| 摘要 |
1,257,937. Making bags; seaming non- metallic sheet material. BRITISH VISQUEEN Ltd. 25 June, 1970 [7 July, 1969], No. 34179/69. Headings B5D and B5K. [Also in Division B8] In a method of making bags in continuous strips by heat sealing a web comprising at least two layers of plastics film to provide side or end seals for the bags, the web is perforated substantially simultaneously with, or before, heat sealing to provide a plurality of ribbons across the width of the web adjacent to the seal position and inclined to the length of the web so that shrinkage of the web when the seal cools is taken up by the ribbons straightening. The perforations may comprise a row of curved slits, or V-shaped slits having their apices directed towards one edge of the web, or two rows of staggered transverse slits. The web may be gripped on either side of the seal position during sealing by stationary or moving clamps. The web may be a tubular film of an unorientated olefine polymer or copolymer. The perforations may also constitute a tear line. Gusseted bags may be formed. |
