| 摘要 |
A method of reducing the solubility of calcium sulfate (or sulphate) dehydra te (CaSO4~2H2O) and method of making the same are disclosed. The suspension of needle-shaped (acicular) calcium sulfate dehydrate particles is prepared by mixing freshly calcined calcium sulfate hemihydrate (CaSO4~1/2H2O), having an avera ge particle size between 1 and 100 micrometers, and water in a reactor at mediu m to high shear rate, with either no additives or together with acids or with calcium or sulfate containing additives. The average length and width of the resulting calcium sulfate dehydrate particles are then about 5 to 35 micrometers and 1 to 5 micrometers, respectively. The calcium sulfate dehydrate particles of reduce d solubility are obtained using a calcium chelating agent, with or without the addition of a weak acid. The resulting product is a suspension of calcium sulfate dehydrate that can be used as a filler in papermaking, more particularly by being directly added to the pulp furnish before the paper sheet formation. These particles have a high retention and provide improved optical properties with minimal filler losses due to solubility.
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