JP2007328161A - Image heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image deterioration resulting from the excessive temperature rise in the whole area of a pressure rotating body and the uneven temperature in the longitudinal direction thereof, and to sufficiently heat the image, regarding an image heating apparatus for heating the image T on a recording material while holding and carrying the recording material P at a nip part N formed by a heating rotating body 21 and the pressure rotating body 28. <P>SOLUTION: The image heating apparatus is provided with: a cooling unit 31 for cooling the pressure rotating body while facing the pressure rotating body 28: and an attaching/detaching mechanism to move the pressure rotating body between a contact position and a retreat position related to the heating rotating body. The cooling unit is moved in linkage with the retreat of the pressure rotating body from the heating rotating body. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is used in an image forming apparatus that employs an electrophotographic system, an electrostatic recording system, or the like typified by a copying machine, a printer, a facsimile machine, or a composite machine thereof, and heats an image on a recording material. Relates to the device.

  In particular, a heating rotator that heats an image on a recording material at the nip portion, a pressure rotator that forms the nip portion with the heating rotator, and the pressure rotator with respect to the heating rotator. The present invention relates to an image heating apparatus having contact / separation means for contacting / separating and cooling means for cooling the pressure rotator.

  As an image heating device, for example, a fixing device that fixes an unfixed toner image formed on a recording material such as plain paper, coated paper, or an OHP sheet as a permanently fixed image, or an image fixed on the recording material is heated. A gloss increasing device that increases the glossiness of an image can be given.

  Conventionally, in the image forming apparatus as described above, as a fixing device for fixing an unfixed toner image on a recording material, a fixing device such as a roller nip method or a belt nip method is often used.

  A roller nip type fixing device is heated by a heating means such as a halogen heater and is adjusted to a predetermined fixing temperature, and a fixing roller as a heating rotator and an elastic pressure as a pressure rotator in pressure contact with the fixing roller. Use a roller. Then, a recording material is introduced into a fixing nip portion that is a pressure contact portion between the pair of rollers, and is nipped and conveyed. Thus, the unfixed toner image formed on the recording material surface is fixed on the recording material surface with heat and pressure.

  A belt nip type fixing device uses an endless belt for either or both of a heating rotator and a pressure rotator that are pressed against each other. The belt nip type fixing device can increase the length (nip width) of the fixing nip portion in the recording material conveyance direction as compared with the roller nip type fixing device. For this reason, it is possible to sufficiently heat the image at a high speed. For example, as a color image forming apparatus, it is suitable as a fixing device for melting and mixing a large amount of multicolor toner images and fixing them on a recording material surface. Yes.

  Patent Documents 1 to 4 describe cooling a non-sheet passing area with cooling air as a countermeasure for increasing the temperature of the non-sheet passing portion of the fixing device.

  Patent Document 5 describes that in a belt fixing device, the belt is cooled by a cooling fan (cooling means) even when the pressure belt is separated from the fixing roller. This prevents the blister phenomenon in which the amount of heat applied to the paper becomes excessive and the coated paper swells up like a fire.

In the belt fixing device, the pressure belt in contact with the fixing roller is cooled by a cooling fan.
Japanese Patent Laid-Open No. 60-136779 JP-A-5-181382 JP 2003-076209 A JP-A-11-175169 JP 2005-292333 A

  However, since the position of the cooling fan (exit of the duct) has been fixed in the past, the distance between the belt and the fan (duct exit) varies depending on whether the belt is attached to the roller or not. Could not be cooled.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to appropriately perform cooling even when a pressure rotating belt such as a pressure belt is attached to a heating rotating member such as a fixing roller or retracted from the heating rotating member.

  In order to achieve the above object, the image heating apparatus according to the present invention has a heating rotating body that heats an image on a recording material at a nip portion, and an additive that forms the nip portion between the heating rotating body. In an image heating apparatus comprising: a pressure rotator; contact / separation means for contacting and separating the pressure rotator with respect to the heating rotator; and cooling means for cooling the pressure rotator. The cooling means is moved in conjunction with the separation operation.

  According to the present invention, it is possible to prevent image temperature deterioration due to excessive temperature increase and longitudinal temperature unevenness in the entire pressure rotating body, and to perform good image heating.

  Hereinafter, it demonstrates in detail based on embodiment of this invention.

(1) Image Forming Unit FIG. 1 is a schematic configuration diagram of an image forming apparatus in this embodiment. This image forming apparatus is an electrophotographic full-color image forming apparatus (composite machine) having a copying machine function, a printer function, and a facsimile function, in which a belt nip type fixing device is mounted as an image heating device.

  Reference numeral 1 denotes a digital color image reader unit. A color image original O is placed on the original platen glass 2 of the reader unit 1 with the image surface facing downward according to a predetermined placement standard, and the original cover 2a is placed thereon. When the copy start key is pressed, the moving optical system 1a moves, the original surface is optically scanned, and the original image is photoelectrically read as a color color separation image signal by the full color sensor (CCD) 3. The image signal is processed by the image processing unit 4 and then sent to the controller unit (control circuit unit) 17 of the digital color image printer unit 5. An original document feeder (ADF, RDF) may be mounted on the document table glass 2 to automatically feed the document O onto the document table glass 2.

  In the printer unit 5, UY, UM, UC, and UK are first to fourth image forming units arranged in tandem. Each image forming unit is an electrophotographic process mechanism using a laser scanning exposure unit 18. Based on the image signal sent from the reader unit 1 to the controller unit 17, a yellow toner image is formed on the photosensitive drum surface of the first image forming unit UY at a predetermined control timing. A magenta toner image is formed on the photosensitive drum surface of the second image forming unit UM at a predetermined control timing. A cyan toner image is formed on the photosensitive drum surface of the third image forming unit UC at a predetermined control timing. A black toner image is formed at a predetermined control timing on the photosensitive drum surface of the fourth image forming unit UK.

  The toner images formed on the photosensitive drum surfaces of the image forming units UY, UM, UC, and UK are sequentially superimposed and transferred onto the surface of the intermediate transfer belt 7 by the primary transfer unit 6. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the intermediate transfer belt 7 by superimposing the four toner images. The full-color toner image is separated and fed by the secondary transfer unit 8 from the multi-stage cassette sheet feeding mechanism unit 9, the deck sheet feeding unit 10, or the MP tray (multi-purpose tray) 11 at a predetermined control timing. Secondary transfer is performed on the surface of the recording material P in a batch. In the image forming apparatus of this example, feeding and transporting of recording materials of various sizes, large and small, is so-called “central reference transport” performed at the center of the recording material.

  The recording material P is separated from the surface of the intermediate transfer belt 7 and introduced into the fixing device 12, and is nipped and conveyed at the fixing nip portion. In this nipping and conveying process, the unfixed full-color toner image is melted and mixed by heat and pressure and fixed as a full-color permanent fixed image on the surface of the recording material P. The recording material P exiting the fixing device 12 is selectively discharged to the face-up discharge tray 14 or the face-down discharge tray 15 by the path switching control by the flapper 13.

