JP2012181546A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which improves durability of a fixation device employing a fixation belt.SOLUTION: A fixation part comprises a fixation belt provided to encompass the outer periphery of an inner roller, which is pressed with a pressure roller 160 from the outside of the fixation belt to form a fixation nip, and induces heat at a magnetic flux generation part 170 to thermally fix an un-fixed image formed on a sheet by letting it pass through the fixation nip. In both end parts of a fixation roller 150 in the axis direction thereof, a pair of flange members 159 are provided to regulate the meander of the belt. The fixation belt comprises: a magnetic shunt alloy layer which changes from ferromagnetism to paramagnetism when a temperature is over a prescribed temperature; and an induction heat generation layer which is mechanically stronger than the magnetic shunt alloy layer and heat-induced. The width of the magnetic shunt alloy layer is narrower than that of the induction heat generation layer, and in both end parts of the fixation belt, the marginal part of the magnetic shunt alloy layer is receded to the center.

Description

  The present invention relates to a fixing device and an image forming apparatus that heat-fix an unfixed image on a recording sheet by heating a fixing belt by induction heating, and particularly relates to a technique for improving durability of the fixing device.

An image forming apparatus such as a copying machine forms a fixing nip by pressing a pressure roller against a fixing roller, and an unfixed image such as toner formed on the recording sheet is fixed by passing the recording sheet through the fixing nip. A fixing device is provided.
The fixing roller is heated to melt and fix an unfixed image on a recording sheet, and in recent years, an electromagnetic induction heating type fixing device capable of raising the temperature in a short time is becoming mainstream.

FIG. 7 shows a schematic configuration of the electromagnetic induction heating type fixing device, and only the fixing roller 1150 is shown in a cross section including its axis.
As shown in the figure, the fixing roller 1150 is configured by extrapolating a cylindrical fixing belt 1153 to an internal roller 1150a in which a heat insulating layer 1152 is formed on the peripheral surface of a cylindrical roller shaft 1151. The

The fixing belt 1153 includes an induction heating layer 1155, a magnetic shunt alloy layer 1156, an elastic layer 1157, and a release layer 1158 that are laminated in that order from the inside.
In addition, a pair of flange members 1180 are fitted to both ends of the roller shaft 1151 to restrict the movement of the fixing belt 1153 in the axial direction.
On the other hand, the pressure roller 1160 is a roller that is arranged in parallel with the fixing roller 1150 and is driven to rotate, and presses the fixing roller 1150 in the X direction to form a fixing nip.

In addition, a magnetic flux generator 1170 made of an induction coil or the like is provided so as to face the fixing roller 1150.
In such a configuration, when an alternating magnetic flux 1170a is generated from the magnetic flux generator 1170, this magnetic flux travels along the induction heat generating layer 1155 and the magnetic shunt alloy layer 1156 of the fixing belt 1153, and the magnetic flux mainly in these two layers. The part facing the generation unit 1170 generates heat and the temperature rises. As a result, when the recording sheet S passes through the fixing nip, the toner image is heated and pressed to be thermally fixed to the recording sheet S.

  At this time, the fixing roller 1150 is deprived of heat by the recording sheet S at the central portion in contact with the recording sheet S (width W). In the portions on both ends (hereinafter referred to as “non-sheet passing portion P”) that do not pass through, the temperature remains high without being deprived of heat, so that the central portion of the fixing roller 1150 is set to the target temperature. When power is continuously supplied to the magnetic flux generation unit 1170, the temperature of the non-sheet passing portion P further increases.

Then, the non-sheet-passing portion P of the magnetic shunt alloy layer 1156 included in the fixing roller 1150 is heated to the Curie temperature or more, and the action of converging the magnetic flux is lost due to the transition from the ferromagnetic material to the paramagnetic material. The magnetic flux density of the non-sheet passing portion P is lowered.
Thereby, since the current density of the eddy current generated in the induction heat generating layer 1155 and the magnetic shunt alloy layer 1156 is decreased, heat generation is suppressed, and the temperature rise in the non-sheet passing portion P is mitigated.

