TWI690498B - Heat treatment method of glass substrate - Google Patents

Abstract

A heat treatment method for a glass substrate, in which the support member 2 supports the glass substrate 1 from below, heat treatment is performed to reduce the thermal shrinkage of the glass substrate 1, and the low-friction sheet 3 is disposed at least on the glass substrate 1 Between the peripheral edge portion 1c of the supported area of the lower surface 1b and the upper surface 2a of the supporting member 2 facing the peripheral edge portion 1c, and the static friction coefficient of the upper surface 3a of the low-friction sheet 3 is set to 0.5 or less In addition, the surface roughness Ra of the upper surface 3a of the low-friction sheet 3 is 5 times or more the surface roughness Ra of the lower surface 1b of the glass substrate 1.

Description

Heat treatment method of glass substrate

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

As we all know, in recent years, mobile terminals such as smart phones and tablet-type terminals have been rapidly popularized to increase the fierce competition in technology development for thinning and lightening mobile terminals and further improving their performance. Therefore, for the substrates of flat panel displays (hereinafter referred to as FPD (flat panel display)) such as liquid crystal displays or organic electroluminescence (EL) displays mounted on mobile terminals, thin glass substrates are also frequently used.

In the manufacturing process of the FPD, a film forming process for forming a thin-film 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 high temperature. Therefore, when the thermal shrinkage rate of the glass substrate is large, a circuit pattern with a predetermined accuracy cannot be formed on the surface of the glass substrate, and the possibility that the desired electrical characteristics cannot be secured increases. Therefore, it is indispensable for the glass substrate for FPD to have a low thermal shrinkage rate and excellent dimensional thermal stability.

Therefore, for example, Patent Document 1 discloses a technique of performing heat treatment on a glass substrate to improve the 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 Literature] [Patent Literature]

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

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

That is, in the manufacturing process of the FPD, in order to improve production efficiency and achieve cost reduction, so-called multi-chamfering is generally performed, that is, after a circuit pattern is uniformly formed on a large glass substrate, from the large glass substrate Cut out multiple glass substrates of product size. In this case, if there is a large strain in the plane direction of the glass substrate, the glass substrate will be deformed as the strain is released after cutting. As a result, when the glass substrates are bonded to each other to produce a panel, there is a deviation between the circuit patterns formed in advance, resulting in defective products.

An object of the present invention is to suppress the occurrence of strain in the glass substrate by heat treatment for reducing the thermal shrinkage of the glass substrate. [Means to solve the problem]

The inventors of the present application performed heat treatment while placing the glass substrate directly on the support member, and observed the behavior of the glass substrate during this period. As a result, it is known that interference fringes are observed as a characteristic of a glass substrate whose strain increases after heat treatment. The interference fringes are caused by voids generated between the supported region on the lower surface of the glass substrate and the upper surface of the support member. It is considered that the main reason for the occurrence of the void is that the peripheral portion of the supported region of the lower surface of the glass substrate (when supporting the entire lower surface of the glass substrate, in particular, the intersection of the lower surface of the glass substrate and the end surface) card 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 filed the invention of the present application based on the findings described above.

That is, the present invention created to solve the above problem is a heat treatment method for a glass substrate, which performs heat treatment to reduce the thermal shrinkage of the glass substrate while supporting the glass substrate from below with a support member, The heat treatment method of the glass substrate is characterized in that a low-friction sheet is arranged at least between the peripheral portion of the supported region on the lower surface of the glass substrate and the upper surface of the supporting member facing 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 5 times the surface roughness Ra of the lower surface of the glass substrate Above the size. Here, "surface roughness Ra" is a value measured based on the method prescribed in JIS B0601:2001, and "static friction coefficient" is a value measured based on the method prescribed in JIS K7125:1999. Moreover, the “supported area” is an area supported by the low-friction sheet in the lower surface of the glass substrate, which is sometimes the entire lower surface of the glass substrate, and sometimes smaller than the lower surface of the glass substrate.

