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    Home > Coatings News > Paints and Coatings Market > Introduction of surface pretreatment of wood products

    Introduction of surface pretreatment of wood products

    • Last Update: 2020-02-25
    • Source: Internet
    • Author: User
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    The surface treatment of wood products is coating Because of the resin, tannin, pigment and moisture in wood, they have influence on the adhesion, dryness and decoration of the coating In order to obtain a smooth and smooth coating with uniform pattern and color and excellent performance, the surface of wood products should also be pretreated before coating The main process of pretreatment includes drying and deburring 1 Dry wood has the characteristics of porous, easy to absorb water and drain water, and has the characteristics of dry shrinkage and wet expansion, which causes blistering, cracking and back sticking of the coating Therefore, new wood needs to be dried to the moisture content of 8% 12% before coating There are two drying methods of wood: natural drying and low temperature drying 2 Deburring: Although the surface of wood products has been planed or polished, there are always some wood fiber residual surfaces that have not been completely separated Once they absorb water or solvent, they will wet and expand and stand up the scraper, and affect the uniformity of surface coloring, leaving some small white spots on the coated coating Therefore, the burr must be removed before the coating For general wood products, only a few times of sanding can be done For high-grade wood products, the following methods can be used: (1) brush a thin shellac varnish (shellac: alcohol = 1:71:8) on the surface, so that the burr can not only stand up, but also become brittle, which is easy to be removed by sanding (2) wipe the surface with a wet cleaning cloth to make the burr absorb water and expand and stand up After the surface is dry, polish it with fine sandpaper or old sandpaper If a little bone glue is added to the water, the effect is better (3) adopt the method of kindling, that is, brush a thin layer of alcohol with a brush pen and light it immediately After burning, the burr becomes hard and brittle, which is easy to be removed by sand grinding This method is only applicable to the treatment of plane 3 Remove the dirt, glue mark, oil mark and other dirt on the surface of wood products, first polish it with sandpaper, and then scrub it with cotton yarn dipped in gasoline If the cleaning is still not clean, the surface can be planed with a short Polish plane 4 Degrease Most coniferous wood contains turpentine Turpentine contains turpentine and rosin, which will affect the adhesion and color uniformity of the coating In the case of high temperature, rosin will overflow from the wood, resulting in sticky coating The commonly used method to remove rosin is to clean it with organic solvent, such as alcohol, turpentine, gasoline, toluene and acetone, or with alkali, such as 5% 6% sodium carbonate solution or 4% 5% caustic soda solution, to saponify rosin, and then clean it with brush or sponge dipped in hot water After the surface is clean, brush 12 layers of shellac paint on the cleaned part to prevent the rosin in the inner layer of wood from seeping out 5 Many bleached wood contains natural pigments, such as mulberry, red sandalwood and so on The pigment of wood sometimes needs to be retained to play a decorative role If the wood products need to be painted in light color or any color unrelated to the original material color, the surface of the white wood products should be bleached In general, bleaching treatment is often carried out on the darker part of the surface to make the color of the wood surface consistent before coating There are many ways to bleach The commonly used bleaching agents are the mixture of hydrogen peroxide (30% concentration) and ammonia (25% concentration) (hydrogen peroxide: water: ammonia = 1:1:0.2) or sodium hydroxide (250g sodium hydroxide dissolved in 500g water) or hydrogen peroxide, etc   When bleaching the veneer with the mixture of hydrogen peroxide and ammonia, if bleaching the veneer, soak the veneer in the mixture; if bleaching the entire surface, apply the solution to the wood surface, and when the surface reaches the bleaching requirements, wipe the surface with a clean wet rag; if bleaching the veneer locally, a small clean one can be used to improve the bleaching effect After the cotton yarn is soaked with bleach, press it on the part to be bleached, and keep the bleach on the cotton yarn until it reaches the bleaching requirements When bleaching with sodium hydroxide solution, apply the solution to the wood surface, and then apply hydrogen peroxide after half an hour After treatment, the wood surface shall be scrubbed with water, neutralized with weak acid (such as 1.2% acetic acid or oxalic acid) solution and sodium hydroxide, and then scrubbed with water The above two methods have good effects on Fraxinus mandshurica, Quercus and so on The bleached surface has no color change for many years 6 Dyeing: in order to get a wood surface with beautiful texture and uniform color, a strand of wood products needs to be dyed The dyeing of wood can be generally divided into water color dyeing and wine color dyeing Water color is the aqueous solution of dye, while wine color is the alcohol solution of dye The best way to prepare water color is to use acid dyes The yellow sodium powder and the black sodium powder are made of several acid dyes When dyeing with water color, the moisture volatilization is slow, the dyeing is even, the price is low, and the use is convenient Its main disadvantage is that water makes wood fluff, and it needs additional sanding to eliminate fluff Alcohol soluble base dyes are the best way to prepare wine color Alcohol is used as the solvent to make wine color It is volatile and does not wet wood It eliminates the phenomenon of wood surface fuzzing, and the color dyed is bright The disadvantage of wine color dyeing is that it is easy to have uneven hue If the wine color is used for dyeing, 6 points of alcohol solution dye, 70 points of alcohol and 24 points of shellac varnish can be weighed After the mixture is even, brush or spray the dye by hand When dissolving dyes, it is better to operate in glass, ceramic tank or enamel basin, no matter it is water color or wine color Do not use metal container to avoid discoloration.
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