JP5105571B2 - Method for producing alkali-free glass - Google Patents

Description

  The present invention relates to an alkali-free glass used for flat display substrates such as liquid crystal displays and EL displays.

  Conventionally, alkali-free glass substrates have been widely used as flat display substrates such as liquid crystal displays and EL displays.

  In particular, electronic devices such as thin film transistor type active matrix liquid crystal displays (TFT-LCDs) are thin and have low power consumption. Therefore, they are suitable for various applications such as car navigation, digital camera viewfinders, and recently PC monitors and TVs in use.

  In the TFT-LCD panel manufacturer, after producing a plurality of devices on a glass substrate (base plate) formed by a glass manufacturer, the product is divided and cut into devices, thereby improving productivity. Cost reduction is planned. In recent years, devices such as TV monitors and personal computer monitors have been required to be large in size, and a glass substrate having a large area of 1000 × 1200 mm has been required in order to obtain a large number of these devices. .

  Further, in portable devices such as mobile phones and notebook computers, weight reduction of devices is required for convenience when being carried, and weight reduction is also required for glass substrates. In order to reduce the weight of the glass substrate, it is effective to reduce the thickness of the substrate. At present, the standard thickness of the glass substrate for TFT-LCD is very thin, about 0.7 mm.

  However, the large and thin glass substrate as described above has a large deflection due to its own weight, which is a big problem in the manufacturing process.

  That is, this type of glass substrate is subjected to processes such as cutting, slow cooling, inspection, and washing after being formed by a glass manufacturer. During these steps, the glass substrate is taken in and out of a cassette having a plurality of stages of shelves. This cassette can be held in the horizontal direction by placing both sides or three sides of the glass substrate on the shelf formed on the left and right inner two surfaces or the left and right and inner three surfaces. However, because large and thin glass substrates have a large amount of deflection, when a glass substrate is placed in a cassette shelf, part of the glass substrate may come into contact with the cassette or another glass substrate, When taking out the glass substrate from the shelf, the glass substrate is likely to swing and become unstable. In addition, the same problem occurs in display makers because the same type of cassette is used.

  The amount of deflection due to the weight of the glass substrate varies in proportion to the density of the glass and in inverse proportion to the Young's modulus. Therefore, in order to keep the amount of deflection of the glass substrate small, it is necessary to increase the specific Young's modulus represented by the ratio of Young's modulus / density. In order to increase the specific Young's modulus, a glass material with a high Young's modulus and a low density is required. Can be thickened. Since the amount of glass deflection changes in inverse proportion to the square of the plate thickness, the effect of reducing the deflection by increasing the plate thickness is very large. Lowering the density of the glass has a great effect on reducing the weight of the glass, so the density of the glass should be as small as possible.

  In general, this kind of alkali-free glass contains a relatively large amount of alkaline earth metal oxide. In order to reduce the density of glass, it is effective to reduce the content of alkaline earth metal oxide, but since alkaline earth metal oxide is a component that promotes the melting property of glass, its When the content is reduced, the meltability is lowered. When the meltability of the glass is lowered, internal defects such as bubbles and foreign matters are likely to occur in the glass. Bubbles and foreign substances in the glass hinder the transmission of light, which is a fatal defect for glass substrates for displays. To suppress such internal defects, the glass must be melted at a high temperature for a long time. Don't be. On the other hand, melting at a high temperature increases the burden on the glass melting furnace. The refractory used in the kiln is eroded more vigorously as the temperature rises, and the life cycle of the kiln becomes shorter.

  In addition, thermal shock resistance is an important requirement for this type of glass substrate. Even if chamfering is performed on the end surface of the glass substrate, fine scratches and cracks are present, and if the tensile stress due to heat is concentrated on the scratches and cracks, the glass substrate sometimes breaks. The glass breakage not only lowers the operating rate of the line, but also causes a fine glass powder generated at the time of breakage to adhere to the glass substrate and cause a disconnection failure or a patterning failure.

  By the way, recent development direction of TFT-LCD includes high performance such as high definition, high speed response, high aperture ratio, etc. in addition to large screen and light weight. Polycrystalline silicon TFT-LCD (p-Si TFT-LCD) has been actively developed for the purpose of reducing the weight and weight. In the conventional p-Si • TFT-LCD, the manufacturing process temperature was as high as 800 ° C. or higher, so that only a quartz glass substrate could be used. However, due to recent developments, the manufacturing process temperature has dropped to 400-600 ° C. As with amorphous silicon TFT-LCDs (a-Si TFT-LCDs) currently produced in large quantities, alkali-free glass substrates have been developed. It has come to be used.

The manufacturing process of p-Si TFT-LCD has more heat treatment processes than the manufacturing process of a-Si TFT-LCD, and the glass substrate is repeatedly subjected to rapid heating and rapid cooling, so the thermal shock to the glass substrate is more It gets bigger. Furthermore, as described above, the glass substrate is enlarged, and not only the glass substrate is likely to have a temperature difference, but also the probability of occurrence of minute scratches and cracks on the end surface is increased, and the substrate is destroyed during the thermal process. Probability increases. The most fundamental and effective method for solving this problem is to reduce the thermal stress resulting from the difference in thermal expansion. Therefore, a glass having a low thermal expansion coefficient is required. Further, when the difference in thermal expansion from the thin film transistor (TFT) material increases, warpage occurs in the glass substrate, and thus approximates the thermal expansion coefficient (about 30 to 33 × 10 ⁻⁷ / ° C.) of the TFT material such as p-Si. It is also required to have a thermal expansion coefficient.

