JP7140582B2 - Glass substrate for display - Google Patents

Description

The present invention relates to glass substrates. In particular, the present invention is a low-temperature polysilicon thin film transistor (hereinafter referred to as LTPS-TFT (Low-Temperature-Polycrystalline-Silicon Thin-Film-Transistor) display, an oxide semiconductor thin film transistor (hereinafter referred to as OS-TFT (Oxide-Semiconductor The present invention relates to a glass substrate suitable for displays, etc. (described as Thin-Film-Transistor). More particularly, the present invention relates to a display glass substrate, wherein the display is a liquid crystal display, an organic EL display, a flat panel display, or the like.

It is desirable to apply LTPS to the manufacture of thin film transistors (TFTs) for displays mounted on mobile devices, etc., for reasons such as the ability to reduce power consumption. Heat treatment at high temperature is required. On the other hand, in recent years, there is an increasing demand for high-definition displays for small portable devices. Therefore, thermal shrinkage of the glass substrate that occurs during the manufacture of the display panel, which causes pitch deviation of the pixels, is a problem. Also, in the glass substrate on which the OS-TFT is formed, suppression of thermal shrinkage is a problem as well.

The thermal shrinkage of a glass substrate can generally be reduced by raising the strain point of the glass or raising the glass transition point (hereinafter referred to as Tg). Against this background, a technique for increasing Tg in order to reduce the thermal shrinkage rate has been disclosed (Patent Document 1). Furthermore, in recent years, there has been an increasing demand for higher definition display panels, so the technique of Patent Document 1 has resulted in an insufficient reduction in the thermal shrinkage rate. For this reason, a technique for increasing the strain point of glass to 725° C. or higher has also been disclosed (Patent Document 2).

Japanese Patent Application Laid-Open No. 2011-126728 Japanese Patent Application Laid-Open No. 2012-106919

Accordingly, an object of the present invention is to provide a glass substrate that satisfies a high strain point or a high Tg while keeping the devitrification temperature low. In particular, it is an object of the present invention to provide a display glass substrate suitable for displays using LTPS-TFTs or OS-TFTs.

In addition, it is required to improve productivity in the manufacture of displays using glass substrates. For example, there is a demand for an improvement in productivity in the process of thinning a glass substrate on which thin film transistors are formed. The productivity of the step of thinning the glass substrate greatly depends on the time required for etching the glass substrate. Therefore, display glass substrates are required to achieve both an improvement in productivity due to an increase in etching rate and a reduction in thermal shrinkage. However, although the glass substrate described in Patent Document 2 has a high strain point, there is a problem that the etching rate is not considered.

An object of the present invention is to provide a glass substrate that preferably takes into consideration the etching rate.

The present invention is as follows.
[1]
SiO ₂ 69-72% in mol % as glass composition
Al ₂ O ₃ 11-15%
_{B2O3 0.5-2.5} %
MgO 1-4%
CaO 4-7%
SrO 0-1%
BaO 4-7%
_K2O 0.01-0.5%
_{P2O5 0.1-2.0} %
B ₂ O ₃ /P ₂ O ₅ 0.2-5
CaO/BaO 0.6-1.2
A glass substrate for a display, made of glass having
[2]
The display glass substrate according to [1], which has a devitrification temperature of 1350° C. or less.
[3]
The glass substrate for display according to [1] or [2], which has a strain point of 710° C. or higher.
[4]
The glass substrate for display according to any one of [1] to [3], which has a glass transition temperature of 779° C. or higher.
[5]
The display glass substrate according to any one of [1] to [4], which has an etching rate of 70 μm/h or more.
[6]
The glass substrate for display according to any one of [1] to [5], wherein SiO ₂ /Al ₂ O ₃ is 4-6.
[7]
The display glass substrate according to any one of [1] to [6], wherein MgO/RO is 0.15 to 0.4, provided that RO=MgO+CaO+SrO+BaO.

According to the present invention, it is possible to provide a glass substrate that satisfies a high strain point or a high Tg while keeping the devitrification temperature low.

In the specification of the present application, unless otherwise specified, the content of the glass composition is indicated by mol %, and the content indicated by % means mol %. The ratio of components constituting the glass composition is indicated by molar ratio.

