TWI758576B - Glass substrate and method for producing the same - Google Patents

Abstract

The technical subject of this invention is to provide the glass substrate and its manufacturing method which are suitable as a high-definition display substrate because the thermal shrinkage rate is small, and are hard to cause peeling electrification. The glass substrate of the present invention is characterized by containing 50-70% of SiO ₂ , 10-25% of Al ₂ O ₃ , 0% or more but less than 3% of B ₂ O ₃ , 0-10% by mass percentage MgO, 0~15% CaO, 0~10% SrO, 0~15% BaO, and 0.005~0.3% Na ₂ O, and the β-OH value does not reach 0.18/mm, the strain point is 735°C above.

Description

Glass substrate and method for producing the same

The present invention relates to a glass substrate and a method for manufacturing the same. The glass substrate is suitable for high-definition displays, and is less likely to be charged by static electricity even if it is peeled off after being in contact with other components.

Glass has been widely used as a substrate for flat panel displays such as liquid crystal displays, hard disks, filters, sensors, and the like. In recent years, in addition to the previous liquid crystal displays, high-definition displays such as low-temperature polysilicon TFT (Thin Film Transistor, thin film transistor) or organic EL (Electroluminescence, electroluminescence) have been widely developed in the industry, and some of them have been put into practical use.

For glass substrates used for high-definition displays, the following characteristics (1) to (5) are particularly required.

(1) It is an alkali-free glass. That is, when the content of the alkali metal oxide in the glass substrate is large, the alkali ions diffuse into the semiconductor substance formed into the film during the heat treatment, and the characteristics of the film are deteriorated.

(2) The thermal shrinkage rate is low and the thermal stability is excellent. That is, the glass substrate is heat-treated to several hundred degrees in steps such as film formation and annealing. During the heat treatment, when the glass substrate is thermally shrunk, pattern shift and the like are likely to occur. For example, there is a heat treatment step of 400~600°C in the manufacturing step of low temperature polysilicon TFT In the heat treatment step, the glass substrate is thermally shrunk, resulting in a dimensional change. If the dimensional change is large, the pixel pitch of the TFT is shifted, which causes display failure. Moreover, in the case of organic EL, even a slight dimensional change may cause display failure, so a glass substrate with an extremely low thermal shrinkage rate is required.

(3) Young's modulus may be higher than Young's modulus in order to suppress abnormality due to deflection of the glass substrate.

(4) From the viewpoint of glass production, it is excellent in meltability and devitrification resistance.

(5) It has chemical resistance or etching performance required in the manufacturing process of the display.

Patent Document 1 discloses an alkali-free glass substrate suitable for high-definition displays.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2016-183091

As described above, an alkali-free glass substrate that does not contain an alkali metal oxide is used as a glass substrate for a display, but there are cases where static charging can cause problems. Glass that is originally an insulator is very easy to be charged, and alkali-free glass is especially easy to be charged, and the temporarily charged static electricity has a tendency to be maintained without escaping. In the production steps of liquid crystal displays, etc., the glass substrate is charged in various steps, and the charging caused by peeling off the glass substrate after contacting the glass substrate with the flat metal or insulator in the film forming step is called peeling charging. The peeling charge of the glass substrate is not only in the step in the atmosphere of normal pressure Occurs, and also occurs in vacuum steps such as the step of etching the thin film on the surface of the substrate or the step of forming the film. Discharge occurs when the conductive substance approaches the charged glass substrate. In addition, since the voltage of the charged static electricity reaches several 10kV, the components or electrode lines on the surface of the glass substrate, or the damage of the glass substrate itself (insulation damage or electrostatic damage) may be caused by the discharge, which will become the cause of poor display. Among liquid crystal displays, especially low-temperature polysilicon TFT displays, fine semiconductor elements or electronic circuits such as thin film transistors are formed on the surface of the glass substrate. However, the elements or circuits are very weak against static electricity, so they are particularly problematic. In addition, it attracts the dust existing in the charged environment and becomes the cause of the contamination of the substrate surface.

As antistatic measures for glass substrates, there are known methods of neutralizing electric charges using an ionizer, or raising the temperature in the environment to discharge accumulated electric charges into the air. However, these countermeasures are not only the cause of the increase in cost, but also cause many points of electrification in the steps, so there is a problem that it is difficult to provide effective countermeasures. Furthermore, these methods cannot be used in vacuum processes such as plasma processes. Therefore, for the use of flat panel displays represented by liquid crystal displays, there is a strong demand for glass substrates that are not easily charged.

