Low-emissive coatings on the outer surface of heat-insulating glasses - a challenge to the flat glass industry

Abstract

The influence of low-emissive coatings on the outer surface of window glazings is reported.They reduce the heat radiation exchange with the open sky respectively the surroundings. However, they are effective and without disadvantages only on the outdoor surface of heat-insulating glasses. Here they diminish the risk of dewing on this surface and the heat loss through the window is not only decreased but it becomes also independent of the inclination of the glazing in the facade. The low-emissivity of coatings is camouflaged by wetting during rain, however, because in this case the sky is overcast, the heat loss is only insignificantly increased. It is known that the covering of dirt by weathering significantly decrease solar transmittance for all kinds of glazings. But surprisingly it has shown that these coverings only insignificantly influence the emissivity of coatings beneath. This proves that the function of heat-insulating glasses with low-emissive coatings on the outdoor surfaces is not impaired by weathering if the coatings have sufficient ageing resistance to environmental attacks.Today, there are low-emissive coatings on the base of SnO2 on the market with high solar transmittance developed forposition 3 of double heat-insulating glasses as well as coatings with reduced solar transmittance for position 2 of solar control glasses. Because the chemical and abrasive resistance of both types of coatings is better than that of untreated float glass, they can also be applied on outdoor surfaces. With these coatings on position 1 a new generation of heat-insulating and solar control glasses with improved functions can be created. In combination with the developing of coatings more advantageous than those on the base of SnO2 this may be a challenge to the flat glass industry in the future.