JP4456941B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and a fixing device installed therein, and more particularly to a fixing device and an image forming apparatus using an electromagnetic induction heating method. It is.

  2. Description of the Related Art Conventionally, a fixing device using an electromagnetic induction heating method for reducing energy consumption by reducing the start-up time of an image forming apparatus such as a copying machine or a printer is known (for example, Patent Documents). 1).

  In Patent Document 1 and the like, an electromagnetic induction heating type fixing device mainly faces a fixing belt stretched between a heating roller (heating roller) and a fixing auxiliary roller (fixing roller), and the heating roller via the fixing belt. It comprises an induction heating unit, a pressure roller facing the fixing auxiliary roller via a fixing belt, and the like. The induction heating unit includes a coil unit extending in the width direction (a direction perpendicular to the conveyance direction of the recording medium), a core facing the coil unit, and the like.

The fixing belt is heated at a position facing the induction heating unit. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, a magnetic field is formed around the coil portion, and an eddy current is generated on the surface of the heating roller. When an eddy current is generated in the heating roller, Joule heat is generated by the electric resistance of the heating roller itself. The fixing belt wound around the heating roller is heated by the Joule heat.
It is known that a fixing device using such an electromagnetic induction heating method can raise the surface temperature (fixing temperature) of a fixing belt to a desired temperature with a small start-up time with low energy consumption.

  On the other hand, in Patent Document 2 and the like, in the fixing device using the electromagnetic induction heating method, the inner periphery of the fixing film is used for the purpose of uniformizing the temperature distribution in the width direction of the fixing film (electromagnetic induction heat generating rotator). A technique for bringing a heat pipe into contact with a surface is disclosed.

JP 2002-82549 A JP 2001-147606 A

  In the conventional image forming apparatus described above, it is difficult to efficiently suppress the temperature rise at both ends in the width direction of the fixing belt, which occurs when a recording medium having a short width direction size is continuously fixed.

Details are as follows.
A general image forming apparatus is configured to form an image on several types of recording media having different sizes in the width direction. Here, the recording media having different sizes in the width direction include recording media of irregular sizes in addition to recording media of various regular sizes in the A and B rows of JIS dimensions. Even in the case of recording media of the same size (for example, A4 size), the transport direction is the short direction (the direction perpendicular to the longitudinal direction) when the longitudinal direction is the transport direction. In some cases, recording media having different sizes in the width direction are handled.

  When fixing such a recording medium having a different size in the width direction with the fixing device, the heat distribution in the width direction of the fixing belt fluctuates according to the width direction size of the recording medium, resulting in temperature unevenness. was there. For example, when fixing by passing a recording medium having a small size in the width direction, a lot of heat is taken away at the position of the fixing belt corresponding to the size in the width direction of the recording medium (the paper passing area). The fixing temperature is lower than at other positions (non-sheet passing area). Such a phenomenon becomes particularly prominent when a recording medium having a small size in the width direction is continuously fed.

  Therefore, when trying to control the fixing temperature in the entire width direction of the fixing belt with reference to the fixing temperature at the center portion in the width direction of the fixing belt, the fixing temperature at the center portion in the width direction of the fixing belt can be controlled to a desired temperature. The fixing temperature at both ends in the direction will increase. As described above, when a recording medium having a large width direction is fixed in a state where the fixing temperature at both ends in the width direction of the fixing belt is increased, a hot offset occurs on the recording medium corresponding to the temperature increase position. Furthermore, when the fixing temperature at both ends in the width direction exceeds the heat resistance temperature of the fixing belt, the fixing belt may be thermally damaged and the life may be shortened.

  When the heat pipe disclosed in the above-mentioned Patent Document 2 is brought into contact with the inner peripheral surface of the fixing belt, there is a possibility that the temperature rise at both ends in the width direction of the fixing belt cannot be sufficiently suppressed. . This is because a sufficient contact area between the fixing belt running in a predetermined direction and the heat pipe cannot be secured. That is, since the heat pipe has a cylindrical shape, the contact between the fixing belt and the heat pipe is close to a line contact. Therefore, heat transfer from the fixing belt to the heat pipe becomes insufficient.

