WO2018123505A1 - Alkali-free glass substrate production method - Google Patents

Abstract

The present invention provides an alkali-free glass substrate production method with which it is possible to produce an alkali-free glass substrate of a higher strain point by lowering the β-OH value of the glass. This method is for continuously producing an alkali-free glass substrate based on SiO₂-Al₂O₃-RO (RO represents at least one selected from among MgO, CaO, BaO, SrO, and ZnO), and is characterized by comprising: a step for preparing a raw material batch that contains a tin compound but does not substantially contain any arsenic compound or antimony compound; a step for electrically melting the prepared raw material batch in a melting furnace that is capable of passing a current and applying heat via a molybdenum electrode; and a step for shaping the molten glass into a plate form by a down-draw process.

Description

Method for producing alkali-free glass substrate

The present invention relates to a method for producing an alkali-free glass substrate, and more specifically, an alkali-free glass suitable for a display including a thin film transistor (TFT: Thin Film Transistor) having a low temperature polysilicon (LTPS: Low Temperature p-Si) film. The present invention relates to a method for manufacturing a substrate.

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

In addition, the glass substrate is exposed to a high-temperature atmosphere in an electric circuit pattern forming process such as a thin film forming process or a thin film patterning process. When the glass substrate is exposed to a high temperature atmosphere, the structural relaxation of the glass proceeds, so that the volume of the glass substrate shrinks (hereinafter, the shrinkage of the glass is referred to as “thermal shrinkage”). If thermal shrinkage occurs in the glass substrate during the electrical circuit pattern formation process, the shape and dimensions of the electrical circuit pattern formed on the glass substrate will deviate from the design values, and a flat panel display having the desired electrical performance is obtained. It will be difficult. For this reason, a glass substrate on which a thin film pattern such as an electric circuit pattern is formed on the surface, such as a glass substrate for a flat panel display, is desired to have a small thermal shrinkage rate.

In particular, in the case of a high-definition glass substrate having a TFT having a low-temperature polysilicon film, when the low-temperature polysilicon film is formed, the glass substrate is exposed to a very high temperature atmosphere, for example, 450 ° C. to 600 ° C. However, since the electric circuit pattern has a high definition, it is difficult to obtain desired electrical performance when heat shrinkage occurs. Therefore, it is strongly desired that the glass substrate used for such applications has a very low thermal shrinkage rate.

Incidentally, as a method for forming a glass substrate used for a flat panel display or the like, a float method, a down draw method represented by an overflow down draw method, or the like is known.

In the float method, molten glass is flowed out onto a float bath filled with molten tin, and stretched in the horizontal direction to form a glass ribbon. This is a method for forming a glass substrate. In the float process, since the conveying direction of the glass ribbon is the horizontal direction, it is easy to lengthen the slow cooling furnace. For this reason, it is easy to make the cooling rate of the glass ribbon in a slow cooling furnace low enough. Therefore, the float method has an advantage that it is easy to obtain a glass substrate having a small heat shrinkage rate.

However, with the float method, it is difficult to mold a thin glass substrate, and after molding, the surface of the glass substrate must be polished to remove tin adhering to the surface of the glass substrate. There are disadvantages.

On the other hand, the downdraw method is a method in which molten glass is drawn downward to form a plate shape. The overflow downdraw method, which is a kind of downdraw method, is a method of forming a glass ribbon by stretching downward a molten glass overflowed from both sides of a forming body having a substantially wedge-shaped cross section. The molten glass overflowing from both sides of the molded body flows down along both side surfaces of the molded body and merges 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. A flat glass substrate can be obtained. Further, the overflow downdraw method has an advantage that a thin glass substrate can be easily formed.

On the other hand, in the downdraw method, since the molten glass flows downward from the molded body, in order to dispose a long slow cooling furnace under the molded body, the molded body must be disposed at a high place. However, in practice, there is a restriction on the height at which the molded body can be disposed due to the height restriction of the ceiling of the factory. That is, in the downdraw 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, so that it becomes difficult to form a glass substrate having a small heat shrinkage rate.

Therefore, it has been proposed to increase the strain point of the glass and reduce the thermal shrinkage of the glass. For example, Patent Document 1 discloses a non-alkali glass composition having a high strain point. The document also describes that the strain point increases as the β-OH value representing the amount of water in the glass decreases.

JP 2013-151407 A JP 2011-020864 A

As shown in FIG. 1, the effect of reducing the heat shrinkage due to the increase in the strain point of the glass becomes smaller as the strain point becomes higher. In addition, the glass whose composition is designed so that the strain point is high has high viscosity, so that it is difficult to melt and mold, and the production efficiency is low. In addition, since such a glass has a high melting temperature and molding temperature, the burden on the production equipment increases. For this reason, as in Patent Document 1, there is a limit to a method for reducing the heat shrinkage rate by adopting a high strain point composition. Therefore, it is important to increase the strain point by lowering the β-OH value, but it is extremely difficult to significantly reduce the β-OH value of glass when mass-producing on an industrial scale. .

The present invention has been made in view of such circumstances, and an object thereof is to produce a non-alkali glass substrate capable of producing a non-alkali glass substrate having a higher strain point by reducing the β-OH value of the glass. Is to provide.

As a result of various investigations, the present inventors have found that the amount of β-OH in the glass can be significantly reduced by optimizing the raw material batch configuration, the melting method, etc., and are proposed as the present invention. is there.

That is, the alkali-free glass production method of the present invention continuously produces a SiO ₂ —Al ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO, and ZnO) -based alkali-free glass substrates. And a step of preparing a raw material batch containing a tin compound and substantially free of an arsenic compound and an antimony compound, and a melting furnace capable of electrically heating the prepared raw material batch with a molybdenum electrode. And a step of forming the molten glass into a plate shape by a down draw method.

