TW202216624A - 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 [beta]-OH value of the obtained low alkali glass plate is referred to as y (/mm), the B2O3 content and the [beta]-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

Low-alkali glass plate manufacturing method and low-alkali glass plate

The present invention relates to a low-alkali glass plate, in detail, to a low-alkali glass plate suitable for displays and the like with thin film transistor (TFT, Thin Film Transistor), the thin film transistor having indium gallium zinc oxide (IGZO) , Indium Gallium Zinc Oxide) and other oxide films.

In flat panel displays, generally, a glass plate is used as a support substrate. Circuit patterns such as TFTs are formed on the surface of the glass plate. Therefore, in order to prevent bad influence on TFT etc., the low alkali glass plate which does not contain an alkali metal component substantially is used as such a glass plate.

In addition, the glass plate is exposed to a high-temperature gas atmosphere in a circuit pattern forming step such as a thin film forming step or a thin film patterning step. When the glass sheet is exposed to a high-temperature gas atmosphere, the structural relaxation of the glass progresses, thereby causing volume shrinkage of the glass sheet (hereinafter, the shrinkage of the glass is referred to as "thermal shrinkage"). In the circuit pattern forming step, if the glass plate is thermally shrunk, the shape and size of the circuit pattern formed on the glass plate may deviate from the design value, making it difficult to obtain a flat panel display with desired electrical properties. Therefore, it is desirable that the thermal shrinkage rate is small for a glass plate on which a thin film pattern such as a circuit pattern is formed on the surface, for example, a glass plate for a flat panel display.

In particular, in the case of a glass plate for a high-definition display including a TFT having an oxide film such as IGZO, when the oxide film is formed, the glass plate is exposed to a very high temperature gas atmosphere such as 400°C to 500°C, Thermal shrinkage is easy to occur. Once thermal shrinkage occurs, it is difficult to obtain the required electrical properties due to high-precision circuit patterns. As such, very little thermal shrinkage is strongly desired for glass sheets for such applications.

In addition, as a shaping|molding method of the glass plate used for a flat panel display etc., a float method, a down-draw method represented by an overflow down-draw method, etc. are known.

The float method refers to a method as follows: molten glass is flowed out over a floating kiln filled with molten tin, stretched in a horizontal direction to form a glass ribbon, and then the glass is heated in a slow cooling furnace installed on the downstream side of the floating kiln. The tape is subjected to slow cooling, thereby forming a glass sheet. In the float method, since the conveying direction of the glass ribbon is the horizontal direction, it is convenient 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 the advantage of easily obtaining a glass sheet with a small thermal shrinkage rate.

However, the float method has the following disadvantages: it is difficult to form a thinner glass plate; and the surface of the glass plate must be ground after forming to remove tin adhering to the surface of the glass plate.

On the other hand, the down-draw method is a method of drawing molten glass downward to form a plate shape. The overflow down-draw method, which is a kind of down-draw method, is a method of forming a glass ribbon by drawing the molten glass overflowing from both sides of a forming body having a substantially wedge-shaped cross section downward. The molten glass overflowing from both sides of the formed body flows down along both sides of the formed body, and merges at the lower part of the formed body. Therefore, in the overflow down-draw method, since the surface of the glass ribbon is formed by surface tension without being in contact with other than air, even if the surface is not polished after forming, no foreign matter will adhere to the surface, and the A glass plate with a flat surface can be obtained. In addition, the overflow down-draw method also has the advantage that it is easy to form a thinner glass plate.

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 arranged below the formed body, the formed body must be arranged at a higher position. However, in practice, there is a limit to the height at which the molded body can be arranged due to the ceiling height of the factory and the like. 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 in some cases. When the length of the slow-cooling furnace is short, the cooling rate of the glass ribbon becomes fast, so that it is difficult to form a glass sheet with a small thermal shrinkage rate.

Therefore, a proposal has been made to increase the strain point of the glass and reduce the thermal shrinkage of the glass. For example, Patent Document 1 discloses a low-alkali glass composition with a high strain point. In addition, this document describes that the lower the β-OH value representing the water content in the glass, the higher the strain point. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2013-151407

[Problems to be Solved by Invention]

As shown in Figure 1, the higher the strain point, the smaller the thermal shrinkage. However, the viscosity of the glass whose composition is designed to increase the strain point is high, so there is a problem that the defoaming is poor, and it is difficult to obtain a glass with excellent foam quality.

The present invention was made in view of the above-mentioned circumstances, and an object thereof is to provide a low-alkali glass plate having a high strain point and excellent bubble quality, and a method for producing the same. [Technical means to solve problems]

The manufacturing method of the low alkali glass plate of the present invention is characterized by comprising the following steps: a batch preparation step, which is to prepare a batch of raw materials so as to contain 50-70% of SiO ₂ , Al ₂ O by mass % ₃ 15～25%, B ₂ O ₃ 2～7.5%, MgO 0～10%, CaO 0～10%, SrO 0～10%, BaO 0～15%, ZnO 0～5%, ZrO ₂ 0～1 %, TiO ₂ 0-5%, P ₂ O ₅ 0-10%, SnO ₂ 0.1-0.5% as a low-alkali glass composed of glass; the melting step is to melt the obtained raw material batch. ; a clarifying step, which clarifies the molten glass; and a forming step, which shapes the clarified glass into a plate shape; and the B ₂ O ₃ content and β-OH value are adjusted so that in the When the content of B ₂ O ₃ is set to x (mass %) and the β-OH value of the obtained low alkali glass plate is set to y (/mm), y=ax+b, 0.01<a<0.04 and 0.03<b The relational expression of <0.06 is established.

