Method of manufacturing tempered glass

Abstract

To increase the strength of glass decreased by a part of the surface being removed after ion exchange treatment.SOLUTION: A method for producing tempered glass has 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 and K ions in molten salt are subjected to ion exchange, causing the maximum compression stress CS3 of a compressive stress layer 2 on a new surface 1a formed by the removal step S5 to be 700 MPa or more.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing tempered glass suitable for, for example, cover glass of mobile phones, digital cameras, PDAs (portable terminals), and touch panel displays.

Background Art

[0002] Devices such as mobile phones (especially smartphones), digital cameras, PDAs, touch panel displays, large TVs, and non-contact power supply are increasingly becoming popular. Tempered glass subjected to ion exchange treatment is used for these applications. In recent years, the use of tempered glass for exterior parts of digital signage, mice, smartphones, etc. has been increasing.

[0003] Tempered glass has a compressive stress layer formed by ion exchange treatment on its surface, thereby suppressing the formation and progression of cracks on the surface and obtaining high strength. The strength of tempered glass can be improved by adjusting the formation mode of such a compressive stress layer.

[0004] Defects may occur on the surface of tempered glass or fine irregularities may remain due to ion exchange treatment. Therefore, it is necessary to remove these defects and irregularities. For example, Patent Document 1 discloses a method for manufacturing tempered glass including a post-strengthening polishing step of polishing the surface of a glass plate after a chemical strengthening step.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the surface of the glass plate is polished in the above-mentioned post-strengthening polishing process, a portion of the compressive stress layer is removed. Therefore, there was a risk that the compressive stress value of the compressive stress layer on the surface of the tempered glass plate would decrease.

[0007] Therefore, the technical problem of the present invention is to increase the strength of glass that has been reduced by the removal of a portion of its surface after ion exchange treatment. [Means for solving the problem]

[0008] The present invention is for solving the above problems and is a method for manufacturing tempered glass having a compressive stress layer on its surface by subjecting glass having a surface to an ion exchange treatment, comprising: a first ion exchange step of bringing the surface of the glass into contact with a first molten salt and exchanging Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of bringing the surface of the glass into contact with a second molten salt and exchanging 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 execution of the first ion exchange step and the second ion exchange step to form a new surface on the tempered glass; and a post-removal ion exchange step of exchanging Na ions in the tempered glass after the removal step with K ions in the molten salt to make the maximum compressive stress CS3 of the compressive stress layer on the new surface 700 MPa or more.

[0009] With this configuration, after the first and second ion exchange processes, the surface of the tempered glass is removed by a removal process, thereby removing minute defects and other imperfections formed on the surface. This allows the tempered glass that had defects to be commercialized, improving the yield. The compressive stress value of the new surface formed on the tempered glass by the removal process will be lower than that of the surface before the removal process, but by performing the post-removal ion exchange process on this new surface, the compressive stress value can be sufficiently increased. This makes it possible to manufacture high-strength tempered glass.

[0010] This method further comprises a post-removal preliminary ion exchange step performed after the removal step but 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, and ion exchange is performed between the Li ions in the tempered glass after the removal step and the Na ions in the molten salt.

[0011] In this method, the concentration of NaNO3 in the third molten salt used in the pre-ion exchange step after removal may be substantially equal to the concentration of NaNO3 in the first molten salt.

[0012] In this method, the concentration of KNO3 in the molten salt used in the post-removal ion exchange step may be substantially equal to the concentration of KNO3 in the second molten salt.

[0013] The ion exchange treatment time in the aforementioned post-removal preliminary ion exchange step may be 10 to 100% of the ion exchange treatment time in the first ion exchange step.

[0014] Furthermore, the ion exchange treatment time in the post-removal ion exchange step may be 50-200% of the ion exchange treatment time in the second ion exchange step.

[0015] The glass is a plate-shaped or sheet-shaped glass with a thickness of 0.05 to 2.0 mm, and the maximum compressive stress CS2 of the compressive stress layer on the new surface after the removal process may be set to 100 MPa or more by removing the main front and back surfaces of the tempered glass in a range shallower than the compressive stress layer after the removal process, before the ion exchange process.

[0016] In the removal step, the surface of the tempered glass after the execution of the first ion exchange step and the second ion exchange step is removed by polishing or etching, and the amount of surface removal Δt in the removal step may be less than the diffusion depth DOL of the K ions introduced in the second ion exchange step.

[0017] In this method, the removal amount Δt in the removal step is 20 μm or less, and after the removal step and before the post-removal ion exchange step, the compressive stress CS2 of the compressive stress layer on the new surface may be less than 700 MPa, and the maximum compressive stress CS3 of the compressive stress layer after the post-removal ion exchange step may be 700 to 1200 MPa.

[0018] The tempered glass after the removal ion exchange process has a stress profile (stress distribution) obtained by measuring the stress in the depth direction from the new surface, which includes a first peak where the compressive stress is at its maximum value at the surface, a first bottom where the stress gradually decreases in the depth direction from the first peak to its minimum value, a second peak where the compressive stress gradually increases in the depth direction from the first bottom to its maximum value, and a second bottom where the tensile stress gradually decreases in the depth direction from the second peak to its minimum value. In the removal ion exchange process, the Na ions in the tempered glass and the K ions in the molten salt may be exchanged so that the compressive stress CSb at the first bottom is 10 MPa or more.

[0019] The concentration of LiNO3 in the molten salt used in the post-removal ion exchange step may be 0.1 to 2% by mass. Furthermore, the concentration of Na ions in the molten salt used in the post-removal ion exchange step may be 5.0% by mass or less when converted to NaNO3.

[0020] 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 may be less than or equal to the ion exchange treatment time in the second ion exchange step.

[0021] In this method, in the second ion exchange step, Na ions in the glass are exchanged with K ions in the second molten salt, and Na ions in the glass are 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 to 5% by mass, and the concentration of KNO3 in the second molten salt is 95 to 99.5% by mass. The ion exchange treatment temperature in the first ion exchange step is 350 to 480°C, the ion exchange treatment temperature in the second ion exchange step is 350 to 480°C, the ion exchange treatment time in the first ion exchange step is 1 to 20 hours, and the ion exchange treatment time in the second ion exchange step may be shorter than the ion exchange treatment time in the first ion exchange step.

[0022] The glass may contain, in terms of mass%, SiO2 40% to 70%, Al2O3 10% to 30%, B2O 30% to 3%, Na2O 5% to 25%, K2O 0% to 5.5%, Li2O 0.1% to 10%, MgO 0% to 6%, and P2O 50% to 15%.

[0023] This method includes an inspection step for checking for defects on the surface of the tempered glass after the first ion exchange step and the second ion exchange step, and before the removal step. If defects are detected on the surface of the tempered glass, at least a portion of the surface can be removed along with the defects in the removal step.

[0024] The present invention is for solving the above problems, and in a method for manufacturing tempered glass for obtaining tempered glass with an adjusted surface compressive stress, at least a part of the surface of the tempered glass having a compressive stress layer on the surface in advance is removed 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 performing an ion exchange treatment on the tempered glass in which the maximum compressive stress CS2 of the compressive stress layer on the new surface is less than 700 MPa. In the post-removal ion exchange step, the Na ions in the tempered glass and the K ions in the molten salt are ion-exchanged to make the maximum compressive stress CS3 of the compressive stress layer on the new surface 700 MPa or more, which is characterized in that.

[0025] According to such a configuration, after the ion exchange treatment, on the new surface formed by removing the surface of the tempered glass, the compressive stress of the compressive stress layer will decrease. However, by performing the post-removal ion exchange step on this new surface, the compressive stress value can be sufficiently increased. Thereby, it becomes possible to manufacture high-strength tempered glass.

[0026] This method may further include a step of measuring, by a measuring device, information regarding the stress of the tempered glass after the removal step and before the post-removal ion exchange step; 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.

[0027] In this method, the measuring device is a device that generates optical interference fringes for the tempered glass after the removal step and before the post-removal ion exchange step, and measures the stress distribution by taking an interference fringe image including the optical interference fringes. The information regarding the stress includes the interference fringe image, the ion exchange conditions include the ion exchange treatment time of 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.

[0028] In this method, the steps include measuring the diffusion depth DOL1 of K ions introduced in the second ion exchange step using the measuring device before the removal step, and determining the amount of removal Δt of the surface of the tempered glass removed in the removal step, wherein the ion exchange condition setting step may set the ion exchange conditions based on a pre-prepared function, the diffusion depth DOL1 of K ions measured by the measuring device, and the amount of removal Δt determined by the removal amount determination step.

[0029] In this method, the ion exchange conditions include the ion exchange treatment time Tx in the post-removal ion exchange step, and the function may include the following equation (1). Tx=a(1-e -b×x ) ···(1) Here, a and b are constants, and x is the ratio (Δt / DOL1) of the removal amount Δt to the diffusion depth DOL1 of the K ions introduced in the second ion exchange step.

[0030] This method may include an inspection step of acquiring defect information of the tempered glass after the execution of the first ion exchange step and the second ion exchange step and before the removal step, and a planned removal amount setting step of setting a planned removal amount to be removed from the surface of the tempered glass after the execution of the first ion exchange step and the second ion exchange step, based on the defect information acquired in the inspection step.

[0031] In this method, the information relating to the stress includes the diffusion depth DOL2 of the K ions remaining in the tempered glass after the removal step and before the post-removal ion exchange step, and in the removal amount determination step, the removal amount Δt may be determined by the difference (DOL1-DOL2) 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.

