October 16, 2006

Volume 84, Number 42

Web Exclusive

All That Glitters

Special effects pigments continue to dazzle by playing with light

Marc S. Reisch

More than 100 years ago, when the automobile industry was in its infancy, buyers could purchase a car in any color they wanted as long as it was black. Today, buyers can get a car that appears to be any number of different colors depending on the angle of view.

"Special effects pigments are growing in popularity," says Shane Dreher, technical marketing group manager for EMD Chemicals, the North American specialty chemicals affiliate of Germany's Merck. "The shimmering, shifting color effects popular in cosmetic and other personal care products are now increasingly popular in a host of other products, including cell phones and small appliances," he notes.

All that glitters, however, is not gold. Many of the gold, silver, and other metallic effects are achieved through layered pigments that artfully reflect different wavelengths of light depending on the viewer's angle of view. For instance, EMD's Miraval Magic pigment line depends on titanium dioxide-coated borosilicate flake. The pigment called Miraval Magic copper seems to glitter in gold, red, or pink tones depending on the angle of view.

But the large, 200-µm-wide flakes in the Miraval line are generally not used in thin automotive coatings because they clog paint spray equipment, and if not oriented properly, can protrude into the clear top coat on a car finish. Instead, Miraval pigments can be used in custom auto refinish coatings or other industrial applications that can accommodate thick coatings.

More suitable for automotive coatings are the Xirallic pigments that are under 35 µm. The titanium dioxide- or iron oxide-coated aluminum oxide platelets produce an intense shimmering glittery color effect, Dreher says.

A newer line of pigments, the Colorstream line, is also suitable for use in car finishes because of the pigments' small size—about 40 µm. These pigments are based on silicon dioxide flakes coated with metal oxides. The thin, smooth pigment particles create iridescent effects allowing shifts in color that can be seen well even in subdued light. Other pigment makers have enhanced their offerings of special effects pigments because of continued interest in the color-shifting effects. BASF recently added three new color tones to its line of Fantasy Color finishes. And when it acquired pigment maker Engelhard earlier this year, BASF also added new mica-based special effects pigments that Engelhard introduced in March.

Engelhard called its then-newest pigments Lumina russet and copper. They offer automotive and other customers metallic rouge and copper tones through "a tight mica particle size distribution and an exclusive multilayer coating technology." Pigments such as these will not only help, as BASF says, to "put us in an even better position to help our customers," but will also help other pigment makers to satisfy customer interest in novel eye-catching colors too.

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