Recently, to achieve higher energy saving in image forming apparatuses of an electrophotographic system, there is a need for a toner for electrostatic image development (hereinafter may be referred to simply as a “toner”) that is heat-fixable at lower temperature.
For example, Patent Literature 1 discloses a toner containing a crystalline polyester resin as a fixing aid.
In such a toner, particularly good low-temperature fixability is obtained, when the compatibility between the crystalline polyester resin and a binder resin during heat fixation is high. However, one problem in this case is that heat-resistant storage stability is low because plasticization of the binder resin proceeds before heat fixation (for example, during storage of the toner). When the compatibility between the crystalline polyester resin and the binder resin is low, there arises a problem in that sufficient low-temperature fixability is not obtained.
In view of the above, Patent Literature 2, for example, proposes that the affinity between the binder resin and the crystalline polyester resin and the concentration of ester groups in the crystalline polyester resin are controlled to achieve both the low-temperature fixability and heat-resistant storage stability simultaneously.
However, in the toner described in Patent Literature 2, the binder resin is an amorphous polyester resin. Since the main skeleton of the amorphous polyester resin is similar to the main skeleton of the crystalline polyester resin, the crystalline polyester resin and the amorphous polyester resin slightly dissolve in each other during production of the toner. Due to this, there arises a problem in that sufficient heat-resistant storage stability is not obtained.
Patent Literature 3 proposes that a combination of a crystalline polyester resin and a copolymer obtained from a styrene-based monomer and a (meth)acrylate-based monomer is used as the binder resin.
However, since the types of these resins are different, the affinity between these resins is low. Therefore, there is a problem in that the crystalline polyester resin is not easily introduced into the toner particles during production of the toner, so that sufficient low-temperature fixability is not obtained.