Glass plate and method for producing glass plate

Abstract

The glass plate (G) has: a peripheral edge region (A1) that has a width along the periphery and in which planar compressive stress is formed; a central region (A2) that occupies the inner circumferential side of the peripheral edge region (A1); and a cross-section which is a cross-section parallel to the vertical direction when the glass plate (G) is installed horizontally in which, when the planar stress at the boundary between the central region (A2) and the peripheral edge region (A1) is taken to be 1 MPa, there is one peak of planar stress in the entire region of the central region (A2) and the peripheral edge region (A1) at one end of the peripheral edge region (A1), the value of the peak is greater than 1 MPa and less than 10 MPa, and the planar stress in the central region (A2) is from -3MPa to 3 MPa throughout the entire central region (A2).

Description

Glass plate and method for manufacturing the same

[0001] The present invention relates to a glass sheet and a method for manufacturing a glass sheet.

[0002] Patent Document 1 discloses a technology relating to a glass sheet made of laminated glass used as window glass for automobiles. Patent Document 1 describes that the glass sheet has a peripheral region having a certain width along the periphery of the glass sheet and in which edge compression is formed, and an intermediate region adjacent to the inner periphery of the peripheral region, having a certain width, and in which inner tension is formed.

[0003] Patent Document 2 discloses a tempered glass sheet having a diagonal central region where the average stress difference is 3 MPa or less, and edge regions, where the edge regions include a first peak and a second peak of the stress difference in at least one of a region within 0.15 × d from the start point of the diagonal and a region within 0.15 × d from the end point of the diagonal, where d is the length of the diagonal.

[0004] International Publication No. 2011 / 096447 Japanese Patent Application Laid-Open No. 2022-122586

[0005] While the techniques disclosed in Patent Documents 1 and 2 increase the strength of glass sheets and suppress cracking, it is desirable to further suppress cracking from the edges, particularly for glass sheets used as cover glass for smartphones and liquid crystal displays. However, adjusting the molding conditions to increase the edge compression in the peripheral region also increases the inner tension in the central region adjacent to the inner periphery of the peripheral region, making cracks more likely to occur at the boundary between the peripheral region and the central region. Furthermore, when stress fluctuations are severe, retardation increases, leading to a problem of deterioration in visibility of the glass sheet.

[0006] Therefore, an object of the present invention is to provide a glass sheet in which cracks originating from the edge are effectively suppressed, and a method for manufacturing the glass sheet.

[0007] The present invention comprises the following configuration: (1) A glass plate having a peripheral region having a width along the periphery and in which a plane compressive stress is formed, and a central region occupying the inner peripheral side of the peripheral region, wherein the glass plate has a cross section parallel to the vertical direction when placed horizontally, in which, when the plane stress at the boundary between the central region and the peripheral region is 1 MPa, there is one plane stress peak in the entire region of the central region and the peripheral region at one end of the peripheral region, the value of the peak is greater than 1 MPa and less than 10 MPa, and the plane stress in the central region is -3 MPa or more and 3 MPa or less throughout the entire central region. (2) A method for manufacturing a glass plate having a curved shape, comprising: placing a flat glass plate on a forming mold; heating the glass plate for 15 seconds to 10 minutes so that the viscosity becomes log η = 19 Poise or less, thereby forming the glass plate into the shape of the forming mold; further, holding the glass plate in a state where the viscosity becomes log η = 13 Poise or less for 1 minute to 10 minutes; and then slowly cooling the glass plate to a strain point or less.

[0008] According to the present invention, it is possible to provide a glass plate in which cracks originating from the edge are effectively suppressed, and a method for manufacturing the glass plate.

[0009] FIG. 1 is a schematic plan view of a glass plate according to this embodiment. FIG. 2 is a graph showing a plane stress distribution A in the widthwise A-A cross section at the longitudinal center of the glass plate. FIG. 3 is a graph showing a plane stress distribution B in the widthwise B-B cross section between the longitudinal center of the glass plate and one longitudinal end of the glass plate. FIG. 4 is a graph showing a plane stress distribution C in the widthwise C-C cross section near one longitudinal end of the glass plate. FIG. 5 is a graph showing a plane stress distribution D in the widthwise D-D cross section from the longitudinal center to one end of the glass plate at the widthwise center. FIG. 6 is a schematic cross-sectional view showing chamfering at the edge of the glass plate. FIG. 7 is a schematic cross-sectional view showing chamfering at the edge of the glass plate. FIG. 8 is a schematic cross-sectional view showing chamfering at the edge of the glass plate. FIG. 9 is a graph showing the retardation distribution in the widthwise A-A cross section at the longitudinal center of the glass plate before and after chemical strengthening. Fig. 10 is a graph showing the plane stress distribution in the A-A cross section in the width direction at the center of the longitudinal direction of a glass plate before and after chemical strengthening. Fig. 11 is a schematic configuration diagram of a forming device that forms a glass plate. Fig. 12 is a schematic cross-sectional view in the width direction of a heating region of the forming device. Fig. 13 is a side view of a forming mold on which a glass plate is placed. Fig. 14 is a graph explaining temperature control in the heating region of the forming device.