[0032] The present invention is for solving the above problems, and provides a method for manufacturing tempered glass having a compressive stress layer on the surface by subjecting a glass having a surface to an ion exchange treatment, comprising: a first ion exchange step of bringing the surface of the glass into contact with a first molten salt and exchanging Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of bringing the surface of the glass into contact with a second molten salt and exchanging Na ions in the glass with K ions in the second molten salt; and at least the surface of the tempered glass after the execution of the first ion exchange step and the second ion exchange step The invention comprises a removal step of forming a new surface on the tempered glass by removing a portion of it; a measurement step of measuring information regarding the stress of the tempered glass after the removal 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 exchange between Na ions in the tempered glass and K ions in the molten salt after the measurement step, wherein the invention further comprises an ion exchange condition setting step of setting the ion exchange conditions in the post-removal ion exchange step based on the information regarding the stress obtained from the measuring device in the measurement step. [Effects of the Invention]

[0033] According to the present invention, the strength of glass, which has decreased due to the removal of a portion of the surface after ion exchange treatment, can be increased. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic diagram showing a cross-section of tempered glass. [Figure 2] This graph shows the stress profile in the thickness direction of tempered glass. [Figure 3] This is a flowchart illustrating a method for manufacturing tempered glass according to the first embodiment. [Figure 4] This is a cross-sectional view of the glass showing the removal process. [Figure 5] This is a flowchart showing a method for manufacturing tempered glass according to the second embodiment. [Figure 6] This is a flowchart illustrating a method for manufacturing tempered glass according to the third embodiment. [Figure 7] This diagram schematically shows interference fringe images of tempered glass. [Figure 8] This diagram schematically shows interference fringe images of tempered glass. [Figure 9] This diagram schematically shows interference fringe images of tempered glass. [Figure 10] This diagram schematically shows interference fringe images of tempered glass. [Figure 11] The stress profile of the tempered glass according to the example is shown. [Figure 12] The stress profile of the tempered glass according to the example is shown. [Modes for carrying out the invention]

[0035] <First Embodiment> Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Figures 1 to 4 show a first embodiment of the method for manufacturing tempered glass according to the present invention.

[0036] As shown in Figure 1, the tempered glass 1 according to the present invention is a plate-shaped or sheet-shaped chemically strengthened glass that has been chemically strengthened by ion exchange. The tempered glass 1 comprises surfaces 1a and 1b, a compressive stress layer 2, and a tensile stress layer 3.

[0037] 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, 0.85 mm or less, even more preferably 0.8 mm or less, 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, 0.6 mm or more, and even more preferably 0.65 mm or more.

[0038] The surfaces 1a and 1b of the tempered glass 1 include a main surface 1a and an end surface 1b, which form the front and back surfaces. The compressive stress layer 2 is formed in the surface layer 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 by ion exchange treatment and a compressive stress layer caused by Na ions introduced by ion exchange treatment. The compressive stress layer caused by K ions is formed at a relatively shallow position on and near 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 K ions introduced by 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 at a deeper position than the compressive stress layer caused by K ions. The tensile stress layer 3 is formed inside the tempered glass 1, i.e., at a deeper position than the compressive stress layer 2.

[0039] The stress profile (stress distribution) of tempered glass 1 is obtained by measuring the stress from the main surface 1a side in the depth direction (direction perpendicular to the main surface 1a), with compressive stress as a positive number and tensile stress as a negative number. The stress profile of tempered glass 1 obtained in this way is shown, for example, as in Figure 2. In the graph of Figure 2, the vertical axis represents stress, and the horizontal axis represents the position (depth) in the thickness direction with respect to one of the main surfaces 1a. In the graph of Figure 2, positive stress values ​​represent compressive stress, and negative stress values ​​represent tensile stress. That is, in the graph of Figure 2, a larger absolute value of the stress indicates a larger stress. Note that Figure 2 is an exaggerated conceptual diagram for illustrative purposes, and the stress profile of tempered glass 1 is not limited to this embodiment.

[0040] The stress profile of the tempered glass 1 comprises, in order from the main surface 1a side in the depth direction (direction perpendicular to the main surface 1a), a first peak P1, a first bottom B1, a second peak P2, and a second bottom B2.

[0041] The first peak P1 is the position where the compressive stress reaches its maximum value and is located on the main surface 1a. The compressive stress CS1 (CSmax) at the first peak P1 is 700 MPa or more, preferably 700 MPa to 900 MPa, and more preferably 750 MPa to 850 MPa.

[0042] At the first bottom B1, the stress gradually decreases in the depth direction from the first peak P1, reaching a minimum value. In Figure 2, the stress CSb at the first bottom B1 is shown as a compressive stress (positive value), but it can also be a tensile stress (negative value). The lower the stress CSb at the first bottom B1, the lower the tensile stress CTmax at the second bottom B2, slowing down the failure behavior.

[0043] The stress CSb at the first bottom B1 is preferably +100 MPa or less, more preferably +90 MPa or less, +80 MPa or less, +70 MPa or less, and +60 MPa or less. However, if the stress CSb at the first bottom B1 is too low, cracks will occur on the surface during the strengthening process, worsening visibility. The stress CSb at the first bottom B1 is preferably -50 MPa or more, more preferably -45 MPa or more, -40 MPa or more, -35 MPa or more, -30 MPa or more, 0 MPa or more, and particularly preferably +10 MPa or more. The stress CSb at the first bottom B1 may be 0 MPa or more and +65 MPa or less, or -30 MPa or more and less than 0 MPa. The depth DOLb at the first bottom 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 bottom B1 is approximately equal to, or slightly deeper than, the depth of the compressive stress layer DOL1, which is the depth of the compressive stress layer caused by K ions (the diffusion depth of K ions) within the compressive stress layer 2. More specifically, DOLb is located within a range of ±10 μm relative to DOL1.

[0044] At the second peak P2, the stress gradually increases in the depth direction from the first bottom B1, and the stress reaches a maximum value. The stress Csp at the second peak P2 is compressive stress. The compressive stress Csp at 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, and 18 MPa to 100 MPa, and more preferably 20 MPa to 80 MPa.

[0045] 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%, and 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%.

[0046] The distance in the depth direction from the first bottom B1 to the second peak P2, i.e., 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.

[0047] At the second bottom B2, the stress gradually decreases in the depth direction from the second peak P2, reaching the minimum value (maximum absolute value) of the tensile stress. The absolute value of the tensile stress CTmax at the second bottom B2 is 70 MPa or less, preferably 65 MPa or less, 60 MPa or less, and more preferably 40 MPa to 55 MPa.

[0048] The product of the tensile stress CTmax of the second bottom B2 and the thickness T is preferably -70 MPa·mm or more, more preferably -65 MPa·mm or more, -60 MPa·mm or more, and -55 MPa·mm or more. Furthermore, the product of the tensile stress CTmax of the second bottom 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, and -30 MPa·mm or less.

[0049] Between the second peak P2 and the second bottom B2 lies a stress zero point Z where the stress is zero. Normally, the depth DOLzero of the stress zero point Z is difficult to exceed 20% of the thickness T, and physically, around 22% is the limit. However, in this embodiment, a DOLzero exceeding this limit can be obtained.

[0050] The greater the depth DOLzero of the stress zero point Z, the higher the strength against penetration by protrusions. Preferably, it is 10% or more of the thickness T, 10.5% or more, 11% or more, 11.5% or more, 12% or more, 12.5% ​​or more, 13% or more, 13.5% or more, 14% or more, 14.5% or more, 15% or more, 15.5% or more, 16% or more, 16.5% or more, 17% or more, 17.5% or more, and 18% or more. More preferably, it is 18.5% or more, 19% or more, 19.5% or more, 20% or more, 20.5% or more, 21% or more, 21.5% or more, 22.0% or more, 22.5% or more, 23% or more, and 23.5% or more. Most preferably, it is 24% or more.

[0051] However, if the depth DOLzero of the stress zero point Z becomes excessively large, it may cause excessive tensile stress in the first bottom B1 and the second bottom 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, and 28% or less of the thickness T, and more preferably 27% or less.

[0052] In this embodiment, the tempered glass 1 also has a similar stress profile on the end face 1b. Specifically, the stress profile of the tempered glass 1 includes a first peak where the compressive stress is at its maximum value at the end face 1b, a first bottom where the stress gradually decreases in the depth direction from the first peak to a minimum value, a second peak where the compressive stress gradually increases in the depth direction from the first bottom to a maximum value, and a second bottom where the tensile stress gradually decreases in the depth direction from the second peak to a minimum value. The compressive stress at the first peak is 700 MPa or more, the compressive stress at the second peak is 15 MPa to 250 MPa, and the second peak is located at a depth of 4% to 20% of the thickness T. Furthermore, the preferred range of the stress profile for the end face 1b can be similarly applied to the preferred range of the stress profile for the main surface 1a.

[0053] The stress and its distribution in the tempered glass 1 can be measured and combined using, for example, the FSM-6000LE and SLP-1000 manufactured by Orihara Manufacturing Co., Ltd.

[0054] The tempered glass 1 configured as described above is manufactured by preparing a plate-shaped glass containing alkali metal oxides as part of its composition (hereinafter referred to as tempered glass) and applying a tempering treatment to this tempered glass.

[0055] The tempered glass preferably contains, in mass percent, SiO2 40% to 70%, Al2O3 10% to 30%, B2O 30% to 3%, Na2O 5% to 25%, K2O 0% to 5.5%, Li2O 0.1% to 10%, MgO 0% to 6%, and P2O 50% to 15%.

[0056] The reasons why the above composition is preferred are explained below. In the description of the content range of each component, percentages refer to mass percentages unless otherwise specified.

[0057] SiO2 is a component that forms the network of glass. If the SiO2 content is too low, vitrification becomes difficult, and acid resistance tends to decrease. Therefore, the preferred lower limit range for SiO2 is 40% or more by mass, preferably 45% or more, and particularly 50% or more. On the other hand, if the SiO2 content is too high, meltability and moldability tend to decrease, and the coefficient of thermal expansion becomes too low, making it difficult to match the coefficient of thermal expansion of the surrounding material. Therefore, the preferred upper limit range for SiO2 is 70% or less by mass, preferably 65% ​​or less, 57% or less, 56% or less, 55% or less, and particularly 54% or less.

