May / June 2018 • Issue 3 • PANELS & FURNITURE ASIA 64 WOOD CLINIC Dear Mr Shen, Our company specialises in panel furniture. We have a contour wrapping machine, and the material for contour wrapping is laminated wood made up of leftover wood chips. The thin veneer contour is coated with EVAhot glue. The company later bought a second-hand contour wrapping machine, which coats the contours with aluminum profiles, PVC and thin veneer, using reactive hot-melt adhesive. Contour wrapping with PVC often reveals the defects, such as blistering and weak adhesion; contour wrapping with thin veneer also shows these defects after spray painting. Why there is blistering and why is the adhesive force always weak? What should we take note of in the contour wrapping process? Yours sincerely, Mr Wu Mr Shim (Shen Yuxin) (I) Why there is blistering and why the adhesive force is weak, and suggesƟons for improvement: 1. Quality of the material for contour wrapping: • The moisture content of the laminated wood material should be controlled at 10±2%. If the moisture content is too high, it will lead to poor adhesion. • Control the quality of the material during the four-sided planing process. In case of serious defects such as tool skipping, rough tool marks, against grain, dent and skips- in-planting in the partial section of the material, the contour will blister partially after wrapping or the adhesive forcewill beweak; defects are usually evident after painting (see Fig. 1). 2. Quality of the thin veneer: • The moisture content of the thin veneer should be controlled at 10±2%. If the moisture content is too high, it will lead to poor adhesion or blistering. • Planing and cutting thin veneer unevenly, or a too-large tolerance will cause poor adhesion. Strictly control and confirm the stability of the veneer. Fig. 1: Skips-in-planting of material or rubber roller damage, insufficient contact pressure between thin veneer and material lead to blistering and weak adhesion.