JP2011118291A - Fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of uneven glossiness in a fixed image due to toner components deposited on a belt member. <P>SOLUTION: An external heat roll 613 heats the fixing belt 610 while stretching the fixing belt 610, which circulation-moves to fix the toner onto paper, from the outside of the fixing belt 610. The external heat roll 613 is configured so that the releasability of the surface of the external heat roll 613 is made to be lower than that of the surface of the fixing belt 610. In the external heat roll 613, a web 651, which cleans the surface of the external heat roll 613 in contact with the external heat roll 613, is disposed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

An image forming apparatus such as a copying machine or a printer having a fixing device for fixing a toner image using a belt member (fixing belt) stretched by a plurality of roll members each having a heating member such as a heater. It has been known.
For example, Patent Document 1 includes a fixing belt stretched between a fixing roller and a heating roller, and a pressure roller that contacts the outer peripheral surface of the fixing belt and forms a nip with the fixing belt. A fixing member having a shape with a large curvature at the exit separation surface is provided inside the fixing belt at a position corresponding to the exit separation portion of the nip formed by the fixing roller and the pressure roller via the belt. A fixing device is described.

No. 2003-5565

  An object of the present invention is to suppress non-uniformity in gloss of a fixed image caused by a toner component adhering to a belt member.

  According to the first aspect of the present invention, the belt member that fixes the toner to the recording material while being circulated and the belt member is heated by a heating element that is arranged inside while stretching the belt member from the outside, An external heating roll member having a surface releasability lower than that of the belt member surface, and a cleaning member disposed in contact with the external heating roll member and cleaning the surface of the external heating roll member And a fixing device.

According to a second aspect of the present invention, the external heating roll member is rotationally driven in response to a rotational driving force from a driving source, and the rotational force received from the belt member is greater than the rotational driving force from the driving source. 2. The fixing device according to claim 1, wherein a rotation transmission limiting member that stops transmission of the rotation driving force when the rotation driving force is larger is disposed in the transmission path of the rotation driving force.
The invention according to claim 3 further includes a support member that supports the belt member while receiving a pressing force from the external heating roll member at a position facing the external heating roll member with the belt member interposed therebetween. The fixing device according to claim 2, wherein:
The invention according to claim 4 is the fixing device according to claim 2, wherein the external heating roll member has a surface hardness higher than that of the cleaning member.

  According to a fifth aspect of the present invention, there is provided a toner image forming unit that forms a toner image, a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material, and a toner image that is transferred onto the recording material. A fixing unit that fixes the toner image to the recording material, and the fixing unit stretches the belt member from the outside, and a belt member that fixes the toner image to the recording material while circulating. While heating the belt member by the heating element disposed inside, the external heating roll member configured to have a surface releasability lower than the releasability of the belt member surface, and the external heating roll member And a cleaning member that cleans the surface of the external heating roll member.

According to a sixth aspect of the present invention, the external heating roll member of the fixing unit is rotationally driven in response to a rotational driving force from a driving source, and the rotational force received from the belt member is from the driving source. 6. The image forming apparatus according to claim 5, wherein a rotation transmission limiting member that stops transmission of the rotation driving force when the rotation driving force is greater is disposed in the transmission path of the rotation driving force.
According to a seventh aspect of the present invention, the fixing unit supports the belt member at a position facing the external heating roll member and the belt member while receiving the pressing force from the external heating roll member. The image forming apparatus according to claim 6, further comprising a member.
The invention according to claim 8 is the image forming apparatus according to claim 6, wherein the external heating roll member of the fixing unit has a surface hardness higher than that of the cleaning member.

According to the first aspect of the present invention, it is possible to suppress the occurrence of non-uniform gloss in the fixed image due to the toner component adhering to the belt member as compared with the case where the present invention is not adopted.
According to the invention of claim 2, in the configuration in which the cleaning member slides for cleaning the surface of the external heating roll member, the moving speed of the belt member is unstable as compared with the case where the present invention is not adopted. Can be suppressed.
According to the invention of claim 3, the function of transferring the toner component adhering to the surface of the belt member to the surface of the external heating roll member can be improved as compared with the case where the present invention is not adopted.
According to the fourth aspect of the present invention, the smoothness of the surface of the external heating roll member is maintained and the toner component adhering to the surface of the belt member is transferred to the surface of the external heating roll member as compared with the case where the present invention is not adopted. Can be maintained.

According to the fifth aspect of the present invention, it is possible to suppress the occurrence of non-uniform gloss in the fixed image due to the toner component adhering to the belt member, as compared with the case where the present invention is not adopted.
According to the invention of claim 6, in the configuration in which the cleaning member slides for cleaning the surface of the external heating roll member, the moving speed of the belt member is unstable as compared with the case where the present invention is not adopted. Can be suppressed.
According to the seventh aspect of the present invention, the function of transferring the toner component adhering to the surface of the belt member to the surface of the external heating roll member can be improved as compared with the case where the present invention is not adopted.
According to the eighth aspect of the present invention, the smoothness of the surface of the external heating roll member is maintained and the toner component adhering to the surface of the belt member is transferred to the surface of the external heating roll member as compared with the case where the present invention is not adopted. Can be maintained.