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

The glass substrate of the present invention invented to solve the above-mentioned problems is characterized in that it contains 50 to 70% by mass of SiO ₂ , 10 to 25% of Al ₂ O ₃ , and 0% or more and less than 3% of B ₂ . O ₃ , 0~10% MgO, 0~15% CaO, 0~10% SrO, 0~15% BaO, and 0.005~0.3% Na ₂ O, and the β-OH value does not reach 0.18/ mm, the strain point is above 735°C.

Moreover, the manufacturing method of the glass substrate of the present invention is characterized by comprising: a raw material preparation step for preparing a glass batch, the glass batch containing 50 to 70% of SiO ₂ and 10 to 25% of SiO 2 by mass percentage. Al ₂ O ₃ , 0% or more but less than 3% B ₂ O ₃ , 0~10% MgO, 0~15% CaO, 0~10% SrO, 0~15% BaO, and 0.005~ 0.3% Na2O glass _; melting step, which melts the glass batch in an electric melting furnace; forming step, which shapes the molten glass into a sheet; slow cooling step, which melts the sheet glass Slow cooling in a slow cooling furnace; and a processing step, which cuts the slowly cooled plate glass into a specific size; and the manufacturing method obtains a β-OH value of less than 0.18/mm and a strain point of 735°C or higher. glass substrate.

According to the knowledge of the present inventors, as the β-OH value of the alkali-free glass substrate decreases, the thermal shrinkage rate decreases. However, when the β-OH value is less than 0.18/mm, it is remarkably easy to be charged. According to the present invention, although the β-OH value is less than 0.18/mm, the electrification of the glass substrate can be suppressed by containing 0.005 mass % or more of Na ₂ O which has the effect of lowering the specific resistance of the glass. On the other hand, when 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 when the glass is melted. Therefore, in the present invention, by limiting B ₂ O ₃ to less than 3 mass %, volatilization of B ₂ O ₃ at the time of glass melting can be suppressed, and the amount of Na ₂ O in the glass can be stabilized. Thereby, the glass substrate with a low thermal shrinkage rate and being hard to be charged can be obtained stably.

In addition, "(beta)-OH value" means the value calculated|required using the following formula by measuring the transmittance|permeability of glass using FT-IR (Fourier Transform Infrared Radiation, Fourier Transform Infrared Spectroscopy).

β-OH value=(1/X)log(T1/T2)

X: glass thickness (mm)

T1: Transmittance (%) at reference wavelength 3846cm ^-1

T2: The minimum transmittance (%) around the hydroxyl absorption wavelength of 3600cm ^-1

As a method of lowering the β-OH value of the glass substrate in the present invention, the following methods are exemplified. (1) Select a glass batch with lower water content (glass raw material with lower water content, or cullet in which the glass body with lower water content is finely pulverized). (2) A component (Cl, SO ₃ , etc.) having the effect of reducing the water content in the glass is added. (3) The moisture content in the furnace atmosphere is reduced. (4) Pour N ₂ into the molten glass. (5) Use a small melting furnace. (6) Increase the flow rate of molten glass. (7) Electric melting furnace is used.

In the case of manufacturing the glass substrate of the present invention as described above, from the viewpoint of lowering the β-OH value, it is preferable to use a glass batch having a lower water content as much as possible, and to use an electric melting furnace. When the glass batch is melted using an electric melting furnace, the increase in the moisture content of the atmosphere due to gas combustion in the melting furnace is suppressed, so that the moisture in the molten glass is more likely to be released than the gas burning furnace. amount decreased. Therefore, the β-OH value of the glass produced by the electric melting furnace decreases. Moreover, 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 lower thermal shrinkage rate. The electric melting furnace is preferably a pure electric melting furnace that does not use a burner, but may be an electric melting furnace provided with a burner or a heater for auxiliary radiant heating in the initial stage of melting.

In the present invention, the thermal shrinkage rate 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. ppm or less, especially 5ppm or less. However, if the thermal shrinkage rate of the glass substrate is set to 0 ppm, the productivity will be significantly reduced, so it is preferably 1 ppm or more, 2 ppm or more, and especially 3 ppm or more. Moreover, it is preferable that the deviation with respect to the target value of the thermal contraction rate of a glass substrate is ±1.0 ppm or less, especially ±0.5 ppm or less. If the thermal shrinkage rate of the glass substrate is high, display failures of low-temperature polysilicon TFT or organic EL displays are likely to occur, and if the thermal shrinkage rate of the glass substrate varies greatly, the display substrate cannot be stably produced. In order to reduce the variation of the thermal shrinkage rate of the glass substrate, it is only necessary to adjust the moisture content of the glass raw material, or to adjust the cooling rate of the slow cooling step.

