Method for producing chemically strengthened glass and method for managing stress characteristics of chemically strengthened glass

Abstract

The present invention relates to a method for producing a chemically strengthened glass comprising the following (1) to (3). (1) A first glass and a second glass are immersed in the same molten salt composition and chemically strengthened at the same time, thereby obtaining a first chemically strengthened glass in which the first glass is chemically strengthened and a second chemically strengthened glass in which the second glass is chemically strengthened, wherein at least one of the K-Na substitution rate and the Na-Li substitution rate in ion exchange of the second glass is faster than that of the first glass. (2) The stress characteristics of the second chemically strengthened glass are measured. (3) Whether the stress characteristics of the second chemically strengthened glass are within the designed range is confirmed.

Description

Technical Field

[0001] The present invention relates to a method for producing chemically strengthened glass and a method for managing stress characteristics of chemically strengthened glass. Background Art

[0002] Chemically strengthened glass is used in the cover glass of portable terminals. Chemically strengthened glass is made by contacting glass with a molten salt such as sodium nitrate, causing ion exchange between the alkali metal ions contained in the glass and the alkali metal ions with a larger ion radius contained in the molten salt, and forming a compressive stress layer on the surface of the glass. The strength of chemically strengthened glass highly depends on the stress characteristics represented by the compressive stress value with the depth from the glass surface as a variable. Therefore, in the manufacture of chemically strengthened glass, it is necessary to properly manage the stress characteristics of chemically strengthened glass.

[0003] As a method for measuring stress characteristics of chemically strengthened glass without destroying it, for example, Patent Document 1 discloses a method for measuring surface stress of strengthened glass (hereinafter also abbreviated as FSM). In addition, Patent Document 2 discloses a method for measuring stress characteristics based on changes in the polarization phase of laser light (hereinafter also abbreviated as SLP).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2017 / 115811

[0007] Patent Document 2: International Publication No. 2018 / 056121 Summary of the invention

[0008] For FSM and SLP, the measurement accuracy of stress characteristics of chemically strengthened glass is low, and the quality is difficult to manage. For example, FSM measures stress characteristics based on the change in refractive index caused by the change in glass composition due to ion exchange. Therefore, if the depth of the compressive stress layer is shallow, or if the glass is not easy to increase the refractive index even after ion exchange, it cannot be measured with good accuracy. In addition, SLP measures stress characteristics based on the change in the polarization phase of laser light, so it cannot be measured with good accuracy when the depth of the compressive stress layer is shallow. In addition, in the manufacture of chemically strengthened glass on an industrial scale, there is a problem that it is difficult to directly manage the manufacturing conditions.

[0009] Therefore, in view of the above circumstances, an object of the present invention is to provide a method for producing chemically strengthened glass which can appropriately manage the stress characteristics of the chemically strengthened glass.

[0010] The present inventors have discovered that the above-mentioned problems can be solved by immersing a first glass and a second glass having at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange faster than that of the first glass in the same molten salt composition, and chemically strengthening the second glass at the same time, and confirming the stress characteristics of the chemically strengthened glass in which the second glass is chemically strengthened, thereby completing the present invention.

[0011] The present invention relates to a method for producing chemically strengthened glass, comprising the following (1) to (3).

[0012] (1) A first glass and a second glass are immersed in the same molten salt composition and chemically strengthened at the same time to obtain a first chemically strengthened glass in which the first glass is chemically strengthened and a second chemically strengthened glass in which the second glass is chemically strengthened, wherein at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange of the second glass is faster than that of the first glass.

[0013] (2) Measuring stress characteristics of the second chemically strengthened glass.

[0014] (3) Confirming whether the stress characteristics of the second chemically strengthened glass are within the designed range.

[0015] The present invention relates to a method for managing stress characteristics of chemically strengthened glass, comprising the following (I) to (III).

[0016] (I) A first glass and a second glass are immersed in the same molten salt composition and chemically strengthened at the same time to obtain a first chemically strengthened glass in which the first glass is chemically strengthened and a second chemically strengthened glass in which the second glass is chemically strengthened, wherein at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange of the second glass is faster than that of the first glass.

[0017] (II) measuring stress characteristics of the second chemically strengthened glass.

[0018] (III) Confirming that the stress characteristics of the second chemically strengthened glass are within a designed range.

[0019] According to the method for producing a chemically strengthened glass of the present invention, it is possible to appropriately manage the stress characteristics of the chemically strengthened glass, which are difficult to measure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flowchart showing one embodiment of the present invention.

[0021] Figure 2 This is a flowchart showing one embodiment of the present invention.

[0022] Figure 3This is a flowchart showing one embodiment of the present invention.

[0023] Figure 4 This is a flowchart showing one embodiment of the present invention. DETAILED DESCRIPTION

[0024] 1. Method for manufacturing chemically strengthened glass

[0025] The method for producing chemically strengthened glass of the present invention (hereinafter also referred to as the production method of the present invention) includes the following steps (1) to (3).

[0026] (1) A first glass and a second glass are immersed in the same molten salt composition and chemically strengthened at the same time to obtain a first chemically strengthened glass in which the first glass is chemically strengthened and a second chemically strengthened glass in which the second glass is chemically strengthened, wherein at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange of the second glass is faster than that of the first glass.

[0027] (2) Measuring stress characteristics of the second chemically strengthened glass.

[0028] (3) Confirming whether the stress characteristics of the second chemically strengthened glass are within the designed range.

[0029] Figure 1 Hereinafter, each step will be described with the second glass being a glass having a faster K—Na substitution rate than the first glass in ion exchange as the first embodiment and the second glass being a glass having a faster Na—Li substitution rate than the first glass as the second embodiment.

