This invention relates to optically transparent or clear elastomers. Transparent plastic materials such as, for example, polycarbonates and polystyrenes, have been known for many years. Being thermoplastic, however, these materials are of limited performance characteristics in terms of physical properties. Often these materials are rigid, or they readily are subject to flex crazing, or flow under stress, or they melt or deform at higher temperatures. Available clear plastic materials in general are not able to meet simultaneous requirements of flexibility, low haze, heat resistance, chemical resistance, and absence of flow under stress.
Some elastomers are known to have a degree of light transmissivity however few are known to be of true optical quality. Known EPDM vulcanizates display a range of characteristics that interfere with optical clarity. Such vulcanizates generally range from slight yellow to black, display considerable haze, tackiness, low permanent set or creasibility, are transluscent to opaque, or display blooming and hazing from constituent migration to the surface and therefore are generally recognized as inferior for optical lens applications. In compounding EPDM, the materials added for imparting strength and for curing generally make the EPDM opaque. A need exists for an EPDM rubber composition that maintains the transparency of the uncured gum without compromising other physical and chemical properties, such as chemical resistance, heat resistance, tensile and tear strengths, etc. A crosslinked thermally stable, chemically resistance and heat resistant flexible elastomer of optical quality would satisfy a long felt need in many optical applications in harsh environments, especially where glass is unsuitable, such as visors for protective suits for air personnel intended to protect against toxic agents, or visors intended for optical coupling to advanced graphic display weapons systems.