JP3513343B2 - Image forming device - Google Patents

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) contacted with a photosensitive drum (image carrier).
There is known a charging device that uniformly charges the surface of the photosensitive drum to a predetermined potential by applying a charging voltage to the power source.

In such a charging device, charged toner such as transfer residual toner adhering to the surface of the photosensitive drum may be transferred and adhered to the surface of the charging roller, resulting in defective charging.

As a preventive measure, for example, a method of transferring dirt on the surface of the charging roller to the surface of the photosensitive drum by rubbing between the surface of the charging roller and the surface of the photosensitive drum based on that the charging roller is driven to rotate by the rotation of the photosensitive drum. Alternatively, a method of gently pressing a cleaning member such as a sponge on the surface of the charging roller to wipe off dirt is used.

[0005]

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

According to the method of pressing the cleaning member, the surface of the charging roller is often scratched.

In recent image forming apparatuses,
There is a strong demand for further extension of the replacement intervals and maintenance intervals of consumable parts by extending the service life of functional members.

Therefore, the present invention provides a charging means (in the above description,
An object of the present invention is to provide an image forming apparatus that extends the life of a charging roller and prevents image unevenness due to charging unevenness for 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 for charging the image carrier by applying a charging voltage from a charging power source, and the image carrier after charging. An exposing unit that exposes the surface to form an electrostatic latent image, a developing unit that adheres charged toner having a predetermined polarity to the electrostatic latent image to form a toner image, and a transfer voltage is applied by a transfer power source. In an image forming apparatus including a transfer member that transfers a toner image on an image carrier to a transfer material, and a cleaning unit that removes deposits on the image carrier,
During non-image formation, the charging voltage, a control means for cleaning sequence by controlling the transfer voltage, the control means, as the cleaning sequence, the charge of the same polarity as the toner to the transfer member by said transfer power supply voltage causes charge to the image bearing member to the charged toner of the same polarity is applied to the, by applying a DC voltage of the charged toner and the opposite polarity to the contact charging member by said charging power source, the charging
A toner having a polarity opposite to that of the toner is transferred from the contact charging member to
It is characterized in that the toner is transferred to the image carrier in the state of being charged to the same polarity as the charged toner .

[0010] The present invention according to claim 2, wherein the contact charging member and at least one of the said cleaning means and said exposure means and said developing means and said image bearing member incorporated integrally in the cartridge container A process cartridge is configured, and the process cartridge is detachably attached to the main body of the image forming apparatus.

In the present invention according to claim 3, the control means controls the charged toner in the cleaning sequence.
After transferring the toner having the opposite polarity to the image carrier, the cleaning sequence of the transfer member is further activated .

The present invention according to claim 4 is characterized in that the contact charging member is a charging roller.

The present invention according to claim 5 is characterized in that 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.

The present invention according to claim 7 is characterized in that the control means performs the cleaning sequence every time the 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.

[0017] For image bearing member, charged toner (negative polarity) the same polarity of voltage to the transfer member by a transfer power source (negative polarity)
Is applied to charge the image carrier to the same polarity as the toner (negative polarity) . Further, a voltage (positive polarity) opposite to the charged toner (negative polarity) is applied to the contact charging member by the charging power source. In this way, toner of the opposite polarity to charged toner (positive electrode)
Contact charging member sex) is adhered, charged toner (negative
Sex) and in reverse polarity (positive polarity), while image carrier, because the charged toner (negative polarity) the same polarity (negative polarity), reverse polarity of the toner on the contact charging member (positive polarity) is contacted Transfer from the charging member to the image carrier. The toner of the opposite polarity (positive polarity) transferred to the image carrier is removed from the image carrier by a cleaning unit that cleans the image carrier.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a vertical cross-sectional view showing a schematic configuration of an image forming apparatus according to the present invention. The image forming apparatus shown in the figure 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 is provided with a scanner unit (exposure means) 1 on the upper part of the apparatus main body. The scanner unit 1 has an optical unit that emits a laser beam emitted according to image information, and a scanning unit that scans the emitted laser beam on a photosensitive drum described later.

