JP2017223746A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can suppress the generation of streak-like wrinkles on a recording medium after the passage through a fixing nip, and an image forming apparatus.SOLUTION: A fixing device comprises a separation member, such as a separation auxiliary member 48 that is arranged at a position not in contact with a pressure member, such as a pressure roller 45 with a fixing belt 43 therebetween on the downstream side in the direction of movement of a recording medium with respect to a nip forming member, such as a fixing roller 41, and is in contact with an inner peripheral surface of the fixing belt 43 to increase the curvature of the fixing belt 43. A holding member 49 in contact with the inner peripheral surface of the fixing belt 43 to hold the fixing belt 43 is arranged from the nip forming member to the separation member in the direction of movement of the recording medium. The fixing device further includes contact/separation means, such as a pressuring/depressuring mechanism that brings the pressure member into contact with or separates the pressure member from the fixing belt 43.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device and an image forming apparatus.

  2. Description of the Related Art Image forming apparatuses such as copying machines, facsimile machines, and printers using electrophotographic technology are provided with a fixing device that fixes an unfixed toner image formed on a recording medium such as paper on the recording medium. As this fixing device, for example, a fixing device that is heated by a heating means such as a heater and includes a fixing belt stretched around a plurality of stretching members is known. A nip such as a fixing nip is formed by the fixing belt and a pressure member such as a pressure roller that rotates while being pressed against a nip forming member such as a fixing roller, which is one of the stretching members, via the fixing belt. A recording medium carrying a toner image is passed through the nip to fix the toner image on the recording medium.

  Japanese Patent Application Laid-Open No. 2004-151858 describes a fixing device provided with a separation mechanism for separating the recording medium that has passed through the nip from the fixing belt as the fixing device. Specifically, it has a separation claw that faces the outer peripheral surface of the fixing belt with a predetermined gap on the downstream side of the nip in the recording medium conveyance direction. In addition, a separation member that abuts on the inner peripheral surface of the fixing belt and increases the curvature of the portion of the fixing belt facing the separation claw (decreasing the curvature radius) is provided. The separation member is disposed at a position away from the pressure member via the fixing belt.

  However, the fixing device described in Patent Document 1 has a problem that streaks are formed on the recording medium after passing through the fixing nip.

  In order to solve the above problems, the present invention provides an endless fixing belt that is stretched around a plurality of stretching members, a nip forming member that is one of the plurality of stretching members, and the nip forming member. A pressure member that forms a nip through the fixing belt opposite to the fixing belt, a heat source that heats the fixing belt, and a downstream side of the nip forming member in the moving direction of the fixing belt through the fixing belt. A fixing device that is disposed at a position spaced apart from the pressure member and includes a separation member that stretches the fixing belt; and a portion between the outlet of the nip and the upstream end of the separation member in the movement direction of the fixing belt. And a pressing member that presses the fixing belt in contact with an inner peripheral surface of the fixing belt, and contact / separation means that contacts and separates the pressing member with respect to the fixing belt. Ah .

  According to the present invention, it is possible to suppress the occurrence of streak-like wrinkles on the recording medium after passing through the fixing nip.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is a schematic sectional view of a fixing device. FIG. 6 is an enlarged view showing the vicinity of a fixing nip outlet of a conventional fixing device. The figure which shows an example of the recording sheet which the wrinkle-like wrinkle produced. FIG. 3 is an enlarged view showing the vicinity of a fixing nip outlet of the fixing device of the present embodiment. The figure explaining the modification of a pressing member. The figure explaining the 2nd modification of a pressing member. The figure explaining the 3rd modification of a pressing member. The figure explaining the 4th modification of a pressing member. A perspective view explaining a moving mechanism The figure which shows the state which has located the pressing member in the contact position. The figure which shows the state which put the pressing member in the cancellation | release position. The schematic block diagram which shows a pressure depressurization mechanism. 6 is a graph showing the temperature of a fixing belt and the temperature of a pressure roller when a printing operation is performed immediately after power-on in the related art. 6 is a graph showing a fixing belt temperature and a pressure roller temperature when a printing operation is performed after waiting for a long period of time in the past. 6 is a graph showing the temperature of the fixing belt and the temperature of the pressure roller when a printing operation is performed immediately after the power is turned on in the present embodiment. 6 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when a printing operation is performed after waiting for a long time in the present embodiment. The flowchart of the pre-heating operation availability.

An embodiment of an electrophotographic printer will be described below as an image forming apparatus to which the present invention is applied.
FIG. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. In this figure, the printer includes four image forming units 2Y, 2M, 2C, and 2K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. ing. The four image forming units 2Y, 2M, 2C, and 2K have a so-called tandem configuration in which an intermediate transfer belt 61 as an image bearing belt described later is arranged along the endless movement direction.

  The printer includes a paper feed path 30, a pre-transfer conveyance path 31, a manual paper feed path 32, a manual feed tray 33, a registration roller pair 34, a conveyance belt unit 35, a fixing device 40, a conveyance switching device 50, a paper discharge path 51, a discharge path 51, and a paper discharge path 51. A paper roller pair 52, a paper discharge tray 53, and the like are also provided. Further, two optical writing units 1YM and 1CK, a primary transfer unit 60, a secondary transfer unit 78, a first paper feed cassette 101, a second paper feed cassette 102, and the like are also provided.

  The image forming units 2Y, 2M, 2C, and 2K have drum-shaped photoconductors 3Y, 3M, 3C, and 3K that are latent image carriers. Each of the first paper feed cassette 101 and the second paper feed cassette 102 accommodates a bundle of recording sheets P therein. Then, the uppermost recording sheet P in the sheet bundle is sent out toward the paper feed path 30 by the rotational driving of the feed rollers 101 a and 102 a.

  A manual feed tray 33 is disposed on the side surface of the printer housing so as to be openable and closable with respect to the housing, and a sheet bundle is manually fed to the upper surface of the tray while being opened with respect to the housing. The uppermost recording sheet P in the manually fed sheet bundle is sent out toward the paper feed path 30 by the feed roller of the manual feed tray 33.

  The two optical writing units 1YM and 1CK each have a laser diode, a polygon mirror, various lenses, and the like. Then, based on image information read by a scanner outside the printer or image information sent from a personal computer, the laser diode is driven, and the photoreceptors 3Y, 3M of the image forming units 2Y, 2M, 2C, 2K. , 3C, 3K are optically scanned. Specifically, the photoreceptors 3Y, 3M, 3C, and 3K of the image forming units 2Y, 2M, 2C, and 2K are rotationally driven in the counterclockwise direction in the drawing by the driving unit. The optical writing unit 1YM performs an optical scanning process by irradiating the driven photoconductors 3Y and 3M while deflecting laser light in the direction of the rotation axis. Thereby, electrostatic latent images based on the Y and M image information are formed on the photoreceptors 3Y and 3M. Further, the optical writing unit 1CK performs an optical scanning process by irradiating the driven photoconductors 3C and 3K while deflecting laser light in the rotation axis direction. Thereby, electrostatic latent images based on the C and K image information are formed on the photoreceptors 3C and 3K.

  Each of the image forming units 2Y, 2M, 2C, and 2K serves as a common support using the photosensitive members 3Y, 3M, 3C, and 3K as latent image carriers and various devices arranged around the photosensitive members 3Y, 3M, 3C, and 3K as one unit. In a supported state, they are integrally attached to and detached from the printer casing. These image forming units have the same configuration except that the colors of the toners used are different from each other. Taking the image forming unit 2Y for Y as an example, this has a developing device 4Y for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image in addition to the photoreceptor 3Y. Further, the transfer residual toner attached to the surface of the photoreceptor 3Y after passing through a primary transfer nip for Y, which will be described later, or a charging device 5Y that uniformly charges the surface of the photoreceptor 3Y that is driven to rotate. A drum cleaning device 6Y is also provided.

  The photoreceptor 3Y has a drum shape in which a photosensitive layer is formed on a base tube made of aluminum or the like by applying a photosensitive organic photosensitive material. An endless belt-shaped belt may be used instead of the drum-shaped belt.

  The developing device 4Y includes a rotatable developing sleeve made of a non-magnetic pipe, and a magnet roller disposed in the hollow so as not to rotate with the sleeve. Then, an electrostatic latent image on the photoreceptor 3Y is obtained by a two-component developer (hereinafter simply referred to as a developer) containing a magnetic carrier carried on the surface of the developing sleeve by the magnetic force generated by the magnet roller and non-magnetic Y toner. Develop. At this time, the developing potential is applied to the Y toner facing the electrostatic latent image on the developing sleeve by the potential difference between the developing bias applied to the developing sleeve and the electrostatic latent image on the photoreceptor 3Y. On the other hand, the background potential is applied to the Y toner facing the background portion of the photoreceptor 3Y on the developing sleeve due to the potential difference between the developing bias and the background portion of the photoreceptor 3Y. Due to these potentials, the Y toner on the developing sleeve is selectively attached only to the electrostatic latent image of the electrostatic latent image and the background portion of the photoreceptor 3Y to develop the electrostatic latent image.

  The Y toner in the Y toner bottle 103Y is appropriately supplied to the developing device 4Y by the Y toner supply device. In the developing device 4Y, a toner concentration sensor is provided as a toner concentration detecting means. The toner concentration sensor detects the magnetic permeability of the developer caused by the carrier that is a magnetic material. The main control unit, which will be described later, controls the driving of the Y toner replenishing device based on the comparison between the output value from the toner density sensor and the output target value from the sensor that is the toner density target value, thereby developing the developer. Is set within a certain range (for example, 4 wt% to 9 wt%). The same toner replenishment control is performed for the developing devices 4M, 4C, and 4K.

  The drum cleaning device 6Y is of a type that scrapes off transfer residual toner from the surface of the photoreceptor 3Y by a polyurethane rubber cleaning blade in contact with the photoreceptor 3Y. Instead of this method, another method may be used. In order to improve the cleaning property, the drum cleaning device 6Y has a rotatable fur brush in contact with the photosensitive member 3Y in addition to the cleaning blade. This fur brush also serves to apply the lubricant to the surface of the photoreceptor 3Y while scraping the lubricant from the solid lubricant to make a fine powder.

