Mita Industrial Co., Ltd.

Hideki Ohta

Masami Tsujihiro

Nobuhiro Hirano

Hiroshi Shimoyama

Toshiro Tokuno

Tatsuo Imafuku

Spheroidal toner for developing electrostatic images is composed of a binding resin as its main component in which at least carbon black and a dispersion stabilizer for the carbon black are contained, the conductivity of the toner being in the range of 5.times.10.sup.-11 to 5.times.10.sup.-9 S/cm. The conductivity of the toner is preferably within the range of 4.times.10.sup.-10 to 5.times.10.sup.-9 S/cm. It is also desirable that the dispersion stabilizer be composed of at least one selected from the group consisting of oil-soluble dyes, coupling agents, and surfactants, and that according to Wadel's practical spheroidicity, the toner be within the range of 0.95 to 1.0. A method of manufacturing the toner includes the steps of: forming grafted carbon black by prepolymerization of a polymerizable composition containing carbon black and a monomer forming a binding resin; adding a carbon black dispersion stabilizer to the prepolymerized composition; and suspending the composition in an aqueous medium and polymerizing the suspended particles in the presence of a polymerization initiator.

Method of manufacturing a toner

Toner for developing electrostatic images contains at least a colorant and a charge control dye in a binding resin which is the main component thereof, the toner having a surface dye density of less than 5.times.10.sup.-3 g/g and containing a monomer having a charge control polar group within the range of 0.01 to 5 weight percent based on the weight of the toner. The binding resin is preferably formed from at least one kind of monomer selected from a group consisting of vinyl aromatic monomers, acrylic type monomers, vinyl ester type monomers, vinyl ether type monomers, diolefin type monomers and monoolefin type monomers, and further preferably from at least one kind of monomer selected from a group consisting of styrene, ester acrylate and ester methacrylate. Also, the binding resin may be formed from at least one kind of monomer selected from a group consisting of polyester, phenol and epoxy resins. It is desirable that the colorant be used in 0.1 to 50 parts by weight for every 100 parts by weight of the polymerizable monomer. A magnetic pigment may also be used in addition to or instead of the colorant. In this case, it is desirable that the magnetic pigment be used in 1 to 200 parts by weight, and preferably in 5 to 100 parts by weight, for every 100 parts by weight of the polymerizable monomer.

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Ikoma, Japan

Hideki Ohta