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. (Glass Sheet) Fig. 1 is a schematic plan view of a glass sheet G according to this embodiment. As shown in Fig. 1, the glass sheet G according to this embodiment has an elongated shape formed into a substantially rectangular shape in a plan view. This glass sheet G is used, for example, as a cover glass for various displays, such as displays of mobile terminals such as smartphones and in-vehicle displays. Note that the planar shape of the glass sheet G is not limited to an elongated rectangular shape, and may be various planar shapes according to the application.

[0011] As shown in FIG. 1 , a glass sheet G has a peripheral region A1 and a central region A2. The peripheral region A1 is a region having a constant width along the periphery of the glass sheet G, and the central region A2 is a region occupying the inner peripheral side of the peripheral region A1. Edge compression is formed in the peripheral region A1 of the glass sheet G. In the present disclosure, planar compressive stress formed on the peripheral edge of the glass sheet is referred to as edge compression. Furthermore, planar tensile stress generated inside the peripheral edge of the glass sheet is referred to as inner tension.

[0012] This glass plate G has been subjected to a chemical strengthening treatment. By subjecting the glass plate G to a chemical strengthening treatment, the overall surface strength of the glass plate G can be increased, making it less likely to break. By the chemical strengthening treatment, the glass plate G has a surface compressive stress (CS: Compressive stress) of 400 MPa to 1400 MPa, and a depth of the surface compressive stress layer (DOL: Depth of layer) of 5 μm to 100 μm. Furthermore, the glass plate G has a plate thickness of 1.5 mm or less. If the plate thickness of the glass plate G is 1.5 mm or less, flexibility can be increased and it can be made more resistant to breakage. The plate thickness of the glass plate G is more preferably 1.3 mm or less. Furthermore, when used as a cover glass for an in-vehicle display device such as a car navigation system, from the viewpoint of strength, the plate thickness of the glass plate G is preferably 0.2 mm or more, more preferably 0.8 mm or more, and even more preferably 1.0 mm or more. Furthermore, the dimensions of the glass plate G can be appropriately selected depending on the application. For example, when used as a cover glass for an in-vehicle display device, the length of the short side is, for example, 50 mm to 500 mm, preferably 100 mm to 300 mm, and the length of the long side is, for example, 50 mm to 1500 mm, preferably 100 mm to 1200 mm. Note that a glass plate that has been subjected to a chemically strengthened treatment is also called chemically strengthened glass.

[0013] Next, the distribution of plane stress, which is the residual stress of the glass sheet G, will be described. FIG. 2 is a graph showing plane stress distribution A in the A-A cross section in the width direction at the longitudinal center of the glass sheet G. The longitudinal direction of the glass sheet G is the left-right direction in FIG. 1, and the width direction of the glass sheet is the up-down direction in FIG. 1. FIG. 3 is a graph showing plane stress distribution B in the B-B cross section in the width direction between the longitudinal center of the glass sheet G and one end of the glass sheet G in the longitudinal direction. FIG. 4 is a graph showing plane stress distribution C in the C-C cross section in the width direction near one end of the glass sheet G in the longitudinal direction. FIG. 5 is a graph showing plane stress distribution D in the D-D cross section from the longitudinal center to one end at the width center of the glass sheet G. In FIGS. 2 to 4, the horizontal axis represents the distance from the lower edge E shown in FIG. 1. In FIG. 5, the horizontal axis represents the distance from the right edge E shown in FIG. 1. In the present disclosure, the one end corresponds to the edge E of the glass plate G, and refers to one of the ends at which plane stress can be measured when the glass plate G is placed horizontally and plane stress in a cross section parallel to the vertical direction is measured using a two-dimensional birefringence distribution evaluation device (for example, WPA-100 manufactured by Photonic Lattice Co., Ltd.).

[0014] Glass plate G has a cross section parallel to the vertical direction when the glass plate is placed horizontally, and when the plane stress at the boundary between central region A2 and peripheral region A1 is 1 MPa, as shown in plane stress distributions A to D, there is one plane stress peak P in the entire area of ​​central region A2 and peripheral region A1 at one end of peripheral region A1.

[0015] Furthermore, as shown in plane stress distributions A to D, the glass sheet G has a peak P value of plane compressive stress in the peripheral region A1 that is greater than 1 MPa and less than 10 MPa. In the glass sheet G, the absolute value of the edge compression in the peripheral region A1 is greater than the absolute value of the inner tension. Furthermore, as shown in plane stress distributions A to D, the glass sheet G has a plane stress in the central region A2 that is greater than -3 MPa and less than 3 MPa throughout the entire central region A2. By having at least one cross section with such a plane stress distribution, the glass sheet G can suppress cracking in the peripheral region A1. Furthermore, distortion can be suppressed to reduce retardation, which is a birefringence phase difference, thereby improving visibility and obtaining a clear transmitted image. It is preferable that the plane stress in the central region A2 be greater than -1 MPa and less than 3 MPa throughout the entire central region A2, as this further suppresses cracking in the peripheral region A1.

[0016] Furthermore, the glass sheet G preferably has a cross section in which the plane stress in the central region A2 exceeds 0 MPa throughout the entire central region, as shown by plane stress distributions B, C, and D. By having at least one cross section with such a plane stress distribution, the strength of the peripheral region A1 of the glass sheet G is increased and inner tension is suppressed. This allows the glass sheet G to be made in a state in which cracks occurring particularly at the edge E are suppressed.

