Film packaging bags are mostly produced by heat sealing methods and also by bonding methods. According to their geometry, they can be basically divided into three categories: pillow-shaped bags, three-side sealed bags, and four-sided sealed bags. It can also be divided into two categories according to whether the bag can stand upright without support: upright bags and non-upright bags.
Pillow-shaped bags, also known as back-sealing bags, have back, upper and lower seams so that they have the shape of a pillow, and many small food bags are often packed in pillow-shaped bags. The back seam of the pillow-shaped bag forms a fin-like package in which the inner layers of the film are placed together and the seam protrudes from behind the packaged bag. Another type of closure overlaps the closure, with the inner layer on one side bonded to the outer layer on the other side to form a flat seal. Since the fin-shaped seal is relatively strong, and the inner layer of the packaging material is heat-sealed, it is widely used. For example, the most common composite film bag, the inner layer is PE and the outer layer is a composite substrate. The overlapping seals are relatively not strong enough, and the inner and outer layers of the bag are required to be heat-sealing materials, so that not many are used, but a little material can be saved. For example, a non-composite pure PE bag can be packaged in this way. The top and bottom seals are bonded to the inner layer of the bag.
The three-side sealing pocket has two side seams and one top seam. The bottom edge of the bag is formed by a horizontally folded film, and all the seals are formed by bonding the inner material of the film. This bag can be folded or not. When there are hem, they can stand upright on the shelf. One of the deformations of the three-side sealing pocket is that the bottom edge formed by the original folding is achieved by bonding, so that it becomes a four-side sealing pocket.
Four side pocket
Four-sided sealing pockets, usually made of top, side and bottom seals of two materials. Compared to the previously mentioned bags, it is possible to use two different plastic resin materials, if they can be bonded to each other, to make a front edge bonded four-side sealing pocket. The four-sided sealing pocket can be made in various shapes such as a heart shape or an oval shape.
The upright bag, when filled with something, can support the weight upright on the shelf. The upright bag has a hem, and the hem will open when something is loaded, so that the bag has a relatively flat bottom to stand up. They are widely used to package liquid products such as kitchen cleaners, and because they can replace hard-pack materials such as cans and bottles, the market and usage are increasing. The stand-up pouch is designed with a horizontal bottom flap that can be made from two flexible packaging materials. In another product, only one film is used, and the film is folded into an M shape to form a bottom edge; it is also possible to design a bottom of a flat sheet that is folded or folded with no side folds to form an overlapping flat sheet. This bag is not as secure as a bag with a hem at the bottom, and is mostly used for dry goods rather than liquid products. In both cases, a certain product weight folds the edges of the package so that the bag can stand on its own.