  In order to solve such a problem, it is conceivable to wrap the fixing belt around the cylindrical heat pipe at a predetermined angle. However, even in such a case, the contact surface between the fixing belt and the heat pipe is only the arc corresponding to the winding angle, and sufficient heat cannot be transferred from the fixing belt to the heat pipe. High nature. Further, in such a case, since it is necessary to secure a space for winding the fixing belt around the heat pipe, the fixing device is increased in size.

  The present invention has been made to solve the above-described problems, and a fixing device and an image forming apparatus that can reliably suppress a temperature rise at both ends in the width direction of the fixing belt with a relatively simple configuration. Is to provide.

According to a first aspect of the present invention, a fixing device includes a heating roller, a fixing roller, a fixing belt wound around the heating roller and the fixing roller, and press-contacting the fixing roller via the fixing belt. and a pressure roller which, in the fixing device for fixing the toner image to a recording medium by heating the toner image at the fixing nip portion to which the pressure roller presses against the fixing nip portion in the traveling direction of the fixing belt And a plate heat pipe that is in contact with the inner peripheral surface of the fixing belt with a flat surface on the upstream side of the heating roller , and the plate heat pipe is orthogonal to the conveyance direction of the recording medium At both ends in the width direction of the fixing belt, it corresponds to a sheet passing area of a recording medium having a size larger than the predetermined size outside the area of the recording medium having a predetermined size. These plates and heat pipes are provided so as to be able to come into contact with and separate from the fixing belt, and when passing the large-sized recording medium, the plates and heat pipes are separated from the fixing belt. It is characterized by being evacuated .

According to a second aspect of the present invention, there is provided a fixing device according to the first aspect, wherein the plate heat pipe is in contact with the fixing belt through a heat radiating member .

According to a third aspect of the present invention, in the fixing device according to the second aspect , the heat dissipating member is a heat dissipating grease .

A fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the plate heat pipe is chamfered on a contact surface with the fixing belt. It is provided with .

According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the fixing belt is pressed against the plate / heat pipe from the outer peripheral surface side. A pressing member is provided .

A fixing device according to a sixth aspect of the invention is the fixing device according to any one of the first to fifth aspects, wherein the heating roller is heated by electromagnetic induction .

According to a seventh aspect of the present invention, an image forming apparatus includes the fixing device according to any one of the first to sixth aspects .

In the present application, the “width direction” is defined as a direction orthogonal to the transport direction in the recording medium.
In the present application, the “fixing belt” is defined as a flexible fixing member that contributes to fixing of a toner image and is stretched and supported by a plurality of roller members. Accordingly, the fixing belt includes a film-like fixing film.

  In the present invention, since the plate heat pipe is brought into contact with the fixing belt, a sufficient contact area between the fixing belt and the plate heat pipe is ensured. Accordingly, it is possible to provide a fixing device and an image forming apparatus in which a temperature increase at both ends in the width direction of the fixing belt is reliably suppressed with a relatively simple configuration.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably. The first and second embodiments will be described as reference examples.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is detachably installed on the apparatus main body 1. A process cartridge as an image forming unit; 7, a transfer unit for transferring a toner image formed on the photosensitive drum 18 to a recording medium P; 10, a paper discharge tray on which an output image is placed; A paper feeding unit in which a recording medium P such as paper is stored, 13 is a registration roller that conveys the recording medium P to the transfer unit 7, and 15 is a recording medium P having a different size from the recording medium P of the paper feeding units 11 and 12. Reference numeral 20 denotes a manual paper feed unit used for transporting the unfixed image on the recording medium P.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 toward the photosensitive drum 18 of the process cartridge 4. The photosensitive drum 18 rotates counterclockwise in the drawing, and a toner image corresponding to image information is formed on the photosensitive drum 18 through a predetermined electrophotographic process (charging process, exposure process, development process). Is done.
Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the recording medium P conveyed by the registration roller 13 in the transfer unit 7.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 11, 12, and 15 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 11 is selected). To do.) Each of the plurality of paper feeding units 11 and 12 stores a recording medium P having a different size and a recording medium P having the same size and different transport directions.

  Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 11 is transported toward the position of the transport path K. Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the recording medium P that has reached the position of the registration roller 13 is conveyed toward the transfer unit 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt and the pressure roller, and the toner image is fixed by the heat received from the fixing belt and the pressure received from the pressure roller. The recording medium P on which the toner image has been fixed is sent from between the fixing belt and the pressure roller, and then is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10.
Thus, a series of image forming processes is completed.

Next, the configuration / operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG.
As shown in FIG. 2, the fixing device 20 mainly includes a fixing auxiliary roller 21, a fixing belt 22, a heating roller 23, an induction heating unit 24, a pressure roller 30, a plate heat pipe 40, a thermostat 37, and an oil application roller 34. , A guide plate 35, a separation plate 36, and the like.

  Here, the fixing auxiliary roller 21 has an elastic layer such as silicone rubber formed on the surface thereof, and is driven to rotate counterclockwise in FIG. 2 by a driving unit (not shown).

  The heating roller 23 is mainly composed of a cylindrical portion made of stainless steel or the like, flanges press-fitted to both ends of the cylindrical portion, and the like. The heating roller 23 rotates counterclockwise in FIG. An inner core 28 made of a ferromagnetic material such as ferrite is installed inside the heating roller 23. The inner core 28 faces the coil portion 25 with the fixing belt 22 interposed therebetween.

  The fixing belt 22 is stretched and supported by the heating roller 23 and the auxiliary fixing roller 21. The fixing belt 22 is an endless belt having a multilayer structure including a base layer made of polyimide resin or the like, a heat generating layer made of silver, nickel, iron, or the like, a release layer (surface layer) made of a fluorine compound, or the like. The releasability for the toner T is secured by the release layer of the fixing belt 22.

The induction heating unit 24 includes a coil unit 25, a core 26, a coil guide 27, and the like.
Here, the coil portion 25 is wound around a litz wire bundled with thin wires so as to cover the outer peripheral portion of the fixing belt 22 wound around the heating roller 23 (in the direction perpendicular to the paper surface of FIG. 2). It is extended. The coil guide 27 is made of a resin material having high heat resistance and holds the coil portion 25. The core 26 is made of a ferromagnetic material such as ferrite, and is provided with a center core 26a and a side core 26b. The core 26 is installed so as to face the coil portion 25 extending in the width direction.

  The pressure roller 30 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on the core metal, and is in pressure contact with the auxiliary fixing roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion between the fixing belt 22 and the pressure roller 30.
A separation plate 36 that guides the conveyance of the recording medium P and promotes the separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30. Yes.

  The plate / heat pipe 40 is in contact with the inner peripheral surface of the fixing belt 22 over almost the entire region in the width direction (the direction perpendicular to the paper surface of FIG. 2). The plate heat pipe 40 is installed on the downstream side of the fixing position, which will be described later, and on the upstream side of the heating position. The plate heat pipe 40 equalizes the temperature distribution in the width direction of the fixing belt 22 after passing through the fixing position. The plate / heat pipe 40 will be described in detail later.

  An oil application roller 34 is in contact with the outer peripheral surface of the fixing belt 22. The oil application roller 34 supplies oil such as silicone oil onto the fixing belt 22. Thereby, the toner releasability on the fixing belt 22 is further ensured. The oil application roller 34 is in contact with a cleaning roller 33 that equalizes the amount of oil applied and removes dirt on the surface.

A thermostat 37 is in contact with the outer peripheral surface of the heating roller 23. Then, when the surface temperature on the heating roller 23 exceeds a predetermined temperature, the thermostat 37 cuts off the power supply to the induction heating unit 24. Thereby, overheating of the heating roller 23 by the induction heating unit 24 is limited.
Although not shown, a thermistor is in contact with the outer peripheral surface of the fixing belt 22. Then, the surface temperature (fixing temperature) on the fixing belt 22 is detected by the thermistor, and the heating amount by the induction heating unit 24 is adjusted.

The fixing device 20 configured as described above operates as follows.
By the rotation driving of the auxiliary fixing roller 21, the fixing belt 22 rotates in the direction of the arrow in FIG. 2, the heating roller 23 also rotates counterclockwise, and the pressure roller 30 also rotates in the direction of the arrow. The fixing belt 22 is heated at a position facing the induction heating unit 24 (a heating position).

