Glass plate and display device

Abstract

To provide a glass plate capable of suppressing surface crystallization of crystallized glass.SOLUTION: A glass plate has a first principal surface and a second principal surface facing the first principal surface, has thickness of 0.30-1.00 mm, and has a crystal growth rate of 100-5,000 μm / hour at any temperature between 950-1,260°C and contains lithium. A content of R2O in a matrix composition is 5.0-15% as represented by mass% based on oxides. At least at the first principal surface, an average content of R2O from the surface to a depth of 10 μm is less than the content of R2O at the thickness center of the plate by 0.5-4.0%, provided that R2O is a total amount of Li2O, Na2O and K2O.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a glass plate and a display device.

Background Art

[0002] For protective members of display devices such as cover glasses of mobile terminals and cover glasses of in-vehicle car navigation systems, high transparency is often required to improve the visibility of the display and the like.

[0003] Devitrified glass is obtained by precipitating crystals in glass, and is harder and less likely to be damaged than non-crystalline glass that does not contain crystals. Due to such characteristics, devitrified glass is suitably used as a protective member of a display device. For example, Patent Document 1 describes devitrified glass suitable as a protective member for portable electronic devices and optical devices.

[0004] Devitrified glass capable of chemical strengthening treatment can achieve high strength while preventing cracking as compared with non-crystalline glass. The chemical strengthening treatment is a treatment for substituting alkali metal ions having a small ionic radius present near the surface of a glass plate with alkali ions having a larger ionic radius by ion exchange at a temperature below the glass transition point. Thereby, a compressive stress remains on the surface of the glass, and the strength of the glass is improved.

[0005] Glass containing Li (hereinafter, lithium-containing glass) is a glass material that can achieve a deep depth of the compressive stress layer (hereinafter, DOL) by high-speed ion exchange (for example, substitution of Li ions with Na ions or K ions). Therefore, in recent years, expectations for the development of lithium-containing glass have been increasing.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] Lithium-containing glass is likely to form crystals during production by the float process. Due to the crystals formed during float process production, surface crystallization is promoted during the crystallization treatment, resulting in a problem that the flatness of the surface deteriorates. When the flatness of the surface deteriorates, the transparency and strength decrease, and also, in the manufacturing process, man-hours for improving the flatness of the surface such as polishing are required, leading to a decrease in production efficiency.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a glass plate capable of suppressing surface crystallization of crystallized glass. [Means for Solving the Problems]

[0009] The present inventors have found that by reducing the total content of alkali metal oxides on the surface, surface crystallization in the crystallization treatment of lithium-containing glass can be suppressed, and completed the present invention.

[0010] That is, the present invention is as follows. 1. A glass plate having a first main surface and a second main surface facing the first main surface, having a thickness of 0.30 to 1.00 mm, having a crystal growth rate at any temperature from 950 ° C to 1260 ° C of 100 to 5000 μm / hour, containing lithium, in terms of mass percentage based on oxides, the content of R2O in the parent composition is 5.0 to 15%, a glass plate in which, at least on the first main surface, the average content of R2O from the surface to a depth of 10 μm is 0.5 to 4.0% less than the content of R2O at the center of the plate thickness. However, R2O is the total of Li2O, Na2O and K2O. 2. A crystallized glass plate obtained by crystallizing the glass plate according to 1 above, a glass plate having an arithmetic mean roughness Ra of the first main surface of 500 nm or less. 3. The mother composition is expressed as a mass percentage based on oxides, SiO2 is 60 to 75%, Al2O3 is 7.0 to 23%, Li2O is 4.5 to 13.0%, and the glass plate according to the above 1 or 2. 4. The mother composition is expressed as a mass percentage based on oxides, SiO2 is 60 to 75%, Al2O3 is 7.0 to 23%, Li2O is 4.5 to 13.0%, Na2O is 0 to 1.5%, SnO2 is 0.10 to 2.5%, ZrO2 is 1.0 to 6.0%, Y2O3 is 1.0 to 9.0%, P2O5 is 0 to 5.0% containing, the glass plate according to any one of the above 1 to 3. 5. The glass plate according to any one of the above 1 to 4, which is chemically strengthened glass. 6. The glass plate according to any one of the above 1 to 5, which is float glass. 7. The glass plate according to any one of the above 1 to 6, wherein the visible light transmittance when converted to a thickness of 0.7 mm is 91.0% or more. 8. A display device including the glass plate according to any one of the above 1 to 7.

Advantages of the Invention

[0011] The glass plate of the present invention contains lithium, and the content of alkali metal oxides is in a specific range, so that surface crystallization in the crystallization treatment is suppressed, and excellent surface flatness is shown.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the glass plate of the present invention will be described in detail based on embodiments. However, the present invention is not limited to the following embodiments and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0014] The devitrified glass is obtained by heat-treating the amorphous glass to cause crystallization. The glass composition of the devitrified glass is the same as that of the amorphous glass before crystallization. In this specification, "chemically strengthened glass" refers to the glass after the chemical strengthening treatment. Also, "glass for chemical strengthening" refers to the glass before the chemical strengthening treatment. In chemically strengthened glass, usually, a compressive stress layer is formed on the surface portion of the glass by ion exchange, so the glass composition of the portion that has not been ion-exchanged is the same as the parent composition of the chemically strengthened glass. Also, even in the ion-exchanged portion, the concentration of components other than alkali metal oxides basically does not change in terms of molar percentage representation based on oxides. Note that although the glass composition in this specification is shown in terms of mass percentage based on oxides, the change in the glass components before and after ion exchange is based on the molar percentage representation based on oxides.