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing device according to an exemplary embodiment is applied. FIG. 3 is a cross-sectional configuration diagram for describing a configuration of a fixing unit. FIG. 4 is a cross-sectional configuration diagram of a region where an external heating roll heats the fixing belt from the outside. It is a section layer lineblock diagram of an external heating roll. It is a figure which shows the drive mechanism for rotating an external heating roll at a constant speed with a fixing belt.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus 1 to which a fixing device (fixing unit) 60 according to the present embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called “tandem type” color printer, and controls an image forming unit 10 that forms an image based on image data, operation control of the entire image forming apparatus 1, for example, a personal computer (PC). A main control unit 50 that performs communication with the user, image processing performed on image data, and the like, and a user interface (UI) unit 90 that receives operation input from the user and displays various information to the user. ing.

<Description of Image Forming Unit>
The image forming unit 10 is a functional unit that forms an image by, for example, electrophotography, and includes six image forming units 11C, 11M, 11HC, 11HM, 11Y as an example of toner image forming units arranged in parallel. 11K (hereinafter “image forming unit 11”). Each image forming unit 11 functions as a functional member, for example, a photosensitive drum 12 on which an electrostatic latent image is formed and then each color toner image is formed, and the surface of the photosensitive drum 12 is charged with a predetermined potential. A charger 13 that exposes the photosensitive drum 12 charged by the charger 13 based on image data, and development that develops the electrostatic latent image formed on the photosensitive drum 12 with toner of each color. And a cleaner 16 for cleaning the surface of the photosensitive drum 12 after transfer.
Each developing unit 15 of each image forming unit 11 is connected to toner containers 17C, 17M, 17HC, 17HM, 17Y, and 17K (hereinafter referred to as “toner containers 17”) for storing toners of respective colors by toner transport paths (not shown). ing. Each color toner is supplied from the toner container 17 to the developing device 15 by a supply screw (not shown) provided in the toner conveyance path.

  Each of the image forming units 11 is configured in substantially the same manner except for the toner accommodated in the developing device 15, and each of them is C (cyan) color, M (magenta) color, HC (high chroma cyan) color, and HM (high chroma magenta). Color, Y (yellow), and K (black) toner images are formed. The HC color here is a cyan color having a cyan hue, a hue that is brighter and higher in saturation than the C color, and the HM color has a magenta hue, and M color. It is a magenta color with a brighter color tone and a relatively high saturation.

The image forming unit 10 intermediates the intermediate transfer belt 20 to which the respective color toner images formed on the photosensitive drums 12 of the respective image forming units 11 are transferred and the respective color toner images formed by the respective image forming units 11. A primary transfer roll 21 for transferring (primary transfer) to the transfer belt 20. Furthermore, a secondary transfer roll 22 that batch-transfers (secondary transfer) each color toner image transferred onto the intermediate transfer belt 20 onto a sheet that is a recording material (recording paper), and each color toner that has been secondarily transferred. And a fixing unit 60 as an example of a fixing unit (fixing device) for fixing the image on the sheet.
In addition, the image forming unit 10 cools each color toner image fixed on the sheet by the fixing unit 60 and promotes fixing of the color toner image on the sheet, and the sheet is bent (curled). And a curl correction unit 85 for correcting the above.
In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit. Further, an area where the secondary transfer roll 22 is disposed and each color toner image on the intermediate transfer belt 20 is secondarily transferred to a sheet is hereinafter referred to as a “secondary transfer area Tr”.

<Description of paper transport system>
In addition, the image forming unit 10 feeds out a plurality of (two in the present embodiment) sheet storage containers 40A and 40B that store sheets and a sheet stored in the sheet storage containers 40A and 40B as a sheet transport system. Feeding rolls 41A and 41B, a first transport path R1 for transporting paper from the paper container 40A, and a second transport path R2 for transporting paper from the paper container 40B. Further, the image forming unit 10 includes a third transport path R3 that transports the paper from the paper storage container 40A and the paper storage container 40B toward the secondary transfer region Tr. In addition, the image forming unit 10 conveys the sheet on which the toner image of each color is transferred in the secondary transfer region Tr so as to pass through the fixing unit 60, the cooling unit 80, and the curl correcting unit 85. And a fifth transport path R5 for transporting the sheet from the curl correction unit 85 toward the sheet stacking section 44 provided in the discharge section of the image forming apparatus 1.
From the first conveyance path R1 to the fifth conveyance path R5, conveyance rolls and conveyance belts are arranged along the respective conveyance paths to sequentially convey the fed sheets.

