JP2015129056A - Method of cutting glass substrate and method of manufacturing glass substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of improving efficiency of grinding processing in cutting of a disk-like glass substrate out of a glass plate using a core drill, and a method of suppressing chipping of the glass substrate.SOLUTION: There is provided a method of cutting a glass substrate in which a disk-like substrate is cut out of a glass plate using a core drill. The core drill has cylindrical grinding parts 42, 52 having abrasive grains 60 fixed with a binder 70, and the grinding parts 42, 52 each have a tip part 80 where the abrasive grains 60 and binder 70 are exposed, and side face parts 82, 83 which each have a protective film 90 formed on a surface of the binder 70 on the side face of the cylindrical shape, the abrasive grain content of the grinding parts 42, 52 being 6-15% in volume percentage.

Description

  The present invention relates to a method for cutting a glass substrate and a method for producing a glass substrate for a magnetic recording medium.

  For example, as a manufacturing method for cutting a disk-shaped glass substrate from a glass plate formed in a flat plate shape, a disk-shaped glass substrate is cut out from a square glass plate having a predetermined dimension, and the surface of the glass substrate is predetermined. There is a method of grinding to the thickness of the glass substrate and then grinding and polishing the end face of the glass substrate (see, for example, Patent Document 1). Moreover, when cutting a disk-shaped glass substrate from a square glass plate, a cutting process is performed using a core drill having a cylindrical diamond grindstone. The core drill thus formed in a cylindrical shape has a predetermined drill width by fixing diamond abrasive grains to the end of the cylindrical base metal by metal bonding. Further, when a glass plate is cut with a core drill, the grain size of the diamond abrasive grains, the concentration of the abrasive grains, the type of bond, the degree of bonding, and the grinding conditions (rotation speed, grinding fluid, feed speed, etc.) are affected.

JP 2008-243292 A

  However, when cutting the disk-shaped glass substrate by bringing the end of the rotating core drill into contact with the glass plate, grinding is performed depending on conditions such as the grain size of the diamond abrasive grains, the concentration of the abrasive grains, and the bonding degree of each abrasive grain. The glass plate, which is a brittle material, when the size of the abrasive grains, the shape of the abrasive grains, the spacing between the abrasive grains, and the bonding force that holds the abrasive grains change to reduce the grinding ability (sharpness) There is a problem that chipping is likely to occur.

  Also, in the core drill that rotates at high speed when cutting the glass substrate, the cylindrical grinding part is not a perfect circle, or the center of the grinding part is the axis (rotation center) when the grinding part is replaced with the base metal If it deviates from the range, it will sway and grinding accuracy will not be maintained. In addition, the core drill may be deformed in the shape of the diamond wheel in the grinding part during grinding and lose its roundness.

  Therefore, in the core drill manufacturing process and maintenance, adjustments such as truing and dressing treatment that adjusts the size and shape variation of each abrasive grain and the variation of the protruding amount of each abrasive grain from the bond layer holding each abrasive grain Doing work. At that time, there is a problem in that the adjustment work for adjusting the shape and the protruding amount of the abrasive grains of the grinding part provided in the core drill takes time and reduces productivity.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method for cutting a glass substrate and a method for manufacturing a glass substrate for a magnetic recording medium that have solved the above problems.

In one proposal, a method for cutting a glass substrate using a core drill to cut a disk-shaped glass substrate from a glass plate,
The core drill has a cylindrical grinding portion in which abrasive grains are fixed with a binder,
The grinding part is a tip part where the abrasive grains and the binder are exposed;
A side surface part formed with a protective film on the surface of the binder on the side surface of the cylindrical shape,
A method for cutting a glass substrate, wherein the abrasive grain content of the grinding part is a volume ratio of 6% to 15%, is provided.

  According to one aspect, the frictional resistance is reduced by the protective film formed on the surface of the binder on the side surface of the grinding part, thereby suppressing the heat generation of the grinding part and the reduction of the grinding ability (sharpness) of the grinding part. And it becomes possible to suppress generation | occurrence | production of the chipping at the time of cut | disconnecting a disk shaped glass substrate from a glass plate. In addition, it is possible to increase the production efficiency of the disk-shaped glass substrate by increasing the number of sheets that can be continuously processed without performing the truing / dressing processing of the grinding part accompanying the grinding process.

