Image forming apparatus, image forming method and developing apparatus

• US 6,684,046 B2
• Filed: 07/30/2001
• Issued: 01/27/2004
• Est. Priority Date: 07/31/2000
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Hibino, Masaru
• Primary Examiner(s): GRAINGER, QUANA MASHELL
• Application Number:
  US09/916,339
• Publication Number:
  US 20020025199A1
• Time in Patent Office: 911 Days
• Field of Search: 399/267, 399/277, 399/254
• US Class Current: 399/267
• CPC Class Codes: G03G 15/09 using magnetic brush
• CPC Class Codes: G03G 15/0921 Details concerning the magnetic brush roller structure, e.g. magnet configuration
• CPC Class Codes: G03G 2215/0822 with wall or blade between agitators

Abstract

An image forming apparatus has a non-magnetic rotatable cylinder having a diameter of 10 mm to 25 mm, a plurality of magnetic field generating means which is inside the non-magnetic cylinder and fixed, a developing container which houses a two component developer containing a magnetic carrier and a non-magnetic toner and has the non-magnetic cylinder rotatably mounted at an opening portion thereof, agitating conveyer means which is inside the developing container and agitates the two component developer and conveys it to the non-magnetic cylinder, and an image bearing member arranged in opposition to the non-magnetic cylinder at intervals. The image forming apparatus is an image forming apparatus which conveys the two component developer by the rotation of the non-magnetic cylinder, and an electrostatic latent image on the image bearing member is magnetic-brush-developed.

Claims

1. An image forming apparatus, comprising:

a non-magnetic rotatable cylinder having a diameter of 10 mm to 25 mm;

a plurality of magnetic field generating means disposed inside the non-magnetic cylinder and fixed relative thereto;

a developing container which houses a two component developer containing a magnetic carrier and a non-magnetic toner, said non-magnetic cylinder being rotatably mounted at an opening portion thereof;

agitating conveyer means, disposed inside the developing container, which agitates the two component developer and conveys it to said non-magnetic cylinder; and

an image bearing member arranged in opposition to the non-magnetic cylinder at intervals,

wherein said image forming apparatus conveys the two component developer by rotation of the non-magnetic cylinder, and an electrostatic latent image on said image bearing member is magnetic-brush-developed,

wherein said magnetic field generating means comprises;

a developer layer thickness control pole for controlling a developer layer thickness on said non-magnetic cylinder of the developer supplied by the agitating conveyer means; and

a stripping off pole having the same magnetic polarity as the developer layer thickness control pole and arranged adjacent to the developer layer thickness control pole in the upper side of the gravitational direction of the developer layer thickness control pole and forming a magnetic field for stripping off the two component developer supplied for development from the non-magnetic cylinder,

wherein the peak value of the strength of the magnetic field of the developer layer thickness control pole in the direction perpendicular to an outer peripheral surface of said non-magnetic cylinder is less than 0 tesla to 0.02 tesla in absolute value greater than the peak value of the strength of the magnetic field of the stripping off pole in the direction perpendicular to the outer peripheral surface of said non-magnetic cylinder,

wherein said agitating conveyer means is installed in such a manner that the topmost surface of the developer conveyed by the agitating conveyer means is situated between the peak position of the strength of the magnetic field of the developer layer thickness control pole in the direction perpendicular to the outer peripheral surface of said non-magnetic cylinder and the peak position of the strength of the magnetic field of the stripping off pole in the direction perpendicular to the outer peripheral surface of said non-magnetic cylinder;

wherein the magnetic carrier in the two component developer has a magnetization of 3.0×

10⁴ A/m to 2.0×

10⁵ A/m in a magnetic field of 0.1 tesla,

the non-magnetic toner has a frictional electrification of −

1×

10<sup>−

2</sup> C/kg to −

4.5×

10<sup>−

2</sup> C/kg,

the non-magnetic toner has a volume average particle size of 4 μ

m to 15 μ

m,

the magnetic carrier has a weight average particle size of 20 μ

m to 70 μ

m,

the non-magnetic toner comprises non-magnetic toner particles and an external additive,

the external additive has a number average particle size of a numerical value of not more than {fraction (1/10)} of the numerical value of the weight average particle size of the non-magnetic toner particles, and

the external additive is used in 0.05 part by weight to 5 parts by weight based on 100 parts by weight of the non-magnetic toner particles.

2. The image forming apparatus according to claim 1, wherein said image bearing member and said non-magnetic cylinder move in opposing directions in a developing portion so that development is performed.

