JP6598071B2 - Method for heat treatment of glass substrate - Google Patents

Description

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

  As is well known, in recent years, mobile terminals such as smartphones and tablet terminals have rapidly spread, and competition for technological development for making mobile terminals thinner and lighter and further improving performance has been intensifying. Yes. For this reason, a thin glass substrate is often used as a substrate for a flat panel display (hereinafter referred to as FPD) such as a liquid crystal display or an organic EL display mounted on a mobile terminal.

  In the FPD manufacturing process, a film forming process for forming a thin-film electric circuit (circuit pattern) on the surface of a glass substrate is usually performed. In the film forming process, the glass substrate to be processed is exposed to a high temperature. Therefore, when the thermal contraction 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 desired electrical characteristics cannot be secured increases. Therefore, it is essential for the glass substrate for FPD to have a low thermal shrinkage rate and excellent thermal dimensional stability.

  Thus, for example, Patent Document 1 discloses that the glass substrate is subjected to heat treatment for the purpose of improving the thermal dimensional stability of the glass substrate. In patent document 1, heat processing is performed in the state which mounted the glass plate of heat processing object directly on the upper surface of a supporting member (heat-resistant glass ceramic plate).

JP-A-5-330835

  However, when a thin glass substrate is subjected to heat treatment by the method disclosed in Patent Document 1, a large strain may occur in the planar direction of the glass substrate after the heat treatment. When such distortion occurs, for example, the following problems may occur.

  That is, in the FPD manufacturing process, in order to increase the production efficiency and reduce the cost, a circuit pattern or the like is formed on a single large glass substrate at a time, and then a large number of glass substrates of a product size are formed from the large glass substrate. In general, so-called multi-chamfering is performed. In this case, if there is a large strain in the plane direction of the glass substrate, the glass substrate is deformed with the release of the strain after cutting. As a result, when manufacturing a panel by bonding glass substrates together, a deviation occurs between circuit patterns formed in advance, which causes a product defect.

  An object of the present invention is to suppress the occurrence of distortion in a glass substrate by heat treatment for reducing the thermal shrinkage rate of the glass substrate.

  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 that time. As a result, it was found that interference fringes were observed as a feature of the glass substrate with increased strain after the heat treatment. This interference fringe is generated due to a gap generated between the supported region on the lower surface of the glass substrate and the upper surface of the supporting member. The main cause of this gap is the peripheral edge of the supported region on the lower surface of the glass substrate (in the case of supporting the entire lower surface of the glass substrate, particularly the intersection where the lower surface of the glass substrate and the end surface intersect). This is considered to be because the glass substrate is prevented from following the upper surface of the support member. Therefore, the inventors of the present application propose the present invention based on such knowledge.

  That is, the present invention devised to solve the above problems is a glass substrate heat treatment method for performing a heat treatment for reducing the thermal shrinkage of the glass substrate in a state where the glass substrate is supported from below by a support member. In addition, a low friction sheet is disposed between at least 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 same, and the static friction coefficient of the upper surface of the low friction sheet is 0.5 or less. In addition, the surface roughness Ra of the upper surface of the low friction sheet is set to be not less than five times the surface roughness Ra of the lower surface of the glass substrate. Here, “surface roughness Ra” is a value measured based on the method defined in JIS B0601: 2001, and “static friction coefficient” is a value measured based on the method defined in JIS K7125: 1999. is there. Further, the “supported region” is a region of the lower surface of the glass substrate that is supported by the low friction sheet, and may be the entire lower surface of the glass substrate or may be smaller than the lower surface of the glass substrate.

  According to such a configuration, at least the peripheral portion of the supported region on 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 edge of the supported region on the lower surface of the glass substrate slides on the low friction sheet, and the glass substrate supports its supporting surface (the upper surface of the low friction sheet, Or it is guided to follow the low friction sheet and the upper surface of the support member. As a result, it is difficult to form a gap between the supported region on the lower surface of the glass substrate and the supporting surface, and it is possible to suppress the occurrence of distortion associated with the heat treatment.

  Here, if the lower peripheral edge of the glass substrate and the upper surface of the low friction sheet are too closely adhered, there is a possibility that the glass substrate cannot be peeled off after the heat treatment. Therefore, in the present invention, 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, thereby relaxing the contact state between them. Thereby, even after heat treatment, the glass substrate can be peeled from the low friction sheet.

