JP4858649B2 - Fixing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a printer, or a facsimile that employs an electrophotographic method, and a multifunction machine having these functions, and an image forming apparatus using the fixing device. The present invention relates to a fixing device capable of preventing or suppressing the occurrence of so-called “waves” on a sheet after fixing processing, and an image forming apparatus using the same.

  Conventionally, in a fixing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions, such as an electrophotographic system of this type, for example, an unfixed toner image is used. The unfixed toner image is fixed on the sheet by heating and pressing while the transferred sheet is conveyed while being sandwiched between the fixing roll and the pressure roll.

  At that time, on the paper immediately after being heated and pressed by the fixing device, the water content of the paper evaporates at the time of heat and pressure, and the water content of the paper changes, so-called “koshi” (rigidity) of the paper. As shown in FIG. 9, it is known that a so-called “wave-out” is generated in which a wave is generated along the sheet conveyance direction as a result of the decrease in image quality or the influence of gravity. . If the paper is cooled in a state where “waves” are generated, the flatness of the paper is lost, leading to a decrease in image quality.

  In view of this, the conventional image forming apparatus employs a mechanism in which a drive conveyance roll is provided in the paper discharge portion of the fixing device, and the discharged paper is pulled by the drive conveyance roll in order to prevent the paper from wobbling. ing.

  However, in the case of such a conventional image forming apparatus, since it is necessary to provide a drive conveyance roll in the paper discharge portion of the fixing device, a drive system for driving the drive conveyance roll is necessary, and the number of parts increases, There was a problem of increasing the cost.

  In view of this, as a technique capable of preventing the paper from spilling without increasing the cost of the apparatus, for example, those disclosed in Japanese Patent Laid-Open Nos. 61-050176 and 5-72937 are already available. Proposed.

  A fixing device according to the above-mentioned Japanese Patent Application Laid-Open No. 61-050176 includes a fixing roller having a built-in heat source, a pressure roller that is pressed and driven by the fixing roller, and a tip disposed on the copy paper discharge side of the fixing roller. A peeling claw that is in contact with the surface of the fixing roller at a position close to a tangent to the center line connecting the center points of the two rollers, and a position that is tangentially below the leading edge of the peeling claw on the copy paper discharge side of the peeling claw The curl correction member is used as a curl correction member, and the curl correction member can be used as a peeling nail by arranging the rear end of the peeling nail below the tangent line or as a guide member. Such a configuration is also disclosed.

  In the fixing device according to the above-mentioned Japanese Patent Application Laid-Open No. 5-72937, a pressure roller is arranged on the upper side and a fixing roller is arranged on the lower side so as to be in pressure contact with each other. In the fixing device of the image forming apparatus, the sheet guide surface of the separation claw is configured to have a convex shape from the front end portion contacting the fixing roller to the rear end portion.

  These technologies disclosed in Japanese Patent Laid-Open Nos. 61-050176 and 5-72937, etc. are arranged such that the peeling claw and the separation claw are arranged so as to form a convex shape with respect to the paper conveyance path. It is configured to stabilize the behavior.

  However, in an image forming apparatus such as a copying machine of the type in which such a configuration is used for vertical conveyance, that is, a sheet is conveyed vertically from the lower side to the upper side in the vertical direction, and the sheet immediately after being discharged is conveyed and discharged in the horizontal direction. However, the separation claw and the like come into strong contact with the surface of the paper immediately after the fixing, and there is a problem in that streaks are generated by the separation claw and the image quality is lowered.

  As for the above-described image forming apparatus such as a vertical transfer copier, as disclosed in Japanese Patent Application Laid-Open No. 2004-233405 relating to the application of the present applicant, Techniques for preventing the wave have already been proposed.

