JP5485665B2 - Manufacturing method of glass blank, upper mold for glass press, press molding apparatus, manufacturing method of substrate for information recording medium, and manufacturing method of information recording medium - Google Patents

Description

  The present invention relates to a method for manufacturing a glass blank, an upper mold for glass press, a press molding apparatus, a method for manufacturing an information recording medium substrate, and a method for manufacturing an information recording medium.

  A direct press method is known as a method for producing a plate-shaped glass semi-product (so-called “glass blank”) used for producing an information recording medium substrate, an optical lens, or the like. In this direct press method, molten glass that continuously flows out from a feeder pipe is supplied onto a lower mold for each predetermined volume, and then a softened glass lump on the lower mold (hereinafter sometimes referred to as “glass gob”) A glass blank is produced through a step of pressing the lower die and the upper die.

  When manufacturing an optical lens by grinding and polishing a glass blank produced by the direct press method, it is important to suppress sink marks generated on the surface of the glass blank in order to reduce the machining allowance during grinding and polishing. is there. This sink mark is generated due to a difference in heat shrinkage between the inside and outside of the glass lump caused by this temperature difference due to a temperature difference between the inside and the outer periphery of the glass lump in a high temperature state during press molding.

  In order to suppress the occurrence of sink marks in such a glass blank for optical glass, the applicant assigns the temperature of the glass gob supplied on the lower mold and the temperature inside and outside the glass lump after this step. A method of pressing the approaching step after implementation has been proposed (see Patent Document 1). In this method, in order to cool the upper surface of the glass gob, cooling air is blown onto the upper surface of the glass gob, or a heat absorbing member made of a metal material having a smooth contact surface is pressed against the upper surface of the glass gob to deform it. The absorbing member and the upper surface of the glass gob are brought into surface contact. Thereby, the heat | fever of the glass gob upper part side is absorbed by the heat absorption member side. The present applicant has also proposed a method of controlling the temperature of the glass gob so that the temperatures of the inside and the outer periphery of the glass gob supplied onto the lower mold are made closer (see Patent Document 2). Also in this method, in order to cool the upper surface of the glass gob, a press member made of a metal material having a smooth contact surface is pressed against the upper surface of the glass gob and deformed to bring the heat absorbing member and the upper surface of the glass gob into surface contact. Thereby, the heat | fever of the glass gob upper part side is absorbed by the heat absorption member side.

  On the other hand, from the viewpoint of ensuring mass production stability of the glass blank, the glass blank is prevented from being burned onto the press surface of the lower mold (for example, see Patent Document 3, Patent Document 4, etc.). It is also important to be able to suppress variations in quality. For this reason, a method is proposed in which a flow path is provided inside the upper mold and the lower mold, and a gas mixed with air and water particles is allowed to flow through the flow path so that the press surface can be controlled at a predetermined temperature. (For example, refer to Patent Document 5, Patent Document 6, etc.).

JP 2002-68757 A (Claim 1, paragraph numbers 0012, 0025, FIG. 3, FIG. 7, etc.) JP 2000-233934 A (Claims 1, 5, 6, 7, paragraph number 0034, etc.) JP 2004-206828 A (paragraph number 0014) JP 2004-203698 A (paragraph number 0011) Japanese Patent Laid-Open No. 10-236831 (paragraph numbers 0032 to 0034, FIG. 6) Japanese Patent Laid-Open No. 10-212127 (paragraph numbers 0013 to 0015, FIG. 1)

  When a glass blank produced by the direct press method is used to produce a substrate for information recording medium (hereinafter sometimes simply referred to as “substrate”), the thickness of the glass blank (the thickness of the area that can ultimately become the substrate) The closer to the thickness of the substrate, the better. This is because the polishing allowance when the glass blank is post-processed into a substrate can be reduced, and the cost can be reduced. For this purpose, as a method for improving the flatness by suppressing the deformation of the glass blank, for example, a glass blank that has undergone deformation immediately after pressing is pressed with a plate heated to an appropriate temperature (so-called warpage correction press), For example, a method of correcting a deformation generated during pressing (a warp correction press method) may be used.

  Actually, when the thickness of the entire glass blank is made thinner than the outer diameter using this warp correction press method, the total warpage amount can be suppressed to some extent. However, in this case, the central portion of the glass blank is locally deformed so as to rise to the side that was in contact with the upper die at the time of pressing, so that the entire glass blank is warped with a substantially flat or substantially uniform and large curvature. I couldn't. And the remaining of such a partial protruding part resulted in the increase in the grinding | polishing margin at the time of processing a glass blank into a board | substrate, and the deterioration of the planarity of the board | substrate after a process.

  This invention is made | formed in view of the said situation, Even when producing a thinner glass blank, the manufacturing method of the glass blank which can obtain the glass blank which has higher planarity, For the glass press used for this It is an object of the present invention to provide an information recording medium substrate manufacturing method and an information recording medium manufacturing method using the upper mold and the press molding apparatus, and the glass blank manufacturing method.

The above-mentioned subject is achieved by the following present invention. That is, in the method for producing a glass blank of the present invention, after supplying the softened glass to the center of the press surface of the lower mold, the press process of press-molding the softened glass between the upper mold and the lower mold At least through this, a glass blank for an information recording medium substrate is produced, and immediately before the press process is performed, the temperature in the vicinity of the center portion of the upper die press surface is lower than the temperature of other regions of the upper die press surface. Features. Here, as the upper die, the upper die for glass press of the present invention described later is used.

One embodiment of the method for producing a glass blank of the present invention preferably satisfies the following formulas (1) and (2).
Formula (1) Tg−200 ≦ Tc <Te ≦ Tg + 50
Formula (2) 0.5 ≦ ΔT ≦ 6
[In the formulas (1) and (2), Tc is a circle in a state where it is assumed that the glass in the softened state has been almost isotropically spread on the lower press surface by press molding to form a disk shape. Represents the temperature (° C.) just before the press molding at the upper die press surface at the position corresponding to the center point of the glass that has finished spreading in a plate shape, Te is the position corresponding to the outermost periphery of the glass that has finished spreading in a disk shape Represents the temperature (° C) immediately before press molding on the upper die press surface, Tg represents the glass transition temperature (° C) of the glass, and ΔT is the midpoint between the center point of the glass that has finished spreading in the shape of a disk and the outermost periphery. Represents a temperature gradient (° C./mm) immediately before press molding on the press surface at a position corresponding to. ]

The upper die for glass press of the present invention is a columnar body portion having a press surface for press-molding a softened glass sandwiched between the upper die and the interior of the body portion, in proximity to the press surface. And a partition member disposed in the space so as to form an outer peripheral side flow path and a central flow path in a space above the cavity part, and The inner diameter in the direction parallel to the press surface is 80% or more of the outer diameter of the glass blank to be press-formed, and the distance between the inner wall surface on the press surface side of the cavity and the press surface in the axial direction of the body portion However, a minimum is formed in the center portion of the press surface, the press surface is a flat surface, and when performing the continuous press, the cooling medium is passed through the lower side from the upper side of the central flow path (1) From the vicinity of the center of the inner wall surface to the outer peripheral side Is dynamic, further outer peripheral flow path is moved from the lower side to the upper side, or, wherein the moving in the direction opposite to the moving direction shown in (2) above (1).

  In one embodiment of the upper die for glass press of the present invention, it is preferable that a concave portion is provided on the inner wall surface on the press surface side of the hollow portion at a position corresponding to the vicinity of the center portion of the press surface.

  In another embodiment of the upper mold for glass press of the present invention, the inner wall surface on the press surface side of the cavity is preferably a curved surface curved so as to be recessed toward the press surface side.

  The press molding apparatus according to the present invention includes at least a lower mold and an upper mold that is disposed opposite to the lower mold and that is relatively movable in a direction approaching and separating from the lower mold. The mold is the upper mold for glass press of the present invention.

