Patent ID: 8394565
Filing Date: 2013-03-12
Classification: G03G

Abstract:
1. A positively charged developer for development of electrostatic images, comprising positively charged toner particles and an external additive, wherein (a) the positively charged toner particles are colored resin particles having a core-shell structure, wherein the colored resin particles having the core-shell structure are obtained by forming a shell formed of an aggregated and fusion-bonded layer of the fine charge control resin particles having positively charging ability on each surface of core particles composed of aggregated and fusion-bonded particles of the fine binder resin particles and the fine colorant particles obtained by an emulsion polymerization aggregation process, and wherein the fine binder resin particles are obtained by polymerizing a monovinyl monomer used as a main component of the polymerizable monomer, (b) the positively charged toner particles have a shape factor SF-1 of 115 to 150, a shape factor SF-2 of 110 to 140 and a ratio (SF-2/SF-1) of 1.00 to 1.10, and (c) the external additive contains positively charged inorganic particles subjected to a hydrophobization treatment with an amino group-containing compound and having a small particle diameter of 5 to 25 nm in terms of a number average primary particle diameter and positively charged inorganic particles subjected to a hydrophobization treatment with an amino group-containing compound and having a large particle diameter of 30 to 300 nm in terms of a number average primary particle diameter, and (d) the charge control resin having positively charging ability is a polymer comprising a quaternary ammonium salt-containing acrylate unit represented by the following structural formula (I): wherein R