Gas barrier enhancement of PET container by plasma based ion implantation

PET（聚对苯二甲酸乙二醇酯）由于易于处理以及成本低而被广泛用作饮料容器和食品或药品包装。但对CO_2、O_2等气体的阻隔性较差，使某些饮料或药品的质量难以长期保持。另一方面，据报道薄DLC（类金刚石碳）层涂层对于增强阻挡特性非常有效。在本研究中，我们打算用离子注入的方法将PET表面改性为类金刚石膜，而不是用类金刚石膜涂覆。采用等离子体基离子注入（PBII）技术对PET薄膜进行表面改性。向膜施加宽度为5微秒的10 kV负脉冲电压。利用衰减全反射红外光谱研究了PET的特征吸收峰是如何降低的，即非晶态是如何增加的。结果表明， ...更多信息 随着剂量的减少。由于倏逝波的穿透深度比PET片材中的PBII改性层宽度大几倍，因此测量的光谱包括来自改性层下的未改性PET的吸收峰。通过计算只穿透改性层的倏逝波功率与总倏逝波功率的比值，可以判断改性层是完全非晶态的，10 keV的氮离子注入使近表面体积中的大部分PET分子被破坏，变成无定形碳。拉曼光谱表明表面有类金刚石碳（DLC）层生成，测量了CO_2和C_2透过率随离子注入量的变化。结果表明，能量为10 keV、剂量为6 × 10 ~（-1）<16>[ions/cm ~ 2]的氮离子注入使PET膜的CO_2和O_2渗透率分别降低到未处理膜的1/10和1/6。利用这些测量值，局部气体阻隔增强，这是限制在改性层，也进行了讨论。由于改性层的厚度小于100 nm（0.1 μ m），即PET片厚度的千分之一，因此离子注入层的局部磁导率降低量分别为CO_2的2 × 10 ~ 4和O_2的1.1 × 10 ~ 4<-4>。我们已经证实，PET瓶的离子注入内表面已经变成了DLC。此外，气体阻隔特性显著增强。少

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 … More 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