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Coating Raw Materials
Polyurethane Coatings for Automotive Exteriors
Since Bayer first introduced polyurethane technology to the coatings industry in 1955, we have been a leader in providing high-quality resins to the automotive industry. We work hand-in-hand with leading automotive manufacturers and paint suppliers to provide cutting-edge coating technology. Our polyurethane coatings raw materials help deliver protection, performance and beauty that last throughout the lifetime of an automobile:
- Long-lasting "new car" look. Clear polyurethane topcoats enhance and help protect the bright, richly colored basecoats on many top-of-the-line automobiles. Polyurethane clearcoats provide gloss and distinctness of image (DOI) that produces a quality "wet look."
- Exceptional resistance to environmental pollutants and chemicals. Polyurethane coatings' resistance to acid rain, bird droppings and other environmental elements have been well demonstrated over the past several years in numerous applications exposed to extremely tough conditions.
- Low-temperature cure capability. Polyurethane's low-temperature cure capability is beneficial for interior and exterior automotive applications that utilize plastic substrates with limited heat resistance.
- Excellent durability and resilience. Polyurethane coatings offer an outstanding combination of durability and resilience, which translates into a high degree of corrosion protection and chip resistance.
- Versatility to match different substrate needs. The versatility inherent in polyurethane coatings provides latitude that allows coatings to be specifically formulated to the performance requirements for a variety of substrates.
- VOC compliance. In addition to offering formulations that meet stringent volatile organic compound (VOC) emission regulations, Bayer provides environmentally friendly systems that can reduce emissions up to 90 percent. In fact, Bayer received the Green Chemistry Award from the U.S. Environmental Protection Agency for developing an industrial coating material that uses water instead of chemical solvents, thus reducing volatile air emissions by as much as 99 percent. To learn more contact us.
To achieve these properties, Bayer's polyurethane coating technology is available at every step of the finishing process:
- Anti-corrosion electrodeposition primer. Electrodeposition is the process by which the paint and the vehicle carry opposite electrical charges in order to deposit a paint film on the vehicle body. Blocked polyisocyanates are used in electrocoats as a crosslinker to provide long-term corrosion protection. Additionally, polymeric MDI products are used as raw materials for the formulation of electrocoat layers. Recommended products include those sold under the Mondur M (MDI) and Desmodur BL polyisocyanate product lines.
- Anti-chip and Chip-resistant coatings. Anti-chip polyurethane coatings, applied after the electrocoat and before the chip-resistant polyurethane primer-surfacer, provide added toughness for a vehicle's most chip-prone areas, such as doors and rocker panels. One-component polyurethane coatings offer excellent chip resistance at low film builds, allowing material cost savings and smoother, high-quality surface appearance.
In addition, anti-chip polyurethane coatings offer good flow and leveling characteristics, ensuring a smooth surface and hence, a quality topcoat finish. The ability of anti-chip polyurethane coatings to be sprayed to a "feather-edge" facilitates selective application to leading edge areas so that demarcation lines are not visible in the final finish. One-component polyurethane primer-surfacers help provide total car body protection from damage caused by flying stones, gravel and other road debris, even at temperatures as low as -20F. They also provide good energy absorption for excellent impact resistance. Recommended products include those from our Desmodur BL polyisocyanate and Desmophen polyol product lines.
- Basecoats. Polyurethane dispersions as basecoat modifiers are used to enhance the mechanical properties of basecoats. Recommended products include those from our Bayhydrol product line.
- Clearcoats. Polyurethane clearcoats provide exceptional appearance attributes measured as gloss and DOI. The transparent finishes highlight the deep, rich colors of today's basecoats and help provide a long-lasting gloss and brilliance.
Clear polyurethane topcoats also provide the highest quality finishes for delivering exceptional resistance to environmental elements such as acid rain, bird droppings, gasoline, road tar, and other substances that can mar the finish of an automobile. The tough polyurethane clearcoats protect car surfaces from these degrading effects, maintaining a smooth, quality appearance long after a car leaves the protective environment of the showroom. Recommended products include those from our Desmodur N and Desmodur Z product lines.
For additional information about polyurethane coatings for the automotive industry, ask your coatings supplier. For more information about Bayer's raw materials, contact us.
Polyurethane Coatings for Automotive Interiors
A growing number of automotive manufacturers are using special-effect polyurethane coatings containing Bayer resins to add a soft, luxurious feel to plastic interior components such as steering wheels, airbag covers, instrument panels, door handles and many other interior trim plastic parts.
Special-effect coatings provide durability and an attractive surface for these high-use hard plastic items. They also provide chemical resistance, scratch and mar resistance, and UV protection. In addition, they eliminate "fogging" associated with PVC plasticizers and frequently yield a cost savings when replacing vinyl wrapping.
Special-effect coatings are two-component (2K) coatings based on the reaction of flexible polyester polyols with mixtures of aliphatic polyisocyanates.