Here, the “non-alkali glass” is a glass to which an alkali metal oxide component is not intentionally added, and specifically, alkali metal oxides (Li ₂ O, Na ₂ O, and K in the glass composition). ₂ O) means a glass having a content of 2000 ppm (mass) or less. “Manufacturing continuously” means that glass is continuously manufactured for a certain period in a continuous melting kiln such as a tank kiln. “SiO ₂ —Al ₂ O ₃ —RO system” means “a glass composition system containing SiO ₂ , Al ₂ O ₃ and RO as essential components.“ Electrical melting ”means that electricity is passed through the glass. The glass is melted by Joule heat generated thereby. It should be noted that the melting method using auxiliary radiation heating by a heater or burner is not excluded here. “Substantially free of arsenic and antimony” means that a glass raw material or glass cullet containing these components is not intentionally added to the glass batch. More specifically, it means that, in the obtained glass, arsenic is 50 ppm or less as As ₂ O ₃ and antimony is 50 ppm or less as Sb ₂ O ₃ on a molar basis. The “down draw method” is a general term for a molding method in which a molten glass is molded while continuously being drawn downward.

Further, the present invention is characterized in that the glass is melted using electric heating. By performing the melting of the glass mainly by electric heating, it is possible to suppress an increase in moisture in the atmosphere. As a result, it becomes possible to greatly suppress the moisture supply of the glass from the atmosphere, and it becomes easy to produce a glass with a high strain point.

Further, in the present invention, a molybdenum electrode is used for conducting heating by heating. Molybdenum electrodes have a high degree of freedom in location and shape. Therefore, even in the case of non-alkali glass that is difficult to conduct electricity, an optimal electrode arrangement and electrode shape can be adopted, and current heating is facilitated.

The present invention is characterized by containing a tin compound as a fining agent and substantially free of an arsenic compound and an antimony compound. Arsenic compounds and antimony compounds function as fining agents, but if these components are present in the glass, the molybdenum electrode is significantly eroded, making it difficult to continuously produce glass on an industrial scale. . On the other hand, tin does not erode the molybdenum electrode. Therefore, by adopting the above-described configuration, it becomes easy to produce glass without bubbles by energization heating.

In the present invention, the glass is formed into a plate shape by a downdraw method. The downdraw method is a method of forming molten glass into a plate shape while extending vertically downward. Compared with the float method in which glass is drawn out in the horizontal direction, the slow cooling furnace is shorter and the slow cooling time (distance) after forming is sufficient. It is difficult to secure. That is, it is a disadvantageous method for obtaining a glass having a small thermal shrinkage rate. Therefore, the merit of increasing the strain point of the glass by reducing the water content is extremely large.

In the present invention, it is desirable not to use radiation heating by burner combustion. “Do not use radiant heating by burner combustion” means that radiant heating by burner combustion is not performed at the time of normal production, and does not exclude the use of a burner at the start of production (at the time of temperature rise). Further, it is not excluded to use radiant heating with a heater at the time of production start-up or normal production. In addition, the time of production start-up refers to a period until the raw material batch is melted to become a glass melt and can be heated by electric current.

If the above configuration is adopted, the amount of moisture contained in the atmosphere in the melting furnace is extremely reduced, and the moisture supplied from the atmosphere into the glass can be greatly reduced. As a result, it becomes possible to produce a glass with a very low water content. The equipment required for combustion heating, such as burner, flue, fuel tank, fuel supply path, air supply device (in the case of air combustion), oxygen generator (in the case of oxygen combustion), exhaust gas treatment device, dust collector, etc. It can be unnecessary or greatly simplified, and it is possible to make the melting kiln compact and to reduce the equipment cost.

In the present invention, it is preferable to add chloride to the raw material batch.

Chloride has the effect of reducing moisture in the glass. When the moisture contained in the glass decreases, the strain point of the glass increases. Therefore, if the above configuration is adopted, it becomes easy to produce a glass having a high strain point.

In the present invention, it is preferable not to add a raw material to be a boron source in the raw material batch.

Since the glass raw material used as a boron source has a hygroscopic property and also contains crystal water, it is easy to bring moisture into the glass. Then, if the said structure is employ | adopted, it will become possible to further reduce the moisture content of the glass obtained. The boron component (B 2 _{O 3),} since a likely component to lower the strain point of the glass, by adopting the above configuration, a high strain point glass is easily obtained.

In the present invention, when producing an alkali-free glass substrate further containing B ₂ O ₃ as a glass composition, it is preferable to use boric anhydride for at least a part of the glass raw material serving as a boron source.

If the said structure is employ | adopted, it will become possible to further reduce the moisture content of the glass obtained. The boron component (B 2 _{O 3),} since a component for improving the meltability of the glass, by adopting the above configuration, it becomes easy to obtain an excellent glass productivity.

In the present invention, it is preferable that no hydroxide raw material is contained in the raw material batch.

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

In the present invention, when producing a non-alkali glass substrate by adding a glass cullet to a raw material batch, a glass cullet made of glass having a β-OH value of 0.4 / mm or less is added to at least a part of the glass cullet. It is preferable to use it. Here, the “glass cullet” means defective glass generated during the production of glass, recycled glass collected from the market, or the like. “Β-OH value” refers to a value obtained by measuring the transmittance of glass using FT-IR and using the following equation.

β-OH value = (1 / X) log (T1 / T2)
X: Glass wall thickness (mm)
T1: Transmittance (%) at a reference wavelength of 3846 cm ⁻¹
T2: Minimum transmittance (%) near the hydroxyl absorption wavelength of 3600 cm ⁻¹
Since alkali-free glass has a high volume resistance, it tends to be difficult to melt compared to glass containing alkali. Therefore, if the above configuration is adopted, the glass can be easily melted and the moisture content of the obtained glass can be further reduced.

In 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 0.2 / mm or less.

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

In the present invention, it is preferable that the obtained glass has a strain point of 690 ° C. or higher. Here, the “strain point” is a value measured based on the method of ASTM C336-71.

If the above configuration is adopted, a glass having a very small heat shrinkage rate can be obtained.

In the present invention, it is preferable that the obtained glass has a thermal shrinkage of 25 ppm or less. Here, “thermal shrinkage” was measured under the condition that the glass was heated from room temperature to 500 ° C. at a rate of 5 ° C./min, held at 500 ° C. for 1 hour, and then cooled at a rate of 5 ° C./min. It is a time value.

If the above configuration is adopted, a glass substrate suitable for forming a low-temperature polysilicon TFT can be obtained.

In the present invention, it is preferably used for manufacturing a glass substrate on which a low-temperature polysilicon TFT is formed.

