PROCESS FOR THE PRODUCTION OF WATER INSOLUBLE NEEDLE-SHAPED PRECIPITATED CALCIUM SULPHATE DIHYDRATE (CASO4-2H2O) AND ITS USE AS A FILLER IN PAPERMAKING

摘要

Needle shape calcium sulphate dehydrate (CaSO4.cndot.2H2O) filler particleswereprepared by mixing freshly calcined calcium sulphate hemihydrate(CaSO4.cndot.1/2H2O)having an average particle size between 1 and 100 micrometers, and water in areactorat high sheer with either no additives or together with acids or with calcium-orsulphate- containing additives. The average length and width of the producedfillerparticles were 5-35 micrometers and 1-5 micrometers respectively. The calciumsulphate dehydrate filler particles were then treated by a calcium chelatingagent,perhaps followed by the addition of a weak acid. The mixture was then held at30-90°C for 5-60min resulting in relatively water insoluble calciumsulphate dehydrate.The filler suspension can be directly added to the pulp furnish before thepaper sheetformation to obtain a high filler retention and improved optical propertieswithminimal filler losses due to solubility. The resulting filler did not causeany operatingdifficulties on the paper machine and provided, depending on the filler level,a 2-15%decreased energy consumption in the drying section.