The method for forming the glass substrate of the present invention is not particularly limited, but the float method is preferred from the viewpoint of prolonging the slow cooling step, and from the viewpoint of improving the surface quality of the glass substrate or reducing the thickness of the glass substrate , preferably the down-draw method, especially the overflow down-draw method. In the overflow down-draw method, the surfaces of the glass substrate that should be the front and back surfaces are not in contact with the molded body, but are molded in the state of free surfaces. Therefore, it is possible to obtain a glass substrate in which the center portion in the plate thickness direction is the overflow confluence surface, and the both surfaces are flame-polished surfaces. Thereby, the glass substrate which is not polished and excellent in surface quality (surface roughness or undulation is small) can be manufactured inexpensively.

In the present invention, when the down-draw method is used, the length (height difference) of the slow cooling furnace is preferably 3 m or more. The slow cooling step is used to remove the strain of the glass substrate. The longer the slow cooling furnace is, the easier it is to adjust the cooling rate of the plate glass and reduce the thermal shrinkage of the glass substrate. Therefore, the length of the slow cooling furnace is preferably 5 m or more, 6 m or more, 7 m or more, 8 m or more, 9 m or more, especially 10 m or more.

In the present invention, the cooling rate of the plate glass in the slow cooling step is preferably 50-1000°C/min, 100-1000°C/min, 100°C within the temperature range from the slow-cooling point to (the slow-cooling point-100°C). Average cooling rate of ~800℃/min, 300℃/min~1000℃/min. The thermal shrinkage rate of the glass substrate also varies depending on the cooling rate when the plate glass is slowly cooled. That is, the thermal contraction rate of the glass substrate cooled rapidly becomes high, and conversely, the thermal shrinkage rate of the glass substrate cooled slowly becomes low.

In the present invention, the slowly cooled plate glass is subjected to cutting processing. That is, the formed plate-shaped glass (glass ribbon) is cut into a predetermined size. After that, in order to prevent breakage from the end face portion, end face grinding or end face grinding may be performed. The short side of the glass substrate thus obtained is preferably 1500 mm or more and the long side is 1850 mm or more. That is, the larger the size of the glass substrate, the higher the production efficiency of the glass substrate, so the short side is preferably 1950mm or more, 2200mm or more, 2800mm or more, especially 2950mm or more, and the long side is preferably 2250mm or more, 2500mm or more, 3000mm or more Above, especially 3400mm or above.

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. The smaller the thickness, the more lightweight the glass substrate can be achieved, and the more suitable it is for a mobile display substrate. However, when the thickness of the glass substrate is too small, breakage is likely to occur due to peeling electrification, so it is preferably 0.1 mm or more, and more preferably 0.2 mm or more.

In order to further suppress the peeling electrification of the glass substrate of the present invention, it is preferable that at least one surface be a fine uneven surface. As the surface shape of the fine concavo-convex surface, the surface roughness Ra may be set to 0.1 to 10 nm. As a method for making the surface of the glass substrate a fine uneven surface, as long as Physical grinding using a grinding device, or chemical etching by spraying an etching solution on a glass substrate may be used. If the latter chemical etching is used, it is not easy to attach glass powder to the glass substrate, and the surface can be cleaned, so it is preferable. Since the glass substrate of the present invention is inherently less likely to cause peeling electrification, even when fine irregularities are formed on the surface thereof, the processing time can be shortened and the productivity can be improved.

According to the present invention, it is possible to stably obtain a glass substrate suitable for use as a substrate for a high-definition display because the thermal shrinkage rate is low, and which does not easily cause peeling and electrification.

1: Support Desk

2: Pad

3: Platform

4: Surface Potentiometer

5: Air gun with ionizer

G: Glass sample (glass substrate)

Ga, Gb: the distance between the marks in the initial stage of the test piece ₁₀

M: mark

ΔL1, ΔL2: offset of mark

Fig.1 (a) - (c) are explanatory views which show the method of measuring the thermal contraction rate of a glass substrate.

Fig. 2 is an explanatory diagram showing an apparatus for measuring the peeled charge amount of a glass substrate, (a) is an explanatory diagram showing a state in which the glass substrate is removed from the stage, and (b) shows a state in which the glass substrate is placed on the stage explanatory diagram.

