JP2008046145A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of correcting the ruggedness of a web by pressing the web against a photoreceptor drum in a double-sided printing and preventing toner printed on the surface of the web from being peeled off in a rear surface printing. <P>SOLUTION: A transfer assist blade 48 is operated in the position where a low friction part 48a at its leading end presses the continuous web 14 against the photoreceptor drum 12 during printing. Since the continuous web 14 is pressed against the periphery of the photoreceptor drum 12 during its passage through a nip area 60, the ruggedness of its surface is corrected. This ensures satisfactory transfer even with the web 14 subjected to the rough surface of paper quality and thermal deformation during fixing. In addition, since the low friction part 48a is curved in a predetermined curvature radius, friction caused when the low friction part 48 slides in contact with the continuous web 14 is decreased. Thus, it is hardly cause to be deviated by the transfer assist blade 48 even on the printed surface of the continuous web 14, and ensures satisfactory image quality in transfer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a printer, a copying machine, and a fax machine configured to transfer a toner image formed on a chargeable photosensitive member to a printing medium.

  Conventionally, continuous paper printers were often used for computer output printing on forms, but recently they have been used for high-speed variable information printing, and for multi-purpose printing such as direct mail, invoices, manuals, and books. Has come to be used. Along with the expansion of the applications used, it is necessary to support various webs from thin paper to thick paper and web types from fine paper to rough paper.

  In addition, there is an increasing need for double-sided printing on the web from the viewpoint of resource saving. For example, when performing double-sided printing with a cut paper printer, the first side (front side) is printed first, and then the web A method is used in which the surface is reversed and the second surface (back surface) is printed the second time.

  In addition, there is an increasing need for double-sided web printing from the viewpoint of resource saving. For example, tandem operation is performed using two continuous paper printers and the first side (front side) is printed on the first side. After that, there is an increasing chance that the continuous paper printer is used in a method of inverting the web surface and printing the second surface (back surface) in the second unit. When dealing with such versatility, in order to obtain an image quality free from image defects, transfer performance at a transfer section having a transfer device is particularly important.

  Further, the image forming apparatus is provided with a fixing unit that fixes the toner image transferred to the web. The fixing unit is provided on the downstream side of the transfer path from the transfer unit, and is configured by a preheater that makes the web contact and preheats, a heating roll that includes the heater, and a backup roll that pressurizes the heating roll. Yes.

  As described above, the fixing unit continues to supply heat to the web during the continuous printing by the pre-heater and the heating roll, and stops supplying heat when printing is stopped. However, immediately after the printing is stopped, the response between the web conveyance speed and the heating amount is poor, and thus overshoot occurs. Therefore, the web portion stopped on the preheater is overheated and thermally contracted, or unevenness is caused by heat damage. Therefore, when printing is restarted, the toner on the photosensitive member is transferred when the web portion stopped on the preheater of the first or first printer passes the second or second transfer portion (image forming portion). A portion where the image is not transferred to the web is formed, and an image defect is likely to occur on the web.

  Further, in the case of double-sided printing, the web is damaged by heat in the first fixing or the first fixing, resulting in unevenness due to thermal shrinkage. Therefore, in the second or second transfer section, the web and the photosensitive drum surface There is a problem in that the adhesiveness is poor and image defects due to transfer defects are likely to occur in the recessed area of the web surface.

Further, Patent Document 1 discloses that a rough surface which has been subjected to fatigue or thermal deformation is obtained by pressing a web against a photoreceptor using a transfer assist blade and correcting the web so as to eliminate the unevenness of the web. It is described to reduce image defects for a state web.
JP-A-6-332325

  However, in the conventional image forming apparatus having the transfer assist blade, in the case of duplex printing, after the first or first printing, the transfer assist blade is inverted when the second or second printing is performed. Since the web is in contact with the front surface of the web and pressed against the photosensitive member, when the end of the transfer assist blade comes into contact with the web, stress concentration occurs in a part of the first image printed first or first time. As a result, fixing toner is peeled off, that is, the image is deteriorated.

