March 21, 2007: In a joint development project with systems supplier fi scher automotive systems, Bayer MaterialScience and Krauss-Maffei tested the practicability of an economical new process that integrates Reaction Injection Moulding (RIM) technology into the injection moulding process, so that the part is coated with polyurethane while it is still in the closed mould. The product chosen for the test was a cupholder trims for a luxury class car. It is otherwise manufactured on the production line by fi scher and coated with an approx. 1.5 mm thick layer of polyurethane using a conventional coating process.
The new technology was developed by Bayer MaterialScience initially as a special form of in-mould coating, in which a twocomponent coating system is injected into a closed mould to coat the part directly. The process was subsequently extended to the coating of parts with polyurethane. In parallel with this, Krauss-Maffei, which manufactures injection moulding machines and polyurethane production machinery, had developed the SkinForm process. Both approaches can be described as “direct methods” - “DirectSkinning” in the case of polyurethane skins and “DirectCoating” in the case of polyurethane coatings. The experience gained by both companies with the new technology was channelled into the joint development project with fi scher.
The processes described above are essentially based on two-component injection moulding, but instead of having a thermoplastic as the second component; it uses a reactive polyurethane system that is injected directly into the mould cavity via a polyurethane mixing head. The fi rst step is to injection-mould the thermoplastic in the fi rst cavity. With the mould open, the moulded part is then moved into a second cavity, for example with a sliding table, rotary table or swivel-platen moulding machine. The mould closes again and a reactive two-component polyurethane system is injected by the RIM process, which immediately cures on the thermoplastic surface. While the polyurethane system is curing, it is possible, using a rotary table or swivel-platen moulding machine, to produce the next part in the fi rst mould cavity, resulting in short cycle times and thus higher productivity.
The new process is variable in terms of layer thickness, tactile properties and cosmetic surface fi nish. It allows either thin polyurethane coatings (≤ 1 mm) or decorative polyurethane skins with a thickness of several millimetres to be applied in solid or expanded form.
