Glass

Abstract

To provide a glass which can achieve both curving workability and devitrification resistance.SOLUTION: The glass of the present invention comprises, as a glass composition in terms of mass%, SiO2: 50-75%, Al2O3: 0-25%, B2O3: 0-25%, Li2O: 0-8%, Na2O: 5-25%, K2O: 0-5%, MgO+CaO+SrO+BaO+ZnO: 0-20%, and P2O5: 0-5%, and is characterized in that the electrical resistivity Logρ at a measuring frequency of 1 kHz and a high-temperature viscosity of 105.0 dPa s is 0.5 Ω cm or more, the electrical resistivity Logρ at a measuring frequency of 1 kHz and a high-temperature viscosity of 103.0 dPa s is 0.1 Ω cm or more, and the softening point is 745°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a glass having a low softening point that is suitable for curved surface processing (thermal processing). [Background technology]

[0002] In recent years, head-mounted displays have been developed, including devices that project images onto a display hanging from the brim of a hat, eyeglass-type devices that display both outside scenery and images on a display, and devices that display images on a see-through light guide plate.

[0003] In devices that display images on a see-through light guide plate, you can see the image displayed on the light guide plate while looking at the outside scenery through glasses. It is also possible to realize 3D display by using technology that projects different images on the left and right, and to realize virtual reality space by using technology that connects the lens of the eye to the retina.

[0004] These devices require optical members with curved surfaces, and these optical members are produced by processing glass plates (plate-shaped glass) into curved surfaces. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2017 / 283305 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] When a glass sheet is curved, it needs to be heat-treated at a temperature equal to or higher than its softening point, but if the heat treatment temperature is too high, the life of the mold used for the curved surface processing will be shortened. If the curved surface processing is performed at a low temperature in order to extend the life of the mold, the glass sheet will have difficulty deforming to conform to the mold, resulting in a decrease in dimensional stability.

[0007] Soda lime glass is commonly used as window glass, but because it has a softening point of approximately 750°C, it is difficult to properly process it into curved surfaces.

[0008] On the other hand, if an attempt is made to improve curved surface workability by lowering the softening point of the glass sheet, the glass becomes unstable and is prone to devitrification during forming.

[0009] The present invention has been made in view of the above circumstances, and its technical object is to create a glass that is both easy to work into curved surfaces and has resistance to devitrification. [Means for solving the problem]

[0010] After repeated experiments, the inventors discovered that the above technical problems can be solved by strictly controlling the content of each component in the glass and controlling the softening point within a predetermined range, and have proposed this finding as the present invention. Specifically, the glass of the present invention contains, by mass, 50-75% SiO2, 0-25% Al2O, 0-25% BO, 0-8% Li2O, 5-25% Na2O, 0-5% KO, and 0-20% MgO, CaO, SrO, BaO, and ZnO, and has a softening point of 745°C or lower. Here, "MgO, CaO, SrO, BaO, and ZnO" refers to the total amount of MgO, CaO, SrO, BaO, and ZnO. The "softening point" refers to a value measured according to the method of ASTM C338.

[0011] In the glass of the present invention, the content of each component is regulated as described above, which makes it possible to lower the softening point and increase the devitrification resistance.

[0012] Furthermore, the softening point of the glass of the present invention is regulated to 745° C. or less. This suppresses thermal deterioration of the mold and the like during curved surface processing, and also makes it easier for the glass sheet to change shape to follow the shape of the mold.

[0013] The glass of the present invention preferably has a glass composition, in mass %, of 60 to 70% SiO2, 3 to less than 10% Al2O3, 0 to 7% B2O3, 0 to 1% Li2O, 13 to 23% Na2O, 0 to 0.1% K2O, 3 to 10% MgO+CaO+SrO+BaO+ZnO, 0 to less than 3% MgO, 2 to 10% CaO, 0 to 2% SrO, 0 to 2% BaO, and 0 to 2% ZnO, and has a softening point of 720°C or lower.

