JP4080561B2 - Manufacturing method of thin sheet glass - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention can be used as a substrate for an information recording medium such as a magnetic recording medium, a magneto-optical recording medium, and an optical recording medium, or as a plate glass such as a camera filter or mask blank. The present invention relates to a method for producing the following thin sheet glass by press molding.
[0002]
[Prior art]
As a method of manufacturing a glass substrate for an information recording medium such as a magnetic recording medium, in addition to a method of cutting out from plate-like glass, a method of directly press-molding from molten glass using a mold, that is, a direct press method is adopted. Yes.
As a conventional example of the direct press method, Japanese Patent Laid-Open No. 7-133121 (Ohara Co., Ltd.) describes that the surface temperature of the upper and lower mold press surfaces is set in the vicinity of the glass transition point, and the inner surface temperature of the barrel mold is set. There is described a method of press-molding a disk-shaped glass product without hindering the extension of the glass in the mold direction by setting the surface temperature higher than the press surface.
[0003]
[Problems to be solved by the invention]
In order to form the molten glass into a thin sheet glass by the direct press method, a process of converting the molten glass gob having a small shape into a sheet glass having a large diameter, that is, a process of well stretching the molten glass in the outer peripheral direction is performed. At this time, in order to stretch the glass well, the temperature of the molten glass is usually set to a relatively high temperature. However, when the temperature of the molten glass is high, the glass is easily fused to the mold, and as a result, it is difficult to stretch the glass thinly.
Also, when forming thin sheet glass, unlike the case of forming thick glass, the contact area between the glass and the mold is large, so the mold receives heat from the hot molten glass and the temperature rises rapidly. Therefore, the burden on the mold is large, and as a result, the mold life is shortened.
[0004]
Japanese Patent Application Laid-Open No. 5-105458 (Corning) discloses a molding method in which a sufficient time is pressed until the temperature of the glass raw material is equal to or lower than the softening point and is in thermal equilibrium. ₂ , BN (Boron Nitride), etc. in a solvent such as water or heat-resistant oil is applied to a mold, and a disk-shaped glass product is formed by forming a release layer on the mold surface as a solidified layer. Is described.
[0005]
However, graphite and MoS ₂ Is unsuitable as a lubricant for a high-temperature mold because it loses its releasability at a low temperature (about 500 ° C.).
Further, the release material layer formed on the molding surface as the solidified layer is easily peeled off when exposed to high temperature, and particularly in the case of a thin plate glass product such as a disk glass product. Once the release material layer is peeled off, it is necessary to form a release material layer again after removing the remaining release material layer, which significantly increases the work efficiency.
[0006]
In particular, in recent years, in all fields including the field of information recording media such as magnetic disks, there is a tendency to demand a glass material having excellent mechanical strength and heat resistance even if it is a very thin flat plate. Since such glass materials are generally in a fairly high temperature range, it is indispensable for the lubricant to be excellent in heat resistance when producing a thin plate glass using the glass material. .
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a method for producing a thin sheet glass by press molding molten glass, and after applying heat-resistant solid lubricant powder to the molding surface of the mold, press molding is performed. It is set as the manufacturing method of the thin sheet glass performed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is applied to a method for producing a thin sheet glass by press molding molten glass. Such molding is usually performed by pressing the lower mold with molten glass and then pressing it with the upper mold placed opposite to the lower mold. At this time, since the molten glass is adjusted to a certain viscosity, it has a thick repellent shape, but is stretched in the outer peripheral direction during pressing to be formed into a thin plate glass.
[0009]
The present invention provides a method for producing a thin sheet glass characterized in that, in the production process of the thin sheet glass, after the heat-resistant solid lubricant powder is adhered to the molding surface of the mold, press molding is performed. is there.
