JP2011063474A - Glass blank, method for manufacturing glass blank, method for manufacturing substrate for information recording medium, and method for manufacturing information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of dent mark, when manufacturing a substrate for information recording medium from glass blank, even reducing the amount of processing by making the thickness of the glass blank thin while excelling in flatness thereof. <P>SOLUTION: The glass blank has a disk-like thin-wall part 10 and a thick-wall part 12 provided so as to form salient parts 12U and 12D to both surfaces of the thin-wall part, along the peripheral part of the thin-wall part 10, where the width W1 of the salient part 12D of one surface side in the diametrical direction of the thin-wall part 10, with respect to the diametrical direction of the thin-wall part 10, is larger than the width W2 of the salient part 12U of the other surface side in the diametrical direction. There are disclosed a method for manufacturing the glass blank; a method for manufacturing a substrate for an information recording medium using the glass blank; and a method for manufacturing the information recording medium. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Glass substrates are widely used as substrates for information recording media such as magnetic recording media. As a method of manufacturing such a glass information recording medium substrate, in addition to a method of cutting glass from a plate-shaped raw glass into a disk shape, a method of pressing molten glass with a pair of molds (so-called direct press) Method) or glass blanks that have been made to a size close to the product, reheated and melted, and pressed more precisely (so-called reheat press), and the glass blanks produced into a predetermined shape are processed into an information recording medium. A substrate is prepared.

  An information recording medium substrate manufactured through such a process needs to have a predetermined thickness and almost no warpage. In addition to this, in order to cope with the cost reduction, it is important to reduce the polishing allowance when manufacturing the information recording medium substrate from the glass blank. For this reason, glass blanks are required not only to be thin, but also to further improve flatness (reduction of warpage). In order to respond to the need for improved flatness, the present applicant has a technology for correcting the warp of the glass blank by performing a warp correction step of re-pressing the softened glass that has become substantially plate-like immediately after pressing. It has been proposed (Patent Document 1).

  Moreover, the warp generated during the press molding remains in the glass blank to some extent. Therefore, even if it grinds in the state which applied the pressure from both surfaces with respect to the glass blank which has such curvature, curvature will generate | occur | produce again when the applied pressure is cancelled | released. In order to solve this problem, when lapping a glass blank, a technique for providing a thick part at the outer peripheral edge of the glass blank, etc., for the purpose of receiving pressure applied to both sides of the glass blank during lapping, This has been proposed by the present applicant (Claim 1, Paragraph 0013, FIG. 2, etc. of Patent Document 2).

Japanese Patent No. 3286756 Patent No. 3714501

  These techniques proposed by the present applicant are very useful in suppressing warpage of a glass blank or an information recording medium substrate as a final product. However, using the technique described in Patent Document 2, an information recording medium substrate is manufactured using a glass blank provided with thick portions so as to be convex on both sides of a peripheral portion of a disk-shaped thin portion. In order to reduce the cost, the glass blank is thinned, and when the processing amount of the glass blank is reduced, a dent formed in a ring shape along the outer peripheral edge is generated on one side of the substrate. There are things to do. A substrate on which such a concave mark remains cannot be used as a substrate for an information recording medium.

  The present invention has been made in view of the above circumstances, and is a glass capable of producing a substrate for an information recording medium that has excellent flatness and suppresses the generation of dents even when the processing amount is reduced by thinning the glass blank. It is an object of the present invention to provide a blank, a manufacturing method thereof, a substrate manufacturing method for an information recording medium using the glass blank, and an information recording medium manufacturing method.

  The above-mentioned subject is achieved by the following present invention. That is, the glass blank of the present invention comprises a disk-shaped thin portion, and a thick portion provided so as to form convex portions on both sides of the thin portion along the peripheral portion of the thin portion. And the radial width of the convex portion on one surface side with respect to the diameter direction of the thin-walled portion is larger than the radial width of the convex portion on the other surface side.

  The glass blank manufacturing method of the present invention, as a pair of molds arranged so as to be movable relative to the vertical direction, is in contact with the glass in a softened state during press molding, and has a circular central portion and the center A first mold having a press surface having an outer edge provided so as to form a recess with respect to the central part on the peripheral side of the part, and a first mold that comes into contact with the softened glass during press molding The second molding provided with a press surface having a circular central portion having a diameter smaller than that of the central portion and an outer edge portion provided on the peripheral side of the central portion so as to form a recess with respect to the central portion. A mold placed on the lower side in the vertical direction is used as the first mold, and a mold placed on the upper side in the vertical direction is used as the second mold. The first mold after placing on the press surface of the mold The first pressing step of pressing the glass lump so as to reach the outer edge of the first mold press surface by the press surface and the press surface of the second mold, and arranged on the lower side in the vertical direction After forming the softened glass lump on the press surface of the second molding die, the molding die to be used as the second molding die, the molding die arranged on the upper side in the vertical direction as the first molding die From the second press step of pressing the glass lump so as to reach the outer edge of the first mold press surface by the press surface of the first mold and the press surface of the second mold. The glass blank of the present invention is manufactured through at least one of the selected pressing steps.

  In one embodiment of the method for producing a glass blank of the present invention, it is preferable to perform a warpage suppressing step for suppressing the occurrence of warpage on the softened glass that has been substantially plate-shaped through a pressing step.

