JP7761879B2 - Glass - Google Patents

Description

The present invention relates to glass, and in particular to glass suitable for use as a substrate for organic EL displays, a carrier glass used when fabricating organic EL elements on a polyimide substrate, etc.

Electronic devices such as organic EL displays are thin, excellent for displaying moving images, and consume little power, making them suitable for use in mobile phone displays and other applications. Furthermore, organic EL displays using polyimide substrates are lightweight and flexible, making them increasingly applicable to a variety of displays.

Glass plates are widely used as substrates for organic EL displays. Glass plates are also used as carrier glass when fabricating organic EL elements on polyimide substrates. Glass plates for these applications are primarily required to have the following properties:
(1) The content of alkali metal oxides is low to prevent alkali ions from diffusing into the semiconductor material formed during the heat treatment process.
(2) To reduce the cost of glass sheets, the glass must be excellent in productivity, particularly in resistance to devitrification and melting.
(3) The strain point must be high in order to reduce the amount of thermal shrinkage during the manufacturing process of p-Si TFTs.

Special Publication No. 2009-525942

To elaborate on the above required characteristic (3), the p-Si TFT film formation process includes a heat treatment step at 400-600°C, which causes minute dimensional changes in the glass plate known as thermal shrinkage. If the amount of thermal shrinkage is large, deviations in the pixel pitch of the TFT occur, resulting in display defects. In the case of organic EL displays, even dimensional shrinkage of a few ppm can result in display defects. The higher the heat treatment temperature to which the glass plate is subjected, the greater the thermal shrinkage.

Furthermore, the carrier glass used when fabricating organic EL elements on a polyimide substrate also undergoes a heat treatment process at the same temperatures as when fabricating organic EL elements on a glass plate. If the glass plate experiences significant thermal shrinkage, that shrinkage is transmitted to the polyimide substrate, causing deviations in the pixel pitch.

As can be seen from the above, glass sheets that are less susceptible to thermal shrinkage are advantageous for these applications. One method for reducing the amount of thermal shrinkage is to anneal the glass sheet near the annealing point after forming it. However, annealing takes a long time, which increases the manufacturing costs of the glass sheet.

Another method is to increase the strain point of the glass plate. The higher the strain point, the less likely thermal shrinkage will occur during the p-Si TFT manufacturing process. For example, Patent Document 1 discloses a glass plate with a high strain point.

However, high strain point glasses generally contain large amounts of refractory _SiO2 and _Al2O3 , which result in poor devitrification resistance and meltability (especially batch meltability), making it difficult _to stably produce inexpensive, high-quality glass. Therefore, it is difficult for high strain point glasses to satisfy the required characteristic (2).

The present invention was developed in light of the above circumstances, and its technical objective is to create a glass that exhibits minimal thermal shrinkage during the p-Si TFT manufacturing process, yet has high resistance to devitrification and melting properties.

As a result of repeated various experiments, the inventors have found that _the above technical problems can be solved by strictly controlling the glass composition of low-alkali glass and the relationship between _Al2O3 and the strain point, and have proposed this finding as the present invention. That is, the glass of the present invention is characterized by having a glass composition containing, in mole percent, 67-73% _SiO2 , _10-15 % _Al2O3 , ₀ to less than 3% _B2O3 , 0-0.5% _Li2O + _Na2O + _K2O , 0-8.5% MgO, 3.5-12% CaO, 0-2.5% SrO, and 1-6% BaO, and having a strain point (° _C ) divided by the _Al2O3 content (mol%) of 51 or more. Here, "Li ₂ O + Na ₂ O + K ₂ O" refers to the total amount of Li ₂ O, Na ₂ O, and K ₂ O. "Strain point" refers to a value measured based on the method of ASTM C336.

The glass of the present invention is characterized by having a glass composition containing, in mole percent, _67-73 % _{SiO2 ,} 10-15% _Al2O3 , _0-1.3 % B2O3, 0-0.5% _Li2O +Na2O+K2O _, 0-3.2% MgO, 3.5-12% CaO, _0-2 % SrO, and 3.5-6% BaO, with CaO-(SrO+BaO) being 3.1% or more, a molar ratio CaO/ _Al2O3 being 1.05 or _less , and a molar ratio SrO/BaO being 0.03-0.50. Here, "CaO-(SrO+BaO)" refers to the value obtained by subtracting the combined amount of SrO and BaO from the CaO content. "CaO/Al ₂ O ₃ " refers to the value obtained by dividing the CaO content by the Al ₂ O ₃ content. "SrO/BaO" refers to the value obtained by dividing the SrO content by the BaO content.

