JP2016011235A - Manufacturing method of glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a glass substrate capable of improving dispersion distribution of a glass substrate in heat-treating a laminate of a plurality of glass substrates molded by a down-draw method to reduce heat shrinkage of the plurality of glass substrates.SOLUTION: A manufacturing method of a glass substrate includes a packaging step for packaging in a case a laminate of glass substrates formed by laminating a plurality of glass substrates molded by a down-draw method in the thickness direction after sandwiching each of the plurality of glass substrates between sheets; and a heat treatment step for heat-treating the laminate of the glass substrates packaged in the packaging step to reduce thermal shrinkage of the plurality of glass substrates. In the heat treatment step, the laminate of the glass substrates is heat-treated so as to reduce distortion and make distortion distribution uniform in an area covering a peripheral region of the glass substrate and a central region enclosed by the peripheral region.

Description

  The present invention relates to a method for manufacturing a glass substrate.

  In recent years, in the field of display panels, higher definition of pixels has progressed in order to improve image quality. With the progress of this high definition, it is desired that the glass substrate used for the display panel has high dimensional accuracy. For example, a glass substrate having a low thermal shrinkage rate is preferable so that the size of the glass substrate is not easily changed even during heat treatment at a high temperature during the manufacturing process of the display panel.

  In general, the thermal shrinkage rate of a glass substrate decreases as the strain point of the glass increases. Moreover, it is known that the thermal shrinkage rate of a glass substrate will become so small that the slow cooling rate in the manufacturing process of a glass substrate is made small. However, if the slow cooling rate is reduced, it is necessary to lengthen the slow cooling furnace that performs the slow cooling process of the glass substrate, but it is difficult to lengthen the slow cooling device on the production line.

  Therefore, the heat shrinkage rate is further lowered by performing heat treatment on a plurality of glass substrates manufactured on the production line over time. For example, a processing method of a glass plate is known that reduces a thermal shrinkage rate by holding a laminated body in which paper is sandwiched between a plurality of glass plates at a predetermined temperature for a required time (Patent Document 1).

JP-A-8-151224

In the glass substrate processing method, a heat treatment is performed on a laminated body of a plurality of glass substrates, so that the thermal shrinkage can be simultaneously reduced for the plurality of glass substrates. The thermal history varies depending on the location of the main surface of the glass substrate, and the degree of thermal contraction of the glass plate tends to vary depending on the location. In this case, although the thermal contraction rate of the glass plate is reduced, distortion is likely to occur in the glass substrate due to the difference in the degree of thermal contraction of the glass substrate. At the start of the heat treatment, for example, the end region including the edge of the glass substrate receives heat conduction from a high-temperature atmosphere, and the temperature rises faster than the central region surrounded by the end region of the glass plate. In addition, before the heat treatment is completed, for example, the atmosphere is cooled down, and the end region of the glass substrate in the high temperature state is exposed to the low temperature atmosphere to dissipate heat, and the temperature is decreased faster than the central region of the glass plate. Such distortion generated in the glass substrate is not preferable because it causes warpage and distortion in the glass substrate.
By the way, conventionally, production of a glass substrate using a downdraw method has been performed. In the downdraw method, when a long sheet glass is conveyed, both ends in the width direction orthogonal to the conveying direction are sandwiched between roller pairs and pulled downward. At this time, the sheet glass is cooled by being sandwiched between the roller pair. Since only the end portion in the width direction of the sheet glass is sandwiched between the pair of rollers, there is a difference in the cooling rate between the end portion in the width direction of the sheet glass and the center portion. Therefore, compared with the glass substrate manufactured by other methods, such as the float process, the difference of the extent of a heat shrink tends to arise. Although the sheet glass is usually cooled in the slow cooling furnace on the downstream side after being conveyed by the roller pair, there is a case where the difference in the degree of thermal shrinkage caused by the cooling by the roller pair is not sufficiently solved. For this reason, distortion tends to occur in the glass substrate.
In order to reduce the occurrence of the distortion of the glass substrate by suppressing the influence of the heat history at the start of the heat treatment and before the end of the heat treatment, the glass substrate is heat-treated for a long time to maintain the atmosphere at the maximum temperature. However, it takes a long time for the heat treatment, which is not preferable in terms of production efficiency of the glass substrate.