A detachable process cartridge 10 is mounted in the substantial center of the apparatus main body. The process cartridge 10 according to the present embodiment includes a drum type photoconductor (hereinafter referred to as “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 onto the photosensitive drum 3; A cleaner (cleaning means) 8 for removing residual toner and the like are integrally incorporated in a cartridge container 9 to form a cartridge. The process cartridge 10 does not have to have all the photosensitive drum 3, the charging roller 4, the developing device 5, and the cleaner 8, and
Any device that has at least one of these devices may be used. For example, only the cleaner 8 may be formed as a cartridge as the cleaning unit 11.

The photosensitive drum 3 in the process cartridge 10 is rotationally driven in the direction of arrow 3, and the surface thereof is uniformly charged by the charging roller 4, and then the scanner unit 1 is used.
The laser light emitted in (1) is applied through the mirror 2 to form an electrostatic latent image. The electrostatic latent image is developed (visualized) as a toner image with toner attached by the developing device 5.

The toner image on the photosensitive drum 3 is transferred onto the transfer material 14 by the transfer roller (transfer means) 7. The transfer material 14 is stored in the paper feed cassette 12, is fed by the paper feed roller 13, and is supplied by the registration roller pair 15 in synchronization with the rotation of the photosensitive drum 3 in the direction of arrow R3. is there.

After the transfer of the toner image, the transfer material 14 is guided by a conveyance guide 16 and conveyed to a fixing device 17, where it is heated and pressed to fix the toner image on the surface, and then a discharge tray 19 discharges the sheet. 18 is discharged.

On the other hand, the photosensitive drum 3 after the toner image transfer is
The so-called transfer residual 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 image forming apparatus having the above structure, the above charging roller 4 is connected to the charging power source 20, and
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 means 22. The charging voltage applied to the charging roller 4 by the charging power source 20 and its application timing are controlled by the control means 22. Similarly, the transfer voltage applied by the transfer power supply 21 to the transfer roller 7 and its application timing are also controlled by the control means 2.
Controlled by two.

Further, the above-mentioned image forming apparatus uses an OPC (organic optical semiconductor) as the photosensitive drum 3, and at the time of image formation, a negative voltage is applied to the charging roller 4 so that the photosensitive drum 3 is negative. Is charged, image exposure is performed by the scanner unit 1, and negatively charged charged toner is attached to the electrostatic latent image by the developing device 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 toner image transfer is positively charged 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 uneven charging. In particular,
When particles that are positively charged are mixed as an externally added component of the toner in order to make the toner more negatively charged, the positively charged particles are likely to adhere to the charging roller 4 and uneven charging is likely to occur. .

Next, the cleaning sequence of the charging roller 4, which is a feature of the present invention, will be described in detail. 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 rotationally driven in the direction of arrow R3. At the same time, the transfer bias (transfer power supply 21) is turned on. This transfer bias is a negative voltage because the toner 6 in the developing device 5 has a negative polarity.

The portion where the transfer bias is turned on is subjected to primary charging (charging power source 2
0) turns on. As described above, since the developing method is reversal development and the toner polarity is negative, the primary charging is positive D
C voltage.

Therefore, the dirt mainly composed of toner particles of positive polarity attached to the surface of the charging roller 4 is charged negatively by the transfer roller 7 while the charging roller 4 is positively charged by the transfer roller 7. The charging roller 4
And the attraction force with the photosensitive drum 3 cause the transfer from being pulled back from the surface of the charging roller 4 to the surface of the photosensitive drum 3.

The time to activate this cleaning sequence is
Minimum, may be Re one rotation der of the charging roller 4, depending on the degree of contamination of the charging roller 4, and further extend the time, or can be shortened.

