阅读说明：本技术 玻璃 (Glass ) 是由 铃木良太 于 2019-02-04 设计创作，主要内容包括：本发明的玻璃板的特征在于,作为玻璃组成,以质量％计含有SiO<Sub>2</Sub> 50～75％、Al<Sub>2</Sub>O<Sub>3</Sub> 0～25％、B<Sub>2</Sub>O<Sub>3</Sub> 0～25％、Li<Sub>2</Sub>O 0～8％、Na<Sub>2</Sub>O 5～25％、K<Sub>2</Sub>O 0～5％、MgO+CaO+SrO+BaO+ZnO 0～20％,软化点为745℃以下。(The glass plate of the present invention is characterized by containing SiO in mass% as a glass composition 2 50～75％、Al 2 O 3 0～25％、B 2 O 3 0～25％、Li 2 O 0～8％、Na 2 O 5～25％、K 2 0-5% of O, 0-20% of MgO + CaO + SrO + BaO + ZnO and a softening point of 745 ℃ or below.)

1. A glass, characterized in that,

the glass composition contains SiO in mass%₂50％～75％、Al₂O₃0％～25％、B₂O₃0％～25％、Li₂O 0％～8％、Na₂O 5％～25％、K₂0 to 5 percent of O, 0 to 20 percent of MgO + CaO + SrO + BaO + ZnO and a softening point below 745 ℃.

2. The glass according to claim 1,

the glass composition contains SiO in mass%₂60％～70％、Al₂O₃More than 3% and less than 10%, B₂O₃0％～7％、Li₂O 0％～1％、Na₂O 13％～23％、K₂0 to 0.1 percent of O, 3 to 10 percent of MgO + CaO + SrO + BaO + ZnO, more than 0 percent and less than 3 percent of MgO, 2 to 10 percent of CaO, 0 to 2 percent of SrO, 0 to 2 percent of BaO and 0 to 2 percent of ZnO, and the softening point is below 720 ℃.

3. The glass according to claim 1 or 2,

the glass is plate-shaped.

4. The glass according to claim 3,

the glass is curved.

5. The glass according to claim 3 or 4,

at least one of the surfaces has a surface roughness Ra of 0.1 to 5 μm.

6. The glass according to any one of claims 3 to 5,

the thickness of the plate is 0.1 mm-3 mm.

7. The glass according to any one of claims 3 to 6,

the functional film is any one of an antireflection film, an antifouling film, a reflective film and a scratch-resistant film on at least one surface.

8. The glass according to any one of claims 1 to 7,

viscosity at liquidus temperature of 10^4.6dPas or more.

9. The glass according to any one of claims 3 to 7,

formed by an overflow downdraw method.

10. The glass according to any one of claims 1 to 8,

the member is used for a head-mounted display.

Technical Field

The present invention relates to a glass having a low softening point suitable for curved surface processing (hot working).

Background

In recent years, as head-mounted displays, devices for projecting images on a display suspended from a visor, glasses-type devices for displaying an external scene and images on the display, devices for displaying images on a transparent light guide plate, and the like have been developed.

In a device that displays an image on a transparent light guide plate, the image displayed on the light guide plate can be viewed while viewing an external scene through glasses. Further, it is possible to realize a 3D display by using a technique of projecting different images to the left and right, or realize a virtual reality space by using a technique of combining the lens of the eye and the retina.

Among these devices, an optical member having a curved surface shape is required, and the optical member is manufactured by curving a glass plate (plate-shaped glass).

Disclosure of Invention

Problems to be solved by the invention

However, in the case of curving a glass sheet, it is necessary to heat treat the glass sheet to a temperature equal to or higher than the softening point, but if the heat treatment temperature is high, the life of a mold or the like for curving becomes short. When the curved surface is processed at a low temperature in order to increase the life of the mold or the like, the glass sheet is less likely to be deformed by the mold, and the dimensional stability is lowered.

Soda lime glass is generally used as a window glass, and has a softening point of about 750 ℃.

On the other hand, when the softening point of the glass sheet is lowered to improve the curved surface workability, the glass becomes unstable and the glass is likely to devitrify during molding.

The present invention has been made in view of the above circumstances, and a technical object thereof is to create glass that can achieve both curved surface workability and devitrification resistance.

