Magnetic carrier for electrophotographic developer and process for producing the same, and two-component system developer

Patent metadata

Field	Value
Publication number	US-9606467-B2
Application number	US-201013375581-A
Country	US
Kind code	B2
Filing date	Jun 4, 2010
Priority date	Jun 4, 2009
Publication date	Mar 28, 2017
Grant date	Mar 28, 2017

Abstract

The present invention relates to a magnetic carrier for an electrophotographic developer comprising spherical magnetic composite particles comprising a phenol resin as a binder and ferromagnetic iron oxide particles bonded to each other through the phenol resin, wherein the spherical magnetic composite particles have a ten-point mean roughness Rz of 0.3 to 2.0 μm. The magnetic carrier for an electrophotographic developer according to the present invention exhibits an excellent durability against peeling-off and abrasion of coating resins formed thereon and a high stability to mechanical stress exerted onto the carrier, is free from occurrence of spent toner, can be stably held over a long period of time without occurrence of fogging and unevenness in density of toner images, and can keep high-quality images with an excellent gradation for a long period of time.

First claim

The invention claimed is:

1. A magnetic carrier for an electrophotographic developer comprising spherical magnetic composite particles comprising a phenol resin as a binder and ferromagnetic iron oxide particles bonded to each other through the phenol resin, and further comprising on the spherical magnet particles a coating layer comprising at least one resin selected from the group consisting of a melamine resin, a silicone-based resin, a fluororesin, an acrylic resin and a styrene-acrylic resin,
wherein the spherical magnetic composite particles before coating with the coating layer have a ten-point mean roughness Rz of 0.3 to 2.0 μm,
a total content of the ferromagnetic iron oxide particles in the spherical magnetic composite particles is 80 to 99% by weight,
the ferromagnetic iron oxide particles are constituted from ferromagnetic iron oxide particles (a) and ferromagnetic iron oxide particles (b) which are different in average particle diameter from each other,
a ratio of an average particle diameter (ra) of the ferromagnetic iron oxide particles (a) having a larger average particle diameter to an average particle diameter (rb) of the ferromagnetic iron oxide particles (b) having a smaller average particle diameter (ra/rb) is more than 1,
a content of the ferromagnetic iron oxide particles (a) is 1 to 50% by weight based on a total amount of the ferromagnetic iron oxide particles (a) and the ferromagnetic iron oxide particles (b), and
the ferromagnetic iron oxide particles (a) and the ferromagnetic iron oxide particles (b) respectively have any shape selected from the group consisting of a spherical shape, a hexahedral shape, an octahedral shape, a polyhedral shape and an amorphous shape.

2. A magnetic carrier for an electrophotographic developer according to claim 1 , wherein a maximum height Ry as measured on a surface of the respective spherical magnetic composite particles is in the range of 0.7 to 2.5 μm.

3. A magnetic carrier for an electrophotographic developer according to claim 1 , wherein an arithmetic mean roughness Ra as measured on a surface of the respective spherical magnetic composite particles is in the range of 0.1 to 0.9 μm, and a mean spacing Sm of profile irregularities thereon is in the range of 0.6 to 6.0 μm.

4. A magnetic carrier for an electrophotographic developer according to claim 1 , wherein the magnetic carrier for an electrophotographic developer has an electric resistance value R 100 of 1×10 8 Ω·cm to 1×10 16 Ωcm as measured when applying a voltage of 100 V thereto, and an electric resistance value R 300 of the magnetic carrier as measured when applying a voltage of 300 V thereto is controlled such that a ratio of R 300 /R 100 satisfies the formula: 0.1≦R 300 /R 100 ≦1.

5. A magnetic carrier for an electrophotographic developer according to claim 1 , wherein the spherical magnetic composite particles further comprise dielectric particles having a relative dielectric constant of not less than 50.

6. A magnetic carrier for an electrophotographic developer according to claim 5 , wherein the dielectric particles are formed of at least one material selected from the group consisting of titanium oxide, a titanate and a zirconate.

7. A magnetic carrier for an electrophotographic developer according to claim 5 , wherein a total content of the dielectric particles and the ferromagnetic iron oxide particles in the spherical magnetic composite particles is 80 to 99% by weight; and a content of the dielectric particles in the spherical magnetic composite particles is 1 to 50% by weight based on a total amount of the ferromagnetic iron oxide particles and the dielectric particles.