[0014] The glass of the present invention is preferably in the form of a plate.

[0015] The glass of the present invention is preferably curved.

[0016] The glass of the present invention preferably has at least one surface with a surface roughness Ra of 0.1 to 5 μm. Here, "surface roughness Ra" refers to the arithmetic mean roughness Ra defined in JIS B0601-2001, but when formed by the down-draw method, it may also be measured with, for example, a commercially available atomic force microscope (AFM).

[0017] The glass of the present invention preferably has a plate thickness of 0.1 to 3 mm.

[0018] The glass of the present invention preferably has a functional film on at least one surface, and the functional film is any one of an anti-reflection film, an anti-fouling film, a reflective film, and an anti-scratch film.

[0019] The glass of the present invention has a viscosity of 10 at the liquidus temperature. 4.6 It is preferable that the viscosity is dPa·s or more. Here, the "viscosity at the liquidus temperature" can be measured by the platinum ball pull-up method. The "liquidus temperature" can be calculated by placing glass powder that passes through a standard 30 mesh (500 μm) sieve and remains on a 50 mesh (300 μm) sieve in a platinum boat, holding it in a temperature gradient furnace for 24 hours, and measuring the temperature at which crystals precipitate.

[0020] The glass of the present invention is preferably formed by an overflow downdraw method.

[0021] The glass of the present invention is preferably used for components for head-mounted displays. DETAILED DESCRIPTION OF THE INVENTION

[0022] The glass of the present invention preferably contains, in mass %, 50-75% SiO2, 0-25% Al2O3, 0-25% B2O3, 0-8% Li2O, 5-25% Na2O, 0-5% K2O, and 0-20% MgO+CaO+SrO+BaO+ZnO. The reasons for limiting the content of each component as described above are as follows. In the explanation of the content of each component, % denotes mass % unless otherwise specified.

[0023] SiO2 is the main component that forms the skeleton of glass. If the SiO2 content is too low, the Young's modulus, acid resistance, and weather resistance tend to decrease. Therefore, the preferred lower limit range of SiO2 is 50% or more, 52% or more, 55% or more, 57% or more, 60% or more, and particularly 62% or more. On the other hand, if the SiO2 content is too high, the softening point will increase unduly, and devitrification crystals will tend to precipitate, making the liquidus temperature likely to rise. Therefore, the preferred upper limit range of SiO2 is 75% or less, 72% or less, 70% or less, 69% or less, 68% or less, and particularly 67% or less.

[0024] Al2O3 is a component that increases Young's modulus and weather resistance. The preferred lower limit of Al2O3 is 0% or more, 1% or more, 3% or more, 4% or more, 5% or more, and particularly 6% or more. On the other hand, if the Al2O3 content is too high, the high-temperature viscosity increases and curved surface workability tends to decrease. Therefore, the preferred upper limit of Al2O3 is 25% or less, 23% or less, less than 20%, less than 15%, 12% or less, 11% or less, less than 10%, and particularly 9% or less.

[0025] B2O3 is a component that forms the glass framework and also acts as a flux. If the B2O3 content is too low, the liquidus temperature is likely to decrease. Therefore, the preferred lower limit of B2O3 is 0% or more, 1% or more, 2% or more, 3% or more, and particularly 4% or more. On the other hand, if the B2O3 content is too high, the high-temperature viscosity increases and curved surface workability is likely to decrease. Therefore, the preferred upper limit of B2O3 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, and particularly 6% or less.

