The present invention relates to vinylidene fluoride ("VDF") polymers having a reduced smoke-generating capability upon ignition and having an increased resistance to ignition (limiting oxygen index or "LOI"), particularly to compositions containing VDF polymers having calcium tungstate dispersed therein.
One of the notable characteristics of fluorinated polymers is their relatively low susceptibility to burning and the low level of smoke generated in such situations as compared with other polymers. This characteristic has been utilized in the wire and cable industry, among others, and more specifically in plenum cable constructions and fiber optic cable applications. Fluoropolymers have LOI values ranging from the 40's to the 90's, as determined by ASTM D-2863, with the higher index numbers being achieved by the least flammable polymers. Polyvinylidene fluoride (PVDF) based resins normally have LOI values in the lower end of that range. Thus, reducing the smoke density and increasing the flame retardancy of the VDF polymers is a desirable goal. The cable constructions would then exhibit a greater tolerance to the inclusion of non-fluorinated components.
Other candidates have been tried for enhancing flame retardation and reduced smoke, such as kaolin clay (U.S. Pat. No. 4,804,702), but are only moderately successful. An improved retardant is highly desirable. The text of U.S. Pat. No. 4,804,702 is incorporated herein by reference for its teaching of typical cable constructions employing such VDF polymers.