Here, the heat-resistant solid lubricant means a solid lubricant that does not lose its lubricity even at a temperature reached by a molding surface that contacts the glass of the mold during press molding. By using a solid lubricant that does not lose lubricity even at such a temperature, the molten glass can be well stretched in the outer peripheral direction, so that a very thin plate glass can be produced. Further, by interposing the heat-resistant solid lubricant between the mold and the molten glass, the amount of heat transferred from the glass to the mold can be reduced at the contact surface between the molten glass and the mold. For this reason, it is relieved that the temperature of the glass suddenly drops due to contact with the mold, and the glass solidified layer can be thinned. As the solidified layer becomes thick, a thin sheet glass having a desired thickness is obtained. It can be prevented from being lost. Furthermore, since there is little transfer of heat to the mold, the mold life can be extended by preventing the temperature of the mold from rising rapidly. Furthermore, even when the press is terminated when the glass is in a softened state, excellent releasability is exhibited when the mold is separated from the thin sheet glass.
[0010]
Here, the temperature reached by the molding surface of the mold during press molding varies depending on the type of glass, the temperature of the molten glass, the desired thickness and diameter of the thin sheet glass, and the like. Usually, the temperature is between the set temperature of the mold and the temperature of the molten glass, but in some cases, a temperature close to the temperature of the molten glass may be reached. Any solid lubricant that does not lose lubricity at such temperatures can be applied as a heat-resistant solid lubricant in the present invention. Among them, boron nitride (BN) that does not lose lubricity up to about 900 ° C., particularly α A type of boron nitride is preferably used.
[0011]
Next, it is preferable that the heat-resistant solid lubricant is adhered to the molding surface of the mold in a powder form. Since it can be made to adhere to a shaping | molding surface in the state containing gas, such as air, between powder particles as it is powder form, the heat insulation by having made the heat-resistant solid lubricant adhere can be improved more. In addition, by attaching it in powder form, it becomes possible to easily remove the heat-resistant solid lubricant remaining on the molding surface after molding by air injection or the like. Can be efficiently manufactured.
The particle size of the heat-resistant solid lubricant powder is not particularly limited. For example, in the case of BN powder, one having an average particle size of 5 to 15 μm can be used.
[0012]
The method for adhering the heat-resistant solid lubricant powder to the molding surface is not particularly limited. For example, in addition to the method of spraying with a gas such as air, a method of applying with a brush or the like can be mentioned. According to the method, it is easy to uniformly adhere to the molding surface, and the cooling effect of the molding surface by the gas injected at the same time can be used.
In order to uniformly adhere a predetermined amount of the heat-resistant solid lubricant powder to the molding surface of the mold, it is also preferable that the molding surface is appropriately formed into a rough surface. Further, as a means for uniformly attaching the heat resistant solid lubricant powder, it is also effective to adjust the water content of the heat resistant solid lubricant powder. When boron nitride powder is used as the heat-resistant solid lubricant powder, the water content is preferably less than 1% by weight.
[0013]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view for explaining an embodiment of the present invention, and is a plan view showing a thin-plate glass forming apparatus, particularly a lower mold apparatus. As shown in FIG. 1, a total of 16 lower molds 11 (heated to 410 ° C.) are arranged at equal intervals on the same circumference on the turntable 12, and the turntable 12 rotates by one pitch. Each of them passes through the positions A to P shown in the drawing in order to go through the following steps.
That is, heat-resistant solid lubricant powder is attached to the molding surface at position O, molten glass flowing down from the pipe is received at position A, press molding is performed at position C, and warp correction pressing is performed at positions D and E. The thin glass sheet is taken out at positions L to N.
[0014]
As described above, the BN powder is injected and adhered to the molding surface of the lower mold 11 at the position O by the injection device 13. FIG. 2 is a configuration diagram specifically showing the injection device 13. In the injection device 13, the BN powder 21 is built in the injection device main body 22, and an air inflow pipe 23 and an air and BN powder 21 outflow pipe 24 are connected to the injection device main body 22. At one end of the air inflow pipe 23, air is supplied at a pressure of 4 kg / cm, for example. ² The other end is inserted into the deposited layer of the BN powder 21 in the injection device main body 22. Therefore, the pressure from the sequencer 25 is 4 kg / cm. ² The air that has flowed out into the inflow pipe 23 in this way is injected from the hole 23a of the inflow pipe 23 in the injection device body 22 to wind up the BN powder 21 in the injection device body 22, and at the same time, the outlet valve 26 is opened to open the BN. It flows out to the outflow pipe 24 together with the powder 21. The outflowed air and BN powder are 4 kg / cm from the accelerator 27 on the outflow pipe 24. ² 1 is injected from the nozzle 28 at the tip of the outflow pipe 24 toward the molding surface of the lower mold 11 in FIG. As a result, BN powder adheres to the molding surface of the lower mold 11 and the lower mold 11 is cooled by heat exchange with the jet air. At this time, for example, by forming the molding surface of the lower mold 11 into a rough surface having a surface roughness (Ra) of 0.5 to 2.0 μm, adhesion of the BN powder can be improved.
