JP2007047195A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus adaptable to continuous paper which can achieve excellent transfer free from an image defect even in transfer to rough surface paper whose surface is largely roughened and also transfer to the second surface of a web which is wrinkled by heat when fixing a toner image on its first surface even when it is the web whose surface is comparatively flat. <P>SOLUTION: The image forming apparatus which is provided with a transfer means opposed to a photoreceptor drum so as to electrostatically transfer a toner image formed on the surface of the photoreceptor drum to the web conveyed to a transfer area between the photoreceptor drum and the transfer means is provided with a guide member at a position where tightness between the web and the photoreceptor drum is enhanced at the entrance of the transfer area, and then provided with a transfer assist roller positioned on a downstream side in the conveyance of the web with reference to the guide member, pressing the web on the photoreceptor in space between the transfer means and itself and also rotating following the traveling of the web. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention has a corona transfer unit facing the photosensitive drum, and a toner image formed on the surface of the photosensitive drum is statically transferred to a web conveyed to a transfer region between the photosensitive drum and the corona transfer unit. In particular, the present invention relates to an image forming apparatus that performs transfer electrically, and in particular, transfer to rough paper having a large surface irregularity, and wrinkles due to heat at the time of fixing a toner image on the first surface, even on a relatively flat web. The present invention also relates to an image forming apparatus capable of good transfer without image defects even when transferring to a second surface of a sheet on which printing has occurred.

  FIG. 4 shows a configuration of a continuous paper printer which is an example of an electrophotographic system. Charge is applied to the surface of the photosensitive drum 1 by the charger 11, and an exposure pattern based on the print data is irradiated from the exposure light source 12 to form an electrostatic latent image on the surface of the photosensitive drum 1. The electrostatic latent image on the surface of the photosensitive drum 1 is developed by the developer on the developing roll of the developing machine 13, and a toner image is formed on the drum 1. The web 7 is conveyed to the transfer unit 10 by the web conveying devices 14, 15, and 16, and the toner image transferred onto the web 7 by the corona transfer device is heated to near the transition temperature of the toner resin when passing through the preheater 17. The toner image is melted and fixed to the web 7 by a fixing machine including a heating roller 18 incorporating a heater and a backup roller 19.

  Conventionally, continuous paper printers were often used for computer output printing on forms, but recently they have been used for multi-purpose printing of direct mail, invoices, manuals, books, etc. by taking advantage of the function of high-speed variable information printing. It came to be. In addition, the web used must be compatible with various types of webs, from thin paper to thick paper, and web types from fine paper to rough paper. Furthermore, from the viewpoint of resource saving, two continuous paper printers are operated in tandem, the first side is printed on the first side, and then the web side is reversed and the second side is printed on the second side. The need for duplex printing is increasing. When dealing with such versatility, transfer performance dominates image quality. In general, many pulp fibers are present on the web surface, whereas the fine fiber paper has a pulp fiber spacing of about 50 μm, while the rough paper has a wide pulp fiber spacing of about 100 μm. The depth of the recess is as large as about 20 μm. For this reason, in the case of rough surface paper, the adhesion between the rough surface paper and the photosensitive drum surface is poor in the transfer portion, and an image defect due to transfer failure occurs in the recessed area on the surface of the rough surface paper. In a printer that supports cut sheets, there has been proposed a method in which a transfer assist blade is provided to press the web against the photoconductor according to the timing when the web passes (see, for example, Patent Documents 1 and 2). For this purpose, the transfer assist blade can be retracted by a solenoid mechanism in the inter-web portion so that the transfer assist blade does not come into direct contact with the surface of the photoconductor layer.

JP-A-9-171308

Japanese Patent Application Laid-Open No. 11-65328

  In the continuous paper printer, printing is performed by transporting perforated box paper or perforated roll paper at a high speed (0.5 to 2 m / sec). Unlike cut paper, the web is continuous and forms a continuous web.

  Problems when the transfer assist blade is applied to a continuous paper printer will be described with reference to FIG. FIG. 3 shows a configuration in which a transfer assist blade 21 is used in the transfer portion. A transfer assist blade 21 such as a plastic plate, a film, or a metal plate is provided on the upstream side of the corona transfer unit 3 when viewed from the web conveyance direction. After being pressed against the surface of the photosensitive drum 1 by the transfer assist blade 21 and reaching the position opposed to the corona transfer device 3 in a closely contacted state, the toner image 9b is transferred to the web 7 by the charge application from the corona transfer device 3. Then, it is sent to a fixing device (not shown) by a web conveying device.

  As a pressing effect of the transfer assist blade 21, it is known that a good transfer can be obtained by reducing the gap between the surface of the rough paper and the photosensitive drum.

  On the other hand, the case where double-sided printing is performed by printing the toner image 9b on the second surface of the web 7 on which the toner image 9a is formed on the first surface is shown. In this case, since the toner image 9a is already formed on the first surface, the first toner image 9a is formed on the surface that contacts the transfer assist blade 21 of the web 7 conveyed to the transfer unit housing 2. The face comes. For this reason, the surface of the toner image 9a fixed by the transfer assist blade 21 is rubbed to cause image deterioration such as missing toner image. In general, when printing the second side, the pressing history of the transfer assist blade 21 is increased in order to improve the adhesion because the web 7 is deformed due to the heat history in the fixing process during the first side printing. It is necessary to increase the size, which will further promote the deterioration of image quality.

