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Figure II.17: Coated polymer part and (wrong) raw part selected for analysis

Figure II.17 shows a coated polymer part and a reference raw part that has been selected for analysis of the surface. The coating on the left sample exhibited adhesion deficiencies (which is not visible in this picture!). The aim of the analyses was to find out, if there are substances on the raw part surface that can have a negative impact on the coating adhesion. However, a close look reveals, that the reference raw part has a different shape. This means, that the raw part does not fit to the coated part. It is inappropriate, because it most likely has been produced in a different moulding tool and thus does not represent the surface condition of the raw parts of the failed bezel. Although, the moulding conditions might seem to be equal, there are always slight differences that may not be obvious.

Figure II.18: a) Coated polymer part showing adhesion deficiencies and b) sound part selected for comparative analysis

Similar considerations apply when not the raw part, but the coating is the target of the analysis. Figure II.18 show a defective bezel which exhibits significant adhesion deficiencies between the black polymer and the grey coating. For this case the coating quality was questioned and a sound reference part which has been coated without failures has been selected for comparative analysis. But the coated bezels in Figure II.18 (failure part with adhesion deficiency and sound part) are obviously not suited for comparative analysis. The coating adhesion visible with the left bezel can be caused e.g. by residues of an injection moulding agent of the polymer. Whether this polymer additive migrates to the surface is a function of the polymer moulding parameters. As the sound part can obviously not have been produced in the same tool or machine, the result of the moulding process must be different. A suitable reference sample for the comparative analysis of the left bezel would have been a sound sample from the same tool machine and lot. With respect to the coating quality there are also doubts, because it is very likely that the reference bezel has not been coated under the same parameters and in the same batch.

The following requirements have to be fulfilled to make sure that analysis of a raw (uncoated) reference part surface delivers reliable information with respect to the above mentioned analytical goal:

 the same moulding tool

 the same raw material lot

 the same moulding parameters

 the same day

 the same environmental conditions

If one of the above mentioned prerequisites are not met, the results are of limited profit for the analytical goal.