  A static elimination lamp is disposed above the photoreceptor 3Y, and this static elimination lamp is also a part of the image forming unit 2Y. The neutralization lamp neutralizes the surface of the photoreceptor 3Y after passing through the drum cleaning device 6Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging device 5Y, and then subjected to optical scanning by the optical writing unit 1YM described above. The charging device 5Y is driven to rotate while receiving a charging bias from a power source. Instead of such a system, a scorotron charger system that performs a non-contact charging process on the photoreceptor 3Y may be employed.

  The image forming unit 2Y for Y has been described, but the image forming units 2M, 2C, and 2K for M, C, and K have the same configuration as the image forming unit 2Y for Y.

  A primary transfer unit 60 is disposed below the four image forming units 2Y, 2M, 2C, and 2K. The primary transfer unit 60 is driven by the rotational drive of any one of the rollers while bringing the intermediate transfer belt 61, which is an image carrier stretched by a plurality of rollers, into contact with the photoreceptors 3Y, 3M, 3C, 3K. It is moved endlessly in the clockwise direction in the figure. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 3Y, 3M, 3C, and 3K abut on the intermediate transfer belt 61 are formed.

  In the vicinity of the primary transfer nips for Y, M, C, and K, the intermediate transfer belt 61 is moved to the photoreceptors 3Y, 3M, 3C, and 3K by primary transfer rollers 62Y, 62M, 62C, and 62K disposed inside the belt loop. It is pushing toward. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, and 62K by a primary transfer power source. As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. Yes.

  In the figure, on the front surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement in the clockwise direction, the Y toner image, the M toner image, and the C The toner image and the K toner image are sequentially superimposed and primarily transferred. By this superimposing primary transfer, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 61.

  A secondary transfer unit 78 is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer unit 78 includes an endless secondary transfer belt 77, a ground driven roller 72, a driving roller, a secondary belt cleaning device 76, a toner adhesion amount detection sensor 64, and the like. The secondary transfer belt 77 is endlessly moved in the counterclockwise direction in the figure as the driving roller rotates while being tensioned by the ground driven roller 72 disposed inside the loop and the driving roller. .

  The secondary transfer belt 77 of the secondary transfer unit 78 has its place where the belt is driven with respect to the ground driven roller 72 abutted with the place where the intermediate transfer belt 61 of the primary transfer unit 60 is applied to the secondary transfer bias roller 68. A secondary transfer nip is formed. A secondary transfer bias output from a secondary transfer power source, which will be described later, is applied to a secondary transfer bias roller 68 inside the loop of the intermediate transfer belt 61, whereas a ground driven roller inside the loop of the secondary transfer belt 77. 72 is grounded. As a result, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 34 is disposed on the right side of the secondary transfer nip in the drawing, and the recording sheet P sandwiched between the rollers can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 61. Send to the secondary transfer nip. In the secondary transfer nip, the four-color toner image on the intermediate transfer belt 61 is secondarily transferred onto the recording sheet P under the influence of the secondary transfer electric field and the nip pressure, and becomes a full color image combined with the white color of the recording sheet P.

  The secondary transfer residual toner adheres to the front surface of the intermediate transfer belt 61 after passing through the secondary transfer nip. The secondary transfer residual toner is removed from the surface of the intermediate transfer belt 61 by the primary belt cleaning device 75 of the primary transfer unit 60.

  The recording sheet P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and the secondary transfer belt 77 and transferred to the transport belt unit 35. The conveyor belt unit 35 moves the endless conveyor belt 36 endlessly in the counterclockwise direction in the figure by the rotational driving of the driving roller 37 while being stretched by the driving roller 37 and the driven roller 38. Then, the recording sheet P delivered from the secondary transfer nip is conveyed along with the endless movement of the belt while being held on the belt upper tension surface, and delivered to the fixing device 40.

  The recording sheet P sent into the fixing device 40 is sandwiched between fixing nips by contact between an endless fixing belt and a pressure roller. Then, the toner image is fixed on the surface by the action of pressure or heating.

  The recording sheet P on which the toner image is transferred to the first surface at the secondary transfer nip and the toner image is fixed on the first surface by the fixing device 40 is sent out toward the conveyance switching device 50. In this printer, the transfer switching device 50, the retransmission path 54, the switchback path 55, the post-switchback transfer path 56, and the like constitute a retransmission means. The conveyance switching device 50 switches the subsequent conveyance destination of the recording sheet P received from the fixing device 40 between the paper discharge path 51 and the retransmission path 54.

  Specifically, when a single-sided mode print job for forming an image only on the first side of the recording sheet P is executed, the conveyance destination is set to the paper discharge path 51. As a result, the recording sheet P on which an image is formed only on the first surface is sent to the discharge roller pair 52 via the discharge path 51 and discharged onto the discharge tray 53 outside the apparatus. Further, when executing a print job in a duplex mode in which images are formed on both sides of the recording sheet P, when the recording sheet P having images fixed on both sides is received from the fixing device 40, the transport destination is also set. The paper discharge path 51 is set. As a result, the recording sheet P with images formed on both sides is discharged onto a discharge tray 53 outside the apparatus.

  On the other hand, when a recording sheet P having an image fixed only on the first side is received from the fixing device 40 during execution of the double-side mode print job, the transport destination is set to the retransmission path 54. A switchback path 55 is connected to the retransmission path 54, and the recording sheet P sent to the retransmission path 54 enters the switchback path 55. When the entire area in the conveyance direction of the recording sheet P enters the switchback path 55, the conveyance direction of the recording sheet P is reversed and the recording sheet P is switched back. In addition to the retransmission path 54, a post-switchback conveyance path 56 is connected to the switchback path 55, and the recording sheet P that has been switched back enters the post-switchback conveyance path 56. At this time, the upper and lower sides of the recording sheet P are reversed. Then, the recording sheet P that is turned upside down is retransmitted to the secondary transfer nip via the post-switchback conveyance path 56 and the sheet feeding path 30 described above. The recording sheet P on which the toner image is also transferred to the second surface at the secondary transfer nip is fixed on the second surface via the fixing device 40, and then the conveyance switching device 50 and the paper discharge path. The paper is discharged onto a paper discharge tray 53 via 51 and a paper discharge roller pair 52.

FIG. 2 is a schematic sectional view of the fixing device 40.
The fixing device 40 according to the present embodiment is a belt fixing method, and includes a fixing belt 43 and a pressure roller 45 as a pressure member that is rotatably provided facing the fixing belt 43. The fixing belt 43 is stretched by a fixing roller 41, a heating roller 42, a tension roller 47, and the like. The fixing roller 41, the pressure roller 45, and the heating roller 42 are pivotally supported so as to be rotatable in the longitudinal direction of the casing of the fixing device 40.

  The fixing belt 43 is an endless belt formed of a PI (polyimide) layer, and has an outer peripheral surface coated with an offset preventing agent such as a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) film. . The fixing roller 41 and the pressure roller 45 are rubber rollers. When the pressure roller 45 is pressed toward the center of the fixing roller 41 through the fixing belt 43, the pressure roller 45 and the fixing belt 43 are interposed. Thus, the fixing nip N1 is formed. The tension roller 47 applies tension to the fixing belt 43 and is formed of a cylindrical aluminum tube.

  The pressure roller 45 is provided so as to be able to come into contact with and separate from the fixing belt 43. When the paper is passed (fixed), the pressure roller 45 presses the fixing belt 43 and fixes it by a pressure depressurization mechanism. A nip N1 is formed. On the other hand, during standby (non-fixing), the pressure is released and the pressure roller 45 is separated from the fixing belt 43.

  The heating roller 42 is a hollow roller made of aluminum or iron and has a heat source 44 including a heater such as a halogen heater inside. The heat source 44 may be an induction heating mechanism. A thermistor 11 that is a temperature sensor element is disposed at a position that opposes the heating roller 42 and the fixing belt 43. Based on the temperature detection of the thermistor 11, the heat source 44 is controlled to reach the set temperature. Yes.

  The fixing roller 41 is connected to driving means constituted by a motor, a reduction gear train, and the like, and is driven to rotate in the direction of the arrow in the figure by this driving means. Due to the rotation of the fixing roller, the pressure roller 45 and the fixing belt 43 that are in pressure contact with the fixing roller 41 rotate at the same speed in the direction of the arrow shown in FIG. The rotation of the fixing roller 41 causes the pressure roller 45 and the fixing belt 43 that are in pressure contact with the fixing roller 41 to rotate at the same speed in the direction of the arrow shown in the drawing. Alternatively, the pressure roller 45 may be rotationally driven by a driving unit, and the fixing belt 43 and the fixing roller 41 that are in pressure contact with the pressure roller 45 may be driven to rotate.

  Further, between the tension roller 47 and the heating roller 42, a polishing device 10 for polishing the outer peripheral surface of the fixing belt 43 is disposed. The polishing apparatus 10 includes a polishing roller 10 a that contacts the outer peripheral surface of the fixing belt 43, and a counter roller 10 b that faces the polishing roller 10 a with the fixing belt 43 interposed therebetween. The polishing roller 10a is pressed against the fixing belt 43 by a pressure spring 10c. The polishing roller 10a and the counter roller 10b are provided so as to be able to contact and separate from the fixing belt 43. When it is not necessary to polish the fixing belt 43, the polishing roller 10a and the counter roller 10b are separated from the fixing belt 43. . Thereby, the life of the fixing belt 43 can be increased.

  When the recording sheet P passes through the fixing nip N1, the surface of the fixing belt 43 is worn by the cutting burr of the recording sheet P. Therefore, in the fixing belt 43, the wear at the portion corresponding to the width of the recording sheet P that is frequently used differs from the wear at the outer portion. As a result, there is a problem that when an image is output using a recording sheet having a width wider than that of a frequently used recording sheet, a worn portion on the fixing belt appears in the image. In the present embodiment, the polishing apparatus 10 is provided and the outer peripheral surface of the fixing belt 43 is polished by the polishing roller 10a, so that the wear of the fixing belt 43 is made uniform in the width direction, and the occurrence of the above problem is suppressed. Yes.

