JPH0915943A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To prevent contamination of a transfer unit due to adhesion of a developer in an image forming apparatus having no cleaning unit for an image carrier. In an apparatus having a charging member and a transfer member arranged in contact with an image carrier and performing image formation by repeating charging, image exposure, development, and transfer steps, between the first and second sheets, and At the time of non-image formation such as after final printing, a voltage for cleaning (for example, −2 kV, +200 V) having the same polarity as that of the developer is applied to the transfer unit and the charging unit,
The developer adhering to the transfer means is returned to the photoconductor to prevent deterioration of image quality due to contamination of the transfer means.

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 apparatus having a charging member and a transfer member which are in contact with a charged surface of an image bearing member such as a photosensitive member.

[0002]

2. Description of the Related Art In an electrophotographic apparatus such as a copying machine or a laser beam printer, or an image forming apparatus such as an electrostatic recording apparatus, a means for charging a surface of an image bearing member such as a photoconductor or a dielectric, and a surface of the image bearing member. Conventionally, a corona discharge device has been widely used as a transfer means for transferring an image formed by a developer onto a transfer material such as paper. However, the corona discharge device requires a high-voltage power source, and is also required as an environmental problem such as generation of ozone due to discharge.

On the other hand, by bringing a semiconductive roller, a blade, a brush, a belt or the like into contact with the surface of the image carrier,
The method of charging the surface of the image carrier and the method of transferring the image of the developer formed on this surface to paper or the like have advantages such as lowering the voltage of the power supply and generating less ozone. For this reason, it has become the mainstream as a charging means and a transfer means for small LBPs and copying machines.

[0004]

However, as the transfer means in contact with the surface of the image carrier is gradually contaminated with the developer as the use progresses, the developed image on the image carrier is transferred. Transfer electric field becomes uneven,
Abnormal discharge is likely to occur and a good transferred image cannot be obtained easily.

Therefore, at the time of non-image formation of the apparatus, a voltage having a polarity opposite to the polarity of the developer that stains the transfer means is applied to the transfer means to remove the developer causing the stain on the image carrier. It is known how to get it back.

However, in recent years, from the viewpoints of downsizing of the apparatus, abrasion of the image carrier, reuse of the developer, etc., there is known an apparatus having no means for cleaning the surface of the image carrier. When the above-mentioned method is carried out by using these devices, the disadvantage that the charging means in contact with the surface of the image carrier is soiled with the developer similarly occurs. The present invention has been made to solve this problem.

[0007]

In order to achieve the above object, in the image forming apparatus according to the present invention, when the developer attached to the transfer means is returned to the image carrier side, the polarity of the developer is set to the charging means. By applying a voltage of the same polarity to prevent the developer from adhering to the charging unit and becoming dirty, the developing unit can be set by setting an appropriate photosensitive potential and developing bias.
By collecting the developer, it is possible to prevent the transfer unit from being soiled, to prevent the transfer electric field from being disturbed, and also to prevent the charging unit from being soiled, so that good image quality can be continuously obtained.

[0008]

【Example】

(First Embodiment) FIG. 2 is a schematic view of an image forming apparatus using the electrophotographic method embodying the present invention. A drum-shaped photosensitive member 1 as an image bearing member rotates in a direction of an arrow (clockwise), and a charging roller (charging member) 2 receives a power source (charging power source).
An appropriate voltage (charging voltage) is applied from 3 to be charged to a desired potential. Next, an electrostatic latent image is formed by image exposure 4 using a laser beam, an LED or the like, and this electrostatic latent image is visualized by a developing device (developing means) 5 to become a toner image. The toner image on the photoconductor 1 is transferred onto a transfer material 6 such as paper by a transfer roller (transfer means) 7 to which an appropriate voltage (transfer voltage) is applied from a power supply (transfer power supply) 8. The transfer material 6 after the toner image transfer is destaticized by a destaticizing needle (destaticizing means) 9 and conveyed to a fixing device (fixing means) 10 to fix the toner image.

On the other hand, the photosensitive member after the toner image transfer reaches the charging roller position again, and similarly enters the next image forming step.

The image forming conditions of this apparatus will be briefly described below.

Photoconductor: Diameter φ30, OPC photoconductor peripheral speed: 90 mm / sec. Charging roller: Diameter φ12 Applied voltage AC component V _PP = 2000V f = 800Hz DC component _VDC = -700V Transfer roller: Applied voltage during transfer DC = + 6kV Static elimination needle: Applied voltage DC = -2kV Photoconductor dark part potential = -700V < Example 1> When the developer (negative polarity) attached to the transfer roller is returned to the photoconductor (hereinafter referred to as a transfer cleaning mode), the transfer roller has a voltage DC = the same polarity as the developer.
-2.5 kV was applied. At this time, the same DC voltage as at the time of latent image formation may be applied to the charging roller.
Further, as the voltage (developing bias) applied to the developing means, DC = -550V was applied at the time of image formation, but DC = + 200V was applied at the time of transfer cleaning so that the developer returned to the photosensitive member was developed. I was supposed to collect it. At this time, the photoconductor potential at the developing position is −700 V, and since DC = + 200 V is applied as the developing bias, the negative polarity developer returned from the transfer roller to the photoconductor is collected by the developing means. .

