WO2011058969A1 - Method for manufacturing glass substrate for use in magnetic recording medium - Google Patents
Method for manufacturing glass substrate for use in magnetic recording medium Download PDFInfo
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- WO2011058969A1 WO2011058969A1 PCT/JP2010/069933 JP2010069933W WO2011058969A1 WO 2011058969 A1 WO2011058969 A1 WO 2011058969A1 JP 2010069933 W JP2010069933 W JP 2010069933W WO 2011058969 A1 WO2011058969 A1 WO 2011058969A1
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- WIPO (PCT)
- Prior art keywords
- glass substrate
- polishing
- diamond
- lapping
- abrasive grains
- Prior art date
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Classifications
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
- G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B37/00—Lapping machines or devices; Accessories
- B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
- B24B37/042—Lapping machines or devices; Accessories designed for working plane surfaces operating processes therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B37/00—Lapping machines or devices; Accessories
- B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
- B24B37/07—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool
- B24B37/08—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool for double side lapping
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B37/00—Lapping machines or devices; Accessories
- B24B37/11—Lapping tools
- B24B37/20—Lapping pads for working plane surfaces
- B24B37/24—Lapping pads for working plane surfaces characterised by the composition or properties of the pad materials
- B24B37/245—Pads with fixed abrasives
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B37/00—Lapping machines or devices; Accessories
- B24B37/11—Lapping tools
- B24B37/20—Lapping pads for working plane surfaces
- B24B37/26—Lapping pads for working plane surfaces characterised by the shape of the lapping pad surface, e.g. grooved
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B9/00—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor
- B24B9/02—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground
- B24B9/06—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground of non-metallic inorganic material, e.g. stone, ceramics, porcelain
- B24B9/065—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground of non-metallic inorganic material, e.g. stone, ceramics, porcelain of thin, brittle parts, e.g. semiconductors, wafers
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C19/00—Surface treatment of glass, not in the form of fibres or filaments, by mechanical means
Definitions
- the present invention relates to a method for producing a glass substrate for a magnetic recording medium.
- This application claims priority based on Japanese Patent Application No. 2009-257112 filed in Japan on November 10, 2009 and Japanese Patent Application No. 2010-182326 filed on August 17, 2010 in Japan, The contents thereof are incorporated herein.
- Magnetic recording media used in hard disk drives are being markedly improved in recording density.
- the increase in surface recording density has become even more intense.
- GMR heads, TMR heads, etc. have been introduced and have continued to increase at a rate of about 1.5 times a year. In the future, it is required to achieve higher recording density.
- the demand for the magnetic recording medium substrate is also increasing.
- aluminum alloy substrates and glass substrates have been used as substrates for magnetic recording media.
- the glass substrate is generally superior to the aluminum alloy substrate with respect to its hardness, surface smoothness, rigidity, and impact resistance. For this reason, the attention degree of the glass substrate for magnetic recording media which can achieve high recording density is increasing.
- a glass substrate for a magnetic recording medium When manufacturing a glass substrate for a magnetic recording medium, it is obtained by cutting a disk-shaped glass substrate from a large plate-shaped glass plate or by directly press-molding a disk-shaped glass substrate from a molten glass using a mold. A lapping (grinding) process and a polishing (polishing) process are performed on the main surface and the end surface of the glass substrate.
- the primary surface of the glass substrate is subjected to primary lapping (grinding), secondary lapping (grinding), primary polishing (polishing), secondary Polishing (polishing) is performed in this order. Then, lapping and polishing are applied to the inner and outer peripheral end faces of the glass substrate during these processing steps.
- Patent Document 1 discloses that surface lapping and scratching / grinding marks are performed by performing a primary lapping process using diamond pellets of resin, metal, vitrified, etc., followed by a secondary lapping process using a diamond pad. -It is disclosed that there are no defects such as suction marks, and that processing in a short time is possible.
- the present invention has been proposed in view of such conventional circumstances, and can provide a high-productivity magnetic recording medium glass substrate for magnetic recording media with high surface smoothness and low surface waviness. It aims at providing the manufacturing method of the glass substrate for media.
- the present invention provides the following means.
- a method for producing a glass substrate for a magnetic recording medium comprising at least a step of subjecting a surface excluding an end surface of the glass substrate to a primary lapping and a step of subjecting to a secondary lapping.
- a diamond pad in which diamond abrasive grains are fixed with a binder is used, and the lapping surface of the diamond pad includes a plurality of tile-shaped convex portions having flat top portions.
- the diamond pad used for the primary lapping process has an average particle size of 4 to 12 ⁇ m of the diamond abrasive grains, and a content of diamond abrasive grains of the convex portions of 5 to 70 vol%.
- the diamond pad used for the secondary lapping process has an average particle diameter of the diamond abrasive grains of 1 to 5 ⁇ m, and a content of the diamond abrasive grains in the convex portions of 5 to 80% by volume.
- (2) The diamond pad used for the primary lapping and the secondary lapping has an outer dimension of the convex part of 1.5 to 5 mm square and a height of 0.2 to 3 mm, and is between adjacent convex parts. 2.
- the diamond pad is used for the primary lapping process and the secondary lapping process, and the diamond pad used for the primary lapping process and the secondary lapping process is optimized to smooth the surface. It is possible to manufacture a glass substrate for a magnetic recording medium with high productivity and low surface waviness with high productivity.
- FIG. 1 is a perspective view illustrating a main surface lapping process, illustrating a process for manufacturing a glass substrate for a magnetic recording medium to which the present invention is applied.
- FIG. 2A is an enlarged plan view showing a pad surface of a diamond pad used in the main surface lapping process.
- FIG. 2B is an enlarged cross-sectional view of the AA ′ cross section of the diamond pad used in the main surface lapping process.
- FIG. 3 is a view for explaining a manufacturing process of the glass substrate for a magnetic recording medium to which the present invention is applied, and is a perspective view showing an inner and outer peripheral end face lapping process.