  As described above, the continuous paper printer has a high need for printing on various webs. However, the width of the web to be used can be used depending on the application. For this reason, recently, long (21 to 22 inches) photosensitive drums have been used, and the widths of webs used vary widely, such as 12 inches, 16 inches, and 22 inches. In the case of printing 12 to 16 inches for forms, manuals, books, and the like are cut after printing, resulting in a 17 inch width that can be chamfered in two A4 sizes, and a 22 inch web that has three chamfers in B5 size. For this reason, when printing a web having a narrow width, unless the transfer assist blade 21 having a width equal to or smaller than the web width is used, the photosensitive drum 1 is contacted and scratched, and the print quality is deteriorated. Therefore, to cope with an arbitrary web width, a method of providing a plurality of transfer assist blades and combining them according to the web width is conceivable, but there is a problem that the configuration is complicated and the size of the transfer assist mechanism is increased.

  Image formation for providing a transfer means facing the photosensitive drum and electrostatically transferring the toner image formed on the surface of the photosensitive drum to a web conveyed to a transfer area between the photosensitive drum and the transfer means In the apparatus, a guide member is provided at a position where the adhesion between the web and the photosensitive drum is increased at the entrance of the transfer region, and the photosensitive member is positioned between the transfer means and the downstream side of the web conveyance with respect to the guide member. A transfer assist roller that is pressed against the drum and rotates in accordance with the running of the web is provided.

  According to the present invention, the transfer assist roller rotates following the web while pressing the web against the photosensitive drum surface with a predetermined pressure. For this reason, the adhesion between the web and the charged photoconductor surface is improved, the voids are reduced, and the transfer performance is improved. At the same time, since the roller is driven, the web is not deformed such as wrinkles.

  Further, by providing the transfer assist roller, the toner image on the first surface is not damaged even during the first surface transfer.

  In addition, by providing a guide member upstream of the transfer assist roller in the web conveyance direction, the adhesion between the web and the photosensitive drum is improved, and the above-described effect can be reliably realized.

  Further, by providing the transfer assist roller and the guide member in the same transfer device housing, the transfer assist roller and the guide member can be retracted from the photosensitive drum, and the conventional effect of separating the web and the photosensitive drum during non-printing is not impaired.

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

  FIG. 1 shows the structure of a transfer portion according to an embodiment of the present invention. In this embodiment, a selenium photoreceptor, a positively charged photoreceptor such as plus OPC, a-Si, or the like is used as the photosensitive drum 1. Show the case. The developing method of the photosensitive drum 1 is a reversal developing method, and the charging polarity of the toner is a positive polarity. A transfer assist roller 4 and a negatively charged corona transfer unit 3 are housed in the transfer unit housing 2 in the transfer unit. The transfer assist roller 4 of this embodiment is obtained by covering a stainless steel round bar having a diameter of 15 mm with a heat-shrinkable tube and heating at 120 to 160 ° C. In the case of an insulating type, a polyethylene terephthalate (PET) tube that has the same charging polarity as the charging polarity of the toner due to charging with the web 7 can be used. Since the conductive type can apply a voltage to the metal core, any of fluororesin, polyimide, and ethylene propylene rubber can be used. In this embodiment, an ethylene propylene rubber tube is used. The thickness after shrinkage of the ethylene propylene rubber tube is about 0.6 mm. Since the surface potential of the unexposed area of the photosensitive drum 1 at the position of the transfer assist roller 4 is +400 to +600 V, a DC voltage of 500 V plus polarity is applied to the metal core. The transfer unit housing 2 in which the corona transfer unit 3 is stored can move forward and backward with respect to the surface of the photosensitive drum 1, and FIG. 2 shows a state in which the transfer unit housing 2 moves backward. Similarly, the transfer assist roller 4 can be brought into contact with and retracted from the surface of the photosensitive drum 1. When the printing operation is interrupted or stopped, the transfer assist roller 4 that is in contact with the surface of the photosensitive drum 1 or the web 7 needs to be quickly retracted. This is because when the web 7 having the transferred toner comes into contact with the transfer assist roller 4, the toner falls off and an image defect occurs.

  Next, a transfer operation using the transfer assist roller 4 will be described.

  When the web 7 is sent from the web conveyance device to the transfer unit and the preparation for the printing operation is completed, the transfer device housing 2 moves to a predetermined distance with respect to the surface of the photosensitive drum 1, and then the transfer assist roller 4 sensitizes the web 7. Press against drum 1. In order to ensure the adhesion between the web 7 and the photosensitive drum 1 and to follow it, it is necessary to optimize the pressing pressure. As a result of the experiment, the pressing pressure of the web 7 by the roller member is 13 g / cm 2 to 40 g / The range was set to cm2.