  Moreover, although the manufacturing process temperature of p-Si * TFT-LCD has recently decreased, it is still considerably higher than the manufacturing process temperature of a-Si * TFT-LCD. If the heat resistance of the glass substrate is low, when the glass substrate is exposed to a high temperature of 400 to 600 ° C. during the manufacturing process of the p-Si • TFT-LCD, minute dimensional shrinkage called thermal shrinkage occurs, which is the TFT. May cause a display defect due to a shift in the pixel pitch. Further, if the heat resistance of the glass substrate is lower, the glass substrate may be deformed or warped. Furthermore, in order to prevent the glass substrate from being thermally contracted in the liquid crystal manufacturing process such as film formation, the glass having excellent heat resistance is required.

  Further, a transparent conductive film, an insulating film, a semiconductor film, a metal film, and the like are formed on the surface of the glass substrate for TFT-LCD, and various circuits and patterns are formed by photolithography etching (photo etching). In these film formation and photoetching steps, the glass substrate is subjected to various heat treatments and chemical treatments.

Therefore, when alkali metal oxides (Na ₂ O, K ₂ O, Li ₂ O) are contained in the glass, alkali ions diffuse into the deposited semiconductor material during the heat treatment, resulting in deterioration of film characteristics. It is considered to be inviting, and is required to have substantially no alkali metal oxide and chemical resistance that does not deteriorate due to various acids and alkalis used in the photoetching process. .

  The glass substrate for TFT-LCD is mainly formed by a down draw method or a float method. Examples of the downdraw method include a slot downdraw method and an overflow downdraw method. A glass substrate formed by the downdraw method does not need to be polished, and thus has an advantage that costs can be easily reduced. However, when a glass substrate is formed by the down draw method, the glass is easily devitrified, so that a glass having excellent devitrification resistance is required.

In view of this, alkali-free glass for substrates has been proposed which satisfies the above-mentioned various characteristics and is characterized by a particularly low density, low expansion and high strain point. (For example, Patent Document 1)
JP 2002-308643 A

The alkali-free glass disclosed in Patent Document 1 has a melting temperature (temperature corresponding to 10 ^2.5 poise) of about 1580 ° C. or higher and requires high-temperature melting, but the density is 2.45 g / cm ³ or less, 30 to The average thermal expansion coefficient in the temperature range of 380 ° C. is 25 to 36 × 10 ⁻⁷ / ° C., and the strain point is 640 ° C. or higher, which satisfies the above requirements.

However, such a low density, when produced on an industrial scale the alkali-free glass of low Rise Zhang, devitrification occurs during forming by a slight variation in the manufacturing conditions.

An object of the present invention may be produced on an industrial scale, it is to provide a manufacturing how moldable alkali-free glass without causing devitrification in the glass.

When producing alkali-free glass that requires high-temperature melting on an industrial scale, it is a high-zirconia refractory with excellent corrosion resistance from the viewpoint of extending the life of manufacturing equipment. (For example, a clarification tank, an adjustment tank, etc.) can be considered. However, according to the study by the present inventors, when alkali-free glass as disclosed in Patent Document 1 is melted in a production facility using a high zirconia refractory, the ZrO ₂ component is eluted from the refractory and the glass. It has been found that the ZrO ₂ concentration in the medium is increased and it is very easy to devitrify, and the present invention has been proposed.

That is, the manufacturing method of the alkali-free glass of the present _{invention, SiO 2 -Al 2 O 3 -B} 2 O 3 -RO (RO is MgO, CaO, BaO, 1 or more SrO and ZnO) have a composition of type The density is 2.45 g / cm ³ or less, the average coefficient of thermal expansion in the temperature range of 30 to 380 ° C. is 25 to 36 × 10 ⁻⁷ / ° C., and the content of BaO is 0 to 0.1% by mass (provided that it is not more than 0. A step of preparing the raw material so as to be an alkali-free glass ( excluding 1% by mass), a melting step of melting the glass raw material in a melting furnace using a high zirconia refractory, and at least a part of platinum or platinum The method includes a supply step of supplying molten glass to a forming device through a supply path formed of an alloy, and a forming step of forming the molten glass supplied to the forming device into a predetermined shape. In the present invention, cullet is also included in the glass raw material. Incidentally, “non-alkali” in the present invention means that the alkali metal oxide (Li ₂ O, Na ₂ O, K ₂ O) is 0.2 mass% or less.

  The method for producing an alkali-free glass of the present invention is characterized in that the glass is melted by direct current heating.

In addition, the alkali-free glass manufacturing method of the present invention is characterized in that direct heating is performed using one or more electrodes selected from SnO ₂ electrodes, Pt electrodes, and Mo electrodes.

  The method for producing alkali-free glass of the present invention is characterized in that glass is formed into a plate shape.

  In addition, the alkali-free glass manufacturing method of the present invention is characterized in that the glass is formed into a plate shape by an overflow down draw method.

Moreover, the method for producing alkali-free glass of the present invention is characterized in that the obtained glass has a ZrO ₂ content of 0.6% or less by mass percentage.

The method for producing an alkali-free glass of the present invention is characterized in that SnO ₂ content of the glass obtained is not more than 0.3% by mass percentage.

  Further, the alkali-free glass production method of the present invention is characterized in that the obtained glass has a β-OH value of 0.2 / mm or more.

The method for producing alkali-free glass of the present invention, SiO ₂ 50-70% in percent by _{mass, Al 2 O 3 10~25%,} B 2 O 3 8.4~20%, 0~10% MgO, CaO 3 -15%, BaO 0-0.1 % (excluding 0.1%) , SrO 0-10%, ZnO 0-10%, TiO ₂ 0-5%, P ₂ O ₅ 0-5% The raw material is prepared so as to become glass.

