WO2022054738A1 - Method for manufacturing low alkali glass plate, and low alkali glass plate - Google Patents

Abstract

Provided are a low alkali glass plate that has a high strain point and excellent bubble quality, and a method for manufacturing the same.　This method for manufacturing a low alkali glass plate is characterized by including: a batch preparation step for preparing a starting material batch so as to yield a low alkali glass that contains, as a glass composition, by mass%, 50-70% of SiO₂, 15-25% of Al₂O₃, 2-7.5% of B₂O₃, 0-10% of MgO, 0-10% of CaO, 0-10% of SrO, 0-15% of BaO, 0-5% of ZnO, 0-1% of ZrO₂, 0-5% of TiO₂, 0-10% of P₂O₅, and 0.1-0.5% of SnO₂; a melting step for melting the starting material batch thus prepared; a refining step for refining the melted glass; and a shaping step for shaping the refined glass into a plate shape. Said method is further characterized in that, when the content of B₂O₃ is referred to as x (mass%) and the β-OH value of the obtained low alkali glass plate is referred to as y (/mm), the B₂O₃ content and the β-OH value are adjusted so as to satisfy the relational expression y=ax+b, wherein 0.01<a<0.04 and 0.03<b<0.06.

Description

Manufacturing method of low-alkali glass plate and low-alkali glass plate

The present invention relates to a low-alkali glass plate, and more particularly to a low-alkali glass plate suitable for a display provided with a thin film transistor (TFT: Thin Film Transistor) having an oxide film such as Indium Gallium Zinc Oxide (IGZO).

A glass plate is generally used as a support substrate in a flat panel display. An electric circuit pattern such as a TFT is formed on the surface of this glass plate. For this reason, a low-alkali glass plate that does not substantially contain an alkali metal component is adopted for this type of glass plate so as not to adversely affect the TFT or the like.

Further, the glass plate is exposed to a high temperature atmosphere in the process of forming an electric circuit pattern such as the process of forming a thin film and the process of patterning a thin film. When the glass plate is exposed to a high temperature atmosphere, the structure of the glass is relaxed, so that the volume of the glass plate shrinks (hereinafter, the shrinkage of the glass is referred to as "heat shrinkage"). When heat shrinkage occurs in the glass plate in the process of forming the electric circuit pattern, the shape and dimensions of the electric circuit pattern formed on the glass plate deviate from the design values, and a flat panel display having desired electrical performance can be obtained. It will be difficult. Therefore, it is desired that a glass plate having a thin film pattern such as an electric circuit pattern formed on the surface thereof, such as a glass plate for a flat panel display, has a small heat shrinkage rate.

In particular, in the case of a glass plate for a high-definition display provided with a TFT having an oxide film such as IGZO, when the oxide film is formed, it is exposed to a very high temperature atmosphere of, for example, 400 ° C to 500 ° C, and heat is generated. Shrinkage is likely to occur, but when thermal shrinkage occurs, it becomes difficult to obtain the desired electrical performance because the electric circuit pattern is high-definition. Therefore, it is strongly desired that the glass plate used for such an application has a very small heat shrinkage rate.

By the way, as a method for forming a glass plate used for a flat panel display or the like, a float method, a downdraw method typified by an overflow downdraw method, and the like are known.

In the float method, molten glass is discharged onto a float bath filled with molten tin and stretched horizontally to form a glass ribbon, and then the glass ribbon is slowly cooled in a slow cooling furnace provided on the downstream side of the float bath. This is a method of forming a glass plate. In the float method, since the transport direction of the glass ribbon is horizontal, it is easy to lengthen the slow cooling furnace. Therefore, it is easy to sufficiently reduce the cooling rate of the glass ribbon in the slow cooling furnace. Therefore, the float method has an advantage that a glass plate having a small heat shrinkage rate can be easily obtained.

However, the float method has the disadvantage that it is difficult to form a thin glass plate, and after molding, the surface of the glass plate must be polished to remove tin adhering to the surface of the glass plate. There are disadvantages.

On the other hand, the down draw method is a method in which molten glass is stretched downward to form a plate. The overflow downdraw method, which is a kind of downdraw method, is a method of forming a glass ribbon by stretching the molten glass overflowing from both sides of a substantially wedge-shaped cross-section (forming body) downward. The molten glass overflowing from both sides of the molded body flows down along both side surfaces of the molded body and joins below the molded body. Therefore, in the overflow down draw method, the surface of the glass ribbon does not come into contact with anything other than air and is formed by surface tension. Therefore, even if the surface is not polished after molding, no foreign matter adheres to the surface and the surface is formed. Can obtain a flat glass plate. Further, according to the overflow down draw method, there is an advantage that a thin glass plate can be easily formed.

On the other hand, in the down draw method, the molten glass flows downward from the molded body. If a long slow cooling furnace is to be placed under the molding, the molding must be placed at a high place. However, in practice, there are restrictions on the height at which the molded product can be placed due to restrictions on the height of the ceiling of the factory. That is, in the down draw method, the length dimension of the slow cooling furnace is limited, and it may be difficult to arrange a sufficiently long slow cooling furnace. When the length of the slow cooling furnace is short, the cooling rate of the glass ribbon becomes high, and it becomes difficult to form a glass plate having a small heat shrinkage rate.

Therefore, it has been proposed to increase the strain point of the glass and reduce the heat shrinkage rate of the glass. For example, Patent Document 1 discloses a low-alkali glass composition having a high strain point. Further, it is described in the same document that the lower the β-OH value representing the amount of water in the glass, the higher the strain point.

Japanese Patent Application Laid-Open No. 2013-151407

As shown in FIG. 1, the higher the strain point, the smaller the heat shrinkage rate. However, since the glass whose composition is designed so that the strain point is high has high viscosity, there is a problem that it is difficult to obtain a glass having excellent foam quality due to poor foam breakage.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a low-alkali glass plate having a high distortion point and excellent foam quality, and a method for producing the same.