  When the double-sided printing mode is selected, the recording material P that has been printed on the first side from the fixing device 12 is sent by the flapper 13 to the sheet path that once leads to the face-down discharged sheet 15. Then, the recording material P is switch-back conveyed, introduced into the re-conveying sheet path 16, turned upside down, and re-introduced into the secondary transfer unit 8. As a result, a toner image is secondarily transferred and formed on the second surface of the recording material P. Thereafter, the recording material P is introduced into the fixing device 12 as in the case of the first side printing, and the recording material on which double-sided printing has been performed is discharged to the face-up discharge tray 14 or the face-down discharge tray 15.

  The above is the case of the copying machine mode. In the printer mode, an image information signal is input to the controller unit 17 from an external host device 19 such as a personal computer or image reader. The controller unit 17 outputs the image information signal to the laser scanner 18 and causes the image forming apparatus to perform an image forming operation as a printer. In the facsimile reception mode, an image information signal is input to the controller unit 17 from the counterpart facsimile machine 19 as an external device. The controller unit 17 outputs the image information signal to the laser scanner 18 to cause the image forming apparatus to perform an image forming operation as a facsimile receiving apparatus. In the facsimile transmission mode, the controller unit 17 transmits the document image information photoelectrically read by the reader unit 1 to the counterpart facsimile receiving device 19.

(2) Fixing device 12
<Overall Outline of Fixing Device 12>
FIG. 2 is a cross-sectional view showing a schematic configuration of the fixing device 12 in this embodiment. The fixing device 12 is a belt nip type device using an endless belt as a pressure rotator. FIG. 3 is a partially enlarged view of FIG. FIG. 4 is a block diagram of a control system of the fixing device 12.

  Here, regarding the constituent members of the fixing device, the longitudinal direction or the longitudinal direction is a direction parallel to the direction orthogonal to the recording material conveyance direction in the conveyance path surface of the recording material P. The upstream side and the downstream side are the upstream side and the downstream side in the recording material conveyance direction. The width of the recording material or the sheet passing width is a recording material dimension in a direction orthogonal to the recording material conveyance direction.

  Reference numeral 21 denotes a fixing roller as a heating rotator, in which both longitudinal end shaft portions are rotatably supported by bearings between front and back side plates of an apparatus housing (not shown). The fixing roller 21 has a cylindrical metal roller 21a made of aluminum or the like as a base (core), and an outer peripheral surface thereof is covered with an elastic layer 21b. The elastic layer 21b has a two-layer structure of a base layer made of silicone rubber (for example, 2.5 mm thick, hardness 40 °) and a surface layer made of fluoro rubber (for example, a coat layer having a thickness of 2.5 μm). It is. The fixing roller 21 receives the driving force of the fixing motor M1 through a transmission mechanism (not shown), and is rotationally driven at a predetermined peripheral speed in the clockwise direction of the arrow.

  In the hollow interior of the fixing roller 21, a halogen lamp H1 is disposed along the roller axial direction as an internal heating means. Further, an auxiliary heating roller 22 as an external heating unit is arranged outside the fixing roller 21 substantially in parallel with the fixing roller 21 and is in pressure contact with a predetermined pressing force. The auxiliary heating roller 22 is disposed with its longitudinal end shafts rotatably supported by bearings between the front and back side plates of the apparatus housing, and rotates following the rotation of the fixing roller 21. The auxiliary heating roller 22 is a cylindrical metal roller formed of aluminum or the like, and a halogen lamp H2 is disposed along the roller axial direction inside the hollow.

  The fixing roller 21 is heated from the inside by supplying power to the halogen lamp H1 from the power supply circuit 51 (FIG. 4), and is also heated by the auxiliary heating roller 22 that is heated by supplying power to the halogen lamp H2 from the power supply circuit 52. Contact heating is also performed from the outside. The surface temperature of the fixing roller 21 is detected by a thermistor TH1 as temperature detecting means disposed in contact with or close to the surface of the fixing roller, and electrical information relating to the roller surface temperature is input from the thermistor TH1 to the controller unit 17. To do. The controller unit 17 supplies power supplied from the power supply circuit 51 to the halogen lamp H1 and supplies the halogen information from the power supply circuit 52 so that the electrical information regarding the roller surface input from the thermistor TH1 corresponds to a predetermined fixing temperature. The power supply to the lamp H2 is controlled. That is, the controller unit 17 controls the temperature of the surface of the fixing roller 21 to a predetermined fixing temperature (for example, 165 ° C.). The thermistor TH1 is disposed at a position that becomes the sheet passing portion region at the longitudinal position of the fixing roller in all the recording materials of various large and small width sizes used for sheet passing.

  TH2 is a thermistor disposed in contact with or close to the surface of the auxiliary heating roller 22. The controller unit 17 manages the temperature of the auxiliary heating roller 22 by controlling the power supply from the power supply circuit 52 to the halogen lamp H2 based on the electrical information regarding the roller surface temperature input from the thermistor TH2.

  A pressure belt unit 23 is disposed below the fixing roller 21. The unit 23 includes first to third rollers 25 to 27 that are disposed between the front and back side plates of the unit frame 24 so as to be substantially parallel to the fixing roller 21 and to be rotatable. It has an endless pressure belt 28 as a pressure rotator suspended and stretched between rollers. Further, on the inner side of the belt, between the fixing roller 21 and the pressure belt 28, a pressure pad 29 for forming a wide fixing nip portion N in the recording material conveyance direction and a lubricant are applied to the inner surface of the belt. An oil application roller 30 is supported by the unit frame 24 and disposed. In addition, a cooling fan unit 31 as a longitudinal temperature distribution fluctuation suppressing unit of the pressure belt 28 is supported on the unit frame 24 outside the pressure belt 28.

  The pressure belt unit 23 has a unit frame 24 supported by a pivot 32 between the front and back side plates of the apparatus housing, and swings up and down with respect to the fixing roller 21 around the pivot 32. It is possible to arrange. As shown in FIGS. 2 and 5, the unit 23 is arranged around the pivot portion 32 by a push-up spring 33 as a pressurizing means disposed on the front side and the back side of the unit frame 24. The front and back sides are pushed up and biased with substantially the same force. The front side and back side push-up springs 33 are respectively arranged on fixed spring receiving seats 34 disposed on the front side and back side plates of the apparatus housing and on the front side and back side plates of the unit frame 24. It is contracted between the spring seat 35 provided.

  Further, an eccentric cam 36 as a pressure releasing means is disposed above the spring seat 35 on each side on the near side and the back side of the unit frame 24. The front and back eccentric cams 36 are attached to the cam shaft 37 with the same size and the same phase, and are intermittently controlled by 180 ° by a cam motor M2 (FIG. 4) controlled by the controller unit 17. Accordingly, each eccentric cam 36 has a first rotation angle posture in which the small diameter portion corresponds to the spring seat 35 as shown in FIG. 5 and a second rotation angle in which the large diameter portion corresponds to the seat 35 as shown in FIG. It can be switched to the rotation angle posture.

  When the eccentric cam 36 is switched to the first rotation angle posture of FIG. 5, the eccentric cam 36 is not in contact with the spring seat 35. As a result, the unit 23 is sufficiently pushed up and rotated with respect to the fixing roller 21 around the pivot portion 32 by the spring 33, and the first roller 25 and the pressure pad 29 are applied as shown in FIGS. The pressure roller 28 is brought into pressure contact with the fixing roller 21 with a predetermined pressing force. The pushed-up state of the unit 23 is a unit wearing state or a pressure belt wearing state.

