JP2012008377A - Image heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heater that prevents bend and crack in an endless belt due to longitudinal bend stress in the case where a side edge face of the endless belt is brought into contact with a skew restricting portion, downstream from a nip area in the rotating direction of the endless belt.SOLUTION: The side edge face of the endless belt is brought into contact with the skew restricting portion in a predetermined area upstream from the nip area. On the other hand, it is separated from the skew restricting portion in the other area in the rotating direction of the endless belt.

Description

  The present invention relates to an image heating apparatus used in an image forming apparatus such as a copying machine or a printer. Examples of the image heating device include a fixing device that heats and fixes an unfixed image formed on a recording material as a fixed image, and a glossiness increasing device that increases the glossiness of an image by heating the image fixed on the recording material. Can be mentioned. In particular, the present invention is applied to an image forming apparatus such as a copying machine or a printer (for example, a laser printer or an LED printer) that uses an electrophotographic method and forms an image on a recording material using an image carrier that forms a latent image. Is preferred.

(Fixing device in general)
2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system or the like develops a latent image formed on, for example, a photosensitive drum serving as an image carrier to form a visible image. Then, the visible image (toner image) is transferred to the recording material using electrostatic force, and then the transferred image is fixed by heat, whereby an image is recorded and formed on the recording material.

(On-demand fixing)
In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a toner image is formed on a sheet as a recording material, and the image is formed by fixing the toner image by heating and pressing. As such a fixing device, a roller fixing method in which a fixing nip portion is formed by pressing a pressure roller against a fixing roller having a heater therein to perform fixing is conventionally employed.

  In the fixing device, the heating member can be instantaneously heated to a predetermined temperature from the viewpoint of saving energy and not causing the user to wait when using the image forming apparatus. A zero-equipped device is required. The above-described heating method using a heating source such as a halogen lamp disposed inside the heating roll cannot be achieved for the following reason. That is, the heating roll as a heating member is a member to which a pressure member such as a pressure roll is pressed, so that it needs to maintain a predetermined rigidity or more, and has a metal core having a certain thickness or more. Yes. Therefore, the heating roll cannot reduce the heat capacity so much. In addition, since the halogen lamp as a heating source is provided inside the heating roll and heats the heating roll from the inside, it takes time until the heat is transmitted to the surface of the heating roll, so a waiting time is inevitably required. It will be long. For the above reasons, the conventional fixing device has a problem that it takes time to warm up and the waiting time becomes long.

  Therefore, in recent years, a film heating type fixing device using a film as a rotatable endless belt having flexibility is known from the viewpoint of quick start and energy saving (Patent Document 1). That is, a fixing nip portion is formed by sandwiching a heat resistant resin film (hereinafter referred to as a fixing film) as a heating member between, for example, a ceramic heater as a heating body and a pressure roller as a pressing member. Then, a recording material on which an unfixed toner image is formed and supported is introduced between the fixing film and the pressure roller in the fixing nip portion, and is nipped and conveyed together with the fixing film. Thus, the unfixed toner image is fixed on the surface of the recording material with the pressure of the fixing nip portion while applying heat of the ceramic heater through the fixing film.

  This film heating type heating apparatus does not require energization of the heater in standby, and after the image forming apparatus receives the print signal, the recording material reaches the heating apparatus even if the heater is energized. It is possible to make it heatable. Therefore, from the viewpoint of energy saving, a film heating type heating device is an excellent fixing device that does not waste energy.

  Also, in this film heating type heating device, when a metal thin sleeve formed using a metal having a higher thermal conductivity than the resin fixing film as the heating layer is used as the heating member, the fixing performance is improved and image formation is achieved. It is possible to sufficiently cope with the speeding up of the apparatus.

JP-A-4-44075

  The present invention is a further improvement of the prior art, and its purpose is to break the bending end due to bending stress in the longitudinal direction when the side end surface of the endless belt is brought into contact with the restricting portion by being shifted downstream of the nip portion in the rotational direction of the endless belt. An object of the present invention is to provide an image heating apparatus capable of preventing cracks and cracks.

In order to achieve the above object, a typical configuration of an apparatus according to the present invention includes a flexible endless belt, a backup member placed inside the endless belt, and the endless belt. A pressure rotator that is in pressure contact with the backup member to form a nip portion with the endless belt, a driving unit that rotationally drives the pressure rotator, and a rotational drive of the pressure rotator The end portion of the endless belt is brought into contact with a guide portion that guides the inner surface of the endless belt in a longitudinal end region that intersects the rotational direction of the endless belt that rotates. A deviation regulating portion that regulates the deviation movement in the longitudinal direction,
In the image heating apparatus that heats the recording material carrying the image at the nip portion while nipping and conveying the side end surface of the endless belt whose inner surface is guided by the guide portion, the rotation direction of the endless belt from the nip portion In the predetermined region on the upstream side, the shift regulating portion is in contact with the shift regulating portion so that the side end surface of the endless belt is separated from the shift regulating portion in the other region in the rotation direction of the endless belt. Steps are provided.