It is a figure which shows an example of each process of the cutting method of a glass substrate, and the manufacturing method of the glass substrate for magnetic recording media. It is a figure which shows the process sequence of the process of extracting a glass substrate from a glass plate. It is a disassembled perspective view which shows the process of extracting a glass substrate from a glass plate. It is a perspective view which illustrates the shape of a glass substrate. It is a longitudinal cross-sectional view which shows the structure of the core drill for internal diameter processing. It is a figure which shows the structure of the core drill for outer diameter processing. It is a longitudinal cross-sectional view which expands and shows the grinding part of each core drill.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

Embodiment 1
FIG. 1 is a diagram showing an example of each step of a method for cutting a glass substrate and a method for producing a glass substrate for a magnetic recording medium. FIG. 2 is a diagram showing a processing procedure in a process of extracting the glass substrate from the glass plate. FIG. 3 is an exploded perspective view showing a step of extracting the glass substrate from the glass plate.

Here, with reference to FIGS. 1-3, each process of the method of cut | disconnecting a glass substrate from a glass plate using a core drill and the manufacturing method of the glass substrate for magnetic recording media is demonstrated.
[Glass plate processing process]
A glass plate is prepared by cutting a glass plate formed into a plate shape by a float method, a press molding method, a redraw method, a fusion method, or the like into a rectangular shape (rectangular shape or square shape) having a predetermined length. Further, the glass plate is processed to a prescribed thickness according to the standard of the glass substrate that is the product (S11).

[Extraction process]
A disk-shaped glass substrate is extracted using a core drill for inner diameter processing and outer diameter processing that rotates at high speed (S12).

  Here, the processing procedure of the extraction process will be described with reference to FIGS.

  As shown in FIG. 2A, in the processing procedure 1, the glass plate 10 cut into a square shape is mounted on the table 20 of the core drilling machine. Then, the center of the glass plate 10 clamped on the table 20 is positioned so as to coincide with the center of rotation of the inner diameter machining core drill 40. The upper surface of the table 20 is provided with a through hole 22 into which a grinding part of the inner diameter machining core drill 40 is inserted, and an annular recess 24 into which a grinding part of the outer diameter machining core drill 50 formed in a cylindrical shape is inserted. ing. The through hole 22 and the annular recess 24 are provided so that the ground portions of the core drills 40 and 50 do not come into contact with each other during the cutting process.

  As shown in FIG. 2B, in the processing procedure 2, the core drill 40 for inner diameter processing is lowered while rotating at high speed, and the tip (end portion) of the grinding portion (diamond wheel) 42 formed in a cylindrical shape is made of glass. The top surface of the plate 10 is brought into contact. Thus, grinding by the inner diameter machining core drill 40 is started and a grinding fluid (coolant) is supplied to the grinding portion 42. When the inner diameter machining core drill 40 is lowered, the grinding portion 42 penetrates the glass plate 10 and the inner peripheral portion is cut from the glass plate 10. Thereby, a center hole is formed at the center of the glass plate 10.

  As shown in FIG. 2C, in the processing procedure 3, the outer diameter processing core drill 50 is lowered from above. Since the rotation center of the outer diameter machining core drill 50 is coaxial with the inner diameter machining core drill 40, it is positioned so as to coincide with the center of the glass plate 10.

  As shown in FIG. 2D, in the processing procedure 4, the outer diameter processing core drill 50 is lowered while rotating at a high speed, and the tip (end) of the grinding portion (diamond wheel) 52 formed in a cylindrical shape is moved. The glass plate 10 is brought into contact with the upper surface. Thus, grinding by the outer diameter machining core drill 50 is started, and a grinding fluid (coolant) is supplied to the grinding part 52. Then, when the outer diameter machining core drill 50 is lowered, the grinding part 52 penetrates the glass plate 10 and the disk-shaped glass substrate 100 is cut from the glass plate 10.