[0015] In this specification, the glass composition of the glass before crystallization or before crystallization and chemical strengthening treatment may be referred to as the parent composition of the devitrified glass. The parent composition of the devitrified glass is equivalent to the composition at the center of the plate thickness.

[0016] In this specification, the glass composition is shown in terms of mass percentage based on oxides, and mass% may be simply denoted as %. Also, "~" indicating a numerical range is used in the sense of including the numerical values described before and after it as the lower limit value and the upper limit value.

[0017] <Glass Plate> The glass plate according to this embodiment has a first main surface and a second main surface facing the first main surface, has a thickness of 0.3 to 1.00 mm, has a crystal growth rate at any temperature between 950 °C and 1260 °C of 50 to 5000 μm / hour, contains lithium, and in terms of mass percentage based on oxides, the content of R2O in the mother composition is 5.0 to 15%. It is characterized in that at least on the first main surface, the average content of R2O from the surface to a depth of 10 μm is 0.5 to 4.0% less than the content of R2O at the center of the plate thickness. However, R2O is the sum of Li2O, Na2O, and K2O.

[0018] The glass plate according to this embodiment is preferably a glass (float glass) plate manufactured by the float process. The float glass plate has a bottom surface that contacts the molten metal during forming and a top surface that faces the bottom surface. In this embodiment, when the crystallized glass plate is a float glass plate, the first main surface is preferably the top surface and the second main surface is preferably the bottom surface.

[0019] (Crystal growth rate) In order for the glass plate according to this embodiment to be a crystallized glass plate in which surface crystallization during the crystallization treatment is suppressed and excellent surface flatness is exhibited, the crystal growth rate at any temperature between 950 °C and 1260 °C is 5000 μm / hour or less, preferably 4000 μm / hour or less, more preferably 3500 μm / hour or less, still more preferably 3000 μm / hour or less, and particularly preferably 2500 μm / hour or less. If the crystal growth is too slow, the time for crystal growth becomes long, so it is 50 μm / hour or more, preferably 80 μm / hour or more, more preferably 100 μm / hour or more, still more preferably 150 μm / hour or more, and particularly preferably 200 μm / hour or more.

[0020] The crystal growth rate can be measured by the following method. (Method) Put the crushed glass particles in a platinum dish, perform heat treatment in an electric furnace controlled at a temperature above the surface devitrification temperature for 15 minutes, take it out at room temperature, and prepare a plurality of samples with nucleation on the glass surface. The prepared nucleated samples are held at intervals of 20 °C for 0.5 to 4 hours in a temperature range where the glass viscosity is 10 4 ~10 6 dPa·s, and crystals are grown at each holding temperature. Measure the crystal size of the samples held at each holding temperature, divide by the holding time, and obtain the crystal growth rate at each holding temperature.

[0021] (R2O concentration) In the glass plate according to this embodiment, at least on the first main surface, the average content of R2O from the surface to a depth of 10 μm is 0.5 to 4.0% less than the content of R2O at the center of the plate thickness. Thereby, the viscosity of the glass surface becomes high, surface crystallization in the crystallization treatment is suppressed, and a crystallized glass plate showing excellent surface flatness can be obtained.

[0022] The difference between the average content of R2O from the surface to a depth of 10 μm and the content of R2O at the center of the plate thickness on at least the first main surface is preferably 0.6% or more, more preferably 0.7% or more, still more preferably 0.8% or more, and particularly preferably 0.9% or more. Also, the difference is preferably 3.5% or less, more preferably 3.2% or less, still more preferably 3.0% or less, and particularly preferably 2.8% or less. The average content of R2O from the surface to a depth of 10 μm on the main surface of the glass can be measured by a wet method.

[0023] Fig. 1 shows the relationship between the depth from the first main surface and the R2O concentration in one aspect of the glass plate according to this embodiment. In Fig. 1, t represents the plate thickness, and t / 2 represents the center of the plate thickness. As shown in Fig. 1, in one aspect, in the region from the first main surface to a depth of x1, as the depth from the first main surface increases, the R2O concentration gradually increases to the R2O concentration at the center of the plate thickness.

[0024] As will be described later, the R2O concentration distribution of the glass plate can be adjusted by, for example, the rare speed, the hydrogen concentration in the air, the temperature of the molten metal bath, the dealcoholization treatment, and the glass composition (for example, the content of SnO2) during the production of the glass plate, such as during forming by the float method.

[0025] (Composition) Hereinafter, the composition of the glass plate according to the present embodiment will be described. The composition of the glass plate is described for the mother composition. The mother composition is equivalent to the composition at the center of the plate thickness.

[0026] As one aspect of the glass plate according to the present embodiment, it is preferable to contain 60 to 75% of SiO2, 7.0 to 23% of Al2O3, and 4.5 to 13.0% of Li2O. As one aspect of a more preferable composition of the glass plate according to the present embodiment, specifically, for example, a composition containing 60 to 75% of SiO2, 7.0 to 23% of Al2O3, 4.5 to 13.0% of Li2O, 0 to 1.5% of Na2O, 0.10 to 2.5% of SnO2, 1.0 to 6.0% of ZrO2, 1.0 to 9.0% of Y2O3, and 0 to 5.0% of P2O5 can be mentioned.

[0027] SiO2 is a component that forms the network structure of the glass. It is also a component that improves chemical durability and can also be a constituent component of precipitated crystals. The content of SiO2 is preferably 60% or more, more preferably 62% or more, still more preferably 64% or more, particularly preferably 66% or more, and most preferably 67% or more. On the other hand, in order to improve the meltability, the content of SiO2 is preferably 75% or less, more preferably 73% or less, still more preferably 71% or less, particularly preferably 70% or less, and most preferably 69% or less.

