JP2010266704A - Image heating device, and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To extend the service life of a fixing device by reducing the bending fatigue by increasing the curvature of the end of a fixing belt. <P>SOLUTION: A guide section for supporting the fixing belt so as to increase the curvature thereof is disposed outside a paper passing region. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image heating apparatus that heats an image carried on a recording material by passing the recording material through a pressure nip portion between a heating member and a pressure member, and in particular, for an image of a copying machine, a printer, or the like. The present invention relates to an image heating apparatus suitable for mounting as an image heating fixing apparatus in a forming apparatus.

  More specifically, an image heating apparatus having a sleeve-like rotator, a guide member that guides the rotator, and a heating unit that heats a recording material conveyed in the nip through the rotator, and the image heating apparatus. The present invention relates to an image forming apparatus provided with a heat fixing apparatus for images.

  In an image forming apparatus such as an electrophotographic copying machine or a printer, an unfixed toner image formed or supported directly (transferred) or directly on a recording material (paper) by an appropriate image forming process means such as an electrophotographic process As a fixing device for heat fixing as a fixed image, a heat roller type heat fixing device has been widely used.

  In recent years, a film heating type fixing device has been put into practical use from the viewpoint of quick start and energy saving. There has also been proposed an electromagnetic induction heating type heating device for generating heat from a metal film itself.

a) Film-type fixing device A film-heating-type fixing device has been proposed in, for example, Japanese Patent Application Laid-Open No. H10-293707. That is, a heat-resistant film (hereinafter referred to as a fixing film) is sandwiched between a ceramic heater as a heating body and a pressure roller as a pressure member to form a pressure nip (hereinafter referred to as a fixing nip portion), and the fixing By introducing a transfer material that forms and supports an unfixed toner image between the fixing film and the pressure roller at the nip, and transporting it with the fixing film, the heat of the ceramic heater is transferred through the fixing film. The unfixed toner image is fixed on the surface of the transfer material by the applied pressure at the fixing nip portion.

  This film heating type fixing device can be configured as an on-demand type device using a ceramic heater and a film having a low heat capacity member, and energizes the ceramic heater as a heat source only at the time of image formation to have a predetermined fixing temperature. This is advantageous in that, for example, the waiting time from the power-on of the image forming apparatus to the image forming executable state is short, and the power consumption during standby can be greatly reduced.

b) Fixing device using metal film (fixing belt) In recent years, with the increase in speed and colorization of image forming devices, a film heating type fixing device uses a metal film such as SUS or nickel as the fixing film, Further, a fixing device using a belt-like member (hereinafter referred to as a fixing belt) in which an elastic layer is provided on a metal film has been proposed.

  Conventionally, heat-resistant resins have been used as the base material for fixing films. However, as the speed of image forming devices increases, the thermal conductivity of the fixing film increases and the heat of the ceramic heater is transferred more efficiently. It was necessary to tell the material.

  For this reason, it is preferable to use a metal having a higher thermal conductivity than the resin as the fixing film substrate. A fixing device using such a metal fixing film is disclosed in Patent Documents 2 and 3, for example.

  Also, with the colorization of image forming apparatuses, it has become necessary to provide an elastic layer on the base material of the fixing film. Examples of such a fixing film and an image forming apparatus are disclosed in Patent Documents 4 and 5, for example.

  This is because when the toner image passes through the fixing nip portion, the conventional film fixing device cannot follow the shape of the toner image transferred in multiple layers of the color image, and partially fixes the toner image. This is because unevenness of sex occurs. The non-uniformity of the fixing property appears as uneven gloss of the image, or becomes non-transparent in OHT (transparent sheet for overhead projector), and the non-uniformity of transparency appears as an image defect when projected. there were.

  By providing an elastic layer on the fixing film, the elastic layer is deformed along the toner layer, so that the toner that is unevenly placed on the image is encased in the elastic layer and uniformly heated by applying heat uniformly. Fixing is achieved.

  However, since the thermal conductivity of the fixing film is inferior due to the provision of the elastic layer, it is necessary to give an extra amount of heat. In particular, in order to ensure the on-demand property of the fixing device, it is necessary to quickly raise the fixing device to a predetermined temperature. Therefore, by making the base material a metal film rather than a normal fixing film, the thermal conductivity can be reduced. The use of an improved fixing belt is advantageous.

  When a film is used in the film heating method, the film may be shifted in the thrust direction, and it is difficult to strictly control this. Therefore, in Patent Documents 6 and 7, etc., the film is loosely suspended, the shifting force of the film is reduced, and the film end is received by the film end regulating surface (hereinafter also referred to as “regulating surface”) of the flange to regulate the shifting. It has been proposed to do. In this apparatus, the film is driven by a pressure rotating body that forms a nip with a heating body through the film, and the restriction surface of the flange is provided except for the nip portion. However, when the edge of the film is regulated by a flange as described above, a phenomenon in which the film is broken and wrinkled or cracked depending on the film thickness and material (hereinafter referred to as “film edge breakage”) As a result, there was a possibility of deterioration of the fixed image in the image heating and fixing device, poor running of the fixing film, a decrease in the durability life, and the occurrence of the noise of regulating the shift of the film. .

