JP2017116921A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device in which a highly thermally conductive member is in direct contact with a film-like thin endless belt with a low heat capacity at a fixing nip, and reduce or eliminate a load on an inner peripheral surface of a belt applied by a corner or an edge of an end in the longitudinal direction of the highly thermally conductive member being brought into point contact or line contact with the inner peripheral surface of the belt.SOLUTION: A fixing device comprises: an endless belt that has flexibility; a heat source that heats the belt; a nip forming unit that is disposed inside the belt and includes a nip forming member and a heat transfer auxiliary member that transfers heat in the longitudinal direction of the belt; and a pressure member that is in pressure contact with the nip forming unit with the belt therebetween to form a fixing nip, the fixing device passing a recording material carrying an unfixed image through the fixing nip to fix the unfixed image on the recording material. An area in non-contact with the belt is formed at an end of the nip forming unit in the longitudinal direction of the heat transfer auxiliary member that is in slide contact with an inner peripheral surface of the belt, and the distance between the belt and the non-contact area is increased toward the end in the longitudinal direction of the belt.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a fixing device that fixes an image on a recording material, and an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having at least two functions of them. .

In recent years, there has been a strong market demand for energy saving and high speed for image forming apparatuses.
In an image forming apparatus, an unfixed toner image is transferred to a recording paper, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, or magnetic recording. Formed on recording material. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

Problems in recent years in such a fixing device include the following.
-When the power is turned on, etc., the warm-up time, which is the time required to reach a predetermined printable temperature (reload temperature) from the normal temperature state, and after receiving a print request, the printing operation is performed and the paper discharge is completed. Further shortening of the first print time, which is the time until the start (Problem 1).
As the speed of the image forming apparatus increases, the number of sheets passing per unit time increases and the required heat quantity increases, so the heat quantity is insufficient particularly at the beginning of continuous printing (problem 2).

  In order to solve the problems as described above, a thin endless belt with a low heat capacity is directly heated without using a metal heat conductor also serving as a support, and is mounted on a high-production image forming apparatus. However, a fixing device capable of obtaining good fixing properties has been proposed (for example, Patent Document 1). In this fixing device, a pressure roller disposed on the outer peripheral side of an endless fixing belt and a nip forming member fixedly disposed inside the fixing belt (in the loop) are brought into pressure contact with each other via the fixing belt, thereby fixing the fixing nip. Is forming.

  In the case of such a fixing configuration using an endless belt having a low heat capacity, there is a difficulty in maintaining a uniform temperature distribution in the longitudinal direction during paper feeding. That is, in the area (sheet passing area) through which a small size recording material passes, heat is consumed to heat the recording material and unfixed toner placed on the recording material. In the non-sheet passing area, heat is consumed by the recording material or the like. Since it is not taken away, heat accumulates in the fixing belt and the pressure roller, and the temperature of the nip portion in the non-sheet passing region becomes higher than the nip portion temperature in the sheet passing region maintained at a predetermined temperature. A so-called end temperature rise occurs. For the problem of temperature rise at the end, a member made of a high thermal conductivity material is attached to the fixing nip side of the nip forming member that is in pressure contact with the fixing belt. It has also been proposed to increase the ability to prevent an end temperature rise (for example, Patent Document 2). This is because the heat transfer in the width direction of the fixing belt, that is, in the longitudinal direction / axial direction of the nip forming member is facilitated by the high thermal conductive material, so that the end region remains heated without being absorbed by the paper passing. Heat is moved in the longitudinal direction to make the temperature distribution as smooth as possible.

  In such a configuration using an endless belt with a low heat capacity, the fixing belt is moved following the driving rotation of the pressure roller, and the fixing belt is located on the fixing nip side of the nip forming member fixed in the loop. Rub with the attached high thermal conductivity member. In order to reduce the rubbing resistance, a low friction sheet is generally disposed on the rubbing surface of the nip forming member / high heat conductive member with the fixing belt. However, the low friction sheet has a thickness of several hundred μm, and the heat energy consumed to heat the low friction sheet is wasted in light of the demand to use heat energy for fixing as much as possible. The sheet should be removed. However, in the configuration in which the low friction sheet is removed and the fixing belt and the high thermal conductivity member are in direct contact with each other, the functionally formed member and the fixing belt are made of a metal having high thermal conductivity such as copper or aluminum. Because of rubbing, point contact or line contact with the belt inner peripheral surface at the corner or edge of the longitudinal end portion of the high thermal conductivity member gives a high load to the belt inner peripheral surface, and belt scraping or kinking ( This may cause damage to the belt due to plastic dents formed on the belt, resulting in a decrease in durability.