  As shown in FIG. 2 (E), after cutting is completed, the outer diameter processing core drill 50 is raised, and the cut disc-shaped glass substrate 100 and the disc-shaped glass substrate 100 are separated on the table 20. The left corner 16 is left. Thereafter, the disk-shaped glass substrate 100 is recovered as a product, and the corners 16 are removed.

  As shown in FIG. 3, the disk-shaped glass substrate 100 and the inner peripheral portion 110 are cut and separated separately from the glass plate 10 by grinding with the inner diameter machining core drill 40 and the outer diameter machining core drill 50. Therefore, the disc-shaped glass substrate 100 having a concentric large-diameter and small-diameter circular cut surface is cut out at the center of the square-shaped glass plate 10.

  On the other hand, the circular hole 12 corresponding to the outer periphery of the disk-shaped glass substrate 100 remains in the glass plate 10 by extracting the disk-shaped glass substrate 100. Since the circular hole 12 is at the center of the square glass plate 10, the connecting portion 14 with each side of the glass plate 10 is narrower than the corner 16 of the glass plate 10. Therefore, when the disk-shaped glass substrate 100 is cut from the glass plate 10, the narrow connection portion 14 becomes weak, and when the grinding parts 42 and 52 penetrate the glass plate 10, The possibility of chipping increases. However, in this embodiment, the occurrence of this chipping can be suppressed by a cutting method using an outer diameter machining core drill 50 described later.

  Here, returning to FIG. 1 again, each step of the manufacturing method of the disk-shaped glass substrate will be described.

[Chamfering process]
The outer peripheral end surface and the inner peripheral end surface of the cut disc-shaped glass substrate are ground with a rotating chamfering grindstone, and each of the outer peripheral end surface and the inner peripheral end surface is chamfered (S13).

  FIG. 4 is a diagram illustrating the shape of a disk-shaped glass substrate. As shown in FIG. 4, the disk-shaped glass substrate 100 has an inner peripheral end surface 103 and an outer peripheral end surface 105 cut into a circular shape by core drills 40 and 50, and is extracted from the glass plate 10. Moreover, after the inner peripheral end surface 103 and the outer peripheral end surface 105 are cut from the glass plate 10, the inner peripheral chamfered surfaces 102a and 102b and the outer peripheral chamfered surfaces 104a and 104b are chamfered by a chamfering grindstone.

  Then, the disk-shaped glass substrate 100 extracted from the glass plate 10 is lapped on the main plane 101 by a double-sided lapping machine, and further, the main plane 101 is polished by a polishing liquid and a polishing pad, and then washed and magnetic recording is performed. It becomes the glass substrate for media.

  The disk-shaped glass substrate 100 is a disk-shaped glass substrate for a magnetic recording medium used as a base material of a magnetic recording medium. For example, (1) for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm. Disc-shaped glass substrate, (2) Disc-shaped glass substrate for magnetic recording medium having outer diameter of 65 mm, inner diameter of 20 mm and plate thickness of 0.8 mm, (3) For magnetic recording medium of outer diameter of 95 mm, inner diameter of 25 mm, plate thickness of 1.27 mm Disc-shaped glass substrate, (4) Disc-shaped glass substrate for magnetic recording medium having an outer diameter of 95 mm, inner diameter of 25 mm, and plate thickness of 1 mm, (5) Disc-shaped for magnetic recording medium having an outer diameter of 95 mm, inner diameter of 25 mm, and plate thickness of 0.8 mm Processing is performed to obtain any glass substrate.

  The inner peripheral chamfered surfaces 102a and 102b and the outer peripheral chamfered surfaces 104a and 104b are chamfered so as to obtain a disk-shaped glass substrate for a magnetic recording medium having a chamfer width of 0.15 mm and a chamfer angle of 45 °, for example.

  The disk-shaped glass substrate for a magnetic recording medium may be amorphous glass, crystallized glass, or tempered glass (for example, chemically tempered glass) having a tempered layer on the surface layer of the glass substrate.

[Lapping process]
The main plane 101 of the disk-shaped glass substrate 100 is lapped by a double-sided lapping device (S14). By this lapping process, the parallelism, flatness, and thickness of the main plane 101 are adjusted to predetermined specified values.

