I am a member of a governmental technical council. I am conducting an investigation of coatings for use in an energy reduction project for my government. I want some information regarding UV-curable liquid and powder coatings. I want to know whether UV-curable liquid and powder coatings contain UV-curable resins or normal resin systems with special additives. Can these additives be added to existing coatings? B. G.
UV-curable liquid and powder coatings, as applied by end users, contain resins that are UV-curable, that is, their curing reactions are activated by photoinitiators and their curing reaction rates are enhanced by photoaccelerators. The chemistry of these reactions is too complex to discuss in the Painting Clinic. Simply stated, the reaction mechanism is free of radical polymerization. Many liquid UV-curable coatings are formulated using reactive diluents in place of solvents to reduce their viscosities so that they are sprayable. Reactive diluents cross-link with the resin and become part of the coating film. In some cases, it is possible to add photoinitiators and photoaccelerators to existing coatings provided they have the “correct” chemistry. However, this comes under the “Don’t try this at home” caveat. You must know what you are doing to achieve success.
On the other hand, powder coatings have their photoinitiators and photoaccelerators built into the formulation as they are manufactured. Since powder coatings are manufactured by dry blending and melt mixing, it would be difficult, if not impossible, to add these curing agents to an existing coating.