JP7256473B2 - Glass substrate and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a glass substrate that is suitable for high-definition displays and that is less likely to be electrostatically charged even when peeled off after being brought into contact with other members, and a method for producing the same.

BACKGROUND ART Conventionally, glass has been widely used as substrates for flat panel displays such as liquid crystal displays, hard disks, filters, sensors, and the like. In recent years, in addition to conventional liquid crystal displays, high-definition displays such as low-temperature polysilicon TFTs and organic ELs have been actively developed, and some have already been put to practical use.

Glass substrates used for high-definition displays are particularly required to have the following properties (1) to (5).

(1) It must be alkali-free glass. That is, if the content of the alkali metal oxide in the glass substrate is large, alkali ions diffuse into the semiconductor material on which the film is formed during heat treatment, resulting in deterioration of film characteristics.
(2) Low thermal shrinkage and excellent thermal stability. That is, the glass substrate is heat-treated to several hundred degrees in processes such as film formation and annealing. If the glass substrate is thermally shrunk during the heat treatment, pattern misalignment and the like are likely to occur. For example, in the manufacturing process of low-temperature polysilicon TFTs, there is a heat treatment process at 400 to 600.degree. If this dimensional change is large, a deviation occurs in the pixel pitch of the TFT, which causes display defects. Further, in the case of organic EL, even a slight change in dimension may cause display failure, so a glass substrate with an extremely low thermal shrinkage is required.
(3) High Young's modulus and specific Young's modulus in order to suppress defects caused by bending of the glass substrate.
(4) Excellent meltability and devitrification resistance from the viewpoint of glass production.
(5) It must have the chemical resistance and etching performance required in the display manufacturing process.

Patent Literature 1 proposes an alkali-free glass substrate suitable for high-definition displays.

JP 2016-183091 A

As described above, alkali-free glass substrates that do not contain alkali metal oxides are used as glass substrates for displays, but static charging may pose a problem. Glass, which is originally an insulator, is very easily charged, but alkali-free glass is particularly easily charged, and once charged static electricity tends to be maintained without escaping. In the manufacturing process of liquid crystal displays, charging of the glass substrate is caused by various processes. called electrification. Separation electrification of a glass substrate occurs not only in a process in the atmosphere of normal pressure but also in a vacuum process such as a process of etching a thin film on the substrate surface or a film forming process. Discharge occurs when a conductive substance approaches a charged glass substrate. Since the voltage of the charged static electricity reaches several tens of kV, the discharge causes breakdown (dielectric breakdown or electrostatic breakdown) of the elements and electrode wires on the surface of the glass substrate, or the glass substrate itself, resulting in display defects. . Among liquid crystal displays, especially low-temperature polysilicon TFT displays have minute semiconductor elements such as thin film transistors and electronic circuits formed on the surface of the glass substrate. It also attracts dust present in the charged environment and causes contamination of the substrate surface.

Well-known antistatic measures for glass substrates include neutralizing electric charges using an ionizer, raising the ambient temperature, and discharging accumulated electric charges into the air. However, these countermeasures cause an increase in cost, and there remains a problem that it is difficult to take effective countermeasures because electrification occurs in a wide variety of places during the process. Furthermore, these means cannot be used in vacuum processes such as plasma processes. Therefore, for flat panel displays such as liquid crystal displays, there is a strong demand for glass substrates that are less likely to be charged.

A technical object of the present invention is to provide a glass substrate that is suitable as a high-definition display substrate because of its low thermal shrinkage and is less likely to cause peeling electrification.

The glass substrate of the present invention, which was invented to solve the above problems, contains, in mass percentage, SiO ₂ 50 to 70%, Al ₂ O ₃ 10 to 25%, B ₂ O ₃ 0% or more to less than 3%, MgO 0 ~10%, CaO 0-15%, SrO 0-10%, BaO 0-15%, Na ₂ O 0.005-0.3%, β-OH value less than 0.18/mm, strain The point is 735° C. or higher.

In addition, the method for producing a glass substrate of the present invention includes, in mass percentage, SiO ₂ 50 to 70%, Al ₂ O ₃ 10 to 25%, B ₂ O ₃ 0% to less than 3%, MgO 0 to 10%, CaO 0 15% SrO 0-10% BaO 0-15% Na ₂ O 0.005-0.3%. It includes the melting process of melting in an electric melting furnace, the forming process of forming the molten glass into a plate shape, the slow cooling process of slowly cooling the plate glass in a slow cooling furnace, and the processing step of cutting the slowly cooled plate glass into specified dimensions. , a β-OH value of less than 0.18/mm, and a strain point of 735° C. or higher.