  As described above, the fixing toner peeled off from the web when the end of the transfer assist blade comes into contact begins to adhere from the end of the transfer assist blade, and gradually accumulates as printing proceeds. Further, the peeled toner deposited on the end of the transfer assist blade may adhere to the subsequent web during the printing operation and cause the first printed image or the first printed image to become dirty.

  Therefore, conventionally, when transferring the toner image on the photoconductor to the web, the image quality of the image transferred to the web is improved by pressing the web against the photoconductor using a transfer assist blade. When printing for the second time, the transfer assist blade contacts the inverted web to deteriorate the image printed by the first or first time, or the release toner deposited on the transfer assist blade is printed on the web surface. There is a problem that it adheres to and gets dirty.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus that solves the above-described problems.

  In order to solve the above problems, the present invention has the following means.

  The present invention relates to a photoconductive photosensitive member on which a toner image is formed, a conveying means for conveying a printing medium having a continuous shape in the conveying direction, and a toner image formed on the surface of the photosensitive member. A transfer unit that transfers to a print medium; a print medium guide unit that is positioned upstream of the transfer unit and guides the print medium to a conveyance path; and the transfer unit, and In the image forming apparatus having a pressing member that presses against the printing medium, the above-described problem is solved by forming a low friction portion having a small friction coefficient in a portion of the pressing member that contacts the printing medium.

  The low friction portion is formed at a tip of the pressing member, and is formed in a shape curved in a direction away from the surface of the photoconductor so as to be in sliding contact with the printing medium with low friction. desirable.

  The low-friction portion is preferably formed so as to warp in a direction away from the printing medium from a position where the printing medium is pressed against the photoreceptor.

  The low friction portion is preferably a roller that rotates while pressing the print medium against the photoconductor.

  Preferably, the low friction portion is provided at a tip of the pressing member, and a pressing force is set by elasticity of the pressing member.

  The present invention provides a first photosensitive member on which a first toner image is formed, a first transfer unit that transfers the first toner image to a first surface of the printing medium, and a second toner image. A second transfer member that transfers the second toner image to the second surface of the printing medium on which the first toner image is transferred to the first surface; An image forming apparatus including: a pressing member that presses the printing medium against the second photosensitive member at least in the second transfer portion; and a friction of a portion of the pressing member that contacts the printing medium The above-described problems are solved by forming a low friction portion having a small coefficient.

  According to the present invention, the low-friction portion having a small friction coefficient is formed in the portion of the pressing member that contacts the printing medium, thereby pressing the printing medium with the pressing member reversed to the photosensitive member when performing double-sided printing. In the process, the unevenness of the printing medium can be corrected, and at the time of printing the second or second time, it is possible to prevent the image printed by the first or first time from being deteriorated and transferred to the printing medium. The quality of the processed image can be improved. Further, since the release toner is unlikely to accumulate on the pressing member, the printing medium can be pressed against the photoconductor so as not to contaminate the printed printing medium surface.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

Hereinafter, the overall configuration of the image forming apparatus according to the present invention will be described, and then the configuration of the transfer portion and the pressing means, which are the main parts of the invention, will be described in this order.
(Overall configuration of image forming apparatus)
FIG. 1 is an overall configuration diagram showing an embodiment of an image forming apparatus according to the present invention. In FIG. 1, the image forming apparatus 10 includes a charger 19, an exposure device 20, a developing device 21, and a corona transfer device 13 serving as transfer means, which are arranged along a rotational peripheral surface of a photosensitive drum 12. After the charger 19 uniformly applies a charge to the surface of the photosensitive drum 12, the exposure device 20 irradiates the surface of the photosensitive drum 12 with laser light according to image data. As a result, an electrostatic latent image is formed on the surface of the photoconductor 12 and is developed by the developing device 21 to form a toner image on the surface of the photoconductor drum 12.

  The continuous web (print medium) 14 is transported by the web transport devices 22 to 24 disposed upstream of the transfer unit 40 and supplied to the transfer unit 40.

