TWI396669B - Method for producing alkali-free glass and alkali-free glass - Google Patents

Description

Method for producing alkali-free glass and alkali-free glass

The present invention relates to an alkali-free glass used for a flat panel display substrate such as a liquid crystal display or an EL display (electroluminescence display).

In the conventional flat display substrates such as liquid crystal displays and EL displays, alkali-free glass substrates are widely used.

In particular, electronic devices such as thin film transistor active matrix liquid crystal displays (TFT-LCDs) are used in car navigation and digital camera finder because they are thin and consume less power, and have been used in personal computers in recent years. Various uses such as screens and TVs.

The TFT-LCD panel factory is manufactured on a glass substrate (unprocessed board) formed in a glass factory, and after making a plurality of parts, the product is divided and cut into products to form a product, thereby improving productivity and reducing costs. . In recent years, in terms of applications such as TVs and personal computer screens, even larger devices are required. In order to carry out the multi-layer state of such devices, a large-area glass substrate of 1000 × 1200 mm is required.

In addition, in the case of a portable device such as a mobile phone or a notebook computer, the convenience of carrying it is required, and the weight of the device is required, and the glass substrate is also required to be lightweight. In order to reduce the weight of the glass substrate, it is an effective method for thinning the substrate. At present, the standard thickness of the glass substrate for TFT-LCD is about 0.7 mm.

However, the large, thin-walled glass substrate as described above is due to its own weight. A large bend occurs, and this situation will cause a major problem in the manufacturing steps.

In other words, the glass substrate is formed into a glass factory and then subjected to steps such as cutting, freezing, inspection, and cleaning. In these steps, the glass substrate will enter and exit the cassette forming the plurality of shelves. The cassette is formed on a frame having two sides on the inner side of the length and the width, or three sides on the inner side of the length, the width, and the height, and is horizontally held in a state in which the glass substrate is placed on both sides or three sides, but the large and thin glass substrate is used. The amount of bending is large, so when the glass substrate is placed on the cassette truss, part of the glass substrate will be damaged by contact with the cassette or other glass substrate, or when the glass substrate is taken out from the frame of the cassette, It is easy to form an unstable state by shaking a lot. In addition, in the display factory, the same problem occurs because the same type of cassette is used.

Such an amount of bending due to the weight of the glass substrate itself is proportional to the density of the glass and inversely proportional to the Young's modulus. Therefore, in order to reduce the amount of bending of the glass substrate, it is necessary to increase the specific elastic modulus represented by the elastic modulus/density ratio. In order to increase the specific elastic modulus, it is necessary to obtain a glass material having a high modulus of elasticity and a low density. However, even if the glass has a lower specific modulus of elasticity and a lower density, the reduced amount of the glass can increase the thickness of the same weight of glass. Since the amount of glass bending varies inversely with the square of the thickness, increasing the thickness as much as possible has a great effect on reducing the bending. Since lowering the glass density is also very effective in achieving weight reduction of the glass, it is preferable to minimize the glass density.

In general, a relatively large amount of alkaline earth metal oxide is contained in such alkali-free glass. In order to achieve low density of glass, reduce alkaline earth metal oxides The content is an effective method, but since the alkaline earth metal oxide is a component which promotes the meltability of the glass, if the content is lowered, the meltability is lowered. When the meltability of the glass is lowered, internal defects such as bubbles and impurities are more likely to occur in the glass. Since bubbles and impurities in the glass hinder the penetration of light, which is a fatal defect of the glass substrate for a display, it is necessary to melt the glass at a high temperature for a long time in order to suppress such internal defects. On the other hand, melting at high temperatures will increase the burden on the glass melting kiln. The higher the temperature, the more refractory the refractory used in the kiln is, resulting in a shortened kiln life cycle.

Furthermore, thermal shock resistance is also an important requirement for such a glass substrate. Even if the end surface of the glass substrate is subjected to the truncation treatment, there are fine flaws or cracks. When the tensile stress is concentrated on the flaw or the crack due to heat, the glass substrate may occasionally crack. The breakage of the glass not only lowers the operation rate of the production line, but also causes the fine glass powder generated at the time of damage to adhere to the glass substrate, which may cause a problem of poor disconnection and poor pattern processing.

However, in recent developments of TFT-LCDs, in addition to large screens and light weight, developments such as high definition, high-speed response, and high aperture ratio have been developed, particularly in recent years, in liquid crystals. For the purpose of high performance and light weight of the display, it is advancing toward the development of polycrystalline germanium TFT-LCD (p-Si. TFT-LCD). Previous p-Si. Since the TFT-LCD has a manufacturing process temperature of up to 800 ° C or more, only a quartz glass substrate can be used. However, according to recent developments, although the manufacturing process temperature has been lowered to 400 to 600 ° C, it is as large as today. The amorphous 矽 TFT-LCD (a-Si. TFT-LCD) is still made of an alkali-free glass substrate.

p-Si. The manufacturing steps of TFT-LCD are compared to a-Si. In the manufacturing steps of the TFT-LCD, the heat treatment step is excessive, because the glass substrate is repeatedly subjected to rapid heating and rapid cooling, and thus the thermal shock to the glass substrate is more serious. Further, as described above, the glass substrate is increased in size, and not only the glass substrate is likely to have a temperature difference, but also the probability of occurrence of minute scratches and cracks at the end faces is improved. Therefore, the probability of the substrate being damaged during the thermal process is increased. The most fundamental and effective way to solve this problem is to reduce the thermal stress caused by the difference in thermal expansion, thus requiring a glass with a lower coefficient of thermal expansion. In addition, when the difference in thermal expansion between the material and the thin film transistor (TFT) material becomes large, since the glass substrate is warped, it is also required to have a thermal expansion coefficient (about 30 to 33 × 10 ^{- with a} TFT material such as p-Si. ⁷ / ° C) similar thermal expansion coefficient.

Furthermore, p-Si. The manufacturing step temperature of TFT-LCD has been reduced recently, but with a-Si. The temperature of the manufacturing steps of the TFT-LCD is still high. If the heat resistance of the glass substrate is low, in p-Si. In the TFT-LCD manufacturing step, when the glass substrate is in a high temperature state of 400 to 600 ° C, shrinkage of a so-called heat shrinkage of a small size is caused, and this phenomenon causes a shift in the pixel pitch of the TFT, which may cause a display failure. Further, when the heat resistance of the glass substrate is lower, the glass substrate may be deformed or warped. Further, in the liquid crystal production step such as film formation, in order to prevent the glass substrate from being shifted due to thermal contraction, a glass excellent in heat resistance is required.

