Investigations on nano- and submicron-particle generation by spray painting processes

Abstract

This paper presents experimental and numerical studies to determine the particle size distributions (PSD) and concentrations in paint overspray. Two kinds of paint materials, solvent borne and water borne paints, both with and without manufactured nanomaterials (pigments), and an industrial spray gun were used. Different aerosol measuring techniques, namely the Spraytec Fraunhofer type particle sizer for micro-sized droplets in the spray jet and the Scanning Mobility Particle Sizer (SMPS) for nano particles in paint overspray were applied. It was found, that solvent borne clear coats create significantly higher number concentration of nano-sized droplets than the water borneprimers. Only small differences in PSD between paints with and without manufactured nanomaterials were found. Numerical simulations of droplet trajectories within the spray booth, for both micro and nano sized droplets, were carried out. Based on the experimental and numerical results, a representative particle size distribution (smaller than 1 μm) for the given spray gun was obtained. Effects of turbulence models on the particle deposition on targets, especially for submicron particles, have been analysed in detailed.Keywords Nano-and submicron-particle, spray coating, aerosol measurement, droplet trajectory calculation IntroductionThe increasing application of manufactured nanomaterials (MNMs) in industrial products requires more knowledge about environmental and human safety. This is especially true for the spray painting process, which produces a high percentage of paint overspray. During the migration of the overspray droplets, solvent continues to evaporate, resulting in the formation of non-volatile fractions of paint aerosols that consist of paint matrix and the applied MNMs, such as TiO2, ZnO, carbon black, etc. The MNMs could remain embedded in paint matrix particles or released from the paint matrix. Thus, the characterization of paint overspray aerosol becomes more and more important. Information about the estimation of worker nanoparticle exposure to paint overspray is limited and particularly the process understanding of nanomaterial release during spray applications. A review of nanoparticle exposure at nanotechnology workplaces has been stated by Kuhlbusch et al. [1]. Carlton and Flynn [2] developed an empirical-conceptual model based on dimensional analysis, to predict breathing zone concentrations of a paint mist during spray painting tasks. Later, they also carried out CFD calculations to simulate production of breathingzone concentration of a paint overspray, for a simple case of the spray painting of a flat plate in a cross-flow ventilated booth [3]. For the risk estimation of exposure to paint overspray, it is also useful to categorize the paint aerosol particles in a spray jet, which can provide important information with regard to the worst case for a given spray atomizer and the applied paint material. Based on the experimental and numerical studies [4][5][6], paint droplet injection models for different atomi...

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