Method and apparatus for making a glass laminate

Abstract

An apparatus for making a glass laminate, including: a source of a glass core sheet; a source of a first force that tensions the glass core sheet in a first axial direction; a source of a second force that tensions the glass core sheet in a second axial direction; and at least one molten glass reservoir extending along a length of the apparatus and on opposite sides of the glass core sheet that delivers a source of at least two glass dads to the opposite side surfaces of the bi-axially tensioned glass core sheet. Also disclosed are methods for making a glass laminate sheet using the disclosed apparatus, as defined herein.

What is claimed is: 
     
         1 . An apparatus for making a glass laminate comprising:
 a source of a glass core sheet;   a source of a first force that produces a first tension on the glass core sheet in a first axial direction;   a source of a second force that produces a second tension on the glass core sheet in a second axial direction; and   at least one molten glass reservoir extending along a length of the apparatus and on opposite sides of the glass core sheet that delivers a source of at least two glass dads to the surface of the first and second axially tensioned glass core sheet.   
     
     
         2 . The apparatus of  claim 1  further comprising the at least one molten glass reservoir having a pass-through region situated between the source of at least two glass dads. 
     
     
         3 . The apparatus of  claim 1  wherein the first axial direction and the second axial direction are orthogonal. 
     
     
         4 . The apparatus of  claim 1  wherein the source of the first force and the source of the second force, when applied to the core glass sheet, produce a biaxial tension on the core glass sheet. 
     
     
         5 . The apparatus of  claim 1  wherein the source of the glass core sheet is selected from at least one of: a preformed sheet; a sheet generated in situ; or a combination thereof. 
     
     
         6 . The apparatus of  claim 1  wherein the source of the glass core sheet is static, semi-static, or dynamic. 
     
     
         7 . The apparatus of  claim 1  wherein the CTE of the core sheet (CTE core ) is greater than the CTE of the clad layer (CTE clad ), and the difference CTE clad −CTE core  is less than 10×10 −7 /° C. 
     
     
         8 . The apparatus of  claim 1  wherein the glass laminate has a compressive stress strength of from 20 to 50 MPa, and the glass laminate is at least one of: alkali-free, a high scratch resistant surface having a Knoop scratch threshold larger than 5 Newton, is free of ion-exchange, or a combination thereof. 
     
     
         9 . A method for strengthening a glass laminate, the glass laminate having a glass core sheet and at least one glass clad layer on at least one of the opposite sides of the glass core sheet, comprising:
 heating the glass laminate, the glass laminate having the glass core sheet has a strain point having a difference of at least 50° C. compared to the strain point of the at least one glass clad layer;   applying biaxial force to the glass core sheet while the glass clad layers are in a state of stress relaxation;   cooling the glass laminate; and   releasing the biaxial force on the glass core sheet.   
     
     
         10 . The method of  claim 9  wherein the strengthened glass laminate has a compressive stress on the clad layers that is increased by from 10 MPa to 200 MPa compared to an un-strengthened glass laminate. 
     
     
         11 . The method of  claim 9  wherein heating the glass laminate is accomplished at from 560 to 600° C. 
     
     
         12 . A method for strengthening a glass laminate, the glass laminate having a glass core sheet and a glass clad layer on at least one of the opposite sides of the glass core sheet, comprising:
 a first heating of the glass laminate to 50° C. below the strain point of the glass core sheet, and the glass core sheet has a strain point of at least 50° C. higher than the strain point of the glass clad layer;   a second heating of the glass laminate to between the anneal point of the glass clad and the strain point of the glass core sheet, the second heating is accomplished at a temperature above the strain point of the clad layer and below the strain point of the core sheet;   bi-axially tensioning the second heated glass laminate at from 10 to 50 MPa for a sufficient time for the stress in the clad layers to relax;   cooling the laminate to ambient temperature; and   removing the bi-axial tensioning.   
     
     
         13 . The method of  claim 12  wherein removing the bi-axial tensioning creates a compressive stress on glass clad layers. 
     
     
         14 . A method for strengthening a glass laminate, the glass laminate having a glass core sheet and a glass clad layer on at least one of the opposite sides of the glass core sheet, comprising:
 contacting the opposite sides of a biaxially tensioned core glass sheet with molten clad glass from a source of molten clad glass.   
     
     
         15 . The method of  claim 14  wherein the glass laminate strengthening is accomplished free of a CTE mismatch condition. 
     
     
         16 . The method of  claim 14  wherein the source of molten clad glass is a modified fusion draw apparatus. 
     
     
         17 . The method of  claim 14  wherein the biaxially tensioned core glass sheet is a preformed single sheet, or is continuously produced in situ by a modified double fusion draw apparatus. 
     
     
         18 . A glass laminate article comprising:
 a glass core sheet; and   at least one glass clad layer on at least one side of the glass core sheet, wherein the glass laminate article is birefringent.   
     
     
         19 . The article of  claim 18  wherein the birefringent property is not attributable to:
 thermal tempering, a polymer, an anisotropic additive, or any combination thereof.