Chemically enhanced glass and methods for its production

Abstract

Glass with chemically enhanced strength, having a compressive stress layer formed in a surface layer therein by an ion exchange process, wherein a surface of the glass has polishing defects, wherein the glass has a texture direction index (STI) of 0.30 or more, the hydrogen concentration Y in a region up to a depth X from an outermost surface of the glass satisfies the following relation equation (I) at X = 0.1 to 0.4 (µm), and the surface strength F (N), measured by a ball-on-ring test under the following conditions, F ≥ 1400 · t² based on the plate thickness t (mm) of the glass is: Y = aX + b, where the meanings of the respective symbols in equation (I) are as follows: Y: hydrogen concentration (as H₂O, mol / L), X: depth from the outermost surface of the glass (µm), a: -0.300 or more, and b: 0.220 or less,The conditions of the ball-on-ring test are as follows: a glass plate with a thickness t (mm) is placed on a stainless steel ring with a diameter of 30 mm and a contact area with a radius of curvature of 2.5 mm. A steel ball with a diameter of 10 mm is held in contact with the glass plate. A load is applied to the center of the ring by the ball under static loading conditions. The breaking load (unit: N) at which the glass breaks is used as the BOR surface strength, and the average of twenty measurements is used as the surface strength F, with the proviso that if the point of breakage of the glass is 2 mm or more away from the point of load on the ball, the obtained value is excluded from the data used to calculate the average value.

Description

TECHNICAL AREA

[0001] The present invention relates to a glass with chemically increased strength and a method for its production. STATE OF THE ART

[0002] In flat-screen display devices, such as digital cameras, mobile phones, personal digital assistants (PDAs), etc., a thin, sheet-like cover glass is placed on the front surface of the display to protect it and improve its appearance, thus providing a wider area than the image display section. Although the glass has high theoretical strength, its strength is greatly reduced when scratched. Therefore, for the cover glass, which must exhibit high strength, a chemically enhanced glass is used, featuring a stress-resistant layer formed on its surface by ion exchange or a similar process.

[0003] With the increasing need for weight and thickness reduction in flat panel display devices, it is desirable to make the cover glass itself thinner. Accordingly, to achieve this, both the surfaces and the edges of the cover glass must exhibit significantly increased strength.

[0004] To increase the strength of chemically enhanced glass, a surface etching treatment is known which must be carried out after the chemical treatment to increase strength (Patent document 1).

[0005] Regarding the strength of glass, it is known that the strength of glass is reduced by the presence of hydrogen (water) in the glass (non-patent documents 1 and 2). DOCUMENTS ON THE STATE OF THE TECHNOLOGY PATENT DOCUMENT

[0006] Patent Document 1: JP-T-2013-516387 NON-PATENT DOCUMENTS

[0007] Non-Patent Document 1: S. ITO et al., “Crack Blunting of High-Silica Glass,” Journal of the American Ceramic Society, Vol. 65, No. 8 (1982), 368-371 Non-Patent Document 2: Won-Taek Han et al., “Effect of residual water in silica glass on static fatigue,” Journal of Non-Crystalline Solids, 127 (1991), 97-104 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] The present inventors have found that concerns exist regarding the potential reduction in glass strength after chemical strengthening, and that the primary cause of this reduction is the penetration of moisture in the air into the glass surface layer, leading to the formation of chemical defects. Furthermore, the present inventors have found that this phenomenon occurs not only through chemical strengthening but also through a heating step in the glass manufacturing process.

[0009] One technique for removing moisture from a glass surface layer is to polish the moisture-containing layer after chemically increasing its strength, or to etch the glass surface after chemical strengthening by immersion in hydrofluoric acid or a similar agent. However, there are concerns that polishing may scratch the glass surface, potentially reducing its strength. Furthermore, if the glass surface has latent defects, there are concerns that etching with hydrofluoric acid or similar agents may enlarge these defects, resulting in unsightly pitting.Furthermore, hydrofluoric acid requires careful handling with regard to safety.

[0010] One object of the present invention is to provide a glass with chemically increased strength, in which a reduction in the strength of the glass itself after carrying out a chemical increase in strength can be effectively prevented. MEANS TO SOLVE THE PROBLEMS

[0011] The present inventors have found that not only by having a hydrogen concentration profile on a surface layer of a glass with chemically enhanced strength lie in a specific range, but also by setting a texture direction index (STI) of a glass surface to a specific value or more, even when the glass surface is polished, the surface strength of the glass is greatly improved, which is how the present invention was made.

[0012] In particular, the present invention is such as is shown below. [1] Glass with chemically enhanced strength, which has a compressive stress layer formed in a surface layer thereof according to an ion exchange process, where one surface of the glass has polishing defects, where the glass has a texture direction index (STI) of 0.30 or more, The hydrogen concentration Y in a region up to a depth X from an outermost surface of the glass satisfies the following relation equation (I) at X = 0.1 to 0.4 (μm), and the surface strength F (N) which was measured by a ball-on-ring test under the following conditions, (F ≥ 1400 × t 2 ) based on the plate thickness t (mm) of the glass is: Y = aX + b (I) where the meanings of the respective symbols in equation (I) are as follows: Y: Hydrogen concentration (as H2O, mol / liter), X: Depth from the outermost surface of the glass (μm), a: -0.300 or more and b: 0.220 or less, the conditions of the ball-on-ring test are as follows: A glass plate with a thickness t (mm) is placed on a stainless steel ring with a diameter of 30 mm and a contact area with a radius of curvature of 2.5 mm. A steel ball with a diameter of 10 mm is held in contact with the glass plate. A load is applied to the center of the ring by the ball under static loading conditions. The breaking load (unit: N) at which the glass breaks is used as the BOR strength, and the average of twenty measurements is used as the surface strength F. In cases where the point of breakage of the glass is 2 mm or more away from the point of load on the ball, the obtained value is excluded from the data used to calculate the average value. [2] Glass with chemically increased strength according to [1], wherein the glass is an aluminosilicate glass, an aluminoborosilicate glass or a soda-lime glass. [3] Glass with chemically increased strength according to [1] or [2], having a texture aspect ratio (Str20) of 0.10 or more. [4] A method for producing a glass with chemically enhanced strength, comprising a step of contacting a glass containing sodium with an inorganic salt containing potassium nitrate, thereby carrying out an ion exchange of Na in the glass with K in the inorganic salt, wherein the inorganic salt contains at least one salt selected from the group consisting of K2CO3, Na2CO3, KHCO3, NaHCO3, K3PO4, Na3PO4, K2SO4, Na2SO4, KOH and NaOH, and the procedure includes: a step of polishing a surface of the glass before ion exchange, a step of washing the glass after ion exchange, one step of acid-treating the glass after washing and a step of alkali-treating the glass after acid-treating it. [5] Glass with chemically increased strength obtained by the manufacturing process according to [4]. ADVANTAGE OF THE INVENTION

[0013] According to the chemically enhanced strength glass of the present invention, the surface strength of the glass can be significantly improved by ensuring that the hydrogen concentration profile on the glass surface layer lies within a specific range and that the texture direction index (STI) of the glass surface is set to a specific value or more. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Fig. Figure 1 is a schematic view to illustrate a ball-on-ring test procedure.

