Method for manufacturing tempered glass

Abstract

The present invention provides a method for producing tempered glass, comprising a first ion exchange step (S2), a second ion exchange step (S3), a removal step (S5), and a post-removal ion exchange step (S7). In the post-removal ion exchange step (S7), Na ions in the glass are ion exchanged with K ions in a molten salt, so that the maximum compressive stress CS3 of the compressive stress layer (2) on the new surface (1a) formed in the removal step (S5) is 700 MPa or more.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a tempered glass suitable for use as a cover glass for, for example, a mobile phone, a digital camera, a PDA (Personal Digital Assistant), or a touch panel display. Background Art

[0002] Mobile phones (especially smartphones), digital cameras, PDAs, touch-panel displays, large-format televisions, and contactless power supplies are becoming increasingly popular. Ion-exchange tempered glass is used in these applications. Furthermore, the use of tempered glass in exterior components such as digital signage, mice, and smartphones has been increasing in recent years.

[0003] Tempered glass has a compressive stress layer formed on its surface by ion exchange treatment, which inhibits the formation and growth of surface cracks and achieves high strength. The strength of tempered glass can be improved by adjusting the formation method of this compressive stress layer.

[0004] Ion exchange treatment may cause defects or leave fine irregularities on the surface of tempered glass. Therefore, these defects and irregularities need to be removed. For example, Patent Document 1 discloses a method for manufacturing tempered glass that includes a post-strengthening polishing step for polishing the surface of a glass sheet after a chemical tempering step.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-137224 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] When the surface of the glass plate is polished in the post-strengthening polishing step, a portion of the compressive stress layer is removed, and thus the compressive stress value of the compressive stress layer on the surface of the tempered glass plate may be reduced.

[0010] Therefore, a technical object of the present invention is to improve the strength of glass which is reduced due to removal of part of the surface after ion exchange treatment.

[0011] Means for solving problems

[0012] The present invention is intended to solve the above-mentioned problems and is a method for producing tempered glass, wherein glass having a surface is subjected to an ion exchange treatment to obtain tempered glass having a compressive stress layer on the surface. The method is characterized by comprising: a first ion exchange step of contacting the surface of the glass with a first molten salt to ion-exchange Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of contacting the surface of the glass with a second molten salt to ion-exchange Na ions in the glass with K ions and Li ions in the second molten salt; a removal step of removing at least a portion of the surface of the tempered glass after the first and second ion exchange steps, thereby forming a new surface in the tempered glass; and a post-removal ion exchange step of ion-exchanging Na ions in the tempered glass after the removal step with K ions in the molten salt, thereby increasing the maximum compressive stress CS3 of the compressive stress layer on the new surface to 700 MPa or higher.

[0013] According to this configuration, after the first and second ion exchange steps, the surface of the tempered glass is removed in a removal step, thereby removing minor defects formed on the surface. This allows tempered glass with defects to be commercialized, improving yield. While the compressive stress value of the new surface of the tempered glass formed by the removal step is lower than the compressive stress value of the surface before the removal step, performing the post-removal ion exchange step on this new surface can significantly increase this compressive stress value. This enables the production of high-strength tempered glass.

[0014] The present method may further include a post-removal preliminary ion exchange step performed after the removal step and before the post-removal ion exchange step, wherein in the post-removal preliminary ion exchange step, the tempered glass after the removal step is brought into contact with a third molten salt, so that Li ions in the tempered glass after the removal step are ion-exchanged with Na ions in the molten salt.

[0015] In this method, the concentration of NaNO 3 in the third molten salt used in the post-removal preliminary ion exchange step may be substantially equal to the concentration of NaNO 3 in the first molten salt.

[0016] In this method, the concentration of KNO 3 in the molten salt used in the post-removal ion exchange step may be substantially equal to the concentration of KNO 3 in the second molten salt.

[0017] The ion exchange treatment time in the post-removal preliminary ion exchange step may be 10 to 100% of the ion exchange treatment time in the first ion exchange step.

[0018] Furthermore, the ion exchange treatment time in the post-removal ion exchange step may be 50 to 200% of the ion exchange treatment time in the second ion exchange step.

[0019] The glass may be a plate or sheet of glass having a thickness of 0.05 to 2.0 mm, and the main surfaces of the front and back surfaces of the tempered glass before the ion exchange step after the removal may be removed in a region shallower than the compressive stress layer, thereby making the maximum compressive stress CS2 of the compressive stress layer in the new surface after the removal step be 100 MPa or more.

[0020] It may be that: in the above-mentioned removal step, the surface of the above-mentioned strengthened glass after the first ion exchange step and the second ion exchange step is polished or etched to remove the above-mentioned material, and the removal amount Δt of the above-mentioned surface in the above-mentioned removal step is smaller than the diffusion depth DOL of the K ions introduced in the above-mentioned second ion exchange step.

[0021] It can be: in the present method, the removal amount Δt in the above-mentioned removal process is less than 20μm, the compressive stress CS2 of the above-mentioned compressive stress layer in the above-mentioned new surface after the above-mentioned removal process and before the above-mentioned post-removal ion exchange process is set to less than 700MPa, and the maximum compressive stress CS3 of the above-mentioned compressive stress layer after the above-mentioned post-removal ion exchange process is set to 700~1200MPa.

[0022] In the tempered glass after the post-removal ion exchange step, a stress curve (stress distribution) obtained by measuring stress in a depth direction from the new surface may include: a first peak at which the compressive stress reaches a maximum value on the surface; a first valley at which the stress gradually decreases in the depth direction from the first peak and reaches a minimum value; a second peak at which the compressive stress reaches a maximum value by gradually increasing in the depth direction from the first valley; and a second valley at which the tensile stress reaches a minimum value by gradually decreasing in the depth direction from the second peak. In the post-removal ion exchange step, Na ions in the tempered glass may be ion-exchanged with K ions in the molten salt so that the compressive stress CSb in the first valley becomes 10 MPa or more.

[0023] The concentration of LiNO3 in the molten salt used in the post-removal ion exchange step may be 0.1 to 2 mass %. In addition, the concentration of Na ions in the molten salt used in the post-removal ion exchange step may be 5.0 mass % or less when converted to NaNO3.

[0024] The ion exchange treatment temperature in the post-removal ion exchange step is 350 to 450° C., and the ion exchange treatment time in the post-removal ion exchange step is less than or equal to the ion exchange treatment time in the second ion exchange step.

[0025] In the present method, it may be that: in the above-mentioned second ion exchange process, the Na ions in the above-mentioned glass are ion-exchanged with the K ions in the above-mentioned second molten salt, and the Na ions in the above-mentioned glass are ion-exchanged with the Li ions in the above-mentioned second molten salt, the concentration of NaNO3 in the above-mentioned first molten salt is more than 50 mass%, the concentration of KNO3 in the above-mentioned first molten salt is less than 50 mass%, the concentration of LiNO3 in the above-mentioned second molten salt is 0.5-5 mass%, and the concentration of KNO3 in the above-mentioned second molten salt is 95-99.5 mass%, the ion exchange treatment temperature of the above-mentioned first ion exchange process is 350-480°C, the ion exchange treatment temperature of the above-mentioned second ion exchange process is 350-480°C, the ion exchange treatment time of the above-mentioned first ion exchange process is 1-20 hours, and the ion exchange treatment time of the above-mentioned second ion exchange process is shorter than the ion exchange treatment time of the above-mentioned first ion exchange process.

[0026] The above-mentioned glass can contain 40% to 70% SiO2, 10% to 30% Al2O3, 0% to 3% B2O3, 5% to 25% Na2O, 0% to 5.5% K2O, 0.1% to 10% Li2O, 0% to 6% MgO, and 0% to 15% P2O5 as glass composition in mass%.

[0027] The method may include an inspection step of inspecting the surface of the tempered glass for defects after performing the first and second ion exchange steps and before the removal step, and if defects are detected on the surface of the tempered glass, removing at least a portion of the surface together with the defects in the removal step.

[0028] The present invention, which aims to solve the above-mentioned problems, is a method for producing tempered glass in which the surface compressive stress of the tempered glass is adjusted. The method is characterized by comprising the following steps: a removal step of removing at least a portion of the surface of the tempered glass previously having a compressive stress layer on the surface to a depth shallower than the depth of the compressive stress layer, thereby forming a new surface on the tempered glass; and a post-removal ion exchange step of subjecting the tempered glass, wherein the maximum compressive stress CS2 of the compressive stress layer on the new surface is less than 700 MPa, to an ion exchange treatment. In the post-removal ion exchange step, the maximum compressive stress CS3 of the compressive stress layer on the new surface is adjusted to 700 MPa or higher by exchanging Na ions in the tempered glass with K ions in a molten salt.

[0029] According to this configuration, after the ion exchange treatment, the compressive stress of the compressive stress layer is reduced in the new surface formed by removing the surface of the tempered glass. However, by performing the post-removal ion exchange step on this new surface, the compressive stress value can be sufficiently increased. This enables the production of high-strength tempered glass.

[0030] The method may further include a step of measuring information related to stress of the tempered glass after the removal step and before the post-removal ion exchange step using a measuring device, and an ion exchange condition setting step of setting ion exchange conditions in the post-removal ion exchange step based on the information measured by the measuring device.

[0031] In the present method, the measuring device may be a device that generates optical interference fringes on the tempered glass after the removal step and before the post-removal ion exchange step, and measures the stress distribution by capturing an interference fringe image including the optical interference fringes; the information related to the stress may include the interference fringe image; the ion exchange conditions may include an ion exchange treatment time in the post-removal ion exchange step; and in the ion exchange condition setting step, the ion exchange treatment time may be set based on the interference fringe image.

[0032] The present method may include: a step of measuring, before the removal step, the diffusion depth DOL1 of the K ions introduced in the second ion exchange step using the measuring device; and a removal amount determining step of determining the amount Δt removed from the surface of the tempered glass in the removal step, wherein the ion exchange condition setting step is configured based on a pre-prepared function, the diffusion depth DOL1 of the K ions measured by the measuring device, and the removal amount Δt determined in the removal amount determining step.

[0033] In the present method, the ion exchange conditions may include the ion exchange treatment time Tx in the post-removal ion exchange step, and the function may include the following formula (1).

[0034] Tx=a(1-e -b×x )...(1)

[0035] Here, a and b are constants, and x is the ratio of the removal amount Δt to the diffusion depth DOL1 of the K ions introduced in the second ion exchange step (Δt / DOL1).

[0036] The method may include: an inspection step of acquiring defect information of the tempered glass after the first ion exchange step and the second ion exchange step and before the removal step; and a predetermined removal amount setting step of setting a predetermined removal amount to be removed from the surface of the tempered glass after the first ion exchange step and the second ion exchange step based on the defect information acquired in the inspection step.

[0037] In the present method, the information related to the stress includes a diffusion depth DOL2 of K ions remaining in the tempered glass after the removal step and before the post-removal ion exchange step. In the removal amount determination step, the removal amount Δt is determined by the difference (DOL1-DOL2) between the diffusion depth DOL1 of K ions introduced in the second ion exchange step and the diffusion depth DOL2 of K ions remaining in the tempered glass.

[0038] The present invention is intended to solve the above-mentioned problems. In a method for producing tempered glass in which glass having a surface is subjected to an ion exchange treatment to obtain tempered glass having a compressive stress layer on the surface, the method comprises: a first ion exchange step of contacting the surface of the glass with a first molten salt to exchange Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of contacting the surface of the glass with a second molten salt to exchange Na ions in the glass with K ions in the second molten salt; and a removal step of removing the tempered glass after the first and second ion exchange steps have been performed. The method for manufacturing strengthened glass further comprises: a step of removing at least a portion of the surface of the tempered glass, thereby forming a new surface in the tempered glass; a measuring step of measuring information related to the stress of the tempered glass after the removing step using a measuring device; and a post-removal ion exchange step of increasing the maximum compressive stress of the compressive stress layer on the new surface by ion-exchanging Na ions in the tempered glass after the measuring step with K ions in a molten salt, the method further comprising an ion exchange condition setting step of setting ion exchange conditions in the post-removal ion exchange step based on the information related to the stress obtained from the measuring device in the measuring step.

