JP2008308343A - Alkali-free glass, alkali-free glass substrate, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide alkali-free glass which satisfies the requirements for a glass substrate for a liquid crystal display, is free of As<SB>2</SB>O<SB>3</SB>and Sb<SB>2</SB>O<SB>3</SB>and is excellent in solarization resistance. <P>SOLUTION: The alkali-free glass is substantially free of alkali metal oxides (R<SB>2</SB>O), As<SB>2</SB>O<SB>3</SB>and Sb<SB>2</SB>O<SB>3</SB>and comprises, by mass, 50-70% SiO<SB>2</SB>, 10-20% Al<SB>2</SB>O<SB>3</SB>, 9-15% B<SB>2</SB>O<SB>3</SB>, 0-2.5% MgO, 6.5-15% CaO, 3-10% SrO, 0-3% BaO, 10-18% MgO+CaO+SrO+BaO and 0.05-1% SnO<SB>2</SB>as a basic composition. In the alkali-free glass, the difference between optical transmittance at the wavelength of 400 nm (wall thickness 0.7 mm) measured before and after ultraviolet exposure is 0-2%, the temperature corresponding to 10<SP>2.5</SP>poise is <1,560°C, and the density is <2.50 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is suitable as a flat panel display substrate such as a liquid crystal display and an EL display, a cover glass of an image sensor such as a charge coupled device (CCD) and a solid-state proximity solid-state imaging device (CIS), and a glass substrate for a solar cell. The present invention relates to an alkali-free glass, a glass substrate using the same, and a method for producing the same.

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

Various items shown below are required for the glass substrate for this application.
(1) If an alkali metal oxide is contained in the glass, alkali ions diffuse into the semiconductor material on which the film is formed during the heat treatment, resulting in deterioration of the film characteristics. Do not contain.
(2) Various chemicals such as acid and alkali used in the photo-etching process, that is, chemical resistance that does not deteriorate due to hydrochloric acid (HCl), buffered hydrofluoric acid (BHF), sulfuric acid, hydrofluoric acid, alkaline solution, etc. Having.
(3) No thermal contraction due to heat treatment in processes such as film formation and annealing. Therefore, it must have a high strain point.
(4) The density should be small in order to reduce the weight of the display.
(5) It has a thermal expansion coefficient approximate to that of the surrounding material.
(6) It has excellent devitrification resistance so that devitrified materials are not generated in the glass melting step or molding step.
(7) Excellent melting property so that undesirable internal defects such as bubbles and foreign matters are not generated in the glass melting step.

  This requirement item (7) will be described in detail below. There is a standard for internal defects such as bubbles and foreign substances in the glass substrate for display. If an internal defect exceeding the standard exists in the glass substrate, it becomes a display defect of the display and becomes a defective product. In order to suppress such internal defects in the glass substrate, the glass must be melted at a high temperature for a long time. However, melting at a high temperature increases the burden on the glass melting furnace. For example, refractories such as alumina and zirconia used in melting kilns are eroded violently as the temperature rises, and are mixed as foreign substances in the glass or the life of the melting kiln is shortened. In addition, the running cost for keeping the inside of the melting furnace at a high temperature is higher than that of glass that melts at a low temperature. For these reasons, a glass that can be melted at as low a temperature as possible is required.

In order to obtain a glass having excellent foam quality, it is important to select a refining agent that generates a refining gas in the temperature range from the vitrification reaction to the homogenization melting. In other words, in the glass refining, the gas generated during the vitrification reaction is expelled from the glass melt by the refining gas, and the fine bubbles remaining due to the refining gas generated again during the homogenization melting are enlarged and removed. The alkali-free glass used for the glass substrate for liquid crystal displays has a high glass melt viscosity and is melted at a higher temperature than glass containing an alkali component. In this kind of alkali-free glass, a vitrification reaction usually occurs at 1200 to 1300 ° C., and defoaming and homogenization are performed at a high temperature of 1400 ° C. or higher. Therefore, As ₂ O ₃ that can generate a clarification gas in a wide temperature range (about 1200 to 1600 ° C.) is mainly used as a clarifier. Further, Sb ₂ O ₃ may be used as a clarifier instead of As ₂ O ₃ , or both may be used in combination. However, since As ₂ O ₃ and Sb ₂ O ₃ are environmentally hazardous substances, it is required to reduce the amount used as much as possible or not at all.

In addition, as display screens of glass substrates for liquid crystal displays have recently become brighter, there has been a strong demand for stable display quality over a long period of time. That is, in applications such as monitors, when the same image is always displayed, a defect called so-called solarization, in which the glass substrate is colored by ultraviolet rays, may occur. When this solarization occurs, only a part of the screen has a low-luminance part, so that the display quality as a display is greatly impaired. Therefore, the solarization resistance which does not color even if exposed to ultraviolet rays for a long time is required. This solarization tends to occur as the amount of As ₂ O ₃ contained in the glass increases.

Under such circumstances, various alkali-free glasses that do not use As ₂ O ₃ or Sb ₂ O ₃ as clarifiers and alkali-free glasses with excellent solarization resistance have been proposed (see, for example, Patent Documents 1 to 3). .
JP 2004-299947 A JP 2006-306690 A JP 2000-302475 A

Patent Documents 1 and ₂ disclose non-alkali glass that uses SnO ₂ as a fining agent and does not contain As ₂ O ₃ or Sb ₂ O _3. It does not fully satisfy the items required for glass substrates. That is, since the alkali-free glass of Patent Document 1 has insufficient meltability, it needs to be melted for a long time at a high temperature, and the alkali-free glass of Patent Document 2 contains a large amount of alkaline earth metal oxide. Therefore, the density is high and it is difficult to reduce the weight. Further, Patent Document 3 discloses an alkali-free glass excellent in solarization resistance, but this alkali-free glass is not considered at all with respect to BHF resistance.

