JP4834654B2 - Thin glass manufacturing method, glass molded product manufacturing apparatus, information recording medium glass substrate manufacturing method, optical component manufacturing method - Google Patents

Description

  The present invention is a method for producing a thin glass used for a substrate for a glass lens or an information recording medium by dividing a glass lump of a required volume from a continuously flowing molten glass and sequentially press-molding the formed glass lump. And a manufacturing apparatus. Furthermore, the present invention relates to a method for manufacturing an optical component or an information recording medium substrate by subjecting the thin glass to grinding and polishing. In particular, the present invention is a thin plate shape such as a substrate for information recording media or a glass blank that is thinner than the outer diameter, and this glass blank is ground and polished to form an optical lens, or information recording The present invention relates to a method for forming an information recording medium by forming an information recording layer on the surface of the substrate for a recording medium.

  There is known a method of obtaining a thin glass that is relatively thin and without bending by a method of directly press-molding from a molten glass using a mold (direct press method).

  The first method is the method disclosed in Japanese Patent Laid-Open No. 5-105458 (Patent Document 1). This method achieves symmetrical heat removal during press molding for some limited time in the direct press method, so that the molding surface and glass temperature are all almost equilibrated below the softening point of the glass. One of the characteristics is that the surface of the receiving molding (lower mold) and the surface of the opposing molding (upper mold) are heated to different predetermined temperatures for a substantial contact time with the molten glass.

  The second method is the method disclosed in Japanese Patent Laid-Open No. 10-236831 (Patent Document 2). This method ends press forming when the glass interior is at a temperature higher than the glass transition point, and the upper die is released, and the inside of the thin sheet glass is lower than the glass transition temperature (lower than the temperature during press molding). It is characterized by applying a press to correct the warp while

The third method is the method disclosed in Japanese Patent Application Laid-Open No. 2004-107098 (Patent Document 3). In this method, after the plate glass is taken out from the mold after press molding, when the glass temperature is below the yield point and exceeds the strain point, pressure is applied to the main surface of the plate glass, or One of the features is that the warp is corrected by applying pressure and annealing.
Japanese Patent Laid-Open No. 5-105458 Japanese Patent Laid-Open No. 10-236831 JP 2004-107098 A

  In the direct press method, after press forming, the sheet glass generally moves with the rotation of the rotary table while being placed on the lower mold, and when it reaches a predetermined position, it is taken out by a take-out device installed beside the rotary table. In general, only the plate-like glass is taken out from the lower mold by a method such as adsorption and transferred to a slow cooling apparatus in the next step. During this time (after the press is finished and the upper mold is released upwards, until the glass sheet is removed from the lower mold), the lower surface and the upper surface of the glass sheet are subjected to extremely different cooling conditions. In other words, the lower surface side has a relatively large heat capacity, and heat exchange is performed (by heat conduction) in a state of being in surface contact with a lower mold of metallic material (such as cast iron), while the upper surface side is Heat exchange is achieved by radiation into the air at about room temperature and heat transfer by convection. Therefore, immediately after pressing for a short time within the limited lower mold stop time, the inside of the plate glass considered to be still in the temperature range where plastic deformation can be solidified by cooling and thermally contracted. It is placed in different cooling conditions, and as a result, it becomes difficult to maintain the shape during pressing. In particular, when the molded shape is close to a thin plate shape having a small strength for maintaining the shape, the stress generated by the difference in cooling rate between the upper and lower surfaces hardly remains as internal stress and is easily released as deformation (warp, swell).

  Here, the lower surface of the glass sheet that is in surface contact with the lower mold, which has a large heat capacity and excellent thermal conductivity, can be cooled with a small temperature difference across the entire surface, making the upper mold separate The upper surface side after exposure is basically exposed to the atmosphere side, and the thinner the glass, the more sensitive it is to the effects of fluctuations in the outside air, including the air flow, and it is difficult to achieve uniform cooling.

  The method shown in Patent Document 1 is that the lower die relative to the upper die on the plate glass from when the glass block starts to contact the lower die until the press between the upper die and the lower die is completed. To eliminate the influence of "excessive contact time", the lower and upper molds are kept at different temperatures during pressing, and heat is removed symmetrically around the center of the glass sheet during pressing. It is said that no warping occurs. At the same time, it is necessary to press the plate glass for a time sufficient to remove sufficient heat from the plate glass. In Example 2, the pressure holding (pressing) time is from 1.35 seconds. 1.65 seconds, and in Examples 1 and 3, 1.5 seconds are indicated. When securing the press time of 1.5 seconds, considering the time required to move the lower die before and after pressing, the time required to stop, the time required to lower the upper die, etc., the number of pressable times per minute is about 25 sheets. However, there is a problem that this long press time becomes a limitation on the number of sheet glass produced per hour in the apparatus.

  In addition, in the press, it is stated that “press for a sufficient time until the temperature of the mold surface and the glass sheet are all below the softening point of the glass sheet and become almost equilibrated.” If the temperature is around the point, the upper and lower surfaces of the glass sheet are exposed to non-uniform cooling conditions, and warpage occurs again. Therefore, this method cannot be said to be a sufficient method as long as the press is continued until it is cooled to a temperature below the glass transition point (more preferably below the strain point) as a method for obtaining a flat glass having no warp. In that case, the pressing time is further increased, and the number of sheet glass produced per hour in the apparatus must be reduced accordingly.