The glass of the present invention has a glass composition containing, in mole percent, 67 to 73% _{SiO2 ,} 12 to 15% _Al2O3 , 0 to less than 1.8% _B2O3 , ₀ to less than 0.5% _Li2O + _Na2O + _K2O , 0 to 6% MgO, 5% or more CaO, 0 to 2% SrO, and 3.5% or more BaO, wherein CaO-(SrO+BaO) is 0.7% or more, the molar ratio SrO/BaO is 0.38 or less, the molar ratio (MgO+CaO+SrO+BaO)/ _Al2O3 is 1.09 to 1.70, and the value obtained by dividing the strain point (°C) by _{the Al2O3} content (mol _% ) is 55 or more. Here, "(MgO+CaO+SrO+BaO)/Al ₂ O ₃ " refers to the value obtained by dividing the total amount of MgO, CaO, SrO and BaO by the content of Al ₂ O ₃ .

The glass of the present invention preferably contains, in mole percent, 67-73% SiO ₂ , 10-15% Al ₂ O _{3 ,} 0 to less than 3% B ₂ O ₃ , 0-0.5% Li ₂ O + Na ₂ O + K ₂ O , 0-8.5% MgO, 3.5-12% CaO, 0-2.5% SrO, and 1-6% BaO as a glass composition. The reasons for specifying the content range of each component as above are as follows. In the explanation of the content range of each component, % means mol % unless otherwise specified.

_SiO2 is a component that forms the glass skeleton and raises the strain point. It also increases chemical resistance to hydrochloric acid and the like. On the other hand, if the _SiO2 content is too high, the melting property significantly decreases and the HF etching rate decreases. Therefore, the preferred lower limit of _SiO2 is 67% or more, 68% or more, 69% or more, and particularly 70% or more, and the preferred upper limit is 73% or less, particularly 72% or less.

Al ₂ O ₃ is a component that increases the strain point and Young's modulus. On the other hand, if the content of Al ₂ O ₃ is too high, the batch solubility during initial melting decreases and the molding temperature increases. The preferred lower limit of Al ₂ O ₃ is 10% or more, 11% or more, particularly 12% or more, and the preferred upper limit is 15% or less, 14% or less, 13% or less, particularly 12.5% or less. When a small amount of B ₂ O ₃ is introduced to reduce meltability and molding viscosity, a relatively large amount of Al ₂ O ₃ can be introduced into the glass composition. On the other hand, when almost no B ₂ O ₃ is contained, it is not possible to introduce too much Al ₂ O ₃ into the glass composition. In this case, it is preferable that the content of Al ₂ O ₃ is as small as possible.

_B2O3 is a component that improves meltability and devitrification resistance, and also lowers the molding temperature. On the other hand, if a large amount _{of B2O3} is introduced, the strain point and Young's modulus also decrease _. The _B2O3 content is preferably less than 3%, 2.5% or less, 2% or less, less than 1.8%, 1.3% or less, particularly 0.8 _% or less.

As will be described in detail later, the raw _material for _B2O3 is a source of much of the moisture in the glass. Therefore, from the viewpoint of reducing the moisture content, it is preferable that the _B2O3 content be as small as possible. Furthermore, when producing glass sheets by full electric melting without using combustion, the lower _{the B2O3} content, the more easily the glass batch spreads uniformly in the melting furnace, and _the more homogeneous the molten glass can be.

Li ₂ O, Na ₂ O, and K ₂ O are components that improve meltability and reduce the electrical resistivity of molten glass, but if the contents of Li ₂ O, Na ₂ O, and K ₂ O are too high, there is a risk of contamination of the semiconductor material due to diffusion of alkali ions. Therefore, the total content of Li ₂ O, Na ₂ O, and K ₂ O is preferably 0 to 0.5%, 0 to less than 0.5%, 0.01 to 0.3%, 0.02 to 0.2%, and particularly 0.03 to less than 0.1%. The content of Na ₂ O is preferably 0 to 0.3%, 0.01 to 0.3%, 0.02 to 0.2%, and particularly 0.03 to less than 0.1%. The content of _{K 2} O is preferably 0 to 0.3%, 0 to 0.2%, and particularly 0 to less than 0.1%.

