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Why Does White Paper Appear Yellowing?
Oct 12, 2017

People are packing cardboard quality requirements are getting higher and higher, coated white board paper as high-grade packaging materials, and its exquisite appearance quality has become the people's pursuit of goals. But the yellowing of coated white paperboard has seriously affected the beauty of the outer packing material. The yellowing of coated white paperboard refers to the phenomenon that the whiteness of the coated product will decline after a certain period of storage or after sunlight irradiation. The mechanism of yellowing of coated white paperboard and the mechanism of its occurrence are studied. The measures and methods to find various factors and stability of yellowing have been paid more and more attention to.

1. forming mechanism of yellowing of coated white paperboard

The latest research results show that the yellowing phenomenon is cardboard in the storage process and the sunlight, oxygen reaction surface material board and the air, change the chemical structure of the surface material, which affect people's 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, ultraviolet light, pH value.

2. factors affecting the yellowing of coated white paperboard

From the oxidation of materials in the process of promoting factors and coated white paper analysis of the factors affecting the coating paper yellowing phenomenon of the main aspects are as follows: white coated paper, fluorescent whitening agent, color pigment, coating adhesive etc..

2.1 coated base paper

2.1.1 paper fiber types and composition: mainly surface fiber composition. Coated white board paper base pulp is usually made of bleached chemical wood pulp, so the return of yellow paper is mainly due to heat induced yellowing. The yellowing of mechanical pulps is mainly due to light induced yellowing, so it is more serious in the storage process than in the chemical pulps.

2.1.2 base paper pH value: acid paperboard is more easy to cause yellowing than alkaline paperboard.

2.1.3 raw materials and other raw materials: such as filling material, retention agent and other raw materials also have a slight impact.

2.2 fluorescent whitening agent

Fluorescent whitening agent is mainly two styrene sulfonic acid (two or four sulfonic acid) derivatives as pulp residual lignin or coating pigment components will cause some cardboard yellowing, while the use of fluorescent whitening agent is to eliminate the yellowish hue, is on the way to improve the appearance quality of board. Although the effect of whitening agent is short, but because it is yellow, more dosage of whitening agent will also affect the yellowing of the paperboard.

2.3 toning paint

2.3.1 different types of colorants often do color pigment for coated white paper coating, the request of them must be light. Direct dyes and basic dyes is cheap, but the low light fastness.

The dosage of 2.3.2 toning pigment is more, it will aggravate the yellowing degree of coated white paper.

2.4 coating adhesive

There are usually three kinds of adhesive used for coating white board paper: acetic acid latex, styrene acrylic latex and styrene butadiene latex. Among them, the acetic acid latex has the least influence on the reversion of yellow latex. Because of its special chemical structure, the latex has the greatest influence on the yellowing.

Comparison of 2.5 kinds of paper base, fiber type and adhesive on yellowing of coated white board