Bayer MaterialScience AG has developed a special flame-retardant polycarbonate (PC)/ABS blend – Bayblend® DP 3008 HR (Hydrolysis Resistant). This new product is highly resistant to the hydrolytic molecular degradation that occurs in extremely warm and humid environments and the detrimental effects this has on material properties.
This major development was revealed in accelerated aging tests that simulated the average lifecycle of domestic appliances (white goods). The yield stress of the blend (ISO 527-1 and -2) was virtually unaffected by being positioned over a water bath at a temperature of 80 °C for 60 days, even despite being in permanent contact with steam. In comparison, such extreme conditions can completely destroy test pieces made from other PC/ABS blends such as Bayblend® FR 2010 that are not specially hydrolysis stabilized and are used, for example, in the housings of IT and audiovisual products. The exceptional hydrolysis resistance of Bayblend® DP 3008 HR was reaffirmed in an accelerated test developed by Bayer MaterialScience, in which plastic granules are stored at 95 °C and almost 100 percent humidity for seven days, after which material degradation is measured using the volume flow index.
“The new material sets an absolute benchmark for halogen-free, flame-retardant PC/ABS blends in terms of hydrolysis stability and also offers the advantage of a perfectly balanced combination of properties,” explains Burkhard Thuermer, who works in technical product support for flame-retardant PC/ABS blends at Bayer MaterialScience. The company’s developers have succeeded in achieving an optimum balance of the thermoplastic’s properties. The material also exhibits excellent flowability, high heat resistance and stiffness and outstanding resistance to chemicals.
“We designed the new material specifically for applications where hydrolysis resistance is of key importance, for example in extreme climates and with white goods. This involved optimizing the hydrolysis resistance of all the blend components,” explains Dr. Thomas Eckel, product developer for flame-retardant PC/ABS blends at Bayer MaterialScience. Potential applications include front panels in spin driers, dishwashers and washing machines, battery housings and parts for copy machines. The material is also ideal for use in components for appliances such as monitors and notebooks that are produced for sale in countries with a warm and humid climate.
High long-term heat resistance, excellent flame retardance
Another strength of Bayblend® DP 3008 HR is its long-term heat resistance. Its relative thermal index (RTI) (UL 746 B) has been established at 80 °C following a two-year test with impact stress and 85 °C without this mechanical stress (wall thickness 1.5 millimeters). This Underwriters Laboratories (UL) test measures the maximum permissible long-term service temperature of the material in air. “This high RTI value opens up a broad range of applications for our material and confirms that components made from it will function reliably and safely at high operating temperatures,” states Thuermer.
The flame-retardance package does not contain chlorine or bromine and meets the requirements of key environmental symbols such as the “TCO 05” and “Blue Angel” marks. It also gives Bayblend® DP 3008 HR its exceptional fire resistance. As a result, the PC/ABS blend not only complies with the relevant UL 94 V and 5V fire tests, but also passes the IEC 60695-2 glow-wire test in accordance with the requirements of the often-quoted household appliance standard IEC 60335-1. A Glow Wire Flammability Index (GWFI) value as per IEC 60695-2-12 of 960 °C (the minimum requirement is 850 °C) was recorded on the UL Yellow Card for test thicknesses of 0.75 to 3.0 mm. The Glow Wire Ignitability Temperature (GWIT) as defined in IEC 60695-2-13 is 800 °C (the minimum requirement is 775 °C) for the same wall thickness range.
Pursuant to performance level category (PLC) classification 2, a range of 250 to 400 was registered on the UL Yellow Card for tracking resistance CTI A (comparative tracking index) in line with IEC 60112. Consequently, the new PC/ABS blend reliably meets standard appliance requirements.
Initial processing tests have shown that Bayblend® DP 3008 HR can be used to manufacture complex components efficiently and cost-effectively with a high dimensional stability and low tendency to distortion. Another advantage of this flame-retardant material is that the potential for outgassing volatile substances is extremely low and is at the same low level as non-reinforced PC/ABS blends without flame retardance. “When it is processed properly, the plate out effect is all but avoided so there is no danger that this effect might damage the surfaces of molded parts. It also means longer periods between cleaning cycles, thereby increasing productivity,” stresses Thuermer.