According to the knowledge of the present inventors, the non-alkali glass substrate has a lower thermal shrinkage rate as the β-OH value decreases, but when the β-OH value is less than 0.18/mm, it becomes remarkably easy to be charged. . According to the present invention, although the β-OH value is less than 0.18/mm, the glass substrate contains 0.005% by mass or more of Na ₂ O, which has the effect of lowering the specific resistance of the glass. can be suppressed. On the other hand, if a glass containing a large amount of B ₂ O ₃ contains Na ₂ O, B ₂ O ₃ tends to volatilize as a sodium compound during melting of the glass. Therefore, in the present invention, the content of B ₂ O ₃ is restricted to less than 3% by mass, so that volatilization of B ₂ O ₃ during melting of the glass can be suppressed and the amount of Na ₂ O in the glass can be stabilized. As a result, it becomes possible to stably obtain a glass substrate that has a low thermal shrinkage rate and is difficult to be charged.

The “β-OH value” refers to a value obtained by measuring the transmittance of glass using FT-IR and using the following formula.
β-OH value = (1/X)log(T1/T2)
X: Glass thickness (mm)
T1: Transmittance (%) at reference wavelength 3846 cm ⁻¹
T2: Minimum transmittance (%) near hydroxyl group absorption wavelength 3600 cm ^-1

Methods for lowering the β-OH value of the glass substrate in the present invention include the following methods. (1) Select a glass batch with a low water content (a glass raw material with a low water content or a glass cullet obtained by finely pulverizing a glass body with a low water content). (2) Addition of components (Cl, _SO3, etc.) that act to reduce the amount of water in the glass. (3) Reduce the moisture content in the furnace atmosphere. (4) _N2 bubbling in the molten glass; (5) Use a small melting furnace. (6) Increase the flow rate of molten glass. (7) Use an electric melting furnace.

As described above, when manufacturing the glass substrate of the present invention, it is preferable to use a glass batch with a water content as low as possible and to use an electric melting furnace from the viewpoint of lowering the β-OH value. When a glass batch is melted using an electric melting furnace, it is easier to reduce the moisture content in the molten glass than in a gas combustion furnace because the increase in moisture content in the atmosphere caused by gas combustion, etc. in the melting furnace can be suppressed. . Therefore, the glass produced in the electric melting furnace has a lower β-OH value. Also, the lower the β-OH value, the higher the strain point of the glass and the easier it is to obtain a glass substrate with a low thermal shrinkage. The electric melting furnace is desirably a completely electric melting furnace that does not use a burner, but it may be an electric melting furnace equipped with a burner or a heater for auxiliary radiant heating in the initial stage of melting.

In the present invention, the heat shrinkage of the glass substrate is preferably 20 ppm or less, 15 ppm or less, 12 ppm or less, 10 ppm or less, 9 ppm or less, 8 ppm or less, 7 ppm or less, 6 ppm or less, particularly 5 ppm or less. However, in order to make the thermal shrinkage rate of the glass substrate 0 ppm, productivity is significantly lowered, so it is preferably 1 ppm or more, 2 ppm or more, and particularly 3 ppm or more. Further, the variation of the thermal shrinkage rate of the glass substrate with respect to the target value is preferably ±1.0 ppm or less, particularly ±0.5 ppm or less. If the heat shrinkage rate of the glass substrate is high, display defects are likely to occur in low-temperature polysilicon TFT or organic EL displays. I can't do it. In order to reduce the variation in the thermal contraction rate of the glass substrate, the water content of the glass raw material may be adjusted, or the cooling rate in the slow cooling step may be adjusted.

The method for forming the glass substrate of the present invention is not particularly limited, but the float method is preferable from the viewpoint that the slow cooling process can be prolonged, and the surface quality of the glass substrate can be improved and the thickness can be reduced. From the viewpoint of doing so, the down-draw method, particularly the overflow down-draw method, is preferred. In the overflow down-draw method, the surfaces to be the front and back surfaces of the glass substrate do not come into contact with the molded body and are molded in a free surface state. As a result, a glass substrate is obtained in which the central portion in the plate thickness direction is the overflow confluence surface and both surfaces are fire-polished surfaces. As a result, an unpolished glass substrate having excellent surface quality (small surface roughness and waviness) can be manufactured at low cost.

In the present invention, when the down-draw method is employed, the length (height difference) of the slow cooling furnace is preferably 3 m or more. The slow cooling process is a process for removing distortion of the glass substrate, and the longer the slow cooling furnace, the easier it is to adjust the cooling rate of the sheet glass and to reduce the thermal shrinkage of the glass substrate. Therefore, the length of the slow cooling furnace is preferably 5 m or longer, 6 m or longer, 7 m or longer, 8 m or longer, 9 m or longer, and particularly preferably 10 m or longer.

