JP2010152198A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus suppressing the undesirable electric fields generated outside the planned area for transcription. <P>SOLUTION: The image forming apparatus has a photoreceptor, an image forming means to form toner images on the photoreceptor surface, a transfer means to transfer the toner images formed on the photoreceptor surface to a recording medium, a first carrier to carry the recording medium to the position between the photoreceptor and the transfer means, a second carrier to carry the recording medium passing through between the photoreceptor and the transfer means to the succeeding step, a guide provided to the transfer means and upstream and downstream the transfer means in the recording medium running path to guide the recording medium in contact with the photoreceptor surface or without touching it, and a presser to press the recording medium to the photoreceptor surface. The presser is charged in a polarity opposite to the image transfer polarity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that transfers a toner image formed on a surface of a photoreceptor to a recording medium using an electrophotographic system, and more particularly to a transfer apparatus that includes a pressing member that assists transfer.

  Conventionally, continuous paper printers were often used for computer output printing on forms, but recently, they have been used for printing direct mail, invoices, manuals, books, etc. by taking advantage of the function of high-speed variable information printing. It has come to be. In particular, the BOOK market is expanding, and there is an increasing demand for the development of high-speed and high-quality printers.

  A typical image quality deterioration of a continuous paper printer is a transfer defect on the second side when duplex printing is performed. Double-sided printing for continuous paper printers includes a system that uses two printers in tandem operation, prints the first side with the first unit, then reverses the web side and prints the second side with the second unit In this system, the transfer defect on the second surface becomes remarkable. In general, a web that has been thermally damaged by the fixing of the first surface is uneven due to thermal contraction, and the adhesion to the photoreceptor is lowered during the transfer of the second surface, causing a transfer defect in the recessed area. . When the tandem operation is performed using two continuous paper printers, the web stopped near the first fixing unit when printing is stopped is greatly affected by thermal damage, and the transfer failure on the second surface becomes more remarkable.

  In order to solve the above problems, a transfer assist blade that mechanically presses a web is generally known. By pressing the transfer assist blade, the unevenness of the web surface and the gap between the photoreceptors are reduced, and good transfer can be obtained.

  On the other hand, transfer dust is an example of other image quality degradation. Transfer dust is a phenomenon in which a toner image is not transferred to a position where it should originally be transferred, but is scattered around the toner image. Image quality such as characters and lines appear to be blurred. In transfer dust, the transfer charge imparted to the web forms an electric field in the gap upstream of the nip position between the web and the photoreceptor (outside the planned transfer area), and a portion of the toner image is transferred to the web (pre- (Transfer). In Patent 3600057, in order to prevent transfer dust, a shield plate that shields the transfer charge from being transferred outside the planned transfer area is provided in the shield case of the corona transfer device, and the shield plate is disposed at a position where no transfer failure occurs. is suggesting. The transfer assist blade described above is also an example of a shielding plate.

  Japanese Laid-Open Patent Publication No. 9-236992 proposes that the web and the photoreceptor are in close contact with the upstream side of the transfer region so that transfer dust can be prevented even if an electric field is formed outside the transfer region. However, since the web is continuous in the continuous paper printer, the web and the photosensitive member need to be separated from each other when the print start is stopped. The first page and the last line of the first page and the last page when the print start is stopped are necessary. From the viewpoint of ensuring print quality, it is difficult to bring the web and the photoconductor into close contact with the upstream side of the transfer region.

Japanese Patent No. 3600057 Japanese Patent Laid-Open No. 9-236992

  The shielding plate that shields the transfer charge from being transferred to the outside of the planned transfer area as in the prior art is effective for shielding the transfer charge directly applied from the transfer means to the outside of the planned transfer area, but has a small electric resistance. When the web is used, there is a problem in that the transfer charge flows from the transfer region to the outside of the transfer scheduled region via the web, thereby causing pre-transfer.

  An object of the present invention is to provide an image forming apparatus that suppresses an undesirable electric field from being generated outside a transfer planned area.

  The first means of the present invention for achieving the above object is a photoconductor, an image forming means for forming a toner image on the surface of the photoconductor, and a transfer for transferring the toner image formed on the surface of the photoconductor to a recording medium. First conveying means for conveying a recording medium between the photosensitive member and the transfer means, a second conveying means for conveying the recording medium that has passed between the photosensitive member and the transferring means to the subsequent stage, and the transferring means And a guide means for guiding the recording medium in contact with or away from the surface of the photoconductor, and a pressing means for pressing the recording medium against the surface of the photoconductor. In the image forming apparatus, the pressing means has a charge opposite in polarity to the transfer charge polarity.

  A second means of the present invention is characterized in that, in the first means, the pressing means is electrically grounded.

  According to a third means of the present invention, in the first or second means, the pressing means is 5 mm downstream of the contact start position from a contact start position of a transfer area where the recording medium and the photosensitive member contact each other. It is characterized by pressing within the range.