[0058] Al2O3 is a component that increases the ion exchange rate and also increases the Young's modulus, thereby increasing the Vickers hardness. Furthermore, it is a component that increases the phase separation viscosity. If the Al2O3 content is too low, the ion exchange rate and Young's modulus tend to decrease. Therefore, the suitable lower limit range for Al2O3 is 10% or more by mass, preferably 15% or more, 18% or more, 24% or more, 25% or more, and especially 26% or more. On the other hand, if the Al2O3 content is too high, devitrified crystals tend to precipitate in the glass, making it difficult to form into a plate shape using methods such as the overflow downdraw method. In particular, when using alumina refractories as the refractory material of the molded body and forming into a plate shape using the overflow downdraw method, devitrified spinel crystals tend to precipitate at the interface with the alumina refractories. Acid resistance also decreases, making it difficult to apply to acid treatment processes. Furthermore, high-temperature viscosity increases, and meltability tends to decrease. Therefore, the suitable upper limit range for Al2O3 is 30% or less by mass, preferably The percentages are 29% or less, 28% or less, and 27% or less.

[0059] B2O3 is a component that reduces high-temperature viscosity and density, as well as improving devitrification resistance. However, if the B2O3 content is too high, the ion exchange rate (especially stress depth) tends to decrease. Ion exchange can also cause discoloration of the glass surface, known as "yellowing," and can reduce acid and water resistance. Therefore, the preferred lower limit range for B2O3 is 0% or more, 0.01% or more, and 0.05% or more by mass%, and the preferred upper limit range for B2O3 is 3% or less, 2% or less, 1% or less, and especially less than 0.3% by mass%.

[0060] Na2O is an ion exchange component and also a component that reduces high-temperature viscosity, thereby improving melting and moldability. Furthermore, Na2O is a component that improves devitrification resistance and devitrification in reaction with refractories of molded articles, especially alumina refractories. If the Na2O content is too low, melting will decrease, the coefficient of thermal expansion will decrease too much, and the ion exchange rate will tend to decrease. Therefore, the suitable lower limit range 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, 12% or more, and especially 12.5% ​​or more. On the other hand, if the Na2O content is too high, the phase separation viscosity tends to decrease. It may also decrease acid resistance, disrupt the balance of components in the glass composition, and conversely decrease devitrification resistance. Therefore, the preferred upper limits for Na2O are 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 especially 15% or less.

[0061] K2O is a component that reduces high-temperature viscosity, thereby improving meltability and moldability. It also improves devitrification resistance and increases Vickers hardness. However, if the K2O content is too high, the phase separation viscosity tends to decrease. Furthermore, acid resistance decreases, the balance of components in the glass composition is disrupted, and devitrification resistance tends to decrease. Therefore, the preferred lower limit range for 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 by mass%, while the preferred upper limit range is 5.5% or less, 5% or less, and especially 4.5% or less.

[0062] Li2O is an ion exchange component and also a component that reduces high-temperature viscosity, thereby improving melting and moldability. Furthermore, it is a component that increases Young's modulus. The preferred lower limit range for Li2O is 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, and especially 2.5% or more by mass%, while the preferred upper limit range is 10% or less, 8% or less, 5% or less, 4.5% or less, 4.0% or less, and especially less than 3.5%.

[0063] MgO is a component that reduces high-temperature viscosity, thereby improving meltability and moldability. It also increases Young's modulus, thereby increasing Vickers hardness and improving acid resistance. Therefore, the preferred lower limit range for MgO is 0% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and especially 2% or more. However, if the MgO content is too high, the ion exchange rate tends to decrease, and the glass tends to devitrify easily. In particular, when using alumina refractories as the refractory material for the molded body and forming it into a plate shape by the overflow downdraw method, devitrified spinel crystals tend to precipitate at the interface with the alumina refractories. Therefore, the preferred upper limit range for MgO is 6% or less, 5.5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, and especially 2.5% or less.

[0064] P2O5 is a component that increases the ion exchange rate while maintaining the compressive stress value. Therefore, the suitable lower limit range for P2O5 is 0% or more, 2% or more, 2.1% or more, 2.5% or more, 3% or more, 4% or more, and especially 4.5% or more. However, if the P2O5 content is too high, clouding due to phase separation may occur in the glass, and the water resistance may decrease. Therefore, the suitable upper limit range for 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 especially 6% or less.

[0065] As a clarifying agent, one or more selected from the group consisting of SnO2, As2O3, Cl, SO3, and CeO2 (preferably from the group consisting of Cl and SO3) may be added in a mass percentage of 0 ppm to 30,000 ppm (0% to 3%).

[0066] The clarifying agent is preferably SnO2, with a preferred content range of 0-10000 ppm, 0-7000 ppm, and particularly 50-6000 ppm by mass. The preferred content range of Cl is 0-1500 ppm, 0-1200 ppm, 0-800 ppm, 0-500 ppm, and particularly 50-300 ppm. The preferred content range of SO3 is 0-100 The ranges are 0 ppm, 0-800 ppm, and especially 10-500 ppm.

[0067] 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 especially less than 300 ppm. This makes it easier to improve the transmittance (400 nm to 770 nm) at a thickness of 1 mm.

[0068] Rare earth oxides such as Nb2O5 and La2O3 are components that increase Young's modulus. However, the raw materials themselves are expensive, and adding large amounts tends to reduce devitrification resistance. Therefore, the content of rare earth oxides is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, and especially 0.1% or less.

[0069] Furthermore, from an environmental perspective, it is preferable that the tempered glass described above substantially does not contain As2O3, Sb2O3, and PbO in its glass composition. It is also preferable, from an environmental perspective, that it substantially does not contain Bi2O3 and F.

[0070] The above-mentioned composition of the tempering glass is merely an example; any tempering glass with a known composition may be used as long as chemical strengthening by ion exchange is possible. Furthermore, the composition of the tempering glass obtained by ion exchange treatment of the above-mentioned tempering glass will be the same as the composition of the tempering glass before ion exchange treatment.

[0071] The following describes a method for manufacturing the tempered glass 1 (tempered glass plate) with the above configuration.

[0072] As shown in Figure 3, this method comprises 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.

[0073] Preparation step S1 is the process of preparing tempered glass. In preparation step S1, glass raw materials mixed to achieve the above glass composition are put into a continuous melting furnace, heated and melted at 1500°C to 1600°C, clarified, supplied to a molding device, molded into a plate or the like, and slowly cooled to produce tempered glass.

[0074] As a method for forming glass plates, it is preferable to employ the overflow downdraw method. The overflow downdraw method is a method that can produce a large quantity of high-quality glass plates, can easily produce large glass plates, and can minimize surface scratches on the glass plates. In the overflow downdraw method, for example, alumina or dense zircon is used as the constituent material of the molded body. The tempered glass according to the present invention has good compatibility with alumina and dense zircon, especially alumina (the components of the molten glass do not easily react with the components of the molded body, making it difficult to generate bubbles or blemishes).

[0075] In addition to the overflow downdraw method, various other molding methods can be employed. For example, the float method, downdraw method (slot-down method, redraw method, etc.), roll-out method, and press method can be used.

[0076] After forming the tempered glass, or simultaneously with the forming process, bending may be performed as needed. Furthermore, cutting, drilling, surface polishing, chamfering, edge polishing, etching, and other processing may be performed as needed.

[0077] The dimensions of the tempered glass can be determined arbitrarily, but the thickness T is preferably 2.0 mm or less, more preferably 0.05 to 1.0 mm, and even more preferably 0.1 mm to 0.9 mm, 0.3 mm to 0.85 mm, or 0.5 mm to 0.8 mm.

[0078] In the first ion exchange step S2, the tempered glass is immersed in a treatment tank filled with a first molten salt containing Na, which has a larger ionic radius than the Li ions contained in the tempered glass, and held at a predetermined temperature for a predetermined time, thereby performing ion exchange treatment on the surface of the tempered glass. This brings the tempered glass into contact with the first molten salt, causing ion exchange between the Li ions in the tempered glass and the Na ions in the first molten salt, and introducing Na ions near the surface (main surface and edge face) of the tempered glass. In addition, ion exchange occurs between the Na ions in the tempered glass and the K ions in the first molten salt. As a result, a compressive stress layer 2 is formed on the surface of the tempered glass, and the tempered glass is strengthened.

[0079] In the first ion exchange step S2, the region in which Na ions are introduced into the tempering glass is preferably a region from the surface of the tempering glass to a depth of 10% or more of the thickness T, and more preferably a region from the surface of the tempering glass to a depth of 12% or more, 14% or more, 15% or more, and 15% to 40% or less of the thickness T.

[0080] The first molten salt used in the first ion exchange step S2 is preferably a mixed salt of NaNO3 and KNO3. The presence of K ions in the first molten salt makes it easier to measure the stress and its distribution in the tempered glass after the first ion exchange step S2, thus being suitable for quality control of the resulting tempered glass. 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, with the remainder being KNO3. The first molten salt may also contain only NaNO3 and no KNO3. Furthermore, the first molten salt may also contain LiNO3.

[0081] The ion exchange treatment temperature in the first ion exchange step S2 is preferably 350 to 480°C, more preferably 360 to 430°C, even more 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 even more preferably 2 to 10 hours.

[0082] 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 the surface of the tempering glass is subjected to ion exchange treatment by holding it at a predetermined temperature for a predetermined time.

[0083] This process brings the tempering glass into contact with the second molten salt, causing reverse ion exchange between the Li ions in the second molten salt and the Na ions in the tempering glass, thereby detaching at least some of the Na ions from the tempering glass. Simultaneously, K ions are exchanged with the Li or Na ions contained in the tempering glass, introducing K ions into the tempering glass to a region shallower than 7% of the thickness T from the surface. In other words, the compressive stress formed in the surface layer of the tempering glass is relieved by reverse ion exchange, while the tempering glass is strengthened by ion exchange, resulting in high compressive stress being formed only near the surface of the surface layer.

