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 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.
2. The method according to claim 1, 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.
3. The method according to claim 1, 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.
4. The method according to claim 1, 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.
5. The method according to claim 1, wherein the non-uniformly ion-exchanged surface layer induces a curvature due to the surface compressive stress.
6. The method according to claim 1, wherein the step of applying, non-uniformly, the ion-exchange treatment to the outer surface comprises non-uniformly applying a paste containing alkaline metal salts to the outer surface.
7. The method according to claim 6, further comprising annealing the thin glass sheet after the step of applying.
8. The method according to claim 7, wherein the step of applying, non-uniformly, the ion-exchange treatment further comprises drying the paste at a temperature of 100 C. and 300 C. for 2 to 10 hours prior to the step of annealing.
9. The method according to claim 1, wherein the step of applying, non-uniformly, an ion-exchange treatment to the outer surface comprises applying the ion-exchange treatment only to the one or more edges so that the ion-exchanged surface layer is not present on the first face or the second face.
10. A method for producing a thin glass article, comprising the steps: providing a thin glass sheet with a first face and a second face, having one or more edges joining the first and the second face, a thickness between the first and the second face, wherein the first and the second face together with the one or more edges form an outer surface of the thin glass sheet; and applying an ion-exchange treatment to the thin glass sheet to produce the thin glass article, the ion-exchange treatment being non-uniformly applied to the outer surface in order to produce a non-uniformly ion-exchanged surface layer of the thin glass article, such that the non-uniformly 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, wherein the non-uniform ion-exchange treatment includes non-uniformly applying a paste containing alkaline metal salts to the outer surface and annealing the thin glass sheet.
11. The method according to claim 10, further comprising drying the paste at a temperature of 100 C. and 300 C. for 2 to 10 hours prior to the step of annealing.
12. The method according to claim 10, wherein the non-uniform ion-exchange treatment is applied such that the minimum value of the surface compressive stress is at most 90% of the maximum value.
13. The method according to claim 10, wherein the non-uniform ion-exchange treatment is applied such that the minimum value of the surface compressive stress is at most 50% of the maximum value.
14. The method according to claim 10, wherein the non-uniform ion-exchange treatment is applied such that the minimum value of the surface compressive stress is at most 30% of the maximum value.
15. The method of claim 10, wherein the non-uniform ion-exchange treatment is selectively applied to one or more designated surface areas on the outer surface in order to produce one or more surface areas of a first kind and one or more surface areas of a second kind, wherein the surface compressive stress and/or the depth of layer is different in the one or more surface areas of the first and second kinds.
16. The method of claim 15, wherein the non-uniform ion-exchange treatment is applied such that the surface compressive stress and/or the depth of layer correspond to the respective maximum value in the one or more surface areas of the first kind and to the respective minimum value in the one or more surface areas of the second kind.
17. The method according to claim 10, wherein the paste comprises alkaline metal salts selected from a group consisting of NaNO3, Na2CO3, NaOH, Na2SO4, NaF, Na3PO4, Na2SiO3, Na2Cr2O7, NaCl, NaBF4, Na2HPO4, K2CO3, KOH, KNO3, K2SO4, KF, K3PO4, K2SiO3, K2Cr2O7, KCl, KBF4, K2HPO4, CsNO3, CsSO4, and CsCl.
18. The method according to claim 10, wherein the non-uniform ion-exchange treatment comprises controlling a slow ion-exchange rate to achieve the ion-exchange surface layer with the maximum value of the depth of layer of equal to or less than 50 m and the maximum value of the surface compressive stress in a range from 10 MPa to 1200 MPa.
19. The method according to claim 18, wherein the depth of layer is equal to or less than 3 m.
20. The method according to claim 10, 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.min0.
[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 CS between the surface areas 24 and the opposing surface areas 25 (CS=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.min=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. CS0, 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 1. The following values for 1/L, CS and DoL have been found to be particular advantageous combinations:
TABLE-US-00017 1/L CS (MPa) DoL (m) 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, refers to the glass transition temperature.
Example 1
[0109] A sheet of 100 mm60 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 mm60 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 m. 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 mm60 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 m. 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 mm60 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 m. 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 m. 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 mm60 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 m. 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 m. 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 mm60 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 m. 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 m. 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 mm60 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 m. 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 m. 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.