  The method for producing a substrate for information recording medium of the present invention produces a substrate for information recording medium through at least a grinding / polishing step of grinding / polishing at least one surface of the glass blank produced by the method for producing a glass blank of the present invention. It is characterized by doing.

  One embodiment of the method for producing an information recording medium substrate of the present invention preferably includes a crystallization step of crystallizing the glass blank by heating.

  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 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.

  ADVANTAGE OF THE INVENTION According to this invention, even when producing a thinner glass blank, the manufacturing method of the glass blank which can obtain the glass blank which has higher planarity, the upper mold | type for glass press and press molding apparatus used for this, and the said An information recording medium substrate manufacturing method and an information recording medium manufacturing method using a glass blank manufacturing method can be provided.

It is explanatory drawing for demonstrating temperature Tc, Te and temperature gradient (DELTA) T. It is explanatory drawing for demonstrating the definition of the aspect-ratio in an example of the glass blank produced using the manufacturing method of the glass blank of this embodiment. It is explanatory drawing for demonstrating the definition of the aspect-ratio in the other example of the glass blank produced using the manufacturing method of the glass blank of this embodiment. It is explanatory drawing for demonstrating the definition of the aspect-ratio in the other example of the glass blank produced using 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. It is a schematic cross section which shows an example of the upper mold | type of this embodiment. It is a schematic cross section which shows the other example of the upper mold | type of this embodiment. It is a graph which shows the example of the temperature distribution with respect to the diameter direction of the upper mold | type press surface just before press molding at the time of manufacturing a glass blank using the upper mold | type of this embodiment. It is a graph which shows the change of the temperature distribution of the lower die press surface at the time of manufacturing a glass blank by the conventional direct press method. It is a schematic cross section showing an example of a conventional upper mold.

(Glass blank manufacturing method)
The manufacturing method of the glass blank of the present embodiment includes a pressing step of press-molding the softened glass between the upper mold and the lower mold after supplying the softened glass to the center of the press surface of the lower mold. At least, a glass blank for an information recording medium substrate is produced. Immediately before the pressing process is performed, the temperature in the vicinity of the center of the upper die press surface is changed to another region (hereinafter referred to as “periphery”). The temperature is lower than the temperature of the “part”.

  As described above, in the glass blank manufacturing method of the present embodiment, the temperature in the vicinity of the center portion of the upper die press surface is controlled to be lower than the temperature of other regions of the upper die press surface immediately before the press process is performed. Is done. For this reason, even in the range where the temperature of the glass blank central portion is equal to or higher than the temperature of the peripheral portion, the temperature difference in the radial direction of the glass blank immediately after press molding can be reduced, and the upper die press surface immediately after pressing. The adhesive force acting between the glass blank that is in contact with the glass blank and the vicinity of the center of the upper press surface can be reduced. As a result, when the glass blank and the upper mold that are still in a state of being easily melted at a high temperature immediately after pressing are separated, the vicinity of the center portion of the glass blank is caused by the adhesive force generated between the press surface of the upper mold, It becomes difficult to be pulled to the upper mold side. As a result, the temperature difference in the radial direction of the glass blank immediately after pressing becomes sufficiently small. And if the curvature correction press method is applied with respect to the glass blank of this state, a glass blank with higher planarity can be obtained.

  In addition, the effect as described above can be obtained by controlling the temperature in the vicinity of the center portion of the upper die press surface to be lower than the temperature in other regions of the upper die press surface immediately before the press process. The reason is as follows. First, when mass-producing glass blanks using the direct press method, a plurality of lower molds arranged so as to be able to circulate in one direction and one upper mold are used to press each lower mold press surface. The softened glass sequentially supplied onto the glass is continuously press-molded. For this reason, on the press surface of the upper die, heat exchange is performed with the softened glass for each press. In addition to continuous pressing, the vicinity of the center of the pressing surface is always in contact with the glass in the softened state from the beginning to the end of the pressing as compared with the peripheral area. Therefore, immediately before the press process is performed, the vicinity of the center portion of the upper die press surface is likely to be relatively hot compared to other portions of the press surface.

  And at the time of continuous press, such a state will be maintained over a long period of time. Therefore, in the vicinity of the center part of the press surface of the upper die, the wettability with respect to the glass in the softened state increases due to the progress of oxidation over time as compared with other portions of the press surface. As a result, (1) With the passage of time, the vicinity of the central portion of the press surface becomes more adhesive to the softened glass than the other portions of the press surface. On the other hand, the softened glass supplied on the press surface of the lower die is in the process of being stretched in a direction parallel to the press surface by the press, in the vicinity of the center of the upper press surface and from the initial stage to the end of the press. In the meantime, you will always be in contact. Therefore, (2) when the glass blank in the softened state has been stretched and the upper glass mold is separated from the upper mold, the glass blank has a central portion in the vicinity of the other portions. Relatively high temperature (ie low viscosity).

  When the warp correction press method is applied to a glass blank after pressing, if the vicinity of the center of the glass blank is excessively hot compared to other parts, a warp correction tool having a substantially uniform temperature is applied to the entire upper surface of the glass blank. When brought into contact, the cooling in the vicinity of the central portion is delayed as compared with other portions. In addition to this, the amount of shrinkage on the lower mold surface side, which is relatively higher than that on the upper mold surface side of the glass blank, is increased. Therefore, in this case, a phenomenon in which only the central portion of the glass blank is raised to the upper mold surface side is likely to occur.

  However, immediately before the pressing process is performed, the temperature in the vicinity of the center portion of the upper die press surface is controlled to be lower than the temperature of other regions of the upper die press surface, so that the glass and the press surface are Even if heat exchange occurs between them, the temperature in the vicinity of the central portion of the press surface of the upper die can be suppressed from becoming relatively high compared to other portions of the press surface. For this reason, generation | occurrence | production of the phenomenon shown in said (1) can be suppressed. Moreover, if it is original, temperature near the center part of the glass blank immediately after a press becomes higher than other parts. However, in the glass blank manufacturing method of the present embodiment, the heat in the vicinity of the center of the glass blank is selectively and intensively taken away by the upper die press surface as compared with other regions of the glass blank. For this reason, when the glass blank and the upper mold are separated from each other, the glass blank is not relatively excessively heated (that is, reduced in viscosity) in the vicinity of the center portion compared to other portions. Therefore, if the warp correction press method is applied to the glass blank in this state, it becomes easier to improve the flatness.

  The same effect can be obtained by (A) a control method immediately before the pressing step so that the temperature in the vicinity of the center portion of the lower die press surface is lower than the temperature in other regions of the lower die press surface, B) It can also be realized by a method in which a cooling member made of, for example, a rod-like metal is brought into contact with the central portion of the upper surface of the softened glass that has become a lump on the lower press surface immediately before pressing. This is because it is possible to suppress the high temperature of the central portion of the glass blank immediately after pressing.

  Here, the method shown in (A) is found by paying attention to a change in temperature distribution of the lower die press surface when a glass blank is manufactured by the conventional direct press method shown in FIG. When a glass blank is manufactured by a conventional direct press method, first, a predetermined amount of molten glass is dropped from the outflow nozzle onto the center of the lower die press surface. Here, the temperature distribution in the diameter direction of the lower die press surface immediately before the molten glass is dripped is substantially flat (a line indicated by a symbol A in FIG. 9. Strictly speaking, since there is heat radiation from the side surface of the lower mold, it is not completely flat, and the temperature near the center is slightly higher than the outer periphery). Next, the glass dripped from the outflow nozzle and formed into a lump on the vicinity of the center of the lower die press surface performs heat exchange with the lower die press surface. For this reason, the temperature distribution in the diameter direction of the lower die press surface increases rapidly in the vicinity of the central portion in contact with the high-temperature glass that has become agglomerated with time, but gradually increases only on the peripheral portion side ( Line indicated by symbol B in FIG. 9). Then, immediately before the massive glass is pressed by the upper mold and the lower mold, the temperature distribution on the lower mold press surface forms a complete convex profile (line indicated by symbol C in FIG. 9). . In this state, the massive glass is pressed by the upper die and the lower die, and stretched from the vicinity of the center portion of the press surface to the peripheral portion side. As a result, in the glass (glass blank) in which the lump of glass has been stretched completely, the temperature difference between the vicinity of the center of the glass blank and the vicinity of the center of the lower press surface is the peripheral edge of the glass blank. And the temperature difference between the peripheral edge of the lower die press surface.

