JPH01302283A - Developing device - Google Patents

Abstract

PURPOSE:To eliminate a void arising in a peripheral part of a solid image by installing an electrode plate, which attracts toner included in developer to the surface of the developer, in the upstream part of a developing area in the developer feeding direction. CONSTITUTION:The developing area 25 is formed in the part where a developing roller 18 faces a photosensitive drum 24. Development is performed in the developing area 25 by bringing the bristle edge of a magnetic brush 20 in contact with the surface of the photosensitive drum 24. In addition, the electrode plate 20 which attracts toner included in the developer forming the magnetic brush 20 to the surface of the magnetic brush 20 is installed in the upstream part of the developing area 25 in a magnetic brush feeding direction. A bias voltage of polarity opposite from the electrified polarity of the toner is applied by a power supply circuit 31 to the electrode plate 20. Therefore, a void occurring in the peripheral part of the solid image is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a developing device, and in particular, the present invention relates to a developing device, and in particular, a developer is conveyed to a developing area by a developer carrier, and a static image formed on the latent image carrier is removed. The present invention relates to a developing device that performs development by supplying toner to an electrostatic latent image.

(Prior Art) Generally, in a magnetic brush developing device that uses a two-component developer installed in an electrophotographic copying machine, etc., the developer in the developing tank is made to stand on a developer carrier to form a magnetic brush. At the same time, the magnetic brush is conveyed to a developing area, and the tip of the brush is brought into sliding contact with the latent image carrier, whereby the electrostatic latent image is developed and visualized. The developer is composed of a magnetic carrier and toner.
Development is performed by selectively transferring toner charged so as to have a certain polarity with respect to the electrostatic latent image in a predetermined potential state toward the electrostatic latent image.

In addition, a developing bias that has a predetermined relationship with the electrostatic latent image and each charging state of the toner is applied to the developer carrier side, and this developing bias prevents toner staining on the background area, etc. This ensures good selective transfer of toner.

FIG. 7 is a schematic diagram showing an example of electric field strength distribution due to solid latent image potential. As shown in this figure, in the solid image area, a developing electric field is formed that attracts toner from the developer carrier side toward the latent image carrier side, and in other background areas, especially the solid image area. A reverse electric field is formed around the periphery of the toner in a direction that pushes the toner toward the developer carrier. The strength of these electric fields is determined by the value of the soul aversion bias described above.

FIG. 8 also shows that when a developing electric field is applied between the latent image carrier 1 and the developer carrier 2, the magnetic brush 3
FIG. 3 is a schematic diagram showing a state in which toner particles therein are moved toward the latent image carrier 1 side. As shown in this figure, the toner particles 3a are moved by the developing electric field from the side of the developer carrier 2 toward the side of the spiked carrier particles 3b, and as a result, the toner particles 3a become latent. It is successfully transferred to the image carrier 1 side.

(Problems to be Solved by the Invention) On the other hand, FIG. 9 shows a case where a reverse electric field is applied between the latent image carrier 1 and the developer carrier 2. In FIG. Such a reverse electric field is formed around the background portion and the solid image portion as described above. The toner particles 3a are moved by this reverse electric field toward the developer carrier 2 side, that is, toward the root side of the carrier particles 3b that have been made into spikes, and as a result, there are fewer toner particles 3a at the ear ends of the carrier particles 3b. . In particular, in the periphery of a solid image area where a strong reverse electric field is formed, the toner particles 3a may not exist at the tip of the carrier particles 3b.

If the magnetic brush 3 enters the developing area with fewer or no toner particles at its tip and comes into contact with the electrostatic latent image, a good developing effect will no longer be achieved and the density will increase. This may result in only a pale image being obtained, or so-called white spots may occur in the image. moreover,
Since the carrier particles are charged to the opposite polarity to the toner particles, if the carrier particle ears come into contact with an image area that has already been developed, the toner in the image area may be taken up by the carrier again. In this case, if a predetermined amount of toner is attached to the carrier side, the lines of electric force generated between the carrier and toner will form a closed system, and no electric force will be applied to the outside. . However, when the amount of toner decreases due to the above-mentioned reverse electric field force, the force of the charged charge of the carrier acts on the outside.

This tendency becomes stronger as the resistance value and dielectric constant of the carrier increases, and the discharge time constant τ (=ρε) of the carrier increases.
Depends on.

In order to solve the above problems, measures such as narrowing the development gap and lowering the resistance of the developer have been considered. However, both of these methods cannot sufficiently reduce white spots, and when narrowing the development gap, the development characteristics will change.
Furthermore, when the developer is made to have a low resistance, there is a problem in that the stability against environmental changes is reduced.

Therefore, the present invention has developed a development method that can effectively eliminate the phenomenon of white spots that occur in the background area, especially in the peripheral area of solid images, with a simple structure, and that can stably obtain high-quality images. The purpose is to provide.

(Means for Solving the Problems) In order to achieve the above object, the invention as set forth in claim 1 is such that the developer carrier is arranged close to the latent image carrier, and the developer carrier is disposed close to the latent image carrier. forming a development area,
In the developing device, the developer is conveyed to the development area by the developer carrier, and development is performed by supplying toner from the developer carrier side to the electrostatic latent image formed on the latent image carrier. , an electrode plate is installed in the upstream portion of the developing area in the developer transport direction to attract the toner in the developer to the surface layer of the developer.