  The fixing device according to Japanese Patent Application Laid-Open No. 2004-233405 has a heat roll, a peeling claw for peeling the paper from the heat roll, and a guide rib for guiding the paper peeled by the peeling claw. Comprises a first guide rib located in the vicinity of the peeling claw and a second guide rib located farther from the peeling claw than the first guide rib. The two guide ribs are configured to have different shapes at least in the contact area where the paper comes into contact, corresponding to the posture of the paper peeled off by the peeling claw.

JP 61-050176 A JP-A-5-72937 JP 2004-233405 A JP 7-128938 A

  However, the conventional technique has the following problems. That is, in the case of the fixing device according to Japanese Patent Application Laid-Open No. 2004-233405, the aim is to eliminate the obstacle to the leading edge of the paper. It has been found that there is a problem that it is not possible to sufficiently prevent the occurrence of.

  More specifically, when applied to a vertically conveyed image forming apparatus such as the fixing apparatus according to Japanese Patent Application Laid-Open No. 2004-233405, the fixing apparatus heats and presses the sheet depending on the moisture content of the sheet, the basis weight of the sheet, and the like. In the paper immediately after being applied, the water content of the paper evaporates at the time of heating and pressurization, the water content of the paper changes, the so-called “stiffness” (rigidity) of the paper is reduced, and the upper direction in the vertical direction after fixing. There is a problem that a so-called “wave wave” may occur in the state of being waved along the paper conveyance direction due to the influence of gravity when being conveyed. all right.

  In order to remedy this problem, a means for avoiding the influence of gravity applied to the paper by abruptly bending the paper transport path near the exit of the fixing device can be considered. In the future, a new problem that the position of the sheet must be set relatively low and the number of sheets that can be stacked on the discharge tray will be reduced.

  In addition, as another technique for preventing the wave of the paper, a means for increasing the stiffness (rigidity) of the paper at the time of fixing by increasing the load at the time of fixing the paper has been proposed. However, there is a problem that the driving torque of the fixing device increases with an increase in the load, resulting in an increase in cost such as an increase in the size of the driving motor.

  Further, as described above, when a mechanism for pulling the sheet immediately after being discharged from the fixing device is provided, there is an inevitable problem that the cost is increased.

  Further, as related prior art, as disclosed in Japanese Patent Laid-Open No. 7-128938, toner image forming means for forming a toner image on a sheet material and fixing for fixing the toner image formed on the sheet material And a conveying path that is arranged downstream of the fixing unit in the conveying direction and conveys the sheet at a higher speed than the fixing unit, and a conveyance path that guides the sheet from the fixing unit to the conveying unit while maintaining a flat surface. A configuration that includes the above has already been proposed.

  However, even in the technique disclosed in Japanese Patent Laid-Open No. 7-128938, a conveyance unit that is disposed downstream in the conveyance direction of the fixing unit and conveys a sheet at a higher speed than the fixing unit, and the conveyance from the fixing unit And a conveyance path for guiding the sheet to the means in a flat state, the structure must be complicated, and the cost of the apparatus is increased. Yes.

  Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and the object of the present invention is to complicate the configuration of the apparatus, which causes an increase in cost and can be loaded on a discharge tray. Provided is a fixing device capable of preventing or suppressing paper ripples and an image forming apparatus using the same, without reducing the number of sheets, and without depending on the water content or basis weight of the paper. There is.

That is, according to the first aspect of the present invention, the heating rotator and the pressing rotator are brought into pressure contact with each other, and an unfixed toner image is formed in a nip portion formed between the heating rotator and the pressing rotator. In a fixing device in which an unfixed toner image is fixed on the paper by passing the paper carrying the paper, and the discharge direction of the paper at the nip portion is set substantially vertically upward.
A guide member provided on the side of the heating rotator on the downstream side where the paper has passed through the nip portion, and provided with a conveyance roller at a position protruding from the rib and the pressure rotator side of the rib;
Among the guide members, a counter member is provided at a position facing the position where the transport roller is provided, and forms a transport path between the guide member and the guide member,
The rib comprises a plurality of first guide ribs and second guide ribs arranged along the axial direction of the heating rotator,
The second guide rib is provided with a lower height in the direction toward the opposing member than the first guide rib at the position of the upstream end portion of the transport roller in the transport direction of the paper , In addition, the fixing device is disposed at a position farther from the transport roller than the first guide rib in the axial direction of the heating rotating body.