[0028] Al2O3 is a component that increases the surface compressive stress by chemical strengthening. The content of Al2O3 is preferably 7.0% or more, more preferably 8.0% or more, still more preferably 8.5% or more, particularly preferably 9% or more, and most preferably 9.5% or more. On the other hand, from the viewpoint of suppressing the excessive increase in the devitrification temperature of the glass, the content of Al2O3 is preferably 23% or less, more preferably 21% or less, still more preferably 20% or less, particularly preferably 19% or less, and most preferably 18% or less.

[0029] Li2O is a component that can form a surface compressive stress by ion exchange and can also be a constituent component of precipitated crystals, and is an essential component. The content of Li2O is preferably 4.5% or more, more preferably 5.0% or more, still more preferably 5.5% or more, particularly preferably 6.0% or more, and most preferably 6.5% or more. On the other hand, for the purpose of stabilizing the glass, the content of Li2O is preferably 13.0% or less, more preferably 12.0% or less, still more preferably 11.0% or less, particularly preferably 10.5% or less, and most preferably 10.0% or less.

[0030] Na2O is a component that improves the meltability of the glass. When containing the content of Na2O, the content is preferably 0.2% or more, more preferably 0.5% or more, particularly preferably 0.7% or more, and most preferably 0.9% or more. If there is too much Na2O, it becomes difficult for crystals to precipitate or the chemical strengthening characteristics deteriorate. Therefore, it is preferably 1.5% or less, more preferably 1.3% or less, still more preferably 1.2% or less, particularly preferably 1.1% or less, and most preferably 1.0% or less.

[0031] K2O, like Na2O, is a component that lowers the melting temperature of glass and may be contained. When containing K2O, the content is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.3% or more, particularly preferably 0.4% or more, and most preferably 0.5% or more. If there is too much K2O, the chemical strengthening property will decrease or the chemical durability will decrease, so 1.5% or less is preferable, more preferably 1.3% or less, still more preferably 1.2% or less, particularly preferably 1.1% or less, and most preferably 1.0% or less.

[0032] For the glass plate according to this embodiment, the total content of Na2O and K2O, Na2O + K2O, is preferably 0% or more and 3.0% or less. From the viewpoint of improving the meltability of the glass, Na2O + K2O is more preferably 0.2% or more, still more preferably 0.4% or more, even more preferably 0.6% or more, particularly preferably 0.7% or more, and most preferably 0.8% or more. Also, if Na2O + K2O is too high, the chemical strengthening property will decrease or the chemical durability will decrease, so 2.7% or less is more preferable, still more preferably 2.5% or less, even more preferably 2.3% or less, particularly preferably 2.2% or less, and most preferably 2.1% or less.

[0033] For the glass plate according to this embodiment, the content of R2O (the total of Li2O, Na2O, and K2O) is 5.0% or more and 15% or less. From the viewpoint of improving the meltability of the glass, the content of R2O is preferably 6.0% or more, still more preferably 6.5% or more, particularly preferably 7.0% or more, and most preferably 7.5% or more. Also, from the viewpoint of enhancing the chemical strengthening property and chemical durability, the content of R2O is preferably 14% or less, more preferably 13% or less, still more preferably 12% or less, and particularly preferably 11% or less.

[0034] From the perspective of enhancing chemical strengthening properties and chemical durability, for the glass sheet according to this embodiment, K2O / R2O is preferably 0.20 or less, more preferably 0.15 or less, still more preferably 0.13 or less, particularly preferably 0.12 or less, and most preferably 0.11 or less. The lower limit of K2O / R2O is not particularly limited, but for example, it is 0.003 or more.

[0035] From the perspective of fining property, for the glass sheet according to this embodiment, the content of SnO2 is preferably 0.10% or more, more preferably in the following order: 0.15% or more, 0.20% or more, 0.25% or more, 0.30% or more, still more preferably 0.35% or more, particularly preferably 0.40% or more, and most preferably 0.45% or more. From the perspective of further suppressing devitrification and coloring, the content of SnO2 is preferably 2.5% or less, more preferably 2.2% or less, particularly preferably 2.0% or less, and most preferably 1.8% or less. Sn can take divalent and tetravalent forms, but in this specification, the concentration is expressed based on SnO2.

[0036] ZrO2 is a component that can form crystal nuclei during the crystallization treatment and may be contained. The content of ZrO2 is preferably 1.0% or more, more preferably 1.5% or more, still more preferably 2.0% or more, particularly preferably 2.5% or more, and most preferably 3.0% or more. On the other hand, in order to suppress devitrification during melting, the content of ZrO2 is preferably 6.0% or less, more preferably 5.5% or less, still more preferably 5.0% or less, particularly preferably 4.5% or less, and most preferably 4.2% or less.

[0037] Also, taking the total content of Li2O, Na2O, and K2O, Li2O + Na2O + K2O, as R2O, from the perspective of enhancing chemical durability, ZrO2 / R2O is preferably 0.1 or more, and more preferably 0.2 or more. From the perspective of enhancing transparency after crystallization, ZrO2 / R2O is preferably 0.8 or less, and more preferably 0.6 or less.

[0038] Y2O3 is a component that makes it difficult for fragments to scatter when the chemically strengthened glass breaks, and it may be contained. The content of Y2O3 is preferably 1.0% or more, more preferably 1.3% or more, still more preferably 1.6% or more, particularly preferably 1.9% or more, and most preferably 2.1% or more. On the other hand, in order to suppress devitrification during melting, the content of Y2O3 is preferably 9.0% or less, more preferably 8.0% or less, still more preferably 7.0% or less, particularly preferably 6.0% or less, and most preferably 5.0% or less.