  According to the present invention, it is possible to prevent the endless belt from being bent or cracked due to the bending stress in the longitudinal direction.

FIG. 3 is a perspective view of a shift regulating portion of the fixing device according to the first embodiment of the present invention. 1 is an explanatory diagram of an image forming apparatus in which a fixing device according to a first embodiment of the present invention is mounted. 1 is a cross-sectional view of a fixing device according to a first embodiment of the present invention. FIG. 3 is a side view of a film unit and a pressure roller constituting the fixing device according to the first embodiment of the present invention. It is explanatory drawing regarding the guide part which the inner surface of the longitudinal direction edge part of a fixing film contacts. It is explanatory drawing regarding the track | orbit with flapping of a fixing film. FIG. 6 is a schematic diagram of a force applied to a fixing film on an upstream side and a downstream side of a fixing nip portion. (A) is a figure which shows the locus | trajectory of a fixing film when not guiding with a guide part, (b) is the enlarged view, (c) is a figure which shows the locus | trajectory of a fixing film when guiding with a guide part. FIG. 3 is a plan view of a shift regulating portion of the fixing device according to the first embodiment of the present invention. It is explanatory drawing regarding the experiment which investigates the relationship between the kind of deviation control part, and film durability. It is explanatory drawing which shows the experimental experiment result which investigates the relationship between the kind of deviation control part, and film durability. (A) is the figure which looked at the guide part and the deviation control part from the longitudinal direction, (b) is the figure which looked at the guide part and the deviation restriction part from the side. FIG. 6 is a schematic front view of a fixing device according to a second embodiment of the present invention. FIG. 6 is a schematic longitudinal sectional front view of a fixing device according to a second embodiment of the present invention.

<< First Embodiment >>
(Image forming device)
FIG. 2 is a cross-sectional view showing a schematic configuration along the sheet (recording material) conveyance direction of a color electrophotographic printer which is an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device. The printer 1 according to the present embodiment forms an image on the recording material P by performing an image forming operation in accordance with input image information from an external host device 200 that is communicably connected to a control circuit unit (control board: CPU) 100. Can be output. The external host device 200 is a computer, an image reader, a facsimile, or the like. The control circuit unit 100 exchanges signals with the external host device 200. It also controls image forming sequence by exchanging signals with various image forming devices on the printer side. The recording material P includes plain paper, resin sheet, cardboard, OHP sheet (overhead projector sheet), envelope, postcard, label, and the like.

  In the printer, first to fourth image forming portions Y, M, C, and Bk are arranged in a horizontal direction from the left side to the right side in the drawing (in-line configuration, tandem type). Each of the image forming units is a laser exposure type electrophotographic process mechanism, and has the same configuration except that the color of the developer (toner) contained in the developing device is different. That is, each of the image forming units Y, M, C, and Bk is a drum type electrophotographic photosensitive member (image carrier: hereinafter referred to as a drum) 2 that is driven to rotate at a predetermined speed in the counterclockwise direction indicated by an arrow. Have Around each drum 2, a primary charger 3, a laser scanner 4, a developing device 5, a primary transfer blade 6, and a cleaner 7 are disposed as process means acting on the drum 2.

  An intermediate transfer belt unit 8 is disposed below the image forming portions Y, M, C, and Bk. The unit 8 includes an endless and flexible intermediate transfer belt (hereinafter referred to as a belt) 9, a driving roller 10, a tension roller 11, and a secondary transfer counter roller 12 that suspends the belt 9. . The primary transfer blades 6 of the respective image forming portions Y, M, C, and Bk are arranged inside the belt 9 and correspond to each other via an ascending belt portion between the tension roller 11 and the driving roller 10 of the belt 9. The drum 2 is pressed against the lower surface of the drum 2. A contact portion between each drum 2 and the belt 9 is a primary transfer portion. A secondary transfer roller 13 is in pressure contact with the secondary transfer counter roller 12 via a belt 9. A contact portion between the belt 9 and the secondary transfer roller 13 is a secondary transfer portion. The belt 9 is circulated and moved by the driving roller 10 in a clockwise direction indicated by an arrow at a speed corresponding to the rotational speed of the drum 2.

  In the present embodiment, the first image forming unit Y contains a yellow (Y) developer in the developing device 5 and forms a Y color toner image on the drum 2. The second image forming unit M stores a magenta (M) developer in the developing unit 5 and forms an M toner image on the drum 2. In the third image forming unit C, cyan (C) developer is accommodated in the developing device 5, and a C color toner image is formed on the drum 2. The fourth image forming unit Bk contains a black (Bk) developer in the developing unit 5 and forms a Bk color toner image on the drum 2.