According to a second aspect of the present invention, the support member also serves as a cover that covers an outlet side of the pressurizing rotator of the nip portion, and an outlet of the pressurizing rotator of the nip portion. 2. A peeling claw portion for peeling the paper at a front end portion on the side, and is pivotally supported so as to open an outlet side of the pressurizing rotating body of the nip portion. The fixing device according to (1).

Furthermore, an invention described in claim 3 is an image forming apparatus comprising the fixing device according to claim 1 or 2.

  According to the present invention, the configuration of the apparatus is complicated, which causes an increase in cost, does not reduce the number of sheets that can be stacked on the discharge tray, and does not depend on the moisture content or basis weight of the sheets. It is possible to provide a fixing device capable of preventing or suppressing paper ripples and an image forming apparatus using the same.

FIG. 1 is a sectional configuration diagram showing a fixing device according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a monochrome multifunction machine as an image forming apparatus to which the fixing device according to Embodiment 1 of the present invention is applied. FIG. 3 is a block diagram showing an image forming unit of a monochrome multifunction peripheral as an image forming apparatus to which the fixing device according to the first embodiment of the present invention is applied. FIG. 4 is an external perspective view showing the fixing device according to Embodiment 1 of the present invention. FIG. 5 is an explanatory view showing the operation of the fixing device according to Embodiment 1 of the present invention. FIG. 6 is an explanatory view showing the operation of the fixing device according to Embodiment 1 of the present invention. FIG. 7 is an explanatory view showing the operation of the conventional fixing device. FIG. 8 is a chart showing experimental results. FIG. 9 is a schematic view showing a wave.

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

Embodiment 1
FIG. 2 is a schematic configuration diagram showing a monochrome multifunction machine employing an electrophotographic system as an image forming apparatus to which the fixing device according to Embodiment 1 of the present invention is applied. This monochrome multifunction device is provided with an image reading device, and is configured as an image forming device having functions as a copying machine, a printer, and a facsimile. Of course, the printer may be configured as a printer that forms an image based on image data output from the network.

  In FIG. 2, reference numeral 1 denotes a monochrome MFP main body, and an automatic document feeder (ADF) that automatically conveys a document (not shown) separated one by one on the monochrome MFP main body 1. 2 and an image reading device 3 that reads an image of a document conveyed by the automatic document conveying device 2 is provided. The image reading device 3 illuminates a document (not shown) placed on a platen glass 4 with a light source 5, and reflects a reflected light image from the document from a full-rate mirror 6, half-rate mirrors 7 and 8, and an imaging lens 9. The image reading element 10 made of a CCD or the like is scanned and exposed through the reduction optical system 11 and the image reading element 10 reads an image of a document at a predetermined dot density (for example, 16 dots / mm). Has been.

  The document image read by the image reading device 3 is sent as image data to an image processing device 12 (IPS) provided inside the monochrome MFP main body 1, and the image processing device 12 uses the image data of the document. On the other hand, if necessary, predetermined image processing such as shading correction, position shift correction, gamma correction, and frame deletion is performed. In addition, the image processing apparatus 12 performs predetermined image processing on image data sent from the personal computer 5 or the like as necessary.

  The image data that has been subjected to the predetermined image processing by the image processing device 12 is sent to a ROS (LaserOutputScanner) 13 as an image exposure means. The ROS 13 uses a polygon mirror, an f-θ lens, etc., not shown. Image exposure with the laser beam LB is performed according to the image data.

  By the way, as shown in FIGS. 2 and 3, an image forming unit 14 configured integrally as a unit is disposed inside the monochrome multifunction device main body 1. The image forming unit 14 includes a photosensitive drum 15 as an image carrier, a charging roll 16 as a charging unit, a developing device 17 as a developing unit, and a cleaning device 19 as a cleaning unit. ing.

