JP3684350B2 - Separation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and the like, and more particularly, to a separation apparatus that neutralizes a recording medium such as a sheet on which a toner image is transferred.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, the surface of an electrostatic latent image bearing member such as a photosensitive drum is uniformly charged by a charging device, and image exposure is performed on the charged area so that a static image corresponding to a document image is obtained. An electrostatic latent image is formed, and the latent image is developed by a developing device to form a visible toner image. The toner image is transferred onto a recording material by a transfer device, and the toner on the recording material is fixed by a fixing device. obtain.
[0003]
In such an image forming apparatus, as a transfer device for transferring a toner image, those using a transfer charger and those using a transfer roller are known. When a transfer roller is used, the transfer roller is pressed against the image carrier or intermediate transfer member with a recording material interposed therebetween, and a voltage having a polarity opposite to that of the toner image is applied to attract the toner to the recording material. For example, when the toner is positively charged, the transfer roller is negatively charged by applying a negative voltage, whereby the positively charged toner image is attracted to the negative charge of the transfer roller. And transferred to the recording material.
[0004]
However, at this time, the recording material pressed by the transfer roller to which a negative voltage is applied is negatively charged when passing between the transfer roller and the image carrier or intermediate transfer member, and further positively charged toner. Since the image carrier that holds the image or the intermediate transfer member itself has a positive charging tendency, the recording material that has passed through the transfer position is attracted to the image carrier or the intermediate transfer member, and the recording material is clogged. It will happen.
These are the same when the charging polarity is reversed.
[0005]
Therefore, in an image forming apparatus that transfers a toner image onto a recording material by a transfer roller, the recording material is usually separated from the image carrier so that the recording material is not attracted and adhered to the image carrier or intermediate transfer member. A separation device is provided, and as such a separation device, one using a separation needle is known.
In this case, the charge of the recording material is released by discharge by the installed separation needle, weakening the adsorption force of the recording material to the image carrier or intermediate transfer member, and the recording material is easily separated from these. It becomes.
[0006]
However, if there is another member near the distance between the tip of the separation needle and the image carrier or intermediate transfer member, discharge will occur from the tip of the separation needle, so that the tip of the separation needle is not provided at that part. The thing of the shape is used.
For example, in JP-A-6-3969, a guide part for guiding the conveyance of a recording material is integrally formed in a part of a holder for supporting a separation needle, and the guide part has a shape extending in the conveyance direction of the recording material. A technique is disclosed in which a notch is provided in a portion of the static elimination needle corresponding to the guide portion.
Specifically, in FIG. 2, when the recording material is conveyed in the direction of the arrow with respect to the photosensitive drum 4 and is neutralized by the separation needle 121, the rib 125 serving as a conveyance guide attached to the guide member 124. 4 is located adjacent to the tip of the separation needle 121, so that a portion corresponding to the rib 125 is provided with a notch 123 so as not to discharge from the separation needle 121 as shown in FIG. Yes.
[0007]
[Problem to be Solved by the Invention]
However, as described above, when the notch 123 is provided in the portion corresponding to the rib 125 that guides the conveyance of the guide member 124, the pointed portion adjacent to the notched portion 123 has a large interval between the adjacent pointed portion. Therefore, such a pointed portion has a problem that charges are concentrated when a bias voltage is applied, and discharge destruction due to abnormal discharge occurs on the photosensitive drum 4 corresponding to this portion, resulting in an image black spot. There was a point.
In particular, in an image forming apparatus using an amorphous silicon photoconductor, if charges are excessively concentrated, pinholes due to discharge breakdown may occur.
The present invention is to solve such problems.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a transfer voltage is applied to a transfer member facing the surface of an image carrier that carries and rotates a toner image, and a sheet or the like that passes through the transfer member The toner image is transferred to a recording medium, and is arranged on the downstream side of the sheet conveyance from the transfer portion, and a plate-like separation needle is attached to the sheet conveyance guide member along the longitudinal direction of the transfer member. in the separation device of the image forming apparatus, the separation needle notches have a pointed end portion adjacent to the cutout portion of the separation needles is formed away from said image bearing member than the other tip By separating the tip of the separation needle at a portion of the photosensitive drum corresponding to the tip of the separation needle that is widened with the adjacent tip, by making a notch. , Photoreceptor Charge on the ram can be prevented discharge breakdown due to abnormal discharge occurring concentrated.
According to a second aspect of the present invention, in the separation device according to the first aspect, the notch portion of the separation needle is formed at a portion corresponding to the reinforcing rib of the conveyance guide member of the paper. Further, it is possible to prevent discharge from the tip of the separation needle to the rib side serving as the conveyance guide of the conveyance guide member for the paper.
According to a third aspect of the present invention, the image carrier is an amorphous silicon photoconductor, which is more effective with an amorphous silicon drum that is easily damaged by discharge due to concentrated charges.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of an image forming apparatus according to the present invention. As shown in FIG. 1, in a copying machine 1 as an example of an image forming apparatus according to the present invention, a photosensitive drum (photosensitive body or image) is rotated in a direction A in the figure by a charging device 3 in a copying machine main body 2. The carrier 4) is uniformly charged, and an electrostatic latent image is formed on the photosensitive drum 4 by the laser beam from the exposure device (laser scanning unit) 6 based on the document image read by the document reader 5. A developing device (developing means) 7 attaches a developer (hereinafter referred to as toner) to the electrostatic latent image to form a toner image. The toner is supplied to the developing device 7 from the toner container 8.
