JPH10236831A - Production of thin planar glass and production of glass substrate for information recording medium as well as magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain thin planar glass having excellent flatness with good mass productivity by supplying fused glass between a lower die and an upper die held at a prescribed temp., press forming the fused glass, ending the press forming at the internal temp. higher than the glass transition temperature and ending the correction of warpage when the inside is above the glass transition point. SOLUTION: The fused glass is supplied onto the forming surface of the lower die stuck with heat resistant solid lubricant powder on the forming surface and thereafter, the upper die is lowered onto the lower die and the fused glass is press formed to the thin planar glass. The press forming is ended by raising the upper die when the temp. in the thin planar glass is at the temp. above the glass transition temperature. Next, this thin planar glass is subjected to warpage correction pressing and the warpage press correction is ended when the temp. in the thin planar glass is at the temp. above the glass transition temperature and thereafter, the planar glass is annealed. As a result, the thin planar glass having a warpage rate of 0.001 to 1% is obtd. and the flat polishing with high accuracy in lap polishing is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used as a substrate of an information recording medium such as a magnetic recording medium, a magneto-optical recording medium and an optical recording medium, or as a plate-like glass such as a filter for a camera and a mask blank. 3m thick
The present invention relates to a method for producing a thin glass plate having a thickness of about m or less by press molding, a method for producing a glass substrate for an information recording medium, and a magnetic recording medium.

[0002]

2. Description of the Related Art Recently, glass substrates are often used as substrates for information recording media such as magnetic recording media. Moreover,
As a method of manufacturing the glass substrate, a method of directly press-molding a molten glass using a molding die, that is, a direct press method, is employed instead of a method of cutting out from a plate-like glass.

As a conventional example of the direct press method, there is a method disclosed in Japanese Patent Application Laid-Open No. 5-105458. In this method, a mold having a release agent layer formed on a molding surface is pressed for a sufficient time until the temperature of the glass raw material is equal to or lower than the softening point and the upper and lower molds are thermally equilibrated. This is a method for producing a disk-shaped glass product having a final shape.

[0004]

However, in the above-described method in which the temperature of the glass raw material is equal to or lower than the softening point, and the press molding is performed for a sufficient time until the glass is thermally equilibrated with the upper and lower molds, the time required for press molding is long, and There was a problem that sex was bad. Further, in the method described in Japanese Patent Application Laid-Open No. 5-105458, it is difficult to completely control the temperature, and the warpage cannot be reduced to a certain degree or more. Glass products obtained by such a manufacturing method may have been able to be used as a substrate for a magnetic recording medium in the past, but recently, demands for higher density of a magnetic recording medium have increased,
Conventionally, a substrate having a smaller warpage has been demanded.
Since a high flatness is required for a substrate for a magnetic recording medium compatible with a head, it is not a preferable manufacturing method. Therefore, even in the method described in JP-A-5-105458, when manufacturing a glass substrate for a magnetic recording medium for an MR head, it is necessary to eventually grind and polish the glass substrate so as to be within a predetermined specification. is there. This grinding is performed in a state where pressure is applied from both sides of the thin glass sheet by a grinding plate. However, since the thin glass sheet having warpage is bent at the time of grinding, both sides of the thin glass sheet after grinding. When the pressure is released, the thick plate-shaped glass is warped again. For this reason, when grinding the thin glass sheet, the pressure applied to the thin glass sheet must always be finely adjusted so that the thin glass sheet does not bend,
For this reason, the grinding time is prolonged, and it is not possible to improve the mass productivity of the thin glass sheet having good flatness from this point.

As another example of the conventional direct press method, there is a method disclosed in JP-A-7-133121. In this method, the surface temperatures of the press surfaces of the upper and lower dies are set near the transition point of the glass to be press-formed, and the inner surface temperature of the body mold is set higher than the surface temperature of the press surface. Under this method, the molten glass is pressed with upper and lower molds to obtain a disk-shaped glass product close to the final product. However, also in this method, it is necessary to grind and polish the obtained glass substrate so as to be within a predetermined specification similarly to the above method, and there is a problem that mass productivity is poor for the same reason as described above.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a thin glass sheet having good flatness with high productivity, and further, a glass for an information recording medium. An object of the present invention is to provide a method of manufacturing a substrate and a magnetic recording medium.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a thin glass sheet, which comprises press-forming between a lower mold to which molten glass is supplied and an upper mold facing the lower mold. Press molding with a lower mold and an upper mold maintained at a temperature of, and when the inside of the thin sheet glass is at a temperature higher than the glass transition point, the press molding is terminated, and then the meat molded by the press molding is finished. Producing a thin glass sheet, wherein a step of correcting the warpage of the thin glass sheet is performed, and the step of correcting the warp is completed when the inside of the thin glass sheet is at a temperature higher than the glass transition point. Method. Preferably, from the viewpoint of shortening the pressing time, it is preferable that the press forming and the warpage correction pressing be completed in a time higher than the softening point of the glass. Further, the temperature of the glass for correcting warpage is preferably lower than the temperature for press molding. Thus, since each press is completed at a glass transition point, a glass softening point, and a higher temperature, the glass at the end of the forming press is:
The shape corresponding to the molding surface of the mold is basically maintained even after the mold is released, and is in a state where it can be minutely deformed by an external force. The time required for each press is preferably within 2 seconds, more preferably within 1.8 seconds. In addition, the above-mentioned glass inside is the main part of the glass covered with the surface layer part of the glass which remarkably radiates heat. The temperature inside the glass affects the shape maintenance and shape deformability. Further, the thin glass plate of the present invention is a thin glass substrate typified by a magnetic disk glass 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.

[0008] The lower mold is designed to sequentially go through a glass gob supplying step, a press forming step, a warp correcting step, a molded article removing step, etc., for example, a plurality of steps on the circumference of a turntable. Although it is preferable to dispose the lower mold and rotate the turntable so that the lower mold goes through each process, it may be designed to move in a linear direction. Also,
The number of lower molds simultaneously provided in each step may be a single number. On the other hand, the upper mold is arranged to face the lower mold located in the step of press molding. Therefore, at least the same number of the upper molds as the lower molds used for one-time press molding is required, but the upper molds may have more numbers. In addition, as long as the heat transferred from the molten glass to the upper mold after press molding can be removed and the temperature of the upper mold can be controlled in a short time so that the temperature of the upper mold becomes an appropriate temperature during molding, one upper mold may be used. .

Next, the temperatures of the molding surfaces of the upper mold and the lower mold (hereinafter, the upper mold and the lower mold are sometimes referred to as molding dies) are adjusted to a predetermined temperature at the start of press molding. It is necessary. Here, the predetermined temperature of the mold refers to a temperature suitable for molding the glass material into a thin plate shape. This temperature is appropriately determined depending on the type of glass, the thickness, the size of the glass plate, and the like.

