KR102133339B1 - Non-alkali glass - Google Patents

Abstract

The present invention has a distortion point of 680 to 735°C, an average coefficient of thermal expansion at 50 to 350°C of 30×10 ^-7 to 43×10 ^-7 /°C, a specific gravity of 2.60 or less, and an oxide-based mass percentage display, SiO ₂ is 58 to 65%, Al ₂ O ₃ is 18 to 22%, B ₂ O ₃ is 3 to 8%, MgO is 0 to 1.3%, CaO is 6.3 to 10%, SrO is 1.7 to 5%, BaO It contains 0.5 to 5%, ZrO ₂ to 0 to 2%, MgO+CaO+SrO+BaO is 12 to 23%, MgO/CaO is 0 to 0.2, MgO/(SrO+BaO) is 0 to 0.4 , And relates to an alkali-free glass having SrO/BaO of 1.2 to 1.6.

Description

Non-alkali glass {NON-ALKALI GLASS}

The present invention relates to an alkali free glass. More specifically, the present invention relates to an alkali-free glass that can be molded by a float method or a fusion method without substantially containing an alkali metal oxide, which is suitable as a substrate glass for various displays and a substrate glass for a photomask.

Conventionally, the properties disclosed below have been required for various display glass plates (glass substrates), particularly glass used for forming a thin film of metal or oxide on the surface.

(1) When the glass contains an alkali metal oxide, since the alkali metal ions diffuse in the thin film and deteriorate the film properties of the thin film, the alkali metal ions should be substantially free.

(2) When the glass plate is exposed to high temperature in the thin film forming process, the distortion point should be high so that the shrinkage (heat shrinkage) caused by deformation of the glass plate and structural stability of the glass can be minimized.

(3) It must have sufficient chemical durability against various chemicals used to form semiconductors. In particular, buffered hydrofluoric acid (BHF: a mixed solution of hydrofluoric acid and ammonium fluoride) for etching SiO _x or SiN _x , chemical solutions containing hydrochloric acid used for etching ITO, and various acids used for etching metal electrodes (nitric acid, sulfuric acid, etc.) ) And alkali of resist stripper.

(4) There should be no defects (bubbles, muffles, inclusions, pits, scratches, etc.) on the interior and surface.

In addition to the above-mentioned demands, the following situations are in recent years.

(5) The weight reduction of a display is requested|required, and glass itself is also desired to have a small specific gravity.

(6) The weight reduction of a display is requested|required, and thinning of a glass plate 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), heat resistance is desired.

(8) In order to increase productivity and increase heat shock resistance by increasing the rate of temperature rise and fall during heat treatment in the production of a liquid crystal display, glass having a small average thermal expansion coefficient of glass is desired.

In recent years, in small and medium-sized displays for mobiles typified by smartphones, high-precision progresses, and the above requirements have become strict.

As glass for liquid crystal display panels, various glass compositions have been proposed (for example, see Patent Documents 1 to 3).

Japanese Patent Publication 2001-172041 Japanese Patent Publication No. Hei 5-232458 Japanese Patent Publication 2012-41217

In patent document 1, an alkali free glass is disclosed. The alkali-free glass disclosed in Patent Literature 1 has a low viscosity at devitrification temperature, and the manufacturing method is limited.

Although alkali-free glass containing 0 to 5 mol% of B ₂ O ₃ and containing BaO is disclosed in Patent Document 2, the alkali-free glass disclosed in Patent Document 2 has an average coefficient of thermal expansion at 50 to 300°C. It exceeds 50×10 ^-7 /℃.

Although the alkali-free glass containing 0.1 to 4.5 mass% of B ₂ O ₃ and 5 to 15 mass% of BaO is disclosed in Patent Document 3, the alkali-free glass disclosed in Patent Document 3 is 50 to 350°C. The average thermal expansion coefficient of exceeds 43×10 ⁻⁷ /° C., and the specific gravity exceeds 2.60.

On the other hand, when inserting the display into the panel, color unevenness caused by stress generated on the glass plate becomes a problem. In order to suppress color unevenness, it is considered effective to reduce the photoelastic constant of glass.

