A review of current flame retardant systems for epoxy resins

The review covers materials currently available or which appear to be in serious development, with emphasis on electrical laminates and encapsulation, and brief coverage of other applications. The dominant technology for FR-4 printed wiring boards uses tetrabromobisphenol-A reacted into the epoxy resin. Nonhalogen systems include additives such as alumina trihydrate, alumina trihydrate plus red phosphorus, and aromatic phosphates. Reactives include a dihydrooxaphosphaphenanthrene oxide and various adducts thereof, and hydroxyl-terminated oligomeric phosphorus-containing esters. A further approach is the modification of the epoxy resin by placement of aromatic groups between the glycidyloxyphenyl groups, and/or by use of a triazine-modified novolac as crosslinker. Flame retardant epoxy coatings continue to make use of ammonium polyphosphate plus char-forming additives.