  The transfer unit 40 transfers the toner image formed on the surface of the photosensitive drum 12 onto the continuous web 14 by the corona transfer unit 13. And the continuous web 14 which passed the transfer part 40 is conveyed by the web conveyance apparatus 25 after that.

  The toner image transferred to the continuous web 14 is heated to near the melting temperature of the toner resin when passing through the preheater 26. Further, the continuous web 14 reaches a fixing unit 30 including a heating roller 27 and a backup roller 28 with a built-in heater. Then, the toner image on the continuous web 14 is heated and pressed by the heating roller 27 and the backup roller 28 and melted and fixed to the continuous web 14.

  In the case of duplex printing, the toner image is transferred and fixed on the front surface (first surface) 14a of the continuous web 14 by the first printing using the image forming apparatus 10, and the second printing is performed. The toner image is transferred and fixed to the back surface (second surface) 14b of the continuous web 14 by printing.

In the case of a tandem printing method capable of double-sided printing on continuous paper, as shown in FIG. 2, two image forming apparatuses 10A and 10B are provided, and continuous between the first and second units. A reversing mechanism 50 for reversing the front surface 14a and the back surface 14b of the web 14 is provided.
(Configuration of transfer unit 40)
FIG. 3 is an enlarged view showing the structure of the transfer unit in the image forming apparatus of the present invention. As shown in FIG. 3, the photosensitive drum 12 of the present embodiment is a positively charged photosensitive member such as a selenium photosensitive member, a positively charged OPC (organic photoconductor), or a-Si (amorphous silicon). The developing method of the photosensitive drum 12 is a reversal developing method, and the charging polarity of the toner is a positive polarity.

  The transfer unit 40 includes a transfer device housing 42, a transfer assist blade (pressing member) 48 and a negatively charged corona transfer device 13 housed therein.

  The transfer assist blade 48 is held by a holding portion 58 a of the blade holder 58 at a position below the corona transfer device 13 in the transfer device housing 42, and is disposed between the upper separator 46 and the lower separator 47 that guide the continuous web 14. Is done. The transfer assist blade 48 is made of, for example, a plastic plate, a film, a metal plate, or the like, and has a width that is wider than the width of the continuous web 14 so that the continuous web 14 can be pressed at the full width. Is formed.

  Then, the continuous web 14 is stretched by the upper separator 46 and the lower separator 47 which are part of the guide means, and thereby passes through the nip region 60 that contacts the photosensitive drum 12. The transfer assist blade 48 is displaced from the lower side of the nip region 60 to a position for pressing the continuous web 14 by the rotation operation of the blade holder 58.

  The transfer device housing 42 is rotatably supported by a shaft 52 provided at an upper portion, and rotates around the shaft 52 when the rotational power of the drive motor 55 is transmitted through the link 54. The driving motor 55 drives the transfer device housing 42 in the direction close to the photosensitive drum 12 in the printing mode, so that the continuous web 14 stretched between the upper separator 46 and the lower separator 47 is placed on the outer periphery of the photosensitive drum 12. Make contact.

  In the stop mode, the transfer motor housing 42 is rotated in the direction away from the photosensitive drum 12 by driving the drive motor 55 in the reverse rotation direction. Thereby, even if the continuous web 14 is separated from the photosensitive drum 12 and the photosensitive drum 12 is rotated by inertia, the conveyance of the continuous web 14 is stopped by stopping the web conveying devices 22 to 25.

  In the printing mode, the low friction portion 48 a provided at the tip of the transfer assist blade 48 operates to a position where the continuous web 14 is pressed against the photosensitive drum 12. As a result, the continuous web 14 is pressed against the outer periphery of the photosensitive drum 12 in the process of passing through the nip region 60, and the surface irregularities are corrected. Therefore, good transfer can be realized even in the case where the paper quality itself is rough or on the web 14 which has been subjected to thermal deformation during fixing. Further, since the low friction portion 48a is curved with a predetermined radius of curvature as will be described later, the friction at the time of sliding contact with the continuous web 14 is reduced. Therefore, rubbing by the transfer assist blade 48 is less likely to occur on the back surface of the continuous web 14, and good image quality is ensured during transfer.

