TWI555715B - Alkali free glass - Google Patents

Description

Alkali-free glass

This invention relates to an alkali-free glass, and more particularly to an alkali-free glass suitable for use in an organic electroluminescence (EL) display.

An electronic device such as an organic EL display is used for a display of a mobile phone or the like because it is thin and has excellent animation display and low power consumption.

As a substrate of an organic EL display, a glass plate is widely used. The glass sheets for this purpose mainly require the following characteristics.

(1) In order to prevent the alkali ions from diffusing into the semiconductor material to be formed in the heat treatment step, it is required to substantially not contain the alkali metal oxide; (2) in order to reduce the glass plate, it is required to have excellent productivity. In particular, it is excellent in resistance to devitrification or melting; (3) In order to reduce heat shrinkage of the glass sheet in a low temperature polysilicon (LTPS) process, a strain point is required to be high.

However, for organic EL displays, portable products are currently in the mainstream, but it is expected that in the future, organic EL TVs will be expanded, and some manufacturers have begun to sell organic EL televisions.

The panel size of organic EL TVs is very large compared to portable products. Therefore, it is expected that the demand for the enlargement and thinning of the glass sheet will be strengthened in the future.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 4445176

The larger the glass sheet is, the thinner the glass sheet is, the more easily the glass sheet is deflected, and various types of defects are easily generated.

The glass sheet formed by the glass manufacturer is subjected to steps of cutting, annealing, inspecting, cleaning, etc., and in these steps, the glass sheet is put into a cassette formed with a multi-stage bracket, and from the card Move out of the shackles. The cassette is usually placed on the opposite sides of the glass plate on the left and right inner side surfaces and can be held in the horizontal direction. However, since the large and thin glass plate has a large amount of deflection, the glass plate is put into the card. In the middle of the process, a part of the glass plate is broken by contact with the cassette, or is shaken a lot when being carried out, and is likely to become unstable. This type of cassette is also used by electronic device manufacturers, so the same problem occurs.

Further, as the electronic device becomes larger and thinner, the glass plate attached to the electronic device is more likely to be bent, so that the image surface of the electronic device may appear to be deformed.

In order to solve the above problems, the following methods have been developed: increasing the specific Young's modulus (Young's modulus/density) or Young's modulus of the glass sheet, and reducing the amount of deflection. For example, Patent Document 1 discloses an alkali-free glass having a Young's modulus of 31 GPa or more and a Young's modulus of 76 GPa or more. However, since the alkali-free glass described in Patent Document 1 has a small amount of SrO and BaO, the devitrification resistance is low, and devitrification is likely to occur during molding. In order to improve the devitrification resistance is necessary to increase the content of B ₂ O _3, B ₂ O ₃ but is Young's modulus and the strain point depressant component together. When the Young's modulus and the strain point are lowered, the glass sheet is easily thermally shrunk in the LTPS process, and when the glass sheet is increased in size and thickness, a problem caused by deflection of the glass sheet may occur.

Therefore, the technical problem of the present invention is to reduce the manufacturing cost of a glass sheet by creating an alkali-free glass which is excellent in productivity (particularly resistance to devitrification) and has a sufficiently high strain point and Young's modulus. In the LTPS process, the heat shrinkage of the glass sheet is suppressed, and when the glass sheet is increased in size and thickness, the defects caused by the deflection of the glass sheet are also prevented.

As a result of various experiments, the inventors of the present invention have found that the above technical problems can be solved by strictly limiting the glass composition range of the alkali-free glass and limiting the glass characteristics to a predetermined range, and have been proposed as the present invention. That is, the alkali-free glass of the present invention is characterized in that it contains 55% to 80% of SiO ₂ and 10% to 25% of Al ₂ O ₃ and 2% to 5.5 as a glass composition by mass% (% by weight). % B ₂ O ₃ , 3% to 8% MgO, 3% to 10% CaO, 0.5% to 5% SrO, and 0.5% to 7% BaO, and the molar ratio of MgO/CaO is 0.5 to 1.5. It is substantially free of alkali metal oxides and has a Young's modulus higher than 80 GPa. Here, the term "substantially free of alkali metal oxide" means a case where the content of the alkali metal oxide (Li ₂ O, Na ₂ O, and K ₂ O) in the glass composition is 1000 ppm by weight or less. "Young's modulus" means a value measured by a bending resonance method. Further, 1 GPa corresponds to about 101.9 Kgf/mm ² .