  The method disclosed in Patent Document 2 is a method in which pressing for correcting warpage is performed when the glass sheet after pressing is at a temperature lower than that during pressing and in a temperature range higher than the glass transition point. However, as with pressing, the time during which heat exchange is possible due to contact with the upper die during warping correction pressing is extremely limited, and even if the flatness is improved once due to contact with the upper die, the glass transition point thereafter. It is inevitable that the sheet glass is cooled at a significantly different speed until the temperature reaches a temperature that cuts in the glass. Therefore, after pressing for a short time of less than about 0.5 seconds, as shown in Table 1 of paragraph 0041 of Patent Document 2, as compared with the case where no forced cooling operation is applied to the upper surface side of the sheet glass, However, it is difficult to make the amount of warpage stably less than 0.03 mm.

  The method disclosed in Patent Document 3 requires another step in order to improve the flatness in addition to the usual slow cooling (annealing) step after the plate-like glass is taken out from the mold. Therefore, it becomes a factor of increasing production cost, and if it is attempted to correct the warpage by forcibly applying heat at the time of annealing the glass sheet that has been cooled to near the strain point once warpage has occurred, surplus due to deformation When flattening the length, there is a problem that a phenomenon that cannot be removed as a small undulation is unavoidable.

  An object of the present invention is to provide a manufacturing method and an apparatus for manufacturing a thin glass molded product that can obtain a thin glass molded product with extremely small warpage without greatly reducing the number of production in the direct press method. And

  Furthermore, the present invention provides a method for producing a glass substrate for information recording medium using the thin glass molded article obtained by the production method of the present invention, and an information recording body using the glass substrate for information recording medium obtained by this production method. Further, the object of the present invention is to provide a method for producing an optical component using the thin glass obtained by the production method of the present invention.

The present invention for solving the above problems is as follows.
[1] A method for producing a thin glass by press-molding a molten glass lump supplied on a pressing lower mold forming surface with a forming surface of an upper pressing mold facing the lower pressing mold,
After the press molding, the upper die for pressing is removed from the press-molded product and then cooled on the press-molded product for at least a part of the period from when the press-molded product is taken out from the lower mold molding surface. A method for producing thin glass, wherein an upper die is placed to balance the cooling state of the upper and lower surfaces of the press-formed product.
[2] The manufacturing method according to [1], in which the cooling upper mold has the same curvature of the contact surface with the press-molded product as the curvature of the upper surface of the molded product.
[3] The manufacturing method according to [1], wherein the cooling upper die approximates at least one of a heat capacity, a surface area, a thermal conductivity characteristic, and a surface emissivity characteristic to a press lower die.
[4] The manufacturing method according to [1], wherein when the upper mold for cooling is placed on the press-molded product, the upper mold for cooling is preheated to substantially the same temperature as the lower mold for press.
[5] The molten glass lump is formed by dividing the molten glass flowing out into a predetermined volume, and is received on a lower mold forming surface for press that sequentially moves,
The press molding is stopped at a predetermined position where the upper die for pressing facing the lower die for pressing is installed, and is performed within a time range of the stop time of the lower die for pressing with the upper die for pressing. I,
Placement of the cooling upper die on the press-molded product is performed from the next stop position of the press molding to the stop position before the take-out position of the press-molded product,
The take-out of the press-molded product is performed after the temperature becomes below the glass yield point,
The press-molded product after taking out is the manufacturing method according to [1], which is gradually cooled.
[6] Intermittent stop at a predetermined indexing position-On the same circumference of the outer peripheral band on the rotating circular table, a lower die for pressing that is replaceable at equal intervals corresponding to the indexing position is arranged.
At the stop position of each lower mold of the above table, the position for receiving at least the broken glass lump, the position for press molding with the upper mold and the lower mold, the position for loading the preheated upper mold for cooling on the press molded product, and for cooling The position to remove the upper mold and the position to take out the press molded product on the lower mold can be set independently,
An upper die for pressing is provided at the press molding position,
It is equipped with a cooling upper die that is loaded on the press-molded product at a position where the cooling upper die is loaded and can be removed from the press-molded product at a position where the cooling upper die is removed. Glass manufacturing equipment.
[7] The manufacturing apparatus according to [6], wherein the upper mold for cooling is similar to the lower mold in at least one of heat capacity, surface area, thermal conductivity characteristics, and surface emissivity characteristics.
[8] The manufacturing apparatus according to [6], further including a heating device capable of setting the cooling upper mold to an arbitrary preheating temperature equal to or lower than a glass softening point.
[9] An information recording medium glass substrate obtained by grinding and polishing a main surface of a thin glass produced by the production method according to any one of [1] to [5]. A method for producing a glass substrate.
[10] An information recording body in which at least an information recording layer is formed on the main surface of the glass substrate for information recording medium manufactured by the manufacturing method according to [9].
[11] A method for producing an optical component, characterized in that an optical component is obtained by grinding and polishing a main surface of a thin glass produced by the production method according to any one of [1] to [5].