[0010]
A sheet is conveyed from the sheet feeding mechanism 9 via the sheet conveyance path 10 toward the photosensitive drum 4 on which the toner image as described above is formed, and the toner image on the surface of the photosensitive drum 4 is transferred by the transfer roller 11 to the sheet. Is transcribed. Then, the sheet on which the toner image is transferred is separated from the photosensitive drum 4 by the separating unit 12 and conveyed to the fixing device 12 having a pair of fixing rollers to fix the toner image. The paper that has passed through the fixing device 13 is sent to a paper conveyance path 14 that is branched in a plurality of directions, and the conveyance direction is sorted by a branching member at a branching point of the paper conveyance path 14 and is sent to the paper conveyance path 18 as it is. After duplex copying, the sheet is discharged from the sheet discharge portion of the upper sheet tray 102a, the lower sheet tray 102b, or the sheet tray 103.
[0011]
The transfer roller 11 is configured to transfer a toner image from the surface of the photosensitive drum 4 by a transfer bias unit (not shown) applying a transfer bias having a polarity opposite to that of the toner to the sheet.
Reference numeral 17 denotes a cleaning unit that removes residual toner on the photosensitive drum 4. The paper feed mechanism 9 is detachably attached to the copier body 2 and includes paper feed cassettes 91 and 92 for storing paper, and a stack bypass 93 provided above the paper feed cassettes 91 and 92. It is connected to an image forming unit including the photosensitive drum 4 and the developing device 7.
[0012]
Next, the separation unit 12 that neutralizes the sheet onto which the toner image is transferred from the photosensitive drum 4 according to the present invention will be described in detail with reference to FIGS.
FIG. 2 is a perspective view showing the conveyance guide member 124 including the photosensitive drum 4 and the separating needle 121 provided adjacent to the photosensitive drum 4 and having the reinforcing rib 125, and around the photosensitive drum 4. FIG. 3 is a cross-sectional view showing how the paper is conveyed and separated. As described above, the positively charged toner that is electrostatically attached by the developing unit 7 to the exposed portion of the photosensitive drum 4 that is uniformly charged to the positive polarity by the charging device 3, and the negative polarity bias is applied to the transfer roller 11. Is applied to the paper transported from the transport path 10. At this time, since the paper also has negative polarity, if it is left as it is, it will be attracted to and wound around the photosensitive drum 4 having the positive polarity.
Therefore, when a positive polarity bias of about 5 KV is applied to the separation needle 121, a discharge occurs on the photosensitive drum 4 side, and when the negatively charged paper is discharged, the paper is wound around the photosensitive drum 4. Instead, the sheet is conveyed along the conveyance guide member 124 in the direction of the arrow in the figure.
[0013]
Next, the shape of the separation needle 121 according to the present invention will be described with reference to FIG. Conventionally, as shown in FIG. 4A, the portion of the separation needle 121 that overlaps the rib 125 of the guide member as shown in FIG. As shown, when the height of the tip 122 of the separation needle 121, that is, the distance from the photosensitive drum 4 is all constant, the separation adjacent to the notch 123 is applied when a bias voltage is applied to the separation needle 121. Charges were concentrated on the tip end portion 122a of the needle 121, and a pinhole due to discharge breakdown due to abnormal discharge occurred in a portion of the photosensitive drum 4 corresponding thereto, and an image black spot was generated.
[0014]
Therefore, as shown in FIG. 4 (b), at the pointed end portion 122 of the separation needle 121, the height of the pointed end portion 122 a ′ adjacent to the notched portion 123 is made lower than the pointed end portion 122 b not adjacent to the notched portion 123, By separating from the photosensitive drum 4, the electric field intensity on the photosensitive drum 4 can be made uniform, and abnormal discharge due to concentration of charges can be prevented.
In the present embodiment, the shape of the separating needle 121 is a saw blade shape, but the tip shape is not limited to this, as shown in FIG. The shape may be cut away from the photosensitive drum 4.
[0015]
【The invention's effect】
According to the present invention, in the separation needle provided with the notch, by separating the tip of the separation needle adjacent to the notch from the photosensitive drum, the tip of the separation needle adjacent to the notch and the corresponding portion. By reducing the electric field strength at the site on the photosensitive drum, the electric charge concentrates on the tip and prevents dielectric breakdown due to abnormal discharge on the photosensitive drum, thereby avoiding image defects such as black spots. I was able to.
[Brief description of the drawings]
FIG. 1 is a schematic mechanical cross-sectional view of an image forming apparatus employing the present invention.
FIG. 2 is a perspective view of a separation unit employing the present invention.
FIG. 3 is a cross-sectional view including a separation unit employing the present invention.
FIG. 4A is a front view of a conventional separation needle.
(B) It is a front view which shows the shape of the separating needle which employ | adopts this invention.
(C) It is a front view which shows the shape of the separation needle in one Example of this invention.
[Explanation of symbols]
3; charging device 4; photosensitive drum 11; transfer roller 12; separation device 121; separation needle 122; separation needle point 122a; separation needle point 122a 'adjacent to the notch in the conventional example; Separation needle point 122b adjacent to the notch; separation needle point 123 not adjacent to the notch 123; notch 124; transport guide member 125; guide member rib

Claims (3)

A transfer voltage is applied to a transfer member that faces the surface of the image carrier that carries and rotates the toner image,
Transferring the toner image to a recording medium such as paper passing through a transfer member;
In the separation apparatus of the image forming apparatus , which is disposed on the downstream side of the transfer of the sheet from the transfer portion and configured to include a plate-like separation needle along the longitudinal direction of the transfer member on the transfer guide member of the sheet.
The separation needle notches have a separation device tip portion adjacent to the cutout portion of the separation needles, characterized in that than the other tip portion is formed away from the image bearing member. 2. The separation apparatus according to claim 1, wherein the notch portion of the separation needle is formed at a portion corresponding to a reinforcing rib of the sheet conveyance guide member . 2. The separation apparatus according to claim 1, wherein the image carrier is an amorphous silicon photosensitive member.

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