Plasma rescues adhesion crisis
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A supplier had a problem. Despite initially appearing to bond reliably, a touch foil applied to a polycarbonate 3D control panel failed the rigorous climatic test demanded by an automotive manufacturer. Bubbles formed in the boundary layer between the plastic substrate and the foil. Rescue came in the form of a pretreatment with atmospheric pressure plasma.
The most likely cause for the inability of additive-free plastics to be bonded or coated effectively, or indeed at all, despite having clean surfaces, is their low polarity and resultant low surface energy. This is ultimately the most important measure for determining the probable adhesion of an adhesive layer, paint or coating. If the surface energy of a plastic is too low, the material surface will require activating. The unexpected failure of an apparently successful adhesive bond sometimes comes to light only when a stress test is performed, for example a climatic test. Automotive component supplier Preh had to make this...