MgO is a component that increases meltability and Young's modulus. On the other hand, MgO lowers the strain point. When reducing Al ₂ O ₃ to lower the melting temperature or molding temperature, it is necessary to incorporate a large amount of SiO ₂ to maintain a high strain point. Introducing a large amount of MgO in a composition region containing a large amount of SiO ₂ facilitates cristobalite precipitation during molding, further lowering the strain point. Therefore, in this case, the MgO content is preferably as low as possible, and the MgO content is preferably 0-8.5%, 0-6%, 0-5%, 0-3.2%, 0-3%, and particularly 0-1%. Furthermore, when introducing a small amount of B ₂ O ₃ to lower the melting temperature or molding temperature, the SiO ₂ content can be relatively low and the Al ₂ O ₃ content can be relatively high. In this case, it is preferable to actively incorporate MgO, and the content of MgO is preferably 1 to 8.5%, 2 to 6%, and particularly preferably 2.5 to 5%.

CaO is a component that improves meltability and batch solubility. Furthermore, among alkaline earth metal oxides, CaO is a component that reduces raw material costs because the raw material used is relatively inexpensive. It also suppresses the precipitation of devitrified crystals containing Mg. On the other hand, if the CaO content is too high, feldspar-based devitrified crystals containing Ca (such as anorthite) are more likely to precipitate during molding. Therefore, the CaO content is preferably 3.5-12%, 4-11%, 5-11%, and particularly 5.5-11%.

SrO is a component that makes it difficult for cristobalite to precipitate during forming, and also lowers the melting temperature without significantly lowering the strain point. On the other hand, as the SrO content increases, the density increases and the Young's modulus tends to decrease. Furthermore, in the composition range where anorthite is likely to precipitate as the primary phase, as the SrO content increases, the liquidus temperature decreases, and the productivity of glass sheets tends to decrease. Therefore, the SrO content is preferably 0-2.5%, 0-2%, and particularly 0.1-1.3%.

Among alkaline earth metal oxides, BaO is a component that suppresses the precipitation of devitrified crystals such as mullite and anorthite, which contain Al, during molding. On the other hand, as the BaO content increases, the density increases and the Young's modulus tends to decrease. The preferred lower limit of BaO is 1% or more, 2% or more, 3% or more, and particularly 3.5% or more, while the preferred upper limit is 12% or less, 11% or less, 10% or less, 8% or less, and particularly 6% or less.

Alkaline earth metal oxides are very important components for increasing the strain point, devitrification resistance, and meltability. A small amount of alkaline earth metal oxide increases the strain point, but _{Al2O3 -} based devitrification crystals are more likely to precipitate during molding, and the high-temperature viscosity increases, making the meltability more likely to decrease. Therefore, the ratio of the total amount of alkaline earth metal oxides (MgO + _CaO + SrO + BaO) to _{the Al2O3} content is very important. Specifically, as the molar ratio (MgO + CaO + SrO + BaO)/ _Al2O3 increases, the meltability and moldability improve, but the strain point tends to decrease. Conversely, as this value decreases, the strain point increases, but the meltability and moldability tend to decrease. Therefore, the preferred lower limit range of the molar ratio (MgO+CaO+SrO+BaO)/Al ₂ O ₃ is 0.95 or more, 1.00 or more, 1.05 or more, particularly 1.09 or more, and the preferred upper limit range is 1.70 or less.

The molar ratio CaO/Al ₂ O ₃ is one of the important indicators for maintaining a high strain point while ensuring meltability. In a composition region containing a large amount of CaO, it is important to design the composition so that the strain point does not decrease. In alkaline earth aluminosilicate glass, Al ₂ O ₃ is the main component other than SiO ₂ that raises the strain point. From these viewpoints, the molar ratio CaO/Al ₂ O ₂ is preferably 1.09 or less, 1.07 or less, or 1.05 or less, particularly 0.25 to 1.05.

In order to produce glass with a high strain point while reducing the manufacturing load, the blending ratio of the four alkaline earth metal oxide components is extremely important. From this perspective, CaO-(SrO+BaO) is preferably -3% or more, -1% or more, 0% or more, 0.7% or more, or 2% or more, and particularly 3.1 to 15%. Increasing the CaO-(SrO+BaO) content reduces the melting temperature and forming temperature, thereby increasing the productivity of glass sheets.

In a composition region containing a large amount of CaO, controlling the molar ratio of SrO/BaO is important from the perspective of devitrification resistance. Specifically, as mentioned above, in a composition region containing a large amount of CaO, anorthite is more likely to precipitate as the primary phase. Among alkaline earth metal oxides, SrO is a component that raises the liquidus temperature of anorthite, while BaO is a component that lowers the liquidus temperature of anorthite. Therefore, the smaller the molar ratio of SrO/BaO, the lower the liquidus temperature of anorthite. However, if no SrO is incorporated at all, devitrification crystals such as cristobalite are more likely to precipitate during molding. Taking these points into consideration, the preferred lower limit of the molar ratio of SrO/BaO is 0 or more, particularly 0.03 or more, and the preferred upper limit is 0.70 or less, 0.63 or less, 0.50 or less, particularly 0.38 or less.

