JPH0792812A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which can surely prevent toner scattered in a developing region from flowing out via a gap between the periphery of a photoreceptor drum and a developing unit even after long-term use and moreover, can be simplified in structure without making the overall size of a device larger and further, generating a noise at the time of actuating. CONSTITUTION:The image forming device is provided with the photoreceptor drum 20 having the formation of an electrostatic latent image on the periphery and rotated, a developing unit 22 developing the electrostatic latent image on the periphery of the drum 20 with the toner by using a magnetic brush developing method, an electrode roller 48a arranged in proximity to the periphery of the photoreceptor drum 20 on the upstream side in the rotational direction of the drum 20 with respect to the developing region where development by the developing unit 22 is attained on the periphery of the drum 20 and having the application of the voltage of the same polarity as that of the toner, to be rotated, a scraping material 52a scraping the toner stuck to the electrode roller 48a and a toner housing tray 54a holding the scraped toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for developing an electrostatic latent image formed on a peripheral surface of a rotating image carrier with toner supplied from a developing means using a magnetic brush developing method. Involved.

[0002]

2. Description of the Related Art In a conventional image forming apparatus of the kind described above, toner not used for development is scattered from a developing area on a peripheral surface of an image carrier by a developing means, and a small part of the toner is scattered around the periphery of the image carrier. It escapes from the developing area to the outside through the gap between the surface and the developing means, and contaminates various components outside the developing area.

Particularly, in an image forming apparatus, when scattered toner adheres to a charger or an optical system for forming an electrostatic latent image on the peripheral surface of an image carrier, uneven image density or so-called fog occurs.
Further, a transfer medium, such as a paper, on which a toner image developed by developing means is transferred from the electrostatic latent image on the peripheral surface of the image carrier is supplied to a transfer area on the peripheral surface of the image carrier. If the above-mentioned scattered toner adheres to the supply means, the scattered toner will eventually stain the transfer medium.

Various means for preventing such escape of scattered toner to the outside of the developing area are known, for example, from Japanese Patent Application Laid-Open No. 4-182683. The above-mentioned means described in this publication has two electrodes arranged close to the image carrier at the upstream end and the downstream end of the developing area in the rotational direction of the image carrier. A voltage having the same polarity as the toner or a voltage obtained by superimposing an AC voltage on the voltage having the same polarity as the toner is applied to the electrodes. The electric field generated between these electrodes and the peripheral surface of the image carrier prevents the scattered toner from escaping to the outside of the developing area as described above.

As another means, it is proposed to shield a gap formed between the peripheral surface of the image carrier at the upstream end and the downstream end of the developing region in the rotational direction of the image carrier with a sheet material or a bristle brush. ing. As still another means, terminal openings of the air suction duct are arranged at the upstream end and the downstream end of the developing area in the rotation direction of the image carrier, and the scattered toner is sucked from the terminal openings to the outside of the developing area. It has also been proposed to prevent such escape of scattered toner.

However, in the above-mentioned first conventional scattered toner escape prevention means, when the amount of scattered toner adhering to the electrodes increases due to long-term use, the above-mentioned scattered toner escape prevention function by the electric field deteriorates. There is a problem of coming. The reason why the scattered toner adheres to the electrode to which the voltage of the same polarity as the toner is applied is that when the negative polarity toner is used as the toner in the developing area, it is usually charged to the negative pole. Figure 6
As shown in Fig. 6, the toner contains a small amount of toner that is charged to the positive pole, which is the opposite of the normal state.The toner that becomes scattered toner is applied with a voltage of the same polarity as the normal negative pole of the toner. It adheres to the existing electrode.

In some cases, positive polarity toner is used as the toner in the developing area. In this case, the same phenomenon as occurs when the negative polarity toner described above is used with the polarity reversed. As shown in FIGS. 7A and 7B, the electric field strength E _G generated between the electrode 10 and the photoconductor 14 when the toner 12 adheres to the electrode 10 can be obtained by the following mathematical formula 1.

[0008]

[Equation 1]

From this equation, the electric field strength E _G depends on the potential V _t of the toner 12 attached to the electrode 10, and
Toner 12 that is positively charged to the opposite of 0
When the amount of adhered particles increases, the inter-gap potential V _G in the gap between the electrode 10 and the peripheral surface of the photoconductor 14
It turns out that is smaller.

