JPH10161500A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong a service life of a charging roller by removing charged toner stuck on the charging roller and to restrain an image unevenness due to the uneven charge. SOLUTION: In this image forming device, a photosensitive drum 3 is charged in negative polarity by applying voltage in the negative polarity to a transferring roller 7 by a transferring power source 21, in order to remove the charged toner in the negative polarity stuck on the charging roller 4. Moreover, the voltage in the positive polarity is applied to the charging roller 4 by the charging power source 20. The toner charged in the positive polarity on the charging roller 4 is forced to transit on the photosensitive drum 3 by forming a strong electric field between the charging roller 4 in the positive polarity and the photosensitive drum 3 in the negative polarity. To the foregoing, the cleaning sequence is performed at the time of non-image forming, by controlling means 22 in a specified timing.

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 an electrophotographic copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a charging roller (contact charging member) brought into contact with a photosensitive drum (image carrier).
There is known a charging device that uniformly charges a surface of a photosensitive drum to a predetermined potential by applying a charging voltage from a power supply to the photosensitive drum.

[0003] In such a charging device, charged toner such as untransferred toner adhering to the surface of the photosensitive drum may transfer and adhere to the surface of the charging roller, resulting in poor charging.

As a preventive measure, for example, based on the fact that the charging roller is driven to rotate by the rotation of the photosensitive drum, dirt on the charging roller surface is transferred to the photosensitive drum surface by sliding friction between the charging roller surface and the photosensitive drum surface. And a method in which a cleaning member such as a sponge is lightly pressed against the surface of a charging roller to wipe off dirt.

[0005]

However, in the above-described method, when image formation (printing) is performed on about 20,000 sheets, image unevenness due to the charging roller may occur. The cause of the image unevenness is that fine powders such as toner components and paper powder gradually adhere to the surface of the charging roller and do not easily peel off. Since the powder is insulative, the charging is disturbed when the photosensitive drum is charged by the charging roller, resulting in uneven charging.

According to the method of pressing the cleaning member, the surface of the charging roller is rather damaged in many cases.

In recent image forming apparatuses,
There is a strong demand for extending the life of the functional member to further extend the replacement interval and maintenance interval of consumable parts.

Therefore, the present invention provides a charging means (in the above description,
It is an object of the present invention to provide an image forming apparatus that extends the life of a charging roller and prevents image unevenness caused by uneven charging over a long period of time.

[0009]

According to a first aspect of the present invention, there is provided an image carrier, a contact charging member to which a charging voltage is applied by a charging power source to charge the image carrier, and the image carrier after charging. Exposing means for exposing the surface to form an electrostatic latent image, developing means for forming a toner image by adhering a charged toner having a predetermined polarity to the electrostatic latent image, and a transfer voltage applied by a transfer power supply; An image forming apparatus comprising: a transfer member configured to transfer a toner image on an image carrier to a transfer material; and a cleaning unit configured to remove deposits on the image carrier.
At the time of non-image formation, the charging voltage, the transfer voltage, and control means for controlling the operation of the contact charging member and the transfer member to perform a cleaning sequence, the control means,
As a cleaning sequence, the transfer power supply applies a voltage having the same polarity as the charged toner to the transfer member to charge the image carrier to the same polarity as the charged toner, and the charging power supply charges the contact charging member to the contact charging member. A DC voltage having a polarity opposite to that of the toner is applied to transfer the charged toner adhering to the contact charging member to the image carrier.

According to a second aspect of the present invention, there is provided a process cartridge in which at least one of the contact charging member, the exposing means, the developing means, and the cleaning means and the image carrier are integrated into a cartridge container. And the process cartridge is detachably mounted to the image forming apparatus main body.

In the present invention according to a third aspect, in the cleaning sequence, after transferring the charged toner adhered to the contact charging member to the image carrier in the cleaning sequence, the control unit further adheres to the transfer member. And transferring the charged toner to the image bearing member.

According to a fourth aspect of the present invention, the contact charging member is a charging roller.

According to a fifth aspect of the present invention, the transfer member is an elastic transfer roller disposed in contact with the image carrier.

