JP2021121835A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that can prevent an excessive increase in temperature to perform temperature control for both ends in the direction of the axis of rotation of a fixing belt.SOLUTION: A fixing device 40 comprises: an endless fixing belt 41; a pressure roller 42; a nip forming member 43; a first heating unit; and a belt guide 46. The first heating unit is arranged opposite to an outer peripheral surface of the fixing belt 41 and heats the fixing belt 41 by electromagnetic induction. The belt guide 46 is in contact with an inner peripheral surface of the fixing belt 41 other than a fixing nip part N to support the fixing belt 41 from the inside. The belt guide 46 has a first area that is arranged in a center part in the direction of the axis of rotation of the fixing belt 41 and formed of a magnetic material and second areas 462 that are arranged on both end sides in the direction of the axis of rotation of the first area and formed of a non-magnetic material, and includes a second heating unit 47 that heats the second areas 462.SELECTED DRAWING: Figure 4

Description

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

In electrophotographic image forming devices such as copiers and printers, the heat fixing method is widely adopted as a method for fixing an unfixed toner image transferred to a recording medium such as paper on paper. The recording medium passes through the fixing nip portion where the fixing member and the pressing member come into contact with each other, so that the recording medium is pressurized and heated to fix the unfixed toner image. Further, as a heat fixing method, an induction heating method in which a fixing member is heated by electromagnetic induction is known. An example of such a fixing device is disclosed in Patent Document 1.

The conventional fixing device disclosed in Patent Document 1 includes a heat generating member (fixing roller) which is a rotating body, a magnetic field generating unit which heats a conductive layer of the heat generating member by electromagnetic induction, and an end portion of the heat generating member in the direction of the rotation axis. It is provided with a magnetic flux shielding member arranged to face each other. Due to the presence of the magnetic flux shielding member, the magnetic flux is concentrated near the end of the heat generating member (fixing roller) in the direction of the rotation axis, and the amount of heat generated is increased. The vicinity of the end of the heat generating member in the direction of the rotation axis is close to the folded portion of the induction coil, and there is a risk that the magnetic flux will decrease and the amount of heat generated will decrease, but this can be avoided by the configuration of the conventional fixing device. Is.

Japanese Unexamined Patent Publication No. 2006-243172

In the fixing nip portion of the fixing device, when the recording medium passes through, the heat of the fixing member is taken away by the recording medium such as paper. The fixing device includes a device that heats the entire width direction of the fixing member in a width direction orthogonal to the transport direction of the recording medium and allows the recording medium to pass along the center of the width direction of the fixing nip portion. In this case, when a recording medium having a size smaller than the entire width direction of the fixing member is passed through the fixing nip portion, heat is not taken by the recording medium at both ends in the width direction of the fixing member, and the heat rises excessively. It sometimes warmed up.

The present invention has been made in view of the above points, and an object of the present invention is to provide a fixing device and an image forming device capable of suppressing an excessive temperature rise at both ends in the rotation axis direction of the fixing belt and adjusting the temperature. And.

In order to solve the above problems, the fixing device of the present invention includes an endless fixing belt, a pressure member, a nip forming member, a first heating unit, and a belt guide. The endless fixing belt can rotate along the transport direction of the recording medium. The pressurizing member contacts the outer peripheral surface of the fixing belt to give a rotational driving force to the fixing belt. The nip forming member is arranged inside the fixing belt so as to face the pressure member across the fixing belt, and contacts the inner peripheral surface of the fixing belt to form the fixing nip portion. The first heating portion is arranged so as to face the outer peripheral surface of the fixing belt, and heats the fixing belt by electromagnetic induction. The belt guide contacts the inner peripheral surface of the fixing belt other than the fixing nip portion and supports the fixing belt from the inside. The belt guide is a first region composed of a magnetic material arranged in the center of the fixing belt in the rotation axis direction, and a non-magnetic material arranged on both ends of the first region in the rotation axis direction. It has a configured second region and a second heating unit that heats the second region.

