METHOD FOR STRENGTHENING AND BENDING GLASS SHEETS

Abstract

Method for strengthening and bending glass sheets, wherein a saturated saline solution is applied to glass sheets, followed by a rapid temperature change, allowing the salt to 5 precipitate. The glass sheets are then evenly coated with a recrystallized salt. Subsequently, the glass sheets are ion exchanged and bent at a predetermined temperature for a predetermined period of time.

Claims

1. A method for strengthening a glass sheet while bending thereof, comprising the steps of: applying a saturated solution at temperature T.sub.1 on the glass sheet at temperature T.sub.2, wherein the saturated solution contains an ionic salt and a liquid solvent, and wherein T.sub.1>T.sub.2; allowing the solution on the glass sheet to cool, thereby precipitating the ionic salt as soon as the solution temperature decrease, leaving a crust of salt adhered to the surface of the glass sheet; heating the glass sheet at a predetermined temperature T.sub.3 for a predetermined period of time t.sub.3 for bending it by a bending process, wherein the temperature T.sub.3 ranges from the temperature at which the viscosity of the glass sheet is 10.sup.14.6 poises to the temperature at which the viscosity of the glass sheet is 10.sup.7.6 poises, and the time t.sub.3 is enough to impart a selected permanent curvature to the glass sheet; and cooling the glass sheet.

2. The method of claim 1, further comprising, between the step of allowing the solution on the glass sheet to cool and the step of heating the glass sheet, the steps of: providing at least an additional glass sheet; and positioning the glass sheet in contact with said at least additional glass sheet, so that the crust of salt on the surface of the glass sheet become trapped between the surfaces in contact during the heating step.

3. The method of claim 1, wherein the step of applying the saturated solution comprises: immersing the glass sheet in the saturated solution; and immediately extracting the glass sheet from said solution.

4. The method of claim 1, wherein the step of applying the saturated solution comprises atomizing the solution on the glass sheet via spray means.

5. The method of claim 1, wherein the step of applying the saturated solution comprises painting the solution on the glass sheet via paint application means.

6. The method of claim 1, wherein the steps of heating the glass sheet and cooling the glass sheet are carried out by a heat source with at least one heat transfer mechanism selected from the group consisting of convection, radiation and conduction.

7. The method of claim 1, wherein in the step of allowing the solution on glass sheet to cool, the cooling rate is from 1 C./min to 100 C./min, preferably from 1 C./min to 50 C./min.

8. The method of claim 1, wherein in the step of allowing the solution on the glass sheet to cool, the thickness of the crust lies between 10 and 600 m, preferably between 10 and 400 m, and even more preferably between 10 and 200 m.

9. The method of claim 1, wherein the glass sheet is selected from the group consisting of soda-lime, alkali aluminosilicate, lithium aluminosilicate and alkali alkaline earth aluminosilicate.

10. The method of claim 1, wherein the ionic salt is selected from the group consisting of ionic salt of the form ANO.sub.3, mixed ionic salt of the form (A, B)NO.sub.3, and a mixture thereof; wherein both A and B are an alkali metal.

11. The method of claim 1, wherein the ionic salt is a mixed ionic salt of the form (C, D)NO.sub.3; wherein C is an alkali metal and D is selected from the group consisting of transition metals and rare-earth metals.

12. The method of claim 1, wherein the ionic salt contains at least one salt selected from the group consisting of sulfides, chlorides, halides and hydrates.

13. The method of claim 1, wherein the liquid solvent is selected from the group consisting of water and at least one organic solvent.

14. The method of claim 1, wherein in the step of heating the glass sheet, the bending process is carried out by a technique selected from the group consisting of gravity bending, press bending and techniques that are hybrids thereof.

15. The method of claim 14, wherein the selected technique is gravity bending, and further comprising, between the step of allowing the solution on the glass sheet to cool and the step of heating the glass sheet, the steps of: providing an additional glass sheet; and positioning the glass sheet above the additional glass sheet, so that the crust of salt on the bottom surface of the glass sheet is retained in contact with said bottom surface of the glass sheet during the heating step.

16. The method of claim 14, wherein the selected technique is press bending, and further comprising, between the step of allowing the solution on the glass sheet to cool and the step of heating the glass sheet, the steps of: providing two additional glass sheets; and sandwiching the glass sheet between the additional glass sheets, so that the crust of salt on both top and bottom surfaces of the glass sheet is retained in contact with said surfaces of the glass sheet during the heating step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These features and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, wherein:

[0018] FIG. 1 shows a saturated solution application process according to one embodiment of the present invention.

