GLASS LAMINATE HAVING INCREASED STRENGTH

Abstract

A method for producing a glass article having a compressive stress zone close to the surface by redrawing a preform having a rectangular cross section is provided. The preform includes at least a first and a second glass, wherein both glasses are not connected to each other in the preform in a force-fitting manner. The second glass has a higher thermal expansion coefficient than the first glass and is located in the preform in the interior of the glass tube of the first glass. A glass laminate having increased strength is also provided, which is composed as an at least three-layer composite material of at least two different glasses. The individual layers of the layer composite are connected to each other over the entire area and in a non-positive manner, in particular by melting, and the glass laminate has a thermally stable compressive stress zone in the areas close to the surface of the layer composite and a tensile stress zone in the inner region of the layer composite.

Claims

1. A method for producing a glass article that has a compressive stress zone close to the surface by redrawing, comprising at least the steps of: providing a preform comprising at least a first glass and a second glass, the second glass having a higher thermal expansion coefficient than the first glass, the first glass being a glass tube of a length (L) with two sides extending over a width (B), and the second glass is located inside the glass tube; and redrawing the preform so that the preform passes through a hot zone to form a drawing onion and is subsequently reshaped by application of mechanical force.

2. A method for producing a glass article that has a compressive stress zone close to the surface by redrawing, comprising at least the steps of: providing a preform comprising at least a first glass and a second glass, the second glass has a higher thermal expansion coefficient than the first glass, the first glass has a length (L) with two sides extending over a width (B), and the second glass is located between the two sides of the first glass, the first glass has lateral portions extending beyond the second glass at lateral sides thereof; redrawing the preform so that the preform passes through a hot zone to form a drawing onion and is subsequently reshaped by application of mechanical force, wherein during the redrawing the lateral portions of the first glass form a laterally sealed body that encloses the second glass.

3. The method as claimed in claim 1, wherein the glass tube has two plane-parallel sides extending over the width and arranged with a spacing (d.sub.1) therebetween, wherein the length is larger than the width and the width is larger than the spacing.

4. The method as claimed in claim 1, wherein the preform has a rectangular or ovaloid cross-sectional shape.

5. The method as claimed in claim 1, wherein the second glass is a sheet glass.

6. The method as claimed in claim 1, wherein the first and second glasses are not connected in force-fitted manner to each other in the preform.

7. The method as claimed in claim 1, wherein the first glass is glass selected from the group consisting of a borosilicate glass, a glass ceramic, and an alkali silicate glass, and/or wherein the second glass is a glass selected from the group consisting of a soda-lime glass, a waterglass, and an alkali silicate glass.

8. The method as claimed in claim 1, further comprising applying a vacuum to the preform.

9. The method as claimed in claim 1, wherein the step of providing the preform comprises: providing a flat preform; producing an angular or ovaloid glass tube made of the first glass; sealing one end of the tube by fusing the tube; and introducing the second glass into the glass tube at an end opposite the sealed one end.

10. The method as claimed in claim 1, wherein the step of redrawing comprises connecting an upper end of the preform to a vacuum generating device.

11. The method as claimed in claim 9, wherein the glass tube is produced by a laser-based reshaping process which comprises hot-forming a sheet glass made of the first glass.

12. The method as claimed in claim 1, wherein, subsequent to the redrawing step, the method further comprises applying a coating to the glass article on one or both sides thereof.

13. The method as claimed in claim 12, wherein the coating is selected from the group consisting of a scratch resistance coating, a sapphire glass coating, an easy-to-clean coating, an anti-fingerprint coating, an anti-glare coating, an anti-reflective coating, an anti-bacterial coating, and combinations thereof.

14. The method as claimed in claim 1, further comprising, subsequent to the redrawing step, the method further comprises the step of thermally and/or chemically tempered the glass article.

15. The method as claimed in claim 1, wherein the redrawing step comprises reshaping the preform into a sheet glass having a thickness of <3 mm.