In addition to the above ingredients, the following ingredients may also be incorporated:

ZnO is a component that improves meltability, but too much ZnO makes the glass more susceptible to devitrification and a lower strain point. Therefore, the ZnO content is preferably 0-5%, 0-3%, 0-0.5%, and particularly 0-0.2%.

P ₂ O ₅ is a component that lowers the liquidus temperature of Al-based devitrified crystals, but if the amount of P ₂ O ₅ increases, the strain point decreases and cristobalite tends to precipitate during molding. Therefore, the content of P ₂ O ₅ is preferably 0 to 1.5%, 0 to 1.2%, and particularly preferably 0 to less than 0.1%.

_TiO2 is a component that reduces high-temperature viscosity, improves meltability, and suppresses solarization. However, if the _TiO2 content is too high, the glass becomes colored and transmittance tends to decrease. Therefore, the _TiO2 content is preferably 0 to 5%, 0 to 3%, 0 to 1%, 0 to 0.1%, and particularly 0 to 0.02%.

ZrO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ , and La ₂ O ₃ have the function of increasing the strain point, Young's modulus, etc. However, if the content of these components increases, the density tends to increase. Therefore, the contents of ZrO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ , and La ₂ O ₃ are preferably 0 to 5%, 0 to 3%, 0 to 1%, and 0 to less than 0.1%, and particularly preferably 0 to less than 0.05%, respectively. Furthermore, the total content of Y ₂ O ₃ and La ₂ O ₃ is preferably less than 0.1%.

_SnO2 is a component that has good fining properties in the high temperature range, as well as a component that increases the strain point and reduces high-temperature viscosity. The SnO2 content is preferably 0 to 1%, 0.001 to 1%, 0.01 to 0.5%, and particularly 0.05 to 0.3%. If _{the SnO2} content is too high, devitrified crystals of _SnO2 are more likely to precipitate during molding.

As long as the glass properties are not impaired, up to 2% of _F2 , _Cl2 , _SO3 , C, or metal powders such as Al and Si can be added as a fining agent. _CeO2 and the like can also be added as a fining agent up to 1%.

_{As2O3 and Sb2O3} are effective as fining agents, and although the glass of the present invention does not completely exclude the incorporation of these components, from an environmental perspective, it is preferable to avoid using these components as much as possible. _Furthermore , since a high content of _As2O3 tends to reduce solarization resistance, its content is preferably 0.1% or less, and it is desirable that it is not substantially contained. Here, "substantially free of _{As2O3 "} refers to a case where the content of _As2O3 in the glass composition is _less than 0.05%. Furthermore, the content of _Sb2O3 is preferably 0.2 _% or less, particularly 0.1 _{% or less, and it is desirable that it is not substantially contained. Here, "substantially free of Sb2O3" refers to a case where the content of Sb2O3 in the glass composition} is less than 0.05%.

Fe ₂ O ₃ is a component that reduces the electrical resistivity of molten glass. The content of Fe ₂ O ₃ is preferably 0 to 0.2%, 0.001 to 0.1%, 0.005 to 0.05%, and particularly 0.008 to 0.015%. If the content of Fe ₂ O ₃ is low, it becomes difficult to achieve the above-mentioned effects. On the other hand, if the content of Fe ₂ O ₃ is high, the transmittance in the ultraviolet range tends to decrease, and the irradiation efficiency when using an ultraviolet laser in the display manufacturing process tends to decrease. Note that when electric melting is performed, it is preferable to actively incorporate Fe ₂ O ₃ , and in that case, the content of Fe ₂ O ₃ is preferably 0.005 to 0.03%, 0.008 to 0.025%, and particularly 0.01 to 0.02%. Furthermore, when it is desired to increase the transmittance in the ultraviolet region, the content of Fe ₂ O ₃ is preferably 0.020% or less, 0.015% or less, 0.011% or less, particularly preferably 0.010% or less.

Furthermore, in relation to Fe ₂ O ₃ , the raw material for introducing MgO is the main source of contamination with Fe ₂ O _3. Therefore, from the viewpoint of increasing the transmittance in the ultraviolet region, it is preferable to reduce the content of MgO as much as possible.

