November 3, 2003
Volume 81, Number 44
CENEAR 81 44 pp. 25-27
ISSN 0009-2347


RAINBOW IN A CAN
T
ake chemistry and physics, mix generously, and voilà! Paint that glitters and sparkles
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DRIVING INNOVATION Xirallic Radiant Red by EMD Chemicals uses platelet Al2O3 crystals to make this Range Rover sparkle.
EMD CHEMICALS PHOTO

MARC S. REISCH, C&EN NORTHEAST NEWS BUREAU

All that glitters is not gold. But if a glitzy paint gives a sales edge to the latest cars and motorcycles, it may as well be as good as gold.

"People are willing to pay for color today," says Steven Kiefer, marketing specialist for Rohm and Haas's powder coatings unit. "Appearance today is as important as the product itself."

Pigments, the finely ground particles that color paint, are a $2.5 billion-a-year U.S. business, according to Steve Nerlfi of the consulting firm Kusumgar, Nerlfi & Growney. About 80% of the 1.9 billion lb of pigments sold to paint makers is the whitening and opacifying agent titanium dioxide. Another 14% is organic pigments, while 6% is other inorganic pigments--mostly mined and purified colorants based on iron oxide.

Average prices for pigments range from $1.10 per lb for inorganic color particles to $13 per lb for the synthetic organic variety. But buyers pay even more for the pearlescent, glittery, special effect pigments, Nerlfi says--an average of $18 per lb.

Producers sold 5 million lb of these eye candy pigments in 2002 with a total value of just over $68 million--a drop in the bucket compared with other types of pigments, he says. Many of the traditional effect pigments are based on coated mica and aluminum flakes. However, newer particles based on metal oxide, coated crystals, and coated glass are spurring demand that is now growing at 5% a year.

"It is always challenging to make paints fresh and innovative," says James G. King, senior research fellow at DuPont Performance Coatings. Before World War II, the only way to get pearlescent effects was by grinding up fish scales. King says it took 10,000 lb of fish to get a few pounds of pearlescent effect crystals. Since the end of that war, specialty pigment makers have worked on coated mica pigments for pearlescence.

Glitter and sparkle effects were widely used in auto paints as far back as the early 1980s, says Stephane Rochard, global marketing manager for Engelhard's pigment business. Today, some 70 to 80% of automotive colors incorporate effect pigments. Aluminum-based pigments, mostly for dramatic metallic effects, and mica-based pearlescent pigments are king and queen, respectively, but other technologies are gaining hold too. With these effect pigments, chemistry and physics conspire to produce dramatic appearances.

Most of the excitement since 1996 has come from color-shifting pigments. Back then, Ford painted a Mustang Cobra show car with a BASF paint containing specialty pigments from Flex Products that shifted from black to purple to a reddish brown.

More recently, DuPont formulated one of the more dramatic effect paints for a 2004 edition Mustang Cobra that debuted at the New York International Auto Show in August. In this instance, the car appears to change from green to blue to purple and then to black as the so-called interference pigments act like prisms to split light into the colors of the rainbow.

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SPARKLY ARCHITECTURE Eckart America's aluminum pigments are used as decorative coatings.
ECKART AMERICA PHOTO
LIKE THEY DID in the 1996 Mustang, the interference pigments DuPont used to formulate the paint came from Flex Products, a division of fiber-optics communications firm JDS Uniphase. According to spokeswoman Mary Ellen King, Flex developed its unique interference pigments in the 1980s using a thin-film deposition technique.

The firm developed unique equipment that uses an electron beam to vaporize a metal coating on a polyester film in a vacuum chamber. Flex removes the coating from the film and grinds it into flakes only 1 mm thick and 17 to 20 mm in diameter. The flakes vary in thickness and opacity at the core, giving rise to a variety of color effects in a manner Flex calls "color by physics."

A number of years' work went into qualifying the pigments to automotive durability standards. Today, many of the interference pigments from firms such as Flex can be used in both solvent and waterborne auto paint systems. The special effects they produce do come at a price: King says the average cost for Flex's ChromaFlair pigments is $3,400 per kg. However, she adds, it only takes a few grams per application to achieve the desired effect.

The firm produces another pigment, SpectraFlair, using a technology similar to that for its ChromaFlair line. However, for this new line, the firm vaporizes a magnesium fluoride and aluminum coating on a diffractive gradient sheet instead of a smooth film. The resulting interference pigments produce an iridescent, liquid silver metal look. Though the color shift is not as dramatic as ChromaFlair, King says the pigments have an iridescent fish-scale-like appearance.

"Interference pigments produce an effect similar to the rainbow effect you see on an oil slick," explains Elisabeth Höner, coatings technical marketing manager for EMD Chemicals, the U.S. affiliate of Germany's Merck KGaA. Some of the company's pigments make use of mica particles coated with layers of titanium dioxide or iron oxide to produce a range of pearlescent effects in green, silver, gold, red, copper, violet, and blue. Light bouncing off the layers creates the effect. For more intense colors, the firm recently decided to cooperate with Toyo Aluminium of Japan to combine the latter's aluminum technology with Merck KGaA's pearlescent know-how.