[0039] P2O5 is not essential, but it has the effect of promoting phase separation of the glass and thus promoting crystallization, and it may be contained. When P2O5 is contained, the content is preferably 0.2% or more, more preferably 0.4% or more, still more preferably 0.6% or more, particularly preferably 0.8% or more, and most preferably 1.0% or more. On the other hand, if the content of P2O5 is too high, it is likely to phase-separate during melting, and the acid resistance will be significantly reduced. The content of P2O5 is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, particularly preferably 3.7% or less, and most preferably 3.5% or less.

[0040] TiO2 is a component that can form crystal nuclei during the crystallization treatment, and it may be contained. TiO2 is not essential, but when it is contained, it is preferably 0.05% or more and 1.0% or less. The content of TiO2 is more preferably 0.08% or more, still more preferably 0.10% or more, particularly preferably 0.15% or more, and most preferably 0.20% or more. On the other hand, in order to suppress devitrification during melting and to impart coloration to the glass, the content of TiO2 is more preferably 0.8% or less, still more preferably 0.6% or less, particularly preferably 0.5% or less, and most preferably 0.4% or less.

[0041] B2O3 is an optional component that can improve the chipping resistance and melting property of chemically strengthened glass, and it may be contained. When B2O3 is contained, its content is preferably 0% or more and 3.0% or less. From the perspective of further improving the melting property, the content of B2O3 is more preferably 0.2% or more, still more preferably 0.4% or more, particularly preferably 0.6% or more, and most preferably 0.8% or more. On the other hand, in order to suppress the occurrence of striae during melting and prevent phase separation and deterioration of glass quality, the content of B2O3 is more preferably 2.0% or less, still more preferably 1.5% or less, particularly preferably 1.0% or less, and most preferably 0.8% or less.

[0042] BaO, SrO, MgO, CaO, and ZnO are components that can improve the melting property of glass and may be contained. When these components are contained, the total content of BaO, SrO, MgO, CaO, and ZnO, BaO + SrO + MgO + CaO + ZnO, is preferably more than 0% and 3.0% or less. From the perspective of further improving the melting property of glass, BaO + SrO + MgO + CaO + ZnO is more preferably 0.1% or more, still more preferably 0.2% or more, particularly preferably 0.3% or more, and most preferably 0.5% or more. On the other hand, from the perspective of suppressing the decrease in ion exchange rate, BaO + SrO + MgO + CaO + ZnO is more preferably 2.5% or less, still more preferably 2.0% or less, particularly preferably 1.8% or less, and most preferably 1.5% or less.

[0043] Among the above components, BaO, SrO, and ZnO may be contained to improve the refractive index of the residual glass and approach the precipitated crystal phase, thereby improving the light transmittance of the crystallized glass and reducing the haze value. In that case, the total content of BaO + SrO + ZnO is preferably 0% or more and 1.0% or less. BaO + SrO + ZnO is more preferably 0.05% or more, still more preferably 0.1% or more, particularly preferably 0.2% or more, and most preferably 0.3% or more. On the other hand, these components may reduce the ion exchange rate. From the viewpoint of improving the chemical strengthening characteristics, BaO + SrO + ZnO is more preferably 0.8% or less, still more preferably 0.6% or less, particularly preferably 0.5% or less, and most preferably 0.4% or less.

[0044] CeO2 has the effect of oxidizing the glass and may suppress coloring, and may be contained. When CeO2 is contained, the content is preferably 0% or more and 1.0% or less. The content of CeO2 is more preferably 0.2% or more, still more preferably 0.3% or more, and particularly preferably 0.4% or more. When CeO2 is used as an oxidizing agent, the content of CeO2 is more preferably 0.8% or less, still more preferably 0.7% or less, particularly preferably 0.6% or less, and most preferably 0.5% or less in order to enhance transparency.

[0045] When the glass is colored and used, a coloring component may be added within a range that does not inhibit the achievement of the desired chemical strengthening characteristics. Examples of the coloring component include CoO, Co3O4, MnO, MnO2, FeO, Fe2O3, NiO, CuO, Cu2O, Cr2O3, V2O5, Bi2O3, SeO2, Se, Er2O3, Nd2O3, Eu2O3, Pr6O 11 are mentioned as suitable ones. The total content of the coloring component is preferably in the range of 1.0% or less. More preferably, it is 0.8% or less, still more preferably 0.6% or less, and most preferably 0.4% or less. When it is desired to increase the visible light transmittance of the glass, it is preferably substantially free of these components.

[0046] As a fining agent during the melting of glass, it may appropriately contain SO3, chlorides, fluorides, etc. It is preferably free of As2O3. When containing As2O3, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not contained.

