JP2010195649A - Glass blank, method for producing the same, method for producing substrate for information recording medium, and method for producing information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass blank with which cracking is suppressed during pressing and to provide a method for producing the same. <P>SOLUTION: The glass blank 1 has a thin part 10 having a disk-like shape and a thick part 12 provided along the peripheral edge part of the thin part 10. When the glass blank is processed into a substrate for an information recording medium, the thick part 12 is removed. The method for producing the glass blank is a method for producing the glass blank 1. The substrate for an information recording medium is produced by using the glass blank 1 or the glass blank 1 produced by the method for producing the glass blank. Further, in the method for producing the information recording medium, a substrate produced by a method for producing a substrate for an information recording medium is used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a glass blank, a method for manufacturing a glass blank, a method for manufacturing a substrate for an information recording medium, and a method for manufacturing an information recording medium.

  As a substrate used for a disk-shaped information recording medium such as a hard disk used as an information recording means such as a personal computer, a substrate made of glass or glass ceramic is widely used. A typical method for manufacturing such an information recording medium substrate is as follows. First, a glass blank is produced using a method (so-called direct press method) in which molten glass is press-molded with a pair of molds composed of an upper mold and a lower mold. Next, post-processing such as polishing is performed on the glass blank to obtain an information recording medium substrate (hereinafter sometimes simply referred to as “substrate”). After that, an information recording medium is obtained by forming an information recording layer or the like on the substrate in accordance with the type of the information recording medium to be manufactured.

  When manufacturing a glass blank using a direct press method, it is known that the curvature and the wave | undulation which generate | occur | produce resulting from press molding will be a problem. And in order to solve these problems, the glass blank which has a thick part in a peripheral part is proposed (refer patent document 1, 2). In addition, from the viewpoint of cost reduction and industrial waste reduction, the thick-walled portion provided on the peripheral edge is entirely in order to suppress the generation of grinding / polishing waste that occurs when processing a glass blank into a substrate. It will not be removed and will eventually form part of the substrate.

JP-A-10-194760

JP 2002-226219 A

  On the other hand, in order to cope with further cost reduction, it is necessary to reduce the polishing allowance when the glass blank is post-processed to form a substrate. For this purpose, the thickness of the glass blank (the thickness of the portion that can eventually become a substrate) is preferably as close as possible to the thickness of the substrate. However, if the thickness of the entire glass blank is to be made thinner, the larger the outer shape of the glass blank, the greater the press thrust required during press molding. Such an increase in press thrust tends to cause cracking of the glass blank.

  The present invention has been made in view of the above-described circumstances, a glass blank for suppressing cracking during pressing, a method for manufacturing the same, a method for manufacturing a substrate for an information recording medium using the glass blank, and an information recording medium. It is an object to provide a manufacturing method.

The above-mentioned subject is achieved by the following present invention.
That is, the glass blank of the present invention has a disk-shaped thin portion and a thick portion provided along the peripheral portion of the thin portion, and is thick when processed into an information recording medium substrate. The portion is removed.

  As one embodiment of the glass blank of this invention, it is preferable that the thickness of a thin part is 0.5 mm or more and less than 1.0 mm.

  As another embodiment of the glass blank of the present invention, the diameter of the thin wall portion is in the range of 65.0 mm to 72.0 mm, in the range of 47.0 mm to 53.0 mm, and in the range of 27.0 mm to 33.0 mm. It is preferable that a value within any one range selected from the following range and the range of 21.0 mm or more and 26.0 mm or less can be taken.

  As still another embodiment of the glass blank of the present invention, it is preferable that the thin portion and the thick portion are formed flush with each other on at least one surface.

  As still another embodiment of the glass blank of the present invention, on the surface on the side where the thin portion and the thick portion are formed to be stepped, it continues from the flat portion of the thin portion to the top of the thick portion. It is preferable that the inclined surface has a curved surface forming a surface continuous with the flat portion.

  One surface of the method for producing a glass blank of the present invention is provided as a circular center portion and a peripheral edge side of the center portion as at least one of an upper die and a lower die, which is in contact with the softened glass during press molding. A press surface having an outer edge is provided, and the outer edge is softened between the upper mold and the lower mold after a softened glass is supplied onto the lower mold using a mold that is concave with respect to the center. A glass blank is produced through at least a pressing step of press-molding the glass so as to reach the outer edge.

  The other surface of the method for producing a glass blank of the present invention is provided as a circular central portion and a peripheral portion of the central portion as a mold of at least one of an upper die and a lower die, which is in contact with the softened glass during press molding. A press surface having an outer edge portion, the outer edge portion being recessed with respect to the center portion, and the diameter of the center portion being in the range of 65.0 mm to 72.0 mm, 47.0 mm to 53.0 mm Glass having a softened state using a mold having a value within one of the ranges selected from the range, the range of 27.0 mm to 33.0 mm, and the range of 21.0 mm to 26.0 mm After the glass is supplied onto the lower mold, a glass blank is produced through at least a pressing step of press-molding the softened glass so as to reach the outer edge portion between the upper mold and the lower mold.