  In order to solve the above-mentioned problem, Patent Document 8 proposes a film restricting surface shape of the flange. In this proposal, as shown in FIG. 16, an endless belt-like (cylindrical) fixing film 403 as a flexible sleeve-like rotating body is loosely suspended around a film guide (not shown) At least when stopped, the tension does not work except for the fixing nip N. The pressure roller 404 is driven via a gear G by a drive source (not shown), and the fixing film 403 rotates and travels only by the frictional force with the pressure roller 404 in the fixing nip N. A ceramic heater (not shown) in contact with a film guide that guides the inner surface of the fixing film 403 in the entire longitudinal direction and the pressure roller 404 are in pressure contact with each other with a predetermined contact pressure by a pressure spring 405 across the fixing film 403. Thus, the fixing nip portion N is formed. Further, flanges (end holders) 402 that restrict the rotation direction trajectory and the thrust direction end of the fixing film 403 are fitted to both ends of the fixing film 403 in the thrust direction. The rotation direction trajectory of the fixing film 403 is regulated by sliding the outer circumferential surface 402a of the flange 402 and the inner circumferential surface of the fixing film 403. The film end regulating surface 402b has the fixing film 403 moved in the thrust direction. Even in this case, the film end is regulated by abutting against the film end regulating surface 402b.

  Further, with respect to the film moving direction shape after the fixing nip N, a portion where the gap between the regulating surface and the fixing film end is gradually reduced is provided to gently regulate the fixing film end after the fixing nip N. . However, in this state, there is a possibility that the fixing film end portion is broken. FIG. 17 shows a state in which the fixing film offset force is generated on the regulating surface in a state where the entire flange 402 is slightly inclined outward in the thrust direction due to the assembly tolerance of the flange 402 that regulates the rotation direction trajectory and the thrust direction end of the fixing film 403. The conceptual diagram when the fixing film edge part bumps is shown. According to FIG. 17, since the entire flange 402 is inclined outward and the restricting surface 402b is also inclined outward, the location on the restricting surface where the end of the fixing film abuts due to the offset force is closer to the fixing nip portion N. It is a local part (the part surrounded by a dotted line). When a strong fixing film shifting force acts in this state, the fixing film end portion is damaged. In addition, when the flange 402 is inclined outward, the fixing film end may be abutted against either upstream or downstream of the fixing nip portion N, and damage may occur due to the offset force.

  This is because the flexibility of the fixing film itself tends to be lost in the vicinity of the fixing nip portion N where the fixing film is sandwiched, and a strong stress is exerted on the end of the fixing film by locally hitting the restriction surface of the flange 402 at such a portion. Is a main factor, and film breakage occurs when the stress exceeds the breaking strength of the fixing film.

  As another example, in a fixing belt using a metal film, although the rigidity of the fixing belt itself is high, in the fixing belt manufacturing process, when the fixing belt is cut into an appropriate length for the fixing device, burrs and minute Cracks were generated, and cracks originating from such burrs and minute cracks were generated by rubbing due to repeated rotation.

  In order to prevent such cracks at the end of the fixing belt, in Patent Document 9, the flange that supports the end of the fixing belt is configured to be supported from the outer peripheral surface of the fixing belt, and is configured to rotate together with the fixing belt. A configuration for preventing rubbing between the belt end and the fixing device is disclosed.

  18 and 19 are a perspective view and a cross-sectional view as seen from the longitudinal direction of an example of a configuration in which the fixing flange 500 is supported from the outer peripheral surface of the fixing belt and rotated together with the fixing belt 501.

  The inner diameter of the fixing flange 500 is set larger than the outer diameter of the fixing belt 501, and the fixing belt 501 is pressed and deformed by the pressure roller 502, so that the surface contacts the inner surface receiving portion 500 a of the fixing flange 500, Generates frictional force. Due to this frictional force, the fixing flange 500 rotates as the fixing belt 501 rotates.

  The fixing flange 500 is supported by the inner surface receiving portion 500a to prevent the fixing belt 501 from falling off the fixing flange 500 even when the fixing belt 501 is shifted in the longitudinal direction.

  However, in the above-mentioned Patent Document 9, the fixing belt 501 is also deformed by the pressure roller 502 in the vicinity of the fixing nip N as the fixing belt 501 rotates. Since the movement in the directions of arrows a and b) is repeated, even if the fixing flange 500 rotates together with the fixing belt 501, some friction between the end surface of the fixing belt 501 and the fixing flange 500 is inevitable.

  As shown in FIG. 21, as shown in a cross-sectional view viewed from a direction perpendicular to the longitudinal direction, the taper shape is formed toward the end of the fixing flange 503, and the longitudinal extension line of the fixing belt 501 and the fixing flange 503 are formed. By setting the angle θ formed with the surface in contact with the end surface of the fixing belt 501 to be 90 ° or more, the fixing belt 501 is deformed by the pressure roller 502 as the rotation rotates, and is rubbed to the end surface of the fixing flange 503 to some extent. Although a structure for preventing this has been proposed, there is always a place where the end surface of the fixing belt 501 and the fixing flange 503 rub against each other in the radial direction at the beginning of the deformation near the fixing nip portion N and the last position where the deformation returns.

