JP2006171475A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve downsizing of an apparatus and bringing down of the cost in a simple constitution in which a bias application, etc., is not necessary and to obtain a good transfer image even with thick paper or in both sides paper passing. <P>SOLUTION: The image forming apparatus is constituted to prevent toner soiling of recording material well by having dispersed toner from a developing apparatus 4 attracted concentrated in the vicinity of a tip part 11a of a recording material guiding member 11 by forming at least the tip part 11a facing a transfer region of the recording material guiding member 11 transporting recording material P to the transfer region from a magnetic member or a magnetized member and providing a tip soiling preventing member 20 projecting toward an image carrier 1 on a paper non passing surface side of the tip part 11a of the recording material guiding member 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus using an electrostatic transfer process in a copying machine or a printer.

  In general, in various image forming apparatuses adopting an electrophotographic system such as a copying machine, a facsimile, or a printer, an image carrier such as a photosensitive drum that is uniformly charged is subjected to an exposure process according to an image pattern. The electrostatic latent image formed on the image carrier is supplied with a developer (toner), which is a chromatic fine powder to which an electrostatic charge is given in the developing device, and the electrostatic latent image Development is performed to make a visible image. The toner image that has been visualized and formed on the image carrier is transferred onto the recording material by an electrostatic transfer process in the transfer region.

  In performing the electrostatic transfer process in the transfer region described above, for example, as shown in FIG. 1, the image is transferred to a transfer device (transfer roller) 5 that transfers the toner image on the image carrier (photosensitive drum) 1. A bias is applied, and a transfer current flowing toward the image carrier 1 flows into the transfer device 5 due to the application of the transfer bias. In addition, transfer inlet guide members 11 and 12 for guiding the recording material to the transfer region are arranged on the upstream side of the transfer device 5 in the recording material conveyance direction. Since these transfer inlet guide members 11 and 12 are arranged so as to be close to the transfer device 5, the charge discharged from the transfer device 5 holds the same polarity (positive polarity) as the transfer current. .

  Since the positive charge held in the transfer inlet guide members 11 and 12 is different from the polarity of the toner (negative polarity), particularly when the toner image on the image carrier 1 enters the transfer device 5. In other words, the toner is attracted to the front end portions 11a of the transfer inlet guide members 11 and 12, which are adjacent portions of the image carrier 1, and becomes dirty. For example, when the front end portion and the rear end portion of the recording material P that has passed through the registration device 13 come into contact with the front end portions 11a of the transfer entrance guide members 11 and 12 where the toner contamination has occurred, the transfer entrance guide member is formed. The toner adhering to the 11 and 12 side may adhere to the recording material P and disturb the image. The toner stains generated in this way are conventionally known as leading edge stains or trailing edge stains, but especially when the recording material P is thick paper or when the curl amount is large due to double-sided printing or the like. Appears prominently.

  In order to deal with such a problem of front end contamination or rear end contamination, in Patent Document 1 below, a transfer entrance guide member is formed of a conductive member, and a repulsion bias having the same polarity as the toner is applied to the transfer entrance guide member. Techniques to do this are disclosed. However, the technique disclosed in Patent Document 1 requires a power source and control means for applying a bias to the conductive member, which complicates the apparatus and leads to an increase in size and cost of the apparatus. There is a problem that.

  Patent Document 2 below discloses a technique in which a conductive member provided on a transfer entrance guide member is grounded, and a friction charging member provided on a conveyance surface of a recording material is frictionally charged to the same polarity as the toner. Has been. However, with the technique disclosed in Patent Document 2, a recording material that has been passed even once, such as automatic double-sided or manual double-sided, does not have a desired bias (negative polarity), and the intended action / effect cannot be obtained. There is a bug that there is.

JP 11-338276 A JP 2002-132058 A

  Accordingly, the present invention provides an image forming apparatus capable of obtaining a good transfer image even when a cardboard or double-sided sheet is passed, while reducing the size and cost of the apparatus with a simple configuration that does not require bias application. With the goal.