  In thin-walled glass molding, the most effective method for suppressing the occurrence of warping is to simulate the thin-walled glass to near the temperature range (near the strain point) where permanent deformation does not newly occur during the thin-glass cooling process. The present inventors considered that the both surfaces are cooled at a speed as close as possible while keeping the “thermally thin shape”. In the present invention, “a shape that is not thermally thin” means that the thin glass is encased in an object having a relatively large heat capacity and a high thermal conductivity in a state where the shape is restricted so that it cannot be deformed. As a result, the objective of slowly cooling the entire thin glass surface with almost no temperature difference can be realized relatively easily. Even if the outside of the encased object is exposed to relatively large thermal environmental fluctuations, the cooling rate difference between the small parts on both sides of the thin glass is suppressed, and there is almost no warping or residual stress, and the strain point Will be interrupted and will not be deformed even if exposed to non-uniform cooling conditions.

  According to the present invention, in the thin glass press molding by the direct press method, the heat treatment conventionally performed for correcting the warp is performed before or after the thin glass is removed from the lower mold and transferred to the slow cooling process. Therefore, it is possible to provide a molding method and an apparatus therefor for obtaining a thin glass with extremely small warpage. Furthermore, according to the present invention, the amount of heat of the molten glass can be used effectively, and the number of production per unit time is not sacrificed. Production of about 45 minutes is also possible.

Hereinafter, the present invention will be described more specifically.
The method for producing a thin glass of the present invention comprises a step of press-molding a molten glass lump supplied on a lower mold forming surface for pressing with a molding surface of an upper mold for pressing opposite to the lower mold for pressing to produce the thin glass. It is a manufacturing method. A method for producing thin glass by press-molding a molten glass lump supplied onto a lower mold surface for pressing with a molding surface of the upper mold for pressing opposed to the lower mold for pressing is a known method. It is.

  The present invention, in the above method, after removing the upper mold for pressing from the press-molded product after the press molding, at least a part of the period until the press-molded product is taken out from the lower mold molding surface for press, An upper die for cooling is placed on the press-formed product to balance the cooling state of the upper and lower surfaces of the press-formed product.

  A typical thin glass has a thickness ratio (thinnest part thickness / planar dimension) of the thinnest part (thinnest part) to planar dimension (for example, diameter in the case of a disk shape) of 1/50. The glass is as follows. In particular, the present invention is suitable for molding a glass having the ratio (thickness of the thinnest portion / planar dimension) of 1/10 or less. Although there is no restriction | limiting in particular in the lower limit of the said ratio, The said ratio is suitable for shaping | molding of the glass of 1/200 or more, and is further suitable for shaping | molding of glass of 1/100 or more. A typical example of such a material is a plate-like glass, and more specifically a disc-like glass.

  Hereinafter, in the present specification, the molds simply referred to as a lower mold and an upper mold mean a lower mold for pressing and an upper mold for pressing.

  The upper mold for cooling used in the present invention is used to balance the cooling state of the upper and lower surfaces of the press-formed product in at least a part of the period from after press molding to before being taken out from the lower mold for press. . Therefore, it is good if it has such a function. In the cooling upper mold, it is preferable that the curvature of the contact surface with the press-molded product is the same as the curvature of the upper surface of the molded product from the viewpoint that the thin glass obtained has a very small warpage. The shape and curvature of the upper and lower surfaces of the press-formed product can be determined as appropriate according to the intended use of the thin glass that is the object, and accordingly, the curvature of the contact surface with the upper mold press-formed product is also determined accordingly. it can.

  The upper mold for cooling is from the time after press molding until before it is taken out from the lower mold for press that at least one of the heat capacity, surface area, thermal conductivity characteristic, and surface emissivity characteristic is similar to the lower mold for press. From the viewpoint of balancing the cooling state of the upper and lower surfaces of the press-formed product in at least a part of the period. The surface emissivity characteristic means the emissivity of the object surface when black body radiation is 1.0. If the emissivity is high (close to 1.0), more heat can be radiated per unit area and unit time.

  “Approximation” of heat capacity, surface area, thermal conductivity characteristic, and surface emissivity characteristic is within ± 20%, preferably within ± 10%, more preferably within ± 5%, most with respect to the lower die for pressing. Preferably, it is within ± 1%. The heat capacity is preferably within ± 20%, and the thermal conductivity and surface emissivity characteristics are preferably substantially the same (within ± 1%). In the present invention, as described above, if the amount of heat deprived by heat conduction per unit time + heat radiation or the like (strictly + convection heat transfer) is approximately equal on the upper surface side and the lower surface side, the predetermined purpose is achieved. Therefore, the cooling state can be grasped by defining the emissivity characteristic of the surface. However, the cooling state can be similarly grasped by making the surface area, volume, material (thermal conductivity), and surface emissivity substantially equal.

  In the method of the present invention, the molten glass lump can be formed by dividing the molten glass flowing out into a predetermined volume, and can be received on the lower mold forming surface for pressing that sequentially moves. .

  In the method of the present invention, the press molding is stopped at a predetermined position where the upper die for pressing opposed to the lower die for pressing is installed, and within the range of the stop time of the lower die for pressing with the upper die for pressing. Can be done in time.

  For example, sheet glass is relatively thin with respect to the planar dimensions of the present invention (the thickness of the thinnest part is 1/10 or less with respect to the diameter), for example, information recording such as a glass substrate for a magnetic disk. It can be a thin plate (disk shape) glass substrate as typified by a substrate for use. However, the thin glass of the present invention is not limited to the information recording substrate, but may be a glass blank for optical components. In the case of an information recording substrate, for example, a glass having a thickness of 2 to 4 mm or less, a diameter and a length of 15 cm or less is typical.

