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In the powder coating of veneered particle boards the highly reactive hybrid epoxy/polyester powder transparent Drylac 530 Series from TIGER Coatings GmbH & Co. KG, Wels, Austria was used. Curing is accelerated by a mixture of catalysts reaching curing times of 3 min at 150 °C or 5 min at 135 °C which allows for energy and time savings making Drylac Series 530 powder suitable for the coating of temperaturesensitive substrates such as MDF and wood.
Powder coatings provide several advantages over traditional coatings: environmental friendliness, freedom of design, robustness and resistance of surfaces, possibility to seamlessly all-around coating, fast production process, cost-effectiveness. In the last years these benefits of the powder coating technology have been adopted from metal to heat-sensitive natural fibre/ wood based substrates (especially medium density fibre boards- MDF) used for interior furniture applications. Powder coated MDF furniture parts are gaining market share already in the classic furniture applications kitchen, bathroom, living and offices. The acceptance of this product is increasing as reflected by excellent growth rates and an increasing customer base. Current efforts of the powder coating industry to develop new powders with higher reactivity (i.e. lower curing temperatures and shorter curing times; e.g. 120°C/5min) will enable the powder coating of other heat-sensitive substrates like natural fibre composites, wood plastic composites, light weight panels and different plastics in the future. The coating could be applied and cured by the conventional powder coating process (electrostatic application, and melting and curing in an IR-oven) or by a new powder coating procedure based on the in-mould-coating (IMC) technique which is already established in the plastic industry. Extra value could be added in the future by the functional powder toner printing of powder coated substrates using the electrophotographic printing technology, meeting the future demand of both individualization of the furniture part surface by applying functional 3D textures and patterns and individually created coloured images and enabling shorter delivery times for these individualized parts. The paper describes the distinctiveness of powder coating on natural fibre/ wood based substrates, the requirements of the substrate and the coating powder.
Mass-customization is a megatrend that also affects the wood industry. To obtain individually designed laminates in batch size one efficient printing and processing technologies are required. Digital printing was envisaged as it does not depend on highly costly printing cylinders (as used in rotogravure printing) and allows rapid exchange of the printing designs. In the present work, two wellestablished digital printing approaches, the multi-pass and the single-pass technique, were investigated and evaluated for their applicability in decorating engineered wood and low-pressure melamine films. Three different possibilities of implementing digital printing in the decorative laminates manufacturing process were studied: (1) digital printing on coated chipboard and subsequently applying a lacquered top-coat or melamine overlay (designated as “direct printing”, since the LPM was the printing substrate), (2) digital printing on decorative paper which was subsequently impregnated before hot pressing (designated as “indirect printing, variant A”) and (3) digital printing on decorative paper with subsequent interlamination of the paper between impregnated under- and overlay paper layers during the pressing process (designated as “indirect printing, variant B”). Due to various advantages of the resulting cured melamine resin surfaces including a much better technological performance and flexibility in surface texture design, it was decided to industrially further pursue only the indirect digital printing process comprising interlamination and the direct printing process with a melamine overlay-finishing. Basis for the successful trials on production and laboratory scales were the identification of applicable inks (in terms of compatibility with melamine resin) and of appropriate printing paper quality (in terms of impregnation and imprinting ability). After selection and fine tuning of suitable materials, the next challenge to overcome was the initially insufficient bond strength between impregnated overlay and the ink layers which led to unsatisfactory quality of the print appearance and delamination effects. However, the optimization of the pressing program and the development of a modified impregnation procedure for the underlay and overlay papers allowed the successful implementation of digital printing in the production line of our industrial partner FunderMax.