Means for solving the problems

The present inventors have repeated various experiments and found that the above technical problems can be solved by strictly limiting the content of each component of the glass and limiting the softening point to a predetermined range, and have proposed the present invention. That is, the glass of the present invention contains SiO in mass%₂50～75％、Al₂O₃0～25％、B₂O₃0～25％、Li₂O 0～8％、Na₂O 5～25％、K₂0 to 5% of O, 0 to 20% of MgO + CaO + SrO + BaO + ZnO, and a softening point of 745 ℃ or lower. Here, "MgO + CaO + SrO + BaO + ZnO" refers to the total amount of MgO, CaO, SrO, BaO, and ZnO. "softening point" refers to a value determined based on the method of ASTM C338.

The glass of the present invention is limited in the content of each component in the above manner. This can lower the softening point and improve resistance to devitrification.

The softening point of the glass of the present invention is limited to 745 ℃ or lower. This can suppress thermal degradation of the mold or the like during curved surface processing, and the glass sheet can easily change its shape in accordance with the shape of the mold.

Further, the glass of the present invention preferably contains SiO in mass%₂60～70％、Al₂O₃More than 3% and less than 10%, B₂O₃0～7％、Li₂O 0～1％、Na₂O 13～23％、K₂0 to 0.1% of O, 3 to 10% of MgO + CaO + SrO + BaO + ZnO, 0% or more and less than 3% of MgO, 2 to 10% of CaO, 0 to 2% of SrO, 0 to 2% of BaO, and 0 to 2% of ZnO, and has a softening point of 720 ℃ or less.

The glass of the present invention is preferably plate-shaped.

The glass of the present invention is preferably curved.

In addition, the glass of the present invention preferably has at least one surface having a surface roughness Ra of 0.1 to 5 μm. The "surface roughness Ra" is an arithmetic average roughness Ra defined in JIS B0601-2001, and can be measured by, for example, a commercially available Atomic Force Microscope (AFM) when formed by a down-draw method.

The glass of the present invention preferably has a thickness of 0.1 to 3 mm.

The glass of the present invention preferably has a functional film on at least one surface, and the functional film is any of an antireflection film, an antifouling film, a reflective film, and a scratch-resistant film.

Further, the glass of the present invention preferably has a viscosity of 10 at the liquidus temperature^4.6dPas or more. Here, "viscosity at liquidus temperature" may be used with platinum ballsAnd (5) a Czochralski method. The "liquidus temperature" can be calculated by placing a glass powder which has passed through a standard sieve of 30 mesh (500 μm) and remained at 50 mesh (300 μm) in a platinum boat, holding the boat in a temperature gradient furnace for 24 hours, and measuring the temperature at which crystals are precipitated.

The glass of the present invention is preferably formed by an overflow downdraw method.

The glass of the present invention is preferably used for a member for a head-mounted display.

Detailed Description

The glass of the present invention preferably contains SiO in mass%₂50～75％、Al₂O₃0～25％、B₂O₃0～25％、Li₂O 0～8％、Na₂O 5～25％、K₂The reason why the glass composition contains 0 to 5% of O and 0 to 20% of MgO + CaO + SrO + BaO + ZnO is as follows. In the description of the content of each component,% represents mass% unless otherwise specified.

SiO₂Is a main component forming the skeleton of the glass. If SiO₂When the content of (b) is too small, the Young's modulus, acid resistance and weather resistance tend to be lowered. Thus, SiO₂The lower limit of the preferable range is 50% or more, 52% or more, 55% or more, 57% or more, 60% or more, particularly 62% or more. On the other hand, if SiO₂When the content of (b) is too large, the softening point is undesirably increased, devitrified crystals are likely to precipitate, and the liquid phase temperature is likely to increase. Thus, SiO₂The preferable upper limit range of (b) is 75% or less, 72% or less, 70% or less, 69% or less, 68% or less, particularly 67% or less.

Al₂O₃Is a component for improving Young's modulus and weather resistance. Al (Al)₂O₃The lower limit of the preferable range is 0% or more, 1% or more, 3% or more, 4% or more, 5% or more, particularly 6% or more. On the other hand, if Al₂O₃When the content (b) is too large, the high-temperature viscosity increases and the curved surface processability is liable to decrease. Thus, Al₂O₃The upper limit of the range is preferably 25% or less, 23% or less, or lessAt 20%, less than 15%, less than 12%, less than 11%, less than 10%, particularly less than 9%.

