JP2000319026A - Die for forming glass substrate, apparatus for producing glass substrate, production of glass substrate and glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a glass substrate of high performance which is optimum for a magnetic disk and has an ultrasmooth and ultraflat surface characteristic by incorporating the characteristics of a direct pressing method which is capable of shortening a tact time and the characteristics of a reheat press method capable of easily producing the shape accuracy of molded goods. SOLUTION: The glass substrate for the magnetic disk is produced by using the die for forming the glass substrate including an outer die and inner die in at least one die of a pair of the dies having press forming surfaces which are flat surfaces by arranging the inner die into a through-hole formed to a concentric circular shape from the central part of at least one die of a pair of the dies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass substrate for a magnetic disk which is most suitable for a recording medium such as a magnetic disk.

[0002]

2. Description of the Related Art In recent years, in the field of magnetic recording, in particular, in magnetic disks, high performance such as miniaturization, thinning, and high capacity has been promoted. Glass substrates with high rigidity, high hardness and easy smoothing have been actively studied because they are extremely advantageous for high density and high reliability.

Conventionally, a glass substrate for a magnetic disk has been cut out to a predetermined size and then cut out to obtain a smooth surface.
It has been manufactured by a polishing method of polishing a glass substrate one by one. However, in recent years, the substrate surface has been required to have extremely high smoothness and high flatness, and this demand is expected to require continuous improvement in accuracy in the future. Therefore, very high precision is required for the polishing step, and there is a concern that the price will increase due to an increase in the number of steps.

On the other hand, a glass material is heated, pressed,
Since the press forming method of cooling and transferring the ultra-smooth surface of the mold by molding does not require post-processing, the productivity is high and the quality is stable, so many studies have been made in the field of manufacturing optical glass elements, It has already been put to practical use.

In the field of optical glass, as a method of obtaining a molded product from a glass material by press molding, there are a so-called reheat press method and a direct press method.

In the reheat press method, a glass blank having a shape approximating a shape to obtain a final molded product is once formed, and the blank material is housed in a molding die unit, heated, pressurized, and cooled. A final molded product corresponding to the shape of the cavity formed by the mold unit is obtained.

In the direct press method, molten glass or glass in a high-temperature softened state is introduced into a molding die unit and pressurized to obtain a final molded product corresponding to the shape of a cavity formed by the die unit. .

In general, the reheat press method has an advantage that the temperature of the glass material follows the mold temperature, so that the shape accuracy is easily obtained. However, since it takes time for heating and cooling, the process is divided, and a plurality of press heads are used. There is a technology to realize a realistic tact. For example, Japanese Patent Application Laid-Open No. 62-292629 proposes that two pre-stages, a pressurizing stage, and a cooling stage are separately provided to heat glass and a mold. Using this technique, it is possible to efficiently mold a highly accurate lens.

However, in the manufacturing method in the reheat press method, it is necessary to introduce a process division using a plurality of press heads in order to reduce the tact time, and there has been a problem of increasing the size and cost of the apparatus.

On the other hand, as a direct pressing method, for example, in JP-A-1-308840, a process in which the surface temperature of molten glass is set lower than the glass softening temperature and the internal temperature is set higher than the softening temperature is described. A method of manufacturing a glass lens includes a step of receiving a lower mirror called a first mirror mold and a step of obtaining a glass lens by press molding with a second mirror mold opposite to the first mold. Proposed. According to this technique, since the glass lump in the high-temperature softened state is directly received and molded by the lower mold, the tact time of the preheating portion can be reduced.

However, since the mold temperature in the direct press method rises to the glass surface temperature, there has been a problem in shortening the molding tact for cooling the mold and the glass substrate in the cooling step.

Conventionally, a substrate which has undergone a polishing step is finished to a final shape by an inner / outer diameter processing machine and an inner / outer peripheral chamfering machine. In order to simplify the substrate production process over a plurality of processes, an approach for introducing a part of the processing process into the molding process has been proposed.

