Rui Sergio Tsukuda
Calcium carbonate is now the dominant mineral used in paper coating. However, wide variations in the extent of its use exist even within the same type of paper or board.
Some of these differences are due to issues of local mineral availability and logistics, but others are due to the experience and sensitivities of individual mills.
In coated wood free grades, especially in Europe, it is not uncommon to be completely clay free. However, learning to run clay free has required a re-think on the control of coating solids, drying profiles and coating application.
Some board mills also run totally clay free, and in general where clay is used, it is used for its specific functionalities of physical coverage of a very rough base, for high uncalendered gloss and for improved activation of laser marking due to its specific beneficial impact on laser energy absorption.
The main benefits of an increased use of CaCO3 are an increase in final sheet whiteness (blue shade), and lower cost of production, however, there may be challenges related to low gloss and coverage of the base. Therefore, the use of formulations containing 100% CaCO3, requires a total system approach.
This presentation first introduces some typical formulations that are used in coated board and paper throughout the different regions of the world, and then explores the different ways in which an increased amount of CaCO3, can generate maximum benefits.
The process of how to optimise coatings containing ultrafine CaCO3is described so that such coating can give equivalent paper and print gloss and physical coverage to those containing traditional amounts of glossing clay. Examples are then given for double coated woodfree and coated board which show that highest levels of performance can be achieved with coating containing up to 100% ultrafine CaCO3 provided that coating colour solids, binder and co-binder concentrations are all optimised at the same time as the mineral.
*Authors' references:1 Imerys Minerals Ltd., Par Moor Centre, Par Moor Rd, Par, Cornwall, UK PL253EH2 Imerys do Brasil - Av. Valentina M.F. Borestein, 545 - 08735-270 - Mogi das Cruzes/S
O PAPEL VOL.78 NUM1 PP82-89 - JAN 2017