Furthermore, a transparent guide is formed on the surface of the glass substrate for TFT-LCD An electric film, an insulating film, a semiconductor film, a metal film, or the like, and various circuits or patterns are formed by photolithography (photolithography). Further, in the film formation and photoetching steps, various heat treatments and drug treatments are performed on the glass substrate.

Therefore, when an alkali metal oxide (Na ₂ O, K ₂ O, or Li ₂ O) is contained in the glass substrate, alkali ions are diffused into the formed semiconductor material during the heat treatment, and it is judged that the film characteristics are deteriorated. Therefore, those who do not substantially contain an alkali metal oxide or which are not resistant to deterioration due to various acids, bases, and the like used in the photolithography step are required.

Further, the glass substrate for a TFT-LCD is mainly formed by a downdraw process or a floating process. Examples of the down-draw method are, for example, a slot downdraw process, an overflow downdraw process, etc., since the glass substrate formed by the down-draw method does not require grinding processing, it is easy to achieve cost reduction. The advantages. However, when a glass substrate is formed by a down-draw method, since the glass substrate is more susceptible to devitrification, a glass excellent in devitrification resistance is also required.

Therefore, there are proposals to satisfy the above characteristics, in particular, alkali-free glass for substrates characterized by low density, low expansion, and high strain point.

(e.g., Japanese Patent Laid-Open Publication No. 2002-308643)

The alkali-free glass disclosed in Japanese Laid-Open Patent Publication No. 2002-308643 has a melting temperature [corresponding to a temperature of 10 ^2.5 poise] of about 1580 ° C or more, which requires high-temperature melting and a density of 2.45 g. Below /cm ³ , the average thermal expansion coefficient in the temperature range of 30 to 380 ° C is 25 to 36 × 10 ^-7 / ° C, and the strain point is 640 ° C or more, which satisfies the above requirements.

However, when such an alkali-free glass having a low density, a low expansion, and a high strain point is produced on an industrial scale, devitrification occurs at the time of molding due to slight variations in manufacturing conditions.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an alkali-free glass which can be molded without causing devitrification of the glass, even if it is produced on an industrial scale, and an alkali-free glass obtained by the method.

When an alkali-free glass which requires high-temperature melting is produced on an industrial scale, it is considered that a high-zirconium refractory excellent in corrosion resistance is used to constitute a molten kiln or is disposed downstream thereof from the viewpoint of long life of the production equipment. Various equipment (such as: clarification tank, adjustment tank, etc.). However, according to the study by the inventors of the present invention, it has been found that ZrO ₂ is melted when the alkali-free glass disclosed in Japanese Laid-Open Patent Publication No. 2002-308643 is melted by a manufacturing apparatus using a high-zirconium refractory. Since the composition is melted from the refractory, the concentration of ZrO ₂ in the glass is increased, and it is extremely likely to be devitrified, and the present invention has been proposed.

That is, the method for producing alkali-free glass of the present invention comprises: preparing a raw material to have SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (RO-based MgO, CaO, BaO, SrO, and ZnO 1 And a step of constituting the alkali-free glass; and a step of melting the glass raw material in a melting kiln using a high zirconium refractory; and melting the glass by using at least a part of a supply passage formed of platinum or a platinum alloy a supply step supplied to the molding apparatus; and a molding step of molding the molten glass supplied to the molding apparatus into a predetermined shape. Also, in the present invention, cullet is also included in the glass raw material. In the present invention, "non-alkaline" means that the alkali metal oxide (Li ₂ O, Na ₂ O, K ₂ O) is 0.2% by mass or less.

Further, in the method for producing an alkali-free glass of the present invention, the glass is melted by direct electric heating.

Further, in the method for producing an alkali-free glass of the present invention, one or more electrodes selected from the group consisting of a SnO ₂ electrode, a Pt electrode, and a Mo electrode are used for direct electric heating.

Further, in the method for producing an alkali-free glass of the present invention, the glass is molded into a plate shape.

Further, in the method for producing an alkali-free glass of the present invention, the glass is formed into a plate shape by an overflow down-draw method.

Further, in the method for producing an alkali-free glass of the present invention, the ZrO ₂ content of the obtained glass is 0.6% or less in terms of mass percentage.

Further, in the method for producing alkali-free glass of the present invention, the SnO ₂ content of the obtained glass is 0.3% or less in terms of mass percentage.

Further, in the method for producing an alkali-free glass of the present invention, the glass obtained has a β-OH value of 0.2/mm or more.

Furthermore, the method for producing alkali-free glass of the present invention is to prepare a raw material to have a density of 2.55 g/cm ³ or less and a temperature coefficient of 30 to 380 ° C, and an average coefficient of thermal expansion of 25 to 40×10 ^-7 /° C. Alkaline-free glass with a strain point above 640 °C.

Furthermore, the method for producing an alkali-free glass of the present invention is to prepare a raw material containing SiO ₂ : 50 to 70% by mass, Al ₂ O ₃ : 10 to 25%, and B ₂ O ₃ : 8.4 to 20 %, MgO: 0 to 10%, CaO: 3 to 15%, BaO: 0 to 10%, SrO: 0 to 10%, ZnO: 0 to 10%, TiO ₂ : 0 to 5%, P ₂ O ₅ : 0 to 5% glass.

The alkali-free glass of the present invention is obtained by the above production method.

Further, the alkali-free glass of the present invention has a composition of SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (one or more of RO-based MgO, CaO, BaO, SrO, and ZnO), and has a density. The average thermal expansion coefficient in the temperature range of 2.55 g/cm ³ or less and 30 to 380 ° C is 25 to 40×10 ^-7 /° C., the strain point is above 640 ° C, and the β-OH value is 0.2/mm or more, and the mass is Percentage, containing a ZrO ₂ content of 0.01 to 0.6% and a SnO ₂ content of 0.005 to 0.3%.

Further, the alkali-free glass of the present invention contains SiO ₂ : 50 to 70% by mass percentage, Al ₂ O ₃ : 10 to 25%, B ₂ O ₃ : 8.4 to 20%, and MgO: 0 to 10 %, CaO: 3 to 15%, BaO: 0 to 10%, SrO: 0 to 10%, ZnO: 0 to 10%, TiO ₂ : 0 to 5%, P ₂ O ₅ : 0 to 5%, ZrO ₂ : 0.01 to 0.6%, and SnO ₂ : 0.005 to 0.3%.

