Electrophotographic toner, method for producing the same, electrophotographic developer, method for producing the developer, and image forming method

1. An electrophotographic toner, comprising a binder resin containing a coloring agent, a crystalline resin and an amorphous resin, wherein the crystalline resin has two or more peaks in weight-average molecular weight as determined by gel permeation chromatography, one of the peaks has a weight-average molecular weight in the range of 15,000 to 40,000, and another peak has a weight-average molecular weight in the range of 2,000 to 10,000.

2. The electrophotographic toner according to claim 1 , wherein the crystalline resin contains a high-molecular weight resin having a peak in the weight-average molecular weight range of 15,000 to 40,000, a low-molecular weight resin having a peak in the weight-average molecular weight range of 2,000 to 10,000, and the high- and low-molecular weight resins are prepared respectively from different monomers.

3. The electrophotographic toner according to claim 1 , wherein the crystalline resin is an aliphatic polyester.

4. The electrophotographic toner according to claim 3 , wherein the ester concentration of the crystalline polyester represented by the following Formula 1 is 0.01 or more and 0.1 or less:

M=K/A   (Formula 1)

wherein in Formula 1, M represents an ester concentration, K represent the number of ester groups in the resin, and A represents the number of atoms constituting the polymer chain in the resin.

5. The electrophotographic toner according to claim 1 , wherein the amorphous resin is a polyester.

6. The electrophotographic toner of according to claim 5 , wherein the amorphous polyester resin has a weight-average molecular weight Mw of from 5,000 to 40,000 and a number-average molecular weight Mn of from 2,000 to 10,000.

7. The electrophotographic toner of according to claim 5 , wherein the amorphous polyester resin has a glass transition temperature of 30° C. to 80° C.

8. The electrophotographic toner according to claim 1 , wherein the content of the amorphous resin is a resin polymerized by a monomer having a vinyl group.

9. The electrophotographic toner according to claim 8 , wherein the resin polymerized by a monomer having a vinyl group has a weight average molecular weight Mw of from 20,000 to 100,000 and a number average molecular weight Mn of from 2,000 to 30,000.

10. The electrophotographic toner according to claim 1 , wherein the content of the crystalline resin is 5% or more and 35% or less by weight with respect to the total amount of the binder resin.

11. The electrophotographic toner according to claim 1 , wherein the toner is prepared by an aggregation process in which aggregated particles containing crystalline particles and amorphous particles are formed in a dispersion containing the crystalline particles and the amorphous particles.

12. An electrophotographic developer employing a carrier containing a magnetic body and the electrophotographic toner according to claim 1 .

13. The electrophotographic developer according to claim 12 , wherein the carrier is coated with a resin, the amount of coated resin being 0.1 to 10 parts by weight relative to 100 parts of the magnetic body.

14. An image-forming process employing the electrophotographic toner of claim 1 , wherein the process comprises:

a latent image forming step of forming an electrostatic latent image on the surface of a latent image-holding member,

a developing step of forming a toner image by developing the electrostatic latent image formed on the surface of the latent image carrier with a developer containing a toner,

a transferring process of transferring the toner image formed on the surface of the latent image carrier onto the surface of an image-receiving member, and

a fixing step of thermally fusing the toner image transferred on the surface of the image-receiving member,

wherein the toner is an electrophotographic toner according to claim 1 .