  The substrate manufacturing method for an information recording medium of the present invention comprises grinding and / or both surfaces of any one of the glass blanks selected from the glass blank of the present invention and the glass blank manufactured by the glass blank manufacturing method of the present invention. Alternatively, the information recording medium substrate is manufactured through at least a polishing process.

  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 the main surface of the information recording medium substrate manufactured by the information recording medium substrate manufacturing method of the present invention, An information recording medium is manufactured.

  According to the present invention, a glass blank capable of producing a substrate for an information recording medium excellent in flatness and capable of producing a substrate for recording with suppressed generation of recesses even if the amount of processing is reduced by thinning the glass blank, and a method for producing the same, and An information recording medium substrate manufacturing method and an information recording medium manufacturing method using a glass blank can be provided.

It is a schematic cross section which shows an example of the glass blank of this embodiment. It is a schematic cross section which shows the other example of the glass blank of this embodiment. It is a schematic cross section which shows an example of a pair of shaping | molding die used for the manufacturing method of the glass blank of this embodiment. It is explanatory drawing for demonstrating the principle which a dent produces | generates when producing the board | substrate for information recording media using the conventional glass blank. It is explanatory drawing for demonstrating the principle which a dent produces | generates when producing the board | substrate for information recording media using the conventional glass blank. It is explanatory drawing for demonstrating the principle which a dent produces | generates when producing the board | substrate for information recording media using the conventional glass blank.

(Glass blank and its manufacturing method)
-Glass blank-
The glass blank of the present embodiment has a disk-shaped thin part and a thick part provided so as to form convex portions on both surfaces of the thin part along the peripheral part of the thin part. The radial width of the convex portion on one surface side with respect to the diameter direction of the thin wall portion is larger than the radial width of the convex portion on the other surface side.

  In the glass blank of this embodiment, the thick part which forms a convex part with respect to both surfaces of a thin part is provided. Therefore, the pressing force applied to both surfaces of the glass blank is received only by this thick part by a pair of grinding machines (lap surface plates) arranged to sandwich the glass blank during lapping. In this state, the lapping is advanced and the thick part is cut, and the thin part is also cut. Therefore, the lapping can be performed without elastically deforming the glass blank by the pressing force received from the grinding machine. Therefore, if the glass blank is processed flat by lapping, the flatness of the glass is maintained even if the pressing force by the grinding machine is removed. On the other hand, when lapping is performed in a state of being elastically deformed, even if the glass blank is intended to be flattened, if the pressing force by the grinder is removed, the deformation of the glass returns and flatness cannot be obtained. Therefore, the flatness of the information recording medium substrate obtained through the lapping process is excellent.

  In addition to this, in the glass blank of the present embodiment, the radial width of the convex portion on one surface side relative to the radial direction of the thin wall portion is larger than the radial width of the convex portion on the other surface side of the thin wall portion. Is also big. This is arranged so as to effectively suppress the warpage of the glass in the cooling process immediately after pressing the glass blank. From the above, in the glass blank of this embodiment, when an information recording medium substrate is produced, it is possible to suppress dents caused by warpage and deformation of the glass blank.

  The effect which can suppress generation | occurrence | production of such a dent is demonstrated more concretely using drawing below, contrasting the glass blank of this embodiment and the conventional glass blank. 4-6 is explanatory drawing for demonstrating the principle which a dent produces | generates when the board | substrate for information recording media is produced using the conventional glass blank. Here, the glass blank 100 shown in FIG. 4 and FIG. 5 includes a disc-shaped thin portion 110 and a thick portion 112 that forms ring-shaped convex portions 112U and 112D on both surfaces of the thin portion 110. Is common to the glass blank of the present embodiment. However, the glass blank of the present embodiment is that the radial width of the convex portion 112D on one surface side D of the glass blank 100 is the same as the radial width of the convex portion 112U on the other surface side U. Is different. FIG. 4 shows a cross-sectional shape in the diametrical direction of a glass blank 100H in a high temperature state immediately after being press-molded by a pair of molds (upper mold and lower mold) and immediately before the upper mold is separated from the glass blank 100. It is a schematic cross section. In FIG. 4, the description of the upper mold and the lower mold is omitted. FIG. 5 is a schematic cross-sectional view showing a cross-sectional shape in the diameter direction of the glass blank 100C after the glass blank 100H shown in FIG. 4 has been cooled to a temperature range equal to or lower than the glass transition temperature Tg. FIG. 6 shows a cross-sectional shape in the diametrical direction of an information recording medium substrate 102 (before end face processing) obtained by performing a post-process such as lapping on the glass blank 100C shown in FIG. It is a schematic cross section. 4 to 5, the surface indicated by the symbol U means the surface that is in contact with the upper die at the time of press molding or the surface that has been in contact, and the surface indicated by the symbol D is the lower surface at the time of press molding. It means the surface that is in contact with the mold or the surface that was in contact with it. In the following description, the surface indicated by the symbol U may be referred to as “upper surface” and the surface indicated by the symbol D may be referred to as “lower surface”.