[0030] [First embodiment]

[0031] <Step (1): Chemical strengthening step>

[0032] Step (1) is a step of immersing a first glass and a second glass in the same molten salt composition and chemically strengthening them simultaneously to obtain a chemically strengthened glass, wherein the second glass is a glass having at least one of a K-Na substitution rate and a Na-Li substitution rate in ion exchange faster than that of the first glass. Using the chemical strengthening conditions of step (1) (hereinafter also referred to as chemical strengthening conditions), the glass obtained by chemically strengthening the first glass is the first chemically strengthened glass, and the glass obtained by chemically strengthening the second glass is the second chemically strengthened glass.

[0033] The glass that becomes the mother material of the first glass and the second glass can be any glass that can be ion exchanged, and can be any one of amorphous glass or crystallized glass. The method for making the glass that becomes the mother material of the first glass and the second glass is, for example, to appropriately coordinate glass raw materials in a manner to obtain a glass of a specified composition, and to utilize a glass melting furnace to heat and melt. Thereafter, the glass can be homogenized by bubbling, stirring, the addition of a clarifier, etc., to be formed into a glass plate of a specified thickness, and slowly cooled and made. Alternatively, it is also possible to utilize a method of being formed into a block and cutting off after slowly cooling to be formed into a plate.

[0034] As a method for forming into a plate, for example, a float process, a press process, a fusion process and a down-draw process can be cited. In particular, when manufacturing a large glass plate, the float process is preferred. In addition, continuous forming methods other than the float process, such as a fusion process and a down-draw process, are also preferred.

[0035] The formed glass ribbon is subjected to grinding and polishing treatment as needed to form a glass plate. It should be noted that when the glass plate is cut into a predetermined shape and size, or when the glass plate is chamfered, it is preferable to cut or chamfer the glass plate before performing the chemical strengthening treatment described later, because a compressive stress layer is also formed on the end surface by the chemical strengthening treatment.

[0036] After the formed glass plate is subjected to chemical strengthening treatment, it is washed and dried to obtain chemically strengthened glass. Chemical strengthening treatment is a treatment in which the glass is brought into contact with the metal salt by immersing the glass in a melt (molten salt composition) of a metal salt (e.g., potassium nitrate) containing metal ions with large ionic radius (typically, sodium ions or potassium ions), so that the metal ions with small ionic radius (typically, lithium ions or sodium ions) in the glass are replaced with metal ions with large ionic radius (typically, sodium ions or potassium ions relative to lithium ions, and potassium ions relative to sodium ions) in the metal salt.

[0037] From the perspectives of fast chemical strengthening treatment speed and the ability to form large compressive stress through ion exchange, it is preferred to use the "Na-Li replacement" method of exchanging lithium ions in the glass with sodium ions in the molten salt or the "K-Na replacement" method of exchanging sodium ions in the glass with potassium ions in the molten salt.

[0038] The treatment conditions of the chemical strengthening treatment are not particularly limited, and appropriate conditions may be selected taking into account the characteristics and composition of the glass, the type of the molten salt composition, and the desired surface compressive stress (CS) of the final chemically strengthened glass, the depth of the compressive stress layer (DOL), and other chemical strengthening characteristics. In addition, in the present invention, the chemical strengthening treatment may be performed only once, or multiple chemical strengthening treatments may be performed using two or more different conditions (multi-step strengthening).

[0039] Although the conditions for the chemical strengthening treatment are not particularly limited, for example, the treatment can be performed by immersing the glass plate in a molten salt composition such as potassium nitrate heated to 360 to 600° C. for 0.1 to 500 hours. It should be noted that the heating temperature of the molten salt composition is preferably 375 to 500° C., and the immersion time of the glass plate in the molten salt composition is preferably 0.3 to 200 hours.

[0040] As molten salts for chemical strengthening treatment, for example, nitrates, sulfates, carbonates and chlorides can be mentioned. Among them, as nitrates, for example, lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate and silver nitrate can be mentioned. As sulfates, for example, lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate and silver sulfate can be mentioned. As carbonates, for example, lithium carbonate, sodium carbonate and potassium carbonate can be mentioned. As chlorides, for example, lithium chloride, sodium chloride, potassium chloride, cesium chloride and silver chloride can be mentioned. These molten salts can be used alone or in combination.

[0041] In the manufacturing method of the present invention, the first glass is a glass to be managed for stress characteristics, and the second glass is a monitoring sample. That is, in the manufacturing method of the present invention, the second glass is used as a monitoring sample, chemically strengthened at the same time as the first glass, and the stress characteristics of the obtained second chemically strengthened glass are used as an index to manage the stress characteristics of the first chemically strengthened glass. The second glass is preferably a glass whose stress characteristics can be measured with high accuracy even when chemically strengthened under the same conditions as the first glass.

[0042] The second glass is a glass in which at least one of the K-Na substitution rate and the Na-Li substitution rate in ion exchange is faster than that of the first glass. Here, the K-Na substitution rate refers to the ion exchange rate of sodium ions in the glass with potassium ions in the molten salt composition. And, the Na-Li substitution rate refers to the ion exchange rate of lithium ions in the glass with sodium ions in the molten salt composition. The ion exchange rate of the glass (hereinafter also referred to as the substitution rate) can be measured based on the chemical strengthening conditions and the ion depth after chemical strengthening.

[0043] Specifically, the diffusion can be calculated using the following Steps 1 to 3 based on Fick's law (the following formula).

[0044]

[0045] In the above formula, D represents the diffusion coefficient (unit: ×10 －12 m 2 / min), C represents the ion concentration (unit: mol%), and x represents the depth from the glass surface (μm).

[0046] [Step 1] Prepare chemically strengthened glass strengthened under the conditions of temperature T (unit: °C) and time t (unit: minute).

[0047] [Step 2] For the chemically strengthened glass prepared in Step 1, an ion diffusion curve in the depth direction is measured.

[0048] Specifically, for example, the composition ratio is evaluated on a cross section of chemically strengthened glass by EPMA, SIMS, etc. In the case of K—Na substitution, the ion depth curve of K ions in the depth direction is measured, and in the case of Na—Li substitution, the ion depth curve of Na ions in the depth direction is measured.

