JPH09311528A - Electrophotographic image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and uniformly electrify an image carrier all the time, without causing an abnormal discharge such as a white streak and dot by preventing the soiling of an electrifying member. SOLUTION: An electrifying roller 2 is provided in proximity to a photoreceptor drum 1 and a preprocessing roller 3 is provided on the upstream side from the electrifying roller 2. Then, a voltage constituted in such a manner that AC and DC voltages are superimposed is applied to the electrifying roller 2 by a power source circuit 4. Further, the voltage constituted in such a manner that the AC and DC voltages are superimposed is applied to the preprocessing roller 3 by a second power source circuit 5. When the DC voltage applied to the electrifying roller 2 in an image region is defined as DC1, the DC voltage applied to the electrifying roller 2 in a nonimage region is defined as DC2 and the DC component voltage of the voltage applied to the roller 3 is defined as D3, the conditions of |DCI|>|DC2|>|DC3| can be satisfied.

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, a printer and a facsimile machine, and more particularly to a technique for uniformly charging the surface of an image carrier (photoreceptor) thereof.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a drum-shaped or belt-shaped photosensitive member is used as an image carrier, and the surface of the photosensitive member is uniformly charged and then exposed or exposed to light. After writing with a beam to form an electrostatic latent image, the electrostatic latent image is developed with toner to be visualized, and then the toner image is transferred onto a transfer paper, fixed and discharged. In such an electrophotographic process, the main charging methods that have been put into practical use for charging the surface of the photoreceptor are a non-contact method using corona discharge by a corona wire and a medium resistance charging member. There is a contact method of charging by contacting with.

Corona discharge using a corona wire has the advantage that the photoconductor can be charged in a non-contact manner, but since the applied voltage is as high as 5 KV or higher, ozone (O3) and nitrogen oxides (NOx) are generated. A large amount is generated, which may accelerate deterioration of the photoconductor or affect the human body.

The contact method is advantageous in that necessary charging can be performed by applying a voltage of 1 to 2 KV, which hardly generates ozone or NOx, but it is difficult to uniformly charge the surface of the photosensitive member. When the charging member such as the roller is contaminated, there are problems that uneven charging occurs and efficiency is reduced. Further, there is also a problem that the components of the charging member bleed from the portion in contact with the photoconductor to contaminate the photoconductor.

Further, since the elastic roller and the blade are in contact with each other, the photosensitive member is driven by the photosensitive member, and the photosensitive member receives pressure.
Therefore, a method has been proposed in which the charging member is disposed in close proximity to the photoconductor in a non-contact manner so that a burden such as bleeding or abrasion is not applied (Japanese Patent Laid-Open Nos. 4-240670 and 4-240671). (See the bulletin, etc.) As described above, it is considered that bleeding and stains can be prevented by not bringing the photoconductor and the charger into contact with each other.

[0006]

There is a cleaning step before the charging step, in which the toner remaining on the photoconductor after the toner image is transferred onto the transfer paper is removed and cleaned.
However, in the current cleaning device, it is often the case that the toner cannot be completely removed due to the deterioration of the blade and the particle size of the toner, so that the toner may remain on the photoreceptor before charging.

Further, it has been attempted to simplify the cleaning device for cost reduction and the like, and there is a situation in which toner may remain on the photoconductor during charging. In addition, the residual toner has passed through the transfer process and is rubbed by the blade to have an electric charge. This charge is often positive even if the initial toner is negatively charged. Therefore, even when the charging member is arranged close to the photoconductor, toner or the like adheres to the charging member from the photoconductor. When the toner adheres to the charging member, the discharge characteristic of that portion changes, which causes an abnormal discharge image such as white lines and white spots.

