13 Jan Better White Top Liner at Lower Cost
FiberLean® on Top Wet-end Coating
FiberLean® on Top has been a major project within FiberLean Technologies Ltd over the last few years. The project is aimed at developing a novel method for making two-layer papers through application of a coating in the paper machine wet-end. This “wet-end coating” is a new unit process in paper making made possible through using microfibrillated cellulose (MFC) as the binder. The binder has to provide sufficient strength, but also prevent penetration of the coating into the base paper. FiberLean® MFC, being a physically entangled MFC-mineral composite, offers ideal properties for this application. FiberLean on Top is primarily aimed at making better White Top Liner at lower cost.
The “proof of concept” now achieved has required a major effort and many days on pilot paper machines. Most of the time has been spent on working out the right equipment, conditions and formulations to make the process run well at high speed. The primary challenges have been related to rheology, drainage and formation. It is clearly a major milestone that has been reached. We now know we have the right product with equipment and a process that works. This means the project focus can shift to scaling-up and adaption to commercial full-scale paper machines.
The FiberLean on Top coating is applied at solids levels similar to the solids content of the base paper at the point of application. Water from the coating is removed through the base paper over the vacuum boxes and in the press section. The level of press solids is increased as a result of the coating, meaning the coated paper can be dried using less energy without requiring any rebuild of driers. This means that the concept offers a low capex solution in combination with low opex and still offers a significant upgrade in paper quality. The MFC-mineral composite coating has the structure and light scattering to optically and physically cover a dark rough base with a smooth white layer suitable for printing.
The major differences to today´s conventional way of producing white top liner are:
- Using simple, low-cost, equipment to apply a coating layer directly onto the base paper with no need for adding any water removal equipment or other paper machinery components (capital avoidance).
- The composition of the layer is substantially different from the conventional approach in that it consists mainly of minerals with a minor amount of MFC, instead of mainly white pulp and a minor amount of mineral.
- The MFC-mineral coating can be applied at lower basis weight compared to conventional white top liner and still meet the market needs in terms of brightness and other properties.
- The MFC-mineral coating has shown particularly good performance when printed in water-intensive print methods, notably digital water-based inkjet printing, an area of exceptionally high growth.