TW201733934A - Heat treatment method for glass substrate carrying out heat treatment for reducing the hot shrinkage rate of the glass substrate 1 - Google Patents

Abstract

This invention discloses a heat treatment method for a glass substrate. The heat treatment method comprises three steps: at least disposing a low-friction sheet 3 between a peripheral side 1c of a supported region of a lower surface 1b of the glass substrate 1 and an upper surface 2a of a supporting member 2 opposite to the peripheral side 1c by carrying out heat treatment for reducing the hot shrinkage rate of the glass substrate 1 in a state of supporting the glass substrate 1 from the downside by using the supporting member 2; setting the static friction coefficient of the upper surface 3a of the low-friction sheet 3 to be lower than 0.5; and setting the surface roughness Ra of the upper surface 3a of the low-friction sheet 3 to be more than 5 times as much as the surface roughness Ra of the lower surface 1b of the glass substrate 1.

Description

Glass substrate heat treatment method

The present invention relates to a heat treatment method for reducing the heat shrinkage rate of a glass substrate.

In recent years, mobile terminals such as smart phones or tablet terminals have been rapidly popularized, and the competition for the development of technologies such as high-performance and high-performance is increasing. Therefore, in the case of a substrate such as a liquid crystal display or an organic electroluminescence (EL) display such as a flat panel display (hereinafter referred to as an FPD), a thin glass substrate is used.

In the manufacturing process of the FPD, a film forming process of forming a film-like circuit (circuit pattern) on the surface of the glass substrate is usually performed. However, in the film forming process, the glass substrate to be processed is exposed to a high temperature. Therefore, when the heat shrinkage rate of the glass substrate is large, a circuit pattern having a predetermined accuracy cannot be formed on the surface of the glass substrate, and there is a high possibility that the desired electrical characteristics cannot be secured. Therefore, it is indispensable for the glass substrate for FPD that the heat shrinkage rate is low and the dimensional thermal stability is excellent.

Therefore, for example, Patent Document 1 discloses a technique of performing heat treatment on a glass substrate to improve dimensional thermal stability of the glass substrate. In Patent Document 1, heat treatment is performed in a state where a glass plate to be heat-treated is directly placed on the upper surface of a support member (heat-resistant glass ceramic plate). [Prior Art Document] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-330835

[Problems to be Solved by the Invention] However, when the thin glass substrate is subjected to heat treatment by the method disclosed in Patent Document 1, a large strain may be generated in the planar direction of the glass substrate after the heat treatment. If such a strain occurs, for example, the following problems occur.

In other words, in the manufacturing process of the FPD, in order to improve the production efficiency and to reduce the cost, a so-called multi-chamfering is generally performed, that is, after a circuit pattern or the like is uniformly formed on a large glass substrate, the large glass substrate is removed from the glass substrate. A plurality of glass substrates of the product size are cut out. In this case, if there is a large strain in the planar direction of the glass substrate, the glass substrate is deformed by strain release after the cutting. As a result, when the glass substrates are bonded to each other to form a panel, variations occur between the circuit patterns formed in advance, resulting in product defects.

An object of the present invention is to suppress strain on a glass substrate by heat treatment for reducing the heat shrinkage rate of the glass substrate. [Means for solving the problem]

The inventors of the present application performed heat treatment in a state where the glass substrate was directly placed on the support member, and observed the behavior of the glass substrate during this period. As a result, it was known that interference fringes were observed as characteristics of a glass substrate in which strain was increased after heat treatment. This interference fringe is caused by a void which is generated between the supported region of the lower surface of the glass substrate and the upper surface of the support member. The main cause of the occurrence of the void is that the peripheral portion of the supported region of the lower surface of the glass substrate (in the case of supporting the entire lower surface of the glass substrate, especially the intersection of the lower surface and the end surface of the glass substrate) is stuck. On the upper surface of the support member, the glass substrate is prevented from following the upper surface of the support member. Therefore, the inventors of the present application and the like have proposed the invention of the present application based on the findings as described above.

In other words, the present invention has been made in order to solve the above problems, and is a heat treatment method for a glass substrate, in which a heat treatment for reducing the heat shrinkage ratio of the glass substrate is performed in a state where the glass substrate is supported from below by a support member. The heat treatment method of the glass substrate is characterized in that the low friction sheet is disposed at least between a peripheral portion of the supported region of the lower surface of the glass substrate and an upper surface of the support member opposed to the peripheral portion, and The static friction coefficient of the upper surface of the low friction sheet is set to 0.5 or less, and the surface roughness Ra of the upper surface of the low friction sheet is set to be 5 times the surface roughness Ra of the lower surface of the glass substrate. The above size. Here, the "surface roughness Ra" is a value measured by a method defined in JIS B0601:2001, and the "static friction coefficient" is a value measured by a method defined in JIS K7125:1999. Further, the "supported region" is a region supported by the low friction sheet in the lower surface of the glass substrate, which may be the entire lower surface of the glass substrate, and may be smaller than the lower surface of the glass substrate.

