Toner for electrostatically charged image development, manufacturing method thereof, image forming method, and image forming apparatus using the image forming method

1. A toner for electrostatically charged image development comprising at least a binder resin, a colorant and a releasing agent, wherein the releasing agent satisfies the following equations (1) and (2):

0.1 ≦η*a ≦1.0  (1)

1.1 ≦η*b/η*a ≦3.5  (2)

wherein

η*a represents a complex viscosity (Pa·s) determined from a first dynamic viscoelasticity measurement at a measuring frequency of the releasing agent of 6.28 rad/s,

η*b represents a complex viscosity (Pa·s) determined from a second dynamic viscoelasticity measurement at a measuring frequency of the releasing agent of 62.8 rad/s,

each of the first and second dynamic viscoelasticities is measured in a temperature range from a temperature that is 15° C. lower than the melting point of the releasing agent to a temperature that is 15° C. higher than the melting point of the releasing agent; and

the shapes of releasing agent particles observed under a transmission electron microscope comprise both rod-like and massive shapes, and the average diameter of the rod-like shapes and the massive shapes is within a range of about 200 to about 1500 nm.

2. The toner for electrostatically charged image development of claim 1 , wherein the releasing agent contains polyalkylene.

3. The toner for electrostatically charged image development of claim 2 , wherein each of the first and second dynamic viscoelasticities is measured at 85° C.

4. The toner for electrostatically charged image development of claim 2 , wherein a maximum endothermic determined by differential thermal analysis of the polyalkylene is within a range of 85 to 95° C., a ratio of a sum of endothermic amounts in a temperature range of not higher than 85° C., which sum is calculated from a partial area obtained from an endothermic curve determined by the differential thermal analysis of the polyalkylene, to a sum of endothermic amounts, which is calculated from a total area obtained from the endothermic curve, is within a range of about 5 to about 15%, and the content of the polyalkylene determined based on a maximum endothermic intensity is within a range of about 6 to about 9% by weight.

5. The toner for electrostatically charged image development of claim 1 , wherein the releasing agent has a viscosity ηs140 at 140° C., determined using an E-type viscometer comprising a cone plate with a cone angle of 1.34°, in a range of about 1.5 to about 5.0 mPa·s.

6. The toner for electrostatically charged image development of claim 1 , wherein an area proportion of the releasing agent having the massive shape observed under a transmission electron microscope is in a range of about 10 to about 30%.

7. The toner for electrostatically charged image development of claim 1 , wherein the toner has a coating layer on a surface thereof, and the thickness of the coating layer determined by a transmission electron microscope is within a range of about 0.1 to about 0.3 μm, and the quantity of the releasing agent on the surface of the toner for electrostatically charged image development determined by X-ray photoelectron spectroscopy is within a range of about 11 to about 30 atm %.

8. A method for producing a toner for electrostatically charged image development, the method comprising:

mixing a dispersion liquid of resin fine particles comprising first resin fine particles having a volume average particle diameter of not more than 1 μm, a dispersion liquid of a colorant, and a dispersion liquid of a releasing agent to prepare a mixed solution; adding a coagulant into the mixed solution to form core aggregates;

adhering second resin fine particles on the surface of the core aggregates to form core/shell aggregates; and

heating the core/shell aggregates to a temperature not lower than the glass transition temperature of the first and/or second resin fine particles to fuse and integrate the core/shell aggregates, wherein the releasing agent satisfies the following equations (1) and (2):

0.1 ≦η*a ≦1.0  (1)

1.1 ≦η*b/η*a ≦3.5  (2)

wherein

η*a represents a complex viscosity (Pa·s) determined from a first dynamic viscoelasticity measurement at a measuring frequency of the releasing agent of 6.28 rad/s,

η*b represents a complex viscosity (Pa·s) determined from a second dynamic viscoelasticity measurement at a measuring frequency of the releasing agent of 62.8 rad/s,

each of the first and second dynamic viscoelasticities is measured in a temperature range from a temperature that is 15° C. lower than the melting point of the releasing agent to a temperature that is 15° C. higher than the melting point of the releasing agent, and

the shapes of releasing agent particles observed under a transmission electron microscope comprise both rod-like and massive shapes, and the average diameter of the rod-like shapes and the massive shapes is within a range of about 200 to about 1500 nm.

9. The method for producing a toner for electrostatically charged image development of claim 8 , wherein the releasing agent contains polyalkylene.

10. The method for producing a toner for electrostatically charged image development of claim 8 , wherein at least a polymer of a metal salt is used as the coagulant.

11. The method for producing a toner for electrostatically charged image development of claim 8 , wherein the mixed solution further includes a dispersion liquid in which inorganic fine particles are dispersed.

12. An image forming method comprising:

uniformly charging a surface of an image holding member;

forming an electrostatic latent image on the surface of the uniformly charged image holding member based on image information;

developing the electrostatic latent image with a developer containing at least a toner to obtain a toner image; and

fusing the toner image on a surface of a recording medium by oilless fusing to form an image on the recording medium;

wherein:

the toner comprising at least a binder resin, a colorant and a releasing agent, and the releasing agent satisfies the following equations (1) and (2):

0.1 ≦η*a ≦1.0  (1)

1.1 ≦η*b/η*a ≦3.5  (2)

wherein

η*a represents a complex viscosity (Pa·s) determined from a first dynamic viscoelasticity measurement at a measuring frequency of the releasing agent of 6.28 rad/s,

η*b represents a complex viscosity (Pa·s) determined from a second dynamic viscoelasticity measurement at a measuring frequency of the releasing agent of 62.8 rad/s,

each of the first and second dynamic viscoelasticities is measured in a temperature range from a temperature that is 15° C. lower than the melting point of the releasing agent to a temperature that is 15° C. higher than the melting point of the releasing agent, and

the shapes of releasing agent particles observed under a transmission electron microscope comprise both rod-like and massive shapes, and the average diameter of the rod-like shapes and the massive shapes is within a range of about 200 to about 1500 nm.