The present invention has been made in view of the above circumstances, satisfies the above requirements (1) to (7), does not contain As ₂ O ₃ or Sb ₂ O ₃ , and has excellent solarization resistance. Another object is to provide alkali-free glass.

The alkali-free glass of the present invention contains substantially no alkali metal oxide (R ₂ O), As ₂ O ₃ , or Sb ₂ O ₃ , and is 50% by mass, SiO ₂ 50 to 70%, Al ₂ O _{3. 10~20%, B 2 O 3 9~15} %, MgO 0~2.5%, CaO 6.5~15%, SrO 3~10%, BaO 0~3%, MgO + CaO + SrO + BaO 10~18%, SnO 2 containing 0.05 to 1% by the basic composition, the difference is 0-2% of the transmittance at a wavelength 400nm before and after UV irradiation (thickness 0.7 mm), temperature corresponding to 10 ^2.5 poise of less than 1560 ° C. The density is less than 2.50 g / cm ³ .

The alkali-free glass of the present invention preferably contains substantially no alkali metal oxide (R ₂ O), As ₂ O ₃ , Sb ₂ O ₃ , SiO ₂ 55-65%, Al ₂ O ₃ 14 _{~18%, B 2 O 3 9.5~13} %, MgO 0~1.9%, CaO 7.2~12%, SrO 3.5~8%, BaO 0~1.5%, MgO + CaO + SrO + BaO 11~ It contains 17% and SnO ₂ 0.05 to 1% as a basic composition.

More preferably, the alkali-free glass of the present invention contains substantially no alkali metal oxide (R ₂ O), As ₂ O ₃ , Sb ₂ O ₃ , SiO ₂ 58 to 63%, Al ₂ O _3. 14.5 to 16.5%, B ₂ O ₃ 9.5 to 12%, MgO 0 to 1%, CaO 7.5 to 10%, SrO 4.1 to 5.4%, BaO 0 to 0.5 %, MgO + CaO + SrO + BaO 12-15%, SnO ₂ 0.1-0.5% as a basic composition.

The alkali-free glass of the present invention preferably contains 0.002 to 0.1% by mass of Fe ₂ O ₃ .

The alkali-free glass of the present invention is preferably characterized in that SnO ₂ / (Fe ₂ O ₃ + SnO ₂ ) is 0.5 or more by mass ratio.

The alkali-free glass of the present invention is preferably characterized in that (CaO + SrO) / (CaO + SrO + Al ₂ O ₃ ) is 0.3 to 0.7 in terms of mass ratio.

  The alkali-free glass of the present invention is preferably characterized by substantially not containing BaO.

  The alkali-free glass of the present invention is preferably characterized by containing 0.01 to 1% by mass of Cl.

The alkali-free glass of the present invention preferably contains 0.0001 to 3% by mass of TiO ₂ .

The alkali-free glass of the present invention is preferably characterized by having a thermal expansion coefficient of 33 to 42 × 10 ⁻⁷ / ° C. in a temperature range of 30 to 380 ° C.

  The alkali-free glass of the present invention is preferably characterized in that the liquidus temperature is less than 1150 ° C.

The alkali-free glass of the present invention is preferably characterized in that the viscosity at the liquidus temperature is 10 ^5.4 dPa · s or more.

The alkali-free glass of the present invention preferably has a specific Young's modulus of 28.0 GPa / (g / cm ³ ) or more.

  The alkali-free glass of the present invention preferably has a strain point of 630 ° C. or higher.

  The alkali-free glass substrate of the present invention is characterized by comprising the alkali-free glass described above.

  The alkali-free glass substrate of the present invention has an average thickness of 0.68 mm or less.

  The alkali-free glass substrate of the present invention is preferably used for a liquid crystal display device.

  A method for producing an alkali-free glass substrate according to the present invention is the method for producing an alkali-free glass substrate as described above, wherein the glass is formed into a plate shape by an overflow down draw method.

The alkali-free glass of the present invention satisfies all of the items (1) to (7) required for the glass substrate for liquid crystal display at the same time, and does not contain As ₂ O ₃ or Sb ₂ O _3. In addition, it is possible to suppress coloring by ultraviolet rays.

In order to obtain alkali-free glass with few bubbles, it is necessary to generate a clear gas that is effective in blowing bubbles when melted at high temperatures, to increase the diameter of microbubbles in the glass melt, and to lift and remove them There is. Therefore, a component that decomposes at a high temperature and generates a large amount of clarified gas is essential, but SnO ₂ releases a large amount of oxygen gas by a chemical reaction due to a valence change of Sn ions in a high temperature range of 1400 ° C. or higher. .

The alkali-free glass of the present invention has a temperature corresponding to 10 ^2.5 poise (melting temperature) as low as less than 1560 ° C. and further contains SnO ₂ as a fining agent, so that a fining effect in a high temperature range can be obtained. The generation of bubbles that can cause display defects can be minimized.

  The reason why the composition range of the alkali-free glass of the present invention is limited as described above is as follows.

