James Bradshaw Mcgee

Silicone resins for protection of first surface reflectors

Abstract Silicone resins were evaluated for use as protective coatings for front or first surface silver and aluminum reflectors. The silicone resins encompassed a broad range of chemical compositions and physical properties. The relevant physical properties of the cured resin films were measured and their soiling characteristics were obtained by measuring the transmissivity of cured films at various periods of outdoor exposure. The spectral hemispherical and specular reflectance of squares of float glass metallized with aluminum and protected with the best candidate coatings were measured before and after exposure to ultraviolet radiation. Float glass squares metallized with both silver and aluminum coated with resin were exposed to moist sulfur dioxide, salt spray and exposed outdoors. These samples were prepared with and without silane coupling agents to promote the adhesion of the resin to the metal surface. Excellent protection and high specular reflectivity was afforded by certain of the silicone resin coatings throughout the various accelerated tests and in outdoor exposure. In general the aluminized reflectors were easier to protect than the silvered reflectors. The most common mode of failure of the silvered float glass samples was loss of adhesion between the glass and the silver. Further work is in progress to diminish this mode of failure and to identify the failure modes which have occurred on both silver and aluminum first surface reflectors.