Automobile companies want to use lightweight plastic parts to reduce the weight of their vehicles and hence fuel consumption. But they also want coating systems for plastic components to contribute to their efforts to reduce manufacturing costs while at the same time satisfying consumers' needs for vibrant colors.
These requirements should be met by molded plastic processes in which the coating of the components is carried out simultaneously with the main production process. One of these technologies is in-mold coating (IMC), which has been striving to make major inroads into the European automobile sector.
With demand for high-performance plastics in cars expected to grow more quickly than the automobile market as a whole in Europe, there should now be openings for IMC and similar technologies.
However, the mature western European automobile market, which has been expanding at an annual rate of less than two percent may be growing too slowly to attract funds necessary for the development of new technologies and the installation of new production equipment.
Coatings systems for molded plastics also have to compete against alternative processes which can cut costs and appear more environmentally sound by eliminating the necessity for paints. These include molded-in finishes, such as laminated paint film.
Bayer MaterialScience (BMS), which specializes in polyurethane coatings for the automobile, electrical, electronic and other sectors, is nonetheless optimistic about new plastic coatings technologies it has been developing. It claims they could "revolutionize" the vehicle components market.
The company believes that the value of the global coatings market for plastic automotive exterior parts will double from ?400 million ($500 million) in 2004 to ?800 by 2014, equivalent to a compound annual growth rate (CAGR) of six percent.
BMS has recently developed a reverse or dual-cure coating system to ensure that the coatings on car bodies have adequate durability, weather fastness and scratch resistance.
Base and clear coats are applied to a film which initially are only partially cured so that the film remains flexible enough to be thermoformed during the next step with a smooth and crack-free surface. Then the coating is cured by UV radiation. The thermoformed films can subsequently be reinforced by injection molding with thermoplastics or by reaction injection molding (RIM) with polyurethanes.
The reverse coating system reduces investment costs for coating lines and ovens with its short drying times and fewer rejects, Hans-Peter Neuwald, head of transportation innovation in Europe at BMS told a recent Bayer Innovation Workshop at Leverkusen, Germany.
The company is also combining RIM with the in-mold coating process in a number of prototype trials and development projects, including with a big customer in the U.S. In a two-step process the plastic part is first injection molded and then transferred to a second cavity where a reactive two-component polyurethane is injected using the RIM process so that it cures within the closed mold to provide functional coatings or decorative finishes.
"The injection molding process and the curing of the two-component polyurethane system takes place simultaneously," explained Rainer Protte, a specialist at Bayer MaterialScience's polycarbonates business unit. "This ensures short cycle times of the sort typically found in normal injection molding of thermoplastics and that means high productivity."
The new coating system means lower investment costs, easier logistics and less demand for space. Injection molded parts do not have to be transported to a coating line in a clean room where they may also have to be stored. The rejection rate is lower and there is no waste resulting from excess spraying of paint.
In comparison with the conventional "open" in-mold process, the closed technology has a much shorter cycle time. With the open method, the cavity surface of the injection molding tool is first sprayed with a coating material after which the cavity is filled with a molten plastic.
In addition to the cost advantage of the simultaneous dual molding and coating processes, another benefit is that textured surfaces like fine grains can be reproduced. BMS sees the application as having big decorative potential not only in the parts for cars but also mobile phone casings, laptop housings, vacuum cleaners, radios and TV sets.
Neuwald told the Leverkusen meeting that trials of the IMC process had now been carried out with a number of different substrates and coating materials. Layer thickness of 200 microns had been achieved with high-quality structured surfaces. The system had also been successfully integrated with film insert molding (FIM).
BMS has also, in co-operation with coatings companies, been commercializing a waterborne two-component (2K) polyurethane coating system for the OEM market. It is already being used for automotive bumper coatings while its introduction into an entire body coatings line could take place within 2-3 years.
However, the waterborne coatings will not be used in the IMC technology. "It makes no sense to combine this process with waterborne 2K technology," said a BMS executive. "That would reduce the efficiency of the reverse and in-mold process because additional flash-off time for the water is necessary."
A swing to in-mold coatings in sectors like automobiles could provide opportunities for powder coatings to establish a stronger foothold in the plastic coatings segment.
In the conventional process, a powder coating is sprayed into the mold cavity before the plastic part is molded. During the molding the coating chemically bonds to the part. But this system has been found to have cost disadvantages and limited color applications.
Irfab Chemical Consultants, Brussels, which has just issued a report on the European powder coatings market over the next 10 years, believes that powder coatings producers are unlikely to invest in the development work to improve the existing process. Nor will their customers want to spend money on the equipment necessary for the application of powders coatings in IMC.
"We have not found much evidence of a big market yet emerging in Europe for powder coatings in in-mold coatings," said Franco Busato, managing partner at Irfab. "Margins are so poor for powder coatings producers at the moment because of rises in raw material costs that they cannot afford to invest in R&D on improvements to technologies like those in in-mold coatings."