TWI477459B - Method for manufacturing glass substrate for flat panel display - Google Patents

Description

Method for manufacturing glass substrate for flat panel display

The present invention relates to a glass substrate for a flat panel display. More specifically, the present invention relates to a method for producing a glass substrate for a flat panel display of a low temperature polycrystalline germanium film transistor (hereinafter referred to as a LTPS. TFT (Low-Temperature-Polycrystalline-Silicon Thin-Film-Transistor)). Moreover, the present invention relates to a method for producing a glass substrate for a flat panel display of a transparent oxide semiconductor thin film transistor (hereinafter referred to as a TOS. TFT (Transparent Oxide-Semiconductor Thin-Film-Transistor)). More specifically, the present invention relates to a method for producing a glass substrate used for a flat panel display produced by forming LTPS or TOS on a substrate surface. More specifically, the present invention relates to a method for producing a glass substrate for a flat panel display in which the flat panel display is a liquid crystal display, and a method for manufacturing a glass substrate for a flat panel display in which the flat panel display is an organic EL (Electroluminescence) display .

In order to reduce the power consumption, etc., it is preferable to use a LTPS for the manufacture of a thin film transistor (TFT) in a small device such as a mobile device, but it is required to be 400 to 600 ° C in the manufacture of the LTPS/TFT. The heat treatment is performed at a relatively high temperature. On the other hand, in recent years, displays for small machines have been increasingly required to have high definition. Therefore, it is preferable to suppress the pitch shift of the pixels as much as possible, thereby suppressing the heat shrinkage of the glass substrate during the manufacture of the display which causes variations in the pitch between pixels. Further, in the glass substrate for TOS/TFT, suppression of heat shrinkage is also a problem.

It is reported that the heat shrinkage rate of the glass substrate can be lowered by lowering the cooling rate in the vicinity of the slow cooling point in the production of the glass substrate (Japanese Patent Laid-Open Publication No. 2009-196879: Patent Document 1, the entire disclosure of which is specifically incorporated herein by reference. this). Further, it is reported that the heat shrinkage rate of the glass substrate can be lowered by setting the cooling rate in the vicinity of the slow cooling point to a value obtained as a function of the slow cooling point of the glass in the production of the glass substrate (Patent Document 2) Japanese Patent Laid-Open No. 2011-20864, the entire disclosure of which is hereby incorporated by reference.

However, as described in Patent Document 1, when the cooling rate in the vicinity of the slow cooling point is excessively lowered in the manufacturing process of the glass substrate, the manufacturing equipment is enlarged and the productivity is also deteriorated. In the method described in Patent Document 2, the cooling rate is controlled in accordance with the slow cooling point of the glass. However, in this method, the productivity in the case of sufficiently reducing the heat shrinkage rate is not high. Further, the glass composition used itself contains relatively large amounts of SrO and BaO, and the obtained glass substrate has a high density and is not suitable for lightweight glass substrates.

In view of the above, it is an object of the present invention to provide a glass substrate for an LTPS/TFT having a heat shrinkage ratio capable of suppressing the variation in the distance between pixels without using the glass which is suitable for weight reduction. Further, an object of the present invention is to provide a glass substrate having a composition suitable for weight reduction, and a method of producing a glass substrate which is also suitable for heat shrinkage for TOS/TFT can be produced without impairing productivity.

The inventors of the present invention have found that the glass substrate for LTPS/TFT having a specific heat shrinkage ratio can be produced without impairing productivity by studying the glass composition, and completed the present invention. Further, it has been found that the above-mentioned glass substrate has a specific heat shrinkage ratio which can be used as a TOS/TFT, and the present invention has been completed.

The present invention is as follows.

[1] (The first aspect of the present invention)

A method for producing a glass substrate for a flat panel display, comprising: (1) a melting step of blending in a manner that a combined amount of SrO and BaO in the glass substrate to be produced is less than 8 mass% and has a strain point of 675 ° C or higher a raw material and melted; (2) a forming step of melting the glass-formed glass ribbon by melt-down method; and (3) a cooling step of cooling the formed glass ribbon under the following condition (A); The average cooling rate from the slow cooling point to the temperature of (strain point -50 ° C): 0.5 ~ less than 5.5 ° C / sec.

[2] The method for producing a glass substrate for a flat panel display according to [1], wherein in the melting step (1), the glass substrate produced has a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) /B ₂ O ₃ blends the raw materials.

[3] The production method according to [1] or [2], wherein the glass substrate produced through the cooling step (3) is heated at a temperature of 10 ° C/min from normal temperature and maintained at 550 ° C for 1 hour, and thereafter at 10 ° C. /min is cooled to normal temperature, again heated at 10 ° C / min and held at 550 ° C for 1 hour, and after 10 ° C / min to room temperature, the heat shrinkage rate represented by the following formula is 75 ppm or less; heat shrinkage rate (ppm) ) = {the amount of shrinkage of the glass before and after the heat treatment / the length of the glass before the heat treatment} × 10 ⁶ .

[4] (Second aspect of the invention)

A method for producing a glass substrate for a flat panel display, comprising: (1) a melting step of producing a glass substrate having a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ a raw material which is substantially free of BaO and has a strain point of 680 ° C or higher and is melted; (2) a forming step which is a molten glass forming glass ribbon which is self-melted by an overflow down-draw method; and (3) a cooling step It is a glass ribbon which is cooled by the following condition (A); (A) an average cooling rate from a temperature not reaching the slow cooling point to a temperature of (strain point - 50 ° C): 0.5 to less than 5.5 ° C / sec.

According to the present invention, it is possible to provide a method for producing a glass substrate for a LTPS/TFT flat panel display and a TOS/TFT flat panel display having a specific heat shrinkage ratio, for example, less than 75 ppm, without impairing productivity.

The present invention relates to a method for producing a glass substrate for a flat panel display such as LTPS/TFT and TOS/TFT. In addition, the glass substrate produced by the production method of the present invention can be used as a glass substrate for a liquid crystal display or an organic EL display. Therefore, the present invention includes a method for producing a glass substrate for a liquid crystal display and a method for producing a glass substrate for an organic EL display.

The method for producing a glass substrate for a flat panel display according to the present invention includes the following melting step (1), forming step (2), and cooling step (3). Hereinafter, a method of manufacturing a glass substrate for an LTPS/TFT flat panel display will be described as an example, but a method of manufacturing a glass substrate for a TOS/TFT flat panel display can also be carried out in the same manner. Further, the method for producing a glass substrate for a liquid crystal display and a glass substrate for an organic EL display can be similarly carried out.

(1) Melting step

In the melting step (1), the raw material is blended, heated, melted, and clarified in such a manner that the produced glass substrate satisfies specific conditions to prepare a molten glass which can be formed. In the present invention, the object is to produce a glass substrate having a specific heat shrinkage ratio, and the object thereof is to perform cooling of the formed glass ribbon in the following cooling step (3) under the condition (A). This glass substrate is produced. Therefore, the raw materials are blended and heated and melted so that the produced glass substrate satisfies specific conditions.

In the first aspect of the invention, the raw material is blended so that the combined amount of SrO and BaO in the glass substrate to be produced is less than 8 mass% and has a strain point of 675 ° C or higher.

SrO and BaO reduce the composition of the devitrification temperature of the glass. The glass substrate of the present invention is not an essential component, but if it is contained, the devitrification resistance and the meltability are improved. However, if the content is too large, the density and the coefficient of thermal expansion increase. When the coefficient of thermal expansion is increased, it is not possible to produce a glass substrate for a LTPS/TFT flat panel display having a specific heat shrinkage ratio of, for example, less than 75 ppm without impairing productivity. Moreover, if the density is increased, the weight of the glass substrate cannot be reduced, which is not preferable for the LTPS/TFT. Therefore, manufactured The amount of SrO and BaO in the glass substrate, that is, the SrO+BaO system was set to be less than 8% by mass. SrO+BaO is preferably 0 to 7% by mass, more preferably 0 to 5% by mass, still more preferably 0 to 3% by mass, still more preferably 0 to 1% by mass, especially for decreasing In the case of the density of the glass substrate, it is preferred that substantially no SrO and BaO are contained.

