JP2016188148A - Alkali-free glass and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkali-free glass with a high Young's modulus, which can be easily melted with a low temperature Tat which glass viscosity reaches 10dPa s, and easily formed by float process with a low temperature Tat which glass viscosity reaches 10dPa s, having a relatively low thermal expansion coefficient and a relatively low specific gravity.SOLUTION: An alkali-free glass has a strain point of 690°C or higher, an average thermal expansion coefficient at 50 to 350°C of 30×10to 43×10/°C, a temperature Tat which glass viscosity reaches 10dPa s of 1710°C or low, a temperature Tat which glass viscosity reaches 10dPa s of 1330°C or low, and a Young's modulus of 80 GPa or more, containing SiO: 57 to 65, AlO: 18 to 23, BO: 0 to 5, MgO: more than 1 to less than 8, CaO: 6 to 12, SrO: 0 or more and less than 2, BaO: 0 or more and less than 5, and MgO+CaO+SrO+BaO: 12 to 23 expressed in mass% in terms of oxides.SELECTED DRAWING: None

Description

  The present invention relates to an alkali-free glass that is suitable for various display substrate glasses and photomask substrate glasses and that is substantially free of alkali metal oxides and can be float-molded.

Conventionally, the following characteristics have been required for various display substrate glasses, particularly those in which a metal or oxide thin film is formed on the surface.
(1) When an alkali metal oxide is contained, alkali metal ions diffuse into the thin film and deteriorate the film characteristics, so that the alkali metal ions are not substantially contained.
(2) When exposed to a high temperature in the thin film forming process, the strain point is high so that the deformation (thermal shrinkage) associated with glass deformation and glass structural stabilization can be minimized.

(3) Sufficient chemical durability against various chemicals used for semiconductor formation. In particular, buffered hydrofluoric acid (BHF: mixture of hydrofluoric acid and ammonium fluoride) for etching SiO _x and SiN _x , and chemicals containing hydrochloric acid used for etching ITO, various acids used for etching metal electrodes (Nitric acid, sulfuric acid, etc.) Resistant to alkali of resist stripping solution.
(4) There are no defects (bubbles, striae, inclusions, pits, scratches, etc.) inside and on the surface.

In addition to the above requirements, in recent years, there are the following situations.
(5) The weight reduction of the display is required, and the glass itself is desired to have a low density glass.
(6) A reduction in the weight of the display is required, and a reduction in the thickness of the substrate glass is desired.

(7) In addition to the conventional amorphous silicon (a-Si) type liquid crystal display, a polycrystalline silicon (p-Si) type liquid crystal display having a slightly higher heat treatment temperature has been produced (a-Si). : About 350 ° C. → p-Si: 350 to 550 ° C.).
(8) A glass having a small average thermal expansion coefficient is required to increase productivity and thermal shock resistance by increasing the temperature raising / lowering rate of the heat treatment for producing a liquid crystal display.

On the other hand, dry etching has progressed, and the demand for BHF resistance has become weaker. As the conventional glass, a glass containing 6 to 10 mol% of B ₂ O ₃ has been often used in order to improve the BHF resistance. However, B ₂ O ₃ tends to lower the strain point. Examples of non-alkali glass not containing B ₂ O ₃ or having a low content are as follows.

Patent Document 1 discloses a glass containing 0 to 3% by weight of B ₂ O ₃ , but the strain point of Examples is 690 ° C. or lower.

Patent Document 2 discloses a glass containing 0 to 5 mol% of B ₂ O ₃ , but the average coefficient of thermal expansion at 50 to 350 ° C. exceeds 50 × 10 ⁻⁷ / ° C.

  In order to solve the problems in the glasses described in Patent Documents 1 and 2, an alkali-free glass described in Patent Document 3 has been proposed. The alkali-free glass described in Patent Document 3 has a high strain point, can be formed by a float process, and is suitable for applications such as a display substrate and a photomask substrate.

JP-A-4-325435 Japanese Patent Laid-Open No. 5-232458 JP-A-9-263421

In recent years, in high-definition small displays such as portable terminals such as smartphones, a method using laser annealing has been adopted as a method for producing high-quality p-Si TFTs. However, in order to further reduce the compaction, the distortion point is high. There is a need for glass. Further, as the glass substrate becomes larger and thinner, a glass having a high Young's modulus and a high specific modulus (Young's modulus / density) is required.
On the other hand, due to demands in the glass manufacturing process, especially float forming, the glass viscosity, particularly the temperature T _{4 at} which the glass viscosity becomes 10 ⁴ dPa · s and the devitrification temperature should be lowered, and the strain point should not be raised excessively. Is required.