According to the configuration of the present invention, the first region of the belt guide is heated by the electromagnetic induction of the first heating portion, but the second region of the belt guide is not heated by the electromagnetic induction of the first heating portion. Therefore, it is possible to suppress excessive temperature rise at both ends of the fixing belt in the direction of the rotation axis. Further, by providing the second heating portion, the second region of the belt guide can be heated as needed. As a result, the temperature of both ends of the fixing belt in the direction of the rotation axis can be adjusted.

It is a schematic cross-sectional front view which shows the structure of the image forming apparatus of embodiment of this invention. It is sectional drawing front view of the fixing device of embodiment of this invention. It is a side view of the cut portion end face of the fixing device of embodiment of this invention. It is a partial cross-sectional front view of the fixing device of 1st Embodiment of this invention, and is the figure which shows the part of the 2nd region of a belt guide. It is a graph which shows the temperature distribution of the fixing belt of the fixing device of the Example of this invention. It is a graph which shows the temperature distribution of the fixing belt of the fixing device of the comparative example with respect to the Example of this invention. It is a graph which shows the temperature distribution of the fixing belt of the fixing device of the Example of this invention, and is the graph which shows the state which operated the 2nd heating part. It is a cross-sectional front view of the fixing device of the 2nd Embodiment of this invention, and is the figure which shows the part of the 2nd region of a belt guide.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following contents.

FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 1 of the embodiment. An example of the image forming apparatus 1 of the present embodiment is a tandem color printer that transfers a toner image onto paper P using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction device having functions such as printing (printing), scanning (image reading), and facsimile transmission.

As shown in FIG. 1, the image forming apparatus 1 includes a paper feeding unit 3, a paper conveying unit 4, an exposure unit 5, an image forming unit 20, a transfer unit 30, a fixing device 40, and a paper discharging unit provided in the main body 2. 7 and control unit 8 are included.

The paper feeding unit 3 accommodates a plurality of sheets of paper P (recording medium), and separates and sends out the paper P one by one at the time of printing. The paper transport unit 4 conveys the paper P fed from the paper feed unit 3 to the secondary transfer unit 33 and the fixing device 40, and further discharges the fixed paper P from the paper ejection port 4a to the paper ejection unit 7. .. When double-sided printing is performed, the paper transport unit 4 distributes the paper P after fixing on the first side to the reverse transport unit 4c by the branch portion 4b, and the paper P is again transferred to the secondary transfer unit 33 and the fixing device 40. Transport. The exposure unit 5 irradiates the image forming unit 20 with a laser beam controlled based on the image data.

The image forming unit 20 is arranged below the intermediate transfer belt 31. The image forming unit 20 includes an image forming unit 20Y for yellow, an image forming unit 20C for cyan, an image forming unit 20M for magenta, and an image forming unit 20B for black. These four image forming units 20 have the same basic configuration. Accordingly, in the following description, the identification codes of "Y", "C", "M", and "B" representing each color may be omitted unless it is particularly necessary to limit them.

The image forming unit 20 includes a photoconductor drum 21 which is an image carrier rotatably supported in a predetermined direction (clockwise in FIG. 1). The image forming unit 20 further includes a charging unit, a developing unit, and a drum cleaning unit around the photoconductor drum 21 along the rotation direction thereof. The primary transfer unit 32 is arranged between the developing unit and the drum cleaning unit.

The charging unit charges the outer peripheral surface of the photoconductor drum 21 to a predetermined potential. Then, an electrostatic latent image of the original image is formed on the outer peripheral surface of the photoconductor drum 21 by the laser light emitted from the exposure unit 5. The developing unit attaches toner to the electrostatic latent image and develops it to form a toner image. Each of the four image forming units 20 forms toner images of different colors.

