Research On The Heat Treatable Low-E Coatings Used For Vehicle Windshield

Vehicle windshield plays a very important role in getting more light from outside while avoiding car from wind and rain. Because of its high visible light transmittance and infrared reflectivity, low-emissivity (Low-E) coating deposited on vehicle windshield can significantly reduce energy consumption of air conditioners.This paper firstly reviews the development of heat insulation film for vehicle windshield over the past two decades. Based on the comparison of various heat insulation films, dual-silver Low-E coating is finally selected for its high visible light transmittance and infrared reflectance. As vehicle windshield has to be annealed at650℃for10min during the fabrication, how to prevent the oxidation, agglomeration and diffusion of Ag component under high temperature is vital for the application of the coating.Low-E film stacks are designed such as SiO2-TiO2-Ti-Ag-Ti-SnO2-Si3N4, SiO2-TiO2-Ti-Ag-Ti-SnO2-Ti-Ag-Ti-SnO2-Si3N4, SiO2-TiO2-Al-Ag-Al-ZnO-Si3N4, SiO2-TiO2-Al-Ag-Al-ZnO-Al-Ag-Al-ZnO-Si3N4, with the use of Ti/Al layer as protective layer and various dielectrice and cladding layer to withstand high temperture. Admittance graphical design theory and Matlab are used to calculate layer thinkness, while Essential Macleod software to simulation optical properties of the stack. The simulation results show that the average visible light transmittance of all designed stack is greater than75%with average infrared reflectivity more than80%, fully satisfying the design requirements.The effect of protective Ti layer in the Low-E stack is verified experimentally. The stacks of TiO2(30nm)-Ag (15nm)-TiO2(30nm) and TiO2(30nm), Ti (2nm)-Ag (15nm)-Ti (2nm)-TiO2(30nm) are fabricatied in JGP560magnetron sputtering deposition machine and then are annealed in air. The test results show that Low-E coating with none protective layer loses its high infrared reflectivity in high temperture while those with Ti protective layer can still keep excellent optical properties:the average transmission remains70%for visible light, less than15%for the light with780～2500nm wavelength and32%for ultraviolet.