阅读说明：本技术 磁盘用玻璃基板的制造方法 (Method for manufacturing glass substrate for magnetic disk ) 是由 东修平 于 2019-01-28 设计创作，主要内容包括：在从玻璃板切出玻璃坯板时,使激光的焦点位置位于所述玻璃板的板厚方向的内部,并且以从所述玻璃板的表面观察时所述焦点位置描绘圆的方式,使第1激光相对于玻璃板相对移动,从而在所述玻璃板内部形成裂纹开始部,然后,使裂纹从裂纹开始部向所述玻璃板的主表面发展,割断玻璃板,将具有分离面的玻璃坯板从所述玻璃板分离,所述分离面的表面粗糙度以算术平均粗糙度Ra计不足0.01μm、正圆度为15μm以下。此后,对所述玻璃坯板的主表面进行磨削或研磨。(When cutting out a glass blank plate from a glass plate, a focal position of a laser is positioned inside the glass plate in a plate thickness direction, and a 1 st laser is relatively moved with respect to the glass plate so that the focal position describes a circle when viewed from the surface of the glass plate, thereby forming a crack initiation portion inside the glass plate, and then, a crack is developed from the crack initiation portion toward the main surface of the glass plate, the glass plate is cut, and the glass blank plate having a separation surface is separated from the glass plate, the separation surface having a surface roughness of less than 0.01 [ mu ] m in terms of arithmetic average roughness Ra and a roundness of 15 [ mu ] m or less. Thereafter, the main surface of the glass blank plate is ground or lapped.)

1. A method for manufacturing a glass substrate for a magnetic disk, comprising:

a separation process of forming a crack initiation portion in the glass sheet by relatively moving a 1 st laser beam with respect to the glass sheet so that a focal position of the laser beam is positioned inside the glass sheet in a sheet thickness direction and the focal position describes a circle when viewed from a main surface of the glass sheet, then growing a crack from the crack initiation portion toward the main surface of the glass sheet, cutting the glass sheet, and separating a glass blank sheet having a separation surface from the glass sheet, the separation surface having a surface roughness of less than 0.01 μm in terms of arithmetic average roughness Ra and a roundness of 15 μm or less; and

and a grinding/polishing process in which at least one of grinding and polishing of the main surface of the glass blank plate is performed.

2. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the focal position is located within a range from 1/3 to 2/3 from a main surface of the glass plate to a thickness of the glass plate.

3. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the focal position is within a range of 1/3 which is less than a thickness of the glass plate from a main surface of the glass substrate.

4. The method for manufacturing a glass substrate for a magnetic disk according to any of claims 1 to 3, wherein a chamfering process is included between the separation process and the grinding/polishing process, and in the chamfering process, a corner formed by the main surface of the glass blank plate and the separation surface is chamfered by a 2 nd laser light of a different type from the 1 st laser light.

5. A method for manufacturing a glass substrate for a magnetic disk, comprising:

a separation process of forming a glass blank plate from which a portion to be removed is separated by moving a 1 st laser beam relative to the glass plate, intermittently forming defects on a circular separation boundary line defined on a main surface of the glass plate by irradiation of the 1 st laser beam, and forming linear defects so as to connect the formed defects;

a chamfering process of forming a chamfered surface on the separation surface by irradiating a 2 nd laser light different from the 1 st laser light from a normal direction of the separation surface of the glass blank from which the removal target portion is separated, and forming the glass blank having a surface roughness of the separation surface of less than 0.01 μm in terms of an arithmetic average roughness Ra and a roundness of 15 μm or less by the irradiation of the 2 nd laser light; and

and a grinding/polishing process in which at least one of grinding and polishing of the main surface of the glass blank plate is performed.

6. The method for producing a glass substrate for a magnetic disk according to claim 5, wherein a thickness of the glass plate is 0.6mm or less.

7. The method for producing a glass substrate for a magnetic disk according to claim 6, wherein a plate thickness of the glass blank plate after the grinding/polishing treatment is less than 0.52 mm.

8. The method for producing a glass substrate for a magnetic disk according to any of claims 1 to 7, wherein the 2 nd laser has a pulse width of 10^-12Pulsed laser light of seconds or less.

9. The method for producing a glass substrate for a magnetic disk according to any of claims 1 to 8,

in the grinding and polishing process, at least one of grinding and polishing is performed on the main surface of the glass blank plate while maintaining the roundness of the glass blank plate obtained by the cutting-out process and maintaining the surface roughness of at least a part of the separation surface.

10. The method for producing a glass substrate for a magnetic disk according to any of claims 1 to 9, wherein the roundness is 0.1 to 15 μm.

Technical Field

The present invention relates to a method for manufacturing a glass substrate for a magnetic disk, including a process of cutting out a glass blank plate from a glass plate using a laser.

Background

In a personal computer, a notebook personal computer, a DVD (digital versatile Disc) recording apparatus, a data center for cloud computing, and the like, a hard disk drive is used for data recording. In a hard disk device, a magnetic disk is used in which a magnetic layer is provided on a disk-shaped non-magnetic disk glass substrate. The magnetic Disk is incorporated in a DFH (Disk Flying Height) type magnetic head having a Flying distance of about 5nm, for example.