In the present invention, the cooling rate of the sheet glass in the annealing step is 50 to 1000°C/min, 100 to 1000°C/min, and 100 to 800°C in the temperature range from the annealing point to (annealing point -100°C). /min, preferably an average cooling rate of 300°C/min to 800°C/min. The thermal contraction rate of the glass substrate also varies depending on the cooling rate when slowly cooling the sheet glass. That is, a glass substrate that is cooled quickly has a high thermal shrinkage rate, and a glass substrate that is cooled slowly has a low thermal shrinkage rate.

In the present invention, the annealed sheet glass is subjected to a cutting process. That is, a molded plate-shaped glass (glass ribbon) is cut into a predetermined size. After that, in order to prevent damage from the end faces, end face grinding or end face polishing may be performed. The glass substrate thus obtained preferably has a short side of 1500 mm or more and a long side of 1850 mm or more. That is, as the size of the glass substrate increases, the production efficiency of the glass substrate improves. , particularly preferably 3400 mm or more.

In the present invention, the thickness of the glass substrate is preferably 0.7 mm or less, 0.6 mm or less, 0.5 mm or less, particularly 0.4 mm or less. As the thickness is reduced, the weight of the glass substrate can be reduced, which is suitable for mobile display substrates. However, if the thickness of the glass substrate is too small, it is likely to be damaged due to separation electrification.

In order to further suppress the separation electrification of the glass substrate of the present invention, it is desirable that at least one surface is a fine uneven surface. The surface shape of the fine uneven surface may be such that the surface roughness Ra is 0.1 to 10 nm. As a method for making the surface of the glass substrate into a fine uneven surface, physical polishing using a polishing apparatus, or a chemical etching method such as applying an etchant to the glass substrate or spraying an etching gas may be adopted. good. The use of the latter chemical etching is preferable because glass powder and the like are less likely to adhere to the glass substrate and the surface can be cleaned. Since the glass substrate of the present invention is originally resistant to peeling electrification, it is possible to shorten the processing time and improve the productivity even when fine irregularities are formed on the surface.

According to the present invention, it is possible to stably obtain a glass substrate that is suitable as a high-definition display substrate because of its low thermal shrinkage and that is less susceptible to peeling electrification.

It is explanatory drawing which shows the method of measuring the heat shrinkage rate of a glass substrate. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows the apparatus used for the measurement of the peeling charge amount of a glass substrate, (a) is explanatory drawing which shows the state which separated the glass substrate from the table, (b) is the state which placed the glass substrate on the table. It is an explanatory diagram showing.

In this specification, the numerical range indicated using "to" means a range including the numerical values before and after "to" as the minimum and maximum values, respectively.

The glass substrate of the present invention contains, in mass percentage, SiO ₂ 50 to 70%, Al ₂ O ₃ 10 to 25%, B ₂ O ₃ 0 to 3%, MgO 0 to 10%, CaO 0 to 15%, It contains 0-10% SrO, 0-15% BaO, and 0.005-0.3% Na ₂ O. The reason why the content of each glass component is regulated as described above will be explained below. In addition, % display of each component below refers to % by mass unless otherwise specified.

When the content of SiO ₂ decreases, the chemical resistance, particularly the acid resistance, tends to decrease, and the strain point tends to decrease. In addition, the density increases, making it difficult to reduce the weight of the glass substrate. The density of the glass is preferably less than 2.70 g/cm ³ , even less than 2.65 g/cm ³ . On the other hand, when the content of SiO ₂ increases, the high-temperature viscosity increases, the meltability tends to decrease, and etching takes a long time. Furthermore, SiO ₂ -based crystals, particularly cristobalite, are precipitated to lower the liquidus viscosity, that is, the devitrification resistance tends to be lowered. Therefore, SiO ₂ is preferably 50% or more, 55% or more, 58% or more, 60.5% or more, further 61% or more, 70% or less, 65% or less, 64% or less, 63.5% or less, 63% or more. % or less, 62.5% or less, and more preferably 62% or less.