The objective of this invention is to solve the said subject. That is, it is a provision of an alkali-free glass having a high distortion point, a low specific gravity and a low photoelastic constant, which is difficult to bend even when thin, and is unlikely to cause problems such as color unevenness even when stress is applied.

The present invention has a distortion point of 680 to 735°C, an average coefficient of thermal expansion at 50 to 350°C of 30×10 ^-7 to 43×10 ^-7 /°C, a specific gravity of 2.60 or less, and an oxide-based mass percentage display,

SiO ₂ to 58 to 65%,

Al ₂ O ₃ to 18 to 22%,

B ₂ O ₃ 3 to 8%,

MgO is 0 to 1.3%,

CaO is 6.3 to 10%,

SrO is 1.7 to 5%,

BaO 0.5 to 5%,

ZrO ₂ containing 0 to 2%,

Provides an alkali-free glass having 12 to 23% MgO + CaO + SrO + BaO, 0 to 0.2 MgO/CaO, 0 to 0.4 MgO/(SrO+BaO), and 1.2 to 1.6 SrO/BaO. .

The alkali-free glass of the present invention has a high distortion point, a low specific gravity and a low photoelastic constant, and although thin, it is difficult to bend, and problems such as color unevenness are unlikely to occur even when stress is applied. Therefore, it can be suitably used in small and medium-sized LCDs, OLEDs, especially portable display fields such as mobiles, digital cameras, and mobile phones. Moreover, it can be used as a glass substrate also in other fields.

Hereinafter, the alkali free glass of this invention is demonstrated.

Next, the composition range of each component is demonstrated.

When the content of SiO ₂ is less than 58% by mass (hereinafter simply referred to as %), the distortion point does not sufficiently increase, and the average thermal expansion coefficient increases, and the specific gravity tends to increase. Therefore, the content of SiO ₂ is 58% or more, preferably 59% or more, and more preferably 60% or more. When the content of SiO ₂ is more than 65%, the solubility of the glass decreases, the Young's modulus decreases, and the devitrification temperature tends to increase. Therefore, the content of SiO ₂ is 65% or less, preferably 64% or less, more preferably 63% or less, still more preferably 62.5% or less, and most preferably 62% or less and 62% or less.

In addition, "the devitrification temperature rises" means that the viscosity at the devitrification temperature becomes low, and devitrification tends to occur when the temperature of the molten glass is higher than the molding temperature.

Al ₂ O ₃ increases the Young's modulus to suppress warpage, further suppresses the glass's crushability, lowers the average coefficient of thermal expansion, raises the distortion point, and improves the fracture toughness value to increase the glass strength. If the content of Al ₂ O ₃ is less than 18%, this effect is unlikely to occur, and the components that increase the average coefficient of thermal expansion are relatively increased. As a result, the average coefficient of thermal expansion tends to be large. Therefore, the content of Al ₂ O ₃ is 18% or more, preferably 18.5% or more, and more preferably 19% or more. When the content of Al ₂ O ₃ is more than 22%, the solubility of the glass is deteriorated, and there is a fear that the devitrification temperature is increased. Therefore, the content of Al ₂ O ₃ is 22% or less, preferably 21.5% or less, and more preferably 21% or less.

B ₂ O ₃ improves the BHF resistance, further improves the dissolution reactivity of the glass, and lowers the devitrification temperature. When the content of B ₂ O ₃ is less than 3%, this effect is unlikely to appear, and BHF resistance tends to deteriorate. Therefore, the content of B ₂ O ₃ is 3% or more, preferably 3.5% or more, and more preferably 4% or more. When the content of B ₂ O ₃ is more than 8%, the photoelastic constant increases, and problems such as color unevenness tend to occur when stress is applied. In addition, when B ₂ O ₃ is too large, the surface roughness of the glass plate after hydrofluoric acid etching treatment (hereinafter also referred to as “thinning treatment”) becomes large, and the strength after the thinning treatment tends to decrease. Moreover, the distortion point also tends to decrease. Therefore, the content of B ₂ O ₃ is 8% or less, preferably 7.5% or less, and more preferably 7% or less.

