JP2001022193A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a transfer sheet from being soiled at its leading end, rear end, side edges, and back during image formation, by separating a transfer entrance guide plate into pieces in the axial direction of a drum-like photoreceptor and insulating them from each other. SOLUTION: A transfer entrance guide plate is disposed such that it is separated into pieces in the axial direction of a drum-like photoreceptor and they are insulated from each other. That is, the transfer entrance guide plate is separated into the pieces in the axial direction of the photoreceptor, (in this example, three metal plates, 46A, 46B, and 46C) and they are connected to each other with a resin plate 47, as an insulator, and electrically completely separated from each other. In this state, in the case the width of 46B has a dimension covering the width of a B4-size transfer sheet for example, the parts of 46A and 46C adjacent thereto cannot accumulate charges through the transfer sheet when the B4-size transfer sheet is passed on 46B. Therefore, even when an A3-size transfer sheet for example is next passed, both side edges of the transfer sheet and back of the part are prevented from being soiled with toner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms a toner image on the surface of a photoreceptor by electrophotography and transfers the toner image onto transfer paper. More specifically, the present invention relates to an image forming apparatus that forms a high-quality image without receiving back stain on transfer paper during transfer.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a charging means, a writing means, and a developing means are provided on a peripheral portion of a rotating photoreceptor, and the surface of the photoreceptor is uniformly charged by the charging means. The latent image of the image is formed by developing means, and the latent image is developed by developing means to form a toner image on the surface of the photoreceptor. On the other hand, the transfer paper fed from the transfer paper storage means or the like is sent to the transfer position, where the toner image is transferred onto the transfer paper at the transfer position.

An electrostatic transfer method is used as a method for transferring a toner image at a transfer position onto transfer paper. In this electrostatic transfer system, the back surface of the transfer paper is charged to the opposite polarity to the charge of the toner by corona discharge from the transfer device, and the toner image on the photoreceptor is transferred to the surface of the transfer paper by Coulomb force and transferred. It is a method. However,
The corona discharge from the transfer unit not only charges the back surface of the transfer paper, but also charges the transfer entry guide plate that guides the transfer paper, which is a nearby member. When the transfer entrance guide plate is charged to a polarity opposite to the charge of the toner, the toner on the photoconductor is transferred to the transfer entrance guide plate by Coulomb force in an area where the transfer entrance guide plate and the surface of the photoconductor are close to each other. The transfer entry guide plate is contaminated with toner, and the toner adheres to the back surface of the passing transfer paper and contaminates the back surface of the transfer paper. I will. Further, when forming images on both sides, the image portion itself on one screen is contaminated.

In order to solve this problem, it is conceivable that the transfer entrance guide plate is grounded to leak the electric charge of the transfer unit, thereby eliminating the contamination due to the adhesion of the toner to the transfer entrance guide plate. However, by grounding the transfer entrance guide plate, the charge of the transfer entrance guide plate can be leaked and the adhesion of the toner can be somewhat prevented. The charged charge on the back side of the transfer paper due to corona discharge leaks to the ground via the transfer entry guide plate that is in contact, and sufficient charge cannot be secured to transfer to the back side of the transfer paper. I will. This phenomenon becomes even more remarkable under high-temperature and high-humidity environmental conditions in which the transfer paper absorbs water to lower the surface resistance of the transfer paper and easily leaks.

To prevent the electric charge on the back surface of the transfer paper from leaking through the transfer entrance guide plate, it is possible to ground the transfer entrance guide plate via a resistor, for example, in Japanese Utility Model Application Laid-Open No. 58-1.
No. 05559, the transfer device is of the OF type.
In the state of F, since the potential of the transfer entry guide plate is at the ground level, a potential difference is generated between the surface of the photoconductor and the transfer entry guide plate due to the residual potential of the photoconductor, and the toner on the photoconductor surface is transferred to the transfer entry guide plate by this potential difference. Transfer and contaminate. To prevent the toner on the surface of the photoconductor from transferring to the transfer entrance guide plate due to this potential difference, the closest distance between the surface of the photoconductor and the transfer entrance guide plate may be increased. In addition, transferability, transfer unevenness, and transfer rate decrease, and image defects such as a decrease in image density, image skip, and image blur occur.

On the other hand, it is conceivable to apply a voltage having the same polarity as that of the toner to the transfer entrance guide plate in order to prevent the toner from adhering to the transfer entrance guide plate, and to apply a voltage using the same high-voltage power supply as the charger. However, the voltage applied to the charger is cut off and the voltage applied to the transfer entry guide plate is also cut off, so that the residual toner on the photoreceptor until the rotation drive of the photoreceptor stops is transferred. It transfers onto the guide plate and contaminates the transfer entry guide plate.