[0026] Alkali metal oxides (Li2O, Na2O, K2O) are components that lower the softening point. However, if incorporated in large amounts, the viscosity of the glass decreases too much, making it difficult to maintain a high liquidus viscosity. Furthermore, the Young's modulus tends to decrease. Therefore, the lower limit of the total amount of Li2O, Na2O, and K2O is preferably 5% or more, 10% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, and particularly 18% or more. The upper limit is preferably 27% or less, 25% or less, 23% or less, 22% or less, 20% or less, and particularly 19% or less. The upper limit of Li2O is preferably 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, and particularly 0.1% or less. The preferred lower limit of NaO is 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 preferred upper limit is 25% or less, 23% or less, 20% or less, 18% or less, particularly 16% or less. The preferred lower limit of KO is 0% or more, particularly 0.1% or more, and the preferred upper limit is 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly 0.1% or less. Note that the KO feedstock contains more harmful impurities (e.g., radiation-emitting elements, coloring elements) than the feedstocks containing other components. Therefore, from the viewpoint of removing harmful impurities, the KO content is preferably 1% or less, 0.5% or less, particularly 0.1% or less.

[0027] The mass % ratio (Na2O-Al2O3) / SiO2 is preferably -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, particularly 0.15 to 0.25. If the mass % ratio (Na2O-Al2O3) / SiO2 is too small, the softening point tends to increase. Note that "(Na2O-Al2O3) / SiO2" refers to the value obtained by subtracting the Al2O3 content from the Na2O content and dividing it by the SiO2 content.

[0028] By restricting the mass percent ratio Na2O / (Li2O + Na2O + K2O) to a predetermined range, it is possible to lower the softening point while improving devitrification resistance. The mass percent ratio Na2O / (Li2O + Na2O + K2O) preferably has a lower limit of 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, and particularly preferably greater than 0.95. Note that "Na2O / (Li2O + Na2O + K2O)" refers to the value obtained by dividing the Na2O content by the combined amount of Li2O, Na2O, and K2O.

[0029] By restricting the mass percent ratio Al2O3 / (Li2O + Na2O + K2O) to a predetermined range, it is possible to lower the softening point while maintaining weather resistance. The mass percent ratio Al2O3 / (Li2O + Na2O + K2O) preferably has a lower limit of 0 or more, 0.1 or more, 0.2 or more, 0.25 or more, or 0.3 or more, particularly more than 0.35, and a preferred upper limit of 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. Note that "Al2O3 / (Li2O + Na2O + K2O)" refers to the value obtained by dividing the Al2O3 content by the combined amount of Li2O, Na2O, and K2O.

[0030] MgO, CaO, SrO, BaO, and ZnO are components that lower the softening point. However, if large amounts of MgO, CaO, SrO, BaO, and ZnO are incorporated, the density becomes excessively high, the Young's modulus tends to decrease, and the high-temperature viscosity decreases too much, making it difficult to ensure a high liquidus 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 is preferably 20% or less, 15% or less, 10% or less, 8% or less, and particularly 6% or less.

[0031] MgO is a component that lowers the softening point and, among alkaline earth metal oxides, is a component that effectively increases the Young's modulus. However, if the MgO content is too high, devitrification resistance and weather resistance tend to decrease. The preferred lower limit of MgO is 0% or more, 0.1% or more, and particularly 0.5% or more, and the preferred upper limit is 8% or less, 5% or less, 3% or less, 2% or less, 1% or less, and particularly 0.9% or less.

[0032] CaO is a component that lowers the softening point and, because it is a relatively inexpensive raw material among alkaline earth metal oxides, reduces raw material costs. However, if the CaO content is too high, devitrification resistance and weather resistance tend to decrease. The preferred lower limit of CaO is 0% or more, 0.1% or more, 1% or more, 2% or more, and particularly 3% or more, and the preferred upper limit is 10% or less, 8% or less, 7% or less, 6% or less, and particularly 5% or less.

[0033] The CaO content is preferably greater than the K2O content, more preferably at least 1 mass % greater than the K2O content, and preferably at least 2 mass % greater than the K2O content. If the CaO content is less than the K2O content, it becomes difficult to achieve both a low softening point and high devitrification resistance.

[0034] By restricting the mass % ratio CaO / (MgO + CaO + SrO + BaO + ZnO) to a predetermined range, it is possible to reduce raw material costs and lower the softening point. The mass % ratio CaO / (MgO + CaO + SrO + BaO + ZnO) preferably has a lower limit of 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, or 0.7 or more, particularly more than 0.8 to 0.95. Note that "CaO / (MgO + CaO + SrO + BaO + ZnO)" refers to the value obtained by dividing the CaO content by the combined amount of MgO, CaO, SrO, BaO, and ZnO.