  For this reason, the heat | fever near the center part of the glass blank immediately after a press is not fully absorbed into the lower mold | type side, and the center part vicinity of the glass blank immediately after a press becomes high temperature (low viscosity) rather than a peripheral part. When paying attention to such a mechanism, it is clear that the temperature in the vicinity of the center portion of the lower die press surface may be controlled to be lower than the temperature in the peripheral portion of the lower die press surface immediately before the press process is performed. It is. Thus, the heat exchange between the glass and the lower mold at the time of pressing can suppress the vicinity of the central portion of the glass stretched in a disc shape from being heated to the peripheral portion, in other words, the glass at the end of press molding. This is because the difference in shrinkage caused by the location near the center of the blank that is relatively high can be suppressed to a small level.

  However, the manufacturing method of the glass blank of this embodiment has the merit demonstrated below further compared with the method shown to said (A) and (B). First, in the method shown in (A) above, the central portion of the softened glass that has become agglomerated on the lower die press surface immediately after the molten glass starts to be dropped onto the lower die and before the press starts. The neighborhood will continue to be cooled. For this reason, the heat | fever of the whole glass of the softened state which became the lump shape before a press is taken away by the lower mold more than necessary, and the viscosity of glass tends to fall more than necessary. On the other hand, in the glass blank manufacturing method of the present embodiment, the softened glass and the upper press surface are in contact only during pressing. For this reason, the heat of the entire soft glass in a lump shape before the start of pressing is not taken away by the upper mold more than necessary, and as a result, the viscosity of the glass is not lowered more than necessary. Therefore, during pressing, glass can maintain high stretchability from the initial stage to the final stage of the press, so that the glass blank can be easily thinned.

  Moreover, when manufacturing a glass blank, a rotary table in which a plurality of lower molds are arranged on the outer edge is usually used. Therefore, when the method shown in the above (A) is adopted, in order to control the cooling so that the temperature in the vicinity of the center portion of the lower die press surface is lower than the temperature of the peripheral portion of the lower die press surface, It is necessary to cool down all the lower molds by flowing cooling water. In order to realize such cooling, it is necessary to extend the piping path of the cooling medium for cooling each lower mold arranged on the rotary table to all the lower molds. However, since the cooling system becomes very complicated, the cooling state of each lower die press surface varies more or less. On the other hand, in the manufacturing method of the glass blank of this embodiment, the shaping | molding die used as the object of cooling is only one upper mold | type. That is, the cooling system for cooling the upper mold is very simple compared to the cooling system employed in the method shown in (A) above. For this reason, it is hard to produce dispersion | variation in the cooling state of an upper die press surface for every press. Therefore, in the manufacturing method of the glass blank of this embodiment, it is easy to suppress the generation | occurrence | production of the quality variation of the glass blank resulting from the variation in the cooling state of the press surface for every press.

  On the other hand, in the method shown in (B) above, the softened glass is cooled in a lump state before being pressed. For this reason, even if the central portion of the upper surface of the massive glass is selectively cooled, when the softened glass is deformed into a disk shape by the press, the selectively cooled region is laterally It will be stretched. For this reason, in the method shown in the above (B), it is fundamental that the press is completely finished and only the heat near the center of the glass blank immediately before the upper die and the glass blank are separated is selectively and intensively taken away. Is difficult.

  On the other hand, in the glass blank manufacturing method of the present embodiment, the upper mold controlled so that the temperature in the vicinity of the center portion of the press surface immediately before pressing is lower than the temperature in other regions is a glass block. Is kept in contact with the softened glass until it has been drawn into a disk shape. For this reason, in the manufacturing method of the glass blank of this embodiment, the press is completely finished, and only the heat in the vicinity of the central portion of the glass blank immediately before the upper mold and the glass blank are separated is selectively and intensively taken away. The state is easy to realize.

  For this reason, the manufacturing method of the glass blank of this embodiment causes the deformation | transformation of a glass blank rather than the method shown to said (B), ie, the center part vicinity of the glass blank, and the center part of an upper mold | type press surface. The adhesive force with the vicinity can be reduced more effectively. Therefore, in the glass blank manufacturing method of the present embodiment, it is easy to further improve the flatness of the glass blank. In addition, when implementing the manufacturing method of the glass blank of this embodiment, in order to improve planarity still more, it combines with the method shown to said (A) and the method shown to (B) as needed. You may implement.

  In the manufacturing method of the glass blank of the present embodiment, the temperature in the vicinity of the center portion of the upper die press surface is lower than the temperature in other regions of the upper die press surface immediately before the press step. Here, the upper die press surface is used as the upper die so that “the temperature near the center of the upper die press surface is lower than the temperature of the other regions of the upper die press surface immediately before the press process”. An upper die is used in which the planar shape of the inner wall surface on the press surface side is substantially circular and a cavity for flowing a cooling medium is provided. A more specific structure of the upper mold will be described later.

  In addition, the state where the temperature near the center of the upper die press surface is lower than the temperature of other regions of the upper die press surface means that the temperature profile in the diametric direction of the press surface is from the outer edge side to the center side. It means a state in which the temperature is lowered (concave profile) as it goes to. On the other hand, in the conventional upper mold used in the conventional method of manufacturing a glass blank, the temperature profile in the diameter direction of the press surface immediately before the pressing process is performed is a convex profile opposite to the above concave profile, Alternatively, it is a substantially flat profile (flat profile). For reference, the term “conventional upper die” refers to the inner side of the upper die press surface, such as the upper die shown in FIG. 6 upper part of Patent Literature 5 and the upper die shown in FIG. Is provided with a cavity for flowing a gas such as air or a cooling gas in which water particles are spray-dispersed in the gas, and the entire inner wall surface on the press surface side of the cavity is opposed to the entire press surface. The upper die has an inner diameter in the range of 80% to 110% in the direction parallel to the pressing surface of the cavity when the outer diameter of the glass blank to be press-formed is set as a reference (100%). Means.

In addition, it is more preferable that the concave profile mentioned above satisfy | fills the following Formula (1) and (2). Thereby, only the central part vicinity of a press surface can be cooled more selectively and efficiently. As a result, the cause of the deformation of the glass blank, that is, the adhesive force between the vicinity of the central portion of the glass blank and the vicinity of the central portion of the upper press surface can be more effectively reduced. Therefore, when a glass blank is manufactured on the conditions which satisfy | fill following Formula (1) and (2), the planarity of a glass blank can be improved further.
Formula (1) Tg−200 ≦ Tc <Te ≦ Tg + 50
Formula (2) 0.5 ≦ ΔT ≦ 6
In the formula (1) and the formula (2), Tc is a disk in a state in which it is assumed that the softened glass is almost isotropically spread on the lower die press surface by press molding to form a disk shape. This represents the temperature (° C.) immediately before press molding at the upper die press surface at the position corresponding to the center point of the glass that has finished spreading in a shape, and Te is the position corresponding to the outermost periphery of the glass that has finished spreading into a disk shape. Tg represents the glass transition temperature (° C) of the glass immediately before press molding on the die press surface, and ΔT is an intermediate point between the center point and the outermost periphery of the glass that has finished spreading in a disk shape. It represents the temperature gradient (° C./mm) immediately before press molding on the press surface at the corresponding position.