The object of the present invention is to solve the above drawbacks, have a high strain point and a high Young's modulus, but have a low temperature T _{2 at} which the glass viscosity becomes 10 ² dPa · s and is easy to melt, and the glass viscosity is 10 An object of the present invention is to provide an alkali-free glass that has a low temperature T _{4 of} ⁴ dPa · s and is easy to float, and that can keep the thermal expansion coefficient and specific gravity relatively low.

The present invention has a strain point of 690 ° C. or higher, an average coefficient of thermal expansion at 50 to 350 ° C. of 30 × 10 ⁻⁷ to 43 × 10 ⁻⁷ / ° C., and a glass viscosity of 10 ² dPa · s. The temperature T ₂ is 1710 ° C. or lower, the temperature T ₄ at which the glass viscosity is 10 ⁴ dPa · s is 1330 ° C. or lower, and the Young's modulus is 80 GPa or higher. SiO ₂ 57-65,
Al ₂ O ₃ 18-23,
B ₂ O ₃ 0-5,
MgO more than 1 and less than 8,
CaO 6-12,
SrO 0 or more and less than 2,
Provided is an alkali-free glass containing BaO 0 or more and less than 5 and having MgO + CaO + SrO + BaO of 12-23.

  The alkali-free glass of the present invention is particularly suitable for a display substrate, a photomask substrate and the like for high strain point use, and is a glass that is easy to float. The alkali-free glass of the present invention can also be used as a glass substrate for a magnetic disk.

Next, the composition range of each component will be described. If the SiO ₂ content is less than 57% (% by mass, the same unless otherwise specified), the strain point is not sufficiently increased, the thermal expansion coefficient is increased, and the density is increased. It is preferably 58% or more, more preferably 59% or more, and further preferably 60% or more. In 65 percent, the solubility decreases, the glass viscosity of 10 ² dPa · s and comprising temperature T ₂ and the temperature T ₄ which is a 10 ⁴ dPa · s is increased, since the devitrification temperature increases, less 65% It is. 64% or less is preferable and 63% or less is more preferable.

Al ₂ O ₃ suppresses the phase separation of the glass, lowers the thermal expansion coefficient and raises the strain point. However, if it is less than 18%, this effect does not appear, and other components that increase the expansion increase. As a result, thermal expansion increases. For this reason, it is 18% or more. 18.5% or more is preferable, and 19% or more is more preferable. If it exceeds 23%, the solubility of the glass may be deteriorated or the devitrification temperature may be increased, so it is 23% or less. It is preferably 22% or less, and more preferably 21% or less.

B ₂ O ₃ can be contained to improve the melting reactivity of the glass, lower the devitrification temperature, and improve the BHF resistance. In order to acquire said effect, 0.1% or more is preferable, 0.3% or more is more preferable, 0.5% or more is further more preferable, and 1% or more is especially preferable. However, if it exceeds 5%, the strain point becomes low and the Young's modulus becomes small, so it is 5% or less. It is preferably 4% or less, more preferably 3% or less, and further preferably 2.5% or less.

  MgO has the characteristics of increasing the Young's modulus while keeping the density low and does not increase expansion in alkaline earths, and improves the solubility, but this effect does not appear sufficiently at 1% or less, Moreover, since the density becomes high because the ratio of other alkaline earths becomes high, it exceeds 1%. It is preferably 2% or more, more preferably 3% or more, further preferably 4% or more, still more preferably 4.5% or more, and particularly preferably 5% or more. Since devitrification temperature rises at 8% or more, it is preferably 7.5% or less, more preferably 7% or less, and even more preferably 6.5% or less, which is less than 8%.

CaO has the characteristics of increasing the Young's modulus while maintaining the low density without increasing the expansion in alkaline earth following MgO, and also improves the solubility. If it is less than 6%, the above-described effect due to the addition of CaO is not sufficiently exhibited, so it is 6% or more. It is preferably 7% or more, more preferably 7.5% or more, and further preferably 8% or more. However, if it exceeds 12%, the devitrification temperature rises, and phosphorus, which is an impurity in limestone (CaCO ₃ ) that is a CaO raw material, may be mixed in a large amount. 11% or less is preferable, 10.5% or less is more preferable, and 10% or less is more preferable.