As described above, the conventional fixing device 1005 is excellent in thermal efficiency because the induction heating layer 1155 and the magnetic shunt alloy layer 1156 themselves provided in the fixing roller 1150 generate heat, and further, the fixing by the action of the magnetic shunt alloy layer 1156. The temperature can be automatically controlled so that the non-sheet passing portion P of the roller 1150 does not overheat.

JP 2008-76508 A

  However, while the pressure roller 1160 is pressed against the fixing roller 1150, while the pressure roller 1160 is driven to rotate, the heat insulating layer 1152 and the fixing belt 1153 of the fixing roller 1150 that follows the pressure roller 1160 are in the thickness direction (fixing roller In the radial direction, the fixing belt 1153 repeats deformation and restoration, or the fixing belt 1153 tends to meander while being displaced in the axial direction with respect to the internal roller 1150a, and the edge thereof strongly contacts one of the flange members 1180.

At this time, the edge portions of the flange member 1180, the heat insulating layer 1152, and the fixing belt 1153 come into contact with each other and rub against each other.
Among these layers, the induction heating layer 1155 and the magnetic shunt alloy layer 1156 are made of a highly rigid metal material, and the degree of increase in internal stress due to deformation is larger than that of the other layers. A large internal stress is generated at the contacting edge.

In particular, the magnetic shunt alloy layer 1156 has a mechanical strength smaller than that of the induction heat generating layer 1155, and therefore, there is a problem that the edge portion thereof is easily cracked due to the frictional force and internal stress.
SUMMARY An advantage of some aspects of the invention is that it improves the durability of a fixing roller in a fixing device using a fixing belt including a magnetic shunt alloy layer and an induction heating layer.

  In order to achieve the above object, in the fixing device according to the present invention, an endless belt is disposed so as to surround the outer periphery of the first roller, and the belt is pressed by the second roller from the outside of the belt. A fixing nip is formed between the surface and the second roller, and the belt is induction-heated by a high-frequency magnetic field generated by an induction coil, and a sheet on which an unfixed image is formed is passed through the fixing nip. In the fixing device for fixing, a pair of flanges for restricting meandering of the belt is provided at both axial ends of the first roller, and the belt is made of ferromagnetic material when a predetermined temperature is exceeded. A magnetic shunt alloy layer that reversibly changes to paramagnetism, an induction heating layer that is higher in mechanical strength than the magnetic shunt alloy layer and that is induction-heated by the induction coil, and the width of the magnetic shunt alloy layer is The induction heating layer Even narrower, in the belt end portions, the edges of the magnetic shunt alloy layer is characterized in that it retracts the belt near the center.

At both ends of the belt, the edge of the magnetic shunt alloy layer recedes toward the center of the belt so that the collar and the magnetic shunt alloy layer do not come into contact with each other. Can be prevented and damage to the edge can be prevented.
Preferably, the magnetic shunt alloy layer is made of an alloy of nickel and iron, and the induction heating layer is made of nickel.

Nickel, which is the material of the induction heating layer, has higher mechanical strength than the alloy of nickel and iron, which is the material of the magnetic shunt alloy layer, so even if the edge of the induction heating layer is brought into contact with the buttocks It can be made difficult to cause damage.
Furthermore, the width of the magnetic shunt alloy layer in the axial direction of the first roller is preferably larger than the maximum width of the recording sheet passing through the fixing nip.
The induction coil is disposed at a position facing the induction heating layer, and the width in the axial direction of the first roller in the magnetic shunt alloy layer and the induction heating layer is the width of the first roller in the induction coil. It is desirable that the width is larger than the axial width.

Thereby, excessive temperature rise in the non-sheet passing region can be effectively suppressed. Moreover, it can prevent that the edge part of an induction heating layer is heated by the magnetic flux which leaked from the both ends of the induction coil.
Note that the present invention may be an image forming apparatus including the fixing device.

1 is a schematic cross-sectional view illustrating an overall configuration of a printer according to an embodiment of the present invention. FIG. 2 is a partially cutaway perspective view showing a configuration of a fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a fixing roller according to an embodiment of the present invention. It is a fragmentary sectional view of the modification (the 1) of the fixing roller of an embodiment of the invention. It is a fragmentary sectional view of the modification (the 2) of the fixing roller of an embodiment of the invention. FIG. 10 is a partial cross-sectional view of a third modification of the fixing roller according to the embodiment of the present invention. FIG. 10 is a cross-sectional view of a fixing device in a conventional image forming apparatus.