B₂O₃Is a component that forms the skeleton of the glass and acts as a flux. If B is₂O₃If the content of (b) is too small, the liquid phase temperature tends to be lowered. Thus, B₂O₃The lower limit of the preferable range is 0% or more, 1% or more, 2% or more, 3% or more, particularly 4% or more. On the other hand, if B₂O₃When the content (b) is too large, the high-temperature viscosity increases and the curved surface processability is liable to decrease. Thus, B₂O₃The preferable upper limit range of (b) is 25% or less, 20% or less, 15% or less, 13% or less, 11% or less, 10% or less, 9% or less, 8% or less, 7% or less, particularly 6% or less.

Alkali metal oxide (Li)₂O、Na₂O、K₂O) is a component that lowers the softening point, but when introduced in a large amount, the viscosity of the glass is too low, and it is difficult to ensure a high liquid phase viscosity. In addition, the Young's modulus is liable to decrease. Thus, Li₂O、Na₂O and K₂The lower limit of the total amount of O is preferably 5% or more, 10% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, particularly 18% or more, and the upper limit thereof is preferably 27% or less, 25% or less, 23% or less, 22% or less, 20% or less, particularly 19% or less. Li₂Suitable upper limit ranges of O are 8% or less, 7% or less, 6% or less, 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly 0.1% or less. Na (Na)₂The lower limit of O is preferably 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, 13% or more, particularly 14% or more, and the upper limit thereof is preferably 25% or less, 23% or less, 20% or less, 18% or less, particularly 16% or less. K₂A suitable lower limit range of O is 0% or more, particularly 0.1% or more, and a suitable upper limit range is 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly 0.1% or less. In addition, K is₂Introduction of OThe material contains more harmful impurities (e.g., radiation emitting elements, coloring elements) than the introduced material of other components. Therefore, from the viewpoint of removing harmful impurities, K₂The content of O is preferably 1% or less, 0.5% or less, particularly 0.1% or less.

Mass% ratio (Na)₂O-Al₂O₃)/SiO₂Preferably-0.3 or more, -0.2 or more, -0.1 or more, -0.05 or more, more than 0, 0.05 or more, 0.1 or more, 0.11 to 0.4, 0.12 to 0.3, and particularly 0.15 to 0.25. In terms of mass% (Na)₂O-Al₂O₃)/SiO₂If it is too small, the softening point tends to increase. "(Na)₂O-Al₂O₃)/SiO₂"means from Na₂O content minus Al₂O₃The amount of (b) is divided by SiO₂The value of (b).

When the mass percent is more than Na₂O/(Li₂O+Na₂O+K₂O) is limited to a predetermined range, the softening point can be lowered and the resistance to devitrification can be improved. Mass% ratio of Na₂O/(Li₂O+Na₂O+K₂O) is preferably 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, particularly more than 0.95. In addition, "Na" is₂O/(Li₂O+Na₂O+K₂O) "means that Na is substituted₂O content divided by Li₂O、Na₂O and K₂Value of the total amount of O.

When the mass% is compared with Al₂O₃/(Li₂O+Na₂O+K₂O) is limited to a predetermined range, the softening point can be lowered while maintaining the weather resistance. Mass% ratio of Al₂O₃/(Li₂O+Na₂O+K₂O) is preferably 0 or more, 0.1 or more, 0.2 or more, 0.25 or more, 0.3 or more, particularly more than 0.35, and preferably 1.6 or less, 1.5 or less, 1.2 or less, 1.1 or less, 1.0 or less, 0.8 or less, 0.7 or less, 0.6 or less, particularly 0.5 or less. In addition, "Al" is₂O₃/(Li₂O+Na₂O+K₂O) "means that Al is substituted₂O₃Is divided by Li₂O、Na₂O and K₂Value of the total amount of O.

MgO, CaO, SrO, BaO and ZnO are components that lower the softening point. However, when a large amount of MgO, CaO, SrO, BaO, and ZnO is introduced, the density becomes too high, the young's modulus is likely to decrease, and the high-temperature viscosity is too low, so that it is difficult to secure a high liquid-phase viscosity. Therefore, the lower limit of the total amount of MgO, CaO, SrO, BaO, and ZnO is preferably 0% or more, 0.1% or more, 0.5% or more, 1% or more, 2% or more, 2.5% or more, 3% or more, 3.5% or more, and particularly 4% or more, and the upper limit thereof is preferably 20% or less, 15% or less, 10% or less, 8% or less, and particularly 6% or less.

