JPH1184881A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of preventing the occurrence of development unevenness corresponding to a magnetic pole pitch at the time of attaining development by using a developing roller consisting of a sleeveless magnet roll having plural magnetic poles. SOLUTION: A covering layer 12 made of a soft magnetic material is formed to cover the surface of a magnet roll, at least in the part corresponding to a latent image of a multimagnetic pole developing roller 2, that is, the region of an image forming width W of the multimagnetic pole developing roller 2 for actualizing the latent image on a photoreceptor drum 1. Thus, the degree of the short circuit of the line of magnetic force between the adjacent magnetic poles of the developing roller 2 is increased, a magnetic flux leaking in the part corresponding to the magnetic pole of the developing roller 2 is reduced and the napping height hH of a magnetic developer 4 at the center of the magnetic pole is suppressed to be the same as the napping height hL of the magnetic developer 4 in the part corresponding to the space between the magnetic poles, to eliminate the occurrence of the development unevenness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device such as a copying machine, a facsimile, a printer, and the like. More specifically, the present invention relates to a magnet roll having a plurality of magnetic poles formed on a surface.
A two-component developer containing toner and magnetic particles (carrier),
Alternatively, the present invention relates to a sleeveless type developing device using a developing roller composed of a sleeveless magnet roll for carrying a developer such as a one-component magnetic toner directly on the surface of the magnet roll while carrying a magnetic force.

[0002]

2. Description of the Related Art A sleeveless developing device using a developing roller composed of the above-mentioned sleeveless magnet roll (hereinafter simply referred to as "magnet roll") has a structure in which a developer is formed by a cylindrical sleeve rotating around a plurality of magnets. Is more easily reduced in size and cost than a sleeve type developing device that transports the toner to the developing area 11, and since toner density control is basically unnecessary, a toner density detection mechanism and a complicated toner density control mechanism are used. There is a merit that can be omitted.

However, in this sleeveless developing device, the thickness of the developer layer formed on the surface of the magnet roll is different between the magnetic poles on and between the magnetic poles as the developing roller, There is a difference in developability with respect to a latent image formed on a photoconductor as a carrier. For this reason, in this sleeveless developing device,
Due to the rotation of the developing roller, the thick and thin portions of the developer layer alternately come into contact with the surface of the image carrier, and the density of the developed image becomes uneven (development unevenness) along the moving direction of the image carrier. (Particularly, the reproducibility of a halftone image is reduced). In order to eliminate such density unevenness, there is a method of rotating the developing roller at a high speed. However, in this method, an increase in driving torque and scattering of the developer are caused, and noise is generated. There are practical problems.

In order to solve this problem, conventionally, as an alternating electric field in which an AC bias is superimposed on a DC bias,
When the magnetic pole of the magnet roll comes closest to the surface of the image carrier, Vmin (valley value of the voltage waveform) is applied, and when the gap between the magnetic poles of the magnet roll comes closest to the surface of the image carrier, Vmax (peak of the voltage waveform). Is applied to develop a latent image on the image carrier (Japanese Patent Application Laid-Open No. 8-166692; hereinafter, this is referred to as “known example 1”). A developing method using an electric means and a mechanical means for equalizing the developability on the magnetic pole and between the magnetic poles (JP-A-8-297414)
JP, hereinafter referred to as “known example 2”), the pitch between the magnetic poles of the magnet roll is set to 0.5 to 10 mm, and the magnet roll and the image carrier in the developing region 11 where the magnet roll and the image carrier face each other. Are set in opposite directions, and the circumferential speed of the magnet roll is Vm (mm / sec).
c) and a developing method in which the ratio of the moving speed Vp (mm / sec) of the image carrier is 5 ≧ Vm / Vp ≧ 1 (Japanese Unexamined Patent Application Publication No.
No. 328387; hereinafter, referred to as “known example 3”).

[0005]

However, in the developing method of "known example 1", since the bias is controlled in synchronization with the developing ability based on the magnetic field distribution of the rotating magnet roll, a magnetic field change is detected by a magnetic sensor. Or it is necessary to take out the timing signal from the rotating shaft of the magnet roll, which causes a problem of high cost.

Further, in the developing method of "known example 2", similarly to the developing method of "known example 1," the electric means and the mechanical means are controlled in synchronization with the change of the developing ability due to the magnetic field distribution of the magnet roll. Must be implemented, which makes it less feasible at low cost.

[0007] Further, in the developing method of "known example 3", the development unevenness corresponding to the magnetic pole pitch is easily eliminated as compared with the developing methods of "known example 1" and "known example 2". Is small, for example, when the outer diameter of the photosensitive drum as the image carrier is 30 mm or less, the effect is small.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof corresponds to a magnetic pole pitch when development is performed using a developing roller including a sleeveless magnet roll having a plurality of magnetic poles. An object of the present invention is to provide a developing device capable of preventing development unevenness from occurring.

[0009]

In order to achieve the above object, the invention of claim 1 has a plurality of magnetic poles, and rotates the developer while carrying a magnetic force to form a latent image on the surface of the image carrier. In a developing device using a developing roller composed of a sleeveless magnet roll for developing, a coating layer made of a soft magnetic material is formed on at least a portion corresponding to a latent image of the developing roller.

In this developing device, since a coating layer made of a soft magnetic material is formed on at least a portion corresponding to the latent image of the developing roller, the developing roller leaks in the normal direction of the developing roller by the action of the coating layer. Lines of magnetic force are reduced. As a result, the height of the spike of the developer at the center of the magnetic pole of the magnet roll as the developing roller is suppressed, and the degree to which the developing characteristics are fluctuated by the fluctuating magnetic field by the rotating magnet roll is reduced.

According to a second aspect of the present invention, in the developing device of the first aspect, the surface roughness of the coating layer is set to be equal to or less than a volume average particle size of the magnetic particles of the developer.