- FIG. 1 is a perspective view illustrating a main surface lapping process, illustrating a process for manufacturing a glass substrate for a magnetic recording medium to which the present invention is applied.
- FIG. 2A is an enlarged plan view showing a pad surface of a diamond pad used in the main surface lapping process.
- FIG. 2B is an enlarged cross-sectional view of the
- FIG. 4 is a view for explaining a manufacturing process of the glass substrate for a magnetic recording medium to which the present invention is applied, and is a perspective view showing an inner peripheral end surface polishing process.
- FIG. 5 is a view for explaining a manufacturing process of the glass substrate for a magnetic recording medium to which the present invention is applied, and is a perspective view showing an outer peripheral end face polishing process.
- FIG. 6 is a diagram for explaining a manufacturing process of the glass substrate for a magnetic recording medium to which the present invention is applied, and is a perspective view showing a main surface polishing process.
- FIG. 7 is a perspective view showing another configuration example of the wrapping machine or polishing machine used in the present invention.
- a glass substrate for a magnetic recording medium manufactured by applying the present invention is a disk-shaped glass substrate having a central hole, and the magnetic recording medium has a magnetic layer, a protective layer, and a lubricating film on the surface of the glass substrate. Etc. are sequentially laminated. Further, in the magnetic recording / reproducing apparatus (HDD), the central portion of the magnetic recording medium is attached to the rotation shaft of the spindle motor, and the magnetic head floats and runs on the surface of the magnetic recording medium rotated by the spindle motor. Information is written to or read from the magnetic recording medium.
- HDD magnetic recording / reproducing apparatus
- SiO 2 —Al 2 O 3 —R 2 O (R represents at least one selected from alkali metal elements) based chemically strengthened glass, SiO 2 2- Al 2 O 3 —Li 2 O glass ceramics, SiO 2 —Al 2 O 3 —MgO—TiO 2 glass ceramics, or the like can be used.
- this glass substrate for magnetic recording media first, the glass substrate is cut out from a large plate-shaped glass plate, or the glass substrate is directly press-molded from a molten glass using a molding die, so that A disk-shaped glass substrate having holes is obtained.
- lapping (grinding) processing and polishing (polishing) processing are performed on the surface (main surface) excluding the end surface of the obtained glass substrate. Moreover, between these processes, the process of performing a lapping process and a polish process with respect to the inner peripheral edge surface of a glass substrate is included. In addition, in this invention, the chamfering process with respect to the inner peripheral edge surface of a glass substrate can also be performed in the same process as the said lapping process.
- the primary main surface lapping step, the inner and outer peripheral end surface lapping step, the inner peripheral end surface polishing step, the secondary main surface lapping step, the outer peripheral end surface polishing step, and the primary main surface are performed in this order.
- a lapping machine 10 as shown in FIG. 1 is used to perform primary lapping on both main surfaces of the glass substrate W (surfaces that will eventually become recording surfaces of the magnetic recording medium).
- the wrapping machine 10 includes a pair of upper and lower surface plates 11, 12, and sandwiches a plurality of glass substrates W between the surface plates 11, 12 rotating in opposite directions to each other. The surface is ground with a grinding pad provided on the surface plates 11 and 12.
- the grinding pad used for the primary lapping is a diamond pad 20A in which diamond abrasive grains are fixed with a bonding agent (bond), and the lapping surface 20a has a flat surface.
- a plurality of tile-shaped convex portions 21 having top portions are provided side by side.
- the diamond pad 20 ⁇ / b> A is formed by arranging a plurality of convex portions 21 on which diamond abrasive grains are fixed with a binder on the surface of the base material 22.
- the outer dimension S of the convex portion 21 is 1.5 to 5 mm square, the height T is 0.2 to 3 mm, and the gap G between adjacent convex portions 21 is G. Is preferably in the range of 0.5 to 3 mm.
- the cooling liquid, the grinding liquid, and the like can be evenly distributed, and the grinding dust and the like can be smoothly discharged from between the convex portions 21 of the lap surface 20a. Is possible.
- the diamond pad 20A used for the primary lapping has an average particle diameter of 4 to 12 ⁇ m, preferably 6 to 12 ⁇ m, and the diamond abrasive content in the convex portion 21 is 5 to 70% by volume. It is preferable to use those in the range, more preferably 5 to 40% by volume, and still more preferably 20 to 30% by volume.
- the grain size and content of the diamond abrasive grains are below the above range, the processing time is increased, resulting in an increase in cost.
- the grain size and content of the diamond abrasive grains exceeds the above range, a desired surface roughness is obtained. It becomes difficult to obtain the degree.
- a resin such as a polyurethane resin, a phenol resin, a melamine resin, or an acrylic resin can be used as the binder of the diamond pad 20A.
- the wrapping machine 30 includes an inner peripheral grindstone 31 and an outer peripheral grindstone 32, and a laminated body X in which a plurality of glass substrates W are stacked with the spacers S in a state where the center holes are aligned with each other around the axis.
- each glass substrate W is sandwiched in the radial direction between the inner peripheral grindstone 31 inserted in the center hole of each glass substrate W and the outer peripheral grindstone 32 disposed on the outer periphery of each glass substrate W, and these inner peripheral grindstones 31 and the outer peripheral grindstone 32 are rotated in the direction opposite to the laminated body X. Then, the inner peripheral end face of each glass substrate W is ground by the inner peripheral grindstone 31, and at the same time, the outer peripheral end face of each glass substrate W is ground by the outer peripheral grindstone 32.
- the surfaces of the inner peripheral grindstone 31 and the outer peripheral grindstone 32 have a corrugated shape in which convex portions and concave portions are alternately arranged in the axial direction, the inner peripheral end surface and the outer peripheral end surface of each glass substrate W are ground.
- the lapping process with respect to the inner and outer peripheral end faces of the glass substrate W is not limited to one stage, and can be performed in two stages (primary and secondary lapping processes).
