Corning Incorporated
COMPOSITIONS AND METHODS FOR PREVENTING BAGGY WARP DEFECT

Abstract:

An aluminosilicate glass, including in mole percent on an oxide basis, MgO+CaO+SrO+Li.sub.2O+ZnO+Y.sub.2O.sub.3+ZrO.sub.2+La.sub.2O.sub.3+TiO.su- b.2+Nb.sub.2O.sub.5+Ta.sub.2O.sub.5 in a range of from 5 mol % to 25 mol %. The glass is processable by (i) flowing the glass in a molten state over forming surfaces to form a glass ribbon, the forming surfaces converging at a root and (ii) drawing the glass ribbon using pulling rollers to form a glass sheet, wherein the pulling rollers are spaced at a pulling roller distance from the root, and wherein the glass exhibits a viscosity curve slope obtained by plotting a temperature gradient to increase a root viscosity of the glass at the root, to a higher viscosity at one of several positions between the root and the pulling rollers, and a viscosity of the glass at the pulling rollers. The glass comprises a liquidus viscosity, the root viscosity being less than the liquidus viscosity, and the glass comprising a viscosity curve slope that prevents a baggy warp defect. In certain embodiments, when the root viscosity of the glass is in a range of from about 70 kP to about 90 kP, and the viscosity of the glass at the pulling rollers is greater than 90 kP and less than or equal 1.times.10.sup.8 kP, the temperature gradient is less than 150.degree. C.