[0015]
FIG. 3 is a front view of the tip opening of the nozzle 28 for injecting BN powder and air. As shown in this figure, the opening of the nozzle 28 is a mesh-like opening by attaching a mesh 29. Further, the central portion of the opening is closed by the closing member 30. Thus, it is preventing that BN powder and air concentrate on the center part of the molding surface of the lower mold | type 11 by setting it as a mesh-shaped opening part and plugging the center part.
[0016]
The molding surface of the lower die 11 is injected with BN powder once every time the lower die 11 reaches the position O. At this time, the water content of the BN powder is preferably less than 1% by weight. Furthermore, as the BN powder, purity: 98%, average particle size: 5 to 15 μm, specific surface area: 3 to 10 m ² / G, bulk density: 0.2-0.6 g / cm ^Three , True specific gravity: 2.26 h-BN powder (manufactured by Mizushima Alloy Iron Co., Ltd., HP) was used.
[0017]
At position C in FIG. 1, although not shown, an upper die (heated to 400 ° C.) is arranged on the lower die 11 for press molding. Also for this upper mold, an injection device as shown in FIG. 2 is provided, and BN powder is injected and adhered to the molding surface.
[0018]
In the method as described above, a plurality of lower molds are arranged and designed such that a glass gob supply process, a press molding process, a molded product removal process, and the like are sequentially performed. For example, as shown in FIG. It is preferable to arrange individual lower molds on the circumference of the substrate and rotate the turntable so that the lower mold passes through each step, but it may be designed to move in a linear direction. Moreover, the number of the lower mold | types simultaneously provided to each process may be single or plural.
On the other hand, the upper mold is arranged to face the lower mold positioned in the press molding process. Therefore, at least the same number of upper molds as the lower molds used for one-time press molding are required, but a larger number may be provided.
[0019]
Next, the temperature of each molding surface of the lower mold and the upper mold needs to be adjusted to a predetermined temperature at the start of press molding.
Here, the predetermined temperature for the mold means a temperature suitable for molding the glass material into a thin plate. This temperature is a temperature that is appropriately determined depending on the glass type, the thickness, the size of the glass plate, and the like.
[0020]
Furthermore, in order to adjust the temperature of the molding surfaces of the lower mold and the upper mold at the start of press molding to the predetermined temperature, means for heating and cooling the lower mold and the upper mold as necessary are provided. It is done.
As a means for heating, for example, a method in which a plurality of nichrome heaters are arranged around the mold and heated, a current is passed through a coil arranged so as to surround the mold, and the mold made of a conductor is induction-heated. Although there are a method and a method of heating with gas, the method by induction heating is preferable in that uniform heating is possible. Unlike the method of heating a single mold with a plurality of heat sources as in the case of heating with a nichrome heater, induction heating can control one or two or more molds with a single coil. There is no problem of variation, and the mold can be heated uniformly by keeping the distance between the mold and the coil constant. In addition, when induction heating is used, induction heating may be performed on both the upper mold and the lower mold, or on either one, and when using a trunk mold, it is applied to the trunk mold. Is also possible.
Here, the current passed through the coil during induction heating is preferably a high-frequency current. At low frequency currents, the device becomes large and noise may be a problem because it is in the human audible range.
[0021]
On the other hand, the temperature of the molding die used for press molding receives heat from the molten glass and is higher than before press molding. Therefore, in order to perform press molding under the same temperature condition for any thin sheet glass, it is preferable that the mold is returned to the temperature before molding before the next press molding. At this time, it is preferable to return the temperature by taking some cooling means, except when it is naturally cooled to the temperature before press molding after being subjected to press molding and then returned to the temperature before press molding. .
