JP2004161564A - Method of manufacturing each of glass blank, substrate for information recording medium and information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass blank which is high in the degree of parallelism and flatness of the main surface by a direct press method, while making use of the merit of the method. <P>SOLUTION: In the method of manufacturing the glass blank, the glass blank is formed by pressing molten glass by using opposing upper and lower molds so as to be processed into a substrate for a disk-like information recording medium having a center hole. As the upper mold and the lower mold, a mold comprising a central mold member and a peripheral mold member is used, and at the time of pressing, pressing is brought to completion before the temperature distribution in the forming surface of the peripheral mold member becomes uniform, or the holding time in the pressing is set to be ≤2 sec. The method of manufacturing the substrate for the information recording medium uses the glass blank manufactured by the method. In the method of manufacturing the information recording medium, an information recording layer is formed on the substrate for the information recording medium manufactured by the method. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for producing a thin glass blank to be processed into a substrate for an information recording medium by press-molding molten glass, and a substrate for an information recording medium by subjecting the glass blank to machining. And a method for producing an information recording medium by forming an information recording layer on the information recording medium substrate.
[0002]
[Prior art]
Glass or crystallized glass obtained by heat-treating glass is used for a substrate of an information recording medium such as a hard disk incorporated in a personal computer. As a method of manufacturing a substrate for an information recording medium from such a glass material, a molten glass is pressed with a press molding die to produce an intermediate molded body made of glass having a shape similar to that of the substrate, and the intermediate molded body is machined. There is known a method of applying the composition to a substrate. The method of press-molding the molten glass to form an intermediate molded body (hereinafter also referred to as “glass blank”) is called a direct press method.
[0003]
An advantage of the direct press method is that a glass blank having a shape and dimensions close to the substrate, such as the overall shape, outer diameter, wall thickness, parallelism of both opposing surfaces (both main surfaces), and flatness, can be obtained. Conversely, if the above advantages are lost, the value of this method will be reduced. The direct press method has a difficulty in that an extremely high-temperature material called molten glass must be formed while satisfying such requirements.
[0004]
On the other hand, there is known a method of manufacturing a glass substrate by incorporating the features of the direct press method and the features of the reheat press method (see Patent Document 1). However, this method has a problem that although a glass substrate having high smoothness and flatness can be obtained, the press time is long and productivity is poor. In addition, it is necessary to heat the mold at the time of pressing, which has been a factor of high cost.
[0005]
[Patent Document 1]
JP-A-12-319026
[0006]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a method of manufacturing a glass blank having a high parallelism and a high flatness of a main surface by a direct press method, utilizing the advantages of the direct press method.
It is a second object of the present invention to provide a method of manufacturing an information recording medium substrate from a glass blank manufactured by the above method, and a method of manufacturing an information recording medium using the substrate.
[0007]
[Means for Solving the Problems]
The object of the present invention is to
Pressing the molten glass using the upper mold and the lower mold facing each other, in a glass blank manufacturing method for forming a glass blank to be processed into a disc-shaped information recording medium substrate having a center hole,
As the upper mold and the lower mold, a mold including a center mold member and a peripheral mold member is used, and
In the press, the press is terminated before the temperature distribution on the molding surface of the peripheral mold member becomes uniform, or
A method for producing a glass blank, wherein the holding time in the press is 2 seconds or less.
Achieved by
In the above-described manufacturing method, it is preferable that a gap is formed between the center mold member and the peripheral mold member, and the gap is a flow path of an airflow from the center of the upper and lower mold forming surfaces to the outside of the upper and lower molds. It is preferable that at least a part of is formed.
Further, in the above manufacturing method, at the time of the pressing, the boundary between the central mold member molding surface for transferring and molding the main surface of the glass blank and the peripheral mold member molding surface falls within a region where the center hole of the glass blank is to be opened. It is preferable to design the mold in such a manner.
