Ultralong Lifetime of Active Surface of Oxygenated PET Films by Plasma-irradiation and Bonding Elements
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Ultralong Lifetime of Active Surface of Oxygenated PET Films by Plasma-irradiation and Bonding Elements Miyoshi Yokura1, 2, Kenichi Uehara1, Guo Xiang 1, Kazuya Hanada1, Yoshinobu Nakamura3, Lakshmi Sanapa Reddy4, Kazuhiro Endo5, Tamio Endo1 1. Mie University, 1577 Kurima, Tsu, Mie 514-8507, Japan. 2. Adwel R&D Co. Ltd., Ritto, Shiga, Japan. 3. The University of Tokyo, Bunkyo-ku, Tokyo, Japan. 4. Department of Physics, S.V.D. College, Kadapa, India. 5. Kanazawa Institute of Technology, Nonoichi, Ishikawa, Japan. ABSTRACT Biaxially oriented polyethylene terephthalate (PET) films can be bonded directly by oxygen plasma irradiation and low temperature heat press around 100°C. The irradiated films were kept in the atmosphere for six years, yet they can be bonded tightly as well. Dry- and wetpeel tests indicate that two bonding elements can be suggested, hydrogen bonding and chemical bonding. The films are bonded by these two elements at lower temperatures, but by the pure chemical bonding at higher temperatures. 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 hydrogen and chemical bondings. Dehydrated condensation reaction is proposed for the chemical bonding. It is briefly mentioned on two origins for the long lifetime of irradiated active surface. INTRODUCTION A clean energy is urgently demanded on the earth, then development for it is accelerated in the world. One of essential technologies is a solar cell [1]. It is necessary to further improve power generation efficiency, weight and durability for wider applications. A cost performance is also an important factor. Usually polyethylene terephthalate (PET) films are used for a backsheet of solar cell panel [2]. It consists of various PET films and these are laminated using glues with organic solvents, causing environmental issues as well as lower performance. We developed a technique of plasma-irradiation-induced direct bonding of plastic films without using any glues [3]. Normally the plasma irradiation effects on the plastic surfaces have very short lifetime, say several days [4]. A reason for it was reported that plasma-generated functional groups diffuse inside away or turn-back inside at the surface [5]. We, however, report here that the PET films, kept for six years in the atmosphere after the plasma irradiation, can still be bonded very tightly in our work. New concepts are proposed for such ultralong lifetime of the plasma-irradiation effect. The plasma-induced activation of plastic film surface is an important technique when we deposit inorganic thin films such as ZnO and TiO2 on plastic films in flexible devices.
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EXPERIMENTAL In this experiment we used PET film samples (Lumirror, Toray) which were produced by two-axes stretch method (biaxially oriented PET). Sample size is 100 mm x 200 mm, and thickness is 1 μm and 100 μm. The film samples were attached on a grounded drum electrode in a vacuum chamber [3]. The chamber was evacuated down to 10 Pa
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