JPH1048958A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the attachment of an isolated carrier generated near the surface of a latent image carrier effectively. SOLUTION: This developing device furnishes a developer carrier in which a magnetic field generating means 23 arraying plural magnetic poles in a nonmagnetic sleeve 22 of the outer diameter 10 to 20mm and the rotary speed 375 to 540mm/sec is fixed and set, a two-component developer G is carried on this developer carrier 21, and an alternating electric field is applied between a latent image carrier 1 and the developer carrier 21 so as to carry out a magnetic brush development. In this case, near the surface of the latent image carrier 1 near the outlet of a developing nip area A, a magnetic field with the radius direction component Br of the magnetic flux more than 68.2mT, and the rate of change in the sleeve rotation direction of the sleeve rotation direction component Bt of the magnetic flux is more than 0.163T/rad, is operated, or a magnetic field in which the index Fr of the radius direction component of a magnetic adsorption force operating to the carrier is more than 2.92, and its direction is toward the center of the developer carrier 21, is operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic copying machine or a printer, and more particularly to a developing device for forming a developer layer of a magnetic brush on a developer carrier. The present invention relates to a developing device that applies an alternating electric field between a latent image carrier and a developer carrier to develop a latent image on the latent image carrier.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system, a magnetic brush developing device has been widely used. This developing device uses a developer carrier (developing roll) in which a magnet roll having a plurality of magnetic poles arranged in a cylindrical non-magnetic sleeve is fixedly installed, and a latent image carrying member is provided to improve image quality and developability. There is known one in which an alternating electric field is applied between a developer and a developer carrier. In such a developing device, an electric field for moving the toner toward the latent image carrier acts to apply an alternating electric field, and an electric field for moving the toner from the latent image carrier toward the developer carrier acts. The case exists. That is, there is a case where an electric field acts to move a carrier having a polarity opposite to that of the toner toward the latent image carrier. For this reason, there is a concern that carrier adhesion to the latent image carrier occurs and image defects occur.

In order to solve such a technical problem,
Conventionally, when a small-diameter sleeve (20 mm or less) is used with a low magnetic force, the carrier is determined by defining the relationship between the magnitude of the radial component and the rotational component of the magnetic flux density and the position of the peak of the radial component. A device that suppresses the adhesion and the flying of the developer has already been proposed (for example, Japanese Patent Laid-Open No. 4-86).
870, JP-A-4-86873 and JP-A-4-278974). In addition, when a carrier having a small diameter is used, carrier adhesion is more likely to occur, so that the magnetic force is related to the change rate of the magnetic flux density in the radial direction, and the peak value of the magnetic force and the peak of the developing main pole are determined. There has also been proposed a device in which the position is specified to prevent carrier adhesion and image roughness (for example, see JP-A-3-4262). Further, there has been proposed an arrangement in which the combined magnetic field vector in the radial direction and the rotation direction is set to be larger than the magnetic force in the developing pole radial direction within 45 ° from the center of the developing pole to prevent carrier adhesion ( For example, Tokuhei 6-9315
No. 3).

[0004]

However, when the difference between the potential of the background portion and the DC component of the bias of the sleeve is large, the carrier adherence to the background portion on the surface of the latent image carrier is substantially chain-like or plural. Are generated in one place, but when the difference between the background portion potential and the DC component of the bias of the sleeve is small, each carrier may be generated in an irregularly isolated manner. In the latter case, it is considered that the carrier is separated from the tip of the chain and is attached to the carrier. For this reason, in the conventional method and apparatus, when a small-diameter sleeve is used at a high rotation speed, isolated carrier adhesion may occur.

At this time, in order to suppress the adhesion of the carrier in the form of a chain and the scattering of the developer, it is conceivable to increase the magnetic flux density of the developing pole to increase the magnetic attraction force. It is difficult to reduce the size and cost of the apparatus because a special magnetic material is required. A method of increasing the magnetic attractive force by sharpening the developing pole can be considered. Particularly, when a small developer carrier is used, it is difficult to obtain a magnetic flux density by sharpening the developing pole. Will be lower. This makes it difficult to reduce the size and cost of the device, as in the case of increasing the magnetic flux density. Further, simply improving the magnetic attraction force on the sleeve is not always effective for the isolated carrier adhesion occurring near the surface of the latent image carrier.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problem, and has an object to provide a developing device capable of effectively preventing isolated carrier adhesion occurring near the surface of a latent image carrier. To provide.