[0047] The glass composition is not particularly limited, but specifically, for example, the following glass compositions can be mentioned. (1) Glass containing 60 - 66% of SiO2, 18.0 - 23% of Al2O3, 4.5 - 9.0% of Li2O, and 1.50 - 2.5% of SnO2, expressed in mass% based on oxides (2) Glass containing 60 - 66% of SiO2, 7.0 - 18% of Al2O3, 7 - 11.0% of Li2O, and 1.00 - 2.5% of SnO2, expressed in mass% based on oxides (3) Glass containing 65 - 75% of SiO2, 8.0 - 13% of Al2O3, 7 - 11.0% of Li2O, and 1.50 - 2.5% of SnO2, expressed in mass% based on oxides (4) Glass containing 65 - 75% of SiO2, 18.0 - 23% of Al2O3, 4.5 - 9.0% of Li2O, and 0.10 - 2.5% of SnO2, expressed in mass% based on oxides (5) Glass containing 60 - 66% of SiO2, 12.0 - 18% of Al2O3, 4.5 - 9.0% of Li2O, and 0.50 - 1.5% of SnO2, expressed in mass% based on oxides

[0048] (Visible light transmittance) The glass plate according to this embodiment has a visible light transmittance of preferably 91.0% or more when converted to a thickness of 0.7 mm. Thus, when used as a protective member of a display device (for example, the cover glass of a mobile display), the display screen is easy to see. The visible light transmittance is more preferably 91.2% or more, and even more preferably 91.4% or more. The higher the visible light transmittance, the better, but it is usually 92% or less. The visible light transmittance of ordinary amorphous glass is about 90%. The visible light transmittance can be measured by a method conforming to JIS R3106 (2019).

[0049] (Haze value) The glass sheet according to the present embodiment preferably has a haze value of 0.5% or less, more preferably 0.3% or less, still more preferably 0.2% or less, particularly preferably 0.1% or less, and most preferably 0.05% or less when measured at a thickness of 0.7 mm. The smaller the haze value, the more preferable. The haze value is a value measured in accordance with JIS K7136 (2000).

[0050] When the total light visible light transmittance of the glass with a plate thickness of t [mm] is T [%] and the surface reflectance on one side is R [%], by applying the Lambert-Beer law, using the constant α, T / 100 = (1 - R / 100) 2 × exp(-αt). From this, expressing α in terms of R, T, and t, and setting t = 0.7 mm, since R does not change with the plate thickness, the total light visible light transmittance T in terms of 0.7 mm 0.7 is T 0.7 / 100 = T / 100 0.7 / t / (1 - R / 100)^(1.4 / t - 2) can be calculated. However, X^Y represents X Y .

[0051] (Thickness) The thickness of the glass sheet according to the present embodiment is 0.30 to 1.00 mm. The thickness is preferably 0.90 mm or less, more preferably 0.80 mm or less, still more preferably 0.70 mm or less, particularly preferably 0.65 mm or less, and most preferably 0.60 mm or less. Also, from the viewpoint of enhancing strength, the thickness is preferably 0.35 mm or more, more preferably 0.40 mm or more, still more preferably 0.45 mm or more, and particularly preferably 0.50 mm or more.

[0052] The shape of the glass plate according to this embodiment may be a shape other than a plate shape according to the product, application, etc. to which it is applied. Further, the glass plate may have a beveled shape with different thicknesses on the outer periphery. Further, the form of the glass plate is not limited to this. For example, the two main surfaces may not be parallel to each other, and all or part of one or both of the two main surfaces may be a curved surface. More specifically, the glass plate may be, for example, a flat glass plate without warping, or a curved glass plate having a curved surface.

[0053] <<Devitrified Glass>> The glass plate according to this embodiment is preferably devitrified glass obtained by crystallizing the above-described glass plate. Devitrified glass is obtained by heat-treating amorphous glass to crystallize it. The glass composition of the devitrified glass is the same as the composition of the amorphous glass before crystallization. That is, the mother composition of the devitrified glass according to this embodiment is the same as the composition of the glass plate according to the above-described this embodiment, and the preferable composition range is also the same.

[0054] In this specification, "devitrified glass" refers to glass in which diffraction peaks indicating crystals are recognized by X-ray diffraction method (XRD: X-ray Diffraction). X-ray diffraction measurement can be performed, for example, by measuring a range of 2θ from 10° to 80° using CuKα rays. Examples of the crystals include β-spodumene-based crystals, lithium disilicate-based crystals, β-quartz-based crystals, lithium metasilicate crystals, and lithium phosphate crystals in crystals containing lithium. These crystals form solid solutions and may dissolve various elements. Particularly, the elements to be dissolved are alkali metals (Na, K) and alkaline earth metals (Mg, Ca, Sr, Ba), but this is not necessarily the case. Further, examples of crystals not containing lithium include ZrO2 and its solid solution crystals. Examples of the elements to be dissolved include Y, Sn, etc., but this is not necessarily the case.

[0055] The crystallization ratio of the crystallized glass is preferably 60% or more, more preferably 65% or more, still more preferably 70% or more, and particularly preferably 75% or more in order to increase the mechanical strength. Also, in order to enhance transparency, it is preferably 90% or less, more preferably 85% or less, and particularly preferably 80% or less. A small crystallization ratio is also excellent in terms of being easy to heat and bend-mold etc.

[0056] The crystallization ratio can be calculated by the Rietveld method from the X-ray diffraction intensity. Regarding the Rietveld method, it is described in "Crystallographic Analysis Handbook" edited by the Editorial Committee of the Crystallographic Society of Japan, "Crystallographic Analysis Handbook" (published by Kyoritsu Shuppan in 1999, p492 - 499).

[0057] The average particle size of the precipitated crystals of the crystallized glass is preferably 150 nm or less, more preferably 100 nm or less, still more preferably 50 nm or less, and particularly preferably 20 nm or less in order to enhance transparency. The average particle size of the precipitated crystals is determined from a transmission electron microscope (TEM) image. Also, it can be estimated from a scanning electron microscope (SEM) image.

