JP6943679B2 - Quartz glass molding mold and molding method - Google Patents

Description

The present invention relates to a quartz glass molding die and a molding method. More specifically, the present invention relates to a mold and method suitable for forming a large quartz glass used for applications such as a large substrate for a liquid crystal display.

Since the product shape of a large substrate product for liquid crystal is rectangular, when starting from a cylindrical synthetic quartz glass block, a step of heat stretching molding using a rectangular molding mold close to the product shape is indispensable. Heat extension molding refers to placing a synthetic quartz glass block in a molding mold and heating it to a temperature higher than the softening temperature to change the shape of the quartz glass. In recent years, large-sized substrate products for liquid crystal displays have been enlarged (6th to 10th generation) from the viewpoint of improving productivity. The sizes of each generation of large LCD substrate products are G6: 800 x 920, G7: 850 x 1200, G8: 1220 x 1400, G10: 1620 x 1780 mm, etc. have been commercialized.

In the manufacture of large substrate products for liquid crystal, a molded product obtained by heating and stretching a cylindrical quartz glass ingot is required to have dimensional accuracy, squareness, flatness and other qualities. In the production of a large-sized substrate molded body for liquid crystal, the temperature and time at the time of forming a quartz glass ingot, the structure, material, release material, etc. of the molding mold are important items for satisfying the quality.

As a method for forming quartz glass, Patent Document 1 (Japanese Patent Publication No. 04-54626) states that when quartz glass is formed under high temperature and pressure into a desired shape, the difference in thermal expansion between the quartz glass and the molded graphite container is caused. A method of using a cushioning material as a component of a graphite container used as a molding die is disclosed in order to relieve the stress. For example, as illustrated below, when the molding size is 130 mm, the molding mold expands to 131 mm at the time of melting, quartz glass is molded at that size, and the molding mold returns to the original size of 130 mm during the cooling process. , The heat expansion difference generated between the quartz glass and the molding die can be absorbed by the cushioning material to obtain a molded body.

Example-1 Mold 130mm
Thermal expansion coefficient of quartz glass: 0.5 × 10 ^-6 / K
Thermal expansion coefficient of graphite (isotropic graphite material): 5 × 10 ^-6 / K
Room temperature: 20 ° C, molding temperature: 1800 ° C
Thermal expansion difference: 130 x (5 x 10 ^-6-0.5 x 10 ^-6 ) x (1800-20) = 1 mm

Special Fair 04-54626 Gazette Tokukousho 62-050414 Gazette Japanese Unexamined Patent Publication No. 05-017174 Japanese Unexamined Patent Publication No. 2012-106869

However, the molding mold of the manufacturing method described in Patent Document 1 has the following problems.
(1) Stress relaxation of molding mold The size of the molded body of the large liquid crystal substrate has increased, and the size of the large liquid crystal substrate has exceeded 1000 mm. With the increase in molding size, the conventional stress relaxation method using a cushion material cannot absorb the difference in thermal expansion. As illustrated below, when the size of the molded body is 1000 mm, the difference in thermal expansion is 8 mm. Due to this difference in thermal expansion (8 mm or more), there are problems such as (i) the dimensional accuracy of the molded body deteriorates, and (ii) the amount of cushioning material used increases to absorb this difference in thermal expansion.

Example-2 Mold 1000mm
Thermal expansion coefficient of quartz glass: 0.5 × 10 ^-6 / K
Thermal expansion coefficient of graphite (isotropic graphite material): 5 × 10 ^-6 / K
Room temperature: 20 ° C, molding temperature: 1800 ° C
Thermal expansion ^{difference: 1000 × (5 × 10 -6} - 0.5 × 10 -6) × (1800-20) = 8mm

On the other hand, Patent Document 2 discloses a method of stretching a graphite fiber cloth as a cushioning material on the inner surface of a molding die to absorb a difference in thermal expansion. When this method was tried on a molded body of a large substrate for liquid crystal, when the glass melted in the molding process, the graphite fiber cloths overlapped with each other, and unevenness of 10 to 20 mm was generated on the outer surface after molding, and the molded body was formed. It was found that there is a problem that the dimensional accuracy of

Further, Patent Document 3 discloses a molding mold in which a carbon molding heat insulating material lining is provided inside the molding mold. In the example, as shown in Example 3 below, the molding die was as small as 270 mm, and therefore the thermal expansion difference was as small as 1 mm. In this case, the stress could be absorbed in the molding die.