The transfer unit 30 includes an intermediate transfer belt 31, a primary transfer unit 32Y, 32C, 32M, 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is arranged above the four image forming portions 20. The intermediate transfer belt 31 is an intermediate transfer body that is rotatably supported in a predetermined direction (counterclockwise in FIG. 1) and in which toner images formed by each of the four image forming portions 20 are sequentially superimposed and primary transferred. .. The four image forming portions 20 are arranged in a so-called tandem system in which the intermediate transfer belt 31 is arranged in a row from the upstream side to the downstream side in the rotation direction.

The primary transfer portions 32Y, 32C, 32M, 32B are arranged above the image forming portions 20Y, 20C, 20M, 20B of each color with the intermediate transfer belt 31 interposed therebetween. The secondary transfer unit 33 is on the upstream side of the paper transfer unit 4 in the paper transfer direction with respect to the fixing device 40, and is an intermediate transfer belt 31 of the transfer unit 30 with respect to the image forming units 20Y, 20C, 20M, and 20B of each color. It is arranged on the downstream side in the rotation direction of. The belt cleaning unit 34 is arranged on the upstream side in the rotation direction of the intermediate transfer belt 31 with respect to the image forming units 20Y, 20C, 20M, and 20B of each color.

The toner image is first transferred to the outer peripheral surface of the intermediate transfer belt 31 by the primary transfer portions 32Y, 32C, 32M, 32B of each color. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming portions 20 are continuously superimposed and transferred to the intermediate transfer belt 31 at a predetermined timing, so that the outer peripheral surface of the intermediate transfer belt 31 is yellow. A color toner image is formed by superimposing four color toner images of cyan, magenta, and black. The drum cleaning unit cleans by removing toner and the like remaining on the outer peripheral surface of the photoconductor drum 21 after the primary transfer.

The color toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the paper P synchronously sent by the paper transport unit 4 by the secondary transfer nip portion formed in the secondary transfer unit 33. The belt cleaning unit 34 cleans by removing toner and the like remaining on the outer peripheral surface of the intermediate transfer belt 31 after the secondary transfer.

The fixing device 40 pressurizes and heats the paper P on which the toner image is transferred to fix the toner image on the paper P.

The control unit 8 includes a CPU (not shown), an image processing unit, a storage unit, other electronic circuits, and electronic components (not shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on the control program or data stored in the storage unit, and performs processing related to the function of the image forming apparatus 1. Each of the paper feed unit 3, the paper transport unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing device 40 receives commands individually from the control unit 8 and prints on the paper P in conjunction with each other. The storage unit is composed of a combination of a non-volatile storage device such as a program ROM (Read Only Memory) and a data ROM (not shown) and a volatile storage device such as a RAM (Random Access Memory).

Subsequently, the configuration of the fixing device 40 of the embodiment will be described with reference to FIGS. 2, 3 and 4. FIG. 2 is a cross-sectional front view of the fixing device 40 of the embodiment. FIG. 3 is a side view of the end face of the cut portion of the fixing device 40 of the embodiment. FIG. 4 is a partial cross-sectional front view of the fixing device 40 of the first embodiment, and is a view showing a portion of a second region 462 of the belt guide 46.

Note that, in FIGS. 2, 3 and 4, for convenience of explanation, a configuration in which the fixing belt 41 is arranged above the fixing nip portion N and the pressure roller 42 (pressurizing member) is arranged below is drawn. bottom. In FIG. 2, the left side is the upstream side in the paper transport direction with respect to the fixing device 40, and the right side is the downstream side in the paper transport direction with respect to the fixing device 40. 2 is a cross-sectional view taken along the line II-II of FIG. 3, FIG. 3 is an end view of the cut portion taken along the line III-III of FIG. 2, and FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. Is.

As shown in FIGS. 2 and 3, the fixing device 40 includes a fixing belt 41, a pressure roller 42 (pressure member), a nip forming member 43, a first heating portion 44, a frame member 45, a belt guide 46, and a first. The heating unit 47 of 2 is provided.

