Material Selection Requirements
In all application methods, parts should be clean and free of surface contamination for good paint adhesion. When possible, design parts to release from the mold easily, so they can be ejected without using external mold release sprays. Oils from hands can also contaminate the part surface. Consider designing designated handling areas or features to reduce contamination in critical painting areas. Part design can have a direct impact on the ease and cost of painting. For instance, spray painting, a line-of-sight process, works within a short nozzle-to-part distance range. To achieve uniform coverage, avoid undercuts and deep, narrow recesses, which may not coat completely. Sharp corners can be difficult to coat sufficiently and may chip or wear through. Consider painting transparent parts on the back surface (or second surface) to protect the paint from scratches and abrasions. Brittle coatings and paints can greatly reduce the impact performance of painted plastic parts. Cracks in the paint or coating act as stress concentrators to initiate fracture in the plastic substrate. Exercise extra care in the design and paint selection for painted parts subjected to impact loads. Flexible paint systems, such as two-part urethanes, tend to perform better in impact applications. |