Here, the term "low alkali glass" refers to a glass in which an alkali metal oxide component is not intentionally added, and specifically refers to the alkali metal oxides (Li ₂ O, Na ₂ O, and K ₂ in the glass composition) Glass with an O) content of 3000 ppm (mass) or less. Furthermore, 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 content of B ₂ O ₃ in the glass composition used is small, a glass plate with a high strain point can be obtained. But generally speaking, glass with high strain point has higher viscosity, and it is difficult to achieve higher foam quality. Therefore, in the present invention, it was further found that as long as the content of B ₂ O ₃ and the β-OH value are controlled as in the above formula, and SnO ₂ having a clarifying effect at relatively high temperature is contained as an essential component, a relatively high High bubble quality.

In the production method of the present invention, it is preferable to prepare a raw material batch in the above-mentioned batch preparation step so as to contain 57-65% of SiO ₂ , 17-22% of Al ₂ O ₃ , and B ₂ O ₃ by mass %. 2.5 to 7%, 1 to 10% of MgO, 0.1 to 15% of BaO, and 0.1 to 0.3% of SnO ₂ are prepared as low-alkali glass of glass composition.

In the production method of the present invention, electrofusion is preferably performed. Here, "electrofusion" refers to a melting method in which electricity is applied to glass, and the glass is heated and melted by Joule heat generated thereby. Furthermore, the simultaneous use of a heater or a burner for radiant heating is not excluded.

According to the above-mentioned configuration, the increase of moisture in the gas atmosphere can be suppressed. As a result, the supply of water from the gas atmosphere to the glass can be greatly suppressed, and the glass with a high strain point can be easily produced. Moreover, since the glass melt is heated by the heat generation (Joule heat) of the glass itself, it is possible to efficiently heat the glass. As such, the raw material batch can be melted at relatively low temperatures.

In the production method of the present invention, it is preferable that the raw material batch contains carbonate raw materials and/or nitrate raw materials.

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

By adopting the above-mentioned configuration, the moisture content of the obtained glass can be adjusted.

In the production method of the present invention, it is preferable that the raw material batch contains the hydroxide raw material.

By adopting the above-mentioned configuration, the moisture content of the obtained glass can be further adjusted.

The production method of the present invention is preferably a method for producing a low-alkali glass plate containing glass chips in the raw material, and at least a part of the glass chips is a glass chip containing glass having a β-OH value of 0.3/mm or less. Here, the so-called "glass dust" refers to defective glass produced in the glass manufacturing process, or recycled glass recovered from the market. The "β-OH value" refers to a value obtained by measuring the transmittance of glass using FT-IR (Fourier Transform Infrared Radiation) and according to the following formula.

β-OH value=(1/X)log(T ₁ /T ₂ ) X: glass thickness (mm) T ₁ : transmittance at reference wavelength 3846 cm ⁻¹ (%) T ₂ : hydroxyl absorption wavelength 3600 cm ⁻ Minimum transmittance around ¹ (%)

Since low-alkali glass has higher volume resistance, it tends to be more difficult to melt than glass containing alkali. Therefore, according to the above-mentioned structure, not only the melting of the glass is facilitated, but also the water content of the obtained glass can be adjusted and reduced.

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

By adopting the above configuration, glass having a high strain point and a low thermal shrinkage rate can be easily obtained.

In the manufacturing method of this invention, it is preferable that the strain point of the glass obtained is 680 degreeC or more. Here, "strain point" is a value measured according to the method of ASTM C336-71.

According to the above-mentioned structure, glass with an extremely small thermal shrinkage rate can be obtained.

In the manufacturing method of this invention, it is preferable that the thermal contraction rate of the glass obtained is 25 ppm or less. Here, the so-called "thermal shrinkage rate" refers to the rate of heating from normal temperature (25°C) to 500°C at a rate of 5°C/min, holding at 500°C for 1 hour, and then cooling down to normal temperature at a rate of 5°C/min. Measured after heat treatment of glass under the same conditions.

With the above-described configuration, a glass plate suitable for forming oxide TFTs can be obtained.

The low alkali glass plate of the present invention is characterized by containing 50 to 70% by mass of SiO ₂ , 15 to 25% of Al ₂ O ₃ , 2 to 7.5% of B ₂ O ₃ , 0 to 10% of MgO, and 0 to 10% of CaO. 10%, SrO 0～10%, BaO 0～15%, ZnO 0～5%, ZrO ₂ 0～1%, TiO ₂ 0～5%, P ₂ O ₅ 0～10%, SnO ₂ 0.1～0.5% As a glass composition, the β-OH value is 0.05 to 0.3/mm, and when the content of B ₂ O ₃ is x (mass %) and the β-OH value is y (/mm), y=ax+b, The relational expressions of 0.01<a<0.04 and 0.03<b<0.06 are established.

The low alkali glass plate of the present invention preferably contains 17-22% by mass of Al ₂ O ₃ , 2.5-7% of B ₂ O ₃ , 0.1-10% of MgO, 0.1-10% of CaO, and 0-0.5 of ZrO ₂ %, TiO ₂ 0-1% as glass composition.

The low alkali glass plate of the present invention preferably contains 57 to 65% by mass of SiO ₂ , 2 to 10% of MgO, 0.1 to 15% of BaO, and 0.1 to 0.3% of SnO ₂ .

