JPH10123849A - Transfer device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent soiling of a paper and blurring of a transfer image caused by a shielding plate by a simple constitution in a transfer device provided with the shielding plate for preventing toner from entering a paper guide. SOLUTION: This device is provided with a photoreceptor 2 on which a toner image is formed, a transfer roll 9 arranged by the side of the photoreceptor 2 and set for forming a transfer area between the photoreceptor 2 and a paper guide 8 having a pair of mutually opposed guide members 12 and 13 arranged at the lower part of the transfer area and set for guiding the paper upward from below toward the transfer area. The guide 8 is provided with the flexible shielding plate 14 brought into contact with the paper P without leaving space when the paper P is passed and brought into contact with the upper end part 13a of one guide member 13 of the guide 8 when the paper P is not passed. Then, the tip part 14a of the flexible plate 14 is bent in the direction of the upper end part 13a of one guide member 13 of the guide 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transfer device used in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, usually, a photoconductor is uniformly charged, and a light carrying image information is irradiated on the photoconductor to form an electrostatic latent image on the photoconductor. An output image is obtained by forming an image, developing the electrostatic latent image with toner to form a toner image, and transferring the toner image to paper using a transfer device.

There are a number of transfer devices for transferring a toner image on a photoreceptor onto a sheet, and even when a transfer device having a transfer roll that comes into contact with the photoreceptor is used,
Generally, a transfer roll is disposed below a photoconductor, and a transfer area where a toner image is transferred to a sheet is formed below the photoconductor. In the transfer, horizontal transfer is performed in which the toner image is transferred while moving in a substantially horizontal direction.Therefore, a paper guide for guiding the paper to the transfer area is provided on the upstream side of the transfer area in the paper transport direction. Are located. This paper guide is a plate-like 2 that is kept at a slightly wider interval than the thickness of the paper in order to guide the paper smoothly to the transfer area.
One guide member is provided on the front surface (the surface on which the toner image is transferred) of the passing paper and on the back surface.

As a transfer method, for example, an electrostatic transfer method in which a voltage having a polarity opposite to that of a toner image is applied to a transfer roll to electrostatically transfer the toner image to paper is used. In this electrostatic transfer method, a toner cloud is generated in a space between the transfer area and the guide member due to a voltage applied to the transfer roll, and a part of the toner cloud is formed in the guide member on the paper surface side.
It may adhere to the surface facing the paper. If the developer adheres to the surface facing the sheet, there is a disadvantage that the surface of the sheet is stained before transfer.

Therefore, in order to prevent such contamination, a voltage of the same polarity as that of the toner image is applied to the guide member on the paper surface side to electrostatically prevent the toner from adhering (Japanese Patent Laid-Open No. 4-2).
No. 08970), a technique of providing a stain prevention cover for preventing toner from adhering above the guide member on the paper surface side (see Japanese Patent Application Laid-Open No. 4-29257), and a technique combining the above two techniques ( JP-A-4-29258) has been proposed.

In recent years, in order to shorten the paper transport distance in the image forming apparatus and reduce the size of the image forming apparatus, a transfer drum is arranged on the side of the photoconductor and a transfer area is formed on the side. A paper guide similar to the paper guide used for horizontal transfer is provided below the transfer area with the outlet facing upward, and the paper is guided by the paper guide and conveyed to the paper from below the transfer area to the transfer area. Vertical transfer is performed in which the toner image is transferred while being moved substantially vertically. When the above-described electrostatic transfer is performed in the vertical transfer, similarly to the case of the horizontal transfer, the toner may adhere to the surface of the guide member on the front surface side of the sheet facing the sheet. In this case, even when the above-described conventional stain prevention technology is used, the toner in the toner cloud drops due to gravity and adheres to the guide member because the exit of the paper guide is provided upward.
For this reason, it is not possible to prevent the toner from adhering to the guide member, and there is a problem that the surface of the sheet before transfer is soiled.

In order to solve such a problem, as shown in FIG. 8, a drum-shaped photosensitive member 2 on which a toner image T is formed and a toner image T disposed on the side of the photosensitive member 2 are moved downward. Roll 9 for transferring the sheet P conveyed upward from the sheet P, and a sheet serving as guide means disposed below a transfer area where the toner image T is transferred to the sheet P and guiding the sheet P to the transfer area In an image forming apparatus including the front side member 12 and the paper back side member 13, it is proposed to provide a flexible shielding plate 14 such as a polyethylene terephthalate sheet whose upper part is in contact with the upper part of the paper back side member 13. Has been filed by the present applicant on February 2, 1995 as Japanese Patent Application No. 7-15919.