<Description of double-sided conveyance system>
In addition, the image forming unit 10 serves as a double-sided conveyance system in which an intermediate paper storage container 42 that temporarily holds the paper on which the toner images of each color are fixed on the first surface by the fixing unit 60 and the paper from the curl correction unit 85 as intermediate paper. A sixth transport path R6 for transporting toward the storage container 42 and a seventh transport path R7 for transporting the paper stored in the intermediate paper storage container 42 toward the third transport path R3 are provided. Further, the image forming unit 10 is disposed on the downstream side of the curl correction unit 85 in the sheet conveyance direction, and conveys the sheet toward the sheet stacking unit 44 and a sixth conveyance path R5 that conveys the sheet to the intermediate sheet storage container 42. A distribution mechanism unit 43 that selectively distributes the sheet to the path R6 and a feeding roll 45 that feeds the sheet stored in the intermediate sheet storage container 42 toward the seventh transport path R7 are provided.

<Description of image forming operation>
Next, a basic image forming operation in the image forming apparatus 1 according to the present embodiment will be described.
Each of the image forming units 11 of the image forming unit 10 forms toner images of C color, M color, HC color, HM color, Y color, and K color by an electrophotographic process using the above functional members. Each color toner image formed by each image forming unit 11 is primary-transferred sequentially on the intermediate transfer belt 20 by the primary transfer roll 21 to form a composite toner image in which the respective color toners are superimposed. The synthetic toner image on the intermediate transfer belt 20 is conveyed to the secondary transfer region Tr in which the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves (in the direction of the arrow).

On the other hand, in the paper transport system, the feeding roll 41 rotates in accordance with the start timing of image formation in each image forming unit 11, and is designated by the UI unit 90 from the paper container 40A and the paper container 40B, for example. The other sheet is fed by the feeding rolls 41A and 41B. The sheet fed by the feeding rolls 41A and 41B is transported along the first transport path R1 or the second transport path R2 and the third transport path R3, and reaches the secondary transfer region Tr.
In the secondary transfer region Tr, the composite toner image held on the intermediate transfer belt 20 is secondarily transferred collectively onto the paper by the transfer electric field formed by the secondary transfer roll 22.

Thereafter, the sheet on which the composite toner image is transferred is separated from the intermediate transfer belt 20 and conveyed to the fixing unit 60 along the fourth conveyance path R4. The synthesized toner image on the paper transported to the fixing unit 60 is fixed on the paper after being subjected to a fixing process by the fixing unit 60. Then, the sheet on which the fixed image is formed is cooled by the cooling unit 80, and the curl correction unit 85 corrects the bending of the sheet. Thereafter, the paper passing through the curl correction unit 85 is guided by the distribution mechanism unit 43 to the fifth transport path R5 during single-sided printing and transported toward the paper stacking unit 44.
The toner (primary transfer residual toner) adhering to the photosensitive drum 12 after the primary transfer and the toner (secondary transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer are respectively cleaner 16, And removed by the belt cleaner 26.

On the other hand, during double-sided printing, the paper on which the fixed image is formed on the first surface of the paper by the above-described process passes through the curl correction unit 85 and is then guided to the sixth transport path R6 by the distribution mechanism unit 43. The sixth transport path R6 is transported toward the intermediate paper storage container. Again, the feeding roll 45 rotates in accordance with the start timing of image formation on the second surface by each image forming unit 11, and the sheet is fed out from the intermediate sheet storage container 42. The sheet fed by the feeding roll 41 is transported along the seventh transport path R7 and the third transport path R3, and reaches the secondary transfer region Tr.
In the secondary transfer region Tr, as in the case of the first surface, the toner images of the respective colors on the second surface held on the intermediate transfer belt 20 are collectively applied to the sheet by the transfer electric field formed by the secondary transfer roll 22. Second transfer is performed.

Then, the paper on which the toner images are transferred on both sides is fixed by the fixing unit 60 as in the case of the first side, cooled by the cooling unit 80, and further corrected by the curl correction unit 85. Is done. Thereafter, the paper that has passed through the curl correction unit 85 is guided to the fifth transport path R5 by the distribution mechanism unit 43 and transported toward the paper stacking unit 44.
In this way, the image forming process in the image forming apparatus 1 is repeatedly executed for the number of printed sheets.

<Description of fixing unit configuration>
Next, the fixing unit 60 used in the image forming apparatus 1 of the present embodiment will be described.
FIG. 2 is a cross-sectional configuration diagram for explaining the configuration of the fixing unit 60 of the present embodiment. The fixing unit 60 includes a fixing belt module 61 that heats a sheet, and an external heating roll member that heats the fixing belt 610 while stretching the fixing belt 610 provided on the fixing belt module 61 from the outside. The main part is composed of a roll 613, a roll cleaning mechanism 65 that cleans the surface of the external heating roll 613, and a pressure roll 62 configured to be able to contact and separate from the fixing belt module 61.