  One side of the manufacturing method of the information recording medium substrate of the present invention is to cut a thick portion of the glass blank selected from the above glass blank and the glass blank produced by the above glass blank manufacturing method. The substrate for an information recording medium is manufactured through at least a thick portion removing step to be removed.

  The other surface of the method for producing the substrate for information recording medium of the present invention comprises a thick part of a glass blank having a disk-like thin part and a thick part provided along the peripheral part of the thin part. A substrate for an information recording medium is manufactured through at least a thick portion removing step that is cut and removed.

  The information recording medium manufacturing method of the present invention includes at least an information recording layer forming step of forming an information recording layer on at least one side of the information recording medium substrate manufactured by the above-described information recording medium substrate manufacturing method. A recording medium is manufactured.

  ADVANTAGE OF THE INVENTION According to this invention, the glass blank which suppresses the crack at the time of a press, its manufacturing method, the manufacturing method of the board | substrate for information recording media using the said glass blank, and the manufacturing method of an information recording medium can be provided.

It is a schematic cross section which shows an example of the glass blank of this embodiment. It is the elements on larger scale which expanded the cross section which cut | disconnected the part near the thick part of the glass blank shown in FIG. 1 in the diameter direction. It is a schematic cross section which shows an example of the type | mold (molding die) used for the manufacturing method of the glass blank of this embodiment. It is explanatory drawing which shows an example of the direct press method of the conventional non-side free press system using a trunk die.

(Glass blank and its manufacturing method)
-Glass blank-
The glass blank of this embodiment has a disk-shaped thin part and a thick part provided along the peripheral part of the thin part, and when processing into a substrate for an information recording medium, the thick part Is removed. In the glass blank which has such a shape, when producing this glass blank, the crack at the time of a press can be suppressed.

  The reason why the inventors found the glass blank of the above-described embodiment is as follows. First, in order to obtain a thinner glass blank from the viewpoint of reducing the polishing allowance, the inventors of the present invention have a thick glass part having a thick part at the peripheral part as shown in Patent Documents 1 and 2. Was also considered unsuitable because it also needed to be polished. For this reason, reducing the thickness of the whole glass blank, without providing a thick part in a peripheral part, was examined. However, it has been found that in such a glass blank, it is necessary to increase the press thrust during press molding, and as a result, cracking is likely to occur. Such cracking is presumed to occur by the following mechanism.

  First, during press molding, softened glass is supplied to the center of the press surface of the lower mold, and then the softened glass is pressed by the lower mold and the upper mold, so that the upper mold and the lower mold The glass is stretched so as to spread in the gap. At this time, the heat of the glass in the softened state is rapidly taken away by coming into contact with the press surface of the upper die or the lower die. As a result, the temperature of the glass decreases, and as a result, the viscosity increases. However, such an increase in viscosity does not occur uniformly in the range from the center side to the outside of the press surface, but is considered to progress as it goes outward from the center side. This is due to the following reason. First, in the softened glass lump sandwiched between the upper mold and the lower mold, the part that extends to the outermost side is deprived of heat by the center of the press surface in the early stage of the press, Is deprived of heat by the outside of the press surface. On the other hand, in the softened glass lump sandwiched between the upper die and the lower die, the portion that is consistently located on the center side of the press surface from the initial stage to the late stage is the center of the press surface in the initial stage of pressing. Although the heat is taken away by the part, in the latter half of the press, the center part of the press surface is heated by heat exchange with the glass block so far, so that the heat is hardly taken away by the center part of the press face.

  Therefore, reducing the thickness of the glass blank means increasing the surface area relative to the volume, so that the outermost periphery of the softened glass mass sandwiched between the upper mold and the lower mold at the time of pressing. Since the increase in the viscosity of the portion extending to the side becomes more remarkable, it is necessary to increase the press thrust as a result, and further, it is considered that the crack is caused. Therefore, the present inventors pay attention to the above-mentioned points, and when the softened glass lump sandwiched between the upper mold and the lower mold is more thinly stretched, the viscosity of the glass lump on the outer peripheral side of the press surface is reduced. It was considered that if the decrease could be suppressed, the increase in press thrust could be suppressed, and further, cracking could hardly occur. This should be realized by increasing the capacity of the softened glass lump and collecting the heat capacity increment at the outer peripheral portion of the press surface, thereby suppressing the temperature drop at the outer peripheral portion during pressing. For this purpose, it is necessary that the peripheral edge of the disk-shaped glass lump is thicker than the center. And as a result, the glass blank produced through such a process will have the same shape as the glass blank of this embodiment. In general, an increase in press thrust tends to improve the transferability of the mold as a result, and the pressed glass tends to stick to the upper mold. However, in the glass blank of this embodiment, even if it thins, as above-mentioned, the increase in press thrust can be suppressed. For this reason, when producing the glass blank of this embodiment, it is also easy to suppress sticking to the upper mold | type of the pressed glass.