SiO ₂ is a component that becomes a glass network, and when its content is too low, the strain point is lowered and the chemical resistance is deteriorated. In addition, it is difficult to reduce the density. On the other hand, if the SiO ₂ content is too high, the high-temperature viscosity becomes high and the meltability deteriorates, and the devitrified material of cristobalite tends to precipitate. Therefore, the content of SiO ₂ is 50 to 70%, preferably 55 to 65%, more preferably 58 to 63%.

Al ₂ O ₃ is a component that improves the heat resistance and Young's modulus of glass. If the content is too small, the meltability, strain point, and Young's modulus are likely to decrease. On the other hand, when the content of Al ₂ O ₃ is too large, the liquidus temperature increases and the devitrification resistance decreases. Therefore, the content of Al ₂ O ₃ is 10 to 20%, preferably 14 to 18%, more preferably 14.5 to 16.5%.

B ₂ O ₃ is a component that works as a flux and lowers the viscosity to facilitate melting. If the content is too small, the effect as a flux becomes insufficient. On the other hand, when the amount of B ₂ O ₃ increases too much, the hydrochloric acid resistance decreases, the strain point decreases, and the heat resistance deteriorates. In addition, the specific Young's modulus decreases. Therefore, the content of B ₂ O ₃ is 9 to 15%, preferably 9.5 to 13%, more preferably 9.5 to 12%.

  MgO is a component that lowers the high-temperature viscosity without lowering the strain point and facilitates melting of the glass. However, if its content is excessive, the resistance to buffered hydrofluoric acid of the glass deteriorates and the devitrification resistance It gets worse. Therefore, the content of MgO is 0 to 2.5%, preferably 0 to 1.9%, more preferably 0 to 1%.

  CaO is a component that lowers the high-temperature viscosity without lowering the strain point and facilitates melting of the glass. However, if the content is too small, the effect as a flux becomes insufficient. On the other hand, when the content of CaO is too large, the buffered hydrofluoric acid resistance of the glass deteriorates. Also, the thermal expansion coefficient and density are too high. Therefore, the CaO content is 6.5 to 15%, preferably 7.2 to 12%, more preferably 7.5 to 11%, and most preferably 7.5 to 10%.

  SrO is a component that improves the chemical resistance of glass and improves devitrification and meltability. If its content is too low, the chemical resistance, devitrification resistance, and meltability deteriorate. On the other hand, when the content of SrO is too large, the density and thermal expansion coefficient are increased, and devitrification resistance and buffered hydrofluoric acid resistance are deteriorated. Therefore, the content of SrO is 3 to 10%, preferably 3.5 to 8%, more preferably 4.1 to 5.4%.

  BaO is a component that functions in the same manner as SrO, but is the component that has the highest effect of increasing the density of glass among alkaline earth metal oxides. When the content of BaO is excessively increased, the density is remarkably increased and the strain point is decreased. Therefore, the content of BaO is 0 to 3%, preferably 0 to 1.5%, more preferably 0 to 0.5%, and most preferably not substantially contained. In the present invention, “substantially free of BaO” means that it contains no BaO other than the amount mixed from the raw material as an impurity component, and the content of BaO is 0. It refers to the case of 2% or less.

  Alkaline earth metal oxides (RO) such as MgO, CaO, SrO and BaO improve the meltability and moldability of the glass by lowering the liquidus temperature of the glass and making it difficult to produce crystalline foreign matter in the glass. At the same time, there is an effect of adjusting the thermal expansion coefficient. However, if the total amount of these is too large, the density of the glass increases and the specific Young's modulus decreases. Therefore, these components should be regulated to a total amount of 10 to 18%, preferably 11 to 17%, and 12 to 15%.

SnO _{2 functions} as a fining agent and has an effect of suppressing the resistance to solarization. However, if the content is too large, the devitrified substance of SnO ₂ is liable to precipitate, which is not preferable. Therefore, the content of SnO ₂ is 0.05 to 1%, preferably 0.1 to 0.5%.

  Moreover, in this invention, it is possible to contain another component other than the said component as needed.

For example, TiO ₂ has the effect of reducing the high temperature viscosity of the glass, improving the meltability, and suppressing solarization. However, if a large amount of TiO ₂ is contained, the glass is colored, and the transmittance is lowered, which is not preferable. Therefore, the content of TiO ₂ is preferably 0.0001 (1 ppm) to 3%, more preferably 0.001 (10 ppm) to 1%, and still more preferably 0.001 (10 ppm) to 0.1%. The total amount of TiO ₂ may be contained as an impurity such as a glass raw material, or may be contained using a reagent raw material.

  In addition, Cl has an effect of promoting the melting of the alkali-free glass, and by adding this, it becomes possible to melt the glass at a low temperature, to make the fining agent work more, and to extend the life of the manufacturing equipment. . However, if the Cl content is too high, the strain point of the glass is lowered, so 0.1 to 1%, more preferably 0.2 to 0.5% is preferable.

  ZnO is a component that improves the buffered hydrofluoric acid resistance of the glass and improves the meltability. However, if the amount is too large, the glass tends to devitrify, the strain point decreases, and the density increases. It is not preferable. Therefore, the content of ZnO is 0 to 5%, preferably 0 to 3%, more preferably 0 to 1%, still more preferably 0 to 0.3%, and most preferably not substantially contained.

CeO ₂ can be used as a refining agent, but if it is too much, the glass is colored, so its content should be regulated to 0 to 0.1%, preferably 0 to 0.05%.

P ₂ O ₅ is a component that improves the devitrification resistance of the glass, but if it is too much, phase separation and milk white occur in the glass, and the acid resistance is remarkably deteriorated. Therefore, the amount of P ₂ O ₅ should be regulated to 0 to 5%, preferably 0 to 3%, more preferably 0 to 1%.