Specifically, the magnetic field lines are alternately switched between the core 26 and the inner core 28 by flowing a high-frequency alternating current through the coil portion 25. Thereby, an eddy current is generated on the surface of the heating roller 23, Joule heat is generated by the electric resistance of the heating roller 23 itself, and the heating roller 23 is heated.
Further, the fixing belt 22 wound around the heating roller 23 is heated by the heating roller 23 heated by electromagnetic induction.

Thereafter, the surface of the fixing belt 22 that generates heat by the induction heating unit 24 reaches a contact portion (a fixing position) with the pressure roller 30. Then, the toner image T on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35 (indicated by the arrow Y). It is movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

The surface of the fixing belt 22 that has passed through the fixing position then passes through the position of the oil application roller 34 and reaches the contact position with the plate / heat pipe 40. The surface of the fixing belt 22 whose surface temperature is made uniform by the plate heat pipe 40 then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

With reference to FIG. 3, the structure and operation of the plate heat pipe 40, which is characteristic in the first embodiment, will be described in more detail.
FIG. 3 is a partially enlarged view showing the vicinity of the plate heat pipe 40 (planar heat pipe) that contacts the inner peripheral surface 22 a of the fixing belt 22. With reference to FIG. 3, the plate heat pipe 40 is a substantially prismatic heat pipe. In the first embodiment, a plate / heat pipe 40 having a length in the width direction substantially equal to the length in the width direction of the fixing belt 22, a length h in the running direction of 9 mm, and a thickness of 1 mm is used. .

  The plate heat pipe 40 is formed by laminating a flat plate and an aluminum plate provided with a working fluid flow path to form a capillary structure therein. With such a structure, on the contact surface of the plate heat pipe 40 that contacts the fixing belt 22, the vapor of the hydraulic fluid evaporated in the high temperature portion moves to the low temperature portion, and the hydraulic fluid condensed in the low temperature portion becomes a capillary phenomenon. To move to the hot part. Such a series of phase changes occur continuously, and the temperature distribution in the width direction of the fixing belt 22 is quickly made uniform. Since the plate heat pipe 40 is in contact with the inner peripheral surface 22 a of the fixing belt 22, there is a side effect on the fixing process performed on the outer peripheral surface of the fixing belt 22 compared with the case of contacting the outer peripheral surface. Does not occur.

FIG. 4 is a graph showing the temperature distribution in the width direction on the fixing belt 22 in the first embodiment.
In FIG. 4, the horizontal axis indicates the position of the fixing belt 22 in the width direction, and the vertical axis indicates the temperature of the fixing belt 22 (fixing temperature). Here, “0” in the width direction position on the horizontal axis indicates the center position in the width direction of the fixing belt 22. A solid line R1 indicates the temperature distribution when the plate / heat pipe 40 is installed (the configuration of the fixing device 20 of the first embodiment), and a broken line R2 indicates when the plate / heat pipe 40 is not installed (conventional fixing). The temperature distribution of the apparatus 20 is shown.

  Note that the temperature measurement in FIG. 4 was performed after continuously passing a small-sized recording medium P having a width direction size L2. Thereafter, a large-sized recording medium P having a width direction size L1 was passed through, and the presence or absence of hot offset in the output image was evaluated.

  From FIG. 4, by installing the plate heat pipe 40, the fixing temperature distribution in the width direction on the fixing belt 22 is made uniform even after the small-sized recording medium P is continuously fed. I can confirm that. That is, the plate / heat pipe 40 performs heat circulation between the high temperature portion (non-sheet passing region) and the low temperature portion (sheet passing region), thereby achieving a uniform fixing temperature. It was also confirmed that the installation of the plate heat pipe 40 suppresses hot offset at both ends in the width direction and thermal damage to the fixing belt 22.

  Here, referring to FIG. 3, chamfered portion 40 a is formed on the contact surface of plate / heat pipe 40 in the first embodiment. As a result, the problem that the inner peripheral surface of the fixing belt 22 traveling in the direction of the arrow is scraped by the edge of the plate heat pipe 40 is suppressed.

