JP2008216555A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which does not cause an image defect by making pressing force to a recording medium equal. <P>SOLUTION: A pressing means for pressing the recording medium against the surface of a photoreceptor includes a first pressing member 22a and a second pressing member 22b provided alongside the photoreceptor and pressing the recording medium against the photoreceptor side by turning, and a slider 24 engaged with a part of the pressing members 22a and 22b and moving along in the arranging direction of the pressing members 22a and 22b. An angle difference is provided in a turning operation direction in a turning standby state between the first pressing member 22a and the second pressing member 22b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus capable of forming a high-quality image without image defects even when an image is formed on a roughened paper or a wrinkled recording 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 applications used, it is necessary to support various recording media from thin paper to thick paper, and from various types of recording media, from fine paper to rough paper.

  On the other hand, from the viewpoint of resource saving, tandem operation is performed using two continuous paper printers, the first side is printed by the first unit, and then the recording medium side is reversed and the second side is printed by the second unit. As a result, the need for duplex printing is increasing. When dealing with such versatility, the transfer performance of the transfer device is particularly important in order to obtain image quality free from image defects.

  However, in general, in the case of tandem printing, the recording medium is damaged due to heat in the first fixing, resulting in unevenness due to heat shrinkage, and the adhesion between the recording medium and the photosensitive drum surface is poor in the second transfer section. In addition, there is a problem that image defects due to transfer defects are likely to occur in the recessed area of the recording medium surface.

  FIG. 16 is a conceptual diagram of a tandem printing method capable of duplex printing on continuous paper. As shown in the figure, a first continuous paper printer P1 that forms an image 504 on a first surface of a continuous recording medium 506 and a second continuous paper printer P2 that forms an image 505 on a second surface are provided. Yes. The continuous paper printers P1 and P2 perform printing by conveying perforated box paper or perforated roll paper at a high speed (0.5 to 2 m / sec). Unlike the cut sheet, the recording medium 506 forms a continuous recording medium without a break in the recording medium.

  For the continuous recording medium 506, after the image 504 is printed by the first printer P1 having an image forming unit such as the photoreceptor 501 and the developing machine 503, the recording medium 506 is reversed by the turn bar T, and further the photoreceptor 502 and the development are developed. An image 505 is printed on the back surface by a second printer P2 having an image forming unit such as a machine 507.

  When printing images on both sides of the recording medium 506 in this way, for example, on the back surface of the recording medium portion stopped in the B part region where the fixing unit (not shown) for fixing the first image 504 to the recording medium 506 is present. When an image is formed by the second printer P2, there is a problem that an image defect occurs.

  FIG. 17 is a schematic diagram showing a recording medium stop state of the fixing unit in which the B section is enlarged. As shown in the figure, the fixing unit includes a pre-heater 602 that preheats by contacting a recording medium 506, a heating roll 603 that includes a heater, and a backup roll 604 that pressurizes the heating roll 603.

  The fixing unit continues to supply heat to the recording medium 506 during continuous printing. When the printing is stopped, the supply of heat is stopped. However, immediately after the printing is stopped, the response is poor and an overshoot occurs. Therefore, the recording medium 506 on the pre-heater 602 is thermally contracted in the direction of the arrow in the drawing, or the recording medium 506 is uneven due to thermal damage. Therefore, when printing is restarted, an image defect is likely to occur when the recording medium portion stopped on the preheater 602 of the first printer P1 passes through the image forming unit of the second printer P2.

  FIG. 18 is a schematic diagram illustrating a toner transfer state in the transfer unit of the second printer P2. The toner image 704 formed on the photoreceptor 701 is positive and is electrostatically adsorbed to the photoreceptor 701, and the recording medium 506 is negatively charged by corona discharge of the corona transfer unit 702, so that the toner image 704 is formed. The image is transferred on the recording medium 506 side. However, if the recording medium 506 is deformed into a concave shape due to heat as shown by a portion C in the drawing, the recording medium 506 remains on the photosensitive member 701 without being transferred, so that a phenomenon of transfer omission occurs.