For example, JP-A-63-248727, JP-A-1-133948 and JP-A-3-22.
No. 8837, a method of sandwiching the molten glass using a pair of molding die members horizontally opposed from both sides thereof while flowing the molten glass down from a nozzle, rapidly cooling and curing the glass to obtain a molded product having a predetermined shape. Has been proposed. According to this technology, a cutting ring is arranged around the mold and cut at the same time as the cavity configuration, or after cooling, the ring can be slid in the press direction and cut, so that the portion protruding outside the mold is removed. It can be removed in the molding process.

However, the magnetic disk substrate needs to treat the hole at the center of the substrate as a waste material, and this technique cannot perform the cutting process in the molding process.

[0015]

SUMMARY OF THE INVENTION The present invention is suitable for a magnetic disk by incorporating the features of a direct press method capable of shortening the tact time and the features of a reheat press method capable of easily obtaining the shape accuracy of a molded product. Therefore, an object of the present invention is to provide a high-performance glass substrate having an ultra-smooth and super-flat surface at a low cost.

[0016]

In order to solve the above-mentioned problems, a glass substrate molding die according to the present invention has a press-formed surface which is flat from at least one of a pair of dies. By arranging the inner mold in the through hole formed concentrically, at least one of the pair of molds is provided with an outer mold and an inner mold.

In the mold for molding a glass substrate of the present invention,
The inner mold is disposed in the same through hole formed concentrically from the center of both molds of the pair of molds, and the concave shape of the lower mold and the upper mold in which the press molding surfaces of the inner mold are fitted. It is preferable to be configured in combination with the convex shape. Also,
Preferably, the outer diameter of the inner mold is the same as the inner diameter of the glass substrate. With such a configuration of the inner mold, the inner diameter of the substrate, that is, the thickness of the waste material is reduced, so that the waste material can be reduced.

Further, it is preferable that the outer mold and the inner mold are arranged insulated from each other, and the press surface of the inner mold has higher heat conductivity and heat capacity than the press surface of the outer mold. It is preferable to be made of a small material.
By making the outer mold and the inner mold have such a configuration, even if a high temperature softened glass lump is dropped on the inner mold,
Since the glass block is not rapidly cooled and kept in a low viscosity state, it can be formed with a small forming pressure.

The apparatus for manufacturing a glass substrate of the present invention is characterized in that the glass receiving mold of the present invention and the inner and outer dies have the same first glass receiving surface height. Positioning means for positioning the inner mold at a second reference position which does not coincide with the position; and arranging the inner mold and the outer mold at a first reference position, press-molding both at the same time, and then pressing the inner mold. Forming means for further pressing only the mold to the second reference position and extracting the inner diameter portion of the glass substrate by shearing force.

The method for producing a glass substrate of the present invention is a method for producing a glass substrate by press-molding a glass lump using the mold for molding a glass substrate of the present invention, wherein the outer mold and the inner mold are separated. It is characterized in that different temperatures are set.
In particular, it is preferable to set the temperature of the outer mold to the glass transition temperature and set the inner mold to a temperature between the glass transition temperature and the glass softening temperature.

Further, in the method for manufacturing a glass substrate of the present invention, after placing both the inner mold and the outer mold at the first reference position where the height of the glass receiving surface coincides with each other, and pressing the both at the same time, It is further preferable that only the inner mold is further pressed to a second reference position where the heights of the glass receiving surfaces of the two molds do not coincide with each other, and the inner diameter of the glass substrate is extracted by a shearing force. According to such a method, the inner diameter portion can be punched in the forming process, so that the manufacturing process can be shortened.

The glass substrate for a magnetic disk of the present invention is obtained by the above-mentioned method of manufacturing a glass substrate of the present invention.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view showing a state in which a glass lump 5 is placed in a glass substrate molding die according to Embodiment 1 of the present invention.