  Said structure WHEREIN: It is preferable that the thickness of a low friction sheet | seat is 0.01 mm-2 mm. In this way, the upper surface of the low friction sheet is less affected by the state of the upper surface of the support member. In addition, there is no problem that the heat capacity of the low friction sheet increases and a large 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. By doing so, the peripheral edge of the lower surface of the glass substrate slides more smoothly on the upper surface of the low friction sheet, so that the glass substrate can easily follow the support surface.

  Said structure WHEREIN: It is preferable to comprise a low friction sheet | seat from the inorganic substance which has a layered crystal structure. If it does in this way, while it becomes easy to reduce a friction coefficient, heat resistance can be improved.

  Said structure WHEREIN: It is preferable that the low friction sheet | seat is laid in the upper surface of a supporting member so that peeling is possible. In this way, even if the low friction sheet is damaged, the low friction sheet can be easily replaced.

  In the above configuration, the low friction sheet may be provided between the entire lower surface of the glass substrate and the upper surface of the support member facing the lower surface so that the entire lower surface of the glass substrate becomes a supported region. In this way, since the entire support surface that supports the glass substrate is formed of the low friction sheet, the glass substrate follows the support surface more smoothly.

  In the above configuration, the peripheral portion of the lower surface of the glass substrate may protrude from the low friction sheet so that the region excluding the peripheral portion of the lower surface of the glass substrate becomes the supported region. In this way, the glass substrate can be handled using the protruding portion of the glass substrate, so that the glass substrate can be placed on the low friction sheet or removed from the low friction sheet. Becomes easier.

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

It is a figure which shows the support aspect of the glass substrate at the time of execution of the heat processing method which concerns on embodiment of this invention, Comprising: (a) is the top view, (b) is AA arrow sectional drawing shown to (a). It is. (A)-(b) is an enlarged view which shows the mode of the change of the mounting aspect of the peripheral part of the glass substrate with respect to the low friction sheet | seat of FIG. It is sectional drawing of the heat processing apparatus used when implementing the heat processing method which concerns on embodiment of this invention. (A)-(c) is a figure for demonstrating the measurement procedure of the thermal contraction rate of a glass substrate.

  Hereinafter, the heat processing method of the glass substrate which concerns on one Embodiment is demonstrated with reference to attached drawing.

  As shown in FIGS. 1A and 1B, the glass substrate 1 to be heat-treated is placed on the upper surface 3 a of the low friction sheet 3 disposed on the upper surface 2 a of the support member (setter) 2. And the heat processing process for reducing the thermal contraction rate of a glass substrate is performed by introduce | transducing and heating the glass substrate 1 to a heat processing apparatus (heat processing furnace) with such a support aspect. A cleaning process for cleaning the glass substrate 1 may be provided before the heat treatment process. By providing such a cleaning process, it is possible to prevent the foreign matter adhering to the surface of the glass substrate 1 from being seized on the surface of the glass substrate 1 due to the heat treatment.

  Hereinafter, each of 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 thereof is preferably 500 mm square or more, more preferably 700 mm square or more, still more 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 distorted. Therefore, the glass substrate 1 having a larger size can easily enjoy the effect of the present embodiment. The glass substrate 1 is not limited to a rectangular shape, and may be a triangle, a pentagon or more polygon, a circle (including an ellipse), 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. Usually, the smaller the thickness, the smaller the own weight, so that it is difficult to follow the upper surface of the support member 2. Therefore, the thinner the glass substrate 1 is, the more effective the low friction sheet 3 is. Further, as the thickness of the glass substrate 1 is reduced, the contribution to the reduction in thickness and weight of a product (for example, FPD) having the glass substrate 1 as a component can be increased. However, when the thickness of the glass substrate 1 is too small, the 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 thermal shrinkage rate. On the other hand, when the strain point becomes 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 less, more preferably 720 ° C. or less, and most preferably 715 ° C. or less. is there. The strain point here is a value measured based on a method defined in ASTM C336.

  The glass substrate 1 having the above-described dimensions, thickness, and strain point can be formed of, for example, silicate glass, silica glass, borosilicate glass, soda glass, non-alkali glass, or the like. In the present embodiment, among the various glasses described above, a glass substrate made of alkali-free glass that hardly causes aging deterioration is used. Here, the alkali-free glass means glass that does not substantially contain an alkali component (alkali metal oxide), and specifically means glass having an alkali component content of 3000 ppm or less. As the alkali-free glass, those having an alkali component content of preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 300 ppm or less are used.