When the content of Al ₂ O ₃ is reduced, the strain point is lowered, the thermal shrinkage rate is increased, and the Young's modulus is lowered, making the glass substrate more flexible. On the other hand, when the content of Al ₂ O ₃ increases, the resistance to BHF (buffered hydrofluoric acid) deteriorates, the surface of the glass tends to become cloudy, and the resistance to cracking deteriorates, making the glass more susceptible to breakage. Furthermore, SiO ₂ —Al ₂ O ₃ system crystals, especially mullite, precipitate in the glass, and the liquidus viscosity tends to decrease. Therefore, Al ₂ O ₃ is preferably 10% or more, 13% or more, 15% or more, 16% or more, 17% or more, 17.5% or more, further 18% or more, 25% or less, 23% or less, 21 % or less, 20% or less, 19% or less, 19.7% or less, and more preferably 19.5% or less.

B ₂ O ₃ is a component that acts as a flux and reduces viscosity to improve meltability. When the content of B ₂ O ₃ increases, the molten glass volatilizes and the glass components tend to fluctuate. Moreover, as the content of B ₂ O ₃ increases, the strain point decreases, and the heat resistance and acid resistance tend to decrease. Furthermore, the Young's modulus is lowered, and the deflection amount of the glass substrate tends to increase. Therefore, B ₂ O ₃ is preferably less than 3%, 2% or less, 1.7% or less, 1.5% or less, 1.4% or less, 1% or less, or substantially not contained. However, from the viewpoint of improving meltability and preventing deterioration of BHF resistance and crack resistance, B ₂ O ₃ is 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more , and may be contained in an amount of 0.5% or more.

As described above, the β-OH value of glass is easily affected by moisture contained in the glass batch fed into the glass melting furnace. Therefore, it is easy to bring moisture into the glass. Therefore, the lower the B ₂ O ₃ content in the glass, the easier it is for the β-OH value of the glass to decrease. Further, the lower the β-OH value, the higher the strain point of the glass and the easier it is to reduce the thermal shrinkage of the glass substrate. For the above reasons, in the present invention, it is preferable to reduce the amount of B ₂ O ₃ as much as possible, and it is desirable to contain substantially no B ₂ O ₃ . Here, “substantially free of B ₂ O _{3 ”} means intentionally not containing B ₂ O ₃ as a raw material, and does not deny contamination from impurities. Specifically, it means that the content of B ₂ O ₃ is 0.1% or less.

MgO is a component that lowers high-temperature viscosity and enhances meltability. Among alkaline earth metal oxides, _MgO is a component that significantly increases Young's modulus. It precipitates and the liquidus viscosity tends to decrease. In addition, MgO is a component that tends to react with BHF to form products. When the content of MgO is too small, it becomes difficult to obtain the above effects, and when the content of MgO is too much, devitrification resistance and strain point tend to be lowered. Therefore, the content of MgO is preferably 10% or less, 9% or less, 8% or less, 6% or less, 5% or less, 4% or less, 3.5% or less, particularly 3% or less. Further, it is preferably 1% or more, 1.5% or more, particularly 2% or more.

CaO is a component that lowers the high-temperature viscosity and remarkably enhances the meltability without lowering the strain point. In addition, among the alkaline earth metal oxides, since the raw material to be introduced is relatively inexpensive, it is a component that reduces the raw material cost. When the content of CaO decreases, it becomes difficult to receive the above effects. On the other hand, if the content of CaO is too high, the glass tends to devitrify and the coefficient of thermal expansion tends to increase. Therefore, the CaO content is preferably 15% or less, 12% or less, 11% or less, 8% or less, particularly 6% or less. Further, it is preferably 1% or more, 2% or more, 3% or more, 4% or more, particularly 5% or more.

SrO is a component that suppresses the phase separation of the glass and increases the resistance to devitrification. Furthermore, it is a component that lowers the high-temperature viscosity without lowering the strain point to enhance the meltability and suppresses the rise in the liquidus temperature. When the content of SrO decreases, it becomes difficult to enjoy the above effects. On the other hand, when the content of SrO increases, strontium silicate-based devitrification crystals tend to precipitate, and devitrification resistance tends to decrease. Therefore, the content of SrO is preferably 10% or less, 7% or less, 5% or less, 4% or less, particularly 3% or less. Further, it is preferably 0.1% or more, 0.2% or more, 0.3% or more, 0.5% or more, 1.0% or more, particularly 1.5% or more.

BaO is a component that remarkably increases devitrification resistance. When the content of BaO decreases, it becomes difficult to receive the above effects. On the other hand, when the content of BaO increases, the density becomes too high and meltability tends to decrease. In addition, devitrified crystals containing BaO tend to precipitate, and the liquidus temperature tends to rise. Therefore, the content of BaO is 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, 10.5% or less, 10% or less, 9.5% or less, particularly 9% or less. is preferred. Further, it is preferably 1% or more, 3% or more, 4% or more, 5% or more, 6% or more, particularly 7% or more.