  The control circuit unit 100 causes each of the image forming units Y, M, C, and Bk to perform an image forming operation based on the color separation image signal input from the external host device 200. As a result, Y, M, C, and Bk color toner images are formed on the surface of the drum 2 that rotates in each of the image forming units Y, M, C, and Bk at predetermined control timings. . The electrophotographic image forming principle and process for forming a toner image on the drum 2 are well-known and will not be described.

  The toner images formed on the surfaces of the drums 2 of the image forming units Y, M, C, and Bk are respectively transferred to the primary transfer unit in the rotation direction and the forward direction of the drums 2 and the rotation speed of the drums 2. Are sequentially superimposed and transferred onto the outer surface of the belt 9 which is rotationally driven at a speed corresponding to the above. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the belt 9 by superimposing the four toner images of the Y, M, C, and Bk colors.

  On the other hand, at a predetermined paper feed timing, each of the selected levels of the upper and lower cassette paper feed units 14A and 14B in which recording materials P (hereinafter referred to as sheets) P of various sizes are stacked and accommodated. The paper feed roller 15 of the paper feed cassette is driven. As a result, the sheets P stacked and stored in the paper feed cassette at that level are separated and fed one by one and conveyed to the registration roller 18 through the conveyance path 16. When manual sheet feeding is selected, the sheet feeding roller 19 is driven. As a result, the sheets P stacked and set on the multi-feed tray 20 are separated and fed one by one and conveyed to the registration roller 18 through the conveyance path 16. The registration roller pair 18 receives the sheet P once and corrects it straight when the sheet is skewed. Then, the registration roller pair 18 sends the sheet P to a secondary transfer portion that is a pressure contact portion between the belt 9 and the secondary transfer roller 13 in synchronization with the toner image on the belt 9. As a result, the full-color composite toner image on the belt 9 is secondarily transferred onto the surface of the sheet P at the secondary transfer portion.

  The sheet P exiting the secondary transfer portion is separated from the surface of the belt 9 and introduced into the fixing device 21. The fixing device 21 melts and mixes toner images of a plurality of colors on the sheet P and fixes them as fixed images on the sheet surface.

  The surface of the belt 8 after separation of the sheet at the secondary transfer portion is cleaned by removing residual deposits such as secondary transfer residual toner by the belt cleaner 22 and repeatedly used for image formation.

  In the monochrome print mode, only the fourth image forming unit Bk that forms a black toner image is controlled in image forming operation.

  In the case of the single-sided printing mode, the sheet P that has exited the fixing device 21 is switched by the switching flapper 23 in accordance with a pre-designation, and is discharged to the face-up discharge tray 25 disposed on the side of the printer. Alternatively, the paper is discharged to a face-down paper discharge tray 28 disposed on the upper surface of the printer. In the case of paper discharge to the tray 25, the sheet P that has exited the fixing device 21 travels straight through the lower surface side of the flapper 23 that has been converted to the first posture, and the first paper discharge roller 24 causes the sheet P to move onto the tray 25. The image is discharged upward. In the case of paper discharge to the tray 28, the sheet P that has exited the fixing device 21 is guided upward through the upper surface side of the flapper 23 that has been changed to the second posture, and is transported upward by the transport path 26. Then, the second paper discharge roller 27 discharges the image onto the tray 28 downward.

  In the double-sided printing mode, the sheet P having undergone image formation and fixing on the first surface exiting the fixing device 21 is guided upward through the upper surface side of the flapper 23 that has been converted to the second posture. It is conveyed upward by the path 26. When the trailing edge reaches the reversal point R during the conveyance of the sheet P, the conveyance path 26 is switched to the reverse conveyance drive. As a result, the sheet P is switched back and enters the double-sided conveyance path 29. Then, it enters the conveyance path 16 again from the double-sided conveyance path 29 and is re-conveyed to the secondary transfer unit in a state where the front and back sides are reversed. As a result, the sheet P receives image transfer on the second surface. The sheet P that has exited the secondary transfer portion is introduced into the fixing device 21. The double-side printed sheet P exiting the fixing device 21 is routed by the switching flapper 23 according to a pre-designation and discharged to the tray 25 or 28 as in the single-sided printing mode. The portion constituted by the flapper 23, the switchback transport path 26, and the like is an example of a reversing unit.

(Fixing device)
FIG. 3 and FIG. 4 are a cross-sectional view and a side view, respectively, of a fixing device 21 according to an embodiment of the present invention as an image heating device that heats a recording material carrying an image at the nip portion while being nipped and conveyed. The fixing device of the present embodiment is a film heating method, and heats a thin fixing film 101 having a conductive layer which is a flexible endless belt having flexibility by a ceramic heater 103.