Further, the alkali-free glass of the present invention is used as a liquid crystal display or an EL display substrate.

According to the production method of the present invention, the molten kiln is made of a high-zirconium refractory having high corrosion resistance, and even when the alkali-free glass which has to be subjected to high-temperature melting is melted, the stable operation can be performed for a long time. Further, at least a part of the supply passage supplied from the melting kiln to the molding apparatus uses platinum or a platinum alloy to reduce the glass contamination caused by the melting of ZrO ₂ . Therefore, it can be molded into glass without devitrification. Devitrification can be further improved by strictly regulating the melting of the electrode, the impurity of the raw material, or the SnO ₂ used as a clarifying agent in the glass. If the amount of water in the glass is increased, the viscosity of the glass can be lowered. Therefore, it is particularly advantageous in the production of alkali-free glass which is melted at a high temperature, and particularly refers to an alkali-free glass which reduces devitrification by lowering the alkaline earth component, lowering the density and lowering the expansion.

Further, the alkali-free glass of the present invention has low density, low expansion, and high strain point, and has a small amount of heat shrinkage and a small amount of warpage, is excellent in thermal shock resistance, and is less likely to cause warpage. At the same time, it has the characteristics of being easily devitrified even if it is produced on an industrial scale. Therefore, it is suitable for glass for substrates of liquid crystal displays and EL displays.

An alkali-free glass having a composition of SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (one or more of RO-based MgO, CaO, BaO, SrO, and ZnO) obtained by the method of the present invention . Among them, it is particularly suitable for the manufacture of glass having a low density, low expansion, and high strain point which must be melted at a high temperature.

Further, the glass system contains ZrO ₂ in an amount of 0.6% or less, preferably 0.5% or less, more preferably 0.3% or less, more preferably 0.2% or less, and particularly preferably 0.1% or less. Preferably, it is preferably 0.01% or more, particularly preferably 0.02% or more. When the ZrO ₂ content exceeds 0.6% or more, devitrification is likely to occur.

From the viewpoint of improving the devitrification, the less ZrO ₂ is, the better. This trend is more pronounced when forming a glass that is closer to a low density, low expansion, high strain point. However, even if a small amount of ZrO _{2 is} added, it has an effect of improving the chemical durability of the alkali-free glass, and therefore it is preferable to contain the compound. Further, the ZrO ₂ is completely prevented from being mixed into the glass raw material with impurities, which leads to an increase in the cost of the raw material. Moreover, it is also possible to mix ZrO ₂ from cullet (for example, when a glass made of a high zirconium refractory is used as cullet, the possibility of containing ZrO ₂ in cullet is extremely high). In addition, cullet is less susceptible to melting, such as alkali-free glass, and is a suitable raw material for glass. Moreover, from the viewpoint of the current high environmental awareness, the necessity of recycling and recycling using broken glass as a raw material has gradually increased. From this point of view, in the present invention, it is preferable to set the lower limit of ZrO ₂ to 0.01%. By containing ZrO ₂ in an amount of 0.01% or more, particularly 0.02% or more, it is expected that the chemical durability of the glass is improved. In addition, there is no need to use a raw material of high purity with respect to ZrO ₂ , so that an increase in the cost of raw materials can be avoided. It is possible to use broken glass.

Further, the content of the glass-based SnO _{2 is} preferably 0.3% or less, more preferably 0.28% or less, more preferably 0.005% or more, particularly preferably 0.02% or more, particularly preferably 0.03% or more, based on the mass percentage. In the present invention, although SnO ₂ is not an essential component, it is a component which can be added as a clarifying agent. Further, when a SnO ₂ electrode electrically melting the glass purposes, the electrodes belonging to the SnO ₂ component from the glass melt. The SnO ₂ content is closely related to the devitrification of the glass caused by ZrO ₂ , and it is easy to devitrify if the amount of SnO ₂ is too large. Further, as in the case of ZrO ₂ , from the viewpoint of improving the devitrification property, the SnO _{2 is} as small as possible. However, SnO _{2 is one of} the few components which can exert a clarifying effect in a high temperature region, and a high clarification effect can be expected in a small amount. Therefore, in the glass of the present invention which is required to be melted at a high temperature and which is difficult to clarify, in order to improve the clarity and reduce the amount of As ₂ O ₃ used, it is preferable that SnO ₂ is contained in an amount of 0.005% or more, preferably 0.01% or more. . In addition, the clarifying effect of SnO ₂ is that even the SnO ₂ melted from the electrode can exert the same effect.

Specific examples of the preferred glass obtained by the production method of the present invention include, for example, a density of 2.55 g/cm ³ or less (preferably 2.45 g/cm ³ or less, particularly preferably 2.42 g/cm ³ or less). ), the average coefficient of thermal expansion in the temperature range of 30 to 380 ° C is 25 to 40 × 10 ^-7 / ° C (preferably 25 to 36 × 10 ^-7 / ° C, especially 28 to 35 × 10 ^-7 / ° C for Preferably, the glass has a strain point above 640 ° C (preferably above 650 ° C). A glass having such characteristics generally has to be melted at a high temperature, but has excellent thermal shock resistance, and can be lightened by approximating the thermal expansion coefficient of the TFT material without causing warpage, and can reduce the amount of bending and heat shrinkage. advantage.

As described above of _{SiO 2 -Al 2 O 3 -B 2} O 3 -RO based glass, typically a temperature corresponding to 10 ^2.5 poise or more at 1580 deg.] C, and the melting temperature must be implemented. Such a glass which must be melted at a high temperature is associated with an improvement in meltability even if the viscosity is slightly lowered. Increasing the moisture of the glass is an effective method for reducing the viscosity of the high temperature. Therefore, in the substrate glass of the present invention, the amount of water of the glass is expressed by β-OH value, and is preferably adjusted to 0.2/mm or more, preferably 0.25/mm or more, and more preferably 0.3/mm or more. It is also preferably at 0.4/mm or more. From the viewpoint of improvement in meltability, the higher the β-OH value, the better, but the higher the tendency to lower the strain point. From this point of view, the upper limit of the β-OH value is preferably 0.65/mm or less, particularly preferably 0.6/mm or less. Further, the β-OH value of the glass is determined by the following formula in the infrared absorption spectrum of the glass.