  Here, Tc, Te, and ΔT shown in the expressions (1) and (2) will be described more specifically with reference to the drawings. FIG. 1 is an explanatory diagram for explaining Tc, Te and ΔT. Here, the upper part of FIG. 1 is a graph showing an example of a profile of the surface temperature change of the press surface with respect to the diameter direction of the upper die press surface immediately before press molding. Moreover, the lower stage of FIG. 1 shows an example of the cross-sectional shape in the diameter direction of the glass that has finished spreading into a disk shape by pressing, and the position in the diameter direction of the glass 1 that has finished spreading into the disk shape shown in the lower stage of FIG. It is explanatory drawing explaining the correspondence with the horizontal axis of the graph shown to the upper stage of FIG. In the example shown in FIG. 1, the temperature profile of the upper die press surface immediately before press molding is represented by a concave curve indicating the minimum temperature Tc at the center point and the maximum temperature Te at the outermost periphery. In addition, the temperature gradient ΔT means the inclination of the tangent line at the intermediate point of the temperature profile more precisely.

  Here, as shown in Formula (1), Tc is preferably a temperature in a range of Tg−200 ° C. or higher and lower than Te ° C. By making Tc Tg−200 ° C. or more, although it depends on the contact time with the glass during pressing, it is possible to suppress cracking of the glass blank due to overcooling. Further, by setting Tc to less than Te, it is possible to realize a temperature distribution (concave profile) in which the temperature in the vicinity of the center portion of the press surface as illustrated in FIG. 1 is low and the temperature on the outer edge side is high. In addition, it is preferable that it is Tg-150 degreeC or more, and, as for the lower limit of Tc, it is more preferable that it is Tg-120 degreeC or more. Further, the difference between Tc and Te (Te−Tc) ° C. is not particularly limited as long as it exceeds 0 ° C., but at least the temperature gradient ΔT is a value that can satisfy the formula (2), and press molding It is necessary that the temperature in the vicinity of the center portion of the subsequent glass blank does not become lower than other portions. Considering this point, Te-Tc is practically preferably 5 ° C. or higher and 150 ° C. or lower, more preferably 10 ° C. or higher and 100 ° C. or lower. Moreover, as shown in Formula (1), the upper limit of Te needs to be Tg + 50 degrees C or less. By making Te within the above range, it is possible to suppress the fusion of the glass during pressing. The upper limit of Te is preferably Tg + 40 ° C. or less, and more preferably Tg + 20 ° C. or less.

  Furthermore, as shown in Formula (2), ΔT is preferably 0.5 ° C./mm or more, and more preferably 1 ° C./mm or more. By setting ΔT to 0.5 ° C./mm or more, as illustrated in FIG. 1, the temperature distribution in the diameter direction of the press surface can be a concave profile. In addition to this, an appropriate temperature difference is obtained between the center portion of the press surface of the upper die and the outer edge side. For this reason, it is possible to selectively and efficiently cool only the vicinity of the center portion of the upper die press surface.

  On the other hand, the upper limit value of ΔT is practically preferably 6 ° C./mm or less, more preferably 3 ° C./mm or less. By setting ΔT to 6 ° C / mm or less, the temperature of the center part of the upper die press surface becomes unnecessarily low, which causes a decrease in stretchability of the glass during pressing and cracks / cracks in the glass blank. Or the temperature on the outer edge side becomes excessively higher than necessary, so that it is possible to reliably prevent the glass blank and the upper mold from fusing at the time of pressing, or the flatness to be worsened due to the increase in the adhesive strength of the outer edge part. .

  It is preferable that the concave temperature distribution on the upper press surface immediately before press molding is as isotropic as possible starting from the center of the upper press surface. From such a viewpoint, the temperature variation in the press surface of Te is preferably ± 2 ° C. or less, and the temperature variation in the press surface of ΔT is preferably ± 0.2 ° C./mm or less.

  As explained above, a glass blank having high flatness can be obtained by using the method for producing a glass blank of the present embodiment and using the warp correction press method in combination after pressing. However, the manufacturing method of the glass blank of this embodiment is more preferably applied when producing a thin glass blank having a smaller ratio of thickness t to diameter d (aspect ratio t / d). The reason is as follows. That is, in a low-aspect-ratio glass blank, the rigidity of the glass blank that is easily deformed immediately after pressing is low. For this reason, in the conventional method for manufacturing a glass blank, it is difficult to avoid deterioration in flatness as the aspect ratio t / d decreases. On the other hand, in the manufacturing method of the glass blank of this embodiment, even if the rigidity reduction which accelerates | stimulates a deformation | transformation of a glass blank occurs because the aspect ratio t / d falls, the root cause which causes a deformation | transformation of a glass blank. That is, the glass blank in a state of being in contact with the upper mold press surface immediately after pressing, and not only reducing the adhesive force in the vicinity of the center of the upper mold press surface, but also the radial temperature difference between the glass blank immediately after pressing Can be reduced. For this reason, in the manufacturing method of the glass blank of this embodiment, even if aspect ratio t / d becomes small, flatness does not deteriorate easily.

  Considering this point, the aspect ratio of the glass blank produced by the glass blank production method of the present embodiment is preferably 0.015 or less, and more preferably 0.014 or less. On the other hand, the lower limit of the aspect ratio is not particularly limited, but is practically preferably 0.01 or more. Thus, for example, if the glass blank is used for producing a 2.5-inch substrate (the diameter is approximately in the range of about 69.0 mm ± 3.0 mm), the thickness corresponding to the aspect ratio of 0.015 is about 1.04 mm. The thickness corresponding to an aspect ratio of 0.01 is about 0.69 mm.

  The aspect ratio of the glass blank is expressed as the ratio (t / d) of the thickness t to the diameter d (mm) of the glass blank. Here, the glass blank includes not only a disk-shaped substrate whose entire surface is flat, but also a glass blank partially provided with a thick portion. In a glass blank partially having such a thick part, the thickness t of the glass blank for defining the aspect ratio is based on the thickness of the thin part. Hereinafter, the definition of the aspect ratio will be described more specifically with reference to the drawings. 2-4 is explanatory drawing for demonstrating the definition of the aspect-ratio in the example of the glass blank manufactured using the manufacturing method of the glass blank of this embodiment. Here, FIG. 2 is a cross-sectional view in the diameter direction of the glass blank 2 composed of only the disk-shaped thin portion 10, and FIG. 3 shows the disk-shaped thin portion 10 and the center in the diameter direction of the thin portion 10. FIG. 4 is a sectional view in the diametrical direction of a glass blank 3 composed of a disk-shaped thick part 12 provided so as to be convex on one side of the thin part 10. FIG. And a diametrical cross-sectional view of the glass blank 4 comprising a ring-shaped thick portion 14 provided so as to be convex on one surface of the thin portion 10 at the peripheral portion in the diameter direction of the thin portion 10. As illustrated in FIGS. 2 to 4, the “aspect ratio” in the present specification refers to the maximum diameter (diameter d) and the thin wall of the glass blanks 2, 3, 4 regardless of the presence or absence of the thick portions 12, 14. The value calculated | required on the basis of the thickness t of the part 10 is meant.

  In addition, the glass blank produced using the manufacturing method of the glass blank of this embodiment may be a perfect flat plate-like thing which does not have a thick part as FIG. 2 shows, As shown in an example in FIG. 4, a part having a thick part may be used. In the example shown in FIG. 4, the thick portion 14 is provided so as to protrude only on one side of the thin portion 10. However, the glass blank produced using the glass blank manufacturing method of the present embodiment may be provided so that the thick portion 14 is convex on both surfaces of the thin portion 10.

  In the direct press method, as illustrated in FIG. 5, as the mold used in the pressing process, in addition to the upper mold 20 and the lower mold 22 used for forming both surfaces of the glass blank, a softened state is applied during pressing. In order to restrict the stretching of the glass lump 26 in the press surface direction, the body mold 24 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 the barrel die 24 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 24. 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 26 supplied on the press surface of the lower die 22 slightly varies, the distance between the press surfaces of the upper die 20 and the lower die 22 is kept constant during pressing, In the example shown in FIG. 4, the capacity fluctuation of the glass lump 20 can be absorbed by the thickness fluctuation of the thick portion 14 provided on the outer peripheral side of the glass blank 4, and in the example shown in FIGS. 3 can be absorbed by fluctuations in the outer diameter. 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. Note that the upper die 20 shown in FIG. 5 is shown for explaining the non-side free press method, and does not explain the upper die of this embodiment described later.

