U.S. Pat. No. 3,426,100 to McDonough relates to copolymers of crystallizable linear polyesters and polycarbonates. Although such polyesters have improved properties, they are not pertinent to the present invention since they do not even suggest melt blends of two different types of polyesters.
British Pat. No. 1,546,698 relates to transparent sheets made from blends of polycarbonate and polyethylene terephthalate. However, once again no suggestion is made of melt blends of applicants' specific polyesters.
"Crystallization Studies of Blends of Polyethylene Terephthalate and Polybutylene Terephthalate" by Escala and Stein, Advances in Chemistry series, 176, 455 (1979) relates to a study wherein a single glass transition temperature for a blend is observed which varies with composition suggesting that the components are compatible in the amorphous phase. This article is not pertinent since it does not relate to any use of a melt blend of polyisophthalate.
A fairly thorough discussion of various polymer blends is set forth in "Polymer Blends," Vol. 1, Chapter 10, by Paul and Newman, Academic Press, 1978. However, no suggestion is contained therein with regard to applicants' melt blends of polyesters.