Bright lights, bold look

Douglas Stratton
Project Leader, Future Business
Automotive Industry Innovation
Bayer MaterialScience LLC
Pittsburgh, Pa.

Automotive OEMs use distinctive styling cues to differentiate their vehicles from the competition. While body styling continues to be a priority, automotive lighting is beginning to emerge as a key design element. Advances in lighting technologies, the desire for distinctive designs and incorporation of color combine to give lighting assemblies bold new looks.

Outer lenses for automotive headlamps have typically been molded from polycarbonate (PC) resin. PC is also increasingly used for inner lenses. PC is well suited for automotive lighting thanks to a combination of high-impact strength, clarity, thermal stability, heat resistance, and ease of injection molding for complex lens designs.

But such recent advances in lighting as light-emitting diodes (LEDs) are complicating the process of picking materials and creating innovative designs. Fortunately, PCs continue to evolve with new grades that are up for the task.

LEDs take the lead
Over the last few years, LEDs have worked their way into automotive lighting — as tail lamps and CHMSLs (center high-mount stop lamps) where PCs serve in bezels and housings. Now LEDs are going into headlamps. The 2007 Cadillac Escalade headlamp assembly, for example, features a row of seven amber LEDs packaged behind amber inner sidemarker lenses molded from Makrolon PC. The headlamp outer lens and chrome bezel are also made from Makrolon PC. This application is significant in that it signals a bright future for LED technologies in such uses.

In fact, white, high-brightness LED (HB-LED) lumen output has steadily risen to a point the bulbs are used on commercial vehicles behind PC lenses in forward lighting day-time running lamps. Automotive OEMs and lighting suppliers are taking the next step: Transforming LEDs from a point light source into a legal beam pattern, thereby paving the way for HB-LEDs in vehicle forward lighting low- and high-beam optics.

The first vehicles featuring HB-LED technology in forward lighting are expected to hit the streets later this year featuring first-generation inner optics likely made of glass. However, polymers have displaced glass in other automotive lenses and will probably do the same in inner lenses. We can expect to see this in 18 to 24 months. Polymers offer several advantages, including lighter weight and can make lens designs more complex. The latter development is particularly important for HB-LED applications.

HB-LED technology can impact both the outer lens and the inner lens. Certain headlamp designs for low and high-beam lighting use internal collimator optical lenses designed to emit light at a certain pattern or “prescription.” These internal lenses are packaged behind an outer PC lens that must offer optimal transmission and excellent thermal resistance. Bayer MaterialScience has engineered grades of PC to meet these outer lens specifications and is developing a new grade for the autointernal lenses.

In some instances, the inner collimator lenses for low and high beams present a processing challenge. A good injection-molded design for lenses has a thickness of approximately 3 to 5 mm. However, some inner lens designs need to be up to 35-mm thick. Fortunately, there are alternatives. One involves casting inner optical lenses using another new material — Baytec optically clear aliphatic polyurethane (PU), which offers excellent clarity, transmission and surface hardness, and is engineered to be cast or milled into precision optics.

The cycle time for the casting process is 3 to 4 hr versus minutes with injection-molded materials. Despite the longer cycle time, there are two key advantages to inner lenses made with Baytec optically clear polyurethane.

First, the cost is less. Building a high-quality, multicavity mold for injection molding can be expensive, ranging from $150,000 to $200,000. Conversely, the nature of the casting process allows much lower setup and tooling costs. Second, casting can quickly and easily create internal lenses featuring radical designs — those requiring extreme thickness, as well as significant variations in wall thickness.

Together, these two advantages fill a critical niche for automotive OEMs and lighting suppliers driven to go from concept to reality more quickly than ever before. Simultaneously, the approach helps keep an eye on the bottom line.

Casting lets lighting suppliers economically produce concepts or prototypes, giving them the freedom to fabricate several design variations — something that would otherwise be to costly and time consuming with injection molding. Optically clear PU is also a candidate for less costly lenses for high-end vehicles such as sports cars where the production volume is typically low — perhaps 3,000 to 5,000 units.

It’s important to note that optically clear PUs and PCs have roughly the same refractive index. This similarity makes it possible to validate a lens’ “prescription” inexpensively using the Baytec material, then move to full-scale commercial production using polycarbonate resin. This flexibility lets resource-conscious suppliers seamlessly move from one material to another as needed.

A new aura
Adding color also creates automotive lighting that is dramatically different. In the near future, new technologies, such as Bayer MaterialScience’s Aura infusion technology, may be used to tint automotive headlamp trim rings and light rods. This can add a splash of color that matches or complements the body paint.

Components custom colored with Aura infusion technology can be ready for market in a matter of hours instead of weeks as is typical with more conventional coloring and color matching techniques. Recently, Apollo Color Coating, Roseville, Mich., licensed the Aura infusion technology and demonstrated its use to create LED amber turn-signal optics. Besides giving a wide variety of colors, the technology can also create special effects such as gradients.

Bayer MaterialScience researchers are exploring other opportunities for introducing color to vehicles.

One of the most recent automotive developments involves using Aura infusion technology for automotive LED lenses and optics. The 2007 Lincoln MKR sports sedan concept, unveiled earlier this year at the North American International Auto Show in Detroit, features LED adaptive headlamps. But, unlike most adaptive headlamps that have multiple lights, the MKR features single LEDs for improved performance and increased lumen output. The light source is a white, HB-LED; the LEDs are packaged in close proximity to the optics. This is not only new in the Lincoln MKR, but also an industry first. Makrolon clear tint PC was selected for the injection-molded headlamp internal optics; Aura infusion technology makes specific optics in the headlamp appear amber when lit.

One recent breakthrough in Aura color infusion technology, for example, can put a variety of metallic colors onto the surface of aluminum wheels.

Looking forward, lighting technologies will continue to evolve at a fast pace, bringing with them new opportunities and new challenges.

Make contact:
Apollo Color Coating, (586) 777-0070, apollocolorcoating.com
Bayer MaterialScience LLC, (800) 662-2927, bayermaterialsciencenafta.com