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The appearance of malt finish or low gloss is created when light is reflected from a surface in a
duff use manner. Such a finish can add a subtle, elegant appearance to a surface, provide better
hiding power for imperfections or the effects of wear, than a high gloss coating. A number of UV
curing applications require low gloss, or perhaps more accurately, gloss control to produce a range of finishes. Two examples are the wear coats for PVC flooring and protective coatings for paper or PVC decorative foils. These represent very different challenges for the formulator, the design of the production and quality control of the finished product. The wearcoats for PVC flooring have long been regarded as "easy" to matt due to the relatively high viscosities of the lacquer and the slow cure speeds of the process; On the other hand, the decorative foil systems require low viscosity formulations curing at very fast speeds and as such are usually regarded as more "difficult" in terms of low gloss. In both cases, identifying the factors which influence the gloss levels and ensuring they are controlled, is essential in meeting a narrow gloss range and producing a consistent high quality product.
The physical process of producing a coating with a matf appearance is well documented. In
simple terms, the impression of low gloss is created by a micro-roughened surface which reflects light in a diffuse manner. This roughening is achieved by the incorporation a matting agents such as Micronesia porous silica particles. In solvent based coatings, matting is aided by a film volume
contraction of up to 30%, as a result of evaporation of the volatile components. This has the effect
of bringing a higher concentration of silica particles to the surface of the film and producing
greater diffusion.: The 100% solids systems used in V curing can hinder the effectiveness of the
matting agents and other measures must be taken to increase the concentration of the silica
particles at;or close to, the surfaceof the wet film.
The gloss level of a IJV cured coating will be influenced by many factors: some from the natureof
the formulation and others from the techniques, equipment and conditions used in the UV
process.