  The fixing belt module 61 rotates while fixing the fixing belt 610 as an example of a belt member that circulates and the fixing belt 610, and the fixing belt module 61 and the pressure roll 62 are pressed against each other (contacted while being pressed against each other). ), A fixing roll 611 that heats the fixing belt 610 from the inside at the nip portion N, and an internal heating roll 612 that heats the fixing belt 610 while stretching the fixing belt 610 from the inside. The fixing belt module 61 includes a tension roll 614 that stretches the fixing belt 610 between the fixing roll 611 and the internal heating roll 612 (upstream of the nip portion N), and a downstream region in the nip portion N. The fixing belt 610 is stretched between the peeling pad 64 as an example of the peeling member disposed in the vicinity of the fixing roll 610 and the nip portion N and the external heating roll 613 (downstream of the nip portion N). A tension roll 615 and a support roll 616 as an example of a support member that supports the fixing belt 610 while receiving a pressing force from the external heating roll 613 are provided. The fixing belt module 61 is configured to be detachable from the image forming apparatus 1.

The fixing belt 610 includes, for example, a base layer formed of a polyimide resin, an elastic layer made of silicone rubber laminated on the surface side (outer peripheral surface side) of the base layer, and a PFA coated on the elastic layer. And a release layer made of (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin). Here, the elastic layer is provided in order to improve the image quality especially for color images. That is, the toner image held on the sheet to be fixed is formed by laminating toners of various colors that are powders. Therefore, in order to supply heat uniformly to the entire toner image at the nip portion N, it is preferable that the surface of the fixing belt 610 be deformed following the unevenness of the toner image on the paper.
The fixing roll 611 is a cylindrical roll formed of, for example, aluminum or SUS, and receives a rotational driving force from a driving motor (not shown) and rotates in the arrow direction in the figure. The fixing roll 611 is heated to a predetermined temperature (for example, 150 ° C.) by, for example, three halogen heaters 71 as an example of a heating element disposed inside the fixing roll 611.

The internal heating roll 612 is a cylindrical roll formed of, for example, aluminum or SUS. Then, the internal heating roll 612 is heated to a predetermined temperature (for example, 190 ° C.) by, for example, four halogen heaters 72 as an example of the heating element disposed inside.
The internal heating roll 612 is provided with spring members (not shown) that press the fixing belt 610 from the inside to the outside at both ends, and the tension of the entire fixing belt 610 is set to 15 kgf, for example.
Further, the internal heating roll 612 is provided with a mechanism for controlling the meandering (belt walk) of the fixing belt 610. That is, a belt edge position detection mechanism (not shown) that detects the end position (edge position) of the fixing belt 610 is disposed in the vicinity of the internal heating roll 612. The internal heating roll 612 is provided with a displacement mechanism (not shown) that displaces one end of the internal heating roll 612 in a direction perpendicular to the axial direction of the internal heating roll 612. The displacement mechanism displaces the fixing belt 610 in the axial direction of the internal heating roll 612 by displacing one end of the internal heating roll 612 according to the detection result of the belt edge position detection mechanism. Thereby, the belt walk of the fixing belt 610 is controlled.

  The peeling pad 64 is a block member made of a metal such as SUS or a rigid body such as resin and having a substantially arc-shaped cross section. The fixing roll 611 is fixedly disposed over the entire axial direction of the fixing roll 611 at a position near the downstream side of the area where the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610 (hereinafter referred to as “roll nip portion N1”). Has been. The peeling pad 64 has a predetermined load (for example, a nip width of 5 mm along the traveling direction of the fixing belt 610) in a predetermined width region (for example, 5 mm along the traveling direction of the fixing belt 610) via the fixing belt 610. For example, it is installed so as to press uniformly at an average of 10 kgf), and a “peeling pad nip portion N2” connected to the roll nip portion N1 is formed.

Next, the external heating roll 613 is a cylindrical roll configured by, for example, nitriding a surface having aluminum or SUS as a base. Then, the external heating roll 613 is heated to a predetermined temperature (for example, 190 ° C.) by, for example, three halogen heaters 73 as an example of a heating element disposed inside. The external heating roll 613 will be described in detail later.
As described above, the fixing unit 60 of the present embodiment employs a configuration in which the fixing belt 610 is heated by the fixing roll 611, the internal heating roll 612, and the external heating roll 613.

  Next, the pressure roll 62 is formed by laminating an elastic layer made of silicone rubber and a release layer made of a PFA tube in this order from the substrate side, for example, using a cylindrical roll made of aluminum or SUS as a base. ing. The pressure roll 62 is disposed so as to be in contact with and separated from the fixing belt module 61. When the pressure roll 62 is set so as to contact (pressure contact) while pressing the fixing belt module 61, the fixing roll of the fixing belt module 61 is used. As 611 rotates in the direction of the arrow, it follows the fixing roll 611 and rotates in the direction of the arrow.