[0049] [Step 3] The measured ion depth curve is fitted using the following formula: In the following formula, C(x) is the ion concentration at a depth x (μm) from the glass surface.

[0050]

[0051] D in the above formula is the diffusion coefficient (×10 －12 m 2 / minute), which is called the replacement speed.

[0052] Since the second glass has at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange faster than the first glass, the stress characteristics of the first chemically strengthened glass can be managed using the stress characteristics of the second chemically strengthened glass as an index.

[0053] The first embodiment of the manufacturing method of the present invention is a method of performing ion exchange (K-Na replacement) of sodium ions in the glass with potassium ions in the molten salt composition during chemical strengthening in step (1). In the first embodiment, the K-Na replacement rate of the second glass is preferably faster than the K-Na replacement rate of the first glass. In the first embodiment, the K-Na replacement rate of the second glass is preferably 1.1 times or more of the K-Na replacement rate of the first glass, more preferably 1.5 times or more, further preferably 2.0 times or more, and particularly preferably 4.0 times or more.

[0054] By making the K—Na substitution rate of the second glass 1.1 times or more of the K—Na substitution rate of the first glass, the stress characteristics of the second chemically strengthened glass are used as a reference index, and the stress characteristics of the first chemically strengthened glass can be further appropriately managed. In addition, the K—Na substitution rate of the second glass is generally 10,000 times or less of the K—Na substitution rate of the first glass.

[0055] It should be noted that the K-Na substitution rate can also be simply evaluated by the ratio of the depth of the compressive stress layer DOL by strengthening the first glass and the second glass under the same strengthening conditions. It should be noted that DOL is basically proportional to the square root of the diffusion rate, so the square of the DOL ratio is equivalent to the substitution rate ratio. Similarly, in FSM, the number of interference fringes is basically proportional to DOL, so it can also be simply evaluated by the ratio of DOL.

[0056] In the first embodiment of the manufacturing method of the present invention, as the first chemically strengthened glass, for example, when the diffusion layer depth of potassium ions is preferably 10 μm or less, it is difficult to accurately measure the stress characteristics, and thus it is more useful to manage the stress characteristics of the first chemically strengthened glass using the stress characteristics of the second chemically strengthened glass as an index. From the viewpoint of reducing the tensile stress balanced with the compressive stress and suppressing the progress of the scratches caused by the tensile stress, the diffusion layer depth of potassium ions in the first chemically strengthened glass is more preferably 8 μm or less, further preferably 6 μm or less, particularly preferably 4 μm or less, and further preferably 2 μm or less. And, typically, it is preferably 1 μm or more.

[0057] The diffusion layer depth of potassium ions in chemically strengthened glass can be measured by EPMA and SIMS. Here, the ion diffusion depth refers to the depth that is greater than the value obtained by adding 5% of the difference between the maximum and minimum values ​​to the minimum value in the ion distribution from the glass surface toward the center of the glass, when the difference between the maximum and minimum values ​​is set to 100%. When there are two or more corresponding values, the one that is closer to the center of the plate thickness and deeper from the glass surface is set as the diffusion layer depth.

[0058] In the first embodiment of the manufacturing method of the present invention, the second glass is preferably a glass whose refractive index is increased by replacing sodium ions in the second glass with potassium ions. As described above, in FSM, it is difficult to accurately measure the stress characteristics of glass whose refractive index does not change even after ion exchange. In one embodiment of the manufacturing method of the present invention, by making the second glass a glass whose refractive index is increased by ion exchange, even if the first glass is a glass whose refractive index does not change by ion exchange, the stress characteristics of the second chemically strengthened glass can be used as an index, and the stress characteristics of the first chemically strengthened glass can be appropriately managed.

[0059] In the first embodiment of the manufacturing method of the present invention, the composition of the second glass preferably contains more Na2O than the composition of the first glass on an oxide basis, preferably by 1 mol% or more, more preferably by 2 mol% or more, and further preferably by 4 mol% or more. By containing more Na2O than the composition of the first glass, preferably by 1 mol% or more, the ion exchange rate can be increased, and thus the stress characteristics of the first chemically strengthened glass can be appropriately managed using the stress characteristics of the second chemically strengthened glass as an indicator.

[0060] From the viewpoint of improving the measurement accuracy of stress characteristics, the thickness of the second glass is preferably 0.2 to 2.5 mm, more preferably 0.3 to 2.0 mm, and further preferably 0.4 to 1.0 mm. Furthermore, from the viewpoint of improving the measurement accuracy of stress characteristics, the thickness of the first glass is preferably 0.3 to 2.5 mm, more preferably 0.4 to 2.0 mm, and further preferably 0.5 to 1.0 mm.

[0061] In one embodiment of the manufacturing method of the present invention, two or more glasses having different compositions are preferably used as the second glass. By using two or more glasses having different compositions as the second glass, the accuracy of managing the stress characteristics of the first chemically strengthened glass can be improved. In addition, by using two or more glasses having different compositions as the second glass, two or more chemical strengthening conditions can be managed.

[0062] In one embodiment of the manufacturing method of the present invention, the first chemically strengthened glass preferably has a visible light transmittance of 80% or more, more preferably 84% or more, and further preferably 86% or more, calculated as a plate thickness of 0.7 mm. In addition, the visible light transmittance of the first chemically strengthened glass calculated as a plate thickness of 0.7 mm is typically 88% or more. The second chemically strengthened glass preferably has a visible light transmittance of 80% or more, more preferably 84% or more, and further preferably 86% or more, calculated as a plate thickness of 0.7 mm. In addition, the visible light transmittance of the second chemically strengthened glass calculated as a plate thickness of 0.7 mm is typically 88% or more.