Cl has the effect of promoting the melting of low-alkali glass, and adding Cl can lower the melting temperature and promote the action of the fining agent. Cl also has the effect of lowering the β-OH value of molten glass. However, if the Cl content is too high, the strain point will decrease and the environmental load will increase. Therefore, the Cl content is preferably 0.5% or less, and in particular 0.001 to 0.2%. Cl can be introduced from sources such as chlorides of alkaline earth metal oxides, such as strontium chloride, or aluminum chloride.

The glass of the present invention preferably has the following properties:

The strain point is preferably 730°C or higher, 735°C or higher, 740°C or higher, and particularly 745°C or higher. If the strain point is low, the glass plate is more likely to undergo thermal shrinkage during the p-Si TFT manufacturing process.

In order to obtain a glass that has small thermal shrinkage and high melting property in the manufacturing process of p-Si TFTs, it is important to simultaneously increase the strain point and batch solubility. On the other hand, Al ₂ O ₃ is a component that significantly reduces batch solubility. Therefore, from the above perspective, it is important to increase the value obtained by dividing the strain point (°C) by the Al ₂ O ₃ content (mol %), and the value obtained by dividing the strain point (°C) by the Al ₂ O ₃ content (mol %) is preferably 51 or more, 53 or more, and particularly 55 to 80.

The density is preferably 2.71 g/cm ^or less, 2.69 g/cm ^{or less} , 2.67 g/cm ^or less, particularly preferably 2.64 g/cm ^or less. If the density is high, the specific Young's modulus increases, making the glass plate more likely to bend under its own weight, and when used as a substrate, increasing the mass of the organic EL display.

Reducing the β-OH value can increase the strain point. The β-OH value is preferably 0.30/mm or less, 0.25/mm or less, 0.20/mm or less, 0.15/mm or less, and particularly 0.10/mm or less. As the β-OH value increases, the strain point tends to decrease. Note that if the β-OH value is made too small, there is a risk of excess Cl in the glass. Therefore, the β-OH value is preferably 0.01/mm or more, and particularly 0.02/mm or more.

The following methods can be used to reduce the β-OH value: (1) Select glass raw materials with a low water content. (2) Add components (Cl, _SO3 , etc.) that reduce the water content in the glass. (3) Reduce the water content in the furnace atmosphere. (4) Bubble _N2 in the molten glass. (5) Use a small melting furnace. (6) Increase the flow rate of the molten glass. (7) Use an electric melting method.

Here, the "β-OH value" refers to a value obtained by measuring the transmittance of glass using FT-IR and using the following formula:
β-OH value = (1/X)log(T ₁ /T ₂ )
X: Glass thickness (mm)
T ₁ : transmittance (%) at a reference wavelength of 3846 cm ⁻¹
T ₂ : Minimum transmittance (%) at a hydroxyl group absorption wavelength of around 3600 cm ⁻¹
The liquidus temperature is preferably less than 1320°C, 1300°C or less, 1280°C or less, 1260°C or less, 1240°C or less, particularly 1220°C or less. If the liquidus temperature is high, devitrified crystals precipitate during forming by an overflow downdraw method or the like, reducing the productivity of the glass sheet. The "liquidus temperature" refers to the value measured by placing glass powder that passes through a standard 30 mesh sieve (sieve opening 500 μm) and remains on a 50 mesh sieve (sieve opening 300 μm) in a platinum boat and holding it in a temperature gradient furnace for 24 hours, at which the temperature at which crystals (primary phase) precipitate is measured.

The liquidus viscosity is preferably 10 ^4.5 dPa s or more, 10 ^4.8 dPa s or more, 10 ^5.0 dPa s or more, 10 ^5.2 dPa s or more, particularly 10 ^5.3 dPa s or more. If the liquidus viscosity is low, devitrification crystals precipitate during forming by the overflow downdraw method or the like, reducing the productivity of glass sheets. The "liquidus viscosity" refers to the viscosity of glass at the liquidus temperature measured by the platinum sphere pull-up method.

The temperature at a high-temperature viscosity of 10 ^4.5 dPa s is preferably less than 1320°C, 1310°C or less, 1305°C or less, particularly 1300°C or less. The temperature at a high-temperature viscosity of 10 ^4.5 dPa s corresponds to the forming temperature when forming by the overflow downdraw method. If the forming temperature is high, creep deformation of the formed body is likely to progress, making it impossible to stably produce high-quality glass sheets. It is possible to produce glass sheets by replacing formed bodies with advanced creep deformation, but since formed bodies are very expensive, the manufacturing cost of glass sheets increases. The "temperature at a high-temperature viscosity of 10 ^4.5 dPa s" can be measured by the platinum sphere pull-up method.