Further, in order to adjust the temperatures of the molding surfaces of the upper mold and the lower mold at the start of press molding to the predetermined temperatures, means for heating the upper mold and the lower mold as necessary, and cooling. Measures are taken. As means for heating, for example, a method of arranging a plurality of nichrome heaters around the lower mold (upper mold) to heat, or applying a current to a coil arranged so as to surround the periphery of the lower mold (upper mold), And a method of heating with a gas. When a plurality of lower molds (upper molds) are arranged, and when a nichrome heater is arranged around each lower mold (upper mold) to heat, each of the lower molds (upper molds) has a temperature variation between the respective nichrome heaters. Since it is difficult to uniformly heat the lower mold (upper mold), it is preferable to use a method based on induction heating that enables uniform heating. According to the induction heating, one coil can heat each lower die (upper die), so that there is no problem of variation in the heat source temperature, and the distance between the coil and each lower die (upper die) is made constant. Thereby, the mold can be heated uniformly. Here, the current flowing through the coil during induction heating is
It is preferably a high-frequency current. At low frequency currents, the device becomes large and noise may be a problem due to the human audible sound range. On the other hand, when there is only one lower die (upper die), there is no problem of temperature variation among the nichrome heaters. Can be adopted.

On the other hand, the temperature of the mold provided for press molding is higher than before the press molding. In order to continuously form the glass, it is necessary to cool the forming die before the next press forming and to form all the formed products under the same temperature conditions. Therefore, a cooling unit is required at the same time as the heating unit. As the cooling means, a method of circulating water or air through the hollow portion of the mold, a method of spraying a liquid such as water onto the inner surface of the hollow portion of the mold to vaporize, and the like can be employed. According to the method of spraying and vaporizing the liquid, the mold can be cooled by the heat of vaporization of the liquid, so that the cooling effect can be obtained with a smaller amount of liquid than in the method of circulating the liquid. Therefore, the method utilizing the heat of vaporization of water or the like is preferable not only from the viewpoint of the cooling effect, but also from the viewpoint of making the cooling device smaller. Furthermore, for example, when it takes time to cool the upper mold, and after the molding, it is not possible to cool to a predetermined temperature by the next molding, a plurality of upper molds are prepared, and one of the upper molds performs press molding. During the operation, the other upper mold may be cooled, and the cooled upper mold may be sequentially subjected to press molding.

In the present invention, at the end of press molding, the temperature of the thin glass plate is higher than the temperature of the forming die, and at this time, the thin glass plate and the forming die are not in thermal equilibrium. However, as described above, since the molding die is kept at a predetermined temperature in advance, the thin glass sheet obtained by cooling after molding has a constant shape with a constant quality such as warpage.・ The shape is easy to polish. Also,
Since it is not necessary to cool the thin-plate glass and the mold until it reaches a thermal equilibrium state, the molding time can be shortened.

In the present invention, the glass body after the press molding has different amounts of heat released through the respective dies, which causes the opposite main surface of the glass body to bend in a curved manner. This warpage is reduced or eliminated in a warp correcting process of the thin glass plate. As a method of correcting the warp, for example, in a thin sheet glass after press molding, a method in which air or the like is blown from the higher temperature of an upper surface and a lower surface to remove heat, or a method of flattening a glass body after press molding. There is a method (hereinafter, referred to as a warpage correction press) of pressing with a pair of bases and deforming into a flat form by an external force. When the glass body is pressed by a pair of flat substrates, the upper die and the lower die used in the press molding may be used as the pair of flat substrates. It is preferable that the viscosity of the glass in the warp correcting step is a value that maintains the shape given by press molding when no external force is applied, and causes slight deformation when the external force is applied. The temperature of the flat substrate used in the warp correction is preferably 400 to 650 ° C. 400 °
If the temperature is lower than C, the glass causes defects. If the temperature exceeds 600 ° C., the glass adheres to the base. This temperature is preferably 250 to 20 ° C lower than the temperature of the glass, and preferably 50 to 200 ° C higher than the mold used in the forming press. This is because the temperature and viscosity of the glass are lower in the warp correction process than in the press molding, and cracks are prevented from occurring in the warp correction.

In the press molding, an amorphous molten glass is molded into a fixed shape corresponding to the inner peripheral molding surface of a molding die. The above-mentioned warping correction press is a thin plate-like glass obtained by press molding. This is not for the purpose of shape processing, but for removing (or reducing) the warpage of the thin-plate glass shaped by press molding and making the thin-plate glass flat or nearly flat. is there. A preferred warp correcting press is to cool a thin plate glass flattened between an upper mold and a lower mold by a pair of flat bases (or an upper mold and a lower mold) having a lower temperature. By doing so, the warpage of the thin glass plate is corrected. The warp correcting press is preferably performed when the inside of the thin plate glass is higher than the glass transition point. If the warp correction press is performed in a state of not higher than the glass transition point, the thin glass sheet tends to be cracked or broken because the thin glass sheet is too hard. On the other hand, if the thin plate glass is too soft, the shape of the thin plate glass changes due to the warp correcting press, which is not preferable. Therefore, the upper limit of the temperature at which the warp correcting press is performed is determined from this viewpoint.

The temperature of the upper mold and the lower mold used for press molding is set from the viewpoint of the type of glass, the releasability of the glass, damage to the mold, and the like. Is preferably 350 to 550 ° C. This is because if the temperature is lower than the lower limit of the mold temperature, the glass does not elongate sufficiently, and if the temperature exceeds the upper limit, seizure or sticking occurs. The temperature of the upper mold is preferably the same as that of the lower mold, or 50 to 100 ° C. lower than the temperature of the lower mold. Further, the temperature of the barrel mold for guiding the lower mold and / or the upper mold is preferably similar to that of the lower mold. The temperature of the lower mold is preferably controlled by the state of warpage of the thin glass sheet after press molding and warpage correction. When the completed sheet glass has a concave warp, lowering the temperature of the lower mold lowers the viscosity of the glass, so that warpage correction in the next step can be properly performed. Conversely, if there is a convex warpage, the lower die can be raised in temperature to increase the viscosity of the glass at the time of correcting the warp, so that the warp can be corrected properly.

