Long Lifetime of Plasma Effect on Bonding of Poly(ethylene terephthalate) Films and Surface Analyses

Abstract

Poly(ethylene terephthalate) (PET) films can be bonded directly by oxygen plasma irradiation and heat press at low temperatures of 100–160 °C. The irradiated films were kept in the atmosphere for six years, yet they can be bonded tightly. The irradiated surface is extremely active just after the irradiation, and it is considerably active after five years. Dry- and wet-peel tests suggest hydrogen bonding and chemical bonding. The films are bonded by these two elements at lower press temperatures, while by the pure chemical bonding at higher temperatures. Fourier transform infrared spectroscopy (FTIR) results on the non-irradiated, irradiated and bonded samples indicate that OH and COOH groups are created at the surface, they are responsible for the both bondings. Dehydrated condensation reaction is proposed for the chemical bonding. The hydrogen bonding is broken by water penetration, causing smaller peel strength under the wet-peel test. Cross-linking layer may be the origin for the long lifetime.

Water adsorption and desorption on plasma-activated PET film surface, indication of hydrogen bonding

“…1) For example, they are used as back sheets for solar cell panels, flexible circuit films, [2][3][4] and insulator sheets in the motor of electric vehicles. [5][6][7] In these applications, the PET films are laminated with other types of plastic films 8,9) such as poly(phenylene sulfide) (PPS) 10) and poly(vinyl fluoride) (PVF) 11) using glues and organic solvents. However, we have to collect the organic solvents in used lamination processes, because they cause environmental problems.…”

“…However, we have to collect the organic solvents in used lamination processes, because they cause environmental problems. 12) We demonstrated the direct bonding between PET and PET, [13][14][15][16] and PET and other plastic films 4) by a plasma irradiation technique and low thermal press 5,[13][14][15][16] without using any glues. The bonding force is stronger than the film cohesion force, as demonstrated in Fig.…”

“…The bonded films have peel strengths larger than 10 N/cm in the 180°peel test, beyond which they show cohesion failure. 5,13) We propose that the mechanism of bonding involves dehydrated condensation reactions between the plasma-created active OH and COOH groups 17,18) at the interface of two irradiated films under the low temperature press. [13][14][15][16] It was found that this plasma irradiation effect on bonding capability can be maintained for more than six years when the irradiated films are kept in the normal atmosphere.…”

“…[13][14][15][16] It was found that this plasma irradiation effect on bonding capability can be maintained for more than six years when the irradiated films are kept in the normal atmosphere. 5,14) One of the origins might be the finding that the irradiated surface having the OH and COOH groups is overspread with atmospheric water. 5,19) Then, in this work, we investigated the activity of irradiated surface of PET films in terms of water adsorption and desorption on the surfaces of films.…”

“…5,14) One of the origins might be the finding that the irradiated surface having the OH and COOH groups is overspread with atmospheric water. 5,19) Then, in this work, we investigated the activity of irradiated surface of PET films in terms of water adsorption and desorption on the surfaces of films.…”