  On the other hand, as described above, the continuous paper printer is also required to support various types of recording media in order to cope with various applications, and the width of the recording medium 506 to be used can be properly used depending on the application. For example, when a long (21 to 22 inch) photosensitive member 701 is used, the width of the recording medium 506 also varies widely, such as 12 inches, 16 inches, and 22 inches. In the case of printing 12 to 16 inches for a form, manuals, books, and the like are cut after printing, so that a recording medium 506 having a 17 inch width capable of two-sided A4 size and a 22-inch 22-inch B5 size is obtained. For this reason, when printing a recording medium 506 having a narrow width, unless a transfer assist blade having a width equal to or less than the width of the recording medium is used, the photosensitive member 701 is contacted and scratched, and the print quality is deteriorated.

Patent Document 1 (Japanese Patent Laid-Open No. 9-171308) proposes a method in which a plurality of transfer assist blades are provided and the transfer assist blades are used in combination according to the recording medium width in order to solve such a problem. ing.
JP-A-9-171308

  However, this method can handle any width of the recording medium, but has a configuration in which each of a plurality of transfer assist blades is individually driven by a plurality of solenoids, so that the transfer assist mechanism becomes large and complicated, and the photosensitive member and transfer There is a problem in that it is difficult to arrange them between the parts, and the cost becomes high.

  The first object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to make the pressing force to the recording medium constant over the width direction of the recording medium, and to rough paper or a recording medium or recording that has been thermally deformed. An object of the present invention is to provide an image forming apparatus that does not cause image defects even on various recording media having different medium widths.

  A second object of the present invention is to provide an image forming apparatus that can prevent uneven charging of a recording medium due to corona discharge and can form a high-quality image.

  In order to achieve the first object, a first means of the present invention includes a transfer means for transferring a toner image formed on the surface of a photosensitive member to a recording medium, and the recording medium between the photosensitive member and the transferring means. And an image forming apparatus including a pressing unit that presses the recording medium passing between the photosensitive member and the transfer unit against the surface of the photosensitive member.

And the pressing means is
A first pressing member such as a transfer assist blade described later and a second pressing member provided side by side with respect to the photosensitive member and pressing the recording medium toward the photosensitive member side by rotation;
A slider that is engageable with a part of the first pressing member and the second pressing member and is movable along an arrangement direction of the first pressing member and the second pressing member;
A rotation means comprising, for example, a cam drive motor, a timing belt, an eccentric cam, a cam follower, and an arm, which will be described later, for rotating the pressing member engaged with the slider to the photosensitive member side;
The first pressing member and the second pressing member are characterized in that an angular difference is provided in the rotation operation direction in the rotation standby state.

  According to a second means of the present invention, in the first means, the slider moves along the arrangement direction of the pressing members based on the width information of the recording medium to be used, and corresponds to the width of the recording medium to be used. The pressing member that rotates is selected.

  In order to achieve the second object, a third means of the present invention is the gap formed between the first pressing member and the adjacent pressing member of the second pressing member in the first means. The longitudinal direction of the recording medium is linked to the conveyance direction of the recording medium.

  In order to achieve the second object, a fourth means of the present invention is the gap formed between the first pressing member and the adjacent pressing members of the second pressing member in the first means. For example, a flexible closing member such as a plastic piece, which will be described later, is provided at the side end of the pressing member.

  The first means of the present invention is configured as described above, and the pressing force to the recording medium can be made constant with respect to the width direction of the recording medium, and the recording medium is rough paper or thermally deformed. Alternatively, image defects do not occur on various recording media having different recording medium widths.

  The third and fourth means of the present invention are configured as described above, and it is possible to prevent uneven charging of the recording medium due to corona discharge caused by a gap generated between the pressing members, thereby forming a high quality image.

Next, an embodiment of the present invention will be described with reference to the drawings.
(Overall configuration of image forming apparatus)
First, the overall schematic configuration of the image forming apparatus will be described with reference to FIG. As shown in the figure, a charger 2, an exposure device 3, a developing device 4, and a corona transfer device 5 are arranged around the photoreceptor 1. After the surface of the photoreceptor 1 is uniformly charged by the charger 2, the exposure device 3 irradiates the surface of the photoreceptor 1 with laser light in accordance with image data. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 1 and is developed by the developing device 4 to form a toner image.

