The electrostatic image developing toner is used in image forming to visualize an electrostatic image in a printer, a copier, a facsimile and the like. To take forming of an image by electrophotographic system as an example, in the first place an electrostatic latent image is formed on a photosensitive drum, in the next place the latent image is developed with a toner and the developed image is transferred to a transfer-receiving paper, and the transferred image is fixed with heat or the like, thus an image is formed. The toner used at that time as the electrostatic image developing toner is generally a toner obtained by what is called a melt-kneading pulverizing method of dry blending a charge controlling agent, a release agent, and a magnetic substance, according to necessity, with a binder resin and a colorant, melt-kneading the mixture by an extruder or the like, in the next place pulverizing and classifying the melt-kneaded product to thereby obtain toner particles, and attaching solid particles such as silica as an external additive on the surfaces of the particles for the purpose of imparting various performances such as a flowing property and the like.
In recent years, heightening of a highly precise image quality is required in image formation such as copiers and printers, and for responding such a requirement, it is necessary that the average particle size of toner particles is 3 μm to 8 μm or so and particle size distribution is narrow. However, it is difficult to control particle size and particle size distribution of toner particles in the melt-kneading pulverizing method, and when it is tried to obtain toner particles having an average particle size of 3 μm to 8 μm, high energy is necessary and, further, when the desired particle size is not obtained, there arises a problem such that a process of classification is further necessary.
As a means for solving such a problem in a melt-kneading pulverization method, manufacturing by a polymerization method such as a suspension polymerization method, an emulsification polymerization aggregation method, and a dissolution suspension method is proposed in place of the melt-kneading pulverizing method.
The suspension polymerization method is a method of manufacturing toner particles by suspension dispersing a composition containing a polymerizable monomer, a polymerization initiator and a colorant as the components in an aqueous medium and then polymerizing.
The emulsification polymerization aggregation method is a method of manufacturing toner particles by emulsifying a polymerizable monomer in an aqueous medium containing a polymerization initiator and an emulsifying agent, polymerizing the polymerizable monomer under stirring to obtain polymer primary particles, adding a colorant and, if necessary, a charge controlling agent or the like thereto to aggregate the polymer primary particles, and aging the obtained aggregated particles.
The dissolution suspension method is a method of manufacturing toner particles by dissolving a binder resin in an organic solvent, adding and dispersing a colorant and the like to obtain a solution phase, dispersing the solution phase with mechanical shearing force in an aqueous phase containing a dispersant and the like to form droplets, and removing the organic solvent from the droplets.
According to these polymerization methods, particle size of toner particles can be easily controlled and small size particles can be obtained in narrow particle size distribution, and so toner particles capable of forming high precise image quality can be obtained.
In particular, since the emulsification polymerization aggregation method is a method of manufacturing toner particles by aggregating polymer primary particles obtained by emulsification polymerization with emulsified particles of a colorant or the like, control of the particle size of primary particles is easier as compared with other polymerization method, and the control of the form of toner particles is also feasible. Further, since it is possible to control the structure of the toner more easily by aggregation control, realization of multifunctional performances including low temperature fixation is feasible.
As characteristics affecting image formation, improvement of charging characteristics has also been eagerly examined.
It is necessary to decide the quantity of charge in conformity with the designs of printers, copiers and the like.
There are minus charge and plus charge in the charge, and either of these is adjusted by a charge controlling agent and a binder resin, and it has been pointed out that there are various problems in the control of the quantity of charge of a positively charging toner as compared with that of a negatively charging toner.
Controlling a charging property has been conventionally performed by selection of a charge controlling agent such as a nigrosine dye, a quaternary ammonium salt, a triphenylmethane, or the like, but when such a positively charging toner is used in a two-component developer, the charge controlling agent is spent on the surface of a magnetic carrier during repeating use for a long term, and frictional charging performance of the carrier reduces, which leads to the reduction of image quality, such as the occurrence of what is called fog, PC contamination, staining, generation of an after image (a ghost), blurring (solid-following up), and cleaning performance.
In addition, a nigrosine dye is a dark brown dye and so it can be used only in a black toner, and a quaternary ammonium salt is colorless but it is inferior in a dispersing property in a binder resin, and a charging property is also inferior. If dispersion in a toner is not uniform, fogging increases and the toner causes spattering, and so a uniform dispersing property of a charge controlling agent is the more required in recent years in particle size miniaturization of a toner for aiming at achieving highly precise image quality.
Accordingly, in recent years, studies have been carried out such that a resin having charge controlling performance is used as a charge controlling agent, or various kinds of functional groups are introduced into a binder resin to thereby improve a charging property by making use of the characteristics thereof. For example, monomers containing an amino group or an amide bond are generally used.
When such monomers are used, it is necessary to use an azo-based polymerization initiator in the polymerization of a resin, but it is pointed out that azo-based polymerization initiators have a tendency to be inferior to other polymerization initiators, e.g., peroxide-based polymerization initiator, in the points of environmental stability and a color developing property of the toner. Further, when ordinary azo-based polymerization initiators are used, a toxic substance having a cyano group is generated as a by-product and also an odor deriving from an amino group occurs.
Further, in addition to these problems, there also remains some fear due to poor dispersion of pigments such that color development unevenness is generated, initial rising of charge is insufficient, and the problems of increase in fog and spattering of toner are not completely solved.
For overcoming the concerns as described above, as a means by the improvement of a binder resin, resins for positively charging toners containing one or more components of an acrylic ester component and methacrylic ester component not having an amino group in a resin have been proposed (Patent Documents 1 to 5).