  The order of performing the lapping process is not limited to S14, and may be performed before the extraction step (S12), before the chamfering step (S13), after the end surface polishing step, and before the main surface polishing step. .

[End face polishing process]
A large number of disk-shaped glass substrates 100 are laminated, and the end surfaces (outer peripheral end surface, inner peripheral end surface) of each disk-shaped glass substrate 100 are polished using a polishing brush and abrasive grains. After polishing, the disc-shaped glass substrate 100 is washed to remove the abrasive grains (S15).

[Main surface polishing process]
Next, the main plane 101 of the disk-shaped glass substrate 100 is polished with a polishing liquid by a double-side polishing apparatus, and the main plane 101 of the disk-shaped glass substrate 100 is polished with a polishing pad to remove scratches and distortions remaining in the lapping process. Thereafter, the disk-shaped glass substrate 100 is washed to remove the polishing liquid and dried (S16). In the main surface polishing step, only primary polishing using the above-described method for polishing a glass substrate for a magnetic recording medium may be performed. However, further secondary polishing and further tertiary to fifth polishing may be performed.

[Washing process]
The cleaning step is a step of cleaning and drying the polished glass substrate (S17). A specific cleaning method is not particularly limited. For example, cleaning can be performed by scrub cleaning using a detergent, ultrasonic cleaning in a state immersed in a detergent solution, ultrasonic cleaning in a state immersed in pure water, or the like. Also, the drying method is not particularly limited, and for example, drying is performed with isopropyl alcohol vapor.

  Further, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the above steps. For example, the inter-process etching is performed by immersing the disc-shaped glass substrate 100 in an acidic solution (hydrofluoric acid, a mixed solution of hydrofluoric acid and sulfuric acid, or the like). Further, when high mechanical strength is required for the glass substrate 100, a strengthening step (for example, a chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate 100 is performed before the polishing step, after the polishing step, or between the polishing steps. You may implement.

  Then, the disk-shaped glass substrate 100 obtained by the manufacturing method including the above steps is used as a magnetic recording medium by further performing a magnetic layer forming step for forming a thin film such as a magnetic layer thereon.

[Configuration of core drill]
FIG. 5 is a longitudinal sectional view showing the configuration of the inner diameter machining core drill. As shown in FIG. 5, the inner diameter core drill 40 includes a grinding part 42 formed in a cylindrical shape, a base part 44 that supports the grinding part 42, and a shaft part 46 formed at the upper end of the base part 44. And have. The grinding part 42 has an outer diameter corresponding to the inner diameter of the disk-shaped glass substrate 100, and diamond abrasive grains are bonded by a binder (metal bond) as will be described later, and on the surface of the cylindrical side binder. A protective film (metal film) is formed. Further, the grinding portion 42 is provided with slits 48 formed of thin grooves extending in the axial direction at a plurality of locations in the circumferential direction.

  FIG. 6 is a diagram showing the configuration of the outer diameter machining core drill. In FIG. 6, the left side of the center line is a cross-sectional view, and the right side of the center line is an external view. As shown in FIG. 6, an outer diameter processing core drill 50 includes a grinding part 52 having an inner diameter corresponding to the outer diameter of the disk-shaped glass substrate 100, a base part 54 that supports the grinding part 52, and a base part And a shaft portion 56 formed at the upper end of 54. The grinding part 52 is formed in a cup shape having a diameter larger than that of the shaft part 56. As will be described later, diamond abrasive grains are bonded by a binder (metal bond), and a protective film (metal film) is formed on the surface of the binder. Is formed. In addition, the grinding part 52 is provided with slits 58 formed of thin grooves extending in the axial direction at a plurality of locations in the circumferential direction.

  In the present embodiment, the slits 48 and 58 are formed such that the circumferential slit width S is 0.5 mm to 1.2 mm. When the slit width is less than 0.5 mm, it becomes difficult to properly supply the grinding liquid (coolant) to the entire tip of the grinding parts 42 and 52, and the glass generated when the glass plate 10 is ground. Clogging due to chips occurs, and it becomes difficult to suppress a reduction in grinding ability (decrease in sharpness) of each abrasive grain (diamond).

