JP2008156006A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device having a simple structure capable of realizing the adequate conveyance timing of a recording medium at post-fixation conveying rollers and subsequent components for conveying the recording medium after passing through a fixing mechanism with an inexpensive constitution without complicating the control constitution for conveying the recording medium. <P>SOLUTION: The image forming device comprises an image forming unit 100 for forming a toner image on a recording medium P by using toner, a fixing mechanism 12 for fixing the toner image on the recording medium P by heat-melting and fixing the toner image formed on the recording medium P, and one or two or more post-fixation conveying rollers 25a, 25b which are arranged along a conveying passage S of the recording medium to convey the recording medium P after passing the fixing mechanism 12. The post-fixation conveying roller 25a is formed of a material with less affinity to a heat deposition component to be heat-deposited out of the component in the toner. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms a toner image on a recording medium using toner and fixes the toner image formed on the recording medium onto the recording medium.

  Conventional image forming apparatuses such as copying machines and printers, for example, form a toner image on a recording medium such as recording paper or an OHP film in an image forming unit, and this is formed on the recording medium by a fixing mechanism. By fixing, an image is formed on the recording medium.

  Among such conventional image forming apparatuses, an image forming apparatus that forms an image by an electrophotographic image forming process, for example, charges the surface of an image carrier such as a photoconductor in an image forming unit, and an image is formed in the charged area. An electrostatic latent image is formed by exposure, a toner image formed by developing the electrostatic latent image is electrostatically transferred to a recording medium, and the toner image transferred to the recording medium by a fixing mechanism By fixing, an image is formed on the recording medium.

  In such a conventional image forming apparatus, generally, a plurality of conveying rollers (for example, a plurality of pairs of conveying rollers arranged opposite to each other) are arranged in a conveying path for conveying a recording medium. The arrangement interval of the plurality of conveyance rollers in the conveyance direction of the recording medium is normally set to be less than the minimum size of the recording medium that allows the image forming apparatus to form an image. As a result, the image forming apparatus is configured to convey the recording medium without staying in the conveyance path (so-called JAM).

  On the other hand, in recent image forming apparatuses, in addition to single-sided image formation for forming a single-sided image with the increase in functionality, the upstream side in the transport direction of the recording medium after passing through the fixing mechanism is in front. In some cases, “double-sided image formation” is performed in which double-sided image formation is performed by forming an image again after transporting (switching back) and reversing the front and back of the recording medium (reversing the recording medium).

  In the image forming apparatus provided with the transport rollers as described above, various transport controls are performed in order to smoothly perform the image forming operation on the recording medium.

  In the following, an example of reverse conveyance by a post-fixing conveyance roller that conveys a recording medium after passing through the fixing mechanism among the conveyance rollers arranged in the conveyance path will be described.

  FIG. 7 is a schematic side view for explaining reversal conveyance of an example of an image forming apparatus that performs single-sided and double-sided image formation.

  In the image forming apparatus shown in FIG. 7, the toner image formed on the photoreceptor 3 in the image forming unit 100 ′ is electrostatically transferred onto the recording medium P by the transfer device 11, and the recording medium P is fixed by the fixing mechanism 12. The toner image formed on the recording medium P is fixed on the recording medium P by heat-melting and fixing the toner image.

  The transport path S in this image forming apparatus is provided with a main transport path S1, a switchback transport path S2, and a reverse transport path S3. The switchback transport path S2 is provided with a pair of post-fixing transport rollers 25a 'and 25b' for transporting the recording medium P after passing through the fixing mechanism 12. Here, of the pair of post-fixing transport rollers 25a ′ and 25b ′, one post-fixing transport roller 25a ′ is a driving roller that is rotationally driven by a drive source (not shown), and the other post-fixing transport roller 25b. 'Is a driven roller arranged opposite to one post-fixing conveying roller 25a'. Further, a detection sensor 26 is provided in the vicinity of the upstream side in the transport direction of the recording medium P of the pair of post-fixing transport rollers 25a 'and 25b'.

  In this image forming apparatus, the conveyance of the recording medium P at the time of image formation is performed by the rotation operation of the branching claw 27 disposed at the connection position between the main conveyance path S1 and the reverse conveyance path S3. . The branch claw 27 rotates in the counterclockwise direction from the first switching position Q1 (the position indicated by the solid line in FIG. 7) and the switchback conveyance path S2 and the reverse conveyance path S3. A second switching position Q2 (a position indicated by a two-dot chain line in FIG. 7) communicating with the second switching position Q2 is provided to be rotatable about a horizontal axis. When the branching claw 27 is at the first switching position Q1, the recording medium P can be discharged from the switchback conveyance path S2 toward the discharging portion (not shown), and when the branching claw 27 is at the second switching position Q2. The recording medium P can be transported from the switchback transport path S2 to the reverse transport path S3.

  In this image forming apparatus, when performing single-sided and double-sided image formation, the following conveyance control of the recording medium P is performed.

  That is, when performing single-sided image formation, the branch claw 27 is switched to the first switching position Q1, and one post-fixing conveyance roller 25a 'is rotated in the direction of the arrow X1 in the drawing by the drive source. As a result, the recording medium P that has passed through the fixing mechanism 12 is transported by the pair of post-fixing transport rollers 25a ′ and 25b ′ with the downstream end P1 in the transport direction forward, and is discharged toward the discharge unit as it is. To do.

  When double-sided image formation is performed, first, similarly to the case of single-sided image formation, the branch claw 27 is switched to the first switching position Q1, and one post-fixing conveyance roller 25a 'is rotated in the direction of the arrow X1. Then, the recording medium P after passing through the fixing mechanism 12 is transported by the pair of post-fixing transport rollers 25a 'and 25b' so that the upstream end P2 in the transport direction is shifted to the switchback transport path S2.

  Next, the detection sensor 26 detects the upstream end portion P2 in the transport direction of the recording medium P, so that the recording medium P is transported while the pair of post-fixing transport rollers 25a ′ and 25b ′ sandwich the recording medium P. The rotation of one post-fixing conveyance roller 25a ′ is temporarily stopped so that the direction upstream side end portion P2 is positioned in the switchback conveyance path S2.

  Then, the branch claw 27 is switched to the second switching position Q2, and one post-fixing conveyance roller 25a 'is rotated in the direction X2 opposite to the rotation direction X1 before stopping. As a result, the recording medium P is transported toward the reverse transport path S3 so that the upstream end P2 in the transport direction before the stop is forward, and the recording medium P is reversed by the reverse transport path S3.

  On the other hand, in the image forming apparatus, regardless of single-sided or double-sided image formation, the recording medium after passing through the fixing mechanism is discharged at a predetermined conveyance speed, thereby obtaining good stacking property of the recording medium in the discharge unit. Be able to. Further, when the image forming apparatus includes a post-processing unit that can perform predetermined post-processing (for example, post-processing such as stapling and punching) on the recording medium after passing through the fixing mechanism, By aligning the recording medium after passing through the fixing mechanism at a predetermined transport timing, good alignment of the recording medium can be obtained. For example, when stapling is performed, the stapling position of the recording medium is well aligned, or when punching is performed, the punch holes of the recording medium are well aligned.

  In this way, the conveyance control of the recording medium is performed in the image forming apparatus, but the conveyance timing of the recording medium after the conveyance roller may deviate from the appropriate timing.

  For example, in the above-described example, in forming an image, the toner on the recording medium P after passing through the image forming unit 100 ′ is subjected to heat and pressure by the pair of fixing rollers 31 and 32 constituting the fixing mechanism 12. And fixed on the recording medium P by melting and fixing. Thus, the recording medium P after passing through the fixing mechanism 12 and the toner fixed on the recording medium P receive heat from the pair of fixing rollers 31 and 32, so that they are at a high temperature for a while although being lower than the fixing temperature. It is in.

