COVER STORY DRIVING INNOVATION Xirallic Radiant Red by EMD Chemicals uses platelet Al203 crystals to make this Rover sparkle.
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.
RAINBOW IN A CAN Take chemistry and physics, mix generously and voilà! Paint that glitters and sparkles MARC S. REISCH, C&EN NORTHEAST NEWS BUREAU
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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 aluminumflakes.However, newer parHTTP://WWW.CEN-ONLINE.ORG
ticles 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," saysJames G. King, senior research fellow at DuPont Performance Coatings. Before World War II, the only way to get pearlescent effects was by grinding upfishscales. King says it took 10,000 lb offish 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 Stéphane 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.
LIKE THEY DID in the 1996 Mustang, the interference pigments DuPont used to formulate the paint came from Flex Products, a division offiber-opticscommunications firm JDS Uniphase. According to spokeswoman Mary Ellen King, Flex developed its unique interference pigments in the 1980s using a thinfilm 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 μιη thick and 17 to 20 μπι in diame ter. The flakes vary in thickness and opac ity 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, ο many of the interference pigx ments from firms such as Flex £ can be used in both solvent and | waterborne auto paint systems. £ The special effects they produce i 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 applica tion 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, thefirmvaporizes a magne sium fluoride and aluminum coating on a diffractive gradient sheet instead of a smooth film. The resulting interference pigments produce an iridescent, liquid sil ver 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 ef fect similar to the rainbow effect you see on an oil slick," explains Elisabeth Hôn-
Cystal Rainow
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COVER STORY er, coatings technical marketing manag thick base coat automotive paint. Coars er for E M D Chemicals, the U.S. affiliate er particles would produce a similar glit of Germany's Merck KGaA. Some of the tery effect but wouldn't allow for the company's pigments make use of mica smooth glasslike finish preferred on new cars. particles coated with layers of titanium dioxide or iron oxide to pro Other chemistries can alter duce a range of pearlescent ef light in paint films to create un fects in green, silver, gold, red, usual appearances. For instance, copper, violet, and blue. Light Wacker produces its Helicone H C S interference pigments bouncing off the layers creates from highly cross-linked organic the effect. For more intense polymer platelets. Like other col colors, the firm recently de or-shifting pigments, these in cided to cooperate with Toyo terference pigments do not ab Aluminium of Japan to com sorb light but reflect and split bine t h e latter's aluminum light. By combining any number technology with Merck KGaAs PAINTS & of substrate colors with Helicone pearlescent know-how. COATINGS pigments, a viewer will experi EMD's Colorstream line pro ence color transitions such as from deep duces more of a color-shifting effect. Like gold to dark green or from copper-red to Flex's SpectraFlair, it is produced using a forest green. plastic substrate. But in EMD's case, sodi um silicate is applied to a plastic spiral and BASF also produces then scratched off, Honer says. The re pigments to give a variety sulting large flakes are ground down and of special effects. Accord then coated with either iron oxide or ti ing to Business Director tanium dioxide. As the viewing angle Werner H. Peter, the com pany's Paliocrom line is a changes, "you get more of a subtle color coated aluminum flake shift than a color flop," she says. that offers new brilliant red, orange, and gold FOR THOSE looking for a "big iridescent metallic effects. He says sparkling effect," EMD has a new pigment the trend today favors a line developed at its Japan R&D center. move from silver metallics "Xirallic pigments are based on homoge to more color. nous α-alumina oxide pigment crystals we grow ourselves and coat with titanium And to satisfy those dioxide and iron oxide," H ô n e r says. who want a color-shifting Though the pigments produce a coarse effect, BASF offers its Variocrom. Sources sparkle, the coated crystals are small say BASF produces these pigments in a enough to be incorporated into a 15-μπιtechnically challenging but cost-effective
fluidized bed oxidative reaction. All BASF will reveal is that they are multilayered light-diffracting pigments with either alu minum or iron oxide cores. Mixing with conventional pigments, formulators can get either dramatic or subtle color-shift ing effects, Peter says. Engelhard's Rochard says that a new generation of metal oxide coated, micabased Lumina colors was first introduced about two years ago. Tight control of par ticle sizes allows for deeper, cleaner colors, he says. The line now includes effect pig ments 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 silvercoated borosilicate glass spheres and flakes, the firm's new StarLight pigments create a brilliant sparkle effect at lower us age levels than traditional metal flake for industrial paint, he says. At a cost of $100 per lb, the pigments work by reflecting both in cident 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 ceram ic structure allows them to reflect infrared radiation are mixed-metal oxides fired at
Before World War II, the only way to get some of the unique pearlescent effects in demand today was by grinding up fish scales.
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COVER STORY 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 bluishWHERE OTHER THAN auto-qualired pigments for automotive and ty sparkle effects are needed, powder coatings. Clariant's HostaEckart America's John A. Kruzel, perm yellow H5G and Novoperm senior account manager, says the SPARKLY ARCHITECTURE Eckart America's SDF-6 series metal pigments, aluminum pigments are used as decorative coatings THI Red are for automotive and industrial use, respectively milled in oleic acid for random disAs important as the base colors are to persion in paints, does the trick. Howev- reduced levels of volatile organic comthe appearance of a coating, the special efer, for automotive use, Eckart does have a pounds, Kruzel says. new line of aluminum pigments made by Tom Wright, marketing manager at All fect pigments are getting the lion's share of vaporization on film. The aluminum is Plastics, says his firm offers water-stabi- development efforts. Some think the rainthen stripped away to produce very fine lized metallic pigments for houseware and bow color effects will be short-lived and water-stabilized particles for use in wa- interior architectural coatings. The Metal- will only appeal to a small segment of terborne coating systems. The new line Lyte line consists of aluminum- and youthful buyers. But many predict that makes it possible for formulators to make bronze-coated mica platelets that are then these specialty pigments, whether subtle or coatings with mirrorlike finishes for car coated with a silica solution. The compa- garish, will endure because of their alluring, interior and dashboard trim that contain ny also produces pigments that impart eye-tickling prowess. • 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.
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