  The cooling upper die can be placed on the press-molded product from the stop position after the press molding to the stop position before the take-out position of the press-molded product. That is, at least a part of the period from after the press molding to before being taken out from the lower die for pressing is the press from the stop position after the press molding to the stop position before the press molded product take-out position. It can be the travel time of the mold. The stop position before the take-out position of the press-molded product may be a stop position immediately before the press-molded product take-out position, but depending on the cooling rate, two or three of the press-molded product take-out positions are used. It can also be the previous stop position.

  It is preferable from the viewpoint of balancing the cooling state that the upper mold for cooling is preheated to substantially the same temperature as the lower mold for press when the upper mold for cooling is placed on the press-molded product.

  In the present invention, as soon as the press is finished and the upper die for pressing is separated from the thin glass, it is heated as soon as possible to a temperature close to the lower die (within ± 50 ° C., preferably within ± 10 ° C.). It is preferable to place the upper mold directly on the glass molded product. From the time of placement, the thin glass is sandwiched between the upper and lower molds with the large heat capacity near the glass transition point while the inside is still in the temperature range where plastic deformation is possible, as described above In other words, it is possible to realize a pseudo “thermally thin shape” and “almost uniform cooling conditions on both sides”. As a result, the temperature difference between the lower mold and the upper mold during press molding, and the internal stress of the thin glass caused by non-uniform cooling after the upper mold is separated, cause the following lower mold and cooling upper mold to It will be relaxed while maintaining a shape without warping due to continuous pinching for a long time.

  The press-molded product is taken out after the temperature reaches the glass yield point or lower, and it is appropriate that the press-molded product after taking out is gradually cooled.

  For example, heat exchange is performed in a state of being sandwiched between upper and lower molds made of metal, for example, in the vicinity of a glass transition point having a heat capacity of 5 times or more and high thermal conductivity while having a surface area within 2 to 3 times that of a press-formed product. As the heat radiation from the mold surface proceeds, the thin glass can be interrupted at the glass transition point with almost uniform temperature distribution with almost no deformation. Thereafter, for example, the upper mold for cooling and then the lower mold are first removed from the thin glass and transferred to the slow cooling apparatus. The lower the glass temperature when removing the cooling upper mold, the less likely the subsequent deformation will occur. Ideally, it is desirable to maintain the sandwiched state between the upper and lower molds until the thin glass temperature falls below the strain point. Realistically, thin glass moldings are placed on the lower mold for pressing and the upper mold for cooling until cooled below the yield point of the glass and as low as possible (most preferably until the glass temperature falls below the strain point). It is appropriate to keep it in a state of being sandwiched between them.

  However, if the timing for loading the upper mold for cooling after pressing is late, for example, if the inside of the thin glass is sufficiently cooled to below the glass transition point, even if it is cooled by sandwiching it with the upper and lower molds to the low temperature, this method The deformation (warpage) suppression effect cannot be expected.

  The method of this invention can be implemented using the manufacturing apparatus of the thin glass of the following this invention.

The apparatus for producing thin glass of the present invention comprises:
On the same circumference of the outer circumferential band on the rotating circular table at a predetermined index position, a lower die for pressing that can be exchanged at equal intervals corresponding to the index position is arranged.
At the stop position of each lower mold of the above table, the position for receiving at least the broken glass lump, the position for press molding with the upper mold and the lower mold, the position for loading the preheated upper mold for cooling on the press molded product, and for cooling The position to remove the upper mold and the position to take out the press molded product on the lower mold can be set independently,
An upper die for pressing is provided at the press molding position,
A cooling upper die that is loaded on the press-molded product at a position for loading the cooling upper die and can be removed from the press-molded product at a position for removing the cooling upper die is provided.

  The upper mold for cooling used in the apparatus for producing thin glass of the present invention is the same as that described in the production method of the present invention.

  The lower mold and upper mold for pressing, and further the material of the upper mold for cooling are preferably heat-resistant and have high thermal conductivity, such as graphite, tungsten alloy, nitride, carbide, refractory metal, etc. Although it is a candidate, cast iron is particularly easy to use because it is inexpensive and easy to process and has sufficient strength and durability.

  The lower die for pressing is designed to go through a glass lump supplying process, a press molding process, a cooling process, a molded product taking process, etc. in order, for example, a plurality of lower molds on the circumference of the turntable. Although it is preferable to arrange the mold and rotate the turntable so that the lower mold passes through each step, it may be designed to move in a linear direction. Moreover, the number of the lower mold | types simultaneously provided to each process may be single. On the other hand, the upper die for pressing is disposed to face the lower die for pressing located in the press molding process. Therefore, at least the same number of upper molds as the lower molds used for one-time press molding are required, but a larger number may be provided. In addition, if the heat transferred from the molten glass to the upper mold after press molding is removed and the temperature of the upper mold can be controlled in a short time so as to be an appropriate temperature at the time of molding, one upper mold may be used. .

  Next, the temperature of each molding surface of the upper mold for pressing and the lower mold (hereinafter, the upper mold and the lower mold may be referred to as a molding mold) is adjusted to a predetermined temperature at the start of press molding. Here, the predetermined temperature for the mold means a temperature suitable for molding the glass material into a thin plate. This temperature is a temperature that is appropriately determined depending on the glass type, the thickness, the size of the glass plate, and the like.