FIG. 1 is a schematic cross-sectional view showing the overall configuration of the printer 1.
As shown in the figure, the printer 1 includes an image processing unit 3, a paper feeding unit 4, a fixing unit 5, and a control unit 60. The printer 1 is connected to a network (for example, a LAN) and is connected to an external terminal device (not connected). When a print job execution instruction is received from (shown), a toner image composed of yellow, magenta, cyan, and black is formed based on the instruction, and a full-color image is formed by multiple transfer of these. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.
<Image process part>
The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K corresponding to each of Y to K colors, an optical unit 10, an intermediate transfer belt 11, and the like.

The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the drum 31Y. The other image forming units 3M to 3K have the same configuration as the image forming unit 3Y, and the reference numerals are omitted in FIG.
The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is rotationally driven in the direction of arrow A.

The optical unit 10 includes a light emitting element such as a laser diode, emits a laser beam L for forming an image of Y to K colors by a drive signal from the control unit 60, and exposes and scans the photosensitive drums 31Y to 31K.
By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 31Y to 31K charged by the chargers 32Y to 32K. The electrostatic latent images are developed by developing units 33Y to 33K, and Y to K color toner images are superimposed on the same positions on the intermediate transfer belt 11 and primarily transferred onto the photosensitive drums 31Y to 31K. It is executed at different timings.

The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 11 by electrostatic forces acting on the primary transfer rollers 34Y to 34K, and a full color toner image is formed.
Move in the direction.
On the other hand, the paper feed unit 4 includes a paper feed cassette 41 that stores the recording sheets S, a feed roller 42 that feeds the recording sheets S in the paper feed cassette 41 one by one onto the transport path 43, and a fed recording sheet S. Are provided with a timing roller pair 44 for taking the timing of feeding the toner to the secondary transfer position 46, and the recording sheet S is transferred from the paper feeding unit 4 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 11. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet S by the action of the secondary transfer roller 45.

The recording sheet S that has passed the secondary transfer position 46 is conveyed to the fixing unit 5, and the toner image (unfixed image) on the recording sheet S is fixed to the recording sheet S by heating and pressurization in the fixing unit 5. Thereafter, the sheet is discharged onto the discharge tray 72 via the discharge roller pair 71.
<Fixing part>
FIG. 2 is a partial cross-sectional perspective view of the fixing unit 5.

As shown in the figure, the fixing unit 5 includes a fixing roller 150, a pressure roller 160, a magnetic flux generation unit 170, and the like.
The fixing roller 150 and the pressure roller 160 are arranged in parallel. By urging the pressure roller 160 toward the fixing roller 150 by an urging mechanism (not shown), a fixing nip is formed between the two rollers. When the recording sheet S passes, the toner image T formed on the recording sheet S is melted and pressed to be fixed.

Details of each part will be described below.
<Magnetic flux generator>
The magnetic flux generator 170 generates an alternating magnetic field toward the fixing roller 150, and includes a lower casing portion 171, a bottom core 172, an induction coil 173, a core 174, and an upper casing portion 175.

The lower casing portion 171 is made of an insulating material such as resin, and an annular groove portion around which the induction coil 173 is wound is provided.
The hem core 172 is a long member made of a ferromagnetic material, and is arranged in parallel to the roller axis (Y axis) along the inner walls of the lower casing portion 171 on the X direction side and the X ′ direction side. Has been.

The induction coil 173 is a litz wire and is covered with a heat resistant resin (not shown).
The induction coil 173 is connected to a high-frequency inverter (not shown), and generates an alternating magnetic field having a predetermined frequency when high-frequency power of 10 to 100 [kHz] and 100 to 2000 [W] is supplied. The fixing roller 150 is heated.
The core 174 is made of a ferromagnetic material and is an arch-shaped member provided across the two hem cores 172.

The upper casing portion 175 is made of an insulating material such as resin, and serves to cover the lower casing portion 171 that houses the bottom core 172, the induction coil 173, and the core 174. <Pressure roller>
As shown in FIG. 2, the pressure roller 160 includes a roller shaft 161, an elastic layer 162, and a release layer 163.