The occurrence of the white stripes or white spots occurs when toner or the like adheres to the charging member, and that portion is apparently close to the photoconductor, and the discharge gap is different, so that the charging start voltage is different and a potential difference occurs. It is conceivable that, depending on the conditions, the adhered toner and the like have a lower resistance than the charging member, and a large discharge occurs. Contamination of the charging member can be removed by installing a cleaning device such as a blade or a brush on the charging member as seen in, for example, Japanese Patent Laid-Open No. 7-64369, but a clean nig device and a means for collecting removed toner are required. Therefore, the number of parts increases, which hinders downsizing and cost reduction.

The present invention has been made in order to solve such a problem, and even if toner remains on the surface of the photosensitive member facing the charging member, the charging device is contaminated even if a cleaning device is not provided. It is an object of the present invention to prevent the occurrence of abnormal discharge and to always stably and uniformly charge the image bearing member (photoreceptor) without causing abnormal discharge such as white lines or white spots. Another object is to prevent unnecessary fatigue of the image bearing member.

[0010]

In order to achieve the above object, the present invention comprises an image carrier and a charging member which is provided in the vicinity of the image carrier and charges the surface of the image carrier. In the electrophotographic image forming apparatus, a first power supply unit for applying a voltage obtained by superposing an AC voltage and a DC voltage to the charging member, and an upstream position in the moving direction of the image carrier relative to the charging member. And a second power supply means for applying a voltage obtained by superimposing an AC voltage and a DC voltage to the voltage applying member, the voltage applying member being disposed in the vicinity of the image carrier.

The peak-to-peak (P-P) voltage of the AC component of the voltage applied to the charging member by the first power supply means is AC1, the voltage of the DC component is DC1, and the second power supply means is the above. When the peak-peak (P-P) voltage of the AC component of the voltage applied to the voltage application member is AC2 and the voltage of the DC component is DC2, it is desirable to satisfy the following conditions. | AC1 |> | AC2 |, | DC1 |> | DC2 | Further, the voltage DC2 of the DC component of the voltage applied to the voltage applying member by the second power source does not reach the charging start voltage for the image carrier. It is recommended to use DC voltage.

Further, in an electrophotographic image forming apparatus including an image carrier and a charging member which is provided near the image carrier and charges the surface of the image carrier, the charging member is the above-mentioned. When facing the image area on the surface of the image carrier, a voltage obtained by superposing AC voltage and DC voltage is applied to the charging member, and the charging member faces the non-image area on the surface of the image carrier. Also, an electrophotographic image forming apparatus provided with a power supply means for applying only a DC voltage to the charging member is provided.

Alternatively, in the electrophotographic image forming apparatus including an image bearing member and a charging member provided in the vicinity of the image bearing member and charging the surface of the image bearing member, the charging member is When facing the image area on the surface of the image carrier, a DC voltage higher than the charging start voltage for the image carrier is applied to the charging member, and the charging member faces the non-image area on the surface of the image carrier. Also provided is an electrophotographic image forming apparatus provided with a power supply means for applying a DC voltage that does not reach the charging start voltage to the image carrier to the charging member.

Further, in this image forming apparatus, a voltage applying member is disposed at a position upstream of the charging member in the moving direction of the image carrier and close to the image carrier, and an alternating current is applied to the voltage applying member. Second power supply means for applying a voltage obtained by superposing the voltage and the DC voltage may also be provided. Further, a DC voltage higher than the charging start voltage applied to the image carrier by the power supply means is DC1, a DC voltage not reaching the charging start voltage is D2, and the second power supply means is the voltage applying member. When the voltage of the DC component of the voltage applied to is set to D3, it is desirable to satisfy the following conditions. | DC1 |> | DC2 |> | DC3 |

[0015]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a main part configuration diagram of an electrophotographic image forming apparatus showing a first embodiment of the present invention, and shows a schematic configuration around an image carrier.

