The effect of temperature of thermal densification of wood substrate, type of lacquer and number of its layers on gloss of finished surface

• Main Authors: Pavlo Bekhta, Yurii Maksymiv, Tomasz Krystofiak
• Format: Article
• Language: English
• Published: Ukrainian National Forestry University 2020-06-01
• Series: Наукові праці Лісівничої академії наук України
• Subjects: thermo-mechanical densification; gloss; waterborne lacquer; polyurethane lac-quer; acrylic lacquer

The surface of the wood substrate is needed to be sanded before applying required amount of lacquer. The main purpose of this study is to find out if it is possible to replace the sanding process of wood substrate before applying a lac-quer, and to determine how strong are effects of the thermal densification tem-perature, type of lacquer and number of lacquer layers on the gloss of the fin-ished surface. As a substrate, were used rotary-cut alder veneer sheets with di-mensions of 300×300×1.5 mm, without any visible damage, with relative humidi-ty 6%. Veneer sheets were bonded to a medium density fiberboard (MDF). Be-fore the bonding process, veneer sheets were exposed to the thermal compression between the platens of the hot press at 150 °C, 180 °C and 210 °C at the pres-sure of 2 MPa within 3 minutes. Three types of lacquers were used: waterborne lacquer (IQ-HY1330-15), polyurethane lacquer (R533-2-15) with adding 10% of hardener RLH6110 and 10% of solvent V721, and acrylic lacquer (UV120-45) cured by ultraviolet radiation. On the thermally densified surface was applied one or two layers of lacquer with or without interlayer sanding for evaluation of the effect of sanding on the gloss of the finished surface. The gloss was evaluated at an angle of light reflection of 60 ° using an Erichsen PICOGLOSS 503 glossme-ter. For the comparison, gloss of lacquered surface was also measured on the sanded substrate. The ANOVA analysis of the obtained results showed that all the variable factors like temperature of densification of veneer, type of applied lacquer and number of lacquer layers are significantly (p ≤ 0.05) affecting the formation of gloss of the lacquered surface on the thermally densified substrate. Type of applied lacquer is the factor with the highest effect on surface gloss (F = 841,041 along fibers, F = 873,409 across fibers). Combined effect of such factors like temperature of densification and absence of interlayer sanding don’t have significant effect on surface gloss (F = 1,333, p = 0,241 along fibers; F = 0,926, p = 0,476 across fibers). The same situation was observed for combined effect of all investigated factors – F = 1,217, p = 0,269 along fibers, F = 1,251, p = 0,246 across fibers. Results of Duncan’s test also showed that the type of applied lac-quer has the greatest effect on the creating surface with the highest gloss unit (GU) number. Lowest values of gloss were observed in case of using waterborne lacquer (GU = 9,52 along fibers and GU = 6,45 across fibers) which is corre-sponding to be a matte surface. Polyurethane lacquer is forming matte and half matte surface gloss with average gloss value number of GU = 11,3 along fibers and GU = 9,09 across fibers. Acrylic lacquer cured by ultraviolet radiation allows to form the lacquer surface with the highest gloss value (average value GU = 45,34 along fibers and GU = 42,93 across fibers). The gloss value increases as the number of lacquer layers increases. Interlayer sanding does not have a signifi-cant effect on the gloss value of the lacquer surface on a thermally densified sub-strate.