The present invention according to claim 6 is characterized in that an AC voltage is applied to the charging roller in addition to a DC voltage having a polarity opposite to that of the charged toner.

According to a seventh aspect of the present invention, the control means performs the cleaning sequence every time a power switch of the image forming apparatus main body is turned on.

[Operation] The main operation (operation corresponding to claim 1) based on the above configuration is as follows.

A voltage having a polarity opposite to that of the charged toner is applied to the transfer member by a transfer power supply to the image carrier to charge the image carrier to a polarity opposite to that of the toner. Further, a voltage having the same polarity as the charged toner is applied to the contact charging member by a charging power source. As described above, the contact charging member to which the charged toner has adhered has the same polarity as the charged toner, while the image carrier has the opposite polarity to the charged toner. From to the image carrier. The charged toner transferred to the image carrier is removed from the image carrier by cleaning means for cleaning the image carrier.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is a laser beam printer of a type in which a process cartridge is detachably attached to an image forming apparatus main body (hereinafter simply referred to as “apparatus main body”).

The image forming apparatus shown in FIG. 1 includes a scanner unit (exposure means) 1 at the top of the apparatus main body. The scanner unit 1 includes an optical unit that irradiates a laser beam emitted according to image information, and a scanning unit that scans the irradiated laser beam on a photosensitive drum described later.

At the approximate center of the apparatus main body, a detachable process cartridge 10 is mounted. The process cartridge 10 in the present embodiment includes a drum-type photosensitive member (hereinafter, referred to as a “photosensitive drum”) 3 as an image carrier.
A charging roller (contact charging member) 4 formed of a semiconductive elastic member; a developing device (developing means) 5 for developing the toner 6 on the photosensitive drum 3; A cartridge (cleaning means) 8 for removing residual toner is integrally incorporated into a cartridge container 9 to form a cartridge. It is not necessary for the process cartridge 10 to have all of the photosensitive drum 3, the charging roller 4, the developing device 5, and the cleaner 8;
What is necessary is just to have at least one of these devices. For example, a cartridge in which only the cleaner 8 is used as the cleaning unit 11 may be used.

The photosensitive drum 3 in the process cartridge 10 is driven to rotate in the direction of arrow 3 and the surface thereof is uniformly charged by the charging roller 4.
Is emitted through the mirror 2 to form an electrostatic latent image. The electrostatic latent image is developed (visualized) as a toner image by attaching toner to the developing unit 5.

The toner image on the photosensitive drum 3 is transferred onto a transfer material 14 by a transfer roller (transfer means) 7. The transfer material 14 is stored in the paper feed cassette 12, fed by the feed roller 13, and supplied by the registration roller pair 15 in synchronization with the rotation of the photosensitive drum 3 in the direction of the arrow R <b> 3. is there.

The transfer material 14 after the transfer of the toner image is conveyed to a fixing device 17 by being guided by a conveyance guide 16, where it is heated and pressed to fix the toner image on its surface. 18 is discharged.

On the other hand, the photosensitive drum 3 after the transfer of the toner image
The so-called untransferred toner remaining on the surface without being transferred to the transfer material 14 is removed by the cleaner 8 and used for the next image formation.

In the above-described image forming apparatus, the charging roller 4 is connected to a charging power source 20.
The transfer roller 7 is connected to a transfer power supply 21, and the charging power supply 20 and the transfer power supply 21 are connected to a control unit 22. The control unit 22 controls the charging voltage applied by the charging power source 20 to the charging roller 4 and the timing of the application. Similarly, the transfer voltage applied by the transfer power supply 21 to the transfer roller 7 and the application timing thereof are also controlled by the control unit 2.
2 is controlled.