In FIG. 1, reference numeral 1 denotes a photosensitive drum which is an image carrier, and a photosensitive layer 1a formed by an OPC (organic photosensitive member) which is negatively charged is covered with an aluminum drum 1b (see FIG. 2). The enlarged view is schematically shown), and rotates in the direction of arrow A. Reference numeral 2 denotes a conductive charging roller which is a charging member, which is opposed to the photosensitive layer 1a of the photosensitive drum 1 via a minute gap G1 and is applied with a voltage by a power supply circuit 4 which is a first power supply means. Photosensitive layer 1
Charge a.

Further, at a predetermined position upstream of the charging roller 2 in the moving direction of the photosensitive drum 1, that is, in the rotating direction,
A roller 3, which is a conductive voltage applying member similar to the charging roller 2, faces the photosensitive layer 1a of the photosensitive drum 1 via a minute gap G2, and is a power supply circuit 5 as a second power supply means. Is applied with a voltage.

Then, the photosensitive layer 1a charged by the charging roller 2 is exposed by a laser beam modulated according to the contrast of the image from a laser writing device (not shown) to form an electrostatic latent image. It is developed with a two-component developer of minus toner by the developing device 6 and visualized. In this embodiment, reversal development is used. At this time, the photosensitive drum 1 is rotating in the arrow A direction at a rotation speed of 180 mm / sec. In the developing device 6, a developing roller 6a and a toner supply roller 6b for supplying toner to the developing roller 6a are provided.

The toner image developed by the developing device 6 is transferred onto a transfer sheet which is conveyed to a transfer section where the photosensitive drum 1 and the transfer roller 7 to which a positive voltage is applied face each other. The transfer sheet is sent from a sheet feeding device or a manual feed tray (not shown) by a sheet feeding roller, stands by before the registration roller, and is sent to the transfer section by the registration roller at a predetermined timing. The transfer roller 7 rotates in the arrow B direction.
In this embodiment, cleaning after transfer is not performed.
However, the blade is installed after the transfer, and the photosensitive drum 1
The toner remaining on the photosensitive layer 1a is collected by an image forming apparatus or a cleaning roller configured to remove the toner remaining on the photosensitive layer 1a, and is returned to the photoconductor in the space between the sheets (non-image area) to be developed. The same can be applied to the image forming apparatus which is returned to the container 6.

The charging device having the charging roller 2 has rollers having a diameter 200 μm larger than the diameter of the charging roller 2 at both ends, and its outer peripheral surface is a non-image area at both ends in the rotation axis direction of the photosensitive drum 1. Are brought into contact with each other and are rotated by being driven by the photosensitive drum 1. Therefore, the gap G1 with the photoconductor drum 1 is 100 μm and faces each other. Similarly, the pre-charging device having the roller 3 also has rollers with a diameter of 200 μm larger than the diameter of the roller 3 at both ends, and the outer peripheral surface of the roller is fixed in the non-image areas at both ends in the rotation axis direction of the photosensitive drum 1. The photoconductor drum 1 is brought into contact with the photoconductor drum 1 and is rotated according to the photoconductor drum 1. Therefore, the photosensitive drum 1
The gap G2 between and also faces each other at 100 microns.

The toner on the photosensitive drum 1 after transfer is
There are toners with background stains, toners remaining after transfer, and the like, which have various polarities and charge amounts, and are often easily attached to the charging roller 2 that is close to the minute gap G1. However, according to this embodiment, a voltage obtained by superimposing an AC peak-peak (PP) voltage of 1 KV on a DC voltage of -300 V is applied to the roller 3 by the power supply circuit 5 before charging, so that the photoconductor drum is charged. The photosensitive layer 1a of No. 1 and the toner adhering thereto are charged to make the polarities of the toner T and the photosensitive layer 1a constant as shown in FIG.

The charging is performed by the power supply circuit 4 and the charging roller 2
In addition, AC peak / peak (P-
P) The voltage is applied by superimposing the voltage of 2000V.
This is performed when the charging roller 2 faces the image area of the photosensitive layer 1a. Further, when the belt roller 2 faces the non-image area of the photosensitive layer 1a, only the DC voltage -900V is applied to the charging roller 2. Gap G1 is 10
Since the discharge start voltage at 0 μm is about −1050V,
Although the battery is not discharged even if a voltage is applied, the electric field E shown in FIG. 2 is formed so that the toner does not adhere.