- the inner peripheral grindstone 31 and the outer peripheral grindstone 32 are composed of diamond abrasive grains fixed with a binder.
- the binder include metals such as copper, copper alloy, cobalt, tungsten carbide, and nickel.
- the diamond abrasive grains contained in the inner peripheral grindstone 31 and the outer peripheral grindstone 32 preferably have an average particle diameter of 4 ⁇ m or more and 12 ⁇ m or less. Further, as the inner peripheral grindstone 31 and the outer peripheral grindstone 32, those containing the diamond abrasive grains in the range of 5 to 95% by volume are preferably used, and more preferably in the range of 20 to 90% by volume.
- the polishing machine 40 includes an inner peripheral polishing brush 41, and rotates the laminated body X about the axis, and the inner peripheral polishing brush 41 inserted into the center hole of each glass substrate W is referred to as the glass substrate W. Move up and down while rotating in the opposite direction. At this time, the polishing liquid is dropped onto the inner peripheral polishing brush 41. Then, the inner peripheral end face of each glass substrate W is polished by the inner peripheral polishing brush 41.
- the edge portion (chamfer surface) of the inner peripheral end face that has been chamfered in the inner and outer peripheral end face lapping step is also polished.
- the polishing liquid for example, a slurry obtained by dispersing cerium oxide abrasive grains in water can be used.
- secondary main surface lapping is performed on both main surfaces of the glass substrate W using the lapping machine 10 as shown in FIG. 1 as in the primary main surface lapping step. That is, while sandwiching a plurality of glass substrates W between a pair of upper and lower surface plates 11 and 12 rotating in opposite directions, both main surfaces of these glass substrates W are grounded by grinding pads provided on the surface plates 11 and 12. Grind.
- the grinding pad used for the secondary lapping is a diamond pad 20B in which diamond abrasive grains are fixed with a bonding agent (bond), and the lapping surface 20a.
- the diamond pad 20 ⁇ / b> B is formed by arranging a plurality of convex portions 21 on which diamond abrasive grains are fixed with a binder on the surface of the base material 22.
- the diamond pad 20B used for the secondary lapping process has an outer dimension S of 1.5 to 5 mm square and a height T of 0. It is preferable to use one having 2 to 3 mm and a distance G between adjacent convex portions 21 in the range of 0.5 to 3 mm.
- the cooling liquid, the grinding liquid, and the like can be evenly distributed, and the grinding dust and the like can be smoothly discharged from between the convex portions 21 of the lap surface 20a. Is possible.
- the diamond pad 20B used for the secondary lapping process has an average particle diameter of diamond abrasive grains of 1 to 5 ⁇ m, preferably 2 to 5 ⁇ m, and a diamond abrasive grain content in the convex portion 21 of 5 to 80 volume%. Those in the range are preferably used, and more preferably in the range of 50 to 70% by volume. When the grain size and content of the diamond abrasive grains are below the above range, the processing time is increased, resulting in an increase in cost. On the other hand, when the grain size and content of the diamond abrasive grains exceeds the above range, a desired surface roughness is obtained. It becomes difficult to obtain the degree.
- a resin such as a polyurethane resin, a phenol resin, a melamine resin, or an acrylic resin can be used as the binder for the diamond pad 20B.
- the polishing machine 50 includes a rotating shaft 51 and an outer peripheral polishing brush 52, and a laminated body X in which a plurality of glass substrates W are stacked with a spacer S interposed therebetween in a state where the center holes are aligned with each other.
- the outer peripheral polishing brush 52 brought into contact with the outer peripheral end surface of each glass substrate W is rotated in the vertical direction while rotating in the direction opposite to the laminate X. Move operation.
- the polishing liquid is dropped onto the outer peripheral polishing brush 52. Then, the outer peripheral end surface of each glass substrate W is polished by the outer peripheral polishing brush 52. At the same time, the edge portion (chamfer surface) of the outer peripheral end face that has been chamfered in the inner and outer peripheral end face lapping step is also polished.
- the polishing liquid for example, a slurry obtained by dispersing cerium oxide abrasive grains in water can be used.
- the polishing machine 60 includes a pair of upper and lower surface plates 61 and 62, and sandwiches a plurality of glass substrates W between the surface plates 61 and 62 that rotate in opposite directions to each other.
- the surface is polished by a polishing pad provided on the surface plates 61 and 62.
- the polishing pad used for the primary polishing is a hard polishing cloth formed of urethane, for example. Further, when polishing both the main surfaces of the glass substrate W with this polishing pad, a polishing liquid is dropped onto the glass substrate W.
- a polishing liquid for example, a slurry obtained by dispersing cerium oxide abrasive grains in water can be used.
- a secondary polishing process is performed on both main surfaces of the glass substrate W using a lapping machine 60 as shown in FIG. That is, while sandwiching a plurality of glass substrates W between the surface plates 61 and 62 rotating in opposite directions, both main surfaces of the glass substrates W are polished by the polishing pads provided on the surface plates 61 and 62.
- the polishing pad used for the secondary polishing process is, for example, a suede-like soft polishing cloth. Further, when polishing both main surfaces of the glass substrate W with this polishing pad, a polishing liquid is dropped onto the glass substrate W.
- a polishing liquid for example, a slurry obtained by dispersing cerium oxide abrasive grains or colloidal silica in a solvent such as water can be used.
- the glass substrate W that has been lapped and polished is sent to the final cleaning process and the inspection process.
- the glass substrate W is cleaned using a method such as chemical cleaning with a detergent (chemical) combined with ultrasonic waves, and the abrasive used in the above step is removed.
- the inspection process for example, the surface (main surface, end surface, and chamfer surface) of the glass substrate W is inspected for scratches and distortions by an optical inspection device using a laser.
