JP2019038708A - Molding die and molding method of quartz glass - Google Patents

Abstract

[PROBLEMS] A new quartz glass mold and quartz glass that solve the problems relating to (1) a method of stress relaxation of the mold, (2) sealability of the molded body, and (3) dimensional accuracy and surface accuracy of the molded body. A method for producing a molded body is provided.
A molding die having a bottom portion and a side wall portion and having a space for molding quartz glass, wherein the bottom portion and the side wall portion of the molding die are each a first made of a C / C composite. A third layer made of a graphite cushioning material, and a third layer made of graphite, and the third layer forms a space for molding the quartz glass. A method for forming quartz glass by using the above-mentioned mold having a bottom part and a side wall part and having a space for forming the quartz glass.
[Selection] Figure 1

Description

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

  Since a large substrate product for liquid crystal has a rectangular product shape, when starting from a cylindrical synthetic quartz glass lump, a process of heating and extending using a rectangular mold close to the product shape is essential. Heat extension molding refers to charging a synthetic quartz glass block into a mold and heating it to a temperature above the softening temperature to change the shape of the quartz glass. In recent years, large-size substrate products for liquid crystals have been increased in size (sixth to tenth generation) from the viewpoint of improving productivity. The size of each generation of large-sized substrate products for LCD is G6: 800 x 920, G7: 850 x 1200, G8: 1220 x 1400, G10: 1620 x 1780mm, and so on.

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

  As a method for forming quartz glass, in Patent Document 1 (Japanese Patent Publication No. 04-54626), when quartz glass is hot-pressed into a desired shape, it is caused by the difference in thermal expansion between the quartz glass and the graphite container of the mold. In order to relieve the stress that occurs, a method of using a cushion material as a constituent component of a graphite container used as a mold is disclosed. For example, as illustrated below, when the molding size is 130 mm, the mold is expanded to 131 mm at the time of melting, quartz glass is molded with that size, and when the mold returns to the original dimension of 130 mm during the cooling process The thermal expansion difference generated between the quartz glass and the mold can be absorbed by the cushion material to obtain a molded body.

Example-1 Mold 130mm
Thermal expansion coefficient of quartz glass: 0.5 × 10 ^-6 / K
Coefficient of thermal expansion 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

Japanese Patent Publication No. 04-54626 Japanese Patent Publication No.62-050414 JP 05-017174 A JP 2012-106869 A

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

Example-2 Mold 1000mm
Thermal expansion coefficient of quartz glass: 0.5 × 10 ^-6 / K
Coefficient of thermal expansion 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

  In contrast, Patent Document 2 discloses a method of stretching a graphite fiber cloth of a cushion material that absorbs a difference in thermal expansion on the inner surface of a mold. When this method was tested on a molded body of a large substrate for liquid crystal, when the glass melted during the molding process, the graphite fiber cloths overlapped, resulting in 10-20 mm irregularities on the outer surface after molding, and the molded body It was found that there was a problem that the dimensional accuracy of the deteriorated.

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

Example-3 Mold 270mm
Thermal expansion coefficient of quartz glass: 0.5 × 10 ^-6
Thermal expansion coefficient of molded insulation: 2.5 × 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 for liquid crystal having a molding size exceeding 1000 mm, the difference in thermal expansion between the quartz glass and the graphite molding die 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 properties is installed inside the mold, the graphite molded heat insulating material cannot absorb the stress generated during the cooling process, and there is a problem that cracks occur in the mold.

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

(2) Sealing property of molded body In general, the mold for large substrates for liquid crystals is assembled by assembling graphite parts together to produce a rectangular mold. When the dimension of one side of the large-sized substrate for liquid crystal exceeds 1000 mm, the difference in thermal expansion between the quartz glass and the mold becomes 8 mm or more as described above. In the mold having the structure described in Patent Document 1, when the cushion material attached to the mold shrinks during the molding, a gap is formed between the graphite parts of the mold. In some cases, the molten glass leaks from the gap and is welded to the graphite material of the mold, causing damage to the mold.