Since the force F applied to the scattered toner from the above electric field is obtained by F = qE _G (q is the charge of the scattered toner), the toner 12 charged to the positive pole of the electrode 10 is opposite to the normal state. When the amount of adhered particles increases and the electric field strength E _G decreases, the force F applied to the scattered toner from the electric field also decreases, so that the scattered toner escapes the electric field and escapes to the outside of the developing area.

In the above-mentioned second conventional scattered toner escape prevention means utilizing a sheet material or a bristle brush, after the sheet material or the bristle brush is developed by the electrostatic latent image on the peripheral surface of the image carrier or the developing means. The toner image may be disturbed, and finally, the image transferred from the image carrier onto the transfer medium such as paper may be disturbed. Further, in the above-mentioned third conventional scattered toner escape preventing means using the air suction duct, the installation of the air suction duct and the air suction device complicates the structure of the image forming apparatus and increases the overall size of the apparatus. Makes loud noise during operation.

[0012]

SUMMARY OF THE INVENTION The present invention has been made under the above circumstances, and an object of the present invention is to allow scattered toner in a developing area to be exposed to the outside through a gap between the peripheral surface of the image carrier and the developing means. It is possible to reliably prevent it from escaping to the end even after a long period of use, yet the structure is simple, the overall size of the device does not increase, and there is no noise during operation. Image forming apparatus.

[0013]

In order to achieve the object of the present invention as described above, an image forming apparatus according to the present invention comprises: a rotating image carrier on which an electrostatic latent image is formed on a peripheral surface. A developing means for developing an electrostatic latent image on the peripheral surface of the image carrier with toner by using a magnetic brush developing method; and a developing area on the peripheral surface of the image carrier for development by the developing means. An electrode roller that is arranged close to the peripheral surface of the image carrier on the upstream side in the rotation direction of the image carrier and that is applied with a voltage of the same polarity as the toner and rotates; and scrapes and holds the toner that has adhered to the electrode roller. And a means for scraping off the toner.

Another image forming apparatus according to the present invention is: a rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; and an electrostatic latent image on the peripheral surface of the image carrier is developed by a magnetic brush. Developing means for developing with toner by using a method; on the peripheral surface of the image bearing member on the upstream side in the rotation direction of the image bearing member with respect to the developing area on the peripheral surface of the image bearing member where the development by the developing means is performed. A first electrode roller which is disposed close to each other and to which a voltage having the same polarity as that of the toner is applied and which rotates; a first toner scraping unit which scrapes and holds the toner adhered to the first electrode roller; and an image It is arranged close to the peripheral surface of the image carrier on the downstream side in the rotation direction of the image carrier with respect to the development area where development is performed on the peripheral surface of the carrier, and a voltage having the same polarity as the toner is applied. The second that is rotated
And an electrode roller; and a second toner scraping unit that scrapes and holds the toner adhered to the second electrode roller.

Still another image forming apparatus according to the present invention is: a rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; and an electrostatic latent image on the peripheral surface of the image carrier is magnetically brushed. Developing means for developing with toner using a developing method; and a peripheral surface of the image carrier on the upstream side in the rotational direction of the image carrier with respect to a developing region on the peripheral surface of the image carrier where development by the developing means is performed. An electrode disposed close to the electrode; a voltage having a polarity opposite to that of the toner is applied to the electrode while the electrostatic latent image does not pass through the position on the peripheral surface of the image bearing member facing the electrode, and the above position is kept static. And an electrode voltage control means for setting the electrode to a grounded state or a floating state while the latent image is passing therethrough.

Another further image forming apparatus according to the present invention is: a rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; and an electrostatic latent image on the peripheral surface of the image carrier. Means for developing with a toner by using a magnetic brush developing method; and an image carrier on an upstream side in a rotation direction of the image carrier with respect to a developing region on the peripheral surface of the image carrier where the developing means develops. A first electrode disposed close to the peripheral surface of the first electrode; toner on the first electrode while the electrostatic latent image does not pass through a position on the peripheral surface of the image carrier facing the first electrode. A first electrode voltage control means for applying a voltage having a polarity opposite to that of the first electrode to bring the first electrode into a grounded state or a floating state while the electrostatic latent image passes through the position; Image bearing member for the developing area on the surface of which the developing means performs development A second electrode disposed close to the peripheral surface of the image carrier on the downstream side in the rotational direction; an electrostatic latent image does not pass through a position on the peripheral surface of the image carrier facing the second electrode. A second electrode voltage that applies a voltage having a polarity opposite to that of the toner to the second electrode in between, and makes the second electrode grounded or floating while the electrostatic latent image passes through the position. And a control means;