  When the toner is in a high temperature state, a part of the components contained in the toner may be deposited on the surface layer of the toner. When the recording medium P is transported by the transport rollers 25a ′ and 25b ′ after fixing in this state, the heat deposition component (for example, wax) deposited on the surface layer of the toner by heating is after the fixing at a lower temperature than the toner. A phenomenon that the diameters of the post-fixing transport rollers 25a ′ and 25b ′ increase (that is, swelling of the post-fixing transport rollers) may occur due to adsorption and absorption by the transport rollers 25a ′ and 25b ′.

  When the post-fixing conveyance roller swells as described above, the conveyance timing of the recording medium after the post-fixation conveyance roller is shifted.

  FIG. 8 is a diagram for explaining a shift in the conveyance timing of the recording medium by the post-fixing conveyance roller when swelling occurs. FIG. 8A is a side view schematically showing a part of one of the post-fixing transport rollers 25a ′, and FIG. 8B is a diagram showing how the recording medium P is chucked by the post-fixing transport rollers 25a ′ and 25b ′. FIG. 8C illustrates a state where the recording medium P is conveyed to the discharge unit, and FIG. FIG. 8D shows a state where the roller is once stopped, and FIG. 8D shows a state in which one post-fixing conveyance roller 25a ′ is rotated in the direction X2 opposite to the direction X1 in FIG. A state is shown in which the recording medium P is guided to the reverse conveyance path S3 by the conveyance rollers 25a ′ and 25b ′.

  As described above, when forming a double-sided image, the rotation of one post-fixing conveyance roller 25a ′ is temporarily stopped (see FIG. 8C). At this time, the post-fixing conveyance rollers 25a ′ and 25b ′ The recording medium P is held (chucked). The distance (rear end chuck distance) d from the nipping portion (chuck portion) by the transport rollers 25a ′ and 25b ′ after fixing of the recording medium P to the upstream end portion P2 in the transport direction before stopping is a processing process of the image forming apparatus. Although there are some differences depending on the speed and the type of the recording medium, when the post-fixing transport rollers 25a ′ and 25b ′ are in the initial state, the range is approximately 30 mm to 50 mm.

  This will be further described with reference to specific numerical values. When post-fixing transport rollers 25a ′ and 25b ′ for transporting the recording medium P after passing through the fixing mechanism 12 are those having a diameter R of about 10 mm, the outer periphery thereof is used. Is 31.4 mm (≈10 mm × π).

  For example, assuming that the diameter R of the post-fixing conveying roller swollen by a thermal precipitation component in the toner is 11 mm (= R + α), the outer periphery thereof is 34.5 mm (≈11 × π). Therefore, the swollen post-fixing conveying roller has an outer circumference that is about 3.1 mm (≈34.5 mm−31.4 mm) longer than that in the initial state. This change in length means an increase in the transport distance of the recording medium P in one post-fixing transport roller 25a 'that is driven to rotate at a predetermined constant number of rotations per unit time by the drive source.

  Here, assuming that an A-4 size recording medium P having a longitudinal length L of 299 mm is transported in the longitudinal direction, and the trailing edge chuck distance d is 30 mm, the recording medium P is 269 mm (= 299 mm-30 mm). Therefore, the post-fixing conveying roller 25a ′ in the initial state rotates by 8.57 rotations (≈269 mm ÷ 31.4 mm / rotation).

  This rotational speed is a value initially set in the image forming apparatus. When this rotational speed is applied to the swollen post-fixing transport roller, the transport distance is 295.7 mm (≈8.57 rotation × 34.5 mm / rotation). It becomes. Accordingly, the rear end chuck distance d is 3.3 mm (≈299 mm−295.7 mm), compared with 30 mm as a reference (in the case of the conveyance roller after fixing in the initial state), and 26.7 mm (≈30 mm−3.3 mm). ) Will also be shorter.

  A summary of this is shown in Table 1 below.

  The rear end chuck distance thus shortened includes various problems. That is, not only the rear end chucking distance may cause a transport JAM by the post-fixing transport roller, but also the rear end chuck distance changes due to the diameter change of the swollen post-fixing transport roller. Even if there is an error in the arrival (conveyance) timing of the recording medium to the sensor of each part that contributes to the conveyance control of the recording medium and the conveyance medium after the fixing is normally conveyed, the recording medium after the conveyance roller after fixing In some cases, a transport JAM may occur due to a transport timing error.

  In the worst case, the upstream end in the conveyance direction of the recording medium passes through the chuck portion of the conveyance roller after fixing, and the switchback cannot be performed, resulting in an apparatus trouble.

  In addition, when the recording medium is transported to the discharge unit in the image forming apparatus regardless of single-sided or double-sided image formation, the recording unit stacks the recording medium at the discharge unit due to the increase in the recording medium transport speed by the swollen post-fixing transport roller. Defects are likely to occur. Further, when the image forming apparatus includes a post-processing unit that performs post-processing such as stapling and punching, the recording medium in the post-processing unit is increased by an increase in the transport speed of the recording medium by the swollen post-fixing transport roller. An error occurs in processing timing. For this reason, inconsistency of the recording medium (for example, when the staple process is performed, the staple position of the recording medium is shifted, and when the punch process is performed, the punch position of the recording medium is not uniform) is caused.

   Further, if the roller diameter of the conveyance roller after fixing becomes too large, it may come into contact with a guide member such as a guide plate in some cases, thereby causing the conveyance timing of the recording medium to deviate.

  In the prior art, it has been proposed that the control means adjust the deviation of the recording medium conveyance timing due to the variation in the position of the recording material at the time of paper feeding or the removal of the conveyance roller.

That is, in order to eliminate the conveyance JAM due to the variation in the position of the recording material at the time of paper feeding and the conveyance roller scraping, the arrival time of the recording medium reaching the registration roller from the paper feeding means is detected, and based on this detection result An image forming apparatus that finely adjusts the control timing of each constituent member has been proposed (see Patent Document 1).
JP 2005-31020 A

  However, since the image forming apparatus described in Patent Document 1 does not take into account the change in the roller diameter of the conveyance roller, the above-described problem associated with the change in the roller diameter of the conveyance roller, that is, the roller diameter is Due to a conveyance failure of the recording medium after the changed conveyance roller, for example, conveyance JAM due to a change in the trailing end chuck distance that may occur when performing double-sided image formation, or device troubles due to inability to switch back, or single-sided and double-sided image formation Regardless of this, it is not possible to cope with a conveyance failure such as a stacking failure of the discharge unit and a poor consistency of the post-processing unit when the post-processing unit is provided.

  Further, as described in Patent Document 1, if the shift of the recording medium conveyance timing is adjusted by the control means, the control configuration for conveying the recording medium becomes complicated, and the apparatus cost increases accordingly.

  The present invention has been made in view of the above problems, and conveys a recording medium after passing through a fixing mechanism without complicating a control structure for conveying the recording medium and having an inexpensive structure. It is an object of the present invention to provide an image forming apparatus having a simple structure capable of optimizing the conveyance timing of the recording medium after the conveyance roller after fixing.

  In order to solve the above-described problems, the present invention provides an image forming unit that forms a toner image on a recording medium using toner, and the toner image formed on the recording medium is heated and melted to be fixed. An image forming apparatus comprising: a fixing mechanism for fixing on a medium; and one or more post-fixing conveyance rollers that are disposed along a conveyance path of the recording medium and convey the recording medium after passing through the fixing mechanism. The at least one post-fixing transport roller of the one or two or more post-fixing transport rollers is made of a material having a low affinity for the thermal precipitation component deposited by heating among the components contained in the toner. Provided is an image forming apparatus that is formed.

