The role of rheological properties and spraying parameters on the spectral selectivity of Thickness Insensitive Spectrally Selective (TISS) paint coatings

TISS paints are complex multi-phase systems consisting of large Al flakes (>50 μm) and small inorganic oxide pigment (<500 nm), embedded in a resin. The large difference between the metallic and inorganic oxide pigment particles poses a problem for paint application in a well reproducible manner, necessary for attaining the highest difference between the solar absorptance and thermal emittance values (i.e., spectral selectivity) of the applied coatings. Due to the complex paint flow through the spray gun nozzle, adjustment of the deposition parameters can be correct only by knowing the detailed rheological properties of the paint, combined with a trial-and-error process.In the present work, we studied the rheological properties of TISS paints and their effect on the spectral selectivity of dry coatings, which were applied on the substrate with the spraying application method. The final aim of our study was to determine the influence of spraying parameters (nozzle, spray gun pressure, and speed of substrate) on the selectivity and to establish the phenomenon of pigment distribution and flake orientation during spraying application.

► Rheological behavior has a major impact on the spectral selectivity of TISS paints.
► Rheological characterization is vital for avoiding poor leveling of dry coatings.
► Spraying parameters are crucial for proper orientation of Al flakes.
► Proper distribution of Al flakes—black pigment is a key to high spectral selectivity.
► Manufacturers of TISS paints should specify technological parameters for spraying.