16. The method as claimed in claim 1, wherein the first glass has a coefficient of thermal expansion in a range from 0.1*10.sup.6/K to 12*10.sup.6/K and/or wherein the second glass has a coefficient of thermal expansion in a range from 0*10.sup.6/K to 12.1*10.sup.6/K.

17. The method as claimed in claim 1, wherein the thermal expansion coefficients of the second and first glasses have a ratio (r.sub.) that is greater than 1, and wherein the ratio has an absolute value of less than 125.

18. The method as claimed in claim 1, wherein the thermal expansion coefficients between the second glass and the first glass have a difference (.sub.) that is 0.1 to 12*10.sup.6/K.

19. The method as claimed in claim 1, wherein the step of providing the preform further comprises providing a third glass in the form of a different glass tube having a rectangular cross-sectional shape and wherein the different glass tube is disposed inside the glass tube, and wherein the second glass is disposed inside the different glass tube.

20. A glass laminate with increased strength, comprising: a layer composite with at least three layers made of two different glasses, wherein the at least three layers are connected to each other over an entire surface area and in a non-positive manner, the layer composite having a compressive stress zone in regions close to a surface of the layer composite and by a tensile stress zone in an inner region of the layer composite, wherein the layer composite has outer layers made of a first glass and an inner layer disposed between the outer layers that is made of a second glass, wherein the first glass has a first coefficient of thermal expansion and the second glass has a second coefficient of thermal expansion, wherein the first coefficient of thermal expansion is smaller than the second coefficient of thermal expansion, and wherein the compressive stress zone is thermally stable.

21. A glass laminate with increased strength, comprising: a layer composite with at least three layers made of two different glasses, wherein the at least three layers are connected to each other over an entire surface area and in a non-positive manner, the layer composite having a compressive stress zone in regions close to a surface of the layer composite and by a tensile stress zone in an inner region of the layer composite, wherein the layer composite has outer layers that are made of a first glass and an inner layer that is disposed between the outer layers that is made of a second glass, wherein the first glass has a first coefficient of thermal expansion and the second glass has a second coefficient of thermal expansion, wherein the first coefficient of thermal expansion is smaller than the second coefficient of thermal expansion, wherein, in a viscosity range from 10.sup.4 to 10.sup.5 dPa.Math.s, the first glass and/or the second glass exhibits a crystallization rate of >0.5 m/min, and wherein the compressive stress zone is thermally stable.

22. A glass laminate with increased strength, comprising: a layer composite with at least five layers made of three different glasses, wherein the at least five layers are connected to each other over an entire surface area and in a non-positive manner, wherein the layer composite has the outer layers that are made of a first glass, an innermost layer that is made of a second glass, a layer made of a third glass disposed between each of the outer layers and the innermost layer, wherein the layer composite has a compressive stress zone in regions of the layer composite close to a surface of the layer composite and by a tensile stress zone in an inner region of the layer composite, wherein the outer layers are made of a first glass, the layer that is disposed between the outer layers and the inner most layer is made of a second glass, wherein the first glass has a first coefficient of thermal expansion and the second glass has a second coefficient of thermal expansion, wherein the first coefficient of thermal expansion is smaller than the second coefficient of thermal expansion, and wherein the compressive stress zone is thermally stable.

23. The glass laminate as claimed in claim 20, comprising a compressive stress of not more than 800 MPa.

24. The glass laminate as claimed in claim 20, wherein the first glass contains alkali ions.

25. The glass laminate as claimed in claim 20, comprising a ratio of layer thicknesses of the first and second glasses of 3:2.

26. The glass laminate as claimed in claim 22, wherein the third glass has a third coefficient of thermal expansion that is smaller than the second coefficient of thermal expansion and greater than the first coefficient of thermal expansion.