In the above-described image forming apparatus, an OPC (organic optical semiconductor) is used as the photosensitive drum 3. When forming an image, a negative voltage is applied to the charging roller 4 so that the photosensitive drum 3 has a negative polarity. Is charged, the image is exposed by the scanner unit 1, and the negatively charged toner is attached to the electrostatic latent image by the developing unit 5, so that a negative toner image is formed on the photosensitive drum 3 by so-called reversal development. Then, a positive transfer voltage is applied to the transfer roller 7 to transfer the toner image onto the transfer material 14. Therefore,
The transfer residual toner remaining on the surface of the photosensitive drum 3 after the transfer of the toner image is charged to a positive polarity by charging by the transfer roller 7, and the positive transfer residual toner passes through the cleaner 8 and adheres to the surface of the charging roller 4. Since the attached charged toner is insulative, it causes charging unevenness. Especially,
When particles that are easily charged to a positive polarity are mixed as an external component of the toner in order to make the toner more negative, the particles of the positive polarity easily adhere to the charging roller 4 and easily cause charging unevenness. .

Next, a cleaning sequence of the charging roller 4 which is a feature of the present invention will be described in detail. Note that the cleaning sequence is performed during non-image formation (other than image formation).

When the main motor (not shown in FIG. 1) starts rotating, the photosensitive drum 3 is driven to rotate in the direction of arrow R3. At the same time, the transfer bias (transfer power supply 21) turns on. This transfer bias is a negative voltage because the toner 6 in the developing device 5 has a negative polarity.

The primary charging (charging power source 2) is performed in accordance with the time when the portion where the transfer bias is turned on passes through the charging roller 4.
0) turns on. As described above, since the developing method is the reversal development and the toner polarity is negative, the primary charging is positive D
C voltage.

Therefore, the contamination mainly composed of the toner particles of the positive polarity adhered to the surface of the charging roller 4 is caused by charging the photosensitive drum 3 to the positive polarity by the transfer roller 7 and charging the charging roller 4 to the negative polarity. Therefore, by the action of the strong electric field formed between the charging roller 4 and the photosensitive drum 3, the toner is returned from the surface of the charging roller 4 to the surface of the photosensitive drum 3 and is transferred.

The time for operating this cleaning sequence is as follows.
At least one turn of the charging roller 4, that is, one turn of the photosensitive drum 3, is sufficient. However, depending on the degree of contamination of the charging roller 4, the time can be further extended or shortened. .

Further, when actuating the cleaning sequence, the surface potential of the photosensitive drum 3, the dark potential V _D is substantially 0
Accordingly, the DC component of the developing bias of the developing device 5 is turned on in response to this, so that the toner 6 in the developing device 5 is not consumed.

When this cleaning sequence is operated, dirt separated from the charging roller 4 is transferred to the transfer roller 7 via the photosensitive drum 3, and there are two methods for preventing this dirt. .

One is a method in which the application of the transfer bias is stopped before the dirt transferred from the charging roller 4 to the photosensitive drum 3 reaches the transfer roller 7. That is, the cleaning sequence is completed by the half rotation of the photosensitive drum 3. According to this method, the transfer bias is turned off before the dirt reaches the transfer roller 7, so that the dirt from the photosensitive drum 3 to the transfer roller 7 is reduced.

The second method is to activate a known cleaning sequence of the transfer roller 7 after the cleaning sequence is completed. This method is a method of cleaning the transfer roller 7 by pre-rotation before image formation, and is a known technique, and thus will not be described in detail here.

Although the present invention has been described with reference to the case where the present invention is applied to a process cartridge type image forming apparatus, it is needless to say that the present invention can be similarly applied to an image forming apparatus which is not a process cartridge type. In image forming apparatuses that are not of the process cartridge type, compared to those of the process cartridge type,
Since the charging roller 4 needs to be used for a long period of time, the effect when the present invention is applied is large.

The above-described cleaning sequence is activated when the power switch of the apparatus main body is turned on,
It may be performed automatically during standby after a certain period of time has elapsed, or may be performed by a key operation by the user from the operation panel of the apparatus main body.

By performing the above-described cleaning sequence, dirt on the surface of the charging roller 4 can be reduced, and the life of the charging roller 4 can be extended.

Hereinafter, the above-described embodiment will be described with reference to a more specific device.

The photosensitive drum 3 is an OPC having a diameter of 30 mm.
Using photoreceptor, process speed is 100mm / se
c.

