Generally, styrenic resins have good processability and mechanical properties and have accordingly been used to produce housing parts for many electrical and electronic goods. However, because styrenic resins can be readily ignited, they are not able to resist fire. Particularly, once styrenic resins catch on fire by external ignition sources, they can further spread fire. Moreover, styrenic resins are subject to various mandatory controls on flammability for safety reasons in countries such as the United States, Japan and Europe, and are required to have high flame retardancy to meet the Underwriter's Laboratories Standard for use in the housings of electrical and electronic appliances. Accordingly, there is a need render styrenic resins flameproof to broaden their use in different applications.
A widely used and known method for imparting good flame retardancy to styrenic resin comprises adding a halogen-containing compound as a flame retardant to a rubber-modified styrenic resin and adding an antimony-containing compound as a flame retardant aid. Examples of halogen-containing compounds used to impart flame retardancy include polybromodiphenyl ether, tetrabromobisphenol-A, epoxy compounds substituted with bromine, chlorinated polyethylene, and the like. Antimony trioxide or antimony pentaoxide is commonly used as an antimony-containing compound.
When a halogen- and antimony-containing compound is used to improve flame retardancy of resins, a desired degree of flame retardancy can readily be imparted to the resulting products without significantly degrading the physical properties thereof. Therefore, the halogen- and antimony-containing compounds are widely used as the primary flame retardant for housing materials of electrical appliances and office equipment formed of ABS resins, PS resins, PBT resins, PET resins or epoxy resins. However, hydrogen halide gases released by halogen-containing compounds during processing can have fatal effects on the human body and have high environmental persistence because these compounds are not naturally degradable. Also these compounds are not soluble in water, and thus can be highly bioaccumulated. Particularly, polybromodiphenyl ether, which is widely used as a halogen-containing flame retardant, may produce toxic gases such as dioxin or furan during combustion, and is consequently harmful to humans and the environment. Accordingly, there is a need to develop flame retardancy methods that do not employ halogen-containing compounds.