  As the photosensitive drum 15, a conductive drum having a photosensitive layer made of OPC or the like on its surface is used. As shown in FIG. 3, the photosensitive drum 15 is driven in the direction of the arrow by a driving unit (not shown). And are rotationally driven at a predetermined speed. After the surface of the photosensitive drum 15 is uniformly charged to a predetermined potential by the charging roll 16, the surface of the photosensitive drum 15 is subjected to image exposure by the ROS 13, and electrostatic charges corresponding to the image data are applied. A latent image is formed. The electrostatic latent image formed on the surface of the photosensitive drum 15 is developed by the developing device 17 using a one-component developer composed only of toner or a two-component developer composed of toner and carrier, and image data. A toner image corresponding to the above is formed. The toner image formed on the photosensitive drum 15 is transferred at a predetermined timing onto a paper 21 having a desired size and material supplied from a paper feed cassette by a transfer roll 18 serving as a transfer unit, as will be described later. Then, it is conveyed to the fixing device 20.

  As shown in FIGS. 2 and 3, the developing device 17 receives toner and developer from the toner cartridge 21 disposed inside the monochrome MFP main body 1 through the toner supply pipe 22 at a predetermined timing. It is configured to be supplied.

  The photosensitive drum 15 after the toner image transfer process is completed is prepared for the next image forming process by removing toner, paper dust, and the like remaining on the surface thereof by the cleaning device 19.

  As shown in FIG. 2, the paper 21 is fed from a paper feed cassette 23 disposed inside the monochrome MFP main body 1 by a paper feed roll 24, or below the monochrome MFP main body 1. From a plurality of stages of the paper feed cassettes 25 to 27, the paper is fed one by one by a paper feed roll 28, a retard roll 29 and a feed roll 30, and is conveyed to a registration roll 32 via a conveyance roll 31. The Then, the sheet 21 is conveyed to a transfer position of the photosensitive drum 15 in synchronization with a toner image formed on the photosensitive drum 15 by a registration roll 32 that is rotationally driven at a predetermined timing. After the toner image is transferred by the transfer roll 18, it is conveyed to the fixing device 20.

  In the case of single-sided printing, the sheet 21 on which the toner image is fixed by the fixing device 20 is discharged as it is onto a discharge tray 34 formed on the upper end surface of the monochrome multifunction peripheral body 1 by a discharge roll 33. When images are formed on both sides of the paper 21, the paper 21 on which the image is formed on one side is not discharged onto the discharge tray 34 by the discharge roll 33 as it is, and the paper 21 is moved behind the paper 21 by the discharge roll 33. In a state where the end is sandwiched, the discharge roll 33 is reversed, and the switching gate 35 provided at the upper part of the fixing device 20 is switched to convey the sheet 21 to the duplex conveyance path 36. Then, the sheet 21 is conveyed again to the registration roll 32 with the front and back sides being reversed through the duplex conveyance path 36, and an image is formed on the back surface of the sheet 21.

  In FIG. 2, reference numeral 37 denotes a manual feed tray, and 38 denotes a paper feed roll for feeding paper from the manual feed tray 37.

By the way, in this embodiment, the heating rotator and the pressurizing rotator are brought into pressure contact with each other, and a sheet carrying an unfixed toner image on the nip formed between the heating rotator and the pressurizing rotator is provided. In a fixing device that fixes an unfixed toner image on the paper by passing it through,
The discharge direction of the paper is set substantially upward in the vertical direction, and the paper peeled from the heating rotator is transported along a guide member provided on the heating rotator side and along the guide member. A support member that supports the back side of the sheet conveyed in this manner is arranged close to the guide member.

