(218f) Development of Solvent Selection Guide for CO2 Spray Coating System

The paint industry is the biggest volatile organic compound (VOC) emission source in Japan. It is urgent issue to reduce VOC emission. CO2 spray coating system, which uses CO2 as alternative diluent of paint, is promising technique for VOC reduction and dry energy saving. However, precipitation of polymer is induced by CO2 dissolution into some paints because CO2 is a poor solvent for the some polymers. It is important to prevent precipitation of polymer in paint solution for spray coating. We have attempted to develop solvent selection guide for the CO2 spray coating system. In this work, phase behavior and phase equilibria of polymer + solvent + CO2 system were experimentally studied. Furthermore, relationship between solubility parameter of the solvent and the phase behavior was investigated.
An acrylate resin as a paint and eight kinds of organic solvents having wide range the solubility parameters were used for phase behavior observation. As a result, precipitation of the resin did not occur in some solvents, and we examined the range of the solubility parameter of effective solvents for the CO2 spray coating system from the observation.
Phase equilibrium data were measured with a synthetic apparatus using three kinds of solvents to obtain CO2 solubility at precipitation pressure observed in the phase behavior experiments. Solubility parameters of CO2 + solvent systems were calculated from the solubility data and the adequate range of the solubility parameter of solvent for the CO2 spray coating system was estimated. Thus it could be noted that solubility parameter is important for solvent selection of CO2 painting.