Toner for developing electrostatic images, process for preparing toner for developing electrostatic images, developer for developing electrostatic images and images forming method

1. A toner for developing electrostatic images, comprising a colorant and a binder resin, said toner containing a reactive polymer which cross-links when heated to a temperature that is higher than 100° C., and having a shape factor SF1 of 110 to 140 represented by:

SF 1 = ML 2 /(4 A/ π×100)

wherein, ML represents a maximum length (μm) of the toner, and A represents a projected area (μm 2 ) of the toner;

wherein the toner has a layered-structure containing at least a shell layer provided so as to cover the surface thereof, and a core layer provided on an inner side of the shell layer; and

the binder resin is contained in the core layer and the shell layer, and a glass transition temperature of a binder resin contained in the core layer is lower than a glass transition temperature of a binder resin contained in the shell layer.

2. A toner for developing electrostatic images according to claim 1 , wherein the toner is prepared at least via an aggregating step of aggregating particles containing at least particles of the binder resin in a dispersion with the particles dispersed therein, to obtain an aggregation of the particles, and a coalescing step of coalescing the aggregation of the particles by heating.

3. A toner for developing electrostatic images according to claim 1 , wherein the reactive polymer contains one or more kinds of cyclic reactive groups which cross-link at a temperature that is higher than 100° C.

4. A toner for developing electrostatic images according to claim 3 , wherein the cyclic reactive group is any one of an epoxy group, an aziridinyl group and an oxazoline group.

5. A toner for developing electrostatic images according to claim 3 , wherein the reactive polymer is a vinyl type resin containing one or more kinds of cyclic reactive groups.

6. A toner for developing electrostatic images according to claim 3 , the toner containing a compound having a carboxyl group.

7. A toner for developing electrostatic images according to claim 6 , wherein the carboxyl group is a dicarboxylic acid.

8. A toner for developing electrostatic images according to claim 1 , wherein the binder resin is the reactive polymer.

9. A toner for developing electrostatic images according to claim 1 , having a surface index value represented by the following formula (2) of 2.0 or less:

(Surface index value)=(measured specific surface area value)/(calculated specific surface area value)  Formula (2)

wherein, in the formula (2), the calculated specific surface area value is represented by 6Σ(n×R 2 )/{ρ×Σ(n×R 3 )}; and, in the above formula representing the specific surface area, n represents a number of particles in a channel (number/1 channel) in the coulter counter, R represents a channel particle diameter (μm) in a coulter counter, Σ represents a toner density (g/μm3), a dividing number of the number of channels is 16, and a size of division is an interval of 0.1 at a log scale.

10. A toner for developing electrostatic images according to claim 1 , wherein a glass transition temperature of the binder resin is in a range of 45° C. to 75° C.

11. A toner for developing electrostatic images according to claim 1 , wherein the reactive polymer is contained at least in the core layer.

12. A toner for developing electrostatic images according to claim 1 , wherein a glass transition temperature of a binder resin contained in the core layer is in a range of 50° C. to 75° C.

13. A developer for developing electrostatic images, comprising a carrier and a toner for developing electrostatic images, said toner comprising a colorant, a binder resin, and a reactive polymer which cross-links when heated to a temperature that is higher than 100° C., and the toner having a shape factor SF1 of 110 to 140 represented by:

SF 1 = ML 2 /(4 A /Σ×100)

wherein, ML represents a maximum length (μm) of the toner, and A represents a projected area (μm 2 ) of the toner;

wherein the toner has a layered-structure containing at least a shell layer provided so as to cover the surface thereof, and a core layer provided on an inner side of the shell layer; and

the binder resin is contained in the core layer and the shell layer, and a glass transition temperature of a binder resin contained in the core layer is lower than a glass transition temperature of a binder resin contained in the shell layer.