The strain point of the produced glass substrate was 675 ° C or more. If the strain point of the glass substrate is low, the heat shrinkage becomes large in the heat treatment step (when the display is manufactured). The strain point of the glass substrate of the present invention is preferably 680 ° C or higher, more preferably 686 ° C or higher, further preferably 690 ° C or higher, further preferably 695 ° C or higher, and still more preferably 700 ° C or higher. The strain point of the glass substrate can be appropriately selected depending on the composition of the glass substrate, and the composition of the glass which can set the strain point to 675 ° C or higher is described below. In the present invention, a glass substrate having a small heat shrinkage rate can be obtained by setting the strain point of the glass substrate to be 675 ° C or higher. However, the heat shrinkage of the glass substrate is not determined solely by the strain point, but also varies depending on other characteristics or manufacturing steps, particularly the cooling conditions in the cooling step.

In the second aspect of the present invention, the glass substrate produced has a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ , and substantially does not contain BaO and has 680 ° C or higher. The material is blended in the manner of the strain point.

In any of the first aspect and the second aspect of the present invention, the glass substrate produced includes glass containing SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ . In the first aspect of the invention, it is preferred that the glass raw material is blended so that the molar ratio (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ in the glass substrate is 9.5 or more. Further, in the second aspect of the present invention, the glass raw material is blended so that the molar ratio (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ in the glass substrate is 9.5 or more. The composition of the glass raw material to be blended and the composition of the manufactured glass substrate may be slightly changed because a part of the components are volatilized and/or scattered during the manufacturing process. In the present invention, the amount of volatilization and the required composition of the scattering and the glass substrate are considered, and the glass raw material is blended. Further, in the present specification, the content of the glass component and the molar ratio refer to values in the glass or the glass substrate unless otherwise specified.

SiO ₂ and 2 times the amount of Al ₂ O ₃ bonding i.e. of _{(SiO 2 + 2 × Al 2} O 3) with respect to B ₂ O ₃ molar ratio of _{(SiO 2 + 2 × Al 2} O 3) / B 2 O ₃ becomes an indicator of high strain point and resistance to devitrification. If (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O _{3 is} less than 9.5, the strain point cannot be sufficiently increased, and it is difficult to produce a LTPS having a specific heat shrinkage ratio of, for example, less than 75 ppm without impairing productivity. / Glass substrate for TFT. On the other hand, in order to sufficiently lower the devitrification temperature to ensure moldability, (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O _{3 is} preferably 25.0 or less, more preferably 19.0 or less. According to the above, (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O _{3 is} preferably in the range of 9.5 to 25.0, more preferably in the range of 9.5 to 19.0, further preferably in the range of 9.5 to 17.0, further It is preferably in the range of 10.0 to 15.5, and more preferably in the range of 11.0 to 15.0.

The glass substrate produced is in the first aspect of the invention, and preferably does not substantially contain BaO. In the second aspect of the invention, BaO is not substantially contained. Therefore, in such cases, when the glass raw material is blended, a compound containing Ba is not used as a glass raw material. However, in the present specification, the term "substantially free of BaO" means consciously containing no BaO in the glass substrate, and is not excluded from the glass raw material or BaO in the production step as an inevitable It is contained in the case where it is mixed with impurities in the glass.

The composition of the glass substrate produced in the production method of the present invention is exemplified by 60 to 78 mol% of SiO ₂ , 3 to 20 mol% of Al ₂ O ₃ , and 0.1 to 15 mol% of B ₂ O ₃ . Glass composition. Alternatively, a glass composition containing 60 to 78 mol% of SiO ₂ , 3 to 20 mol% of Al ₂ O ₃ , and 3 to 15 mol% of B ₂ O ₃ may be exemplified. The glass may further contain 0 to 15 mol% of MgO, 0 to 20 mol% of CaO, 0 to 10 mol% of SrO, 0 to 5 mol% of ZnO, 0 to 0.8 mol% of K ₂ O, and 0 to 0.1. Mol% of Fe ₂ O ₃ , other clarifying agents, and the like. Further, it is preferable that substantially no Sb ₂ O ₃ is contained and substantially no As ₂ O ₃ is contained. These aspects are common to the first aspect and the second aspect described above.

Since the SiO ₂ -based glass has a skeleton component, it is an essential component. When the content is small, there is a tendency that the strain point is lowered and the thermal expansion coefficient is increased. Moreover, when the SiO ₂ content is too small, it is difficult to reduce the density of the glass substrate. On the other hand, when the content of SiO _{2 is} too large, the melting temperature is remarkably high and it tends to be difficult to be melted. When the content of SiO _{2 is} too large, the devitrification resistance tends to be lowered, so that the moldability tends to be deteriorated. From this point of view, the content of SiO ₂ is preferably in the range of 60 to 78 mol%. The content of SiO ₂ is more preferably 62 to 75 mol%, still more preferably 63 to 72 mol%, still more preferably 65 to 71 mol%.

The Al ₂ O ₃ system is an essential component for increasing the strain point. If the content is too small, the strain point is lowered. Further, there is a tendency that the Young's modulus is also lowered and the etching rate is also lowered. When the content of Al ₂ O _{3 is} too large, the devitrification temperature of the glass increases and the formability tends to be deteriorated. From this point of view, the content of Al ₂ O ₃ is preferably in the range of 3 to 20 mol%. The content of Al ₂ O ₃ is more preferably 5 to 18 mol%, still more preferably 5 to 15 mol%, still more preferably 7 to 14 mol%, still more preferably 10 to 14 mol%.

B ₂ O ₃ is an essential component for lowering the melting temperature of the glass to improve the meltability. When the B ₂ O ₃ content is too small, there is a tendency that the meltability is lowered, the devitrification resistance is lowered, and the thermal expansion coefficient is increased. Moreover, when the B ₂ O ₃ content is too small, it is difficult to achieve a low density. If the content of B ₂ O _{3 is} too large, a strain point and a decrease in Young's modulus are generated. From this point of view, the B ₂ O ₃ content is preferably in the range of 0.1 to 15 mol%, more preferably in the range of 3 to 15 mol%, still more preferably 3 to 9.5 mol%, still more preferably 3 to not It is 8.9 mol%, more preferably 4 to less than 8.9 mol%, further preferably 5 to 8.5 mol%, still more preferably 6 to 8 mol%. Further, in terms of sufficiently preventing devitrification, the B ₂ O ₃ content is preferably in the range of 0.1 to 15 mol%, more preferably in the range of 3 to 15 mol%, still more preferably 5 to 13 mol%, further It is preferably 5 to 12 mol%, more preferably 6 to less than 10 mol%.

The MgO system enhances the composition of the meltability. Further, since it is difficult to increase the density of the alkaline earth metal, if the content is relatively increased, the density is easily lowered. It is not essential but the meltability can be improved by inclusion. However, when the content of MgO is too large, the devitrification temperature of the glass is rapidly increased, and the formability is deteriorated. In particular, in the case where the devitrification temperature is to be lowered, it is preferred that substantially no MgO is contained. From this point of view, the MgO content is preferably from 0 to 15 mol%, more preferably from 0 to 10 mol%, further preferably from 0 to 5 mol%, further preferably from 0 to less than 2 mol%, further It is preferably 0 to 1.5 mol%, further preferably 0 to 1 mol%, still more preferably 0 to 0.5 mol%, and still more preferably 0 to less than 0.2 mol%, most preferably Jia is not actually included.

The CaO system is an effective component for increasing the devitrification temperature of the glass without increasing the devitrification temperature of the glass. Further, since it is difficult to increase the density of the alkaline earth metal, if the content is relatively increased, the density is easily lowered. When the content is too small, there is a tendency that the meltability due to an increase in the melting temperature is lowered and the devitrification property due to an increase in the devitrification temperature is lowered. If the CaO content is too large, there is a tendency for an increase in the coefficient of thermal expansion and an increase in density. The CaO content is preferably 0 to 20 mol%, more preferably 3.6 to 16 mol%, still more preferably 4 to 16 mol%, still more preferably 6 to 16 mol%, still more preferably more than 7 to 16 mol. %, further preferably 8 to 15 mol%, further preferably 9 to 13 mol%.

The SrO system reduces the composition of the devitrification temperature. SrO is not essential, but if it is contained, the devitrification resistance is improved, and the meltability is also improved. If the SrO content is too large, the density increases. The SrO content is preferably 0 to 10 mol%, more preferably 0 to 5 mol%, still more preferably 0 to 3 mol%, still more preferably 0 to 2 mol%, still more preferably 0 to 1 mol%. Further, it is further preferably 0 to less than 0.5 mol%, and still more preferably 0 to less than 0.1 mol%. In the case where the density of the glass is to be lowered, it is preferred that substantially no SrO is contained.