The method for producing a low-alkali glass plate of the present invention has a glass composition of SiO ₂ 50 to 70%, Al ₂ O ₃ 15 to 25%, B ₂ O ₃ 2 to 7.5%, MgO 0 to% by mass. ₁₀ %, CaO 0-10%, SrO 0-10%, BaO 0-15%, ZnO _0-5 %, ZrO 20-1%, TiO 20-5%, _{P2O 50-10} %, A batch preparation step for preparing a raw material batch so as to have a low alkaline glass containing SnO ₂ 0.1 to 0.5%, a melting step for melting the prepared raw material batch, and a clarification step for clarifying the melted glass. _The content of B2O3 is x ₍ mass%), and the β-OH value of the obtained low-alkali glass plate is y (/ mm). Then, the content of B ₂ O ₃ and the β-OH value should be adjusted so that the relational expressions of y = ax + b, 0.01 <a <0.04 and 0.03 <b <0.06 are established. It is a feature.

Here, the "low alkaline glass" is a glass to which an alkali metal oxide component is not intentionally added, and specifically, the alkali metal oxides (Li ₂ O, Na ₂ O, and K) in the glass composition. ₂ O) means glass having a content of 3000 ppm (mass) or less. The content of Na ₂ O in the glass composition is preferably 500 ppm or less, particularly preferably 300 ppm or less.

_In the present invention, since the _B2O3 content of the glass composition used is small, it is possible to obtain a glass plate having a high strain point. However, glass having a high strain point generally has a high viscosity, and it is difficult to achieve high foam quality. Therefore, in the present invention, if the B ₂ O ₃ content and the β-OH value are controlled according to the above formula and SnO ₂ having a clarifying effect at a relatively high temperature is contained as an essential component, high foam quality can be achieved. I found out what I could do.

In the production method of the present invention, in the batch preparation step, the glass composition is SiO ₂ 57 to 65%, Al ₂ O ₃ 17 to 22%, B ₂ O ₃ 2.5 to 7%, MgO in mass%. It is preferable to prepare the raw material batch so as to be a low alkaline glass containing 1 to 10%, BaO 0.1 to 15%, and SnO ₂ 0.1 to 0.3%.

In the production method of the present invention, it is preferable to electrically melt. Here, "electric melting" is a melting method in which electricity is applied to the glass and the Joule heat generated by the electricity is used to heat and melt the glass. It does not exclude the case where radiant heating by a heater or a burner is used together.

If the above configuration is adopted, it is possible to suppress an increase in moisture in the atmosphere. As a result, it becomes possible to significantly suppress the water supply from the atmosphere to the glass, and it becomes easy to manufacture the glass having a high strain point. Further, since the glass melt is heated by using the heat generated by the glass itself (Joule heat), the glass can be heated efficiently. Therefore, it is possible to melt the raw material batch at a relatively low temperature.

In the production method of the present invention, it is preferable to contain a carbonate raw material and / or a nitrate raw material in the raw material batch.

In the production method of the present invention, it is preferable to use orthoboric acid and / or anhydrous boric acid as at least a part of the glass raw material as a boron source.

If the above configuration is adopted, it becomes possible to adjust the water content of the obtained glass.

In the production method of the present invention, it is preferable to contain the hydroxide raw material in the raw material batch.

If the above configuration is adopted, it becomes possible to further adjust the water content of the obtained glass.

In the production method of the present invention, a glass cullet is contained in the raw material to produce a low-alkali glass plate, and the β-OH value is 0.3 / mm or less in at least a part of the glass cullet. It is preferable to use a glass cullet made of glass. Here, "glass cullet" means defective glass generated during the production of glass, recycled glass recovered from the market, and the like. 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 (T ₁ / T ₂ )
X: Glass wall thickness (mm)
T ₁ : Transmittance (%) at a reference wavelength of 3846 cm ^-1
T ₂ : Minimum transmittance (%) near hydroxyl group absorption wavelength 3600 cm ^-1

Low alkaline glass has a high volume resistance, so it tends to be harder to melt than glass containing alkali. Therefore, if the above configuration is adopted, the glass can be easily melted, and the water content of the obtained glass can be reduced and adjusted.

In the production method of the present invention, it is preferable to adjust the glass raw material and / or the melting conditions so that the β-OH value of the obtained glass is 0.3 / mm or less.

If the above configuration is adopted, it becomes easy to obtain glass having a high strain point and a low heat shrinkage rate.

In the production method of the present invention, it is preferable that the strain point of the obtained glass is 680 ° C. or higher. Here, the "distortion point" is a value measured based on the method of ASTM C336-71.

If the above configuration is adopted, it is possible to obtain glass having an extremely small heat shrinkage rate.

In the production method of the present invention, the heat shrinkage of the obtained glass is preferably 25 ppm or less. Here, the "heat shrinkage rate" means that the glass is 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 to room temperature at a rate of 5 ° C./min. It is a value when measured after heat treatment under the condition of lowering the temperature.

If the above configuration is adopted, a glass plate suitable for forming an oxide TFT can be obtained.

The low-alkali glass plate of the present invention has a glass composition of 40% by mass, SiO ₂ 50 to 70%, Al ₂ O ₃ 15 to 25%, B ₂ O ₃ 2 to 7.5%, MgO 0 to 10%, CaO. 0 to 10%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 to 5%, ZrO ₂₀ to 1%, TiO ₂₀ to 5%, P ₂ O ₅₀ to 10%, SnO ₂₀ . It contains 1 to 0.5%, has a β-OH value of 0.05 to 0.3 / mm, has a B ₂ O ₃ content of x (mass%), and has a β-OH value of y (/ mm). ), It is characterized in that the relational expressions of y = ax + b, 0.01 <a <0.04 and 0.03 <b <0.06 are established.

