JPH09114239A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reuse toner and to remove the toner filming of an image carrier with a compact device. SOLUTION: A cleaning roller 9 is provided to reuse the toner remaining on the image carrier 1, after a transfer is performed and the toner filming which can not be removed by the cleaning roller 9 is eliminated by a developing roller 5. Concretely, at the time of removing the toner filming, the rotational speed of the developing roller 5 is made faster than that at the time of executing development and recovering the toner or the strength of magnetic force at a position where the image carrier 1 faces the developing roller 5 is made greater. Moreover, the toner filming is eliminated at regular intervals in consideration of the life of the image carrier 1.

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 such as a copying machine, a facsimile or a printer, which forms a recorded image by an electrophotographic process using toner.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus is capable of high speed and high density, and its process is as follows. After applying a uniform charge to the image carrier composed of a photoconductive material, an electrostatic latent image is formed by irradiating the image carrier with light based on image information, and the electrostatic latent image is formed by charged particles. The toner image on the image carrier is transferred to a transfer material such as plain paper, and the unfixed toner image is fixed by applying heat and pressure.

Toner that has not been transferred in the transfer process (hereinafter referred to as transfer residual toner) is collected by a cleaning device. The cleaning device may be a blade, a cleaning roller, a magnetic brush cleaning device, or the like. Toner filming on the image bearing member means that toner adheres to the image bearing member and does not separate from the image bearing member during the transfer process or the developing process. Call)
If is not removed, the potential of the exposed portion in that portion does not drop, resulting in image loss.

In a blade cleaning device, the blade can usually remove toner filming. As a technique for removing toner filming when a magnetic brush cleaning device is used, Japanese Patent Application Laid-Open No. 3-155588 discloses a device for performing magnetic brush cleaning with a cleaning sleeve after a transfer means, except for the time of image formation. Techniques for performing filming removal operations in time are shown.

By the way, the toner collected by the cleaning device is put in a container and discarded, or a mechanism for returning the toner to the developing device through a toner conveying path such as a pipe is required for reuse, which leads to an increase in size of the device.

On the other hand, in order to reuse the toner and downsize the apparatus, Japanese Patent Laid-Open No. 6-51672 discloses
A biasing cleaning roller is provided to collect toner by electrostatic force when the image area corresponding to the paper passing portion of the image carrier passes, and toner is passed when the non-image area corresponding to the non-paper passing portion passes. There is shown a technique for adhering to the image carrier.

[0007]

However, of the above-mentioned conventional techniques, the former has a drawback that toner filming can be removed but toner cannot be reused. In the latter case, since the cleaning roller is used, the toner filming on the image carrier cannot be removed.

In view of the above problems, it is an object of the present invention to provide an image forming apparatus capable of reusing toner and removing toner filming of an image carrier with a small apparatus.

[0009]

To achieve the above object, a first invention is to form an electrostatic latent image around an image carrier that rotates or moves in one direction in order along the moving direction. In the image forming apparatus in which the developing unit, the developing unit, the transferring unit, and the cleaning unit are arranged, the developing unit has a function of developing the electrostatic latent image, a function of collecting the toner adhering to the image carrier, and a function of collecting the toner on the image carrier. The cleaning unit has a function of removing toner filming, and has a function of cleaning the toner on the image carrier to hold it on the surface and a function of discharging the held toner to the image carrier. The filming removal function is performed every fixed number of copies or when the power is turned on.

[0010] The second invention is the first invention, wherein:
The toner filming removing function of the developing means is the rotational speed of the developer carrying member V when developing the electrostatic latent image, U when collecting the toner adhering to the image carrying member, and W when removing the toner filming. Is achieved by setting W> V and W> U.

The third invention is based on the first invention.
The toner filming removal function of the developing means is characterized in that it is achieved by switching the strength of the magnetic force at the position where the image carrier and the developer carrier face each other to a level higher than that during development.