[0084] In the second ion exchange step S3, the region where Na ions are released from the reinforcing glass is preferably a region from the surface of the reinforcing glass to a depth of 15% or less of the thickness T, and more preferably a region from the surface of the reinforcing glass to a depth of 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 1% or more to 10% or less, 2% or more to 10% or less, 3% or more to 10% or less, 4% or more to 10% or less, and 5% or more to 10% or less of the thickness T. Also, in the second ion exchange step S3, the region where K ions are introduced into the reinforcing glass is preferably a region from the surface of the reinforcing glass to a depth of 7% or less of the thickness T, and more preferably a region from the surface of the reinforcing glass to a depth of 6.5% or less, 6% or less, 5.5% or less, and 5% or less of the thickness T.

[0085] 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. 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%, and 1-2% by mass. The concentration of KNO3 in the second molten salt is preferably 95-99.8%, 97-99.6%, 98-99.5%, and 99-99.7% by mass.

[0086] Furthermore, the concentration of Li ions in the second molten salt is preferably 100 ppm by mass or more. In this case, the concentration of Li ions in the second molten salt can be determined by multiplying the LiNO3 expressed in mass percent by 0.101.

[0087] The ion exchange treatment temperature in the second ion exchange step S3 is preferably 350 to 480°C, more preferably 360 to 430°C, 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 more, more preferably 0.3 to 2 hours, 0.4 to 1.5 hours, or even more preferably 0.5 to 1 hour.

[0088] The tempering glass immersed in the molten salt in each ion exchange step S2 and S3 may be preheated to the temperature of the molten salt in the ion exchange treatment of each ion exchange step S2 and S3, or it may be immersed in the molten salt at room temperature (for example, 1°C to 40°C).

[0089] It is preferable to include a washing step between the first ion exchange step S2 and the second ion exchange step S3 to wash the tempering glass drawn from the molten salt. Washing makes it easier to remove any deposits adhering to the tempering glass, allowing for a more uniform ion exchange process in the second ion exchange step S2.

[0090] In the first inspection step S4, the quality (presence or absence of defects, unevenness, etc.) of the tempered glass 1 formed through the first ion exchange step S2 and the second ion exchange step S3 is inspected before the removal step S5. If minute defects such as scratches are found on the surface of the tempered glass 1, for example, on the main surface 1a, in the first inspection step S4, the subsequent removal step S5 is performed on that tempered glass 1. On the other hand, if no minute defects are found and the tempered glass 1 otherwise conforms to the standards for a product, it becomes a product.

[0091] As shown in Figure 4, in removal step S5, the front and back main surfaces 1a of the tempered glass 1 are removed in a range 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 preferable to polish the surface 1a0 of the tempered glass 1 with an abrasive tool such as an abrasive pad. However, the surface 1a0 may also be removed by etching the tempered glass 1.

[0092] In removal step S5, regardless of the removal method used, it is preferable that the amount of material removed from each of the front and back main surfaces 1a be the same. More specifically, it is preferable that the difference in the amount of material removed from the front and back main surfaces 1a be 1 μm or less, more preferably 0.5 μm or less, and more preferably 0.3 μm or less. By limiting the difference in the amount of material removed from the front and back main surfaces 1a to a small amount, the occurrence of warping of the tempered glass 1 caused by removal can be suppressed. Therefore, when removal is performed by polishing, it is preferable to use a double-sided polishing device.

[0093] The amount removed from the tempered glass 1 (removal amount) Δt is preferably 0.5 to 20 μm. This removal amount Δt is preferably set to be constant over the entire area of ​​the main surface 1a, but portions of the main surface 1a0 without defects may be left unremoved. That is, in the removal step S5, at least a portion of the main surface 1a0 of the tempered glass 1 can be removed. This removal amount Δt is preferably smaller than the depth DOLzero of the compressive stress layer 2, and more preferably smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3. If defects occur on the end face 1b, a portion of the end face 1b may be removed by polishing or etching.

[0094] In the removal process S5, the surface 1a0 of the tempered glass 1 is removed, and a new surface 1a is formed on the tempered glass 1. Hereinafter, the glass on which the new surface 1a has been formed will be referred to as "second tempered glass". As described above, if the removal amount Δt is made smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange process S3, a portion of the compressive stress layer caused by these K ions will remain on the new surface 1a.

[0095] As a result of the removal process S5, the compressive stress value (maximum compressive stress value) CS2 of the compressive stress layer 2 on the new surface 1a of the second tempering glass is lower than the compressive stress value on surface 1a0 before the removal process S5. The compressive stress value CS2 of the new surface 1a after the removal process S5 and before the post-removal ion exchange process S7 is 80 MPa or more, preferably 100 MPa or more, more preferably 150 MPa or more, and 200 MPa or more. Furthermore, the compressive stress value of the new surface 1a will be less than 700 MPa, 600 MPa or less, 500 MPa or less, and 400 MPa or less, depending on the amount Δt of tempering glass 1 removed in the removal process S5.

[0096] The removal step S5 forms a new surface 1a on the second tempering glass, and the depth (diffusion depth) of the compressive stress layer (diffusion depth) caused by K ions that was formed on the second tempering glass decreases in proportion to the amount removed Δt. The diffusion depth DOL2 of K ions in the compressive stress layer 2 remaining on the second tempering glass after the removal step S5 (before the post-removal ion exchange step S7) is preferably 0.02% to 3.00% of the thickness T1 of the second tempering glass, and more preferably 0.05% to 2.00% of the thickness T1.

[0097] In the second inspection step S6, it is inspected whether or not defects remain on the new surface 1a formed on the second tempering glass. In addition to checking for defects, the second inspection step S6 may also check whether the dimensions of the second tempering glass, such as its thickness, conform to the specified standards. If defects remain in the second tempering glass, the removal step S5 is performed again on that second tempering glass, and then the second inspection step S6 is performed again. For second tempering glass that conforms to the standards for defects and dimensions set in the second inspection step S6, the next post-removal ion exchange step S7 is performed. On the other hand, if the second tempering glass does not conform to the standards for defects and dimensions set in the second inspection step S6, the removal step S5 is performed again on that second tempering glass, and then the second inspection step S6 is performed again.

[0098] In the post-removal ion exchange step S7, the second strengthening glass is strengthened so that the first peak P1, first bottom B1, second peak P2, second bottom B2, and other strengthening characteristics of the stress profile fall within the above numerical range.

[0099] In the post-removal ion exchange step S7, the second strengthening glass, which has undergone the second inspection step S6, is subjected to ion exchange treatment. Specifically, in the post-removal ion exchange step S7, the second strengthening glass, on which a new surface 1a has been formed by the removal step S5, is immersed in a treatment tank filled with a molten salt containing K ions and Li ions. By holding the second strengthening glass in contact with the molten salt at a predetermined temperature for a predetermined time, ion exchange treatment is performed on the new surface 1a of the second strengthening glass.

[0100] This process involves reverse ion exchange between Li ions in the molten salt and Na ions in the second strengthening glass, releasing at least some of the Na ions from the second strengthening glass. Simultaneously, K ions are exchanged with either Li or Na ions in the second strengthening glass. In other words, the compressive stress formed on the surface of the second strengthening glass is relieved by reverse ion exchange, while the glass is strengthened by ion exchange, resulting in high compressive stress being formed only near the surface of the surface layer.

[0101] 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. Specifically, 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% by mass, with the remainder being KNO3. The molten salt may also contain NaNO3. In this case, the concentration of Na ions in the molten salt is preferably 5% by mass or less, more preferably 1.8% by mass or less, when converted to NaNO3. Furthermore, the concentration of Na ions in the molten salt is preferably 5000 ppm by mass or less relative to the total amount of molten salt.

[0102] Furthermore, the concentration of Li ions in the molten salt is preferably 100 ppm by mass or more relative to the total amount of molten salt. In this case, the concentration of Li ions in the molten salt can be determined by multiplying the mass percentage of LiNO3 by 0.101.

[0103] The ion exchange treatment temperature in the post-removal ion exchange step S7 is preferably 350-480°C, 350-450°C, more preferably 360-430°C, and even more preferably 370-400°C, 370-390°C.

[0104] 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 or equal to 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 more, more preferably 0.3 to 2 hours, 0.4 to 0.1 hours, and even more preferably 0.5 to 0.075 hours. However, it is not limited to this, and the ion exchange treatment time in the post-removal ion exchange step S7 may be 0.1 to 200% of the ion exchange treatment time in the second ion exchange step S3, preferably 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 may be set shorter than the ion exchange treatment time in the second ion exchange step S3.

[0105] The compressive stress value (maximum compressive stress value) CS3 of the compressive stress layer 2 on 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 on the surface 1a0 before the removal step S5. The compressive stress value CS3 on the surface 1a after the post-removal ion exchange step S7 is 700 MPa or higher, preferably 700 to 1200 MPa.

[0106] Furthermore, in the post-removal ion exchange step S7, it is preferable that the ion exchange conditions be 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, and 20 MPa or less.

[0107] Furthermore, in the post-removal ion exchange step S7, it is preferable to adjust the ion exchange conditions 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 CS1. However, it is permissible for CS3 to be greater than or equal to CS1, as long as the strength of the tempered glass 1 is improved.

[0108] The post-removal ion exchange step S7 increases the depth of the compressive stress layer 2 in the tempered glass 1. The diffusion depth DOL3 of K ions in the compressive stress layer 2 of the tempered glass 1 after the post-removal ion exchange step S7 is preferably 0.02% to 3.00% of the thickness T1 of the tempered glass 1, and more preferably 0.05% to 2.00% of the thickness T1.

[0109] In the third inspection step S8, the tempered glass 1 formed by the post-removal ion exchange step S7 is subjected to inspections such as checking for defects and measuring the stress profile. The tempered glass 1 becomes a product when it meets the standards set in the third inspection step S8.

[0110] According to the manufacturing method of the tempered glass 1 of this embodiment described above, by removing the surface (main surface 1a0) of the tempered glass 1 in the removal step S5, minute defects formed on this surface can be removed. In this removal step S5, the compressive stress value of the compressive stress layer 2 on the new surface (new main surface 1a) formed will decrease, but by performing the ion exchange step S7 after removal, the compressive stress value of the surface (main surface 1a) of the tempered glass 1 can be adjusted to 700 MPa or more.

