Today, plastics dominate the automotive interior. Components are typically injection-molded from a thermoplastic and then, in a second step, coated on a coating line at a different location to create the desired appearance and haptic properties.
The DirectCoating process produces a component in just one step. After production in the injection mold, the plastic substrate is then transferred to a second, minimally larger cavity, into which the coating system is injected via a reaction injection molding (RIM) mixing head. This creates a polyurethane (PU) coated component with outstanding properties that requires virtually no post-processing.
“Compared with the conventional process, the integrated process offers substantial savings potential with respect to logistics effort, energy consumption and space requirements,” said automotive coatings expert Dr. Jan Weikard. “All you need is an injection molding machine and a RIM system.”
The component itself can be transparent, translucent or opaque. Its surface can be coated in various colors, decorated with a matte or high-gloss finish or protected with scratch-resistant functional coatings. There are also various haptic and surface structuring options.
This is another advantage the DirectCoating process has over spray coating. The injected coating can also reproduce contours such as sharp or rounded edges and raised surfaces because it accurately depicts the mold surface. Ultrafine grain patterns with a sharp contrast between high-gloss and matte areas are one possible variant.
One example is the prototype of a redesigned steering wheel cover that Covestro is presenting at the European Coatings Show 2017. This development demonstrates the wide range of colors, surface structures and tactile properties that can be reproduced on the same component from a single mold using DirectCoating. Located in the driver’s direct field of vision, the steering wheel cover meets the most demanding appearance requirements.
The raw materials for PU layers applied by DirectCoating cannot contain any solvents, not even water. The process therefore requires low-viscosity raw materials that display sufficient flow at 50 to 90 degrees Celsius to quickly fill the cavity. Aliphatic polyisocyanates are particularly well-suited materials, as are polyester and polyether diols and polyols as well as polycarbonate diols as the polyol components. Characteristics such as elasticity, weathering resistance, self-healing and scratch resistance can be defined by the appropriate selection of raw materials.
Mold filling with the polyurethane coating can be computed in advance using a material data set created by Covestro for Moldflow simulation software. The simulation model considers various parameters so that problems such as air pockets can be prevented. Trials with the model have now reached the stage where Covestro is offering its customers and their mold makers the project service of computing the ideal sprue and vent design for the coating component.
Critical to the continued success of the technology are customized materials, optimum combination of the thermoplastic with the PU raw materials, special formulation expertise with solvent-free coatings, effective use of simulation and testing methods, and solid processing know-how. DirectCoating technology then has good chances of becoming established in the automotive industry.