The alkali-free glass of the present invention limits the glass composition range as described above. When it is set as such, the devitrification resistance, the strain point, and the Young's modulus can be sufficiently improved. In particular, if the molar ratio of MgO/CaO is limited to 0.5 to 1.5, the devitrification resistance or the Young's modulus can be remarkably improved.

Second, the alkali-free glass of the present invention preferably further contains 0.001% by mass to 1% by mass of SnO ₂ .

Third, the alkali-free glass of the present invention preferably has a strain point higher than 680 °C. Here, the "strain point" means a value measured according to the method of ASTM C336.

Fourth, the alkali-free glass of the present invention preferably has a liquidus temperature of less than 1210 °C. Here, the "liquidus temperature" can be calculated by placing a glass powder which has passed through a standard sieve of 30 mesh (500 μm) and remaining on 50 mesh (300 μm) into a platinum boat, and then maintains it in a temperature gradient furnace. The temperature at which the crystals were precipitated was measured for 24 hours.

Fifth, the alkali-free glass of the present invention preferably has an average thermal expansion coefficient of 30 × 10 ^-7 / ° C to 50 × 10 ^-7 / ° C in a temperature range of from 30 ° C to 380 ° C. Here, the "average thermal expansion coefficient in a temperature range of 30 ° C to 380 ° C" can be measured by a dilatometer.

Sixth, the alkali-free glass of the present invention preferably has a temperature of less than 1600 ° C at 10 ^2.5 poise. Here, "the temperature at 10 ^2.5 poise" can be measured by a platinum ball pulling method.

Seventh, the alkali-free glass of the present invention preferably has a viscosity at a liquidus temperature of 10 ^4.8 poise or more. Further, the "viscosity at the liquidus temperature" can be measured by a platinum ball pulling method.

Eighth, the alkali-free glass of the present invention is preferably formed by an overflow down draw method.

Ninth, the alkali-free glass of the present invention preferably has a thickness of less than 0.5 mm.

Tenth, the alkali-free glass of the present invention is preferably used in an organic EL device.

In the alkali-free glass according to the embodiment of the present invention, as a glass composition, 55% to 80% of SiO ₂ , 10% to 25% of Al ₂ O ₃ , and 2% to 5.5% of B ₂ O are contained by mass%. ₃ , 3%~8% MgO, 3%~10% CaO, 0.5%~5% SrO and 0.5%~7% BaO, Moor than MgO/CaO is 0.5~1.5, substantially no alkali Metal oxide. The reason why the range of each component is limited as described above is shown below. In addition, unless otherwise indicated, in the description of the content of each component, % means the mol% (% of moles).

SiO ₂ is a component that forms a skeleton of the glass. The content of SiO ₂ is 55% to 80%, preferably 55% to 75%, more preferably 55% to 70%, and further preferably 55% to 65%. When the content of SiO ₂ is too small, it is difficult to increase the Young's modulus. In addition, the acid resistance is liable to lower and the density becomes too high. On the other hand, when the content of SiO ₂ is too large, the high-temperature viscosity is high, and the meltability is liable to lower. Further, devitrified crystals such as cristobalite are likely to be precipitated, and the liquidus temperature is likely to rise.

Al ₂ O ₃ is a component that forms a skeleton of the glass, and is a component that increases the Young's modulus, and further a component that suppresses phase separation. The content of Al ₂ O ₃ is from 10% to 25%, preferably from 12% to 20%, more preferably from 14% to 20%. When the content of Al ₂ O ₃ is too small, the Young's modulus is liable to lower, and the glass is easily separated into phases. On the other hand, when the content of Al ₂ O ₃ is too large, devitrified crystals such as mullite or anorthite are easily precipitated, and the liquidus temperature tends to rise.