Na ₂ O is a component that lowers the resistivity of glass. When the content of Na ₂ O decreases, it becomes difficult to receive the above effects. On the other hand, when the content of Na ₂ O increases, alkali ions diffuse into the semiconductor material on which the film is formed during heat treatment, resulting in deterioration of film characteristics. Therefore, Na ₂ O is 0.005% or more, 0.008% or more, 0.01% or more, 0.02% or more, 0.025% or more, 0.03% or more, and further 0.05% or more It is preferably 0.3% or less, more preferably 0.2% or less.

K ₂ O may be added as an alkali metal oxide other than Na ₂ O. K ₂ O is also a component that lowers the resistivity of glass. When the content of K ₂ O decreases, it becomes difficult to enjoy the above effects. On the other hand, if the content of K ₂ O increases, alkali ions will diffuse into the semiconductor material on which the film is formed during heat treatment, resulting in deterioration of film characteristics. Therefore, K ₂ O is 0.001% or more, 0.002% or more, 0.005% or more, 0.01% or more, 0.02% or more, 0.025% or more, 0.03% or more, and further 0.05% or more is preferable, and 0.3% or less, and more preferably 0.2% or less. K ₂ O can be contained more than Na ₂ O.

Furthermore, Li ₂ O, which is an alkali metal oxide other than Na ₂ O and K ₂ O, can be added as appropriate. However, if the content of alkali metal oxides increases, alkali ions will diffuse into the semiconductor material on which the film is formed during heat treatment, resulting in deterioration of film _{characteristics .} The total amount of O and K ₂ O) is preferably 0.4% or less.

In the present invention, the glass substrate may contain the following components in addition to the above components.

The glass substrate of the present invention preferably contains 0.005 to 0.1% of Fe ₂ O ₃ . Fe ₂ O ₃ , like Na ₂ O, is a component that has the effect of lowering the specific resistance of the glass. By containing a certain amount or more of Fe ₂ O ₃ , the effect of suppressing electrification of the glass substrate is further enhanced. . Fe ₂ O ₃ is preferably contained in an amount of 0.005% or more, 0.008% or more, particularly 0.01% or more. However, if the content of Fe ₂ O ₃ exceeds 0.1%, the transmittance of the glass is lowered, which may not be _preferable as a display substrate _.

The glass substrate of the present invention preferably contains 0.001 to 0.5% SnO ₂ . SnO ₂ is a component that has a good refining action in a high temperature range, raises the strain point and lowers the high temperature viscosity. Also, in the case of an electric melting furnace using molybdenum electrodes, there is an advantage that the electrodes are not eroded. On the other hand, when the content of SnO ₂ increases, the precipitation of devitrified crystals of SnO ₂ tends to occur, and the precipitation of devitrified crystals of ZrO ₂ tends to be promoted. Therefore, the content of SnO ₂ is 0.001-0.5%, 0.001-0.45%, 0.001-0.4%, 0.01-0.35%, 0.1-0. 3%, particularly preferably 0.15 to 0.3%.

Further, other components that the glass substrate of the present invention may contain will be described.

ZnO is a component that enhances meltability. However, when the content of ZnO increases, the glass tends to devitrify and the strain point tends to decrease. The content of ZnO is preferably 0-5%, 0-4%, 0-3%, especially 0-2%.

ZrO ₂ is a component that enhances chemical durability, but when the content of ZrO ₂ increases, devitrification lumps of ZrSiO ₄ tend to occur. The content of ZrO ₂ is preferably 0-5%, 0-4%, 0-3%, especially 0.01-2%.

TiO ₂ is a component that lowers the high-temperature viscosity and enhances the meltability, as _well as suppressing coloration due to solarization. The content of TiO ₂ is preferably 0-5%, 0-4%, 0-3%, 0-2%, especially 0-0.1%.

P ₂ O ₅ is a component that raises the strain point and suppresses the precipitation of alkaline earth aluminosilicate-based devitrified crystals such as anorthite. However, when a large amount of P ₂ O ₅ is contained, the glass tends to undergo phase separation. The content of P ₂ O ₅ is preferably 0 to less than 0.15%, 0 to 1%, 0 to 0.1%, and is substantially free from the viewpoint of facilitating glass recycling. Specifically, it is preferably less than 0.01%.

Metal powders such as Cl, F, SO ₃ , C, CeO ₂ or Al, Si can be contained up to a total amount of 3%. As ₂ O ₃ and Sb ₂ O ₃ are useful as clarifiers, but from the viewpoint of the environment and electrode erosion prevention, it is desirable that they should not be substantially contained. Here, "substantially free" means that the total amount of As ₂ O ₃ and Sb ₂ O ₃ is 0.1% or less.

