Glass plate and method for manufacturing glass plate

Abstract

The present invention relates to a glass plate which contains at least one heavy metal oxide selected from among Sb2O3, PbO, and As2O3, wherein: the total content of the heavy metal oxide satisfies being 0-0.40 mass% at least on one main surface; the ratio expressed by (the total content of the heavy metal oxide on the main surface) / (the total content of the heavy metal oxide inside the glass plate) is 0-0.8; and the absolute value of the difference between the visible light transmittance Uvc% after the surface layers of the pair of main surfaces are removed by 100 μm and the visible light transmittance Tvc% in the plate thickness direction is 2% or less.

Description

Glass plate and method for manufacturing a glass plate

[0001] This invention relates to a glass plate and a method for manufacturing a glass plate.

[0002] Typically, a large amount of CO2 is used during glass manufacturing. ２ CO2 emissions are produced, mainly from the combustion of heavy oil during the melting of glass raw materials and the decomposition of carbonate raw materials. Therefore, CO2 emissions occur during glass manufacturing. ２ To reduce emissions, it is useful to reuse glass cullet to manufacture glass.

[0003] As an example of glass cullet reuse, Patent Document 1 discloses a glass recycling method that can improve the value of recycled amorphous glass cullet. Also, Patent Document 2 discloses a method for reprocessing glass plates, such as tempered glass substrates used in solar panels, and a method for recycling solar panels, for the effective reuse of glass plates.

[0004] Japanese Patent Publication No. 2021-109122 Japanese Patent Publication No. 2021-151634

[0005] As mentioned in the above-mentioned literature, one type of glass cullet is PV cullet obtained by crushing solar panels. Currently, the majority of PV cullet is landfilled, so there is a strong social demand for the reuse of PV cullet. The glass used in the original solar panels that become the PV cullet contains Sb to adjust the Fe-Redox (oxidation-reduction state of Fe) and to ensure high transparency. ２ O ３ Where antimony is added, it is important to note that antimony may cause a certain environmental burden through leaching into landfills. Furthermore, attention must be paid to the leaching of antimony when PV cullet is dismantled and cleaned for reuse. The same applies to glass from other sources and types, in addition to glass derived from PV cullet as described above. That is, Sb ２ O ３ In addition, PbO and As are heavy metal oxides. ２ O ３ Also, from the perspective of being a hazardous substance, it will be subject to removal. And, Sb２ O ３ the same mechanism can also be applied to the aforementioned PbO and As ２ O ３ as well.

[0006] Accordingly, an object of the present invention is to provide a glass plate containing a heavy metal element, in which elution of the heavy metal element to the outside environment is suppressed. Another object of the present invention is to provide a method for producing the above glass plate.

[0007] As a result of intensive studies conducted by the present inventors, even if the glass plate contains a heavy metal oxide such as Sb ２ O ３ , the inventors have found that if the content of the heavy metal oxide in the main surface of the glass plate can be reduced, elution of the heavy metal element to the outside environment can be suppressed. As a result of further studies, the present inventors have completed the present invention by finding that by subjecting a glass plate to a specific treatment, the content of heavy metal oxide in the main surface of the glass plate can be reduced, thereby obtaining a glass plate in which the total content of the heavy metal oxide in the main surface is relatively lower than that in the interior of the glass plate.

[0008] That is, the gist of an embodiment of the present invention is as follows. [1] A glass plate having a pair of opposing main surfaces, wherein the glass plate contains Sb ２ O ３ , PbO, and As ２ O ３ selected from at least one heavy metal oxide, wherein the glass plate satisfies, on at least one main surface, a total content of the heavy metal oxides of 0 to 0.40% by mass based on oxide; in the glass plate, using the content expressed in mass% based on oxide, the ratio represented by {[total content of the heavy metal oxides in the main surface] / [total content of the heavy metal oxides in the interior of the glass plate]} is 0 to 0.8; let T be the visible light transmittance in the thickness direction of the glass plate ｖｃ %, and let U be the visible light transmittance after removing 100 μm each from the surface layers of the pair of main surfaces of the glass plate ｖｃ %, then |U ｖｃ -T ｖｃA glass plate in which the absolute value of the difference in transmittance represented by | is 2% or less. [2] The glass plate according to [1], wherein the content of the heavy metal oxides in the interior, expressed as mass % on an oxide basis, satisfies the total of the heavy metal oxides: 0.0005 to 0.50%. [3] The glass plate in which the content of the heavy metal oxides in the interior, expressed as mass % on an oxide basis, is SiO ２ :60-80%, Na ２ O: 5-20%, K ２ O: 0-3%, MgO: 0-15%, CaO: 5-20%, Al ２ O ３ : 0-10%, Fe ２ O ３ : 0-3%, CeO ２ : 0-2%, TiO ２ : 0-3%, SO ３ : 0-2%, Cr ２ O ３ A glass plate according to [1] or [2] above, satisfying the following: 0-0.2% of solids, 0-0.2% of CoO, 0-0.2% of NiO, and a total of 0.0005% or more of the heavy metal oxides. [4] A glass plate according to any one of [1] to [3] above, wherein the glass plate, which is 30 mm square and 4 mm thick, is immersed in 120 mL of a 1 mol / L NaOH solution at a liquid temperature of 85°C for 5 hours, and the total amount of heavy metal oxides eluted into the NaOH solution is less than 0.4 ppm by mass. [5] A glass plate according to any one of [1] to [4] above, having a plate thickness of 0.5 to 20 mm.

[0009] [6] A method for manufacturing a glass plate having a pair of opposing main surfaces, wherein Sb ２ O ３ , PbO, and As ２ O ３ A method for manufacturing a glass plate, comprising in order: preparing a glass plate containing at least one heavy metal oxide selected from; contacting a reducing agent with at least one main surface of the glass plate; and heating the glass plate at a temperature of 700°C or higher. [7] A method for manufacturing a glass plate having a pair of opposing main surfaces, wherein Sb ２ O ３ , PbO, and As２ O ３ A method for manufacturing a glass plate, comprising in order: preparing a glass plate containing at least one heavy metal oxide selected from; and heating the glass plate in a reducing atmosphere at a temperature of 700°C or higher. [8] The glass plate contains Sb as the heavy metal oxide. ２ O ３ A method for manufacturing a glass plate according to [6] or [7], wherein the glass plate contains and the glass plate is a recycled product obtained from PV cullet, which is made by crushing glass that constitutes a solar panel.

[0010] According to the present invention, it is possible to suppress the leaching of heavy metal elements from a glass plate containing heavy metal oxides into the outside environment.

[0011] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention. Furthermore, the "~" indicating a numerical range is used to mean that the numbers written before and after it are included as the lower limit and upper limit. In this specification, mass% and weight%, and mass ppm and weight ppm are synonymous.

[0012] In this specification, the composition of the main surface of a glass plate, i.e., the constituent components and their content, is determined by performing laser ablation inductively coupled plasma mass spectrometry at 1 μm intervals from the main surface (outermost surface) of the glass plate to a depth of 3 μm, and calculating the average value. Furthermore, the composition of the interior of the glass plate, i.e., the constituent components and their content, refers to the composition in the portion of the glass plate that is 100 μm or more deep from the main surface (outermost surface). If the thickness of the glass plate is insufficient, the composition of the central portion in the thickness direction of the glass plate may be considered as the composition of the interior of the glass plate. The composition of the interior of the glass plate is determined by using X-ray fluorescence analysis (XRF) on a surface of the glass plate that has been polished to a thickness of 100 μm.