[0035] SrO is a component that improves devitrification resistance, but if its content is too high, the component balance of the glass composition is disrupted, which in turn reduces devitrification resistance. It also makes it easier for harmful impurities to be mixed in. Therefore, the preferred upper limit of SrO is 10% or less, 3% or less, 2% or less, 1% or less, and particularly 0.1% or less.

[0036] BaO is a component that improves devitrification resistance, but if its content is too high, the balance of the components in the glass composition is disrupted, which in turn reduces devitrification resistance. It also makes it easier for harmful impurities to be mixed in. Therefore, the preferred upper limit of BaO is 10% or less, 3% or less, 2% or less, 1% or less, and particularly 0.1% or less.

[0037] ZnO is a component that significantly lowers the softening point, but if its content is too high, the glass is prone to devitrification. Therefore, the preferred lower limit of ZnO content is 0% or more, 0.1% or more, 0.3% or more, and particularly 0.5% or more, and the preferred upper limit is 15% or less, 10% or less, 5% or less, 3% or less, 2% or less, and particularly less than 1%.

[0038] By restricting the mass percentage ratio ZnO / (MgO+CaO+SrO+BaO+ZnO) to a predetermined range, it is possible to lower the softening point while maintaining devitrification resistance. The mass percentage ratio ZnO / (MgO+CaO+SrO+BaO+ZnO) preferably has a lower limit of 0 or more, 0.05 or more, 0.07 to 1.0, 0.08 to 0.75, 0.1 to 0.55, or 0.15 to 0.5, particularly 0.2 to 0.4. Note that "ZnO / (MgO+CaO+SrO+BaO+ZnO)" refers to the value obtained by dividing the ZnO content by the combined amount of MgO, CaO, SrO, BaO, and ZnO.

[0039] In addition to the above components, other components may be incorporated. From the viewpoint of accurately enjoying the effects of the present invention, the content of other components other than the above components is preferably 12% or less, 10% or less, 8% or less, particularly preferably 5% or less in total.

[0040] P2O5 is a component that forms the glass skeleton. It also stabilizes the glass and improves devitrification resistance. On the other hand, if the P2O5 content is too high, the glass tends to undergo phase separation and the water resistance tends to decrease. The upper limit of P2O5 is preferably 5% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less, and particularly preferably less than 0.1%.

[0041] TiO2 and ZrO2 are components that enhance acid resistance. However, if the TiO2 and ZrO2 contents are too high, devitrification resistance and transmittance tend to decrease. Harmful impurities also tend to be mixed in. The preferred upper limit of TiO2 is 5% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less, particularly less than 0.1%. The preferred upper limit of ZrO2 is 5% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less, particularly less than 0.1%.

[0042] Fe2O3 is an unavoidable impurity component, and its content is 0.001 to 0.05%, 0.003 to 0.03%, and particularly 0.005 to 0.019%. If the Fe2O3 content is too low, high-purity raw materials are required, which can easily increase raw material costs. On the other hand, if the Fe2O3 content is too high, the transmittance is likely to decrease.

[0043] As a fining agent, one or more selected from the group consisting of As2O3, Sb2O3, CeO2, SnO2, F, Cl, and SO3 can be added in an amount of 0 to 2%. However, from an environmental perspective, it is preferable that As2O3 and F are substantially absent, i.e., less than 0.1%. In particular, considering fining ability and environmental impact, SnO2 is preferred as a fining agent. The preferred lower limit of SnO2 is 0% or more, 0.1% or more, and particularly 0.15% or more, while the preferred upper limit is 1% or less, 0.5% or less, 0.4% or less, and particularly 0.3% or less. The preferred lower limit of Sb2O3 is 0% or more, 0.03% or more, 0.05% or more, and particularly 0.07% or more, while the preferred upper limit is 1% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, and particularly 0.1% or less.