  Therefore, the present invention provides a glass substrate capable of improving the strain distribution of the glass substrate when heat treatment is performed on the laminated body of the plurality of glass substrates formed by the downdraw method to reduce the thermal shrinkage rate of the plurality of glass substrates. It aims at providing the manufacturing method of.

One aspect of the present invention is a method for producing a glass plate,
A glass substrate is formed by the downdraw method, and a forming step of cutting the formed glass substrate into a predetermined size,
A plurality of glass substrates obtained in the forming step are laminated in the thickness direction in a state of being sandwiched between sheet bodies to produce a laminated body of glass substrates, and the laminated body of glass substrates is packed in a packaging body. Packing process;
A heat treatment step of reducing the thermal shrinkage rate of the plurality of glass substrates by heat-treating the laminate of the glass substrates packed in the packing step,
In the heat treatment step, heat treatment is performed on the glass substrate laminate so as to reduce the generation of strain and make the strain distribution uniform from the end region of the glass substrate to the central region surrounded by the end region. It is characterized by.

  In the heat treatment step, in the laminated body of the glass substrates, from one end to the other end in the thickness direction, the occurrence of strain of the laminated glass substrates is reduced, and the strain distribution of the glass substrates is made uniform. It is preferable to heat-treat the laminate.

The strain is preferably 9 kgf / cm ² or less.

  The sheet body is preferably made of one or a combination selected from carbon graphite, alumina fiber, silica fiber, glass fiber, and porous ceramics.

  It is preferable that the distortion of the glass substrate reduced in the heat treatment step is smaller than the distortion of the glass substrate reduced in the forming step.

  ADVANTAGE OF THE INVENTION According to this invention, when performing the heat processing to the laminated body of the several glass substrate shape | molded by the down draw method and reducing the thermal contraction rate of several glass substrate, the strain distribution of a glass substrate can be improved. .

It is a flowchart which shows the flow of the manufacturing method of the glass plate of this embodiment. It is a side view which shows the pallet on which the laminated body of the glass substrate was mounted in the heat processing performed by this embodiment. (A) is the figure which showed the position on a glass substrate, (b) is a figure which shows the thermal history in each position on a glass substrate. It is a graph which shows the relationship between the area which shows the difference of a thermal history, and distortion.

Hereinafter, the manufacturing method of the glass substrate of this invention is demonstrated in detail.
FIG. 1 is a flowchart showing the flow of the glass substrate manufacturing method of the present embodiment. Although the glass substrate manufactured is not specifically limited, For example, it is preferable that each of the vertical dimension and the horizontal dimension is 500 mm to 3500 mm. The glass substrate is preferably a very thin rectangular plate having a thickness of 0.1 to 1.1 mm.

As a method for forming sheet glass from molten glass in the present embodiment, a float method or a down draw method such as a fusion method (overflow down draw method) is used. The substrate manufacturing method is suitable for the downdraw method and particularly the fusion method because it is difficult to lengthen the slow cooling device on the production line in the downdraw method.

First, the melted glass is formed into a sheet glass that is a strip-shaped glass having a predetermined thickness by a known method such as a fusion method or a float method (step S1).
Next, the formed sheet glass is sequentially sampled on a glass substrate which is a base plate having a predetermined length (step S2). In step S2, after cutting the edge part of the width direction of a sheet glass called an ear | edge part among sheet glass, it plate | plates for every predetermined size. And the glass substrate laminated body (bundle of glass substrates) of the structure which laminated | stacked the glass substrate sequentially obtained by the boarding between each sheet | seat body, and laminated | stacked the glass substrate in the thickness direction of the glass substrate is produced ( Laminate production process: Step S3). Next, a heat treatment for heating the glass substrate laminate produced for the glass substrate laminate is performed (heat treatment step: step S4). The process of step S3 and the process of step S4 are the annealing process of this embodiment. Details of the annealing step will be described later.