In this specification, the numerical range represented by "~" means the range which includes the numerical value described before and after "~" as a minimum value and a maximum value, respectively.

The glass substrate of the present invention contains 50-70% SiO ₂ , 10-25% Al ₂ O ₃ , 0% or more but less than 3% B ₂ O ₃ , 0-10% MgO, O ~15% CaO, 0~10% SrO, ₀ ~15% BaO, and 0.005~0.3% Na2O. The reason for restricting the content of each glass constituent as described above will be explained below. In addition, the following % of each component means mass % unless otherwise specified.

When the content of SiO ₂ decreases, chemical resistance, especially acid resistance, tends to decrease, and the strain point tends to decrease. Moreover, the density becomes high, and it becomes difficult to achieve weight reduction of a glass substrate. The density of the glass is preferably less than 2.70 g/cm ³ , and more preferably less than 2.65 g/cm ³ . On the other hand, when the content of SiO ₂ increases, the high temperature viscosity becomes high, the meltability tends to decrease, and it takes time in the case of etching. Furthermore, _SiO2 -based crystals, especially cristobalite, are precipitated, and the liquidus viscosity tends to decrease, that is, the devitrification resistance tends to decrease. Therefore, SiO ₂ is preferably 50% or more, 55% or more, 58% or more, 60.5% or more, and further 61% or more, and preferably 70% or less, 65% or less, 64% or less, 63.5% or less, 63% or less, 62.5% or less, and further 62% or less.

When the content of Al ₂ O ₃ decreases, the strain point decreases, the thermal shrinkage rate increases, the Young's modulus decreases, and the glass substrate is easily flexed. On the other hand, when the content of Al ₂ O ₃ is increased, the BHF (Buffered Hydrogen Fluoride) resistance is reduced, cloudiness is likely to occur on the glass surface, and the crack resistance is reduced and breakage is likely to occur. Furthermore, SiO ₂ -Al ₂ O ₃ crystals, especially mullite, are precipitated 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, and further 18% or more, and preferably 25% or less, 23% or less, 21% or less, 20% or less, 19% or less, 19.7% or less, and further 19.5% or less.

B ₂ O ₃ acts as a flux to reduce viscosity and improve meltability. When the content of B ₂ O ₃ increases, the molten glass volatilizes and the glass component is liable to fluctuate. In addition, as the content of B ₂ O ₃ increases, the strain point decreases, and the heat resistance or acid resistance decreases more easily. Furthermore, the Young's modulus decreases, 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, and more preferably substantially not contained. However, from the viewpoint of improving meltability and preventing a decrease in BHF resistance or crack resistance, B ₂ O may be contained in an amount of 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, and further 0.5% or more. ₃ .

As mentioned above, the β-OH value of glass is easily affected by the moisture contained in the glass batch that is put into the glass melting furnace, especially the glass raw material that becomes the boron source because it is hygroscopic and also contains crystal water. Therefore, it is easy to bring moisture into the glass. Therefore, the more the content of B ₂ O ₃ in the glass decreases, the easier the β-OH value of the glass decreases. In addition, the lower the β-OH value, the higher the strain point of the glass, and the easier it is to reduce the thermal contraction rate of the glass substrate. For the above reasons, in the present invention, it is preferable to reduce B ₂ O ₃ as much as possible, and it is preferable that B ₂ O ₃ is not substantially contained. Here, B ₂ O ₃ is not substantially contained means that B ₂ O ₃ is not intentionally contained as a raw material, and mixing of impurities from impurities is not denied. Specifically, it means that the content of B ₂ O ₃ is 0.1% or less.

MgO is a component that reduces high temperature viscosity and improves melting properties. Among alkaline earth metal oxides, it is a component that significantly increases Young's modulus. However, if excessively introduced, SiO ₂ crystals, especially cristobalite, will be precipitated. , the liquidus viscosity is easy to decrease. Furthermore, MgO is a component that easily reacts with BHF to form a product. When the content of MgO is small, it is difficult to enjoy the above-mentioned effects, and when the content of MgO is large, the devitrification resistance and the strain point are likely 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, especially 3% or less. Moreover, 1% or more, 1.5% or more, especially 2% or more are preferable.