ZrO ₂ is a component that improves the chemical resistance of glass, particularly acid resistance, and improves the specific Young's modulus. However, if it is contained in a large amount, the liquidus temperature rises and zircon devitrified substances precipitate. It becomes easy and meltability is greatly impaired. Therefore, ZrO ₂ is 0 to 3%, preferably 0 to 1%, more preferably 0 to 0.3%, and most preferably not substantially contained.

In order to improve the solarization resistance of the glass, it is desirable to reduce the amount of Fe ₂ O ₃ in the glass as much as possible. However, if the amount of Fe ₂ O ₃ is extremely reduced, it is necessary to use an expensive high-purity glass raw material, which is not preferable from the viewpoint of cost. Therefore, the amount of Fe ₂ O ₃ is 0.001 to 0.1%, preferably 0.005 to 0.08%, more preferably 0.005 to 0.05%, and still more preferably 0.007 to 0.03. % Should be regulated. The total amount of Fe ₂ O ₃ may be contained as an impurity such as a glass raw material, or may be contained using a reagent raw material.

Y ₂ O ₃ , Nb ₂ O ₃ , and La ₂ O ₃ have the effect of increasing the strain point and specific Young's modulus. However, if contained in a large amount, the density increases, so each should be suppressed to 5% or less. . Furthermore, metal powders such as F ₂ , Cl ₂ , SO ₃ , C, Al, Si, etc. can be contained up to 5% each as a fining agent.

In the present invention, it is preferable to adjust the contents of SnO ₂ and Fe ₂ O ₃ which affect the resistance to solarization. That is, SnO ₂ / (SnO ₂ + Fe ₂ O ₃ ) is 0.5 or more, preferably 0.8 or more, more preferably 0.9 or more, further preferably 0.92 or more, and most preferably 0.95 or more. By adjusting so that it becomes, it becomes easy to improve the solarization resistance.

In the alkali-free glass of the present invention, cristobalite tends to precipitate as devitrified crystals. The degree of precipitation of devitrified crystals is a mass ratio, and the composition ratio of (CaO + SrO) / (CaO + SrO + Al ₂ O ₃ ) has a great influence. When this ratio is less than 0.3, the tendency to devitrification is increased and the moldability is lowered, which is not preferable. On the other hand, if it exceeds 0.7, the density and the thermal expansion coefficient become too high, which is not preferable. The range of this ratio is preferably 0.3 to 0.6, more preferably 0.4 to 0.6, and more preferably 0.4 to 0.5.

However, if an alkali metal oxide (R ₂ O) such as Na ₂ O, K ₂ O, or Li ₂ O is contained, alkali ions diffuse into the deposited semiconductor material during the heat treatment, leading to deterioration of film characteristics. It is necessary that substantially no alkali metal oxide is contained. In the present invention, “substantially does not contain an alkali metal oxide” means that it contains no alkali metal oxide (R ₂ O) other than the amount mixed from the raw material as an impurity component. In the composition, the content of R ₂ O is 0.1% or less.

Further, As ₂ O ₃ and Sb ₂ O ₃ are environmentally hazardous substances, so it is necessary that they are not substantially contained. In particular, the alkali-free glass substrate containing As ₂ O ₃ has a problem that solarization is likely to occur. In the present invention, “substantially free of As ₂ O ₃ and Sb ₂ O ₃ ” means that As ₂ O ₃ and Sb ₂ O ₃ are not included in addition to the amount mixed from the raw materials as impurity components. Meaning, and refers to the case where As ₂ O ₃ and Sb ₂ O ₃ are each 0.1% or less in the glass composition.

The alkali-free glass of the present invention is characterized in that the difference in transmittance (wall thickness: 0.7 mm) at a wavelength of 400 nm before and after irradiation with ultraviolet rays is 0 to 2%. As described above, the glass substrate for a liquid crystal display may have a problem of so-called solarization, in which the glass substrate is colored by ultraviolet rays. However, the difference in the transmittance of the glass at a wavelength of 400 nm before and after irradiation with ultraviolet rays is zero. It can prevent that the display quality as a display falls that it is -2%. Here, the difference in transmittance at a wavelength of 400 nm before and after irradiation with ultraviolet rays indicates a value measured by the following method. First, after preparing a 0.7 mm thick glass substrate, the transmittance (T ₄₀₀ ) at a wavelength of 400 nm is measured with a spectrophotometer UV-3100PC manufactured by Shimadzu Corporation. Next, using a low-pressure mercury lamp, the glass substrate is irradiated with ultraviolet rays having a wavelength of 185 nm (2.7 mW / cm ² ) and a wavelength of 254 nm (13 W / cm ² ) for 12 hours. After ultraviolet irradiation, the transmittance at a wavelength of 400 nm (t ₄₀₀ ) is measured with the above spectrophotometer, and the difference between the transmittance before irradiation with ultraviolet rays and the transmittance after irradiation (T ₄₀₀ −t ₄₀₀ ) is determined.

The alkali-free glass of the present invention is characterized in that, in addition to the glass composition, the temperature at 10 ^2.5 dPa · s is less than 1560 ° C. The temperature (melting temperature) at 10 ^2.5 dPa · s, which is a high-temperature viscosity, can be measured by a well-known platinum ball pulling method. The lower this temperature, the more the glass can be melted at a lower temperature and the clarification with SnO ₂ becomes easier. It is also possible to suppress erosion of the refractory used in the glass melting furnace. Therefore, the temperature at 10 ^2.5 dPa · s is more preferably less than 1550 ° C., and more preferably less than 1540 ° C.

