Tempered glazings, and glass for use therein

Abstract

Glazing, thermally tempered to required standards, are produced more readily by tempering panes having a high coefficient of thermal expansion (greater than 93×10 −7 per degree Centigrade) and for a low Fracture Toughness (less than 0.72 MPam 1/2 ). Use of glasses selected according to the invention enables thin glazings (especially glazings less than 3 mm thick) to be tempered to automotive standard with improved yields using conventional tempering methods, and thicker glazings to be tempered at lower quench pressure than required hitherto. Suitable glasses include glasses comprising, in percentages by weight, 64 to 75%, SiO 2 , 0 to 5% Al 2 O 3 , 0 to 5% B 2 O 3 , 9 to 16% alkaline earth metal oxide other than MgO, 0 to 2% MgO, 15 to 18% alkali metal oxide and at least 0.05% total iron (calculated as Fe 2 O 3 ).

1 . A thermally tempered glazing of soda lime silica glass produced by tempering a pane of glass having a coefficient of thermal expansion greater than 93×10 −7  per degree Centigrade and a Fracture Toughness of less than 0.72 MPam 1/2 .  
     
     
         2 . A thermally tempered glazing as claimed in  claim 1  having a thickness of less than 3 mm.  
     
     
         3 . A thermally tempered glazing as claimed in  claim 1  or  claim 2  wherein the glass has a coefficient of thermal expansion of at least 95×10 −7  per degree Centigrade.  
     
     
         4 . A thermally tempered glazing as claimed in any of the preceding claims wherein the glass has a Fracture Toughness of less than 0.70 MPam 1/2 .  
     
     
         5 . A thermally tempered glazing as claimed in any of the preceding claims wherein the coefficient of thermal expansion α per degree Centigrade and Fracture Toughness FT (in MPam 1/2 ) of the glass are such that  
       
         
           
             
               
                 
                   α 
                   × 
                   
                     10 
                     7 
                   
                 
                 FT 
               
               ≥ 
               135 
             
           
           
           
               
           
         
       
     
     
         6 . A thermally tempered glazing as claimed in any of the preceding claims wherein the glass has an alkali metal oxide content greater than 15% by weight.  
     
     
         7 . A thermally tempered glazing as claimed in any of the preceding claims wherein the glass has an alkali metal oxide content in the range 15 to 18% by weight.  
     
     
         8 . A thermally tempered glazing as claimed in any of the preceding claims wherein the glass has a ferrous oxide content (calculated as ferric oxide) of at least 0.2% by weight.  
     
     
         9 . A thermally tempered glazing as claimed in  claim 8  wherein the glass has a ferrous oxide content (calculated as ferric oxide) of at least 0.3% by weight.  
     
     
         10 . A thermally tempered glazing as claimed in any of the preceding claims wherein the glass has a magnesium oxide content of less than 2% by weight.  
     
     
         11 . A thermally tempered glazing as claimed in any of the preceding claims wherein the glass has a content of alkaline earth metal oxide (other than magnesium oxide) of at least 9% by weight.  
     
     
         12 . A thermally tempered glazing as claimed in any of the preceding claims having a thickness in the range 2.3 to 2.9 mm.  
     
     
         13 . A laminated automotive glazing comprising at least one semi-tempered glass pane having a thickness in the range 1.5 mm to 2.5 mm, produced by semi-tempering a pane of glass as defined in any of  claims 1  to  11 .  
     
     
         14 . A method of tempering a glazing comprised of glass as defined in any of  claims 1  to  11  characterised by operating at a quench pressure at least 20% than the quench pressure required to temper a corresponding glazing of standard composition to the required standards under otherwise similar conditions.  
     
     
         15 . A method as claimed in  claim 14  wherever the quench pressure is at least 25% less than the quench pressure required to temper a corresponding glazing of standard composition to the required standards under otherwise similar conditions.  
     
     
         16 . A method as claimed in  claim 14  or  claim 15  wherein the glazing is of float glass having a thickness in the range 3 mm to 5 mm.  
     
     
         17 . A method as claimed in  claim 16  wherein the quench pressures used range from not more than 12.5 kPa for 3 mm glass to not more than 5kPa for 5 mm glass.  
     
     
         18 . A method as claimed in  claim 17  wherein the quench pressures used range from not more than 10 kPa for 3 mm glass to not more than 5 kPa for 5 mm glass.  
     
     
         19 . A method of tempering a glazing comprised of glass as defined in any of  claims 1  to  11  characterised by operating at a quench pressure of not more than 12.5 kPa for 3 mm glass.  
     
     
         20 . A method of tempering a glazing comprised of glass as defined in any of  claims 1  to  11  characterised by operating at a quench pressure of not more than 10 kPa for 4 mm glass.  
     
     
         21 . A method of tempering a glazing comprised of glass as defined in any of  claims 1  to  11  characterised by operating at a quench pressure of not more than 6 kPa for 5 mm glass.  
     
     
         22 . A thermally tempered glazing of soda lime silica glass having a thickness of less than 3 mm, optionally being a glazing as claimed in any of  claims 1  to  11 , the glass being green glass containing at least 14.5% by weight Na 2 O, at least 10.5% by weight CaO, at least 0.5% by weight total iron (measured as Fe 2 O 3 ) and being substantially magnesium-free, the glass having a ferrous value (% ferrous) of at least 30%.  
     
     
         23 . A laminated automotive glazing, optionally being a glazing as claimed in  claim 13 , comprising at least one semi tempered glass pane having a thickness in the range 1.5 mm to 2.5 mm, and being of green glass having a composition as specified in  claim 18 .  
     
     
         24 . A method of tempering an automotive glazing, optionally being a method as claimed in any of  claims 14  to  21 , the automotive glazing being of glass having a composition as specified in  claim 18  characterised by operating at a quench pressure 10% less, preferably 25% less than the quench pressure required to toughen a corresponding glazing of standard composition to the required standards under otherwise similar conditions.  
     
     
         25 . A soda lime silica glass in sheet form of composition comprising, in percentages by weight  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   SiO 2   
                   64-75% 
                 
                     
                   Al 2 O 3   
                    0-5% 
                 
                     
                   B 2 O 3   
                    0-5% 
                 
                     
                   Alkaline earth metal oxide (other than MgO) 
                    9-16% 
                 
                     
                   Alkali metal oxide 
                   15-18% 
                 
                     
                   MgO 
                   <2% 
                 
                     
                   Total iron (calculated as Fe 2 O 3 ) 
                   ≧0.05% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         26 . A soda lime silica glass as claimed in  claim 25  of composition comprising, in percentages by weight:  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   SiO 2   
                   67-73% 
                 
                     
                   Al 2 O 3   
                    0-3% 
                 
                     
                   B 2 O 3   
                    0-3% 
                 
                     
                   Alkaline earth metal oxide (other than MgO) 
                   10-14% 
                 
                     
                   Alkali metal oxide 
                   15-17% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         27 . A soda lime silica glass as claimed in  claim 25  or  26  wherein the ratio of ferrous iron (calculated as ferric oxide) to total iron (calculated as ferric oxide) is less than 30%.  
     
     
         28 . A soda lime silica glass as claimed in any of  claims 25  to  27  having a thickness less than 2.8 mm.  
     
     
         29 . A thermally tempered pane of soda lime silica glass of composition as claimed in any of  claims 25  to  28 .