According to this configuration, the peripheral edge portion of the supported region of at least the lower surface of the glass substrate is in contact with the upper surface of the low friction sheet. Since the static friction coefficient of the upper surface of the low friction sheet is as small as 0.5 or less, the peripheral portion of the supported region of the lower surface of the glass substrate slides on the low friction sheet, and the glass substrate follows the support surface (low friction sheet) The manner of the upper surface, or the upper surface of the low friction sheet and the support member, is guided. As a result, it is difficult to form a void between the supported region on the lower surface of the glass substrate and the support surface thereof, and it is possible to suppress the occurrence of strain accompanying the heat treatment.

Here, when the peripheral edge portion of the lower surface of the glass substrate is too close to the upper surface of the low friction sheet, there is a possibility that the glass substrate cannot be peeled off after the heat treatment. Therefore, in the invention of the present application, the surface roughness Ra of the upper surface of the low friction sheet is set to be five times or more the surface roughness Ra of the lower surface of the glass substrate, thereby relaxing the adhesion state of the two. . Thereby, the glass substrate can be peeled off from the low friction sheet even after the heat treatment.

In the above configuration, the thickness of the low friction sheet is preferably from 0.01 mm to 2 mm. Thereby, the upper surface of the low friction sheet is less susceptible to the state of the upper surface of the support member. Further, there is no problem that the heat capacity of the low friction sheet is increased, and a large energy loss is generated at the time of heat treatment.

In the above configuration, the static friction coefficient of the low friction sheet is preferably 0.2 or less. Thereby, the peripheral portion of the lower surface of the glass substrate slides more smoothly on the upper surface of the low friction sheet, and therefore, the glass substrate easily follows the support surface.

In the above configuration, the low friction sheet preferably contains an inorganic substance having a layered crystal structure. Thereby, the friction coefficient is easily reduced, and heat resistance can be improved.

In the above configuration, the low friction sheet is preferably peelably laid on the upper surface of the support member. Thereby, even in the case where the low friction sheet is damaged, the low friction sheet can be easily replaced.

In the above configuration, the entire lower surface of the glass substrate may be a supported region, and the low friction sheet may be provided on the entire lower surface of the glass substrate and the supporting member opposed to the entire lower surface. Between the surfaces. Thereby, the entire supporting surface of the supporting glass substrate contains the low friction sheet, and therefore, the glass substrate can more smoothly follow the supporting surface.

In the above configuration, the peripheral portion of the lower surface of the glass substrate may be extended from the low friction sheet so that the region other than the peripheral portion of the lower surface of the glass substrate is the supported region. Thereby, since the glass substrate can be operated by the extending portion of the glass substrate, the mounting operation of placing the glass substrate on the low friction sheet or taking out the glass substrate from the low friction sheet can be taken out. The job becomes easy. [Effects of the Invention]

As described above, according to the present invention, strain can be suppressed from occurring in the glass substrate by heat treatment for reducing the heat shrinkage rate of the glass substrate.

Hereinafter, a heat treatment method of a glass substrate according to an embodiment will be described with reference to the accompanying drawings.

As shown in Fig. 1 (a) and Fig. 1 (b), the glass substrate 1 as a heat treatment target is placed on the upper surface 3a of the low friction sheet 3, and the low friction sheet 3 is placed on a support member (carrier plate). The upper surface 2a of 2. Further, in such a support form, the glass substrate 1 is introduced into a heat treatment apparatus (heat treatment furnace) and heated, whereby a heat treatment step for reducing the heat shrinkage rate of the glass substrate is performed. Further, a washing step of washing the glass substrate 1 may be provided before the heat treatment step. When such a cleaning step is provided in advance, it is possible to prevent foreign matter adhering to the surface of the glass substrate 1 from being sintered on the surface of the glass substrate 1 by heat treatment.

Hereinafter, the glass substrate 1 and the low friction sheet 3, the support member 2, and the heat treatment apparatus 10 used in the heat treatment step will be described in detail.

[Glass substrate] The glass substrate 1 has a rectangular shape in plan view, and the size of the glass substrate 1 is preferably 500 mm square or more, more preferably 700 mm square or more, further preferably 1000 mm square or more, and most preferably 1300 mm square or more. . In general, the larger the size of the glass substrate 1, the more easily the glass substrate 1 after heat treatment is strained. Therefore, the larger the size of the glass substrate 1, the easier it is to enjoy the effects of the present embodiment. Further, the glass substrate 1 is not limited to a rectangular shape, and may be a polygon having a triangle or a pentagon or more, a circular shape (including an elliptical shape), an irregular shape, or the like.