[0008]
Further, a second object of the present invention is to provide a method for manufacturing a substrate for an information recording medium, wherein a glass blank manufactured by the above manufacturing method is used, and the glass blank is machined, and a substrate for an information recording medium manufactured by this method is provided. This is achieved by a method for manufacturing an information recording medium in which an information recording layer is formed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a glass molded body having a shape similar to the shape of the information recording medium substrate and finished on the substrate by a step including machining is referred to as a glass blank.
The information recording medium substrate generally has a disk shape with a smaller thickness than the outer diameter. Therefore, the glass blank is formed into a shape similar to this shape. When press-molding a thin glass plate such as a glass blank, it is not easy to form both main surfaces of the glass blank corresponding to the bottom surface of the disk so as to have extremely high parallelism and flatness. The present inventor considered the reason and obtained the following knowledge.
[0010]
In the direct press method, extremely high-temperature molten glass is supplied to the molding surface of the lower mold (hereinafter referred to as "casting"), or the molten glass is pressed by the upper and lower molds while it is in a softened state. And the temperature of the upper mold before pressing must be adjusted to a temperature that does not cause fusion with the glass. Generally, the temperature is adjusted based on the temperature near the transition point of the glass to be pressed. The mold whose temperature has been adjusted in this way is heated by the heat of the glass when it comes into contact with high-temperature glass during casting or pressing. Conversely, the calorific value of the glass is quickly taken away from the contact area with the mold. Such heat radiation from the glass to the mold starts from the position where the molten glass is cast on the lower mold forming surface. Then, when the press is started, the upper mold forming surface starts to contact the glass, so that the upper mold forming surface also advances. As the glass is pushed by the press into the cavity formed between the upper and lower molding surfaces, the glass expands to the periphery of the upper and lower molding surfaces. In this process, the highest temperature is the position where the molten glass is cast on the lower mold forming surface, and the position where the upper mold forming surface comes into contact with the glass first at the time of pressing, that is, the lower mold forming surface It is considered to be a part facing the cast position of. As a result, large thermal expansion occurs locally in the portion of the press molding surface that is rapidly heated by the glass, and stress is generated in the mold. This stress causes the molding surface to warp. When casting the molten glass at the center of the lower mold forming surface, the temperature near the center of the forming surface of both the upper and lower molds becomes high, so the forming surface warps in a convex shape. When such a molding surface is transferred to glass, the parallelism and flatness of the molded glass blank are reduced. On the other hand, if the pressing is continued until the temperature distribution of the forming die becomes uniform, the warping of the forming surface does not occur, and the above problem can be avoided. However, in this case, since a long time is required for pressing, there is a problem that productivity is significantly reduced.
Therefore, the present inventors, while performing press molding in a short time, to prevent such a decrease in parallelism and flatness, it suffices to relax the stress due to thermal expansion that causes warpage of the molding surface. And completed the present invention. Hereinafter, this point will be described in more detail.
[0011]
In the present invention, the upper and lower molds are constituted by the center mold member and the peripheral mold member. By dividing the upper and lower molds into two mold members as described above, stress in the mold due to thermal expansion that causes warpage during pressing can be reduced. Preferably, a gap is formed between the center mold member and the peripheral mold member. Since the gap is formed, the gap is narrowed by thermal expansion of the center mold member and the peripheral mold member, and as a result, stress due to thermal expansion can be further reduced. The gap facing the upper and lower mold forming surfaces is preferably provided along the entire periphery of the center mold member. In the case where stress is not completely relieved by providing the above gaps in the upper and lower dies, the shape of the upper and lower dies can be corrected so as to be flat at the time of pressing. The material of the press mold such as the center mold member and the peripheral mold member is a heat-resistant material, and is preferably a metal material or the like which is excellent in workability and is used in a normal direct press method. Further, in the present invention, the materials of the peripheral mold member and the central mold member may be the same or different. In general, the heat conductivity of the heat-resistant alloy is low, and when this material is applied to the center mold member, the supplied molten glass tends to stick to the center mold member. Therefore, when using a heat-resistant alloy for the peripheral mold member, it is preferable to change the material of the peripheral mold member and the center mold member. In this case, as the material of the center mold member, stainless steel, cast iron, or the like can be used.
