TEMPERED GLASS PLATE

Abstract

Tempered glass plate that has been hardened by a cooling medium sprayed from a plurality of nozzles, where the thickness of the tempered glass plate is less than or equal to 2.7 mm, where a plurality of stress traces have been formed on a surface of the tempered glass plate by the cooling medium, which is sprayed by the plurality of nozzles, where the distance between the nearest stress traces of the majority of stress traces is less than or equal to 20 mm, wherein the surface of the tempered glass plate comprises a first imaginary circle formed by connecting points separated from the center by one of the plurality of stress traces by 2.5 mm, wherein the tempered glass plate includes an area that is free from an elastic wave and is not affected by an elastic wave generated during breaking, and where, during fracturing in the area free from an elastic wave, the average number of cracks present in the first imaginary circle is greater than or equal to 3.4.

Description

[0001] The present invention relates to a tempered or prestressed glass plate and in particular to a tempered glass plate with a small plate thickness, which is adapted for a weight reduction of a vehicle that has been planned in recent years.

[0002] Until now, tempered glass has been used as the window glass in vehicles. The tempered glass comprises a compressive stress layer formed on its surface and a tensile stress layer in a central section running along the thickness of the glass. The tempered glass can be produced by applying a tempering process to the surface of the glass at a high temperature, such as 650 °C to 700 °C, by blowing air through it.

[0003] In recent years, in order to achieve a reduction in vehicle weight with a view to saving fuel, there has been a need for a glass plate with a low plate thickness that meets a safety standard required for tempered glass for the vehicle.

[0004] Patent document 1 and patent document 2 disclose a tempered glass plate, which is a glass plate with a low plate thickness and which meets the safety standard required for the tempered glass plate for the vehicle. [Patent document 1] Japanese unexamined patent JP S59 - 19 050 B2 [Patent document 2] Japanese unexamined patent JP S52 - 121 620 A

[0005] In the case of applying the disclosure of patent document 1 and patent document 2 to a glass plate with a small plate thickness, such as a glass plate with a thickness of less than or equal to 2.7 mm, there is a tendency to obtain an elongated fragment (splinter) with a length greater than 75 mm and a large fragment with an area of ​​3 cm. 2 exceeds the limit, so that the safety standard cannot be stably met.

[0006] In light of the background described above, the present application provides a tempered glass plate which can easily meet a breakage standard for vehicle window glass and which has a low plate thickness.

[0007] To solve the aforementioned problem, the present invention provides a tempered glass plate which has been tempered by a cooling medium sprayed from a plurality of nozzles, wherein the thickness of the tempered glass plate is less than or equal to 2.7 mm, wherein a plurality of stress marks have been formed on a surface of the tempered glass plate by the cooling medium sprayed from the plurality of nozzles, wherein the distance between the nearest stress marks of the plurality of stress marks is less than or equal to 20 mm, wherein the surface of the tempered glass plate comprises a first imaginary circle formed by connecting points separated from the center of one of the plurality of stress marks by 2.5 mm, wherein the tempered glass plate comprises an area free of an elastic wave generated during fracture.is not affected, and wherein, during fracturing in the area free from an elastic wave, the average number of cracks present in the first imaginary circle is greater than or equal to 3.4.

[0008] According to the present invention, a tempered glass plate is provided which can easily meet a breakage standard for vehicle window glass and which has a low plate thickness.

[0009] Other tasks, features and advantages of the present invention will become clearer from the following detailed description when read in conjunction with the accompanying drawings. Fig. Figure 1 is a schematic diagram showing the main components of a thermal tempering device for producing a tempered glass plate according to one embodiment. Fig. Figure 2 is a front view of the tempered glass plate G, which is tempered by the thermal tempering device. Fig. Figure 3 is a schematic diagram showing an area of ​​an elastic wave and an area free of an elastic wave. Fig. Figure 4 is a diagram showing an example of a procedure for counting the number of cracks present in a first imaginary circle. Fig. Figure 5 is a diagram showing a largest fragment and a smallest fragment. Fig. 6A, Fig. 6B and Fig. 6C are diagrams that show the state of a fragment during breaking, Fig. Figure 7 is a diagram showing a relationship between the distance of the back-and-forth movement and the number of cracks present in the first imaginary circle, and Fig. Figure 8 is a diagram showing a relationship between the distance of the back-and-forth movement and the number of cracks present in the second imaginary circle.

[0010] A tempered glass plate according to an embodiment of the present invention is described below with reference to the accompanying drawings.

[0011] This description refers to the tempered glass plate G, which has a rectangular shape in plan view; however, the shape of the tempered glass plate G is not limited to this. For example, the tempered glass plate G may have a polygonal shape, such as a trapezoid or a triangle, and an edge and / or corner section of the polygonal shape may have an arc shape.

[0012] It should be noted that in the following part of this description, "parallel" allows for a deviation of a degree that does not impair the effect of the present invention. For example, a deviation of ± 3 degrees from "parallel" in the strict sense is permissible.

[0013] The Fig. Figure 1 is a schematic diagram illustrating, by way of example, the main components of a thermal tempering device 10 for producing a tempered glass plate according to the embodiment. Fig. Figure 2 is a front view of the tempered glass plate G, which is tempered by the thermal tempering device 10. Fig. Figure 3 is a schematic diagram showing an area of ​​an elastic wave and an area that is free of an elastic wave.

[0014] The tempered glass plate G is tempered by the thermal tempering device 10. The tempered glass plate G comprises a first surface G1, a second surface G2 opposite the first surface G1, and a side surface G3 connecting the first surface G1 and the second surface G2.