_SiO2 is a framework component of glass and is therefore an essential component. As the content decreases, the strain point tends to decrease and the coefficient of thermal expansion tends to increase. Also, if the SiO ₂ content is too low, it will be difficult to reduce the density of the glass substrate. On the other hand, if the SiO ₂ content is too high, the glass melt tends to have an increased specific resistance and a remarkably high melting temperature, making melting difficult. Furthermore, too much _SiO2 content slows down the etching rate. From such a point of view, the content of SiO ₂ can be appropriately adjusted. The SiO ₂ content of the glass is in the range of 69-72%, preferably in the range of 69.0-72.0%. The content of SiO ₂ is more preferably in the range of 69.5-71.5%, still more preferably 69.7-71.3%.

Al ₂ O ₃ is an essential component that raises the strain point. Too little Al ₂ O ₃ content lowers the strain point. Furthermore, if the Al ₂ O ₃ content is too low, the Young's modulus and acid etching rate tend to decrease. On the other hand, if the Al ₂ O ₃ content is too high, the devitrification temperature of the glass will rise and the devitrification resistance will decrease, so that the formability tends to deteriorate. From such a point of view, it can be adjusted as appropriate. The Al ₂ O ₃ content of the glass is in the range of 11-15%. The content of Al ₂ O ₃ is preferably in the range of 11.0-15.0%, more preferably 12.0-14.8%, more preferably 12.5-14.5%, still more preferably 12.7-14.3%.

B ₂ O ₃ is a component that lowers the high temperature viscosity of the glass and improves the meltability. That is, the meltability is improved by lowering the viscosity near the melting temperature. It is also a component that lowers the devitrification temperature. When the B ₂ O ₃ content is small, the meltability and devitrification resistance tend to be lowered. Too much B ₂ O ₃ content lowers the strain point and Young's modulus. In addition, devitrification tends to occur due to volatilization of B ₂ O ₃ during glass molding. In particular, glass with a high strain point tends to have a high molding temperature, which promotes the above volatilization and causes a significant problem of devitrification. In addition, volatilization of B ₂ O ₃ during melting of the glass makes the glass significantly non-uniform, and striae are likely to occur. From this point of view, the B ₂ O ₃ content is in the range of 0.5% to 2.5%. The B ₂ O ₃ content is preferably 0.5-2.0%, more preferably 0.5-1.8%, even more preferably 0.5-1.7%, more preferably 0.5-1.6%, even more preferably 0.5-1.5 % range.

MgO is a component that improves the meltability and is an essential component. Further, since it is a component that is difficult to increase the density among the alkaline earth metals, relatively increasing the content thereof facilitates the reduction of the density. By containing it, the specific resistance and melting temperature of the molten glass can be lowered. However, if the content of MgO is too high, the devitrification temperature of the glass rises sharply, making devitrification particularly likely during the molding process. From such a viewpoint, the MgO content is 1 to 4%, preferably 1.0 to 4.0%, more preferably 1.5 to 3.5%, still more preferably 2.0 to 3.5%, and even more preferably 2.3 to 3.3%. Range.

CaO is an effective component for improving the meltability of the glass without sharply increasing the devitrification temperature of the glass, and is essential. In addition, since it is a component that is difficult to increase the density among alkaline earth metal oxides, relatively increasing the content thereof facilitates the reduction of the density. If the content is too small, the glass melt tends to have an increase in resistivity and a decrease in devitrification resistance. Too much CaO content tends to increase the coefficient of thermal expansion and increase the density. From this point of view, the CaO content is in the range of 4-7%, preferably 4.0-7.0%, more preferably 4.5-6.5%, still more preferably 5.0-6.0%.

SrO is a component that can lower the devitrification temperature of glass. SrO is not essential, but its inclusion improves devitrification resistance and meltability. However, if the SrO content is too high, the density will increase. From this point of view, the SrO content is 0 to 1%, preferably 0 to 0.5%, and more preferably substantially free.

BaO is a component capable of effectively lowering the devitrification temperature of glass and the specific resistance of molten glass, and is an essential component. Inclusion of BaO improves devitrification resistance and meltability. However, if the BaO content is too high, the density will increase. In addition, the BaO content is 4 to 7% from the viewpoint of environmental load and the tendency of the coefficient of thermal expansion to increase. The BaO content is preferably in the range of 4.0-7.0%, more preferably 4.5-6.5%, still more preferably 5.0-6.0%.

