JP5497612B2 - GLASS BLANK AND ITS MANUFACTURING METHOD, MAGNETIC RECORDING MEDIUM SUBSTRATE, AND MAGNETIC RECORDING MEDIUM MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to a glass blank, which is a thin plate-shaped glass molded product, a method for manufacturing the same, a magnetic recording medium substrate manufactured from the glass blank, and a method for manufacturing the magnetic recording medium.

As a base material of a high-density recording medium such as a hard disk, a glass blank which is a thin plate-like glass molded product as shown in Patent Document 1 is used. A sectional view of a conventional glass blank is shown in FIG. As shown in FIG. 8, the conventional glass blank 201 has a cross-sectional shape like a letter “D” formed by protruding portions 211 and 221 formed on the edges of the first surface 210 and the second surface 220. Is formed. Corner portions 212 and 222 are formed between the first surface 210 and the protruding portion 211 of the glass blank 201 and between the second surface 220 and the protruding portion 221. In the conventional glass blank, the angles of the corner portions 212 and 222 are approximately 90 °. By forming the glass blank in such a shape, the lapping in a state where the glass blank is elastically deformed can be avoided by receiving the pressure of the grinding machine at the protruding portion at the time of lapping, and a flat magnetic recording medium substrate Can be produced.

  The glass blank is generally formed by a press device. The press apparatus is manufactured by sandwiching a glass lump (gob) that has been heated and melted between an upper mold and a lower mold and molding the glass lump while cooling. More specifically, the gob is dropped on the lower mold, and then the upper mold is driven toward the lower mold, and the gob is pressed between the upper mold and the lower mold.

  In order to improve the production efficiency of the glass blank, normally, a plurality of lower molds are used for one upper mold, and once pressed, the glass blank is placed on the lower mold even after the upper mold is separated. It is cooled as it is. Moreover, in order to form said protrusion part in a glass blank, the level | step-difference part is formed in the upper mold | type and the lower mold | type.

Patent No. 3714501

  In the cooling step, the glass blank is cooled by natural heat dissipation. Further, at the time of pressing, the temperature of the upper mold is lower than that of the lower mold. However, since the pressing time is short, the temperature of the glass is higher on the upper surface than on the lower surface. Therefore, as for the glass blank in the cooling process, the temperature decrease width increases as the portion is closer to the upper mold. As a result, the glass blank 201 contracts more greatly on the upper side, and as shown in FIG. 9, the glass blank 201 is warped so as to protrude downward.

  Once cooled, the glass blank is pressed again between the lower die and the upper die for flatness correction press maintained in the vicinity of the glass transition point, and the warpage is corrected (flatness correction press). However, when the glass blank 201 is warped, the holding of the glass blank 201 by the lower mold D becomes unstable, and for example, a part of the protruding portion 221 of the glass blank 201 rides on the stepped portion D1 of the lower shape D. There is a possibility that flatness correction press will be performed in the state. As a result, the protruding portions 211 and 221 are pressed between the step portions of the lower mold and the upper mold, and the flatness accuracy of the glass blank is low. Further, when the upper portion of the glass blank 201 contracts in the cooling process, the lower corner portion 222 of the glass blank 201 is caught, and the first surface 210 of the glass blank 201 is stretched and deformed, and the glass blank 201 The flatness accuracy may be reduced.

  The present invention has been made to solve the above problems. That is, an object of the present invention is to provide a glass blank having high flatness accuracy, a method for manufacturing the glass blank, a magnetic recording medium substrate manufactured from the glass blank, and a method for manufacturing the magnetic recording medium.

  In order to achieve the above object, in the glass blank of the present invention, the first and second protrusions project in the normal direction of the first surface and the second surface from the edges of the first surface and the second surface of the glass blank, respectively. The top surfaces of the first and second protrusions are formed substantially parallel to the first surface and the second surface, respectively, and the top surfaces of the first and second protrusions are provided. First and second inclined surfaces are formed from the respective surfaces over the first surface and the second surface.

  With such a configuration, when the flatness correction press is performed, the inclined surface of the glass blank slides along the mold, and the flatness correction press is performed in substantially the same state as when the glass blank was first formed. As a result, a glass blank with high flatness accuracy is obtained.