  As shown in FIG. 4, in the glass blank 100 </ b> H that maintains the high temperature state immediately after pressing, the shape of the mold is transferred to the glass blank, and no warpage occurs. However, if the cooling process on the upper surface side and the lower surface side is different after pressing, the warpage of the glass blank due to the difference in thermal shrinkage of the glass becomes significant. Therefore, when the glass blank 100H shown in FIG. 4 is cooled, as shown in FIG. 5, the glass blank 100C is curved so as to warp on the upper surface side.

For this reason, when the glass blank 100C is used to produce the information recording medium substrate 102, when the polishing allowance is reduced due to the thinning of the glass blank 100C, a concave portion is formed in the corner portion 114C on the lower surface and the central portion on the upper surface. 114P and 114Q are generated (FIG. 6).
Such recesses 114P and 114Q have a smaller warpage when the glass blank 100C is warped and / or when the glass blank 100C is thinner (that is, when the information recording medium substrate 102 is manufactured). It will become noticeable.

  Moreover, in order to correct the curvature of the glass blank 100C, the curvature correction press as shown by patent document 1 etc. may be implemented with respect to the glass blank 100C. In this case, the warp correction press presses the entire upper surface side (the region indicated by the symbol RP shown in FIG. 5) of the thin portion 110 of the glass blank 100C that has a deformable temperature with the warp correction press member.

  FIG. 1 is a schematic cross-sectional view showing an example of the glass blank of the present embodiment. The symbols RP, U, and D shown in the figure are the same as those shown in FIGS. The glass blank 1 shown in FIG. 1 has a disk-shaped thin portion 10 and a thickness that forms ring-shaped convex portions 12U and 12D on both surfaces of the thin portion 10 along the peripheral portion of the thin portion 10. It is common to the conventional glass blank 100 illustrated in FIGS. 4 and 5 in that the meat portion 12 is provided. However, the glass blank 1 is conventional in that the radial width W1 of the convex portion 12D on the one surface side D of the glass blank 1 is larger than the radial width W2 of the convex portion 12U on the other surface side U. This is different from the glass blank 100.

That is, the width W2 of the convex portion 12U has a function of receiving the pressing force applied by the grinding machine at the time of lapping (the pressing force receiving), as in the case of the conventional glass blank 100 illustrated in FIGS. Function) is determined. On the other hand, the width W1 of the convex portion 12D is determined in consideration of the viewpoint of further improving the rigidity of the glass blank 1 as compared with the conventional glass blank 100 in addition to the pressing force receiving function. That is, the temperature history in advance with respect to the warp of the glass blank in the process in which the upper surface of the glass blank 1 is separated from the upper mold and cooled to the glass transition temperature Tg or less from the state immediately after pressing the glass blank in a high temperature state. The direction which a glass blank warps is calculated | required from, and the curvature of glass is suppressed by changing the width | variety of the convex parts 12U and 12D provided in each surface with respect to the direction.
For this reason, when a substrate for an information recording medium is produced by performing a post-process such as lapping using this glass blank 1, even if the polishing allowance is reduced by thinning the glass blank 1, FIG. Generation | occurrence | production of the dent 114P resulting from curvature as shown in FIG. 6 is also suppressed.

  Moreover, you may implement the curvature correction press with respect to the glass blank 1 similarly to the past. In this case, the outermost peripheral end of the warp correction press region RP is set outside the inner peripheral side surface (line indicated by the dotted line in FIG. 1) of the convex portion 12D. When the warp correction press is performed in such a state, not only the thin portion 10 but also a part of the thick portion 12 (in the diameter direction, on the inner peripheral side than the inner peripheral side surface of the convex portion 12U, and The pressing force may also be applied to the outer peripheral side portion of the convex portion 12D.

  In addition, in the glass blank 1 shown in FIG. 1, the surface on the side where the narrow convex portion 12U is provided is in contact with the upper mold during pressing, and when performing a warp correction press, a warp correction press member is used. The surface to be pressed (upper surface) is used. At the time of warp correction press, the upper surface of the glass blank 1 is pressed by a member different from the upper mold used in press molding. At the time of warping correction press, the thick portion 12 of the glass blank 1 has a lower viscosity than the thin portion 10 and pressing the thick portion 12 may cause the thick portion 12 to be deformed. It is preferable to press only, and it is preferable to press the thin portion 10 over a wide range. However, since the warp correction press is pressed by a member different from the upper die as described above, if the entire thin portion 10 is pressed with the member slightly displaced, a part of the thick portion 12 is also pressed. There is a fear. Therefore, in order to press the upper surface of the glass blank 1 over a wide range without pressing the thick wall portion 12, the narrow convex portion 12U becomes the upper surface, that is, the wider side of the thin wall portion 10 becomes the upper surface. It is desirable to perform press molding. When the warp correction press is not performed, the surface on the side provided with the narrow convex portion 12U may be a surface in contact with the upper die or a surface in contact with the lower die at the time of pressing. . In any case, the ratio of the region that is relatively thick with respect to the diameter direction of the glass blank 1 is increased, the rigidity is further improved, and the warpage is suppressed.

  In the glass blank 1 shown in FIG. 1, the inner peripheral side surface of the convex portion 12 </ b> D is a surface perpendicular to the lower surface of the thin portion 10. However, the inner peripheral side surface of the convex portion 12D is inclined with respect to the lower surface of the thin portion 10 so that the skirt extends from the top side of the convex portion 12D to the lower surface side of the thin portion 10 as shown in FIG. The surface 12S may be sufficient. In this case, the inclination angle (angle θ shown in FIG. 2) is preferably not less than 30 degrees and less than 90 degrees from the viewpoint of preventing breakage of the portion where the inclined surface 12S intersects the top surface of the convex portion 12D. Further, it is more preferably 40 degrees or more and less than 80 degrees.

