Specifically, 53.0 g (0.300 mol) of benzyl methacrylate, 11.7 g (0.090 mol) of 2-hydroxyethyl methacrylate, 7.92 g (0.110 mol) of methacrylic acid, and 50 g of propylene glycol monomethylether acetate were placed in a 300-ml four-necked flask and stirred at 80° C. under a nitrogen atmosphere. A solution prepared by dissolving 0.3118 g (1.91×10−3 mol) of a thermal polymerization initiator (2,2′-azobisisobutylnitrile (AIBN) in 10 g of propylene glycol monomethylether acetate) was added thereto, and stirred for 6 hours. Subsequently, the supply of nitrogen was stopped, and a solution of 0.22 g (1.5×10−3 mol) of p-methoxyphenol dissolved in 15 g of propylene glycol monomethylether acetate was added thereto, and the temperature was elevated to 95° C. and stirred for 2 hours. A binder (benzyl methacrylate/methacrylic acid/2-hydroxyethyl methacrylate copolymer) was thus obtained. The resulting binder had an acid value of 30 mgKOH/g and a weight average molecular weight of 15,000.