  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, further preferably 0.5 nm or less, and most preferably 0.2 nm or less. is there. In addition, surface roughness Ra of the upper surface 1a of the glass substrate 1 may be the same as that of the lower surface 1b, and may differ.

  The glass substrate 1 is manufactured by, for example, an overflow downdraw method, a slot downdraw method, a rollout method, a float method, an updraw method, or a redraw method. In this embodiment, a glass substrate manufactured by the overflow downdraw 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 1 b of the glass substrate 1 is a supported region of the glass substrate 1. Furthermore, the low friction sheet 3 has a protruding portion 3 c that protrudes outward from the glass substrate 1. In addition, the low friction sheet 3 may be provided only in the area | region corresponding to the peripheral part 1c (hatching part in a figure) in the lower surface 1b of the glass substrate 1. FIG. Further, 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 may be flush. 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 region of the glass substrate 1 is smaller than the lower surface 1b of the glass substrate 1.

  In order to suppress the occurrence of distortion of the glass substrate 1 due to the heat treatment, it is necessary to start the heat treatment with the glass substrate 1 sufficiently following 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. As the static friction coefficient is smaller, the planar distortion of the glass substrate 1 caused by the heat treatment can be suppressed. 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 or different from the upper surface 3a.

  Here, when 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 are excessively adhered to each other, the glass substrate 1 is broken during the heat treatment, or the glass substrate 1 is low after the heat treatment. In some cases, the friction sheet 3 may stick to the friction sheet 3 and cannot be separated. Further, when the glass substrate 1 is placed on the upper surface 3 a of the low friction sheet 3, the contact portions may be attached in sequence, and the glass substrate 1 may be difficult to follow the upper surface 3 a of the low friction sheet 3. In particular, since glass substrates used in display applications require high surface smoothness, glass substrates with extremely small surface roughness Ra (for example, Ra of about 0.2 nm) are generally used. Such a problem is likely to occur. Therefore, in order to alleviate the adhesion between the upper surface 3a of the low friction sheet 3 and 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 equal to the surface roughness Ra of the lower surface 1b of the glass substrate 1. The size is set to 5 times or more. Preferably it is 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 micrometer or more, More preferably, it is 0.1 micrometer or more, More preferably, it is 0.2 micrometer or more, Most preferably, it is 0.5 micrometer or more. By setting within the above range, sticking between the glass substrate 1 and the low friction sheet 3 can be suppressed. On the other hand, if the surface roughness Ra is too large, the coefficient of static friction increases, so the surface roughness Ra of the upper surface 3a of the low friction sheet 3 is preferably 5 μm or less. 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 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 the sum of Ra1 and Ra2. . 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 to the said range, the glass substrate 1 and the supporting member 2 can be isolate | separated easily, and it will become easy to enjoy the function of the low friction sheet | seat 3. FIG. 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. In addition, the production cost of the low friction sheet 3 may increase. Therefore, the thickness of the low friction sheet 3 is preferably set to Ra1 + Ra2 + 2000 μm or less. Specifically, the thickness of the low friction sheet 3 is preferably 0.01 mm to 2 mm.

  It is preferable that the low friction sheet 3 be removable from the support member 2. In this way, when the low friction sheet 3 is damaged, it can be easily replaced. As a result, it becomes easy to suppress the quality deterioration of the glass substrate 1 accompanying the damage of the low friction sheet 3. Specifically, for example, the low friction sheet 3 is directly laid on the upper surface 2 a of the support member 2 without using an adhesive layer or the like, and the surface roughness Ra of the lower surface 3 b of the low friction sheet 3 is set to be the upper surface of the support member 2. It is set larger than the surface roughness Ra of 2a.

  The low friction sheet 3 is preferably composed of an inorganic material 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, it is preferable to use graphite because it is inexpensive and easy to manufacture in a sheet form. The purity of the inorganic material constituting the low friction sheet 3 is preferably 99.0% or more by mass%. More preferably, it is 99.5% or more, More preferably, it is 99.8% or more, Most preferably, it is 99.9% or more. As the purity is higher, for example, scratches on the glass substrate due to impurities such as metals can be suppressed. In the present embodiment, among the various inorganic materials described above, graphite having a purity of 99.9% that is relatively inexpensive and easy to increase in size 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 of the strain and the heat shrinkage rate. In this way, the glass substrate 1 can be easily placed and taken out. In consideration of workability, the ratio of the area of the low friction sheet 3 to the entire area of the lower surface 1b of the glass substrate 1 is preferably 0.5 or more and 1.0 or less. More preferably, it is 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.

