| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain alumina powder for a toner additive adaptable to the increase of the amount of a toner used due to the colorization of an electronic photograph, upgrading an image, having good durability and excellent in grinding performance in an electrophotographic developer used in an electrophotographic device and to obtain a developer using the alumina powder. SOLUTION: The alumina powder comprises polyhedralα-alumina particles substantially having no crushed face. The ratio (D/H) of the maximum particle diameter D of the particles parallel to a hexagonal close-packed lattice face ofα-alumina to the particle diameter H perpendicular to the hexagonal close- packed lattice face is 0.5-3.0. The number average particle diameter of theα-alumina particles is 0.1-1.0μm. The ratio (D90/D10) of the particle diameter D90 of cumulative 90% of the cumulative particle size distribution from the fine particle side to the particle diameter D10 of cumulative 10% is <=7.</p> |