[0013] 《Glass Plate》 The glass plate according to this embodiment has a pair of opposing main surfaces, and Sb ２ O ３ , PbO, and As ２ O ３It contains at least one heavy metal oxide selected from the above. The glass plate satisfies the requirement that the total content of heavy metal oxides, expressed as mass percent on at least one main surface based on oxides, is 0 to 0.40%. Furthermore, the ratio expressed as {[Total content of heavy metal oxides on the main surface] / [Total content of heavy metal oxides inside the glass plate]}, using the content expressed as mass percent on oxides, is 0 to 0.8. The visible light transmittance of the glass plate in the thickness direction is T ｖｃ U is the visible light transmittance in the thickness direction of a glass plate after removing 100 μm of the surface layer of each of the two main surfaces mentioned above. ｖｃ When expressed as a percentage, |U ｖｃ -T ｖｃ The absolute value of the difference in transmittance represented by | is 2% or less.

[0014] The glass plate according to this embodiment has Sb as a constituent component. ２ O ３ , PbO, and As ２ O ３ The glass plate contains at least one heavy metal oxide selected from the following. Conventionally, when alkaline cleaning or the like is performed on such a glass plate, there is concern about the leaching of heavy metal elements into the outside environment. In contrast, the glass plate according to this embodiment has been found to effectively suppress the above-mentioned leaching by setting the ratio of the total content of heavy metal oxides on the main surface of the glass plate to the total content of heavy metal oxides inside the glass plate, that is, the ratio expressed as {[total content of heavy metal oxides on the main surface of the glass plate] / [total content of heavy metal oxides inside the glass plate]} to 0.8 or less.

[0015] In this embodiment, the glass plate has a ratio of 0 to 0.8 expressed as {[Total content of heavy metal oxides on the main surface of the glass plate] / [Total content of heavy metal oxides inside the glass plate]}. Here, from the viewpoint of suitably suppressing the elution of heavy metal elements into the outside environment, the above ratio is 0.8 or less, preferably 0.6 or less, more preferably 0.4 or less, and the lower the ratio, the better. On the other hand, the lower limit of the above ratio is not particularly limited and may be 0, that is, it may not contain the above heavy metal oxides. However, since the above heavy metal oxides are contained inside the glass plate, it may be difficult to make the total content of heavy metal oxides on the main surface of the glass plate 0. From this viewpoint, it may be greater than 0, may be 0.001 or more, and may be 0.01 or more. Furthermore, the above ratio only needs to be satisfied by the total content of heavy metal oxides on at least one of the main surfaces of the glass plate, and it is preferable that the total content of heavy metal oxides on both main surfaces satisfy the ratio, as this can further reduce the elution of heavy metal elements into the outside environment.

[0016] In this specification, the total content of heavy metal oxides refers to the average Sb content (Sb) in the main surface or interior of the glass plate. ５＋ Sb ３＋ (made of Sb metal) ２ O ３ Converted to the standard, and the average Pb content (Pb ２＋ Pb ４＋ (consisting of Pb metal) converted to PbO standards, and the average As content (As ５＋ As ３＋ (made of As metal) ２ O ３ This represents the sum of the value converted to the standard.

[0017] In this embodiment, the content of heavy metal oxides in mass percentage on at least one main surface of the glass plate is preferably 0 to 0.40% of the total heavy metal oxides. Here, from the viewpoint of further reducing the amount of heavy metal elements leached into the outside environment, the content is preferably 0.40% or less, more preferably 0.35% or less, and even more preferably 0.30% or less. On the other hand, the lower limit of the content is not particularly limited and may be 0%, i.e., it may not contain any heavy metal oxides. However, since heavy metal oxides are contained inside the glass plate, it can be difficult to make the total content of heavy metal oxides on the main surface of the glass plate 0. From this viewpoint, the content may be greater than 0%, may be 0.0005% or more, or may be 0.0010% or more. Furthermore, the total content of heavy metal oxides only needs to be satisfied on at least one of the main surfaces of the glass plate, and it is preferable that both main surfaces satisfy this condition.

[0018] <Composition> The composition inside the glass plate according to this embodiment will be described below. The content here is expressed as mass percent based on oxides.

[0019] Sb ２ O ３ In the glass plate according to this embodiment, Sb ２ O ３ From the perspective of leaching into the environment and harmfulness to the human body, it is preferable not to include it. On the other hand, as mentioned above, in order to achieve high transparency, such as in the glass that makes up solar panels, Sb ２ O ３ It often contains Sb ２ O ３ This can be included, whether intentionally or inevitably. ２ O ３ The content may be greater than 0% and less than or equal to 0.50%, greater than 0% and less than or equal to 0.40%, and also between 0.0010% and 0.40%. Here, Sb ２ O ３ The content of is greater than 0%, may be 0.0005% or more, 0.0010% or more, or 0.0020% or more. Also, Sb ２ O ３From the perspective of suppressing the absolute amount of [the relevant component] and reducing the amount of antimony that can be eluted into the external environment, the content may be 0.50% or less, may be 0.40% or less, or may be 0.35% or less.

[0020] ・PbO In the glass sheet according to the present embodiment, it is preferable not to contain PbO from the viewpoints of elution into the environment and harmfulness to the human body. On the other hand, since PbO may be mixed in as an impurity during production, it can be contained regardless of whether it is intentionally or unavoidably introduced. The content of PbO may be 0 to 0.50%, may be more than 0% and 0.50% or less, or may be 0.0010 to 0.40%. Here, the content of PbO is 0% or more, may be more than 0%, may be 0.0005% or more, may be 0.0010% or more, or may be 0.0020% or more. Furthermore, from the perspective of suppressing the absolute amount of PbO and reducing the amount of lead that can be eluted into the external environment, the content may be 0.50% or less, may be 0.40% or less, or may be 0.35% or less.

[0021] ・As ２ ₂O₃ ３ In the glass sheet according to the present embodiment, As ２ ₂O₃ ３ is preferably not contained from the viewpoints of elution into the environment and harmfulness to the human body. On the other hand, As ２ ₂O₃ ３ may be contained in old solar panels for purposes such as fining agents and oxidizing agents, so As ２ ₂O₃ ３ can be contained regardless of whether it is intentionally or unavoidably introduced. As ２ ₂O₃ ３ has a content that may be 0 to 0.50%, may be more than 0% and 0.50% or less, or may be 0.0010 to 0.40%. Here, the content of As ２ ₂O₃ ３ is 0% or more, may be more than 0%, may be 0.0005% or more, may be 0.0010% or more, or may be 0.0020% or more. Furthermore, from the perspective of suppressing the absolute amount of As ２ ₂O₃ ３ and reducing the amount of arsenic that can be eluted into the external environment, the content may be 0.50% or less, may be 0.40% or less, or may be 0.35% or less.

[0022] ・Total heavy metal oxide In the glass sheet according to the present embodiment, the total content of heavy metal oxides, that is, Sb ２ O ３ , PbO, and As ２ O ３ The total content may be 0.0005 to 0.50%. Here, the total content may be 0.0005% or more, 0.0010% or more, or 0.0020% or more. Further, from the viewpoint of suppressing the absolute amount of heavy metal oxides and reducing the total amount of heavy metals that can be eluted into the external environment, the content may be 0.50% or less, 0.40% or less, or 0.35% or less.

[0023] ・SiO ２ In the glass sheet according to the present embodiment, SiO ２ is a component that contributes to improving Young's modulus, thereby making it easy to secure the strength required for a glass sheet. The content of SiO ２ is preferably 60 to 80%. Here, from the viewpoint of obtaining good weather resistance and suppressing thermal cracking of the glass sheet caused by an excessively high average linear expansion coefficient, the content is preferably 60% or more, more preferably 65% or more, still more preferably 68% or more, and particularly preferably 70% or more. Further, from the viewpoint of reducing difficulty in glass production associated with an increase in viscosity during melting, the content is preferably 80% or less, more preferably 78% or less, still more preferably 76% or less, and particularly preferably 74% or less.