[0015] Fig. 2 A schematic view showing a method for producing a glass with chemically enhanced strength according to the present invention is shown in (a) to (d) of Fig. 2 shown.

[0016] Fig. Figure 3 is a graph showing the hydrogen concentration profile in the surface layer of each chemically enhanced strength glass obtained in Examples 1 and 2 and in Comparison Examples 1 and 2.

[0017] Fig. Figure 4 is an explanatory view for deriving the relation equation (I) from the graph where the hydrogen concentration profile in the surface layer of the chemically enhanced strength glass obtained in Example 1 is plotted.

[0018] Fig. Figure 5 is an explanatory view for deriving the relation equation (I) from the graph in which the hydrogen concentration profile in the surface layer of the chemically enhanced strength glass is plotted, which was obtained in comparative example 1.

[0019] Fig. Figure 6 is an atomic force microscope (AFM) image of a glass surface from Example 1.

[0020] Fig. 7 is an AFM image of a glass surface from example 2.

[0021] Fig. Figure 8 is an AFM image of a glass surface from Example 3.

[0022] Fig. 9 is an AFM image of a glass surface from comparison example 1.

[0023] Fig. 10 is an AFM image of a glass surface from comparison example 2.

[0024] Fig. 11 is an AFM image of a glass surface from comparison example 3.

[0025] Fig. 12 is an AFM image of a glass surface from reference example 1.

[0026] Fig. 13 is an AFM image of a glass surface from reference example 2.

[0027] Fig. Figure 14 is a Weibull plot of the BOR strength rating of each chemically enhanced strength glass obtained in Example 1 and Comparative Example 1. MODE FOR EXECUTING THE INVENTION

[0028] The present invention is described in detail below; however, this should not be interpreted as limiting the present invention to the following embodiments, and the present invention may be modified and carried out in any way within the scope in which the essence of the present invention is not deviated from. <Glas mit chemisch erhöhter Festigkeit>

[0029] The chemically enhanced glass according to the present invention is a chemically enhanced glass having a compressive stress layer formed in its surface layer according to an ion exchange process in which the hydrogen concentration in the area up to a certain depth from the outermost surface of the glass satisfies the following relation equation (I) and the glass surface has polishing defects.

[0030] The compressive stress layer is a high-density layer formed by an ion exchange of Na ions in a glass surface with K ions in a molten salt by contacting a glass starting material with an inorganic molten salt, such as potassium nitrate.

[0031] In the chemically enhanced glass of the present invention, the hydrogen concentration profile in the glass surface layer lies within a specific range. In particular, the hydrogen concentration Y in a range up to a depth X from the outermost surface of the glass satisfies the following relation equation (I) at X = 0.1 to 0.4 (μm). Y = aX + b (I) [In equation (I), the meanings of the respective symbols are as follows: Y: Hydrogen concentration (as H2O, mol / liter) X: Depth from the outermost surface of the glass (μm) a: -0.300 or more b: 0.220 or less]

[0032] Regarding the strength of glass, it is known that the strength of glass decreases due to the presence of hydrogen (moisture) within the glass. However, the present inventors have found that concerns exist regarding the potential reduction in glass strength after chemical treatments aimed at increasing its strength. The primary reason for this reduction is the penetration of moisture from the air into the glass, leading to the formation of chemical defects. Furthermore, the present inventors have discovered that this phenomenon occurs not only through chemical strength enhancement but also through a heating step in the glass manufacturing process.

[0033] When the hydrogen concentration in a glass is high, hydrogen penetrates the Si-O-Si bond network in the glass in the form of Si-OH, thereby cleaving the Si-O-Si bonds. High hydrogen concentrations in the glass are thought to result in an increased number of broken Si-O-Si bonds, which can easily lead to chemical defects and thus reduce the glass's strength.

[0034] The aforementioned relational equation (I) applies in a region from the outermost surface to a depth X = 0.1 to 0.4 μm. The thickness of the compressive stress layer, which is to be formed by ion exchange, lies within a range of 5 to 50 μm, although this depends on the degree of chemical strength enhancement. The hydrogen penetration depth in glass depends on the diffusion coefficient, temperature, and time, and the amount of hydrogen penetration is additionally influenced by the amount of moisture in the air. The hydrogen concentration after chemical strength enhancement is highest in the outermost layer and gradually decreases towards the deeper part (main mass), where the compressive stress layer does not form.The aforementioned relation equation (I) defines the reduction profile and in the outermost surface (X = 0 μm) there is the possibility that the moisture concentration may vary due to time-dependent degradation and therefore the equation is defined such that it applies in a region of the near surface (X = 0.1 to 0.4 μm) which is not affected by the variation.

[0035] In equation (I), a represents a slope that defines the profile of the hydrogen concentration reduction. The range of a is -0.300 or more, preferably -0.270 to -0.005, more preferably -0.240 to -0.030.

[0036] In equation (I), b corresponds to the hydrogen concentration at the outermost surface (X = 0 μm). The range of b is 0.220 or less, preferably 0.020 to 0.215, more preferably 0.030 to 0.210.

[0037] It is generally assumed that the reduction in the strength of a glass is caused by the growth of microcracks present in the glass surface due to external mechanical stress. According to non-patent document 2, it is assumed that if the glass structure at the tip of a crack is in a Si-OH-richer state, the cracks will grow readily. Assuming that the tips of cracks are exposed to air, the amount of Si-OH at the crack tip is assumed to have a positive relationship to the hydrogen concentration at the outermost surface of the glass. Accordingly, b, which corresponds to the hydrogen concentration at the outermost surface, is preferably within a low range, as shown above.

[0038] As it is in the Fig. As shown in Figure 3, the glass processed by a chemical strength enhancement step showed no significant difference in hydrogen penetration depth. While it is possible that the hydrogen penetration depth could vary depending on the conditions of the chemical strength enhancement step, a negative correlation occurs when the depth does not change at all between b, which corresponds to the hydrogen concentration at the outermost surface, and a, which corresponds to the slope used to define the hydrogen concentration reduction profile. Accordingly, a is preferably within a high range, as shown above.

[0039] As described above, it has been found in the present invention that the strength of a chemically enhanced glass can be greatly improved not only by setting the hydrogen concentration itself in the surface layer, but also by setting the hydrogen concentration in the surface layer and its reduction profile, such that they each lie in a specific range, with particular attention paid to the hydrogen concentration profile. [Method for measuring the hydrogen concentration profile]

[0040] The hydrogen concentration profile (H2O concentration, mol / liter) of a glass is a profile that is measured under the following analytical conditions.