The roller shaft 161 is rotationally driven by a drive mechanism (not shown), and is, for example, a cylindrical aluminum shaft having a thickness of 3 mm and an outer diameter of approximately 30 mm.
The elastic layer 162 is a cylindrical body made of silicone sponge rubber having a thickness of 3 mm to 10 mm.
The release layer 158 is an endless belt made of a fluororesin such as PFFE or PFA having a thickness of 10 μm or more and 50 μm or less.
<Fixing roller>
As shown in FIG. 3, the fixing roller 150 is formed by inserting an internal roller 150 a inside a cylindrical fixing belt 153.

Here, a gap of 0 μm or more and 200 μm or less is provided between the internal roller 150a and the fixing belt 153.
The internal roller 150 a is formed by forming a heat insulating layer 152 on the peripheral surface of the roller shaft 151.
The roller shaft 151 is a metal pipe made of, for example, aluminum, and both ends thereof are supported by bearings 180.

More specifically, the roller shaft 151 is, for example, a cylindrical shaft having an outer diameter of 20 mm and a thickness of 4 mm.
Further, the roller shaft 151 is provided with a pair of flange members 159 that restrict the position of the fixing belt 153 in the axial direction at both ends.
The heat insulating layer 152 is made of a highly elastic and highly heat insulating material having a thickness of 2 mm or more and 10 mm or less (preferably 3 mm or more and 7 mm or less), for example, a sponge body of silicone rubber. It is provided so as to cover the excluded part.

The fixing belt 153 is an endless belt in which an induction heating layer 155, a magnetic shunt alloy layer 156, an elastic layer 157, and a release layer 158 are laminated in this order.
The induction heat generating layer 155 is an endless nickel electroformed belt having a thickness of 5 μm or more and 100 μm or less (preferably 15 μm or more and 30 μm or less), and its tensile strength is 1000 MPa or more and 2500 MPa or less.

The magnetic shunt alloy layer 156 is made of an alloy of nickel and iron, and is an endless belt having a thickness of 5 μm or more and 100 μm or less (preferably 15 μm or more and 30 μm or less). However, when it exceeds the Curie temperature, it has the property of becoming paramagnetic, and its tensile strength is 400 MPa or more and 500 MPa or less.
As other materials, nickel, iron, chromium, or the like having a tensile strength of 400 MPa or more and 500 MPa or less may be used.

The elastic layer 157 is, for example, a silicone rubber cylindrical body having a thickness of 10 μm or more and 800 μm or less (preferably 100 μm or more and 300 μm or less), and is attached to the outer periphery of the induction heating layer 155.
Here, when the thickness of the elastic layer 157 is less than 10 μm, it is difficult to obtain the desired elasticity in the thickness direction.

On the other hand, when the thickness of the elastic layer 157 exceeds 800 μm, the heat generated in the induction heating layer 155 hardly reaches the outer peripheral surface of the release layer 158, and the thermal efficiency tends to deteriorate.
The release layer 158 is made of, for example, silicone rubber, PTFE or PFA, and is an endless belt having a thickness of 5 μm or more and 100 μm or less (preferably 10 μm or more and 50 μm or less), and improves the release property on the surface of the fixing roller. ing.

Here, the heat insulating layer 152, the induction heat generating layer 155, the elastic layer 157, and the release layer 158 all have the same length in the X-axis direction.
On the other hand, the magnetic shunt alloy layer 156 has a shorter length in the X-axis direction than these layers.
More specifically, at both ends of the fixing roller 150, the edge of the magnetic shunt alloy layer 156 retreats by a length of 3 mm or more and 10 mm or less from the edge of the induction heating layer 155, and the retreated portion An induction heat generating layer 155 is formed, and the flange member 159 and the magnetic shunt alloy layer 156 are configured not to be in direct contact with each other.

This is to reduce stress concentration on the edge of the magnetic shunt alloy layer 156 that is inferior in mechanical strength to the induction heating layer 155 and to prevent damage to the magnetic shunt alloy layer 156.
In addition, the edge of the magnetic shunt alloy layer 156 projects outward in the range of 2 mm or more and 3 mm or less from both ends in the width direction (YY ′ direction) of the induction coil 173.
This is because the leakage magnetic flux 201 existing at both ends in the width direction (YY ′ direction) of the induction coil 173 wraps around the outside of both edges of the magnetic shunt alloy layer 156 and enters the induction heating layer 155. In this part, even if the magnetic shunt alloy layer 156 becomes paramagnetic, the induction heat generating layer 155 is heated, and the self-temperature control function described later does not function well, so that this is prevented.

