Patent GB-1281401-A (GB)
Title: Valved plastics bag
Inventor: WORNDL JOHN
IPC: B31B29/84
Filed: 1969-02-17
Abstract: 1281401 Valved plastics-film bags CANADIAN INDUSTRIES Ltd 27 Jan 1970 [17 Feb 1969] 8507/69 Heading B8K [Also in Division B5] A valved plastics bag comprises front and back panels 1, 2 which are sealed together along their sides 3, 4 and which have their ends joined together by gussetted panels 5, 6 having mitred ends 7, the gusset 6 at the top end having a plastics film patch 10 sealed, by a U-shaped seal 11, to its inner surface, and a slit 9, located. within the area of the seal to form, with the patch, a one-way valve. The top panel 6 is joined to the upper edge of the front panel 1 by an overlapping sealed joint 8. The valve patch 10 has an extension 12 of thinner gauge film sealed, at 13, to its free end. In a machine for making a valved bag, a length of plastics tube 14, unwound from a supply reel, is intermittently advanced, in increments equal to a bag width, by a draw-roll assembly 46 over rolls 15, 16 to a slitting assembly 21 which slits the upper ply of the tube longitudinally at a position spaced from a tube edge by half the desired width of a bag top, the free edge of the upper ply then being folded outwardly to form a protruding border of the lower panel which eventually forms the top gusset 5. The two-ply length of film may alternatively be formed by longitudinally folding a length of single ply. While the machine is stationary the valve slit 9 is cut by a knife 23 in the outwardly folded border, and the thicker and thinner materials for the valve patch 10 are drawn respectively from rolls 25, 24 and are passed through a heat seal 26 which bonds together their overlapping edges. A cut-off knife (96), Fig. 11 (not shown), cuts off a length of valve panel 10 and a clamp (113) descends to hold the panel 10 in contact with the protruding border while a U-shaped seal 29 then descends to make the U-shaped seal 11, Fig. 4, and form a valve. The tubular film next passes around a former plate 30 and a wedge and U-shaped guide (34, 35), Fig. 8 (not shown), which fold the lower border upwardly and over for sealing, by sealing bars at 36, in overlapping relationship with the upper panel and form the seat 8, Fig. 5. The gussets are then formed along the sides of the tube by sets of interiorly located double discs 41, 42 which expand the tube into rectangular cross-section and which co-operate with exterior discs 43. The tube then moves forward to a roll assembly 44 which compresses the gussetted edges before they are heated by clamp plates 45 and subsequently passed through the draw-roll assembly 46. V-shaped seals, corresponding to the seals 7, Fig. 3, are then formed in the edges of the tube by sealing and cutting bars 50 before the tube is passed to a gusset-turn-over guide 51 which folds the upper gusset against the middle portion of the tube to facilitate its passage between succeeding rolls. A photo-electric assembly 52, sensing batches of printed information on the tube, actuates a controller (5, 3), Fig. 12 (not shown), forregulating the various operations of the machine. The tube is finally passed. through a unit 54 which transversely cuts and seals the tube between the apices of each pair of opposed V-shaped gusset seals to form the side seals 4, 5, Fig. 3. A unit 54 ejects the finished bags on to a conveyer 55. The valve-forming mechanism is described in detail with respect to Figs. 9-12 (not shown).