The alkali-free glass of the present invention is characterized in that the density is less than 2.50 g / cm ³ . Liquid crystal displays and organic EL displays are required to be thinner and lighter, and glass substrates are also required to be thinner and lighter. For this reason, a glass substrate having a thickness of 0.4 to 0.7 mm is mainly used as the glass substrate for these applications. However, in order to further reduce the weight, a reduction in density is required. The lower the density of the glass, the lighter the glass and the better for mobile device applications, but when trying to reduce the density of alkali-free glass to an extremely low level, it is necessary to reduce the alkali metal oxide (RO), As a result, there is a problem that the temperature at 10 ^2.5 dPa · s increases and the meltability decreases. Therefore, the density is more preferably 2.38 to 2.48 g / cm ³ , and further preferably 2.40 to 2.47 g / cm ³ . Here, in the present invention, the density refers to a value measured by a well-known Archimedes method based on JIS Z8807.

The alkali-free glass of the present invention preferably has a thermal expansion coefficient of 33 to 42 × 10 ⁻⁷ / ° C. in a temperature range of 30 to 380 ° C., more preferably 34 to 40 × 10 ⁻⁷ / ° C. preferable. Conventionally, it is desirable that the thermal expansion coefficient of an alkali-free glass substrate used for a liquid crystal display is consistent with the thermal expansion coefficient of an a-Si film or a p-Si film formed on the glass substrate. ^Therefore, alkali-free glass substrates having a size of less than 33 × 10 ⁻⁷ / ° C. are mainly commercially available. However, if the coefficient of thermal expansion of the alkali-free glass is to be less than 33 × 10 ⁻⁷ / ° C., it is necessary to reduce the alkaline earth metal oxide, which tends to lower the meltability of the glass. Therefore, it has been considered that it is impossible to improve the meltability while reducing the coefficient of thermal expansion of alkali-free glass. However, in practice, an a-Si film or a p-Si film can be satisfactorily formed even when the thermal expansion coefficient of the alkali-free glass substrate is 33 × 10 ⁻⁷ / ° C. or higher. There was found. When a liquid crystal panel is produced by bonding two alkali-free glass substrates, even if an alkali-free glass substrate having a thermal expansion coefficient of 33 × 10 ⁻⁷ / ° C. or more is used, it is commercially available. It has also been found that a non-alkali glass substrate (thermal expansion coefficient: less than 33 × 10 ⁻⁷ / ° C.) can be well bonded to form a panel. Therefore, in the present invention, a relatively large amount of alkaline earth metal oxide is contained, whereby the thermal expansion coefficient is 33 to 42 × 10 ⁻⁷ / ° C., and the temperature corresponding to 10 ^2.5 poise is 1560 ° C. or lower. Was possible.

The alkali-free glass substrate of the present invention preferably has a liquidus temperature of less than 1150 ° C. and a viscosity at the liquidus temperature (liquidus viscosity) of 10 ^5.4 dP · as or more. As the liquidus temperature becomes lower and the viscosity at the liquidus temperature becomes higher, devitrification is less likely to occur at the time of molding the glass, so that molding by the overflow downdraw method becomes easier. In other words, the overflow downdraw method has an advantage that a glass substrate with excellent surface quality can be obtained as compared with the float method, but the glass temperature at the time of molding is low, and thus devitrified substances are easily generated in the glass. . Here, devitrification is a process of cooling a high-temperature glass melt to form glass, and means that crystalline foreign substances are deposited inside or on the surface of the glass. Therefore, when the glass substrate is formed by the overflow down draw method, it is necessary to sufficiently consider the liquid phase temperature and the liquid phase viscosity. Therefore, the liquidus temperature is preferably less than 1100 ° C., more preferably less than 1080 ° C. The viscosity at the liquidus temperature is more preferably 10 ^5.5 dP · as or more, 10 ^5.6 dP · as or more, and further preferably 10 ^5.8 dP · as or more.

In addition, the alkali-free glass of the present invention preferably has a specific Young's modulus (Young's modulus / density) of 28.0 GPa / (g / cm ³ ) or more because the deflection of the glass substrate is reduced. In other words, as the glass substrate becomes larger or thinner, the deflection due to its own weight increases, and it becomes more likely to swing and fall during handling in the transport process and packing process, or to be damaged by contact with other members. . The amount of deflection of the glass substrate changes in proportion to the density of the glass and in inverse proportion to the Young's modulus. Therefore, in order to reduce the amount of deflection of the glass substrate, it is necessary to increase the specific Young's modulus. Therefore specific Young's modulus ^{is, 28.5GPa / (g / cm 3} ) or more, and further preferably 29.0GPa / (g / cm ³⁾ or ^{more, 29.5GPa / (g / cm 3} ) or more and most preferably .

