Magnetic carrier and two-component developer

• US 7,939,233 B2
• Filed: 01/21/2010
• Issued: 05/10/2011
• Est. Priority Date: 08/04/2008
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakamura, Kunihiko, Inoue, Chika, Endo, Tomoko, Fujikawa, Hiroyuki, Komatsu, Nozomu, Ishigami, Koh, Baba, Yoshinobu, Itakura, Takayuki
• Primary Examiner(s): Chapman; Mark A
• Application Number:
  US12/691,033
• Publication Number:
  US 20100119967A1
• Time in Patent Office: 474 Days
• Field of Search: 430/111.3, 430/111.35, 430/111.4
• US Class Current: 430/111.3
• CPC Class Codes: G03G 9/0821 characterised by physical parameters magnetic parameters G03G9/083
• CPC Class Codes: G03G 9/0827 characterised by their shape, e.g. degree of sphericity
• CPC Class Codes: G03G 9/1075 Structural characteristics of the carrier particles, e.g. shape or crystallographic structure
• CPC Class Codes: G03G 9/1085 with non-ferrous metal oxide, e.g. MgO-Fe2O3
• CPC Class Codes: G03G 9/113 having coatings applied thereto
• CPC Class Codes: G03G 9/1131 Coating methods; Structure of coatings
• CPC Class Codes: G03G 9/1132 Macromolecular components of coatings

Abstract

A magnetic carrier and a two-component developer are provided which have remedied blank areas, fog after leaving, carrier sticking during running, and image density variations before and after running. The magnetic carrier has magnetic carrier particles having at least porous magnetic core particles and a resin. The magnetic carrier particles satisfying the specific conditions (a), (b) and (c) where, in a reflected electron image of cross sections of the magnetic carrier particles as photographed with a scanning electron microscope, straight lines that divide a cross section of a magnetic carrier particle into 72 at intervals of 5° are drawn from a reference point of the cross section thereof toward the surface of the magnetic carrier particle; the magnetic carrier particles being contained in an amount of 60% by number or more.

Claims

1. A magnetic carrier which comprises:

magnetic carrier particles containing porous magnetic core particles which are filled in pores thereof with a first resin;

wherein the porous magnetic carrier particles filled in pores thereof with the first resin are further coated on the surfaces thereof with a second resin, which is the same or different from the first resin; and

wherein 60% by number or more of the magnetic carrier particles satisfies the following (a), (b) and (c) when cross-sectional reflected electron image of the magnetic carrier particle photographed by a SEM is divided into 72 with straight lines drawn from a reference point in a radial fashion towards the surface of the magnetic carrier particle at an interval of 5°

;

(a) the number “

A”

of the straight lines on which the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle is from 0.0 μ

m or more to 0.3 μ

m or less, is from 7 lines or more to 36 lines or less, among the 72 straight lines;

(b) the number “

B”

of the straight lines on which the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle is from 1.5 μ

m or more to 5.0 μ

m or less, is from 7 lines or more to 36 lines or less, among the 72 straight lines; and

(c) the number “

C”

of the straight lines on which the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle is from 0.0 μ

m or more to 5.0 μ

m or less, is 70 lines or more, among the 72 straight lines.

2. The magnetic carrier according to claim 1, wherein the “

A”

is from 11 lines or more to 32 lines or less, among the 72 straight lines, and the B is from 11 lines or more to 32 lines or less, among the 72 straight lines.

3. The magnetic carrier according to claim 1, wherein, where an average value of the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle along straight lines of from the 1st line to the 18th line among the 72 straight lines is set as an average value (1), an average value of the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle along straight lines of from the 19th line to the 36th line among the 72 straight lines is set as an average value (2), an average value of the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle along straight lines of from the 37th line to the 54th line among the 72 straight lines is set as an average value (3) and an average value of the distance from the surface of the magnetic carrier particle to the surface of the porous magnetic core particle along straight lines of from the 55th line to the 72nd line among the 72 straight lines is set as an average value (4), a difference between the maximum value and the minimum value in the average values (1) to (4) is 1.5 μ

m or less.

4. A two-component developer which comprises the magnetic carrier according to claim 1 and a toner.

5. The two-component developer according to claim 4, wherein the toner has an average circularity of from 0.940 or more to 1.000 or less where particles having a circle-equivalent diameter of from 1.985 μ

m or more to less than 39.69 μ

m as measured with a flow type particle image analyzer having an image processing resolution of 512×

512 pixels (0.37 μ

m×

0.37 μ

m per pixel) are divided into 800 in the range of circularities of from 0.200 to 1.000 to make analysis.

6. The two-component developer according to claim 4, wherein the toner has a circularity of 0.910 or more at cumulative 10% by number from lower circularities in circularity distribution of particles with a circle-equivalent diameter of from 1.985 μ

m or more to less than 39.69 μ

m of the toner.