According to the production method of the present invention, a high zirconia refractory having high corrosion resistance is used in the melting furnace, and stable operation over a long period of time can be performed even when non-alkali glass that requires high-temperature melting is melted. . In addition, platinum or a platinum alloy is used in at least a part of the supply path for introducing the molten glass from the melting furnace to the molding apparatus, and the glass is less contaminated by elution of ZrO ₂ . For this reason, glass can be shape | molded without producing devitrification. It is possible to further improve devitrification by strictly regulating elution from the electrode, impurities of the raw material, or SnO ₂ contained in the glass as a fining agent. If the moisture content of the glass is increased, the viscosity of the glass can be reduced. Therefore, it is particularly advantageous when producing an alkali-free glass that is melted at a high temperature, particularly an alkali-free glass having reduced devitrification due to reduction in density and expansion by reducing alkaline earth components.

The alkali-free glass produced by the method of the present invention, low density, low Rise Zhang was Wami amount is small, excellent thermal shock resistance, also warpage hardly occurs. Moreover, it has a feature that it is not easily devitrified even if it is produced on an industrial scale. Therefore, it is suitable as glass for substrates of liquid crystal displays and EL displays.

The glass produced by the method of the present invention is a non-alkali glass having a composition of SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO and ZnO). It is. Of these low-density requiring a hot melt, it is suitable for the production of glass of a low Rise Zhang.

The glass has a ZrO ₂ content by mass of 0.6% or less, preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.2% or less, and optimally 0.1%. In addition, it is preferable to contain 0.01% or more, particularly 0.02% or more. If ZrO ₂ exceeds 0.6%, devitrification tends to occur.

From the viewpoint of improvement in devitrification, the better ZrO ₂ is small. This tendency becomes more prominent as the glass has a lower density, lower expansion, and higher strain point. However, ZrO ₂ has a function of improving the chemical durability of the alkali-free glass even when added in a small amount, and it is desirable to contain this. Further, completely preventing ZrO ₂ mixed as an impurity from the glass raw material causes an increase in raw material cost. Furthermore, there is a possibility that ZrO ₂ is mixed from the glass cullet (for example, when a glass produced using a high zirconia refractory is used as the cullet, the possibility that the cullet contains a ZrO ₂ component is very high. ). Glass cullet is a preferred raw material for glass that is difficult to melt, such as alkali-free glass. Moreover, with the recent increase in environmental awareness, there is an increasing need to recycle and use glass cullet as a raw material. For these reasons, in the present invention, it is desirable to set the lower limit of ZrO ₂ to 0.01%. By containing 0.01% or more, particularly 0.02% or more of ZrO ₂ , improvement in the chemical durability of the glass can be expected. Further, with respect to ZrO ₂ , it is not necessary to use an excessively high-purity raw material, and an increase in raw material cost can be avoided. In addition, glass cullet can be used.

Further, the glass has a SnO ₂ content of 0.3% or less, particularly 0.28% or less, preferably 0.005% or more, particularly 0.02% or more, and further preferably 0.002% or less. It is desirable that it is 03% or more. SnO ₂ is not an essential component in the present invention, but is a component that can be added as a fining agent. In the case of electrically melting the glass with SnO ₂ electrode, SnO ₂ which is an electrode component is dissolved in the glass. The SnO ₂ content is closely related to the devitrification of the glass due to ZrO _{2. When} the SnO ₂ content is large, devitrification tends to occur. As in the case of ZrO _2, the smaller the SnO ₂ , the better from the viewpoint of improving devitrification. However, SnO ₂ is a few components that exhibit a clarification effect at high temperatures, and a high clarification effect can be expected in a small amount. Therefore, in the glass of the present invention that requires high-temperature melting and is difficult to clarify, it contains SnO ₂ in an amount of 0.005% or more, particularly 0.01% or more in order to improve the clarity or reduce the amount of As ₂ O ₃ used. It is desirable. Note refining effect of SnO ₂ is the same even SnO ₂ eluted from the electrode.

Glass that is by Ri Manufacturing the production method of the present invention has a density of 2. 45 g / cm ³ or less, good Mashiku is 2.42 g / cm ³ hereinafter, the average thermal expansion coefficient of 2 5~36 × 10 ^-7 / ℃ in the temperature range of 30 to 380 ° C., the good Mashiku 28-35 × a 10 ^-7 / ° C. of glass. Glass having such characteristics, generally requires a high temperature melting, excellent thermal shock resistance, without the occurrence of warp to approximate the thermal expansion coefficient of a TFT material, also can be lightweight, the amount of deflection there is an advantage that Ru can be reduced.
Further, if the strain point of the glass is 640 ° C. or higher, preferably 650 ° C. or higher, it is more preferable because the thermal shock resistance is further improved and the thermal shrinkage can be reduced.

The above-described SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ —RO-based glass generally has a temperature corresponding to 10 ^2.5 poise of 1580 ° C. or higher and requires high-temperature melting. In such a glass that requires high-temperature melting, reducing the viscosity as much as possible leads to improvement of the meltability. Increasing the water content of the glass is effective in reducing the high temperature viscosity. Therefore, in the substrate glass of the present invention, the moisture content of the glass is expressed by a β-OH value and is 0.2 / mm or more, particularly 0.25 / mm or more, further 0.3 / mm or more, preferably 0. It is preferable to adjust to 4 / mm or more. From the viewpoint of improving the meltability, the higher the β-OH value, the better, but on the other hand, the higher the value, the lower the strain point. For these reasons, it is desirable that the upper limit of the β-OH value is 0.65 / mm or less, particularly 0.6 / mm or less. Note that the β-OH value of glass is determined by the following equation in the infrared absorption spectrum of glass.

