Patent ID: 7946128

Claim:
A method for producing alkali-metal-oxide-free glass sheets by a downdraw process comprising selecting, melting, and fining batch materials so that the glass making up the sheets comprises SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO and BaO, and, on an oxide basis, comprises in mole percent: SiO 2 67.0-70.0 B 2 O 3 8.0-11.0 Al 2 O 3 9.5-12.0 MgO <3.7 CaO 5.5-11.2 SrO ≦2.2 BaO ≦2.2 MgO/CaO ≦0.7 wherein: (a) 1.0≦Σ(MgO+CaO+SrO+BaO)/(Al 2 O 3 )≦1.25, where Al 2 O 3 , MgO, CaO, SrO, and BaO represent the mole percents of the respective oxide components; (b) 2.5 MgO+5 CaO+6 SrO+7 BaO≦59; (c) the fining is performed without the use of substantial amounts of either arsenic or antimony, the glass making up the glass sheets comprising, on an oxide basis, at most 0.05 mole percent As 2 O 3 and at most 0.05 mole percent Sb 2 O 3 ; (d) the glass making up the glass sheets has a coefficient of thermal expansion less than or equal to 36×10 −7 /° C. over the temperature range of 0 to 300° C.; (e) the glass making up the glass sheets has a density less than or equal to 2.46 g/cc; (f) the glass making up the glass sheets has a liquidus temperature minus softening point up to 200° C.; and (g) a population of 50 sequential glass sheets produced by the downdraw process from the melted and fined batch materials comprising an average gaseous inclusion level of less than 0.10 gaseous inclusions/cubic centimeter, where each sheet in the population has a volume of at least 500 cubic centimeters.