An unusual process uses uv radiation to cause microcellular foaming in narrow bands on the surface of thin t-butylacrylate/methylmethacrylate copolymer sheet.

An unusual process uses uv radiation to cause microcellular foaming in narrow bands on the surface of thin t-butylacrylate/methylmethacrylate copolymer sheet. The process was reported by Oji Paper Co. of Tokyo in a paper at the Foams TopCon 2006 conference in Elk Grove Village, Ill., last month, sponsored by the Society of Plastics Engineers. Because the high-resolution foamed patterns selectively change the transparency of the film, Oji Paper is exploring the process for making optical diffusion films, light guides, and optical wave guides. To make the film, acrylic copolymer containing a photosensitive acid generator is solvent cast onto a supporting PET sheet, then peeled off and treated in two separate steps. The sheet is first uv-irradiated and then heated. The combination induces chemical reactions that release isobutene gas, forming cells smaller than 10 microns. Cell size is controlled by temperature. This photochemistry reportedly foams much thinner film than is possible by extrusion with supercritical CO2, which tends to lose gas from the film surface. Patterns can be photochemically foamed into sheet by masking the uv light or drawing lines with a uv laser. Oji Paper: +81 (3) 3533-7008/www.ojipaper.co.jp . SPE: (203) 775-0471/www.4spe.org