CaO is a component that reduces the high temperature viscosity without lowering the strain point and significantly improves the meltability. In addition, since the raw material to be introduced into the alkaline earth metal oxide is relatively inexpensive, it is a component for reducing the cost of the raw material. When the content of CaO is reduced, it is difficult to enjoy the above-mentioned effects. On the other hand, when the content of CaO is too large, the glass tends to devitrify and the thermal expansion coefficient tends to increase. Therefore, the content of CaO is preferably 15% or less, 12% or less, 11% or less, 8% or less, especially 6% or less. Moreover, 1% or more, 2% or more, 3% or more, 4% or more, especially 5% or more are preferable.

SrO is a component that suppresses phase separation of glass and improves devitrification resistance. Furthermore, it is a component that reduces the high temperature viscosity without lowering the strain point, thereby improving the meltability, and suppressing the rise of the liquidus temperature. When the content of SrO is reduced, the above-mentioned effects cannot be obtained easily. On the other hand, when the content of SrO increases, devitrification crystals of strontium silicate series are likely to be precipitated, and the devitrification resistance is likely to decrease. Therefore, the content of SrO is preferably 10% or less, 7% or less, 5% or less, 4% or less, especially 3% or less. Moreover, 0.1% or more, 0.2% or more, 0.3% or more, 0.5% or more, 1.0% or more, especially 1.5% or more are preferable.

BaO is a component that significantly improves devitrification resistance. When the content of BaO is reduced, it is difficult to enjoy the above-mentioned effects. On the other hand, when the content of BaO increases, the density becomes too high, and the meltability tends to decrease. In addition, devitrification crystals containing BaO tend to precipitate, and the liquidus temperature tends to rise. Therefore, the content of BaO is preferably 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, especially 9% or less. Moreover, 1% or more, 3% or more, 4% or more, 5% or more, 6% or more, especially 7% or more are preferable.

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

K ₂ O may also be added as an alkali metal oxide other than Na ₂ O. K ₂ O is also a component that reduces the specific resistance of glass. When the content of K ₂ O is reduced, the above-mentioned effects cannot be obtained easily. On the other hand, when the content of K ₂ O increases, alkali ions diffuse into the film-formed semiconductor material during heat treatment, resulting in poor film properties. Therefore, K ₂ O is preferably 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, further 0.05% or more, and preferably 0.3% or less, and further 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 also be appropriately added. However, if the content of alkali metal oxides increases, alkali ions diffuse into the film-formed semiconductor material during heat treatment, resulting in poor film characteristics. Therefore, the total amount of alkali metal oxides (Na ₂ O, The total amount of Li ₂ O and K ₂ O) is preferably 0.4% or less.

In the present invention, the glass substrate can contain the following components in addition to the above-mentioned components.

The glass substrate of the present invention preferably contains 0.005-0.1% Fe ₂ O ₃ . _Fe2O3 is a component which has the effect of reducing the specific resistance _of glass similarly to _Na2O , and the effect of suppressing the electrification _of a glass substrate is further improved by containing _Fe2O3 in a certain amount or more. Fe ₂ O ₃ is preferably contained at 0.005% or more, 0.008% or more, especially 0.01% or more. However, if Fe ₂ O ₃ is contained in an amount exceeding 0.1%, the transmittance of the glass may be lowered, which may be unsatisfactory as a display substrate. Therefore, Fe ₂ O ₃ is preferably 0.1% or less.

The glass substrate of the present invention preferably contains 0.001 to 0.5% of SnO ₂ . SnO ₂ is a component that has a good clarifying effect in the high temperature region, increases the strain point and reduces the high temperature viscosity. Furthermore, in the case of an electric melting furnace using a molybdenum electrode, there is an advantage that the electrode is not eroded. On the other hand, when the content of SnO ₂ increases, devitrification crystals of SnO ₂ are easily precipitated, and precipitation of devitrification crystals of ZrO ₂ is easily accelerated. Therefore, the content of SnO ₂ is preferably 0.001-0.5%, 0.001-0.45%, 0.001-0.4%, 0.01-0.35%, 0.1-0.3%, especially 0.15-0.3%.

Furthermore, the other component which the glass substrate of this invention can contain is demonstrated.

ZnO is a component that improves 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 improves chemical durability, but when the content of ZrO ₂ increases, devitrification and agglomeration of ZrSiO ₄ is likely 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 reduces high-temperature viscosity, improves meltability, and suppresses coloring due to exposure to sunlight. However, when the content of TiO ₂ increases, the glass is colored and transmittance tends to decrease. 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 increases the strain point and suppresses the precipitation of devitrified crystals of alkaline earth aluminosilicates such as anorthite. However, when a large amount of P ₂ O ₅ is contained, the glass tends to separate phases. The content of P ₂ O ₅ is preferably 0 to less than 0.15%, 0 to 1%, and 0 to 0.1%, and in particular, from the viewpoint of facilitating the reuse of glass, it is preferably not substantially contained. In terms of less than 0.01%.

