Patent ID: 7772331

Claim:
A method of producing a low viscosity liquid phenol-modified aromatic hydrocarbon formaldehyde resin, including subjecting an aromatic hydrocarbon formaldehyde resin (A) and a phenol (B), in which a weight ratio between the aromatic hydrocarbon formaldehyde resin (A): the phenol resin (B) is 90:10 to 70:30, to condensation reaction in the presence of an acid catalyst to obtain a low viscosity liquid phenol-modified aromatic hydrocarbon formaldehyde resin (C) having a viscosity at 25° C. of 1,500 to 10,000 mPa·S, wherein the acid catalyst comprises para-toluene sulfonic acid; wherein the aromatic hydrocarbon formaldehyde resin (A) comprises a xylene formaldehyde resin or a mesitylene formaldehyde resin and the viscosity of the aromatic hydrocarbon formaldehyde resin (A) at 25° C. is 30 to 500 mPa·S; and wherein the acid catalyst is added in an amount of 5 to 50 ppm with respect to a total amount of the aromatic hydrocarbon formaldehyde resin (A) and the phenol (B), the method also comprising: terminating, when a reaction mixture has a viscosity at 25° C. of 400 to 1000 mPa·S, the condensation reaction by adding an inorganic basic compound and/or a tertiary amine compound having a boiling point of 300° C. or more; distilling and removing the phenol (B) unreacted and a low boiling component after termination of the condensation reaction, such that the low viscosity liquid phenol-modified aromatic hydrocarbon formaldehyde resin (C) comprises the unreacted phenol (B) in a content of 0.5% by weight or less; and reusing unreacted phenol (B) and the low boiling component, distilled and removed after termination of the condensation reaction, as a part of a reaction raw material.