The thickness of the glass substrate 1 is 0.7 mm or less, preferably 0.5 mm or less, more preferably 0.4 mm or less, and most preferably 0.3 mm or less. In general, the smaller the thickness, the smaller the self-weight, and therefore it is difficult to follow the upper surface of the support member 2. Therefore, the thinner the glass substrate 1 is, the more the effect of the low friction sheet 3 is. Further, as the thickness of the glass substrate 1 is smaller, the contribution to the thinning or weight reduction of a product (for example, FPD) having the glass substrate 1 as a constituent component can be made higher. However, if the thickness of the glass substrate 1 is too small, the minimum strength required for the glass substrate 1 cannot be ensured. Therefore, the thickness of the glass substrate 1 is preferably 1 μm or more, more preferably 3 μm or more, and most preferably 5 μm or more.

The strain point of the glass substrate 1 is 650 ° C or higher, preferably 660 ° C or higher, more preferably 670 ° C or higher, and most preferably 680 ° C or higher. The higher the strain point, the easier it is to reduce the heat shrinkage rate. On the other hand, when the strain point is too high, the productivity of the glass substrate 1 is remarkably lowered. Therefore, the strain point of the glass substrate 1 is preferably 725 ° C or lower, more preferably 720 ° C or lower, and most preferably 715 ° C or lower. Further, the strain point referred to herein is a value measured by a method defined by American Society for Testing and Materials (ASTM) C336.

The glass substrate 1 having the above-described size, thickness, and strain point can be formed, for example, of tellurite glass, ceria glass, borosilicate glass, soda glass, alkali-free glass, or the like. In the present embodiment, a glass substrate formed of an alkali-free glass which is less likely to cause deterioration over time among the various glasses is used. Here, the alkali-free glass means a glass which does not substantially contain an alkali component (alkali metal oxide), and specifically refers to a glass having an alkali component content of 3,000 ppm or less. As the alkali-free glass, the alkali component content is preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 300 ppm or less.

The surface roughness Ra of the lower surface 1b of the glass substrate 1 is preferably 2.0 nm or less, more preferably 1.0 nm or less, still more preferably 0.5 nm or less, and most preferably 0.2 nm or less. Further, the surface roughness Ra of the upper surface 1a of the glass substrate 1 may be the same as that of the lower surface 1b or may be different from the lower surface 1b.

The glass substrate 1 is subjected to, for example, an overflow down-draw method, a slot down-draw method, a roll out method, a float method, and an up draw. Method, redraw method. In the present embodiment, a glass substrate produced by an overflow down-draw method is used.

[low friction sheet]

In this embodiment, the low friction sheet 3 is disposed between the entire lower surface 1b of the glass substrate 1 and the upper surface 2a of the support member 2 opposed to the lower surface 1b. That is, in this embodiment, the entire lower surface 1b of the glass substrate 1 is a supported region of the glass substrate 1. Further, the low friction sheet 3 has a projecting portion 3c that protrudes toward the outer side of the glass substrate 1. Further, the low friction sheet 3 may be provided only in a region corresponding to the peripheral portion 1c (hatched portion in the drawing) in the lower surface 1b of the glass substrate 1. Moreover, the extension portion 3c can also be omitted. That is, the end surface of the glass substrate 1 is on the same surface as the end surface of the low friction sheet 3. Of course, the end surface of the low friction sheet 3 may be located slightly inside the end surface of the glass substrate 1. In this case, the supported area of the glass substrate 1 is smaller than the lower surface 1b of the glass substrate 1.

In order to suppress the generation of the strain of the glass substrate 1 accompanying the heat treatment, it is necessary to start the heat treatment in a state where the glass substrate 1 sufficiently follows the upper surface 3a of the low friction sheet 3. Therefore, the static friction coefficient of the upper surface 3a of the low friction sheet 3 is set to 0.5 or less. The static friction coefficient of the upper surface 3a of the low friction sheet 3 is preferably 0.4 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less. The smaller the static friction coefficient is, the more the strain in the planar direction of the glass substrate 1 due to the heat treatment can be suppressed. Further, the static friction coefficient of the lower surface 3b of the low friction sheet 3 is not particularly limited, and may be the same as the upper surface 3a or may be different from the upper surface 3a.

Here, if the surface smoothness of the upper surface 3a of the low friction sheet 3 is too high, the low friction sheet 3 and the glass substrate 1 may excessively adhere to each other, causing the glass substrate 1 to be cracked during heat treatment, or After the heat treatment, the glass substrate 1 is attached to the low friction sheet 3, and the two cannot be separated. Further, when the glass substrate 1 is placed on the upper surface 3a of the low-friction sheet 3, there is also a case where the contact portions are sequentially attached, and it is difficult for the glass substrate 1 to sufficiently follow the upper surface of the low-friction sheet 3. 3a. In particular, since a glass substrate used for display applications requires high surface smoothness, a glass substrate having a very small surface roughness Ra (for example, Ra is about 0.2 nm) is generally used, and thus the above-described problems are apt to occur. Therefore, in order to alleviate the adhesion of the upper surface 3a of the low friction sheet 3 to the lower surface 1b of the glass substrate 1, the surface roughness Ra of the upper surface 3a of the low friction sheet 3 is set to the surface of the lower surface 1b of the glass substrate 1. The size of the roughness Ra is more than 5 times. It is preferably 10 times or more, more preferably 20 times or more, and most preferably 50 times or more.