[0015] The thickness of the tempered glass plate G is greater than or equal to 1.8 mm and less than or equal to 2.7 mm. In particular, with a view to reducing the weight of a vehicle, the thickness of the tempered glass plate G is preferably less than or equal to 2.5 mm and more preferably less than or equal to 2.3 mm. Furthermore, if the plate thickness is greater than or equal to 1.8 mm, there is a tendency for a surface compressive stress that meets a fracture standard and a tensile stress that occurs together with the surface compressive stress to be generated in a thermal tempering process.

[0016] The thermal curing device 10 comprises a plurality of nozzles 12 for spraying a cooling medium towards the entire areas of the first surface G1 and the second surface G2. Air can be given as an example of the cooling medium. The nozzles 12 are arranged symmetrically (staggered arrangement).

[0017] The arrangement of the majority of nozzles is not limited to a staggered arrangement and the majority of nozzles can, for example, be arranged in the form of a square grid.

[0018] The cooling medium from the nozzles 12 is sprayed onto the surface of the tempered glass plate G, which is hardened by the thermal tempering device 10. This creates stress marks 14, as described in the Fig. Figure 2 shows that stress marks 14 are formed on the surface of the tempered glass plate G immediately below the respective nozzles 12; in particular, the stress marks 14 are formed at the positions corresponding to the sections exhibiting a higher quenching capacity. Such positions tend to be more quenched compared to other sections. Consequently, when these sections are viewed from a top view, a strong plane compressive stress is generated. Accordingly, the stress marks 14 can be viewed through a polarizing plate or a sensitive color plate. Fig. 2. The stress traces 14 are shown by circles; however, the shapes of the stress traces 14 are not limited to circles. The shapes of the stress traces 14 can be various forms, such as elliptical shapes, a rectangular shape, and a polygonal shape, or the shapes of the stress traces 14 can be point shapes.

[0019] As described above, the stress traces 14 are formed at the positions immediately below the nozzles 12. Consequently, the stress traces 14 are arranged symmetrically, like the nozzles 12 (staggered arrangement). As described in the Fig. As shown in Figure 2, the voltage traces 14 comprise a first voltage trace 14A, a second voltage trace 14B, a third voltage trace 14C and a fourth voltage trace 14D.

[0020] The second voltage track 14B, the third voltage track 14C, and the fourth voltage track 140 are arranged such that they are spaced apart from the first voltage track 14A by a reference distance “a”. In particular, if the first voltage track 14A is considered to be the center, the reference distance “a” is a distance between the first voltage track 14A and the voltage tracks that are closest to the first voltage track 14A. The spacing between the voltage tracks specifies a distance between the center of a specific voltage track and the center of another voltage track that is closest to the specific voltage track. There can be more than one voltage track that has the same spacing between the voltage tracks. In this embodiment, there are six voltage tracks for the first voltage track 14 that have the same spacing between the voltage tracks.

[0021] It should be noted that in the case of a staggered arrangement as in this embodiment, the reference distance “a” is equal to the length of a short axis of the parallelogram described below.

[0022] It is preferred that the reference distance “a” is less than or equal to 20 mm, more preferably less than or equal to 18 mm, even more preferably less than or equal to 16 mm, even more preferably less than or equal to 14 mm, even more preferably less than or equal to 13.5 mm, even more preferably less than or equal to 12 mm and even more preferably less than or equal to 10 mm.

[0023] By setting such a reference distance "a", the stress traces 14 are formed with a small spacing. A high internal tensile stress is generated on an inner side of the stress trace 14 in the thickness direction of the plate, which is an energy source for crack propagation and branching. Consequently, when the spacing of the stress traces 14 is small and the stress traces 14 are densely packed, the energy sources for crack propagation and branching are concentrated. Therefore, in the event of a fracture, the formation of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² is possible. 2 be prevented.

[0024] In general, a plane compressive stress is generated in the tempered glass plate in the areas where the stress traces 14 are formed, and a plane tensile stress is generated in the areas between the stress traces 14. If the difference between the plane compressive stress and the plane tensile stress becomes too large at an interface, significant optical distortion is generated in the tempered glass plate at that interface. This was a source of discomfort for a driver, such as a distortion of location or process. Consequently, during thermal tempering, after a pattern has formed on the tempered glass plate due to the plane compressive and plane tensile stresses, the pattern is frosted by moving the glass plate back and forth, particularly frosting the interface between the plane compressive and plane tensile stresses.

[0025] In contrast, the inventors of the present invention have found that when the reference distance "a" is set to less than or equal to a specific constant value, as is the case in the embodiment, a driver of a vehicle tends not to perceive the boundary section as a significant optical distortion. This is because, when the gap between the stress traces 14 is reduced, even if a large difference is generated at a boundary section between the plane compressive stress and the plane tensile stress, the distance at which the boundary sections are repeatedly formed is also small, so that the driver tends not to perceive the boundary sections as a significant optical distortion. Consequently, it is not necessary to mattify the boundary sections between the plane compressive stress and the plane tensile stress, and the distance of the reciprocating motion can be reduced.Alternatively, a back-and-forth movement cannot be performed.

[0026] Particularly in cases where the tempered glass plate G has a complexly shaped surface, the distance between the tip of the nozzle 12 and the glass plate G, as well as the reciprocating distance of the glass plate G, are limited to prevent contact between the nozzle tip 12 and the glass plate G during the reciprocating motion. Consequently, it was difficult to provide a tempered glass plate that could easily meet the fracture standard for automotive window glass and had a low plate thickness. In contrast, with the reference distance “a” described above, the reciprocating distance can be reduced, so that even if the tempered glass plate has a complexly shaped surface, the glass plate can be obtained with sufficient quality.

