TWI530469B - Glass substrate for display and method for manufacturing the same - Google Patents

Description

Glass substrate for display and manufacturing method thereof

The present invention relates to a glass substrate for a display and a method of manufacturing the same. In particular, the present invention relates to a low temperature polycrystalline germanium thin film transistor (hereinafter referred to as a LTPS-TFT (Low-Temperature-Polycrystalline-Silicon Thin-Film-Transistor)) glass substrate for display. Further, the present invention relates to an oxide semiconductor thin film transistor (hereinafter referred to as an OS-TFT (Oxide-Semiconductor Thin-Film-Transistor)) glass substrate for display. More specifically, the present invention relates to a glass substrate for a display in which the above display is a liquid crystal display. Or a glass substrate for a display in which the above display is an organic EL display. Furthermore, the present invention relates to a glass substrate for a flat panel display in which the display is a flat panel display.

A display mounted on a mobile device or the like is expected to use LTPS for manufacturing a thin film transistor (TFT) based on the reason that power consumption can be reduced. However, in the manufacture of LTPS-TFT, a relatively high temperature heat treatment of 400 to 600 ° C is required. On the other hand, displays for small mobile devices have been increasingly demanding in recent years. Therefore, heat shrinkage of the glass substrate generated when the display panel is manufactured, which causes variations in pixel pitch, becomes a problem. Moreover, the glass substrate which forms an OS-TFT has also been aimed at suppressing heat shrinkage similarly.

The heat shrinkage rate of the glass substrate can generally be lowered by increasing the strain point of the glass; increasing the glass transition point (hereinafter, Tg); or lowering the slow cooling rate.

Based on the above background, a technique for increasing the strain point of glass in order to reduce the heat shrinkage rate has been disclosed (Patent Document 1). Also, it is revealed that by adjusting the slow cooling point to the temperature near the strain point A technique in which the ratio of the slope of the average density curve in the degree region to the average linear expansion coefficient reduces heat shrinkage (Patent Document 2). Further, a technique for increasing the Tg in order to reduce the heat shrinkage ratio has been disclosed (Patent Document 3). Further, in recent years, the display panel has been increasingly refined, and the technique of Patent Document 3 has been insufficient for the reduction of the heat shrinkage rate. For this reason, a technique of making the strain point of the glass 725 ° C or higher is also disclosed (Patent Document 4).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-6649

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2004-315354

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2011-126728

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2012-106919

In recent years, due to the increasing demand for high definition, it has been sought to further reduce the heat shrinkage rate. When the strain point of the glass substrate is increased in order to further reduce the heat shrinkage rate, it is necessary to increase the content of SiO ₂ or Al ₂ O _{3 in} the glass, but as a result, the specific resistance of the molten glass tends to increase. In recent years, in order to efficiently melt glass in a melting tank, direct energization heating may be used. When the direct electric heating is used, when the specific resistance of the molten glass rises, the electric current flows not only to the molten glass but also to the refractory constituting the melting tank, and as a result, there is a problem that the melting groove is melted. However, in the invention described in the above Patent Document 1, there is no consideration of the specific resistance of the molten glass. Therefore, in the case where the glass described in Patent Document 1 is to be produced by melting by direct current heating, there is a strong concern that the melting loss of the melting tank occurs. Further, in recent years, in order to increase the refinement of the glass and to further increase the strain point of the glass, the above problems have become more apparent.

Moreover, since the strain point of the glass disclosed in the above Patent Document 2 is 682 to 699 ° C, Therefore, in order to sufficiently reduce the slope of the average density curve of heat shrinkage, it is necessary to minimize the slow cooling rate, and there is a problem that productivity is lowered. Further, in the glass disclosed in Patent Document 2, since the devitrification temperature is 1287 ° C or higher, there is a problem that devitrification easily occurs. Moreover, the above problems become particularly noticeable in the case of forming using the down-draw method.

Further, in the production of a display using a glass substrate, productivity is improved, and for example, productivity in a step of thinning a glass substrate on which a thin film transistor is formed is also improved. The productivity of the step of thinning the glass substrate largely depends on the time taken for the etching of the glass substrate. Therefore, in the display glass substrate, improvement in productivity and reduction in heat shrinkage rate due to an increase in etching rate are simultaneously achieved. However, the glass substrate described in Patent Document 4 has a problem that the strain point is high but the etching rate is not considered.

As described above, if the heat shrinkage rate of the glass substrate is to be lowered, there is a problem that the melting groove is melted by the increase in the specific resistance of the glass; the glass is devitrified; or it is difficult to simultaneously achieve productivity improvement due to an increase in the etching rate. Reduced heat shrinkage.

Therefore, the object of the present embodiment is to provide (1) a glass substrate which simultaneously achieves a high strain point and prevents melting of the melting tank caused by direct electric heating during melting of the glass, or (2) simultaneously achieving high strain point and suppressing forming. A glass substrate that is devitrified in the step, or (3) a glass substrate that simultaneously achieves a high strain point and a high etching rate, and a manufacturing method therefor. In particular, it is an object of the present embodiment to provide a glass substrate for a display suitable for use in a display using LTPS-TFT or OS-TFT and a method of manufacturing the same.

This embodiment has the following aspects.

[1] A glass substrate for a display, which is formed of glass containing SiO ₂ or Al ₂ O ₃ and expressed by mol%, B ₂ O ₃ is 0 to 8%, and R ₂ O is 0.01. ~0.8%, BaO/RO indicates that the content of the component in the formula is 0.05~1, and the strain point is 670 °C or more. Here, RO means (MgO+CaO+SrO+BaO), R ₂ O represents (Li ₂ O+Na ₂ O+K ₂ O).

[2] The glass substrate according to [1], wherein the content of SiO ₂ , Al ₂ O ₃ , and BaO is represented by mol%, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 8 to 20%, and BaO is 0.1. ~15%.

[3] The glass substrate of [1] or [2], wherein (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) The value calculated from the content of the component in the formula is 2.5 or more.

[4] A glass substrate for a display, which is formed of glass containing SiO ₂ 60 to 80%, Al ₂ O ₃ 8 to 20%, and B ₂ O ₃ 0 to 8%. , R ₂ O is 0.01 to 0.8%, and (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) The content of the component is calculated to be 2.5 or more, BaO/RO is 0.05 to 1, and the strain point is 670 ° C or more. Here, RO means (MgO + CaO + SrO + BaO), and R ₂ O means (Li ₂ O+Na ₂ O +K ₂ O).

[5] The glass substrate according to any one of [1] to [4], which contains MgO 0 to 15%, CaO 0 to 20%, SrO 0 to 15%, and BaO 0.1 to 15% in terms of mol%.

[6] The glass substrate according to any one of [1] to [5] wherein the molar ratio represented by SiO ₂ /Al ₂ O ₃ is less than 10.

[7] The glass substrate according to any one of [1] to [6] wherein, in terms of % by mol, the value of the component represented by the formula represented by B ₂ O ₃ +RO+ZnO is 15 ~25%.

[8] The glass substrate according to any one of [1] to [7] which further contains SnO ₂ and Fe ₂ O ₃ , expressed as % by mol, and the content of SnO ₂ is 0.03 to 0.15%, and SnO ₂ and Fe The total content of ₂ O ₃ is 0.05 to 0.2%.

[9] The glass substrate according to any one of [1] to [8], which is represented by mol%, containing SiO ₂ 66 to 72%, Al ₂ O ₃ 11 to 15%, and B ₂ O ₃ 0 to 8%. , MgO 0~6%, CaO 2~11%, SrO 0~1%, BaO 1~10%.

[10] The glass substrate according to any one of [1] to [9], which is represented by mol%, containing SiO ₂ 66 to 72%, Al ₂ O ₃ 11 to 15%, and B ₂ O ₃ 0 to 8%. , MgO 0~6%, CaO 2~11%, SrO 0~1%, BaO 1~10%, BaO/RO value is 0.1~0.5, CaO/RO value is 0.2~0.6, MgO/(RO+ The value of ZnO) is 0.15 to 0.6.

[11] The glass substrate according to any one of [1] to [10] which does not substantially contain La ₂ O ₃ and Y ₂ O ₃ .

[12] A glass substrate for a display comprising glass containing SiO ₂ , Al ₂ O ₃ , MgO, expressed in mole %, having MgO/(RO+ZnO) of 0.1 to 0.9 and a strain point of 700 ° C or more, The temperature was raised at a temperature increase rate of 10 ° C /min, and the temperature was maintained at 550 ° C for 2 hours, and the temperature was lowered to 400 ° C in 55 minutes, and then the heat shrinkage rate shown in the following formula was 5 ppm to 75 ppm when it was cooled to normal temperature. Heat shrinkage rate (ppm) = {shrinkage of glass before and after heat treatment / length of glass before heat treatment} × 10 ⁶

Here, RO means (MgO + CaO + SrO + BaO).

[13] A glass substrate for a display comprising SiO ₂ , Al ₂ O ₃ , and BaO, represented by mol%, BaO of 1 to 15%, substantially no Sb ₂ O ₃ , and strain point of 700 ° C or more The glass was heated at a temperature elevation rate of 10 ° C /min, held at 550 ° C for 2 hours, cooled to 400 ° C in 55 minutes, and then placed at room temperature to cool to room temperature, the heat shrinkage rate shown by the following formula 5ppm~75ppm.