  Here, the width W2 of the convex portion 12U can be set to around 2.0 mm as exemplified in paragraph 0008 of Patent Document 2 from the viewpoint of securing a pressure receiving function during lapping. Specifically, it is preferably in the range of 1 mm to 6 mm, and more preferably in the range of 1 mm to 4.5 mm. By setting the width W2 to 1 mm or more, the pressure receiving function at the time of lapping can be reliably exhibited by the convex portion 12U. Further, by setting the width W2 to 4.5 mm or less, it is possible to prevent the polishing rate from being lowered more than necessary during lapping, and to prevent the manufacturing efficiency of the information recording medium substrate from being lowered.

  The direction in which the glass blank 1 warps is obtained in advance from the thermal history of the glass, and the side on which the glass blank 1 warps and becomes a convex surface is defined as W1, and the side on which the glass blank 1 becomes a concave surface is defined as W2. At this time, the ratio (W1 / W2) of the width W1 of the convex portion 12D to the width W2 of the convex portion 12U is preferably 1.0 or more, more preferably 2.0 or more, and more preferably 3.0 or more. preferable. In addition, W1 / W2 is preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.5 or less from the easiness of glass processing (lap processing time).

  The height of the convex portion 12U (the height with the upper surface of the thin portion 10 indicated by reference numeral H1 in FIG. 1 as a reference surface) is not particularly limited, but is preferably in the range of 0.05 mm to 0.1 mm. By setting the height of the convex portion 12U to be 0.05 mm or more, the convex portion 12U can reliably exert a pressure receiving function during lapping. In addition, by setting the height H1 of the convex portion 12U to 0.1 mm or less, it is possible to prevent the polishing margin from being increased more than necessary at the time of lapping and prevent a decrease in the manufacturing efficiency of the information recording medium substrate. .

  The height of the convex portion 12D (the height with the lower surface of the thin portion 10 indicated by reference numeral H2 in FIG. 1 as the reference surface) is not particularly limited, but is preferably in the range of 0.05 mm to 0.1 mm. By setting the height of the convex portion 12D to be 0.05 mm or more, the convex portion 12D can reliably exert the pressure receiving function during lapping. Further, by setting the height H2 of the convex portion 12D to 0.1 mm or less, it is possible to prevent the polishing margin from being increased more than necessary at the time of lapping and prevent a decrease in the manufacturing efficiency of the information recording medium substrate. .

  In addition, as described above, when the information recording medium substrate 102 is manufactured from the conventional glass blank 100 illustrated in FIGS. 4 and 5, the generation of the recesses 114 </ b> P and 114 </ b> Q is caused by the thinning of the glass blank 100. That is, the aspect ratio of the glass blank 100 (the ratio of the thickness t of the thin portion 110 to the diameter d of the glass blank 100, t / d) tends to become more prominent. However, the glass blank 1 of the present embodiment has a larger proportion of the thick portion in the diameter direction than the conventional glass blank 100. For this reason, the glass blank 1 of the present embodiment is less likely to generate the indentation 114P because the decrease in rigidity is small and the warp is small even when the aspect ratio is smaller than that of the conventional glass blank 100. Considering this point, the aspect ratio of the glass blank 1 of the present embodiment is preferably 0.018 or less, and more preferably in the range of 0.013 to 0.017. In the glass blank of this embodiment, even if the aspect ratio is 0.018 or less, the generation of the dents 114P and 114Q that are difficult to avoid in the conventional glass blank 100 can be more reliably suppressed. In addition, the lower limit of the aspect ratio is not particularly limited, but if the aspect ratio is too small, it is difficult to stretch the glass thinly at the time of pressing, and it becomes impossible to manufacture the glass blank itself from a practical viewpoint. , 0.010 or more is preferable. In the present specification, the thickness t used for determining the aspect ratio means the thickness of the thin portions 10 and 110 as shown in FIGS. In addition, in the glass blank of this embodiment, even if an aspect ratio is 0.018 or less, generation | occurrence | production of the dent 114Q can be suppressed more reliably, but this dent 114Q is finally used for information recording media. When a hole is drilled in the center of the substrate 102, it may remain. This is because the recess 114Q is removed by drilling, and therefore the recess 114Q does not remain on the information recording medium substrate (finished product) that has undergone drilling.

-Glass blank manufacturing method-
The glass blank 1 of this embodiment is produced by the direct press method. Here, at the time of press molding, as a pair of molds, it comes into contact with the softened glass at the time of press molding, and a circular central portion and a dent to the central portion on the peripheral side of the central portion. A first mold having a press surface having an outer edge portion provided, a circular central portion in contact with the glass in a softened state during press molding, and having a smaller diameter than the central portion of the first mold; and A second mold having a press surface having an outer edge portion provided so as to form a recess with respect to the central portion on the peripheral side of the central portion is used. A pair of shaping | molding die shall be arrange | positioned so that relative movement with respect to a perpendicular direction is possible, for example.