  The film fixing device includes a method of transporting the fixing film between the pressure roller while applying tension using a dedicated transport roller and a driven roller to transport the fixing film, and pressurizing the cylindrical fixing film. There is a tensionless method of driving with the conveying force of the roller. The former has the advantage that the transportability of the fixing film can be increased, and the latter has the advantage that the apparatus configuration can be simplified and a low-cost fixing device can be realized.

  This tensionless type film heating type heating device uses a heat-resistant endless film which is a cylindrical endless belt. At least a part of the circumference of the film is always tension-free, that is, no tension is applied to the film, and the film is rotated by the rotational driving force of a pressure roller as a pressure rotation member.

  In FIG. 3, a heater 103 is basically composed of an elongated thin plate-like ceramic substrate whose longitudinal direction is perpendicular to the drawing, and an energization heating resistor layer provided on the substrate surface. This is a low heat capacity heater that raises the temperature with a steep rise characteristic as a whole.

  The heater support member 104 fixes and supports the heater 103. The heater support member 104 is a heat insulating member such as a heat resistant resin having a substantially semicircular arc shape in cross section and having a longitudinal direction as a longitudinal direction in the drawing. A stay 105 is provided inside the support member 104. The heater 103 is disposed in a groove formed along the length of the lower surface of the heater support member 104 so that the heater surface is exposed downward and fixed with a heat resistant adhesive or the like. A temperature detection element (not shown) such as a thermistor for detecting the heater temperature is disposed on the surface of the heater 103 on the support member 104 side.

  The fixing film 101 which is an endless belt is a cylindrical (endless) heat-resistant film as a heating member that transmits heat, and is loosely fitted on a support member including the heater 103. The fixing film 101 has a reduced heat capacity to improve quick start performance. The film thickness is 100 μm or less, preferably 50 μm or less and 20 μm or more. The film material is a single layer of heat-resistant polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), or tetrafluoroethylene / hexafluoropropylene copolymer (FEP). Or it is the following composite layers. That is, it is a layer in which PTFE, PFA, FEP, etc. are coated on the outer peripheral surface of polyimide (PI), polyamide imide (PAI), polyether ether ketone (PEEK), polyether sulfone (PES), polyphenylene sulfide (PPS), etc. is there. The fixing film 101 as an endless belt can be made of metal.

  Reference numeral 102 denotes a pressure roller as a heat-resistant elastic pressure member, which is rotationally driven by a driving means M (FIG. 1). The pressure roller 102 is composed of a cored bar and an elastic layer made of a heat-resistant rubber such as silicone rubber or fluororubber, or a foam of silicone rubber, and is disposed with both ends of the cored bar supported rotatably. is there. The above-described assembly of the heater 103, the support member 104, the fixing film 101, and the stay 105 is arranged in parallel with the pressure roller 102 with the heater 103 side facing downward. Then, by pressing the stay 105 downward, the lower surface of the heater 103 is pressed against the upper surface of the pressure roller 102 via the fixing film 101 against the elasticity of the roller elastic layer, thereby fixing the fixing nip having a predetermined width as a heating unit. Part N (FIG. 6) is formed. In other words, the heater 103, the support member 104, and the stay 105 constitute a backup member disposed inside the fixing film 101. Then, the backup member and a pressure roller as a pressure rotator are brought into pressure contact with each other through the fixing film 101 to form a nip portion N between the fixing film 101.

  Reference numeral 107 denotes a shift regulating portion that is fitted and disposed on the front side and back side ends (both ends) of the support member 104, and receives the side end in the longitudinal direction of the fixing film 101. It plays a role of restricting the movement of the supporting member 104 along the longitudinal direction. In FIG. 4, which shows the film unit and the pressure roller, reference numeral 106 denotes a guide portion that receives the inner surface of the fixing film 101 and serves to regulate the rotation path, and both end portions in the direction intersecting the rotation direction of the fixing film. Provided on the side.

(Stabilization of fixing film trajectory)
When the fixing film 101 is driven by the conveying force of the pressure roller 102 without applying tension to the thin fixing film 101, the fixing film 101 flutters in the rotation direction.

  8A and 8B show the results of measuring the trajectory of the fixing film 101 when the fixing film 101 is driven by the conveying force of the pressure roller 102 without guiding the fixing film 101 by the guide unit 106. It is. When the fixing film 101 is driven by the pressure roller 102 at the fixing nip portion N without being guided, the fixing film 101 flutters in the circumferential direction (rotating direction). When the fixing film 101 flutters in the circumferential direction, the end portion of the fixing film 101 in the longitudinal direction (direction intersecting the rotation direction) comes into contact with the shift restricting portion 107, so that the frictional force and the buckling force can be obtained. The area which receives the composite stress of is created. Therefore, it is necessary to stabilize the locus of the fixing film 101.

