JP3599218B2 - Transfer device for image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transfer device used in an electrophotographic image forming apparatus.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, usually, a photoconductor is uniformly charged, and an electrostatic latent image is formed on the photoconductor by irradiating the photoconductor with light carrying image information, The electrostatic latent image is developed with toner to form a toner image, and the toner image is transferred to paper using a transfer device, thereby obtaining an output image.
[0003]
There are several types of transfer devices for transferring the toner image on the photoreceptor to paper, and even when a transfer device having a transfer roll that comes into contact with the photoreceptor is used, the transfer device is generally provided below the photoreceptor. The transfer area where the toner image is transferred to the sheet is formed below the photoreceptor. In the transfer, horizontal transfer is performed in which the toner image is transferred while being moved 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. The paper guide passes through two plate-like guide members, which are kept at a slightly wider interval than the thickness of the paper in order to smoothly guide the paper to the transfer area, the surface of the paper (the surface on which the toner image is transferred). Side and back side.
[0004]
Further, as a transfer method, for example, an electrostatic transfer method in which a voltage having a polarity opposite to that of the toner image is applied to a transfer roll and the toner image is electrostatically transferred to paper is used. In this electrostatic transfer method, a toner cloud is generated in the space between the transfer area and the guide member due to the voltage applied to the transfer roll, and a part of the toner cloud faces the paper of the guide member on the paper surface side. It may adhere to the surface. If the developer adheres to the surface facing the sheet, there is an inconvenience that the surface of the sheet is stained before transfer.
[0005]
Therefore, in order to prevent this contamination, a technique of applying a voltage having the same polarity as the toner image to the guide member on the paper surface side to electrostatically prevent the toner from adhering (see Japanese Patent Laid-Open No. 4-208970). A technique of providing a dirt prevention cover for preventing toner from adhering above the guide member on the paper surface side (see JP-A-4-29257), or a technique combining the above two techniques (JP-A-4-29258). Reference) has been proposed.
[0006]
By the way, in recent years, in order to shorten the sheet conveyance distance in the image forming apparatus and downsize the image forming apparatus, a transfer drum is arranged on the side of the photoconductor, and a transfer area is formed on the side of the transfer drum. A paper guide similar to the paper guide used in horizontal transfer is provided below the area, with the exit facing upward, the paper is guided by this paper guide, and the paper is conveyed to the paper from below the transfer area to the transfer area, and the toner image is formed. Is performed while moving the image almost 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 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 outlet 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.
[0007]
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 arranged on the side of the photosensitive member 2 are moved upward from below. A transfer roll 9 for transferring the sheet P conveyed toward the sheet P, and a sheet surface side member which is disposed below a transfer area where the toner image T is transferred to the sheet P and guides the sheet P to the transfer area It has been 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 in an image forming apparatus provided with the paper back side member 13 and the paper back side member 13. Filed on Feb. 2, 1995 as Japanese Patent Application No. 7-15919 by the present applicant.
[0008]
According to the transfer device of the prior application described in the above-mentioned application specification, when the paper P does not pass, the leading end portion 14a of the flexible shielding plate 14 comes into contact with the upper end portion 13a of the paper back side member 13. Therefore, 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 side member 13 During the period, the flexible shielding plate 14 is deformed by the passage of the sheet P, and is 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]
[Problems to be solved by the invention]
However, some problems still remain in the transfer device of the prior application.
[0010]
First, as shown in FIG. 8, the front end of the shielding plate 14 is located above the contact position with the paper P and is separated from the paper P, so that the toner in the toner cloud It may fall between P and the tip of the shielding plate 14 and 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.
[0011]
When the transfer device is used for a long period of time, the shielding plate 14 frictions with the paper P, and the surface of the shielding plate 14 is positively charged, so that the negatively charged toner on the surface of the photoconductor 2 is electrostatically attracted. The surface of the plate 14 is stained with toner. Then, the toner adheres to the sheet and causes stain on the sheet.
[0012]
Secondly, since the sheet P frictions with the shielding plate 14 and the surface of the sheet P is alternately charged positively and negatively by peeling charging, the gap between the transfer roll 52 and the photosensitive member 2 immediately before transfer is formed. Then, 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.
[0013]
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 an electrostatic charge is applied to the negatively charged toner on the surface of the photoconductor 2. The repelling force is applied to prevent the toner from adhering to the tip of the shielding plate 14 and the vicinity of the tip, 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.