  Next, the typical example of the manufacturing method of the glass blank of 1st 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. In addition, the temperature of a lower mold | type is adjusted in the range with which the said Formula (1) is satisfy | filled so that the glass blank obtained may not be broken by overcooling a glass lump. In addition, if necessary, heat-resistant solid lubricant powder such as boron nitride (BN) powder is attached to the lower press surface in advance in order to improve the lubricity of the molten glass to be cast. You may leave it.

  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 temperature of the upper die is adjusted so as to satisfy the equations (1) and (2), and the temperature of the lower die press surface is adjusted within a range of 350 to 650 ° C. The upper mold temperature can be set in the range of the lower mold temperature to [lower mold temperature−150 ° C.] within a range satisfying the expressions (1) and (2). 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 for take-out (removal). 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 adsorbing 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 a glass blank can be obtained through such a series of processes.

-Glass composition-
Although it can select suitably according to the board | substrate and information recording medium which are produced using this as a glass composition of the glass blank produced by the manufacturing method of the glass blank of this embodiment, For example, aluminosilicate glass, soda lime glass Soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, and the like. 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.

(Upper mold for glass press)
In the upper mold for glass press (upper mold) used in the method for producing a glass blank of the present embodiment, the temperature in the vicinity of the center of the upper mold press surface is in the other area of the upper mold press surface immediately before the press process is performed. The structure is not particularly limited as long as it can be controlled lower than the temperature. However, as the upper mold used in the method for manufacturing the glass blank of the present embodiment, it is easier to realize a temperature profile that satisfies the expressions (1) and (2). The upper mold of the embodiment is particularly suitable.

  That is, the upper die of this embodiment is a columnar body portion having a press surface for press-molding the softened glass between the upper die and the inside of the body portion, and is close to the press surface. A cavity portion provided at a position where the inner diameter in the direction parallel to the press surface of the cavity portion is 80% or more of the outer diameter of the glass blank to be press-formed, and the cavity portion in the axial direction of the body portion The distance between the inner wall surface on the press surface side and the press surface (hereinafter sometimes referred to as “bottom wall thickness”) has a structure that is minimized at the center portion of the press surface. Here, the “outer diameter of the glass blank to be press-molded” is 65 to 71 mm for a glass blank used for manufacturing a 2.5-inch substrate and 27 for a glass blank used for manufacturing a 1.0-inch substrate. 4 to 30 mm. These values are typical values (representative values), and the outer diameter of the glass blank actually manufactured by the glass blank manufacturing method of the present embodiment is limited to the above values only. It is not something.

  In the upper mold of the present embodiment, the inner diameter D (in) of the cavity is slightly smaller than the outer diameter of the glass blank to be press-formed as described above, that is, 80% of the outer diameter of the glass blank to be press-formed. It is necessary to set it above, and it is preferable to set it to 85% or more.

  By setting the inner diameter D (in) of the hollow portion to 80% or more of the outer diameter of the glass blank to be press-formed, substantially the region of the upper die press surface that is in contact with the glass blank is substantially pressed. The entire surface is forcibly cooled. For this reason, the upper mold of this embodiment is a deformation of the glass blank due to an increase in adhesive force between the peripheral edge of the glass blank and the peripheral edge of the upper press surface due to insufficient cooling power on the peripheral edge of the upper mold press surface. It is easy to prevent sticking between the upper mold and the glass blank. In addition, the bottom wall thickness is minimal at the center of the upper press surface. Therefore, even when the upper die press surface is heated by heat exchange with the glass blank during pressing, the vicinity of the central portion of the upper die press surface is more efficiently and intensively cooled than the peripheral portion. Therefore, immediately after the upper mold and the glass blank are separated from each other, that is, by heat exchange with the glass blank, the temperature profile in the state where the upper mold press surface is most heated temporarily becomes a flat profile or a convex profile. However, the temperature profile of the upper die press surface can be a concave profile until immediately before the next pressing step. On the other hand, the upper limit of the outer diameter of the glass blank for press-molding the inner diameter D (in) of the cavity is not particularly limited, but is preferably 110% or less from a practical viewpoint.

  Note that the bottom wall thickness (that is, the minimum bottom wall thickness) at the center of the upper mold press surface is such that the temperature profile of the upper mold press surface can be a concave profile immediately before the press process is performed, and is continuous. From the viewpoint of ensuring strength that can avoid deformation and breakage of the upper die press surface by pressing, 10 mm to 20 mm is preferable, and 12 mm to 18 mm is more preferable. Moreover, it is preferable that the inner diameter D (in) of the hollow portion is 60% or less of the outer diameter D (out) of the body portion. In this case, since the thickness of the outer peripheral wall constituting the body portion can be ensured, the strength of the upper mold can be ensured.

  In the present specification, “inner diameter D (in)” means the diameter of the cavity when the cross-sectional shape in the direction parallel to the press surface of the cavity is circular, and the direction parallel to the press surface of the cavity When the cross-sectional shape is a substantially circular shape or a polygonal shape close to a circular shape, it means the diameter of a circle having the same area as the cross-section of the hollow portion (equivalent circular area diameter). The “outer diameter D (out)” means the diameter of the body part when the cross-sectional shape in the direction parallel to the press surface of the body part is circular, and the cross-sectional shape in the direction parallel to the press surface of the body part. Is a substantially circular shape or a polygonal shape close to a circular shape, it means the diameter of a circle having the same area as the cross section of the body portion (equivalent diameter of a circular area).

  Here, in the axial direction of the body portion, as a specific configuration for minimizing the distance between the inner wall surface on the upper press surface side of the cavity and the upper press surface at the center portion of the press surface (1) A configuration in which a concave portion is provided on the inner wall surface on the press surface side of the cavity portion at a position corresponding to the vicinity of the center portion of the press surface, or (2) an inner wall surface on the press surface side of the cavity portion is pressed. The structure made into the curved surface curved so that it may become depressed on the surface side is mentioned.

  FIG. 6 is a schematic cross-sectional view showing an example of the upper die of this embodiment. Specifically, a recess is provided on the inner wall surface on the press surface side of the cavity portion corresponding to the vicinity of the center portion of the press surface. It shows about the upper mold | type which has the structure comprised. The upper die 30 shown in FIG. 6 includes a cylindrical or prismatic body portion 42 having a press surface 40, a hollow portion 44 provided in a position close to the press surface 40 inside the body portion 42, It has. Of the inner wall 46 on the press surface 40 side of the cavity 44, the disk-shaped inner wall 46 </ b> A at a position corresponding to the vicinity of the center of the press surface 40 corresponds to a region other than the vicinity of the center of the press surface 40. It is recessed toward the pressing surface 40 side from the ring-shaped inner wall surface 46 </ b> B at the position to be a disk-shaped concave portion 48. That is, the distance (bottom wall thickness) between the press surface 40 and the inner wall surface 46 on the press surface side of the cavity 44 in the axial direction of the body portion 42 (a straight line indicated by a one-dot chain line in the drawing) It is minimal at the center of the surface 40. Here, the bottom thickness Ta corresponding to the distance between the inner wall surface 46A and the press surface 40 (that is, the minimum bottom thickness) is preferably within the above-described range. Further, the ratio (Ta / Tb) between the bottom wall thickness Tb corresponding to the distance between the inner wall surface 46B and the press surface 40 and the bottom wall thickness Ta (Ta / Tb) is preferably within a range of 12 mm to 22 mm, and 14 mm to 20 mm. Within the range is more preferable. By setting Ta / Tb within the above range, a concave profile can be easily formed. Moreover, the internal diameter D (in) in the direction parallel to the press surface 40 of the cavity part 44 is set to 80% or more of the outer diameter of the glass blank to press-mold as mentioned above. Further, the upper side of the hollow portion 44 is partitioned by a pair of partition members 50R and 50L. In the drawing, the partition member 50R and the partition member 50L are depicted as separate members, but may be a cross section of one pipe, for example. That is, it can be set as the structure by which the cylindrical member was formed by the partition members 50R and 50L, and the hole penetrated the center was formed.