[0016] In order to form the molten glass into a thin plate, it is necessary to stretch the molten glass in the outer circumferential direction. Therefore, a solid lubricant is attached to the molding surface of the molding die to improve the lubricity of the molten glass. It is preferred to raise. At this time, the forming die for forming the thin-plate glass receives a higher amount of heat from the molten glass than in the case of forming a thick-walled glass by press forming, and thus has a high temperature. Therefore, the solid lubricant is preferably a heat-resistant one that does not lose lubricity even in a high temperature range. Such a heat-resistant solid lubricant is not particularly limited as long as it has excellent heat resistance,
Boron nitride (BN) is preferred. Further, in order to obtain a sheet glass having excellent mechanical strength even in the case of an extremely thin sheet glass, a glass material having a high melting temperature may be used. In such a case, since the temperature of the mold also becomes considerably high, the heat resistance required of the solid lubricant becomes very high. Even in such a case, a high heat-resistant solid lubricant powder such as BN powder is preferably used. By using a powdered heat-resistant solid lubricant, uniform adhesion of the glass to the molding surface and removal of excess can be easily performed.

Further, the material of the molding die may be any material having heat resistance, and graphite, tungsten alloy, nitride, carbide, heat-resistant metal, etc. are used. Particularly, cast iron has excellent strength and durability. preferable.

The thin glass sheet completed through the forming press and the warpage correcting press of the present invention has a case where warpage is completely removed and a case where warpage remains. If the warpage can be removed by mechanical grinding or polishing, a finished press with warpage remaining may be used. If a warped glass substrate is simply ground and polished, the finished product will still be warped. Therefore, in order to grind and polish a warped pressed product, a device is required. In order to realize a good grinding method, the point is that, when grinding, it is sufficient to carry out grinding while suppressing the curvature of the pressed product from being deformed by the load of the grinding lapping machine. Specifically, the load on the lapping machine is gradually increased with the passage of time from the start of grinding, and after a flat glass substrate is formed, the load is further increased so that the plate thickness becomes a predetermined size. I just need. As another method of suppressing the bending deformation of the pressed product, instead of making the shape of the pressed product a simple disk shape, a pressure receiving portion that supports the pressure of the lapping machine is pressed around the pressed product. It may be formed at the stage. In the case of such a shape, since the pressure of the lapping machine is received by the pressure receiving portion, the deformation of the curved portion can be easily suppressed. The invention of grinding and polishing such a warped glass substrate flat is disclosed in JP-A-5-105458 and JP-A-7-133.
The invention can also be applied to a pressed product obtained by the method described in the pressing method described in JP-A-121.

The thin-plate glass obtained by the above-mentioned manufacturing method becomes 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) rough (rough polishing),
(2) Sanding (fine grinding, lapping), (3) first polishing (polishing), and (4) second polishing (final polishing, polishing). In some cases, (1)
Roughing (rough polishing) may be omitted.

Further, the above-mentioned glass substrate for an information recording medium constitutes a magnetic recording medium by sequentially laminating an underlayer, a magnetic layer, a protective layer and a lubricating layer on the glass substrate. Here, as the material of the glass substrate of the magnetic recording medium, for example, aluminosilicate glass, soda lime glass, sodaaluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass And the like. Further, glass having the following composition is preferably used. (1) Crystallized glass 1% by weight, SiO _2: 60 to 87%, Li ₂ O: 5%
To 20% Na ₂ O is 0 to 5% K ₂ O 0-10%
Na ₂ O and K ₂ O 0.5 to 10% in total, MgO is 0.5 to 7.5%, CaO is from 0 to 9.5%, SrO 0
-15%, BaO 0-13%, ZnO 0-13%,
B ₂ O ₃ is 0~10%, Al ₂ O ₃ is 0%, P ₂
O ₅ is 0.5 to 8%, TiO ₂ is 0 to 5%, ZrO ₂ is 0 to 3%, SnO ₂ is 0~3%, As ₂ O ₃ and Sb ₂ O
₃ contains 0 to 2% in total, and 0 to 5% of a fluoride of one or more metal elements of the metal oxide as a total amount of F,
V ₂ O ₅ , CuO, MnO may be optionally used as a coloring component.
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 , E
at least one selected from the group of r ₂ O ₃ containing 0 to 5%, lithium disilicate case, by containing alpha-cristobalite, alpha-quartz, lithium monosilicate, beta-spodumene, etc. as a main crystal, A crystallized glass having a crystal grain size of 3.0 μm or less. (2) crystallized glass 2 wt% display, SiO ₂ is 45 to 75%, CaO is 4
30% Na ₂ O is 2 to 15% K ₂ O 0 to 20%
Al ₂ O ₃ 0-7%, MgO 0-2%, ZnO 0
２2%, SnO ₂ is 0 to 2%, Sb ₂ O ₃ is 0 to 1%,
B ₂ O ₃ is 0~6%, ZrO ₂ is 0~12%, Li ₂ O
Contains 0 to 3%, a fluoride of one or more metal elements of the metal oxide described above in a total amount of 3 to 12% of F, and optionally contains Cr ₂ O ₃ , Co ₃ O _{4 and the} like as coloring components. And
A crystallized glass containing canasite or potassium fluororichterite as a main crystal and having a crystal grain size of 1.0 μm or less. (3) a glass 3 wt% display, SiO ₂ is 62~75%, Al ₂ O ₃ is 4 to 18%, ZrO ₂ is 0 to 15%, Li ₂ O is 3-1
Glass containing 2% and ₃ to 13% of Na2O. weight%
With 62-75% SiO ₂ , 5-15% Al
₂ O ₃ , 4-10% Li ₂ O, 4-12% Na
Contains 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;
Further, the weight ratio of Al ₂ O ₃ / ZrO ₂ is 0.4 to 2.5.
Is a glass for chemical strengthening.

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

As the underlayer, for example, Cr, Mo, T
a, an underlayer made of at least one material selected from nonmagnetic metals such as Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic properties. The underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, Cr / Cr, Cr / CrMo, Cr / CrV, Cr
V / CrV, Al / Cr / CrMo, Al / Cr / C
r, a multilayer base layer of Al / Cr / CrV, Al / CrV / CrV and the like.

As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiCr, C
oCrTa, CoPtCr, CoNiPt, CoNi
CrPt, CoNiCrTa, CoCrTaPt, Co
A magnetic thin film such as CrPtSiO may be used. The magnetic layer is made of a non-magnetic film (for example, Cr, CrMo, Cr).
V, etc. to reduce noise (for example, CoPtCr / CrMo / CoPtCr, CoC
rTaPt / CrMo / CoCrTaPt). As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head),
Co, Y, Si, rare earth elements, Hf, Ge, S
An impurity element selected from n and Zn or an element containing an oxide of these impurity elements is also included. As the magnetic layer, in addition to the above, ferritic, iron - rare-earth and, in a non-magnetic film made of SiO _2, BN F
Granules having a structure in which magnetic particles such as e, Co, FeCo, and CoNiPt are dispersed may be used. Also,
The magnetic layer may be of any of an internal recording type and a vertical recording 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 with an underlayer, a magnetic layer, and the like by an in-line type sputtering apparatus. Also,
These protective layers may be a single layer, or may have a multilayer structure composed of the same or different films. further,
Another protective layer may be formed on the protective layer or in place of the protective layer. For example, instead of the above protective layer,
Colloidal silica fine particles may be dispersed and applied in a state where tetraalkoxylan is diluted with an alcohol-based solvent on the Cr film, followed by firing to form a silicon oxide (SiO ₂ ) film.