FIG. 6 is a timing chart showing the operation of this image forming apparatus. That is, the roller 3 before charging
At the same time, AC and DC are applied at the same time when the main motor that rotationally drives the photosensitive drum 1 is turned on, and the application is continued until the main motor is turned off. Only direct current is applied to the charging roller 2 when the main motor is turned on. Then, an alternating current is also applied in the image area from the image tip. After that, when the non-image area is reached after the trailing edge of the image, the alternating current is turned off again and only the direct current is applied.

By applying the voltage at such a timing, it is possible to prevent the charging roller 2 from being soiled. The charging roller 2 used was a single-layered one in which carbon was added to silicon rubber and the volume low efficiency was adjusted to 10 ⁷ to 10 ⁸ Ω · cm, and the aluminum core was coated with a thickness of 0.5 mm. For the roller 3 before charging, urethane in which carbon is dispersed is used.

FIG. 3 is a view similar to FIG. 1 showing another embodiment of the present invention. In FIG. 1, the number of rollers before charging is three.
In place of the above, a roll-shaped brush 8 is provided, which can also have the same function. For the brush, a resin fiber such as nylon to which carbon is added to have conductivity is used.

FIG. 4 is a view similar to FIG. 1 showing still another embodiment of the present invention. In FIG. 1, the roller 3 before charging is replaced by 3 and a flat blade 9 is used as the photosensitive drum 1.
It is arranged close to the photosensitive layer 1a. The same function can be provided by this. The blade 9 is made of rubber such as chloroprene or urethane, or urethane resin having conductive carbon added thereto. As the conductive agent added, an ion conductive conductive agent or the like is used.

The charging roller 2 has an aluminum core with a diameter of 10 ⁵ -1.
It may be composed of an elastic layer of 0 ⁶ Ω · cm and a coat layer of 10 ⁹ to 10 ¹² Ω · cm. Reference numeral 10 is a transfer sheet that is passing through the transfer section. Further, as in yet another embodiment shown in FIG. 5, instead of the charging roller 2 as the charging member,
The flat charging plate 11 may be used.

As described above, according to the above-described embodiments,
The charging member such as the charging roller 2 faces the photoconductor in a non-contact manner,
In the image area, a voltage in which an AC voltage and a DC voltage are superposed is applied in order to stabilize the potential. By applying this voltage, uniform charging with stable charging potential is performed.

Further, in the pre-charging step, a voltage in which an AC voltage and a DC voltage are superposed is applied to a voltage applying member such as a roller 3 which is placed in close proximity to the photoconductor without contacting the photoconductor and the photoconductor layer. The remaining toner is charged. The toner remaining on the photoconductor includes toner that is attached to the background of the photoconductor and residual toner after transfer, and the polarity is negatively charged even if the photoconductor is reversely developed with negative toner. Are mixed. Some transfer residual toner is negative. In order to align the polarities of such toners before charging, the toners are charged by superposing an AC voltage and a negative DC voltage in the previous step, and the toners are uniformly negatively charged. It can be negatively charged and can be uniformly charged by an AC voltage.

However, the applied voltage before charging must be smaller than the voltage applied to the charging member in the charging step, both AC voltage and DC voltage. The reason will be described. An object of the present invention is to prevent toner from adhering to the charging member. In order to prevent the toner remaining on the photoconductor from adhering to the charging member, when the residual toner has a negative polarity, the electric field is directed toward the charging roller 2 which is the charging member as shown in FIG. (The charging member has a lower potential). In order to form such an electric field, it is necessary to carry out a lower charging in the pre-charging step of the photoconductor than in the charging.

