The Preparation Of Highly Adhesive Polyimide Coating By Low Temperature Imidization

Polyimide coating refers to the pre-polymer of thermoplastic polyimide---polyamic acid solution which has a great adhesion. It plays an important role in many high-tech fields. However, polyimide coating must be imidized totally at high temperature(300℃) which limits its application in many fields. And because of the rigid molecule, strong intermolecular action and low surface energy, the adhesion of polyimide coating to the substratethes is weak. Therefore, the preparation of highly adhesive polyimide coating at low temperature has a very important significance.2,2-bis[4-(4-aminophenoxy) phenyl]propane(BAPP),4,4’-diaminodiphenyl ether (ODA), 3,3’,4,4’-benzophenone tetracarboxylic dianhydride(BTDA),4,4’-oxydiphthalic anhydride (ODPA) were firstly used to prepare six different kinds of polyimide coatings. Then low-temperature curing agents were added to the BAPP-ODA-BTDA type polyamic acid for reducing the imidized temperature and the optimal reaction condition of low temperature imidization was explored. In addition, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyl disiloxane (GAPD) and aminopropyl terminated polydimethylsiloxane(PDMS) were copolymerized with BAPP、ODA、BTDA separately, and the influences of different silicon-containing monomers and different amounts on the overall performance of the material were discussed. Finally, with the 3-aminopropyl triethoxysilane(APTS) monomers, BAPP-ODA-BTDA-PDMS-APTS typy polyamic acid contained different molecular weights were synthesized by controlling the amounts of monomer and the reaction time. The effect of blending two polyamic acid solutions of different molecular weight on the material properties was studied.Chemical structures, mechanical properties, thermal properties, surface morphology, contact angles of polyimide films were characterized by fourier transform infrared spectroscopy(FTIR), nuclear magnetic resonance(’H-NMR), electronic universal tensile testing machine, thermogravimetric(TG), scanning electron microscopy(SEM), contact angle measurement. Apparent viscosity, molecular weight and molecular weight distribution of polyamic acid were measured by viscometer, gel permeation chromatography(GPC). The adhesion between cured coatings and various substrates were determined by cross-cut test, cooking test, tensile shear strength and T-peel strength test.The results showed that:the adhesion of the coating can be improved by introducing the flexible BAPP and polar BTDA. While adding ODA to be copolymerized, BAPP-ODA-BTDA type polyimide coating had a better adhesion to the substrate with good mechanical properties and thermal stability which is the best formula. When the solids content of polyimide coating was 20% and the ratio of the amount of quinoline and dianhydride was 1:5, BAPP-ODA-BTDA type polyamic acid can be completely imidized at 200℃ and the overall performance of the obtained polyimide films were excellent by using quinoline as the catalyst. The mechanical properties of the material were reduced by introducing GAPD copolymer, while the mechanical properties and thermal stability of the material maintained well by adding suitable PDMS. The tensile strength and T5% temperature of BAPP-ODA-BTDA-PDMS type polyimide film were 110.72Mpa and 519.7℃. And the adhesion of BAPP-ODA-BTDA-PDMS type polyamic acid coating were improved. Through blending two different molecular weight of BAPP-ODA-BTDA-PDMS-APTS type polyamic acid solutions, the adhesion between cured coatings and various substrates can be effectively improved. When the weight average molecular weight of the polyimide coating were 25664 and 4279, the tensile shear strength and T-peel strength between cured coatings and aluminum had the largest values, the adhesion grade between cured coatings and copper, aluminum, glass plate reached the optimal level of 0 rank, the attached time between cured coatings and glass substrate was more than 2280h. And the obtained polyimide films had a good comprehensive performance with the the tensile strength and T5% temperature of the films were 108.75Mpa and 495.99℃, which was a highly adhesive polyimide coating prepared at low temperature.