When this cleaning sequence is operated, the surface potential of the photosensitive drum 3 is such that the dark portion potential V _{D is} almost zero.
Therefore, the DC component of the developing bias of the developing device 5 is turned on so that the toner 6 in the developing device 5 is not consumed.

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

One is a method of stopping the application of the transfer bias 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 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 adhesion of the dirt from the photosensitive drum 3 to the transfer roller 7 is reduced.

The second method is to operate 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. Therefore, it will not be described in detail here.

The present invention has been described above in the case of being applied to the image forming apparatus of the process cartridge system, but it is needless to say that the present invention can be similarly applied to the image forming apparatus of the process cartridge system. In the image forming apparatus that is not the process cartridge system, compared to the process cartridge system,
Since it is necessary to use the charging roller 4 for a long period of time, the effect of applying the present invention is great.

The timing for activating the above cleaning sequence is when the power switch of the main body of the apparatus is turned on,
It may be automatically performed during standby after a certain time has passed, or may be performed by a user operating a key on the operation panel of the apparatus body.

By performing the cleaning sequence described above, it is possible to reduce the contamination of the surface of the charging roller 4 and extend the life of the charging roller 4.

The above embodiment will be described below with reference to a more specific device.

The photosensitive drum 3 is an OPC having a diameter of 30 mm.
Using a photoconductor, the 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. The material of this sponge is
Examples thereof include urethane rubber, EPDM, and silicone rubber.
A thin layer is formed on the surface layer to prevent contamination and leak to the OPC photosensitive member. The charging roller 4 has a DC of -140
When the voltage of 0V is applied, the charging start voltage is about -700V
The photosensitive drum 3 is charged to about -700V. During the cleaning sequence, a DC voltage of + 1400V is applied.

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

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

About 5% of Teflon powder is mixed in the surface layer of the OPC photosensitive member to reduce the abrasion of the surface.

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 at the time of image formation, but a transfer bias of about −2 kV is applied to the transfer roller 7 during the cleaning sequence. Applied to. As a result, the photosensitive drum 3 is about -200 to -3.
It will be charged to 00V.

Therefore, the toner on the charging roller 4 (positive
When the (polarity) is transferred to the photosensitive drum 3, the charging roller 4 is +1400 V and the photosensitive drum 3 is -2.
The electric potential is between 0 and -300V, and a strong electric field is formed between them by the electric potential difference, and the electric field causes particles such as toner (positive polarity) on the charging roller 4 to be on the photosensitive drum 3.
Transfer to the top.

<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, and the material of this sponge is urethane rubber, EPDM, silicone rubber or the like. A thin layer is formed on the surface layer to prevent contamination and leak to the OPC photosensitive member. -700V DC is applied to the charging roller 4.
A charging bias in which an AC voltage having a constant current of 1 mA is superposed on the voltage is applied. +700 during cleaning sequence
A voltage obtained by superposing the AC voltage on the DC voltage of V is applied.

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

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

About 5% of Teflon powder is mixed in the surface layer of the OPC photosensitive member to reduce 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 at the time of 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.

[0053] During the cleaning sequence in this embodiment, the charging roller 4, 1 mA to a DC voltage of + 700 V
Since the charging bias in which the AC voltage of the constant current is superimposed is applied, the peeling of the toner (positive polarity) from the surface of the charging roller 4 can be promoted by applying the AC voltage.

<Third Embodiment> FIG. 3 shows the third embodiment.
FIG. 3 is a vertical sectional view showing a schematic configuration of the image forming apparatus of FIG.

In the third embodiment, instead of the transfer roller 7 used in the first embodiment shown in FIG. 1, a transfer charger 23 utilizing corona discharge is used. The rest of the configuration is similar to that of the first embodiment,
A duplicate description will be omitted.

When the transfer charger 23 is used, ozone is generated by corona discharge. However, 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. Quite few. Although it has a negative polarity during the cleaning sequence, the amount of ozone generated is small because it is a short time.