[0058] For the crystallized glass plate according to this embodiment, the arithmetic mean roughness Ra of the first main surface is preferably 500 nm or less, more preferably 450 nm or less, still more preferably 400 nm or less, particularly preferably 350 nm or less, and most preferably 300 nm or less. When the arithmetic mean roughness Ra of the first main surface is 500 nm or less, the flatness of the surface is excellent and the production efficiency can be improved. The lower limit of the arithmetic mean roughness Ra of the first main surface is not particularly limited, but for example, it is 5 nm or more.

[0059] The arithmetic mean roughness Ra can be measured by a method according to JIS B0601:1994. Note that for the crystallized glass according to this embodiment, it is preferable that the arithmetic mean roughness Ra of the first main surface in the unpolished state is 500 nm or less.

[0060] As a crystallization treatment for obtaining a crystallized glass plate showing the arithmetic mean roughness Ra, after treating at a first treatment temperature for a certain period of time, treating at a second treatment temperature for a certain period of time can be mentioned. As the conditions of the crystallization treatment, it is preferable that the second treatment temperature is higher than the first treatment temperature. Specifically, the following conditions can be mentioned. Conditions: The first treatment temperature is 550°C to 800°C, the second treatment temperature is 750°C to 1000°C, hold at the first treatment temperature for 1 hour to 10 hours, and then hold at the second treatment temperature for 10 minutes to 10 hours. The heating rate and cooling rate in each stage of heat treatment are 5 to 120°C / min.

[0061] <<Chemically strengthened glass>> The glass plate according to the present embodiment is preferably chemically strengthened glass. The chemically strengthened glass according to the present embodiment is obtained by chemically strengthening the glass plate according to the above-described present embodiment. That is, the base composition of the chemically strengthened glass according to the present embodiment is the same as the compositions of the glass plate and the crystallized glass according to the above-described present embodiment, and the preferable composition ranges are also the same.

[0062] When the chemically strengthened glass is plate-shaped, the content ratio of the alkali metal element is different between the surface layer and the center in the thickness direction. On the other hand, except for the case where an extreme ion exchange treatment is performed, the glass composition at the deepest part from the surface of the chemically strengthened glass is the same as the base composition of the chemically strengthened glass. When the chemically strengthened glass is plate-shaped, the deepest part from the glass surface is, for example, the depth of 1 / 2 of the plate thickness t.

[0063] (Stress characteristics) In this specification, the "depth of the compression stress layer (DOL)" is the depth at which the compression stress value CS becomes zero. The surface compression stress value CS0 and the depth of the compression stress layer DOL can be measured using a surface stress meter [for example, the surface stress meter (FSM-6000) manufactured by Orimoto Seisakusho]. The preferable plate thickness (t) and the preferable shape of the chemically strengthened glass according to the present embodiment are the same as the preferable plate thickness (t) and the shape of the glass plate according to the above-described present embodiment.

[0064] The chemically strengthened glass according to this embodiment preferably has a surface compressive stress value CS0 of 300 MPa or more, more preferably 350 MPa or more, still more preferably 400 MPa or more, and even more preferably 450 MPa or more. The upper limit value of the surface compressive stress value CS0 is not particularly limited, but the surface compressive stress value CS0 may be, for example, 1400 MPa or less.

[0065] For the chemically strengthened glass according to this embodiment, if the depth of the compressive stress layer DOL is too large with respect to the thickness t (mm), CT may become too large. Therefore, it is preferably 0.30t or less, and more preferably 0.20t or more. Further, from the viewpoint of improving strength, DOL is preferably 0.10t or more, and more preferably 0.15t or more. <Use>

[0066] The glass sheet according to this embodiment can be used as a cover glass for mobile electronic devices such as mobile phones, smartphones, personal digital assistants (PDAs), and tablet terminals. It is also useful as a cover glass for electronic devices such as televisions (TVs), personal computers (PCs), and touch panels that are not intended for portability. Further, it is also useful as building materials such as window glass, table tops, interior decorations of automobiles and airplanes, etc., and their cover glasses (for example, in-vehicle cover glasses).

[0067] The glass sheet according to this embodiment can be bent or formed before or after chemical strengthening to have a shape other than a flat plate shape, and is therefore also useful for applications such as housings having a curved surface shape.

[0068] <<Manufacturing method of glass sheet>> The manufacturing method of the glass sheet according to this embodiment preferably includes at least the following step (1), more preferably includes at least one of the following steps (2) and (3) in addition to step (1), and still more preferably includes the following steps (1) to (3). (1) Step of producing amorphous glass (2) Step of heat-treating the glass to obtain crystallized glass (3) Step of ion-exchanging the glass to obtain chemically strengthened glass The following describes each step.

[0069] (1) Step of producing amorphous glass Amorphous glass can be produced, for example, by the following method. Glass raw materials are formulated so as to obtain glass of a preferable composition, and are heated and melted in a glass melting furnace. Thereafter, the molten glass is homogenized by bubbling, stirring, addition of a fining agent, etc., formed into a glass plate of a predetermined thickness by a known forming method, and gradually cooled.

[0070] As the forming method, the float method is preferable. The float method refers to a method of flowing molten glass onto a molten metal bath and forming it into a plate shape. In this specification, the upstream of the molten metal bath refers to the side where the molten glass flows in, and the downstream refers to the side where the glass formed into a ribbon shape is carried out.

[0071] Fig. 2 shows a schematic diagram of an apparatus for manufacturing glass by the float method. As shown in Fig. 2, the apparatus for manufacturing glass by the float method includes a melting furnace 10, a float bath 20, and a lehr (annealing furnace) 30. In the manufacture of glass by the float method, first, glass raw materials are melted in the melting furnace 10 to obtain molten glass. The melting furnace 10 has a melting kiln 11, and in the melting kiln 11, the introduced glass raw materials 1 are melted to obtain molten glass 2. More specifically, the melting kiln 11 includes a melting tank 12 on the upstream side and a cooling tank 13 on the downstream side, and these are connected by a neck 14 (or throat), and the glass raw materials 1 are melted into molten glass 2 on the upstream side (i.e., the melting tank), and the temperature of the molten glass 2 is adjusted on the downstream side.