When the temperature at a high-temperature viscosity of 10 ^2.5 dPa·s is η _2.5 and the temperature at a high-temperature viscosity of 10 ^4.0 dPa·s is η _4.0 , (η _2.5 - _{η 4.0} )/η _2.5 is preferably 0.158 or greater, 0.163 or greater, and particularly 0.170 or greater. The temperature at a high-temperature viscosity of 10 ^2.5 dPa·s is generally an indicator of meltability, and the lower this temperature, the higher the meltability. However, when a composition is designed to achieve a high strain point, as in the present invention, the temperature at a high-temperature viscosity of 10 ^2.5 dPa·s inevitably becomes high. Furthermore, when a heat-resistant metal such as platinum is used in a fining vessel (fining pipe), it becomes difficult to raise the temperature of the fining vessel (fining pipe) to a temperature sufficient for fining due to the heat-resistance limit of platinum, with such a high-melting-point glass. However, even in such a case, if the temperature change relative to the viscosity change near the temperature at which the high-temperature viscosity is 10 ^2.5 dPa·s is large, the process window will be wider, which is advantageous for improving the foam quality. Note that "(η _2.5 - η _4.0 )/η _2.5 " is the value obtained by subtracting the temperature at which the high-temperature viscosity is 10 ^4.0 dPa·s from the temperature at which the high-temperature viscosity is 10 ^2.5 dPa·s, and dividing the result by the temperature at which the high-temperature viscosity is 10 ^{2.5 dPa·s. Furthermore, the "temperature at which the high-temperature viscosity is 10 2.5 dPa} ·s" and the "temperature at which the high-temperature viscosity is 10 ^4.0 dPa·s" can be measured by the platinum sphere pull-up method.

The specific Young's modulus is preferably 29.5 GPa/g cm ^-3 or more, 29.7 GPa/g cm ^-3 or more, 30 GPa/g cm ^-3 or more, 31 GPa/g cm ^-3 or more, 31.5 GPa/g cm ^-3 or more, particularly 32 GPa/g cm ^-3 or more. If the specific Young's modulus is low, the glass plate will be easily bent under its own weight, and the glass plate will be easily damaged during the film formation process of the p-Si TFT. The "specific Young's modulus" is the value obtained by dividing the Young's modulus by the density. The "Young's modulus" can be measured by the well-known resonance method.

The HF etching rate is preferably 0.8 μm/min or more, 0.9 μm/min or more, and particularly 1.0 μm/min or more. When glass plates are used as substrates for mobile devices, etc., they are thinned (slimmed) by hydrofluoric acid (HF) etching. If the HF etching rate is low, slimming takes a long time, which increases costs. Here, "HF etching rate" refers to the etching depth when a mirror-polished glass surface is etched with a 10% by weight HF aqueous solution at 20°C for 30 minutes.

The glass of the present invention preferably has a flat plate shape and an overflow confluence surface in the center in the plate thickness direction. In other words, it is preferably formed by the overflow downdraw method. The overflow downdraw method is a method in which molten glass is allowed to overflow from both sides of a wedge-shaped refractory, and the overflowing molten glass is drawn downward while being joined at the bottom end of the wedge to form a flat plate. In the overflow downdraw method, the surface that will become the surface of the glass plate does not come into contact with the refractory and is formed in a free surface state. This makes it possible to inexpensively produce unpolished glass plates with good surface quality. Furthermore, it is easy to make the glass larger and thinner.

In addition to the overflow downdraw method, glass sheets can also be formed using methods such as the slot-down method, redraw method, float method, and roll-out method.

The thickness of the glass of the present invention (in the case of a glass plate) is not particularly limited, but is preferably 1.0 mm or less, 0.7 mm or less, 0.5 mm or less, and particularly 0.05 to 0.4 mm. The smaller the thickness, the easier it is to reduce the weight of the organic EL display. The thickness can be adjusted by the flow rate and forming speed (plate drawing speed) during glass production, etc.

A method for industrially producing the glass of the present invention preferably includes a melting step of charging a glass batch prepared so as to contain, in mole percent, 67 to 73% of SiO ₂ , 10 to 15% of Al ₂ O ₃ , 0 to less than 3% of B ₂ O ₃ , 0 to 0.5% of Li ₂ O + Na ₂ O + K ₂ O , 0 to 8.5% of MgO, 3.5 to 12% of CaO, 0 to 2.5% of SrO, and 1 to 6% of BaO into a melting furnace and subjecting the batch to electrical heating using heating electrodes to obtain molten glass, and a forming step of forming the obtained molten glass into a flat glass plate having a thickness of 0.1 to 0.7 mm by an overflow downdraw method.