According to a fourth aspect of the invention, in the second or third aspect of the invention, when removing the toner filming by the developing means, a bias is applied to the developer carrying member so that the toner is attached to the developer carrying member. Is characterized by.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is premised on the use of cleaning means for recycling the toner remaining on the image bearing member after transfer, specifically, a cleaning roller, and toner filming that cannot be removed by the cleaning roller is performed. It is intended to be removed by the developing roller. Specifically, at the time of removing the toner filming, the rotation speed of the developing roller is made higher than that at the time of developing or collecting the toner, or the strength of the magnetic force at the position where the image carrier and the developing roller are opposed to each other is increased. It should be noted that this is performed at predetermined intervals in consideration of the life of the image carrier.

A detailed description will be given below with reference to the accompanying drawings. FIG. 1 is a schematic diagram centering on an image forming unit of an image forming apparatus according to an embodiment of the present invention. Around the drum-shaped image carrier 1, a charging roller 2, a laser optical system 3 for performing optical writing with a laser beam 4, a developing roller (developer carrier).
5, a developing device 6, a transfer roller 7, a separation charger 8, a cleaning roller 9, and a pre-cleaning charger 1.
A cleaning device 11 having zero and a charge eliminating lamp 12 are arranged, and an image is formed by the following operation. A series of image forming processes will be described by reversal development.

As is well known, the reversal development means that the polarity of the charge uniformly charged before the latent image formation is negative.
This is an image forming method in which after irradiating a background portion with light by image exposure, the background portion is developed with a negatively charged toner, and a positive charge is applied from the back surface of the transfer material at a transfer portion to transfer it to the transfer material.

The image carrier 1 which is a photoconductor (OPC) having an organic photoconductive layer is neutralized by the static elimination lamp 12 and uniformly negatively charged (-700 V) by the charging roller 2, and then the laser optical system 4 drives it. A latent image is formed (the exposed portion potential is −100 V) by the laser light 3 that is irradiated. The laser light 3 is emitted from a semiconductor laser (not shown) and is deflected by a polygonal mirror (polygon mirror) (not shown) having a hexagonal column that rotates at high speed. The deflected laser light passes through an element such as an fθ lens and scans the surface of the image carrier at a constant speed. The writing optical system may be an LED.

The latent image thus formed is developed by the magnetic brush of the developing roller 5 (applied voltage is -550.
V), and a toner image is formed. The developer used is a two-component developer composed of a non-magnetic toner and a magnetic carrier.

On the other hand, a transfer sheet (transfer material) is conveyed from a sheet feeding mechanism (not shown), and a pair of upper and lower registration rollers (not shown) synchronizes with the image front end and the image carrier 1 and the transfer roller 7.
And the toner image is transferred onto this transfer paper. At this time, the transfer bias applied to the transfer roller 7 is + 950V. Then, the transfer paper is separated from the image carrier 1 and is discharged as a copy through the fixing device 13.

Although the toner developed by the developing roller 5 is almost entirely charged to the negative polarity, the transfer roller 7 is supplied with a positive charge, so that a part of the transfer residual toner is charged from the transfer roller 7. When injected, it becomes a positive polarity toner. The pre-cleaning charger 10 supplies a negative corona to these toners, and the toners are recharged to the negative side.

Thus, the transfer residual toner on the image carrier 1 which is almost all negatively charged is cleaned by the cleaning roller 9 and is retained on the cleaning roller 9. At this time, a positive bias is applied to the cleaning roller 9. An image is formed by the above operation.

When one sheet of image is formed, at least one of the rotation direction and the speed of the cleaning roller 9 is switched, and at the same time, a negative bias is applied, and the collected toner is discharged to the image carrier 1. The discharged toner is conveyed to the developing area as the image carrier 1 rotates. At this time, it is desirable that the charging roller 2 be separated from the image carrier 1.

A positive bias is applied to the developing roller 5. In the developing area, the magnetic brush gives an impact force to the toner on the image carrier 1 to collect the toner by the bias. The above operation realizes toner recycling.

