Adhesion Promoter
Requirements: Thermoplastic polyolefin, also known as TPO is widely used in flexible automotive exterior trim such as fascia, cladding and body side moldings. TPO is inherently difficult to wet due to its low surface energy and therefore difficult to paint. Methods such as plasma or flame have been very successful in overcoming this issue by oxidizing the TPO surface thereby raising the surface energy. Another well established and widely practiced method is through the use of air atomized adhesion promoters. These adhesion promoters are normally formulated with chlorinated polyolefin (CPO) as well as conductive resins. These conductive resins are particularly important because they provide a continuous conductive surface once the adhesion promoter film has coalesced. This enables subsequently applied paint layers to be applied electroscatically and therefore enhance transfer efficiency.
Adhesion promoters are available as 1K solventborne and waterborne systems. Primer or topcoat is then applied after the adhesion promoter has been flashed. Typically adhesion promoters are applied to achieve a dry film thickness of 0.3 – 0.5 mils (7.5 – 12.5mm)
DuPont Adhesion Promoter Products: DuPont Performance Coatings offers both solventborne and waterborne adhesion promoters. Both are highly conductive and offer excellent adhesion to TPO and subsequent applied coating layers. Color keyed and clear offerings are available without the conductive properties.
Primer
Requirements: Priming automotive plastic is a prerequisite for topcoating rigid plastics such as SMC, polyester or nylon based substrates. The role of primer is to fill in any small imperfection, which may be present due to the molding process or the plastic itself. It also acts to provide a conductive layer to facilitate the electrostatic application of subsequently applied coating layers. Primer also protects the substrate from potentially damaging UV energy from the sun. Often, primers are formulated to be color keyed to allow minimum basecoat film thickness and to minimize the effect of stone chipping.
DuPont Primer Products: DuPont Automotive Systems offers a complete line of primers including solventborne, waterborne, water slurry and powder. The VOC of water slurry primers is less than 0.4 lbs/gal (48 g/l). DuPont Herberts Automotive Systems frequently recommends specific primer combinations with topcoats to optimize application robustness and field performance.
Also underdevelopment are two approaches to SMC: liquid (1K solvent and waterborne) and UV dual cure system.
Basecoat
Requirements: Basecoat is the coating layer that provides color and aesthetic effects. Basecoat must provide uniform appearance initially and for many years without fading. Modern requirements for appealing vehicles often require micas, aluminum flakes and other effect pigmentation. These can be incorporated in one basecoat layer or in a separate layer. If two layers are used, the sandwich with the clearcoat is called a tricoat topcoat. DuPont Automotive Systems is the world leader in wet-on-wet tricoat application in both solventborne and waterborne basecoat topcoats.
DuPont Basecoat Products: DuPont Automotive Systems offers a complete color palette in solventborne and waterborne basecoats. For the solventborne portion, color mastering is achieved in either a low bake (120°F/49°C) 2K system or a high bake (250°F/121°C) 1K systems. DuPont also has an extensive color styling effort and works closely with designers from all major automotive manufacturers. Styling options range from familiar solid colors through interesting metallics to eye-catching effects. DuPont provides wet-on-wet tricoat and two-tone capability in both waterborne and solventborne forms – and all of these basecoat forms are available in combination with various clearcoat alternatives.
Clearcoat
Requirements: The clearcoat is the coating layer that forms the last interface to the environment. It carries the biggest part of the technological performance and must be able to resist environmental etch, bird droppings, car wash scratches and other outside influences. To improve performance against all these influences, OEM coating systems move from colored topcoats to basecoat/clearcoat systems. The clearcoat in combination with the basecoat forms the automotive topcoat, which gives the vehicle its external appearance. One and two component clearcoats (1K and 2K) are applied over solventborne and waterborne basecoats.
Clearcoats may also be tinted to provide a richer, more saturated color.
The driving forces for clearcoat development are cost of material and process, appearance, etch and scratch resistance and the environmental footprint.
DuPont Clearcoat Products: Since the time when solventborne acrylic-melamine 1K systems were the predominant clearcoats, many technological improvements have been made. Requirements for long-term technological performance led to a portfolio of clearcoats that today fulfill various customer demands. Product specifications are adapted based on customer requirements and the application conditions in the different application facilities, but are based on common chemical approaches and formulating principles.
1K and 2K clearcoats are widely used where plastic components are painted outside of the assembly plant. The 1K clearcoats are subdivided into traditional high solids high bake solventborne acrylic melamine or silane systems with the latter offering enhanced etch resistance. The 2K clearcoats include solventborne and super high-solids versions. In either case, rigid or elastomeric versions are available. For low bake (120°F/49°C) requirements, a 2K offering is the product of choice.
DuPont Performance Coatings is the only coatings supplier that supplies every type of clearcoat system and is a major global supplier of plastic finishing systems to the worldwide automotive industry.
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