That is, the peak-to-peak voltage of the AC component of the voltage applied to the charging member such as the charging roller 2 by the power supply circuit 4 is AC1, the voltage of the DC component is DC1, and the power supply circuit 5
, AC1 |> | AC2 |, | DC1 |> | DC2, where AC2 is the peak-to-peak voltage of the AC component of the voltage applied to the voltage applying member before charging, such as the roller 3, Make sure the condition of | is satisfied.

Further, when the image area of the photoconductor is being charged, the charging member is inevitably applied with a voltage under the charging condition, so that the above situation is maintained, but in the non-image area. If nothing is done, the potential of the charging member will be zero. Even in the non-image area, the toner on the background may be left on the photoconductor, and the photoconductor is biased negatively due to the residual potential. Will be suitable for. Then, the toner on the photoconductor adheres to the charging member.

Therefore, even in the non-image area, the charging member is required to have a negative potential as compared with the photoconductor. In the non-image area, it is not necessary to charge the photoconductor, and the charging of the photoconductor causes fatigue of the photoconductor instead. Therefore, only the potential needs to be negative. Therefore, it is optimal to apply only the DC voltage to the charging member. As this DC voltage, a voltage that does not reach the discharge start voltage is applied. By applying a voltage that does not reach the discharge start voltage, the potential difference can be maintained without discharging and toner can be prevented from adhering to the charging member even in the non-image area.

Since the toner remaining on the photosensitive member is negatively charged, the toner on the background of the image is collected by the developing device 6. The discharge start voltage means a voltage value applied to the charging member when a charging of the photosensitive member, which is the member to be charged, starts by applying a DC voltage to the charging member. The AC voltage waveform may be a sine wave, a rectangular wave, a triangular wave, or the like.

Next, a further different embodiment of the present invention will be described, and FIGS. 1 to 5 used in the embodiment described above will be commonly used. However, only the power supply circuit 4 has a function different from that of the previous embodiment. This embodiment will be described by taking the configuration of FIG. 1 as an example. In this power supply circuit 4, as shown in the timing chart of FIG.
When the charging roller 2 faces the image area (from the front end of the image to the rear end of the addition), a DC voltage of -1800 V is applied to the charging roller 2, the main motor is turned on, and the charging roller 2 moves to the photosensitive drum 1. When the charging roller 2 faces the non-image area, the DC voltage of −900 V is applied to the charging roller 2 to maintain the potential.

When the gap G1 is 100 μm, the discharge start voltage is about −1050 V, and therefore discharge does not occur even if a voltage is applied at −900 V, but the electric field E shown in FIG. 2 is formed so that toner does not adhere. . In this case, the power supply circuit 4 applies the photosensitive drum 1 to the charging roller in the image area.
DC voltage higher than the charging start voltage for DC1, DC voltage not reaching the charging start voltage applied in the non-image area is D
2. When the DC component voltage of the voltage applied to the roller 3 by the power supply circuit 5 is D3, | DC1 |> | DC2 |> | D
C3 | should be satisfied.

Even in this case, the same effect as that of the above-described embodiment can be obtained. It should be noted that each of the configurations shown in FIGS. 3 to 5 is the same as each of the above-described embodiments except that the function of the power supply circuit 4 is as described above.
Their description is omitted. The present invention can be similarly applied to an electrophotographic image forming apparatus using a photoconductor belt or the like instead of the photoconductor drum as the image carrier.

[0037]

As described above, even if the toner remains on the surface of the image carrier (photoreceptor) facing the charging member, the adjoining charging member can be prevented from becoming dirty without a cleaning device. The image carrier can always be stably and uniformly charged without abnormal discharge such as streaks or white spots. It is also possible to prevent unnecessary fatigue of the image carrier.

[Brief description of drawings]

FIG. 1 is a configuration diagram of main parts of an electrophotographic image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a developed sectional view showing a facing portion of a photosensitive drum and a charging roller in FIG. 1 in an enlarged manner.

FIG. 3 is a main part configuration diagram similar to FIG. 1 showing another embodiment of the present invention.

