Image forming apparatus and image forming method

1. An image forming apparatus comprising:

an electrostatic-latent-image holding member;

a charging unit that charges the electrostatic-latent-image holding member;

an electrostatic-latent-image forming unit that forms an electrostatic latent image on a surface of the charged electrostatic-latent-image holding member;

a plurality of developing units that each supply a developer containing a toner to the electrostatic latent image formed on the surface of the electrostatic-latent-image holding member and form a toner image;

a transfer unit that transfers the toner image onto a recording medium to form a transfer image; and

a fixing unit that fixes the transfer image,

wherein the plurality of developing units separately contain a toner A and a toner B that satisfy relationships (1) and (2) below and have similar colors;

the toner A includes a binder resin containing a polyester about 90 mass % or more of the binder resin, the polyester contains an amorphous polyester having an alkyl side chain and a crystalline polyester, and when a glass transition temperature of the amorphous polyester is defined as Tga, the crystalline polyester has a melting temperature Tma of about (Tga+10)° C. or more and about (Tga+30)° C. or less;

the toner B contains a binder resin containing a polyester about 90 mass % or more of the binder resin, the polyester contains an amorphous polyester having an alkyl side chain and a crystalline polyester, and when a glass transition temperature of the amorphous polyester is defined as Tgb, the crystalline polyester has a melting temperature Tmb of about (Tgb+10)° C. or more and about (Tgb+30)° C. or less; and about 90 mass % of the binder resin of the toner A and about 90 mass % of the binder resin of the toner B are the same resin;

(1) relationship of Ta>Tb where Ta represents a flow tester ½ effluent temperature of the toner A and Tb represents a flow tester ½ effluent temperature of the toner B; and

(2) relationship of Aa>Ab where Aa represents an amount of an aluminum (with reference to net intensity) in the toner A measured with fluorescent X-ray and Ab represents an amount of an aluminum (with reference to net intensity) in the toner B measured with fluorescent X-ray.

2. The image forming apparatus according to claim 1 , wherein the toner A and the toner B further satisfy a relationship (3) below,

(3) relationship of Naa>Nab where Naa represents an amount of a sodium in the toner A measured with fluorescent X-ray and Nab represents an amount of a sodium in the toner B measured with fluorescent X-ray.

3. The image forming apparatus according to claim 1 , wherein the similar colors of the toner A and the toner B are selected from black, cyan, magenta, and yellow.

4. The image forming apparatus according to claim 3 , wherein the similar colors of the toner A and the toner B are black.

5. The image forming apparatus according to claim 1 , wherein the melting temperature Tma and the melting temperature Tmb are about 50° C. or more and about 120° C. or less.

6. The image forming apparatus according to claim 1 , wherein the glass transition temperature Tga and the glass transition temperature Tgb are about 45° C. or more and about 70° C. or less.

7. The image forming apparatus according to claim 1 , wherein a content of the amorphous polyester in the binder resin is about 60 mass % or more.

8. An image forming method comprising performing a plurality of developments with a toner A and a toner B that satisfy relationships (1) and (2) below and have similar colors,

wherein the toner A includes a binder resin containing a polyester about 90 mass % or more of the binder resin, the polyester contains an amorphous polyester having an alkyl side chain and a crystalline polyester, and when a glass transition temperature of the amorphous polyester is defined as Tga, the crystalline polyester has a melting temperature Tma of about (Tga+10)° C. or more and about (Tga+30)° C. or less;

the toner B contains a binder resin containing a polyester about 90 mass % or more of the binder resin, the polyester contains an amorphous polyester having an alkyl side chain and a crystalline polyester, and when a glass transition temperature of the amorphous polyester is defined as Tgb, the crystalline polyester has a melting temperature Tmb of about (Tgb+10)° C. or more and about (Tgb+30)° C. or less; and about 90 mass % of the binder resin of the toner A and about 90 mass % of the binder resin of the toner B are the same resin;

(1) relationship of Ta>Tb where Ta represents a flow tester ½ effluent temperature of the toner A and Tb represents a flow tester ½ effluent temperature of the toner B; and

(2) relationship of Aa>Ab where Aa represents an amount of an aluminum (with reference to net intensity) in the toner A measured with fluorescent X-ray and Ab represents an amount of an aluminum (with reference to net intensity) in the toner B measured with fluorescent X-ray.

9. The image forming method according to claim 8 , wherein the toner A and the toner B further satisfy a relationship (3) below,

(3) relationship of Naa>Nab where Naa represents an amount of a sodium in the toner A measured with fluorescent X-ray and Nab represents an amount of a sodium in the toner B measured with fluorescent X-ray.

10. The image forming method according to claim 8 , wherein the similar colors of the toner A and the toner B are selected from black, cyan, magenta, and yellow.

11. The image forming method according to claim 10 , wherein the similar colors of the toner A and the toner B are black.

12. The image forming method according to claim 8 , wherein the melting temperature Tma and the melting temperature Tmb are about 50° C. or more and about 120° C. or less.

13. The image forming method according to claim 8 , wherein the glass transition temperature Tga and the glass transition temperature Tgb are about 45° C. or more and about 70° C. or less.

14. The image forming method according to claim 8 , wherein a content of the amorphous polyester in the binder resin is about 60 mass % or more.