In such a DFH type magnetic head, since the floating distance is short, it is necessary to avoid the adhesion of fine particles and the like to the main surface of the magnetic disk. In order to suppress the adhesion of the fine particles, it is preferable that the glass substrate is polished with high precision not only to the main surface but also to the end face, and that the surface roughness is small. In order to stably rotate the magnetic disk at high speed, the disk-shaped magnetic disk preferably has high roundness.

In order to meet the requirements of such magnetic disks, end face polishing is performed to reduce the surface roughness of the end faces (inner end faces and outer end faces) of the magnetic disk glass substrate and to improve the roundness.

The glass substrate for a magnetic disk was obtained by cutting out a glass plate, chamfering an end face, polishing the end face, grinding and polishing the main surface, and cleaning the glass plate.

In cutting out the glass plate, a technique of cutting out a glass blank plate from the glass plate using a laser instead of scribing (scribes) and cutting by a cutter has been proposed (patent document 1).

In the above-described technique, a laser beam focal line of a pulse laser beam is made incident into a glass sheet at a predetermined incident angle, the glass sheet and the laser beam are relatively moved in parallel, and an operation of generating a defect line (a hole) along the laser beam focal line in the glass sheet is repeatedly performed, thereby forming a plurality of defect lines (holes). At this time, since the crack propagates between the adjacent defect lines (through holes), the glass blank sheet having a desired shape can be cut out from the glass sheet. The spacing of the defect lines (perforations) was 2 μm apart.

Prior art documents

[ patent document ]

[ patent document 1] Japanese patent application laid-open No. 2017-511777

Disclosure of Invention

Problems to be solved by the invention

In the above-described technique, a disc-shaped glass blank can be produced from a glass plate, but since the glass blank is cut out based on a defect line (perforation), a part of the cross-sectional shape of a hole constituting the defect line remains on the end face of the cut glass blank. Therefore, in order to obtain a magnetic disk glass plate having not only a small surface roughness of the main surface but also a small surface roughness of the end face from the cut glass blank plate, it is necessary to perform end face polishing. The grinding time for end face grinding is long, and is not preferable in terms of not only production efficiency but also production cost. The cutting is preferably performed by using a laser beam which requires a shorter polishing time than the conventional laser beam even if the end face polishing is performed, or which does not perform the end face polishing at all.

Accordingly, an object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk, the method comprising the following processes: when a glass blank plate as a raw material of a glass plate for a magnetic disk is cut out from a glass plate by using a laser, it is possible to cut out a glass blank plate having a surface roughness and a roundness which are significantly reduced in an end face polishing time as compared with the conventional one, and preferably, even if the end face polishing is not performed.

Means for solving the problems

As described above, when a disc-shaped glass blank is cut out based on a plurality of defect lines formed by punching holes in a glass sheet, the end face cannot be formed into a preferable shape satisfying both surface roughness and roundness.

On the other hand, the glass blank sheet can be cut out by irradiating the glass sheet with laser light so that the focal position reaches the main surface of the glass sheet to form a defect on the main surface and to propagate a crack from the defect into the glass sheet. In contrast, the following was found: when a glass blank sheet is cut out by forming a defect in the glass sheet and by causing a crack to progress from the defect to the main surfaces on both sides, the surface roughness of the end face is small and the roundness is high.

Further, it was found that: even in a glass blank plate which is not formed into a shape satisfying both the surface roughness and the roundness of the end face, in order to form the chamfered surface of the glass blank plate, the laser beam is irradiated from the normal direction of the separating surface which is the cut surface of the glass blank plate to the separating surface, and the glass in the vicinity of the separating surface is melted to form the chamfered surface. Based on these facts, the present inventors conceived the following modes of the invention.

One embodiment of the present invention is a method for manufacturing a glass substrate for a magnetic disk. The manufacturing method comprises the following steps: a separation process of forming a crack initiation portion in the glass sheet by relatively moving a 1 st laser beam with respect to the glass sheet so that a focal position of the laser beam is positioned inside the glass sheet in a sheet thickness direction and the focal position describes a circle when viewed from a main surface of the glass sheet, then growing a crack from the crack initiation portion toward the main surface of the glass sheet, cutting the glass sheet, and separating a glass blank sheet having a separation surface from the glass sheet, the separation surface having a surface roughness of less than 0.01 μm in terms of arithmetic average roughness Ra and a roundness of 15 μm or less; and a grinding/polishing process in which the main surface of the glass blank plate is ground or polished.

Preferably, the focal point position is within a range of 1/3 to 2/3 from the main surface of the glass sheet to the thickness of the glass sheet.

The focal point position is within 1/3 of the thickness of the glass plate from the main surface of the glass substrate.

Preferably, a chamfering process is included between the separation process and the grinding/polishing process, and a corner formed by the main surface of the glass blank plate and the separation surface is chamfered by a 2 nd laser different from the 1 st laser in the chamfering process.