EMD's Colorstream line produces more of a color-shifting effect. Like Flex's SpectraFlair, it is produced using a plastic substrate. But in EMD's case, sodium silicate is applied to a plastic spiral and then scratched off, Höner says. The resulting large flakes are ground down and then coated with either iron oxide or titanium dioxide. As the viewing angle changes, "you get more of a subtle color shift than a color flop," she says.

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FLEX PRODUCTS PHOTO
FOR THOSE looking for a "big iridescent sparkling effect," EMD has a new pigment line developed at its Japan R&D center. "Xirallic pigments are based on homogenous -alumina oxide pigment crystals we grow ourselves and coat with titanium dioxide and iron oxide," Höner says. Though the pigments produce a coarse sparkle, the coated crystals are small enough to be incorporated into a 15-mm-thick base coat automotive paint. Coarser particles would produce a similar glittery effect but wouldn't allow for the smooth glasslike finish preferred on new cars.

Other chemistries can alter light in paint films to create unusual appearances. For instance, Wacker produces its Helicone HC S interference pigments from highly cross-linked organic polymer platelets. Like other color-shifting pigments, these interference pigments do not absorb light but reflect and split light. By combining any number of substrate colors with Helicone pigments, a viewer will experience color transitions such as from deep gold to dark green or from copper-red to forest green.

BASF also produces pigments to give a variety of special effects. According to Business Director Werner H. Peter, the company's Paliocrom line is a coated aluminum flake that offers new brilliant red, orange, and gold metallic effects. He says the trend today favors a move from silver metallics to more color.

And to satisfy those who want a color-shifting effect, BASF offers its Variocrom. Sources say BASF produces these pigments in a technically challenging but cost-effective fluidized bed oxidative reaction. All BASF will reveal is that they are multilayered light-diffracting pigments with either aluminum or iron oxide cores. Mixing with conventional pigments, formulators can get either dramatic or subtle color-shifting effects, Peter says.

Engelhard's Rochard says that a new generation of metal oxide coated, mica-based Lumina colors was first introduced about two years ago. Tight control of particle sizes allows for deeper, cleaner colors, he says. The line now includes effect pigments in red, green, and blue, and a new gold effect pigment called Lumina Brass.

"We don't know why, but the trend is for more pronounced effects across the board," says Jeff Nixon, a marketing manager at Shepherd Color. Using proprietary silver-coated borosilicate glass spheres and flakes, the firm's new StarLight pigments create a brilliant sparkle effect at lower usage levels than traditional metal flake for industrial paint, he says. At a cost of $100 per lb, the pigments work by reflecting both incident light and color from other pigments in paint.

The firm, a well-known maker of durable ceramic colorants, has also come up with pigments whose attributes are felt more than they are seen. A line of Arctic pigments whose unique ceramic structure allows them to reflect infrared radiation are mixed-metal oxides fired at high temperature. These synthetic minerals can reduce heat buildup on coated roofs by 20 to 40 °F compared to identically colored coatings formulated with conventional pigments, Nixon says. Cooler roofs decrease costs to cool buildings, so roofing materials containing these pigments may get an EnergyStar rating from the Department of Energy.

WHERE OTHER THAN auto-quality sparkle effects are needed, Eckart America's John A. Kruzel, senior account manager, says the SDF-6 series metal pigments, milled in oleic acid for random dispersion in paints, does the trick. However, for automotive use, Eckart does have a new line of aluminum pigments made by vaporization on film. The aluminum is then stripped away to produce very fine water-stabilized particles for use in waterborne coating systems. The new line makes it possible for formulators to make coatings with mirrorlike finishes for car interior and dashboard trim that contain reduced levels of volatile organic compounds, Kruzel says.

Tom Wright, marketing manager at All Plastics, says his firm offers water-stabilized metallic pigments for houseware and interior architectural coatings. The Metal-Lyte line consists of aluminum- and bronze-coated mica platelets that are then coated with a silica solution. The company also produces pigments that impart stone and granite effects by controlling the size, distribution, and color of mica particles.

And lest anyone think that traditional color pigment makers are neglecting new developments in preference for the effect pigment specialists, both Ciba Specialty Chemicals and Clariant recently introduced new color variants. Ciba put out a new diketo pyrrollo-pyrrole ultra-opaque red to meet demand for high-performance bluish-red pigments for automotive and powder coatings. Clariant's Hostaperm yellow H5G and Novoperm THI Red are for automotive and industrial use, respectively.

As important as the base colors are to the appearance of a coating, the special effect pigments are getting the lion's share of development efforts. Some think the rainbow color effects will be short-lived and will only appeal to a small segment of youthful buyers. But many predict that these specialty pigments, whether subtle or garish, will endure because of their alluring, eye-tickling prowess.





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