(Shapes of guide part and offset control part)
Therefore, in this embodiment, when the fixing device 21 is driven as shown in FIG. 4, the inner surface of the fixing film 101 is guided in the end region in the longitudinal direction of the guide portion 106 for stabilizing the locus of the fixing film 101. Are provided at both ends. As the material of the guide portion 106, PPS, or heat-resistant material such as PET or PES can be used. However, in order to reduce the load on the fixing film 101, the guide portion 106 is designed so that the guide portion is smaller than the inner diameter of the fixing film 101 so that the guide portion 106 is not pressed against the fixing film 101 over the entire surface of the guide portion. .

  Here, in the area where the fixing film 101 of the guide portion 106 is in pressure contact, the area where the inner surface of the fixing film 101 and the outer surface of the guide portion 106 are constantly in pressure contact is A, and the inner surface of the fixing film 101 and the outer surface of the guide portion 106 are Let B be a region where pressure welding and separation are repeated. FIG. 5 is a perspective view of the region A and the region B viewed from an oblique direction. The fixing film 101 is not shown. FIG. 6 is a view of the region as seen from the cross-sectional direction, and 101a and 101b are views showing a state where the fixing film 101 flutters in the circumferential direction (rotation direction). The fixing film 101 is regulated by the nip portion N, and when rotating in the circumferential direction, a region A that is tensioned in the circumferential direction is always provided in a part of the guide portion 106 (a predetermined region upstream of the nip portion N). Exists.

  In the region A where the tension is applied in the circumferential direction, the guide portion 106 is always regulated in the circumferential direction and does not flutter in the circumferential direction. On the other hand, since there is nothing to regulate in the region where no tension is applied, the fixing film 101 flutters in the circumferential direction under various conditions such as the temperature state of the fixing film 101 and the rotation speed of the fixing film.

FIG. 7 is a diagram schematically showing the direction of the force received by the end face of the fixing film 101. S represents the force in the rubbing direction, and Z represents the buckling force in the longitudinal direction. In FIG. 7, the upper side is the upstream side with respect to the fixing nip N, and the lower side in FIG. In the predetermined area A upstream of the fixing nip portion N, the fixing film 101 receives only a rubbing force in the rotation direction (circumferential direction) between the fixing film 101 and the shift regulating portion 107. On the other hand, in the region B where the trajectory of the fixing film 101 is not stable in the rotation direction, the rubbing force in the rotation direction and the buckling in the longitudinal direction (direction perpendicular to the rotation direction) with the shift restricting portion 107. You will receive power.
As shown in FIG. 7, the buckling force in the longitudinal direction is greater on the downstream side than the nip portion N on the upstream side.

  Therefore, in the present embodiment, the side end surface of the fixing film 101 whose inner surface is guided by the guide portion 106 comes into contact with the shift restricting portion in a predetermined region upstream of the nip portion N (the rotation direction of the fixing film 101). To. Then, in the rotation direction of the endless belt, a step portion is provided in the shift regulating portion so that the side end surface of the endless belt is separated from the shift regulating portion in other regions.

  Here, the “upstream side” in the rotation direction of the endless belt with respect to the nip portion N refers to a region that does not include the nip portion N and goes from the zenith portion with respect to the nip portion N toward the nip portion N along the rotation direction. Shall.

  As a result, even if the fixing film flutters on the downstream side, since the side end surface of the film is separated from the deviation regulating portion on the downstream side, the film does not receive a force from the deviation regulating portion and prevents film damage. it can. Here, the “downstream side” in the rotation direction of the endless belt with respect to the nip portion N refers to a region that does not include the nip portion N and goes from the nip portion N to the zenith portion with respect to the nip portion N along the rotation direction. Shall.

  Regarding the stepped portion of the shift regulating portion 107, FIG. 1 is a view of the shift regulating portion 107 seen from an oblique direction, and FIG. 9 is a view seen from the top. In FIG. 1 and FIG. 9, the surface of the shift restricting portion 107 is C (protrusion portion), which is protruding in the contact direction when viewed from the shift direction Y, and is not protruding, that is, the side end surface of the fixing film 101. The non-abutting surface that did not contact was designated as D (non-protruding portion). Since the abutting surface C does not always contact the fixing film 101 perpendicularly with parts accuracy and assembly accuracy, the non-abutting surface D that does not protrude in the abutting direction is 0 with respect to the protruding surface C. It is desirable to recede 5mm or more.

  Here, if the area of the abutting surface C for receiving the offset force is in the area A where the inner surface of the fixing film 101 and the outer surface of the guide portion 106 are constantly in pressure contact, the end face of the fixing film 101 is shifted. Only the rubbing force in the rotation direction is received between the restricting portion 107 and the control portion 107. For this reason, since it does not receive the buckling force in the longitudinal direction and does not need to receive two combined stresses of the rubbing force and the buckling force, the fixing film 101 can be prevented from cracking or cracking.

