P - Polymer Processing Glossary of Terms

Parting line - Line, visible on the mold part, where mold separates to release the molded part from the cavity.
Pearlescent pigments - A class of pigments consisting of particles that are essentially transparent crystals of a high refractive index. The optical effect is one on partial reflection from the two sides of each flake. When reflections from parallel plates reinforce each other, the result is a silvery luster, iridescent effects and metallic sheen resembling natural pearl.
PET - Polyethylene Terephthalate, known as a thermoplastic polyester. Has the unusual ability to exist in either an amorphous or highly crystalline state.
Plasticize - To soften a material and make it plastic or moldable, either by means of an extruder or by heat or both.
Platen - The plates on which the mold assembly is mounted. Large metal blocks on clamping ends of molding machine used to support mold.
Polycarbonate resins - Polymers derived from the direct reaction between aromatic and aliphatic dihydroxy compounds with phosgene or by the ester exchange reaction with appropriate phosgene- derived precursors.
Polyethylene - A polyolefin composed of polymers of ethylene. Exists in three classes: low, medium and high density.
Polymer - A high-molecular weight organic compound whose structure can be represented by repeated small units.
Polymerization - A chemical reaction in which the molecules of a monomer are linked together to form large molecules whose molecular weight is a multiple of that of the original substance.
Polypropylene - A tough, light-weight polyolefin plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.
Process - A set of conditions or set of causes working together to produce an outcome. In injection molding the key process variables are Time, Temperature, Pressure, and Flow Rate
Process capability - The common variation of a process; the short term variation under controlled conditions. This variation is always present in a process and capability measured as the best the process will ever produce unless changed.
Purging - The forcing out of resin from the extruder.