  In this embodiment, the line connecting the center of the heating rotator and the pressurizing rotator is inclined toward the heating rotator with respect to the horizontal direction so that the paper discharge direction from the nip portion is heated. Since it is on the rotating body side, the sheet is configured to be more reliably conveyed along a guide member provided on the heating rotating body side.

  In this embodiment, the guide member is configured to include a rotatable transport roller for transporting the paper.

  Furthermore, in this embodiment, the paper discharge direction is determined by a straight line connecting a gap formed by the outlet of the nip portion of the heating rotator and the pressure rotator, and the guide member and the support member. Is also set on the heating rotor side.

  That is, as shown in FIGS. 1 and 4, the fixing device 20 according to this embodiment is integrally formed as a unit, and can be integrally attached to and detached from the monochrome multifunction peripheral body 1 as a fixing unit. It is configured. The fixing device 20 is formed in a substantially rectangular parallelepiped elongated box shape by a fixing device housing 40 made of a heat-resistant synthetic resin.

  In the fixing device housing 40, as shown in FIG. 1, a fixing roll 41 as a heating rotator and a pressure roll 42 as a pressing rotator are pressed against each other at a relatively low predetermined pressure. A nip portion 43 is formed between the fixing roll 41 and the pressure roll 42 so as to follow the outer peripheral shape of the fixing roll 41. The fixing roll 41 is composed of a core metal 44 formed in a relatively thin cylindrical shape with a metal such as stainless steel or aluminum, and a heat-resistant silicone rubber coated on the surface of the core metal 44 relatively thinly. The heat-resistant elastic body layer 45 and a release layer 46 made of tetrafluoroethylene, PFA, or the like coated on the surface of the heat-resistant elastic body layer 45 are configured. In addition, a halogen lamp 47 is provided as a heating source inside the fixing roll 41. The fixing roll 41 is heated by the halogen lamp 47 from the inside, and the surface temperature of the fixing roll 47 is a predetermined value. The temperature detection sensor 48 detects the surface temperature so as to reach the temperature, and the energization to the halogen lamp 47 is controlled.

  Further, as shown in FIG. 1, the pressure roll 42 includes a metal core 49 formed into a solid cylindrical shape with a metal such as stainless steel or aluminum, and a heat resistance that is thickly coated on the surface of the metal core 49. And a release layer 51 made of tetrafluoroethylene, PFA or the like coated on the surface of the heat resistant elastic layer 50.

As shown in FIG. 1, the fixing roll 41 and the pressure roll 42 are pressed against each other at a relatively low predetermined pressure by a coil spring (not shown) as described above. As shown in FIG. 1, a nip portion 43 having a concave shape on the side of the pressure roll 42 is formed between the rolls 42, as shown in FIG. 1. Then, the sheet 21 on which the unfixed toner image T is transferred is conveyed from the lower side to the upper side in the vertical direction, and passes through the nip portion 43 formed between the fixing roll 41 and the pressure roll 42. The unfixed toner image T is configured to be fixed by being heated and pressed on the paper 21. In FIG. 1 , reference numeral 52 denotes a chute on the inlet side of the fixing device 20.

 In this embodiment, the center line L1 connecting the centers O and O ′ of the fixing roll 41 and the pressure roll 42 is fixed not at the horizontal direction but at a predetermined angle θ (for example, 5 °) with respect to the horizontal direction. It arrange | positions so that it may incline to the roll 41 side.

 Further, as shown in FIG. 1, the fixing device 20 is provided with a peeling claw 53 for peeling the paper 21 from the fixing roll 41 on the downstream side of the outlet of the nip portion 53. The tip of the peeling claw 53 is disposed at a position retracted by a predetermined amount downstream from the outlet of the nip portion 43 in the rotation direction of the fixing roll 41, and the surface 53 a of the peeling claw 53 is formed on the nip portion 43. While forming a substantially parallel surface with the straight line L2 connecting both ends of the fixing roller 41, the fixing roller 41 is disposed at a position retracted by a predetermined amount T on the downstream side in the rotation direction. The peeling claw 53 is attached to the fixing device housing 40 so as to be rotatable about a fulcrum 54. Further, as shown in FIG. 4, a plurality of the peeling claws 53 are arranged at predetermined positions along the axial direction of the fixing roll 41.