B ₂ O ₃ is a component which improves meltability and improves resistance to devitrification. The content of B ₂ O ₃ is 2% to 5.5%, preferably 2.5% to 5.5%, more preferably 3% to 5.5%, and further preferably 3% to 5%. When the content of B ₂ O ₃ is too small, the meltability or the devitrification resistance is liable to lower, and the resistance to the hydrofluoric acid-based chemical liquid is liable to lower. On the other hand, when the content of B ₂ O ₃ is too large, the Young's modulus or acid resistance is liable to lower.

MgO is a component which lowers the high-temperature viscosity and improves the meltability, and is a component which significantly increases the Young's modulus in the alkaline earth metal oxide. The content of MgO is 3% to 8%, preferably 3.5% to 8%, more preferably 4% to 8%, and further preferably 4.5% to 8%, particularly preferably 5% to 8%. When the content of MgO is too small, the meltability or Young's modulus is liable to lower. On the other hand, when the content of MgO is too large, the devitrification resistance is liable to lower.

CaO is a component which does not lower the strain point and lowers the high temperature viscosity and remarkably improves the meltability. Further, in the alkaline earth metal oxide, since the raw material to be introduced is relatively inexpensive, it is a component which makes the raw material cost low. The content of CaO is 3% to 10%, preferably 3.5% to 9%, more preferably 4% to 8.5%, and further preferably 4% to 8%, particularly preferably 4% to 7.5%. If the content of CaO is too small, it is difficult to enjoy the above effects. On the other hand, if the content of CaO is too large, the glass is easily devitrified.

SrO is a component that suppresses phase separation and improves resistance to devitrification. Further, it is a component that does not lower the strain point, lowers the high-temperature viscosity, improves the meltability, and is a component that suppresses an increase in the liquidus temperature. The content of SrO is from 0.5% to 5%, preferably from 0.5% to 4%, more preferably from 0.5% to 3.5%. If the content of SrO is less than 0.5%, it is difficult to enjoy the above effects. On the other hand, if When the content of SrO is too large, the devitrified crystal of the strontium silicate system is likely to be precipitated, and the devitrification resistance is liable to be lowered.

BaO is a component that improves resistance to devitrification. The content of BaO is from 0.5% to 7%, preferably from 0.5% to 6%, more preferably from 0.5% to 5%, and even more preferably from 0.5% to 4.5%. If the content of BaO is too small, it is difficult to enjoy the above effects. On the other hand, when the content of BaO is too large, the high-temperature viscosity is too high, and the meltability is liable to lower, and the devitrified crystal containing BaO is likely to be precipitated, and the liquidus temperature is likely to rise.

The molar ratio of CaO/MgO is an important component ratio in terms of both high Young's modulus and high resistance to devitrification, and the cost of manufacturing the glass sheet is reduced. The molar ratio CaO/MgO is 0.5 to 1.5, preferably 0.5 to 1.3, 0.5 to 1.2, 0.5 to 1.1, and particularly preferably 0.5 to 1.0. When the molar ratio of CaO/MgO is too small, the devitrified crystal of the chalk is easily precipitated, the devitrification resistance is likely to be lowered, and the raw material cost is likely to be high. On the other hand, when the molar ratio of CaO/MgO is too large, the devitrified crystal of the alkaline earth aluminum silicate such as anorthite is easily precipitated, and the devitrification resistance is liable to be lowered, and the Young's modulus is hard to be improved.

In addition to the above components, for example, the following components may be added as an optional component. In addition, the content of the other components other than the above-mentioned components is preferably 10% or less, and particularly preferably 5% or less from the viewpoint of the effect of the present invention.

ZnO is a component that improves the meltability. However, if a large amount of ZnO is contained, the glass is easily devitrified, and the strain point is liable to lower. The content of ZnO is preferably 0% to 5%, 0% to 4%, 0% to 3%, and particularly preferably 0% to 2%.

SnO ₂ is a component having a good clarifying action in a high temperature range, and is a component for improving strain point and a component for lowering high temperature viscosity. The content of SnO ₂ is preferably 0% to 1%, 0.001% to 1%, 0.01% to 0.5%, and particularly preferably 0.05% to 0.3%. When the content of SnO ₂ is too large, devitrified crystals of SnO ₂ are easily precipitated. Further, when the content of SnO ₂ is less than 0.001%, it is difficult to enjoy the above effects.