  Preferably, the angle of the first and second inclined surfaces with respect to the first surface and the second surface is 30 ° or less. With such a configuration, the inclined surface becomes more slippery with respect to the mold during the flatness correction press.

  Preferably, the corner portion between the first and second surfaces and the first and second inclined surfaces is rounded. Preferably, a corner portion between the top surfaces of the first and second protrusions and the first and second inclined surfaces is rounded. Moreover, Preferably, the corner part between the top surface of the 1st and 2nd protrusion part and the side surface of a glass blank is rounded.

  When the glass blank is cooled, heat easily escapes from the convex corners, while heat hardly escapes from the concave corners. For this reason, at the time of cooling, a large thermal stress is likely to be generated in the corner portion, and there is a possibility that the glass blank is greatly deformed. In the present invention, since the corner portion is rounded as described above, heat is more difficult to escape at the convex corner portion, and heat is more easily escaped at the concave corner portion. As a result, in the configuration of the present invention, a highly accurate glass blank with less thermal deformation at the corner is realized.

  Moreover, in the glass blank of this invention, all of the top surface of the said 1st and 2nd protrusion part, the part enclosed by the inclined surface in the said 1st surface, and the part enclosed by the inclined surface in the 2nd surface. Are preferably substantially parallel to each other, more preferably the top surfaces of the first protrusions are on the same plane, and the top surfaces of the second protrusions are on the same plane. By making the glass blank in such a shape, the glass blank can be cooled more uniformly after press molding, the flatness of the glass blank can be improved, and the flatness of the glass blank can be easily evaluated. Can be done. In addition, in the lapping process when producing a magnetic recording medium substrate from a glass blank, it is possible to lapping while uniformly receiving the pressure of the grinding machine over the entire top surface of the protruding portion of the glass blank. Property can be further improved, and the effect of preventing chipping of the protrusions can also be obtained.

  Moreover, in order to achieve said objective, the manufacturing method of the glass blank of this invention presses the glass material softened between the upper mold | type and the lower mold | type, and presses the glass blank which is a thin plate-shaped glass molded product. The upper die and the lower die in the pressing step are each formed on a substantially horizontal plane portion and the entire circumference of the peripheral portion of the plane portion, and the bottom surface thereof becomes substantially horizontal and is recessed with respect to the plane portion. And a sloping surface formed between the flat portion and the bottom surface of the peripheral portion.

  Preferably, the method for producing a glass blank of the present invention further includes a cooling step that is performed after the pressing step and separates the upper die from the lower die and cools the glass blank on the lower die.

  In order to achieve the above object, the method of manufacturing the magnetic recording medium substrate of the present invention is a method of processing the glass blank of the present invention into a disk-shaped substrate, or the glass blank by the method of manufacturing a glass blank of the present invention. And the glass blank is processed into a disk-shaped substrate.

  In order to achieve the above object, the method for producing a magnetic recording medium of the present invention comprises processing the glass blank of the present invention into a disk-shaped substrate and forming at least a magnetic recording layer on the substrate, or A glass blank is produced by the method for producing a glass blank of the present invention, the glass blank is processed into a disk-shaped substrate, and at least a magnetic recording layer is formed on the substrate.

  As described above, according to the present invention, it is possible to obtain a glass blank with high flatness accuracy. Further, by manufacturing a magnetic recording medium substrate or magnetic recording medium using the glass blank, it is possible to save labor in the process of manufacturing the substrate from the glass blank.

FIG. 1 is a cross-sectional view of a glass blank according to an embodiment of the present invention. FIG. 2 shows a glass blank manufacturing apparatus according to an embodiment of the present invention in a state where molten glass is supplied to the lower mold. FIG. 3 shows a cross-sectional view of a glass blank manufacturing apparatus according to an embodiment of the present invention in a state in which molten glass gob is formed by cutting molten glass. FIG. 4 shows a glass blank manufacturing apparatus according to an embodiment of the present invention in a state where an upper mold is disposed on a lower mold. FIG. 5 shows a cross-sectional view of the glass blank manufacturing apparatus according to the embodiment of the present invention in a state where pressing is performed between the upper mold and the lower mold. FIG. 6: shows sectional drawing of the manufacturing apparatus of the glass blank which concerns on embodiment of this invention of the state which is cooling the glass blank on a lower mold | type. FIG. 7 shows a cross-sectional view of the glass blank manufacturing apparatus according to the embodiment of the present invention in a state where the glass blank is warped on the lower mold. FIG. 8 is a cross-sectional view of a conventional glass blank. FIG. 9 shows a cross-sectional view of a conventional glass blank manufacturing apparatus in a state where the glass blank is warped on the lower mold.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a glass blank according to an embodiment of the present invention. As shown in FIG. 1, the glass blank 101 of the present embodiment is a disk-shaped glass molded product having a diameter of 66 mm and a thickness of about 1 mm.