[0019] FIG. 2 shows an embodiment of the present invention wherein the bending process is carried out by the gravity bending technique.

[0020] FIG. 3 shows an embodiment of the present invention wherein the bending process is carried out by the press bending technique.

[0021] FIG. 4 shows a first example of a glass package configuration according to one embodiment of the present invention.

[0022] FIG. 5 shows a second example of a glass package configuration according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring now to the drawings, there are shown preferred embodiments of the method according to the present invention.

[0024] FIG. 1 shows spray means 1 applying a saturated solution 2 on a glass sheet 3. The saturated solution 2 is previously prepared by dissolving ionic salt in a liquid solvent (e.g. deionized water) at a temperature T.sub.1, wherein the solubility of the salt is higher as T1 increases according to the solubility curve of said salt which plots the changes of the solubility of a salt at different temperatures in a solvent. The ionic salt is a salt with the generic formula ANO.sub.3, or a mixed ionic salt (A, B)NO.sub.3, or a mixture thereof; wherein both A and B are an alkali metal (e.g. NaNO.sub.3, KNO.sub.3 and LiNO.sub.3, among others). The saturated solution 2 at temperature T.sub.1 is applied on the glass sheet 3 at temperature T.sub.2, wherein T.sub.1 is greater than T.sub.2. Next, the solution 2 on the glass sheet 3 is allowed to cool at a cooling rate from 1 C./min to 100 C./min, preferably from 1 C./min to 50 C./min, thereby precipitating the ionic salt as soon as the solution temperature decrease along the solubility curve of said ionic salt, i.e. as temperature decreases it precipitates as much ionic salt as corresponds to the change of temperature at the curve. As a result, the glass sheet 3 is evenly coated with a recrystallized salt, forming a crust of salt on the surface of the glass sheet 3. Next, the glass sheet 3 is heated inside a heat source 8 (FIG. 2) at a predetermined temperature T.sub.3 for a predetermined period of time t.sub.3 for bending it by a bending process, wherein the temperature T.sub.3 ranges from the temperature at which the viscosity of the glass sheet is 10.sup.14.6 poises to the temperature at which the viscosity of the glass sheet is 10.sup.7.6 poises, and the time t.sub.3 is enough to impart a selected permanent curvature to the glass sheet 3. Lastly, the glass sheet 3 is cooled inside the heat source in a controlled manner, preventing the glass sheet from shattering due to sudden temperature change.

[0025] FIG. 2 shows an embodiment wherein the bending process is carried out by the gravity bending technique. In this technique, between the step of allowing the solution on the glass sheet to cool and the step of heating the glass sheet, an additional glass sheet 4 is positioned below the glass sheet 3, forming a glass package 5, so that the crust of salt on the bottom surface 6 of the glass sheet 3 is retained in contact with said bottom surface 6 during the heating step. The glass package 5 is supported on a bending mold 7, and then placed in the heat source 8 for performing the heating step, wherein the force of gravity acts on the glass package 5, causing to sag under its own weight onto the bending mold 7.

[0026] FIG. 3 shows an embodiment wherein the bending process is carried out by the press bending technique. In this technique, between the step of allowing the solution on the glass sheet to cool and the step of heating the glass sheet, the glass sheet 3 is sandwiched between two additional glass sheets 9, forming a glass package 10, so that the crust of salt on both top 11 and bottom 12 surfaces of the glass sheet 3 is retained in contact with said surfaces 11-12 during the heating step. The glass package 10 is heated inside a heat source and then compression forces are applied to it by press members 13-14 having complementary surfaces corresponding to the desired shape.

[0027] In certain applications, wherein it is required to bend two or more glass sheets simultaneously (e.g. production process of a laminated glass), the glass sheets are disposed one above the other, forming a glass package. Thus, depending on the glass package configuration, some of these glass sheets can be used as additional glass sheets. For example, according to the present invention, in a production process of two laminated glass, wherein the selected bending technique is gravitational bending, and the required laminated glass has the follow composition:

[0028] Laminated glass I: a chemically strengthened alkali aluminosilicate glass sheet and a borosilicate glass sheet; and

[0029] Laminated glass II: two chemically strengthened alkali aluminosilicate glass sheets;

[0030] the glass package 15, in the former case, comprises a borosilicate glass sheet 16 at the bottom and an alkali aluminosilicate glass sheet 17 at the top (FIG. 4), wherein the alkali aluminosilicate glass sheet 17 has a crust of salt adhered to its surface, so that the borosilicate glass sheet 16 acts as an additional glass sheet, which retains in contact the crust of salt on the bottom surface 18 of the alkali aluminosilicate glass sheet 17 with said surface 18 during the heating step.

