A novel technique to enhance surface properties of DLC films deposited on the inner wall of cylindrical PET barrel by DC-RF hybrid discharge

A newly proposed technique has been utilized to improve surface properties of gas barriering DLC films deposited on PET bottle. The discharge in the bottle is induced by radio-frequency discharge and an external DC system is coupled to the RF power supply to control the potential of discharge electrode. In contrast to conventional discharge configuration, this leads to the capability to optimize the ion bombardment energy and surface properties of deposited films. The effect of negative DC voltage on the adhesion strength, optical transmittance, surface profile, roughness, and permeability of DLC coated PET samples has been investigated using immersion test, UV-visible spectroscopy, optical profilometry, and gas permeability tester, respectively. The results have demonstrated that the DLC coated PET samples with external bias show slight damage during beer immersion tests. Lower light transmittance is induced for the films deposited at high negative bias due to larger ion bombardment effect. There exists a proper bias to give rise to a small surface roughness. The gas permeability of DLC coated PET samples deposited with external bias has been substantially decreased compared to that of untreated one.