  At the edges of the first surface 110 and the second surface 120 of the glass blank 101, annular projecting portions 111 and 121 projecting in the normal direction of the respective surfaces are formed. The top surfaces 111a and 121a of the protrusions 111 and 121 are formed substantially parallel to the first surface 110 and the second surface 120, respectively. The protrusions 111 and 121 function as support portions (pedestals) when the glass blank 101 is lapped. In this embodiment, since the top surfaces 111a and 121a of the protrusions 111 and 121 are formed substantially parallel to the first surface 110 and the second surface 120, respectively, the glass blank 101 is used when lapping is performed as a subsequent process. Is held stably. In addition, the preferable minimum of the height of the protrusion parts 111 and 121 is 0.01 mm, the more preferable minimum is 0.02 mm, the still more preferable minimum is 0.03 mm, and a still more preferable minimum is 0.04 mm. A preferable upper limit of the height of the protrusions 111 and 121 is 0.10 mm, a more preferable upper limit is 0.09 mm, a still more preferable upper limit is 0.08 mm, and a still more preferable upper limit is 0.07 mm. If the heights of the protrusions 111 and 121 are excessive, the cooling speed of the protrusions is increased in the cooling step after press molding, and it becomes difficult to cool the glass blank uniformly, and the flatness of the glass blank is lowered. If the heights of the protrusions 111 and 121 are too small, it becomes difficult to receive the pressure of the grinding machine only by the protrusions in the lapping process, and the glass blank is wrapped in an elastically deformed state. It becomes difficult to obtain the effect of the protruding portion. The dimension of the protruding portion in the radial direction of the glass blank (disc shape) is preferably 0.5 mm or more, more preferably 0.8 mm or more from the viewpoint of obtaining the effect of the protruding portion, and 1 mm or more. Is preferably 10 mm or less, more preferably 8 mm or less, further preferably 7 mm or less, still more preferably 6 mm or less, and even more preferably 5 mm or less. In the present embodiment, the heights of the protrusions 111 and 121 (the distances of the top surfaces 111a and 121a from the first surface 110 and the second surface 120) are about 0.05 mm.

  In addition, inclined surfaces 112 and 122 are formed between the first surface 110 and the protruding portion 111 and between the second surface 120 and the protruding portion 121, respectively. The angle θ1 between the first surface 110 and the inclined surface 112 and the angle θ2 between the second surface 120 and the inclined surface 122 are both substantially the same angle. Further, a corner portion 113 between the first surface 110 and the inclined surface 112, a corner portion 114 between the inclined surface 112 and the top surface 111 a of the protruding portion 111, and a corner between the second surface 120 and the inclined surface 122. Both the portion 123 and the corner portion 124 between the inclined surface 122 and the top surface 121a of the protruding portion 121 are rounded. Further, the corner portions 115 and 125 between the circumferential surface 130 of the glass blank 101 and the protruding portions 111 and 121 are also rounded. From the viewpoint of obtaining the effect of rounding the corner portion described later, the radius of curvature of each corner portion is preferably 0.05 mm or more, more preferably 0.1 mm or more, and further preferably 0.2 mm or more. Preferably, it is 0.3 mm or more. If the upper limit of the radius of curvature is excessive, the protruding portion cannot be formed. Therefore, the upper limit of the radius of curvature may be determined in consideration of the outer diameter of the glass blank, the thickness, the width of the protruding portion, and the like. It should be noted that the projecting portions of both the first surface and the second surface annularly surround the outer periphery of each of the first surface and the second surface, so that the glass blank can be cooled uniformly and the grinding machine during lapping It is preferable from the viewpoint of receiving pressure evenly.

  Subsequently, the manufacturing procedure of the glass blank 101 of this embodiment is demonstrated. The glass blank 101 is manufactured by a press device. 2, 3, 4, 5, and 6 are cross-sectional views of the pressing device in each manufacturing process of the glass blank 101.

