Methods for molding composite polyester articles having rigid and flexible regions

A method of molding a composite molded article having discrete regions of relatively rigid and flexible resins bonded to one another along an interfacial fusion zone, said method comprising the steps of:

• positioning within a mold cavity a solid preform which will constitute said discrete region of said relatively rigid resin of said composite article and which consists essentially of a thermoplastic polyalkylene terephthalate resin selected from the group consisting of homopolymers of polybutylene terephthalate or polyethylene terephthalate, and copolymers mainly comprised of recurring polybutylene terephthalate or polyethylene terephthalate units and no greater than 30% by weight of other comonomeric units;
• and then
• forming said discrete regions of said flexible resin of said composite article which is bonded to said rigid region by introducing, into said mold cavity at a temperature which is between 10.degree. C. to 70.degree. C. greater than the melt temperature of said polyester resin forming said solid preform, a thermoplastic polyester elastomer resin which is the polycondensation reaction product of (a) a dicarboxylic acid or its ester-forming derivative, (b) a low molecular weight glycol or its ester-forming derivative, and (c) a polyoxyalkylene glycol having an average molecular weight of between 400 to 6000 or its ester-forming derivatives;
• establishing an interfacial fusion zone between said thermoplastic polyester and a surface region of said solid preform by allowing said introduced thermoplastic polyester elastomer resin to contact and at least partially melt said surface region of said solid preform by virtue of said thermoplastic polyester elastomer resin being at a temperature which is between 10.degree. C. to 70.degree. C. greater than the melt temperature of said polyester resin forming said solid preform thereby to establish said interfacial fusion zone and to cause said polyester elastomer resin to coalesce with said at least partially melted surface region of said polyester resin;
• and then
• allowing said at least partially melted surface region of said thermoplastic polyester resin and said molten polyester elastomer to solidify thereby fusing said solid preform and said polyester elastomer along said interfacial fusion zone, whereby said discrete regions of relatively rigid and flexible resins of said composite article are bonded one to another with increased fusion strength along said interfacial fusion zone.