  In order to reduce the friction on the contact surface between the plate / heat pipe 40 and the fixing belt 22, heat radiation grease as a heat radiation member can be applied to the contact surface. Accordingly, wear of the fixing belt 22 and the plate / heat pipe 40 is reduced while suppressing a temperature rise at both ends in the width direction of the fixing belt 22.

  As described above, according to the configuration of the first embodiment, since the fixing belt 22 and the plate / heat pipe 40 are in surface contact with each other, a sufficient contact area is secured, and the high temperature portion of the fixing belt 22 is secured. Sufficient heat is transferred to the plate / heat pipe 40. As a result, a temperature rise at both ends in the width direction of the fixing belt 22 is surely suppressed, and temperature unevenness in the width direction is also reduced.

Embodiment 2. FIG.
The second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is a partially enlarged view showing the vicinity of the plate heat pipe 40 in the fixing device 20 according to the second embodiment, and corresponds to FIG. 3 in the first embodiment. The fixing device 20 of the second embodiment is different from that of the first embodiment in that a pressing member 43 and an urging member 44 are provided in the vicinity of the plate / heat pipe 40.

  As shown in FIG. 5, the plate / heat pipe 40 is in contact with the inner peripheral surface 22 a of the fixing belt 22 as in the first embodiment. Further, two pairs of pressing members 43 are in contact with the outer peripheral surface of the fixing belt 22. The two pairs of pressing members 43 abut on the outer peripheral surface of the fixing belt 22 in a region exceeding the maximum sheet passing region (the region in which the width direction size of the recording medium P is maximum). As a result, side effects (for example, damage to the fixing surface) to the fixing process performed on the outer peripheral surface of the fixing belt 22 do not occur.

  Of the two pairs of pressing members 43, one pair of pressing members 43 is installed on the upstream side of the plate / heat pipe 40, and the other pair of pressing members 43 is installed on the downstream side of the plate / heat pipe 40. Yes. Each of the two pairs of pressing members 43 is provided with an urging member 44 and is given an urging force in a direction in which the fixing belt 22 is pressed.

  With such a configuration, the adhesion of the fixing belt 22 to the plate heat pipe 40 is improved. Therefore, even when the fixing belt 22 travels in the direction of the arrow, there is no gap between the plate and the heat pipe 40, and the surface contact between both members is maintained well.

  As described above, also in the second embodiment, as in the first embodiment, since the fixing belt 22 and the plate / heat pipe 40 are in surface contact with each other, a sufficient contact area is ensured. Thus, sufficient heat is transferred from the high temperature portion of the fixing belt 22 to the plate / heat pipe 40. As a result, a temperature rise at both ends in the width direction of the fixing belt 22 is surely suppressed, and temperature unevenness in the width direction is also reduced.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 6 is a partially enlarged view showing the vicinity of the plate and heat pipe in the fixing device 20 according to the third embodiment, and corresponds to FIG. 3 in the first embodiment. FIG. 7 is a view of the plate / heat pipe of FIG. 6 as viewed from the inner peripheral surface 22a side.
In the fixing device 20 according to the third embodiment, two plates and heat pipes 40A and 40B are provided at both ends in the width direction, and the plates and heat pipes 40A and 40B can be brought into and out of contact with the fixing belt 22. The structure is different from that of the first embodiment.

  As shown in FIG. 6, the plate / heat pipes 40 </ b> A and 40 </ b> B are brought into contact with the inner peripheral surface 22 a of the fixing belt 22 as in the first embodiment. In the third embodiment, as shown in FIG. 7, two plates and heat pipes 40A and 40B are respectively installed at both ends in the width direction of the inner peripheral surface 22a.

  Specifically, as shown in FIG. 7, the two plates and heat pipes 40A and 40B include a small size recording medium P having a width direction size L2 and a large size recording medium P having a width direction size L1. , So as to correspond to the above. That is, the two plate / heat pipes 40A and 40B are configured to come into contact with the fixing bell 22 outside the small size area.

  Here, the two plates / heat pipes 40A and 40B are brought into and out of contact with the fixing belt 22 at a predetermined timing by a contact / separation mechanism (not shown) (both between the solid line portion and the broken line portion in FIG. 6). Move in the direction of the arrow.) Specifically, when the small-sized recording medium P is continuously passed, the two plates and heat pipes 40A and 40B are brought into contact with the fixing belt 22 (the position of the solid line portion). On the other hand, when the large-sized recording medium P is passed, the two plates / heat pipes 40A and 40B are retracted from the fixing belt 22 (the position of the broken line).