  The press apparatus 10 that manufactures the glass blank 101 presses the gob GG, which is a lump of molten glass material GM, between the upper mold 11 (FIGS. 4 and 5) and the lower mold 12, so that the glass blank 101 Is a device for manufacturing.

  In manufacturing the glass blank 101, first, the gob GG needs to be placed on the lower mold 12. For this purpose, as shown in FIG. 2, the lower mold 12 is moved under the nozzle 13 that discharges the molten glass material GM.

  As shown in FIG. 2, a pair of cutting blades 14 are provided between the discharge port 13 a of the nozzle 13 and the lower mold 12. The pair of cutting blades 14 are spaced apart from each other in a first state in which the glass material GM can pass from between the pair of cutting blades 14 and a second state in which the pair of cutting blades 14 abut against each other so as not to pass the glass material GM It is possible to switch between these states.

  In FIG. 2, the cutting blade 14 is in the first state, and the glass material GM discharged from the discharge port 13 a of the nozzle 13 passes between the cutting blades 14 and is placed on the lower mold 12.

  In addition, as FIG. 2 shows, the 2nd surface 120 of the glass blank 101 (FIG. 1), the protrusion part 121, the inclined surface 122, the circumferential surface 130, and the corner parts 123-125 are shown in the upper surface of the lower mold | type 12. As shown in FIG. A recess 12a having the same shape as that of FIG. A contact portion 12b that contacts the upper mold 11 is formed on the periphery of the recess 12a. The recess 12a is located at the center and has a substantially horizontal flat surface portion 12d and a peripheral concave flat surface 12e formed on the outer edge of the flat surface portion 12d and recessed downward with respect to the flat surface portion 12d. In addition, the surface which shape | molds the corner part of a glass blank in an upper mold | type and a lower mold is processed into the shape which reversed the roundness of the corner part. If the rounded corner portion can be formed by transferring the molding surface of the press mold, a portion for transferring the corner portion may be provided in addition to the above portion of the press mold.

  After a predetermined amount of the glass material GM is placed on the recess 12a of the lower mold 12, the cutting blade 14 is in the second state. In this state, as shown in FIG. 3, the glass material is cut by the cutting blade 14 to form the gob GG.

  The lower mold 12 then moves below the upper mold 11 with the gob GG placed on the recess 12a. As shown in FIG. 4, the upper mold 11 has a cylinder part 11a and a piston part 11b. The piston portion 11b is driven so as to move up and down in the cylinder portion 11a, and the contact surface 11c, which is the lower surface of the cylinder portion 11a of the upper die 11, is brought into contact with the contact surface 12b of the lower die 12. Then, the lower mold 12 is surrounded by the concave portion 12a, the lower surface 11d of the piston portion 11b of the upper die 11, and the protruding portion die portion 11e formed inside the contact surface 11c of the cylinder portion 11a of the upper die 11. A sealed space P is formed. As shown in FIG. 4, the gob GG is housed in the sealed space P when the contact surface 11 c of the upper mold 11 and the contact surface 12 b of the lower mold 12 are in contact.

  Next, the piston portion 11 b of the upper mold 11 descends toward the lower mold 12. The lower surface 11d of the piston portion 11b has the same shape as the first surface 110 of the glass blank 101 (FIG. 1). Further, the protruding portion mold portion 11e of the cylinder portion 11a of the upper mold 11 includes an inclined surface 11e1 having the same shape as the inclined surface 112 of the glass blank 101 and a peripheral concave surface 11e2 having the same shape as the top surface 111a of the protruding portion 111. Is formed. Therefore, in the state where the piston portion 11b is lowered, the sealed space P has the same shape as the glass blank 101 as shown in FIG.

  When the piston portion 11b of the upper mold 11 is lowered, the gob GG is rapidly formed into a thin plate as shown in FIG. At this time, since the contact area between the gob GG and the upper mold 11 and the lower mold 12 increases rapidly, the heat of the gob GG is suddenly taken away by the upper mold 11 and the lower mold 12, which is a disk-shaped glass product. A glass blank 101 is formed.

