ETPs when used for electrical/electronic applications require fire resistance. For the fire protection of thermoplastic engineering resins, phosphinate-based flame retardants (FRs) are the alternative to established products such as halogenated FRs.
Products based on organic phosphinic acid salts have been established for fiberglass reinforced polyamides (PAs). Organic phosphinates are hydrophobic fine powders with a very low residual solubility in water. For PA6 and 66, synergistic blends with melamine derivatives are the products of choice. Phosphinate-based FRs is mainly used to achieve a V-0 classification according to the UL 94 test. Class 5V A can be reached as well. The required loading depends on several parameters, such as the type of PA polymer or blend, thickness of material and fiberglass content. Unlike other halogen-free FRs, such as melamine cyanurate or red phosphorus, the phosphinate based systems can be used at nearly all glass levels up to 50%. Apart from the self-extinguishing ability of the materials, other tests simulating electrical failures are crucial for the electrical/electronics market. In the hot-wire ignition (HWI) test according to UL 746 A (IEC 60 695-2-20), a fiber glass-reinforced PA66 containing Exolit OP 1312 reaches the highest performance level category 0 (PLC 0), corresponding to a mean ignition time of more than 120 seconds. The required dosages are equivalent to the UL 94 5V A level. PLC 0 is achieved in the high-current arc ignition (HAI) test as well. More than 200 arcs are needed to ignite the flame retarded PA 66 GR.
The revised glow-wire test according to the European standard EN/IEC 60695 measures two key figures: GWFI (glow wire flammability index) and GWIT (glow wire ignition temperature). For electrical components used in household appliances, it is particularly important to reach levels of 960°C (GWFI) and 775°C (GWIT). PA compounds with phosphinate-based FRs usually pass both test levels. However, the GWIT performance can be border line for finished parts so adaptations of the formulation may be necessary.
Since the heat-release rate is the most important factor for the speed of fire propagation, these results confirm an excellent degree of protection against fire spread. PA66 GR with the synergistic blend Exolit OP 1312 at the UL 94 V-0 level features relatively low loading, low material density and a high comparative tracking index. PAs with high heat-deflection temperatures known as polyphthalamides with HDT/A 280°C, are a rapidly growing group of specialty products in the electrical/electronics industry.
As flame retarded compounds, they are used in sophisticated applications such as surface mount technology (SMT) of semiconductor components. Facing the stringent requirement of lead-free reflow soldering, these materials have to withstand peak temperatures of 260°C and more during the soldering process. HPPAs can only compete with more expensive materials such as LCPs (liquid crystal polymers) if the FR system keeps their properties on the high level required by the application.
The phosphinate Exolit OP 1230 has proven to be stable enough and provides efficient flame retardancy for HPPAs. Apart from very good mechanical and electrical properties of the polymer compound, the process-related performance is very important. Unlike other FR materials, compounds based on Exolit show no blistering after reflow test at 260°C (lead-free soldering).
Compounders, moulders and OEMs eagerly anticipated the development of an Exolit OP grade for thermoplastic polyesters that can comply with UL 94 V-0 also at low thickness. With Clariant’s new synergistic formulations, another stronghold of halogenated FRs is crumbling, as they are already used for halogen-free flame-retarded PBT, PET or TPE-E. The synergistic formulations used in thermoplastic polyesters are tailored to this family of polymers and therefore different from those developed for PAs. The new FR polyester compounds are superior to materials based on brominates FRs in terms of density and electrical properties. The CTI values that can be reached allow a broader range of applications and miniaturization of appliances. However, due to the filler-like behaviour of the Exolit OP, the physical properties of the compound do not completely match the properties of their halogenated counterparts.
Although they are a relatively young product group, the phosphinate containing FRs have been intensively studied in view of their toxicological and environmental properties. The results are very satisfying and do not generate any concern related to their use in plastics. Moreover, phosphinate containing materials do not require separation under the European Regulation on Waste Electrical and Electronic Equipment (WEEE). The highly effective phosphinates fill a gap in the fire protection of the widely used engineering plastics due to their overall good property profile and the possibilities they offer. |
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