  FIG. 12 shows a specific step region between the abutting surface C and the non-abutting surface D of the deviation regulating portion 107. FIG. 12A is a view of the guide portion and the shift restricting portion viewed from the longitudinal direction, and FIG. 12B is a view of the guide portion and the shift restricting portion viewed from the side. About this level | step difference formation, you may form the non-abutting surface D by grinding etc. on the basis of the abutting surface C, and additionally form the abutting surface C on the non-abutting surface D by the screw coupling etc. Also good.

  In the present embodiment, the guide portion 106 and the shift restriction portion 107 may be configured as the same integrated member or may be configured as separate members.

(Measurement of film trajectory)
Here, an experiment was conducted in which the outer track of the fixing film 101 was measured with a laser displacement meter. In this experiment, the inner peripheral position is calculated by subtracting the thickness of the fixing film 101 from the outer peripheral position, and the area A and the area B are defined. As a result, the contact area between the shift restricting portion 107 and the side end portion of the fixing film 101 can be controlled to prevent the end portion of the fixing film 101 from being damaged. Hereinafter, the experimental method will be described. The inventor prepared the first model to the sixth model with respect to the abutting surface C of the shift regulating portion 107.

  First, when the region where the film inner surface is constantly in contact with the guide portion 106 is A, the region in the rotation direction of the abutting surface C of the deviation regulating portion 107 with which the film side end surface is in contact is equal to the region A. Or the form made into the smaller area | region was made into the 1st model 107a. In the first model, the film fluttering is zero within the area of the abutting surface C of the deviation regulating portion 107.

Next, five types of models were considered in which the region where the film side end surface is in contact with the abutting surface C of the shift restricting portion 107 is larger than the region A in the film rotation direction. That is, the second model 107b has a configuration in which the area of the abutting surface C of the shift restricting portion 107 is widened so that the side end surface comes into contact with a region where the film fluttering changes to 0.1 mm at the maximum. Similarly, the third model 107c is a form in which the area of the abutting surface C of the shift restricting portion 107 is widened so that the side end face comes into contact with a region where the film fluttering changes to 0.2 mm at the maximum. Furthermore, a form in which the area of the abutting surface C of the shift restricting portion 107 is widened so that the side end surface comes into contact with a region where the film fluttering changes to a maximum of 0.3 mm is defined as a fourth model 107d. In addition, the fifth model 107e is a form in which the area of the abutting surface C of the shift restricting portion 107 is widened so that the side end surface comes into contact with a region where the film fluttering changes to 0.4 mm at the maximum.
In addition, the sixth model 107f is a form in which the area of the abutting surface C of the shift restricting portion 107 is widened so that the side end face comes into contact with a region where the film fluttering changes to a maximum of 0.5 mm. For the first model 107a to the sixth model 107f, an experiment in which the fixing device is idled was performed, and the time until the end of the fixing film 101 was cracked was compared. FIG. 11 shows the above experimental results.

(Experimental result)
The first model 107a cracked around 3000 hours idling, the second model 107b cracked around 2900 hours idling, and the third model 107c cracked around 2600 hours idling. The fourth model 107d cracked in 1200 hours. The fifth model 107e cracked in 600 hours, and the sixth model 107f cracked in 200 hours. From the above experimental results, it is determined that the first model, the second model, and the third model are good, that is, even if the abutting surface C of the shift restricting portion 107 is expanded to a region where the film flutter is displaced within 0.2 mm. It was confirmed that there was not much problem.

  As described above, based on the result of this experiment, with respect to the abutting surface C of the shift regulating portion 107, the inner surface of the endless belt is determined to be somewhat wider on the upstream side in the rotational direction of the endless belt, based on the region A that constantly contacts the guide portion. It can be a region (second model, third model). Of course, it is needless to say that the first model in which the region in the rotation direction of the abutting surface C of the shift restricting portion 107 is the same as or narrower than the region A may be used.

<< Second Embodiment >>
(Fixing device having induction heating element)
This embodiment is different from the first embodiment in that the rotatable endless belt having flexibility is a ferromagnetic member and includes magnetic field generating means for generating an eddy current in the endless belt and generating heat in the endless belt. Different. The other points are the same as in the first embodiment. FIG. 13 is a schematic front view of the fixing device 21, and FIG. 14 is a longitudinal schematic front view of the fixing device 21.

