PIGMENTS | SPECIAL EFFECTS
Right: Drop tests show how pigments can impact on ageing. The part on the left uses a tradi- tional colouring method, the part on the left Merck’s WAY technology
impact. However, says Gordon Price, Technical Marketing Manager Plastics, at German pigments specialist Merck, recent environmental, regulatory, and sustainability developments — together with the trend towards paint replacement — means effect pigments are appearing more and more in non-packaging areas, where new and modified grades are often required to suit the specific application needs. Many of these application areas tend to use engineering polymers employing compounding as the colouring route. “A prime consideration in most of these non-
packaging applications, which are commonly for outdoors or long lifetime goods, tends to be weatherability, light stability and the inertness of the effect pigment in the polymer. Ordinary pearlescent effect pigments, intended for packag- ing, have a surface that can react with light and chemicals to degrade the polymer from within over a prolonged time period. Single trip or short lifecycle packaging doesn’t necessarily need to retain long term properties, although one could argue the quality of any recyclate from recycled packaging may be reduced,” Price says.
Long-term performance “Exterior applications do need the longer term properties. Merck has developed the WAY range of pigments [WAY stands for Weathering and Anti- Yellowing] to give an effect pigment that has high light stability and a stabilised pigment surface that reduces the interactivity between the pigment and the polymer and additives package,” he says. According to Price, the inorganic treatment it uses withstands all plastic processing tempera- tures. In addition, because there is almost no photochemical reaction between the pigment and polymer, he says it will allow any polymer additive package to work, so retaining the desired physical
28 COMPOUNDING WORLD | March 2021
properties for a longer time and exposure. The WAY range enables a variety of metallic looking colour effects to be developed without the use of metal. Price cites an example in personal transportation, where mass coloured plastics are progressively replacing painted metal parts. “Here the long-term physical strength of the polymer system needs to be retained and WAY technology helps this. In tests exposing samples to real world exposure, pigment based on WAY technology retained physical properties far longer than alternative methods of creating the same effect.” Effect pigments including WAY technology can also have less attenuation and effect on systems used for autonomous driving, such as Radar and Lidar, than metal-based colouring systems, Price claims. “Another ongoing development, using an
innovative inorganic post treatment of effect pigments to reduce UV-instigated polymer decomposition, also has the property that creates mass tone coloured metallic effects without having to add other colorants that may exhibit low light stability,” he says.
Sustainable trends Changing requirements among brand owners and consumers are also highlighted by Sun Chemical Performance Pigments. “More sustainable, easier to recycle, identification, more durable, higher loadings, and lower cost are all part of every discussion we have with our customers,” says Scott Heitzman, Business Development Manager Plastics. Sun Chemical has several platforms of pearles- cent and metallic pigments. Pearlescents include natural and synthetic mica-based grades — SunMica and SunMica LUX — as well as the SunGem XST glass-based types. The company says these platforms provide a full gamut of whites, interfer-
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IMAGE: MERCK
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