[0044] PbO and Bi2O3 are components that reduce high temperature viscosity, but from an environmental point of view, it is preferable that they are not contained substantially, that is, that their content be less than 0.1%.

[0045] Y2O3, La2O3, Nb2O5, Gd2O3, Ta2O5, and WO3 have the effect of increasing Young's modulus, etc. However, if the content of each of these components exceeds 5%, especially 1%, the cost of raw materials will rise.

[0046] The glass of the present invention preferably has the following properties:

[0047] The softening point is 745° C. or lower, preferably 730° C. or lower, particularly 600 to 720° C. If the softening point is too high, thermal deterioration of the mold and the like is accelerated during curved surface processing, and the glass becomes difficult to change shape to follow the shape of the mold.

[0048] The average linear thermal expansion coefficient in the temperature range of 30 to 380°C 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 / ℃, especially 88×10 -7 ~98×10 -7 / °C. If the average linear thermal expansion coefficient is outside the above range, it becomes difficult to match the thermal expansion coefficient of various peripheral components (especially various metal films, etc.), and the glass plate is more likely to crack or break when incorporated into a device. Note that the "average linear thermal expansion coefficient in the temperature range of 30 to 380°C" refers to a value measured with a dilatometer.

[0049] The liquidus temperature is preferably less than 850° C., 825° C. or less, 800° C. or less, 780° C. or less, 760° C. or less, particularly 750° C. or less. The viscosity at the liquidus temperature is preferably 10 4.6 dPa·s or more, 10 5.2 dPa·s or more, 10 5.5 dPa·s or more, 10 5.8 dPa·s or more, especially 10 6.0 The viscosity is dPa·s or more. This makes it easier to form glass sheets by the down-draw method, particularly the overflow down-draw method, and makes it easier to produce glass sheets with small thicknesses. Furthermore, devitrification crystals are less likely to occur in the glass during forming. As a result, the manufacturing cost of glass sheets can be reduced.

[0050] High temperature viscosity 10 2.5 The temperature in dPa·s is preferably 1500°C or less, 1400°C or less, 1350°C or less, 1320°C or less, particularly 1300°C or less. 2.5 As the temperature at dPa·s increases, the melting property decreases and the manufacturing cost of the glass rises. 2.5 The "temperature at dPa·s" can be measured using the platinum sphere pull-up method.

[0051] In a glass manufacturing process, molten glass may be heated by directly applying an electric current to an electrode inserted in a melting tank, or by indirectly applying an electric current to a feeder, a forming device, etc. However, when the molten glass is electrically heated, if a potential difference occurs between different metal members in contact with the molten glass, an electrical circuit is formed via the molten glass, and bubbles may be generated at the metal / molten glass interface, which corresponds to the positive and negative electrodes.

[0052] Specifically, when an electrical circuit is formed, the following reaction occurs, which can cause bubbles to form in the portion that becomes the positive electrode side. Positive side: O 2- → 0.5O2+ 2e - Negative electrode: 0.5O2+ 2e - → O 2-

[0053] According to Faraday's law of electrolysis, the mass of a substance that changes at each electrode through electrolysis is proportional to the amount of electricity flowing (see Equation 1 below).

[0054] [Number 1] m = (Q M) / (F Z) m: mass of the substance changed (g) Q: Amount of electricity flowing (C) M: Molar mass of the substance (g / mol) F: Faraday constant (C / mol) Z: Number of electrons involved in the change of one molecule of material

[0055] Here, the quantity of electricity Q is expressed as the product of the current I and the time t (see Equation 2). Also, according to Ohm's law, the voltage is expressed as the product of the resistance and the current (see Equation 3).

[0056] [Number 2] Q=I·t I: Current (A) t: time (seconds)

[0057] [Number 3] E=R·I E: Voltage (V) R: Resistance (Ω) I: Current (A)

[0058] Resistance R (Ω) is determined by the electrical resistivity ρ (Ω cm) of the glass and the cell constant κ (cm -1 ) (see Equation 4).