  SrO can be contained in order to improve the solubility without increasing the devitrification temperature of the glass. However, if it is 2% or more, the expansion coefficient may increase, so it is less than 2%. It is preferably 1.5% or less, more preferably 1% or less, still more preferably 0.7% or less, and particularly preferably less than 0.5%.

  BaO can be included to improve solubility. 1% or more is preferable, 1.5% or more is more preferable, and 2% or more is more preferable. However, if it is too much, the expansion and density of the glass are excessively increased, so the content is made less than 5%. 4.5% or less is preferable and 4% or less is more preferable.

If the total amount of MgO, CaO, SrO, and BaO is less than 12%, the temperature T _{4 at} which the glass viscosity becomes 10 ⁴ dPa · s increases, and the float bath casing structure and heater are used during float forming. It is 12% or more because there is a risk of extremely shortening the service life. 14% or more is preferable, and 16% or more is more preferable. If it exceeds 23%, there is a possibility that the thermal expansion coefficient cannot be reduced, so that it is 23% or less. 21% or less is preferable and 19% or less is more preferable.

The glass of the present invention does not contain an alkali metal oxide in excess of the impurity level (ie substantially) in order not to cause deterioration of the characteristics of the metal or oxide thin film provided on the glass surface during panel production. In order to facilitate recycling of the glass, it is preferable that PbO, As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained.

Furthermore, for the same reason, it is preferable that the P ₂ O ₅ content is not substantially contained.

The alkali-free glass of the present invention improves ZrO ₂ , ZnO, Fe ₂ O ₃ , SO ₃ , F, Cl, SnO ₂ in order to improve the solubility, clarity and formability (float formability) of the glass in addition to the above components. In a total amount of 5% or less, preferably 1% or less, more preferably 0.5% or less, and still more preferably 0.1% or less. More preferably, ZrO ₂ and ZnO are not substantially contained.

Since the alkali-free glass of the present invention has a strain point of 690 ° C. or higher, thermal shrinkage during panel production can be suppressed. Further, a laser annealing method can be applied as a method for manufacturing the p-Si TFT. 695 ° C or higher is more preferable, 700 ° C or higher is more preferable, and 705 ° C or higher is particularly preferable.
Since the alkali-free glass of the present invention has a strain point of 690 ° C. or higher, it is used for high strain points (for example, for organic EL having a thickness of 0.7 mm or less, preferably 0.5 mm or less, more preferably 0.3 mm or less). Suitable for display substrates or illumination substrates, or thin display substrates or illumination substrates having a thickness of 0.3 mm or less, preferably 0.1 mm or less.
When forming a sheet glass having a plate thickness of 0.7 mm or less, further 0.5 mm or less, further 0.3 mm or less, and further 0.1 mm or less, the drawing speed at the time of forming tends to increase. Rises and the compaction of the glass tends to increase. In this case, compaction can be suppressed when the glass is a high strain point glass.

  The alkali-free glass of the present invention has a glass transition point of preferably 740 ° C. or higher, more preferably 750 ° C. or higher, and further preferably 760 ° C. or higher for the same reason as the strain point.

The alkali-free glass of the present invention has an average coefficient of thermal expansion at 50 to 350 ° C. of 30 × 10 ⁻⁷ to 43 × 10 ⁻⁷ / ° C., has high thermal shock resistance, and has high productivity during panel production. it can. In the alkali-free glass of the present invention, the average thermal expansion coefficient at 50 to 350 ° C. is preferably 35 × 10 ⁻⁷ or more. The average thermal expansion coefficient at 50 to 350 ° C. is preferably 42.5 × 10 ⁻⁷ / ° C. or less, more preferably 42 × 10 ⁻⁷ / ° C. or less, and further preferably 41.5 × 10 ⁻⁷ / ° C. or less. is there.

  Furthermore, the alkali-free glass of the present invention has a specific gravity of preferably 2.7 or less, more preferably 2.65 or less, and even more preferably 2.6 or less.

The alkali-free glass of the present invention has a temperature T _{2 at} which the viscosity becomes 10 ² dPa · s is 1710 ° C. or less, preferably 1690 ° C. or less, more preferably 1670 ° C. or less, further preferably 1650 ° C. or less, particularly Since it is preferably 1640 ° C. or lower, dissolution is relatively easy.

