| 摘要 |
PROBLEM TO BE SOLVED: To control the molecular weight of a polyurethane resin in a proper range to suppress variations in molecular weight between products.SOLUTION: An urethane prepolymer having a molecular weight Mu, which contains an acidic group and an isocyanate group, is synthesized, and the urethane prepolymer is mixed with an aqueous solvent containing a basic substance to prepare a mixture, and mixture temperature T thereof is measured. The mixture is then stirred to disperse the urethane prepolymer into the aqueous solvent, whereby a water dispersion prepared. A chain elongation agent is added to the water dispersion to increase the molecular weight of the urethane prepolymer so that molecular weight Mw becomes a target value, whereby a polyurethane resin is produced. At that time, the total time t of the mixing treatment time tm from the start of the preparation of the mixture to the end thereof and the dispersion treatment time td from the start of the preparation of the water dispersion to the end thereof is determined based on the target value for the molecular weight Mw of the polyurethane resin, the mixture temperature T and the molecular weight Mu of the urethane prepolymer. |