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

(3) Dimensional accuracy and surface accuracy of the molded product When a deformable cushion material is installed in a mold having the structure described in Patent Document 1, the cushion material collapses due to the liquid pressure of the fused quartz glass in the molding process. The side plate constituting the molding die is slanted and the perpendicularity of the molded body is deteriorated. In the case of the mold having the structure described in Patent Document 2, the cushion material is installed inside the mold, and the cushion material is crushed along the liquid pressure distribution of the molten glass. The side surface of the molded body is inclined, and the perpendicularity between the upper surface and the side surface of the molded body is deteriorated (86 to 87 °). In the molding process, the side wall of the mold moves outward due to the thermal expansion and hydraulic pressure of the bottom plate, but is restrained by the upper frame of the mold and the mold is maintained. When the process proceeds to the cooling process, the upper frame of the mold is shrunk, and the cushion material on the wall of the mold is further shrunk under the stress that squeezes the side wall of the mold inward. Due to this action, the phenomenon that the side wall portion of the mold is inclined with the bottom plate as a fulcrum is observed. In addition, the cushion material installed inside the mold is flexible, so as the glass moves during the molding process, “wrinkles” occur due to the overlapping and swelling of the cushion material itself, and the molded product surface is molded. As a result, irregularities are formed, and the surface accuracy of the molded article deteriorates. Due to these factors, the defective width of the outer surface of the large-sized substrate for liquid crystal is increased and the yield is lowered.

  The present invention solves the above problems (1) to (3) that occur when a large-sized substrate for liquid crystal exceeds 1000 mm by using a conventional mold or molding method. It is an object of the present invention to provide a new molding die and molding method that can improve the quality (crack, dimension / surface accuracy) of the molded body and improve the yield (productivity). is there.

The present invention is as follows.
[1]
A mold having a bottom part and a side wall part and having a space for molding quartz glass,
The bottom and side walls of the mold have, from the outside, a first layer made of C / C composite, a second layer made of carbon cushion material, and a third layer made of graphite molded heat insulating material, respectively, The mold, wherein a third layer forms a space for molding the quartz glass.
[2]
The mold according to [1], wherein a difference between a coefficient of thermal expansion of the C / C composite and a coefficient of thermal expansion of quartz glass is in a range of 0 to 1.0 × 10 ⁻⁶ / K.
[3]
The mold according to [1], wherein the difference between the thermal expansion coefficient of the C / C composite and the thermal expansion coefficient of quartz glass is in the range of 0 to 0.5 × 10 ⁻⁶ / K.
[4]
The mold according to any one of [1] to [3], wherein the graphite formed heat insulating material has a density in a range of 0.1 to 0.5 g / cm ³ .
[5]
The mold according to any one of [1] to [4], wherein the carbon cushion material is a carbon fiber felt.
[6]
The carbon-made 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, according to any one of [1] to [5]. .
[7]
The bottom part of the said 3rd layer consists of two or more members, The manufacturing type in any one of [1]-[6] which has a crevice between each member.
[8]
A method of molding quartz glass using a molding die having a bottom and a side wall and having a space for molding quartz glass, wherein the molding die is any one of [1] to [7]. The method as described above.
[9]
The quartz glass ingot is accommodated in the space for forming the quartz glass, heated to a temperature equal to or higher than the melting point of the quartz glass, and the side surface of the fused quartz glass ingot is the space side of the third layer forming the space The method according to [8], wherein the temperature is maintained until 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 body is 1000 mm or more.
[11]
The method according to [8] or [9], wherein the length of both sides of the quartz glass molded body is 1000 mm or more.

  According to the present invention, even when the size of the large substrate for liquid crystal exceeds 1000 mm, the quality (cracks, dimensions / surface accuracy) of the molded body can be improved, and the yield (productivity) can be improved.

Side surface sectional drawing of an example of the shaping | molding die used by this invention is shown. The top view (figure from upper direction) of the shaping | molding die shown in FIG. 1 is shown. FIG. 3 is an explanatory view of side cross-section molding of Example 1. FIG. 4 is a side sectional view explanatory view of Example 2. Side surface molding explanatory drawing used by the comparative examples 1 and 2 which manufactured the large substrate for liquid crystals of 850 * 1400mm of G7 with the method of patent document 1 is shown.