[0039] Effects of the Invention

[0040] According to the present invention, it is possible to improve the strength of glass which is reduced due to removal of part of the surface after ion exchange treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram showing a cross section of tempered glass.

[0042] Figure 2This is a graph showing a stress curve in the thickness direction of tempered glass.

[0043] Figure 3 This is a flowchart showing the method for producing tempered glass according to the first embodiment.

[0044] Figure 4 It is a cross-sectional view of the glass showing the removal step.

[0045] Figure 5 This is a flowchart showing a method for producing tempered glass according to the second embodiment.

[0046] Figure 6 This is a flowchart showing a method for producing tempered glass according to a third embodiment.

[0047] Figure 7 This is a diagram schematically showing an interference fringe image of tempered glass.

[0048] Figure 8 This is a diagram schematically showing an interference fringe image of tempered glass.

[0049] Figure 9 This is a diagram schematically showing an interference fringe image of tempered glass.

[0050] Figure 10 This is a diagram schematically showing an interference fringe image of tempered glass.

[0051] Figure 11 The stress curves of the tempered glasses of Examples are shown.

[0052] Figure 12 The stress curves of the tempered glasses of Examples are shown.

[0053] Description of Reference Numerals

[0054] 1 Tempered Glass

[0055] 1a0 Surface of the removed glass

[0056] 1a New surface of glass

[0057] 3 Compressive stress layer

[0058] B1 First Valley

[0059] B2 Second Valley

[0060] Maximum compressive stress of the compressive stress layer after CS2 removal process

[0061] Maximum compressive stress of the compressive stress layer after ion exchange process after CS3 removal

[0062] CSb compressive stress of the first valley

[0063] DOL1 Diffusion depth of K ions introduced in the second ion exchange step

[0064] P1 First Peak

[0065] P2 Second Peak

[0066] S2 First ion exchange step

[0067] S3 Second ion exchange process

[0068] S4 First inspection process

[0069] S5 Removal process

[0070] S7a removal and preparatory ion exchange process

[0071] S7 removal after ion exchange process

[0072] S41 First measurement step

[0073] S42 Predetermined removal amount setting step

[0074] S61 Second measurement step

[0075] S62 Removal amount determination process

[0076] S63 Ion exchange condition setting process

[0077] Δt0 Expected removal amount

[0078] Δt removal amount DETAILED DESCRIPTION

[0079] <First embodiment>

[0080] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figures 1 to 4 A first embodiment of the method for producing tempered glass of the present invention will be described.

[0081] like Figure 1 As shown in FIG. 1 , the tempered glass 1 of the present invention is a plate-shaped or sheet-shaped chemically tempered glass that has been chemically tempered by ion exchange. The tempered glass 1 includes surfaces 1 a and 1 b , a compressive stress layer 2 , and a tensile stress layer 3 .

[0082] The thickness T of the tempered glass 1 can be arbitrarily determined, but is preferably 2.0 mm or less, more preferably 1.8 mm or less, 1.6 mm or less, 1.4 mm or less, 1.2 mm or less, 1.0 mm or less, 0.9 mm or less, or 0.85 mm or less, and even more preferably 0.8 mm or less. It is preferably 0.03 mm or more, 0.05 mm or more, 0.1 mm or more, 0.15 mm or more, 0.2 mm or more, 0.25 mm or more, 0.3 mm or more, 0.35 mm or more, 0.4 mm or more, 0.45 mm or more, 0.5 mm or more, or 0.6 mm or more, and even more preferably 0.65 mm or more.

[0083] The surfaces 1a and 1b of the tempered glass 1 include the main surface 1a and the end surface 1b, which form the front and back surfaces. A compressive stress layer 2 is formed in the surface portion of the tempered glass 1, including the main surface 1a and the end surface 1b. The compressive stress layer 2 includes a compressive stress layer caused by K ions introduced through ion exchange and a compressive stress layer caused by Na ions introduced through ion exchange. The compressive stress layer caused by K ions is formed at a relatively shallow position near and on the surfaces 1a and 1b of the tempered glass 1. The depth of the compressive stress layer caused by K ions, i.e., the diffusion depth DOL1 (not shown) of the K ions introduced through ion exchange, is preferably 0.02% to 3.00% of the thickness T of the tempered glass 1, and more preferably 0.05% to 2.00% of the thickness T. The compressive stress layer caused by Na ions is formed deeper than the compressive stress layer caused by K ions. A tensile stress layer 3 is formed within the tempered glass 1, i.e., deeper than the compressive stress layer 2.

[0084] The stress curve (stress distribution) of the tempered glass 1 is obtained by measuring the stress in the depth direction (direction perpendicular to the main surface 1a) from the main surface 1a side, with compressive stress as a positive number and tensile stress as a negative number. The stress curve of the tempered glass 1 obtained in this way is, for example, Figure 2 As shown. Figure 2 In the graph of , the vertical axis represents stress, and the horizontal axis represents the position (depth) in the thickness direction based on one main surface 1a. Figure 2 In the graph, positive stress indicates compressive stress, and negative stress indicates tensile stress. Figure 2 The greater the absolute value of stress in the graph, the greater the stress. Figure 2 This is a schematic diagram exaggerated for the sake of understanding, and the stress curve of the tempered glass 1 is not limited to this form.

[0085] The stress curve of the tempered glass 1 includes a first peak P1, a first valley B1, a second peak P2, and a second valley B2 in this order from the main surface 1a side in the depth direction (a direction perpendicular to the main surface 1a).

[0086] The first peak P1 is the position where the compressive stress reaches its maximum value and exists on the main surface 1a. The compressive stress CS1 (CSmax) of the first peak P1 is 700 MPa or more, preferably 700 MPa to 900 MPa, and more preferably 750 MPa to 850 MPa.

[0087] The stress decreases along the depth direction from the first peak P1 and reaches the minimum value at the first valley B1. The stress CSb of the first valley B1 is Figure 2 The example in FIG shows a case where compressive stress (positive value) is present, but tensile stress (negative value) may also be present. The lower the stress CSb of the first valley B1, the lower the tensile stress CTmax of the second valley B2, which slows down the behavior during fracture.

[0088] The stress CSb at the first valley B1 is preferably less than +100 MPa, more preferably less than +90 MPa, less than +80 MPa, less than +70 MPa, or less than +60 MPa. However, if the stress CSb of the first valley B1 is too low, cracks will be generated on the surface during the strengthening process, which will deteriorate the visual recognition. The stress CSb of the first valley B1 is preferably greater than -50 MPa, more preferably greater than -45 MPa, greater than -40 MPa, greater than -35 MPa, greater than -30 MPa, or greater than 0 MPa, and particularly preferably greater than +10 MPa. The stress CSb of the first valley B1 can be greater than 0 MPa and less than +65 MPa, or greater than -30 MPa and less than 0 MPa. The depth DOLb of the first valley B1 is preferably 0.5% to 12% of the thickness T, more preferably 1% to 7% of the thickness T. The depth DOLb of the first valley B1 is substantially equal to or slightly deeper than the depth DOL1 of the compressive stress layer caused by K ions (diffusion depth of K ions) in the compressive stress layer 2. More specifically, DOLb is within a range of ±10 μm relative to DOL1.

[0089] The stress increases in the depth direction from the first valley B1, and reaches a maximum value at the second peak P2. The stress CSp of the second peak P2 is a compressive stress. The compressive stress CSp of the second peak P2 is 15 MPa to 250 MPa, preferably 15 MPa to 240 MPa, 15 MPa to 230 MPa, 15 MPa to 220 MPa, 15 MPa to 210 MPa, 15 MPa to 200 MPa, 15 MPa to 190 MPa, 15 MPa to 180 MPa, 15 MPa to 175 MPa, 15 MPa to 170 MPa, 15 MPa to 165 MPa, 15 MPa to 160 MPa, 18 MPa to 100 MPa, and more preferably 20 MPa to 80 MPa.

[0090] The depth DOLp of the second peak P2 is 4% to 20% of the thickness T, preferably 4% to 19%, 4% to 18.5%, 4% to 18%, 4% to 17.5%, 4% to 17% of the thickness T, and more preferably 4.5% to 17%, 5% to 17%, 6% to 17%, 7.3% to 17%, and 8% to 15%.

[0091] The distance in the depth direction from the first valley B1 to the second peak P2 , ie, DOLp-DOLb, is 3% or more of the thickness T, preferably 4% or more of the thickness T, and more preferably 5% to 13% of the thickness T.

[0092] The stress decreases in the depth direction from the second peak P2, reaching the minimum tensile stress value (maximum absolute value) at the second valley B2. The absolute value of the tensile stress CTmax in the second valley B2 is 70 MPa or less, preferably 65 MPa or less, 60 MPa or less, and more preferably 40 MPa to 55 MPa.

[0093] The product of the tensile stress CTmax of the second valley B2 and the thickness T is preferably -70 MPa·mm or greater, more preferably -65 MPa·mm or greater, -60 MPa·mm or greater, or -55 MPa·mm or greater. Furthermore, the product of the tensile stress CTmax of the second valley B2 and the thickness T is preferably -5 MPa·mm or less, -10 MPa·mm or less, -15 MPa·mm or less, -20 MPa·mm or less, -25 MPa·mm or less, or -30 MPa or less.

[0094] Between the second peak P2 and the second valley B2 lies a stress zero point Z where stress is zero. Typically, the depth DOLzero of the stress zero point Z rarely exceeds 20% of the thickness T, with a physical limit of approximately 22%. However, in this embodiment, a DOLzero exceeding this limit can be achieved.

[0095] The greater the depth DOLzero of the stress zero point Z, the higher the strength relative to the penetration of the protrusion. It is preferably more than 10%, more than 10.5%, more than 11%, more than 11.5%, more than 12%, more than 12.5%, more than 13%, more than 13.5%, more than 14%, more than 14.5%, more than 15%, more than 15.5%, more than 16%, more than 16.5%, more than 17%, more than 17.5%, more than 18%, more preferably more than 18.5%, more than 19%, more than 19.5%, more than 20%, more than 20.5%, more than 21%, more than 21.5%, more than 22.0%, more than 22.5%, more than 23%, more than 23.5%, and most preferably more than 24%.

[0096] However, if the depth DOLzero of the stress zero point Z is too large, excessive tensile stress may be generated in the first valley B1 and the second valley B2. Therefore, the depth DOLzero of the stress zero point Z is preferably 35% or less, 34.5% or less, 34% or less, 33.5% or less, 33% or less, 32.5% or less, 32% or less, 31.5% or less, 31% or less, 30.5% or less, 30% or less, 29.5% or less, 29% or less, 28.5% or less, or 28% or less of the thickness T, and more preferably 27% or less.

[0097] In this embodiment, the tempered glass 1 also exhibits a similar stress curve at the end surface 1b. Specifically, the stress curve of the tempered glass 1 includes a first peak at which the compressive stress reaches a maximum value at the end surface 1b; a first valley where the stress gradually decreases in the depth direction from the first peak and reaches a minimum value; a second peak where the compressive stress gradually increases in the depth direction from the first valley and reaches a maximum value; and a second valley where the tensile stress decreases in the depth direction from the second peak and reaches a minimum value. The compressive stress at the first peak is 700 MPa or higher, while the compressive stress at the second peak is 15 MPa to 250 MPa. The second peak exists at a depth of 4% to 20% of the thickness T. The preferred range of the stress curve for the end surface 1b also applies to the preferred range of the stress curve for the main surface 1a.

[0098] In addition, the stress and its distribution of the tempered glass 1 can be measured and synthesized using, for example, FSM-6000LE and SLP-1000 manufactured by Orihara Seisakusho Co., Ltd.