  On the other hand, the recording medium 6 made of continuous paper is conveyed to a transfer unit by recording medium conveying devices 7, 8, 9, and the toner image is transferred onto the recording medium 6 by a corona transfer device 5. The toner image on the recording medium 6 is heated to near the glass transition temperature of the toner resin by passing through the preheater 10, and the toner image is recorded on the recording medium 6 by the fixing device 13 including the heating roller 11 and the backup roller 12 incorporating the heater. It is melted and fixed to. In the case of duplex printing, two image forming apparatuses are connected and used as shown in FIG.

(Configuration of transfer unit 14)
Next, the configuration of the transfer unit 14 will be described with reference to FIGS. FIG. 1 is a configuration diagram of the transfer unit showing a state where the transfer assist blade is operating during printing, FIG. 2 is a configuration diagram of the transfer unit showing a state where the transfer assist blade is not operating during printing, and FIG. It is a block diagram of the transfer part which shows the state at the time of standby.

  The transfer unit 14 includes a transfer unit housing 15 having a U-shaped cross section that opens toward the photoreceptor 1, and the corona transfer unit 5 is attached to the inside thereof. A housing moving motor 16 is installed behind the transfer device housing 15, and its rotational power is transmitted to the transfer device housing 15 via the link 17. One end of the link 17 is rotated by the housing moving motor 16. Eccentric with respect to the center and attached to the rotating shaft of the housing moving motor 16. The transfer device housing 15 is supported so as to be able to vibrate about a ring-shaped rotation support portion 18.

  In order to guide the recording medium 6 between the photosensitive member 1 and the corona transfer device 5, a lower guide 19 is attached to the lower portion of the opening of the transfer device housing 15, and an upper guide 20 is attached to the upper portion of the opening.

  A transfer assist mechanism 21 is installed in the vicinity of the lower part inside the transfer device housing 15. The transfer assist mechanism 21 includes a transfer assist blade 22, a blade holder 23 that supports the base end portion of the transfer assist blade 22, and a recording that is engaged with the blade holder 23 and orthogonal to the conveyance direction X of the recording medium 6. A slider 24 that is movable in the width direction Y of the medium 6, a hinge shaft 25 that rotatably supports the blade holder 23, an arm 26 that is coupled to the blade holder 23 (first blade holder 23a described later), and the arm 26, a cam follower 27 attached to the free end of the cam 26, an eccentric cam 28 provided at a position close to the cam follower 27, a cam drive motor 29 for rotationally driving the eccentric cam 28, and the cam drive motor 29 A driving pulley 30 fixed to the rotating shaft, and a timing belt stretched between the eccentric cam 28 and the driving pulley 30. It is mainly composed of a door 31..

  For example, as shown in FIG. 1, the transfer assist blade 221 is disposed in the vicinity of the corona transfer device 5, does not block corona discharge from the corona transfer device 5, and performs recording in the nip region between the photoreceptor 1 and the recording medium 6. It arrange | positions in the position which can press the medium 6. FIG.

(Operation of the transfer unit 14)
Next, a rough operation of the transfer unit 14 will be described. As shown in FIG. 3, at the time of printing standby, the transfer device housing 15 is separated from the peripheral surface of the photoreceptor 1, and therefore the recording medium 6 stretched between the lower guide 19 and the upper guide 20 is also included in the photoreceptor 1. Separated from the circumferential surface.

  When the preparation for the printing operation is completed, the housing drive motor 16 rotates, the transfer device housing 15 is pushed by the link 17, and the transfer device housing 15 rotates around the rotation support portion 18 toward the photoreceptor 1. By this rotation, the lower guide 19 and the upper guide 20 are moved together with the recording medium 6 to the vicinity of the surface of the photoreceptor 1.

  This state is shown in FIG. 2, and the recording medium 6 contacts the peripheral surface of the photoreceptor 1 with a predetermined nip width. If the normal printing, that is, the recording medium 6 is not damaged by heat, the transfer unit 14 can transfer the toner image onto the recording medium 6 in the state shown in FIG. 2, and the transfer assist blade 22 needs to be operated. No.