In this developing device, the surface roughness of the coating layer is not more than the volume average particle size of the magnetic particles of the developer, so that the developer can be more easily captured on the surface of the coating layer. Thereby, the unevenness of the transport amount of the developer supplied to the developing area by the developing roller is reduced.

According to a third aspect of the present invention, in the developing device of the first aspect, the average thickness of the coating layer is set to be equal to or less than the volume average particle size of the magnetic particles of the developer.

In this developing device, since the average thickness of the coating layer is equal to or less than the volume average particle diameter of the magnetic particles of the developer, it acts on the developer of the developing roller due to the formation of the coating layer. The drop in magnetic force is suppressed. As a result, the developer magnetically supported by the developing roller falls to the outside of the developing device, and when the two-component developer including the toner and the carrier is used as the developer, the developer is applied to the image carrier (photoconductor). Carrier adhesion is eliminated.

According to a fourth aspect of the present invention, in the developing device of the first aspect, the coating layer is formed as an integral film.

In this developing device, the coating layer is
By being formed as an integral film, the adhesion of the film layer to the surface of the magnet roller is enhanced. Thereby, for example, even if the adhesive strength of the coating layer to the surface of the magnet roller is partially reduced due to long-term use of the developing roller, another portion adjacent to the portion where the adhesive strength of the coating layer is reduced may be removed by the magnet. Since the film layer is firmly adhered and held on the roller surface, peeling damage of the film layer is avoided.

According to a fifth aspect of the present invention, in the developing device of the first aspect, the coating layer is formed of an aggregate of soft magnetic material particles.

In this developing device, the coating layer is
Since the soft magnetic material is composed of aggregates of particles, appropriate irregularities are formed on the surface of the coating layer. As a result, the amount of developer transported by the developing roller and the height of the spike are stabilized, and development unevenness is eliminated.

According to a sixth aspect of the present invention, in the developing device of the fifth aspect, the volume average particle diameter of the soft magnetic material particles is equal to or less than the volume average particle diameter of the magnetic particles of the developer. Things.

In this developing device, the volume average particle diameter of the soft magnetic material particles is equal to or smaller than the volume average particle diameter of the magnetic particles of the developer. Is done. Thereby, the unevenness of the transport amount of the developer supplied to the developing area by the developing roller is reduced.

According to a seventh aspect of the present invention, there is provided a developing device using a developing roller comprising a plurality of magnetic poles and a sleeveless magnet roll for rotating a developer while carrying a magnetic force to develop a latent image on the surface of the image carrier. The developing roller at a distance within a distance between the tip of a developer regulating member and the surface of the developing roller for regulating the amount of developer supplied to a developing area on the surface of the developing roller. In which the maximum magnetic flux density in the tangential direction is larger than the maximum magnetic flux density in the normal direction of the developing roller.

In this developing device, the magnetized state of the developing roller depends on the distance between the tip of the developer regulating member for regulating the amount of developer supplied to the developing area 11 on the surface of the developing roller and the surface of the developing roller. Since the maximum magnetic flux density in the tangential direction of the developing roller at a distance within the interval is larger than the maximum magnetic flux density in the normal direction of the developing roller, the leakage magnetic flux on the magnetic pole of the developing roller is Is reduced. As a result, the height of the spike of the developer at the center of the magnetic pole of the magnet roll as the developing roller is suppressed, the height of the spike is stabilized, and the development unevenness is improved.

According to a further aspect of the present invention, there is provided a developing apparatus having a plurality of magnetic poles and a developing roller comprising a sleeveless magnet roll for rotating a developer while carrying a magnetic force to develop a latent image on the surface of the image carrier. In the above, the position of the developer regulating member for regulating the amount of developer supplied to the developing area on the surface of the developing roller, where the distance between the developing roller and the developer regulating member is minimized, and prior to regulating the amount of developer by the developer regulating member. The position of the developer regulating auxiliary member, which is arranged on the upstream side in the developing roller rotation direction of the developer regulating member for regulating the amount of the developer, is at a position where the distance between the developer regulating member and the developing roller is minimum, and The angle θd is an angle θd ≠ p · θm (p: an integer) that does not become an integral multiple of the angle θm between the adjacent magnetic poles of the developing roller and the center of the developing roller. A.

In this developing device, a position where the distance between the developing roller and the developer regulating member for regulating the amount of developer supplied to the developing area on the surface of the developing roller is minimized. Prior to the regulation of the developer amount, a position between the developer regulating member and the developer regulating auxiliary member disposed on the upstream side in the developing roller rotation direction of the developer regulating member for regulating the developer amount is set at a position where the distance between the developer regulating member and the developing roller is minimized. Since the angle θd formed with respect to the center of the developing roller is not an integral multiple of the angle θm formed between the magnetic poles adjacent to each other with respect to the center of the developing roller, θd ≠ p · θm (p: integer), Fluctuations in the rotational load of the developing roller, which occur each time the magnetic pole of the developing roller faces a doctor as the developer regulating member or a pre-doctor as the developer regulating auxiliary member, are suppressed. As a result, the unevenness of the density and magnification of the image, which is assumed to be caused by the uneven rotation of the developing roller and the image carrier (photoconductor), which corresponds to the magnetic pole pitch of the developing roller, is eliminated.

According to a ninth aspect of the present invention, in the developing device of the eighth aspect, the angle 2θd which is twice the angle θd is an angle 2θd = q · θm (q: integer) which is an integral multiple of the angle θm. It is characterized by the following.

In this developing device, the angle 2θd, which is twice the angle θd, is set to an angle 2θd = q · θm (q: integer) which is an integral multiple of the angle θm. Therefore, for example, when the load on the developing roller is maximized when the magnetic pole of the developing roller faces the doctor, the load on the portion of the developing roller facing the pre-doctor is minimized. This cancels out the respective loads at the portions where the doctor and the pre-doctor of the developing roller face each other, reduces the fluctuation range of the load of the developing roller, and corresponds to the magnetic pole pitch of the developing roller. And unevenness such as density and magnification of the image, which is presumed to be caused by uneven rotation of the image carrier (photoconductor).