[0099] The tempered glass 1 having the above-described structure is produced by preparing a plate-shaped glass containing an alkali metal oxide as a composition (hereinafter referred to as tempering glass) and subjecting the tempering glass to a tempering treatment.

[0100] The tempered glass preferably contains, in mass %, 40% to 70% SiO2, 10% to 30% Al2O3, 0% to 3% B2O3, 5% to 25% Na2O, 0% to 5.5% K2O, 0.1% to 10% Li2O, 0% to 6% MgO, and 0% to 15% P2O5 as a glass composition.

[0101] The reasons why the above composition is preferred are as follows: In the description of the content range of each component, unless otherwise specified, the expression % means mass %.

[0102] SiO2 is a component that forms a network of glass. If the content of SiO2 is too little, it is difficult to vitrify, and the acid resistance is easily reduced. Therefore, the suitable lower limit range of SiO2 is calculated by mass% to be more than 40%, preferably more than 45%, and particularly preferably more than 50%. On the other hand, if the content of SiO2 is too much, then the meltability and formability are easily reduced, and in addition, the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of the surrounding materials. Therefore, the suitable upper limit range of SiO2 is calculated by mass% to be less than 70%, preferably less than 65%, less than 57%, less than 56%, less than 55%, and particularly preferably less than 54%.

[0103] Al2O3 is a component that increases the ion exchange rate and is a component that increases Young's modulus and Vickers hardness. In addition, it is a component that increases the viscosity of phase separation. If the content of Al2O3 is too little, the ion exchange rate and Young's modulus are likely to decrease. Therefore, the suitable lower limit range of Al2O3 is 10% or more by mass%, preferably 15% or more, 18% or more, 24% or more, 25% or more, and particularly preferably 26% or more. On the other hand, if the content of Al2O3 is too much, devitrified crystals are easily precipitated in the glass, making it difficult to form the glass into a plate by overflow downdrawing or the like. In particular, when using alumina refractory as a forming body refractory and forming the glass into a plate by overflow downdrawing, devitrified crystals of spinel are easily precipitated at the interface with the alumina refractory. In addition, acid resistance is also reduced, making it difficult to apply to the acid treatment process. In addition, high-temperature viscosity increases, and meltability is easily reduced. Therefore, the suitable upper limit range of Al2O3 is 30% or less in mass %, preferably 29% or less, 28% or less, or 27% or less.

[0104] B2O3 is a component that reduces high-temperature viscosity and density and improves resistance to devitrification. However, if the B2O3 content is too high, the ion exchange rate (especially stress depth) is likely to decrease. In addition, ion exchange can easily cause coloring of the glass surface, known as burning, or reduce acid resistance and water resistance. Therefore, the suitable lower limit range of B2O3 is 0% or more, 0.01% or more, and 0.05% or more in mass %, and the suitable upper limit range of B2O3 is 3% or less, 2% or less, and 1% or less in mass %, especially less than 0.3%.

[0105] Na2O is an ion exchange component that reduces high-temperature viscosity, improves meltability, and improves formability. It also improves devitrification resistance and its reaction with formed refractory materials, particularly alumina refractory materials. If the Na2O content is too low, meltability decreases, the thermal expansion coefficient decreases excessively, or the ion exchange rate tends to slow. Therefore, the suitable lower limit for Na2O is 5% or more, 7% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 11% or more, or 12% or more, particularly 12.5% or more. On the other hand, excessive Na2O content can cause phase separation and reduce viscosity. Furthermore, acid resistance can sometimes decrease, or the glass composition may lack a balanced composition, leading to a decrease in devitrification resistance. Therefore, the suitable upper limit range of Na2O is 20% or less, 19.5% or less, 19% or less, 18% or less, 17% or less, 16.5% or less, 16% or less, 15.5% or less, and particularly 15% or less.

[0106] K2O is a component that reduces high-temperature viscosity and improves meltability and formability. It is also a component that improves devitrification resistance or increases Vickers hardness. However, if the K2O content is too high, phase separation occurs and the viscosity is easily reduced. In addition, there is a tendency for the acid resistance to decrease or the component balance of the glass composition to be lacking, and the devitrification resistance to decrease instead. Therefore, the suitable lower limit range of K2O is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, 2% or more, 2.5% or more, 3% or more, and especially 3.5% or more, and the suitable upper limit range is 5.5% or less, 5% or less, and especially 4.5% or less.

[0107] Li2O is an ion exchange component that reduces high-temperature viscosity, improving meltability and formability. It also increases Young's modulus. The suitable lower limit range for Li2O, in mass %, is 0.1% or higher, 0.5% or higher, 1.0% or higher, 1.5% or higher, 2.0% or higher, and particularly 2.5% or higher. The suitable upper limit range is 10% or lower, 8% or lower, 5% or lower, 4.5% or lower, 4.0% or lower, and particularly less than 3.5%.

[0108] MgO is a component that reduces high-temperature viscosity, improves meltability and formability. It is also a component that increases Young's modulus and Vickers hardness, or improves acid resistance. Therefore, the suitable lower limit range of MgO is 0% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. However, if the MgO content is too high, there is a tendency for the ion exchange rate to decrease and the glass to become devitrified. In particular, when using alumina refractory as a forming body refractory and forming the glass into a plate by overflow downdrawing, spinel devitrified crystals are easily precipitated at the interface with the alumina refractory. Therefore, the suitable upper limit range of MgO is 6% or less, 5.5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, and particularly 2.5% or less.

[0109] P2O5 is a component that increases the ion exchange rate while maintaining the compressive stress value. Therefore, the suitable lower limit range of P2O5 is 0% or more, 2% or more, 2.1% or more, 2.5% or more, 3% or more, 4% or more, and particularly 4.5% or more. However, if the P2O5 content is too high, the glass will easily become cloudy due to phase separation, or its water resistance will be easily reduced. Therefore, the suitable upper limit range of P2O5 is 15% or less, 10% or less, 9.5% or less, 9% or less, 8.5% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, 6.3% or less, and particularly 6% or less.

[0110] As a clarifier, one or more selected from the group consisting of SnO2, As2O3, Cl, SO3, and CeO2 (preferably the group consisting of Cl and SO3) can be added in an amount of 0 ppm to 30,000 ppm (0% to 3%) by mass.

[0111] As a clarifier, SnO₂ is particularly preferably included. Suitable SnO₂ content ranges, in mass %, are 0 to 10,000 ppm, 0 to 7,000 ppm, and particularly 50 to 6,000 ppm. Suitable Cl content ranges are 0 to 1,500 ppm, 0 to 1,200 ppm, 0 to 800 ppm, 0 to 500 ppm, and particularly 50 to 300 ppm. Suitable SO₃ content ranges are 0 to 1,000 ppm, 0 to 800 ppm, and particularly 10 to 500 ppm.

[0112] The Fe2O3 content is preferably less than 1000 ppm (less than 0.1%), less than 800 ppm, less than 600 ppm, less than 400 ppm, and particularly less than 300 ppm. This tends to improve the transmittance (400 nm to 770 nm) at a thickness of 1 mm.

[0113] Rare earth oxides such as Nb2O5 and La2O3 are components that increase Young's modulus. However, the raw material costs themselves are high, and if added in large quantities, devitrification resistance tends to decrease. Therefore, the rare earth oxide content is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, and particularly preferably 0.1% or less.

[0114] Furthermore, from an environmental perspective, the tempering glass preferably contains substantially no As2O3, Sb2O3, or PbO as a glass composition. Furthermore, from an environmental perspective, it preferably contains substantially no Bi2O3 or F.

[0115] It should be noted that the composition of the tempered glass described above is merely an example, and any tempered glass having a known composition may be used as long as it can be chemically tempered by ion exchange. Furthermore, the composition of the tempered glass obtained by ion-exchanging the tempered glass described above is the same as the composition of the tempered glass before the ion-exchange treatment.

[0116] Hereinafter, a method for producing the tempered glass 1 (tempered glass sheet) having the above-described configuration will be described.

[0117] like Figure 3 As shown, the method includes a preparation step S1, a first ion exchange step S2, a second ion exchange step S3, a first inspection step S4, a removal step S5, a second inspection step S6, a post-removal ion exchange step S7, and a third inspection step S8.

[0118] Preparation step S1 is the step of preparing the tempered glass. In preparation step S1, glass raw materials prepared to achieve the above-mentioned glass composition are placed in a continuous melting furnace, heated and melted at 1500°C to 1600°C, clarified, and then supplied to a forming device, where they are formed into a sheet or other form and slowly cooled to produce the tempered glass.

[0119] As a method for forming a glass sheet, the overflow down-draw method is preferably used. The overflow down-draw method is a method that can produce high-quality glass sheets in large quantities, and can also easily produce large glass sheets. In addition, it can minimize damage to the surface of the glass sheet. It should be noted that in the overflow down-draw method, as the constituent materials of the formed body, for example, alumina and dense zircon are used. The tempered glass of the present invention has good compatibility with alumina and dense zircon, and particularly good compatibility with alumina (the components of the molten glass are unlikely to react with the components of the formed body, and bubbles, pitting, etc. are unlikely to occur).

[0120] In addition to the overflow down-draw method, various forming methods can be used. For example, a float method, a down-draw method (slot down-draw method, re-draw method, etc.), a roll-out method, a press method, etc. can be used.

[0121] The tempered glass may be subjected to bending processing after being formed or simultaneously with the forming as required. In addition, processing such as cutting processing, hole processing, surface grinding processing, chamfering processing, end surface grinding processing, etching processing, etc. may be performed as required.

[0122] The size of the tempered glass can be arbitrarily determined, but the thickness T is preferably 2.0 mm or less, more preferably 0.05 to 1.0 mm, further preferably 0.1 to 0.9 mm, 0.3 to 0.85 mm, or 0.5 to 0.8 mm.

[0123] In the first ion exchange step S2, the surface of the strengthened glass is ion-exchanged by immersing it in a treatment tank filled with a first molten salt containing Na, whose ionic radius is larger than the Li ions contained in the strengthened glass, and maintaining it at a predetermined temperature for a predetermined time. Thus, the strengthened glass is brought into contact with the first molten salt, and the Li ions in the strengthened glass are ion-exchanged with the Na ions in the first molten salt, thereby introducing Na ions near the surface (main surface and end face) of the strengthened glass. Furthermore, the Na ions in the strengthened glass are ion-exchanged with the K ions in the first molten salt. As a result, a compressive stress layer 2 is formed on the surface of the strengthened glass, strengthening the strengthened glass.

[0124] In the first ion exchange step S2, the region into which Na ions are introduced into the strengthening glass is preferably a region from the surface of the strengthening glass to a depth of 10% or more of the thickness T, and more preferably a region from the surface of the strengthening glass to a depth of 12% or more, 14% or more, 15% or more, or 15% or more and 40% or less of the thickness T.

[0125] The first molten salt used in the first ion exchange step S2 is preferably a mixed salt of NaNO3 and KNO3. If the first molten salt contains K ions, it is easy to measure the stress and distribution of the tempered glass after the first ion exchange step S2, which is suitable for quality management of the obtained tempered glass. Preferably, the concentration of NaNO3 in the first molten salt is preferably 50% or more by mass, and the concentration of KNO3 in the first molten salt is preferably less than 90% by mass. However, the concentration of NaNO3 in the first molten salt is preferably 100-10%, 100-20%, 100-30%, 100-40%, or 100-50% by mass, and the remainder is preferably KNO3. It should be noted that the first molten salt can be composed only of NaNO3 and does not contain KNO3. In addition, the first molten salt may contain LiNO3.

[0126] The ion exchange treatment temperature in the first ion exchange step S2 is preferably 350 to 480° C., more preferably 360 to 430° C., further preferably 370 to 400° C. or 370 to 390° C. The ion exchange treatment time in the first ion exchange step S2 is preferably 1 to 20 hours, more preferably 1.5 to 15 hours, and further preferably 2 to 10 hours.