[14] The glass substrate according to [12] or [13], wherein the content of SiO ₂ and Al ₂ O ₃ is expressed by mol%, SiO ₂ is 60 to 80%, and Al ₂ O ₃ is 8 to 20%.

[15] The glass substrate according to any one of [12] to [14] wherein, in terms of % of mol, MgO is from 1 to 15%.

[16] A glass substrate for display comprising 60% to 80% of SiO ₂ , 8 to 20% of Al ₂ O ₃ , 0 to 15% of B ₂ O _{3 ,} 1 to 15% of BaO, and MgO/ in terms of mol%. (RO + ZnO) is 0.1 to 0.9, the strain point is 700 ° C or more glass, the temperature is raised at a temperature increase rate of 10 ° C / min, held at 550 ° C for 2 hours, cooled to 400 ° C in 55 minutes, and then placed in cooling The heat shrinkage rate shown by the following formula at the normal temperature is 5 ppm to 75 ppm, and the heat shrinkage ratio (ppm) = {the shrinkage amount of the glass before and after the heat treatment/the length of the glass before the heat treatment} × 10 ⁶

Here, RO means (MgO + CaO + SrO + BaO).

[17] The glass substrate according to any one of [12] to [16] wherein, in terms of mol%, (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO) is 2.8~20.

[18] The glass substrate according to any one of [12] to [17] wherein, in terms of mol%, MgO is 1 to 15%, CaO is 0 to 20%, SrO 0~15%.

[19] The glass substrate according to any one of [12] to [18] wherein, in terms of mol%, SiO ₂ /Al ₂ O ₃ is 6.0 or less.

[20] The glass substrate according to any one of [12] to [19] which contains SnO ₂ and Fe ₂ O ₃ , expressed in mol%, SnO ₂ is 0.03 to 0.15%, and SnO ₂ and Fe ₂ O ₃ The total amount is 0.05~0.2%.

[21] The glass substrate according to any one of [12] to [20], which is represented by mol%, containing SiO ₂ 66 to 72%, Al ₂ O ₃ 11 to 15%, and B ₂ O ₃ 0 to 7%. , MgO 1~6%, CaO 2~11%, SrO 0~1%, BaO 1~10%.

[22] The glass substrate according to any one of [12] to [21], which is represented by mol%, containing SiO ₂ 66 to 72%, Al ₂ O ₃ 11 to 15%, and B ₂ O ₃ 0 to 7%. , MgO 1~6%, CaO 2~11%, SrO 0~1%, BaO 1~10%, BaO/RO value is 0.1~0.5, Ca/RO value is 0.2~0.6, MgO/(RO+ The value of ZnO) is 0.15 to 0.6.

[23] A glass substrate for a display, which is formed of glass containing SiO ₂ , Al ₂ O ₃ , and BaO, expressed by mol%, B ₂ O ₃ being 0 to 7%, and BaO being 1 ~15%, SiO ₂ /Al ₂ O ₃ is 6.0 or less, and the strain point is 700 ° C or more.

[24] The glass substrate according to [23], wherein the content of SiO ₂ and Al ₂ O ₃ is represented by mol%, SiO ₂ is 60 to 80%, and Al ₂ O ₃ is 10.5 to 20%.

[25] A glass substrate for a display, which is formed of glass containing SiO ₂ 60 to 80%, Al ₂ O ₃ 10.5 to 20%, and B ₂ O ₃ 0 to 7%. BaO 1~15%, substantially does not contain As ₂ O ₃ , RO is 10.0~18.0%, SiO ₂ /Al ₂ O ₃ is 3 or more, 5.7 or less, SrO<0.25×CaO, strain point is 700°C or more. Glass, here, RO means (MgO + CaO + SrO + BaO).

[26] The glass substrate according to any one of [23] to [25], which contains MgO 0 to 15%, CaO 0 to 20%, and SrO 0 to 8% in terms of mol%.

[27] The glass substrate of any one of [23] to [26], wherein SrO/RO is 0~0.1.

[28] The glass substrate according to any one of [23] to [27] wherein the CaO/RO is 0.1 to 0.8.

[29] The glass substrate according to any one of [23] to [28] which contains SnO ₂ and Fe ₂ O ₃ , expressed in mol%, SnO ₂ is 0.03 to 0.15%, and SnO ₂ and Fe ₂ O ₃ The total amount is in the range of 0.05 to 0.2%.

[30] The glass substrate according to any one of [23] to [29], which is represented by mol%, containing SiO ₂ 66 to 72%, Al ₂ O ₃ 11 to 15%, and B ₂ O ₃ 0 to 7%. , MgO 0~6%, CaO 2~11%, SrO 0~1%, BaO 1~10%.

[31] The glass substrate according to any one of [23] to [30], which is represented by mol%, containing SiO ₂ 66 to 72%, Al ₂ O ₃ 11 to 15%, and B ₂ O ₃ 0 to 7%. , MgO 0~6%, CaO 2~11%, SrO 0~1%, BaO 1~10%, BaO/RO value is 0.1~0.5, Ca/RO value is 0.2~0.6, MgO/(RO+ The value of ZnO) is 0.15 to 0.6.

[32] The glass substrate according to any one of [23] to [31] wherein the average thermal expansion coefficient at 100 to 300 ° C is 28.0 to 45.0 × 10 ^-7 ° C ^-1 .

[33] The glass substrate according to any one of [1] to [11], wherein (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O _{3 )} The value represented by +RO) is 3.1 or more.

[34] The glass substrate according to any one of [1] to [33] wherein the SiO ₂ -(1/2 × Al ₂ O ₃ ) is represented by the content of the component in the formula The value is less than 65%.

[35] The glass substrate according to any one of [1] to [34] which does not substantially contain As ₂ O ₃ .

[36] The glass substrate according to any one of [1] to [35] which does not substantially contain Sb ₂ O ₃ .

[37] The glass substrate according to any one of [1] to [22] wherein R ₂ O (Li ₂ O + Na ₂ O + K ₂ O) is 0.1 to 0.4%.

[38] The glass substrate according to any one of [1] to [22] wherein the average thermal expansion coefficient at 100 to 300 ° C is 28.0 to 50.0 × 10 ^-7 ° C ^-1 .

[39] The glass substrate according to any one of [1] to [38] which is a glass substrate formed by an overflow down-draw method.

[40] The glass substrate according to any one of [1] to [39] wherein a glass substrate for a flat panel display formed using a thin film transistor formed of a low temperature polycrystalline silicon or an oxide semiconductor is formed on a surface of the glass substrate.

[41] The glass substrate according to [1] to [40], which is a glass substrate for a liquid crystal display or an organic EL display.

[42] The glass substrate according to [1] to [41] wherein the glass substrate is a glass substrate for a display other than a CRT (Brown Tube) display.

[43] A method for producing a glass substrate for a display according to any one of [1] to [42], comprising the step of melting a glass raw material of a predetermined composition by at least direct electric heating; a step of forming the molten glass melted by the melting step into a flat glass; and The flat glass is slowly cooled, and a slow cooling step of cooling the flat glass is controlled so as to lower the heat shrinkage rate of the flat glass.

[44] The production method according to [43], wherein the melting step is to melt the glass raw material in a melting tank composed of at least a high zirconia-based refractory.

[45] The method according to [43] or [44] wherein the slow cooling step is in a temperature range of Tg to (Tg - 100 ° C), and the cooling rate of the flat glass is 30 to 300 ° C / min. The method is to slowly cool the flat glass.

[46] A display using the glass substrate for a display according to any one of [1] to [45].

According to one aspect of the above-mentioned glass substrate, it becomes possible to suppress or avoid the melt loss of the glass melting tank, and to manufacture a high strain point glass.

Further, according to one aspect of the above-described glass substrate, it is possible to manufacture a glass having a high strain point and suppressing devitrification at the time of molding.

Further, according to one aspect of the above-described glass substrate, it is possible to manufacture a glass substrate which simultaneously realizes a high strain point and a high etching rate.

Thereby, it is possible to provide a glass substrate for a display which can reduce heat shrinkage when manufacturing a display, and in particular, a glass substrate for display suitable for a flat panel display using LTPS-TFT or OS-TFT.

In the specification of the present application, the composition of the glass is expressed by mol% (mol%) unless otherwise specified, and the mol% means an index indicating the content in %. The ratio of the constituents constituting the glass composition is expressed by the molar ratio.

In one embodiment of the glass substrate for a display of the present embodiment, the high strain point is simultaneously achieved and the melting groove of the melting tank caused by direct electric heating during melting of the glass is prevented. The glass substrate contains SiO ₂ and Al ₂ O ₃ and is expressed by mol%, B ₂ O ₃ is 0 to 8%, R ₂ O is 0.01 to 0.8%, BaO/RO is 0.05 to 1, and strain point is 670 ° C. the above.

