Method for making hot-pressed thermoplastic elements for glass-plastic lenses

A method for reforming thin, tough thermoplastic film to provide a curved plastic element of nominally zero focal power, precise curvature, and optical quality, while avoiding the introduction of heat loop defects into the element, which comprises the steps of:

• selecting for reforming a tough thermoplastic film having a thickness less than or equal to about 0.015 inches;
• heating the thermoplastic film to a temperature above its glass transition temperature while pressing the film between a rigid reforming surface of convex curvature and a rigid reforming surface of concave curvature, each of said surfaces being finished to optical quality and having the same nominal diopter curvature, the convex reforming surface having a radius of curvature which is about 1-25 mils less than the radius of curvature of the concave reforming surface;
• and cooling the thermoplastic film to a temperature at least below its glass transition temperature prior to separating the film from the reforming surfaces.