- the wrapping is performed by using the diamond pads 20A and 20B as shown in FIGS. 2A and 2B in the primary wrap processing and the secondary wrap processing described above. It is possible to finish the surface excluding the end face of the glass substrate W smoothly in a short time while smoothly discharging grinding waste from between the convex portions 21 of the surface 20a. In addition, the processing time in the subsequent primary main surface polishing step and secondary main surface polishing step can be shortened. Therefore, according to the present invention, it is possible to manufacture a glass substrate for a magnetic recording medium with high surface smoothness and less surface waviness with high productivity.
- a commercially available grinding fluid can be used as the grinding fluid used in the above-described primary lapping and secondary lapping.
- the grinding fluid is roughly classified into an aqueous grinding fluid and an oily grinding fluid.
- the water-based grinding fluid is obtained by adding pure water, an appropriate amount of alcohol, polyethylene glycol as a viscosity modifier, an amine, a surfactant, and the like.
- the oil-based grinding fluid is obtained by adding an appropriate amount of oil or stearic acid as an extreme pressure additive.
- water-based Sabrelube® 9016 manufactured by Chemetall
- a polishing aid and an anticorrosive agent are added to the grinding liquid used in the primary lapping process and the secondary lapping process described above, and the polishing liquid used in the primary polishing process and the secondary polishing process. May be.
- the polishing aid contains at least an organic polymer having a sulfonic acid group or a carboxylic acid group, and among them, an organic polymer having an average molecular weight of 4000 to 10,000 having sodium sulfonate or sodium carboxylate is used. It is preferable to use it. Thereby, the surface of the glass substrate W can be smoothed more in the said process.
- Examples of the organic polymer containing sodium sulfonate or sodium carboxylate include GEROPON OP SC / 213 (trade name / Rhodia), GEROPON T / 36 (trade name / Rhodia), GEROPON TA / 10 (trade name / Rhodia).
- a magnetic recording medium manufactured using the glass substrate W generally contains a corrosive substance such as Co, Ni, and Fe in the magnetic layer. Therefore, by adding an anticorrosive agent to the above-described grinding liquid or polishing liquid, it is possible to prevent the magnetic layer from being corroded and obtain a magnetic recording medium excellent in electromagnetic conversion characteristics.
- benzotriazole or a derivative thereof is preferably used.
- a derivative of benzotriazole for example, one obtained by substituting one or two or more hydrogen atoms of benzotriazole with a carboxyl group, a methyl group, an amino group, a hydroxyl group, or the like can be used.
- 4-carboxylbenzotriazole or a salt thereof, 7-carboxybenzotriazole or a salt thereof benzotriazole butyl ester, 1-hydroxymethylbenzotriazole, 1-hydroxybenzotriazole, or the like can be used.
- the addition amount of the anticorrosive is preferably 1% by mass or less, more preferably 0.001 to 0.1% by mass with respect to the total amount when the diamond slurry is used.
- this invention is not necessarily limited to the thing of the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
- the lapping machine 10 used in the primary main surface lapping process and the secondary main surface lapping process and the polishing machine 50 used in the primary main surface polishing process and the secondary main surface polishing process described above are illustrated in FIG.
- a plurality of are provided with a pair of upper and lower lower surface plates 71 and upper surface plate 72, and a plurality of carriers 73 disposed on a surface facing upper surface plate 72 of lower surface plate 71.
- a glass substrate (not shown) is set in the opening 74 of 35 in this embodiment. Both main surfaces of the plurality of glass substrates are ground by a grinding pad provided on the lower surface plate 71 and the upper surface plate 72. It is also possible to adopt a configuration in which grinding or polishing with a polishing pad is performed.
- the lower surface plate 71 and the upper surface plate 72 are rotationally driven by a drive motor (not shown) with the rotation shafts 71a and 72a provided at the center portions thereof, so that the respective center axes coincide with each other. It can be rotated in the opposite direction in a state where Further, a concave portion 75 for arranging a plurality of (five in this embodiment) carriers 73 is provided on the surface facing the upper surface plate 72 of the lower surface plate 71.
- the plurality of carriers 73 are made of, for example, a disk-shaped epoxy resin reinforced by mixing aramid fibers or glass fibers.
- the plurality of carriers 73 are arranged side by side around the rotation shaft 71 a inside the recess 75.
- a planetary gear portion 76 is provided on the outer peripheral portion of each carrier 73 over the entire circumference.
- the sun gear portion 77 that rotates together with the rotating shaft 71 a in mesh with the planetary gear 76 of each carrier 73 is provided in the inner peripheral portion of the recess 75, and the planet of each carrier 73 is provided in the outer peripheral portion of the recess 75.
- a fixed gear portion 78 that meshes with the gear portion 76 is provided.
- Example 1 In Example 1, first, a glass substrate (TS-10SX, manufactured by OHARA) having an outer diameter of 48 mm, a central hole of 12 mm, and a thickness of 0.560 mm was used.
- T-10SX glass substrate having an outer diameter of 48 mm, a central hole of 12 mm, and a thickness of 0.560 mm was used.
- a primary main surface lapping step, an inner and outer peripheral end surface lapping step, an inner peripheral end surface polishing step, a secondary main surface lapping step, an outer peripheral end surface polishing step, and a primary main surface polishing The process and the secondary main surface polishing process were performed in this order.
- a wrapping machine having a pair of upper and lower surface plates is used to sandwich both glass substrates while sandwiching a plurality of glass substrates between surface plates rotating in opposite directions.
- the main surface was ground with a grinding pad provided on the surface plate.
- a diamond pad (Trizact (trade name) manufactured by Sumitomo 3M) was used as a grinding pad for primary lapping.
- This diamond pad has a convex outer dimension of 2.6 mm square, a height of 2 mm, an interval between adjacent convex parts of 1 mm, and an average grain size of diamond abrasive grains of 9 ⁇ m. Is about 20% by volume, and an acrylic resin is used as a binder.
- a lapping machine a 4-way double-side polishing machine (Type 16B, manufactured by Hamai Sangyo Co., Ltd.) was used, and the surface plate was rotated at 25 rpm and the processing pressure was 120 g / cm 2 for 15 minutes.