[0012]
The molding die composed of the central mold member and the peripheral mold member used in the present invention can be constituted by fitting the central mold member into the peripheral mold member. The outer diameter of the center mold member and the inner diameter of the center hole of the peripheral mold member can be appropriately set in consideration of the thermal expansion during casting and pressing of the mold member. In particular, in order to prevent glass from entering the boundary between the two mold members at the time of pressing, at room temperature, the temperature is set higher than room temperature and lower than the mold temperature at the time of pressing, while ensuring that the center mold member cannot be fitted into the peripheral mold member. It is preferable to fit the central mold member while the peripheral mold member is heated.
[0013]
The boundary between the central mold member and the peripheral mold member is transferred to the main surface of the glass blank to form a part of the molding surface, and a step is formed on the main surface of the glass blank. Further, when a gap is present at the boundary at the time of pressing, when glass enters the gap by viscous flow, steps and projections are formed on the main surface of the glass blank. Such steps and projections are considered to be inconvenient in obtaining a glass blank having high parallelism and flatness. Therefore, in the present invention, at the time of pressing, the boundary between the central mold member molding surface and the peripheral mold member molding surface for transferring and molding the main surface of the glass blank, so as to enter the region where the center hole of the glass blank is to be opened. It is preferable to design the mold. That is, it is preferable to set the positional relationship between the center mold member and the peripheral mold members in the upper and lower molds so that the boundary is transferred to an area where the center hole of the glass blank is to be formed. As a result, even if the boundary is transferred to the glass blank by pressing, this portion is removed by the center boring process, so that the flattening of the main surface of the information recording medium substrate is not adversely affected.
[0014]
Next, the casting position of the molten glass will be described. As described above, in the temperature history of the lower mold surface, the position exposed to the highest temperature is the position where the molten glass is cast, and in the temperature history of the upper mold surface, the position exposed to the highest temperature is the lower mold This is the position facing the casting position on the molding surface. Therefore, it is considered that the amount of thermal expansion at these positions is the largest. If a boundary is provided so that the cast portion is placed on the surface of the center mold member, the stress due to thermal expansion can be more effectively reduced. In the present invention, the position of the boundary is preferably in a region where the center hole of the glass blank is opened, and by setting the casting position to the center of the lower mold forming surface, the stress can be effectively alleviated. it can. Further, setting the casting position at the center of the lower mold forming surface is advantageous in uniformly spreading the glass into the cavity formed between the upper and lower mold forming surfaces during pressing. For the above reasons, it is preferable to supply the molten glass to the center of the lower mold forming surface.
[0015]
In the present invention, when a gap is formed between the center mold member and the peripheral mold member, the gap forms at least a part of a gas flow path leading from the center of the upper and lower mold forming surfaces to the outside of the upper and lower molds. Is preferred. At the time of pressing, the atmospheric gas loses an escape space between the molding surface and the glass and may be trapped. If press molding is performed in this state, a dent corresponding to the shape of the trapped gas may remain on the surface of the molded product, resulting in defective molding. Such a phenomenon is called a gas trap. In the present invention, the gas between the upper and lower mold forming surfaces and the glass can be discharged from the gap to the outside of the mold by penetrating the gap from the center of the mold forming surface to the outside of the mold. Can be prevented.
