FLAME RETARDANT CASES

UL94 is one of the primary standards for testing the flammability of plastic materials used for parts in devices and appliances. It is now harmonized with IEC 60707, 60695-11-10 and 60695-11-20 as well as ISO 9772 and 9773.  Standard size plaques of material are tested for how they respond to a small open flame or radiant heat.  The results of the testing should only be used as an indicator of performance in real world situations.  Other specific testing may also be required. 

HB - Slow burning on a horizontal specimen; burning rate < 76 mm/min for thickness < 3 mm or burning stops before 100 mm 

V-2 - Burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.

V-1 - Burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed. 

V-0 - Burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed. 

5VB - Burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may develop a hole. 

5VA - Burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may not develop a hole.

There are a number of materials that can be blended into the basic plastic resins used to mold cases. These include minerals, organohalogen and organophosphorus compounds, and some other miscellaneous organic compounds. Many cannot be used due to the requirements of environmental standards such as California Prop 65, REACH and RoHS. These additives react in different ways.

Some undergo a reaction that lowers the temperature of the plastic, thus reducing the heat source. Another technique is to actually induce a char of the surface of the plastic, thus separating it from the flame. Others release inert gases that dilute the combustible gases and lower the flame.

Chlorinated and brominated flame retardants release gases that react with the burning gases to reduce or extinguish the flame.