FLAME RETARDANTS
Figure 3 - Cone calorimeter : Rate of heat release of 30 % GF PA 6 V-0 compounds with Exolit OP
Figure 4 - Colour appearance of PA 66 GF with Exolit OP before & after storage for seven days at 150 ° C
The advantages of PFRs in PAs include a comparative tracking index ( CTI ) of 600V and above . High CTI values are important for the design of connectors for the creepage distance . The higher the CTI , the lower the minimum creepage distance can be , facilitating miniaturisation or higher currents . Optical smoke density and smoke toxicity are also different when using PFRs or BFRs . Due to their low smoke density according to IEC 45545 standard , PAs with PFRs are used in , for example , railway interiors .
New options
Modifying a PFR to pass the GWIT and UL 94 with the same recipe has been a challenge . However , with the newly developed Exolit OP grades , it is possible to achieve V-0 and GWIT of 775 ° C at reasonable FR dosages . This achievement comes from adding a new synergist that induces more of a foamed char after the application of the glowing wires and prevents ignition . During the product development , it was found that GF PA 6 and 6,6 need different systems , due to different thermal degradation pathways . Consequently , Clariant is launching Exolit OP 1466 ( TP ) and Exolit OP 1480 ( TP ) for each of them respectively . For high temperature PAs , which normally give a better glow wire performance , OP 1466 ( TP ) is the preferred option . The outstanding thermal stability of Exolit OP 1400 is seen in the new GWIT blends , meaning that both grades can be processed at
high throughputs ( Tables 1 & 2 ). No blooming and no deposits in injection moulding are observed . Both Exolit OP 1466 ( TP ) and 1480 ( TP ) have passed the criteria for EcoTain . The tested dosage of the new Exolit OP grades in GF PA 6 and 66 GF is in the range of 20-24 %. Robust GWIT results above 775 ° C were observed in test specimens with varying thicknesses . Glow wire tests with PA specimens at the UL TTC lab in Krefeld and at VDE in Offenbach have confirmed their excellent glow wire performance . First trials with the glow wire end product test , where only two-second afterburning times are allowed , have shown promising results as well .
In application
A typical application of flame retarded PA compounds for household appliances is Raster-Anschluss- Steck-Technik ( RAST , meaning ‘ grid connection plug-in technique ’) connectors . RAST standards 2.5 and 5 – the numbers indicate the distance in millimeters between the contact centres – apply to household appliances . The technical requirements for the use of PAs in RAST connectors are UL 94 V-0 and GWIT 775 ° C , as well as high flowability and good mechanical properties . The new Exolit OP grades meet these and also show lower heat release in case of fire compared to the former grades . This was measured in a cone colorimeter according to ISO 5660-1 , which makes them suitable for railway interior applications , where maximum
average rate of heat emission data is required ( Figure 3 ). In addition , PAs with OP 1466 ( TP ) show lower optical smoke density . Exolit OP 1466 ( TP ) and OP 1480 ( TP ) also deliver superior colour stability after heat ageing compared to Exolit OP 1400 . This performance was assessed by storing naturally coloured , 30 % GF PA 6,6 compounds with Exolit OP 1400 and with OP 1480 ( TP ) and OP 1466 ( TP ) at 150 ° C for seven days ( Figure 4 ). The improvement can be mainly attributed to the new grades ’ superior hiding effect .
Summary
Exolit OP halogen-free FRs are widely used in PAs as they combine favourable sustainability profiles with excellent technical performance . The addition of new grades for glow wire performance opens opportunities for halogen-free flame retarded PAs to be used in all kinds of white goods . Further applications of such flame retarded PAs are envisaged in railway applications , due to lower heat and smoke release rates , as well as in e-mobility and 5G-related applications . •
* - Exolit and EcoTain are registered trademarks of Clariant
Dr Sebastian Hoerold
HEAD OF TECHNICAL SERVICE FLAME RETARDANTS FOR PLASTICS
CLARIANT PLASTICS & COATINGS ( DEUTSCHLAND ) GMBH
k + 49 821 479 2506 J sebastian . hoerold @ clariant . com j www . clariant . com
52 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981