The outer diameter of the charging roller 4 is 12 mm, and a sponge is used as an elastic body.
Examples include urethane rubber, EPDM, and silicone rubber.
A thin layer is formed on the surface to prevent contamination and leakage to the OPC photoconductor. The charging roller 4 has a DC of -140
0V voltage is applied, and the charging start voltage is about -700V
Are charged to about -700V. During the cleaning sequence, a voltage of +1400 V is applied at DC.

The developing method of the developing device 5 is a jumping developing method, and a bias voltage obtained by superposing an AC voltage of 1600 V _{PP on} a DC voltage of -500 V is applied at the time of image formation. During the cleaning sequence, no AC voltage is applied,
Only DC voltage.

The average particle diameter of the toner was about 6 μm.

The surface layer of the OPC photoreceptor contains about 5% of Teflon powder mixed therein so as to reduce the surface shaving.

As the transfer roller, a sponge roller having a diameter of 18 mm is used, and the voltage is set so that a current of about 5 μA flows during image formation. However, during the cleaning sequence, a transfer bias of about -2 kV is applied to the transfer roller 7. Is applied to As a result, the photosensitive drum 3 becomes approximately -200 to -3.
It will be charged to 00V.

Therefore, when the toner on the charging roller 4 is transferred to the photosensitive drum 3, the charging roller 4 is set at +1400 V and the photosensitive drum 3 is set at -200 to -3.
The voltage becomes 00 V, and a strong electric field is formed between the two by this potential difference, and particles such as toner on the charging roller 4 are transferred onto the photosensitive drum 3 by this electric field.

Second Embodiment In the second embodiment, an OPC photosensitive member having a diameter of 30 mm is used as the photosensitive drum 3, and the process speed is set to about 100 mm / sec.

The outer diameter of the charging roller is 12 mm, and a sponge is used as an elastic body. The sponge is made of urethane rubber, EPDM, silicone rubber or the like. A thin layer is formed on the surface to prevent contamination and leakage to the OPC photoconductor. -700 V DC is applied to the charging roller 4.
A charging bias in which an AC voltage having a constant current of 1 mA is superimposed on the voltage is applied. +700 during cleaning sequence
A voltage obtained by superimposing an AC voltage on a DC voltage of V is applied.

The developing method is a jumping developing method, in which a DC voltage of -500 V is applied to 1600 during image formation.
A bias voltage in which the AC voltage of V _PP is superimposed is applied.
During the cleaning sequence, no AC voltage is applied, and only DC voltage is applied.

A toner having an average particle diameter of about 6 μm was used.

The OPC photoreceptor has about 5% of Teflon powder mixed in the surface layer, thereby reducing the abrasion of the surface of the photosensitive drum 3.

As the transfer roller 7, a sponge roller having a diameter of 18 mm is used, and the voltage is set so that about 5 μA flows during image formation, but about -2 kV is applied to the transfer roller 7 during the cleaning sequence. . As a result, the photosensitive drum 3 is charged to about -200 to -300V.

At the time of the cleaning sequence in this embodiment, the charging roller 4 is applied with a DC voltage of -700 V at 1 mA.
Since the charging bias in which the constant current AC voltage is superimposed is applied, the separation of the toner from the surface of the charging roller 4 can be promoted by applying the AC voltage.

<Embodiment 3> FIG. 3 shows Embodiment 3 of the present invention.
1 is a longitudinal sectional view illustrating a schematic configuration of the image forming apparatus of FIG.

In the third embodiment, a transfer charger 23 utilizing corona discharge is used instead of the transfer roller 7 used in the first embodiment shown in FIG. Other configurations are the same as those in the first embodiment.
Duplicate description is omitted.

When the transfer charger 23 is used, ozone is generated by corona discharge. In the present invention, since the transfer charge during image formation is positive, the amount of ozone generated is smaller than that in the case of negative polarity. You need quite a few. During the cleaning sequence, the polarity is negative, but the amount of ozone generated is small because of the short time.

In the cleaning sequence in the third embodiment, the transfer charger 23 operates at the transfer charging timing shown in FIG.
Should be activated.

