| 摘要 |
PURPOSE: To produce sheets of base paper for an electrical insulating laminated sheet excellent in dimensional stability and silver migration resistance by forming the sheet from wood pulp as a raw material and regulating the moisture content and water retention value within specific ranges. CONSTITUTION: A hardwood chip produced in Hokkaido, Japan is digested by a kraft process to provide an unbleached pulp having 18±0.5 Kappa number and the resultant pulp is then bleached with oxygen, an alkali, chlorine and chlorine dioxide in many stages to afford a bleached kraft pulp, which is used as a raw material. A melamine resin in an amount within 1% is internally added thereto and the resultant stock is formed into sheets of paper. Thereby, the sheets of base paper for a laminated sheet having >=5 and <=7% moisture content and >=85% water retention value are formed and then impregnated with a phenol resin to prepare prepregs. A prescribed number of he prepared prepregs are then laminated and hot press molded to afford the electrical insulating laminated sheet.
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