The low-temperature polysilicon TFT has a heat treatment temperature as high as 450 to 600 ° C. when formed on the substrate, and the circuit pattern becomes finer. Therefore, a glass substrate used for this type of application requires a particularly low thermal shrinkage rate. Therefore, the merit of adopting the method of the present invention capable of producing a glass substrate having a very high strain point is extremely great.

It is a graph which shows the relationship between the strain point of glass, and a thermal contraction rate. It is explanatory drawing which shows schematic structure of the glass manufacturing equipment for enforcing the manufacturing method of this invention. It is a top view for demonstrating the measurement procedure of the thermal contraction rate of a glass substrate.

Hereinafter, the method for producing the alkali-free glass of the present invention will be described in detail.

The method of the present invention includes a step of preparing a raw material batch, a step of electrically melting the prepared batch, and a step of forming the molten glass into a plate shape.

(1) Step of preparing raw material batch First, SiO ₂ —Al ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO and ZnO) based composition, more specifically, in mol%. A glass raw material is prepared so as to be an alkali-free glass containing 50 to 75% of SiO ₂ , 5 to 20% of Al ₂ O _{3 and} 5 to 30% of RO. A suitable glass composition will be described later.

As the glass raw material, for example, silica sand (SiO ₂ ) or the like can be used as a silicon source.

As the aluminum source, alumina (Al ₂ O ₃ ), aluminum hydroxide (Al (OH) ₃ ), or the like can be used. In addition, since aluminum hydroxide contains crystal water, when the usage rate is large, it becomes difficult to reduce the moisture content of the glass. Therefore, it is preferable not to use aluminum hydroxide as much as possible. Specifically, the usage rate of aluminum hydroxide may be 50% or less, 40% or less, 30% or less, 20% or less, 10% or less with respect to 100% of the aluminum source (Al ₂ O ₃ conversion). Preferably, it is desirable not to use it if possible.

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 ), or the like can be used. In addition, since magnesium hydroxide contains crystal water, when the usage rate is large, it becomes difficult to reduce the moisture content of the glass. Therefore, it is preferable not to use magnesium hydroxide as much as possible. Specifically, magnesium hydroxide is preferably 50% or less, 40% or less, 30% or less, 20% or less, 10% or less with respect to 100% magnesium source (MgO conversion), and should not be used if possible. Is desirable.

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

Furthermore, in the present invention, it is preferable that the batch contains chloride. Chloride functions as a dehydrating agent that significantly reduces the moisture content of the glass. Moreover, there exists an effect which accelerates | stimulates the effect | action of the tin compound which is a clarifier. Furthermore, chloride decomposes and volatilizes in a temperature range of 1200 ° C. or higher to generate a clear gas, and suppresses the formation of a heterogeneous layer due to the stirring effect. In addition, the chloride has an effect of taking in and dissolving a silica raw material such as silica sand at the time of decomposition. As the chloride, for example, alkaline earth metal chloride such as strontium chloride, aluminum chloride and the like can be used.

Furthermore, in this invention, a tin compound is included in a batch. The tin compound functions as a fining agent. It also has the function of increasing the strain point and lowering the high temperature viscosity. As the tin compound, for example, tin oxide (SnO ₂ ) can be used. When tin oxide is used, it is preferable to use tin oxide having an average particle diameter D _{50 in} the range of 0.3 to 50 μm. When the average particle diameter D _{50 of the} tin oxide powder is small, aggregation between the particles occurs and clogging in the blending plant is likely to occur. On the other hand, when the average particle diameter D ₅₀ of the tin oxide powder larger, the dissolution reaction of the glass melt of the tin oxide powder is delayed, no progress has fining of the melt. As a result, oxygen gas cannot be sufficiently released at an appropriate time of glass melting, bubbles are likely to remain in the glass product, and it becomes difficult to obtain a product excellent in foam quality. Also in the glass product, easily causing a so undissolved lumps of SnO ₂ crystal appears. A preferable range of the average particle diameter D ₅₀ of the tin oxide powder is 2 to 50 μm, particularly 5 to 50 μm.

Further, in the present invention do not contain ingredients which the boron source (not containing B ₂ O ₃ as a glass composition in other words) is preferred. In other words, orthoboric acid (H ₃ BO ₃ ) and boric anhydride (B ₂ O ₃ ) are known as boron sources, but these raw materials are hygroscopic, so depending on the storage conditions, a large amount of boron may be contained in the glass. Bring in moisture. In addition, since orthoboric acid contains crystallization water, it becomes difficult to reduce the water content of the glass when the use ratio is large. In the case containing forced to B ₂ O ₃ as a glass composition, increasing the proportion of boric anhydride as possible are preferable. Specifically, it is desirable to use boric anhydride in an amount of 50% or more, 70% or more, 90% or more, particularly 100% for the boron source (B ₂ O ₃ conversion).

Furthermore, in the present invention, various glass materials can be used in addition to the above depending on the glass composition. For example, zircon (ZrSiO ₄ ) or the like as a zirconia source, titanium oxide (TiO ₂ ) or the like as a titanium source, aluminum metaphosphate (Al (PO ₃ ) ₃ ), magnesium pyrophosphate (Mg ₂ P ₂ O ₇ ) or the like as a phosphate source. Can be used respectively.

In the present invention, it is important that the batch does not substantially contain an arsenic compound and an antimony compound. When these components are contained, the molybdenum electrode is eroded, so that it is difficult to stably melt the electrode for a long time. Moreover, these components are not preferable from an environmental viewpoint.

In the present invention, it is preferable to use glass cullet in addition to the glass raw material described above. When glass cullet is used, the ratio of the glass cullet used relative 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. Although there is no restriction | limiting in the upper limit of the usage rate of glass cullet, it is preferable that it is 50 mass% or less, 40 mass% or less, especially 30 mass% or less. Further, at least a part of the glass cullet used has a β-OH value of 0.4 / mm or less, 0.35 / mm or less, 0.3 / mm or less, 0.25 / m or less, 0.2 / mm or less. In particular, a low moisture glass cullet made of glass of 0.15 / mm or less is desirable. The lower limit value of the β-OH value of the low moisture glass cullet is not particularly limited, but is practically 0.01 / mm or more.