[0059] [Number 4] R=ρ·κ R: Resistance (Ω) ρ: Electrical resistivity (Ω cm) κ: Cell constant (cm -1 )

[0060] From Equations 2 to 4, the relationship between the quantity of electricity Q and the electrical resistivity ρ is expressed as Equation 5, and the quantity of electricity Q and the electrical resistivity ρ are inversely proportional. In other words, the higher the electrical resistivity ρ, the smaller the quantity of electricity Q, and the mass m of the changed substance = the amount of bubbles decreases.

[0061] [Number 5] Q=(E t) / (ρ κ)

[0062] Furthermore, the viscosity of molten glass during molding is approximately constant regardless of the glass composition, so the higher the electrical resistivity at the same viscosity, the fewer bubbles are generated during molding.

[0063] Therefore, the higher the electrical resistivity of the molten glass, the better. 5.0 The electrical resistivity Logρ in 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, particularly 1.1 Ω·cm or more. 5.0 If the electrical resistivity Logρ in dPa·s is too low, bubbles will be generated in the molten glass, resulting in an increase in bubble defects and an increase in the glass manufacturing cost. 5.0 Electrical resistivity Logρ in dPa·s can be measured by the two-terminal method. If the amount of B2O3 in the glass composition is increased, the measurement frequency can be increased to 1 kHz and the high-temperature viscosity to 10 5.0The electrical resistivity Logρ in dPa·s can be increased.

[0064] Measurement frequency 1kHz, high temperature viscosity 10 3.0 The electrical resistivity Logρ in 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, particularly 0.7 Ω·cm or more. 3.0 If the electrical resistivity Logρ in dPa·s is too low, bubbles will be generated in the molten glass, resulting in an increase in bubble defects and an increase in the glass manufacturing cost. 3.0 Electrical resistivity Logρ in dPa·s can be measured by the two-terminal method. If the amount of B2O3 in the glass composition is increased, the measurement frequency can be increased to 1 kHz and the high-temperature viscosity to 10 3.0 The electrical resistivity Logρ in dPa·s can be increased.

[0065] When the measurement temperature for electrical resistivity is fixed (for example, when measuring electrical resistivity at a measurement frequency of 1 kHz and 1300°C), increasing the amount of SiO2 in the glass composition increases the electrical resistivity, and increasing the amount of alkali metal oxides tends to decrease the electrical resistivity.

[0066] The glass of the present invention is preferably formed by a downdraw method, particularly an overflow downdraw method. The overflow downdraw method is a method for producing a glass sheet by overflowing molten glass from both sides of a heat-resistant trough-shaped structure, and drawing the overflowed molten glass downward while joining at the lower end of the trough-shaped structure. In the overflow downdraw method, the surface that will become the surface of the glass sheet does not contact the trough-shaped refractory and is formed in a free surface state. This makes it easier to produce a glass sheet with high surface smoothness.

[0067] As a method for forming a glass sheet, in addition to the overflow downdraw method, for example, a slot down method, a redraw method, a float method, a roll out method, etc. can also be adopted.

[0068] As described above, the glass of the present invention has a low softening point, and therefore can be appropriately curved to match the shape of a mold or the like. Therefore, the glass of the present invention is preferably curved into a plate shape, and more preferably curved by heat treatment. Furthermore, when a curved shape is formed by curved surface processing, the radius of curvature of the curved surface is preferably 100 to 2000 mm, particularly 200 to 1000 mm. This facilitates application to components for head-mounted displays.

[0069] In the glass of the present invention, the surface roughness Ra of at least one surface is preferably 0.1 to 5 μm, particularly 0.3 to 3 μm. In particular, when curved surface processing is performed by heat treatment using a mold, it is preferable to restrict the surface roughness Ra of the surface in contact with the mold to 0.1 to 5 μm, particularly 0.3 to 3 μm. This can increase the efficiency of curved surface processing without blurring the displayed image. If the surface roughness Ra of the surface in contact with the mold is high, the surface roughness Ra can be reduced by fire polishing the surface.