The manufacturing process for glass sheets generally includes a melting process, a fining process, a supplying process, a stirring process, and a forming process. The melting process is a process in which a glass batch containing glass raw materials is melted to obtain molten glass. The fining process is a process in which the molten glass obtained in the melting process is clarified using a fining agent or the like. The supplying process is a process in which the molten glass is transported between each process. The stirring process is a process in which the molten glass is stirred and homogenized. The forming process is a process in which the molten glass is formed into a glass sheet. Note that, if necessary, processes other than those mentioned above, such as a conditioning process in which the molten glass is adjusted to a state suitable for forming, may be incorporated after the stirring process.

Conventional low-alkali glass is typically melted industrially by heating with a burner combustion flame. The burner is typically located above the melting furnace and uses a fossil fuel, specifically a liquid fuel such as heavy oil or a gaseous fuel such as LPG, as fuel. The combustion flame can be obtained by mixing a fossil fuel with oxygen gas. However, this method results in a large amount of moisture being mixed into the molten glass during melting, which tends to increase the β-OH value. Therefore, when producing the glass of the present invention, electrical heating using a heating electrode is preferred. It is preferable to melt the glass by electrical heating using a heating electrode without heating with a burner combustion flame, i.e., completely electric melting. This reduces the likelihood of moisture being mixed into the molten glass during melting, making it easier to regulate the β-OH value to 0.30/mm or less, 0.25/mm or less, 0.20/mm or less, 0.15/mm or less, and particularly 0.10/mm or less. Furthermore, when electrical heating is performed using heating electrodes, the amount of energy per mass required to obtain molten glass is reduced, and the amount of molten volatiles is also reduced, thereby reducing the environmental impact.

Furthermore, with regard to this electrical heating, the lower the moisture content in the glass batch, the easier it is to reduce the moisture content in the glass sheet. The B ₂ O ₃ raw material introduced is likely to be the largest source of moisture contamination. Therefore, from the viewpoint of producing a glass sheet with low moisture content, it is preferable to keep the B ₂ O ₃ content as low as possible. Furthermore, the lower the moisture content in the glass batch, the easier it is for the glass batch to spread uniformly in the melting furnace, making it easier to produce a homogeneous, high-quality glass sheet.

Electrical heating using a heating electrode is preferably carried out by applying an AC voltage to a heating electrode installed at the bottom or side of the melting furnace so that it comes into contact with the molten glass inside the melting furnace. The material used for the heating electrode is preferably heat-resistant and corrosion-resistant to molten glass. For example, tin oxide, molybdenum, platinum, rhodium, etc. can be used, with molybdenum being particularly preferred from the standpoint of flexibility in furnace installation.

The glass of the present invention has a high electrical resistivity due to its low alkali metal oxide content. Therefore, when applying electrical heating using heating electrodes to low-alkali glass, current flows not only through the molten glass but also through the refractories constituting the melting furnace, which may prematurely damage the refractories constituting the melting furnace. To prevent this, it is preferable to use a zirconia-based refractory with high electrical resistivity, particularly electrocast zirconia bricks, as the furnace refractory. It is also preferable to incorporate small amounts of components that reduce electrical resistivity (such as Li ₂ O, Na 2 O, K ₂ O, and Fe ₂ O ₃ ) into the molten glass (glass composition), and it is particularly preferable to incorporate small amounts of Li ₂ O, Na ₂ O, and K ₂ O (for example, 0.01 _% by mass or more, particularly 0.02% by mass or more). The content of Fe ₂ O ₃ is preferably 0.005 to 0.03 mass%, 0.008 to 0.025 mass%, particularly preferably 0.01 to 0.02 mass%. Furthermore, the content of ZrO ₂ in the zirconia-based refractory is preferably 85 mass% or more, particularly preferably 90 mass% or more.

The present invention will now be described based on examples. However, the following examples are merely illustrative. The present invention is not limited to the following examples in any way.

Tables 1 to 6 show examples of the present invention (samples No. 1 to 91). Note that "N.A." in the tables means that the data has not been measured.