β-OH value=(1/X)log10(T ₁ /T ₂ ) X: glass thickness (mm) T ₁ : light transmittance (%) in reference wavelength 3846 cm ^-1 T ₂ : absorption wavelength at 3600 cm ^- Minimum transmittance near ¹ (%)

Further, in addition to the above characteristics, the liquidus temperature is preferably 1150 ° C or less (especially preferably 1130 ° C or less, more preferably 1100 ° C or less), and the viscosity in the liquid phase temperature is preferably 10 ^5.4 dPa. Above s (especially 10 ^6.0 dPa.s or more is preferred). By satisfying this condition, even if it is formed into a plate shape by the lower drawing method, devitrification does not occur, and the grinding step can be omitted, and the production cost can be reduced. In particular, in a 10% HCl aqueous solution, when the treatment is carried out at 80 ° C for 24 hours, the amount of erosion is 10 μm or less, and in a 10% aqueous HCl solution, when the treatment is carried out at 80 ° C for 1 hour, depending on the visual inspection, The surface was observed to be turbid and rough, and when it was treated in a 130 BHF solution at a temperature of 20 ° C for 30 minutes, the amount of erosion was 0.8 μm or less, and when it was used in a 63 BHF solution for 20 minutes to 30 minutes. When the condition was applied, no turbidity or roughness was observed depending on the visual observation surface, and a better condition was exhibited. In addition, the specific elastic modulus is preferably 27.5GPa/g. Cm ^-3 or more (especially 29.0 GPa.s or more is preferred). By satisfying this condition, the amount of bending of the glass substrate can be reduced. If 10 ^2.5 dPa. When the temperature of the glass melt in the viscosity is below 1650 ° C, the meltability will be better.

Further, preferred glass composition examples produced by the production method of the present invention include, for example, SiO ₂ : 50 to 70% by mass, Al ₂ O ₃ : 10 to 25%, and B ₂ O _{3 .} : 8.4 to 20%, MgO: 0 to 10%, CaO: 3 to 15%, BaO: 0 to 10%, SrO: 0 to 10%, ZnO: 0 to 10%, TiO ₂ : 0 to 5%, P ₂ O ₅ : 0 to 5% glass. A glass having such a composition generally has to be subjected to high-temperature melting, but the strain point, density, thermal expansion coefficient, chemical resistance, specific modulus of elasticity, meltability, moldability, and the like which are required for use as a substrate such as a liquid crystal display can be obtained as described above. characteristic. The reason for limiting the composition range will be described below.

The SiO ₂ content is 50 to 70%. If it is less than 50%, the chemical resistance, in particular, the acid resistance will be deteriorated, and it is difficult to achieve a low density. On the other hand, when it is more than 70%, the high-temperature viscosity is increased, and the meltability is deteriorated, and at the same time, defects of devitrified foreign matter (white smectite) are easily generated in the glass. The content of SiO _{2 is} preferably 58% or more, particularly preferably 60% or more, more preferably 62% or more, and most preferably 68% or less, particularly preferably 66% or less.

The Al ₂ O ₃ content is 10 to 25%. If it is less than 10%, it is quite difficult to reach the strain point above 640 °C. Moreover, Al ₂ O ₃ has a function of increasing the glass elastic modulus and increasing the specific modulus of elasticity, and if it is less than 10%, the modulus of elasticity is lowered. The Al ₂ O ₃ content is preferably at least 12%, more preferably 14.5% or more, and most preferably 19% or less, particularly preferably 18.0% or less. On the other hand, when it is more than 19%, the liquidus temperature rises and the devitrification resistance decreases.

B ₂ O ₃ has a function as a fluxing agent, and is a component which lowers viscosity and improves meltability. However, the glass substrate used in the liquid crystal display is required to have high acid resistance, and the more the B ₂ O _{3 is, the} more the acid resistance tends to decrease. The B ₂ O ₃ content is 8.4 to 20%. If it is less than 8.4%, the role as a flux will be insufficient, and the buffer-resistant hydrofluoric acid will deteriorate. On the other hand, when it is more than 20%, the strain point of the glass is lowered, the heat resistance is lowered, and the acid resistance is deteriorated. In particular, since the modulus of elasticity is lowered, the specific modulus of elasticity is also lowered. The content of B ₂ O _{3 is} preferably 8.6% or more, and preferably 15% or less, particularly preferably 14% or less, more preferably 12% or less.

The MgO content is 0 to 10%. MgO does not cause the strain point to decrease, but lowers the high temperature viscosity and improves the glass meltability. And in the alkaline earth metal oxide, the effect of reducing the density is the most. However, when a large amount is contained, the liquidus temperature rises and the devitrification resistance decreases. Moreover, since MgO will react with buffered hydrofluoric acid to form a product, and it is fixed on a member on the surface of the glass substrate or attached to the glass substrate, but this may cause white turbidity, and thus the content thereof may be Limited. Therefore, the MgO content is preferably from 0 to 2%, particularly preferably from 0 to 1%, more preferably from 0 to 0.5%, and particularly preferably not included.

CaO is also like MgO, which is a component that does not lower the strain point, but lowers the high temperature viscosity and significantly improves the glass meltability, and its content is 3 to 15%. Such an alkali-free glass substrate is generally important in terms of improving the meltability in order to supply a large amount of a high-quality glass substrate which is difficult to melt and inexpensive. The reduction of SiO ₂ in the glass composition system of the present invention is the most effective method for improving the meltability. However, when the amount of SiO ₂ is decreased, the acid resistance is extremely lowered, and since the density and thermal expansion coefficient of the glass are increased, the most Good to avoid. Therefore, in the present invention, in order to improve the meltability of the glass, it contains 3% or more of CaO. On the other hand, when CaO is more than 15%, the buffer-resistant hydrofluoric acid of the glass is deteriorated, the surface of the glass substrate is more likely to be corroded, and the reaction product adheres to the surface of the glass substrate to make the glass white and turbid, and the coefficient of thermal expansion becomes Too high, so it is best to avoid it. The CaO content is preferably 4% or more, more preferably 5% or more, more preferably 6% or more, and most preferably 12% or less, particularly preferably 10% or less, and more preferably 9% or less. .

BaO is a component that enhances glass resistance and devitrification resistance and contains 0 to 10%. However, it is a component which greatly increases the density of glass and the coefficient of thermal expansion. When it is low density and low expansion, it is preferable not to contain it as much as possible. Moreover, from the environmental point of view, it is also best not to contain too much. The BaO content is preferably 5% or less, and particularly preferably 2% or less. However, in order to reduce the density and the low expansion of the glass, it is preferably 1% or less, more preferably 0.1% or less.