  The transfer assist blade 48 is rotatably supported by a hinge shaft 49 attached to the lower separator 47, and a cam follower 70 fixed to the transfer housing 42 is attached to the tip of the hinge shaft 49. . A cam 71 is provided at a position close to the cam follower 70, and the cam 71 is connected to a drive pulley 74 driven by a motor 73 via a timing belt 72.

  Therefore, the transfer assist blade 48 is displaced by a driving force of the motor 73 between a position where the continuous web 14 passing through the nip region 60 is pressed and a position where the transfer assist blade 48 is separated from the continuous web 14 and released. For example, in the printing mode, the driving force of the motor 73 is transmitted to the driving pulley 74, the timing belt 72, the cam 71, and the cam follower 70 to rotate the blade holder 58 that holds the transfer assist blade 48 in the clockwise direction.

  Accordingly, the transfer assist blade 48 presses the continuous web 14 against the photosensitive drum 12 by bringing the low friction portion 48 a into contact with the continuous web 14. At that time, the transfer assist blade 48 is elastically deformed with the holding portion 58a of the blade holder 58 as a fulcrum, and generates a spring force that presses the low friction portion 48a against the continuous web 14. The spring force (pressing force) of the transfer assist blade 48 is set by the material and thickness of the transfer assist blade 48 and the support blade 59, the distance between the low friction portion 48a and the holding portion 58a, and the like.

In the stop mode, the blade holder 58 is rotated counterclockwise by driving the motor 73 in the reverse rotation direction. As a result, the continuous web 14 is released from being pressed by the transfer assist blade 48 and separated from the photosensitive drum 12.
(Configuration of pressing member)
Next, the configuration of the transfer assist blade 48 that is a pressing member will be described. FIG. 4 is a side view showing the transfer assist blade 48. As shown in FIG. 4, a blade holder 58 that holds the transfer assist blade 48 has a hinge shaft 49 inserted through the shaft hole 56 and is supported so as to rotate about the hinge shaft 49. A support blade 59 is fixed to the holding portion 58 a of the blade holder 58, and the transfer assist blade 48 is fixed to the support blade 59.

  The transfer assist blade 48 has a low friction portion 48a that is in sliding contact with the continuous web 14 with low friction at the tip. The low friction portion 48 a is formed in an R shape that is curved in a direction away from the surface of the photosensitive drum 12.

  The transfer assist blade 48 of the present embodiment is formed of, for example, an elastically deformable PET (polyethylene terephthalate) resin sheet having a thickness t of about t = 0.1 mm to 1.0 mm. The support blade 59 is also formed of the same spring material as the transfer assist blade 48 (resin sheet having elasticity).

  The transfer assist blade 48 is fixed at a portion where the transfer assist blade 48 is joined to the support blade 59 in an overlapped manner, and the low friction portion 48a extending to the tip side from the support blade 59 is held in a state having a spring.

  Since the low friction portion 48a slidably contacting the continuous web 14 of the transfer assist blade 48 is formed in a curved R shape, it has a shape that avoids contact with the continuous web 14. If the curvature of the low friction portion 48a is too small, stress concentration generated when contacting the continuous web 14 is likely to occur. Therefore, it is desirable to have as large a curvature as possible. It is desirable that the contact portion has a curvature similar to that of the continuous web 14 that passes therethrough.

  In this embodiment, a load of 0.5 to 2 kg / cm is applied to the continuous web 14 in the width direction, and the transfer assist blade 48 is transferred to the continuous web 14 by setting the radius of curvature to 0.5 mm or more. It is possible to ensure a good transfer assisting effect with no defects in the image.