  Furthermore, in order to adjust the temperature of the molding surfaces of the upper die and the lower die at the start of press molding to the predetermined temperature, means for heating and cooling means are provided for the upper die and the lower die as necessary. It is done. As a heating means, for example, a plurality of nichrome heaters are arranged around the lower mold (upper mold) and heated, and a current is passed through a coil arranged so as to surround the lower mold (upper mold). There are means for inductively heating a mold made of the above, means for heating with gas, and the like.

  On the other hand, the temperature of the molding die used for press molding is higher than that before press molding due to heat transfer from high-temperature glass. In order to perform glass molding continuously with one or a small number of molds, it is necessary to cool the molds until the next press molding, and to mold all molded products under equivalent temperature conditions. In this case, therefore, a cooling means is provided simultaneously with the heating means. As the cooling means, means for circulating water or air in the hollow portion of the mold, means for spraying liquid such as water on the inner surface of the hollow portion of the mold, and the like can be employed. If it takes time to cool the upper die for pressing and it cannot be cooled to the predetermined temperature before molding after molding, prepare multiple upper die for pressing. During press molding, the other upper molds for pressing may be cooled, and the upper mold for pressing after cooling may be sequentially subjected to press molding.

  The thin glass manufacturing apparatus of the present invention will be described with reference to FIG. Table 1 below describes each stop position and its function.

  A feeder through which molten glass continuously flows out is installed immediately above P-1 in FIG. 1, and a predetermined volume of glass lump is placed on the lower mold of P-1 by a glass cutting device in which two cutting blades operate intermittently. To be supplied. The glass temperature at this time is not the most suitable temperature for press molding, and in the case of the direct press method, the glass liquid phase temperature is often greatly restricted, and the viscosity is much lower than the viscosity suitable for molding. In many cases, it must be done. The mold temperature is maintained in a sufficiently high temperature (specifically, a temperature slightly higher than the glass transition point) so that the surface of the glass lump is not baked on the mold surface, and the surface is not cooled more than necessary before pressing. In order to prevent the seizure of the glass, a powder called a mold release agent can be applied to the lower mold surface.

  When the table is moved to the position P-2 by stopping the operation, the upper die for pressing is placed opposite the lower die, and the glass lump is moved between the lower die and the lower die by the lowering operation of the upper die. Press molding is performed, and then the upper die is retracted upward and the press is finished before the lower die starts to move by table rotation.

  Next, when the lower mold moves to P-3, the upper mold for cooling preheated near the lower mold temperature by the upper mold preheating apparatus for cooling is taken out at the take-out position of the upper mold preheating apparatus for cooling, and comes into contact with each other. Are placed on the thin glass molded product on the lower mold by a placing device (not shown) while being kept parallel. At this time, it is appropriate to place the cooling upper mold softly so as not to damage the surface of the thin glass molded product.

  During the period from P-3 to P-8, when the lower mold repeatedly moves and stops while the upper mold for cooling is placed on the thin glass molded product, the temperature gradually decreases while both are naturally cooled. Go. It is preferable that the upper die for cooling has a position shift prevention mechanism that does not shift in the horizontal direction on the glass molded product when the lower die is moved. Specifically, the prevention mechanism can be configured by, for example, positioning protrusions installed at a plurality of locations on the outer periphery of the cooling upper mold covering the outer periphery of the lower mold.

  When the position of P-8 is reached, the upper mold for cooling is removed from the thin glass and returned to the return position of the upper mold preheating device for cooling.

  In P-9, only a thin glass molded product is removed from the lower mold by a thin glass molded product take-out device (not shown) and transferred to a slow cooling device. The lower mold whose temperature has been lowered by natural cooling until P-9 is not shown, for example, by a high-frequency mold heating device, from P-10 to P- to a temperature suitable for receiving molten glass at P-1. Heats rapidly between twelve.

  The upper mold for cooling which has returned to the return position of the upper mold preheating apparatus for cooling is reheated to a predetermined temperature before moving to the take-out position on the upper mold preheating apparatus for cooling.

  The above example shows an embodiment with a rotary table type press device, but an upper mold for cooling is loaded on the upper surface side of the thin glass early after pressing, and when the thin glass becomes below the required temperature, Application of the method based on the present invention of removing the thin glass from the mold and the lower mold is not limited to the rotary table type.

  The thin glass completed through the cooling by the molding press and the cooling upper mold stack according to the present invention may have no warp or may remain slightly warped. If the warpage can be removed by mechanical grinding or polishing, a finished press product with warpage remaining may be used. If the glass substrate warped with low rigidity due to its thin wall is simply ground and polished normally, it will be temporarily elastically deformed by the load (load) during processing and become apparently flat. Will return to warped again. Therefore, ingenuity is required to grind and polish a pressed product that is slightly warped. In order to realize a good grinding method, the main point is that the grinding of the press product is suppressed while suppressing the elastic deformation of the press product due to the load of the lapping machine for grinding. Specifically, the load on the lapping machine is gradually increased over time from the start of grinding, and after forming a flat glass substrate, the load is further increased so that the plate thickness becomes a predetermined dimension. That's fine.