  Further, when the biasing force of the fixing belt 501 is large, a frictional force is generated at the receiving portion of the fixing flange 503, and the fixing flange 503 may not rotate in synchronization with the rotation of the fixing belt 501. In such a case, since the rotation speeds of the fixing flange 503 and the fixing belt 501 are different, a relatively large force acts on the fixing belt when the slidability between the fixing flange 503 and the fixing belt 501 is low. At this time, the fixing flange or the fixing belt is tilted, and if the fixing belt and the fixing flange come into contact with each other in the vicinity of the nip, a very large buckling pressing force works, and the fixing belt may be cracked.

  Further, when θ is increased, the fixing flange 503 is pulled in the direction of the arrow in FIG. 21 due to the longitudinal displacement of the fixing belt 501, and the fixing belt 501 is distorted in the longitudinal direction. Since the stress increases, there is a problem that the fixing belt 501 causes fatigue failure.

  In particular, in the fixing belt 501 in which the base layer is formed by plastic processing such as ironing, the residual stress of the metal layer is large, and the fixing belt end surface has minute cracks due to sliding friction and longitudinal distortion. It tends to cause cracks starting from, and fatigue failure.

  In particular, in the color image forming apparatus, it is necessary to increase the pressure in the fixing nip portion N as compared with the monochrome image forming apparatus. This is because a color image is formed by superimposing a plurality of colors of toner, so that the toner image height is higher than that of a black and white image forming apparatus, and a higher pressure is required in order to obtain a uniformly smooth image in the fixing unit. Is necessary.

  When the pressure at the fixing nip portion N is increased, the force that the fixing belt approaches in the longitudinal direction also increases, so that cracking due to buckling of the fixing belt is likely to occur.

  Therefore, as shown in FIG. 22, the fixing belt end regulating surface 109 c and the fixing flange 108 of the end holder 109 have a fixing belt circumferential length that is a straight line parallel to the nip line of the fixing nip N at the fixing belt end. When divided into approximately two equal parts, the fixing nip N does not come into contact, but only a part of the region facing the fixing nip N and outside the outer periphery of the fixing belt 103, and the fixing belt 103 is thrust. The fixing flange 108 is inclined by the fixing belt 103 from the two-dot chain line to the solid line, and the end of the fixing belt 103 restricts the thrust direction only on the side facing the fixing nip N. A configuration is disclosed.

JP-A-63-313182 JP 2003-045615 A JP 2003-156554 A Japanese Patent Laid-Open No. 10-10893 Japanese Patent Laid-Open No. 11-15303 JP-A-4-44075 JP-A-4-204980 Japanese Patent Laid-Open No. 5-208750 JP 2002-231419 A

  However, even if the stress that the fixing belt receives from the fixing flange due to the offset force and the friction with the fixing flange are reduced, cracks starting from the end portions have occurred. In this regard, as another stress applied to the end portion of the fixing belt, fatigue due to repeated “bending” during rotation can be considered. As shown by the broken line portion in FIG. 23, this is caused by the minimum curvature portion a of the fixing belt 601 that occurs before and after the press-contact two-ply when the fixing belt rotates. With the miniaturization of equipment, this minimum curvature tends to become smaller and smaller.

  In the case of a thin film SUS having a thickness of 34 μm, it was confirmed by repeated bending tests that increasing the minimum curvature by 10% doubled the life until fatigue failure. In fact, cracks are unlikely to occur in other configurations having a large minimum curvature. From the above, the permanent stress due to repeated “bending” during rotation is intermittently combined with the stress due to the offset force, thereby causing cracks starting from the ends and reducing the life of the fixing belt.

  For these reasons, it is required to increase the curvature during rotation of the fixing belt and relieve stress due to repeated “bending”. However, since the shape of the heater holder 602 that guides the rotation of the fixing belt in the sheet passing area is optimized to satisfy the fixing conditions, it is necessary to maintain the conventional heater holder shape. The shape will inevitably be determined according to this. Therefore, it is necessary to configure such that only the end portion of the fixing belt 601 has a large curvature during rotation.

  Accordingly, the present invention aims to reduce fatigue caused by “bending” during rotation by supporting the fixing belt 601 to have a minimum curvature larger outside the paper passing area when the press-fitting dip is formed. And

  In order to achieve the above object, an invention relating to the present application includes a sleeve-like rotating body, a heating unit that heats the rotating body, and heats a recording material that carries an image along with the rotation of the rotating body, and the rotation An image heating apparatus having a pressure member that forms a pressure nip with a body, a first guide surface that supports an inner surface of the rotating body in a substantially paper passing area, and an inner surface of the rotating body substantially outside the paper passing area When the press-contact nip is formed, the second guide surface is outside the position of the inner peripheral surface of the rotating body supported by the first guide surface. It is characterized by this.

  As described above, according to the present invention, it is possible to reduce fatigue caused by repeated “bending” occurring at the end of the fixing belt while satisfying the fixing conditions. This makes it possible to delay the occurrence of cracks at the end of the fixing belt, and provide a long-life image heating apparatus.

