| 摘要 |
PURPOSE:To obtain a high insulation crude ceramic board having excellent void occupation ratio and insulation breakdown strength by forming a green sheet having special crude density or more of a ceramic material having relatively low alumina purity by a roll compaction method, and baking it at a special temperature or lower. CONSTITUTION:Even if a ceramic material having relatively low alumina purity of 90-99wt.% Al2O3 content is used, voids are reduced thereby to provide excellent insulation. That is, the material is subjected to a roll compaction molding to form a green sheet having a density of 2.4g/cm<3>. Thus, the voids in the sheet are reduced. Its baking temperature can be 1600 deg.C or lower due to high density, and grain growth of its crystal is suppressed to reduce the voids. Therefore, obtained ceramic board has 8.5 or less of void occupying ratio in section of a thickness direction and 20kV/mm or more of insulation breakdown strength. |
