Polybutylene Terephthalate (PBT)
Ultradur® – The polybutylene terephthalate (PBT) for high-quality components
Ultradur® is BASF’s brand name for its line of partially crystalline, thermoplastic, saturated polyesters derived from polybutylene terephthalate (PBT). They are employed as materials for high-quality technical components in many industry sectors.
Ultradur® shows its strengths wherever high-quality and above all heavy-duty parts are required – for example in the automotive industry, in the electrics and electronic sectors. The range of applications which benefit from these properties of Ultradur® in both industry and everyday life is vast. A feature that is particularly important is the low water absorption and thus the fact that the mechanical and electrical properties are largely independent of the moisture content or the climatic surrounding conditions. Particularly for components that are safety-relevant and have to work reliably for the entire lifetime of a component, Ultradur® is indispensable.
Ultradur® product range (PBT, PBT+ASA, PBT+PET)
The most important applications of Ultradur® are automotive engineering, electrical engineering, electronics and telecommunications as well as precision engineering and general mechanical engineering. For these applications, a variety of Ultradur® types is available.
The Ultradur® range includes a variety of PBT grades which differ in their flow properties, demolding and setting behavior. The unreinforced grades are used for parts with very good surface quality, with applications ranging from packaging film to filigree connectors in electrical engineering and functional parts such as gear wheels.
Ultradur® demonstrates the full potential of its positive properties in a wide range of glass-fiber reinforced grades. Ultradur® types with different glass-fiber contents are available on demand as standard, including types with a glass-fiber content of over 50%. Processed to molded parts, these Ultradur® grades are key players in assemblies that withstand high mechanical stress even at elevated temperatures, such as in the engine compartment of cars.
In addition to the pure PBT/glass-fiber compounds, the range of reinforced grades also includes glass-fiber reinforced PBT blends which have been further optimized with regard to surface quality and dimensional stability. Well-known manufacturers of electronic assemblies have confidence in the reinforced Ultradur® grades as a housing material because of its outstanding performance profile and high consistency of product quality.
With the innovative Ultradur® High Speed grades, it is possible not only to fill intricate molds, but also to significantly reduce cycle times compared with standard materials. These particularly economic Ultradur® High Speed grades have different glass-fiber contents and are also available as PBT/ASA blends, the S 4090 grades.
Manufacturing large, dimensionally stable parts, e. g. ventilation grids in cars, is a major challenge for plastic processors. The warpage-reduced grades make processing easier. These materials have lower contents of anisotropic fillers and reinforcing materials. At special settings, it is possible to achieve roughly equal processing rates in longitudinal and transverse direction – the best conditions for the production of visible low-warpage parts.
Special additives make the robust Ultradur® even more resistant if it is exposed to water or moisture at elevated temperatures. It was possible to show in various test systems that these specialty grades are resistant to hydrolytic attack for much longer than standard PBT. Further information on Ultradur® HR can be found in the brochure “Ultradur® HR – PBT for hot-damp environments”.
In principle, laser welding of partially crystalline thermoplastics is more difficult than that of amorphous plastics as the laser beam is scattered on the spherulites. This problem, which is shared by all partially crystalline plastics, was particularly pronounced with PBT: Ultradur® LUX now provides a partially crystalline PBT with optical properties that have never been reached before. In comparison with conventional PBT, Ultradur® LUX lets through much more laser light; the widening of the beam is much lower.
The improved laser transparency means that considerably higher welding speeds are now possible, and at the same time the process window is much wider. Thicker components for joining can also be welded than was previously the case. This gives access to applications that were previously reserved for other joining methods. More detailed information about Ultradur® LUX can be found in the brochure “Ultradur® LUX – PBT for laser welding”.
Many flame-retardant grades are available in the product range. Ultradur® for applications in the construction and electrical appliances sectors, which place special requirements on PBT’s flammability. The standard fire-retardant grades are unreinforced and available with 10 to 30 percent glass-fiber reinforcement.
With the suffixes FC (Food Contact) and Aqua®, Ultradur® grades are offered specifically for components that come into contact with food and drinking water. The Ultradur® FC grades make it possible to develop applications in contact with food and to meet the different food safety regulations, e. g. FDA, European Food Contact No. 2002 / 72 / EC and GMP (EC) No. 2023/2006.
Ultradur® FC Aqua® grades have the approvals in accordance with the KTW, DVGW and WRAS guidelines in cold water applications. The special requirements on plastics that come into contact with drinking water include particularly low migration values, a high level of taste neutrality and the confirmation that long-term contact with the plastic will not cause accelerated algae growth. More detailed information about the Aqua® range can be found in the brochure “From the idea to production. The Aqua® plastics portfolio for the sanitary and water industries”.
Ultradur® B 4520 PRO is suitable in particular for injection molding applications in the medical sector. It is noted for its low warpage and shrinkage behavior. This means that Ultradur® B 4520 PRO is able to meet the strict requirements placed on medical components in terms of dimensional stability. Other advantages that are significant for use in medical equipment include the low water absorption and the excellent resistance to many chemicals that are used in the medical sector.
Among other things, gamma rays or ethylene oxide are used for sterilizing the components. More detailed information about Ultradur® PRO can be found in the brochure entitled “Engineering plastics for medical solutions – Ultraform® PRO and Ultradur® PRO”.
Properties of Ultradur®
The Ultradur® grades are polyalkylene terephthalate molding compounds based on polybutylene terephthalate. Ultradur® is produced by polycondensation of terephthalic acid or dimethyl terephthalate with 1,4-butanediol using special catalysts. Terephthalic acid, dimethyl terephthalate and 1,4-butanediol are obtained from petrochemical feedstocks, such as xylene and acetylene.
The processing of Ultradur®
Ultradur® can be processed by all methods known for thermoplastics. The main methods, however, are injection molding and extrusion. Complex moldings are economically manufactured in large numbers from Ultradur® by injection molding. The extrusion process is used to produce film, semi-finished products, pipes, profiled parts, sheet and monofilaments. Semi-finished products are for the most part machined further by means of cutting tools to form finished moldings.