  The specific configuration of the image forming unit includes an image carrier, a charging device that charges the surface of the image carrier, and the surface of the image carrier that is charged by the charging device. An exposure device that forms an electrostatic latent image, a developing device that visualizes an electrostatic latent image formed on the image carrier using toner with a toner image, and a toner image that is formed on the image carrier. An image forming unit including a transfer device for transferring to a medium and a cleaning device for removing residual toner on the image carrier remaining without being transferred by the transfer device can be exemplified.

  According to the image forming apparatus of the present invention, the at least one post-fixing transport roller is formed of a material having a low affinity for the thermal precipitation component in the toner. The occurrence of swelling of the post-fixing conveyance roller can be effectively prevented, thereby making it possible to optimize the conveyance timing of the recording medium after the post-fixation conveyance roller.

  That is, since the at least one post-fixing conveying roller is only formed of a material having a low affinity for the thermal precipitation component in the toner, the control configuration for conveying the recording medium is not complicated. The conveyance timing of the recording medium after the post-fixing conveyance roller can be made appropriate.

  In the image forming apparatus according to the present invention, the at least one post-fixing transport roller formed of a material having a low affinity for the thermal precipitation component in the toner is a pair of post-fixing transport rollers arranged to face each other. The case where it is at least one of these can be illustrated. Preferably, the at least one post-fixing transport roller formed of a material having a low affinity for the thermal precipitation component in the toner may be both the pair of post-fixing transport rollers.

  The at least one post-fixing transport roller formed of a material having a low affinity for the thermal precipitation component in the toner includes a post-fixing transport roller that transports the recording medium immediately after passing through the fixing mechanism. In other words, it is preferably a post-fixing conveyance roller that first conveys the recording medium that has passed through the fixing mechanism.

  Further, the case where the at least one post-fixing conveyance roller formed of a material having a low affinity for the thermal precipitation component in the toner is a driving roller that is rotationally driven by a driving source. In this case, for example, a pair of post-fixing conveyance rollers can be configured by a post-fixing conveyance roller that is the driving roller and a post-fixing conveyance roller that is a driven roller disposed opposite thereto. Of course, the post-fixing conveyance roller as the driven roller may be formed of a material having a low affinity for the thermal precipitation component in the toner.

  In the image forming apparatus according to the present invention, a case where at least one of the pair of fixing rollers constituting the fixing mechanism is a heating roller having a heat source can be exemplified.

  Here, when the toner image on the recording medium is fixed by the fixing mechanism, the toner on the recording medium can usually be heated by a heating roller. From this point of view, the at least one post-fixing transport roller formed of a material having a low affinity for the thermal precipitation component in the toner has the transport path in the transport path based on the recording medium transported. It is preferable that it is arranged on the heating roller side.

  In the image forming apparatus according to the present invention, the at least one post-fixing conveyance roller formed of a material having a low affinity for the thermal precipitation component in the toner is the post-fixation conveyance roller caused by the thermal precipitation component. The case where it forms with the material which does not participate in the swelling of a roller can be illustrated. By doing so, it is possible to reliably prevent the post-fixing conveyance roller from swelling. In this case, the at least one post-fixing conveyance roller formed of a material having a low affinity for the thermal precipitation component in the toner is a silicon-based roller, and the thermal precipitation component in the toner is a paraffin wax. The case of being can be illustrated.

  In order to solve the above problems, the present invention also provides an image forming unit that forms a toner image on a recording medium using toner and a toner image formed on the recording medium by heating and fixing the toner image. Image forming comprising: a fixing mechanism for fixing on a recording medium; and one or more post-fixing conveying rollers disposed along a recording medium conveying path and conveying the recording medium after passing through the fixing mechanism. The toner has an affinity for at least one post-fixing conveyance roller among the one or two or more post-fixing conveyance rollers, wherein the thermal precipitation component deposited by heating among the components contained in the toner is There is also provided an image forming apparatus characterized by being made of a small material.

  In this image forming apparatus, the thermal precipitation component in the toner is made of a material having a low affinity for the at least one post-fixing transport roller. The occurrence of swelling of the post-fixing conveyance roller due to the components can be effectively prevented, whereby the conveyance timing of the recording medium after the post-fixing conveyance roller can be optimized.

  That is, since the thermal precipitation component in the toner is only composed of a material having a low affinity for the at least one post-fixing conveyance roller, the control configuration for conveying the recording medium is not complicated. With the existing control configuration, the conveyance timing of the recording medium after the post-fixing conveyance roller can be made appropriate.

  The at least one post-fixing transport roller is a post-fixing transport roller that transports the recording medium immediately after passing through the fixing mechanism (in other words, a post-fixing transport roller that transports the recording medium that has passed through the fixing mechanism first). It is preferable that

  In this image forming apparatus, the case where the thermal precipitation component of the toner is made of a material that does not contribute to the swelling of the at least one post-fixing conveyance roller due to the thermal precipitation component can be exemplified. By doing so, it is possible to reliably prevent the post-fixing conveyance roller from swelling. In this case, it can be exemplified that the at least one post-fixing transport roller is a silicon-based roller, and the thermal precipitation component in the toner is a paraffin wax.

  As described above, according to the present invention, the post-fixing transport roller that transports the recording medium after passing through the fixing mechanism without complicating the control configuration for transporting the recording medium and having an inexpensive configuration. It is possible to provide an image forming apparatus with a simple structure capable of optimizing the subsequent conveyance timing of the recording medium.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a schematic configuration of the image forming apparatus according to the present embodiment. The image forming apparatus A shown in FIG. 1 includes an image forming unit 100 that forms a toner image on a sheet-like recording medium (hereinafter referred to as paper) P such as recording paper or an OHP film using toner.

  The image forming unit 100 includes an image carrier (here, a photoconductive drum) 3 (3a, 3b, 3c, 3d) and a charging device (here) for charging the surface of the photoconductor 3 (3a, 3b, 3c, 3d). A charging device) 5 (5a, 5b, 5c, 5d), an exposure device (here, an exposure unit) 1 for forming an electrostatic latent image on the photoreceptor 3 (3a, 3b, 3c, 3d), A developing device (here, a developing unit) 2 (2a, 2b, 2c, 2d) for visualizing the electrostatic latent image with toner and forming a toner image on the photoreceptor 3 (3a, 3b, 3c, 3d) A primary transfer device (here, the intermediate transfer member (here, intermediate transfer member belt) 7 and a toner image on the photosensitive drum 3 (3a, 3b, 3c, 3d) once transferred onto the intermediate transfer belt 7 Intermediate transfer roller) 6 (6a, 6b, 6c, 6d) and intermediate transfer roller Primary cleaning device (here, cleaner unit) 4 (4a) that removes residual toner remaining on the surface of the photoreceptor 3 (3a, 3b, 3c, 3d) without being transferred by the roller 6 (6a, 6b, 6c, 6d). , 4b, 4c, 4d), a secondary transfer device (here, secondary transfer unit) 11 for transferring the toner image on the intermediate transfer belt 7 onto the paper P, and an intermediate image without being transferred by the secondary transfer unit 11. A secondary cleaning device (here, an intermediate transfer belt cleaning unit) 9 for removing residual toner remaining on the surface of the transfer belt 7 is provided.

  In addition to the image forming unit 100, the image forming apparatus A includes a pair of fixing rollers 31 and 32 that fix the toner image formed on the paper P by heating and melting and fixing the toner image on the paper P. A mechanism 12, a transport path S for the paper P, and transport rollers disposed along both sides of the transport path S are provided.

  Further, the image forming apparatus A includes a document reading device (here, a scanner device) B, a paper feeding device 10, and a discharge unit 15, and image data corresponding to a document read by the document reading device B or externally. Multi-color and single-color images are formed on the paper P in accordance with the transmitted image data.