(Quartz glass mold)
The quartz glass molding die of the present invention is a quartz glass molding die using a molding die having a bottom part and a side wall part and having a space for molding quartz glass,
The bottom and side walls of the mold have, from the outside, a first layer made of C / C composite, a second layer made of carbon cushion material, and a third layer made of graphite molded heat insulating material, respectively, 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 die having a bottom portion and a side wall portion and having a space for molding the quartz glass, wherein the molding die is the above-mentioned present invention. It is the method which is a shaping | molding die.

  The molding die of the present invention has a C / C composite (also called graphite / graphite composite material, carbon / carbon composite material, carbon fiber reinforced carbon composite material, etc.) having a thermal expansion coefficient close to that of quartz glass as an outer layer. This is a mold (see Example 4) having a three-layer structure in which a carbon cushioning material (for example, felt) and a graphite molded heat insulating material are sequentially provided inside. This mold is used in the molding method of the present invention. By using this mold, especially in the production of large substrates for liquid crystals exceeding 1000 mm, the dimensions and perpendicularity of the molded body, the surface accuracy of the molded body and the generation of cracks in the molded body are improved. The quality and yield of large substrates can be improved.

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

  The bottom 10 has a first layer 11 made of C / C composite on the outer side (lower side), and then a second layer 12 made of a carbon cushion material is provided on the inner side of the first layer 11. The third layer 13 made of a graphite molded heat insulating material is provided inside. In addition, the side wall 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. A third layer 23 made of a graphite molded heat insulating material is provided inside. In the vicinity of the upper end portions of the four side wall portions 20, a mold 30 for maintaining the structure of the side wall portions 20 can be provided. The mold frame 30 is made of a C / C composite, and the inside of the planar shape thereof corresponds to the planar shape outside the planar shape of the side wall portion 20.

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

The first layer 11 of the bottom 10 and the first layer 21 of the side wall 20 are structural members that maintain the hydraulic pressure when the glass in the molding process is melted. The thicknesses of the first layer 11 and the first layer 21 are 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 mold and the mass of the quartz glass block to be molded. The thickness of the first layer 21 can be set as appropriate so that the deformation (deflection) due to the hydraulic pressure when the quartz glass is melted is less than a predetermined value. The thickness of the 1st layer 11 can be made into the range of 10-100 mm, for example, and the thickness of the 1st layer 21 can be made into the range of 3-50 mm, for example. In the C / C composite, it is preferable that the difference between the thermal expansion coefficient and the thermal expansion coefficient of the quartz glass is small from the viewpoint of improving the mold accuracy, for example, the difference in the thermal expansion coefficient 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, still more preferably 0 to 0.4 × 10 10. ^-6 / K.

(Second layers 12 and 22)
The second layers 12 and 22 are provided for the purpose of reducing the difference in thermal expansion between the first layer and the third layer, and are made of a carbon cushion material. Furthermore, it also has a function of sealing the gap between the first layer and the third layer, which have poor cushioning properties and flexibility. The bulk density and thickness of the carbon cushion material can be determined in accordance with the degree of thermal expansion and contraction caused by the size of the quartz glass molded body at the time of molding and taking into account the desired dimensional accuracy. The cushion material of the second layer 12 and the cushion material of the second layer 22 may be the same material or thickness, or may be different materials and thicknesses. In particular, the thickness of the cushion material of the second layer 22 is desirably as thin as possible within a range that can absorb the difference in thermal expansion, from the viewpoint of molding accuracy and the like. The carbon cushion material is preferably a carbon fiber felt, for example, 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. Preferably there is. 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 to 7 mm.

