New patent application published for: DEVELOPING DEVICE AND IMAGE FORMING APPARATUS

DEVELOPING DEVICE AND IMAGE FORMING APPARATUS

Claims

1. A developing device comprising a developing roller having a developer carrying surface for carrying a two-component developer containing toner particles and carrier particles, so as to supply the toner particles in the two-component developer carried on the developer carrying surface to an electrostatic latent image at a development position, thereby developing the electrostatic latent image, wherein the developing roller includes a shaft extending in a predetermined direction, a magnet fixed to an outer peripheral surface of the shaft, so as to have a plurality of magnetic poles in a circumferential direction of the shaft, and a development sleeve as a cylindrical member in which the shaft is inserted, the development sleeve having an outer peripheral surface of the cylindrical member as the developer carrying surface, and being supported in a rotatable manner about the shaft, the magnet including, as the magnetic poles, at least a first magnetic pole disposed on the downstream side of the development position in the rotation direction of the development sleeve, and a second magnetic pole disposed on the downstream side of the first magnetic pole in the rotation direction of the development sleeve, so as to have the same polarity as the first magnetic pole, thereby attracting the two-component developer to the developer carrying surface, the developing roller has a part from the first magnetic pole to the second magnetic pole on the downstream side in the rotation direction of the development sleeve, as a developer separating part for allowing the two-component developer to separate from the developer carrying surface, the developer separating part has a magnetic force reversal region, in which a resultant force of a vertical magnetic force and a horizontal magnetic force of the developer separating part increases as being apart from the developer carrying surface in the normal direction, supposing that position P represents a position on the developer carrying surface, at which a ratio of the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part at 0.5 mm apart from the developer carrying surface in the normal direction, to the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part at 0.05 mm apart from the developer carrying surface in the normal direction, becomes maximum, supposing that position Q represents an intermediate position in the circumferential direction between a position Q1 on the developer carrying surface, at which the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part is 20 mT, on the first magnetic pole side of the developer separating part, and a position Q2 on the developer carrying surface, at which the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part is 20 mT, on the second magnetic pole side of the developer separating part, supposing that a distance in the circumferential direction on the developer carrying surface, from the position Q1 on the first magnetic pole side to the position Q2 on the second magnetic pole side of the magnetic force reversal region, is α (mm), supposing that a distance between the position Q1 and the position Q2 in the circumferential direction is β (mm), supposing that a distance between the position P and the position Q in the circumferential direction is γ (mm), supposing that γ has a positive value when the position Q is on the upstream side of the position P in the rotation direction of the development sleeve, and that γ has a negative value when the position Q is on the downstream side of the position P in the rotation direction of the development sleeve, then the following inequality (F1) is satisfied, and when the inequality (F1) is satisfied, a variation width of a shear friction coefficient of the two-component developer is 0.02 or less, within a range where a surface coverage of toner particles with respect to one carrier particle is 22.7% or more and 45.4% or less.
α−(18.9×(γ/β).sup.2+20.8×(γ/β))>6  (F1)
2. A developing device comprising a developing roller having a developer carrying surface for carrying a two-component developer containing toner particles and carrier particles, so as to supply the toner particles in the two-component developer carried on the developer carrying surface to an electrostatic latent image at a development position, thereby developing the electrostatic latent image, wherein the developing roller includes a shaft extending in a predetermined direction, a magnet fixed to an outer peripheral surface of the shaft, so as to have a plurality of magnetic poles in a circumferential direction of the shaft, and a development sleeve as a cylindrical member in which the shaft is inserted, the development sleeve having an outer peripheral surface of the cylindrical member as the developer carrying surface, and being supported in a rotatable manner about the shaft, the magnet including, as the magnetic poles, at least a first magnetic pole disposed on the downstream side of the development position in the rotation direction of the development sleeve, and a second magnetic pole disposed on the downstream side of the first magnetic pole in the rotation direction of the development sleeve, so as to have the same polarity as the first magnetic pole, thereby attracting the two-component developer to the developer carrying surface, the developing roller has a part from the first magnetic pole to the second magnetic pole on the downstream side in the rotation direction of the development sleeve, as a developer separating part for allowing the two-component developer to separate from the developer carrying surface, the developer separating part has a magnetic force reversal region, in which a resultant force of a vertical magnetic force and a horizontal magnetic force of the developer separating part increases as being apart from the developer carrying surface in the normal direction, supposing that position P represents a position on the developer carrying surface, at which a ratio of the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part at 0.5 mm apart from the developer carrying surface in the normal direction, to the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part