  In order to achieve the above object, in the image forming apparatus according to the present invention, the toner image formed on the image carrier by the developing means on the recording material conveyed to the transfer region along the guide surface provided on the recording material guide member. In the image forming apparatus configured to perform image formation by transferring the image by the action of the transfer means, a tip contamination preventing member is provided on the back surface side of the guide surface of the recording material guide member and facing the transfer region. Is provided.

  According to the image forming apparatus of the present invention having such a configuration, the toner scattered from the developing device or the photosensitive drum adheres to the leading end contamination preventing member provided at the leading end portion on the back side of the recording material guiding member. Thus, toner contamination on the recording material is prevented well.

  As described above, the present invention provides a developing device and a photosensitive drum by providing a tip contamination preventing member at the tip of the guide surface of the recording material guide member that conveys the recording material to the transfer region and facing the transfer region. Since the toner scattered from above is attached to the tip of the recording material guide member to prevent toner contamination of the recording material, the device is compact with a simple configuration that does not require bias application etc. A good transfer image can be obtained even at the time of thick paper and double-sided paper feeding, and the usefulness of the image forming apparatus can be greatly improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Prior to that, an example of a schematic structure of a laser beam printer as an image forming apparatus to which the present invention is applied will be described.

  The laser beam printer shown in FIG. 1 includes a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is driven to rotate at a process speed of 131 mm / sec in the direction of arrow A by a driving unit (not shown). Around the photosensitive drum 1, a charging roller 2 as a charging device that uniformly charges the surface of the photosensitive drum 1 in almost the order along the rotation direction indicated by the arrow A, and exposure for forming an electrostatic latent image. A laser scanner 3 as a means, a developing device 4 for forming a toner image by visualizing an electrostatic latent image, and a transfer roller 5 as a transfer device for transferring the toner image on the photosensitive drum 1 to the recording material P A cleaning device 6 for collecting untransferred toner remaining on the photosensitive drum 1 is disposed. A fixing device 8 is disposed above the photosensitive drum 1.

  On the other hand, on the lower side of the apparatus main body M described above, a paper feed cassette 7 containing a sheet-like recording material P such as paper is disposed. A registration roller 13 is disposed for conveying the. In addition, a transfer inlet guide upper 11 that plays a main role for stabilizing the conveyance of the recording material P is disposed at a portion from the registration roller 13 to the transfer roller 5 described above, and the transfer inlet guide upper 11 An auxiliary transfer entrance guide lower 12 is arranged so as to face the surface. Further, a control board 9 for controlling an image forming operation and the like is attached to the back side of the apparatus main body M.

  Next, the operation of the laser beam printer having such a configuration will be described. First, the surface of the photosensitive drum 1 that is rotationally driven in the direction of arrow A by a driving unit (not shown) is moved by the charging roller 2. The battery is uniformly charged with a predetermined polarity and a predetermined potential (−585 V). The uniformly charged photosensitive drum 1 is subjected to image exposure based on image information by an image beam L irradiated from the laser scanner 3 as an exposure unit to the surface, and the charge corresponding to the exposed portion is removed. Thus, an electrostatic latent image is formed. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by the developing device 4 to be visualized to obtain a toner image. The developing device 4 is composed of, for example, a developing sleeve 4a having a diameter of 20 mm coated with carbon on the surface of an aluminum roller, and a toner chamber 4b for storing toner. A magnet roller 4c is included in the developing sleeve 4a. .

  On the other hand, as the toner in the present embodiment, for example, as in claim 7 of the claims, a one-component magnetic toner in which carbon black or a magnetic material is dispersed in a resin is used, and the developing sleeve 4a is used as the toner. A predetermined developing bias (AC: 2400 Hz, 1.6 KVpp / DC: -455 V) is applied to cause the toner to fly onto the electrostatic latent image on the photosensitive drum 1, whereby the electrostatic latent image is developed as a toner image (visible). Imaged). The obtained toner image is transferred to the recording material P side such as paper by the electrostatic transfer process of the transfer roller 5.

