Overview of Plastic Coatings and Dip Molded Plastics
- Plastic coating is the application of liquid polymers or plastic on the surface of a workpiece by dipping or immersion. The result is a plastic layer for protective, convenience, and decorative purposes. It increases the piece‘s durability, strength, corrosion, and chemical resistance. It also gives heat and electrical insulation.
- The main desirable property of polymers to be used in a dip coating and dip molding process is high viscosity which enables the polymer to resist flowing off the tool‘s surface. Also, it must be readily available in liquid form. Commonly used polymers are Plastisol, Latex, Neoprene, Polyurethane, and Epoxy.
- Pre-treatment steps in a dip coating process are categorized as follows: (1) removal of surface impurities (degreasing and stripping); (2) modification of substrate properties (phosphating, shot peening, blasting, and de-embrittlement); and (3) improvement of coating quality (addition of primers and undercoats). Pre-treatment in a dip molding process requires the use of mold release agents.
- Production process steps in a dip coating and dip molding are pre-heating of the tool, dipping in a polymer solution, draining excess solution, curing, cooling of the part and tool, and unloading.
- Coating thickness is dependent on dwell time, the temperature of the tool, rate of immersion and withdrawal of the tooling in the polymer solution, and physical properties of the polymer solution.
- Advantages of dip coating and dip molding over other molding methods are: (1) gives accurate internal dimensions; (2) produces seamless and double-walled parts, hence increasing durability; (3) limited restrictions on product size and design, and flexibility in tooling modification; (4) low operational and investment cost; and (5) minimal polymer wastage.
- The disadvantages of dip coating and dip molding are difficulty in obtaining accurate coating thickness and long cycle times.