SrO is a component that enhances glass resistance and devitrification resistance and contains 0 to 10%. However, if too much is contained, the density and thermal expansion coefficient of the glass will increase. The SrO content is preferably 4% or less, particularly 2.7% or less, more preferably 1.5% or less.

Further, BaO and SrO are components which have a property of improving the resistance to buffered hydrofluoric acid (BHF resistance). Therefore, in order to improve the BHF resistance, the total amount of the components is preferably 0.1% or more (especially preferably 0.3% or more, and more preferably 0.5% or more). However, as described above, when too much BaO and SrO are contained, the total amount of the glass is preferably suppressed to 6% or less because of the increase in the density and thermal expansion coefficient of the glass. In this range, the total amount of BaO and SrO is preferably as large as possible from the viewpoint of improving the resistance to BHF and devitrification resistance, and conversely, from the viewpoint of a decrease in density or coefficient of thermal expansion or environmental concerns. In terms of content, it is best to reduce the content as much as possible.

ZnO is a component which improves the buffer-resistant hydrofluoric acidity of a glass substrate and improves the meltability. When the content is too large, the glass is easily devitrified, the strain point is lowered, and the density is increased, so that it is preferably avoided. Therefore, its content is It is preferably 0 to 10%, preferably 0 to 7%, particularly preferably 5% or less, more preferably 3% or less, particularly preferably 0.9% or less, and most preferably 0.5% or less.

Each component containing MgO, CaO, BaO, SrO, and ZnO is mixed by the phase to significantly lower the liquidus temperature of the glass, and it is difficult to cause crystal foreign matter in the glass to improve the meltability and moldability of the glass. effect. However, when the total amount of each of the above components is too small, the effect as a flux is insufficient, the meltability is deteriorated, and the thermal expansion coefficient is too low, and the integration with the TFT material is lowered. On the other hand, if it is too large, the density will increase, and in addition to the inability to reduce the weight of the glass substrate, the specific elastic modulus is lowered, so that it is preferably avoided. The total amount of the components is preferably from 6 to 20%, preferably from 6 to 15%, particularly preferably from 6 to 12%.

TiO ₂ is a component that improves the resistance of glass, in particular, it improves the acid resistance and lowers the viscosity at high temperature and enhances the meltability. However, if the content is too large, the glass will be colored, and in order to reduce the light transmittance, Therefore, it is not suitable for glass substrates for displays. Therefore, TiO ₂ should be limited to 0 to 5%, preferably 0 to 3%, particularly preferably 0 to 1%.

P ₂ O ₅ is a component that enhances the devitrification resistance of glass. However, if the content is too large, it is preferably avoided because it causes phase separation and milk whiteness in the glass and the acid resistance is also significantly deteriorated. Therefore, P ₂ O ₅ should be limited to 0 to 5%, preferably 0 to 3%, particularly preferably 0 to 1%.

Further, in addition to the above components, in the present invention, the total amount of Y ₂ O ₃ , Nb ₂ O ₃ , and La ₂ O _{3 may be} within 5%. Although these components have the effects of increasing the strain point and the elastic modulus, if the content is too large, it is preferably avoided because the density is increased. In addition, it can be clarified by adding metal powder such as As ₂ O ₃ , Sb ₂ O ₃ , Sb ₂ O ₅ , F ₂ , Cl ₂ , SO ₃ , C, or Al or Si without damaging the glass characteristics. The total amount of the agent is less than 5%. It may also contain a clarifying agent such as CeO ₂ or Fe ₂ O ₃ in a total amount of 5%. In addition, As ₂ O ₃ is best not to be used from an environmental point of view.

Next, a method of producing the alkali-free glass of the present invention will be described in detail. The method of the present invention comprises: a compounding step, a melting step, a supplying step, and a forming step.

The mixing step is a batch preparation in which a glass raw material is blended into a glass having a composition of SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (one or more of RO-based MgO, CaO, BaO, SrO, and ZnO). step. In particular, as described above, it is preferable to formulate a glass having a characteristic of a thermal expansion coefficient of 25 to 40 × 10 ^-7 /° C. and a strain point of 640 ° C or more in a temperature range of 2.55 g/cm ³ or less and 30 to 380 ° C. And, in terms of mass percentage, contains SiO ₂ : 50 to 70%, Al ₂ O ₃ : 10 to 25%, B ₂ O ₃ : 8.4 to 20%, MgO: 0 to 10%, CaO: 3 to 15%, BaO: 0 to 10%, SrO: 0 to 10%, ZnO: 0 to 10%, TiO ₂ : 0 to 5%, and P ₂ O ₅ : 0 to 5% of glass.

Further, the ZrO ₂ component which causes the devitrification causes an increase in the content due to the melting from the refractory in the subsequent melting step. It is important to limit the amount of ZrO ₂ component to be mixed into the glass raw material, and even if it is used in an attempt to improve chemical durability, etc., the amount of addition must be kept to a minimum. When the SnO ₂ component which strengthens the devitrification of ZrO _{2 is} electrically melted by the SnO ₂ electrode, the content of the SnO ₂ component may be increased due to melting from the electrode. Therefore, it is important to limit the incorporation of SnO ₂ from the glass raw material as much as possible, and the amount of addition must be kept to a minimum when it is deliberately used for obtaining a clarifying effect or the like.

The melting step is a step of melting the raw material by a melting kiln using a high zirconium refractory. The high zirconium refractory is preferably a ZrO ₂ electroformed refractory which is excellent in corrosion resistance and can be used for a long period of time. When the melting temperature is in the alkali-free glass of the above composition, it is about 1,500 to 1,650 °C.

Further, by using an SnO ₂ electrode, a Pt electrode, a Mo electrode, or the like, direct electric heating is performed to perform electric melting, and high-temperature melting can be easily performed. In this case, it is of course also possible to combine the combustion of heavy oil or gas to perform melting. In addition, the type of the electrode is not particularly limited, and it is only necessary to consider the factors such as the electrode life and the degree of erosion, and then determine the appropriate type. Further, the number of electrodes to be used is not necessarily one, and two or more types of electrodes may be used in combination after considering various conditions. For example, when Pt melts in the glass and causes problems, the SnO ₂ electrode or the Mo electrode is used for the portion where the electrode component is more easily melted, and the Pt electrode is used for other portions. In particular, since the SnO ₂ electrode is composed of an oxide itself, even if the electrode component is melted in the glass, it has a characteristic that it is less likely to adversely affect the glass.