  A separation assisting member 48 as a separation member is provided inside the fixing belt 43 and downstream of the fixing nip N1 in the movement direction of the fixing belt surface. The separation assisting member 48 is a block member formed of a metal such as SUS or a rigid body such as a resin and having a substantially arc-shaped cross section. The separation assisting member 48 contacts the inner peripheral surface of the fixing belt 43 on the downstream side of the fixing nip N1 in the moving direction of the fixing belt, stretches the fixing belt 43 in a direction away from the fixing roller 41, and fixes the fixing belt 43. The direction of travel is changing rapidly. By abruptly changing the advancing direction of the fixing belt 43, the curvature of the fixing belt 43 can be increased (the radius of curvature is decreased), and the recording sheet P can be separated by this curvature, thereby improving the separation performance. it can.

  In the present embodiment, since the contact surface of the separation assisting member 48 with the fixing belt 43 has an arc shape, the fixing belt 43 can be moved smoothly along the arc-shaped contact surface.

  In addition, the surface of the separation assisting member 48 facing the fixing roller 41 is also formed in an arc shape along the surface of the fixing roller 41. Thereby, the separation assisting member 48 can be disposed in a narrow space without contacting the fixing roller 41.

  The separation assisting member 48 is provided over the entire axial direction of the fixing roller 41, and both ends thereof are fixed to the side surface of the casing of the fixing device 40. Further, the separation assisting member 48 is disposed at a position where it does not come into contact with the pressure roller 45, and is configured to prevent the durability of the pressure roller 45 and the motor torque from increasing.

  A separation plate 46 as a second separation member is disposed so as to face the separation assisting member 48 with the fixing belt 43 interposed therebetween. The front end of the separation plate 46 is disposed so as to have a minute gap with the fixing belt 43. The tip of the separation plate 46 is tapered and has a tapered shape. In this embodiment, a pressing member 49 is provided between the fixing nip and the separation assisting member 48 so as to contact the inner peripheral surface of the fixing belt 43 and to contact the fixing belt 43 to the pressure roller 45. Yes.

Hereinafter, the basic operation of the fixing device 40 of the present embodiment will be described.
The recording sheet P on which the toner image is formed is conveyed to the fixing nip N1, and the toner image on the recording sheet is heated and melted at the fixing nip N1, whereby the toner image is fixed. Thereafter, the recording sheet P is separated from the fixing belt 43 by the separation plate 46 after the nip exit and discharged from the fixing device 40. In order to confirm that the recording sheet P has passed at a predetermined timing, a paper discharge sensor is disposed at the exit of the fixing device 40. Then, when the recording sheet P is not discharged at a predetermined timing, the processing shifts to a jam processing mode such as notifying the user that a paper jam has occurred.

Next, the characteristic part of this embodiment is demonstrated.
FIG. 3 is an enlarged view showing the vicinity of the exit of the fixing nip N1 of the conventional fixing device.
The separation plate 46 mainly separates the recording sheet P from the fixing belt 43 by bringing the leading end of the recording sheet P, which is difficult to separate due to the curvature of the fixing belt 43, into contact with the leading end of the separation plate 46. It takes on the function. Further, when the tip of the separation plate 46 comes into contact with the fixing belt 43, the fixing belt 43 is scraped by the separation plate 46 and the life of the fixing belt 43 is reduced. As described above, in order to ensure that the leading end of the separation plate 46 does not contact the fixing belt 43 and the thin paper is surely brought into contact with the separation plate 46, the gap d (about approximately) between the fixing belt 43 and the separation plate 46. 0.2 mm) must be managed with high accuracy.

  Therefore, the separation assisting member 48 facing the separation plate 46 via the fixing belt 43 is formed of a rigid body, and fluctuations in the gap d between the fixing belt 43 and the separation plate 46 due to deformation of the separation assisting member 48 are suppressed. Further, when the rigid separation auxiliary member 48 is configured to contact the pressure roller 45 via the fixing belt 43, the separation auxiliary member 48 is elastically deformed by the pressure of the pressure roller 45 and separated from the fixing belt 43. There is a risk that the gap d with the plate 46 will fluctuate. There is also a problem that the durability of the pressure roller 45 is lowered. As shown in Table 1 below, when the separation assisting member 48 is retracted 2 mm from the pressure roller 45, the lifespan of the pressure roller 45 and the fixing belt 43 can be increased approximately twice.

However, by providing the separation assisting member 48 at a position separated from the pressure roller 45, pressure is applied to the recording sheet P attached to the fixing belt 43 from the fixing nip N1 to the separation portion where the leading end of the separation plate 46 faces. Will not be applied. When the recording sheet P is heated in the fixing nip N1, moisture contained in the recording sheet P is vaporized to become water vapor. The fixing nip N1 is pressurized with a strong surface pressure of about 40 [N / cm ² ], so that no water vapor is released from the recording sheet P. However, since there is no pressure on the recording sheet P that has exited the fixing nip N1, water vapor is released from the recording sheet P.

  As shown in FIG. 3, the gap between the fixing belt 43 and the pressure roller 45 at the fixing nip exit is narrower than when the fixing belt 43 is wound around the fixing roller 41. Therefore, heat is easily generated in the narrow region, the temperature of the recording sheet does not decrease, and a lot of water vapor is released. The water vapor is mainly released from the surface (back surface) of the recording sheet P facing the pressure roller 45. In addition, the recording sheet that has exited the fixing nip N1 is conveyed to a separation unit that is opposed to the front end of the separation plate 46 while being attached to the fixing belt 43. Since the non-image portion of the recording sheet P is lower than the image portion on which the toner image is formed, a gap is formed between the fixing belt 43 and the non-image portion, and water vapor is also released into this gap. Is done. When the water vapor is released, the fibers of the recording sheet P are dried and the undulation is generated.

  Further, water vapor mainly released from the surface (back surface) of the recording sheet P facing the pressure roller 45 stays in this narrow gap, and is again absorbed by the recording sheet and wets the recording sheet. Further, the water vapor released between the fixing belt 43 and the non-image portion remains in the gap, and is absorbed again by the recording sheet and wets the recording sheet. When the recording sheet P gets wet, the fibers extend and the recording sheet is wavy.

  As described above, in the conventional configuration shown in FIG. 3, during the period from when the recording sheet P is conveyed from the fixing nip N <b> 1 to the separation portion where the leading edge of the separation plate 46 faces, The fibers of the recording sheet P are expanded and contracted by wetting due to absorption, and the recording sheet P is wavy during this time. Then, the wrinkles S are generated on the recording sheet P as shown in FIG.

  Therefore, in the present embodiment, a pressing member 49 that contacts the inner peripheral surface of the fixing belt 43 between the fixing roller 41 and the separation assisting member 48 and presses the fixing belt is provided.

FIG. 5 is an enlarged view showing the vicinity of the exit of the fixing nip N1 of the fixing device of the present embodiment.
In this embodiment, a pressing member 49 is disposed between the fixing roller 41 and the separation assisting member 48 inside the fixing belt 43. The pressing member 49 is a plate-like member having a thickness of about 0.2 mm formed of a metal such as SUS. One end is supported by the support plate 24, and extends from the support plate 24 to the pressure roller side. Thus, the plate spring is bent toward the fixing nip N1. In this way, by bending in the middle, the pressing portion 49b that makes contact with the inner peripheral surface of the fixing belt 43 and makes the fixing belt 43 contact with the pressure roller 45, and the surface movement direction of the fixing belt 43 rather than the pressing portion 49b. A bent peeling portion 49a is formed on the downstream side.

  The pressing member 49 is provided so as to bite 0.4 mm into the pressure roller 45 and is installed so as to be elastically deformed and press the fixing belt 43 against the pressure roller 45 with a predetermined load. As a result, a post nip portion N2 is formed by the pressing member 49 downstream of the fixing nip N1 in the recording sheet conveyance direction.

  Further, the shape of the pressing portion 49 b of the pressing member 49 is made to conform to the surface shape of the pressure roller 45, and the fixing belt 43 is uniformly pressed against the pressure roller 45. Further, at the outlet of the post nip portion N2, the moving direction of the fixing belt 43 is suddenly changed along the bending of the peeling portion 49a of the pressing member 49. Thereby, the curvature of the fixing belt 43 at the exit of the post nip portion N2 can be increased (the radius of curvature is decreased). In the present embodiment, the peeling portion 49a of the pressing member 49 is configured so that the radius of curvature of the fixing belt 43 at the exit of the post nip portion N2 is 6 mm.

  In the present embodiment, the recording sheet P that has exited the fixing nip N1 is conveyed while receiving pressure at the post nip portion N2. Since the pressure at the post nip portion N2 is lower than that at the fixing nip N1, water vapor is discharged from the recording sheet at the post nip portion N2. By releasing water vapor from such a recording medium, the fiber of the paper dries and shrinks, but the recording sheet is pressed by the pressing roller 49 by the pressing member 49 via the fixing belt 43. The fibers are not shrunk and the undulation of the recording sheet due to the release of water vapor is suppressed.

  Further, the water vapor released from the post nip portion N2 remains as bubbles between the recording sheet P and the fixing belt 43, and is absorbed again by the recording sheet P to wet the recording sheet P. However, during the absorption of water vapor, the recording sheet P is pressed by the pressing roller 45 by the pressing member 49 via the fixing belt 43. Accordingly, paper fibers are wetted by the absorption of water vapor and the paper fibers tend to stretch. However, since the recording sheet P is pressed by the pressure roller 45 by the pressing member 49 via the fixing belt 43, the fibers can stretch. Accordingly, the undulation of the recording sheet P due to the absorption of water vapor is suppressed.

  In this way, by suppressing the undulation of the recording sheet, when the recording sheet after passing through the fixing nip is nipped and conveyed by the pair of paper discharge rollers, the recording sheet is as shown in FIG. Generation of streak-like wrinkles can be suppressed.

