Oxygen transmission of transparent diamond-like carbon films

Recently, gas barrier properties of diamond-like carbon (DLC) films have been investigated and are started to apply to food packaging field such as an inner coating for polyethylene terephthalate (PET) bottles. Recycling PET bottles has been promoted on environmental and economic grounds. However, it is difficult to recycle DLC-coated PET bottles because of the brownish color of DLC films. In this study, we successfully synthesized transparent and colorless DLC films on PET substrates from CH4 and H-2 gases by the RF-CVD method. Further, we investigated the relationship between oxygen transmission and optical transparency from the viewpoint of microstructure and hardness of the films. The results showed the optical transparency were gradually improved as decreasing RF power and increasing deposition pressure. In particular, the films deposited at 15 W and 40 Pa was almost completely transparent; however the oxygen transmission increased. (c) 2004 Elsevier B.V. All rights reserved.