  Further, when the eccentric cam 36 is switched to the second rotational angle posture of FIG. 6, the large diameter portion of the eccentric cam 36 pushes down the spring seat 35 against the spring 33. As a result, the unit 23 is rotated downward from the fixing roller 21 around the pivot 32, and the first roller 25, the pressure pad 29, and the pressure belt 28 are fixed to the fixing roller as shown in FIGS. It will be in a state completely away from 21. The pushed-down state of the unit 23 is a unit detached state or a pressure belt detached state.

  The pressure belt 28 is configured such that the surface of a base material made of a resin such as polyimide or a metal such as nickel is covered with an elastic body layer such as silicone rubber or fluorine rubber. For example, a flexible endless belt in which a fluorine base is coated to a thickness of 180 μm on a belt base material made of a polyimide film having a thickness of 70 μm, a circumferential length of 185 mm, and a width of 245 mm.

  The first roller 25 is made of stainless steel, and is pressed against the fixing roller 21 with a pressure belt 28 interposed therebetween to form a fixing nip portion N together with the pressure pad 29, and recording of the fixing nip portion N is performed. This roller separates the recording material from the surface of the fixing roller at the material outlet. Hereinafter, this roller 25 is referred to as a separation roller.

  The second roller 26 is a roller disposed on the entry side of the recording material P to the fixing nip portion N. Hereinafter, this roller 26 is referred to as an entrance roller. By heating the entrance roller 26, the pressure belt 28 is slightly warmed. That is, the entrance roller 26 is a cylindrical metal roller formed of aluminum or the like, and the halogen lamp H3 is disposed along the roller axis direction in the hollow interior. The entrance roller 26 is heated by supplying power to the halogen lamp H3 from the power supply circuit 53 (FIG. 4). The roller surface temperature is detected by the thermistor TH3. The controller unit 17 manages the surface temperature of the entrance roller 26 in a predetermined manner based on the electrical information regarding the roller surface temperature input from the thermistor TH3.

  In the above, the target temperature of the pressure belt 28 is about 100 ° C. The reason for warming the pressure belt 28 is to shorten the return time from the standby state by adjusting the temperature of the pressure belt (rotated) separated from the fixing roller 21. The reason why the pressure belt 28 is cooled is that the time during which the pressure belt 28 is in contact with the fixing roller 21 is increased to cope with the blister phenomenon, and the temperature of the non-sheet passing portion of the fixing roller 21 is increased. This is to cope with the situation.

  The third roller 27 is disposed below the separation roller 25 and the entrance roller 26 and functions as a tension roller that applies tension to the pressure belt 28. Further, it functions as a roller that controls the lateral movement (belt movement along the length of the roller) during rotation of the pressure belt 28. Hereinafter, this roller 27 is referred to as a steering roller. The steering roller 27 is formed by forming an elastic layer on the surface of a metal roller, and is urged to move in a direction in which the pressure belt 28 is tensioned. The steering roller 27 is controlled to be displaced in the direction of the roller axis so that the belt shift is returned by a roller swinging mechanism (not illustrated) that is controlled based on belt shift detection information from a belt shift detection sensor (not shown). .

  The pressure pad 29 is formed by forming an elastic pad 29b made of a silicone rubber foam having a thickness of about 3.5 mm on a support plate (metal base plate) 29a (FIG. 3) having a width of about 25 mm. A φ29 wire 29c made of SUS is disposed along the length of the pad at the distal end of the elastic pad 29b on the downstream side in the recording material conveyance direction. The pressure pad 29 is configured by covering the surface of the elastic pad 29b including the wire 29c with a low friction sheet 29d (for example, a sheet obtained by impregnating a glass fiber with a tetrafluoroethylene resin) 29d. . The pressure pad 29 is disposed inside the pressure belt 28 and on the upstream side of the separation roller 25 in the recording material conveyance direction, with the wire 29c portion approaching the separation roller 25.

  2 and 3, the separation roller 25 is pressed into contact with the fixing roller 21 with the pressure belt 23 sandwiched between the separation roller 25 and the elastic layer 21 b of the fixing roller 21. Such elastic deformation of the elastic layer 21b caused by the biting pressure contact of the separation roller 25 prevents the recording material from being wound around the fixing roller 21 at the recording material outlet portion of the fixing nip portion N, so Recording material separation performance can be obtained. The pressure pad 29 is also pressed against the fixing roller 21 with a predetermined pressing force with the pressure belt 23 interposed therebetween. Thus, the pressure belt 28 is wound around and pressed against the fixing roller 21 by the pressing force of the separation roller 25 and the pressure pad 29, so that a wide fixing nip portion N is formed in the recording material conveyance direction. . In the apparatus of this embodiment, the width of the fixing nip portion N is about 20 mm. FIG. 9 shows a pressure distribution in the width direction of the fixing knitted portion N formed by the separation roller 25 and the pressure pad 29. It can be seen that pressure is continuously generated between the separation roller 25 and the pressure pad 29. Thereby, it is possible to prevent image defects such as image displacement. Further, since the pressure roller 25 is formed of a rigid body, it is possible to sufficiently secure a pressure capable of ensuring the recording material separation near the recording material outlet of the fixing nip portion N.

  The pressure belt 28 rotates following the rotation driving of the fixing roller 21 in a state where the pressure belt 28 is pressed against the fixing roller 21 by the separation roller 25 and the pressure pad 29. The separation roller 25, the entrance roller 26, and the steering roller 27 are accompanied by the rotation of the pressure belt 28. The pressure belt 28 rotates while its inner surface is in close contact with the pressure pad 29 and slides. However, since the surface of the pressure pad 29 is covered with the low friction sheet 29d, the sliding resistance is small. Further, the sliding resistance is further reduced by applying silicone oil as a lubricant to the inner surface of the pressure belt 28 by the oil application roller 30.

  When the main power switch of the image forming apparatus is turned on, the image forming apparatus enters a warm-up mode. If the pressure belt unit 23 of the fixing device 12 is in the detached state, the controller 17 switches to the wearing state. Further, the fixing roller 21 is rotated and power supply to the halogen lamps H1, H2, and H3 is started, and the temperature rise of the fixing roller 21 and the entrance roller 26 is started. As a result, the fixing roller 21 is heated to a predetermined temperature. Further, the pressure belt 28 is also slightly warmed by the entrance roller 26 heated by the halogen lamp H3. Then, when the fixing roller 21 is heated to a predetermined temperature and then idly rotates for a predetermined time, the fixing device 12 becomes in a state capable of fixing, and is controlled to the predetermined temperature until the image forming process is started and the fixing process is started. Waiting while being.

  Then, the recording material P on which the unfixed toner image T is transferred from the image forming process side is conveyed to the fixing device 12. The recording material P is guided by the guide 38 and introduced into the fixing nip portion N. SW is a recording material detection sensor disposed in the guide 38, and the arrival / passage of the recording material P is detected by this sensor, and the detection signal is input to the controller 17. The recording material P faces the toner image carrying surface facing the fixing roller 21, enters the fixing nip portion N and is nipped and conveyed, and the toner image carrying surface side is pressed against the heated peripheral surface of the fixing roller 21. As a result, the unfixed toner image T is melted and fixed on the recording material P.