According to a fourth means of the present invention, in the first means, the pressing means has a blade shape, and has a volume resistivity of 10 ³ to 10 ⁹ Ω · cm.

  According to a fifth means of the present invention, in the first or second means, a shielding shield is provided between the transfer means and the pressing means.

  According to a sixth means of the present invention, in the first or second means, the pressing means is formed of a plurality of blades with an insulating material on a surface facing the transfer means. .

  Photoconductor, image forming unit for forming a toner image on the surface of the photoconductor, transfer unit for transferring the toner image formed on the surface of the photoconductor to a recording medium, and recording between the photoconductor and the transfer unit. A first conveying means for conveying the medium; a second conveying means for conveying the recording medium that has passed between the photosensitive member and the transferring means; and an upstream side and a downstream side in the conveying direction of the recording medium with respect to the transferring means. In the image forming apparatus, the image forming apparatus includes: a guide unit that guides the recording medium in contact with or away from the surface of the photoconductor; and a pressing unit that presses the recording medium against the surface of the photoconductor. By having a charge of opposite polarity, it is possible to suppress the generation of an undesirable electric field outside the transfer scheduled region, and to prevent transfer dust.

  Alternatively, by electrically grounding the pressing means, it is possible to suppress the generation of an undesirable electric field outside the transfer scheduled area, and to prevent transfer dust.

  Embodiments according to the present invention will be described below with reference to FIGS.

  FIG. 4 shows the overall configuration of the image forming apparatus according to the present invention. First, a charge is applied to the photosensitive member 2 from the charger 10, and then an exposure pattern based on the print data is irradiated from the exposure device 11 to form an electrostatic latent image on the photosensitive member 2. The electrostatic latent image on the photoreceptor 2 is developed by the developing machine 12, and a toner image is formed on the photoreceptor 2. The web 7 is conveyed to the transfer unit by the web conveying devices 13 and 14, and the toner image is transferred onto the web 7 by the corona transfer device 3. The toner image on the web 7 is heated to the vicinity of the transition temperature of the toner resin when passing through the pre-heater 15, and then melted and fixed to the web 7 by a fixing machine including a heating roller 16 and a backup roller 17 incorporating the heater.

FIG. 3 shows a transfer portion of the image forming apparatus. The photosensitive member 2 is a positively charged photosensitive member such as a selenium photosensitive member, an organic photosensitive member (OPC), or amorphous silicon (a-Si). The developing method is a reversal developing method, and the toner charging polarity is a positive polarity. A transfer assist blade 1 and a negatively charged corona transfer device 3 are housed inside the transfer device housing 4, and the transfer assist blade 1 has a volume resistivity of 10 ⁶ Ω · cm and a semiconductive polyurethane (PU) 1a. In addition, an insulating type polyethylene terephthalate (PET) 1b having a volume resistivity of 5 × 10 ¹⁶ Ω · cm or more was superposed. Here, the insulation type polyethylene terephthalate 1b is provided as a shielding plate to prevent electrical interference between the corona transfer device 3 and the semiconductive polyurethane 1a. In order to obtain, it was used by superimposing with the semiconductive type polyurethane 1a. The transfer assist blade 1 has a thickness of about 1.0 mm to 3.0 mm, the surface that contacts the web 7 is a semiconductive polyurethane 1a, and the surface that faces the corona transfer unit 3 is an insulating polyethylene terephthalate 1b.

  The transfer housing 4 serving as the guide means for the web 7 is rotated about the center of rotation in the figure by the rotation power transmitted through the link 9 by the rotation of the drive motor 8. When the transfer housing 4 rotates, the web 7 is guided by the upper web guide 6 and the lower web guide 5 attached to the transfer housing 4 so that the web 7 contacts the photoconductor 2 from a position separated from the surface of the photoconductor 2. Move to the position you want.

  FIG. 1 shows a difference in potential distribution on the surface of the web 7 caused by the presence / absence of the transfer assist blade 1 and the presence / absence of charge supply to the transfer assist blade 1. As shown in FIG. 1- (c), when a shielding plate that shields the transfer charge from being transferred outside the planned transfer area is not provided, -aV and web that are directly applied from the corona transfer unit 3 to the outside of the planned transfer area. The transfer dust becomes conspicuous due to the formation of an electric field by -bV flowing from the transfer region to the outside of the transfer planned region via 7. As shown in FIG. 1- (b), when the transfer assist blade 1 is provided as a shielding plate, -aV applied from the corona transfer device 3 is shielded, and only -bV flowing through the web 7 is outside the planned transfer region. Since an electric field is formed, transfer dust can be reduced. However, since -bV varies greatly depending on the environment and the type of web 7, it is necessary to block -bV flowing through web 7. Therefore, as shown in FIG. 1- (a), -bV flowing through the web 7 is blocked by applying a charge having a reverse polarity to the transfer charging polarity to the transfer assist blade 1a. As a result, the potential on the surface of the web 7 outside the transfer scheduled area becomes + cV, which is the same polarity as the charging polarity of the toner, and transfer dust can be suppressed by the repulsive force between the web 7 and the toner.