According to this configuration, at least the peripheral portion of the supported region of 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 area on the lower surface of the glass substrate slides on the low-friction sheet, and the glass substrate follows its supporting surface (low-friction sheet The upper surface, or the upper surface of the low-friction sheet and the supporting member) is guided. As a result, it is not easy to form a gap between the supported region on the lower surface of the glass substrate and its supporting surface, and it is possible to suppress the generation of strain accompanying heat treatment.

Here, if the periphery 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 5 times or more the surface roughness Ra of the lower surface of the glass substrate, so as to ease the adhesion state of the two . Thereby, even after the heat treatment, the glass substrate can be peeled from the low-friction sheet.

In the above configuration, the thickness of the low-friction sheet is preferably 0.01 mm to 2 mm. With this, the upper surface of the low-friction sheet is not easily affected by the state of the upper surface of the support member. Furthermore, there is no problem that the heat capacity of the low-friction sheet increases and a large energy loss (energy loss) occurs during heat treatment.

In the above configuration, the static friction coefficient of the low-friction sheet is preferably 0.2 or less. As a result, the peripheral portion of the lower surface of the glass substrate slides on the upper surface of the low-friction sheet more smoothly, so the glass substrate easily follows the supporting surface.

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

In the above configuration, the low-friction sheet is preferably detachably 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 on the support member facing the entire lower surface Between the surfaces. As a result, the entire supporting surface supporting the glass substrate includes the low-friction sheet, so the glass substrate will follow its supporting surface more smoothly.

In the above configuration, the region of the lower surface of the glass substrate other than the peripheral portion may be a supported region, and the peripheral portion of the lower surface of the glass substrate may protrude from the low-friction sheet. Thereby, the glass substrate can be manipulated by the extending portion of the glass substrate. Therefore, the placement operation of placing the glass substrate on the low-friction sheet or the removal of the glass substrate from the low-friction sheet Homework becomes easy. [Effect of invention]

As described above, according to the present invention, it is possible to suppress the occurrence of strain in the glass substrate by the heat treatment for reducing the thermal shrinkage rate of the glass substrate.

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

As shown in FIGS. 1( a) and 1 (b ), the glass substrate 1 as the heat treatment target is placed on the upper surface 3 a of the low-friction sheet 3 that is disposed on the support member (carrier plate) 2's upper surface 2a. Furthermore, in such a supporting form, the glass substrate 1 is introduced into a heat treatment device (heat treatment furnace) and heated, thereby performing a heat treatment step to reduce the thermal shrinkage rate of the glass substrate. Furthermore, before the heat treatment step, a washing step for washing the glass substrate 1 may be provided. If such a washing step is provided in advance, it is possible to prevent foreign materials adhering to the surface of the glass substrate 1 from being sintered on the surface of the glass substrate 1 with heat treatment.

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

[Glass substrate] The glass substrate 1 has a rectangular shape in plan view. The size of the glass substrate 1 is preferably 500 mm square or more, more preferably 700 mm square or more, and 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. In addition, 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 circle (including an ellipse), and an irregular shape.

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. Generally, the smaller the thickness, the smaller the dead 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 greater the effect of the low-friction sheet 3 is. Furthermore, the smaller the thickness of the glass substrate 1, the higher the degree of contribution to thinning, lightening, and the like of products (for example, FPD) that use the glass substrate 1 as a component. However, if the thickness of the glass substrate 1 is too small, the minimum strength required by 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 thermal shrinkage. On the other hand, if the strain point is too high, the productivity of the glass substrate 1 significantly decreases. 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. In addition, the strain point here is the value measured based on the method prescribed by the American Society for Testing and Materials (ASTM) C336.

