Bleaching process of veneer in artificial thin wood production (2)

The system is usually achieved by adding sodium hydroxide or sodium silicate.

3.4 Post-processing
After the bleached veneer, there is still unreacted hydrogen peroxide and other alkali liquids and auxiliaries, which affect the normal dyeing of the veneers. Therefore, the post-treatment must thoroughly clean the veneers to neutral with a large amount of clean water. Drain dry.

4 Determination of main parameters

4.1 Bleach concentration

Bleach concentration is an important factor affecting the quality of bleaching. Too high concentration will cause waste, affecting economic and technical indicators; too low will affect bleaching effect. The experiment found that when the concentration of hydrogen peroxide exceeds 6%, the increase of the concentration of the bleaching liquid is not obvious to the increase of the whiteness of the veneer; and when the concentration of the bleaching liquid is less than 2%, even if the bleaching time is prolonged, the bleaching effect is not satisfactory. Especially when bleaching a darker board, it is difficult to drift through. Experiments have shown that the suitable concentration of bleached veneers should be between 3% and 6%, preferably around 5%.

4.2 Bleach temperature

Bleaching temperature is also one of the main factors affecting the bleaching index. The temperature of the bleaching liquid is low, the decomposition of hydrogen peroxide is slow, and the bleaching speed is slowed down. Especially when the temperature is lower than 15 °C, the bleaching process is extremely slow and the drift rate is extremely low. As the temperature increases, the double-oxygen double decomposition accelerates, and the bleaching speed also accelerates. However, if the temperature is too high, the hydrogen peroxide decomposes too fast, and the effective action time is shortened. According to the experimental research, the temperature of the bleaching liquid is 25-35 C, which not only increases the production cost, but also achieves better bleaching effect.

4.3 Bleaching time

Bleaching time is another important parameter in the bleaching process. The time is too short, the bleaching is not transparent, there will be obvious color difference inside and outside, which directly affects the bleaching effect; too long will prolong the working hours and production cycle, directly affecting economic benefits. Therefore, we must master the bleaching time. Table 1 shows the corresponding relationship between veneer thickness and bleaching time of wood such as poplar, elm and birch in the production of artificial thin wood under the conditions of 5% hydrogen peroxide concentration, 25 C and pH=10.5.

Table 1 Correspondence between veneer thickness and bleaching time

Single table thickness (mm) - "time (h)

<0. 5―————————0.5

<0. 75―————————1

<0. 80——————————1.5

<0. 85―————————2

<0. 90——————————2.5

<0. 95―————————3



When the thickness of the veneer is 0.85mm or more, the penetrant and auxiliary agent should be added. The experiment proves that when the thickness of the veneer is <0.85mm, better bleaching effect can be achieved without adding any additives, but when the veneer thickness is >0.85mm, it is necessary to add additives and penetrants. Over. Taking bleached lmm thick veneer as an example, when adding additives and penetrants, it only needs 4 hours to completely float and evenly float. Otherwise, even if it is bleached for 6 hours, it is difficult to float, often deep inside and outside.

5 Conclusion

1 bleaching the veneer with hydrogen peroxide as the main agent, the suitable process conditions should be: hydrogen peroxide concentration 3% to 6%, temperature 25-35 C, pH 9.5-11, depending on the thickness of the veneer, when the veneer When thicker, it should be added with additives and penetrants.

2 After bleaching, the veneers are lighter in color and uniform in color tone, and eliminate the stains and stains on the surface of the veneer, which greatly improves the dyeing quality of the veneers.

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