β-OH value = (1 / X) log 10 (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
In addition to the above characteristics, the liquidus temperature is 1150 ° C. or lower (especially 1130 ° C. or lower, more preferably 1100 ° C. or lower), and the viscosity at the liquidus temperature is 10 ^5.4 dPa · s or higher (especially 10 ^6.0 dPa · s or higher). Is desirable. By satisfying this condition, devitrification does not occur even if it is formed into a plate shape by the downdraw method, and it is possible to reduce the production cost by omitting the polishing step. Further, when the 10% HCl aqueous solution was treated at 80 ° C. for 24 hours, the erosion amount was 10 μm or less, and when the 10% HCl aqueous solution was treated at 80 ° C. for 1 hour, the surface was visually observed. When no white turbidity or roughness is observed, and the 130 BHF solution is treated at 20 ° C. for 30 minutes, the erosion amount is 0.8 μm or less, and the 63 BHF solution is treated at 20 ° C. for 30 minutes. It is desirable that no white turbidity or roughness is observed by visual surface observation. The specific Young's modulus is desirably 27.5 GPa / g · cm ⁻³ or more (particularly 29.0 GPa · s or more). By satisfying this condition, the amount of deflection of the glass substrate can be reduced. Furthermore, if the temperature of the glass melt at a viscosity of 10 ^2.5 dPa · s is 1650 ° C. or lower, the meltability will be good.

Further a composition example of the glass which is preferably produced by the production method of the present invention, SiO ₂ 50-70% in percent by _{mass, Al 2 O 3 10~25%,} B 2 O 3 8.4~20%, MgO 0 ~10%, CaO 3~15%, BaO 0~ 0.1% ( excluding 0.1%), SrO 0~10%, 0~10% ZnO, TiO 2 0~5%, P 2 O 5 Glass containing 0 to 5% is mentioned. Glass having such a composition generally requires high-temperature melting, but the strain point, density, thermal expansion coefficient, chemical resistance, specific Young's modulus, meltability, and the like required for substrates such as liquid crystal displays as described above, It is possible to obtain characteristics such as moldability. The reason for limiting the composition range will be described below.

The content of SiO ₂ is 50 to 70%. If it is less than 50%, chemical resistance, particularly acid resistance is deteriorated, and it is difficult to reduce the density. On the other hand, if it exceeds 70%, the high-temperature viscosity becomes high, the meltability becomes poor, and a defect of devitrified foreign matter (cristobalite) tends to occur in the glass. The SiO ₂ content is preferably 58% or more, particularly 60% or more, more preferably 62% or more, and 68% or less, particularly preferably 66% or less.

The content of Al ₂ O ₃ is 10 to 25%. If it is less than 10%, it becomes difficult to set the strain point to 640 ° C. or higher. Al ₂ O ₃ has a function of improving the Young's modulus of the glass and increasing the specific Young's modulus, but if it is less than 10%, the Young's modulus is lowered. The content of Al ₂ O ₃ is preferably 12% or more, particularly preferably 14.5% or more, and is preferably 19% or less, particularly preferably 18.0% or less. If it exceeds 19%, the liquidus temperature increases and the devitrification resistance decreases.

B ₂ O ₃ is a component that acts as a flux and lowers viscosity to improve meltability. On the other hand, a glass substrate used for a liquid crystal display is required to have high acid resistance, but the acid resistance tends to decrease as the amount of B ₂ O ₃ increases. The content of B ₂ O ₃ is 8.4 to 20%. If it is less than 8.4%, the function as a flux becomes insufficient and the buffered hydrofluoric acid resistance deteriorates. On the other hand, if it exceeds 20%, the strain point of the glass is lowered, the heat resistance is lowered and the acid resistance is deteriorated. Furthermore, since the Young's modulus decreases, the specific Young's modulus decreases. The content of B ₂ O ₃ is preferably 8.6% or more, 15% or less, particularly 14% or less, more preferably 12% or less.

  The content of MgO is 0 to 10%. MgO lowers the high temperature viscosity without lowering the strain point and improves the meltability of the glass. In addition, the alkaline earth metal oxide is most effective in reducing the density. However, if it is contained in a large amount, the liquidus temperature rises and the devitrification resistance decreases. In addition, MgO reacts with buffered hydrofluoric acid to form a product, which may adhere to the element on the glass substrate surface or adhere to the glass substrate and cause it to become cloudy. is there. Therefore, the content of MgO is 0 to 2%, particularly 0 to 1%, more preferably 0 to 0.5%, and preferably it is not substantially contained.

CaO is also a component that lowers the high temperature viscosity and remarkably improves the meltability of the glass without lowering the strain point, like MgO, and its content is 3 to 15%. This kind of alkali-free glass substrate is generally difficult to melt, and in order to supply a large amount of a high-quality glass substrate at a low cost, it is important to improve its melting property. In the glass composition system of the present invention, reducing SiO ₂ is most effective for increasing the meltability. However, reducing the amount of SiO ₂ results in extremely low acid resistance and increases the density and thermal expansion of the glass. This is not preferable because the coefficient increases. Therefore, in this invention, in order to improve the meltability of glass, 3% or more of CaO is contained. On the other hand, if the CaO content exceeds 15%, the buffered hydrofluoric acid resistance of the glass deteriorates, and the glass substrate surface is easily eroded, and the reaction product adheres to the glass substrate surface, causing the glass to become cloudy and further thermal expansion. Since the coefficient becomes too high, it is not preferable. The CaO content is preferably 4% or more, particularly 5% or more, and more preferably 6% or more, and is preferably 12% or less, particularly 10% or less, and more preferably 9% or less.