The strain point of the low alkali glass plate of the present invention is preferably 680°C or higher.

The thermal shrinkage rate of the low alkali glass plate of the present invention is preferably 25 ppm or less.

The low-alkali glass plate of the present invention is preferably used as a glass plate on which oxide TFTs are formed.

Regarding oxide TFTs, when they are formed on a substrate, the heat treatment temperature is high (around 400 to 500° C.), and the circuit pattern is finer. Therefore, it is particularly desirable for glass sheets to be used for this purpose that the thermal shrinkage is small. For this reason, the use of the glass sheet of the present invention with a high strain point is extremely advantageous.

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

Hereinafter, the manufacturing method of the low alkali glass plate of this invention is demonstrated in detail. In this specification, the numerical range represented using "-" means the range which includes the numerical value described before and after "-" as a minimum value and a maximum value, respectively.

The method of the present invention is a method for continuously manufacturing a low-alkali glass plate, and includes the following steps: a batch preparation step, which is to prepare a raw material batch; a melting step, which is to melt the prepared raw material batch; clarifying step, which is to clear the molten glass; and a forming step, which is to form the clear glass. Hereinafter, detailed description will be given step by step.

(1) Batch Preparation Step First, glass raw materials are prepared so as to contain 50 to 70% of SiO ₂ , 15 to 25% of Al ₂ O ₃ , 2 to 7.5% of B ₂ O ₃ , and 0 to 10% of MgO in mass %. , CaO 0～10%, SrO 0～10%, BaO 0～15%, ZnO 0～5%, ZrO ₂ 0～1%, TiO ₂ 0～5%, P ₂ O ₅ 0～10%, SnO ₂ 0.1 to 0.5% is prepared as a low-alkali glass with a glass composition. The reason for restricting the content of each component as described above will be explained below. In addition, unless otherwise specified, the % symbol in the description of each component below represents mass %. In addition, the raw material used will be demonstrated later.

SiO ₂ is a component that forms the glass skeleton. The lower limit of the content of SiO ₂ is preferably 50%, 51%, 51.5%, 52%, 55%, 56%, 57%, and particularly preferably 58%. In addition, the upper limit of the content of SiO ₂ is preferably 70%, 69%, 68%, 67%, 66%, 65%, 64%, 63%, and more preferably 62%. When the content of SiO ₂ is too small, not only the density is too high, but also the acid resistance tends to decrease. On the other hand, when the content of SiO ₂ is too large, the high temperature viscosity becomes high and the meltability tends to decrease. In addition, devitrification 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 a glass skeleton, and is also a component that increases the strain point and Young's modulus, and is also a component that 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%, and particularly preferably 18%. In addition, the upper limit of the content of Al ₂ O ₃ is preferably 25%, 24%, 23%, 22%, 21.5%, and particularly preferably 21%. When the content of Al ₂ O ₃ is too small, the strain point and the Young's modulus tend to decrease, and the glass tends to phase-separate. On the other hand, when the content of Al ₂ O ₃ is too large, devitrification crystals such as mullite and anorthite are likely to be precipitated, and the liquidus temperature is likely to rise.

B ₂ O ₃ is a component that improves not only meltability but also devitrification resistance. The lower limit of the content of B ₂ O ₃ is preferably 2%, 2.2%, and particularly preferably 2.5%. Moreover, the upper limit _of content of B2O3 _becomes like this. Preferably it is 7.5%, More preferably, it is 7%. When 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 chemical solutions such as buffered hydrofluoric acid tends to decrease. In addition, there is a possibility that the amount of water brought in from the batch is too low. On the other hand, when 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 reduces high temperature viscosity and improves melting properties, and is a component that significantly increases Young's modulus among alkaline earth metal oxides. The lower limit of the content of MgO is preferably 0%, 0.1%, 0.5%, 1%, 1.5%, and particularly preferably 2%. Moreover, the upper limit of the content of MgO is preferably 10%, 9%, 8%, 7.5%, 7%, 6%, and more preferably 5%. When the content of MgO is too small, meltability and Young's modulus tend to decrease. On the other hand, when the content of MgO is too large, not only the devitrification resistance but also the strain point tends to decrease easily.

CaO is a component that reduces high temperature viscosity and significantly improves meltability without lowering the strain point. In addition, among the alkaline earth metal oxides, the introduction raw material of CaO is relatively inexpensive, so it is a component that reduces the cost of the raw material. The lower limit of the content of CaO is preferably 0%, 0.1%, 1%, 2%, 3%, and particularly preferably 3.5%. In addition, the upper limit of the content of CaO is preferably 10%, 9%, or 8%, and particularly preferably 7%. When the content of CaO is too small, it is difficult to have the above-mentioned effects. On the other hand, when the content of CaO is too large, not only the glass tends to devitrify, but also the thermal expansion coefficient tends to become high.

SrO is a component that suppresses phase separation and also improves devitrification resistance. Furthermore, SrO is a component that reduces high temperature viscosity and improves meltability without lowering the strain point. It is also a component that suppresses the rise in liquidus temperature. The lower limit of the content of SrO is preferably 0%, 0.1%, and particularly preferably 0.3%. In addition, the upper limit of the content of SrO is preferably 10%, 9%, 8%, 7%, 6%, and particularly preferably 5%. When the content of SrO is too small, it is difficult to obtain the above-mentioned effects. On the other hand, when the content of SrO is too large, not only the density is too high, but also devitrification crystals containing SrO tend to precipitate, and the devitrification resistance tends to decrease.