  More specifically, the image data handled in the image forming apparatus A corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y), or a single color ( For example, it corresponds to a monochrome image using black). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the charger 5 (5a, 5b, 5c, 5d), the cleaner unit 4 (4a, 4b, 4c, 4d) and four intermediate transfer rollers 6 (6a, 6b, 6c, 6d) are provided in order to form four types of images corresponding to the respective colors. The end codes a, b, c, and d correspond to black (K), cyan (C), magenta (M), and yellow (Y), respectively.

  That is, the image forming unit 100 includes a developing device 2a, a photosensitive drum 3a, a charger 5a, a cleaner unit 4a, and an intermediate transfer roller 6a, a black (K) image station, a developing device 2b, and a photosensitive drum 3b. A cyan (C) image station having a charger 5b, a cleaner unit 4b and an intermediate transfer roller 6b, and a magenta having a developing device 2c, a photosensitive drum 3c, a charger 5c, a cleaner unit 4c and an intermediate transfer roller 6c. An (M) image station and a yellow (Y) image station including a developing device 2d, a photosensitive drum 3d, a charger 5d, a cleaner unit 4d, and an intermediate transfer roller 6d are provided. Hereinafter, the last reference numerals of these members will be omitted.

  The image forming unit 100 is provided below the discharge unit 15 provided in the upper part of the image forming apparatus A.

  The charger 5 is a charging unit for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. As the charger 5, a contact type charger (for example, a roller type or a brush type) or a charger type charger as shown in FIG. 1 can be used.

  The exposure unit 1 has a function of forming an electrostatic latent image corresponding to image data on the surface by exposing the surface of the charged photosensitive drum 3 according to input image data. .

  As the exposure unit 1, a laser scanning unit (LSU) provided with a laser irradiation unit and a reflection mirror, or a writing device (for example, a writing head) in which light emitting elements such as EL and LED are arranged in an array can be used.

  The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners of each color (K, C, M, Y). The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  An intermediate transfer belt unit 8 is disposed above the photosensitive drum 3. The intermediate transfer belt unit 8 includes an intermediate transfer belt driving roller 81, intermediate transfer belt tension rollers 83 and 83, and an intermediate transfer belt driven in addition to the intermediate transfer belt 7, the intermediate transfer roller 6, and the intermediate transfer belt cleaning unit 9. A roller 82 is provided.

  The intermediate transfer belt drive roller 81, intermediate transfer belt tension rollers 83 and 83, intermediate transfer roller 6, intermediate transfer belt driven roller 82, and other rollers stretch and support the intermediate transfer belt 7. Can be moved in a predetermined direction (arrow D direction in the figure).

  The intermediate transfer roller 6 is rotatably supported on the side opposite to the photosensitive drum 3 with the intermediate transfer belt 7 interposed therebetween. The intermediate transfer roller 6 gives a transfer bias to the intermediate transfer belt 7 for the toner image on the photosensitive drum 3.

  The intermediate transfer belt 7 is provided so as to come into contact with the respective photosensitive drums 3, and the toner images of the respective colors formed on the photosensitive drums 3 are sequentially transferred onto the intermediate transfer belt 7. Thus, a color toner image (multicolor toner image) is formed on the intermediate transfer belt 7. Here, the intermediate transfer belt 7 is formed in an endless shape using a film having a thickness of about 100 μm to 150 μm.

  The toner image is transferred from the photosensitive drum 3 to the intermediate transfer belt 7 by the intermediate transfer roller 6 that is in contact with the back side of the intermediate transfer belt 7 (that is, the side opposite to the photosensitive drum 3 of the intermediate transfer belt 7). Done. The intermediate transfer roller 6 has a high-voltage transfer bias for transferring the toner image to the intermediate transfer belt 7, that is, a high-voltage transfer having a polarity (for example, a positive electrode) opposite to the toner charging polarity (for example, a negative electrode). A bias is applied. Here, the intermediate transfer roller 6 is based on a rotating shaft made of a metal having a diameter of 8 mm to 10 mm (for example, stainless steel), and the surface thereof is made of a conductive elastic material (for example, a material such as EPDM or urethane foam). ). The intermediate transfer roller 6 can apply a high voltage uniformly to the intermediate transfer belt 7 by the conductive elastic material. In this embodiment, a roller-shaped transfer electrode is used. However, the present invention is not limited to this, and a brush-shaped electrode can also be used.

  As described above, the toner image visualized with the toner of each color on the photosensitive drum 3 by the image data corresponding to the document read by the document reading device B or the image data received from the outside is an intermediate image. Laminated with the transfer belt 7. The toner images of the respective colors stacked in this manner are transferred to the sheet by the secondary transfer unit 11 disposed at the transfer portion where the sheet P and the intermediate transfer belt 7 face each other by the surface movement of the intermediate transfer belt 7 in the direction of arrow D. Transferred onto P.

  The intermediate transfer belt 7 and the transfer belt 11a of the secondary transfer unit 11 are pressed against each other to form a nip region. Also, the transfer belt 11a of the secondary transfer unit 11 has a voltage (that is, a negative polarity) opposite to the voltage for transferring the toner image of each color on the intermediate transfer belt 7 onto the paper P, that is, the toner charging polarity (for example, a negative electrode). For example, a positive electrode) voltage is applied. Further, in order to constantly obtain the nip region, either the roller of the secondary transfer unit 11 or the intermediate transfer belt drive roller 81 is made of a hard material such as a metal roller, and the other is a soft material such as an elastic roller. (For example, soft materials such as elastic rubber and foamable resin).

  By the way, the toner image of each color on the intermediate transfer belt 7 may not be completely transferred onto the paper P by the secondary transfer unit 11, and the toner may remain on the intermediate transfer belt 7. This residual toner causes toner color mixing in the next step.

  Therefore, the intermediate transfer belt cleaning unit 9 is configured to remove and collect the residual toner. For example, the intermediate transfer belt cleaning unit 9 includes a cleaning blade that contacts the intermediate transfer belt 7 as a cleaning member. The cleaning blade is supported on the back side of the intermediate transfer belt 7 at a position facing the intermediate transfer belt driven roller 82 (that is, the side opposite to the driven roller 82 of the intermediate transfer belt 7).

  The paper feed tray 10 is a tray for storing the paper P, and is provided below the image forming unit 100 of the image forming apparatus A. The discharge unit 15 is provided on the lower side of the document reading device B. In the present embodiment, the discharge unit 15 includes a discharge tray 15a. The paper discharge tray 15a is a tray for placing printed paper P face down.

  Further, the image forming apparatus A is provided with a substantially S-shaped main transport path S1 for sending the paper P in the paper feed tray 10 to the paper discharge tray 15a via the secondary transfer unit 11 and the fixing mechanism 12. It has been.

  Further, a pickup roller 16, a registration roller 14, and a fixing mechanism 12 are disposed along the main conveyance path S1 from the paper feed tray 10 to the paper discharge tray 15a.

  The image forming apparatus A is provided with a transport roller (not shown) for transporting the paper P. The transport rollers are, for example, small rollers for promoting and assisting the transport of the paper P, and a plurality of the transport rollers are provided along the transport path S. The transport path S includes a main transport path S1, a switchback transport path S2 and a reverse transport path S3, which will be described later.

  The pickup roller 16 is a pull-in roller that is provided at the end of the paper feed tray 10 and supplies the paper P from the paper feed tray 10 to the main transport path S1 one by one.

  The registration roller 14 temporarily stops the paper P conveyed from the paper feed tray 10 and aligns the leading ends of the paper P. The registration roller 14 has a function of conveying the paper P in a timely manner in synchronization with the toner image on the intermediate transfer belt 7.