Since MgO increases the Young's modulus without increasing the specific gravity, the problem of warpage can be alleviated by increasing the inelasticity, and the fracture toughness value is improved to increase the glass strength. In addition, among the alkaline earth metals, it has the characteristic of not increasing the average coefficient of thermal expansion and improving solubility. However, when the content of Al ₂ O ₃ in the glass composition is 18% or more, when the MgO content is large, the devitrification temperature tends to increase. Therefore, the content of MgO is 1.3% or less, preferably 1.2% or less, more preferably 1.1% or less, still more preferably 1.0% or less.

CaO has a characteristic that, after MgO, among the alkaline earth metals, the inelastic rate is increased, the average thermal expansion coefficient is not increased, and the distortion point is not excessively lowered, and solubility is improved like MgO. In addition, it has a feature that the devitrification temperature is less likely to be higher than that of MgO, and devitrification is hardly a problem in the production of glass. When the content of CaO is less than 6.3%, this effect does not appear, and the devitrification temperature tends to rise. Therefore, the content of CaO is 6.3% or more, preferably 6.7% or more, and more preferably 7% or more. When the content of CaO is more than 10%, the average thermal expansion coefficient increases, and the devitrification temperature becomes high, and devitrification tends to be a problem in the production of glass. Therefore, the content of CaO is 10% or less, preferably 9% or less, and more preferably 8.5% or less.

SrO has the characteristic of not increasing the devitrification temperature of glass, improving solubility and reducing the photoelastic constant. However, since the effect is lower than BaO and the effect of increasing the specific gravity is larger, it is preferable not to contain much.

On the other hand, in the alkali-free glass, if the SrO content is less than 1.7%, solubility decreases and there is a fear that the devitrification temperature increases. Therefore, the content of SrO is 1.7% or more, preferably 2% or more. When the SrO content is more than 5%, the specific gravity tends to increase, and the average thermal expansion coefficient tends to increase. Therefore, the content of SrO is 5% or less, preferably 4.5% or less, and more preferably 4% or less.

BaO has a feature that the solubility is improved without increasing the devitrification temperature of the glass, and the photoelastic constant is reduced. However, if it contains a lot, specific gravity will become large and there exists a tendency for an average thermal expansion coefficient to become large.

On the other hand, in the alkali-free glass, if the BaO content is less than 0.5%, the photoelastic constant increases, solubility decreases, and there is a fear that the devitrification temperature increases. Therefore, the content of BaO is 0.5% or more, preferably 1.0% or more, and more preferably 1.5% or more. When the content of BaO is more than 5%, the specific gravity increases, and there is a fear that the average thermal expansion coefficient increases. Therefore, the content of BaO is 5% or less, preferably 4.5% or less, and more preferably 4% or less.

ZrO ₂ may be contained up to 2% in order to increase the Young's modulus, to lower the glass melting temperature, and to promote crystal precipitation during firing. When the content of ZrO ₂ exceeds 2%, the glass tends to become unstable, or the relative dielectric constant ε of the glass tends to increase. The content of ZrO ₂ is preferably 1.5% or less, more preferably 1.0% or less, still more preferably 0.5% or less, and particularly preferably not substantially contained.

In addition, in the present invention, "substantially free" means that it does not contain other than inevitable impurities mixed from raw materials or the like, that is, it does not contain intentionally.

If the content of MgO, CaO, SrO, and BaO is less than 12% in total, the temperature T4 at which the glass viscosity becomes 10 ⁴ dPa·s increases, and there is a concern that the heater life of the molding equipment may be shortened during plate glass molding. Therefore, the content of MgO, CaO, SrO and BaO is 12% or more in total, 13% or more is preferable, and 14% or more is more preferable. If the content of MgO, CaO, SrO and BaO is more than 23% in total, there is a fear that the average thermal expansion coefficient cannot be reduced. Therefore, the content of MgO, CaO, SrO, and BaO is 23% or less in total, preferably 21% or less, and more preferably 19% or less.

By the sum of the contents of MgO, CaO, SrO and BaO satisfying the above and also satisfying the following conditions (MgO/CaO, MgO/(SrO+BaO), SrO/BaO each being a specific numerical range), Without increasing the devitrification temperature, the phase separation can be suppressed, the Young's modulus and the inelasticity can be increased, and the glass viscosity, particularly T4, can be lowered.

MgO/CaO is made 0.2 or less. MgO/CaO is preferably 0.16 or less.

