Abstract
A thin glass article is provided that has a first face, a second face, one or more edges joining the first and second faces, and a thickness between the first and second faces, where the faces and the one or more edges together form an outer surface of the thin glass article. The thin glass article has an ion-exchanged surface layer on its outer surface. The ion-exchanged surface layer is non-uniform, wherein the non-uniform ion-exchanged surface layer has an associated compressive surface stress which varies between a minimum and a maximum value over the outer surface and/or a depth of layer which varies between a minimum and a maximum value over the outer surface. A method for producing a thin glass article and a use of a thin glass article are also provided.
Claims
1. A thin glass article, comprising: a first face; a second face one or more edges joining the first and second faces; a thickness between the first and second faces, the first and second faces and the one or more edges together forming an outer surface; and an ion-exchanged surface layer on the outer surface, the ion-exchanged surface layer being non-uniform and having a compressive surface stress and/or a depth of layer that varies between a minimum value and a maximum value over the outer surface.
2. The thin glass article according to claim 1, wherein the minimum value is at most 90% of the maximum value.
3. The thin glass article according to claim 1, wherein the minimum value is zero.
4. The thin glass article according to claim 1, wherein the ion-exchanged surface layer is formed by exchanged K.sup.+ and/or Na.sup.+ ions.
5. The thin glass article according to claim 1, wherein the maximum value of the depth of layer is equal or less than 50 μm and the maximum value of the surface compressive stress lies in a range from 10 MPa to 1200 MPa.
6. The thin glass article according to claim 1, wherein the thickness is equal or less than 1 mm.
7. The thin glass article according to claim 1, comprising one or more surface areas of a first kind and one or more surface areas of a second kind on the outer surface, the first kind corresponding to the maximum value and the second kind corresponding to the minimum value.
8. The thin glass article according to claim 7, wherein the first kind covers equal to or more than 15% of the outer surface.
9. The thin glass article according to claim 7, wherein the first kind covers equal to or more than 50% of the outer surface
10. The thin glass article according to claim 7, the first kind completely covers at least one of the first and second faces.
11. The thin glass article according to claim 7, wherein the first kind covers completely covers the one or more edges.
12. The thin glass article according to claim 7, wherein the one or more surface areas of the first kind comprise more than one surface area.
13. The thin glass article according to claim 12, wherein the more than one surface area of the first kind cover part both of the first and second faces.
14. The thin glass article according to claim 12, wherein the more than one surface areas of the first kind are arranged in a regular pattern on the first and/or second face.
15. The thin glass article according to claim 14, wherein the regular pattern is selected from the group consisting of a chess-board pattern, a stripe pattern, a circle pattern, and a wave pattern.
16. The thin glass article according to claim 7, wherein each area of the first kind on one of the first or second face is opposed on the other of the first or second face by an area of the second kind.
17. The thin glass article according to claim 7, wherein the one or more areas of the first and the second kind has a refractive index that differ by at least 0.004 to 0.009.
18. The thin glass article according to claim 1, further comprising at least one curved region with a surface curvature resulting from the ion-exchanged surface layer.
19. The thin glass article according to claim 18, comprising one or more surface areas of a first kind and one or more surface areas of a second kind on the outer surface, the first kind corresponding to the maximum value and the second kind corresponding to the minimum value, wherein the at least one curved region is associated with at least one of the one or more areas of the first kind.
20. The thin glass article according to claim 18, wherein the at least one curved region is exactly one curved region, the exactly one curved region extending over an entirety of the thin glass article and having a cylindrical curvature.
21. The thin glass article according to claim 1, wherein the ion-exchanged surface layer has a refractive index that varies by at least 0.001 up to 0.1 across the outer surface.
22. A method for producing a thin glass article, comprising: providing a thin glass sheet with a first face, a second face, one or more edges joining the first and second faces, and a thickness between the first and second faces, the first and second faces together with the one or more edges form an outer surface; and applying, non-uniformly, an ion-exchange treatment to the outer surface to produce a non-uniformly ion-exchanged surface layer, the non-uniformly ion-exchanged surface layer having a compressive surface stress and/or a depth of layer that varies between a minimum value and a maximum value over the outer surface.
23. The method according to claim 22, wherein the step of applying, non-uniformly, the ion-exchange treatment to the outer surface comprises applying the ion-exchange treatment such that the minimum value is at most 90% of the maximum value.
24. The method according to claim 22, wherein the step of applying, non-uniformly, the ion-exchange treatment to the outer surface comprises applying the ion-exchange treatment such that the minimum value is at most 30% of the maximum value.
