In Living Color - molded-in-color plastics for automobiles

Automotive Industries, Nov, 2000 by Lindsay Brooke

Molded-in-color plastics are moving closer to production -- and to eliminating the paint shop from assembly plants.

The dream ot eliminating a $500 million paint line from assembly plants -- and the traditional production bottlenecks that often go with it -- remains just that: a dream. Within a few years, however, glossy, scratch resistant, recyclable molded-in-color (MIC) plastic body panels needing no coatings will finally be ready for automotive prime time.

It won't necessarily be "good-bye, paint shop," notes Nipponi Rao, senior specialist, exterior panels, at DaimlerChrysler's tech center in Auburn Hills, Mich. But the MIC technology is making swift progress into the exterior panel arena.

"It's coming along quite fast," Rao observes. "Maybe faster than I'd imagined even two years ago. There are still some issues that must be solved before we can go to MIC in high volume, however."

The issues include a lack of true metallic colors and the question of weatherability in extreme temperature and sunlight conditions. A solution to these issues is appearing in a new generation of extrudable plastic films. These films will be molded into various plastic substrates (either thermoplastics or thermosets) for major body panel applications. Their advantage is in the thickness of the film -- at .030 inch, it can withstand deep draws and radical part geometries.

GE Plastics fired the latest shot in the evolution of MIC body panels with its new Sollx brand. Sollx film seems to have a lot of the qualities that OEMs are looking for in MIC technology: super high gloss ([greater than]100 at 60 degrees); the ability to thermoform deep-draw parts; resistance to chemicals and fuels; weatherability (it has passed GE's 10-year accelerated outdoor tests); and it's available in a wide color pallet, including some metallics.

The material is produced in sheet stock by GE Plastics' Structured Products division, which will supply it to molders, color-matched, in roll form.

"Our goal was to do molded colors that didn't need a coating," explains Venkatakrishnan Umamaheswaran, GE Plastics' market development manager in Southfield, Mich. (He goes by the nickname "UV" for obvious reasons.) "So about three years ago, our R&D center in Schenectady, N.Y., began looking at polymers that are capable of long-term durability and colorability."

Development of MIC materials and process technology for exterior-panel use has been ongoing since the late 1980s. Early applications, often in polycarbonates, focused on exterior trim and were limited to shades or grey or black. By the late 1990s, it became possible to mold body fascias in color -- a pioneer being the 1999 Chrysler Neon fascias. The material was DuPont Surlyn, a resin with excellent color-matching to the body color and superior scratch resistance.

But automakers still need MIC materials for use on major exterior panels, in both structural and non-structural roles.

Cell Manufacturing is Key

The current Surlyn Reflection series materials are not targeted for structural applications. "We're pursuing structural technologies," notes John Wahl, executive marketing manager at DuPont. "We're looking at co-injection molding or two-shot molding, where Surlyn can be combined with one of our structural materials, such as Rynite or glass-reinforced Zytel."

With a .030-inch-wall thickness, sheet-film such as GE's Sollx can withstand (depending on the part geometry and depth of draw) a thermoforming operation that will thin out the sheet to .015 inch on the edges. Prototyping of various high-draw parts, such as fascias and fenders, is now underway at GE Plastics.

UV explains that Sollx will arrive at the molder or thermoformer in rolls, or it can be blanked to pre-cut sheets. "The ideal is, we're developing a cell-manufacturing concept at our Pittsfield, Mass., facility. In the cell, you start with a roll of Sollx film that's fed continuously into the thermoformer. There it gets thermoformed as well as trimmed and then fed into the injection molding machine."

Asked about Sollx's coefficient of thermal expansion, UV explains that Solix acts basically like a surface coating. It's dominated by the substrate's thermal properties.

The color issue for MIC materials is being pursued aggressively by the plastics industry, Rao notes. "We're seeing very promising solutions from the leaders -- Solvay, Besell (formerly Montell) and A. Schulman, in addition to GE and DuPont," he says. Molding thermoplastics in metallic colors is still a bit of a black art.

"We don't have it figured out completely yet," admits UV. "We're making a huge investment in fundamental technologies to create and synthesize colorants that are compatible with thermoplastics, have long-term durability, weatherability, because the pigment itself has to be weatherable as well as the polymer."

Others are moving aggressively in the same direction. "Film technologies are one of the ways to go," notes Wahl.

Of nearly 4,000 pigments now available to automakers, only about 25 or so are truly weatherable. The Sollx development team is working on expanding those 25, as well as working with additive suppliers to develop mica and aluminum flakes for the metallics. This will improve appearance and impact properties.