[0007]

The inventor of the present invention has analyzed the isolated carrier adhesion phenomenon occurring near the surface of the latent image carrier, and found that the developer, especially the developer, is located near the surface of the latent image carrier. It was found that isolated carrier adhesion occurred near the most downstream portion of the area where the carrier was rubbed (the development nip area). Based on this fact, the present inventor has found that it is necessary to apply a sufficient magnetic attraction force near the most downstream portion of the development nip region in order to effectively avoid the above-mentioned carrier adhesion. I came up with the invention.

That is, in order to solve the above-mentioned problems, the present invention is directed to a case where a small developer carrier is used at a high rotation speed, and a magnetic flux near the most downstream portion of a developing nip near the surface of a latent image carrier. An object of the present invention is to provide a developing device for preventing carrier adhesion by efficiently obtaining a magnetic attraction force by defining the magnitude of the density and the rate of change.

More specifically, as shown in FIG. 1, the present invention faces the latent image carrier 1 and at the position facing the latent image carrier 1 in the same direction as the latent image carrier 1. 10-20mm outer diameter and 375-540mm peripheral speed
Developer carrier 21 in which a magnetic field generating means 23 in which a plurality of magnetic poles are arranged is fixedly installed in a non-magnetic sleeve 22 at a speed of / sec.
A two-component developer G comprising a magnetic carrier C and a non-magnetic toner T is carried on the developer carrier 21, and an alternating electric field is applied between the latent image carrier 1 and the developer carrier 21. In the developing device for performing the magnetic brush development, the radial component Br of the magnetic flux density is 68.2 (mT) or more in the rotational direction of the sleeve near the surface of the latent image carrier 1 near the exit of the developing nip area A. A magnetic field having a rate of change of the component Bt in the sleeve rotation direction of 0.163 (T / rad) or more is applied.

From another point of view, the present invention relates to FIG.
As shown in the figure, in the vicinity of the surface of the latent image carrier 1 near the exit of the development nip area A, the index Fr of the radial component of the magnetic attractive force acting on the carrier is 2.92 or more and the developer carrier 21
Characterized by applying a magnetic field in a direction toward the center.

Next, the operation of the above technical means will be described. It is possible to effectively prevent the unnecessary carrier C from adhering to the latent image carrier 1 and being transported to the transfer area, thereby causing image defects. This is considered to be due to the following reasons. The forces mainly related to the easiness of carrier adhesion include electrostatic force due to an electric field applied between the latent image carrier 1 and the developer carrier 21, centrifugal force due to rotation of the sleeve 22, A magnetic attraction force on the sleeve 22 may be considered.

Here, when the diameter of the developer carrying member 21 is reduced with the downsizing of the image forming apparatus, the centrifugal force increases. For this reason, as the rotational speed of the sleeve 22 increases and the radius r of the sleeve 22 decreases, the adhesion of the carrier becomes remarkable. This is because the centrifugal force has increased, and the gap between the sleeve 22 and the latent image carrier ₁ at the most downstream portion P1 of the development nip area A has increased, making it difficult for the magnetic field to spread. is there. Therefore, in the most downstream portion P ₁ of the developing nip region A, it is contemplated that carrier adhesion can be prevented if Oyobose sufficient magnetic attraction force.

The magnetic attraction force is related to the magnetic flux density vector B = (Br, Bt) and the rate of change of B , as expressed by Equation 1.

[0014]

(Equation 1)

Then, the most downstream portion P ₁ of the development nip area A
Attention was paid to the magnetic flux density and the rate of change of the magnetic flux density in the sleeve radial direction and the sleeve rotation direction, and the relationship between the carrier adhesion amounts was examined. The results shown in FIGS. 2 and 3 were obtained. The measuring device used was manufactured by ADS. According to FIGS. 2 and 3, the radial component Br of the magnetic flux density
(P ₁ ) and the component Bt (P ₁ ) in the sleeve rotation direction of the magnetic flux density
It has been found that carrier adhesion has occurred in relation to the rate of change in the radial direction (ΔBt / Δφ).

