Formation mechanism of yellowing phenomenon of the

Formation mechanism of yellowing phenomenon of Coated Whiteboard

people have higher and higher requirements for the quality of packaging board. As a high-end packaging material, Coated Whiteboard has also become the goal of people to pursue its exquisite appearance quality. However, the yellowing phenomenon of coated white board has seriously affected the appearance of outer packaging materials. Yellowing of Coated Whiteboard refers to the phenomenon that the whiteness of the product will decrease after a certain period of storage or sunlight exposure. We have paid more and more attention to studying the yellowing phenomenon of coated white board and its mechanism, finding out various factors of yellowing and the measures and methods to stabilize the whiteness. Based on the production practice of our company, this paper analyzes the yellowing phenomenon of coated white board, and discusses how to prevent and solve the yellowing phenomenon

1. The latest research results show that the yellowing phenomenon is that the paperboard surface material reacts with oxygen in the air during storage and after sunlight, which changes the chemical structure of the surface material, thus affecting the visual effect of people. The degree of oxidation determines the severity of yellowing. The oxidation process is mainly promoted by the following three factors: ① high temperature, ② ultraviolet light, and ③ pH value

2. Factors affecting the yellowing phenomenon of coated white board

from the analysis of the promoting factors in the oxidation process and the material composition of coated white board, the factors affecting the yellowing phenomenon of coated white board mainly include the following aspects: coated white board base paper, fluorescent brightener, toner pigment, coating adhesive, etc

3. Prevention and solution of yellowing phenomenon of coated white board

3.1 process adjustment of coated base paper: bleached chemical wood pulp is used as the surface pulp fiber of base paper, and the amount of surface pulp is increased to strengthen the coverage of lining mechanical pulp. The medium alkaline sizing process is adopted to reduce the amount of aluminum sulfate in the face pulp and improve the 13h value of the base paper. It is proved by experiments that the pH value of the base paper surface is between 6.5 and 8.0, which has a good effect. In the process of papermaking, the drying temperature should be strictly controlled. When the paperboard is dry, the drying temperature should be reduced as much as possible, and good use of base paper and coated paper will have a good strategy on the first day of the merger; In addition, we should have a strict rules of conduct and an experienced M & a team

3.2 choose liquid brightener with good quality: experiments have proved that the application of liquid brightener can reduce the yellowing degree of coated products. While ensuring to improve the self-sufficiency of the product, its effect on yellowing is significantly lower than that of powdered brightener. The liquid brightener with good quality must have high purity. The liquid brightener with poor purity will not only cause unnecessary waste, but also easy to form the phenomenon of yellowing. In addition, the fluorescent brightener should be used well in the paint formula, and the application of brightener carrier (auxiliary adhesive) should also be paid attention to

3.3 rational application of tinting pigments: the use of tinting 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 Whiteboard, the selection of color matching pigments requires not only easy operation, good affinity, but also high sun fastness. Therefore, it is best to choose high-quality organic pigments, whose performance in all aspects is relatively ideal. More attention should be paid to the amount of color pigments, because too high or too low amount can not achieve the purpose of color matching. Too high, it will aggravate the yellowing degree of Coated Whiteboard; If it is too low, the required appropriate whiteness cannot be achieved

3.4 select and then carefully measure the coating adhesive proportion of the sensor feedback value: in the coating formula, in order to prevent and solve the yellowing phenomenon of coated white board, it is almost impossible to use a single styrene butadiene latex as the coating adhesive under the requirements of balancing the formula cost and product performance. Therefore, according to the product performance requirements, styrene butadiene latex can be mixed with other latex, such as cheap styrene acrylic latex, which can not only ensure the strength performance of coated white board paper, but also reduce its yellowing process for a variety of mechanical properties experiments of various wood-based panels and decorative wood-based panels

3.5 select new chemical additives: the author found that nano silicon based oxide has obvious potential in reducing coating yellow due to its unique molecular structure. In the eye aging test, the absolute value of chromaticity b value decreases very little. In addition, UV absorbers and antioxidants can also reduce the yellowing of the whiteboard coating

3.6 other factors that should be paid attention to: for example, the pH value of coating, the purification of coating water, the use of coated starch, the moisture of coated paperboard, the packaging and storage of coated paperboard, etc. Although these are not the main reasons for yellowing, as long as the prevention is strengthened in all aspects without foreign technology, it is also very effective to solve the yellowing of Coated Whiteboard

4. Conclusion

4 In the production practice of solving the problem of yellowing of coated white board, the main factors affecting yellowing are coated base paper, fluorescent brightener, toner pigments and adhesives. Improve the process conditions of base paper production, select high-quality fluorescent brighteners and color pigments, and adjust the optimal dosage; Scientific determination of the best combination of adhesives can effectively reduce the yellowing phenomenon of Coated Whiteboard

4.2 the use of new chemical additives, such as nano silicon-based oxides, UV absorbers and antioxidants, will also reduce the yellowing phenomenon of Coated Whiteboard

4.3 strengthening the production control of coated white board and the prevention of all aspects of packaging and storage conditions is also a favorable way to solve the yellowing of coated white board