According to the transfer device of the prior application described in the above specification, when the paper P does not pass through, the leading end 14a of the flexible shielding plate 14 is in contact with the upper end 13a of the paper back side member 13. Because of the contact, the toner in the toner cloud can be prevented from dropping between the shielding plate 14 and the paper back side member 13, and when the paper P passes, the flexible shielding plate 14 and the paper back surface Between the side members 13, the paper P
As a result, the flexible shielding plate 14 is deformed by the passage of the sheet, and the sheet is pushed and expanded by an amount by which the sheet can pass. Therefore, toner contamination between the shielding plate 14 and the paper back side member 13 can be prevented without any difficulty in passing the paper P.

[0009]

However, the transfer apparatus of the prior application still has some problems.

[0010] First, as shown in FIG.
4 is located above the contact position with the sheet P and is separated from the sheet P, so that the toner in the toner cloud falls between the sheet P and the tip of the shielding plate 14. And may adhere to the shielding plate 14. In this case, there is a problem that the toner adhered to the shielding plate 14 adheres to the surface of the paper P and stains the surface of the paper P, particularly, the front and rear ends.

When the transfer device is used for a long period of time, the shielding plate 14 rubs against the paper P to positively charge the surface of the shielding plate 14 and electrostatically attracts the negatively charged toner on the surface of the photosensitive member 2. Therefore, the surface of the shielding plate 14 is stained with the toner.
Then, the toner adheres to the sheet, and stains the sheet.

Second, the paper P rubs against the shielding plate 14,
Since the surface of the paper P is alternately charged positively and negatively by the peeling charging, the transfer roll 52 and the photosensitive member 2 just before the transfer are transferred.
, The negatively charged toner on the surface of the photoconductor 2 flies toward the positively charged portion of the paper P, and blurring of the transferred image such as “character blur” occurs.

In the transfer device of the prior application, it is described that a negative bias voltage is applied to the back surface of the shielding plate 14, whereby the negatively charged toner on the surface of the photoconductor 2 is removed. Giving electrostatic repulsion,
The toner is prevented from adhering to the front end and the vicinity of the front end of the shielding plate 14, thereby preventing the paper from being stained. However, this method alone does not provide a sufficient effect, and requires the provision of a new bias supply means, which causes a problem that the structure is complicated and the manufacturing cost is increased.

Accordingly, the present invention provides a transfer device provided with a shielding plate for preventing toner from entering a paper guide, and with a simple structure, prevents contamination of paper and bleeding of a transferred image due to the shielding plate. That is the task.

[0015]

According to the present invention, there is provided an image bearing member on which a toner image is formed, and a transfer device disposed on a side of the image bearing member, wherein a transfer area is provided between the image bearing member and the image bearing member. And a guide unit having a pair of opposed guide members disposed below the transfer area and guiding the sheet upward from below toward the transfer area, and the image carrier in the transfer area. In the transfer device of the image forming apparatus for transferring the toner image onto the sheet, the guide unit is configured such that an upper end of one of the guide members of the guide unit is elastically pressed against the sheet when the sheet passes, and when the sheet does not pass. It has a flexible shielding plate that contacts the upper end of one of the guiding members of the guiding means, and the distal end of the flexible shielding plate has
The guide means may be bent in the direction of the upper end of one of the guide members.

According to the present invention, there is provided an image carrier on which a toner image is formed, and a transfer device disposed on a side of the image carrier, wherein a transfer area is formed between the image carrier and the image carrier. When,
Guide means having a pair of opposing guide members disposed below the transfer area and guiding the sheet upward from the bottom toward the transfer area, and transferring the toner image of the image carrier to the sheet in the transfer area In the transfer device of the image forming apparatus, the guide unit is configured such that an upper end portion of one of the guide members of the guide unit is elastically pressed against the sheet when the sheet passes, and one guide of the guide unit when the sheet does not pass. A flexible shielding plate that contacts the upper end of the member is provided, and a stress concentration portion having lower mechanical strength than other portions is formed near the base end of the flexible shielding plate. It is characterized by having done.