  The recording material P discharged from the recording material outlet side of the fixing nip N after this fixing passes through the fixing roller elastic body layer portion elastically deformed by the separation roller 25 and is peeled off from the surface of the fixing roller 21 by itself. Even when the recording material P is not peeled off from the fixing roller 21 by itself, it is surely peeled off from the fixing roller 21 by the peeling claw 40. Even if the recording material P wraps around the pressure belt 28, it is surely peeled off from the pressure belt 28 by the peeling claw 41. After the fixing is completed, the recording material P passes through the fixing nip portion N, and then is sent out from the fixing device by the discharge conveying roller 39.

  The surface of the fixing roller 21 after the recording material is separated is cleaned by a cleaning device 42 to remove contaminants such as toner and paper dust attached to the roller surface. The cleaning device 42 in this embodiment is a web-type device, and is configured to clean the roller surface by pressing the cleaning web 42a against the surface of the fixing roller 21 by the pressure roller 42d. 42b is a web feed roller, and 42c is a web take-up roller, and the web portion pressed against the surface of the fixing roller 21 by the pressure roller 42d is gradually updated by web feed. Further, a release agent application device (not shown) applies silicone oil or the like as a release agent to the surface of the fixing roller 21 to facilitate separation of the recording material P from the fixing roller 21 and to prevent toner offset. May be achieved.

<Cooling fan unit 31>
Here, in the following description, a recording material having the maximum sheet passing width that can be used in the apparatus is referred to as a large size recording material, and a recording material having a smaller width is referred to as a small size recording material.

  In the fixing device 12 as described above, at the time of passing a small-size recording material, the portion that becomes the non-sheet passing portion and the portion that becomes the sheet passing portion of the pressure belt 28 that is in contact with the fixing roller 21 It is heated by the heat from the fixing roller 21. Further, the separation roller 25 and the pressure pad 29 that are in pressure contact with the fixing roller 21 via the pressure belt 28 are heated as described above, so that a portion that becomes a non-sheet passing portion and The portion that becomes the paper passing portion is heated. In particular, when a continuous image forming operation and consequently a fixing operation are performed, if no action is taken, the non-sheet passing portion and the sheet passing portion of the pressure belt 28, the separation roller 25, and the pressure pad 29 are provided. This part is in a situation where the temperature rises excessively. As a result, particularly when continuous image formation is performed on the recording material P such as coated paper, image deterioration occurs in the non-sheet passing portion and the sheet passing portion.

  Therefore, in the fixing device 12 of the present embodiment, the temperature detection means detects the temperatures at the center and both ends in the longitudinal direction of the pressure belt 28, and the temperature detection signal values from these temperature detection means and a predetermined threshold value are detected. From this comparison, the overheated portion position in the longitudinal direction of the pressure belt 28 is predicted. And the cooling fan unit 31 as a longitudinal temperature distribution fluctuation suppression means of the pressurizing belt 28 is operated to cool the overheated portion position of the pressurizing belt 28 to a temperature within a certain range.

  As described above, by cooling the overheated portion of the pressure belt 28, the temperature of the separation roller portion and the pressure pad portion corresponding to the overheated portion is also lowered. Further, the excessive temperature rise of the fixing roller 21 is reduced by cooling the pressure belt 28.

  This will be specifically described below. FIG. 10 is a view taken along line (10)-(10) in FIG. A is the central reference conveyance line (virtual line) of the recording material P, B is the effective heating area width of the fixing roller 21, and C is the maximum sheet passing width of the recording material P (= sheet passing portion of a large size recording material). The effective heating area width B is set to be substantially the same width as the maximum sheet passing width C or slightly wider. D and E are a paper passing portion and a non-paper passing portion of the small size recording material.

  In the present embodiment, the cooling fan units 31 are arranged along the longitudinal direction of the pressure belt and fixed to and supported by the unit frame 24. The first to fourth four cooling fan devices 31 (1) that are the same as each other. It is composed of 31 (2), 31 (3), and 31 (4). Each cooling fan device is provided at a fan part 31a including a motor and a fan, a duct part 31b that guides air generated by the rotation of the fan, and a tip part of the duct part 31b. An air blowing opening 31c for intensively blowing is provided.

  The four cooling fan devices are located between the separation roller 25 and the steering roller 27 on the outside of the pressure belt 28, and at least the separation roller 25 is exposed to air via the pressure belt 28. It is located near. Each cooling fan device is arranged at substantially equal intervals in the effective heating area width B of the fixing roller 21 along the longitudinal direction of the pressure belt with the air blowing opening 31c facing the outer surface of the pressure belt. The distance a between the air blowing opening 31c and the pressure belt 28 of each cooling fan device is set to be substantially the same.

  The cooling fan devices are first, second, third, and fourth cooling fan devices in order from the back side to the near side of the unit frame 24. The first and fourth cooling fan devices 31 (1) and 31 (4) correspond to the non-sheet passing portion E when the small size recording material is passed through the fixing device 12, and the second and third cooling fans Fan devices 31 (2) and 31 (3) correspond to the sheet passing portion D. In the state where all of the first to fourth cooling fan devices are turned on, air is blown substantially uniformly over the entire length of the pressure belt longitudinal region substantially corresponding to the effective heating region width B of the fixing roller 21. It is supposed to be in a state that has been.

  TH4, TH5, and TH6 are three thermistors as temperature detecting means for detecting temperature distribution fluctuations in the longitudinal direction of the pressure belt 28. These thermistors TH4, TH5, and TH6 are arranged in contact with or close to the surface of the pressure belt 28 along the pressure belt longitudinal direction in the pressure belt suspension portion of the separation roller 25. The thermistor TH4 and the thermistor TH6 are arranged at positions near the back end and near the end within the maximum sheet passing width C, respectively, and the thermistor TH5 is arranged at a position approximately at the center of the maximum sheet passing width C. It is set up. Hereinafter, the thermistor TH4 is referred to as the back side thermistor, the thermistor TH6 is referred to as the front side thermistor, and the thermistor TH5 is referred to as the central thermistor.

  Electrical information related to the temperature of the pressure belt 28 detected by the thermistors TH4, TH5, and TH6 is input to the controller unit 17. The controller unit 17 performs on / off control of the first cooling fan device 31 (1) based on detection information input from the back side thermistor TH4. In addition, the controller unit 17 performs on / off control of the fourth cooling fan device 31 (4) based on detection information input from the near-side thermistor TH6. The controller unit 17 controls the second and third cooling fan devices 31 (2) and 31 (3) on and off based on detection information input from the central thermistor TH5.

  In other words, the controller unit 17 compares the temperature detection information value input from the back side thermistor TH4 with a predetermined threshold value, and if the temperature detection information value exceeds the threshold value (temperature outside a certain range), the pressure belt 28. It is determined that the non-sheet passing portion on the back side of the temperature has risen beyond the allowable range. And the controller part 17 drives the 1st cooling fan apparatus 31 (1), and makes it the state which sprayed air with respect to the non-sheet passing part of the back | inner side of the pressurization belt 28. FIG. Thereby, the non-sheet passing portion on the back side of the pressure belt 28 is cooled by air and the temperature is lowered. When the controller 17 detects that the back side thermistor TH4 has lowered the temperature of the non-sheet passing part on the back side of the pressure belt 28 to a temperature equal to or lower than a threshold (temperature within a certain range), the first cooling fan The drive of the device 31 (1) is stopped.