  Accordingly, the present invention provides a fixing device having a structure in which a high thermal conductivity member is in direct contact with a thin endless belt in a film shape with a low heat capacity at a fixing nip, and corners and edges of the longitudinal end portion of the high thermal conductivity member are in the belt. An object is to reduce or eliminate the load applied to the inner peripheral surface of the belt by making point or line contact with the peripheral surface.

  In order to achieve the above object, according to the present invention, an endless belt having flexibility, a fixing heat source for heating the belt, and a nip forming member disposed in the longitudinal direction of the belt are disposed in the belt. A recording material for carrying an unfixed image, comprising: a nip forming unit having a heat transfer auxiliary member that moves heat; and a pressure member that presses against the nip forming unit with the belt interposed therebetween to form a fixing nip. In the fixing device for fixing the unfixed image on the recording material by passing through the fixing nip, the longitudinal end of the heat transfer assisting member in sliding contact with the inner peripheral surface of the belt of the nip forming unit A region that is not in contact with the belt is formed, and this non-contact region increases the distance from the belt toward the longitudinal end portion of the belt.

  According to the present invention, the non-contact region is formed in the longitudinal direction of the belt at the longitudinal end portion of the heat transfer assisting member that is in sliding contact with the inner peripheral surface of the belt of the nip forming unit. Since the distance from the belt increases toward the end, the longitudinal end of the belt sliding contact surface of the heat transfer auxiliary member does not make point contact or line contact with the inner peripheral surface of the belt. Can be prevented.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view illustrating an embodiment of a fixing device. It is a disassembled perspective view which shows the basic positional relationship of the nip formation member which comprises a nip formation unit, a supporting member, a heat transfer auxiliary member, and an edge part heater. It is a figure which shows the basic cross-sectional structure of a heat transfer auxiliary member. It is a perspective view of the form which lost the corner of the U-shaped heat transfer auxiliary member where the section was square. FIG. 3 is a schematic diagram of a configuration that regulates rotation of the fixing belt. FIG. 7A is a diagram showing the relationship between the heat transfer assisting member and the belt shape, FIG. 7A shows the relationship at the end position, and FIG. 7B shows the relationship at the center position. It is a related figure of a heat transfer auxiliary member at the time of adding an end flank and a belt shape. It is a perspective view of another form which eliminated the corner | angular part of the U-shaped heat transfer auxiliary | assistant member where the cross section was square. FIG. 6 is a perspective view corresponding to FIG. 5 in which the longitudinal start position of the flank is substantially the same on the nip inlet side and the nip outlet side. FIG. 10 is a perspective view corresponding to FIG. 9 in which the longitudinal start position of the flank is substantially the same on the nip inlet side and the nip outlet side. The end flank is provided only on the nip outlet side. FIG. 13A is a perspective view, FIG. 13B is a side view, and FIG. 13C is a side view of the fixing nip side. FIG. 13A is a perspective view, FIG. 13B is a side view, and FIG. It is a perspective view of the example which cut the whole edge. FIG. 14A is a perspective view, and FIG. 14B is a side view. FIG. 14A is a perspective view, and FIG. 14B is a side view. It is sectional drawing which shows another embodiment of the fixing device which can use the heat transfer auxiliary member which concerns on each form.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 1 is a color laser printer. In the center of the printer body, four image forming units 4Y, 4C, 4M, and 4K are provided side by side along the extending direction of the intermediate transfer belt 30. Yes. Each of the image forming units 4Y, 4C, 4M, and 4K stores developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and A developing device 7 that supplies toner to the surface of the photoreceptor 5 and a cleaning device 8 that cleans the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are assigned color codes, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M The reference numerals are omitted.

  Below the image forming units 4Y, 4C, 4M, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. In addition, each primary transfer roller 31 is connected to a power source of a printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. .