With this configuration, the width of the magnetic shunt alloy layer 156 is longer than the maximum width Wm of the recording sheet S, and the protrusion L3 from the maximum width Wm is about 15 mm to 18 mm. .
The flange member 159 is in contact with the edge of the fixing belt 153 to prevent the fixing belt 153 from moving and meandering in the Y-axis direction, and is fitted into both ends of the roller shaft 151.

In such a configuration, when the magnetic shunt alloy layer 156 becomes equal to or higher than the Curie temperature, the portion changes from a ferromagnetic material to paramagnetism, and the action of converging the magnetic flux is lost. Density decreases.
As a result, the current density of the eddy current generated in the induction heating layer 1155 and the magnetic shunt alloy layer 1156 also decreases, so that heat generation is suppressed and the temperature rise in the non-sheet passing portion P is mitigated.

  The Curie temperature is set to a temperature that is approximately 20 ° C. higher than the temperature suitable for fixing (target temperature). With this, when a large number of small-sized recording sheets S (width W) are continuously printed. In the fixing roller 150, the temperature of the non-sheet passing portion P where the recording sheet S does not pass through the portion heated by induction in the belt width direction, that is, the temperature of the non-sheet passing portion P is not deprived of heat by the recording sheet S. For this reason, even if the temperature exceeds the target temperature, the Curie temperature is not significantly exceeded, and a high temperature that damages the fixing roller 150 is prevented.

The Curie temperature to be set is not limited to the above temperature, and the fixing unit 5 is configured so that the non-sheet passing part P does not overheat while the temperature of the sheet passing part maintains a predetermined fixing temperature. Accordingly, it is appropriately set by experiment.
Thus, the fixing unit 5 is excellent in thermal efficiency because the induction heating layer 155 and the magnetic shunt alloy layer 156 itself provided in the fixing roller 150 generate heat, and further, due to the action of the magnetic shunt alloy layer 156, the fixing roller 150 The excessive temperature rise of the non-sheet passing portion P can be automatically suppressed.

Further, since the flange member 159 and the magnetic shunt alloy layer 156 are configured so as not to be in direct contact with each other, the edge portion of the magnetic shunt alloy layer 156 having a relatively low mechanical strength can be hardly damaged.
<Method for Producing Induction Heating Layer 155 and Magnetic Shunt Alloy Layer 156>
Here, a combination of the induction heating layer 155 and the magnetic shunt alloy layer 156 is referred to as a laminated metal layer 154.

Hereinafter, a method for manufacturing the laminated metal layer 154 will be described.
About manufacture of the laminated metal layer 154, what is necessary is just to perform the following procedures using a well-known manufacturing method.
1) A nickel layer (hereinafter referred to as “nickel belt”) is formed on the surface of a cylindrical core by nickel electroforming until the thickness becomes 5 μm or more and 100 μm or less (preferably 15 μm or more and 30 μm or less). To do.
2) Separately, use a drawing process such as spatula drawing (spinning), squeezing drawing (DI), etc., or an alloy of nickel and iron, and a thickness of 5μm to 100μm (desirable) Is an endless belt (hereinafter referred to as “magnetic shunt alloy belt”) having a cylindrical shape with a diameter equal to or greater than the outer diameter of the nickel belt and shorter than the nickel belt. .
3) Press-fit the magnetic shunt alloy belt into the nickel belt with the core inserted.
4) Mask the surface of the magnetic shunt alloy belt with tape.
5) The plating process is again performed by nickel electroforming until the thickness of the nickel layer at both ends of the belt becomes the same as the surface of the magnetic shunt alloy portion at the center.
6) Remove masking.

By performing the steps as described above, the laminated metal layer 154 having a uniform thickness can be formed.
7) Furthermore, a 1 μm to 2 μm thin nickel layer may be formed on the surface of the laminated metal layer 154 in a state where the core is inserted after the step 6) by using nickel electroforming.
By doing so, as shown in FIG. 4, a laminated metal layer 154a in which the magnetic shunt alloy layer 156a is embedded in the induction heating layer 155a can be formed.