Example-3 Mold 270mm
Coefficient of thermal expansion of quartz glass: 0.5 × 10 ^-6
Coefficient of thermal expansion of molded insulation: 2.5 x 10 ^-6
Room temperature: 20 ° C, molding temperature: 1800 ° C
Thermal expansion ^{difference: 270 × (2.5 × 10 -6} - 0.5 × 10 -6) × (1800-20) = 1mm

However, as shown in Example-2, in the production of a large substrate molded body for a liquid crystal display having a molding size of more than 1000 mm, the difference in thermal expansion between the quartz glass and the graphite molding mold is as large as 8 mm or more. The graphite molded heat insulating material has a density in ^{the range of 0.1 to 0.5 g / cm 3} , and has poor cushioning properties. When a graphite molded heat insulating material having poor cushioning property is installed inside the molding mold, the graphite molded heat insulating material cannot absorb the stress generated in the cooling process, and there is a problem that cracks occur in the molding mold.

As described above, the conventional method cannot sufficiently cope with the stress relaxation of the molding mold in the production of the large-sized substrate molded body for liquid crystal display having the molding size exceeding 1000 mm. Furthermore, in addition to the problems of (1) stress relaxation of the molding die, (2) the sealing property of the molded body and (3) the dimensional accuracy and surface accuracy of the molded body are also the conventional methods in the production of the large substrate molded body. There was a problem with the method.

(2) Sealing property of molded product Generally, a molding mold for a large substrate for a liquid crystal display is made by assembling graphite parts to form a rectangular molding mold. When the size of one side of the molded body of the large liquid crystal substrate exceeds 1000 mm, the difference in thermal expansion between the quartz glass and the molding mold becomes 8 mm or more as described above. In a molding die having the structure described in Patent Document 1, when the cushion material attached to the molding die shrinks during molding, a gap is formed between the graphite parts of the molding die. In some cases, the molten glass leaks from the gap and is welded to the graphite material of the mold, damaging the mold.

Further, when the large liquid crystal substrate molded body becomes thick, the cushion material is crushed by the hydraulic pressure of the glass at the time of melting, and a gap is formed between the molded graphite parts. Due to this phenomenon, glass leaks from the gaps in the mold, the glass is fused to the mold, cracks are formed in the lower corners of the large substrate molded body for liquid crystal on the glass side during the cooling process, and the yield deteriorates.

(3) Dimensional accuracy and surface accuracy of the molded body When a deformable cushion material is installed in a molding mold having the structure described in Patent Document 1, the cushion material is crushed by the hydraulic pressure of the quartz glass melted in the molding process. , The side plates constituting the molding die become slanted, and the squareness of the molded body becomes worse. In the case of the molding die having the structure described in Patent Document 2, the cushioning material is installed inside the molding die, and the cushioning material is crushed along the hydraulic pressure distribution of the molten glass. The side surface of the molded body becomes slanted, and the squareness between the top surface and the side surface of the molded body deteriorates (86 to 87 °). In the molding process, the side wall portion of the molding die moves outward due to the thermal expansion and hydraulic pressure of the bottom plate, but is restrained by the upper frame of the molding die, and the molding die is maintained. When the cooling process is started, the upper frame of the molding die shrinks, and the cushioning material on the wall of the molding die further shrinks due to the stress of squeezing the side wall of the molding die inward. Due to this action, a phenomenon is observed in which the side wall portion of the mold is tilted with the bottom plate as a fulcrum. In addition, since the cushion material installed inside the mold is flexible, "wrinkles" occur due to the overlap and swelling of the cushion material itself as the glass moves during the molding process, and the surface of the molded body after molding Is formed uneven, and the surface accuracy of the molded product deteriorates. Due to these factors, the defective width of the outer surface of the large substrate molded body for liquid crystal display increases, and the yield decreases.

In order to solve the above-mentioned problems (1) to (3) that occur in molding in which the size of a large substrate for liquid crystal exceeds 1000 mm by using a conventional molding die or molding method, the present invention has a structure and material of the molding die. It is an object of the present invention to provide a new molding die and molding method capable of improving the quality (crack, size / surface accuracy) of the molded product and improving the yield (productivity). be.