[0027] The invention according to claim 10 has a plurality of magnetic poles,
In a developing device using a developing roller composed of a sleeveless magnet roll that develops a latent image on the surface of an image carrier by rotating the developer while carrying a magnetic force, the amount of the developer supplied to a developing area on the surface of the developing roller is controlled. A developer regulating member for regulating, or a developer arranged upstream of the developer regulating member in the developing roller rotation direction of the developer regulating member for regulating the amount of developer prior to regulating the amount of developer by the developer regulating member. The angle θw between the rubbing surface of the developer regulating auxiliary member, which faces the developing roller and rubs against the developer magnetically supported by the developing roller, with respect to the center of the developing roller, is defined by the magnetic poles adjacent to each other of the developing roller. Angle θ to the center of the developing roller
Angle θw = r · θm (r: integer) which is an integral multiple of m.

In this developing device, a doctor serving as a developer regulating member or a pre-doctor serving as a developer regulating auxiliary member slides against a developer magnetically supported by the developing roller so as to face the developing roller. The angle θw of the rubbing surface with respect to the center of the developing roller is set to an angle θw = r · θm (r: integer) that is an integral multiple of the angle θm of the adjacent magnetic poles of the developing roller with the center of the developing roller. Therefore, as in the case of the ninth aspect of the present invention, the respective loads at the portions where the doctor and the pre-doctor of the developing roller face each other are offset, and the fluctuation range of the load of the developing roller is reduced.
As a result, the rotational load fluctuation rate of the developing roller is reduced, and unevenness such as image density and magnification is eliminated.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a developing device of an electrophotographic copying machine (hereinafter referred to as "copier") will be described below.

FIG. 1A is a schematic configuration diagram of a developing device according to the present embodiment. This developing device is a sleeveless type developing device that directly carries a magnetic force on a magnet roll without using a sleeve as a developer carrying means, and is composed of a magnet roll having a plurality of magnetic poles N and S formed on a surface thereof. And a multi-pole developing roller 2 for carrying a magnetic developer 4 such as a two-component developer or a one-component magnetic toner containing magnetic particles (carrier) directly on the surface while carrying a magnetic force, and a cylinder as a latent image carrier of a copying machine A main body container of a developing device provided with an opening 9a which is disposed on the side of the photosensitive drum 1 and exposes a portion of the developing roller facing the developing area 11 toward the photosensitive drum 1. Developing device case 9
A toner container 6 having a toner supply port 7 for replenishing toner 5 to a portion of the developing roller in the developing device case 9; and a magnetic developer 4 carried on the developing roller and conveyed. A doctor 3 as a developer regulating member for regulating the amount, a developing bias power supply 8 for applying a developing bias to the developing roller, and the like are provided.

In a developer storage section 10 formed by a gap between the developing case 9 and the multi-pole developing roller 2 adjacent to the doctor 3 in the upstream side in the developer conveying direction, a developing area opposed to the photosensitive drum 1 is provided. The magnetic developer 4 which is not conveyed to the side 11 and whose movement is prevented by the doctor 3 is stored. The toner container 6 is formed in a part of the developing case 9 so as to be adjacent to the developer storage 10 from the upstream side in the developer conveying direction, and the multi-pole developing roller 2 of the developing case 9 is formed. The toner supply port 7 is formed by the inner wall end 9b along the line and the upstream end of the developer storage section 10 in the developer transport direction.

Next, the developing operation in the sleeveless developing device will be described. First, an initial agent, for example, a developer having a toner concentration of 10 wt% and a carrier of 35 g is set in the developing device, and the multi-pole developing roller 2 is rotationally driven clockwise as indicated by an arrow a in FIG. The developer 4 is divided into one that is attracted to the surface of the multi-pole developing roller 2 by magnetic force and one that is stored in the developer storage unit 10. The magnetic developer 4 stored in the developer storage unit 10 is rotated by 1 mm / s in the direction opposite to the arrow a by the magnetic force of the multi-pole developing roller 2 with the rotation of the multi-pole developing roller 2 in the direction of the arrow a. It circulates at the above moving speed.
Then, an interface is formed at the boundary between the surface of the developer magnetically supported on the surface of the multi-pole developing roller 2 and the surface of the developer moving in the developer storage unit 10.

Next, when the toner 5 is set in the toner container 6, the multi-pole developing roller 2 is supplied through the toner supply port 7.
The toner 5 is supplied to the developer carried by the magnetic force. The developer on the multi-pole developing roller 2 to which the toner has been supplied is transported to the developer storage 10 together with the toner. During the transportation, the toner supplied to the developer slightly enters the axial center of the multi-pole developing roller 2, and the portion between the developers where the toner enters enters the axial center of the multi-pole developing roller 2. The frictional force applied from the developer to the outer developer decreases. As a result, the transport force applied from the developer on the axial center side of the multi-pole developing roller 2 to the outer developer decreases.

In the developer storing section 10, the force of stopping the transport of the developer transported by the multi-pole developing roller 2 is exerted by the gravity and magnetic force of the stored magnetic developer 4. is working. When the toner 5 present on the surface of the developer magnetically supported by the multi-pole developing roller 2 is conveyed to the interface, the frictional force between the developers near the interface decreases, and the developer near the interface decreases. The transport force of the developer decreases, thereby reducing the transport amount of the developer near the interface. (Hereinafter, margin)

On the other hand, unlike the inside of the developer storage section 10 described above, gravity does not act on the developer on the upstream side in the rotation direction of the multi-pole developing roller 2 from the junction of the toner 5 and the magnetic developer 4. The force acting to stop the conveyance of the developer conveyed by the multi-pole developing roller 2 is smaller than that in the developer storage unit 10. For this reason, the balance between the amount of the developer conveyed to the junction and the amount of the conveyed developer conveyed at the interface is broken, causing a state of collision of the developer. The unfollowable developer escapes outside the surface of the multi-pole developing roller 2. Then, such a developer raises the position of the junction and increases the layer thickness of the developer including the interface. After passing through the doctor 3 and being supplied to the developing area 11, the layer thickness of the developer returned to the developing device case 9 also gradually increases. The state is controlled by the unit 9b. Then, the developer that does not pass through the gap between the inner wall end portion 9b and the multi-pole developing roller 2 is scraped off.

