Understanding the Importance of Double Coated Paper Structure in Printing

Double coated papers are usually high quality paper grades. The double coating structure contains a precoat, which usually serves to fill-in the surface pores while the topcoat, which will be printed on, is of a higher quality. We have investigated the effect of the precoat on the printing characteristics of double coated papers as measured by the Deltack method. We found that both the precoat and the topcoat influence the final ink holdout.We propose a model based on preferential filtration and pigment packing that varies from the precoat to the topcoat to explain how the precoat may be used to improve the printing characteristics of papers.

The model is based on preferential filtration of ink components on the topcoat structure while the topcoat structure is itself controlled by the precoat. As a consequence, it is possible to obtain the same maximum in the Deltack force (which is an evaluation of ink holdout and force exerted on the paper surface) with very different double coated paper structures having either the same pore diameters and different pore volumes or having the same pore volume but different pore diameters. The pore volume and pore diameters can be modified and optimized by changing the mineral pigments included in the coating colour.