  FIG. 2 shows the potential distribution on the surface of the web 7 when the transfer assist blade 1a is electrically grounded. The transfer assist blade 1a may be a conductive type such as a metal plate. By electrically grounding the transfer assist blade 1a, -bV flowing through the web 7 is blocked, and the potential outside the transfer scheduled region becomes 0V, so that transfer dust can be suppressed. This configuration does not require a high-voltage power supply for supplying charges to the transfer assist blade 1a, and can provide an inexpensive apparatus. However, since the efficiency of blocking −bV flowing through the web 7 is reduced as compared with the method of supplying electric charge, there are restrictions on the environment and the use conditions of the web 7.

  On the other hand, the pressing position of the transfer assist blade 1 is preferably in the vicinity of the nip start position between the web 7 and the photoreceptor 2. In this embodiment, the pressing position of the transfer assist blade is set within the range of 5 mm downstream from the nip start position between the web 7 and the photoreceptor 2. As described above, when a charge having a polarity opposite to the transfer charge polarity is applied to the transfer assist blade 1, it is effective for suppressing transfer dust, but the total charge applied to the transfer is decreased and the transfer capability is decreased. Direction. In addition, since the web 7 is continuous in the continuous paper printer, the web 7 and the photosensitive member 2 need to be separated from each other when the print start is stopped. The first page and the last line of the last page when the print start is stopped The nip area (transfer area) between the web 7 and the photoreceptor 2 is small in terms of ensuring the print quality of the last line. In order to perform a sufficient transfer in a limited transfer region, the transfer assist blade 1 is disposed at a position where it is pressed near the nip start position between the web 7 and the photosensitive member 2, and the transfer assist blade 1 has a polarity opposite to the charging polarity of the transfer. Therefore, it is necessary to minimize the decrease in transfer ability when the charge is applied.

It is a figure which shows the electric potential distribution of the web surface at the time of providing the electric charge of reverse polarity to the charging polarity of a transfer to a press means. It is a figure which shows the electric potential distribution of the web surface at the time of electrically grounding a press means. It is sectional drawing which shows the structure of the transfer part in this invention. 1 is an overall view showing a configuration of a continuous paper printer.

Explanation of symbols

  1: Transfer assist blade, 1a: Conductive transfer assist blade, 1b: Insulation type transfer assist blade, 2: Photoconductor, 3: Corona transfer device, 4: Transfer housing, 5: Lower web guide, 6: Upper web Guide: 7: Web, 8: Drive motor, 9: Link, 10: Charger, 11: Exposure device, 12: Developer, 13, 14: Web transport device, 15: Preheater, 16: Heating roller, 17: Backup roller.

Claims (6)

  Photoconductor, image forming unit for forming a toner image on the surface of the photoconductor, transfer unit for transferring the toner image formed on the surface of the photoconductor to a recording medium, and recording between the photoconductor and the transfer unit. A first conveying means for conveying the medium; a second conveying means for conveying the recording medium that has passed between the photosensitive member and the transferring means; and an upstream side and a downstream side in the conveying direction of the recording medium with respect to the transferring means. The image forming apparatus includes a guide unit that guides the recording medium in contact with or away from the surface of the photoreceptor, and a pressing unit that presses the recording medium against the surface of the photoreceptor. Has a charge of opposite polarity.   Photoconductor, image forming unit for forming a toner image on the surface of the photoconductor, transfer unit for transferring the toner image formed on the surface of the photoconductor to a recording medium, and recording between the photoconductor and the transfer unit. A first conveying means for conveying the medium; a second conveying means for conveying the recording medium that has passed between the photosensitive member and the transferring means; and an upstream side and a downstream side in the conveying direction of the recording medium with respect to the transferring means. In the image forming apparatus, the image forming apparatus includes: a guide unit that guides the recording medium in contact with or away from the surface of the photosensitive member; and a pressing unit that presses the recording medium against the surface of the photosensitive member. An image forming apparatus.   3. The pressing unit according to claim 1, wherein the pressing unit presses within a range of 5 mm downstream of the contact start position from a contact start position of a transfer area where the recording medium and the photoconductor contact each other. Image forming apparatus. The image forming apparatus according to claim 1, wherein the pressing unit has a blade shape and has a volume resistivity of 10 ³ to 10 ⁹ Ω · cm.   The image forming apparatus according to claim 1, wherein a shielding shield is provided between the transfer unit and the pressing unit.   3. The image forming apparatus according to claim 1, wherein the pressing unit includes an insulating material on a surface facing the transfer unit and includes a plurality of blades.

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