US Patent 7331917 Bag making machine

Plastic bag making apparatus by which it is arranged that even if a bottom gusset member is not specially supplied, a bottom gusset can be incorporated into a plastic bag. As continuous trunk members (1,2) are fed, they are guided by a trunk guide mechanism (16-29) and folded along a longitudinal fold line (8). Then, the folded portion (4) is folded back along a longitudinal fold-back line (10), whereby a twofold section is formed of the trunk members, with the continuous trunk members forming the trunk of the plastic bag, the twofold section forming the bottom gusset of the plastic bag.