  In this embodiment, the recording sheet may be pressed so that the fibers of the recording sheet do not expand or contract due to the release or absorption of water vapor, and the pressure may be sufficiently lower than the pressure in the fixing nip. In the present embodiment, the pressure of the post nip portion N2 may be about 5 [N]. Further, the waviness of the recording sheet may be suppressed to such an extent that no streak-like wrinkles as shown in FIG. Therefore, the fixing belt 43 may be pressed by the pressing member 49 so as to be close to the pressure roller, and there may be a slight gap between the fixing belt 43 and the pressure roller 45. In this case, the recording sheet P that has exited the nip N1 hits the pressure roller 45 and the fixing belt when the undulation is caused by the release or absorption of water vapor, and further undulation is suppressed. Therefore, even if there is a slight gap between the fixing belt 43 and the pressure roller 45 by pressing the fixing belt 43 with the pressing member 49 so as to be close to the pressure roller, the undulation can be suppressed. Further, when the fixing belt 43 is not brought into contact with the pressure roller 45 by the pressing member 49, if the gap described above is the thickness of the recording sheet P, the recording sheet exiting the fixing nip N1 is pressed against the fixing belt. Since the sheet is conveyed while being sandwiched between the rollers, it is possible to more effectively suppress the undulation of the recording sheet.

  Further, at the exit of the post nip portion N2, the fixing belt 43 is rapidly changed in the moving direction along the bending of the peeling portion 49a of the pressing member 49. As a result, the recording sheet P is separated from the fixing belt 43 by the curvature separation at the exit of the post nip portion N2. In addition, the recording sheet P having a weak stiffness such as thin paper and the recording sheet P on which an image is formed up to the leading end portion of the recording sheet P are not separated in curvature at the exit of the post nip portion N2, and are attached to the fixing belt 43. It is conveyed to the separation unit. However, the water vapor generated in the fixing nip N1 has already been released in the post nip portion N2. Therefore, there is almost no water vapor released until it moves to the separation part. Further, the gap between the fixing belt 43 and the pressure roller 45 at the exit of the post nip portion N2 is wider than that in FIG. Accordingly, the heat is not released near the exit of the post nip portion N2, but is released to the surroundings. Therefore, the recording sheet is heated by the heat in the vicinity of the outlet of the post nip portion N2 until it moves to the separation portion, and almost no water vapor is released. Therefore, there is almost no undulation caused by drying due to the discharge of water vapor between the post-nip portion N2 and the separation portion.

  Further, water vapor that has not been reabsorbed by the recording sheet at the post nip portion N2 is discharged to the periphery at the outlet of the post nip portion N2. However, since the gap between the fixing belt 43 and the pressure roller 45 at the exit of the post nip portion N2 is wider than that in FIG. 3, it does not stay near the exit of the post nip portion N2. Therefore, reabsorption of water vapor hardly occurs between the post nip portion N2 and the separation portion. Therefore, there is almost no undulation due to wetting due to reabsorption of water vapor between the post-nip portion N2 and the separation portion.

  Further, when the fixing belt 43 is pressed by the pressing member 49, a region where the fixing belt 43 is not stretched and is in a free state is between the outlet of the post nip portion N2 and the separation assisting member 48. Compared to FIG. The free region can be narrowed.

  Further, by making the pressing member 49 a plate-like member, the heat capacity can be reduced and the temperature loss due to the pressing member 49 can be suppressed as compared with the case where the pressing member 49 is a block-like member. As a result, the waiting time until the temperature of the fixing belt 43 is raised to a necessary temperature can be shortened as compared with the case where the pressing member 49 is a block-shaped member. Moreover, compared with the case where the pressing member 49 is a block-shaped member, an increase in power consumption can be suppressed and energy saving can be achieved.

  Also, by using the pressing member 49 as an elastic member, it is possible to make it easier to follow the pressure roller 45 than when the pressing member 49 is a rigid body. Accordingly, the fixing belt can be pressed uniformly against the pressure roller with a predetermined load.

  In the present embodiment, the recording sheet P has three separation portions that can be separated from the fixing belt 43. That is, there are three portions: the curvature portion of the fixing belt at the exit of the post nip portion N2 formed by the peeling portion 49a of the pressing member 49, the curvature portion of the fixing belt 43 formed by the separation auxiliary member, and the tip of the separation plate 46. . Thereby, the recording sheet P can be reliably separated from the fixing belt 43, and the occurrence of paper jam can be suppressed satisfactorily.

  In addition, the configuration of the pressing member 49 is not limited to the above-described configuration, and for example, as illustrated in FIG. 6, a portion of the pressing member 49 that extends from the support plate 24 toward the pressure roller may be bent. With such a configuration, the pressing member 49 is easily elastically deformed, the followability to the pressure roller 45 can be increased, and the durability of the pressure roller 45 can be increased.

  In addition, as shown in FIG. 7, the peeling portion 49 a may have a shape protruding toward the downstream side in the conveyance direction of the recording sheet P. With this configuration, the curvature of the fixing belt 43 at the exit of the post nip portion N2 formed by the peeling portion 49a can be increased (the radius of curvature is decreased), and the separation property of the recording sheet P at the exit of the post nip portion N2 can be improved. it can.

  Further, as shown in FIGS. 8 and 9, an opening 49 c may be provided in the pressing portion 49 b of the pressing member 49. With this configuration, the heat capacity of the pressing member 49 can be further reduced, the waiting time until the fixing belt 43 is heated to a necessary temperature can be shortened, and energy saving can be achieved. Can do.

  In addition, it is preferable to arrange the tip of the pressing portion 49 b of the pressing member 49 as close to the fixing roller 41 as possible. As shown in FIG. 5, this is pressed by the member from the inside between the post nip portion N2 pressed against the pressure roller 45 by the pressing portion 49b of the pressing member 49 and the fixing nip N1. An unbounded boundary region N2s is generated. The contact pressure to the pressure roller 45 in the boundary region N2s is lower than the contact pressure of the post nip portion N2. As described above, when there is a portion where the contact pressure on the upstream side in the recording sheet conveyance direction is lower than that on the downstream side, the following problem occurs. That is, since the pressure in the boundary region N2s is lower than that of the fixing nip N1, as described above, water vapor is released from the recording sheet, and bubbles are generated between the recording sheet and the fixing belt. Also, air in the toner image leaks due to thermal expansion, and bubbles are generated between the recording sheet and the fixing belt. When the recording sheet enters the post nip portion N2 having a pressure higher than that of the boundary region N2s, the bubbles are pushed out by the pressing force of the pressing member 49 and move on the surface of the recording sheet P. The toner image on the recording sheet is immediately after exiting the fixing nip N1, and is not completely solidified. The toner image is disturbed by the movement of bubbles on the surface of the recording sheet, and an abnormal image such as uneven glossiness is generated.

  Therefore, it is preferable that the fixing belt 43 is pressed to the vicinity of the fixing nip N1 by the pressing member 49 to narrow the boundary region N2s. By narrowing the boundary region N2s, it is possible to suppress the generation of bubbles in the boundary region. For this reason, in this embodiment, the pressing member 49 is configured to extend from the fixed end fixed to the support plate 24 to the pressure roller side and bend to the fixing nip N1 side in the middle. The upstream end in the direction was defined as a free end. As a result, the pressing member 49 can be disposed near the fixing nip N1 as compared with the case where the end on the downstream side in the recording sheet conveyance direction is bent to the side opposite to the fixing nip side and the free end. The boundary region N2s can be narrowed.

  For the same reason, the pressing force of the pressing member 49 to the fixing belt is also uniform or decreased as it goes downstream in the recording sheet conveyance direction, so that the downstream pressing force is higher than the upstream pressing force. It is preferable not to become. Thereby, it is possible to prevent the bubbles of the released water vapor from being pushed out and moved on the surface of the recording sheet at the post nip portion N2. Thereby, it is possible to suppress the occurrence of abnormal images such as uneven gloss in the post nip portion N2.

  Table 2 below shows the results of an evaluation test for the width of the boundary region N2s.

In the evaluation test in Table 2, the surface pressure of the fixing nip N1 is 40 [N / cm ² ], and the surface pressure of the post nip N2 is 2.84 [N / cm ² ] (0.29 [kg / cm ² ]). A solid image was created on A3 paper, and the created image was visually evaluated for uneven gloss. Each surface pressure was measured using ISCAN. The case where gloss unevenness could not be confirmed was designated as “OK level”, and the case where gloss unevenness was confirmed was designated as “NG level (bad level)”. The surface pressure of the boundary region N2S is an average surface pressure from the fixing nip outlet to the upstream end of the pressing member, and the surface pressure of the post nip N2 is downstream from the upstream end of the pressing member in the fixing belt moving direction. Average surface pressure to the side edge. The surface pressure of the post nip portion N2 is monotonously decreased from the upstream side toward the downstream side in the fixing belt moving direction, and the surface pressure at the upstream end portion of the post nip portion N2 is about 8 [N / cm ² ].

  As can be seen from Table 2, by setting the width of the boundary region N2s to 2.8 mm or less, it is possible to suppress the generation of bubbles in the boundary region N2s, and the surface of the recording sheet is pushed out by the post nip portion N2. It can suppress moving. As a result, it is considered that gloss unevenness did not occur and the gloss unevenness could be set to “OK level”.

  As shown in FIG. 5, it is preferable that the angle θ formed between the tangent line X1 of the pressure roller 45 and the tangent line X2 of the fixing roller 41 at the exit of the fixing nip N1 is 45 ° or more. The applicant conducted an evaluation test when the angle θ was 13 ° and when the angle θ was 45 °. When the angle θ was 13 °, uneven gloss occurred, and the angle θ was 45. When it was °, no gloss unevenness occurred. This is because when the angle θ is 13 °, the distance between the recording sheet P and the fixing roller 41 near the exit of the fixing nip N1 is short. Therefore, the recording sheet P1 exiting the fixing nip N1 is affected by the heat of the fixing roller 41. As a result, the release of water vapor in the boundary region N2s and the thermal expansion of air in the toner image increase, and the bubbles generated in the boundary region N2s tend to increase. As a result, even if the difference between the surface pressure of the boundary region N2s and the surface pressure of the post nip portion N2 is small, the volume of the air bubbles is large, so that the expansion of the air bubbles when being crushed at the post nip portion N2 increases. It is thought that unevenness occurred. On the other hand, by setting the angle θ to 45 ° or more, the influence of the heat of the fixing roller 41 received by the recording sheet P in the boundary region N2s can be reduced. Thereby, in the boundary region N2s, the release of water vapor from the recording sheet P and the thermal expansion of the air in the toner can be suppressed, and the bubble can be prevented from becoming large. As a result, it is considered that the expansion of the bubbles when the bubbles are crushed in the post nip portion is suppressed, and the level of gloss unevenness cannot be confirmed.