[0014]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a transfer device having a shielding plate for preventing toner from entering a paper guide, with a simple configuration, to prevent contamination of paper and bleeding of a transferred image due to the shielding plate. And
[0015]
[Means for Solving the Problems]
The present invention provides an image carrier on which a toner image is formed, a transfer device disposed on a side of the image carrier, and a transfer device for forming a transfer area between the image carrier and the transfer device. An image for transferring a toner image of the image carrier to a sheet in the transfer area, the guide means having a pair of opposed guide members disposed below the area to guide the sheet from bottom to top toward the transfer area; In the transfer device of the forming apparatus, 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 the one of the guide members of the guide unit when the sheet does not pass. It is provided with a flexible shielding plate that comes into contact with the upper end portion, and the distal end portion of the flexible shielding plate is bent in the direction of the upper end portion of one of the guide members of the guide means. Features.
[0017]
[Action]
In 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 guiding means, the leading end of the shielding plate comes into contact with the sheet, so that There is no gap between one guide member and the front end of the shielding plate, and no toner adheres to the paper side of the front end of the shielding plate.
[0019]
Further, since the frictional charging between the sheet and the shielding plate is reduced, the bleeding of the transferred image is improved.
[0020]
【Example】
Hereinafter, an embodiment of a transfer device of an image forming apparatus of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a basic configuration of a transfer device of an image forming apparatus.
[0021]
The image forming apparatus 1 forms a drum-shaped photoreceptor 2 rotating in a direction indicated by an arrow 2a, a charger 3 for uniformly charging the photoreceptor 2, and exposes the photoreceptor 2 to form a latent image. An exposure unit (not shown) for forming the developing unit 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 includes a pair of transport rollers 5a, 5b and a pair of transport rollers that transport a sheet P supplied from a plurality of sheet trays (not shown) each containing sheets of various sizes. Guides 6a and 6b, a sheet guide 8 disposed below transfer area 7 for guiding sheet P conveyed by these to transfer area 7, and sheet P guided to transfer area 7 by sheet guide 8. A transfer roller 9 is provided on the side of the photoreceptor 2 for transferring a toner image to the sheet P. The sheet P is guided by a sheet guide 8 from below the transfer area 7 to above and the toner image is transferred. After that, it is sent to a fixing device (not shown), where it is fixed and discharged to the outside.
[0022]
In order to transfer the toner image onto the paper P, a voltage having a polarity (positive in this embodiment) opposite to the charging polarity (minus in this embodiment) of the toner image is applied to the transfer roll 9 from a power supply 10. Due to this voltage, a toner cloud 11 is generated in a space between the sheet P and the photoconductor 2 below the transfer area 7.
[0023]
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 passes through the paper guide 8. A sheet back side member 13 disposed on the back side of the middle sheet P, and a polyethylene having a lower end fixed to the sheet front side member 12 and an upper end elastically contacting the upper end of the sheet back side member 13. A shielding plate 14 made of terephthalate or the like and having insulating flexibility and functioning as a shielding plate for the toner cloud 11 is provided.
[0024]
The upper end portion 13a of the sheet back side member 13 and the tip end portion 14a of the flexible shielding plate 14 are in elastic contact with each other, and the sheet P has a flexible shielding The plate 14 is bent, and the shielding plate 14 having flexibility by the thickness of the sheet P is pushed out. That is, the sheet back side member 13 and the flexible shielding plate 14 are in contact with each other when the sheet P does not pass, and contact with the surface of the passing sheet P when the sheet P passes. I do. 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. Stain by toner can be reduced. In this embodiment, the paper surface side member 12 is configured as a part of the photoconductor protection cover.
[0025]
Here, in the present invention, by forming the flexible shielding plate 14 into a specific shape as shown in each of the following embodiments, the contamination of the paper due to the flexible shielding plate 14 is achieved. In addition, the bleeding of the transferred image is prevented.
[0026]
<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 toward the upper end portion 13a of the paper back side member 13 to provide flexibility. The front end portion 14a of the shielding plate 14 having elasticity is brought into elastic contact with the upper end portion 13a of the paper back side member 13. As a result, there is no gap between the paper back side member 13 and the flexible shielding plate 14 at the leading end 14a of the flexible shielding plate 14, and the toner near the transfer gap has flexibility. It does not adhere to the surface of the shielding plate 14 on the side of the sheet P, and the surface of the sheet P can be prevented from being stained.