The amount of low-moisture glass cullet used is preferably 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more, particularly the total amount of the glass cullet used. Is preferably a low moisture glass cullet. When the β-OH value of the low moisture glass cullet is not sufficiently low, or when the usage rate of the low moisture glass cullet is small, the effect of lowering the β-OH value of the obtained glass becomes small.
In addition, the glass raw material, the glass cullet, or the raw material batch prepared by mixing these may contain moisture. It may also absorb moisture from 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 pre-furnace silo for feeding a prepared raw material batch into a melting furnace, and the like.

(2) Step of electromelting the prepared raw material batch Next, the prepared raw material batch is put into a melting kiln and is electrically melted.

The melting kiln has a plurality of molybdenum electrodes. When electricity is applied between the molybdenum electrodes, electricity is passed through the glass melt, and the glass is continuously melted by the Joule heat. In addition, radiant heating with a heater or a burner may be supplementarily used, but from the viewpoint of lowering the β-OH value of the glass, it is desirable to achieve complete electric melting without using a burner. When heating with a burner, moisture generated by combustion is taken into the glass, making it difficult to sufficiently reduce the moisture content of the glass.

As described above, since the molybdenum electrode has a high degree of freedom in the location and shape of the electrode, even if it is non-alkali glass that is difficult to conduct electricity, the optimal electrode arrangement and electrode shape can be adopted, It becomes easy. The electrode shape is preferably a rod shape. If it is rod-shaped, it is possible to arrange a desired number of electrodes at an arbitrary position on the side wall surface or bottom wall surface of the melting furnace while maintaining a desired inter-electrode distance. As for the arrangement of the electrodes, it is desirable to arrange a plurality of pairs on the wall surface (side wall surface, bottom wall surface, etc.), particularly the bottom wall surface of the melting furnace, with the distance between the electrodes shortened. When glass contains an arsenic component or an antimony component, a molybdenum electrode cannot be used for the reasons described above, and instead, a tin electrode that is not subject to erosion by these components must be used. However, since the tin electrode has a very low degree of freedom in the location and the electrode shape, it becomes difficult to electrically melt the alkali-free glass.

The raw material batch charged into the melting kiln is melted by energization heating to become a glass melt (molten glass). At that time, the chloride contained in the raw material batch decomposes and volatilizes, thereby removing moisture in the glass into the atmosphere and reducing the β-OH value of the glass. Moreover, the tin compound contained in the raw material batch dissolves in the glass melt and acts as a fining agent. More specifically, the tin component releases oxygen bubbles during the temperature rising process. The released oxygen bubbles are removed from the glass by expanding and floating the bubbles contained in the glass melt. Further, the tin component absorbs oxygen bubbles in the temperature lowering process, thereby eliminating bubbles remaining in the glass.

The glass melted in the melting kiln is supplied to the molding apparatus, but a clarification tank, a stirring tank, a state adjustment tank, etc. are arranged between the melting kiln and the molding apparatus, and after passing these, You may make it supply. Further, it is preferable that at least the contact surface with the glass of the communication flow path connecting between the melting furnace and the molding apparatus (or each tank provided therebetween) is made of platinum or a platinum alloy in order to prevent contamination of the glass.

(3) The process of shape | molding the fuse | melted glass in plate shape Next, the glass fuse | melted with the melting furnace is supplied to a shaping | molding apparatus, and it shape | molds in plate shape by the down draw method.

It is preferable to adopt the overflow downdraw method as the downdraw method. The overflow down-draw method is a method in which molten glass overflows from both sides of a saddle-shaped refractory with a wedge-shaped cross section, and the overflowed molten glass is joined at the lower end of the saddle-shaped refractory and stretched downward to form a glass plate. It is the method of shape | molding in a shape. In the overflow down draw method, the surface to be the surface of the glass substrate is not in contact with the bowl-shaped refractory, and is formed in a free surface state. Therefore, an unpolished glass substrate having a good surface quality can be manufactured at a low cost, and the glass can be easily made large and thin. The structure and material of the bowl-shaped refractory used in the overflow downdraw method are not particularly limited as long as desired dimensions and surface accuracy can be realized. In addition, the method of applying a force when performing downward stretch molding is not particularly limited. For example, a method may be adopted in which a heat-resistant roll having a sufficiently large width is rotated and stretched in contact with the glass, or a plurality of pairs of heat-resistant rolls are contacted only near the end face of the glass. It is also possible to adopt a method of stretching by stretching. In addition to the overflow down draw method, for example, a slot down method or the like can be adopted.

Note that the glass thus formed into a plate shape is cut into a predetermined size and subjected to various chemical or mechanical processing as required to form a glass substrate.

(4) Composition of alkali-free glass As a composition of alkali-free glass to which the production method of the present invention can be suitably applied, it is SiO ₂ 60 to 75%, Al ₂ O ₃ 9.5 to 17%, B ₂ O in mol%. ₃ to 9%, MgO 0 to 8%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 10%, SnO ₂ 0.001 to 1%, Cl 0 to 3%, As ₂ Examples thereof include glass that does not substantially contain O ₃ and Sb ₂ O _{3 and} has a molar ratio (CaO + SrO + BaO) / Al ₂ O ₃ of 0.5 to 1.0. The reason for limiting the content of each component as described above will be described below. In addition, in description of content of each component,% display represents mol% unless there is particular notice.

SiO ₂ is a component that forms a glass skeleton. The SiO ₂ content is preferably 60 to 75%, 62 to 75%, 63 to 75%, 64 to 75%, 64 to 74%, particularly 65 to 74%. When the content of SiO ₂ is too small, the density becomes too high, the acid resistance is likely 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, and devitrification crystals such as cristobalite are likely to precipitate, and the liquidus temperature is likely to rise. Become.

Al ₂ O ₃ is a component that forms a glass skeleton, a component that increases the strain point and Young's modulus, and a component that further suppresses phase separation. The content of Al ₂ O ₃ is preferably 9.5 to 17%, 9.5 to 16%, 9.5 to 15.5%, particularly preferably 10 to 15%. When the content of Al ₂ O ₃ is too small, the strain point, the Young's modulus tends to decrease, also tends glass phase separation. 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 precipitate, and the liquidus temperature is likely to rise.