[0016]
Next, an example of the structure of the press mold will be specifically described. FIG. 1 is a sectional view of an upper mold 10 and a lower mold 20 used for press molding. This cross-sectional view shows a cross section perpendicular to each of the molding surface of the upper mold 10 and the molding surface of the lower mold 20 and including the center of each molding surface. The upper mold 10 and the lower mold 20 have the following structures. At the center of the peripheral mold members 11, 21, a circular central hole for inserting the central mold members 12, 22 is provided. A fixing hole for fixing the center mold member is provided at the back of the center hole. The upper die has a retaining ring 16 and an O-ring 17, and the lower die has a retaining ring 25. The center mold members 12 and 22 include a columnar portion formed in consideration of a gap at a temperature during molding, and a fixing portion to be inserted and fixed in a fixing hole of the peripheral mold member. When the central mold members 12 and 22 are inserted into the central holes of the peripheral mold members 11 and 21 and the fixing portion is fixed by the fixing holes, the side surfaces of the columnar portions of the central mold members 12 and 22 and the peripheral mold members at the temperature during molding. Uniform gaps 13 and 23 are formed between the center holes 11 and 21 over the entire circumference. In this state, the upper and lower mold forming surfaces are formed by the molding surfaces of the center mold members 12 and 22 (the bottom surfaces of the cylindrical portions) and the molding surfaces of the peripheral mold members. It is preferable to arrange the molding surfaces of the center mold members 12 and 22 and the molding surfaces of the peripheral mold members 11 and 21 on the same plane, but the center is taken into consideration in view of press moldability and reduction of glass intrusion into the gaps 13 and 23. The molding surfaces of the mold members 12, 22 may be slightly protruded or retracted from the molding surfaces of the peripheral mold members 11, 21. Gas vent holes 14 and 24 penetrating into the center hole are provided on the side surfaces of the peripheral mold members 11 and 21, and the upper and lower mold forming surfaces and the glass are interposed through the gaps 13 and 23 and the gas vent holes 14 and 24. The gas between them is discharged to the outside of the upper and lower molds. In other words, in this case, the gaps 13 and 23 form a part of a gas flow path from the center of the upper and lower mold forming surfaces to the outside of the upper and lower molds. In addition, the gaps 13 and 23 may form the entire gas flow path from the center of the upper and lower mold forming surfaces to the outside of the upper and lower molds. The inner diameter of the center holes of the peripheral mold members 11 and 21 is equal to or less than the diameter of the area where the center hole of the glass blank is to be opened (diameter of the center hole), and is preferably 75 to 90% of the diameter of the center hole. Just fine. On the other hand, the outer diameter of the cylindrical portion of each of the center mold members 12 and 22 is preferably 99.8 to 100.2% of the inner diameter of the center hole of each of the peripheral mold members 11 and 21 from the viewpoint of making the gap interval appropriate.
[0017]
The surface roughness of the peripheral mold member forming surface in the vicinity of the gaps 13 and 23 is made larger than other portions of the molding surface of the peripheral mold members 11 and 21 to reduce or prevent glass from entering the gaps 13 and 23. It is also possible to promote the discharge of the gas between the upper and lower mold forming surfaces and the glass from the gaps 13 and 23 to the outside of the mold. Examples of a method for increasing the surface roughness include a method in which the molding surfaces of the peripheral mold members 11 and 21 are formed smoothly by lathing or the like, and only the vicinity of the center hole is sandblasted. When the center of the glass blank including the part to be sandblasted is put in the area where the center hole is formed, the part to which the sandblasted molding surface is transferred is removed by the center hole forming. Even if the sandblasted molding surface extends outside the area where the center hole is drilled, if the surface roughness of this part falls within the allowance for flattening and smoothing of the main surface, the substrate by sandblasting An adverse effect on the surface smoothness can also be avoided. Note that the upper mold 10 and the lower mold 20 may be used while being cooled by providing a cooling means.
[0018]
On the outer periphery of the molding surface of the peripheral mold member 11 of the upper mold 10, a side wall portion 15 that comes into contact with the lower mold 20 when the press mold is clamped is provided over the entire periphery. The height of the side wall portion 15 with respect to the molding surface of the peripheral mold member 11 is uniform over the entire circumference, and the thickness of the glass blank is regulated by this height. The molding surface of the central mold member 12 of the mold 10 and the molding surface of the peripheral mold member 12 become parallel.
When the glass comes into contact with the side wall portion 15, the portion is rapidly cooled, the in-plane temperature distribution of the glass in the cavity when viewed from the pressing direction becomes large, and undulation-like deformation is easily generated in the glass blank. . Further, when the progress of the glass is hindered by the side wall portion 15, the glass easily enters the gaps 13 and 23 between the central mold members 12 and 22 and the peripheral mold members 11 and 21. If the inner diameter of the side wall 15 is made larger than the outer diameter of the glass blank, it is possible to reduce or prevent the glass from entering the gaps 13 and 23. Therefore, it is preferable that the inner diameter of the side wall portion 15 is larger than the outer diameter of the glass blank to be press-formed. By doing so, the pressed glass does not reach the side wall 15.
