Standard test is 90 degree peel test with using standardized scotch tape. Which type of plastic is used will effect which ink is best. Low energy plastics such as PE or PP will need to have their surface modified by flame or corona to get the best adhesion. The people who make the pad print machines such as Tampoprint in Chicagoland IL are your best source of infro. If the part material can be attacked by a solvent such as ABS,PVC etc, an ink with specialized solvent is your answer. There are lots of people out there in this business to help you.