As described above, SnO _{2 is} suitable as the clarifying agent. However, as long as the glass characteristics are not impaired, 5% or less of metal powders of F, Cl, SO ₃ , C, Al, Si, or the like may be added as a clarifying agent. Further, CeO ₂ or the like of 5% or less may be added as a clarifying agent.

As a clarifying agent, As ₂ O ₃ and Sb ₂ O _{3 are} also effective. The alkali-free glass of the present invention does not completely exclude the inclusion of such components, but from the viewpoint of environmental properties, it is preferred to use as few components as possible. Further, when As ₂ O ₃ is contained in a large amount, the solarization resistance tends to decrease. The content of As ₂ O ₃ is preferably 1% or less and 0.5% or less, particularly preferably 0.1% or less, and is preferably substantially not contained. Here, "substantially free of As ₂ O ₃ " means that the content of As ₂ O ₃ in the glass composition is less than 0.05%. Further, the content of Sb ₂ O ₃ is preferably 1% or less, particularly preferably 0.5% or less, and is preferably substantially not contained. Here, "substantially free of Sb ₂ O ₃ " means that the content of Sb ₂ O ₃ in the glass composition is less than 0.05%.

Cl has an effect of promoting the melting of the alkali-free glass. When Cl is added, the melting temperature can be lowered and the action of the clarifying agent can be promoted. As a result, the melting cost can be reduced, and the life of the glass-making kiln can be extended. However, if the content of Cl is too large, the strain point is liable to lower. Therefore, the content of Cl is preferably 3% or less and 1% or less, and particularly preferably 0.5% or less. Furthermore, chlorine can be used. A raw material such as chloride of an alkaline earth metal oxide such as hydrazine or aluminum chloride is used as a raw material for introduction of Cl.

P ₂ O ₅ is a component which increases the strain point, and is a component which can remarkably suppress precipitation of an alkaline earth aluminosilicate devitrified crystal such as anorthite. However, if P ₂ O ₅ is contained in a large amount, the glass is easily phase-separated. The content of P ₂ O ₅ is 0% to 2.5%, preferably 0% to 1.5%, more preferably 0% to 0.5%, and further preferably 0% to 0.3%.

TiO ₂ is a component which lowers the high-temperature viscosity and improves the meltability, and is a component which suppresses aging. However, when TiO ₂ is contained in a large amount, the glass is colored, and the transmittance is liable to lower. The content of TiO ₂ is preferably 0% to 5%, 0% to 3%, 0% to 1%, and particularly preferably 0% to 0.02%.

For Y ₂ O ₃ , Nb ₂ O ₅ , and La ₂ O ₃ , there is an effect of increasing the strain point, the Young's modulus, and the like. However, if the content of these components is more than 5%, respectively, the density is liable to increase.

In the alkali-free glass of the present invention, the strain point is preferably more than 680 ° C, 685 ° C or more, 690 ° C or more, and particularly preferably 695 ° C or more. If so set, the heat shrinkage of the glass sheet can be suppressed in the LTPS process.

In the alkali-free glass of the present invention, the Young's modulus exceeds 80 GPa, preferably 82 GPa or more, 83 GPa or more, and particularly preferably 83.5 GPa or more. If the Young's modulus is too low, it is likely to cause a problem caused by the deflection of the glass plate.

In the alkali-free glass of the present embodiment, the average thermal expansion coefficient in the temperature range of 30 ° C to 380 ° C is preferably 30 × 10 ^-7 / ° C to 50 × 10 ^-7 / ° C, 32 × 10 ^-7 / ° C - 50 ×10 ^-7 /°C, 33×10 ^-7 /°C~50×10 ^-7 /°C, 34×10 ^-7 /°C~50×10 ^-7 /°C, especially good 35×10 ^-7 /°C~ 50 × 10 ^-7 / ° C. If it is set as such, it is easy to integrate with the thermal expansion coefficient of Si for TFT.

In the alkali-free glass of the present embodiment, the liquidus temperature is preferably less than 1210 ° C and 1200 ° C or less, and particularly preferably 1190 ° C or less. When it is set as such, it is easy to prevent devitrification crystallization at the time of glass manufacture, and productivity may fall. Further, since the molding is easy by the overflow down-draw method, the surface quality of the glass sheet can be easily improved, and the production cost of the glass sheet can be reduced. Further, the liquidus temperature is an index of resistance to devitrification, and the lower the liquidus temperature, the more excellent the devitrification resistance.