- the grinding liquid Sabrelube 9016 (manufactured by Chemetall) was diluted 10-fold with water and the grinding amount per side of the glass substrate was about 100 ⁇ m.
- a laminated body in which a plurality of glass substrates are laminated with a spacer sandwiched in a state where the center holes are aligned is rotated around the axis.
- Each glass substrate is sandwiched in the radial direction between the inner peripheral grindstone inserted in the center hole of each glass substrate and the outer peripheral grindstone disposed on the outer periphery of each glass substrate W, and the inner peripheral grindstone and the outer peripheral grindstone are laminated.
- the inner peripheral end face of each glass substrate was ground with the inner peripheral grindstone, and at the same time, the outer peripheral end face of each glass substrate was ground with the outer peripheral grindstone.
- the inner peripheral grindstone and the outer peripheral grindstone were used with a grindstone containing 80% by volume of diamond abrasive grains having an average particle diameter of 10 ⁇ m and using a copper alloy as a binder. Then, grinding was performed for 30 seconds with the rotation speed of the inner peripheral grindstone being 1200 rpm and the rotation speed of the outer peripheral grindstone being 600 rpm.
- the laminate is rotated about its axis while being dropped on the inner peripheral polishing brush, and inserted into the center hole of each glass substrate.
- the inner peripheral end face of each glass substrate was polished by moving the inner peripheral polishing brush up and down while rotating it in the direction opposite to the glass substrate.
- a nylon brush was used as the inner peripheral polishing brush, and ceria slurry was used as the polishing liquid. Then, polishing was performed for 10 minutes with the rotation speed of the inner peripheral polishing brush being 300 rpm.
- a wrapping machine having a pair of upper and lower surface plates is used to sandwich both glass surfaces while sandwiching a plurality of glass substrates between surface plates that rotate in opposite directions. It ground with the grinding pad provided in the board.
- a diamond pad (Trizact (trade name) manufactured by Sumitomo 3M) was used as a grinding pad for secondary lapping.
- This diamond pad has an outer dimension of a convex part of 2.6 mm square, a height of 2 mm, an interval between adjacent convex parts of 1 mm, and an average grain size of diamond abrasive grains of 4 ⁇ m. Is about 50% by volume, and an acrylic resin is used as a binder.
- a lapping machine a 4-way double-side polishing machine (Type 16B manufactured by Hamai Sangyo Co., Ltd.) was used, and the surface plate was rotated at 25 rpm and the processing pressure was 120 g / cm 2 for 10 minutes.
- the grinding fluid Sabrelube 9016 (manufactured by Chemetall) was diluted 10 times with water and the grinding amount per side of the glass substrate was about 30 ⁇ m.
- a polishing machine equipped with an outer peripheral polishing brush is used, and a plurality of glass substrates are laminated with spacers in between in a state where the center holes are aligned again while dripping the polishing liquid onto the outer peripheral polishing brush.
- the laminated body is rotated around the axis by a rotating shaft inserted into the center hole of each glass substrate, and the outer peripheral polishing brush that is in contact with the outer peripheral end surface of each glass substrate is rotated in the opposite direction to the laminated body.
- the outer peripheral end face of each glass substrate was polished by moving in the direction.
- a nylon brush was used as the outer peripheral polishing brush, and ceria slurry was used as the polishing liquid. And it grind
- the primary main surface polishing step using a polishing machine having a pair of upper and lower surface plates, a plurality of glass substrates are sandwiched between surface plates rotating in opposite directions, and a polishing liquid is dropped on the glass substrate, Both main surfaces of these glass substrates were polished with a polishing pad provided on a surface plate.
- a suede type manufactured by Filwel
- a commercially available ceria-based abrasive SHOROX, manufactured by Tohoku Metal Chemical Co., Ltd., particle size: 1.0 ⁇ m
- a polishing slurry prepared so that the ceria content was 0.6% by mass was used.
- the lapping machine uses a 4-way double-side polishing machine (Type 16B, manufactured by Hamai Sangyo Co., Ltd.), while supplying the polishing liquid at 8 liters / minute, rotating the platen at 30 rpm and processing pressure at 110 g / min. Grinding was performed for 40 minutes as cm 2 . The grinding amount per side of the glass substrate was about 15 ⁇ m.
- the secondary main surface polishing step using a polishing machine having a pair of upper and lower surface plates, sandwiching a plurality of glass substrates between surface plates rotating in opposite directions, while dropping a polishing liquid on the glass substrate, Both main surfaces of these glass substrates were polished with a polishing pad provided on a surface plate.
- a suede type manufactured by Filwel
- a ceria abrasive-containing solution having a solid content of 12% by mass (average particle size of 0.5 ⁇ m, Showa) SHORX manufactured by Denko) and a silica abrasive solution having a solid content of 40% by mass (average particle size 0.08 ⁇ m, Compol manufactured by Fujimi) are added to water, the ceria content is 0.6% by mass, and the silica content is The polishing slurry prepared so that it might become 0.2 mass% was used.
- the lapping machine uses a 4-way double-side polishing machine (Type 16B, manufactured by Hamai Sangyo Co., Ltd.), supplying the polishing liquid at 7 liters / minute, and rotating the platen at 25 rpm and processing pressure at 110 g / min. Grinding was performed for 30 minutes as cm 2 . The grinding amount per side of the glass substrate was about 2 ⁇ m.
- the obtained glass substrate was chemically washed with an anionic surfactant combined with ultrasonic waves and washed with pure water to obtain a glass substrate for a magnetic recording medium of Example 1.
- Comparative Example 1 In Comparative Example 1, in the primary main surface lapping step, a lapping machine having a pair of upper and lower surface plates is used, a plurality of glass substrates are sandwiched between surface plates that rotate in opposite directions, and a grinding liquid is sandwiched between the glass substrates. While dripping, both the main surfaces of these glass substrates were ground with the grinding pad provided in the surface plate. At this time, a resin bond diamond lapping machine using diamond abrasive grains having an average particle diameter of 9 ⁇ m was used as a grinding pad for primary lapping, and water was used as a grinding liquid. In the lapping machine used for the primary lapping, diamond grains are bonded to the entire ground surface via a binder, and the surface is flat. The content of diamond abrasive grains is about 20% by volume, and a polyurethane resin is used as a binder.
