Oberflächenmodifizierung und -analytik von Polyimid
The present work concerns the characterisation of the chemical and physical properties of the surface, which arise when switching the wetting characteristics of the polyimide surface. A reversible loop consists of four processes: the hydrolysis of the polyimide surface to generate a hydrophilic surface, the UV-exposure, rubbing of the exposed areas and the erasure of the structures with a commercial cleaning agent. The structured surface can be used in an offset printing press as a printing-plate. After the erasure the loop is closed. All processes are limited to a thin layer on the surface of the polyimide. Therefore, surface sensitive-characterisation methods are required for their investigation. To acquire information about the chemical modification after the individual process steps measurements with infrared spectroscopy in attenuated total reflexion (FTIR-ATR spectroscopy) and X-ray photoelectron spectroscopy (XPS) were carried out. The structures produced by light exposure could be mapped with white light interference microscopy, scanning electron microscopy and atomic force microscopy. The important wetting characteristics for the offset printing could be determined macroscopically with contact angle measurements and microscopically by means of special atomic force microscopy procedures. The generation of hydrophilic zones on the polyimide was accomplished by the hydrolysis of its surface. The samples were brought into contact with an alkaline solution. The cyclic imide groups were opened. Upon opening amide and carboxylate groups are formed, which were detected by means of FTIR-ATR and XP-spectroscopy. The patterning of the surfaces was realized by two different UV light sources: a mercury vapor lamp and a laser system (Ti:Sa laser). Although the physical and chemical process induced by the UV irradiation is very diverse, due to the energy density, the result of the UV irradiation namely the destruction of the polymer chain at the surface is comparable. Residues of the gradest polyimide chain stays as debris. After exposure to irradiation the surfaces did not show uniform wettability. Therefore, subsequently a development step was carried out for removing the polyimide which was destroyed by the UV irradiation. This was done via rubbing the surface with a cellulose pad. By removing the ablated material, indentations on the surface of the polyimide arose. These could be mapped by atomic force microscopy and white light interference microscopy. The depth of these structures depends on the kind and the fluence of the UV source. It varied between 100 and 200 nm. The exposed and rubbed zones were hydrophobic. For obtaining a rewritable printing plate it is necessary to erase the surface at the end of the cycle, so that a new print format on the same surface can be produced. This takes place via abrasion the surface with a commercial cleaning agent. The XPS analysis showed that both element composition and chemical shift of the treated surface corresponds to that of the untreated polyimide surface. This surface behaved in each regard like the original surface, so that the entire cycle could be repeated several times with reproducible results.
info:eu-repo/classification/ddc/540, Offsetdruckplatte, Polyimide, Oberfläche, Modifizierung, Oberflächenanalyse, Chemie, Oberflächenchemie, Polymere, Ablation, Benetzung, Drucktechnik
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