B ₂ O ₃ is a component that enhances meltability and increases devitrification resistance. The content of B ₂ O ₃ is preferably 0 to 9%, 0 to 8.5%, 0 to 8%, 0 to 7.5%, particularly preferably 0 to 7.5%. When B ₂ content of O ₃ is too small, it tends to decrease. Meltability and devitrification resistance, also resistance tends to decrease with respect to hydrofluoric acid chemical. On the other hand, when the content of B ₂ O ₃ is too large, the Young's modulus and the strain point tends to decrease. In addition, the amount of water brought in increases. In the case where priority is given to an increase in strain point and a reduction in water content, the content of B ₂ O ₃ is preferably 0 to 3%, 0 to 2%, particularly preferably 0 to 1%. More preferably not. Note that “substantially free of B ₂ O ₃ ” means that B ₂ O ₃ is not intentionally added, that is, a raw material that becomes a boron source is not added, and the case where it is mixed as an impurity is excluded. is not. More objectively, it means that the content of B ₂ O ₃ is 0.1% or less.

MgO is a component that lowers the viscosity at high temperature and increases the meltability, and among alkaline earth metal oxides, it is a component that significantly increases the Young's modulus. The MgO content is preferably 0 to 8%, 0 to 7%, 0 to 6.7%, 0 to 6.4%, particularly preferably 0 to 6%. When there is too little content of MgO, a meltability and a Young's modulus will fall easily. On the other hand, when there is too much content of MgO, devitrification resistance will fall easily and a strain point will fall easily.

CaO is a component that lowers the high-temperature viscosity without lowering the strain point and significantly increases the meltability. Further, among the alkaline earth metal oxides, since the introduced raw material is relatively inexpensive, it is a component that lowers the raw material cost. The CaO content is preferably 0 to 10%, 2 to 15%, 2 to 14%, 2 to 13%, 2 to 12%, particularly preferably 2 to 11%. When there is too little content of CaO, it will become difficult to receive the said effect. On the other hand, when there is too much content of CaO, while glass will become easy to devitrify, a thermal expansion coefficient will become high easily.

SrO is a component that suppresses phase separation and increases devitrification resistance. Furthermore, it is a component that lowers the high-temperature viscosity without increasing the strain point and increases the meltability, and also suppresses the rise in the liquidus temperature. The SrO content is preferably 0 to 10%, 0.1 to 10%, 0.1 to 9%, 0.1 to 8%, 0.1 to 7%, particularly preferably 0.1 to 6%. . When there is too little content of SrO, it will become difficult to receive the said effect. On the other hand, when the content of SrO is too large, strontium silicate devitrification crystals are likely to precipitate, and devitrification resistance is likely to be lowered.

BaO is a component that significantly increases devitrification resistance. The BaO content is preferably 0 to 10%, 0 to 7%, 0 to 6%, 0 to 5%, particularly preferably 0.1 to 5%. When there is too little content of BaO, it will become difficult to receive the said effect. On the other hand, when there is too much content of BaO, while a density will become high too much, a meltability will fall easily. Further, devitrified crystals containing BaO are likely to precipitate, and the liquidus temperature is likely to rise.

SnO ₂ is a component that has a good clarification action in a high temperature range, a component that increases the strain point, and a component that decreases high temperature viscosity. There is also an advantage that the molybdenum electrode is not eroded. The SnO ₂ content is preferably 0.001 to 1%, 0.001 to 0.5%, 0.001 to 0.3%, and particularly preferably 0.01 to 0.3%. When the content of SnO ₂ is too large, the devitrified crystal of SnO ₂ is likely to precipitate, and the precipitation of the devitrified crystal of ZrO ₂ is easily promoted. Incidentally, when the content of SnO ₂ is less than 0.001%, it becomes difficult to enjoy the above-mentioned effects.

Cl has a dehydrating effect, that is, an effect of reducing the amount of water in the glass. In addition, Cl has an effect of promoting melting of the alkali-free glass. If Cl is added, the melting temperature can be lowered and the action of the clarifying agent is promoted. As a result, the melting cost is reduced and the glass manufacturing kiln is reduced. It is possible to extend the service life. However, if the Cl content is too large, the strain point tends to decrease. For this reason, the Cl content is preferably 0 to 3%, 0.001 to 3%, 0.001 to 2%, and particularly preferably 0.001 to 1%.

As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained. Specifically, it means that the contents of As ₂ O ₃ and Sb ₂ O ₃ are both 50 ppm or less. These components are useful as fining agents, but should not be used because they erode the molybdenum electrode and make electromelting difficult on an industrial scale. Moreover, it is preferable not to use from an environmental viewpoint.

The molar ratio (CaO + SrO + BaO) / Al ₂ O ₃ is an important component ratio in order to achieve both a high specific Young's modulus and a high strain point and to improve devitrification resistance. The molar ratio (CaO + SrO + BaO) / Al ₂ O ₃ is 0.5 to 1.5, 0.5 to 1.3, 0.5 to 1.2, 0.5 to 1.1, 0.6 to 1 .1, particularly 0.7 to 1.1. When the molar ratio (CaO + SrO + BaO) / Al ₂ O ₃ is too small, devitrification crystals caused by mullite and alkaline earth are likely to precipitate, and the devitrification resistance is significantly reduced. On the other hand, when the molar ratio (CaO + SrO + BaO) / Al ₂ O ₃ increases, alkaline earth aluminosilicate devitrification crystals such as cristobalite and anorthite tend to precipitate, and devitrification resistance tends to decrease. Therefore, it is difficult to increase the specific Young's modulus and the strain point.

In addition to the above components, for example, the following components may be added as optional components. In addition, the content of other components other than the above components is preferably 10% or less, and particularly preferably 5% or less in total, from the viewpoint of accurately enjoying the effects of the present invention.

ZnO is a component that enhances meltability. However, when ZnO is contained in a large amount, the glass tends to be devitrified and the strain point tends to be lowered. The content of ZnO is preferably 0 to 5%, 0 to 4%, 0 to 3%, particularly preferably 0 to 2%.