FIG. 1 is a sequence diagram when printing is performed in the continuous two-sheet mode. In this example, the transfer cleaning mode is performed between the first sheet and the second sheet (between sheets) and at the time of the post-rotation of the photoconductor after the final printing. That is, -2 kV is applied to the transfer roller, the developing bias is set to +200 V, and the developing material is returned to the photoreceptor. The timing of performing the transfer cleaning mode is not limited to this example, and may be, for example, only during the post-rotation, or may be performed for every certain number of sheets by detecting the number of sheets. Further, it may be performed at the time of pre-rotation of the photoconductor before image formation.

<Embodiment 2> In Embodiment 1, the reversal development system in which the charging polarity of the photoconductor and the charging polarity of the developer are the same has been described. Next, the charging polarity of the photoconductor and the polarity of the developer are The different regular development systems will be described.

The image forming conditions are different from those in Example 1 in that the polarity of the developer is positive, the applied voltage at the time of transfer of the transfer roller DC = -6 kV, the voltage applied to the discharging needle DC = + 2 kV, the voltage applied at the cleaning mode of the transfer roller DC = + 2 0.5 kV Development bias DC = -250V During image formation DC = -250V During transfer roller cleaning mode DC = -250V Charging roller applied voltage DC component During image formation DC = -700V During transfer roller cleaning mode DC = + 300V (AC component Is the same as in the first embodiment).

FIG. 3 shows an example of a sequence for continuous two-sheet printing. Similar to the first embodiment, this is an example in which the transfer cleaning mode is performed at the time of the paper interval and the post-rotation of the photoconductor.

The positive polarity developer attached to the transfer roller is returned to the surface of the photosensitive member by applying a transfer voltage of +2.5 kV. When the returned developer passes through the charging roller portion, a voltage of DC = + 300V is applied to the charging roller, and the developer is electrically repelled and reaches the developing position. When passing through the developing position, the potential of the photosensitive member is +300 V due to the voltage applied to the charging roller, and the developing bias is applied to DC = -250 V, so that it is electrically recovered by the developing means.

As a result of experiments according to Examples 1 and 2, when the present invention is not used, the number of durable sheets is about 40,000 at room temperature of 23 ° C. and relative humidity of 60%, and at room temperature of 23 ° C. and relative humidity. Under 10%, an abnormal image occurred on about 30,000 sheets.

When the present invention is used, about 90,000 sheets are produced under a relative humidity of 60% and 6 even under a relative humidity of 10%.
It has become possible to obtain a sufficiently good image in actual use even at the endurance of 10,000 sheets.

<Other Embodiments> In the above description, a roller is used as the charging means and the transfer means. However, the means for contacting the image carrier is not limited to the roller, and the present invention is also applicable to the following. Applied.

For example, an example as shown in FIG. 4 can be given as the charging means. That is, the charging or transfer blade 21 as shown in FIG. 4A, the charging brush or transfer brush 22 as shown in FIGS.
The magnetic brush 23 as shown in FIG. Also,
A belt type transfer means 11 as shown in FIG. 5 is also applied to the present invention.

[0021]

As described above, according to the present invention,
In an image forming apparatus that does not have a cleaning means for the image carrier and has a charging means and a transfer means that come into contact with the image carrier, a voltage for returning the developer adhering to the transfer means to the image carrier side during non-image formation is set. While applying to the transfer means,
A voltage having the same polarity as that of the developer is applied to the charging means to prevent the developer from adhering, and a voltage to recover the developer is applied to the developing means. Thus, it is possible to prevent the transfer unit and the charging unit from being soiled.

As a result, as the use of the device progresses,
It is possible to prevent the deterioration of a good image quality due to the unevenness of the transfer electric field due to the dirt of the transfer means, and it is possible to improve the reliability of the apparatus.

[Brief description of the drawings]

FIG. 1 is a sequence diagram illustrating a first embodiment of the present invention.

FIG. 2 is a schematic view of an image forming apparatus for carrying out the present invention.

FIG. 3 is a sequence diagram illustrating a second embodiment of the present invention.

FIG. 4 is a sequence diagram illustrating another embodiment of the present invention.

FIG. 5 is a sequence diagram illustrating still another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier 2 ... Charging means 3 ... Charging means power supply 4 ... Image exposure 5 ... Developing means 6 ... Transfer material 7 ... Transfer means 8 ... Transfer means power supply 9 ... Eliminating means 10 ... Fixing means 11 ... Transfer belt 21 ... Charging Or transfer blade 22 ... charging or transfer brush 23 ... magnetic brush

Claims (2)

[Claims] 1. An apparatus having a charging member and a transfer member disposed in contact with an image bearing member and performing image formation by repeating charging, image exposure, development and transfer steps, at the time of non-image formation, a transfer unit and a charging unit. An image forming apparatus, wherein a voltage having the same polarity as that of the developer is applied to the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein when a non-image is formed, a voltage having the same polarity as that of the developer is applied to the transfer means and the charging means, and an image is applied as a voltage to the developing means. An image forming apparatus, wherein a voltage for recovering the developer from the image carrier to the developing means is applied by an electric field created by the potential of the carrier and the applied voltage of the developing means.