Two-component developer, developer cartridge, process cartridge, and image forming apparatus
A two-component developer includes: a toner; a carrier having a surface energy of from about 23 dyne/cm to about 37 dyne/cm; and an external additive having a shape factor SF1 of from about 130 to about 150 and a number-average particle diameter of from about 80 nm to about 1 μm; and an existence ratio A of the external additive on a surface of the toner and an existence ratio B of the external additive on a surface of the carrier satisfying the relationship of the following Expression 1: 0.04≦B/A≦0.4.
1. A two-component developer comprising:
a toner;
a carrier having a surface energy of from about 23 dyne/cm to about 37 dyne/cm; and
an external additive having a shape factor SF1 of from about 130 to about 150 and a number-average particle diameter of from about 80 nm to about 1 μm;
wherein:
an existence ratio A of the external additive on a surface of the toner and an existence ratio B of the external additive on a surface of the carrier satisfying the relationship of the following Expression 1:
0.04 ≦B/A≦ 0.4; Expression 1:
the carrier comprises a core and a coating layer thereon; and
the coating layer comprises a resin selected from the group consisting of a perfluorohexylethyl methacrylate/methyl methacrylate copolymer, a perfluorobutylethyl methacrylate/methyl methacrylate copolymer, isobornyl methacrylate, adamantane methacrylate, and alkoxysilyl methacrylate.
2. The two-component developer according to claim 1 , wherein the external additive comprises a hydrophobized surface layer.
3. The two-component developer according to claim 1 , wherein the toner further comprises a binder resin, a colorant, and a release agent.
4. The two-component developer according to claim 3 , wherein the binder resin comprises a styrene-acrylic resin having a weight-average molecular weight Mw of from about 20,000 to about 100,000.
5. The two-component developer according to claim 3 , wherein the binder resin comprises a polyester resin having a weight-average molecular weight Mw of from about 5,000 to about 40,000.
6. The two-component developer according to claim 3 , wherein the binder resin has a glass transition temperature of from about 40° C. to about 80° C.
7. The two-component developer according to claim 3 , wherein the release agent has a melting point of from about 50° C. to about 110° C.
8. The two-component developer according to claim 3 , wherein the content of the release agent in the toner is from about 1% by weight to about 15% by weight with respect to the toner.
9. The two-component developer according to claim 1 , wherein the toner has a volume-average particle diameter of from about 2 μm to about 10 μm.
10. The two-component developer according to claim 1 , wherein the toner has a shape factor SF1 of from about 120 to about 140.
11. The two-component developer according to claim 1 , wherein the carrier has a volume resistivity of from about 1×105Ω·cm to about 1×1015Ω·cm.
12. A developer cartridge accommodating the two-component developer according to claim 1 .
13. A process cartridge comprising:
the two-component developer according to claim 1 ; and
a developer holder which holds and transfers the two-component developer.
14. An image forming apparatus comprising:
an image holder;
a charging device that charges a surface of the image holder;
a latent image forming device that forms an electrostatic latent image on the charged surface of the image holder;
a developing device that holds the two-component developer according to claim 1 and develops the electrostatic latent image using the toner included in the two-component developer to form a toner image; and
a transfer device that transfers the toner image formed on the surface of the image holder to a transfer medium.