[0017] In addition, it is preferable that the plane stress peak P of the glass sheet G is present in a region less than 50 mm from the boundary between the central region A2 and the peripheral region A1. In other words, it is preferable that the peripheral region A1 of the glass sheet G is a region less than 50 mm from the edge E. In this way, if the plane stress peak P is present in a region less than 50 mm from the edge E, distortion at the edge E can be suppressed and a good appearance can be achieved. It is more preferable that the peripheral region A1 of the glass sheet G is a region less than 20 mm from the edge E. If the plane stress peak P is present in a region less than 20 mm from the edge E, the region that is distorted at the edge E can be narrowed and the region with a good appearance can be widened.

[0018] Furthermore, the glass plate G may include, for example, a curved region having a curvature radius of 5 mm or more in a portion of the central region A2 or the peripheral region A1. The curvature radius is preferably 50 mm or more, more preferably 100 mm or more, and even more preferably 200 mm or more. Thus, the provision of a curved region can improve the design and visibility of the glass plate G. In this case, when the curvature radius is small, such as 200 mm or less, it is preferable to measure the plane stress in a state in which the irradiation direction of the above-mentioned two-dimensional birefringence distribution evaluation device is approximately equal to the normal direction of the plane tangent to the measured curved surface. By using such a measurement method, separation between the thickness of the glass plate G and the optical path length in the vertical direction of the glass is less likely to occur, allowing for more accurate plane stress measurement. On the other hand, the curvature radius is, for example, 10,000 mm or less, preferably 5,000 mm or less, and more preferably 3,000 mm or less. It is preferable that the glass sheet G has a curved shape without a flat portion and has the same radius of curvature throughout the entire bent region, but the bent region may be a spline curve in which the radius of curvature changes continuously.

[0019] Furthermore, if the glass plate G, which has increased strength in the peripheral region A1 and reduced inner tension, is used as a cover glass for a display for a mobile terminal or an in-vehicle display, the display can be strongly protected while ensuring good visibility.

[0020] Furthermore, the glass sheet G is chamfered on at least one side of the cross section of its edge E. By chamfering the edge E in this manner, cracks caused by minute chips remaining on the edge E can be suppressed.

[0021] 6 to 8 show the chamfered shape of the edge E. Examples of chamfering the edge E include R-chamfering, in which the entire edge E, including the corners Ea and Eb, is polished into an arc shape, as shown in FIG. 6 , and C-chamfering, in which the corners Ea and Eb of the edge E are polished flat, as shown in FIG. 7 . Among these, R-chamfering at least one of the corners Ea and Eb of the edge E is preferred because it is more likely to suppress cracks caused by minute chips remaining in the edge E. Furthermore, as shown in FIG. 8 , the corner Ea on the front side of the edge E may be mirror-polished to form a curved surface. In this case, it is preferable to perform C-chamfering or R-chamfering on the corners Ea and Eb of the edge E. When R-chamfering the corners Ea and Eb of the edge E, it is preferable that the radius R of the arc be 0.5 mm or more. By setting the radius R to 0.5 mm or more, cracks at the edge E can be prevented. On the other hand, it is preferable that the radius R be 1000 mm or less. By setting the radius R of the arc to 1000 mm or less, the design of the glass plate G can be improved.

[0022] The glass sheet G may also have a buttonhole or an inner curve, and in this case, by providing the above-mentioned plane stress distribution, the strength of the peripheral region A1 can be increased and cracks occurring from the edge E can be suppressed.