The low-alkali glass plate of the present invention has a glass composition of Al ₂ O ₃ 17 to 22%, B ₂ O ₃ 2.5 to 7%, MgO 0.1 to 10%, and CaO 0.1 to 20% by mass. It preferably contains 10%, ZrO ₂₀ to 0.5%, and TiO ₂₀ to 1%.

The low-alkali glass plate of the present invention preferably contains SiO 257 to 65%, MgO ₂ to 10%, BaO 0.1 to 15%, and SnO ₂ 0.1 to 0.3% by mass. ..

The low alkaline glass plate of the present invention preferably has a strain point of 680 ° C. or higher.

The low alkaline glass plate of the present invention preferably has a heat shrinkage rate of 25 ppm or less.

The low alkaline glass plate of the present invention is preferably used as a glass plate on which an oxide TFT is formed.

The oxide TFT has a high heat treatment temperature (around 400 to 500 ° C.) when it is formed on the substrate, and the circuit pattern becomes finer. Therefore, a glass plate used for this type of application is required to have a particularly small heat shrinkage rate. Therefore, the merit of adopting the glass plate of the present invention having a high strain point is extremely large.

The low-alkali glass plate of the present invention preferably has a substrate area of 4 m ² or more.

It is a graph which shows the relationship between the strain point of a glass, and the heat shrinkage rate. It is a top view for demonstrating the procedure of measuring the heat shrinkage rate of a glass plate.

Hereinafter, the method for manufacturing the low alkaline glass plate of the present invention will be described in detail. The numerical range indicated by using "-" in the present specification means a range including the numerical values before and after "-" as the minimum value and the maximum value, respectively.

The method of the present invention is a method for continuously producing a low-alkali glass plate, which is a batch preparation step for preparing a raw material batch, a melting step for melting the prepared raw material batch, and a clarification step for clarifying the melted glass. And a molding step of molding the clarified glass. Hereinafter, each step will be described in detail.

(1) Batch preparation step First, as the glass composition, SiO ₂ 50 to 70%, Al ₂ O ₃ 15 to 25%, B ₂ O ₃ 2 to 7.5%, MgO 0 to 10%, CaO in terms of mass%. 0 to 10%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 to 5%, ZrO ₂₀ to 1%, TiO ₂₀ to 5%, P ₂ O ₅₀ to 10%, SnO ₂₀ . The glass raw material is prepared so as to be a low-alkali glass containing 1 to 0.5%. As described above, the reason for restricting the content of each component will be described below. In the following description of each component,% notation indicates mass% unless otherwise specified. The raw materials used will be described later.

SiO ₂ is a component that forms the skeleton of glass. The lower limit of the content of SiO ₂ is preferably 50%, 51%, 51.5%, 52%, 55%, 56%, 57%, particularly 58%. Further, the upper limit of the content of SiO ₂ is preferably 70%, 69%, 68%, 67%, 66%, 65%, 64%, 63%, particularly 62%. If the content of SiO ₂ is too small, the density becomes too high and the acid resistance tends to decrease. On the other hand, if the content of SiO ₂ is too large, the high-temperature viscosity becomes high and the meltability tends to decrease. In addition, devitrified crystals such as cristobalite are likely to precipitate, and the liquidus temperature is likely to rise.

Al ₂ O ₃ is a component that forms the skeleton of glass, is a component that increases the strain point and Young's modulus, and is a component that further suppresses phase separation. The lower limit of the content of Al ₂ O ₃ is preferably 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, particularly 18%. The upper limit of the content of Al ₂ O ₃ is preferably 25%, 24%, 23%, 22%, 21.5%, and particularly preferably 21%. If the content of Al ₂ O ₃ is too small, the strain point and Young's modulus tend to decrease, and the glass tends to be phase-separated. On the other hand, if the content of Al ₂ O ₃ is too large, devitrified crystals such as mullite and anorthite are likely to precipitate, and the liquidus temperature is likely to rise.

B ₂ O ₃ is a component that enhances meltability and devitrification resistance. The lower limit of the content of B ₂ O ₃ is preferably 2%, 2.2%, and particularly preferably 2.5%. The upper limit of the content of B ₂ O ₃ is preferably 7.5%, particularly preferably 7%. If the content of B ₂ O ₃ is too small, the meltability and devitrification resistance tend to decrease, and the resistance to hydrofluoric acid-based chemicals such as buffered hydrofluoric acid tends to decrease. In addition, the amount of water brought in from the batch may decrease too much. On the other hand, if the content of B ₂ O ₃ is too large, the strain point and Young's modulus tend to decrease. In addition, the amount of water brought in from the batch increases.

MgO is a component that lowers high-temperature viscosity and enhances meltability, and is a component that significantly increases Young's modulus among alkaline earth metal oxides. The lower limit of the MgO content is preferably 0%, 0.1%, 0.5%, 1%, 1.5%, particularly 2%. The upper limit of the MgO content is preferably 10%, 9%, 8%, 7.5%, 7%, 6%, and particularly preferably 5%. If the content of MgO is too small, the meltability and Young's modulus tend to decrease. On the other hand, if the content of MgO is too large, the devitrification resistance tends to decrease and the strain point tends to decrease.

CaO is a component that lowers the high-temperature viscosity and remarkably enhances the meltability without lowering the strain point. Further, among the alkaline earth metal oxides, since the introduced raw material is relatively inexpensive, it is a component that reduces the raw material cost. The lower limit of the CaO content is preferably 0%, 0.1%, 1%, 2%, 3%, particularly 3.5%. The upper limit of the CaO content is preferably 10%, 9%, 8%, and particularly preferably 7%. If the CaO content is too low, it becomes difficult to enjoy the above effects. On the other hand, if the content of CaO is too large, the glass tends to be devitrified and the coefficient of thermal expansion tends to be high.

