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Ten parts of a styrene/acrylic acid copolymer (acid value: 250; molecular weight: 5,000) as a dispersing agent were dissolved in 80 parts of dimethyl sulfoxide, and 10 parts of a quinacridone pigment (C.I. Pigment Red 122) were suspended in the resultant solution in a flask at 25° C. under an air atmosphere. A 30% methanol solution of potassium hydroxide was then added dropwise little by little to dissolve the quinacridone pigment. After the pigment solution was stirred for 3 hours, it was quickly poured into ion-exchanged water (400 parts of ion-exchanged water per 10 parts of the pigment; 0° C.) stirred by an impellor type agitating blade (800 rpm) and cooled and temperature-maintained by means of two system dispensers (manufactured by Musashi Engineering K.K.; needle internal diameter: 0.57 mm; delivery pressure: 4.0 kgf/cm2) to obtain an aqueous dispersion of quinacridone-pigment-containing particles having an average particle diameter of 27.6 nm.

1. stirringagitating blade (800 rpm)
2. temperaturecooled
3. temperaturetemperature-maintained by means of two system dispensers (manufactured by Musashi Engineering K.K.; needle internal diameter: 0.57 mm; delivery pressure: 4.0 kgf/cm2)