[0023] The glass sheet G may be made of alkali-free glass, soda-lime glass, soda-lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, borosilicate glass, or the like. ２ O.K. ２The term "glass substantially free of alkali metal oxides" refers to glass that is substantially free of alkali metal oxides such as SiO. Here, "substantially free of alkali metal oxides" means that the total content of alkali metal oxides is 0.1 mass % or less. When the glass plate G is used as a cover glass for a display device, it is preferable to use glass that contains alkali metal oxides such as those shown below. When glass that contains alkali metal oxides is subjected to a chemical strengthening treatment after molding, a compressive stress layer is formed on the glass surface, thereby increasing the strength. The glass that contains alkali metal oxides is not particularly limited, but may contain, for example, SiO, expressed in mole % based on the oxides. ２ 50% to 80%, Al ２ O ３ 0.1% to 25%, Li ２ O + Na ２ O+K ２ O 3% to 30%, MgO 0% to 25%, CaO 0% to 25%, and ZrO ２ Contains 0% to 5% of. Specific examples include the following glasses (i) to (v). The following glass (i) is included in soda lime silicate glass. The following glasses (ii), (iii), and (iv) are included in aluminosilicate glass. The following glass (v) is included in lithium aluminosilicate glass. (i) Indicated in mole percent on an oxide basis, SiO ２ 63% to 73%, Al ２ O ３ 0.1% to 5.2%, Na ２ O 10% to 16%, K ２ O from 0% to 1.5%, Li ２ Glass containing 0% to 5% of O, 5% to 13% of MgO, and 4% to 10% of CaO. ２ "Contains 0% to 1.5% of O" means that K ２ This means that O is not essential but may be contained up to 1.5%. Hereinafter, the same applies when the content of other substances is described as "0% or more". (ii) Indicated in mole percent based on oxides, SiO ２ 50% to 74%, Al ２ O ３ 1% to 10%, Na ２ O 6% to 14%, K ２ O from 3% to 11%, Li２ O 0% to 5%, MgO 2% to 15%, CaO 0% to 6%, and ZrO ２ Contains 0% to 5% of SiO ２ and Al ２ O ３ The total content of is 75% or less, Na ２ O and K ２ (iii) A glass having a total content of O of 12% to 25% and a total content of MgO and CaO of 7% to 15%. ２ 68% to 80%, Al ２ O ３ 4% to 10%, Na ２ O 5% to 15%, K ２ O from 0% to 1%, Li ２ O 0% to 5%, MgO 4% to 15% and ZrO ２ (iv) A glass containing, in mole percent on an oxide basis, SiO ２ 67% to 75%, Al ２ O ３ 0% to 4%, Na ２ O 7% to 15%, K ２ 1% to 9% O, Li ２ O 0% to 5%, MgO 6% to 14% and ZrO ２ Contains 0% to 1.5% of SiO ２ and Al ２ O ３ The total content of 71% to 75%, Na ２ O and K ２ (v) A glass having a total content of O of 12% to 20%, and when CaO is contained, the content of CaO is less than 1%. ２ 56% to 73%, Al ２ O ３ 10% to 24%, B ２ O ３ 0% to 6%, P ２ O ５ 0% to 6%, Li ２ 2% to 7% O, Na ２ O 3% to 11%, K ２O 0% to 2%, MgO 0% to 8%, CaO 0% to 2%, SrO 0% to 5%, BaO 0% to 5%, ZnO 0% to 5%, TiO ２ 0% to 2%, ZrO ２ (vi) A glass containing 0% to 4% of SiO ２ 58 to 80%, Al ２ O ３ 13-18%, B ２ O ３ 0 to 5%, P ２ O ５ 0.5-4%, Li ２ 3-10% O, Na ２ O 5-20%, K ２ O 0-2%, MgO 0-11%, CaO 0-20%, SrO 0-20%, BaO 0-15%, ZnO 0-10%, TiO ２ 0 to 1%, ZrO ２ Glass containing 0 to 2% of

[0024] In the above example, the glass sheet G after being subjected to chemical strengthening treatment has been described, but the present invention may also be applied to a glass sheet G before being strengthened by chemical strengthening treatment.

[0025] FIG. 9 is a graph showing the distribution of retardation (birefringence phase difference) in a widthwise cross section (A-A cross section) passing through the center of the longitudinal direction of the glass plate G before and after chemical strengthening, and is the result of measurement from the main surface side of the glass plate G using a birefringence phase difference measurement device. FIG. 10 is a graph showing the plane stress distribution in a widthwise cross section (A-A cross section) passing through the center of the longitudinal direction of the glass plate G before and after chemical strengthening, and is the result of calculation based on the measured retardation of the glass plate G. Since a predetermined calculation formula (retardation / (glass plate thickness × photoelastic coefficient) = plane stress) holds between retardation and plane stress, it is possible to calculate one value from the other value. As shown in FIG. 9, the glass plate G preferably has a cross section in which the retardation in the cross section of the central region A2 is greater than 0 nm and less than 11 nm throughout the entire central region A2. By having at least one cross section with such a retardation distribution, the glass plate G can suppress distortion and reduce retardation, thereby improving visibility and providing a clear transmitted image.

[0026] As shown in Figures 9 and 10, the retardation and plane stress distribution of the glass sheet G hardly change before and after strengthening by chemical strengthening. In other words, even before strengthening by chemical strengthening, the retardation distribution of the glass sheet G is the same as that after strengthening, and the plane stress distribution is also the same as that after strengthening. Therefore, by having the above-mentioned plane stress distribution even before strengthening, the strength of the peripheral region A1 of the glass sheet G is increased and inner tension is suppressed. Then, by performing a chemical strengthening treatment on this glass sheet G before strengthening, the overall surface strength is increased and it becomes more resistant to breakage. Furthermore, the glass sheet G may have at least one layer of an AG layer, an AR layer, an AFP layer, and a printed layer (not shown). The AG layer, AR layer, and AFP layer are formed in this order on one main surface of the glass sheet G (on the main surface facing the viewer if the glass sheet G is a cover glass for a display). The printed layer is formed on the other main surface of the glass sheet G. The AG layer, AR layer, AFP layer, and printed layer each have a curved surface shape that conforms to the glass plate G. The AG (Anti-Glare) layer is an anti-glare layer that imparts anti-glare properties to the glass plate G. The AG layer has an uneven surface. The surface roughness (root mean square roughness, RMS) of this uneven surface is preferably 25 nm to 1000 nm, more preferably 10 nm to 500 nm. The AG layer may be formed by etching the glass plate G, or may be formed separately from the glass plate G. In the latter case, the AG layer may be a coating film containing a plurality of dispersed particles, or may be a transparent resin film having an uneven pattern transferred onto its surface. The AR (Anti-Reflection) layer is an anti-reflection layer that reduces glare caused by reflected light. The AR layer improves the visibility of images on the display. The AR layer is configured by alternately laminating, for example, high-refractive index layers having a refractive index of 1.9 or more at a wavelength of 550 nm and low-refractive index layers having a refractive index of 1.6 or less at a wavelength of 550 nm. The AR layer may be provided on the AG layer or directly on the glass plate G. The AFP (Anti-Fingerprint) layer is an anti-fouling layer that suppresses the adhesion of dirt. The dirt includes at least one of fingerprints, sweat, and dust. Due to its characteristics, the AFP layer is preferably formed on the outermost surface of the glass plate G.The AFP layer is preferably made of a fluorine-containing organic compound (a compound having a fluorine-containing organic group) that can impart antifouling, water repellency, and oil repellency. Examples of fluorine-containing organic compounds include fluorine-containing organosilicon compounds. The printed layer is provided along at least a portion (preferably the entire) of the periphery of the glass plate G. The printed layer conceals, for example, the wiring of the display, thereby improving the design of the display. The color of the printed layer is, for example, black, but is not limited to black as long as it has high light-blocking properties, and may be wood grain, for example. Note that the plane stress of the glass plate G refers to the plane stress of the glass plate G alone, excluding the printed layer. When a printed layer is provided on the glass plate G, the printed layer on the glass plate G is removed, and then the plane stress of the glass plate G is measured. Removal of the printed layer does not change the value of the plane stress of the glass plate G alone.