  As described above, if the static friction coefficient and the surface roughness Ra of the low friction sheet 3 are set, the following effects can be enjoyed. That is, as shown in FIG. 2 (a), the peripheral edge 1c of the lower surface 1b of the glass substrate 1 (particularly, the intersection 1x of the lower surface 1b and the end surface 1d) is caught by the upper surface 3a of the low friction sheet 3, and the glass substrate 1 It is difficult to maintain the state in which the gap C is formed between the low friction sheet 3 and the low friction sheet 3. Even if the state of FIG. 2 (a) occurs temporarily, the peripheral edge portion 1c of the lower surface 1b of the glass substrate 1 slides on the upper surface 3a of the low friction sheet 3 toward the outer side (X direction). The lower surface 1b of the glass substrate 1 approaches the low friction sheet 3 while descending (Y direction). Further, even when the glass substrate 1 is further lowered from the state of FIG. 2A, the peripheral portion 1 c of the lower surface 1 b of the glass substrate 1 starts to come into surface contact with the upper surface 3 a of the low friction sheet 3. The peripheral edge 1c of the lower surface 1b of the glass substrate 1 slides outward (X direction) on the upper surface 3a of the low friction sheet 3, and the lower surface 1b of the glass substrate 1 descends (Y direction) along with this. To approach. Thereby, as shown in FIG. 2 (b), the glass substrate 1 correctly follows the upper surface 3 a of the low friction sheet 3. As a result, it becomes difficult to form the gap 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 occurrence of distortion associated with the heat treatment. Further, as shown in FIG. 2 (b), even when the heat treatment is performed in a state where the glass substrate 1 follows the low friction sheet 3, both are not excessively adhered to each other. 1 can be easily separated.

[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 heat-resistant material such as glass, ceramics, or metal can be used. Among these, as the support member 2, it is preferable to use crystallized glass having a low thermal expansion coefficient and high thermal shock resistance.

  The thickness of the support member 2 is preferably 0.5 to 4.0 mm. More preferably, it is 0.5-3.5 mm, More preferably, it is 0.5-3.0 mm, More preferably, it is 0.5-2.5 mm, Most preferably, it is 1.0-2.5 mm. By setting it in the above range, the support member 2 is less likely to be thermally deformed, and the heat capacity of the support member 2 is increased, so that a large energy loss does not occur during heat treatment. Therefore, the heat treatment of the glass substrate 1 can be performed accurately and efficiently.

[Heat treatment equipment]

  It is preferable to use a batch-type furnace or a single-wafer type furnace that does not include a transfer device as a heat treatment apparatus that performs heat treatment. Such a furnace can suppress the sliding of the glass substrate 1 accompanying conveyance, since the glass substrate 1 receives heat processing in a stationary state. As a result, it becomes easy to maintain a uniform temperature distribution in the surface of the glass substrate 1, and it is possible to suppress variations in the thermal shrinkage rate, and distortion and shape deterioration due to the temperature distribution. Moreover, the possibility of breakage due to collision with the in-furnace member during the heat treatment can be reduced. In this 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, a lifting platform 13 that moves up and down relative to the glass chamber 11 with the glass shelf 12 placed thereon, and a furnace wall 14 that houses the glass chamber 11. And a heater 15 for heating the glass chamber 11 from the outside. This heat treatment apparatus 10 is disposed in a clean room. In short, the heat treatment process is performed in a clean room.

  The glass chamber 11 has a covered cylindrical shape with an open lower end, and has a heat treatment space S therein. The glass chamber 11 is formed into a covered cylinder by integrally molding quartz glass, and the heat treatment space S is defined by a continuous surface without a joint.