[0063] In addition, sometimes, the visible light transmittance is preferably 80% or less based on design properties (e.g., colored AG glass). In this case, since it is difficult to measure the stress characteristics using non-destructive tests such as SLP when the visible light transmittance converted to a plate thickness of 0.7 mm is preferably 60% or less as the first chemically strengthened glass, it is more useful to manage the stress characteristics of the first chemically strengthened glass using the stress characteristics of the second chemically strengthened glass as an indicator. From the above viewpoints, the visible light transmittance is more preferably 40% or less, and further preferably 20% or less. And, typically, it is 0.01% or more.

[0064] In one embodiment of the manufacturing method of the present invention, when the interference fringes observed by a surface stress meter using the optical waveguide effect as the observation principle are preferably 2 or less as the first chemically strengthened glass, it is difficult to measure the stress characteristics by non-destructive tests such as FSM, so it is useful to manage the stress characteristics of the first chemically strengthened glass using the stress characteristics of the second chemically strengthened glass as an indicator. From the above viewpoint, it is more preferable that the first chemically strengthened glass has 1 or less interference fringes.

[0065] In one embodiment of the manufacturing method of the present invention, when the refractive index of the first chemically strengthened glass is preferably outside the range of 1.40 to 1.62, for example, it is difficult to measure the stress characteristics by non-destructive testing such as FSM, so it is more useful to manage the stress characteristics of the first chemically strengthened glass using the stress characteristics of the second chemically strengthened glass as an index. From the above viewpoint, the refractive index of the first chemically strengthened glass is more preferably outside the range of 1.4 to 1.7.

[0066] <Step (2): Stress property measurement step>

[0067] Step (2) is a step of measuring the stress characteristics of the second chemically strengthened glass obtained in step (1). Examples of stress characteristics include surface compressive stress (CS), depth of compressive stress layer (DOL), tensile stress at the center of plate thickness (CT), plate thickness, bending strength, crack initiation load, diffusion layer depth of potassium ions, diffusion layer depth of sodium ions, etc. From the perspective of improving the accuracy of management of the stress characteristics of the first chemically strengthened glass, it is preferred to select at least one of CS, DOL and CT, more preferably at least CS and DOL, further preferably CS, DOL and CT, and particularly preferably curves showing the diffusion layer depth of potassium ions and the diffusion layer depth of sodium ions.

[0068] The method for measuring stress characteristics can be appropriately selected from conventionally known methods without particular limitation, and for example, a sample obtained by thinning a cross section of a glass plate is used for measurement using a birefringence stress meter. A birefringence stress meter is a device that uses a polarizing microscope and a liquid crystal display compensator to measure the magnitude of retardation caused by stress, and an example of such device is the birefringence imaging system Abrio-IM manufactured by CRi.

[0069] The compressive stress value near the surface of the glass plate can be measured using, for example, an optical waveguide surface stress meter (eg, FSM-6000 manufactured by Orihara Corporation). The optical waveguide surface stress meter can measure the stress value without performing processing such as thinning the glass sample.

[0070] The stress value inside the glass can be measured, for example, using a scattered light photoelastic stress meter (e.g., SLP-2000 manufactured by Orihara Corporation). The scattered light photoelastic stress meter is independent of the refractive index distribution inside the glass and can measure the stress value without performing processing such as thinning the glass sample.

[0071] <Step (3): Stress characteristics evaluation step>

[0072] Step (3) is a step of confirming whether the stress characteristics of the second chemically strengthened glass measured in step (2) are within the designed range, and the stress characteristics of the first chemically strengthened glass are managed by setting the stress characteristics of the second chemically strengthened glass within the management range. In step (3), if the stress characteristics of the second chemically strengthened glass are within the designed range, it can be determined that the stress characteristics of the first chemically strengthened glass are within the designed range.

[0073] For the stress characteristics of the first chemically strengthened glass, the "design range" is set from the perspective of quality design. As an example, the stress characteristics of the first chemically strengthened glass are difficult to measure in FSM and SLP, but if it is a destructive test (Abrio, etc.), stress measurement can be performed. By measuring the stress characteristics in advance using a destructive test, the allowable range of the stress characteristics of the first chemically strengthened glass that meets the required characteristics can be determined. In order to set the stress characteristics of the first chemically strengthened glass within the designed range, the first glass is chemically strengthened using conditions within the designed range. As conditions for chemical strengthening, for example, temperature, time, and salt concentration contained in the molten salt composition can be cited.

[0074] Whether the chemical strengthening conditions of the first glass are "conditions within the designed range" can be determined by judging whether the stress characteristics of the second chemically strengthened glass are within the range of stress characteristics when the second glass is chemically strengthened under the conditions within the designed range. The fact that the stress characteristics of the second chemically strengthened glass are within the range of stress characteristics when the second glass is chemically strengthened under the conditions within the designed range is referred to as "the stress characteristics of the second chemically strengthened glass are within the designed range". The stress characteristics of the second chemically strengthened glass and the conditions for chemical strengthening are known.

[0075] As one aspect of step (3), for example, a aspect of confirming whether the stress characteristic of the second chemically strengthened glass is within a designed range for the value of the stress characteristic of the second chemically strengthened glass measured in step (2) (e.g., CS, DOL) can be cited. If the value of the stress characteristic of the second chemically strengthened glass is within the designed range, it can be determined that the stress characteristic of the first chemically strengthened glass is within the designed range. In addition, if the value of the stress characteristic of the second chemically strengthened glass is within the designed range, it can be determined that the conditions for chemically strengthening the first glass are within the designed range.

[0076] As a range of stress characteristics of the second chemically strengthened glass for judging that the conditions for chemically strengthening the first glass are within the designed range, for example, CS is preferably managed within the range of ±100 MPa of the designed value, more preferably ±50 MPa of the designed value, and further preferably ±30 MPa. In addition, for example, DOL is preferably managed within the range of ±10 μm of the designed value, more preferably ±5 μm of the designed value, and further preferably ±3 μm.