The fixing belt 41 is rotatably supported by the housing portion of the fixing device 40 around a horizontal axis. The fixing belt 41 has an endless shape, for example, has a cylindrical shape with an outer diameter of 20 mm to 50 mm, and has substantially the same length as the pressure roller 42 in the rotation axis direction (width direction orthogonal to the transport direction of the paper P). Have. The fixing belt 41 can rotate along the conveying direction of the paper P, which is a recording medium.

The fixing belt 41 has a laminated structure in which an elastic layer and a release layer are provided on the outer peripheral side of a heat generating layer which is a base material layer. The heat generating layer is composed of, for example, a metal film having a thickness of 30 μm to 50 μm such as nickel, or a polyimide film having a thickness of 50 μm to 100 μm mixed with a metal powder such as copper, silver, or aluminum. The elastic layer is made of, for example, silicon rubber having a thickness of 100 μm to 500 μm. The release layer is composed of a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) having a thickness of 30 μm to 50 μm, for example.

The pressure roller 42 is rotatably supported by the housing portion of the fixing device 40 around a horizontal axis. The pressure roller 42 has a cylindrical shape and has substantially the same length as the fixing belt 41 in the rotation axis direction (width direction of the paper P). A predetermined pressure is applied to the pressurizing roller 42 toward the fixing belt 41 by a pressurizing mechanism (not shown). The outer peripheral surface of the pressure roller 42 presses the nip forming member 43 via the fixing belt 41 and comes into contact with the outer peripheral surface of the fixing belt 41 to form the fixing nip portion N.

The pressurizing roller 42 is connected to a drive source (not shown) including a motor, receives power from the motor, and rotates clockwise in FIG. The pressure roller 42 comes into contact with the outer peripheral surface of the fixing belt 41 and applies a rotational driving force to the fixing belt 41.

The pressure roller 42 has a laminated structure in which an elastic layer and a release layer are provided on the outer peripheral side of the core metal. The core metal is made of a metal such as aluminum having a diameter of about 20 mm, for example. The elastic layer is made of, for example, silicon rubber having a thickness of about 8 mm. The release layer is made of a fluorine-based resin such as PFA having a thickness of, for example, about 10 μm to 50 μm.

The nip forming member 43 is arranged inside the fixing belt 41 so as to face the pressure roller 42 across the fixing belt 41. The nip forming member 43 comes into contact with the inner peripheral surface of the fixing belt 41, and forms a fixing nip portion N between the fixing belt 41 and the pressure roller 42.

The nip forming member 43 has a substantially rectangular parallelepiped shape extending along the rotation axis direction (paper width direction) of the fixing belt 41 with substantially the same length as the fixing belt 41. The nip forming member 43 has a base material made of a metal such as aluminum or a heat-resistant resin such as a liquid crystal polymer. The nip forming member 43 may have an elastic layer made of, for example, an elastomer, silicon rubber, or the like on the side of the base material facing the fixing belt 41. Further, the nip forming member 43 has a sheet material (release layer) made of a fluorine-based resin such as PFA in a region facing the fixing belt 41. The sheet material comes into contact with the inner peripheral surface of the fixing belt 41 at the fixing nip portion N, and extends to a region on the upstream side and the downstream side of the fixing nip portion N in the rotational direction of the fixing belt 41, which does not contact the fixing belt 41.

The first heating unit 44 is arranged to face the outer peripheral surface of the fixing belt 41 with a predetermined gap in the region opposite to the side where the pressure roller 42 is arranged with respect to the fixing belt 41. The first heating unit 44 extends longer than the fixing belt 41 and the belt guide 46 along the rotation axis direction (paper width direction) of the fixing belt 41.

The first heating unit 44 includes an exciting coil 441, a holding member (not shown), a core, and the like. The exciting coil 441 and the core are held in place by the holding member. The exciting coil 441 is composed of a litz wire in which a plurality of conducting wires are bundled, and is wound so as to extend along the rotation axis direction (paper width direction) of the fixing belt 41. The exciting coil 441 is formed in an arc shape along the outer peripheral surface of the fixing belt 41 in the circumferential direction of the fixing belt 41.

