Coating of paper with highly filled powders

• Powders with 100 parts of CaCO3, and 10 and 20 parts of polymer were studied.
• Such powders can be charged and deposited onto paper by electrostatic means.
• Pressing in a hot roll nip essential for both cohesion and adhesion
• Coatings have uneven thickness and low mechanical interlocking with paper.

The purpose of this study was to evaluate the feasibility of using highly filled powders as electrostatically applied paper coatings. Powders prepared by two different methods were suitable for electrostatic deposition and they attached to the paper surface with a grounded backing. Pressing at elevated temperatures turned out to be a crucial process step for improving the adhesive and cohesive strengths of the powder coating layer on paper. Limited mechanical interlocking with the base paper and an uneven pressure profile were factors impairing the surface strength of the coated paper. On the other hand, factors such as higher polymer content, higher pressing temperature, pre-heating the paper prior to coating, and increasing the number of hot roll nips increased adhesion between the coating and the base paper. Powder coatings as such had uneven thickness, and they displayed a relatively broad pore size distribution.

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