The mold for forming a glass substrate includes a lower mold 25 and an upper mold 30 for a molding outer mold, and a press molding surface arranged in a through hole formed in the center of the outer molds 25 and 30. A lower mold 10 having a concave inner mold, an upper mold 85 having an inner mold having a press-formed convex surface, and an outer mold 2 upon completion of molding.
And a regulating ring 35 for regulating the gaps of 5, 30. Since the glass block 5 in a high temperature softened state is placed on the lower mold 10 of the inner mold, a material having good releasability at a high temperature,
For example, carbide and carbon such as SiC, AlN and TiN
And other materials. The entire lower mold 10 of the inner mold may be made of the above material,
The material may be formed only on the receiving surface 10a by various film forming techniques such as the CVD method. The coating layer does not need to be a single layer, and an underlayer may be provided to improve adhesion strength and heat resistance. Further, a polishing treatment can be performed to make the surface of the coating layer have a good surface roughness.

The outer dies 25, 30 and the regulating ring 35 are made of a cemented carbide (linear expansion coefficient α = 58 × 10 ⁻⁷ ) containing tungsten carbide (WC) as a main component, and have molding surfaces 25a, 30a. Is processed to a desired surface roughness and is coated with a platinum (Pt) -based alloy protective film.

FIGS. 2 to 7 are cross-sectional views schematically showing a glass substrate manufacturing apparatus according to the first embodiment of the present invention for forming a glass substrate using the glass substrate forming die shown in FIG. .

FIG. 2 shows a glass mass 5 in a high-temperature softened state to be dropped.
FIG. 2 is an external view showing a state in which the inner mold is received by a lower mold 10 of an inner mold. Before receiving the glass block 5, the lower mold 10 is heated to a predetermined temperature equal to or higher than the glass softening temperature (about ± 50 ° C.) by a heating device (not shown). Therefore, even if the glass lump in the high temperature softened state is dropped, the vicinity of the glass surface is not rapidly cooled, the inside of the glass lump 5 is maintained at a high temperature, and even if the temperature of the outer mold for molding is low, the conventional method is used. Molding can be performed with a normal molding pressure.

Further, the shape of the receiving surface 10a is a gentle concave surface in order to form a glass block having a predetermined weight into an appropriate thickness and size. That is, when the temperature of the lower mold 10 is set to a predetermined temperature equal to or higher than the glass softening temperature,
Is required to have an outer diameter substantially equal to the outer diameter of the lower mold 10 of the inner mold.

The lower mold 10 of the inner mold is held adiabatically by the mold conveying member 15 and conveyed below the dropping port 2 of the glass melting furnace 1 to drop a predetermined amount of the glass mass 5 in a high temperature softened state. .

FIG. 3 is a schematic cross-sectional view of the molding apparatus for illustrating a step of installing the lower mold of the inner mold in the molding apparatus. The molding device 20 includes the heater blocks 50 and 53 and the heat insulating member 5.
The cooling members 60 and 65 are fixed to each other by fastening members such as bolts, and a pair of outer molding dies 25 and 30 are fixed to the heater blocks 50 and 53 via fixing rings 40 and 45, respectively. .

The regulating ring 35 is installed on the flange of the upper die 30 of the outer mold, and is fixed integrally with the upper die 30 by the fixing ring 45. At the time of molding, the end surface 35a of the regulating ring 35 contacts the flange 25b of the lower mold 25 of the outer mold,
This will determine the thickness of the molded article. Outer mold for molding 2
Reference numerals 5 and 30 denote predetermined temperatures between the vicinity of the glass softening temperature (about ± 50 ° C.) and the vicinity of the glass transition temperature (about ± 50 ° C.) by a plurality of straight tube type cartridge heaters 51 and 54 embedded in the heater blocks 50 and 53. Heated to temperature. The support member 70 is fixed to the cooling member 60 via the heat insulating member 55.