  The glass shelf 12 has a plurality of storage portions 16 provided in a multi-stage shape in the vertical direction, and each storage portion 16 has at least a pair of column portions 12a erected on a lifting platform and a column portion 12a. And a shelf board 12b that is detachably attached. Both the column part 12a and the shelf board 12b are formed of quartz glass. In the present embodiment, a grid-like frame is adopted as the shelf plate 12b, and a plurality of pin-like protrusions are provided on the upper surface of the shelf plate 12b. Then, the horizontal glass substrate 1 is supported from below by a support member 2 having a low friction sheet 3 (hereinafter also referred to as “assembly”), and is supported from below by pin-shaped protrusions.

  The elevator 13 has a quartz glass mounting portion 13a on which the glass shelf 12 is mounted. When the mounting 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 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 on the glass shelf 12 placed on the placing portion 13a.

  The furnace wall 14 has a covered cylindrical shape with the lower end opened, and the whole is made of a refractory material. A heater 15 is attached to the side inner wall surface of the furnace wall 14. As the heater 15, for example, a metal heating element typified by a nichrome heating element is used.

  The heat treatment apparatus 10 may be separately provided with a cooling means (for example, a blower) for cooling the glass chamber 11 from the outside. By providing such a cooling means, the atmosphere of the heat treatment space heated by the heater 15 can be efficiently cooled.

  Next, a heat treatment process executed by the heat treatment apparatus having the above configuration will be described. In the heat treatment process, a temperature raising step, a heat retaining step, and a temperature lowering step are sequentially performed.

  Prior to carrying out the temperature raising step, the mounting portion 13a of the lifting / lowering base 13 is positioned at the lowered position, and the assembly is loaded on each receiving portion 16 of the glass shelf 12, and then the lifting / lowering base 13 is moved up and down to move the glass shelf 12. Is disposed in the heat treatment space S in the glass chamber 11. In addition, loading of the assembly with respect to each accommodating part 16 (and unloading of the assembly from each accommodating part 16 after heat processing) is performed by the robot fork which can support an assembly from the downward side, for example.

  The temperature raising step is a step of raising the temperature of the glass substrate 1 to a predetermined temperature. Here, the glass substrate 1 is raised by 10 ° C./min or more, preferably 15 ° C./min or more, more preferably 20 ° C./min or more. The output of the heater is adjusted so that the temperature is increased at a temperature rate. However, if the rate of temperature increase of the glass substrate 1 is too high, the possibility of the glass substrate 1 being damaged or the like increases, so the rate of temperature increase is 100 ° C./min or less, more preferably 80 ° C./min or less.

  In the temperature raising 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 temperature of the glass substrate 1 is preferably T ° C or less, more preferably (T-10 ° C) or less, and even more preferably (T-20 ° C). ), More preferably (T-30 ° C.) or less, particularly preferably (T-40 ° C.) or less, most preferably (T-50 ° C.) or less until the glass chamber 11 is heated. Thereby, the thermal contraction rate of the glass substrate 1 can be reduced, preventing the shape change of the glass substrate 1 accompanying heat processing as much as possible. However, if the glass substrate 1 is not sufficiently heated, the thermal shrinkage rate of the glass substrate 1 cannot be reduced appropriately. Therefore, the glass chamber 11 is heated until the temperature of the glass substrate 1 becomes (T-200 ° C.) or higher.

  In the heat retaining step, the glass substrate 1 heated to a predetermined temperature is held at the predetermined temperature for a predetermined time (specifically, 0.5 to 60 minutes). Thereby, the variation in the thermal contraction rate between the glass substrates 1 can be reduced while appropriately reducing the thermal contraction rate of the individual glass substrates 1.

  In the temperature lowering step, the temperature of the glass substrate 1 is gradually decreased. The temperature lowering rate is preferably 1 ° C./min or more, more preferably 5 ° C./min or more, and even more preferably 10 ° C./min or more. Thereby, productivity of the glass substrate 1 can be improved, shortening the processing time of a temperature-falling step. However, if the temperature lowering rate is too fast, the thermal shrinkage rate of the glass substrate 1 cannot be sufficiently reduced, and the possibility that the warp of the glass substrate 1 will increase increases. Therefore, the temperature lowering rate is preferably 100 ° C./min or less, and more preferably 80 ° C./min or less.

  The strain remaining in the glass substrate 1 is measured by the method described below as a stress caused by the strain. The strain in the glass substrate 1 can be estimated by measuring optical birefringence, that is, measuring the optical path difference of orthogonally polarized light waves. When the optical path difference is R (nm), the stress (exactly the deviation stress) F (MPa) generated by the strain is expressed as F = R / (C × L). Here, L is the distance (cm) through which the polarized wave has passed, and C (nm / cm) is a proportionality constant determined by glass and is called a photoelastic constant.