K ₂ O is a component that increases the basicity of the glass and promotes clarity. Also, it is a component that lowers the specific resistance of the molten glass. When it is contained, the specific resistance of the molten glass is lowered, so that it is possible to prevent the current from flowing through the refractory constituting the melting tank and to suppress the erosion of the melting tank. In addition, when the refractory constituting the melting tank contains zirconia, it is possible to suppress the melting tank from being eroded and eluting zirconia from the melting tank into the glass melt, so devitrification due to zirconia can also be suppressed. . Further, since the viscosity of the glass is lowered in the vicinity of the melting temperature, the meltability and the clarity are improved. On the other hand, if the K ₂ O content is too high, the coefficient of thermal expansion tends to increase and the strain point tends to decrease. From this point of view, the K ₂ O content is in the range of 0.01-0.5%, preferably 0.1-0.4%, more preferably 0.1-0.3%.

P ₂ O ₅ is a component that lowers high-temperature viscosity and improves meltability, and is an essential component. Too much P ₂ O ₅ content lowers the strain point. In addition, due to volatilization of P ₂ O ₅ during melting of the glass, the non-uniformity of the glass becomes remarkable, and striae are likely to occur. From this point of view, the P ₂ O ₅ content is in the range of 0.1-2.0%, more preferably 0.2-1.9%, and still more preferably 0.3-1.7%.

If the _molar ratio _B2O3 / _P2O5 of _B2O3 and _P2O5 is too small _, the _{devitrification} temperature tends to increase _, and if it is too large, the glass transition temperature tends to decrease. . Therefore, B ₂ O ₃ /P ₂ O ₅ is in the range of 0.2-5, preferably 0.25-4.5%, more preferably 0.30-4.0%, still more preferably 0.30-3.5%.

If the molar ratio CaO/BaO is too small, the devitrification temperature tends to rise, and if it is too large, the devitrification temperature tends to rise. The molar ratio CaO/BaO is in the range 0.6-1.2, preferably 0.7-1.2, preferably 0.8-1.2, more preferably 0.9-1.1.

If the molar ratio SiO ₂ /Al ₂ O ₃ is too large, the etching rate may decrease, and if the value is too small, the devitrification resistance may decrease. From this point of view, the molar ratio SiO ₂ /Al ₂ O ₃ is preferably 4 to 6, more preferably 4.3 to 5.8, still more preferably 4.4 to 5.7. In addition, in glasses having compositions in which the values of SiO ₂ +Al ₂ O ₃ are close to each other, the etching rate remarkably depends on SiO ₂ /Al ₂ O ₃ . From the viewpoint of achieving both high strain point, devitrification resistance, and etching rate, SiO ₂ +Al ₂ O ₃ should be 80 to 90% and SiO ₂ /Al ₂ O ₃ should be 4 to 6. more preferably, SiO ₂ +Al ₂ O ₃ is 82-88%, and SiO ₂ /Al ₂ O ₃ is preferably in the range of 4.3-5.8.

MgO, CaO, SrO and BaO are components that lower the specific resistance and melting temperature of the glass melt and improve the meltability. If the total content of MgO, CaO, SrO and BaO, MgO+CaO+SrO+BaO (hereinafter referred to as RO), is too small, the meltability deteriorates. Too much RO lowers the strain point and Young's modulus and raises the density and coefficient of thermal expansion. In order to effectively lower the devitrification temperature without excessively increasing the density, MgO/RO is preferably in the range of 0.15-0.4, more preferably 0.18-0.38, and still more preferably 0.20-0.36. RO is preferably in the range of 9-19%, more preferably in the range of 11-17%.

The glass substrate of the present invention has a devitrification temperature of 1,350°C or lower, preferably 1,300°C or lower, more preferably 1,280°C or lower, and still more preferably lower than 1,250°C. The lower the devitrification temperature, the easier it is to form a glass sheet by the overflow down-draw method. By applying the overflow down-draw method, the step of polishing the surface of the glass substrate can be omitted, so that the surface quality of the glass substrate can be improved. Also, production costs can be reduced. If the devitrification temperature is too high, devitrification tends to occur easily, making it difficult to apply the overflow downdraw method.