The surface roughness Ra of the upper surface 3a of the low friction sheet 3 is preferably 0.02 μm or more. More preferably, it is 0.05 μm or more, further preferably 0.1 μm or more, further preferably 0.2 μm or more, and most preferably 0.5 μm or more. By setting in advance within the above range, the adhesion of the glass substrate 1 and the low friction sheet 3 can be suppressed. On the other hand, when the surface roughness Ra is too large, the static friction coefficient is increased. Therefore, the surface roughness Ra of the upper surface 3a of the low friction sheet 3 is preferably 5 μm or less. Further, the surface roughness Ra of the lower surface 3b of the low friction sheet 3 is not particularly limited, and may be the same as the upper surface 3a or may be different from the upper surface 3a.

When the surface roughness Ra of the lower surface 1b of the glass substrate 1 is Ra1 and the surface roughness Ra of the upper surface 2a of the support member 2 is Ra2, the thickness of the low friction sheet 3 is preferably larger than Ra1 and Ra2. The added value. More preferably, Ra1+Ra2+ is 10 μm or more, and further preferably Ra1+Ra2+50 μm or more, and most preferably Ra1+Ra2+100 μm or more. By setting in advance in the above range, the glass substrate 1 and the support member 2 can be easily separated, and the function of the low friction sheet 3 can be easily enjoyed. On the other hand, if the thickness of the low friction sheet 3 is too large, the heat capacity increases, and the energy loss at the time of heat treatment increases. Moreover, the manufacturing cost of the low friction sheet 3 is also likely to increase. Therefore, the thickness of the low friction sheet 3 is preferably set to be Ra1 + Ra 2+ 2000 μm or less. Specifically, the thickness of the low friction sheet 3 is preferably from 0.01 mm to 2 mm.

The low friction sheet 3 is preferably in a form that can be removed from the support member 2 in advance. Thereby, when the low friction sheet 3 is damaged, it can be easily replaced. As a result, it is easy to suppress the deterioration of the quality of the glass substrate 1 due to the damage of the low friction sheet 3. Specifically, for example, the low friction sheet 3 is directly laid on the upper surface 2a of the support member 2 without passing through an adhesive layer or the like, and the surface roughness Ra of the lower surface 3b of the low friction sheet 3 is set larger than the support member. The surface roughness Ra of the upper surface 2a of 2.

The low friction sheet 3 preferably contains an inorganic substance having a layered crystal structure. Examples of the inorganic material having a layered crystal structure include graphite, boron nitride, molybdenum disulfide, talc, mica, and the like. Among them, graphite is preferably used in view of being inexpensive and easy to manufacture into a sheet shape. The purity of the inorganic material constituting the low friction sheet 3 is preferably 99.0% by mass or more. More preferably, it is 99.5% or more, further preferably 99.8% or more, and most preferably 99.9% or more. The higher the purity, the more it is possible to suppress scratches on the glass substrate caused by impurities such as metal. In the present embodiment, graphite which is relatively inexpensive and which is easy to increase in size and has a purity of 99.9% is used.

In the glass substrate 1 after the heat treatment, the size of the low friction sheet 3 with respect to the glass substrate 1 can be reduced within a range that does not affect the variation or the unevenness of the heat shrinkage rate. Thereby, the mounting and taking-out work of the glass substrate 1 becomes easy. When the workability is considered, the ratio of the area of the low friction sheet 3 to the area of the entire lower surface 1b of the glass substrate 1 is preferably 0.5 or more and 1.0 or less. It is more preferably 0.6 or more and less than 1.0, more preferably 0.7 or more and less than 1.0, and most preferably 0.7 or more and 0.9 or less.

When the static friction coefficient and the surface roughness Ra of the low friction sheet 3 are set as described above, the following effects can be enjoyed. In other words, it is difficult to maintain a state in which the peripheral edge portion 1c of the lower surface 1b of the glass substrate 1 (particularly, the intersection portion 1x of the lower surface 1b and the end surface 1d) is caught in the low friction sheet 3 as shown in Fig. 2(a). On the upper surface 3a, a gap C is formed between the glass substrate 1 and the low friction sheet 3. Even if the state of FIG. 2(a) is temporarily generated, the peripheral edge portion 1c of the lower surface 1b of the glass substrate 1 slides on the outer side (X direction) on the upper surface 3a of the low friction sheet 3, and accordingly, the glass substrate The lower surface 1b of 1 is lowered on one side (Y direction), and the low friction sheet 3 is approached on one side. Further, the glass substrate 1 is further lowered from the state of FIG. 2(a), whereby even if the peripheral edge portion 1c of the lower surface 1b of the glass substrate 1 comes into surface contact with the upper surface 3a of the low friction sheet 3, the glass substrate 1 The peripheral edge portion 1c of the lower surface 1b also slides outward (X direction) on the upper surface 3a of the low friction sheet 3, and accordingly, the lower surface 1b of the glass substrate 1 is lowered (Y direction), and the surface is nearly low. Friction sheet 3. Thereby, as shown in FIG. 2(b), the glass substrate 1 correctly follows the upper surface 3a of the low friction sheet 3. As a result, it is difficult to form the void C between the lower surface 1b of the glass substrate 1 and the upper surface 3a of the low friction sheet 3, and the occurrence of strain accompanying the heat treatment can be suppressed. Further, as shown in FIG. 2(b), even if the heat treatment is performed in a state where the glass substrate 1 follows the low friction sheet 3, since the two are not excessively adhered, it is possible to easily remove the low friction sheet after the heat treatment. The glass substrate 1 is separated on the material 3.