  Further, when the slit width S of the slits 48 and 58 exceeds 1.2 mm, the durability of the core drills 40 and 50 may be lowered. Moreover, the grinding parts 42 and 52 vibrate during the grinding of the glass plate 10, and the accuracy in cutting out the disc-shaped glass substrate 100 from the glass plate 10 may be reduced, and chipping may occur. The number of the slits 48 and 58 is appropriately increased or decreased according to the diameter of the grinding portions 42 and 52 and the distance between the slits.

[Configuration of grinding section]
FIG. 7 is an enlarged longitudinal sectional view showing a grinding portion of each core drill. As shown in FIG. 7, in the grinding parts 42 and 52 of the core drills 40 and 50, a metal protective film 90 is formed on the surface of a metal bond grindstone in which abrasive grains 60 are fixed with a binder 70.

  As the abrasive grains 60, diamond abrasive grains are mainly used. The grinding parts 42 and 52 use a metal bond grindstone obtained by sintering abrasive grains 60 mainly having a predetermined grain size with a binder 70 made of metal, and are fixed to the lower ends of the base metal parts 44 and 54.

  Further, the grinding parts 42 and 52 include a tip part 80 where the abrasive grains 60 and the binder 70 are exposed, and inner and outer side surfaces 82 where the protective film 90 formed on the surface of the binder 70 is exposed. 83. The tip 80 is in a state in which the abrasive grains 60 are exposed from the binder 70, the glass plate 10 can be ground, and the abrasive grains 60 whose grinding ability (sharpness) has dropped can be self-acting. . On the other hand, the side portions 82 and 83 have a bonding strength to each abrasive grain 60 increased by the protective film 90 formed on the surface of the binder 70, and the holding power of each abrasive grain 60 is improved.

  Furthermore, the grinding parts 42 and 52 have a volume ratio of 6% to 15% with respect to the entire volume formed in a cylindrical shape. The particle size display of the grinding parts 42 and 52 is, for example, # 270 (particle size JIS display 270/325, average particle size 53 μm) or # 325 (particle size JIS display 325/400, average particle size 44 μm). Moreover, the average particle diameter of the abrasive grains 60 of the grinding portions 42 and 52 in the present embodiment is preferably 40 μm to 65 μm (number is # 250 to # 400).

  Further, the drill width (radial thickness) t of the grinding portions 42 and 52 is formed to be 0.5 mm to 1.2 mm, and preferably 0.7 mm to 1.2 mm.

  The protective film 90 is mainly formed of a metal film obtained by coating a metal (nickel-based or titanium-based plating film) by electrodeposition. Moreover, the film thickness (thickness) of the protective film 90 is 1 μm to 10 μm. The protective film 90 is formed so as to cover the surface of the binder 70 and the joint portions (boundary portions) between the end portions of the base metal portion 54 and the grinding portions 42 and 52. Therefore, the bonding strength between the end portion of the base metal portion 54 and the grinding portions 42 and 52 is reinforced, and a sufficient and stable holding force can be obtained with respect to the grinding resistance at the time of grinding. Therefore, the shake (radial vibration) of the grinding parts 42 and 52 during high-speed rotation is suppressed.

  Here, the operation and effect of the configuration of the grinding parts 42 and 52 and the cutting method will be described.

  (A1) The abrasive grains content of the grinding parts 42 and 52 is set to a volume ratio of 6% to 15% (diamond concentration is 25 or more and 60 or less), and the side parts 82 and 83 of the grinding parts 42 and 52 A protective film 90 is formed on the surface of the binder 70. Thereby, the disk-shaped glass substrate 100 can be cut from the glass plate 10 with high precision while maintaining the grinding ability (sharpness) of the abrasive grains 60 without applying a high processing load to the cut surface of the glass plate 10. It becomes possible.

  And it can prevent that a big chipping arises in the processed disk shaped glass substrate 10. FIG.

  In addition, since the abrasive grains 60 whose grinding ability (sharpness) is reduced due to the self-generated action are dropped at the tip portions 80 of the grinding portions 40 and 50, the reduction of the grinding ability at the tip portion 80 can be suppressed, and the truing / dressing processing interval Can be made longer. That is, it is possible to increase the number of processed disk-shaped glass substrates 100 that can be cut out from the glass plate 10 without subjecting the grinding parts 40 and 50 to truing and dressing, thereby improving productivity and reducing costs. .