BaO is a component that improves the chemical resistance and devitrification resistance of glass, but it is a component that greatly increases the density and thermal expansion coefficient of glass, and is not included as much as possible in the case of low density and low expansion. Is preferred. Also, a large amount is not preferable from the viewpoint of the environment. The content of BaO is 0 . 1% or less (excluding 0.1%) .

  SrO is a component that improves the chemical resistance and devitrification resistance of glass, and is contained in an amount of 0 to 10%. However, if contained in a large amount, the density and thermal expansion coefficient of the glass increase. The SrO content is preferably 4% or less, particularly 2.7%, and more preferably 1.5% or less.

  Further, BaO and SrO are components having a property of particularly improving BHF resistance. Therefore, in order to improve the BHF resistance, it is preferable to contain these components in a total amount of 0.1% or more (preferably 0.3% or more, more preferably 0.5% or more). However, as described above, if too much BaO and SrO are contained, the density and thermal expansion coefficient of the glass increase, so it is desirable to keep the total amount at 6% or less. Within that range, the total amount of BaO and SrO is preferably contained as much as possible from the viewpoint of improving BFH resistance and devitrification resistance, while reducing the density and thermal expansion coefficient, or environmental aspects. From the viewpoint of consideration, it is desirable to reduce as much as possible.

  ZnO is a component that improves the buffered hydrofluoric acid resistance of the glass substrate and improves the meltability. However, if it is contained in a large amount, it tends to devitrify the glass, lowering the strain point, and increasing the density. Absent. Therefore, the content is 0 to 10%, preferably 0 to 7%, more preferably 5% or less, further preferably 3% or less, particularly 0.9% or less, and most preferably 0.5% or less.

  Each component of MgO, CaO, BaO, SrO, ZnO is mixed and contained, so that the liquidus temperature of the glass is remarkably lowered, and it is difficult to produce crystalline foreign matters in the glass, thereby improving the meltability and moldability of the glass. There is an effect to improve. However, if the total amount of these is small, the function as a flux is not sufficient, the meltability is deteriorated, the thermal expansion coefficient becomes too low, and the consistency with the TFT material is lowered. On the other hand, when the amount is too large, the density increases, the weight of the glass substrate cannot be reduced, and the specific Young's modulus decreases, which is not preferable. The total amount of these components is preferably 6 to 20%, particularly 6 to 15%, and more preferably 6 to 12%.

TiO ₂ is a component that improves the chemical resistance of glass, especially acid resistance, and lowers the viscosity at high temperature to improve the melting property. It is not preferable as a glass substrate. Thus TiO ₂ is 0 to 5%, should be regulated preferably 0-3%, more preferably 0 to 1%.

P ₂ O ₅ is a component that improves the devitrification resistance of the glass. However, if contained in a large amount, P ₂ O ₅ is not preferable because phase separation and milk white occur in the glass and the acid resistance is significantly deteriorated. Therefore, P ₂ O ₅ should be regulated to 0 to 5%, preferably 0 to 3%, more preferably 0 to 1%.

In addition to the above components, in the present invention, Y ₂ O ₃ , Nb ₂ O ₃ , and La ₂ O ₃ can be contained up to about 5% in total. These components have a function of increasing the strain point, Young's modulus, etc., but if they are contained in a large amount, the density increases, which is not preferable. Furthermore, as long as the glass properties are not impaired, the total amount of clarifier such as metal powder such as As ₂ O ₃ , Sb ₂ O ₃ , Sb ₂ O ₅ , F ₂ , Cl ₂ , SO ₃ , C, Al, Si, etc. Up to 5%. Further, CeO ₂ , Fe ₂ O _{3 and the} like can be contained as a fining agent in a total amount of up to 5%. As ₂ O ₃ is desirably not used from the environmental viewpoint.

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

In the blending step, glass raw materials are blended so that the glass has a composition of SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO and ZnO). This is a process for preparing a batch. In particular, as described above, the glass has the characteristics that the density is 2.55 g / cm ³ or less, the average thermal expansion coefficient is 25 to 40 × 10 ⁻⁷ / ° C., and the strain point is 640 ° C. or higher in the temperature range of 30 to 380 ° C. Also, by mass percentage, 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 It is desirable to prepare such a glass that contains 10% to 10%, SrO 0 to 10%, ZnO 0 to 10%, TiO ₂ 0 to 5%, and P ₂ O ₅ 0 to 5%.

Further, the ZrO ₂ component that causes devitrification may increase in content due to elution from the refractory in the subsequent melting step. For this reason, it is important to limit the incorporation of ZrO ₂ component from the glass raw material as much as possible, and when it is intended to improve chemical durability, the amount of addition must be kept to a minimum. . If the SnO ₂ component that enhances the devitrification property of ZrO ₂ is electrically melted using a SnO ₂ electrode, the content may increase due to elution from the electrode. For this reason, it is important to limit the mixing from the glass raw material as much as possible, and when it is intentionally used to obtain a clarification effect or the like, the addition amount must be kept to a minimum.

