Alkali metal-containing glass plate, and method for producing alkali metal-containing glass plate

Abstract

The present invention has been made to meet the demand for imparting high transparency (light transmissivity) to a glass plate. The present invention comprises a preparation step #1 for preparing a glass plate, and a content adjustment step #2 for varying the content of a first alkali metal in the thickness direction of the glass plate.

Description

A glass plate containing alkali metals and a method for manufacturing a glass plate containing alkali metals

[0001] The present invention relates to a glass plate containing an alkali metal and a method for manufacturing a glass plate containing an alkali metal.

[0002] For example, this type of glass plate is used in a variety of applications. For instance, Patent Document 1 discloses low-reflection glass.

[0003] Special table 2016-504260 publication

[0004] For example, when applying glass plates to display devices, depending on the application of the glass plate, it may be necessary to impart high transparency (light transmittance) to the glass plate.

[0005] The present invention relates to a method for manufacturing a glass plate containing a first alkali metal, comprising: a preparation step of preparing a glass plate; and a content adjustment step of varying the content of the first alkali metal in the thickness direction of the glass plate.

[0006] With the above configuration, high transparency can be imparted to the glass plate, as shown in the embodiment.

[0007] In the above, the glass plate preferably contains a second alkali metal having a smaller ionic radius than the first alkali metal, and the content adjustment step preferably includes a substitution step in which the second alkali metal is replaced with the first alkali metal by ion exchange between the ions of the second alkali metal and the ions of the first alkali metal.

[0008] Furthermore, in the above, it is preferable that the content adjustment step includes a layer formation step in which multiple layers with different content levels of the first alkali metal are formed.

[0009] Furthermore, in the above, it is preferable that the layer formation step includes an etching step in which the surface of the glass plate is chemically etched with an alkaline aqueous solution containing ions of the first alkali metal.

[0010] Furthermore, in the above, the first alkali metal is preferably potassium, and the alkaline aqueous solution is preferably a potassium bicarbonate aqueous solution.

[0011] Furthermore, in the above, the plurality of layers preferably include a first layer located on the surface portion of the glass plate and a second layer located inside the first layer in the thickness direction, wherein the content of the first alkali metal and the second alkali metal in the first layer is less than the content of the first alkali metal and the second alkali metal in the second layer.

[0012] Furthermore, it is preferable that the second layer is a layer in which the content of the first alkali metal and the content of the second alkali metal change in the thickness direction.

[0013] Furthermore, it is preferable that the second layer has discontinuous regions in which the content of the first alkali metal and the content of the second alkali metal change discontinuously in the thickness direction.

[0014] Furthermore, it is preferable that in the second layer, the ratio of the first alkali metal to the second alkali metal changes continuously in the thickness direction in the region inward from the discontinuous region in the thickness direction.

[0015] The glass plate of the present invention is a glass plate containing a first alkali metal and a second alkali metal having a smaller ionic radius than the first alkali metal, comprising a first layer located on the surface portion of the glass plate and a second layer located inside the first layer in the thickness direction of the glass plate, wherein the content of the first alkali metal and the second alkali metal in the first layer is less than the content of the first alkali metal and the second alkali metal in the second layer.

[0016] With the above configuration, a glass plate with high transparency can be obtained, as shown in the example.

[0017] Furthermore, it is preferable that the second layer is a layer in which the content of the first alkali metal and the content of the second alkali metal change in the thickness direction.

[0018] Furthermore, it is preferable that the second layer has discontinuous regions in which the content of the first alkali metal and the content of the second alkali metal change discontinuously in the thickness direction.

[0019] Furthermore, it is preferable that in the second layer, the ratio of the first alkali metal to the second alkali metal changes continuously in the thickness direction in the region inward from the discontinuous region in the thickness direction.

[0020] In the above, it is preferable that the third layer is located inside the second layer in the thickness direction, and that the content of the second alkali metal in the third layer is greater than the content of the second alkali metal in the first layer and the content of the second alkali metal in the second layer.