  For example, the registration roller 14 conveys the paper P so that the image position of the toner image on the photosensitive drum 3 matches the image position on the paper P based on a detection signal from a pre-registration detection switch (not shown). It has become.

  The fixing mechanism 12 fixes a toner image formed on the paper P by heating and melting and fixing the toner image on the paper P, and includes a pair of fixing rollers 31 and 32. The pair of fixing rollers 31 and 32 can rotate with the paper P interposed therebetween, and at least one of them is a heating roller having a heat source 33. In the present embodiment, both of the pair of fixing rollers 31 and 32 are heating rollers.

  The pair of fixing rollers 31 and 32 are controlled so as to reach a predetermined fixing temperature by the control unit 200 described later based on a signal from the temperature detector 34. The pair of fixing rollers 31 and 32 has a function of thermally fixing the paper P to the paper P by fusing, mixing, and pressing the multicolor toner image transferred to the paper P by thermocompression bonding of the paper P. .

  The image forming apparatus A transports (switches back) the paper P after passing through the fixing mechanism 12 so that the upstream end P2 in the transport direction is forward, and reverses the front and back of the paper P (the paper P). And a reverse conveyance mechanism C that performs double-sided printing by forming an image again (hereinafter, image formation may be referred to as printing).

  FIG. 2 is a schematic side view centering on the reverse conveyance mechanism C in the image forming apparatus A shown in FIG. In the following description, the conveyance direction of the paper P is simply referred to as “conveyance direction”, and the width direction of the paper P orthogonal thereto is simply referred to as “width direction”.

  FIG. 3 is a schematic view of the pair of post-fixing transport rollers 25a and 25b and the drive source 28 as viewed from the transport direction.

  The reverse conveyance mechanism C includes a pair of post-fixing conveyance rollers 25a and 25b disposed opposite to each other to convey the paper P after passing through the fixing mechanism 12 (here, the first paper P after passing through the fixing mechanism 12). A switchback transport path S2 that allows the paper P sent from the main transport path S1 to be transported to the upstream end P2 in the transport direction by the pair of post-fixing transport rollers 25a and 25b, and stopped from the switchback transport path S2. A reversing conveyance path S3 for guiding the sheet P conveyed in front of the upstream end P2 in the previous conveyance direction to the main conveyance path S1 upstream in the conveyance direction from the image forming unit 100 so as to reverse the front and back, and the fixing mechanism 12. The paper P after passing through the fixing mechanism 12 and the paper detection sensor 26 for detecting the paper P after passing through the fixing mechanism 12 as the main transport. A first switching position Q1 (a position indicated by a solid line in FIG. 2) for switching so as to transport from S1 to the switchback transport path S2 and a switch to transport the paper P from the switchback transport path S2 to the reverse transport path S3. A switching member (here, a branching claw) 27 that is selectively switchable so as to be able to take a second switching position Q2 (a position indicated by a two-dot chain line in FIG. 2) is provided.

  In the present embodiment, one post-fixing conveyance roller 25a is a reversing roller that switches back the paper P, and is also a discharging roller that discharges the paper P to the discharging unit 15, and the reversing roller, the discharging roller, Is also used. Accordingly, the switchback transport path S2 also serves as a part of the main transport path S1 (portion downstream in the transport direction toward the discharge unit 15).

  Further, one post-fixing conveyance roller 25 a that serves both as a reverse roller and a discharge roller is a drive roller that is rotationally driven by a drive source 28, and is connected to the drive source 28. Further, the other post-fixing transport roller 25b disposed opposite to the one post-fixing transport roller 25a is a driven roller (see FIG. 3).

  Specifically, the pair of post-fixing transport rollers 25a and 25b are relative to the rotation shafts H and H that are supported by the apparatus frames F and F disposed at both ends in the width direction so as to be rotatable about the axis along the width direction. It is supported so that it cannot rotate. The rotation shaft H that supports the other post-fixing conveyance roller 25b is movable in the vertical direction with respect to the rotation shaft H that supports the one post-fixation conveyance roller 25a. The rotation shaft H that supports one post-fixing conveyance roller 25a is connected to a drive source 28 via a drive transmission mechanism E. The rotating shafts H and H are provided with urging members G and G at both ends so that the pair of post-fixing transport rollers 25a and 25b are pressed against each other with a predetermined pressure.

  The control unit 200 illustrated in FIG. 2 includes a CPU (Central Processing Unit) 201 and a storage unit 202. The storage unit 202 stores various control programs and necessary functions, and includes a ROM (Read Only Memory) and a RAM (Random Access Memory).

  The control unit 200 is configured to perform a printing process control by reading various control programs from the storage unit 202 by the CPU 201 and executing the read control programs.

  The paper detection sensor 26 inputs a predetermined first signal (here, an ON signal) to the control unit 200 when the downstream end P1 in the transport direction of the transported paper P passes, and the transport direction of the transported paper P It is electrically connected to the input system of the control unit 200 so that a predetermined second signal (here, an off signal) different from the first signal can be input to the control unit 200 when the upstream end P2 passes. Yes.

  The drive source 28 is electrically connected to the output system of the control unit 200 so that an operation signal from the control unit 200 is input.

  When performing single-sided printing and double-sided printing in the image forming apparatus A, the following conveyance control of the paper P is performed.

  That is, when performing single-sided printing, the branch claw 27 is switched to the switching position Q1, and one post-fixing conveyance roller 25a is rotated by the drive source 28 in a predetermined rotation direction (arrow X1 direction in FIG. 2). As a result, the sheet P after passing through the fixing mechanism 12 is transported in the main transport path S1 by the pair of post-fixing transport rollers 25a and 25b so that the downstream end P1 in the transport direction is forward, and is discharged as it is. Discharge towards the department.

  When performing double-sided printing, first, similarly to the case of single-sided printing, the branch claw 27 is switched to the switching position Q1, and one post-fixing conveyance roller 25a is rotated in a predetermined rotational direction X1. Then, the sheet P after passing through the fixing mechanism 12 is transported by the pair of post-fixing transport rollers 25a and 25b so that the upstream end P2 in the transport direction is shifted to the switchback transport path S2.

  Next, the sheet detection sensor 26 detects the upstream end portion P2 in the transport direction of the paper P, so that the upstream end in the transport direction of the paper P in a state where the pair of post-fixing transport rollers 25a and 25b sandwich the paper P. The rotation of one post-fixing conveyance roller 25a is temporarily stopped so that the portion P2 is positioned in the switchback conveyance path S2. For example, the rear end chuck distance d (see FIG. 8C) from the chuck portion of the paper P by the transport rollers 25a and 25b to the upstream end in the transport direction before stopping may be 30 mm.

  Then, the branch claw 27 is switched to the switching position Q2, and one post-fixing conveyance roller 25a is rotated in a direction opposite to the rotation direction X1 before the stop (in the direction of arrow X2 in FIG. 2). Then, the paper P is transported toward the reverse transport path S3 so that the upstream end P2 in the transport direction before the stop is forward, and the paper P is reversed by the reverse transport path S3.

  With such a configuration, in the image forming apparatus A, the sheet P after the fixing of the multicolor toner image is conveyed to the reverse conveyance path S3 by the pair of post-fixation conveyance rollers 25a and 25b, and is reversed (the front and back are reversed). In this state, the multicolor toner image is directed downward and an image is formed, and then discharged onto the paper discharge tray 15a.

  Further, as shown in FIG. 1, the image forming apparatus A is provided with an insertion tray 20 in addition to a sheet feeding cassette 10 that stores sheets in advance.

  As in the paper feed cassette 10, a pickup roller 16 ′ is disposed on the insertion tray 20, and guides the paper P one by one to the main transport path S 1.