[0041] A secondary ion mass spectrometry (SIMS) method is used to measure the hydrogen concentration profile of a glass substrate. In cases where a quantitative hydrogen concentration profile is obtained using SIMS, a standard sample with a known hydrogen concentration is required. A method for preparing the standard sample and a method for determining its hydrogen concentration are described below. 1) A portion of the glass substrate to be analyzed is cut out. 2) A layer of 50 μm or more from the surface of the cut glass substrate is removed by polishing or chemical etching. The removal treatment is performed on both surfaces. In particular, the thickness to be removed from both surfaces is 100 μm or more. The glass substrate that has undergone the removal treatment is used as the standard specimen. 3) The standard sample is analyzed using infrared spectroscopy (IR) and the extinction height A is determined. 3550 at the peak near 3550 cm –1 in the IR spectrum and the extinction height A 4000 (Baseline) at 4000 cm –1 will be determined. 4) The thickness d (cm) of the standard sample is measured using a thickness measuring device, such as a micrometer. 5) Referring to reference A, the hydrogen concentration (as H2O, mol / Liter) in the standard sample is determined using formula II, in which the practical infrared extinction index of H2O in glass ε prakt (L / (mol·cm))75. Hydrogen concentration in the standard sample = (A 3550 – A 4000 ) / (ε prakt ·d) Formula II Reference A): S. Ilievski et al., Glastech. Ber. Glass Sci. Technol., 73 (2000), 39.

[0042] The glass substrate to be analyzed and the standard sample, whose hydrogen concentration is known, are prepared according to the above-mentioned procedure, are simultaneously introduced into a SIMS device and analyzed sequentially, so that the depth-direction profiles of the intensities of 1 H – and 30 Si – will be received. Then the 1 H – -profile through the 30 Si – -profile divided, so that a depth direction profile of the 1 H – / 30 Si – -intensity ratio is obtained. From the depth-direction profile of the 1 H – / 30 Si – -Intensity ratio of the standard sample is an average 1 H – / 30Si –The intensity ratio is calculated over a depth range of 1 μm to 2 μm, and a calibration curve of this value and the hydrogen concentration is plotted so that it passes through the origin (calibration curve with a standard sample at a level). Using the calibration curve, the 1 H – / 30 Si – The intensity ratio on the vertical axis of the profile of the glass substrate to be analyzed is converted into the hydrogen concentration. Accordingly, the hydrogen concentration profile of the glass substrate to be analyzed is obtained. The measurement conditions for SIMS and IR are as follows. [SIMS measurement conditions] Device: ADEPT1010, manufactured by ULVAC-PHI, Inc. Primary ion species: Cs + Primary ion acceleration voltage: 5 kV Primary ion current value: 500 nA Primary ion incidence angle: 60° relative to the perpendicular to the sample plane Primary ion beam size: 300 × 300 μm 2 Secondary ion polarity: Minus Secondary ion detection range: 60 × 60 μm 2 (4% of the primary ion beam size) ESA input lens: 0 Use of a neutralization device: Yes Method for converting the horizontal axis from sputtering time to depth: The depth of the analysis crater is measured using a stylus surface profile analyzer (Dektak 150, manufactured by Veeco Inc.), and the primary ion sputtering velocity is determined. Using the sputtering velocity, the horizontal axis is converted from sputtering time to depth. Field axis potential at the 1 H – -Detection: The optimal value can vary from device to device.

[0043] The user should carefully set the value so that the background is completely separated. [IR measurement conditions] Device: Nic-plan / Nicolet 6700, manufactured by Thermo Fisher Scientific Co., Ltd. Resolution: 4 cm –1 Number of samples: 16 Detector: TGS detector

[0044] The following procedure is used to derive the relational equation [I] from the hydrogen concentration profile (H2O concentration, mol / liter) of the glass, which was determined under the aforementioned analytical conditions. As described in the Fig. 5 and Fig. As shown in Figure 6, a linear approximation is applied to the hydrogen concentration profile in a depth range of 0.1 to 0.4 μm. The equation of the resulting approximation line is referred to as the relation equation [I].

[0045] Methods for adjusting a and b include, for example, changing the melting agent concentration, the sodium concentration, the temperature, and the time during the chemical strength-enhancing step.

[0046] The chemically enhanced glass of the present invention has polishing defects on its surface. Polishing in the present invention means that the surface of a glass is polished with abrasives to smooth it. The surface polishing method is not specifically limited, and examples include common methods. The presence or absence of polishing defects can be distinguished by surface examination using an AFM (atomic force microscope). A case in which one or more scratches, each with a length of 5 μm or more, are present in an area of ​​10 μm × 5 μm is considered to be a condition in which the surface has polishing defects. Fig. Figure 6 shows a condition exhibiting surface polishing defects (in example 1, shown below), and the Fig. Figure 12 shows a condition that has no surface polishing defects (in reference example 1, which is given below). (Glass surface strength)

[0047] The surface strength of the chemically enhanced glass of the present invention can be evaluated according to a ball-on-ring test. (Ball-on-ring test)

[0048] The chemically enhanced glass of the present invention is evaluated with respect to the BOR strength F(N) measured by a ball-on-ring (BOR) test in which a glass plate is arranged on a stainless steel ring having a diameter of 30 mm and a contact part having a roundness with a radius of curvature of 2.5 mm, and in which, while a steel ball with a diameter of 10 mm is held in contact with the glass plate, a load is exerted on the center of the ring by the ball under static loading conditions.

[0049] The chemically enhanced glass of the present invention meets F ≥ 1400 × t 2 , preferably F ≥ 1800 × t 2[In the formulas, F represents the BOR strength (N) measured by the ball-on-ring test, and t represents the thickness (mm) of the glass plate.] If the BOR strength F(N) is within this range, the glass exhibits excellent strength even when formed into a thin plate.

[0050] The Fig. Figure 1 shows a schematic view to illustrate the ball-on-ring test used in the present invention. In the ball-on-ring (BOR) test, a glass plate 1 , while it is held horizontally, by a pressure application device 2 , which is made of SUS304 (hardened steel, diameter: 10 mm, polished to a mirror finish), is subjected to pressure, so that the strength of the glass plate 1 is measured.

[0051] In the Fig. 1 is the glass plate 1, which is a sample, horizontally on a recording device 3 arranged, which is made of SUS304 (diameter: 30 mm, radius of curvature of the contact part R: 2.5 mm, the contact part is hardened steel, polished to a mirror finish). Above the glass plate 1 is a pressure application device 2 to apply pressure to the glass plate 1 arranged under pressure.

[0052] In this embodiment, the central area of ​​the glass plate 1 The sample obtained in the examples and comparison examples is subjected to pressure from above. The test conditions are as specified below. Lowering speed of the pressure application device 2 : 1.0 (mm / min)

[0053] In this test, the breaking load (unit: N) at which the glass breaks is used as the BOR strength. The average of twenty measurements is used as the average BOR strength. In cases where the point of fracture of the glass plate is 2 mm or more away from the ball impact point, the measured value is excluded from the data used to calculate the average. (Texture Direction Index (STI))

[0054] Furthermore, in the chemically enhanced strength glass of the present invention, its texture direction index (STI) is 0.30 or more, preferably 0.45 or more, and more preferably 0.50 or more. The texture direction index (STI) referred to herein is an index that indicates the quality of the directional dependence of the texture formed on the surface and has a value from 0 to 1. In the case where the texture has a pronounced direction, the STI approaches 0. Conversely, in the case where the texture has no directional dependence, the STI approaches 1. That is, in the case where the texture has a pronounced direction, as is the case in polishing defects, the STI approaches a value of 0. However, if the polishing defects become smooth and the texture becomes indistinct, it can be assumed that the STI approaches 1.It can be assumed that, in view of the fact that the texture direction index (Sti) of the chemically enhanced strength glass of the present invention lies within the aforementioned range, the chemically enhanced strength glass of the present invention has smooth polishing defects.