[0021] The glass plate of the present invention is a glass plate containing alkali metals, alkaline earth metals, and aluminum, wherein the glass plate includes a first layer located on the surface and a second layer located inside the first layer in the thickness direction of the glass plate, and the aluminum content in the first layer is greater than the aluminum content in the second layer.

[0022] With the above configuration, a glass plate with high transparency can be obtained, as shown in the examples. Note that "containing alkali metals, alkaline earth metals, and aluminum" includes configurations that primarily contain alkali metals, alkaline earth metals, and aluminum in the form of oxides.

[0023] In the above, it is preferable that the content of alkaline earth metals in the first layer is less than the content of alkaline earth metals in the second layer.

[0024] Furthermore, in the above, the first layer is preferably a void layer having air pockets.

[0025] In the above, it is preferable that the thickness of the first layer is smaller than the thickness of the second layer.

[0026] In the above, the thickness of the first layer is preferably 30 nm to 2 μm.

[0027] If the thickness of the first layer is too thin, its effect on transmittance will be reduced. For this reason, a thickness of 30 nm or more is preferable. Also, if the thickness of the first layer is too thick, the mechanical strength will decrease. For this reason, the thickness is 2 μm or less, preferably 1 μm or less, and more preferably 800 nm or less.

[0028] In the above, the thickness of the second layer is preferably 8 to 100 μm.

[0029] If the thickness of the second layer is too thin, its effect on transmittance will be reduced. For this reason, a thickness of 8 μm or more is preferable. Also, if the thickness of the second layer is too thick, there is a possibility that the glass plate itself will warp. For this reason, the thickness is 100 μm or less, preferably 80 μm or less, and more preferably 60 μm or less.

[0030] In the above, the thickness of the glass plate is preferably 0.3 to 3 mm.

[0031] In the above, it is preferable that the first alkali metal is potassium and the second alkali metal is sodium.

[0032] This is a cross-sectional view showing the glass plate of the present invention. This is a cross-sectional view showing the details of the layer structure of the glass plate of the present invention. This is a flowchart showing the manufacturing method of the glass plate of the present invention. This is an SEM image of an embodiment of the present invention. This is an SEM image of a comparative example. This is an SEM image of an embodiment of the present invention. This is an image showing the distribution of aluminum elements. This is an image showing the distribution of potassium elements. This is an image showing the distribution of sodium elements. This is an image showing the distribution of magnesium elements. This is an image showing the distribution of calcium elements. This is an image showing the distribution of silicon elements. This is a graph showing the results of thickness direction profile measurement by EDX method.

[0033] The following describes embodiments of the alkali metal oxide-containing glass plate and the method for manufacturing the alkali metal oxide-containing glass plate according to the present invention, based on the drawings. However, the invention is not limited to the following embodiments, and various modifications are possible without departing from the gist of the invention.

[0034] As shown in FIG. 1, for example, this glass plate 1 has a rectangular shape with a first major surface 1a (upper surface) and a second major surface 1b (lower surface).

[0035] This glass plate 1 mainly contains potassium (an example of a first alkali metal) and sodium (an example of a second alkali metal) having an ionic radius smaller than that of potassium in the form of oxides in its network structure. Further, this glass plate contains magnesium (an example of an alkaline earth metal) and calcium (an example of an alkaline earth metal) mainly in the form of oxides in its network structure.

[0036] The glass plate is not particularly limited, but at least as its composition, it contains silicon oxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), and alkali metal oxide. Further, the glass plate is not particularly limited, but it is preferably free of boric acid (B ２ O ３ ). This is because when the glass plate contains boric acid, its water resistance is inferior compared to a glass plate free of boric acid.

[0037] As shown in FIG. 1, the glass plate 1 includes a first layer 11 located on the first major surface 1a and the second major surface 1b, a second layer 12 located inside the first layer in the thickness direction, and a third layer 13 located inside the second layer 12 in the thickness direction.

[0038] The first layer 11 is formed, for example, by forming irregularities on the surface portion (the portion on the first major surface 1a side and the portion on the second major surface 1b side) of the chemically strengthened layer by an etching process.

[0039] The chemically strengthened layer is a layer in which all or part of sodium ions are exchanged with potassium ions by ion exchange on the surface of the glass plate, and is a layer having a residual compressive stress.