In the present specification, RO means (MgO + CaO + SrO + BaO), and R ₂ O means (Li ₂ O + Na ₂ O + K ₂ O).

The content of SiO ₂ , Al ₂ O ₃ and BaO is preferably expressed by mol%, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 8 to 20%, and BaO is 0.1 to 15%.

More preferably, the glass substrate for a display of the present invention contains 60% to 80% of SiO ₂ , 8 to 20% of Al ₂ O ₃ , 0 to 8% of B ₂ O ₃ , and 0.01 to 0.8% of R ₂ O. (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) is 2.5 or more, BaO / RO is 0.05 - 1, and the strain point is 670 ° C the above.

The glass substrate described above is described as a glass substrate (A) in the following examples.

In another embodiment of the glass substrate for a display of the present embodiment, the high strain point is simultaneously achieved and the devitrification in the molding step is suppressed. The glass substrate comprises glass containing SiO ₂ , Al ₂ O ₃ , MgO, expressed in mole %, MgO/(RO+ZnO) of 0.1 to 0.9, strain point of 700 ° C or more, and a temperature increase rate of 10 ° C/min. The temperature was raised, the temperature was maintained at 550 ° C for 2 hours, the temperature was lowered to 400 ° C in 55 minutes, and the heat shrinkage ratio shown by the following formula when it was left to cool to room temperature was 5 ppm to 75 ppm.

Here, RO means (MgO + CaO + SrO + BaO).

In this form, since MgO/(RO+ZnO) is set to 0.1 to 0.9, a high strain point can be maintained, and devitrification at the time of molding can be suppressed. Further, by setting MgO/(RO+ZnO) to 0.1 to 0.9, the meltability of the glass can be maintained. Further, since the heat shrinkage ratio is 5 ppm to 75 ppm, it is suitably used as a glass substrate for a display suitable for a display using LTPS-TFT or a glass substrate for a display using OS-TFT.

Further, it includes glass containing SiO ₂ , Al ₂ O ₃ , and BaO, expressed as mole %, BaO being 1 to 15%, substantially containing no Sb ₂ O ₃ , and having a strain point of 700 ° C or more, at 10 ° C / min. The temperature was raised at a temperature rising rate, and the temperature was raised at 550 ° C for 2 hours, and the temperature was lowered to 400 ° C in 55 minutes. Thereafter, when the temperature was cooled to normal temperature, the heat shrinkage ratio shown by the following formula was 5 ppm to 75 ppm.

In this form, since the content of BaO is set to 1 to 15%, the high strain point can be maintained, and the devitrification temperature of the glass can be effectively lowered. Since the heat shrinkage ratio is 5 ppm to 75 ppm, it is suitably used as a glass substrate for a display suitable for a display using LTPS-TFT or a glass substrate for a display using OS-TFT.

Further, the content of SiO ₂ and Al ₂ O _{3 is} preferably expressed by mol%, SiO ₂ is 60 to 80%, and Al ₂ O ₃ is 8 to 20%.

More preferably, one form of the glass substrate for a display according to the present embodiment includes 60% to 80% of SiO ₂ , 8 to 20% of Al ₂ O ₃ , 0 to 15% of B ₂ O ₃ , and BaO 1 to 15 in terms of mol%. %, MgO / (RO + ZnO) is 0.1 ~ 0.9, the strain point is 700 ° C or more glass, the temperature is raised at 10 ° C / min, the temperature is maintained at 550 ° C for 2 hours, 55 minutes to 450 ° C, Thereafter, the heat shrinkage ratio shown by the following formula when it is cooled to normal temperature is 5 ppm to 75 ppm.

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

In this embodiment, since MgO/(RO+ZnO) is set to 0.1 to 0.9, the content of BaO is set to 1 to 15%, so that a low devitrification temperature can be maintained and the strain point of the glass can be increased. Further, since the heat shrinkage ratio is 5 ppm to 75 ppm, it is suitably used as a glass substrate for a display suitable for a display using LTPS-TFT or a glass substrate for a display using OS-TFT.

The glass substrate described above is described as a glass substrate (B) in the following examples.

In still another embodiment of the glass substrate for a display of the present embodiment, a high strain point and a high etching rate are simultaneously achieved. The glass substrate contains SiO ₂ , Al ₂ O ₃ , and BaO, and is expressed by mol%, B ₂ O ₃ is 0 to 7%, BaO is 1 to 15%, and SiO ₂ /Al ₂ O ₃ is 6.0 or less. It is above 700 °C.

By setting the B ₂ O ₃ content to 0 to 7%, the high temperature viscosity of the glass can be lowered, and the meltability can be improved.

By setting the content of BaO to 1 to 15%, the devitrification temperature can be effectively lowered while maintaining the strain point of the glass high.

By setting SiO ₂ /Al ₂ O ₃ to 6.0 or less, the etching rate can be improved.

Further, by setting the strain point of the glass to 700 ° C or higher, the heat shrinkage rate can be controlled to a specific range.

Further, the content of SiO ₂ and Al ₂ O _{3 is} preferably expressed by mol%, SiO ₂ is 60 to 80%, and Al ₂ O ₃ is 10.5 to 20%.

By setting SiO ₂ to 60 to 80%, it is possible to reduce the density of the glass while suppressing an increase in the thermal expansion coefficient of the glass. Further, by setting Al ₂ O ₃ to 10.5 to 20%, it is possible to suppress an increase in the devitrification temperature while suppressing a decrease in the strain point.

More preferably, it contains SiO ₂ 60-80%, Al ₂ O ₃ 10.5-20%, B ₂ O ₃ 0-7%, BaO 1-15%, and substantially no As ₂ O ₃ , RO. It is 10.0 to 18.0%, SiO ₂ /Al ₂ O ₃ is 3 or more and 5.7 or less, SrO < 0.25 × CaO, and the strain point is 700 ° C or more.

Here, RO means (MgO + CaO + SrO + BaO).

By setting RO to 10.0 to 18.0%, it is possible to reduce the density while maintaining the meltability, and to suppress an increase in the thermal expansion coefficient.

By setting SiO ₂ /Al ₂ O ₃ to 3 or more and 5.7 or less, high strain point, devitrification resistance, and etching rate can be simultaneously achieved.

By setting SrO < 0.25 x CaO, the devitrification temperature of the glass can be effectively lowered.

Further, by setting the strain point of the glass to 700 ° C or higher, the heat shrinkage rate can be controlled to a specific range.

The glass substrate described above is described as a glass substrate (C) in the following examples.

Hereinafter, an embodiment of the glass substrate for a display of the present embodiment will be described.

Since the SiO ₂ -based glass has a skeleton component, it is an essential component. If the content is decreased, there is a tendency that the strain point is lowered and the coefficient of thermal expansion 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 specific resistance of the molten glass increases, the melting temperature remarkably increases, and melting tends to be difficult. When the content of SiO _{2 is} too large, the devitrification temperature increases and the devitrification resistance tends to decrease. Further, when the content of SiO _{2 is} too large, the etching rate becomes slow. From this point of view, the content of SiO ₂ is preferably in the range of 60 to 80 mol%. The content of SiO ₂ is more preferably 64 to 73 mol% or 65 to 75 mol%, more preferably 66 to 72 mol%, still more preferably 67 to 71 mol%.

The Al ₂ O ₃ system is an essential component for increasing the strain point. If the Al ₂ O ₃ content is too small, the strain point is lowered. Further, when the content of Al ₂ O _{3 is} too small, the Young's modulus and the etching rate by the acid tend to decrease. On the other hand, when the content of Al ₂ O _{3 is} too large, the devitrification temperature of the glass increases, and the devitrification resistance decreases, so that the moldability tends to be deteriorated. From this point of view, the content of Al ₂ O ₃ is in the range of 8 to 20 mol%. The content of Al ₂ O ₃ is preferably from 10 to 17 mol%, more preferably from 10.5 to 17 mol%, still more preferably from 11 to 15 mol%, still more preferably from 12 to 15 mol%.

B ₂ O ₃ is a component which lowers the high temperature viscosity of glass and improves the meltability. That is, since the viscosity in the vicinity of the melting temperature is lowered, the meltability is improved. Further, B ₂ O _{3 is} also a component which lowers the devitrification temperature. When the content of B ₂ O _{3 is} small, there is a tendency that the meltability and the devitrification resistance are lowered. If the B ₂ O ₃ content is too large, the strain point and the Young's modulus are lowered. Further, devitrification is likely to occur due to volatilization of B ₂ O ₃ during glass forming. In particular, since the glass having a high strain point tends to have a high molding temperature, the above-described volatilization is promoted, and the occurrence of devitrification becomes conspicuous. Further, due to the volatilization of B ₂ O ₃ at the time of glass melting, the unevenness of the glass becomes conspicuous, and streaks are likely to occur. In this regard, the B ₂ O ₃ content is 0 to 15 mol%, preferably 0 to 8 mol%, more preferably 0 to 7 mol%, more preferably 0.1 to 6 mol%, more preferably The ratio is preferably 1 to 5 mol%, more preferably 1.5 to 4.5 mol%.