  Similarly, the controller unit 17 compares the temperature detection information value input from the front side thermistor TH6 with a predetermined threshold value, and if the temperature detection information value exceeds the predetermined threshold value, the controller unit 17 detects the value on the front side of the pressure belt 28. It is determined that the temperature of the non-sheet passing portion has exceeded the allowable level. And the controller part 17 drives the 4th cooling fan apparatus 31 (4), and makes it the state which sprayed air with respect to the non-sheet passing part of the near side of the pressurization belt 28. FIG. Thereby, the non-sheet passing portion on the front side of the pressure belt 28 is cooled by air and the temperature is lowered. When the controller unit 17 detects that the front side thermistor TH6 has lowered the temperature of the non-sheet passing portion on the front side of the pressure belt 28 to a temperature equal to or lower than the threshold value, the controller unit 17 drives the fourth cooling fan device 31 (4). Stop.

  Further, the controller unit 17 compares the temperature detection information value input from the central thermistor TH5 with a predetermined threshold value, and when the temperature detection information value exceeds the predetermined threshold value, the controller unit 17 It is determined that the temperature has risen to an unacceptable level. Then, the controller unit 17 drives the second and third cooling fan devices 31 (2) and 31 (3) to bring air into the paper passing portion of the pressure belt 28. Thereby, the pressure belt 28 is cooled by air and the temperature is lowered. If the controller 17 detects that the temperature of the sheet passing portion of the pressure belt 28 has fallen within the allowable temperature by the central thermistor TH5, the second and third cooling fan devices 31 (2) and 31 (3). Stop driving.

  Thus, the temperature distribution fluctuation in the width direction of the pressure belt 28 is suppressed by the selective drive control of the first to fourth cooling fan devices as described above. Further, since the pressure belt 28 is cooled as described above, the temperature rise of the non-sheet passing portion of the fixing roller 21 is also suppressed.

  That is, in the fixing roller 21, the temperature rise of the non-sheet passing portion is relieved indirectly by the cooling of the pressure belt 28. A plurality of cooling fans are installed side by side, and only the fan on the end side is operated to cool the end of the belt, and the end of the roller in contact therewith is cooled.

  FIG. 11 shows the temperature transition of the non-sheet passing portion when the small size recording material is continuously fed 100 sheets, and shows the case where cooling is performed and the case where cooling is not performed. In the experiment of this graph, the temperature adjustment temperature of the fixing roller 21 is set to 165 ° C.

  By controlling the cooling fan unit 31 as described above, the temperature of the pressure belt 28 is prevented from excessively rising due to heat from the fixing roller 21 even if the recording material P does not pass through. As a result, heat from the fixing roller 21 is not easily transmitted to the separation roller 25 and the pressure pad 29 that are pressed against the fixing roller 21 via the pressure belt 28 in the fixing nip portion N, and the temperature distribution along the length thereof. Fluctuations are suppressed and overheating is prevented.

  Accordingly, since the pressure pad 29 does not cause a significant temperature difference between the non-sheet passing portion and the sheet passing portion, the heat with respect to the fixing roller axial direction of the pad portion 29b mainly made of a silicone rubber foam. The degree of expansion is almost uniform without variation. As a result, the nip pressure along the longitudinal direction in the fixing nip portion N is not largely lost between the non-sheet passing portion and the sheet passing portion, and is maintained in a substantially required pressure distribution. For this reason, even in the recording material P that passes through the fixing nip portion N where the balance of the pressure distribution hardly changes, the end image defect occurs due to the heating being performed uniformly and the substantially uniform fixing property being ensured. Can be suppressed.

  The drive control of the first to fourth cooling fan devices can be performed as follows. That is, when the corresponding thermistors TH4 to 6 each detect a temperature exceeding a predetermined threshold temperature (a temperature outside a certain range), the voltage applied to the motor of the fan unit 31a is varied so that the temperature exceeds the threshold temperature. Accordingly, it is possible to adopt a configuration in which the wind speed of the cooling fan device is controlled in intensity.

  Cooling of the pressure belt 28 by the cooling fan unit 31 is performed in a state where the pressure belt 28 is separated from the fixing roller 21 and the heat supply from the fixing roller 21 is cut off, so that the cooling efficiency is increased. That is, as one means for sufficiently exerting and assisting the cooling capacity, the pressure belt 28 that is in pressure contact with the fixing roller 21 is provided with a pressure releasing mechanism, and is separated to a position where it is completely separated from the fixing roller 21. In this way, it is sufficient if there is a cooling assist mechanism that completely cuts off the heat supply from the fixing roller 21 to the pressure belt 28, and the configuration has the advantage of greatly increasing the cooling efficiency.

  Therefore, when the pressure belt 28 is cooled by the cooling fan unit 31, the controller unit 17 interrupts the image forming operation and puts the pressure belt unit 23 of the fixing device 12 on the fixing roller 21 (FIG. 2). 3. Switch from 3 ・ 5) to detached state (Fig.6 ・ 7 ・ 8). As a result, the pressure belt 28 is separated from the fixing roller 21. Then, the controller unit 17 turns on the cooling fan device to be driven by the cooling fan unit 31 and causes the pressure belt 28 to be cooled. When it is detected that the temperature of the pressure belt 28 falls within the allowable temperature, the controller unit 17 stops the cooling of the pressure belt 28 by the cooling fan unit 31, and switches the pressure belt unit 23 to the wearing state. The image forming operation is resumed.

  FIG. 12 is a pressure belt cooling time graph according to the presence or absence of cooling by the cooling fan unit 31 when the pressure belt unit 20 is detached and when it is worn. a is a temperature transition of the heating belt when the unit is in a worn state and there is no cooling. b is the temperature change of the heating belt when the unit is worn and with cooling. c is the heating belt temperature transition when the unit is in a detached state and without cooling. d is the temperature change of the heating belt when the unit is detached and with cooling. In the experiment of this graph, the temperature adjustment temperature of the fixing roller 21 is set to 165 ° C.

  In c (when the unit is removed and there is no cooling), although the pressure belt 28 is separated from the fixing roller 21, the temperature rises as time passes. This is because standby temperature control is carried out even if it is removed. That is, the pressure belt 28 continues to rotate even during standby, and heating by the entrance roller 26 is performed.

  The cooling fan unit 31 always obtains the same cooling effect without changing the positional relationship between the cooling fan device and the pressure belt 20 as a cooling object in conjunction with the attaching / detaching operation of the pressure belt unit 23. Means are effective. Without changing the positional relationship between the cooling fan device and the pressure belt from the mechanism that connects the unit 23 to the part to be attached and removed, and the cooling fan device performs the same attachment / detachment operation, and the part different from the unit attachment / detachment part, Any cooling mechanism such as providing another mechanism for obtaining the same cooling effect may be used.

  In the fixing device described above, the first to fourth four cooling fan devices 31 (1), 31 (2), 31 () in which the cooling fan unit 31 is configured with respect to the unit frame 24 of the pressure belt unit 23. 3) 31 (4) is fixedly supported. Accordingly, the positional relationship between these cooling fan devices and the pressure belt 20 (the distance a between the air blowing opening 31c of each cooling fan device and the pressure belt 28) is different from that when the unit 23 is worn (FIG. 3). It does not change with the state (FIG. 8).