FIG. 1 shows the printing of the second surface on the web 7 on which the toner image 9a is printed on the first surface. Since the surface of the transfer assist roller 4 is an ethylene propylene (EPDM) rubber layer and is driven by the web 7, the toner image 9a on the first surface is not damaged. Further, even when the web 7 is a web having a rough surface such as rough paper, the voids are reduced, and the adhesion to the surface of the photosensitive drum 1 is improved, so that good transfer can be performed. However,
A large amount of paper dust generated by the rubbing on the edge and surface of the web 7 by the traveling mechanism of the web 7 floats inside the printer device, and if the printing is continued for a long time, the paper is formed on the surface of the transfer assist roller 4. Since dust, dust, or the like adheres, the effect of pressing the transfer assist roller 4 against the web 7 is reduced, and the first-side printed image that comes into contact with the transfer assist roller 4 is induced. Therefore, the function of the transfer assist roller 4 is compensated for by increasing the adhesion between the web 7 and the photosensitive drum 1 by providing the guide member 5. In the embodiment of the present invention, the guide member 5 has a fixed roller shape, but the guide member 5 may have a plate shape.

  Next, the mechanical mechanism of the present invention will be described. In FIG. 1, as described above, the transfer unit includes a transfer assist roller 4, a guide member 5, a negatively charged corona transfer device 3, a transfer assist roller 4, a guide member 5, and a stopper 6. A transfer assist roller holder 8 is provided. The transfer assist roller 4 is brought into contact with the photosensitive drum 1 by the optimum pressing pressure as described above by a spring 20 applied to the transfer housing 2 and the transfer assist roller holder 8 with the shaft center of the guide member 5 as the rotation center. The guide member 5 guides the web 7 from the first surface printed image 9 a side, and is held in a positional relationship that improves the adhesion between the photosensitive drum 1 and the web 7. Reference numerals 22 and 23 are guide plates for guiding the web 7 to the transfer section. The guide plate 22 is fixed to the link 24, and the link 24 has a function for moving the guide plate 22 backward when the transfer device housing 2 moves backward. Have

  FIG. 2 shows a state in which the transfer unit is moved backward and stopped, that is, a state in which the printing operation is interrupted or stopped. The transfer assist roller holder 8 moves away from the photosensitive drum 1 at the same time as the transfer housing 6 moves backward, and the pressure for pressing the transfer assist roller 4 against the photosensitive drum 1 disappears. Then, as the spring 20 contracts, the stopper 6 comes into contact with the bottom surface of the transfer housing 2, the transfer assist roller holder 8 stops, and the transfer assist roller 4 and the guide member 5 are held in a state of being retracted from the photosensitive drum 1. Is separated from the photosensitive drum 1.

  Electrophotographic printers can be used in a wide range of fields from the field of business printing to personal use, taking advantage of the fact that variable information can be printed on a web such as paper at high speed. In particular, since continuous paper printers do not cause jams during web conveyance like cut paper, various webs can be conveyed and printed at high speed. Recently, printing needs for individuals such as direct mail and fee schedules have increased, and it has been required to print faster, in large quantities, and at lower prices. In addition, paper usage by double-sided printing from the viewpoint of protecting the global environment Reduction, use of recycled paper and roughened paper using recycled pulp, etc. are desired. The present invention solves transfer defects during double-sided printing and improves transferability to low-cost webs such as recycled paper and roughened paper, thus saving resources in addition to realizing high-quality high-speed printers. Can contribute.

The figure which shows the transcription | transfer part in this invention. The figure which shows the transcription | transfer part in this invention. The figure which shows the conventional transcription | transfer part using a transcription | transfer assist blade. 1 is an overall view showing a configuration of a continuous paper printing compatible printer. FIG.

Explanation of symbols

1 is a photosensitive drum, 2 is a transfer device housing, 3 is a corona transfer device, 4 is a transfer assist roller, 5 is a guide member, 6 is a stopper, 7 is a web, 8 is a transfer assist roller holder, and 9a is a first side print image. 9b is a second side printed image, 10 is a transfer unit, 11 is a charger, 12 is an exposure light source, 13 is a developing unit, 14, 15 and 16 are paper conveying devices, 17 is a preheater, 18 is a heating roller, and 19 is A backup roller, 20 is a spring, 21 is a transfer assist blade, 22 and 23 are guide plates, and 24 is a link.

Claims (2)

  Image formation for providing a transfer means facing the photosensitive drum and electrostatically transferring the toner image formed on the surface of the photosensitive drum to a web conveyed to a transfer area between the photosensitive drum and the transfer means In the apparatus, a guide member is provided at a position where the adhesion between the web and the photosensitive drum is increased at the entrance of the transfer region, and the photosensitive member is positioned between the transfer means and the downstream side of the web conveyance with respect to the guide member. An image forming apparatus comprising a transfer assist roller that is pressed against a drum and rotates in accordance with web travel. The transfer means is a corona transfer device, and the corona transfer device, the transfer assist roller, and the guide member are stored in the same housing, the housing can be retracted from the photosensitive drum, and the housing is retracted. The image forming apparatus according to claim 1, wherein the transfer assist roller and the guide member are completely retractable from the photosensitive drum.

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