The glass substrate 1 having the size, thickness, and strain point can be formed of, for example, silicate glass, silica glass, borosilicate glass, soda glass, alkali-free glass, or the like. In this embodiment, a glass substrate made of alkali-free glass that is the least likely to deteriorate over time among the various glasses is used. Here, the alkali-free glass refers to glass that does not substantially contain an alkali component (alkali metal oxide), and specifically refers to glass having an alkali component content of 3000 ppm or less. As the alkali-free glass, the content of the alkali component 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. In addition, 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, for example, an overflow down-draw method, a slot down-draw method, a roll out method, a float method, and an up draw method Method and redraw method. In this embodiment, the glass substrate manufactured by the 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 facing the lower surface 1b. That is, in this embodiment, the entire lower surface 1b of the glass substrate 1 is set as the supported region of the glass substrate 1. Furthermore, the low-friction sheet 3 has an extension portion 3c that extends outward of the glass substrate 1. Furthermore, the low-friction sheet 3 may be provided only in the region corresponding to the peripheral edge portion 1c (hatched portion in the figure) in the lower surface 1b of the glass substrate 1. Furthermore, the protruding portion 3c may be omitted. That is, the end surface of the glass substrate 1 and the end surface of the low-friction sheet 3 are on the same surface. Of course, the end surface of the low-friction sheet 3 may be located slightly inside from 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 1 b of the glass substrate 1.

In order to suppress the occurrence 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 3 a 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, the more it is possible to suppress the strain in the plane direction of the glass substrate 1 accompanying heat treatment. In addition, 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 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 be excessively adhered, causing the glass substrate 1 to crack 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. Moreover, when the glass substrate 1 is placed on the upper surface 3a of the low-friction sheet 3, there may also be a case where the contact parts 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, glass substrates used for display applications require high surface smoothness. Therefore, glass substrates with extremely small surface roughness Ra (for example, Ra is about 0.2 nm) are generally used, so the above-mentioned problems are likely to occur. Therefore, in order to ease 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 roughness Ra is more than 5 times the size. 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. It is more preferably 0.05 μm or more, further preferably 0.1 μm or more, still more preferably 0.2 μm or more, and most preferably 0.5 μm or more. By setting in the above range in advance, it is possible to suppress the adhesion of the glass substrate 1 and the low-friction sheet 3. On the other hand, if the surface roughness Ra is too large, the static friction coefficient becomes large. Therefore, the surface roughness Ra of the upper surface 3a of the low-friction sheet 3 is preferably 5 μm or less. In addition, 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 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 of. More preferably, it is Ra1+Ra2++10 μm or more, more preferably Ra1+Ra2++50 μm or more, and most preferably Ra1+Ra2++100 μm or more. By setting in this range in advance, 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 during heat treatment increases. Moreover, the production cost of the low-friction sheet 3 may also increase. Therefore, the thickness of the low-friction sheet 3 is preferably Ra1 + Ra2 + 2000 μm or less. Specifically, the thickness of the low-friction sheet 3 is preferably 0.01 mm to 2 mm.

The low-friction sheet 3 is preferably in a form that can be detached 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 caused by 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 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 substance having a layered crystal structure include graphite, boron nitride, molybdenum disulfide, talc, and mica. Among them, graphite is preferably used because it is inexpensive and easy to manufacture in a sheet shape. The purity of the inorganic substance constituting the low-friction sheet 3 is, in mass%, preferably 99.0% or more. More preferably, it is more than 99.5%, further preferably, it is more than 99.8%, and most preferably, it is more than 99.9%. The higher the purity, the more it is possible to suppress scratches caused by impurities such as metals on the glass substrate. In the present embodiment, graphite which is relatively inexpensive among the various inorganic substances, is easy to enlarge, and has a purity of 99.9% is used.

For the glass substrate 1 after heat treatment, the size of the low-friction sheet 3 relative to the glass substrate 1 can be reduced within a range that does not affect the strain or unevenness of the thermal shrinkage rate. This makes it easy to place and take out the glass substrate 1. In consideration of workability, 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, still more preferably 0.7 or more and less than 1.0, and most preferably 0.7 or more and 0.9 or less.