[0024] ・Na ２ O In the glass sheet according to the present embodiment, Na ２ O is a component that improves the meltability of glass. The content of Na ２ O is preferably 5 to 20%. Here, from the viewpoint of lowering viscosity to improve moldability, the content is preferably 5% or more, more preferably 8% or more, still more preferably 10% or more, and particularly preferably 12% or more. Further, from the viewpoint of suppressing thermal cracking of the glass sheet caused by an excessively high average linear expansion coefficient, the content is preferably 20% or less, more preferably 18% or less, still more preferably 16% or less, and particularly preferably 14% or less.

[0025] ・K ２O In the glass plate according to this embodiment, K ２ O is a component that improves the solubility of glass. K ２ The O content is preferably 0 to 3%. Here, K ２ O does not need to be included, but if it is included, K ２ From the viewpoint of reducing viscosity and improving moldability, the O content is more preferably 0.01% or more, even more preferably 0.03% or more, and particularly preferably 0.1% or more. Furthermore, from the viewpoint of suppressing thermal cracking of the glass plate due to an excessively large average coefficient of linear expansion, the above content is preferably 3% or less, more preferably 2.5% or less, even more preferably 2% or less, and particularly preferably 1.5% or less.

[0026] • MgO In the glass plate according to this embodiment, MgO is a component that promotes the dissolution of the glass raw material and improves weather resistance and Young's modulus. The MgO content is preferably 0 to 15%. Here, MgO may not be included, but if it is included, the MgO content is preferably 1% or more, and more preferably 2% or more, from the viewpoint of weather resistance and Young's modulus. Furthermore, from the viewpoint of suppressing devitrification, the above content is preferably 15% or less, more preferably 10% or less, even more preferably 7% or less, and particularly preferably 5% or less.

[0027] CaO In the glass plate according to this embodiment, CaO is a component that improves the solubility of the glass raw material. The CaO content is preferably 5 to 20%. Here, from the viewpoint of improving the solubility of the glass raw material, the CaO content is preferably 5% or more, more preferably 6% or more, and even more preferably 7% or more. Furthermore, from the viewpoint of avoiding an increase in the specific gravity of the glass and maintaining low brittleness and strength, the above content is preferably 20% or less, more preferably 15% or less, even more preferably 12% or less, and particularly preferably 10% or less.

[0028] Al ２ O ３ In the glass plate according to this embodiment, Al ２ O ３ Al is a component that makes up the mesh structure of glass. ２ O ３ The content of is preferably 0 to 10%. Here, Al２ O ３ It is not necessary to include it, but if it is included, Al ２ O ３ The content of is preferably 0.3% or more, and more preferably 0.5% or more, from the viewpoint of Young's modulus, weather resistance, moisture resistance, chemical durability, and suppression of thermal cracking. Furthermore, from the viewpoint of suppressing the increase in viscosity when the glass raw materials are melted and facilitating glass manufacturing, and from the viewpoint of moldability, the above content is preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, and particularly preferably 2% or less.

[0029] Fe ２ O ３ In the glass plate according to this embodiment, Fe ２ O ３ Fe is an unavoidable component that is mixed in as an impurity from raw materials, etc. ２ O ３ The content of is preferably 0 to 3%. ２ O ３ The content refers to the content of FeO, an oxide of divalent iron, and Fe, an oxide of trivalent iron. ２ O ３ Total iron content (Fe ２ O ３ This refers to the amount converted to Fe. Here, the glass plate in this embodiment is Fe ２ O ３ It is not necessary to contain Fe, but if it is included ２ O ３ From the viewpoint of raw material costs, the content of is preferably more than 0%, more preferably 0.001% or more, and even more preferably 0.005% or more. Furthermore, from the viewpoint of obtaining high permeability, the above content is preferably 3% or less, more preferably 2.5% or less, and even more preferably 2% or less.

[0030] ・CEO ２ In the glass plate according to this embodiment, CeO ２ This is a solarization component. CeO ２ The content of is preferably 0 to 2%. Here, the glass plate according to this embodiment is CeO ２ It does not have to include, but CeO ２If it contains, the content is preferably 0.0001% or more, more preferably 0.0010% or more, and even more preferably 0.0050% or more from the viewpoint of coloring. Furthermore, from the viewpoint of coloring and raw material cost, the above content is preferably 2% or less, more preferably 1.5% or less, even more preferably 0.5% or less, and even more preferably 0.05% or less.

[0031] ・TiO ２ In the glass plate according to this embodiment, TiO ２ TiO is a coloring agent. ２ The content of is preferably 0 to 3%. Here, the glass plate according to this embodiment is TiO ２ It does not have to include TiO ２ If it contains, the content is preferably 0.0001% or more, more preferably 0.0010% or more, and even more preferably 0.0050% or more from the viewpoint of coloring. Furthermore, from the viewpoint of suppressing devitrification and suppressing coloring, the above content is preferably 3% or less, more preferably 1% or less, and even more preferably 0.2% or less.

[0032] ・SO ３ In the glass plate according to this embodiment, SO ３ SO4 is an ingredient that functions as a fining agent, but usually most of it is produced during the glass plate manufacturing process. ２ and O ２ It breaks down into SO4 and is released out of the system as bubbles. ３ The content may be 0 to 2%. Considering the release outside the system as described above, the glass plate according to this embodiment is SO ３ It does not have to include SO ３ If it contains, its content may be 0.01% or more, 0.05% or more, or 0.1% or more. Furthermore, from the viewpoint of suppressing the increase of white foam, i.e., sulfate defects, and the resulting deterioration of quality, the above content is preferably 1% or less, more preferably 0.7% or less, and even more preferably 0.5% or less.

[0033] ・Cr ２ O ３ In the glass plate according to this embodiment, Cr ２ O ３ Cr is an ingredient that adjusts the color of glass. ２ O３ The content of is preferably 0 to 0.2%. Here, the glass plate according to this embodiment is Cr ２ O ３ It does not have to include Cr ２ O ３ If it contains, the amount may be 0.00001% or more, 0.0001% or more, or 0.001% or more from the viewpoint of color. Furthermore, from the viewpoint of color adjustment, the above amount is preferably 0.2% or less, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0034] • CoO In the glass plate according to this embodiment, CoO is a component that adjusts the color of the glass. The CoO content is preferably 0 to 0.2%. Here, the glass plate according to this embodiment does not have to contain CoO, but if it does contain CoO, the content may be 0.00001% or more, 0.0001% or more, or 0.0005% or more from the viewpoint of color. Furthermore, from the viewpoint of color adjustment, the above content is preferably 0.2% or less, more preferably 0.1% or less, and even more preferably 0.05% or less.

[0035] NiO In the glass plate according to this embodiment, NiO is a component that adjusts the color of the glass. The NiO content is preferably 0 to 0.2%. Here, the glass plate according to this embodiment does not have to contain NiO, but if it does contain NiO, the content is preferably 0.00001% or more, more preferably 0.0001% or more, and even more preferably 0.001% or more from the viewpoint of coloring. Furthermore, from the viewpoint of coloring, the above content is preferably 0.2% or less, more preferably 0.05% or less, and even more preferably 0.01% or less.