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, the secondary transfer roller 36 is also connected to the power source of the printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30.
A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K containing replenishing toner are detachably attached to the bottle container 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development from each toner bottle 2Y, 2C, 2M, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 containing paper P as a recording material, a paper feed roller 11 for carrying out the paper P from the paper feed tray 10, and the like are provided. Here, the recording material includes, in addition to plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

  The basic operation of the printer according to this embodiment is as follows. When the image forming operation is started, the photoconductors 5 in the image forming units 4Y, 4C, 4M, and 4K are rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is set to a predetermined polarity by the charging device 6. Uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is formed by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized, and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed in the nip. Are collectively transferred onto the paper P. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container placed in the printer body. To be recovered.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4C, 4M, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

FIG. 2 is a schematic cross-sectional configuration diagram showing an embodiment of the fixing device 20.
The fixing device 20 includes an endless fixing belt 21 that is a thin and flexible cylindrical fixing member, and a pressure roller 22 that is a pressure member that abuts from the outer peripheral side of the fixing belt 21. ing. The fixing belt 21 is heated by the radiant heat of the heaters 23A and 23B as a plurality of heat sources arranged inside (in the loop). A halogen heater is generally used as the heat source, but an induction heating device, a resistance heating element, a carbon heater, or the like may be used.

  Further, a nip forming member 24 that forms a fixing nip N with the pressure roller 22 via the fixing belt 21 and a stay 25 (support member) that supports the nip forming member 24 are disposed inside the fixing belt 21. ing. The nip forming member 24 arranged in the width direction of the fixing belt 21 is fixedly supported by the stay 25, so that the nip forming member 24 is prevented from being bent by the pressure from the pressure roller 22, and added. A uniform nip width can be obtained in the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly heat-resistant resins such as polyimide (PI) resin, polyether ether ketone (PEEK) resin, and reinforced them with glass fiber. Is made up of. This prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature range, ensures a stable fixing nip state, and stabilizes the output image quality. The stay 25 and the heaters 23A and 23B are fixed and held at both ends in the longitudinal direction on a side plate of the fixing device 20 or a separately provided holder. End heaters 26 as end heat sources different from the main heat source (fixing heat source) are integrally attached to both ends in the longitudinal direction of the nip forming member 24. Generally, the end heat source is a contact heat transfer type heater such as a ceramic saver.

  A heat transfer auxiliary member 27, also referred to as a soaking member, that facilitates heat transfer in the longitudinal direction of the fixing belt, has each surface facing the inner peripheral surface of the fixing belt 21 of each of the nip forming member 24 and the end heater 26. The cover belt is arranged so as to prevent heat from staying in the end region of the fixing belt 21 when passing small-size paper or when the end heater 26 is turned on, and thus positively in the width direction of the fixing belt 21, that is, The heat is transferred in the longitudinal direction of the heat transfer assisting member 27 to eliminate the temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer auxiliary member 27 is formed of a material having high thermal conductivity that enables heat transfer in a short time. In the depiction in FIG. 2, the surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21 and is a nip forming surface that is formed flat. However, it may be a concave shape or other shapes. When the nip forming surface has a concave shape, the discharge direction at the front end of the sheet is closer to the pressure roller, the separation is improved, and jamming is suppressed.

  As is well known, a temperature sensor 29 for detecting the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 21, and the sheet P from the fixing belt 21 is disposed downstream of the fixing device 20 in the sheet conveyance direction. A separating member 40 that separates the pressure roller 22 and a releasable pressure unit that pressurizes the pressure roller 22 to the fixing belt 21 is also provided.

  In order to reduce the heat capacity, the endless fixing belt 21 that is thin and small in diameter like a film is composed of a base material on the inner peripheral side formed of a metal material such as nickel or SUS, or a resin material such as polyimide, and a PFA. It is comprised by the mold release layer of the outer peripheral side formed with (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), etc. An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. When the thickness of the elastic layer is about 100 μm, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface can be absorbed by the elastic deformation of the elastic layer, and uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to a thickness of 1 mm or less and a diameter of 20 to 40 mm as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, more preferably 0.16 mm or less, and the diameter is 30 mm. The following is desirable.