- a 4-way double-side polishing machine (Type 16B manufactured by Hamai Sangyo Co., Ltd.) was used. While supplying the grinding liquid to the surface plate, the rotation speed of the surface plate was 25 rpm, and the processing pressure was 120 g / cm 2 . Grinding was performed for 15 minutes. Other than that was carried out similarly to Example 1, and manufactured the glass substrate for magnetic recording media.
- Example 2 a metal bond diamond pad was used as a grinding pad in the primary main surface lapping step of Example 1 above.
- This diamond pad is obtained by fixing diamond abrasive grains to a polyurethane resin base material by electroless nickel plating.
- the outer dimensions of the convex portion are 2.6 mm square, the height is 2 mm, and the adjacent convex portion. Is 1 mm, the average grain diameter of the diamond abrasive grains is 9 ⁇ m, and the content of the diamond abrasive grains in the convex portion is about 20% by volume.
- the other production conditions were the same as in Example 1.
- Example 3 a metal bond diamond pad was used as a grinding pad in the secondary main surface lapping step of Example 1 described above.
- This diamond pad is obtained by fixing diamond abrasive grains to a polyurethane resin base material by electroless nickel plating.
- the outer dimensions of the convex portion are 2.6 mm square, the height is 2 mm, and the adjacent convex portion. Is 1 mm, the average grain size of the diamond abrasive grains is 4 ⁇ m, and the content of the diamond abrasive grains in the convex portion is about 50% by volume.
- the other production conditions were the same as in Example 1 above.
- the surface roughness Ra of each of the glass substrates for magnetic recording media of Examples 1 to 3 and Comparative Example 1 was measured. Note that an atomic force microscope (D3000 manufactured by Digital Instruments) was used for the measurement of the surface roughness Ra.
- the surface roughness Ra of the glass substrate for magnetic recording medium of Example 1 was 0.3 nm
- the surface roughness Ra of the glass substrate for magnetic recording medium of Example 2 was 0.4 nm.
- the surface roughness Ra of the glass substrate for magnetic recording media of Example 3 was 0.6 nm.
- the surface roughness Ra of the glass substrate for magnetic recording media of Comparative Example 1 was 0.9 nm.
- the waviness was worse by about 5% than in Example 1, but Example 3 was the same as that in Example 1.
- Examples 1 to 3 were all compared to Comparative Example 1. The swell was small.
- a glass substrate (glass substrate for magnetic recording medium) having a higher surface smoothness than Comparative Example 1 could be produced.
- Example 2 a metal bond diamond pad using electroless nickel plating as the above-mentioned binder is used as a grinding pad for primary or secondary lapping.
- this metal bond diamond pad the holding power of diamond abrasive grains is increased, and the life of the pad is expected to be extended.
- Example 2 the use of a metal bond diamond pad in the primary lapping process increases the holding power of the diamond abrasive grains. As a result, the polishing ability of the pad slightly decreased.
- Example 3 a metal bond diamond pad was used for secondary lapping, but since the content of diamond abrasive grains was high, the holding power of the diamond abrasive grains was not so high.
- the polishing ability of the pad slightly decreased.
- the diamond pad which used resin for the binder is used, and it has elastic force rather than the diamond pad of the said metal bond, from the case of the said Examples 2 and 3 A glass substrate having a good surface roughness Ra was obtained.
- the present invention can be applied to the manufacture of a glass substrate for a magnetic recording medium.
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Abstract
Description
本願は、2009年11月10日に、日本に出願された特願2009-257112号、および2010年8月17日に日本に出願された特願2010-182326号に基づく優先権を主張し、それらの内容をここに援用する。 The present invention relates to a method for producing a glass substrate for a magnetic recording medium.
This application claims priority based on Japanese Patent Application No. 2009-257112 filed in Japan on November 10, 2009 and Japanese Patent Application No. 2010-182326 filed on August 17, 2010 in Japan, The contents thereof are incorporated herein.
(1) 少なくともガラス基板の端面を除く表面に1次ラップ加工を施す工程と2次ラップ加工を施す工程とを含む磁気記録媒体用ガラス基板の製造方法であって、
前記1次ラップ加工及び2次ラップ加工には、ダイヤモンド砥粒が結合剤で固定されたダイヤモンドパッドを用い、このダイヤモンドパッドのラップ面は、平坦な頂部を有するタイル状の凸部が複数並んで設けられた構造を有し、
前記1次ラップ加工に用いるダイヤモンドパッドは、前記ダイヤモンド砥粒の平均粒径が4~12μmであり、前記凸部におけるダイヤモンド砥粒の含有量が5~70体積%であり、
前記2次ラップ加工に用いるダイヤモンドパッドは、前記ダイヤモンド砥粒の平均粒径が1~5μmであり、前記凸部におけるダイヤモンド砥粒の含有量が5~80体積%であることを特徴とする磁気記録媒体用ガラス基板の製造方法。
(2) 前記1次ラップ加工及び2次ラップ加工に用いるダイヤモンドパッドは、前記凸部の外形寸法が1.5~5mm角、高さが0.2~3mmであり、隣接する凸部の間の間隔が0.5~3mmであることを特徴とする請求項1に記載の磁気記録媒体用ガラス基板の製造方法。 The present invention provides the following means.
(1) A method for producing a glass substrate for a magnetic recording medium, comprising at least a step of subjecting a surface excluding an end surface of the glass substrate to a primary lapping and a step of subjecting to a secondary lapping.