  In the image forming apparatus A described above, when requesting single-sided printing, first, the paper P transported from the paper feed cassette 10 is transported to the registration roller 14 by a transport roller (not shown) in the main transport path S1. Is done. Next, the sheet P is conveyed to the transfer portion in synchronization with the toner image on the intermediate transfer belt 7 by the registration roller 14. The toner image on the intermediate transfer belt 7 is transferred onto the paper P conveyed to the transfer site by a transfer electric field applied to the secondary transfer unit 11. Thereafter, the sheet P passes through the fixing mechanism 12, whereby unfixed toner transferred onto the sheet P receives heat and pressure from the pair of fixing rollers 31 and 32 constituting the fixing mechanism 12. Melted, fixed and fixed on paper. The paper P on which the toner image is fixed is then discharged onto the paper discharge tray 15a through a pair of post-fixing transport rollers 25a and 25b.

  Further, the paper P loaded on the manual paper feed tray 20 is fed by the pickup roller 16 ', reaches the registration roller 14 through a plurality of transport rollers (not shown), and thereafter feeds from the paper feed cassette 10. The paper is discharged to the paper discharge tray 15a through the same route as the paper P to be printed.

  On the other hand, when requesting double-sided printing, the single-sided printing is completed as described above, and the paper P that has passed through the fixing mechanism 12 is chucked by the post-fixing transport rollers 25a and 25b, and is transported by one post-fixing. When the roller (here, the discharge / reverse roller) 25a rotates in the reverse direction, the roller 25a is transported to the reverse transport path S3 so that the upstream end P2 in the transport direction before the stop comes forward. The paper P transported to the reverse transport path S3 is guided upstream in the transport direction from the image forming unit 100, and then is printed on the back surface through the registration rollers 14 and discharged to the paper discharge tray 15a.

  Although printing is performed as described above, the sheet P after passing through the fixing mechanism 12 and the toner fixed on the sheet P are at a lower temperature than the surface temperatures of the heating rollers 31 and 32. It is in a state higher than the ambient temperature.

  The toner used in the image forming apparatus generally contains a resin as a main component, but additionally contains a charge control agent, a colorant, and wax. FIG. 4 schematically shows substances constituting the toner and an example of the content ratio. The content ratio of the charge control agent, the colorant, the wax and the resin is appropriately selected from the content ratio range shown in FIG. 4 depending on the required toner characteristics, and is 100% as a whole toner. For example, if the charge control agent is 2%, the colorant is 10%, and the wax is 8%, the resin is 80%.

  The toner melted by heating softens and melts the resin component that is the main component of the toner at the time of melting, so components such as a charge control agent, a colorant, and wax dispersed in the toner component are on the surface of the melted toner. May precipitate.

  Of the thermal precipitation components precipitated by heating in this way, for example, wax is an effective component for improving the surface gloss of the toner in a solidified state, but the softening temperature of the wax itself is low, and in the softened state It may adhere to other members.

  When the toner in the high temperature state on the paper passes through a pair of post-fixing transport rollers that are in a low temperature state (for example, the ambient temperature inside the apparatus) compared to the toner and the paper, the pair of post-fixing transport rollers It is rapidly cooled, so that it not only adheres to the conveyance roller after fixing, but also a wax component adheres. In this way, the wax in the toner adhering to the post-fixing transport roller penetrates into the post-fixing transport roller by the applied pressure of the post-fixing transport rollers arranged opposite to each other, and increases the diameter of the post-fixing transport roller. Causes a “swelling effect”.

  FIG. 5 is a diagram showing a result of analyzing the post-fixing conveyance roller and the wax, which is a component contained in the toner, by FT-IR (Fourier Transform InfraRed spectrometer).

  FIG. 5 (a) shows the result of analysis by pressing the rubber cross section of the post-fixing conveyance roller made of EPDM (ethylene-propylene-diene rubber) whose life has passed to the crystal for measurement for 1 minute. FIG. 5B shows the result of analysis by pressing the rubber cross section of the post-fixing conveyance roller made of EPDM in the initial state (new) against the crystal for measurement for 1 minute. FIGS. 5C and 5D show the results of analyzing the paraffin wax component in the toner.

  In FIG. 5 (a), as indicated by α, the wax component in the toner indicated by γ in FIGS. 5 (c) and 5 (d) is expressed. It can be seen that the wax is attached and impregnated.

  When the post-fixing conveyance roller swells in this way, the conveyance timing of the paper after the post-fixation conveyance roller deviates from the appropriate timing.

  From this point of view, in the image forming apparatus A according to the embodiment of the present invention, at least one of the pair of post-fixing transport roller pairs 25a and 25b (here, one post-fixing transport roller pair 25a) is included in the toner. It is formed of a material having a low affinity for a thermal precipitation component (for example, wax) that is deposited by heating.

  As described above, in the image forming apparatus A according to the embodiment of the present invention, the post-fixing conveyance roller 25a is formed of a material having a low affinity for the thermal precipitation component (for example, wax) in the toner. It is possible to effectively prevent the occurrence of swelling of the conveyance roller due to the deposited component, and thereby it is possible to optimize the conveyance timing of the paper P after the conveyance roller 25a after fixing.

  That is, since the occurrence of swelling of the conveying roller after fixing can be effectively prevented, the diameter of the roller can be kept constant at the initial diameter (for example, 10 mm). Thereby, for example, when performing double-sided printing, the switchback timing of the paper P can be optimized, that is, the trailing edge chuck distance d (for example, 30 mm) can be made constant. Accordingly, it is possible to avoid the occurrence of a conveyance JAM or an apparatus trouble due to a change in the rear end chuck distance d.

  In addition, since the image position on one side and the image position on the other side of the paper P can be aligned with each other at an appropriate position, it is possible to improve the printing quality during double-sided printing.

  Further, since the diameter of the post-fixing transport roller 25a can be kept constant at the initial diameter (for example, 10 mm), the transport timing of the paper P can be made constant. Therefore, regardless of single-sided and double-sided printing, the control configuration for conveying the paper P can be made as it is without complicating the control configuration, and the load on the control unit 200 can be reduced accordingly.

  Further, the diameter of the roller can be made constant, and therefore, the number of rotations per unit time of the post-fixing conveyance roller 25a (that is, the conveyance speed of the paper P) can be made constant. It becomes possible to make it.

  Furthermore, since the post-fixing conveyance roller can be effectively prevented from swelling, the post-fixation conveyance roller can have a long service life.

  Note that at least one of the pair of post-fixing transport rollers 25a and 25b is preferably disposed on the heating rollers 31 and 32 side in the main transport path S1 with respect to the transported paper P. By doing so, the post-fixing transport roller on the side in contact with the toner heated by the heating rollers 31 and 32 can be a transport roller made of a material having a low affinity with the thermal precipitation component, and thereby the post-fixing transport roller is swollen. Can be more effectively prevented. By the way, after the paper P passes through the pair of post-fixing conveying rollers 25a and 25b, the thermal precipitation component adhering to one roller tends to adhere to the other roller. From such a viewpoint, it is more preferable that both of the pair of post-fixing transport rollers 25a and 25b are made of a material having a low affinity for the thermal precipitation component.

  In the present embodiment, the post-fixing transport roller 25a is formed of a material that does not participate in the post-fixing transport roller due to the thermal precipitation component. By doing this, it is possible to prevent the conveyance roller from swelling after fixing.

  Here, the post-fixing conveyance roller 25a is a silicon roller, and the thermal precipitation component in the toner is paraffin wax.

  For example, when the material of the conveying roller after fixing is “EPDM (ethylene-propylene-diene rubber)” and the wax used for the toner is “paraffinic wax”, the molecular structures of “EPDM” and “paraffinic wax” are as follows: The structure is shown as follows.