  The alkali-free glass of the present invention preferably has a strain point of 630 ° C. or higher because there is little shrinkage due to heat treatment. In the case of a glass substrate for a display, a transparent conductive film, an insulating film, a semiconductor film, a metal film, and the like are formed on the glass substrate in a process of forming an electronic circuit such as a TFT and a wiring. Circuits and patterns are formed. In these film formation and photolithography etching processes, the glass substrate is subjected to various heat treatments and chemical treatments. For example, in an active matrix liquid crystal display, an insulating film or a transparent conductive film is formed on a glass substrate, and a large number of amorphous silicon or polycrystalline silicon TFTs are formed on the glass substrate through a photolithography etching process. . In these steps, the glass substrate is subjected to heat treatment at 300 to 600 ° C. By this heat treatment, the glass substrate may undergo a dimensional change of about several ppm (several μm with respect to the length of the glass substrate 1 m: this dimensional change is generally called thermal shrinkage). If the thermal shrinkage of the glass substrate is large, the TFT pattern will be displaced, and it will not be possible to accurately form an element in which multiple thin films are laminated. In order to suppress the thermal shrinkage, it is effective to increase the heat resistance of the glass, specifically to increase the strain point. Therefore, the strain point is more preferably 640 ° C. or higher, and further preferably 650 ° C. or higher. However, if the strain point becomes too high, the temperature at the time of melting and forming the glass substrate rises, increasing the load on the glass production equipment, which is not preferable because it causes a cost increase. Therefore, if other characteristics are taken into consideration, the strain point should be set to 750 ° C. or lower, particularly 700 ° C. or lower.

The alkali-free glass of the present invention has an erosion amount of preferably 10 μm or less and more preferably 6 μm or less when immersed in a 10% HCl aqueous solution at 80 ° C. for 24 hours. Further, when immersed in a 10% HCl aqueous solution at 80 ° C. for 3 hours, it is preferable that no white turbidity or roughness is observed by visual surface observation. Furthermore, when the alkali-free glass of the present invention is immersed in a 130 BHF solution at 20 ° C. for 30 minutes, the erosion amount is preferably 2 μm or less, and more preferably 1 μm or less. Further, when immersed in a 63 BHF solution at 20 ° C. for 30 minutes, it is preferable that no white turbidity or roughness is observed by visual surface observation. That is, as described above, the glass substrate for liquid crystal display is subjected to various heat treatments and chemical treatments. Generally, in the TFT array process, a series of processes of film formation process → resist pattern formation → etching process → resist stripping process. Is repeated. At that time, a chemical treatment such as HCl or BHF is applied as an etching solution. These chemical solutions are not disposable but are circulated liquid system flows in consideration of cost reduction. If the chemical resistance of the glass is poor, the reaction product between the chemical and the glass substrate will clog the filter of the circulating liquid system during etching, or the glass surface may become cloudy due to inhomogeneous etching, or the etching solution The change in the components may cause various problems such as an unstable etching rate. In particular, a hydrofluoric acid chemical represented by BHF erodes the glass substrate strongly, so the above-mentioned problems are likely to occur, and the glass substrate is required to have excellent BHF resistance. That is, it is very important that the amount of erosion to the chemical solution of glass is small from the viewpoint of preventing contamination of the chemical solution and clogging of the filter during the process due to reaction products. In addition, regarding the chemical resistance of the glass, it is important that not only the amount of erosion is small but also the appearance change is not caused. It is an indispensable characteristic for a glass substrate for a liquid crystal display, in which light transmittance is important, that the appearance of the glass does not change due to chemical treatment, such as white turbidity or roughness. The evaluation results of the amount of erosion and the change in appearance do not necessarily coincide with each other particularly with respect to BHF resistance. For example, even if the glass shows the same amount of erosion, the appearance may or may not change after chemical treatment depending on the composition. There is. In that respect, according to the alkali-free glass of the present invention, even when immersed in a 130 BHF solution at 20 ° C. for 30 minutes, the erosion amount is 2 mg / cm ² or less, and immersed in a 63 BHF solution at 20 ° C. for 30 minutes. However, since the cloudiness and roughness cannot be recognized by visual observation of the surface, the above-mentioned problems can be reliably solved.

  Moreover, when the Vickers hardness is low, the alkali-free glass of the present invention tends to scratch the surface of the glass substrate, and this scratch may cause disconnection of the electronic circuit formed on the glass substrate. Therefore, the Vickers hardness is preferably 560 or more, more preferably 570 or more, and further preferably 580 or more.

  Since the alkali-free glass of the present invention has a low density and a high specific Young's modulus, it is difficult to bend even if the thickness of the glass substrate is reduced. That is, since the alkali-free glass substrate of the present invention has a small amount of deflection, it is possible to minimize a decrease in workability during transportation and packaging. Therefore, by reducing the average thickness to 0.68 mm or less, preferably 0.65 mm or less, more preferably 0.60 mm or less, it is possible to reduce the weight of the glass substrate without significantly reducing workability. .

When producing the alkali-free glass substrate of the present invention, first, a glass raw material prepared so as to be a glass having a desired composition is put into a melting furnace, melted under predetermined conditions, and defoamed. At this time, a large amount of oxygen gas is generated by a chemical reaction due to a change in the valence of SnO ₂ , and a large number of bubbles present in the glass float with the oxygen gas and are removed. Thereafter, the molten glass is formed into a plate shape by using an overflow down draw method, and is slowly cooled.

  Here, the overflow down draw method means that the molten glass overflows from both sides of the heat-resistant (for example, zircon refractory) bowl-like structure, and the overflowed molten glass is joined at the lower end of the bowl-like refractory, This is a method for producing a glass plate (glass substrate) by stretching. When a glass plate is formed by this method, the surfaces (both surfaces) that become the surface of the glass substrate are not contacted with the bowl-shaped refractory, and are formed in a free surface state. Further, it is possible to obtain a glass substrate having a small surface roughness and undulation and excellent appearance quality.

  Hereinafter, the alkali-free glass of the present invention will be described in detail based on examples.