  The stay 25 having a T-shaped cross section has an upright portion 25a standing upright on the side opposite to the fixing nip N side, and is arranged so that the heaters 23A and 23B as main heat sources are separated by the upright portion 25a. One of the heaters 23A and 23B has a heat generation region at the center in the longitudinal direction corresponding to the small size paper, and the other has heat generation regions at both ends in the longitudinal direction corresponding to the large size paper. The heaters 23 </ b> A and 23 </ b> B are configured to generate heat by being output controlled by a power supply unit provided in the printer main body, and the output control is performed by detecting the temperature of the belt surface by a temperature sensor provided on the outer periphery of the fixing belt 21. Based on the results. By such heater output control, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  Reflecting members 28A and 28B are disposed between the stay 25 and the heaters 23A and 23B, so that the heating efficiency of the heaters 23A and 23B to the fixing belt 21 is increased and the stay 25 is heated by the radiant heat from the heaters 23A and 23B. This reduces wasteful energy consumption. The same effect can be obtained even if the stay 25 surface is heat-insulated or mirror-finished instead of including the reflecting members 28A and 28B.

  The pressure roller 22 includes a cored bar, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the cored bar, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. It is configured. At a location where the pressure roller 22 is pressed against the fixing belt 21 by the spring of the pressure unit and is in pressure contact with the fixing belt 21, the elastic layer of the pressure roller 22 is crushed, thereby forming a fixing nip N having a predetermined width. Yes. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 through the fixing nip N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched and rotated at the fixing nip N, and travels by being guided by flanges disposed at both ends outside the fixing nip N.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  In the nip forming unit constituted by the nip forming member 24, the stay 25, the heat transfer auxiliary member 27, and the end heater 26, as can be seen from FIG. The opposite surface is integrated with the flat surface on the fixing nip N side of the stay 25. At this time, uneven shapes such as bosses and pins may be formed on the respective surfaces, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. The integral structure of the heat transfer assisting member 27 and the nip forming member 24 may be provided by engaging a claw or the like, but may be bonded or the like. Concave portions 24a and 24b as stepped portions are formed at both ends in the longitudinal direction of the nip forming member 24, and end heaters 26a and 26b are accommodated and fixed at these portions.

  The surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is configured as a belt sliding contact surface 27a. However, in terms of mechanical strength, the nip forming surface is substantially the nip forming surface. The surface 24c is opposed to the pressure roller 22. As shown in FIG. 4, the heat transfer assisting member 27 has a basically square U shape. If no treatment is performed, the nip inlet side (upstream side in the sheet conveying direction) at both ends in the longitudinal direction is used. ), The corners 27b and 27c exist on the exit side (downstream side in the sheet conveyance direction). In particular, in order to improve the separation of the paper, the nip outlet is inclined and protrudes toward the fixing belt toward the outlet. Therefore, on the outlet side, the corner portion 27b at the end in the longitudinal direction comes into strong contact with the inner peripheral surface of the belt and applies a high load to the inner peripheral surface of the belt, causing scraping, kinking, or breakage of the inner peripheral surface of the belt. Also on the entrance side, in the process where the fixing belt 21 is pulled into the fixing nip N, the corner portion 27b on the entrance side and the inner peripheral surface of the belt come into strong contact, and similarly, the inner peripheral surface of the belt is scraped, kinked, or damaged. End up.

  Therefore, in the heat transfer auxiliary member 27 in the present embodiment, as shown in FIG. 5, the nip inlet side at the both ends in the longitudinal direction on the belt sliding contact surface side, the corners 27 b and 27 c on the outlet side are taken or crushed, A portion corresponding to the corner portion is a region that is not in contact with the fixing belt 21. The distance between the surface of the non-contact area and the fixing belt 21 increases as it goes outward in the width direction of the fixing belt 21. The belt sliding contact surface 27a of the heat transfer assisting member 27 and the fixing belt 21 are in sliding contact with triangular relief surfaces 27d and 27e formed by taking the corners of the longitudinal end portions of the heat transfer assisting member 27. At this time, the load on the inner peripheral surface of the belt at the corner portion is greatly reduced, and it is possible to prevent the inner peripheral surface of the belt from being scraped, kinked or damaged. In order to ensure the functionality of the end heaters 26a and 26b which are contact heat transfer type heaters, the flank surfaces 27d and 27e need to be separated from each other in the sheet passing direction. That is, the end heaters 26a and 26b are present in the region of the belt sliding contact surface 27a between the flank 27d and the flank 27e.