  The fixing device 20 is configured to perform a fixing process while transporting the sheet 21 with the center along the axial direction of the fixing roll 41 as a reference (center registration), and the peeling claw 53 A plurality (five in the illustrated example) are arranged so as to be located slightly inside the both end edges of the papers 21 of various sizes according to the sizes of the papers 21 to which the fixing device 20 performs the fixing process. Yes.

  Further, as shown in FIG. 4, at the outlet of the fixing device housing 40, a first guide rib 55 and a second guide rib as guide members for guiding the paper 21 are provided on the same side as the peeling claw 53. 56 are arranged along the axial direction of the fixing roll 41. As shown in FIG. 1, the first guide rib 55 is disposed adjacent to the peeling claw 53, and the sheet 41 guided by the surface 53a of the peeling claw 53 is shown in FIG. Then, the first curved surface 55a that is bent toward the pressure roll 42 to improve the rigidity as viewed from the cross-sectional shape of the paper 21, and the paper 21 guided by the first curved surface 55a is moved again to the fixing roll 41 side. The second curved surface 55b is provided to bend and improve the rigidity as seen from the cross-sectional shape of the paper 21.

  Further, as shown in FIG. 1, the first guide rib 55 includes a guide roller 57 as a guide member at a position protruding from the first guide rib 55 closest to the pressure roll 42. The sheet 21 guided by the first guide rib 55 is smoothly guided downstream in the transport direction.

  Further, as shown in FIGS. 4 and 6, the second rib 56 is formed in a curved shape lower than the first rib 55, and conveys the paper 21 at a position away from the peeling claw 53. It is comprised so that it may convey smoothly to the downstream side along a direction.

  Further, in the fixing device 20, as shown in FIG. 1, as a support member on the pressure roll 41 side so as to face the first and second guide ribs 55 and 56 and the guide roller 57 on the fixing roll 41 side. The peeling member 58 is provided. As shown in FIG. 4, the peeling member 58 also serves as a cover that covers the outlet side of the pressure roll 42, and the peeling member 58 is configured to be openable and closable around the fulcrum 59. Yes. As shown in FIG. 4, the peeling member 58 extends along the axial direction of the pressure roll 42 at the substantially flat plate-like portion 60 that covers the outlet side of the pressure roll 42 and the tip of the substantially flat plate-like portion 60. And peeling claw portions 61 arranged at predetermined intervals.

  As shown in FIG. 1, the peeling claw portion 61 of the peeling member 58 has a lower end slightly extended toward the surface side of the pressure roll 42, and the surface of the peeling claw portion 61 is a nip. It is formed so as to intersect the straight line L2 connecting both ends of the portion 53 with a small inclination angle. Even if the front end of the paper 21 subjected to the fixing process faces the pressure roll 42 side in the nip portion 43 between the fixing roll 41 and the pressure roll 42, the nip portion is formed by the surface of the peeling claw portion 61. 43 is configured to assist the peeling action so as to be directed in the direction of a straight line L2 connecting both ends of 43. The straight line L2 also represents a straight line connecting a gap 62 formed by the outlet of the nip portion 43 of the fixing roll 41 and the pressure roll 42 and the first guide rib 55 and the peeling member 58. The discharge direction of the paper 21 is more than the straight line L2 connecting the gap 62 formed by the outlet of the nip portion 43 of the fixing roll 41 and the pressure roll 42 and the first guide rib 55 and the peeling member 58. 41 side is set.