Then, the magnetic developer 4 having passed through the doctor 3
When the toner concentration reaches a predetermined toner concentration, the increased amount of developer scraped off and layered by the regulation by the inner wall end portion 9b closes the toner supply port 7, and the developer conveyed by the multi-pole developing roller 2 The toner 5 from the inside of the storage section 5 does not contact. Then, in this state, the taking in of the toner 5 ends. At this time, the bulk of the magnetic developer 4 increases due to an increase in the toner concentration in the developer reservoir 10,
As a result, the space inside the developer storage section 10 becomes narrower, so that the moving speed of the magnetic developer 4 circulating decreases.

In the developing device in the above state, of the magnetic developer 4 conveyed by the rotation of the multi-pole developing roller 2 in the direction of the arrow a, the gap between the multi-pole developing roller 2 and the doctor 3 (hereinafter referred to as the gap). The developer that has passed the gap through the “doctor gap Gd” is the gap between the photoconductor drum 1 rotating in the clockwise direction indicated by the arrow b and the multi-pole developing roller 2 (hereinafter, this gap is referred to as the “development gap Gp”). ) Is transported to the developing area 11 formed. Then, in the developing area 11, the toner 5 is supplied from the multi-pole developing roller 2 to the electrostatic latent image formed on the photosensitive drum 1, and the electrostatic latent image is visualized ( Visualization)
Is done.

Next, the operation when the toner is consumed will be described. When the toner on the multi-pole developing roller 2 is consumed by the development after the intake of the toner 5 is completed and the toner concentration becomes constant, the toner supply port 7
The toner in the developer layer formed so as to block the toner is consumed. Then, the toner density in this portion decreases, and the conveying force acting on the magnetic developer 4 by the multi-pole developing roller 2 increases. Further, the toner is also consumed in the developer storage unit 10, so that the toner density decreases and the conveying force acting on the magnetic developer 4 by the multi-pole developing roller 2 increases. Then, the layer of the developer regulated by the inner wall end 9b decreases, and the layer of the developer accumulated near the toner supply port 7 decreases. Then, at the toner supply port 7, the magnetic developer 4 conveyed by the multi-pole developing roller 2 and the toner 5
Comes into contact with the toner, and the toner 5
Is taken in, and the toner concentration of the magnetic developer 4 increases.

As described above, the regulation state of the magnetic developer 4 on the multi-pole developing roller 2 by the inner wall end 9b changes in accordance with the change in the toner density on the multi-pole developing roller 2, and the toner The concentration is self-controlled. As a result, the toner concentration of the magnetic developer 4 is always kept in a substantially constant range. Therefore, the developing device according to the present embodiment does not require a complicated toner density control mechanism such as a toner density sensor and a toner replenishing member.

In this sleeveless developing device, as shown in FIG. 2, at the portion corresponding to the magnetic pole of the multi-pole developing roller 2, the magnetic developer 4 is sprinkled by the action of the magnetic force lines in the normal direction. The thickness of the magnetic developer 4 supported by the magnetic force, that is, the height at which the magnetic developer 4 stands, hH
However, since the direction of the line of magnetic force is tangential to the multi-pole developing roller 2 between the magnetic poles, the spike height hL of the magnetic developer 4 is reduced.

For this reason, in the conventional sleeveless developing device, the spike height hH of the magnetic developer 4 at the portion corresponding to the magnetic pole of the multi-pole developing roller 2 and the magnetic developer at the portion corresponding to between the magnetic poles The difference from the ear height hL of 4 is 0.1 m
m, and the rotation of the multi-pole developing roller 2 causes the thick and thin portions of the developer layer of the developer magnetically supported by the multi-pole developing roller 2 to alternately contact the surface of the photosensitive drum 1 However, uneven density (developing unevenness) has occurred in the image density visualized along the moving direction of the photosensitive drum 1.

The difference between the spike height hH of the magnetic developer 4 at the center of the magnetic pole of the multi-pole developing roller 2 and the spike height hL of the magnetic developer 4 at a portion corresponding to the position between the magnetic poles. If the height hH of the magnetic developer 4 at the center of the magnetic pole of the multi-pole developing roller 2 is reduced by simply lowering the magnetic flux density at the center of the magnetic pole to eliminate the Due to the decrease, the phenomenon that the magnetic developer 4 magnetically supported by the multi-pole developing roller 2 falls out of the developing device and the carrier adheres to the photosensitive drum 1 easily occurs.

Therefore, in the developing device according to the present embodiment,
As shown in FIGS. 1B and 1C, at least a portion corresponding to the latent image of the multi-pole developing roller 2, that is, image formation of the multi-pole developing roller 2 for visualizing the latent image on the photosensitive drum 1. A coating layer 12 made of a soft magnetic material is formed in the region of the width W so as to cover the surface of the magnet roll.

As described above, by forming the coating layer 12 made of a soft magnetic material in the area of the image forming width W of the multi-pole developing roller 2, the coating layer 12 acts so as to be adjacent to the multi-pole developing roller 2. The degree of short-circuit of the magnetic field lines between the magnetic poles is increased, and the magnetic field lines leaking in the normal direction, that is,
Leakage magnetic flux at a portion corresponding to the magnetic pole of the multi-pole developing roller 2 is reduced. Thereby, the spike height hH of the magnetic developer 4 at the center of the magnetic pole of the multi-pole developing roller 2 becomes the same as the spike height hL of the magnetic developer 4 at a portion corresponding to between the magnetic poles. Is suppressed. As a result, as described above, the magnetic flux density at the center of the magnetic pole is simply lowered to reduce the magnetic head height hH of the magnetic developer 4 at the center of the magnetic pole of the multi-pole developing roller 2. Without causing phenomena such as dropping of the developer 4 and adhesion of the carrier to the photosensitive drum 1,
The occurrence of development unevenness was able to be surely eliminated.

