Effects of treatment using ammonia plasma on poly(lactic acid) (PLA), poly(ethylene terephthalate) (PET), and liquid-crystal polymer (LCP) were investigated to elucidate differences related to polymer structures and the mode of introduction of nitrogen functional groups onto the polyester surfaces. Nitrogen functional groups were introduced into PET and LCP, but were not introduced into PLA. Those results indicate reductions in the contact angle for PET and LCP. No decrease in the contact angle was observed for PLA. Reasons for differences in attachment of nitrogen functional groups by ammonia plasma processing on polyester surfaces were discussed. The respective actions of active species were investigated for radicals, electrons, and ions in plasma.

The power dependence of nitrogen functional group introduction treated with ammonia plasma on poly(ethylene terephthalate) (PET) and liquid crystal polymer (LCP) was investigated. The ratios of NH2 and N–C=O groups, which are the introduced functional groups, differ depending on the power used for plasma generation. The ratio of N–C=O groups increases with increasing power. For PET, the introduction of oxygen functional groups occurs at low power. Power dependences of contact angles were found for PET and LCP. They are related to the different types and quantities of functional groups with respect to the power. A considerable decrease in contact angles is apparent at the low-power side of 0–15 W.

The surfaces of three kinds of polymer were treated using pulsed oxygen plasma: poly(ether ether ketone) (PEEK), liquid crystalline polymer (LCP), and linear-low-density polyethylene (L-LDPE). Also using pulsed oxygen plasma, oxygen functional groups were introduced on polymer surfaces. The effects of oxygen functional group introduction were investigated to elucidate whether any differences exist in the manner of introduction of oxygen functional groups on the polymer surface, arising from differences in polymer structures. The introduction of oxygen functional groups formed hydrophilic polymer surfaces. Fewer oxygen functional groups were introduced on PEEK and LCP surfaces by pulsed plasma treatment than by continuous oxygen plasma. On the other hand, many oxygen functional groups were introduced on L-LDPE surfaces than by continuous oxygen plasma. Reasons for different attachment of oxygen functional groups by pulsed oxygen plasma processing on polymer surfaces were discussed.

The effects of primary amino groups' introduction treated by ammonia plasma on linear low-density polyethylene (L-LDPE) were investigated. The introduction of the primary amino groups on the L-LDPE surface was carried out by three kinds of approaches. These approaches were the use of conventional ammonia plasma, plasma treatment of hydrogen gas blended into ammonia gas, and ammonia plasma treatment under hydrogen. Primary amino groups could be introduced with three kinds of ammonia plasma. Amide groups were also introduced simultaneously, which suggested the oxidation of polyethylene surfaces. The ammonia plasma treatment under a hydrogen gas atmosphere is the most effective to introduce primary amino groups into a polyethylene surface selectively.

Surface modification of aromatic LCP surfaces with plasma treatment was carried out to improve the adhesive strength at LCP/Cu interfaces. Plasma treatment to a polymer surface is known to introduce functional groups and to bring about etching action thereon. This study was intended to investigate which or both functional group introduction and etching action contributes to adhesive strength improvement. The effect on the adhesive strength of ordinary plasma treatment and remote plasma treatment was evaluated. Remote plasma treatment is possible to irradiate mainly radicals on LCP surface. The following three subjects were discussed in this study : (1) plasma treatment increases the adhesive strength at LCP/Cu interfaces ; (2) plasma treatment produces oxygen functional groups and nitrogen functional groups and led to etch LCP surfaces, all of which contribute to adhesive strength ; and (3) the oxygen functional groups, nitrogen functional groups, and etching action work simultaneously to enhance adhesive strength by their synergistic effects.