[0040] The second layer 12 is a portion inside the first layer 11 in the thickness direction of the chemically strengthened layer.

[0041] The third layer 13 is a portion inside the chemically strengthened layer (inside the second layer 12) in the thickness direction of the glass plate.

[0042] The thickness of the glass plate 1 is not particularly limited, but is preferably 0.3 to 3 mm. The thickness of the first layer 11 is not particularly limited, but is preferably 30 nm to 2 μm. In other words, if the thickness of the first layer 11 is too thin, its effect on the transmittance will be small. For this reason, a thickness of 30 nm or more is preferred. Also, if the thickness of the first layer 11 is too thick, the mechanical strength will decrease. For this reason, the thickness is 2 μm or less, preferably 1 μm or less, and more preferably 800 nm or less. The thickness of the second layer 12 is not particularly limited, but is preferably 8 to 100 μm. In other words, if the thickness of the second layer 12 is too thin, its effect on the transmittance will be small. For this reason, a thickness of 8 μm or more is preferred. Also, if the thickness of the second layer 12 is too thick, there is a possibility that the glass plate itself will warp. For this reason, the thickness is 100 μm or less, preferably 80 μm or less, and more preferably 60 μm or less. Thus, preferably, the thickness of the first layer 11 is smaller than the thickness of the second layer 12. Figures 1 and 2 are schematic diagrams illustrating the order of the layers in the thickness direction of the glass plate 1, and the thicknesses of the first layer 11 and the second layer 12 in Figure 1 do not necessarily correspond to the above range and ratio.

[0043] The potassium and sodium content in the first layer 11 is less than the potassium and sodium content in the second layer 12 (see Figure 13).

[0044] Furthermore, the magnesium and calcium content in the first layer 11 is less than the magnesium and calcium content in the second layer 12.

[0045] As shown in Figure 2, the second layer 12 has a discontinuous region 12c in which the potassium content and sodium content change discontinuously in the thickness direction. It has a first region 12a on the surface side (first layer 11 side) and a second region 12b on the inside side (third layer 13 side) of the discontinuous region (see Figure 13).

[0046] The potassium-sodium ratio in the second region 12b of the second layer 12 changes continuously in the thickness direction of the glass plate. That is, as you approach the third layer 13 side (the center side in the thickness direction of the glass plate), the potassium content decreases and the sodium content increases (see Figure 13). Furthermore, in the etching process described later, when the glass plate is immersed in an alkaline aqueous solution (for example, an aqueous solution of potassium bicarbonate), sodium, potassium, magnesium, calcium, and others dissolve from the surface part of the second layer 12 (the surface part of the first region 12a of the second layer 12), and silicon oxide (SiO₂) is released. ２ ), and aluminum oxide (Al ２ O ３ A first layer 11 of a void layer having voids mainly composed of ) is formed. Note that the alkaline aqueous solution is not limited to potassium bicarbonate aqueous solution, but can be selected as appropriate.

[0047] <Manufacturing Method> As shown in Figure 3, the manufacturing method of the glass plate of the present invention comprises a preparation step #1 for preparing the glass plate and a content adjustment step #2 for varying the content of the first alkali metal oxide in the thickness direction of the glass plate. In the embodiments described below, the content adjustment step #2 includes a chemical strengthening step #21 and an etching step #22. Each step is described below.

[0048] (Preparation Step) In preparation step #1, prepare a glass plate. The glass plate is not particularly limited, but for example, a float glass plate can be used. Note that the glass plate is not limited to a float glass plate; any flat glass plate can be used without any particular restrictions on the manufacturing method. Surface-polished glass plates may also be used. Furthermore, it is not limited to flat glass plates, but can also be applied to curved glass such as lenses.

[0049] (Chemical Strengthening Process) Chemical strengthening process #21 (an example of a substitution process) is a process in which a residual compressive stress layer is formed on the surface of a glass plate by replacing all or part of the sodium contained near the surface of the glass plate with potassium through ion exchange between sodium ions and potassium ions on the surface of the glass plate.