In this case, the glass blank of this embodiment can be produced through at least one pressing step shown in the following (1) or (2).
(1) A mold (lower mold) disposed on the lower side in the vertical direction is a first mold, and a mold (upper mold) disposed on the upper side in the vertical direction is a second mold. After placing the glass lump on the press surface of the first mold, the glass lump is formed on the press surface of the first mold by the press surface of the first mold and the press surface of the second mold. Pressing process for pressing to reach the outer edge (first pressing process)
(2) The mold (lower mold) disposed on the lower side in the vertical direction is the second mold, and the mold (upper mold) disposed on the upper side in the vertical direction is the first mold. After placing the glass lump on the press surface of the second mold, the glass lump is placed on the press surface of the first mold by the press surface of the first mold and the press surface of the second mold. Pressing process for pressing to reach the outer edge (second pressing process)

  Here, FIG. 3 is a schematic cross-sectional view showing an example of a pair of molds used in the glass blank manufacturing method of the present embodiment. Specifically, the molds are orthogonal to the press surface. Fig. 3 shows a cross section when cut. A pair of forming dies shown in FIG. 3 includes an upper die 20 and a lower die 30. During pressing, the upper die 20 is arranged on the upper side in the vertical direction, and the lower die 20 is arranged on the lower side in the vertical direction. The upper die 20 includes a circular center portion 22A and a press surface 22 having a ring-shaped outer edge portion 22B provided so as to be recessed with respect to the center portion 22A on the peripheral side of the center portion 22A. The lower mold 30 includes a circular center portion 32A and a press surface 32 having a ring-shaped outer edge portion 32B provided on the peripheral side of the center portion 32A so as to be recessed with respect to the center portion 32A. . However, the diameter of the central portion 32A of the press surface 32 of the lower die 30 is smaller than the diameter of the central portion 22A of the press surface 22 of the upper die 20. Note that each of the pair of molds may be constituted by one member, or may be constituted by combining a plurality of members. When a plurality of members are combined and configured, the members may be fixed to each other, or the molding die may be configured with the members movable relative to each other.

  When manufacturing the glass blank 1 of this embodiment as illustrated in FIG. 1, the softened glass lump is supplied onto the central portion 32 </ b> A of the press surface 32 of the lower mold 30, and then the upper mold 20 and the lower mold are used. 30, the glass lump is press-molded so as to reach the outer edge 22 </ b> B of the press surface 22 of the upper mold 20. In addition, when obtaining the glass blank of the same shape as the glass blank 1 shown in FIG. 1, the arrangement | positioning relationship of the upper mold | type 20 and the lower mold | type 30 with respect to a perpendicular direction may be upside down.

  For this reason, it is preferable to implement the curvature suppression process which suppresses generation | occurrence | production of curvature with respect to the glass of the soft state which became a substantially plate shape after passing through a press process. In the warpage suppressing step for suppressing the occurrence of warpage, it can be broadly classified as follows: (1) a method of forcibly correcting warpage once generated by applying external force (warpage correction press), and (2) a rough plate immediately after pressing. It is possible to use at least one of the methods of preventing the difference between the cooling conditions of the upper and lower surfaces of the softened glass that has become a shape and cooling the upper and lower surfaces under substantially the same conditions.

  As described above, as the warp correction press of (1), after obtaining a glass blank 1 as shown in FIG. 1, it is pressed with a pair of flat substrates in a state where it is heated again to a temperature at which it can be easily deformed. Then, a method of deforming to a flat form by an external force or a glass in a softened state immediately after press molding (as a shape, a glass having the same shape as the glass blank 1 of the present embodiment illustrated in FIG. 1) is flat. There is a method in which a pair of substrates is pressed and deformed so as to have a flat shape by an external force.

  Here, the temperature inside the glass blank 1 when performing the warp correction press is preferably higher than the glass transition temperature Tg. Thereby, since the glass blank 1 has the softness which is moderately easy to deform | transform, even if an external force is added to the glass blank 1, it can suppress more reliably that a crack and a crack generate | occur | produce. In addition, although the upper limit of the temperature inside the glass blank 1 is not specifically limited, It is preferable to set it as glass transition temperature Tg + 80 degrees C or less practically. Thereby, since it becomes difficult to maintain the glass blank 1 in a soft and easy-to-deform state even after the warp correction press is performed, the second deformation after the warp correction press can be suppressed. The temperature of the flat substrate used in the warp correction press is preferably in the range of 400 to 650 ° C. from the viewpoint of preventing the glass from fusing to the substrate while preventing the glass from cracking.

  Also, (2) soaking and cooling on the upper and lower surfaces is the same as that of the lower die so as to be close to or in contact with the upper surface of the softened glass that is substantially plate-like immediately after the upper die is separated from the upper surface. In a state where a planar member heated to a certain temperature is placed, cooling is performed until the temperature of the softened glass that has become substantially plate-shaped is equal to or lower than the temperature at which deformation is difficult (that is, the glass transition temperature). Is called. If such cooling is performed, the deviation of the cooling conditions on both sides of the softened glass that has become substantially plate-like after press molding is suppressed, and almost uniform thermal shrinkage occurs on both sides, thus suppressing the occurrence of warpage. it can.