MgO/(SrO+BaO) is made 0.4 or less. MgO/(SrO+BaO) is preferably 0.38 or less, more preferably 0.36 or less, still more preferably 0.27 or less, and most preferably 0.23 or less.

When SrO/BaO is less than 1.2, specific gravity and average thermal expansion coefficient tend to increase. Therefore, SrO/BaO is made 1.2 or more. Preferably it is 1.25 or more, 1.3 or more, 1.35 or more, 1.4 or more. When SrO/BaO exceeds 1.6, the devitrification temperature tends to rise. Therefore, SrO/BaO is made 1.6 or less. It is preferably 1.55 or less, and more preferably 1.5 or less.

It does not substantially contain alkali metal oxides such as Na ₂ O and K ₂ O. For example, it is 0.1% or less.

In addition, when the glass plate containing the alkali-free glass of the present invention is used for display production as a glass plate for a display, the alkali-free glass of the present invention is not produced in order not to cause deterioration of properties of thin films such as metals or oxides provided on the surface of the glass plate. It is preferable that P ₂ O ₅ is not substantially contained. In addition, in order to facilitate recycling of the glass, it is preferable that the alkali-free glass of the present invention does not substantially contain PbO, As ₂ O ₃ and Sb ₂ O ₃ . In order to improve the solubility, clarity, and formability of the glass, ZnO, Fe ₂ O ₃ , SO ₃ , F, Cl, SnO ₂ in the alkali free glass of the present invention is 2% or less in total, preferably 1% or less , More preferably, it may contain 0.5% or less.

The alkali-free glass of the present invention can be produced, for example, by the following procedure.

The raw materials for each of the above components are combined to have a target content in the glass composition, which is continuously introduced into a melting furnace, heated to 1500 to 1800°C and dissolved to obtain molten glass. An alkali-free glass plate containing the alkali-free glass of the present invention can be obtained by molding the obtained molten glass into a glass ribbon having a predetermined plate thickness using a molding apparatus, and then cooling the glass ribbon, followed by cutting.

In this invention, it is preferable to shape|mold into a glass plate by a float method or a fusion method, etc. Especially, it is preferable to shape|mold into a glass plate by a fusion method. By using the fusion method, the average cooling rate in the vicinity of the glass transition point is increased, and when the obtained glass plate is further thinned by a hydrofluoric acid (HF) etching treatment, the surface roughness of the glass plate on the side subjected to the hydrofluoric acid (HF) etching treatment is small. It is easy to lose, and the strength is easily improved. In consideration of stably producing large plate glass (for example, 2 m or more on one side), the float method is preferable.

In the present invention, it is preferable to form a glass plate having a thickness of 0.7 mm or less. By making the plate thickness thin, the weight reduction of the display can be easily achieved. The plate thickness of the glass plate obtained by molding is more preferably 0.5 mm or less, more preferably 0.4 mm or less, even more preferably 0.35 mm or less, particularly preferably 0.25 mm or less, and more particularly preferably 0.1 mm. Below, it is most preferably 0.05 mm or less. However, if the plate thickness is less than 0.005 mm, when the glass plate in the present invention is used for display production as a glass plate for display, it is not preferable because there may be a problem of self-weight bending in a device process performed during display production. When self-weight bending is a particular problem, the plate thickness is preferably 0.1 mm or more, and more preferably 0.2 mm or more.

In the present invention, it is preferable that at least one surface of the alkali-free glass plate containing the alkali-free glass of the present invention is subjected to a hydrofluoric acid (HF) etching treatment with a depth of 5 µm or more from the surface. By thinning by the etching process, the thickness of the display using an alkali-free glass plate (glass substrate) can be reduced, and the display can be made lighter.

The alkali-free glass of the present invention has a distortion point of 680°C or higher and 735°C or lower. Thereby, when the said alkali free glass is used for display manufacture as a glass plate for a display, heat shrinkage at the time of display manufacture can be suppressed. It is preferably 685°C or higher, more preferably 690°C or higher, and even more preferably 695°C or higher. When the distortion point is 680°C or higher, it is suitable for a purpose (for example, a substrate for OLED display or a substrate for lighting) aiming at a high distortion point.

However, if the distortion point of the alkali-free glass is too high, it is necessary to increase the temperature of the molding apparatus accordingly, and the life of the molding apparatus tends to decrease. For this reason, the alkali-free glass of this invention has a distortion point of 735 degreeC or less.