  When the volume ratio of each abrasive grain 60 with respect to the total volume of the grinding parts 40 and 50 is less than 6% by volume, when the glass plate 10 is ground and cut, the grinding parts 40 and 50 wear quickly, so one core drill can be used. The number of processed disk-shaped glass substrates 100 that can be processed is reduced.

  Moreover, when the volume ratio of each abrasive grain 60 with respect to the whole volume of the grinding parts 40 and 50 exceeds 15 volume%, the abrasive grain 60 of the front-end | tip part 80 will be clogged at the early stage from a process start. Further, the abrasive grains 60 at the tip end portion 80 are not properly regenerated, and the abrasive grains 60 in a state where the corners of the abrasive grains 60 are rounded and the grinding ability (sharpness) is reduced are not dropped by the self-generated action. As a result, the abrasive grains 60 with reduced grinding ability remain at the tip 80, and the processing load when grinding the glass plate 10 is increased, causing chipping of the cut glass substrate 100.

  Further, when the volume ratio of the abrasive grains 60 exceeds 15% by volume, the load applied to the glass plate 10 becomes large and chipping occurs at the initial stage where the tip 80 of the grinding part contacts the glass plate 10 and starts grinding. There is also a fear.

  Furthermore, by forming the protective film 90 on the surface of the binder 70 on the side surface portions 82 and 83, glass chips generated when the glass plate 10 is ground can be easily removed, and the grinding portion can be removed. The supply of the grinding fluid can be performed appropriately, clogging of the grinding part is suppressed, and heat generation when the glass plate 10 is ground can be suppressed.

  And by suppressing the heat generation when the glass plate 10 is ground, it is possible to suppress a reduction in the grinding ability of the abrasive grains 60 (a reduction in sharpness). Moreover, by suppressing the heat generation when the glass plate 10 is ground, it is possible to prevent the grinding ability of the abrasive grains 60 from being reduced (sharpness is reduced) and to prevent the processing load during grinding of the glass plate 10 from being increased. It is possible to suppress the occurrence of chipping in the disk-shaped glass substrate 100.

  By forming the protective film 90 on the surface of the binder 70 of the side surface portions 82 and 83, the frictional resistance of the side surface portions 82 and 83 is reduced, so that the grinding portions 42 and 52 are removed from the glass plate 10 during grinding with a core drill. When it comes off, it comes into sliding contact with the cut surface of the glass plate 10 with low friction, and the occurrence of chipping can be suppressed accordingly.

  (A2) By making the film thickness of the protective film 90 electrodeposited with metal (nickel-based or titanium-based plating film) 1 μm to 10 μm, it is possible to sufficiently suppress the occurrence of chipping in the processed glass substrate 10. it can. That is, the glass chips generated when the glass plate 10 is ground are less likely to be eliminated because the friction with the surface of the protective film 90 is reduced and clogging of the abrasive grains 60 is suppressed. Therefore, heat generation when the glass plate 10 is ground can be sufficiently suppressed. Thereby, since the fall of the grinding capability of the abrasive grain 60 can be suppressed and the sharpness of the abrasive grain 60 can be maintained, the interval of a truing dressing process can be lengthened. As a result, the sharpness is appropriately maintained, the grinding parts 42 and 52 can be continuously processed without truing and dressing, the number of processed glass substrates 10 that can be ground can be increased, and the productivity can be improved. Costs can be reduced.

  Moreover, when the film thickness of the protective film 90 is less than 1 μm, the glass chips generated when the glass plate is ground are not sufficiently removed, and the abrasive grains 60 may be clogged. And it becomes difficult to suppress the grinding ability decline (a sharpness falls) of the abrasive grain 60, the processing load of glass plate grinding rises (a sharpness worsens), and chipping generate | occur | produces in the cut disc shaped glass substrate 100. There is a risk.

  Further, when the thickness of the protective film 90 is less than 1 μm, the frictional resistance of the side portions 82 and 83 cannot be sufficiently reduced, and the grinding portions 42 and 52 pass through the glass plate 10 and come out below the glass plate 10. There is also a risk of causing chipping.