[0036] In this embodiment, the glass plate has a total content of heavy metal oxides on at least one main surface of the glass plate that is less than the total content inside the glass plate. On the other hand, the components other than heavy metal oxides, i.e., SiO ２ Na ２ O, K ２ O, MgO, CaO, Al ２ O ３ Fe ２ O ３ , CEO２ , TiO ２ SO ３ , Cr ２ O ３ With respect to CoO and NiO, there are no particular limitations on the amount of each component between the content on at least one main surface of the glass plate and the content inside the glass plate. For example, for any component other than heavy metal oxides, the difference between the content on the main surface of the glass and the content inside the glass plate may be 2% or less, 1% or less, or 0.5% or less, respectively. Furthermore, the lower limit of the above difference is not particularly limited and may be 0%, i.e., the same content, 0.05% or more, or 0.1% or more.

[0037] The glass plate according to this embodiment may contain other components in addition to the above-mentioned components. The above-mentioned other components are not particularly limited, but for example, Li ２ O, B ２ O ３ , SrO, BaO, ZrO ２ , Y ２ O ３ , Nd ２ O ５ GaO ２ , GeO ２ MnO ２ , V ２ O ５ Er ２ O ３ Au ２ O ３ Ag ２ O, CuO, CdO, MoO ３ Cl, F, SnO ２ ZnO, SeO ２ These are some examples.

[0038] The above-mentioned other components are optional as long as they do not impair the effects of the present invention, and their content is not particularly limited. For example, the total content of the other components may be 0-20% or 0-10%. In this case, if the above-mentioned other components are included, the total content may be 20% or less, 10% or less, or 5% or less, from the viewpoint of reactivity.

[0039] <Characteristics and Physical Properties> The glass plate according to this embodiment has a visible light transmittance in the thickness direction of the plate Tｖｃ U is the visible light transmittance in the thickness direction of a glass plate after removing 100 μm of the surface layer from each of the two main surfaces. ｖｃ When expressed as a percentage, |U ｖｃ -T ｖｃ The absolute value of the difference in transmittance represented by | is 2% or less. Here, the visible light transmittance mentioned above is the visible light transmittance measured in accordance with JIS R 3106:2019 and calculated using the relative spectral distribution of the C light source described in JIS Z 8701:1999. Furthermore, all visible light transmittances in this specification are values ​​converted to the visible light transmittance for a glass plate with a thickness of 4 mm.

[0040] Above | U ｖｃ -T ｖｃ A small absolute value of the difference in transmittance represented by | means that the effect on the optical properties for visible light is small because the total content of heavy metal oxides on at least one main surface of the glass plate is less than the total content inside the glass plate.

[0041] In this embodiment, |U ｖｃ -T ｖｃ The absolute value of the difference in transmittance represented by | is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.3% or less, and even more preferably 1.0% or less. Furthermore, the lower limit of the above difference in transmittance is not particularly limited and may be 0%, 0.001% or more, or 0.01% or more.

[0042] The visible light transmittance T in the thickness direction of the glass plate according to this embodiment. ｖｃ A transmittance of 80-95% is preferred. Here, from the viewpoint of power generation efficiency and transparency, the above transmittance T ｖｃ The transmittance T is preferably 80% or more, more preferably 83% or more, and even more preferably 88% or more. ｖｃ There is no particular upper limit, but considering the absorption, scattering, and reflection of the glass, it may be 95% or less, or even 93% or less.

[0043] The haze of the glass plate according to this embodiment is not particularly limited, but as an indicator that the glass plate is free from cloudiness and has good transparency, the haze is preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.0% or less. The lower limit of the haze is also not particularly limited, but may be, for example, 0.01% or more. In this specification, haze refers to the value converted to haze at a thickness of 4 mm, measured with a D65 light source in accordance with JIS K 7136:2000.

[0044] In this embodiment, the glass plate may leach heavy metal elements into the environment, such as into landfills or during washing. However, in this embodiment, the amount of heavy metal elements leached into a 1 M NaOH solution is used as one indicator of the degree of heavy metal element leaching into the environment. Specifically, the glass plate according to this embodiment is prepared as a test material measuring 30 mm square and 4 mm thick, and immersed in 120 mL of a 1 M NaOH solution at a liquid temperature of 85°C for 5 hours. The total amount of heavy metal oxides leached into the 1 M NaOH solution after the immersion is determined. The amount of leaching is preferably 0.4 ppm by mass or less, more preferably less than 0.4 ppm by mass, even more preferably 0.35 ppm by mass or less, and even more preferably 0.3 ppm by mass or less. The less the amount, the better.

[0045] Furthermore, the amount of elution can also be calculated by integrating the heavy metal oxide content up to the etching depth, based on the main surface area of ​​the glass plate, the change in weight of the glass plate before and after immersion, and the profile of the heavy metal oxide content in the thickness direction of the glass plate.

[0046] The thickness of the glass plate according to this embodiment is preferably 0.5 to 20 mm. Here, from the viewpoint of strength, the plate thickness is preferably 0.5 mm or more, more preferably 1 mm or more, even more preferably 1.5 mm or more, and even more preferably 2 mm or more. Furthermore, from the viewpoint of productivity, lightness, and transmittance, the plate thickness is preferably 20 mm or less, more preferably 10 mm or less, even more preferably 6 mm or less, and even more preferably 4 mm or less.

[0047] The shape of the main surface of the glass plate according to this embodiment is not particularly limited, and any shape such as rectangle, polygon, circle, or ellipse can be adopted. Furthermore, the area of ​​the main surface is not particularly limited and can be adjusted as appropriate depending on the application. For example, the area of ​​the main surface of the glass plate according to this embodiment is 0.0001 to 100 m². ２ But that's fine.

[0048] The glass plate according to this embodiment may be a flat glass plate or a glass plate that has been molded or bent to include a curved surface.

[0049] The glass plate according to this embodiment may have a functional layer on at least one of the pair of opposing main surfaces. Examples of such functional layers include ultraviolet-cutting layers, infrared-cutting layers, anti-fouling layers, water-repellent layers, hydrophilic layers, conductive layers, decorative layers, and optical functional layers. The functional layer may consist of only one layer or multiple layers. The method for forming the functional layer is not particularly limited and can be formed using known methods depending on the type of functional layer.

[0050] <Applications> The glass plate according to this embodiment can be used for a variety of purposes, and is not particularly limited, but examples include cover glass for solar cells, glass plates for building materials, and glass plates for automobiles. More specifically, examples include glass plates used for partitions, exterior and interior finishes of buildings, and automobile doors. The glass plate according to this embodiment is very significant because, even when the glass plate is cleaned before application to these purposes, and even while it is actually used in the above-mentioned applications, the concern about environmental burden and impact on human health due to the leaching of heavy metal elements from the main surface of the glass plate is extremely small. In addition to its use in the above-mentioned various applications, the glass plate according to this embodiment is also very significant from the viewpoint of reducing environmental burden, even when disposed of in a landfill, due to the low content of heavy metal oxides on the surface.

[0051] 《Method for Manufacturing Glass Plates》 The method for manufacturing glass plates according to this embodiment is not particularly limited as long as the glass plate described in the above-mentioned "Glass Plates" can be obtained, and preferred embodiments of the obtained glass plate are the same as the preferred embodiments of the glass plate described in the above-mentioned "Glass Plates".

[0052] A first embodiment, which is an example of a method for manufacturing a glass plate according to this embodiment, includes the following steps 1A to 3A in order. Step 1A: Having a pair of opposing main surfaces, Sb ２ O ３ , PbO, and As ２ O ３ Step 1: Prepare a glass plate containing at least one heavy metal oxide selected from the above. Step 2A: Contact a reducing agent with at least one main surface of the glass plate from Step 1A. Step 3A: Heat the glass plate from Step 2A at a temperature of 700°C or higher.

