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Pressure sensitive adhesives (PSAs) are widely used in the industrial application and in our daily life, such as packaging, labels, tapes, and so on, because of their excellent characteristics - easy to stick to many kind of substrate without any activation, and easy to peel. Among many kind of PSAs, solvent-borne or water-borne acrylic PSAs are one of the most popular PSA due to their wide variation of adhesion properties and high cost performance. Recently, strong demand for environment-friendly technology is increasing and development of solvent free system is becoming important. The UV curable acrylic PSA system has been proposed as a solvent free system, however, some technical problems to be solved remains 1]. As the acrylic system polymerizes through photo-initiated radical polymerization, oxygen in the air interferes with the polymerization of monomers 2]. This fact results in residual unreacted monomers, which cause odor problem and skin irritation. To solve these problems of acrylic radical system, the cationic polymerization system, which is able to cure under air atmosphere and to form thin coating, has been introduced. For example, a PSA system consists of heterotelechelic polymer and tackifier was proposed 3]. The cured PSA sheet was reported to exhibit good adhesion properties, still some problems seems to remain. High viscosity of the formulations requires rather high heating during coating process, and the low compatibility of polymer limits the variation of formulation. These problems could be a barrier to the industrial application of this system. Oxetanes have been proved to possess many superior characteristics 4]. First, high reactivity of oxetane enables to give high molecular weight polymer. Second, even low molecular weight monomers developed so far were AMES Test negative. And third, mono-functional oxetanes, especially alkyl oxetanes with alkyl side chain, possess low viscosity and good compatibility with other monomers; Using alkyl oxetanes, wide range of useful PSA formulations seems to be possible. In this paper, the photo-curing properties of PSA formulations of a mono-functional alkyl oxetane in combination with monomers listed below were investigated, and the adhesion properties of the cured PSA sheet were evaluated.