In this process, a cleaning blade which is commonly used cannot be used for returning the cleaned toner to the image carrier 1 in the non-image area. Usually, toner filming on the image carrier 1 can be removed by a cleaning blade, but this process requires another means.

Therefore, in the present invention, the developing device 6 is provided with a function of removing toner filming. In order to remove the toner filming, it is necessary to increase the impact force and contact pressure of the magnetic brush more than when collecting the toner.
When the toner is collected, the toner can be collected even under the condition that the developing device 6 removes the toner filming. However, since the toner is collected for each copy operation, the surface of the image carrier 1 is more than necessary. It will be scraped off, and the life of the image carrier 1 will be shortened. Therefore, in the present invention, the toner filming on the image carrier 1 is removed every fixed number of copies or when the copy power is turned on.

(Specific Example 1) When the toner is collected by the magnetic brush, the surface of the carrier is covered with the toner to some extent. The toner is collected by attaching the toner to the uncoated portion of the carrier. Therefore, in order to collect almost 100% of the toner on the image carrier 1, it is necessary to increase the number of contact between the image carrier 1 and the magnetic brush.

However, at the time of development, if the rotational speed of the developing roller 5 is increased, the adverse effect such as the trailing edge of the halftone image coming off may occur, so the rotational speed of the developing roller 5 has an upper limit. Therefore, in the case of recovery, if the rotation speed is the same as that at the time of development, almost 100% recovery may not be possible. Whether or not the rotation speed needs to be changed depends on the rotation speed of the image carrier 1 and the conditions such as the developer. If necessary, the rotation speed V of the developing roller 5 when developing the electrostatic latent image, the image carrier When the rotational speed for collecting the toner attached to the body 1 is U, the rotational speed of the developing roller 5 is switched so that U> V. As a result, the developing roller 5 with respect to the linear velocity of the image carrier 1 when the toner is collected
It is possible to increase the ratio of the linear velocities and increase the number of contact between the image carrier 1 and the magnetic brush.

However, when removing the toner filming, it is necessary to further increase the rotation speed to further increase the impact force of the magnetic brush. Therefore, assuming that the rotation speed for removing toner filming is W, W>
V and W> U. The mechanism for switching the rotation speed of the developing roller 5 may be a known mechanism such as an electromagnetic clutch.

(Specific Example 2) As described above, when removing toner filming, it is necessary to increase the impact force of the magnetic brush more than when recovering toner. Therefore, the effect of removing toner filming can be improved by switching the strength of the magnetic force at the position where the image carrier 1 and the developing roller 5 face each other. At the time of removing the toner filming, the magnetic force between the image carrier 1 and the developing roller 5 is increased,
Harden the magnetic brush ears. At the time of development, if the brush of the magnetic brush is made too hard, a sweep pattern is generated in the image, so it is not preferable to increase the magnetic force above a certain level. Further, by using it in combination with the technique of changing the linear velocity shown in Example 1, the effect of removing toner filming can be further enhanced.

FIG. 2 is a constitutional view of a general developing roller schematically showing the magnetic force distribution. The developing roller 5 has a cylindrical developing sleeve 5a and a cylindrical magnet roller 5b provided therein. Further, magnetic poles P1 to P6 are arranged inside the magnet roller 5b as shown in the drawing to create a magnetic force distribution as shown in the drawing. FIG. 2
The horizontal and vertical directions of are in agreement with FIG. Normally, FIG.
As shown in FIG. 5, stable developing conditions are obtained when the peak of the magnetic force of the main pole is located at an upper position about 7 ° from the position facing the image carrier 1.