  The thin glass obtained by the production method of the present invention becomes, for example, a glass substrate for an information recording medium through mechanical processing such as grinding and polishing. The grinding and polishing processes at that time are generally roughly divided into (1) roughing (rough polishing), (2) sanding (fine grinding, lapping), (3) first polishing (polish), (4 ) It consists of each step of the second polishing (final polishing, polishing). In some cases, (1) roughening (rough polishing) may be omitted.

Next, application of the present invention exemplifies the shape and dimensions of a thin glass (glass blank) for a glass substrate for an information recording medium that is suitable from a practical aspect.
(1) The thickness of the portion to be processed into a glass blank (for an information recording medium substrate having a diameter of 1 inch) having an outer diameter of 27.4 to 30 mm is uniform within a range of 0.44 to 0.8 mm. Some are preferred. Thickness in the range where the center hole can be drilled is in the range of 0.8 to 1.0 mm, which increases the volume and total heat of the glass. This is preferable in forming the glass blank of the portion to be formed. Both main surfaces are flat, the machining allowance in the smoothing process is 0.05 to 0.4 mm, the diameter of the central thick part is 4 to 6 mm, the outer diameter of the target substrate is 27.4 mm, the thickness is 0.381 mm, The inner diameter of the center hole is preferably 7.0 mm.

(2) The thickness of the portion to be processed into a glass blank (for an information recording medium substrate having a diameter of 2.5 inches) having an outer diameter of 65 to 68 mm is uniform within a range of 0.7 to 1.0 mm. Some are preferred. The thickness of the part where the center hole can be made is in the range of 1.1 to 1.5 mm, which increases the volume and total heat of the glass, and even a thin glass blank has a uniform thickness (processed on the substrate) to the full outer diameter by pressing. This is preferable in forming the glass blank of the portion to be formed. Both main surfaces are flat, the machining allowance in the smoothing process is 0.05 to 0.4 mm, the diameter of the central thick part is 16 to 19 mm, the outer diameter of the target substrate is 65.0 mm, the thickness is 0.635 mm, The inner diameter of the center hole is preferably 20.0 mm.

(3) The thickness of the portion to be processed into a glass blank (for an information recording medium substrate having a diameter of 3.5 inches) having an outer diameter of 95 to 98 mm is uniform within a range of 1.05 to 1.4 mm. Some are preferred. Thickness in the range of 1.5 to 2.1 mm where the center hole can be drilled increases the volume and total heat of the glass, and even a thin glass blank has a uniform thickness (processed on the substrate) to the full outer diameter by pressing This is preferable in forming the glass blank of the portion to be formed. Both main surfaces are flat, the machining allowance in the smoothing process is 0.05 to 0.4 mm, the diameter of the central thick part is 21 to 24 mm, the outer diameter of the target substrate is 95.0 mm, the thickness is 1.0 mm, The center hole inner diameter is preferably 25.0 mm.

  In the present invention, an annealed glass blank (thin glass) is cooled to room temperature and then machined to produce an information recording medium substrate. Machining includes center hole drilling, outer diameter processing for adjusting the outer diameter to a desired dimension, chamfering processing for chamfering, lapping processing for flattening and smoothing the main surface of a glass blank, polishing processing, and the like. . Although the glass blank is a press-molded product, there is no warpage or it is greatly reduced, so the burden on the planarization of the main surface can be reduced. For example, the primary lapping process using the count # 400 abrasive grains and the secondary lapping process using the count # 1000 abrasive grains is performed, the primary lapping process is omitted, and the secondary lapping process is performed. And the main surface can be flattened and smoothed by subsequent polishing. Furthermore, the produced glass substrate may be chemically strengthened to form a compressive stress layer on the surface.

  In addition, if the material of a glass blank is made into the crystallized glass base material, the glass blank which consists of crystallized glass can also be produced by heat-processing a glass blank. And if the said mechanical processing is given to this glass blank, the board | substrate for information recording media made from crystallized glass can also be produced.

  As the glass substrate material that does not include the crystal phase and the glass substrate material that does not include the crystal phase and is chemically strengthened, a known glass such as an aluminosilicate glass or aluminoborosilicate glass containing an alkali metal oxide may be used. it can. Known glass can also be used as the crystallized glass substrate material. For example, a silicate glass containing a component that can be a crystal nucleus such as titanium can be shown.

  As described above, various types of substrates for information recording media, such as a glass substrate that does not contain a crystal phase, a glass substrate that does not contain a crystal phase and has a compressive stress layer on the surface, and a crystallized glass substrate, can be produced.

  An information recording medium can be produced by providing an information recording layer on the substrate thus obtained. If a magnetic layer is formed as an information recording layer on this substrate, a magnetic recording medium such as a magnetic disk or a magneto-optical recording medium can be produced. Furthermore, an optical recording medium can be produced by providing an optical recording layer. A known structure may be applied to the film structure on the substrate, the type of film, the formation method, and the like.

  Further, the glass substrate for information recording medium can constitute a magnetic recording medium by sequentially laminating an underlayer, a magnetic layer, a protective layer and a lubricating layer on the glass substrate. Here, the material of the glass substrate of the magnetic recording medium is, for example, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass. Examples thereof include glass ceramics. Further, preferably, a glass having the following composition is used.