  Then, by arranging the partition members 50R and 50L above the cavity portion 44, the space above the cavity portion 44 is a space formed between the right inner wall surface of the cavity portion 44 and the partition member 50R ( (Right outer peripheral flow path), a space formed between the left inner wall surface of the cavity 44 and the partition member 50L (left outer peripheral flow path), and a space formed between the pair of partition members 50R and 50L ( It is divided into three (central flow path). During continuous pressing, for example, as indicated by an arrow F in the figure, the cooling medium passes from the upper side to the lower side of the central flow path, and the bottom surface side of the cavity portion 44 is located near the central portion of the inner wall surface 46. It is possible to flow from the side to the outer peripheral side, and to move the right outer peripheral side channel and the left outer peripheral side channel from the lower side to the upper side. The flow of the cooling medium may be in the opposite direction. Further, the right outer peripheral channel and the left outer peripheral channel may be independent channels, but they may be connected to form an integral ring-shaped channel.

  FIG. 7 is a schematic cross-sectional view showing another example of the upper die of the present embodiment. Specifically, a cavity is formed on the inner wall surface on the press surface side of the cavity portion corresponding to the vicinity of the center portion of the press surface. It shows about the upper mold | type which has the structure which made the inner wall surface by the side of the press surface of a part the curved surface curved so that it might become depressed at the press surface side. Here, in FIG. 7, parts having substantially the same functions and configurations as those shown in FIG. The upper die 32 shown in FIG. 7 has basically the same structure as the upper die 30 shown in FIG. 6, but the inner wall surface 46 is closer to the press surface 40 than the upper die 30 shown in FIG. It is different in that it is a curved surface curved so as to be depressed. Further, the curved inner wall surface 46 has a dome shape, and the bottom wall thickness is set to be minimal at the center portion of the press surface 40. Here, the ratio (Tmin / Tmax) between the bottom wall thickness Tmin at the center of the press surface 40 and the bottom wall thickness Tmax at the position corresponding to the outermost side of the inner wall surface 46 is in the range of 0.4 to 0.95. The inside is preferable, and the range of 0.5 to 0.9 is more preferable. By setting Tmin / Tmax within the above range, a concave profile can be easily formed.

  In both of the upper molds 30 and 32 of the present embodiment shown in FIGS. 6 and 7, the temperature profile of the press surface can be a concave profile immediately before the press process is performed. However, the size and shape of each part of the upper molds 30 and 32, particularly the relative ratio of the inner diameter D (in) of the hollow portion to the outer diameter D (out) of the body portion 42, the cross-sectional shape of the inner wall surface 46, the bottom meat By adjusting the thickness and the like, the shape of the concave profile can be controlled to a desired shape.

  FIG. 8 is a graph showing an example of a temperature distribution with respect to the diameter direction of the upper die press surface immediately before press molding when a glass blank is manufactured using the upper die of this embodiment. In the figure, the vertical axis and the horizontal axis are the same as those shown in FIG. 1, and the description of the glass blank 1 corresponding to the horizontal axis is omitted. In the graph of FIG. 8, two types of concave profiles indicated by reference signs A and B are shown as temperature profiles. The temperature profile A is a concave profile in which the temperature gradually decreases as it approaches the vicinity of the center of the press surface corresponding to the vicinity of the center point in the graph, whereas the temperature profile B increases as it approaches the vicinity of the center of the press surface. It is a concave profile in which the temperature rapidly decreases. Whether the temperature profile A or the temperature profile B is selected as the shape of the temperature profile immediately before the pressing process is performed depends on the diameter and cross-sectional shape of the glass blank to be manufactured, the temperature of the softened glass at the time of pressing, etc. Can be selected as appropriate. However, when the vicinity of the central portion of the upper press surface is more easily heated at the time of pressing, for example, when the diameter of the glass blank to be produced is larger, or a glass blank having a thick portion 12 at the central portion as shown in FIG. When producing 3, it is preferable to select the temperature profile B. In many other cases, it is preferable to select the temperature profile A.

  Here, when it is desired to control the shape of the temperature profile just before the pressing step as in the temperature profile A, it is preferable to use the upper mold 32 of the present embodiment of the type illustrated in FIG. In this case, the difference between the maximum temperature and the minimum temperature in the temperature profile A can be in the range of about 5 ° C to 40 ° C. On the other hand, when it is desired to control the shape of the temperature profile immediately before the pressing process as in the temperature profile B, it is preferable to use the upper mold 30 of the present embodiment of the type illustrated in FIG. In this case, the difference between the maximum temperature and the minimum temperature in the temperature profile B can be in the range of about 20 ° C to 60 ° C.

  In addition, the upper mold | types 30 and 32 of this embodiment cool the press surface 40 heated at the time of a press by flowing a cooling medium in the cavity part 44. FIG. Here, as the cooling medium, the cooling effect is very high, and the temperature in the vicinity of the center portion of the upper die press surface can be controlled to be lower than the temperature of other regions of the upper die press surface immediately before the press process. From an easy viewpoint, it is particularly preferable to use a liquid such as water. Even when a gas such as air or a gaseous cooling medium having a high cooling effect in which water particles having a high specific heat are dispersed in a gas such as air is used as the cooling medium, the specific heat of the cooling medium is too small. For this reason, it is difficult to control the temperature in the vicinity of the center portion of the upper die press surface to be lower than the temperature in other regions of the upper die press surface immediately before the press process.

  Here, as the cooling liquid, it is preferable to use a liquid having a specific heat at 20 ° C. of 0.6 cal / g · ° C. to 1.2 cal / g · ° C. By controlling the temperature near the center of the upper die press surface immediately before the pressing step by controlling the specific heat to be 0.6 cal / g · ° C. or lower than the temperature of other regions of the upper die press surface, A sufficient cooling effect can be obtained. In addition, from a practical viewpoint such as material availability, the specific heat is preferably set to 1.2 cal / g · ° C. or less as described above. A typical example of the cooling liquid having such specific heat is water (specific heat at 20 ° C. = 1.0 cal / g · ° C.). A mixed solution in which an organic solvent is mixed can also be used. In adjusting these mixed liquids, the material type and the mixing ratio are appropriately selected so that the specific heat of the mixed liquid is within the above range.

(Press molding equipment)
Considering the points described above, it is preferable that the press molding apparatus of the present embodiment includes the above-described upper mold of the present embodiment. More specifically, the press molding apparatus of this embodiment is arranged so as to face the lower mold and the lower mold, and is relatively movable in a direction approaching and separating from the lower mold. It is particularly preferable that the upper mold is used as an upper mold.

  The configuration other than the upper mold of the press molding apparatus of the present embodiment can be adopted by appropriately combining known configurations. For example, the press molding apparatus according to the present embodiment includes one upper mold and a plurality of lower molds according to the present embodiment each having a press surface for press-molding a predetermined volume of molten glass, and a spindle serving as a rotation center. A circular rotary table in which the lower molds are arranged on the peripheral edge at equal intervals and 360 degrees is divided by the number of the lower molds, and is rotated and stopped in one direction at every rotation angle, and a molten glass supply source A glass supply means for cutting molten glass continuously flowing out from a nozzle connected to a predetermined volume and supplying the molten glass onto a lower press surface that stops at any one stop position of the rotary table; With respect to one stop position, it is opposed to the lower die press surface that stops at the stop position downstream in the rotation direction of the turntable and is movable in the vertical direction, and is positioned on the lower die press surface. Molten glass The upper die having a pressing surface that is pressed into a substantially plate shape, and one or more stop positions on the basis of the stop position where the upper die is disposed, and on the downstream side in the rotation direction of the rotary table It can be set as the structure provided with the taking-out means which takes out the substantially plate-shaped glass (glass blank) located on the lower die press surface of the stop position located.