FIG. 3 is a cross-sectional view illustrating the shape of the heater holder and the fixing belt on the sheet passing area and the outside of the sheet passing area in the first embodiment. FIG. 3 is an external perspective view of a heater holder and a fixing belt in Embodiment 1. The conceptual diagram of the heater holder in Example 1. FIG. FIG. 6 is an external perspective view of a heater, a guide member, and a fixing belt in Embodiment 2. The conceptual diagram of the edge part flange in Example 3. FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus in Embodiment 1. FIG. The perspective view of a fixing device. FIG. FIG. 9 is a cross-sectional view taken along line (5)-(5) in FIG. 8. The block diagram of the electric power feeding system with respect to a heater. FIG. 3 is a cross-sectional model diagram illustrating a layer configuration of a fixing belt. FIG. 3 is an external perspective view of a heating assembly and a pressure roller with a fixing belt removed. The exploded perspective view of the one end part side of the heating assembly which removed the fixing belt. The figure of the inner surface side of a fixing flange and an end holder. The figure explaining the contact position of a fixing belt and a fixing flange. FIG. 6 is a diagram illustrating a configuration of a fixing device in a conventional example. The conceptual diagram near a film when a flange inclines outside in a prior art example. The perspective view explaining the structure of the fixing flange in a prior art example. Sectional drawing explaining the structure of the fixing flange in a prior art example. The figure explaining the rubbing state of the fixing belt and fixing flange in a conventional example. The figure explaining the regulation state of the fixing belt in a conventional example. FIG. 6 is an enlarged vertical cross-sectional view of one end side of a fixing device in a conventional example. External perspective view of heater holder and fixing belt in the conventional example

Example 1
(1) Example of Image Forming Apparatus FIG. 6 is a schematic configuration diagram of an example of an image forming apparatus in which the image heating apparatus of the present invention is mounted as a fixing device. The image forming apparatus of this example is a four-color full-color laser beam printer using an electrophotographic process.

a) Outline of Overall Configuration of Image Forming Apparatus This image forming apparatus A includes, as an image forming unit, a photosensitive drum 1 as an image carrier, a charging device 2 for charging the photosensitive drum 1, and a photosensitive drum 1. Exposure means (laser scanner) 3 for forming an electrostatic latent image by exposure, four developing units for developing the electrostatic latent image as a toner image, that is, a yellow developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, A rotary developing device holder 4 holding the black developing device 4Bk, an intermediate transfer member unit 5, a drum cleaning unit (cleaning blade) 6 for cleaning the surface of the photosensitive drum 1, and the like.

  The intermediate transfer body unit 5 presses the intermediate transfer belt 5a, a driving roller 40 and a tension roller 41 that are suspended from the intermediate transfer belt 5a, and the intermediate transfer belt 5a against the photosensitive drum 1 to form a primary transfer portion. At the intermediate transfer belt winding portion of the primary transfer roller 5j and the driving roller 40, the secondary transfer roller 11 controlled to move toward and away from the outer surface of the intermediate transfer belt 5a, the charging roller 5f as a belt cleaning unit, etc. Have

  Further, the transfer material feeding unit includes a paper feed cassette 19 in which a transfer material (not shown) as a final recording medium is stacked and stored, a feed roller 18, a registration sensor 14, and the like, and image formation on the transfer material. As a subsequent fixing and discharging unit, an on-demand fixing device 8, a discharge roller pair 13, a discharge guide 15, a discharge roller pair 9, a discharge tray 10, and the like are provided.

  The intermediate transfer belt 5a is driven to rotate in the clockwise direction indicated by the arrow at a predetermined peripheral speed, and the photosensitive drum 1 is rotated counterclockwise as indicated by the arrow in synchronization with the rotation of the intermediate transfer belt 5a. Is uniformly charged by the charging device 2, and the yellow (Y) image is irradiated by the exposure unit 3 to form an electrostatic latent image corresponding to the yellow image on the photosensitive drum 1.

  Simultaneously with the formation of the electrostatic latent image, the developing device holder 4 is driven to place the yellow developing device 4Y at the developing position with respect to the photosensitive drum 1, so that yellow toner adheres to the electrostatic latent image on the photosensitive drum 1. A voltage having the same polarity as the charging polarity of the photosensitive drum 1 and substantially the same potential is applied to cause yellow toner to adhere to the electrostatic latent image for development. Thereafter, a voltage having a reverse polarity to the toner is applied to the primary transfer roller 5j to primarily transfer the yellow toner image on the photosensitive drum 1 onto the intermediate transfer belt 5a.

  When the primary transfer of the yellow toner image is completed as described above, the developing device for the next color rotates and is positioned at the developing position opposite to the photosensitive drum 1, and magenta (M ), Cyan (C), and black (Bk), the electrostatic latent image is formed and developed, and the primary transfer to the intermediate transfer belt 5a is sequentially performed, and four color toner images are superimposed on the intermediate transfer belt 5a. Match.

  During this time, the secondary transfer roller 11 is not in contact with the intermediate transfer belt 5a. The charging roller 5f as a cleaning unit is also in a non-contact state with the intermediate transfer belt 5a.