SrO is a component that suppresses phase separation and enhances devitrification resistance. Further, it is a component that lowers the high-temperature viscosity and enhances the meltability without lowering the strain point. It is also a component that suppresses the rise in liquid phase temperature. The lower limit of the SrO content is preferably 0%, 0.1%, and particularly preferably 0.3%. The upper limit of the SrO content is preferably 10%, 9%, 8%, 7%, 6%, particularly 5%. If the content of SrO is too small, it becomes difficult to enjoy the above effect. On the other hand, if the content of SrO is too large, the density becomes too high, and devitrification crystals containing SrO tend to precipitate, so that the devitrification resistance tends to decrease.

BaO is a component that significantly enhances devitrification resistance. The lower limit of the BaO content is preferably 0%, 0.1%, 0.5%, particularly 1%. The upper limit of the BaO content is preferably 15%, 14%, 13%, 12%, 11%, particularly 10.5%. If the BaO content is too low, it becomes difficult to enjoy the above effects. On the other hand, if the BaO content is too high, the density becomes too high and the meltability tends to decrease. In addition, devitrified crystals containing BaO are likely to precipitate, and the liquidus temperature is likely to rise.

ZnO is a component that enhances meltability. The ZnO content is preferably 0 to 5%, 0 to 4%, 0 to 3%, and particularly preferably 0 to 2%. If the ZnO content is too high, the glass tends to be devitrified and the strain point tends to decrease.

ZrO ₂ is a component that enhances chemical durability. The lower limit of the content of ZrO ₂ is preferably 0%, particularly preferably 0.01%. The upper limit of the content of ZrO ₂ is preferably 1%, 0.5%, 0.2%, 0.1%, and particularly preferably 0.05%. If the content of ZrO ₂ is too large, devitrification of ZrSiO ₄ is likely to occur.

TiO ₂ is a component that lowers high-temperature viscosity and enhances meltability. It is also a component that suppresses solarization. The content of TiO ₂ is preferably 0 to 5%, 0 to 4%, 0 to 3%, 0 to 2%, 0-1%, and particularly preferably 0 to 0.1%. If the content of TiO ₂ is too high, the glass is colored and the transmittance tends to decrease.

P ₂ O ₅ is a component that enhances the strain point and is a component that can suppress the precipitation of devitrified crystals of alkaline earth aluminosilicate type such as anorthite. The content of P ₂ O ₅ is 0 to 10%, 0 to 9%, 0 to 8%, 0 to 7%, 0 to 6%, 0 to 5%, 0 to 4%, and particularly 0 to 3%. Is preferable. If the content of P ₂ O ₅ is too large, the glass tends to be phase-separated.

SnO ₂ is a component having a good clarifying action in a high temperature range, a component that increases a strain point, and a component that lowers a high temperature viscosity. It also has the advantage of not eroding the molybdenum electrode. The lower limit of the SnO ₂ content is preferably 0.1%, particularly preferably 0.15%. The upper limit of the SnO ₂ content is preferably 0.5%, 0.45%, 0.4%, 0.35%, and particularly preferably 0.3%. If the content of SnO ₂ is too small, it becomes difficult to enjoy the above effects. On the other hand, if the content of SnO ₂ is too large, the devitrified crystals of SnO ₂ are likely to precipitate, and the precipitation of the devitrified crystals of ZrO ₂ is likely to be promoted.

In addition to the above components, other components can be contained in a total amount of 5% or less. However, it is preferable that As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained from the viewpoint of the environment and the prevention of electrode erosion. Here, "substantially free" means that the glass raw material or glass cullet containing these components is not intentionally added to the glass batch. More specifically, it means that arsenic is 50 ppm or less as As ₂ O ₃ and antimony is 50 ppm or less as Sb ₂ O ₃ in the obtained glass.

Further, Cl and F may be contained in the glass, but the Cl content is preferably less than 0.1%, particularly preferably less than 0.05%, and the F content is 0.1%. Less than, especially less than 0.05%. Further, Cl + F (total amount of Cl and F) is preferably less than 0.1%.

Next, the glass raw materials that make up the batch will be explained. In the following description of each raw material,% indication indicates mass% unless otherwise specified.

As the silicon source, silica sand, stone powder (SiO ₂ ) or the like can be used.

As the aluminum source, alumina (Al ₂ O ₃ ), aluminum hydroxide (Al (OH) ₃ ) and the like can be used.

As the boron source, orthoboric acid (H ₃ BO ₃ ) or anhydrous boric acid (B ₂ O ₃ ) can be used. Since orthoboric acid contains water of crystallization, the water content of the glass can be adjusted to be relatively high when the usage ratio is large. Therefore, it is preferable to use both orthoboric acid and anhydrous boric acid and adjust the usage ratio according to the target β-OH content.

Alkaline earth metal sources include calcium carbonate (CaCO ₃ ), magnesium oxide (MgO), magnesium hydroxide (Mg (OH) ₂ ), barium carbonate (BaCO ₃ ), barium nitrate (Ba (NO ₃ ) ₂ ), Strontium carbonate (SrCO ₃ ), strontium nitrate (Sr (NO ₃ ) ₂ ) and the like can be used.

Zinc oxide (ZnO) or the like can be used as the zinc source.

Zircon (ZrSiO ₄ ) or the like can be used as the zirconia source. When a Zr-containing refractory such as zirconia electrocasting refractory or dense zircon is used as the refractory constituting the molten kiln, the zirconia component is eluted from the refractory. These eluted components may also be used as a zirconia source.

Titanium oxide (TiO ₂ ) or the like can be used as the titanium source.

As a phosphorus source, aluminum metaphosphate (Al (PO ₃ ) ₃ ), magnesium pyrophosphate (Mg ₂ P ₂ O ₇ ) and the like can be used.