  Table 1 shows Examples (Sample Nos. 1 to 7) and Comparative Examples (Sample No. 8) of the present invention.

  Each glass sample of Table 1 was produced as follows.

  First, a batch prepared so as to have the glass composition in the table was put in a platinum crucible, melted at 1600 ° C. for 24 hours in an electric furnace, poured out on a carbon plate, and formed into a plate shape.

Each glass sample thus obtained, the density, thermal expansion coefficient, strain point, 10 ^2.5 poise temperature, liquidus temperature, liquidus viscosity, Young's modulus, specific modulus, HCl resistance, BHF resistance, ultraviolet irradiation before and after The transmittance difference was measured and the results are shown in the table.

As can be seen from the table, the sample No. 1-7 has a density of 2.45 g / cm ³ or less, a thermal expansion coefficient of 38 to 39 × 10 ⁻⁷ / ° C., a strain point of 660 ° C. or more, a temperature corresponding to 10 ^2.5 poise, 1550 ° C. or less, a liquid phase It has a temperature of 1115 ° C. or lower, a liquid phase viscosity of 10 ^5.4 dPa · s or higher, a specific Young's modulus of 29.3 GPa / (g / cm ³ ) or higher, excellent HCl resistance and BHF resistance, and transmission before and after UV irradiation. The difference in rate was as small as 1.5%, and all the characteristics were good.

On the other hand, sample No. which is a comparative example. No. 8 is not environmentally friendly because it contains As ₂ O ₃ , the temperature of 10 ^2.5 poise is as high as 1584 ° C., and the transmittance difference between before and after UV irradiation is 2.5%, so that it has melting and solarization resistance. It was inferior to. Furthermore, sample no. Since No. 8 has a specific Young's modulus of 27.8 GPa / (g / cm ³ ), it is presumed that the amount of deflection when the glass substrate is formed increases.

  In addition, the density in a table | surface 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 was measured based on the method of ASTM C336-71. The higher this value, the higher the heat resistance of the glass.

10 ^2.5 dPa · s indicates a temperature of 10 ^2.5 poise, which is a high temperature viscosity, and was measured by a well-known platinum ball pulling method. The lower this value, the better the meltability.

  The liquid phase temperature was obtained by grinding each glass sample, passing through a standard sieve 30 mesh (500 μm), putting the glass powder remaining on 50 mesh (300 μm) into a platinum boat and holding it in a temperature gradient furnace for 24 hours. The temperature at which devitrification (crystalline foreign matter) was generated in the glass was measured by observing with a microscope.

  The liquid phase viscosity indicates the viscosity of the glass at the liquid phase temperature. The lower the liquidus temperature and the higher the liquidus viscosity, the better the devitrification resistance and the moldability.

  The Young's modulus was measured by a resonance method, and the specific Young's modulus was obtained by calculating from the Young's modulus and density values using the Young's modulus / density formula.

The HCl resistance and BHF resistance were evaluated by the following methods. First, after both surfaces of each glass sample were optically polished, they were immersed at a predetermined temperature and time in a chemical solution prepared by masking a part and then preparing a predetermined concentration. After the chemical treatment, the mask was removed, and the level difference between the mask portion and the erosion portion was measured with a surface roughness meter, and the value was taken as the erosion amount. The HCl resistance was evaluated as ○ when the erosion amount was 10 μm or less, and ◎ when the erosion amount was 6 μm or less. The BHF resistance was evaluated as ○ when the erosion amount was 2 μm or less, and ◎ when the erosion amount was 1 μm or less. For appearance evaluation, after both surfaces of each glass sample are optically polished, immersed in a chemical solution prepared to a predetermined concentration at a predetermined temperature and time, the glass surface is visually observed, and the glass surface becomes cloudy. Or rough, or cracked was marked with ×, and no change was marked with ○. In addition, a chemical | medical solution and process conditions are as follows. The amount of HCl-resistant erosion was measured using a 10% by mass HCl aqueous solution at 80 ° C. for 24 hours, and the appearance was evaluated using a 10% by mass HCl aqueous solution at 80 ° C. for 3 hours. It was. The amount of erosion of BHF resistance was measured using a 130 BHF solution (NH ₄ HF: 4.6% by mass, NH ₄ F: 36% by mass) under the treatment conditions of 20 ° C. for 30 minutes. (HF: 6% by mass, NH ₄ F: 30% by mass) was carried out at 20 ° C. for 30 minutes.

The transmittance difference before and after UV irradiation was measured as follows. After polishing the glass sample to a thickness of 0.7 mm, the transmittance (T ₄₀₀ ) at a wavelength of 400 nm was measured with a spectrophotometer UV-3100PC manufactured by Shimadzu Corporation. Next, using a low-pressure mercury lamp, the glass sample was irradiated with ultraviolet rays having a wavelength of 185 nm (2.7 mW / cm ² ) and a wavelength of 254 nm (13 mW / cm ² ) for 12 hours, and then the transmittance (t ₄₀₀ ) at a wavelength of 400 nm was obtained. The transmittance difference T ₄₀₀ -t ₄₀₀ was determined by calculation.

