Andrew Donkin of LATI UK explains the considerations when colouring flame retardant plastics.
An Underwriter’s Laboratory (UL) yellow card is a globally recognised guarantee of safety and quality. It lists multiple properties for a polymeric material tested by UL to appropriate standards. The most commonly requested property we are asked to provide confirmation of via a yellow card is the flammability rating according to the UL94 standard, with the most commonly requested rating being ‘V0’. Although not always the case, for many manufacturers the approval of their end product is based on the use of plastic parts which have themselves been made using polymeric materials which are covered by UL Yellow Cards. In a world where differentiation through colour is an increasing trend, care must be taken to ensure that the colouring of a flame retardant plastic does not in some way compromise this important ‘Yellow Card’.
The considerations in this regard differ considerably depending on what exactly the flame classification is. For some electrical applications a yellow card is requested even for HB flame classifications, which do not imply the material is at all ‘self extinguishing’. In these instances colouring of the material by use of a masterbatch, or issuing to a third party to compound in the colour, can be quite acceptable as long as the colouration does not affect the HB rating.
The same does not apply however to self extinguishing materials carrying a V0 or V2 rating. In these cases, the yellow card will cover the colours in which the manufacturer can supply their polymer or compound. This could cover any of natural, black and various specific colours or, ideally, an ‘all colours’ rating. However, the coloured product has to come directly from the manufacturer as introducing the colour by means of a non-UL approved masterbatch, or by passing the natural on to a third party to colour, will mean the yellow card no longer applies.
Unfortunately, UL approved masterbatches have restricted applicability also. There are a small number of UL approved masterbatches, but these are only approved for use in combination with specified grades of material, and use in other materials, even those carrying a yellow card, will render the V0 flammability classification invalid.
Lati is a leading manufacturer of flame retardant compounds with many approved for ‘all colours’. However, there are no UL approved masterbatches for use in our grades, and the same applies to many other manufacturers. So, if you are called upon to produce a coloured product that is V0 rated, do ensure the colour / raw material combination carries the appropriate certification – it’s not an area in which to make mistakes.