[0027] It should be noted that in the present description, a complex shaped surface refers to a surface that is curved in two directions, namely a specific direction and a direction perpendicular to the specific direction.

[0028] A deviation of ± 1 mm is permissible for the reference distance "a" so that the effect is not impaired. For example, a deviation of ± 1 mm is permissible.

[0029] It should be noted that the embodiment is not limited to the case where no back-and-forth movement is performed. As described below, for example, back-and-forth movement is permissible to such an extent that the distance of the back-and-forth movement is less than or equal to approximately 25 mm.

[0030] Additionally, a parallelogram surface 16 is formed on the surface of the tempered glass plate G by the first stress track 14A, the second stress track 14B, the third stress track 14C, and the fourth stress track 14D. The parallelogram surface 16 is formed by connecting the centers of the first stress track 14A, the second stress track 14B, the third stress track 14C, and the fourth stress track 14D, and the parallelogram surface 16 is in the Fig. 2 the area enclosed by the dotted line. The length of an edge of the parallelogram surface 16 is the reference distance “a”, the length of the short axis of the parallelogram surface 16 is the reference distance “a”, and the length of the long axis of the parallelogram surface 16 is obtained geometrically from the reference distance “a”.

[0031] The surface of the tempered glass G comprises a compressive stress layer, and an inner section of the tempered glass G in the thickness direction of the sheet comprises a tensile stress layer. Applying a localized impact to the tempered glass sheet induces cracks on its surface. When these cracks reach the tensile stress layer after traversing the compressive stress layer, the tensile stress propagates the cracks in various directions along the glass sheet, causing the tempered glass sheet G to fracture. This fracture generates an elastic wave, which propagates within the tempered glass sheet G along a circumferential edge.

[0032] The elastic wave is generated at the same time as when the cracks reach the tensile stress layer and begin to propagate in different directions across the glass plate. The elastic wave propagates concentrically from the fracture origin (i.e., the starting point of the cracks). The propagation speed of the elastic wave is higher than the crack propagation speed, generally ranging from 1.1 to 2.3 times the crack propagation speed.

[0033] After the elastic wave is reflected at the circumferential edge of the tempered glass plate G, it encounters a crack tip, which is subsequently extended. Following the collision of the crack tip and the elastic wave, an energy fluctuation occurs, resulting in a tendency for the cracks to branch. Consequently, the size of a fragment in a region (referred to below as the "elastic wave region 38") located farther from the point of impact of the elastic wave and the crack is smaller relative to the size of a fragment in a region (referred to as the "elastic wave-free region 39") located closer to the point of impact of the crack, compared to the size of a fragment in a region (referred to as the "elastic wave-free region 39") located closer to the point of impact of the crack.Consequently, the breaking within the area 39, which is free of an elastic wave, is important for determining whether the tempered glass plate G meets the breaking standard for vehicle window glass.

[0034] Assuming that the tempered glass plate G breaks at the center of gravity A and that the propagation speed of the elastic wave is twice the elongation speed of the crack, the elastic wave region 38 and the elastic wave-free region 39 are defined below with reference to the Fig. 3 described.

[0035] According to the Fig. 3. If the tempered glass plate G breaks at its center of gravity A, the elastic wave, after propagating along line 36, which extends from the center of gravity A to a point B on the lower edge section of the tempered glass plate G, is regularly reflected at point B and propagates along line 37. Consequently, the crack, which extends from the center of gravity A along line 35 in the direction of the lower edge of the tempered glass plate G, encounters the elastic wave propagating along line 37 at a point C.

[0036] The dashed line 31 is a line obtained by connecting the points where the elastic wave, which is regularly reflected at the bottom edge of the tempered glass plate G, hits the crack extending from the center of gravity A as the starting point in the direction of the bottom edge.Accordingly, the dashed line 32 is a line obtained by connecting the points where the elastic wave, which is regularly reflected at the left edge of the tempered glass plate G, strikes the crack that propagates from the center of mass A as the starting point in the direction of the left edge; the dashed line 33 is a line obtained by connecting the points where the elastic wave, which is regularly reflected at the top edge of the tempered glass plate G, strikes the crack that propagates from the center of mass A as the starting point in the direction of the top edge; and the dashed line 34 is a line obtained by connecting the points where the elastic wave, which is regularly reflected at the right edge of the tempered glass plate G, strikes the crack that propagates from the center of mass A as the starting point in the direction of the right edge.

[0037] As described above, the area (hatched area) enclosed by the dashed lines 31, 32, 33 and 34 is the area 39 which is free of an elastic wave, and the area which is different from the area 39 which is free of an elastic wave is the area of ​​an elastic wave 38.

[0038] The area 39, which is free of an elastic wave, can be varied depending on the propagation speed of the elastic wave.For example, the region 39, which is free of an elastic wave, can be a region with a width corresponding to the distance between the line obtained by connecting the points where the elastic wave, normally reflected at the circumferential edge of the tempered glass plate G, strikes the crack propagating from the centroid A, where the propagation speed of the elastic wave is assumed to be 1.7 times the elongation speed of the crack, and the line obtained by connecting the points where the elastic wave, normally reflected at the circumferential edge of the tempered glass plate G, strikes the crack propagating from the centroid A, where the propagation speed of the elastic wave is assumed to be 2.3 times the elongation speed of the crack.

[0039] During the breaking of the tempered glass plate G, in the area 39 which is free from an elastic wave, the average number of cracks present within a first imaginary circle 18, which is obtained by connecting the points separated by 2.5 mm from the center of the stress track 14, is preferably greater than or equal to 3.4, more preferably greater than or equal to 4 and even more preferably greater than or equal to 4.2.