Description

DESCRIPTION OF THE FIGURES

[0076] The invention will now be described in more detail by way of exemplary embodiments and with reference to FIGS. 1 to 9, wherein:

[0077] FIG. 1 schematically illustrates a first embodiment of the method according to the invention;

[0078] FIG. 2 schematically illustrates a further embodiment of the method according to the invention;

[0079] FIG. 3 is a schematic view of one embodiment of the laminate according to the invention;

[0080] FIG. 4 is a schematic view of a further embodiment of the glass laminate, in which the glass laminate is coated on one face thereof;

[0081] FIG. 5 is a schematic view of a further embodiment of the glass laminate, in which the glass laminate comprises a third glass;

[0082] FIG. 6a is a view of the lower end of the glass tube having a rectangular cross section;

[0083] FIG. 6b is a view of the lower end of the glass tube having a hexagonal cross section; and

[0084] FIG. 6c is a view of the lower end of the glass tube having rounded edges;

[0085] FIG. 7 is a schematic cross-sectional view of a preferred embodiment of a preform according to the invention prior to redrawing;

[0086] FIG. 8 is a schematic cross-sectional view of the preferred embodiment of a preform according to the invention shown in FIG. 7 during hot reshaping thereof, in particular during redrawing;

[0087] FIG. 9 is a schematic cross-sectional view of the preferred embodiment of a preform according to the invention shown in FIGS. 7 and 8 during hot reshaping thereof, in particular after application of a vacuum.

DETAILED DESCRIPTION

[0088] In the following detailed description of preferred embodiments, the same reference numerals designate substantially similar or identical components or features.

[0089] FIG. 1 schematically illustrates a sequence of method steps according to a first embodiment of the inventive method, the items employed in the method steps being shown in a longitudinal cross-sectional view.

[0090] First, a glass tube 1 of length L is provided, which has a preferably rectangular or oval cross-sectional shape. Glass tube 1 is made of a first glass and has an inner spacing, also referred to as inner diameter d.sub.1, and a wall thickness wd.sub.1.

[0091] The long plane-parallel sides of the glass tube extend over a width B (see FIGS. 6a to 6c) and are spaced from each other by an inner spacing d1. For these parameters, the relationship L>B>d1 applies.

[0092] In step a), the glass tube 1 is preferably sealed at one end thereof, by fusing.

[0093] In step b), a sheet glass of a thickness d.sub.2 and made of a second glass 3 is introduced into the glass tube 2 sealed at one end.

[0094] Sheet glass 3 has a thickness d.sub.2 which is smaller than the inner spacing d.sub.1 of the first tube 1, so that the sheet glass 3 can be inserted into the glass tube 2.

[0095] The glasses of first glass tube 1 and of sheet glass 3 differ in their coefficients of thermal expansion, the thermal expansion coefficient of the first glass being smaller than the thermal expansion coefficient of the second glass.

[0096] The two interposed glasses, i.e. glass tube 2 and sheet glass 3, define the preform 4.

[0097] The outer dimension, also referred to as the outer diameter D.sub.V of preform 4 corresponds to the outer dimension of the first glass tube 1.

[0098] Preform 4 is introduced into a redrawing apparatus 10 by means of rollers 6.

[0099] The apparatus 10 shown in FIG. 1 is illustrated in simplified form and merely represents one example of a possible redrawing apparatus. The walls 5 of apparatus 10 include heaters (not shown), by means of which the preform 4 is heated.

[0100] Preform 4 is passed through apparatus 10 by rollers 6 and 8, the arrows symbolizing the advancement direction of the preform.

[0101] During redrawing, a common drawing onion of the two glasses 1 and 3 in their viscous state is being formed within hot zone 7. As a result of the redrawing, a full-surface and non-positive connection is created between the first and second glasses 1, 3, in particular by fusion along the surfaces thereof.

[0102] Thus, a three-layered glass laminate 9 is provided as the result of redrawing. Contact is established between the walls of the first tube 1 and the surfaces of sheet glass 3. Sheet glass 3 thus forms the inner layer of the laminate, while the two outer layers of the laminate are defined by the glass of first glass tube 1.