The MgO system enhances the composition of the meltability. Moreover, since it is a component which does not easily increase density in an alkaline earth metal, it is easy to reduce density by relatively increasing the content. By containing MgO, the specific resistance and melting temperature of the molten glass can be lowered. However, if the content of MgO is too large, the devitrification temperature of the glass rises sharply, and thus it becomes easy to devitrify especially in the molding step. From this point of view, the MgO content is 0 to 15 mol%, preferably 1 to 15 mol%, more preferably 0 to 6 mol%, still more preferably 1 to 6 mol%. Or the MgO content is preferably from 0 to 15 mol%, more preferably from 0 to 6 mol%, more preferably from 1 to 6 mol%.

The CaO system is a component which is effective for improving the meltability of the glass without impairing the devitrification temperature of the glass. Further, since it is a component which is less likely to increase in density in the alkaline earth metal oxide, when the content is relatively increased, it is easy to reduce the density. If the content is too small, the specific resistance of the molten glass increases and the devitrification resistance tends to decrease. If the CaO content is too large, the coefficient of thermal expansion increases and the density tends to increase. From this point of view, the CaO content is 0 to 20 mol%, preferably 1 to 15 mol%, more preferably 2 to 11 mol%, still more preferably 4 to 9 mol%.

The SrO system reduces the composition of the devitrification temperature of the glass. SrO is not an essential component, and if it is contained, devitrification resistance and meltability are improved. However, if the SrO content is too large, the density will increase. From this point of view, the SrO content is 0 to 15 mol%, preferably 0 to 8 mol%, more preferably 0 to 3 mol%, more preferably 0 to 1 mol%, more preferably 0. A range of ~0.5% by mole, more preferably substantially not contained.

The BaO system can effectively reduce the devitrification temperature of the glass and the essential components of the specific resistance of the molten glass. When BaO is contained, devitrification resistance and meltability are improved. However, if the content of BaO is too large, the density will increase. Further, the BaO content is 0 to 15 mol% or 0.1 to 15 mol%, preferably 1 to 15 mol%, more preferably 1 based on the viewpoint of the environmental burden and the tendency to increase the coefficient of thermal expansion. ~10% by mole, more preferably 1.5 to 6% by mole.

Li ₂ O and Na ₂ O are components which increase the thermal expansion coefficient of the glass and may cause damage to the substrate during heat treatment. Also, it is to reduce the composition of the strain point. On the other hand, since the specific resistance of the molten glass can be lowered, by containing these components, corrosion of the melting tank can be suppressed. From the above viewpoints, the content of Li ₂ O is preferably from 0 to 0.5 mol%, more preferably substantially not contained. The content of Na ₂ O is preferably 0 to 0.5 mol%, more preferably 0 to 0.2 mol%. Further, since Na ₂ O is more difficult to lower the composition of the strain point than Li ₂ O, Na ₂ O>Li ₂ O is preferable. Further, from the viewpoint of preventing the TFT characteristics from being melted from the glass substrate, Li ₂ O and Na ₂ O are preferably substantially not contained.

K ₂ O is a component that enhances the basicity of the glass and promotes clarification. Further, in order to lower the specific resistance of the molten glass. When K ₂ O is contained, the specific resistance of the molten glass is lowered, so that the current can be prevented from flowing to the refractory constituting the melting tank, and the melting tank can be prevented from being corroded. Further, when the refractory material constituting the melting tank contains zirconia, it is possible to suppress the corrosion of the melting tank and melt the zirconia from the melting tank to the molten glass, so that devitrification caused by zirconia can also be suppressed. Further, since the glass viscosity in the vicinity of the melting temperature is lowered, the meltability and the clarity are improved. On the other hand, when the K ₂ O content is too large, the thermal expansion coefficient increases and the strain point tends to decrease. From this point of view, 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%.

ZrO ₂ and TiO ₂ are components that increase the strain point of the glass. However, when the amount of ZrO _{2 and the} amount of TiO ₂ become too large, the devitrification temperature is remarkably increased, and thus the devitrification resistance tends to be lowered. In particular, since ZrO ₂ is hard to melt due to a high melting point, it causes a problem that a part of the raw material is deposited on the bottom of the melting tank. When these unmelted components are mixed into the glass slab, the quality of the glass is deteriorated as an inclusion. Further, since TiO ₂ is a component that colors the glass, it is not preferable for the substrate for display. In this regard, in the glass substrate of the present embodiment, the content of ZrO ₂ and TiO ₂ is preferably 0 to 5 mol %, more preferably 0 to 2 mol %, more preferably substantially Does not contain.

ZnO is a component that improves the meltability. But it is not an essential ingredient. When the ZnO content is too large, the devitrification temperature rises, the strain point decreases, and the density tends to increase. From this point of view, the ZnO content is preferably from 0 to 5 mol%, more preferably from 0 to 2 mol%, and more preferably substantially not contained.

P ₂ O ₅ is a component that lowers high temperature viscosity and improves meltability. But it is not an essential ingredient. If the P ₂ O ₅ content is too large, the strain point is lowered. Further, due to the volatilization of P ₂ O ₅ at the time of glass melting, the unevenness of the glass becomes conspicuous, and streaks are likely to occur. From this point of view, the P ₂ O ₅ content is preferably 0 to 3 mol%, more preferably 0 to 1 mol%, more preferably 0 to 0.5 mol%, and more preferably substantially no content. .

The glass substrate of this embodiment may contain a clarifying agent. The clarifying agent is not particularly limited as long as it has a small burden on the environment and excellent transparency of the glass, and examples thereof include a metal oxide selected from the group consisting of Sn, Fe, Ce, Tb, Mo, Sb, and W. At least one of the groups. As the clarifying agent, SnO _{2 is} suitably used. When the content of the clarifying agent is too small, the quality of the bubbles is deteriorated, and if it is too large, devitrification, coloring, or the like may occur. The amount of clarifying agent also depends on the type of clarifying agent or the composition of the glass. For example, the total amount of SnO ₂ , Fe ₂ O ₃ and Sb ₂ O ₃ is preferably 0.05 to 0.50 mol%, more preferably 0.05 to 0.20 mol%.

The SnO ₂ system can obtain a clarifying agent for clarifying effects even at a temperature of 1600 ° C or higher, and can be used for producing a glass substrate for a flat panel display (for example, Li) which can contain only a small amount of Li ₂ O, Na ₂ O, and K ₂ O. ₂ O, Na ₂ O and K ₂ O of the total amount of 0.01 to 0.8 mole%) of a few refining agents. However, since SnO ₂ itself is a component which is prone to devitrification and is a component which promotes devitrification of other components, it is not preferable to add a large amount from the viewpoint of suppressing devitrification.

Also, glass with a higher strain point (for example, glass with a strain point of 670 ° C or higher or glass with a temperature of 700 ° C or higher) and glass with a lower strain point (for example, glass with a strain point of less than 670 ° C or glass of less than 700 ° C) In contrast, the devitrification temperature tends to be high, and in order to suppress devitrification, it is necessary to make the temperature of the molten glass in the molding step higher than the glass having a lower strain point. Here, from the viewpoint of resistance to latent denaturation and heat resistance, the molded body used in the overflow down-draw method preferably comprises a refractory containing zirconia. In the case where the overflow down drawing is employed as the forming method, it is necessary to increase the temperature of the formed body in accordance with the attempt to increase the temperature of the molten glass in the forming step. However, when the temperature of the molded body is increased, zirconia is melted from the molded body, and there is a problem that the zirconia is devitrified. And, in particular, contains a large amount of SnO ₂ in the glass, there is likely to occur due to the loss of the zirconium oxide SnO ₂ of the lens, zirconium devitrification tendency caused by the oxidation of the SnO _2.

Further, a glass having a higher strain point (for example, a glass having a strain point of 670 ° C or more or a glass of 700 ° C or higher) and a glass having a lower strain point (for example, a glass having a strain point of less than 670 ° C or a glass of less than 700 ° C) In contrast, there is a tendency that the temperature at which the glass raw material is melted is also likely to become high. Here, from the viewpoint of corrosion resistance, the melting tank that performs the melting step is preferably composed of a high zirconia-based refractory containing zirconia. Further, from the viewpoint of energy efficiency, it is preferred to melt the glass raw material by electrofusion or electrofusion in combination with other heating methods. However, when the glass having a high strain point described in the present embodiment and containing only a small amount of Li ₂ O, Na ₂ O, and K ₂ O is melted, the specific resistance of the molten glass is large, and the current flows high. The zirconia-based refractory material has a problem that zirconia is easily melted into the molten glass. If the zirconia is melted, the devitrification of the above-mentioned zirconia and the devitrification of SnO ₂ tend to occur.

That is, from the viewpoint of suppressing devitrification of zirconia and SnO ₂ , in the glass substrate of the present embodiment, SnO _{2 is} not preferably contained in an amount exceeding 0.5 mol%. From this point of view, the SnO ₂ content is, for example, preferably 0 or more and less than 0.5 mol%, preferably 0.01 to 0.5 mol%, more preferably 0.01 to 0.2 mol%, still more preferably 0.03 to 0.15 mol. The ear % is more preferably in the range of 0.05 to 0.12 mol%.