The glass substrate of the present invention has a β-OH value of less than 0.18/mm. The lower the β-OH value of the glass, the higher the strain point of the glass and the lower the thermal shrinkage rate. /mm or less, preferably 0.07/mm or less, particularly 0.05/mm or less. However, from the viewpoint of suppressing electrification of the glass substrate, the β-OH value is preferably 0.01/mm or more, 0.02/mm or more, particularly 0.03/mm or more.

The glass substrate of the present invention has a strain point of 735° C. or higher. In order to reduce the thermal shrinkage of the glass substrate, it is desirable to make the strain point as high as possible, preferably 740° C. or higher, 745° C. or higher, more preferably 750° C. or higher. However, the higher the strain point, the higher the temperature during melting and molding of the glass and the higher the manufacturing cost of the glass substrate.

For the same reason as the strain point, the glass substrate of the present invention preferably has an annealing point of 780° C. or higher, 790° C. or higher, 800° C. or higher, 810° C. or higher, particularly 820° C. or higher. However, the higher the annealing point, the higher the temperature during melting and molding of the glass, and the higher the manufacturing cost of the glass substrate. .

The glass substrate of the present invention preferably has a Young's modulus of 80 GPa or more. The higher the Young's modulus, the smaller the bending of the glass substrate and the easier the handling during transportation and packaging. Young's modulus is preferably 81 GPa or more, 82 GPa or more, 83 GPa or more, 84 GPa or more, and more preferably 85 GPa or more.

The glass substrate of the present invention preferably has a temperature corresponding to 10 ^4.5 dPa·s of 1330° C. or lower, 1320° C. or lower, particularly 1310° C. or lower. If the temperature corresponding to 10 ^4.5 dPa·s increases, the temperature during molding becomes too high, and the production yield tends to decrease.

The glass substrate of the present invention preferably has a temperature corresponding to 10 ^2.5 dPa·s of 1670° C. or lower, 1660° C. or lower, particularly 1650° C. or lower. When the temperature corresponding to 10 ^2.5 dPa·s becomes high, the glass becomes difficult to melt, defects such as bubbles increase, and the production yield tends to decrease.

The glass substrate of the present invention preferably has a liquidus temperature of less than 1250°C, less than 1240°C, less than 1230°C, particularly less than 1220°C. In this way, devitrified crystals are less likely to occur during glass production, so that the glass can be easily formed into a plate shape by the overflow down-draw method. As a result, the surface quality of the glass substrate can be improved, and a decrease in manufacturing yield can be suppressed. From the viewpoint of increasing the size of glass substrates and increasing the definition of displays, it is of great significance to improve the devitrification resistance of glass and to minimize devitrification substances that may become surface defects.

The glass substrate of the present invention has a viscosity at the liquidus temperature of 10 ^4.9 dPa·s or more, 10 ^5.0 dPa·s or more, 10 ^5.1 dPa·s or more, 10 ^5.2 dPa·s or more, particularly 10 5.2 dPa·s ^{or more.} It is preferably ³ dPa·s or more. In this way, devitrification is less likely to occur during glass molding, so that it is easier to mold into a plate shape by the overflow down-draw method, and the surface quality of the glass substrate can be improved. The viscosity at the liquidus temperature is an index of moldability, and the higher the viscosity at the liquidus temperature, the better the moldability.

(Example 1)
Tables 1 and 2 show example glasses of the present invention (Sample Nos. 1 to 9) and conventional glass (Sample No. 10). The contents of components other than Na ₂ O, K ₂ O, Fe ₂ O ₃ and ZrO ₂ in the table are rounded off to the second decimal place.

The glass samples in Tables 1 and 2 were produced as follows. First, a glass batch prepared by mixing glass raw materials so as to have the composition shown in the table was placed in a platinum crucible and then melted at 1600 to 1650° C. for 24 hours. In melting the glass batch, a platinum stirrer was used to stir and homogenize the glass batch. Then, the molten glass was poured onto a carbon plate to form a plate, and then slowly cooled at a temperature near the annealing point for 30 minutes. For each sample thus obtained, strain point, annealing point, density, Young's modulus, temperature corresponding to 10 ^4.5 dPa s, temperature corresponding to 10 ^2.5 dPa s, liquidus temperature TL, liquid Log ₁₀ ηTL was measured for viscosity ηTL (dPa·s) at phase temperature.

The strain point and annealing point in Tables 1 and 2 were measured according to ASTM C336.

Density was measured by the Archimedes method according to ASTM C693.