  On the other hand, the feeding roller 18 of the feeding unit is driven, and the transfer material loaded and stored in the paper feeding cassette 19 is separated and fed one by one and conveyed toward the registration roller pair 7d. Immediately after the registration roller pair 7d, there is provided a registration sensor 14 that detects the leading edge of the transfer material, interrupts the rotational driving force of the registration roller pair 7d, and waits the transfer material at a predetermined position. As a result, the transfer material is temporarily put into a standby state at a predetermined position near the registration roller pair 7d.

  After the four color toner images have been formed on the intermediate transfer belt 5a, the secondary transfer roller 11 is pressed against the intermediate transfer belt 5a (the state shown in FIG. 6), and further in synchronization with the rotation of the intermediate transfer belt 5a. The transfer material waiting at a predetermined position in the vicinity of the registration roller pair 7d is sent out to the secondary transfer portion which is a nip portion between the intermediate transfer belt 5a and the secondary transfer roller 11 by re-driving the registration roller pair 7d. The re-feeding of the transfer material by the registration roller pair 7d is such that when the front end portion of the four color toner image formed on the intermediate transfer belt 5a reaches the secondary transfer portion, the front end portion of the transfer material is also subjected to the secondary transfer. This is done at the timing of reaching the part. Further, a voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 11, and the four color toner images on the intermediate transfer belt 5 a are secondarily transferred onto the surface of the transfer material at once in the secondary transfer portion. .

  In this way, the transfer material that has been secondarily transferred reaches the fixing device 8 via the conveyance belt unit 12, and after fixing (melting and mixing) a plurality of color toner images, the discharge roller pair 13 is then received. Is discharged along the discharge guide 15 and discharged to the face-down discharge tray 10 above the image forming apparatus A by the discharge roller pair 9 to complete the image formation.

  On the other hand, after the secondary transfer of the toner image from the intermediate transfer belt 5a to the transfer material in the secondary transfer portion, the charging roller 5f as a belt cleaning unit is pressed against the intermediate transfer belt 5a and remains on the intermediate transfer belt 5a. The residual toner is given a charge opposite to that at the time of transfer. The residual toner to which the reverse charge is applied is electrostatically attached to the photosensitive drum 1 and then collected by the drum cleaning unit 6 for the photosensitive drum 1. The collected residual toner is collected and accumulated in the waste toner box 16 as waste toner.

(2) Fixing device 8
FIG. 7 is a perspective view of the fixing device 8, FIG. 8 is a front view of the intermediate part omitted, and FIG. 9 is a transverse sectional view taken along line (5)-(5) of FIG.

  Reference numerals 100 and 104 denote a heating assembly as a heating member forming a nip portion (fixing nip portion) N for nipping and transporting the recording material and heating the image on the recording material, and an additional pressure member as a pressure member. It is a pressure roller.

The heating assembly 100 includes:
a: heater holder 101 formed of a liquid crystal polymer resin having high heat resistance;
b: A thin and long ceramic heater H as a heating means disposed along the length of the holder on the lower surface of the heater holder 101;
c: A U-shaped fixing stay 110 having a downward cross section disposed inside the heater holder 101;
d: a fixing belt 103 as a flexible sleeve-shaped rotating body loosely fitted to the assembly of the heater holder 101, the heater H, and the fixing stay 110;
e: Fixing flanges 108 as fixing belt support members, which are disposed on both ends of the fixing belt 103, respectively, as a fixing belt support member that rotatably supports the radial direction of the end of the fixing belt 103 from the outer peripheral surface and the thrust direction from the side (end surface) And a boss 109b that rotatably supports the inner peripheral surface of the fixing flange 108, and an end as a regulating member provided with a fixing belt end regulating surface 109c that regulates the thrust direction end of the fixing belt 103 via the fixing flange 108. Part holder 109,
f: As a temperature measuring element which is held at the tip of a stainless steel elastic arm 102 (FIG. 9) whose base is fixed to the heater holder 101 and elastically contacts the inner surface of the fixing belt 103 by the elastic arm 102. Thermistor TH,
Etc. is an assembly.

  The pressure roller 104 is formed by forming a silicone rubber layer 104b with a thickness of about 3.5 mm on a stainless steel core metal 104a by injection molding, and covering a PFA resin tube (release layer) 104c with a thickness of about 40 μm thereon. It becomes. As shown in FIG. 8, the pressure roller 104 is arranged such that both ends of the cored bar 104a are rotatably supported via a bearing member 107b between the front and back side plates 107a of the apparatus frame 107, respectively. It is. G is a drive gear fixedly disposed at one end of the cored bar 104a. As the rotational force is transmitted from the drive system M to the drive gear G, the pressure roller 104 is rotationally driven at a predetermined speed in the counterclockwise direction of the arrow in FIG.

  The heating assembly 100 is arranged above the pressure roller 104 and in parallel with the pressure roller 104 with the heater H side facing downward. The end holders 109 on both ends protrude outwardly from the vertical slit holes 107c formed in the front and back side plates 107a of the apparatus frame 107, and the vertical guides are formed at the vertical edges of the vertical slit holes 107c. The groove portion 109d is engaged, and is freely slidable in the vertical direction along the vertical edge of the vertical slit hole portion 107c.