[0111] <Second Embodiment> Figure 5 shows a second embodiment of the present invention. The manufacturing method of the tempered glass 1 according to this embodiment differs from the first embodiment in that it includes a post-removal preliminary ion exchange step S7a, which is performed after the second inspection step S6 and before the post-removal ion exchange step S7.

[0112] In the post-removal preliminary ion exchange step S7a, the second strengthening glass, which has undergone the removal step S5 and the second inspection step S6, is immersed in a treatment tank filled with the third molten salt. That is, the second strengthening glass is brought into contact with the third molten salt, and ion exchange occurs between the Li ions in the second strengthening glass and the Na ions in the third molten salt. In addition, ion exchange occurs between the Na ions in the second strengthening glass and the K ions in the third molten salt.

[0113] In the post-removal preliminary ion exchange step S7a, the region in which Na ions are introduced into the second strengthening glass is preferably a region from the new surface 1a of the second strengthening glass to a depth of 10% or more of the thickness T1, and more preferably a region from the surface of the second strengthening glass to a depth of 12% or more, 14% or more, 15% or more, and 15% to 40% or less of the thickness T1.

[0114] 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 concentrations" means that the difference in concentration (absolute value) 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.

[0115] In this embodiment, the second strengthening glass is immersed in a processing tank containing the third molten salt as described above, but the configuration of 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 strengthening glass that has gone through the second inspection step S6 may be immersed in a processing tank containing the first molten salt used in the first ion exchange step.

[0116] Thus, in the post-removal preliminary ion exchange step S7a, by using a first molten salt having concentrations of NaNO3 and KNO3 substantially equal to those of the third molten salt, the post-removal preliminary ion exchange step S7a can be performed without preparing a processing tank to accommodate the third molten salt. This reduces the cost of the manufacturing equipment for the tempered glass 1 and also saves space. Furthermore, the ion exchange conditions (time, temperature) in the post-removal preliminary ion exchange step S7a may be the same as those in the first ion exchange step S2.

[0117] 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 concentration of NaNO3 in the third molten salt is preferably 100-10%, 100-20%, 100-30%, 100-40%, or 100-50% by mass, with the remainder being KNO3. The third molten salt may contain only NaNO3 and no KNO3. The third molten salt may also contain LiNO3.

[0118] Furthermore, the Li ion concentration in the third molten salt is preferably ±2000 ppm for Li ions alone.

[0119] The ion exchange treatment temperature in the pre-ion exchange step S7a after removal is preferably 350-480°C, more preferably 360-430°C, and even more preferably 370-400°C or 370-390°C.

[0120] The ion exchange treatment time in the pre-ion exchange step S7a after removal is preferably 10-100% of the ion exchange treatment time in the first ion exchange step S2, and more preferably 50-100%.

[0121] In this embodiment, the post-removal ion exchange step S7 is performed after the post-removal preliminary ion exchange step S7a. In the post-removal ion exchange step S7, the second strengthening glass is immersed in a treatment tank containing the molten salt, similar to the first embodiment. In this case, it is preferable that the concentration of KNO3 in the molten salt used in the post-removal ion exchange step S7 is substantially equal to the concentration of KNO3 in the second molten salt. It is also preferable that the concentration of LiNO3 in the molten salt used in the post-removal ion exchange step S7 is substantially equal to the concentration of LiNO3 in the second molten salt.

[0122] In this embodiment, as described above, in the post-removal ion exchange step S7, the second strengthening glass is immersed in a treatment tank containing a predetermined molten salt. However, the configuration 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 strengthening glass that has gone through 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.

[0123] Thus, by using a second molten salt having substantially the same concentration of LiNO3 and KNO3 as the concentration of LiNO3 and KNO3 in the molten salt in the post-removal ion exchange step S7, this post-removal ion exchange step S7 can be performed without preparing a dedicated treatment tank for it. This reduces the cost of the manufacturing equipment for the tempered glass 1 and also enables space saving.

[0124] In this case, the ion exchange treatment time in the post-removal ion exchange step S7 may be 0.1 to 200% of the ion exchange treatment time in the second ion exchange step S3, and preferably 1 to 200%, 10 to 200%, 50 to 200%, or 50 to 100%.

[0125] The third inspection step S8, which is performed after the removal ion exchange step S7, is carried out in the same manner as the third inspection step S8 in the first embodiment.

[0126] In this embodiment, it is preferable that the ion exchange conditions of the ion exchange process after the removal process S5 (post-removal preliminary ion exchange process S7a and / or post-removal ion exchange process S7) are adjusted so that the absolute value of the difference between the stress CSb at the first bottom of the tempered glass 1 obtained after the removal ion exchange process S7 and the stress CSb at the first bottom of the tempered glass 1 after the second ion exchange process S3 and before the removal process S5 is preferably 50 MPa or less, more preferably 40 MPa or less, and 30 MPa or less.

[0127] If the bottom portion is not clearly observed, CSb can be attributed to compressive stress at the potassium ion diffusion end or DOL.

[0128] Furthermore, it is preferable to adjust the ion exchange conditions of the ion exchange process after the removal process S5 (removal pre-ion exchange process S7a and / or removal ion exchange process S7) so that the stress CSb at the first bottom of the tempered glass 1 obtained after the removal ion exchange process S7 is 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 at the first bottom of the tempered glass 1 obtained after the second ion exchange process S3 and before the removal process S5.

[0129] Furthermore, as long as the strength of the tempered glass 1 is improved, it is permissible for the stress CSb at the first bottom of the tempered glass 1 obtained after the removal ion exchange step S7 to be equal to or greater than the stress CSb at the first bottom of the tempered glass 1 after the second ion exchange step S3 and before the removal step S5.

[0130] In this embodiment, it is preferable that the ion exchange conditions of the ion exchange process after the removal process S5 (post-removal preliminary ion exchange process S7a and / or post-removal ion exchange process S7) are adjusted so that the absolute value of the difference between the stress CSp at the second peak of the tempered glass 1 obtained after the removal ion exchange process S7 and the stress CSp at the second peak of the tempered glass 1 after the second ion exchange process S3 and before the removal process S5 is preferably 50 MPa or less, more preferably 30 MPa or less, and 20 MPa or less.

[0131] If a clear peak is not observed, the difference in the average stress values ​​from depth DOL to DOC can be used as an alternative to calculating the difference in CSp.

[0132] Furthermore, it is preferable to adjust the ion exchange conditions of the ion exchange process after the removal process S5 (removal pre-ion exchange process S7a and / or removal ion exchange process S7) so that the stress CSp at the first peak of the tempered glass 1 obtained after the removal ion exchange process S7 is 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 tempered glass 1 obtained after the second ion exchange process S3 and before the removal process S5.

[0133] Furthermore, as long as the strength of the tempered glass 1 is improved, it is permissible for the stress CSp at the second peak of the tempered glass 1 obtained after the removal ion exchange process S7 to be greater than or equal to the stress CSp at the second peak of the tempered glass 1 after the second ion exchange process S3 and before the removal process S5.

[0134] According to the manufacturing method of the tempered glass 1 of the second embodiment described above, even if, for example, the removal step S5 removes material to the depths of the glass and reduces not only the compressive stress CS1 of the surface layer but also the compressive stresses of the first bottom B1 (CSb) and the second stress P2 (CSp), the inclusion of a post-removal preliminary ion exchange step S7a allows for ion exchange to be performed again to the depths, thereby regenerating the compressive stresses of CSb and CSp. As a result, the strength characteristics of the tempered glass 1 lost in the removal step S5 can be suitably restored (reproduced).

[0135] <Variation> Furthermore, the present invention is not limited to the configuration of the above embodiments, nor is it limited to the effects described above. The present invention can be modified in various ways without departing from the spirit of the invention.

[0136] In the above embodiment, an example was shown in which the second ion exchange step S3 is performed after the first ion exchange step S2, 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.

[0137] In the above embodiment, the first ion exchange step S2 is exemplified as an example in which ion exchange is performed between Li ions in the reinforcing glass and Na ions in the first molten salt. However, the first ion exchange step S2 may also be an embodiment in which ion exchange is performed between Na ions in the reinforcing glass and K ions in the molten salt.

[0138] In the above embodiment, an example was given in which one ion exchange treatment is performed as a post-removal ion exchange treatment after the removal treatment. However, a preliminary ion exchange treatment (post-removal preliminary ion exchange treatment) may be added after the removal treatment and before the post-removal ion exchange treatment. That is, multiple ion exchange treatments, including a post-removal preliminary ion exchange treatment, may be performed after the removal treatment and before the post-removal ion exchange treatment. The composition and temperature of the molten salt used in the post-removal preliminary ion exchange treatment can be, for example, the same as those of the first ion exchange treatment described above, and the ion exchange treatment time can be less than or equal to the ion exchange treatment time in the first ion exchange treatment.

[0139] In the above embodiment, the removal step S5 removes the surface 1a0 of the tempered glass 1, 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 canceling the compressive stress of the tempered glass 1 by such a reverse ion exchange treatment.

[0140] In the second embodiment described above, an example was explained in which, in the post-removal preliminary ion exchange step S7a, the concentrations of NaNO3 and KNO3 in the third molten salt were substantially equal to the concentrations of NaNO3 and KNO3 in the first molten salt. However, the embodiment is not limited to this example, and these concentrations may be different.

[0141] In the second embodiment described above, an example was explained in which, in the post-removal ion exchange step S7, the concentrations of LiNO3 and KNO3 in the molten salt were substantially equal to the concentrations of LiNO3 and KNO3 in the first molten salt. However, the embodiment is not limited to this example, and these concentrations may be different.