  Here, as described above, the fixing belt 21 is sandwiched and rotated at the fixing nip N and is guided by the flanges disposed at both ends except for the fixing nip N, and thus travels at the axial end portion. The belt rotation trajectory is restricted by this, and there is no restriction at the center in the axial direction, and the belt is pressed by the fixing nip N. As shown in FIG. 6, a flange 41 as a belt holding member is inserted into the end portion of the fixing belt 21, and the end portion of the fixing belt 21 is rotatably held by the flange 41. Specifically, the flange 41 is fixed to an insertion portion 41a inserted into the end portion of the fixing belt, a restriction portion 41b formed to have a larger outer diameter than the insertion portion 41a, and a housing (not shown) of the fixing device 20. And a fixing portion 41c. The restricting portion 41b is formed to be at least larger than the outer diameter of the fixing belt 21, and restricts movement of the fixing belt 21 when the fixing belt 21 is displaced in the axial direction. Further, the flange 41 as a belt holding member is formed in a C-shaped cross section opened at the position of the fixing nip N. The end portion of the stay 25 is fixed and positioned on the flange 41 as the belt holding member.

  In addition, a slip ring 42 as an annular protective member that protects the end portion of the fixing belt 21 is provided between the end surface of the fixing belt 21 and the restriction portion 41 b of the flange 41 facing the fixing belt 21. Accordingly, as shown in FIGS. 7a and 7b, the belt trajectory during rotation differs in the width direction. As shown in FIG. 7a, the fixing belt 21 rotates in a shape close to a circle by being restricted by the flange 41 at the end, while the influence of the flange restriction decreases toward the center, as shown in FIG. 7b. In the center position, it can exist in a free state with little influence of flange restriction. For this reason, the contact pressure with the heat transfer auxiliary member entrance / exit is stronger at the end than at the center, and in particular, the entrance side comes into contact more strongly because the fixing belt 21 is drawn. Therefore, in the exit side corner portion 27c and the entrance corner portion 27b of the heat transfer assisting member at the end position, as shown in FIG. 8, the flank face is prevented from coming into contact with the belt shape affected by the flange regulation. 27d, 27e escape amounts are set, and the longitudinal relief start position also reaches a position where the contact pressure between the entrance / exit of the heat transfer auxiliary member 27 and the fixing belt 21 is weakened so that the inner peripheral surface of the belt is not scraped, kinked or damaged. It is desirable to keep away from the flange 41 toward the center. In other words, it is desirable to form the flank so as to follow the shape of the fixing belt 21 that spans from the portion restricted by the flange at the end to the fixing nip in the center.

  Here, the escape amounts of the flank surfaces 27d and 27e and the longitudinal start position, that is, the longitudinal inner position may not be the same on the nip inlet side and the outlet side. This is because the effect exerted by the invention is that the load on the inner peripheral surface of the belt by the corners of the heat transfer assisting member 27 is reduced.

  The flank surfaces 27d and 27e of the entrance / exit are formed so that the flank surfaces do not step into the nip region 27f. Here, the nip region is a region where the pressure roller 22 presses the belt sliding contact surface 27a with a predetermined pressure or more. When the flank exists in the nip region 27f, the region pressed against the pressure roller 22 with a predetermined pressure is not a single plane, and the belt is distorted at the inflection point of the plane, and the pressure roller is also locally May cause deformation of the fixing belt and the pressure roller. This can be prevented by forming the flank so as not to step into the nip region 27f. Here, the longitudinal width 27g of the belt sliding contact surface entrance of the heat transfer assisting member 27 may be shortened as long as the flank 27d does not exist in the nip region 27f. That is, the longitudinal start position of the flank 27d on the nip entrance side may be inside the longitudinal end position of the fixing nip N.

  On the nip exit side, it is necessary to bend the belt in order to improve the paper separation, and as shown in FIG. 4, the belt protrudes toward the fixing belt side toward the nip exit of the belt sliding contact surface 27a. Inclined. Therefore, in order to increase the inclination angle when the fixing belt 21 moves away from the belt sliding contact surface 27a, the exit side of the belt sliding contact surface 27a has no flank 27e in the nip region, and the longitudinal width 27h is The width in the longitudinal direction of the maximum sheet that is supposed to be passed is larger. That is, the longitudinal start position of the flank 27e on the nip exit side is outside the end position in the longitudinal region through which the paper passes.