The lower mold 10 of the inner mold held by the mold conveying member 15 is conveyed to a through hole 26 formed at the center of the outer mold 25 for molding, and the fitting portion 10b of the lower mold 10 is supported. Inserted into the through hole 71 of the member 70, the bottom surface 10 of the lower die 10
c is positioned at a height at which it contacts the height adjustment member 79. In this state, the lower mold 10 is supported by the through hole 71 of the support member 70 so as to be able to stand by itself from the mold conveying member 15, and the mold conveying member 15 is removed from the molding apparatus 20.

FIG. 4 is a schematic sectional view of a molding apparatus for illustrating a step of arranging the lower mold of the inner mold at a position where molding is possible. When the mounting of the lower mold 10 is completed, the height adjusting member 79 is housed in the mold receiving base 75 by a driving means (not shown). The lower mold 10 in contact with the tip of the height adjustment member 79 also slides in synchronization with the height adjustment member 79 to a position where it contacts the end face 75a of the mold receiving base 75.

The mold receiving base 75 is formed via a press shaft 77,
The hydraulic cylinder 7 is engaged with the hydraulic cylinder -78.
8, the base member 21 is pressed and positioned on the positioning surface 21a of the base member 21.

At this time, the lower mold 10 is adiabatically arranged with the lower mold 25 of the outer mold for molding through a gap of 200 to 300 μm to prevent a rapid temperature change of the lower mold 10. Further, the support member 70 which is in contact with the fitting portion 10b of the lower mold 10 is fixed via the heat insulating member 55, and is also insulated with the heater block 50 via a gap of 200 to 300 μm. Sudden temperature fluctuation of the ten fitting portions 10b is prevented. In addition, S
If a ceramic material such as a carbide molded body such as iC or a nitride molded body such as AlN or TiN is used, it is not necessary to provide a gap with the outer mold.

FIG. 5 is a schematic sectional view of a molding apparatus for illustrating a molding process of a glass substrate. A press shaft 80 is fixed to the upper cooling member 65, and the press shaft 80 is incorporated in a hydraulic cylinder 81. Upper die 85 of the inner die placed in the through hole of the upper die 30 of the outer die for molding
Are incorporated in a hydraulic cylinder 83 via a press shaft 82. The hydraulic cylinder 83 is fixed to a press shaft 80 of the cooling member 65. Therefore, the upper mold 30 of the outer mold and the upper mold 85 of the inner mold are supported by the hydraulic cylinder 81 and the hydraulic cylinder 83 so as to be capable of relative movement.

The contact surface 85a of the upper mold 85 of the inner mold with the glass block has the same convex shape that fits into the concave shape of the lower mold 10 of the inner mold. Thus, when molded, the thickness of the glass substrate becomes uniform. The portion formed by the lower mold 10 and the upper mold 85 is the inner diameter of the glass substrate and is treated as waste material. Therefore, by having such a mold shape in the present invention, it is possible to reduce the amount of waste material and the material cost. A heater (not shown) is disposed inside the upper die 85 to heat the upper die to a predetermined temperature between a glass softening temperature and a glass transition temperature. Therefore, since the glass lump can be molded in a state of high viscosity, there is no need to increase the molding pressure.

The regulating ring 35 is installed on the flange of the upper die 30 of the outer mold for molding to determine the thickness of the molded glass substrate 6, and is fixed integrally with the upper die 30 by the fixing ring 45. . During molding, the end surface 35 of the regulating ring 35
A is pushed off until it contacts the flange 25b of the lower mold 25 of the outer mold for molding, and after a certain period of time, the upper mold is opened to complete the molding. At this time, the lower mold 10 and the upper mold 8 of the inner mold
Reference numeral 5 denotes a first reference position at which a glass substrate can be formed.

The outer molds 25 and 30 are preferably made of a material having excellent mechanical strength at a high temperature, such as a cemented carbide or quartz glass mainly containing tungsten carbide (WC) as a base material, and having a small coefficient of thermal expansion. desirable.