  In addition, the glass blank of this embodiment and the glass blank of patent document 1, 2 have a disk-shaped thin part, and a thick part provided along the circumferential part of the thin part. In common. However, when producing a substrate of the same size from a glass blank, the glass blanks described in Patent Documents 1 and 2 are part of the substrate, whereas the glass blank of the present embodiment, Since all the thick portions are removed, they do not constitute part of the substrate. That is, when producing the board | substrate which has the same thickness and diameter, the glass blank of this embodiment has a larger diameter of the glass blank than the glass blank of patent document 1,2. That is, the diameters of the glass blanks described in Patent Documents 1 and 2 are small. For this reason, in the glass blanks described in Patent Documents 1 and 2, it is not necessary to stretch the glass lump sandwiched between the upper mold and the lower mold at the time of pressing in the production thereof. The problem itself is unlikely to occur.

  On the other hand, in the glass blank of this embodiment, when processing into a substrate, the thick portion is usually removed by cutting before polishing. For this reason, compared with the glass blank of patent documents 1 and 2, it has the big merit on processing cost that the processing time required for grinding | polishing processing can be reduced significantly. However, conversely, all of the thick portion is discarded without being used as a part of the substrate, which is considered to be uneconomical. However, when the thick wall portion is cut and removed, it becomes a chip shape and is easy to collect. And the collect | recovered chip | tip can be easily reused as a molten glass raw material (what is called cullet) for glass blanks. On the other hand, in the glass blanks described in Patent Documents 1 and 2, although a part of the thick part is used as a substrate, the remaining part is pulverized and removed by polishing or the like. Since the thick part removed in such a form is mixed with the polishing liquid or the like, it cannot be recovered and reused. Therefore, the glass blank of this embodiment is superior to the glass blanks described in Patent Documents 1 and 2 in terms of the recycling efficiency of the thick part.

  In addition, the crack accompanying increase in press thrust becomes easy to generate | occur | produce, so that the thickness of the thin part of the glass blank assumed that the thick part is not provided in a peripheral part is thin. Considering these points, the thickness of the thin portion of the glass blank of the present embodiment is preferably 1.0 mm or less, and more preferably 0.9 mm or less. In consideration of the diameter of the substrate finally produced using the glass blank, the glass blank for a so-called 2.5 inch substrate (diameter = 65 mm) preferably has a thickness of 0.9 mm or less, and 0 .8 mm or less is more preferable. In a glass blank for a 1.8 inch substrate (diameter = 48 mm), the thickness of the thin portion is preferably 0.8 mm or less, and more preferably 0.6 mm or less. In a glass blank for a 1.0 inch substrate (diameter = 27.4 mm), the thickness of the thin portion is preferably 0.7 mm or less, and more preferably 0.5 mm or less. In a glass blank for a 0.85-inch substrate (diameter = 21.6 mm), the thickness of the thin portion is preferably 0.7 mm or less, and more preferably 0.5 mm or less. The lower limit of the thickness of the thin wall portion is not particularly limited regardless of the size of the target substrate, but as the glass blank thickness decreases, it becomes difficult to maintain flatness at the material stage. It is preferable to set it to 0.5 mm or more.

  Moreover, in the glass blank of this embodiment, when processing into a board | substrate, the part (thin-wall part) which remained after removing the thick part will comprise a board | substrate substantially. From such a viewpoint, the processing cost in the subsequent process can be reduced as the diameter of the thin wall portion is closer to the target substrate diameter. However, it is also necessary to secure a certain margin in consideration of variations during processing in the subsequent process. Considering these points, in the glass blank for a 2.5-inch substrate, the diameter of the thin portion is preferably in the range of 66.0 mm to 72.0 mm. In a glass blank for a 1.8 inch substrate, the diameter of the thin portion is preferably in the range of 48.0 mm to 53.0 mm. In a glass blank for a 1.0 inch substrate, the diameter of the thin portion is preferably in the range of 27.6 mm to 33.0 mm. In the glass blank for 0.85 inch substrates, the diameter of the thin part is preferably in the range of 21.8 mm to 26.0 mm.