[0053] In this embodiment, the first aspect preferably includes the following step 4A in addition to steps 1A to 3A described above. Step 4A: A step of heating the glass plate from step 3A to 100°C or higher in an atmospheric environment.

[0054] A second embodiment, which is an example of a method for manufacturing a glass plate according to this embodiment, includes steps 1B and 2B in order below. Step 1B: Having a pair of opposing main surfaces, Sb ２ O ３ , PbO, and As ２ O ３ Step 1B: A step of preparing a glass plate containing at least one heavy metal oxide selected from the above. Step 2B: A step of heating the glass plate from Step 1B at a temperature of 700°C or higher in a reducing atmosphere.

[0055] <First Embodiment> The first embodiment of the method for manufacturing a glass plate according to this embodiment will be described below.

[0056] Step 1A: Step 1A in this embodiment has a pair of opposing main surfaces, Sb ２ O ３ , PbO, and As ２ O ３The process involves preparing a glass plate containing at least one heavy metal oxide selected from the above. The glass plate has a pair of opposing main surfaces and contains the heavy metal oxide; however, the method of preparation is not particularly limited. For example, the glass plate may be manufactured to have a desired composition, or a commercially available one may be used. Alternatively, recycled glass obtained from glass cullet may be used. The recycled glass may be one that is commercially available as recycled glass, or a glass plate may be manufactured from the glass cullet and used as recycled glass. Specifically, for example, the glass constituting the solar cell panel may contain Sb ２ O ３ It often contains Sb. Therefore, the glass plate in this embodiment has Sb as a heavy metal oxide. ２ O ３ It is also preferable that the glass constituting the solar cell panel is a recycled product obtained from crushed PV cullet. However, the recycled product is not limited to that obtained from the above-mentioned PV cullet; it may also be obtained from glass cullet containing the above-mentioned heavy metal oxides from other sources and types. Alternatively, it may be a recycled product that is a mixture of glass cullet containing the above-mentioned heavy metal oxides from multiple sources and types.

[0057] The glass plate containing the above heavy metal oxide preferably satisfies the following requirements in terms of the content expressed as mass percentage based on the oxide. Furthermore, as the above heavy metal oxide, Sb ２ O ３ It is more preferable to contain Sb ２ O ３ It is even more preferable to contain 0.0005 to 0.50% of SiO. ２ :60-80%, Na ２ O: 5-20%, K ２ O: 0-3%, MgO: 0-15%, CaO: 5-20%, Al ２ O ３ : 0-10%, Fe ２ O ３ : 0-2%, CeO ２ : 0-2%, TiO ２ : 0-3%, SO ３: 0-2%, Cr ２ O ３ : 0-0.2%, CoO: 0-0.2%, NiO: 0-0.2%, and total of the above heavy metal oxides: 0.0005-0.50%.

[0058] Step 2A: Step 2A in this embodiment is a step of bringing a reducing agent into contact with at least one main surface of the glass plate prepared in Step 1A.

[0059] The reducing agent described above is not particularly limited as long as it can reduce heavy metal oxides. The reducing agent may be in solid, liquid, or gaseous state, but a liquid state is preferred from the viewpoint of efficiently reacting even in small amounts. As a method of contacting the reducing agent with the main surface of the glass plate, for example, when using solid thermocompression bonding, examples of the reducing agent include organic compounds such as ethylene vinyl acetate copolymer (EVA) and carbon powder such as carbon. When contacting the reducing agent with the main surface of the glass plate by solution coating, it is preferable to dissolve the reducing agent in a liquid medium, and when water is used as the liquid medium, a water-soluble organic compound is preferred as the reducing agent. However, it is not essential that the reducing agent be dissolved in the liquid medium; it may also be dispersed in the liquid medium. When a gaseous reducing agent is directly contacted with the main surface of the glass plate, CO gas, H ２ Reducing gases such as gases are preferred.

[0060] The above organic compound preferably has a boiling point of 250°C or higher, from the viewpoint of functioning suitably as a reducing agent during heating in the subsequent step 3A.

[0061] Examples of water-soluble organic compounds include sugars, glycols, hydroxy acids, amino acids, carboxylic acids, esters, proteins, gelatin, and polymers (such as polyvinyl alcohol, polyamide, polyethylene oxide, polyacrylic acid, polyacrylamide, polyethyleneimine, and polyvinyl chloride). Among these, sugars are preferred due to their high solubility in water.

[0062] Sugars are classified into monosaccharides, disaccharides, and polysaccharides. Examples of monosaccharides include glucose and fructose. Examples of disaccharides include sucrose, lactose, maltose, trehalose, and sucralose. Among these, sucrose (table sugar) is preferred from the viewpoint of availability. In addition, since sucralose contains chlorine, it can also play a role in assisting halogenating agents, which will be discussed later. Examples of polysaccharides include starch, glycogen, agarose (agar), pectin, and gums.

[0063] Water is preferred as the liquid medium for dissolving or dispersing the reducing agent, but it is not limited to water; for example, an organic solvent may also be used.

[0064] When using an organic solvent as a liquid medium, examples of organic solvents include ether-based solvents, alcohol-based solvents, ester-based solvents, ketone-based solvents, and other hydrocarbon-based solvents.

[0065] When an organic solvent is used as the liquid medium, a resin is preferred as the reducing agent. Examples of resins include cellulose, acrylic, polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), polyamide (PA), polycarbonate (PC), butyral, melamine, rosin, silicone, polyester, and epoxy.

[0066] In this embodiment, when the reducing agent is brought into contact with the solution by means of solution coating or immersion in the solution, and a liquid reducing agent is used, the content of the reducing agent in the solution is not particularly limited, but for example, 20 to 90% by mass is preferred. Here, from the viewpoint of reducing power, the content of the reducing agent is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Furthermore, from the viewpoint of not leaving a large amount of reducing agent residue after heating in step 3A, the content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0067] When applying a solution containing a reducing agent to the main surface of a glass plate, the main surface of the glass plate is 1 cm ２ It is preferable to apply the reducing agent so that the amount per unit is 0.001 to 50 mg. Here, from the viewpoint of reducing power, the above amount is preferably 0.001 mg or more, more preferably 0.05 mg or more, and even more preferably 0.1 mg or more. Furthermore, from the viewpoint of not leaving a large amount of reducing agent residue after heating in step 3A, the above amount is preferably 50 mg or less, more preferably 30 mg or less, and even more preferably 10 mg or less.

[0068] The solution containing the above reducing agent may also contain other optional components. Examples of other optional components include halogenating agents, reducing aids, halogen scavengers, etc.

[0069] The halogenating agent is preferably one that can convert heavy metal oxides into halides, and halogen-containing organic polymer compounds and halogen-containing inorganic compounds are preferred from the viewpoint of availability and other factors.

[0070] Halogen-containing organic polymer compounds are organic polymer compounds that contain halogen atoms, and examples include polyvinylidene chloride and polyvinyl chloride. Furthermore, because halogen-containing organic polymer compounds contain carbon (C), they can also play a supporting role as reducing agents. Examples of halogen-containing inorganic compounds include CaCl. ２ CaCl ２ ・2H ２ O, CaCl ２ 4H ２ O, CaCl ２ 6H ２ O, CaBr ２ CaBr ２ ・2H ２ O, CaBr ２ 4H ２ O, CaBr ２ 6H ２ O, CaF ２ , KCl, NaCl, NaF, MgCl ２ MgCl ２ 6H ２ O, NH ４ Examples include Cl. Among them, CaCl is considered to be a good choice from the perspective of cost and halogen content. ２ CaCl ２・2H ２ O and NaCl are particularly preferred.