[Support member] The support member 2 supports the glass substrate 1 and the low friction sheet 3 to be heat-treated from the lower side, and a material having heat resistance such as glass, ceramics, or metal can be used. Among them, it is preferable to use a crystallized glass having a low coefficient of thermal expansion and high thermal shock resistance as the support member 2.

The thickness of the support member 2 is preferably from 0.5 mm to 4.0 mm. More preferably, it is 0.5 mm to 3.5 mm, further preferably 0.5 mm to 3.0 mm, more preferably 0.5 mm to 2.5 mm, and most preferably 1.0 mm to 2.5 mm. By setting in advance in the above range, the possibility that the support member 2 is thermally deformed is low, and the heat capacity of the support member 2 does not increase, and a large energy loss does not occur at the time of heat treatment. Therefore, the glass substrate 1 can be heat-treated with high precision and efficiency.

[heat treatment device]

The heat treatment apparatus that performs the heat treatment preferably uses a batch furnace or a sheet-by-piece furnace that does not include the conveying device. In such a furnace, the glass substrate 1 is subjected to heat treatment in a standing state, and therefore, the sliding of the glass substrate 1 accompanying the conveyance can be suppressed. As a result, it is easy to maintain a uniform temperature distribution in the plane of the glass substrate 1, and it is possible to suppress unevenness in heat shrinkage rate or deterioration in strain or shape due to temperature distribution. Moreover, it is also possible to reduce the possibility of breakage due to collision with the inner member of the furnace during the heat treatment. In the present embodiment, as shown in Fig. 3, a heat treatment apparatus 10 for a batch furnace is used.

As shown in FIG. 3, the heat treatment apparatus 10 includes a glass chamber 11 and a lifting table 13 that moves up and down with respect to the glass chamber 11 in a state in which the glass frame 12 is placed; the furnace wall 14 houses the glass. a chamber 11; and a heater 15 that heats the glass chamber 11 from the outside. The heat treatment device 10 is disposed in a clean room. In summary, the heat treatment step is performed in a clean room.

The glass chamber 11 has a lid-shaped cylindrical shape with a lower end open, and has a heat treatment space S inside. The glass chamber 11 is formed into a lid-shaped cylindrical shape by integrally molding quartz glass, and the heat treatment space S is defined by a continuous surface having no seam.

The glass frame 12 has a plurality of accommodating portions 16 which are provided in a plurality of stages in the vertical direction, and each of the accommodating portions 16 is at least a pair of column portions 12a erected on the elevating table and detachably attached to the column portion 12a. The board 12b is divided and formed. Both the column portion 12a and the shelf plate 12b are formed of quartz glass. In the present embodiment, a lattice-shaped frame body is used as the shelf plate 12b, and a plurality of pin-shaped projections are provided on the upper surface of the shelf plate 12b. In addition, the glass substrate 1 in the horizontal state is supported by the support member 2 including the low friction sheet 3 from the lower side (hereinafter also referred to as "assembly"), and is supported by the plug-like projection from the lower side.

The lifting table 13 has a mounting portion 13a made of quartz glass on which the glass frame 12 is placed. When the placing portion 13a is at the raised position, the lower end opening of the glass chamber 11 is closed, and the glass frame 12 is disposed in the heat treatment space S. On the other hand, when the placing portion 13a is lowered to the lowered position, the assembly is loaded and unloaded with respect to the glass frame 12 placed on the placing portion 13a.

The furnace wall 14 has a closed cylindrical shape with a lower end open and contains a refractory as a whole. A heater 15 is attached to the inner wall surface of the side wall of the furnace wall 14. For example, a metal-based heating element typified by a nichrome-based heating element is used as the heater 15.

A cooling unit (for example, a blower) that cools the glass chamber 11 from the outside may be additionally provided in the heat treatment apparatus 10. By providing such a cooling unit in advance, it is possible to efficiently cool the environment of the heat treatment space heated by the heater 15.

Next, the heat treatment step performed by the heat treatment apparatus having the above configuration will be described. In the heat treatment step, the temperature increasing step, the holding step, and the cooling step are sequentially performed.

