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Plastic edge with metallic look replaces decorative aluminium ring

Bayer MaterialScience AG : 15 October, 2004  (Application Story)
The dial of the current Golf from Volkswagen is made of the printed polycarbonate film Makrofol DE 1-4 from Bayer MaterialScience AG. At the edge, it is formed such that the circumference has a matte metallic look.
Dials for automobile speedometers are often surrounded by a mounted decorative aluminium ring. However, the current Golf from Volkswagen demonstrates that this decorative feature can be produced without a separate ring. Its dial is made of the printed polycarbonate film Makrofol DE 1-4 from Bayer MaterialScience AG. At the edge, it is formed such that the circumference has a matte metallic look. 'This integration means that several steps in the component assembly process are no longer required, resulting in savings in materials and logistics and removing the need for a complex electroplating step. Moreover, the formed film looks more homogeneous than an equivalent component with a mounted ring,' explains Hans Braun, expert on plastic films at Bayer MaterialScience. The manufacturer of the complete speedometer unit is Siemens VDO Automotive AG.

The 375 microns thick film is printed on both sides with more than 10 layers of ink using the screen printing method. The translucent symbols are grey and are backlit by coloured LEDs (backlit effect for nighttime use). The edge is formed using the 'High Pressure Forming' method patented by Bayer MaterialScience. This has the advantage that the film can be formed with great precision significantly below the glass temperature TG of the polycarbonate and the matte surface of the material is retained.

The experts from the film group of Bayer MaterialScience cooperated closely with Siemens VDO Automotive to develop the component. One particularly tough challenge was to meet the exacting demands made on the positioning accuracy of the printed symbols. This is very important because the speedometer is a measuring instrument that has a direct effect on the driving behaviour of car drivers and therefore on safety. Any deviations in printing and forming must be kept to an absolute minimum. 'For example, we made precise adjustments to the heating system of the high pressure forming equipment using a thermal imaging camera in order to achieve an optimum forming process with controlled shrinkage of the film,' comments Armin Berger, film specialist at Bayer MaterialScience. Due to the precision with which the symbols can be positioned, he sees great opportunities for the use of polycarbonate films in measuring scales and displays in mechanical engineering as well as for clock and watch faces.

Bayer MaterialScience is currently working to develop materials and technologies to make the manufacturing process for automotive dials more cost-effective and give designers greater creative freedom. One example of this is the new light-diffusing film Makrofol TP 243, which disperses light to a greater extent than the PMMA films which have until now set the standards in this field. It also offers greater light permeability. Dials made of this material can therefore be backlit with light diodes which emit less light and are thus considerably cheaper. Further design possibilities are also likely to be opened up by films that are 'back injected' with a thermoplastic using the film insert moulding (FIM) process to produce and stabilise curvature of the dial.
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