The BaO system reduces the composition of the devitrification temperature. BaO is not essential, but if it is contained, the devitrification resistance is improved and the meltability is also improved. Further, when the BaO content is too large, an increase in density and an increase in thermal expansion coefficient occur. The BaO content is preferably from 0 to 10 mol%, more preferably from 0 to less than 5 mol%, further preferably from 0 to 3 mol%, further preferably from 0 to 2 mol%, still more preferably from 0 to 1 The range of mol%. Furthermore, in terms of the environmental burden, it is better It does not contain BaO in quality.

Li ₂ O and Na ₂ O are components which improve the meltability, but they are components which are melted from the glass substrate to deteriorate the TFT characteristics or increase the thermal expansion coefficient of the glass. The content of Li ₂ O and Na ₂ O is preferably 0 to 0.5 mol%, more preferably 0 to 0.1 mol%, still more preferably 0 to 0.01 mol%, further preferably substantially no Li ₂ O and Na ₂ O.

K ₂ O is a component that increases the alkalinity of the glass and promotes clarification. Further, it is a component which lowers the specific resistance and lowers the melting temperature to improve the meltability. Although it is not essential, if it is contained, the clarification property is improved and the meltability is also improved. When the content of K ₂ O is too large, there is a possibility that the characteristics of the TFT are deteriorated by melting from the glass substrate. Moreover, there is a tendency that the coefficient of thermal expansion also increases. The K ₂ O content is preferably from 0 to 0.8 mol%, more preferably from 0.01 to 0.5 mol%, still more preferably from 0.1 to 0.3 mol%.

The glass substrate obtained by the production method of the present invention may contain a fining agent. As the clarifying agent, SnO _{2 is} preferred. If the content of SnO ₂ is too small, the quality of the bubbles deteriorates. If the content of SnO ₂ is too large, devitrification is likely to occur. The content of SnO ₂ is preferably in the range of 0.01 to 0.2 mol%, more preferably 0.03 to 0.15 mol%, still more preferably 0.05 to 0.12 mol%.

The Fe ₂ O ₃ system has a component which lowers the specific resistance of the glass in addition to the action as a clarifying agent. Among the glasses which have high viscosity in a high temperature region and are difficult to be melted, it is preferable to contain Fe ₂ O ₃ to lower the specific resistance of the glass. However, when the content of Fe ₂ O _{3 is} too large, the glass is colored and the transmittance is lowered. Therefore, the Fe ₂ O ₃ content is in the range of 0 to 0.1 mol%, preferably 0 to 0.05 mol%, more preferably 0.001 to 0.05 mol%, still more preferably 0.005 to 0.05 mol%, still more preferably 0.005~ 0.02 mol% range.

The glass substrate obtained by the production method of the present invention preferably contains substantially no As ₂ O _{3 in} terms of environmental burden. In the glass substrate of the present invention, Sb ₂ O _{3 is} preferably 0 to 0.5 mol%, more preferably 0 to 0.1 mol%, and most preferably substantially no Sb ₂ O ₃ , in terms of environmental burden.

In the present specification, the term "substantially not contained" means that the raw material of the components is not used as the raw material of the components, and the components contained in the form of impurities in the glass raw materials of the other components are not excluded. And the incorporation of components that are melted from the manufacturing device to the glass.

If the content of SiO ₂ of from minus total content of Al ₂ O ₃ of 1/2 _{(SiO 2 O 3/2 2} -Al) the value is too small, although the etching rate increase, but the devitrification resistance decreases danger . If the value is too high, there is a problem that the etching rate is lowered. From this point of view, (SiO ₂ -Al ₂ O ₃ /2) is preferably 66 mol% or less, more preferably 50 to 66 mol%, still more preferably 56 to 64 mol%, still more preferably 57 to 57. 63 mol%, further preferably 58 to 62 mol%.

If the amount of SiO ₂ and Al ₂ O ₃ of co i.e. SiO ₂ + Al ₂ O ₃ is too small, the strain point tends to decrease, if too large, the devitrification resistance tends to deteriorate it. Therefore, SiO ₂ + Al ₂ O _{3 is} preferably 75 mol% or more, more preferably 76 to 88 mol%, still more preferably 77 to 85 mol%, still more preferably 78 to 82 mol%.

When the amount of B ₂ O ₃ and P ₂ O ₅ , that is, B ₂ O ₃ + P ₂ O _{5 is} too small, the meltability tends to decrease, and if it is too large, the volatilization by B ₂ O ₃ + P ₂ O ₅ The unevenness of the glass is obvious, and it is easy to produce streaks. Further, there is a tendency that the strain point is lowered. Therefore, B ₂ O ₃ + P ₂ O _{5 is} preferably 0.1 to 15 mol%, more preferably 3 to 15 mol%, still more preferably 3 to 9.5 mol%, still more preferably 4 to 9 mol%, more preferably Further preferably, it is 5 to 9 mol%, and further preferably 6 to 8 mol%. Further, from the viewpoint of sufficiently preventing devitrification, B ₂ O ₃ + P ₂ O _{5 is} preferably in the range of 0.1 to 15 mol%, more preferably 3 to 15 mol%, still more preferably 5 to 13 mol%. Further, it is preferably from 5 to 12 mol%, more preferably from 6 to less than 10 mol%.

To prevent a reduction in the strain point of the side of one side in terms of the viewpoint of improving meltability, CaO B ₂ O ₃ with respect to the molar ratio of CaO / B ₂ O ₃ is preferably 0.5 or more, more preferably 0.9 or more, and further preferably more than 1.2, further preferably in the range of more than 1.2 to 5, further preferably in the range of more than 1.2 to 3, further preferably in the range of 1.3 to 2.5, and most preferably in the range of 1.3 to 2. Further, from the viewpoint of sufficiently improving the meltability, it is preferably from 0.5 to 5, more preferably from 0.9 to 3, still more preferably from 1 to 2.5, still more preferably more than 1.2 to 2, still more preferably more than The range of 1.2~1.5.

More ratio CaO/RO is an indicator of meltability and resistance to devitrification. CaO/RO is preferably from 0.5 to 1, more preferably from 0.7 to 1, further preferably from more than 0.85 to 1, further preferably from 0.88 to 1, further preferably from 0.90 to 1, further preferably 0.92~1, the best is 0.95~1. By setting these ranges, it is possible to achieve both devitrification resistance and meltability. Further, it is possible to achieve a low density.

When the combined amount of RO, ZnO, and B ₂ O ₃ , that is, RO + ZnO + B ₂ O _{3 is} too small, the meltability tends to decrease. On the other hand, if it is too much, there exists a tendency for a strain point to fall. Therefore, RO + ZnO + B ₂ O _{3 is} preferably 7 to 30%, more preferably 7 to less than 25 mol%, more preferably 10 to 23 mol%, and even more preferably 12 to 22 mol%, further It is preferably 14 to 21 mol%, more preferably 16 to 21 mol%. Further, from the viewpoint of sufficiently improving the meltability, it is preferably from 7 to 30%, more preferably from 12 to 27%, still more preferably from 14 to 25 mol%, still more preferably from 17 to 23 mol%.

RO with respect to the amount of SiO ₂ and Al alloy (SiO ₂ + Al ₂ O ₃₎ of the ₂ O ₃ molar ratio of _{RO / (SiO 2 + Al 2} O 3) becomes a strain point of index and meltability. From the viewpoint of taking into consideration the high strain point and the meltability, and also the reduction of the high strain point and the specific resistance of the glass, it is preferably in the range of 0.07 to 0.2, more preferably 0.08 to 0.18, still more preferably 0.13 to 0.18, Further preferably, it is in the range of 0.13 to 0.16.

The combination of Li ₂ O, Na ₂ O and K ₂ O, that is, R ₂ O, is a component which increases the basicity of the glass and facilitates oxidation of the clarifying agent to exhibit clarity. Further, it is a component which lowers the specific resistance and the melting temperature to improve the meltability. R ₂ O is not essential, but if it is contained, the bubble quality and the meltability are improved. However, if the R ₂ O content is too large, the coefficient of thermal expansion tends to increase. R ₂ O is preferably 0 to 0.8 mol%, more preferably 0.01 to 0.5 mol%, still more preferably 0.1 to 0.3 mol%.

Since the K ₂ O system has a larger molecular weight than Li ₂ O or Na ₂ O, it is difficult to melt from the glass substrate. Therefore, in the case of containing R ₂ O, it is preferred to contain K ₂ O. That is, it is preferably a mol% content of K ₂ O > a mol% content of Li ₂ O and/or a mol % content of K ₂ O > a mol% content of N ₂ O. When the ratio of Li ₂ O and Na ₂ O is large, the glass substrate is melted to deteriorate the TFT characteristics. The molar ratio K ₂ O/R ₂ O is preferably from 0.3 to 1, more preferably from 0.5 to 1, further preferably from 0.8 to 1, further preferably from 0.9 to 1.