[0017]

First, in the image forming apparatus described above, an electric field generated between the electrode roller on the upstream side in the rotational direction of the image carrier and the peripheral surface of the image carrier causes the peripheral surface of the image carrier and the peripheral surface of the image carrier. The scattered toner in the developing area is prevented from escaping to the outside through the gap between the developing means on the upstream side in the rotation direction.

In the developing means for developing the electrostatic latent image on the peripheral surface of the image bearing member with toner using the magnetic brush developing method,
Since the amount of toner scattered on the upstream side in the rotation direction of the image carrier is larger than that on the downstream side in the developing area on the peripheral surface of the image carrier where the development is performed by the developing means, the electrode roller is located above the upstream side. It is important for the toner to be disposed on the side close to the peripheral surface of the image bearing member in order to prevent the scattered toner in the developing area from escaping to the outside.

Since the scattered toner adhering to the peripheral surface of the electrode roller is scraped off and held by the toner peeling means, the electric field strength is always maintained in the initial state, and even after long-term use, it remains in the developing area. It is possible to reliably prevent the scattered toner from escaping to the outside. Secondly, in the image forming apparatus described above, an electric field generated between the first and second electrode rollers on the upstream and downstream sides of the image carrier in the rotation direction of the image carrier and the peripheral surface of the image carrier is an image carrier. The scattered toner in the developing area is prevented from escaping to the outside through the gap between the peripheral surface of the developing device and the developing means on the upstream side and the downstream side in the rotation direction of the image carrier.

In the third image forming apparatus described above, while the electrostatic latent image does not pass through a position on the peripheral surface of the image bearing member facing the electrode on the upstream side in the rotation direction of the image bearing member, for example, the image forming apparatus. During warming up or automatic setup of, the electric field generated between the electrode and the peripheral surface of the image carrier by applying a voltage of the opposite polarity to the toner to the electrode,
The scattered toner in the developing area is prevented from escaping to the outside through the gap between the peripheral surface of the image carrier and the developing device on the upstream side in the rotation direction of the image carrier.

Also in this case, the amount of toner scattered on the upstream side in the rotational direction of the image carrier is larger than that on the downstream side with respect to the developing area on the peripheral surface of the image carrier where the development is performed by the developing means. Therefore, it is important that the electrode is arranged close to the peripheral surface of the image carrier on the upstream side in order to prevent the scattered toner in the developing area from escaping to the outside.

In this case, the normal scattered toner charged to the electrode in the opposite polarity to the charged polarity of the image carrier is forcibly and rapidly attached. While the electrostatic latent image passes through the position facing the electrode on the peripheral surface of the image carrier, the electrode voltage control means sets the electrode to the ground state or the floating state, so that the toner adhered to the electrode. Due to this, an electret state is formed, and due to the electric field generated by this electret state, the normal scattered toner receives a force in the direction toward the image carrier and adheres to the electrostatic latent image. Therefore, the amount of normal scattered toner attached to the electrode does not increase even after long-term use.

In the fourth image forming apparatus described above, the electrostatic latent image is formed on the peripheral surface of the image bearing member at the positions facing the first and second electrodes on the upstream side and the downstream side in the rotation direction of the image bearing member. The electric field generated between the first and second electrodes and the peripheral surface of the image carrier by applying a voltage having a polarity opposite to that of the toner to the first and second electrodes while the image carrier does not pass through the image carrier. The scattered toner in the developing area is prevented from escaping to the outside through the gap between the peripheral surface of the body and the developing means on the upstream side and the downstream side in the rotation direction of the image carrier.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will now be described in detail with reference to FIGS. 1 to 7 in the accompanying drawings. FIG. 1 is an enlarged vertical sectional view of a main part of an image forming apparatus according to a first embodiment of the present invention, in which an electrostatic latent image is formed on a peripheral surface of a rotating image carrier. A photoconductor drum 20 as a body and a developing device 22 as a developing unit adjacent to the photoconductor drum 20 are shown.