  As shown in FIG. 3, the eccentric cam 28 is in the position of the top dead center in the print standby state. Therefore, even if the transfer device housing 15 rotates about the rotation support portion 18 toward the photosensitive member 1 side, FIG. As shown in FIG. 2, the cam follower 27 is not in contact with the eccentric cam 28 and is in a separated state, so that the transfer assist blade 22 is in a non-operating state.

  As in the case where the portion of the recording medium 6 stopped on the preheater 10 (see FIG. 15) of the first printer (for front side printing) passes through the transfer unit 14 of the second printer (for back side printing), Next, the case where the transfer assist blade 22 is operated will be described.

  In this case, the eccentric cam 28 is rotated to the position of the bottom dead center shown in FIG. By this rotational operation, the eccentric cam 28 comes into contact with the cam follower 27 and pushes up the cam follower 27, whereby the transfer assist blade 22 is tilted toward the photoreceptor 1 around the hinge shaft 25, and as shown in FIG. 22 presses the recording medium 6 against the peripheral surface of the photoreceptor 1. Therefore, even if the recording medium 6 is thermally damaged and the surface has irregularities, the recording medium 6 can be brought into close contact with the surface of the photoreceptor 1 to perform good transfer due to the pressing by the transfer assist blade 22. it can.

  In the present embodiment, the pressing timing and pressing time of the transfer assist blade 22 are set as follows.

  In the tandem printer system, when the path length of the recording medium 6 from the preheater 10 of the first printer to the transfer unit 14 of the second printer is, for example, 110 inches, and the recording medium conveyance speed is 30 inches / second, The time required for the recording medium 6 on the preheater 10 to enter the transfer section 14 is about 3.6 seconds. Accordingly, the pressing timing of the transfer assist blade 22 is determined with a margin of about ± 1 second before and after. The pressing time of the transfer assist blade 22 is determined with a slight margin based on the length of the preheater 10 and the conveyance speed of the recording medium 6.

(Configuration of the transfer assist mechanism 21)
Next, the configuration of the transfer assist mechanism 21 will be described. The transfer assist blade 22 is made of a synthetic resin or metal thin plate, and has a thickness of about 0.1 mm to 1.0 mm. For example, as shown in FIG. 5, the transfer assist blade 22 includes a first blade 22a and a plurality of second blades 22b _{1 to} 22b _n arranged in parallel on one end side of the first blade 22a.

The pressing width L1 of the pressing tip portion of the first blade 22a corresponds to the minimum width Lmin of the recording medium 6 that can be used in the image forming apparatus, and in this embodiment, the pressing width L1 is any value from 6 inches to 12 inches. ing. The pressing width L2 of each of the second blade _22b 1 _{~22b n} is a value of either 1 inch 0.5 inches to correspond with a variety of recording medium 6, the pressing width of the first blade 22a It is shorter than L1. The grand total width of the pressing width L1 and pressing width L2 of each of the second blade _22b 1 _{~22b n} of the first blade 22a is corresponding to the maximum width Lmax of the recording medium 6 can be used in the image forming apparatus.

Also the blade holder 23 for holding the transfer assist blade 22 corresponds to the first blade 22a and a second blade _22b 1 _{~22b n,} is composed of a first blade holder 23a and second blade holder _23b 1 _{~23b n} . In this embodiment, the transfer assist blade 22 and the blade holder 23 are separated, and the base of the transfer assist blade 22 is fixed to the side surface of the blade holder 23 by an appropriate means. It is also possible to mold integrally.

  A single hinge shaft 25 passes through each blade holder 23 and is supported so as to be rotatable about the hinge shaft 25.

  As shown in FIG. 4, the slider 24 that engages with the blade holder 23 and moves in the width direction Y of the recording medium 6 includes a first slider 32 and a second slider 33. The cross-sectional shape of the first slider 32 is square and substantially C-shaped, and the engaging portions 32a and 32b provided at both ends thereof are first engaging grooves 34a formed on the side surface and the upper surface of the blade holder 23, 34b is engaged. The cross-sectional shape of the second slider 33 is L-shaped, and the engaging portions 33a and 33b provided at both ends thereof are second engaging grooves 34c and 34d formed on the side surface and the upper surface of the blade holder 23, respectively. Is engaged. By this engagement, the first slider 32 and the second slider 33 can slide in the Y direction without dropping from the blade holder 23. Therefore, the blade holder 23 functions as a rail for the sliders 32 and 33.