25. The method according to claim 22, wherein the step of applying, non-uniformly, the ion-exchange treatment to the outer surface comprises applying a masking to cover regions of the outer surface prior to applying the ion-exchange treatment, the masking preventing an ion-exchange at the regions.
26. The method according to claim 22, wherein the non-uniformly ion-exchanged surface layer induces a curvature due to the surface compressive stress.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] The exemplary figures used for illustration of the invention schematically show:
[0078] FIG. 1 is a thin glass sheet with rectangular shape;
[0079] FIGS. 2a-2e are sectional views of several thin glass articles with non-uniform ion-exchanged surface layers according to the invention;
[0080] FIGS. 3a-3f are several frontal views of thin glass articles with patterned non-uniform ion-exchanged surface layers according to the invention;
[0081] FIG. 4a is a sectional view of a thin glass article with a patterned non-uniform ion-exchanged surface layer on both faces of the glass article;
[0082] FIG. 4b is an alternatingly curved thin glass article resulting from the patterned non-uniform ion-exchanged surface layer according to FIG. 4a;
[0083] FIG. 5a is a sectional view of a thin glass article with a non-uniformly ion-exchanged surface layer where one face has a constant ion-exchanged surface layer and the other face has a no ion-exchanged surface layer;
[0084] FIG. 5b is a thin glass article with constant curvature resulting from the non-uniformly ion-exchanged surface layer according to FIG. 5a;
[0085] FIG. 6 is a perspective view of a thin glass article with a non-uniformly ion-exchanged surface layer covering the edges of the glass article.
[0086] The dimensions and aspect ratios in the figures are not to scale and have been oversized in part for better visualization. Corresponding elements in the figures are generally referred to by the same reference numerals.
DETAILED DESCRIPTION
[0087] FIG. 1 shows a rectangular shaped thin glass article 1 (henceforth referred to as “glass article 1”) with a length L, a width W and a thickness t. The glass article 1 has a first face 2 and an opposing second face 3 which are joined by four linear edges 4. The faces 2 and 3 together with the edges 4 form an outer surface 5 of the glass article 1. It is to be understood that the glass article can also have other shapes as e.g. a circular shape or any other shape as required by the desired application. According to the invention, the glass article 1 has a non-uniformly ion-exchanged surface layer 8 (henceforth referred to as “surface layer 8”, see e.g. FIG. 2a-2e) which varies over the outer surface 5.
[0088] FIGS. 2a-2e show partial sectional views of the glass article 1 with several different surface layers 8 according to the invention. FIGS. 2a-2e do not indicate the surface compressive stress (CS) associated with the surface layers 8 and rely on the depth of layer (DoL) for illustration of the invention. Separators of different surface areas are indicated by thin dashed lines where appropriate.
[0089] FIG. 2a shows a continuously varying ion-exchanged layer 8 of the first face 2 of the glass article 1. The ion-exchanged layer 8 varies from a minimal depth of layer DoL.sub.min=0 to a maximum value DoL.sub.max. The transition from DoL.sub.min to DoL.sub.max extends along a dimension x over a comparatively large distance which can be of the same order of magnitude as a characteristic dimension of the glass article 1.
[0090] FIG. 2b shows a regularly patterned surface layer 8 with surface areas 9 of a first kind having a DoL of DoL.sub.max whereas surface areas 10 of a second kind have a DoL of DoL.sub.min=0. The surface areas 9 and 10 are arranged in a regularly alternating sequence. The surface areas 9 and 10 directly border to each other in this embodiment and the transition in DoL from the surface areas 9 to the neighboring surface areas 10 is abrupt, i.e. on a length scale that is small compared to the extension of the surface areas 9 and 10. The transition is indicated as a step function in FIG. 2b.
[0091] FIG. 2c shows an irregularly patterned surface layer 8 with a surface area 9 of a first kind having a DoL of DoL.sub.max surface areas 10 of a second kind having a DoL of DoL.sub.min=0 and a surface area 11 of a third kind having a DoL of DoL.sub.2 with DoL.sub.min<DoL.sub.2<DoL.sub.max.
[0092] FIG. 2d shows an irregularly patterned surface layer 8 with a surface area 9 of a first kind having a DoL of DoL.sub.max and surface areas 10 of a second kind having a DoL of DoL.sub.min≠0.
[0093] FIG. 2e shows a regularly patterned surface layer 8 with surface areas 9 of a first kind having a DoL varying from DoL.sub.min=0 to DoL.sub.max and surface areas 10 of a second kind having a DoL of DoL.sub.min=0.
