Improvements in or relating to sacks

988,946. Plastic valve bags. BOWATER RESEARCH & DEVELOPMENT CO. Ltd. Aug. 2, 1962 [Aug. 16, 1961], No. 29635/61. Heading B8K. A valve 20 (Fig. 4) is formed in a flattened gussetted bag of heat-sealable thermoplastics by an extension of the gusset 3, 4 folded in, together with parts of the side walls, about the line 21, 22, 23 to form a sleeve, and welded at 24 to the overlying walls of the bag. The bag illustrated opens to block-bottom form (Fig. 5) closed by a central weld 13. Part of the valve may be cut away at 27, and the outer wall of the sleeve may be welded to the bag bottom. The bag may be of polyvinyl chloride, or of paper coated on one or both sides with a thermoplastic material. The Provisional Specification also describes a block-bottom bag formed from a squared-off length of flattened gussetted tube, by means of an end closure weld and of corner welds at 45 degrees to the sides of the bag and joining each wall of the gusset to its overlying bag wall but not joining the walls of the gusset together.