  The pressing portion 109 a on the upper surface of each end holder 109 receives a downward pressing force F by a pressure plate (pressure lever) 112, so that the heating assembly 100 is pressed in the direction of the pressure roller 104 by the fixing stay 110. The silicone rubber layer 104b of the roller 104 is pushed down against the elasticity. As a result, the heater H is pressed against the pressure roller 104 with the fixing belt 103 interposed therebetween, and a fixing nip portion (pressure nip portion) N having a predetermined width is formed between the heating assembly 100 and the pressure roller 104. .

  The total length of the fixing belt 103 is set to be larger than the contact surface length of the pressure roller 104 (longitudinal length of the fixing nip portion N).

  The pressure plate 112 is rotatably provided with one end pivotally supported on the front side and the rear side plate 107 a of the apparatus frame 107, and the lower surface of the middle portion of the pressure plate is the upper surface pressing portion 109 a of the end holder 109. The pressure spring 111 is contracted between the upper surface of the pressure plate free end side and the fixed bent portion 107d of the side plate 107a, and a pressure F is applied to the upper surface pressing portion 109a of each end holder 109. ing. In this embodiment, the heating assembly 100 is pressed toward the pressure roller 104 with a total pressure of 20 kgf (10 kgf on one side).

  The pressure mechanisms 111 and 112 have a pressure release mechanism (not shown), and are configured so that the pressure can be released and the transfer material can be easily removed at the time of jam processing or the like.

  The heater holder 101 has extension arm portions 101a projecting outward from vertical slit holes 107c formed in the front and back side plates 107a of the device frame 107 at both ends thereof. Both ends of the heater H are extended to the extension arm portion 101a. As shown in FIG. 5, a power supply electrical contact a is provided at one end, and a temperature is provided at the other end. A regulating electrical contact b is provided. A power feeding connector 121 is fitted to the extension arm portion 101 a on one side of the heater holder 101. As a result, the electric contact on the power feeding connector 121 side and the electric power feeding contact a on the heater H side are conducted, and the heater H and the power feeding circuit 120 on the image forming apparatus main body side are brought into electrical communication. A temperature adjustment connector 122 is fitted to the extension arm portion 101 a on the other side of the heater holder 101. As a result, the electrical contact on the temperature adjustment connector 122 side and the electrical contact b on the heater H side are conducted, and electrical temperature measurement information of the thermistor TH (FIG. 9) is transmitted via the electrical contact b for temperature adjustment and the temperature adjustment connector 122. The image forming apparatus can be input to the control circuit (CPU) 106 on the main body side.

  In the fixing device 8 of this embodiment, when the pressure roller 104 is driven to rotate, the fixing belt 103 moves outwardly around the heater holder 101 and the fixing stay 110 by the pressure friction force at the fixing nip portion N as indicated by the arrows in FIG. Follows clockwise rotation. At this time, the inner surface of the fixing belt 103, the heater 100, and the heater holder 101 are configured to slide. Grease is applied to the sliding surface of the heater 100, and the fixing belt 103 rotates, so that the grease spreads over the entire inner surface of the fixing belt and ensures the slidability between the heater 100 and the heater holder 101 and the inner surface of the fixing belt 103. ing.

  In normal use, power supply from the power supply circuit 120 to the heater H is started simultaneously with the start of rotation of the fixing device (rotation driving of the pressure roller 104 and accompanying rotation of the fixing belt 103). The heater H quickly rises in temperature, and the rotating fixing belt 103 is heated by the generated heat. The rise of the fixing belt 103 is detected by the thermistor TH in contact with the inner surface of the fixing belt 103, and the electrical temperature measurement information is input to the control circuit 106. The control circuit 106 controls the electric power supplied from the power supply circuit 120 to the heater H so that the temperature detection information of the fixing belt 103 input from the thermistor TH is maintained at a predetermined fixing temperature, thereby controlling the temperature of the heater H, that is, the fixing belt 103. Adjust the temperature to a predetermined level. The thermistor TH has a thermistor element attached to the tip of a stainless steel arm 102, and even if the movement of the inner surface of the fixing belt 103 becomes unstable due to the swinging of the arm 102, the thermistor element has an inner surface of the fixing belt 103. It is always kept in contact.

  Then, rotation of the fixing device is started, power supply to the heater H is started, and the fixing belt 103 is temperature-controlled at a predetermined fixing temperature, and the transfer material S to be image-fixed enters the entrance as shown in FIG. Guided by the guide 105 and introduced into the fixing nip N. The entrance guide 105 is assembled to the apparatus frame 107 and serves to guide the transfer material so that the transfer material S that has passed through the secondary transfer nip is accurately guided to the fixing nip N.

  The transfer material S introduced into the fixing nip N is nipped and conveyed by the fixing nip N, and is heated by the heat of the fixing belt 103 in the nipping and conveying process, and is pressurized by the pressure of the fixing nip N. The four color toner images on the transfer material S are fixed (melted and mixed) as fixed images on the transfer material S. The transfer material S exiting the fixing nip N is separated from the surface of the fixing belt 103 by the curvature, conveyed along the discharge guide 15 by the discharge roller pair 13, and discharged face-down on the upper part of the image forming apparatus A by the discharge roller pair 9. It is discharged to the tray 10 to complete image formation.