On the press-formed surfaces 25a and 30a, a target made of a noble metal-based metal such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), or iridium (Ir) or an alloy material is used. A thin protective film is formed by sputtering, preventing adhesion to the press surface due to repeated press forming of glass under high temperature and high pressure, and deterioration of surface smoothness due to surface roughening of the base metal press formed surface. I do. Further, the smoothness of the protective film is suitably 5 nm or less for a magnetic disk, preferably 2 nm or less.
More preferably, the thickness is 1 nm or less, and such a smooth surface can be obtained by polishing using fine particles of cerium oxide.

The temperatures of the outer molding dies 25 and 30 are set near the glass transition temperature (about ± 50 ° C.), and are lower than the temperatures of the inner dies 10 and 85 at the center. Therefore, when the glass lump 5 is formed into a substrate shape, the glass substrate 6 is rapidly cooled from the vicinity of the glass softening temperature (approximately ± 50 ° C.) to the vicinity of the glass transition temperature, so that the molding tact can be significantly reduced. . Furthermore, since the press forming surfaces 25a and 30a of the forming die have good smoothness, no post-process is required after the polishing process on the glass forming surface.

FIG. 6 is a schematic sectional view of a forming apparatus showing a processing step of cutting the inner diameter portion of the formed glass substrate.

The hydraulic cylinder 81 is driven to suppress the upper mold 30 of the outer mold for molding and the upper mold 85 of the inner mold at a predetermined pressure, and the restricting ring 35 is engaged with the flange of the lower mold 25 of the outer mold for molding. 25b, when the substrate molding is completed, the upper die 85 of the inner mold is driven by the hydraulic cylinder 83 and further pressed. Thereby, the glass substrate 6 is subjected to the punching process by the shearing force along the pressing surface of the upper die 85 by the shearing force, and is separated into the glass substrate 6 and the inner diameter portion 7. At the same time, the pressing force of the hydraulic cylinder 78 integrally engaging with the lower mold 10 of the inner mold is released, and the lower mold 10 is moved to the hydraulic cylinder 78 via the mold receiving base 75, the substrate inner diameter portion 7, and the upper mold 85. 83, the positioning surface 22a of the base 22
Is pressed and positioned.

The thickness of the glass substrate 6 and the inner diameter portion 7 do not need to be the same, and if the thickness of the inner diameter portion 7 is made relatively thin,
Not only the amount of waste material can be reduced, but also punching can be performed with a smaller press pressure.

FIG. 7 is a schematic sectional view of the molding apparatus for showing a step of transferring the glass substrate from the molding apparatus to the next step.

The unit including the upper mold 30 of the outer mold for molding is raised by the upper hydraulic cylinder 81,
The transfer member 95 moves above the glass substrate 6. The transfer member 95 has a projection 95a in contact with the glass substrate 6 and a projection 95b in contact with the inner diameter section 7. Holes 95c and 95d for introducing air are independently formed in each projection. Have been. Therefore, when transferring from the molding apparatus 20 to the outside, air is sucked in from the holes 95c and 95d, the glass substrate 6 and the inner diameter portion 7 are sucked, and air is discharged from the hole 95d at a predetermined place to remove the inner diameter portion 7. In the next step, air is discharged from the hole 95c to remove the glass substrate 6, and the transfer to the next step is completed.

(Embodiment 2) FIG. 8 is a sectional view showing a state in which a glass lump 5 is placed in a glass substrate molding die according to Embodiment 2 of the present invention.

