higher the glass transition temperature Tg, the more it is possible to suppress thermal shrinkage and deformation caused by thermal shrinkage when the glass plate 10 is heat-treated. Therefore, considering the heat treatment when forming a magnetic film of a magnetic disk on the substrate 1, the glass transition temperature Tg is preferably 500°C or more, and more preferably 650°C or more.

[0164] According to one embodiment, the glass plate 10 is preferably made of a glass having a linear expansion coefficient of 100×10 -7 [1 / K] or less, and more preferably a material with a linear expansion coefficient of 95×10 -7 [1 / K] or less, and more preferably, a material with a linear expansion coefficient of 70×10 -7 [1 / K] or less, and preferably has a linear expansion coefficient of 60×10 -7 [1 / K] or less. The lower limit of the linear expansion coefficient of the glass plate 10 is not particularly limited, but in the case of the glass plate 10, for example, 5×10 -7[1 / K][1 / K]. The linear expansion coefficient referred to here is a linear expansion coefficient obtained by the difference in thermal expansion between 100°C and 300°C. By using such a linear expansion coefficient, thermal expansion can be suppressed during the heating process when forming a magnetic film, etc., and when the holding part of the film forming device fixes the glass plate 10 and holds the end surface 14 of the outer peripheral end, thermal deformation of the glass plate 10 around the holding part can be suppressed. For example, in the existing aluminum alloy substrate, the linear expansion coefficient is 242×10 -7 [1 / K], and the linear expansion coefficient of the glass plate 10 in one embodiment is 51×10 -7 [1 / K].

[0165] [Experimental example]

[0166] In the manufacturing method of the glass plate 10 of the present embodiment, the glass plate 10 is suspended from the mounting surface 18 of the base during irradiation with the laser light L, thereby investigating the effect of suppressing the in-plane strain distribution in the main surface 12 of the glass plate 10. The outer diameter of the glass plate 10 is 95 mm, the inner diameter of the inner hole is 25 mm, and the thickness Th is 0.7 mm. The glass composition of the glass plate 10 is the above-mentioned glass 1.

[0167] During the heating performed before and during the irradiation of the laser light L, the heating was adjusted so that the heating temperature of the glass plate 10 became 350° C. at a position 30 mm away from the center of the glass plate 10 .

[0168] (Strain distribution measurement)

[0169] The deviation of the delay value is used in the strain distribution of the main surface 12. As the deviation of the delay value, the difference between the maximum and minimum values ​​of the delay value at 12 measurement points in the circumferential direction and radial direction of the main surface 12 is calculated. Regarding the radial positions of the 12 measurement points, the inner circumferential end face of the disk-shaped glass plate 10 is 0% and the outer circumferential end face is 100%, and there are three positions at 25%, 50%, and 75% radially outward from the inner circumferential end face. On the other hand, the circumferential position of the measurement point is four positions (0, 90, 180, and 270 degrees) separated by 90 degrees on the circumference. Linearly polarized light is irradiated at the above 12 measurement points, and the delay value of the polarized light that has passed through the glass plate 10 is measured.

[0170] (Temperature distribution measurement)

[0171] Regarding the temperature distribution of the heated glass plate 10, the deviation of the measured temperature of the glass plate 10 is used. In the measurement of the temperature distribution, the glass plate 10 is heated by the same method as when the laser light L is irradiated without irradiating the end surface 14, and the temperature of the above 12 measurement points of the main surface 12 is measured at the same timing as the timing of starting the irradiation of the laser light L at this time. In the temperature measurement, a non-contact thermometer (thermal imager) is used. The difference between the highest temperature and the lowest temperature of the temperatures at the 12 measurement points is calculated, and the difference is used as the temperature deviation.

[0172] Regarding the irradiation conditions of the laser L, the width W1 is 1 mm, the length W2 is 10 mm, and the Pd is 5.1 [W / mm 2 The moving speed of the laser light L along the end surface 14 is 20 [mm / sec].