The supplying step is a step of supplying the molten glass melted in the melting kiln to the molding apparatus by using at least a part of a supply passage formed of platinum or a platinum alloy. The reason why the supply passage is formed by using platinum or a platinum alloy is to prevent the ZrO _{2 from being} more melted into the glass. In addition, the incorporation of ZrO ₂ not only causes devitrification of the glass, but also affects homogeneity. In the production of glass which can be used even without grinding, it is necessary to improve the homogeneity of the glass, and it is therefore necessary to prevent the occurrence of glass contamination due to the melting of ZrO ₂ in the supply passage. The use of platinum or a platinum alloy for the supply passage has an effect on the homogeneity of the glass. Therefore, the more the portion formed by using platinum or a platinum alloy, the better, and it is desirable that the contact surface with the glass is formed entirely of platinum or a platinum alloy. In addition, the "supply passage" means an integral device provided between the melting kiln and the molding apparatus. It includes, for example, a clarification tank, an adjustment tank, a stirring tank, and the like, and a communication flow path connecting the grooves. Further, in the supply step, not only the glass is supplied to the molding apparatus, but also the glass is preferably clarified and homogenized.

Further, the "supply passage formed by using platinum or a platinum alloy" means a supply passage not only made of platinum or a platinum alloy but also a supply passage for covering the surface of the refractory with platinum.

The molding step is a step of molding the molten glass supplied to the molding device into a predetermined shape. In terms of display use, the glass can be formed into a thin plate shape by a method such as an overflow down-draw method, a slot down draw process, a floating method, or a roll out method. In particular, when molding is carried out by the overflow down-draw method, a glass plate excellent in surface quality can be obtained without polishing, which is preferable.

According to the above, the alkali-free glass of the present invention can be obtained.

Further, in the production method of the present invention, the ZrO ₂ tolerance should be limited to the content of the obtained glass in terms of mass percentage, below 0.6%, preferably at 0.5, from the viewpoint of preventing devitrification in the molding step. % or less, preferably 0.3% or less, more preferably 0.2% or less, and most preferably 0.1% or less. Further, it is preferably 0.01% or more, and particularly preferably 0.02% or more. When the ZrO ₂ content in the obtained glass is 0.6% or less, the devitrification property can be improved. In addition, the amount of ZrO ₂ in the glass can be determined according to factors such as the amount of ZrO ₂ raw materials used in the compounding step or impurity management, refractory temperature management or current amount adjustment in the melting step, and the use area of platinum or platinum alloy in the supply step. And make adjustments.

Further, in the same manner, the SnO ₂ tolerance is preferably 0.3% or less, more preferably 0.28% or less, and most preferably 0.005% or more, particularly preferably 0.01% or more, based on the mass percentage. It is better. When the SnO ₂ content in the obtained glass is 0.3% or less, the devitrification caused by ZrO ₂ can be greatly suppressed. Further, the amount of SnO ₂ in the glass can be adjusted depending on factors such as the amount of use of the SnO ₂ raw material in the compounding step or the management of the impurities, the number of uses of the SnO ₂ electrode in the melting step, or the temperature management of the electrode.

Further, in order to reduce the viscosity of the glass to improve the meltability as much as possible, it is preferable to increase the moisture content of the glass. Specifically, the β-OH value is preferably adjusted to 0.2/mm or more, particularly preferably 0.25/mm or more, more preferably 0.3/mm or more, and particularly preferably 0.4/mm or more. In adjusting the amount of water in the glass, it is possible to select a raw material having a high water content (for example, a hydroxylated raw material), to add water to the raw material, to limit the content of a component such as chlorine to reduce the amount of water in the glass, and to melt the glass. In the case of oxygen combustion, the amount of water in the furnace environment is increased, water vapor is directly introduced into the furnace, and water vapor bubbles are applied to the molten glass.

(Example 1)

Tables 1 and 2 show the experimental results of the influence of the SnO ₂ content on the devitrification phenomenon caused by ZrO ₂ . The glass 1 contains, by mass%, SiO ₂ : 60%, Al ₂ O ₃ : 15%, B ₂ O ₃ : 10%, CaO: 5%, BaO: 5%, SrO: 5%, and density. 2.5 g/cm ³ , 30 to 380 ° C thermal expansion coefficient of 37 × 10 ^-7 / ° C, strain point of 655 ° C glass. The glass 2 contains, by mass%, SiO ₂ : 64%, Al ₂ O ₃ : 16%, B ₂ O ₃ : 11%, CaO: 8%, SrO: 1%, and a density of 2.4 g/cm ^{3 .} A glass having a thermal expansion coefficient of 32 × 10 ^-7 / ° C at 30 to 380 ° C and a strain point of 660 ° C.

Each sample was prepared as follows. First, the glass raw material is formulated so that the amount of ZrO _{2 and the} amount of SnO ₂ are changed to have the above composition. This raw material was placed in a white gold crucible in batches, and melted at 1600 ° C for 24 hours to be molded. Then, the obtained glass was pulverized, and passed through a standard sieve 30 mesh (500 μm), and the glass powder remaining in 50 mesh (300 μm) was placed in a platinum boat and subjected to a temperature-gradient furnace. ) Take it out after 24 hours. For the sample obtained, the ZrO _{2 in the} glass was observed by a microscope. The highest temperature exhibited by SiO ₂ crystals. In addition, the "-" part in the table refers to the uninvestigated person.

From the above results, it is known that the glass 2 having a low density, a low expansion, and a high strain point, which is reduced in alkaline earth components such as BaO, is more likely to be devitrified by a small amount of ZrO ₂ . Further, it was confirmed that the higher the ZrO ₂ content and the SnO ₂ content, the stronger the devitrification property.

(Example 2)

Next, an embodiment of the method of the present invention will be described with reference to the drawings. Fig. 1 is a schematic explanatory view showing a glass manufacturing apparatus 1 for carrying out the production method of the present invention.

First, the configuration of the glass manufacturing equipment will be described. The glass manufacturing equipment 1 includes a slightly rectangular melting kiln 2 constituting a molten glass supply source, a clarification tank 3 provided at a downstream end of the melting kiln 2, an adjustment tank 4 provided at a downstream end of the clarification tank 3, and The molding apparatus 5 at the downstream end of the tank 4 is adjusted; and the melting kiln 2, the clarification tank 3, the adjustment tank 4, and the molding apparatus 5 are connected by the collateral flow paths 6, 7, and 8, respectively.