[0007]

As described above, at the time of transfer, toner stains easily occur on the edges of the leading and trailing edges of the transfer paper and on the back side of the transfer paper. In addition, such toner stains occur not only on the leading edge, the trailing edge, and the back surface of the transfer paper, but also, for example, when the size of the transfer paper is changed from B4 size to A3 size, on the side edges of the transfer paper and the back surface. Had occurred. This means that when performing double-sided copying, the image itself is contaminated, and the image quality itself is greatly impaired, which is very undesirable.

Further, in order to avoid contamination of the transfer entrance guide plate by toner, when the guide plate is separated from the optimum position of the photoreceptor, the adhesion of the transfer paper to the photoreceptor is reduced, so that transfer slippage, transfer unevenness and unevenness of transfer are reduced. A decrease in the transfer rate occurs, and image defects such as a decrease in image density, image blur, and image blur occur.

The present invention pursues the shape of the transfer entrance guide plate and the means for applying a voltage to the guide plate to eliminate the above-mentioned drawbacks, and to form the leading edge, the trailing edge, and the like at the time of image formation on transfer paper. It is an object of the present invention to provide an image forming apparatus capable of maintaining a stable and high-quality image without generating a stain on a side surface or a back surface.

[0010]

This object is achieved by any of the following technical means (1) to (4).

(1) In an image forming apparatus having at least a drum-shaped photosensitive member, a charging device, a developing device, a transfer device, and a transfer entrance guide plate for guiding transfer paper to the transfer device, the transfer entrance guide plate is formed of the drum shape. An image forming apparatus, wherein the photosensitive member is divided into a plurality of parts in the axial direction of the photosensitive member.

(2) The image forming apparatus according to (1), wherein each of the divided transfer approach guide plates is provided with a voltage applying means for applying a voltage.

(3) The image forming apparatus according to item (2), wherein a voltage is applied to each of the divided transfer approach guide plates from the voltage applying means via a resistor.

(4) In an image forming apparatus having at least a drum-shaped photosensitive member, a charger, a developing unit, a transfer unit, and a transfer entrance guide plate for guiding transfer paper to the transfer unit, a voltage is applied to the transfer entrance guide plate. A dedicated high-voltage power supply is provided as a voltage applying means for applying the voltage, and the voltage Vg applied to the transfer approach guide plate is set in absolute value to a value between the charging potential Vh and the exposure potential Vw of the photoreceptor. An image forming apparatus comprising: a control unit that outputs a signal while the photoconductor is rotating.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the image forming apparatus according to the present invention will be described first with reference to the overall configuration diagram shown in FIG.

The image forming apparatus shown in FIG. 1 is a digital type image forming apparatus, and includes an image reading section A, an image processing section B (not shown), an image forming section C, and transfer paper transport as transfer paper transport means. It is composed of a section D.

An automatic document feeder for automatically transporting a document is provided above the image reading section A.
The original placed on the original 1 is moved by the original transport roller 12 to the original
The sheets are separated and conveyed, and the image is read at the reading position 13a. The document for which the reading of the document has been completed is discharged onto the document discharge tray 14 by the document conveying roller 12.

On the other hand, the image of the original placed on the platen glass 13 is composed of a first mirror unit 15 composed of an illumination lamp and a first mirror constituting a scanning optical system, and a second mirror positioned in a V-shape. The second mirror unit 16 composed of a mirror and a third mirror is read by a reading operation at the speed V of the first mirror unit 15 and a moving exposure by the second mirror unit 16 at the speed V / 2 in the same direction.

The read image is formed on a light receiving surface of an image sensor CCD as a line sensor through a projection lens 17. The linear optical image formed on the image pickup device CCD is sequentially photoelectrically converted into an electric signal, and subjected to image processing such as density conversion and filter processing in an image processing unit B, and then the image data is temporarily stored in a memory. Is done.

In the image forming section C, a drum-shaped photosensitive member 21 serving as an image forming unit, a charger 22 serving as a charging unit, a developing unit 23 serving as a developing unit, and a transfer unit are provided as image forming units. A transfer device 24, a separator 25 as a separating unit, and a cleaning device 2 as a cleaning unit
6 and a PCL (precharge lamp) 27 are arranged in the order of operation. The photoconductor 21 is formed by applying a photoconductive compound on a drum substrate, and uses, for example, an organic photoconductor (OPC) and is driven and rotated clockwise in the drawing.

