Nowadays, more complain for the box caused by paper yellowing discoloration which has been a big trouble for package printing companies. Coated paper yellowing discoloration means whiteness dropped with a period time’s storage or after the sunshine.

Here we will analyze the phenomena of yellowing and discuss how to prevent and solve it combined with production practice.

1.  Formation principle of the yellowing for the coated paper

   With latest research, yellowing discoloration is cause by oxidation between the material on paper surface and air under storage and sunshine which will lead to the change of chemical structure for the surface material. Then it will effect human visual.

 The degree of oxidation determines the severity of yellowing. The following 3 factors has promotion function in the process of oxidation 1. high temperature 2 ultraviolet light 3. PH value

2. Factors for yellowing of coated whiteboard paper

Analysis  from the promoting factors in oxidation and material structure of coated whiteboard paper, we think the main factors for yellowing in concluding below: the base paper of the coated whiteboard paper, fluorescent brightener, color pigments,  coating binder and so on.

3. Prevention and solution of the yellowing

1. Process adjustment:  Maijiang fiber use bleached chemical wood pulp and increase the dosage of Maijiang to keep a more coverage of lining mechanical pulp. With sizing process in neutral and alkaline environment and less usage of AL3SO4 to increase the PH value. It proves with experiments, the PH value of base paper between 6.5 and 8.0 is better. In the copying process, strict control of drying temperature, the lower temperature is better. At the same time, we need to use good quality cooling cylinder.

2. Good quality of liquid brightener: proved by research, using the liquid brightener can decrease the standard of yellowing. And the effect is better than the powder brightener. But we need the high purity, low purity is no use for the yellowing even it may cause the yellowing. Another hand, we need use better fluorescent.

3. Color pigments reasonable application. To use the pigments is to improve the CIE ,decrease the usage of the fluorescent brightener, and balance different chemical raw materials to get the needed color. We’d like to choose high quality organic pigments which is more fusional and better sun block and will help us use it easily . We also need to pay attention on the usage amount, if more, it will accelerate the yellowing, but if less, it have no help for the whitening .

4.  Reasonable coating adhesive ratio. According to the product performance, we need to use the mixture of styrene-butadiene latex and other latex which will add the strength of coated whiteboard paper and decrease the yellowing.

5. New chemical additive Nanosilicon oxide has special molecular structure which is help for decreasing the yellowing . In the experiment, chroma value of B will low. And ultraviolet light absorber and antioxidant can decrease the yellowing.

6. Other considerations. Such as the PH value of paint, pure of the paint water, water content of the coated board, package and storage of the board, they’re not the main factors for the yellowing, but we also need to pay attention for it.

Conclusion

1.     In the process to prevent the yellowing, we need to pay attention the main factors which mentioned above.

2.     Choosing new chemical additive will also decrease the yellowing.

3.     Strengthening production control of the coated board and the storage of the package are also a big help of the yellowing.