[0072] Next, molten glass 2 is continuously supplied from the upstream side to the surface of the molten metal bath 21 stored in the float bath 20 to form a glass ribbon 3. Then, the formed glass ribbon 3 is drawn out from the downstream end of the float bath 20 and introduced into a lehr (rare) 30 for slow cooling to produce a plate-like glass. The glass ribbon 3 introduced into the lehr 30 is slowly cooled while being conveyed by a conveying means such as a roller conveyor to a lehr (not shown). Since the molten glass 2 on the molten metal bath 21 and the glass ribbon 3 in the lehr 30 are continuous, the conveying speed (lehr speed) in the lehr 30 depends on the speed at which the molten glass 2 flows from upstream to downstream on the molten metal bath 21. Although the glass ribbon 3 in the lehr 30 is solidified, the molten glass 2 flows, so the speed of the molten glass 2 is slower than the lehr speed, and the speed of the molten glass 2 on the molten metal bath 21 tends to be faster towards the downstream. The type of molten metal is not particularly limited, but generally molten tin is used.

[0073] As described above, in the present embodiment, the SnO2 concentration distribution in the glass plate can be adjusted by 1) the lehr speed, 2) the hydrogen concentration in the air, 3) the temperature of the molten metal bath, and 4) the glass composition (for example, the content of SnO2) during forming by the float process. Each item will be described below.

[0074] 1) The lehr speed during float forming The lehr speed is preferably 20 m / h or more, more preferably 100 m / h or more, still more preferably 200 m / h or more, particularly preferably 300 m / h or more, and most preferably 400 m / h or more. If the lehr speed is too high, the quality of the glass is likely to deteriorate, so it is preferably 1200 m / h or less, more preferably 1000 m / h or less, still more preferably 900 m / h or less, particularly preferably 850 m / h or less, and most preferably 800 m / h or less.

[0075] 2) The hydrogen concentration in the atmosphere during float forming The hydrogen concentration in the atmosphere during float forming can be adjusted by the concentration of gases such as reducing gases and oxidizing gases supplied to the glass during float forming, the spraying amount, the main surface to be sprayed, the treatment temperature and time, etc. Examples of the supply of such gases include supply from holes in the ceiling arranged at an interval from the molten metal bath 21, and spraying of gas onto the glass sheet in the lehr.

[0076] Examples of the reducing gas include nitrogen gas, hydrogen gas, carbon monoxide gas, or a mixed gas thereof. The reducing gas may contain an inert gas such as air, nitrogen, or argon as a carrier gas. The reducing gas can be supplied, for example, from holes in the ceiling arranged at an interval from the molten metal bath 21. Specific examples of the treatment conditions for the reducing gas include conditions such as setting the mixed gas to 0.1 to 100 cc / min and the treatment temperature to 600 to 1200 °C. The mixed gas is, for example, a mixed gas of nitrogen gas and hydrogen gas, and contains 80 to 99.5 vol% of nitrogen gas and 0.5 to 20 vol% of hydrogen gas.

[0077] Examples of the oxidizing gas include sulfurous acid gas (SO2 gas), hydrofluoric acid gas, oxygen gas, or a mixed gas thereof. The oxidizing gas may contain an inert gas such as air, nitrogen, or argon as a carrier gas. The oxidizing gas may further contain water vapor. The oxidizing gas is sprayed, for example, onto the main surface of the glass sheet (preferably at least the top surface, specifically, for example, only the first main surface or both the first main surface and the second main surface) in the lehr. Specific examples of the treatment conditions for the oxidizing gas include conditions such as setting the mixed gas to 0.1 to 100 cc / min and the treatment temperature to 600 to 1200 °C. The mixed gas may vary, for example, in the oxygen content in the range of 0.5 to 10 vol% or higher. In some embodiments, the mixed gas may be oxygen gas having a maximum of 100 vol%.

[0078] 3) Temperature of the molten metal bath during float forming The temperature of the molten metal bath is preferably 700 °C or higher, more preferably 800 °C or higher, still more preferably 850 °C or higher, and particularly preferably 900 °C or higher. From the viewpoint of volatilization of metallic tin, it is preferably 1300 °C or lower, more preferably 1250 °C or lower, still more preferably 1200 °C or lower, and particularly preferably 1150 °C or lower.

[0079] 4) Glass composition The SnO2 concentration distribution in the glass plate can also be adjusted by adjusting the SnO2 concentration of the base composition. The preferred range of the SnO2 concentration of the base composition is the same as the range described above in the section of <Glass plate> (composition).

[0080] (2) Step of heat-treating the glass to obtain a crystallized glass A crystallized glass can be obtained by heat-treating (heat treatment) the amorphous glass obtained by the above procedure. In that case, the heat treatment includes a multi-step heat treatment of two or more steps. The multi-step heat treatment refers to a heat treatment in which holding at a predetermined temperature range for a predetermined time is performed a plurality of times while changing the temperature range and the like. Specifically, as the multi-step heat treatment, for example, a two-step heat treatment in which the temperature is raised from room temperature to a first treatment temperature and held for a certain time, and then held at a second treatment temperature higher than the first treatment temperature for a certain time can be mentioned.

