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A low gloss or matt effect is frequently a key feature or requirement of many coating materials applied to the surfaces of man-made objects or constructions. In traditional low to medium solids, solvent- and water-borne coatings film shrinkage resulting from the evaporation of volatile components and crosslinking or polymerisation reactions of the binder materials, together with a sufficient number of matting agent particles of a suitable size, enable the formation of a micro-rough film surface structure. This structure is necessary for the diffuse light-scattering responsible for creating the visual effect of reduced gloss (figure 1 in paper). Specially designed matting agents are available, to provide the "particles" required. Above all the micronised porous synthetic silica products, with their high purity, low particle density and well-defined particle size distribution represent ideal materials for this purpose.
On the other hand, formulating low-gloss or matt UV-curable coating systems is considered difficult. Low volume-shrinkage, associated with the 100% VOC-free nature of these systems, is the main obstacle to the development of sufficient micro-roughness in the coating film surface to provide a matt appearance. The challenge is becoming increasingly severe due to a trend to higher line speeds and the consequent need for more reactive, faster curing systems.