The present invention is as follows.
[1]
A molding die having a bottom and a side wall and having a space for molding quartz glass.
From the outside, the bottom and side walls of the molding mold have a first layer made of C / C composite, a second layer made of carbon cushioning material, and a third layer made of graphite molded heat insulating material. The mold in which the third layer forms a space for molding the quartz glass.
[2]
The mold according to [1], wherein the difference between the coefficient of thermal expansion of the C / C composite and the coefficient of thermal expansion of quartz glass ^{is in the range of 0 to 1.0 × 10 -6 / K.}
[3]
The mold according to [1], wherein the difference between the coefficient of thermal expansion of the C / C composite and the coefficient of thermal expansion of quartz glass ^{is in the range of 0 to 0.5 × 10 -6 / K.}
[4]
The type according to any one of [1] to [3], wherein the graphite molded heat insulating material has a density in ^{the range of 0.1 to 0.5 g / cm 3.}
[5]
The type according to any one of [1] to [4], wherein the carbon cushion material is a carbon fiber felt.
[6]
The production mold according to any one of [1] to [5], wherein the carbon cushion material has a bulk density in ^{the range of 0.07 to 0.12 g / cm 3 and a thickness in the range of 1 to 10 mm.} ..
[7]
The production mold according to any one of [1] to [6], wherein the bottom portion of the third layer is composed of two or more members and has a gap between the members.
[8]
A method for molding quartz glass using a molding die having a bottom portion and a side wall portion and having a space for molding quartz glass, wherein the molding die is described in any one of [1] to [7]. The above-mentioned method, which is a molding mold of.
[9]
A quartz glass ingot is housed in the space for molding quartz glass, the temperature is raised to a temperature equal to or higher than the melting point of the quartz glass, and the side surface of the fused silica glass ingot is the space side of the third layer forming the space. The method according to [8], wherein the temperature is maintained until it comes into contact with the surface, and then cooled to obtain a quartz glass molded body having a planar shape substantially equal to the planar shape of the space.
[10]
The method according to [8] or [9], wherein the length of at least one side of the quartz glass molded product is 1000 mm or more.
[11]
The method according to [8] or [9], wherein the length of both sides of the quartz glass molded product is 1000 mm or more.

According to the present invention, it is possible to improve the quality (cracks, dimensions / surface accuracy) of the molded product and improve the yield (productivity) even in the molding in which the size of the large substrate for liquid crystal display exceeds 1000 mm.

A side sectional view of an example of a molding mold used in the present invention is shown. A plan view (view from above) of the molding die shown in FIG. 1 is shown. The side cross-sectional molding explanatory drawing of Example 1 is shown. The side cross-sectional molding explanatory drawing of Example 2 is shown. An explanatory view of side cross-sectional molding used in Comparative Examples 1 and 2 in which a large G7 850 × 1400 mm liquid crystal display substrate was manufactured by the method described in Patent Document 1 is shown.

(Quartz glass molding mold)
The quartz glass molding die of the present invention is a quartz glass molding die using a molding die having a bottom portion and a side wall portion and having a space for molding quartz glass.
From the outside, the bottom and side walls of the molding mold have a first layer made of C / C composite, a second layer made of carbon cushioning material, and a third layer made of graphite molded heat insulating material. The third layer is a mold that forms a space for molding the quartz glass.

(Quartz glass molding method)
The quartz glass molding method of the present invention is a method of molding quartz glass using a molding mold having a bottom portion and a side wall portion and having a space for molding quartz glass, and the molding die is the above-mentioned present invention. It is a method that is a molding mold of.

In the molding mold of the present invention, a C / C composite (also called a graphite / graphite composite material, a carbon / carbon composite material, a carbon fiber reinforced carbon composite material, etc.) having a thermal expansion coefficient close to that of quartz glass is used as an outer layer thereof. It is a molding die having a three-layer structure (see Example 4) in which a carbon cushioning material (for example, felt) and a graphite molded heat insulating material are sequentially provided inside. This molding die is used in the molding method of the present invention. By using this molding mold, especially in the production of a large substrate for liquid crystal display in which the size exceeds 1000 mm, the dimensions and squareness of the molded body, the surface accuracy of the molded body are improved, and the crack generation of the molded body is improved, and the liquid crystal display is used. It is possible to improve the quality and yield of large-sized substrates for manufacturing.

FIG. 1 shows a side cross section of an example of a molding die used in the present invention.
It has a bottom portion 10 and a side wall portion 20, and the side wall portions 20 are provided on four sides, and one bottom portion 10 and four side wall portions 20 form a space S for forming quartz glass. The planar shape of the space S for molding quartz glass is square, preferably rectangular. The four side wall portions 20 are fixed by being incorporated into the four grooves 14 provided on the upper surface of the bottom portion 10 in the vicinity of the bottom portion thereof, and a molding die is assembled.

The bottom portion 10 has a first layer 11 made of C / C composite on the outside (lower side), and then a second layer 12 made of carbon cushioning material is provided inside the first layer 11 to provide a second layer 12 A third layer 13 made of a graphite molded heat insulating material is provided inside the structure. Further, the side wall portion 20 has a first layer 21 made of C / C composite on the outside, and then a second layer 22 made of a carbon cushion material is provided inside the first layer 21 to form a second layer 22. A third layer 23 made of a graphite molded heat insulating material is provided inside. A formwork 30 for maintaining the structure of the side wall portion 20 can be provided in the vicinity of the upper end portions of the four side wall portions 20. The mold 30 is made of a C / C composite, and the inside of the plane shape corresponds to the outside plane shape of the plane shape of the side wall portion 20.