MgO is a component that lowers the softening point, and among the alkaline earth metal oxides, is a component that effectively increases the young's modulus. However, if the content of MgO is too large, devitrification resistance and weather resistance are liable to be lowered. The lower limit of MgO is preferably 0% or more, 0.1% or more, particularly 0.5% or more, and the upper limit of MgO is preferably 8% or less, 5% or less, 3% or less, 2% or less, 1% or less, particularly 0.9% or less.

CaO is a component that lowers the softening point, and is a component that lowers the cost of raw materials because the raw materials are relatively inexpensive to introduce into the alkaline earth metal oxide. However, if the content of CaO is too large, devitrification resistance and weather resistance are liable to be lowered. The lower limit of CaO is preferably 0% or more, 0.1% or more, 1% or more, 2% or more, particularly 3% or more, and the upper limit thereof is preferably 10% or less, 8% or less, 7% or less, 6% or less, particularly 5% or less.

Preferable content ratio K of CaO₂The content of O is large, and more preferably larger than K₂The content of O is more than 1 mass%, preferably more than K₂The O content is more than 2 mass%. If the content of CaO is less than K₂The content of O makes it difficult to achieve both a low softening point and high resistance to devitrification.

If the mass% ratio CaO/(MgO + CaO + SrO + BaO + ZnO) is limited to a predetermined range, the softening point can be lowered while the raw material cost is reduced. A suitable lower limit range of the mass% ratio CaO/(MgO + CaO + SrO + BaO + ZnO) is 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, and particularly more than 0.8 and 0.95 or less. The term "CaO/(MgO + CaO + SrO + BaO + ZnO)" refers to a value obtained by dividing the content of CaO by the total amount of MgO, CaO, SrO, BaO, and ZnO.

SrO is a component for improving the devitrification resistance, but if the content thereof is too large, the components of the glass composition become unbalanced, and conversely the devitrification resistance is liable to be lowered. In addition, harmful impurities are easily mixed. Therefore, a suitable upper limit range of SrO is 10% or less, 3% or less, 2% or less, 1% or less, and particularly 0.1% or less.

BaO is a component for improving the devitrification resistance, but if the content thereof is too large, the components of the glass composition become unbalanced, and conversely the devitrification resistance is liable to be lowered. In addition, harmful impurities are easily mixed. Therefore, a suitable upper limit range of BaO is 10% or less, 3% or less, 2% or less, 1% or less, and particularly 0.1% or less.

ZnO is a component that significantly lowers the softening point, but if the content is too large, the glass is easily devitrified. Accordingly, a suitable lower limit range of ZnO is 0% or more, 0.1% or more, 0.3% or more, particularly 0.5% or more, and a suitable upper limit range is 15% or less, 10% or less, 5% or less, 3% or less, 2% or less, particularly less than 1%.

When the mass% ratio ZnO/(MgO + CaO + SrO + BaO + ZnO) is limited to a predetermined range, the softening point can be lowered while maintaining devitrification resistance. A preferable lower limit of the mass% ratio ZnO/(MgO + CaO + SrO + BaO + ZnO) is 0 or more, 0.05 or more, 0.07 to 1.0, 0.08 to 0.75, 0.1 to 0.55, 0.15 to 0.5, and particularly more than 0.2 and 0.4 or less. The term "ZnO/(MgO + CaO + SrO + BaO + ZnO)" means a value obtained by dividing the ZnO content by the total amount of MgO, CaO, SrO, BaO, and ZnO.

In addition to the above components, other components may be introduced. From the viewpoint of reliably obtaining the effects of the present invention, the content of the other components than the above components is preferably 12% or less, 10% or less, 8% or less, and particularly 5% or less, in total.

P₂O₅Is a component forming the glass skeleton. And a component for stabilizing the glass or improving resistance to devitrification. On the other hand, if P₂O₅When the content of (b) is too large, glass phase separation tends to occur, or water resistance tends to be lowered. P₂O₅The preferable upper limit range of (b) is 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly less than 0.1%.

