Surface modification of polymers using excimer lasers and short-pulse flashlamps

Exposure of oriented, semicrystalline polymers, such as poly(ethylene terephthalate), poly(ethylene naphthalate) and polyimides, to the output of pulsed light sources, such as excimer lasers or short pulse flashlamps, at energy densities less than the ablation threshold can produce an amorphous layer on the polymer surfaces. Time resolved spectroscopy has shown that this amorphous layer is produced by a transient heating of the surface region to temperatures exceeding the polymer melting point (300-500 degree(s)C) resulting in rapid melting and the production of the thin disordered surface layer. Static SIMS, XPS, and infrared spectroscopy measurements have shown that this surface amorphization occurs without any decomposition or crosslinking of the polymer surface. The amorphous layers produced by this rapid thermal process provide increased adhesion of a wide range of coatings and films to the treated polymers due to the increased fracture toughness of their disordered morphology. The amorphous surface layer also can antireflect the polymers, provide increased autoadhesion, and increase coating penetration into the treated polymer substrates. This last characteristic can be exploited to provide photoimaging properties, as negative photoresists, to polyimides. The rapid thermal surface modification technology shows potential for economic industrial implementation, using short pulse flashlamps, provided that reliable, large-scale flashlamp systems can be made available.