Note that the thin film nickel layer may be formed by replacing the steps 6) and later with steps 8) and 9) described below.
8) Plating is performed by nickel electroforming until the thickness of the nickel layer at both ends of the belt is thicker than the surface of the magnetic shunt alloy portion at the center.
9) Polish the surface so that the belt surface is flat.

By carrying out these steps, the laminated metal layer 154a having a more uniform thickness can be created.
The fixing belt described above is annealed after being machined.
This annealing may be performed at 700 ° C. to 1000 ° C. for about 30 minutes to 2 hours.
This is because if internal distortion occurs due to drawing processing during the production of the magnetic shunt alloy belt, the magnetic permeability of the magnetic shunt alloy decreases, the magnetic flux density decreases, and the heat generation efficiency deteriorates. It is for removing.
<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be implemented.
(1) In the above embodiment, the fixing belt 153 is an endless belt in which the induction heating layer 155, the magnetic shunt alloy layer 156, the elastic layer 157, and the release layer 158 are laminated in this order. The fixing belt is not limited to the configuration, and may be a fixing belt including at least the induction heating layer 155 and the magnetic shunt alloy layer 156.
(2) In the above embodiment, the edge of the magnetic shunt alloy layer 156 is retracted from the edge of the induction heat generating layer 155, and the induction heat generating layer 155 is formed in the retracted portion. The magnetic shunt alloy layer 156 is configured not to be in direct contact with the magnetic shunt alloy layer 156, but is not limited to this configuration. For example, as shown in FIG. 5, the edge of the magnetic shunt alloy layer 156b is simply It may be configured to recede from the edge of the induction heating layer 155b.

Even in this case, the magnetic shunt alloy layer 156b and the induction heating layer 155b are in contact with each other without any gap, and are pressed from the outer periphery by the action of the elastic force of the elastic layer 157. Thus, it does not move in the axial direction and come into contact with the flange member 159.
(3) In the above embodiment, in the fixing roller 150, the roller shaft 151 having the heat insulating layer 152 formed on the peripheral surface is inserted inside the cylindrical fixing belt 153. Although a gap of 0 μm or more and 200 μm or less is provided between the heat generation layer 155, the present invention is not limited to this configuration.

For example, as shown in FIG. 6, the outer diameter of the fixing belt 153 is enlarged (hereinafter referred to as “fixing belt 253”), the clearance is secured about several millimeters, and the clearance extends in the roller axis direction. The present invention may be applied to a so-called loose-fitting type fixing device provided with a guide plate 254 having a circular cross section.
In short, the fixing belt is arranged so as to surround the outer periphery of the first roller, and is pressed by the second roller from the outside of the fixing belt to form a fixing nip between the surface of the fixing belt and the second roller. Any fixing device may be used that heats the recording sheet S on which an unfixed image is formed by passing through the fixing nip by induction heating with an induction coil while rotating around.

In such a configuration, since the heat insulating layer 152 is in contact with only a part of the outer periphery of the fixing belt 253, there is an advantage that the heat insulating efficiency is high and the warm-up time can be shortened.
(4) Although the tandem type color printer has been described in the above embodiment, the present invention is not limited to this, and is applicable to all image forming apparatuses including an induction heating type fixing device. is there.

  The present invention can be widely applied to a fixing device and an image forming apparatus that heat-fix an unfixed image on a recording sheet by heating a fixing belt by induction heating.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y, 3M, 3C, 3K Image creation part 4 Paper feed part 5 Fixing part 10 Optical part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 31 Photoreceptor drum 32 Charger 33 Developer 34 Primary transfer roller 35 Cleaner 41 Paper Feed Cassette 42 Roller 43 Conveying Path 44 Timing Roller Pair 45 Secondary Transfer Roller 46 Secondary Transfer Position 60 Control Unit 71 Discharge Roller Pair 72 Discharge Tray 150 Fixing Roller 151 Roller Shaft 150a Internal Roller 151 Roller Shaft 152 Heat Insulating Layer 153, 153a Fusing belt 154, 154a Laminated metal layer 155, 155a, 155b Induction heating layer 156, 156a, 156b Magnetic shunt alloy layer 157 Elastic layer 158 Release layer 159 Gutter member 160 Pressure roller 161 Roller shaft 162 Elastic layer 163 Separation Mold layer 170 Magnetic flux Generator 173 Induction coil 201 Leakage magnetic flux 254 Guide plate

