2.4 coating adhesive
There are usually three types of adhesives for coating white paper: acetic acid latex, styrene-acrylic latex, and styrene-butadiene latex. Among them, acetic acid latex has the least effect on yellowing, and styrene-butadiene latex has the greatest impact on yellowing due to its special chemical structure.

2.5 Comparison of Effect of Cardboard Paper Fiber Types and Adhesives on Yellowing of Coated Whiteboard Paper

3. Prevention and remedy of yellowing of coated white paper

3.1 Adjustment of the process of coating base paper: The surface pulp fibers of the base paper are all bleached chemical pulp, and the amount of batter is increased to increase the coverage of the mechanical pulp of the liner. The use of alkaline sizing process to reduce the amount of aluminum sulfate bake, increase the 13H value of the original paper. The experiment proved that the pH of the paper surface layer was between 6.5 and 8. O2_ asks better results. In the process of papermaking, the temperature of the drying should be strictly controlled to ensure that the board is dry, the drying temperature should be reduced as much as possible, and the cold paper of the base paper and coated paper should be used.

3.2 Select better-quality liquid whitening agent: The experiment proves that the application of liquid brightener can reduce the yellowing degree of the coated product. It ensures that the self-degree of the product is improved while the effect on yellowing is obviously lower than that of powdery whitening agent. Better quality liquid brighteners must require higher purity. Poorly pure liquid brighteners not only cause unnecessary waste, but also tend to form yellowing. In addition to the use of fluorescent whitening agents in coating formulations, attention should be paid to the use of brightener carriers (adhesives).

3.3 Reasonable application of color pigments: The use of color pigments is to maximize whiteness (CIE), reduce the amount of fluorescent brighteners, and balance different chemical raw materials to achieve the desired hue. In order to reduce the yellowing of coated white paper, the use of color pigments requires not only easy operation, good affinity, but also high lightfastness. Therefore, it is best to use high quality organic pigments, and its performance in various aspects is ideal. More attention should be paid to the amount of hueing pigments, because too high or too low amounts can not achieve the purpose of color hue. Too high will exacerbate the degree of yellowing of the coated white paper; if it is too low, the desired whiteness will not be achieved.

3.4 Choosing a reasonable coating adhesive proportion: In order to prevent and solve the phenomenon of yellowing of coated white paper in the coating formulation, a single styrene-butadiene latex is used as the coating adhesive under the requirements of balanced formulation cost and product performance. It is almost impossible. Therefore, according to product performance requirements, you can choose styrene-butadiene latex and other latex mixed use, such as low-cost styrene-acrylic latex, both to ensure the strength of coated white paper, but also reduce the degree of return to yellow.

3.5 Selection of New Chemical Auxiliaries: In the study of nano-silicon oxides used in coating formulations, the authors found that nano-silicon oxides have a clear tendency to reduce coating yellow due to their unique molecular structure. In the aging test, the absolute value of the color b value decreases very little. In addition, UV absorbers and antioxidants can also reduce yellowing of the coated white paper coating.

3.6 Other factors that should be taken care of: such as the pH value of the paint, 'cleaning paint water, use of coated starch, moisture of coated paperboard, packaging and storage of coated paperboard, etc. should be strengthened. Although these are not the main reasons for the formation of yellowing, as long as prevention is strengthened in all aspects, it is also effective to solve the problem of yellowing of coated white paper.

4. in conclusion
4,l In the production practice of solving the problem of yellowing of coated whiteboard paper, coating base paper, fluorescent whitening agent, color pigment and adhesive are the main factors that affect yellowing. Improve the process conditions of raw paper production, use high-quality fluorescent whitening agents, color pigments, adjust the best dosage; scientifically determine the best mix of adhesives, can effectively reduce the yellowing phenomenon of coated white paper.

4.2 The use of new chemical additives, such as nano-silicon oxides, UV absorbers and antioxidants, will also reduce the yellowing of coated whiteboard.

4.3 Strengthen the prevention of coating whiteboard production control and packaging storage conditions is also an advantageous way to solve the yellowing of coated whiteboard paper.