Adhesive Property Enhancement by Photochemical Modification on Polyimide Sheet Surface by Irradiation with Excimer Lamp
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ABSTRACT Polyimide sheet surface was photochemically modified to be hydrophilic property with Xe 2* excimer lamp (A =172nm) irradiation and pure water solution. The solution was sandwiched between the surface and fused silica glass. With the excimer lamp irradiation, the solution and the surface were excited; the surface was dehydrogenated by the hydrogen atoms which were photodissociated from pure water and replaced the photodissociated OH radicals. The hydrophilic property of the modified surface was evaluated by measuring the contact angle with water. The replacement of the OH radicals were confirmed by FTIR. The modified surface was bonded to stainless steel with an epoxy resin for evaluation of the adhesive strength by the shearing tensile test. As a result, the adhesion was increased to 1.4 times that of the non-irradiated sample. INTRODUCTION In engineering plastics, polyimide is far superior in heat resistance, mechanical strength and chemical stability, and is widely used as aerospace materials and flexible printed substrates. These excellent properties, on the other hand, make surface modification difficult. Laser-ablation has been extensively studied for making holes in the material by irradiating polyimide with high energy excimer laser [I]. When the surface is photochemically modified, it allows different materials to be joined to the irradiated part. Examples of photochemical surface modification previously reported include ArF laser modification of an oleophilic surface by substituting methyl groups, teflon surface modification of hydrophilic surfaces in the presence of water solution[2-4]. There are also the reports by using Xe 2* excimer lamp [5]. Aiming for photochemical modification of polyimide surface, we used the Xe 2* excimer lamp light ( A = I 72nm) as a light source and pure water or methyl alcohol as a reaction solution, and have successfully formed a hydrophilic polyimide surface without surface deformation [7]. The FTIR analysis confirmed the substitution reaction of the OH radicals. After modification, we put epoxy resin on the surface and measured the adhesive strength, which increased to 1.4 times that of the non-irradiated sample. This result shows the effect of photochemical modification. Furthermore, in order to investigate the dependence of the excited wavelength upon the photoreaction on the surface, the efficiency of the photodissociation from the solution with ArF excimer laser instead of Xe 2*excimer lamp was measured. The surface was excited with the ArF excimer laser. Accordingly, the production of the radicals from the solution depends on the excited wavelength. As a result, the use of 555 Mat. Res. Soc. Symp. Proc. Vol. 397 01996 Materials Research Society
photochemical surface modification made possible an adhesion of polyimide to different kinds of materials while keeping their properties. PHOTOCHEMICAL REACTIONS Polyimide has imide groups in molecules, as shown in Fig. 1; the C-H bond energy of benzene ring is 80.6kcal/mol. Xe2*excimer lamp or ArF excimer laser (165kc
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