[0077] <Step (4): Step of determining chemical strengthening conditions>

[0078] The manufacturing method of the present invention may further include step (4) after steps (1) to (3). Step (4) is a step of determining the chemical strengthening conditions of step (1) based on the stress characteristics of the second chemically strengthened glass, and the chemical strengthening conditions are calculated and managed based on the stress characteristics of the second chemically strengthened glass. A flowchart for explaining an embodiment including steps (1) to (4) is shown in Figure 2 .

[0079] As one embodiment of step (4), for example, based on the measurement result of the stress characteristics of the second chemically strengthened glass in step (2), the chemical strengthening conditions in step (1) are identified, compared with a pre-set "design range of chemical strengthening conditions for the first glass", and it is determined whether the chemical strengthening conditions in step (1) are within the designed range.

[0080] <Step (1'): Step of determining the relationship between stress characteristics and chemical strengthening conditions>

[0081] When the relationship between the stress characteristics of the second glass and the chemical strengthening conditions is not known, the manufacturing method of the present invention may include a step (1') before the step (1). The step (1') is a step of finding the relationship between the chemical strengthening conditions of the composition of the second glass and the stress characteristics. Specifically, it is performed as follows. The step (1') is a step of obtaining a third chemically strengthened glass by chemically strengthening a third glass having the same composition as the second glass, measuring the stress characteristics of the third chemically strengthened glass, and finding the correlation between the stress characteristics of the third chemically strengthened glass and the chemical strengthening conditions of the step (1'). It is preferred to use the correlation between the stress characteristics of the third chemically strengthened glass and the chemical strengthening conditions of the step (1') to find the design range of the step (3).

[0082] Figure 3 Schematic diagram for explaining an embodiment in which step (1') is included before step (1) and step (4) is included after steps (1) to (3).

[0083] As a method for determining stress characteristics and chemical strengthening conditions, for example, there can be mentioned the method described in Maya Hatano et al., Key Engineering Materials, 1662-9795, Vol. 702, p. 32-36.

[0084] The second glass and the third glass have the same composition. From the viewpoint of improving the prediction accuracy of the relationship between the stress characteristics and the chemical strengthening conditions in the step (1'), the second glass and the third glass preferably have the same thickness.

[0085] As one embodiment of the step (1'), for example, the following step (1'a) or (1'b) can be cited. (1'a) The third glass is chemically strengthened under a plurality of different conditions (e.g., temperature, time, salt concentration), and the correlation between each stress characteristic (e.g., CS, DOL) and temperature, time, and salt concentration is obtained. Using the correlation obtained from the experimental point, the stress characteristic assumed by the strengthening condition is set as (CS sim 、DOL sim (1'b) Using a strengthening simulation (finite element method, etc.), the stress characteristics (e.g., CS, DOL) of the chemically strengthened glass obtained by chemically strengthening the third glass under a plurality of different conditions (e.g., temperature, time, salt concentration) are calculated, and the simulated value of the obtained stress characteristics is set as (CS sim 、DOL sim ).

[0086] As step (4) in the embodiment including the above-mentioned step (1') and steps (1) to (4), for example, there can be mentioned a step including the following steps (4-1) to (4-3). The flowchart of this embodiment is shown in Figure 4 .

[0087] (4-1) Based on the correlation obtained by using the step (1'), candidate conditions are obtained for the chemical strengthening conditions (e.g., temperature, time, salt concentration) of the step (1). The number of candidate conditions may be two or more. As a method for obtaining the candidate conditions, for example, the simulated value of the stress characteristic obtained in the step (1') (e.g., CS sim and DOL sim ) and the measured values ​​of stress characteristics of the second chemically strengthened glass (e.g. CS exp and DOL exp ) is used as a candidate condition for an approximate value; a method for investigating the relationship between chemical strengthening conditions and stress characteristics using the finite element method, and a method for inferring chemical strengthening conditions from stress characteristics, etc.

[0088] (4-2) For each candidate condition obtained in step (4-1), the measured values ​​of the stress characteristics of the second chemically strengthened glass (e.g., CS exp and DOL exp ) and analog values ​​(such as CS sim and DOL sim ), and find the error of the stress characteristic value (for example, CS error and DOL error) shown in the following formula (i).

[0089] Error of stress characteristic value = (measured value of stress characteristic - simulated value of stress characteristic) / measured value of stress characteristic ... formula (i)

[0090] When the stress characteristics are, for example, CS and DOL, the CS error and the DOL error are respectively expressed by the following equations (ii) and (iii).

[0091] CS error = (CS exp -CS sim ) / CS exp …Formula (ii)

[0092] DOL error = (DOL exp -DOL sim ) / DOL exp …Formula (iii)

[0093] (4-3) For each candidate condition, the sum of squares of the errors of each stress characteristic value is calculated, and the condition with the smallest sum of squares of the errors is determined as the chemical strengthening condition of step (1). When the stress characteristic values ​​are, for example, CS and DOL, the sum of squares of the errors is expressed by the following formula (iv).

[0094] The sum of squared errors = squared CS error + squared DOL error…Formula (iv)

[0095] When two or more glasses having different compositions are used as the second glass, in the step (4-3), the sum of squares of errors of the second chemically strengthened glasses of respective compositions is calculated one by one, and the chemical strengthening condition that minimizes the sum is determined as the chemical strengthening condition of the step (1).

[0096] Specifically, for example, when two or more glasses (second glass a, second glass b) having different compositions are used as the second glass, the step (4) includes, for example, the following steps (4'-1) to (4'-3).

[0097] (4′-1) Based on the correlation obtained in the step (1′), candidates for the chemical strengthening conditions (eg, temperature, time, salt concentration) of (1) are obtained.

[0098] (4′-2) For each of the second chemically strengthened glasses a and b under the candidate conditions selected in (4′-1), an error in the stress characteristic value is obtained.