The lubricating layer is prepared, for example, by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying the diluted lubricant to the medium surface by dipping, spin coating, or spraying. It is formed by performing heat treatment.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for producing a thin glass sheet according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a conceptual diagram of a temperature change characteristic of a raw glass, and FIG.
FIG. 3 is a process diagram of the manufacturing method. The composition of the raw glass whose temperature change characteristics are shown in FIG. 1 is as follows. That is, Si
O ₂ is 63.7, Al ₂ O ₃ is 14, Li ₂ O is 7, N
a ₂ O is 9, ZrO ₂ is 6, Sb ₂ O ₃ is the weight percent of 0.3. As shown in FIG. 2, in the manufacturing method according to the embodiment of the present invention, first, in step 1, a heat-resistant solid lubricant powder is attached to a molding surface of a lower die. The heat-resistant solid lubricant powder is made of hexagonal BN (boron nitride) powder, and is sprayed together with gas to adhere to the molding surface of the lower die. By adhering the heat-resistant solid lubricant powder to the molding surface, it is possible to improve the releasability and the extension of the molten glass.
Next, in step 2, an appropriate amount of molten glass (1200 ° C. as shown in FIG. 1) is supplied onto the molding surface of the lower mold to obtain an ohashi-shaped glass gob that is rounded by surface tension. Next, in step 3, the upper mold is lowered onto the lower mold, and the glass gob is press-molded into thin plate-like glass using the upper and lower molds. At this time, the press molding is performed in a very short time of about 1 second, and when the thin sheet glass is in a softened state, that is, the inside of the thin sheet glass has a softening point (Ts) of 690 ° C. as shown in FIG. ) When the temperature is equal to or higher than the above, the upper mold is raised to end the press molding. The upper mold used for the press molding has a heat-resistant solid lubricant powder (hexagonal BN powder) adhered to the molding surface in advance similarly to the lower mold. Therefore, it is possible to prevent the glass from being fused to the upper mold when the upper mold is separated from the soft, high-temperature sheet glass.

Next, a step of correcting the warpage rate is performed on the thin glass sheet left on the lower mold. Here, a warp correcting press was performed using a mold having a molding surface similar to that of the upper mold. In this case, the warp correction press is performed twice, and when the first warp correction press is performed as shown in step 4 of FIG. 2, the thin glass sheet is still at 690 ° C. as shown in FIG. Above the softening point. next,
When the second warp correcting press is performed on the thin glass in step 5, the thin glass has a softening point of 690 ° C. and a transition point (Tg) of 500 ° C. as shown in FIG. At an intermediate temperature. Thereafter, the thin glass sheet is taken out of the lower mold in a state where the temperature is lowered to a transition point temperature of 500 ° C. or lower (however, a temperature higher than a strain point of 380 ° C.) (Step 6), and an annealing step of Step 7 (9 hours) Transfer to

According to such a method, since the thin sheet glass is in a softened state and the press forming is completed when the forming die and the glass are not in thermal equilibrium, the press forming is started. Time is shortened. In addition to shortening the press time, the warp correction press is terminated when the inside of the thin glass plate is higher than the glass transition point, and the time from the end of press molding to the end of the warp correction press is also set short. Therefore, according to this method, mass productivity of the thin plate glass is improved. Further, in this method, the pressing time is short, the amount of heat transferred from the thin plate glass to the upper mold and the lower mold is not uniform, and the upper mold side and the lower mold side of the thin plate glass are thermally unbalanced. In this state, the thin glass plate is warped to some extent, but the warp is corrected by the warp correcting press, so that a thin flat glass plate with good flatness is manufactured.

FIG. 3 is a plan view showing one specific example of the upper die device 11 and the lower die device 12 used in the above method. The lower mold device 12 is provided with 16 lower molds 14 at equal intervals on the same circumference on a turntable 13 that rotates by one pitch at a rate of once every two seconds around a rotation axis (not shown) at the center. The lower mold 14 sequentially moves from the position A to P shown in the figure each time the turntable 13 rotates by one pitch. As for the lower mold 14, the heat-resistant solid lubricant powder is adhered to the molding surface at the position O as shown in step 1 of FIGS. 1 and 2, and at the position A as shown in step 2 of FIGS. Is supplied with a glass gob and the position C
In FIG. 1 and FIG. 2, press forming is performed as shown in step 3; at position D, the first warp correction press is performed as shown in step 4 in FIG. 1 and FIG. A second warp correcting press is performed as shown in step 5 of FIG. 2 and the thin glass sheet is taken out at positions L to N as shown in step 6 of FIGS. Also, one high-frequency coil 15 is provided so as to surround the outside and inside of the 16 lower dies 14. In other words, in this device, one common high-frequency coil 15
The lower dies 14 are subjected to high-frequency induction heating in a lump. Moreover, in order to heat each lower mold to the same temperature, the high-frequency coil 15 surrounds the outer and inner sides of the lower mold arranged on the circumference so that the distance between the lower mold and the coil is constant. Are located. Thereby, the sixteen lower dies 14 can be uniformly heated. Moreover, the 16 lower dies 14 rotate,
Since the positional relationship between the 16 lower molds 14 and the high-frequency coil 15 becomes uniform, the 16 lower molds 14 can be more uniformly heated. For this reason, when the mold is heated by high-frequency induction heating, a partial temperature difference does not occur in one mold, so that it is possible to prevent partial stretching failure of glass and fusion to the mold. . In addition, all the molds can be controlled to a desired temperature, and thin-plate glass of the same quality can be mass-produced.