BaO is a component that significantly improves devitrification resistance. The lower limit of the content of BaO is preferably 0%, 0.1%, 0.5%, and particularly preferably 1%. In addition, the upper limit of the content of BaO is preferably 15%, 14%, 13%, 12%, 11%, and particularly preferably 10.5%. When the content of BaO is too small, it is difficult to obtain the above-mentioned effects. On the other hand, when the content of BaO is too large, not only the density is too high, but also the meltability tends to decrease. In addition, devitrification crystals containing BaO tend to precipitate, and the liquidus temperature tends to rise.

ZnO is a component that improves meltability. The content of ZnO is preferably 0 to 5%, 0 to 4%, 0 to 3%, and particularly preferably 0 to 2%. When the content of ZnO is too large, the glass tends to devitrify and the strain point tends to decrease.

ZrO ₂ is an ingredient that enhances chemical durability. The lower limit of the content of ZrO ₂ is preferably 0%, particularly preferably 0.01%. In addition, 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 agglomerated particles of ZrSiO ₄ are easily generated.

TiO ₂ is a component that reduces high temperature viscosity and improves meltability. It is also an ingredient that inhibits the aging effect of sun exposure. The content of TiO ₂ is preferably 0-5%, 0-4%, 0-3%, 0-2%, 0-1%, particularly preferably 0-0.1%. When the content of TiO ₂ is too large, the glass is colored and the transmittance tends to decrease.

P ₂ O ₅ is not only a component that raises the strain point, but also a component that can suppress the precipitation of alkaline-earth aluminosilicate-based devitrification crystals such as anorthite. The content of P ₂ O ₅ is preferably 0-10%, 0-9%, 0-8%, 0-7%, 0-6%, 0-5%, 0-4%, particularly preferably 0-3% %. When the content of P ₂ O ₅ is too large, the glass tends to be phase-separated.

SnO ₂ is not only a component that has a good clarifying effect in a high temperature region, but also a component that increases the strain point, and is also a component that reduces high temperature viscosity. In addition, SnO ₂ has the advantage of not corroding the molybdenum electrode. The lower limit of the content of SnO ₂ is preferably 0.1%, particularly preferably 0.15%. In addition, the upper limit of the content of SnO ₂ is preferably 0.5%, 0.45%, 0.4%, 0.35%, and particularly preferably 0.3%. When the content of SnO ₂ is too small, it is difficult to have the above-mentioned effects. On the other hand, when the content of SnO ₂ is too large, the devitrification crystals of SnO ₂ are easily precipitated, and the precipitation of devitrification crystals of ZrO ₂ is easily promoted.

In addition to the above-mentioned components, other components may 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 or from the viewpoint of preventing corrosion of the electrode. Here, "substantially free" means that glass raw materials or glass chips containing these components are not intentionally added to the glass batch. More specifically, in the obtained glass, 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 addition, although Cl and F may be contained in glass, the content of Cl is preferably less than 0.1%, more preferably less than 0.05%. The content of F is preferably less than 0.1%, more preferably less than 0.05%. Moreover, it is preferable that Cl+F (total total amount of Cl and F) is less than 0.1%.

Next, the glass raw material which comprises a batch is demonstrated. In addition, unless otherwise specified, the % symbol in the description of each raw material below represents mass %.

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 ), or the like can be used.

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

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

As the zinc source, zinc oxide (ZnO) or the like can be used.

As a zirconia source, zircon (ZrSiO ₄ ) or the like can be used. Furthermore, when Zr-containing refractories such as zirconia electroformed refractories and dense zircon are used as refractories constituting the melting kiln, zirconia components are eluted from the refractories. These leaching components can also be used as a source of zirconia.

As the titanium source, titanium oxide (TiO ₂ ) or the like can be used.

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

As the tin source, tin oxide (SnO ₂ ) or the like can be used. Furthermore, in the case of using tin oxide, it is preferable to use tin oxide whose average particle size _D50 is in the range of 0.3-50 μm, 2-50 μm, especially 5-50 μm. If the average particle diameter _D50 of the tin oxide powder is small, the particles will cohere, and clogging is likely to occur in the blending equipment. On the other hand, when the average particle diameter _D50 of the tin oxide powder is large, the reaction in which the tin oxide powder is melted in the glass melt is slow, and the melt does not become clear. As a result, oxygen gas cannot be sufficiently released at an appropriate timing when glass is melted, bubbles tend to remain in glass products, and it is difficult to obtain products with excellent bubble quality. In addition, it is easy to cause unmelted agglomerated particles of SnO ₂ crystals to appear in glass products.

In the present invention, the raw material batch may also contain carbonate raw materials. The carbonate raw material enables SnO ₂ to function efficiently as a fining agent. As a carbonate raw material, calcium carbonate (CaCO3), barium carbonate (BaCO3 ₎ , strontium carbonate ( _{SrCO3 )} , etc. can be used, for example.

In the present invention, the raw material batch may also contain nitrate raw materials. The nitrate raw material enables SnO ₂ to function efficiently as a clarifying agent. As a 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 raw material batch may also contain hydroxide raw materials. The hydroxide raw material can adjust the moisture content. As a 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 preferable that the batch is substantially free of arsenic compounds and antimony compounds. When these components are contained, the molybdenum electrode is corroded, so that it is difficult to perform electrofusion stably for a long time. Also, from an environmental point of view, these ingredients are not good.