[0127] In the second ion exchange step S3 , the tempering glass is immersed in a treatment tank filled with a second molten salt containing K ions and Li ions and maintained at a predetermined temperature for a predetermined time, thereby performing ion exchange treatment on the surface of the tempering glass.

[0128] Thus, the tempered glass is brought into contact with the second molten salt, and the Li ions in the second molten salt undergo reverse ion exchange with the Na ions in the tempered glass, causing at least a portion of the Na ions to be removed from the tempered glass. Simultaneously, K ions undergo ion exchange with the Li or Na ions contained in the tempered glass, causing the K ions to be introduced into the tempered glass from the surface to a region shallower than 7% of the thickness T. Specifically, the reverse ion exchange relaxes the compressive stress formed in the surface portion of the tempered glass, and the ion exchange strengthens the tempered glass, resulting in high compressive stress only near the surface in the surface portion.

[0129] In the second ion exchange step S3, the region where Na ions are desorbed from the strengthening glass is preferably the region from the surface of the strengthening glass to a depth of 15% or less of the thickness T, and more preferably the region from the surface of the strengthening glass to a depth of 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 1% or more and 10% or less, 2% or more and 10% or less, 3% or more and 10% or less, 4% or more and 10% or less, or 5% or more and 10% or less of the thickness T. Furthermore, in the second ion exchange step S3, the region where K ions are introduced into the strengthening glass is preferably the region from the surface of the strengthening glass to a depth of 7% or less of the thickness T, and more preferably the region from the surface of the strengthening glass to a depth of 6.5% or less, 6% or less, 5.5% or less, or 5% or less of the thickness T.

[0130] The second molten salt used in the second ion exchange step S3 is preferably a mixed salt of LiNO3 and KNO3. The concentration of LiNO3 in the second molten salt is preferably lower than the concentration of KNO3 in the second molten salt. Specifically, the concentration of LiNO3 in the second molten salt is preferably 0.1-5%, 0.2-5%, 0.3-5%, 0.4-5%, 0.5-5%, 0.5-4%, 0.5-3%, 0.5-2.5%, 0.5-2%, or 1-2% by mass%. The concentration of KNO3 in the second molten salt is preferably 95-99.8%, 97-99.6%, 98-99.5%, or 99-99.7% by mass.

[0131] The concentration of Li ions in the second molten salt is preferably 100 mass ppm or more. The concentration of Li ions in the second molten salt is obtained by multiplying LiNO 3 expressed in mass % by 0.101.

[0132] The ion exchange treatment temperature in the second ion exchange step S3 is preferably 350 to 480°C, more preferably 360 to 430°C, and even more preferably 370 to 400°C or 370 to 390°C. The ion exchange treatment time in the second ion exchange step S3 is preferably shorter than the ion exchange treatment time in the first ion exchange step S2. The ion exchange treatment time in the second ion exchange step S3 is preferably 0.2 hours or longer, more preferably 0.3 to 2 hours, 0.4 to 1.5 hours, and even more preferably 0.5 to 1 hour.

[0133] The tempered glass immersed in the molten salt in each ion exchange step S2, S3 may be preheated to the temperature of the molten salt in the ion exchange treatment in each ion exchange step S2, S3, or may be immersed in each molten salt at room temperature (eg, 1°C to 40°C).

[0134] A cleaning step for cleaning the tempered glass drawn from the molten salt is preferably provided between the first ion exchange step S2 and the second ion exchange step S3. This cleaning facilitates the removal of deposits adhering to the tempered glass, allowing for more uniform ion exchange in the second ion exchange step S2.

[0135] In the first inspection step S4, the quality of the tempered glass 1 formed through the first and second ion exchange steps S2 and S3 is inspected for defects (such as the presence of defects, irregularities, etc.) before the removal step S5. If minor defects, such as scratches, are found on the surface of the tempered glass 1, for example, the main surface 1a, during the first inspection step S4, the tempered glass 1 is subjected to the subsequent removal step S5. On the other hand, if no minor defects are found and the tempered glass 1 meets the standards for other products, the tempered glass 1 is finalized.

[0136] like Figure 4 As shown, in the removal step S5, the front and back main surfaces 1a of the tempered glass 1 are removed in an area shallower than the compressive stress layer 2. Specifically, the portion from the surface 1a0 of the tempered glass 1 where the defect was found to a predetermined depth Δt is removed. As a method for removing the surface 1a0 of the tempered glass 1, it is preferred to polish the surface 1a0 of the tempered glass 1 using a polishing tool such as a polishing pad. However, this is not limiting; the surface 1a0 may also be removed by etching the tempered glass 1.

[0137] In the removal step S5, regardless of the removal method used, it is preferable to ensure that the amount of material removed from the front and back main surfaces 1a is equal. More specifically, the difference in the amount of material removed from the front and back main surfaces 1a is preferably 1 μm or less, more preferably 0.5 μm or less, or 0.3 μm or less. By minimizing the difference in the amount of material removed from the front and back main surfaces 1a, warping of the tempered glass 1 caused by the removal can be suppressed. Therefore, when removing the material by polishing, it is preferable to use a double-side polishing machine.

[0138] The amount (removal amount) Δt removed from the tempered glass 1 is preferably 0.5 to 20 μm. The removal amount Δt is preferably set to be constant over the entire range of the main surface 1a, but it is also possible to leave a portion of the main surface 1a0 without defects without removing it. That is, in the removal step S5, at least a portion of the main surface 1a0 of the tempered glass 1 can be removed. The removal amount Δt is preferably less than the depth DOLzero of the compressive stress layer 2, and further preferably less than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3. It should be noted that in the case where defects occur on the end surface 1b, the end surface 1b can be subjected to grinding or etching to remove a portion of the end surface 1b.

[0139] In the removal step S5, the surface 1a0 of the tempered glass 1 is removed, thereby forming a new surface 1a in the tempered glass 1. Hereinafter, the glass with the new surface 1a is referred to as the "second tempered glass." As described above, when the removal amount Δt is smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3, a portion of the compressive stress layer caused by the K ions remains on the new surface 1a.

[0140] The removal step S5 reduces the compressive stress value (maximum compressive stress value) CS2 of the compressive stress layer 2 on the new surface 1a of the second tempered glass compared to the compressive stress value of the surface 1a0 before the removal step S5. The compressive stress value CS2 of the new surface 1a after the removal step S5 and before the post-removal ion exchange step S7 is 80 MPa or greater, preferably 100 MPa or greater, and more preferably 150 MPa or greater or 200 MPa or greater. Furthermore, the compressive stress value of the new surface 1a is adjusted to less than 700 MPa, 600 MPa or less, 500 MPa or less, or 400 MPa or less, depending on the amount Δt removed from the tempered glass 1 in the removal step S5.

[0141] By forming a new surface 1a in the second strengthened glass during the removal step S5, the depth (diffusion depth) of the compressive stress layer caused by K ions formed in the second strengthened glass is reduced according to the removal amount Δt. The diffusion depth DOL2 of the K ions remaining in the compressive stress layer 2 of the second strengthened glass after the removal step S5 (and before the post-removal ion exchange step S7) is preferably 0.02% to 3.00% of the thickness T1 of the second strengthened glass, and more preferably 0.05% to 2.00% of the thickness T1.

[0142] In the second inspection step S6, the newly formed surface 1a of the second tempered glass is inspected for remaining defects. Alternatively, the second inspection step S6 may not only inspect for defects but also inspect whether the dimensions of the second tempered glass, such as thickness, meet specified criteria. If defects remain in the second tempered glass, the second tempered glass is subjected to the removal step S5 again, followed by the second inspection step S6. If the second tempered glass meets the defect and dimensional criteria set in the second inspection step S6, the subsequent post-removal ion exchange step S7 is performed. On the other hand, if the second tempered glass does not meet the defect and dimensional criteria set in the second inspection step S6, the second tempered glass is subjected to the removal step S5 again, followed by the second inspection step S6.

[0143] In the post-removal ion exchange step S7 , the second glass for strengthening is strengthened so that the first peak P1 , the first valley B1 , the second peak P2 , the second valley B2 and other strengthening characteristics of the stress curve fall within the above-mentioned numerical ranges.

[0144] In the post-removal ion exchange step S7, the second tempered glass that has undergone the second inspection step S6 is subjected to an ion exchange treatment. Specifically, in the post-removal ion exchange step S7, the second tempered glass, having a new surface 1a formed in the removal step S5, is immersed in a treatment tank filled with a molten salt containing K ions and Li ions. While the second tempered glass is immersed in (contacting) the molten salt, it is maintained at a predetermined temperature for a predetermined time, thereby subjecting the new surface 1a of the second tempered glass to an ion exchange treatment.

[0145] Thus, the Li ions in the molten salt undergo reverse ion exchange with the Na ions in the second tempered glass, causing at least a portion of the Na ions to be removed from the second tempered glass. Simultaneously, K ions undergo ion exchange with the Li or Na ions in the second tempered glass. Specifically, the reverse ion exchange relaxes the compressive stress formed in the surface layer of the second tempered glass, while the ion exchange strengthens the second tempered glass, resulting in high compressive stress only near the surface of the surface layer.

[0146] The molten salt used in the post-removal ion exchange step S7 is preferably a mixed salt of LiNO3 and KNO3. The concentration of LiNO3 in the molten salt is preferably lower than the concentration of KNO3 in the molten salt. In detail, the concentration of LiNO3 in the molten salt is preferably 0.1-2%, 0.2-2%, 0.3-2%, 0.4-2%, 0.5-2% in mass%, and the remainder is preferably KNO3. The molten salt may contain NaNO3. In this case, when the concentration of Na ions in the molten salt is converted into NaNO3, it is preferably 5% by mass or less, more preferably 1.8% by mass or less. In addition, relative to the total amount of the molten salt, the concentration of Na ions in the molten salt is preferably 5000 mass ppm or less.

[0147] The Li ion concentration in the molten salt is preferably 100 ppm by mass or more relative to the total amount of the molten salt. The concentration of Li ions in the molten salt is calculated by multiplying LiNO 3 expressed in mass % by 0.101.

[0148] The ion exchange treatment temperature in the post-removal ion exchange step S7 is preferably 350 to 480°C, 350 to 450°C, more preferably 360 to 430°C, further preferably 370 to 400°C, 370 to 390°C.

[0149] The ion exchange treatment time in the post-removal ion exchange step S7 is preferably shorter than the ion exchange treatment time in the first ion exchange step S2 and less than the ion exchange treatment time in the second ion exchange step S3. The ion exchange treatment time in the post-removal ion exchange step S7 is preferably 0.2 hours or longer, more preferably 0.3 to 2 hours, 0.4 to 1 hour, and even more preferably 0.5 to 0.75 hours. Without limitation, the ion exchange treatment time in the post-removal ion exchange step S7 can be 0.1 to 200% of the ion exchange treatment time in the second ion exchange step S3, and can preferably be 1 to 200%, 10 to 200%, 50 to 200%, or 50 to 100%. In other words, the ion exchange treatment time in the post-removal ion exchange step S7 can be set to be shorter than the ion exchange treatment time in the second ion exchange step S3.

[0150] The compressive stress value (maximum compressive stress value) CS3 of the compressive stress layer 2 of the surface 1a of the tempered glass 1 formed by the post-removal ion exchange step S7 is an increase from the compressive stress value CS2 of the surface 1a0 before the removal step S5. The compressive stress value CS3 of the surface 1a after the post-removal ion exchange step S7 is 700 MPa or greater, preferably 700 to 1200 MPa.

[0151] In the post-removal ion exchange step S7 , the ion exchange conditions are preferably adjusted so that the absolute value of the difference between the compressive stress value CS3 and the compressive stress CS1 is preferably 100 MPa or less, preferably 50 MPa or less, more preferably 30 MPa or less, or 20 MPa or less.