  In addition, sample No. as an example. A glass substrate for a liquid crystal display having a substrate size of 900 mm × 1100 mm and a thickness of 0.5 mm was produced by melting the glass No. 7 in a test melting furnace and forming it into a plate shape by an overflow down draw method. This glass substrate has a warpage of 0.075%, waviness (WCA) of 0.15 μm or less (cutoff fh: 0.8 mm, fl: 8 mm), and surface roughness (Ra) of 100 mm or less (cutoff λc: 9 μm). It was excellent in surface quality, had no bubbles and devitrification that would cause display defects, and was suitable as a glass substrate for liquid crystal displays. In the overflow downdraw method, the temperature of the molten glass, the rotational speed of the stirring stirrer, the flow rate of the glass, the speed of the pulling roller for pulling the formed glass plate downward, and both edges of the glass plate are cooled. The surface quality of the glass substrate was adjusted by appropriately adjusting the speed of the cooling roller. Further, “warping” of the glass substrate was measured using a gap gauge described in JIS B-7524 by placing the glass substrate on an optical surface plate. “Waviness” is a value obtained by measuring WCA (filtered center line waviness) described in JIS B-0610 using a stylus type surface shape measuring device. This measurement is performed by SEMI STD D15-1296 “ It is measured by a method according to “Measurement Method of Surface Waviness of FPD Glass Substrate” and is measured with a length of 300 mm in a direction perpendicular to the drawing direction of the glass substrate. Further, “average surface roughness (Ra)” is a value measured by a method based on SEMI D7-97 “Measurement method of surface roughness of FPD glass substrate”.

The alkali-free glass of the present invention satisfies all of the above requirements (1) to (7) at the same time, and is preferable in terms of environment since it does not contain As ₂ O ₃ and Sb ₂ O ₃ , and further has resistance to solarization. It is excellent as a glass substrate for a liquid crystal display because it is excellent in coloration due to ultraviolet rays. In addition, the alkali-free glass of the present invention is used for other flat panel display substrates such as organic EL displays, charge coupled devices (CCDs), image sensors such as close proximity solid-state imaging devices (CIS), and glass for solar cells. It can be used as a transparent substrate material for various applications such as a glass substrate.

Claims (18)

Alkali metal oxide (R ₂ O), As ₂ O ₃ , Sb ₂ O ₃ are not substantially contained, and by mass%, SiO ₂ 50 to 70%, Al ₂ O ₃ 10 to 20%, B ₂ O _{3 Based on} 9-15%, MgO 0-2.5%, CaO 6.5-15%, SrO 3-10%, BaO 0-3%, MgO + CaO + SrO + BaO 10-18%, SnO ₂ 0.05-1% Contained as a composition, the difference in transmittance (wall thickness 0.7 mm) at a wavelength of 400 nm before and after UV irradiation is 0 to 2%, the temperature corresponding to 10 ^2.5 poise is less than 1560 ° C., and the density is 2.50 g / cm ³ Alkali-free glass characterized by being less than. Alkali metal oxide (R ₂ O), As ₂ O ₃ , Sb ₂ O ₃ are not substantially contained, and by mass%, SiO ₂ 55 to 65%, Al ₂ O ₃ 14 to 18%, B ₂ O ₃ 9.5-13%, MgO 0-1.9%, CaO 7.2-12%, SrO 3.5-8%, BaO 0-1.5%, MgO + CaO + SrO + BaO 11-17%, SnO ₂ 0. The alkali-free glass according to claim 1, which contains 05 to 1% as a basic composition. Alkali metal oxide (R ₂ O), As ₂ O ₃ , Sb ₂ O ₃ are not substantially contained, and by mass%, SiO ₂ 58 to 63%, Al ₂ O ₃ 14.5 to 16.5% _{, B 2 O 3 9.5~12%,} 0~1% MgO, CaO 7.5~10%, SrO 4.1~5.4%, BaO 0~0.5%, MgO + CaO + SrO + BaO 12~15%, _{3. The} alkali-free glass according to claim 1, comprising 0.1 to 0.5% of SnO ₂ as a basic composition. Alkali-free glass according to claim 1, the Fe ₂ O _3, characterized in that it contains 0.001 to 0.1 wt%. The alkali-free glass according to claim 1, wherein SnO ₂ / (SnO ₂ + Fe ₂ O ₃ ) is 0.5 or more in terms of mass ratio. The alkali-free glass according to claim 1, wherein (CaO + SrO) / (CaO + SrO + Al ₂ O ₃ ) is 0.3 to 0.7 in terms of mass ratio.   The alkali-free glass according to any one of claims 1 to 6, which is substantially free of BaO.   The alkali-free glass according to any one of claims 1 to 7, which contains 0.01 to 1% by mass of Cl. Alkali-free glass according to claim 1, characterized in that it contains TiO ₂ 0.0001 to 3 wt%. 10. The alkali-free glass according to claim 1, wherein the coefficient of thermal expansion in a temperature range of 30 to 380 ° C. is 33 to 42 × 10 ⁻⁷ / ° C. 10.   Liquid phase temperature is less than 1150 degreeC, The alkali free glass in any one of Claims 1-10 characterized by the above-mentioned. The alkali-free glass according to any one of claims 1 to 11, wherein a viscosity at a liquidus temperature is 10 ^5.4 dPa · s or more. The non-alkali glass according to claim 1, wherein the specific Young's modulus is 28.0 GPa / (g / cm ³ ) or more.   The alkali-free glass according to any one of claims 1 to 13, wherein the strain point is 630 ° C or higher.   An alkali-free glass substrate comprising the alkali-free glass according to any one of claims 1 to 14.   The alkali-free glass substrate according to claim 15, wherein the average thickness is 0.68 mm or less.   The alkali-free glass substrate according to claim 15 or 16, which is used for a liquid crystal display device.   The method for producing an alkali-free glass substrate according to any one of claims 15 to 17, wherein the glass is formed into a plate shape by an overflow down draw method.