(First layers 11 and 21)
The first layers 11 and 21 are made of C / C composite. The coefficient of thermal expansion of the C / C composite is 1 × 10 ^-6 / K or less. The layered C / C composite has a different thermal expansion coefficient in the vertical direction (thickness direction) and the parallel direction (in-plane direction of the main surface) (the thermal expansion coefficient of the C / C composite is, for example, the vertical direction: ~ 8). × 10 ^-6 / K, parallel direction: <1 × 10 ^-6 / K), it is preferable to manufacture the molding mold parts in the parallel direction of the C / C composite in the part where the dimensional accuracy of the molding mold is required.

The first layer 11 of the bottom portion 10 and the first layer 21 of the side wall portion 20 are structural members that maintain the hydraulic pressure when the glass in the molding process is melted. The thickness of the first layer 11 and the first layer 21 is not particularly limited, but the thickness of the first layer 11 can be appropriately selected so as to have a strength that can withstand the mass of the entire molding die and the mass of the quartz glass gob to be molded. The thickness of the first layer 21 can be appropriately set so that the deformation (deflection) due to the hydraulic pressure at the time of melting the quartz glass is less than a predetermined value. The thickness of the first layer 11 can be in the range of 10 to 100 mm, for example, and the thickness of the first layer 21 can be in the range of 3 to 50 mm, for example. In the C / C composite, it is preferable that the difference in the coefficient of thermal expansion from the coefficient of thermal expansion of the quartz glass is small from the viewpoint of improving the molding accuracy. For example, the difference in the coefficient of thermal expansion between the C / C composite and the quartz glass. Is preferably in the range of 0 to 1.0 × 10 ^-6 / K, more preferably in ^{the range of 0 to 0.5 × 10 -6} / K, and even more preferably in the range of 0 to 0.4 × 10. It is in the range of ^{-6 / K.}

(Second layers 12 and 22)
The second layers 12 and 22 are provided for the purpose of alleviating the difference in thermal expansion between the first layer and the third layer, and are made of a carbon cushioning material. Furthermore, it also has a function of sealing the gap between the first layer and the third layer, which have poor cushioning and flexibility. The bulk density and thickness of the carbon cushioning material can be determined according to the degree of thermal expansion and contraction due to the size of the quartz glass molded body at the time of molding, and in consideration of the desired dimensional accuracy. The cushioning material of the second layer 12 and the cushioning material of the second layer 22 may have the same material and thickness, or may have different materials and thicknesses. In particular, it is desirable that the thickness of the cushioning material of the second layer 22 is as thin as possible within the range in which the difference in thermal expansion can be absorbed from the viewpoint of molding accuracy and the like. The carbon cushion material is preferably, for example, carbon fiber felt, and the carbon cushion material has a bulk density in ^{the range of 0.07 to 0.12 g / cm 3} and a thickness in the range of 1 to 10 mm. It is preferable to have. The density is more preferably in ^{the range of 0.08 to 0.10 g / cm 3} , and the thickness is more preferably in the range of 2-7 mm.

(Third layers 13 and 23)
The third layers 13 and 23 are members that come into contact with the quartz glass molded body and determine the surface accuracy of the surface of the molded body. Therefore, it is preferable that the molded heat insulating material used for the third layers 13 and 23 has a smooth surface and strength not to be deformed by the hydraulic pressure of the glass, and further has peelability. Further, the third layer 13 provided on the bottom portion 10 is preferably made of a material having a small shrinkage deformation value because it receives a load due to the hydraulic pressure of the glass during molding. The graphite molded heat insulating material preferably has a density in the range of ^{0.1 to 0.5 g / cm 3 from the viewpoint of balancing air permeability and strength.} In particular, the graphite molded heat insulating material used for the third layer 13 is preferably a material having a small shrinkage deformation value, and therefore has a density preferably in the range of ^{0.13 to 0.16 g / cm 3.}

The graphite molded heat insulating material has a larger thermal expansion than the C / C composite. Therefore, as shown in FIG. 2 (plan view seen from above of the molding die shown in FIG. 1), the outer edge dimension of the plane of the third layer 13 made of the graphite molded heat insulating material is the first made of C / C composite. It is desirable that the layers are erected on the layer 11 and shorter than the internal dimensions of the third layers 23a to 23d of the four fixed side wall portions.

For example, when the molding mold is 1000 mm, the molding mold: 1000 mm
Coefficient of thermal expansion (C / C) of graphite / graphite composite material: 0.8 × 10 ^-6 / K
Graphite molded insulation: 2.5 x 10 ^-6 / K
Thermal expansion of graphite / graphite composite material (C / C composite)
1000 x (0.8 x 10 ^-6 ) x (1800-20) = 1.4 mm
Graphite molded insulation
1000 x (2.5 x 10 ^-6 ) x (1800-20) = 4.5 mm
Thermal expansion difference 4.5 --1.4 = 3.1mm
Therefore, it is desirable that the molded heat insulating material has a shorter thermal expansion difference with respect to the internal dimensions of the molding mold of graphite / graphite composite material (C / C).

