%0 Research article
%T Plastic coating of plywood using extrusion technique
%A Kuusipalo, Jurkka
%D 2001
%J Silva Fennica
%V 35
%N 1
%R doi:10.14214/sf.607
%U https://silvafennica.fi/article/607
%X The target was to study and develop industrially suitable methods to  apply thermoplastic coatings on plywood. Typically, wear and climatic  resistance for wooden sheets, such as chip board and plywood, is  achieved by thermosetting resin coating (e.g. phenol-formaldehyde).  However, economical and environmental issues are driving towards  thermoplastic coatings (e.g. polyethylene) in such products. Several  technologies, such as film gluing and laminating, have been introduced,  but the costs and processing are limiting factors. This study  concentrates on direct coating of plywood with extruded molten plastic  film, in other words extrusion coating of plywood. This technique  provides fast coating process and cheap raw materials. In the study it  was found that extrusion coating of plywood is difficult. The high heat  energy of the molten plastic causes moisture evaporation of the top  veneer, and the only possible escape direction of the evaporated  moisture is through the plastic, which causes bubbling in the plastic  coating. Another disadvantage of the plywood is its rigidity, which  limits the development of the process. In this work, a new technique was  applied for coating the flexible veneers with typical extrusion coating  equipment, where the escape of the evaporated moisture was possible  through the top veneer to the atmosphere. Another main issue was to  reach sufficient adhesion between plastic and plywood. Target was  achieved using either monolayer polyethylene (PE-LD) or 2-layer  polypropylene/adhesion polymer plastic coatings.