[0027]
When the paper P passes between the paper back side member 13 and the flexible shielding plate 14, the leading end 14 a of the flexible shielding plate 14 comes into contact with the paper P in a linear manner. Since the intermediate portion 16 of the flexible shielding plate 14 does not contact the paper P or only contacts the paper P lightly, the contact area is reduced, and the positive polarity triboelectric charging of the paper P is reduced. Blurring of the transferred image can be prevented.
[0028]
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.
[0029]
Note that the bent portion 15 is basically formed in a direction orthogonal to the transport direction of the paper P, but 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 resisting force is not applied to the leading end of the sheet at once. The occurrence of paper jam can be prevented.
[0030]
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 paper P enters the bent portion 15, the resistance applied to the leading end of the paper P decreases, so that the occurrence of paper jam can be prevented.
[0031]
<Second embodiment>
In the second embodiment, as shown in FIG. 4, a stress concentration portion 17 having lower mechanical strength than other portions is formed near a base end of a flexible shielding plate 14, 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 since 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.
[0032]
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 the bleeding of the 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 configuration in which a plurality of holes 14c are continuously formed in a direction orthogonal to the direction can be adopted. Reference numeral 14d denotes a mounting hole for the shielding plate 14. Further, as shown in FIG. 5B, the shielding plate 14 having flexibility 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 formed of a rigid member. The end 14f is made of a flexible member, or as shown in FIG. 5C, near the lower end 14 of the flexible shielding plate 14 with respect to the transport direction of the sheet P. The long groove 14g is formed in the direction perpendicular to the direction of the axis, or as shown in FIG. 5 (d), the portion excluding the base end of the flexible shielding plate 14 is formed of two plate-like members 14h and 14i. The base end of the shielding plate 14 having flexibility is formed by bonding and the base end is formed by a single plate-like member 14h, or the thickness of the base end of the flexible shielding plate 14 is compared with other portions by molding or plate material additional processing. Techniques such as thinning can be adopted.
[0033]
Further, when a flexible shielding plate 14 is formed by laminating two plate-like members 14h and 14i, as shown in FIG. The plate member 14i on the side may be formed of a conductive member, and a bias voltage having a polarity opposite to the charging polarity of the toner may be applied from the power supply 18 to the plate member 14i formed of the conductive member. In this case, it is possible to prevent the toner from flying from the surface of the photoreceptor 2 in the direction of the paper guide, thereby further preventing the toner from adhering.
[0034]
FIG. 7 is a schematic diagram showing a third embodiment of the transfer device of the image forming apparatus of the present invention. The third embodiment has a configuration similar to that of the example shown in FIG. 3, except that a conductive pattern 14 b is provided on the back surface of the shielding plate 14, and the conductive pattern 14 b is attached to the transfer roll 9. The difference is that a voltage having a polarity opposite to the transfer voltage applied from the high-voltage power supply 19 is applied from the power supply 18.
[0035]
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 photoreceptor 2 in the direction of the paper guide, thereby further adhering the toner. Can be prevented.
[0036]
【The invention's effect】
As described above, according to the present invention, the tip portion of the shielding plate, than that is bent toward the upper end portion of one of the guide members of the guide means, the tip portion of the shield plate is in contact with the paper, 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. Therefore, it is possible to prevent the sheet from being stained due to the shielding plate. Further, since there is no frictional electrification 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 showing 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 ... Charger, 4 ... Developing device, 5a, 5b ... Conveying rollers, 6a, 6b ... Conveying 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 distal end, 14f proximal end, 14g long groove, 14h, 14i plate-like member, 15 bending part, 16 intermediate part, 17 stress concentration part, 18 power supply, 19: High voltage power supply, P: Paper

Claims (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 a transfer device below the transfer region. An image forming apparatus, comprising: a guide unit having a pair of opposed guide members arranged to guide the sheet from bottom to top toward the transfer area, and to transfer the toner image of the image carrier onto the sheet in the transfer area. In the device,
The guide means is configured such that the upper end of one of the guide members of the guide means is elastically pressed against the paper when the paper passes, and the upper end of the one of the guide means contacts the upper end of the guide means when the paper does not pass. Equipped with a shielding plate
An end portion of the flexible shielding plate is bent in a direction toward an upper end of one of the guide members of the guide means. 2. The transfer device according to claim 1, wherein a stress concentration portion having lower mechanical strength than other portions is formed near a base end portion of the flexible shielding plate. 3. The transfer of the image forming apparatus according to claim 1, wherein a portion to which a voltage having a polarity opposite to a polarity of a transfer voltage is applied is provided on a back surface of the flexible shielding plate. apparatus.

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