[0142] <Third Embodiment> The first embodiment described above can be transformed into a third embodiment by the following modifications. Figure 6 is a flowchart of the method for manufacturing tempered glass according to the third embodiment. In the method for manufacturing tempered glass according to the third embodiment, information on the tempered glass 1 after the second ion exchange step S3 and information on the second tempering glass after the removal step S5 are obtained before the post-removal ion exchange step S7, and the ion exchange conditions in the post-removal ion exchange step S7 can be set based on this information. The ion exchange conditions include, for example, the ion exchange processing time and ion exchange processing temperature in the post-removal ion exchange step S7. The following describes the case in which the ion exchange processing time, which is an ion exchange condition, is set.

[0143] The first inspection step S4 in the method for manufacturing tempered glass 1 includes a first measurement step S41 for inspecting the tempered glass 1 formed through the first ion exchange step S2 and the second ion exchange step S3 for the presence or absence of defects, and for acquiring information regarding the stress of 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.

[0144] Furthermore, the second inspection step S6 in this method includes a second measurement step S61 which inspects whether defects remain on the new surface 1a formed on the second tempering glass and obtains information on the stress of the second tempering glass; a removal amount determination step S62 which determines the amount Δt of tempering glass 1 actually removed in the removal step S5; and an ion exchange condition setting step S63 which sets the ion exchange conditions in the post-removal ion exchange step S7.

[0145] Furthermore, the third inspection step S8 in this method includes a third measurement step S81 which inspects the tempered glass 1 formed by the ion exchange step S7 after removal for defects, and also obtains information regarding the stress of the tempered glass 1.

[0146] In the first measurement step S41 of the first inspection step S4, information regarding the stress of the tempered glass 1 after the second ion exchange step S3 is measured using a measuring device. A surface stress meter (for example, FSM-6000LE or SLP-1000 manufactured by Orihara Corporation) is preferably used as the measuring device for the first measurement step S41.

[0147] The surface stress meter can generate optical interference fringes on the tempered glass 1, capture an interference fringe image including these fringes, and save it as image data. Based on this image data, the surface stress meter can measure the stress profile (stress distribution) of the tempered glass 1. Information regarding the stress of the tempered glass 1 includes the diffusion depth DOL1 of K ions introduced into the tempered glass 1, in addition to this interference fringe image. Furthermore, information regarding the stress of the tempered glass 1 may also include information such as the first peak P1, first bottom B1, second peak P2, second bottom B2, and their depths in the stress profile described above.

[0148] Furthermore, in the first measurement step S41, the thickness of the tempered glass 1 is measured. The thickness of the tempered glass 1 is measured using a measuring device such as a micrometer or a laser displacement meter.

[0149] 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, the planned removal amount Δt0 to be removed from the tempered glass 1 in order to remove the defect is set based on the defect information (information such as the type, size, and depth of the defect) and information such as the thickness of the tempered glass 1.

[0150] In addition, in the planned removal amount setting step S42, it is also possible to set the planned removal amount Δt0 without relying on the results of the first measurement step S41. For example, if it is clear that there is a certain trend in the occurrence of defects in tempered glass during the preparation step (manufacturing step of tempered glass), it is possible to set the planned removal amount Δt0 uniformly for multiple tempered glass pieces 1 without using the measurement results of the first measurement step S41.

[0151] In the second measurement step S61 of the second inspection step S6, information regarding the stress of the second strengthening glass is measured using the measuring device (surface stress meter) used in the first measurement step S41. Specifically, the measuring device generates optical interference fringes in the second strengthening glass, similar to the first measurement step S41, captures an interference fringe image, and saves the image data as information regarding the stress. The information regarding the stress of the second strengthening glass includes this interference fringe image as well as the diffusion depth DOL2 of K ions remaining in the second strengthening glass.

[0152] Furthermore, in the second measurement step S61, the thickness of the second tempering glass may be measured by the same means as in the first measurement step S41.

[0153] In the removal amount determination step S62, the amount actually removed from the tempered glass 1 in the removal step S5 (removal amount) Δt can be calculated from 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.

[0154] The determination of the removal amount Δt is not limited to the method described above. In the removal amount determination step S62, for example, the difference between the K ion diffusion depth DOL2 related to the second reinforcing glass measured in the second measurement step S61 and the K ion diffusion depth DOL1 measured in the first measurement step S41 (DOL1-DOL2) may be determined as the removal amount Δt.

[0155] 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 processing time is set as an ion exchange condition based on a pre-prepared function. This function is given by the following equation (1).

[0156] Tx=a(1-e -b×x ) ···(1)

[0157] In equation (1), Tx is the ion exchange treatment time, and a and b are constants that vary depending on the second ion exchange treatment time, the strengthening conditions such as 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 a number that is twice the ion exchange treatment time in the second ion exchange step. A preferred range for b is, for example, 1 to 5.

[0158] In equation (1), the variable x is the ratio (Δt / DOL1) between the amount removed Δt from one of the front and back main surfaces of the second strengthening glass, which was identified in the removal amount identification step S62, and the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3.

[0159] Equation (1) is created by conducting manufacturing tests on several pre-prepared samples of tempered glass. These manufacturing tests are carried out as follows:

[0160] First, a first ion exchange process and a second ion exchange process are performed on each sample to produce tempered glass. Next, information regarding the stress of each tempered glass is obtained.

[0161] Subsequently, different planned removal amounts are set for each tempered glass, and the removal process is carried out. Next, information regarding the stress of the second tempering glass is obtained. Then, different ion exchange conditions (ion exchange processing time) are set for each second tempering glass, and the post-removal ion exchange process is carried out. Finally, information regarding the stress of the tempered glass after the post-removal ion exchange process is obtained.

[0162] Subsequently, the stress information obtained for the tempered glass after the removal and ion exchange process is verified. That is, it is confirmed whether the stress information for each tempered glass satisfies the predetermined criteria. Next, based on the data of the tempered glass that satisfies the criteria, a function is created using analysis software on a computing device (e.g., a PC) based on data such as the removal amount Δt for each sample, DOL1 after the second ion exchange process, DOL2 after the removal process, and the ion exchange processing time of the removal ion exchange process S7. Equation (1) is created through the above procedure.

[0163] The ion exchange condition setting step S63 is performed by a processing unit capable of performing the calculation of equation (1).

[0164] In the third measurement step S81 of the third inspection step S8, information regarding the stress of the tempered glass 1 after the removal ion exchange step S7 is measured by a measuring device (surface stress diameter). Subsequently, in the third inspection step S8, it is determined whether or not the measured stress information meets the standard value (determination step). This determination step is performed, for example, by a computing device.

[0165] The removal amount Δt may be set independently of the presence or absence of defects, and is not limited to the embodiments and modified methods described above. In this case, the removal amount Δt may be set based on various information obtained in the manufacturing process (preparation process) of tempered glass.

[0166] <Fourth Embodiment> In the third embodiment described above, an example was given in which the removal amount Δt is specified and the ion exchange processing time is set based on the removal amount Δt. However, the method may be modified to set the ion exchange processing time without specifying the removal amount Δt, as shown below. That is, in the ion exchange condition setting step S63, the ion exchange conditions can be set without using the above equation (1). Specifically, in the ion exchange condition setting step S63, the ion exchange processing time can be set based on, for example, an interference fringe image.

[0167] In the ion exchange condition setting step S63, the ion exchange processing time for the post-removal ion exchange step S7 can be set based on the interference fringe image data of the reinforced glass 1 acquired in the first measurement step S41 and the interference fringe image data acquired in the second measurement step S61. In this case, the removal amount specification step S62 can be omitted. A specific embodiment of this ion exchange condition setting step S63 will be described below with reference to Figures 7 to 10.

[0168] Figure 7 is a schematic diagram of the interference fringe image (hereinafter referred to as the "first interference fringe image") of the tempered glass 1 after the second ion exchange step S3. Figures 8 to 10 are schematic diagrams of the interference fringe images (hereinafter referred to as the "second interference fringe images") of the second tempering glass acquired after the removal step S5.

[0169] As shown in Figure 7, the first interference fringe image includes a first region A1 and a second region A2 (the same applies to the second interference fringe image). Each region A1 and A2 includes multiple bright and dark lines L1a to L1c, L2a to L2c, and the boundary BP of the optical interference fringes. The measuring device creates this first interference fringe image and can calculate the stress value and depth of the compressive stress layer of the tempered glass based on the distance D0 between the dark lines L1a to L1c (or bright lines) in the first region A1 and the dark lines L2a to L2c in the second region A2.

[0170] Each region A1 and A2 contains, for example, three dark lines L1a-L1c and L2a-L2c. Hereinafter, the three dark lines L1a-L1c and L2a-L2c in each region A1 and A2 will be referred to as the first dark lines L1a and L2a, the second dark lines L1b and L2b, and the third dark lines L1c and L2c, respectively.

[0171] In Figure 7, the distance between the boundary BP of the first region A1 and the first dark line L1a (hereinafter referred to as the "first distance") is indicated by the 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 the 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 the symbol D13. Similarly, the first distance between the boundary BP of the second region A2 and the first dark line L2a is indicated by the symbol D21, the second distance between the first dark line L2a and the second dark line L2b is indicated by the symbol D22, and the third distance between the second dark line L2b and the third dark line L2c is indicated by the symbol D23.

[0172] As shown in Figure 8, the first region A1 and the second region A2 of the second interference fringe image include the first dark lines L1a, L2a to the third dark lines L1c, L2c and the boundary BP, similar to the first interference fringe image. In this second interference fringe image, the first distances D11, D21 to the third distances D13, D23 related to each dark line L1a~L1c, L2a~L2c are different from the first distances D11, D21 to the third distances D11, D23 in the first interference fringe image.

[0173] In this case, the distances D11-D13 and D21-D23 in the second interference fringe image change as a result of performing the post-removal ion exchange step S7. In the ion exchange condition setting step S63, the ion exchange processing time of the post-removal ion exchange step S7 is set so that the distances D11-D13 and D21-D23 in the second interference fringe image are equal to the distances D11-D13 and D21-D23 in the first interference fringe image. When there are three dark lines in the second interference fringe image, the ion exchange processing time of the post-removal ion exchange step S7 is preferably 0.1-50%, more preferably 10-50% or 20-45%, of the ion exchange processing time of the second ion exchange step S3.

