Light-Stable Decorative Skins in RIM Technology Shortens Cycle Times and Good Mold Reproduction

Brightly colored, light-stable decorative skins made of polyurethane can now be produced directly in a Reaction Injection Molding (RIM) process. This is the result of close cooperation between Bayer MaterialScience AG and Faurecia that focused on large decorative skins for mid- and high-end motor vehicles. Working together, they optimized the manufacturing process and an aliphatic polyurethane system to enable production of a high-quality decorative skin in a pre-production mold. "This solution is a cost-effective alternative to both polyurethane spray-on skin technology and in-mold coating RIM technology. We envisage huge potential for this application, particularly with decorative skins for components in automotive and commercial vehicle interiors, such as instrument panels, arm rests, center consoles, and door trims," says Gregor Murlowski, an expert in polyurethane skins in the Polyurethanes Business Unit of Bayer MaterialScience. The light-stable BayflexR LS (Light Stable) is the tailor-made polyurethane material used in this new process.

The aliphatic RIM skin is produced in a one-step process, making it a more cost-effective solution than the in-mold coating (IMC) RIM process, in which a decorative coating is first sprayed into the mold before an aromatic polyurethane system is injected in a second step using RIM technology. However, although polyurethane skins produced in this way offer a very high level of quality, the disadvantages of this two-stage process - such as longer cycle times and higher investments for molds and equipment - must be taken into account.

Polyurethane spray-on skin production in an open mold can also lead to unwanted material build-up, which causes irregular haptic features on the surface.

"By contrast, the advantage of the RIM process is that it enables wall thickness to be determined accurately, even at edges that are difficult to reach and in geometrically complex situations where a spray head cannot be positioned precisely. This prevents material build-up," explains Murlowski. This high level of precision in determining the wall thickness offers the advantage that rip seams for concealed airbags can be created with absolute precision. A further benefit of this RIM process is its cost-effectiveness. "Depending on the component being manufactured, we anticipate that this process will be up to 50 percent faster than polyurethane spray-on skin technology," reveals Murlowski.

Among other substances, BayflexR LS is based on a UV-resistant, aliphatic polyisocyanate, which means that it can be pigmented in bright colors. The material's flowability, elongation at break, haptic properties and scratch resistance were optimized for the production of colored RIM skins. BayflexR LS produces matt and visually attractive surfaces.

Bayer MaterialScience provides more than just optimized materials for manufacturers producing polyurethane decorative skins using the new RIM process. The company also performs extensive checks on the skins to OEM specifications, for example, heat and light aging, emission behavior and tensile strength. The service also includes support in the mold design process, providing software to optimize flowability and gating, for instance.

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