  The first slider 32 and the second slider 33 can be individually slid relative to the blade holder 23, and the length in the width direction (Y direction) of the first slider 32 and the second slider 33 is substantially the same as that of the first blade 22a. Designed to the size.

  As shown in FIG. 5, a connecting portion 35 having a U-shaped planar shape is provided at a substantially central portion on the back side (opposite to the transfer assist 22) of the first slider 32. The connecting portion 35 has a wire shown in FIG. The lower part of the clamper 36 is connected (see FIG. 6).

(Configuration of pressing range adjusting mechanism 37)
Next, the configuration of the pressing range adjustment mechanism 37 will be described. As shown in FIG. 7, the pressing range adjusting mechanism 37 includes an endless wire 39 connected to a bracket 38 of a tractor 9a on one side of the recording medium transport device 9, and a plurality of pulleys 40 on which the wire 39 is mounted. Have. The wire 39 is wound around the inside of the transfer device housing 15, and the wire clamper 36 is fastened in the middle of the wire 39 outside the transfer device housing 15. The tractor 9a is slidably supported on the support shaft 43 and is automatically moved and positioned in the Y direction based on the width information of the recording medium 6 to be used. The direction movement operation and the movement operation of the first slider 32 are interlocked.

  Further, as shown in FIG. 7, one end 41a of the corotron mask 41 is connected to the middle of the wire 39, and the other end of the corotron mask 41 is wound on a reel 42 installed outside the recording medium conveyance area. It has become. The corotron mask 41 is disposed on the front surface of the corona transfer device 5 and blocks the corona transfer device 5 and the photosensitive member 1 in the non-sheet passing region B, thereby preventing corona discharge therebetween. The photosensitive member 1 is protected.

(Operation of the transfer assist mechanism 21)
Next, the operation of the transfer assist mechanism 21 will be described. The length of the first slider 32 and the second slider 33 in the width direction (Y direction) is designed to be approximately the same as the length of the first blade 22 (first blade holder 23a). Therefore, when the recording medium 6 to be used is set to the minimum width, the first slider 32 and the second slider 33 are moved most in the Y2 direction, and the second slider 33 is moved to the first slider 32 as shown in FIG. Between the first blade holder 23a and the first blade holder 23a. The first slider 32 and second slider 33 is engaged seen engaging the first blade holder 23a, is disengaged away from the second blade holder _23b 1 _{~23b n.}

  In this state, when the first slider 32 is moved in the Y1 direction by a length L1 or more by the wire 39, the rear end 32c (see FIG. 5) of the first slider 32 is moved in the moving direction (Y1 direction) of the second slider 33. By engaging the front end 33d and moving the second slider 33 in the same direction, the wide recording medium 6 can be handled.

  Further, when the first slider 32 is moved by the wire 39 in the opposite Y2 direction by a distance of the length L1 or more, the front end 32d of the first slider 32 is now moved to the rear end 33c of the second slider 33 in the moving direction (Y2 direction). Engage and move the second slider 33 so as to push it in the same direction, so that the narrow recording medium 6 can be handled.

Thus, the pressable range of the blade holder 23 (23a, 23b _{1 to} 23b _n ) is adjusted by the movement positions of the first slider 32 and the second slider 33. For example, when the recording medium 6 to be used is set to the minimum width, and the first slider 32 and the second slider 33 are moved most in the Y2 direction so as to face the first blade holder 23a, the first slider 32 and The second slider 33 is engaged only with the first blade holder 23a. When the cam drive motor 29 (see FIG. 6) is driven in this state, only the first blade holder 23a moves toward the photoreceptor 1 with the hinge shaft 25 as the center through the timing belt 31, the eccentric cam 28, the cam follower 27, and the like. The recording medium 6 is pressed in the arrow Z direction by the first assist blade 22a held by the first blade holder 23a.