TiO₂And ZrO₂Is a component for improving acid resistance. However, if TiO₂And ZrO₂When the content of (b) is too large, the devitrification resistance is lowered or the transmittance is liable to be lowered. In addition, harmful impurities are easily mixed. TiO 2₂The preferable upper limit range of (b) is 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly less than 0.1%. ZrO (ZrO)₂The preferable upper limit range of (b) is 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly less than 0.1%.

Fe₂O₃Is an inevitable impurity component, and the content thereof is 0.001-0.05%, 0.003-0.03%, particularly 0.005-0.019%. If Fe₂O₃If the content of (b) is too small, a high-purity raw material is required, and the raw material cost tends to rise. On the other hand, if Fe₂O₃If the content of (b) is too large, the transmittance tends to decrease.

As a clarifying agent, 0 to 2% of As selected from the group consisting of₂O₃、Sb₂O₃、CeO₂、SnO₂、F、Cl、SO₃One or more than two of them. However, As₂O₃And F are preferably substantially absent, i.e., less than 0.1%, from the viewpoint of environment. Particularly, SnO is preferable in consideration of fining ability and environmental influence₂As a clarifying agent. SnO₂The lower limit of (b) is preferably 0% or more, more preferably 0.1% or more, particularly preferably 0.15% or more, and the upper limit of (b) is preferably 1% or less, more preferably 0.5% or less, more preferably 0.4% or less, particularly preferably 0.3% or less. Sb₂O₃The lower limit of the preferable range is 0% or more, 0.03% or more, 0.05% or more, particularly 0.07% or more,the upper limit is preferably 1% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, particularly 0.1% or less.

PbO and Bi₂O₃Is a component for reducing the high-temperature viscosity, but is preferably substantially not contained, that is, less than 0.1% from the viewpoint of environment.

Y₂O₃、La₂O₃、Nb2O₅、Gd₂O₃、Ta₂O₅、WO₃Has the effect of improving Young's modulus. However, if the content of each of these components is more than 5%, particularly more than 1%, the raw material cost increases.

The glass of the present invention preferably has the following characteristics.

The softening point is 745 ℃ or lower, preferably 730 ℃ or lower, particularly 600 to 720 ℃. If the softening point is too high, thermal degradation of the mold or the like is promoted during curved surface processing, and the glass is difficult to change its shape in accordance with the shape of the mold.

The average linear thermal expansion coefficient within the temperature range of 30-380 ℃ is preferably 50 × 10^-7～125×10^-7/℃、65×10^-7～110×10^-7/℃、80×10^-7～105×10^-7/℃、85×10^-7～100×10^-7/° c, in particular 88 × 10^-7～98×10^-7V. C. If the average linear thermal expansion coefficient is outside the above range, it is difficult to match the thermal expansion coefficients of various peripheral members (particularly, various metal films and the like), and when the glass plate is assembled into a device, the glass plate is likely to be broken or damaged. The "average linear thermal expansion coefficient in a temperature range of 30 to 380 ℃" means a value measured by an dilatometer.

The liquid phase temperature is preferably less than 850 ℃, 825 ℃ or less, 800 ℃ or less, 780 ℃ or less, 760 ℃ or less, particularly 750 ℃ or less. The viscosity at the liquidus temperature is preferably 10^4.610 dPas or more^5.210 dPas or more^5.510 dPas or more^5.8dPas or more, particularly 10^6.0dPas or more. Thus, the glass sheet can be easily formed by the down-draw method, particularly the overflow down-draw method, and therefore, the glass sheet can be easily formedA glass plate having a small plate thickness is produced. Further, devitrification crystals are hardly generated in the glass during forming. As a result, the manufacturing cost of the glass plate can be reduced.

High temperature viscosity 10^2.The temperature at 5 dPas is preferably 1500 ℃ or lower, 1400 ℃ or lower, 1350 ℃ or lower, 1320 ℃ or lower, particularly 1300 ℃ or lower. Viscosity at high temperature 10^2.5When the temperature at dpas is high, the meltability is lowered, and the production cost of the glass increases. Here, "high temperature viscosity 10^2.5The temperature "at dPa · s" can be measured by the platinum ball pulling method.

In the glass production process, in order to heat the molten glass, an electrode is inserted into the melting tank to perform direct electric heating, and in some cases, indirect electric heating is performed to a feeder, a forming device, or the like. However, when the molten glass is heated by energization, if a potential difference is generated between different metal members in contact with the molten glass, an electrical circuit is formed by the molten glass, and bubbles may be generated at the metal/molten glass interface corresponding to the positive electrode and the negative electrode.

