Reheat stretch blow molding

As was the case for ketchup bottles, most uses of coinjection blow molding have the aim of improving the barrier characteristics of the container, to extend the shelf life, and to better preserve the flavor, aroma, or other characteristics of the product. Reheat stretch blow molding is the most common process, with three to five layers of resin forming the parison. The skin layers, both inside and outside. 

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

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. 

The two-stage PET stretch blow molding system is usually referred to as the reheat blow molding... 

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). 

Most commonly used for molding PET bottles and jars, there are two methods of stre blow molding the 1 -stage method and the 2-stage, or reheat and blow (R B), method. Tte plastic is stretched to improve its physical properties. 

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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