In the present specification, the term "substantially free of" means that the raw materials for these components are not used in the frit, and components contained as impurities in frit of other components, It does not exclude the contamination of components eluted into the glass from manufacturing equipment such as melting tanks and moldings.

The glass substrate of the present invention can contain a fining agent. The refining agent is not particularly limited as long as it has a small environmental load and is excellent in refining of the glass. At least one selected from can be mentioned. _The glass substrate of the present invention is _{substantially} free of _Sb2O3 and _As2O3 . Substantially free of Sb ₂ O ₃ and As ₂ O ₃ can reduce environmental load. SnO ₂ is suitable as a refining agent. If the content of the clarifying agent is too small, the quality of the foam will deteriorate, and if it is too large, it may cause devitrification or coloration. The content of the refining agent depends on the type of refining agent and the composition of the glass. For example, the SnO ₂ content is preferably 0.05-0.50%, more preferably 0.05-0.40%.

_{SnO 2} is a _{refining agent} that can obtain a refining effect even at 1600° C. or _{higher .} and K ₂ O in a total amount of 0.01-0.8%). However, SnO ₂ is a component that tends to cause devitrification by itself, and is also a component that promotes devitrification of other components, so from the viewpoint of suppressing devitrification, it is not preferable to add a large amount.

In addition, glass with a high strain point (e.g., glass with a strain point of 730°C or higher) tends to have a higher devitrification temperature than glass with a low strain point (e.g., glass with a strain point of less than 730°C). Therefore, in order to suppress devitrification, it may be necessary to raise the temperature of the molten glass in the forming process as compared with glass having a low strain point. Here, from the viewpoint of creep resistance and heat resistance, the molded body used in the overflow down-draw method preferably contains a refractory material containing zirconia. When overflow down-draw is employed as the molding method, the temperature of the molded body needs to be increased as the temperature of the molten glass in the molding process is increased. However, when the temperature of the molded body rises, there is a problem that zirconia is eluted from the molded body, and devitrification of the zirconia tends to occur. In addition, particularly in glass containing a large amount of SnO ₂ , devitrification of SnO ₂ due to zirconia and devitrification of zirconia due to SnO ₂ tend to occur easily.

Furthermore, glass with a high strain point (e.g., glass with a strain point of 730°C or higher) has a melting temperature of glass raw materials compared to glass with a low strain point (e.g., glass with a strain point of less than 730°C). tends to be higher. Here, from the viewpoint of corrosion resistance, the melting tank in which the melting step is performed preferably contains a high zirconia-based refractory containing zirconia. Moreover, from the viewpoint of energy efficiency, it is preferable to melt the glass raw materials by electric melting or a combination of electric melting and other heating means. However, when melting a glass having a high strain point as described in the present invention and containing only trace amounts of Li ₂ O, Na ₂ O, and K ₂ O, the specific resistance of the molten glass is large. Current flows through the zirconia-based refractory, which easily causes the problem of elution of zirconia into the molten glass. When zirconia is eluted, devitrification of zirconia and devitrification of SnO ₂ described above tend to occur.

In other words, from the viewpoint of suppressing the devitrification of zirconia and SnO ₂ , it is not preferable that the SnO ₂ content exceeds 0.5% in the glass substrate of the present invention.

Fe ₂ O ₃ is a component that lowers the specific resistance of molten glass in addition to functioning as a clarifier. In the case of a glass that is highly viscous at high temperature and difficult to melt, it is preferable to contain it in order to reduce the specific resistance of the molten glass. However, if the Fe ₂ O ₃ content is too high, the glass will be colored and the transmittance will decrease. Therefore, the Fe ₂ O ₃ content is in the range 0-0.1%, preferably 0-0.08%, more preferably 0.001-0.06%, even more preferably 0.001-0.05%, more preferably 0.001-0.04%. is.

_The refining agent can also be used in combination with _SnO2 and _Fe2O3 . As described above, from the viewpoint of suppressing devitrification, it is not preferable to contain a large amount of SnO ₂ . However, in order to obtain a sufficient fining effect, it is required that the fining agent is contained in a predetermined amount or more. Therefore, by using SnO ₂ and Fe ₂ O ₃ together, it is possible to obtain a sufficient refining effect and produce a glass substrate with few bubbles without increasing the content of SnO ₂ so as to cause devitrification. The total amount of SnO ₂ and Fe ₂ O ₃ is preferably in the range of 0.05-0.50%, more preferably 0.05-0.20%, still more preferably 0.05-0.40%.