[0040] The center of voltage track 14 means the center of voltage track 14, which is determined by a polarizing plate or a sensitive color plate.

[0041] The first imaginary circle 18 is a circle with a radius of 2.5 mm and is formed in an imaginary way on the surface of the tempered glass plate G. In the Fig. 2 is the first imaginary circle 18 shown such that the size of the first imaginary circle 18 is smaller than the size of the voltage trace 14; however, the size of the first imaginary circle 18 may be identical to the size of the voltage trace 14 or the size of the first imaginary circle 18 may be smaller than the size of the voltage trace 14.

[0042] The Fig. Figure 4 is a diagram showing an example of a procedure for counting the number of cracks present within the first imaginary circle 18. The number of cracks present within the first imaginary circle 18 indicates the number of cracks to be counted, without distinguishing between cracks that are predominantly elongating (referred to below as "main cracks") and cracks that branch at the bifurcation point, as described in the Fig. Figure 4 shows that the main crack is such that the angle of the crack does not change almost at all before and after the bifurcation point.

[0043] Furthermore, the average number of cracks present within the first imaginary circle 18 gives the average number of cracks present within each of the first imaginary circles corresponding to all stress traces 14 in the region 39 that is free of an elastic wave. It should be noted that if the number of first imaginary circles in the region 39 that is free of an elastic wave exceeds 100, the average number of cracks present within each of the twenty first imaginary circles of the first imaginary circles included in the region 39 that is free of an elastic wave can be used as a reference.

[0044] If the number of cracks present within the first imaginary circle 18 is as described above, the cracks passing through the respective first imaginary circles 18 tend to connect with each other in the area between the first imaginary circles 18. Consequently, the formation of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² may occur. 2 be prevented.

[0045] Furthermore, if the reference distance “a” lies within the aforementioned range and the number of cracks present within the first imaginary circle 18 is as described above, the tempered glass plate G can more easily meet the fracture standard. This is because, in the area between the first imaginary circles 18, the cracks passing through each of these first imaginary circles 18 can more easily connect to one another.

[0046] In addition, the tempered glass plate G further comprises a second imaginary circle, which is obtained by connecting the points that are separated from the center of the stress track 14 by 5 mm, and the average number of cracks that are present within the second imaginary circle is preferably greater than or equal to 8.8, more preferably greater than or equal to 9.1, even more preferably greater than or equal to 9.5 and even more preferably greater than or equal to 10.

[0047] The second imaginary circle is a circle with a radius of 5 mm and the second imaginary circle is formed in an imaginary way on the surface of the tempered glass plate G.

[0048] If the number of cracks present within the second imaginary circle is as described above, the cracks passing through the respective second imaginary circles tend to connect in the area between the second imaginary circles. Consequently, the formation of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² may occur. 2 be prevented.

[0049] Furthermore, if the reference distance “a” lies within the range described above and the number of cracks present within the second imaginary circle is as described above, the tempered glass plate G can more easily meet the fracture standard. This is because, in the area between the second imaginary circles, the cracks passing through the respective second imaginary circles can more easily connect to one another.

[0050] Additionally, during the breaking of the tempered glass plate G in the area 39, which is free from an elastic wave, the average number of branching points that are present within the first imaginary circle 18 is preferably greater than or equal to 1.5, more preferably greater than or equal to 1.7 and even more preferably greater than or equal to 2.

[0051] The branching point refers to a point where two or more cracks intersect, and in the example given in the Fig. As shown in Figure 4, there are three branching points.

[0052] If the number of branching points within the first imaginary circle 18 is as described above, many cracks with different angles of extension are generated around the branching point, so that in the area between the first imaginary circles 18, the cracks passing through the respective first imaginary circles 18 tend to connect with each other. Consequently, the formation of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² can occur. 2 be prevented.

[0053] Furthermore, if the reference distance “a” lies within the area described above and the number of branching points within the first imaginary circle 18 is as described above, the tempered glass plate G can more easily meet the fracture standard. This is because, in the area between the first imaginary circles 18, the cracks passing through each of these first imaginary circles 18 can more easily connect to one another.

[0054] The Fig. Figure 5 is a diagram showing a largest fragment 50 and a smallest fragment 51. During the breaking of the tempered glass plate G, in the area 39 which is free of an elastic wave, the ratio between the area of ​​the largest fragment 50, at least a part of which lies within the parallelogram area 16, and the area of ​​the smallest fragment 51, at least a part of which lies within the parallelogram area 16, is preferably greater than or equal to 15, more preferably greater than or equal to 17, even more preferably greater than or equal to 20, even more preferably greater than or equal to 23, and even more preferably greater than or equal to 25.

[0055] The largest fragment 50, wherein at least a part of it lies within the parallelogram area 16, refers to a fragment with the largest area of ​​the fragments, wherein at least a part of each of them lies within the parallelogram area 16.

[0056] Furthermore, the smallest fragment 51, wherein at least a part of it lies within the parallelogram area 16, refers to a fragment with the smallest area of ​​the fragments, wherein at least a part of each of them lies within the parallelogram area 16.

[0057] Furthermore, the long axis b of the parallelogram surface 16 lies in any direction from the starting point of the crack in the direction of the edge of the tempered glass plate G.

[0058] The ratio between the area of ​​the largest fraction 50 and the area of ​​the smallest fraction 51 represents a value obtained by dividing the area of ​​the largest fraction 50 by the area of ​​the smallest fraction 51.