The first heating unit 44 heats the fixing belt 41 by electromagnetic induction. More specifically, the first heating unit 44 heats the fixing belt 41 by generating heat in the heat generating layer of the fixing belt 41 by induction heating.

The frame member 45 is a substantially central portion in the radial direction of the fixing belt 41, and is arranged between the nip forming member 43 and the contact portions 4611 and 4621 of the belt guide 46 described later. The frame member 45 extends longer than the fixing belt 41 along the rotation axis direction (paper width direction) of the fixing belt 41.

The frame member 45 holds the nip forming member 43 and the belt guide 46. The nip forming member 43 is fixed to the nip facing wall portion 451 facing the fixing nip portion N of the frame member 45. The belt guide 46 is connected to the side wall portions 452 of the frame member 45 on the upstream side and the downstream side of the fixing nip portion N of the fixing belt 41 in the rotational direction.

The belt guide 46 is arranged inside the fixing belt 41 so as to face the first heating portion 44 across the fixing belt 41. The belt guide 46 comes into contact with the inner peripheral surface of the fixing belt 41 other than the fixing nip portion N, and supports the fixing belt 41 from the inside. The belt guide 46 is composed of a sheet metal extending along the rotation axis direction (paper width direction) of the fixing belt 41 with substantially the same length as the fixing belt 41.

As shown in FIG. 3, the belt guide 46 has a first region 461 and a second region 462 arranged along the rotation axis direction (paper width direction) of the fixing belt 41. Each of the first region 461 and the second region 462 includes contact portions 4611, 4621 and connection portions 4612, 4622, respectively, as shown in FIGS. 2 and 4.

The contact portions 4611 and 4621 are arranged on the opposite side of the fixing nip portion N with the radial center portion of the fixing belt 41 separated from each other. The contact portions 4611 and 4621 are curved in an arc shape along the inner peripheral surface of the fixing belt 41. The contact portions 4611 and 4621 come into contact with the inner peripheral surface of the fixing belt 41 over almost the entire area. The contact portions 4611 and 4621 face the exciting coil 441 with the fixing belt 41 in between.

The connecting portions 4612 and 4622 are arranged on the downstream side of the contact portions 4611 and 4621 in the rotational direction of the fixing belt 41. The connecting portions 4612 and 4622 are connected to one end in the circumferential direction of the contact portions 4611 and 4621. The connecting portions 4612 and 4622 bend and extend inward in the radial direction of the fixing belt 41 from one end in the circumferential direction of the contact portions 4611 and 4621, and further bend toward the fixing nip portion N adjacent to the frame member 45. .. The connecting portions 4612 and 4622 do not come into contact with the fixing belt 41. The connecting portions 4612 and 4622 are connected to the side wall portion 452 of the frame member 45.

As shown in FIG. 3, the first region 461 of the belt guide 46 is arranged at the center of the fixing belt 41 in the rotation axis direction (paper width direction). The first region 461 is made of an elastic magnetic material such as SUS430 having a thickness of 0.1 mm to 0.5 mm.

As shown in FIG. 3, the second region 462 of the belt guide 46 is arranged on each end side of the first region 461 in the rotation axis direction (paper width direction) of the fixing belt 41. The second region 462 is made of a non-magnetic material such as aluminum.

As shown in FIG. 4, the second heating unit 47 includes a power supply unit 471 and is electrically connected to the second region 462 of the belt guide 46. The current sent from the power supply unit 471 flows along the circumferential direction through the contact portion 4621 of the second region 462. The second heating unit 47 heats the second region 462 by passing an electric current, and heats the second region 462.

According to the above configuration, the first region 461 of the belt guide 46 is heated by the electromagnetic induction of the first heating unit 44, while the second region 462 of the belt guide 46 is electromagnetically induced by the first heating unit 44. Not heated by induction. Therefore, it is possible to suppress excessive temperature rise at both ends of the fixing belt 41 in the direction of the rotation axis. Further, by providing the second heating unit 47, the second region 462 of the belt guide 46 can be heated as needed. As a result, the temperature of both ends of the fixing belt 41 in the direction of the rotation axis can be adjusted.