[0094] FIGS. 3a-3e show differently patterned surface layers 8 with surface areas 12, 14, 16, 18, 20, 22 of a first kind (hatched) and surface areas 13, 15, 17, 19, 21, 23 of a second kind (white) on the face 2 of the glass article 1 in a frontal view. It is to be understood that the surface areas 12, 14, 16, 18, 20, 22 can have e.g. a larger DoL and/or CS than the surface areas 13, 15, 17, 19, 21, 23 or vice versa. The patterns shown in FIG. 3a-3e also represent a masking by e.g. a coating used during production of the thin glass article in order to achieve the non-uniform ion-exchanged surface layer 8.
[0095] FIG. 3a shows a regular pattern of regular shaped surface areas 12 which are circularly shaped. The surface areas 12 are arranged in an array and are disconnected. The surface areas 12 are fully surrounded by a surface area 13 covering the remaining area of the face 2. The surface areas 12 and 13 together fully cover the face 2. Such a regular pattern can be applied as e.g. optical diffusors.
[0096] FIG. 3b shows a regular pattern of regular shaped surface areas 14 and 15 which have a congruent quadratic shape i.e. the same shape and the same size. The surface areas 14 and 15 are alternatingly arranged in a chess-board pattern. The surface areas 14 and 15 together fully cover the face 2. Such chess-board patterns can be applied as e.g. optical diffusors.
[0097] FIG. 3c shows a regular pattern of irregularly shaped surface areas 16. The surface areas 16 are arranged in an array and are disconnected. The surface areas 16 are fully surrounded by a surface area 17 covering the remaining area of the face 2. The surface areas 16 and 17 together fully cover the face 2. Such a regular pattern can be applied as e.g. optical diffusors
[0098] FIG. 3d shows a stripe pattern which is regular in one half of the face 2 (left side) and, for illustration purposes, irregular in the other half. The stripe pattern is formed by stripe shaped surface areas 18 which are separated by also stripe shaped surface areas 19. The surface areas 19 in the regular half have identical width whereas the width is increasing in the irregular half of face 2. The surface areas 18 and 19 together fully cover the face 2. Such stripe patterns can be applied as regular or irregular patterns as e.g. optical grids or linear optical lenses or if a wave shaped glass article is required (see also FIGS. 4a and 4b).
[0099] FIG. 3e shows an irregular pattern of irregular shaped surface areas 20. The surface areas 20 are arranged in an array and are disconnected. The surface areas 20 are fully surrounded by a surface area 21 covering the remaining area of the face 2. The surface areas 20 and 21 together fully cover the face 2. Such irregular patterns can e.g. be applied as optical diffusors.
[0100] FIG. 3e shows concentric ring shaped surface areas 22 which are separated by correspondingly shaped surface areas 23. The surface areas 22 and 23 together fully cover the face 2. Such a surface layer 8 can e.g. be applied as optical lens or grating.
[0101] FIG. 4a shows a partial sectional view of the glass article 1 with another embodiment of the surface layer 8 according to the invention. The surface layer 8 in this embodiment corresponds to a stripe pattern with surface areas 24 of a first kind on the face 2 and surface areas 24′ of a first kind on face 3. The surface areas 24 and 24′ have a DoL=DoL.sub.max and a surface compressive stress CS=CS.sub.max (see also FIG. 4b). The surface layer 8 further comprises surface areas 25 of a second kind on face 2 and surface areas 25′ of a second kind on face 3. The surface areas 25 and 25′ of the second kind have a DoL=DoL.sub.min=0 and also have a surface compressive stress CS=CS.sub.min=0. The surface areas 24 and 25 are arranged with respect to the surface areas 24′ and 25′ such that each surface area 24 and 24′ on the respective face 2 or 3 is opposed by a surface area 25′ or 25 on the other face, respectively.
[0102] FIG. 4b shows a perspective view of the glass article 1 of FIG. 4a in a relaxed state. Due to the compressive surface stresses CS=CS.sub.max in the surface areas 24 on face 2 and 24′ on face 3 which are not opposed by any surface compressive stresses on the respective areas on the opposing face, the glass article 1 experiences an unbalanced surface force. If the difference in surface compressive stress ΔCS between the surface areas 24 and the opposing surface areas 25′ (ΔCS=CS.sub.max in the present example) is large enough, the glass article 1 experiences a bending force and relaxes into a curved shape until the surface compressive stresses are balanced. Since the glass article 1 of FIGS. 4a and 4b has an alternating stripe pattern, the unbalanced surface compressive stresses result in a wave-like shape of the glass article 1 as shown in FIG. 4b. The curved regions are thereby associated with e.g. the surface areas 24 and 24′ of the first kind and have a (minimal) curvature radius R.
