Sheet structure

Abstract

The new composite flexible sheet material comprises a base sheet structure made up of a thermoplastic resin layer which is flowable or fusible at predetermined sealing conditions, plus a polyester backing layer non-flowable or non-fusible at said conditions. The thermoplastic layer is thicker than the backing layer. Adhered to the thermoplastic layer is a layer of polyester fibrous material not flowable or fusible at said sealing conditions. The fibrous material layer is capable of being substantially submerged into the thermoplastic layer upon the application of sealing conditions. A preferred invertible envelope-type packet is formed by using a composite sheet having a thermoplastic fusible layer and a non-fusible backing layer, and involves placing the thermoplastic layer inwardly and the backing layer on the exterior of the envelope. Opposing walls of the envelope are united along portions thereof adjacent the envelope cavity. The expanse of the sheet material forming each opposing wall extends beyond a seal structure along one edge of the envelope cavity to form a pair of outwardly projecting ear-flaps. Sheet material forming one of the ear-flaps is folded back upon itself over the thermoplastic layer side thereof. Part of this folded back portion extends as a partition member substantially throughout the seal structure along the one edge; and this seal structure along said one edge is temporary and rupturable at the interface between the backing layer of the partition member and the thermoplastic layer of the opposing sheet.