If the mass ratio of the SnO ₂ content to the total amount of SnO ₂ and Fe ₂ O ₃ (SnO ₂ /(SnO ₂ +Fe ₂ O ₃ )) is too large, devitrification tends to occur, and if it is too small, it is insufficient. The fining effect cannot be obtained, and the glass may become colored. Therefore, it is preferably in the range of 0.6 to 1.0, more preferably in the range of 0.7 to 1.0.

It is preferable that the glass substrate of the present invention does not substantially contain As ₂ O ₃ from the viewpoint of environmental load. The glass substrate of the present invention does not substantially contain Sb ₂ O ₃ due to the environmental burden.

The glass substrate of the present invention preferably does not substantially contain PbO and F for environmental reasons.

The glass substrate of the present invention has an average thermal expansion coefficient (100-300°C) at 100°C to 300°C of 50.0 × 10 ^-7 °C ^-1 or less and 28.0 to 50.0 × 10 ^-7 °C ^-1 . is preferably 33.0 to 47.0×10 ^-7 ° C. ^-1 , still more preferably 33.0 to 46.0×10 ^-7 ° C. ^-1 , still more preferably 35.0 to 44.0×10 ^-7 ° C. ^-1 , still more preferably 36.0 It is in the range of ~43.0×10 ^-7 °C ^-1 . When the coefficient of thermal expansion is large, thermal shock and thermal shrinkage tend to increase in the heat treatment process. Moreover, if the thermal expansion coefficient is large, it becomes difficult to reduce the thermal contraction rate. Regardless of whether the coefficient of thermal expansion is large or small, it is difficult to match the coefficient of thermal expansion with the peripheral materials such as metals and thin films formed on the glass substrate, and there is a risk that the peripheral members will peel off.

In general, when a glass substrate has a low strain point, thermal shrinkage tends to occur in a heat treatment process in manufacturing a display. The glass substrate of the present invention preferably has a strain point of 710° C. or higher, more preferably 720° C. or higher, still more preferably 730° C. or higher, and still more preferably 735° C. or higher.

The glass substrate of the present invention preferably has a thermal shrinkage rate of 15 ppm or less, more preferably 13 ppm or less, and more preferably 10 ppm or less. If the heat shrinkage ratio becomes too large, it causes a large pitch deviation of the pixels, making it impossible to realize a high-definition display. In order to control the thermal shrinkage rate within a predetermined range, the strain point of the glass substrate is preferably 700° C. or higher, or 715° C. or higher. In order to make the thermal shrinkage rate 0ppm, it is required to make the slow cooling process extremely long, and to apply heat shrink reduction treatment (offline slow cooling) after slow cooling and cutting process, but in this case, productivity decreases and costs rise. Considering productivity and cost, the thermal shrinkage rate is, for example, preferably 0.1 ppm to 15 ppm, or 0.5 ppm to 15 ppm, more preferably 1 ppm to 15 ppm, still more preferably 1 ppm to 13 ppm, and still more preferably 2 ppm to 10ppm.

Incidentally, the thermal shrinkage rate is shown by the following formula after the glass substrate is held at a temperature of 500° C. for 30 minutes and then subjected to a heat treatment by allowing it to cool to room temperature.
Thermal shrinkage rate (ppm) = {Amount of shrinkage of glass before and after heat treatment/Length of glass before heat treatment} x ¹⁰⁶
At this time, "the amount of shrinkage of the glass before and after the heat treatment" is "the length of the glass before the heat treatment - the length of the glass after the heat treatment".

The density of the glass substrate of the present invention is preferably 3.0 g/cm ³ or less, more preferably 2.9 g/cm ³ or less, still more preferably 2.8 g/cm ³ from the viewpoint of weight reduction of the glass substrate and weight reduction of the display. It is below. If the density becomes too high, it becomes difficult to reduce the weight of the glass substrate, and it becomes difficult to reduce the weight of the display.