Tin oxide (SnO ₂ ) or the like can be used as the tin source. When tin oxide is used, it is preferable to use tin oxide having an average particle size D ₅₀ in the range of 0.3 to 50 μm, 2 to 50 μm, and particularly 5 to 50 μm. If the average particle size _D50 of the tin oxide powder is small, agglutination between the particles occurs, and clogging in the compounding plant is likely to occur. On the other hand, if the average particle size _D50 of the tin oxide powder is large, the dissolution reaction of the tin oxide powder in the glass melt is delayed, and the clarification of the melt does not proceed. As a result, oxygen gas cannot be sufficiently released at an appropriate time for melting the glass, bubbles tend to remain in the glass product, and it becomes difficult to obtain a product having excellent foam quality. In addition, undissolved lumps of SnO ₂ crystals are likely to appear in the glass product.

In the present invention, the carbonate raw material may be contained in the raw material batch. The carbonate raw material can efficiently function SnO ₂ , which is a clarifying agent. As the carbonate raw material, for example, calcium carbonate (CaCO ₃ ), barium carbonate (BaCO ₃ ), strontium carbonate (SrCO ₃ ) and the like can be used.

In the present invention, the nitrate raw material may be contained in the raw material batch. The nitrate raw material can efficiently function SnO ₂ , which is a clarifying agent. As the nitrate raw material, for example, barium nitrate (Ba (NO ₃ ) ₂ ), strontium nitrate (Sr (NO ₃ ) ₂ ) and the like can be used.

In the present invention, the hydroxide raw material may be contained in the raw material batch. The water content of the hydroxide raw material can be adjusted. As the hydroxide raw material, aluminum hydroxide (Al (OH) ₃ ), magnesium hydroxide (Mg (OH) ₂ ), calcium hydroxide (Ca (OH) ₂ ) and the like can be used.

In the present invention, it is desirable that the batch contains substantially no arsenic compound and antimony compound. If these components are contained, the molybdenum electrode is eroded, which makes it difficult to stably electrically melt the molybdenum electrode for a long period of time. Moreover, these components are environmentally unfavorable.

In the present invention, it is preferable to use a glass cullet in addition to the above-mentioned glass raw material. When the glass cullet is used, the ratio of the glass cullet to the total amount of the raw material batch is preferably 1% by mass or more, 5% by mass or more, and particularly preferably 10% by mass or more. There is no limitation on the upper limit of the usage ratio of the glass cullet, but it is preferably 50% by mass or less, 40% by mass or less, and particularly preferably 30% by mass or less. Further, it is preferable that at least a part of the glass cullet used is a low-moisture glass cullet made of glass having a β-OH value of 0.3 / mm or less, 0.25 / mm or less, particularly 0.2 / m or less. .. The lower limit of the β-OH value of the low-moisture glass cullet is not particularly limited, but is preferably 0.05 / mm or more.

Note that the glass raw material, the glass cullet, or the raw material batch containing these may contain water. It may also absorb moisture in the atmosphere during storage. Therefore, in the present invention, it is preferable to introduce dry air into a raw material silo for weighing and supplying individual glass raw materials, a furnace front silo for putting the prepared raw material batch into a melting kiln, and the like.

(2) Melting step Next, the prepared raw material batch is melted.

To melt the raw material batch, use a melting kiln that can be heated by radiant heat generated by burner combustion and Joule heat generated by energization between electrodes. In particular, it is preferable to use a melting kiln capable of electric melting.

A melting kiln that can be electrically melted has a plurality of electrodes made of molybdenum, platinum, tin, etc. By applying electricity between these electrodes, electricity is energized in the glass melt, and the Joule heat causes electricity to flow through the glass melt. The glass is continuously melted. In addition, radiant heating by a heater or a burner may be used in combination as an auxiliary. When heating with a burner, the water generated by combustion is taken into the glass and the water content of the glass increases. Therefore, by adjusting the combustion amount and temperature, the number of burners used in the melting equipment, and the raw material. , The water content of the glass can be adjusted as appropriate.

It is preferable to use a molybdenum electrode as the electrode. Since the molybdenum electrode has a high degree of freedom in the arrangement location and the electrode shape, the optimum electrode arrangement and electrode shape can be adopted even for low-alkali glass that is difficult to conduct electricity, and energization heating becomes easy. The electrode shape is preferably rod-shaped. If it is rod-shaped, it is possible to arrange a desired number of electrodes at arbitrary positions on the side wall surface and the bottom wall surface of the melting kiln while maintaining a desired distance between the electrodes. It is desirable to arrange the electrodes on the wall surface (side wall surface, bottom wall surface, etc.) of the melting kiln, particularly on the bottom wall surface, in a plurality of pairs with a short distance between the electrodes. If the glass contains an arsenic component or an antimony component, the molybdenum electrode cannot be used for the reason described above, and instead, it is necessary to use a tin electrode that is not eroded by these components. However, since the tin electrode has a very low degree of freedom in the arrangement location and the electrode shape, it is difficult to electrically melt the low-alkali glass.

The raw material batch put into the melting kiln is melted by radiant heat or Joule heat and becomes a glass melt (molten glass). Multivalent oxides such as tin compounds contained in the raw material batch dissolve in the glass melt and act as a clarifying agent. For example, the tin component releases oxygen bubbles in the process of raising the temperature. The released oxygen bubbles expand and float the bubbles contained in the glass melt and remove them from the glass. In addition, the tin component absorbs oxygen bubbles in the temperature lowering process to eliminate the bubbles remaining in the glass.

(3) Clarification step Next, the temperature of the molten glass is raised and clarified. The clarification step may be performed in an independent clarification tank, or may be performed in a downstream portion in a melting kiln or the like.

When the temperature of the glass melt becomes higher than that at the time of melting, oxygen bubbles are released from the clarifying agent component by the above reaction, and the bubbles contained in the glass melt can be expanded and floated to be removed from the glass. At this time, the larger the temperature difference between the melting temperature and the clarification temperature, the higher the clarification effect. Therefore, it is desirable to keep the melting temperature as low as possible.