If the conditions on the inlet side and the outlet side are satisfied, the longitudinal start positions of the flank surfaces 27d and 27e can be arbitrarily set.
FIG. 9 shows another configuration example of the heat transfer auxiliary member. In this heat transfer auxiliary member 47, instead of the flat relief surfaces 27d and 27e of the heat transfer auxiliary member 27 of FIG. 5, the relief surfaces 47d and 47e which are curved surfaces are used as the surfaces of the non-contact area. Since the locus of the nip inlet and outlet during rotation of the fixing belt 21 has a curved shape, the load on the fixing belt can be further reduced by making the belt sliding contact portion a curved surface.

  As shown in FIGS. 10 and 11, the longitudinal start position of the flank may be substantially the same on the inlet side and the outlet side. Further, only one of the inlet side and the outlet side may be provided with a relief surface. FIG. 12 shows a configuration in which a flank 27e is provided only on the outlet side.

  In the embodiment relating to the heat transfer assisting member 27 and the heat transfer assisting member 47 of the modified example, the heat transfer assisting member is positioned so as to cover the nip forming member 24, so that a long thin plate is formed in a U shape. In this shape, the shape of the heat transfer assisting members 27 and 47 can be realized by drawing to crush the corners. A heat transfer auxiliary member formed of a metal having high thermal conductivity such as copper or aluminum can be easily bent such as drawing. The heat transfer auxiliary member generates wear powder on the sliding contact surface, and it is assumed that the wear powder damages the heat transfer auxiliary member itself and the inner peripheral surface of the belt. It is also desirable to use it as an auxiliary member.

  The heat transfer auxiliary member 27 in FIGS. 5 and 10 and the heat transfer auxiliary member 47 in FIGS. 9 and 11 are fitted and integrated so as to cover the surface of the nip forming member 24 that faces the inner peripheral surface of the fixing belt 21. Although it is a member having a U-shaped cross section, it does not need to have a U-shaped cross section if it is bonded and fixed to the nip forming member 24 or if the heat transfer assisting member also serves as the nip forming member. That is, a rectangular parallelepiped long plate having a large plate thickness and the corners at both ends in the longitudinal direction can be used as the heat transfer assisting member. As an example, as shown in FIGS. 13a and 13b, flank surfaces 57c and 57d are formed by removal processing such as cutting processing including not only the corners at both ends in the longitudinal direction of the thick plate, but also the edges. Thus, the heat transfer assisting member 57 is used.

  The drawing process for crushing the corners of the heat transfer assisting member 27 in FIGS. 5 and 10 and the heat transfer assisting member 47 in FIGS. 9 and 11 makes the desired shape by bending the metal. It is necessary to consider the processing of other adjacent members. On the other hand, the cutting process creates a shape by removing a member, and a predetermined material thickness is required, but a large shape change is possible with high accuracy. Therefore, in the heat transfer assisting member 57 having a rectangular parallelepiped shape, the end flank surfaces 57c and 57d of the heat transfer assisting member 57 can be formed by cutting not only the corners but also the end edges. . Thereby, the load to the belt inner peripheral surface by the point contact of a corner | angular part vertex and the contact of an edge part edge can be reduced.

  Further, in the cutting process, finer processing is possible, and each edge and vertex of the belt sliding contact surface can be finished into an arc-shaped curved surface 67g like the heat transfer auxiliary member 67 shown in FIG. 13c. Thereby, the load itself by the point contact of the corner | angular part vertex of a belt sliding contact surface or the line contact of an edge can be eliminated.

  Further, as shown in FIG. 14, the end flank of the thick long plate may be curved. This heat transfer assisting member 77 has arcuate curved surfaces 77c and 77d at both ends in the longitudinal direction of the belt sliding contact surface 77a, and the edges on the nip inlet side and the outlet side are curved in a range that does not affect the paper separation property. It is. The corners and edges at the end in the longitudinal direction are allowed to escape into a curved shape, which not only eliminates the load caused by point contact at the corners and line contact at the edges, but also prevents excessive bending of the belt. Inner surface wear can be reduced.

