Posted in: Formulators Forum

Unveiling the World of Effect Pigments

Posted on Tuesday, April 30, 2024

Effect pigments play a crucial role in the visual aesthetics and functional properties of powder coatings. A diverse selection of effect pigments is accessible for powder coatings, including aluminum, pearlescent, gold and bronze, stainless steel, and zinc. Aluminum pigments stand as the largest class utilized in powder coatings due to their versatility and effectiveness.

Aluminum pigments are classified as leafing and non- leafing and are available in a variety of particle sizes that range from fine to sparkle effect. Leafing pigments are produced using stearic acid, typically not found in powder coatings. As a result, during the curing cycle, the metallic pigment tends to migrate to the upper surface of the coatings, where it will orient parallel to the surface, resulting in a chrome-like finish. Non-leafing aluminum pigments are produced using oleic acid and are compatible with polymers which orient randomly through the film, resulting in a bright silver finish.

Non-leafing aluminum pigments are available in various degrees of resistance with single or double encapsulation: standard (silica treatment), stable (acrylic treatment), and ultra-stable (sol-gel and acrylic treatment), providing excellent chemical and weathering resistance. These pigments are used in a wide range of applications such as automotive parts and bicycles, façade elements and window frames in architecture, metal furniture, shelving units, and household appliances such as refrigerators, stoves, and washing machines.

As industries worldwide strive towards more sustainable practices, effect pigment manufacturers now supply aluminum pigments with a reduced carbon footprint. This remarkable achievement is possible through utilizing low- carbon aluminum as a raw material, coupled with a commitment to sourcing electricity from renewable sources.

Pearlescent pigments typically consist of synthetic or natural mica that have been coated with metal oxides such as titanium dioxide or iron oxide. Utilizing synthetic substrates can present an advantage over conventional natural pigments. Synthetic pearlescent pigments offer several key benefits, including high color purity, absence of yellow undertones, and exceptional chemical and weather resistance.

Gold and bronze pigments are utilized to achieve copper and gold shade effects. These pigments contain pure copper which is evenly encapsulated by a dense silicate layer. This protective layer ensures higher heat resistance and color consistency compared to uncoated bronze pigments. These pigments are not recommended for exterior application due to copper’s high reactivity with oxygen.

There are three methods of producing metallic effects: post-blend, co-extrusion, and bonding. The post-blend method involves the mixing or tumbling of the base powder with aluminum flakes. The advantages of this method include low cost and retention of flake integrity due to the low energy mixing. However, the post-blend method is limited to spray-to-waste applications due to the inability to reclaim and reuse the material, stemming from varying concentrations of aluminum pigments within the mixture.

In the co-extrusion process, aluminum pigment flakes are incorporated with raw materials during the pre-mixing stage. The resulting homogenous mixture proceeds through the extruder, followed by chill roll, cooling, breaking, grinding, sieving, and packing. This method ensures uniform dispersion of the aluminum pigments, resulting in consistent quality and performance in powder coating applications.

Bonding is a thermo-mechanical process in which the metallic and pearlescent pigments are fixed on the surfaces of the spherical particles of the base powder coatings. Bonding is recommended for high volume metallic powder effect as it provides a consistent color and enables the recovery of overspray as overspray material is not significantly different from the virgin material.

Effect pigments provide optical effects in a variety of end markets, including but not limited to, cosmetics, plastics, and of course, coatings. They represent a significant leap forward in advancing the capabilities of powder coatings, enhancing both sustainability and aesthetics. As the industry continues to innovate, the integration of effect pigments promises to play a pivotal role in shaping the future of coatings technology.

Archita Patel Naik is marketing and technical services manager–powder coatings, Eckart America Corporation.