Patent ID: 8137882

Claim:
A toner for developing electrostatic images which is obtained by melt mixing a binder resin and a coloring agent to obtain a mixture, pulverizing the mixture after cooling to obtain a powder material, treating the powder material by heating under a floating condition to obtain rounded particles and removing rough particles and fine particles from the rounded particles by classification to obtain mother particles of the toner having an average circularity of 0.930 to 0.980, wherein inorganic fine particles having a roundness of 1.00 to 1.30, an average of diameter of primary particles of 0.05 to 0.45 μm and a ratio of a standard deviation to the average of diameter of primary particles of 0.25 or smaller are added to the mother particles of the toner as an external additive, wherein said inorganic fine particles are particles of barium titanate produced in accordance with an alkoxide process, and wherein an average circularity of the mother particles is determined with respect to particles having a diameter corresponding to the diameter of a circle of 3 μm or greater by using a flow type analyzer of particle images in accordance with the following equation: average circularity=(length of circumference of a circle having the same area as the projected area of a particle)/(length of circumference of the projected image of the particle), and said roundness of the inorganic fine particles is determined by taking pictures of particles of an outside additive at a magnification of 20,000 using a scanning electron microscope and determining a length of the circumference and the area of 100 particles using software for an image analysis, and calculating the roundness in accordance with the following equation: roundness=(length of circumference) 2 /{4π×(area)}.