  Furthermore, if necessary, before supplying molten glass to the lower mold press surface, solid lubricant powder spraying means for attaching a heat-resistant solid lubricant powder such as BN onto the lower mold press surface, press Other mechanisms and means may be provided such as a warp correction means comprising a plate member for press used for correcting the warpage of the glass that has become substantially plate-like later. In addition, the number of the lower mold | types arrange | positioned at a rotary table is four processes which must be implemented at least when producing a glass blank; That is, (1) Molten glass is supplied on the press surface of a lower mold | type. A glass supplying step, (2) a pressing step of pressing the softened glass supplied on the pressing surface of the lower die with the upper die and the lower die, and (3) a glass substantially plate-shaped by pressing on the lower die. In the process of transporting together with the lower mold from the stop position for pressing to the stop position for taking out in the state of being placed on, soaking / cooling process for cooling while soaking using natural cooling or forced cooling, And (4) in the sense that it corresponds to the step of taking out the substantially plate-shaped glass (glass blank) that has been soaked and cooled on the press surface of the lower die from the lower die using vacuum adsorption or the like. There should be at least four. However, considering the securing of the cooling period of the glass that has become a substantially plate shape from the press molding to the removal, and the securing of the remaining heat time of the lower mold press surface before press molding, the number of lower molds is practically About 6 or more and 30 or less are preferable.

  The material of the lower mold and the upper mold is preferably a material having heat resistance and high thermal conductivity. Examples of such materials include graphite, tungsten alloys, nitrides, carbides, refractory metals, and the like, and cast iron is particularly preferable from the viewpoint of being inexpensive and easy to process and having sufficient strength and durability.

(Method for manufacturing substrate for information recording medium)
About the glass blank produced by the manufacturing method of the glass blank of this embodiment mentioned above, the board | substrate for information recording media can be produced at least through the grinding | polishing and grinding | polishing process of grinding and grind | polishing at least one surface of this glass blank. . Moreover, when the glass which comprises a glass blank has a glass composition which can be crystallized by heat processing, the crystallizing process crystallized by heating a glass blank other than the said process can also be combined. As typical examples of manufacturing the information recording medium substrate, for example, (1) a first lapping step, (2) a cutting step (coring, forming), (3) an end surface grinding step, (4) a second The lapping step, (5) end surface polishing 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.

(1) First lapping step In the first lapping step, a disk-shaped glass base plate is obtained by lapping both main surfaces of the glass blank. 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, the main surface can be mirror-polished using a soft foam 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 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, you may make it 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 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)
For the evaluation, 16 lower dies are arranged at equal intervals along the outer peripheral edge, and a press equipped with a rotary table that rotates while repeatedly moving and stopping every 22.5 degrees in one direction at the time of pressing. A device was used. Further, when 16 lower mold stop positions corresponding to the 16 lower molds arranged on the outer peripheral edge of the rotary table are numbered P1 to P16 along the rotation direction of the rotary table, The following members are respectively arranged on the lower die press surface or the lower die side at the following lower die stop position.
Lower mold stop position P1: Glass supply means Lower mold stop position P2: Upper mold Lower mold stop position P4: Upper mold for warping correction press Lower mold stop position P12: Extraction means (vacuum suction device)

  Further, when the lower mold moves to the stop positions P2 to P12, a soaking / cooling step is performed, and when moving to the stop positions P12 to P16, the lower mold is preheated using a heater. .

(Upper type)
For the evaluation, the following lower mold was used.
-Upper mold A1-
As the upper mold A1, an upper mold made of cast iron having the shape shown in FIG. 6 was prepared. The main dimensions of each part are as follows.
-Outer diameter D (out) of the body part 42 = 120 mm
-Inner diameter D (in) of cavity 44 = 66 mm
D (in) / outer diameter of the glass blank to be formed (71 mm) = 93%
-Diameter D (h) of recess 48 = 15 mm
・ Bottom thickness Ta = 13mm on the inner wall surface 46A
-Bottom wall thickness Tb = 18mm on the inner wall surface 46B
・ Ta / Tb = 0.72

  In the test, water around room temperature (22 ° C.) was used as the cooling liquid and the hollow portion 44 was flowed in the direction of arrow F. In the test, the flow rate of the cooling liquid and the preheating of the upper die before the press were controlled so that the temperature profile of the press surface immediately before pressing was as shown in Table 1.

-Upper mold A2-
The upper mold A2 was prepared by changing the following dimensions with respect to the upper mold A1. Except for this change, the upper mold A2 is the same as the upper mold A1.
-Inner diameter D (in) of cavity 44 = 58 mm
D (in) / outer diameter of the glass blank to be formed (71 mm) = 82%

-Upper mold A3-
The upper mold A3 was prepared by changing the following dimensions with respect to the upper mold A1. Except for this change, the upper mold A3 is the same as the upper mold A1.
-Inner diameter D (in) of the cavity 44 = 76 mm
D (in) / outer diameter of the glass blank to be formed (71 mm) = 107%

-Upper mold A4-
The upper mold A4 was prepared by changing the following dimensions with respect to the upper mold A1. Except for this change, the upper mold A4 is the same as the upper mold A1.
・ Bottom wall thickness Ta = 12mm on the inner wall surface 46A
-Bottom wall thickness Tb = 20mm on the inner wall surface 46B
・ Ta / Tb = 0.6

-Upper mold A5-
The upper mold A5 was prepared by changing the following dimensions with respect to the upper mold A1. Except for this change, the upper mold A5 is the same as the upper mold A1.
-Diameter D (h) of the recess 48 = 20 mm

-Upper mold B1-
As the upper mold B1, an upper mold made of cast iron having the shape shown in FIG. 7 was prepared. The main dimensions of each part are as follows.
-Outer diameter D (out) of the body part 42 = 120 mm
-Inner diameter D (in) of cavity 44 = 66 mm
D (in) / outer diameter of glass blank (71 mm) = 93%
-Curvature radius of inner wall surface = 140 mm
-Minimum bottom wall thickness Tmin of the inner wall surface 46 (wall thickness at the center of the inner wall surface) = 13 mm
・ Maximum bottom wall thickness Tmax of inner wall surface 46 (thickness of inner wall outermost surface) = 21 mm

-Upper mold C1-
The upper mold C1 was prepared by changing the following dimensions with respect to the upper mold A1. Except for this change, the upper die C1 is the same as the upper die A1.
-Inner diameter D (in) of the cavity 44 = 53 mm
D (in) / outer diameter of glass blank to be formed (71 mm) = 75%

-Upper mold D1-
As the upper mold D1, an upper mold made of cast iron having the shape shown in FIG. 10 was prepared. The main dimensions of each part are as follows. FIG. 10 is a schematic cross-sectional view showing an example of a conventional upper mold. The upper mold 100 shown in FIG. 10 has the same configuration as the upper mold 30 shown in FIG. It is what has. In the figure, members having the same functions and structures as those shown in FIG. 6 are denoted by the same reference numerals.
-Outer diameter D (out) of the body part 42 = 120 mm
-Inner diameter D (in) of cavity 44 = 66 mm
D (in) / outer diameter of glass blank (71 mm) = 93%
・ Bottom thickness T = 18mm on the inner wall 46

  In the test, water around room temperature (22 ° C.) or a gas at room temperature (22 ° C.) in which water particles are spray-dispersed in air is used as a cooling medium in the direction of arrow F. Washed away. In the test, the flow rate of the cooling medium and the upper mold before pressing so that the temperature at the center of the press surface (temperature Tc at the position corresponding to the center point in FIG. 1) becomes the temperature shown in Table 1. Controlled preheating.

