All-plastic heat-sealable container material and method of making

Claim 1

A multiple-layer composite blank product in flattened tube form from which containers can be made, said blank comprising a core layer of high density thermoplastic polymeric material having a specific gravity of about 0.950 to about 0.965, a thickness of 15 mils to about 17.5 mils, and a first predetermined softening point, and an outer layer of lower density thermoplastic polymeric material on each side of said core layer, said outer layers having a specific gravity of about 0.918 to about 0.930, a thickness of about 0.75 mils to about 2.0 mils, and a second predetermined softening point lower than said first predetermined softening point such that said outer layers, at unconfined edge portions of said blank, can be dynamically heated to sufficient molten condition for heat sealing while said core layer is not significantly thermally affected and provides structural support for said outer layer without distortion or shrivelling, said blank product being formed by the process of joining the polymeric materials while in molten condition and co-extruding them, and said flattened tube form having a heat-sealed side-seam and being formed by the process of dynamically heating said outer layers at unconfined edge portions of said blank to sufficient molten condition for heat-sealing, and thereafter joining edge portions of said blank together to form said side-seam in predetermined areas wherein said outer layers are molten, said core layer providing, during and after said dynamic heating, the sole structural support for said unconfined molten outer layers.