  In the glass blank of this embodiment, the thick part may be provided so as to be convex on both surfaces of the thin part, but the thin part and the thick part are flush with each other on at least one surface. Preferably it is formed. In the so-called direct press method, a large number of lower molds are sequentially moved to receive a predetermined amount of molten glass gob and press molding is performed with one upper mold, so that the mold contacts the glass blank surface. As for the time, the upper mold can secure only a very short time compared to the lower mold. Therefore, although the degree of the glass blank formed varies depending on the temperature of the lower mold, the cooling rate on the upper mold surface side of the glass blank becomes slow unless a special cooling measure is taken after the upper mold surface is detached. It is inevitable that the blank outer periphery has a warp characteristic that tends to warp toward the upper mold surface. Here, in the present embodiment, if the shape is such that the thin portion and the thick portion are formed flush with each other on the upper die surface side, the glass blank is on the lower die surface side by the thick portion formed on the outer edge portion. Therefore, the amount of warpage when the stress in the direction in which the outer periphery of the glass blank warps to the upper die surface due to heat shrinkage during the cooling process after pressing is reduced by that amount. Will be. Since the deformation is suppressed, the stress remains inside, but since the stress is relaxed in the subsequent slow cooling step, the deformation is maintained while being suppressed.

  The thickness of the thick part is not particularly limited as long as it is thicker than the thin part. However, the thickness of the thick part is preferably the thickness of the thin part + 0.4 mm or more, and more preferably the thickness of the thin part + 0.8 mm or more. Moreover, it is preferable that the width | variety of a thick part is 2 mm or more, and it is preferable that it is 3 mm or more. By setting the thickness and width of the thick part within the above ranges, the temperature drop of the portion extending most outward from the softened glass lump sandwiched between the upper die and the lower die during pressing ( Viscosity increase) can be more effectively suppressed. Therefore, as a result, it is possible to more reliably suppress an increase in press thrust and further cracking. The upper limit value of the thickness of the thick part is not particularly limited, but from a practical viewpoint such as reducing the amount of disposal when producing a substrate by processing a glass blank, The thickness is preferably 2 mm or less. From the same viewpoint, the width of the thick portion is preferably 7 mm or less.

-Specific examples of glass blanks-
Next, specific examples of the glass blank of this embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the glass blank of the present embodiment, and specifically, a cross-sectional view when the glass blank is cut in the diameter direction. Further, the glass blank 1 shown in FIG. 1 includes a disk-shaped thin portion 10 and a thick portion that is provided along the peripheral portion of the thin portion 10 and whose one surface is flush with the thin portion 10. Twelve. When processing into a board | substrate using this glass blank 1, the thick part 12 is removed from the glass blank 1. FIG. Then, the substrate is obtained by post-processing only the thin portion 10 after the thick portion 12 is removed. In this case, for example, the range indicated by the double arrow D in the thin portion 10 is finally used as a portion constituting the substrate.

  In addition, when producing the glass blank 1, it is inevitable that the heat shrinkage amount of the thick portion 12 becomes larger than the heat shrinkage amount of the thin portion 10 in the process of cooling the glass blank 1 in a high temperature state immediately after pressing. . A response to the problem resulting from this phenomenon will be described with reference to FIG. FIG. 2 is a partially enlarged view of an enlarged cross section of a portion near the thick portion of the glass blank shown in FIG. The tensile stress generated inside the glass blank 1 due to such an unbalanced amount of heat shrinkage is the surface on the side where the thin portion 10 and the thick portion 12 have a step (the lower surface in FIG. 2), and the thin portion It tends to concentrate in the vicinity of the region where the thickness changes from 10 to the thick portion 12 (near the boundary portion 16 between the outermost peripheral side of the flat portion 14 of the thin portion 10 and the innermost peripheral side of the thick portion 12). Such stress concentration causes cracking of the glass blank 1 after pressing. In order to suppress the occurrence of such cracks, on the side where the thin portion 10 and the thick portion 12 are formed so as to form a step, the flat portion 14 of the thin portion 10 to the outermost portion of the thick portion 12 is formed. The inclined surface 20 that continues to the top 18 preferably has a curved surface that forms a surface that is continuous with the flat portion 14. This is because, if such a configuration is employed, stress concentration in one place is alleviated. In addition, this curved surface can be made into the shape which comprises a part of a perfect circle, an ellipse, a parabola, or a hyperbola, for example.

-Manufacturing method of glass blank-
The glass blank 1 of this embodiment can be produced by a direct press method. Here, the glass blank 1 is produced as follows. That is, after supplying the softened glass onto the lower mold, at least a press process for press-molding the softened glass so as to reach the outer edge portion between the upper mold and the lower mold. A glass blank can be obtained.

  However, as at least one of the upper mold and the lower mold used for press molding, a press surface having a circular central portion and an outer edge portion provided on the peripheral side of the central portion in contact with the softened glass during press molding. , And the outer edge portion is recessed with respect to the central portion. Here, FIG. 3 is a schematic cross-sectional view showing an example of a die (molding die) used in the glass blank manufacturing method of the present embodiment. Specifically, the molding die is orthogonal to the press surface. It shows about the cross section at the time of cut | disconnecting like this. In the molding die 30 shown in FIG. 3, the outer edge portion 32A of the press surface 32 is provided so as to be recessed with respect to the central portion 32B. Here, the step portion 34 between the central portion 32B and the outer edge portion 32A can be made to correspond to the curved inclined surface 20 shown in FIG. Further, at the time of pressing, the softened glass (not shown in the drawing) is stretched so as to be in contact with a part of the outer edge portion 32A (a region indicated by a double arrow E in the drawing) from the central portion 32B. This mold 30 may be used as an upper mold and a lower mold, or may be used as one of the upper mold and the lower mold. In the latter case, a conventionally known mold such as a mold having the entire press surface as a flat surface can be used as the other mold.