The melting step is a step of melting the raw material in a melting kiln using a high zirconia refractory. As the high zirconia refractory, it is preferable to use a ZrO ₂ electroformed refractory that has excellent corrosion resistance and can be used for a long time. The melting temperature is about 1500 to 1650 ° C. in the case of the alkali-free glass having the above composition.

Moreover, high temperature melting can be easily performed by performing electric melting by direct current heating using a SnO ₂ electrode, a Pt electrode, a Mo electrode or the like. In this case, it goes without saying that there is no problem even if it is melted together with combustion of heavy oil or gas. The type of electrode is not particularly limited, and an appropriate type may be determined in consideration of the life of the electrode, the degree of erosion, and the like. Moreover, the electrode to be used does not necessarily need to be one type, and two or more types of electrodes can be used in combination in consideration of various conditions. For example, when elution of Pt into the glass is a problem, a SnO ₂ electrode or a Mo electrode can be used in a part where the electrode component is easily eluted, and a Pt electrode can be used in other parts. In particular, since the SnO ₂ electrode itself is made of an oxide, it has a feature that it does not adversely affect the glass even if the electrode component is dissolved in the glass.

The supply step is a step of supplying molten glass melted in a melting furnace to a molding apparatus using a supply path formed at least partially from platinum or a platinum alloy. The reason for forming the supply path with platinum or a platinum alloy is to prevent further ZrO ₂ from dissolving into the glass. Further, the penetration of ZrO ₂ affects not only the devitrification property of the glass but also the homogeneity. In order to produce a glass that can be used even if it is not polished, the glass must have high homogeneity, and for this purpose, it is necessary to prevent contamination of the glass due to ZrO ₂ dissolution in the supply path. Using platinum or a platinum alloy in the supply path contributes to maintaining the homogeneity of the glass. Therefore, it is preferable that the number of parts formed of platinum or a platinum alloy is larger. Ideally, the entire contact surface with glass is formed of platinum or a platinum alloy. In addition, a supply path | route points out the whole installation provided between a melting kiln and a shaping | molding apparatus. For example, a clarification tank, an adjustment tank, a stirring tank, and the like, and a communication channel connecting the tanks are included. Further, in the supplying step, it is desirable that the glass is not limited to simply supplying glass to a forming facility, but the glass is clarified and homogenized.

  The “supply path formed of platinum or a platinum alloy” includes not only a supply path made of only platinum or a platinum alloy but also a supply path in which the refractory surface is covered with platinum.

  The forming step is a step of forming the molten glass supplied to the forming apparatus into a predetermined shape. For display applications, the glass is formed into a thin plate using a method such as an overflow downdraw method, a slot downdraw method, a float method, or a rollout method. In particular, molding by the overflow downdraw method is preferable because a glass plate having excellent surface quality can be obtained even when unpolished.

  The alkali-free glass of the present invention can be produced as described above.

In the production method of the present invention, from the viewpoint of preventing devitrification in the molding step, the ZrO ₂ allowable amount should be limited so that the content of the glass to be obtained is 0.6% or less by mass percentage. , Preferably 0.5% or less, more preferably 0.3% or less, further preferably 0.2% or less, and optimally 0.1% or less. Moreover, it is desirable that it is 0.01% or more, especially 0.02% or more. If the ZrO ₂ content in the obtained glass is 0.6% or less, the devitrification can be improved. The amount of ZrO ₂ in the glass is the amount of ZrO ₂ raw material used and impurities in the preparation process, the temperature control of the refractory in the melting process and the adjustment of the current amount, and the area of platinum or platinum alloy used in the supply process. It is possible to adjust by such as.

Similarly, the SnO ₂ tolerance is such that the glass content obtained is 0.3% or less, particularly 0.28% or less in terms of mass percentage, and 0.005% or more, particularly 0.01%. It is preferable to be as described above. If the SnO ₂ content in the obtained glass is 0.3% or less, the occurrence of devitrification due to ZrO ₂ can be significantly suppressed. The amount of SnO ₂ in the glass can be adjusted by controlling the amount of SnO ₂ raw material used and impurities in the blending process, the number of SnO ₂ electrodes used in the melting process, and the temperature control of the electrodes.

  Further, it is preferable to increase the water content of the glass for the purpose of reducing the viscosity of the glass and improving the meltability as much as possible. Specifically, it is preferable to adjust to 0.2 / mm or more, particularly 0.25 / mm or more, more preferably 0.3 / mm or more, particularly 0.4 / mm or more, expressed by β-OH value. . To adjust the moisture content of the glass, select a raw material with a high water content (for example, a hydroxide raw material), add moisture to the raw material, or contain ingredients that reduce the moisture content in the glass, such as chlorine. Methods such as limiting the amount, adopting oxygen combustion during glass melting to increase the amount of moisture in the furnace atmosphere, introducing water vapor directly into the furnace, or performing water vapor bubbling in the molten glass Can be performed.

Tables 1 and 2 show the experimental results showing that the SnO ₂ content affects devitrification caused by ZrO ₂ . Glass 1 contains SiO ₂ 60% by mass, Al ₂ O ₃ 15%, B ₂ O ₃ 10%, CaO 5%, BaO 5%, SrO 5%, and a density of 2.5 g / cm ³ , 30 A glass having a thermal expansion coefficient of 37 × 10 ⁻⁷ / ° C. and a strain point of 655 ° C. at 380 ° C., and glass 2 is SiO ₂ 64%, Al ₂ O ₃ 16%, B ₂ O ₃ 11 in mass%. %, CaO 8%, SrO 1%, a density of 2.4 g / cm ³ , a coefficient of thermal expansion at 30 to 380 ° C. of 32 × 10 ⁻⁷ / ° C., and a strain point of 660 ° C.