Specifically, when an electric circuit is formed, the following reaction occurs, and air bubbles may be generated in a portion to be the positive electrode side.

On the positive side: o is^2-→0.5O₂+2e^-

Negative electrode side: 0.5O₂+2e^-→O^2-

According to the faraday's law of electrolysis, the mass of a substance that changes at each electrode by electrolysis is proportional to the amount of electricity flowing (see the following equation 1).

[ mathematical formula 1]

m＝(Q·M)/(F·Z)

m: mass of the substance varied (g)

Q: electric quantity flowing (C)

M: molar Mass of substances (g/mol)

F: faraday constant (C/mol)

Z: number of electrons involved in change of substance of 1 molecule

Here, the charge Q is represented by the product of the current I and the time t (see equation 2). In addition, according to ohm's law, voltage is expressed by the product of resistance and current (see equation 3).

[ mathematical formula 2]

Q＝I·t

I: current (A)

t: time (seconds)

[ mathematical formula 3]

E＝R·I

E: voltage (V)

R: resistance (omega)

I: current (A)

The resistance R (Ω) is determined by the resistivity ρ (Ω · cm) of the glass and the electrode constant κ (cm) determined by the measuring apparatus^-1) The product of (see equation 4).

[ mathematical formula 4]

R＝ρ·κ

R: resistance (omega)

ρ: resistivity (omega cm)

Kappa: electrode constant (cm)^-1)

The relation between the electric quantity Q and the resistivity rho is as shown in the formula 5 according to the formulas 2 to 4, and the electric quantity Q and the resistivity rho are inversely proportional. That is, it is found that the higher the resistivity ρ is, the smaller the electric quantity Q is, and the smaller the mass m of the changed substance is, the smaller the amount of bubbles is.

[ math figure 5]

Q＝(E·t)/(ρ·κ)

Since the viscosity of the molten glass during molding is substantially constant regardless of the glass composition, the higher the resistivity at the same viscosity, the smaller the amount of bubbles generated during molding.

Therefore, it is preferable that the molten glass has a high resistivity, a measurement frequency of 1kHz, and a high-temperature viscosity of 10^5.0The resistivity Log ρ at dPa · s is preferably 0.5 Ω · cm or more, 0.6 Ω · cm or more, 0.7 Ω · cm or more, 0.8 Ω · cm or more, 0.9 Ω · cm or more, 1.0 Ω · cm or more, and particularly 1.1 Ω · cm or more. When the measurement frequency is 1kHz and the high-temperature viscosity is 10^5.0If the resistivity Log ρ at dpas is too low, bubbles are generated in the molten glass, bubble defects increase, and the production cost of the glass rises. Here, "measurement frequency 1kHz, high temperature viscosityDegree 10^5.0The resistivity Log ρ ″ at dPa · s can be measured by a two-terminal method. In addition, if B is added to the glass composition₂O₃The measurement frequency can be increased by 1kHz and the high-temperature viscosity can be increased by 10^5.0Resistivity Log ρ at dPa · s.

Measurement frequency 1kHz, high temperature viscosity 10^3.0The resistivity Log ρ at dPa · s is preferably 0.1 Ω · cm or more, 0.2 Ω · cm or more, 0.3 Ω · cm or more, 0.4 Ω · cm or more, 0.5 Ω · cm or more, 0.6 Ω · cm or more, and particularly 0.7 Ω · cm or more. When the measurement frequency is 1kHz and the high-temperature viscosity is 10^3.0If the resistivity Log ρ at dpas is too low, bubbles are generated in the molten glass, bubble defects increase, and the production cost of the glass rises. Here, "measurement frequency 1kHz, high temperature viscosity 10^3.0The resistivity Log ρ ″ at dPa · s can be measured by a two-terminal method. In addition, if B is added to the glass composition₂O₃The measurement frequency can be increased by 1kHz and the high-temperature viscosity can be increased by 10^3.0Resistivity Log ρ at dPa · s.

When the temperature for measuring the resistivity is fixed (for example, when the resistivity is measured at a measurement frequency of 1kHz or 1300 ℃), SiO in the glass composition is increased₂The resistivity increases, and the resistivity is likely to decrease when the alkali metal oxide is added.

