The application of metallic pigments and pearlescent pigments in powder coatings

With the improvement of aesthetic demands, the pursuit of high aesthetic coatings has become a trend.
Powder coatings with metallic or pearlescent effects present luxurious decorative effects, from crystal-like metallic luster to satin-like pearl brightness.
So metallic and pearlescent pigments are widely used in spraying furniture, sports equipment, and automobiles.
These decorative powders differ from functional powders like pure epoxy, polyester, and acrylic.
While they provide some protection to the substrate, their weather resistance, corrosion resistance, and heat resistance are not as high as specialized functional powders.

Types and Characteristics of Metallic and Pearlescent Pigments

Metallic and pearlescent pigments used in powder coatings are typically flake-shaped particles.
Generally the commercial products have a D50 particle size ranging from 3 to 75μm.
These include aluminum powder (commonly known as silver powder), copper powder (gold powder), zinc powder, nickel powder, stainless steel powder,
and inorganic mica flake powder coated with oxide (commonly known as pearlescent powder). Aluminum powder is used in the largest quantity in powder coatings, followed by copper (gold) powder, pearlescent powder, zinc powder, and stainless steel powder, which are often used in anti-corrosion coatings.
These pigments play different roles in powder coatings due to their distinct characteristics (see Table 1)

Application of Metallic Powder Pigments and Pearlescent Pigments

Aluminum Pigments

Aluminum pigment is the most commonly used flake effect pigment in industrial applications.
It is divided into floating and non-floating types, with non-floating aluminum powder occupying over 80% of the market share.
Non-floating aluminum powder includes varieties with larger particle sizes and a crystal-like luster, as well as finer particle sizes with a satin-like luster.
These powders have good pigment wetting properties due to their organic color film surface and distribute evenly in powder coatings.
Floating aluminum powder mainly arranges on the coating surface, showing a bright, chrome-like effect.
It provides excellent opacity, and metallic aluminum powder presents the following characteristics on powder coatings or film surfaces.

Copper gold powder

Ordinary copper (gold) powder is a floating flake pigment made from a specific ratio of copper, zinc, and aluminum alloy.
The mixture undergoes ball milling and classification to achieve the final product.
Furthermore variations in copper content result in distinct hue differences.

Coarser copper gold powder particles in shades like cyan, red, and bronze exhibit stronger metallic effects but poorer coverage.
Paint formulas require higher quantities of coarse-particle copper gold powder.
On the other hand iner particles produce weaker metallic effects, softer hues, and enhanced coverage capabilities.
Powder coating designers can select copper gold powder varieties by particle size and hue based on client needs.

Surface coatings of organic materials reduce copper gold powder density while increasing surface tension and heat resistance.
Different copper gold powder types may discolor under specific climates or chemical exposures, reducing coating gloss.

Pearlescent Pigments

Pearlescent pigments display pearl-like luster and consist of mica substrates coated with titanium dioxide. As a result multilayer light reflection and transmission through coated particles create pearlescent optical effects.

Varied metal oxide coatings generate distinct interference light effects.
These variations produce broad pearlescent color shifts and even “color travel” phenomena.

Modern pearlescent pigments fall into silver-white, iridescent, and colored categories. Surface chemical treatments and coating modifications enable compatibility with all natural/synthetic resin systems. They suit both thermosetting and thermoplastic powder coatings.

Application Cases

Automotive industry: A car manufacturer developed “Starlight Silver” metallic paint using a three-layer spraying process.
The top layer contains 20% aluminum powder, the middle layer has 15% mica pearlescent pigment, and the bottom layer is 85% epoxy resin.
So This results in a BOSCH reflectivity test value of 92%.

Conclusion

Effect pigments provide rich visual effects for powder coatings, but their performance is highly influenced by the coating system.
The application of effect pigments in powder coatings is not as mature as in liquid coatings.
With continuous improvements in powder coating technology, key technical challenges for effect pigments will be addressed.
The widespread use of effect pigments will significantly increase the added value and appearance of powder coatings, enhancing product competitiveness.

Company News