ES8703342A3 - Synthetic film sacks with double block bottoms - Google Patents

Abstract

At the place where the bottom cross weld is to be formed for the prodn. of a continuous run of sacks with harmonica pleats on their long sides, from a tubular film, third harmonica pleat part welds are aligned at right angles to the long axis of the tube. In a following step the bottom cross weld is formed by welding together the earlier formed pleat part welds and the opposing film layers, between the inner ends of the third pleat part welds. The side harmonica pleats have central and two outer long edges delimiting a first and a second harmonica pleat section and the sack has a bottom welded seam across its full width. At one end of the tubular film close to the first bottom welded seam, two first pleat part welds are formed. These part welds bond the outer film layer to the part fold opposite to it. Close to the other end of the sack at least two second pleat part welds are formed, which bond an outer film layer to the opposing harmonica pleat section. First pleat part welds extend between the inner and outer long edges of the pleats in the direction of the closed end of the sack. These first part welds or their extension intersect the first bottom cross weld in the zone of the point of intersection of the bottom cross weld and the central long edge of the fold. The bottom weld together with the first pleat welds may or may not close the tube, and the first bottom cross weld is formed after the forming of at least a pair of first and second pleat part welds on each side of the tubular film, and after the tubular film is transported over a distance which is at least equal to the greatest distance between the first and second pleat part welds. Eliminates the need to change over from a two layer to a four layer weld which weakens the film material. The technique outlined gives a better bottom weld and the speed of output is increased.