In the primary lapping process and the secondary lapping process, a diamond pad in which diamond abrasive grains are fixed with a binder is used, and the lapping surface of the diamond pad includes a plurality of tile-shaped convex portions having flat top portions. Having a provided structure,
The diamond pad used for the primary lapping process has an average particle size of 4 to 12 μm of the diamond abrasive grains, and a content of diamond abrasive grains of the convex portions of 5 to 70 vol%.
The diamond pad used for the secondary lapping process has an average particle diameter of the diamond abrasive grains of 1 to 5 μm, and a content of the diamond abrasive grains in the convex portions of 5 to 80% by volume. A method for producing a glass substrate for a recording medium.
(2) The diamond pad used for the primary lapping and the secondary lapping has an outer dimension of the convex part of 1.5 to 5 mm square and a height of 0.2 to 3 mm, and is between adjacent convex parts. 2. The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein the distance between the two is 0.5 to 3 mm.
本発明を適用して製造される磁気記録媒体用ガラス基板は、中心孔を有する円盤状のガラス基板であり、磁気記録媒体は、このガラス基板の面上に、磁性層、保護層及び潤滑膜等を順次積層したものからなる。また、磁気記録再生装置(HDD)では、この磁気記録媒体の中心部をスピンドルモータの回転軸に取り付けて、スピンドルモータにより回転駆動される磁気記録媒体の面上を磁気ヘッドが浮上走行しながら、磁気記録媒体に対して情報の書き込み又は読み出しを行う。 Hereinafter, a method for producing a glass substrate for a magnetic recording medium to which the present invention is applied will be described in detail with reference to the drawings.
A glass substrate for a magnetic recording medium manufactured by applying the present invention is a disk-shaped glass substrate having a central hole, and the magnetic recording medium has a magnetic layer, a protective layer, and a lubricating film on the surface of the glass substrate. Etc. are sequentially laminated. Further, in the magnetic recording / reproducing apparatus (HDD), the central portion of the magnetic recording medium is attached to the rotation shaft of the spindle motor, and the magnetic head floats and runs on the surface of the magnetic recording medium rotated by the spindle motor. Information is written to or read from the magnetic recording medium.
例えば、上述した1次主面ラップ工程及び2次主面ラップ工程で用いられるラッピングマシーン10及び1次主面ポリッシュ工程及び2次主面ポリッシュ工程で用いられるポリッシングマシーン50については、例えば図7に示すように、上下一対の下定盤71及び上定盤72と、下定盤71の上定盤72と対向する面に配置された複数のキャリア73とを備え、各キャリア73に設けられた複数(本実施形態では35つ。)の開口部74にガラス基板(図示せず。)をセットし、これら複数のガラス基板の両主面を下定盤71及び上定盤72に設けられた研削パッドにより研削する又は研磨パッドにより研磨する構成とすることも可能である。 In addition, this invention is not necessarily limited to the thing of the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, the lapping
実施例1では、先ず、外径48mm、中央孔12mm、厚さ0.560mmのガラス基板(オハラ社製、TS-10SX)を用いた。 Example 1
In Example 1, first, a glass substrate (TS-10SX, manufactured by OHARA) having an outer diameter of 48 mm, a central hole of 12 mm, and a thickness of 0.560 mm was used.
比較例1では、上記1次主面ラップ工程において、上下一対の定盤を備えるラッピングマシーンを用い、互いに逆向きに回転する定盤の間で複数枚のガラス基板を挟み込み、ガラス基板に研削液を滴下しながら、これらガラス基板の両主面を定盤に設けられた研削パッドにより研削した。このとき、1次ラップ加工の研削パッドには、平均粒径9μmのダイヤモンド砥粒を用いたレジンボンドダイヤモンドラップ盤を用い、研削液には、水を用いた。なお、1次ラップ加工に用いたラップ盤は、研削面の全面にダイヤモンド粒が結合剤を介してボンディングされており、その表面は平坦である。また、ダイヤモンド砥粒の含有量は約20体積%であり、結合剤としてポリウレタン系樹脂を用いている。 (Comparative Example 1)
In Comparative Example 1, in the primary main surface lapping step, a lapping machine having a pair of upper and lower surface plates is used, a plurality of glass substrates are sandwiched between surface plates that rotate in opposite directions, and a grinding liquid is sandwiched between the glass substrates. While dripping, both the main surfaces of these glass substrates were ground with the grinding pad provided in the surface plate. At this time, a resin bond diamond lapping machine using diamond abrasive grains having an average particle diameter of 9 μm was used as a grinding pad for primary lapping, and water was used as a grinding liquid. In the lapping machine used for the primary lapping, diamond grains are bonded to the entire ground surface via a binder, and the surface is flat. The content of diamond abrasive grains is about 20% by volume, and a polyurethane resin is used as a binder.
実施例2では、上記実施例1の1次主面ラップ工程において、研削パッドとしてメタルボンドのダイヤモンドパッドを用いた。このダイヤモンドパッドは、ポリウレタン系樹脂製の基材に、無電解ニッケルめっきによって、ダイヤモンド砥粒を固着したものであり、凸部の外形寸法が2.6mm角、高さが2mm、隣接する凸部の間の間隔が1mm、ダイヤモンド砥粒の平均粒径が9μmであり、凸部におけるダイヤモンド砥粒の含有量が約20体積%である。そして、それ以外の製造条件は、上記実施例1と同様にした。 (Example 2)
In Example 2, a metal bond diamond pad was used as a grinding pad in the primary main surface lapping step of Example 1 above. This diamond pad is obtained by fixing diamond abrasive grains to a polyurethane resin base material by electroless nickel plating. The outer dimensions of the convex portion are 2.6 mm square, the height is 2 mm, and the adjacent convex portion. Is 1 mm, the average grain diameter of the diamond abrasive grains is 9 μm, and the content of the diamond abrasive grains in the convex portion is about 20% by volume. The other production conditions were the same as in Example 1.