(Third layer 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 molded body surface. Therefore, it is preferable that the molded heat insulating material used for the third layers 13 and 23 has a strength that does not deform due to the smooth surface and the liquid pressure of the glass, and further has releasability. The third layer 13 provided on the bottom 10 is preferably made of a material having a small shrinkage deformation value because it is subjected to a load due to the liquid pressure of the glass during molding. From the viewpoint of balance between air permeability and strength, the graphite molded heat insulating material preferably has a density in the range of 0.1 to 0.5 g / cm ³ . In particular, since the graphite molded heat insulating material used for the third layer 13 is preferably a material having a small shrinkage deformation value, the density is preferably in the range of 0.13 to 0.16 g / cm ³ .

  Graphite molded insulation has a larger thermal expansion than C / C composite. Therefore, the dimension of the outer edge of the plane of the third layer 13 made of graphite is as shown in FIG. 2 (plan view seen from above the mold shown in FIG. 1). It is desirable that the length is shorter than the inner dimensions of the third layers 23a to 23d of the four side walls that are erected on the first layer 11 and fixed.

For example, when the mold is 1000 mm as an example Mold: 1000 mm
Coefficient of thermal expansion (C / C) of graphite / graphite composite: 0.8 × 10 ⁻⁶ / K
Graphite molded insulation: 2.5 × 10 ^-6 / K
Thermal expansion of graphite / graphite composite (C / C composite)
1000 x (0.8 x ^10-6 ) x (1800-20) = 1.4mm
Graphite molded insulation
1000 x (2.5 x ^10-6 ) x (1800-20) = 4.5mm
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 than the inner dimension of the graphite / graphite composite (C / C) mold.

  The three side layers 23a to 23d of the four side walls are in contact with the side end surfaces of the two opposite third layers 23a and 23c without gaps in the vicinity of the edges of the two opposite third layers 23b and 23d, Alternatively, one side end face of each of the third layers 23a, 23b, 23c, and 23d of the four side wall portions abuts in the vicinity of the edge portions of the adjacent side wall portions 23b, 23c, 23d, and 23a without any gap. Similarly, the second side layers 22a to 22d of the four side wall portions are arranged so that the side end surfaces of the two opposing second layers 22a and 22c are not exposed in the vicinity of the edges of the two opposing second layers 22b and 22d. Or one side end face of the second layer 22a, 22b, 22c, 22d of the four side wall parts abuts in the vicinity of the edge part of the adjacent side wall parts 22b, 22c, 22d, 22a without any gap. Further, similarly, the side layers of the two first layers 21a and 21c facing each other have gaps in the vicinity of the edges of the two first layers 21b and 21d facing each other. Or one side end surface of the first layers 21a, 21b, 21c, and 21d of the four side wall portions abuts in the vicinity of the edge portions of the adjacent side wall portions 21b, 21c, 21d, and 21a without gaps. . These four side wall third layers 23a to 23d, the four side wall second layers 22a to 22d and the four side wall first layers 21a to 21d form four side walls and a bottom portion. 13 and a space S for forming quartz glass are formed inside.

  As shown in FIG. 2, second layers 22a to 22d are provided on the first layers 21a to 21d, and third layers 23a to 23d are provided thereon. The four side walls 20 of the mold are preferably arranged so that the second layer 22 and the third layer 23 are staggered. In order to maintain the shape of the mold, it is appropriate that the first layers 21a to 21d to the third layers 23a to 23d are fixed to all layers using carbon yarn or graphite bolts and nuts, respectively. 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. Therefore, depending on the length of the side wall portion 20, the distance between the third layers 23a to 23d. It is appropriate to appropriately provide a gap for differential thermal expansion.

  In the mold of the present invention, the structure of the contact portion between the second layer 12 and the third layer 13 of the bottom 10 and the second layer 22 and the third layer 23 of the side wall 20 is not limited, but there is no gap. Alternatively, it is preferable that the structure is such that a gap is not easily formed, or even if there is a gap, there is no hindrance to molding. In the structure of the 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 thereof. On the other hand, in the mold of the present invention shown in FIGS. 3 and 4, the third layer 23 of the side wall 20 is erected closer to the inside of the mold than the third layer 13 of the bottom 10, and the second layer of the side wall 20. The layer 22 is thinner at the periphery of the third layer 13 at the bottom 10 than between the third layer 23 and the first layer 21 at the other side wall 20.