The upper die device 11 has an upper die 17 attached to the tip of each leg of an octopus-shaped rotary unit 16, and eight upper die 17 are integrated with the rotary unit 16 to form a turntable 13.
Similarly to the above, the positions a to h are rotated by one pitch at a rate of once every two seconds. The upper mold 17 is also heated by high-frequency induction heating. In this case, one high-frequency coil 1 surrounds the inside and outside of the eight upper molds 17.
8 are provided, and eight upper dies 17 are provided by the high-frequency coil 18.
It is preferable to perform high-frequency induction heating in a lump. The upper mold 17 has heat-resistant solid lubricant powder adhered to the molding surface. This adhesion can be performed at any position other than the position where the upper mold 17 is subjected to pressing. It can be carried out. In addition, the upper mold 17
Is the lower mold 1 of the position C at the position a directly opposite to the position e.
4 and is subjected to press molding (in the figure, it is shifted to the left for convenience of illustration). Therefore, in this device, when each upper die 17 is rotated to the position a, that is, 8
Since press molding is performed once per press molding, and the same upper mold is used for press molding after a certain time, abnormal heating of the upper mold 17 can be prevented. That is, the upper mold 17 receives heat from the glass gob and rises in temperature when subjected to press molding, and when this is repeated continuously, an abnormal heating state occurs, causing problems such as sticking of the glass to the molding surface. According to 1 press for 8 press moldings
Since the same upper mold is used at intervals of time, the upper mold 17 does not enter an abnormally heated state, is maintained at a predetermined temperature controlled by high-frequency induction heating, and can prevent glass sticking and the like. .

It is preferable that both the high-frequency coil 18 of the upper die device 11 and the high-frequency coil 15 of the lower die device 12 are water-cooled to prevent the high-frequency coil from being heated by the heat radiated by the molding die. Further, for example, when the upper die is singular, as shown in FIG. 4, the coil 18 is disposed so that the distance between the upper die 17 and the coil 18 is constant, so that the upper die 17 is uniformly heated. be able to. Further, when the upper die is singular as shown in FIG. 4, a method may be adopted in which a nichrome heater is similarly arranged around the upper die instead of the coil 18 and heating is performed.

The upper mold 17 and the lower mold 14 can have various structures, and FIG. 5 shows a specific example. Upper mold 17
Is composed of a cylindrical upper mold body 21 and a support rod 22 formed at the center of the upper surface of the upper mold body 21 to support the upper mold body 21. The flat lower surface of the upper mold body 21 A pressing surface (forming surface) 23 is provided. Further, when the support rod 22 is moved up and down by a driving means (not shown), the upper die 17 is moved up and down. In the center of the upper die body 21 and the support rod 22, a hollow portion 24 is formed which is open on the upper surface of the support rod 22, and the upper die portion around the hollow portion 24 has a hollow portion 24. 8 are formed at the back of the support rod 22 so as to communicate with the hollow portion 24 and open to the upper surface of the support rod 22 as shown in the plan view of FIG. Here, when water is sprayed into the cavity 24 together with air, the upper mold 17 can be cooled using the heat of vaporization of water. The vaporized water is discharged from the discharge hole 25. Since the heat of vaporization of water per unit volume is larger than the specific heat, the cooling method using this heat of vaporization can be efficiently cooled without requiring larger equipment than the method of circulating water as a cooling medium.

The upper die 17 is provided with a body die 26 surrounding the upper die 17. The body die 26 has a cylindrical body 27 and an upper end portion of the body 27 inside. An annular flange portion 28 is formed so as to protrude. Here, the inner peripheral surface of the lower surface of the body 27 has a larger diameter than the others, and has a downwardly extending slope 29 for forming a chamfer on the press-formed thin glass plate. The upper die 17 is provided slidably up and down on the inner peripheral surface of such a trunk die 26.

The lower mold 14 has a cylindrical lower mold main body 31 and a lower mold main body 31 formed at the center of the lower surface of the lower mold main body 31.
And a support rod 32 that supports
The flat upper surface of the lower die body 31 is a pressing surface (forming surface) 33. Further, when the support rod 32 is moved up and down by a driving means (not shown), the lower die 14 is moved up and down. In the center of the lower die body 31 and the support rod 32, a hollow portion 34 is formed which is open on the lower surface of the support rod 32. In the lower die portion around the hollow portion 34, a hollow portion 34 is formed. The discharge hole 35 communicating with the hollow portion 34 at the back of the support rod 32 and opening on the lower surface of the support rod 32 is formed as shown in the bottom view of FIG. Here, water is sprayed into the cavity 34 together with air. The lower mold 14 is cooled using the heat of vaporization of the sprayed water. The vaporized water is discharged from the discharge hole 35. The above cooling is PID controlled by a signal from a thermocouple installed in the mold, the mold is controlled to a predetermined temperature, and the molten glass is always kept at a constant temperature even when continuously molded. It can be molded with a mold.

The lower die 14 is provided with a trunk die 36 surrounding the lower die 14. The trunk die 36 has a cylindrical trunk die body 37 and a lower end part of the trunk die body 37. An annular flange portion 38 is formed so as to protrude. Here, the inner peripheral surface of the upper surface portion of the trunk die body 36 is larger in diameter than the others, and the inner peripheral surface of the portion changed to the larger diameter is formed by chamfering the press-formed thin plate glass. The slope 39 is widened upward. The lower mold 14 is
The inner peripheral surface of such a die 36 is provided so as to be slidable up and down.

The pressing surface 33 of the lower die 14 and the pressing surface 23 of the upper die 17 have, for example, a surface roughness (Ra) of 0.5.
It is formed on a rough surface of about 2.0 μm. This rough surface may be formed on the entire press surfaces 33 and 23 or may be formed only on a part of the press surfaces 33 and 23. By forming the rough surface on the press surfaces 33 and 23, it is possible to improve heat insulation, prevent sticking of glass, and improve adhesion of the heat-resistant solid lubricant powder. In the above configuration,
Slope 29 for forming a chamfered portion on the inner peripheral surface of body dies 26, 36,
Although 39 is formed, the durability of such a slope forming method is improved as compared with a method of forming a slope with a projection or the like on a molding die.

In addition to the upper die 17 and the lower die 14 as described above, at positions D and E in FIG. As shown in the cavities 24, 34 and the discharge holes 25, 35, upper dies (molding dies) 71, 72 for warpage correcting press are provided. The upper dies 71 and 72 for the warpage correcting press are provided with body dies 71A and 72A, and have the same configuration as the upper die 17 for press forming described above. However, while the temperature of the forming surface of the upper die for press forming 17 is 410 ° C., the temperature of the forming surface of the upper die 71 for the first warpage correcting press is 600 ° C. The temperature of the molding surface of the mold 72 is adjusted to 560 ° C.