[0173] The results of strain distribution measurement and temperature distribution measurement in Comparative Examples 1 and 2 and Examples 1 to 4 are shown in Table 1 below.

[0174] In Comparative Example 1, the glass plate 10 was placed on a hot plate heater having a cylindrical base with a circular hole inner diameter of 45 mm and an outer diameter of 75 mm for heating. In Comparative Example 2, the glass plate 10 was placed on a hot plate heater having a cylindrical base with a circular hole inner diameter of 35 mm and an outer diameter of 85 mm for heating.

[0175] In Examples 1 and 2, the glass plate 10 is suspended from the mounting surface 18 and heated using a spot type halogen lamp heater capable of adjusting the heating area from above. The distance between the halogen lamp heater and the glass plate 10 and the input power of the halogen lamp heater are different between Examples 1 and 2.

[0176] In Example 3, the glass plate 10 is suspended from the mounting surface 18 and heated using a spot-type carbon heater capable of adjusting the heating area from above.

[0177] In Example 4, main surface 12 is heated by irradiating laser light in a circular irradiation region having a diameter of 100 mm.

[0178] In Examples 1 to 4, a non-contact chuck using the Bernoulli effect is disposed as a base on the lower surface side of the main surface 12 to float and fix the glass plate 10 .

[0179] [Table 1]

[0180]

[0181] In Examples 1 to 4, in which the glass plate 10 is suspended from the mounting surface 18 and heated, the deviation of the strain (retardation value) is 30 [nm] or less, which is smaller than that of Comparative Examples 1 and 2, in which the glass plate 10 is heated in contact with the mounting surface 18, and is preferred. In Examples 2 to 4, the above deviation is 20 [nm] or less, which is more preferred. In addition, from the comparison between Example 1 and Comparative Example 2, it can be seen that by suspending the glass plate 10, the deviation of the strain can be reduced even with the same temperature deviation.

[0182] This shows that the in-plane strain distribution in the main surface 12 of the glass plate 10 can be suppressed by floating the glass plate 10 from the mounting surface 18 of the base.

[0183] The above describes in detail the method for manufacturing a glass plate and a magnetic disk of the present invention, but the method for manufacturing a glass plate and a magnetic disk of the present invention are not limited to the above-mentioned embodiments, and various improvements and changes can be made without departing from the scope of the present invention.

[0184] Explanation of symbols

[0185] 10 Glass Pane

[0186] 12 Main surface

[0187] 14 End face

[0188] 14c Chamfered face

[0189] 14t Sidewall

[0190] 16 Round hole

[0191] 18 Loading surface

[0192] 20 Laser light source

[0193] 22 Optical system

[0194] 24 converging lens.

Claims

1. A glass plate, which is a disc-shaped glass plate, in, The glass plate is a glass substrate for a magnetic disk or a raw material for a glass substrate for a magnetic disk. A circular hole is provided at the center of the glass plate. The glass plate has a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface along the circular hole. The outer peripheral end surface and / or the inner peripheral end surface has: a side wall surface extending in a direction substantially orthogonal to the main surface; and a chamfered surface interposed between the side wall surface and the main surface and formed into a curved shape convex outward, The thickness Th of the glass plate is less than 0.7 mm, In the main surface, the difference between the maximum and minimum delay values ​​at 12 locations in total is less than 30 nm, and the 12 locations in total are: assuming that the inner circumferential end face is at 0% and the outer circumferential end face is at 100%, and that there are 4 locations on the circle 90 degrees apart at each of the three radial positions of 25%, 50%, and 75% radially outward from the inner circumferential end face.

2. The glass sheet according to claim 1, in, A ratio C / Th of a length C of the chamfered surface in a radial direction of the main surface to a thickness Th of the glass sheet is 0.1 to 0.

7.

3. The glass sheet according to claim 1 or 2, in, The arithmetic mean roughness Ra of the outer peripheral end surface and / or the inner peripheral end surface is 0.02 μm or less. 4 . A method for producing a glass substrate for a magnetic disk, the method comprising polishing the main surface of the glass plate according to claim 1 .

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