Further, the alkali-free glass of the present invention has a temperature T _{4 at} which the viscosity becomes 10 ⁴ dPa · s is 1330 ° C. or less, preferably 1320 ° C. or less, more preferably 1310 ° C. or less, still more preferably 1300 ° C. or less, particularly preferably Is 1290 ° C. or lower, which is preferable for float molding.
In addition, the alkali-free glass of the present invention preferably has a devitrification temperature of 1320 ° C. or lower because the molding by the float method becomes easy. Preferably they are 1310 degrees C or less, 1300 degrees C or less, and 1290 degrees C or less. Further, the difference between the temperature T ₄ (temperature at which the glass viscosity becomes 10 ⁴ dPa · s, unit: ° C.) and the devitrification temperature (T ₄ −devitrification temperature), which is a standard of float moldability and fusion moldability, Preferably it is -20 degreeC or more, -10 degreeC or more, Furthermore, it is 0 degreeC or more, More preferably, it is 10 degreeC or more, More preferably, it is 20 degreeC or more, Most preferably, it is 30 degreeC or more.
In this specification, the devitrification temperature is obtained by putting crushed glass particles in a platinum dish and performing heat treatment for 17 hours in an electric furnace controlled at a constant temperature. It is an average value of the maximum temperature at which crystals are deposited inside and the minimum temperature at which crystals are not deposited.

  The alkali-free glass of the present invention preferably has a Young's modulus of 80 GPa or more, 81 GPa or more, 82 GPa or more, 84 GPa or more, more preferably 85 GPa or more, and more preferably 86 GPa or more.

The alkali-free glass of the present invention preferably has a photoelastic constant of 31 nm / MPa / cm or less.
Due to the birefringence of the glass substrate due to stress generated during the manufacturing process of the liquid crystal display panel and the liquid crystal display device, a phenomenon in which the black display becomes gray and the contrast of the liquid crystal display decreases may be observed. By setting the photoelastic constant to 31 nm / MPa / cm or less, this phenomenon can be suppressed small. Preferably it is 30 nm / MPa / cm or less, More preferably, it is 29 nm / MPa / cm or less, More preferably, it is 28.5 nm / MPa / cm or less, Most preferably, it is 28 nm / MPa / cm or less.
The alkali-free glass of the present invention has a photoelastic constant of preferably 23 nm / MPa / cm or more, more preferably 25 nm / MPa / cm or more, considering the ease of securing other physical properties.
The photoelastic constant can be measured by a disk compression method at a measurement wavelength of 546 nm.

  Further, the alkali-free glass of the present invention preferably has a small shrinkage during heat treatment. In liquid crystal panel manufacturing, the heat treatment process is different between the array side and the color filter side. Therefore, particularly in a high-definition panel, when the thermal shrinkage rate of glass is large, there is a problem in that dot displacement occurs during fitting. The evaluation of the heat shrinkage rate can be measured by the following procedure. The sample is held at a temperature of glass transition point + 100 ° C. for 10 minutes and then cooled to room temperature at 40 ° C. per minute. Here, the total length of the sample is measured. Thereafter, the sample is heated to 600 ° C at 100 ° C per minute, held at 600 ° C for 80 minutes, cooled to room temperature at 100 ° C per minute, and the total length of the sample is measured again. The ratio between the amount of shrinkage of the sample before and after the heat treatment at 600 ° C. and the total length of the sample before the heat treatment at 600 ° C. is defined as the thermal shrinkage rate. In the above evaluation method, the heat shrinkage rate is preferably 100 ppm or less, more preferably 80 ppm or less, further preferably 60 ppm or less, further 55 ppm or less, and particularly preferably 50 ppm or less.

The alkali-free glass of the present invention can be produced, for example, by the following method. The raw materials of each component normally used are mixed so as to become target components, which are continuously charged into a melting furnace and heated to 1500 to 1800 ° C. to melt. A plate glass can be obtained by forming this molten glass into a predetermined plate thickness by a float method (or a fusion method), and then cutting after slow cooling.
Since the glass of the present invention has relatively low solubility, it is preferable to use the following as a raw material for each component. However, the float method is preferable in view of stably producing a large plate glass (for example, one side of 2 m or more).

  In the following, Examples 1 to 8 are Examples, and Examples 9 to 10 are Comparative Examples. The raw material of each component was prepared so that it might become a target composition, and it melt | dissolved at the temperature of 1550-1650 degreeC using the platinum crucible. In melting, the mixture was stirred using a platinum stirrer to homogenize the glass. Next, the molten glass was poured out, formed into a plate shape, and then slowly cooled.