[0050] Specifically, for example, a glass plate is immersed in a potassium nitrate molten solution. This causes all or part of the sodium contained near the surface of the glass plate to be replaced with potassium through ion exchange between sodium ions and potassium ions.

[0051] The temperature of the molten potassium nitrate in chemical strengthening step #21 is not particularly limited, but is preferably between 380°C and 500°C. In other words, considering the ion exchange between sodium ions and potassium ions in chemical strengthening step #21, a temperature of 380°C or higher is preferred, and considering the heat resistance of the glass plate, a temperature of 500°C or lower is preferred. Furthermore, within the above range, the temperature of the molten potassium nitrate is preferably 400°C or higher, and more preferably 420°C or higher. Furthermore, the immersion time is not particularly limited, but is preferably between 20 minutes and 4000 minutes. If the temperature of the molten potassium nitrate is low, the ion exchange rate will be slow, and it will take time to reach the desired compressive stress value. Also, if the temperature of the molten potassium nitrate is high, it will be difficult to increase the compressive stress value. From this viewpoint as well, the above temperature range is preferred.

[0052] Although the chemical strengthening process #21 was explained using the example of using a molten potassium nitrate, it is not limited to this. For example, a molten mixed salt of potassium nitrate and sodium nitrate, or a molten mixed salt of potassium nitrate and silver nitrate may also be used.

[0053] (Etching process) Etching process #22 (an example of a layer formation process and a replacement process) is a process in which the glass plate after the chemical strengthening process #21 is etched to form an uneven layer on the surface of the glass plate.

[0054] Specifically, the glass plate after chemical strengthening process #21 is chemically etched by immersion in an alkaline aqueous solution. For example, a potassium bicarbonate aqueous solution can be used as the alkaline aqueous solution.

[0055] The concentration of the potassium hydrogen carbonate aqueous solution in the etching step #22 is not particularly limited, but is preferably from 0.1 mol / l to 3 mol / l. Although not particularly limited, the temperature of the potassium hydrogen carbonate aqueous solution in the etching step is not particularly limited, but is preferably from 50°C to 130°C, more preferably from 50°C to 100°C. Further, the immersion time is not particularly limited, but is preferably from 30 minutes to 2880 minutes.

[0056] In the etching step #22, the case of using a potassium hydrogen carbonate aqueous solution as the alkaline aqueous solution has been described as an example, but the present invention is not limited thereto. For example, an alkaline aqueous solution other than the potassium hydrogen carbonate aqueous solution such as a sodium hydrogen carbonate aqueous solution may be used.

[0057] By the above manufacturing method, as shown in the following examples, the light transmittance of the glass plate is improved. That is, as shown in the following examples, it is considered that the reflection on the surface portion of the glass plate is reduced because the surface portion of the glass plate becomes a void layer having voids by etching. Further, as shown in the following examples, by forming a gradient in the composition distribution in the glass plate by etching and ion exchange, the light transmission state changes, leading to an improvement in light transmittance.

[0058] <Examples> Hereinafter, examples according to the present invention will be described. However, the present invention is not limited to the following examples.

[0059] (1) Glass plate preparation step The glass plates used in the examples and comparative examples were prepared as follows. A rectangular float glass plate having a size of 50 × 50 mm and a thickness of 1 mm was prepared. The composition of this glass plate was as follows. In addition, trace components are included in addition to the following components. SiO ２ : 70.5 mol% Al2O ３ : 1.0 mol% MgO : 5.9 mol% CaO : 8.6 mol% Na ２ O : 13.3 mol% K ２ O : 0.6 mol% Fe ２ O ３ : (less than 0.1 mol%)

[0060] (2) Chemical strengthening process The glass plate described above was immersed in a potassium nitrate melt. The temperature of the potassium nitrate melt was 460°C. The immersion time was 360 minutes to 3840 minutes.

[0061] (3) Etching Process A glass plate after the chemical strengthening process or a glass plate that has not undergone the chemical strengthening process was immersed in a 0.5 mol / l potassium bicarbonate aqueous solution. The temperature of the potassium bicarbonate aqueous solution was 70°C. The immersion time ranged from 360 minutes to 1440 minutes.

