|Budget Amount *help
¥2,500,000 (Direct Cost : ¥2,500,000)
Fiscal Year 2004 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 2003 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 2002 : ¥1,000,000 (Direct Cost : ¥1,000,000)
PET (polyethylene terephthalate) is widely used as beverage containers and food or medicine packages due to the easy handling as well as the low cost It is also suitable for recycling. However, the barrier characteristics to some gases such as CO_2 and O_2 are not so good that the long-period maintenance of quality is hard for some beverages or medicines. On the other hand, thin DLC (Diamond Like Carbon) layer coating has been reported to be very effective for enhancing the barrier characteristics. In this research, we intend to change the PET surface to DLC by ion implantation instead of coating with the DLC film. The surface of PET film is modified by PBII (plasma-based ion implantation) with nitrogen plasma. 10kV negative-pulse voltage of 5 micro second in width is applied to the film. Attenuated total reflection FTIR is used to investigate how the characteristic absorption peaks for PET decrease, that is, how the amorphous state increases. The result shows that the absorption peaks
decrease with the dose. Since the penetration depth of the evanescent wave is several times larger than the PBII modified-layer width in the PET sheet, the measured spectrum includes the absorption peaks from the unmodified PET under the modified layer. By calculating the ratio of the evanescent-wave power penetrating only into the modified layer to the total evanescent wave power, we can estimate that the modified layer is fully amorphous.
Most PET molecules in the near surface volume are destroyed and made into amorphous carbon by 10 keV nitrogen ion implantation. Raman spectra have indicated the generation of DLC (diamond like carbon) layer, we measure the variations of CO_2 and C_2 permeability through the surface-modified PET sheets as a function of ion dose. As a result, nitrogen ion implantation with 10 keV in energy and 6x10^<16> [ions/cm^2] in dose reduces CO_2 and O_2 permeability for the PET sheets down to 1/10 and 1/6 of times the values for those of the untreated sheets, respectively. Using these measured values, the local gas-barrier enhancement, which is restricted to the modified layer, is also discussed. Since the modified-layer thickness is less than 100 nm (0.1 micron), i.e. one thousandth of the PET sheet thickness, the reductions of local permeability for ion-implanted layer are 2x10^4 for CO_2 and 1.1x10^<-4> for O_2, respectively.
Finally, we implanted nitrogen ions into the inner surface. We have confirmed that the ion implanted inner surface of a PET bottle has been changed into DLC. Furthermore, the gas barrier characteristics have been remarkably enhanced. Less