  Next, the typical example of the manufacturing method of the glass blank 1 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 mold and the lower mold, the pressing pressure, and the pressing time are appropriately set in consideration of the thermal properties of the glass such as the glass transition temperature, the diameter and thickness of the glass blank to be manufactured, and the like. For example, the upper mold temperature can be set to 250 to 550 ° C., and the lower mold temperature can be set to 350 to 650 ° C. 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 completed, 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 position (takeout position) where the molded product is taken out from the lower mold. In addition, the lower die is stopped between the press position and the take-out position, the upper surface of the molded product on the lower die is pressed with the pressing die, and the warp correction press is performed to correct the warpage of the molded product, and then the take-out position. Each lower mold may be transferred to Alternatively, while the lower die is transferred from the press position to the take-out position, it is heated to a temperature similar to that of the lower die so as to be close to or in contact with the upper surface of the molded product placed on the lower die, and The temperature history of the glass may be adjusted by arranging a flat plate member that covers the entire top surface of the molded product.

  Further, the molded product is put into an annealing furnace and annealed in order to remove strain. And the glass blank of this embodiment can be obtained through such a series of processes. Moreover, you may implement a curvature correction press with respect to the glass blank after annealing as needed.

-Glass composition-
The glass composition of the glass blank 1 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, aluminoboro Examples thereof include silicate glass, borosilicate glass, quartz glass, and chain silicate glass. 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 2% by mass to 10% by mass, Na ₂ O. May be an aluminosilicate glass containing 5% by mass or more and 18% by mass or less as a main component (however, an aluminosilicate glass containing no phosphorus oxide). For example, SiO ₂ is 62 mass% to 75 mass%, Al ₂ O ₃ is 5 mass% to 20 mass%, Li ₂ O is 2 mass% to 8 mass%, and Na ₂ O is 6 mass% to 15 mass%. It may be an amorphous aluminosilicate glass containing, as a main component, 0 mass% or less and ZrO ₂ of 0 mass% or more and 8 mass% or less.

(Information Recording Medium Substrate Manufacturing Method)
Next, a case where an information recording medium substrate (hereinafter, simply referred to as “substrate” in some cases) is manufactured using the glass blank 1 of the present embodiment will be described. In this case, the information recording medium substrate can be manufactured through at least a lapping step of lapping the glass blank 1 of the present embodiment while being sandwiched between lap surface plates. Moreover, when the glass which comprises the glass blank 1 has a glass composition which can be crystallized by heat processing, the crystallizing process crystallized by heating substantially plate-like glass other than the said process can also be combined. As a typical example of manufacturing an information recording medium substrate, for example, (1) lapping step, (2) drilling step and end face processing step, (3) main surface polishing step, and (4) chemical strengthening step are performed. can do. Note that the order of these steps may be changed.

(1) Lapping process In a lapping process, a disk-shaped glass base plate is obtained by lapping both the main surfaces of the glass blank 1. This lapping process can be performed using alumina free abrasive grains or the like by a double-sided lapping apparatus using a planetary gear mechanism.

(2) Drilling step and end face processing step Next, using a diamond drill, a circular hole is formed in the center of the glass substrate to obtain a donut-shaped glass substrate. Chamfering and polishing can be performed on the outer and inner diameter portions of the glass substrate.

(3) Main surface polishing step The main surface is subjected to a polishing step mainly for removing residual scratches and distortions. As a polishing liquid, for example, cerium oxide abrasive grains or colloidal silica can be used.

(4) Chemical strengthening process When the substantially plate-like glass 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 process and the polishing process described above, 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.

  Chemical strengthening is performed by immersing glass in a chemical strengthening solution in which potassium nitrate and sodium nitrate are mixed. Thereby, 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.

  These series of steps may not be in this order. The surface roughness of the information recording medium produced through these can be set to an order of sub-nanometers by Ra. The surface roughness can be appropriately adjusted by selecting conditions. The information recording medium substrate obtained through the above 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. In particular, it is suitable for use in producing a magnetic recording medium.

(Information recording medium manufacturing method)
The information recording medium can be manufactured through at least an information recording layer forming step for forming an information recording layer on the main 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 can be 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. .

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

(Press molding equipment)
In the production of the glass blank of each example and each comparative example, a plurality of lower molds are arranged at equal intervals along the outer peripheral edge, and when pressing, a press device provided with a rotary table that rotates an index in one direction is used. Using. In this press apparatus, at a predetermined position where the lower mold stops along the direction of index rotation of the rotary table, (1) a position P (cast) for supplying molten glass onto the lower mold press surface, (2) lower Position P (press) where molten glass (glass gob) supplied on the mold press surface is pressed using the upper mold placed above the lower mold press surface and the lower mold, (3) Position P (press) From the upper surface of the glass blank formed in step (2), the position P (press # 2) to press (warp correction press) using a warp correction press die that is a separate article from the upper die, (4) A position P (take-out) to be taken out from the lower die press surface is assigned.

  This press apparatus includes 16 lower molds, and the position where each lower mold stops is the outer edge of the rotary table and is provided at equal intervals in the circumferential direction. Here, if the position where the lower mold stops is numbered 1 to 16 in the rotation direction and the position P (cast) is the first, the position P (press) is the third position P (press # 2) is fourth, and position P (take-out) is twelfth.

