عنوان مقاله [English]
Background and objectives: The purpose of this research is to reduce amount and speed of absorption of the liquids coating substances of the particleboard surface (lacquer, paint and enamel in the lacquer painting process and glue in the lamination method). In this context, the researchers found that the increasing of the average density of particleboard increases the minimum and maximum density of its surface layers. According to the researches, increasing the surface layers density of particleboard decreases their liquid finishing materials absorption. Since at the present the main solvent of liquid finishing materials for finishing the surface of wooden boards is on the water-based, researchers have invented a method of surface absorption test of wooden boards by water instead of toluene. After several studies, they performed water absorption test by the surface layer of wooden boards during the test period of 60-minute.
Materials and methods: In this study, the large particles with 1% moisture in the middle layer and industrial fine particles in the surface layers were used for production three layers particleboard. Knowing that by increasing the wood moisture to fiber saturation point (30%), perpendicular compressive strength to the wood fibers significantly is reduced, in this study, the moisture of the surface layer particles was increased to 5% and 10 % with water spray method. The wood particles of surface and middle layers were mixed with resin separately. For wood particles of surface layers was used UF with concentration of 55 % and commercial resin UF with concentration of 68.8 % (with purpose of control the surface layers moisture of three layers mats in the desired limit). Commercial resin UF was heated to temperature of 60 °C with the purpose of reducing its viscosity. Then, three layers particleboard with medium density of 650 kg/m3 were obtained by 2.7 MPa specific press pressure and at temperature by 220 °C. The analyses of mechanical strengths, water and toluene absorption were performed to evaluation the properties of the particleboards surface layer.
Results: According to the results of the density gradient graph in the thickness of the samples, increasing wood particle moisture of the surface layer increases the density of samples surface layer.
The results of the mechanical strengths and liquid absorption analysis showed that, by increasing wood particle moisture of the surface layer increases flexural strength and surface soundness of samples and decreases absorption and absorption speed of the samples surface layer.
Conclusion: Increasing wood particle moisture of the surface layers increases the quality of particleboard surface layer for finishing. The moisture optimal amount of the surface layer wood particle is 5% in treatment 7 (made by commercial urea-formaldehyde resin).