  The diameter of the central portion 32B of the press surface 32 of the mold whose outer edge portion 32A is concave with respect to the central portion 32B (however, as shown in FIG. 3, the stepped portion 34 is not perpendicular to the press surface 32). In this case, it is preferable that the area excluding the step portion 34 (meaning the diameter of the area indicated by the double-headed arrow d in FIG. 3) be within the following range depending on the size of the substrate to be finally produced. That is, when producing a glass blank for a 2.5 inch substrate, the diameter of the central part is preferably in the range of 66.0 mm or more and 72.0 mm or less. When producing a glass blank for a 1.8 inch substrate, the diameter of the central part is preferably within the range of 48.0 mm or more and 53.0 mm or less. When producing a glass blank for a 1.0-inch substrate, the diameter of the central part is preferably in the range of 27.6 mm or more and 33.0 mm or less. When producing a glass blank for a 0.85-inch substrate, the diameter of the central part is preferably in the range of 21.8 mm or more and 26.0 mm or less.

  In the direct press method, as illustrated in FIG. 4, as the mold used in the pressing process, in addition to the upper mold 40 and the lower mold 42 used for forming both surfaces of the glass blank, a softened state during pressing is used. In order to restrict the stretching of the glass lump 50 in the press surface direction, the body die 44 may be used in combination. Also in the production of the glass blank of the present embodiment, a press method (non-side free press method) using a restricting member such as a barrel die 44 that restricts free stretching of the softened glass lump in the press surface direction is employed. Although it is possible, it is more preferable to employ a press method (side free press method) that does not use a regulating member such as the body mold 44. The reason for this is that in the side free press method, free stretching of the softened glass lump in the press surface direction during pressing is not regulated. Therefore, even if the capacity of the softened glass lump 50 supplied on the press surface of the lower die 42 is slightly changed, the distance between the press surfaces of the upper die 40 and the lower die 42 is kept constant during pressing. The capacity fluctuation of the glass lump 50 can be absorbed by the thick part. Therefore, when the side free press method is adopted, the thickness variation between the glass blanks can be made smaller than when the non-side free press method is adopted, and as a result, the load of the polishing process, which is a subsequent process, can be made smaller. Can do. FIG. 4 shows an example of a conventional non-side free press type direct press method using a body mold. When the glass blank manufacturing method of this embodiment is performed, for example, The lower mold 30 illustrated in FIG. 3 can be used as the mold 42.

  Next, the typical example of the manufacturing method of the glass blank of this embodiment including a press process is demonstrated below. First, molten glass made of these glass materials that has been melted, clarified, and stirred and homogenized is continuously discharged from the outflow nozzle at a constant outflow speed, and this molten glass flow is always kept at a constant mass by a cutting machine called shear. Periodically cut to obtain a softened glass lump. The softened glass lump that has been cut is supplied (cast) onto the press surface of the lower mold waiting just under the outflow nozzle. The molten glass discharged from the outflow nozzle is in a softened state and has a viscosity of about 0.3 to 100 Pa · s. Although the temperature of the lower mold is lower than the temperature of the glass lump, the temperature of the lower mold is adjusted to a temperature at which the temperature of the glass lump suddenly drops and is not pressable. In addition, in order to improve the lubricity with respect to the press surface of the molten glass to be cast, a solid lubricant such as boron nitride (BN) powder may be attached to the lower mold press surface in advance. Good.

  The lower mold in which the cast is finished and the softened glass is placed on the press surface is transferred to a press position where the upper mold is waiting, and is pressed by the upper mold and the lower mold. At this time, the temperature of the upper and lower molds, the pressing pressure, and the pressing time take into consideration the thermal properties of the glass such as the glass transition temperature, the diameter and thickness of the glass blank to be produced, and whether or not the side free press method is used. Set as appropriate. For example, the upper mold temperature may be set to 250 to 550 ° C., the lower mold temperature may be set to 350 to 650 ° C., and the upper mold temperature may be set within a range of the lower mold temperature to [lower mold temperature−100 ° C.]. it can. The pressing force during pressing can be about several GPa, but is not particularly limited to this range, and can be adjusted as appropriate.