Around the photoconductor drum 20, the peripheral surface of the photoconductor drum 20 is evenly arranged at the upstream side of the developing device 22 in the rotation direction of the photoconductor drum 20 indicated by an arrow A.
A charger for charging a positive pole having a surface potential of about 900 V and an exposure unit for uniformly forming an electrostatic latent image on the peripheral surface of the photosensitive drum 20 charged to the positive pole are arranged in this order. Further, the toner image developed from the electrostatic latent image by the toner in the developing device 22 is provided on the downstream side of the developing device 22 in the rotation direction of the photosensitive drum 20 indicated by the arrow A. A transfer / fixing device that is transferred from a supply path 24 to a transfer target such as paper and fixes it on the transfer target, and a cleaner 26 that collects the toner remaining on the peripheral surface of the photosensitive drum 20 after the transfer are in this order. It is located in.

Such an overall structure of the image forming apparatus is known. Developing device 22 including a constitution characteristic of the present invention
The structure of the developing device 22 will be described in detail. The developing device 22 includes a developing roller 28 adjacent to the photosensitive drum 20. The developing roller 28 includes a fixed magnet roller 32 having a plurality of magnets 30N and 30S having different magnetic poles, which are separated from each other in the circumferential direction on the circumferential surface, and the magnet roller 32 is concentrically provided on the circumferential surface of the magnet roller 32. Placed magnet roller 3
2, a magnetic brush conveying roller 34 that rotates in a counterclockwise direction indicated by an arrow B symmetrically to the photosensitive drum 20 in the circumferential direction and conveys a magnetic brush.

The developing device 22 has a developer accommodating chamber 36 adjacent to the developing roller 28 on the side opposite to the photosensitive drum 20. A two-component developer composed of toner and carrier is contained in the developer accommodating chamber 36, and the toner and carrier are agitated to form a region on the peripheral surface of the developing roller 28 opposite to the photosensitive drum 20. A toner charging mixer 38 for accumulating the toner and the carrier and agitating the toner is stored. Toner is the developer storage chamber 3
6 is frictionally charged by being stirred by the toner charging mixer 38, and is charged to a negative pole different from the positive pole which is the polarity of the electrostatic latent image on the peripheral surface of the photoconductor drum 20.

The developing device 22 further has a toner storage chamber 40 adjacent to the developer storage chamber 36 on the side opposite to the developing roller 28, and the toner storage chamber 40 is supplied to the toner storage chamber 40 from the outside. A toner supply mixer 42 that supplies toner to the developer storage chamber 36 is stored. The arrangement of the plurality of magnets 30N and 30S in the magnet roller 32 is as follows.

The magnetic brush cleaner 4 is provided on the side opposite to the photosensitive drum 20 with respect to the peripheral surface of the magnetic brush conveying roller 34.
4 is arranged, the magnet 30N of the N pole has a peripheral position on the downstream side in the rotation direction of the magnetic brush transport roller 34 with respect to the magnetic brush cleaner 44 and the peripheral surface of the magnetic brush transport roller 34 at the photosensitive drum 20. The position closest to the position (on the line connecting the center of rotation of the photosensitive drum 20 and the center of the magnetic brush transfer roller 34) and the position near the upstream side of the magnetic brush cleaner 44 in the rotational direction of the magnetic brush transfer roller 34. It is located in and. Further, the S pole magnet 30S is arranged between these three N pole magnets 30N, and is not arranged between the first and last N pole magnets 30N. The plurality of N-pole magnets 30N and S
The pole magnets 30S may be arranged differently from each other.

The magnetic brush in the developer accommodating chamber 36 is moved around the magnetic brush transport roller 34 by the magnetic force of the N-pole magnet 30N located at the downstream side of the magnetic brush cleaner 44 in the rotational direction of the magnetic brush transport roller 34. Stand up with toner charged to the negative pole on the surface. As the magnetic brush transport roller 34 rotates, the magnetic brush transport roller 34
The magnetic brush on the peripheral surface of the magnetic brush is attracted by the S pole magnet 30S and moves together with the magnetic brush conveying roller 34, and the magnetic brush on the magnetic brush before the position where the peripheral surface of the magnetic brush conveying roller 34 comes closest to the photosensitive drum 20. Toner charged to the negative pole is struck on the peripheral surface of the photoconductor drum 20, and if there is an electrostatic latent image charged to the positive pole on the peripheral surface of the photoconductor drum 20, the toner of the negative pole is electrostatic latent image. Attached to.