[0152] Furthermore, in the post-removal ion exchange step S7, the ion exchange conditions are preferably adjusted so that the compressive stress value CS3 is 0.7 to 1.3 times, preferably 0.8 to 1.2 times, and particularly preferably 0.9 to 1.1 times, the compressive stress value CS1. It should be noted that CS3 may be greater than CS1 as long as the strength of the tempered glass 1 is improved.

[0153] By eliminating the post-ion exchange step S7, the depth of the compressive stress layer 2 in the strengthened glass 1 is increased. The diffusion depth DOL3 of K ions in the compressive stress layer 2 of the strengthened glass 1 after eliminating the post-ion exchange step S7 is preferably 0.02% to 3.00% of the thickness T1 of the strengthened glass 1, and more preferably 0.05% to 2.00% of the thickness T1.

[0154] In the third inspection step S8, the tempered glass 1 formed in the post-removal ion exchange step S7 is inspected for defects and subjected to stress curve measurement. Tempered glass 1 becomes a product if it meets the criteria determined in the third inspection step S8.

[0155] According to the method for manufacturing the tempered glass 1 of the present embodiment described above, the surface (main surface 1a0) of the tempered glass 1 is removed in the removal step S5, thereby removing minute defects formed on the surface. While the compressive stress value of the compressive stress layer 2 on the new surface (new main surface 1a) formed by the removal step S5 is reduced, the compressive stress value of the surface (main surface 1a) of the tempered glass 1 can be adjusted to 700 MPa or higher by performing the post-removal ion exchange step S7.

[0156] <Second embodiment>

[0157] Figure 5 The second embodiment of the present invention is shown. The method for producing the tempered glass 1 of this embodiment differs from the first embodiment in that it includes a post-removal preliminary ion exchange step S7 a performed after the second inspection step S6 and before the post-removal ion exchange step S7 .

[0158] In the post-removal preliminary ion exchange step S7a, the second tempered glass, which has undergone the removal step S5 and the second inspection step S6, is immersed in a treatment tank filled with a third molten salt. Specifically, the second tempered glass is brought into contact with the third molten salt, and the Li ions in the second tempered glass are ion-exchanged with the Na ions in the third molten salt. Furthermore, the Na ions in the second tempered glass are ion-exchanged with the K ions in the third molten salt.

[0159] In the post-removal preliminary ion exchange step S7a, the region into which Na ions are introduced into the second tempered glass is preferably a region from the new surface 1a of the second tempered glass to a depth of 10% or more of the thickness T1, and more preferably a region from the surface of the second tempered glass to a depth of 12% or more, 14% or more, 15% or more, or 15% or more and 40% or less of the thickness T1.

[0160] The third molten salt used in the post-removal preliminary ion exchange step S7a is preferably a mixed salt of NaNO3 and KNO3. The concentration of NaNO3 in the third molten salt is preferably substantially equal to the concentration of NaNO3 in the first molten salt. Here, "substantially equal concentration" means that the difference (absolute value) between the concentrations is 1% or less. Similarly, the concentration of KNO3 in the third molten salt is preferably substantially equal to the concentration of KNO3 in the first molten salt.

[0161] In this embodiment, the second tempering glass is immersed in the treatment tank containing the third molten salt as described above. However, the method of performing the post-removal preliminary ion exchange step S7a is not limited to this embodiment. For example, in the post-removal preliminary ion exchange step S7a, the second tempering glass that has undergone the second inspection step S6 may be immersed in the treatment tank containing the first molten salt used in the first ion exchange step.

[0162] By using a first molten salt having a concentration of NaNO₃ and KNO₃ substantially equal to the concentration of NaNO₃ and KNO₃ in the third molten salt in the post-removal preliminary ion exchange step S7a, the post-removal preliminary ion exchange step S7a can be performed without requiring a treatment tank for the third molten salt. This reduces the cost of equipment for manufacturing the tempered glass 1 and also saves space. Furthermore, the ion exchange conditions (time and temperature) in the post-removal preliminary ion exchange step S7a can be the same as those in the first ion exchange step S2.

[0163] The concentration of NaNO3 in the third molten salt is preferably 20% or more by mass, and the concentration of KNO3 in the first molten salt is preferably less than 90% by mass. However, the present invention is not limited thereto. The concentration of NaNO3 in the third molten salt is preferably 100-10%, 100-20%, 100-30%, 100-40%, or 100-50% by mass, and the remainder is preferably KNO3. It should be noted that the third molten salt may be a composition containing only NaNO3 but not KNO3. In addition, the third molten salt may contain LiNO3.

[0164] In addition, the Li ion concentration in the third molten salt is preferably ±2000 ppm in terms of Li ions alone.

[0165] The ion exchange treatment temperature in the post-removal preliminary ion exchange step S7a is preferably 350 to 480°C, more preferably 360 to 430°C, further preferably 370 to 400°C or 370 to 390°C.

[0166] The ion exchange treatment time in the post-removal preliminary ion exchange step S7a is preferably 10 to 100% of the ion exchange treatment time in the first ion exchange step S2, and more preferably 50 to 100%.

[0167] The post-removal ion exchange step S7 of this embodiment is performed after the post-removal preliminary ion exchange step S7a. In the post-removal ion exchange step S7, as in the first embodiment, the second tempering glass is immersed in a treatment tank containing a molten salt. In this case, the concentration of KNO3 in the molten salt used in the post-removal ion exchange step S7 is preferably substantially equal to the concentration of KNO3 in the second molten salt. In addition, the concentration of LiNO3 in the molten salt used in the post-removal ion exchange step S7 is preferably substantially equal to the concentration of LiNO3 in the second molten salt.

[0168] In this embodiment, as described above, in the post-removal ion exchange step S7, the second tempering glass is immersed in a treatment tank containing a predetermined molten salt. However, the method of the post-removal ion exchange step S7 is not limited to this embodiment. For example, in the post-removal ion exchange step S7, the second tempering glass that has undergone the post-removal preliminary ion exchange step S7a may be immersed in a treatment tank containing the second molten salt used in the second ion exchange step.

[0169] Thus, in the post-removal ion exchange step S7, by using a second molten salt having a concentration of LiNO₃ and KNO₃ substantially equal to the concentration of LiNO₃ and KNO₃ in the molten salt, the post-removal ion exchange step S7 can be performed even without preparing a dedicated treatment tank for the post-removal ion exchange step S7. This can reduce the cost of the manufacturing equipment for the tempered glass 1 and also achieve space saving.

[0170] In this case, the ion exchange treatment time in the post-removal ion exchange step S7 is preferably 0.1 to 200% of the ion exchange treatment time in the second ion exchange step S3, and more preferably 1 to 200%, 10 to 200%, 50 to 200%, or 50 to 100%.

[0171] The third inspection step S8 performed after the post-removal ion exchange step S7 is performed in the same manner as the third inspection step S8 in the first embodiment.

[0172] In this embodiment, the ion exchange conditions of the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and / or the post-removal ion exchange step S7) are preferably adjusted so that the absolute value of the difference between the stress CSb in the first valley of the strengthened glass 1 obtained after the post-removal ion exchange step S7 and the stress CSb in the first valley of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5 is preferably 50 MPa or less, more preferably 40 MPa or less, or 30 MPa or less.

[0173] In the case where no valley is clearly observed, CSb may adopt compressive stress in the end of potassium ion diffusion or DOL.

[0174] Furthermore, it is preferable to adjust the ion exchange conditions of the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and / or the post-removal ion exchange step S7) so that the stress CSb in the first valley of the strengthened glass 1 obtained after the post-removal ion exchange step S7 becomes 0.5 to 2.0 times, preferably 0.7 to 1.5 times, more preferably 0.7 to 1.5 times, and particularly preferably 0.8 to 1.3 times the stress CSb in the first valley of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5.

[0175] It should be noted that, as long as the strength of the strengthened glass 1 is improved, the stress CSb in the first valley of the strengthened glass 1 obtained after the removal of the post-ion exchange step S7 is allowed to be greater than the stress CSb in the first valley of the strengthened glass 1 after the second ion exchange step S3 and before the removal of the step S5.

[0176] In this embodiment, the ion exchange conditions of the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and / or the post-removal ion exchange step S7) are preferably adjusted so that the absolute value of the difference between the stress CSp at the second peak of the strengthened glass 1 obtained after the post-removal ion exchange step S7 and the stress CSp at the second peak of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5 is preferably 50 MPa or less, more preferably 30 MPa or less, or 20 MPa or less.

[0177] When no peak is clearly observed, the difference in CSp can be replaced by comparing the average difference in stress values at depth positions DOL to DOC.

[0178] Furthermore, it is preferable to adjust the ion exchange conditions of the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and / or the post-removal ion exchange step S7) so that the stress CSp at the first peak of the strengthened glass 1 obtained after the post-removal ion exchange step S7 becomes 0.5 to 2.0 times, preferably 0.7 to 1.5 times, more preferably 0.7 to 1.5 times, and particularly preferably 0.8 to 1.3 times the stress CSp at the second peak of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5.

[0179] It should be noted that, as long as the strength of the strengthened glass 1 is improved, the stress CSp at the second peak of the strengthened glass 1 obtained after the removal of the post-ion exchange step S7 is allowed to be greater than the stress CSp at the second peak of the strengthened glass 1 after the second ion exchange step S3 and before the removal of the step S5.

[0180] According to the method for producing the tempered glass 1 of the second embodiment described above, even if the removal step S5 involves removing the glass deep into the glass, reducing not only the compressive stress CS1 of the surface layer but also the compressive stresses CSb of the first valley B1 and CSp of the second stress P2, the inclusion of the post-removal preliminary ion exchange step S7a allows ion exchange to be performed again deep into the glass to restore the compressive stresses of CSb and CSp. Consequently, the strength characteristics of the tempered glass 1 lost in the removal step S5 can be appropriately restored (reproduced).

[0181] <Modification>

[0182] It should be noted that the present invention is not limited to the configuration of the above-described embodiment, nor is it limited to the above-described effects. The present invention can be modified in various ways without departing from the spirit of the present invention.

[0183] In the above embodiment, an example is shown in which the second ion exchange step S3 is performed after the first ion exchange step S2 is performed, but the present invention is not limited to this configuration. The first ion exchange step S2 and the second ion exchange step S3 may be performed simultaneously.

[0184] In the above embodiment, the case where the Li ions in the tempering glass are exchanged with the Na ions in the first molten salt in the first ion exchange step S2 is exemplified. However, the first ion exchange step S2 may alternatively be a method of exchanging the Na ions in the tempering glass with the K ions in the molten salt.

[0185] In the above embodiment, a single ion exchange treatment is performed after the removal step as the post-removal ion exchange step. However, a preliminary ion exchange treatment (post-removal preliminary ion exchange step) may be added after the removal step and before the post-removal ion exchange step. That is, multiple ion exchange treatments, including a post-removal preliminary ion exchange step, may be performed after the removal step and before the post-removal ion exchange step. The composition and temperature of the molten salt used in the post-removal preliminary ion exchange step may be the same as those in the first ion exchange step, and the ion exchange treatment time may be less than the ion exchange treatment time in the first ion exchange step.

[0186] In the above embodiment, the surface 1a0 of the tempered glass 1 is removed in the removal step S5, thereby reducing the compressive stress value in the compressive stress layer 2 of the tempered glass 1. Another method for reducing the compressive stress value is to perform a reverse ion exchange treatment on the tempered glass 1 that has undergone the first ion exchange step S2 and the second ion exchange step S3. The removal step S5 of the present invention does not include a method of eliminating the compressive stress of the tempered glass 1 through such a reverse ion exchange treatment.

[0187] In the second embodiment, in the post-removal preliminary ion exchange step S7a, the concentrations of NaNO3 and KNO3 in the third molten salt are substantially equal to the concentrations of NaNO3 and KNO3 in the first molten salt. However, the present invention is not limited thereto and their concentrations may be different.