  Further, in this embodiment, as shown in FIG. 1, the peeling member 58 is arranged close to the first guide rib 55 side and provided on the peeling member 58 and the first guide rib 55. A narrow conveyance passage 62 is formed between the guide roller 57 and the guide roller 57. Further, in this embodiment, as described above, the first guide rib 55 is configured to include the rotatable guide roller 57 that conveys the paper 21. As a result, in this embodiment, the peeling member 58 is disposed close to the guide roller 57 provided on the first guide rib 55, and the narrow conveyance between the peeling member 57 and the guide roller 57 is performed. The passage 62 is formed. The peeling member 57 plays a role of supporting the back surface of the sheet 21 conveyed in a state guided by the first guide rib 55 and the guide roller 57. For this reason, it is desirable that the conveyance path 62 is relatively narrow. However, if the conveyance path 62 is too narrow, the passage of the paper 1 is hindered, which causes a jam or the like.

  The gap G of the transfer path 62 is set to 0.2 mm or more and 1.3 mm or less. In this embodiment, the gap G of the transfer path 62 is set to 0.9 mm.

  In the above configuration, in the monochrome multifunction device to which the fixing device according to this embodiment is applied, the configuration of the device is complicated as described below, resulting in an increase in cost or the number of sheets that can be stacked on the discharge tray. It is possible to prevent or suppress paper ripples without reducing the number of sheets and without depending on the water content or basis weight of the paper.

  That is, in the monochrome multifunction peripheral according to this embodiment, as shown in FIG. 2, an electrostatic latent image corresponding to image data is formed on the photosensitive drum 15 and formed on the surface of the photosensitive drum 15. The electrostatic latent image is developed by the developing device 17 to form a toner image. After the toner image formed on the photosensitive drum 15 is transferred onto the paper 21, the unfixed toner transferred onto the paper 21 is transferred. The image T is fixed by the fixing device 20.

  At that time, in the fixing device 20, as shown in FIG. 5, the paper 21 carrying the unfixed toner image T passes through the nip portion 43 formed between the fixing roll 41 and the pressure roll 41, After being heated and pressurized to fix the unfixed toner image T on the paper 21, it is discharged from the nip 43. The discharge direction of the sheet 21 is such that a straight line L1 connecting the centers O and O ′ of the fixing roll 41 and the pressure roll 41 is inclined toward the fixing roll 41 with respect to the horizontal direction. The heat-resistant elastic body layer 50 is formed thick, and the nip portion 43 is formed so as to have a concave shape on the pressure roll 42 side. Therefore, the sheet 21 that has passed through the nip portion 43 has an inclination of a straight line L1 that connects the centers O and O ′ of the fixing roll 41 and the pressure roll 41, and the shape of the nip portion 43 that has a concave shape on the pressure roll 42 side. At the same time, the sheet 21 is discharged to the fixing roll 41 side by the stiffness (rigidity) of the sheet 21 itself.

  Then, after the sheet 21 discharged to the fixing roll 41 side is peeled off from the fixing roll 41 by the peeling claw 53, the first and second sheets provided on the fixing roll 41 side as shown in FIGS. It is conveyed along the second guide ribs 55 and 56. Thereafter, the sheet 21 is transported along the first and second guide ribs 55 and 56 and is moved upward by a guide roller 57 provided on the first guide rib 55 as shown in FIG. It is conveyed.

  As shown in FIG. 5, since the switching gate 35 is disposed at the exit of the fixing device 20, the conveyance direction is changed diagonally upward to the upper right by the switching gate 35, as shown in FIG. As shown, the discharge roll 33 is reached, and the discharge roll 33 is discharged onto a discharge tray 34 provided on the upper portion of the monochrome MFP main body 1.

  By the way, in the fixing device, the stiffness (rigidity) of the paper 21 that has passed through the nip 43 may be extremely reduced depending on the moisture content or size of the paper 21, and the stiffness (rigidity) of the paper 21 is extremely low. When the pressure decreases, the paper 21 sags due to its own weight or the like while being conveyed along the first and second guide ribs 55 and 56 and the guide roller 57 through the nip portion 43, and the paper 21 is wavy. May occur.