Before the temperature increasing step is performed, the placing portion 13a of the lifting platform 13 is placed at the lowered position, and after the assembly is placed in each of the accommodating portions 16 of the glass frame 12, the lifting table 13 is moved upward, and the glass frame 12 is placed. The heat treatment space S in the glass chamber 11. Further, for example, the assembly is attached to each of the housing portions 16 (and the assembly is discharged from each of the housing portions 16 after heat treatment) by a robot fork that can support the assembly from the lower side.

The temperature increasing step is a step of raising the temperature of the glass substrate 1 to a predetermined temperature. Here, the output of the heater is adjusted so that the glass substrate 1 is 10 ° C / min or more, preferably 15 ° C / min or more, more preferably The temperature rise rate of 20 ° C / min or more is raised. However, if the temperature rise rate of the glass substrate 1 is too fast, the possibility that the glass substrate 1 is broken or the like is increased. Therefore, the temperature increase rate is 100 ° C / min or less, and more preferably 80 ° C / min or less.

Next, in the temperature increasing step, the glass chamber 11 (heat treatment space S in the glass chamber 11) is heated from the outside until the temperature of the glass substrate 1 is a predetermined temperature. When the strain point of the glass substrate 1 is T [unit: ° C], the glass chamber 11 is heated until the temperature of the glass substrate 1 is preferably T ° C or less, more preferably (T - 10 ° C) or less, and further It is preferably (T-20 ° C) or less, more preferably (T-30 ° C) or less, still more preferably (T-40 ° C) or less, and most preferably (T-50 ° C) or less. Thereby, the shape change of the glass substrate 1 accompanying heat processing can be prevented as much as possible, and the heat shrinkage rate of the glass substrate 1 can be reduced. However, if the glass substrate 1 is not sufficiently heated, the heat shrinkage rate of the glass substrate 1 cannot be appropriately reduced. Therefore, the glass chamber 11 is heated until the temperature of the glass substrate 1 is (T-200 ° C) or more.

In the heat retention step, the glass substrate 1 heated to a predetermined temperature is held at the predetermined temperature for a predetermined time (specifically, 0.5 minute to 60 minutes). Thereby, the heat shrinkage rate of each of the glass substrates 1 can be appropriately reduced, and the unevenness of the heat shrinkage ratio between the glass substrates 1 can be reduced.

In the temperature lowering step, the temperature of the glass substrate 1 is gradually lowered. The cooling rate is preferably 1 ° C / min or more, more preferably 5 ° C / min or more, and still more preferably 10 ° C / min or more. Thereby, the processing time of the temperature decreasing step can be shortened, and the productivity of the glass substrate 1 can be improved. However, if the temperature drop rate is too fast, the heat shrinkage rate of the glass substrate 1 cannot be sufficiently reduced, and the possibility that the warpage of the glass substrate 1 increases increases. Therefore, the temperature drop rate is preferably 100 ° C / min or less, more preferably 80 ° C / min or less.

Further, the strain remaining in the glass substrate 1 was measured as a stress due to strain by the method described below. The strain in the glass substrate 1 can be estimated by measurement of optical birefringence, that is, measurement of optical path difference of orthogonal linearly polarized waves. The optical path difference is set to R (nm), and the stress (accurately, the deviation stress) F (MPa) due to the strain is expressed as F = R / (C × L). Here, L is a distance (cm) through which a polarized wave passes, and C (nm/cm) is a proportional constant depending on glass, and is called a photoelastic constant.

In the glass substrate 1 after the heat treatment, the maximum stress due to the residual strain is preferably 1 MPa or less. More preferably, it is 0.8 MPa or less, further preferably 0.6 MPa or less, and most preferably 0.5 MPa or less. When it is in the above range, deformation of the glass substrate 1 can be suppressed even if the division is performed.

In the above, the heat treatment method of the glass substrate of the embodiment of the present invention has been described. However, the embodiment of the present invention is not limited thereto, and various modifications can be made without departing from the spirit and scope of the invention. [Examples]

The heat treatment is performed in a state where the low friction sheet is placed on the upper surface of the support member and the glass substrate is placed on the upper surface of the low friction sheet (hereinafter, also referred to as "the embodiment"). In the case where the heat treatment is performed in a state where the glass substrate is directly placed on the upper surface of the support member (hereinafter, also referred to as "Comparative Example 1 and Comparative Example 2"), it is carried out before and after the heat treatment. A confirmation test for confirming the strain in the plane direction of the glass substrate was performed.

When the confirmation test was carried out, in the examples, four assemblies including the supporting member/low friction sheet/glass substrate were prepared, and in Comparative Example 1 and Comparative Example 2, four combinations including the supporting member/glass substrate were prepared. Pieces. Next, heat treatment is performed on each of the assemblies.

The glass substrate to be subjected to heat treatment was used in Examples, Comparative Example 1, and Comparative Example 2. As the glass substrate, a 730 mm × 920 mm rectangular-shaped glass substrate (specifically, an alkali-free glass substrate OA-11 manufactured by Nippon Electric Glass Co., Ltd.) having a thickness of 0.5 mm was used. The glass substrate has a linear thermal expansion coefficient of 37 × 10 ^-7 / ° C (30 ° C to 380 ° C), a strain point of 685 ° C, and a photoelastic constant of 30 nm / cm. Further, the surface roughness Ra of the lower surface of the glass substrate was 0.2 nm. Further, although the surface roughness Ra of the upper surface of the glass substrate did not directly affect the result of the confirmation test, it was the same as the lower surface of the glass substrate.