  With such a configuration and control, when the small-sized recording medium P is continuously fed, the heat of the contact surface that has become high temperature is moved to the opposite surface side by the two plates / heat pipes 40A and 40B. To do. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 is suppressed. On the other hand, when a large-sized recording medium P is passed, since the temperature rise at both ends does not occur, the functions of the plate heat pipes 40A and 40B are retracted to limit their functions.

  In the first embodiment, the case where the size of the recording medium P is two (L1 and L2) has been described in order to facilitate understanding. On the other hand, when the size of the recording medium P is three or more, the number of plate / heat pipe pairs corresponding to the number of the sizes is installed. The plurality of pairs of plates and heat pipes are controlled to contact and separate according to the width direction size of the recording medium P.

  As described above, also in the third embodiment, since the fixing belt 22 and the plate / heat pipes 40A and 40B are in surface contact with each other, a sufficient contact area is secured, and the high temperature of the fixing belt 22 is ensured. A sufficient amount of heat is transferred from the section to the plate / heat pipe 40. As a result, a temperature rise at both ends in the width direction of the fixing belt 22 is surely suppressed, and temperature unevenness in the width direction is also reduced.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a partially enlarged view showing the vicinity of a plate / heat pipe installed in the fixing device of FIG. 2. 3 is a graph showing a temperature distribution in a width direction on a fixing belt in the fixing device of FIG. 2. It is the elements on larger scale which show the vicinity of the plate heat pipe in Embodiment 2 of this invention. It is the elements on larger scale which show the vicinity of the plate heat pipe in Embodiment 3 of this invention. FIG. 7 is a view of the plate heat pipe of FIG. 6 as viewed from the inner peripheral surface side of the fixing belt.

Explanation of symbols

1 image forming apparatus main body (apparatus main body), 3 exposure unit, 4 image forming unit,
7 Transfer section, 10 Paper discharge tray, 11, 12 Paper feed section,
20 fixing device, 21 fixing auxiliary roller, 22 fixing belt,
22a inner peripheral surface, 23 heating roller, 24 induction heating part, 25 coil part,
26 core, 26a center core, 26b side core,
28 inner core, 30 pressure roller, 33 cleaning roller,
34 oil application roller, 35 guide plate,
36 separators, 37 thermostats,
40, 40A, 40B plate heat pipe, 40a chamfered part,
43 pressing member, 44 urging member.

Claims (7)

A heating roller, a fixing roller, a fixing belt wound around the heating roller and the fixing roller, and a pressure roller pressed against the fixing roller via the fixing belt, the pressure roller being in pressure contact in the fixing nip portion by heating the toner image in a fixing device for fixing the toner image to a recording medium,
A plate heat pipe that is in contact with the inner peripheral surface of the fixing belt with a flat surface downstream of the fixing nip portion in the traveling direction of the fixing belt and upstream of the heating roller ;
The plate heat pipe passes through a recording medium having a size larger than the predetermined size outside the area of the recording medium having a predetermined size at both ends in the width direction of the fixing belt perpendicular to the conveyance direction of the recording medium. These plates and heat pipes are respectively installed at positions corresponding to the paper areas, and are provided so as to be able to contact with and separate from the fixing belt, and when passing the large-sized recording medium, the plates and heat pipes are A fixing device retracted from the fixing belt . The fixing device according to claim 1, wherein the plate heat pipe is in contact with the fixing belt via a heat radiating member . The fixing device according to claim 2, wherein the heat radiating member is a heat radiating grease . The plate heat pipe fixing device according to any one of claims 1 to 3, further comprising a chamfered portion at the surface in contact with the fixing belt. The fixing device according to any one of claims 1 to 4, characterized in that a pressing member that presses the fixing belt from an outer peripheral surface side with respect to the plate heat pipe. The fixing device according to claim 1 , wherein the heating roller is heated by electromagnetic induction . An image forming apparatus comprising the fixing device according to claim 1 .

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