  Further, if the fixing belt 43 is always in contact with the pressure member 45 by the pressing member 49, the pressing force of the pressing member 49 is constantly applied to the pressure roller 45 and the fixing belt 43, and the pressure roller 45 and the fixing belt 43 are fixed. There is a possibility that the life of the belt 43 may be reduced. Further, when the fixing belt 43 is brought into contact with the pressure roller 45 by the pressing member 49 at the time of rotational driving other than the paper passing time such as warm-up, the friction between the fixing belt inner peripheral surface and the pressing member 49 is caused. As a result, the fixing belt 43 is worn early. For this reason, it is preferable to release the contact of the pressing member 49 when the sheet is not passed or when a recording sheet such as thick paper or OHP which hardly generates undulation due to the release or absorption of water vapor. In the case of thick paper, the leading end of the thick paper collides with the free end of the pressing member 49, the pressing member 49 bends downstream in the recording sheet conveyance direction, or the fixing belt 43 is placed between the leading end of the thick paper and the free end of the pressing member 49. The fixing belt 43 may be damaged due to being pinched. Therefore, when the recording sheet is thick paper, it is preferable to position the pressing member at the release position.

FIG. 10 is a perspective view illustrating a moving mechanism that moves the pressing member 49 between a contact position where the fixing belt 43 contacts the pressure roller 45 and a release position where the contact is released.
As shown in FIG. 10, the moving mechanism 20 includes a bent support plate 24 to which the pressing member 49 is fixed and supported. The holding member 49 is screwed to the lower end portion of the support plate 24. Arm members 23 and guide members 21 are provided on both ends of the support plate 24 in the axial direction of the fixing roller. A connecting member 22 connected to a driving means constituted by a cam or the like is fixed to the tip of the arm member 23. The connection member 22 is held in an arc-shaped slot that is centered on the rotation center of the fixing roller provided on the side surface of the fixing device casing.

FIG. 11 is a diagram illustrating a state in which the pressing member 49 is positioned at a contact position where the fixing belt 43 contacts the pressure roller. FIG. 12 illustrates the pressing member 49 in the pressure roller of the fixing belt 43. It is a figure which shows the state located in the cancellation | release position which cancel | released contact | abutting to 45. FIG.
As shown in FIGS. 11 and 12, the guide member 21 is attached to the cored bar portion 41 a of the fixing roller 41. When the recording sheet P conveyed to the fixing nip N1 is a recording sheet that is unlikely to be wavy, the pressing member 49 is positioned at the release position. Examples of the recording sheet in which undulation is unlikely to occur include a strong recording sheet such as cardboard and a recording sheet that does not contain moisture such as OHP. In a strong recording sheet such as cardboard, even if the recording sheet is dried by the release of water vapor or absorbs the water vapor, it is difficult for the paper to be wavy due to its own elasticity. A recording sheet that does not contain water such as OHP does not generate water vapor and absorbs water in the first place.

  When the pressing member 49 is positioned at the release position, the connecting member 22 is pushed upward in the figure by the driving means. Then, the moving mechanism 20 rotates in the direction of the arrow A in the figure with the center of the fixing roller being guided by the guide member 21. Then, as shown in FIG. 12, the pressing member 49 moves in a direction away from the pressure roller 45, the pressing member is separated from the fixing belt, and the contact with the pressure roller is released.

  As described above, when the recording sheet conveyed to the fixing nip N1 is a recording sheet such as thick paper or OHP that is unlikely to be undulated, the pressing roller 49 and the fixing belt 43 are disposed by positioning the pressing member 49 at the release position. , And the life of the pressure roller 45 and the fixing belt 43 can be extended. Further, friction between the fixing belt 43 and the pressing member 49 can be reduced. In particular, in the present embodiment, when the pressing member 49 is located at the release position, the pressing member 49 is separated from the inner peripheral surface of the fixing belt 43. For this reason, when it is positioned at the release position, friction between the inner peripheral surface of the fixing belt 43 and the pressing member 49 does not occur, and wear of the fixing belt 43 can be further suppressed.

  In particular, by positioning the pressing member 49 at the release position for thick paper, the free end of the pressing member 49 does not collide with the leading end in the transport direction of the thick paper, and the life of the fixing belt 43 and the pressing member 49 can be extended. .

  Further, even when the recording sheet is not passed through the fixing device, the pressing member 49 is positioned at the release position, so that wear of the pressure roller 45 and the fixing belt 43 can be suppressed. The life of the pressure roller 45 and the fixing belt 43 can be extended. Specifically, at the time of standby, the pressing member 49 is positioned at the release position, for example, the recording member is moved from the release position to the contact position at the timing when the recording sheet passes through the secondary transfer nip, and the recording sheet is moved to the fixing device. Prior to entering, the pressing member is positioned at the contact position. When the recording sheet is discharged from the fixing device, the pressing member 49 is moved to the release position and separated from the fixing belt. As a result, it is possible to reduce the load caused by pressing the fixing member of the fixing belt or the pressure roller.

FIG. 13 is a schematic configuration diagram showing the pressurization / decompression mechanism 201.
As shown in FIG. 13, there is a pressure arm 201a that is in contact with the core of the pressure roller 45 and is rotatably supported at one end side, and a pressure cam 201b that is in contact with the other end side of the pressure arm 201a. doing. Further, the pressure cam 201b is rotated by driving means 201c such as a motor to displace the pressure arm 201a in contact with the pressure cam 201b, and the pressure roller 45 is displaced accordingly. The pressure release / pressure contact state of the roller 45 can be switched. The driving unit 201c is connected to the control unit 202, and the control unit 202 controls the driving of the driving unit 201c. In this embodiment, after the fixing operation is completed, the pressure cam 201b is driven to shift from a pressure contact state where the pressure roller 45 is pressed against the fixing belt 43 to a pressure release state where the pressure roller 45 is separated from the fixing belt 43. To do. As a result, the load on the pressure roller, the fixing belt, and the fixing roller can be reduced, and the durability can be improved.

  In the double-side mode, when the image formed on the second surface of the recording sheet is fixed, the pressure roller is separated from the fixing belt when the fixing operation is completed. That is, in the double-sided mode, after the image is fixed on one side of the recording sheet, the pressure roller is not separated from the fixing belt. In continuous printing, when the fixing operation is performed on the image of the last recording sheet, the pressure roller is separated from the fixing belt when the fixing operation is completed.

  When the pressure roller is separated after the fixing operation, the following problem may occur. That is, there is a problem in that gloss unevenness may occur in an image formed by an image forming operation after the standby mode continues for a long period of time or an image formed by the first image forming operation after the power is turned on. Hereinafter, the problem will be specifically described.

FIG. 14 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when the conventional printing operation is performed immediately after the power is turned on.
As shown in FIG. 14, when the power is turned on, the warm-up operation is started in a state where the pressure roller 45 is separated from the fixing belt 43, and the temperature of the fixing belt 43 rises to a predetermined temperature t1. If an image forming signal is received during the warm-up operation, the operation proceeds to the pre-sheet passing operation without shifting to the standby mode. When the pre-passage operation is started, the fixing belt 43 is heated to a temperature t2 corresponding to the recording sheet to be passed with the pressure roller 45 being separated from the fixing belt 43. When the temperature is raised to the temperature t2, feeding of the recording sheet is started. The pressure roller 45 is brought into contact with the fixing belt 43 at a predetermined timing after the recording sheet starts to be fed until the recording sheet reaches the fixing nip.

  After the power is turned on, the temperature of the pressure roller 45 is lowered. Therefore, even if the pressure roller is brought into contact with the fixing belt at a predetermined timing after the recording sheet feeding is started until the recording sheet reaches the fixing nip, heat is sufficiently stored in the pressure roller 45. Not enough thermal expansion. As a result, the amount of elastic deformation of the pressing member 49 decreases, the tip of the pressing member 49 moves away from the fixing nip N1, and the width of the boundary region N2S exceeds 2.8 mm. As a result, it is considered that uneven gloss occurred in the image formed first after the power was turned on.

FIG. 15 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when a printing operation is performed after waiting for a long period of time in the related art.
Even during standby for a long period of time, as shown in FIG. 15, the temperature of the pressure roller 45 is lowered. Therefore, even if the pressure roller 45 is brought into contact with the fixing belt 43 at a predetermined timing from when the recording sheet feeding is started until it reaches the fixing nip N1, heat is sufficiently accumulated in the pressure roller 45. Not enough thermal expansion. As a result, the amount of elastic deformation of the pressing member 49 decreases, the tip of the pressing member 49 moves away from the fixing nip N1, and the width of the boundary region N2S exceeds 2.8 mm. As a result, gloss unevenness also occurs in an image formed after waiting for a long time.

  Therefore, in the present embodiment, the pressure roller 45 is brought into contact with the fixing belt 43 during the pre-sheet feeding operation so that the pressure roller 45 is preheated.

FIG. 16 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when the printing operation is performed immediately after the power is turned on in the present embodiment.
As shown in FIG. 16, in the warm-up operation, the fixing belt 43 increases the temperature to a predetermined temperature t1. If an image forming signal is received during the warm-up operation, the operation proceeds to the pre-sheet passing operation after the warm-up operation is completed. After shifting to the pre-sheet passing operation, a pre-heating operation for bringing the pressure roller 45 into contact with the fixing belt for a predetermined time is executed. As a result, heat is transferred from the fixing belt 43 to the pressure roller 45, heat is stored in the pressure roller 45, and the pressure roller 45 is thermally expanded. When the predetermined time has elapsed, the pressure roller 45 is separated from the fixing belt 43. In this way, when the predetermined time has elapsed, the pressure roller 45 is separated from the fixing belt 43, and thereafter, the fixing belt 43 is passed through the pressure roller 45 without the heat of the fixing belt 43 being taken away. The temperature can be quickly raised to the temperature t2 corresponding to the recording sheet to be recorded. Thereby, it is possible to suppress an increase in the operation time before passing paper. When the fixing belt 43 rises to a temperature t2 corresponding to the recording sheet to be passed, the recording sheet is fed and the pressure roller 45 is fixed at a predetermined timing before the recording sheet reaches the fixing nip. It abuts on the belt 43.