Table 1 shows the glass composition (unit: mass%), the coefficient of thermal expansion at 50 to 350 ° C. (unit: × 10 ⁻⁷ / ° C.), the strain point (unit: ° C.), the glass transition point (unit: ° C.), Specific gravity, Young's modulus (GPa) (measured by ultrasonic method), high temperature viscosity value, temperature T ₂ (temperature at which glass viscosity becomes 10 ² dPa · s, unit: ° C.) and float molding T ₄ (temperature at which the glass viscosity becomes 10 ⁴ dPa · s, unit: ° C.), devitrification temperature (unit: ° C.), photoelastic constant (unit: nm / MPa / cm) ) (Measured by a disk compression method at a measurement wavelength of 546 nm). Evaluation of the heat shrinkage rate was performed according to the following procedure. The sample is held at a temperature of glass transition point + 100 ° C. for 10 minutes and then cooled to room temperature at 40 ° C. per minute. Here, the total length of the sample is measured. Then, it heats to 600 degreeC at 100 degreeC / min, hold | maintains at 600 degreeC for 80 minutes, cools to room temperature at 100 degreeC / minute, and measures the full length of a sample again. The ratio between the amount of shrinkage of the sample before and after heat treatment at 600 ° C. and the total length of the sample before heat treatment at 600 ° C. was defined as the heat shrinkage rate.
In Table 1, values shown in parentheses are calculated values.

As is apparent from the table, all the glasses of the examples have a thermal expansion coefficient as low as 30 × 10 ⁻⁷ to 43 × 10 ⁻⁷ / ° C., and a temperature T _{2 at} which the glass viscosity becomes 10 ² dPa · s is 1710 ° C. Since the temperature T ₄ at which the glass viscosity is 10 ⁴ dPa · s is 1330 ° C. or lower, the glass has excellent solubility and is located in the float bath and on the downstream side of the float bath. It has little effect on the life of the metal member and the heater used in the part that enters the annealing furnace from the float bath outlet. Further, the strain point is as high as 690 ° C. or higher, the Young's modulus is as high as 80 GPa or higher, the specific gravity is as low as 2.7 or less, the thermal shrinkage is as low as 100 ppm or less, and the photoelastic constant is 31 nm / MPa / cm or less.

  Further, the devitrification temperature is 1320 ° C. or less, and devitrification is unlikely to occur during float molding.

  The alkali-free glass of the present invention has a high strain point and a high Young's modulus, and is suitable for uses such as a display substrate and a photomask substrate. Moreover, it is suitable also for uses, such as a substrate for information recording media and a substrate for solar cells.

Claims (5)

The temperature T at which the strain point is 690 ° C. or higher, the average thermal expansion coefficient at 50 to 350 ° C. is 30 × 10 ⁻⁷ to 43 × 10 ⁻⁷ / ° C., and the glass viscosity is 10 ² dPa · s. ₂ is 1710 ° C. or lower, the temperature T ₄ at which the glass viscosity becomes 10 ⁴ dPa · s is 1330 ° C. or lower, the Young's modulus is 80 GPa or higher, and the SiO ₂ 57 is expressed in terms of mass% on the oxide basis. ~ 65,
Al ₂ O ₃ 18-23,
B ₂ O ₃ 0-5,
MgO more than 1 and less than 8,
CaO 6-12,
SrO 0 or more and less than 2,
BaO contains 0 or more and less than 5,
Alkali-free glass whose MgO + CaO + SrO + BaO is 12-23. SiO ₂ 58 to 64 in terms of mass% based on oxide,
Al ₂ O ₃ 19-22,
B ₂ O ₃ 0.1-4,
MgO 2-7.5,
CaO 7-11,
SrO 0-1.5,
BaO 1 to 4.5
Containing
The alkali-free glass according to claim 1, wherein MgO + CaO + SrO + BaO 2 is 14-21. SiO ₂ 59 to 64 in terms of mass% based on oxide,
Al ₂ O ₃ 19-22,
B ₂ O ₃ 0.1-3,
MgO 3-7,
CaO 7.5-10.5,
SrO 0-1,
BaO 1-4
Containing
The alkali-free glass according to claim 2, wherein MgO + CaO + SrO + BaO is 14-21.   The alkali-free glass according to any one of claims 1 to 3, wherein the specific gravity is 2.7 or less.   Devitrification temperature is 1320 degrees C or less, The alkali free glass in any one of Claims 1-4.