Particles Emission from an Industrial Spray Coating Process Using Nano-Materials.

Industrial spray coating processes are known to produce excellent coatings on large surfaces and are thus often used for in-line production. However, they could be one of the most critical sources of worker exposure to ultrafine particles (UFPs). A monitoring campaign at the Witek s.r.l. (Florence, Italy) was deployed to characterize the release of TiO ₂ NPs doped with nitrogen (TiO ₂ -N) and Ag capped with hydroxyethyl cellulose (AgHEC) during automatic industrial spray-coating of polymethyl methacrylate (PMMA) and polyester. Aerosol particles were characterized inside the spray chamber at near field (NF) and far field (FF) locations using on-line and off-line instruments. Results showed that TiO ₂ -N suspension produced higher particle number concentrations than AgHEC in the size range 0.3-1 µm (on average 1.9 10 ² p/cm ³ and 2.5 10 ¹ p/cm ³ , respectively) after background removing. At FF, especially at worst case scenario (4 nozzles, 800 mL/min flow rate) for TiO ₂ -N, the spray spikes were correlated with NF, with an observed time lag of 1 minute corresponding to a diffusion speed of 0.1 m/s. The averaged ratio between particles mass concentrations in the NF position and inside the spray chamber was 1.7% and 1.5% for TiO ₂ -N and for AgHEC suspensions, respectively. The released particles' number concentration of TiO ₂ -N in the size particles range 0.3-1 µm was comparable for both PMMA and polyester substrates, about 1.5 and 1.6 10 ² p/cm ³ . In the size range 0.01-30 µm, the aerosol number concentration at NF for both suspensions was lower than the nano reference values (NRVs) of 16·10 ³ p/cm ^-3 .