Polymers, commonly called plastics, are artificial products that are not available in nature. They are produced artificially from basic organic materials, crude oil, natural gas, or even biomass. The initial products, so-called monomers, are low molecular weight gases or liquids. High molecular weight macromolecules with solid consistency are synthesized through chain reactions and sometimes through cross-linking.
The first step in making polymer packaging is to melt the thermoplastic resins and then form them into films or sheets or into an end product like a cap, bottle, or cup. The machines with which this is done are called extruders. An extruder has two main components, a barrel and a screw. Both are made of alloy steel and are very robustly constructed because a pressure of several hundred bars arises during melting. The resins are furnished sometimes with additives that are abrasive; the extruder must be able to work such a product without getting damaged.
Converting means upgrading of a packaging material. A monolayer web (single layer) can be converted to a multilayer composite through a suitable procedure to get better performance. Better performance means better mechanical properties like sealing or puncture strength. It may also mean better barrier properties against light, oxygen, moisture, or aroma or better ESCR (environmental stress crack resistance). Converting may also fulfill marketing aspects like an attractive surface through special printing, lacquering, or a soft touch.