[0017]

According to the present invention, in which the leading end of the flexible shielding plate is bent in the direction of the upper end of one of the guide members of the guide means, the leading end of the shielding plate comes into contact with the sheet. There is no gap between one guide member of the guide means and the front end of the shielding plate, and no toner adheres to the paper side of the front end of the shielding plate.

Further, in the present invention in which a stress concentration portion having lower mechanical strength than other portions is formed near the base end portion of the flexible shielding plate, the shielding plate is bent from the stress concentration portion. Since the leading end of the shielding plate is flat, there is no gap between one of the guide members of the guiding means and the leading end of the shielding plate, and toner adheres to the paper side of the leading end of the shielding plate. Absent.

Further, since the frictional charging between the sheet and the shielding plate is reduced, the bleeding of the transferred image is improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a transfer device of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating a basic configuration of a transfer device of an image forming apparatus.

The image forming apparatus 1 includes a drum-shaped photosensitive member 2 rotating in a direction indicated by an arrow 2a, a charger 3 for uniformly charging the photosensitive member 2, and a photosensitive member 2 by exposing the photosensitive member 2 to light. An exposure unit (not shown) for forming a latent image and a developing device 4 for developing a latent image on the photoconductor 2 with a developer to form a toner image are provided. Further, the image forming apparatus 1
A pair of transport rollers 5a, 5b and a pair of transport guides 6 for transporting the paper P supplied from a plurality of paper trays (not shown) each storing various sizes of paper.
a and 6b, a sheet guide 8 disposed below the transfer area 7 for guiding the sheet P conveyed by these to the transfer area 7, and a sheet P guided to the transfer area 7 by the sheet guide 8. A transfer roll 9 for transferring the toner image is provided on the side of the photoreceptor 2, and the sheet P is guided by a sheet guide 8 from below the transfer area 7 to the top and the toner image is transferred. Thereafter, the sheet is sent to a fixing device (not shown), where it is fixed and discharged to the outside.

On the transfer roll 9, a toner image
In order to transfer the toner image onto the transfer area 7, a voltage having a polarity (positive in this embodiment) opposite to the charge polarity (minus in this embodiment) of the toner image is applied from the power supply 10.
A toner cloud 11 is generated in a space between the sheet P and the photosensitive member 2 below the sheet P.

Next, the paper guide 8 will be described. The paper guide 8 is disposed on the front side of the paper P to which the toner image passing through the paper guide 8 is transferred, and determines a posture of the paper P entering the paper P, and the paper guide 8
The paper back side member 13 arranged on the back side of the paper P passing through the paper P, the lower end portion is fixed to the paper front side member 12, and the upper end portion elastically contacts the upper end portion of the paper back side member 13. A shielding plate 14 made of polyethylene terephthalate or the like and having insulation and functioning as a shielding plate for the toner cloud 11 is provided.

The upper end portion 13a of the sheet back side member 13 and the distal end portion 14a of the flexible shielding plate 14 are in elastic contact with each other, and when the sheet P passes through this contact portion, the sheet P becomes flexible. Is bent, and the flexible shielding plate 14 is expanded by the thickness of the paper P. That is, the paper back side member 13 and the flexible shielding plate 14
Are in contact with each other when the paper P does not pass, and come in contact with the surface of the passing paper P when the paper P is passing. For this reason, the toner in the toner cloud 11 hardly enters the inside of the paper guide 8 from the contact portion between the paper back side member 13 and the flexible shielding plate 14, and the surface of the paper P before transfer is removed. The contamination by the toner can be reduced. In this embodiment, the paper surface side member 12 is configured as a part of the photoconductor protection cover.

Here, in the present invention, as shown in each of the following embodiments, the flexible shielding plate 14 is formed into a specific shape, which results from the flexible shielding plate 14. This is to prevent paper stains and bleeding of the transferred image.

<First Embodiment> In the first embodiment, as shown in FIG. 2, the front end portion 14a of the flexible shielding plate 14 is bent from the bent portion 15 to the upper end portion of the paper back side member 13. 13a, which is bent toward the 13a side and has flexibility
4 is connected to the upper end 13a of the sheet back side member 13.
Is elastically contacted. Thereby, the sheet back side member 1 at the front end portion 14a of the flexible shielding plate 14
3, the gap between the flexible shielding plate 14 and the flexible shielding plate 14 disappears, and the toner near the transfer gap does not adhere to the surface of the flexible shielding plate 14 on the paper P side.
Surface can prevent contamination.