After the rotating photoconductor 21 is uniformly charged by the charger 22, the exposure optical system 30 performs image exposure based on the image signal called from the memory of the image processing unit B. The exposure optical system 30 serving as a writing unit uses a laser diode (not shown) as a light emitting light source, passes through a rotating polygon mirror 31, an fθ lens (no symbol), and a cylindrical lens (no symbol) to bend an optical path by a reflection mirror 32, thereby performing main scanning. The photoreceptor 21
Image exposure is performed at the upper Ao position, and a latent image is formed by sub-scanning due to rotation of the photoconductor 21. In the present embodiment, a character portion is exposed to form a latent image.

The latent image on the photoreceptor 21 is subjected to reversal development by the developing device 23, and a visible toner image is formed on the surface of the photoreceptor 21. In the transfer paper transport section D, paper feed units 41 (A) and 41 serving as transfer paper storage means in which transfer papers P of different sizes are stored below the image forming unit.
(B) and 41 (C) are provided, and a manual paper feed unit 42 for performing manual paper feed is provided on the side, and the transfer paper P selected from any of them is supplied to a guide roller 43.
The transfer paper P is fed along the transport path 40, and the transfer paper P is temporarily stopped and then re-fed by a pair of registration rollers 44 for correcting the inclination and deviation of the fed transfer paper.
2, the toner image on the photoconductor 21 is guided by the transport path 40, the pre-transfer roller 43a, and the transfer entrance guide plate 46 at the transfer position Bo.
The transfer paper P is transferred to the transfer paper P by 4 and then discharged by the separator 25 to separate the transfer paper P from the surface of the photoconductor 21, and is conveyed to the fixing device 50 by the conveyance device 45.

The fixing device 50 has a fixing roller 51 and a pressure roller 52. By passing the transfer paper P between the fixing roller 51 and the pressure roller 52, the transfer paper P is heated and pressed to remove toner. Weld. The transfer paper P on which the toner image on one side has been fixed is subjected to double-sided image formation for forming a toner image on the other side according to a mode described below, or is discharged onto the paper output tray 64 in a state of a single-sided image.

When the double-sided image forming mode is selected,
The transfer paper P after the image fixing on the front surface is guided by the conveyance direction switching member 62 and descends along the reverse conveyance path 60,
After being once carried into the switchback path 60a, it is carried out and reversed between the front surface and the back surface.
Is further re-fed along the conveyance path 40 by the guide roller 43, and the transfer paper P is temporarily stopped by the registration roller pair 44 for correcting the inclination and deviation of the transfer paper. After that, re-feeding is performed, and the toner image of the back surface image formed on the photoreceptor 21 is transferred to the back surface of the transfer paper P by the transfer device 24 at the transfer position Bo, then separated and conveyed, and fixed. The paper is discharged onto the paper discharge tray 64.

When the one-sided image forming mode is selected,
The transfer paper P on which the front surface image has been fixed proceeds straight and is discharged onto the paper discharge tray 64, or is guided to the reversing conveyance path 60 by the conveyance direction switching member 62, and then the upper and lower surfaces are reversed by switchback. The paper is discharged onto the paper discharge tray 64.

A major feature of the present invention is to prevent the occurrence of toner stains on the edges of the leading and trailing edges of the transfer sheet and the back side of the transfer sheet during transfer, and to prevent the toner image itself from being disturbed. This is to prevent the occurrence of a failure.

The present inventor has continued to study why the toner stain is likely to occur on the edges of the leading and trailing edges of the transfer paper and on the back side of the transfer paper during transfer, and obtained the following findings. That is, when the transfer entrance guide plate 46 is formed of a metal plate as before, the resistance of the transfer paper at the time of transfer output is originally low, and particularly high, as shown in FIG. 2 which is an enlarged view of a main part of FIG. In a humid environment, the transfer charge is lower, and the transfer charge flows through the transfer paper and flows into the transfer entry guide plate 46, where the transfer entry guide plate 46
Has the same polarity as the transfer device 24. As a result, the fog toner on the photoconductor 21 on the outer side of the leading and trailing edges of the transfer paper in the paper passing direction on the photoconductor 21 and the outer side of the paper passing width adhere to the transfer approach guide plate 46, and the adhered toner is transferred to the next It was found that the edge and the back surface of the leading edge and the trailing edge of the transfer paper were stained.

Therefore, in the present invention, as shown in the perspective view of FIG. 3, a plurality of transfer entry guide plates 46 are provided in the axial direction of the photosensitive member 21 (in the example of the present embodiment, three transfer plates, ie, a metal plate 46A,
46B and 46C), and each of them is connected by an insulating resin plate 47 to be electrically divided completely. In this state, for example, when the width of 46B is set to be large enough to fit the width of the transfer paper in B4 size,
When the transfer paper of A3 size is passed, the above-mentioned charges are not stored in the adjacent portions 46A and 46C through the transfer paper. The toner stain on the edge and the back surface of the edge is eliminated. However, some toner stains remain on the edge of the leading or trailing edge of the transfer paper and on the back surface of that portion.