  As described above, the fixing device of the present embodiment has a mode (first mode) in which the pressure belt 28 is cooled by controlling the cooling fan unit 31 on and off while the pressure belt unit 23 is in the worn state. Further, there is a mode (second mode) in which the pressure belt unit 23 is removed and the cooling fan unit 31 is controlled to be turned on / off to cool the pressure belt 28. These two modes are controlled separately. That is, the first mode is executed in order to cope with the temperature rise of the non-sheet passing portion of the fixing roller. Therefore, the first mode is implemented by using the temperature at the end of the fixing roller 21 or the number of small-size paper sheets as a trigger. The second mode is executed to remove the pressure belt 28 from the fixing roller 21 and quickly cool it when the pressure belt 28 has excessively heated due to contact with the fixing roller 21. Therefore, the second mode is performed using the temperature of the pressure belt 28 as a trigger.

  FIG. 13 shows another configuration example of the cooling fan unit 31. Reference numeral 45 denotes a fixed stay disposed between the front and back side plates of the fixing device casing. Each fan unit 31a including the motors and fans of the first to fourth four cooling fan devices 31 (1), 31 (2), 31 (3), and 31 (4) constituting the cooling fan unit 31 is as described above. The fixed stays 45 are arranged along the length of the fixed stay 45 and fixedly supported. Further, the air blowing opening 31c of each cooling fan device faces the outer surface of the pressure belt and is within the effective heating area width B of the fixing roller 21 along the longitudinal direction of the pressure belt with respect to the unit frame 24. They are arranged at substantially equal intervals. The distance a between the air blowing opening 31c and the pressure belt 28 of each cooling fan device is set to be substantially the same. And it is the structure which connected between the fan part 31a and each air blowing opening part 31c of each cooling fan apparatus with the bellows type duct part 31b which can be expanded-contracted. Therefore, also in the configuration example of FIG. 13, the positional relationship between the cooling fan device and the pressure belt 20 (air blowing of each cooling fan device) when the unit 23 is attached (a) and when it is detached (b). The distance a) between the opening 31c and the pressure belt 28 does not change.

  FIG. 14 shows still another configuration example of the cooling fan unit 31. This configuration example is obtained by changing the bellows type duct portion 31b to the telescopic type expansion / contraction duct portion 31b in the configuration example of FIG. Also in this configuration example, the positional relationship between the cooling fan device and the pressure belt 20 (when the unit 23 is in the attached state (a) and in the detached state (b)) The distance a) with the pressure belt 28 does not change.

  If the fixing roller 21 and the pressure belt 20 cannot be separated without being completely separated, the pressure down, roller hardness, fixing roller core metal thickness, fixing roller surface layer thickness, etc. are changed, and the fixing nip N Reduce the width. This also shortens the heating time of the pressure belt 20 by the fixing roller 21, so that the heat supply to the pressure belt 20 can be reduced.

  Applying at least one of the two means for sufficiently demonstrating and assisting the cooling capacity can lead to improvement of cooling and cooling efficiency.

  Further, it is desirable that the pressure pad 29 be shaped to take into account the flattening of the longitudinal pressure distribution at the fixing nip N and the non-sheet passing portion temperature rise that occurs when the small size recording material is continuously fed. Therefore, at least one of means for providing a spacer that forms a crown on the bottom surface of the elastic pad of the pressure pad 29, or means for forming a crown on the pressure pad support plate 29a, and a pressure contact with the fixing roller 21 is provided. The shape of the pressure pad length is determined. As an effect of this, by flattening the longitudinal pressure distribution in the fixing nip portion N in consideration of the temperature rise of the non-sheet passing portion, the longitudinal temperature distribution is flattened and the cooling temperature in the longitudinal direction of the pressure belt 28 and the pressure pad 29 is reduced. By making it uniform, image deterioration can be prevented evenly.

  In addition, the saturation of moisture contained in the recording material or the toner differs depending on the pressure belt temperature in the pressure relief portion, which is one of the causes of deterioration of the fixed image, with respect to the width direction of the fixing nip portion N. The degree of deterioration of the fixed image has also changed greatly. Therefore, in order to make the cooling effect effective for the fixed image, it is important to secure the pressure distribution in the width direction of the fixing nip portion N, which is an indispensable condition for improving the cooling effectiveness.

  Since the cooling fan device and the pressure belt are both arranged at a position where cooling is possible without changing the distance, the heat received from the pressure belt may be directly affected by the temperature rise of the cooling fan device. There may be. In such a case, risk can be avoided by small-scale measures such as discharging hot air through the exhaust duct or arranging a cooling FAN for the cooling fan device itself.

  In addition, when the cold air blown from the cooling fan device hits the pressure belt, the pressure belt can be cooled, but the cold air turns into hot air and remains in the atmosphere, which causes the temperature rise problem of many sensors arranged in the fixing device. There is a risk of development. Although it is sufficient that the sensors arranged in the fixing device are densely located at a certain location, in the case of the fixing device in which the sensors are complimented in the entire area, it is expected that dealing with the temperature rise of the sensor will be large-scale. For example, since there is a problem of space, a problem of power distributed to the fixing device due to addition of FAN, a cost, and the like, it is important to arrange the cooling device in consideration of the flow of cold air blown from the cooling device.

  Furthermore, since the pressure belt is cooled in conjunction with the attachment / detachment of the pressure belt unit 23 from the fixing roller 21, the cooling capacity differs between the unit detached state and the worn state. When the recording material feed speed is different, the cooling time is different, so the cooling capacity is also different. Further, in order to lower the temperature to a level at which the fixed image does not deteriorate, the cooling is performed depending on the temperature of the pressure belt and the pressure condition (after continuous paper feeding: after the intermittent paper feeding, the pressure time difference when the recording material feed speed is different). Ability is different. Among these different cooling times, it is important to ensure high productivity and separation cooling time during high-speed paper feeding, or to secure pressurization time during high-speed paper feeding. . However, it is an advantageous invention for outputting a higher-quality fixed image, and if the constraint condition can be established, the fixing ability with respect to the image deteriorated under the temperature condition can be satisfied.

  In the apparatus having the configuration shown in FIGS. 13 and 14 described above, the duct portion 31b of the cooling fan device expands and contracts or slides in conjunction with the detaching operation of the pressure belt unit 23, and cools the temperature rise of the pressure belt 20. This is a means configuration for obtaining a stable fixed image with suppression. That is, the same cooling effect is always obtained without changing the positional relationship between the air blowing opening 31c of the cooling fan device and the pressure belt 20 in conjunction with the attaching / detaching operation of the pressure belt unit 23.

  The cooling fan device itself is separated from the pressure belt 20 that raises the temperature, that is, the temperature of the cooling fan device itself is prevented by increasing the distance from the pressure belt that raises the temperature when the pressure belt is separated. Is effective. As shown in FIG. 13 and FIG. 14, a mechanism in which the duct portion 31 b that can be expanded or contracted provided in the cooling fan device is operated by being coupled with a part of a portion where the pressure belt is attached or detached, or a mechanism that drives sliding expansion and contraction by a motor It is sufficient if there is a moving mechanism such as. As for the cooling effect, even if compared with the configuration of FIG. 11, there is no significant decrease in the cooling capacity, and almost the same cooling capacity is exhibited. This is considered to be because the distance a from the air blowing opening 31c of the cooling fan device to the pressure belt can be ensured in the case of FIG. 11, FIG. 13, or FIG. Furthermore, the distance from the fan part 31a generating the air of the cooling fan device to the air blowing opening part 31c does not change significantly in any of the cases of FIG. 11, FIG. 13, and FIG. It is thought that the cooling capacity is maintained without changing the air volume and the wind speed. Therefore, in consideration of the temperature rise of the cooling fan device and the maintenance of the cooling capacity, the cooling fan device provided with the expansion / contraction / sliding mechanism is effective as in the case of FIGS.