If the static friction coefficient and the surface roughness Ra of the low-friction sheet 3 are set in this way, the following effects can be enjoyed. That is, it is difficult to maintain a state where the peripheral portion 1c of the lower surface 1b of the glass substrate 1 (especially the intersection 1x of the lower surface 1b and the end surface 1d) is stuck in the low-friction sheet 3 as shown in FIG. 2(a). A gap C is formed between the glass substrate 1 and the low-friction sheet 3 on the upper surface 3a of. 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 will slide outward (in the X direction) on the upper surface 3a of the low-friction sheet 3, and the glass substrate The lower surface 1b of 1 is lowered (in the Y direction) while approaching the low-friction sheet 3. Furthermore, 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 The peripheral edge portion 1c of the lower surface 1b also slides on the upper surface 3a of the low-friction sheet 3 to the outward side (X direction), and accordingly, the lower surface 1b of the glass substrate 1 descends (Y direction) and approaches low Friction sheet 3. Thereby, as shown in FIG. 2( b ), the glass substrate 1 accurately follows the upper surface 3 a of the low-friction sheet 3. As a result, it is not easy to form a void C between the lower surface 1b of the glass substrate 1 and the upper surface 3a of the low-friction sheet 3, and it is possible to suppress the generation of strain accompanying the heat treatment. Moreover, as shown in FIG. 2(b), even if the glass substrate 1 follows the low-friction sheet 3 and the heat treatment is performed, since the two are not excessively adhered, the low-friction sheet can be easily removed 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 materials having heat resistance such as glass, ceramics, and metal can be used. Among them, it is preferable to use crystallized glass having a low thermal expansion coefficient and high thermal shock resistance as the support member 2.

The thickness of the support member 2 is preferably 0.5 mm to 4.0 mm. It is more preferably 0.5 mm to 3.5 mm, further preferably 0.5 mm to 3.0 mm, still more preferably 0.5 mm to 2.5 mm, and most preferably 1.0 mm to 2.5 mm. By setting in the above-mentioned range in advance, the support member 2 has a low possibility of thermal deformation, and the heat capacity of the support member 2 does not increase, and a large energy loss during heat treatment does not occur. Therefore, the glass substrate 1 can be heat-treated with high accuracy and efficiency.

[Heat treatment device]

The heat treatment apparatus that performs heat treatment is preferably a batch furnace or a piece-by-piece furnace that does not include a transfer device. In such a furnace, the glass substrate 1 is subjected to heat treatment in a static state, and therefore, it is possible to suppress the sliding of the glass substrate 1 accompanying the conveyance. As a result, it is easy to maintain a uniform temperature distribution in the surface of the glass substrate 1, and it is possible to suppress the unevenness of the thermal shrinkage rate or the deterioration of the strain or shape caused by the temperature distribution. Furthermore, it is possible to reduce the possibility of damage due to collision with members in the furnace during heat treatment. In this embodiment, as shown in FIG. 3, the heat treatment apparatus 10 of a batch furnace is used.

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

The glass chamber 11 is in the form of a covered cylinder with an open lower end, and has a heat treatment space S inside. The glass chamber 11 is formed into a covered cylindrical shape by integrally forming quartz glass, and a heat treatment space S is defined by a continuous surface without a seam.

The glass shelf 12 has a plurality of storage portions 16 arranged in multiple stages along the up-down direction. Each storage portion 16 is composed of at least a pair of column portions 12a erected on an elevating platform and a rack detachably attached to the column portions 12a The board 12b is divided and formed. Both the column portion 12a and the shelf plate 12b are formed of quartz glass. In this embodiment, a lattice-shaped frame is used as the shelf plate 12b, and a plurality of latch-shaped protrusions are provided on the upper surface of the shelf plate 12b. Further, the glass substrate 1 in the horizontal state is supported from the lower side by the supporting member 2 including the low-friction sheet 3 and is supported from the lower side by the latch-shaped protrusions. Hereinafter, the support member 2 supporting the glass substrate 1 is also referred to as a package.

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

The furnace wall 14 is in the shape of a covered cylinder with an open lower end, and contains refractory as a whole. A heater 15 is attached to the side inner wall surface 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.