3. An image forming method, comprising:

providing a non-magnetic rotatable cylinder having a diameter of 10 mm to 25 mm;

providing a plurality of magnetic field generating means disposed inside the non-magnetic cylinder and fixed relative thereto;

providing a developing container which houses a two component developer containing a magnetic carrier and a non-magnetic toner, the non-magnetic cylinder being rotatably mounted at an opening portion thereof;

providing agitating conveyer means, disposed inside the developing container, which agitates the two component developer and conveys it to the non-magnetic cylinder;

providing an image bearing member arranged in opposition to the non-magnetic cylinder at intervals, and

rotating the non-magnetic cylinder so as to convey the two component developer and magnetic-brush-develop an electrostatic latent image on the image bearing member,

wherein providing the magnetic field generating means comprises;

providing a developer layer thickness control pole for controlling a developer layer thickness on the non-magnetic cylinder of the developer supplied by the agitating conveyer means; and

providing a stripping off pole having the same magnetic polarity as the developer layer thickness control pole and arranged adjacent to the developer layer thickness control pole in the upper side of the gravitational direction of the developer layer thickness control pole and forming the magnetic field for stripping off the two component developer supplied for development from the non-magnetic cylinder,

wherein the peak value of the strength of the magnetic field of the developer layer thickness control pole in the direction perpendicular to an outer peripheral surface of the non-magnetic cylinder is less than 0 tesla to 0.02 tesla in absolute value greater than the peak value of the strength of the magnetic field of the stripping off pole in the direction perpendicular to the outer peripheral surface of the non-magnetic cylinder,

wherein the agitating conveyer means is installed in such a manner that the topmost surface of the developer conveyed by the agitating conveyer means is situated between the peak position of the strength of the magnetic field of the developer layer thickness control pole in the direction perpendicular to the outer peripheral surface of the non-magnetic cylinder and the peak position of the strength of the magnetic field of the stripping off pole in the direction perpendicular to the outer peripheral surface of the non-magnetic cylinder;

wherein the magnetic carrier in the two component developer has a magnetization of 3.0×

10⁴ A/m to 2.0×

10⁵ A/m in a magnetic field of 0.1 tesla,

the non-magnetic toner has a frictional electrification of −

1×

10<sup>−

2</sup> C/kg to −

4.5×

10<sup>−

2</sup> C/kg,

the non-magnetic toner has a volume average particle size of 4 μ

m to 15 μ

m,

the magnetic carrier has a weight average particle size of 20 μ

m to 70 μ

m,

the non-magnetic toner comprises non-magnetic toner particles and an external additive,

the external additive has a number average particle size of a numerical value of not more than {fraction (1/10)} of the numerical value of the weight average particle size of the non-magnetic toner particles, and

the external additive is used in 0.05 part by weight to 5 parts by weight based on 100 parts by weight of the non-magnetic toner particles.

4. The image forming method according to claim 3, wherein the image bearing member and the non-magnetic cylinder move in opposing directions in a developing portion so that development is performed.

5. A developing apparatus, comprising:

a non-magnetic rotatable cylinder having a diameter of 10 mm to 25 mm;

a plurality of magnetic field generating means disposed inside the non-magnetic cylinder and fixed relative thereto;

a developing container which houses a two component developer containing a magnetic carrier and a non-magnetic toner, said non-magnetic cylinder rotatably mounted at an opening portion thereof; and

agitating conveyer means, disposed inside the developing container, which agitates the two component developer and conveys it to said non-magnetic cylinder,

wherein said developing apparatus conveys the two component developer by rotation of the non-magnetic cylinder and an electrostatic latent image on an image bearing member of an image forming apparatus is magnetic-brush-developed, the image bearing member being arranged in opposition to the non-magnetic cylinder at intervals,

wherein said magnetic field generating means comprises;

a developer layer thickness control pole for controlling a developer layer thickness on said non-magnetic cylinder of the developer supplied by the agitating conveyer means; and

a stripping off pole having the same magnetic polarity as the developer layer thickness control pole and arranged adjacent to the developer layer thickness control pole in the upper side of the gravitational direction of the developer layer thickness control pole and forming the magnetic field for stripping off the two component developer supplied for development from the non-magnetic cylinder,

wherein the peak value of the strength of the magnetic field of the developer layer thickness control pole in the direction perpendicular to an outer peripheral surface of said non-magnetic cylinder is less than 0 tesla to 0.02 tesla in absolute value greater than the peak value of the strength of the magnetic field of the stripping off pole in the direction perpendicular to the outer peripheral surface of said non-magnetic cylinder,

wherein said agitating conveyer means is installed in such a manner that the topmost surface of the developer conveyed by the agitating conveyer means is situated between the peak position of the strength of the magnetic field of the developer layer thickness control pole in the direction perpendicular to the outer peripheral surface of said non-magnetic cylinder and the peak position of the strength of the magnetic field of the stripping off pole in the direction perpendicular to the outer peripheral surface of said non-magnetic cylinder;

wherein the magnetic carrier in the two component developer has a magnetization of 3.0×

10⁴ A/m to 2.0×

10⁵ A/m in a magnetic field of 0.1 tesla,

the non-magnetic toner has a frictional electrification of −

1×

10−

2 C/kg to −

4.5×

10−

2 C/kg,

the non-magnetic toner has a volume average particle size of 4 μ

m to 15 μ

m,

the magnetic carrier has a weight average particle size of 20 μ

m to 70 μ

m,

the non-magnetic toner comprises non-magnetic toner particles and an external additive,

the external additive has a number average particle size of a numerical value of not more than {fraction (1/10)} of the numerical value of the weight average particle size of the non-magnetic toner particles, and

the external additive is used in 0.05 part by weight to 5 parts by weight based on 100 parts by weight of the non-magnetic toner particles.

6. The developing apparatus according to claim 5, wherein said image bearing member and said non-magnetic cylinder move in opposing directions in a developing portion so that development is performed.