[0055] After obtaining a shape image using an atomic force microscope (AFM), the texture direction index (STI) can be determined using image analysis software. (Texture aspect ratio (Str20))

[0056] The chemically enhanced glass of the present invention also has a texture aspect ratio (Str20) of 0.10 or more, preferably 0.35 or more, and more preferably 0.55 or more. It can be assumed that when the texture aspect ratio (Str20) falls within the aforementioned range, the chemically enhanced glass of the present invention exhibits smooth polishing defects.

[0057] After obtaining a shape image using an atomic force microscope (AFM), the texture aspect ratio (Str20) can be determined using image analysis software.

[0058] Furthermore, the chemically enhanced strength glass of the present invention exhibits reduced light scattering caused by depressions and has an excellent surface appearance. <Verfahren zur Herstellung eines Glases mit chemisch erhöhter Festigkeit>

[0059] One embodiment of the method for producing a glass with chemically increased strength is described below, although the present invention is not limited thereto. (Glass composition)

[0060] The glass used in the present invention can be any glass containing sodium, and as long as it has a composition that can be shaped and whose strength can be increased by a chemical treatment, various types of compositions can be used. In particular, examples include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkali barium glass, aluminoborosilicate glass, etc.

[0061] The manufacturing process for glass is not specifically limited. Desired glass raw materials are placed in a continuous melting furnace and melted under heating, preferably at 1500 to 1600°C. The molten glass is then refined and placed in a molding device to form it into a plate-like shape. It is then gradually cooled to produce a glass.

[0062] Various methods can be used to shape glass. For example, different forming processes can be used, such as a down-draw process (e.g., a flow-down-draw process, a slot-down process, a draw-post-forming process, etc.), a float process, a roll-out process, and a pressing process.

[0063] The thickness of a glass is not specifically limited, however, for effective implementation of the treatment to chemically increase strength, its thickness is generally preferably 5 mm or less, more preferably 3 mm or less.

[0064] The shape of a glass for use in the present invention is not specifically limited. For example, various shapes of a glass can be used, such as a plate-like shape with a uniform thickness, a curved shape in which at least one of the front or back surfaces is curved, and a three-dimensional shape having a curved section.

[0065] Although the composition of the chemically enhanced strength glass of the present invention is not specifically limited, the following glass compositions, for example, can be mentioned. (i) Glass comprising, in mol%, 50 to 80% SiO2, 2 to 25% Al2O3, 0 to 10% Li2O, 0 to 18% Na2O, 0 to 10% K2O, 0 to 15% MgO, 0 to 5% CaO and 0 to 5% ZrO2. (ii) Glass comprising, in mol%, 50 to 74% SiO2, 1 to 10% Al2O3, 6 to 14% Na2O, 3 to 11% K2O, 2 to 15% MgO, 0 to 6% CaO and 0 to 5% ZrO2, wherein the total content of SiO2 and Al2O3 is 75% or less, the total content of Na2O and K2O is 12 to 25% and the total content of MgO and CaO is 7 to 15%. (iii) Glass comprising, in mol%, 68 to 80% SiO2, 4 to 10% Al2O3, 5 to 15% Na2O, 0 to 1% K2O, 4 to 15% MgO and 0 to 1% ZrO2. (iv) Glass comprising, in mol%, 67 to 75% SiO2, 0 to 4% Al2O3, 7 to 15% Na2O, 1 to 9% K2O, 6 to 14% MgO and 0 to 1.5% ZrO2, wherein the total content of SiO2 and Al2O3 is 71 to 75%, the total content of Na2O and K2O is 12 to 20% and the total content of CaO, if present, is less than 1%.

[0066] The chemically enhanced glass of the present invention has an ion-exchanged compressive stress layer on its surface. In the ion exchange process, the surface of a glass is ion-exchanged, so that a surface layer is formed in which a compressive stress remains. In particular, the alkali metal ions (typically Li ions, Na ions), which have a small ionic radius, are replaced in the surface of a glass plate by alkali ions with a larger ionic radius (typically Na ions or K ions for Li ions and K ions for Na ions) by means of an ion exchange at a temperature not higher than the glass transition temperature. Accordingly, a compressive stress remains in the surface of the glass, and the strength of the glass is thereby increased.

[0067] In the manufacturing process of the present invention, a chemical increase in strength is achieved by contacting a glass with an inorganic salt containing potassium nitrate (KNO3). Accordingly, the sodium ions in the glass surface are exchanged with the potassium ions in the inorganic salt, forming a high-density compressive stress layer. The process of contacting a glass with an inorganic salt comprises a method in which a paste-like inorganic salt is applied to a glass, a method in which a glass is sprayed with an aqueous solution of an inorganic salt, and a method in which a glass is immersed in a salt bath of molten salt heated to a temperature not below its melting point; of these methods, immersion in molten salt is preferred.

[0068] The inorganic salt is preferably a salt having a melting point not higher than the lower annealing temperature of the glass whose strength is to be increased (generally 500 to 600°C), and in the present invention, a salt containing potassium nitrate (melting point: 330°C) is preferred. The potassium nitrate-containing salt is preferred because it can exist in a molten state at a temperature not higher than the lower annealing temperature of the glass, and because, moreover, it can be easily handled within the operating temperature range. The potassium nitrate content in the inorganic salt is preferably 50% by weight or more.

[0069] In addition, the inorganic salt preferably contains at least one salt selected from the group consisting of K2CO3, Na2CO3, KHCO3, NaHCO3, K3PO4, Na3PO4, K2SO4, Na2SO4, KOH and NaOH, and more preferably contains at least one salt selected from the group consisting of K2CO3, Na2CO3, KHCO3 and NaHCO3.

[0070] The aforementioned salt (hereinafter referred to as the "melting agent") has the property of cleaving the network of a glass, which is typically a Si-O-Si bond. Since the temperature at which the chemical strength-enhancing treatment is carried out is high, such as several hundred degrees Celsius, the covalent Si-O bond in the glass is cleaved appropriately at this temperature, and therefore the density reduction treatment described below can proceed smoothly for the glass.

[0071] The degree of cleavage of the covalent bond can vary depending on the glass composition, the type of salt (melting agent) to be used, and the conditions of treatment for chemically increasing strength, such as temperature and time; however, the conditions are preferably selected such that 1 to 2 of the four covalent bonds extending from Si can be cleaved.

[0072] For example, in a case where K2CO3 is used as a melting agent, the melting agent content in the inorganic salt is 0.1 mol% or more, and the temperature of the treatment for chemical strength enhancement is from 350 to 500°C, the time of the treatment for chemical strength enhancement is preferably from 1 minute to 10 hours, more preferably from 5 minutes to 8 hours, and even more preferably from 10 minutes to 4 hours.