(4) Molding step Next, the clarified glass is supplied to the molding apparatus and molded into a plate shape. A stirring tank, a state adjusting tank, or the like may be arranged between the clarification tank and the molding apparatus, and the glass may be supplied to the molding apparatus after passing through these. In addition, in order to prevent contamination of the glass, at least the contact surface with the glass of the connecting flow path connecting the melting kiln, the clarification tank, and the molding equipment (or the tanks provided between them) must be made of platinum or a platinum alloy. Is preferable.

The molding method is not particularly limited, but if the down-draw method is adopted, which has restrictions on the length of the slow cooling furnace and it is difficult to reduce the heat shrinkage rate, the effect of the present invention can be easily enjoyed. As the downdraw method, it is preferable to adopt the overflow downdraw method. The overflow down draw method is to overflow the molten glass from both sides of a gutter-shaped refractory with a wedge-shaped cross section, and while merging the overflowed molten glass at the lower end of the gutter-shaped refractory, stretch the glass downward to form a plate. It is a method of molding into a shape. In the overflow down draw method, the surface of the glass plate, which should be the surface, does not come into contact with the gutter-shaped refractory and is formed in a free surface state. Therefore, it is possible to inexpensively manufacture a glass plate that is unpolished and has good surface quality, and it is easy to increase the size and thickness of the glass. The structure and material of the gutter-shaped refractory used in the overflow downdraw method are not particularly limited as long as they can achieve desired dimensions and surface accuracy. Further, the method of applying a force when performing downward stretching molding is not particularly limited. For example, a method of rotating and stretching a heat-resistant roll having a sufficiently large width in contact with the glass may be adopted, or a plurality of pairs of heat-resistant rolls may be brought into contact with only the vicinity of the end face of the glass. You may adopt the method of letting and stretching. In addition to the overflow down draw method, for example, a slot down method or the like can be adopted.

The glass thus formed into a plate shape is cut into a predetermined size and subjected to various chemical or mechanical processing as necessary to become a glass plate.

Next, a low-alkali glass plate that can be produced by the method of the present invention will be described.

The low alkaline glass plate obtained by the method of the present invention heats the glass from room temperature (25 ° C.) to 500 ° C. at a rate of 5 ° C./min, holds the glass at 500 ° C. for 1 hour, and then has a rate of 5 ° C./min. The heat shrinkage when the temperature is lowered to room temperature is preferably 25 ppm or less, 22 ppm or less, 20 ppm or less, 19 ppm or less, 18 ppm or less, 17 ppm or less, 16 ppm or less, 15 ppm or less, 14 ppm or less, and particularly preferably 13 ppm or less. If the heat shrinkage rate is large, it becomes difficult to use it as a substrate for forming an oxide TFT. The lower limit of the heat shrinkage rate is not limited, but is preferably 2 ppm or more, particularly preferably 3 ppm or more.

The low alkaline glass plate obtained by the method of the present invention preferably has a β-OH value of 0.3 / mm or less, particularly preferably 0.25 / mm or less. If the β-OH value is too large, the strain point of the glass will not be sufficiently high, and it will be difficult to significantly reduce the heat shrinkage rate. Further, the lower limit of the β-OH value is preferably 0.06 / mm or more, particularly preferably 0.1 / mm or more. If the β-OH value is too small, the glass dough must be melted at a high temperature, so that the refractory that comes into contact with the glass melt erodes, and foreign matter caused by the refractory may increase in the glass. be. In addition, there is a risk that the life of the melting equipment will be shortened, or that undissolved foreign material will flow out and the homogeneity of the glass will deteriorate, leading to deterioration of quality and deterioration of foam quality.

The low alkaline glass plate obtained by the method of the present invention has a B ₂ O ₃ content of x (mass%) and a β-OH value of y (/ mm), y = ax + b, 0.01 <a. It is preferable that the relational expressions <0.04 and 0.03 <b <0.06 hold. Further, the lower limit of a is preferably 0.015 or more, particularly preferably 0.02 or more, and the lower limit of b is preferably 0.035 or more, particularly preferably 0.04 or more. By doing so, it becomes easy to obtain a low-alkali glass plate having a high strain point and a small heat shrinkage rate.

The low alkaline glass plate obtained by the method of the present invention is made of glass having a strain point of 680 ° C or higher, 685 ° C or higher, 690 ° C or higher, 695 ° C or higher, 700 ° C or higher, 705 ° C or higher, and particularly 710 ° C or higher. preferable. By doing so, it becomes easy to suppress the heat shrinkage of the glass plate in the manufacturing process of the oxide TFT. If the strain point is too high, the temperature at the time of molding or melting becomes too high, and the manufacturing cost of the glass plate tends to rise. Therefore, the upper limit of the strain point is 750 ° C. or lower, 740 ° C. or lower, especially 730 ° C. or lower. It is preferable to have.

The low alkaline glass plate obtained by the method of the present invention is a glass having a temperature of 1630 ° C. or lower, 1620 ° C. or lower, 1610 ° C. or lower, 1600 ° C. or lower, 1590 ° C. or lower, particularly 1580 ° C. or lower at 10 ^2.5 dPa · s. It is preferably composed of. If the temperature at 10 ^2.5 dPa · s is too high, the glass becomes difficult to melt, the manufacturing cost of the glass plate rises, and defects such as bubbles are likely to occur. If the temperature at 10 ^2.5 dPa · s is too low, the viscosity at the liquid phase temperature will be high and it will be difficult to design. Therefore, the lower limit of the temperature at 10 ^2.5 dPa · s is 1500 ° C or higher, 1510 ° C or higher, especially 1520 ° C. The above is preferable. The "temperature corresponding to 10 ^2.5 dPa · s" is a value measured by the platinum ball pulling method.