(3) Fixing belt 103
The fixing belt 103 is formed by forming an elastic layer and a release layer on a metal base layer. FIG. 11 is a schematic cross-sectional view showing the layer structure of the fixing belt 103 used in this embodiment.

For the fixing belt 103, a silicone rubber layer (elastic layer) 103b is formed by a ring coating method on a SUS belt (base layer) 103a formed into a seamless belt shape having a thickness of 34 μm by drawing a SUS base tube. In addition, a PFA resin tube having a thickness of 30 μm is coated as the releasable layer 103c. For the silicone rubber layer 103b, it is desirable from the viewpoint of temperature rise to use a material having as high a thermal conductivity as possible and to reduce the heat capacity of the fixing belt 103. In this embodiment, the material having a thermal conductivity of about 1.0 × 10 ⁻³ cal / sec · cm · K and a silicone rubber having a high thermal conductivity were used.

  On the other hand, it is desirable that the silicone rubber layer 103b of the fixing belt 103 is made as thick as possible from the viewpoint of image quality such as OHT permeability and “s” (small gloss unevenness) on the image. According to the study by the present inventors, it has been found that a rubber thickness of 200 μm or more is necessary to obtain a satisfactory level of image quality.

  The silicone rubber layer 103b in this example has a thickness of 275 μm. Further, the inner diameter of the fixing belt 103 in this embodiment is set to 24 mm.

  Furthermore, by providing a fluororesin layer on the surface of the fixing belt 103, the surface releasability is improved, and the offset phenomenon that occurs when the toner once adheres to the surface of the fixing belt 103 and moves to the transfer material S again is prevented. can do.

  Further, by using a PFA tube as the releasable layer 103c on the surface of the fixing belt 103, a uniform releasable layer can be formed more easily.

(4) Fixing flange 108, end holder 109
12 is an external perspective view of the heating assembly and the pressure roller from which the fixing belt 103 has been removed, FIG. 13 is an exploded perspective view of one end portion of the heating assembly from which the fixing belt 103 has been removed, and FIG. It is a figure of the inner surface side of the part holder 109.

  The fixing flange 108 is an annular short cylindrical member as a fixing belt supporting member that rotatably supports the radial direction of the end portion of the fixing belt 103 from the outer peripheral surface side and the thrust direction from the side surface (end surface).

  The end holder 109 rotatably supports the inner peripheral surface of the fixing flange 108 at the boss portion 109b and restricts the movement of the fixing flange 108 in the thrust direction. That is, the end holder 109 is provided with a boss portion 109b that rotatably supports the inner peripheral surface of the fixing flange 108, and a fixing belt end portion regulating surface 109c that regulates the thrust direction end portion of the fixing belt 103 via the fixing flange 108. It functions as a regulating member.

  As shown in FIG. 14, the fixing flange 108 has an inner diameter φ 26 larger than the outer diameter of the fixing belt 103, and the fixing belt 103 deformed by the pressure roller 104 is inscribed in the fixing flange 108 to generate a frictional force. The fixing belt 103 and the fixing flange 108 rotate together to prevent the end surface of the fixing belt 103 from rubbing.

  Further, in this embodiment, the rubbing surface (fixing belt end regulating surface) 109c of the end holder 109 with the fixing flange 108, as shown in FIG. In the approaching direction, a portion near the fixing nip N is tapered in a direction away from the fixing belt 103. As a result, the fixing belt 103 and the fixing flange 108 are in contact with each other only at a portion that is far from the fixing nip portion N and has flexibility (contact point 113). Even in such a case, no great stress is applied to the end of the fixing belt. Further, since the rubbing force does not act on the fixing belt 103 even in a region deformed by nip formation (shaded region β in FIG. 15), defects such as microcracks existing at the end of the fixing belt are not enlarged.

  Here, a configuration related to the present invention will be described with reference to FIGS. 1 to 3 are diagrams in which only the heater holder 101, the heater H, the fixing belt 103, and the pressure roller 104 referred to in FIG. 8 are extracted and simplified, and the shape claimed in the present invention is added. First, in FIG. 2, a protrusion 101p that guides the inner surface of the sleeve is provided at the entrance / exit of the heater H storage portion outside the paper passing area. FIG. 1 shows only the heater holder 101 extracted from these, and the protrusion 101p is provided only on the outside of the paper passing area and disappears gradually toward the paper passing area. In this embodiment, as shown in FIG. 2, the distance y between the fixing belt end and the pressure roller end is 5 mm, whereas the height x of the protrusion 101p is set to 0.5 mm. Note that the height x of the protrusion is determined in accordance with the distance y between the end of the fixing belt and the end of the pressure roller, and if y increases, x needs to be increased. On the other hand, the shape of the sheet passing area is optimized so as to satisfy the fixing conditions, so the conventional heater holder shape is maintained and no change is made. Next, the cross-sectional shape of the fixing belt when the pressure nip is formed outside the paper passing area and the paper passing area will be described with reference to FIG. As indicated by the broken line portion, the shape of the fixing belt before and after the two-pipe follows the shape of the heater holder, so that the minimum curvature b outside the sheet passing area is larger than the minimum curvature c in the sheet passing area. In this embodiment, the minimum curvature b outside the sheet passing area is approximately R8.0 on the upstream side, and the minimum curvature c in the sheet passing area is approximately R7.0 on the upstream side. In this way, by reducing the curvature by about 10%, compared to the conventional example (FIG. 23) in which the minimum curvature outside the paper passing area is equivalent to that of the paper passing area, fatigue due to repeated “bending” at the fixing belt end portion. And a life-prolonging effect twice or more against fatigue failure can be expected.