[0071] In this embodiment, when the solution containing the reducing agent also contains a halogenating agent, the content of the halogenating agent in the solution containing the reducing agent is not particularly limited, but for example, 5 to 70% by mass is preferred. Here, from the viewpoint of sufficiently halogenating heavy metal oxides, the content of the halogenating agent is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, from the viewpoint of reducing volatilized halogen-containing gases, the content is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0072] Examples of reducing aids include metal powders, water-insoluble organic powders, and carbon powders. It is preferable that these do not dissolve in the liquid medium. Adding a reducing aid further promotes the reduction of heavy metal oxides, thereby facilitating the vaporization of heavy metal oxides from the main surface of the glass plate in the subsequent step 3A. The reducing aid may also be used as a reducing agent.

[0073] Examples of the above metal powders include Al, Si, Cu, and Fe. These may be used individually or in combination of two or more. As for the above non-aqueous organic powder, polymeric organic materials are preferred, and resins such as EVA, PVB, and silicone are particularly preferred.

[0074] In this embodiment, if the solution containing the reducing agent also contains a reducing agent, the content of the reducing agent in the solution containing the reducing agent is not particularly limited, but for example, 0 to 20% by mass is preferred. Here, the reducing agent may not be included, but if it is included, the content is preferably greater than 0% by mass, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, from the viewpoint of reducing properties and reactivity of heavy metal oxides. Furthermore, from the viewpoint of appropriately controlling the composition of the resulting glass plate, the content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0075] In this embodiment, if the solution containing the reducing agent also contains a halogen scavenger, the halogen scavenger may be, for example, Ca(OH)２ Examples include hydroxides of alkaline earth metals. When the solution containing the reducing agent in this embodiment also contains a halogen scavenger, the content of the halogen scavenger in the solution containing the reducing agent is not particularly limited, but for example, more than 0% by mass and 20% by mass or less is preferred. Here, the content of the halogen scavenger may be more than 0% by mass, and from the viewpoint of sufficiently capturing halogens, 0.1% by mass or more is preferred, 0.5% by mass or more is more preferred, and 1% by mass or more is even more preferred. Also, from the viewpoint of reactivity, the above content is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0076] As a method for applying a reducing agent to at least one main surface of a glass plate, when applying a solution containing the reducing agent, the specific method is not particularly limited and examples include a roll coater, spray coater, bar coater, spin coater, etc. Furthermore, when applying to both main surfaces of a glass plate, the glass plate may be immersed in a solution containing the reducing agent.

[0077] The glass plate obtained in step 2A may be dried as needed before being subjected to heating in the subsequent step 3A. The drying method is not particularly limited, and for example, drying using equipment such as an oven or drying in sunlight can be employed. Specifically, for example, it may be dried in an oven at 30 to 250°C for 1 minute to 600 minutes. Alternatively, it may be dried in sunlight for several hours to several months. It should be noted that the above drying does not necessarily require the complete removal of moisture.

[0078] Step 3A: Step 3A in this embodiment is a step of heating the glass plate from step 2A, that is, the glass plate on which a solution containing a reducing agent has been applied to at least one main surface, to a temperature of 700°C or higher.

[0079] The heating described above causes the heavy metal oxides on the main surface of the glass plate, which were reduced in step 2A, to vaporize. In some cases, the heavy metal oxides on the main surface of the glass plate may also react with the halogenating agent and then with the reducing agent, resulting in a reduced state that vaporizes. As a result, the total content of heavy metal oxides on the main surface of the glass plate is reduced compared to the interior, and a glass plate with the desired properties is obtained.

[0080] The heating temperature is preferably 700°C or higher, and more preferably 700 to 1400°C. Here, from the viewpoint of efficiently removing heavy metal oxides from the main surface of the glass plate, the heating temperature is preferably 700°C or higher, more preferably 800°C or higher, even more preferably 900°C or higher, and even more preferably 1000°C or higher. Furthermore, from the viewpoint of energy saving and protection of the heating device, the heating temperature is preferably 1400°C or lower, more preferably 1300°C or lower, and even more preferably 1200°C or lower.

[0081] The heating time is not particularly limited, but may be, for example, 0.01 to 10 hours. Here, from the viewpoint of heavy metal oxide removal efficiency, the heating time is preferably 0.01 hours or more, more preferably 0.05 hours or more, and even more preferably 0.1 hours or more. Also, from the viewpoint of productivity, the heating time is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0082] When performing the above heating, a reducing atmosphere is preferred from the viewpoint of enhancing the reducing properties of heavy metal oxides. A reducing atmosphere, as used here, is an atmosphere with a lower oxygen concentration than the atmosphere and containing a reducing gas or an inert gas.

[0083] Furthermore, from the viewpoint of promoting the vaporization of heavy metal oxides, the above atmosphere preferably contains water vapor, and it is also preferable that the dew point temperature is 0°C or higher, and it is more preferable that it contains water vapor and has a dew point temperature of 0°C or higher.

[0084] The above dew point temperature is preferably 0°C or higher, more preferably 40°C or higher, even more preferably 55°C or higher, and particularly preferably 70°C or higher. Superheated steam may be used for dew point control.

[0085] The atmosphere during heating preferably contains 30% by mass or less of oxygen among components other than water vapor. This promotes the reduction and vaporization of heavy metal oxides on the main surface of the glass plate. The oxygen content is preferably 30% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 1% by mass or less, and may even be 0% by mass, i.e., no oxygen is present.

[0086] The atmosphere during heating preferably contains 70% by mass or more of inert gas among components other than water vapor. That is, when the entire atmosphere during heating is considered to be 100% by mass, assuming there is no water vapor, it is preferable that the atmosphere contains 70% by mass or more of inert gas. This promotes the reaction between heavy metal oxides and the reducing agent on the main surface of the glass plate, and promotes the vaporization of heavy metal oxides. The content of the above inert gas is preferably 70% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, especially preferably 98% by mass or more, particularly preferably 99% by mass or more, and may also be 100% by mass.

[0087] Examples of the above-mentioned inert gases include nitrogen, argon, helium, neon, and xenon, and one or more of these may be used. When two or more are used, it is preferable that the total content ratio of these gases satisfies the above range.

[0088] For example, when nitrogen gas is used as the inert gas, the atmosphere during heating should preferably contain 70% by mass or more of nitrogen gas among the components other than water vapor, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, especially preferably 98% by mass or more, particularly preferably 99% by mass or more, and may even be 100% by mass.

[0089] The internal composition of the glass plate obtained by the above method can be considered to be the same as the composition of the glass plate prepared in step 1A. On the other hand, the glass plate obtained by the above method preferably has a total heavy metal oxide content on the main surface that came into contact with the reducing agent that is less than the total heavy metal oxide content inside the glass plate, and the content expressed as mass percent based on oxides is preferably 0% or more and 0.40% or less. In addition, the ratio expressed as {[total heavy metal oxide content on the main surface] / [total heavy metal oxide content inside the glass plate]} is preferably 0 or more and 0.8 or less.

[0090] Step 4A: In this embodiment, Step 4A is a step of heating the glass plate from Step 3A to 100°C or higher in an atmospheric environment. By going through Step 4A, residual carbon in the glass plate that has gone through Step 3A can be removed.

[0091] The heating temperature in step 4A is preferably 100°C or higher, and more preferably 100 to 600°C. Here, from the viewpoint of properly volatilizing carbon, the above temperature is preferably 100°C or higher, more preferably 200°C or higher, and even more preferably 300°C or higher. Furthermore, from the viewpoint of properly maintaining the surface shape of the glass, the above temperature is preferably 600°C or lower, more preferably 550°C or lower, and even more preferably 500°C or lower.