The melting kiln 2 has a bottom wall, a side wall, and a top wall, and each of the walls is formed of a high zirconium refractory such as a ZrO ₂ electroformed refractory. The side wall system is designed to have a thin wall thickness to make the refractory easy to cool. Further, a plurality of pairs of electrodes are disposed on the lower end and the bottom wall of the left and right side walls, and a plurality of burners are respectively disposed at the upper ends of the left and right side walls. A cooling device is provided in each of the electrodes so that the temperature of the electrodes does not rise excessively. In addition, if the burner is subjected to oxy-combustion heating using an oxygen burner, higher temperature heating can be performed, and the moisture of the glass can be easily increased. Then, by applying electric power between the electrodes, the glass can be directly electrically heated. Further, by irradiating the flame of the burner toward the upper end space of the molten glass, the molten glass can be heated from above.

An air outlet is formed at a side wall of the downstream end of the melting kiln 2, and the outlet port communicates with the melting kiln 2 and the clarification tank 3 through a narrow contact flow path 6 provided at the upstream end.

The clarification tank 3 has a bottom wall, a side wall, and a top wall, and the walls are formed of a high zirconium refractory. Further, the contact flow path 6 has a bottom wall, a side wall, and a top wall, and each of the walls is formed of a high-zirconium refractory such as a ZrO ₂ electroformed refractory. The clarification tank 3 has a smaller volume than the melting kiln 2, and a platinum or platinum alloy is adhered to the inner wall surface of the bottom wall and the side wall (at least in contact with the inner wall surface of the molten glass). Platinum or a platinum alloy is also adhered to the inner wall surface of the bottom wall and the side wall. This clarification tank 3 is on the side wall of the upstream end, and an opening is provided at the downstream end of the above-mentioned collateral flow path 6. The clarification tank 3 is mainly a portion where glass clarification is carried out, and fine bubbles contained in the glass will be expanded and removed from the glass by the clarified gas released from the clarifying agent.

Forming an outflow port on the downstream end side wall of the above clarification tank 3, and flowing The outlet has a narrow contact flow path 7 at the upstream end and a regulating groove 4 at the downstream end of the clarification tank 3.

The adjustment groove 4 has a bottom wall, a side wall, and a top wall, and the walls are formed of a high zirconium refractory. Further, the contact flow path 7 has a bottom wall, a side wall, and a top wall, and each of the walls is also formed of a high zirconium refractory such as a ZrO ₂ electroformed refractory. The inner wall surface of the adjusting groove 4 and the inner wall surface of the side wall (at least in contact with the inner wall surface portion of the molten glass) are adhered with platinum or a platinum alloy, and are also disposed on the inner wall surface of the bottom wall and the side wall of the connecting flow path 7 Platinum or platinum alloy is attached. This adjustment groove 4 mainly adjusts the glass to a position suitable for the molding state, and reduces the temperature of the molten glass to a viscosity suitable for molding.

An outflow port is formed on the downstream end side wall of the adjustment groove 4, and the outflow port is transmitted through the narrow contact flow path 8 at the upstream end, and communicates with the molding device 5 at the downstream end of the adjustment groove 4.

The molding apparatus 5 is a sheet glass molding apparatus used for molding a substrate glass for a display such as a liquid crystal panel glass, for example, an overflow down-draw apparatus. The inner wall surface of the bottom wall and the side wall of the contact flow path 8 is provided with platinum or a platinum alloy.

In the present embodiment, the "supply flow path" means the contact flow path 8 provided from the downstream flow path 6 provided downstream of the melting furnace to the upstream end of the molding apparatus. Further, although the glass manufacturing equipment including the melting kiln, the clarification tank, the adjustment tank, and the molding apparatus has been exemplified as described above, for example, a stirring for homogenizing the glass may be provided between the adjustment tank and the molding apparatus. groove. Further, each of the above devices is exemplified by attaching platinum or a platinum alloy to a refractory, but it is of course possible to use A device consisting of platinum or platinum alloy itself.

A method of manufacturing glass using the glass manufacturing apparatus having the above configuration will be described.

First, the glass raw material is blended into a glass having a composition of SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (one or more of RO-based MgO, CaO, BaO, SrO, and ZnO). Specifically, the glass raw material is formulated to contain SiO ₂ : 50 to 70%, Al ₂ O ₃ : 10 to 25%, B ₂ O ₃ : 8.4 to 20%, MgO: 0 to 10%, CaO. : 3 to 15%, BaO: 0 to 10%, SrO: 0 to 10%, ZnO: 0 to 10%, TiO ₂ : 0 to 5%, and P ₂ O ₅ : 0 to 5% of glass. Further, in addition to the above components, various components such as a clarifying agent may be added. However, it is extremely important to prevent the ZrO ₂ or SnO ₂ component from being mixed into the glass raw material as much as possible. Further, when such components are deliberately used, it is necessary to carefully consider the amount of addition from the manufacturing equipment and carefully determine the amount of addition. Further, when it is desired to increase the amount of moisture of the glass, a raw material such as a hydroxylate is used.

Next, the prepared glass raw material is put into the melting kiln 2 to be melted and vitrified. A voltage is applied to the electrodes in the melting kiln 2, and the glass is directly energized and heated. Moreover, the glass is heated from above by the combustion flame of the burner. Accordingly, the glass is melted at a high temperature of about 1,500 to 1,650 °C. Further, when the side wall and the electrode are sufficiently cooled and simultaneously melted, the melting of ZrO ₂ or SnO ₂ can be effectively suppressed.

The molten glass which has been vitrified in the melting kiln 2 is introduced into the clarification tank 3 through the communication flow path 6. Although the initial bubbles generated during the vitrification reaction are contained in the molten glass, in the clarification tank 3, the initial bubbles are removed by the expansion of the clarified gas released from the clarifier component.

The clarified molten glass in the clarification tank 3 is introduced into the adjustment tank through the venting flow path 7. The molten glass introduced into the adjustment tank 4 is at a high temperature and has a low viscosity, and cannot be directly molded by the molding apparatus in this state. Here, it is convenient to use the adjustment groove to lower the temperature of the glass and adjust it to a viscosity suitable for molding.

The molten glass which has been adjusted to be viscous by the adjustment groove 4 is introduced into the overflow down-feeding device through the contact flow path 8, and is formed into a thin plate shape. Then, cutting, end surface processing, or the like is performed to obtain a substrate glass composed of alkali-free glass.