Each sample was prepared as follows. First, glass materials were prepared by changing the amount of ZrO _{2 and the} amount of SnO ₂ so as to obtain the above composition. This raw material batch was put in a platinum crucible, melted at 1600 ° C. for 24 hours, and then molded. Thereafter, the obtained glass was pulverized, passed through a standard sieve 30 mesh (500 μm), and the glass powder remaining on 50 mesh (300 μm) was placed in a platinum boat, held in a temperature gradient furnace for 24 hours, and then taken out. With respect to the obtained sample, the maximum temperature at which ZrO ₂ · SiO ₂ crystals were observed in the glass was displayed by microscopic observation. The “-” part in the table indicates that no investigation has been made.

From the above results, it was found that the glass 2 having a reduced density, a low expansion, and a high strain point by reducing alkaline earth components such as BaO easily devitrifies with a small amount of ZrO ₂ . It was also confirmed that devitrification tends to increase as the ZrO ₂ content and the SnO ₂ content increase.

  Next, an embodiment of the method of the present invention will be described based on the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of a glass manufacturing facility 1 for carrying out the manufacturing method of the present invention.

  First, the configuration of the glass manufacturing facility will be described. The glass production facility 1 includes a substantially rectangular melting furnace 2 serving as a molten glass supply source, a clarification tank 3 provided on the downstream side of the melting furnace 2, and an adjustment tank provided on the downstream side of the clarification tank 3. 4 and a molding apparatus 5 provided on the downstream side of the adjustment tank 4, and the melting furnace 2, the clarification tank 3, the adjustment tank 4, and the molding apparatus 5 are connected by communication channels 6, 7, and 8, respectively. ing.

The melting furnace 2 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 a ZrO ₂ electroformed refractory. The side wall is designed to be thin so that the refractory is easily cooled. In addition, a plurality of pairs of electrodes are installed on the lower and bottom walls of the left and right side walls, and a plurality of burners are installed above the left and right side walls. Each electrode is provided with cooling means so that the electrode temperature does not rise excessively. Further, if an oxygen burner is used for the burner and oxygen combustion heating is performed, heating at a higher temperature becomes possible, and the moisture of the glass can be easily increased. The glass can be directly energized and heated by applying electricity between the electrodes. Moreover, the molten glass can be heated from above by radiating the flame of the burner toward the upper space of the molten glass.

  An outlet is formed on the downstream side wall of the melting furnace 2, and the melting furnace 2 and the clarification tank 3 communicate with each other via a narrow communication channel 6 having the outlet at the upstream end. Yes.

The clarification tank 3 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 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 clarification tank 3 has a smaller volume than the melting furnace 2, 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 6 and the inner wall surface of the side wall. In the clarification tank 3, the downstream end of the outflow passage 6 is opened on the upstream side wall. The clarification tank 3 is a part where clarification of the glass is mainly performed, and fine bubbles contained in the glass are levitated and clarified by the clarification gas released from the clarifier, and are removed from the glass.

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

The said adjustment tank 4 has a bottom wall, a side wall, and a ceiling wall, and each of these walls is formed with the high zirconia refractory. The communication channel 7 has a bottom wall, a side wall, 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 4 (at least the inner wall surface part in contact with the molten glass) is lined with platinum or a platinum alloy, and is attached to the bottom wall and the inner wall surface of the side wall of the communication channel 7. Also, platinum or a platinum alloy is lined. The adjustment tank 4 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 on the downstream side wall of the adjustment tank 4, and the molding device 5 communicates with the downstream side of the adjustment tank 4 via a narrow communication channel 8 having the outlet at the upstream end. .

  The forming device 5 is a plate glass forming device used for forming a display substrate glass such as a liquid crystal plate glass, and is, for example, an overflow down draw device. The bottom wall and the inner wall surface of the side wall of the communication channel 8 are lined with platinum or a platinum alloy.

  In addition, the supply path in a present Example points out from the connection flow path 6 provided in the downstream of a melting furnace to the connection flow path 8 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 of manufacturing glass using the glass manufacturing facility having the above-described configuration will be described.

First, a glass raw material is prepared so as to be a glass having a composition of SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO and ZnO). Specifically SiO ₂ 50-70% by mass _{percentage, Al 2 O 3 10~25%,} B 2 O 3 8.4~20%, 0~10% MgO, CaO 3~15%, BaO 0~10 %, SrO 0~10%, 0~10% ZnO, TiO 2 0~5%, to formulate a glass raw material so that the glass containing P ₂ O ₅ 0~5%. In addition to the above, various components such as a refining agent can be added, but it is important to limit the incorporation of ZrO ₂ and SnO ₂ components from glass raw materials as much as possible. In addition, when these components are intentionally used, it is necessary to carefully determine the addition amount after taking into consideration the amount of mixing from the production equipment. When it is desired to increase the moisture content of the glass, for example, a hydroxide raw material is used.

Subsequently, the prepared glass raw material is put into the melting furnace 2 and melted and vitrified. In the melting furnace 2, a voltage is applied to the electrodes and the glass is directly energized and heated. The glass is heated from above by a burner flame. In this way, the glass is melted at a high temperature of about 1500 to 1650 ° C. If melting is performed while sufficiently cooling the side walls and electrodes, elution of ZrO ₂ and SnO ₂ can be effectively suppressed.

  The molten glass vitrified in the melting furnace 2 is guided to the clarification tank 3 through the communication channel 6. The molten glass contains initial bubbles generated during the vitrification reaction. In the clarification tank 3, the initial bubbles are lifted and removed by the clarification gas released from the clarifier component.