FIG. 4 is a main part configuration diagram similar to FIG. 1 showing still another embodiment of the present invention.

FIG. 5 is a view showing still another embodiment of the present invention.
It is a principal part block diagram similar to.

FIG. 6 is a timing chart diagram for explaining the operation of the image forming apparatus according to the present invention.

FIG. 7 is a timing chart diagram for explaining an operation of another image forming apparatus according to the present invention.

[Explanation of symbols]

 1: Photosensitive drum 1a: Photosensitive layer 2: Charging roller (charging member) 3: Roller before charging (voltage applying member) 4: Power supply circuit (first power supply means) 5: Power supply circuit (first power supply means) 6: Developing device 7: Transfer roller 8: Brush before charging (voltage applying member) 9: Blade before charging (voltage applying member) 10: Transfer paper 11: Charging plate

Claims (7)

[Claims] 1. An electrophotographic image forming apparatus comprising an image carrier and a charging member which is provided in the vicinity of the image carrier and charges the surface of the image carrier. First power supply means for applying a voltage in which an alternating voltage and a direct current voltage are superposed, and a voltage application disposed closer to the image carrier at a position upstream of the charging member in the moving direction of the image carrier. An electrophotographic image forming apparatus comprising: a member; and a second power supply unit for applying a voltage obtained by superposing an AC voltage and a DC voltage to the voltage applying member. 2. The electrophotographic image forming apparatus according to claim 1, wherein a peak-peak voltage of an AC component of the voltage applied by the first power supply unit to the charging member is AC1, and a voltage of the DC component is DC1. And the peak-to-peak voltage of the AC component of the voltage applied by the second power supply means to the voltage applying member is AC.
2. When the DC component voltage is DC2, an electrophotographic image forming apparatus characterized by satisfying the following conditions: | AC1 |> | AC2 |, | DC1 |> | DC2 |. 3. The electrophotographic image forming apparatus according to claim 2, wherein the voltage DC2 of the DC component of the voltage applied to the voltage applying member by the second power supply means is the charging start voltage for the image carrier. An electrophotographic image forming apparatus characterized by a DC voltage not exceeding 4. An electrophotographic image forming apparatus comprising an image carrier and a charging member which is provided in the vicinity of the image carrier and charges the surface of the image carrier, wherein the charging member is the When facing the image area on the surface of the image carrier, a voltage obtained by superimposing AC voltage and DC voltage is applied to the charging member so that the charging member faces the non-image area on the surface of the image carrier. The electrophotographic image forming apparatus is characterized in that a power supply means for applying only a DC voltage to the charging member is provided. 5. An electrophotographic image forming apparatus comprising an image bearing member and a charging member which is provided in the vicinity of the image bearing member and charges the surface of the image bearing member. When facing the image area on the surface of the image carrier, a DC voltage equal to or higher than the charging start voltage for the image carrier is applied to the charging member, and the charging member is applied to the non-image area on the surface of the image carrier. An electrophotographic image forming apparatus, characterized in that, when facing each other, a power supply means for applying a DC voltage not reaching a charging start voltage to the image carrier to the charging member is provided. 6. The electrophotographic image forming apparatus according to claim 5, further comprising a voltage applying member disposed closer to the image bearing member at a position upstream of the charging member in the moving direction of the image bearing member. An electrophotographic image forming apparatus, comprising: a second power supply unit that applies a voltage obtained by superposing an AC voltage and a DC voltage to the voltage applying member. 7. The electrophotographic image forming apparatus according to claim 6, wherein a DC voltage equal to or higher than a charging start voltage applied to the charging member by the power source means for the image carrier reaches DC1 and a charging start voltage. A direct current voltage is D2, and a voltage of a direct current component of the voltage applied to the voltage applying member by the second power supply means is D
3, the electrophotographic image forming apparatus is characterized in that the condition of | DC1 |> | DC2 |> | DC3 | is satisfied.