Metal powders such as Cl, F, SO ₃ , C, CeO ₂ , or Al and Si may be contained in a total amount of up to 3%. Although As ₂ O ₃ or Sb ₂ O ₃ is useful as a clarifying agent, from the viewpoint of the environment or the prevention of electrode corrosion, it is preferable that it is not substantially contained. Here, "substantially not containing" means that the total amount of As ₂ O ₃ and Sb ₂ O ₃ is 0.1% or less.

The β-OH value of the glass substrate of the present invention is less than 0.18/mm. Since the β-OH value of the glass decreases, the strain point of the glass increases, and the thermal shrinkage rate decreases, so the β-OH value is preferably less than 0.15/mm, 0.12/mm or less, 0.1/mm or less, and 0.07/mm. mm or less, especially 0.05/mm or less. However, from the viewpoint of suppressing the electrification of the glass substrate, the β-OH value is preferably 0.01/mm or more, 0.02/mm or more, and particularly 0.03/mm or more.

The strain point of the glass substrate of the present invention is 735° C. or higher. In order to reduce the thermal shrinkage rate of the glass substrate, it is desirable to increase the strain point as much as possible, and it is preferably 740°C or higher, 745°C or higher, and further 750°C or higher. However, as the strain point is increased, the temperature at the time of glass melting or molding becomes higher, and the manufacturing cost of the glass substrate increases, so the strain point is preferably made 800° C. or lower.

For the glass substrate of the present invention, for the same reason as the strain point, the slow cooling point is preferably 780°C or higher above, 790°C or higher, 800°C or higher, 810°C or higher, especially 820°C or higher. However, the higher the annealing point, the higher the temperature at the time of glass melting or molding, and the higher the manufacturing cost of the glass substrate. Therefore, the annealing point is preferably 850°C or lower, and more preferably 840°C or lower.

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 deflection of the glass substrate, and the easier the handling during transportation or packaging. The Young's modulus is preferably 81GPa or more, 82GPa or more, 83GPa or more, 84GPa or more, and further 85GPa 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, and 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 manufacturing 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, and particularly 1650°C or lower. When the temperature corresponding to 10 ^2.5 dPa·s becomes high, the glass is less likely to be melted, defects such as bubbles increase, and the production yield tends to decrease.

The liquidus temperature of the glass substrate of the present invention is preferably less than 1250°C, less than 1240°C, less than 1230°C, especially less than 1220°C. In this way, since devitrification crystals are not easily generated during glass production, it is easy to form into a plate shape by the overflow down-draw method. Thereby, the surface quality of a glass substrate can be improved, and the fall of a manufacturing yield can be suppressed. From the viewpoint of increasing the size of glass substrates or increasing the definition of displays, it is very significant to improve the devitrification resistance of glass and to suppress as much as possible devitrification substances that may become surface defects.

The glass substrate of the present invention preferably has a viscosity at 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, especially 10 ^5.3 dPa·s above. In this way, since devitrification does not easily occur during glass forming, it is easy to form into a plate shape by the overflow down-draw method, and the surface quality of the glass substrate can be improved. Furthermore, the viscosity at the liquidus temperature is an indicator of the formability, and the higher the viscosity at the liquidus temperature, the better the formability.

[Example] (Example 1)

Tables 1 and 2 show the example glasses (sample No. 1 to 9) and the conventional glass (sample No. 10) of the present invention. In addition, the content of components other than Na ₂ O, K ₂ O, Fe ₂ O ₃ , and ZrO ₂ in the table is obtained by rounding off the second decimal place.

The glass samples of Tables 1 and 2 were produced as follows. First, the glass batch obtained by preparing the glass raw material so as to have the composition shown in the table is put into a platinum crucible, and then melted at 1600 to 1650° C. for 24 hours. When the glass batch was melted, it was homogenized by stirring with a platinum stirrer. Next, after pouring the molten glass out onto a carbon plate and shape|molding into a plate shape, it cooled slowly for 30 minutes at the temperature of a annealing point vicinity. The strain point, slow cooling point, density, Young's modulus, temperature corresponding to 10 ^4.5 dPa·s, temperature corresponding to 10 ^2.5 dPa·s, liquidus temperature TL were measured for each sample thus obtained, and about the liquid The viscosity ηTL (dPa·s) at the phase temperature was measured as Log ₁₀ ηTL.