When the paper P passes between the paper back side member 13 and the flexible shielding plate 14, the leading end 14a of the flexible shielding plate 14 contacts the paper P linearly. Since the intermediate portion 16 of the flexible shielding plate 14 does not touch the paper P or only touches it lightly, the contact area is reduced, and the positive polarity triboelectric charging of the paper P is reduced. As a result, the bleeding of the transferred image can be prevented.

Further, as shown in FIG. 3, by making the intermediate portion 16 of the flexible shielding plate 14 completely float from the paper P, the influence of triboelectric charging can be greatly reduced.

Although the bent portion 15 is basically formed in a direction perpendicular to the direction in which the sheet P is conveyed, it may be formed slightly inclined from this direction. In this case, the leading end of the sheet P enters the bent portion of the leading end of the flexible shielding plate 14 with a time difference, so that the resistive force is not applied to the leading end of the sheet at once. The paper jam can be prevented from occurring.

Further, the bent portion 15 may be formed not in a square shape but in a round shape or a polygonal bent shape. Also in this case, when the leading end of the sheet P enters the bent portion 15, the resistance applied to the leading end of the sheet P is reduced, so that the occurrence of a paper jam can be prevented.

<Second Embodiment> In the second embodiment, as shown in FIG. 4, the mechanical strength is higher near the base end of the flexible shielding plate 14 than at other portions. A weak stress concentration portion 17 is formed, and the flexible shielding plate 14 is bent at the stress concentration portion 17. Accordingly, the distal end portion 14a of the flexible shielding plate 14 can be prevented from warping, and the flexible shielding plate 14 has a substantially flat plate shape from the base end to the distal end portion 14a. The distal end portion 14a of the flexible shielding plate 14 comes into contact with the paper back side member 13 without being lifted. Therefore, similarly to the first embodiment, the toner does not adhere to the surface of the flexible shielding plate 14 on the paper P side, and the surface of the paper P can be prevented from being stained. Further, since the strength does not decrease from the base end to the distal end of the flexible shielding plate 14, the flexible shielding plate 14 does not bend in the longitudinal direction.

Further, since only the leading end portion 14a of the flexible shielding plate 14 comes into contact with the paper P, the influence of frictional charging can be greatly reduced, and bleeding of a transferred image can be prevented. As a means for forming the stress concentration portion 17 on the flexible shielding plate 14, as shown in FIG. 5A, the paper P is conveyed to the vicinity of the lower end portion 14b of the flexible shielding plate 14. A plurality of holes 14c continuously in a direction orthogonal to the direction.
Can be adopted. Note that reference numeral 1
4d is a mounting hole for the shielding plate 14. FIG.
As shown in (b), the flexible shielding plate 14 has a two-part structure that is divided into a distal end part 14e and a base end part 14f, and the distal end part 14e is made of a rigid member. It is made of a flexible member, or FIG.
As shown in FIG. 5C, a long groove 14g is formed in the vicinity of the lower end portion 14 of the flexible shielding plate 14 in a direction perpendicular to the transport direction of the sheet P, or as shown in FIG. As shown, the portion of the flexible shielding plate 14 excluding the base end is formed by laminating two plate members 14h and 14i, and the base end is formed by one plate member 14h. thing,
Alternatively, a technique of reducing the thickness of the proximal end portion of the flexible shielding plate 14 by molding or additional processing of the plate material as compared with other portions can be adopted.

Further, when a flexible shielding plate 14 is formed by bonding two plate members 14h and 14i together, as shown in FIG. 6, the back side of the shielding plate 14, that is,
The plate-like member 14i on the side opposite to the sheet P is formed of a conductive member, and the plate-like member 14i made of the conductive member is connected to the power supply 1.
From 8, a bias voltage having a polarity opposite to the polarity of the charged toner may be applied. In this case, it is possible to prevent the toner from flying from the surface of the photoconductor 2 in the direction of the paper guide, thereby further preventing the toner from adhering.

FIG. 7 is a schematic view showing a third embodiment of the transfer device of the image forming apparatus according to the present invention. A third embodiment is:
It has the same configuration as the example shown in FIG.
A conductive pattern 14b is provided on the back surface of the transfer roll 9 and the high-voltage power supply 19 is connected to the conductive pattern 14b.
The voltage of the opposite polarity to the transfer voltage applied from the
8 is applied.