In addition to the function as a clarifying agent, the Fe ₂ O ₃ system also lowers the specific resistance of the molten glass. Among the glasses having high viscosity at high temperature and difficult to be melted, it is preferred to contain Fe ₂ O _{3 in} order to lower the specific resistance of the molten glass. However, if the Fe ₂ O ₃ content is too large, the glass will be colored and the transmittance will be 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%, more preferably 0.003 to 0.05 mol%, more preferably 0.005~0.03% of the range of moles.

In the present embodiment, the clarifying agent is preferably used in combination of SnO ₂ and Fe ₂ O ₃ . From the viewpoint of suppressing devitrification, it is not preferable to contain a large amount of SnO ₂ as described above. However, in order to sufficiently obtain a clarifying effect, it is required to contain a clarifying agent having a specific value or more. Therefore, by using SnO _{2 in} combination with Fe ₂ O ₃ , a sufficient clarifying effect can be obtained without deteriorating the content of SnO ₂ as much as possible, and a glass substrate having few bubbles can be produced. The total amount of SnO ₂ and Fe ₂ O ₃ is preferably in the range of 0.05 to 0.2 mol%, more preferably 0.07 to 0.2 mol%, still more preferably 0.08 to 0.18 mol%, still more preferably 0.09 to 0.15 mol%. The range of %.

When the content of SnO ₂ is too large relative to the molar ratio of SnO ₂ and Fe ₂ O ₃ (SnO ₂ /(SnO ₂ +Fe ₂ O ₃ )), devitrification is likely to occur, and if it is too small, sufficient seizure cannot be obtained. The clarifying effect is the case of glass coloring. Therefore, it is preferably in the range of 0.6 to 0.95, more preferably in the range of 0.65 to 0.9.

The glass substrate of the present embodiment preferably contains substantially no As ₂ O ₃ based on the environmental burden. The glass substrate of the present embodiment has a problem of environmental burden, and Sb ₂ O _{3 is} preferably 0 to 0.5 mol% (including 0), more preferably 0 to 0.3 mol%, and even more preferably 0 to 0.05 mol%. The range is preferably not substantially contained.

The glass substrate of the present embodiment preferably contains substantially no PbO or F for environmental reasons.

In the present specification, the term "substantially not contained" means that the glass raw material is not used as a raw material of the components, and is not excluded from the glass raw material of other components as a component contained as an impurity. Manufacturing device for self-melting tank, molded body, etc. The incorporation of the components that are melted into the glass.

When the amount of SiO _{2 and} the content of Al ₂ O _{3 are} twice as large as SiO ₂ + (2 × Al ₂ O ₃ ), the strain point tends to decrease, and if it is too large, the devitrification resistance is deteriorated. The tendency. Therefore, SiO ₂ + (2 × Al ₂ O ₃ ) is preferably 100 mol% or less, preferably 75 to 100 mol%, more preferably 80 to 100 mol%, and even more preferably 92 to 98 mol. The range of ear %.

If the difference between the ₂ O ₃ content of 1/2 of the content of SiO ₂ and _{Al SiO 2 - (1/2} × Al 2 O 3) the value is too large, there is reduced risk of the etching rate. From this point of view, SiO ₂ -(1/2 × Al ₂ O ₃ ) is preferably 69 mol% or less, more preferably less than 65 mol%. On the other hand, when the value of SiO ₂ -(1/2 × Al ₂ O ₃ ) is too small, the devitrification resistance is lowered. From this point of view, SiO ₂ -(1/2×Al ₂ O ₃ ) is preferably from 45 mol% to 69 mol%, more preferably 55 mol% or more and less than 65 mol%, more preferably It is 60~64% by mole.

If the value of Mohr is too large for SiO ₂ /Al ₂ O ₃ , there is a possibility that the etching rate is lowered. From this point of view, the molar ratio of SiO ₂ /Al ₂ O _{3 is} preferably less than 10, more preferably 6.0 or less, still more preferably 5.7 or less, or less than 5.7. On the other hand, when the value of SiO ₂ /Al ₂ O ₃ is too small, the devitrification resistance is lowered. From this point of view, the molar ratio of SiO ₂ /Al ₂ O _{3 is} preferably 3.5 or more and less than 10, more preferably 4.0 to 6.0, still more preferably 4.5 or more and less than 5.7. Or the molar ratio of SiO ₂ /Al ₂ O _{3 is} preferably 3.0 to 5.7, more preferably 3.5 to 5.7, still more preferably 4.0 to 5.7, still more preferably 4.5 to 5.6.

Further, regarding the glass having a composition having an approximate value of SiO ₂ + (2 × Al ₂ O ₃ ), the etching rate more significantly depends on SiO ₂ /Al ₂ O ₃ . From the viewpoint of achieving high strain point, devitrification resistance, and etching rate at the same time, SiO ₂ + (2 × Al ₂ O ₃ ) is preferably 75 to 100 mol% and SiO ₂ /Al ₂ O _{3 is} preferable. It is 3.5 or more and less than 10, more preferably SiO ₂ + (2 × Al ₂ O ₃ ) is 92 to 98 mol% and SiO ₂ /Al ₂ O ₃ is in the range of 4.0 to 6.0.

If the B ₂ O ₃ and P the total amount of B ₂ O ₅ of the ₂ O ₃ + P ₂ O ₅ is too small, it tends to melting decrease of, if too large, the B ₂ O ₃ + P glass ₂ O ₅ of inhomogeneous It becomes obvious that it becomes easy to produce streaks, and there is a tendency that strain points are lowered. Therefore, B ₂ O ₃ + P ₂ O _{5 is} preferably 0 to 15 mol%, preferably 0 to 8 mol%, more preferably 0 to 7 mol%, still more preferably 0.1 to 6 mol%. More preferably, it is 1 to 5 mol%, more preferably 1.5 to 4.5 mol%.

MgO, CaO, SrO, and BaO are components which lower the specific resistance and melting temperature of the molten glass to improve the meltability. When the total amount of MgO, CaO, SrO, and BaO is too small, MgO+CaO+SrO+BaO (hereinafter referred to as RO) is too small, and the meltability is deteriorated. If the RO is too large, the strain point and the Young's modulus are lowered, and the density and the coefficient of thermal expansion are increased. In this regard, the RO is preferably in the range of 5 to 25 mol%, more preferably 8 to 18 mol%, more preferably 10 to 18 mol%, still more preferably 10 to 17 mol%. .

Mohr ratio (SiO ₂ + (2 × Al ₂ O ₃ )) / (2 × B ₂ O ₃ ) + RO) is mainly an indicator of strain point and resistance to devitrification. If the value is too small, the strain point is lowered. On the other hand, if the value is too large, the meltability and the devitrification resistance are lowered. Therefore, the molar ratio (SiO ₂ + (2 × Al ₂ O ₃ )) / (2 × B ₂ O ₃ ) + RO) is preferably 2.8 to 20, more preferably 3.1 to 20, still more preferably 3.1 to 15 More preferably, it is 3.5 to 10, more preferably 3.7 to 7.

In order to effectively lower the devitrification temperature without excessively reducing the strain point, or to effectively lower the devitrification temperature without excessively reducing the strain point without excessively increasing the specific resistance, BaO/RO is 0.05 to 1, More preferably, it is 0.05 to 0.6, more preferably 0.1 to 0.5.

In order to effectively lower the devitrification temperature without excessively increasing the density, CaO/RO is preferably from 0.1 to 0.8, more preferably from 0.2 to 0.7, still more preferably from 0.2 to 0.6, still more preferably from 0.2 to 0.5.

Moerbi MgO/(RO+ZnO) is an indicator of resistance to devitrification and melting. The MgO/(RO+ZnO) is preferably 0.1 to 1, more preferably 0.1 to 0.9, still more preferably 0.1 to 0.85, still more preferably 0.15 to 0.7, still more preferably 0.15 to 0.6. By setting these ranges, the devitrification resistance and the meltability can be simultaneously achieved. Further, it is possible to reduce the density.

In order to reduce the content of SiO ₂ (for example, the content of SiO ₂ is 80 mol% or less) and the content of Al ₂ O ₃ is large (for example, the content of Al ₂ O ₃ is 8 mol% or more) The temperature is effectively lowered, preferably SrO < 0.25 x CaO. That is, it is preferable that the SrO content is less than 0.25 times the CaO content, more preferably SrO < 0.2 × CaO, more preferably SrO < 0.1 × CaO. Or the molar ratio SrO/RO is preferably 0 to 0.1.