In the heat treatment apparatus 10, a cooling unit (for example, a blower) which cools the glass chamber 11 from the outside may be additionally provided. By providing such a cooling unit in advance, the environment of the heat treatment space heated by the heater 15 can be efficiently cooled.

Next, the heat treatment steps performed by the heat treatment apparatus having the above configuration will be described. In the heat treatment step, the temperature increase step, the heat preservation step, and the temperature decrease step are sequentially performed.

Before performing the temperature raising step, first place the mounting portion 13a of the lifting table 13 at the lowered position, and after loading the assembly into each receiving portion 16 of the glass shelf 12, the lifting table 13 is moved up to arrange the glass shelf 12 The heat treatment space S in the glass chamber 11. Furthermore, for example, by a robot fork capable of supporting the assembly from the lower side, the assembly is loaded into each storage section 16 (and after heat treatment, the assembly is removed from each storage section 16).

The temperature raising 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 A temperature increase rate of 20°C/min or more increases the temperature. However, if the temperature increase rate of the glass substrate 1 is too fast, the possibility of breakage or the like of the glass substrate 1 increases. Therefore, the temperature increase rate is set to 100° C./min or less, more preferably 80° C./min or less.

Next, in the temperature increasing step, the glass chamber 11 (the heat treatment space S in the glass chamber 11) is heated from the outside until the temperature of the glass substrate 1 reaches 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 It is preferably (T-20°C) or lower, more preferably (T-30°C) or lower, particularly preferably (T-40°C) or lower, and most preferably (T-50°C) or lower. Thereby, the shape change of the glass substrate 1 accompanying heat treatment can be prevented as much as possible, and the thermal shrinkage rate of the glass substrate 1 can be reduced. However, if the glass substrate 1 is not sufficiently heated, the thermal 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 higher.

In the heat retention step, the glass substrate 1 that has been heated to a predetermined temperature is maintained at the predetermined temperature for a predetermined time (specifically, 0.5 minutes to 60 minutes). Thereby, the thermal shrinkage rate of each glass substrate 1 can be reduced appropriately, and the unevenness of the thermal shrinkage rate 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. As a result, the processing time of the cooling step can be shortened, and the productivity of the glass substrate 1 can be improved. However, if the cooling rate is too fast, the thermal shrinkage rate of the glass substrate 1 cannot be sufficiently reduced, and the possibility of increased warpage of the glass substrate 1 increases. Therefore, the cooling rate is preferably 100°C/min or less, and more preferably 80°C/min or less.

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

For the glass substrate 1 after heat treatment, the maximum stress due to residual strain is preferably 1 MPa or less. It is more preferably 0.8 MPa or less, still more preferably 0.6 MPa or less, and most preferably 0.5 MPa or less. If it is within the above range, the deformation of the glass substrate 1 can be suppressed even if it is divided and cut.

In the above, the heat treatment method of the glass substrate according to the embodiment of the present invention has been described, but the embodiment of the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. [Example]

When the low friction sheet is arranged on the upper surface of the support member and the glass substrate is placed on the upper surface of the low friction sheet, the heat treatment is performed (hereinafter, it will also be referred to as "Example") ), and in the case where the heat treatment is performed with the glass substrate directly placed on the upper surface of the support member (hereinafter, also referred to as "Comparative Example 1 and Comparative Example 2"), before and after the heat treatment, A confirmation test to confirm the strain in the plane direction of the glass substrate.

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

The glass substrates to be heat-treated are common to Examples, Comparative Examples 1 and 2. As the glass substrate, a rectangular glass substrate with a thickness of 0.5 mm of 730 mm×920 mm (specifically, an alkali-free glass substrate OA-11 manufactured by NEC Glass Co., Ltd.) was used. The linear thermal expansion coefficient of the glass substrate is 37×10 ^-7 /℃ (30℃～380℃), the strain point is 685℃, and the photoelastic constant is 30 nm/cm. Furthermore, the surface roughness Ra of the lower surface of the glass substrate is 0.2 nm. In addition, although the surface roughness Ra of the upper surface of the glass substrate does not directly affect the result of the confirmation test, it is the same level as the lower surface of the glass substrate.

