THERMAL DIMENSIONAL STABILITY TREATMENT OF VITREOUS SHEET MATERIAL BY CONTACTING WITH A MOLTEN ALKALI METAL SALT

摘要

A sheet of vitreous material for use as a substrate is produced by contacting the sheet with a molten alkali metal salt prior to any firing step or other heat treatment associated with the application of coating layers. The so-treated sheet has improved thermal dimensional stability, such that wide ranges of heating and cooling applied by the heat treatment do not create an unacceptable amount of shrinkage of the vitreous material.