  Further, in order to reduce wear on the inner peripheral surface of the belt, it is also desirable to apply a resin coating to the belt sliding contact surface of the heat transfer assisting member to improve the sliding property between the belt sliding contact surface and the belt inner peripheral surface. . In particular, since PTFE resin is excellent in non-adhesiveness (releasing properties and water repellency), it is highly slippery with the belt inner peripheral surface and can reduce belt inner peripheral surface wear. In addition to slipperiness, PAI (polyamideimide) resin has extremely high heat resistance and wear resistance. By coating the resin containing PAI resin, both the heat transfer assisting member and the inner peripheral surface of the belt can be used. Wear can be reduced. Furthermore, by interposing a lubricant between the inner peripheral surface of the belt and the sliding contact surface of the heat transfer auxiliary member, wear of both the heat transfer auxiliary member and the belt can be remarkably reduced. In particular, by using a highly viscous (low fluidity) grease as the lubricant, the grease always stays between the heat transfer assisting member and the belt inner peripheral surface, and the lubricity can be maintained for a long time. As the base oil of the grease, a fluorine type having excellent heat resistance is desirable.

  Also, as shown in FIGS. 4 and 6, a convex shape is formed on the exit side of the heat transfer assisting member 27 in the sheet conveyance direction in order to increase the separation of the sheet that has exited the fixing nip in the longitudinal direction of the sheet passing area. A portion 27i is provided. Further, in the nip forming member 24, as can be seen from FIG. 6, the portions facing the heat transfer auxiliary member flank on the entrance side and the exit side in the paper transport direction are processed into a shape along the flank. Further, the nip forming member 24 is processed into a shape along the convex shape on the exit side of the heat transfer auxiliary member at a location facing the convex shape on the exit side of the heat transfer auxiliary member.

  Note that the heat transfer auxiliary member according to each of the above embodiments can be applied not only to a fixing device provided with an end heater on a nip forming member, but also to a known fixing device not provided with an end heater. It can be done. FIG. 15 is a schematic cross-sectional view of a fixing device 80 that does not include an end heater. This fixing device basically differs from the fixing device 20 provided with the end heater 26 in the nip forming member 24 shown in FIG. 2 only in the presence or absence of the end heater and the number of main heat sources. By omitting the reference numerals, the description is omitted. The nip forming member 24 will be described with reference to FIG. 6. The end contact heater 26 a is accommodated in a recess 24 a provided in the nip forming member 24. In the case of a fixing device that does not use an end heater, the recess 24a is not provided, and a flat surface 24c facing the pressure roller 22 is uniformly formed in the longitudinal direction.

DESCRIPTION OF SYMBOLS 20 Fixing device 21 Fixing belt 22 Pressure roller 23 Heater 24 Nip forming member 25 Stay 26 End heater 27, 47, 57, 67, 77 Heat transfer auxiliary member

JP 2010-32631 A Japanese Patent Laying-Open No. 2015-64561

Claims (9)

A nip having a flexible endless belt, a heat source for heating the belt, a nip forming member and a heat transfer assisting member that moves heat in the longitudinal direction of the belt. And a pressure member that presses against the nip forming unit with the belt interposed therebetween to form a fixing nip, and passes a recording material carrying an unfixed image through the fixing nip, thereby allowing the recording material to pass through the fixing nip. In a fixing device for fixing an unfixed image,
In the nip forming unit, a region that is not in contact with the belt is formed at a longitudinal end of the heat transfer assisting member that is in sliding contact with the inner peripheral surface of the belt. A fixing device characterized in that the distance from the belt increases toward the end.   2. The fixing device according to claim 1, wherein an inner position in the longitudinal direction of the non-contact region is outside an end position in the longitudinal direction of the fixing nip on an upstream side in the recording material conveyance direction of the fixing nip.   The inner position in the longitudinal direction of the non-contact area is outside the end position in the longitudinal area of the maximum recording material on which the sheet is supposed to pass on the downstream side in the recording material conveyance direction of the fixing nip. The fixing device according to claim 1 or 2.   The fixing device according to claim 1, wherein the non-contact area is flat.   The fixing device according to claim 1, wherein the non-contact area is curved.   The fixing device according to claim 1, wherein a coating for reducing wear on the inner peripheral surface of the belt is provided on a fixing nip side of the heat transfer auxiliary member.   The fixing device according to claim 1, wherein a lubricant is interposed between a fixing nip side of the heat transfer auxiliary member and an inner peripheral surface of the belt.   The fixing device according to claim 1, wherein a contact heat transfer type end heat source is disposed at an end in a longitudinal direction of the nip forming member.   An image forming apparatus comprising the fixing device according to claim 1.

Images