In the third embodiment, the transfer charger 2
3 does not come into contact with the photosensitive drum 3, the toner transferred from the charging roller 4 to the photosensitive drum 3 is further transferred to the photosensitive drum 3.
Does not transfer to the transfer charger 23, the sequence for cleaning the transfer roller 7, which is required in the first and second embodiments, is not required, and the cleaning sequence can be simplified. Becomes

In the first, second and third embodiments, the image formation is performed by reversal development using a photosensitive drum 3 of an OPC photosensitive member having a negative charging characteristic. I explained the cleaning sequence,
The present invention is not limited to this. For example, the present invention can be applied to a sequence using a photosensitive drum made of amorphous silicon having a positive charging characteristic, and also to a cleaning sequence in the case of performing normal development. However, in these cases, the polarity of the voltage applied to the charging roller and the transfer roller during image formation, the polarity of the charged toner, and the polarity of the voltage applied to the charging roller and the transfer roller during the cleaning sequence, the charged toner , Etc., should be appropriately selected. In any case, in the cleaning sequence, a transfer voltage having the same polarity as that of the charged toner may be applied to the transfer roller, and a charging voltage having a polarity opposite to that of the charged toner may be applied to the charging roller.

[0060]

As described above, according to the present invention,
The transfer unit charges the image carrier to the same polarity as the charged toner, and charges the contact charging member to the opposite polarity to the charged toner, thereby removing stains mainly composed of the charged toner attached to the contact charging member. And effectively removes dirt on the surface of the contact charging member, eliminates charging unevenness caused by dirt, extends the life of the contact charging member, and provides a good image free from image unevenness due to charging unevenness. It can be formed over a long period.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus (laser beam printer) according to a first embodiment.

FIG. 2 is a timing chart showing a cleaning sequence according to the first embodiment.

FIG. 3 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus (laser beam printer) according to a third embodiment.

[Description of Signs] 3 Image carrier (photosensitive drum) 4 Contact charging member (charging roller) 5 Developing device 7 Transfer member (transfer roller) 9 Photosensitive drum container 10 Process cartridge 11 Cleaning unit 20 Charging power supply 21 Transfer power supply 22 Control means 23 Transfer charger

Claims (7)

[Claims] An image bearing member; a contact charging member to which a charging voltage is applied by a charging power source to charge the image bearing member;
Exposure means for exposing the charged surface of the image carrier to form an electrostatic latent image, developing means for forming a toner image by attaching a charged toner of a predetermined polarity to the electrostatic latent image, and a transfer power supply A transfer member to which a transfer voltage is applied to transfer the toner image on the image carrier to a transfer material, and a cleaning means for removing the deposits on the image carrier. Control means for controlling the charging voltage, the transfer voltage, and the operation of the contact charging member and the transfer member to perform a cleaning sequence, wherein the control means controls the transfer power supply to the transfer member by the transfer power supply as a cleaning sequence. A voltage having the same polarity as the charged toner is applied to charge the image carrier to the same polarity as the charged toner, and the charging power supply causes the contact charging member to be opposite to the charged toner. By applying a sexual DC voltage to transfer the charged toner adhering to the contact charging member to said image bearing member, an image forming apparatus characterized by. 2. A process cartridge comprising at least one of the contact charging member, the exposing means, the developing means, and the cleaning means and the image carrier integrally incorporated in a cartridge container. The image forming apparatus according to claim 1, wherein the image forming apparatus is detachably attached to the image forming apparatus main body. 3. The control unit according to claim 1, wherein, in the cleaning sequence, after the charged toner attached to the contact charging member is transferred to the image carrier, the control unit further removes the charged toner attached to the transfer member. The image forming apparatus according to claim 1, wherein the image is transferred to an image carrier. 4. The device according to claim 1, wherein the contact charging member is a charging roller.
An image forming apparatus. 5. The transfer member according to claim 1, wherein the transfer member is an elastic transfer roller disposed in contact with the image carrier.
An image forming apparatus according to any one of the preceding claims. 6. The image forming apparatus according to claim 4, wherein an AC voltage is applied to the charging roller in addition to a DC voltage having a polarity opposite to that of the charged toner. 7. The image forming apparatus according to claim 1, wherein the control unit performs the cleaning sequence each time a power switch of the image forming apparatus main body is turned on.
An image forming apparatus according to any one of the preceding claims.