Colors have always played an important role in human life. Today this is above all true of colorful products, which are designed to draw attention and convey brand messages, thereby securing their place among the competition. Colors elicit desired emotions in consumers and lend products specific quality characteristics.
Fabricating colored plastic articles, however, requires much more than just knowledge of the coloring process, because materials and products today have to be highly functional to be accepted: Used outdoors they must be resistant to UV light; in hot environments, like laser welding or in the vicinity of fires, a plastic must protect the human eyes against the harmful effects of infrared radiation. The surface of plastic articles must not be altered in any way by the coloring process, or only precisely in the manner intended.
For decades now, Covestro – formerly Bayer MaterialScience – has been active in the field of coloring polycarbonate plastics. “We have unique and comprehensive knowledge of colorants, plastics and coloring technologies,” said color expert Gianmaria Malvestiti. “Through our global network of Color Competence and Design Centers, we support customers in fulfilling a wide variety of requirements.”
Focus on polycarbonate
Covestro’s color activities center on the polycarbonate Makrolon®, invented in 1953 by the Bayer chemist Dr. Hermann Schnell. It is transparent and offers unique opportunities for coloration, from transparent, translucent and opaque, and that in an endless array of shades and effects. At the Fakuma trade fair in Friedrichshafen, Germany, from October 13 to 17, 2015, the company is exhibiting a number of examples.
The colorants must not impair the flow properties of a plastic during processing. If a plastic needs to exhibit good ductility, a dark Marsala red colorant must not alter its mechanical properties. If the viscosity of the melt is important for processing, a grass-green shade must not influence its flow properties.
Comprehensive expertise is important
Covestro’s know-how also encompasses the sometimes complex interactions between colorants and UV absorbers. The latter are added to a plastic when the articles fabricated from it are to be exposed to sunlight and must last a long time. “The type and amount of absorber has to be adapted to the respective situation,” said Malvestiti. “A few hours of sunlight in a kitchen is not as stressful as sunlight shining all day long on cars parked in an unshaded parking lot in Florida.”
Combined protection against UV radiation, visible light and heat creates new possibilities in the field of automotive glazing. Panorama roofs made of Makrolon® let in the desired level of daylight, while protecting passengers from UV radiation. Infrared absorption creates a pleasant climate inside, but also reduces fuel consumption, since the air-conditioning does not have to work as hard.
Variable composite surfaces
The surface of a product is another important aspect of its visual appearance. Composites have a disadvantage in this regard, because the reinforcing fibers can diminish the quality of the surface. Covestro has extensive knowledge of process technologies that circumvent such drawbacks.
One common method is Rapid Heat Cycle Molding, in which the mold is rapidly heated and cooled. Surface quality can be significantly enhanced by using modern laser engraving processes. It is even possible to render both glossy and matte sections on the same surface.
LED revolution gives rise to new requirements
Energy-efficient LED lighting technology opens up new fields of application for polycarbonates, but also requires new product grades with different properties. Covestro has tailored the Makrolon® LED line of products to meet these requirements.
Many applications depend on distributing the bright light of these point sources in such a way that an observer perceives a uniformly illuminated surface. This is where polycarbonate with high light diffusion comes in, because it is formulated to have a backscattering effect even when totally transparent in order to meet requirements and achieve the desired appearance. It is even possible to have LED light appear warmer (yellower) or colder (bluer).