  The glass substrate after the heat treatment is conveyed to a cutting process, and is cut into a product size to obtain a glass substrate (step S5). The obtained glass substrate is subjected to end face processing including end face grinding, polishing and corner cutting, and then the glass substrate is washed (step S6). The cleaned glass substrate is optically inspected for scratches, dust, dirt, or scratches including optical defects (step S7). A glass substrate having a quality suitable by inspection is loaded on a pallet and packed as a laminated body alternately laminated with paper protecting the glass substrate (step S8). The packed glass substrate is shipped to a supplier.

  The glass substrate manufactured in this embodiment is suitable as a glass substrate used for a display panel, for example, a glass substrate for liquid crystal display or a glass substrate for organic EL display. Furthermore, the glass substrate manufactured in this embodiment is particularly suitable as a glass substrate for LTPS (Low-temperature poly silicon) TFT display used for high-definition displays, or a glass substrate for oxide semiconductor TFT displays. .

The glass substrate of this embodiment preferably has a heat shrinkage rate of 10 ppm or less from the viewpoint of being used for a glass substrate for a high-definition display panel, and more preferably has a heat shrinkage rate of 6 ppm or less. The distortion of the glass substrate is preferably 9 kgf / cm ² or less from the viewpoint of suppressing the change in optical characteristics due to the distortion, for example, the change in refractive index, without causing warpage, and is 4 kgf / cm ² or less. preferable. The lower limit of the strain is not particularly limited, but is substantially 2 kgf / cm ² . In this embodiment, it is preferable that the distortion of the glass substrate reduced in the heat treatment step is smaller than the distortion reduced in the sheet glass formed in step S1. In other words, the distortion of the glass substrate is preferably reduced by the heat treatment step. The thermal contraction rate of the glass substrate before the heat treatment step is preferably 1000 ppm or less, and more preferably 50 ppm or less. By performing the heat treatment step, the strain becomes less than the allowable value while reducing the thermal shrinkage rate of the glass substrate.
The strain point of the glass substrate is preferably 600 ° C. to 760 ° C. in order to obtain a glass substrate for a high-definition display. For example, the strain point is 661 ° C.

As such a glass substrate, the glass substrate of the following glass compositions is illustrated. That is, the raw material of molten glass is prepared so that the glass substrate of the following glass compositions is manufactured.
SiO ₂ 55~80 mol%,
Al ₂ O ₃ 8-20 mol%,
B ₂ O ₃ 0 to 12 mol%,
RO 0 to 17 mol% (RO is the total amount of MgO, CaO, SrO and BaO).

SiO ₂ is preferably 60 to 75 mol%, and more preferably 63 to 72 mol%, from the viewpoint of reducing the heat shrinkage rate.
Among RO, it is preferable that MgO is 0-10 mol%, CaO is 0-10 mol%, SrO is 0-10%, and BaO is 0-10%.

Further, at least SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and RO are included, and the molar ratio ((2 × SiO ₂ ) + Al ₂ O ₃ ) / ((2 × B ₂ O ₃ ) + RO) is 4. The glass which is 5 or more may be sufficient. In addition, it is preferable that at least one of MgO, CaO, SrO, and BaO is included, and the molar ratio (BaO + SrO) / RO is 0.1 or more.

The total content of 2-fold and mol% of RO for the content of mol% of B ₂ O ₃ is 30 mol% or less, it is preferred that preferably 10 to 30 mol%.
Moreover, 0 mol% or more and 0.4 mol% or less may be sufficient as the content rate of the alkali metal oxide in the glass substrate of the said glass composition.
Further, it contains 0.05 to 1.5 mol% of metal oxides (tin oxide and iron oxide) whose valence fluctuates in the glass, and substantially contains As ₂ O ₃ , Sb ₂ O ₃ and PbO. It is not essential but optional.

[Laminate production process]
FIG. 2 is a side view showing a pallet (packaging body) 20 on which the laminated body 10 (hereinafter referred to as the laminated body 10) of the glass substrate 11 used in the laminated body laminating process of step S3. Here, the left side of FIG. 2 is the front side of the pallet 20, and the right side of FIG. The stacked body 10 is placed on the pallet 20 with the stacking direction approximately in the front-rear direction. Here, the stacking direction of the stacked body 10 does not have to completely coincide with the front-rear direction. For example, as shown in FIG. 2, when the glass substrate 11 is tilted diagonally, the angle formed by the stacking direction and the front-rear direction is the angle formed by the vertical direction of the glass substrate 11.