Li ₂ O, Na ₂ O, and K ₂ O are components which increase the basicity of the glass and facilitate the oxidation of the clarifying agent to exhibit clarification. Further, it is a component which lowers the viscosity at the melting temperature and improves the meltability. Further, it is also a component that lowers the specific resistance of the molten glass. When Li ₂ O, Na ₂ O, and K ₂ O are contained, the specific resistance of the molten glass is lowered, and the clarity and meltability are improved. In particular, it is possible to prevent excessive current from flowing to the refractory constituting the melting tank, and it is possible to suppress corrosion of the melting tank. Further, when the melting bath contains zirconia, it is possible to suppress the zirconia from being melted from the melting tank to the glass, so that devitrification caused by zirconia can also be suppressed. Further, since the viscosity of the molten glass is lowered, the meltability and the clarification property are improved. However, when the total amount of the contents of Li ₂ O, Na ₂ O, and K ₂ O is too large, these may be melted from the glass substrate, and the TFT characteristics may be deteriorated. Further, there is a tendency that the strain point is lowered and the coefficient of thermal expansion is increased. The total content of Li ₂ O, Na ₂ O and K ₂ O (hereinafter referred to as R ₂ O) is 0 to 0.8 mol%, more preferably 0.01 to 0.8 mol%, more preferably 0.01 to 0.5 mol. The ear % is more preferably 0.1 to 0.4 mol%, more preferably 0.2 to 0.3 mol%.

K ₂ O has a larger molecular weight than Li ₂ O or Na ₂ O, and thus is not easily melted from the glass substrate. Thus, preferred ₂ O or Na ₂ O and K is comprising more than Li ₂ O. When the ratio of Li ₂ O and Na ₂ O is large, these may be melted from the glass substrate, which may increase the fear of deteriorating the TFT characteristics. The molar ratio K ₂ O/R ₂ O is preferably from 0.5 to 1, more preferably from 0.6 to 1, more preferably from 0.65 to 1, more preferably from 0.7 to 1.

The molar ratio (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) mainly becomes an index of strain point and meltability. If the value is too small, the strain point is lowered. Therefore, the molar ratio (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) is 2.5 or more, preferably 3.0 or more. On the other hand, if the value is too large, the meltability and the devitrification resistance are lowered. Therefore, the molar ratio ((SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O))) is preferably 2.5 to 22, more preferably 3.0 The range of ~10. (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) is preferably 3.5 to 7.

RE ₂ O ₃ refers to the total amount of rare earth metal oxides, and examples of the rare earth metal oxide include Sc ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , Pr ₂ O ₃ , Nd ₂ O ₃ , and Sm _{2 .} O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ . RE ₂ O ₃ is a component that increases the density and coefficient of thermal expansion. Moreover, it is a component with a high cost. Therefore, RE ₂ O ₃ is 0 or more and less than 1.0 mol% (including 0), more preferably 0 to 0.5 mol% (including 0), and particularly preferably substantially not contained.

From the viewpoint of preventing an increase in density and thermal expansion coefficient and reducing cost, Y ₂ O ₃ and La ₂ O are preferably substantially not contained.

In the glass substrate of the present embodiment, the devitrification temperature is preferably 1280 ° C or lower, more preferably 1250 ° C or lower, and still more preferably 1210 ° C or lower. The lower the devitrification temperature, the easier the formation of the glass sheet by the overflow down-draw method. By applying the overflow down-draw method, the step of grinding the surface of the glass substrate can be omitted, so that the surface quality of the glass substrate can be improved. In addition, production costs can also be reduced. If the devitrification temperature is too high, devitrification tends to occur, and thus it tends to be difficult to apply to the overflow down-draw method.

The average thermal expansion coefficient (100 to 300 ° C) of the glass substrate of the present embodiment at 100 ° C to 300 ° C is 50.0 × 10 ^-7 ° C ^-1 or less, preferably 28.0 to 50.0 × 10 ^-7 ° C ^-1 , more preferably It is 33.0 to 46.0 × 10 ^-7 ° C ^-1 , more preferably 33.0 to 45.0 × 10 ^-7 ° C ^-1 , more preferably 35.0 or more and less than 43.0 × 10 ^-7 ° C ^-1 , more preferably 38.0 to 43.0 × 10 ^-7 °C ^-1 range. If the coefficient of thermal expansion is large, there is a tendency that the thermal shock or the heat shrinkage rate increases in the heat treatment step. Moreover, if the coefficient of thermal expansion is large, it becomes difficult to lower the heat shrinkage rate. Further, regardless of whether the coefficient of thermal expansion is large or small, it becomes difficult to achieve integration with the thermal expansion coefficient of a peripheral material such as a metal or a film formed on a glass substrate, and there is a possibility that the peripheral member is peeled off.

In general, if the glass substrate has a low strain point, heat shrinkage easily occurs in the heat treatment step at the time of manufacturing the display. Regarding the glass substrate of the present embodiment, the strain point It is 670 ° C or higher, more preferably 700 ° C or higher, and even more preferably 710 ° C or higher.

The glass substrate of the present embodiment preferably has a heat shrinkage ratio of 90 ppm or less or 75 ppm or less. If the heat shrinkage rate becomes too large, a large deviation of the pixels is caused, and it becomes impossible to realize a high-definition display. In order to control the heat shrinkage rate to a specific range, it is preferable to set the strain point of the glass substrate to 670 ° C or higher or 700 ° C or higher. In addition, when the heat shrinkage rate is set to 0 ppm, it is required to extend the slow cooling step as much as possible, or to perform the heat shrinkage reduction treatment (offline slow cooling) after the slow cooling and cutting steps. In this case, the productivity is lowered and the cost is lowered. high. The heat shrinkage ratio is preferably, for example, 3 to 90 ppm, 3 to 75 ppm, or 5 to 75 ppm, more preferably 5 ppm to 60 ppm, still more preferably 10 ppm to 55 ppm, still more preferably 15 ppm to 50 ppm, in view of productivity and cost.

Further, the heat shrinkage ratio is a value represented by the following formula after heat treatment of the glass substrate, the heat treatment is carried out at a temperature increase rate of 10 ° C /min, and the temperature is maintained at 550 ° C for 2 hours, and the temperature is lowered for 55 minutes. (The cooling rate is about 2.7 ° C / min) to 400 ° C, and then left to cool to room temperature.

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

In this case, the "shrinkage amount of the glass before and after the heat treatment" means "the length of the glass before the heat treatment - the length of the glass after the heat treatment".

The glass substrate of the present embodiment has a density of preferably 3.0 g/cm ³ or less, more preferably 2.8 g/cm ³ or less, and still more preferably 2.65 g from the viewpoint of weight reduction of the glass substrate and weight reduction of the display. /cm ³ or less. When the density is too high, the weight of the glass substrate becomes difficult, and it is also difficult to reduce the weight of the display.

When the transition point of the glass (hereinafter referred to as Tg) is lowered, there is a tendency that heat shrinkage tends to occur in the heat treatment step of manufacturing the display. In the glass substrate of the present embodiment, the Tg is preferably 720 ° C or higher, more preferably 750 ° C or higher, and still more preferably 760 ° C or higher. In order to make the Tg of the glass substrate into the above range, in the composition range of the glass substrate of the present embodiment, for example, components such as SiO ₂ and Al ₂ O ₃ are appropriately added, or B ₂ O ₃ , RO, and R ₂ O components are reduced.

Regarding the glass of the present embodiment, the viscosity is shown to be 10 ^2.5 [dPa. The temperature of s] (hereinafter referred to as melting temperature) is preferably 1680 ° C or less, more preferably 1500 to 1680 ° C, more preferably 1520 to 1660 ° C, still more preferably 1560 to 1640 ° C. For glass with a lower melting temperature, the strain point is easily lowered. In order to increase the strain point, it is also necessary to increase the melting temperature to some extent. However, if the melting temperature is high, the burden on the melting tank increases. Moreover, since a large amount of energy is consumed, the cost is also high. Further, when electric melting is applied to the glass melting, the current does not flow to the glass, but flows to the heat-resistant brick forming the melting tank, and the melting tank is broken. In order to set the melting temperature of the glass to the above range, components such as B ₂ O ₃ and RO which have a reduced viscosity are appropriately contained in the composition range of the glass substrate of the present embodiment.

The molten glass in the case of producing the glass substrate of the present embodiment preferably has a specific resistance (1550 ° C) of 30 to 700 Ω. Cm, more preferably 30~400Ω. Cm, more preferably 30~300Ω. Cm, more preferably 50~300Ω. The range of cm. If the specific resistance becomes too small, the current value required for melting becomes too large, and there is a case where equipment restriction occurs. Moreover, there is also a tendency for the consumption of electrodes to increase. If the specific resistance of the molten glass becomes too large, the current does not flow to the glass, but flows to the heat-resistant brick forming the melting tank, and the melting tank is melted. The specific resistance of the molten glass can be mainly adjusted to the above range by controlling the contents of RO, R ₂ O, and Fe ₂ O ₃ .

The glass constituting the glass substrate of the present embodiment preferably has an etching rate of 50 μm/h or more. If the etching speed is increased, the productivity is improved. In particular, when the glass substrate is bonded to the glass substrate on the color filter side and the glass substrate is etched to reduce the weight, the etching rate determines the productivity. However, if the etching rate is too high, the productivity in manufacturing the display is improved, but the devitrification resistance of the glass is lowered. Moreover, the heat shrinkage rate is also likely to increase. The etching rate is preferably 60 to 140 μm/h, more preferably 65 to 120 μm/h, still more preferably 70 to 120 μm/h. In order to increase the etching rate of the glass, it is only necessary to reduce the value of SiO ₂ -(1/2 × Al ₂ O ₃ ) or SiO ₂ /Al ₂ O ₃ . In the present embodiment, the etching rate is defined as being measured under the following conditions. The etching rate (μm/h) in the present specification means that the glass substrate is immersed in an etching solution adjusted to an HF concentration of 1 mol/kg and a HCl concentration of 5 mol/kg for 1 hour per unit time (1 hour). The thickness reduction (μm) of the surface of one of the glass substrates.