[0059] Furthermore, the area of ​​the largest fragment 50 is preferably greater than or equal to 1.5 cm². 2 and less than or equal to 3.0 cm 2 , preferably larger than or equal to 1.8 cm2 and less than or equal to 2.9 cm 2 and even more preferably larger than or equal to 2.0 cm 2 and less than or equal to 2.8 cm 2 .

[0060] If the largest fragment 50 and the smallest fragment 51 are incorporated into at least one parallelogram surface 16 within the area 39, which is free of an elastic wave, with the ratio described above, the production of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² is possible. 2 be prevented.

[0061] Furthermore, it is more preferred that the largest fragment 50 encompasses the centroid of the parallelogram surface 16. By arranging at least one parallelogram surface 16 within the region 39, which is free of an elastic wave, the generation of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² can be avoided. 2 be prevented.

[0062] Furthermore, for a circle 52 with a diameter which is the greatest length of the largest fragment 50, a part of the area of ​​the circle 52 occupied by the largest fragment 50 is preferably greater than or equal to 30%, more preferably greater than or equal to 40%, even more preferably greater than or equal to 50%, even more preferably greater than or equal to 55%, and even more preferably greater than or equal to 60%.

[0063] As indicated by the double arrow in the Fig. As shown in Figure 5, for example, the largest length of the largest fragment 50 represents the largest length of lengths of straight lines obtained by connecting two points on the outline of the largest fragment 50.

[0064] Circle 52 with the diameter which is the greatest length of the largest fragment 50, represents, for example, circle 52, which is defined by a dot-dash line in the Fig. 5 is shown.

[0065] If such a largest fragment 50 is included in at least one parallelogram surface 16 within the area 39 which is free of an elastic wave, the generation of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² can be achieved. 2 be prevented.

[0066] The reason why the ratio between the largest fragment 50 and the smallest fragment 51 is determined in the manner described above, and the reason why the largest fragment 50 is determined in the manner described above, are described below by comparing the technical concept of the prior art with the technical concept of the present application.

[0067] In many cases, according to the prior art, to meet the fracture standard, a pattern of plane compressive stress and a pattern of plane tensile stress are formed in the tempered glass plate, such that the crack extension directions are bent and the cracks are interconnected. Furthermore, there is a tendency to produce a large fragment near the centroid of the parallelogram surface. Consequently, the crack extension directions are bent so that the cracks are guided to pass through an area near the centroid of the parallelogram surface. In particular, the prior art technical concept is to cause the tempered glass plate to break into fragments of uniform size. However, even with this technical concept, there is a tendency to produce a large fragment within the parallelogram surface.The reason for this is as follows. In a case where the cracks are guided in such a way that they pass through the region near the centroid of the parallelogram surface, cracks that were originally intended to pass through a section of the parallelogram surface that differs from the region near the centroid are also guided to the region near the centroid, so that there is a tendency for a large fragment to be formed in the section of the parallelogram surface that differs from the region near the centroid.

[0068] In contrast, it was found in the embodiment that the fracture standard can be easily met without introducing cracks within the parallelogram surface 16 through a pattern of plane stress, provided that the reference distance “a” is small, the number of cracks is greater than or equal to the number described above, and the number of branching points near the center of the stress track 14, where an internal tensile stress is high, is greater than or equal to the number described above. In particular, the technical concept is to cause the largest fragment to be produced near the centroid of the parallelogram surface, and for the tempered glass plate to break into small fragments by joining cracks in a section that differs from the area near the centroid.Since the number of cracks and the number of branching points are greater than or identical to a predetermined number, as described above, the crack density is high, and the cracks tend to join in a section different from the area near the centroid. Furthermore, the reference distance "a" is small, so the largest fragment tends to be neither large nor elongated. Consequently, a glass plate can be obtained that easily meets the fracture standard.

[0069] The average surface compressive stress of the tempered glass plate G is preferably greater than or equal to 100 MPa and less than or equal to 165 MPa, more preferably greater than or equal to 105 MPa and less than or equal to 160 MPa, and even more preferably greater than or equal to 110 MPa and less than or equal to 155 MPa.

[0070] With such a value of average surface compressive stress, an internal tensile stress can be generated in the entire tempered glass plate G that is sufficient to cause the propagation and branching of the cracks.

[0071] It should be noted that in the tempered glass plate G, which is produced by spraying a cooling medium from openings of the plurality of nozzles 12 onto the heated glass plate, the surface compressive stress at a point where a jet stream of the cooling medium hits the glass plate (the stress track 14) differs from the surface compressive stress at a point between the stress tracks 14.Consequently, the average surface compressive stress G of the tempered glass plate is defined as an average value obtained by averaging a value at a point immediately below the nozzle 12 (the first stress track 14A) and a value at the centroid of a triangle formed by the first stress track 14A and two points (the second stress track 14B and the third stress track 14C), where these are the stress tracks closest to and closest to the first stress track 14A. The first point is expected to be close to the maximum value of the surface compressive stress, and the second point is expected to be close to the minimum value of the surface compressive stress.Surface compressive stress can be measured using a Babinet-type surface compressive stress measuring instrument using the photoelasticity of scattered light, based on the "via-scope" method.

[0072] Furthermore, the value of the surface compressive stress at the stress track 14 is preferably greater than or equal to 120 MPa and less than or equal to 175 MPa, more preferably greater than or equal to 130 MPa and less than or equal to 175 MPa, even more preferably greater than or equal to 140 MPa and less than or equal to 175 MPa, even more preferably greater than or equal to 143 MPa and less than or equal to 175 MPa, and even more preferably greater than or equal to 145 MPa and less than or equal to 175 MPa.