Young's modulus was measured by the bending resonance method according to JISR1602.

The temperatures corresponding to 10 ^4.5 dPa·s and 10 ^2.5 dPa·s were measured by the platinum ball pull-up method.

The liquidus temperature TL is measured by passing through a standard sieve of 30 meshes (500 μm), putting the glass powder remaining on the 50 meshes (300 μm) into a platinum boat, and holding it in a temperature gradient furnace set at 1100° C. to 1350° C. for 24 hours. After that, the platinum boat was taken out, and the temperature at which devitrification (crystal foreign matter) was observed in the glass was measured.

The viscosity Log ₁₀ ηTL at the liquidus temperature was calculated by measuring the viscosity ηTL of the glass at the liquidus temperature by _the platinum ball pull-up method.

The β-OH value was obtained by measuring the transmittance of the glass using FT-IR and using the following formula.
β-OH value = (1/X)log(T1/T2)
X: Glass thickness (mm)
T1: Transmittance (%) at reference wavelength 3846 cm ⁻¹
T2: Minimum transmittance (%) near hydroxyl group absorption wavelength 3600 cm ^-1

As is clear from Tables 1 and 2, each of the samples Nos. 1 to 9 has a strain point of 735° C. or higher and an annealing point of 785° C. or higher, so that the glass easily has a thermal shrinkage of 20 ppm or less. In addition, since the Young's modulus is 80.4 GPa or more, it is difficult to bend, and since the liquidus temperature TL is 1246 ° C. or less and the viscosity ηTL at the liquidus temperature is 10 ^4.9 dPa s or more, devitrification hardly occurs during molding. . Especially No. Each of samples 1, 2, 7 to 9 had a viscosity ηTL of 10 ^5.2 dPa·s or more at the liquidus temperature, and was therefore suitable for the overflow downdraw method.

(Example 2)
Sample No. in Table 2. Glass batches were prepared to be 8 and 10 glasses. Next, this glass batch was put into an electric melting furnace and melted at 1600 to 1650° C. After the molten glass was clarified and homogenized in a clarification tank and a homogenization tank, it was adjusted to a viscosity suitable for molding in a pot. . Then, after forming the molten glass into a plate with an overflow down-draw device, set the average cooling rate to 385 ° C./min in the temperature range from the annealing point to (annealing point -100 ° C.) in a slow cooling furnace with a length of 5 m. and cooled slowly. After that, the sheet glass was cut and the edges were processed to produce a glass substrate having dimensions of 1500×1850×0.7 mm.

The β-OH value and thermal shrinkage of each glass substrate thus obtained were measured. The glass substrate No. 8 had a β-OH value of 0.1/mm and a thermal shrinkage of 10 ppm. On the other hand, sample no. The glass substrate No. 10 had a β-OH value of 0.3/mm and a thermal shrinkage of 25 ppm.

The thermal contraction rate of the glass substrate was measured by the following method. First, as shown in FIG. 1A, a strip-shaped sample G of 160 mm×30 mm was prepared as a glass substrate sample. Markings M were formed at positions 20 to 40 mm away from the edge of the strip-shaped sample G using #1000 water-resistant abrasive paper on both ends of the strip-shaped sample G in the long side direction. After that, as shown in FIG. 1(b), the strip-shaped sample G with the markings M formed thereon was folded in two along the direction perpendicular to the markings M to prepare sample pieces Ga and Gb. Then, only one sample piece Gb was heated from room temperature (25° C.) to 500° C. at a rate of 5° C./min, held at 500° C. for 1 hour, and then subjected to heat treatment in which the temperature was lowered to room temperature at a rate of 5° C./min. . After the heat treatment, as shown in FIG. 1(c), the sample piece Ga not subjected to the heat treatment and the sample piece Gb subjected to the heat treatment are arranged in parallel, and the markings M of the two sample pieces Ga and Gb are marked. The amount of misalignment (ΔL1, ΔL2) was read with a laser microscope, and the thermal shrinkage rate was calculated by the following formula. Note that l ₀ in the formula is the initial distance between the markings M.
Thermal shrinkage = [{ΔLl (μm)+ΔL2 (μm)}×10 ³ ]/l ₀ (mm) (ppm)

Next, the sample no. For each of the glass substrates Nos. 8 and 10, the peel electrification was evaluated using the apparatus shown in FIG.

