Reheat injection stretch blow molding

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. 

An alternative approach is to cool the parison completely after the injection molding step, and remove it from the core rod. The parison can then be stored or shipped elsewhere before blow molding. In this case, it is necessary to reheat the parison to the desired temperature before the blow-molding step. This approach is seldom used for ordinary injection blow molding, but is not uncommon for stretch blow molding, which is discussed in Section 12.4. 

Preform injection followed by reheat stretch blow molding (RSBM)... 

FIGURE 17.7 Stretch blow molding 1, parison injection molded 2, parison is reheated 3-A, arod stretches the parison, imparting axial orientation 3-B, air expands parison against mold walls, imparting tangential orientation 4, finished bottle ejected from mold. Vmm Modem Plastics 55(10), 22 (1978). 

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... 

The prefemps mdided in a standard injection molding m hine. The cold preforms am then shipped randomly to a special sttetch blow machine, wto% they are oriented, reheated, stretch and blown. 

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