| 摘要 |
PURPOSE:To obtain the title binder which does not cause environmental pollution, has excellent curability, storage stability and working efficiency and is suitable for use in shell molds, by blending a specified liquid resol type phenolic resin contg. no free HCHO with a solid phenolic resin. CONSTITUTION:A phenol compd. (a) (e.g., phenol) is condensed with HCHO (b) in a molar ratio of 1:3-8 in an alkaline aq. medium contg. 0.02-0.2mol [per mol of the component (a)] of NaOH (c) dissolved in water at 40-100 deg.C (reflux temp.) for 1-10hr. The reaction mixture is cooled and the pH thereof is adjusted to 4-7 with an acid, NH3 and/or an ammonium salt [e.g., (NH4)2CO3] are/is added thereto to convert the remaining free HCHO into hexamethyleneteramine. If desired, the mixture is dehydrated in a vacuum to obtain a liquid resol type phenolic resin (B) contg. no free HCHO. At least one solid phenolic resin (A) such as novolak, resol or benzyl ether type phenolic resin is blended with at least 2wt% (on a solid basis) component B.
|