[0103] FIG. 5a shows a partial sectional view of the glass article 1 with another embodiment of the surface layer 8 according to the invention. The glass article 1 has a constant DoL=DoL.sub.max and an associated surface compressive stress CS=CS.sub.max over the whole face 2 or, in other words, a surface area 26 of a first kind that covers the whole face 2. The surface layer 8 has a DoL=DoL.sub.max=0 over the whole opposing face 3 or in other words has a surface area 27 of a second kind that covers the whole face 3. Due to the thus unbalanced surface compressive stresses, i.e. ΔCS≠0, between the both faces 2 and 3, the glass article 1 experiences an unbalanced surface force which causes the glass article 1 to bend into a curved shape until the surface compressive stresses on both faces 2 and 3 are balanced. Since the surface layer 8 is essentially constant on each face, the glass article 1 achieves a shape that has an essentially constant cylindrical curvature R as shown in FIG. 5b.
[0104] FIG. 6 shows another embodiment of the glass article 1 with a surface layer 8 according to the invention. In this embodiment, the surface layer 8 has a surface area 28 (hatched) of a first kind that covers the edges 4 of the glass article 1 and extends onto the faces 2 and 3 in a border region along the edges 4. The surface area 28 has a DoL=DoL.sub.max and a surface compressive stress CS=CS.sub.max. The remaining area of the face 2 is covered by a surface area 29 of a second kind and the remaining area of face 3 by a corresponding surface area (not visible in FIG. 6), The surface area 29 has a DoL=DoL.sub.min and a surface compressive stress CS=CS.sub.min. The border regions on the faces 2 and 3 have a width l. The following values for l/L, CS and DoL have been found to be particular advantageous combinations:
TABLE-US-00017 l/L CS (MPa) DoL (μm) ≦0.3 ≧20 ≧5 ≦0.1 ≧50 ≧10 ≦0.01 ≧100 ≧20 ≦0.001 ≧300 ≧50
[0105] It is, however, to be understood that other combinations can also be advantageous and the particular choice may depend on the specific requirements.
Exemplary Embodiments
[0106] The glass compositions A and B as listed in the below Table 2 are used for the exemplary embodiments 1-8 as described below:
TABLE-US-00018 TABLE 2 Exemplary glass compositions Glass A Glass B Composition weight-% Composition weight-% SiO.sub.2 64.0 SiO.sub.2 62 B.sub.2O.sub.3 8.3 Al.sub.2O.sub.3 17 Al.sub.2O.sub.3 4.0 Na.sub.2O 13 Na.sub.2O 6.5 K.sub.2O 3.5 K.sub.2O 7.0 MgO 3.5 ZnO 5.5 CaO 0.3 TiO.sub.2 4.0 SnO.sub.2 0.1 Sb.sub.2O.sub.3 0.6 TiO.sub.2 0.6 Cl.sup.− 0.1
[0107] Glasses A and B have the following selected properties:
TABLE-US-00019 TABLE 3 Parameters of glasses A and B according to Table 2 Parameter Glass A Glass B CTE (20-300° C.) [10.sup.−6/K] 7.2 8.3 T.sub.g [° C.] 557 623 Density [g/cm.sup.3] 2.5 2.4
[0108] CTE in Table 3 refers to the coefficient of thermal expansion and T.sub.g refers to the glass transition temperature.
Example 1
[0109] A sheet of 100 mm×60 mm was cut from glass A (see Table 2) with a thickness of 0.05 mm. The glass sheet was pasted with an ink mixed with KNO.sub.3 powder by a screen printing method fully covering one of its faces. Subsequently, the sheet was dried at 180° C. during 1 hour to remove the ink. After drying, the sheet was annealed at 330° C. for 2 hours to drive an ion-exchange process. As a result, the in this example ultrathin glass sheet experienced a bending into a widely cylindrical curved shape with a curvature radius of 52 mm (corresponding to the shape shown in FIG. 5b).
Example 2
[0110] A sheet of 100 mm×60 mm was cut from glass A (Table 2) with a thickness of 0.05 mm. The sheet was coated with an indium tin oxide (ITO) film on one of its faces in order to prevent ion-exchange and was subsequently submersed into a KNO.sub.3 salt bath. The ultrathin glass sheet was toughened at a temperature of 400° C. for 1 hour. The CS is approximately 270 MPa and the DoL is approximately 7 μm. As a result, the in this example ultrathin glass sheet experienced a bending into a widely cylindrical curved shape with a curvature radius of 48 mm (corresponding to the shape shown in FIG. 5b).