In this invention, it is preferable to use glass dust in addition to the said glass raw material. In the case of using glass scraps, the usage ratio of the glass scraps with respect to the total amount of the raw material batch is preferably 1 mass % or more, 5 mass % or more, and particularly preferably 10 mass % or more. The upper limit of the usage ratio of the glass dust is not limited, but it is preferably 50 mass % or less, 40 mass % or less, and particularly preferably 30 mass % or less. Moreover, it is preferable that at least a part of the glass dust to be used is low-moisture glass dust containing glass whose β-OH value is 0.3/mm or less, 0.25/mm or less, especially 0.2/m or less. In addition, the lower limit value of the β-OH value of the low-moisture glass shavings is not particularly limited, but is preferably 0.05/mm or more.

Furthermore, glass raw materials, glass flakes, or raw material batches obtained by blending these components sometimes contain moisture. In addition, it may also absorb moisture in the atmosphere during storage. Therefore, in the present invention, it is preferable to introduce drying into the raw material storage bin for weighing and supplying each glass raw material, or the furnace front storage bin for throwing the obtained raw material batch into the melting kiln, etc. Air.

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

The melting of the raw material batch uses a melting kiln that can be heated by the radiant heat generated by the combustion of the burner or the Joule heat generated by the conduction of electricity between the electrodes. In particular, it is preferable to use a melting furnace capable of electric melting.

A melting kiln capable of electro-melting has a plurality of electrodes including molybdenum, platinum, tin, etc., by applying electricity between these electrodes, electricity is energized in the glass melt, and the glass is continuously energized by Joule heat generated by the electricity. molten. Furthermore, it is also possible to simultaneously use a heater or a burner for radiant heating as an auxiliary. In the case of heating with a burner, the moisture content of the glass is increased due to the moisture generated by the combustion being brought into the glass. Therefore, the amount and temperature of the burning and the number of burners used in the melting equipment are determined. , and the raw materials are adjusted, so that the moisture content of the glass can be appropriately adjusted.

As the electrode, a molybdenum electrode is preferably used. Due to the high degree of freedom in the arrangement position and electrode shape of the molybdenum electrode, the most suitable electrode arrangement and electrode shape can be adopted even for low-alkali glass, which is difficult to energize, which makes energization and heating easier. The electrode shape is preferably a rod shape. If it is a rod shape, a desired number of electrodes can be arranged at any position on the side wall surface or bottom wall surface of the melting kiln while maintaining a desired distance between electrodes. As for the arrangement of electrodes, it is preferable to arrange a plurality of pairs by shortening the distance between electrodes on the wall surface (side wall surface, bottom wall surface, etc.) of the melting kiln, especially the bottom wall surface. Furthermore, in the case where the glass contains arsenic or antimony, for the reasons already explained, molybdenum electrodes cannot be used, and tin electrodes that are not corroded by these components must be used instead. However, since the degree of freedom in the arrangement position of the tin electrode and the shape of the electrode is very low, it is difficult to electrofuse the low-alkali glass.

The raw material batch thrown into the melting kiln is melted by radiant heat or Joule heat, and becomes a glass melt (molten glass). Polyvalent oxides such as tin compounds contained in the raw material batch melt in the glass melt and function as a clarifying agent. For example, the tin component releases oxygen bubbles during the heating process. The released oxygen bubbles enlarge and float the bubbles contained in the glass melt to remove them from the glass. In addition, the tin component absorbs oxygen bubbles during the cooling process, thereby eliminating bubbles remaining in the glass.

(3) Clarification step Next, the molten glass is heated and clarified. The clarification step can be carried out in a separate clarification tank, or in a downstream part of the melting kiln.

When the temperature of the glass melt is higher than the temperature during melting, oxygen bubbles are released from the clarifying agent component due to the above reaction, so that the bubbles contained in the glass melt can be enlarged and floated to be removed from the glass. . At this time, the larger the difference between the temperature during melting and the temperature during clarification, the better the clarification effect. Therefore, it is desirable to lower the temperature at the time of melting as much as possible.

(4) Forming step Next, the clarified glass is supplied to a forming apparatus and formed into a plate shape. In addition, a stirring tank, a state adjustment tank, etc. may be arrange|positioned between a clarification tank and a shaping|molding apparatus, and after passing through these tanks, you may supply glass to a shaping|molding apparatus. In addition, in order to prevent the contamination of the glass, it is preferable that at least the contact surface with the glass be platinum or platinum as for the communication flow path connecting the melting kiln, the clarification tank, and the molding device (or each tank provided therebetween). Alloy.

Although the forming method is not particularly limited, the length of the slow-cooling furnace is limited, and the effect of the present invention is likely to be obtained if the down-draw method is used, which is not easy to reduce the thermal shrinkage rate. As the down-draw method, an overflow down-draw method is preferably used. The overflow down-draw method refers to the method described below: the molten glass overflows from both sides of the gutter-shaped refractory with a wedge-shaped cross-section, and on the other hand, the overflowing molten glass is confluent at the lower end of the gutter-shaped refractory, One face is extended downward to shape the glass into a plate shape. In the overflow down-draw method, the surface of the glass plate should not be in contact with the gutter-shaped refractory, and should be formed in the state of a free surface. Therefore, a glass plate with good surface quality can be produced at a low cost in an unpolished state, and it is easy to achieve an increase in size or thickness of the glass. Furthermore, the structure and material of the gutter-shaped refractory used in the overflow down-draw method are not particularly limited, as long as required dimensions and surface accuracy can be achieved. In addition, the method of applying a force is not particularly limited when the stretching is performed downward. For example, a method of rotating and extending a heat-resistant roll having a sufficiently large width in contact with the glass may be employed, or a method of extending a plurality of pairs of heat-resistant rolls only in contact with the vicinity of the end surface of the glass may be employed. Furthermore, in addition to the overflow down-draw method, for example, an orifice down-draw method may also be employed.