  As a means for obtaining a stable fixed image by suppressing the temperature rise of the pressure belt, the pressure belt 28 for raising the temperature of the duct portion 31b that is extendable and slidable that operates in conjunction with the attachment / detachment operation of the pressure belt. As close as possible. Proximity is a non-contacting distance in consideration of vibration of the pressure belt and vibration due to thermal deformation. Thus, a means for preventing the temperature of the fixing device and its peripheral functions from rising without diffusing the air hitting the pressure belt as much as possible is effective.

  The position and distance between the cooling fan device and the pressure belt, or the air volume and the wind speed of the cross-sectional area where the air blown from the cooling fan device hits the pressure belt are calculated based on certain conditions. This is provided with a condition that is determined according to the required cooling capacity provided by the specifications and configuration of the fixing device.

  For example, the graph illustrated in FIG. 15 examines the correlation between the distance between the pressure belt 28 and the cooling fan device and the cooling time when the pressure belt 28 is cooled from about 140 ° C. to about 100 ° C. by the cooling fan device. It is the experimental result.

  Further, in the specifications on the cooling fan device side, when trying to determine the conditions of the average wind speed Vs and the air volume Qs per cross-sectional area Ss of the cooling assist mechanism, the cooling effect is determined according to the formula described in the JIS standard shown below. The optimal value of is calculated.

Qs (m ³ / s) = Vs (m / s) × Ss (m ² )
The conditions of the cooling fan unit 31 as the longitudinal temperature distribution fluctuation suppressing means using the cooling action described above vary depending on the configuration and specifications of the fixing device, and the required cooling capacity is calculated based on the above conditions. As a result, the toner (developer) is fixed on the recording material by pressurizing and heating and melting at the fixing nip, which is the original role of the fixing device, and it is ensured that a stable fixed image can be obtained. Any image that can obtain a fixed image with any color may be used. For example, in the case of the fixing cooling capacity having the characteristics as shown in FIG. 16, the cooling capacity to be used is one of the points on the curve of the graph.

  When a part or the entire temperature distribution along the longitudinal direction of the pressure belt 28 is detected at a temperature outside a certain range, it is sufficient that the cooling capacity can be varied and maintained according to the detected temperature.

  As such means, in the operation of the cooling device provided with the cooling assist mechanism as described above, for example, by performing a cooling operation in conjunction with the attachment and detachment of the pressure belt, the cooling capacity during paper passing and non-paper passing is at the same level. To keep it stable.

  In addition, when a part or all of the temperature distribution in the longitudinal direction of the pressure belt is detected at a temperature outside a certain range, each cooling fan device can be operated independently and connected, and the rotation speed of the fan can be adjusted at full speed. Set the half-speed mode. This makes the cooling capacity variable according to the detected temperature, and even if multiple problems such as non-sheet passing part temperature rise and whole area temperature rise occur at the same time, the pressure belt can be cooled evenly and uniformly. To do.

  In addition, the cooling assist mechanism operates independently and connected according to the detected temperature, so that the cooling capacity can be varied according to the detected temperature to increase the temperature of the non-sheet passing portion and the entire area. Even if the above problems occur at the same time, the pressure belt is uniformly and uniformly cooled.

  When a part or the whole temperature distribution along the longitudinal direction of the pressure belt is detected at a temperature outside a certain range by the above means, the cooling capacity is varied and maintained according to the detected temperature. I can do it.

  In addition, the cooling fan device is arranged at a position where the pressure belt to be cooled is shielded by the area of the recording material passing portion and the non-sheet passing portion. At least one of the front side (sheet passing portion, non-sheet passing portion), central portion (sheet passing portion), and back side (sheet passing portion, non-sheet passing portion) in the longitudinal direction of the pressure belt can be shielded. Exists. It is only necessary to be able to cool both ends and the center at the same time or to cool either the both ends or the center. For example, it is a means for cooling with the arrangement of the cooling device as shown in FIG.

  Further, the longitudinal temperature distribution fluctuation suppressing means utilizing the heat supply blocking action acts directly or indirectly to block the heat from the fixing roller 21 transmitted to the pressure pad 29 forming at least the fixing nip portion of the pressure belt. What is necessary is just to obtain. For example, it is a means for releasing the pressure contact between the fixing roller 21 and the pressure belt and completely shutting off the heat supply from the fixing roller 21. Alternatively, a pressure pad for reducing the heat capacity between the fixing roller and at least the non-sheet passing portion of the pressure belt in order to suppress the temperature rise of the non-sheet passing portion of the pressure pad forming the fixing nip portion. The material and the shape are arranged. In addition, the heat supply shut-off function operates in conjunction with the attachment / detachment of the pressure belt, similarly to the role of the cooling assist mechanism included in the cooling action, regardless of the pressure belt attachment / detachment position depending on the presence or absence of the copy job. It will play a role in maintaining the cooling effect.

  Further, the longitudinal temperature distribution fluctuation suppressing means utilizing the longitudinal pressure action in the shape of the pressure pad is configured such that at least the non-sheet passing portion of the pressure belt reduces the deformation amount of the heating temperature of the pressure pad by the pressure and heat from the fixing roller. It is a means to adjust. Moreover, the amount of change in which the pressure pad is heated may be long as long as the effect of further suppressing the amount of change is obtained. For example, as a countermeasure against the temperature rise of the non-sheet passing portion, in order to suppress the temperature change amount in the length of the pressure pad, the pressure on the non-sheet passing portion side in the shape of the pressure pad, that is, the end pressure of the fixing nip portion is set. A crown is formed so as to form a nip at the lowest possible pressure. As a result, the pressure distribution in the fixing nip portion forms a slightly higher central pressure distribution than the end partial pressure, and the thermal conductivity from the fixing roller due to a decrease in linear pressure between the fixing roller and the pressure pad at the end portion. Is a means for reducing the change in the heating temperature.

  The longitudinal temperature distribution variation suppressing means may use a combination of a plurality of such cooling actions, heat supply blocking actions, and longitudinal pressure actions in the shape of the pressure pad.

  The non-sheet passing portion of the pressure belt is a so-called recording material that is generated by the size of the width in the feeding direction of the recording material, including a portion where the recording material is not expected to pass at all in a normal fixing operation. The non-passing region is also included.

  The heating rotator is mainly roll-shaped, but may be belt-shaped. Further, the pressure rotator may be in a roll shape. You may provide the heating means which heats the pressurization rotary body side supplementarily.

  Therefore, in the present invention, the image heating device (fixing device) may be a roller nip type device in which both the heating rotator and the pressure rotator are in a roll shape.

  By providing the longitudinal temperature distribution fluctuation suppressing means as described above, excessive temperature rise in the pressure belt at least in the non-sheet passing portion (a state in which the temperature rises abnormally compared to the temperature rise in the sheet passing portion) and pressurization A longitudinal temperature difference caused by an excessive temperature rise in the entire belt is suppressed.