(1) In the crystallized glass 1 wt% displayed, SiO ₂ is 60~87%, Li ₂ O is 5 to 20%, Na ₂ O is 0 to 5%, K ₂ O is 0%, Na ₂ O And K ₂ O in total 0.5 to 10%, MgO 0.5 to 7.5%, CaO 0 to 9.5%, SrO 0 to 15%, BaO 0 to 13%, ZnO 0~13%, B ₂ O ₃ is 0~10%, Al ₂ O ₃ is 0~10%, P ₂ O ₅ is 0.5 to 8%, TiO ₂ is 0 to 5%, ZrO ₂ is 0 3%, SnO ₂ is 0 to 3%, As ₂ O ₃ and Sb ₂ O ₃ are 0 to 2% in total, and fluoride of one or more metal elements of the above metal oxide is 0 to 0 as the total amount of F 5% contained, and optionally as coloring components, V ₂ O ₅ , CuO, MnO ₂ , Cr ₂ O ₃ , CoO, MoO ₃ , NiO, Fe ₂ O ₃ , TeO ₂ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Er ₂ O Containing 0 to 5% of at least one selected from the group of ₃ and containing lithium disilicate as the main crystal, optionally α-cristobalite, α-quartz, lithium monosilicate, β-spodumene, etc. Crystallized glass having a size of 3.0 μm or less.

(2) crystallized glass 2 wt% display, SiO ₂ is 45 to 75%, CaO is 4 to 30%, Na ₂ O is 2 to 15%, K ₂ O 0 to 20%, the Al ₂ O ₃ 0 to 7%, MgO is 0 to 2%, ZnO is 0 to 2%, SnO ₂ is 0~2%, Sb ₂ O ₃ is 0~1%, B ₂ O ₃ is 0~6%, ZrO ₂ is 0-12% of Li ₂ O, 0-12% of Li ₂ O, one or more metal element fluorides of the above-mentioned metal oxides are contained in a total amount of 3-12% of F, and in some cases Cr ₂ O ₃ as a coloring component A crystallized glass containing Co ₃ O _{4 and the} like, containing canasite or potassium fluoro-richitelite as a main crystal, and having a crystal grain size of 1.0 μm or less.

(3) Glass 3% by weight, SiO ₂ 62-75%, Al ₂ O ₃ 4-18%, ZrO ₂ 0-15%, Li ₂ O 3-12%, Na ₂ O 3 Glass containing ~ 13%. In weight percent, 62-75% of SiO _2, 5 to 15% of Al ₂ O _3, 4 to 10% of Li ₂ O, 4 to 12% of Na ₂ O, and 5.5 to 15% of ZrO ₂ And a weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, and a weight ratio of Al ₂ O ₃ / ZrO ₂ is 0.4 to 2.5. .

  Such a glass substrate can be subjected to chemical strengthening treatment by a low-temperature ion exchange method on the surface for the purpose of improving impact resistance, vibration resistance and the like. Here, the chemical strengthening method is not particularly limited as long as it is a known chemical strengthening method. For example, low-temperature chemical strengthening in which ion exchange is performed in a region not exceeding the transition temperature is preferable from the viewpoint of the glass transition point. Examples of the alkali molten salt used for chemical strengthening include potassium nitrate, sodium nitrate, and nitrates obtained by mixing them.

  Examples of the underlayer include an underlayer made of at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the base layer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. Examples thereof include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, CrV / CrV, Al / Cr / CrMo, Al / Cr / Cr, Al / Cr / CrV, and Al / CrV / CrV. .

Examples of the magnetic layer include magnetic thin films such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrTaPt, and CoCrPtSiO. The magnetic layer may be a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrTaPt / CrMo / CoCrTaPt, etc.) in which the magnetic film is divided by a non-magnetic film (for example, Cr, CrMo, CrV) to reduce noise. Good. As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), an impurity element selected from Co, alloys, Y, Si, rare earth elements, Hf, Ge, Sn, Zn Or those containing oxides of these impurity elements. As the magnetic layer, in addition to the above, ferritic, iron - rare-earth and, Fe in a non-magnetic film made of SiO _2, BN, Co, FeCo, the structure in which the magnetic particles are dispersed, such CoNiPt granular Etc. Further, the magnetic layer may be of an internal type or a vertical type.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective layers can be continuously formed together with the underlayer, the magnetic layer and the like by an in-line type sputtering apparatus. These protective layers may be a single layer, or may have a multilayer structure composed of the same or different films. Furthermore, another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, colloidal silica fine particles are dispersed and applied in a tetraalkoxylane diluted with an alcohol-based solvent on a Cr film, and further baked to form a silicon oxide (SiO ₂ ) film. It may be formed.

  For example, the lubricating layer may be obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying it to the surface of the medium by dipping, spin coating, or spraying. Go and form.

  It is also possible to produce a thin glass (press-molded product) having a circular planar shape, one main surface being concave and the other main surface being convex, and grinding and polishing the press-formed product to produce a meniscus lens. . In that case, the press-molded product is called a lens blank, and is molded into a shape that approximates the lens of the finished product. The concave and convex surfaces having a central thickness thinner than the peripheral thickness are suitable as lens blanks for concave meniscus lenses, and conversely the concave and convex surfaces having a central thickness thicker than the peripheral thickness. Is suitable as a lens blank of a convex meniscus lens. Thus, various lenses can be made by producing various lens blanks, grinding and polishing.