The glass substrate forming die is composed of a lower die 25 and an upper die 30 for forming an outer die and an inner die disposed in a through hole formed in the center of the outer die 25 and 30. Lower mold 10
And an upper mold 85, and a regulating ring 35 for regulating the gap between the outer molds 25 and 30 when the molding is completed. The receiving surface 10d of the lower mold 10 of the inner mold is flat and made of carbide such as SiC, glassy carbon or the like having good heat conductivity and small heat capacity, and the glass mass 5 in a high temperature softened state is placed thereon. However, since the glass block is not rapidly cooled, wrinkles due to cooling do not occur on the surface of the glass block. Therefore, a glass substrate having good surface properties can be obtained even when molded.

The outer molds 25, 30 and the inner molds 10, 85 are insulated from each other by arranging them with a gap therebetween.

The forming process is the same as that of the first embodiment except for the method of placing the glass block. That is, the glass lump 5 in the second embodiment is carried by the placing member (not shown) to the receiving surface 10d of the lower die 10 of the inner mold arranged in the forming apparatus and is placed.

Here, the case where the upper and lower dies are separated into the outer die and the inner die has been described. However, either the upper die or the lower die may be separated. In such a case, a substrate in which the inner diameter portion of the glass substrate is not punched may be manufactured, but by adjusting the positioning of the inner mold with respect to the outer mold, a glass substrate having a thin inner diameter portion is manufactured. It is possible to shorten the processing time, facilitate the processing, and reduce the amount of waste material in the subsequent step of removing the inner diameter portion.

[0053]

(Embodiment 1) Next, a method for manufacturing a magnetic disk substrate according to the present invention will be specifically described with reference to FIGS.

Aluminosilicate glass having a glass transition temperature Tg = 501 ° C., a glass softening temperature Ts = 670 ° C., and a coefficient of linear expansion α = 95 × 10 ⁻⁷ was stably dropped from a platinum nozzle having an inner diameter of 6 mm with a viscosity of 200 poise. I let it.

The lower mold 10 of the inner mold was made of heat-resistant steel (stainless steel). In addition, CV
A SiC thin film is formed by the D method. In addition, receiving surface 1
The outer diameter of Oa is 24 mm.

Since the entire lower mold of the inner mold is heated to 700 ° C., even if a glass lump in a high-temperature softened state is dropped, the vicinity of the glass surface is not rapidly cooled.
The inside is maintained at a high temperature, the viscosity at the conventional molding pressure becomes 3.16 million poise even when the temperature of the outer mold is low, the weight is 6.5 g ± 0.5 g, and the outer diameter is 22.3 mm ± 0. 3m
m, a marble-shaped glass lump having a thickness of 8 mm ± 0.5 mm is obtained.

As the molding conditions, the outer molding dies 25, 3
0 is 500 ° C., the upper mold 85 of the inner mold is 700 ° C., the molding pressure is 400 kg / cm ² , the molding time is 1 minute,
In the meantime, the inner die was punched by the upper die 85 of the inner die. Thereafter, the heating was stopped and the pressing pressure was increased to 100
kg / cm ² , cooling was performed, and the temperature monitor of the heater was released from the mold at 400 ° C.
And the inner diameter portion 7 is adsorbed and transferred to the next step to complete the molding.

The shape of the glass substrate 6 for a magnetic disk thus obtained has an outer diameter of 70 mm and a thickness of 0.635 m.
m, inner diameter 24 mm.

The smoothness is Ra = 0.5 nm ± 0.2 nm, and the press forming surfaces 25 of the outer molds 25 and 30 are formed.
It was confirmed that the smoothness of a and 30a was transferred almost as it was.

Although the embodiment of the present invention has been described above, the temperature of the outer mold for molding is not limited to the glass transition temperature, but can be set within a temperature range of ± 100 ° C. .

[0061]

According to the present invention, a high-precision glass substrate for a magnetic disk having an ultra-smooth and ultra-flat surface property can be manufactured inexpensively and in large quantities. Further, according to the present invention, it is possible to reduce the material cost by reducing the weight of the waste material at the inner diameter portion of the disk, and furthermore, it is possible to simultaneously perform the punching process in the molding process, so that it is possible to reduce the process and increase the tact time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which a glass lump is placed in a glass substrate molding die according to a first embodiment.