P ₂ O ₅ is a component that increases the strain point and is a component that can suppress precipitation of devitrified crystals of alkaline earth aluminosilicates such as anorthite. However, when P ₂ O ₅ is contained in a large amount, the glass is likely to be phase-separated. The content of P ₂ O ₅ is preferably 0 to 2.5%, 0 to 1.5%, 0 to 1%, particularly 0 to 0.5%.

TiO ₂ is a component that lowers the viscosity at high temperature and increases the meltability, and is a component that suppresses solarization. However, when TiO ₂ is contained in a large amount, the glass is colored and the transmittance tends to decrease. . The content of TiO ₂ is preferably 0 to 4%, 0 to 3%, 0 to 2%, particularly preferably 0 to 0.1%.

Y ₂ O ₃ and Nb ₂ O ₅ have a function of increasing the strain point, Young's modulus, and the like. However, when the content of these components is more than 2%, the density tends to increase.

La ₂ O ₃ also has a function of increasing the strain point, Young's modulus, and the like, but in recent years, the price of the introduced raw material has been rising. The alkali-free glass of the present invention does not completely exclude the inclusion of La ₂ O ₃ , but from the viewpoint of batch cost, it is preferable not to add it substantially. The content of La ₂ O ₃ is preferably 2% or less, 1% or less, 0.5% or less, and is not substantially contained (0.1% or less).

ZrO ₂ functions to increase the strain point and Young's modulus. However, when the content of ZrO ₂ is too large, the devitrification resistance is significantly decreased. In particular, when SnO ₂ is contained, it is necessary to strictly regulate the content of ZrO ₂ . The content of ZrO ₂ is preferably 0.2% or less, 0.15% or less, and particularly preferably 0.1% or less.

(5) Characteristics of alkali-free glass substrate, etc. Next, the alkali-free glass substrate obtained by the method of the present invention will be described.

The alkali-free glass substrate obtained by the method of the present invention was heated at a rate of 5 ° C./min from room temperature to 500 ° C., held at 500 ° C. for 1 hour, and then cooled at a rate of 5 ° C./min. It is preferable that the thermal shrinkage rate is 25 ppm or less, 20 ppm or less, 15 ppm or less, 12 ppm or less, particularly 10 ppm or less. When the thermal shrinkage rate is large, it becomes difficult to use as a substrate for forming a low-temperature polysilicon TFT.

The alkali-free glass substrate obtained by the method of the present invention is made of a glass having a β-OH value of 0.2 / mm or less, 0.18 / mm or less, 0.16 / mm or less, particularly 0.15 / mm or less. It is preferable to become. The lower limit of the β-OH value is not limited, but is preferably 0.01 / mm or more, particularly preferably 0.05 / mm or more. If the β-OH value is large, the strain point of the glass will not be sufficiently high, and it will be difficult to significantly reduce the thermal shrinkage rate.

The alkali-free glass obtained by the method of the present invention has a strain point of more than 670 ° C, more than 675 ° C, more than 680 ° C, more than 685 ° C, more than 690 ° C, more than 700 ° C, more than 710 ° C, particularly more than 720 ° C. Is preferred. If it does in this way, in the manufacturing process of a low-temperature polysilicon TFT, it will become easy to suppress the thermal contraction of a glass substrate.

The alkali-free glass substrate obtained by the method of the present invention has a temperature corresponding to 10 ^4.0 dPa · s at 1350 ° C. or lower, 1345 ° C. or lower, 1340 ° C. or lower, 1335 ° C. or lower, 1330 ° C. or lower, especially 1325 ° C. or lower. It is preferable to consist of a certain glass. When the temperature at 10 ^4.0 dPa · s increases, the temperature at the time of molding becomes too high, and the manufacturing cost of the glass substrate tends to increase. The “temperature corresponding to 10 ^4.0 dPa · s” is a value measured by a platinum ball pulling method.

The alkali-free glass substrate obtained by the method of the present invention is preferably made of glass having a temperature at 10 ^2.5 dPa · s of 1700 ° C. or lower, 1695 ° C. or lower, 1690 ° C. or lower, particularly 1680 ° C. or lower. When the temperature at 10 ^2.5 dPa · s increases, it becomes difficult to melt the glass, the manufacturing cost of the glass substrate rises, and defects such as bubbles easily occur. The “temperature corresponding to 10 ^2.5 dPa · s” is a value measured by a platinum ball pulling method.

The alkali-free glass obtained by the method of the present invention has a liquidus temperature of less than 1300 ° C, 1290 ° C or less, 1210 ° C or less, 1200 ° C or less, 1190 ° C or less, 1180 ° C or less, 1170 ° C or less, 1160 ° C or less, particularly 1150. The glass is preferably made of glass having a temperature of not higher than ° C. If it does in this way, it will become easy to prevent the situation where devitrification crystal occurs at the time of glass manufacture, and productivity falls. Furthermore, since it becomes easy to shape | mold by the overflow down draw method, while it becomes easy to improve the surface quality of a glass substrate, the manufacturing cost of a glass substrate can be reduced. And from the viewpoint of increasing the size of a glass substrate in recent years and increasing the definition of a display, the significance of increasing the devitrification resistance is extremely great in order to suppress devitrification substances that can be surface defects as much as possible. The liquidus temperature is an index of devitrification resistance. The lower the liquidus temperature, the better the devitrification resistance. “Liquid phase temperature” is obtained by passing the standard sieve 30 mesh (500 μm) and putting the glass powder remaining in 50 mesh (300 μm) into a platinum boat for 24 hours in a temperature gradient furnace set at 1100 ° C. to 1350 ° C. After holding, the platinum boat is taken out and refers to the temperature at which devitrification (crystal foreign matter) is observed in the glass.

The alkali-free glass substrate obtained by the method of the present invention has a viscosity at a liquidus temperature of 10 ^4.8 dPa · s or more, 10 ^4.9 dPa · s or more, 10 ^5.0 dPa · s or more, 10 ^5.1. dPa · s or more, 10 ^5.2 dPa · s or more, preferably 10 ^5.3 dPa · s or more, particularly preferably 10 ^5.4 dPa · s or more. In this way, devitrification is less likely to occur at the time of molding, so it becomes easier to mold the glass substrate by the overflow downdraw method, and as a result, the surface quality of the glass substrate can be improved, and the glass substrate is manufactured. Cost can be reduced. The viscosity at the liquidus temperature is an index of moldability. The higher the viscosity at the liquidus temperature, the better the moldability. The “viscosity at the liquidus temperature” refers to the viscosity of the glass at the liquidus temperature and can be measured by, for example, a platinum ball pulling method.