[0073] The amount of flux to be added, for the purpose of adjusting the surface hydrogen concentration, is preferably 0.1 mol% or more, more preferably 1 mol% or more, and particularly preferably 2 mol% or more. For productivity reasons, its amount is preferably not more than the saturation solubility of each salt. If the flux is added in excess, there is a concern that glass corrosion may occur. For example, in a case where K₂CO₃ is used as the flux, its amount is preferably 24 mol% or less, more preferably 12 mol% or less, and particularly preferably 8 mol% or less.

[0074] In addition to potassium nitrate and the melting agent, the inorganic salt may contain any other chemical species within a range that does not impair the advantageous effects of the present invention. For example, alkali chloride salts or alkali borate salts, such as sodium chloride, potassium chloride, sodium borate, and potassium borate, may be included. One or more of these may be added either individually or in combination. (Step 1: Polishing a glass surface)

[0075] In step 1, the glass surface is polished. The polishing conditions are not specifically restricted, and polishing can be carried out under conditions such that a desired surface roughness is achieved. As a polishing agent, a general procedure can be used in which, for example, cerium oxide with an average particle diameter of approximately 0.7 μm is dispersed in water to produce a slurry with a density of 0.9, and the glass surface is polished to a depth of 0.5 μm or more per surface using a non-woven or velour polishing pad under a polishing pressure of 10 kPa.

[0076] Polishing the glass surface removes macro-defects, thereby improving surface strength. This polishing is preferably performed prior to the chemical strength-enhancing (ion exchange) treatment of step 4, as described later. The manufacturing process of the present invention is described below with reference to examples of an embodiment in which chemical strength enhancement is carried out by immersing a glass in a molten salt. (Production of a molten salt) 1 )

[0077] A molten salt can be produced according to the steps outlined below.

[0078] Step 2a: Production of molten potassium nitrate salt

[0079] Step 3a: Adding a melting agent to the molten potassium nitrate salt (Step 2a – Production of molten potassium nitrate salt –)

[0080] In step 2a, potassium nitrate is placed in a container and melted by heating at a temperature not lower than its melting point, thus producing a molten salt. The melting is carried out at a temperature ranging from the melting point (330°C) of potassium nitrate to its boiling point (500°C). In particular, with regard to the balance between the surface compressive stress (CS) to be imparted to a glass and the depth of the compressive stress layer (DOL), as well as the time required to increase strength, it is more preferred that the melting temperature be between 350°C and 470°C.

[0081] Regarding the container for melting potassium nitrate, metals, quartz, ceramics, and the like can be used. In particular, metallic materials are preferred with regard to durability, and stainless steel (SUS) is preferred with regard to corrosion resistance. (Step 3a – Adding a melting agent to the molten potassium nitrate salt –)

[0082] In step 3a, the aforementioned melting agent is added to the molten potassium nitrate salt prepared in step 2a and, while maintained at a temperature within a specified range, is mixed with a paddle stirrer or the like until the mixture is homogeneous. If multiple melting agents are used, the order in which they are added is not specifically restricted, and they may be added simultaneously.

[0083] The temperature is preferably not lower than the melting point of potassium nitrate, i.e., preferably 330°C or higher, more preferably 350 to 500°C. The stirring time is preferably from 1 minute to 10 hours, more preferably from 10 minutes to 2 hours. (Production of a molten salt 2)

[0084] In the above-described production of a molten salt 1, a method of adding a melting agent after the production of a molten salt of potassium nitrate is mentioned as an example; however, apart from this method, the molten salt can also be produced according to the following steps.

[0085] Step 2b: Mixing potassium nitrate and a melting agent

[0086] Step 3b: Melting the mixed salt of potassium nitrate and melting agent (Step 2b – Mixing potassium nitrate and a melting agent –)

[0087] In step 2b, potassium nitrate and a melting agent are placed in a container and mixed with a paddle stirrer or similar device. If multiple melting agents are used, the order in which they are added is not specifically restricted, and they may be added simultaneously. The container used may be the same as the one used in step 2a above. (Step 3b – Melting the mixed salt of potassium nitrate and melting agent –)

[0088] In step 3b, the mixed salt obtained in step 1b is melted by heating. The melting is carried out at a temperature ranging from the melting point (330°C) of potassium nitrate to its boiling point (500°C). In particular, with regard to the balance between the surface compressive stress (CS) to be imparted to a glass and the depth of the compressive stress layer (DOL), as well as the time required to increase strength, a melting temperature of 350 to 470°C is preferred. The stirring time is preferably from 1 minute to 10 hours, more preferably from 10 minutes to 2 hours.

[0089] In a case where deposits form in the molten salt obtained by steps 2a and 3a or 2b and 3b above upon the addition of a flux, the molten salt is kept undisturbed before chemical strengthening treatment until the deposits have settled at the bottom of the container. The deposits contain the flux, which has exceeded its saturation solubility, and salts formed by the exchange of cations in the flux within the molten salt.

[0090] The molten salt for use in the manufacturing process of the present invention has a sodium concentration of preferably 500 ppm by weight or more, more preferably 1000 ppm by weight or more. A sodium concentration of 500 ppm by weight or more in the molten salt is preferred because the low-density layer can be easily made deeper in the acid treatment step described below. The upper limit of the sodium concentration is not specifically defined and is acceptable up to a level at which a desired surface compressive stress (CS) can be obtained.

[0091] The molten salt used once or several times for chemical strength enhancement treatment contains sodium released from the glass. Therefore, if the sodium concentration is already within the aforementioned range, sodium originating from the glass can be used as a sodium source. Alternatively, if the sodium concentration is insufficient, or if fresh molten salt is used that has not previously undergone chemical strength enhancement treatment, the sodium concentration can be adjusted by adding an inorganic sodium salt, such as sodium nitrate.

[0092] As described above, a molten salt can be produced according to step 2a and step 3a or step 2b and step 3b mentioned above. (Chemical increase in strength)

[0093] Next, a chemical strength-enhancing treatment is carried out using the prepared molten salt. In this treatment, a glass is immersed in molten salt, and the metal ions (Na ions) in the glass are replaced by metal ions (K ions) with a larger ionic radius in the molten salt. This ion exchange alters the composition of the glass surface, resulting in a denser surface and the formation of a compressive stress layer. 20 is formed [(a) to (b) in the Fig. 2]. The compaction of the glass surface creates compressive stress, thus increasing the strength of the glass.

[0094] In particular, the density of the chemically enhanced glass decreases from the outer edge of the intermediate layer. 30(Main mass), which is present in the center of the glass, gradually increases to the surface of the compressive stress layer and therefore lies between the intermediate layer 30 and the compressive stress layer 20 There is no clear boundary at which the density abruptly changes. The intermediate layer refers to a layer located in the central part of the glass and surrounded by the stress-pressure layer. The intermediate layer is a layer that has not undergone any ion exchange, which distinguishes it from the stress-pressure layer.

[0095] In particular, the treatment for chemically increasing the strength in the present invention is carried out by the following step 4.

[0096] Step 4: Chemical treatment to increase the strength of glass

[0097] In step 4, a glass is preheated, and the temperature of the molten salt, prepared in steps 2a and 3a or 2b and 3b as described above, is adjusted to the temperature required for chemical strength enhancement. Next, the preheated glass is immersed in the molten salt for a predetermined period, after which the glass is removed from the molten salt and allowed to cool. Preferably, prior to the chemical strength enhancement treatment, the glass is shaped according to its intended use, for example, by mechanical processing such as cutting, surface finishing, drilling, etc.