[0070] The glass of the present invention can also be used as a plate-shaped glass formed by a down-draw method without undergoing curved surface processing. In this case, the surface roughness Ra is preferably 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, and particularly preferably 1 nm or less.

[0071] The glass of the present invention preferably does not have a compressive stress layer formed on the surface thereof due to ion exchange, which allows the production cost of the glass to be reduced.

[0072] The glass of the present invention preferably has a plate shape, and its plate thickness is preferably 3.0 mm or less, 2.5 mm or less, 2.0 mm or less, 1.5 mm or less, 1.0 mm or less, particularly 0.9 mm or less. The thinner the plate thickness, the easier it is to reduce the weight of the glass plate and to perform curved surface processing. On the other hand, if the plate thickness is too thin, the strength of the glass plate itself decreases. Therefore, the plate thickness is preferably 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, 0.4 mm or more, 0.5 mm or more, 0.6 mm or more, particularly more than 0.7 mm.

[0073] 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 anti-reflection film, an anti-fouling film, a reflective film, and an anti-scratch film.

[0074] The antireflection film is preferably a dielectric multilayer film in which low-refractive index layers with a relatively low refractive index and high-refractive index layers with a relatively high refractive index are alternately stacked. This makes it easier to control the reflectance at each wavelength. The antireflection film can be formed by, for example, a sputtering method or a CVD method. 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 preferably 0.1% or less.

[0075] The antifouling film is preferably prepared by incorporating a fluorine-containing silane compound into the antifouling layer-forming composition and coating a solution of a silane compound having a fluoroalkyl group or a fluoroalkyl ether group. In particular, the fluorine-containing silane compound is preferably a silazane or an alkoxysilane. Among the silane compounds having a fluoroalkyl group or a fluoroalkyl ether group, preferred are those in which the fluoroalkyl groups in the silane compound are bonded to Si atoms at a ratio of one or less per Si atom, with the remainder being hydrolyzable groups or siloxane-bonded groups. The hydrolyzable group referred to here is, for example, an alkoxy group, which hydrolyzes to a hydroxyl group, thereby forming a polycondensate of the silane compound.

[0076] The reflective film is preferably a metal film such as Al, and the scratch-resistant film is preferably an inorganic film such as SiO2 or Si3N4. Example 1

[0077] The present invention will be described below based on examples. Note that the following examples are merely illustrative and the present invention is not limited to the following examples.

[0078] Tables 1 to 6 show examples of the present invention (samples Nos. 1 to 87) and comparative examples (samples Nos. 88 and 89).

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] [Table 4]

[0083] [Table 5]

[0084] [Table 6]

[0085] First, a glass batch prepared by blending glass raw materials to obtain the glass composition shown in the table was placed in a platinum crucible and melted at 1200 to 1500°C for 4 hours. When melting the glass batch, it was stirred using a platinum stirrer to homogenize it. Next, the obtained molten glass was poured onto a carbon plate and formed into a plate, after which it was slowly cooled from a temperature about 20°C higher than the annealing point Ta to room temperature at a rate of 3°C / min. For each of the obtained samples, the average linear thermal expansion coefficient α in the temperature range of 30 to 380°C, density ρ, strain point Ps, annealing point Ta, softening point Ts, high-temperature viscosity 10 4.0 Temperature in dPa·s, high temperature viscosity 10 3.0 Temperature in dPa·s, high temperature viscosity 10 2.5 The temperature in dPa·s, the liquidus temperature TL, the viscosity η at the liquidus temperature TL, and the electrical resistivity Logρ were evaluated.

[0086] The average coefficient of linear thermal expansion α in the temperature range of 30 to 380° C. is a value measured with a dilatometer.

[0087] The density ρ is a value measured by the well-known Archimedes method.

[0088] The strain point Ps, annealing point Ta, and softening point Ts are values measured based on the method of ASTM C336 or ASTM C338.

