Written on 13.03.2013 - Technology
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New impact-resistant ester TPUs with better inherent colour, less discolouration

With Desmopan DP 3862D and DP 3856D, Bayer MaterialScience has developed the first two representatives of a new generation of impact-resistant, modified ester TPUs primarily for applications in the winter sports segment. They are intended to replace the ester TPUs Desmopan DP 8377 and DP 8715, which have long been established in the production of ski boots, for example.

Fig. 1: Desmopan DP 3862D and DP 3856D have an improved inherent colour and a reduced tendency to yellow

According to the company, this development was prompted by its aim to offer products with improved optical properties, greater UV stability and consistent quality, enabling its customers to respond more flexibly and rapidly to new design and colour trends.

Bayer is planning to expand the portfolio of this new product generation. For instance, the company intends to produce Desmopan DP 3868D as a successor of Desmopan DP 8417 in the first quarter of 2013. The objective is to provide customers with the entire range of hardnesses available from the current line of product grades. Additional material variants with other hardnesses can then be added as demand dictates, says the company.

Fig. 2: Yellowness Index according to DIN 5036 after 0, 24, and 120 h exposure to UV radiation

Tendency to yellow reduced

The special strength of the two newcomers, Desmopan DP 3862D and DP 3856D, is their improved inherent colour and reduced tendency to yellow (fig. 1), which is attributable to a different impact resistance modifier, among other things. For example, Desmopan DP 3862D has a Yellowness Index (YI) value of only 2 (fig. 2). To compare, the YI value of its predecessor, Desmopan DP 8377, averages about 10.

The low tendency towards yellowing is expressed in lower colour difference values. After 24 hours of exposure to UV radiation, Desmopan DP 3862D has a colour difference DE of only 16. Bayer says that both of the new TPU grades possess the same high-level mechanical properties as their “older siblings.” They therefore display similarly good low-temperature flexibility, low-temperature impact resistance and wear resistance, says the company.

Fig. 3: The inherent colour of the new TPUs has been improved

Premium variants with higher UV resistance

Bayer also offers premium variants of both of the new ester TPUs: Desmopan DP 3856DU and DP 3862DU. The “U” at the end of the product designation stands for a new UV protection additive. It ensures that both structural materials are particularly resistant to ultraviolet radiation compared with their predecessors. For instance, the colour difference DE after 24 hours of exposure to UV radiation is less than 4 in the case of Desmopan DP 3862DU. The inherent colour of the premium variants has also been considerably improved (fig. 3). As a result, they can also be coloured in light tones, and are suitable for such things as the production of bright white ski boot shells.

Bayer says it has succeeded with all the new ester TPUs in reducing the number of additives so as to simplify the formulation. The result is greater consistency in the properties of the production batches. Furthermore, the additives used are more readily available than the previous materials, providing for greater supply reliability.