The above-mentioned division is performed by dividing the transfer paper by the center with reference to the center, and dividing the transfer paper into three parts by way of example. do it.

Then, as shown in the wiring diagram of FIG. 4, a voltage is positively applied from a high-voltage power supply 72 independent of the charging voltage power supply to transfer the outside of the paper passing portion (paper passing direction and paper passing width). The potential of the entrance guide plate 46 is not set to the same polarity as that of the transfer device 24. As a result, the toner on the photosensitive member 21 is not attracted to the transfer entry guide plate 46. Therefore, there was no toner stain on the leading edge, the trailing edge and the back surface of the transfer paper. And each divided metal plate 46
A voltage is preferably applied to A, 46B, and 46C via the resistor 73 because the voltage is stabilized.

When applying such a voltage,
It is effective even if the transfer entrance guide plate 46 is not divided. However, it is desirable to divide it because it is more stable.

The above is an example of each of the first to third embodiments. Next, an example of the fourth embodiment will be described.

This is provided with a dedicated high-voltage power supply 72 as voltage applying means for applying a voltage to the transfer approach guide plate 46. The voltage Vg applied to the transfer approach guide plate 46 is converted into an absolute value by the photosensitive member 21. Charge potential Vh and exposure potential V
The control means 75 is set to a value between w and outputs an applied voltage from the dedicated high-voltage power supply 72 at least while the photoconductor 21 is rotating.

As an example of such an embodiment, when the transfer potential due to the discharge from the transfer unit 24 is +500 V, the charging potential Vh on the photoconductor 21 is -750 V, Vw is -50 V, and Vg is -500 V. When controlled, very good results were obtained.

That is, it was found that good results were obtained when the relationship of | Vh | ≧ | Vg | ≧ | Vw | was maintained. However, these voltage potentials and transfer potentials have opposite signs of + and-as described above.

FIG. 5 is a timing chart when the image forming apparatus is operated for two cycles and stopped. The operation of the drive motor for the photosensitive member, the charger, the writing, the developing sleeve, the bias, the voltage of the transfer entry guide plate, and the transfer device is performed. It shows the time. As shown in the timing chart of FIG. 5, the output of the voltage potential of the transfer entrance guide plate 46 continues for a time indicated by T1 until the drive motor of the photosensitive member is stopped even after the output of the charger is turned off. are doing. By doing so, a satisfactory result free from toner contamination could be completely maintained.

[0037]

According to the present invention, in forming an image on a transfer sheet, the adhesion between the transfer sheet and the photoreceptor is well maintained without causing toner stain on the leading edge, the trailing edge, the side edge, and the rear face. It has become possible to provide an image forming apparatus capable of maintaining stable, high-quality images without causing image defects such as transfer defects.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged view of an example of a main part of FIG.

FIG. 3 is a perspective view of a transfer approach guide plate used in the present invention.

FIG. 4 is a wiring diagram showing a state of voltage application to a transfer approach guide plate used in the present invention.

FIG. 5 is a timing chart of the image forming apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Photoreceptor 22 Charger 23 Developing device 24 Transfer device 25 Separator 30 Exposure optical system 44 Registration roller pair 46 Transfer entry guide plate 47 Resin plate 72 Dedicated high voltage power supply 73 Resistance

Claims (4)

[Claims] 1. A drum-like photoconductor, a charger,
In an image forming apparatus having a developing unit, a transfer unit, and a transfer entrance guide plate for guiding transfer paper to the transfer unit, the transfer entrance guide plate is divided into a plurality of pieces in the axial direction of the drum-shaped photoconductor while being insulated from each other. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein each of the divided transfer approach guide plates is provided with a voltage applying unit for applying a voltage. 3. The image forming apparatus according to claim 2, wherein a voltage is applied to each of the divided transfer approach guide plates from the voltage applying unit via a resistor. 4. At least a drum-shaped photoconductor, a charger,
In an image forming apparatus having a developing unit, a transfer unit, and a transfer entrance guide plate for guiding transfer paper to the transfer unit, the transfer entrance guide plate is provided with a dedicated high-voltage power supply as a voltage application unit for applying a voltage. The voltage Vg applied to the entrance guide plate is represented by an absolute value and the charging potential Vh of the photoconductor and the exposure potential Vw
An image forming apparatus comprising: a control unit that sets a value between the values and outputs the output at least while the drum-shaped photosensitive member is rotating.