The magnetic brush cleaner 44 does not drop the magnetic brush that has not fallen from the peripheral surface of the magnetic brush conveying roller 34 even when the peripheral surface of the magnetic brush conveying roller 34 is closest to the photosensitive drum 20. The magnetic force of the N-pole magnet 30N immediately before and the action of the magnetic brush cleaner 44 forcefully drop the magnetic brush transport roller 34 from the peripheral surface to the separated magnetic brush receiver 46, and recirculate the toner charging mixer 38.

In the above-described structure, the toner charged to the negative pole on the magnetic brush before the position where the peripheral surface of the magnetic brush conveying roller 34 comes closest to the photosensitive drum 20 is the peripheral surface of the photosensitive drum 20. When the toner is struck by the toner, the toner scatters, and in the gap between the photoconductor drum 20 and the developing device 22, the photoconductor drum 20 and the magnetic brush conveying roller 34 from the upstream side and the downstream side of the rotation of the photoconductor drum 20.
The airflow generated by the rotation of the roller easily escapes to the outside of the developing device 22.

It has been described in the "Prior Art" section of this specification that the scattered toner that has escaped to the outside of the developing device 22 eventually deteriorates the quality of the toner image transferred onto the transfer target. . In order to prevent the scattered toner from escaping to the outside of the developing device 22, in the first embodiment, the upstream side and the downstream side of the rotation of the photosensitive drum 20 in the gap between the photosensitive drum 20 and the developing device 22. A pair of upper and lower electrode rollers 48 that approach the peripheral surface of the photoconductor drum 20 on the side and extend parallel to the rotation center line of the photoconductor drum 20.
a and 48b are rotatably arranged.

The pair of upper and lower electrode rollers 48a and 48b are given a rotational force separately from the magnetic brush conveying roller 34 of the photosensitive drum 20 or the developing device 22, and inside the developing device 22 at a position facing the photosensitive drum 20. That is, the rotation direction of the upper electrode roller 48a is the same counterclockwise direction as the rotation direction of the magnetic brush transport roller 34, and the rotation direction of the lower electrode roller 48b is opposite to the rotation direction of the magnetic brush transport roller 34. Rotate clockwise.

A predetermined voltage having a predetermined polarity is applied from the DC power supplies 50a and 50b to the pair of upper and lower electrode rollers 48a and 48b, respectively. In this embodiment, the predetermined polarity is the same as the negative polarity which is the normal polarity of the toner in the developing device 22. As a result, a pair of upper and lower electrode rollers 48a, 4a
The electric field generated between each of the photoconductors 8b and the photoconductor drum 20 prevents the scattered toner from escaping to the outside of the developing device 22.

However, when the toner having a positive polarity opposite to the negative polarity which is a normal polarity contained in the developing device 22 becomes a scattered toner, the pair of upper and lower electrode rollers 48a and 48b are provided. It becomes easy to adhere, and it is 1 above and below
When the amount of the toner having the positive polarity attached to the pair of electrode rollers 48a and 48b increases, the electric field becomes weak, and thus the scattered toner can easily escape to the outside of the developing device 22.

Therefore, a pair of upper and lower electrode rollers 48a, 48
To scrape the scattered toner adhering to b, the toner scraping materials 52a and 52b are pressed against the peripheral surfaces of the pair of upper and lower electrode rollers 48a and 48b. Each of the toner scraping materials 52a and 52b can be a plate blade type or a pad pressing type. Then, the elasticity of these materials is used to press the corresponding peripheral surfaces of the pair of upper and lower electrode rollers 48a and 48b with a predetermined pressure.

The toner scraped off from the peripheral surfaces of the pair of upper and lower electrode rollers 48a and 48b by the toner scraping materials 52a and 52b is a pair of upper and lower electrode rollers 48a and 48b.
scraped-off toner storage trays 5 provided below the respective b
It is accommodated in 4a and 54b. Scraped toner storage tray 5
4a and 54b are toner storage trays 54 even when the developing device 22 is tilted during inspection of the developing device 22 or inspection of the image forming apparatus.
The toner contained in the a and 54b is configured not to spill. Further scraped toner storage tray 5
The respective capacities of 4a and 54b are sufficient so that no inspection is required until the life of the developing device 22.