First, a glass batch prepared by blending glass raw materials to obtain the glass composition shown in the table was placed in a platinum crucible and melted at 1600 to 1650°C for 24 hours. The glass batch was stirred and homogenized using a platinum stirrer during melting. The molten glass was then poured onto a carbon plate, formed into a plate, and annealed at a temperature near the annealing point for 1 hour. For each sample obtained, the density ρ, average coefficient of thermal expansion α in the temperature range of 30 to 380°C, β-OH value, strain point Ps, annealing point Ta, softening point Ts, temperature at high-temperature viscosity 10 ^4.5 dPa s, temperature at high-temperature viscosity 10 ^4.0 dPa s, temperature at high-temperature viscosity 10 ^3.0 dPa s, temperature at high-temperature viscosity 10 ^2.5 dPa s, liquidus viscosity logη at TL, Young's modulus E, modulus of rigidity G, Poisson's ratio γ, specific Young's modulus E/ρ, and HF etching rate were evaluated.

Density ρ is a value measured using the well-known Archimedes method.

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

The β-OH value is measured using the method described above.

The strain point Ps, annealing point Ta, and softening point Ts were measured according to the methods of ASTM C336 and C338.

The temperatures at which the high temperature viscosities are 10 ^4.5 dPa·s, 10 ^4.0 dPa·s, 10 ^3.0 dPa·s and 10 ^2.5 dPa·s are values measured by the platinum sphere pull-up method.

The liquidus viscosity logηatTL is the viscosity of glass at the liquidus temperature TL, measured using the platinum ball pull-up method. The liquidus temperature TL is measured by placing glass powder that passes through a standard 30-mesh sieve (sieve openings 500μm) and remains on a 50-mesh sieve (sieve openings 300μm) in a platinum boat and holding it in a temperature gradient furnace for 24 hours, and then measuring the temperature at which crystals (primary phase) precipitate.

Young's modulus E and modulus of rigidity G are values measured using the well-known resonance method. Poisson's ratio is a value calculated from Young's modulus E and modulus of rigidity G. Specific Young's modulus E/ρ is the value obtained by dividing Young's modulus by density.

The HF etching rate is the etching depth when a mirror-polished glass surface is etched with a 10% by weight HF aqueous solution at 20°C for 30 minutes.

As is clear from Tables 1 to 9, Samples No. 1 to 91 had a low alkali metal oxide content, a strain point Ps of 734°C or higher, a temperature at which the high-temperature viscosity reached 10 ^2.5 dPa s was 1693°C or lower, and a liquidus viscosity of 10 ^4.32 dPa s or higher. Therefore, Samples No. 1 to 91 are considered suitable for use as substrates for organic EL displays and as carrier glasses used when fabricating organic EL elements on polyimide substrates.

Claims (3)

The glass has a glass composition, in mole percent _, of _SiO2 67-73%, _{Al2O3 12.3-15} %, B2O3 0-2 % , Li2O+ _Na2O + _K2O 0-0.5%, MgO 0-8.5%, CaO 3.5-6.1%, SrO 0-2.5%, _BaO 1-6%, and TiO2 _0-5 %, wherein the _molar ratio (MgO+CaO+SrO+BaO)/ _Al2O3 is 1.31 or _more , and the value obtained by dividing the strain point (°C) by _{the Al2O3} content (mol%) is 51 or more. 2. The glass according to claim 1, characterized in that the glass composition contains, in mole percent _, 67-73% SiO2 _, 12.3-15% _Al2O3 , _0-1.3 % B2O3, _0-0.5 % Li2O+ _Na2O +K2O, 0-3.2% MgO, _3.5-6.1 % CaO, 0-2% SrO, 3.5-6% BaO, and 0-5% _TiO2 , _wherein CaO-(SrO+BaO) is 0.7% or more, the molar ratio (MgO+CaO+SrO+BaO)/ _Al2O3 is 1.31 or more, _the molar ratio CaO/ _Al2O3 is 1.05 or less, and the molar ratio _SrO /BaO is 0.03-0.50. 2. The glass according to claim 1, characterized in that it has a glass composition, in mole percent, of _SiO2 67-73%, _{Al2O3 12.3-15} %, _{B2O3 0} to less than 1.8%, _Li2O + _Na2O + _K2O 0 to less than 0.5%, MgO 0-6%, CaO 5-6.1%, SrO 0-2%, BaO _3.5 % or more, and TiO2 0-5%, wherein CaO-(SrO+BaO) is 0.7% or more, the molar ratio SrO/BaO is 0.38 or less, the molar ratio (MgO+ _CaO +SrO+BaO)/ _Al2O3 is 1.31 to 1.70, and the value obtained by dividing the strain point (°C) by the _Al2O3 content ₍ mol %) is 55 or more.