Another embodiment of the present invention is a method for manufacturing a glass substrate for a magnetic disk. The manufacturing method comprises the following steps: a separation process of moving a 1 st laser beam relative to a glass plate, intermittently forming defects on a circular separation boundary line defined on a main surface of the glass plate by irradiation of the 1 st laser beam, and forming linear defects so as to connect the formed defects, thereby separating a glass blank plate from the glass plate; a chamfering process in which a chamfered surface is formed on a separating surface of the glass blank plate by irradiating a 2 nd laser light of a different kind from the 1 st laser light from a normal direction of the separating surface, and the glass blank plate having a surface roughness of the separating surface of less than 0.01 μm in terms of arithmetic average roughness Ra and a roundness of 15 μm or less is formed by the irradiation of the 2 nd laser light; and a grinding/polishing process for performing at least one of grinding and polishing of the main surface of the glass blank plate.

The thickness of the glass plate is 0.6mm or less.

Further, it is preferable that the thickness of the glass raw plate after the grinding/polishing treatment is less than 0.52 mm.

Preferably, the 2 nd laser has a pulse width of 10^-12Pulsed laser light of seconds or less.

Preferably, in the grinding/polishing process, at least one of grinding and polishing is performed on the main surface of the glass blank plate while maintaining the roundness of the glass blank plate obtained by the cutting-out process and maintaining the surface roughness of at least a part of the separation surface.

The roundness is 0.1-15 mu m.

[ Effect of the invention ]

According to the above-described method for producing a glass substrate for a magnetic disk, a glass blank plate having a surface roughness and a roundness of an end face which are significantly reduced in end face polishing time compared to conventional ones, preferably without end face polishing, can be cut.

Drawings

Fig. 1 (a) is a perspective view of an example of a magnetic disk glass substrate produced in the present embodiment, and (b) is a view showing an example of a cross section of an outer end surface of the magnetic disk glass substrate shown in (a).

Fig. 2 (a) and (b) are diagrams for explaining an example of the method of cutting out the glass blank plate from the glass plate according to the present embodiment.

Fig. 3 is a diagram for explaining an example of the method of cutting out the glass blank plate from the glass plate according to the present embodiment.

Fig. 4 is a diagram for explaining an example of chamfering processing performed in the present embodiment.

Fig. 5 is a diagram for explaining an example of the process of forming the chamfered surface in the present embodiment.

Detailed Description

In the method of manufacturing a glass substrate for a magnetic disk of the present embodiment, a disk-shaped glass blank is cut out from a glass plate along an inner circle and an outer circle which are concentric circles, and after chamfering processing of a corner portion of a connecting portion between an end face (parting face) of the cut-out disk-shaped glass blank and a main surface is performed, grinding and polishing of the main surface are performed to manufacture a glass substrate for a magnetic disk.

Here, the surface roughness of the separating surface, i.e., the end surface (inner end surface, outer end surface), of the glass blank cut out from the glass plate using the conventional laser, i.e., the arithmetic mean roughness Ra and the roundness do not satisfy the required ranges of the end surfaces of the glass plate for a magnetic disk. Although the arithmetic average roughness Ra can be made within a desired range by polishing the end faces of the glass blank plate cut out by the conventional method, the end face polishing requires a lot of time and is inefficient in production. On the other hand, it is difficult to adjust the roundness of the glass blank sheet having low roundness.

In view of this, in the present embodiment, the glass blank plate is cut out from the glass plate using the laser, but the glass blank plate is cut out in a different manner from the conventional one.

Specifically, in the 1 st process as one embodiment, the focal position of the 1 st laser beam is positioned inside the glass sheet in the sheet thickness direction, and the 1 st laser beam is moved relative to the glass sheet so that the focal position describes a circle when viewed from the main surface of the glass sheet, thereby forming a circular crack initiation portion inside the glass sheet. Then, the glass sheet is cut by advancing the crack from each position of the circular crack initiation portion toward the main surface of the glass sheet, and a glass blank sheet having a separation surface (cut surface) with a surface roughness of less than 0.01 μm in terms of arithmetic average roughness Ra and a roundness of 15 μm or less is separated from the glass sheet.

The crack initiation portion is a portion that is damaged, melted, deteriorated, or altered by irradiation with laser light, for example. For example, by heating the glass sheet, cracks develop from the crack initiation portion to both main surfaces of the glass sheet.

Then, before grinding and polishing treatment described later, chamfering treatment for forming a chamfered surface by using a 2 nd laser is performed. Therefore, between the separation process of separating the glass blank plate from the glass plate and the grinding/polishing process, the corner portion formed by the main surface and the separation surface of the glass blank plate is chamfered by the 2 nd laser light of a different type from the 1 st laser light.