As shown in FIG. 3, the fixing nip portion N is a paper P having a size in the paper width direction of the first size Wp1 and a second size Wp2 having a size in the paper width direction larger than the first size Wp1. A certain sheet P and can be passed through. The size Wb1 of the first region 461 of the belt guide 46 in the paper width direction is larger than the first size Wp1 of the paper P that can pass the fixing nip portion N and smaller than the second size Wp2.

According to this configuration, for example, in the image forming apparatus 1 of the present embodiment, when the size of the paper P used as standard in the width direction is the first size Wp1, the electromagnetic induction of the first heating unit 44 Allows only the first region 461 of the belt guide 46 to be heated. Therefore, it is possible to prevent the second region 462 of the belt guide 46 through which the paper P does not pass from being heated for a longer period of time when the paper P of the first size Wp1 is used.

Next, a comparison between the fixing device 40 of the embodiment of the present invention and the fixing device of the comparative example having the conventional configuration different from the embodiment will be described below. FIG. 5 is a graph showing the temperature distribution of the fixing belt 41 of the fixing device 40 of the embodiment. FIG. 6 is a graph showing the temperature distribution of the fixing belt of the fixing device of the comparative example with respect to the example. FIG. 7 is a graph showing the temperature distribution of the fixing belt 41 of the fixing device 40 of the embodiment, and is a graph showing a state in which the second heating unit 47 is operated. The horizontal axes of FIGS. 5, 6 and 7 represent the positions of the fixing belt in the rotation axis direction (paper width direction). The vertical axis of FIGS. 5, 6 and 7 represents the surface temperature of the fixing belt.

In the fixing device of the comparative example in which the temperature distribution of the fixing belt is shown in FIG. 6, the fixing device is heated over the entire area in the width direction of the fixing belt, and the paper is passed along the center of the fixing nip portion in the width direction. According to FIG. 6, in the case of the fixing device of the comparative example, when a paper having a size Wp0 smaller than the entire area in the paper width direction of the fixing belt is passed through the fixing nip portion, heat is generated at both ends Be in the width direction of the fixing belt. It can be seen that the surface temperature of the fixing belt has risen excessively without being robbed by the paper.

On the other hand, in the fixing device 40 of the embodiment in which the temperature distribution of the fixing belt 41 is shown in FIG. 5, the first region 461 of the belt guide 46 is heated by the electromagnetic induction of the first heating unit 44. , The second region 462 is not heated. As a result, the surface temperature of the region of the fixing belt 41 adjacent to the second region 462 is lower than that of the region adjacent to the first region 461. That is, it can be seen that excessive temperature rise at both ends of the fixing belt 41 in the rotation axis direction (paper width direction) can be suppressed.

Further, in the fixing device 40 of the embodiment in which the temperature distribution of the fixing belt 41 is shown in FIG. 7, the second region 462 of the belt guide 46 is heated by the second heating unit 47. As a result, the passing region of the paper P, which is the region adjacent to the second region 462 of the fixing belt 41 and is the second size Wp2 larger than the first size Wp1, is outside the paper width direction. The surface temperature is higher than the region. That is, when the paper P having the second size Wp2 is passed through the fixing nip portion N, the paper P can be heated appropriately. In this way, the fixing device 40 of the embodiment can adjust the temperature of both ends of the fixing belt 41 in the rotation axis direction (paper width direction).

As shown in FIG. 3, the belt guide 46 has a gap G between the first region 461 and the second region 462. That is, since the first region 461 of the belt guide 46 and the second region 462 are separated from each other, it is possible to prevent the heat of the first region 461 from being transferred to the second region 462. Therefore, it is possible to improve the action of maintaining only the first region 461 at a high temperature without raising the temperature of the second region 462.