[0019]
In the present invention, the pressing by the forming die is completed before the temperature distribution on the forming surface of the peripheral die member becomes uniform. By using the above-described mold while improving productivity by short-time press molding, a glass blank excellent in flatness and smoothness can be obtained. The temperature distribution on the molding surface of the peripheral mold member can be measured by a contact thermometer, a thermocouple, an infrared radiation thermometer, or the like.
[0020]
In the present invention, specifically, the holding time in the press (press holding time) is set to 2 seconds or less. Preferably it is 1 second or less. Here, the press holding time refers to the time from when the pressurization of the glass by the upper and lower molds is started to when the glass molded article is separated from the upper mold after the molding is completed. If the press holding time exceeds 2 seconds, the temperature of the glass decreases and the fluidity decreases, so that the glass does not stretch to the desired outer diameter, and the obtained glass blank is thick and has a small diameter. turn into. In addition, the press holding time is preferably set to 0.3 seconds or more in order to allow time for the glass to sufficiently elongate. The press holding time may be obtained based on a control signal of the press forming apparatus, or the movement of the press forming die may be photographed by a video camera or a high-speed video camera, and may be obtained from a reproduced image.
[0021]
In addition, assuming that the time until the glass gob is formed into a plate-shaped molded product by pressing is the press time, the press time is 0.5 second or less in order to obtain a molded product having a desired thickness and shape. It is more preferable to set it to 0.1 second or less. The lower limit of the pressing time is determined by the performance of the pressing device, but by pressing in a shorter time, a molded product having a good wall thickness can be obtained.
[0022]
In order to perform press molding in a short time as described above in the present invention, the glass viscosity is preferably 200 to 1000 dPa · S, and the press pressure is 10 to 100 kg / cm.²It is preferable that
[0023]
In the present invention, since the press molding is performed in a very short time as described above, it is not necessary to heat the molding die with a heater or the like during the period from casting of the glass to takeout. Therefore, the temperature of the glass decreases monotonously from the casting of the glass to the takeout. According to the present invention, it is possible to obtain a glass blank excellent in flatness and smoothness while performing press molding in an extremely short time without requiring a step such as heating of a mold.
[0024]
Next, when press-molding a thin glass blank with a press mold having a gap between the peripheral mold member and the center mold member, the upper mold side is asked how to eliminate the gas trap. A description will be given with reference to FIGS. By casting, the molten glass is supplied to the center of the lower mold forming surface. In order to form this into a thin glass blank, it is necessary to press the upper and lower dies in a short time to spread the glass thinly. FIGS. 2A to 2D are schematic diagrams showing how the glass spreads in such a short press. As shown in FIGS. 2B and 2C, the transitional wall thickness of the glass is the thickest at the center, then the tip (peripheral portion) that is going to spread around is thick, and the gap between the center and the tip is large. Becomes thinner. If the distance between the upper mold and the lower mold is reduced as it is, a gas trap is generated on the upper mold side between the center part and the tip part. However, according to the mold structure of this embodiment, the center part and the tip part are formed. The gas between the thin portion in the middle and the molding surface of the upper die passes through the gas vent hole from the gap in the upper die and is discharged to the outside of the die, so that a gas trap can be prevented.
Also, when a gas trap is provided on the lower mold side, press molding can be performed while preventing the gas trap, as shown in the schematic views of FIGS.
[0025]
Upon completion of the pressing, the upper mold is released from the glass blank, and cooled on the lower mold forming surface until the surface temperature of the glass blank falls below the yield point, preferably below the transition point. Cooling on the lower mold forming surface to this temperature is preferable because the glass is not deformed when removed from the mold. At the time of cooling, a member having a lower temperature than glass may be brought into contact with the upper surface of the glass blank, or the upper surface may be pressed by this member to promote cooling and correct the warpage of the glass blank. After the glass blank is cooled as described above, it is removed from the lower mold and annealed.