The combination of MgO, CaO, SrO, and BaO is a component in which RO is improved in meltability. If the RO content is too small, the meltability is deteriorated. If the RO content is too large, there is a tendency that the strain point is lowered, the density is increased, and the Young's modulus is lowered. Moreover, if the RO content is too large, there is also a tendency to increase the coefficient of thermal expansion. to. In this regard, the RO is preferably in the range of 3 to 25 mol%, preferably 4 to 16 mol%, more preferably 4 to 15 mol%, and even more preferably 5 to less than 14 mol%. Further, it is preferably in the range of 6 to 14 mol%, more preferably in the range of 8 to 13 mol%, still more preferably in the range of 9 to 12 mol%.

The devitrification temperature of the glass substrate of the present invention is preferably 1270 ° C or lower, more preferably 1260 ° C or lower, further preferably 1250 ° C or lower, and further preferably 1200 ° C or lower. When the devitrification temperature is 1270 ° C or less, it is easy to form a glass plate by a down-draw method. If the devitrification temperature is too high, devitrification is likely to occur and it is not suitable for the down-draw method.

The average thermal expansion coefficient (100 to 300 ° C) of the glass substrate of the present invention is preferably less than 55 × 10 ^-7 ° C ^-1 , more preferably 28 × 10 ^-7 ° C ^-1 ~ less than 40 × 10 ^-7 ° C ^{- 1} , further preferably 30 × 10 ^-7 ° C ^-1 ~ less than 39 × 10 ^-7 ° C ^-1 , further preferably 32 × 10 ^-7 ° C ^-1 ~ less than 38 × 10 ^-7 ° C ^-1 , It is further preferably in the range of 34 × 10 ^-7 ° C ^-1 to less than 38 × 10 ^-7 ° C ^-1 . Further, from the viewpoint of further reducing the heat shrinkage ratio, it is preferably less than 37 × 10 ^-7 ° C ^-1 , more preferably 28 × 10 ^-7 ° C ^-1 to less than 36 × 10 ^-7 ° C ^-1 . Further preferably, it is 30 × 10 ^-7 ° C ^-1 ~ less than 36 × 10 ^-7 ° C ^-1 , further preferably 31 × 10 ^-7 ° C ^-1 to 35 × 10 ^-7 ° C ^-1 , further preferably It is in the range of 32 × 10 ^-7 ° C ^-1 ~ less than 35 × 10 ^-7 ° C ^-1 . If the coefficient of thermal expansion is large, the heat shrinkage rate tends to increase. On the other hand, when the coefficient of thermal expansion is small, it is difficult to obtain a match between the peripheral material such as a metal or an organic binder formed on the glass substrate and the thermal expansion coefficient, and the peripheral member is peeled off. The thermal stress caused by the difference in thermal expansion can be reduced by setting the thermal expansion coefficient to the above range.

The heat shrinkage rate of the glass substrate of the present invention is preferably 75 ppm or less, more preferably 60 ppm or less, further preferably 55 ppm or less, further preferably 50 ppm or less, further preferably 48 ppm or less, further preferably less than 45 ppm, and still more preferably 43 ppm or less. If the heat shrinkage rate (amount) is too large, a large deviation between pixels is caused, and a high-definition display cannot be realized. In order to control the heat shrinkage rate (amount) to a specific range, it is preferable to set the strain point of the glass substrate to 675 ° C or higher. Further, if the heat shrinkage rate is to be 0 ppm, it is necessary to reduce the cooling rate of the cooling step (for example, the second cooling step) as much as possible, or to provide a heat shrinkage reduction treatment step differently from the cooling step described below. Specifically, the heat shrinkage rate (offline annealing) can be reduced by providing a heat shrinkage reduction treatment step after the cutting step described below. However, if the cooling rate is lowered as much as possible or the heat shrinkage reduction treatment step is set differently from the cooling step, the productivity is lowered and the cost is increased. In view of productivity and cost, the heat shrinkage ratio is preferably from 5 to 75 ppm, more preferably from 5 to 60 ppm, further preferably from 8 to 55 ppm, further preferably from 8 to 50 ppm, still more preferably 10 to 48 ppm, further preferably 10 to less than 45 ppm, and further preferably 15 to 43 ppm.

Further, the heat shrinkage ratio was expressed by the following formula after performing heat treatment at twice the temperature rise and fall rate of 10 ° C / min and holding at 550 ° C for 1 hour. More specifically, the temperature was raised from normal temperature at 10 ° C / min and maintained at 550 ° C for 1 hour, and thereafter, the temperature was lowered to normal temperature at 10 ° C / minute, and the temperature was again raised at 10 ° C / minute and held at 550 ° C for 1 hour. Cool down to room temperature at 10 ° C / min.

Heat shrinkage rate (ppm) = {shrinkage of glass before and after heat treatment / length of glass before heat treatment} × 10 ⁶

The density of the glass substrate of the present invention is preferably 2.6 g/cm ³ or less, more preferably 2.5 g/cm ³ or less, still more preferably 2.45 g/cm ³ or less, still more preferably 2.42 g/cm ³ or less. If the density is too high, the weight of the glass substrate is difficult, and the weight of the display is not reduced.

When the Tg of the glass is lowered, there is a tendency that heat shrinkage tends to occur in the heat treatment step at the time of manufacture of the display. The Tg of the glass substrate of the present invention is preferably 720 ° C or higher, more preferably 730 ° C or higher, further preferably 740 ° C or higher, and further preferably 750 ° C or higher. In order to set the Tg of the glass substrate to the above range, it is preferable to increase the Tg such as SiO ₂ and Al ₂ O _{3 in} the range of the composition of the glass substrate of the present invention.

The temperature (melting temperature) at which the viscosity (100 dPa.s) of the glass melt of the present invention is expressed is preferably 1750 ° C or lower, more preferably 1600 to 1750 ° C, still more preferably 1620 to 1730 ° C, further preferably It is in the range of 1650~1720 °C. The strain point of the glass having a lower melting temperature tends to become lower. In order to increase the strain point, it is necessary to also increase the melting temperature to some extent. However, if the melting temperature is high, the burden on the melting tank becomes large. Moreover, since energy is used in a large amount, the cost is also high. In order to set the melting of the glass to the above range, it is preferable to contain a component such as B ₂ O ₃ or RO having a reduced viscosity in the range of the composition of the glass substrate of the present invention.

The specific resistance of the molten glass of the present invention (at 1550 ° C) is preferably 50 to 300 Ω. Cm, more preferably 50~250 Ω. Cm, and further preferably 50 to 200 Ω. Cm, further preferably 100 to 200 Ω. The range of cm. If the specific resistance is too small, there is a problem that the current value required for melting is too large and there is a restriction on the device. If the specific resistance of the molten glass is too large, there is a possibility that the current does not flow in the glass but flows in the heat-resistant brick forming the melting tank to cause melting of the melting tank. The specific resistance of the molten glass can be mainly adjusted to the above range by controlling the contents of RO, K ₂ O, and Fe ₂ O ₃ .

The liquid viscosity of the glass of the invention is preferably 30,000 dPa. Above s, more preferably 40,000 dPa. Above s, further preferably 50,000 dPa. s above the range. By being in the above range, it is difficult to generate a devitrified crystal during molding, and thus it is easy to form the glass substrate by the overflow down-draw method.

The Young's modulus of the glass substrate of the present invention is preferably 70 GPa or more, more preferably 73 GPa or more, still more preferably 74 GPa or more, still more preferably 75 GPa or more. If the Young's modulus (GPa) is small, the glass is easily broken by the deflection of the glass due to the glass weight. The Young's modulus (GPa) of the glass substrate can be increased by increasing the content of the glass substrate of the present invention such that the Young's modulus (GPa) tends to fluctuate, for example, the content of Al ₂ O ₃ or the like is increased. Big.

The specific modulus (Young's modulus/density) of the glass substrate of the present invention is preferably 28 or more, more preferably 29 or more, still more preferably 30 or more, still more preferably 31 or more. If the specific modulus of elasticity is small, the glass is easily broken by the deflection of the glass due to the self-weight of the glass.

(2) Forming step

In the forming step (2), the molten glass forming glass ribbon is melted and clarified by heating by an overflow down-draw method. The method of the overflow down-draw method is itself a well-known method. For the overflow down-draw method, for example, Japanese Laid-Open Patent Publication No. 2009-298665, JP-A-2010-215428, and JP-A-2011-168494, and the like, herein. The device used in the overflow down-draw method The illustrations are shown in Figures 1 and 2.