Hereinafter, the present invention will be described in more detail by way of examples.
P-1 position where aluminosilicate glass containing Li ₂ O, Na ₂ O, ZrO ₂ that has been melted, degassed, homogenized, and continuously flowing out from the outflow feeder was cut into a predetermined volume and the surface was kept at 500 ° C. Supplied on a lower mold made of metal (cast iron). The glass temperature at the outflow is about 1150 ° C. On the surface of the lower mold, a fine powder of boron nitride is applied in advance so that the molten glass is not easily seized. The yield point of the glass is 560 ° C., the glass transition point is 485 ° C., and the strain point is 462 ° C. After moving to the P-2 position, the surface is pressed with an upper mold of about 400 ° C. for 0.3 seconds to form a thin glass with a thickness of 1.2 mm and an outer diameter of 66 mm, and then moved to the next P-3 position A cylindrical cooling upper die, which is preheated to about 500 ° C and is the same metal material as the lower die and has almost the same volume and surface area, is placed with care not to damage the upper surface of the thin glass. . The upper die for cooling is removed when it moves to P-8 while naturally cooling through P-4, P-5, P-6, and P-7. Further, at position P-9, only the thin glass is removed from the lower mold by the vacuum suction device and conveyed into the slow cooling device. When the flatness of the thin glass sampled at this time was measured, the average value was less than 20 μm, and the maximum was less than 30 μm.

A disk-shaped magnetic disk substrate, that is, a substrate for a magnetic recording medium, was produced by wrapping, thinning a center hole and polishing the thin glass.
Further, a magnetic recording medium was manufactured by forming a film including a magnetic recording layer on the substrate.
Note that a film including a magnetic recording layer may be formed after the substrate is chemically strengthened.

  The above example relates to the production of a magnetic recording medium substrate, but various types of lens blanks such as a concave meniscus lens blank and a convex meniscus lens blank can also be formed with the desired shape of each mold. . These blanks were ground and polished to obtain various lenses such as a concave meniscus lens and a convex meniscus lens.

  The present invention is useful in the field of manufacturing thin glass to be glass blanks for information recording substrates and optical components.

It is explanatory drawing of an example of the apparatus of this invention.

Claims (11)

A method for producing a thin glass by press molding a molten glass lump supplied on a lower mold surface for pressing with a molding surface of an upper mold facing the lower mold for pressing,
After the press molding, the upper die for pressing is removed from the press-molded product and then cooled on the press-molded product for at least a part of the period from when the press-molded product is taken out from the lower mold molding surface. A method for producing thin glass, wherein an upper die is placed and the cooling conditions of the upper and lower surfaces of the press-formed product are substantially uniformed to balance the cooling state of the upper and lower surfaces of the press-formed product. The manufacturing method according to claim 1, wherein the cooling upper die has a curvature of a contact surface with the press-molded product that is the same as a curvature of an upper surface of the molded product. The manufacturing method according to claim 1, wherein the cooling upper die has at least one of a heat capacity, a surface area, a thermal conductivity characteristic, and a surface emissivity characteristic that is similar to a lower die for pressing. The manufacturing method according to claim 1, wherein when the upper mold for cooling is placed on the press-molded product, the upper mold for cooling is preheated to substantially the same temperature as the lower mold for press. The molten glass lump is formed by dividing the molten glass flowing out into a predetermined volume, and is received on the lower mold forming surface for pressing that sequentially moves,
The press molding is stopped at a predetermined position where the upper die for pressing facing the lower die for pressing is installed, and is performed within a time range of the stop time of the lower die for pressing with the upper die for pressing. I,
Placement of the cooling upper die on the press-molded product is performed from the next stop position of the press molding to the stop position before the take-out position of the press-molded product,
The take-out of the press-molded product is performed after the temperature becomes below the glass yield point,
The manufacturing method according to claim 1, wherein the press-molded product after taking out is gradually cooled. On the same circumference of the outer circumferential band on the rotating circular table at a predetermined index position, a lower die for pressing that can be exchanged at equal intervals corresponding to the index position is arranged.
At the stop position of each lower mold of the above table, the position for receiving at least the broken glass lump, the position for press molding with the upper mold and the lower mold, the position for loading the preheated upper mold for cooling on the press molded product, and for cooling The position to remove the upper mold and the position to take out the press molded product on the lower mold can be set independently,
An upper die for pressing is provided at the press molding position,
In the position for stacking the cooling upper die is stacked on the press-in position to remove the cooling upper mold, wherein characterized in that it comprises a cooling upper mold can be removed from the press-molded product An apparatus for producing thin glass for use in the production method according to Item 1 . The manufacturing apparatus according to claim 6, wherein the cooling upper mold has at least one of a heat capacity, a surface area, a thermal conductivity characteristic, and a surface emissivity characteristic similar to the lower mold. The manufacturing apparatus of Claim 6 which further contains the heating apparatus which can set the said upper mold | type for cooling to the arbitrary preheating temperature below a glass softening point. A method for producing a glass substrate for an information recording medium, comprising obtaining a glass substrate for an information recording medium by grinding and polishing a main surface of the thin glass produced by the production method according to claim 1. . An information recording body comprising at least an information recording layer formed on a main surface of a glass substrate for information recording medium manufactured by the manufacturing method according to claim 9. A method for producing an optical component, characterized in that an optical component is obtained by grinding and polishing a main surface of a thin glass produced by the production method according to claim 1.

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