[0026]
After annealing, the glass blank cooled to room temperature preferably has a parallelism of 10 to 30 μm and a flatness of 20 to 50 μm. On the other hand, the upper mold was composed of one member, and after performing press molding in the same manner, the parallelism and flatness of the annealed glass blank cooled to room temperature were measured. The degree was 70-100 μm.
[0027]
Next, the dimensions of the glass blank to which the present invention is suitable will be exemplified.
▲ 1 ▼ Outer diameter φ₀Is 27.4 to 30 mm (for 1 inch diameter information recording medium substrates)
The thickness of the portion pressed by the peripheral mold member is 0.8 mm or less, preferably 0.44 to 0.8 mm.
The thickness of the part pressed by the center mold member is 0.8 to 1.0 mm.
The allowance for flattening and smoothing of both main surfaces is 0.05 to 0.4 mm.
The diameter of the part pressed by the center mold member is 4 to 6 mm.
Parallelism is 5 to 10 μm.
Flatness is 10 to 20 μm.
The outer diameter of the substrate is 27.4 mm, the thickness is 0.381 mm, and the inner diameter of the center hole is 7.0 mm.
(2) Outer diameter φ₀Is 65-68 mm (for 2.5 inch diameter information recording medium substrate)
The thickness of the part pressed by the peripheral mold member is 1.0 mm or less, preferably 0.7 to 1.0 mm.
The thickness of the part pressed by the center mold member is 1.1 to 1.5 mm.
The allowance for flattening and smoothing of both main surfaces is 0.05 to 0.4 mm.
The diameter of the part pressed by the central mold member is 16 to 19 mm.
Parallelism is 10 to 20 μm.
Flatness is 20 to 40 μm.
The outer diameter of the substrate is 65.0 mm, the thickness is 0.635 mm, and the inner diameter of the center hole is 20.0 mm.
(3) Outer diameter φ₀Is 95 to 98 mm (for 3.5 inch diameter information recording medium substrate)
The thickness of the part pressed by the peripheral mold member is 1.4 mm or less, preferably 1.05 to 1.4 mm.
The thickness of the portion pressed by the center mold member is 1.5 to 2.1 mm.
The allowance for flattening and smoothing of both main surfaces is 0.05 to 0.4 mm.
The diameter of the part pressed by the center mold member is 21 to 24 mm.
Parallelism is 10 to 30 μm.
Flatness is 20 to 50 μm.
The outer diameter of the substrate is 95.0 mm, the thickness is 1.0 mm, and the inner diameter of the center hole is 25.0 mm.
[0028]
The glass used in the present invention is a known glass material as a glass material for a substrate for an information recording medium or a glass material from which a crystallized glass substrate is obtained by crystallization by heat treatment, which can be press-molded. Can be used. Examples of such a glass material include aluminosilicate glass containing an alkali metal oxide, glass obtained by introducing an alkaline earth metal oxide or titanium oxide into the above glass, and glass containing a rare earth oxide.
[0029]
After being annealed and cooled to room temperature, the glass blank is subjected to, for example, center drilling, finishing of inner and outer diameters (including chamfering), flattening and smoothing of both main surfaces (lapping, rough polishing) Finish polishing). The lapping process is usually performed by lapping with # 400 abrasive grains and lapping with # 1000 abrasive grains. However, the lapping process is performed by reducing the warping of the press mold as described above. If the removal allowance is reduced, sufficient flatness and smoothness can be obtained only by lapping with # 1000 abrasive grains, and lapping with # 400 abrasive, which was conventionally required, can be omitted. You can also.
In the present invention, by flattening and smoothing the two main surfaces after the center hole drilling process, it is possible to eliminate the need for flattening and smoothing the portion where the gap between the upper and lower mold forming surfaces is transferred.
[0030]
In the present invention, when obtaining a crystallized glass substrate, it is desirable to perform a heat treatment step for crystallization before flattening and smoothing both main surfaces. If it does not crystallize, the glass may be chemically strengthened by an ion exchange method or the like to form a substrate. A washing step may be appropriately provided between the above steps.