<Description of the fixing operation in the fixing unit>
Subsequently, a fixing operation in the fixing unit 60 of the present embodiment will be described.
The sheet on which the composite toner image (unfixed toner image) is electrostatically transferred in the secondary transfer region Tr (see FIG. 1) of the image forming apparatus 1 is fixed along the fourth conveyance path R4 (see FIG. 1). It is conveyed toward the nip portion N (see FIG. 2). The unfixed toner image on the paper surface passing through the nip portion N is fixed to the paper mainly by pressure and heat acting on the roll nip portion N1.

  That is, in the fixing unit 60 of the present embodiment, the heat acting on the roll nip portion N1 is mainly supplied by the fixing belt 610. The fixing belt 610 is supplied with heat supplied from the halogen heater 71 arranged inside the fixing roll 611 via the fixing roll 611 and from the halogen heater 72 arranged inside the internal heating roll 612 via the internal heating roll 612. And the heat supplied from the halogen heater 73 disposed inside the external heating roll 613 through the external heating roll 613. As a result, not only the fixing roll 611 but also the internal heating roll 612 and the external heating roll 613 are replenished with heat energy, so that a sufficient amount of heat is secured at the roll nip portion N1 even if the process speed is high. .

In the fixing unit 60 of the present embodiment, the fixing belt 610 that functions as a direct fixing member can be configured to have a very small heat capacity. In addition, the fixing belt 610 is configured to come into contact with the fixing roll 611 that is a heat supply member, and the internal heating roll 612 and the external heating roll 613 with a wide lap area (large wrap angle). Therefore, since a sufficient amount of heat is supplied from the fixing roll 611, the internal heating roll 612, and the external heating roll 613 in a short period of one rotation of the fixing belt 610, the fixing belt 610 is returned to the necessary fixing temperature in a short time. It becomes possible. Thereby, a predetermined fixing temperature is maintained in the roll nip portion N1.
As a result, in the fixing unit 60 of the present embodiment, the fixing temperature is maintained substantially constant even when the paper is continuously fed at a high speed. In addition, the phenomenon that the fixing temperature drops at the start of the fixing operation at high speed (so-called “temperature droop phenomenon”) is suppressed. In particular, when fixing to thick paper having a large heat capacity, the maintenance of the fixing temperature and the occurrence of temperature droop are suppressed, and furthermore, the fixing temperature is switched halfway according to the type of paper (both the fixing temperature is increased and decreased). Even if necessary, the fixing belt 610 has a small heat capacity, so that the temperature can be easily switched by adjusting the output of the halogen heater 71, and further, the halogen heater 72 and the halogen heater 73.

  In the fixing unit 60 of the present embodiment, the fixing roll 611 is a hard roll formed of aluminum, SUS, or the like, and the pressure roll 62 is a soft roll that covers an elastic layer. Therefore, in the roll nip portion N1, the fixing roll 611 hardly bends, and the surface of the pressure roll 62 is bent, so that a nip region having a width in the traveling direction of the fixing belt 610 is formed. As described above, in the roll nip portion N1, the fixing roll 611 on the side where the fixing belt 610 is wrapped is hardly deformed. Therefore, the fixing belt 610 passes through the roll nip portion N1 while maintaining the moving speed substantially constant. As a result, the fixing belt 610 is prevented from being wrinkled or distorted at the roll nip portion N1, so that a high-quality fixed image is stably provided.

Subsequently, after passing through the roll nip portion N1, the sheet is conveyed to the peeling pad nip portion N2. The peeling pad nip portion N <b> 2 is configured so that the peeling pad 64 is pressed against the pressure roll 62 and the fixing belt 610 is pressed against the pressure roll 62. Accordingly, the roll nip portion N1 has a curved shape that is convex downward due to the curvature of the fixing roll 611, whereas the peeling pad nip portion N2 has a curved shape that is convex upward due to the curvature of the pressure roll 62. Yes.
Therefore, the traveling direction of the sheet heated and pressed under the curvature of the fixing roll 611 in the roll nip portion N1 is changed to the curvature directed in the opposite direction by the pressure roll 62 in the peeling pad nip portion N2. At that time, a minute micro slip occurs between the toner image on the paper and the surface of the fixing belt 610. As a result, the adhesion between the toner image and the fixing belt 610 is weakened, and a state is formed in which the paper is easily peeled off from the fixing belt 610. As described above, the peeling pad nip portion N2 is also positioned in a preparation process for surely peeling in the final peeling process.

  Since the fixing belt 610 is conveyed so as to be wound around the peeling pad 64 at the exit of the peeling pad nip portion N2, the conveyance direction of the fixing belt 610 changes abruptly there. That is, since the fixing belt 610 moves along the outer surface of the peeling pad 64, the bending of the fixing belt 610 becomes large. Therefore, the paper whose adhesion with the fixing belt 610 is weakened in advance in the peeling pad nip portion N2 is separated from the fixing belt 610 by the stiffness of the paper that the paper itself has.