at 0.05 mm apart from the developer carrying surface in the normal direction, becomes maximum, supposing that position Q represents an intermediate position in the circumferential direction between a position Q1 on the developer carrying surface, at which the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part is 20 mT, on the first magnetic pole side of the developer separating part, and a position Q2 on the developer carrying surface, at which the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part is 20 mT, on the second magnetic pole side of the developer separating part, supposing that a distance in the circumferential direction on the developer carrying surface, from the position Q1 on the first magnetic pole side to the position Q2 on the second magnetic pole side of the magnetic force reversal region, is α (mm), supposing that a distance between the position Q1 and the position Q2 in the circumferential direction is β (mm), supposing that a distance between the position P and the position Q in the circumferential direction is γ (mm), supposing that γ has a positive value when the position Q is on the upstream side of the position P in the rotation direction of the development sleeve, and that γ has a negative value when the position Q is on the downstream side of the position P in the rotation direction of the development sleeve, then the following inequality (F2) is satisfied, and when the inequality (F2) is satisfied, a variation width of the shear friction coefficient of the two-component developer is 0.037 or less, within the range where a surface coverage of the toner particles with respect to one carrier particle is 22.7% or more and 45.4% or less.
α−(18.9×(γ/β).sup.2+20.8×(γ/β))>7  (F2)
3. A developing device comprising a developing roller having a developer carrying surface for carrying a two-component developer containing toner particles and carrier particles, so as to supply the toner particles in the two-component developer carried on the developer carrying surface to an electrostatic latent image at a development position, thereby developing the electrostatic latent image, wherein the developing roller includes a shaft extending in a predetermined direction, a magnet fixed to an outer peripheral surface of the shaft, so as to have a plurality of magnetic poles in a circumferential direction of the shaft, and a development sleeve as a cylindrical member in which the shaft is inserted, the development sleeve having an outer peripheral surface of the cylindrical member as the developer carrying surface, and being supported in a rotatable manner about the shaft, the magnet including, as the magnetic poles, at least a first magnetic pole disposed on the downstream side of the development position in the rotation direction of the development sleeve, and a second magnetic pole disposed on the downstream side of the first magnetic pole in the rotation direction of the development sleeve, so as to have the same polarity as the first magnetic pole, thereby attracting the two-component developer to the developer carrying surface, the developing roller has a part from the first magnetic pole to the second magnetic pole on the downstream side in the rotation direction of the development sleeve, as a developer separating part for allowing the two-component developer to separate from the developer carrying surface, the developer separating part has a magnetic force reversal region, in which a resultant force of a vertical magnetic force and a horizontal magnetic force of the developer separating part increases as being apart from the developer carrying surface in the normal direction, supposing that position P represents a position on the developer carrying surface, at which a ratio of the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part at 0.5 mm apart from the developer carrying surface in the normal direction, to the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part at 0.05 mm apart from the developer carrying surface in the normal direction, becomes maximum, supposing that a value of the ratio at the position P is “A”, supposing that position Q represents an intermediate position in the circumferential direction between a position Q1 on the developer carrying surface, at which the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part is 20 mT, on the first magnetic pole side of the developer separating part, and a position Q2 on the developer carrying surface, at which the resultant force of the vertical magnetic force and the horizontal magnetic force of the developer separating part is 20 mT, on the second magnetic pole side of the developer separating part, supposing that a distance in the circumferential direction on the developer carrying surface, from the position Q1 on the first magnetic pole side to the position Q2 on the second magnetic pole side of the magnetic force reversal region, is α (mm), supposing that a distance between the position Q1 and the position Q2 in the circumferential direction is β (mm), supposing that a distance between the position P and the position Q in the circumferential direction is γ (mm), supposing that γ has a positive value when the position Q is on the upstream side of the position P in the rotation direction of the development sleeve, and that γ has a negative value when the position Q is on the downstream side of the position P in the rotation direction of the development sleeve, then the following inequality (F3) is satisfied, and when the inequality (F3) is satisfied, a variation width of the shear friction coefficient of the two-component developer is 0.02 or less, within the range where a surface coverage of the toner particles with respect to one carrier particle is 22.7% or more and 45.4% or less.
A/α+0.8334×(γ/β)≤0.275  (F3)
4. An image forming apparatus comprising the developing device according to claim 1, so as to print an image developed by the developing device on a sheet.
5. An image forming apparatus comprising the developing device according to claim 2, so as to print an image developed by the developing device on a sheet.
6. An image forming apparatus comprising the developing device according to claim 3, so as to print an image developed by the developing device on a sheet.