[0103] FIG. 2 schematically shows the process sequence of a further embodiment of the method, the method steps being illustrated in a longitudinal cross-sectional view.

[0104] The further embodiment shown in FIG. 2 differs from the exemplary embodiment of FIG. 1 in that a glass tube 50 made of a third glass is additionally used.

[0105] Glass tube 1 is made of a first glass and has an inner spacing d.sub.1 and a wall thickness wd.sub.1. In step a), the glass tube 1 is sealed at one end thereof by fusing.

[0106] A further glass tube 50 having a wall thickness wd.sub.2 is introduced into the so obtained glass tube 2 sealed at one end, in step b). Glass tube 50 has a rectangular or ovaloid cross section and an outer dimension d.sub.2 which is smaller than the inner spacing d.sub.1 of the first tube 1, so that the glass tube 50 can be inserted into the glass tube 2.

[0107] Glass tube 50 is made of a third glass. Subsequently, a glass 30 in the form of a sheet glass is inserted into glass tube 50.

[0108] The first and second glasses differ in their thermal expansion coefficients, the thermal expansion coefficient of the first glass being smaller than the thermal expansion coefficient of the second glass.

[0109] Depending on the embodiment, the third glass, i.e. the glass of glass tube 50, may have a thermal expansion coefficient between the expansion coefficients of the first and second glasses. Alternatively or additionally, the third glass may contain coloring components.

[0110] The interleaved glass tubes 2 and 50 together with sheet glass 30 define the preform 41. The outer dimension D.sub.V of preform 41 corresponds to the outer dimension of the first glass tube 1.

[0111] Preform 41 is introduced into a redrawing apparatus 10 by means of rollers 6. As a result of the redrawing, a full-surface and non-positive connection is created between the three components 2, 50, and 30 of the preform 41, in particular by fusion. Thus, a five-layered glass laminate 90 is provided as the result of redrawing.

[0112] Surface contact is established between the walls of the first tube 1 and the walls of tube 50 and also between the two walls of tube 50 and the two faces of sheet glass 30. Sheet glass 30 defines the inner layer of the laminate, while the walls of glass tube 50 each define an intermediate layer and the walls of the first glass tube 1 define the two outer layers of the laminate 90.

[0113] Preferably, in this case, the respective glasses are selected so that the glasses disposed further inwards have a higher coefficient of thermal expansion than the glasses disposed further outwards or at least than the outermost first glass of glass tube 1. In this way, a gradient-like increase of compressive stress from the interior towards the exterior of laminate 90 can be achieved, which may even be stronger than in the case of glass laminates comprising a smaller number of glasses, and nevertheless the warp arising during shaping, in particular during redrawing, will usually be less pronounced.

[0114] FIG. 3 schematically illustrates a cross-sectional view through glass laminate 9. In this embodiment, the glass laminate comprises three glass layers 11a, 12, and 11b in the form of a layer composite. The outer layers 11a and 11b are made of the first glass. The inner glass layer 12 is disposed between outer layers 11a and 11b, the individual glass layers sharing common interfaces. Inner glass layer 12 is made of the second glass.

[0115] Layers 11a and 11b each have a layer thickness d.sub.a, the layer thickness of the inner layer 12 is denoted by d.sub.i. The glass laminate 9 has a total thickness D.sub.L. Depending on the selected process parameters during the redrawing process, the total thickness D.sub.L of the glass laminate is smaller than the total thickness D.sub.V of the preform, which corresponds to the outer dimension of glass tube 2.

[0116] FIG. 4 schematically illustrates a further embodiment of the glass laminate according to the invention. In this embodiment, the glass laminate 13 is coated on one face thereof. The coating 14 may, for example, be a coating 14 for increasing scratch resistance, a sapphire glass coating, an easy-to-clean coating, an anti-fingerprint coating, an anti-glare coating, an anti-reflective coating, and/or an anti-bacterial coating.