1 and 2 show a schematic configuration of a molding apparatus 40 used in the overflow down-draw method. 1 is a cross-sectional view of a forming device 40. 2 is a side view of the forming device 40.

The forming device 40 includes a passage through which the glass ribbon GR passes and a space surrounding the passage. The space surrounding the passage includes an overflow chamber 20, a forming chamber 30, and a cooling chamber 80.

The molding apparatus 40 mainly includes a molded body 41, a spacer member 50, a cooling roller 51, a temperature adjustment unit 60, pull-down rollers 81a to 81d, heaters 82a to 82h, and a cutting device 90. Further, the molding device 40 includes a control device 91 (not shown). The overflow chamber 20 is formed by molding a molten glass conveyed from a clarification device (not shown) into a space of the glass ribbon GR. The grinding step of the surface of the glass substrate after the formation is not required by using the overflow down-draw method.

(3) Cooling step

In the cooling step (3), the glass ribbon formed in the forming step is cooled under the following condition (A).

(A) Average cooling rate from slow cooling point to (strain point -50 ° C): 0.5 ~ less than 5.5 ° C / sec

The formed glass ribbon is cooled while facing downward. The usual methods and conditions for the extension and cooling of the glass ribbon are well known. In the method of the present invention, the glass ribbon formed in the overflow forming apparatus is directly annealed by in-line annealing, and further cut to produce a glass sheet.

The forming chamber 30 is disposed below the overflow chamber 20 and is used to adjust the thickness of the glass ribbon GR and the amount of warpage. In the forming chamber 30, the execution is performed One of the first cooling steps S41 is described. Specifically, in the forming chamber 30, the upstream region of the glass ribbon GR is cooled. The upstream region of the glass ribbon GR is the region where the temperature of the central portion C of the glass ribbon GR is higher than the glass ribbon GR of the slow cooling point. The center portion C of the glass ribbon GR is the center in the width direction of the glass ribbon GR. The temperature in the center portion C including the glass ribbon GR in the upstream region becomes a temperature region near the slow cooling point. After passing through the forming chamber 30, the glass ribbon GR passes through the cooling chamber 80 described below.

The cooling chambers 80 shown in Figures 1 and 2 are disposed below the overflow chamber 20 and the forming chamber 30 for adjusting the space of the strain gauge of the glass ribbon GR. In the overflow chamber 20, one of the first cooling step S41, the second cooling step S42, and the third cooling step S43 are performed. Specifically, in the cooling chamber 80, the glass ribbon GR passing through the forming chamber 30 passes through a slow cooling point and a strain point, and is cooled to a temperature near room temperature. Further, the inside of the cooling chamber 80 is divided into a plurality of spaces by the heat insulating member 80b.

The cooling step of the glass ribbon includes: a first cooling step of cooling the glass ribbon of about 1,100 ° C to 1,250 ° C formed in the overflow forming apparatus to exceed the slow cooling point; and a second cooling step of slow cooling The temperature is cooled to a temperature of (strain point - 50 ° C); and the third cooling step is cooled from a temperature not reached (strain point - 50 ° C) to a temperature near (strain point - 200 ° C). Further, in the present invention, the average cooling rate of the center portion of the glass ribbon in the second cooling step is set to 0.5 to less than 5.5 ° C / sec (condition A). By setting the average cooling rate of the center portion of the glass ribbon in the second cooling step to the above range, a glass substrate which can reduce the heat shrinkage rate without impairing productivity can be obtained. Furthermore, in the present specification, the cooling rate of the glass ribbon is referred to unless otherwise specified. The average cooling rate at the center of the glass ribbon. More specifically, Japanese Patent Application No. 2012-525566, etc., the entire disclosure of which is hereby incorporated by reference. Further, in the present specification, (strain point - 50 ° C) means a temperature 50 ° C lower than the strain point, and (strain point - 200 ° C) means a temperature 200 ° C lower than the strain point.

In the cooling step of the formed glass ribbon in the production method of the present invention, it is preferred to cool the glass ribbon under the following conditions (B) and (C) in addition to the above condition (A).

(B) The average cooling rate of the glass ribbon formed in the molding step (2) at a slow cooling point: 5.5 ° C / sec or more; (C) The average temperature of the glass ribbon in the above (B) becomes a slow cooling point The cooling rate is faster than the average cooling rate of the glass ribbon from the above (strain point - 50 ° C) to (strain point - 200 ° C).

The cooling step of the formed glass ribbon in the production method of the present invention may satisfy the condition (D) in addition to the above conditions (A) or (A) to (C). (D) the temperature of the glass ribbon from the above (strain point -50 ° C) to the above (strain point -200 ° C), the average cooling rate is faster than the temperature of the glass ribbon from the slow cooling point to (strain point) The average cooling rate up to -50 ° C).

The condition (B) is a cooling condition in the first cooling step until the temperature of the glass ribbon becomes a slow cooling point, and the average cooling rate of the center portion of the glass ribbon formed in the molding step is 5.5 ° C /sec or more. The average cooling rate of the central portion of the glass ribbon in the first cooling step is preferably from 5.5 ° C / sec to 50.0 ° C / sec, more preferably from 8.0 ° C / sec to 16.5 ° C / sec. If the average cooling rate of the center portion of the glass ribbon in the first cooling step is less than 5.5 ° C / sec, the productivity is lowered. on the other hand, When the average cooling rate of the center portion of the glass ribbon in the first cooling step exceeds 50.0 ° C / sec, it is difficult to control the temperature in the width direction of the glass ribbon to suppress plane strain or warpage. Further, the first edge portion cooling rate in the first cooling step S41 is preferably 5.5 ° C / sec to 52.0 ° C / sec, more preferably 8.3 ° C / sec to 17.5 ° C / sec. Further, the average cooling rate of the central portion of the glass ribbon in the first cooling step is preferably faster than the average cooling rate at the central portion of the glass ribbon in the second cooling step and the third cooling step. Condition (C) The average cooling rate in the first cooling step until the temperature of the glass ribbon becomes the slow cooling point is faster than the temperature of the glass ribbon from the above (strain point -50 ° C) to (strain point -200 ° C) The average cooling rate in the third cooling step up to that. By doing so, the accuracy of temperature control in the width direction of the glass ribbon can be improved.

Condition (A) is the cooling condition of the glass ribbon in the second cooling step, and the average cooling rate of the center portion of the glass ribbon at the temperature from the slow cooling point to the (strain point - 50 ° C) is 0.5 to less than 5.5 ° C / sec. Preferably, it is 1.0 ° C / sec to 5.5 ° C / sec, more preferably 1.5 ° C / sec ~ 5.0 ° C / sec. If the average cooling rate of the center portion of the glass ribbon in the second cooling step is less than 0.5 ° C / sec, the manufacturing equipment becomes large and the productivity is lowered. On the other hand, when it is 5.5 ° C / sec or more, the heat shrinkage rate cannot be sufficiently reduced. Further, the edge portion cooling rate in the second cooling step is preferably from 0.3 ° C / sec to 5.3 ° C / sec, more preferably from 0.8 ° C / sec to 2.8 ° C / sec. Further, the average cooling rate of the central portion of the glass ribbon in the second cooling step is preferably slower than the average cooling rate at the central portion of the glass ribbon in the first cooling step.

In the present invention, the cooling rate of the central portion of the glass ribbon in the third cooling step is not particularly limited, but is preferably from 1.5 ° C / sec to 7.0 ° C / sec, more preferably from 2.0 ° C / sec to 5.5 ° C / sec. If the cooling rate of the center of the glass ribbon in the third cooling step When the degree is less than 1.5 ° C / sec, the productivity is lowered. On the other hand, when it is 7.0 ° C / sec or more, the glass ribbon is ruptured due to the glass quenching. Further, the edge portion cooling rate in the third cooling step S43 is preferably from 1.3 ° C / sec to 6.8 ° C / sec, more preferably from 1.5 ° C / sec to 5.0 ° C / sec.

Further, the average cooling rate of the center portion of the glass ribbon in the third cooling step may be faster than the average cooling rate of the central portion of the glass ribbon in the second cooling step. The condition (D) is that the temperature of the glass ribbon is slower than the temperature of the glass ribbon in the third cooling step from the above (strain point - 50 ° C) to the above (strain point - 200 ° C). The average cooling rate in the second cooling step up to the (strain point -50 ° C) from the cold point. Thus, there is a case where the accuracy of temperature control in the width direction of the glass ribbon can be further improved. However, even if the temperature of the glass ribbon is less than the above (strain point - 50 ° C) to the above (strain point - 200 ° C), the average cooling rate in the third cooling step is slower than the temperature of the glass ribbon from the slow cooling point. The average cooling rate in the second cooling step up to (strain point -50 ° C) can also control the temperature in the width direction of the glass ribbon with the required accuracy as long as the above conditions (A) to (C) are satisfied. . The accuracy can be further improved by satisfying the condition (D).

