| 摘要 |
PROBLEM TO BE SOLVED: To obtain a water-absorbing resin which does not discolor extracting water by setting a pH value of a phenol resin within a specific range by employing an alkylsulfonic acid having a specific number of carbon atoms as a neutralizing agent in the synthesis of the phenol resin. SOLUTION: Phenols and aldehydes in equimolar amounts or with the excess of the aldehydes over the phenols are charged into a reactor and allowed to react under heat in the presence of an alkaline catalyst such as potassium hydroxide or the like. Subsequently, an alkylsulfonic acid represented by the formula: R-SO3H (wherein R is a 1-3C lower alkyl) such as methanesulfonic acid or the like is added as a neutralizing agent to the reaction product thereby adjusting the pH to 5-9 to give a resol type phenol resin for a foam. As the phenols, there can be mentioned alkylphenols such as cresol, xylenol and the like, polyhydric phenols such as resorcinol, catechol and the like, phenol, bisphenol A and the like. As the aldehydes, there can be mentioned formalin, acetaldehyde, furfural and the like. |