In the third embodiment, in addition to the effect of the transfer device of the image forming apparatus shown in FIG. 3, the toner is prevented from flying from the surface of the photosensitive member 2 in the direction of the paper guide.
The adhesion of the toner can be further prevented.

[0036]

As described above, according to the present invention,
The distal end of the shielding plate is bent in the direction of the upper end of one of the guide members of the guide means, or has a mechanical strength closer to the base end of the flexible shielding plate than other portions. Formed a weak stress concentration part, so that the leading end of the shielding plate was in contact with the paper, and there was no gap between one of the guide members of the guiding means and the leading end of the shielding plate. No toner adheres to the paper side. Therefore, it is possible to prevent the sheet from being stained due to the shielding plate. In addition, since there is no frictional charging due to surface contact between the sheet and the shielding plate, bleeding of the transferred image is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a basic configuration of a transfer device of an image forming apparatus.

FIG. 2 is a schematic diagram illustrating a first embodiment of a transfer device of the image forming apparatus according to the present invention.

FIG. 3 is a schematic diagram showing a modification of the first embodiment.

FIG. 4 is a schematic view showing a second embodiment of the transfer device of the image forming apparatus of the present invention.

FIG. 5 is a schematic view showing a means for forming a stress concentration portion on a flexible shielding plate.

FIG. 6 is a schematic diagram illustrating an example in which a means for applying a bias voltage is provided to a shielding plate.

FIG. 7 is a schematic view showing a third embodiment of the transfer device of the image forming apparatus of the present invention.

FIG. 8 is a schematic diagram illustrating a transfer device of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2a ... Arrow, 2 ... Photoconductor, 3 ... Charging device, 4 ... Developing device, 5a, 5b ... Conveying rollers, 6a, 6
b: conveyance guide, 7: transfer area, 8: paper guide, 9:
Transfer roll, 10 ... Power supply, 11 ... Toner cloud, 12
... Paper front side member, 13 ... Paper back side member, 14 ... Flexible shielding plate, 14a ... Top end, lower 14b ... End
14c: hole, 14d: mounting hole, 14e: tip, 1
4f: base end portion, 14g: long groove, 14h, 14i: plate member, 15: bent portion, 16: middle portion, 17: stress concentration portion,
18 power supply, 19 high voltage power supply, P paper

Claims (4)

[Claims] An image carrier on which a toner image is formed, a transfer device disposed on a side of the image carrier, the transfer device forming a transfer area between the image carrier and the transfer device; Guide means having a pair of opposing guide members disposed below the transfer area and guiding the sheet upward from the bottom toward the transfer area; and transferring the toner image of the image carrier to the sheet in the transfer area. In the transfer device of the image forming apparatus, the guide unit is configured such that an upper end portion of one of the guide members of the guide unit is elastically pressed against the sheet when the sheet passes, and one of the guide members of the guide unit when the sheet does not pass. A flexible shielding plate that comes into contact with the upper end of the guide means, and the distal end of the flexible shielding plate is bent in the direction of the upper end of one of the guide members of the guide means. Of an image forming apparatus characterized by Apparatus. 2. The image forming apparatus according to claim 1, wherein a stress concentration portion having lower mechanical strength than other portions is formed near a base end of the flexible shielding plate. Transfer device. 3. An image carrier on which a toner image is formed, a transfer device disposed on a side of the image carrier, the transfer device forming a transfer area between the image carrier and the transfer device, Guide means having a pair of opposing guide members disposed below the transfer area and guiding the sheet upward from the bottom toward the transfer area; and transferring the toner image of the image carrier to the sheet in the transfer area. In the transfer device of the image forming apparatus, the guide unit is configured such that an upper end portion of one of the guide members of the guide unit is elastically pressed against the sheet when the sheet passes, and one of the guide members of the guide unit when the sheet does not pass. A flexible shielding plate that contacts the upper end of the flexible shielding plate, and a stress concentration portion having lower mechanical strength than other portions is formed near a base end of the flexible shielding plate. Transfer of image forming apparatus characterized by the following: Location. 4. The apparatus according to claim 1, wherein a portion to which a voltage having a polarity opposite to the polarity of the transfer voltage is applied is provided on a back surface of the flexible shielding plate. Transfer device of the image forming apparatus.