[0117] FIG. 5 illustrates a further embodiment of the invention in which the glass laminate 15 comprises layers made of a third glass, 16a and 16b.

[0118] Layers 16a and 16b are disposed between layers 11a and 11b, respectively, and the inner layer 12. In this case, the ratio of the thickness d.sub.a of the two outer layers 11a and 11b to the thickness d.sub.m of layers 16a and 16b corresponds to the ratio of wall thicknesses wd.sub.1 and wd.sub.2 of the two glass tubes 1 and 50 in the preform 41 (see FIG. 2). Thus, the following applies:

2d.sub.a/d.sub.m=wd.sub.1/wd.sub.2

[0119] FIGS. 6a, 6b, 6c show views of the lower end of the glass tube 1, corresponding to the respective cross section thereof, with different configurations of the small sides, or edges.

[0120] In FIG. 6a the lower end of glass tube 1 has the shape of a rectangle and in FIG. 6b the shape of a hexagon. In FIG. 6c, the lower end has rounded lateral sides, or edges.

[0121] In all three FIGS. 6a, 6b, and 6c, the thickness D.sub.V and the width B or extension of the plane-parallel sides or faces are indicated.

[0122] Reference is now made to FIG. 7 which shows a schematic cross-sectional view of a further preform 42 prior to being redrawn, which is in particular employed for a further embodiment of the inventive method for producing a glass article.

[0123] In this embodiment, again, reference numerals already mentioned above designate the same or equivalent components.

[0124] In this further embodiment, the method for producing a glass article with a compressive stress zone close to the surface by redrawing comprises at least the steps of: a) providing a preform 42, the preform 42 comprising at least a first and a second glass 3, wherein the second glass 3 has a higher thermal expansion coefficient than the first glass, wherein the first glass has a length L with two sides extending over a width B, and wherein the second glass 3 is arranged between the two sides of the first glass 1 extending over a length L.

[0125] As an alternative to the first embodiment according to the invention, the first glass has lateral portions 44, 45, 46, 47 extending beyond the second glass at lateral sides thereof and is provided in the form of a respective sheet glass in step b).

[0126] FIG. 8 is a schematic cross-sectional view of the preferred embodiment of a preform 42 according to the invention shown in FIG. 7 during hot reshaping, in particular while being redrawn.

[0127] The lateral portions 44, 45, 46, 47 laterally extending beyond the second glass 3, are contacted to each other by appropriate means, such as for example by further, preferably heated rollers, not shown in the figures, during the viscous state of the first glass during hot-forming thereof in the hot zone, and in this embodiment, too, one end of the preform 42 may be sealed, for example also by hot-forming, in order to permit to subsequently apply a vacuum.

[0128] According to a preferred embodiment, in this embodiment too, the air located between the individual components of the preform 42 is removed in a subsequent step by applying a vacuum, which results in the deformation illustrated in FIG. 9.

[0129] Accordingly, FIG. 9 is a schematic cross-sectional view of the preform 42 shown in FIGS. 7 and 8 during hot-forming thereof, in particular during redrawing after a vacuum was applied.

[0130] Here, the portions 44, 45, 46, 47 of the first glass extending laterally beyond the second glass form a laterally sealed body during the redrawing, in particular in the form of an ovaloid glass tube of non-round cross section, which encloses the second glass 3.

[0131] Subsequently or essentially simultaneously, the redrawing of the preform 42 is effected by passing the preform 42 through the hot zone in order to form a drawing onion and then further shaping it by application of mechanical force.

