Correctly solve the quality problems that occur during the dyeing process of veneers

August 17, 2019

Many companies often have problems such as veneer bursting, uneven thickness, color flower, color difference, color drop, and opening of glue in the process of veneer veneer veneer processing, which affects the quality of veneer decoration and waste. Based on our many years of production experience, the analysis is as follows.

1 Preparation of the wood segment The preparation of the wood segment is the first process of veneer production, which directly affects the quality of the veneer. Therefore, the wood segment requires no flaws, no knots, no cracks, otherwise the veneer after the rotary cutting has a large amount of excavation, which affects the quality of the board surface. Secondly, the wood section requires no bending, because the bending rate of the wood section is low, resulting in More waste; third, the wood section of the village requires no mildew, with mildewed wood segments, the veneer after the veneer is not easy to bleach and dye, affecting the appearance quality of the board.

2 Rotary cutting of the wooden section During the cutting process of the wooden section, due to the uneven adjustment of the knife door or the sharpness of the cutting edge, it is easy to cause uneven thickness of the veneer after the rotary cutting and perforation of the veneer. Therefore, it must be before the rotary cutting Check the adjustment of the device.

3 veneer dyeing

3.1 veneer cooking in the wood structure, although the cellulose content is more than 50%, but still have 20% lignin, 3% ash and resin, etc., their presence directly affects the bleaching of veneers Degree and dyeing effect, so it must be removed. The purpose of cooking is to remove lignin and other substances in the veneer by the action of chemicals. Since caustic soda is more erosive to cellulose than neutral sulfite, and the removal of lignin is not as high as that of neutral sulfite, the cooking of veneers is carried out by the neutral sulfite method.

3.2 Bleaching of veneers Most wood-based panels have a light background, so the cooked veneers must be bleached. In the process of high temperature treatment of hydrogen peroxide, it is necessary to control the temperature and pH of the bleach. After the veneer is floated, it should be rinsed with hot water in time. On the one hand, it can effectively remove the silicon scale generated by sodium silicate (sodium silicate as a stabilizer for the bleaching liquid) on the surface of the veneer; on the other hand, the veneer can be effectively removed. Residual hydrogen peroxide. If the veneer returns to yellow, it can be treated with dilute acid at a concentration of 1-2 g/L at room temperature for about 10 minutes.

3.3 Dyeing of veneers Because the material of the veneers is hard and the penetrating performance is poor, the heating curve must be strictly controlled during the dyeing process to avoid the local temperature being too high and causing the color flower. It is dyed with acid dye. The pH value of the dyeing solution changes greatly during the dyeing process. It should be adjusted according to the measured pH value. When adding sulfuric acid to the dyeing solution, it should be evenly added to prevent the local acidity from being too high and the surface of the wood to be carbonized. Use reactive dyeing, salt and other dyes should be added in two parts, the fixing temperature can not be lower than 85Y. After the veneer is dyed, it should be rinsed with hot water in time to remove the floating color of the plate surface and keep the pH of the plate surface neutral.

4 After the drying board of the veneer has been bleached and dyed, the water content is too high. Therefore, the board after washing with water should be drained for 30-40 minutes, and then dried in the dryer, which can save dry energy. It also reduces drying time. Strictly control the drying curve of the veneer to avoid the local temperature is too high and cause the veneer to burst. The moisture content of the veneer after drying is controlled at about 7% to 10%. The surface of the board will be too cracked, and if it is too wet, it will affect the amount of glue.

5 The purpose of the veneer coating of the veneer is to bond the plates of different colors together. Because the veneer is thin, the amount of glue applied between the veneers should not be too much, otherwise it will affect the color of the light-colored plate, and it will be easy to crack and waste. For dark boards, when adding glue, add appropriate amount of dye to the rubber to avoid the phenomenon of “white core” layer, so as to ensure the uniform color of the board after processing. Since the General Administration of Quality Supervision, Inspection and Quarantine has strictly restricted the amount of formaldehyde released from wood-based panels, it is necessary to select odorless and harmless environmentally-friendly rubber compounds for the selection of rubber compounds in order to make the products acceptable to consumers.

6 After pre-pressing and gluing the veneer after the rubber table, the pressure must be controlled at 2MPa during the pre-pressing and setting process. The pressure will cause the veneer to burst; the pressure will not be fixed. The pre-pressing time is about 24h, which ensures the shaping effect of the veneer.

7 Sewage treatment Start with the process of controlling pollution sources, continuously improve the process, and then carry out centralized decontamination to further treat the sewage. First, the two-bath method of boiling and rinsing was changed to one-bath method to reduce the water consumption and the displacement; secondly, the environmentally-friendly reactive dye was used to replace the more heavily contaminated acid dye, and the original intermittent dyeing was changed to continuous, and the foot water was used. The secondary utilization reduces the discharge of colored sewage and saves the dyeing materials. Finally, the sewage is treated by air flotation, and after sedimentation and filtration, the sewage discharge requirements are met. There are many processing steps for veneer dyeing and veneering, and there are many problems. Therefore, it is necessary to strictly follow the requirements of the process for each process, so as to solve the problems in production in time.

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