  The paper separated from the fixing belt 610 is guided in the traveling direction by a peeling guide plate 69 disposed on the downstream side of the peeling pad nip portion N2. The paper guided by the peeling guide plate 69 is then conveyed toward the cooling unit 80 by the paper discharge guide 78 and the paper discharge belt 79, whereby the fixing process in the fixing unit 60 is completed.

<Description of external heating roll>
Next, the external heating roll 613 of this embodiment will be described.
FIG. 3 is a cross-sectional configuration diagram of a region where the external heating roll 613 heats the fixing belt 610 from the outside. As shown in FIG. 3, the external heating roll 613 contacts the fixing belt 610 while pressing the fixing belt 610 with the pressing force F1. On the other hand, on the inner side of the fixing belt 610 at a position where the external heating roll 613 contacts the fixing belt 610 (position facing the external heating roll 613 and the fixing belt 610), it opposes the pressing force F1 from the external heating roll 613. A support roll 616 as an example of a support member that supports the fixing belt 610 while a pressing force F2 (F1 = F2) is applied is disposed. Thereby, a pressing force F1 of, for example, 0.75 kgf / cm ² or more is set between the external heating roll 613 and the fixing belt 610, for example, with a nip width of 3 mm.

The external heating roll 613 is provided with a roll cleaning mechanism 65 that cleans the surface of the external heating roll 613. The roll cleaning mechanism 65 includes a winding roll 652 around which a web 651 as an example of a cleaning member in which fibers are formed into a sheet shape, and a winding roll that gradually winds up the web 651 wound around the winding roll 652. 653 and a pressing roll 654 that makes the web 651 contact the surface of the external heating roll 613 while pressing it with a pressing force F3 (for example, 3 to 6 kgf / cm ² ).
The winding roll 653 gradually winds the web 651 in the direction opposite to the rotation direction of the external heating roll 613 at a moving speed slower than the peripheral speed of the external heating roll 613. The winding roll 653 and the winding roll 652 are configured to be detachable, and when the winding roll 653 winds up all the web 651 wound around the winding roll 652, the winding roll 652 and the winding roll 653. Will be replaced with a new one.

<Description of the surface layer of the external heating roll>
The external heating roll 613 of the present embodiment is configured by, for example, nitriding the surface that contacts the fixing belt 610 using, for example, aluminum or SUS as a base.
Here, FIG. 4 is a cross-sectional layer configuration diagram of the external heating roll 613. As shown in FIG. 4, the external heating roll 613 includes a base layer 613a made of, for example, SUS, and a surface layer 613b. For example, the surface layer 613b is configured by one of chromium nitride represented by a chemical formula CrN and chromium nitride represented by a chemical formula Cr ₂ N, or a mixture of both. . The "mixed" with chromium nitride represented by the chemical formula 2 chromium nitride and chemical formula Cr represented by CrN _N, is configured in a multilayer by a composed layer formed layer and Cr 2 _N in CrN And a case where CrN and Cr ₂ N are mixed to form a single layer.
By thus nitriding the surface layer 613b of the external heating roll 613, the surface layer 613b of the external heating roll 613 is separated from the surface of the fixing belt 610 formed of a release layer made of PFA, for example. The type is set low.

  As described above, in the fixing unit 60 of the present embodiment, the unfixed toner image on the paper surface passing through the nip portion N is fixed to the paper by receiving heat from the fixing belt 610 by contact with the fixing belt 610. Is done. Therefore, toner components such as polypropylene (PP) and polyethylene (PE) constituting the toner are likely to adhere (offset) to the surface of the fixing belt 610. As a result, toner components such as PP and PE adhere to the surface portion of the fixing belt 610 that is in direct contact with the image portion on which the toner image is formed by fixing. On the other hand, the toner component does not adhere to the surface portion of the fixing belt 610 in contact with the non-image portion where the toner image is not formed. Therefore, a portion where the toner component is adhered and a portion where the toner component is not adhered are formed on the surface of the fixing belt 610.

  When a surface portion to which the toner component is adhered and a surface portion to which the toner component is not adhered are formed on the fixing belt 610, an unfixed toner image is formed on the surface of the fixing belt 610 from the fixing belt 610 at the next fixing time. It makes a difference in the conduction of heat to. That is, in the region where the toner component is attached on the surface of the fixing belt 610, heat conduction from the fixing belt 610 to the unfixed toner image is relatively small due to the presence of the toner component, and in the region where the toner component is not attached, Heat conduction to the unfixed toner image becomes relatively large. For this reason, in the next (this) fixing after the previous fixing that caused the adhesion of the toner component, the toner is melted in the portion in the current image area that contacts the surface of the fixing belt 610 to which the toner component has adhered. It becomes relatively insufficient, and the gloss is low compared to other image areas. As a result, a low-gloss area is formed in the current fixed image as the history of the previous image portion, and the image quality is degraded.