[0099] (4′-3) For each of the second chemically strengthened glasses a and b, the sum of the squares of the errors of the stress characteristic values ​​is obtained, and the sum of the squares of the errors of the second chemically strengthened glass a and the squares of the errors of the second chemically strengthened glass b, that is, the sum of the squares of the errors represented by the following formula (v) is obtained. The chemical strengthening condition under which the sum of the squares of the errors is minimized is determined as the chemical strengthening condition of step (1).

[0100] The sum of the squares of the errors = (the sum of the squares of the errors of the second chemically strengthened glass a) + (the sum of the squares of the errors of the second chemically strengthened glass b) Formula (v)

[0101] [Second embodiment]

[0102] The second embodiment of the manufacturing method of the present invention is a case where lithium ions in the glass are exchanged with sodium ions in the molten salt composition during chemical strengthening. The second embodiment is the same as the first embodiment except for the following points. In the second embodiment, the Na-Li replacement rate of the second glass is preferably faster than the Na-Li replacement rate of the first glass.

[0103] In the second embodiment of the manufacturing method of the present invention, the Na-Li substitution rate of the second glass is preferably 1.1 times or more of the Na-Li substitution rate of the first glass, more preferably 1.5 times or more, further 2.0 times or more, and particularly preferably 4.0 times or more. By making the Na-Li substitution rate of the second glass 1.1 times or more of the Na-Li substitution rate of the first glass, it is easy to appropriately manage the stress characteristics of the first chemically strengthened glass using the stress characteristics of the second chemically strengthened glass as an index. In addition, from the viewpoint of appropriately managing the stress characteristics of the first chemically strengthened glass, the Na-Li substitution rate of the second glass is preferably 10,000 times or less of the Na-Li substitution rate of the first glass.

[0104] It should be noted that the first glass and the second glass can be strengthened under the same strengthening conditions and the ratio of the depth of the compressive stress layer DOL can be used for simple evaluation. It should be noted that DOL is roughly proportional to the square root of the diffusion rate, so the square of the DOL ratio is equivalent to the substitution rate factor.

[0105] In the second embodiment of the manufacturing method of the present invention, as the first chemically strengthened glass, for example, if the diffusion layer depth of sodium ions is preferably 50 μm or less, it is difficult to accurately measure the stress characteristics using SLP, and thus it is useful to manage the stress characteristics of the first chemically strengthened glass using the stress characteristics of the second chemically strengthened glass as an index. From this viewpoint, the diffusion layer depth of sodium ions in the first chemically strengthened glass is more preferably 45 μm or less, further preferably 40 μm or less, and particularly preferably 35 μm or less. And, typically, it is preferably 30 μm or more.

[0106] The depth of the sodium ion diffusion layer in chemically strengthened glass can be measured by SIMS.

[0107] 2. Methods for managing stress characteristics of chemically strengthened glass

[0108] The method for managing stress characteristics of the chemically strengthened glass of the present invention (hereinafter also referred to as the management method of the present invention) includes the following steps (I) to (III).

[0109] (I) A first glass and a second glass are immersed in the same molten salt composition and chemically strengthened at the same time to obtain a first chemically strengthened glass in which the first glass is chemically strengthened and a second chemically strengthened glass in which the second glass is chemically strengthened, wherein at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange of the second glass is faster than that of the first glass.

[0110] (II) measuring stress characteristics of the second chemically strengthened glass.

[0111] (III) Confirming that the stress characteristics of the second chemically strengthened glass are within a designed range.

[0112] The steps (I) to (III) are respectively the same as the steps (1) to (3) described in the section of the method for producing chemically strengthened glass. According to the management method of the present invention, even if the first glass is a glass whose stress characteristics are difficult to measure by non-destructive testing, the stress characteristics of the first chemically strengthened glass can be estimated by using the stress characteristics of the second chemically strengthened glass as an index, thereby appropriately managing the stress characteristics of the chemically strengthened glass.

[0113] Example

[0114] The following is a detailed description of the embodiments of the present invention, but the present invention is not limited to these. Examples 1 and 2 are embodiments.

[0115] [Measurement method]

[0116] (CS and DOL)

[0117] CS was measured using an optical waveguide surface stress meter (FSM-6000 manufactured by Orihara Corporation), and DOL was measured using a birefringence stress meter (Abrio manufactured by Orihara Corporation).

[0118] (Replacement speed)

[0119] The replacement speed is obtained using Steps 1 to 3 above.

[0120] [Example 1]

[0121] <Step (1')> A step of chemically strengthening a third glass having the same composition as the second glass to obtain a third chemically strengthened glass, and determining the relationship between the stress characteristics of the third chemically strengthened glass and the chemical strengthening conditions in step (1')

[0122] (Production of chemically strengthened glass)

[0123] Glass raw materials are mixed in a manner to form glass compositions 2A and 2B described later in <Step (1)>, and are melted and ground to produce a glass plate for chemical strengthening. As glass raw materials, general glass raw materials such as oxides, hydroxides, carbonates, etc. are appropriately selected, and 900 g of glass is weighed. The mixed glass raw materials are placed in a platinum crucible, melted and degassed at 1700°C. The glass is flowed onto a carbon plate to obtain a glass block. The obtained peeling is processed and mirror-polished to obtain a glass plate of chemically strengthened glass with a thickness t of 0.7 mm.

