Protective layer for cycloolefin polymer against an aromatic solvent prepared by chemical vapor deposition using cyclosiloxane as a raw molecule

A chemical vapor deposition (CVD) process on the basis of a closed cell system for organosilane coating on cycloolefin polymer (COP) has been developed in order to provide the polymer with the resistivity against aromatic solvents. Prior to the CVD coating, a COP substrate had been made hydrophilic through the surface oxidation with active oxygen species, that is, atomic oxygen and ozone, generated with vacuum ultra-violet (VUV) irradiation at 172 nm in wavelength to atmospheric oxygen molecules. Next, the substrate, cyclosiloxane (tetramethyl-cyclotetrasiloxane, TMCTS) and water liquids were sealed in a closed reaction cell and kept at 80 °C. The substrate was exposed for 3 h to vaporize TMCTS and water so that hydrolyzed TMCTS molecules were chemisorbed and then condensed on the hydrophilic surface, resulting in the formation of a thin film with a thickness about 50 nm. The film was transparent in the visible range. The COP substrate coated with a TMCTS-CVD film showed a resistivity to m-xylene to some extent. When a second TMCTS layer was deposited on a first TMCTS layer that had been rinsed in water and then hydrophilized with VUV oxidation, the resistivity to m-xylene has been much improved. As another approach to improve the solvent resistivity, a monolayer of fluoroalkylsilane (FAS, 1H,1H,2H,2H-tridecafluoro-n-octyltriethoxysilane) was formed on the hydrophilized TMCTS film by a vapor phase method. This FAS-TMCTS double layered film showed an excellent resistivity against m-xylene, most likely because a solvent repellency was provided by the FAS monolayer.