[0132] Below, preferred glasses for carrying out the invention are given. Since the invention is not limited to a specific one of the glasses mentioned below, it is not a priori predefined whether the respective glass is an inner or outer glass, that is to say the first or second glass. For the purposes of the invention it suffice to take into account the values of the thermal expansion coefficients given in the independent claims by selecting the corresponding glasses. For this purpose, the thermal expansion coefficients, determined for a temperature range from 20 C. to 300 C. in each case, are also given below for each of the glasses. Wherever the thermal expansion coefficients are not specified as an exact value but as a range, the respective value of the thermal expansion coefficient for the respective exact composition employed need to be used, which may as well be determined, for example, by measurement on the respective employed glass.

[0133] According to one embodiment, at least one of the aforementioned glasses is a lithium aluminosilicate glass having a thermal expansion coefficient from 3.3 to 5.7*10.sup.6/K and the following composition (in wt %):

TABLE-US-00001 TABLE 1 Composition (wt %) SiO.sub.2 55-69 Al.sub.2O.sub.3 18-25 Li.sub.2O 3-5 Na.sub.2O + K.sub.2O 0-30 MgO + CaO + SrO + 0-5 BaO ZnO 0-4 TiO.sub.2 0-5 ZrO.sub.2 0-5 TiO.sub.2 + ZrO.sub.2 + SnO.sub.2 2-6 P.sub.2O.sub.5 0-8 F 0-1 B.sub.2O.sub.3 0-2

[0134] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0135] Preferably, the lithium aluminosilicate glass of one embodiment the invention has the following composition (in wt %), with a thermal expansion coefficient from 4.76 to 5.7*10.sup.6/K:

TABLE-US-00002 TABLE 2 Composition (wt %) SiO.sub.2 57-66 Al.sub.2O.sub.3 18-23 Li.sub.2O 3-5 Na.sub.2O + K.sub.2O 3-25 MgO + CaO + SrO + 1-4 BaO ZnO 0-4 TiO.sub.2 0-4 ZrO.sub.2 0-5 TiO.sub.2 + ZrO.sub.2 + SnO.sub.2 2-6 P.sub.2O.sub.5 0-7 F 0-1 B.sub.2O.sub.3 0-2

[0136] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0137] Most preferably, the lithium aluminosilicate glass of a preferred embodiment of the invention has the following composition (in wt %), with a thermal expansion coefficient from 0.068 to 1.16*10.sup.6/K as a glass ceramic and with a thermal expansion coefficient from 5 to 7*10.sup.6/K as a glass:

TABLE-US-00003 TABLE 3 Composition (wt %) SiO.sub.2 57-63 Al.sub.2O.sub.3 18-22 Li.sub.2O 3.5-5 Na.sub.2O + K.sub.2O 5-20 MgO + CaO + SrO + 0-5 BaO ZnO 0-3 TiO.sub.2 0-3 ZrO.sub.2 0-5 TiO.sub.2 + ZrO.sub.2 + SnO.sub.2 2-5 P.sub.2O.sub.5 0-5 F 0-1 B.sub.2O.sub.3 0-2

[0138] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0139] According to one embodiment, the glass is a soda-lime glass, comprising the following composition (in wt %), and with a thermal expansion coefficient from 5.33 to 9.77*10.sup.6/K:

TABLE-US-00004 TABLE 4 Composition (wt %) SiO.sub.2 40-81 Al.sub.2O.sub.3 0-6 B.sub.2O.sub.3 0-5 Li.sub.2O + Na.sub.2O + K.sub.2O 5-30 MgO + CaO + SrO + BaO + 5-30 ZnO TiO.sub.2 + ZrO.sub.2 0-7 P.sub.2O.sub.5 0-2

[0140] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0141] Preferably, the soda-lime glass of one embodiment of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 4.94 to 10.25*10.sup.6/K:

TABLE-US-00005 TABLE 5 Composition (wt %) SiO.sub.2 50-81 Al.sub.2O.sub.3 0-5 B.sub.2O.sub.3 0-5 Li.sub.2O + Na.sub.2O + K.sub.2O 5-28 MgO + CaO + SrO + BaO + 5-25 ZnO TiO.sub.2 + ZrO.sub.2 0-6 P.sub.2O.sub.5 0-2