  On the other hand, the recording material P is stored in the above-described paper feeding cassette 7 and is conveyed so as to be pulled out by a paper feeding roller and a registration roller 13 (not shown), and the recording material P that has passed through the registration roller 13 is transferred to the transfer entrance. It is conveyed along the guide top 11 to a transfer nip (transfer area) between the photosensitive drum 1 and the transfer roller 5.

  Then, the recording material P carrying the unfixed toner image on the surface by the electrostatic transfer process in the transfer nip portion is transported to the fixing device 8 along a transport guide (not shown), where the unfixed toner image is heated. The toner image is fixed on the surface of the recording material P by pressurizing and melting the toner. Residual toner that has not been transferred to the recording material P remains on the surface of the photosensitive drum 1 after the transfer of the toner image, but the residual toner is removed by being scraped off by the cleaning blade 6 a of the cleaning device 6. The photosensitive drum 1 whose surface is cleaned is used for the next image formation. By repeating the above operation, image formation can be performed one after another.

  Next, a detailed configuration of the transfer entrance guide members 11 and 12 according to the present embodiment described above and the periphery thereof will be described with reference to FIG.

  The transfer entrance guide members 11 and 12 described above are provided so as to prevent image deterioration such as scattering of character images and blurring of dots, but the recording material P that has passed through the registration roller 13 is transferred to these transfer entrance guides. The members 11 and 12 are mainly conveyed along a guide surface (the left surface in the drawing) provided on the transfer entrance guide 11 and reach the transfer nip portion (transfer region) between the photosensitive drum 1 and the transfer roller 5. .

  At this time, the recording material P is configured to enter the transfer nip portion (transfer area) from the upstream side in the rotation direction of the photosensitive drum 1 by about 3 mm from the contact center between the photosensitive drum 1 and the transfer roller 5. However, at this time, the lower transfer inlet guide 12 described above is arranged so that the recording material P conveyed so as not to follow the upper transfer inlet guide 11 is pulled by the fixing device 8 or the transfer roller 5. Even in such a state, the recording material P smoothly enters toward the transfer nip portion between the photosensitive drum 1 and the transfer roller 5.

  In particular, as shown in FIG. 2, the back side of the above-described transfer inlet guide 11, that is, the non-sheet-passing surface (developing sleeve proximity surface) that is the right side of the transfer inlet guide 11 shown in the drawing, A thin plate-like tip contamination preventing member 20 is provided by pasting or the like. The tip contamination preventing member 20 is provided so as to prevent the toner scattered from the developing device 4 and the photosensitive drum 1 from fouling the tip end portion 11a on the upper side of the transfer entrance guide 11 shown in the figure. In this case, the transfer entrance guide 11 is arranged so as to protrude from the front end edge (upper end edge in the drawing) toward the photosensitive drum 1 side.

  In the first embodiment of the transfer entrance guide top 11 and the tip contamination prevention member 20 as described above, the entire transfer entrance guide top 11 is formed of a gin-coated steel plate having a magnetic thickness of 1.2 mm. The material of the transfer entrance guide top 11 may be a magnetic material, and is not particularly limited as long as it is a material that can be magnetized by cutting or bending by processing.

  On the other hand, the tip contamination preventing member 20 in the first embodiment is formed of a mylar having a thickness of 100 μm, which is a resin sheet material, and the protruding amount from the tip edge portion of the transfer entrance guide upper 11 is set to 2.5 mm. Has been. The material of the tip contamination preventing member 20 is not particularly limited, and the thickness may be set thinner than the transfer entrance guide upper 11 as described in claim 5 of the claims. preferable. Further, the amount of protrusion of the tip contamination preventing member 20 from the tip edge portion of the transfer entrance guide top 11 is, for example, 1.0 mm or more as described in claim 4 to capture the toner. The height is not particularly limited as long as the height is not in contact with the photosensitive drum 1 (the amount of protrusion).