The glass substrate of the present embodiment may have a thickness of, for example, 0.1 to 1.1 mm or 0.3 to 1.1 mm. However, it is not intentionally limited to the scope. The plate thickness may be, for example, in the range of 0.3 to 0.7 mm and 0.3 to 0.5 mm. If the thickness of the glass plate is too thin, the strength of the glass substrate itself is lowered. For example, when a flat panel display is manufactured, damage is likely to occur. If the thickness of the plate is too thick, it is not preferable for a display that is required to be thin. Further, since the weight of the glass substrate is increased, the weight of the flat panel display cannot be reduced. Further, in the case where the etching treatment of the glass substrate is performed after the TFT is formed, the amount of etching treatment is increased, which is costly and time consuming.

The glass substrate of this embodiment is used, for example, in the manufacture of a flat panel display which etches the surface of a glass substrate after bonding an array and a color filter. The glass substrate of this embodiment is suitable for a glass substrate for a display (excluding a CRT (Brown Tube) display). In particular, the glass substrate of the present embodiment is suitable for forming a glass substrate for a flat panel display of an LTPS-TFT or an OS-TFT. Specifically, it is suitable for a glass substrate for a liquid crystal display or a glass substrate for an organic EL display. Particularly suitable for a glass substrate for an LTPS-TFT liquid crystal display or a glass substrate for an LTPS-TFT organic EL display. In particular, it is suitable for a glass substrate for a display that requires a high-definition mobile terminal or the like.

<flat panel display>

This embodiment includes a flat panel display in which an LTPS-TFT or an OS-TFT is formed on the surface of a glass substrate, and the glass substrate of the flat panel display is the glass substrate of the above-described embodiment. The flat panel display of this embodiment may be, for example, a liquid crystal display or an organic EL display.

<Method of Manufacturing Glass Substrate>

The method for producing a glass substrate for a display according to the present embodiment includes the steps of: melting a glass raw material having a predetermined composition at least by direct electric heating; and melting the molten glass melted by the melting step into a flat shape. a step of forming a glass; a step of slow cooling of the flat glass described above.

In particular, it is preferable that the slow cooling step is a step of controlling the cooling condition of the flat glass so as to lower the heat shrinkage rate of the flat glass.

[melting step]

In the melting step, for example, direct electric heating and/or combustion heating is used to melt the glass raw material having a predetermined composition. The glass raw material can be suitably selected from known materials. From the viewpoint of energy efficiency, it is preferred in the melting step to melt the glass raw material using at least direct electric heating. Further, it is preferable that the melting tank in which the melting step is performed includes a high zirconia-based refractory. The above-described predetermined composition can be appropriately adjusted, for example, within a range that satisfies the content described above for each component of the glass.

[Forming step]

In the forming step, the molten glass melted by the melting step is formed into a flat glass. For the molding method of forming a flat glass, for example, a glass ribbon is formed in a flat glass state by a down-draw method, in particular, an overflow down-draw method. Further, a floating method, a re-drawing method, a rolling method, or the like can be applied. By using the down-draw method, the main surface of the obtained glass substrate is formed by a free surface which is not in contact with the environment, and thus has a high smoothness and variation as compared with the case of using other forming methods such as a floating method. The grinding step of the surface of the formed glass substrate is not required, so that the manufacturing cost can be reduced and the productivity can be improved. Further, since the two main surfaces of the glass substrate formed by the down-draw method have a uniform composition, when the etching treatment is performed, the surface and the back surface can be uniformly etched regardless of the molding. engraved.

[slow cooling step]

The heat shrinkage rate of the glass substrate can be controlled by appropriately adjusting the conditions at the time of slow cooling. In particular, it is preferred to control the cooling conditions of the flat glass in such a manner as to lower the heat shrinkage rate of the flat glass. The heat shrinkage ratio of the glass substrate is 90 ppm or less as described above, preferably 75 ppm or less, more preferably 5 to 75 ppm. In order to produce a glass substrate having such a numerical heat shrinkage rate, for example, in the case of using a down-draw method, it is preferred to set the cooling rate of the glass ribbon as the flat glass to a temperature range of Tg to (Tg - 100 ° C). Slowly cool at 30 to 300 ° C / min. If the cooling rate is too fast, the heat shrinkage rate cannot be sufficiently lowered. On the other hand, if the cooling rate is too slow, there is a problem that the productivity is lowered and the glass manufacturing apparatus (slow cooling furnace) is enlarged. The cooling rate is preferably in the range of 30 to 300 ° C / min, more preferably 50 to 200 ° C / min, more preferably 60 to 120 ° C / min. By setting the cooling rate to 30 to 300 ° C /min, the glass substrate of the present embodiment can be more reliably produced. Further, after the flat glass is cut downstream of the slow cooling step, the heat shrinkage rate can be lowered by additionally performing offline slow cooling, but in this case, in addition to the equipment for performing the slow cooling step, an additional offline is required. Slow cooling equipment. Therefore, as described above, it is preferable to omit offline slow cooling and to reduce the heat shrinkage rate in the slow cooling step, and it is preferable from the viewpoint of productivity and cost. In addition, the cooling rate of the glass ribbon in this specification shows the cooling rate of the center part of the width direction of a glass ribbon.

[Examples]

Hereinafter, the present embodiment will be described in more detail based on examples. However, this embodiment is not limited by the embodiment. In the following examples and comparative examples, the physical properties described below were measured.

(strain point)

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

(devitrification temperature)

The glass was pulverized, and glass granules which passed through a 2380 μm sieve and remained on a 1000 μm sieve were added to a platinum boat. The platinum boat was kept in an electric furnace having a temperature gradient of 1,050 to 1,380 ° C for 5 hours, and then taken out from the furnace, and devitrification occurring 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.

(specific resistance at 1550 ° C)

The specific resistance of the molten glass was measured by a four-probe method using a 4192A LF impedance analyzer manufactured by Hewlett Packard Co., Ltd., and the specific resistance at 1550 ° C was calculated from the above measurement results.

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

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

(heat shrinkage rate)

The heat shrinkage ratio is determined by a scribing method for a glass having a size of 90 mm to 200 mm × 15 mm 30 mm × 0.5 mm to 1 mm. As a heat treatment for heat shrinkage measurement, an air recirculation furnace (N120/85HA manufactured by Nabertherm) was used, and the temperature was raised from room temperature at 10 ° C /min, held at 550 ° C for 2 hours, and cooled at 55 minutes (cooling rate was about 2.7 ° C / Minutes to 400 ° C, after which the door of the air recirculation furnace is half opened and left to cool to room temperature.

Heat shrinkage rate (ppm) = {shrinkage of glass under heat treatment / line spacing of glass before heat treatment} × 10 ⁶

Further, in the case of measuring the heat shrinkage of the glass obtained by melting the glass raw material in the platinum crucible and flowing out to the iron plate and cooling and solidifying, it is cut, ground, and ground to a thickness of 0.7 mm, using an electric furnace. After holding at a temperature of Tg + 15 ° C for 30 minutes, the glass outside the furnace was taken out in 4 minutes. At this time, the average cooling rate in the range of Tg + 15 to 150 ° C is 100 to 200 ° C / min.

(density)

The density of the glass is determined by the Archimedes method.

(etching speed)

The etching rate (μm/h) was determined by measuring glass (12.5 mm × 20 mm × 0.7 mm) in an etching solution (200 mL) adjusted to an HF concentration of 1 mol/kg and a HCl concentration of 5 mol/kg at 40 °C. The thickness reduction amount (μm) in the case of immersion for 1 hour, and the thickness reduction amount (μm) of one surface of the glass substrate per unit time (1 hour) was calculated.

Hereinafter, the composition and evaluation of the examples and comparative examples will be described in three aspects of the glass substrates (A) to (C).

(Glass substrate (A): Examples 1 to 60, Comparative Examples 1 to 3)

The glass of Examples 1 to 60 and Comparative Examples 1 to 3 were produced in the following order so as to have the glass compositions shown in Tables 1 to 4. With respect to the obtained glass, the strain point, the devitrification temperature, Tg, and the average thermal expansion coefficient (α) in the range of 100 to 300 ° C, the heat shrinkage ratio, the density, and the etching rate were determined.

The raw materials of the respective components were blended in such a manner as to have the composition of the glass shown in Tables 1 to 4, and melted, clarified, and formed.

Among the glasses thus obtained, the heat shrinkage ratios of Examples 1 to 60 were 90 ppm or less. Moreover, the specific resistance of the molten glass at 1550 ° C is also 700 Ω. Below cm. Further, when the glass raw material was melted by direct electric heating and the glass substrate was produced by the overflow down-draw method, the same result was obtained. Therefore, by using these glasses, a glass substrate which can be used for a display using an LTPS-TFT can be manufactured by an overflow down-draw method. Moreover, these glass substrates are also suitable as a glass substrate for OS-TFT.