FIG. 17 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when the printing operation is performed after waiting for a long time in the present embodiment.
When the image forming signal is received, the operation shifts from the standby mode to the pre-passage operation, and the temperature is raised to the temperature t2 corresponding to the recording sheet passing through the fixing belt 43. Also, a preheating operation is executed simultaneously with the pre-sheet passing operation, the pressure roller 45 is brought into contact with the fixing belt 43, and the pressure roller 45 is preheated for a predetermined time. The pressure roller 45 is heated to the temperature t3 by this preheating. Then, after preheating for a predetermined time, the pressure roller 45 is separated from the fixing belt 43, and the pressure roller 45 is brought into contact with the fixing belt 43 again at a predetermined timing after feeding of the recording sheet is started.

  Table 3 below shows the width of the boundary region N2s when the pressure roller 45 is brought into contact with the fixing belt 43 without performing the preheating operation, and the pressure roller 45 that has performed the preheating operation. The width of the boundary region N2s when it is brought into contact with is shown.

  As can be seen from Table 3, it can be seen that the boundary region N2s is shortened by about 0.7 mm compared to the case where the preheating operation is not performed. Thus, by preheating, the pressure roller 45 can be thermally expanded, the amount of pressing against the pressing member 49 is increased, and the amount of elastic deformation of the pressing member 49 can be increased. Thereby, for example, when the preheating operation is not performed, as shown in Table 3, the one having the boundary region N2s of 3 mm can be shortened to 2.3 mm by performing the preheating operation, and uneven gloss is generated. Can be suppressed.

  Further, when the pre-heating operation is not performed, the boundary region N2s is about 0.7 mm from 2.8 mm in which the occurrence of uneven gloss is suppressed in consideration of the case where the pressure roller 45 is not thermally expanded. It is necessary to set it narrowly. However, there is also an advantage that the margin of the boundary region N2s can be increased by performing the preheating operation.

  The preheating operation time (the time during which the pressure roller 45 is brought into contact with the fixing belt 43) may be changed based on the temperature of the pressure roller 45 before the operation before passing paper. For example, when the standby time is short and the pressure roller 45 is sufficiently storing heat, the preheating operation may be shortened or the preheating operation may not be performed. Table 4 below is a table showing an example of the relationship between the temperature before the sheet passing operation of the pressure roller 45 and the preheating operation time.

  In an example shown in Table 4, when the temperature of the pressure roller 45 before the operation before passing the sheet is 30 ° C. or less, the heat accumulation of the pressure roller 45 is small. Therefore, even if the pressure roller 45 is brought into contact with the fixing belt 43 at a predetermined timing after the feeding of the recording sheet is started, the thermal expansion does not sufficiently occur until the recording sheet reaches the fixing nip. Accordingly, when the temperature of the pressure roller 45 before the operation before passing the sheet is 30 ° C. or less, the pressure roller 45 is sufficiently heated in advance by performing a preheating operation for 45 seconds. On the other hand, when the temperature of the pressure roller 45 before the operation before paper passing is 110 ° C., the pressure roller 45 stores heat to some extent, so that the occurrence of the gloss unevenness can be suppressed by the preheating operation for 5 seconds. . Further, when the temperature of the pressure roller 45 before the operation before passing the paper is 120 ° C., the preheating operation is not performed.

  Thus, by changing the preheating time based on the temperature of the pressure roller 45 before the pre-paper operation, occurrence of gloss unevenness can be suppressed. In addition, by minimizing the preheating time, it is possible to suppress the heat of the fixing belt 43 from being taken away by the pressure roller 45 in the operation before passing the sheet, and the fixing belt 43 is adapted to the recording sheet. The time until the temperature is raised can be shortened. Thereby, it is possible to shorten the operation time before passing paper.

  Further, when the temperature of the pressure roller 45 reaches a specified temperature, the preheating operation may be terminated. Even in such a configuration, when the temperature of the pressure roller 45 before the operation before paper passing is high, the preheating operation time is shortened, and the time for the operation before paper passing can be shortened. The preheating time may be determined based on the standby mode time. The longer the standby mode time is, the more the heat of the pressure roller 45 escapes, and the temperature of the pressure roller 45 before the operation before passing the sheet decreases. Therefore, when the standby mode time is long or during the first image forming operation after the power is turned on, the preheating operation time is lengthened to heat the pressure roller firmly. On the other hand, when the standby time is short, the pre-heating operation time is shortened or the pre-heating operation is not performed, so that the pre-paper feeding operation is shortened. Further, by determining the preheating time based on the standby mode time, a temperature sensor for detecting the temperature of the pressure roller 45 becomes unnecessary, and the cost of the apparatus can be reduced.

  In the case where the moving mechanism for moving the pressing member shown in FIGS. 10 and 11 to the release position is not provided, the fixing member 49 is brought into contact with the fixing belt even in the case of thick paper to perform the fixing operation. . In this case, whether or not gloss unevenness occurs depends on the thickness of the recording sheet. Specifically, gloss unevenness is more likely to occur on thick paper than on thin paper, and gloss unevenness is more likely to occur on coated paper than on uncoated paper. Table 5 below is a table showing an example of the relationship between the paper type and the preheating operation.

  As shown in Table 5, for example, when the recording sheet to be passed is uncoated paper, the preheating operation is performed when the recording sheet exceeds the basis weight 220 [gsm]. When the recording sheet to be passed is coated paper, the preheating operation is performed when the recording sheet exceeds the basis weight 163 [gsm].

  This is because, as the paper thickness increases, more moisture is contained, so that water vapor is likely to be released from the recording sheet in the boundary region N2s, and bubbles are likely to be generated in the boundary region N2s. Therefore, gloss unevenness is more likely to occur on thick paper than on thin paper. Also, the coated paper is more likely to disturb the toner image when the bubbles generated in the boundary region N2s move on the surface of the recording sheet P than the uncoated paper, and gloss unevenness is more likely to occur. Accordingly, when the recording sheet to be passed is coated paper and the basis weight exceeds 163 [gsm], the preheating operation is performed to narrow the width of the boundary region N2s. Thereby, generation | occurrence | production of the bubble in boundary region N2s can be suppressed, and it can suppress that gloss unevenness arises. On the other hand, in the case of non-coated paper, the toner image is less likely to be disturbed by air bubbles than in the case of coated paper. Therefore, when the basis weight is a recording sheet exceeding 220 [gsm], a preheating operation is performed. On the other hand, since the thin paper contains a small amount of moisture, bubbles are hardly generated in the boundary region N2s, and uneven gloss is hardly generated. Therefore, when the recording sheet to be passed is thin paper (basis weight of 163 [gsm] or less for coated paper, 220 [gsm] or less for uncoated paper), preheating may not be performed. As a result, it is possible to shorten the pre-sheet passing operation for raising the temperature of the fixing belt 43 to a temperature corresponding to the recording sheet to be passed.

  When adjusting the position of the pressure roller 45 according to the paper thickness of the recording sheet to be passed through, the type of paper such as an envelope, image information, etc., is the preheating operation performed according to the position of the pressure roller 45? You may decide whether or not. Table 6 below shows an example of the relationship between the position of the pressure roller, the fixing nip width, and the preheating operation.

  In Table 6, the pressure contact position of the pressure roller 45 with the fixing belt 43 can be adjusted in four stages. One stage is located at the position farthest from the fixing roller 41, the pressure applied to the fixing belt 43 is the lowest, and the fourth stage is located closest to the fixing roller 41, and the pressure applied to the fixing belt 43 is the highest. For example, if the image to be recorded on the recording sheet is a large amount of toner on the recording sheet such as a full-color image, a large amount of heat is required to obtain good fixability. Therefore, for example, when the amount of toner adhering to the image recording sheet is large, the pressure contact position is set to “4”, and the amount of heat applied at the fixing nip is increased by increasing the fixing nip width. Further, when the recording paper is thick, such as an envelope or thick paper, for example, the pressure contact position is set to “1”, and the pressure applied to the fixing belt 43 by the pressure roller is lowered. In this way, good fixability is maintained by setting the pressure contact position of the pressure roller and changing the fixing nip width based on the amount of toner on the recording sheet to be passed and the type of paper. be able to.

  When the pressure contact position of the pressure roller 45 is “1” or “2” in Table 6, the amount of elastic deformation of the pressing member 49 decreases, and the width of the boundary region N2s exceeds 2.8 mm. There is a fear. Therefore, when the pressure contact position of the pressure roller 45 is “1” or “2” in Table 5, a pre-heating operation is performed to thermally expand the pressure roller 45. Thereby, the boundary region N2s can be made 2.8 mm or less. On the other hand, when the pressure contact position of the pressure roller 45 is “3” or “4” in Table 5, the front end of the pressing member 49 approaches the fixing nip. Even if not, there is no possibility that the boundary region N2s exceeds 2.8 mm. Therefore, when the pressure contact position of the pressure roller 45 is “3” or “4” in Table 5, the preheating operation is not performed. As a result, it is possible to shorten the pre-sheet passing operation.

FIG. 18 is a flowchart of whether or not the preheating operation is possible.
First, when an image forming signal is received, the control unit 202 (see FIG. 13) acquires paper type information to be passed through the fixing nip N1. Specifically, the user inputs the paper type information set in the first paper feed cassette 101 or the second paper feed cassette 102 by using an operation unit of the image forming apparatus, software installed in a personal computer, or the like. A table in which the seed information is associated with the sheet cassette is stored in the nonvolatile memory. When receiving the image forming signal, the control unit 202 acquires a paper cassette to be used, and acquires paper type information from the paper cassette information and a table stored in the nonvolatile memory. Then, based on the acquired paper type information, if the recording sheet to be passed through the fixing nip is coated paper, it is checked whether the basis weight is 163.1 [gsm] or more. It is checked whether the basis weight is 20.1 [gsm] or more (S1).

  When the recording sheet passed through the fixing nip has a basis weight of less than 163.1 [gsm] in the case of coated paper and less than 220.1 [gsm] in the case of uncoated paper (No in S1) Do not perform pre-heating operation. On the other hand, when the recording sheet to be passed through the fixing nip has a basis weight of 163.1 [gsm] or more in the case of coated paper and a basis weight of 220.1 [gsm] or more in the case of uncoated paper (YES in S1) ) Checks the pressure contact position of the pressure roller 45 when the recording sheet is passed through the fixing nip (S2).

