Synthesis of practical high-gas-barrier carbon films at low and atmospheric pressure for PET bottles

In this paper, the high-gas-barrier properties of a-C:H films are summarized and the possibility of the wider applications of a-C:H films for food and beverage containers is discussed. Coating a-C:H films inside polyethylene terephthalate (PET) bottles dramatically improves the gas barrier property and accordingly, the oxygen transmission rate (OTR) becomes extremely low (∼1/30 of uncoated bottles). In fact, the coating equipment for PET bottles operated by the radio-frequency plasma-enhanced chemical vapor deposition (CVD) method under low pressure has been developed and has already been in practical use. Recently, a unique and cost-effective atmospheric-pressure glow plasma CVD technique was introduced by our group as the substitute for the low-pressure CVD technique. Homogeneous and highly stable plasma was constantly generated under an atmosphere of acetylene gas (C₂H₂) without using any other dilution gases such as He, Ar and N₂. It was found that by using a pulsed power supply operated at a frequency of 35 kHz with a voltage of 24 kV, high gas-barrier a-C:H films were synthesized under atmospheric pressure, which implies that the new power supply would eventually lead to the development of a new atmospheric-pressure glow plasma CVD technique.