When the paper is transported in a state where the wax component is precipitated from the toner melted by the heating roller of the fixing mechanism and is in pressure contact with the pair of post-fixing transport rollers, the [CH in the paraffin wax] ₂ ] The group is bonded to [—CH ₂ —CH ₂ —] in “EPDM”, and the molecular structure is different from that of “EPDM”. That is, the post-fixing transport roller is “swelled” due to intermolecular bonding between the wax component contained in the toner and the surface of the post-fixing transport roller.

  In order to avoid such a swollen state of the post-fixing conveyance roller, in the image forming apparatus A according to the embodiment of the present invention, as described above, the material of the post-fixing conveyance roller 25a is “silicon-based”. To do. The “silicon-based” molecular structure is shown below.

  As described above, the “silicon-based” molecular structure is bonded with Si and R (resin) having a strong intermolecular bonding force and is in a stable state. Therefore, even if the deposited wax component passes through the pair of post-fixing transport rollers 25a and 25b and adheres to the post-fixing transport roller 25a, the post-fixing transport roller 25a can be prevented from being swollen. In addition, it is possible to eliminate the change in the circumferential length of the conveyance roller 25a after fixing. Then, the wax adhering to the post-fixing conveyance roller 25a may re-adhere, for example, to the sheet P that next passes through the post-fixing conveyance roller 25a.

  The image forming apparatus A may further include a post-processing unit that can perform predetermined post-processing on the printed paper P.

  FIG. 6 is an explanatory diagram illustrating an example of a post-processing unit provided in the discharge unit 15 of the image forming apparatus illustrated in FIG. 1 and a schematic configuration of the discharge tray 15a.

  The post-processing unit 50 provided in the discharge unit 15 enables a plurality of post-processing such as punching processing and stapling processing on the paper P discharged from the apparatus main body after the print processing is completed. Hereinafter, the post-processing unit 50 and the paper discharge tray 15a will be described in detail with reference to FIG.

  As shown in FIG. 6, the post-processing unit 50 is disposed on the downstream side in the transport direction from the pair of post-fixing transport rollers 25a and 25b of the apparatus main body. The post-processing unit 50 includes a punching unit 60 having a punching hole function and a staple unit 70 having a stapling function as post-processing units. In the post-processing unit 50, the punching unit 60 is disposed on the upstream side in the transport direction, and the staple unit 70 is disposed on the downstream side in the transport direction. A paper discharge tray 15 a is provided on the downstream side in the transport direction of the staple unit 70. With such a configuration, the discharge unit 15 allows the paper P discharged from the pair of post-fixing conveyance rollers 25a and 25b to be discharged to the paper discharge tray 15a through the punching unit 60 and the staple unit 70. ing.

  As described above, in the post-processing unit 50, the punching unit 60 is disposed on the upstream side, and the staple unit 70 is disposed on the downstream side. This is because, in the staple unit 70, punching processing is performed on a plurality of sheets P 1.

  The punching unit 60 performs punching processing (punching processing) on the paper P discharged from the pair of post-fixing transport rollers 25a and 25b. The punching unit 60 is provided with a punch hole punching mechanism 61, a guide plate 62, and a punch waste storage box 63. Further, the punching unit 60 is provided with transport rollers 56, 56 in the middle of the main transport path S1.

  When there is a request for punching processing, the punching unit 60 stops the sheet P conveyed to the punching unit 60 on the guide plate 62 and opens punch holes by the punch hole forming mechanism 61 for each sheet. It is configured as follows. At this time, punch holes are made at positions determined based on the size of the paper P.

  The punch hole punching mechanism 61 is arranged on the upper part of the punching unit 60. The punch hole punching mechanism 61 has a core material 64 having a diameter that matches the diameter of the punch hole at a predetermined interval along the width direction. It is provided in two places. The core material 64 is provided so as to be movable up and down, and opens a punch hole in the paper P when the core material 64 descends. The core member 64 is provided so as to be reciprocally movable in a direction along the width direction of the paper P.

  The guide plate 62 is disposed below the punch hole punching mechanism 61, and the guide plate 62 is formed with an opening corresponding to a predetermined position for punch holes. The punch scrap storage box 63 is disposed below the punching unit 60 and collects punch scrap generated by punch punching processing by the punch scrap storage box 63.

  When the punching process is performed by the punching unit 60, the core member 64 of the punch hole punching mechanism 61 is moved to a position corresponding to the position determined based on the size of the paper P described above.

   In this punching unit 60, the conveyance timing of the paper P after passing through the fixing mechanism 12 is made appropriate so that it matches the timing of the punching process, so that the punch holes of the paper P are aligned well. It has become.

  The staple unit 70 performs a staple process on the paper P conveyed from the punching unit 60 on the upstream side in the conveyance direction.

  The staple unit 70 includes a staple mechanism unit 71, a staple table 72, alignment plates 73 and 73, and paper discharge rollers 74 and 74. Discharge rollers 54 and 54 for discharging the paper P to the staple table 72 are provided on the downstream side in the transport direction of the main transport path S1.

  In the staple unit 70, when there is a request for staple processing, the staple mechanism unit 71 performs staple processing on a predetermined number of sheets P stacked on the staple table 72. At this time, stapling is performed at a position determined based on the size of the paper P and the desired staple position. The desired staple position is a position where the user performs a desired staple process such as one stop at the upper left corner of the paper P or two stops at the left end.

  The staple mechanism unit 71 is disposed below the discharge rollers 54 and 54, and binds the upstream end portion P2 in the transport direction of the paper P stacked on the staple table 72 with a staple needle. The stapling mechanism unit 71 is configured to be capable of reciprocating along the width direction of the paper P so that stapling can be performed at a position determined based on the size of the paper P and the desired staple position. It has become.

  When stapling is performed by the staple unit 70, the staple mechanism 71 is moved to a position corresponding to a position determined based on the size of the paper P and the desired staple position.

  The staple table 72 is used to stack the sheets P discharged from the discharge rollers 54 and 54, and serves as a processing table for staple processing by the staple mechanism unit 71. The staple table 72 is arranged with the downstream side in the transport direction inclined upward. When the staple process is performed, the paper P discharged from the discharge rollers 54 and 54 slides down to the upstream side of the staple table 72 in the transport direction along the inclination of the staple table 72 due to its own weight. On the other hand, when the stapling process is not performed, the sheet P is discharged from the discharge rollers 74 and 74 to the discharge tray 15a as will be described later.

  The alignment plates 73 and 73 are disposed to face both sides in the direction along the width direction of the upper surface (surface from which the paper P is discharged) of the staple table 72. The pair of alignment plates 73, 73 are provided so as to be capable of reciprocating along the width direction. When the stapling unit 70 performs stapling, the alignment plates 73 and 73 are moved along the width direction so that the sheets P discharged onto the staple table 72 can be aligned in the width direction one by one. I have to. At this time, the alignment plates 73 and 73 are moved in accordance with the movable width determined based on the size of the conveyed paper P. Note that the reciprocating movement of the pair of alignment plates 73 and 73 is enabled by, for example, a rack and pinion mechanism.

   In this staple unit 70, the conveyance timing of the paper P after passing through the fixing mechanism 12 is made appropriate, so that it matches the movement timing of the alignment plates 73, 73, whereby the staple position of the paper P is adjusted. It is designed to be well aligned.

  The paper discharge rollers 74 and 74 are arranged in a pair of upper and lower sides on the most downstream side in the transport direction of the staple table 72 so as to face the paper discharge tray 15a, and discharge the paper P on the staple table 72 to the paper discharge tray 15a. Is. The upper and lower paper discharge rollers 74 and 74 are both provided as drive rollers. That is, the upper and lower paper discharge rollers 74 and 74 are both connected to the drive source.