In recent years, with the increase in the definition of the display, the circuit pattern tends to be fine. Therefore, tiny foreign objects that have not been problematic before have gradually become the cause of disconnection or short circuit. In terms of preventing such problems, the significance of improving resistance to devitrification is also large.

In the alkali-free glass of the present embodiment, the viscosity at the liquidus temperature is preferably 10 ^4.8 poise or more, 10 ^5.0 poise or more, 10 ^5.2 poise or more, and particularly preferably 10 ^5.5 poise or more. When it is set as described above, devitrification is less likely to occur during molding, so that the glass sheet can be easily formed by the overflow down-draw method. As a result, the surface quality of the glass sheet can be improved, and the production cost of the glass sheet can be reduced. Further, the viscosity at the liquidus temperature is an index of formability, and the higher the viscosity at the liquidus temperature, the more the formability is improved.

In the alkali-free glass of the present embodiment, the temperature at 10 ^2.5 poise is preferably 1600 ° C or lower and 1580 ° C or lower, and particularly preferably 1570 ° C or lower. When the temperature at 10 ^2.5 poise is high, it is difficult to melt the glass, and the manufacturing cost of the glass sheet becomes high. Further, the temperature at 10 ^2.5 poise corresponds to the melting temperature, and the lower the temperature, the higher the meltability.

The alkali-free glass of the present embodiment is preferably formed by an overflow down-draw method. The overflow down-draw method is a method in which molten glass is allowed to overflow from both sides of a heat-resistant flow-like structure, and the molten glass that has overflowed merges at the lower end of the flow-like structure, and is formed by extending downward to form a glass plate. . In the overflow down-draw method, the surface to be the surface of the glass sheet is not in contact with the flow-like refractory, but is formed in a state of a free surface. Therefore, it is possible to inexpensively manufacture a glass plate which is not polished and has a good surface quality, and is also easy to be thinned. Further, the structure or material of the launder structure used in the overflow down-draw method is not particularly limited as long as the required size or surface precision can be achieved. Further, the method of applying a force when performing the downward stretching molding is not particularly limited. For example, a method of rotating and extending in a state where a heat-resistant roller having a sufficiently large width is brought into contact with the glass, or a method of bringing a plurality of pairs of heat-resistant rollers into contact with and extending only near the end surface of the glass may be employed.

In addition to the overflow down-draw method, for example, a glass plate can be formed by a down-draw method (such as a gully type down method) or a floating method.

In the alkali-free glass of the present embodiment, the thickness is not particularly limited, but is preferably less than 0.5 mm, 0.4 mm or less, and 0.35 mm or less, and particularly preferably 0.3 mm or less. The thinner the thickness, the more lightweight the device can be. The thickness can be adjusted by using the flow rate at the time of glass manufacture, the speed of the pull plate, and the like.

The alkali-free glass of the present embodiment is preferably used in an organic EL device, particularly an organic EL display. Especially for TV applications, after making multiple devices on a glass plate, the devices are divided and cut one by one, which can reduce the cost. (so-called multi-chamfering). Since the alkali-free glass of the present invention has a low liquidus temperature and a high viscosity at a liquidus temperature, it is easy to form a large glass plate, and this requirement can be satisfied.

[Example]

Hereinafter, examples of the invention will be described. Furthermore, the following examples are merely illustrative. The invention is not limited by the following examples.

Examples (Examples No. 1 to No. 13) and Comparative Examples (Sample No. 14, No. 15) of the present invention are shown in Tables 1 and 2.

First, a glass batch prepared by blending a glass raw material into a platinum crucible so as to have a glass composition in the table was melted at 1600 ° C to 1650 ° C for 24 hours. When the glass batch was melted, it was stirred using a platinum stir bar to homogenize. Then, the molten glass was discharged onto a carbon plate, formed into a plate shape, and annealed at a temperature near the annealing point for 30 minutes. The obtained samples were evaluated for density, average thermal expansion coefficient CTE at a temperature range of 30 ° C to 380 ° C, strain point Ps, annealing point Ta, softening point Ts, temperature at a high temperature viscosity of 10 ⁴ dPa ‧ s, and high temperature viscosity 10 ³ The temperature at dPa‧s, the temperature at high temperature viscosity of 10 ^2.5 dPa‧s, the liquidus temperature TL and the viscosity log ₁₀ ηTL at liquidus temperature TL.

