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The impact of surface preparation of wood on the adhesion of certain types of coatings In order to achieve an enhancement of adhesion of specific type of coating to the surface of beech wood (Fagus Sylvatica L.), the optimum substrate preparation system was determined regarding the specific coating formulation. The results showed that lower values of surface roughness parameters can be obtained by the sanding process than by the planning process. These lower values of surface roughness enable higher adhesion of a 2K acrylic-isocyanate coating. In cases where coating is performed with a 1K waterborne coating, higher values of adhesion were observed on the surfaces with higher surface roughness. Direct correlation between surface roughness and adhesion of a 2K polyurethane coating was not found. The adhesion between a 1K waterborne coating and the wood substrate is primarily based on a mechanical bonding (entanglement), while the adhesion of a 2K acrylic-isocyanate coating is primarily based on the other bonding mechanisms.

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The cured finishes always contain certain irregularities that result from the technique and conditions of application. For this reason, in order to achieve smooth high gloss finished surfaces, it is necessary to polish ("rub-out")

This paper presents the research of influence of wood surface preparation on the wetting ability of polyurethane coatings, by the method of contact angle. The samples were made of two species of Paulownia (Paulownia elongata and Paulownia fortunei). All the samples were processed by planing (molding). After molding, the samples were arranged in groups and sanded. In relation with wood grain direction, each group had a particular system of sanding, based on the numbering of sanding paper, program of displacement of sanding papers with different numbering and the direction of sanding. The quality of wood surface after sanding was expressed by the values of roughness parameters in the system 'M': Ra, Rz, Rv, Rp and Rt. The contact angle was measured using transparent polyurethane (PU) coating and distilled water. The influence of the system of sanding on the values of contact angle was analyzed by roughness parameter Ra