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A real fast mover: New super-flow PBT |
Progress in engineering plastics
A real fast mover: New super-flow PBT
Presented by Dr. Carsten Weiss, Marketing Ultradur®
Trade Press Conference K 2004, June 22, 2004, Ludwigshafen, Germany
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With the help of a specially developed polymer system, BASF researchers have succeeded in significantly reducing the melt viscosity of PBT (polybutylene terephthalate), making it much easier to process. The new easy-flow product is a really fast mover: depending on the glass-fibre content, it flows at least twice as far as comparable standard Ultradur® grades. Other characteristics of the polymer – like mechanical properties, shrinkage and heat distort resistance – are scarcely affected by the modification (figure 1).
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Nano particles modify rheology
The key to this innovation lies in the addition of a nano structured additive. Nano particles are tiny particles that have a distinct influence on the properties of a material – if distributed homogeneously. The diameter of the nano particles in the new Ultradur grade ranges between 50 and 300 nm (figure 2). The additive, along with the special way it is incorporated, causes a fundamental change in the rheology of the base polymer: while the melt still behaves as a non-Newtonian fluid, there is a big drop in its viscosity – of about 50% for an Ultradur with 30% glass fibres (moulding temperature of approx. 260° Celsius).
The increased flowability can be demonstrated in a spiral flow test. Here, the rheology-modified version of Ultradur B4300 G6 flows twice as far as the corresponding standard product under the same processing conditions (both materials having a glass fibre content of 30%) (figure 3).
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Benefits for converters and designers
The change in rheology brings a series of benefits for injection moulders. The lower viscosity means that smaller injection and holding pressures can be applied. Alternatively, the moulding temperature can be lowered and holding time shortened (figure 4).
During their development, the rheology-modified products were tested successfully under production conditions with three of BASF's big Ultradur customers in the automotive and electrical sectors. Depending on the part involved, it was possible to reduce the moulding temperature and holding time by up to 20% compared with the usual Ultradur grades – resulting in a significant increase in output (figure 5).
Another aspect is design opportunities, particularly where thin-walled mouldings are concerned. Easier flow will allow articles with higher filler contents (e.g., glass fibres) to be moulded, resulting in better mechanical properties at reduced wall thickness (figure 6).
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Nomen est omen (a name is an omen)
And because the rheology-modified PBT sets entirely new standards of flow, BASF researchers decided on a rather unconventional name for the new product: Ultradur® High Speed. Ultradur High Speed versions of B4300 G2, B4300 G4 and B4300 G6 (10, 20 and 30% GF) will be available initially (figure 8).
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