[0062] (4) Examples Table 1 below shows the immersion times in the chemical strengthening step and etching step for each example and comparative example. In the table, "-" indicates that the step was not performed (immersion time 0 minutes).

[0063] (5) Transmittance Tables 2 to 5 show the light transmittance of the glass plates for each example at each wavelength. The light transmittance is shown as a value with the light transmittance of the glass plate for each wavelength at the comparative example set to 100. In all examples, the light transmittance exceeded 100 at all wavelengths. From this, it was confirmed that the light transmittance was improved in all examples.

[0064] It is believed that etching creates a void layer on the surface of the glass plate, reducing reflection from the surface. Furthermore, etching and ion exchange create a gradient in the compositional distribution within the glass plate, altering the light transmission characteristics and leading to improved light transmission. As a result, it is believed that light transmittance improved in all examples. (6) SEM image of the glass plate of the present invention An SEM image of the glass plate of Example 13 below was prepared. In Example 13, the above glass plate was immersed in a potassium nitrate melt during the chemical strengthening process. The temperature of the potassium nitrate melt was 460°C. The immersion time was 170 minutes. This glass plate was immersed in a 0.5 mol / l potassium bicarbonate aqueous solution during the etching process. The temperature of the potassium bicarbonate aqueous solution was 70°C. The immersion time was 1440 minutes.

[0065] Figure 4 shows an SEM image of the glass plate of Example 13. Figure 5 shows an SEM image of a comparative example (a glass plate that has not undergone chemical strengthening and etching processes). Figures 4 and 5 are SEM images of the thickness portion of the glass plate taken from an oblique angle above. In Figures 4 and 5, the upper side is the surface of the glass plate (first main surface 11a or second main surface 11b), and the lower side is the inner side in the thickness direction of the glass plate. In Figure 4, it can be seen that the surface of the first layer 11 has irregularities. It can also be seen that the first layer 11 is a void layer with voids, and that the density of the first layer 11 is lower than the density of the second layer 12.

[0066] (7) Elemental distribution analysis The elemental distribution of the glass plate of Example 13 was analyzed by EDX analysis. The results of the elemental distribution analysis are shown in Figures 7 to 12. Figure 6 is an SEM image at the same scale as Figures 7 to 12. Figure 7 shows the distribution of aluminum, Figure 8 shows the distribution of potassium, Figure 9 shows the distribution of sodium, Figure 10 shows the distribution of magnesium, Figure 11 shows the distribution of calcium, and Figure 12 shows the distribution of silicon.

[0067] In each diagram (image) showing the elements, 11 corresponds to the position of the first layer 11, and 12 corresponds to the position of the second layer 12.

[0068] As shown in Figure 7, it can be seen that the number of bright spots indicating the element aluminum has increased at the location corresponding to the first layer 11 formed by the etching process. From this, it was confirmed that an aluminum-rich layer was formed at the location corresponding to the first layer 11. In other words, the first layer 11 has a higher proportion of aluminum compared to the second layer 12 and the third layer 13.

[0069] Furthermore, Figure 9 shows that the bright spot indicating the element sodium is lower at the position corresponding to the first layer 11 than at the position corresponding to the second layer 12. Also, Figure 8 shows that the bright spot indicating the element potassium is lower at the position corresponding to the first layer 11 than at the position corresponding to the second layer 12. In other words, it can be seen that the potassium and sodium content in the first layer 11 is lower than the potassium and sodium content in the second layer 12.

[0070] Furthermore, Figure 9 shows that the bright spots indicating magnesium are lower at the position corresponding to the first layer 11 than at the position corresponding to the second layer 12. Also, Figure 10 shows that the bright spots indicating calcium are lower at the position corresponding to the first layer 11 than at the position corresponding to the second layer 12. In other words, the magnesium and calcium content in the first layer 11 is lower than the magnesium and calcium content in the second layer 12.

[0071] Furthermore, Figure 12 shows bright spots indicating the silicon element at positions corresponding to the first layer 11, confirming the presence of silicon in the first layer 11. Based on this and the results in Figure 7 above, it was confirmed that the first layer 11 is composed of silicon and aluminum, which form the glass framework.