The glass formed into a plate shape in this way is cut into a specific size, and is subjected to various chemical processing, mechanical processing, etc. as necessary to form a glass plate.

Next, the low alkali glass plate which can be produced by the method of this invention is demonstrated.

Regarding the low alkali glass plate obtained by the method of the present invention, when the glass is heated from normal temperature (25°C) to 500°C at a rate of 5°C/min, and kept at 500°C for 1 hour, the temperature is increased at a rate of 5°C/min. When cooling to room temperature, the thermal shrinkage rate 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, especially 13 ppm or less. If the thermal shrinkage rate is large, it is difficult to use as a substrate for forming oxide TFTs. In addition, the lower limit value of the thermal shrinkage rate is not limited, but is preferably 2 ppm or more, particularly preferably 3 ppm or more.

The β-OH value of the low alkali glass plate obtained by the method of the present invention is preferably 0.3/mm or less, particularly preferably 0.25/mm or less. When the β-OH value is too large, the strain point of the glass is not high enough, and it is difficult to significantly reduce the thermal shrinkage. Further, the lower limit value 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 green glass must be melted at a high temperature, so that the erosion of the refractory in contact with the glass melt increases, and there is a possibility that foreign matter or the like generated by the refractory in the glass increases. In addition, there is also a possibility that the life of the melting equipment will be shortened, or the unmelted heterogeneous green body may flow out, resulting in a decrease in the homogeneity of the glass, deterioration in quality, and deterioration in bubble quality.

For the low alkali glass plate obtained by the method of the present invention, when the content of B ₂ O ₃ is set to x (mass %) and the β-OH value is set to y (/mm), y=ax+b, The relational expressions of 0.01<a<0.04 and 0.03<b<0.06 are established. Furthermore, the lower limit value of a is preferably 0.015 or more, particularly preferably 0.02 or more, and the lower limit value of b is preferably 0.035 or more, particularly preferably 0.04 or more. In this way, it is easy to obtain a low-alkali glass plate with a high strain point and a small thermal shrinkage rate.

The low-alkali glass plate obtained by the method of the present invention preferably includes glass with 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, especially 710°C or higher . In this way, the thermal shrinkage of the glass plate can be easily suppressed in the manufacturing step of the oxide TFT. If the strain point is too high, the temperature at the time of forming and melting becomes too high, and the manufacturing cost of the glass plate tends to increase. Therefore, the upper limit of the strain point is preferably 750°C or lower, 740°C or lower, and particularly preferably 730°C or lower.

The low alkali glass plate obtained by the method of the present invention preferably includes a temperature of 1630°C or lower, 1620°C or lower, 1610°C or lower, 1600°C or lower, 1590°C or lower, especially 1580°C or lower at 10 ^2.5 dPa·s. of glass. If the temperature under 10 ^2.5 dPa·s is too high, the glass will not be easily melted, the manufacturing cost of the glass plate will increase, and defects such as bubbles will easily occur. If the temperature at 10 ^2.5 dPa·s is too low, it is difficult to design the viscosity at the liquidus temperature to a higher viscosity. Therefore, the lower limit of the temperature at 10 ^2.5 dPa·s is preferably 1500°C or higher, 1510°C or higher, especially Preferably, it is 1520 degreeC or more. In addition, "the temperature equivalent to 10 ^2.5 dPa·s" is the value measured by the platinum ball pulling method.

The low alkali glass plate obtained by the method of the present invention preferably has a liquidus temperature of less than 1250°C, less than 1240°C, less than 1230°C, less than 1220°C, less than 1210°C, especially less than 1200°C of glass. In this way, devitrification crystals are less likely to be produced when glass is produced, and it is easy to prevent a reduction in productivity. Furthermore, since it is easy to form by the overflow down-draw method, not only the surface quality of the glass plate can be easily improved, but also the manufacturing cost of the glass plate can be reduced. In addition, from the viewpoints of the recent enlargement of glass plates and the high definition of displays, improving devitrification resistance is also very significant for suppressing devitrification substances that may become surface defects as much as possible. In addition, the liquidus temperature is an index of devitrification resistance, and the lower the liquidus temperature, the more excellent the devitrification resistance. "Liquidus temperature" means that the glass powder that passed through a standard sieve of 30 mesh (500 μm mesh) and remained in 50 mesh (300 μm mesh) was put into a platinum boat, and the temperature was set at 1100°C to 1350°C After being kept in the temperature gradient furnace for 24 hours, the platinum boat was taken out, and the temperature at which devitrification (crystalline foreign matter) was observed in the glass.

The low alkali glass plate obtained by the method of the present invention preferably 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, 10 ^4.5 dPa·s or more, 10 ^4.6 Glass above dPa·s, above 10 ^4.7 dPa·s, above 10 ^4.8 dPa·s, above 10 ^4.9 dPa·s, especially above 10 ^5.0 dPa·s. In this way, devitrification does not easily occur during forming, so that the glass plate can be easily formed by the overflow down-draw method. As a result, the surface quality of the glass plate can be improved, and the manufacturing cost of the glass plate can be reduced. Furthermore, the liquid phase viscosity is an index of formability, and the higher the liquid phase viscosity, the higher the formability. In addition, "liquidus viscosity" means the viscosity of the glass in liquidus temperature, for example, it can measure by the platinum ball pulling method.