[0073] With such a value of surface compressive stress at stress track 14, an internal tensile stress can be generated at a central section in the plate thickness direction corresponding to the position of stress track 14, which is sufficient to cause crack elongation and branching, so that near the center of stress track 14 the number of cracks tends to be greater than or identical to the number described above, and the number of branching points tends to be greater than or identical to the number described above.

[0074] Furthermore, a value obtained by dividing the value of the surface compressive stress at stress trace 14 by the value of the surface compressive stress at the centroid of the triangle described above is preferably greater than or equal to 1.05, more preferably greater than or equal to 1.07, and even more preferably greater than or equal to 1.10. With such a value, it can be ensured that the number of cracks is greater than or identical to the number described above, and that the number of branching points is greater than or identical to the number described above, and that the largest fragment lies within the specified parameters described above, thus preventing the formation of an elongated fragment with a length greater than 75 mm and / or a large fragment with an area greater than 3 cm². 2 can be prevented.

[0075] The type of glass used for the tempered glass plate G according to the embodiment is soda-lime glass. Soda-lime glass is a glass comprising SiO₂, CaO, Na₂O, and K₂O as its main components. It should be noted that the type of glass used for the tempered glass plate G according to the present invention is not specifically limited and can be either an alkali-free glass or an aluminosilicate glass.

[0076] The tempered glass plate G according to the embodiment preferably comprises, as an oxide, the following glass composition. With the following glass composition, a high surface compressive stress and an internal tensile stress, generated together with the surface compressive stress, can be produced by the thermal tempering process even if the plate thickness is small. Furthermore, the glass plate can easily be formed into a complex shape, such as a complexly shaped surface.

[0077] It should be noted that a range of numbers “x to y” described below is used to indicate that the range of numbers includes “x” and “y” as the lower limit and the upper limit, respectively, and in the following part of this description “x to y” will be used with the same meaning unless otherwise stated. (First example) Al2O3: 0 wt.% to 3.5 wt.% Total Na2O and K2O: 12.0 wt.% to 14.5 wt.% (Second example) Al2O3: 0 wt.% to 2.0 wt.% Total Na2O and K2O: 13.0 wt.% to 15.5 wt.%

[0078] The tempered glass plates G described above, according to the first and second examples, can contain at least 65 wt.% to 75 wt.% SiO2 and 7 wt.% to 14 wt.% CaO and Al2O3, Na2O and K2O in the areas described above. (Third example) SiO2: 68.0 wt.% to 75.0 wt.% Al2O3: 0 wt.% to 3.5 wt.% CaO: 7.0 wt.% to 13.0 wt.% MgO: 0 wt.% to 7.0 wt.% Na2O: 12.0 wt.% to 15.0 wt.% K2O: 0 wt.% to 3.0 wt.% Total Na2O and K2O: 12.0 wt.% to 14.5 wt.% (Fourth example) SiO2: 68.0 wt.% to 75.0 wt.% Al2O3: 0 wt.% to 2.0 wt.% CaO: 7.0 wt.% to 13.0 wt.% MgO: 0 wt.% to 7.0 wt.% Na2O: 12.0 wt.% to 15.0 wt.% K2O: 0 wt.% to 3.0 wt.% Total Na2O and K2O: 13.0 wt.% to 15.5 wt.%

[0079] Al₂O₃ is a component used to ensure weather resistance, and it is preferably present in an amount greater than or equal to 1.7 wt.% and more preferably greater than or equal to 1.8 wt.%. If more than 3.5 wt.% Al₂O₃ is present, the viscosity increases and melting can be difficult. In this respect, more preferably less than or equal to 3.3 wt.% and particularly preferably less than or equal to 2.0 wt.% Al₂O₃ is present.

[0080] Na₂O is a component used to improve meltability, and if less than 12.0 wt% Na₂O is present, the meltability may be impaired. Preferably, more than or equal to 12.8 wt% Na₂O is present, and particularly preferably more than or equal to 13.0 wt%. Furthermore, if more than 15.0 wt% Na₂O is present, the weather resistance may be impaired. Therefore, more preferably less than or equal to 14.8 wt% Na₂O is present, and particularly preferably less than or equal to 13.8 wt% Na₂O.

[0081] K₂O is a component for improving meltability and is preferably present in an amount of more than or equal to 0.5 wt.% and more preferably more than or equal to 0.9 wt.%. Furthermore, if more than 3.0 wt.% K₂O is present, the weather resistance may be impaired and the cost of the glass plate increased. More preferably less than or equal to 1.8 wt.% and particularly preferably less than or equal to 1.6 wt.% K₂O is present.

[0082] It should be noted that the composition of the glass plate can be measured by fluorescence X-ray spectroscopy.

[0083] Additionally, the coefficient of thermal expansion of the glass plate to be used for the production of the tempered glass plate G according to the embodiment is preferably greater than or equal to 90 × 10 -7 / K and less than or equal to 100 × 10 -7 / K, preferably greater than or equal to 91 × 10 -7 / K and less than or equal to 95 × 10 -7 / K. It should be noted that in the present description the coefficient of thermal expansion represents the average coefficient of thermal expansion from 50 °C to 350 °C.

[0084] The coefficient of thermal expansion depends, for example, on the β-OH value (mm²). -1 ) which represents the glass composition and moisture content. In the case of soda-lime glass, for example, the coefficient of thermal expansion increases when the content of alkali metal oxides (such as Na₂O and K₂O) in the glass decreases and when the β-OH value (mm) -1 ) becomes smaller.