In the second process 2 as another embodiment, the 1 st laser beam is moved relative to the glass plate, and the 1 st laser beam is irradiated to intermittently form the defects on the separation boundary line of the circular shape defined on the main surface of the glass plate, and the linear defects are formed so as to connect the formed defects, thereby separating the glass blank plate from the glass plate. A chamfer surface is formed on a separating surface of the separated glass blank plate by irradiating a 2 nd laser from a normal direction of the separating surface, and the glass blank plate having an arithmetic average roughness Ra of a surface roughness of the separating surface of less than 0.01 [ mu ] m and a roundness of 15 [ mu ] m or less is formed by the irradiation of the 2 nd laser.

The defects include flaws, melted portions, deteriorated or modified portions (hereinafter referred to as flaws, etc.) formed in the glass, and holes (including through holes and non-through holes) having a small hole cross section and rapidly recessed from the main surface of the glass sheet, cracks, and the like. Such defects become the core of the crack growth that progresses.

The intermittent formation of defects includes the formation of a plurality of holes (including through holes and non-through holes) in the glass plate, which have small hole cross sections and are cut at intervals in the depth direction of the glass plate to form flaws or the like serving as cores for crack generation.

The formation of the linear defects includes formation of cracks connecting the intermittently formed defects in a linear manner. The cracks include not only cracks in which physical gaps are clearly formed in the glass material but also potential cracks in which boundary surfaces are formed without forming physical gaps.

Separating the glass blank from the glass sheet comprises: removing an outer portion of the surrounding glass blank to form a separated edge into a circular periphery; and removing the inner portion surrounded by the glass gob to form a circular inner hole.

In the measurement of the roundness, for example, a plate-shaped probe having a thickness thicker than the plate thickness of the glass blank plate is disposed so as to face the end face in a direction perpendicular to the main surface of the glass substrate, the glass blank plate is rotated in the circumferential direction to obtain a contour line, and the difference between the radii of an inscribed circle and a circumscribed circle of the contour line is calculated as the roundness of the glass substrate. For example, a roundness/cylinder shape measuring device can be used for measuring roundness.

The arithmetic average roughness Ra is measured in accordance with JIS B0601: 2001, respectively. The arithmetic average roughness Ra was determined by measuring the surface shape of the end face of the glass blank plate in the evaluation region of 50 μm square using a laser microscope under the following conditions.

Observation magnification: the weight of the mixture is 3000 times that of the mixture,

measurement pitch in height direction (Z axis): the thickness of the film is 0.01 mu m,

cutoff λ s: the thickness of the film is 0.25 mu m,

cutoff λ c: 80 μm.

The resolution in the height direction is preferably 1nm or less. In the present embodiment, the observation magnification is 3000 times, but the observation magnification may be appropriately selected in a range of about 1000 to 3000 times according to the size of the measurement surface.

In the above-described process 1, the optical system of the laser light source is adjusted so that the focal position of the 1 st laser light is positioned inside the glass sheet in the thickness direction, and therefore, the light energy is concentrated at the focal position and locally heated, and the crack initiation portion is formed inside the glass. Thereafter, the glass sheet is heated, for example, to cause cracks to develop from the crack initiation portion toward the main surface. The surface roughness of the cut surface formed by the crack is small. Further, a circle which is a locus of a focal position can be highly rounded by a moving mechanism or the like which can relatively move the 1 st laser beam on the glass plate with high accuracy. Therefore, although the accuracy of the roundness of the glass blank sheet depends on the straightness of the crack extending from the focal point position toward the main surface, the crack extends from the inside in the thickness direction of the glass sheet, and therefore the distance of progression is shorter than that of the crack progressing from one main surface toward the other main surface. Therefore, deterioration in roundness can be suppressed.

In addition, in the 2 nd process, in the case of separating the glass blank plate by forming the crack connecting the defects intermittently formed with defects by irradiation with the 1 st laser beam, the arithmetic average roughness Ra of the separation surface may be large and the roundness may be low, but since the 2 nd laser beam is irradiated to the separation surface from the normal direction of the separation surface to form the chamfered surface while melting the glass in the vicinity of the separation surface by heat, the chamfered surface is formed by irradiation with the 2 nd laser beam, and the surface roughness of the separation surface can be reduced and the accuracy of the roundness can be improved by irradiation with the 2 nd laser beam. Thus, the arithmetic average roughness Ra of the surface roughness of the separating surface can be made smaller than 0.01 μm, and the roundness can be made 15 μm or less. According to one embodiment, the roundness may be 0.1 to 15 μm. The circularity is preferably 10 μm or less, more preferably 7 μm or less, and still more preferably 5 μm or less.

Hereinafter, a method for manufacturing a magnetic disk glass substrate according to the present embodiment will be described with reference to the drawings. Fig. 1 (a) is a perspective view of an example of a magnetic disk glass substrate produced in the present embodiment. Fig. 1 (b) is a view showing an example of a cross section of the outer end surface of the magnetic disk glass substrate shown in fig. 1 (a).