-Lower mold and upper mold for warping correction press-
The lower mold and the upper mold for warp correction press used in all the experimental examples to be described later have the same structure as the upper mold made of cast iron shown in FIG. In the test, a gas at room temperature (22 ° C.) in which water particles were sprayed and dispersed in air as a cooling medium was used to flow in the direction of arrow F through the cavity 44. The gas flow rate at this time was set to the same value in all the experimental examples.

(Experimental example 1)
A glass blank 2 having a cross-sectional shape shown in FIG. 2 is obtained by supplying molten glass obtained by melting aluminosilicate glass onto a press surface of a lower mold and then pressing the upper mold and the lower mold in a side-free manner. 1000 sheets having a thickness of t0.9 mm, a diameter of d71 mm, and t / d = 0.013) were produced. In producing the glass blank, the lower mold A1 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.)
・ Dispersion of solid lubricant powder on the lower press surface before pressing: None (no solid lubricant powder used)
・ Temperature of the upper die surface during pressing: 450 ℃ (in-plane average temperature)
・ Viscosity of molten glass put on the lower mold: 40 Pa · s
・ Press time (time to apply pressure to glass): 0.6 seconds ・ Material constituting upper die press surface: cast iron ・ Glass blank temperature when taking out glass blank from lower die: 520 ° C.
・ Glass blank leaving environment after take-out: normal temperature atmospheric environment

  In addition, when the temperature characteristics of the press surface of the upper die immediately before press molding (the upper die when waiting above the lower die stop position P2 for pressing) were measured using an infrared radiation thermometer, The temperature profile was as shown in Table 1. The pressing pressure during pressing was adjusted so that the target aspect ratio shown in Table 1 was obtained.

(Experimental Examples 2 to 10)
The target aspect ratio shown in Table 1 can be obtained by controlling the press pressure at the time of pressing after controlling the type of the lower die used and the temperature characteristics of the press surface of the upper die immediately before press molding to the state shown in Table 1. A glass blank was produced in the same manner as in Experimental Example 1 except that the glass blank was adjusted.

(Evaluation results)
Table 1 shows the results of the press test of each experimental example. In Table 1, Experimental Examples 1 to 8 correspond to examples of the glass blank manufacturing method of the present invention, and Experimental Examples 9 and 10 correspond to comparative examples of the glass blank manufacturing method of the present invention. Is. Experimental Examples 1 to 7 correspond to upper mold examples of the present invention, and Experimental Examples 8 to 10 correspond to upper mold comparative examples of the present invention.

-Flatness-
In addition, the flatness shown in Table 1 is the glass blank for a total of 1000 samples of 9001 to 10000 when a continuous 10,000-sheet press test is performed using the warp correction press method. 2 was evaluated by measuring the bulging height with respect to the reference surface formed outside by a surfcom (manufactured by Tokyo Seimitsu Co., Ltd.) in the diameter direction. In addition, the product whose bulge height from the reference surface exceeded 20 μm was counted as a defective product. The evaluation criteria are as follows.
A: No defective product is generated.
B: 1 to less than 5 defective products per 1000 sheets C: 6 to 10 defective products per 1000 sheets D: 10 to 100 defective products per 1000 sheets E: More than 100 defective products per 1000 sheets

1 Glass 2, 3, 4 glass blank 10 that has finished spreading into a disk shape 10 Thin portion 12, 14 Thick portion 20 Upper die 22 Lower die 24 Body die 26 Glass lump 30, 32 Upper die 40 Press surface 42 Body portion 44 Cavity Portions 46, 46A, 46B Inner wall surface 48 Recesses 50, 50R, 50L Partition member 100 Upper mold

Claims (10)

After supplying the softened glass to the center of the press surface of the lower die, at least through a pressing step of press-molding the softened glass between the upper die and the lower die, for the information recording medium substrate A glass blank is produced,
In an immediately preceding pressing step, the temperature of the vicinity of the center portion of the upper die press surface is rather low than the temperature of other regions of the upper die press surface,
The upper mold is
A columnar body having a press surface for press-molding the softened glass with the upper mold; and
A hollow portion provided in a position close to the press surface inside the body portion;
A partition member disposed in the space so as to form an outer peripheral side flow path and a central flow path in a space above the hollow portion;
With
The inner diameter in the direction parallel to the press surface of the cavity is 80% or more of the outer diameter of the glass blank to be press-molded,
In the axial direction of the body portion, the distance between the inner wall surface on the press surface side of the cavity portion and the press surface forms a minimum at the center portion of the press surface,
The press surface is a flat surface,
When carrying out continuous pressing, (1) the cooling medium is moved from the upper side to the lower side of the central flow path, and the bottom surface side of the hollow portion is moved from the vicinity of the central portion of the inner wall surface to the outer peripheral side. And the outer peripheral flow path is further moved from the lower side to the upper side, or (2) is moved in the direction opposite to the moving direction shown in (1) above . In the manufacturing method of the glass blank of Claim 1,
The manufacturing method of the glass blank characterized by the recessed part being provided in the inner wall surface by the side of the said press surface of the said cavity part of the position corresponding to the center part vicinity of the said press surface . In the manufacturing method of the glass blank of Claim 1,
An inner wall surface on the press surface side of the hollow portion is a curved surface curved so as to be recessed toward the press surface side . A columnar body having a press surface for press-molding the softened glass with the upper mold; and
A hollow portion provided in a position close to the press surface inside the body portion;
A partition member disposed in the space so as to form an outer peripheral side flow path and a central flow path in a space above the hollow portion;
With
The inner diameter in the direction parallel to the press surface of the cavity is 80% or more of the outer diameter of the glass blank to be press-molded,
In the axial direction of the body portion, the distance between the inner wall surface on the press surface side of the cavity portion and the press surface forms a minimum at the center portion of the press surface ,
The press surface is a flat surface,
When carrying out continuous pressing, (1) the cooling medium is moved from the upper side to the lower side of the central flow path, and the bottom surface side of the hollow portion is moved from the vicinity of the central portion of the inner wall surface to the outer peripheral side. And further moving the outer peripheral flow path from the lower side to the upper side, or (2) moving in the direction opposite to the moving direction shown in (1) above . In the upper mold for glass press according to claim 4 ,
An upper die for a glass press, wherein a concave portion is provided on an inner wall surface on the press surface side of the hollow portion at a position corresponding to the vicinity of the center portion of the press surface. In the upper mold for glass press according to claim 4 ,
An upper die for a glass press, wherein an inner wall surface on the press surface side of the hollow portion is a curved surface curved so as to be recessed toward the press surface side. With the lower mold,
An upper mold that is disposed opposite to the lower mold and is relatively movable in a direction approaching and separating from the lower mold;
Comprising at least
The upper mold is
A columnar body having a press surface for press-molding the softened glass with the upper mold; and
A hollow portion provided in a position close to the press surface inside the body portion;
A partition member disposed in the space so as to form an outer peripheral side flow path and a central flow path in a space above the hollow portion;
With
The inner diameter in the direction parallel to the press surface of the cavity is 80% or more of the outer diameter of the glass blank to be press-molded,
In the axial direction of the body portion, the distance between the inner wall surface on the press surface side of the cavity portion and the press surface forms a minimum at the center portion of the press surface,
The press surface is a flat surface,
When carrying out continuous pressing, (1) the cooling medium is moved from the upper side to the lower side of the central flow path, and the bottom surface side of the hollow portion is moved from the vicinity of the central portion of the inner wall surface to the outer peripheral side. Further, the outer peripheral side flow path is moved from the lower side to the upper side, or (2) is moved in the direction opposite to the moving direction shown in (1) above . A substrate for an information recording medium is produced through at least a grinding / polishing step of grinding / polishing at least one surface of a glass blank produced by the method for producing a glass blank according to any one of claims 1 to 3. A method for manufacturing a substrate for an information recording medium. In the manufacturing method of the board | substrate for information recording media of Claim 8 ,
A method for producing a substrate for an information recording medium, comprising a crystallization step of crystallizing the glass blank by heating. 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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