Bayer also offers environmentally friendly products and technologies. In fact, Bayer received the Green Chemistry award from the U.S. Environmental Protection Agency for developing an industrial coating material that uses water instead of chemical solvents, thus reducing volatile air emissions by as much as 99 percent.
Special-effect coatings can be tailored to protect and enhance the many different types of plastics commonly used for interior automotive components. They offer:
- Excellent adhesion to most plastics
- Flexibility needed to match various types of plastics
- Low-temperature curability essential for many heat-sensitive plastics
- Easy repairs with scuff sanding of defects and then full coat application
- Easy application using conventional or electrostatic spray equipment
- Wide range of colors and gloss options
Recommended products include those sold under the Desmodur, Bayhydur, Desmophen and Bayhydrol tradenames.
For additional information about special-effect polyurethane coatings for interior automotive parts, ask your coatings supplier. For information about coating raw materials, contact us.
Polyurethane Coatings for Automotive Plastic Components
More than two billion pounds of plastic are used annually in the North American Automotive Industry for exterior and interior parts ranging from body panels and fascias to instrument panels and steering wheels. Polyurethane coating systems using Bayer raw materials and colorants help provide a durable, long-lasting and high-quality surface finish for these components.
Two-component (2K) solventborne, and waterborne systems are the most common polyurethane coating formulations, and they deliver key properties such as:
- Environmental etch and chemical resistance
- Class A surface finish
- Low-temperature cure
- Good adhesion properties
- Variable flexibility
- Mild solvent use
- Low VOC capability
Bayer's polyurethane coatings can be applied to the most widely used plastics in the automotive industry including TPO, TSOP, PUR-RIM, PUR-RRIM, PUR-SRIM, Polypropylene, Polycarbonate, ABS, PC/ABS blends, thermoset polyesters, PC/PET blends, PC/PBT blends, polyamide 6 and SMA/ABS.
In addition to offering a full line of polyurethane coating raw materials for the automotive industry, Bayer also provides high-performance adhesive and specialty technology for both interior and exterior components.
Polyurethane Coatings Provide Exceptional Durability
Automobile exteriors in particular are subjected to a wide range of potentially degrading effects. These include temperature extremes, sunlight, acid rain, as well as exposure to flying stones, dirt and other debris that can lead to scratches and abrasion marks. Of particular importance for some plastic substrates is polyurethane coatings' excellent chemical resistance. Plastics such as ABS and polycarbonate generally have poor resistance to solvents and other harmful materials and will degrade if exposed. The strong, tightly crosslinked nature of polyurethane coatings results in a durable film that is nearly impervious to these types of degrading elements, which can cause some other paint films to break down. Also, when scratched, polyurethane coatings have a "self healing" tendency in that minor scratches close up in time.
Properly Coated Plastics Can Provide Class A Finishes
The coating of plastic automotive parts is different in several ways from the coating of metal parts. However, with some basic knowledge about both the plastic to be coated and techniques for the application of coatings, a class A surface finish rivaling that of coated metals can be obtained despite the more difficult surface morphology of plastics.
Cryogenic polishing is an effective way to recover the gloss of a flexible polyurethane coating after sanding. High-speed robotic paint operations are often used to apply two-component (2K) polyurethane coatings.
Power Wash Is Most Technologically Advanced Cleaning Method
Like all substrates, plastics should be cleaned before any type of coating is applied. Mold release, fingerprints and other greasy marks must be removed with a more rigorous, multi-stage cleaning system. The most widely used cleaning method is power washing, whereby a hot alkaline or acid solution is sprayed at high pressures followed by a rinse of deionized water.
Polyurethanes Can Be Applied Using Conventional or Electrostatic Spray Equipment
The coating of plastic automotive parts is usually done off-line and the parts are then installed after the rest of the car has been painted. Plastics with thermal deflection temperatures can be painted on-line without deformation of the plastic. However, some of these plastics may experience other problems at high temperature, such as shrinking and blistering. Structural supports and other part-fixturing methods help avoid shrinking of some of the more thermal-resistant plastics.
Polyurethane coatings can be applied with either conventional or electrostatic spray equipment. Robots often are employed for the bulk of the operation, with touch-ups or hard-to-reach areas painted manually. When using any type of paint system, including polyurethane coatings, good engineering controls, ventilation and use of proper personal protection equipment should be used to ensure safe handling. Relevant Material Safety Data Sheets and other pertinent information should be studied before any new paint operation is initiated.
Polyurethane primers or primer-surfacers can be applied directly to a cleaned substrate to fill in porous areas of the substrate and thus improve surface smoothness. Although specifications can vary widely, a primer applied to exterior body panels or bumpers may be specified for a dry film thickness (DFT) of 1.0 to 1.5 mils. Typical bake schedule is 30 minutes at 180F or the equivalent.