6 and 7 show a case where the recording medium 6 having a width A is used. The wire 39 is moved based on the width information of the recording medium 6 to be used, whereby the first slider 32 and the second slider 33 are engaged with the first blade holder 23a and the second blade holders 23b _{1 to} 23b _α . When the cam drive motor 29 is driven in this state, the second blade holders 23b _{1 to} 23b _α are centered on the hinge shaft 25 through the first blade holder 23a and the first slider 32 and the second slider 33 engaged therewith. Thus, the first assist blade 22a held on the first blade holder 23a and the second assist blades 22b _{1 to} 22b _α held on the second blade holders 23b _{1 to} 23b _α are also brought together. Falls to the photoreceptor 1 side.

Further, since one end 41a of the corotron mask 41 is connected to the wire 39, the corona transfer device 5 and the photosensitive member 1 are blocked in the non-sheet passing region B in accordance with the width of the recording medium 6 to be used. . FIG. 7 shows a state where the first assist blade 22 a and the second assist blades 22 b _{1 to} 22 b _α have fallen and the non-sheet passing region B is blocked by the corotron mask 41.

  FIGS. 8A and 8B are views for explaining a first inconvenience of the transfer assist mechanism 21. FIG. 8A shows a state where the transfer assist mechanism 21 is not operating, and FIG. Indicates a state in which the transfer assist mechanism 21 is operating.

  Since the slider 24 is engaged with the blade holder 23 and the plurality of transfer assist blades 22 are tilted according to an arbitrary width of the recording medium 6, a certain gap is required between the blade holder 23 and the slider 24. Since the slider 24 itself is also tall, twisting occurs. For this reason, when the transfer assist blades 22 are engaged with the sliders 24 via the blade holders 23, the second transfer assist is performed with respect to the first transfer assist blades 22a as shown in FIG. In some cases, the blade 22b may be displaced by an angle α2 in the direction of the arrow. The reason for shifting in the direction of the arrow is that there is a force acting to return the transfer assist blade 22 to the initial position by a spring (not shown).

  In this state, when the transfer assist blade 22 is rotated in the operation of pressing the recording medium 6 toward the photosensitive member 1, that is, in the direction shown in FIG. 5B, the first transfer assist blade 22a is rotated by an angle β1. The second transfer assist blade 22b can rotate only by an angle β2 (= β1-α2) which is smaller than the angle β1 by an angle α2. Thus, the further away from the first transfer assist blade 22a, the weaker the pressing force of the second transfer assist blade 22b, so that the recording medium 6 cannot be sufficiently pressed against the photosensitive member 1 side, and the effect of the transfer assist blade 22 is sufficiently achieved. I can't demonstrate it.

  Therefore, in the present invention, as shown in FIG. 9A, the second transfer assist blade 22b is previously tilted toward the photoreceptor 1 by an angle α with respect to the first transfer assist blade 22a, that is, the first transfer assist blade. It attaches to the 2nd blade holder 22b in the state which protruded from 22a.

  In this way, when the transfer assist blade 22 is rotated by an angle β in the operation of pressing the recording medium 6 toward the photosensitive member 1, that is, in the direction shown in FIG. 5B, the first transfer assist blade 22a and the second transfer assist blade 22a are moved. The assist blade 22b falls to a substantially equivalent position and can press the recording medium 6 evenly in the width direction, and the effect of the transfer assist blade 22 can be sufficiently exhibited.

  Since a large number of the second transfer assist blades 22b are installed, the angles α of the respective second transfer assist blades 22b can be made constant, or the angle α can be set according to the state of each of the second transfer assist blades 22b. Can also be changed slightly. As means for inclining the second transfer assist blade 22b in advance, the surface of the second blade holder 23b that contacts the slider 24, the surface that contacts the second transfer assist blade 22b, or the second blade assist blade 22b contacts the second blade holder 23b. There are means for forming an inclined surface on the surface.

  FIG. 10 is a diagram for explaining a second inconvenience of the transfer assist mechanism 21. As shown in the figure, the transfer assist blade 22 is divided into a large number of sheets, and a gap 44 is generated between adjacent transfer assist blades 22.