The toner scraping materials 52a and 52b and the corresponding toner storage trays 54a and 54b are placed one above the other.
Toner scraping means for scraping off the toner from the peripheral surfaces of the pair of electrode rollers 48a and 48b and accommodating the scraped toner is configured. A pair of upper and lower electrode rollers 48
The rotational speeds of a and 48b can be selected depending on the condition of the scattered toner in the vicinity of the pair of upper and lower electrode rollers 48a and 48b in the developing device 22.
The same peripheral speed as the peripheral speed when rotating 0
It is preferable to obtain each of the pair of electrode rollers 48a and 48b.

The gap between each of the pair of upper and lower electrode rollers 48a and 48b and the photosensitive drum 20 and the voltage applied to each of the pair of upper and lower electrode rollers 48a and 48b are an electric field below the Paschen's discharge curve. In this embodiment, the surface potential of the photosensitive drum 20 is 700 to 900V.
Was 0.5-1.0 mm and 500 V-1 kV.

In the above-described embodiment, the toner scraping member 5 is a means for supplying power from the corresponding DC power sources 50a and 50b to the pair of upper and lower electrode rollers 48a and 48b.
2a and 52b, which are independent of the conductive wires, the toner scraping materials 52a and 52b (only the former is shown in FIG. 2) are made of elastic material having conductivity as shown in an enlarged view in FIG. This is formed by a member (for example, a strip of a conductive material such as metal or carbon or an elastic member such as plastic containing powder), so that the DC power source 50 can be used.
It can be used as a power supply means from a, 50b to the toner scraping material 52a, 52b.

Further, in the above-described embodiment, the peripheral surface of the magnetic brush carrying roller 34 among the plurality of magnets 30N and 30S in the magnet roller 32 of the developing roller 28 of the developing device 22 is located at the position closest to the photosensitive drum 20. What was disposed was on the line connecting the center of rotation of the photoconductor drum 20 and the center of the magnetic brush transport roller 34, but as shown in the enlarged view of FIG. By slightly shifting to the side, the angle at which the tip of the magnetic brush rising with the toner on the magnetic brush conveying roller 34 collides with the peripheral surface of the photoconductor drum 20 can be weakened, and the sliding contact distance can be increased. The efficiency of toner development by the magnetic brush on the peripheral surface of the photosensitive drum 20 is improved.

In this case, most of the scattered toner generated is on the upstream side described above, and as shown in FIG. 3, the electrode roller on the downstream side and the DC power source corresponding thereto can be omitted. Even in the embodiment shown in FIG. 1, depending on the toner scattering condition in the developing area of the developing device 22, the downstream electrode roller and the DC power source corresponding thereto can be omitted as shown in FIG. .

FIG. 4 is an enlarged vertical sectional view of the main part of the image forming apparatus according to the second embodiment of the present invention. Most of the structure of the main part of the image forming apparatus is shown in FIG. Figure 1
The structure of the main part of the image forming apparatus according to the first embodiment of the present invention shown in FIG. Therefore,
In the second embodiment of FIG. 4, the same components as those of the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

The second embodiment of FIG. 4 differs from the first embodiment of FIG. 1 in that a pair of upper and lower electrode rollers 4 of the first embodiment is used.
8a and 48b instead of electrode plates 60a and 60 at the same position
b is used, and a pair of electrode rollers 48
Toner scraping materials 52a and 52b for a and 48b and a toner storage tray 54 for storing the scraped toner
a and 54b are omitted.

The photosensitive drum 2 is attached to the electrode plates 60a and 60b.
The DC power supply 50a corresponding to the voltage of the negative pole, which is the polarity opposite to the polarity of the normal toner, and the positive pole, which is the polarity opposite to the normal polarity of the toner, while the electrostatic latent image does not pass through the positions facing the electrode plates 60a and 60b on the peripheral surface of 0. , 50b. As a result, most of the scattered toner having a negative polarity, which is the normal polarity, inside the developing device 22 is generated in the electrode plates 60a and 60b.
Is forced to adhere rapidly. However, the photosensitive drum 2
As described above, the problematic scattered toner is not attached because 0 is charged to the positive polarity which is the same polarity as the charged polarity.

