Process for producing toner for developing electrostatic image and apparatus system therefor

A process for producing a toner for developing an electrostatic latent image, comprising the step of;

• melt-kneading a composition comprising at least a binder resin and a coloring agent, cooling the kneaded product to solidification, and pulverizing the solidified product to produce a pulverized feed material;
• feeding the pulverized feed material to a first classifying means to classify the feed material into coarse powder and fine powder;
• feeding the classified coarse powder to a pulverizing means and thereafter feeding back the pulverized product to the first classifying means;
• introducing the classified fine powder to a second classifying means having a multi-division classification zone divided into at least three sections, to which the particles of the fine powder are allowed to fall along curved lines by the Coanda effect, where a coarse powder portion mainly comprised of particles having a particle size above a prescribed range is dividedly collected in a first divided section, a median powder portion mainly comprised of particles having a particle size within the prescribed range is dividedly collected in a second divided section, and a fine powder portion mainly comprised of particles having a particle size below the prescribed range is dividedly collected in a third divided section;
• and
• feeding back said classified coarse powder collected in the first divided section, to one of said pulverizing means and said first classifying means;
• wherein said median powder collected in the second divided section has a volume average particle diameter of from 4 .mu.m to 10 .mu.m and a coefficient of variation of number distribution, represented by A, satisfying the following condition:
• 20.ltoreq.A.ltoreq.45
• wherein A represents the coefficient of variation (S/D.sub.1).times.100 in the number distribution of the median powder, wherein S represents the standard deviation in the number distribution of the median powder and D.sub.1 represents the number average particle diameter (.mu.m) of the median powder;
• and
• when the weight per unit time of the pulverized feed material fed to the first classifying means is represented by B, the weight per unit time of the fine powder introduced to the second classifying means is represented by C, the weight per unit time of the coarse powder collected in the first divided section and fed back to the pulverizing means or the first classifying means is represented by G, the weight per unit time of the median powder collected in the second divided section is represented by M and the weight per unit time of the fine powder collected in the third divided section is represented by F, the weights B, C, F, G and M are controlled to satisfy the following expressions:
• 0.3.ltoreq.weight B/weight C.ltoreq.0.8,
• 0.2.ltoreq.weight G/weight C.ltoreq.0.7, and
• 0.8.ltoreq.weight B/(weight F+weight M).ltoreq.1.2.