As described above, according to the present invention, a glass blank having high parallelism and flatness of the main surface can be manufactured by the direct press method while making use of the advantages of the direct press method.
Further, by improving the parallelism and flatness of the main surface of the glass blank according to the present invention, it is possible to reduce the burden on the flattening process of the main surface by machining, and it is possible to reduce the load on the substrate for magnetic recording media and magneto-optical recording. A substrate for an information recording medium such as a substrate for a medium and a substrate for an optical recording medium, and various information recording media using the substrate can be manufactured with high productivity.
Manufacturing information recording media such as magnetic recording media, magneto-optical recording media, and optical recording media by providing a magnetic recording layer, a magneto-optical recording layer, an optical recording layer, and the like on the main surface of the substrate according to the recording method. Can be.
[0031]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
(Example 1)
First, a central mold member and a peripheral mold member, both made of ductile cast iron, are assembled into a structure as shown in FIG. The outer diameter of the lower mold surface and the upper mold surface is φ90 mm, and the inner diameter of the center hole of the peripheral mold member is 16.0 mm.₀ ^+0.01, The diameter of the cylindrical portion of the center mold member is 16.0 mm_+0.02 ^+0.01(Here, the superscript and the subscript are processing tolerances), and the configuration is such that the central mold member cannot be fitted into the central through hole of the peripheral mold member at room temperature, and the peripheral mold member is heated to 150 ° C. The center mold member was fitted. A gap of about 0.01 mm was formed between the central mold member and the peripheral mold member over the entire circumference during press molding. Further, the molding surface of the center mold member on the lower mold side was arranged and fixed at a position having a depth of 0.4 mm from the molding surface of the peripheral mold member. Further, the molding surface of the center mold member on the upper mold side was arranged and fixed so as to protrude 0.2 mm from the molding surface of the peripheral mold member.
Next, the molten glass of the aluminosilicate glass containing the alkali metal oxide is melted, clarified and homogenized, and the molten glass is caused to flow down from a platinum alloy feeder at a constant speed, and the molten glass flow is cut by a cutting blade to a predetermined value. A heavy molten glass gob was cast in the center of the lower mold forming surface. The dimensions of the glass gob at the time of casting were Φ25 mm, and the height at the center was 8 mm. The transition point of the glass to be cast was 485 ° C., and the viscosity of the glass at the time of casting and the temperature of the lower mold forming surface were 400 poise and 500 ° C.
[0032]
The cast glass is transferred together with the lower mold to a press position where the upper mold waits above, where it is pressed by the lower mold and the upper mold. The press holding time was 0.5 to 0.8 seconds, and the pressing time was about 0.01 seconds. Here, it was confirmed with a contact thermometer that the temperature distribution of the peripheral mold member was not uniform. The temperature distribution of the peripheral mold member can also be measured with a thermocouple, an infrared radiation thermometer, or the like. Next, the upper mold is retracted upward, separated from the upper surface of the formed glass blank, and waits until the temperature of the glass blank drops to near the glass transition temperature on the lower mold forming surface. After the temperature of the glass blank has dropped to near the glass transition temperature, the glass blank on the lower mold is taken out to the atmosphere. Direct press molding is performed in the atmosphere, but the glass blank is not rapidly cooled while in contact with the high-temperature lower mold, but the entire surface is exposed to the room temperature atmosphere from near the glass transition temperature at the moment of taking out from the lower mold. And quenched. In addition, the temperature of the glass monotonously decreases from casting to takeout. After annealing the glass blank in a rare furnace, it was cooled to room temperature, and then the parallelism and flatness were measured.
The outer diameter of the obtained glass blank was 66 mm, the wall thickness was 0.9 mm, the parallelism was 15 μm, and the flatness was 30 μm, which were favorable results. Also, no shape deterioration due to the gas trap was observed.