[0092] The heating time in step 4A is preferably, for example, 0.1 to 20 hours. Here, from the viewpoint of sufficiently volatilizing carbon, the above time is preferably 0.1 hours or more, more preferably 0.3 hours or more, and even more preferably 0.5 hours or more. Also, from the viewpoint of productivity, the above time is preferably 20 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less.

[0093] Steps 2A and 3A, or steps 2A to 4A, may be repeated multiple times. Depending on the conditions adopted, repeating the above steps multiple times may remove more heavy metal oxides from the main surface of the glass plate, or increase the thickness range from the surface of the glass plate to which heavy metal oxides are removed. The number of repetitions is not particularly limited, but may be 2 to 10 times or 2 to 5 times. Here, from the viewpoint of removing more heavy metal oxides, the number of repetitions may be 2 or more times or 3 or more times, and from the viewpoint of productivity, it may be 10 or less times or 5 or less. However, this does not preclude performing steps 2A and 3A, or steps 2A to 4A, only once. In some cases, a sufficient amount of heavy metal oxides can be removed even with only one repetition, and in some cases, a sufficient thickness of heavy metal oxides can be removed.

[0094] <Second Embodiment> Next, a second embodiment of the method for manufacturing a glass plate according to this embodiment will be described.

[0095] • Process 1B: In this embodiment, process 1B has a pair of opposing main surfaces, Sb ２ O ３ , PbO, and As ２ O ３ This step involves preparing a glass plate containing at least one heavy metal oxide selected from the following. This step is the same as step 1A in the first embodiment described above, and the preferred embodiment is also the same.

[0096] Step 2B: In this embodiment, Step 2B is a step of heating the glass plate from Step 1B at a temperature of 700°C or higher in a reducing atmosphere.

[0097] The heating process reduces and vaporizes the heavy metal oxides on the main surface of the glass plate. This reduces the total amount of heavy metal oxides on the main surface of the glass plate compared to the interior, resulting in a glass plate with the desired properties.

[0098] A reducing atmosphere is an atmosphere with a lower oxygen concentration than the atmosphere, containing a reducing gas or an inert gas, and is not particularly limited as long as it reacts with the heavy metal oxides on the main surface of the glass plate and removes the heavy metal oxides by heating. Examples of reducing gases include hydrogen gas and carbon monoxide gas. Among these, hydrogen gas is preferred from the viewpoint of reactivity.

[0099] From a safety standpoint, the above-mentioned reducing gas is preferably used as a mixed gas with an inert gas. Examples of inert gases include nitrogen, argon, helium, neon, and xenon, and one or more of these may be used.

[0100] Furthermore, the reducing gas may further contain a halogenating agent. Examples of halogenating agents include gases containing halogen elements, such as fluorine gas, chlorine gas, and bromine gas.

[0101] As a reducing atmosphere, the content of reducing gas to the total of reducing gases and inert gases is preferably, for example, 0 to 100 volume%. Here, from the viewpoint of reactivity, the above content is preferably 1 volume% or more, more preferably 3 volume% or more, and even more preferably 5 volume% or more. The above content may also be 100 volume%, i.e., all reducing gases, but from the viewpoint of safety, the above content is preferably 50 volume% or less, more preferably 20 volume% or less, and even more preferably 10 volume% or less. Furthermore, the content of reducing gas to the total of reducing gases, inert gases, and gases containing halogen elements is also preferably within the above range, and the content of reducing gas to the total of reducing gases and gases containing halogen elements is also preferably within the above range.

[0102] The dew point temperature of the reducing atmosphere used for the above heating is not particularly limited, but from the viewpoint of promoting the vaporization of heavy metal oxides, it is preferably 0°C or higher, more preferably 40°C or higher, even more preferably 55°C or higher, and particularly preferably 70°C or higher. Superheated steam may be used for dew point control.

[0103] The heating temperature is preferably 700°C or higher, and more preferably 700 to 1400°C. Here, from the viewpoint of efficiently promoting the vaporization of heavy metal oxides on the main surface of the glass plate, the heating temperature is preferably 700°C or higher, more preferably 800°C or higher, even more preferably 900°C or higher, and even more preferably 1000°C or higher. Furthermore, from the viewpoint of energy saving and protection of the heating device, the heating temperature may be 1400°C or lower.

[0104] The heating time is not particularly limited, but may be, for example, 0.01 to 10 hours. From the viewpoint of reactivity, the heating time is preferably 0.01 hours or more, more preferably 0.05 hours or more, and even more preferably 0.1 hours or more. From the viewpoint of productivity, the heating time is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0105] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. Examples 1, 2, and 4 to 6 are examples, and Example 3 is a comparative example.

[0106] 《Manufacturing of Glass Plates》 〈Example 1〉 Glass raw materials were mixed to obtain the glass composition (Composition A) shown in Table 1 in mass % based on oxides, and weighed to obtain 1000 g of glass. Next, the mixed glass raw materials were placed in a platinum crucible and placed in an electric furnace at 1500°C to melt for about 5 hours, then degassed and homogenized. The obtained molten glass was poured into a mold, held at 600°C for 2 hours, and then cooled to room temperature at a rate of 0.5°C / min to obtain glass blocks. The obtained glass blocks were each processed into plates of 30 mm × 30 mm × 4 mm thickness to obtain initial glass plates. (Process 1A)

[0107] Next, a solution containing a reducing agent was applied to both main surfaces of the obtained initial glass plate using a brush. The solution containing the reducing agent was an aqueous solution prepared by dissolving sucrose in water so that the reducing agent content was 33% by mass. The above application was carried out on the main surface of the initial glass plate, up to 1 cm. ２ The amount of sucrose applied per unit was adjusted to 10 mg. (Step 2A)

[0108] After drying this at room temperature for 30 minutes, it was heated at 1000°C for 20 minutes under a reducing atmosphere (99.99% nitrogen by volume, 0.01% oxygen by volume, dew point -70°C) to obtain a glass plate. (Step 3A) Subsequently, it was heated again under an atmospheric environment at 400°C for 5 hours to obtain the desired glass plate. (Step 4A)

[0109] <Example 2> Using the same method as in step 1A of Example 1, the initial glass plate was subjected to steps 2A to 4A of Example 1, and the desired glass plate was obtained by repeating these steps three times.

[0110] <Example 3> The initial glass plate obtained by the same method as in step 1A of Example 1 was used as the glass plate for Example 3.

[0111] <Examples 4 to 6> Glass raw materials were mixed to obtain the glass compositions (compositions B to D) shown in Table 1 in mass % based on oxides, and initial glass plates were obtained in the same manner as in step 1A of Example 1.

[0112] Next, a solution containing a reducing agent was applied to both main surfaces of the obtained initial glass plates using a spin coater (MS-B200, Mikasa Corporation). The solution containing the reducing agent was an aqueous solution prepared by dissolving sucrose in water so that the reducing agent content was 33% by mass. The above coating was applied to the main surface of the initial glass plates up to 1 cm. ２ The amount of sucrose applied per unit was adjusted to 1 mg. (Step 2A)

[0113] This was then subjected to the same process as in step 3A in Example 1 to obtain the desired glass plate. Note that in Table 2, for Examples 4 to 6, the "Number of Processing Sessions (Steps 2A to 4A)" is listed as "1," but this means that since step 4A was not performed, the number of processing sessions for steps 2A to 3A was 1.