[0098] The glass preheating temperature depends on the temperature at which the glass is immersed in molten glass, but this is generally preferably 100°C or higher.

[0099] The temperature during the chemical increase of strength is preferably not higher than the lower relaxation temperature of the glass whose strength is to be increased (generally 500 to 600°C), however, to obtain a greater depth of the compressive stress layer, it is particularly preferred to be 350°C or higher.

[0100] The immersion time of the glass in a molten salt is preferably from 1 minute to 10 hours, more preferably from 5 minutes to 8 hours, and even more preferably from 10 minutes to 4 hours. Within this range, it is possible to obtain a glass with chemically enhanced strength that exhibits an excellent balance between strength and the depth of the compressive stress layer.

[0101] In the manufacturing process of the present invention, the following steps are carried out after the treatment to chemically increase the strength.

[0102] Step 5: Washing the glass

[0103] Step 6: Acid treatment of the glass after step 5

[0104] At the time after the aforementioned step 6, the glass surface also exhibits a low-density layer. 10 on, in which the surface layer of the compressive stress layer has been denatured, in particular its density has been reduced [(b) to (c) in the Fig. 2]. The low-density layer is formed by leaching of Na and K from the outermost surface of the compressive stress layer, and H has penetrated (substituted) it instead.

[0105] Steps 5 and 6 are described in detail below. (Step 5 – Washing the glass –)

[0106] In step 5, the glass is washed with process water, ion-exchanged water, or the like. Ion-exchanged water is particularly preferred. The washing conditions can vary depending on the washing liquid used; however, in the case where ion-exchanged water is used, it is preferred that the glass be washed at 0 to 100°C to ensure the complete removal of the adhering salts. (Step 6 – Acid Treatment –)

[0107] In step 6, the glass washed in step 5 is further subjected to acid treatment.

[0108] In acid treatment for a glass, a glass with chemically increased strength is immersed in an acidic solution, whereby Na and / or K in the surface of the glass with chemically increased strength can be replaced by H.

[0109] The solution is not specifically limited as long as it is acidic and has a pH of less than 7, and the acid used may be weak or strong. In particular, the acid is preferably hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid, citric acid, etc. These acids may be used individually or in combination.

[0110] The temperature for carrying out the acid treatment varies depending on the type and concentration of the acid to be used and the treatment time, but is preferably 100°C or lower.

[0111] The time required to carry out the acid treatment also varies depending on the type, concentration and temperature of the acid to be used and the treatment time, but with regard to productivity, it is preferably from 10 seconds to 5 hours, more preferably from 1 minute to 2 hours.

[0112] The concentration of the solution used for the acid treatment varies depending on the type and temperature of the acid to be used and the treatment time, but is preferably a concentration at which the risk of container corrosion is lower and in particular its concentration is preferably from 0.1 wt.% to 20 wt.%.

[0113] The low-density layer is removed during the alkaline treatment described below, and a thicker low-density layer is preferred because it is easier to remove from the glass surface. Accordingly, the thickness of the low-density layer is preferably 5 nm or more, more preferably 20 nm or more, depending on the amount of glass surface removed. The thickness of the low-density layer can be adjusted by modifying the concentration of the flux, the sodium concentration, the temperature, the time, and other parameters during the chemical strength enhancement step.

[0114] With regard to the removability of the glass surface, the density of the low-density layer is preferably lower than the density in the area (main mass) that lies below the ion-exchanged compressive stress layer.

[0115] The thickness of the low-density layer can be determined from the period (Δθ) measured by X-ray reflectometry (XRR).

[0116] The density of the low-density layer can be determined from the critical angle (θc) measured in the XRR.

[0117] In a simplified way, the formation of a low-density layer and the thickness of the layer can be confirmed by examining the cross-section of a glass using a scanning electron microscope (SEM).

[0118] In the manufacturing process of the present invention, the following step is carried out after the acid treatment.

[0119] Step 7: Alkali treatment

[0120] In step 7, part or all of the low-density layer formed up to step 6 can be removed [(c) to (d) in the Fig. 2].

[0121] Step 7 is described in detail below. (Step 7 – Alkali treatment –)

[0122] In step 7, the glass, which has undergone acid treatment in step 6, is further subjected to alkali treatment.

[0123] In alkaline treatment, the chemically enhanced glass is immersed in a basic solution, which removes part or all of the low-density layer.

[0124] The solution is not specifically restricted as long as it is basic and has a pH greater than 7, and any weak or strong base may be used. In particular, a base such as sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, or the like is preferred. These bases may be used either individually or in combination.

[0125] The temperature for carrying out the alkaline treatment varies depending on the type and concentration of the base used and the treatment time, but is preferably from 0 to 100°C, more preferably from 10 to 80°C, and even more preferably from 20 to 60°C. This temperature range is preferred because it does not pose a risk of glass corrosion.

[0126] The time required to carry out the alkali treatment also varies depending on the type, concentration and temperature of the base used, but with regard to productivity, it is preferably from 10 seconds to 5 hours, more preferably from 1 minute to 2 hours.

[0127] The concentration of the solution for carrying out the alkali treatment varies depending on the type and temperature of the base to be used and the treatment time, but is preferably from 0.1 wt.% to 20 wt.% with regard to the removability of the glass surface.

[0128] The aforementioned alkaline treatment removes part or all of the low-density layer containing hydrogen, exposing the surface layer where the hydrogen concentration profile satisfies the specific equation (I) described above. Consequently, a glass with chemically enhanced strength and improved surface strength can be obtained. Furthermore, since the low-density layer is removed, defects present in the glass surface are also eliminated. Therefore, this is also expected to contribute to the improvement in strength.

[0129] In addition, in the manufacturing process of the present invention, large surface defects are removed in advance by polishing the glass surface prior to the chemical strengthening treatment. It is assumed that, according to this pre-polishing, the chemical strengthening treatment, and the acid and alkali treatments, macro- and micro-defects on the glass surface are removed, thereby considerably improving the surface strength of the glass.

[0130] Between the acid treatment step 6 and the alkali treatment step 7 mentioned above, or after the alkali treatment step 7, it is preferred to carry out a washing step such as step 5.

[0131] In the manufacturing process of the present invention, the chemical liquids that need to be handled are very safe, and therefore the process does not require any special equipment. Accordingly, a glass with chemically enhanced strength, whose surface strength has been greatly increased, can be obtained safely and efficiently.

[0132] The amount of low-density layer to be removed depends on the alkali treatment conditions. One embodiment in which the low-density layer 10 has been completely removed, is in (d) of Fig. 2 shown, however, a part of the layer is low density 10It can be removed, while some of it remains. With regard to improving strength, the effect can be achieved even if not the entire low-density layer is removed; however, to ensure stable light transmission of the glass, it is preferable to remove the entire low-density layer.