[Example 1]
Hereinafter, embodiments of the production method of the present invention will be described. FIG. 2 is an explanatory diagram showing a schematic configuration of the glass manufacturing facility 1 for carrying out the manufacturing method of the present invention.

First, the structure of the glass manufacturing facility will be explained. The glass production facility 10 includes a melting furnace 1 for electrically melting a raw material batch, a clarification tank 2 provided on the downstream side of the melting furnace 2, an adjustment tank 3 provided on the downstream side of the clarification tank 2, and an adjustment. The melting furnace 1, the clarification tank 2, the adjustment tank 3, and the molding apparatus 4 are connected by connecting flow paths 5, 6, and 7, respectively.

The melting furnace 1 has a bottom wall, a side wall, and a ceiling wall, and each of these walls is formed of a high zirconia refractory such as ZrO ₂ electroformed refractory or dense zircon. The side wall is designed to be thin so that the refractory is easily cooled. In addition, a plurality of pairs of molybdenum electrodes are installed on the left and right side wall lower portions and bottom walls. Each electrode is provided with cooling means so that the electrode temperature does not rise excessively. The glass can be directly energized and heated by applying electricity between the electrodes. In this embodiment, there is no burner (except for the burner at the start of production) or heater used during normal production.

The upstream side wall of the melting furnace 1 is provided with an inlet for raw material supplied from a furnace silo (not shown), and an outlet is formed on the downstream side wall. The melting furnace 1 and the clarification tank 2 communicate with each other through a narrow communication flow path 5 having an upstream end.

The clarification tank 2 has a bottom wall, a side wall, and a ceiling wall, and each of these walls is formed of a high zirconia refractory. The communication channel 5 has a bottom wall, side walls, and a ceiling wall, and each of these walls is also formed of a high zirconia refractory such as a ZrO ₂ electroformed refractory. The clarification tank 2 has a smaller volume than the melting furnace 1, and the bottom wall and the inner wall surface of the side wall (at least the inner wall surface part in contact with the molten glass) are lined with platinum or a platinum alloy, Platinum or a platinum alloy is also lined on the bottom wall of the path 5 and the inner wall surface of the side wall. In the clarification tank 2, the downstream end of the outflow path 5 is opened on the upstream side wall. The clarification tank 2 is a part where clarification of the glass is mainly performed, and fine bubbles contained in the glass are floated up by the clarification gas released from the clarifier and removed from the glass.

An outlet is formed in the downstream side wall of the clarification tank 2, and the adjustment tank 3 communicates with the downstream side of the clarification tank 2 via a narrow communication channel 6 having the outlet at the upstream end. .

The said adjustment tank 3 has a bottom wall, a side wall, and a ceiling wall, and these each wall is formed with the high zirconia refractory. The communication channel 6 has a bottom wall, side walls, and a ceiling wall, and each of these walls is also formed of a high zirconia refractory such as a ZrO ₂ electroformed refractory. The inner wall surface of the bottom wall and the side wall of the adjustment tank 3 (at least the inner wall surface part in contact with the molten glass) is lined with platinum or a platinum alloy, and the bottom wall of the communication channel 7 and the inner wall surface of the side wall Also, platinum or a platinum alloy is lined. The adjustment tank 3 is a part that mainly adjusts the glass to a state suitable for molding, and gradually adjusts the temperature of the molten glass to a viscosity suitable for molding.

An outlet is formed in the side wall on the downstream side of the adjustment tank 3, and the molding device 4 communicates with the downstream side of the adjustment tank 3 via a narrow communication channel 7 having the outlet at the upstream end. .

The molding apparatus 4 is a downdraw molding apparatus, for example, an overflow downdraw molding apparatus. The bottom wall and the inner wall surface of the side wall of the communication channel 7 are lined with platinum or a platinum alloy.

In addition, the supply path in a present Example points out from the communication flow path 5 provided in the downstream of a melting kiln to the communication flow path 7 provided in the shaping | molding apparatus upstream. Moreover, although the glass manufacturing equipment which consists of each part of a melting kiln, a clarification tank, an adjustment tank, and a shaping | molding apparatus was illustrated here, for example, between the adjustment tank and the shaping | molding apparatus, the stirring tank which stirs and homogenizes glass should be provided. Is also possible. Furthermore, although each said equipment showed what formed platinum or a platinum alloy by lining a refractory material, it cannot be overemphasized that the equipment comprised with platinum or platinum alloy itself may be used instead of this.

A method for producing glass using the glass production equipment having the above-described configuration will be described.

First, a raw material batch is prepared so as to be SiO ₂ —Al ₂ O ₃ — (B ₂ O ₃ ) —RO-based alkali-free glass. For example, a raw material batch is prepared so as to have the composition shown in Table 1. In preparing raw material batches, boric anhydride is actively used as the boron source, no boron source material is used, hydroxide raw material is not used, and glass cullet with a low β-OH value is actively used. The raw materials are appropriately selected so that the obtained glass has a low β-OH value.

Subsequently, the prepared glass material is put into the melting furnace 1 and melted and vitrified. In the melting furnace 1, a voltage is applied to the molybdenum electrode and the glass is directly energized and heated. In this embodiment, since radiation heating by burner combustion is not performed, moisture in the atmosphere does not increase, and the amount of moisture supplied from the atmosphere into the glass is greatly reduced. In this embodiment, when starting production, the glass raw material is heated using a burner, and when the initially charged glass raw material is melted, the burner is stopped and the process proceeds to direct current heating.

The molten glass vitrified in the melting furnace 1 is guided to the clarification tank 2 through the communication channel 5. The molten glass contains a large number of bubbles trapped in the melt, which are present between the bubbles generated during the vitrification reaction and the raw material particles. It is lifted and removed by a clear gas released from a certain SnO ₂ .