[0124] (Production of the Third Chemically Strengthened Glass and Evaluation of the Relationship between Stress Characteristics and Chemical Strengthening Conditions)

[0125] The obtained chemically strengthened glass was used as the third chemically strengthened glass, and the relationship between stress characteristics and chemical strengthening conditions was evaluated. For the chemically strengthened glass obtained above, the stress characteristics (CS) of the chemically strengthened glass obtained by chemical strengthening under the conditions of changing the salt concentration (KNO3 content in the molten salt composition) in the range of 95 to 100 mass% by 0.5 mass% scale, changing the temperature in the range of 380 to 450°C by 5°C scale, and changing the time in the range of 15 to 180 minutes by 5 minutes scale were obtained by simulation. sim and DOL sim ). In each condition, the chemically strengthened glass obtained by chemically strengthening the chemically strengthened glass having the same composition as the glass composition 2A is collectively referred to as 3A, and the chemically strengthened glass obtained by chemically strengthening the chemically strengthened glass having the same composition as the glass composition 2B is collectively referred to as 3B.

[0126] <Step (1)> Step of obtaining first chemically strengthened glass and second chemically strengthened glass

[0127] (Production of chemically strengthened glass)

[0128] Next, mirror polishing was performed in the same manner as in step (1′) so as to obtain a glass plate for chemical strengthening having a thickness t of 0.7 mm, so as to obtain glass composition 1, 2A or 2B represented by molar percentage based on oxides.

[0129] Glass composition 1: Composition containing SiO2, Al2O3, Li2O and 4.8% Na2O

[0130] Glass composition 2A: A composition containing SiO2 64%, Al2O3 8%, Na2O 13%, K2O 4%, and MgO 11%.

[0131] Glass composition 2B: having a composition of SiO2 64%, Al2O3 11%, Na2O 16%, K2O 1%, and MgO 8%.

[0132] A 0.7 mm thick chemically strengthened glass plate composed of glass composition 1, glass composition 2A or glass composition 2B was chemically strengthened at 390° C. for 4 hours using a molten salt composition containing 96.5 mass % of KNO3 and 3.5 mass % of NaNO3. The stress characteristics and substitution rate ratio of the obtained chemically strengthened glass were evaluated, and the results are shown in Table 1. The substitution rate ratio is obtained by squaring the DOL ratio.

[0133] Table 1

[0134] Glass composition 1 2A 2B CS(MPa) 976 605 860 DOL(μm) 4.1 26.2 20.1 DOL Ratio 1.0 6.4 4.9 Replacement speed ratio 1.0 40.8 24.0

[0135] (Production of Chemically Strengthened Glass 1, 2A, and 2B)

[0136] The glass plate for chemical strengthening was subjected to ion exchange treatment under the conditions shown in Table 2A to obtain the first chemically strengthened glass (chemically strengthened glass 1) and the second chemically strengthened glass (chemically strengthened glass 2A, 2B). The salt concentration in Table 2A refers to the KNO3 content in the molten salt composition, and the rest is NaNO3.

[0137] <Step (2)> Step of measuring stress characteristics of second chemically strengthened glass

[0138] The CS and DOL of the chemically strengthened glasses 2A and 2B produced in step (1) were evaluated. The results were denoted as CS and DOL, respectively. exp and DOL exp Shown in Table 2A.

[0139] <Step (3)> Step of confirming whether the stress characteristics of the second chemically strengthened glass are within the designed range

[0140] The designed range of the stress characteristics of the second chemically strengthened glass obtained in advance is shown in Table 2B. It was confirmed that the results of Table 2A were within the range of Table 2B.

[0141] <Step (4)> Step of determining chemical strengthening conditions

[0142] The stress characteristics (CS) of the chemically strengthened glasses 3A and 3B obtained in step (1′) sim and DOL sim ), and the stress characteristic value (CS exp and DOL exp The conditions closest to ) were selected as candidate conditions 1-1 to 1-5. The results are shown in Table 3.

[0143] For the candidate conditions 1-1 to 1-5 obtained, according to the stress characteristic values ​​(CS sim and DOL sim ) and the stress characteristic values ​​(CS exp and DOL exp ), using the above formulas (ii) to (iv), calculate the sum of the squares of the errors (Δ3A, Δ3B), and using the above formula (v), calculate the sum of the sums of the squares of the errors (Sum).

[0144] Table 2A

[0145]

[0146] Table 2B

[0147]

[0148]

Table 3

[0149]

[0150] As shown in Table 2A and Table 2B, the results shown in Table 2A are within the range shown in Table 2B. In Table 3, the sum of the squares of the errors Δ3A, Δ3B and the sum of the squares of the errors enclosed by the thick frame are the minimum values. As shown in Table 3, candidate condition 1-1, in which the sum of the squares is the minimum, is the same condition as the chemical strengthening conditions of the chemically strengthened glasses 2A and 2B shown in Table 2A. It can be seen that by using two types of second glasses, the chemical strengthening conditions for strengthening the first glass can be identified.

[0151] [Example 2]

[0152] <Step (1')> A step of chemically strengthening a third glass having the same composition as the second glass to obtain a third chemically strengthened glass, and determining the relationship between the stress characteristics of the third chemically strengthened glass and the chemical strengthening conditions of step (1')

[0153] As in Example 1, as the third chemically strengthened glass, the stress characteristics (CS sim and DOL sim ).

[0154] <Step (1)> Step of obtaining first chemically strengthened glass and second chemically strengthened glass

[0155] The chemical strengthening conditions of Example 1 were changed to the conditions shown in Table 4A. The chemical strengthening glass was chemically strengthened in the same manner as in Example 1 to produce the first chemically strengthened glass (chemically strengthened glass 1), chemically strengthened glasses 2A and 2B. The salt concentration in Table 4A refers to the KNO3 content in the molten salt composition, and the remainder is NaNO3.

[0156] <Step (2)> Step of measuring stress characteristics of second chemically strengthened glass

[0157] The CS and DOL of the chemically strengthened glasses 2A and 2B produced in step (1) were evaluated in the same manner as in Example 1. The results were given as CS and DOL, respectively. exp and DOL exp Shown in Table 4A.

[0158] <Step (3)> Step of confirming whether the stress characteristics of the second chemically strengthened glass are within the designed range

[0159] The designed range of the stress characteristics of the second chemically strengthened glass obtained in advance is shown in Table 4B. It was confirmed that the results of Table 4A were within the range of Table 4B.