Further, in the invention described in claim 2, a developer carrier is installed close to the latent image carrier to form a development area in the opposing portion of these two members, and the developer carrier is used to develop the image. By transporting the agent to the development area,
In a developing device that performs development by supplying toner to an electrostatic latent image formed on a latent image carrier from the developer carrier side, the developer conveying direction of the developing area, which is the developer carrying area with respect to the developing area. An electrode plate is installed on the upstream side to draw the toner in the developer to the surface layer of the developer, and the electrode plate is installed so as to cover a part of the development area.

(Function) In the means having the configurations described in claims 1 and 2, until the magnetic brush is carried into the developing area or immediately after it is carried into the developing area, the toner particles in the magnetic brush are moved by the electrode plate to the tip of the brush. As a result, the effect of attracting the toner toward the developer carrier due to the reverse electric field force is weakened.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 shows a developing device 11 to which the present invention is applied. A toner hopper part 13 is provided at the rear end side (right end side in the figure) of the casing 12 that houses the two-component developer, and a toner cartridge 14 is detachably attached to this toner hopper part 13. It is installed. An agitator 15 is installed inside the toner cartridge 14 to agitate the new toner stored inside.
A toner replenishment roller 6 is pivotally supported at an outlet portion provided at a lower portion of the toner hopper portion 13. The toner sent out from the toner cartridge 14 by the agitation action of the agitator 15 is transferred to the toner hopper part 13.
Once stored, the toner replenishing roller 6 is driven to rotate intermittently to supply a predetermined amount to the vicinity of the paddle wheel 17 provided in the casing 12.

Further, a developing roller 18 as a developer carrier is arranged in front of the paddle wheel 17 (on the left side in the drawing), and the toner and carrier are pumped onto the developing roller 8 while being stirred by the paddle wheel 17. The developer consisting of is made to stand on the surface of the sleeve by a magnet 19 installed in the hollow sleeve of the developing roller 8, thereby forming a magnetic brush 20. This magnetic brush 20 is conveyed in the direction of the arrow, and a doctor blade 21 as a developer regulating member is disposed on the downstream side in the conveyance direction. This doctor blade 21 has a magnetic brush 20
It has the function of regulating the height of the ears, that is, the amount of developer. Further, the excess developer scraped off by the doctor blade 21 is returned to the paddle wheel 17 side while being laterally stirred by the separator 22F3 and the stirring screw 23 installed immediately after the doctor blade 21.

Furthermore, the hollow sleeve forming the developing roller 8 is
A part of the outer surface of the front end thereof is exposed from the front end opening of the casing 12 so as to face the photosensitive drum 24 side as a latent image carrier, and in particular, as shown in FIG. A developing area 11i25 is formed in a portion facing the photosensitive drum 24. In this developing area 25, the tip of the magnetic brush 20 comes into contact with the surface of the photosensitive drum 24, thereby performing a developing action. In this embodiment, the photosensitive drum 24 is moved in the direction of the arrow V (aa+
/sec), and the developing roller 8 is rotated so as to be conveyed at a speed of V/sec).
(ao+/sec), and the relationship between the two is set to be >V and Sp.

Furthermore, an electrode plate 3 is provided on the upstream side of the developing area 25 in the magnetic brush conveying direction to attract the toner in the developer forming the magnetic brush 20 to the surface layer of the magnetic brush 20.
0 is set. This electrode plate 30 is connected to the developing row 51.
It is formed from a thin plate member made of a conductive material and has a predetermined length in the direction of the rotation axis of the magnetic brush 8 and a predetermined width in the conveying direction of the magnetic brush 20 . An insulating layer can also be coated on the surface of the thin plate member. This electrode plate 30
are placed in contact with or close to the tip of the magnetic brush 20, and extend to the boundary of the developing area 25. A bias voltage having a polarity opposite to the charge polarity of the toner is applied to such an electrode plate 30 by a power supply circuit 31, and this bias voltage causes the magnetic brush 20, that is, the toner in the developer, to be transferred to the surface layer of the magnetic brush 20. It seems that people are drawn to it.

In such an embodiment, as particularly shown in FIG. 3, the toner in the magnetic brush 20 is removed from the background by the electric field force of the electrode plate 30 until just before the magnetic brush 20 is carried into the developing area 25. The magnetic brush 20 is attracted to the surface layer of the magnetic brush 20 against the reverse electric field force caused by the magnetic brush 20 . Therefore, a situation in which toner particles decrease or disappear at the tip of the magnetic brush 20 is avoided, and the magnetic brush 20 moves to the development area 1ii in a normal state. A good developing effect is achieved by entering the electrostatic latent image 25 and coming into contact with the electrostatic latent image. Therefore, it is possible to prevent an image with a low density from being obtained or to cause so-called white spots to occur in the image, which is the case with the conventional method.