[0072] (8) Thickness direction profile measurement by EDX The strength profile of the glass plate in the thickness direction of the glass plate of Example 13 was measured using line analysis by the EDX method. Figure 13 shows the measurement results of the thickness direction profile.

[0073] Figure 13 shows that the intensity of potassium at the position corresponding to the first layer 11 is lower than at the position corresponding to the second layer 12. Furthermore, the intensity of sodium at the position corresponding to the first layer 11 is lower than at the position corresponding to the second layer 12. In other words, the potassium and sodium content in the first layer 11 is lower than the potassium and sodium content in the second layer 12.

[0074] Furthermore, Figure 13 shows that the intensity of potassium and sodium elements changes in the thickness direction of the glass plate at the location corresponding to the second layer. In other words, it can be seen that the potassium and sodium content in the second layer 12 changes in the thickness direction of the glass plate.

[0075] Furthermore, Figure 13 shows that there are points where the potassium and sodium concentrations change discontinuously in the position corresponding to the second layer. Specifically, in the position corresponding to the first region 12a of the second layer, the potassium and sodium concentrations, which had been continuously increasing slightly towards the center in the thickness direction, increase sharply in the position corresponding to the discontinuous region 12c. In other words, it can be seen that the second layer has a discontinuous region 12c in which the potassium and sodium content changes discontinuously in the thickness direction.

[0076] Furthermore, Figure 13 shows that in the second layer, in the region inward in the thickness direction from the discontinuous region 12c (corresponding to the second region 12b), the intensity of the potassium element continuously decreases as you move towards the center in the thickness direction. Also, it can be seen that the intensity of the sodium element continuously increases as you move towards the center in the thickness direction. In other words, in the region corresponding to the second region 12b, it can be seen that the potassium content continuously decreases in the thickness direction as you move towards the center in the thickness direction, and the sodium content continuously increases in the thickness direction. That is, in the second region 12b, the composition ratio of potassium to sodium changes continuously.

[0077] Furthermore, Figure 13 shows that, at the location corresponding to the third layer 13, the intensity of potassium and sodium elements is approximately constant in the thickness direction. In other words, at the location corresponding to the third layer 13, the potassium content and sodium content are approximately constant in the thickness direction.

[0078] (9) Elemental distribution analysis using glass plates with different compositions Elemental distribution analysis was also performed in the same manner as above using glass with a different composition from the glass plates described above. The composition of this glass plate is as follows. Note that it also contains trace components in addition to the components listed below. SiO ２ : 67.2mol% Al ２ O ３ : 2.7 mol% MgO: 13.1 mol% CaO: 1.7 mol% Na ２ O: 15.0 mol% K ２ O: 0.2 mol% Fe ２ O ３ : (less than 0.1 mol%)

[0079] The "chemical strengthening process" and "etching process" for this glass plate were carried out in the same manner as described above. That is, the glass plate was immersed in a potassium nitrate melt. The temperature of the potassium nitrate melt was 460°C. The immersion time was 360 minutes to 3840 minutes. After the chemical strengthening process, the glass plate was immersed in a 0.5 mol / l potassium bicarbonate aqueous solution. The temperature of the potassium bicarbonate aqueous solution was 70°C. The immersion time was 360 minutes to 1440 minutes.

[0080] The same results as above were obtained when this glass plate was used. In other words, it could be seen that the first layer 11 had a higher proportion of A1 compared to the second layer 12 and the third layer 13. It could also be seen that the potassium and sodium content in the first layer 11 was less than the potassium and sodium content in the second layer 12. Furthermore, it could be seen that the magnesium and calcium content in the first layer 11 was less than the magnesium and calcium content in the second layer 12.

[0081] This invention can be widely used as a glass plate for image display devices, light-emitting devices, architectural applications, automotive applications, and other applications. Furthermore, it can be applied not only to flat glass plates but also to curved glass such as lenses.