In addition, the strain point and slow cooling point in Tables 1 and 2 were measured by the method of ASTM (American Society for Testing Materials, American Society for Testing Materials) C336.

Density is measured using the Archimedes method according to ASTM C693.

Young's modulus was measured by the bending resonance method based on JISR1602.

The temperatures corresponding to 10 ^4.5 dPa·s and 10 ^2.5 dPa·s were determined by the platinum ball pulling method.

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

Viscosity at liquidus temperature Log _{10 ηTL} is calculated by measuring the viscosity ηTL of glass at liquidus temperature by the platinum ball pulling method.

The β-OH value is 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 3846cm ^-1

T2: The minimum transmittance (%) around the hydroxyl absorption wavelength of 3600cm ^-1

As can be seen from Tables 1 and 2, since the strain point of each sample No. 1 to 9 is 735°C or higher and the slow cooling point is 785°C or higher, it is easy to make the thermal shrinkage rate 20 ppm or less glass. In addition, since the Young's modulus is 80.4GPa or more, it is not easy to bend, and because 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, it is difficult to produce loss during molding. through. In particular, the samples No. 1, 2, and 7 to 9 are suitable for the overflow down-draw method because the viscosity ηTL at the liquidus temperature is 10 ^5.2 dPa·s or more.

(Example 2)

Glass batches were prepared in such a way as to become the glasses of Sample Nos. 8 and 10 of Table 2. Then, the glass batch is put into an electric melting furnace, and after melting at 1600-1650° C., the molten glass is clarified and homogenized in a clarification tank and a homogenization tank, and then adjusted in a crucible (pot) to be suitable for forming. viscosity. Then, after the molten glass was formed into a plate shape by an overflow down-drawing device, in a slow cooling furnace with a length of 5 m, the average cooling rate in the temperature range from the slow cooling point to (slow cooling point -100°C) was set to 385°C/ Chill for minutes. Then, the glass substrate having a size of 1500×1850×0.7 mm was produced by cutting the plate glass and performing end surface processing.

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

The thermal contraction rate of a glass substrate was measured by the following method. First, as shown in FIG. 1( a ), a short strip-shaped sample G of 160 mm×30 mm was prepared as a sample of the glass substrate. For each of the both ends in the longitudinal direction of the short strip-shaped sample G, a mark M was formed at a position 20 to 40 mm from the edge using #1000 water-resistant abrasive paper. Thereafter, as shown in FIG. 1( b ), the short strip-shaped sample G with the mark M formed thereon is folded and cut into two pieces along the direction orthogonal to the mark M, and test pieces Ga and Gb are produced. Then, only one test piece Gb was subjected to a heat treatment in which the temperature was raised from normal temperature (25°C) to 500°C at 5°C/min, held at 500°C for 1 hour, and then lowered to normal temperature at 5°C/min. After the above heat treatment, as shown in FIG. 1( c ), in a state where the test piece Ga without heat treatment and the test piece Gb with heat treatment are arranged side by side, the two test pieces Ga and Gb are read by a laser microscope. The amount of positional shift (ΔL1, ΔL2) of the mark M, and the thermal shrinkage rate was calculated according to the following formula. Furthermore, _l0 in the formula is the distance between the markers M in the initial stage.

Thermal shrinkage=[{ΔL1(μm)+ΔL2(μm)}×10 ³ ]/l ₀ (mm)(ppm)

Next, the evaluation of peeling electrification was performed using the apparatus shown in FIG. 2 with respect to each glass substrate of the said sample No. 8 and 10.

As shown in FIG.2(a), the support base 1 of the glass substrate G is provided with the pad 2 made of Teflon (registered trademark) which supports the four corners of the glass substrate G. As shown in FIG. The support table 1 is provided with a metal aluminum platform 3 that can be lifted and lowered. As shown in FIG. 2(b), the glass substrate G is brought into contact with the platform 3 by lifting and lowering the platform 3, and then the glass substrate G is peeled off. The glass substrate G is charged. Furthermore, the platform 3 is grounded. In addition, singular or plural holes (not shown) are formed in the stage 3, and the holes are connected to a diaphragm-type vacuum pump (not shown). When the vacuum pump is driven, air is sucked from the hole of the stage 3 , whereby the glass substrate G can be vacuum adsorbed on the stage 3 . Moreover, the surface potentiometer 4 was provided in the position of 10 mm above the glass substrate G, and the electric charge amount which generate|occur|produced in the center part of the glass substrate G was measured continuously by this. Moreover, the air gun 5 with an ionizer is provided above the glass substrate G, and the electrification of the glass substrate G can be eliminated by this.