[0027] (Method for manufacturing glass plate) Next, a method for manufacturing a glass plate G will be described. Here, a glass plate used as a cover glass for a display or the like is formed into a target shape in a size that matches the display. Methods for manufacturing such a glass plate include, for example, a method in which a glass plate is formed and then processed (hereinafter referred to as an oversize method) and a method in which a glass plate is processed and then shaped (hereinafter referred to as a just edge method).

[0028] In the oversize method, a glass sheet larger than the target size is formed into the target shape and then the peripheral portion is cut off to achieve the target size. In contrast, in the just-edge method, a glass sheet processed to the same size as the target size is formed to match the target shape.

[0029] The oversizing method can easily process the size of the glass sheet G to the target size, but because the peripheral portion where high plane stress remains is cut and removed, it is difficult to form appropriate edge compression in the peripheral region A1. Therefore, in this example, the glass sheet G is formed by the just-edge method, which forms a glass sheet G of the same size as the target size into the target shape. Glass sheet forming using the just-edge method allows mirror finishing to be applied to edges with appropriate edge compression (see FIG. 8 ), so the glass sheet G and its manufacturing method of this embodiment are also useful for glass sheets that require mirror finishing.

[0030] Fig. 11 is a schematic diagram of a forming device 10 that forms a glass sheet G. Fig. 12 is a schematic cross-sectional view in the width direction of a heating zone Zhe of the forming device 10. Fig. 13 is a side view of a forming mold 20 on which a glass sheet G is placed. Fig. 14 is a graph illustrating temperature control in the heating zone Zhe of the forming device 10.

[0031] As shown in Figure 11, a glass sheet G forming apparatus 10 includes multiple (three in this example) heating furnaces 11A, 11B, and 11C, multiple (two in this example) annealing furnaces 13A and 13B, and a cooling furnace 15, which are arranged in this order. In this forming apparatus 10, the heating furnaces 11A, 11B, and 11C form a heating zone Zhe, the annealing furnaces 13A and 13B form an annealing zone Zsc, and the cooling furnace 15 forms a cooling zone Zco. A glass sheet G placed on a forming mold 20 transported in the transport direction X passes through the forming apparatus 10. That is, in the forming apparatus 10, the glass sheet G placed on the forming mold 20 is carried in from the heating furnace 11A side, passed through the heating zone Zhe, the annealing zone Zsc, and the cooling zone Zco, and then carried out from the cooling furnace 15 side.

[0032] 12, the heating furnaces 11A, 11B, and 11C each include an upper heater 31 and a lower heater 33, and the glass sheet G passes between the upper heater 31 and the lower heater 33 while being placed on the forming mold 20. The upper heater 31 includes a plurality of (five in this example) thermocouples Hu1 to Hu5, and the lower heater 33 includes a plurality of (five in this example) thermocouples Hd1 to Hd5. The thermocouples Hu1 to Hu5 of the upper heater 31 and the thermocouples Hd1 to Hd5 of the lower heater 33 are arranged in a direction intersecting the transport direction X of the forming mold 20, and are independently temperature-controlled.

[0033] In the forming apparatus 10 having the above configuration, the glass sheet G is placed on the forming mold 20 and passed through the heating zone Zhe, the annealing zone Zsc, and the cooling zone Zco of the forming apparatus 10, and formed into a target shape.

[0034] Next, a description will be given of each step in manufacturing the glass sheet G. (Placement Step) As shown in Fig. 13 , a glass sheet G having a planar shape cut to a size equivalent to a target size is placed on a forming mold 20. The upper surface of the forming mold 20 serves as a forming surface 21 for forming the glass sheet G into the target shape.

[0035] (Heating Step) The glass sheet G placed on the forming mold 20 is carried in together with the forming mold 20 from the heating furnace 11A side, and this glass sheet G is heated in the heating region Zhe.