[0188] In the second embodiment, in the post-removal ion exchange step S7, the concentrations of LiNO3 and KNO3 in the molten salt are substantially equal to the concentrations of LiNO3 and KNO3 in the first molten salt. However, the present invention is not limited thereto and their concentrations may be different.

[0189] <Third embodiment>

[0190] The first embodiment described above can be modified as follows to form a third embodiment. Figure 6 This is a flowchart illustrating a method for manufacturing tempered glass according to a third embodiment. In the method for manufacturing tempered glass according to the third embodiment, information about the tempered glass 1 after the second ion exchange step S3 and information about the second tempered glass after the removal step S5 can be obtained before the post-removal ion exchange step S7. Based on this information, ion exchange conditions in the post-removal ion exchange step S7 can be set. Examples of ion exchange conditions include the ion exchange treatment time and the ion exchange treatment temperature in the post-removal ion exchange step S7. The following describes the case where the ion exchange treatment time is set as an ion exchange condition.

[0191] The first inspection step S4 in the method for manufacturing the tempered glass 1 includes, in addition to inspecting the tempered glass 1 formed through the first ion exchange step S2 and the second ion exchange step S3 for defects, a first measurement step S41 for acquiring information related to stress in the tempered glass 1, and a planned removal amount setting step S42 for setting a planned removal amount Δt0 to be removed from the tempered glass 1.

[0192] Furthermore, the second inspection step S6 in the present method includes, in addition to inspecting whether defects remain on the new surface 1 a formed on the second strengthening glass, a second measurement step S61 for acquiring information related to the stress of the second strengthening glass, a removal amount determination step S62 for determining the removal amount Δt of the strengthened glass 1 actually removed in the removal step S5, and an ion exchange condition setting step S63 for setting ion exchange conditions in the post-removal ion exchange step S7.

[0193] Furthermore, the third inspection step S8 in this method includes, in addition to inspecting the presence or absence of defects in the tempered glass 1 formed in the post-removal ion exchange step S7 , a third measurement step S81 for acquiring information on stress in the tempered glass 1 .

[0194] In the first measuring step S41 of the first inspection step S4, information related to the stress of the tempered glass 1 after the second ion exchange step S3 is measured using a measuring device. A surface stress meter (e.g., FSM-6000LE or SLP-1000 manufactured by Orihara Manufacturing Co., Ltd.) is preferably used as the measuring device used in the first measuring step S41.

[0195] The surface stress meter generates optical interference fringes on the tempered glass 1, captures an interference fringe image containing the optical interference fringes, and stores it as image data. Based on this image data, the surface stress meter can measure the stress curve (stress distribution) of the tempered glass 1. Information related to the stress of the tempered glass 1 includes, in addition to the interference fringe image, the diffusion depth DOL1 of the K ions introduced into the tempered glass 1. Furthermore, information related to the stress of the tempered glass 1 may include information such as the first peak P1, first valley B1, second peak P2, second valley B2 in the aforementioned stress curve, and their depths.

[0196] In addition, in the first measurement step S41, the thickness of the tempered glass 1 is measured. The thickness of the tempered glass 1 is measured by a measuring device such as a micrometer or a laser displacement meter.

[0197] In the planned removal amount setting step S42, for example, if a defect is detected in the tempered glass 1 in the first inspection step S4, a planned removal amount Δt0 to be removed from the tempered glass 1 to remove the defect is set based on the defect information (such as the type, size, and depth of the defect) and information such as the thickness of the tempered glass 1.

[0198] Furthermore, in the predetermined removal amount setting step S42, the predetermined removal amount Δt0 can be set independently of the results of the first measurement step S41. For example, in the preparation step (the step of manufacturing the tempered glass), if it is clear that there is a consistent trend in the occurrence of defects in the tempered glass, the predetermined removal amount Δt0 can be uniformly set for a plurality of tempered glasses 1 without utilizing the measurement results of the first measurement step S41.

[0199] In the second measurement step S61 of the second inspection step S6, information related to the stress of the second tempered glass is measured using the measurement device (surface stress meter) used in the first measurement step S41. Specifically, similar to the first measurement step S41, the measurement device generates optical interference fringes on the second tempered glass, captures the interference fringe image, and stores the image data as stress-related information. Information related to the stress of the second tempered glass includes, in addition to the interference fringe image, the diffusion depth DOL2 of K ions remaining in the second tempered glass.

[0200] In the second measuring step S61 , the thickness of the second tempering glass can be measured by the same method as in the first measuring step S41 .

[0201] In the removal amount determination step S62 , the amount (removal amount) Δt actually removed from the tempered glass 1 in the removal step S5 can be calculated based on the difference between the thickness of the second tempering glass and the thickness of the tempered glass 1 measured in the first measurement step S41 .

[0202] Determination of the removal amount Δt is not limited to the above-described method. In the removal amount determination step S62, for example, the difference (DOL1-DOL2) between the diffusion depth DOL2 of K ions in the second tempered glass measured in the second measurement step S61 and the diffusion depth DOL1 of K ions measured in the first measurement step S41 can be determined as the removal amount Δt.

[0203] In the ion exchange condition setting step S63, the ion exchange conditions for the post-removal ion exchange step S7 are set based on the measurement results of the first measurement step S41 and the second measurement step S61. In the ion exchange condition setting step S63, the ion exchange treatment time as the ion exchange condition is set based on a pre-prepared function. An example of this function is the following formula (1).

[0204] Tx=a(1-e -b×x )…(1)

[0205] In formula (1), Tx represents the ion exchange treatment time, and a and b represent constants that vary depending on various strengthening conditions, such as the second ion exchange treatment time and the strengthening temperature, and the thickness of the strengthened glass 1. A preferred range for a is, for example, from the ion effect treatment time in the second ion exchange step to twice the ion exchange treatment time in the second ion exchange step. A preferred range for b is, for example, 1 to 5.

[0206] The variable x in formula (1) is the ratio (Δt / DOL1) of the removal amount Δt of one (one) of the front and back main surfaces of the second tempered glass determined in the removal amount determination step S62 to the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3.

[0207] Formula (1) was obtained by performing a production test on a plurality of samples of tempered glass prepared in advance. The production test was performed as follows.

[0208] First, each sample was subjected to a first ion exchange step and a second ion exchange step to produce a tempered glass. Next, information related to stress of each tempered glass was obtained.

[0209] Then, a removal step is performed with different predetermined removal amounts set for each tempered glass. Next, information related to the stress of the second tempered glass is obtained. Then, a post-removal ion exchange step is performed with different ion exchange conditions (ion exchange treatment time) set for each second tempered glass. Finally, information related to the stress of the tempered glass after the post-removal ion exchange step is obtained.

[0210] Next, the stress information obtained for the tempered glass after the post-removal ion exchange step is verified. Specifically, the stress information for each tempered glass is checked to see if it meets a pre-set benchmark. Next, based on the data for the tempered glass that meets the benchmark, a function is created using analysis software on a processing device (e.g., a PC) based on the removal amount Δt, DOL1 after the second ion exchange step, DOL2 after the removal step, and the ion exchange treatment time in the post-removal ion exchange step S7 for each sample. The above steps yield Equation (1).

[0211] The ion exchange condition setting step S63 is executed by a calculation processing device capable of performing calculation processing of the formula (1).

[0212] In the third measurement step S81 of the third inspection step S8, information related to stress in the tempered glass 1 after excluding the post-ion exchange step S7 is measured using a measuring device (surface stress gauge). Then, in the third inspection step S8, a determination is made as to whether the measured stress information satisfies a reference value (determination step). This determination step is performed, for example, by a processing unit.

[0213] The method of each embodiment and modification example described above is not limited thereto, and the removal amount Δt may not be set based on the presence or absence of defects. In this case, the removal amount Δt may be set based on various information obtained in the manufacturing process (preparatory process) of the tempered glass.

[0214] <Fourth embodiment>

[0215] In the third embodiment described above, the ion exchange treatment time is set based on the removal amount Δt. However, a modification may be made as follows, in which the ion exchange treatment time is set without determining the removal amount Δt. That is, in the ion exchange condition setting step S63, the ion exchange conditions may be set without using the above-mentioned formula (1). Specifically, in the ion exchange condition setting step S63, the ion exchange treatment time may be set based on, for example, an interference fringe image.

[0216] In the ion exchange condition setting step S63, the ion exchange treatment time of the post-removal ion exchange step S7 can be set based on the interference fringe image data of the tempered glass 1 obtained in the first measurement step S41 and the interference fringe image data obtained in the second measurement step S61. In this case, the removal amount determination step S62 can be omitted. Figures 7 to 10 A specific embodiment of the ion exchange condition setting step S63 will be described.

[0217] Figure 7 Schematic diagram of an interference fringe image (hereinafter referred to as a “first interference fringe image”) of the tempered glass 1 after the second ion exchange step S3 . Figures 8 to 10 Schematic diagram of the interference fringe image of the second tempering glass obtained after step S5 is removed (hereinafter referred to as “second interference fringe image”).

[0218] like Figure 7 As shown, the first interference fringe image includes a first area A1 and a second area A2 (the same in the second interference fringe image). Each area A1 and A2 includes a plurality of bright and dark lines L1a-L1c, L2a-L2c, and a boundary BP of the light interference fringes. The measurement device can generate this first interference fringe image and calculate the stress value and depth of the compressive stress layer of the strengthened glass based on the distance D0 between the dark lines L1a-L1c (or bright lines) in the first area A1 and the dark lines L2a-L2c in the second area A2.

[0219] Each area A1, A2 includes, for example, three dark lines L1a to L1c, L2a to L2c. Hereinafter, the three dark lines L1a to L1c, L2a to L2c in each area A1, A2 are referred to as first dark lines L1a, L2a, second dark lines L1b, L2b, and third dark lines L1c, L2c, respectively.

[0220] exist Figure 7 In the diagram, the distance between the boundary portion BP of the first area A1 and the first dark line L1a (hereinafter referred to as the "first distance") is indicated by symbol D11, the distance between the first dark line L1a and the second dark line L1b (hereinafter referred to as the "second distance") is indicated by symbol D12, and the distance between the second dark line L1b and the third dark line L1c (hereinafter referred to as the "third distance") is indicated by symbol D13. Similarly, the first distance between the boundary portion BP of the second area A2 and the first dark line L2a is indicated by symbol D21, the second distance between the first dark line L2a and the second dark line L2b is indicated by symbol D22, and the third distance between the second dark line L2b and the third dark line L2c is indicated by symbol D23.

[0221] like Figure 8As shown, the first and second regions A1 and A2 of the second interference fringe image, like the first interference fringe image, include first dark lines L1a, L2a through third dark lines L1c, L2c and a boundary portion BP. In this second interference fringe image, the first distances D11, D21 through third distances D13, D23 of the dark lines L1a through L1c, L2a through L2c differ from the first distances D11, D21 through third distances D11, D23 of the first interference fringe image.

[0222] In this case, the distances D11 to D13 and D21 to D23 in the second interference fringe image change by performing the post-removal ion exchange step S7. In the ion exchange condition setting step S63, the ion exchange treatment time of the post-removal ion exchange step S7 is set so that the distances D11 to D13 and D21 to D23 in the second interference fringe image are equal to the distances D11 to D13 and D21 to D23 in the first interference fringe image. If the number of dark lines in the second interference fringe image is three, the ion exchange treatment time of the post-removal ion exchange step S7 is preferably 0.1 to 50% of the ion exchange treatment time of the second ion exchange step S3, and more preferably 10 to 50% or 20 to 45%.

[0223] It should be noted that in Figure 8 In the example shown in FIG5 , if the ion exchange treatment time of the post-ion exchange step S7 exceeds 50% of the ion exchange treatment time of the second ion exchange step S3, when an interference fringe image of the tempered glass 1 after the post-ion exchange step S7 is obtained, the number of dark lines included in the image is greater than the number of dark lines (3) in the first interference fringe image, which is not preferable.

