Feature Story
Jan 1st, 2008                                Print this article

Get the paint out

By Tony Deligio

In addition to the environmental and cost benefits of eliminating paint in markets like automotive, creating designs that apply molded-in color can produce a robust manufacturing process as well.

RTP Co. (Winona, MN) has combined its color and long-fiber know-how in a new line of long-cut color masterbatches, which mimic the shape of long-fiber thermoplastics (LFT), and thereby reduce separation during handling. In addition to additives in long-cut masterbatch pellets for dry blending, RTP supplies additives in precompounded LFT pellets. Ampacet’s LiquidMetal promises designers a polished metal appearance in plastic. Solvay Engineered Polymer’s Indure polypropylene blend was used as a molded-in color replacement for a painted PA/PPO in this school bus application. The Smart fortwo, which arrives in North America in 2008, is the first commercial vehicle to feature polypropylene body panels, applying molded-in color instead of paint.

Beyond any ancillary benefits, however, appearance and customer acceptance trump all other considerations, especially in hues and products with ingrained expectations. That’s certainly the case with “school bus yellow,” a hue that evokes a singular image. In a 2008 model-year project, Solvay Engineered Polymers (Auburn Hills, MI, and now part of Basell) took on just that task, supplying a polyolefin alloy with molded-in color to replace a nylon-polyphenylene oxide (PA/PPO) blend, that had been painted, for two body panels that transition the bus’s exterior from the engine enclosure to the passenger compartment.

IC Corp. (Mansfield, TX), which manufactures the CE model school bus, said using molded-in color in Solvay’s Indure X-210A polyolefin alloy, versus paint, saves more than $350,000 annually on the parts.

Regardless of the economics, the components still needed to conform with appearance and performance standards, including gloss levels and scratch, mar, and UV resistance. The Class A unpainted parts are specified to gloss levels of 80-85% at a 45° angle, and this was accomplished by polishing the surface of the two-cavity tool which molds the parts. Otherwise, IC was able to use the original tooling, since Solvay worked to match the shrinkage rates of the PA/PPO predecessor with its TPO replacement.

According to Mitesh Shah, technical manager of automotive operations at Solvay Engineered Polymers, molded-in color ultimately offers more stone-and-gravel protection than painted parts, since their weatherability is lowered once paint begins to chip off. “These materials have been developed to achieve, in molded-in-color parts, an appearance and a durability that is similar to painted parts,” Shah said in a release. Solvay says the Indure material provides the flexural modulus, tensile strength, and impact resistance needed in the application, while featuring no flow or weld lines in spite of vent holes.

Smart design

The bus application will be joined on the road in 2008 by the Smart fortwo, which, according to polyolefin supplier Borealis (Beringen, Netherlands), will become the first commercialized car to have full body panels made from polypropylene (PP). Here, too, molded-in color is applied, although a secondary step to add a clear coat is used (initially reported in MPW’s K Show Daily).

Smart sourced Borealis’ Daplen ED230HP TPO for the panels, replacing polycarbonate/polybutylene terephthalate (PC/PBT) compounds traditionally used in such applications. The parts are molded by Plastal, which also assisted in developing the material. The Tier One supplier required a material that would enable high production levels. With the design calling for in-mass colored compounded material, secondary production steps are eliminated and Borealis reports the result is a part that offers UV resistance and good clear-coat adhesion.

In addition to lowering volatile organic compound (VOC) emissions by reducing paint, sourcing PP also lowered overall vehicle weight by 15%, which means less fuel is needed and less exhaust is created. On the mechanical property side, there is a low thermal expansion of the material so there’s zero gap tolerance between the parts, and the panels exhibit a strong impact to stiffness ratio.

The fortwo is slated to launch in North American starting this month, with six colors (deep black, light yellow, crystal white, blue metallic, red metallic, and silver metallic) available. The vehicle itself only measures 8.8 ft in length, 5.1 ft in height, and 5.1 ft in width. The company overcomes safety concerns regarding PP body panels by surrounding the cockpit in a tridion safety cell, made from standard and high-strength steel. Smart says the safety-management system is designed to achieve a four-star U.S. crash rating. Dealers will begin to fill U.S. orders for the vehicle in 2008, with 30,000 already placed on hold with a $99 deposit.

Making plastics look like metals

On the packaging front, polyethylene terephthalate (PET) is prized for its clarity, but several colorant suppliers have launched new color portfolios to jazz up polyester. In addition to adding seven new shades to its LiquidMetal Colors line, Ampacet (Tarrytown, NY) has launched Blue Edge masterbatch, which it says gives PET bottles a blue halo silhouette, as well as enhancing bottle brightness and giving a soft glow in ultraviolet light. The company says that since pigment isn’t used, light transmission isn’t affected. Alcoholic drinks consumed in clubs that employ black lights are one potential target product.

For its LiquidMetal line, Ampacet has added bronze, gold, red, silver, midnight blue, brown, and bright chrome to the preexisting brass, chrome, copper, onyx, graphite, and gun-metal blue shades. Ampacet says the line sees use in packaging that looks to simulate polished metal for cosmetics, specialty foods, beverage, and car-care product packaging. The product uses Ampacet’s Formula X PET technology, which eliminates the need to pre-dry PET colors and allows for extruder-throat feeding. This technology also reportedly reduces feed-throat clogging and screw slippage, while improving color dispersion.

Teknor Color Co. (New York) has new custom-colored concentrates that allow designers to achieve color-shift effects in packaging. The ColorMorph line has colorants that shift from gold to bright red, depending on viewing angle, and from transparent to opaque. The latter orients the color in this PET sheet so that printing or contents would be visible, depending on the angle.

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