Surface gloss of fibreboard panels veneered with birch wood

The effect of thermal compression temperature, veneer side (loose vs. tight), the number of lacquer layers and spread rates on the gloss unit (GU) of lacquer coatings were determined. Rotary-cut birch veneer sheets were thermally compressed at various temperatures (150, 180 and 210 °C) and afterwards they were bonded to the surfaces of MDF panels. The lacquer was applied to the surface of veneered MDF panels in 1, 2 and 3 layers at the various spread rates, appropriate 50, 75 and 100 g/m².

The values of GU parameter were measured at three angles − 20, 60 and 85°. Statistical evaluation of GU parameter showed, that the number of layers, the amount of lacquer, the direction of wood fibers, the side of veneer and compression temperature significantly affect gloss of the surfaces of veneered MDF panels.

Thermal compression improves surface gloss

Gloss increased with the number of layers and the amount of applied lacquer. Brightness decreases with the increase in temperature from 150 to 180 °C, while a further increase in temperature from 180 to 210 °C enhances GU. There is a significant difference between values of gloss (except for the 20° angle) measured along and across grain direction. The values of gloss measured along the wood fibers are higher than those measured across the grains.

Thermal compression of veneer homogenises the surface and as a result the gloss of the loose and tight sides is uniform. Thermal compression of birch wood surface instead of its sanding before finishing improves aesthetic properties of wood, in particular surface gloss as well as reduces the required lacquer application rate. These findings make it possible to improve the technology of lacquer coatings of thermally compressed wood.

The study is published in: Progress in Organic Coatings Volume 117, April 2018, Pages 10-19.