[0224] exist Figure 9 In the example shown, each area A1 and A2 of the second interference fringe image includes two dark lines, L1a, L1b, L2a, and L2b. In the ion exchange condition setting step S63, the ion exchange conditions (ion exchange treatment time) are set so that the two dark lines L1a, L1b, L2a, and L2b become three dark lines after the post-removal ion exchange step S7, and so that the positions of these three dark lines coincide with the positions of the three dark lines L1a to L1c and L2a to L2c in the first interference fringe image. In other words, in this example, the post-removal ion exchange step S7 changes the number of dark lines in the interference fringe image of the tempered glass 1 from two to three, and the ion exchange conditions (ion exchange treatment time) are set so that the first, second, and third distances of these three dark lines are equal to the first distances D11, D21, second distances D12, D22, and third distances D13, D23, respectively, in the corresponding first interference fringe image.

[0225] If the Figure 9 As in the example shown in FIG. 1 , when the number of dark lines L1a, L1b, L2a, and L2b included in the second interference fringe image is two, the ion exchange treatment time of the post-removal ion exchange step S7 is preferably 50 to 100% of the ion exchange treatment time of the second ion exchange step S3.

[0226] exist Figure 10 In the example shown, each area A1 and A2 of the second interference fringe image includes one dark line L1a and one dark line L2a. In the ion exchange condition setting step S63, the ion exchange conditions (ion exchange treatment time) are set so that the one dark line L1a and one dark line L2a are removed and converted into three dark lines by performing the post-ion exchange step S7, and so that the positions of these three dark lines coincide with the positions of the three dark lines L1a to L1c and L2a to L2c in the first interference fringe image.

[0227] Like the Figure 10 As in the example of , when the number of dark lines included in the second interference fringe image is one, the ion exchange treatment time of the post-removal ion exchange step S7 is preferably 100 to 150% of the ion exchange treatment time of the second ion exchange step S3.

[0228] As described above, in the ion exchange condition setting step S63, the optimal ion exchange treatment time can be set based on the interference fringe pattern of the second tempering glass after step S5. The ion exchange treatment time is obtained by performing manufacturing tests on a plurality of tempering glass samples prepared in advance.

[0229] The manufacturing test was conducted as follows: First, each sample was subjected to a first ion exchange step and a second ion exchange step to produce a tempered glass. Next, information related to stress of each tempered glass was obtained.

[0230] Then, a removal step is performed with different removal amounts set for each tempered glass. Next, information related to the stress of the second tempered glass after the removal step is obtained. Next, a post-removal ion exchange step is performed with different ion exchange conditions (ion exchange treatment time) set for each second tempered glass. Next, information related to the stress of the tempered glass after the post-removal ion exchange step is obtained.

[0231] Then, in the first interference fringe image, the second interference fringe image and the interference fringe image after the post-ion exchange process, the positions and distances of the dark lines of each light interference fringe are compared and verified. If the state of the light interference fringes in the first interference fringe image is consistent with the state of the light interference fringes in the interference fringe image after the post-ion exchange process, it can be said that the ion exchange treatment time in the post-ion exchange process is optimal relative to the removal amount Δt. The relationship between the removal amount Δt obtained in this way and the optimal ion exchange conditions can be constructed as a database. The database is stored in an operation processing device (such as a computer such as a PC) that can execute the ion exchange condition setting process S63. By operating the operation processing device, in the ion exchange condition setting process S63, the ion exchange conditions in the post-ion exchange process can be set based on the second interference fringe image.

[0232] Example

[0233] Hereinafter, the tempered glass of the present invention will be described based on examples. It should be noted that the following examples are merely illustrative and the present invention is not limited to the following examples.

[0234] The samples were prepared as follows. First, a tempered glass plate was prepared for ion exchange treatment. The tempered glass plate had a glass composition, by mass%, of 51.6% SiO2, 27.9% Al2O3, 0.3% B2O3, 0.6% K2O, 7.5% Na2O, 3.3% Li2O, 0.3% MgO, 8.4% P2O5, and 0.1% SnO2.

[0235] Glass raw materials are prepared to form the above-mentioned composition and melted in a platinum kettle at 1600°C for 21 hours. The resulting molten glass is then formed by flowing down from a refractory forming body using an overflow downdraw method. The thus-formed glass ribbon is cut into predetermined sizes to obtain a strengthened glass plate as a test piece. The strengthened glass plate has a thickness of 0.55, 0.7, or 0.8 mm. Next, the strengthened glass is immersed in a molten salt bath and subjected to an ion exchange treatment based on a first ion exchange step and a second ion exchange step to obtain a strengthened glass plate.

[0236] In the first ion exchange step, the weight concentration ratio of KNO₃ to NaNO₃ in the molten salt was set to 40(%):60(%) or 70(%):30(%). Furthermore, the ion exchange treatment temperature of the molten salt in the first ion exchange step was 380°C. The ion exchange treatment time in the first ion exchange step was set to 90 minutes or 180 minutes.

[0237] In the second ion exchange step, each test piece was subjected to ion exchange using a molten salt containing different weight ratios of KNO₃, NaNO₃, and LiNO₃. The ion exchange time in the second ion exchange step was varied for each test piece. The ion exchange temperature of the molten salt in the second ion exchange step was 380°C.

[0238] Then, each test piece was subjected to a removal step. In the removal step, both main surfaces of each test piece were removed by grinding. At this time, the amount of removal (grinding amount) of each main surface in each test piece was made different.

[0239] Then, a post-removal preliminary ion exchange step was performed on some of the test pieces. In this post-removal preliminary ion exchange step, the weight concentration ratio of KNO₃ to NaNO₃ in the molten salt was set to 40%:60%. The ion exchange treatment time in this post-removal preliminary ion exchange step was varied for each test piece. The ion exchange treatment temperature of the molten salt in this post-removal preliminary ion exchange step was 380°C.

[0240] Each test piece was then subjected to a post-removal ion exchange step. The ion exchange treatment time in the post-removal ion exchange step was varied for each test piece. The ion exchange treatment temperature of the molten salt in the post-removal ion exchange step was 380°C.

[0241] The stress curve of each test piece was then measured. The stress curve was measured using a surface stress meter FSM-6000LE and SLP-1000 manufactured by Orihara Manufacturing Co., Ltd. The measurements were performed with a refractive index of 1.50 and a photoelastic constant of 28.9 [(nm / cm) / MPa] for each test piece.

[0242] Tables 1 to 23 show the conditions for each of the above-mentioned steps and the results of the measurement of the strengthening properties. Of the sample pieces Nos. 1 to 174 shown in Tables 1 to 23, Nos. 1 to 8, 11, 12, 15, 16, 19, 20, 23 to 47, 84 to 110, 112 to 115, 117 to 164, and 166 to 174 represent examples in which a post-removal ion exchange step was performed after the second ion exchange step, rather than a post-removal preliminary ion exchange step. Nos. 52 to 83 represent examples in which a post-removal ion exchange step was performed after the post-removal preliminary ion exchange step. Furthermore, Nos. 9, 10, 13, 14, 17, 18, 21, 22, 48 to 51, 111, 116, 165, and 170 represent comparative examples. For the comparative example, the test pieces of sample Nos. 48 to 51 were not polished (removal step) after the second ion exchange step. In Tables 1 to 23, "grinding amount" is the value obtained by adding up the grinding amounts of each main surface (both sides) in each test piece. The grinding amount of one main surface is equal to the grinding amount of the other main surface. In addition, the grinding amounts shown in Tables 1 to 11 are theoretical estimates calculated based on the grinding rate and grinding time of the sample, and the strict actual grinding amount may contain deviations. In Tables 1 to 7, 12 to 20, "Δt" is the removal amount of tempered glass in the removal process (DOL1-DOL2). In addition, the value of "Δt / DOL1" is expressed as a percentage.

[0243] Among Samples No. 1 to 174, the thickness of the tempering glass of No. 1 to 120 was 0.7 mm, the thickness of the tempering glass of No. 121 to 144 was 0.55 mm, and the thickness of the tempering glass of No. 145 to 174 was 0.8 mm.

[0244] "DOC" in the table is the DOLzero value in the above embodiment. "CT" in the table is the maximum tensile stress value (CTmax) at the center of the test piece in the plate thickness direction. "CS50" in the table is the compressive stress value at a depth of 50 μm from the surface of the test piece.

[0245] The "DOC Reproducibility" in the table is the ratio of the DOC of the Examples or Comparative Examples that underwent a removal step and a post-removal ion exchange step to the DOC of the Comparative Example that did not undergo the removal step. Specifically, the DOC reproducibility for Nos. 1-10, 23-26, 39-47, 52-55, and 68-71 is expressed as a percentage by dividing the measured DOC by the DOC (150.5 μm) of Comparative Example No. 48, produced under the same conditions. Similarly, the DOC reproducibility for Nos. 11-14, 27-30, 56-59, and 72-75 is the measured DOC divided by the DOC (146.2 μm) of Comparative Example No. 49. The DOC reproducibility for Nos. 15-18, 31-34, 60-63, and 76-79 is the measured DOC divided by the DOC (143.0 μm) of Comparative Example No. 50. The DOC reproducibility of Nos. 19 to 22, 35 to 38, 64 to 67, and 80 to 83 is the value obtained by dividing the measured values by the DOC (140.4 μm) of the corresponding comparative example, No. 51. Similarly, the DOC reproducibility of Nos. 84 to 110, 112 to 115, 117 to 164, 166 to 169, and 171 to 174 is the value obtained by dividing the measured values by the DOC of the corresponding comparative example (not shown).

[0246] The "CT Reproducibility" in the table is the ratio of the CT of the Examples or Comparative Examples that underwent the removal step and the post-removal ion exchange step to the CT of the Comparative Example that did not undergo the removal step. Specifically, the CT reproducibility for Nos. 1-10, 23-26, 39-47, 52-55, and 68-71 is expressed as a percentage by dividing the measured DOC by the CT (-60.0 MPa) of Comparative Example No. 48, produced under the same conditions. The CT reproducibility for Nos. 11-14, 27-30, 56-59, and 72-75 is expressed as a percentage by dividing the measured DOC by the CT (-63.4 MPa) of Comparative Example No. 49. The CT reproducibility for Nos. 15-18, 31-34, 60-63, and 76-79 is expressed as a percentage by dividing the measured DOC by the CT (-63.6 MPa) of Comparative Example No. 50. The CT reproducibility of Nos. 19-22, 35-38, 64-67, and 80-83 is the value obtained by dividing the measured values by the CT (-66.7 MPa) of the corresponding comparative example, No. 51. Similarly, the CT reproducibility of Nos. 84-110, 112-115, 117-164, 166-169, and 171-174 is the value obtained by dividing the measured values by the CT of the corresponding comparative example (not shown).

[0247]

Table 1

[0248]

[0249]

Table 2

[0250]

[0251]

Table 3

[0252]

[0253]

Table 4

[0254]

[0255]

Table 5

[0256]

[0257]

Table 6

[0258]

[0259]

Table 7

[0260]

[0261]

Table 8

[0262]

[0263]

Table 9

[0264]

[0265]

Table 10

[0266]

[0267]

Table 11

[0268]

[0269]

Table 12

[0270]

[0271]

Table 13

[0272]

[0273]

Table 14

[0274]

[0275]

Table 15

[0276]

[0277] Table 16

[0278]

[0279]

Table 17

[0280]

[0281]

Table 18

[0282]

[0283]

Table 19

[0284]

[0285] Table 20

[0286]

[0287] Table 21

[0288]

[0289] Table 22

[0290]

[0291] Table 23

[0292]

[0293] The measurement results showed that, in all examples, the post-removal ion exchange step achieved strengthening properties comparable to those of the comparative example, which was a product without polishing. In particular, in the example that performed the post-removal preliminary ion exchange step, various strengthening properties could be measured even when the polishing amount was increased to 10 μm or more, and the DOC and CT reproduction rates showed relatively high values.