In the third layers 23a to 23d of the four side wall portions, the side end faces of the two opposing third layers 23a and 23c, respectively, come into contact with each other in the vicinity of the edges of the two opposing third layers 23b and 23d without a gap. Alternatively, one side end surface of the third layer 23a, 23b, 23c, 23d of the four side wall portions abuts without a gap near the edges of the adjacent side wall portions 23b, 23c, 23d, 23a, respectively. Similarly, in the second layers 22a to 22d of the four side wall portions, the side end faces of the two opposing second layers 22a and 22c, respectively, are in contact with each other in the vicinity of the edges of the two opposing second layers 22b and 22d without any gap. Either they are in contact with each other, or one side end surface of the second layer 22a, 22b, 22c, 22d of the four side wall portions is in close contact with each other near the edges of the adjacent side wall portions 22b, 22c, 22d, 22a, respectively. Further, similarly, in the first layers 21a to 21d of the four side wall portions, the side end faces of the two first layers 21a and 21c facing each other have gaps in the vicinity of the edges of the two facing first layers 21b and 21d, respectively. The first layers 21a, 21b, 21c, 21d of the four side wall portions are in contact with each other without gaps, or one side end surface of the four side wall portions 21a, 21b, 21c, 21d is in contact with each other without a gap near the edges of the adjacent side wall portions 21b, 21c, 21d, 21a, respectively. .. The third layers 23a to 23d of these four side walls, the second layers 22a to 22d of the four side walls, and the first layers 21a to 21d of the four side walls form the four side walls of the molding mold, and the bottom portion. Together with 13, a space S for forming quartz glass is formed inside.

As shown in FIG. 2, the second layers 22a to 22d are provided on each of the first layers 21a to 21d, and the third layers 23a to 23d are further provided on the second layers 22a to 22d, respectively. It is preferable that the four side wall portions 20 of the molding die are arranged so that the second layer 22 and the third layer 23 are staggered. It is appropriate to fix all the layers of the first layers 21a to 21d to the third layers 23a to 23d using carbon yarn or graphite bolts and nuts in order to maintain the shape of the mold. As described in the previous section, the C / C composite of the first layer 21 and the molded heat insulating material of the third layer 23 have different coefficients of thermal expansion, and therefore, depending on the length of the side wall portion 20, between the third layers 23a to 23d. It is appropriate to appropriately provide a gap for the difference in thermal expansion.

In the molding mold of the present invention, the structure of the contact portion between the second layer 12 and the third layer 13 of the bottom portion 10 and the second layer 22 and the third layer 23 of the side wall portion 20 is not limited, but there is no gap. Alternatively, it is preferable that the structure is such that a gap is unlikely to occur, or even if there is a gap, the molding is not hindered. In the structure of the molding mold shown in FIG. 1, the second layer 12 and the second layer 22 are provided without a gap, and the third layer 13 and the third layer 23 are provided inside the second layer 12 and the second layer 22. On the other hand, in the molding mold of the present invention shown in FIGS. 3 and 4, the third layer 23 of the side wall portion 20 is erected closer to the inside of the molding mold than the third layer 13 of the bottom portion 10, and the second side wall portion 20 The layer 22 is thinner at the peripheral portion of the third layer 13 of the bottom portion 10 than between the third layer 23 and the first layer 21 of the other side wall portion 20.

Further, the third layer 13 of the bottom portion 10 may be composed of two or more members, and a gap may be provided between the members to have a structure capable of absorbing thermal expansion. FIG. 4 shows an example in which the third layer 13 is divided into two members, 13a and 13b. The third layer 13 of the bottom portion 10 may be, for example, a member divided into four parts.

Table 1 below shows the typical characteristics of typical materials of the C / C composite used for the first layer of the molding die and the molded heat insulating material used for the third layer. These are merely examples and are not intended to be limited to them. For comparison, the material of graphite material (CIP) is also described.

The degree of thermal expansion and contraction of the molding mold when the C / C composite used for the first layer and the molded heat insulating material used for the third layer are the above-mentioned graphite molded heat insulating materials are shown below.