  Furthermore, the third layer 13 of the bottom 10 can be made of two or more members, and a structure can be provided in which a gap is provided between each member to absorb thermal expansion. FIG. 4 shows an example in which the third layer 13 is divided into two members 13a and 13b. For example, the third layer 13 of the bottom 10 may be a member divided into four parts.

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

  The degree of thermal expansion and contraction of the 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-described graphite formed 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 × 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) = 1.4mm
Thermal expansion difference 1.4-0.9 = 0.5mm
(For graphite (CIP) mold: 8mm)

(Hot-extension molding of quartz glass)
In the method of the present invention, the quartz glass ingot is accommodated in a space for molding the quartz glass of the mold. The quartz glass ingot can be manufactured by a known method, and the shape thereof is not particularly limited. The quartz glass ingot stored in the mold is heated to a temperature equal to or higher than the melting point of the quartz glass. There are no particular restrictions on the temperature raising conditions and the temperature at which the temperature is raised. When the temperature is raised to a predetermined temperature equal to or higher than the melting point of the quartz glass (for example, 1800 to 1900 ° C.), the quartz glass ingot melts, and the side surface of the fused quartz glass contacts the space side surface of the third layer forming the molding space. And hold until the desired substrate shape or approximate substrate shape is obtained.

  At this stage, due to the mass and liquid pressure of the fused quartz glass, the side surface of the fused quartz glass gives stress to 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 have dimensions that are thermally expanded from room temperature at the elevated temperature. However, the second layer is a cushion material, and is thermally expanded and contracted by stress. After the fused silica glass has a desired substrate shape or substrate approximate shape, the mold and the molded body are cooled. In the process, the mold and the molded body contract according to the thermal expansion coefficient. Typical thermal expansion coefficients of the quartz glass, the first layer (C / C composite) and the third layer (graphite molded heat insulating material) are as shown in Table 1 above. The first layer and the quartz glass molded body. As a result, since the thermal contraction of the third layer is larger than that of the quartz glass molded body, the bottom third layer and the side wall third layer are fixed as the bottom third layer contracts during the cooling process. The side wall portion third layer is pushed outward by the side surface of the molded body. On the other hand, since the thermal contraction of the first layer is larger than that of the quartz glass molded body, the bottom first layer and the side wall first layer are fixed along with the shrinkage of the bottom first layer in the cooling process. The side wall portion first layer is also pushed outward through the second layer and the third layer. However, the pressure from this quartz glass molded body is absorbed by the second side wall portion (cushion material).

  As described above, for example, the difference in thermal expansion between the first layer and the molded body in the case of a molded body of 1000 mm is 0.5 mm, and this is the side wall portion second layer (cushion material) in the molding die of the present invention. Can be absorbed. The stress from the molded body on the side wall first layer is absorbed by the second side wall layer (cushion material), while the stress on the third side wall from the molded body is the side wall third layer 23. 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 third layer and can move horizontally is, for example, the third layer 13 of the bottom portion 10 of the forming die as shown in FIG. The structure can 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 part 20 can also move with the thermal expansion / contraction of the bottom part 10.

  In this way, a quartz glass molded body having a planar shape substantially equal to the planar shape of the space can be obtained.

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

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

(Manufacture of quartz glass ingots)
As in Patent Document 4 (Japanese Patent Laid-Open No. 2012-106869), a cylindrical synthetic quartz glass lump supplies raw material SiCl ₄ and combustion hydrogen and oxygen to the burner, and generates SiO ₂ fine particles by a flame hydrolysis reaction. A quartz glass ingot was produced by a so-called direct method in which the produced fine particles were made into a transparent glass upon deposition.
Next, the defective portion on the outer surface of the ingot was removed and charged into a molding die to produce a molded body of a large substrate for liquid crystal.

