A novel formulation approach for improving fibre coverage during blade coating

• It is generally understood that increased pigment aggregation and structuring of wet coating colour improves fibre coverage, but reduces runnability on the blade coater. This paper presents a formulation approach which results in formation of a significant coating structure only after the blade. The approach is based on the laboratory observation that the structuring effect of small amounts of a salt is inversely dependent on coating colour pH. The combination of calcium chloride addition and the use of ammonia for pH control is therefore proposed. The evaporation of ammonia after the blade results in pH reduction and allows the formation of pigment structure during coating consolidation. Results from laboratory studies and pilot coater trials are presented. The latter suggest that the proposed approach provides significant improvements in fibre coverage, surface smoothness and opacity, but that surface strength is reduced. Laboratory results and the observed good blade runnability indicate that the coating structuring is obtained only after the blade, as the ammonia evaporates.

Nyckelord

Coating

coated papers

paper properties

agglomeration

adsorption

elipsometry

polyacrylates

rheology

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