[0036] As shown in FIG. 14 , in the heating region Zhe, the glass sheet G is heated in the heating furnace 11A to a peak temperature of 500°C to 750°C. Next, the glass sheet G is heated to a peak temperature of 550°C to 850°C in the heating furnace 11B, and then the glass sheet G is maintained at a temperature of 550°C to 850°C in the heating furnace 11C. At this time, in the heating furnaces 11A, 11B, and 11C, the temperatures of the thermocouples Hu1 to Hu5 of the upper heater 31 are each controlled to uniformly heat the glass sheet G. As shown in FIG. 14 , in the heating furnaces 11A and 11B, it is preferable, from the viewpoint of shape accuracy, to control the temperatures of the thermocouples so that the heater heating temperatures (temperatures of thermocouples Hu1 and Hu5) at both ends of the glass sheet G in the longitudinal direction are higher than the heater heating temperature (temperature of thermocouple Hu3) at the center of the glass sheet G in the longitudinal direction. Furthermore, in order to suppress cracking, it is preferable that the temperature distribution peak of the glass sheet G in the heating region Zhe exists at one end of the peripheral region A1. Specifically, as shown in FIG. 14, it is preferable to control the temperature of the thermocouples so that the peaks of the temperature distribution of the glass sheet G in the heating furnaces 11A and 11B exist at both longitudinal ends of the glass sheet G (parts corresponding to thermocouples Hu1 and Hu5). Note that the heating temperature of the glass sheet G may be gradually increased as it progresses through the heating furnaces 11A to 11C, as exemplified above, or it may be heated to a constant temperature from the heating furnaces 11A to 11C. The glass sheet G is softened by being heated in the heating region Zhe and is formed by its own weight into a shape that conforms to the forming surface 21 of the forming mold 20. Note that forming of the glass sheet G by its own weight is preferable, as temperature change is suppressed. However, forming by pressing from above, forming by blowing air or the like from above, or forming by vacuum suction from the forming surface 21 may also be used.

[0037] Then, the glass sheet G is heated in the heating region Zhe for 15 seconds to 10 minutes to form the glass sheet G so that the viscosity becomes log η = 19 Poise or less. By heating the glass sheet G in this manner, cracking of the glass sheet G due to rapid heating can be suppressed, and the occurrence of foreign matter defects on the surface of the glass sheet G can be suppressed. The heating time is preferably 30 seconds to 7 minutes, and more preferably 30 seconds to 5 minutes.

[0038] Furthermore, the glass sheet G is maintained at a viscosity of log η = 13 Poise or less for 1 minute to 10 minutes. This suppresses the occurrence of appearance defects in the glass sheet G, and the glass sheet G is formed into a target shape that conforms to the forming surface 21 of the forming mold 20. When the viscosity of the glass sheet G is in a state where log η > 13 Poise, the viscosity is high, making it difficult to form the glass sheet G into a desired curved shape, and as a result, the surface shape accuracy of the glass sheet G is likely to deteriorate. Furthermore, by setting the heating time while maintaining this viscosity to 10 minutes or less, not only can the appearance quality of the glass sheet G be improved, but the takt time can be shortened, thereby improving manufacturing efficiency. The heating time while maintaining this viscosity is preferably 2 minutes to 8 minutes, and more preferably 4 minutes to 6 minutes.

[0039] Furthermore, when maintaining the viscosity of the glass sheet G, it is preferable to suppress the viscosity distribution in the in-plane direction of the glass sheet G to log η = 8.5 Poise or more and log η = 13 Poise or less. This is expected to eliminate residual stress in the glass sheet G and reduce retardation. Note that this viscosity distribution is preferably log η = 9 Poise or more and log η = 12 Poise or less.

[0040] (Slow-cooling process) The glass sheet G on the forming mold 20 heated in the heating region Zhe is sent sequentially to the slow-cooling furnaces 13A and 13B in the slow-cooling region Zsc. Then, in this slow-cooling region Zsc, the glass sheet G is slowly cooled to room temperature in accordance with the heating peak in the heating region Zhe, thereby being slowly cooled to below the strain point. This is expected to remove residual stress in the glass sheet G and reduce retardation. Then, this slow-cooling makes the viscosity of the glass sheet G log η = 12.5 Poise or more. The slow-cooling time to achieve this viscosity is preferably 30 seconds to 10 minutes, more preferably 1 minute to 4 minutes.

[0041] (Cooling process) The glass sheet G on the forming mold 20 that has been annealed in the annealing region Zsc is sent to the cooling furnace 15 in the cooling region Zco, where it is cooled and then carried out. This results in a cooled, shaped glass sheet G. The glass sheet G is removed from the forming mold 20 and transported to the next process, and the forming mold 20 is returned to the carry-in position of the forming device 10. The glass sheet G shaped in this manner has a high strength in the peripheral region A1, and also has reduced inner tension, resulting in a glass sheet that is particularly resistant to cracking that occurs from the edge E.

[0042] (Chemical Strengthening Treatment Step) The glass sheet G formed by the forming device 10 is subjected to a chemical strengthening treatment by a chemical strengthening method.