The pallet 20 includes a base portion 21, a placement portion 22, a back plate 23, and the like.
The base part 21, the mounting part 22, and the back plate 23 are made of a metal such as steel, for example, and are integrally formed by welding or the like.
The base portion 21 has a substantially rectangular plate shape, and is provided with an opening 21a for inserting a forklift claw on an end surface.
The mounting part 22 is fixed to the upper part of the base part 21, and the laminated body 10 of the glass substrate is placed on the upper part of the mounting part 22. Here, the upper surface of the mounting portion 22 does not have to be completely horizontal. For example, as shown in FIG. 2, when the glass substrate 11 is leaned diagonally, the upper surface of the mounting portion 22 may be inclined according to the leaning angle of the glass substrate 11.
The back plate 23 has a substantially rectangular plate shape, and is fixed to the rear end of the mounting portion 22 substantially perpendicularly to the mounting portion 22 in the upper part of the base portion 21. The back plate 23 supports the rear end portion in the stacking direction of the stacked body 10 placed on the mounting portion 22. Here, the back plate 23 does not have to be completely vertical. For example, as shown in FIG. 2, when the glass substrate 11 is leaned diagonally, the back plate 23 may be inclined according to the leaning angle of the glass substrate 11.

  Next, the laminate 10 will be described. The laminated body 10 includes a plurality of glass substrates 11 and a plurality of sheet bodies 12.

The sheet body 12 is sandwiched between the glass substrates 11. In the laminated body 10, the sheet body 12, the glass substrate 11, the sheet body 12, the glass substrate 11,.
The sheet body 12 plays a role of preventing adhesion between the laminated glass substrates 11. The sheet body 12 is made of a material having a heat resistance higher than the temperature (heat treatment temperature) when the laminated body 10 is heat treated. For example, a material having a heat resistant temperature of 500 ° C. or higher is used. By performing heat treatment using such a sheet body 12, the heat distribution becomes uniform, and the variation in the thermal shrinkage rate in the in-plane direction of the glass substrate can be reduced.
It is preferable that the sheet body 12 has a higher thermal conductivity than that of the glass substrate 11 from the viewpoint that the degree of heat treatment of the plurality of glass substrates 11 can be made uniform in the heat treatment step described later. Specifically, the thermal conductivity of the sheet body 12 exceeds 1 W / mK in the plane direction, preferably 2 to 2000 W / mK, more preferably 50 to 1000 W / mK. Although an upper limit is not specifically limited, For example, it is 2000 W / mK. The material of the sheet body 12 is preferably made of, for example, one selected from carbon graphite, alumina fiber, silica fiber, glass fiber, and porous ceramics, or a combination thereof. Among these materials, for example, carbon graphite can be used as a sheet-like carbon graphite sheet, and alumina fiber, silica fiber, and glass fiber can be used as a cloth, a knitted fabric, or the like containing each as a main component. The porous ceramics can be used as a thin plate formed by sintering powder ceramics such as alumina, silica, zirconia, and SiC. The material and form of the sheet body 12 are not limited to these, but may be, for example, a cloth or knitted fabric mainly containing glass fibers, and paper-made paper containing glass fibers or ceramic fibers as a main component. It may be. The sheet body 12 may have a thermal conductivity equal to or lower than that of the glass substrate 11. For example, a heat insulating material such as iso-wool paper may be used.

