These 2K systems are normally applied "off line" with the coated plastic parts fixed to the painted metallic body. The clear coats applied to the plastic components like the bumpers and wing mirrors however are 2K systems since they can normally only accept temperatures up to about 90 ☌. Car manufacturer ( OEM) clear coats applied to the metal bodies of cars are normally 1K systems since they can be heated to around 140 ☌ to effect cure. One part and two part formulations are often referred to as "1K" and "2K" respectively. Clearcoat can be either solvent or water-borne. For this reason, clearcoat must be durable enough to resist abrasion and chemically stable enough to withstand UV light. Usually sprayed on top of a colored basecoat, clearcoat is a glossy and transparent coating that forms the final interface with the environment. Pearlescent paints can be two stage in nature (pearl base color + clear) or 3 stage in nature (basecoat + pearl mid-coat + clear-coat). Pearl pigments impart a colored sparkle to the finish which works to create depth of color. Pearlescent paints contain special iridescent pigments commonly referred to as "pearls".A similar mode of action occurs with pearlescent pigmented basecoats. The formulation of the clear coat needs to be carefully chosen so that it will not "re-dissolve" the basecoat and thus affect the orientation of the metallic flake but will still exhibit enough adhesion between the coatings so as to avoid delamination of the clear coat. This orientation then needs to be unaffected by the application of the clear coat solvents. Subsequent evaporation of the solvent (or water), leads to a reduction in the film thickness of the drying coating, causing the aluminium flake to be dragged into an orientation parallel to the substrate. The "flop" is maximised if the basecoat increases in viscosity shortly after application so that the aluminium flake which is in a random orientation after spraying is locked into this position while there is still much solvent (or water) in the coating. This is the difference in the brightness between looking perpendicularly at the paint and that at an acute angle. Metallic basecoats are formulated so that the aluminium flake is parallel to the substrate. Metallic and pearlescent paints must be applied evenly to ensure a consistent looking finish without light and dark spots which are often called "mottling". This paint is harder to manage than solid paints because of the extra dimensions to consider. Metallic paints contain aluminium flakes to create a sparkling and grainy effect, generally referred to as a metallic look.Clear coat was not used on solid colors until the early 1990s. It is also widely used on cars, trucks, and motorcycles. This is the easiest type of paint to apply, and the most common type of paint for heavy transportation vehicles, construction equipment and aircraft. Solid paints have no sparkle effects except the color. Base coat used in automotive applications is commonly divided into three categories: solid, metallic, and pearlescent pigments. This coat contains the visual properties of color and effects, and is usually the one referred to as the paint. The base coat is applied after the primer coat. In E-Coat, also called CED paint, use is approximately 99.9% and provides superior salt spray resistance compared to other painting processes. The body works as a cathode and the paint as an anode sticking on the body surface. The body is dipped into the Electro-Coat Paint Operation (ELPO/E-Coat), then a high voltage is applied. A phosphate coat is necessary to protect the body against corrosion effects and prepares the surface for the E-Coat. Without proper pretreatment, premature failure of the finish system can almost be guaranteed. High-pressure water spray jets are directed to the body. Water-based acrylic polyurethane enamels are now almost universally used as the basecoat with a clearcoat. Enamel paint is better for the environment and replaced lacquer paint in the late 20th century. Up to 85% of Lacquer paint can evaporate into the air, polluting the atmosphere. Environmental laws have prohibited this, which has resulted in a move to water-based paints. Until several decades ago lead, chromium, and other heavy metals were used in automotive paint. Nowadays, two-component (catalyzed) paint is usually applied by robotic arms and cures in just a few hours either at room temperature or in heated booths. As mass production of cars made the process untenable, paint began to be dried in ovens. In the early days of the automobile industry, paint was applied manually and dried for weeks at room temperature because it was a single component paint that dried by solvent evaporation.
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