To achieve the above object, a fixing device according to the present invention is an endless, belt rotatably supported in the circumferential direction that is the endless, in contact with the outer peripheral surface of the belt, the belt A pressure member that forms a fixing nip with the surface, the belt is induction-heated by a high-frequency magnetic field generated by an induction coil, and a sheet on which an unfixed image is formed is sandwiched by the fixing nip A fixing device that performs heat fixing while being conveyed with rotation of the belt, and is provided with a pair of flanges that regulate meandering of the belt on both ends of the belt in a direction perpendicular to the circumferential direction. The belt has a magnetic shunt alloy layer that reversibly changes from ferromagnetic to paramagnetic when a predetermined temperature is exceeded, and has a mechanical strength higher than that of the magnetic shunt alloy layer, and is induction-heated by the induction coil. Including heating layer The width of the magnetic shunt alloy layer is smaller than the induction heating layer, at both ends in a direction orthogonal to the circumferential direction of the belt, the edge of the magnetic shunt alloy layer has retreated to the belt near the center, the The induction coil is disposed at a position facing the induction heating layer, and the width of the magnetic shunt alloy layer and the induction heating layer is larger than the width of the induction coil in a direction orthogonal to the circumferential direction. And

At both ends of the belt, the edge of the magnetic shunt alloy layer recedes toward the center of the belt so that the collar and the magnetic shunt alloy layer do not come into contact with each other. Can be prevented and damage to the edge can be prevented.
Moreover, it can prevent that the edge part of an induction heating layer is heated by the magnetic flux which leaked from the both ends of the induction coil.
Preferably, the magnetic shunt alloy layer is made of an alloy of nickel and iron, and the induction heating layer is made of nickel.

Nickel, which is the material of the induction heating layer, has higher mechanical strength than the alloy of nickel and iron, which is the material of the magnetic shunt alloy layer, so even if the edge of the induction heating layer is brought into contact with the buttocks It can be made difficult to cause damage.
Furthermore, it is preferable that the width of the magnetic shunt alloy layer in the direction orthogonal to the circumferential direction is larger than the maximum width of the recording sheet passing through the fixing nip .

Thereby, excessive temperature rise in the non-sheet passing region can be effectively suppressed.
In addition, it is desirable that the induction heating layer is formed in a portion where the edge portion of the magnetic shunt alloy layer recedes closer to the center of the belt than the induction heating layer.
Note that the present invention may be an image forming apparatus including the fixing device.

Claims (5)

An endless belt is disposed so as to surround the outer periphery of the first roller, and is pressed by the second roller from the outside of the belt to form a fixing nip between the belt surface and the second roller. And a fixing device for inductively heating the belt with a high-frequency magnetic field generated by an induction coil, and thermally fixing a sheet on which an unfixed image is formed through the fixing nip,
A pair of flanges that regulate meandering of the belt are provided at both axial ends of the first roller,
The belt is
A magnetic shunt alloy layer that reversibly changes from ferromagnetic to paramagnetic above a predetermined temperature;
A mechanical strength higher than that of the magnetic shunt alloy layer, and an induction heating layer that is induction-heated by the induction coil,
The fixing device according to claim 1, wherein a width of the magnetic shunt alloy layer is narrower than that of the induction heating layer, and an edge portion of the magnetic shunt alloy layer recedes toward the belt center at both ends of the belt. The magnetic shunt alloy layer is made of an alloy of nickel and iron,
The fixing device according to claim 1, wherein the induction heating layer is made of nickel.   The fixing device according to claim 1, wherein a width of the magnetic shunt alloy layer in an axial direction of the first roller is larger than a maximum width of a recording sheet passing through the fixing nip. The induction coil is disposed at a position facing the induction heating layer,
4. The width in the axial direction of the first roller in the magnetic shunt alloy layer and the induction heating layer is larger than the axial width of the first roller in the induction coil. 5. The fixing device described.   An image forming apparatus having the fixing device according to claim 4.

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