[0114] 《Evaluation》 〈Sb on the main surface of the glass plate ２ O ３ Content: Sb content on the main surface of the obtained glass plate ２ O ３ The content was determined by measuring it using a laser microscope with laser ablation inductively coupled plasma mass spectrometry. NIST SRM610 and 612 were used as standard samples. ２９The measurement was normalized using Si. The equipment used and the measurement conditions for laser ablation (hereinafter referred to as LA) are as follows: <Equipment Used> LA: JUPITER manufactured by ST Japan Co., Ltd. Inductively coupled plasma mass spectrometer: iCAP-TQ manufactured by Thermo Fisher Scientific Co., Ltd. Laser microscope: Lext OLS4000 manufactured by Olympus Corporation <LA Measurement Conditions> Output: 6 mW Irradiation size: 0.5 mm x 0.5 mm Frequency: 4 kW Irradiation pitch: 2 μm Speed: 9 mm / s

[0115] Sb on the main surface of the glass plates obtained in Examples 1 to 6 ２ O ３ Content, and {[Sb on the main surface} ２ O ３ [Content] / [Sb content inside the glass plate] ２ O ３ The ratio expressed as "Content]" is shown in Table 2 as "Main surface Sb ２ O ３ Content (mass%)” and “Sb ２ O ３ The content ratio (main surface / internal) (-) is shown. Note that in Table 2, "Internal Sb ２ O ３ "Content (mass%)" refers to the amount of Sb inside the glass plate. ２ O ３ It refers to the content.

[0116] <Transmittance> Using a spectrophotometer (Hitachi High-Technologies Corporation, UH4150), the visible light transmittance T was measured for a glass plate. ｖｃ The following measurements were taken. The measurements were performed in accordance with JIS R 3106:2019, and the relative spectral distribution of the C light source described in JIS Z 8701:1999 was used to calculate the value, which was then converted to a value for a 4 mm thickness. In addition, the above transmittance T was measured for glass plates in which the top 100 μm of the surface layer on both main surfaces was removed by mirror polishing. ｖｃ Similarly, visible light transmittance U ｖｃ The values ​​were measured and converted to values ​​for a 4 mm thickness. The transmittance Tvc and transmittance U obtained above were then calculated. ｖｃ , and | U ｖｃ -T ｖｃ Table 2 shows the absolute values ​​of the difference in transmittance, represented by the | symbol.

[0117] Here, the value converted to a plate thickness of 4 mm is the value of the glass plate (here, visible light transmittance T) calculated by measuring the refractive index of the glass plate whose transmittance was measured, and then using Selmeyer's formula to calculate the reflectance of the glass plate from the refractive index, taking into account multiple reflections. ｖｃ or visible light transmittance U ｖｃ This value is converted to a value for a plate thickness of 4 mm.

[0118] <Elution Amount> A glass plate was immersed in a 1 M NaOH solution at a liquid temperature of 85°C for 5 hours, and the amount of Sb eluted into 120 mL of the 1 M NaOH solution was measured. Specifically, the obtained eluate was diluted 10-fold with ultrapure water, and quantitative analysis of Sb was performed using ICP emission spectrometry. The measurement wavelength used was 206.834 nm, and the calibration curve method was used for quantification. An Agilent 5800 instrument manufactured by Agilent Technologies was used. The results are shown in Table 2 as "Sb Elution Amount (mass ppm)".

[0119]

[0120]

[0121] From the above results, it was found that the glass plate according to this embodiment had a total heavy metal oxide content of 0 to 0.40% on its main surface, and the ratio expressed as {[Total heavy metal oxide content on the main surface] / [Total heavy metal oxide content inside the glass plate]} satisfied 0 to 0.8, indicating that the amount of heavy metal oxides on the main surface was reduced compared to the inside of the glass plate. As a result, it was shown that the elution of heavy metal elements into the outside environment could be suppressed. Furthermore, when the processing of steps 2A to 4A was performed multiple times in Example 2, the total heavy metal oxide content on the main surface was higher than in Example 1. We believe this is because heavy metal oxides diffused from deeper regions of the glass plate toward the main surface in order to remove heavy metal oxides from those regions. In other words, although the total heavy metal oxide content on the main surface, which is the outermost surface of the glass plate in Example 2, is higher than in Example 1, we believe that if a heavy metal element elution test were performed under more severe conditions, the amount of heavy metal elements eluted would be smaller in Example 2. In Examples 4 to 6, by reducing the amount of reducing agent applied to one-tenth of that in Examples 1 and 2, step 4A can be omitted, and Tｖｃ While keeping it high, Sb on the main surface ２ O ３ We were able to reduce the amount of reducing agent. We believe this is because reducing the amount of reducing agent suppressed discoloration caused by excessive reduction.

[0122] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2025-039530, filed on 12 March 2025, the contents of which are incorporated herein by reference.

Claims

A glass plate having a pair of opposing main surfaces, The aforementioned glass plate is Sb ２ O ３ , PbO, and As ２ O ３ It contains at least one heavy metal oxide selected from, The glass plate has a content in at least one main surface that satisfies the total of the heavy metal oxides, expressed as mass percent based on oxides: 0 to 0.40%. The glass plate has a ratio expressed as {[Total content of the heavy metal oxides on the main surface] / [Total content of the heavy metal oxides inside the glass plate]}, using the content expressed in mass percent based on oxides, which is between 0 and 0.

8. The visible light transmittance of the glass plate in the thickness direction is T. ｖｃ U ｖｃ When expressed as a percentage, |U ｖｃ -T ｖｃ A glass plate in which the absolute value of the difference in transmittance, represented by |, is 2% or less. 　 The glass plate according to claim 1, wherein the content of the heavy metal oxides in the interior, expressed as a mass percentage based on oxides, satisfies the total of the heavy metal oxides: 0.0005 to 0.50%. 　 The glass plate has an oxide content expressed as a mass percentage based on the oxide within it. Yes ２ :60~80%, Na ２ O:5~20%、 K ２ O: 0~3%, MgO: 0-15%, CaO: 5-20%, Al ２ O ３ :0~10%、 Fe ２ O ３ :0~3%、 CeO ２ :0~2%、 TO ２ :0~3%, SO ３ :0~2%、 Cr ２ O ３ :0~0.2%、 CoO: 0-0.2%, NiO: 0-0.2%, , and The glass plate according to claim 1 or 2, satisfying the total amount of the heavy metal oxides: 0.0005 to 0.50%. 　 The glass plate according to claim 1 or 2, wherein the glass plate, which is 30 mm square and 4 mm thick, is immersed in 120 mL of a 1 mol / L NaOH solution at a liquid temperature of 85°C for 5 hours, and the total amount of heavy metal oxides eluted into the NaOH solution is less than 0.4 ppm by mass. 　 A glass plate according to claim 1 or 2, wherein the plate thickness is 0.5 to 20 mm. 　 A method for manufacturing a glass plate having a pair of opposing main surfaces, Sb ２ O ３ , PbO, and As ２ O ３ To prepare a glass plate containing at least one heavy metal oxide selected from, The reducing agent is brought into contact with at least one main surface of the glass plate, and A method for manufacturing a glass plate, comprising, in order, heating the glass plate to a temperature of 700°C or higher. 　 A method for manufacturing a glass plate having a pair of opposing main surfaces, Sb ２ O ３ , PbO, and As ２ O ３ To prepare a glass plate containing at least one heavy metal oxide selected from, and A method for manufacturing a glass plate, comprising the steps of heating the glass plate in a reducing atmosphere at a temperature of 700°C or higher. 　 The glass plate is made of Sb as the heavy metal oxide. ２ O ３ It contains, The method for manufacturing a glass plate according to claim 6 or 7, wherein the glass plate is a recycled product obtained from PV cullet, which is obtained by crushing glass that constitutes a solar panel.

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