SURFACE PHOTOGRAFTING OF LOW-DENSITY POLYETHYLENE FILMS AND ITS RELEVANCE TO PHOTOLAMINATION

Surface modifications of pristine and ozone-pretreated low-density pol yethylene (LDPE) films were carried out via UV-induced graft copolymer ization with a photoinitiator-containing, epoxy-based commercial monom er (DuPont Somos(TM) 6100 for solid imaging and optical lithography) a nd also with the photoinitiator-free acrylic acid (AAc). The chemical composition and microstructure of the graft copolymerized surfaces wer e studied by angle-resolved X-ray photoelectron spectroscopy (XPS). Th e concentration of surface grafted polymer increased with the UV illum ination time and the monomer concentration. For LDPE films graft copol ymerized with the epoxy-based monomer, surface chain rearrangement was not observed or was less well pronounced, due to the partial crosslin king of the grafted chains. Simultaneous photografting and photolamina tion between two LDPE films, or between a LDPE film and a poly(ethylen e terephthalate) (PET) film, in the presence of either monomer system, were also investigated. The photolamination rates and strengths depen d on the ozone pretreatment time, the UV illumination time, and the UV wavelength, as well as on the nature of the substrate materials. A sh ear adhesion strength approaching 150 N/cm(2) could be achieved with e ither monomer system, provided that the polymer films were pretreated with ozone. The failure mode of the photolaminated surfaces was cohesi ve in nature in the case of the photoinitiator-containing epoxy monome r, but was either cohesive or adhesional in nature (depending on the s ubstrate assembly) in the case of the photoinitiator-free AAc monomer.