Research On The Process And Coating Properties Of Beech Timber Epoxy-Polyester Powder Coating

As a material with high structural performance, Beech timber, generally decorated with oil paint, is widely used in home decoration, easels, toys and other fields. Organic solvent coatings process is complex and time-consuming, with low efficiency, VOC emissions, and pollution to the environment. Powder coating, as a kind of 100% solid powder coating without any solvent, is environmentally friendly, safe, recycling, widely applicable, etc. Low-temperature-fast-curing powder coating has been successfully applicated on the medium density fiberboard(MDF) in recent years. Powder coating is a new type of environmentally friendly coating methods on wood materials, which makes its application on Beech timber possible. Therefore, in this study, the low-temperature fast curing powder coating, instead of oil paint is sprayed on the Beech timber surface to improve its surface performance, which can make the processes of production and use environmentally friendly and thus offer a new environmentally friendly, energy-saving, and efficient coating method for the Beech timber surface decoration. The main results of this study are as follows:(1) The constant temperature and humidity box is utilized to adjust temperatures and the moisture content of timber. On the condition of normal temperature 25℃, Beech timber moisture content is in the range of 7.0% to 9.0%, timber surface resistance was ≤ 109 ?, the suitable weight of powder coating on the average size was about 100g·m-2, there is no serious pinhole, cracking and other phenomena on the surface of Beech timber coating, coating adhesive force was grade 1, and coating thickness was 85μm. When Beech timber temperature is rising, constantly at 45℃ and 65℃, the higher temperature can lead to smaller surface resistance in the same range of moisture content. When the moisture content was controlled in the range of 7%-8% and the surface resistance was in 109 ? orders of magnitude, coating surface quality was good, there were no obvious flaws, adhesive force was grade 1, and coating thickness was about 95μm. On the condition of same moisture content, by comparing the results of 25 ℃、45 ℃ and 65 ℃, raising the temperature leads to the decrease of timber surface resistance, which contributes to electrostatic powder coating.(2)On the condition of preheating, the range of the resistance decrease due to the temperature was more than the range of resistance increasing due to the decrease of the surface moisture content. The moisture evaporating speed of the surface and inside was slow and uniform on the condition of low preheating temperature. While the moisture evaporating speed of the surface was faster than that of inside on the condition of relatively high preheating temperature. With comprehensive consideration, when the temperature is 105℃ and the heating time is 9min, the resistance is 1.518 × 107 Ω, the coating appearance was good, the coating performances meet the veneer man-made board physical and chemical performance requirements.(3)The sample surface was processed separatedly by preheating, polyurethane primer coating, waterborne primer coating, and preheating and spraying powder coating. The processed samples were treated by electrostatic powder coating and the coating curing process to obtain Beech timber powder coating. Coating properties of the samples were tested according to the relevant national standards, and physical and chemical properties such as surface coating adhesive force and pencil hardness were analyzed and compared. As a result, the best method of surface treatment was sanding, preheating, and two electrostatic powder coating, on the condition of certain moisture content.(4) The epoxy polyester powder coating and the cured coating were analysised by infrared spectroscopy and DSC in order to check the curing degree of coating formed on the surface of the samples; Optical microscope was utilized to observe the concave and convex of coating surface.(5)Beech timber with powder coating was with high-temperature resistance, but it was combustionsupporting, not antiflaming when the timber was burning.