[0174] In the example shown in Figure 8, if the ion exchange processing time of the post-removal ion exchange step S7 exceeds 50% of the ion exchange processing time of the second ion exchange step S3, the number of dark lines in the interference fringe image of the reinforced glass 1 after the post-removal ion exchange step S7 will be greater than the number of dark lines (3) in the first interference fringe image, which is undesirable.

[0175] In the example shown in Figure 9, each region A1 and A2 of the second interference fringe image contains two dark lines L1a, L1b, L2a, and L2b. In the ion exchange condition setting step S63, the ion exchange conditions (ion exchange processing time) are set so that these two dark lines L1a, L1b, L2a, and L2b become three dark lines after the removal ion exchange step S7 is performed, and so that these three dark lines coincide with the positions of the three dark lines L1a-L1c and L2a-L2c in the first interference fringe image. In other words, in this example, by performing the post-removal ion exchange process S7, the number of dark lines in the interference fringe image of the reinforced glass 1 changes from two to three, and the ion exchange conditions (ion exchange processing time) are set so that the first, second, and third distances related to these three dark lines are equal to the first distances D11, D21, the second distances D12, D22, and the third distances D13, D23 in the corresponding first interference fringe image.

[0176] As shown in the example in Figure 9, when there are two dark lines L1a, L1b, L2a, and L2b in the second interference fringe image, the ion exchange processing time in the post-removal ion exchange step S7 is preferably 50-100% of the ion exchange processing time in the second ion exchange step S3.

[0177] In the example shown in Figure 10, each region A1 and A2 of the second interference fringe image contains one dark line L1a and L2a. In the ion exchange condition setting step S63, the ion exchange conditions (ion exchange processing time) are set so that the one dark line L1a and L2a is removed and then the ion exchange step S7 is performed, resulting in three dark lines, and so that the positions of these three dark lines coincide with the positions of the three dark lines L1a-L1c and L2a-L2c in the first interference fringe image.

[0178] As shown in the example in Figure 10, when there is only one dark line in the second interference fringe image, the ion exchange processing time in the post-removal ion exchange step S7 is preferably 100-150% of the ion exchange processing time in the second ion exchange step S3.

[0179] As described above, in the ion exchange condition setting step S63, the optimal ion exchange processing time can be set based on the interference fringe image of the second strengthening glass after the removal step S5. This ion exchange processing time is obtained by conducting manufacturing tests on several pre-prepared samples of strengthening glass.

[0180] This manufacturing test will be conducted as follows: First, a first ion exchange process and a second ion exchange process will be performed on each sample to produce tempered glass. Next, information regarding the stress of each tempered glass will be obtained.

[0181] Subsequently, different removal amounts are set for each tempered glass, and the removal process is carried out. Next, information regarding the stress of the second tempering glass after the removal process is obtained. Then, different ion exchange conditions (ion exchange processing time) are set for each second tempering glass, and the post-removal ion exchange process is carried out. Next, information regarding the stress of the tempered glass after the post-removal ion exchange process is obtained.

[0182] Subsequently, the positions and distances of the dark lines of each optical interference fringe are compared and verified in the first interference fringe image, the second interference fringe image, and the interference fringe image after the post-removal ion exchange process. If the state of the optical interference fringe in the first interference fringe image matches the state of the optical interference fringe in the interference fringe image after the post-removal ion exchange process, it can be said that the ion exchange processing time in the post-removal ion exchange process is optimal for 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 a computing device (e.g., a PC or other computer) capable of executing the ion exchange condition setting process S63. By operating this computing device, it becomes possible to set the ion exchange conditions in the post-removal ion exchange process based on the second interference fringe image in the ion exchange condition setting process S63. [Examples]

[0183] The tempered glass according to the present invention will be described below based on examples. Note that the following examples are merely illustrative, and the present invention is not limited in any way to these examples.

[0184] The sample was prepared as follows. First, a tempering glass plate for ion exchange treatment was prepared. The tempering glass plate had the following glass composition by mass%, consisting of SiO2 51.6%, Al2O3 27.9%, B2O 30.3%, K2O 0.6%, Na2O 7.5%, Li2O 3.3%, MgO 0.3%, P2O 58.4%, and SnO 20.1%.

[0185] The glass raw materials were mixed to achieve the above composition and melted in a platinum pot at 1600°C for 21 hours. The resulting molten glass was then formed by flow-down drawing from a refractory molded body using the overflow down-draw method. The resulting glass ribbon was cut to predetermined dimensions to obtain tempered glass plates for test specimens. The thickness of the tempered glass plates was 0.55, 0.7, or 0.8 mm. Next, the tempered glass was immersed in a molten salt bath and subjected to ion exchange treatment in a first ion exchange step and a second ion exchange step to obtain tempered glass plates.

[0186] 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%. 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.

[0187] In the second ion exchange step, each test specimen was subjected to ion exchange treatment using molten salts with different weight concentration ratios of KNO3, NaNO3, and LiNO3. The ion exchange treatment time in the second ion exchange step was varied for each test specimen. The ion exchange treatment temperature of the molten salt in the second ion exchange step was 380°C.

[0188] Subsequently, a removal process was performed on each test specimen. In the removal process, both main surfaces of each test specimen were removed by polishing. At this time, the amount of material removed (amount of polishing) from each main surface was varied for each test specimen.

[0189] Subsequently, a pre-ion exchange process was performed on some of the test specimens. In the pre-ion exchange process, the weight concentration ratio of KNO3 to NaNO3 in the molten salt was set to 40%:60%. The ion exchange treatment time in the pre-ion exchange process was varied for each test specimen. The ion exchange treatment temperature of the molten salt in the pre-ion exchange process was 380°C.

[0190] Subsequently, a post-removal ion exchange process was performed on each test specimen. In the post-removal ion exchange process, the ion exchange treatment time was varied for each test specimen. The ion exchange treatment temperature of the molten salt in the post-removal ion exchange process was 380°C.

[0191] Subsequently, the stress profiles of each test specimen were measured. The stress profiles were measured using surface stress meters FSM-6000LE and SLP-1000 manufactured by Orihara Seisakusho Co., Ltd. For the measurements, the refractive index of each test specimen was set to 1.50 and the optical elastic constant to 28.9 [(nm / cm) / MPa].

[0192] Tables 1 to 23 show the conditions for each of the above processes and the measurement results of the strengthening characteristics. Of the samples No. 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 are examples in which the post-removal ion exchange process was performed without performing the post-removal pre-ion exchange process after the second ion exchange process, while Nos. 52 to 83 are examples in which the post-removal ion exchange process was performed after the post-removal pre-ion exchange process. In addition, Nos. 9, 10, 13, 14, 17, 18, 21, 22, 48 to 51, 111, 116, 165, and 170 are comparative examples. For the comparative example samples Nos. 48 to 51, polishing (removal process) was not performed after the second ion exchange process. In Tables 1-23, "Polishing Amount" is the sum of the polishing amounts of each main surface (both sides) in each test specimen. The polishing amount of one main surface is equal to the polishing amount of the other main surface. Furthermore, the polishing amounts shown in Tables 1-11 are theoretical estimates calculated based on the polishing rate and polishing time of the sample, and the exact actual polishing amount may vary. In Tables 1-7 and 12-20, "Δt" is the amount of tempered glass removed in the removal process (DOL1-DOL2). The value of "Δt / DOL1" is shown as a percentage.

[0193] Of the samples No. 1 to 174, the thickness of the tempered glass for No. 1 to 120 is 0.7 mm. The thickness of the tempered glass for No. 121 to 144 is 0.55 mm. The thickness of the tempered glass for No. 145 to 174 is 0.8 mm.

[0194] In the table, "DOC" represents the DOLzero value in the above embodiment. In the table, "CT" represents the maximum tensile stress value (CTmax) at the center of the thickness direction of the test specimen. In the table, "CS50" represents the compressive stress value at a depth of 50 μm from the surface of the test specimen.

[0195] In the table, "DOC Recall Rate" is the ratio of the DOC of an example or comparative example that underwent a removal process and a post-removal ion exchange process to the DOC of a comparative example that did not undergo a removal process. Specifically, the DOC recall rates for Nos. 1-10, 23-26, 39-47, 52-55, and 68-71 are shown as a percentage obtained by dividing the measured DOC by the DOC (150.5 μm) of comparative example No. 48, which was prepared under the same conditions. Similarly, the DOC recall rates for Nos. 11-14, 27-30, 56-59, and 72-75 are obtained by dividing the measured value by the DOC (146.2 μm) of the corresponding comparative example No. 49. The DOC recall rates for Nos. 15-18, 31-34, 60-63, and 76-79 are obtained by dividing the measured value by the DOC (143.0 μm) of the corresponding comparative example No. 50. The DOC recall rates for Nos. 19-22, 35-38, 64-67, and 80-83 were calculated by dividing the measured value by the DOC (140.4 μm) of the corresponding comparative example No. 51. Similarly, the DOC recall rates for Nos. 84-110, 112-115, 117-164, 166-169, and 171-174 were calculated by dividing the measured value by the DOC of the corresponding comparative example (details omitted).

[0196] In the table, "CT Reproducibility" is the ratio of the CT of an example or comparative example that underwent a removal process and a post-removal ion exchange process to the CT of a comparative example that did not undergo a removal process. Specifically, the CT reproducibility for Nos. 1-10, 23-26, 39-47, 52-55, and 68-71 is shown as a percentage obtained by dividing the measured DOC by the CT (-60.0 MPa) of comparative example No. 48, which was prepared under the same conditions. The CT reproducibility for Nos. 11-14, 27-30, 56-59, and 72-75 is obtained by dividing the measured value by the CT (-63.4 MPa) of the corresponding comparative example No. 49. The CT reproducibility for Nos. 15-18, 31-34, 60-63, and 76-79 is obtained by dividing the measured value by the CT (-63.6 MPa) of the corresponding comparative example No. 50. The CT recall rates for Nos. 19-22, 35-38, 64-67, and 80-83 are calculated by dividing the measured value by the CT (-66.7 MPa) of the corresponding comparative example No. 51. Similarly, the CT recall rates for Nos. 84-110, 112-115, 117-164, 166-169, and 171-174 are calculated by dividing the measured value by the CT of the corresponding comparative example (details omitted).