That is, it is preferable that the above-described aspect is that the three flat cooling steps S41 to S43 included in the cooling step S4 of the glass ribbon GR cool the sheet glass SG at at least the cooling steps S41 and S42 at different cooling rates. The cooling rate of the cooling steps S42 and S43 can be faster regardless of which one. Specifically, the cooling rate of the first cooling step S41 among the three cooling steps S41 to S43 is the fastest, and the cooling rate of the second cooling step S42 and the cooling rate of the third cooling step S43 are faster or even For the same speed, you can maintain a higher life. The productivity side improves the temperature control of the glass ribbon, especially the temperature control in the width direction.

Hereinafter, the temperature management of the glass ribbon GR in each of the cooling steps S41 to S43 will be described in detail with reference to FIGS. 3 and 4 . Figure 3 shows the temperature distribution at a specific height position of the glass ribbon GR. Fig. 4 shows the cooling rate of the glass ribbon GR (0.7 mm) manufactured in Example 1 which satisfies the condition (D).

(3-1) First cooling step

The first cooling step S41 is a step of cooling the molten glass that is joined immediately below the molded body 41 to a temperature near the slow cooling point. Specifically, in the first cooling step, the glass ribbon GR of about 1,100 ° C to 1,250 ° C is cooled to a temperature near the slow cooling point (see FIG. 4 ). Here, the slow cooling point viscosity is 10 ¹³ dPa. The temperature of s.

In the first cooling step S41, the temperature management of the glass ribbon GR is performed based on the first temperature distribution TP1 to the fourth temperature distribution TP4. The first cooling step includes a first temperature control step in which the temperature of the end portion in the width direction of the glass ribbon GR is lower than the temperature of the central portion CA sandwiched by the end portion and the temperature of the central portion CA becomes uniform. And the second temperature control step is performed such that the temperature in the width direction of the glass ribbon GR decreases from the central portion toward the end portion after the first temperature control step. Here, the uniform temperature of the central region CA means that the temperature of the central region CA is included in a specific temperature region. The specific temperature range is the range of the reference temperature ± 20 ° C. The reference temperature is the average temperature in the width direction of the central area CA. The temperature in the width direction of the glass ribbon GR decreases from the center portion toward the end portion, which means that the temperature at the center portion C and the temperature at the edge portions R, L form a gradient (warm) Degree gradient). Here, the temperature gradient is obtained by dividing the temperature of the edge portion R, L from the temperature of the center portion C by the width W of the glass ribbon GR (for example, 1650 mm, see FIG. 3) divided by 2. Value ((temperature of center C - temperature of edge portion R, L) / (width of flat glass W/2)).

The first temperature distribution TP1 shown in FIG. 3 is realized by controlling the cooling rolls 51 and the temperature adjusting unit 60 in the forming chamber 30. Specifically, the edge portions R, L of the glass ribbon GR are cooled by the cooling roller 51. The temperature of the edge portions R and L of the glass ribbon GR is cooled to a temperature lower than the temperature of the central region CA by a specific temperature (for example, 200 ° C to 250 ° C). The first temperature distribution TP1 suppresses shrinkage of the glass ribbon GR in the width direction by quenching the edge portion, thereby making the thickness of the glass ribbon GR uniform.

The second temperature distribution TP2 and the third temperature distribution TP3 are realized by controlling the temperature adjustment unit 60 in the forming chamber 30. Specifically, the edge portions R, L of the glass ribbon GR are cooled by the cooling units 64, 65, and the central region CA of the flat glass is cooled by the cooling units 62, 63. By performing such cooling, tension can be continuously applied to the center portion of the glass ribbon GR, and warpage of the glass ribbon GR can be suppressed.

Further, the fourth temperature distribution TP4 is realized by controlling the heater 82a in the cooling chamber 80. By making the temperature gradient TG4 in the fourth temperature distribution TP4 smaller than the temperature gradient TG3 in the upstream third temperature distribution TP3, tension can be continuously applied to the center portion of the glass ribbon GR, and warpage of the glass ribbon GR can be suppressed.

(3-2) second cooling step

The second cooling step S42 is a step of cooling the glass ribbon GR having a temperature near the slow cooling point to a vicinity of a strain point of -50 ° C (see FIG. 4). Here, the viscosity of the strain point glass is 10 ^14.5 dPa. s temperature.

In the second cooling step S42, the temperature management of the glass ribbon GR is performed based on the fifth temperature distribution TP5 and the sixth temperature distribution TP6. The second cooling step includes a third temperature control step in which the temperature gradient between the end portion and the central portion in the width direction of the flat glass is lowered as it approaches the strain point of the glass.

The fifth temperature distribution TP5 is achieved by controlling the heater 82b in the cooling chamber 80. By making the temperature gradient TG5 in the fifth temperature distribution TP5 smaller than the temperature gradient TG4 in the upstream fourth temperature distribution TP4, tension can be continuously applied to the center portion of the glass ribbon GR, and warpage of the glass ribbon GR can be suppressed.

The temperature in the width direction of the sixth temperature distribution TP6-based glass ribbon GR (the temperature of the edge portions R and L in the width direction to the center portion C) is uniform. In other words, the sixth temperature distribution TP6 is a temperature distribution in which the temperature gradient around the edge portions R and L and the temperature around the center portion C is the smallest in the width direction of the glass ribbon GR, and the temperature around the edge portions R and L is The temperature around the center portion C is the same.

Here, the term “uniform” means that the temperature around the edge portions R and L and the temperature around the center portion C are included in a specific temperature region. The specific temperature range is the range of the reference temperature ± 5 ° C. The reference temperature is the average temperature in the width direction of the glass ribbon GR.

Further, the sixth temperature distribution TP6 is realized by controlling the heater 82c in the cooling chamber 80. Further, the sixth temperature distribution TP6 is realized in the vicinity of the strain point. Here, the vicinity of the strain point refers to the specific temperature including the strain point. region. The specific temperature range is the area of "(slow cooling point + strain point)/2" to "strain point -50 °C". The sixth temperature distribution TP6 is achieved at least at a point near the strain point (at one of the flow directions).

(3-3) third cooling step

The third cooling step S43 is a step of cooling the glass ribbon GR reaching the temperature near the strain point of -50 ° C to a temperature near the strain point of -200 ° C (refer to FIG. 4 ).

In the third cooling step S43, the temperature management of the glass ribbon GR is performed based on the seventh temperature distribution TP7 to the tenth temperature distribution TP10. The third cooling step includes a fourth temperature control step in which the temperature in the width direction of the flat glass is lowered from the end portion in the width direction of the flat glass toward the center portion. In other words, in the third cooling step S43, it is preferable that the temperature in the central portion is not near the glass strain point, and the lower portion is formed from the both end portions (edge portions) of the glass ribbon toward the central portion. The manner in which the temperature of the glass ribbon is controlled is controlled.

Further, the seventh temperature distribution TP7 to the tenth temperature distribution TP10 are realized by controlling the heaters 82d to 82g in the cooling chamber 80. Specifically, the seventh temperature distribution TP7 is realized by the heater 82d, the eighth temperature distribution TP8 is realized by the heater 82e, and the ninth temperature distribution TP9 is realized by the heater 82f, and is realized by the heater 82g. The 10th temperature distribution TP10. The central portion CA has the lowest temperature at the central portion C, the highest temperature at the edge portions R and L, and the temperature gradient TG7~10 in the seventh temperature distribution TP7 to the tenth temperature distribution TP10 gradually increases along the flow direction of the glass ribbon GR. Thereby, the tension can be continuously applied to the center portion of the glass ribbon GR, and the warpage of the glass ribbon GR can be suppressed.

Further, in the first to third cooling steps, in order to use the glass ribbon The central portion in the width direction acts on the direction in which the glass ribbon is conveyed, and temperature control can be performed in such a manner that a temperature of at least 150 ° C is applied from the slow cooling point of the glass at a temperature at a central portion in the width direction of the glass ribbon. (slow cooling point +150 ° C) in the temperature region where the glass strain point is reduced by 200 ° C (strain point - 200 ° C), the cooling rate of the central portion in the width direction of the glass ribbon is faster than the width direction The cooling rate of the end.

