CoolSun: organic paints for cool buildings

Poor attention has been paid so far to the 50% of NIR radiation flux (750-2500 nm), coming from direct, diffused and reflected sun radiation, which contributes to increase the temperature in urban areas. To reduce the increasing demand for energy consumption for air conditioning or to produce cool fabrics, there is a need for NIR reflective pigments and coatings formulation since reflecting the sun’s radiation minimizes the amount of energy absorbed by the surface1. NIR reflective property is useful in applications where solar heating must be attenuated, such as leather goods, greenhouse coverings, roofing and transporting of heat-sensitive materials2 Today, NIR reflectivity is obtained with the use of inorganic pigments (TiO2, metal oxides and complexes) that are expensive and, in some cases, toxic2. The challenge is the development of a fully organic NIR reflective coating. This can be possible by mixing NIR non-absorbing pigments with polymeric NIR-reflective additives in the formulation of coatings. This work aims at the preparation of paints starting from waterborne-dispersion of resin and NIR reflective organic pigments and additives. As pigment we used different perylene bis-imide derivatives, already known for their NIR reflective properties4. Aswell, we studied the synergic cool effect adding thermoplastic hollow microspheres (Expancel®)5 and their comparison with a standard black dye.