[0160] <Step (4)> Step of determining chemical strengthening conditions

[0161] The stress characteristics (CS) of the chemically strengthened glasses 3A and 3B obtained in step (1′) sim and DOL sim ), and the stress characteristic value (CS exp and DOL exp The conditions closest to ) were selected as candidate conditions 2-1 to 2-5. The results are shown in Table 5.

[0162] For each of the candidate conditions 2-1 to 2-5 obtained, the stress characteristic value (CS sim and DOL sim) and the stress characteristic value (CS exp and DOL exp ), find the sum of the squares of the errors (Δ3A, Δ3B), and find the sum of the sums of the squares of the errors (Sum). The results are shown in Table 5.

[0163] Table 4A

[0164]

[0165] Table 4B

[0166]

[0167] Table 5

[0168]

[0169] As shown in Table 4A and Table 4B, the result shown in Table 4A is within the range shown in 4B. In Table 5, the sum of squares of errors Δ3A, Δ3B and the sum of squares of errors are the minimum values ​​surrounded by bold frames. As shown in Table 5, candidate condition 2-1, in which the sum of squares of errors Δ3A, Δ3B and the sum of squares of errors are the minimum values, is the same condition as the chemical strengthening conditions of chemically strengthened glasses 2A and 2B shown in Table 4A. It can be seen that by using any of the second glasses, the chemical strengthening conditions for strengthening the first glass can be identified.

[0170] From the above results, it is understood that according to the production method of the present invention, the stress characteristics of the chemically strengthened glass can be appropriately managed, and the chemically strengthened glass 1 obtained by chemically strengthening the first glass can be produced.

[0171] In addition, by preliminarily investigating the range of stress characteristics (e.g., CS and DOL) that can determine the candidate conditions as 2-1, for example, it is possible to confirm whether the stress characteristics of the second chemically strengthened glass are within the "design range" of the above-mentioned step (3) or step (III), thereby enabling efficient evaluation or management of the stress characteristics of the chemically strengthened glass.

[0172] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to one skilled in the art that various modifications and changes can be made without departing from the scope and spirit of the present invention.

[0173] This application is made based on Japanese Patent Application No. 2020-092689 filed on May 27, 2020, the contents of which are incorporated herein by reference.

Claims

1. A method for managing stress characteristics of a chemically strengthened glass, comprising: using a second glass as a monitoring sample, chemically strengthening the second glass at the same time as the first glass, and using the stress characteristics of the obtained second chemically strengthened glass as an indicator to manage the stress characteristics of the first chemically strengthened glass as a management target of the stress characteristics, the method comprising the following (1) to (4): (1) immersing a first glass and a second glass in the same molten salt composition and chemically strengthening them simultaneously, thereby obtaining a first chemically strengthened glass in which the first glass is chemically strengthened and a second chemically strengthened glass in which the second glass is chemically strengthened, wherein at least one of a K—Na substitution rate and a Na—Li substitution rate in ion exchange of the second glass is faster than that of the first glass; (2) measuring stress characteristics of the second chemically strengthened glass, (3) confirming whether the stress characteristics of the second chemically strengthened glass are within the designed range, (4) The chemical strengthening conditions of (1) are determined based on stress characteristics of the second chemically strengthened glass.

2. The method according to claim 1, wherein: Before the above (1), the following (1') is included: (1′) A third glass having the same composition as the second glass is chemically strengthened to obtain a third chemically strengthened glass, and the relationship between the chemical strengthening conditions and the stress characteristics of the composition of the second glass is obtained by measuring the stress characteristics of the third chemically strengthened glass.

3. The method according to claim 1 or 2, wherein: The stress characteristic in (2) is at least one selected from the group consisting of surface compressive stress CS, compressive stress layer depth DOL, and tensile stress CT at the center of plate thickness.

4. The method according to claim 1 or 2, wherein: The chemical strengthening conditions of (1) include the immersion time of the first glass and the second glass in the molten salt composition and the temperature of the molten salt composition.

5. The method according to claim 1 or 2, wherein: The second glass has a thickness of 0.3 to 2.5 mm.

6. The method according to claim 2, wherein: The thickness of the second glass is the same as the thickness of the third glass.

7. The method according to claim 1 or 2, wherein: As the second glass, two or more types of glasses having compositions different from each other are used.

8. The method according to claim 1 or 2, wherein: The K—Na substitution rate of the second glass is faster than that of the first glass.

9. The method according to claim 8, wherein: The potassium ion diffusion layer depth of the first chemically strengthened glass is 10 μm or less.

10. The method according to claim 8, wherein: The K—Na substitution rate of the second glass is 1.1 times or more the K—Na substitution rate of the first glass.

11. The method according to claim 8, wherein: The second glass is glass in which the refractive index is increased by replacing sodium ions in the second glass with potassium ions.

12. The method according to claim 8, wherein: The composition of the second glass contains 1 mol% or more of Na2O on an oxide basis, compared with the composition of the first glass.

13. The method according to claim 1 or 2, wherein: The Na—Li replacement rate of the second glass is faster than that of the first glass.

14. The method according to claim 13, wherein: The first chemically strengthened glass has a sodium ion diffusion layer depth of 50 μm or less.

15. The method according to claim 13, wherein: The Na—Li replacement rate of the second glass is 1.1 times or more the Na—Li replacement rate of the first glass.

16. The method according to claim 1 or 2, wherein: The first chemically strengthened glass has a visible light transmittance of 80% or less based on a plate thickness of 0.7 mm.

17. The method according to claim 1 or 2, wherein: The first chemically strengthened glass has one or less interference fringe observed using a surface stress meter using the optical waveguide effect as an observation principle.

18. The method according to claim 1 or 2, wherein: The refractive index of the first chemically strengthened glass is outside the range of 1.40 to 1.62.

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