  As a result of such a configuration, the tip end portion 11a of the magnetic transfer entrance guide top 11 is close to the developing sleeve 4a including the magnet 4c having a strong magnetic force of 90 mT, for example, at the edge portion. A concentrated magnetic field is generated. Therefore, the toner scattered from the developing device 4 and the photosensitive drum 1 is magnetically attracted only to the vicinity of the front end of the transfer entrance guide 11 where a concentrated magnetic field is generated. The toner attracted in a concentrated manner adheres to the non-sheet-passing surface side of the mylar (tip contamination prevention member) 20 attached to the non-sheet-passing surface (developing sleeve proximity surface) side which is the back surface side of the transfer entrance guide 11. . As a result, the sheet passing surface at the leading end portion 11a of the transfer entrance guide 11 on the conveying surface side of the recording material P and the leading end portion of the leading contamination preventing member 20 protruding therefrom is not contaminated with scattered toner. Even when paper with a large curl is passed, the leading and trailing end portions of the recording material P are not soiled by the leading end portion 11a of the transfer entrance guide top 11 and the leading end portion of the leading end contamination preventing member 20, and the leading and trailing ends are prevented. Occurrence of image abnormalities such as edge smearing can be satisfactorily prevented.

  For example, in the first embodiment of the present invention described above, SUS316 is used on the transfer inlet guide so as to reduce contamination due to scattered toner by a conventional model, for example, a non-magnetic conductive member, and the toner on the transfer inlet guide. Compared with the case where a repulsive bias having the same polarity (−600 V) is applied, the level of the trailing edge stain when passing 1000 sheets of A4 size solid black is almost the same as that applying the repulsive bias. Yes, it was confirmed that the level is better than SUS316 which is not magnetized.

  Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment shown in FIG. 3 as well, the recording material P that has passed through the registration roller 13 is mainly placed on the transfer entrance guide 11 in order to prevent image deterioration such as scattering of character images and dot bleeding. Along the transfer nip portion between the photosensitive drum 1 and the transfer roller 5, the transfer nip portion is entered from the upstream side of the photosensitive drum by about 3 mm.

  In the example of the second embodiment, the transfer entrance guide top 11 is formed of a gin-coated steel plate having a thickness of 1.2 mm, and only the tip portion 11a adjacent to the photosensitive drum 1 is magnetized to 10 mT by a magnet. ing. The polarity to be magnetized is the opposite polarity of the closest polarity of the magnet 4c included in the developing sleeve 4a. In this embodiment, the polarity is N polarity opposite to the S polarity of the developing pole which is the main pole of the magnet 4c. Magnetized. For magnetization at the tip end portion 11a of the transfer entrance guide upper 11, another member (magnet or the like) having a desired polarity and magnetic force may be provided.

  Also, the tip contamination preventing member 20 in the present embodiment is a mylar having a thickness of 100 μm, which is a resin sheet material, and the protrusion amount from the tip edge portion of the transfer entrance guide upper 11 is 2.5 mm. The material of the tip contamination preventing member 20 is not particularly limited, and the thickness is not particularly specified as long as it is thinner than the transfer entrance guide 11 as described in claim 5. Absent. Furthermore, the amount of protrusion of the tip contamination preventing member 20 from the leading edge of the transfer entrance guide 11 is not particularly specified as long as it is 1.0 mm or more as described in claim 4 of the claims, The height is not particularly limited as long as it does not contact the photosensitive drum 1 (the amount of protrusion).