(Example 2)
As shown in FIG. 4, the same effect as described above can be obtained by interposing a member 205 for guiding the inner surface of the fixing belt end between the heater H end and the fixing belt end outside the sheet passing area. Can be obtained. The member 205 may be realized by placing a heat resistant resin on the heater H.

(Example 3)
Example 3 will be described below. The overall configuration of the apparatus is the same as that of FIG. 6 shown in the first embodiment, but the following configuration is also conceivable for the fixing device. That is, regarding the relationship between the heater holder 301, the heater H, the fixing belt 303, and the end flange 305, as shown in FIG. 5, the outer peripheral surface 305a of the end flange 305 and the inner peripheral surface of the fixing belt 303 are slid. Thus, the rotation belt trajectory of the fixing belt 303 is regulated, and the fixing belt end regulating surface 305b regulates the fixing belt end portion by abutting against the fixing belt end regulating surface 305b even when the fixing belt 303 approaches the thrust direction. is doing. Furthermore, in Example 1, when the press contact dip is formed so that the end flange 305 has the function of the protrusion 101p that the heater holder had on the outside of the sheet passing region, A guide is provided on the end flange as in 305c so that the minimum curvature of the fixing belt outside the sheet passing area is larger than the minimum curvature in the sheet passing area.

  With the configuration as described above, without changing the shape of the heater holder in the paper-passing area, that is, maintaining the fixing conditions, reducing the fatigue caused by repeated “bending” of the stress generated at the end of the fixing belt I can do it.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Photosensitive drum charging roller 3 Exposure means 4 Developing apparatus (development rotary)
5 Intermediate transfer unit 5a Intermediate transfer belt 5f according to the first embodiment 5f Cleaning charging roller 5j according to the first embodiment 5j Primary transfer roller according to the first embodiment 6 Cleaning blade 7d according to the first embodiment Registration roller pair according to the first embodiment 8 Fixing device 9 Discharge roller according to the first embodiment 10 Discharge tray according to the first embodiment 11 Secondary transfer roller according to the first embodiment 13 First transfer A pair of paper discharge rollers according to the embodiment 14 A registration sensor according to the first embodiment 15 A paper discharge guide according to the first embodiment 16 A waste toner box according to the first embodiment 19 A paper feed cassette according to the first embodiment 40 Belt Drive Roller According to the First Example 41 Belt Driven Roller According to the First Example H Heater According to the First Example 101 Heater Holder According to the First Example 10 p Projection of Heater Holder According to First Example TH Thermistor According to First Example 103 Fixing Belt According to First Example 104 Pressure Roller According to First Example 105 First Example The entrance guide 106 according to the first embodiment.
107 Frame according to the first embodiment 108 Fixing flange according to the first embodiment 109 End holder 110 according to the first embodiment 110 Fixing stay 111 according to the first embodiment 111 Pressure according to the first embodiment Spring 112 Pressure plate according to the first embodiment 113 Contact point between the fixing belt and the fixing flange according to the first embodiment 201 Heater holder according to the second embodiment 203 Fixing belt 204 according to the second embodiment 204 Second Pressure roller according to the embodiment 205 Inclusion according to the second embodiment 300 Fixing flange according to the third embodiment 301 Fixing belt 303 according to the third embodiment 303 Pressure roller 305 according to the third embodiment Fixing flange according to third embodiment 402 End holder according to conventional example 403 Fixing film according to conventional example 404 Pressure roller according to conventional example 405 Addition according to conventional example Pressure spring 500 Fixing flange according to conventional example 501 Fixing belt according to conventional example 502 Pressure roller according to conventional example 503 Fixing flange according to conventional example 601 Fixing belt according to conventional example 602 Heater holder according to conventional example

Claims (4)

  An image having a sleeve-like rotator, heating means for heating the rotator, heating the recording material carrying the image as the rotator rotates, and a pressure member forming a pressure nip with the rotator The heating device has a first guide surface that supports the inner surface of the rotator within the sheet passing area and a second guide surface that supports the inner surface of the rotator outside the sheet passing area to form a pressure nip. In this case, the image heating apparatus is characterized in that the second guide surface is outside the position of the inner peripheral surface of the rotating body supported by the first guide surface.   The image heating apparatus according to claim 1, wherein the second guide surface is provided in the vicinity of the upstream and downstream of the heating unit.   The image heating apparatus according to claim 1, wherein the second guide surface is provided between the heating unit and the rotating body.   The image heating apparatus according to claim 1, wherein a restricting member in a thrust direction of the rotating body also serves as the second guide surface.