When the glass transition point (hereinafter referred to as Tg) is lowered, thermal shrinkage tends to occur more easily in the heat treatment process for manufacturing displays. The glass substrate of the present invention preferably has a Tg of 779° C. or higher, more preferably 790° C. or higher, and still more preferably 795° C. or higher. In order to make the Tg of the glass substrate within the above range, for example, components such as SiO ₂ and Al ₂ O ₃ are increased, or B ₂ O ₃ , RO, R ₂ are added within the composition range of the glass substrate of the present invention. It is appropriate to reduce the O component.

The temperature at which the glass of the present invention exhibits a viscosity of 10 ^2.5 [dPa s] (hereinafter referred to as melting temperature) is preferably 1680 ° C. or less, more preferably in the range of 1500 to 1680 ° C., still more preferably 1520 ° C. ~1660°C, more preferably 1540-1640°C. A glass with a low melting temperature tends to have a low strain point. In order to raise the strain point, it is necessary to raise the melting temperature to some extent. However, if the melting temperature is high, the load on the melting tank increases. Moreover, since a large amount of energy is used, the cost is also high. Moreover, when electromelting is applied to melting the glass, the electric current may flow through the heat-resistant bricks forming the melting tank instead of the glass, and the melting tank may be damaged. In order to set the melting temperature of the glass in the above range, it is appropriate to contain, within the range of the composition of the glass substrate of the present invention, components that lower the viscosity, such as B ₂ O ₃ and RO, within the above range. be.

The glass melt used to produce the glass substrate of the present invention has a specific resistance (at 1550°C) of preferably 30 to 700 Ω·cm, more preferably 30 to 400 Ω·cm, still more preferably 30 to 300 Ω·cm, and even more preferably 30 to 300 Ω·cm. is in the range of 50 to 300Ω·cm. If the resistivity is too low, the current value required for melting will be too high, which may impose restrictions on facilities. In addition, there is a tendency that the consumption of the electrodes increases. If the specific resistance of the molten glass becomes too large, the electric current may flow not through the glass but through the heat-resistant bricks forming the melting tank, resulting in the melting damage of the melting tank. The specific resistance of the molten glass can be adjusted within the above range mainly by controlling the contents of RO _{, R2O} and _Fe2O3 .

The glass constituting the glass substrate of the present invention preferably has an etching rate of 70 μm/h or more. A faster etching rate improves productivity. In particular, when the glass substrates on the TFT side and the color filter side are laminated together and then etched to reduce the weight, the etching rate affects the productivity. However, if the etching rate is too high, the productivity of the display is improved, but the devitrification resistance of the glass is lowered. Also, the thermal shrinkage rate tends to increase. The etching rate is preferably 70-100 μm/h, more preferably 72-95 μm/h, still more preferably 75-90 μm/h. In order to increase the etching rate of glass, the value of SiO ₂ -(1/4×Al ₂ O ₃ ) or SiO ₂ /Al ₂ O ₃ should be decreased. In the present invention, the above etching rate is defined as measured under the following conditions. Etching rate (μm/h) as used herein means the unit time when a glass substrate is immersed for 1 hour in an etching solution adjusted to have an HF concentration of 1 mol/kg and an HCl concentration of 5 mol/kg at 40°C. It is the thickness reduction amount (μm) of one surface of the glass substrate per (1 hour).

The thickness of the glass substrate of the present invention can be, for example, in the range of 0.1-1.1 mm, or 0.3-1.1 mm. However, it is not the intention to limit to this range. The plate thickness can also range, for example, from 0.3 to 0.7 mm, from 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, damage during flat panel display manufacturing is more likely to occur. If the plate thickness is too thick, it is not preferable for displays that are required to be thin. Moreover, since the weight of the glass substrate increases, it becomes difficult to reduce the weight of the flat panel display. Furthermore, if the glass substrate is etched after the formation of the TFTs, the amount of etching process increases, resulting in cost and time.

The glass substrate of the present invention is used, for example, in the manufacture of flat panel displays in which the surface of the glass substrate is etched after bonding an array and color filter. The glass substrate of the present invention is suitable as a glass substrate for displays (excluding CRT (cathode-ray tube) displays). In particular, the glass substrate of the present invention is suitable for flat panel display glass substrates on which LTPS-TFTs or OS-TFTs are formed. Specifically, it is suitable for liquid crystal display glass substrates and organic EL display glass substrates. In particular, it is suitable for LTPS-TFT liquid crystal display glass substrates and LTPS-TFT organic EL display glass substrates. Among others, it is suitable for glass substrates for displays such as mobile terminals that require high definition.

