| 摘要 |
PURPOSE:To obtain an extender pigment which has excellent dispersibility in a water-based coating and gives a coating film with high gloss, by wet-milling an aqueous suspension of calcium carbonate on which a polycarboxylic acid dispersing agent of a specified composition has been adsorbed, in a manner to satisfy specified conditions. CONSTITUTION:A precipitated calcium carbonate having an average particle diameter of 0.01-0.5mum is allowed to adsorb a sodium salt, an ammonium salt and/or an amino salt of a polymer of at least one alpha,beta-unsaturated monocarboxylic acid (I) selected from among acrylic acid, methacrylic acid and crotonic acid and/or a copolymer of (I) with at least one alpha,beta-unsaturated dicarboxylic acid (II) selected from maleic acid and itaconic acid. This calcium carbonate is allowed to stay in a continuous wet disperser for at least 0.5min to be wet-milled so that the value S calculated by the equation from the particle size distribution determined with an apparatus by photo extinction method of the centrifugal sedimentation analysis may satisfy the equation. The wet- milled calcium carbonate is then dried to form a powder.
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