Orientation blow molding

In injection blow molding, the parison is formed by injection molding rather than extrusion. A variation known as stretch (or orientation) blow molding is responsible for the now ubiquitous plastic soda-pop bottle. In this process, parisons (often called preforms in this case) are injection molded with the bottom end closed and the threads and neck molded on the open top. They are allowed to cool to room temperature. Prior to blowing, they are reheated in a radiant-heat oven in which close control is exercised over the temperature profile of the parison. When introduced to the blow mold, the parison is normally a fraction of the length of the mold (Figure 17.7), but before blowing, a rod... 

Soft-drink bottles made from poly(ethylene terephthalate) (PET) are usuady made by stretch-blow mol ding in a two-step process. Eirst, a test-tube-shaped preform is molded, which is then reheated to just above its glass-transition temperature, stretched, and blown. Stretching the PET produces biaxial orientation, which improves transparency, strength, and toughness of the botde (54,56). A one-step process is used for many custom containers that are injection stretch-blow molded. 

PS or copolymers are used extensively in injection blow mol ding. Tough and cra2e-resistant PS containers have been made by multiaxiaHy oriented injection-molded parisons (238). This process permits the design of blow-molded objects with a high degree of controlled orientation, independent of blow ratio or shape. 

This technique is also called nonaxisym-metric blow molding. In conventional EBM the parison enters the mold rather in a straight tube. In 3-D BM the parison is laid or oriented in the mold prior to closing. It is manipulated in the tool cavity providing complex geometric products that can have... 

How is orientation introduced into an injection blow molded part Compare this to orientation in a stretch blow part ... 

In the injection blow molding process, the parison is formed by injection molding of the preshaped parison onto a steel rod, as shown in Fig. 14.18. The rod with the molded thread already completed is moved to the blowing station, where the article is inflated free of scrap. The parison thickness distribution is determined in the injection mold without the need of further control. Some axial orientation is introduced during injection, resulting in an article with partial biaxial orientation. 

A process that greatly improves blow molded product properties is that of injection stretch blow molding, which introduces biaxial orientation in crystallizable polymers. There are two variants of this process involving the molding of a preform as the first step. The thermomechanical paths of the two process variants are shown in Fig. 14.19. In the... 

Stretch blow molding holds the parison above its glass transition temperature (7 ) and stretch-orients it to increase modulus, strength, impact resistance, transparency, and impermeability. This is most important for PET, and is also used for PVC, polypropylene, and polyacrylonitrile. 

EVOH have superior gas barrier properties.80 89 They are often used as the internal layer in multilayer food packaging films, blow molded rigid containers, gasoline tanks for automobiles for a variety of purposes, etc. EVOH can be fabricated by the usual melt processing methods. The barrier properties of films decrease in the presence of moisture, so multilayer with protective polypropylene (especially biaxially oriented material), low-density polyethylene, nylons, or other moisture barrier films provides films or products that are useful even with liquids. The... 

PET s broad range of properties make them ideal replacements in certain applications for such metals as die-cast aluminum or zinc also in thermoset switches, relays, sensors, etc. Applications include packaging (particularly stretched injection blow molded beverage bottles and film), appliances, electrical/electronics, etc. PET finds applications in such diverse end uses as fibers for clothing, films, botdes, food containers, and engineering plastics for precision molded parts.118-120 A wide range of applications is possible because of the excellent balance of properties PET possesses and because the degree of crystallinity and the level of orientation in the finished product can be controlled. 

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