  Incidentally, in the case of the longitudinal temperature distribution fluctuation suppressing means using the cooling action or the heat supply shut-off action, the excessive temperature rise in at least the non-sheet passing portion of the heating body and the excessive temperature rise in the entire pressure belt are prevented. The Thereby, as a result of the temperature of the non-sheet passing portion and the vicinity thereof becoming constant, fluctuations in the longitudinal temperature distribution are suppressed.

  Further, in the case of the longitudinal temperature distribution fluctuation suppressing means using the longitudinal pressure action in the shape of the pressure pad, the pressure distribution in the fixing nip portion is varied. For this reason, when the pressure tends to be shifted toward the center or the end portion, there is a possibility that image fluctuation occurs due to speed fluctuation, that is, slippage due to fluctuation of the friction coefficient μ in the fixing nip portion. Depending on the shape of the pressure pad, the pressure distribution is made almost flat with respect to the pressure belt width direction, so that the speed fluctuation in the pressure belt width direction is eliminated, and image displacement is prevented. Also, the transportability of the fixing nip can be stably performed.

  As a result, if the pressure distribution in the fixing nip is set to be flat or slightly centrally high, the temperature difference between the non-sheet passing portion and the sheet passing portion of the pressure belt tends not to be noticeable.

  Such a longitudinal temperature distribution fluctuation suppressing means is particularly effective when employed in a belt nip type image fixing apparatus as shown in the embodiments.

  Of course, the pressure belt is effective even when it is employed in another component, for example, a roller nip type image fixing apparatus including a pressure roll as described above.

  In the belt nip type image fixing device, an action of cooling at least a portion of the pressure belt corresponding to the non-sheet passing portion of the pressure pad or an action of blocking heat transfer from the fixing roller to the pressure pad side. It is preferable to provide a longitudinal temperature distribution fluctuation suppressing means to be used.

  In this case, the pressure belt is cooled to indirectly cool the non-sheet passing portion or the sheet passing portion of the pressure pad, or to the non-sheet passing portion or the sheet passing portion of the pressure pad. As a result, abnormal temperature rises in the non-sheet passing portion and the sheet passing portion are prevented.

  Further, such a configuration of the longitudinal temperature distribution fluctuation suppressing means is advantageous even when there is no installation space or the like for disposing the longitudinal temperature distribution fluctuation suppressing means having the action of directly cooling the pressure pad or blocking the heat supply. is there.

  In the belt nip type image fixing apparatus, when the longitudinal temperature distribution fluctuation suppressing means utilizing the cooling action is used, the suppressing means is a pressure pad forming the fixing nip portion of the pressure belt. It is good to arrange | position so that it may cool intensively. Or it is good to arrange | position so that it may cool before the pressurization belt conveys to a nip part. In this case, the endless belt is efficiently cooled by the longitudinal temperature distribution fluctuation suppressing means.

  Among the temperature detection means of the pressure belt using these longitudinal temperature distribution fluctuation suppression means, the temperature detection signal in the fixing device is detected at a temperature outside a certain range, and the temperature increase in the pressure belt width direction is predicted. However, it is preferable to set the cooling operation.

  Furthermore, regardless of the fixing nip method, when using the longitudinal temperature distribution fluctuation suppressing means that uses the cooling action, it is preferable to set the cooling operation to allow for a certain temperature margin. That is, the cooling by the suppression means predicts at least the temperature when the pressure belt is removed before the recording material is conveyed to the fixing nip or the temperature when the pressure belt is attached, and cools it with a certain temperature margin. It is good to set it so that the action can be entered.

  In this case, overheating of at least the non-sheet passing portion of the pressure belt that is likely to occur depending on the presence or absence of the recording material passing through the fixing nip portion can be prevented simply and efficiently. Moreover, in this case, while the recording material does not pass through the fixing nip portion, the temperature rise in the pressure belt width direction is predicted based on the signal detected at a temperature outside the predetermined range, and the cooling operation is turned ON / OFF. Setting is possible. From this, it is possible to prevent the pressure belt from being cooled by the cooling action of the longitudinal temperature distribution fluctuation suppressing means. Therefore, there is no possibility of adversely affecting the temperature control of the fixing temperature in the fixing device (for example, temperature control during warm-up or idling) (unnecessary temperature decrease or the like).

  In addition to the above setting, in order to detect the temperature of the pressure belt within a certain range, a control for performing idling for a certain time and entering a cooling operation may be set. In the cooling operation during paper passing, the temperature of the pressure belt is detected by the temperature detection means at the center and both ends of the pressure belt in the width direction, and the temperature of the pressure belt is raised. Foresee. Then, only that position may be set to be feedback-controlled so as to perform a cooling operation to a temperature within a certain range.

  Such an image heating apparatus of the present invention is applied to an image forming apparatus that needs to fix an unfixed toner image on a recording material to form a permanent image. There are no particular restrictions on the configuration of the image forming apparatus, but in particular, when applied to an image forming apparatus having a configuration capable of performing continuous image formation using coated paper as a recording material, the image as described above is used. This is particularly beneficial since good fixing without deterioration occurs.

Schematic configuration diagram of an example of an image forming apparatus Cross-sectional view showing schematic configuration of fixing device Partial enlarged view of FIG. Block diagram of the fixing device control system Side view of the front side of the fixing device (when the pressure belt unit is worn) Side view of the front side of the fixing device (when the pressure belt unit is removed) Cross-sectional view of FIG. Partial enlarged view of FIG. Pressure distribution diagram in the width direction of the fixing nip (10)-(10) line view of FIG. Temperature transition graph of the pressure belt belt passing part and non-sheet passing part when 100 sheets of small size recording material are continuously passed Pressure belt cooling time graph with and without cooling by the cooling fan unit when the pressure belt unit is detached and worn Cross-sectional view of another configuration example of cooling fan unit Cross-sectional view of still another configuration example of the cooling fan unit Experimental result graph in which the correlation between the distance between the pressure belt and the cooling fan device and the cooling time when the pressure belt is cooled from about 140 ° C. to about 100 ° C. by the cooling fan device Transition graph of cooling capacity by wind speed

Explanation of symbols

  12 .. Fixing device (image heating device) 21.. Fixing roller (heating rotator) 23.. Pressure belt unit 28.. Pressure belt (pressure rotator) 31. Cooling unit), 36 ・ ・ Eccentric cam (detachment mechanism)

Claims (3)

A heating rotator for heating the image on the recording material at the nip portion, a pressure rotator for forming the nip portion between the heating rotator, and the pressure rotator for contacting and separating from the heating rotator. In an image heating apparatus comprising: a contacting / separating unit for causing cooling; and a cooling unit for cooling the pressurizing rotating body.
An image heating apparatus, wherein the cooling means is moved in conjunction with the contact / separation operation of the contact / separation means.   The image heating apparatus according to claim 1, further comprising a holding unit that holds the cooling unit and the pressurizing rotating body, and the holding unit is moved in conjunction with a contact / separation operation of the contact / separation unit.   The cooling means includes a fan, and a duct that includes a blower opening that blows air from the fan toward the pressurizing rotating body and expands and contracts in conjunction with the contacting / separating operation of the contacting / separating means. The image heating apparatus according to claim 1.