Study On Photocatalytic Surface Modification Of Flexible Plastic Substrate

The poly (ethylene terephthalate) (PET) and polyimide (PI) are the most commonly used engineering plastic because of their excellent properties, such as: excellent mechanical properties, stable physicochemical properties, high resistance to common solvents and thermal stability. They have been widely used in microelectronic industry, the flexible printed circuits, medical materials, mechanical equipment and the daily living equipments.Through the surface metallization of the PET and PI films, many specific properties of the PET and PI films can be enhanced and their application areas can be widened. However, the adhesion strength between the PET and PI films and the electroless copper film is very weak. Therefore, in order to improve the surface hydrophily and the adhesion strength between the PET and PI films and the electroless copper film, the surface modification process is necessary. Many surface modification methods have been introduced to enhance the surface hydrophily and the surface roughness of the film surface, such as wet chemical treatment, surface graft copolymerization treatments, plasma treatment. Though the wet chemical treatment brings a lot of serious environmental problems, due to simplicity and production cost, the TiO2 photocatalytic treatment was used for metallization of the PET and PI films.The TiO2 photocatalytic treatment has received extensive attention in recent years because of its high good stability, high catalytic activity, and environment-friendly system. So the TiO2 photocatalytic treatment is used for the surface modification of the PET and PI films.In this dissertation, an environmentally friendly surface modification system was used to modify the PET and PI films. After the films were treated properly by the TiO2 photocatalytic treatment, the desired effects were obtained. The main works of the dissertation are as follows:1. In this dissertation, a surface modification of the PET film was investigated by TiO2 photocatalytic system. The mild swelling system containing Dimethylsulfoxide (DMSO) and ethanol was designed. And the effects of the photocatalytic condition on the surface contact angle of PET were investigated after swelling treatment. In order to enhance the adhesion strength between the PET film and the electroless copper film, the effects of TiO2 crystal forms, TiO2 particle sizes, and TiO2 content, as well as treatment condition, upon the surface contact angle, surface characterization, and adhesion strength were investigated. Anatase TiO2 with a particle size of 5 nm had a high catalytic activity and dispersibility in aqueous solution, which has a better photocatalytic treatment effect. After the optimal photocatalytic treatment, the surface contact angle of the PET film decreased from 84.4 to 19.8°. The results of SEM observation indicated that many dense uniform cavities appeared on the PET surface after the proper photocatalytic treatment, and the surface roughness of the PET film increased from 36 to 117 nm. The adhesion strength between the PET film and the electroless copper film reached 0.89 KN·m-1. Fourier trans-form-infrared spectroscopy (FT-IR) indicated the carbonyl group was formed on the PET surface after photocatalytic treatment. X-ray photoelectron spectroscopy (XPS) analysis further demonstrated that some ether carbon groups were oxidized to carboxyl groups with the photocatalytic treatment, so the surface hydrophilicity was improved. Consequently, TiO2 photocatalytic treatment is an environmentally friendly and effective method for the surface modification of the PET film.2. Because the PI contains the stable imide ring structure, which is against the effect of TiO2 photocatalytic treatment. And so, only TiO2 photocatalytic treatment is not suitable for the modification of the PI films. The swelling process is very necessary before the TiO2 photocatalytic treatment. In this dissertation, the effects of different swelling system and swelling condition, TiO2 content, as well as photocatalytic treatment time upon the surface contact angle, surface characterization, and adhesion strength were investigated. The swelling system containing N, N-dimethylformamide (DMF),water, Dimethylsulfoxide (DMSO) and Tetramethylammoniumhydroxide (TMAH) was designed in the experiment. And the effects of the swelling solution on the TiO2 photocatalytic treatment of the PI were investigated after swelling and photocatalytic treatment at the fixed swelling condition. The study results indicated that when DMF:H2O:DMSO1:2:1,TMAH was 5 g/L, swelling time was 15 min, photocatalytic treatment was 30 min, an optimal modification performance of PI films was obtained.After the swelling and the TiO2 photocatalytic treatment, the surface contact angle decreased to 28.7°, and the surface topography of the PI films had no obvious change with the TiO2 the photocatalytic treatment. XPS analyses indicated -COOH group was formed on the PI surface after photocatalytic treatment, the surface hydrophilicity was improved, and the adhesion strength between the PI film and electroless copper film was increased accordingly.