  The lower die and the upper die are formed by a molding die (outer edge concave portion) having a center portion having a circular press surface and an outer edge portion provided at the peripheral edge portion of the central portion so as to be recessed with respect to the central portion. Type molding die) or a molding die having a flat pressing surface (full flat type molding die) was used. And in the production of the glass blank of each example and each comparative example, according to the shape of the glass blank to be produced, as a mold used as an upper mold or a lower mold, an outer edge concave mold or an entire flat type A mold was selected. Moreover, when the outer edge concave mold was used, a mold having a different diameter between the central part and a step between the peripheral part and the central part was appropriately used according to the shape of the glass blank to be produced.

  Moreover, about the diameter of the press surface of the curvature correction press type | mold used for the curvature correction press, the convex parts 12U and 112U are provided in the upper surface U side like the glass blank 1 shown in FIG. 1, and the glass blank 100 shown in FIG. When manufacturing the glass blank to be manufactured, the thing which can press only the thin part (meaning the area | region shown by RP shown in FIG. 1) in which the convex parts 12U and 112U are not provided was used. In this case, the diameter of the press surface was selected so that the margin (the length indicated by the symbol M in FIG. 1) was 1.5 mm. On the other hand, in FIG. 1 and FIG. 4, when manufacturing the glass blank which does not provide the convex parts 12U and 112U on the upper surface U side, the diameter of the press surface of the warp correction press mold was selected so that the entire upper surface could be pressed.

Example 1
-Direct press-
A glass blank 1 having a cross-sectional shape shown in FIG. 1 was obtained by supplying the molten glass obtained by melting the aluminosilicate glass onto the press surface of the lower mold and then pressing it with the upper mold and the lower mold. The ratio of the thickness t to the diameter d of the thin wall portion 10 of the glass blank 1, that is, the aspect ratio (t / d), the width W2 and height of the convex portion 12U, and the width W2 and height of the convex portion 12D are W1 / W2 is as shown in Table 1. The diameter d is 66.0 mm, which is the same for the glass blanks produced in other examples and comparative examples.

  When manufacturing the glass blank 1 by the direct press method in Example 1, each process was implemented in the following procedures. That is, molten glass is supplied onto the lower mold at P (cast), pressed at the lower mold stop position P (press), and the warp correction arranged above at the lower mold stop position P (press # 2) is corrected. The upper surface of the glass blank on the lower die press surface is warped and corrected by the press die, and the lower die moves from the lower die stop position P (press # 2) to P (take-out). The glass that has become substantially plate-like in the placed state is naturally allowed to cool, and the glass blank that has become substantially plate-like cooled at the lower die stop position P (take-out) is taken out, and the lower die stop position P (take) is taken. The lower mold is circulated and transferred again from -out) to the lower mold stop position P (cast). In addition, the taken-out glass blank was put into the slow cooling furnace, and was cooled to normal temperature.

Here, main production conditions 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: 500 ° C.
・ Temperature of upper die press surface during pressing: 450 ℃
・ Viscosity of molten glass put on the lower mold: 40 Pa · s
・ Press time (time to apply pressure to glass): 1 second ・ War correction press time: 1 second ・ Material composing upper and lower press surfaces: cast iron (no coating treatment)
-Temperature of the glass blank 1 when the glass blank 1 is taken out from the lower mold: 520 ° C

-Fabrication of substrate for information recording medium-
About the glass blank 1 obtained through the above process, (1) lapping step, (2) drilling step and end face processing step, (3) main surface polishing step and (4) chemical strengthening step are performed, The substrate for information recording medium (outer diameter: 65.0 mm, thickness: 0.635 mm, center hole inner diameter: 20.0 mm) was obtained by washing. The obtained information recording medium substrate was evaluated for dents and flatness, and for ease of processing based on the time required for lapping.

(Examples 2 to 11)
When the glass blank 1 was produced, direct pressing was performed in the same manner as in Example 1 except that the mold used was appropriately changed so that the convex portions 12D and 12U had the shapes shown in Table 1. Moreover, the conditions for producing an information recording medium substrate using the obtained glass blank 1 were the same as in Example 1, and an information recording medium substrate was obtained.

(Comparative Example 1)
A glass blank 100 shown in FIG. 4 was produced. When the glass blank 100 was produced, direct pressing was performed in the same manner as in Example 1 except that the mold used was appropriately changed so that the shapes of the convex portions 112D and 112U were as shown in Table 2. Moreover, the conditions at the time of producing the information recording medium substrate using the obtained glass blank 100 were the same as those in Example 1, and an information recording medium substrate was obtained.

(Comparative Example 2)
A glass blank having no convex portions as illustrated in FIGS. 1 and 4 on both the upper and lower surfaces and a flat surface on both surfaces was produced. In producing this glass blank, direct pressing was performed in the same manner as in Example 1 except that the mold used was appropriately changed. Moreover, the conditions at the time of producing the information recording medium substrate using the obtained glass blank 100 were the same as those in Example 1, and an information recording medium substrate was obtained.

(Comparative Examples 3 and 4)
In FIG. 4, the glass blank which does not have the convex part 112U in the lower surface was produced. In producing this glass blank, direct pressing was performed in the same manner as in Example 1 except that the forming die used was appropriately changed so that the shape of the convex portion 112D was as shown in Table 2. Moreover, the conditions at the time of producing the information recording medium substrate using the obtained glass blank 100 were the same as those in Example 1, and an information recording medium substrate was obtained.

