The blow molding process is a common method of forming plastic packaging containers. Blow molding is to put a semi-molten tube blank (or parison) obtained by extrusion or injection molding into a mold, and then close the mold, and introduce and compress the compressed air into the tube blank to make it adhere to On the wall of the cavity, a method of processing a certain hollow product is obtained by cooling and demoulding.

The blow molding process can be classified into a variety of types depending on the molding method.

1. Stretch blow molding

Stretch blow molding is a molding method in which a preformed preform has been shaped, a bottomed parison heated at a suitable temperature below the melting point is placed in a mold, and a stretched rod is used for axial stretching and then blown immediately. At the same time of molding, the orientation of the macromolecules in the wall of the product is aligned and fixed, thereby greatly improving the performance of the plastic container.

The characteristics of this molding method are: low scrap rate, high production efficiency and easy weight control. The impact toughness of the product is high, the rigidity is improved, the transparency and gloss are improved, the barrier property and the airtightness are good, but the control of the stretching temperature is high, and the equipment investment is large. Most PP and PET bottles are formed by injection-blowing, such as cola bottles.

2. Multi-layer blow molding

Multi-layer blow molding is a molding method for preparing a multi-layered container by using a multi-layer composite parison by a blow molding process. Through the reasonable matching of various plastic layers, the effective complementarity of the properties of the various layers of plastics is achieved, thereby overcoming some inherent disadvantages of single-layer plastic containers.

The characteristics of this molding method are: improving the physical and mechanical properties of the plastic container and improving the performance of the container, such as light blocking, heat insulation, flammability, and printability.