As described above, in the first to third cooling steps, it is preferable that (1) the width direction of the glass ribbon is in a region where the temperature in the central portion in the width direction of the glass ribbon is equal to or higher than the glass softening point. The both end portions are lower than the temperature of the central portion sandwiched by the both end portions, and the temperature of the central portion is controlled to control the temperature of the glass ribbon; (2) for the center of the width direction of the glass ribbon The tension acts in the direction in which the glass ribbon is conveyed, and the temperature distribution in the width direction of the glass ribbon is from the center in a region where the temperature of the central portion of the glass ribbon is less than the glass softening point and the glass strain point is And controlling the temperature of the glass ribbon so that the both end portions become lower; and (3) the temperature direction of the glass ribbon in the temperature region of the glass portion of the glass ribbon The temperature of the glass ribbon is controlled such that the temperature gradient between the both end portions and the central portion disappears.

Example

Hereinafter, the present invention will be described in further detail by way of examples. However, the invention is not intended to be limited by the examples.

Example 1

(production of sample glass)

In the manner of the composition of the glass shown in Table 1, the usual glass materials, namely ceria, alumina, boria, potassium carbonate, basic magnesium carbonate, calcium carbonate, barium carbonate, tin dioxide and ferric oxide, are used. , blending glass raw material batch (hereinafter referred to as batch).

The batch prepared by the use of a continuous melting device having a refractory brick melting tank and a platinum alloy adjusting tank is melted at 1560 to 1640 ° C, clarified at 1620 to 1670 ° C, and stirred at 1440 to 1530 ° C. The glass substrate manufacturing apparatus shown in FIGS. 1 and 2 was formed into a thin plate shape having a width of 1600 mm and a thickness of 0.7 mm by an overflow down-draw method, and was slowly cooled under specific conditions to obtain a liquid crystal display. A glass substrate (for organic EL display) is used. Specific slow cooling conditions are shown in Tables 2-6. Further, regarding each of the following characteristics, a test glass substrate of 30 mm × 40 mm × 0.7 mm was produced from the glass substrate obtained under the slow cooling conditions of Table 3.

(strain point, slow cooling point)

The measurement was performed using a curved beam measuring device (manufactured by Tokyo Industrial Co., Ltd.), and the strain point and the slow cooling point were obtained by calculation according to the curved beam method (ASTM C-598).

(heat shrinkage rate)

The heat shrinkage rate was raised at a temperature of 10 ° C / min from normal temperature and maintained at 550 ° C for 1 hour. Thereafter, the temperature was lowered to 10 ° C / minute to room temperature, and the temperature was again raised at 10 ° C / minute and held at 550 ° C for 1 hour. The amount of shrinkage of the glass substrate after cooling to room temperature at 10 ° C /min was determined by the following formula.

Heat shrinkage rate (ppm) = {shrinkage of glass before and after heat treatment / length of glass before heat treatment} × 10 ⁶

In the present embodiment, specifically, the measurement of the amount of shrinkage was carried out by the following method.

(Method for measuring devitrification temperature)

The above glass substrate was pulverized and passed through a sieve of 2380 μm to obtain glass granules remaining on a sieve of 1000 μm. After the glass granules were immersed in ethanol and subjected to ultrasonic cleaning, they were dried in a thermostatic chamber. The dried glass granules were placed on a platinum boat having a width of 12 mm, a length of 200 mm, and a depth of 10 mm so that the glass granules 25 g were substantially fixed in thickness. The platinum boat was held in an electric furnace having a temperature gradient of 1080 to 1320 ° C for 5 hours, and then taken out from the furnace, and the devitrification generated inside the glass was observed by a 50-fold optical microscope. The highest temperature at which devitrification was observed was set as the devitrification temperature.

(Method for measuring the average thermal expansion coefficient α and Tg in the range of 100 to 300 ° C)

The temperature at the temperature rise and the amount of expansion and contraction of the glass were measured using a differential thermal dilatometer (Thermo Plus 2 TMA8310). The rate of temperature rise at this time was set to 5 ° C / min. Based on the measurement results of the above temperature and the amount of expansion and contraction of the glass, the average thermal expansion coefficient and Tg in the temperature range of 100 to 300 ° C were measured.

(density)

The density of the glass was measured by the Archimedes method described above for the Young's modulus measurement sample.

(Young's modulus, specific elastic modulus)

The Young's modulus is used to make a glass having a thickness of 5 mm, which is measured by an ultrasonic pulse method. The specific elastic modulus is calculated from Young's modulus and density.

(melting temperature, liquid viscosity)

The melting temperature is based on the measurement results using a platinum ball pull-type automatic viscosity measuring device, and the viscosity is calculated to be 102.5 dPa. Obtained at the temperature of s. The liquidus viscosity is obtained by calculating the viscosity at the devitrification temperature based on the above measurement results.

(specific resistance)

The measurement was carried out by a four-terminal method using a 4192A LF impedance analyzer manufactured by HP, and the specific resistance at 1550 ° C was calculated from the above measurement results.

Glass composition (mol%), devitrification temperature (°C), slow cooling point (°C), strain point (°C), average thermal expansion coefficient (×10 ^-7 °C ^-1 ), density (g/cm ³ ), Yang The modulus (GPa), the specific modulus of elasticity, the melting temperature (°C), the liquidus viscosity (dPa.s), the Tg (°C), and the specific resistance (Ω.cm) are shown in Table 1.

Tables 2 to 5 show the measured values of the temperature change (°C) of the glass ribbon GR and the time (second) required for the temperature change in the cooling step S4, and the average cooling rate (° C/sec) of the center portion C of the glass ribbon GR. Tables 2 to 5 show values at which the average cooling rate (° C./sec) in S42 (the range of the temperature from the slow cooling point to the strain point of -50 ° C) is 0.9, 1.1, 2.9, and 5.1, respectively. Further, Table 8 shows the heat shrinkage ratio of the glass substrate produced in the case where the average cooling rate (° C./sec) in S42 is 0.9, 1.1, 2.9, and 5.1, respectively.

Example 2

Glass composition (mol%), devitrification temperature (°C), slow cooling point (°C), strain point (°C), average thermal expansion coefficient (×10 ^-7 °C ^-1 ), density (g/cm ³ ), Yang The modulus (GPa), the specific modulus of elasticity, the melting temperature (°C), the liquidus viscosity (dPa.s), the Tg (°C), and the specific resistance (Ω.cm) are shown in Table 1. Further, the width of the glass ribbon GR was set to 1600 mm and the thickness was set to 0.7 mm.

Tables 6 to 7 show the measured values of the temperature change (°C) of the glass ribbon GR and the time (seconds) required for the temperature change in the cooling step S4, and the average cooling rate (°C/sec) of the center portion C of the glass ribbon GR. Tables 6 to 7 show the values of the average cooling rate (°C/sec) in S42 of 2.1 and 3.0, respectively. Further, in Table 8, the heat shrinkage ratio of the glass substrate produced in the case where the average cooling rate (° C./sec) in S42 was 2.1 and 3.0, respectively.

According to the results shown in Table 8, it was found that the average cooling rate in the second cooling step was 0.5 to less than 5.5 ° C / sec, and a glass substrate having a heat shrinkage ratio of 60 ppm or less was obtained.

Comparative example

Glass composition (mol%), devitrification temperature (°C), slow cooling point (°C), strain point (°C), average thermal expansion coefficient (×10 ^-7 °C ^-1 ), density (g/cm ³ ), Yang The modulus (GPa), the specific modulus of elasticity, the melting temperature (°C), the liquidus viscosity (dPa.s), the Tg (°C), and the specific resistance (Ω.cm) are shown in Table 1. Further, the width of the glass ribbon GR was set to 1600 mm and the thickness was set to 0.7 mm.

Table 9 shows the measured values of the temperature change (°C) of the glass ribbon GR and the time (seconds) required for the temperature change in the cooling step S4, based on the measured values interpolated to reach the slow cooling point (715 ° C), the strain point. a value (interpolated value) of -50 ° C (610 ° C) and a strain point -200 ° C (460 ° C), and a cooling rate (° C / sec) of the center portion C.

In the cooling step S4, the cooling rate in the first cooling step S41 becomes the maximum value, and the cooling rate in the third cooling step S43 becomes the second largest value and the second cooling. The cooling step is performed in such a manner that the cooling rate in step S42 becomes the minimum value. The heat shrinkage rate of the obtained glass substrate was also 86 ppm as shown in Table 8.