On the other hand, in Comparative Examples 1 to 3, the specific resistance of the molten glass at 1550 ° C was 700 Ω. Below cm, but the strain point is less than 670 °C. Further, the heat shrinkage ratio of Comparative Example 1 was far more than 90 ppm.

(Glass substrate (B): Examples 101 to 148 and Comparative Example 101)

The glass of Examples 101 to 148 and Comparative Example 101 were produced in the following order so as to have the glass compositions shown in Tables 5 to 7. With respect to the obtained glass, the strain point, the devitrification temperature, Tg, and the average thermal expansion coefficient (α) in the range of 100 to 300 ° C, the heat shrinkage ratio, the density, and the etching rate were determined.

The raw materials of the respective components were blended in such a manner as to have the composition of the glass shown in Tables 5 to 7, and melted, clarified, and formed.

The heat shrinkage of the glass of Examples 101 to 148 thus obtained was 5 to 75 ppm. Further, the devitrification temperature is also 1280 ° C or lower. On the other hand, in Comparative Example 101 in which MgO/(RO+ZnO) was 0.95, the heat shrinkage rate was 5 to 75 ppm, but the devitrification temperature exceeded 1280 °C.

Further, when the glass raw material was melted by direct electric heating and the glass substrate was produced by the overflow down-draw method, the same result was obtained. Therefore, by using the glasses of Examples 101 to 148, a glass substrate which can be used for a display using an LTPS-TFT can be manufactured by an overflow down-draw method. Further, the glass substrates of Examples 101 to 148 are also suitably used as a glass substrate for OS-TFT.

(Glass substrate (C): Examples 201 to 255 and Comparative Examples 201 to 203)

The glass of Examples 201 to 255 and Comparative Examples 201 to 203 were produced in the following order so as to have the glass compositions shown in Tables 8 to 11. With respect to the obtained glass, the strain point, the devitrification temperature, Tg, and the average thermal expansion coefficient (α) in the range of 100 to 300 ° C, the heat shrinkage ratio, the density, and the etching rate were determined.

The raw materials of the respective components were blended in such a manner as to have the composition of the glass shown in Tables 8 to 11, and melted, clarified, and formed.

The strain point of the glass thus obtained is 700 ° C or more. Further, the etching rate is also 50 μm/h or more. Therefore, by using these glasses, a glass substrate which can be used for a display using an LTPS-TFT can be manufactured by an overflow down-draw method. Moreover, these glass substrates are also suitable as a glass substrate for OS-TFT.

In Examples 201 to 255 and Comparative Example 203 in which SiO ₂ /Al ₂ O ₃ was 6.0 or less, the etching rate was 65 (μm/h) or more and was good. On the other hand, in Comparative Examples 201 and 202 in which SiO ₂ /Al ₂ O ₃ exceeded 6.0, the etching rate was 62 (μm/h) or less and was inferior.

In Examples 1 to 55 and Comparative Examples 1 and 2 in which the content of B ₂ O ₃ was 7% or less, the strain point was higher than 700 °C. The devitrification temperature is above 1100 °C.

On the other hand, in Comparative Example 203 in which the content of B ₂ O ₃ was 12.0%, the devitrification temperature was lowered to 1,050 ° C, but the strain point was lowered to 660 ° C.

Claims (14)

A glass substrate for a display, which is formed of glass containing SiO ₂ or Al ₂ O ₃ and expressed by mol%, B ₂ O ₃ is 0 to 8%, and R ₂ O is 0.01 to 0.8%. , BaO is 1~15%, BaO/RO is 0.05~1, and the strain point is 670°C or more. Here, RO means (MgO+CaO+SrO+BaO), and R ₂ O means (Li ₂ O+Na ₂ O+K ₂ O). A glass substrate for a display, which is formed of glass containing SiO ₂ 60-80%, Al ₂ O ₃ 8-20%, B ₂ O ₃ 0-8%, R _{2 in} terms of mole % O is 0.01 to 0.8%, BaO is 1 to 15%, and (SiO ₂ + (2 × Al ₂ O ₃ )) / ((2 × B ₂ O ₃ ) + RO + (10 × R ₂ O)) is 2.5 or more. , BaO / RO is 0.05 ~ 1, the strain point is 670 ° C or more glass, where RO means (MgO + CaO + SrO + BaO), R ₂ O means (Li ₂ O + Na ₂ O + K ₂ O) . The glass substrate of claim 1 or 2, which is represented by mol%, containing MgO 0~15%, CaO 0~20%, SrO 0~15%, and BaO 0.1~15%. The glass substrate of claim 1 or 2, wherein SiO ₂ -(1/2 × Al ₂ O ₃ ) is less than 65%, expressed as % by mole. The glass substrate of claim 1 or 2, wherein expressed in mole %, B ₂ O ₃ +RO + ZnO is 15 to 25%. The glass substrate according to claim 1 or 2, which contains SnO ₂ and Fe ₂ O ₃ , expressed in mol%, SnO ₂ is 0.03 to 0.15%, and the total amount of SnO ₂ and Fe ₂ O ₃ is 0.05 to 0.2%. The glass substrate of claim 1 or 2, which comprises SiO ₂ 66-72%, Al ₂ O ₃ 11-15%, B ₂ O ₃ 0-8%, MgO 0-6%, CaO 2 in terms of mole % ~11%, SrO 0~1%, BaO 1~10%. The glass substrate of claim 1 or 2 which does not substantially contain As ₂ O ₃ . A glass substrate for a display device, which comprises comprising _{SiO 2, Al 2 O 3,} MgO, expressed in mole%, BaO is 1 ~ 15%, MgO / ( RO + ZnO) is _{0.1 ~ 0.9, (SiO 2 +} 2Al 2 O ₃ ) / (2B ₂ O ₃ + RO) is 3.5 or more, and the glass having a strain point of 700 ° C or higher is heated at a temperature increase rate of 10 ° C / min, held at 550 ° C for 2 hours, and cooled to 400 at 55 minutes. °C, after the cooling to normal temperature, the heat shrinkage rate shown in the following formula is 5 ppm to 75 ppm, and the heat shrinkage ratio (ppm) = {the shrinkage amount of the glass before and after the heat treatment/the length of the glass before the heat treatment} × ¹⁰⁶ here, RO represents a (MgO + CaO + SrO + BaO ). A glass substrate for display comprising SiO ₂ , Al ₂ O ₃ , BaO, expressed in mole %, BaO is 1 to 15%, (SiO ₂ + 2Al ₂ O ₃ ) / (2B ₂ O ₃ + RO) It is 3.5 or more, substantially does not contain Sb ₂ O ₃ , and has a strain point of 700 ° C or higher, and is heated at a temperature increase rate of 10 ° C / min, held at 550 ° C for 2 hours, and cooled to 400 ° C in 55 minutes. The heat shrinkage ratio shown by the following formula when it is cooled to normal temperature is 5 ppm to 75 ppm, and the heat 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 glass substrate for display comprising 60% to 80% of SiO ₂ , 8 to 20% of Al ₂ O ₃ , 0 to 15% of B ₂ O _{3 ,} 1 to 15% of BaO, and MgO/(RO+) ZnO) is 0.1 to 0.9, (SiO ₂ +2Al ₂ O ₃ )/(2B ₂ O ₃ +RO) is 3.5 or more, and the glass having a strain point of 700 ° C or higher is heated at a temperature increase rate of 10 ° C /min. The temperature is kept at 550 ° C for 2 hours, and the temperature is lowered to 400 ° C in 55 minutes. Thereafter, when it is cooled to normal temperature, the heat shrinkage rate shown in the following formula is 5 ppm to 75 ppm, and the heat shrinkage ratio (ppm) = {before and after heat treatment. The amount of shrinkage of the glass / the length of the glass before the heat treatment} × 10 ⁶ Here, RO represents (MgO + CaO + SrO + BaO). A glass substrate for a display, which is formed of glass containing SiO ₂ , Al ₂ O ₃ , and BaO, expressed in mole %, B ₂ O ₃ being 0 to 7%, and BaO being 1 to 15%. SiO ₂ /Al ₂ O ₃ is 6.0 or less, and the strain point is 700 ° C or more. A glass substrate for a display, which is formed of glass containing SiO ₂ 60-80%, Al ₂ O ₃ 10.5-20%, B ₂ O ₃ 0-7%, BaO 1 ~15%, substantially does not contain As ₂ O ₃ , RO is 10.0 to 18.0%, SiO ₂ /Al ₂ O ₃ is 3 or more, 5.7 or less, SrO < 0.25 × CaO, and the strain point is 700 ° C or higher. A display for manufacturing a glass substrate according to any one of claims 1 to 2 and claims 9 to 13 A method for producing a glass substrate for a display, comprising the steps of: melting a melting of a glass raw material having a predetermined composition by at least direct electric heating; and forming a molten glass melted by the melting step into a flat glass. And a step of slow cooling of the flat glass by controlling the cooling condition of the flat glass so as to reduce the heat shrinkage rate of the flat glass.