The substrate area of the low-alkali glass plate obtained by the method of the present invention is preferably 4 m ² or more. If the substrate area is too small, it is difficult to efficiently manufacture large LCD (Liquid Crystal Display, liquid crystal display device) and OLED (Organic Light-Emitting Diode, organic light emitting diode) displays including TFTs having oxide films such as IGZO. [Example]

Next, the glass obtained by the method of this invention is demonstrated. Table 1 shows Examples (No. 1 to 8) and Comparative Example (No. 9) of the present invention.

[Table 1] quality% No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 No.9 _SiO2 60.3 62.0 60.0 59.2 59.1 60.0 60.0 59.8 59.1 Al ₂ O ₃ 20.0 20.0 19.0 19.0 18.0 18.0 18.0 20.0 18.0 B ₂ O ₃ 4.0 3.0 3.0 6.0 7.0 5.5 7.5 2.5 9.0 MgO 3.5 2.0 3.0 2.5 3.0 4.0 4.0 2.5 3.0 CaO 5.5 4.5 5.0 6.5 6.0 4.0 5.0 5.0 5.0 SrO 2.5 1.5 1.0 1.0 2.0 3.0 0.5 5.0 1.0 BaO 4.0 6.9 8.8 5.5 4.5 5.2 5.0 5.0 4.5 ZnO 0.2 0.2 ZrO ₂ 0.02 0.01 0.03 0.03 0.01 0.01 0.02 0.15 0.01 SnO ₂ 0.2 0.15 0.25 0.25 0.15 0.3 0.2 0.2 0.15 β-OH value[/mm] 0.16 0.15 0.17 0.20 0.24 0.18 0.19 0.15 0.44 Strain point [℃] 720 730 715 699 692 705 685 735 672 10 Temperature at ^2.5 dPa·s [℃] 1565 1640 1570 1540 1525 1550 1532 1585 1485 Liquidus temperature [℃] 1180 1200 1180 1120 1100 1130 1101 1205 1070 Liquid Viscosity (log η at TL) [dPa·s] 5.3 5 5.2 5.6 5.6 5.4 5.7 5.1 5.7 bubble quality ○ ○ ○ ○ ○ ○ ○ ○ ○ Thermal shrinkage [ppm] 13 15 16 18 20 17 twenty three 15 32 y=ax+b ○ ○ ○ ○ ○ ○ ○ ○ ×

First, to obtain the composition of Table 1, silica sand, alumina, ortho-boric acid, boric anhydride, calcium carbonate, strontium carbonate, strontium nitrate, barium carbonate, and tin dioxide were mixed and blended. In addition, glass flakes with the same composition as the target composition (β-OH value: 0.2/mm, used in an amount of 35% by mass with respect to the total amount of the raw material batch) were used in combination.

Next, the glass raw material is supplied to an electric melting furnace which is not combusted with a burner to be melted, and then the molten glass is clarified and homogenized in a clarification tank and an adjustment tank, and its viscosity is adjusted so as to be suitable for molding.

Next, after supplying the molten glass to an overflow down-draw forming apparatus and forming it into a plate shape, it was cut to obtain a glass sample having a thickness of 0.5 mm. Furthermore, the molten glass discharged from the melting kiln is supplied to a forming apparatus while being in contact with only platinum or a platinum alloy.

The obtained glass samples were evaluated for β-OH value, strain point, temperature at 10 ^2.5 dPa·s, liquidus temperature, liquidus viscosity, thermal shrinkage, bubble quality, and whether the formula y=ax+b (x system) was satisfied. The content (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 results are shown in Table 1.

As can be seen from Table 1, Examples No. 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 more, a low thermal shrinkage rate of 23 ppm or less, and excellent foam quality. On the other hand, in Comparative Example No. 9, since the content of B ₂ O ₃ was large and the above formula was not satisfied, the strain point was low at 672° C., and the thermal shrinkage rate was high at 32 ppm.

In addition, the β-OH value of glass was calculated|required by the following formula by measuring the transmittance|permeability of glass using FT-IR.

β-OH value=(1/X)log10(T ₁ /T ₂ ) X: glass thickness (mm) T ₁ : transmittance at reference wavelength 3846 cm ⁻¹ (%) T ₂ : hydroxyl absorption wavelength 3600 cm ⁻ Minimum transmittance around ¹ (%)

The strain point is determined based on the method of ASTM C336-71.

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

Liquidus temperature system The glass powder that passed through a standard sieve of 30 mesh (500 μm mesh) and remained in 50 mesh (300 μm mesh) was put into a platinum boat, and the temperature gradient furnace was set at 1100 ° C to 1350 ° C. After 24 hours, the platinum boat was taken out, and the temperature at which devitrification (crystalline foreign matter) was observed in the glass.

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

The thermal shrinkage rate was measured by the following method. First, as shown in FIG. 2( a ), a short strip-shaped sample G of 160 mm×30 mm is prepared as a sample of the glass plate 1 . Using #1000 water-resistant abrasive paper, marks M were formed on both ends of the short strip-shaped sample G in the longitudinal direction at positions 20 to 40 mm from the edge. Thereafter, as shown in FIG. 2( b ), the short strip-shaped sample G on which the mark M was formed was folded in half along the direction orthogonal to the mark M, and separated into two pieces to obtain test pieces Ga and Gb. Then, only one of the test pieces Gb was heat-treated, that is, 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. 2( 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 deviation (ΔL ₁ , ΔL ₂ ) of the mark M, and the thermal shrinkage rate was calculated according to the following formula. Furthermore, l ₀ in the formula is the initial distance between marks M.