However, the rate of change in the radial direction was measured by measuring the magnetic flux density at a position 50 μm away from the sleeve 22 in the absence of the developer, and the rate of change of the magnetic flux density was determined.
Here, the magnetic flux density is measured by rotating the sleeve 22 by 0.36 ° in the rotation direction, and the rate of change was determined by the difference between two points sandwiching the calculation point. Here coordinates, the sleeve rotation center O _M as the origin, and the direction away from the O _M and radial axis to the positive direction, and cylindrical coordinates consisting rotational axis of the sleeve rotation direction as a positive direction .

Equation (1) is rewritten as equation (2).
This can be considered as an index proportional to the magnetic attraction.

[0018]

(Equation 2)

Here, the most downstream portion P of the development nip region A
Paying attention to the magnetic attraction force in _1,
As a result, it was found that there was a relationship with carrier adhesion as shown in FIG. Thus, it was found that the carrier attachment can be prevented by the action of magnetic flux density required for the most downstream portion P ₁ and the change rate of the development nip area A.

Here, the weight average particle size is 30 to 80 μm.
A carrier coated with resin on ferrite particles of
A two-component developer composed of a non-magnetic toner having a weight average particle diameter of 10 μm or less is used.
^It was conveyed by 2-800 g / m ² . At this time, it was found by the most downstream portion P ₁ position is viewed from the closest position of the sleeve 22 and the latent image bearing member 1 is about 1mm~2mm downstream side of the developing nip area A. However, the observation is on the sleeve 22 after image formation, M ₀ by measuring the distance between M ₀ -M ₁ shown in FIG. 1, the rotation center O _M and the angle ∠M of M _{1 0} -O sleeve 22 _M -M ₁ from the closest distance M ₀ -M ₁ was determined P _1.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 5 is an example of an image forming apparatus configured using the developing device 2 according to the first embodiment of the present invention. The latent image carrier 1 is
A photoconductive drum having a surface layer made of a negatively charged organic photoreceptor on its surface, which is uniformly charged by a charging device 3 and then irradiated with light corresponding to an image by an exposure device 4, An electrostatic latent image due to the difference can be formed. The surface potential when an electrostatic latent image is formed is, for example, −
100 V and -700 V in the background. The electrostatic latent image formed on the latent image carrier 1 is reversely developed by the developing device 2, and a toner image is formed on the latent image carrier 1. This toner image is uniformly exposed by the pre-transfer exposure device 5, transferred to the recording paper 8, and then fixed by a fixing device (not shown).

As shown in FIG. 6, the developer carrier 21 of the developing device 2 is provided to face the latent image carrier 1, and conveys the developer G adhered to the surface by rotating. The gap in the region closest to the latent image carrier 1 is set to about 400 to 600 μm. The developer carrier 21 has a rotating non-magnetic developing sleeve 22. Inside the developing sleeve 22, a plurality of magnetic poles are arranged along the peripheral surface, and are fixed and supported so as not to rotate. A roll 23 is provided. As a result, a magnetic field is formed along the peripheral surface of the developing sleeve 22, and a two-component developer (not shown) composed of a magnetic carrier and a non-magnetic toner is applied to the developer carrier 2 according to the magnetic field.
1 can be adsorbed to the surface.

The two-component developer transported to the developer supply area by the developer transport stirring member 26 such as an auger is transferred to the developer carrier 21 by a developer supply member 25 such as a paddle.
The developer is further conveyed to the developing area with the transport amount regulated by the developer layer regulating member 24. A DC superimposed AC voltage, which is a bias voltage, is applied to the developer carrier 21 by a high-voltage AC power supply (not shown) and a DC power supply (not shown), and the developer carrier 21 and the latent image carrier 1 are applied.
In the developing nip area A (see FIG. 1) where the electrodes are close to each other, an alternating electric field is generated between the latent image carrier 1 and the grounded electrode under the photosensitive layer. This bias voltage can be set, for example, such that the frequency of the AC component is 6.0 kHz, the peak-to-peak voltage is 1.5 kV, and the DC component is -500 V.