FIG. 1C shows a schematic configuration example of the multi-pole developing roller 2 according to the present embodiment, in which a coating layer 12 made of a soft magnetic material is formed in the area of the image forming width W on the surface of the magnet roll. The multi-pole developing roller 2 is shown. The non-image forming areas (surfaces at both ends of the magnet roll) other than the image forming width W of the multi-pole developing roller 2 are covered with the coating layer 12.
May be coated with a soft magnetic material or a conductive material as necessary to assure the adhesive strength of the film or to secure a developing bias conductive path.

The soft magnetic material used for the coating layer 12 includes Supermalloy, Sendust, silicon steel plate, 7
8 permalloy, Mn-Zn ferrite, hypersil,
Examples include soft iron and nickel. These soft magnetic materials are
High permeability and low developer holding power. Therefore, for example, by bringing these soft magnetic materials into contact with a magnet roll in which a hard magnetic material is magnetized in the form of a permanent magnet, the lines of magnetic force leaking to the surface thereof can be reduced.

The coating layer 12 preferably has conductivity, and the resistance of the coating layer 12 and the resistance between the coating layer 12 and the bias power supply are effective so that the developing bias effect is effectively exerted. Therefore, a low resistance is preferable. The magnetic pole density peak of the multi-pole developing roller 2 is 40
８０80 mT, and the pitch of each magnetic pole is preferably 0.5 to 3 mm.

The developing bias applied to the multi-pole developing roller 2 by the developing bias power supply 8 has a frequency f of 0.5 to 5 kHz and a voltage Vpp between the (+) side peak and the (−) side peak. Is preferably 0.5 to 1.5 kV, in which an AC bias and a DC bias are superimposed.

The doctor gap Gd between the multi-pole developing roller 2 and the doctor 3 is preferably 0.15 to 0.35 mm, and the developing gap Gp between the photosensitive drum 1 and the multi-pole developing roller 2 is An average of 0.10 to 0.15 mm is preferred.

As shown in FIG. 3, the surface roughness Rz of the coating layer 12 of the multi-pole developing roller 2 (JisB0601)
Is smaller than or equal to the volume average particle diameter rc of the magnetic particles of the magnetic developer 4 (carrier for a two-component developer, toner itself for a one-component magnetic toner) (Rz ≦ rc)
By doing so, the capturing property of the magnetic developer 4 on the surface of the coating layer 12 is improved, and unevenness in the transport amount of the magnetic developer 4 supplied to the developing area 11 by the multi-pole developing roller 2 can be reduced. . That is, with such a configuration, the transport amount of the developer transported by the coating layer 12 becomes more uniform, and together with the effect of reducing the difference in the height of the ears of the magnetic developer 4, the development unevenness is further reduced. Can be further improved. Here, the magnetic particles trapped in the concave portions on the surface of the coating layer 12 of the multi-pole developing roller 2 allow a large number of magnetic lines of force between adjacent magnetic poles formed by the coating layer 12 to pass therethrough, thereby providing a stable and strong magnetic field. Magnetic force works. In the normal direction of the surface of the center of the magnetic pole, the leakage of the lines of magnetic force is small. Further, in the multi-pole developing roller 2, the magnetic flux density and its gradient are large and a strong magnetic force acts on the convex portion on the surface of the coating layer 12, so that the magnetic force acts strongly between the magnetic poles and at the center of the magnetic pole. It is considered that this greatly contributes to stabilization of the transport amount of the agent. It is desirable that the coating layer 12 be made of a conductive material in order to improve the bias application effect.

If the thickness t of the coating layer 12 is too large, the magnetic flux density on the surface of the multi-pole developing roller 2 drops significantly, and the magnetic force acting on the developer when a proper amount of the developer is conveyed is insufficient. As a result, phenomena such as dropping of the developer from the multi-pole developing roller 2 and adhesion of the carrier to the photosensitive drum 1 occur. As a result of various examinations of conditions that can avoid such a phenomenon, the preferable thickness t of the coating layer 12 is equal to (1/1) the volume average particle diameter of the carrier in the two-component developer.
In the case of the one-component magnetic toner, the volume average particle diameter of the toner itself was equal to (1/1) to 1/2.

Further, it is desirable that the coating layer 12 is formed as an integral film. That is, by forming the coating layer 12 into an integral film, the adhesion of the coating layer 12 to the surface of the magnet roller is enhanced. Thereby, for example, even if the adhesive force of the coating layer 12 to the surface of the magnet roller is partially reduced due to long-term use of the multi-pole developing roller 2, even if the adhesive force of the coating layer 12 is reduced to another portion adjacent to the portion where the adhesive force is reduced. Since the portion is firmly adhered and held on the surface of the magnet roller, peeling damage of the coating layer 12 can be prevented.

The coating layer 12 is formed as shown in FIG.
As shown in (b), the coating layer is formed by forming an aggregate of soft magnetic material particles (soft magnetic particles) 12a and a binder resin 12b for binding the soft magnetic particles 12a. 12 can form moderate irregularities on the surface,
It is easy to stabilize the transport amount of the developer and the height of the spikes, and it is possible to improve development unevenness. Here, the volume average particle diameter rs of the soft magnetic particles 12a is equal to or smaller than the volume average particle diameter rc of the magnetic particles of the magnetic developer 4 (carrier for a two-component developer, toner itself for a one-component magnetic toner) (Rs ≦ rc). That is, with this configuration, as in the case of the embodiment shown in FIG. 3, the ability to capture the magnetic developer 4 on the surface of the coating layer 12 is improved, and the developer is transported by the coating layer 12. The amount becomes more uniform, and the development unevenness can be further improved in addition to the effect of reducing the difference in height of the ears of the magnetic developer 4. It is desirable that the coating layer 12 be made of a conductive material in order to improve the bias application effect.

