Blow molding has developed into several main processes depending on the products manufactured and the methods used.
Injection blow molding involves first creating a bottomed preform from plastic using injection molding, then transferring the preform to a blow mold to blow-form a hollow product. Based on the degree of automation, the process can be divided into one-step and two-step methods. One-step methods (such as three-station or two-station injection blow molding machines) complete both the injection preform and blow molding on the same equipment, offering a high degree of automation and excellent bottle neck flatness and sealing, suitable for high-volume, high-quality production (such as pharmaceutical packaging). Two-step methods separate the injection preform and heated blow molding into two separate machines, resulting in lower equipment investment, but challenges exist in product consistency and hygiene control.
Extrusion blow molding involves first creating a bottomed preform from plastic using extrusion, then transferring the preform to a blow mold to blow-form a hollow product. The difference between extrusion and injection blow molding lies in the method of preform manufacturing; the blow molding process is essentially the same. This process requires relatively simple equipment and low investment, making it one of the most common methods for producing hollow containers, especially suitable for processing materials such as polyethylene (PE) and polyvinyl chloride (PVC).
Stretch blow molding is a type of biaxially oriented stretching blow molding. The method involves first stretching the preform longitudinally, then inflating it with compressed air to achieve transverse stretching. Stretch blow molding can significantly improve the transparency, impact strength, surface hardness, and rigidity of the product, and is suitable for blow molding polypropylene and polyethylene terephthalate (PET). Depending on the source of the preform, it can be divided into injection preform oriented stretch blow molding, extrusion preform oriented stretch blow molding, and multilayer oriented stretch blow molding.
Blow molding film is a method for forming thermoplastic films. Plastic is first extruded into a tube using an extrusion method, and then continuously expanded into a tubular film of a certain size by blowing air into the tube. After cooling, it is folded and rolled into a double-layer flat film. This method, with blow molding being the most widely used, is suitable for manufacturing films of polyethylene, polyvinyl chloride, and polyamide.
Multi-layer blow molding refers to the co-extrusion of multiple layers of materials with different properties (such as ethylene-vinyl alcohol copolymer EVOH, which has high gas barrier properties, extruded simultaneously). Containers manufactured using this process have excellent barrier properties and are suitable for packaging products sensitive to oxygen and moisture, such as edible oils, condiments, and automotive fuel tanks.
Three-dimensional blow molding is a process that can create three-dimensional shapes. This technology avoids material sagging and burrs caused by its own weight, and can manufacture products with curved sections or complex, serpentine shapes with high quality, such as automotive air conditioning hoses and irregularly shaped piping.