The glass of the present invention is preferably formed by a down-draw process, particularly an overflow down-draw process. The overflow downdraw method is a method of producing a glass sheet by overflowing molten glass from both sides of a heat-resistant gutter-shaped structure and extending the molten glass downward while merging the overflowing molten glass at the lower tip of the gutter-shaped structure. In the overflow down-draw method, the surface of the glass sheet to be formed is formed in a free surface state without contacting the refractory material in the form of a trough. Therefore, a glass plate having high surface smoothness can be easily produced.

As the method of forming a glass sheet, for example, a slot down-draw method, a redraw method, a float method, a roll-out method, or the like can be used in addition to the overflow down-draw method.

The glass of the present invention has a low softening point as described above, and therefore can be curved appropriately in accordance with the shape of a mold or the like. Therefore, the glass plate of the present invention is preferably curved, and more preferably curved by heat treatment. When the curved surface is formed by curved surface machining, the curvature radius of the curved surface is preferably 100 to 2000mm, particularly 200 to 1000 mm. Thus, the present invention can be easily applied to a head-mounted display device.

In the glass of the present invention, the surface roughness Ra of at least one surface is preferably 0.1 to 5 μm, and particularly preferably 0.3 to 3 μm. Particularly, when the curved surface is processed by heat treatment using a mold, the surface roughness Ra of the contact surface of the mold and the mold is preferably limited to 0.1 to 5 μm, particularly 0.3 to 3 μm. Therefore, the displayed image is not unclear, and the efficiency of curved surface processing can be improved. When the surface roughness Ra of the contact surface between the mold and the mold is large, the surface roughness Ra can be reduced by fire-polishing the surface.

Further, as the glass of the present invention, a plate-like glass formed by a down-draw method without performing a curved surface processing may be used as it is. In this case, the surface roughness Ra of the surface is preferably 10nm or less, 9nm or less, 8nm or less, 7nm or less, 6nm or less, 5nm or less, 4nm or less, 3nm or less, 2nm or less, and particularly 1nm or less.

The glass of the present invention preferably does not have a compressive stress layer formed on the surface thereof by ion exchange. Thus, the manufacturing cost of the glass can be reduced.

The glass of the present invention preferably has a plate shape, and the plate thickness thereof is preferably 3.0mm or less, 2.5mm or less, 2.0mm or less, 1.5mm or less, 1.0mm or less, and particularly 0.9mm or less. The thinner the plate thickness is, the more easily the glass plate is reduced in weight and the more easily the curved surface is worked. On the other hand, if the thickness is too small, the strength of the glass sheet itself is reduced. Therefore, the plate thickness is preferably 0.1mm or more, 0.2mm or more, 0.3mm or more, 0.4mm or more, 0.5mm or more, 0.6mm or more, and particularly more than 0.7 mm.

The glass of the present invention has a plate shape and has a functional film on at least one surface, and the functional film is preferably any one of an antireflection film, an antifouling film, a reflective film, and a scratch-resistant film.

As the antireflection film, for example, a dielectric multilayer film in which a low refractive index layer having a relatively low refractive index and a high refractive index layer having a relatively high refractive index are alternately laminated is preferable. This makes it easy to control the reflectance at each wavelength. The antireflection film can be formed by, for example, a sputtering method, a CVD method, or the like. The reflectance of the antireflection film at each wavelength is preferably, for example, 1% or less, 0.5% or less, 0.3% or less, and particularly 0.1% or less.

The antifouling film is preferably produced by applying a silane compound solution having a fluoroalkyl group or fluoroalkyl ether group to a composition for forming an antifouling layer, the composition containing a fluorine-containing silane compound. Particularly preferred fluorine-containing silane compounds are silazanes or alkoxysilanes. Among the silane compounds having a fluoroalkyl group or fluoroalkyl ether group, a silane compound in which a fluoroalkyl group is bonded to an Si atom at a ratio of 1 or less to 1 Si atom and the remainder is a hydrolyzable group or siloxane bonding group is preferable. The hydrolyzable group referred to herein is, for example, a group such as an alkoxy group, and the group is converted into a hydroxyl group by hydrolysis, whereby the silane compound forms a polycondensate.

As the reflective film, a metal film of Al or the like is preferable. SiO is preferred as the scratch-resistant film₂、Si₃N₄And the like.