VERFAHREN ZUM FESTIGEN VON AUS FLOAT-GLAS HERGESTELLTEN GLASGEGENSTAENDEN DURCH IONENAUSTAUSCH UND GEFESTIGTER GLASGEGENSTAND

摘要

The invention relates to a method of strengthening a glass article formed of sheet glass produced by the float process. The strengthening method includes a known ion exchange treatment to replace alkali metal ions in the surface layers of the glass with, e.g., alkali metal ions larger in ionic radius such as potassium ions. To prevent warping of the glass article during the ion exchange treatment by the influence of a metal element such as tin used as the molten metal in the float process and diffused into one surface of the sheet glass, the glass article is pretreated by contacting at least said surface with an external source of sodium ions and/or lithium ions and heating the glass article together with the external source of the alkali metal ions at 350 DEG -650 DEG C. for 0.01-100 hr. The pretreatment is neither preceded nor followed by grinding or polishing of said surface of the glass. By incorporating the pretreatment, the ion exchange strenthening can be accomplished to a high degree without degrading flatness and surface smoothness of the glass even when the glass thickness is not more than about 3 mm.