On the other hand, as shown in FIG. 5, the magnetized state of the multi-pole developing roller 2 is changed at a distance within a distance (doctor gap Gd) between the tip of the doctor 3 and the surface of the multi-pole developing roller 2. By setting the magnetized state in which the maximum magnetic flux density BY in the tangential direction of the multi-pole developing roller 2 is larger than the maximum magnetic flux density BZ in the normal direction of the multi-pole developing roller 2 (BY> BZ), The leakage magnetic flux on the magnetic pole of the developing roller 2 is reduced. As a result, the height of the magnetic developer 4 at the center of the magnetic pole of the multi-pole developing roller 2 is suppressed, and the amount of the developer transported and the height of the ear are stabilized, so that the development unevenness can be improved. When the multi-pole developing roller 2 is magnetized in this way, a special magnetizing yoke having a strong magnetic field strength of not only the vertical component but also the tangential component of the multi-pole developing roller 2 is used.

By the way, the rotating members involved in image formation, for example, the photosensitive drum 1 and the multi-pole developing roller 2 often do not rotate uniformly due to the load fluctuation. In particular, in the sleeveless developing device in which the magnet roll is rotated as described above, the magnetic pole of the magnet roll regulates the amount of developer prior to the doctor 3 and the regulation of the amount of developer by the doctor 3. Each time the doctor 3 faces a developer regulating auxiliary member (hereinafter, referred to as a “pre-doctor 13”) disposed upstream of the doctor 3 in the rotation direction of the multi-pole developing roller. The rotation load of the multi-pole developing roller fluctuates so that it becomes a maximum value. As a result, the rotation unevenness of the multi-pole developing roller 2 corresponding to the magnetic pole pitch of the magnet roll and the rotation unevenness of the photosensitive drum 1 (when the drive source of the photosensitive drum 1 and the multi-pole developing roller 2 are common, Especially easy to notice)
The unevenness (image unevenness) such as the density and magnification of the image, which is presumed to be the cause, occurred.

Therefore, in the developing device according to the present embodiment,
As shown in FIG. 6, the position where the distance between the multi-pole developing roller 2 of the doctor 3, which is a main source of the rotational load of the multi-pole developing roller 2, and the multi-pole developing roller of the pre-doctor 13 are minimized. The angle θd (the angle formed by the doctor unit and the pre-doctor unit) with respect to the roller center (rotation center) of the multi-pole developing roller 2 with respect to the position where the interval between the multi-pole developing roller 2 and the multi-pole developing roller 2 is minimized. An angle θd ≠ p · θm (p: p: θm) which is not an integral multiple of an angle (an angle corresponding to a magnetic pole pitch) θm between adjacent magnetic poles and the center of the multi-pole developing roller 2.
Integer).

In this developing device, the angle θd between the doctor section and the pre-doctor section is determined by the multi-pole developing roller 2.
Θd that is not an integral multiple of the angle θm equivalent to the magnetic pole pitch
≠ p · θm (p: integer), that is, an angle at which the magnetic poles of the multi-pole developing roller 2 do not simultaneously face the doctor 3 and the pre-doctor 13 when the multi-pole developing roller 2 rotates. Since the setting is set, the fluctuation of the rotational load of the multi-pole developing roller 2 caused by the magnetic pole of the multi-pole developing roller 2 facing the doctor 3 or the pre-doctor 13 is suppressed. Thereby, it was possible to eliminate the occurrence of image unevenness corresponding to the magnetic pole pitch of the multi-pole developing roller 2, which is presumed to be caused by rotation unevenness of the multi-pole developing roller 2 and the photosensitive drum 1.

Here, the angle 2θd, which is twice as large as the angle θd between the doctor section and the pre-doctor section shown in FIG. 6, is changed to an angle 2θd = q · multiple of the angle θm corresponding to the magnetic pole pitch of the multi-pole developing roller 2. θm (q: integer), for example, FIG.
As shown in FIG. 7A, when the angle 2θd is configured to be an angle three times the magnetic pole pitch equivalent angle θm (2θd = 3 · θm), as shown in FIG. When the rotational load F of the developing roller 2 has a maximum load at the doctor section, it has a minimum load at the pre-doctor section. This allows
The doctor 3 and the pre-doctor 13 of the multi-pole developing roller 2
The respective loads at the opposing portions are canceled out, and the variation width of the load of the multi-pole developing roller 2 is reduced. Therefore, in the developing device having this configuration, the combined load of the load of the doctor section and the load of the pre-doctor section becomes a stable load with a small fluctuation width to a substantially constant value, and the magnetic pole of the multi-pole developing roller 2 is changed to the doctor 3 or the pre-doctor. 13, the fluctuation of the rotational load of the multi-pole developing roller 2, which is caused by facing, can be suppressed more reliably, and the above-mentioned image unevenness can be further improved.