Therefore, in the fixing unit 60 of the present embodiment, the surface layer 613b of the external heating roll 613 is configured by nitriding, for example. Accordingly, the releasability at the surface layer 613 b of the external heating roll 613 is configured to be lower than the releasability at the surface of the fixing belt 610.
In other words, in the present embodiment, the surface of the fixing belt 610 is configured to have lower adhesion energy to toner components such as PP and PE than the surface layer 613b of the external heating roll 613. Therefore, in the region where the surface of the fixing belt 610 and the surface layer 613b of the external heating roll 613 are in contact, the toner component adhering to the surface of the fixing belt 610 is relatively easily separated from the surface of the fixing belt 610 (release property). Is high), a state of being easily attached to the surface layer 613b of the external heating roll 613 (low releasability) is formed. As a result, the toner component adhering to the surface of the fixing belt 610 is transferred (adsorbed) to the surface layer 613 b of the external heating roll 613 in the contact area between the fixing belt 610 and the external heating roll 613. As a result, the toner component adhering to the surface of the fixing belt 610 is removed to the external heating roll 613 side.

  In this case, the surface smoothness of the external heating roll 613 is improved (for example, Ra ≦ 0.2), and the external heating roll 613 presses the fixing belt 610 with a pressing force F1 of, for example, 0.75 kg / cm or more. It is preferable to do. As a result, the adhesion between the surface of the external heating roll 613 and the surface of the fixing belt 610 is improved, so that the function of transferring the toner component adhering to the surface of the fixing belt 610 to the surface layer 613b of the external heating roll 613 is improved.

<Description of cleaning of the surface of the external heating roll>
As described above, the external heating roll 613 is provided with the roll cleaning mechanism 65 that cleans the surface of the external heating roll 613. Then, the web 651 moves while being pressed against the surface of the external heating roll 613 by the pressing roll 654. As a result, the toner component and toner transferred from the surface of the fixing belt 610 to the surface of the external heating roll 613 are scraped off by the fibers of the web 651, and the toner adsorption capability of the surface layer 613b of the external heating roll 613 is maintained.

In this case, the web 651 moves while being pressed against the surface of the external heating roll 613 by the pressing roll 654, but the winding speed of the winding roll 653 at that time is slower than the peripheral speed of the external heating roll 613. Therefore, rubbing occurs between the surface of the external heating roll 613 and the web 651. However, the surface layer 613b of the external heating roll 613 of this embodiment is configured by nitriding with, for example, chromium nitride whose chemical formula is represented by CrN or Cr ₂ N. Therefore, the Vickers hardness of the surface of the external heating roll 613 (surface layer 613) is 1000 to 2500 Hv and harder than the web 651. Accordingly, the surface layer 613b of the external heating roll 613 is hardly damaged even by rubbing with the web 651, and external heating for improving the adhesion between the surface of the external heating roll 613 and the surface of the fixing belt 610 is performed. The smoothness of the surface of the roll 613 is maintained. As a result, the function of transferring the toner component adhering to the surface of the fixing belt 610 to the surface layer 613b of the external heating roll 613 is maintained.

On the other hand, due to the rubbing between the surface of the external heating roll 613 and the web 651, the external heating roll 613 receives sliding friction in a direction that reduces the rotation speed. Thereby, the structure which decelerates the rotational speed of the external heating roll 613 is set. When the rotation speed of the external heating roll 613 is reduced, sliding friction occurs in the contact area between the fixing belt 610 and the external heating roll 613 in a direction that reduces the moving speed of the fixing belt 610, and the moving speed of the fixing belt 610 is reduced. It becomes a factor to stabilize.
Therefore, in the fixing unit 60 of the present embodiment, a drive mechanism for rotating the external heating roll 613 at a constant speed with the fixing belt 610 is provided.

<Description of driving mechanism of external heating roll>
Next, FIG. 5 is a diagram showing a drive mechanism for rotating the external heating roll 613 at a constant speed with the fixing belt 610.
As shown in FIG. 5, the rotation shaft 92 to which the drive side gear 91 is fixed is connected to a drive motor (not shown) as an example of a drive source, and the rotational drive force from the drive motor is transmitted. A roll side gear 97 that receives a rotational driving force is fixed to the rotation shaft 613 c of the external heating roll 613. Then, the rotational driving force from the driving side gear 91 is transmitted to the roll side gear 97 by the first transmission gear member 93 and the second transmission gear member 95 fixed coaxially to the rotating shaft 94. That is, the first transmission gear member 93 is gear-coupled to the drive-side gear 91 on the drive motor side, and the second transmission gear member 95 is gear-coupled to the roll-side gear 97 on the external heating roll 613 side. As a result, the rotational driving force of the drive motor is transmitted through the path of the rotation shaft 92 → the drive side gear 91 → the first transmission gear member 93 → the rotation shaft 94 → the second transmission gear member 95 → the roll side gear 97. .
Here, in the fixing unit 60 of the present embodiment, the gear ratio of the drive side gear 91, the first transmission gear member 93, the second transmission gear member 95, and the roll side gear 97 is determined by the external heating roll. The peripheral speed of 613 is set to be slightly faster (for example, 1%) than the moving speed of the fixing belt 610.
The rotating shaft 613c, the rotating shaft 94, and the rotating shaft 92 of the external heating roll 613 are supported by a housing (not shown) of the fixing unit 60 main body.