[0081] In the case of a two-step heat treatment, the first treatment temperature is preferably a temperature range in which the crystal nucleation rate becomes large in the glass composition, and the second treatment temperature is preferably a temperature range in which the crystal growth rate becomes large in the glass composition. Also, the holding time at the first treatment temperature is preferably long so that a sufficient number of crystal nuclei are generated. By generating a large number of crystal nuclei, the size of each crystal becomes small, and a highly transparent crystallized glass can be obtained.

[0082] In the case of a two-step heat treatment, the first treatment temperature is, for example, 550 °C to 800 °C, the second treatment temperature is, for example, 850 °C to 1000 °C, and after holding at the first treatment temperature for 2 hours to 10 hours, it is held at the second treatment temperature for 2 hours to 10 hours.

[0083] The heating rate and the cooling rate in each heat treatment stage are preferably 5 to 120 °C / min. Since the crystal growth rate in the material can be followed when the heating rate and the cooling rate are 5 °C / min or more, it is preferable. On the other hand, since the deformation of the material can be suppressed when the heating rate and the cooling rate are 120 °C / min or less, it is preferable.

[0084] The molten glass may be homogenized and formed into a glass plate with a predetermined thickness, or the molten glass may be formed into a block shape, and subsequently, a crystallization treatment may be continuously performed. The crystallized glass obtained by the above procedure is ground and polished as necessary to form a crystallized glass plate.

[0085] (3) Step of obtaining chemically strengthened glass by ion-exchanging glass In the present embodiment, the chemical strengthening treatment (ion-exchange treatment) can be performed, for example, by immersing a glass plate in a molten salt such as potassium nitrate heated to 360 to 600 °C for 0.1 to 500 hours. The heating temperature of the molten salt is preferably 375 to 500 °C, and the immersion time of the glass plate in the molten salt is preferably 0.3 to 200 hours.

[0086] Examples of the molten salt for performing the chemical strengthening treatment include nitrates, sulfates, carbonates, chlorides, etc. Examples of the nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, silver nitrate, etc. Examples of the sulfates include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, silver sulfate, etc. Examples of the carbonates include lithium carbonate, sodium carbonate, potassium carbonate, etc. Examples of the chlorides include lithium chloride, sodium chloride, potassium chloride, cesium chloride, silver chloride, etc. These molten salts may be used alone or in combination of multiple types.

[0087] In this embodiment, the treatment conditions for chemical strengthening treatment may be appropriately selected in consideration of the characteristics and composition of the glass for chemical strengthening, the type of molten salt, and chemical strengthening characteristics such as the surface compressive stress and the depth of the compressive stress layer desired for the finally obtained chemically strengthened glass.

[0088] In particular, it is preferable to perform chemical strengthening treatment on an amorphous glass or a crystallized glass having a large fracture toughness value for a long time. When the ion exchange reaction proceeds by the long-time chemical strengthening treatment, a large compressive stress is generated in the surface layer portion, and at the same time, due to structural relaxation, a decrease in the compressive stress mainly occurs near the surface, and the compressive stress balance of this embodiment is easily obtained.

[0089] Also, in this embodiment, the chemical strengthening treatment may be performed only once, or the chemical strengthening treatment (multi-stage strengthening) may be performed a plurality of times under two or more different conditions.

[0090] <Display device> The display device according to this embodiment includes the glass plate according to the above-described embodiment. Examples of the display device in this embodiment include a display device such as an in-vehicle car navigation system and a portable display device such as a smartphone.

Description of reference numerals

[0091] 1 Glass raw material; 2 Molten glass; 3 Glass ribbon; 10 Melting furnace; 11 Melting kiln; 12 Melting tank; 13 Cooling tank; 14 Neck; 20 Float bath; 21 Molten metal bath; 22 Top roll; 23 Restrictor; 30 Slow cooling furnace (rearer)

Claims

1. It has a first main surface and a second main surface facing the first main surface, with a thickness of 0.30 to 1.00 mm, and a crystal growth rate at any temperature from 950 °C to 1260 °C of 100 to 5000 μm / hour, contains lithium, in terms of mass percentage based on oxides, the content of RO in the mother composition ２ is 5.0 to 15%, at least on the first main surface, the average content of RO from the surface to a depth of 10 μm ２ is 0.5 to 4.0% less than the content of RO at the center of the plate thickness, a glass plate. However, RO ２ is the sum of Li ２ O, Na ２ O and K ２ O. ２

2. A crystallized glass plate obtained by crystallizing the glass plate according to Claim 1, and the arithmetic mean roughness Ra of the first main surface is 500 nm or less.

3. The mother composition, in terms of mass percentage based on oxides, contains 60 to 75% of SiO ２ , 7.0 to 23% of Al ２ O ３ , and 4.5 to 13.0% of Li ２ O, the glass plate according to Claim 1.

4. The mother composition, in terms of mass percentage based on oxides, contains 60 to 75% of SiO ２ , 7.0 to 23% of Al ２ O ３ , 4.5 to 13.0% of Li ２ O, 0 to 1.5% of Na ２ O, and 0.10 to 2.5% of SnO ２ ​ ZrO ２ is 1.0 to 6.0%, Y ２ O ３ is 1.0 to 9.0%, P ２ O ５ is 0 to 5.0% The glass sheet according to claim 3, comprising.

5. The glass sheet according to claim 1, which is chemically strengthened glass.

6. The glass sheet according to claim 1, which is float glass.

7. The glass sheet according to claim 1, having a visible light transmittance of 91.0% or more when converted to a thickness of 0.7 mm.

8. A display device including the glass sheet according to any one of claims 1 to 7.

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