Furthermore, since the magnetic brush 20 is prevented from being in a state where only the carrier is present as described above, the brush consisting only of the carrier will not come into contact with the image area that has already been developed, and as a result, the image area This prevents the toner from being taken up by the carrier again. Furthermore, by obtaining the magnetic brush 20 in which the toner is well distributed in this way, the image density of the solid image area is increased, and it becomes possible to form a homogeneous image without white spots in the -layer. Note that the image density can be set to a desired value by adjusting the bias voltage value applied to the electrode plate 30.

Further, in the embodiment shown in FIG. 4, the electrode plate 40
is formed to be curved with a constant curvature, so that the electrode plate 40 is arranged along the curvature of the developing roller 18. Such a configuration is convenient because the electrode plate 40 can be extended in a long shape without coming into contact with the photoreceptor drum 24 side.

Furthermore, in the embodiment shown in FIG. 5, a bias application device 51 is attached to the electrode plate 50, and this bias application device 51 includes a control device 52 that performs output control based on image forming timing. It is attached. When the developer comes into contact with the non-image area, the control device 52 switches the bias voltage generated from the bias application device 51 to the same polarity as the toner. According to this embodiment, when a developing operation is not performed, the toner particles are moved toward the developing roller 18, thereby removing the toner adhered to the electrode plate 50 and preventing the toner from sticking. Inconveniences such as generation of oppositely charged toner due to friction between toners can be avoided. A bias applying device 53 that applies a developing bias to the developing roller 18 is also provided with a control device 54 that performs output control based on image forming timing. By controlling the output of the developing bias using the control device 54 as described above, it becomes possible to perform the above-described operation of removing the adhered toner on the electrode plate 50 even more effectively.

Note that each of the bias application devices 51 and 53 is configured in a circuit such that it can output two or more different bias values. .

Furthermore, in the embodiment shown in FIG. 6, an electrode plate 60 is placed over a portion of the development area. Even in such embodiments, the same functions and effects as those of the above-mentioned embodiments can be obtained. In this embodiment, the portion of the electrode plate 6° that comes into contact with the photoreceptor drum 24 is insulated, thereby preventing leakage of the electrostatic latent image. As for insulation treatment,
Depositing aluminum on polyethylene terephthalate (PET) can be employed.

In each of the above embodiments, if alternating current is superimposed on the bias applied to the electrode plate, similar effects such as improving white spots can be obtained, and at the same time, toner adhesion to the electrode plate can be prevented by the action of the alternating current voltage. This is also possible and convenient.

Note that the present invention can be applied regardless of whether the development is normal rotation development or reverse development.

(Effects of the Invention) As described above, in the developing device according to the invention described in claims 1 and 2, the toner in the magnetic brush is The electrode plate that attracts the toner to the surface layer of the magnetic brush is ms#AI to prevent the toner from penetrating into the deep layer.
T! , it is possible to maintain a good distribution of toner particles against the above-mentioned reverse electric field, and with a simple structure, toner particles that tend to occur in the background area, especially in the periphery of solid images, can be maintained. The phenomenon of white spots can be effectively eliminated, and at the same time, the image density of solid image areas can be further increased. Therefore, according to the present invention, high quality images can be stably obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an enlarged part of a developing device according to an embodiment of the present invention, FIG. 2 is a schematic vertical sectional view showing the entire developing device, and FIG. 3 is an electrode plate. FIG. 4 is a schematic explanatory diagram showing an enlarged part of a developing device in another embodiment of the present invention, and FIGS. 5 and 6 are schematic illustrations of the present invention. 7 is a schematic explanatory diagram showing a part of the developing device in another embodiment, FIG. 7 is a schematic distribution diagram showing an example of the electric field intensity distribution formed by the potential of a solid latent image, and FIG. Schematic explanatory diagram showing a state in which a developing electric field is applied between a carrier and a developer carrier, No. 9
The figure is a schematic explanatory diagram showing a state in which a reverse electric field is applied between the latent image carrier and the developer carrier. 11...Developing device, 18...Developing roller, 24...
・Photosensitive drum, 25...Development area, 30.40,5
0°60...electrode plate. (% 1 Ru) 77h5 Kusakui (Tie ζ〉7゛

Claims (1)

[Scope of Claims] 1. A developer carrier is installed close to the latent image carrier to form a development area in the opposing portion of these two members, and the developer is transferred to the development area by the developer carrier. In a developing device, in which toner is supplied from the developer carrier side to an electrostatic latent image formed on a latent image carrier to perform development by conveying the toner to A developing device characterized in that an electrode plate is installed in an upstream portion of a certain developing region in a developer conveying direction to attract toner in the developer to a surface layer portion of the developer. 2. By installing a developer carrier close to the latent image carrier to form a development area in the opposing portion of these two members, and by causing the developer carrier to transport the developer to the development area, In a developing device that performs development by supplying toner to an electrostatic latent image formed on a latent image carrier from the developer carrier side, the developer conveying direction of the developing area, which is the developer carrying area with respect to the developing area. A developing device characterized in that an electrode plate is installed in an upstream portion to attract toner in the developer to a surface layer portion of the developer, and the electrode plate is installed so as to cover a part of the development area. Device.