  Moreover, when the film thickness of the protective film 90 exceeds 10 μm, the protrusion amount of the abrasive grains 60 from the surface of the protective film 90 decreases, the sharpness becomes poor, and the processing load when grinding the glass plate 10 increases. There is a possibility that chipping may occur in the cut disc-shaped glass substrate 100.

  Further, when the thickness of the protective film 90 exceeds 10 μm, the drill width t becomes large, and a load is applied to the outer side surface portions of the grinding portions 42 and 52 to generate heat. Therefore, the processing load at the time of grinding the glass plate 10 is increased, the sharpness is deteriorated, and chipping may occur in the cut disc-shaped glass substrate 100. Moreover, the processing load at the time of grinding the glass plate 10 becomes high, and the sharpness is deteriorated, which may increase the load of rotational driving of the core drill. In that case, there is a possibility that the grinding apparatus stops due to an increase in load during grinding.

  (A3) The drill width (thickness in the radial direction) t of the grinding portions 42 and 52 is formed to be 0.5 mm to 1.2 mm. When the drill width t is less than 0.5 mm, the strength of the grinding parts 42 and 52 becomes insufficient, and the grinding parts 42 and 52 may be damaged while the glass plate 10 is being ground.

  In addition, when the drill width t exceeds 1.2 mm, when the glass plate is ground, the wear of the tip portion becomes uneven between the inner side surface portion and the outer side surface portion of the core drill so that the outer side surface portion of the core drill is loaded. Thus, heat due to grinding resistance is generated on the outer side surface portion of the core drill, the grinding ability (sharpness) of the abrasive grains is lowered, and chipping may occur on the cut disc-shaped glass substrate.

  Moreover, the processing load when grinding the glass plate 10 is increased, and the sharpness may be deteriorated. For this reason, if the load of rotational driving of the core drill at the time of grinding increases, the grinding apparatus may stop.

  (A4) The average particle diameter of the abrasive grains 60 of the grinding portions 42 and 52 is 40 μm to 65 μm (the count is # 250 to # 400). When the average particle diameter of the abrasive grains 60 is less than 40 μm, clogging due to glass chips generated when the glass plate 10 is ground tends to occur. That is, it becomes difficult to suppress the grinding ability of the abrasive grains 60 from being lowered and the sharpness from being lowered. Therefore, when the glass plate 10 is ground, the processing load increases (sharpness is deteriorated) and heat is generated, and there is a possibility that chipping occurs in the cut disc-shaped glass substrate 100.

  Moreover, when the average particle diameter of the abrasive grains 60 is less than 40 μm, the grinding resistance becomes high and heat is generated, and the sharpness due to the reduction of the grinding ability of the abrasive grains 60 may be reduced.

  Further, when the average particle diameter of the abrasive grains 60 exceeds 65 μm, the load applied to the glass plate 10 becomes large during the initial stage of starting the grinding of the glass plate 10 at the tip 80 of the grinding portions 42 and 52 and during grinding, and chipping. May increase. Further, a deep work-affected layer (scratch) may occur in the ground disc-shaped glass substrate 100.

[Evaluation of cutting method with core drill]
Here, referring to Table 1, the experimental results of Examples 1 to 3, which are examples using the cutting method by the core drill in which the protective film 90 of the present invention is formed, and the cutting method by the core drill without the protective film 90 are shown. The experimental results of Examples 4 to 6, which are comparative examples used, are compared.

尚、表１に記載したチッピング発生率（％）は、１ｍｍ以上のチッピングが生じたガラス基板の発生率を示す。また、表１に記載した加工枚数は、内径用加工コアドリル４０を用いて、研削部４２をツルーイング・ドレッシング処理することなく加工できる円盤状ガラス基板１００の枚数を示す。

In addition, the chipping incidence (%) described in Table 1 indicates the incidence of a glass substrate on which chipping of 1 mm or more has occurred. The number of processed sheets shown in Table 1 indicates the number of disk-shaped glass substrates 100 that can be processed by using the inner diameter processing core drill 40 without subjecting the grinding part 42 to truing and dressing.