Next, a method for press-molding a disk-shaped thin glass plate using the molding apparatus having the above-described configuration will be described with reference to FIG. 3 and FIGS. 7 to 9, illustration of the cavities 24 and 34 and the discharge holes 25 and 35 is omitted for simplification of the drawing, as in FIG. When the lower mold 14 rotates to the position A in FIG. 3, as shown in FIG. 7A and the position A in FIG.
The molten glass 42 heated to 1200 ° C. from the platinum pipe 41 is supplied to the lower mold 14 at a constant flow rate (450 ° C. on the molding surface).
When the molten glass 42 is supplied to the
Is cut by the cutting blade 43 as shown in FIG. The cut molten glass 42 becomes an ohashi-like glass gob that is rounded due to surface tension. Next, when the lower mold 14 rotates to the position C in FIG. 3, as shown in FIG.
(Temperature of the molding surface 410 ° C.) is lowered integrally with the body mold 26,
The lower surface of the trunk die 26 contacts the upper surface of the lower die 36. Next, as shown in FIG. 8B and the position C in FIG. 10, the upper mold 17 slides down the inner peripheral surface of the body mold 26 and descends, and the upper mold 17 and the lower mold 14 press-mold a glass gob. I do. Then, the glass gob spreads over the entire flat space surrounded by the trunk molds 26 and 36 to become the thin-plate glass 44. At this time, the both sides of the outer peripheral portion of the thin-plate glass 44 are provided with body molds 26 and 36.
A chamfer for preventing chipping is formed by the slopes 29 and 39 on the inner peripheral surface. The time required for molding is about 1.7 seconds.

Next, as shown in FIG. 9A, the upper die 17 slides on the inner peripheral surface of the barrel die 26 and rises. At this time, there is a possibility that the thin plate glass 44 may rise by sticking to the upper mold 17, but in this apparatus, the inner surface (the slope 29 is removed) of a large part of the inner peripheral surface diameter of the lower surface of the upper mold body 26. Since the thin glass 44 is pressed by the inner surface of the portion having the thin glass 44, the thin glass 44 does not rise integrally with the upper mold 17, and the thin glass 44 is held on the lower mold 14. Then, FIG.
As shown in (b), the upper mold barrel 26 rises. At this time, since the contact area between the upper die 26 and the thin plate glass 44 is small, the thin glass 44 does not stick to the upper die 26 and rise.

Next, when the lower mold 14 is rotated to the position D in FIG. 3, the lower mold 14 and the body mold 3 are rotated as shown in the position D in FIG.
The upper mold 71 and the body mold 71A for the first warp correction press are lowered onto 6, and the first warp correction press is performed on the thin glass plate 44 held on the lower mold 14. Further, when the lower mold 14 rotates to the position E in FIG. 3, the upper mold 72 and the body mold 72A for the second warpage correction press are placed on the lower mold 14 and the body mold 36 as shown in the position E in FIG.
Is lowered, and a second warp correcting press is performed on the thin glass plate 44 held on the lower mold 14. 1
The time required to correct the warpage is about 1.7 seconds. Thereafter, when the lower mold 14 rotates to the positions L to N in FIG.
4 slides on the inner peripheral surface of the barrel die 36 and rises, so that the thin glass sheet 44 is taken out. Thereafter, the lower mold 14 rotates to the positions O, P, A,... In FIG. 3 and is again subjected to press molding. The upper mold used in the warp correction may be the upper mold 73 in FIG. 16 in which the upper mold 71 (or 72) in FIG. 10 and the body mold 71A (or 72A) are integrated.

In this way, a disk-shaped glass 61 having a diameter of 66 mm and a wall thickness of 1.3 mm shown in FIG. 11 was actually manufactured. Further, the warpage ratio of the disk-shaped thin glass plate manufactured as described above was examined. The magnitude of the warpage ratio was a value of the ratio (b / a) of the warpage amount b to the reference length (diameter of the disc-shaped glass 61) a in FIG. As is evident from Table 1, the warp b of the disc-shaped glass becomes smaller each time the warp correcting press step is performed.

[Table 1] The thin glass sheet pressed in this way is formed thicker than the final product, and both main surfaces are ground by lap polishing or the like. At this time, in the thin-plate glass of this example, the magnitude of the warp could be made constant to some extent, and the direction of the warp could also be made constant upward and concave. For this reason,
In the subsequent lap polishing, the warp directions could be aligned and the flat grinding could be performed with high precision. On the other hand, if the direction of the warp is upward or downward, the so-called unsuitable products, in which lap polishing is not stable and cannot be ground and polished flat with high precision, increase. Here, it is considered that the reason why the directions of the warp were all constant was that the manner in which the heat of the molten glass was deprived in the manufacturing process was constant in all the glasses.

Hereinafter, the machining will be described in detail.
As for the machining, specifically, the surface of the above glass is washed with water, and the following (1) roughing (rough polishing), (2) sanding (fine grinding, lapping), and (3) first polishing (Polish) and (4) Second polishing (final polishing, polishing).

(1) Roughing Step First, both surfaces of the above glass substrate were ground one by one with a fine diamond grindstone. The load at this time is 10
It was about 0 kg. Thereby, the surface roughness of both surfaces of the glass substrate was finished to about 10 μm by Rmax (measured according to JIS B 0601). Next, a hole was made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end face was also ground to reduce the diameter to 6 mm.
After 5 mmφ, a predetermined chamfering process was performed on the outer peripheral end surface and the inner peripheral surface.

(2) Sanding (Lapping) Step Next, the glass substrate was sanded. This sanding step aims at improving dimensional accuracy and shape accuracy.
The sanding process was performed using a lapping device, and was performed twice while changing the grain size of the abrasive grains to # 400 and # 1000. Specifically, first, both sides of the glass substrate housed in the carrier are 0 to 1 μm in both precision and surface roughness (Rmax) by rotating the internal rotation gear and the external rotation gear using alumina abrasive grains of particle size # 400. Lapping was performed to about 6 μm. In this lapping, the load was gradually increased from 80 kg to 120 kg. Next, lapping was performed by changing the particle size of the alumina abrasive grains to # 1000, to obtain a surface roughness (Rmax) of about 2 μm. The glass substrate that had been subjected to the sanding process was washed by sequentially immersing it in a neutral detergent and water washing tank.

(3) First Polishing (Polishing) Step Next, a first polishing step was performed. This first polishing step is intended to remove scratches and distortion remaining in the above sanding step, and was performed using a polishing apparatus. For details, use a hard polisher (cerium pad M) as polisher (polishing powder).
HCl (manufactured by Speed Fam) under the following polishing conditions. Polishing liquid: cerium oxide + water Load: 300 g / cm ² (L = 238 kg) Polishing time: 15 minutes Removal amount: 30 μm Lower platen rotation speed: 40 rpm Upper platen rotation speed: 35 rpm Inner gear rotation speed: 14 rpm Outer gear rotation speed : 29 rpm The glass substrate after the above first polishing step was washed with a neutral detergent, pure water, pure water, IPA (isopropylene alcohol), IP
A (steam drying) was sequentially immersed in each cleaning tank for cleaning.