<Flat panel display>
The present invention includes a flat panel display in which LTPS-TFT or OS-TFT is formed on the surface of a glass substrate, and the glass substrate of this flat panel display is the above glass substrate of the present invention. A flat panel display of the present invention can be, for example, a liquid crystal display or an organic EL display.

<Method for manufacturing glass substrate>
The method for producing a glass substrate for a display of the present invention includes a melting step of melting glass raw materials prepared to have a predetermined composition, for example, by using at least direct electric heating, and forming the molten glass melted in the melting step into a flat plate. It has a forming step of forming into glass and a slow cooling step of slowly cooling the flat glass. In particular, the slow cooling step is preferably a step of controlling the cooling conditions of the flat glass so as to reduce the thermal shrinkage of the flat glass.

[Melting process]
In the melting step, glass raw materials prepared to have a predetermined composition are melted using, for example, direct electric heating and/or combustion heating. Glass raw materials can be appropriately selected from known materials. From the viewpoint of energy efficiency, in the melting step, it is preferable to melt the glass raw materials at least by using direct electric heating. Moreover, it is preferable that the melting tank for performing the melting step is configured to contain a high zirconia-based refractory. The predetermined composition can be adjusted as appropriate within a range that satisfies the above-described content of each component of the glass, for example.

[Molding process]
In the forming step, the molten glass melted in the melting step is formed into flat glass. A down-draw method, particularly an overflow down-draw method, is suitable as a method for forming flat glass, and a glass ribbon is formed as flat glass. In addition, a float method, a redraw method, a rollout method, and the like can be applied. By adopting the down-draw method, the main surface of the obtained glass substrate is formed as a free surface that does not come into contact with anything other than the atmosphere, compared to the case of using other molding methods such as the float method. Since it has high smoothness and does not require a step of polishing the surface of the glass substrate after molding, the manufacturing cost can be reduced and productivity can also be improved. Furthermore, since both main surfaces of the glass substrate molded using the down-draw method have a uniform composition, etching can be performed uniformly regardless of the front and back surfaces during molding. can be done.

[Slow cooling process]
The heat shrinkage rate of the glass substrate can be controlled by appropriately adjusting the conditions during slow cooling. In particular, it is preferable to control the cooling conditions of the flat glass so as to reduce the thermal shrinkage of the flat glass. As described above, the thermal contraction rate of the glass substrate is 15 ppm or less, preferably 13 ppm or less, and more preferably 1 to 13 ppm. In order to manufacture a glass substrate having such a numerical value of thermal shrinkage, for example, when using the down-draw method, the cooling rate of the glass ribbon as flat glass is changed from Tg to (Tg-100°C) Slow cooling is preferably performed within the temperature range of 30 to 300°C/min. If the cooling rate is too fast, the thermal shrinkage cannot be sufficiently reduced. On the other hand, if the cooling rate is too slow, there arises a problem that the productivity is lowered and the size of the glass manufacturing apparatus (annealer) is increased. A preferable range of the cooling rate is 30 to 300°C/min, more preferably 50 to 200°C/min, and even more preferably 60 to 120°C/min. By setting the cooling rate to 30 to 300° C./min, the glass substrate of the present invention can be produced more reliably. The thermal shrinkage rate can also be reduced by separately performing slow cooling offline after cutting the flat glass downstream of the slow cooling process. Off-line slow cooling equipment is required. Therefore, as described above, it is preferable from the viewpoint of productivity and cost to control the rate of thermal shrinkage in the slow cooling step so as to omit the off-line slow cooling. In this specification, the cooling rate of the glass ribbon indicates the cooling rate of the central portion in the width direction of the glass ribbon.

Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the examples. In the examples and comparative examples shown below, the physical properties described below were measured.

(Strain point)
Using a differential thermal dilatometer (Thermo Plus2 TMA8310 manufactured by Rigaku Corporation), the low-temperature viscosity of the glass was measured by the isothermal penetration method. The viscosity was approximated using the Vogel Fulcher Tammann equation, and the temperature at which the viscosity of the glass was 10^14.5[dPa・s] was calculated. This temperature was taken as the strain point.

