| 摘要 |
PURPOSE:To improve the characteristics of a novolack type phenolic resin formed by controlling the ortho rate of tetranuclide and higher nuclides to a specific % range and limiting the total content of dinuclide and trinuclide components. CONSTITUTION:The novolack type phenolic resin is formed by dehydrating and concentrating a phenol and formaldehyde respectively at prescribed ratios by an acidic catalyst, bivalent metallic salt catalyst, etc., heating and mixing two kinds of the resultant resins and further dehydrating and concentrating the mixed resins. The ortho rate of the tetranuclide and higher nuclide components of the phenolic resin is controlled to >=40% and <50% in this stage; at the same time, the ratio of the ortho rate of the dinuclide and trinuclide components to the tetranuclide and higher nuclide components is controlled to <1.05 and further the total content of the dinuclide and trinuclide components is controlled to >=20% and <45%. The strength and curing speed characteristics of the casting mold are both improved by using such phenolic resin as the essential component for the binder.
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