Patent ID: 7851120

Claim:
A method for producing a developing agent comprising: forming a dispersion liquid of mixture particles containing at least a mixture of a polyester resin and a colorant by dispersing the mixture particles in an aqueous medium; introducing the dispersion liquid into a mechanical shearing device including a heating unit, a mechanical shearing unit, and a cooling unit; heating the dispersion liquid to a temperature not lower than the glass transition temperature of the polyester resin through the heating unit; granulating the mixture particles by subjecting the heated dispersion liquid to mechanical shearing through the mechanical shearing unit; and obtaining fine particles by cooling the dispersion liquid to a temperature lower than the glass transition temperature of the polyester resin through the cooling unit, wherein when a volume of a portion in which the dispersion liquid flows in the heating unit and the mechanical shearing unit is expressed as A cc; a volume of a portion in which the dispersion liquid flows in the cooling unit is expressed as B cc; and a flow rate of the dispersion liquid is expressed as C cc/min, the following relationship (1) is satisfied: −2<log(( A+B )/ C )<2 (1).