  When the set heating contact position is “3” or more shown in Table 6 above (No in S2), the preheating operation is not executed. On the other hand, when the set heating contact position is “2” or less shown in Table 6 above (Yes in S2), it is checked whether or not the temperature of the pressure roller 45 is 120 ° C. or less (S3). .

  When the temperature of the pressure roller 45 is 120 ° C. or higher (No in S3), the preheating operation is not executed. On the other hand, when the temperature of the pressure roller 45 is less than 120 ° C. (Yes in S3), the preheating operation is executed for the number of seconds set for each temperature of the pressure roller shown in Table 4 (S4).

  In the example shown in FIG. 18, the preheating operation is performed when all of the above conditions S1, S2, and S3 are satisfied. However, any one of the above conditions S1, S2, and S3 You may make it perform preheating operation | movement when satisfy | filling.

  In the above description, an embodiment in which the fixing device of the present invention is applied to an image forming apparatus such as a copying machine or a printer using an electrophotographic system has been described. For example, image forming such as a copying machine or a printer using an ink jet system is used. The fixing device of the present invention can also be applied to a fixing device that dries an undried ink image carried on a recording paper (paper) of the apparatus.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect 1)
An endless fixing belt 43 stretched between a plurality of stretching members, a nip forming member such as a fixing roller 41 that is one of the plurality of stretching members, and the fixing facing the nip forming member A pressure member such as a pressure roller 45 that forms a nip via the belt 43, a heat source 44 that heats the fixing belt 43, and the fixing belt on the downstream side of the nip forming member in the movement direction of the fixing belt 43. In a fixing device including a separation member such as a separation auxiliary member 48 that is disposed at a position spaced apart from the pressure member via a belt 43 and stretches the fixing belt 43, the separation member Between the upstream end portion in the fixing belt moving direction, a pressing member 49 that contacts the inner peripheral surface of the fixing belt 43 and presses the fixing belt 43, and the pressure member is fixed to the fixing belt 43. Fixing device is characterized in that a moving means such as a pressurized 圧脱 pressure mechanism 201 for contacting and separating with respect to belt.
In Patent Document 1, streaky wrinkles of the recording medium after passing through the fixing nip are generated when the recording medium after passing through the fixing nip is wavy, and the recording medium in which the waviness is conveyed is conveyed to a pair of paper discharge rollers. To occur. The undulation of the recording medium after passing through the fixing nip occurs until the recording medium that has exited the nip such as the fixing nip N1 moves to the separation position of the separation member. This occurs for the following reasons. That is, in the fixing device described in Patent Document 1 described above, the surface of the recording medium on which the toner image is formed is heated while being pressed against the fixing belt at the nip, whereby the toner melts and the toner image is formed on the recording medium. It is fixed. The recording medium exiting the nip is conveyed to the separation position of the separation member in a state where the toner melted at the nip adheres to the fixing belt, and is separated from the fixing belt at the separation position. When the recording medium is heated in the fixing nip, the moisture contained in the recording medium is vaporized to become water vapor. However, in the nip, since the recording medium is pressed with a high nip pressure, the water vapor is removed from the recording medium. Hard to be released. However, while the toner image on the recording medium from the nip to the separation position is conveyed while being attached to the fixing belt, no pressure is applied to the recording medium. Cheap. The water vapor is mainly released from the surface opposite to the surface on the fixing belt side of the recording medium. Further, the height is lower than the image portion on which the toner image is formed, and a gap is formed between the fixing belt and the non-image portion, and water vapor is also released into this gap. When the water vapor is released, the fibers of the recording medium are dried and the undulation is generated.
Further, the water vapor released into the gap between the fixing belt and the non-image portion remains in the gap and is again absorbed by the recording medium. The water vapor released by itself is reabsorbed, so that the recording medium is wetted and the fibers are extended, and the recording medium is wavy.
Thus, until the recording medium exiting the nip moves to the separation position, the fibers of the recording medium expand and contract due to drying due to the release of water vapor and wetting due to the reabsorption of water vapor. The undulations occur.
On the other hand, in (Aspect 1), the recording medium exiting from the nip is fixed so as to be conveyed in a state of being sandwiched between the fixing belt and the pressure member, or having almost no gap between the pressure member and the pressure member. By pressing the belt with the pressing member, the following advantages are obtained. That is, while the recording medium moves to the separation position, if the recording medium undulates by drying due to the release of water vapor from the recording medium, the recording medium hits the fixing belt or the pressure member and the undulation is inhibited. As a result, the undulation of the recording medium due to the release of water vapor between the nip and the separating member is suppressed.
Further, even when the released water vapor is reabsorbed between the nip and the separating member to cause the recording medium to undulate, the waving is inhibited by the fixing belt and the pressure member. As a result, the undulation of the recording medium due to the reabsorption of water vapor is also suppressed between the nip and the separating member.
In this way, by suppressing the undulation of the recording medium after passing through the nip, the recording medium in which the undulation has occurred can be suppressed from being conveyed by the discharge roller pair, and the recording medium after passing through the fixing nip. It is possible to suppress the generation of streak-like wrinkles.
Further, in the first aspect, by providing contact / separation means such as a pressure depressurization mechanism 201 that contacts and separates the pressure member with respect to the fixing belt, the pressure member is separated from the fixing belt after completion of the fixing operation. be able to. Thereby, it can suppress that the wrinkle of the shape which carried out the elastic deformation at the time of the said nip formation on a pressurization member etc., and can improve durability.

(Aspect 2)
In the first aspect, after the fixing operation is finished, the pressing member such as the pressing roller 45 is controlled to be separated from the fixing belt 43 by the contact / separation means such as the pressing / depressurizing mechanism 201. A pressure member is brought into contact with the fixing belt during a start-up operation such as a pre-sheet passing operation for heating to a predetermined temperature, and a pre-heating operation for heating the pressure member for a predetermined time is performed.
According to this, as described in the embodiment, a pressure member such as a pressure roller can be thermally expanded by the preheating operation. Thus, when the pressing member is brought into contact with the fixing belt 43, the pressing member can be elastically deformed by a predetermined amount, and the contact pressure of the fixing belt on the pressing roller between the pressing member and the fixing nip. The boundary region N2s, which is lower than the contact pressure of the region pressed by the pressing member such as the post nip portion N2, can be prevented from expanding beyond a specified width (2.8 mm in the present embodiment). Thereby, it is possible to suppress the release of water vapor from the recording medium in the boundary region N2s and the generation of water vapor bubbles in the boundary region N2s. As a result, it is possible to suppress the occurrence of uneven glossiness by causing the water vapor bubbles to move on the recording medium in a region pressed by the pressing member and disturb the toner on the recording medium.

(Aspect 3)
In the aspect 2, the start-up operation is a pre-sheet feeding operation before the recording medium conveyance to the nip is started.
As a result, the recording medium is conveyed to the nip in a short time after the pressure member such as the pressure roller is thermally expanded by the preheating operation, so that the boundary region N2s has a predetermined width (this embodiment). In this case, the recording medium can be conveyed to the boundary region N2s in a state of 2.8 mm or less. Thereby, generation | occurrence | production of gloss unevenness can be suppressed favorably.

(Aspect 4)
In the aspect 3, it is determined whether or not to perform the preheating operation according to the type of the recording medium that passes through the nip.
According to this, as described in the embodiment, gloss unevenness does not occur even if the width of the boundary region N2s is somewhat wide depending on the type of paper such as thin paper. Therefore, when such a paper type is passed, the pre-heating operation is not performed, and the fixing belt is heated up to a temperature corresponding to the recording medium as compared with the case where the pre-heating operation is performed. The time can be shortened and the pre-sheet feeding operation can be shortened. Further, when the width of the boundary region N2s is large, such as thick paper, the occurrence of gloss unevenness can be suppressed by performing the pre-heating operation for a paper type that may cause gloss unevenness.

(Aspect 5)
In the aspect 3 or 4, the control unit 202 or the like that changes the pressure position of the pressure member such as the pressure roller 45 to the fixing belt 43 by controlling the contact / separation means such as the pressure depressurization mechanism 201 is added. Pressure adjusting means is provided, and it is determined whether or not to perform the pre-heating operation according to the pressure position of the pressure member to the fixing belt.
According to this, as described in the embodiment, the closer the pressure position of the pressure member such as the pressure roller is to the fixing roller 41 and the nip forming member, the greater the elastic variable of the pressing member and the fixing nip. Since the width also increases, the boundary region N2s can be set to a specified width (2.8 mm or less) without performing the preheating operation. On the other hand, as the pressure position of the pressure member such as the pressure roller is further away from the nip forming member, the elastic variable of the pressing member is reduced and the fixing nip width N1 is also narrowed. 2.8 mm or less).
Accordingly, by determining whether or not to perform the pre-heating operation according to the pressure position of the pressure member to the fixing belt, both suppression of gloss unevenness and shortening of the pre-sheet feeding operation are achieved. be able to.

(Aspect 6)
In any one of modes 3 to 5, the preheating operation time is set according to the temperature of a pressure member such as the pressure roller 45 before the operation before paper passing.
When the temperature of a pressure member such as a pressure roller is high, the boundary region has a specified width (in this embodiment, 2 when the pressure member is brought into contact with the fixing belt, even if the preheating time is short. .8 mm) or less, the pressure member can be thermally expanded. Therefore, by setting the preheating operation time according to the temperature of the pressure member such as the pressure roller 45 before the operation before paper passing, the preheating time is always compared with the case where the preheating operation is always performed for the same time. Can be shortened. By shortening the preheating operation, the heat transfer from the fixing belt to the pressure member is suppressed in the pre-sheet feeding operation, and the temperature is quickly raised to the temperature corresponding to the recording medium to which the fixing belt is passed. be able to. As a result, it is possible to shorten the operation before paper passing.

(Aspect 7)
In the fixing device according to any one of Embodiments 2 to 6, when a plurality of recording media are continuously passed through the nip, the pressing member is separated from the fixing belt after the continuous passing and both sides of the recording medium are disposed. When the image is fixed, the pressure member is separated from the fixing belt after the image fixing on both sides is completed.
As a result, the paper width of continuous paper passing can be shortened and the double-sided printing time can be shortened as compared with the case where the pressure member such as the pressure roller 45 is separated from the fixing belt for each sheet passing. be able to.

