Press method of making expanded thermoplastic sheet

Claim 1

The method of claim 1 wherein the final sheet is a laminate comprising an interior core portion formed of expanded ABS resinous material and unexpanded thermoplastic polymeric resinous facing sheets integrally bonded to said core portion on each side thereof.

Claim 5

The method of making an expanded thermoplastic polymeric resinous sheet having an expanded core portion faced on both sides with a layer of non-expanded thermoplastic polymeric resinous material, each layer of non-expanded thermoplastic material being integrally bonded to the expanded thermoplastic sheet, said method comprising: positioning one or more plies of expandable thermoplastic polymeric resinous material within a frame, said expandable thermoplastic material being disposed between plies of a non-expandable thermoplastic polymeric resinous material to form a stack of plies of non-expandable and expandable thermoplastic material, at least one ply of said expandable thermoplastic material containing a solid decomposeable blowing agent therefor, said frame having a thickness less than said stack of plies of thermpolastic material and being of a size such that free space is provided between the inner periphery of said frame and the outer periphery of said stack of plies; placing said frame with said stack of plies positioned therein between upper and lower clamping plate means to provide a stacked assemblage, the area of said clamping plate means being at least equal to the area encompassed by said frame; clamping said stacked assemblage between upper and lower platen press means, said platen press means having an area at least slightly larger than the area of said clamping plate means and at least one of said platens being a driven platen, said clamping exerting sufficient pressure to said stacked assemblage to expel air from said stack of plies and cause said frame to contact only one of said clamping plate means such that said expelled air is free to escape from said assemblage through said free space; applying pressure to said stacked assemblage causing said frame member to contact both of said clamping plates and completely enclose said stack of plies, and concurrently heating said stacked assemblage, said pressure and said heating being sufficient to decompose said blowing agent and fuse said non-expandable thermoplastic material to said expandable thermoplastic material and said expandable thermoplastic material to itself, lateral flow of said expandable thermoplastic material being limited by said frame; instantaneously relieving said applied pressure enabling said platnes to move apart while concurrently continuing to heat said assemblage to effect vertical expansion of said expandable thermoplastic material, the relief of said pressure being controlled so as to maintain surface-to-surface contact between said spaced-apart platens and said clamping plates, between said clamping plates and the plies of said non-expandable thermoplastic material, and between the plies of said non-expandable thermoplastic material and the expanding thermoplastic material without permitting any free space to develop within said expanding thermoplastic material, between said expanding thermoplastic material and said non-expandable thermoplastic material, between said non-expandable thermoplastic material and said clamping plates, and between said clamping plates and said platens during said vertical expansion; cooling said assemblage while retaining contact between said platens and said clamping plates, between said clamping plates and said non-expandable thermoplastic material, and between said non-expandable thermoplastic material and said expanded thermoplastic material at the desired, final thickness of the expanded thermoplastic material until said expanded thermoplastic material has solidified and stabilized to form an expanded thermoplastic polymeric resinous sheet; and, removing from said assemblage said expanded thermoplastic polymeric resinous sheet having a layer of non-expandable thermoplastic polymeric resinous material integrally bonded to both faces thereof.