[0085] Furthermore, the β-OH value (mm) varies -1The β-OH value of the glass plate depends, for example, on the water content in the starting materials, the type of heat source used to melt the starting materials (e.g., heavy oil, liquefied gas, electricity, etc.), the water vapor concentration in a dissolver, and the residence time of the molten glass in the dissolver. -1 The water content of the glass plate is preferably adjusted, for example, by a process in which a hydroxide is used instead of an oxide as the starting material for the glass (e.g., magnesium hydroxide (Mg(OH)₂) is used as a magnesium source instead of magnesium oxide (MgO)). In this embodiment, the water content in the glass plate is expressed as the β-OH value (mm²). -1 ) from 0.1 to 0.4 and preferably from 0.2 to 0.3.

[0086] With such a coefficient of thermal expansion, the thermal hardening process can generate high surface compressive stress and internal tensile stress, which is generated simultaneously with the surface compressive stress, even with a thin glass plate. Furthermore, the glass plate can easily be formed into a complex shape, such as a complexly shaped surface. [Examples]

[0087] The following describes results for cases where the tempered glass plates were produced using the thermal tempering device 10, which is described in the Fig. 1 is shown, and these were broken. <Beispiel 1>

[0088] The conditions under which the tempered glass according to Example 1 and the tempered glass according to a comparison example were manufactured are described below. Glass plate thickness: 2.3 mm Coefficient of thermal expansion: 90 × 10 -7 / K Temperature of the glass before quenching: 680 °C Nozzle diameter: 3.4 mm Distance between the nozzle tip and the glass: 15 mm Reference distance “a” (short axis a): 13.2 mm Long axis b: 22.9 mm Blowing pressure: 29 kPa Quenching time: 5 seconds

[0089] Each sample was prepared while the distance of the back-and-forth movement during quenching (also referred to as the back-and-forth movement distance) was set to 0 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 45 mm and 60 mm.

[0090] The average surface compressive stress at a distance of 0 mm during the back-and-forth movement was 145 MPa. Furthermore, the surface compressive stress value at stress track 14 was 152 MPa. Finally, the value obtained by dividing the surface compressive stress value at stress track 14 by the surface compressive stress value at the centroid of the triangle described above was 1.11.

[0091] Each sample produced under the conditions described above was broken at its center of gravity as the starting point. Fig. Figure 6A shows a state of the fragments during breaking in the case where the distance of the back-and-forth movement was 0 mm. Fig. Figure 6B shows a state of the fragments during breaking in the case where the back-and-forth movement distance was 30 mm, and the Fig. Figure 6C shows a state of the fragments during breaking in the case where the back-and-forth movement distance was 60 mm. Furthermore, the Fig. 7 the result of counting the number of cracks in each of the first imaginary circles obtained by connecting the points spaced 2.5 mm from the corresponding center of the stress trace, in the area free of an elastic wave. Accordingly, the Fig. 8 the result of counting the number of cracks in the second imaginary circle obtained by connecting the points spaced 5 mm apart from the center of the stress trace.

[0092] It should be noted that in the Fig. 6A, Fig. 6B and Fig. 6C points are shown as traces, indicating the centers of the stress traces.

[0093] From the Fig. 6A, Fig. 6B and Fig. 6C shows that in the case of Fig. 6A compared to the cases of Fig. 6B and Fig. 6C the production of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm 2 can be prevented.

[0094] From the Fig. It is evident from paragraph 7 that if the average number of cracks present within the first imaginary circle formed by connecting the points spaced 2.5 mm apart from the center of the stress trace is greater than or equal to 3.4, the production of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² is likely. 2 can be prevented.

[0095] From the Fig.It is evident from paragraph 8 that if the average number of cracks present within the second imaginary circle formed by connecting the points spaced 5 mm apart from the center of the stress trace is greater than or equal to 8.8, the production of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² will occur. 2 can be prevented. <Beispiel 2>

[0096] The conditions under which the tempered glass according to Example 2 was manufactured are described below. Glass plate thickness: 2.3 mm Coefficient of thermal expansion: 90 × 10 -7 / K Temperature of the glass before quenching: 665 °C Nozzle diameter: 4 mm Distance between the nozzle tip and the glass: 20 mm Reference distance “a” (short axis a): 18 mm Long axis b: 31.2 mm Blowing pressure: 22 kPa Quenching time: 5 seconds Distance of back-and-forth movement: 0 mm

[0097] In Example 2, the average surface compressive stress was 117 MPa. Furthermore, the surface compressive stress value at stress trace 14 was 123 MPa. Additionally, the value obtained by dividing the surface compressive stress value at stress trace 14 by the surface compressive stress value at the centroid of the triangle described above was 1.10.

[0098] In Example 2, the number of cracks and the number of branching points present during the fracture within the first circle, formed by connecting the points spaced 2.5 mm from the center of the stress track, and the number of cracks and / or the number of branching points present during the fracture within the second circle, formed by connecting the points spaced 5 mm from the center of the stress track, exceed the specified values ​​according to this description, so that the production of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² also occurs. 2 can be prevented. <Beispiel 3>

[0099] The conditions under which the tempered glass according to Example 3 was manufactured are described below. Glass plate thickness: 2.3 mm Coefficient of thermal expansion: 90 × 10 -7 / K Temperature of the glass before quenching: 680 °C Nozzle diameter: 2.5 mm Distance between the nozzle tip and the glass: 11 mm Reference distance “a” (short axis a): 9.8 mm Long axis b: 17 mm Blowing pressure: 28 kPa Quenching time: 5 seconds Distance of back-and-forth movement: 0 mm

[0100] In Example 3, the average surface compressive stress was 139 MPa. Furthermore, the surface compressive stress value at stress trace 14 was 147 MPa. Additionally, the value obtained by dividing the surface compressive stress value at stress trace 14 by the surface compressive stress value at the centroid of the triangle described above was 1.12.