In the examples, the comparative examples 1 and the comparative example 2, the conditions of the support member other than the surface roughness Ra and the static friction coefficient were common. A 830 mm × 1020 mm rectangular crystallized glass plate (specifically, NEOCERAM N-0 manufactured by Nippon Electric Glass Co., Ltd.) having a thickness of 4 mm was used as a supporting member. The support member has a coefficient of linear thermal expansion of -1 x 10 ^-7 / ° C (30 ° C to 750 ° C). The surface roughness Ra of the upper surface of the support member was 0.8 μm in Comparative Example 1, and 0.5 nm in Comparative Example 2. The static friction coefficient of the upper surface of the support member was 1.3 in Comparative Example 1, and 0.8 in Comparative Example 2. Further, in Comparative Examples 1 and 2, a crystallized glass plate obtained by adjusting the surface of the crystallized glass plate by polishing was used. The surface roughness Ra and the static friction coefficient of the upper surface of the support member in the examples did not directly affect the results of the confirmation test. Therefore, the surface roughness Ra and the static friction coefficient were the same as those of Comparative Example 1, and the measurement was not performed.

A rectangular shape graphite of 730 mm × 920 mm (purity of 99.9% or more) having a thickness of 200 μm was used as the low friction sheet. The upper surface of the low friction sheet has a surface roughness Ra of 1.0 μm and a static friction coefficient of 0.1 to 0.2. Further, although the surface roughness Ra and the static friction coefficient of the lower surface of the low friction sheet did not directly affect the results of the confirmation test, they were the same as the upper surface of the low friction sheet.

The heat treatment conditions were common to the examples, Comparative Example 1 and Comparative Example 2. The heat treatment conditions were such that the glass substrate at room temperature was heated to 650 ° C at a temperature increase rate of 10 ° C /min, and then held at 650 ° C for 3 minutes, and then the glass substrate was cooled to room temperature at a temperature drop rate of 60 ° C / min. Further, in all the glass substrates used for the test, the maximum stress value due to the strain before the heat treatment was 0.3 MPa to 0.4 MPa.

The test results of the confirmation test are shown in Table 1.

[Table 1]

Table 1 also shows that in the embodiment, the static friction coefficient of the upper surface of the low friction sheet constituting the support surface of the glass substrate is 0.5 or less, and the surface roughness Ra of the upper surface of the low friction sheet is the surface roughness of the glass substrate. Ra is more than 5 times. On the other hand, in Comparative Example 1, the static friction coefficient of the upper surface of the support member constituting the support surface of the glass substrate exceeded 0.5, and the surface roughness Ra of the upper surface of the support member was 5 times the surface roughness Ra of the glass substrate. the above. Further, in Comparative Example 2, the static friction coefficient of the upper surface of the support member constituting the support surface of the glass substrate exceeded 0.5, and the surface roughness Ra of the upper surface of the support member was less than 5 times the surface roughness Ra of the glass substrate.

As a result, in the examples, the maximum stress due to the strain of the glass substrate after the heat treatment was 0.3 MPa to 0.4 MPa for all the samples, and no change due to the heat treatment occurred. On the other hand, in Comparative Example 1, the maximum stress value of the glass substrate after the heat treatment was a large value exceeding 1.0 MPa. Further, in Comparative Example 2, the surface roughness Ra of the upper surface of the support member was less than 5 times the surface roughness Ra of the glass substrate. Therefore, when the glass substrate and the support member were excessively adhered, a glass substrate was generated during the heat treatment. When the thermal expansion of the support member is inferior, the glass substrate is broken (broken during heat treatment) due to the difference in thermal expansion. Therefore, the heat treatment method of the present invention can be said to be useful in suppressing the generation of strain accompanying heat treatment.

In conjunction with the confirmation test, it was evaluated how much the glass substrate was thermally contracted with heat treatment, that is, the heat shrinkage rate of the glass substrate was evaluated. The heat shrinkage ratio of the glass substrate was measured and calculated in the order shown by the following (1)-(5). (1) As shown in Fig. 4 (a), a short strip sample G of 160 mm × 30 mm was prepared as a sample of a glass substrate. (2) The water-resistant abrasive paper having a particle size of 1000 is used, and the end portions of the short-length sample G in the longitudinal direction are shifted from the end edge to the center in the longitudinal direction by about 20 mm to 40 mm, respectively. A mark M extending in the short side direction is formed. (3) The short strip sample formed with the mark M is divided into two along the longitudinal direction to prepare sample pieces Ga and Gb. (4) Only one of the two sample pieces Ga and Gb (here, the sample piece Gb) is heat-treated by the heat treatment apparatus. The heat treatment was carried out in the following order, i.e., the temperature was raised from normal temperature to 500 ° C at a temperature increase rate of 5 ° C / minute → at 500 ° C for one hour → at a temperature drop rate of 5 ° C / minute to a normal temperature. (5) After heat-treating the sample piece Gb in the above-described form, the sample piece Ga not subjected to the heat treatment and the sample piece Gb after the heat treatment are placed side by side, and two samples are read by a laser microscope. The positional shift amounts ΔL ₁ and ΔL ₂ of the marks M in the sheets Ga and Gb are calculated based on the following equations (unit: ppm). Further, L ₀ in the following formula is a separation distance between the marks M before heat treatment. Heat shrinkage rate = [{ΔL ₁ (μm) + ΔL ₂ (μm)} × 10 ³ ] / L ₀ (mm)