8. A magnetic carrier for an electrophotographic developer according to claim 5 , wherein the ferromagnetic iron oxide particles consist of one kind of ferromagnetic iron oxide particles (b′) solely; a ratio of an average particle diameter (rc) of the dielectric particles to an average particle diameter (rb′) of the ferromagnetic iron oxide particles (b′) (rc/rb′) is more than 1; and the ferromagnetic iron oxide particles (b′) have any particle shape selected from the group consisting of a spherical shape, a hexahedral shape, an octahedral shape, a polyhedral shape and an amorphous shape.

9. A magnetic carrier for an electrophotographic developer according to claim 5 , wherein the ferromagnetic iron oxide particles are constituted from ferromagnetic iron oxide particles (a″) and ferromagnetic iron oxide particles (b″) which are different in average particle diameter from each other; a ratio of an average particle diameter (ra″) of the ferromagnetic iron oxide particles (a″) to an average particle diameter (rb″) of the ferromagnetic iron oxide particles (b″) (ra″/rb″) is more than 1; a ratio of the average particle diameter (rc) of the dielectric particles to the average particle diameter (rb″) of the ferromagnetic iron oxide particles (b″) (rc/rb″) is more than 1; a content of the ferromagnetic iron oxide particles (a″) is less than 49% by weight based on a total amount of the ferromagnetic iron oxide particles (a″), the ferromagnetic iron oxide particles (b″) and the dielectric particles; and the ferromagnetic iron oxide particles (a″) and the ferromagnetic iron oxide particles (b″) respectively have any shape selected from the group consisting of a spherical shape, a hexahedral shape, an octahedral shape, a polyhedral shape and an amorphous shape.

10. A process for producing the magnetic carrier for an electrophotographic developer as defined in claim 1 , said process comprising the step of mixing and reacting mixed particles comprising two kinds of ferromagnetic iron oxide particles which are different in average particle diameter from each other, with a phenol compound and an aldehyde compound in an aqueous medium while stirring to obtain a cured product, thereby producing spherical magnetic composite particles comprising the ferromagnetic iron oxide particles and a phenol resin, wherein the spherical magnetic composite particles are provided, on a surface thereof, with fine irregularities owing to a shape of the ferromagnetic iron oxide particles having a larger average particle diameter.

11. A process for producing the magnetic carrier for an electrophotographic developer as defined in claim 5 , said process comprising the step of reacting ferromagnetic iron oxide particles and dielectric particles having a relative dielectric constant of not less than 50, with a phenol compound and an aldehyde compound in an aqueous medium to obtain a cured product, thereby producing spherical magnetic composite particles comprising the ferromagnetic iron oxide particles, the dielectric particles and a phenol resin, wherein the spherical magnetic composite particles are provided, on a surface thereof, with fine irregularities owing to a shape of the dielectric particles.

12. A process for producing the magnetic carrier for an electrophotographic developer as defined in claim 5 , said process comprising the step of reacting two kinds of ferromagnetic iron oxide particles which are different in average particle diameter from each other and dielectric particles having a relative dielectric constant of not less than 50, with a phenol compound and an aldehyde compound in an aqueous medium to obtain a cured product, thereby producing spherical magnetic composite particles comprising the ferromagnetic iron oxide particles, the dielectric particles and a phenol resin, wherein the spherical magnetic composite particles are provided, on a surface thereof, with fine irregularities owing to shapes of the ferromagnetic iron oxide particles having a larger average particle diameter and the dielectric particles.

Assignees

• Iwami Katsuji
• Harada Shigenori
• Kurita Eiichi
• Kinoshita Kaori
• Toda Kogyo Corp

Inventors

• Iwami Katsuji
• Harada Shigenori
• Kurita Eiichi
• Kinoshita Kaori

Classifications

• G03G9/1135

  obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds · CPC title

• G03G9/1133 Primary

  obtained by reactions only involving carbon-to-carbon unsaturated bonds · CPC title

• G03G9/1136

  containing silicon atoms · CPC title

• G03G9/1134

  containing fluorine atoms · CPC title

• G03G9/107 Primary

  having magnetic components · CPC title