  Next, the upper mold 11 is separated from the lower mold 12, and the glass blank 101 is cooled on the recess 12 a of the lower mold 12. At the time of pressing, the temperature of the upper die 11 is set lower than that of the lower die 12, but since the pressing time is short, the temperature of the glass blank 101 is lower on the upper die 11 side when pressing is completed. It is higher than the mold 12 side. For this reason, the temperature decrease amount of the first surface 110 on the upper mold 11 side in the cooling process is larger than the temperature decrease amount of the second surface 120. For this reason, in the cooling process, as shown in FIG. 7, the first surface 110 contracts more than the second surface 120, and a warp that protrudes downward occurs in the glass blank 101.

  Next, after the glass blank 101 is cooled to some extent in the cooling process, the lower die 12 has the same shape as the upper die 11 and is maintained at a higher temperature than the upper die 11 (not shown) for flatness correction press. The glass blank 101 is pressed again between the lower mold 12 and the upper mold for flatness correction press. As a result, the warp of the glass blank 101 generated in the cooling process is removed.

  In the present embodiment, as described above, the inclined surfaces 112 and 122 are formed between the first surface 110 and the second surface 120 of the glass blank 101 and the protruding portions 111 and 121. Similar inclined surfaces 12c and 11e1 are formed on the lower die 12 and the upper die for flatness correction press.

  Further, as described above, when the glass blank 101 is warped, the holding of the glass blank 101 by the lower mold 12 becomes unstable, and the glass blank 101 can move on the flat portion 12d of the lower mold 12. There is sex. In the present embodiment, the angles θ1 and θ2 of the inclined surfaces 112 and 122 of the glass blank 101 with respect to the first surface 110 and the second surface 120 are 30 ° or less, and when performing a flatness correction press, The inclined surfaces 112 and 122 of the glass blank 101 slide along the inclined surfaces of the lower die 12 and the flatness correcting press upper die and the lower die, and the sealed space between the lower die 12 and the flatness correcting press upper die. The flatness correction press is performed in a state where the glass blank 101 is securely accommodated in the sealed space P (corresponding to the sealed space P in FIG. 5).

  For this reason, in this embodiment, the shape defect of the glass blank which may arise when the flatness correction press is performed without the glass blank 101 being accommodated in the sealed space between the lower die 12 and the upper die for flatness correction press. Is prevented.

  The angles θ1 and θ2 may be 30 ° or more, but when the angles θ1 and θ2 are particularly 30 ° or less, the inclined surfaces 112 and 122 of the glass blank 101 are the lower die 12 and the upper die for annealing press. This is preferable because it becomes easier to slide along the inclined surface.

  In addition, even if the second surface 120 side of the glass blank 101 contracts in the cooling process, the inclined surface 122 on the second surface 120 side of the glass blank 101 slides along the inclined surface 12c of the lower mold 12, so that the glass blank The protruding portion 121 of 101 is caught by the lower mold 12 and the first surface 110 and the second surface 120 are not deformed.

  Further, as described above, the glass blank 101 according to the present embodiment includes the corner portion 113 between the first surface 110 and the inclined surface 112, and the corner portion between the inclined surface 112 and the top surface 111 a of the protruding portion 111. 114, a corner portion 123 between the second surface 120 and the inclined surface 122, a corner portion 124 between the inclined surface 122 and the top surface 121a of the protruding portion 121, the circumferential surface 130 of the glass blank 101, and the protruding portion 111. The corners 115 and 125 between the first and second parts 121 and 121 are rounded. In general, the convex corner portion easily escapes heat to the flat portion, and the concave corner portion hardly releases heat to the flat portion. For this reason, a large thermal deformation may occur in the vicinity of the corner while the glass blank is cooled. In the present embodiment, by rounding the corner portion, heat is less likely to escape to the outside at the convex corner portion, and heat is more likely to escape to the outside at the corner portion that is concave. For this reason, thermal deformation that may occur at the corners during cooling is alleviated.

  The flatness of the glass blank produced in this way was 18 μm. According to the present invention, a glass blank excellent in flatness with a flatness of 20 μm or less could be obtained. On the other hand, the flatness of the glass blank press-molded without providing inclined surfaces on the first and second surfaces is 50 μm. The flatness of the glass blank is 100 μm with both the first surface and the second surface being concave, and the corners between the first and second surfaces and the side surfaces are not rounded corners but edges. there were. Thus, the flatness of the glass blank which does not satisfy the requirements of the present invention is 50 μm or more, and the flatness and the like are insufficient.

