How to prevent and solve the yellowing phenomenon of coated white board paper in the printing of color box packaging boxes

The color boxes used for product packaging and the packaging boxes used for packaging various commodities are mostly made of white cardboard. The newly purchased white cardboard goes through cutting, printing, and post-processing to become our product packaging boxes. However, the yellowing of the packaging box during the use of coated white board paper has seriously affected the appearance of the outer packaging material. Yellowing of coated whiteboard paper means that the whiteness of the product will decrease to a certain extent after being stored for a certain period of time or exposed to sunlight. This article mainly analyzes the yellowing phenomenon of coated whiteboard paper based on production practice, and discusses how to prevent and solve the yellowing phenomenon.

1. The formation mechanism of yellowing phenomenon of coated whiteboard paper

The latest research results show that the yellowing phenomenon is caused by the reaction of the cardboard surface material with oxygen in the air during the storage process and after exposure to sunlight, changing the chemical structure of the surface material, thereby affecting human visual effects. The degree of oxidation determines the severity of yellowing. The oxidation process is mainly due to the promotion of the following three factors: ① high temperature, ② ultraviolet light, and ③ pH value.

2. Factors affecting the yellowing phenomenon of coated whiteboard paper

From the analysis of the promoting factors in the oxidation process and the material composition of coated whiteboard paper, the factors that affect the yellowing phenomenon of coated whiteboard paper mainly include the following aspects: coated whiteboard paper base paper, fluorescent whitening agent, toning pigment, coating Cloth adhesives, etc.

3. Preventive and solution measures for yellowing of coated whiteboard paper

3.1. Adjustment of the process of coating base paper: all the pulp fibers of the base paper are bleached chemical wood pulp, and the amount of pulp is increased to enhance the coverage of the mechanical pulp of the lining layer. Use a medium-alkaline sizing process to reduce the amount of aluminum sulfate in the batter and increase the 13H value of the base paper. Experiments have proven that the pH value of the base paper surface layer is better between 6.5 and 8.0. During the papermaking process, the drying temperature must be strictly controlled. While ensuring that the cardboard is dry, the drying temperature should be reduced as much as possible, and the cold cylinders for base paper and coated paper should be used well.

3.2. Choose a liquid whitening agent of good quality: Experiments have proven that the application of liquid whitening agent can reduce the yellowing degree of coated products. While ensuring that the product's brightness is improved, its impact on yellowing is significantly lower than that of powdery whitening agents. Better quality liquid whitening agents must require higher purity. Liquid whitening agents with poor purity will not only cause unnecessary waste, but also easily cause yellowing. In addition, fluorescent whitening agents should be used well in the coating formula, and attention should be paid to the application of the whitening agent carrier (auxiliary adhesive).

3.3. Reasonable application of tinting pigments: The use of tinting pigments is to maximize the whiteness (CIE), reduce the amount of fluorescent whitening agents, and balance different chemical raw materials to achieve the required hue. In order to reduce the yellowing of coated whiteboard paper, the selection of toning pigments must not only be easy to operate, have good affinity, but also have high light fastness. Therefore, it is best to choose high-quality organic pigments, whose performance in all aspects is relatively ideal. Pay more attention to the amount of coloring pigments used, because too high or too low a dosage will not achieve the purpose of coloring. If it is too high, the yellowing of the coated whiteboard paper will be aggravated; if it is too low, the required appropriate whiteness will not be achieved.

3.4. Choose a reasonable proportion of coating adhesive: In the coating formula, in order to prevent and solve the yellowing phenomenon of coated whiteboard paper, and under the requirements of balancing formula cost and product performance, it is almost impossible to use a single styrene-butadiene latex as the coating adhesive. It's impossible. Therefore, according to product performance requirements, you can choose to mix styrene-butadiene latex with other latexes, such as cheap styrene-acrylic latex, which can not only ensure the strength performance of coated whiteboard paper, but also reduce its yellowing degree.

3.5. Selection of new chemical additives: The author’s research on the application of nano-silicon-based oxides in coating formulations found that nano-silicon-based oxides have obvious potential in reducing coating yellowing due to their unique molecular structure. In the eye aging test, the absolute value of the chromaticity b value decreased very little. In addition, ultraviolet absorbers and antioxidants can also reduce the yellowing of the coated whiteboard paper coating.