Float glass process for making thin flat glass and thin flat glass substrate made with same

Abstract

The thin flat glass substrate, especially for display engineering, has a thickness of less than 1.5 mm, a length of at least 1800 mm, a width of at least 1800 mm and a difference between a smallest thickness and largest thickness of less than 50 μm. The float glass process for making the improved flat glass substrate provides flags ( 9 ) in the molten metal bath in the hot-spread region on both sides of the forming glass sheet to minimize the variation in thickness of the thin flat glass substrate formed by the process.

1 . A flat glass substrate, especially for display engineering, with a thickness of less than 1.5 mm, a length of at least 1800 mm, a width of at least 1800 mm and a difference between a smallest value of said thickness and a largest value of said thickness of less than 50 μm;
 wherein said flat glass substrate is made by a float glass process comprising the steps of:   a) pouring a hot glass melt ( 4 ) on a molten metal bath ( 2 ) contained in a float tank, so that melted glass freely spreads out in a hot spread region (I) of the molten metal bath, said hot spread region being a section of the molten metal bath in which the melted glass freely spreads under the influence of gravity;   b) arranging flags ( 9 ), which do not contact a glass sheet ( 3 ,  3 ′) forming from the melted glass, in the molten metal bath in the hot spread region on both sides of the melted glass with a height, an orientation, and with a spacing from a side wall of the float tank, a spacing from the melted glass, and a spacing from a bottom ( 11 ) of the float tank, so that thickness variations in the glass sheet forming from the melted glass are minimized;   c) engaging the glass sheet with top rollers in a region of the metal bath that is downstream from the hot spread region to further draw out the glass sheet; and   d) imparting a final outlet speed to the glass sheet ( 3 ,  3 ′) by accelerating the glass sheet.   
     
     
         2 . The flat glass substrate as defined in  claim 1 , wherein said thickness is from 0.4 mm to 1.1 mm. 
     
     
         3 . The flat glass substrate as defined in  claim 1 , with an edge length of up to 2500 mm. 
     
     
         4 . The flat glass substrate as defined in  claim 1 , wherein said difference is less than 30 μm. 
     
     
         5 . The flat glass substrate as defined in  claim 1 , wherein said difference is less than 15 μm. 
     
     
         6 . The flat glass substrate as defined in  claim 1 , containing at most 1000 ppm of sodium ions. 
     
     
         7 . The flat glass substrate as defined in  claim 1 , wherein in said float glass process each of the flags is a plate immersed in the molten metal bath between the side wall of the float tank and an outer edge of the glass sheet ( 3 , 3 ′) without contacting the glass sheet. 
     
     
         8 . The flat glass substrate as defined in  claim 1 , wherein in said float glass process said flag extends above the molten metal bath in a side region adjacent to said side wall and is oriented substantially transverse to a feed direction of the glass sheet on the molten melt bath. 
     
     
         9 . The flat glass substrate as defined in  claim 1 , wherein in said float glass process said flags ( 9 ) are made of graphite and oriented at an angle of 90° to 30° to a feed direction of the glass sheet ( 3 ,  3 ′).