Comparative Example 1
-A large-sized substrate for G7 850 x 1400 mm liquid crystal was manufactured by the method described in Patent Document 1.
Molding condition charging ingot: 560kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Mold: Vertical 900 x Horizontal 1450 x Height 1000 mm
Mold material: Graphite (isotropic graphite)
Release material: Graphite fiber cloth
Thickness of cushion material: 10mm / side (carbon fiber felt)
-Refer to the example of Patent Document 2 for the release material.
As shown in FIG. 5, a molding test was conducted with cushion materials (4) placed on the four sides of the mold. However, the upper frame (1) of the mold was broken after molding, and the side plate of the mold was broken and damaged.
・ The molded body was cracked and the large substrate for G7 liquid crystal could not be obtained.

Comparative Example 2
In Comparative Example 2, the same test as in Comparative Example 1 was performed with the thickness of the cushion material increased by 25 mm.
Molding condition charging ingot: 560kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Mold: Vertical 900 x Horizontal 1450 x Height 1000 mm
Mold material: Graphite (isotropic graphite)
Release material: Graphite fiber cloth
Thickness of cushion material: 25mm / side (carbon fiber felt)

・ The mold did not break, but 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 vertical: 875 mm (average value), horizontal: 1425 mm (average value), and thickness: 190 mm (minimum value). When the molded body was observed from the side, it was formed into a trapezoidal shape, and the dimensional difference between the upper and lower bases of the trapezoid was about 10 to 15 mm.
・ This is because, as shown in FIG. 5, when the quartz glass is melted, the side surface of the mold is pushed, the cushion material is crushed, and in the cooling process, the upper frame is subjected to stress due to thermal contraction and the side plate is inclined became.

・ When acquiring 850x1400mm from this molded body,
Molded body thickness: 190mm Crack: 55mm Effective length: 135mm Product yield: 63%
It became.
-Furthermore, since the dimension of the side surface of the molded body is trapezoidal, a rough cutting process is required.
As described above, it has been found that the molding method described in Patent Document 1 (Patent No. 1865417) is not suitable for manufacturing a large substrate for liquid crystal having a thickness of 1000 mm or more.

FIG. Molding explanatory diagram of Comparative Examples 1 and 2: Upper frame (made of graphite)
2: Preparation 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 mold of the present invention, a molded body of 850 × 1400 mm in which the size of the large substrate for liquid crystal is G7 was manufactured, and the effect was confirmed. FIG. 3 is an explanatory view of molding.
・ Molding condition charging ingot: 560kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Mold: Vertical 900 x Horizontal 1450 x Height 1000 mm

Material 1st layer: C / C composite 2nd layer: Carbon fiber felt 3rd layer: Graphite molded insulation and molded body
Top: Vertical: 851 mm, Horizontal: 1401 mm Bottom: Vertical 853 mm, Horizontal: 1403 mm
A thickness of 200 mm was manufactured.

The breakage of the mold and the liquid leakage of the glass from the mold as observed in Comparative Examples 1 and 2 were not observed.
・ The quality of the molded body is
Dimensional difference of molded product (maximum-minimum): 2mm Surface accuracy of molded product (standard deviation): 0.5 to 07,
Angle: 89-90 degrees
Molded body cracks: none A molded body with good quality was obtained.

  When obtaining 850 x 1400 mm from this molded body, the product yield improved to 91%. Furthermore, since the dimensional accuracy of the side surface of the molded body is good, rough cutting is not necessary, and productivity can be improved and costs can be reduced. With the molding die of the present invention and the molding method of the present invention using the same, it is possible to produce a molded product having a size of the large substrate for liquid crystal exceeding 1000 mm.

