The force required to separate a metallic coating from its plastic substrate is determined by the interaction of several factors: the generic type and quality of the plastic molding compound, the molding process, the process used to prepare the substrate for electroplating, and the thickness and mechanical properties of the metallic coating. By holding all others constant, the effect on the peel strength by a change in any one of the above listed factors may be noted. Routine use of the test in a production operation can detect changes in any of the above listed factors.
The peel test values do not directly correlate to the adhesion of metallic coatings on the actual product.
This test method gives two procedures for measuring the force required to peel a metallic coating from a plastic substrate. One procedure (Procedure A) utilizes a universal testing machine and yields reproducible measurements that can be used in research and development, in quality control and product acceptance, in the description of material and process characteristics, and in communications. The other procedure (Procedure B) utilizes an indicating force instrument that is less accurate and that is sensitive to operator technique. It is suitable for process control use.
The tests are performed on standard molded plaques. This method does not cover the testing of production electroplated parts.
The tests do not necessarily measure the adhesion of a metallic coating to a plastic substrate because in properly prepared test specimens, separation usually occurs in the plastic just beneath the coating-substrate interface rather than at the interface. It does, however, reflect the degree that the process is controlled.
Before conducting ASTM B533, it is important to read the entire specification. Standards can be obtained from appropriate standard authorities.