The heat shrinkage rate of the glass substrate measured and calculated according to the above procedure was a very small value of about 10 ppm.

From the above, it can be understood that the present invention is useful in reducing the heat shrinkage rate of the glass substrate and suppressing the generation of strain accompanying the heat treatment.

1‧‧‧Glass substrate 1a‧‧‧ Upper surface 1b‧‧‧ Lower surface 1c‧‧‧ Peripheral part 1d‧‧‧ End face 1x‧‧‧ Intersection 2‧‧‧ Supporting member 2a‧‧‧ Upper surface 3‧‧ ‧ Low-friction sheet 3a‧‧‧ Upper surface 3b‧‧‧ Lower surface 3c‧‧‧ Extension 10‧‧‧ Heat treatment unit 11‧‧‧Glass room 12‧‧‧ Glass holder 12a‧‧‧ Column 12b‧ ‧‧板板13‧‧‧Elevator 13a‧‧‧Loading Department 14‧‧‧Walls 15‧‧‧Heaters 16‧‧‧Inclusion Department AA‧‧‧C‧‧‧Gap G‧‧‧ Short Strip sample Ga‧‧‧sample piece Gb‧‧‧sample piece L ₀ ‧‧‧Separation distance M‧‧‧Market S‧‧‧ Heat treatment space X‧‧‧ Direction Y‧‧‧ Direction ΔL ₁ ‧ ‧ Position offset ΔL ₂ ‧‧‧ position offset

1(a) to 1(b) are views showing a support form of a glass substrate at the time of execution of the heat treatment method according to the embodiment of the present invention, wherein Fig. 1(a) is a plan view thereof, and Fig. 1(b) is a view of Fig. 1(a). ) AA line arrow view of the cross section shown. 2( a ) to 2 ( b ) are enlarged views showing changes in the mounting form of the peripheral edge portion of the glass substrate of the low friction sheet of FIGS. 1( a ) to 1 ( b ). Fig. 3 is a cross-sectional view showing a heat treatment apparatus used in carrying out the heat treatment method according to the embodiment of the present invention. 4( a ) to 4 ( c ) are diagrams for explaining a procedure for measuring the heat shrinkage rate of the glass substrate.

1‧‧‧ glass substrate

1a‧‧‧ upper surface

1c‧‧‧The Peripheral Department

2‧‧‧Support components

2a‧‧‧Upper surface

3‧‧‧Low-friction sheet

3a‧‧‧Upper surface

3c‧‧‧Outreach

A-A‧‧‧ line

Claims (7)

A heat treatment method for a glass substrate, wherein a heat treatment for reducing a heat shrinkage rate of the glass substrate is performed in a state where a glass substrate is supported from below by a support member, and the heat treatment method for the glass substrate is characterized by: The friction sheet is disposed at least between a peripheral portion of the supported region of the lower surface of the glass substrate and an upper surface of the support member opposite to the peripheral portion, and the upper surface of the low friction sheet The static friction coefficient of the surface is set to 0.5 or less, and the surface roughness Ra of the upper surface of the low friction sheet is set to be 5 or more times the surface roughness Ra of the lower surface of the glass substrate. The method for heat-treating a glass substrate according to claim 1, wherein the low-friction sheet has a thickness of 0.01 mm to 2 mm. The method for heat-treating a glass substrate according to the first or second aspect of the invention, wherein the low friction sheet has a static friction coefficient of 0.2 or less. The heat treatment method for a glass substrate according to any one of claims 1 to 3, wherein the low friction sheet contains an inorganic material having a layered crystal structure. The heat treatment method for a glass substrate according to any one of claims 1 to 4, wherein the low friction sheet is peelably laid on an upper surface of the support member. The method for heat-treating a glass substrate according to any one of the items 1 to 5, wherein the low friction sheet is formed such that the entire lower surface of the glass substrate becomes the supported region. The material is disposed between the entire lower surface of the glass substrate and the upper surface of the support member opposite to the entire lower surface. The method for heat-treating a glass substrate according to any one of the first aspect of the present invention, wherein the region of the lower surface of the glass substrate other than the peripheral portion is the supported region. A peripheral portion of the lower surface of the glass substrate is projected from the low friction sheet.