Effect of mold stiffness on surface flatness of mold-pressed glass

This paper presents the effect of mold stiffness on the surface flatness of mold-pressed glass for glass molding and imprint processes. Phosphate and borosilicate glasses were pressed at their viscoelastic temperature region using flat molds of several kinds and subsequently cooled to room temperature. Surface flatness of the mold-pressed glasses was examined using a stylus surface profilometer. The glass surface curvature was observed after spontaneous demolding by thermal shrinkage stress of the glass and the mold during cooling. The curvature decreased with increasing mold stiffness, as determined by the Young’s modulus and mold thickness. The curvature also decreased with decreasing cooling rate during cooling, which was discussed in terms of the glass fragility. It was demonstrated that the Young’s modulus, mold thickness, and cooling rate are key factors for the control of the molded glass surface flatness.