| 摘要 |
PROBLEM TO BE SOLVED: To improve a binding degree of water-soluble binding film 2 to original sand grain 1. SOLUTION: A porous shell 3 is provided between the original sand grain 1 having small diameter and the water-soluble binding film 2 coated on the surface part of the original sand grain, and this porous shell 3 is effectively functioned, and the binding degree of the water-soluble binding film 2 to the original sand grain 1, is sufficiently secured. COPYRIGHT: (C)2004,JPO
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