The developer carrier 21 used in the present embodiment
Includes a developing sleeve 22 formed in the axial direction of the V-shaped grooves at a constant pitch in the aluminum sleeve substrate surface with an outer diameter of 18 mm, as shown in FIG. 1, the developing nip region A most downstream portion P ₁ The radial component Br of the magnetic flux density is 68.2 (m
T), the change rate of the sleeve rotation direction component Bt of the magnetic flux density in the sleeve rotation direction becomes 0.163 (T / rad) or more, or the radial direction component of the magnetic attraction force calculated by Expression 2 And a magnet roll 23 having magnetic poles formed so as to apply a magnetic field having an index Fr of 2.92 or more.

FIG. 7 shows a magnetic field pattern on the surface of the developing sleeve 22 of the developer carrier 21 used in the present embodiment. In the present embodiment, a V-shaped groove is used on the surface of the developing sleeve 22, but a square groove, a U-shaped groove, a sand blast treatment, or the like may be used as long as the developer can be stably conveyed.

First, an experiment was performed under the following conditions. (1) Experiment 1 Photosensitive drum - Proximity most developing sleeve distance _{P 0 -M 0: (a)} 400μm, (b) 500μm · ∠M 0 -O M - developing pole S1 peak position: + 5 ° (sleeve rotation direction (Upstream side) ・ Weight ratio of toner in developer: 6.0 wt% (Tribo:
(About 25 μC / g) ・ Carrier resistance value: 10 ^8.5 to ^109.5 Ω · cm ・ Developing sleeve rotation speed / photosensitive drum rotation speed: 1.
6 (developing sleeve rotation speed: 480 mm / sec, photoconductor drum rotation speed: 300 mm / sec)-Photoconductor drum surface potential (background portion): -7
00V Sleeve bias potential: DC bias -500 V AC bias 1.5 kV (peak-to-peak voltage) 6.0 kHz, rectangular wave

At this time, when the transport amount of the developer is stopped when the sleeve is stopped, (a) 400 to 550 g / m ² (a) 550 to 700 g / m ² (c) 700 to 800 g / The gap between the developer layer regulating member (blade) 24 and the sleeve was adjusted to be m ² .

When the distance between M _{0 and} M ₁ was measured under these conditions, (a) was about 1.5 mm, and (b)
Was about 1.7 mm. The amount of the developer in the upstream region of (c) In the development nip region A increased, but the position of the P ₁ has not changed much. The magnetic field pattern at a position including the vicinity of P ₁ illustrated in FIGS. Also, P
The magnetic flux density in the vicinity of _1, the index Fr of change rate and the magnetic attraction force of the magnetic flux density shown in Table 1.

[0029]

[Table 1]

When the surface of the photosensitive member was examined under the above conditions, no carrier adhesion was observed in any of (a) to (c).

(2) Experiment 2 Next, the weight ratio of the toner in the developer was set to (a) 3.0 wt%,
(B) 4.0 wt%, (c) 10.0 wt%, the carrier resistance value is (A) 10 ^8.5 to 10 ^9.5 Ω · cm, (A) 10
And ^{13 ~10 14 Ω} · cm, the other conditions (1) -
(B) Carrier adhesion was examined in the same manner as in (a).

As a result, in the case of the condition (A), carrier adhesion occurred to the extent that no problem occurred (several 40 mm × 40 mm) in (a), but carrier adhesion occurred in (b) and (c). Did not. In the case of condition (a), (a)
No carrier adhesion occurred in any of (c) to (c).

(3) Experiment 3 The rotation speed of the developing sleeve / the rotation speed of the photosensitive drum was set to (a) 1.5 (the rotation speed of the developing sleeve was 350 mm / sec, and the rotation speed of the photosensitive drum was 200 mm / sec). Sleeve rotation speed 480 mm / sec Photoconductor drum rotation speed 300 mm / sec) (c) 1.8 (Development sleeve rotation speed 540 mm / sec Photoconductor drum rotation speed 300 mm / sec), and other conditions (1)-(b) ) -Carrier adhesion was examined in the same manner as in (a). As a result, (a) to (c)
No carrier adhesion occurred in any of the above.

Embodiment 2 Using a developer carrier 21 whose magnetic field pattern on the surface of the developing sleeve 22 is as shown in FIG. As a result, the carrier adhesion was not observed as in the case of the first embodiment. FIG. 11 shows a magnetic field pattern at a position including the vicinity of P _1, and Table 2 shows a magnetic flux density, a change rate of the magnetic flux density, and an index Fr of a radial component of the magnetic attractive force near P ₁ .

