On plasma processing of polymers and the stability of the surface properties for enhanced adhesion to metals

This paper deals with the plasma surface treatment of polymers in a low fre quency bell jar reactor with non-symmetrical configuration of electrodes. T he highly energetic character of this discharge due to its low excitation f requency and electrode configuration, as well as its small discharge volume makes it a very efficient and fast functionalization process. Amongst the different plasma gases used for the adhesion improvement of polypropylene t o aluminum, ammonia has shown to be the most suitable one for this applicat ion. Since the NH and NH2 radicals play an important role in the kinetics o f nitrogen incorporation in polymers, mixtures of N-2 and H-2 were also use d as possible substitutes for ammonia. The former are more environmentally friendly and easier to handle in industry than ammonia. The efficiency of n itrogen rich mixtures in the case of the second application, i.e. adhesion improvement of copper to fluoropolymers has been compared to that of ammoni a which still shows faster nitrogen incorporation. The last part of this pa per is devoted to the study of the energetic character of plasmas of mixtur es of He + NH3 by OES and electrical measurements in the whole range of com position of the two gases. The results show that an ammonia percentage rang ing from 5 to 10% in plasmas of mixtures of He/NH3 represents a transition between two different discharge regimes. Plasmas of mixtures of He + 2% NH3 , characterized by highly energetic electrons, ions and probably metastable s of helium give rise to enhanced adhesion of PP to aluminum which remains stable with time. (C) 2001 Elsevier Science B.V. All rights reserved.