[0197] [Table 1]

[0198] [Table 2]

[0199] [Table 3]

[0200] [Table 4]

[0201] [Table 5]

[0202] Table 6

[0203] Table 7

[0204] Table 8

[0205] Table 9

[0206] Table 10

[0207] Table 11

[0208] Table 12

[0209] Table 13

[0210] Table 14

[0211] Table 15

[0212] Table 16

[0213] [Table 17]

[0214] [Table 18]

[0215] [Table 19]

[0216] [Table 20]

[0217] [Table 21]

[0218] [Table 22]

[0219] [Table 23]

[0220] The measurement results showed that in all of the examples, performing the post-removal ion exchange process allowed for enhancement characteristics comparable to those of the comparative example, which was an unpolished product. In particular, in the example where a pre-removal ion exchange process was performed, it was possible to measure each enhancement characteristic even when the amount of polishing was large (10 μm or more), and the DOC and CT recall rates were also relatively high.

[0221] As an example, Figure 11 shows the stress profiles of samples No. 1, No. 4, and No. 48. The stress profiles of the tempered glass samples No. 1 and No. 4, which are examples, clearly have a first peak, first bottom, second peak, and second bottom, similar to comparative example sample No. 48, which did not undergo the removal process. As shown in Figure 11, it can be seen that the examples are sufficiently strengthened, to the same extent as or even more so than the comparative example, by performing the ion exchange process after removal.

[0222] Figure 12 shows the stress profiles of samples No. 6, No. 48, No. 57, and No. 73. As shown in Figure 12, the stress profile of sample No. 57, which is an example in which a pre-ion exchange step after removal and a post-ion exchange step were performed, has a clearly larger first bottom and second peak compared to No. 6, which is an example in which only the post-ion exchange step was performed without the pre-ion exchange step, indicating a favorable recovery of the compressive stress in the deep regions. Therefore, performing a pre-ion exchange step after removal can favorably increase the strength of the glass that has been reduced by polishing (removal step). [Explanation of Symbols]

[0223] 1. Tempered glass 1a0 Surface of the glass to be removed 1a New surface of glass 3. Compressive stress layer B1 1st bottom B2 Second Bottom Maximum compressive stress of the compressive stress layer after the CS2 removal process Maximum compressive stress of the compressive stress layer after ion exchange process following CS3 removal Compressive stress at the first bottom of CSb Diffusion depth of K ions introduced in the second ion exchange process of DOL1 P1 (First Peak) P2 (Second Peak) S2 First ion exchange process S3 Second ion exchange process S4 First Inspection Process S5 removal process S7a Preliminary ion exchange process after removal S7 Ion exchange process after removal S41 1st measurement process S42 Planned removal amount setting process S61 2nd measurement process S62 Removal amount identification process S63 Ion exchange condition setting process Δt0 Planned removal amount Δt removal amount

Claims

1. In a method for manufacturing tempered glass, in which glass having a surface is subjected to ion exchange treatment to obtain tempered glass having a compressive stress layer on the surface, A first ion exchange step involves bringing the surface of the glass into contact with a first molten salt and performing an ion exchange between Li ions in the glass and Na ions in the first molten salt. A second ion exchange step involves bringing the surface of the glass into contact with a second molten salt and exchanging Na ions in the glass with K ions in the second molten salt. A removal step is performed to remove at least a portion of the surface of the tempered glass after the first ion exchange step and the second ion exchange step has been performed, thereby forming a new surface on the tempered glass. A post-removal ion exchange step is performed by ion exchange between Na ions in the reinforced glass and K ions in the molten salt after the removal step, thereby setting the maximum compressive stress CS3 of the compressive stress layer on the new surface to 700 MPa or more. After the first ion exchange step and the second ion exchange step are performed, an inspection step is performed to check for defects on the surface of the tempered glass before the removal step, The process includes a planned removal amount setting step for setting a planned removal amount to be removed from the surface of the tempered glass after the execution of the first ion exchange step and the second ion exchange step, A method for manufacturing tempered glass, characterized in that, if a defect is detected on the surface of the tempered glass in the inspection step, at least a portion of the surface is removed in the removal step based on the planned removal amount set in the planned removal amount setting step.

2. The process further comprises a pre-removal ion exchange step performed after the removal step and before the post-removal ion exchange step, The method for manufacturing tempered glass according to claim 1, wherein in the pre-ion exchange step after removal, 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 exchanged with Na ions in the third molten salt.

3. The third molten salt used in the aforementioned pre-ion exchange step after removal contains NaNO ３ The concentration of is the amount of NaNO in the first molten salt. ３ A method for producing tempered glass according to claim 2, wherein the concentration is substantially equal to that of the above.

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

5. The method for manufacturing tempered glass according to any one of claims 2 to 4, wherein the ion exchange treatment time in the pre-ion exchange step after removal is 10 to 100% of the ion exchange treatment time in the first ion exchange step.

6. The method for manufacturing tempered glass according to any one of claims 2 to 5, 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 glass is a plate-shaped or sheet-shaped glass with a thickness of 0.05 to 2.0 mm. A method for manufacturing tempered glass according to any one of claims 1 to 6, wherein the main front and back surfaces of the tempered glass before the removal-after ion exchange step are removed in a range shallower than the compressive stress layer, thereby making the maximum compressive stress CS2 of the compressive stress layer on the new surface after the removal step 100 MPa or more.

8. In the removal step, the surface of the tempered glass after the execution of the first ion exchange step and the second ion exchange step is polished or etched to remove the material. A method for manufacturing tempered glass according to any one of claims 1 to 7, wherein the amount of surface removal Δt in the removal step is smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step.

9. The removal amount Δt in the removal step is 20 μm or less. After the removal step, the compressive stress CS2 of the compressive stress layer on the new surface before the ion exchange step after removal is set to less than 700 MPa. A method for manufacturing tempered glass according to any one of claims 1 to 8, wherein the maximum compressive stress CS3 of the compressive stress layer after the removal and ion exchange step is set to 700 to 1200 MPa.

10. The stress profile obtained by measuring the stress in the depth direction from the new surface of the tempered glass after the removal and ion exchange process is, The first peak on the surface where the compressive stress reaches its maximum value, The stress gradually decreases in the depth direction from the first peak to the first bottom where the stress is at its minimum, The second peak, which gradually increases in the depth direction from the first bottom and reaches a maximum value of compressive stress, The structure comprises a second bottom, which gradually decreases in the depth direction from the second peak until the tensile stress reaches its minimum value, The method for manufacturing tempered glass according to any one of claims 1 to 9, wherein in the post-removal ion exchange step, ion exchange is performed between Na ions in the tempered glass and K ions in the molten salt so that the compressive stress CSb of the first bottom becomes 10 MPa or more.

11. LiNOx in the molten salt used in the ion exchange step after removal ３ The method for manufacturing tempered glass according to any one of claims 1 to 10, wherein the concentration of is 0.1 to 2% by mass.

12. The concentration of Na ions in the molten salt used in the ion exchange step after removal is NaNO ３ A method for manufacturing tempered glass according to any one of claims 1 to 11, wherein the amount is 5% by mass or less when converted to a certain percentage.

13. The ion exchange treatment temperature in the ion exchange step after removal is 350 to 450°C. The method for manufacturing tempered glass according to any one of claims 1 to 12, wherein 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. In the second ion exchange step, the Na ions in the glass are exchanged with the K ions in the second molten salt, and the Na ions in the glass are exchanged with the Li ions in the second molten salt. NaNO in the first molten salt ３ The concentration is 50% by mass or more. KNO in the first molten salt ３ The concentration is less than 50% by mass. The concentration of LiNO in the second molten salt is 0.5 to 5% by mass, and ３ is 0.5 to 5% by mass, and KNO in the second molten salt ３ The concentration is 95-99.5% by mass. The ion exchange treatment temperature in the first ion exchange step is 350 to 480°C. The ion exchange treatment temperature in the second ion exchange step is 350 to 480°C. The ion exchange treatment time for the first ion exchange step is 1 to 20 hours. A method for manufacturing tempered glass according to any one of claims 1 to 13, wherein the ion exchange processing time of the second ion exchange step is shorter than the ion exchange processing time of the first ion exchange step.

15. The aforementioned glass has a glass composition of SiO2 by mass%. ２ 40%~70%, Al ２ O ３ 10% to 30%, B ２ O ３ 0% to 3%, Na ２ O 5% to 25%, K ２ O 0% to 5.5%, Li ２ O 0.1% to 10%, MgO 0% to 6%, P ２ O ５ A method for producing tempered glass according to any one of claims 1 to 14, comprising 0% to 15%.

16. In a method for manufacturing tempered glass in which the compressive stress on the surface is adjusted, A removal step in which a new surface is formed on tempered glass by removing at least a portion of the surface of tempered glass that has a compressive stress layer on its surface to a depth shallower than the depth of the compressive stress layer, The process includes a post-removal ion exchange step in which the tempered glass, in which the maximum compressive stress CS2 of the compressive stress layer on the new surface is less than 700 MPa, is subjected to ion exchange treatment. In the aforementioned 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 ion exchange between the Na ions in the reinforced glass and the K ions in the molten salt. An inspection step is performed to inspect the surface of the tempered glass for defects before the removal step, The system further comprises a planned removal amount setting step, which sets a planned removal amount to be removed from the surface of the tempered glass, A method for manufacturing tempered glass, characterized in that, if a defect is detected on the surface of the tempered glass in the inspection step, at least a portion of the surface is removed in the removal step based on the planned removal amount set in the planned removal amount setting step.

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