As shown in FIG. 8, a rubbing surface 3a of a doctor 3, which rubs against a magnetic developer 4 magnetically supported by the multi-pole developing roller 2 so as to face the multi-pole developing roller 2, and
The rubbing surface 13a of the pre-doctor 13 is formed to have a large width, and an angle θw1 between the rubbing surface 3a of the doctor 3 and the center of the multi-pole developing roller 2 or the rubbing surface 13 of the pre-doctor 13
a with respect to the center of the multi-pole developing roller 2 in FIG.
Is an angle θw1 = r · θm, θw2 = r · θm (r: integer) that is an integral multiple of the angle θm between the magnetic poles adjacent to each other of the multi-pole developing roller 2 with respect to the center of the multi-pole developing roller 2. The rubbing surface 3a of the doctor 3 and the pre-doctor 1
An even number of magnetic poles having different polarities of the multi-pole developing roller 2 alternately face the third rubbing surface 13a. Accordingly, in the developing device having this configuration, as shown in FIG. 9, as in the case described above, each rotational load F at the opposed portion between the doctor 3 and the pre-doctor 13 of the multi-pole developing roller 2 is used.
Are offset, and the fluctuation range of the load of the multi-pole developing roller 2 is reduced. As a result, the rotational load fluctuation rate of the multi-pole developing roller 2 is reduced, and image unevenness such as image density and magnification can be eliminated. In this configuration, the doctor 3
When the width of the rubbing surface 3a and the rubbing surface 13a of the pre-doctor 13 are narrow, the number of magnetic poles opposing them is one by one, and therefore, as shown by a broken line in FIG. Periodic load fluctuations occur due to the magnetic pole pitch.

[0060]

According to the first to fifth aspects of the present invention, leakage occurs in the normal direction of the developing roller due to the action of the coating layer made of a soft magnetic material formed on at least the portion corresponding to the latent image of the developing roller. Since the lines of magnetic force are reduced, the height of the spike of the developer at the center of the magnetic pole of the magnet roll as the developing roller is suppressed, and the degree to which the developing characteristics are fluctuated by the fluctuating magnetic field due to the rotating magnet roll can be reduced. Has an excellent effect.

In particular, according to the second aspect of the present invention, the surface roughness of the coating layer is equal to or less than the volume average particle diameter of the magnetic particles of the developer. Thus, there is an excellent effect that the unevenness of the transport amount of the developer supplied to the developing area by the developing roller can be reduced. (Hereinafter, margin)

According to the third aspect of the present invention, since the average thickness of the coating layer is equal to or less than the volume average particle diameter of the magnetic particles of the developer, the developing roller is formed by forming the coating layer. The drop of the magnetic force acting on the developer can be suppressed, and the developer magnetically supported by the developing roller falls out of the developing device, and when a two-component developer including a toner and a carrier is used as the developer, There is an excellent effect that the carrier can be prevented from adhering to the image carrier (photoconductor).

According to the fourth aspect of the present invention, since the coating layer is formed as an integral film, the adhesion of the coating layer to the surface of the magnet roller is enhanced. Thereby, for example, even if the adhesive strength of the coating layer to the surface of the magnet roller is partially reduced due to long-term use of the developing roller, another portion adjacent to the portion where the adhesive strength of the coating layer is reduced may be removed by the magnet. Since the film layer is firmly adhered and held on the roller surface, there is an excellent effect that peeling and destruction of the film layer can be avoided.

According to the fifth aspect of the present invention, since the coating layer is formed of an aggregate of particles of a soft magnetic material, appropriate irregularities can be formed on the surface of the coating layer, and the amount of developer transported by the developing roller can be increased. There is an excellent effect that the unevenness of development can be eliminated by stabilizing the height of the spike and the height of the spike.

According to the invention of claim 6, since the volume average particle diameter of the soft magnetic material particles in claim 5 is less than the volume average particle diameter of the magnetic particles of the developer, the developer on the surface of the coating layer Of the developer supplied to the developing area by the developing roller can be reduced.

In particular, according to the seventh aspect of the present invention, the magnetized state of the developing roller is changed to the developing area 11 on the surface of the developing roller.
The maximum magnetic flux density in the tangential direction of the developing roller at a distance within the distance between the tip of the developer regulating member for regulating the amount of developer supplied to the developing roller and the surface of the developing roller is the maximum in the normal direction of the developing roller. Since the magnetized state is larger than the magnetic flux density, the leakage magnetic flux on the magnetic pole of the developing roller is reduced, and the degree of the development characteristics fluctuated by the fluctuating magnetic field generated by the rotating magnet roll can be reduced. Accordingly, there is an excellent effect that the height of the spike of the developer at the center of the magnetic pole of the magnet roll as the developing roller is suppressed, the height of the spike is stabilized, and the uneven development can be improved.

According to the invention of claim 8, the position of the developer regulating member for regulating the amount of developer supplied to the developing area on the surface of the developing roller is minimized, and Prior to the regulation of the amount of developer by the developer regulating member, the distance between the developer regulating member and the developing roller of the developer regulating auxiliary member arranged upstream of the developer regulating member in the direction of rotation of the developing roller is minimum. And the angle θd formed with respect to the center of the developing roller with respect to the center of the developing roller.
The angle θd ≠ p · θm (p: integer) is set so as not to be an integral multiple of the following formula, so that the magnetic pole of the developing roller can be used as a doctor as the developer regulating member or a pre-doctor as the developer regulating auxiliary member. Fluctuations in the rotational load of the developing roller, which occur each time they face each other, can be suppressed, and the image of an image that is presumed to be caused by uneven rotation of the developing roller or image carrier (photoconductor) corresponding to the magnetic pole pitch of the developing roller can be suppressed. There is an excellent effect that occurrence of image unevenness such as density and magnification can be prevented.

According to the ninth aspect of the present invention, there is provided an eighth aspect of the present invention.
Angle between the doctor and pre-doctor in the developing device of
The angle 2θd which is twice as large as d is an integer 2θd = q · θm which is an integral multiple of the angle θm corresponding to the magnetic pole pitch of the developing roller.
(Q: an integer), when the load on the developing roller is maximized when the magnetic pole of the developing roller faces the doctor, the load on the portion of the developing roller facing the pre-doctor is reduced. It is extremely small. This cancels out the respective loads at the portions where the doctor and the pre-doctor of the developing roller face each other, reduces the fluctuation range of the load of the developing roller, and corresponds to the magnetic pole pitch of the developing roller. There is an excellent effect that it is possible to more reliably prevent the occurrence of image unevenness such as density and magnification of an image which is presumed to be caused by uneven rotation of the image carrier (photoconductor).