(4) Second Polishing Step Next, the polishing apparatus used in the first polishing step is performed, and the polisher is changed from a hard polisher to a soft polisher (Polyak: manufactured by Speed Fam). Carried out. The polishing conditions were the same as in the first polishing step, except that the load was 100 g / cm ² , the polishing time was 5 minutes, and the removal amount was 5 μm. The glass substrate after the second polishing step was immersed in each of a washing tank of a neutral detergent, a neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) to be washed. In addition, ultrasonic waves were applied to each cleaning tank. Thus, a disc-shaped glass substrate for an information recording medium having an outer diameter of 65 mmφ, a central hole diameter of 20 mmφ, a thickness of 0.5 mm, Rmax of 40 Å, and Ra of about 8 Å was obtained.

In the manufacturing method according to the above-described embodiment of the present invention, a plurality of lower dies 14 are arranged on the turntable 13, and each lower die is sequentially conveyed to a pressing position to perform a pressing step and the like. Since the molded thin-plate glass is taken out from each lower mold, and each lower mold 14 is again used for manufacturing the thin-plate glass, the thin-plate glass can be mass-produced. In addition,
In the above embodiment, the warp correcting press is performed at the position D and the position E. However, if the flatness is not so required, it may be performed at one of the position D and the position E.
However, after the position F, the thin glass plate 44 becomes too hard, and when the warpage correction press is performed, cracks and cracks tend to occur.

Further, in the above embodiment, the same upper mold as the press-formed upper mold is used as the upper mold for the warpage correcting press, but the upper mold as shown in FIGS. 12 to 14 is used. You may. As shown in FIG.
A small-diameter cylindrical member 51 having a groove 52 serving as a passage of cooling air and a bottomed large-diameter cylindrical member 53 having a flange 54 formed on the opening side are welded at a welding portion 57. Things. Such an upper mold 50 has a cylindrical body mold 56.
The upper die 50 is reciprocated along the axial direction in the body die 56 by an air cylinder (not shown). The upper mold 50 is configured such that the downward movement of the upper mold 50 is restricted by the flange 54 contacting a step surface 56B formed inside the upper end of the body mold 56.

The trunk 53 of the large-diameter cylindrical member 53 of the upper die 50
The outer diameter of A is smaller than the diameter of the press surface 61 of the lower die 60 shown in FIG. 13 (enlarged view of the circle A in FIG. 12), and the lower end of the body 53A has a chamfered portion 53B. It is formed along the entire circumferential direction. Thereby, at the time of the warpage correction press, the cooling speed of the thin plate glass 44 is high and the press surface 55 of the upper mold 50 does not hit the hardened peripheral portion, and the thin plate glass 44 is not cracked or broken. It is prevented from occurring.

As shown in FIG. 14, a plurality of v-shaped grooves 55A are radially formed on the press surface 55 of the upper die 50. Each groove 55A is for facilitating separation of the thin glass plate 44 from the press surface 55 of the upper die 50 after the warp correction press. As described above, the warp correcting press is performed when the shape of the thin glass sheet 44 is not deformed, so that the groove 5 is formed in the shape of the thin glass sheet 44.
5A has no effect.

A groove 56A for centering with the lower mold 60 shown in FIG. 13 is formed on the inner surface of the lower end of the body mold 56 along the entire circumferential direction. A groove 56A is formed in the protrusion 60A of the lower mold 60.
The upper die 50 and the lower die 60
Are aligned with each other.

The upper die 50 is particularly effective when the support portion 45 described later with reference to FIG. 15 is subjected to a warp correction press of the thin glass plate 44 formed at the outer peripheral end. That is, since the support portion 45 has a portion protruding toward the upper die, the protruding portion has a press surface 55 of the upper die 50.
, Cracks and cracks are likely to occur at the projection and at the boundary 58 with the projection of the thin plate glass 44. However, if the chamfered portion 53B is formed on the upper die 50, the pressing surface of the upper die 50 is pressed. 55 is prevented from hitting the support portion 45.

The thin glass plate formed by press molding is formed thicker than the final product, and it is necessary to grind both main surfaces by lap polishing or the like in order to obtain the final product. At this time, if the thin glass sheet is warped, the thin glass sheet bends when pressure is applied from both sides of the thin glass sheet by the grinding plate. Therefore, even if the thin glass sheet is flattened by grinding in this state, when the pressure is released from both sides, the thin glass sheet warps again, and it is difficult to obtain a flat thin glass sheet. Therefore, a portion that receives pressure from both surface sides of the thin plate glass may be provided in a part of the thin plate glass. As a specific example, as shown in FIG.
A support portion 45 (height: 1.5 mm) as a pressure receiving portion is provided along the entire circumferential direction of the thin plate glass 44 on the outer peripheral end of the thin plate glass 44 having a curved portion having a thickness of 1.3 mm.
To form It is preferable that the support portion 45 is formed so as to protrude from each of the front and back surfaces of the thin plate glass 44. When the surface of the thin plate glass 44 protrudes from the support portion 45, the curved portion of the thin plate glass 44 hits the upper platen 46 before the support portion 45 comes into contact with the upper platen 46 during grinding. This is because the state of the portion changes and the thin glass plate 44 warps after grinding.

The thin plate glass 44 is disposed between the upper platen 46 and the lower platen 47 as shown in FIG.
The thin plate glass 44 is ground while applying pressure from both sides by 6 and 47 to flatten the thin plate glass 44 and process it to a predetermined thickness. In this grinding, the pressure from both sides by the upper platen 46 and the lower platen 47 is received by the support portion 45, so that the thin glass sheet 44 is prevented from bending, and the curved state of the thin glass sheet 44 changes. Is ground in a state where is suppressed. Therefore, upper surface plate 4
Even when the pressure from both sides by the platen 6 and the lower platen 47 is released, the thin plate glass 44 does not warp, and it becomes easier to obtain the thin plate glass 44 with much better flatness. Also, the support portion 45
As a result, the curved portion of the thin plate glass 44 is not moved by receiving pressure from both sides by the upper platen 46 and the lower platen 47, so that the curved portion of the thin plate glass 44 does not move in the grinding process. Like thin glass 44
It is not necessary to finely adjust the pressure applied to the thin plate glass 44, the thin plate glass 44 can be efficiently ground, and the thin plate glass 44 with good flatness can be mass-produced.

In the above-mentioned grinding, the grinding proceeds in the latter half of the grinding, and the thin plate glass 44 and the upper platen 46 (the lower platen 4)
Since the contact area with 7) is large, it is preferable to apply a larger pressure than in the first half to carry out the grinding. Also, the support portion 45
May be provided on the center side with respect to the outer peripheral end of the thin plate glass in addition to the outer peripheral end in FIG. Further, such a support portion 45 can be easily obtained by providing a concave portion on the molding surface of the above-described upper die, lower die, and body die.