According to the above method, the glass obtained from the melting kiln will be contacted only with less contaminated platinum or platinum alloy, without being exposed to a high zirconium refractory or the like, and supplied to the molding apparatus, so that excessive mixing of ZrO ₂ is not caused. In addition, the content of SnO ₂ can be tightly controlled. Moreover, it is also possible to adjust for moisture. Therefore, the obtained alkali-free glass can form a ZrO ₂ content of 0.6% or less, a SnO ₂ content of 0.3% or less, and a β-OH value of 0.2/mm or more. The composition is less likely to cause devitrification and is excellent in meltability. Glass.

(Example 3)

Next, the glass produced by the method of the present invention will be described.

First, glass materials such as cerium, alumina, boric acid, calcium carbonate, and cerium nitrate are blended and mixed according to % by mass: SiO ₂ : 64%, Al ₂ O ₃ : 16%, B ₂ O ₃ : 11% , CaO: 8%, SrO: 1% composition. Further, both the ZrO ₂ content and the SnO ₂ content in the above raw materials are 0.01% or less. Further, the clarifying agent used was cerium pentoxide in an amount of 1.0% in terms of Sb ₂ O ₃ .

Next, the glass raw material was supplied to a melting kiln composed of a high zirconium refractory, and direct electric heating and oxycombustion heating by a SnO ₂ electrode were used in combination, and the mixture was melted at a maximum temperature of 1,650 °C. Next, in the clarification tank and the adjustment tank, the molten glass is clarified and homogenized, and adjusted to a viscosity suitable for molding. Then, after the molten glass was supplied to the overflow down-drawing device and formed into a plate shape, a glass sample having a thickness of 0.7 mm was obtained by cutting. Further, the molten glass obtained from the melting kiln is supplied to the molding apparatus while being in contact with only platinum or a platinum alloy.

The content of ZrO ₂ and SnO ₂ and the β-OH value of the glass were confirmed for the obtained glass sample, and the phenomenon of devitrification or the like was evaluated. The results are shown in Table 3.

The ZrO ₂ and SnO ₂ contents in the glass were confirmed by fluorescent X-ray analysis.

The β-OH value of the glass was measured by a FT-IR (Fourier transform infrared spectro-photometer) to measure the transmittance of the glass, and was obtained by the following formula.

β-OH value=(1/X)log10(T ₁ /T ₂ ) X: glass thickness (mm) T ₁ : light transmittance (%) in reference wavelength 3846 cm ^-1 T ₂ : absorption wavelength at 3600 cm ^- Minimum transmittance near ¹ (%)

The devitrification property was 10 cm ² parts of the obtained substrate glass, and the presence or absence of devitrification was observed by a microscope.

The clarification system counts the number of bubbles of 100 μm or more in the glass substrate, and evaluates by converting the number of bubbles to an average of 1 kg.

Density is measured using the well-known sub-mimimeter method.

The coefficient of thermal expansion is measured by a dilatometer to measure the average coefficient of thermal expansion in the temperature range of 30 to 380 °C.

The strain point and the cold point were measured in accordance with the method of ASTM C336-71.

The softening point was measured in accordance with the method of ASTM C338-73. Further, each temperature corresponding to the viscosity of 10 ⁴ , 10 ³ , and 10 ^2.5 was measured by a platinum ball drawing method.

The alkali-free glass which can be manufactured according to the method of the present invention is not only suitable for display applications, but also can be used for image sensors such as a charge coupled device (CCD), a double contact solid image sensor (CIS), Glass for solar cells Glass substrate material.

1‧‧‧Glass manufacturing equipment

2‧‧‧melting kiln

3‧‧‧Clarification tank

4‧‧‧Adjustment slot

5‧‧‧Molding device

6,7,8‧‧‧Contact flow path

Fig. 1 is a schematic explanatory view showing a glass manufacturing apparatus used in the production method of the present invention.

1‧‧‧Glass manufacturing equipment

2‧‧‧melting kiln

3‧‧‧Clarification tank

4‧‧‧Adjustment slot

5‧‧‧Molding device

6,7,8‧‧‧Contact flow path

Claims (6)

A method for producing an alkali-free glass, comprising: preparing a raw material to have SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (one or more of RO-based MgO, CaO, BaO, SrO, and ZnO) a mixing step of a glass raw material having a composition, wherein the glass raw material has a density of 2.55 g/cm ³ or less and an average thermal expansion coefficient of 25 to 40×10 ^-7 /° C. at a strain point in a temperature range of 30 to 380 ° C a melting step of melting the glass raw material; a supplying step of supplying the molten glass to the molding apparatus; and a molding step of molding the molten glass supplied to the molding apparatus into a predetermined shape, wherein the raw material is blended into a glass The content of the ZrO ₂ contained in the raw material (excluding the cullet) is 0.01% by mass or less; and the glass raw material is melted by a melting kiln using a high zirconium refractory so that the ZrO ₂ content of the molten glass becomes 0.01 to 0.6% by mass, SnO _{2 after the} content becomes 0.005 to 0.3% by mass, and the β-OH value becomes 0.2 to 0.65/mm; the molten glass is supplied to the molding device by a supply passage formed of at least a portion in contact with the molten glass by platinum or a platinum alloy; Among them, before The supply passage is an integral device provided between the aforementioned melting kiln and the aforementioned molding device. The method for producing an alkali-free glass according to the first aspect of the invention, wherein the glass raw material is melted by direct electric heating. In the method of producing a non-alkali glass according to the _second aspect of the invention, the electrode is selected from the SnO ₂ electrode, the Pt electrode, and the Mo electrode, and the direct current heating is performed. A method for producing an alkali-free glass according to the first aspect of the invention, wherein the molten glass is formed into a plate shape. The method for producing an alkali-free glass according to claim 1 or 4, wherein the molten glass is formed into a plate shape by an overflow down-draw method. The method for producing an alkali-free glass according to the first aspect of the invention, wherein the raw material is formulated to contain SiO ₂ : 50 to 70% by mass percentage, Al ₂ O ₃ : 10 to 25%, and B ₂ O ₃ : 8.4 to 20%, MgO: 0 to 10%, CaO: 3 to 15%, BaO: 0 to 10%, SrO: 0 to 10%, ZnO: 0 to 10%, TiO ₂ : 0 to 5%, P ₂ O ₅ : 0 to 5% of glass raw material.