[0101] In Example 3, the number of cracks and the number of branching points present during the fracture within the first circle formed by connecting the points spaced 2.5 mm from the center of the stress track, and / or the number of cracks and the number of branching points present during the fracture within the second circle formed by connecting the points spaced 5 mm from the center of the stress track, exceed the specified values ​​of this description, so that the production of an elongated fragment with a length of more than 75 mm and / or a large fragment with an area of ​​more than 3 cm² also occurs. 2 can be prevented. DESCRIPTION OF REFERENCE MARKS 10 Thermal hardening device 12 nozzle 14 Tension trail 14A First voltage trace 14B Second voltage track 14C Third voltage track 14D Fourth Tension Track 16 Parallelogram area Line 31 to 34 connecting points where a crack meets an elastic wave 35 Extension of a crack 36 Propagation of an elastic wave 37 Propagation of a regularly reflected elastic wave 38 Area of ​​an elastic wave 39 Area that is free of an elastic wave 50 Largest fragment 51 Smallest fragment 52 Circle with a diameter that is the greatest length of the largest fragment a reference distance, short axis b Long axis G Tempered glass plate G1 First surface G2 Second Surface G3 side surface

Claims

[1] Tempered glass plate which has been hardened by a cooling medium sprayed from a plurality of nozzles, where the thickness of the tempered glass plate is less than or equal to 2.7 mm, where a plurality of stress traces have been formed on a surface of the tempered glass plate by the cooling medium, which is sprayed by the plurality of nozzles, where the distance between the nearest stress traces of the majority of stress traces is less than or equal to 20 mm, wherein the surface of the tempered glass plate comprises a first imaginary circle formed by connecting points separated from the center by one of the plurality of stress traces by 2.5 mm, wherein the tempered glass plate includes an area that is free from an elastic wave and is not affected by an elastic wave generated during breaking, and where, during fracturing in the area free from an elastic wave, the average number of cracks present in the first imaginary circle is greater than or equal to 3.

4. [2] Tempered glass plate according to claim 1, wherein during breaking in the area which is free from an elastic wave the average number of cracks which are present in the first imaginary circle is greater than or equal to 4. [3] Tempered plate according to claim 1 or 2, wherein the surface of the tempered glass plate further comprises a second imaginary circle formed by connecting points separated by 5 mm from the center of one or the plurality of stress traces, wherein during breaking in the area free from an elastic wave the average number of cracks present in the second imaginary circle is greater than or equal to 8.

8. [4] Tempered glass plate according to claim 3, wherein during breaking in the area which is free from an elastic wave the average number of cracks which are present in the second imaginary circle is greater than or equal to 9.

5. [5] Tempered glass plate according to any one of claims 1 to 4, wherein the average surface compressive stress of the tempered glass plate is greater than or equal to 100 MPa and less than or equal to 165 MPa. [6] Tempered glass plate according to any one of claims 1 to 5, wherein the surface compressive stress value at one of the plurality of stress traces is greater than or equal to 120 MPa and less than or equal to 175 MPa. [7] Tempered glass plate according to any one of claims 1 to 6, wherein the majority of stress traces comprises a first stress trace, wherein the majority of voltage traces further comprise a second voltage trace and a third voltage trace, wherein the second voltage trace and the third voltage trace are closest to the first voltage trace and the second voltage trace and the third voltage trace are closest to each other, wherein the tempered glass plate encompasses a triangle formed by the first stress track, the second stress track and the third stress track, and where a value obtained by dividing a value of a surface compressive stress at the first stress trace by a surface compressive stress at a centroid of the triangle is greater than or equal to 1.

05. [8] Tempered glass plate according to any one of claims 1 to 7, wherein the majority of stress traces comprises a first stress trace, wherein the majority of voltage traces further comprise a second voltage trace, a third voltage trace and a fourth voltage trace, wherein the second voltage trace, the third voltage trace and the fourth voltage trace are located closest to the first voltage trace, wherein the tempered glass plate forms a parallelogram surface formed by the first stress track, the second stress track, the third stress track and the fourth stress track, and where the parallelogram area is included in the region that is free of an elastic wave and is not affected by the elastic wave during breaking, wherein the long axis of the parallelogram surface is located in any direction from a starting point of a crack in the direction of an edge of the tempered glass plate and wherein the ratio between the area of ​​a largest fragment, where at least part of the largest fragment is located in the parallelogram area, and the area of ​​a smallest fragment, where at least part of the smallest fragment is located in the parallelogram area, is greater than or equal to 15. [9] Tempered glass plate according to claim 8, wherein the area of ​​the largest fragment is greater than or equal to 1.5 cm² 2 and less than or equal to 3.0 cm 2 is. [10] Tempered glass plate according to claim 8 or 9, wherein the largest fragment comprises a center of gravity of the parallelogram surface. [11] Tempered glass plate according to any one of claims 8 to 10, wherein in a circle having a diameter which is the greatest length of the largest fragment, a part of an area of ​​the circle occupied by the largest fragment is greater than or equal to 30%. [12] Tempered glass plate according to any one of claims 1 to 11, wherein the thickness of the tempered glass plate is greater than or equal to 1.8 mm and less than or equal to 2.5 mm. [13] Tempered glass plate according to any one of claims 1 to 12, wherein the average coefficient of thermal expansion of the tempered glass plate from 50 °C to 350 °C is greater than or equal to 90 × 10 -7 / K and less than or equal to 100 × 10 -7 / K is.

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