While the electrostatic latent image passes through the position facing the electrode plates 60a and 60b on the peripheral surface of the photosensitive drum 20, it is interposed between the DC power supplies 50a and 50b and the electrode plates 60a and 60b. Electrode voltage control means (not shown) brings these electrode plates 60a and 60b into a grounded state or a floating state. By doing so, the electrode plates 60a, 60
The electric charge of the attached toner itself is held in b. The charge of the toner attached to the electrode plates 60a and 60b in the grounded state or the floating state has little attenuation even if left for a long time. Thereby, the electrode plates 60a, 6
An electric field is generated between the toner adhering to 0b and the photoconductor drum 20, and the action of this electric field prevents escape of scattered toner from the gap between the electrode plates 60a and 60b and the photoconductor drum 20.

A CPU, for example, can be used as the electrode voltage control means (not shown) for controlling in this way. A gap between each of the pair of upper and lower electrode plates 60a and 60b and the photosensitive drum 20, and a pair of upper and lower electrode plates 60a and 6b
The voltage applied to each of 0b is set to be an electric field equal to or lower than Paschen's discharge curve, and in this embodiment, 0.5 when the surface potential of the photosensitive drum 20 is 700 to 900V.
˜1.0 mm and 0.2V to 500V.

The respective dimensions of the pair of upper and lower electrode plates 60a and 60b in the rotation direction of the photosensitive drum 20 are as follows: the flow velocity of air around the photosensitive drum 20 and the magnetic brush conveying roller 34, and the pair of upper and lower electrode plates 60a. , 60b and the photoconductor drum 20, and a pair of upper and lower electrode plates 60.
Optimum values are designed in consideration of the applied voltage to each of a and 60b, the layout size constraint of the developing device 22 in the image forming apparatus, and the like.

FIG. 5A shows a pair of upper and lower electrode plates 60a,
60B is a diagram showing a model of a potential when a voltage having a polarity opposite to the most negative polarity, which is the normal polarity, is applied to the toner inside the developing device 22 in each of 60b,
a is a potential having a polarity opposite to the minus polarity which is the normal polarity of most of the toner inside the developing device 22 applied to each of the pair of upper and lower electrode plates 60a and 60b, and Vs is the photosensitivity. Vt is a potential on the peripheral surface of the body drum 20, Vt is a potential of scattered toner attached to each of the pair of upper and lower electrode plates 60a and 60b, and VG is a potential of the pair of upper and lower electrode plates 60a and 60b and the photosensitive drum 20. It is the potential in the gap between and.

The electric field voltage Vt of the scattered toner attached to each of the pair of upper and lower electrode plates 60a and 60b is -200V to -5.
Reach 00V. Then, a pair of upper and lower electrode plates 60a, 6
The scattered toner attached to each of 0b constitutes an electret, and there is almost no attenuation after several hours. FIG. 5B
After the state of FIG. 5A, a pair of upper and lower electrode plates 60a,
It is a figure which shows the model of the electric potential when each of 60b is made into a grounding state (Va = 0).

In the state of FIG. 5B, the strength E _{G of the} electric field generated between each of the pair of upper and lower electrode plates 60a and 60b and the photosensitive drum 20 can be obtained by the following mathematical formula 2. .

[0053]

[Equation 2]

The meanings of various symbols here are the same as those of the above-mentioned mathematical expression 1.

[0055]

As described above in detail, in the image forming apparatus according to the present invention, the scattered toner in the developing area escapes to the outside through the gap between the peripheral surface of the image carrier and the developing means. It can be reliably prevented even after long-term use, and the structure is simple, the overall size of the device is not increased, and noise is not generated during operation.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a main part of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged vertical cross-sectional view showing a modified example in which the toner scraping material for the electrode roller in the embodiment of FIG. 1 functions as a power supply unit for the electrode roller.

FIG. 3 is a schematic vertical cross-sectional view showing a modification of the arrangement of the electrode rollers in the developing device of the image forming apparatus of the embodiment of FIG. 1 and a modification of the arrangement of the magnets in the magnet roller of the developing roller.

FIG. 4 is a schematic vertical sectional view of a main part of an image forming apparatus according to a second embodiment of the present invention.

5A is an electrode plate when a voltage having a polarity opposite to the normal polarity of most of the toner inside the developing device is applied to the electrode plate in the developing device of the image forming apparatus of the embodiment of FIG. It is a figure which shows the model of the electric potential between a photoreceptor and (B) is (A).
It is a figure which shows the model of the electric potential between an electrode plate and a photoreceptor when the electrode plate is grounded after the above state.