  If the longitudinal direction of the gap 44 is parallel to the conveyance direction X of the recording medium 6, unevenness occurs in charging of the recording medium 6 due to corona discharge during transfer, and a black portion is formed in a portion corresponding to the gap 44 of the recording medium 6. Streaks may occur.

  Therefore, in the present invention, as shown in FIG. 11, a gap 44 is generated between adjacent transfer assist blades 22. The longitudinal direction of the gap 44 is an angle of γ with respect to the conveyance direction X of the recording medium 6 (for example, 30). Degree). In this way, the uneven charging due to the gap 44 can be dispersed in the width direction of the recording medium 6, and the uneven charging is suppressed and the occurrence of black streaks is eliminated.

FIG. 12 is a partially enlarged sectional view showing a first modification for suppressing the occurrence of black streaks. In this example, for example, the plastic pieces 45 of the ultrathin fixed to the second transfer assist blade 22b ₁ and the side portion opposite the first transfer assist blade 22a, the second transfer assist blade adjacent the leading edge of the plastic piece 45 superposed on the receiving portion 46 of 22b _1, a gap 44 which occurs between the first transfer assist blade 22a of the second transfer assist blade 22b ₁ Seki plastic piece 45, to prevent uneven charging due to the gap 44. Although not shown, the plastic piece 45 is similarly attached to the side surface of each second transfer assist blade 22b.

If kill only the first transfer assist blade 22a in a standing state a second transfer assist blade 22b ₁ as shown in the figure pressing direction Y, the distal end portion of the plastic piece 45 is easily elastically deformed by it's flexibility Thus, only the first transfer assist blade 22a can be tilted. An escape portion 47 is provided on the back side of the receiving portion 46 of the second transfer assist blade 22b ₁ so as not to prevent the deformation of the plastic piece 45.

May return the first transfer assist blade 22a from the tilted state to the original upright position, the distal end portion of the plastic piece 45 is easily elastically deformed, by superposing on the back side of the second transfer assist blade 22b ₁ of the receiving portion 46 The gap 44 can be closed.

In the case defeat the first transfer assist blade 22a and the pressing direction Y together second transfer assist blade 22b _1, can be tilted both in a state of blocking the gap 44 with a plastic piece 45.

  FIG. 13 is a partially enlarged cross-sectional view showing a second modification for suppressing the occurrence of black stripes. In the case of this example, a stepped overlapping portion 48 having a single step thickness is formed on the side surface portion of each transfer assist blade 22, and the gap 44 is substantially formed by the overlapping of the overlapping portions 48. It becomes a blocked state. As shown in the figure, the overlapping portion 48 protrudes to the side that does not hinder when the transfer assist blade 22 is individually tilted.

  There are a one-side reference and a center reference in the conveyance mode of the recording medium 6. The transfer assist blade 22 shown in FIG. 5 corresponds to one-side reference, and a large number of second transfer assist blades 22b are arranged in parallel on one end side of the first transfer assist blade 22a. FIG. 14 is a front view showing the transfer assist blade 22 in which the conveyance mode of the recording medium 6 corresponds to the central base preparation. As shown in the drawing, a large number of second transfer assist blades 22b having a relatively short width are arranged in parallel on both ends of the first transfer assist blade 22a having a relatively large width.

  According to the image forming apparatus of the present invention, good transfer without image defects is possible even when rough paper having large irregularities on the surface is used. Further, when performing double-sided printing with a tandem image forming apparatus using the corona transfer method, even if the recording medium is thermally deformed by the first image forming apparatus, an image is transferred during transfer in the second image forming apparatus. Transfer failure can be prevented.

