UV curing is used to cure coatings and adhesives on many different types of automotive parts and components. A few examples are described below. Click here for information about curing three dimensional parts.
Lighting Reflector Housings
Acrylic Tail Lens
Body Side Moldings
SMC Body Panels
UV Automotive Clearcoats
Safety and Handling for UV-Curing Automotive Coatings
A UV curable hardcoat is applied and cured onto polycarbonate plastic lenses to provide scratch and chip resistance. The thermal process that UV curing replaces takes up to three hours, requires lenses to be heat-annealed, cooled, coated with a primer, baked, cooled, top-coated, baked and cooled. The UV process takes less than 10 minutes, reducing parts-in-process, allowing quicker part changes, and lowering energy costs. Fusion UV Systems’ UV curing systems are installed on many headlamp lens lines throughout the world.
UV technology offers fast processing with improved performance for reflector housings for automotive lighting. UV light is used to pre-treat the housing surface improving adhesion of the UV-curable primer. The primer provides an extremely smooth surface for the subsequent vacuum deposition of aluminum and a superior reflective surface. The reflector is then top-coated with a protective UV-cured clearcoat to preserve the mirror-like finish of the soft aluminum. The thermal process that UV replaces took a total of three hours. The UV process decreases parts inventory and space and energy costs, while improving yields and product performance.
Acrylic tail lenses are first decorated with a UV-cured silk-screen coating. Then a UV clearcoat is applied to protect the decoration while providing a uniform, high-gloss finish. The UV clearcoat also provides superior abrasion resistance and gloss retention compared to urethane and acrylic clearcoats, but the UV coating is flexible enough to match the thermal expansion rate of the coatings beneath it, which the brittle, thermal silicones could not. This flexibility prevents cracking of the clearcoat during subsequent cyclic thermal testing.
One of the most cost-effective processes for body side moldings is the extrusion of pigmented vinyl. The materials are very inexpensive and efficient to form, but tend to yellow and stain in the field. To overcome these deficiencies, a UV-cured clearcoat is applied to substantially improve the products performance without significantly increasing the process time. Second generation products, such as a 100% solid liquid coating and UV-curable powder coating, are under development.
Two examples of UV-coated under-hood components are preassembled radiators and starter motors. UV-curable powder coatings are used to coat the radiators because the assembly has a heat-sensitive rubber gasket that could not withstand the high temperatures associated with traditional powder coating. UV powders melt, flow and cure at much lower temperatures (only 90-100 degrees Celsius) and the UV cure is much faster and takes up much less floor space.
UV technology was chosen for the housing and the balancing of the starter motor to reduce VOCs and because low-temperature processing is possible. Traditionally, metal subtraction by a drill press had been used to remove metal from the armature windings to balance the motor. However, removal of metal decreases the motor efficiency and can result in a scrapped part if too much material needs to be removed. The UV technology uses additive balancing. A small amount of UV-curable material is applied to the armature, cured and then tested. If still unbalanced, the process is repeated, just like the subtractive process. However, there is no scrap and the motor efficiency is not adversely affected.
Read about how Unit Parts uses UV curing for their aftermarket starters and alternators.
Low-gloss coatings are used extensively on plastic parts. A waterborne UV-curable clearcoat provides excellent mar and chemical resistance as a very low gloss on flexible vinyl-wrapped parts. The coating provides higher performance than solvent-borne and waterborne thermally cured coatings, with a very low VOC content.
UV-curable liquids and powders for aluminum wheels is a promising development. The UV process reduces processing and cool-down time, space requirements, as well as energy costs. Helios Coatings, Inc. has developed a chrome plated look which uses UV coatings.
BASF developed a UV curable primer/sealer for SMC body panels that creates a strong enough coating layer to eliminate outgassing from the SMC during the subsequent high temperature thermal paint-curing process. Prior to this development, a typical SMC body panel would have paint pops that required hand repair or sanding, followed by another run through the paint line. (The paint pops are due to porosity of SMC materials which outgas during the paint curing.) The UV curable primer/sealer eliminates the need for hand repair and rework, significantly increasing production rates and reducing labor requirements.
Process Conditions For UV Sealer On SMC Body Panels, a paper given by Kevin Joesel at a RadTech Europe Conference is available for download.
Request a free publication: Safety and Handling for UV-Curing Automotive Coatings. This 16-page guide includes detailed information on the safe handling, processing, mixing, clean-up, storage and disposal of ultraviolet materials used in automotive refinish surface operations.
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