The peeling charge of the glass substrate was measured in the following procedure using this apparatus. Furthermore, the experiment was performed in a clean room with a temperature of 25°C and a humidity of 40%. Since the charged amount will be greatly affected by the atmosphere, especially the humidity in the atmosphere, it is especially necessary to consider the adjustment of the humidity.

(1) The glass substrate G is placed on the support pad 2 of the support table 1 .

(2) The static electricity of the glass substrate G is eliminated by using the air gun 5 with an ionizer.

(3) The stage 3 is raised and brought into contact with the glass substrate G, and vacuum suction is performed to make the stage 3 and the glass substrate G in close contact with each other for 20 seconds.

(4) The glass substrate G is peeled off from the table 3 by lowering the table 3 , and the surface potentiometer 4 is used to continuously measure the amount of charge generated in the center portion of the glass substrate G.

(5) By repeating the above-mentioned steps (3) and (4), the peeling evaluation was continuously performed 5 times in total.

The maximum charge amount in each measurement was obtained, and the value was accumulated as the peeling charge amount.

As a result, the peeling charge amount of the glass substrate of Sample No. 8 was 1000V, whereas the peeling charge amount of Sample No. 10 was 2000V, which was relatively large. Moreover, after spraying an etching gas to one surface of the glass substrate of the sample No. 8, after making the surface roughness Ra 1 nm, the peeling charge amount was measured, and it was 800V.

Claims (14)

A glass substrate, characterized in that it contains 50-70% of SiO ₂ , 10-25% of Al ₂ O ₃ , 0% or more but less than 3% of B ₂ O ₃ , and 0-10% of B 2 O 3 by mass percentage. MgO, 0~15% CaO, 0~10% SrO, 0~15% BaO, 0.005~0.3% Na ₂ O, and 0~1% P ₂ O ₅ , and the β-OH value does not reach 0.18/mm, the strain point is above 735℃. As claimed in claim 1, the glass substrate contains 0.005-0.1% Fe ₂ O ₃ in mass percentage. The glass substrate of claim 1 or 2 contains 0.001-0.5% SnO ₂ in mass percentage. The glass substrate of claim 1 or 2 has a Young's modulus of 80 GPa or more. The glass substrate of claim 1 or 2 has a thermal shrinkage rate of 20 ppm or less. For the glass substrate of claim 1 or 2, the content of P ₂ O ₅ is less than 0.01%. According to the glass substrate of claim 1 or 2, its thickness is 0.7 mm or less. The glass substrate of claim 1 or 2, wherein at least one surface thereof is a fine uneven surface. As in the glass substrate of claim 8, the surface roughness Ra of the fine uneven surface is 0.1 to 10 nm. A method for manufacturing a glass substrate, characterized by comprising: a raw material preparation step, which prepares a glass batch material, wherein the glass batch material contains 50-70% of SiO ₂ and 10-25% of Al ₂ O in terms of mass percentage. _3. More than 0% but less than 3% B ₂ O ₃ , 0~10% MgO, 0~15% CaO, 0~10% SrO, 0~15% BaO, 0.005~0.3% Na ₂ O, and 0-1% P ₂ O ₅ glass; melting step, which melts the glass batch in an electric melting furnace; forming step, which shapes the molten glass into a plate shape; slow cooling step , which slowly cools the plate-shaped glass in a slow-cooling furnace; and a processing step, which cuts the slowly-cooled plate-shaped glass into a specific size; and the manufacturing method obtains a β-OH value of less than 0.18/mm , The glass substrate whose strain point is above 735℃. The method for producing a glass substrate according to claim 10, wherein the cooling rate of the plate glass in the slow cooling step is 50°C/min to 1000°C/min within the temperature range from the slow cooling point to (the slow cooling point -100°C). the average cooling rate. The method for manufacturing a glass substrate according to claim 10 or 11, wherein chemical etching is performed on at least one surface. The manufacturing method of the glass substrate according to claim 10 or 11, wherein at least one surface is physically ground. The manufacturing method of the glass substrate according to claim 10 or 11, wherein the surface roughness Ra is set to 0.1 to 10 nm.

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