[0035]

[Table 2]

[0036]

As described above, according to the present invention, a sufficient magnetic attraction force is defined by defining the magnitude and the rate of change of the magnetic flux density near the most downstream part of the developing nip area near the surface of the latent image carrier. , Carrier adhesion to the latent image carrier can be avoided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a developing device according to the present invention.

FIG. 2 is a graph showing a relationship between a magnetic flux density radial direction component Br and a carrier adhesion amount near the most downstream portion of a developing nip region.

FIG. 3 is a graph showing a relationship between a change rate ΔBt / Δφ of a magnetic flux density sleeve rotation direction component Bt in a sleeve rotation direction and a carrier adhesion amount near a most downstream portion of a development nip region.

FIG. 4 is a graph showing a relationship between an index Fr of a radial component of a magnetic attraction force acting on a carrier and a carrier adhesion amount.

FIG. 5 is an explanatory diagram illustrating Embodiment 1 of an image forming apparatus incorporating a developing device to which the present invention has been applied;

FIG. 6 is an explanatory diagram illustrating a configuration of a developing device according to the first embodiment.

FIG. 7 is an explanatory diagram showing a magnetic flux density pattern on a sleeve of the developer carrier used in the first embodiment.

FIG. 8 is an explanatory diagram showing a magnetic flux density pattern at a position separated from the sleeve of the developer carrier used in the first embodiment by a distance P ₁ -M ₁ (P ₁ -M ₁ = 550 μm).

FIG. 9 is an explanatory diagram showing a magnetic flux density pattern at a distance P ₁ -M ₁ (P ₁ -M ₁ = 700 μm) from the sleeve of the developer carrier used in the first embodiment.

FIG. 10 is an explanatory diagram showing a magnetic flux density pattern on a sleeve of the developer carrying member used in the second embodiment.

FIG. 11 is an explanatory diagram showing a magnetic flux density pattern at a position separated by a distance P ₁ -M ₁ (P ₁ -M ₁ = 700 μm) from a sleeve of a developer carrier used in the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Latent image carrier (photosensitive drum), 2 ... Developing device, 21
... developer carrying member, 22 ... nonmagnetic sleeve (developing sleeve) 23: magnetic field generating means (magnet roll), A ... developing nip region, the closest position between the developing sleeve of P ₀ ... image bearing member, P ₁ development nip region most downstream part of ... latent image carrier, O _M
... center of rotation of the developing sleeve, the closest position between the latent image bearing member M ₀ ... developing sleeve, M ₁ ... development nip region most downstream portion of the developing sleeve, G ... developer

Claims (2)

[Claims] An outer diameter of 10 to 20 mm and a peripheral speed of 375 to 540 mm / s, which face the latent image carrier and rotate in the same direction as the latent image carrier at a position facing the latent image carrier.
a non-magnetic sleeve having a magnetic field generating means in which a plurality of magnetic poles are arranged and fixed, and a two-component developer comprising a magnetic carrier and a non-magnetic toner is carried on the developer carrier. In a developing device that applies an alternating electric field between the latent image carrier and the developer carrier to perform magnetic brush development, the magnetic flux density in the radial direction of the magnetic flux density near the surface of the latent image carrier near the exit of the development nip area A developing device, wherein a magnetic field having a component Br of 68.2 (mT) or more and a change rate of a magnetic flux density component Bt in a sleeve rotation direction of a sleeve rotation direction of 0.163 (T / rad) or more is applied. 2. An outer diameter of 10 to 20 mm facing the latent image carrier and rotating in the same direction as the latent image carrier at a position facing the latent image carrier, and a peripheral speed of 375 to 540 mm / s.
a non-magnetic sleeve having a magnetic field generating means in which a plurality of magnetic poles are arranged and fixed, and a two-component developer comprising a magnetic carrier and a non-magnetic toner is carried on the developer carrier. Then, in a developing device in which an alternating electric field is applied between the latent image carrier and the developer carrier to perform magnetic brush development, magnetic attraction acting on the carrier is provided near the surface of the latent image carrier near the exit of the development nip area. Index Fr of radial component of force
A magnetic field which is directed to the center of the developer carrying member when the pressure is 2.92 or more.