(Aspect 8)
In any one of the first to seventh aspects, the front end includes a second separation member such as a separation plate 46 that is not in contact with the outer peripheral surface of the fixing belt 43 and faces the separation member such as the separation assisting member 48, and the separation member includes: The rigidity is higher than that of the pressing member 49.
According to this, as described in the embodiment, deformation of the separation member such as the separation auxiliary member 48 can be suppressed, and the minute gap between the second separation member such as the separation plate 46 and the fixing belt 43 varies. Can be suppressed. Thereby, it is possible to suppress the fixing belt 43 from coming into contact with the tip of the second separation member and damaging the outer peripheral surface of the fixing belt 43. Further, the leading end in the conveyance direction of a recording medium such as a recording sheet attached to the fixing belt does not come into contact with the second separation member, and it is possible to suppress the occurrence of poor separation.

(Aspect 9)
In any one of the first to eighth aspects, the contact surface of the separation member such as the separation auxiliary member 48 with the fixing belt 43 has an arc shape.
According to this, as described in the embodiment, the fixing belt 43 can be smoothly moved along the arcuate contact surface.

(Aspect 10)
In any one of the first to ninth aspects, the pressing member is configured to contact the pressure member via the fixing belt, and the pressing member 49 is a plate-like member having spring elasticity.
According to this, as described in the embodiment, the heat capacity of the pressing member can be reduced as compared with the case where the pressing member is configured by a block member. Thereby, the temperature loss by the pressing member 49 can be suppressed. As a result, the waiting time until the temperature of the fixing belt 43 is raised to a necessary temperature can be shortened as compared with the case where the pressing member 49 is a block-shaped member. Moreover, compared with the case where the pressing member 49 is a block-shaped member, an increase in power consumption can be suppressed and energy saving can be achieved.
Further, since the pressing member 49 has spring elasticity, it can follow the pressure member such as the pressure roller 45 well, and the fixing belt 43 can be brought into good contact with the pressure member.

(Aspect 11)
In the tenth aspect, the pressing portion 49b that contacts the inner peripheral surface of the fixing belt 43 and presses the fixing belt 43 against a pressure member such as the pressure roller 45, and the recording sheet P than the pressing portion 49b. And a peeling portion 49a bent in a direction away from the pressure member on the downstream side in the moving direction of the recording medium.
According to this, the recording medium can be favorably pressed against the pressure member such as the pressure roller 45 by the pressing portion 49b. Further, the fixing belt 43 sandwiched between the pressing portion 49b and the pressure member moves along the bent peeling portion 49a, and the moving direction thereof changes abruptly. As a result, the recording medium can be separated in curvature at the peeling portion 49a. As a result, the recording medium can be separated from the fixing belt 43 by separating the recording medium at a plurality of locations with the curvature at the peeling portion 49a and the curvature at the separation member such as the separation assisting member. .

(Aspect 12)
In the aspect 10 or 11, the pressing member 49 has a pressing portion 49b that contacts the inner peripheral surface of the fixing belt 43 and contacts the pressing belt such as the pressure roller 45 with the fixing belt 43. The pressing portion 49b has a shape that follows the surface shape of the pressure member.
As a result, as described in the embodiment, the fixing belt 43 can be uniformly brought into contact with the pressure member by the pressing member 49. As a result, it is possible to prevent air bubbles between the recording medium and the fixing belt from being pushed out and moving on the surface of the recording medium in the pressing range of the pressing member 49 such as the post nip portion N2. Thereby, it is possible to suppress the occurrence of abnormal images such as uneven gloss in the post nip portion N2.

(Aspect 13)
In any one of modes 10 to 12, the upstream end of the pressing member 49 in the fixing belt moving direction is a free end.
According to this, as described in the embodiment, the pressing member 49 can be brought close to the fixing nip N1, and a boundary region between the fixing nip N1 and a pressing range of the pressing member 49 such as the post nip portion N2. The width of N2s can be narrowed, and the occurrence of uneven gloss can be suppressed.

(Aspect 14)
In any one of Aspects 1 to 13, the distance from the exit of the nip such as the fixing nip N1 to the upstream end of the pressing member 49 in the fixing belt moving direction is 2.8 mm or less.
According to this, as described in the embodiment, it is possible to suppress a decrease in the surface pressure in the boundary region between the nip such as the fixing nip N1 and the pressing range of the pressing member 49 such as the post nip portion N2. Generation of uneven gloss can be suppressed.

(Aspect 15)
In any one of the first to fourteenth aspects, the pressing force on the downstream side of the pressing member 49 in the fixing belt moving direction is set to be equal to or lower than the pressing force on the upstream side.
According to this, as described in the embodiment, it is possible to suppress the occurrence of uneven gloss in the pressing range of the pressing member 49 such as the post nip portion N2.

(Aspect 16)
A latent image carrier such as a photoreceptor 3, toner image forming means (comprising charging device 5, optical writing unit 1, developing device 4, etc.) for forming a toner image on the latent image carrier; Transfer means (consisting of a primary transfer unit and a secondary transfer unit) for transferring onto the recording medium from the latent image carrier, and a fixing means for fixing the toner image transferred onto the recording material to the recording material; The fixing device according to any one of aspects 1 to 15 is used as the fixing unit.
According to this, it is possible to suppress the generation of streak-like wrinkles on the output recording medium.

1: Optical writing unit 2: Image forming unit 3: Photoconductor 4: Developing device 5: Charging device 10: Polishing device 21: Polishing device 21: Guide member 22: Connection member 23: Arm member 24: Support plate 40: Fixing device 41: Fixing Roller 41a: Metal core part 42: Heating roller 43: Fixing belt 44: Heat source 45: Pressure roller 46: Separating plate 47: Tension roller 48: Separation auxiliary member 49: Holding member 49a: Peeling part 49b: Holding part 60: Primary Transfer unit 78: Secondary transfer unit 201: Pressure depressurization mechanism 201a: Pressure arm 201b: Pressure cam 201c: Driving means 202: Control unit N1: Fixing nip N2: Post nip N2s: Boundary area P: Recording sheet

Japanese Patent Laying-Open No. 2015-18906

Claims (16)

An endless fixing belt stretched over a plurality of stretch members;
A nip forming member that is one of the plurality of stretching members;
A pressure member that forms a nip through the fixing belt opposite the nip forming member;
A heat source for heating the fixing belt;
A fixing device including a separating member that is disposed downstream of the nip forming member in the moving direction of the fixing belt and spaced from the pressure member via the fixing belt, and stretches the fixing belt; ,
A pressing member that contacts the inner peripheral surface of the fixing belt and presses the fixing belt between the outlet of the nip and the upstream end of the separation member in the fixing belt moving direction;
A fixing device comprising: a contacting / separating unit that contacts and separates the pressing member with respect to the fixing belt. The fixing device according to claim 1,
After the fixing operation is finished, the pressing member is controlled to be separated from the fixing belt by the contacting / separating means,
A fixing device that performs a preheating operation in which the pressure member is brought into contact with the fixing belt during a start-up operation for heating the fixing belt to a predetermined temperature and the pressure member is heated for a predetermined time. . The fixing device according to claim 2,
The fixing device according to claim 1, wherein the start-up operation is a pre-sheet-passing operation for raising the temperature of the fixing belt to a temperature corresponding to a recording medium to be fed before starting the conveyance of the recording medium to the nip. The fixing device according to claim 3.
A fixing device that determines whether or not to perform the preheating operation according to a type of a recording medium that passes through the nip. In the fixing device according to claim 3 or 4,
A pressure adjusting means for controlling the contact / separation means to change the pressure position of the pressure member to the fixing belt;
A fixing device that determines whether or not to perform the preheating operation in accordance with a pressure position of the pressure member to the fixing belt. The fixing device according to any one of claims 3 to 5,
The fixing device, wherein the preheating operation time is set according to a temperature of the pressure member before the start of the pre-sheet passing operation. The fixing device according to claim 2,
When a plurality of recording media are continuously passed through the nip, the pressure member is separated from the fixing belt after completion of continuous feeding, and when fixing images on both sides of the recording medium, both-side image fixing is performed. A fixing device, wherein after completion, the pressure member is separated from the fixing belt. The fixing device according to any one of claims 1 to 7,
A leading end is not in contact with the outer peripheral surface of the fixing belt, and includes a second separating member facing the separating member;
A fixing device characterized in that the separating member has higher rigidity than the pressing member. The fixing device according to claim 1,
The fixing device according to claim 1, wherein a contact surface of the separation member with the fixing belt has an arc shape. The fixing device according to any one of claims 1 to 9,
The pressing member is for bringing the fixing belt into contact with the pressure member,
A fixing device, wherein the pressing member is a plate-like member having spring elasticity. The fixing device according to claim 10.
The pressing member is in contact with an inner peripheral surface of the fixing belt and presses the pressing belt against the pressing member, and the pressing member is located on the downstream side of the pressing belt in the fixing belt moving direction. A fixing device comprising: a peeling portion bent in a direction away from the member. The fixing device according to claim 10 or 11,
The pressing member has a pressing portion that contacts the inner peripheral surface of the fixing belt and causes the fixing belt to contact the pressure member,
The fixing device, wherein the pressing portion has a shape that follows the surface shape of the pressure member. The fixing device according to any one of claims 10 to 12,
A fixing device characterized in that the upstream end of the pressing member in the fixing belt moving direction is a free end. The fixing device according to claim 1,
The fixing device is characterized in that the distance from the exit of the nip to the upstream end of the pressing member in the moving direction of the fixing belt is 2.8 mm or less. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the pressing force of the pressing member on the downstream side in the fixing belt moving direction is equal to or lower than the pressing force on the upstream side. A latent image carrier;
Toner image forming means for forming a toner image on the latent image carrier;
Transfer means for transferring the toner image from the latent image carrier onto a recording medium;
A fixing unit that fixes the toner image transferred onto the recording material to the recording medium;
An image forming apparatus using the fixing device according to claim 1 as the fixing unit.

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