  A one-way clutch 96 as an example of a rotation transmission limiting member is disposed between the second transmission gear member 95 and the rotation shaft 94 so as to be coaxial with the rotation shaft 94. When the rotational torque (rotational force) received by the external heating roll 613 from the fixing belt 610 is larger than the rotational torque (rotational driving force) from the drive motor, the one-way clutch 96 is applied to the external heating roll 613 from the drive motor. It acts to stop the transmission of rotational driving force. Thereby, the external heating roll 613 rotates at a peripheral speed equal to the moving speed of the fixing belt 610.

Thus, the external heating roll 613 is configured to rotate by receiving a rotational driving force from a drive motor (not shown) so as to maintain the rotational speed against the sliding friction from the web 651. . Then, the gear ratio of each gear is set so that the peripheral speed of the external heating roll 613 is slightly faster than the moving speed of the fixing belt 610, and at the same time, the rotational driving force is transmitted from the drive motor to the external heating roll 613. A one-way clutch 96 is disposed in the route. Accordingly, when the rotational torque received by the external heating roll 613 from the fixing belt 610 becomes larger than the rotational torque from the drive motor, the transmission of the rotational driving force from the drive motor to the external heating roll 613 is stopped. Thereby, in the contact region between the fixing belt 610 and the external heating roll 613, the external heating roll 613 rotates stably at a peripheral speed equal to the moving speed of the fixing belt 610.
Therefore, even if the surface of the external heating roll 613 is cleaned by sliding with the web 651, the movement speed of the fixing belt 610 is suppressed from becoming unstable.

As described above, the fixing unit 60 of the present embodiment is configured such that the releasability at the surface layer 613 b of the external heating roll 613 is lower than the releasability at the surface of the fixing belt 610. . Accordingly, the toner component adhering to the surface of the fixing belt 610 is transferred to the external heating roll 613 to remove the toner component from the surface of the fixing belt 610. Thereby, since the image portion fixed before that is formed as a low gloss region in the next fixed image as a history, it is suppressed that the image quality is deteriorated.
Further, the external heating roll 613 is configured to rotate by receiving the rotational driving force from the drive motor via the one-way clutch 96. Accordingly, even if the surface of the external heating roll 613 is cleaned by sliding with the web 651, the movement speed of the fixing belt 610 is suppressed from becoming unstable.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing unit, 61 ... Fixing belt module, 65 ... Roll cleaning mechanism part, 71, 72, 73 ... Halogen heater, 96 ... One-way clutch, 610 ... Fixing belt, 611 ... Fixing roll, 612 ... Internal heating roll, 613 ... External heating roll

Claims (8)

A belt member for fixing the toner to the recording material while circulatingly moving;
An external heating roll member configured to heat the belt member by a heating element arranged inside while stretching the belt member from the outside and whose surface releasability is lower than the releasability of the belt member surface When,
A fixing device comprising: a cleaning member disposed in contact with the external heating roll member and cleaning the surface of the external heating roll member.   The external heating roll member is rotationally driven in response to a rotational driving force from a driving source, and when the rotational force received from the belt member is greater than the rotational driving force from the driving source, 2. The fixing device according to claim 1, wherein a rotation transmission limiting member for stopping transmission is disposed in a transmission path of the rotational driving force.   The support member which supports the said belt member is further provided in the position which opposes the said external heating roll member on both sides of the said belt member, receiving the pressing force from the said external heating roll member. Fixing device.   The fixing device according to claim 2, wherein the external heating roll member has a surface hardness higher than that of the cleaning member. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A belt member for fixing the toner image to the recording material while circulatingly moving;
An external heating roll member configured to heat the belt member by a heating element arranged inside while stretching the belt member from the outside and whose surface releasability is lower than the releasability of the belt member surface When,
An image forming apparatus comprising: a cleaning member disposed in contact with the external heating roll member and cleaning the surface of the external heating roll member.   The external heating roll member of the fixing unit is rotationally driven in response to a rotational driving force from a driving source, and the rotational heating force received from the belt member is greater than the rotational driving force from the driving source. 6. The image forming apparatus according to claim 5, wherein a rotation transmission limiting member for stopping transmission of the rotational driving force is disposed in the transmission path of the rotational driving force.   The fixing unit further includes a support member that supports the belt member while receiving a pressing force from the external heating roll member at a position facing the external heating roll member with the belt member interposed therebetween. The image forming apparatus according to claim 6.   The image forming apparatus according to claim 6, wherein the external heating roll member of the fixing unit has a surface hardness higher than that of the cleaning member.

Images