TABLE OF CONTENTS Formulation of plastics materials consists of the polymeric or resin material and additives for affecting specific functions such as foaming. Solvents can be added for cast molding (Rubin, 1974) of parts, but cannot be used for injection molding because heating the solvent would cause explosive pressures. Also, nonsolvent or thermally melted resins can be poured into a mold and are said to be cast molded.
Plastics formulations are usually simple compared to paint, adhesives, and inks. The resins for molding, for example, are usually preformulated and sold to the molder. Injected, extruded, or blow molded parts contain small amounts of pigment or other fillers, no solvents, and small amounts of additives. The additives are introduced for specific purposes as plasticizer for PVC, gas releasing/foaming agents for low-density parts, and others. The basic material in a molded part is the resin. The resin is usually thermoplastic and to a lesser degree, thermoset. Detailed material information is presented in Chapter 8.
Formulations for molded plastic parts are simpler than paint, adhesive, or ink dispersions. The resin/polymer is usually over 95% of the formulation. A typical plastics formulation consists primarily of some or all of the following components:
Resin/polymer
Pigment/dye
Flow agent
Mold release agent
Plasticizer
Antioxidant
UV stabilizer
Polymers and resins that flow when heated and do not chemically react or cross-link are called thermoplastics materials. Examples of thermoplastics are polyethylene (PE) and nylon. After injection molding parts from these materials, they can be reheated above...