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

The bubble quality was counted as the bubbles with a diameter of 100 μm or more, and the case where the number of bubbles was 0.05/kg or less was represented by “○”, and the case where the number of bubbles was more than 0.05/kg was represented by “×”.

The cases satisfying the formula y=ax+b (x is the content of B ₂ O ₃ (mass %), y is the β-OH value (/mm), 0.01<a<0.04 and 0.03<b<0.06) are marked as “○” , the case where the formula y=ax+b is not satisfied is marked as “×”. [Industrial Availability]

According to the present invention, it is possible to easily obtain a glass plate with a high strain point, good bubble quality, and a small thermal shrinkage rate suitable for the production of oxide TFTs.

G: Sample Ga: Test piece Gb: Test piece l ₀ : Distance M: Mark ΔL ₁ : Position deviation amount ΔL ₂ : Position deviation amount

FIG. 1 is a graph showing the relationship between the strain point of glass and the thermal shrinkage rate. Fig.2 (a)-(c) is a top view for demonstrating the measurement procedure of the thermal contraction rate of a glass plate.

Claims (17)

A method for manufacturing a low-alkali glass plate, characterized in that it includes the following steps: a batch preparation step, which is to prepare a batch of raw materials so as to have 50-70% SiO ₂ , Al ₂ O ₃ by mass % 15～25%, B ₂ O ₃ 2～7.5%, MgO 0～10%, CaO 0～10%, SrO 0～10%, BaO 0～15%, ZnO 0～5%, ZrO ₂ 0～1% , TiO ₂ 0-5%, P ₂ O ₅ 0-10%, SnO ₂ 0.1-0.5% are prepared in the manner of low alkali glass composed of glass; the melting step is to melt the obtained raw material batch; A clarifying step, which clarifies the molten glass; and a forming step, which shapes the clarified glass into a plate shape; and the content of B ₂ O ₃ and the β-OH value are adjusted so that in the When the content of B ₂ O ₃ is set to x (mass %) and the β-OH value of the obtained low alkali glass plate is set to y (/mm), y=ax+b, 0.01<a<0.04 and 0.03<b< The relational expression of 0.06 is established. The method for producing a low-alkali glass plate according to claim 1, wherein the raw material batch is prepared in the above-mentioned batch preparation step so as to contain 57-65% of SiO ₂ , 17-22% of Al ₂ O ₃ , B 2.5 to 7% of ₂ O ₃ , 1 to 10% of MgO, 0.1 to 15% of BaO, and 0.1 to 0.3% of SnO ₂ are prepared as low-alkali glass of glass composition. The method for producing a low-alkali glass plate according to claim 1 or 2, wherein electrofusion is performed on the obtained raw material batch. The method for producing a low-alkali glass plate according to any one of claims 1 to 3, wherein the raw material batch contains carbonate raw materials and/or nitrate raw materials. The method for producing a low-alkali glass plate according to any one of claims 1 to 4, wherein orthoboric acid and/or boric anhydride are used in at least a part of the glass raw material as the boron source. 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. The method for producing a low-alkali glass plate according to any one of claims 1 to 6, wherein the raw material batch contains glass dust, and at least a part of the glass dust is glass dust containing glass with a β-OH value of 0.3/mm or less. The method for producing a 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. The method for producing a low-alkali glass plate according to any one of claims 1 to 8, wherein the obtained glass has a strain point of 680° C. or higher. The method for producing low-alkali glass according to any one of claims 1 to 9, wherein the thermal shrinkage of the obtained glass is 25 ppm or less. A low-alkali glass plate, characterized in that it contains 50-70% of SiO ₂ , 15-25% of Al ₂ O ₃ , 2-7.5% of B ₂ O ₃ , 0-10% of MgO, 0-10% of CaO 10%, SrO 0～10%, BaO 0～15%, ZnO 0～5%, ZrO ₂ 0～1%, TiO ₂ 0～5%, P ₂ O ₅ 0～10%, SnO ₂ 0.1～0.5% As a glass composition, the β-OH value is 0.05 to 0.3/mm, and when the content of B ₂ O ₃ is x (mass %) and the β-OH value is y (/mm), y=ax+b, The relational expressions of 0.01<a<0.04 and 0.03<b<0.06 are established. The low-alkali glass plate according to claim 11, which in mass % contains Al ₂ O ₃ 17-22%, B ₂ O ₃ 2.5-7%, MgO 0.1-10%, CaO 0.1-10%, ZrO ₂ 0- 0.5%, TiO ₂ 0-1% as glass composition. The low-alkali glass plate according to claim 11 or 12, which contains 57-65% SiO ₂ , 2-10% MgO 2-15%, 0.1-15% BaO, and 0.1-0.3% SnO ₂ as a glass composition in mass %. The low alkali glass plate according to any one of claims 11 to 13, wherein the strain point is 680° C. or higher. The low-alkali glass plate according to any one of claims 11 to 14, which has a thermal shrinkage rate of 25 ppm or less. The low-alkali glass plate according to any one of claims 11 to 15, which is used as a glass plate on which oxide TFTs are formed. 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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