A magnetic disk glass substrate (hereinafter referred to as a glass substrate) 1 shown in fig. 1 (a) is an annular thin-plate glass substrate. The glass substrate for a magnetic disk is, for example, a glass substrate for a magnetic disk having a nominal diameter of 2.5 inches or 3.5 inches, regardless of the size of the glass substrate for a magnetic disk. In the case of a magnetic disk glass substrate having a nominal diameter of 2.5 inches, for example, the outer diameter is 65mm and the diameter of the center hole is 20 mm. The glass substrate 1 has a thickness of 1.0mm or less, for example, 0.6mm to 1.0 mm. Alternatively, the thickness is less than 0.6mm, for example less than 0.52 mm. A magnetic disk was produced by forming a magnetic layer on the main surface of the glass substrate 1.

The glass substrate 1 includes: a pair of main surfaces 11p, 12 p; a side wall surface 11w formed on the outer end surface; chamfered surfaces 11c, 12c interposed between the side wall surface 11w and the main surfaces 11p, 12 p; a side wall surface, not shown, formed on the inner end surface in the same manner as the outer end surface; and chamfered surfaces, not shown, interposed between the side wall surfaces and the main surfaces 11p and 12 p.

The glass substrate 1 has a circular hole in the center. The side wall surface 11w includes the center position in the plate thickness direction of the glass substrate 1. The inclination angle of the chamfered surfaces 11c, 12c with respect to the main surfaces 11p, 12p is not particularly limited, and is, for example, 45 °. The boundary between the side wall surface 11w and the chamfered surfaces 11c and 12c is not limited to the shape having an edge as shown in the figure, and may be a smoothly continuous curved surface. As shown in fig. 1 (b), the chamfered surfaces 11c and 12c may be curved instead of being linearly inclined in their cross-sectional shape.

(treatment No. 1)

In the production of the glass substrate 1, a separation process of cutting out a glass blank plate from a previously produced glass plate using a laser is performed. Fig. 2 (a), (b) and 3 are diagrams for explaining the separation process according to the embodiment of cutting out a glass blank plate from the glass plate 20.

The glass sheet 20 is a glass sheet having a constant thickness by the float method or the down-draw method, for example. Alternatively, the glass plate may be formed by press-molding a glass block using a mold. The thickness of the glass plate 20 is larger by the removal amount of grinding and polishing, for example, by about several μm, than the target thickness when the final product, that is, the glass substrate for a magnetic disk is obtained.

The laser light source 30 is a device that emits laser light L1 (1 st laser light), and for example, YAG laser light or ND: YAG laser, and the like. Therefore, the wavelength of the laser light is, for example, in the range of 1030nm to 1070 nm.

The laser beam L1 is a pulsed laser beam, and in one embodiment, the pulse width of the laser beam L1 is preferably set to 10 from the viewpoint of suppressing excessive glass deterioration at the focal position F of the laser beam L1^-12Seconds or less (1 picosecond or less). The optical energy of the laser beam L1 can be appropriately adjusted according to the pulse width and the repetition frequency of the pulse width. When light energy is supplied excessively with respect to the pulse width and the repetition frequency, the glass is liable to be excessively deteriorated and residues are liable to be present at the focal position F.

As shown in fig. 2 (b), since the optical system of the laser light source 30 is adjusted so that the focal position F of the laser light L1 is located inside the glass sheet 20 in the sheet thickness direction, the light energy is concentrated at the focal position F and locally heated, and a crack starting portion (core of crack generation) due to damage, melting, deterioration, or alteration is formed. Since the focal point position F moves relative to the glass plate 20 so as to draw a circle when viewed from the surface of the glass plate 20, the crack initiation portion has a circular shape. By heating the glass plate 20 or the like, as shown in fig. 3, a crack C starts to be generated in the glass from each position of the crack starting portion, and the crack C progresses toward the main surface. Thus, the glass blank can be easily separated from the glass sheet 10 without applying a large force for cutting.

Thus, the surface roughness of the parting surface (cut surface) is less than 0.01 μm in terms of the arithmetic average roughness Ra, and a glass blank plate having a roundness of 15 μm or less can be obtained. The circularity is preferably 10 μm or less, more preferably 7 μm or less, and still more preferably 5 μm or less. The separation surface (cut surface) is an end surface that satisfies the requirements of the end surface of the magnetic disk glass substrate. Therefore, the separation surface (cut surface) does not need to be ground.

In addition, according to one embodiment, the focal point position F is preferably located within a range of 1/3 to 2/3 from the main surface of the glass sheet 20 to the thickness of the glass sheet 20. By setting the focal position F within this range, the parting surface (cut surface) satisfying the requirements of roundness and surface roughness can be directly used as the side wall surface 11w shown in fig. 1 (b), and therefore, unnecessary processing such as end surface grinding is not required, and the production efficiency can be improved.

Further, according to one embodiment, the focal point position F is preferably located within a range of 1/3 which is smaller than the plate thickness of the glass plate from the main surface of the glass plate. In this case, the vicinity of the focal position F where the residue is more likely to be formed than the parting surface (cut surface) formed by the crack and the surface roughness is reduced becomes a portion to be removed by the chamfering process described later. Therefore, in the case of further improving the surface roughness, the focal point position F is preferably located within a range of 1/3 which is smaller than the plate thickness of the glass plate from the main surface of the glass plate.