As shown in FIG. 2(a), the support 1 for the glass substrate G has pads 2 made of Teflon (registered trademark) for supporting the four corners of the glass substrate G. As shown in FIG. The support table 1 is provided with a metal aluminum table 3 that can be raised and lowered. By moving the table 3 up and down as shown in FIG. By separating the glass substrate G, the glass substrate G can be charged. Note that the table 3 is grounded. One or more holes (not shown) are formed in the table 3, and these holes are connected to a diaphragm-type vacuum pump (not shown). When the vacuum pump is driven, air is sucked from the holes of the table 3, whereby the glass substrate G can be vacuum-adsorbed to the table 3. As shown in FIG. A surface potential meter 4 is installed at a position 10 mm above the glass substrate G to continuously measure the amount of charge generated in the central portion of the glass substrate G. FIG. Also, an air gun 5 with an ionizer is installed above the glass substrate G, so that the charge on the glass substrate G can be eliminated.

Using this device, the separation electrification of the glass substrate was measured in the next step. The experiment was conducted in a clean booth at a temperature of 25° C. and a humidity of 40%. Since the amount of charge varies greatly depending on the atmosphere, especially the humidity in the air, it is necessary to pay particular attention to the adjustment of the humidity.

(1) Place the glass substrate G on the support pad 2 of the support table 1 .
(2) Eliminating the charge on the glass substrate G with an air gun 5 with an ionizer.
(3) The table 3 is lifted to come into contact with the glass substrate G, and the table 3 and the glass substrate G are brought into close contact with each other for 20 seconds by vacuum suction.
(4) The glass substrate G is separated from the table 3 by lowering the table 3, and the charge amount generated in the central portion of the glass substrate G is continuously measured by the surface potential meter 4.
(5) By repeating the above steps (3) and (4), a total of five peel evaluations are continuously performed.
The maximum electrification amount in each measurement is obtained, and these are integrated to obtain the peeling electrification amount.

As a result, sample no. While the peeling charge amount of the glass substrate of sample No. 8 was 1000 V, the sample No. No. 10 had a peeling charge amount as large as 2000V. Also sample no. Etching gas was sprayed on one surface of the glass substrate No. 8 to set the surface roughness Ra to 1 nm, and then the peeling electrification amount was measured to be 800V.

G glass sample (glass substrate)
M Marking 1 Support base 2 Pad 3 Table 4 Surface potential body 5 Air gun with ionizer

Claims (13)

In mass percentage, SiO ₂ 50-70%, Al ₂ O ₃ 18-25 %, B ₂ O ₃ 0-3%, MgO 0-10%, CaO 0-15%, SrO 0-10%, BaO 0-15%, Na ₂ O 0.005-0.3%, P ₂ O ₅ 0-1%, β-OH value less than 0.18/mm, strain point 735°C or higher A glass substrate characterized by: 2. The glass substrate according to claim 1, containing 0.005 to 0.1% of Fe ₂ O ₃ in mass percentage. 3. The glass substrate according to claim 1, containing 0.001 to 0.5% SnO ₂ in mass percentage. 4. The glass substrate according to claim 1, which has a Young's modulus of 80 GPa or more. 5. The glass substrate according to any one of claims 1 to 4, which has a heat shrinkage rate of 20 ppm or less. 6. The glass substrate according to any one of claims 1 to 5, wherein at least one surface is a fine uneven surface. 7. The glass substrate according to claim 6, wherein the fine uneven surface has a surface roughness Ra of 0.1 to 10 nm. 8. The glass substrate according to any one of claims 1 to 7, wherein the content of P ₂ O ₅ is less than 0.01% in mass percentage. In mass percentage, SiO ₂ 50-70%, Al ₂ O ₃ 18-25 %, B ₂ O ₃ 0-3%, MgO 0-10%, CaO 0-15%, SrO 0-10%, BaO 0-15% Na ₂ O 0.005-0.3% P ₂ O ₅ 0-1% P 2 O 5 0-1%; It includes a melting step of melting in a furnace, a forming step of forming the molten glass into a plate shape, a slow cooling step of slowly cooling the plate glass in a slow cooling furnace, and a processing step of cutting the slowly cooled plate glass into a predetermined size. A method for producing a glass substrate, comprising obtaining a glass substrate having a −OH value of less than 0.18/mm and a strain point of 735° C. or higher. The cooling rate of the sheet glass in the annealing step is an average cooling rate of 50° C./min to 1000° C./min in the temperature range from the annealing point to (annealing point −100° C.). 9. The method for producing a glass substrate according to 9. 11. The method for producing a glass substrate according to claim 9, wherein at least one surface is chemically etched. 11. The method of manufacturing a glass substrate according to claim 9, wherein at least one surface is physically polished. The method for producing a glass substrate according to any one of claims 9 to 12, wherein the content of P ₂ O ₅ is less than 0.01% in mass percentage.

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