Adhesion LPCAT-treated

It is evident in Figures 30.18 and 30.19 that, after the accelerated adhesion test, the primer-coated air LPCAT treated TPOs showed poor adhesion performance as compared to argon and methane LPCAT-treated TPOs. This is a clear indication that air-plasma treatment can achieve the paintable surface but cannot provide the treated surface that can be painted in a durable manner. The poor durability can be attributed to (1) the water-sensitive nature of adhesion and (2) the excessive degradation of polypropylene that causes weaker boundary layer. 

Plasma treatment of Parylene C films has proved to be very effective in improving the painting properties of Parylene C polymers with respect to a solvent-borne primer as described above. The similar effect of LPCAT plasma treatment on the adhesion of Parylene C polymer to water-borne primer (44-GN-36, Deft Corp.) was also observed. Table 30.3 summarizes the tape test results for the Deft primer coatings on Parylene C surfaces treated by LPCAT under different plasma conditions. 

LPCAT-CH4 treatment deposits plasma polymer of methane on the substrate surface. Since the energetic species are consumed in building up the layer of plasma polymer, the irradiation eflfects of plasma onto the exposed substrate polymer is much less. The excellent adhesion of a primer to the LPCAT-CH4-treated TPO was interpreted due to the replacement of the weak boundary layer by the interaction of tight network of plasma polymer of methane [23]. Plasma deposition from organic compounds, such as methane and ethane, can produce a thin layer of plasma polymer coating with tight networks. 

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