The low alkaline glass plate obtained by the method of the present invention is preferably made of glass having a liquid phase temperature of less than 1250 ° C., less than 1240 ° C., less than 1230 ° C., less than 1220 ° C., less than 1210 ° C., and particularly less than 1200 ° C. By doing so, devitrification crystals are less likely to occur during glass production, and it becomes easier to prevent a situation in which productivity is lowered. Further, since it is easy to mold by the overflow down draw method, it is easy to improve the surface quality of the glass plate and it is possible to reduce the manufacturing cost of the glass plate. From the viewpoint of increasing the size of the glass plate and increasing the definition of the display in recent years, it is very significant to improve the devitrification resistance in order to suppress the devitrification material which may be a surface defect as much as possible. The liquidus temperature is an index of devitrification resistance, and the lower the liquidus temperature, the better the devitrification resistance. The "liquid phase temperature" is a temperature gradient furnace set to 1100 ° C. to 1350 ° C. by putting the glass powder that has passed through a standard sieve of 30 mesh (opening 500 μm) and remains in 50 mesh (opening 300 μm) into a platinum boat. After holding the glass for 24 hours, the platinum boat is taken out, and it refers to the temperature at which devitrification (crystal foreign matter) is observed in the glass.

The low alkaline glass plate obtained by the method of the present invention has a liquid phase viscosity of 10 ^4.0 dPa · s or more, 10 ^4.2 dPa · s or more, 10 ^4.4 dPa · s or more, and 10 ^4.5 dPa ·. s or more, 10 ^4.6 dPa · s or more, 10 ^4.7 dPa · s or more, 10 ^4.8 dPa · s or more, 10 ^4.9 dPa · s or more, especially 10 ^5.0 dPa · s or more. It is preferably made of glass. By doing so, devitrification is less likely to occur during molding, so that the glass plate can be easily formed by the overflow downdraw method, and as a result, the surface quality of the glass plate can be improved, and the glass plate can be manufactured. The cost can be reduced. The liquidus viscosity is an index of moldability, and the higher the liquidus viscosity, the better the moldability. The "liquid phase viscosity" refers to the viscosity of the glass at the liquid phase temperature, and can be measured by, for example, a platinum ball pulling method.

The low alkaline glass plate obtained by the method of the present invention preferably has a substrate area of 4 m ² or more. If the substrate area is too small, it becomes difficult to efficiently manufacture a large LCD or OLED display provided with a TFT having an oxide film such as IGZO.

Next, the glass manufactured by using the method of the present invention will be described. Table 1 shows Examples (No. 1 to 8) and Comparative Examples (No. 9) of the present invention.

 

First, silica sand, aluminum oxide, orthoboric acid, anhydrous boric acid, calcium carbonate, strontium carbonate, strontium nitrate, barium carbonate, and ferric oxide were mixed and prepared so as to have the composition shown in Table 1. A glass cullet having the same composition as the target composition (β-OH value 0.2 / mm, 35% by mass with respect to the total amount of the raw material batch was used) was also used.

Next, the glass raw material was supplied to an electric melting kiln that did not use burner combustion to melt it, and then the molten glass was clarified and homogenized in the clarification tank and the adjustment tank, and the viscosity was adjusted to be suitable for molding.

Subsequently, the molten glass was supplied to an overflow down draw molding apparatus, molded into a plate shape, and then cut to obtain a glass sample having a thickness of 0.5 mm. The molten glass that came out of the molten kiln was supplied to the molding apparatus while in contact with only platinum or a platinum alloy.

For the obtained glass sample, β-OH value, strain point, temperature at 10 ^2.5 dPa · s, liquid phase temperature, liquid phase viscosity, heat shrinkage rate, foam grade, y = ax + b (x is B ₂ O ₃ ). Content (% by mass) and y were evaluated as to whether the β-OH value (/ mm) and the formulas of 0.01 <a <0.04 and 0.03 <b <0.06) were satisfied. The results are shown in Table 1.

As is clear from Table 1, No. 1 which is an example. Nos. 1 to 8 satisfy the above formula, have a low β-OH value of 0.24 / mm or less, a high strain point of 685 ° C. or higher, a low heat shrinkage rate of 23 ppm or less, and excellent foam quality. .. On the other hand, No. No. 9 had a high B ₂ O ₃ content and did not satisfy the above formula, so that the strain point was as low as 672 ° C. and the heat shrinkage rate was as high as 32 ppm.

The β-OH value of glass was determined by measuring the transmittance of glass using FT-IR and using the following formula.

β-OH value = (1 / X) log10 (T ₁ / T ₂ )
X: Glass wall thickness (mm)
T ₁ : Transmittance (%) at a reference wavelength of 3846 cm ^-1
T ₂ : Minimum transmittance (%) near hydroxyl group absorption wavelength 3600 cm ^-1

The strain point was measured based on the method of ASTM C336-71.

The temperature at 10 ^2.5 dPa · s is a value measured by the platinum ball pulling method.

The liquidus temperature passes through a standard sieve of 30 mesh (opening 500 μm), and the glass powder remaining in 50 mesh (opening 300 μm) is placed in a platinum boat and placed in a temperature gradient furnace set at 1100 ° C to 1350 ° C. After holding for 24 hours, the platinum boat was taken out, and the temperature was such that devitrification (crystal foreign matter) was observed in the glass.

The liquid phase viscosity is a value obtained by measuring the viscosity of glass at the liquid phase temperature by the platinum ball pulling method.

The heat shrinkage was measured by the following method. First, as shown in FIG. 2A, a strip-shaped sample G having a size of 160 mm × 30 mm was prepared as a sample of the glass plate 1. Marking M was formed on each of both ends of the strip-shaped sample G in the long side direction at a position 20 to 40 mm away from the edge using # 1000 water-resistant abrasive paper. Then, as shown in FIG. 2B, the strip-shaped sample G on which the marking M was formed was folded in two along the direction orthogonal to the marking M to prepare sample pieces Ga and Gb. Then, only one sample piece Gb was subjected to a heat treatment in which the temperature was raised from room temperature (25 ° C.) to 500 ° C. at 5 ° C./min, held at 500 ° C. for 1 hour, and then lowered to room temperature at 5 ° C./min. .. After the heat treatment, as shown in FIG. 2C, the marking M of the two sample pieces Ga and Gb in a state where the heat-treated sample piece Ga and the heat-treated sample piece Gb are arranged in parallel. The amount of misalignment (ΔL ₁ , ΔL ₂ ) was read with a laser microscope, and the heat shrinkage rate was calculated by the following formula. Note that l ₀ in the equation is the distance between the initial markings M.