According to one embodiment, laser light L1 is preferably pulsed at 10 widths^-12Pulsed laser light of seconds or less. At pulse widths in excess of 10^-12In the case of seconds, the light energy is concentrated at the focal position F, and the glass near the focal position F is changed in quality, which tends to reduce the surface roughness.

The chamfering process is performed in this way for chamfering the corner portion formed by the main surface and the end face as the separation surface (cut surface) of the glass blank plate separated from the glass plate 20. Specifically, the corners are chamfered with a laser beam L2 (2 nd laser beam) of a different type from the laser beam L1. Fig. 4 is a diagram illustrating an example of chamfering. The corner 40 is irradiated with the laser light L2 from a direction inclined at an inclination angle of 30 to 60 degrees with respect to the main surface, and the corner 40 is heated and softened to be evaporated, whereby the corner 40 can be chamfered. For example, CO may be preferably used₂And (4) laser. In this case, the laser light L2 is a pulse laser light having a repetition period of 5KHz or more and a power density of 100W/cm per 1 pulse per unit area²The following. Such chamfering enables formation of a chamfered surface having low surface roughness and high roundness.

Thus, the corner formed by the lower main surface and the sidewall surface shown in fig. 3 can be chamfered using the same laser L2. Since the corner portion 40 is chamfered by the laser L2, the productivity is higher than that in the case of chamfering with a grinding wheel or the like.

In this way, since end face polishing is not required from the cutting-out to chamfering of the glass blank 30, the production efficiency is improved.

(treatment No. 2)

In the 2 nd process of the other embodiment, the laser light L1 (the 1 st laser light) is moved relative to the glass sheet 20, and the laser light L1 is irradiated to intermittently form defects on the separation boundary line of the circular shape defined on the glass sheet 20, and linear defects are formed to connect the formed defects, thereby separating the glass blank sheet from the glass sheet 20. The distance between the intermittently formed defect and the adjacent defect is about several μm, for example, 1 to 10 μm.

In this case, as shown in fig. 2 (b), the focal position F of the laser light L1 may not necessarily be located inside the thickness of the glass sheet 20 in the thickness direction, and the focal position F is not limited. For example, the focal position F may also be located on the main surface of the glass plate 20. By irradiation with the laser light L1, the light energy is concentrated and locally heated at the irradiation position, and a defect caused by a flaw, melting, deterioration, or alteration is formed as a crack initiation portion (a core of crack generation). By heating the glass plate 20 or the like, cracks develop from each position of the crack initiation portion until the cracks are linearly connected to adjacent defects. This enables a linear defect to be formed on the separation boundary line, and the glass blank plate can be separated from the glass plate 20. In order to facilitate separation when separating the glass blank plate from the glass plate 20, the glass plate 20 may be heated by a heater or a laser beam to form a gap due to a difference in thermal expansion between the glass blank plate and the other portions.

The laser light L1 (1 st laser light) for intermittently forming defects is, for example, YAG laser light or ND: YAG laser, and the like. Therefore, the wavelength of the laser light is, for example, in the range of 1030nm to 1070 nm.

The laser beam L1 is a pulsed laser beam, and in one embodiment, the pulse width of the laser beam L1 is preferably 10 from the viewpoint of suppressing excessive glass deterioration^-12Seconds or less (1 picosecond or less).

The optical energy of the laser beam L1 can be appropriately adjusted according to the pulse width and the repetition frequency of the pulse width. When light energy is supplied excessively with respect to the pulse width and the repetition frequency, the glass is likely to be excessively deteriorated, and residues are likely to be present at the irradiation position.

In the case of the process 2, since the crack initiation end is not limited to the inside of the glass sheet 20, the surface roughness and roundness of the separation surface of the separated glass blank sheet may not be sufficient. However, when a chamfer surface is formed on the separation surface as shown in fig. 5, the separation surface is irradiated with laser light L2 from the normal direction of the separation surface, whereby a part of the glass in the vicinity of the separation surface is heated and melted by the irradiation of the laser light L2. Therefore, the surface roughness of the separating surface can be reduced and the roundness can be improved by the irradiation of the 2 nd laser beam. Fig. 5 is a diagram illustrating an example of the process of forming the chamfered surface. By appropriately setting the intensity and spot size of the laser light L2, the chamfer surface can be formed, and the surface roughness of the separating surface can be reduced to improve the roundness. By adjusting the intensity of the light energy irradiated to the separating surface by the 2 nd laser beam and the spot size on the separating surface, a chamfered surface having a desired shape can be formed, and a preferable separating surface having a small surface roughness and a high degree of roundness can be formed.

The laser beam L2 is formed by making a laser beam L2 emitted from a laser light source into parallel light by an optical system including a collimator lens or the like, then converging a 2 nd laser beam L2 through a converging lens 34, and then irradiating the spread laser beam L2 to a separation surface. On the other hand, the glass plate 20 rotates at a constant speed with the center position of the glass plate 20 as the rotation center. Thus, the laser beam L2 is irradiated to the entire circumference of the separation surface of the glass plate 20 while the laser beam L2 and the separation surface are moved relative to each other in the circumferential direction of the glass plate 20.