[0294] As an example, in Figure 11 The stress curves of samples No. 1, No. 4, and No. 48 are shown in FIG. The stress curves of the tempered glasses of samples No. 1 and No. 4 as examples clearly have a first peak, a first valley, a second peak, and a second valley, similar to the stress curves of sample No. 48 as a comparative example in which the removal process was not performed. Figure 11 As shown, it can be seen that the Examples were sufficiently strengthened to be equal to or better than the Comparative Examples by carrying out the post-removal ion exchange step.

[0295] exist Figure 12 The stress curves of samples No.6, No.48, No.57 and No.73 are shown in FIG. Figure 12As shown, the stress curve of Sample No. 57, an example of an embodiment that performed both the post-removal preliminary ion exchange step and the post-removal ion exchange step, clearly has a larger first valley and a larger second peak than that of Sample No. 6, an example of an embodiment that performed the post-removal preliminary ion exchange step without performing the post-removal preliminary ion exchange step, indicating that the deep compressive stress has been appropriately restored. Therefore, performing the post-removal preliminary ion exchange step can appropriately improve the strength of the glass that has been reduced by grinding (the removal step).

Claims

1. A method for producing tempered glass, comprising subjecting glass having a surface to an ion exchange treatment to obtain tempered glass having a compressive stress layer on the surface, wherein: With the following processes: a first ion exchange step of contacting the surface of the glass with a first molten salt to exchange Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of contacting the surface of the glass with a second molten salt to exchange Na ions in the glass with K ions in the second molten salt; a removing step of removing at least a portion of the surface of the strengthened glass after the first and second ion exchange steps have been performed, thereby forming a new surface on the strengthened glass; a post-removal ion exchange step of exchanging Na ions in the tempered glass after the removal step with K ions in a molten salt, thereby making the maximum compressive stress CS3 of the compressive stress layer in the new surface greater than or equal to 700 MPa; an inspection step of inspecting the surface of the tempered glass for defects after performing the first ion exchange step and the second ion exchange step and before the removal step; and a predetermined removal amount setting step of setting a predetermined removal amount to be removed from the surface of the tempered glass after performing the first ion exchange step and the second ion exchange step; If a defect on the surface of the tempered glass is detected in the inspection step, at least a portion of the surface is removed together with the defect in the removal step based on the planned removal amount set in the planned removal amount setting step.

2. The method for producing tempered glass according to claim 1, wherein: further comprising a post-removal preliminary ion exchange step performed after the removal step and before the post-removal ion exchange step, In the post-removal preliminary ion exchange step, the tempered glass after the removal step is brought into contact with a third molten salt, and Li ions in the tempered glass after the removal step are ion-exchanged with Na ions in the third molten salt.

3. The method for producing tempered glass according to claim 2, wherein: The concentration of NaNO 3 in the third molten salt used in the post-removal preliminary ion exchange step is substantially equal to the concentration of NaNO 3 in the first molten salt.

4. The method for producing tempered glass according to claim 2 or 3, wherein: The concentration of KNO 3 in the molten salt used in the post-removal ion exchange step is substantially equal to the concentration of KNO 3 in the second molten salt.

5. The method for producing tempered glass according to claim 2 or 3, wherein: The ion exchange treatment time in the post-removal preliminary ion exchange step is 10% to 100% of the ion exchange treatment time in the first ion exchange step.

6. The method for producing tempered glass according to claim 2 or 3, wherein: The ion exchange treatment time in the post-removal ion exchange step is 50% to 200% of the ion exchange treatment time in the second ion exchange step.

7. The method for producing tempered glass according to any one of claims 1 to 3, wherein: The glass is a sheet glass with a thickness of 0.05 mm to 2.0 mm. By removing the front and back main surfaces of the tempered glass before the post-removal ion exchange step in a region shallower than the compressive stress layer, the maximum compressive stress CS2 of the compressive stress layer in the new surface after the removal step is set to 100 MPa or more.

8. The method for producing tempered glass according to any one of claims 1 to 3, wherein In the removing step, the surface of the tempered glass after the first and second ion exchange steps is polished or etched to remove the glass. The amount Δt removed from the surface in the removal step is smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step.

9. The method for producing tempered glass according to any one of claims 1 to 3, wherein: The removal amount Δt in the removal step is 20 μm or less. The compressive stress CS2 of the compressive stress layer in the new surface after the removal step and before the post-removal ion exchange step is set to less than 700 MPa, The maximum compressive stress CS3 of the compressive stress layer after the post-removal ion exchange step is set to 700 MPa to 1200 MPa.

10. The method for producing tempered glass according to any one of claims 1 to 3, wherein In the tempered glass after the post-removal ion exchange step, a stress distribution obtained by measuring stress in a depth direction from the new surface includes: a first peak where the compressive stress becomes a maximum on the surface; a first valley where the stress decreases gradually from the first peak in the depth direction and becomes a minimum stress; a second peak where the compressive stress increases gradually in the depth direction from the first valley and reaches a maximum value; as well as A second valley where the tensile stress decreases gradually from the second peak in the depth direction to a minimum value, In the post-removal ion exchange step, Na ions in the tempered glass are ion-exchanged with K ions in the molten salt so that the compressive stress CSb of the first valley becomes 10 MPa or more.

11. The method for producing tempered glass according to any one of claims 1 to 3, wherein: The concentration of LiNO 3 in the molten salt used in the post-removal ion exchange step is 0.1% by mass to 2% by mass.

12. The method for producing tempered glass according to any one of claims 1 to 3, wherein: The concentration of Na ions in the molten salt used in the post-removal ion exchange step is 5% by mass or less when converted to NaNO 3 .

13. The method for producing tempered glass according to any one of claims 1 to 3, wherein: The ion exchange treatment temperature in the post-removal ion exchange step is 350°C to 450°C. The ion exchange treatment time in the post-removal ion exchange step is less than or equal to the ion exchange treatment time in the second ion exchange step.

14. The method for producing tempered glass according to any one of claims 1 to 3, wherein: In the second ion exchange step, Na ions in the glass are ion-exchanged with K ions in the second molten salt, and Na ions in the glass are ion-exchanged with Li ions in the second molten salt. The concentration of NaNO3 in the first molten salt is 50% by mass or more, The concentration of KNO3 in the first molten salt is less than 50% by mass. The concentration of LiNO3 in the second molten salt is 0.5% by mass to 5% by mass. The concentration of KNO3 in the second molten salt is 95% to 99.5% by mass. The ion exchange treatment temperature of the first ion exchange step is 350°C to 480°C. The ion exchange treatment temperature of the second ion exchange step is 350°C to 480°C. The ion exchange treatment time of the first ion exchange step is 1 hour to 20 hours. The ion exchange treatment time of the second ion exchange step is shorter than the ion exchange treatment time of the first ion exchange step.

15. The method for producing tempered glass according to any one of claims 1 to 3, wherein: The glass contains, by mass%, 40% to 70% SiO2, 10% to 30% Al2O3, 0% to 3% B2O3, 5% to 25% Na2O, 0% to 5.5% K2O, 0.1% to 10% Li2O, 0% to 6% MgO, and 0% to 15% P2O5 as a glass composition.

16. The method for producing tempered glass according to claim 1, wherein: have: a step of measuring information related to stress of the tempered glass after the removal step and before the post-removal ion exchange step using a measuring device; and an ion exchange condition setting step of setting ion exchange conditions in the post-removal ion exchange step based on the information measured by the measuring device.

17. The method for producing tempered glass according to claim 16, wherein: The measuring device generates optical interference fringes on the tempered glass after the removal step and before the post-removal ion exchange step, and measures stress distribution by capturing an interference fringes image including the optical interference fringes. The information related to the stress includes the interference fringe image, The ion exchange conditions include the ion exchange treatment time of the post-removal ion exchange step, In the ion exchange condition setting step, the ion exchange treatment time is set based on the interference fringe image.

18. The method for producing tempered glass according to claim 16, wherein: have: a step of measuring the diffusion depth DOL1 of the K ions introduced in the second ion exchange step using the measuring device before the removal step; and a removal amount determining step of determining a removal amount Δt of the surface of the tempered glass removed in the removing step, In the ion exchange condition setting step, the ion exchange condition is set based on a pre-prepared function, the diffusion depth DOL1 of K ions measured by the measuring device, and the removal amount Δt determined in the removal amount determining step.

19. The method for producing tempered glass according to claim 18, wherein: The ion exchange conditions include the ion exchange treatment time Tx in the post-removal ion exchange step, The function includes the following formula (1), Tx=a(1-e -b×x )・・・(1) Here, a and b are constants, and x is Δt / DOL1, which is the ratio of the removal amount Δt to the diffusion depth DOL1 of K ions introduced in the second ion exchange step.

20. The method for producing tempered glass according to claim 18 or 19, wherein: have: an inspection step of acquiring defect information of the strengthened glass after performing the first ion exchange step and the second ion exchange step and before the removal step; The planned removal amount setting step sets the planned removal amount to be removed from the surface of the tempered glass after the first ion exchange step and the second ion exchange step based on the defect information acquired in the inspection step.

21. The method for producing tempered glass according to claim 18 or 19, wherein: The information related to the stress includes a diffusion depth DOL2 of K ions remaining in the strengthened glass after the removal step and before the post-removal ion exchange step, In the removal amount determination step, the removal amount Δt is determined by the difference between the diffusion depth DOL1 of the K ions introduced in the second ion exchange step and the diffusion depth DOL2 of the K ions remaining in the tempered glass, ie, DOL1 - DOL2.

22. A method for producing tempered glass, wherein the method is a method for producing tempered glass having adjusted surface compressive stress, characterized in that: With the following processes: a removing step of removing at least a portion of the surface of the tempered glass having a compressive stress layer on the surface thereof to a depth shallower than the depth of the compressive stress layer, thereby forming a new surface on the tempered glass; as well as After removing the post-ion exchange step, the tempered glass having the maximum compressive stress CS2 of the compressive stress layer on the new surface being less than 700 MPa is subjected to ion exchange treatment. In the post-removal ion exchange step, the maximum compressive stress CS3 of the compressive stress layer on the new surface is set to 700 MPa or more by exchanging Na ions in the tempered glass with K ions in the molten salt. Also features: an inspection step of inspecting the surface of the tempered glass for defects before the removal step; and a predetermined removal amount setting step of setting a predetermined removal amount to be removed from the surface of the tempered glass having a compressive stress layer on the surface in advance, If a defect on the surface of the tempered glass is detected in the inspection step, at least a portion of the surface is removed together with the defect in the removal step based on the planned removal amount set in the planned removal amount setting step.

23. A method for producing tempered glass, comprising subjecting glass having a surface to an ion exchange treatment to obtain tempered glass having a compressive stress layer on the surface, wherein: have: a first ion exchange step of contacting the surface of the glass with a first molten salt to exchange Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of contacting the surface of the glass with a second molten salt to exchange Na ions in the glass with K ions in the second molten salt; a removing step of removing at least a portion of the surface of the strengthened glass after the first and second ion exchange steps have been performed, thereby forming a new surface on the strengthened glass; a measuring step of measuring information related to stress of the tempered glass after the removing step using a measuring device; as well as a post-removal ion exchange step of exchanging Na ions in the tempered glass after the measurement step with K ions in the molten salt, thereby increasing the maximum compressive stress of the compressive stress layer on the new surface; The method for manufacturing the tempered glass further comprises: an ion exchange condition setting step of setting ion exchange conditions in the post-removal ion exchange step based on the information related to the stress obtained from the measuring device in the measuring step; an inspection step of inspecting the presence or absence of defects on the surface of the tempered glass after performing the first and second ion exchange steps and before the removal step; and a predetermined removal amount setting step of setting a predetermined removal amount to be removed from the surface of the tempered glass after performing the first and second ion exchange steps. If a defect on the surface of the tempered glass is detected in the inspection step, at least a portion of the surface is removed together with the defect in the removal step based on the planned removal amount set in the planned removal amount setting step.

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