TABLE OF CONTENTS The basic components of a UV-curable formulation (resins, diluents, photoinitiators) alone hardly ever produce a coating of acceptable quality. The wetting of the surface or pigments, which is often facilitated by the solvent, and the removal of entrained air, which is difficult due to short or no flash off times before cure, are only two examples of specific difficulties related to the film quality of UV-curable coatings. Therefore, as in classical coatings, various additives are used. The additives are in principle the same as used in classical solvent-based formulations, however, often tailor made for specific needs.73
De-aeration additives are based on polyacrylates as silicon-free additives and organically modified siloxanes. They replace surfactants, which stabilize the bubbles, and due to a balanced incompatibility lead to a raise and burst of the bubbles at the surface. In almost all powder coatings benzoine is used as a de-aeration additive.
Substrate wetting additives have to reduce the surface tension of the coating system and maintain these properties in highly dynamic processes like printing. For UV-curable formulations often low molecular weight silicones, hydrocarbon organics or fluorinated surfactants are used.
Surface control additives are used to improve flow and levelling as well as slip and scratch resistance. Here also silicones, however, with higher molecular weights and often containing polymerizable groups are used. These compounds show a strong tendency to migrate to the surface and provide improved slip and scratch resistant properties.
Surface-active additives, such as flow, levelling, de-aeration, slip additives, are...