[0043] Here, chemical strengthening is a process in which alkali metal ions with a small ionic radius present on the main surface of a glass plate (workpiece) are exchanged with alkali metal ions with a larger ionic radius using a molten salt at just under 450°C, thereby forming a surface compressive stress layer on the surface of the glass plate. The alkali metal ions with a small ionic radius present on the main surface of the glass plate are typically Li ions or Na ions. The alkali metal ions with a larger ionic radius contained in the molten salt are typically Na ions for Li ions and K ions for Na ions. The chemical strengthening process can be carried out by a conventionally known method, for example, by immersing the glass in a molten salt such as potassium nitrate molten salt. This molten salt may contain approximately 10% by mass of potassium carbonate.

[0044] This chemical strengthening method forms a surface compressive stress layer on the surface of the glass sheet G, thereby obtaining a high-strength glass sheet G. By mixing a silver component such as silver nitrate into the molten salt during chemical strengthening, the glass undergoes ion exchange, resulting in silver ions on the surface, which can impart antibacterial properties. Furthermore, the chemical strengthening treatment is not limited to one time, and may be performed, for example, two or more times under different conditions. After the chemical strengthening treatment, the glass sheet G may be washed. For example, in addition to water washing, acid treatment, alkali treatment, or alkali brush washing may be performed as the washing.

[0045] By performing chemical strengthening treatment using this chemical strengthening method, the surface compressive stress (CS) of the glass sheet G after molding is set to 400 MPa or more and 1400 MPa or less, and the depth of the surface compressive stress layer (DOL) is set to 5 μm or more and 100 μm or less, thereby increasing the overall surface strength and making the glass sheet G more shatter-resistant.

[0046] Even if the glass sheet G is rapidly cooled in this chemical strengthening treatment, the rapid cooling does not affect the plane stress because the temperature is below the strain point, and no deformation occurs due to the release of inner tension.

[0047] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these modifications and applications are included in the scope of protection sought.

[0048] As described above, this specification discloses the following: (1) A glass plate having a peripheral region having a width along the periphery and in which a plane compressive stress is formed, and a central region occupying the inner periphery of the peripheral region, wherein the glass plate has a cross section parallel to the vertical direction when the glass plate is placed horizontally, in which, when the plane stress at the boundary between the central region and the peripheral region is 1 MPa, there is one plane stress peak in the entire region of the central region and the peripheral region at one end of the peripheral region, the value of the peak is greater than 1 MPa and less than 10 MPa, and the plane stress in the central region is -3 MPa or more and 3 MPa or less throughout the entire central region. This glass plate enhances the strength of the peripheral region, and cracks occurring particularly at the edges are suppressed. Moreover, this glass plate can suppress distortion and reduce retardation, thereby improving visibility and providing a clear transmitted image. (2) The glass plate according to (1), having a cross section in which the plane stress in the central region is -1 MPa or more and 3 MPa or less throughout the entire central region. This glass plate further suppresses cracking in the peripheral region. (3) The glass plate according to (1) or (2), having a cross section in which the plane stress in the central region is greater than 0 MPa throughout the entire central region. This glass plate further suppresses cracking in the peripheral region. Moreover, this glass plate suppresses inner tension, thereby further suppressing cracking, particularly from the edges. (4) The glass plate according to any one of (1) to (3), having a thickness of 1.5 mm or less. This glass plate can be made more flexible and less susceptible to cracking. (5) The glass plate according to any one of (1) to (4), having the peak of the plane stress present in a region less than 50 mm from the boundary between the central region and the peripheral region. This glass plate can suppress distortion at the edges, resulting in a good appearance. (6) The glass plate according to any one of (1) to (6), wherein the peak of the plane stress is present in a region less than 20 mm from the boundary between the central region and the peripheral region. This glass plate can narrow the region that is distorted at the edge, thereby widening the region that has a good appearance. (7) The glass plate according to any one of (1) to (6), wherein the glass plate includes a bent region having a radius of curvature of 5 mm or more.This glass plate can improve design and visibility. (8) The glass plate according to (7), which includes a bent region having a radius of curvature of 50 mm or more. This glass plate can improve design and visibility. (9) The glass plate according to any one of (1) to (8), in which the absolute value of the edge compression in the peripheral region is larger than the absolute value of the inner tension. This glass plate can prevent cracks that can occur when the absolute value of the inner tension is larger than the absolute value of the edge compression. (10) The glass plate according to any one of (1) to (9), in which at least one side of the edge cross section is rounded. This glass plate is likely to be effective in suppressing cracks caused by fine chips remaining on the edge. (11) The glass plate according to any one of (1) to (10), which is used as a cover glass for a display. When used as a cover glass for a display, this glass plate can strongly protect the display while ensuring good visibility. (12) The glass plate according to any one of (1) to (11), which is used as a cover glass for an in-vehicle display. When used as a cover glass for an in-vehicle display, this glass plate can firmly protect the in-vehicle display while ensuring good visibility. (13) The glass plate according to any one of (1) to (12), which has a cross section in which the retardation in the cross section of the central region is greater than 0 nm and less than or equal to 11 nm throughout the entire central region. This glass plate suppresses distortion, thereby improving visibility and providing a clear transmitted image. (14) The glass plate according to any one of (1) to (13), which is chemically strengthened glass, having a surface compressive stress of 400 MPa to 1400 MPa, and a surface compressive stress layer depth of 5 μm to 100 μm. This glass plate increases the overall surface strength and makes it more resistant to breakage.(15) A method for manufacturing a glass sheet including a curved shape, comprising: placing a flat glass sheet on a forming mold; heating the glass sheet so that the viscosity becomes log η = 19 Poise or less within 15 seconds to 10 minutes to form the glass sheet into the shape of the forming mold; holding the glass sheet at a state where the viscosity becomes log η = 13 Poise or less for 1 minute to 10 minutes; and then slowly cooling the glass sheet to below its strain point. This method for manufacturing a glass sheet can produce a glass sheet that has high strength in the peripheral region, suppresses inner tension, and particularly suppresses cracks occurring at the edges. (16) The method for manufacturing a glass sheet according to (15), wherein, during the heating, the heating temperature at both ends of the glass sheet in the longitudinal direction is higher than the heating temperature at the center of the glass sheet in the longitudinal direction. This method for manufacturing a glass sheet is preferable in terms of the shape precision of the glass sheet. (17) The method for producing a glass plate according to (15) or (16), wherein, during the heating, a peak in the temperature distribution of the glass plate exists at one end of the peripheral region of the glass plate. This method for producing a glass plate is preferable for suppressing cracking of the glass plate. (18) The method for producing a glass plate according to any one of (15) to (17), wherein the glass plate after shaping is subjected to a chemical strengthening treatment. This method for producing a glass plate increases the overall surface strength and makes it possible to produce a glass plate that is more resistant to cracking.