Heat shrinkage rate = [{ΔL ₁ (μm) + ΔL ₂ (μm)} × 10 ³ ] / l ₀ (mm) (ppm)

As for the foam quality, bubbles with a diameter of 100 μm or more were counted, and those having a diameter of 0.05 / kg or less were indicated as “〇”, and those having a diameter of more than 0.05 / kg were indicated as “x”.

y = ax + b (x is the content (% by mass) of B ₂ O ₃ , y is the β-OH value (/ mm), 0.01 <a <0.04 and 0.03 <b <0.06). The case where the expression was satisfied was evaluated as "○", and the case where the expression was not satisfied was evaluated as "×".

According to the present invention, it is possible to easily obtain a glass plate having a high strain point, good foam quality, and a small heat shrinkage ratio suitable for producing an oxide TFT.

Claims (17)

1. As the glass composition, in terms of mass%, SiO ₂ 50 to 70%, Al ₂ O ₃ 15 to 25%, B ₂ O ₃ 2 to 7.5%, MgO 0 to 10%, CaO 0 to 10%, SrO 0 to Contains 10%, BaO 0 to 15%, ZnO 0 to 5%, ZrO ₂₀ to 1%, TiO ₂₀ to 5%, P ₂ O ₅₀ to 10%, SnO ₂ 0.1 to 0.5%. A batch preparation process that prepares a raw material batch so that it becomes low-alkali glass.
   It includes a melting step of melting the prepared raw material batch, a clarification step of clarifying the melted glass, and a molding step of forming the clarified glass into a plate shape.
   When the content of B ₂ O ₃ is x (mass%) and the β-OH value of the obtained low alkaline glass plate is y (/ mm), y = ax + b, 0.01 <a <0.04 and 0. A method for producing a low-alkali glass plate, which comprises adjusting the content of B ₂ O ₃ and the β-OH value so that the relational expression of .03 <b <0.06 holds.
2. In the batch preparation step, the glass composition in terms of glass composition is SiO ₂ 57 to 65%, Al ₂ O ₃ 17 to 22%, B ₂ O ₃ 2.5 to 7%, MgO 1 to 10%, BaO 0. The method for producing a low-alkali glass plate according to claim 1, wherein a raw material batch is prepared so as to be a low-alkali glass containing 1 to 15% and SnO ₂ 0.1 to 0.3%.
3. The method for producing a low-alkali glass plate according to claim 1 or 2, wherein the prepared raw material batch is electrically melted.
4. The method for producing a low-alkali glass plate according to any one of claims 1 to 3, wherein the raw material batch contains a carbonate raw material and / or a nitrate raw material.
5. The method for producing a low-alkali glass plate according to any one of claims 1 to 4, wherein orthoboric acid and / or anhydrous boric acid is used as at least a part of the glass raw material as a boron source.
6. The method for producing a low-alkali glass plate according to any one of claims 1 to 5, wherein the raw material batch contains a hydroxide raw material.
7. Claims 1 to 7, wherein the raw material batch contains a glass cullet, and at least a part of the glass cullet is a glass cullet made of glass having a β-OH value of 0.3 / mm or less. The method for manufacturing a low-alkali glass plate according to any one.
8. The low-alkali glass plate according to any one of claims 1 to 7, wherein the glass raw material and / or the melting conditions are adjusted so that the β-OH value of the obtained glass is 0.3 / mm or less. Manufacturing method.
9. The method for manufacturing a low-alkali glass plate according to any one of claims 1 to 8, wherein the strain point of the obtained glass is 680 ° C. or higher.
10. The method for producing low alkaline glass according to any one of claims 1 to 9, wherein the obtained glass has a heat shrinkage rate of 25 ppm or less.
11. As the glass composition, in terms of mass%, SiO ₂ 50 to 70%, Al ₂ O ₃ 15 to 25%, B ₂ O ₃ 2 to 7.5%, MgO 0 to 10%, CaO 0 to 10%, SrO 0 to Contains 10%, BaO 0 to 15%, ZnO 0 to 5%, ZrO ₂₀ to 1%, TiO ₂₀ to 5%, P ₂ O ₅₀ to 10%, SnO ₂ 0.1 to 0.5%. However, the β-OH value is 0.05 to 0.3 / mm, and the β-OH value is 0.05 to 0.3 / mm.
    When the content of B ₂ O ₃ is x (mass%) and the β-OH value is y (/ mm), y = ax + b, 0.01 <a <0.04 and 0.03 <b <0. A low-alkali glass plate characterized in that the relational expression of 06 holds.
12. As the glass composition, in terms of mass%, Al ₂ O ₃ 17 to 22%, B ₂ O ₃ 2.5 to 7%, MgO 0.1 to 10%, CaO 0.1 to 10%, ZrO ₂₀ to 0. The low alkaline glass plate according to claim 11, which contains 5% and ₂₀ to 1% of TiO.
13. 11. The glass composition is characterized by containing SiO ₂ 57 to 65%, MgO 2 to 10%, BaO 0.1 to 15%, and SnO ₂ 0.1 to 0.3% in mass%. Or the low alkaline glass plate according to 12.
14. The low alkaline glass plate according to any one of claims 11 to 13, wherein the strain point is 680 ° C. or higher.
15. The low alkaline glass plate according to any one of claims 11 to 14, wherein the heat shrinkage rate is 25 ppm or less.
16. The low-alkali glass plate according to any one of claims 11 to 15, characterized in that it is used as a glass plate on which an oxide TFT is formed.
17. The low-alkali glass plate according to any one of claims 11 to 16, wherein the substrate area is 4 m ² or more.
    

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