Basic Paint Technology
Automotive paint technology has made significant advancements over the years, more or less you could basically class the products into 2 categorized, Thermoset & Thermoplastics.
Thermosets – These are the products that cure irreversibly. They require a catalyst that causes a chemical reaction creating a cross-linked product. This would typically include your clearcoats, primers, sealers,panel bond, bumper repair materials & even plastic bumpers themselves.
Thermoplastics – These are products that remain soluble after drying. They are usually 1 component (no hardener) and do not cross-link. They can be broken down by whatever solvent they are being reduced with. This would include your basecoats, 1 component primers/paints, 1 part repair materials (ie.. window urethane/seam sealers).
What is Crosslinking?
Crosslinking is a chemical reaction that causes a group of polymers (synthetic or naturally existing materials) to bond together with a linkage. Crosslinking produces one large molecule of your paint film, it makes it very strong and durable. The linkage depends on the resin (ie epoxy, urethane, polyester) & each linkage has its advantages and disadvantages. Here\’s a look at a few different types of resins:
Epoxy – Epoxy forms the strongest bond because of the unique crosslinking network produced. Epoxy provides superior adhesion and corrosion resistance. The biggest advantage epoxy offers is its strength and durability, drying times are generally slower. Epoxy resins are also broken down easily by UV rays which do not make epoxy coatings ideal for topcoats.
Urethane – Urethanes are produced by the reaction of diisocyanates and di-alcohols. They produce a strong cross-linked urethane chain. Urethane has a great deal of flexibility in the types of products it can be created for. It is known for its quick drying times. Uses include primers, clearcoats, basecoats, structural adhesives, bumper repair adhesives.
Polyester – Polyester forms a strong bond utilizing the ester linkage and can be further reinforced with fibers to improve it. Polyester has the highest tendency to shrink but is low in cost compared to the other resins. Uses include body filler, fiberglass, primers & some basecoats.
Factory vs Refinishing Procedures
For the most part, the same resins are used just in a different way. Epoxy can be applied through the electro-deposition rather then spraying. Urethane products are usually sprayed and then heat activated. The products are provided with the hardener in it and are designed not to activate until they reach a certain temperature, usually around 200 degrees. There is little difference in the durability of these types of applications. Factory paint is baked only for the purpose of activating the urethane clearcoat and producing more vehicles.
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