  When press molding is finished, the upper surface of the molded product is released from the upper mold, and the lower mold on which the molded product is placed is transferred to a take-out position. In addition, the lower mold is stopped between the press position and the take-out position, the upper surface of the molded product on the lower mold is pressed with the pressing mold, the warpage of the molded product is corrected, and each lower mold is transferred to the take-out position. May be. The molded product is cooled to near the glass transition temperature or lower than the glass transition temperature before being transferred to the take-out position. This is to prevent the molded product from being deformed by the force applied during take-out. Take-out is performed by adsorbing and holding the upper surface of the molded product with an adsorption means. The take-out molded product is rapidly cooled in the atmosphere, and then placed in an annealing furnace and annealed for strain removal. And the glass blank of this embodiment can be obtained through such a series of processes.

-Glass composition-
The glass composition of the glass blank of the present embodiment can be appropriately selected according to the substrate and information recording medium produced using the glass blank. For example, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate Glass, borosilicate glass, quartz glass, chain silicate glass, and the like can be given. These glasses may be crystallized glass that crystallizes by heat treatment.

As the aluminosilicate glass, SiO ₂ is 58% by mass to 75% by mass, Al ₂ O ₃ is 5% by mass to 23% by mass, Li ₂ O is 3% by mass to 10% by mass, Na ₂ O. May be an aluminosilicate glass containing 4 mass% or more and 13 mass% or less as a main component (however, an aluminosilicate glass not containing a phosphorus oxide). For example, SiO ₂ is 62% by mass to 75% by mass, Al ₂ O ₃ is 5% by mass to 15% by mass, Li ₂ O is 4% by mass to 10% by mass, and Na ₂ O is 4% by mass to 12% by mass. Mass% or less, ZrO ₂ contains 5.5 mass% or more and 15 mass% or less as a main component, and the mass ratio of Na ₂ O / ZrO ₂ is 0.5 or more and 2.0 or less, Al ₂ O ₃ / ZrO. It is good also as an amorphous aluminosilicate glass which does not contain the phosphorus oxide whose mass ratio of ₂ is 0.4-2.5. In addition, it is desirable that the glass does not contain an alkaline earth metal oxide such as CaO or MgO. Examples of such glass include N5 glass (trade name) manufactured by HOYA Corporation.

(Method for manufacturing substrate for information recording medium)
A substrate for an information recording medium can be produced by at least a thick part removing step of cutting and removing the thick part of the glass blank obtained through the above-described steps. The thick part can be cut using a diamond cutter. After removing the thick portion from the glass blank, the information recording medium substrate can be usually obtained by performing post-processing such as shape processing such as end face processing and center hole cutting and double-side polishing processing. More specifically, for example, (1) first lapping step, (2) cutout step (coring, forming), (3) end surface grinding step, (4) second lapping step, and (5) end surface polishing. The step, (6) main surface polishing step, (7) chemical strengthening step and cooling step, and (8) precision cleaning step can be performed in this order. Hereinafter, these eight steps will be described more specifically. The disk-shaped glass having a diameter sufficiently larger than the diameter of the substrate is press-molded, the concentric disk-shaped glass is taken out from the disk-shaped glass by scribing, and the taken-out disk-shaped glass is taken from the above (1) to (8 ) Can be formed into a substrate.

(1) 1st lapping process In a 1st lapping process, a disk-shaped glass base plate is obtained by lapping the both main surfaces of the glass blank after cut | disconnecting a thick part. This lapping process can be performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the glass base plate from above and below, and a grinding liquid containing free abrasive grains is supplied onto the main surface of the glass base plate, and these are moved relatively to perform lapping processing. It can be carried out. By this lapping process, a glass base plate having a flat main surface is obtained.

(2) Cutting process (coring, forming)
Next, the glass base plate is cut using a diamond cutter, and a disk-shaped glass substrate is cut out from the glass base plate. Next, using a cylindrical diamond drill, a circular hole is formed in the center of the glass substrate to obtain a donut-shaped glass substrate (coring).

(3) End surface grinding process And an inner peripheral end surface and an outer peripheral end surface are ground with a diamond grindstone, and a predetermined chamfering process is performed (forming).

(4) Second Lapping Step Next, a second lapping process is performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Can be completed in time.

(5) End surface polishing step Next, the end surface of the glass substrate is mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains can be used. By this end surface polishing step, generation of particles and the like from the end surface of the glass substrate can be prevented.

(6) Main surface polishing step As the first half step of the main surface polishing step, a first polishing step is first performed. This first polishing process is mainly intended to remove scratches and distortions remaining on the main surface in the lapping process described above. In the first polishing step, the main surface is polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. For example, cerium oxide abrasive grains can be used as the polishing liquid. And the glass substrate which finished this 1st grinding | polishing process is immersed in each washing tank of a neutral detergent, a pure water, and IPA (isopropyl alcohol) sequentially, and is wash | cleaned.

  Next, a second polishing step is performed as the latter half of the main surface polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface is performed using a soft foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the polishing liquid, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step can be used. The glass substrate that has finished the second polishing step is sequentially immersed in each cleaning bath of neutral detergent, pure water, and IPA (isopropyl alcohol) to be cleaned. An ultrasonic wave is applied to each cleaning tank.