The sheet body 12 is made of a material whose density does not change before and after the heat treatment, and preferably has a tensile elastic modulus of 500 GPa or less. A material whose density does not change before and after the heat treatment can be said to be a material that does not change in quality due to the heat treatment. Further, as a material whose density does not change before and after the heat treatment, a material whose contact area with the glass substrate 11 does not change before and after the heat treatment may be used. The density in particular of the sheet | seat body 12 is not restrict | limited, For example, it is 1-5 g / cm < ³ >. When the sheet body 12 is repeatedly used for heat treatment, a material that shrinks in the first heat treatment and does not shrink in the subsequent heat treatment is also used as a material whose density does not change before and after the heat treatment. The degree of shrinkage in this case is, for example, a shrinkage rate within 5%. As the sheet body 12 having a tensile elastic modulus in the above range, for example, the above-described carbon graphite can be preferably used. The tensile elastic modulus is a value measured according to JIS K7161 or JIS K7113.
The thickness of the sheet body 12 is preferably thick in terms of enhancing the thermal conductivity in the in-plane direction of the glass substrate 11. On the other hand, the thickness of the sheet body 12 is preferably thin in order to increase the thermal conductivity in the out-of-plane direction and reduce the volume of the laminated body 10. For this reason, it is preferable that the thickness of the sheet | seat body 12 is about 0.02 mm-3 mm, for example, is about 0.25 mm. The area of the sheet body 12 is preferably about the same as or larger than that of the glass substrate 11.
In addition, even if the sheet body 12 is adjacent to the laminated body 10 in the thickness direction and the portion located outside the end of the glass substrate 11 is connected with a buffer material made of the same material as the sheet body 12, for example. Good. Thereby, the heat distribution of the thickness direction of the laminated body 10 can be approximated more uniformly.

[Heat treatment process]
Next, the heat treatment in step S4 will be described.
The laminated body 10 produced in the laminated body production process is subjected to heat treatment off-line from the production line. In this heat treatment, the laminated body of the glass substrates 11 is left for a predetermined time in an atmosphere at a predetermined temperature.

  Specifically, the pallet 20 on which the laminate 10 is placed is loaded into a furnace for heat treatment, the air in the furnace is heated to raise the temperature of the atmosphere from room temperature, and then the temperature is kept constant. The glass substrate 11 is heat-treated by allowing it to stand for a predetermined time (maintained at the maximum temperature) and then lowering the temperature of the atmosphere to room temperature. In this embodiment, the maximum temperature is kept constant, but the temperature profile of the atmosphere in the heat treatment is not particularly limited. However, the temperature of the atmosphere in the heat treatment is preferably at least in the temperature range from the strain point of the glass substrate 11 to −400 ° C. to the strain point from the viewpoint of reducing the thermal shrinkage rate. The time during which the temperature of the atmosphere is in the above temperature range is, for example, 1 to 120 hours. If the time during which the temperature of the atmosphere is in the above temperature range is less than 1 hour, the heat shrinkage rate is not sufficiently reduced, and if it is longer than 120 hours, the heat shrinkage rate is sufficiently reduced, but the production efficiency of the glass substrate 11 is improved. descend.

Although the strain point varies depending on the type of glass, the glass substrate 11 preferably has a glass composition with a high strain point in order to reduce thermal shrinkage. For example, the strain point of the glass of the glass substrate 11 is 600 ° C. It is preferably ˜760 ° C., more preferably 655 ° C. or higher. For example, the strain point is 661 ° C. Even a glass substrate having a low strain point can achieve a thermal contraction rate comparable to that of a glass substrate having a high strain point by heat treatment. In this case, the minimum temperature of the heat treatment temperature is 200 ° C. (= 600 ° C.-400 ° C.) or more.
The high temperature atmosphere to which the laminate 10 of the glass substrate 11 is exposed is not particularly limited, and may be an atmosphere having an oxygen content of 5 to 50%, for example, an air atmosphere composed of air.

  FIGS. 3A and 3B are diagrams showing thermal histories at points A and B on the glass substrate 11. Here, the thermal history indicates a history of the temperature of the glass substrate 11 that changes due to heat treatment. When the laminated body 10 of the glass substrate 11 is sandwiched in the laminating direction and the laminated body 10 is carried into a furnace for heat treatment and the temperature of the atmosphere in the furnace is raised, the heat of the atmosphere is increased in the laminating direction of the laminated body 10. It is transmitted to the glass substrate 11 from the outside. The edge region 11 a including the edge of the glass substrate 11 receives heat conduction from a high-temperature atmosphere and heats up faster than the central region 11 b surrounded by the edge region 11 a of the glass substrate 11. Further, the temperature is lowered, the edge region 11a of the glass substrate 11 in the high temperature state is exposed to the atmosphere that has become low temperature, and heat is dissipated, so that the temperature is lowered faster than the central region 11b of the glass substrate 11. For this reason, as shown in FIG.3 (b), on the glass substrate 11, the temperature around the point A rises and falls faster than the area around the point B. When there is a difference in the thermal history in this way, the thermal contraction rate is different from the edge region 11a to the central region 11b (from the periphery of the point A to the periphery of the point B), and distortion occurs because tensile and compressive stress are generated. In order to make the thermal shrinkage rate uniform within the surface of the glass substrate 11 and suppress the occurrence of distortion, the difference in temperature change from the edge region 11a to the central region 11b of the glass substrate 11 is eliminated, that is, the thermal history. It is necessary to reduce the difference.