  In the fixing device 21, a fixing belt unit (hereinafter referred to as a belt unit) 31 is disposed between the left and right opposing side plates 51 </ b> L and 51 </ b> R of an apparatus frame (chassis, frame) 50 while holding both ends in the longitudinal direction. . Further, a pressure roller 32 having elasticity as a pressure rotator (rotatable pressure member) is disposed by holding both ends in the longitudinal direction between the side plates 51L and 51R. The belt unit 31 and the pressure roller 32 are arranged vertically in parallel between the side plates 51L and 51R. Then, both 31 and 32 are pressed against each other, and a nip portion having a predetermined width in the sheet conveying direction (short direction) between the fixing belt (hereinafter referred to as a belt) 34 on the belt unit 31 side and the pressure roller 32. A fixing nip portion N) is formed. On the opposite side of the belt unit 31 from the pressure roller 32 side, the exciting coil unit (hereinafter referred to as a coil unit) 33 as a magnetic field generating means that is held by the apparatus frame 50 and generates a magnetic flux. Are arranged in parallel with the belt unit 31. The coil unit 33 is disposed between the left and right opposing side plates 51L and 51R by being attached to the device frame 50 via brackets 57L and 57R. The coil unit 33 is opposed to the belt 34 on the outside of the belt 34 of the belt unit 31 while maintaining a substantially constant gap α in a non-contact manner.

  The coil unit 33 includes an exciting coil 41, a first magnetic core 42a provided at the winding center of the coil 41, and a second magnetic core 42b provided on the opposite side of the coil 41 from the belt 34 side. The coil 41 and the magnetic cores 42a and 42b are stored in a holder (casing) 43 as a support member. The first and second magnetic cores 42a and 42b and the in-belt magnetic core 37 are made of a ferromagnetic material. A material having a low high magnetic permeability residual magnetic flux density such as ferrite may be used.

  In the belt unit 31, the belt 34 can restrain more magnetic flux generated from the coil unit 33 inside the metal by using a ferromagnetic metal such as iron (a metal having high permeability). That is, by increasing the magnetic flux density, an eddy current is generated on the metal surface, and the belt can be efficiently heated. The belt unit 31 includes a fixing pad 35 (FIG. 14) as a backup member and a pressure stay 36 as a pressure member, which are inserted and arranged inside the belt 34. The fixing pad 35 is a heat insulating member such as a heat resistant resin. The pressure stay 36 is a die steel material having rigidity such as U-shaped SUS having a downward cross section. The pressure stay 36 supports the fixing pad 35. Further, the belt unit 31 includes an in-belt magnetic core (magnetic shielding core) 37 made of a ferromagnetic material having a U-shaped cross-section facing downward as a magnetic shielding member and disposed outside the pressure stay 36. Have. The fixing pad 35 and the pressure stay 36 are longer than the belt 34, and the left and right end portions protrude outward from the left and right end portions of the belt 34, respectively. The cap members 38L and 38R are fitted to the left and right projecting ends.

  The left cap member 38L and the right cap member 38R are heat insulating members such as a heat resistant resin, and are molded bodies having the same shape. The cap members 38 </ b> L and 38 </ b> R have a pressure receiving portion 38 a that covers and fits the left end portion and the right end portion of the pressure stay 36 that supports the fixing pad 35. Further, a flange portion 38b (first portion) which is integrated with the pressure receiving portion 38a and has a stepped portion which is formed in a disc shape and is formed of an abutting surface C and a non-abutting surface D, facing the left end surface and the right end surface of the belt 34. Corresponding to the shift restriction portion 107 of the embodiment and having the same function). Further, on the inner surface side of the flange portion 38b opposite to the pressure receiving portion 38a side, the flange portion 38b is integrated with the flange portion 38b so as to enter the inside of the belt 34 and restrict the rotation trajectory of the belt from the inside of the belt. Corresponding to the guide unit 106 of the first embodiment and having the same function). That is, the guide portion 38 c has a function of supporting the belt 34 from the inside at both ends of the belt 34 and guiding the rotation trajectory of the belt 34. The guide portion 38c and the flange portion 38b as the shift restricting portion can be configured by separate members in addition to the integrated same member.

  The pressure roller 32 is disposed so that the left and right ends of the cored bar 32a are rotatably supported by the left and right opposing side plates 51L and 51R of the device frame 50 via bearing members 54L and 54R, respectively. A drive gear G is fixedly disposed at the left end of the cored bar 32a. Pressure springs 56L and 56R are contracted between the pressure receiving portions 38a of the left and right cap members 38L and 38R of the belt unit 31 and the left and right spring receiving seats 55L and 55R provided in the device frame 50, respectively. Has been. The predetermined tension force F of the left and right pressure springs 56L and 56R acts on the fixing pad 35 via the pressure receiving portions 38a and the pressure stays 36 of the left and right cap members 38L and 38R. As a result, the fixing pad 35 is pressed against the pressure roller 32 against the elasticity of the elastic layer 32b with the belt 34 interposed therebetween, and a nip portion having a predetermined width between the belt 34 and the pressure roller 32 in the sheet conveyance direction. N is formed. The fixing pad 35 assists in forming the pressure profile of the nip portion N.