Here, the irradiation of the laser light L to the separating surface is performed from the normal direction of the irradiated separating surface, but the normal direction includes, as an allowable error range, a direction inclined within a range of an inclination angle of 0 degree ± 10 degrees with respect to the normal direction in addition to the perfect normal direction (inclination angle of 0 degree).

In the example shown in fig. 5, the chamfered surface is formed using the outer peripheral end surface 24 of the glass plate 20 as the parting surface, but the chamfered surface may be formed using the inner peripheral end surface 26 along the inner hole of the disc-shaped glass plate 20 as the parting surface.

As an example of the laser light L2, CO is used₂The laser light is not limited to CO as long as it has an oscillation wavelength that absorbs glass₂And (4) laser. Examples thereof include a CO laser (oscillation wavelength: 5 μm), an Er-YAG laser (oscillation wavelength: 2.94 μm), and the like.

Thus, a glass blank plate having a surface roughness of the parting surface of less than 0.01 μm in terms of arithmetic average roughness Ra and a roundness of 15 μm or less can be obtained. The circularity is preferably 10 μm or less, more preferably 7 μm or less, and still more preferably 5 μm or less. The separating surface is an end surface that satisfies the requirements of the end surface of the magnetic disk glass substrate. Therefore, the end face does not need to be polished.

Since the thinner the glass sheet is, the more easily the glass near the separation surface is melted in a short time by irradiation of the laser light L2 to the separation surface, such a 2 nd treatment is effective for an extremely thin glass sheet having a sheet thickness of 0.6mm or less. In this case, the thickness of the glass blank after grinding and polishing treatment described later is preferably set to less than 0.52 mm.

By performing the above-described processes 1 and 2, a disk-shaped glass blank having a circular outer periphery and having concentric inner holes formed in the circular outer periphery is obtained.

(grinding and polishing treatment of Main surface)

The glass blank plate separated from the glass plate and having the chamfered surface is subjected to grinding and polishing treatment of the main surface.

In the grinding and polishing treatment, the glass blank plate is ground and then polished.

In the grinding process, the main surface of the glass blank plate is ground using a double-side grinding apparatus provided with a planetary gear mechanism. Specifically, the main surfaces on both sides of the glass blank sheet are ground while holding the outer peripheral end face of the glass blank sheet in a holding hole provided in a holding member of the double-side grinding apparatus. The double-side grinding device has a pair of upper and lower stages (upper stage and lower stage) between which a glass blank plate is held. Further, by moving either or both of the upper and lower surface plates, the glass blank plate and the surface plates can be moved relative to each other while supplying the coolant, and both main surfaces of the glass blank plate can be ground. For example, a grinding member formed by fixing diamond particles with resin and forming a sheet may be attached to a table and subjected to grinding treatment.

Next, the main surface of the glass blank after grinding was subjected to the 1 st polishing. Specifically, the main surfaces on both sides of the glass blank sheet are polished while holding the outer peripheral end face of the glass blank sheet in a holding hole provided in a polishing carrier of a double-side polishing apparatus. The purpose of the 1 st polishing is to remove scratches and deformation remaining on the main surface after the grinding treatment, or to adjust fine surface irregularities (microwaviness and roughness).

In the 1 st polishing process, a double-side polishing apparatus having the same structure as that of the double-side polishing apparatus used in the above-described polishing process using fixed abrasive grains was used to polish the glass blank plate while supplying the polishing slurry. In the 1 st polishing treatment, a slurry containing free abrasive grains was used. As the free abrasive grains used for the 1 st polishing, for example, abrasive grains of cerium oxide, zirconium oxide, or the like are used. The double-side polishing apparatus also holds the glass blank plate between a pair of upper and lower platens, as in the double-side polishing apparatus. A flat polishing pad (e.g., a resin Polisher) having an annular shape as a whole is attached to the upper surface of the lower platen and the bottom surface of the upper platen. Then, by moving either or both of the upper platen and the lower platen, the glass blank plate and each platen are moved relative to each other, whereby both main surfaces of the glass blank plate are polished. The abrasive grains preferably have a size in the range of 0.5 to 3 μm in terms of average particle diameter (D50).

The glass blank may be chemically strengthened after the 1 st polishing. In this case, the glass blank is immersed in the chemical strengthening solution using, for example, a mixed solution of potassium nitrate and sodium sulfate. Thereby, a compressive stress layer can be formed on the surface of the glass blank by ion exchange.

Next, the glass green sheet was subjected to the 2 nd polishing. The purpose of the 2 nd polishing process is to mirror-polish the main surface. In the 2 nd polishing, a double-side polishing apparatus having the same configuration as that of the double-side polishing apparatus used in the 1 st polishing was also used. Specifically, the main surfaces on both sides of the glass blank sheet are polished while holding the outer peripheral end face of the glass blank sheet in a holding hole formed in a polishing carrier of a double-side polishing apparatus. In the 2 nd polishing process, the hardness of the resin polisher differs from that of the 1 st polishing process in the type and particle size of the free abrasive grains. The hardness of the resin polisher is preferably lower than that of the 1 st grinding treatment. For example, a polishing liquid containing colloidal silica as free abrasive grains is supplied between a polishing pad of a double-side polishing apparatus and the main surface of a glass blank plate, and the main surface of the glass blank plate is polished. The abrasive grains used for the 2 nd grinding preferably have a size in the range of 5 to 50nm in terms of an average grain diameter (d 50).