Example-4 Mold 1000mm
Thermal expansion coefficient of quartz glass: 0.5 × 10 ^-6 / K
Thermal expansion coefficient of C / C composite: 0.8 × 10 ^-6 / K
Graphite molded insulation: 2.5 x 10 ^-6 / K
Room temperature: 20 ° C, molding temperature: 1800 ° C

Thermal expansion of quartz glass
1000 x (0.5 x 10 ^-6 ) x (1800-20) = 0.9 mm
Thermal expansion of C / C composite
1000 x (0.8 x 10 ^-6 ) x (1800-20) = 1.4 mm
Thermal expansion difference 1.4 --0.9 = 0.5mm
(For graphite (CIP) molding: 8 mm)

(Heat extension molding of quartz glass)
In the method of the present invention, the quartz glass ingot is housed in the space for molding the molded quartz glass. The quartz glass ingot can be manufactured by a known method, and the shape thereof is not particularly limited. The temperature of the quartz glass ingot stored in the mold is raised to a temperature equal to or higher than the melting point of the quartz glass. There are no particular restrictions on the heating conditions and the temperature at which the temperature is raised. When the temperature rises to a predetermined temperature (for example, 1800 to 1900 ° C.) equal to or higher than the melting point of the quartz glass, the quartz glass ingot melts, and the side surface of the melted quartz glass comes into contact with the space side surface of the third layer forming the molding space. Then, the glass is held until it has a desired substrate shape or a substrate-like shape.

At this stage, the mass and hydraulic pressure of the fused silica glass causes the sides of the fused silica glass to stress the third layer. This stress causes the second layer to shrink. Further, the quartz glass, the first layer, the second layer and the third layer show the dimensions of thermal expansion from room temperature at a raised temperature. However, the second layer is a cushioning material, which undergoes thermal expansion and contraction due to stress. After the fused silica glass has a desired substrate shape or a substrate-approximate shape, the molding die and the molded body are cooled. In the process, the molding die and the molded body shrink according to the coefficient of thermal expansion. Typical thermal expansion coefficients of quartz glass, the first layer (C / C composite) and the third layer (graphite molded heat insulating material) are as shown in Table 1 above, and the third layer from the one with the largest shrinkage. The first layer and the quartz glass molded body. As a result, since the heat shrinkage of the third layer is larger than that of the quartz glass molded product, when the bottom third layer and the side wall third layer are fixed due to the shrinkage of the bottom third layer in the cooling process. The third layer of the side wall is pushed outward by the side surface of the molded body. On the other hand, since the heat shrinkage of the first layer is also larger than that of the quartz glass molded body, the bottom first layer and the side wall first layer are fixed as the bottom first layer shrinks in the cooling process. The first layer of the side wall is also pushed outward via the second and third layers. However, the pressure from this quartz glass molded body is absorbed by the second layer (cushion material) of the side wall portion.

As described above, for example, in the case of a molded body of 1000 mm, the difference in thermal expansion between the first layer and the molded body is 0.5 mm, and in the molding mold of the present invention, this is used as the second layer of the side wall portion (cushion material). Can be absorbed by. The stress from the molded body to the first layer of the side wall is absorbed by the second layer (cushion material) of the side wall, whereas the stress to the third layer of the side wall from the molded body is the third layer 23 of the side wall. However, if it is not fixed to the bottom third layer and can move horizontally, it can be relaxed. The structure in which the side wall portion third layer 23 is not fixed to the bottom portion third layer and can move horizontally is a structure of the third layer 13 of the bottom portion 10 of the molding die, for example, as in the molding die shown in FIG. The structure may be such that the second layer 22 and the third layer 23 of the side wall portion 20 are arranged on the molded heat insulating material. In this structure, the first layer 21 to the third layer 23 of the side wall portion 20 can also move with the thermal expansion and contraction of the bottom portion 10.

In this way, it is possible to obtain a quartz glass molded product whose planar shape is substantially equal to the planar shape of the space.

In the method of the present invention, a quartz glass molded body having at least one side length of 1000 mm or more can be molded, and a quartz glass molded body having both side lengths of 1000 mm or more can also be molded. can.

Hereinafter, the present invention will be described in more detail based on examples. However, the examples are examples of the present invention, and the present invention is not intended to be limited to the examples.

(Manufacturing of quartz glass ingot)
As in Patent Document 4 (Japanese Unexamined Patent Publication No. 2012-106869), the columnar synthetic quartz glass block _{supplies SiCl 4 as a} raw material and hydrogen and oxygen for combustion to a burner, and SiO ₂ fine particles are produced by a flame hydrolysis reaction. A quartz glass ingot was produced by a so-called direct method in which the produced fine particles were formed and the produced fine particles were vitrified at the same time as the deposition.
Next, the defective portion on the outer surface of the ingot was removed and charged into a molding die to manufacture a molded body of a large substrate for liquid crystal display.