The density is a value measured by the well-known Archimedes method.

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

The strain point Ps, the annealing point Ta, and the softening point Ts are values measured according to the method of ASTM C336.

The temperature at a high temperature viscosity of 10 ⁴ dPa ‧ s, 10 ³ dPa ‧ s, and 10 ^2.5 dPa ‧ s is a value measured by a platinum ball pulling method.

The liquidus temperature TL is a glass powder which has passed through a standard sieve of 30 mesh (500 μm) and remains on 50 mesh (300 μm), and is placed in a platinum boat, and maintained in a temperature gradient furnace for 24 hours, and then the temperature of the crystallization is measured. The value obtained.

The viscosity log ₁₀ ηTL at the liquidus temperature is a value obtained by measuring the viscosity of the glass at the liquidus temperature TL by a platinum ball pulling method.

Tables 1 and 2 show that samples No. 1 to No. 13 have a Young's modulus of 80 GPa or more, a strain point of more than 680 ° C, and a liquidus temperature of less than 1210 ° C because the glass composition is limited to a predetermined range. Therefore, heat shrinkage in the LTPS process can be reduced, and even if the glass plate is enlarged and thinned, it is less likely to cause a problem caused by deflection. Therefore, Sample Nos. 1 to No. 13 are considered to be suitable as substrates for organic EL displays.

On the other hand, since sample No. 14 did not restrict the glass composition to a predetermined range, the liquidus temperature was high and the devitrification resistance was low. Therefore, the sample No. 14 is inferior in formability, and the quality or reliability of the display may be degraded due to minute foreign matter. Further, since Sample No. 15 did not limit the glass composition to a predetermined range, the temperature of 10 ^2.5 was high and the Young's modulus was low. Therefore, the sample No. 15 is inferior in meltability, and if the glass plate is increased in size and thickness, defects due to deflection may occur.

[Industrial availability]

The alkali-free glass of the present invention is suitable for a flat panel display substrate such as a liquid crystal display or an EL display, a charge coupled device (CCD), and a similar proximity solid-state imaging device (Contact Image Sensor (CIS)). The cover glass for image sensors, the substrate for solar cells, the cover glass, and the substrate for organic EL illumination are particularly suitable as substrates for organic EL displays.

Claims (10)

An alkali-free glass characterized by containing 55% to 80% of SiO ₂ , 10% to 25% of Al ₂ O ₃ , and 2% to 5.5% of B ₂ O ₃ as a glass composition. 3%~8% MgO, 3%~7.5% CaO, 0.5%~5% SrO, 0.5%~7% BaO and 0%~5% ZnO, molar ratio MgO/CaO is 0.5~1.3 It does not substantially contain an alkali metal oxide, the liquidus temperature is below 1210 ° C, and the Young's modulus is higher than 80 GPa. The alkali-free glass according to claim 1, wherein the alkali-containing glass further contains 0.001% by mass to 1% by mass of SnO ₂ . The alkali-free glass according to claim 1 or 2, wherein the strain point is higher than 680 °C. The alkali-free glass according to claim 1 or 2, wherein the liquidus temperature is lower than 1210 °C. The alkali-free glass according to claim 1 or 2, wherein the average thermal expansion coefficient in the temperature range of 30 ° C to 380 ° C is 30 × 10 ^-7 / ° C to 50 × 10 ^-7 / ° C. The alkali-free glass according to claim 1 or 2, wherein the temperature at 10 ^2.5 poise is lower than 1600 °C. The alkali-free glass according to claim 1 or 2, wherein the viscosity at the liquidus temperature is 10 ^4.8 poise or more. The alkali-free glass according to claim 1 or 2, which is formed by an overflow down-draw method. The alkali-free glass according to claim 1 or 2, wherein the thickness is thinner than 0.5 mm. An alkali-free glass as described in claim 1 or 2, which is used in an organic EL device.