[0133] According to the method for producing chemically enhanced glass of the present invention, a chemically enhanced glass with improved surface strength can be obtained even after polishing. Since the treatment can also be carried out by immersion in the solution, the manufacturing process is efficient in that it is suitable for various glass shapes and large-area glass, and both surfaces of the glass can be treated simultaneously. Furthermore, even in cases where latent defects are pre-existing on the glass surface, a chemically enhanced glass can be obtained that does not exhibit an unsightly appearance due to depressions and that displays improved surface strength.Furthermore, the treatment in the present invention is very safe and cost-effective compared to an etching treatment using hydrofluoric acid or the like. EXAMPLES

[0134] The present invention is specifically described with reference to the examples given below, but the present invention is not limited thereto. <bewertungsverfahren>

[0135] Various assessments in the present examples were carried out according to the analytical procedures mentioned below. (Evaluation of a glass: surface tension)

[0136] The compressive stress value and the depth of the compressive stress layer in the chemically enhanced glass of the present invention can be measured using an EPMA (electron probe microanalyzer) or a surface tension meter (e.g., FSM-6000, manufactured by Orihara Manufacturing Co., Ltd.), etc. In the examples, the surface compressive stress value (CS, unit: MPa) and the depth of the compressive stress layer (DOL, unit: μm) were measured using a surface tension meter (FSM-6000) manufactured by Orihara Manufacturing Co., Ltd. (Evaluation of a glass: Distance measurement)

[0137] The distance dimension thickness of a glass was determined by measuring its weight before and after treatment with a chemical liquid using an electronic analytical balance (HR-202i, manufactured by AND Company, Limited) and converting the determined value into a thickness according to the following equation. (Distance thickness per surface) = ((Weight before treatment) – (Weight after treatment) / (Glass density) / treated area / 2

[0138] The calculation was performed using a value of 2.41 (g / cm²). 3 ) determined glass density. (Rating of a glass: Texture Direction Index (STI))

[0139] First, a shape image was acquired using an atomic force microscope (XE-HDM, manufactured by Park Systems Corporation) under the following conditions: measurement mode: non-contact, sampling size: 10 μm × 5 μm, color scale: ±1 nm, sampling rate: 1 Hz, arm: non-contact arm (item: PPP-NCHR 10M, manufactured by Park Systems Corporation). Subsequently, the shape image underwent calibration and L-filter treatment (ISO value: 2.0 μm) using image analysis software (SPIP 6.2.6, manufactured by Image Metrology Inc.), and the texture direction index (STI) was determined by roughness analysis. (Evaluation of a glass: Texture aspect ratio (Str20))

[0140] First, a shape image was acquired using an atomic force microscope (XE-HDM, manufactured by Park Systems Corporation) under the following conditions: measurement mode: non-contact, sampling size: 10 μm × 5 μm, color scale: ±1 nm, sampling rate: 1 Hz, boom: non-contact boom (item: PPP-NCHR 10M, manufactured by Park Systems Corporation). Subsequently, the shape image underwent calibration and L-filter treatment (ISO value: 2.0 μm) using image analysis software (SPIP 6.2.6, manufactured by Image Metrology Inc.), and a texture aspect ratio index (Str20) was determined by roughness analysis. (Evaluation of a glass: surface strength)

[0141] The glass surface strength was measured according to the ball-on-ring (BOR) test. Fig. Figure 1 shows a schematic view to illustrate the ball-on-ring test used in the present invention. A glass plate 1 was, while held horizontally, by a pressure-exercising device 2 , which was made of SUS304 (hardened steel, diameter: 10 mm, polished to a mirror finish), was subjected to pressure, so that the strength of the glass plate 1 was measured.

[0142] In the Fig. 1 is the glass plate 1 , which is a sample, horizontally on a recording device 3 arranged, which is made of SUS304 (diameter: 30 mm, radius of curvature of the contact part R: 2.5 mm, the contact part is hardened steel, polished to a mirror finish). Above the glass plate 1 is a pressure application device 2 to apply pressure to the glass plate 1 arranged under pressure.

[0143] In this embodiment, the central area of ​​the glass plate was 1 , which was obtained in the examples and the comparative examples, from above the glass plate 1 The test conditions are as follows. Lowering speed of the pressure application device 2 : 1.0 (mm / min)

[0144] In this test, the breaking load (unit: N) at which the glass broke was used as the BOR strength. The average of twenty measurements was used as the average BOR strength. In one case where the breakage point of the glass plate was 2 mm or more away from the ball impact point, the measured value was excluded from the data used to calculate the average. (Evaluation of a glass: hydrogen concentration)

[0145] According to the procedure described in the preceding section [Procedure for measuring the hydrogen concentration profile], the hydrogen concentration profile was determined and the relational equation [I] was derived from it. <Beispiel 1> (Polishing step)

[0146] An aluminosilicate glass with dimensions 50 mm × 50 mm × 0.70 mm was produced. Cerium oxide with an average particle diameter of 1.2 μm was dispersed in water to create a slurry with a density of 0.9. Both surfaces of the aluminosilicate glass were simultaneously polished to a depth of 3.0 μm per surface using a polishing pad (non-woven type) under a polishing pressure of 10 kPa. The surface roughness (Ra), measured by AFM, was 0.45 nm. AFM measurement conditions: Atomic force microscope (XE-HDM, manufactured by Park Systems Corporation), sampling size: 10 μm × 5 μm, color scale: ±1 nm, sampling rate: 1 Hz. (Step of chemically increasing strength)

[0147] In a beaker made of SUS, 9700 g of potassium nitrate, 890 g of potassium carbonate, and 400 g of sodium nitrate were placed and the contents heated to 450°C using a heating jacket, producing a molten salt containing 6 mol% potassium carbonate and 10,000 ppm sodium by weight. The glass obtained in the polishing step was preheated to 200–400°C and then subjected to a chemical strength-enhancing treatment by immersion in the molten salt at 450°C for 2 hours for ion exchange and cooling to approximately room temperature. The resulting chemically strengthened glass was washed with water and subjected to the next step. Composition (in mol-%) of the aluminosilicate glass (density: 2.41): SiO2 68%, Al2O3 10%, Na2O 14%, MgO 8%. (Acid treatment step)

[0148] In a plastic tank, 6.0 wt% nitric acid (HNO3, manufactured by Kanto Chemical Co., Inc.) was prepared and heated to 41°C using a fluoropolymer-coated heating device (KKS14A, manufactured by Hakko Electric Co., Ltd.). The glass obtained in the preceding step for chemical strength enhancement was immersed in the temperature-controlled nitric acid for 120 seconds to perform the acid treatment and then rinsed several times with clean water. The resulting glass was then subjected to the next step. (Alkali treatment step)

[0149] An aqueous solution of 4.0 wt% sodium hydroxide was prepared in a plastic tank and heated to 40°C using a fluoropolymer-coated heating device (KKS14A, manufactured by Hakko Electric Co., Ltd.). The glass obtained in the acid treatment step was immersed in the temperature-controlled aqueous sodium hydroxide solution for 120 seconds to perform the alkali treatment, then rinsed several times with clean water and dried with an air stream.