Figure 3 (Main components)
30: Formwork (upper frame) (C / C composite)
21: First layer side wall (C / C composite)
11: Bottom of the first layer (C / C composite)
12: Second layer (carbon fiber felt)
13: Third layer (molded insulation)
40: Preparation ingot (quartz glass)
50: Molded body (quartz glass)

Molding yield = 850 ^a) mm x 1400 ^a) mm x effective length ^b) mm x 2.2 ^c) (g / cm ³ ) / 1000000 / charge weight kg x 100
a) Length of the short side and long side of the product b) Effective length = Minimum thickness of the molded article−Defect thickness c) Density of quartz glass

Example 2
-Although it is desirable to use an integral type for the third layer of the graphite molded heat insulating material, the size of the graphite molded heat insulating material is limited, so it may be divided and attached to the mold.
In Example 2, the third layer of graphite molded heat insulating material was divided into two parts 13a and 13b and placed in a mold. FIG. 4 shows an explanatory diagram of the mold.

・ Molding condition charging ingot: 560 kg
Temperature x time: 1800 ° C x 3h (nitrogen atmosphere)
Mold: Vertical 900 x Horizontal 1450 x Height 1000 mm
Material first layer: C / C composite second layer: Carbon fiber felt
Third layer: Graphite molded insulation (2 splits) Butt gap: 5mm

・ The size of the molded body was 852 × 1402 × 200 mm.
-When the molded body was observed, a convex “burr” (3-4 mm wide × about 500 mm long) was observed on the bottom of the molded body, but there were no progressive cracks in the molded body.
This “burr” is generated when molten quartz glass leaks into the gap between the two parts of the molded insulation, and the second layer of felt beneath the molded insulation stops the glass from flowing out. The effect of the sealing property of the felt of the second layer was confirmed.
-It is desirable that the gap between the formed heat insulating materials is narrow, so that glass leakage is suppressed. To prevent glass leakage, the gap is preferably less than 10 mm.

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

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

  Also, by using a C / C composite (graphite / graphite composite material) for the first layer of the mold, the thermal expansion difference between the mold and quartz glass is less than 1/10, and the third layer has cushioning properties. It has become possible to use almost no graphite molded insulation. Thereby, the unevenness | corrugation of the molded object of the large sized substrate for liquid crystal which had arisen when using the soft carbon fiber felt described in the subject (3) can be improved from 10 mm to <1 mm.

  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: mold 40: charged ingot (quartz Glass)
50: Molded body S: Molding space

Claims (11)

A mold having a bottom part and a side wall part and having a space for molding quartz glass,
The bottom and side walls of the mold have, from the outside, a first layer made of C / C composite, a second layer made of carbon cushion material, and a third layer made of graphite molded heat insulating material, respectively, The mold, wherein a third layer forms a space for molding the quartz glass. The mold according to claim 1, wherein a difference between a thermal expansion coefficient of the C / C composite and a thermal expansion coefficient of quartz glass is in a range of 0 to 1.0 x ^10-6 / K. The mold according to claim 1, wherein a difference between a thermal expansion coefficient of the C / C composite and a thermal expansion coefficient of quartz glass is in a range of 0 to 0.5 × 10 ⁻⁶ / K. The mold according to any one of claims 1 to 3, wherein the graphite molded heat insulating material has a density in a range of 0.1 to 0.5 g / cm ³ . The mold according to any one of claims 1 to 4, wherein the carbon cushioning material is a carbon fiber felt. The carbon steel cushion member is in the range of bulk density 0.07~0.12g / cm ^3, a thickness ranging 1 to 10 mm, manufacturing mold according to claim 1. The bottom part of the said 3rd layer consists of two or more members, The manufacturing type | mold in any one of Claims 1-6 which has a clearance gap between each member. It is a method of shape | molding quartz glass using the shaping | molding die which has a bottom part and a side wall part and has a space for shape | molding quartz glass, Comprising: The said shaping | molding die is a shaping | molding in any one of Claims 1-7. Said method being a mold. The quartz glass ingot is accommodated in the space for forming the quartz glass, heated to a temperature equal to or higher than the melting point of the quartz glass, and the side surface of the fused quartz 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 the surface is contacted, and then cooled to obtain a quartz glass molded body having a planar shape substantially equal to the planar shape of the space. The method according to claim 8 or 9, wherein a length of at least one side of the quartz glass molded body is 1000 mm or more. The method according to claim 8 or 9, wherein the length of both sides of the quartz glass molded body is 1000 mm or more.