According to the tenth aspect of the present invention, the doctor as the developer regulating member or the pre-doctor as the developer regulating auxiliary member slides on the developer which is magnetically supported by the developing roller so as to face the developing roller. The angle θw of the rubbing surface to be rubbed with respect to the center of the developing roller is an integral multiple of the angle θm with respect to the center of the developing roller of the magnetic poles adjacent to each other. ), The loads of the developing roller at the portions where the doctor and the pre-doctor are opposed to each other are offset to reduce the fluctuation range of the load of the developing roller. Thus, there is an excellent effect that the fluctuation rate of the rotation load of the developing roller can be reduced to prevent the occurrence of image unevenness such as image density and magnification.

[Brief description of the drawings]

FIG. 1A is a schematic configuration diagram of a main part of a developing device according to an embodiment. (B) is an explanatory view of a configuration of a main part of a multi-pole developing roller of the developing device. (C) is a schematic configuration diagram of the multi-pole developing roller.

FIG. 2 is an explanatory view showing a state of a developer spike on a conventional multi-pole developing roller.

FIG. 3 is a schematic diagram illustrating another configuration example of the multi-pole developing roller of the developing device according to the embodiment.

FIG. 4A is a schematic diagram showing still another configuration example of the multi-pole developing roller. (B) is a schematic configuration diagram of a main part of the multi-pole developing roller.

FIG. 5 is a graph showing a magnetic flux density distribution in another configuration example of the multi-pole developing roller of the developing device according to the embodiment.

FIG. 6 is a schematic diagram of another configuration example of the multi-pole developing roller of the developing device according to the embodiment.

FIG. 7A is an explanatory diagram of a preferred configuration example of the multi-pole developing roller shown in FIG. 6; 7B is a graph showing the magnetic flux density distribution of the multi-pole developing roller shown in FIG.

FIG. 8 is a schematic diagram of still another configuration example of the multi-pole developing roller of the developing device according to the embodiment.

9 is a graph showing a magnetic flux density distribution of the multi-pole developing roller shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 multi-pole developing roller 3 doctor 3a doctor rubbing surface 4 magnetic developer 5 toner 6 toner container 7 toner supply port 8 developing bias power supply 9 developing device case 10 developer storing unit 11 developing area 12 coating layer 12a Soft magnetic particles 13 Predactor 13a Sliding surface of predactor BY Maximum magnetic flux density in the tangential direction of BY multi-pole developing roller BZ Maximum magnetic flux density in the normal direction of multi-pole developing roller hH Height of spike at developer magnetic pole center hL Height of spike between magnetic poles of developer Gd Doctor gap Gp Development gap t Thickness of coating layer W Image forming width θd Angle between doctor and pre-doctor θm Angle equivalent to magnetic pole pitch of multi-pole developing roller

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Nobuhiko Umezawa 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (10)

[Claims] 1. A developing device using a developing roller having a plurality of magnetic poles and a sleeveless magnet roll for rotating a developer while carrying a magnetic force to develop a latent image on the surface of an image carrier. A coating layer made of a soft magnetic material is formed on at least a portion corresponding to the latent image. 2. The developing device according to claim 1, wherein the surface roughness of the coating layer is equal to or less than the volume average particle size of the magnetic particles of the developer. 3. The developing device according to claim 1, wherein the average thickness of the coating layer is equal to or less than the volume average particle size of the magnetic particles of the developer. 4. The developing device according to claim 1, wherein said coating layer is formed as an integral film. 5. The developing device according to claim 1, wherein said coating layer is formed of an aggregate of particles of a soft magnetic material. 6. The developing device according to claim 5, wherein the volume average particle diameter of the soft magnetic material particles is equal to or less than the volume average particle diameter of the magnetic particles of the developer. 7. A developing device using a developing roller having a plurality of magnetic poles, and a sleeveless magnet roll for rotating a developer while carrying a magnetic force to develop a latent image on the surface of the image bearing member. The magnetized state of the developing roller is controlled in the tangential direction of the developing roller at a distance within the distance between the tip of the developer regulating member for regulating the amount of developer supplied to the developing area on the developing roller surface and the developing roller surface. A developing device wherein a magnetic flux density is set to a magnetized state in which the magnetic flux density is larger than a maximum magnetic flux density in a normal direction of the developing roller. 8. A developing device using a developing roller having a plurality of magnetic poles, and a sleeveless magnet roll for rotating a developer while carrying a magnetic force to develop a latent image on the surface of the image bearing member. A position where the distance between the developing roller and the developer regulating member for regulating the amount of the developer supplied to the developing area on the front surface is minimized, and the amount of the developer is regulated prior to regulating the amount of the developer by the developer regulating member. An angle θd with respect to the center of the developing roller between the developer regulating member and the position where the distance between the developer regulating auxiliary member and the developing roller disposed at the upstream side in the developing roller rotation direction of the developer regulating member is minimized, An angle θd ≠ p · θm that is not an integral multiple of an angle θm between the adjacent magnetic poles of the developing roller and the center of the developing roller.
(P: integer). 9. The developing device according to claim 8, wherein the angle 2θd that is twice the angle θd is an angle 2θd = q · θm (q: integer) that is an integral multiple of the angle θm. apparatus. 10. A developing device using a developing roller having a plurality of magnetic poles, and a sleeveless magnet roll for rotating a developer while carrying a magnetic force to develop a latent image on an image carrier surface. A developer regulating member for regulating the amount of developer supplied to the development region on the surface, or a developer regulating member for regulating the amount of developer prior to regulating the amount of developer by the developer regulating member. The angle between the center of the developing roller and the rubbing surface of the developer regulating auxiliary member arranged on the upstream side in the rotation direction of the developing roller, the rubbing surface facing the developing roller and rubbing against the developer magnetically supported by the developing roller. A developing device, wherein θw is an angle θw = r · θm (r: an integer) that is an integral multiple of an angle θm formed between the magnetic poles adjacent to each other and the center of the developing roller.