[0049] This application is based on a Japanese patent application (Patent Application No. 2023-223477) filed on December 28, 2023, the contents of which are incorporated herein by reference.

[0050] A1 Peripheral region A2 Central region E Edge G Glass plate P Peak of plane stress

Claims

1. A glass plate having a peripheral region with a width along its periphery and in which a planar compressive stress is formed, and a central region occupying the inner peripheral side of the peripheral region, the glass plate having a cross-section parallel to the vertical direction when the glass plate is horizontally installed, when the planar stress at the boundary between the central region and the peripheral region is 1 MPa, there is one peak of the planar stress in the entire region of the central region and the peripheral region at one end of the peripheral region, the value of the peak is greater than 1 MPa and less than 10 MPa, and the planar stress in the central region is -3 MPa or more and 3 MPa or less over the entire central region.

2. The glass plate according to claim 1, having a cross-section in which the planar stress in the central region is -1 MPa or more and 3 MPa or less over the entire central region.

3. The glass plate according to claim 1 or claim 2, having a cross-section in which the planar stress in the central region exceeds 0 MPa over the entire central region.

4. The glass plate according to claim 1 or claim 2, having a plate thickness of 1.5 mm or less.

5. The glass plate according to claim 1 or claim 2, wherein the peak of the planar stress exists in a region less than 50 mm from the boundary between the central region and the peripheral region.

6. The glass plate according to claim 5, wherein the peak of the planar stress exists in a region less than 20 mm from the boundary between the central region and the peripheral region.

7. The glass plate according to claim 1 or claim 2, including a bending region having a radius of curvature of 5 mm or more.

8. The glass plate according to claim 7, including a bending region having a radius of curvature of 50 mm or more.

9. The glass plate according to claim 1 or claim 2, wherein the absolute value of the edge compression in the peripheral region is made larger than the absolute value of the inner tension.

10. The glass plate according to claim 1 or claim 2, wherein at least one side of the edge cross-section is chamfered with an R.

11. The glass plate according to claim 1 or claim 2, used as a cover glass for a display.

12. The glass plate according to claim 1 or claim 2, used as a cover glass for an in-vehicle display.

13. The glass plate according to claim 1 or claim 2, having a cross-section in which the retardation in the cross-section of the central region exceeds 0 nm and is 11 nm or less over the entire central region.

14. A chemically strengthened glass, wherein the surface compressive stress is 400 MPa or more and 1400 MPa or less, and the depth of the surface compressive stress layer is 5 μm or more and 100 μm or less, the glass plate according to claim 1 or claim 2.

15. A method for manufacturing a glass plate including a curved surface shape, wherein a glass plate having a planar shape is placed on a molding die, the glass plate is heated so that the viscosity becomes log η = 19 Poise or less within 15 seconds or more and 10 minutes or less to be formed into the shape of the molding die, further, the glass plate is held for 1 minute or more and 10 minutes or less in a state where the viscosity of the glass plate becomes log η = 13 Poise or less, and then, the glass plate is gradually cooled to a temperature below the strain point, a method for manufacturing a glass plate.

16. The method for manufacturing a glass plate according to claim 15, wherein when heating, the heating temperature at both ends in the longitudinal direction of the glass plate is higher than the heating temperature at the central portion in the longitudinal direction of the glass plate.

17. The method for manufacturing a glass plate according to claim 15 or claim 16, wherein when heating, there is one peak of the temperature distribution of the glass plate at one end of the peripheral region of the glass plate.

18. The method for manufacturing a glass plate according to claim 15 or claim 16, wherein a chemical strengthening treatment is performed on the glass plate after molding.

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