by David W. Bynon
<font size="1">Copyright©, 1999-2002, Autopia Car Care -- All Rights Reserved</font>
Not long ago, I had an unfortunate parking lot accident with my Porsche. A tired employee backed into my Carrera, crumpling and tearing the plastic bumper cap on the rear of the car. The end result was a $4,200 repair bill. The repair was perfect, but it left me wondering and asking a lot of questions about the use of plastics on cars. Here’s what I discovered.
Most modern cars use plastic bumper systems and fascias made of thermoplastic olefins (TPOs), polycarbonates, polyesters, polypropylene, polyurethanes, polyamides, or blends of these compounds. Often, glass fibers are added to provide more strength and structural rigidity. Plastics allow automotive engineers to have a lot of freedom in styling, building, and placing components.
Plastic also lends itself to combining several complex parts into a single, integrated piece, such as a front bumper and spoiler. From bumpers to door panels, plastics give designers and engineers the freedom to create car shapes and designs that otherwise would never be possible.
With all of its benefits, plastic body parts do have limitations and drawbacks. One of the issues that I have discovered over the years is that painted plastic body parts components easily stain and dull. To understand why, I researched the process of painting plastic bumpers and how it differs from painting metal body panels.
I have long known that it’s necessary to add a “flex� agent to paint for plastics. The flex agent allows the paint to flex with the plastic part and not crack or delaminate. What I did not understand is how the flex agents work. It’s very interesting, and explains why painted plastic parts are so susceptible to staining and dulling.
Paint flex agents cause the paint to be more porous. In essence, the flex agent makes the paint foam, creating microscopic pockets. These pockets allow the paint to remain spongy and flexible. Most of the pockets are deep in the layers of paint, but some float to the surface. The flex agent also causes the paint to remain soft. Paint on TPO resists chips very well, but it will dent (small ping marks) from road stones.
The porosity and softness afforded by the flex agent creates a couple of challenges. First, the paint does not resist stains as well as paint without a flex agent. Second, the flex agent paint cannot be buffed or polished with anything more than the finest polish, or the finish will be ruined. Buffing does not increase the gloss on this paint as it does with a hard paint finish. It smears it.
I’ve seen a dozen or more cases of botched repair jobs, where an inexperienced painter used a buffer to blend paint and put permanent buffer burns and smudges in the bumper cap. I’ve seen even more cases of a car owner using a rubbing compound on their soft plastic bumper caps to remove bug stains. The paint dulls and never returns to full gloss. I have also noticed that etching from hard water and bird droppings is much worse on the painted plastic parts.
General care of plastic bumper caps and fascias is really no different than caring for the rest of the body. Keep it clean and keep it waxed. If you get bug splats, remove them before they harden and have a chance to stain. Low abrasive paint cleansing lotions and polishes are okay to use, but stay away from rubbing compounds and don’t use a high-speed buffer. These areas need waxing more often than the rest of the car, too. Because the front is low and often a complex shape, most people neglect waxing and polishing this area, even though it needs it most.
<font size="1">Copyright©, 1999-2002, Autopia Car Care -- All Rights Reserved</font>
Not long ago, I had an unfortunate parking lot accident with my Porsche. A tired employee backed into my Carrera, crumpling and tearing the plastic bumper cap on the rear of the car. The end result was a $4,200 repair bill. The repair was perfect, but it left me wondering and asking a lot of questions about the use of plastics on cars. Here’s what I discovered.
Most modern cars use plastic bumper systems and fascias made of thermoplastic olefins (TPOs), polycarbonates, polyesters, polypropylene, polyurethanes, polyamides, or blends of these compounds. Often, glass fibers are added to provide more strength and structural rigidity. Plastics allow automotive engineers to have a lot of freedom in styling, building, and placing components.
Plastic also lends itself to combining several complex parts into a single, integrated piece, such as a front bumper and spoiler. From bumpers to door panels, plastics give designers and engineers the freedom to create car shapes and designs that otherwise would never be possible.
With all of its benefits, plastic body parts do have limitations and drawbacks. One of the issues that I have discovered over the years is that painted plastic body parts components easily stain and dull. To understand why, I researched the process of painting plastic bumpers and how it differs from painting metal body panels.
I have long known that it’s necessary to add a “flex� agent to paint for plastics. The flex agent allows the paint to flex with the plastic part and not crack or delaminate. What I did not understand is how the flex agents work. It’s very interesting, and explains why painted plastic parts are so susceptible to staining and dulling.
Paint flex agents cause the paint to be more porous. In essence, the flex agent makes the paint foam, creating microscopic pockets. These pockets allow the paint to remain spongy and flexible. Most of the pockets are deep in the layers of paint, but some float to the surface. The flex agent also causes the paint to remain soft. Paint on TPO resists chips very well, but it will dent (small ping marks) from road stones.
The porosity and softness afforded by the flex agent creates a couple of challenges. First, the paint does not resist stains as well as paint without a flex agent. Second, the flex agent paint cannot be buffed or polished with anything more than the finest polish, or the finish will be ruined. Buffing does not increase the gloss on this paint as it does with a hard paint finish. It smears it.
I’ve seen a dozen or more cases of botched repair jobs, where an inexperienced painter used a buffer to blend paint and put permanent buffer burns and smudges in the bumper cap. I’ve seen even more cases of a car owner using a rubbing compound on their soft plastic bumper caps to remove bug stains. The paint dulls and never returns to full gloss. I have also noticed that etching from hard water and bird droppings is much worse on the painted plastic parts.
General care of plastic bumper caps and fascias is really no different than caring for the rest of the body. Keep it clean and keep it waxed. If you get bug splats, remove them before they harden and have a chance to stain. Low abrasive paint cleansing lotions and polishes are okay to use, but stay away from rubbing compounds and don’t use a high-speed buffer. These areas need waxing more often than the rest of the car, too. Because the front is low and often a complex shape, most people neglect waxing and polishing this area, even though it needs it most.