  The molten glass clarified in the clarification tank 3 is guided to the adjustment tank through the communication channel 7. The molten glass led to the adjustment tank 4 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 adjustment tank 4 is guided to the overflow downdraw apparatus through the communication channel 8 and formed into a thin plate shape. Furthermore, cutting, end face processing, etc. are given, and the substrate glass which consists of an alkali free glass can be obtained.

According to the above method, the glass that has exited the melting furnace is in contact with only platinum or a platinum alloy with little contamination, and is supplied to the molding apparatus without contact with high zirconia refractories, etc., and excessive ZrO ₂ Mixing does not occur. In addition, the SnO ₂ content can be strictly controlled. Furthermore, the moisture can be adjusted. Therefore, the alkali-free glass obtained can have 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, and devitrification. Is less likely to occur and has excellent meltability.

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

First, silica sand, aluminum oxide, boric acid, calcium carbonate, strontium nitrate so as to have a composition of 64% by mass of SiO ₂ 64%, Al ₂ O ₃ 16%, B ₂ O ₃ 11%, CaO 8%, SrO 1%. Glass raw materials were prepared and mixed. The contents of ZrO ₂ and SnO _{2 in} the raw material were both set to 0.01% or less. Moreover, 1.0% of antimony pentoxide was used as a clarifying agent in terms of Sb ₂ O ₃ .

Next, the glass raw material was supplied to a melting kiln made of a high zirconia refractory, and melted at a maximum temperature of 1650 ° C. by using both direct current heating and oxycombustion heating with a SnO ₂ electrode. Subsequently, the molten glass was clarified and homogenized in a clarification tank and an adjustment tank, and adjusted to a viscosity suitable for molding. Further, the molten glass was supplied to an overflow downdraw apparatus, formed into a plate shape, and then cut to obtain a 0.7 mm thick glass sample. The molten glass exiting the melting kiln is supplied to the molding apparatus while only in contact with platinum or a platinum alloy.

The obtained glass samples, the content of ZrO ₂ and SnO _2, and reaffirmed beta-OH value of the glass were evaluated for the presence of devitrification or the like. The results are shown in Table 3.

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

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

β-OH value = (1 / X) log 10 (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
Regarding devitrification, the presence or absence of devitrified substances was observed with a microscope for 10 m ² of the obtained substrate glass.

  The clarity was evaluated by counting the number of bubbles of 100 μm or more in the glass substrate and converting it to the number of bubbles per kg.

  The density was measured by the well-known Archimedes method.

  The coefficient of thermal expansion was determined by measuring an average coefficient of thermal expansion in a temperature range of 30 to 380 ° C. using a dilatometer.

  The strain point and annealing point were measured based on the method of ASTM C336-71.

The softening point was measured based on the method of ASTM C338-73. Each temperature corresponding to a viscosity of 10 ⁴ , 10 ³ , 10 ^2.5 was measured by a platinum ball pulling method.

  The alkali-free glass that can be produced by the method of the present invention is not only used for displays, but also as a glass substrate material for image sensors such as charge coupled devices (CCD), equal-magnification proximity solid-state imaging devices (CIS), and solar cells. Can also be used.

It is a schematic explanatory drawing of the glass manufacturing equipment used with the manufacturing method method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass manufacturing equipment 2 Melting kiln 3 Clarification tank 4 Adjustment tank 5 Molding device 6, 7, 8 Connection flow path

Claims (9)

It has a composition of SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ —RO (RO is one or more of MgO, CaO, BaO, SrO and ZnO), and has a density of 2.45 g / cm ³ or less, 30 to An alkali-free glass having an average thermal expansion coefficient of 25 to 36 × 10 ⁻⁷ / ° C. in a temperature range of 380 ° C. and a BaO content of 0 to 0.1 mass% (excluding 0.1 mass%). The molten glass is formed by a process of preparing the raw material, a melting process of melting the glass raw material in a melting kiln using a high zirconia refractory, and a supply path at least partially formed of platinum or a platinum alloy A method for producing alkali-free glass, comprising: a supplying step for supplying to the apparatus; and a forming step for forming the molten glass supplied to the forming apparatus into a predetermined shape. The method for producing alkali-free glass according to claim 1, wherein the glass is melted by direct current heating. _{3. The} method for producing alkali-free glass according to claim 2, wherein direct heating is carried out using one or more electrodes selected from SnO ₂ electrodes, Pt electrodes, and Mo electrodes. The method for producing alkali-free glass according to claim 1, wherein the glass is formed into a plate shape. The method for producing alkali-free glass according to claim 1 or 4, wherein the glass is formed into a plate shape by an overflow down draw method. Any of the manufacturing method of the alkali-free glass according to claim 1 to 5, ZrO ₂ content of the resulting glass is equal to or less than 0.6% by mass percentage. The method for producing an alkali-free glass according to any one of claims 1 to 6, wherein the SnO ₂ content of the obtained glass is 0.3% or less by mass percentage. The β-OH value of the obtained glass is 0.2 / mm or more, The method for producing alkali-free glass according to any one of claims 1 to 7. _SiO 2 _50-70% in percent by _{mass, Al 2 O 3 10~25%,} B 2 O 3 8.4~20%, 0~10% MgO, CaO 3~15%, BaO 0~ 0.1% ( (Except 0.1%) , SrO 0 to 10%, ZnO 0 to 10%, TiO ₂ 0 to 5%, P ₂ O ₅ The method for producing alkali-free glass according to claim 1.