The cleaning sequence in the third embodiment is performed by the transfer charger 23 at the transfer charging timing shown in FIG.
Should be activated.

In the third embodiment, the transfer charger 2 is used.
Since 3 does not contact the photosensitive drum 3, the toner (positive polarity) transferred from the charging roller 4 to the photosensitive drum 3 does not transfer from the photosensitive drum 3 to the transfer charger 23. Was required for Form 2,
A sequence for cleaning the transfer roller 7 is unnecessary, and the cleaning sequence can be simplified.

In the first, second and third embodiments described above, image formation is performed by reversal development using the photosensitive drum 3 of the 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 a cleaning sequence when performing regular 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 The polarity and the like of the above shall be appropriately selected. In either case, in the cleaning sequence, the transfer roller is charged with charged toner.
( Transfer voltage of the same polarity as the regular polarity toner used for developing the electrostatic latent image), and charging toner (electrostatic
A charging voltage having a polarity opposite to that of the regular polarity toner used for developing the latent image) may be applied.

[0060]

As described above, according to the present invention,
The image bearing member is charged with toner by a transfer unit (developing an electrostatic latent image.
The toner is charged to the same polarity as that of the normal polarity toner used for the contact charging member, and the contact charging member is charged to the normal polarity used for developing the electrostatic latent image.
By charging to the opposite polarity to the toner of the polarity) , the toner of the opposite polarity adhered to the contact charging member (developing the electrostatic latent image)
Toner having a polarity opposite to that of the regular polarity used in the above) can be transferred to the image carrier, and stains on the surface of the contact charging member can be effectively removed to eliminate charge unevenness caused by the stain. It is possible to extend the life and form a good image without image unevenness caused by charging unevenness for a long period of time.

[Brief description of drawings]

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

[Explanation of symbols]

3 Image carrier (photosensitive drum) 4 Contact charging member (charging roller) 5 Developer 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

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 21/10

Claims (7)

(57) [Claims] 1. An image carrier, and a contact charging member for charging the image carrier by applying a charging voltage from a charging power source,
Exposure means for exposing the surface of the image carrier after charging to form an electrostatic latent image; developing means for forming charged toner of a predetermined polarity on the electrostatic latent image to form a toner image; and transfer power source. In the image forming apparatus, the transfer member applies a transfer voltage to transfer the toner image on the image carrier to the transfer material, and the cleaning unit removes the deposits on the image carrier. , the charging voltage, a control means for cleaning sequence by controlling the transfer voltage, the control means, as the cleaning sequence, applying the charged toner of the same polarity of the voltage to the transfer member by said transfer power supply with charging the image bearing member to the charged toner of the same polarity and, by applying a DC voltage of the charged toner and the opposite polarity to the contact charging member by said charging power source, the charging toner The contact charging unit the opposite polarity of the toner and
The material is charged to the same polarity as the charged toner.
The image forming apparatus, wherein the image forming apparatus is transferred to the image carrier. Wherein at least one of said contact charging member and the exposing means and the <br/> developing means and said cleaning means, the process cartridge incorporates integrally with said image bearing member to the cartridge container The image forming apparatus according to claim 1, wherein the process cartridge is configured to be detachably attached to the main body of the image forming apparatus. 3. The control means controls the cleaning sequence.
Be carefulToner of the opposite polarity to the charged tonerThe image bearing
After transferring to the body, further transfer memberCleaning sequence
To activate the The image formation according to claim 1 or 2, wherein
apparatus. 4. The contact charging member is a charging roller, and the contact charging member is a charging roller.
The image forming apparatus according to the item. 5. The elastic transfer roller, wherein the transfer member is disposed in contact with the image carrier, and the transfer member is an elastic transfer roller.
The image forming apparatus according to the item. 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 charging toner. 7. The control unit performs the cleaning sequence each time the power switch of the image forming apparatus main body is turned on.
The image forming apparatus according to the item.