  The upper and lower paper discharge rollers 74 and 74 are provided so as to be able to come into contact with and separate from each other. It is provided to be movable. When the paper P is discharged to the paper discharge tray 15a, the upper and lower paper discharge rollers 74 and 74 are brought into pressure contact with each other. When the staple process is performed on the paper P, the upper and lower paper discharge rollers 74 are used. , 74 are separated from each other.

  In this way, when performing the stapling process, the upper and lower paper discharge rollers 74 and 74 are separated from each other, and the downstream end P1 in the transport direction of the paper P sent to the staple table 72 is moved to the upper and lower paper discharge rollers 74 and 74. It can be made to project from between 74. After the stapling process, the upper and lower discharge rollers 74, 74 can be brought into a pressure contact state so that the bundle of sheets P after the stapling process can be discharged to the discharge tray 15a.

  The conveyance of the paper P in the post-processing unit 50 is performed as follows.

  That is, the main transport path S1 is formed from the pair of post-fixing transport rollers 25a and 25b of the apparatus main body to the discharge rollers 54 and 54 disposed in the middle of the staple unit 70 through the punching unit 60. The paper P discharged from the pair of post-fixing conveyance rollers 25a and 25b of the apparatus main body is conveyed to the staple table 72 of the staple unit 70 along the main conveyance path S1. When the punching process is selected, the sheet P transported to the main transport path S1 is stopped on the guide plate 62 after the double-sided printing process or the single-sided printing process is completed. Then, the core material 64 of the punch hole punching mechanism 61 is lowered, and a punch hole is opened at a predetermined position on the upstream end P2 in the transport direction of the paper P.

  Further, the paper P discharged from the discharge rollers 54 and 54 toward the staple table 72 gradually comes into contact with the staple table 72 from the front end. While the paper P is being discharged from the discharge rollers 54 and 54, the downstream end P <b> 1 in the transport direction of the paper P reaches the discharge rollers 74 and 74 on the most downstream side in the transport direction of the staple table 72. Subsequent conveyance of the paper P differs depending on whether or not the staple processing is performed by the staple unit 70.

  When the stapling process is not performed, since the upper and lower paper discharge rollers 74 and 74 are in a pressure contact state, the paper P is sent by the paper discharge rollers 74 and 74 and discharged to the paper discharge tray 15a.

  On the other hand, when performing stapling, the upper and lower paper discharge rollers 74 are in a separated state. For this reason, the sheet P is not sent by the discharge rollers 74, 74 even if the downstream end P1 in the conveyance direction of the sheet P is sent between the upper and lower discharge rollers 74, 74 by the discharge rollers 54, 54. . Therefore, if the upstream end P2 in the transport direction of the paper P moves away from the discharge rollers 54 and 54 and loses the transport force toward the downstream side in the transport direction, the paper P is now along the staple table 72 inclined by its own weight. Slip down to the upstream side in the transport direction.

  Then, after a predetermined number of sheets P are discharged from the discharge rollers 54 and 54, aligned and stacked on the staple table 72, the stapling process is performed on the upstream end P <b> 2 in the transport direction of the sheet P by the staple mechanism 71. . During this stapling process, the middle portion of the paper P is between the upper and lower paper discharge rollers 74 and 74 in a separated state. After the stapling process is completed, the upper and lower paper discharge rollers 74 and 74 are pressed against each other, and the paper discharge rollers 74 and 74 are driven to discharge the bundle of sheets P onto the paper discharge tray 15a.

  In the image forming apparatus A provided with the post-processing unit 50 as described above, the post-fixing conveyance roller 25a is formed of a material having a low affinity for the thermal precipitation component (for example, wax) in the toner. In addition, it is possible to effectively prevent the post-fixing conveyance roller from being swelled due to the thermal precipitation component, thereby making it possible to optimize the conveyance timing of the paper P after the post-fixing conveyance roller 25a, as described above. The same effect as when the post-processing unit 50 is not provided can be obtained.

  Further, as shown in FIG. 6, when the image forming apparatus A includes the post-processing unit 50, for example, the positional accuracy of the staple position of the paper P by the staple processing in the post-processing unit 50 can be improved and the paper P by the punching process can be improved. Therefore, it is possible to effectively prevent misalignment of the paper P such as a staple position shift or a punch position irregularity. Therefore, it is possible to contribute to improving the appearance of the discharged paper P.

  In the present embodiment, the post-fixing conveyance roller is formed of a material having a low affinity for the thermal precipitation component in the toner. However, the thermal precipitation component in the toner is applied to the post-fixation conveyance roller. You may comprise with a material with little affinity. By doing this, the same effect can be obtained.

1 is a side view showing a schematic configuration of an image forming apparatus according to the present embodiment. FIG. 2 is a schematic side view mainly showing a reverse conveyance mechanism in the image forming apparatus shown in FIG. 1. FIG. 5 is a schematic view of a pair of post-fixing conveyance rollers and a driving source when viewed from a conveyance direction. FIG. 3 is a diagram schematically illustrating substances constituting the toner and an example of a content ratio thereof. It is a figure which shows the result of having analyzed the conveyance roller after fixing, and the wax which is a component contained in a toner by FT-IR (Fourier transform infrared spectrophotometer). FIG. 2 is an explanatory diagram illustrating an example of a post-processing unit provided in a discharge unit of the image forming apparatus illustrated in FIG. 1 and a schematic configuration of paper discharge. It is a schematic side view for explaining reversal conveyance of an example of an image forming apparatus that performs single-sided and double-sided printing. FIG. 7 is a diagram for explaining a shift in the conveyance timing of a recording medium by a post-fixing conveyance roller when swelling occurs.

Explanation of symbols

12 Fixing mechanism 25a, 25b Conveyor roller after fixing 28 Drive source 31, 32 Fixing roller 100 Image forming part A Image forming apparatus P Recording medium (paper)
S transport path

Claims (7)

An image forming unit that forms a toner image on a recording medium using toner, a fixing mechanism that fixes the toner image formed on the recording medium by heating and melting and fixing the toner image, and a recording medium An image forming apparatus including one or more post-fixing transport rollers that are disposed along a transport path and transport the recording medium after passing through the fixing mechanism,
Of the one or more post-fixing transport rollers, at least one post-fixing transport roller is formed of a material having a low affinity for a thermal precipitation component deposited by heating among the components contained in the toner. An image forming apparatus.   2. The at least one post-fixing transport roller formed of a material having a low affinity for the thermal precipitation component in the toner is a drive roller that is rotationally driven by a drive source. The image forming apparatus described. At least one of the pair of fixing rollers constituting the fixing mechanism is a heating roller having a heat source;
The at least one post-fixing transport roller formed of a material having a low affinity for the thermal precipitation component in the toner is disposed on the heating roller side in the transport path with reference to the transported recording medium. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The at least one post-fixing conveyance roller formed of a material having a low affinity for the thermal precipitation component in the toner is formed of a material that does not contribute to the post-fixation conveyance roller due to the thermal precipitation component. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An image forming unit that forms a toner image on a recording medium using toner, a fixing mechanism that fixes the toner image formed on the recording medium by heating and melting and fixing the toner image, and a recording medium An image forming apparatus including one or more post-fixing transport rollers that are disposed along a transport path and transport the recording medium after passing through the fixing mechanism,
The toner is made of a material in which a thermal precipitation component deposited by heating among the components contained in the toner has a low affinity for at least one of the one or more post-fixing transport rollers. An image forming apparatus.   The image forming apparatus according to claim 5, wherein the thermal precipitation component of the toner is made of a material that does not contribute to swelling of the at least one post-fixing conveyance roller due to the thermal precipitation component.   The image forming apparatus according to claim 4, wherein the at least one post-fixing conveying roller is a silicon-based roller, and the thermal precipitation component in the toner is paraffin-based wax.

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