[0150] In this way, a glass with chemically increased strength was obtained from Example 1. <Beispiel 2>

[0151] A glass with chemically increased strength was produced in the same way as in Example 1, however, in the polishing step, cerium oxide with an average particle diameter of 0.9 μm was used as the polishing agent and the polishing pad was changed to a velour-type polishing pad. <Beispiel 3>

[0152] A glass with chemically increased strength was produced in the same way as in Example 2, except that in the polishing step the polishing pad was changed to a polishing pad of a hard urethane type, and in the chemical strength enhancement step the amount of sodium in the molten salt, the temperature during the chemical strength enhancement treatment, and the time during the chemical strength enhancement treatment were each changed to the values ​​shown in Table 1. <Vergleichsbeispiel 1>

[0153] A glass with chemically increased strength was produced in the same way as in Example 1, except that in the chemically increasing strength step the amount of sodium in the molten salt was changed to a value shown in Table 1, the amount of potassium carbonate added was changed to 0 g, and the acid treatment step and the alkali treatment step were omitted. <Vergleichsbeispiel 2>

[0154] A glass with chemically increased strength was produced in the same way as in Example 2, except that in the polishing step cerium oxide with an average particle diameter of 0.7 μm was used as the polishing agent, in the chemically increasing strength step the amount of sodium in the molten salt was changed to a value shown in Table 1, and the amount of potassium carbonate added was changed to 0 g, and the acid treatment step and the alkali treatment step were omitted. <Vergleichsbeispiel 3>

[0155] A glass with chemically increased strength was produced in the same way as in Example 2, except that in the step of chemically increasing the strength, the amount of sodium in the molten salt was changed to a value shown in Table 1, the amount of potassium carbonate added was changed to 0 g, and the acid treatment step and the alkali treatment step were omitted. <Referenzbeispiel 1>

[0156] A glass with chemically increased strength was produced in the same way as in Example 2, but cerium oxide with an average particle diameter of 0.7 μm was used as the polishing agent in the polishing step. <Referenzbeispiel 2>

[0157] A glass with chemically increased strength was produced in the same way as in Example 2, except that in the polishing step cerium oxide with an average particle diameter of 0.7 μm was used as the polishing agent, and in the chemical strength enhancement step the amount of sodium in the molten salt, the temperature during the chemical strength enhancement treatment, and the time during the chemical strength enhancement treatment were each changed to the values ​​shown in Table 1.

[0158] The resulting glass with chemically enhanced strength was evaluated with respect to various properties. The results are shown in Table 1.

[0159] The Fig. 3 to Fig. Figure 5 shows graphs in which the hydrogen concentration profile in the surface layer of each chemically enhanced strength glass obtained in the respective examples and comparison examples has been plotted.

[0160] Furthermore, the Fig. 6 to Fig. 13 images taken with an AFM regarding glass surfaces before and after acid treatment and alkali treatment of the respective glasses with chemically increased strength, which were obtained in the respective examples, comparison examples and reference examples.

[0161] Furthermore, the Fig. 14. A Weibull plot of the BOR strength rating of each of the chemically enhanced strength glasses obtained in Example 1 and Comparative Example 1. Fig. Figure 14 shows a Weibull plot of the BOR strength rating of an aluminosilicate glass plate sample with a thickness of 0.70 mm. The horizontal axis of the graph shows the logarithm In (σ) of the failure load σ (N) and its vertical axis shows a cumulative failure probability percentage P (%) based on the sample in each of the two groups.

[0162] The results in Table 1 show that examples 1 to 3, each with a texture direction index (Sti) of 0.30 or more and satisfying equation (I), exhibited significantly improved surface strength compared to the control examples 1 to 3. Furthermore, examples 1 and 2, each with a texture aspect ratio (Str20) of 0.10 or more, showed even greater improvements in surface strength than example 3.

[0163] Furthermore, the results in the Fig. It can be seen from Figure 14 that the average breaking load in Example 1 was 1303 N, whereas it was 564 N in Comparison Example 1. The 10% breaking load (B10) was 1128 N in Example 1, whereas it was 488 N in Comparison Example 1, and the 1% breaking load (B1) was 927 N in Example 1, whereas it was 402 N in Comparison Example 1. From these results, it is evident that no low-strength products are produced in Example 1 and that the products obtained exhibit significantly improved reliability with respect to surface strength.

[0164] While the invention has been described in detail with reference to specific embodiments thereof, it is apparent to a person skilled in the art that the present invention can be altered and modified in various ways without altering its essence and scope. This application is based on a Japanese patent application filed on July 19, 2013 (Japanese patent application no. 2013-151116), the contents of which are incorporated herein by reference. COMMERCIAL APPLICABILITY

[0165] According to the present invention, a chemically enhanced glass with a significantly improved surface strength can be produced safely and cost-effectively. The chemically enhanced glass of the present invention can be used as a cover glass for displays such as those for mobile phones, digital cameras, and touchscreen displays. Reference symbol list 10 low-density layers 20 Pressure stress layer 30 Intermediate shift< / bewertungsverfahren>

Claims

[1] Glass with chemically enhanced strength, which has a compressive stress layer formed in a surface layer thereof according to an ion exchange process, where one surface of the glass has polishing defects, where the glass has a texture direction index (STI) of 0.30 or more, The hydrogen concentration Y in a region up to a depth X from an outermost surface of the glass satisfies the following relation equation (I) at X = 0.1 to 0.4 (μm), and the surface strength F (N) which was measured by a ball-on-ring test under the following conditions, (F ≥ 1400 × t 2 ) based on the plate thickness t (mm) of the glass is: Y = aX + b (I) where the meanings of the respective symbols in equation (I) are as follows: Y: Hydrogen concentration (as H2O, mol / liter), X: Depth from the outermost surface of the glass (μm), a: -0.300 or more and b: 0.220 or less, the conditions of the ball-on-ring test are as follows: A glass plate with a thickness t (mm) is placed on a stainless steel ring with a diameter of 30 mm and a contact area with a radius of curvature of 2.5 mm. A steel ball with a diameter of 10 mm is held in contact with the glass plate. A load is applied to the center of the ring by the ball under static loading conditions. The breaking load (unit: N) at which the glass breaks is used as the BOR strength, and the average of twenty measurements is used as the surface strength F. In cases where the point of breakage of the glass is 2 mm or more away from the point of load on the ball, the obtained value is excluded from the data used to calculate the average value. [2] Glass with chemically increased strength according to claim 1, wherein the glass is an aluminosilicate glass, an aluminoborosilicate glass or a soda-lime glass. [3] Glass with chemically enhanced strength according to claim 1 or 2, having a texture aspect ratio (Str20) of 0.10 or more. [4] A method for producing a glass with chemically enhanced strength, comprising a step of contacting a glass containing sodium with an inorganic salt containing potassium nitrate, thereby carrying out an ion exchange of Na in the glass with K in the inorganic salt, wherein the inorganic salt contains at least one salt from the group consisting of K2CO3, Na2CO3, KHCO3, NaHCO3, K3P O4 , Na3PO4, K2SO4, Na2SO4, KOH and NaOH, is selected, and the procedure includes: a step of polishing a surface of the glass before ion exchange, a step of washing the glass after ion exchange, one step of acid-treating the glass after washing and a step of alkali-treating the glass after acid-treating it. [5] Glass with chemically increased strength obtained by the manufacturing process according to claim 4.