Analysis on Pre-printing Surface Treatment of Paper and Paperboard

Surface treatment technology refers to artificial crafts done by mechanical or physical to meet the requirements of anti-corrosion or wear resistance, decoration, etc.

There are various kinds of printing materials, some can be printed with or without surface treatment for example paper packaging products, for example, paper boxes or gift bags. From commercial perspective, surface treatment is a value adding method, which can be considered as a good way to lower the net cost of the materials. From material perspective, it is a good way to improve the performance of paper or paper board. There are strength performance including stiffness, tensile strength, compressive strength, optical properties including whiteness, brightness, and opacity, absorptivity including wettability, and absorptivity, and surface properties including roughness, smoothness and friction properties.

Humidity control is the first surface treatment for paper printing. And humidity control influences the paper deformation a lot. The cellulose contained in the paper have multiple hydroxyl groups, which determines its strong hydrophilicity. The paper materials get swollen after water absorbed and gets wrinkled after dried, which affects the printing quality badly. High humidity leads to low surface strength and even paper crack. Low humidity gets paper crispy and lowers the burst strength, making paper feeding quite difficult to be accomplished, which finally influences the preciseness of printing. Therefore, before printing, humidity control should be strictly executed by following methods like equal humidity adaptation method, moisture absorption method, wet solution method, cold water reprinting method, etc.

Most surface treatment applications lay the foundation for further coating, especially for improving positioning control, i.e. Z-direction coverage and surface performance, X-Y direction variability. Base paper affects the effect of surface treatment. The effect of positioning control is subject to the base paper itself. And the appropriate control of base paper performance is still a big challenge. Although the surface sizing can control the wettability, it has little influence on paper appearance. And the surface structure can be deformed at the bottom of its forming.

Functional coatings as surface treatment should not be confusing. Not all the coatings should be dyed. The improvement of adhesives, protectants and strippable coatings usually begins with in-machine application of surface sizing agents. Whether it is silicon peel coating, or adhesive and protective coating, the covering ability and economy of functional coating layer are improved.

The coverage capability control of any additional layer (whether silicon or printing ink) is an important part in terms of coating function. Protective coated paper and paperboard are commonly found in food packaging bags, paperboard, label, packaging of roll and paper and protective paper. At present, most of the researches are developing in this area.