(Comparative Examples 5 and 6)
In FIG. 4, a glass blank having no protrusions 112D on the upper surface was produced. In producing this glass blank, direct pressing was performed in the same manner as in Example 1 except that the mold used was appropriately changed so that the shape of the convex portion 112U was as shown in Table 2. Moreover, the conditions at the time of producing the information recording medium substrate using the obtained glass blank 100 were the same as those in Example 1, and an information recording medium substrate was obtained.

(Evaluation)
The substrate for information recording medium obtained in each example and comparative example was evaluated for the dents and flatness. The ease of processing during lapping was also evaluated. The results are shown in Table 1 and Table 2 below.

In Tables 1 and 2, the evaluation method and evaluation criteria for the dents and flatness are as follows.
-Recess-
The dents on the surface of the substrate for the information recording medium were obtained by irradiating the surface of the substrate with light from a visual inspection light source (Olympus long-life halogen light source device ILK-7C) in a dark room environment for 1000 samples. Whether or not a ring-shaped dent was observed along the outer peripheral edge of the substrate was evaluated. The evaluation criteria are as follows.
A: None of the dents are observed in 1000 sheets.
◯: In 1000 sheets, dents are observed in the range of 1 or more and less than 5 sheets.
(Triangle | delta): In 1000 sheets, a dent is observed in the range of 5 sheets or more and less than 20 sheets.
X: 20 or more dents are observed in 1000 sheets.

-Flatness-
The flatness of the portion excluding the convex portion was measured with 10 samples, and the average value was obtained. The flatness was obtained by measuring the displacement at a 1 mm pitch with a laser focus displacement meter while moving the sample placed on the XY stage. Then, the difference between the maximum value and the minimum value of the displacement obtained after correcting the inclination of the measured value was obtained for each sample, and the average value of these values was defined as flatness. The evaluation criteria are as follows.
A: Less than 4 μm B: 4 μm or more and less than 10 μm
Δ: 10 μm or more and less than 20 μm ×: 20 μm or more

-Ease of processing (processing time)-
The time required for the lapping process was relatively evaluated based on the lapping process time in Example 1. The evaluation criteria are as follows.
A: Processing time is less than + 5% with respect to Example 1. B: Processing time is + 5% or more and less than + 10% with respect to Example 1. Δ: Processing time is + 10% or more with respect to Example 1 and less than + 15%. Processing time + 15% or more with respect to Example 1

DESCRIPTION OF SYMBOLS 1 Glass blank 10 Thin part 12 Thick part 12U, 12D Convex part 12S Inclined surface 14C Corner | angular part 20 Upper mold | type 30 Lower mold | type 22 Press surface 22A Center part 22B Outer edge part 32 Press surface 32A Central part 32B Outer edge part 100, 100H, 100C Glass blank 102 Information recording medium substrate 110 Thin portion 112 Thick portion 112U, 112D Convex portion 114C Corner portion 114P, 114Q Concavity

Claims (5)

A thin disk-shaped part,
A thick portion provided so as to form convex portions on both sides of the thin portion along the peripheral portion of the thin portion;
A glass blank, wherein a radial width of the convex portion on one surface side with respect to a diameter direction of the thin-walled portion is larger than a radial width of the convex portion on the other surface side. As a pair of molds arranged to be movable relative to the vertical direction,
A press surface provided with a press surface having a circular center portion and an outer edge portion provided so as to form a recess with respect to the center portion on the peripheral side of the center portion in contact with the softened glass during press molding. One mold,
It is in contact with the softened glass at the time of press molding, and a circular central portion having a smaller diameter than the central portion of the first mold and a dent to the central portion on the peripheral side of the central portion. Using a second mold having a press surface having an outer edge provided in
The mold placed on the lower side in the vertical direction is the first mold, and the mold placed on the upper side in the vertical direction is the second mold.
After the softened glass lump is disposed on the press surface of the first mold, the glass lump is moved by the press surface of the first mold and the press surface of the second mold. A first pressing step for pressing to reach the outer edge of one mold press surface; and
The mold placed on the lower side in the vertical direction is the second mold, and the mold placed on the upper side in the vertical direction is the first mold.
After the softened glass lump is disposed on the press surface of the second mold, the glass lump is moved by the press surface of the first mold and the press surface of the second mold. Through at least one pressing step selected from a second pressing step that presses to reach the outer edge of one mold press surface,
A glass blank manufacturing method characterized by manufacturing a glass blank. In the glass blank manufacturing method of Claim 2,
A glass blank manufacturing method, wherein a warp suppressing step for suppressing warpage is performed on a softened glass that has been substantially plate-shaped through the pressing step. The both sides of the glass blank selected from the glass blank of Claim 1, and the glass blank manufactured by the glass blank manufacturing method of Claim 2 or 3,
An information recording medium substrate manufacturing method comprising manufacturing an information recording medium substrate through at least a process of grinding and / or polishing.   An information recording medium is manufactured through at least an information recording layer forming step of forming an information recording layer on the main surface of the information recording medium substrate manufactured by the information recording medium substrate manufacturing method according to claim 4. An information recording medium manufacturing method characterized by the above.

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