Comparative Example 1
-A large G7 LCD substrate of 850 x 1400 mm was manufactured by the method described in Patent Document 1.
Molding conditions Preparation ingot: 560 kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Molding mold: length 900 x width 1450 x height 1000 mm
Mold material: Made of graphite (isotropic graphite)
Release material: Graphite fiber cloth
Cushion material thickness: 10 mm / side (carbon fiber felt)
-For the release material, the example of Patent Document 2 was referred to.
-As shown in FIG. 5, a cushioning material (4) was put on the four sides of the molding die and a molding test was carried out. However, the upper frame (1) of the molding die was broken after molding, and the side plate of the molding die also collapsed and was damaged.
-The molded product also cracked, and it was not possible to obtain a large substrate for G7 liquid crystal display.

Comparative Example 2
In Comparative Example 2, the thickness of the cushion material was increased by 25 mm, and the same test as in Comparative Example 1 was performed.
Molding conditions Preparation ingot: 560 kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Molding mold: length 900 x width 1450 x height 1000 mm
Mold material: Made of graphite (isotropic graphite)
Release material: Graphite fiber cloth
Cushion material thickness: 25 mm / side (carbon fiber felt)

-Although the mold was not damaged, glass leaked from the gaps between the side plates of the mold, causing cracks in the molded body.
-The dimensions of the molded body are: length: 875 mm (average value), width: 1425 mm (average value), thickness: 190 mm (minimum value). When the molded body was observed from the side, it was molded into a trapezoid, and the dimensional difference between the upper and lower bases of the trapezoid was about 10 to 15 mm.
・ As shown in FIG. 5, this pushes the side surface of the molding die when the quartz glass is melted, the cushioning material is crushed, and during the cooling process, the upper frame is heat-shrinked and stress acts on the inside of the molding die, and the side plate is slanted. became.

・ When acquiring 850 x 1400 mm from this molded body
Mold thickness: 190mm Crack: 55mm Effective length: 135mm Product yield: 63%
It became.
-Furthermore, since the dimensions of the side surface of the molded body are trapezoidal, a rough cutting process is required.
-As described above, it has been found that the molding method (Patent No. 1865417) described in Patent Document 1 is not suitable for manufacturing a large substrate for a liquid crystal display having a size of 1000 mm or more.

Figure 5. Explanatory drawing of molding of Comparative Examples 1 and 2 1: Upper frame (made of graphite)
2: Prepared ingot (quartz glass)
3: Side plate (made of graphite)
4: Cushion material (carbon fiber felt)
5: Bottom plate (made of graphite)
6: Molded body (quartz glass)

Example 1
-In the molding die of the present invention, a molded body having a size of a large substrate for liquid crystal display of G7 of 850 x 1400 mm was manufactured, and the effect was confirmed. FIG. 3 shows an explanatory diagram of molding.
・ Molding conditions Ingot: 560kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Molding mold: length 900 x width 1450 x height 1000 mm

Material 1st layer: C / C composite 2nd layer: Carbon fiber felt 3rd layer: Graphite molded heat insulating material / molded body
Top surface: Length: 851 mm, Width: 1401 mm Bottom surface: Length 853 mm, Width: 1403 mm
Thickness: 200 mm was manufactured.

No breakage of the mold and leakage of glass from the mold as observed in Comparative Examples 1 and 2 were observed.
・ The quality of the molded body is
Dimensional difference of molded body (maximum-minimum): 2 mm Surface accuracy of molded body (standard deviation): 0.5 to 07,
Angle: 89-90 degrees,
Mold cracks: None A molded body with good quality was obtained.

When 850 x 1400 mm was obtained from this molded body, the product yield was improved to 91%. Further, since the dimensional accuracy of the side surface of the molded body is good, it is not necessary to cut the rough processing, and the productivity can be improved and the cost can be reduced. The molding die of the present invention and the molding method of the present invention using the molding die have made it possible to manufacture a molded body having a size of a large substrate for a liquid crystal display exceeding 1000 mm.

Fig. 3 (main members)
30: Formwork (upper frame) (C / C composite)
21: First layer side wall (C / C composite)
11: First layer bottom (C / C composite)
12: Second layer (carbon fiber felt)
13: Third layer (molded insulation)
40: Prepared ingot (quartz glass)
50: Molded body (quartz glass)

Molding yield = 850 ^a) mm × 1400 ^a) mm × effective length ^b) mm × 2.2 ^c) (g / cm ³ ) / 100000 / Charge weight kg × 100
a) Length of short and long sides of the product b) Effective length = minimum thickness of molded body-defective thickness c) Density of quartz glass

Example 2
-It is desirable to use an integrated type for the graphite molded heat insulating material of the third layer, but since the graphite molded heat insulating material has a size limitation, it may be divided and attached to the molding mold.
-In Example 2, the graphite molded heat insulating material of the third layer was divided into 13a and 13b and installed in the molding mold. FIG. 4 shows an explanatory view of the molding die.

