Preparation and characterization of a new low infrared-emissivity coating based on modified aluminum

A low infrared-emissivity coating was prepared using modified Al powder and polyurethane as metallic pigment and adhesive. Al powder was coated with polyethylene wax by the flux-capping method to reduce the emissivity and gloss of the coating. The surface morphology and chemical composition of pure and modified Al powders were characterized by scanning electron microscopy and X-ray diffraction. The infrared emissivity of the product was measured by an infrared emissometer. The influences of the modified Al powder content, substrate material, coating thickness, and aging time on infrared emissivity were systematically investigated. The results indicate that modified Al powder decreases not only the gloss of the coating, but also its emissivity within the wavelength range of 8–14 μm. The polyethylene wax/Al composites have a homogenous sheet structure at 30 wt.% Al content, and a lower infrared emissivity. The optimum content of modified Al powder is around 18 wt.%. The coating exhibits a lower emissivity value and excellent optical properties. The infrared emissivity of the composite coating significantly increases with increased thickness, and approaches a constant value when the thickness is more than 80 μm. Accelerated aging test results show that with increased aging time, the coating with modified Al powder has a better aging resistance and lower infrared emissivity than that with pure Al powder.