  Here, the temperature at which the semiconductor layer composed of LTPS and IGZO is formed on the glass substrate 11 is 400 ° C. to 600 ° C. (when the strain point is 661 ° C., the temperature is 60 ° C. to 260 ° C. lower than the strain point). Therefore, it is only necessary to reduce the thermal contraction rate of the glass substrate 11 in this temperature range. For this reason, in this embodiment, heat treatment is performed so that the temperature around the points A and B of the glass substrate 11 is in the temperature range of 400 ° C. to 500 ° C. The thermal shrinkage rate changes not only with the maximum temperature when the glass substrate 11 is heat-treated, but also with the heat history. In particular, as shown in FIG. 3 (b), the heat history from the maximum temperature of the heat treatment temperature (for example, 500 ° C.) to the temperature 50 ° C. to 300 ° C. lower than the maximum temperature (for example, 450 ° C. to 200 ° C.) The heat shrinkage rate is greatly affected. The thermal shrinkage rate is a temperature at which the thermal shrinkage rate is evaluated, here, a temperature at which a semiconductor layer composed of LTPS and IGZO is formed on the glass substrate 11, for example, at a temperature range of 400 ° C. to 500 ° C. The heat shrinkage rate decreases. Further, thermal shrinkage is reduced even in the temperature range of 400 ° C. to 500 ° C. or less. That is, the temperature close to the temperature at which the thermal contraction rate is evaluated has a large effect on the thermal contraction rate, and the temperature away from the temperature at which the thermal contraction rate is evaluated has a smaller effect on the thermal contraction rate. For this reason, in the present embodiment, the heat treatment is performed so that the difference in thermal history in the surface direction of the glass substrate 11 is suppressed in the temperature range from the highest heat treatment temperature to a temperature lower by 50 ° C. to 300 ° C. In FIG.3 (b), the difference of the thermal history in the temperature range of 300 to 500 degreeC is shown. By reducing the difference in thermal history (area S in FIG. 3B) between the edge region 11a (around point A) and the central region 11b (around point B) of the glass substrate 11, the heat on the surface of the glass substrate 11 is reduced. Variations in shrinkage rate are suppressed, and the occurrence of distortion can be suppressed.

The smaller the area S formed by the difference between the thermal history at point A and the thermal history at point B, the smaller the strain value. FIG. 4 is a graph showing the relationship between the area indicating the difference in thermal history and the strain. As shown in the figure, when the strain is set to 2 kgf / cm ² or less, the glass substrate 11 is heat-treated so that the area is S1 or less. Further, the glass substrate 11 is heat-treated so that the area is S2 or less when the strain is 4 kgf / cm ² or less, and the area is S3 or less when the strain is 9 kgf / cm ² or less. The values of the areas S1 to S3 are time × temperature, that is, the amount of heat. The values of the areas S1 to S3 can be arbitrarily changed depending on the size, thickness, composition, and the like of the glass substrate 11. Thereby, the temperature and time in the heat treatment of the glass substrate 11 can be appropriately changed according to the allowable strain value required when manufacturing the panel of the high-definition display.