In addition, for the same reason as the distortion point, the alkali-free glass of the present invention has a glass transition point of preferably 730°C or higher, more preferably 735°C or higher, and even more preferably 740°C or higher.

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. Thereby, thermal shock resistance is large and productivity of a display can be raised when the said alkali free glass is used for display manufacture as a glass plate for a display. The alkali-free glass of the present invention preferably has an average coefficient of thermal expansion of 35×10 ^-7 to 40×10 ^-7 /°C.

Further, the alkali-free glass of the present invention has a specific gravity of 2.60 or less, preferably 2.59 or less, more preferably 2.58 or less, and even more preferably 2.56 or less.

It is preferable that the alkali-free glass of the present invention has an inelasticity of 29 MNm/kg or more. When the inelasticity is less than 29 MNm/kg, problems such as conveyance troubles and cracks due to self-weight bending tend to occur. More preferably, it is 29.5 MNm/kg or more, still more preferably 30 MNm/kg or more, particularly preferably 30.5 MNm/kg or more.

The alkali-free glass of the present invention preferably has a Young's modulus of 74 GPa or more, more preferably 74.5 GPa or more, still more preferably 75 GPa or more, and particularly preferably 75.5 GPa or more. The Young's modulus can be measured by an ultrasonic method.

It is preferable that the alkali-free glass of the present invention has a photoelastic constant of 31 nm/MPa/cm or less.

When the alkali-free glass of the present invention is used as a glass plate for a display, the black plate becomes gray and the contrast of the liquid crystal display decreases due to the birefringence of the glass plate due to the stress generated during the LCD manufacturing process or the use of the LCD device. There may be a phenomenon. By setting the photoelastic constant to 31 nm/MPa/cm or less, this phenomenon can be suppressed small. More preferably, it is 30.5 nm/MPa/cm or less, still more preferably 30 nm/MPa/cm or less, particularly preferably 29.5 nm/MPa/cm or less, and most preferably 29 nm/MPa/cm or less.

Considering the ease of securing other physical properties, it is preferable that the photoelastic constant is 25 nm/MPa/cm or more.

In addition, the photoelastic constant can be measured at a measurement wavelength of 546 nm by a disk compression method.

In addition, the alkali-free glass of the present invention preferably has a temperature T2 of 1780° C. or less, and more preferably 1750° C. or less, more preferably a glass viscosity as a reference for solubility of 10 ² poise (dPa·s). 1720°C or lower. Thereby, dissolution becomes relatively easy.

In addition, the alkali-free glass of the present invention preferably has a temperature T4 of 1360° C. or less, with a glass viscosity of 10 ⁴ poise (dPa·s) as a reference for float formability or fusion formability, and more preferably 1350° C. or less. , More preferably 1340°C or less, particularly preferably 1330°C or less.

In addition, the alkali-free glass of the present invention preferably has a viscosity (devitrification viscosity) of 10 ^{3. 8} poise (dPa·s) or higher at devitrification temperature. This makes it difficult for devitrification to be a problem during molding by the fusion method or the float method. More preferably, it is 10 ^{4. 0} poise or more, more preferably 10 ^{4. 2} poise or more, particularly preferably 10 ^{4. 4} poise or more, particularly preferably 10 ^4.6 poise or more.

The devitrification temperature is preferably 1330°C or lower, more preferably 1325°C or lower, even more preferably 1320°C or lower, particularly preferably 1315°C or lower.

The devitrification temperature in the present invention is determined as follows. Pulverized glass particles are placed in a platinum plate, and heat-treated for 17 hours in an electric furnace controlled at a constant temperature, and after heat treatment, an optical microscope is used to obtain the highest temperature and crystal precipitation of crystals on the surface and inside of the glass. The lowest temperature that does not precipitate is observed, and the average value is taken as the devitrification temperature.

The viscosity at the devitrification temperature is obtained by measuring the viscosity of the glass at the devitrification temperature.

Moreover, it is preferable that the alkali-free glass of this invention has a small shrinkage rate (heat shrinkage rate) at the time of heat processing. In liquid crystal panel production, the heat treatment process is different on the array side and the color filter side. Therefore, especially in a high-precision panel, there is a problem that, when the heat shrinkage ratio of the glass is large, misalignment of dots occurs during fitting.

