Study On The Viscosity Properties Of Kaolin Used In Paper Coating

As t he important r aw m aterials i n p aper coating, K aolin has ireplaceable positions because of its special structure and properties. But most of the productions of the civil kaolin factories can not reach the requirement of paper coating in the viscosity at present. Therefore how to better the viscosity properties of civil kaolin, improve its viscosity concentration to 68-70%, better its fluidity, and finally reach the requirement of paper coating, are very important. This is the difficult and hot subject in the kaolin trade.In the tests, Suzhou and Maoming kaolin are selected as the materials which are the most representative kaolin in China. By adding dispersants to the kaolin slurry and using machines, the viscosity properties of the two kaolin materials are bettered, their viscosity concentrations are all improved above of 69%, and meet the requirement of paper coating. Studies on the mechanism of disperse and changing of the fluidity are also carried out.The tests of the main factors that influence the dispersing of the kaolin slurry are carried in the first, and the optimum operating conditions are made certain. Those are the follows: the pH value of the slurry should be controlled among 7. 0-8.0; the velocity of stirrer should be controlled among 2500-3000 r/min; and the stirring time should be controlled within 10-15 minutes.The tests that the viscosity of kaolin slurry influenced by dispersants solely are carried at the concentration of 63% and 68% respectively. The result of the tests proved that the influence of regent 1 is the greatest in inorganic dispersants, and the influence of regent 5 is the greatest in organic dispersants. But the consumption of inorganic dispersants is too high and their functions are limited at high concentration; the influence of organic dispersants is marked but its cost is too high. Therefore, inorganic and organic dispersants are all not suitable for uses eparately, and t he d ispersant of their mixture i s considered of using in the follow tests.The tests of mixture dispersants that composed of regent 1 and otherorganic d ispersants are c arried. T he r esult p roved t hat m ixture d ispersant o f regent 1 and regent 5 is the best regent for the two kaolin materials, and their optimum dosage are respectively the follow: the dosage of regent 1 is 1. 0 kg/t, and the dosage of regent 5 is 3. 0 kg/t. The test of the viscosity concentration proved that the viscosity concentration of Suzhou kaolin is improved from 61. 43% to 68. 33%, the viscosity concentration of Maoming kaolin is improved from 64. 02% to 69. 56%.The tests of machines are carried consequently for the further development. The result of the tests proved that by using double-screw extruder after adding the mixture dispersant to the slurry, the viscosity concentration of Suzhou kaolin can be improved to 69. 14%, and the viscosity concentration of Maoming kaolin can be improved to 70. 32%.The disperse mechanism of kaolin slurry is also discussed finally. So conclusion can be draw that the dispersants c an adhere to the surface of the kaolins and increase the minus value of Zeta potential of their surface, the hydrophilities between particles increased, the flocculation construction of "T" type is broken, so the viscosity of kaolin is lowered. The function of machines is to make the particles arrange along slice directional and their construction is broken, so the construction viscosity of kaolin is lowered and its viscosity concentration is improved.The result of the tests of fluidity of kaolin and studies on the rheology proved that the kaolin slurry change from plastic fluid to yield-pseudoplastic fluid, the behaviors of the slurry are bettered, and is suitable for paper coating.kaolin; viscosity properties; dispersant; viscosity concentration;fluidity...