  Further, heat treatment is performed so that the temperature of the central region 11b (around point B) of the glass substrate 11 reaches the same maximum temperature as the temperature of the edge region 11a (around point A). When the temperature of the central region 11b (around the point B) of the glass substrate 11 reaches the maximum temperature, the difference in thermal shrinkage between the edge region 11a (around the point A) and the central region 11b (around the point B) becomes small. Generation of distortion can be reduced. The time for which the temperature of the central region 11b (around the point B) continues (maintains) the maximum temperature is arbitrary, and is, for example, 1 hour to 4 hours, and more preferably 1 hour to 2 hours. In order to achieve a predetermined heat shrinkage rate, heat treatment is performed so that the temperature of the glass substrate 11 from the edge region 11a (around the point A) to the central region 11b (around the point B) reaches the maximum temperature, thereby generating distortion. In order to suppress the heat treatment, the glass substrate 11 is heat-treated so that the difference in thermal history in the surface direction becomes small.

  By such heat treatment, the thermal shrinkage rate of the glass substrate 11 can be set to 0 to 12 ppm. The thermal contraction rate of the glass substrate 11 is preferably 0 to 6 ppm, and more preferably 0 to 3 ppm. Such a thermal contraction rate can be achieved by adjusting the glass composition of the glass substrate, the temperature of the heat treatment, and the heat treatment time.

In the heat treatment, from one end of the glass substrate to the other end in the thickness direction, the heat shrinkage rate of the laminated glass substrate is reduced, and the glass substrate laminate is formed so that the distribution of the heat shrinkage rate is uniform. It is preferable to heat-treat. Such heat treatment can be performed, for example, by interposing a heating plate between the glass substrates of the laminated body or sandwiching the glass substrate with a heat insulating plate.
The said heating plate is for heating the laminated body 10, For example, the electrode plate which generate | occur | produces heat when an electric current is sent can be used. In this case, since the resistance value of the electrode plate changes according to the temperature of the electrode plate, the amount of current flowing through the electrode plate changes according to the temperature of the electrode plate. For this reason, the temperature of the heating plate can be controlled based on the amount of current flowing through the electrode plate. Thereby, a laminated body is heated so that the heat distribution of the thickness direction may become equal.
When sandwiching a glass substrate with a heat insulating plate, it is preferable to arrange a pair of heat insulating plates at both ends in the stacking direction of the laminate 10. In the case of the laminate 10 shown in FIG. 2, the front end of the laminate 10 and A heat insulating plate is arranged at the rear end. Thereby, the glass substrate 11 located in the front end (front end part) of the laminated body 10 suppresses the heat flowing from the atmosphere to the glass substrate 11 through the main surface of the glass substrate 11, and the glass substrate 11 is laminated in the stacking direction. The central portion can have a form similar to the form of heat conduction that flows from the outside in the surface direction of the main surface of the glass substrate 11. As a result, the heat distribution of the laminate can be made equal in the thickness direction.

  According to the manufacturing method of the glass substrate of this embodiment, the thermal contraction rate in the in-plane direction of a glass substrate can be reduced by performing heat processing using the above-mentioned sheet | seat body 12. FIG. Thereby, the distribution of the thermal shrinkage rate in the glass substrate becomes uniform, and the glass substrate is less likely to be warped or distorted. Further, since the distribution of the heat shrinkage rate becomes uniform, the generation of strain is suppressed and the strain distribution becomes uniform. In particular, the glass substrate formed by the downdraw method may not sufficiently eliminate the difference in the degree of thermal shrinkage between the end region and the central region. Since the heat shrinkage rate is reduced by the heat treatment using the sheet member 12, the distribution of the heat shrinkage rate and the strain distribution in the glass substrate become uniform.

[Experimental example]
A plurality of glass substrates having the following glass compositions were produced by the overflow down draw method. The strain point of the glass substrate was 660 ° C.

(Glass composition)
SiO ₂ 67.0 mol%,
Al ₂ O ₃ 10.6 mol%,
B ₂ O ₃ 11.0 mol%,
RO 11.4 mol% (RO is the total amount of MgO, CaO, SrO and BaO).

In each of the example and the conventional example, a glass substrate was laminated using a sheet body to form a laminate, and heat treatment was performed. As the sheet body, a carbon graphite sheet was used in the example, and paper was used in the conventional example. A carbon graphite sheet having a heat resistant temperature of 550 ° C., a density of 1.5 g / cm ³ , a tensile elastic modulus of 4 MPa or more, a thickness of 0.08 mm, and a thermal conductivity of 400 to 450 W / mK was used. On the other hand, recycled paper having a resin component of 0.3% was used as the paper. The heat treatment was performed under the same conditions for both the example and the conventional example, the ambient temperature was 500 ° C., and the standing time was 8 hours.
After the heat treatment, the thermal shrinkage and strain of the glass substrates produced in the examples and the conventional examples were measured.