20‧‧‧Overflow chamber

30‧‧‧Forming chamber

40‧‧‧Forming device

41‧‧‧Formed body

50‧‧‧ spacer components

51‧‧‧Cooling roller

60‧‧‧Temperature adjustment unit

80‧‧‧Cooling chamber

81a‧‧‧ Pull down the roller

81b‧‧‧ Pull down the roller

81c‧‧‧ Pull down the roller

81d‧‧‧ Pull down the roller

82a‧‧‧heater

82b‧‧‧heater

82c‧‧‧heater

82d‧‧‧heater

82e‧‧‧heater

82f‧‧‧heater

82h‧‧‧heater

90‧‧‧cutting device

Fig. 1 is a schematic (cross-sectional view) of an overflow down-draw forming apparatus.

Fig. 2 is a schematic diagram (side view) of an overflow down-draw forming apparatus.

Figure 3 is a graph showing the temperature distribution at a particular height position of the glass ribbon.

Fig. 4 is a view showing an example of the cooling rate of the glass ribbon of Example 1 (an example of a cooling rate of 1 ° C / sec).

Claims (10)

A method for producing a glass substrate for a flat panel display, comprising: (1) a melting step of blending in a manner that a combined amount of SrO and BaO in the glass substrate to be produced is less than 8 mass% and has a strain point of 675 ° C or higher a raw material and melted; (2) a forming step of melting the glass-formed glass ribbon by melt-down method; and (3) a cooling step of cooling the formed glass ribbon; the cooling step comprising: first cooling a step of cooling to a temperature exceeding a slow cooling point; a second cooling step of cooling from a slow cooling point to a temperature of (strain point - 50 ° C); and a third cooling step of self-supplied (strain) The temperature at a point of -50 ° C) is cooled to a temperature near (strain point - 200 ° C); the average cooling rate in the first cooling step is 5.5 to 50.0 ° C / sec, and the average cooling rate in the second cooling step is 0.5 ~ less than 5.5 ° C / sec; (1) In the cooling step, the temperature in the center portion of the center of the width direction of the glass ribbon is in the region above the glass softening point, and is located in the width direction of the glass ribbon. The temperature at both ends of the end is lower than the above The temperature of the core portion is controlled such that the temperature of the central portion sandwiched by the two edge portions becomes uniform, and the temperature of the center portion in the width direction of the glass ribbon is not reached. In the region where the glass softening point is above the glass strain point, the temperature distribution in the width direction of the glass ribbon becomes lower toward the both edge portions from the center portion And controlling the temperature of the glass ribbon; and (3) the two edge portions in the width direction of the glass ribbon and the central portion in a temperature region where the temperature of the central portion of the glass ribbon is a glass strain point The temperature gradient disappears in such a way as to control the temperature of the glass ribbon. A method for producing a glass substrate for a flat panel display, comprising: (1) a melting step of blending in a manner that a combined amount of SrO and BaO in the glass substrate to be produced is less than 8 mass% and has a strain point of 675 ° C or higher a raw material and melted; (2) a forming step of melting the glass-formed glass ribbon by melt-down method; and (3) a cooling step of cooling the formed glass ribbon; the cooling step comprising: first cooling a step of cooling to a temperature exceeding a slow cooling point; a second cooling step of cooling from a slow cooling point to a temperature of (strain point - 50 ° C); and a third cooling step of self-supplied (strain) The temperature at a point of -50 ° C) is cooled to a temperature near (strain point - 200 ° C); the average cooling rate in the first cooling step is 5.5 to 50.0 ° C / sec, and the average cooling rate in the second cooling step is 0.5 ~ less than 5.5 ° C / sec; in the above cooling step, the temperature is controlled in such a manner that at least the temperature at the center of the center of the width direction of the glass ribbon is increased from the slow cooling point of the glass by 150 ° C. Cold point +150 ° C) becomes the glass strain point minus In the temperature range of 200 ° C (strain point -200 ° C), the cooling rate of the center portion in the width direction of the glass ribbon is faster than the position The cooling rate of both edge portions at both ends in the width direction. The method for producing a glass substrate for a flat panel display according to claim 1, wherein in the melting step (1), the glass substrate produced exhibits a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ is a blend of raw materials. The method for producing a glass substrate for a flat panel display according to claim 2, wherein in the melting step (1), the glass substrate produced exhibits a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ is a blend of raw materials. The method for producing a glass substrate for a flat panel display according to any one of claims 1 to 4, wherein the glass substrate produced through the cooling step (3) is heated at a temperature of 10 ° C /min from normal temperature and maintained at 550 ° C for 1 hour. Thereafter, the temperature was lowered to room temperature at 10° C./min, and the temperature was raised again at 10° C./min and held at 550° C. for 1 hour. After the temperature was lowered to 10° C./min to room temperature, the heat shrinkage ratio represented by the following formula was 75 ppm or less; The shrinkage ratio (ppm) = {the amount of shrinkage of the glass before and after the heat treatment / the length of the glass before the heat treatment} × 10 ⁶ . A method for producing a glass substrate for a flat panel display, comprising: (1) a melting step of producing a glass substrate having a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ a raw material which is substantially free of BaO and has a strain point of 680 ° C or higher and is melted; (2) a forming step which is a molten glass forming glass ribbon which is self-melted by an overflow down-draw method; and (3) a cooling step The cooling zone is formed by cooling; the cooling step includes: a first cooling step of cooling to a point beyond the slow cooling point; and a second cooling step of cooling from a slow cooling point to (strain point -50 ° C) And the third cooling step, which is cooled from a temperature less than (strain point - 50 ° C) to a temperature near (strain point - 200 ° C); the average cooling rate of the first cooling step is 5.5 ~50.0 ° C / sec, the average cooling rate of the second cooling step is 0.5 to less than 5.5 ° C / sec; in the cooling step, (1) the temperature at the center of the center of the width direction of the glass ribbon is In the region above the softening point of the glass, in the width direction of the above glass ribbon The temperature of the both edge portions of the end is lower than the temperature of the central portion, and the temperature of the glass ribbon is controlled by the temperature of the central region sandwiched by the two edge portions, and (2) the width of the glass ribbon The glass ribbon is controlled such that the temperature in the central portion of the direction is not higher than the glass softening point and is higher than the glass strain point, and the temperature distribution in the width direction of the glass ribbon is lowered from the center portion toward the both edge portions. And (3) controlling the temperature gradient of the both edge portions and the center portion in the width direction of the glass ribbon in a temperature region in which the temperature of the center portion of the glass ribbon is a glass strain point is controlled The temperature of the above glass ribbon. A method for producing a glass substrate for a flat panel display, comprising: (1) a melting step of producing a glass substrate having a molar ratio of 9.5 or more (SiO ₂ + 2 × Al ₂ O ₃ ) / B ₂ O ₃ a raw material which is substantially free of BaO and has a strain point of 680 ° C or higher and is melted; (2) a forming step which is a molten glass forming glass ribbon which is self-melted by an overflow down-draw method; and (3) a cooling step The cooling zone is formed by cooling; the cooling step includes: a first cooling step of cooling to a point beyond the slow cooling point; and a second cooling step of cooling from a slow cooling point to (strain point -50 ° C) And the third cooling step, which is cooled from a temperature less than (strain point - 50 ° C) to a temperature near (strain point - 200 ° C); the average cooling rate of the first cooling step is 5.5 ~50.0 ° C / sec, the average cooling rate of the second cooling step is 0.5 to less than 5.5 ° C / sec; in the cooling step, the temperature is controlled as follows: at least as the center of the width direction of the glass ribbon The temperature at the center is increased from the slow cooling point of the glass to 150 ° C ( In the temperature region where the glass strain point is reduced by 200 ° C (strain point - 200 ° C), the cooling rate of the center portion in the width direction of the glass ribbon is faster than the both ends in the width direction. The cooling rate of the two edges. The method for producing a glass substrate for a flat panel display according to any one of claims 2 to 4, wherein the first cooling step includes a first temperature control step of both edge portions in a width direction of the glass ribbon. The temperature is lower than the temperature of the central portion sandwiched by the both edge portions, and the temperature of the central portion becomes uniform. The method for producing a glass substrate for a flat panel display according to any one of claims 2 to 4, wherein the second cooling step includes a third temperature control step of the glass in the vicinity of the strain point near the glass The temperature gradient of the edge portion and the center portion in the width direction of the belt is lowered. The method for producing a glass substrate for a flat panel display according to claim 8, wherein the second cooling step includes a third temperature control step of arranging the edge portion in the width direction of the glass ribbon as it approaches the strain point of the glass. The temperature gradient in the center portion is reduced.