  However, in the fixing device 20 according to this embodiment, the peeling member 58 that supports the back side of the sheet 21 so as to face the first and second guide ribs 55 and 56 and the guide roller 57 is the first guide. The rib 55 and the guide roller 57 are disposed in the vicinity. Therefore, the back side of the paper 21 is peeled off even in a situation where the stiffness (rigidity) of the paper 21 is extremely lowered due to the moisture content, size, etc. of the paper 21 and the paper 21 is sag due to its own weight. It will be supported by the member 58. Therefore, in the fixing device 20, it is possible to prevent or suppress the occurrence of undulation in the paper 21 due to its own weight or the like.

  On the other hand, when the peeling member 58 that supports the back side of the paper 21 is not provided, as shown in FIG. 7, when the stiffness (rigidity) of the paper 21 is reduced, the first guide rib 55 side Thus, the sheet 21 discharged to the bottom is lifted from the guide roller 57 provided on the first guide rib 55, and the sheet 21 is wavy due to its own weight or the like.

Experimental Example Next, the present inventors modified the monochrome multifunction device DocuCenter 155/185 manufactured by Fuji Xerox Co., Ltd., and prototyped an image forming apparatus as shown in FIGS. 1 and 2 in a high temperature and high humidity environment. The paper was left in a packaged state for a long time, and A3 size (P-paper manufactured by Fuji Xerox Co., Ltd.) was fixed immediately after opening, and an experiment was conducted to check the occurrence of ripples on the paper.

  At that time, the guide roller 57 was used in a state where the gap T of the transport passage 62 was changed by using various guide rollers 57 having different diameters.

  FIG. 8 shows the results of the above experimental example.

  As can be seen from FIG. 8, by setting the gap T of the conveyance path 62 to 1.3 mm or less, the number of waves generated on the paper 21 can be suppressed or prevented to 2 or less to about 0. It can be seen that, in actual use, the number of waves generated on the paper 21 can be brought to a level with no problem.

  Further, if the gap T of the conveyance path 62 is set to less than 0.2 mm, the conveyance path 62 through which the paper 21 passes becomes too narrow and a jam may occur in the paper 21, and is set to 0.2 mm or more. It is desirable to do.

  On the other hand, when the gap T of the transport passage 62 is set to 1.4 mm or more, the number of undulations generated on the paper 21 is four or more, and the allowable range is less than four. It is not possible and not desirable.

20: fixing device, 40: fixing device housing, 41: fixing roll, 42: pressure roll, 43: nip portion, 55: first guide rib, 56: second guide rib, 57: guide roller.

Claims (3)

The paper for carrying the unfixed toner image is passed through a nip portion formed between the heating rotator and the pressure rotator by bringing the heating rotator and the pressure rotator into pressure contact with each other. In the fixing device in which the unfixed toner image is fixed on the top, and the discharge direction of the paper in the nip portion is set substantially vertically upward.
A guide member provided on the side of the heating rotator on the downstream side where the paper has passed through the nip portion, and provided with a conveyance roller at a position protruding from the rib and the pressure rotator side of the rib;
Among the guide members, a counter member is provided at a position facing the position where the transport roller is provided, and forms a transport path between the guide member and the guide member,
The rib comprises a plurality of first guide ribs and second guide ribs arranged along the axial direction of the heating rotator,
The second guide rib is provided with a lower height in the direction toward the opposing member than the first guide rib at the position of the upstream end portion of the transport roller in the transport direction of the paper , In addition, the fixing device is disposed at a position farther from the transport roller than the first guide rib in the axial direction of the heating rotating body.   The support member also serves as a cover that covers the outlet side of the pressurizing rotator of the nip portion, and a peeling claw that peels the paper from the tip of the nip portion on the outlet side of the pressurizing rotary member 2. The fixing device according to claim 1, further comprising a portion, and being pivotally supported so as to open an outlet side of the pressing rotary body of the nip portion.   An image forming apparatus comprising the fixing device according to claim 1.

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