  In the glass substrate 1 after the heat treatment, the maximum stress generated by the remaining strain is preferably 1 MPa or less. More preferably, it is 0.8 MPa or less, More preferably, it is 0.6 MPa or less, Most preferably, it is 0.5 MPa or less. If it is the said range, even if it cut | divides and cut | disconnects, the deformation | transformation of the glass substrate 1 can be suppressed.

  As mentioned above, although the heat processing method of the glass substrate which concerns on embodiment of this invention was demonstrated, embodiment of this invention is not necessarily limited to this, A various change is performed in the range which does not deviate from the summary of this invention. It is possible.

  When a low friction sheet is disposed on the upper surface of the support member and heat treatment is performed with a glass substrate placed on the upper surface of the low friction sheet (hereinafter, also referred to as “example”), Confirmation test for confirming the strain in the planar direction of the glass substrate before and after the heat treatment in each case where the heat treatment is performed with the glass substrate directly placed (hereinafter also referred to as “Comparative Example 1 and Comparative Example 2”). Went.

  In carrying out the confirmation test, four assemblies consisting of a support member / low friction sheet / glass substrate were prepared in the examples, and four assemblies consisting of support members / glass substrates were prepared in Comparative Examples 1 and 2. Each of these assemblies was subjected to heat treatment.

The glass substrate to be heat-treated is common to the examples, comparative example 1 and comparative example 2. As the glass substrate, a rectangular glass substrate having a thickness of 0.5 mm and a size of 730 mm × 920 mm (specifically, an alkali-free glass substrate OA-11 manufactured by Nippon Electric Glass Co., Ltd.) was used. The glass substrate has a linear thermal expansion coefficient of 37 × 10 ⁻⁷ / ° C. (30 to 380 ° C.), a strain point of 685 ° C., and a photoelastic constant of 30 nm / cm. The surface roughness Ra of the lower surface of the glass substrate is 0.2 nm. Note that the surface roughness Ra of the upper surface of the glass substrate does not directly affect the result of the confirmation test, but is approximately the same as the lower surface of the glass substrate.

The support member is the same in Examples, Comparative Example 1 and Comparative Example 2, except for the surface roughness Ra and the static friction coefficient. As the support member, a rectangular crystallized glass plate (specifically, Neoceram N-0 manufactured by Nippon Electric Glass Co., Ltd.) having a thickness of 4 mm and a size of 830 mm × 1020 mm was used. The linear thermal expansion coefficient of this support member is −1 × 10 ⁻⁷ / ° C. (30 to 750 ° C.). The surface roughness Ra of the upper surface of the support member is 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 is 1.3 in Comparative Example 1 and 0.8 in Comparative Example 2. In Comparative Examples 1 and 2, a crystallized glass plate whose surface was adjusted by polishing was used. The surface roughness Ra and the coefficient of static friction of the upper surface of the support member in the examples were not measured because they did not directly affect the results of the confirmation test, but those similar to those in Comparative Example 1 were used.

  As the low friction sheet, rectangular graphite (purity: 99.9% or more) having a thickness of 200 μm and a size of 730 mm × 920 mm was used. 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. The surface roughness Ra and the static friction coefficient of the lower surface of the low friction sheet do not directly affect the result of the confirmation test, but are approximately the same as the upper surface of the low friction sheet.

  The heat treatment conditions are common to the examples, comparative example 1 and comparative example 2. The heat treatment conditions were as follows: a glass substrate at room temperature was heated to 650 ° C. at a temperature increase rate of 10 ° C./min, held at 650 ° C. for 3 minutes, and then the glass substrate was cooled at a temperature decrease rate of 60 ° C./min. The temperature is lowered to room temperature. In addition, with all the glass substrates used for the test, the maximum stress value generated by the strain before the heat treatment was 0.3 to 0.4 MPa.

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

  As is clear from Table 1, in the example, 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 5 times or more of the surface roughness Ra of the glass substrate. 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 is more than 0.5, and the surface roughness Ra of the upper surface of the support member is the surface roughness Ra of the glass substrate. 5 times or more. In Comparative Example 2, the static friction coefficient of the upper surface of the support member constituting the support surface of the glass substrate is more than 0.5, and the surface roughness Ra of the upper surface of the support member is the surface roughness Ra of the glass substrate. Less than 5 times.

