Ageing time of wettability on polypropylene surfaces processed by cold plasma

The increasing use of polymeric materials in high technological fields, such as automotive, has forced the need to overcome some of their limitations by means of innovative processing. In the automobile industry, a complex and critical process is used in order to enhance both wettability and adhesive properties of polypropylene bumper surfaces. Cold plasma treatment represents an efficient, clean and economic alternative to activate polymeric surfaces. The aim of this work has been to value the ageing time of cold plasma treatment, applied to polypropylene surface, as a function of process parameters. The evaluation of ageing time represents a fundamental step to plan the insertion of the plasma process inside the industrial system of bumper production. In fact, once the ageing time has been determined, it is possible to establish how much time has to pass between the surface activation of a bumper, obtained by cold plasma treatment, and the following paint process. A set of process variables (voltage, time and air flow rate) has been identified and used to carry out some experimental tests on the basis of design of experiment techniques. The cold plasma process has proved to give a long ageing time in all process conditions.