  As a result of the configuration as in the second embodiment, the tip end portion 11a of the transfer entrance guide top 11 is magnetized to 10 mT, so that the toner scattered from the developing device 4 and the photosensitive drum 1 is transferred to the transfer entrance guide. It is attracted more positively to the magnetized portion of the top end portion 11a of the top 11, and can be satisfactorily adhered to the non-sheet passing surface side which is the back side of the tip contamination preventing member 20. Therefore, the tip portion 11 a of the transfer inlet guide upper 11 where the toner attracted intensively becomes the conveying surface of the recording material P and the tip portion of the tip contamination preventing member 20 protruding from the tip portion of the transfer inlet guide upper 11 are also included. Even if thick paper or paper with large curl is passed, the recording material P is recorded even if the leading and trailing ends of the recording material P touch the leading end of the transfer entrance guide 11 or the leading end of the leading antifouling prevention member 20 even if the scattered toner is not soiled. Image abnormalities such as dirt on the front and rear ends of the material P do not occur.

  For example, in the above-described second embodiment of the present invention, SUS316 is used on the transfer inlet guide so as to reduce contamination due to scattered toner by a nonmagnetic conductive member, for example, and the same polarity as the toner on the transfer inlet guide When comparing with each conventional model to which a repulsive bias of (−600 V) is applied, when comparing with the first embodiment described above, when 1000 sheets of A4 size solid black were passed. It was confirmed that the level of the trailing edge dirt was the best result.

  As mentioned above, although the embodiment of the invention made by the present inventor has been specifically described, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Not too long.

  For example, each of the embodiments described above applies the present invention to a laser beam printer, but the present invention can be similarly applied to other image forming apparatuses such as copying machines and facsimiles. .

  The image forming apparatus according to the present invention described above can be widely applied to a wide variety of image forming apparatuses such as copying machines as well as image forming apparatuses such as printers.

1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus to which the present invention is applied. It is a longitudinal cross-sectional view which shows schematic structure of the transfer guide member concerning the 1st Embodiment of this invention, and its peripheral part. It is a longitudinal cross-sectional view which shows schematic structure of the transfer guide member concerning the 2nd Embodiment of this invention, and its peripheral part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Laser scanner 4 Developing device 4a Developing sleeve 4b Toner chamber 4c Developing magnet 5 Transfer roller 6 Cleaning device 6a Cleaning blade
7 Paper cassette
DESCRIPTION OF SYMBOLS 8 Fixing device 9 Control board 11 Transfer entrance guide top 11a Transfer entrance guide top tip 12 Transfer entrance guide bottom 13 Registration roller 20 Tip contamination prevention member M Device main body L Laser beam path P Recording material

Claims (7)

Configuration in which image formation is performed by transferring the toner image formed on the image carrier by the developing means to the recording material conveyed to the transfer area along the guide surface provided on the recording material guide member by the action of the transferring means. In the image forming apparatus made in
An image forming apparatus, wherein a leading end contamination preventing member is provided at a leading end portion facing the transfer area on the back side of the guiding surface of the recording material guiding member. The recording material guide member has at least a tip portion facing the transfer region formed of a magnetic member,
2. The image forming apparatus according to claim 1, wherein the antifouling member is provided so as to protrude from the recording material guide member toward the image carrier. The recording material guide member is formed from a member magnetized at least at a tip portion facing the transfer region,
2. The image forming apparatus according to claim 1, wherein the antifouling member is provided so as to protrude from the recording material guide member toward the image carrier. The recording material guide member is disposed on the developing means side and has a first recording material guide member having a main conveyance function for the recording material, and a first recording material guide member disposed so as to face the first recording material guide member. Two recording material guide members,
4. The image forming apparatus according to claim 1, wherein the magnetic member and the tip contamination preventing member are provided on the first recording material guide member. 5.   The tip contamination prevention member is formed of a non-magnetic member, and is arranged so that the tip portion of the tip contamination prevention member protrudes 1.0 mm or more from the tip edge portion of the recording material guide member. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   6. The image forming apparatus according to claim 1, wherein the antifouling member is formed of a resin sheet material. The image forming apparatus according to claim 1, wherein the developer contained in the developing unit to visualize the electrostatic latent image is made of toner having a single component and magnetism.

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