  As shown in FIG. 2, in the case of a tandem printing method capable of double-sided printing of the continuous web 14, the image forming apparatuses 10A and 10B use a box paper with a perforation or a roll paper without a perforation at high speed (0.5). (2m / sec) and printing. Unlike the cut paper, the continuous web 14 is continuously formed without any breaks in the web.

  The first image forming unit such as the first photoconductor 12A, the first developing machine 21A, and the first transfer unit 40A of the first image forming apparatus 10A has a first surface on the front surface 14a of the continuous web 14. After the image 80 is printed, the continuous web 14 is reversed by the reversing mechanism 50, and the second photoconductor 12B, the second developing device 21B, the second transfer unit 40B, and the like of the second image forming apparatus 10B. The second image 90 is printed on the back surface 14b of the continuous web 14 by the second image forming unit.

  When the images 80 and 90 are printed on both sides of the continuous web 14 in this way, for example, the back side of the web portion stopped in the heating region K where the first fixing unit 30A for fixing the first image 80 to the continuous web 14 is present. In addition, when the second transfer unit 40B performs the second or second transfer, the transfer assist blade 48 may come into contact with the first image 80 to cause an image defect.

  FIG. 5 is an enlarged perspective view showing the web stop state of the fixing unit 30. As shown in FIG. 5, the fixing unit 30 includes a pre-heater 26 that makes the continuous web 14 contact and preheats, a heating roll 27 that includes a heater, and a backup roll 28 that pressurizes the heating roll 27.

  The fixing unit 30 continues to supply heat to the continuous web 14 during continuous printing. When the printing is stopped, the supply of heat is stopped. However, since the conveyance of the continuous web 14 is also stopped, the response is poor immediately after the printing is stopped. Therefore, a thermal overshoot of the continuous web 14 occurs. Therefore, the continuous web 14 on the preheater 26 is thermally contracted in the Y direction (paper width direction) in the drawing, and unevenness is generated on the surface due to thermal damage. Therefore, when printing is restarted after stopping, the heated portion of the web 14 stopped on the pre-heater 26 of the first image forming apparatus 10A passes through the transfer unit 40 of the second image forming apparatus 10B. Image defects are likely to occur.

  However, in this embodiment, as described above, the low friction portion 48 a of the transfer assist blade 48 provided in the transfer portion 40 presses the continuous web 14 against the photosensitive drum 12. As a result, the continuous web 14 is pressed against the outer periphery of the photosensitive drum 12 in the process of passing through the nip region 60, and the surface irregularities are corrected. Therefore, even in the web 14 that has been subjected to thermal deformation by the fixing unit 30 of the first image forming apparatus 10A (or the first time), good transfer can be performed in the second image forming apparatus 10B (or the second time). Can be realized.

  Moreover, since the low friction part 48a is curving with the predetermined curvature radius, the friction at the time of sliding-contacting the continuous web 14 is reduced. Therefore, in the second image forming apparatus 10B (or the second time), rubbing by the transfer assist blade 48 hardly occurs on the back surface 14b of the continuous web 14, and good image quality is ensured during transfer.

  FIG. 6 is a diagram schematically illustrating a toner transfer state in the transfer unit 30B of the second image forming apparatus 10B. As shown in FIG. 6, the toner image 100 formed on the photoreceptor 12 </ b> B has a positive polarity and is electrostatically adsorbed to the photoreceptor 12 b, and the continuous web 14 has a negative polarity due to corona discharge of the corona transfer unit 13. The toner image 100 is transferred to the continuous web 14 side.

  However, if the web 14 is deformed in a concave shape due to heat as indicated by C in FIG. 6 (shown by a broken line), it remains on the photoconductor 12B without being transferred. The trouble that occurred is generated.

  The deformation of the portion C is flattened as indicated by a broken line by the low friction portion 48a of the transfer assist blade 48 pressing the continuous web 14 toward the photosensitive drum 12, and the image transferred to the continuous web 14 is also transferred. A good transfer assisting effect can be ensured without causing any defects.