It is a block diagram of a transfer unit showing a state in which a transfer assist blade is operating during printing according to an embodiment of the present invention. It is a block diagram of a transfer unit showing a state where the transfer assist blade is not operating during printing according to an embodiment of the present invention. It is a block diagram of the transfer part which shows the state at the time of the printing standby which concerns on embodiment of this invention. FIG. 3 is a partially enlarged cross-sectional view of a transfer assist mechanism according to an embodiment of the present invention. It is a partial perspective view of a transfer assist mechanism according to an embodiment of the present invention. It is a partial perspective view of a transfer assist mechanism according to an embodiment of the present invention. It is a partial perspective view of a transfer assist mechanism according to an embodiment of the present invention. It is a partially expanded sectional view for demonstrating the 1st inconvenience of a transfer assist mechanism. FIG. 3 is a partially enlarged cross-sectional view of a transfer assist mechanism according to an embodiment of the present invention. FIG. 10 is a partially enlarged plan view for explaining a second inconvenience of the transfer assist mechanism. FIG. 3 is a partially enlarged plan view of a transfer assist mechanism according to an embodiment of the present invention. FIG. 3 is a partially enlarged cross-sectional view of a transfer assist mechanism according to an embodiment of the present invention. FIG. 3 is a partially enlarged cross-sectional view of a transfer assist mechanism according to an embodiment of the present invention. It is a front view of a transfer assist blade according to an embodiment of the present invention. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a conceptual diagram of a tandem printing method capable of duplex printing on continuous paper. FIG. 6 is an explanatory diagram illustrating a state of a recording medium stopped on a fixing device when printing is stopped. It is explanatory drawing which shows the state of transfer omission.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charger, 3 ... Exposure device, 4 ... Developing machine, 5 ... Corona transfer device, 6 ... Recording medium, 7-9 ... Recording medium conveyance apparatus, 10 ... Preheater, 11 ... Heating roller, 12 DESCRIPTION OF SYMBOLS ... Backup roller, 13 ... Fixing device, 14 ... Transfer part, 15 ... Transfer device housing, 16 ... Housing movement motor, 17 ... Link, 18 ... Rotation support, 19 ... Lower guide, 20 ... Upper guide, 21 ... Transfer assist mechanism 22 ... Transfer assist blade, 22a ... First transfer assist blade, 22b ... Second transfer assist blade, 23 ... Blade holder, 23a ... First blade holder, 23b ... Second blade holder, 24 ... Slider, 25 ... Hinge shaft , 26 ... arm, 27 ... cam follower, 28 ... eccentric cam, 29 ... cam drive motor, 30 ... drive pulley, 31 ... timing belt, 32 First slider, 32a, 32b ... engaging portion, 33 ... second slider, 33a, 33b ... engaging portion, 34a, 34b ... first engaging groove, 34c, 34d ... second engaging groove, 35 ... connecting portion , 36 ... wire clamp, 37 ... pressing range adjusting mechanism, 38 ... bracket, 39 ... wire, 40 ... pulley, 41 ... corotron mask, 42 ... reel, 43 ... spindle, 44 ... gap, 45 ... plastic piece, 46 ... receiving part, 47 ... escape part, 48 ... overlapping part, X ... half-way of recording medium, Y ... width direction of recording medium, Z ... pressing direction.

Claims (4)

Transfer means for transferring a toner image formed on the surface of the photoreceptor to a recording medium;
Conveying means for passing the recording medium between the photoconductor and transfer means;
In the image forming apparatus comprising a pressing unit that presses the recording medium passing between the photosensitive member and the transfer unit against the surface of the photosensitive member.
The pressing means is
A first pressing member and a second pressing member which are provided side by side with respect to the photoconductor and press the recording medium toward the photoconductor by rotation;
A slider that is engageable with a part of the first pressing member and the second pressing member and is movable along an arrangement direction of the first pressing member and the second pressing member;
A rotating means for rotating the pressing member engaged with the slider to the photosensitive member side;
The image forming apparatus according to claim 1, wherein the first pressing member and the second pressing member are provided with an angular difference in a rotation operation direction in a rotation standby state.   2. The image forming apparatus according to claim 1, wherein the slider moves along the arrangement direction of the pressing members based on width information of the recording medium to be used, and rotates according to the width of the recording medium to be used. 2. The image forming apparatus according to claim 1, wherein the pressing member is selected.   2. The image forming apparatus according to claim 1, wherein a longitudinal direction of a gap formed between the adjacent pressing members of the first pressing member and the second pressing member is chained with respect to a conveyance direction of the recording medium. An image forming apparatus characterized by crossing.   2. The image forming apparatus according to claim 1, wherein a flexible closing member that closes a gap formed between the adjacent pressing members of the first pressing member and the second pressing member is provided on a side of the pressing member. An image forming apparatus provided at an end.

Images