In Examples, Comparative Examples 1 and 2, the conditions of the support member other than the surface roughness Ra and the static friction coefficient are common. A rectangular-shaped crystallized glass plate (specifically, NEOCERAM N-0 manufactured by Nippon Electric Glass Co., Ltd.) of 830 mm×1020 mm with a thickness of 4 mm was used as a support member. The linear thermal expansion coefficient of the support member is -1×10 ^-7 /℃ (30℃～750℃). 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. In addition, in Comparative Examples 1 and 2, a crystallized glass plate whose surface was adjusted 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 of the same degree as in Comparative Example 1 were not measured.

As a low-friction sheet, a 730 mm × 920 mm rectangular graphite (purity of 99.9% or more) with a thickness of 200 μm was used. The surface roughness Ra of the upper surface of the low-friction sheet is 1.0 μm, and the static friction coefficient is 0.1 to 0.2. In addition, although the surface roughness Ra and the static friction coefficient of the lower surface of the low-friction sheet do not directly affect the results of the confirmation test, they are the same as the upper surface of the low-friction sheet.

The heat treatment conditions are common to Examples, Comparative Examples 1 and 2. The heat treatment condition is to raise the temperature of the glass substrate around room temperature to 650°C at a temperature increase rate of 10°C/min, hold it at 650°C for 3 minutes, and then cool the glass substrate to room temperature at a temperature decrease rate of 60°C/min. In addition, in all the glass substrates used for the test, the maximum stress value due to strain before 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 examples, 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 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. Furthermore, in Comparative Example 2, the static friction coefficient of the upper surface of the support member constituting the support surface of the glass substrate exceeds 0.5, and the surface roughness Ra of the upper surface of the support member is less than 5 times the surface roughness Ra of the glass substrate.

As a result, in the examples, for all the samples, the value of the maximum stress due to the strain of the glass substrate after the heat treatment was 0.3 MPa to 0.4 MPa, and no change due to the heat treatment occurred. In contrast, in Comparative Example 1, the maximum stress value of the glass substrate after the heat treatment was a large value exceeding 1.0 MPa. Furthermore, 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, the glass substrate was generated during the heat treatment When there is a difference in thermal expansion from the support member, the glass substrate is damaged due to the difference in thermal expansion (breakage during heat treatment). 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, the degree to which the glass substrate thermally shrinks along with the heat treatment, that is, the thermal shrinkage rate of the glass substrate is evaluated. The thermal shrinkage rate of the glass substrate was measured and calculated according to the procedures shown in (1) to (5) below. (1) As shown in FIG. 4(a), a short strip-shaped sample G of 160 mm×30 mm is prepared as a glass substrate sample. (2) Using water-resistant abrasive paper with a particle size of 1000, the positions of both ends of the short strip G in the longitudinal direction are offset by about 20 mm to 40 mm from the edge to the central side in the longitudinal direction, A mark M extending in the short-side direction is formed. (3) Along the longitudinal direction, the short strip-shaped sample on which the mark M is formed is divided into two to prepare sample pieces Ga and Gb. (4) Using a heat treatment apparatus, only one of the two sample pieces Ga and Gb (here, the sample piece Gb) is heat-treated. The heat treatment was performed in the following order, that is, the temperature was raised from normal temperature to 500°C at a temperature increase rate of 5°C/min → held at 500°C for one hour → the temperature was lowered to normal temperature at a temperature decrease rate of 5°C/min. (5) In the above-mentioned form, after the heat treatment of the sample piece Gb, the unheated sample piece Ga and the heat-treated sample piece Gb are arranged side by side, and two samples are read by a laser microscope The positional deviation amounts ΔL ₁ and ΔL ₂ of the mark M in the sheets Ga and Gb were calculated based on the following formulas [unit: ppm]. In addition, L ₀ in the following formula is the separation distance between the marks M before heat treatment. Thermal shrinkage rate = [{ΔL ₁ (μm) + ΔL ₂ (μm)} × 10 ³ ]/L ₀ (mm)

The thermal shrinkage rates of the glass substrates measured and calculated in this order are very small values around 10 ppm.