Example 3
[0111] A sheet of 100 mm×60 mm was cut from glass A (Table 2) with a thickness of 0.1 mm. The sheet was masked according to the surface areas 24 and 24′ in a regular stripe pattern as shown in FIG. 4a (see also FIG. 3d). The sheet was then coated with an ITO-film, resulting in coated areas corresponding to the surface areas 25 and 25′ in order to prevent ion-exchange in the coated areas. After removing the masking of the surface areas 24 and 24′, the ultrathin glass sheet was submersed into a KNO.sub.3 salt bath and toughened at a temperature of 400° C. for 1 hour. This resulted in an ion-exchange in the surface areas 24 and 24′ and in no ion-exchange in the ITO-coated surface areas 25 and 25′. The CS is approximately 270 MPa and the DoL is approximately 7 μm. As a result, the in this example ultrathin glass sheet experienced an alternating bending into a wave shape as shown in FIG. 4b.
Example 4
[0112] A sheet of 100 mm×60 mm was cut from glass B (Table 2) with a thickness of 0.3 mm. The sheet was masked according to the surface areas 18 in the regular stripe pattern shown in FIG. 3d. The sheet was then coated with an ITO-film, resulting in coated areas corresponding to the surface areas 19 in order to prevent ion-exchange in the coated areas. The widths of all stripe shaped surface areas 18 and 19 were 5 μm. After removing the masking of the surface areas 18, the in this example ultrathin glass sheet was submersed into a KNO.sub.3 salt bath and toughened at a temperature of 420° C. for 3 hours. The CS is approximately 900 MPa and the DoL is approximately 35 μm. The refractive index variation is about 0.008. The resulting ultrathin glass article can be applied as an optical grating.
Example 5
[0113] A sheet of 100 mm×60 mm was cut from glass B (Table 2) with a thickness of 0.3 mm. The sheet was masked according to the surface areas 14 in the chess-board pattern shown in FIG. 3b. The sheet was then coated with an ITO-film, resulting in coated areas corresponding to the surface areas 15 in order to prevent ion-exchange in the coated areas. The edge lengths of all square surface areas 14 and 15 were 5 μm. After removing the masking of the surface areas 14, the in this example ultrathin glass sheet was submersed into a KNO.sub.3 salt bath and toughened at a temperature of 420° C. for 3 hours. The CS is approximately 900 MPa and the resulting DoL is approximately 35 μm. The refractive index variation is about 0.008. The resulting ultrathin glass article can be applied as an optical diffusor.
Example 6
[0114] A sheet of 100 mm×60 mm was cut from glass B (Table 2) with a thickness of 0.3 mm. The sheet was masked according to the surface areas 12 in the circle pattern shown in FIG. 3a. The sheet was then coated with an ITO-film, resulting in a coated area corresponding to the surface area 13 in order to prevent ion-exchange in the coated area. The diameter of each circular surface area 12 was 5 μm. After removing the masking of the surface areas 12, the in this example ultrathin glass sheet was submersed into a KNO.sub.3 salt bath and toughened at a temperature of 420° C. for 3 hours. The CS is approximately 900 MPa and the DoL is approximately 35 μm. The refractive index variation is about 0.008. The resulting ultrathin glass article can be applied as an optical diffusor.
Example 7
[0115] A sheet of 100 mm×60 mm was cut from glass B (Table 2) with a thickness of 0.3 mm. The sheet was masked according to the surface areas 16 in the regular pattern of irregular shapes as shown in FIG. 3c. The sheet was then coated with an ITO-film, resulting in a coated area corresponding to the surface area 17 in order to prevent ion-exchange in the coated area. The characteristic dimension of each irregular surface area 16 was 5 μm. After removing the masking of the surface areas 16, the in this example ultrathin glass sheet was submersed into a KNO.sub.3 salt bath and toughened at a temperature of 420° C. for 3 hours. The CS is approximately 900 MPa and the DoL is approximately 35 μm. The refractive index variation is about 0.008. The resulting ultrathin glass article can be applied as an optical diffusor.
Example 8
[0116] Tests have been performed on the change in refractive index R.sub.i due to an Na.sup.+/K.sup.+-exchanged surface layer in a glass sheet of glass B (Table 2). It has been found that the change in refractive index R.sub.i linearly depends on the CS resulting from the ion-exchanged surface layer (see Table 4 where a refractive index R.sub.i=0 is assumed at the glass surface):
TABLE-US-00020 TABLE 4 Refractive index R.sub.i in dependence of surface compressive stress CS. CS (MPa) R.sub.i 900 0.008 700 0.007 500 0.006
[0117] The refractive index was measured by a prism coupler (Metricon 2010/M). It has also been found that the refractive index R.sub.i decreases as DoL increases.