(devitrification temperature)
The glass was crushed, passed through a 2380 μm sieve, and the glass grains retained on the 1000 μm sieve were placed in a platinum boat. This platinum boat was held in an electric furnace with a temperature gradient of 1050 to 1380° C. for 16 hours, then taken out from the furnace and devitrification generated inside the glass was observed with a 50-fold optical microscope. The maximum temperature at which devitrification was observed was taken as the devitrification temperature.

(Measuring method of average coefficient of thermal expansion α and Tg in the range of 100 to 300°C)
It was measured using a differential thermal dilatometer (Thermo Plus2 TMA8310). The heating rate at this time was 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.

(Thermal shrinkage rate)
The heat shrinkage rate was determined by the marking line method on a glass having a size of 90 mm to 200 mm×15 to 30 mm×0.3 to 1 mm. As the heat treatment for the heat shrinkage measurement, an air circulation furnace (N120/85HA manufactured by Nabertherm) was used, the temperature was maintained at 500°C for 30 minutes, and the material was allowed to cool to room temperature.
Thermal shrinkage rate (ppm) = {Amount of shrinkage of glass during heat treatment/Distance between marking lines of glass before heat treatment} x 10 ⁶

When measuring the heat shrinkage of the glass obtained by melting the glass raw materials in a platinum crucible, pouring them onto an iron plate, and cooling and solidifying them, the glass should be cut, ground, and polished to a thickness of 0.5 mm, and an electric Using a furnace, the glass was held at a temperature of Tg+15° C. for 30 minutes and then removed from the furnace at a cooling rate of 150 to 250° C./min.

(density)
The density of the glass was measured by the Archimedes method.

(Etching rate)
Etching rate (μm/h) is obtained by immersing glass (12.5 mm x 20 mm x 0.7 mm) in an etching solution (200 mL) at 40°C with an HF concentration of 1 mol/kg and an HCl concentration of 5 mol/kg for 1 hour. The thickness reduction amount (μm) was measured, and the thickness reduction amount (μm) of one surface of the glass substrate per unit time (1 hour) was calculated.

Compositions and evaluations of examples will be described below.
Glasses of Examples 1 to 32 were produced according to the following procedure so as to have the glass compositions shown in Table 1. The strain point, devitrification temperature, Tg, average thermal expansion coefficient (α) in the range of 100 to 300° C., thermal contraction rate, density and etching rate of the obtained glass were determined.

Raw materials for each component were mixed so as to obtain the glass composition shown in Table 1, and then melted, clarified, and molded.

Examples 1 to 32 obtained as described above have a devitrification temperature of 1350° C. or lower, a strain point of 710° C. or higher, a glass transition temperature of 779° C. or higher, and an etching rate of 70 μm/h or higher. Met. Similar results were also obtained when glass raw materials were melted using direct electric heating and glass substrates were manufactured by the overflow down-draw method. Therefore, by using these glasses, it is possible to manufacture glass substrates that can be used in displays to which LTPS-TFTs are applied by the overflow down-draw method. These glass substrates are also suitable as OS-TFT glass substrates.

INDUSTRIAL APPLICABILITY The present invention is useful in fields related to glass substrates.

Claims (7)

SiO ₂ 69-72% in mol % as glass composition
Al ₂ O ₃ 11-15%
_{B2O3 0.5-1.8} %
MgO 1-4%
CaO 4-7%
SrO 0-1%
BaO 4-7%
_K2O 0.01-0.5%
_{P2O5 0.1-2.0} %
B ₂ O ₃ /P ₂ O ₅ 0.25-5
CaO/BaO 0.6-1.2
made of glass having
The strain point is 730 ° C. or higher,
The glass transition temperature is 779° C. or higher,
A display glass substrate having an etching rate of 78 μm/h or more . 2. The display glass substrate according to claim 1, which has a devitrification temperature of 1350[deg.] C. or lower. 3. The display glass substrate according to claim 1, which has a strain point of 735[ deg.] C. or higher. 4. The display glass substrate according to claim 1, which has a glass transition temperature of 790 ° C. or higher. 5. The display glass substrate according to claim 1, which has an etching rate of 80 μm/h or more. 6. The display glass substrate according to claim 1, wherein SiO ₂ /Al ₂ O ₃ is 4-6. The display glass substrate according to any one of claims 1 to 6, wherein MgO/RO is 0.15 to 0.4, provided that RO=MgO+CaO+SrO+BaO.