FIG. 3 is a block diagram showing an example of the developing roller used in the present invention. FIG. 3A shows a state in which the magnetic pole P1 is separated from the inner peripheral side of the magnet roller 5b, in other words, separated from the image carrier 1. Indicates the status. On the contrary, (b) shows a state of approaching. The magnetic pole P1 has a magnetic force stronger than that of the normal magnetic pole shown in FIG. 2 and is kept away from the inner peripheral surface of the magnet roller 5b during development as shown in FIG. 3A. With this, it is possible to perform the development with the conventional magnetic force. Further, when removing the toner filming, as shown in FIG.
As shown in (b), the magnetic pole P1 is connected to the magnet roller 5b.
Approach the inner surface of. As a result, the magnetic force of the main pole can be increased when removing the toner filming.

(Specific Example 3) To remove toner filming, the effect of the bias applied to the developing roller 5 is not so great. However, when the rotation speed of the developing roller 5 (developing sleeve 5a) is increased as in the specific example 1 or the magnetic brush of the magnetic brush is hardened as in the specific example 2, the toner is carried on the image carrier even if the bias is not applied. The toner adheres to the upper part of the sheet 1 and wastes toner. Therefore, by applying a bias to the developing roller 5 in the direction of adhering the toner to the developing roller 5, wasteful consumption of toner can be prevented.

[0032]

According to the image forming apparatus of the first aspect, the function of the developing means to develop the electrostatic latent image, the function of collecting the toner adhering to the image carrier, and the removal of the toner filming on the image carrier. Since it has the above function, even a small-sized image forming apparatus that recycles toner can prevent image deterioration due to toner filming and obtain stable and reliable image quality.

According to the image forming apparatus of the second aspect, the toner filming removal function is achieved because the number of contact between the image carrier and the magnetic brush can be increased by increasing the rotation speed of the developer carrier. can do.

According to the image forming apparatus of the third aspect, the impact force of the magnetic brush can be increased by switching the strength of the magnetic force at the position where the image carrier and the developer carrier face each other. The toner filming removal function can be achieved.

According to the image forming apparatus of the fourth aspect, since bias is applied to the developer carrying member in the direction of adhering the toner to the developer carrying member when removing the toner filming, wasteful toner consumption can be prevented. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram centering on an image forming unit of an image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a general developing roller schematically showing a magnetic force distribution.

FIG. 3 is a configuration diagram showing an example of a developing roller used in the present invention.

[Explanation of symbols]

 1 Image Carrier 2 Charging Roller 3 Laser Optical System 4 Laser Light 5 Developing Roller 5a Developing Sleeve 5b Magnet Roller 6 Developing Device 7 Transfer Roller 8 Separation Charger 9 Cleaning Roller 10 Pre-Cleaning Charger 11 Cleaning Device 12 Electrification Lamp

Claims (4)

[Claims] 1. An image forming apparatus in which an electrostatic latent image forming unit, a developing unit, a transfer unit, and a cleaning unit are sequentially arranged around an image carrier that rotates or moves in one direction along a moving direction. The developing means has a function of developing the electrostatic latent image, a function of collecting the toner adhering to the image carrier, and a function of removing toner filming on the image carrier, and the cleaning means is a function of cleaning the image carrier. Has a function of cleaning the toner of the above and holding it on the surface once and a function of discharging the held toner to the image carrier, and the function of removing the toner filming by the developing means is
An image forming apparatus, which is performed every fixed number of copies or when the power is turned on. 2. The image forming apparatus according to claim 1, wherein
The toner filming removing function of the developing means is the rotational speed of the developer carrying member V when developing the electrostatic latent image, U when collecting the toner adhering to the image carrying member, and W when removing the toner filming. Then, the image forming apparatus is achieved by setting W> V and W> U. 3. The image forming apparatus according to claim 1, wherein
The image forming apparatus is characterized in that the function of removing toner filming by the developing means is achieved by switching the strength of the magnetic force at the position where the image carrier and the developer carrier face each other to a higher strength than that during development. 4. The image forming apparatus according to claim 2, wherein the toner filming is removed by the developing unit,
An image forming apparatus characterized in that a bias is applied to the developer carrying member so that the toner is attached to the developer carrying member.