FIG. 6 is a diagram showing a polarity distribution of toner in a developing device of a normal image forming apparatus.

7A and 7B are diagrams showing a model of a potential generated between a scattered toner and a photoconductor drum when the scattered toner adheres to a scattered toner splashing prevention electrode in a conventional image forming apparatus.

[Explanation of symbols]

20 ... Photosensitive drum (image bearing member), 22 ... Developing device, 24
... Transferred material supply path, 26 ... Cleaner, 28 ... Developing roller, 30N, 30S ... Magnet, 32 ... Magnet roller,
34 ... Magnetic brush transport roller, 36 ... Developer storage chamber, 3
8 ... Toner charging mixer, 40 ... Toner storage chamber, 42 ... Toner supply mixer, 44 ... Magnetic brush cleaner, 46 ... Separation magnetic brush receiver, 48a, 48b ... Electrode roller, 50
a, 50b ... DC power source, 52a, 52b ... Toner scraping material (toner scraping means), 54a, 54b ... Toner storage tray (toner scraping means), 60a, 60b
… Electrode plate.

Claims (4)

[Claims] 1. A rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; and a developing process for developing the electrostatic latent image on the peripheral surface of the image carrier with toner using a magnetic brush developing method. And means arranged on the peripheral surface of the image bearing member close to the peripheral surface of the image bearing member on the upstream side in the rotation direction of the image bearing member with respect to the developing area where development is performed by the developing means, and has the same polarity as the toner. An image forming apparatus comprising: an electrode roller that is rotated by applying the voltage of 1. and a toner scraping unit that scrapes and holds toner attached to the electrode roller. 2. A rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; and a developing process for developing the electrostatic latent image on the peripheral surface of the image carrier with toner using a magnetic brush developing method. And means arranged on the peripheral surface of the image bearing member close to the peripheral surface of the image bearing member on the upstream side in the rotation direction of the image bearing member with respect to the developing area where development is performed by the developing means, and has the same polarity as the toner. A first electrode roller that is rotated by applying a voltage of 1; a first toner scraping unit that scrapes and holds the toner adhered to the first electrode roller; and a developing unit on the peripheral surface of the image carrier. A second electrode roller which is arranged on the downstream side in the rotation direction of the image carrier with respect to the developing area where development is performed, close to the peripheral surface of the image carrier, and to which a voltage having the same polarity as that of the toner is applied and which rotates. The toner attached to the second electrode roller An image forming apparatus, comprising: a second toner scraping unit that scrapes and holds. 3. A rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; a developing process for developing the electrostatic latent image on the peripheral surface of the image carrier with toner using a magnetic brush developing method. And an electrode disposed on the peripheral surface of the image carrier on the upstream side in the rotational direction of the image carrier with respect to the development area where the development is performed by the developing means, and an electrode arranged near the peripheral surface of the image carrier. While the electrostatic latent image does not pass through the position facing the electrode on the peripheral surface of the carrier, a voltage having a polarity opposite to that of the toner is applied to the electrode, and the electrode passes while the electrostatic latent image passes through the position. And an electrode voltage control means for bringing the electrode into a grounded state or a floating state. 4. A rotating image carrier on which an electrostatic latent image is formed on the peripheral surface; a developing process for developing the electrostatic latent image on the peripheral surface of the image carrier with toner using a magnetic brush developing method. And a first electrode disposed on the peripheral surface of the image bearing member on the upstream side in the rotation direction of the image bearing member with respect to the developing region where the development is performed by the developing unit. While the electrostatic latent image does not pass through the position facing the first electrode on the peripheral surface of the image carrier, a voltage having a polarity opposite to that of the toner is applied to the first electrode to keep the position static. First electrode voltage control means for bringing the first electrode into a grounded state or a floating state while the latent image is passing; to a developing area on the peripheral surface of the image carrier where the developing means develops. Of the image carrier on the downstream side in the direction of rotation of the image carrier. A second electrode placed on the second electrode; a voltage having a polarity opposite to that of the toner is applied to the second electrode while the electrostatic latent image does not pass through a position on the peripheral surface of the image carrier facing the second electrode. An image forming apparatus comprising: a second electrode voltage control unit that applies the second electrode voltage to the ground state or the floating state while the electrostatic latent image passes through the position.