  As a result, in the examples, the value of the maximum stress generated by strain in the glass substrate after the heat treatment in all the samples was 0.3 to 0.4 MPa, and no change due to the heat treatment was observed. 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. Furthermore, in Comparative Example 2, since 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, the glass substrate and the support member are in close contact, and the glass substrate and the support member are subjected to heat treatment. When the difference in thermal expansion occurred, the glass substrate was damaged by the difference in thermal expansion (damaged during heat treatment). Therefore, it can be said that the heat treatment method according to the present invention is useful in suppressing the generation of strain accompanying heat treatment.

In addition to the above confirmation test, how much the glass substrate thermally contracted with the heat treatment, that is, the thermal contraction rate of the glass substrate was evaluated. The thermal shrinkage rate of the glass substrate was measured and calculated according to the following procedures (1) to (5).
(1) As shown in FIG. 4A, a 160 mm × 30 mm strip sample G is prepared as a glass substrate sample.
(2) Using water-resistant abrasive paper having a particle size of 1000, in each of both ends in the long side direction of the strip-shaped sample G, it extends in the short side direction to a position shifted by about 20 to 40 mm from the edge to the central side in the long side direction. Marking M is formed.
(3) The strip-shaped sample on which the marking M is formed is divided into two along the long side direction, and sample pieces Ga and Gb are produced.
(4) Only one of the sample pieces Ga and Gb (here, the sample piece Gb) is heat-treated with a heat treatment apparatus. The heat treatment was carried out by the procedure of increasing the temperature from normal temperature to 500 ° C. at a temperature increase rate of 5 ° C./minute→holding at 500 ° C. for 1 hour → decreasing the temperature to room temperature at a temperature decrease rate of 5 ° C./minute.
(5) After heat-treating the sample piece Gb in the above-described manner, the non-heat-treated sample piece Ga and the heat-treated sample piece Gb are arranged in parallel, and the marking M on both the sample pieces Ga and Gb The positional deviation amounts ΔL ₁ and ΔL ₂ are read with a laser microscope, and the thermal contraction rate [unit: ppm] is calculated based on the following mathematical formula. Incidentally, L ₀ in the following equations is the distance between the front heat treatment marking M.
Thermal contraction rate = [{ΔL ₁ (μm) + ΔL ₂ (μm)} × 10 ³ ] / L ₀ (mm)

  The thermal contraction 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 is understood that the present invention is useful in suppressing the generation of strain accompanying heat treatment while reducing the thermal shrinkage rate of the glass substrate.

DESCRIPTION OF SYMBOLS 1 Glass substrate 1a Upper surface 1b Lower surface 1c Peripheral part 2 Support member 2a Upper surface 3 Low friction sheet 3a Upper surface 3b Lower surface 3c Projection part 10 Heat processing apparatus

Claims (7)

In a state where the glass substrate is supported from below by a support member, a heat treatment method of the glass substrate is performed to reduce the heat shrinkage rate of the glass substrate,
While disposing a low friction sheet at least between the peripheral edge of the supported region on the lower surface of the glass substrate and the upper surface of the support member facing the same,
The static friction coefficient of the upper surface of the low friction sheet is 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. A method for heat-treating a glass substrate.   The glass substrate heat treatment method according to claim 1, wherein the low friction sheet has a thickness of 0.01 mm to 2 mm.   The glass substrate heat treatment method according to claim 1, wherein the low friction sheet has a static friction coefficient of 0.2 or less.   The said low-friction sheet | seat consists of an inorganic substance which has a layered crystal structure, The heat processing method of the glass substrate in any one of Claims 1-3 characterized by the above-mentioned.   The heat treatment method for a glass substrate according to any one of claims 1 to 4, wherein the low friction sheet is detachably laid on an upper surface of the support member.   The low friction sheet is provided between the entire lower surface of the glass substrate and the upper surface of the support member facing the lower surface so that the entire lower surface of the glass substrate becomes the supported region. The heat processing method of the glass substrate of any one of Claims 1-5 to do.   6. The peripheral portion of the lower surface of the glass substrate protrudes from the low friction sheet so that the region excluding the peripheral portion of the lower surface of the glass substrate becomes the supported region. The heat processing method of the glass substrate of any one of these.

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