  By using a conductive material such as an elastomer resin for the transfer assist blade 48 and being electrically grounded and controlled to an arbitrary potential state, the low friction portion 48a is in contact with the continuous web 14, and the continuous web 14 is transferred to the transfer corona. It is possible to prevent negative charging due to exposure from 13. Therefore, the transfer assist blade 48 is grounded, and static electricity charged on the continuous web 14 is removed to prevent adhesion of electrostatic dirt, and accumulation of dirt over time can be prevented.

  Further, when the continuous web 14 and the fixing toner are charged in advance, it is conceivable to prevent the accumulation of dirt by charging the transfer assist blade 48 with the same polarity. Thus, if it can prevent that a dirt accumulates, since the adhesion to the printing surface of the continuous web 14 can also be prevented, favorable printing image quality can be ensured.

  In this way, in this embodiment, the transfer defect during double-sided printing can be solved, and the transferability to a low-cost web such as a recycled web or a web with poor surface irregularity can be improved. In addition to realizing high-speed printers, it can also contribute to resource saving.

  Here, a modified example will be described.

  FIG. 7 is a diagram showing a first modification of the transfer assist blade 48. In FIG. 7, the same parts as those in FIG.

  As shown in FIG. 7, the transfer assist blade 48 of the first modification has a low friction part 48b having a D-shaped cross section at the tip. The low friction portion 48b is molded and joined separately from the transfer assist blade 48. For example, the low friction portion 48b is formed of a low friction resin material having a small coefficient of friction such as a material such as tetrafluoroethylene resin. .

  As the shape of the low friction part 48b, it is possible to form an arbitrary curved surface by a resin molding method, and it is also possible to mold the curvature radius to be relatively large. Therefore, the low friction portion 48 b can be formed in a shape corresponding to the radius of curvature of the conveyance path of the continuous web 14 that passes through the nip region 60.

  Accordingly, when the low friction portion 48b presses the continuous web 14 against the photosensitive drum 12, the continuous web 14 is pressed against the outer periphery of the photosensitive drum 12 in the process of passing through the nip region 60, and the unevenness of the surface is corrected. The Therefore, even on the web 14 that has been thermally deformed by the fixing unit 30 of the first image forming apparatus 10A (or the first time), the back surface 14b is printed by the second image forming apparatus 10B (or the second time). In this case, good transfer can be realized.

  Further, since the friction when the continuous web 14 is slid in contact with the low friction portion 48b is reduced, when the back surface 14b of the continuous web 14 is printed in the second image forming apparatus 10B (or the second time). The front surface 14a is less likely to be rubbed by the transfer assist blade 48, and good image quality is ensured during transfer.

  As described above, the first modification can solve the transfer failure at the time of double-sided printing and improve the transferability to a low-cost web such as a recycled web or a web with a poor surface irregularity state. In addition to realizing high-speed printers, it can also contribute to resource saving.

  FIG. 8 is a diagram showing a second modification of the transfer assist blade 48. In FIG. 8, the same parts as those in FIG. 4 described above are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 8, the transfer assist blade 48 of Modification 2 is provided with a roller 48 c that rotates while pressing the continuous web 14 against the photosensitive drum 12 at the tip.

  The roller 48 c is rotatably supported by a shaft 48 d held at the tip of the transfer assist blade 48, and can reduce friction with respect to the continuous web 14 by rolling due to friction when contacting the continuous web 14. it can.

  When the roller 48c presses the continuous web 14 against the photoconductive drum 12, the continuous web 14 is pressed against the outer periphery of the photoconductive drum 12 in the process of passing through the nip region 60, and the surface unevenness is corrected. Therefore, even on the web 14 that has been thermally deformed by the fixing unit 30 of the first image forming apparatus 10A (or the first time), the back surface 14b is printed by the second image forming apparatus 10B (or the second time). In this case, good transfer can be realized.

  Moreover, since the roller 48c rotates, the friction at the time of sliding-contacting the continuous web 14 is reduced significantly. Therefore, in the second image forming apparatus 10B (or the second time), rubbing by the transfer assist blade 48 hardly occurs on the front surface 14a of the continuous web 14, and good image quality is ensured during transfer.