Although the present invention has been described in detail, it goes without saying that the above-described embodiment is merely one specific example.
The specific configuration of the upper and lower dies, the number of upper and lower dies, the relationship between the positions of the upper and lower dies and each process, the specific configuration of the upper and lower dies can be variously modified. . In the upper die and the lower die, the inner surface temperature of the barrel die can be set higher than the surface temperature of the press surface. Further, it is appropriate that the warp rate of the thin glass sheet is about 0.001% to 1%, and if the warp direction is constant in one of the upward and downward directions, the subsequent wrapping is performed. It becomes possible to grind flat with high precision in polishing.

[0057]

As described above, according to the present invention, a thin plate glass having good flatness can be manufactured with high mass productivity.
As a result, a high quality, high performance glass substrate for an information recording medium and a magnetic recording medium can be manufactured with high mass productivity.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a temperature change characteristic of raw glass in an embodiment of a method of manufacturing a thin plate glass according to the present invention.

FIG. 2 is a process chart showing an embodiment of a method for manufacturing a thin plate glass according to the present invention.

FIG. 3 is a plan view of an upper die device and a lower die device used in the method of FIG. 2;

FIG. 4 is a plan view showing another example of the relationship between the upper die and the high-frequency coil.

FIG. 5 is a sectional view showing a specific example of an upper die and a lower die of the apparatus of FIG. 3;

FIG. 6 is a plan view and a bottom view of the upper die and the lower die of FIG. 5;

FIG. 7 is a cross-sectional view for explaining press molding.

FIG. 8 is a cross-sectional view for explaining the press molding.

FIG. 9 is a cross-sectional view for explaining the press molding.

FIG. 10 is a cross-sectional view for explaining press forming and warpage correcting press.

FIG. 11 is a sectional view showing a disc-shaped glass manufactured according to the embodiment of the present invention.

FIG. 12 is a cross-sectional view showing another example of the upper die for the warpage correction press.

FIG. 13 is an enlarged sectional view showing a portion A in FIG. 12;

FIG. 14 is a bottom view showing the press surface of the upper die for warpage correction press in FIG. 12;

FIG. 15 is a sectional view showing another example of the thin plate glass according to the present invention and a grinding step.

FIG. 16 is a cross-sectional view showing another example of the upper die for the warpage correction press.

[Explanation of symbols]

 14 Lower die 17 Upper die 42 Molten glass 44 Thin glass plate 45 Supporting parts 71, 72, 73, 50 Upper die for warpage correcting press

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shizuo Suzuki 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Inside the Hoya Corporation (72) Inventor Takumi 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Inside of Hoya Co., Ltd. (72) Tetsuya Saito 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Inside of Hoya Co., Ltd. (72) Atsushi Saito 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Hoya (72) Inventor Katsuya Nagakura 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Inside Hoya Corporation

Claims (14)

[Claims] 1. A method for producing a thin glass sheet, comprising press-forming between a lower mold to which molten glass is supplied and an upper mold facing the lower mold, wherein the lower mold is maintained at a predetermined temperature. And press-molding with an upper mold, and ending press-forming when the inside of the thin-plate glass is at a temperature higher than the glass transition point, and then correcting the warpage of the thin-plate glass formed by press-forming. A method for producing a thin glass sheet, wherein the step of performing the step and correcting the warpage is completed when the inside of the thin glass sheet is at a temperature higher than the glass transition point. 2. The thin glass sheet according to claim 1, wherein the step of correcting the warp comprises pressing the thin glass sheet in a deformable state after press molding with a pair of flat bases. Production method. 3. The method for producing a thin plate glass according to claim 1, wherein the press forming is terminated when the inside of the thin plate glass is at a temperature higher than the softening point. 4. The method according to claim 1, wherein the press forming is completed in a state where the upper mold side and the lower mold side of the thin plate glass are thermally unbalanced. . 5. The method for producing a thin glass sheet according to claim 1, wherein the thin glass sheet and the upper mold and / or the lower mold are thermally unbalanced. 6. The method according to claim 1, wherein the upper mold and the lower mold after the press molding are cooled so that at least at the start of the next press, the molding surface of the upper mold and the molding surface of the lower mold are maintained at a predetermined temperature. 2. The method for producing a thin plate glass according to 1. 7. A method for producing a thin glass plate by press-molding a molten glass with a molding die, wherein a predetermined processing is performed on a press surface of an upper die and a lower die to thereby form one main surface of the thin glass plate. And forming a pressure receiving portion projecting from each of the other main surfaces from each of the main surfaces. 8. The method for manufacturing a thin plate glass according to claim 1, wherein a plurality of said lower dies are provided, and each lower die is supplied with molten glass at a predetermined position while sequentially moving, and said press forming is performed. A method for manufacturing a thin plate glass, wherein the warp correction and the glass removal are sequentially performed, and the lower mold after the glass removal is again provided for manufacturing the thin plate glass. 9. A glass substrate for an information recording medium, wherein the glass substrate for an information recording medium is obtained by grinding and polishing the main surface of the thin plate glass produced by the production method according to claim 1. Method. 10. A method for manufacturing a glass substrate for an information recording medium, wherein a glass substrate obtained by press-molding a molten glass with a molding die and finely curved is ground and polished. An information recording medium characterized by comprising a step of flattening a thin glass sheet while suppressing deformation of a thin glass sheet in a curved state, and a step of removing a predetermined amount of a surface to obtain a desired thickness. A method for manufacturing a glass substrate. 11. The method for manufacturing a glass substrate for an information recording medium according to claim 10, wherein in the flattening, the pressure of the lapping machine is increased continuously or stepwise from the start to the end of the grinding. 12. A method of manufacturing a glass substrate for an information recording medium for grinding and polishing a glass substrate obtained by press-molding a molten glass with at least a pair of molds, wherein a load of a lapping machine in the grinding step is: A method for manufacturing a glass substrate for an information recording medium, wherein a flat glass substrate is formed by setting a value at which deformation of a curved shape of a glass substrate can be suppressed. 13. A method for manufacturing a thin glass sheet according to claim 7, wherein each of the pressure receiving portions of the thin glass sheet manufactured by the method for manufacturing a thin glass sheet is subjected to a grinding pressure. And then polishing to obtain a glass substrate for an information recording medium. 14. A magnetic recording medium comprising at least a magnetic layer formed on a main surface of a glass substrate for an information recording medium manufactured by the manufacturing method according to claim 9.