The effect of high wood moisture content on the coating of solid wood furniture
Wood must contain a certain proportion of water. If there is no water, it will not form wood. However, since the moisture content in the wood changes with the change of environmental humidity, it will cause great trouble and inconvenience to the painting work, so the wood before painting Be sure to dry.
The state of moisture in the wood: the water in the wood, according to its combination with the wood and its location, is generally divided into chemical water, free water and sorbed water, (the percentage of water content is usually the ratio of water weight to wood weight) It is expressed as % moisture content).
Soaking water: also known as combining water. It exists in the microcapillary between wood molecules and is physically and chemically bonded to wood. The amount of water absorbed depends on the size of the wood surface and the amount of free radicals. Generally, the average is about 24%. We usually say that the effect of moisture on the properties of wood refers to the absorption of water.
When the wood is improperly dried and the moisture content does not reach the equilibrium point compatible with the local environment, the coating starts, which generally causes poor coating film, affects color and gloss, and causes coating defects such as bubbles, pinholes, whitening, etc. Poor, the wood is swelled and contracted after painting, causing cracking and peeling of the coating film. The specific impact is as follows:
1. Cause whitening of the wet coating. When the wood is poorly dried, the moisture in the wood will enter the coating with the volatilization of the thinner, and whitening will occur. The release of moisture can also affect the transparency of the paint.
2. Produce pinholes and bubbles. Since the PU paint easily reacts with moisture to generate gas, bubbles are formed when the gas escapes, and pinholes are generated when the bubbles are broken, causing coating film defects.
3. Affect the drying and curing of the coating. Due to the high moisture content of the wood, the contact surface of the coating and the wood is wet, which affects the volatilization of the thinner and the crosslinking reaction between the resin and the curing agent, thereby also affecting the drying speed and smooth curing of the coating, resulting in drying or drying. incomplete.
4, the impact of the color of the bright. High water content affects the coloration of wood. When the moisture content of wood changes, the coating will change color with the shrinkage of wood and the color will be unclear.
5. Affect the adhesion of paint. For wood with a high water content, the coating will crack, bulge, and peel off as the water evaporates, resulting in poor adhesion.
6, causing fungi breeding. Due to the high water content, the growth of decaying bacteria, mold and discoloring bacteria may occur, causing deterioration and damage of wood products.
7, causing deformation of wood products. Due to the high water content, the lacquered wood products can still transfer moisture to the outside world, causing the wood products to warp and deform due to shrinkage, resulting in damage to the coating film and wood products.
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