UV curable powder coatings for the finishing of leather
A novel powder coating binder system based on UV-curable, semi-crystalline polyurethane acrylates has been developed for heat-sensitive and highly flexible substrates, such as leather. The developed powder coating film had good abrasion and adhesion properties. The concepts applied in this work were based on the adjustment and control of the degree of crystallinity of hinders by three ways: (i) formulating different molecular weight monomers for random copolymerization, (ii) introducing functional monomer with pendant groups and (iii) cross-linking during curing. Amongst the three approaches explored in this work, a combination of branching and cross-linking was found most successful. A crystalline binder with cross-linkable pendant groups was employed as the powder coating main binder; this is the major difference from other work on powder coatings where amorphous resin alone or partially blended with a crystalline component are used as binders. The preparation of UV curable powder coating binder resins and their properties, such as crystallinity, viscosity and tensile modulus and elongation to break have been studied by DSC, SEM, FTIR-ATR and DMTA methods. It was found that the polyurethane acrylate binders (made from DHBA, BEP, DEG and HDI etc.) are potentially useful for formulating novel powder coatings. The properties of the developed powder coating finished leather have been tested. Hot plating processes and an EMB application method for leather finishing have been discussed as well. Nano-scale silica particles surface modified with acrylate has been studied, and their properties or properties of powder coatings formulated with the particles have been characterized. The powder coating rub fastness was improved by formulation with surface modified nano-scale silica particles
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