[0089] High temperature viscosity 10 4.0 dPa·s, 10 3.0 dPa·s, 10 2.5 The temperature at dPa·s was measured by the platinum sphere pulling method.

[0090] Electrical resistivity Logρ is measured at a frequency of 1 kHz and a high-temperature viscosity of 10 5.0 dPa·s and 10 3.0 The electrical resistivity in dPa·s was measured using the two-terminal method.

[0091] The liquidus temperature TL is the temperature at which crystals precipitate when glass powder that passes through a standard 30 mesh (500 μm) sieve and remains on a 50 mesh (300 μm) sieve is placed in a platinum boat and held in a temperature gradient furnace for 24 hours, after which the temperature at which crystals precipitate is measured by microscopic observation. The viscosity η at the liquidus temperature TL is the viscosity of the glass at the liquidus temperature TL, measured by the platinum sphere pull-up method.

[0092] As is clear from Tables 1 to 6, samples Nos. 1 to 87 have a softening point Ts of 596 to 744°C and a viscosity η at the liquidus temperature TL of 10 3.7 Therefore, samples Nos. 1 to 87 have good curved surface workability and devitrification resistance. On the other hand, samples Nos. 88 and 89 have softening points Ts of 837°C or higher, which is thought to make them difficult to curve. Example 2

[0093] The glass (plate thickness 0.8 mm) of samples No. 1 to 87 was subjected to curved processing at a temperature near the softening point Ts to match the shape of the mold, and then a concave mirror was produced by forming an Al reflective film on the surface on the recess side that should reflect the display light.

[0094] On the other hand, for the glasses (plate thickness 0.8 mm) of Samples No. 88 and 89, curved surfaces were processed at a temperature near the softening point Ts so as to follow the shape of the mold, but because the temperature during curved surface processing was high, thermal degradation of the mold was observed. [Industrial Applicability]

[0095] The glass of the present invention is suitable for use as a member for head-mounted displays because of its excellent curved surface processability and devitrification resistance. In addition, because of its excellent devitrification resistance, the glass is also suitable for use as a cover glass for CCD or CMOS type image sensors, a cover glass for photodiodes in LiDAR (Light Detection and Ranging) used to measure inter-vehicle distances, and the like. Because of its excellent curved surface processability (thermal processability), the glass is also suitable for medical tubing and vehicle center information displays.

Claims

1. The glass composition is, in mass%, SiO 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 1. A glass characterized by containing 0 to 5% of O and 0 to 20% of MgO+CaO+SrO+BaO+ZnO, and having a softening point of 745° C. or lower.

2. The glass composition is, in mass%, SiO ２ 60-70%, Al ２ O ３ 3 to less than 10%, B ２ O ３ 0-7%, Li ２ O 0-1%, Na ２ O 13-23%, K ２ 2. The glass according to claim 1, comprising 0 to 0.1% O, 3 to 10% MgO+CaO+SrO+BaO+ZnO, 0 to less than 3% MgO, 2 to 10% CaO, 0 to 2% SrO, 0 to 2% BaO, and 0 to 2% ZnO, and having a softening point of 720°C or lower.

3. 3. The glass according to claim 1, which is in the form of a plate.

4. 4. The glass according to claim 3, characterized in that it is curved.

5. 5. The glass according to claim 3, wherein at least one surface has a surface roughness Ra of 0.1 to 5 μm.

6. 6. The glass according to claim 3, wherein the thickness of the glass is 0.1 to 3 mm.

7. 7. The glass according to claim 3, further comprising a functional film on at least one surface thereof, the functional film being any one of an anti-reflection film, an anti-fouling film, a reflective film, and an anti-scratch film.

8. Viscosity at liquidus temperature is 10 ４．６ 8. The glass according to claim 1, wherein the viscosity is dPa·s or more.

9. 8. The glass according to claim 3, which is formed by an overflow downdraw method.

10. The glass according to any one of claims 1 to 8, which is used as a member for a head-mounted display.

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