[0033]
The glass blank thus produced was subjected to processing for forming a center hole, inner and outer diameter processing, lapping on both main surfaces, rough polishing, and precision polishing to obtain a glass substrate for a magnetic recording medium. In these steps, a washing step can be included as appropriate. If necessary, the obtained glass substrate may be immersed in a molten alkali metal salt and subjected to chemical strengthening by ion exchange.
[0034]
(Example 2)
Components from which crystallized glass is obtained by heat treatment, for example, SiO 2₂, Al₂O₃, TiO₂, Na₂O, MgO, CaO, Y₂O₃The molten glass containing each component such as is directly press-molded, and a glass blank is made in the same manner as in Example 1. The glass blank is appropriately subjected to a heat treatment step, a grinding step, and a polishing step for crystallization. Thus, a disk-shaped substrate having a central hole was obtained.
Each substrate thus obtained is suitable not only as a substrate for a magnetic recording medium, but also as a substrate for a magneto-optical recording medium and a substrate for an information recording medium such as an optical disk.
[0035]
(Comparative Example 1)
Except that the upper mold was constituted by an integral member, the same press molding as in the above example was performed, annealed and cooled to room temperature, and the parallelism and flatness were measured. The obtained degree of parallelism was 60 μm and the degree of flatness was 80 μm, which were lower values than those of the examples. When the glass blank was machined to produce an information recording medium substrate, the labor required for flattening was about 150%, which was larger than that of the above example.
[0036]
(Comparative Example 2)
The same press molding as in the above example was performed except that the pressing time was 4 seconds. The outer diameter of the molded product did not reach 66 mm and the wall thickness was large, and this press molding was determined to be poor elongation of glass.
[0037]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the glass blank with high parallelism and flatness of a main surface can be manufactured by a direct press method, taking advantage of the direct press method.
In addition, by improving the parallelism and flatness of the main surface of the glass blank, the burden on flattening the main surface by machining can be reduced. Thus, a substrate for an information recording medium such as a substrate for an optical recording medium, and various information recording media using the substrate can be manufactured with high productivity.
[Brief description of the drawings]
FIG. 1 is a sectional view of an upper die and a lower die used for press molding.
FIG. 2 is a drawing of the glass in a short press.
[Explanation of symbols]
10 ... upper mold
11: Upper die peripheral die member
12: Upper mold center mold member
13: Upper die gap
14 ... Upper mold vent hole
15 ... side wall
16 ... Upper retaining ring
17… O-ring
20 ... lower mold
21: Lower die peripheral die member
22 ... Lower mold center mold member
23 ... Lower mold gap
24 ... Lower gas vent hole
25 ... Lower retaining ring

Claims (7)

Pressing the molten glass using the upper mold and the lower mold facing each other, in a glass blank manufacturing method for forming a glass blank to be processed into a disc-shaped information recording medium substrate having a center hole,
As the upper mold and the lower mold, a mold composed of a central mold member and a peripheral mold member is used, and in the press, the press is completed before the temperature distribution on the molding surface of the peripheral mold member becomes uniform. Manufacturing method of glass blank. Pressing the molten glass using the upper mold and the lower mold facing each other, in a glass blank manufacturing method for forming a glass blank to be processed into a disc-shaped information recording medium substrate having a center hole,
A method for producing a glass blank, wherein a mold comprising a central mold member and a peripheral mold member is used as the upper mold and the lower mold, and a holding time in the press is 2 seconds or less. The method according to claim 1, wherein a gap is formed between the center member and the peripheral mold member. The method for manufacturing a glass blank according to claim 3, wherein the gap forms at least a part of a flow path of an airflow from the center of the upper and lower mold forming surfaces to the outside of the upper and lower molds. At the time of the pressing, the mold should be designed such that the boundary between the central mold member molding surface for transferring and molding the main surface of the glass blank and the peripheral mold member molding surface falls within the region where the center hole of the glass blank is to be opened. The method for producing a glass blank according to any one of claims 1 to 4, wherein A method for producing a substrate for an information recording medium, wherein the glass blank is machined by using the glass blank produced by the method according to claim 1. A method for producing an information recording medium, comprising forming an information recording layer on an information recording medium substrate produced by the method according to claim 6.

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