[0142] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0143] Most preferably, the soda-lime glass of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 4.93 to 10.25*10.sup.6/K:

TABLE-US-00006 TABLE 6 Composition (wt %) SiO.sub.2 55-76 Al.sub.2O.sub.3 0-5 B.sub.2O.sub.3 0-5 Li.sub.2O + Na.sub.2O + K.sub.2O 5-25 MgO + CaO + SrO + BaO + 5-20 ZnO TiO.sub.2 + ZrO.sub.2 0-5 P.sub.2O.sub.5 0-2

[0144] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0145] According to one embodiment of the invention, the glass is a borosilicate glass of the following composition (in wt %), with a thermal expansion coefficient from 3.0 to 9.01*10.sup.6/K:

TABLE-US-00007 TABLE 7 Composition (wt %) SiO.sub.2 60-85 Al.sub.2O.sub.3 0-10 B.sub.2O.sub.3 5-20 Li.sub.2O + Na.sub.2O + K.sub.2O 2-16 MgO + CaO + SrO + BaO + 0-15 ZnO TiO.sub.2 + ZrO.sub.2 0-5 P.sub.2O.sub.5 0-2

[0146] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0147] More preferably, the borosilicate glass of one embodiment of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 2.8 to 7.5*10.sup.6/K:

TABLE-US-00008 TABLE 8 Composition (wt %) SiO.sub.2 63-84 Al.sub.2O.sub.3 0-8 B.sub.2O.sub.3 5-18 Li.sub.2O + Na.sub.2O + K.sub.2O 3-14 MgO + CaO + SrO + BaO + 0-12 ZnO TiO.sub.2 + ZrO.sub.2 0-4 P.sub.2O.sub.5 0-2

[0148] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0149] Most preferably, the borosilicate glass of one embodiment of the present invention has the following composition (in wt %) with a thermal expansion coefficient from 3.18 to 7.5*10.sup.6/K:

TABLE-US-00009 TABLE 9 Composition (wt %) SiO.sub.2 63-83 Al.sub.2O.sub.3 0-7 B.sub.2O.sub.3 5-18 Li.sub.2O + Na.sub.2O + K.sub.2O 4-14 MgO + CaO + SrO + BaO + 0-10 ZnO TiO.sub.2 + ZrO.sub.2 0-3 P.sub.2O.sub.5 0-2

[0150] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0151] According to one embodiment, the glass is an alkali metal aluminosilicate glass of the following composition (in wt %), with a thermal expansion coefficient from 3.3 to 10.0*10.sup.6/K:

TABLE-US-00010 TABLE 10 Composition (wt %) SiO.sub.2 40-75 Al.sub.2O.sub.3 10-30 B.sub.2O.sub.3 0-20 Li.sub.2O + Na.sub.2O + K.sub.2O 4-30 MgO + CaO + SrO + BaO + 0-15 ZnO TiO.sub.2 + ZrO.sub.2 0-15 P.sub.2O.sub.5 0-10

[0152] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0153] More preferably, the alkali metal aluminosilicate glass of one embodiment of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 3.99 to 10.22*10.sup.6/K:

TABLE-US-00011 TABLE 11 Composition (wt %) SiO.sub.2 50-70 Al.sub.2O.sub.3 10-27 B.sub.2O.sub.3 0-18 Li.sub.2O + Na.sub.2O + K.sub.2O 5-28 MgO + CaO + SrO + BaO + ZnO 0-13 TiO.sub.2 + ZrO.sub.2 0-13 P.sub.2O.sub.5 0-9

[0154] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0155] Most preferably, the alkali aluminosilicate glass of one embodiment of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 4.4 to 9.08*10.sup.6/K:

TABLE-US-00012 TABLE 12 Composition (wt %) SiO.sub.2 55-68 Al.sub.2O.sub.3 10-27 B.sub.2O.sub.3 0-15 Li.sub.2O + Na.sub.2O + K.sub.2O 4-27 MgO + CaO + SrO + BaO + 0-12 ZnO TiO.sub.2 + ZrO.sub.2 0-10 P.sub.2O.sub.5 0-8

[0156] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0157] In one embodiment of the invention, the glass is an aluminosilicate glass having a low alkali content, with the following composition (in wt %) and with a thermal expansion coefficient from 2.8 to 6.5*10.sup.6/K:

TABLE-US-00013 TABLE 13 Composition (wt %) SiO.sub.2 50-75 Al.sub.2O.sub.3 7-25 B.sub.2O.sub.3 0-20 Li.sub.2O + Na.sub.2O + K.sub.2O 0-4 MgO + CaO + SrO + BaO + 5-25 ZnO TiO.sub.2 + ZrO.sub.2 0-10 P.sub.2O.sub.5 0-5

[0158] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0159] More preferably, the aluminosilicate glass of low alkali content according to one embodiment of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 2.8 to 6.5*10.sup.6/K:

TABLE-US-00014 TABLE 14 Composition (wt %) SiO.sub.2 52-73 Al.sub.2O.sub.3 7-23 B.sub.2O.sub.3 0-18 Li.sub.2O + Na.sub.2O + K.sub.2O 0-4 MgO + CaO + SrO + BaO + 5-23 ZnO TiO.sub.2 + ZrO.sub.2 0-10 P.sub.2O.sub.5 0-5

[0160] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0161] Most preferably, the aluminosilicate glass of low alkali content according to one embodiment of the present invention has the following composition (in wt %), with a thermal expansion coefficient from 2.8 to 6.5*10.sup.6/K:

TABLE-US-00015 TABLE 15 Composition (wt %) SiO.sub.2 53-71 Al.sub.2O.sub.3 7-22 B.sub.2O.sub.3 0-18 Li.sub.2O + Na.sub.2O + K.sub.2O 0-4 MgO + CaO + SrO + BaO + 5-22 ZnO TiO.sub.2 + ZrO.sub.2 0-8 P.sub.2O.sub.5 0-5

[0162] Optionally, coloring oxides may be added, such as Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, TiO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, from 0 to 2 wt % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.3, Cl, F, and/or CeO.sub.2 may be added as a refining agent, and from 0 to 5 wt % of rare earth oxides may further be added to impart magnetic, photonic or optical functions to the glass layer or glass sheet, and the total amount of the total composition is 100 wt %.

[0163] Generally, the intermediate glass, i.e. the second glass or any of the glasses located inside the first glass may as well be introduced into the space between core glass and outer glass in the form of a powder or as a sheet, this means as sheet glass.

[0164] The inner and intermediate glasses may as well be introduced as a coated glass into the angular or ovaloid first (outer) glass.

[0165] In one embodiment, an amorphous mixture of silicon dioxide and aluminum oxide is used for this purpose, and through the mixing ratio thereof it is possible to adjust the amount of thermal expansion a and hence the prestress of the later redrawn glass laminate.

[0166] In case of a pure SiO.sub.2 layer, the thermal expansion behavior is approximately that of quartz glass, and with an increasing proportion of Al.sub.2O.sub.3 (=6.5 . . . 8.9*10.sup.6/K) in the mixture, the value and therefore the coefficient of thermal expansion will correspondingly change to larger values. This permits to achieve predefined values of compressive stress by adjusting the thermal expansion coefficient.

[0167] In a further embodiment, glasses of a specific predetermined composition are ground to powder and are applied to the second glass, i.e. the core glass, or to one of the inner glasses in a spraying or dipping process or in a screen printing process. In a dipping process, for example, coating thicknesses in a range from 10 nm to about 300 nm can be achieved (with a single application), greater layer thicknesses can be achieved by repeated application of the glass layer.