Toner for electrostatic image development, toner cartridge, process cartridge and image forming apparatus

1. A toner for electrostatic image development, comprising a toner particle and external additive particles adhered to the surface of the toner particle, each of the external additive particles being constituted of a plurality of irreversibly coalesced primary particles, and the shape factor SF2 of the external additive particles, represented by the following formula (1), being in the range from 110 to 160:

[(particle perimeter) 2 /(particle projected area×4×π)]×100  (1).

2. The toner for electrostatic image development of claim 1 , wherein the amount of the external additive particles adhered to the surface of the toner particle is from 5 to 300 in terms of number-average number of the particles adhered to one toner particle.

3. The toner for electrostatic image development of claim 1 , wherein the number-average particle diameter D1 of the primary particles constituting the external additive particles and the number-average long axis diameter D2 of the external additive particles satisfy the relationship represented by the following formula (2):

1.5 ≦D 2 /D 1≦15  (2).

4. The toner for electrostatic image development of claim 1 , wherein the number-average long axis diameter of the external additive particles is from 0.06 μm to 1 μm.

5. The toner for electrostatic image development of claim 1 , wherein the number-average long axis diameter of the primary particles is from 0.02 μm to 0.50 μm.

6. The toner for electrostatic image development of claim 1 , wherein each of the external additive particle is obtained by coalescing from 2 to 300 primary particles on a projected area.

7. The toner for electrostatic image development of claim 1 , wherein the glass transition temperature of the toner particle is from 35° C. to 70° C.

8. A toner cartridge that is attachable to and detachable from an image forming apparatus provided with a development unit, and accommodates the toner for electrostatic image development of claim 1 to be supplied to the development unit.

9. The toner for electrostatic image development of claim 1 , wherein the irreversibly coalesced primary particles are organic particles, or inorganic particles that are adhered to one another with a binder resin.

10. A method of forming an image, the method comprising:

forming an electrostatic latent image on the surface of a latent image holding member;

developing the electrostatic latent image with a developer comprising the toner for electrostatic image development of claim 1 , thereby forming a toner image;

transferring the toner image formed on the latent image holding member to the surface of a recording medium; and

fixing the toner image on the surface of the recording medium, wherein

the external additive particles included in the toner for electrostatic image development are constituted of a plurality of irreversibly coalesced organic primary particles.

11. A method of forming an image, the method comprising:

forming an electrostatic latent image on the surface of a latent image holding member;

developing the electrostatic latent image with a developer comprising the toner for electrostatic image development of claim 1 , thereby forming a toner image;

transferring the toner image formed on the latent image holding member to the surface of a recording medium; and

fixing the toner image on the surface of the recording medium, wherein

the external additive particles included in the toner for electrostatic image development are constituted of a plurality of irreversibly coalesced inorganic primary particles that are adhered to one another with a binder resin.

12. A method for producing the toner for electrostatic image development of claim 1 , the method comprising:

producing external additive particles, each of the external additive particles being produced by irreversibly coalescing a plurality of organic primary particles, and the shape factor SF2 of the external additive particles, represented by the following formula (1), being in the range from 110 to 160; and

mixing the external additive particles with toner particles so that the external additive particles adhere to the surface of each of the toner particles:

[(particle perimeter) 2 /(particle projected area×4×π)]×100  (1).

13. A method for producing the toner for electrostatic image development of claim 1 , the method comprising:

producing external additive particles, each of the external additive particles being produced by irreversibly coalescing a plurality of inorganic primary particles by adhering the plurality of inorganic primary particles to one another with a binder resin, and the shape factor SF2 of the external additive particles, represented by the following formula (1), being in the range from 110 to 160; and

mixing the external additive particles with toner particles so that the external additive particles adhere to the surface of each of the toner particles:

[(particle perimeter) 2 /(particle projected area×4×π)]×100  (1).

14. A toner for electrostatic image development, comprising a toner particle and external additive particles adhered to the surface of the surface of the toner particle, each of the external additive particles being constituted of a plurality of irreversibly coalesced organic primary particles or a plurality of irreversibly coalesced inorganic primary particles that are adhered to one another with a binder resin.