People have higher and higher quality requirements for packaging paperboard, coated white paper as high-grade packaging materials, and its exquisite appearance quality has also become the goal of people. However, the yellowing phenomenon of coated white paper has seriously affected the aesthetic appearance of the outer packaging material. The yellowing of coated white paper means that after the product is stored for a certain period of time, or after exposure to sunlight, the whiteness of the product will decrease. The phenomenon of the yellowing of the coated whiteboard paper and the mechanism of the occurrence of the yellowing paper were studied. The measures to find the various factors of yellowing and the stability of the whiteness were increasingly attracted by our attention. This article mainly combines the production practice of our company, analyzes the phenomenon of yellowing of coated white paper, and discusses how to prevent and solve the phenomenon of yellowing.

1, coating white paper yellow back phenomenon formation mechanism

The latest research results show that the phenomenon of yellowing is the reaction of cardboard surface materials with oxygen in the air during the storage process and after sunlight exposure, which changes the chemical structure of the surface layer material, and thus affects the human visual effect. The degree of oxidation determines the severity of yellowing. The oxidation process is mainly due to the following three factors: 1 high temperature, 2 UV, 3 pH.

2. Factors affecting the yellowing of coated white paper
From the promotion factors in the oxidation process and the analysis of the material composition of the coated whiteboard paper, the factors affecting the yellowing of the coated whiteboard paper mainly include the following aspects: coated white paper base paper, fluorescent whitening agent, color pigment, and coating Cloth adhesive and so on.

2.1 coating base paper

2.1.1 Fiber type and composition of the base paper: It is mainly the composition of the surface fiber. The base paper batter of coated white paper is generally composed of bleached chemical wood pulp, so the yellowing of the base paper is mainly due to heat induced yellowing. The yellowing of mechanical pulp is mainly caused by light induced yellowing, so it is more severe than yellowing in chemical pulp during storage.

2.1.2 pH value of base paper: Acid paperboard is more likely to cause yellowing than alkaline paperboard.

2.1.3 Other raw materials of raw paper: such as filling materials, retention aids and other raw materials also have a slight impact.

2.2 Fluorescent Brightener

Fluorescent brighteners are mainly derivatives of stilbene disulfonic acid (or tetrasulfonic acid) because residual lignin in the pulp or some of the pigment components in the paint will cause yellowing of the paperboard, and the fluorescent whitening agent The use is to eliminate the yellowish tint, which is a way to improve the quality of the cardboard. Although the effect of brighteners is short-lived, because it is yellow in itself, more brighteners will also affect the yellowing of the paperboard.

2.3 color pigment
2.3.1 Different types of colorants are often used as tinting pigments for coated white paper coatings, and their requirements must be lightfast. Direct dyes and basic dyes are cheaper, but they have lower light fastness.

2.3.2 The use of more color pigments will exacerbate the yellowing of coated white paper.