Depending on the surface smoothness of the substrate or performance requirements, a primer may be applied directly to cleaned substrates or to primed and cured surfaces. The basecoat can be pigmented in virtually any metallic or nonmetallic shade and is generally applied to a DFT of 0.5 to 1.2 mils.
Typically, a 2K polyurethane clearcoat then is applied "wet-on-wet" over the basecoat. The clearcoat provides excellent distinctness of image (DOI), gloss and weatherability. DFT generally ranges from 1.0 to 2.0 mils. The basecoat/clearcoat system is commonly baked for 30 to 45 minutes at temperatures ranging form 150F to 250F.
Polishing and Repairing Flexible Coatings
In the automotive industry, it is common practice to correct small surface imperfections, such as those arising from dust or dirt particles and scratches, by sanding and polishing. However, until recently, only the more rigid polyurethane coatings could be polished.
Restoring a flexible polyurethane coating to its original high-gloss finish, such as those formulated for fascia, was extremely difficult or impossible by sanding and polishing small imperfections. As a result, complete sanding and refinishing of the entire part were required, which slowed production and raised finishing costs.
One option is "cold air polishing," which has been found to be effective for polishing flexible polyurethane coatings. Using this equipment, highly flexible coatings can be re-polished after sanding to recover more than 95 percent of their original gloss. This is comparable to the amount of gloss recovered when conventional polishing is employed on rigid coatings.
Low-Temperature-Curing Polyurethane Coatings are Compatible With Plastics That Have Low Thermal Deflection Temperatures
The thermal deflection temperature of a thermoplastic or, similarly, the heat sag of a thermoset material, is another important consideration in coating selection. Auto makers' painting lines for metal bodies typically operate at baking temperatures ranging from 250F to 350F. Some rigid paints can only cure at these higher temperatures. For many plastics, exposure to such high-heat conditions can cause part deformation, buckling, shrinking and other problems. For this reason, many plastic parts are painted off-line with coatings that cure below the plastics thermal deflection temperature.
Polyurethane coatings have low-temperature-cure capability. Most polyurethane paint systems will cure at ambient temperatures (although elevated temperatures often are used to accelerate curing). The ability to specify a curing temperature from a wide range of options permits the use of polyurethane coatings on many different types of plastics. The precise cure temperature for a particular application can be optimized to ensure that it is safely below the thermal deflection temperature of the substrate, yet as high as possible to minimize cure time.
Polyurethane Coatings Adhere to Plastics
Polyurethane coatings exhibit good adhesion to most plastic substrates, and exceptional adhesion to substrates made of RIM polyurethanes because of the chemical similarity of the two materials.
Polyurethane Coatings Provide Flexible Properties
The flexibility of a plastic substrate is critical in determining
its proper coating, which is true for coating all types of plastics,
but is especially important when coating flexible plastics. Some automotive
body parts, such as front and rear bumpers, must meet federally established
impact standards. Plastics used for bumper systems typically have
a high degree of flexibility, which allows for minor collisions without
permanent damage to the part. It is important that the coating applied
to these components helps to retain, not impair, the plastic's impact
resistance.
The flexibility of a plastic can be determined by measuring its tensile elongation at break. The elongation of plastics used in front and rear bumpers generally is in the range of 100 to 220 percent, as measured by ASTM method D 638.
Typical thermoset acrylic coating systems for metal have a tensile elongation at break of about three percent at room temperature. This type of rigid coating applied to a flexible plastic an reduce the plastic's impact resistance. Upon impact, small cracks can form in the coating due to the coatings inability to stretch in the plastic. Since the coating is adhered to the substrate, these small cracks in the coating can then spread down into the plastic and cause premature failure of the otherwise flexible painted part.
In contrast, polyurethane coating systems can be tailored to have an elongation at break up to 160 percent. This flexibility means the coating can match the flexibility of the substrate. The coating can stretch with the substrate, inhibiting premature failure of the component.
Plastics used in less impact-prone applications, such as side body panels and exterior rigid trim, require less flexibility and, similarly, less flexible coatings. A coating that is more flexible than the substrate is not desirable because, although impact strength is not affected, a softer surface is obtained. More rigid polyurethane coatings (with elongation at break as low as 30 percent) can be prepared for these uses.
Polyurethane Coatings Compatible with Mild Solvents
The ability to use mild solvents with polyurethane coatings can facilitate application to chemical-sensitive plastics.
Bayer's Polyurethane Coating Systems Help Reduce VOC Emissions
In addition to offering formulations that meet stringent volatile organic compound (VOC) emission regulations, Bayer provides environmentally friendly systems that can reduce emissions up to 90 percent. In fact, Bayer received the Green Chemistry Award from the U.S. Environmental Protection Agency for developing an industrial coating material that uses water instead of chemical solvents, thus reducing volatile air emissions by as much as 99 percent. To learn more contact us.
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