As the cooling means, a method of circulating water or air in the hollow portion of the mold, a method of spraying a liquid such as water on the inner surface of the hollow portion of the mold, 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 the method of circulating the liquid. Therefore, the method of using the heat of vaporization such as water 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 it cannot be cooled to a predetermined temperature after molding, the upper mold can be easily formed, and one of the upper molds is press-molded. When performing the above, another upper mold may be cooled and a plurality of upper molds may be circulated.
[0022]
In press molding, the press is terminated when the glass is in a softened state. Therefore, at the end of press molding, the temperature of the thin sheet glass is higher than the temperature of the mold, and at this point, molding with the thin sheet glass is performed. The mold is not in thermal equilibrium. However, since the mold is maintained at a predetermined temperature in advance, the thin glass sheet obtained by cooling after molding has a constant shape such as warpage and is easy to grind and polish. It has a shape. Further, since it is not necessary to cool the thin sheet glass and the mold until the thermal equilibrium state is reached, the molding time can be shortened.
Furthermore, for the purpose of shortening the press time, the press molding may be terminated at a temperature at which the central portion of the thin sheet glass is equal to or higher than the softening point of the glass material.
Moreover, since the thin sheet glass after press molding is in a softened state, a step of correcting the warpage of the thin sheet glass may be performed after press molding. The process of correcting the warpage of the thin sheet glass is, for example, by blowing air on only one side of the thin sheet glass, taking heat non-uniformly, or by a molding die having a molding surface similar to the upper mold. This is a step of correcting the magnitude of the warp by pressing again.
[0023]
In addition, when using a body mold, the mold temperature is set so that the surface temperature of the upper and lower press surfaces is near the glass transition point, and the inner surface temperature of the body mold is set higher than the surface temperature of the press surface. May be.
Further, the mold is formed of a heat-resistant material such as graphite, tungsten alloy, nitride, carbide, refractory metal, etc., but when performing high-frequency heating, it is limited to a refractory metal that can be heated by this. . In that case, cast iron is particularly preferable because of its excellent strength and durability.
[0024]
The thin plate-like glass obtained by the above manufacturing method becomes a glass substrate for information recording media, for example, through mechanical processing such as grinding and polishing.
Hereinafter, machining will be described in detail. For machining, specifically, the above glass surface is washed with water, and (1) roughing (rough polishing), (2) sanding (fine grinding, lapping), and (3) first polishing. Steps (polishing) and (4) second polishing (final polishing, polishing) are performed.
[0025]
(1) Roughing process
First, both surfaces of the glass substrate were ground one by one with a fine diamond grindstone. The load at this time was about 100 kg. Thus, the surface roughness on both surfaces of the glass substrate was finished to about 10 μm by Rmax (measured by JIS B 0601).
Next, a hole was made in the central portion of the glass substrate using a cylindrical grindstone, and the outer peripheral end face was ground to a diameter of 65 mmφ, and then a predetermined chamfering process was performed on the outer peripheral end face and the inner peripheral face.
[0026]
(2) Sanding (wrapping) process
Next, the glass substrate was sanded. This sanding step is intended to improve dimensional accuracy and shape accuracy. The sanding process was performed using a lapping apparatus, and was performed twice with the grain size of the abrasive grains being changed to # 400 and # 1000.
Specifically, first, using alumina abrasive grains having a particle size of # 400, setting the load to about 100 kg, and rotating the inner and outer rotation gears, both the surfaces of the glass substrate housed in the carrier have both accuracy of 0. Lapping was performed to ˜1 μm and surface roughness (Rmax) of about 6 μm.
Subsequently, 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 sequentially immersed in each washing bath of neutral detergent and water and washed.
[0027]
(3) First polishing process
Next, a first polishing step was performed. This first polishing step is intended to remove scratches and distortions remaining in the sanding step described above, and was performed using a polishing apparatus.
Specifically, a hard polisher (cerium pad MHCl: manufactured by Speed Fam Co., Ltd.) was used as the polisher (polishing powder), and the first polishing step was performed under the following polishing conditions.
