Adhesion enhancement and lamination of polyimide films

Fully imidized polyimide films were joined together in a lamination process to form a structure that is flexible and has superior thermal stability. This process was demonstrated using the commercially available films KaptonH and UpilexS, as well as spuncast and thermally imidized pyromellitic dianhydride/4-amino phenyl ether (PMDA-ODA) films. When any of these films without prior surface treatment, were placed together and laminated, the interface was very weak, always with a fracture energy G_c<10 J/m² as measured by a T-peel test. However, we were able to form a strong laminate structure by modifying the surface of the base film, causing the region within 2000 Å of the surface to convert to polyamic acid. We subsequently coated this surface modified base film with a thin layer of poly 4,4´-oxydiphenylene oxydiphthalimide (ODPA-ODA), a polyimide with T_g=270°C, and laminated two such surface clad films together at 350°C. For the case of the KaptonH films, the interfacial fracture energy was too large to be measured with the T-peel test (G_c⩾1300 J/m²). The ODPA-ODA clad UpilexS films had a G_c=440±80 J/m². The ODPA-ODA can also be used to bind sequentially spuncast layers together. In this case it is applied as a thin layer onto a fully imidized PMDA-ODA layer before deposition and thermal imidization of a second PMDA-ODA layer. This interlayer increased the fracture energy by about an order of magnitude with the exact amount of increase dependent upon the molecular weight of the interlayer and the annealing temperature