Complete shear rate analysis provides a new means ofoptimizing coating performance on high speed coaters

摘要

Increased quality demand for coated papers together with higher coating production rates and efficiencyrequirements, have resulted in the need for improved coating formulations that are further optimized inperformance quality and cost. This has resulted in the increased need for coating rheology studies to ensurethat the coatings achieve the desired end product quality, particularly important at high coating speeds.The rapidly growing number of high speed; and often low coat weight, blade and film type coaters havemade it difficult for both coated paper producers and coating suppliers to predict the high shearperformance of their coating formulations. For example coaters operating above 800 m/min {2600 ft/min}experience shear rates well in excess of one (1) million s-1 that have, up until now, been impossible tomeasure and analyze. With new viscometer technology coating R & D can now better, faster and with lesscost determine the runnability requirements of their high speed coating formulations by accuratelydetermining the products viscosity behavior at very high shear rates.Complete shear rate analysis starting at 100 s-1 and going all the way up to ultra high.shear rates of 2.5million s-1, can now be achieved by using a electronically controlled, mechanical piston driven unit calledthe ACAV™ A2 UltraHigh Shear Viscometer. The new A2 model uses a hydraulically driven piston toforce the sample through the desired capillary at a precise, computer controlled flow rate, and is capable ofgenerating pressures up to 350 bars (5150 psi). This pressure safely generates shear rates several timeshigher than conventional capillary viscometers, when compared to equivalent capillary diameters. Theviscosity data can be measured in a simple, repeatable and rapid manner and correction factors such kineticenergy and Rabinowitsch-Mooney, are available. It can also accurately analyze all Newtonian and non-Newtonian samples.