(7) Chemical strengthening step and cooling step When the glass blank used for the production of the information recording medium substrate is made of glass containing an alkali metal such as lithium or sodium, the glass substrate that has been subjected to the lapping step and polishing step described above is used. It is preferable to apply chemical strengthening. By performing the chemical strengthening step, a high compressive stress can be generated in the surface layer portion of the information recording medium substrate. For this reason, the impact resistance of the surface of the information recording medium substrate can be improved. Such chemical strengthening treatment is very suitable for producing a magnetic recording medium in which a head for recording / reproducing information may mechanically come into contact with the surface of the information recording medium.

  The chemical strengthening is performed by preparing a chemical strengthening solution in which potassium nitrate and sodium nitrate are mixed, heating the chemical strengthening solution, preheating the cleaned glass substrate, and immersing it in the chemical strengthening solution. Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened.

  Then, the glass substrate which finished the chemical strengthening process is immersed in a water bath, cooled, and maintained for a while. Then, the cooled glass substrate is cleaned by immersing it in heated concentrated sulfuric acid. Further, the glass substrate after the sulfuric acid cleaning is cleaned by immersing in a cleaning bath of pure water and IPA (isopropyl alcohol) sequentially. In addition, an ultrasonic wave is applied to each washing tank.

(8) Precision cleaning step Next, it is preferable to carry out a precision cleaning step in order to remove abrasive residues and foreign iron-based contaminants, and to make the surface of the glass substrate smoother and cleaner. Such a precision cleaning process is very suitable for producing a magnetic recording medium in which a head for recording / reproducing information may mechanically contact the surface of the information recording medium. This is because the occurrence of head crashes and thermal asperities can be suppressed by carrying out precision cleaning. In addition, as a precision washing | cleaning process, it is preferable to perform a water rinse washing | cleaning and an IPA washing | cleaning process after washing | cleaning by alkaline aqueous solution.

  The surface roughness of the information recording medium produced through these series of steps can be on the order of sub-nanometers with Ra. The surface roughness can be appropriately adjusted by selecting main surface polishing conditions and cleaning conditions. The information recording medium substrate obtained through the above-described eight steps can be used for production of an information recording medium employing various known recording methods such as known magnetic recording, optical recording, and magneto-optical recording. However, it is particularly suitable for use in producing a magnetic recording medium. Further, in the case of an information recording medium substrate that is not required to have cleanness, smoothness, and impact resistance on the surface of the information recording medium substrate as much as the magnetic recording medium substrate, one of the above eight steps is performed as necessary. The steps may not be performed, and each process may be simplified or performed under rougher conditions.

(Method of manufacturing information recording medium)
The information recording medium can be manufactured by performing at least an information recording layer forming step of forming an information recording layer on at least one surface of the information recording medium substrate thus obtained. When a magnetic recording medium is manufactured, a magnetic recording layer is provided as an information recording layer. The magnetic recording medium may be either a horizontal magnetic recording system or a perpendicular magnetic recording system, but is preferably a perpendicular magnetic recording system. When a perpendicular magnetic recording type magnetic recording medium is manufactured, for example, an adhesion layer made of Cr alloy, a soft magnetic layer made of FeCoCrB alloy, an underlayer made of Ru, and CoCrPt—TiO _{2 on} both surfaces of an information recording medium substrate. A perpendicular magnetic recording layer made of an alloy, a protective layer made of hydrogenated carbon, and a lubricating layer made of perfluoropolyether are sequentially formed in this order. The adhesion layer, the soft magnetic layer, the underlayer, and the perpendicular magnetic recording layer can be formed by a sputtering method, and the protective layer can be formed by a sputtering method or a CVD method (Chemical Vapor Deposition method). The lubricating layer can be formed by a dip coating method. Further, in-line type or single-wafer type sputtering apparatus capable of continuous film formation of each layer can be used for film formation from the adhesion layer to the protective layer, and immersion coating apparatus can be used for film formation of the lubricating layer. .

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
A glass blank having a cross-sectional shape shown in FIG. 1 is obtained by supplying a molten glass obtained by melting an aluminosilicate glass onto a pressing surface of a lower die and then pressing the upper die and the lower die in a side-free manner. 1000 pieces of part thickness: 0.85 mm, thin part diameter: 68 mm, thick part width 4 mm, thick part thickness: 1.8 mm) were produced. In the production of this glass blank, a lower mold in which the outer edge portion of the press surface is concave with respect to the central portion was used as the lower mold. The main production conditions for producing a glass blank are as follows.
Glass transition temperature Tg: 485 ° C
-Average linear expansion coefficient of glass: 95 × 10 ⁻⁷ / K (100 to 300 ° C.), 98 × 10 ⁻⁷ / K (300 to Tg ° C.), 37 × 10 ⁻⁶ / K (Tg to 530 ° C.),
・ Pressing surface temperature when supplying molten glass onto the pressing surface of the lower mold: 450 ° C.
・ Temperature of the upper press surface during pressing: 360 ° C
・ Viscosity of molten glass put on the lower mold: 40 Pa · s
・ Pressing time (time for applying pressure to glass): 0.8 seconds ・ Material constituting upper and lower mold pressing surfaces: cast iron ・ Average temperature of glass blank when taking out glass blank from lower mold: 510 ° C.