FIG. 2 is an external view showing a state in which a dropped glass lump in a high-temperature softened state is received by a lower mold of an inner mold in the first embodiment.

FIG. 3 is a schematic cross-sectional view of the molding apparatus for illustrating a step of installing the lower mold of the inner mold in the molding apparatus in the first embodiment.

FIG. 4 is a schematic cross-sectional view of a molding apparatus for illustrating a step of disposing a lower mold of an inner mold at a position where molding is possible in the first embodiment.

FIG. 5 is a schematic sectional view of a molding apparatus for illustrating a molding step in the first embodiment.

FIG. 6 is a schematic cross-sectional view of a forming apparatus for illustrating a processing step of cutting an inner diameter portion of a formed glass substrate in the first embodiment.

FIG. 7 is a schematic cross-sectional view of the forming apparatus for illustrating a step of transferring the glass substrate from the forming apparatus to the next step in the first embodiment.

FIG. 8 is a cross-sectional view showing a state in which a glass lump is placed in a glass substrate molding die according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass melting furnace 5 Glass lump 10 Lower mold of inner mold 15 Mold conveying member 20 Molding device 25 Lower mold of outer mold for molding 30 Upper mold of outer mold for molding 35 Regulation ring 40 Fixing ring 45 Fixing ring 50 Heater block 53 Heater block 55 Insulating member 56 Insulating member 60 Cooling member 65 Cooling member 70 Supporting member 75 Mold receiving stand 79 Height adjusting member 85 Upper mold of inner mold 95 Transferring member

Continuing on the front page (72) Inventor Kazuaki Takagi 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] An inner mold is disposed in a through hole formed concentrically from a center of at least one of a pair of molds having a flat press-molded surface, so that a pair of molds is formed. A mold for molding a glass substrate, wherein at least one of the molds includes an outer mold and an inner mold. 2. An inner mold is disposed in the same through hole formed concentrically from the center of both molds of the pair of molds,
And a combination of a concave shape of the lower die and a convex shape of the upper die into which the press-formed surface of the inner die is fitted.
4. The mold for molding a glass substrate according to item 1. 3. The glass substrate molding die according to claim 1, wherein the outer diameter of the inner die is the same as the inner diameter of the glass substrate. 4. The glass substrate molding die according to claim 1, wherein the outer die and the inner die are arranged insulated from each other. 5. The glass according to claim 1, wherein the pressed surface of the inner mold is made of a material having a higher thermal conductivity and a smaller heat capacity than the pressed surface of the outer mold. Mold for substrate molding. 6. A first glass substrate molding die according to claim 1, wherein the inner and outer dies have the same glass receiving surface height. Positioning means for positioning the inner mold at a second reference position which does not coincide with the reference position; and arranging the inner mold and the outer mold at the first reference position, press-molding both at the same time, A molding means for further pressing the mold only to the second reference position and extracting the inner diameter portion of the glass substrate by a shearing force. 7. A method for producing a glass substrate by press-molding a glass lump using the glass substrate molding die according to any one of claims 1 to 5, wherein the outer die and the inner die are provided. A glass substrate at a different temperature. 8. The method according to claim 7, wherein the temperature of the outer mold is set to a glass transition temperature, and the temperature of the inner mold is set to a temperature between the glass transition temperature and the glass softening temperature. 9. After placing both the inner mold and the outer mold at a first reference position where the heights of the glass receiving surfaces are the same, press-molding the two molds at the same time, and then setting only the inner mold to the two glass molds. 9. The method of manufacturing a glass substrate according to claim 7, wherein the glass substrate is further pressed to a second reference position where the surface heights do not match, and the inner diameter of the glass substrate is extracted by a shearing force. 10. A glass substrate for a magnetic disk obtained by the method for manufacturing a glass substrate according to claim 7. Description: