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Paint and polymer durability (2)
Polymer films are generally produced by a drawing process, such as that depicted below for Poly Ethylene Terephthalate (PET):
 A representation of the film forming process. “u” indicates the part of the
process in which uniaxially drawn film is produced and “b” indicates the part
in which biaxially drawn material is produced. (Diagram courtesy of DuPont
Teijin Films.)
PET
films are commonly manufactured by the process depicted in the figure in which blended
and dried polymer is melt extruded onto a cooled casting drum from which it is then drawn between sets of rollers with a surface speed differential – ie. the film is subjected to a uniaxial draw. After this the film is deformed in the transverse direction to produce biaxially drawn film. Thus, samples with different polymer orientation and or
crystallinity are obtained in the form of as-cast film and uniaxial and biaxial films.
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