Polishing liquid: Cerium oxide + water
Load: 300 g / cm ² (L = 238kg)
Polishing time: 15 minutes
Removal amount: 30 μm
Lower platen rotation speed: 40rpm
Upper platen rotation speed: 35rpm
Inner gear speed: 14rpm
Outer gear speed: 29rpm
The glass substrate which finished the said 1st grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, a pure water, IPA (isopropylene alcohol), and IPA (steam drying) sequentially, and was wash | cleaned.
[0028]
(4) Second polishing step
Next, the polishing apparatus used in the first polishing step was performed, and the second polishing step was performed by changing the polisher from a hard polisher to a soft polisher (Porelax: manufactured by Speedfam). Polishing conditions are 100 g / cm load. ² The first polishing step was the same as the polishing step except that the polishing time was 5 minutes and the removal amount was 5 μm.
The glass substrate after the second polishing step was washed by sequentially immersing it in each washing tank of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying). In addition, the ultrasonic wave was applied to each washing tank.
In this manner, a disk-shaped glass substrate for information recording media having an outer diameter of 65 mmφ, a central hole diameter of 20 mmφ, a thickness of 0.5 mm, Rmax of 40 angstroms, and Ra8 angstroms was obtained.
[0029]
The glass substrate for an information recording medium manufactured by the method as described above constitutes a magnetic recording medium by sequentially laminating an underlayer, a magnetic layer, a protective layer, and a lubricating layer on the glass substrate.
[0030]
Here, as the material of the glass substrate of the magnetic recording medium, for example, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass Examples thereof include glass ceramics. Further, preferably, a glass having the following composition is used.
(1) Crystallized glass 1
SiO in weight% ₂ 60-87%, Li ₂ O is 5 to 20%, Na ₂ O is 0 to 5%, K ₂ 0 to 10% of O, Na ₂ O and K ₂ O in total 0.5-10%, MgO 0.5-7.5%, CaO 0-9.5%, SrO 0-15%, BaO 0-13%, ZnO 0-13 %, B ₂ O _Three 0-10%, Al ₂ O _Three 0-10%, P ₂ O _Five 0.5-8%, TiO ₂ 0-5%, ZrO ₂ 0 to 3%, SnO ₂ 0-3%, As ₂ O _Three And Sb ₂ O _Three 0 to 2% in total, 0 to 5% of the fluoride of one or more metal elements of the above metal oxide as a total amount of F, and optionally as a coloring component, V ₂ O _Five , CuO, MnO ₂ , Cr ₂ O _Three , CoO, MoO _Three , NiO, Fe ₂ O _Three , TeO ₂ , CeO ₂ , Pr ₂ O _Three , Nd ₂ O _Three , Er ₂ O _Three 0 to 5% of at least one selected from the group consisting of lithium disilicate as the main crystal, optionally containing α-cristobalite, α-quartz, lithium monosilicate, β-spodumene, etc. Crystallized glass whose length is 3.0 μm or less.
(2) Crystallized glass 2
SiO in weight% ₂ Is 45 to 75%, CaO is 4 to 30%, Na ₂ O is 2 to 15%, K ₂ O is 0 to 20%, Al ₂ O _Three 0-7%, MgO 0-2%, ZnO 0-2%, SnO ₂ 0-2%, Sb ₂ O _Three 0-1%, B ₂ O _Three 0-6%, ZrO ₂ 0-12%, Li ₂ O is contained in an amount of 0 to 3%, and fluoride of one or more metal elements of the above metal oxide is contained in an amount of 3 to 12% as a total amount of F. ₂ O _Three , Co _Three O _Four And the like, kanasite or potassium / fluoro / richerite as the main crystal, and the crystal grain size is 1.0 μm or less.
(3) Glass 3
SiO in weight% ₂ 62-75%, Al ₂ O _Three 4-18%, ZrO ₂ 0-15%, Li ₂ 3-12% O, Na ₂ Glass containing 3 to 13% of O.