  In Table 1, Examples 1 to 3 each have a protective film 90 made of a metal film having a thickness of 8 μm, 5 μm, and 2 μm, an abrasive content of 11.3 vol%, and an abrasive 60 Inner diameter with an average particle diameter of 53 μm, a drill width t of the grinding portion 42 of 0.7 mm, a slit width S of 1 mm, and a protective film 90 electrodeposited with a nickel-based metal film This is a case of cutting with the machining core drill 40.

  Further, in Table 1, Examples 4 to 6 each have no protective film 90, have an abrasive content of 7.5% by volume, 11.3% by volume, 18.8% by volume, and 60 The average particle size of the material was 53 μm, the drill width t of the grinding part 42 was 0.7 mm, the slit width S was 1 mm, and the protective film 90 was electrodeposited with a nickel-based metal film. This is the case of cutting with the inner diameter machining core drill 40.

  The number of sheets that can be continuously processed from the glass plate 10 to the disk-shaped glass substrate 100 without performing the truing / dressing treatment using the inner diameter processing core drill 40 of the first embodiment was 350,000, 348,000, and 348,000. . The chipping occurrence rates (%) at this time were 0.03%, 0.02%, and 0.03%, respectively.

  On the other hand, in Examples 4-6, the number of sheets that can be continuously processed from the glass plate 10 to the disk-shaped glass substrate 100 without using a truing / dressing treatment using a core drill without the protective film 90 is 18,000, 147,000. 65,000 sheets. The chipping occurrence rates (%) at this time were 0.04%, 0.06%, and 0.14%, respectively.

  As a result of this experiment, by forming a protective film 90 by electrodepositing a metal film on the surface of the binder 70 on the side surfaces 82 and 83 of the grinding parts 42 and 52, the number of continuous processing of the disk-shaped glass substrate 100 is dramatically increased. It has been proved that the production efficiency is increased and the chipping rate is lowered.

  In addition, although the said experimental result was performed using the inside diameter processing core drill 40, since the structure of the grinding part 52 of the outside diameter core drill 50 is the same as that of the grinding part 42 of the inside diameter processing core drill 40, it is outside diameter. Even when the disk-shaped glass substrate 100 is continuously processed using the processing core drill 50, it is presumed that the same experimental results as those in Table 1 can be obtained.

DESCRIPTION OF SYMBOLS 10 Glass plate 12 Circular hole 14 Connection part 16 Corner | angular part 20 Table 40 Core drill 42 for internal diameter processing, 52 Grinding part 44, 54 Base part 46, 56 Shaft part 48, 58 Slit 50 Core drill 60 for external diameter processing Abrasive grain 70 Coupling Agent 80 Tip portion 82, 83 Side surface portion 90 Protective film 100 Disc-shaped glass substrate 101 Main plane 103 Inner peripheral end surface 102a, 102b Inner peripheral chamfered surface 104a, 104b Outer peripheral chamfered surface 105 Outer peripheral end surface

Claims (7)

A method for cutting a glass substrate by cutting a disk-shaped glass substrate from a glass plate using a core drill,
The core drill has a cylindrical grinding portion in which abrasive grains are fixed with a binder,
The grinding part is a tip part where the abrasive grains and the binder are exposed;
A side surface part formed with a protective film on the surface of the binder on the side surface of the cylindrical shape,
The method for cutting a glass substrate, wherein the abrasive grain content of the grinding part is a volume ratio of 6% to 15%.   The glass substrate cutting method according to claim 1, wherein the protective film has a thickness of 1 μm to 10 μm.   The said core drill is a cutting method of the glass substrate of Claim 1 or 2 whose drill width of the said grinding part is 0.5 mm-1.2 mm.   The method for cutting a glass substrate according to any one of claims 1 to 3, wherein an average particle diameter of the abrasive grains is 40 µm to 65 µm.   The said core drill is a cutting method of the glass substrate in any one of Claims 1-4 by which the slit was formed in the front-end | tip of the said grinding part.   The method for cutting a glass substrate according to claim 1, wherein the protective film is a metal.   A method for producing a magnetic recording medium, comprising a cutting step using the method for cutting a glass substrate according to claim 1.

Images