In addition, evaluation of a heat shrinkage rate can be measured with the following procedure. A glass plate sample (a sample of 100 mm long x 10 mm wide x 1 mm thick) mirror-polished with cerium oxide is held at a temperature of +100°C for 10 minutes, and then cooled to 40°C per minute to room temperature. Here, the total length (longitudinal direction) L1 of the sample is measured. Thereafter, heating is performed at 100°C to 600°C every hour, held at 600°C for 80 minutes, cooled to 100°C per hour to room temperature, and the total length L2 of the sample is measured again. The ratio (L1-L2)/L1 of the difference (L1-L2) of the total length before and after heat treatment at 600°C and the total length L1 of the sample before heat treatment at 600°C is taken as the heat shrinkage ratio. In the above evaluation method, the heat shrinkage rate is preferably 120 ppm or less, more preferably 100 ppm or less, more preferably 80 ppm or less, even more preferably 60 ppm or less, particularly preferably 50 ppm or less.

Example

(Examples: Examples 1 to 6 and Examples 9 to 15, Comparative Examples: Examples 7 to 8)

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The raw materials of each component were combined so that the glass composition was the target composition shown in Tables 1 and 2 (glass composition (unit: mass%)), and dissolved at a temperature of 1600°C for 1 hour using a platinum crucible. After dissolving, it flowed on a carbon plate, and after holding at a glass transition point of +30°C for 60 minutes, it was cooled to room temperature at 1°C every minute. The obtained glass was mirror-polished to obtain a glass plate, and various evaluations were performed.

In Tables 1 and 2, the average coefficient of thermal expansion at 50 to 350°C (unit: × 10 ^-7 /°C), specific gravity, Young's modulus (GPa), distortion point (unit: °C), glass transition point (unit: °C), Inelastic modulus (MNm/kg), T4 (temperature at which glass viscosity is 10 ⁴ dPa·s, unit: °C), T2 (temperature at which glass viscosity is 10 ² dPa·s, unit: °C), devitrification temperature (unit : ℃), viscosity at devitrification temperature (unit: dPa·s), photoelastic constant (unit: nm/MPa/cm), and thermal contraction rate (unit: ppm). Each measurement was performed by the method mentioned above.

In addition, in Table 1, the values in parentheses are calculated values.

The glass of Examples 7 and 8 does not apply to the alkali free glass of the present invention, and since the ratio of BaO to SrO is large, as a result, the average coefficient of thermal expansion is large and the specific gravity is high.

Although the present invention has been described in detail and with reference to specific embodiments, it is clear to those skilled in the art that various modifications and modifications can be made without departing from the spirit and scope of the present invention.

This application is based on the JP Patent application 2013-195793 of an application on September 20, 2013, The content is taken in here as a reference.

(Industrial availability)

ADVANTAGE OF THE INVENTION According to this invention, the alkali free glass which has a high distortion point, low specific gravity and low photoelasticity constant, is hard to bend even if it is thin, and is hard to generate|occur|produce the problem of color unevenness even when stress is applied can be provided.

Claims (3)

The distortion point is 680 to 735°C, the average coefficient of thermal expansion at 50 to 350°C is 30×10 ^-7 to 43×10 ^-7 /°C, specific gravity is 2.60 or less, and the mass percentage display based on oxide is
SiO ₂ to 58 to 65%,
Al ₂ O ₃ to 18 to 22%,
B ₂ O ₃ 3 to 8%,
MgO is 0 to 1.3%,
CaO is 6.3 to 10%,
SrO is 1.7 to 5%,
BaO 0.5 to 5%,
ZrO ₂ containing 0 to 2%,
Non-alkali glass with MgO+CaO+SrO+BaO of 12-23%, MgO/CaO 0-0.2, MgO/(SrO+BaO) 0-0.4, SrO/BaO 1.2-1.6. The alkali-free glass according to claim 1, wherein the photoelastic constant is 31 nm/MPa/cm or less. The alkali-free glass according to claim 1 or 2, wherein the viscosity at devitrification temperature is 10 ^{3. 8} poise (dPa·s) or more.