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

1‧‧‧Glass substrate 1a‧‧‧Upper surface 1b‧‧‧Lower surface 1c‧‧‧Peripheral part 1d‧‧‧End surface 1x‧‧‧Intersection 2‧‧‧Support member 2a‧‧‧‧Upper surface 3‧‧ ‧Low friction sheet 3a‧‧‧Upper surface 3b‧‧‧Lower surface 3c‧‧‧Extended part 10‧‧‧ Heat treatment device 11‧‧‧Glass chamber 12‧‧‧Glass frame 12a‧‧‧Column part 12b‧ ‧‧Sheet 13‧‧‧Elevating table 13a‧‧‧ Placement part 14‧‧‧ Furnace wall 15‧‧‧ Heater 16‧‧‧ Containment part AA‧‧‧ Line C‧‧‧Gap G‧‧‧ short Strip sample Ga ‧‧‧ sample piece Gb ‧‧‧ sample piece L ₀ ‧‧‧ separation distance M ‧‧‧ mark S ‧‧‧ heat treatment space X‧‧‧ direction Y‧‧‧ direction ΔL ₁ ‧‧ ‧Position offset ΔL ₂ ‧‧‧Position offset

1(a) to 1(b) are diagrams showing the supporting form of the glass substrate when the heat treatment method of the embodiment of the present invention is executed, FIG. 1(a) is a plan view thereof, and FIG. 1(b) is FIG. 1(a). ) Shows the arrow AA line sectional view. FIGS. 2( a) to 2 (b) are enlarged views showing changes in the mounting form of the peripheral portion of the glass substrate with respect to the low-friction sheet of FIGS. 1 (a) to 1 (b ). 3 is a cross-sectional view of a heat treatment apparatus used when implementing the heat treatment method according to the embodiment of the present invention. 4( a) to 4 (c) are diagrams for explaining the measurement procedure of the thermal shrinkage rate of the glass substrate.

1‧‧‧Glass substrate

1a‧‧‧upper surface

1c‧‧‧Perimeter

2‧‧‧Support component

2a‧‧‧upper surface

3‧‧‧Low friction sheet

3a‧‧‧upper surface

3c‧‧‧Extended part

A-A‧‧‧line

Claims (7)

A heat treatment method for a glass substrate, which performs heat treatment to reduce the thermal shrinkage of the glass substrate in a state where the support member supports the glass substrate from below, the heat treatment method of the glass substrate is characterized by The friction sheet is disposed at least between the peripheral edge of the supported region on the lower surface of the glass substrate and the upper surface of the supporting member facing the peripheral edge, 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 5 times or more the surface roughness Ra of the lower surface of the glass substrate. The heat treatment method for a glass substrate as described in item 1 of the patent application range, wherein the thickness of the low-friction sheet is 0.01 mm to 2 mm. The heat treatment method for a glass substrate as described in the first or second patent application, wherein the static friction coefficient of the low-friction sheet is 0.2 or less. The heat treatment method for a glass substrate according to the first or second patent application, wherein the low-friction sheet contains an inorganic substance having a layered crystal structure. The heat treatment method for a glass substrate according to the first or second patent application, wherein the low-friction sheet is detachably laid on the upper surface of the support member. The heat treatment method for a glass substrate according to item 1 or item 2 of the patent application scope, wherein the low-friction sheet is provided on all the lower surfaces of the glass substrate as the supported region Between the entire lower surface of the glass substrate and the upper surface of the support member facing the entire lower surface. The heat treatment method for a glass substrate according to claim 1 or claim 2, wherein the glass is made such that the area of the lower surface of the glass substrate except the peripheral portion becomes the supported area The peripheral portion of the lower surface of the substrate protrudes from the low-friction sheet.

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