Substrates & Automotive Paints:
Questions to Consider
Substrates & Automotive Paints:
Questions to Consider
In the world of automotive paint, consistent results are key – not only to the folks in quality control, but more importantly, to the folks in the showroom (and I don’t mean the salespeople!).
A Mix of Substrates
The modern automobile has come a long way from Henry Ford’s Model T, which was primarily a steel box, painted inside and out (“any color you like – as long as it’s black!”). A bit of brass trim around the headlights, natural wood spokes in the wheels, and leather seats, and you have the classic look.
Today’s automobiles are a very different animal.
In addition to the sleek lines and seemingly endless color combinations, the modern iteration is a complex combination of high-tech alloys, composites, plastics, and countless other natural and man-made materials. The contemporary consumer is far more critical when it comes to fit and finish than their parents and grandparents were.
All these factors combine to significantly complicate the task of applying the myriad finishes available for both the exterior and the interior of the modern automobile!
Drivers of Modern Material Choices
Though Henry Ford was very concerned with the ruggedness and reliability of his Model T, it’s clearly no match for today’s offerings. It’s obvious that safety and fuel economy were secondary concerns in those early designs.
Now, safety requirements are paramount. “Crumple zones” – areas made from a combination of high-strength and malleable metals – make up the body and frame and enable a car to pass demanding crash tests.
Also on the tip of every automotive engineer’s tongue is the term “light-weighting”, which refers to using modern materials (aluminum, plastics, composites, etc.) to remove weight wherever possible. Light-weighting reduces vehicle mass, which in turn improves its fuel economy and its crash test survivability. Noise, vibration, and harshness are also greatly reduced for the driver and passengers.
What’s All This Got to Do With Paint?
All these different materials pose their own respective challenges to the paint team. From an appearance perspective, the plastic thermoformed bumpers and fascias must match the body color and gloss (as must the molded door handles, mirror housings, gas filler doors, etc.). And that means they all should be painted with the same paint…right?
Not exactly.
Many considerations go into the design of a modern automotive paint. Let’s start with curing it on the surface after application. We’re all familiar with the concept of “baking” the paint to cure it. But you can’t heat the plastic parts to the same temperature as the metal parts. That means the paint used on the plastic parts must cure at a lower temperature than the paint used on the metal parts.
Then there’s the question of adhesion. The paint must stick to the parts you’re putting it on for a very long time and through a wide variety of conditions. But a metal surface is very different from a plastic surface, and each reacts very differently to changes in things like temperature, humidity, etc. For instance, the metal parts are more prone to expand in the hot sun than the plastic parts, and therefore formulations have to be “tweaked” accordingly.
Speaking of humidity: another aspect of paint that most people don’t think about is protection. Protecting the substrate from external factors is just as important as appearance. But different substrates have different vulnerabilities. Steel parts are highly susceptible to moisture (so the paint must protect the metal parts from water exposure), whereas plastic is virtually impervious to water (so this is less of a concern for the paint). Conversely, plastic is very susceptible to damage from UV exposure, whereas steel and aluminum are unaffected. All of these factors drive changes in paint formulation.
Distance is No Excuse
Another rarely considered factor is that all of these diverse parts that make up the modern automobile are manufactured (and painted) by a variety of vendors in various locations – often in different states and even in different countries, and climates, using an assortment of processes, and a diverse set of operators.
But in the end, they all must come together in the assembly plant and match perfectly when placed next to one another on the finished product.
Why?
Because the final assembly has to pass inspection by the most critical color detection instrument on the planet: my wife’s eye.