(Measurement of heat shrinkage rate)
Before heat treatment, a glass substrate is cut into a rectangle of a predetermined size, a marking line is put on both ends of the long side, and cut in half at the center of the short side to obtain two glass samples. One of the glass samples is heat-treated (temperature rising rate is 10 ° C./min, left at 450 ° C. for 1 hour). Measure the length of the other glass sample without heat treatment. Further, the heat-treated glass sample and the untreated glass sample are put together to measure the deviation amount of the marking line with a laser microscope or the like, and the difference in the length of the glass sample is obtained to obtain the thermal contraction amount of the sample. be able to. Using the difference as the amount of heat shrinkage and the length of the glass sample before the heat treatment, the heat shrinkage rate is obtained by the following equation. The thermal shrinkage rate of this glass sample was taken as the thermal shrinkage rate of the glass substrate.
Thermal contraction rate (ppm) = (difference) / (length of glass sample before heat treatment) × 10 ⁶

[Measurement of strain]
Since the refractive index of a glass substrate changes with distortion, the retardation value resulting from the birefringence of a glass substrate was measured. The larger the retardation value, the greater the distortion. For the measurement of the retardation value, a birefringence measuring device ABR-10A manufactured by UNIOPT was used.
Strain was measured at 10 or more different positions on the surface of the glass substrate, and the maximum value among the measured strain values was defined as the strain value.

The thermal shrinkage rates of the glass substrates of the examples and the conventional examples were 6 ppm and 20 ppm, respectively, and the thermal shrinkage rates of the examples were extremely low.
In addition, regarding the retardation value of the glass substrate of the example and the conventional example, the maximum measured value of the glass substrate of the example is 2 kgf / cm ² , and the maximum measured value of the glass substrate of the conventional example is 15 kgf / cm ^2. It was. From this, it can be seen that the glass substrate of the example has a small strain.
From this, the effect of the manufacturing method of the glass substrate of this embodiment is clear.

  As mentioned above, although the manufacturing method of the glass substrate of this invention was demonstrated in detail, this invention is not limited to the said embodiment and Example, In the range which does not deviate from the main point of this invention, you may carry out various improvement and change. Of course.

10 Laminated body 11 Glass substrate 12 Sheet body 20 Pallet (packaging body)
21 base part 22 mounting part 23 back plate

Claims (5)

A glass substrate is formed by the downdraw method, and a forming step of cutting the formed glass substrate into a predetermined size,
A plurality of glass substrates obtained in the forming step are laminated in the thickness direction in a state of being sandwiched between sheet bodies to produce a laminated body of glass substrates, and the laminated body of glass substrates is packed in a packaging body. Packing process;
A heat treatment step of reducing the thermal shrinkage rate of the plurality of glass substrates by heat-treating the laminate of the glass substrates packed in the packing step,
In the heat treatment step, heat treatment is performed on the glass substrate laminate so as to reduce the generation of strain and make the strain distribution uniform from the end region of the glass substrate to the central region surrounded by the end region. A method for producing a glass substrate, comprising:   In the heat treatment step, in the laminated body of the glass substrates, from one end to the other end in the thickness direction, the occurrence of strain of the laminated glass substrates is reduced, and the strain distribution of the glass substrates is made uniform. The manufacturing method of the glass substrate of Claim 1 which heat-processes a laminated body.   The method for producing a glass substrate according to claim 1, wherein the strain is 10 ppm or less.   The glass according to any one of claims 1 to 3, wherein the sheet body is composed of one kind selected from carbon graphite, alumina fiber, silica fiber, glass fiber, and porous ceramics, or a combination thereof. A method for manufacturing a substrate.   The glass substrate manufacturing method according to any one of claims 1 to 4, wherein the distortion of the glass substrate reduced in the heat treatment step is smaller than the distortion of the glass substrate reduced in the forming step.

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