[0031]
Such a glass substrate can be subjected to chemical strengthening treatment by a low-temperature ion exchange method on the surface for the purpose of improving impact resistance, vibration resistance and the like. Here, the chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method. For example, low-temperature chemical strengthening in which ion exchange is performed in a region not exceeding the transition temperature is preferable from the viewpoint of the glass transition point. . Examples of the alkali molten salt used for chemical strengthening include potassium nitrate, sodium nitrate, and nitrates obtained by mixing them.
[0032]
Examples of the underlayer include an underlayer made of at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. Examples thereof include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, CrV / CrV, Al / Cr / CrMo, Al / Cr / Cr, Al / Cr / CrV, and Al / CrV / CrV. .
[0033]
Examples of the magnetic layer include magnetic thin films such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrTaPt, and CoCrPtSiO. The magnetic layer may be a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrTaPt / CrMo / CoCrTaPt, etc.) in which the magnetic film is divided by a non-magnetic film (for example, Cr, CrMo, CrV) to reduce noise. Good. As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), an impurity element selected from Co, alloys, Y, Si, rare earth elements, Hf, Ge, Sn, Zn Or those containing oxides of these impurity elements. As the magnetic layer, in addition to the above, ferrite, iron-rare earth, and SiO ₂ A granular material having a structure in which magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of BN or the like may be used. Further, the magnetic layer may be of an internal type or a vertical type.
[0034]
Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective layers can be continuously formed together with the underlayer, the magnetic layer and the like by an in-line type sputtering apparatus. In addition, these protective layers may be a single layer, or may have a multilayer structure composed of the same or different films. Furthermore, another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, colloidal silica fine particles are dispersed and coated on a Cr film with tetraalkoxylane diluted with an alcohol solvent, and then fired to form silicon oxide (SiO 2). ₂ ) A film may be formed.
[0035]
For example, the lubricating layer may be obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying it to the surface of the medium by dipping, spin coating, or spraying. Go and form.
[0036]
The present invention has been described in detail above, and the above embodiment is a case where a disk-shaped (disk-shaped) glass is press-molded. The invention is applicable. Further, the heat-resistant solid lubricant powder adhesion device is not limited to the injection device shown in FIG.
[0037]
【The invention's effect】
As described above, according to the method for producing a thin sheet glass of the present invention, since the heat-resistant solid lubricant powder is adhered to the molding surface of the molding die, the molten glass is hot and the molding die is hot. Excellent release properties can be obtained even in press molding of a thin sheet glass heated to a high temperature, and a thin sheet glass can be obtained with high productivity by improving the elongation of the molten glass. Furthermore, since the heat-resistant solid lubricant powder can be easily adhered and removed, the working efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a plan view for explaining an embodiment of a method for producing a thin sheet glass according to the present invention.
FIG. 2 is a configuration diagram specifically showing an injection device used in the embodiment of the present invention.
FIG. 3 is a front view of a nozzle tip of the injection device of FIG. 2;
[Explanation of symbols]
11 Lower mold
13 Injection device
21 BN powder

Claims (5)

In a method for producing thin sheet glass by press molding molten glass, the molding surface of the mold is roughened, and a heat-resistant solid lubricant powder is injected along with gas onto the molding surface of the roughened mold. to, performs cooling of the mold by heat exchange with the mold and the gas, after increasing the thermal insulation in the molding surface by adhering the heat-resistant solid lubricant powder on the molding surface, wherein Receiving the molten glass on the molding surface, performing press molding, and repeatedly using the molding die after removing the heat-resistant solid lubricant powder remaining on the molding surface after the molding, and the thin plate shape A method for producing a thin glass sheet, wherein the glass is processed into a glass substrate for an information recording medium by performing at least a polishing step .   The method for producing a thin glass sheet according to claim 1, wherein the heat-resistant solid lubricant powder is BN powder. The method for producing a thin sheet glass according to claim 1 or 2 , further comprising a step of correcting warpage of the thin sheet glass in a softened state after press molding. A method for producing a glass substrate for an information recording medium, wherein at least a polishing step is performed after producing a thin sheet glass by the production method according to any one of claims 1 to 3 . 5. A method for producing an information recording medium, comprising producing at least a magnetic layer after producing a glass substrate for an information recording medium by the production method according to claim 4 .

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