Production of paper and paperboard

Abstract From the Canadian patent

The fines retention or drainage properties of mechanical pulps in the paper making process are improved by including in the thin stock, not after the last point of high shear particles of a water-dispersible colloid siliceous material such as a bentonite clay in intimate association with a low molecular weight water soluble high anionic charge density polymer, such as polyacrylic acid having a molecular weight below 50,000 and a charge density of at least 4 m eq/g and further including in the thin stock, after the last point of high shear, a non-ionic high molecular weight polyelectrolyte such as polyacrylamide having a molecular weight of at least 100,000.