[0031] In the latter case, the glass package 19 comprises an alkali aluminosilicate glass sheet 20 sandwiched by a sacrificial glass sheet 21 (e.g. borosilicate glass sheet) at the bottom and an alkali aluminosilicate glass sheet 22 at the top (FIG. 5), wherein both alkali aluminosilicate glass sheets 20, 22 have a crust of salt adhered to their surface. Despite not being part of the laminated glass composition, the sacrificial glass sheet 21 is required as an additional glass sheet during the heating step in order to retain in contact the crust of salt on the bottom surface 23 of the sandwiched alkali aluminosilicate glass sheet 20 with said surface 23.

[0032] In the embodiments depicted in FIGS. 1-5, the heat source is a furnace. In all embodiments, the heat source is provided with at least one heat transfer mechanism selected from the group consisting of convection, radiation and conduction.

[0033] Moreover, in the embodiments depicted in FIGS. 1-5, the thickness of the crust lies between 10 and 60 m. However, in other embodiments, the thickness of the crust lies between 10 and 600 m, preferably between 10 and 400 m, and even more preferably between 10 and 200 m.

[0034] Additionally, in the embodiment illustrated in FIG. 1, the saturated solution is atomized on the glass sheet. However, in other embodiments, the saturated solution is applied to the glass sheet by others means. In an embodiment, the application step is performed by immersing the glass sheet in the saturated solution. In an alternative embodiment, the saturated solution is applied to glass sheet by painting the saturated solution via paint application means.

[0035] As can be noted, the present invention is not limited to a particular shape, geometry or size of the glass sheet. Furthermore, the invention can be used independently of the glass type and/or composition used, provided that the glass sheet contains alkalis or transition metals in its composition. Moreover, the present invention is able to take advantage of the chemical strengthening process to change others glass surface properties such as luminescence, index of refraction, antimicrobial properties and antibacterial properties, among others. Therefore, in the embodiments in which at least one of these properties are required, the ionic salt is a mixed ionic salt of the form (C, D)NO.sub.3; wherein C is an alkali metal and D is selected from the group consisting of transition metals and rare-earth metals.

[0036] Alternatively, in some embodiments, the ionic salt contains at least one salt selected from the group consisting of sulfides, chlorides, halides or hydrates.

[0037] In several embodiments, the glass sheets are made of soda-lime, alkali aluminosilicate, lithium aluminosilicate, alkali alkaline earth aluminosilicate or another silicate.

[0038] In all embodiments, the liquid solvent is water or at least one organic solvent (e.g. ammonia and glycerol, among others). In some embodiments, wherein the liquid solvent is water, the liquid solvent is selected from the group consisting of deionized water, distilled water and potable water.

[0039] Although, only two bending techniques were exemplified herein, one of ordinary skill in the art would appreciate that the present invention can be performed with other well-known bending techniques (e.g. hybrid techniques).

[0040] Subsequently, a practical example will be set forth to clarify the effects of the present invention.

EXAMPLE

[0041] A mixture of equal parts of KNO.sub.3 and deionized water were mixed at 80 C. The saturated solution was painted with a brush on a cold alkali aluminosilicate glass sheet (AAS). The KNO.sub.3 precipitated almost immediately after contacting the surface of the glass sheet. The painted glass sheet was then sandwiched by a soda-lime silicate glass sheet at the bottom and a borosilicate glass sheet at the top, forming a glass package. The glass package entered to a gravity forming furnace preset at 625 C. and hold it for 420 seconds. During this time, the glass package decreased the temperature to 576 C. After that, the furnace was allowed to cool down to about 300 C., before removing the curved glass. The total time of the glass package inside the furnace and above the melting point of KNO.sub.3 was of 16 minutes. The result of the painted glass sheet is reported as follow:

TABLE-US-00001 TABLE 1 Compressive StressCS Depth of LayerDOL Type of glass (MPa) (m) AAS 507 20

[0042] In the example, the compressive strength and depth of layer values obtained (TABLE 1) are typically what have been reported in the literature for the conventional ion exchange method.

[0043] It must be understood that this invention is not limited to the embodiments described and illustrated above. A person skilled in the art will understand that numerous variations and/or modifications can be carried out that do not depart from the spirit of the invention, which is only defined by the following claims.