(Comparative Example 1)
As the lower mold, a lower mold whose entire pressing surface is flat is used, and the pressure during pressing is the same as in Example 1 except that the glass blank having the same thickness as the thin part of the glass blank of Example 1 is adjusted. Thus, 1000 glass blanks were produced. The obtained glass blank has substantially the same volume except for the difference in shape with respect to the glass blank produced in Example 1 that does not have a thick part and has a larger outer diameter. is there.

<Evaluation>
In Example 1 and Comparative Example 1, Table 1 shows the results of evaluating the number of cracks generated when 1000 glass blanks were produced. Moreover, the relative press thrust in the comparative example 1 when the press thrust at the time of pressing in Example 1 is set to 100 is shown with these results. Moreover, in the production of the glass blank, the presence or absence of sticking was also confirmed. As a result, when forming 1000 sheets, sticking did not occur in Example 1, but sticking occurred in the middle of Comparative Example 1, making it impossible to continue forming, and after several interruptions in forming. 1000 samples were collected

DESCRIPTION OF SYMBOLS 1 Glass blank 10 Thin part 12 Thick part 14 Plane part 16 Boundary part 18 Top part 20 Inclined surface 30 Forming die 32 Press surface 32A Outer edge part 32B Central part 34 Step part 40 Upper mold 42 Lower mold 44 Trunk mold 50 Soft state Glass lump

Claims (10)

A thin disk-shaped part,
A thick part provided along the peripheral edge of the thin part;
Have
The glass blank, wherein the thick portion is removed when processing into an information recording medium substrate. The glass blank according to claim 1,
The glass blank, wherein the thin portion has a thickness of 0.5 mm or more and less than 0.9 mm. In the glass blank of Claim 1 or 2,
The diameter of the thin portion is in the range of 66.0 mm to 72.0 mm, in the range of 48.0 mm to 53.0 mm, in the range of 27.6 mm to 33.0 mm, and 21.8 mm to 26 A glass blank characterized by being able to take a value in any one range selected from within a range of 0.0 mm or less. In the glass blank as described in any one of Claims 1-3,
The glass blank, wherein the thin portion and the thick portion are formed flush with each other on at least one of the surfaces. In the glass blank as described in any one of Claims 1-4,
In the surface on the side where the thin-walled portion and the thick-walled portion are formed to form a step, an inclined surface that continues from the flat surface portion of the thin-walled portion to the topmost portion of the thick-walled portion is continuous with the flat-surface portion. A glass blank having a curved surface. As the at least one of the upper mold and the lower mold, a press surface having a circular center portion and an outer edge portion provided on a peripheral side of the center portion, which is in contact with the softened glass at the time of press molding, is provided. Use a mold whose part is concave with respect to the central part,
2. After supplying the softened glass onto the lower mold, at least through a pressing step of press-molding the softened glass so as to reach the outer edge portion between the upper mold and the lower mold. The manufacturing method of the glass blank characterized by producing the glass blank as described in any one of -5. As the at least one of the upper mold and the lower mold, a press surface having a circular center portion and an outer edge portion provided on a peripheral side of the center portion, which is in contact with the softened glass at the time of press molding, is provided. The portion is concave with respect to the central portion, and the diameter of the central portion is in the range of 66.0 mm to 72.0 mm, in the range of 48.0 mm to 53.0 mm, and in the range of 27.6 mm to 33.0 mm. Using a mold having a value in any one range selected from the following range and a range of 21.8 mm or more and 26.0 mm or less,
After supplying the softened glass onto the lower mold, the glass blank is passed through at least a pressing step of press-molding the softened glass so as to reach the outer edge portion between the upper mold and the lower mold. A method for producing a glass blank, which is characterized by being produced.   A thick part of a glass blank selected from the glass blank according to any one of claims 1 to 5 and the glass blank produced by the glass blank production method according to claim 7 is cut. An information recording medium substrate manufacturing method comprising producing an information recording medium substrate through at least a thick portion removing step to be removed.   At least through a thick part removing step of cutting and removing the thick part of the glass blank having a disk-like thin part and a thick part provided along the peripheral part of the thin part, information A method for manufacturing a substrate for information recording media, comprising producing a substrate for recording media.   An information recording medium is formed through at least an information recording layer forming step of forming an information recording layer on at least one side of the information recording medium substrate manufactured by the method for manufacturing an information recording medium substrate according to claim 8 or 9. A method of manufacturing an information recording medium, characterized by manufacturing.

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