DirectSkinning technology

DirectSkinning technology is a new production process designed to improve cost efficiency in the production of injection moulded parts. It has now been used for the first time with an aliphatic polyurethane material in the series production of vehicle interior parts.

As part of a technology project devoted to the DirectSkinning process, fischer automotive systems and Bayer MaterialScience claim to have developed a decorative panel which is now manufactured in series production. The component seals off a kinematic drawer located on the dashboard of the BMW 5 Gran Turismo series directly above the central console.

Dr Michael Baumeister, head of production and logistics at the Horb, Germany plant of fischer automotive systems, said: "Our joint project demonstrates that DirectSkinning is ready for series production and can be used to manufacture injection mouldings with high quality, coloured decorative polyurethane surfaces for vehicle interiors."

The approximately 1.4mm thick covering for the panel is based on the polyurethane system Bayflex LS (LS = Light Stable) from BaySystems - the global umbrella brand for the polyurethane systems operations of Bayer MaterialScience.

The system used was specially developed for the DirectSkinning process. The panel is produced in five colours, including ivory white, light beige and grey. "Our polyurethane systems meet the growing demand for light colours in vehicle interiors as they deliver lasting UV resistance and colour fastness. They also give the surfaces a high level of scratch and abrasion resistance," observed Gregor Murlowski, a polyurethanes expert at Bayer MaterialScience. The panel's thermoplastic substrate consists of the heat and impact resistant polycarbonate acrylonitrile-butadiene-styrene (PC/ABS) blend Bayblend T85, another material from the Leverkusen based company.

DirectSkinning technology combines injection moulding of thermoplastics with the reaction injection moulding (RIM) process for polyurethane processing. The coated component is produced directly on the injection moulding machine in a single mould (multiple moulds are also possible) in a process that is comparable to multi-component injection moulding. After manufacturing of the thermoplastic substrate, the polyurethane system is injected into the closed mould via a polyurethane mixing head and the thermoplastic surface is thus coated.

Andreas Bürkle, head of the DirectSkinning project at fischer automotive, added: "When a rotary table or swivel platen mould is used, the two production steps can be performed in parallel, for example, thus ensuring short cycle times and high productivity."

According to Bürkle, parts produced in this way require little secondary finishing. The thickness and colour of the polyurethane layer can be varied over a broad range. As the component is produced in a single mould, DirectSkinning does not require a separate coating system, in contrast to traditional methods. "The investment and space needed for the machines are reduced accordingly," noted Rainer Protte, special injection molding processes at Bayer MaterialScience. Transportation and interim storage of the fresh injection mouldings become a thing of the past, simplifying logistical processes and minimising the risk of contamination and damage."

Hot light aging tests passed
The light stability of the decorative panel's polyurethane surfaces has been thoroughly tested. This process included heat aging, hot light aging, climatic change and solar simulation testing. Testing showed that virtually no surface defects, discolouring, yellowing or hardness fluctuations occur over the service life of the component, thus satisfying automakers' stringent requirements concerning the yellowing stability of plastic surfaces in vehicle interiors.

It was also possible to precisely map the mould, the surface of which has a leather like grain, adapt the polyurethane surface exactly to the colour specifications and match its optical effect to neighbouring surfaces made from other materials (colour matching). This series development was preceded by extensive joint work. For instance, the feasibility of the DirectSkinning process was tested on a prototype component from a series application - decorative trim for a cup holder.

Author
Dr Frank Rothbarth, Bayer MaterialScience

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