[0082] 1 Glass plate 11 First layer 12 Second layer 13 Third layer #1 Preparation process #2 Content adjustment process

Claims

1. A method for manufacturing a glass plate containing a first alkali metal, comprising: a preparation step of preparing a glass plate; and a content adjustment step of varying the content of the first alkali metal in the thickness direction of the glass plate.

2. The method for manufacturing a glass plate according to claim 1, wherein the glass plate contains a second alkali metal having a smaller ionic radius than the first alkali metal, and the content adjustment step comprises a substitution step of substituting the second alkali metal with the first alkali metal by ion exchange between ions of the second alkali metal and ions of the first alkali metal.

3. The method for manufacturing a glass plate according to claim 2, wherein the content adjustment step comprises a layering step of forming a plurality of layers having different content of the first alkali metal.

4. The method for manufacturing a glass plate according to claim 3, wherein the layer formation step comprises an etching step of chemically etching the surface of the glass plate with an alkaline aqueous solution containing ions of the first alkali metal.

5. The method for producing a glass plate according to claim 4, wherein the first alkali metal is potassium and the alkaline aqueous solution is an aqueous solution of potassium bicarbonate.

6. The method for manufacturing a glass plate according to claim 3, wherein the plurality of layers include a first layer located on the surface portion of the glass plate and a second layer located inside the first layer in the thickness direction, and the content of the first alkali metal and the second alkali metal in the first layer is less than the content of the first alkali metal and the second alkali metal in the second layer.

7. The method for manufacturing a glass plate according to claim 6, wherein the second layer is a layer in which the content of the first alkali metal and the content of the second alkali metal change in the thickness direction.

8. The method for manufacturing a glass plate according to claim 6, wherein the second layer has discontinuous regions in which the content of the first alkali metal and the content of the second alkali metal change discontinuously in the thickness direction.

9. The method for manufacturing a glass plate according to claim 8, wherein in the region of the second layer that is inside the discontinuous region in the thickness direction, the ratio of the first alkali metal to the second alkali metal changes continuously in the thickness direction.

10. A glass plate containing a first alkali metal and a second alkali metal having a smaller ionic radius than the first alkali metal, comprising a first layer located on the surface portion of the glass plate and a second layer located inside the first layer in the thickness direction of the glass plate, wherein the content of the first alkali metal and the second alkali metal in the first layer is less than the content of the first alkali metal and the second alkali metal in the second layer.

11. The glass plate according to claim 10, wherein the second layer is a layer in which the content of the first alkali metal and the content of the second alkali metal change in the thickness direction.

12. The glass plate according to claim 10, wherein the second layer has discontinuous regions in which the content of the first alkali metal and the content of the second alkali metal change discontinuously in the thickness direction.

13. The glass plate according to claim 11, wherein in the region of the second layer that is inward in the thickness direction from the discontinuous region, the composition ratio of the first alkali metal and the second alkali metal changes continuously in the thickness direction.

14. The glass plate according to claim 11, having a third layer located inside the second layer in the thickness direction, wherein the content of the second alkali metal in the third layer is greater than the content of the second alkali metal in the first layer and the content of the second alkali metal in the second layer.

15. A glass plate containing alkali metals, alkaline earth metals, and aluminum, wherein the glass plate comprises a first layer located on the surface and a second layer located inside the first layer in the thickness direction of the glass plate, and the aluminum content in the first layer is greater than the aluminum content in the second layer.

16. The glass plate according to claim 15, wherein the content of alkaline earth metals in the first layer is less than the content of alkaline earth metals in the second layer.

17. The glass plate according to claim 10 or 15, wherein the first layer is a void layer having voids.

18. The glass plate according to claim 10 or 15, wherein the thickness of the first layer is smaller than the thickness of the second layer.

19. The glass plate according to claim 18, wherein the thickness of the first layer is 30 nm to 2 μm.

20. The glass plate according to claim 19, wherein the thickness of the second layer is 8 to 100 μm.

21. The glass plate according to claim 20, wherein the thickness of the glass plate is 0.3 to 3 mm.

22. The glass plate according to any one of claims 10 to 14, wherein the first alkali metal is potassium and the second alkali metal is sodium.

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