Next, the fixing device 40 of the second embodiment will be described. FIG. 8 is a cross-sectional front view of the fixing device 40 of the second embodiment, and is a view showing a portion of a second region 463 of the belt guide 46. Since the basic configuration of the second embodiment is the same as that of the first embodiment (see FIGS. 1 to 3) described above, the common components are given the same reference numerals or the same names as before. In some cases, the description thereof may be omitted, and the description of the configuration other than the featured parts may be omitted.

The belt guide 46 of the fixing device 40 of the second embodiment has a second region 463 as shown in FIG. The second region 463 has a contact portion 4631, a connection portion 4632, and a recess 4633.

The recess 4633 is provided on the inner peripheral portion of the contact portion 4631 curved in an arc shape. The recess 4633 is recessed from the inner peripheral surface of the contact portion 4631 toward the outside in the radial direction. At least one recess 4633 is provided, and for example, five recesses 4633 are provided in the present embodiment. The five recesses 4633 are arranged at predetermined intervals in the circumferential direction.

In the second region 463, the second heating unit 47 including the power supply unit 471 is electrically connected. The current sent from the power supply unit 471 flows along the circumferential direction through the contact portion 4631 of the second region 463. The recess 4633 is formed so as to extend in a direction orthogonal to the direction in which the current flows, that is, in the direction of the rotation axis of the fixing belt 41 (direction of the depth of the paper surface in FIG. 8). As a result, the thickness of the second region 463 is reduced at the portion of the recess 4633. In other words, the second region 463 has a narrow radial interval at the recess 4633.

According to this configuration, the current sent from the power supply unit 471 receives a resistance at the recess 4633. As a result, the amount of heat generated increases at the recess 4633. Therefore, it is possible to improve the heating efficiency by the second heating unit 47.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to this, and various modifications can be made without departing from the gist of the invention.

For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem type image forming apparatus for color printing in which images of a plurality of colors are sequentially superimposed, but the image forming apparatus 1 is limited to such a model. Instead, it may be an image forming apparatus for color printing or an image forming apparatus for monochrome printing, which is not a tandem type.

The present invention can be used in fixing devices and image forming devices.

1 Image forming device 40 Fixing device 41 Fixing belt 42 Pressurizing roller (pressurizing member)
43 Nip forming member 44 First heating part 45 Frame member 46 Belt guide 47 Second heating part 461 First area 462, 463 Second area 471 Power supply part 4611, 4621, 4631 Contact parts 4612, 4622, 4632 Connection Part 4633 Recess G Gap N Fixing Nip part P Paper Wp1 First size Wp2 Second size

Claims (5)

An endless fixing belt that can rotate along the transport direction of the recording medium,
A pressure member that comes into contact with the outer peripheral surface of the fixing belt and gives a rotational driving force to the fixing belt.
A nip forming member which is arranged inside the fixing belt so as to face the pressure member across the fixing belt and contacts the inner peripheral surface of the fixing belt to form a fixing nip portion.
A first heating unit, which is arranged to face the outer peripheral surface of the fixing belt and heats the fixing belt by electromagnetic induction,
A belt guide that contacts the inner peripheral surface of the fixing belt other than the fixing nip portion and supports the fixing belt from the inside, and
With
The belt guide
A first region made of a magnetic material arranged at the center of the fixing belt in the direction of the rotation axis, and
A second region made of a non-magnetic material arranged on both ends of the first region in the direction of the rotation axis, and a second region.
A fixing device comprising a second heating portion for heating the second region. The fixing nip portion has a size in the width direction orthogonal to the transport direction of the recording medium, which is the first size, and the recording medium, which has a second size larger than the first size. And, it is possible to pass through,
The fixing device according to claim 1, wherein the size of the first region in the width direction is larger than the first size and smaller than the second size. The fixing device according to claim 1 or 2, wherein the belt guide has a gap between the first region and the second region. The second heating unit generates heat in the second region by passing an electric current through it.
Any one of claims 1 to 3, wherein the second region has a recess extending in a direction orthogonal to the direction in which the current flows, and the thickness of the recess is reduced at the portion of the recess. The fixing device according to. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 4.

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