  The pressure roller 32 is driven by turning on the fixing motor M (drive means for rotationally driving the pressure rotator). The driving force of the fixing motor M is transmitted to the drive gear G via a power transmission system (not shown), and the pressure roller 32 as a pressure rotator is rotationally driven at a predetermined speed. By the rotation of the pressure roller 32, a rotational force acts on the belt 34 by the frictional force between the surface of the pressure roller 32 and the surface of the belt 34 in the fixing nip portion N. As a result, the inner surface of the belt 34 is driven to rotate at substantially the same speed as the rotation speed of the pressure roller 32 while sliding in contact with the lower surface of the fixing pad 35 in the fixing nip portion N.

  The shift in the longitudinal direction accompanying the rotation of the belt 34 is restricted by receiving the belt left end surface from the flange portion 38b (corresponding to 107 in the first embodiment) of the cap member 38L. Alternatively, the belt right end surface is received by the flange portion 38a of the right-side cap member 38R, thereby being restricted.

  The guide part 38c is the same as that described in the guide part 106 of the first embodiment. That is, when the belt 34 is driven by the conveying force of the pressure roller 32 without applying tension to the thin belt 34 having flexibility (the free belt method), the belt 34 flutters in the circumferential direction (FIG. 8A ), (B)).

  Therefore, it is necessary to stabilize the trajectory of the belt 34. Therefore, in the present embodiment, each of the left and right cap members 38L and 38R is provided with a guide portion 38c that regulates the rotation trajectory of the belt 34 from the inside thereof with respect to the belt 34 that rotates following the rotation drive of the pressure roller 32. ing. The rotation trajectory of the belt 34 is restricted only at both ends in the belt longitudinal direction. That is, the guides 38c arranged at both ends in the longitudinal direction of the belt 34 guide the rotation trajectory of the belt 34 when driven by the pressure roller 32 only at both ends.

  The guide portions 38c are the same as those in the first embodiment, but are arranged at both ends of the non-sheet passing area of the sheet, that is, on both outer sides of the maximum sheet passing width area Wmax of the sheet P as shown in FIG. The rotation trajectory of the belt 34 is regulated at both ends in the belt longitudinal direction. More specifically, the guide portion 38 c enters the inside of the belt 34 from the left and right ends of the belt 34, supports the belt 34 from the inside at both ends of the belt 34, and guides the rotation trajectory of the belt 34. It has a function.

  In the present embodiment, as the belt 34, a flexible thin belt having the following specifications is used.

Inner layer 34a: 30 μm polyimide (PI)
Conductive layer 34b: Ni having an inner diameter of 30 mm (thickness 30 or 40 μm)
Elastic layer 43c: silicone rubber 300 μm
Surface release layer 43d: tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA) 40 μm
In the present embodiment, the thermistor TH as temperature detecting means for detecting the belt temperature for temperature control of the belt 34 is disposed outside the belt 34. The thermistor TH is held at the tip of the elastic member 53, and the temperature detector is brought into elastic contact with the outer surface of the belt 34 by the spring property of the elastic member 53. The thermistor TH may be disposed inside the belt 34, and the temperature detection unit may be elastically brought into contact with the inner surface of the belt.

102 ..Pressure roller, 104 ..Heater support member, 105 ..Stay, 106 ..Guide part, 107 ..Deviation restriction part, N ..Nip part, C .. Abutting surface of deviation restriction part, D ..Non-abutting surface of the shift regulation part

Claims (5)

A rotatable endless belt having flexibility;
A backup member disposed inside the endless belt;
A pressure rotator that presses against the backup member via the endless belt to form a nip portion with the endless belt; and
Drive means for rotationally driving the pressure rotator;
A guide portion that guides an inner surface of the endless belt in an end region in a longitudinal direction intersecting a rotation direction of the endless belt that rotates following the rotation drive of the pressure rotator;
A deviation regulating portion that regulates a deviation movement of the endless belt in the longitudinal direction by contacting a side end surface of the endless belt;
In the image heating apparatus for heating while sandwiching and conveying the recording material carrying the image at the nip portion,
A side end surface of the endless belt whose inner surface is guided by the guide portion contacts the shift regulating portion in a predetermined region upstream of the nip portion in the rotation direction of the endless belt, while the endless belt rotates. An image heating apparatus, wherein a stepped portion is provided in the shift regulating portion so that a side end surface of the endless belt is separated from the shift regulating portion in another region in the direction.   2. The image heating apparatus according to claim 1, wherein the predetermined region on the upstream side in the rotation direction of the endless belt is a region determined based on a region where the inner surface of the endless belt constantly contacts the guide portion.   The predetermined region on the upstream side in the rotational direction of the endless belt is a region equal to or narrower than a region where the inner surface of the endless belt constantly contacts the guide portion. Image heating device.   The image heating apparatus according to claim 1, wherein the backup member includes a heating member, and the endless belt is heated by the heating member. The image heating according to any one of claims 1 to 3, wherein the endless belt is a ferromagnetic member, and includes magnetic field generation means for generating an eddy current in the endless belt and generating heat in the endless belt. apparatus.