・ Molding conditions Ingot: 560 kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Molding mold: length 900 x width 1450 x height 1000 mm
Material 1st layer: C / C composite 2nd layer: Carbon fiber felt
Third layer: Graphite molded heat insulating material (divided into two) Butt gap: 5 mm

-The size of the molded body was 852 x 1402 x 200 mm.
-When observing the molded body, a convex "burr" (width 3 to 4 mm x length about 500 mm) was observed on the bottom surface of the molded body, but there were no progressive cracks in the molded body.
-This "burr" is generated by the molten quartz glass leaking into the gap where the two-part molded heat insulating material is abutted, and the outflow of the glass is stopped by the second layer felt under the molded heat insulating material. The effect of the sealing property of the felt of the second layer was confirmed.
-The narrower the gap between the molded heat insulating materials, the more the glass leakage is suppressed, and it is desirable that the gap is less than 10 mm in order to prevent the glass leakage.

According to the present invention, regarding the problem (1) that has become apparent in the molded body of a large substrate for liquid crystal exceeding 1000 mm, the difference in thermal expansion between the molded mold and the quartz glass can be reduced from, for example, 8 mm to 0.5 mm. can. As a result, the dimensional accuracy and squareness of the molded product can be improved.

Regarding the problem (2), as described above, the gap between the parts of the molding mold due to the difference in thermal expansion in the molding process is reduced, and the sealing property is improved. There is little change in the shape of the molding die in the molding process (heating → cooling), the dimensional accuracy of the molded body after molding is greatly improved, and the yield is improved.

In addition, by using C / C composite (graphite / graphite composite material) for the first layer of the mold, the difference in thermal expansion between the mold and quartz glass is reduced to 1/10 or less, and the third layer has cushioning properties. It has become possible to use almost no graphite molded insulation. As a result, the unevenness of the molded body of the large substrate for liquid crystal display, which is generated when the soft carbon fiber felt described in the problem (3) is used, can be improved from 10 mm to <1 mm.

It is useful in fields related to quartz glass molding technology.

10: Bottom 11: First layer 12: Second layer 13: Third layer 14: Groove 20: Side wall 21: First layer 22: Second layer 23: Third layer 30: Formwork 40: Preparation ingot (quartz) Glass)
50: Molded body S: Space for molding

Claims (11)

Has one bottom and four side wall portions, have a space for molding quartz glass, since the length of at least one side of the cylindrical quartz glass ingot is formed on a quartz glass substrate is more than 1000mm It is a molding mold used for
Bottom and side wall of the mold, has from the outside, a first layer of C / C composite, respectively, a second layer made of carbon steel cushion member, and a third layer consisting of graphite mold heat insulating material, wherein The first layer of the four side wall portions is fixed by being incorporated into each of the four grooves provided on the upper surface of the first layer of the bottom portion near the bottom, and the third layer is a flat surface for forming the quartz glass. The molding die that forms a rectangular space on the shape. The difference between the coefficient of thermal expansion of the C / C composite and the coefficient of thermal expansion of quartz glass is in the range of ^{0 to 1.0 × 10 -6} / K or 0 to 0.5 × 10 ^-6 / K. , The molding die according to claim 1. The molding according to claim 1 or 2 , wherein the bottoms of the second layer and the third layer of the side wall portion are provided so as to be in contact with the upper surface of the second layer of the bottom portion or the upper surface of the third layer of the bottom portion. Mold. The graphite mold heat insulating material, the mold according to any one of claims 1 to 3 density is in the range of 0.1 to 0.5 g / cm ^3. The molding die according to any one of claims 1 to 4, wherein the carbon cushion material is a carbon fiber felt. The molding die according to any one of claims 1 to 5, wherein the carbon cushion material has a bulk density in ^{the range of 0.07 to 0.12 g / cm 3} and a thickness in the range of 1 to 10 mm. The molding die according to any one of claims 1 to 6, wherein the third layer of the bottom is composed of two or more members and has a gap between the members. A cylindrical quartz glass ingot is molded using a molding mold having a bottom and a side wall and a space for molding quartz glass, and a quartz glass substrate having at least one side length of 1000 mm or more is formed. The method according to any one of claims 1 to 7, wherein the molding die is the molding die according to any one of claims 1 to 7. A quartz glass ingot is housed in the space for molding quartz glass, the temperature is raised to a temperature equal to or higher than the melting point of the quartz glass, and the side surface of the fused silica glass ingot is the space side of the third layer forming the space. The method according to claim 8, wherein the temperature is maintained until it comes into contact with the surface, and then cooled to obtain a quartz glass substrate whose planar shape is substantially equal to the planar shape of the space. The method according to claim 8 or 9, wherein the lengths of both sides of the quartz glass substrate are 1000 mm or more. The molding die according to any one of claims 1 to 7, wherein the lengths of both sides of the quartz glass substrate are 1000 mm or more.

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