The molten glass clarified in the clarification tank 2 is guided to the adjustment tank through the communication channel 6. The molten glass led to the adjustment tank 3 is high temperature, has a low viscosity, and cannot be directly molded by a molding apparatus. Therefore, the temperature of the glass is lowered in an adjustment tank and adjusted to a viscosity suitable for molding.

The molten glass whose viscosity has been adjusted in the adjusting tank 3 is guided to the overflow downdraw molding device through the communication channel 7 and formed into a thin plate shape. Further, cutting, end face processing and the like are performed, and a glass substrate made of alkali-free glass can be obtained.

According to the above method, it is possible to reduce the moisture supplied into the glass as much as possible, so that the β-OH value can be reduced to 0.2 / mm or less, and a glass having a low thermal shrinkage rate can be obtained. Obtainable.
[Example 2]
Next, the glass manufactured using the method of the present invention will be described.

First, in mol%, SiO ₂ 66.1%, Al ₂ O ₃ 12.9%, B ₂ O ₃ 6.0%, MgO 3.8%, CaO 7.5%, SrO 1.0%, BaO 2. Silica sand, aluminum oxide, orthoboric acid, boric anhydride, calcium carbonate, strontium nitrate, barium carbonate, tin oxide, strontium chloride, chloride so that the composition contains 5%, SnO ₂ 0.1%, Cl 0.1% Barium and glass cullet having the above composition were mixed and prepared. Tables 2 and 3 show the ratio of boric anhydride to the boric acid raw material and the glass cullet usage ratio to the entire raw material. The total amount of the alkali metal oxide component in the raw material was 0.01%.

Next, the glass raw material was supplied to the melting furnace and melted, and then the molten glass was clarified and homogenized in the clarification tank and the adjustment tank, and adjusted to a viscosity suitable for molding. Melting conditions were as shown in Tables 2 and 3. In the table, “energization” means current heating by a molybdenum electrode, and “burner” means radiant heating by oxyfuel combustion using a burner.

Subsequently, the molten glass was supplied to an overflow downdraw molding apparatus, formed into a plate shape, and then cut to obtain a glass sample having a thickness of 0.5 mm. The molten glass exiting the melting kiln was supplied to the molding apparatus while contacting only platinum or a platinum alloy.

The obtained glass samples were evaluated for β-OH value, glass strain point and heat shrinkage. The results are shown in Tables 2 and 3.

The β-OH value of glass was determined by measuring the transmittance of the 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 (%) in the vicinity of a hydroxyl group absorption wavelength of 3600 cm ⁻¹
The strain point was measured based on the method of ASTM C336-71.

The thermal shrinkage was measured by the following method. First, as shown in FIG. 3A, a 160 mm × 30 mm strip sample G is prepared as a sample of the glass substrate 1. A marking M is formed on each end of the strip-shaped sample G in the long side direction at a position 20 to 40 mm away from the edge by using # 1000 water-resistant abrasive paper. After that, as shown in FIG. 3B, the strip-shaped sample G on which the marking M is formed is folded in two along the direction orthogonal to the marking M to produce sample pieces Ga and Gb. Then, only one sample piece Gb is heated from room temperature to 500 ° C. at 5 ° C./min, held at 500 ° C. for 1 hour, and then heat-treated to lower the temperature at 5 ° C./min. After the heat treatment, as shown in FIG. 3C, in the state where the sample piece Ga that has not been heat-treated and the sample piece Gb that has been heat-treated are arranged in parallel, the markings M of the two sample pieces Ga and Gb The amount of displacement (ΔL1, ΔL2) is read with a laser microscope, and the thermal contraction rate is calculated by the following equation. Note that l ₀ in the equation is a distance between the initial markings M.

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

According to the method of the present invention, it is possible to easily obtain a glass substrate having a small thermal shrinkage rate, which is suitable for producing a low-temperature polysilicon TFT.

DESCRIPTION OF SYMBOLS 1 Melting kiln 2 Clarification tank 3 Adjustment layer 4 Molding apparatus 5, 6, 7 Connecting flow path 10 Glass manufacturing equipment

Claims (11)

1. A method of continuously producing a non-alkali glass substrate of SiO ₂ —Al ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO and ZnO), comprising a tin compound, and Preparing a raw material batch so that it does not substantially contain an arsenic compound and an antimony compound, electrically melting the prepared raw material batch in a melting furnace capable of conducting heating with a molybdenum electrode, and lowering the molten glass And a step of forming into a plate shape by a draw method.
2. The method for producing an alkali-free glass substrate according to claim 1, wherein radiation heating by burner combustion is not used in combination.
3. 3. A method for producing an alkali-free glass substrate according to claim 1 or 2, wherein chloride is added to the raw material batch.
4. The method for producing an alkali-free glass substrate according to any one of claims 1 to 3, wherein a raw material serving as a boron source is not added to the raw material batch.
5. _2. A method for producing an alkali-free glass substrate further containing B ₂ O ₃ as a glass composition, wherein boric anhydride is used as at least a part of a glass raw material to be a boron source. 4. A method for producing an alkali-free glass substrate according to any one of items 1 to 3.
6. 6. The method for producing an alkali-free glass substrate according to claim 1, wherein the raw material batch does not contain a hydroxide raw material.
7. A method for producing a non-alkali glass substrate by adding glass cullet to a raw material batch, wherein a glass cullet made of glass having a β-OH value of 0.4 / mm or less is used as at least a part of the glass cullet. The method for producing an alkali-free glass substrate according to any one of claims 1 to 6.
8. 8. The alkali-free glass substrate according to claim 1, wherein the glass raw material and / or the melting conditions are adjusted so that the obtained glass has a β-OH value of 0.2 / mm or less. Manufacturing method.
9. The method for producing an alkali-free glass substrate according to any one of claims 1 to 8, wherein the obtained glass has a strain point higher than 690 ° C.
10. The method for producing an alkali-free glass according to any one of claims 1 to 9, wherein the glass has a heat shrinkage rate of 25 ppm or less.
11. The method for producing an alkali-free glass substrate according to any one of claims 1 to 10, which is used for producing a glass substrate on which a low-temperature p-Si TFT is formed.

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