| 摘要 |
PROBLEM TO BE SOLVED: To provide an inexpensive production method for a white pigment using a deinked sludge of pigment-coated waste paper as the raw material whereby the whiteness and brightness of the pigment is high, the slurry solution of the pigment does not solidify, a paper-making wire used for the white pigment is hardly abraded, and that the cost as the difference between the treatment cost and the disposal cost is low. SOLUTION: The deinked sludge disposed of at a deinking step for recovering pulp from pigment-coated waste paper is used as the raw material. The deinked sludge is dehydrated to dray and baked in a baking oven at 650-700 deg.C to give a white incineration residue, which is subjected to primary grinding with a grinding machine to give particles with the maximum particle size of 150μm or lower, then dispersed in water to give an aqueous dispersion, and subjected to secondary grinding with a wet grinding machine to give a white pigment having an average particle size of 0.5-5μm. The pH of the pigment is adjusted to 6-11 pH by blowing carbon dioxide gas into the aqueous dispersion after the primary grinding or into both the aqueous dispersion after the primary grinding and after the secondary grinding.
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