実施例3では、上記実施例1の2次主面ラップ工程において、研削パッドとしてメタルボンドのダイヤモンドパッドを用いた。このダイヤモンドパッドは、ポリウレタン系樹脂製の基材に、無電解ニッケルめっきによって、ダイヤモンド砥粒を固着したものであり、凸部の外形寸法が2.6mm角、高さが2mm、隣接する凸部の間の間隔が1mm、ダイヤモンド砥粒の平均粒径が4μmであり、凸部におけるダイヤモンド砥粒の含有量が約50体積%である。それ以外の製造条件は、上記実施例1と同様にした。 (Example 3)
In Example 3, a metal bond diamond pad was used as a grinding pad in the secondary main surface lapping step of Example 1 described above. This diamond pad is obtained by fixing diamond abrasive grains to a polyurethane resin base material by electroless nickel plating. The outer dimensions of the convex portion are 2.6 mm square, the height is 2 mm, and the adjacent convex portion. Is 1 mm, the average grain size of the diamond abrasive grains is 4 μm, and the content of the diamond abrasive grains in the convex portion is about 50% by volume. The other production conditions were the same as in Example 1 above.
また、実施例2は、実施例1よりもうねりが5%ほど悪化したものの、実施例3は、実施例1と同等のうねりであり、実施例1~3は、何れも比較例1よりもうねりが小さかった。
以上のように、実施例1~3では、比較例1よりも表面の平滑性が高いガラス基板(磁気記録媒体用ガラス基板)を製造することができた。 As a result, the surface roughness Ra of the glass substrate for magnetic recording medium of Example 1 was 0.3 nm, and the surface roughness Ra of the glass substrate for magnetic recording medium of Example 2 was 0.4 nm. The surface roughness Ra of the glass substrate for magnetic recording media of Example 3 was 0.6 nm. On the other hand, the surface roughness Ra of the glass substrate for magnetic recording media of Comparative Example 1 was 0.9 nm.
In Example 2, the waviness was worse by about 5% than in Example 1, but Example 3 was the same as that in Example 1. Examples 1 to 3 were all compared to Comparative Example 1. The swell was small.
As described above, in Examples 1 to 3, a glass substrate (glass substrate for magnetic recording medium) having a higher surface smoothness than Comparative Example 1 could be produced.
11,12…定盤
20A,20B…ダイヤモンドパッド
20a…ラップ面
21…凸部
22…基材
30…ラッピングマシーン
31…内周砥石
32…外周砥石
40…ポリッシングマシーン
41…内周研磨ブラシ
50…ポリッシングマシーン
51…回転シャフト
52…外周研磨ブラシ
60…ポリッシングマシーン
61,62…定盤
71…下定盤
72…上定盤
73…キャリア
74…開口部
75…凹部
76…遊星ギア部
77…太陽ギア部
78…固定ギア部
W…ガラス基板
X…積層体
S…スペーサ DESCRIPTION OF
Claims (2)
- 少なくともガラス基板の端面を除く表面に1次ラップ加工を施す工程と2次ラップ加工を施す工程とを含む磁気記録媒体用ガラス基板の製造方法であって、
前記1次ラップ加工及び2次ラップ加工には、ダイヤモンド砥粒が結合剤で固定されたダイヤモンドパッドを用い、このダイヤモンドパッドのラップ面は、平坦な頂部を有するタイル状の凸部が複数並んで設けられた構造を有し、
前記1次ラップ加工に用いるダイヤモンドパッドは、前記ダイヤモンド砥粒の平均粒径が4~12μmであり、前記凸部におけるダイヤモンド砥粒の含有量が5~70体積%であり、
前記2次ラップ加工に用いるダイヤモンドパッドは、前記ダイヤモンド砥粒の平均粒径が1~5μmであり、前記凸部におけるダイヤモンド砥粒の含有量が5~80体積%であることを特徴とする磁気記録媒体用ガラス基板の製造方法。 A method for producing a glass substrate for a magnetic recording medium, comprising at least a step of subjecting a surface excluding an end surface of the glass substrate to a primary lap process and a step of subjecting the surface to a secondary lap process,
In the primary lapping process and the secondary lapping process, a diamond pad in which diamond abrasive grains are fixed with a binder is used, and the lapping surface of the diamond pad includes a plurality of tile-shaped convex portions having flat top portions. Having a provided structure,
The diamond pad used for the primary lapping process has an average particle size of 4 to 12 μm of the diamond abrasive grains, and a content of diamond abrasive grains of the convex portions of 5 to 70 vol%.
The diamond pad used for the secondary lapping process has an average particle diameter of the diamond abrasive grains of 1 to 5 μm, and a content of the diamond abrasive grains in the convex portions of 5 to 80% by volume. A method for producing a glass substrate for a recording medium. - 前記1次ラップ加工及び2次ラップ加工に用いるダイヤモンドパッドは、前記凸部の外形寸法が1.5~5mm角、高さが0.2~3mmであり、隣接する凸部の間の間隔が0.5~3mmであることを特徴とする請求項1に記載の磁気記録媒体用ガラス基板の製造方法。 The diamond pad used for the primary lapping process and the secondary lapping process has an outer dimension of the projection of 1.5 to 5 mm square and a height of 0.2 to 3 mm, and the spacing between adjacent projections is 2. The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein the thickness is 0.5 to 3 mm.
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WO2013015752A1 (en) * | 2011-07-28 | 2013-01-31 | Hoya Glass Disk (Thailand) Ltd. | Chamfering apparatus and method of manufacturing glass substrate for information recording medium |
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JPWO2016047535A1 (en) * | 2014-09-26 | 2017-07-20 | バンドー化学株式会社 | Polishing pad and polishing pad manufacturing method |
JP2021020314A (en) * | 2014-09-26 | 2021-02-18 | バンドー化学株式会社 | Polishing pad and method for producing polishing pad |
Also Published As
Publication number | Publication date |
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US20120225610A1 (en) | 2012-09-06 |
CN102714042A (en) | 2012-10-03 |
JP2012064295A (en) | 2012-03-29 |
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