In one embodiment, whether or not the chemical strengthening treatment is required may be appropriately selected in consideration of the glass composition and the necessity. In addition to the 1 st polishing process and the 2 nd polishing process, other polishing processes may be added, and the polishing process of both main surfaces may be completed by one polishing process. The order of the above-described processes may be changed as appropriate.

Thus, the main surface of the glass blank 20 is polished to obtain a magnetic disk glass substrate satisfying the conditions required for the magnetic disk glass substrate.

Grinding and polishing of the main surface of the glass raw plate 20 are not always performed, and at least either one may be performed. For example, polishing may be performed without grinding.

The glass starting sheet 20 may be subjected to an end face polishing process of polishing the end face (separation face) of the glass starting sheet 20 before the 1 st polishing, for example, after the 1 st polishing, before the 1 st polishing, or before the 1 st polishing.

Even when such an end face polishing treatment is performed, the time required for the end face polishing treatment is short because the arithmetic mean roughness Ra of the end face of the raw glass plate 20 is less than 0.01 μm and the roundness is 15 μm or less. The end face polishing treatment may be performed by a polishing brush method in which the end face is polished with a polishing brush while supplying the free abrasive grains thereto, or a polishing method using a magnetically functional fluid. The grinding method using the magnetic functional fluid is, for example, the following method: the slurry containing abrasive grains in the magnetorheological fluid is formed into a lump by a magnetic field, the end face of the glass blank plate 20 is inserted into the lump, and the lump and the glass blank plate 20 are rotated relative to each other to grind the end face.

However, in order to improve the production efficiency, it is preferable not to perform the end face polishing treatment. In this case, in the grinding and polishing process of the main surface, the main surface of the glass blank plate is ground or polished while maintaining the roundness of the glass blank plate obtained by the cutting-out process and further maintaining the surface roughness of at least a part of the separation surface.

As a material of the magnetic disk glass substrate in the present embodiment, aluminosilicate glass, soda-lime glass, borosilicate glass, or the like can be used. In particular, aluminosilicate glass can be preferably used from the viewpoint of being able to perform chemical strengthening and being able to produce a magnetic disk glass substrate having excellent flatness of the main surface and excellent substrate strength. More preferably amorphous aluminosilicate glass.

The composition of the magnetic disk glass substrate of the present embodiment is not limited, but the glass substrate of the present embodiment is preferably an amorphous aluminosilicate glass having the following composition: SiO in mol% converted to oxide₂50 to 75% of Al₂O₃1 to 15% of Li₂O、Na₂O and K₂5 to 35% in total of at least one selected from O, 0 to 20% in total of at least one selected from MgO, CaO, SrO, BaO and ZnO, and ZrO₂、TiO₂、La₂O₃、Y₂O₃、Ta₂O₅、Nb₂O₅And HfO₂At least one component selected from (1) is 0 to 10% in total.

The glass substrate of the present embodiment is preferably an amorphous aluminosilicate glass having the following composition: for example, 57 to 75% by mass of SiO₂5 to 20% of Al₂O₃(wherein, SiO)₂And Al₂O₃The total amount of (B) is 74% or more), ZrO₂、HfO₂、Nb₂O₅、Ta₂O₅、La₂O₃、Y₂O₃And TiO₂More than 0% and not more than 6% in total, Li₂O is more than 1% and not more than 9%, Na₂O is 5 to 28% (wherein, the mass ratio of Li to O is Li₂O/Na₂O is less than 0.5), K₂0 to 6% of O, 0 to 4% of MgO, more than 0% and not more than 5% of CaO (wherein the total amount of MgO and CaO is not more than 5%, and the content of CaO is more than that of MgO), and 0 to 3% of SrO + BaO.

The composition of the magnetic disk glass substrate of the present embodiment comprises SiO₂、Li₂O、Na₂O and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO and BaO, wherein the molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO/(MgO + CaO + SrO + BaO)) may be 0.20 or less, and the glass transition temperature may be 650 ℃ or more. The glass substrate for a magnetic disk having such a composition is suitable for a glass substrate for a magnetic disk used for a magnetic disk for energy assisted magnetic recording.

The method for producing a glass substrate for a magnetic disk of the present invention has been described above in detail, but the method for producing a glass substrate for a magnetic disk of the present invention is not limited to the above embodiment, and various improvements and modifications can be made without departing from the scope of the present invention.

Description of the reference symbols

1 glass substrate for magnetic disk

11p, 12p major surface

11w side wall surface

11c, 12c chamfer

20 glass plate

24 peripheral end face

26 inner peripheral end face

30 laser light source

34 converging lens

40 corner