  Using a glass blank having a flatness of 18 μm, known processes such as center drilling, peripheral processing, lapping, and polishing were performed, followed by washing and drying to produce a magnetic recording medium substrate. Since the glass blank excellent in flatness was used, the lapping process was able to be shortened. The magnetic recording medium substrate may be chemically strengthened as necessary. A known film including a magnetic recording layer was formed on the magnetic recording medium substrate to obtain a magnetic disk, that is, a magnetic recording medium.

DESCRIPTION OF SYMBOLS 10 Press apparatus 11 Upper mold | type 12 Lower mold | type 101 Glass blank 110 1st surface 111, 121 Protrusion part 111a, 121a Top surface 112, 122 Inclined surface 120 2nd surface

Claims (16)

A glass blank which is a thin plate-shaped glass molded article,
From the edges of the first surface and the second surface of the glass blank, the first and second protrusions that protrude in the normal direction of the first surface and the second surface, respectively,
The top surfaces of the first and second protrusions are formed substantially parallel to the first surface and the second surface, respectively.
A glass blank, wherein first and second inclined surfaces are formed from the top surfaces of the first and second protrusions to the first surface and the second surface, respectively.   The glass blank according to claim 1, wherein an angle of the first and second inclined surfaces with respect to the first surface and the second surface is 30 ° or less.   The glass blank according to claim 1 or 2, wherein a corner portion between the first surface and the second surface and the first and second inclined surfaces is rounded.   The corner part between the top surface of the said 1st and 2nd protrusion part and the said 1st and 2nd inclined surface is rounded, The any one of Claims 1-3 characterized by the above-mentioned. A glass blank according to item   The corner part between the top surface of the said 1st and 2nd protrusion part and the side surface of the said glass blank is rounded, The Claim 1 characterized by the above-mentioned. Glass blank.   All of the top surfaces of the first and second protrusions, the portion surrounded by the inclined surface on the first surface, and the portion surrounded by the inclined surface on the second surface are flat surfaces and are substantially parallel to each other. The glass blank according to any one of claims 1 to 5. Between the upper mold and the lower mold, it has a pressing step of pressing a softened glass material to form a glass blank that is a thin plate-like glass molded product,
The upper die and the lower die at the time of the pressing step are each formed on a substantially horizontal flat part and an entire periphery of the peripheral part of the flat part, and its peripheral part is substantially horizontal and concave with respect to the flat part. And a slanted surface formed between the flat portion and the bottom surface of the peripheral edge portion.   The glass blank according to claim 7, further comprising a cooling step of cooling the glass blank on the lower die by separating the upper die from the lower die, which is performed after the pressing step. Manufacturing method.   9. The method for producing a glass blank according to claim 7, wherein an angle of the inclined surfaces of the upper mold and the lower mold with respect to a plane portion is 30 ° or less.   The method for producing a glass blank according to any one of claims 7 to 9, wherein a corner portion between the flat portion and the inclined surface of the upper die and the lower die is rounded.   The method for producing a glass blank according to any one of claims 7 to 10, wherein a corner portion between the bottom surface and the inclined surface of the peripheral portion of the upper mold and the lower mold is rounded. .   The corner part between the bottom face of the peripheral part of the said upper mold | type and a lower mold | type and the outer peripheral surface of this peripheral part is rounded, The Claim 7 characterized by the above-mentioned. Manufacturing method of glass blank. In the method of manufacturing a glass magnetic recording medium substrate,
A method for manufacturing a magnetic recording medium substrate, comprising processing the glass blank according to any one of claims 1 to 6 into a disk-shaped substrate. In the method of manufacturing a glass magnetic recording medium substrate,
A method for producing a magnetic recording medium substrate, comprising producing a glass blank by the method according to claim 7 and processing the glass blank into a disk-shaped substrate.   A method for producing a magnetic recording medium, comprising: processing the glass blank according to any one of claims 1 to 6 into a disk-shaped substrate; and forming at least a magnetic recording layer on the substrate.   A glass blank is produced by the method according to any one of claims 7 to 12, the glass blank is processed into a disk-shaped substrate, and at least a magnetic recording layer is formed on the substrate. Method.

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