  Further, by forming the roller 48c with a conductive material, as described above, the static electricity charged on the continuous web 14 is removed to prevent the adhesion of electrostatic dirt, and the accumulation of dirt over time is prevented. be able to.

  As described above, in the second modification, the transfer failure during double-sided printing can be solved, and the transferability to a low-cost web such as a recycled web or a web with a poor surface irregularity can be improved. In addition to realizing high-speed printers, it can also contribute to resource saving.

  In the above-described embodiment and modifications 1 and 2, duplex printing using a continuous web printer has been described. Needless to say, the presser of the present invention can also be applied to a cut sheet web printer.

  In the above-described embodiment, the case where double-sided printing is performed using two image forming apparatuses 10A and 10B has been described as an example. However, the present invention is not limited to this. Of course, the present invention can also be applied to a configuration having a first image forming unit that prints the surface and a second image forming unit that prints the second surface of the web.

1 is an overall configuration diagram showing an embodiment of an image forming apparatus according to the present invention. It is a figure which shows typically the tandem printing system in which double-sided printing is possible. FIG. 3 is an enlarged view showing a configuration of a transfer unit in the image forming apparatus of the present invention. 5 is a side view showing a transfer assist blade 48. FIG. 3 is an enlarged perspective view illustrating a web stop state of the fixing unit 30. FIG. FIG. 6 is a diagram schematically illustrating a toner transfer state in a transfer unit 30B of a second image forming apparatus 10B. FIG. 10 is a diagram showing a first modification of the transfer assist blade 48. FIG. 10 is a diagram showing a second modification of the transfer assist blade 48.

Explanation of symbols

10, 10A, 10B Image forming apparatus 12, 12A, 12B Photosensitive drum 13 Corona transfer device 14 Continuous web 22-25 Web transport device 26 Preheater 27 Heating roller 28 Backup roller 30 Fixing unit 40 Transfer unit 42 Transfer device housing 46 Upper separator 47 Lower separator 50 Reverse mechanism 58 Blade holder 48 Transfer assist blades 48a, 48b Low friction portion 48c Roller 59 Support blade 60 Nip region 80 First image 90 Second image

Claims (6)

A photoconductive photoreceptor on which a toner image is formed;
A conveying means for conveying a printing medium having a continuous shape in the conveying direction;
A transfer portion for transferring a toner image formed on the surface of the photoreceptor to the printing medium;
A printing medium guide unit that is located upstream of the transfer unit and guides the printing medium to a conveyance path;
An image forming apparatus having a pressing member that is provided in the transfer unit and presses the printing medium against the photoconductor;
An image forming apparatus, wherein a low friction portion having a small friction coefficient is formed on a portion of the pressing member that contacts the printing medium.   The low friction portion is formed at a tip of the pressing member and formed in a shape curved in a direction away from the surface of the photoconductor so as to be in sliding contact with the printing medium with low friction. The image forming apparatus according to claim 1, wherein:   The low friction portion is formed so as to warp in a direction away from the printing medium with respect to a conveyance direction of the printing medium from a position where the printing medium is pressed against the photosensitive member. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the low friction portion includes a roller that rotates while pressing the printing medium against the photosensitive member.   The image forming apparatus according to claim 1, wherein the low friction portion is provided at a tip of the pressing member, and a pressing force is set by elasticity of the pressing member. A first photoreceptor on which a first toner image is formed;
A first transfer unit that transfers the first toner image to the first surface of the printing medium;
A second photoreceptor on which a second toner image is formed;
A second transfer unit for transferring the second toner image to the second surface of the printing medium having the first toner image transferred to the first surface;
An image forming apparatus having
A pressing member that presses the printing medium against the second photosensitive member at least in the second transfer portion;
An image forming apparatus, wherein a low friction portion having a small friction coefficient is formed on a portion of the pressing member that contacts the printing medium.

Images