Improvement of oxygen barrier of PET film with diamond-like carbon film by plasma-source ion implantation

Plasma-source ion implantation is employed to deposit amorphous carbon layers on polyethylene terepthalate (PET) film as a means of improving the oxygen barrier characteristics. This process is performed using pulsed, high negative voltage (∼15 kV, 10 μs pulse width, 300 pulses/s) and C2H2 gas at 5.5 Pa. The effect of adding Ar or CH4 to the gas mixture is also examined. The amorphous carbon layer deposited on the PET film is found to consist primarily of hydrogenated graphite crystal with minor CH, CH2 and CH3 components, and to have the characteristics of diamond-like carbon. The film reduces the oxygen transmission rate (OTR) of the PET film by ∼150 times at a film thickness of only 290–700 nm, and is seen to decrease with decreasing ratio of the disorder peak to the graphite peak. It is predicted that there exists an optimum gas pressure to obtain the highest gas barrier at a minimal thickness using this technique. The relationships between the conditions of discharge and the OTR of the PET are also discussed.