JP2010217841A - Fixing device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the durability of a fixing device using a fixing belt. <P>SOLUTION: The fixing belt 153 is arranged to surround the outer periphery of an internal roller 150a and is pressed from outside of the fixing belt 153 by a pressing roller 160 to form a fixing nip. A fixing part 5 is thermally fixed by induction heating at a magnetic field generation part 170 and passing a sheet on which an unfixed image is formed through the fixing nip. A pair of collar members 159 which regulate meandering of a belt is provided to both ends in the axial direction of the fixing roller 150. The fixing belt 153 includes: a first metal heat-generating layer 156 made of a diamagnetic material; and a second metal heat-generating layer 155 which is made of a ferromagnetic material, has a higher mechanical strength, a larger specific resistance, and a larger thickness than the first metal heat generating layer 156. The width of the first metal heat-generating layer 156 is smaller than that of the second metal heat-generating layer 155. On both ends of the fixing belt 153, the edge of the first metal heat-generating layer 156 shifts backward to the center. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 fixes an unfixed image such as toner formed on the recording sheet 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. 9 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 is formed by laminating a release layer 1158, an elastic layer 1157, a first metal heating layer 1156, and a second metal heating layer 1155 in this order from the outside.
Here, the first metal heating layer is made of a diamagnetic material such as copper having a thickness smaller than that of the second metal heating layer 1155.
The second metal heating layer 1155 is made of a ferromagnetic material such as nickel, and has a higher specific resistance than the first metal heating layer 1156.

A pair of flange members 1180 are fitted into both ends of the roller shaft 1151 in order to restrict 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 the alternating magnetic flux 1170a is generated from the magnetic flux generator 1170, the portion of the second metal heat generating layer 1155, which is a ferromagnetic material, mainly facing the magnetic flux generator 1170 tries to draw the alternating magnetic flux 1170a. To do. At this time, since the first metal heat generating layer 1156 is provided between the magnetic flux generator 1170 and the second metal heat generating layer 1155, the magnetic flux passes through the first metal heat generating layer 1156, so An electric current is generated.

Here, the first metal heat generating layer 1156 is thinner than the skin depth of the eddy current and has a lower specific resistance than the second metal heat generating layer 1155, so that the eddy current is applied to the first metal heat generating layer 1156. Concentrated and generates heat.
Further, the alternating magnetic flux 1170a that penetrates through the first metal heat generating layer 1156 and enters the second metal heat generating layer 1155 generates a current in the second metal heat generating layer 1155 to generate heat.

  In this way, by combining the first metal heat generating layer 1156 and the second metal heat generating layer 1155 having different magnetism as heat generating layers and appropriately selecting the thickness of each layer so that the total amount of heat generated by both layers is increased, Efficient heating can be performed.

Patent No. 4077410

  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 1150). The fixing belt 1153 repeats deformation and restoration in the radial direction), or the edge of the fixing belt 1153 comes into strong contact with one of the flange members 1180 in an attempt to meander with respect to the internal roller 1150a.

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 first metal heat generating layer 1156 and the second metal heat generating layer 1155 are made of a highly rigid metal material, and the degree of increase in internal stress due to deformation is larger than other layers. A large internal stress is generated at the edge in contact with the member 1180.

In particular, since the first metal heat generating layer 1156 has a mechanical strength smaller than that of the second metal heat generating layer 1155, there is a problem that a crack is easily generated at the edge due to the frictional force or the internal stress.
The present invention has been made in view of the above problems, and improves the durability of a fixing roller in a fixing device using a fixing belt including a first metal heating layer and a second metal heating layer having different magnetism. With the goal.

  In order to achieve the above object, the fixing device according to the present invention has an endless belt 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 A fixing nip is formed between the first roller 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 and thermally fixed. In the fixing device, a pair of flanges for restricting meandering of the belt is provided at both axial end portions of the first roller, and the belt is a first metal heating layer made of a diamagnetic material. And a second metal heat generating layer having a mechanical strength higher than that of the first metal heat generating layer, a higher specific resistance, and a greater thickness than the first metal heat generating layer. In the axial direction of one roller Width is narrower than the second metal heating layer in the belt end portions, the edge portions of the first metal heating layer is characterized in that it retracts the belt near the center.

At both ends of the belt, the edge of the first metal heat generating layer is configured so that the edge of the first metal heat generating layer recedes toward the center of the belt so that the collar portion and the first metal heat generating layer do not contact each other. This reduces the stress generated at the edge and prevents the edge from being damaged.
The first metal heating layer may be made of any one of copper, aluminum, brass, gold, and silver, and the second metal heating layer may be made of nickel.

Since nickel which is the material of the second metal heating layer has higher mechanical strength than any of copper, aluminum, brass, gold and silver which can be the material of the first metal heating layer, the edge of the second metal heating layer Even if the part is brought into contact with the collar part, it is possible to make it difficult to cause breakage.
Furthermore, it is preferable that the width of the first metal heating layer in the axial direction of the first roller is larger than the maximum width of the recording sheet passing through the fixing nip.

The induction coil is disposed at a position facing the second metal heating layer, and the width of the first metal heating layer and the second metal heating layer in the axial direction of the first roller is the induction coil. It is desirable that it is larger than the width of the first roller in the axial direction.
When leakage magnetic flux existing at both ends of the induction coil wraps around the outer sides of the first metal heating layer and enters the second metal heating layer, the first metal heating layer and the second metal heating layer are separated. The ratio of the current density of the generated eddy current may change, and the amount of heat generated may be different from the central portion.

With the above configuration, the wraparound of the leakage magnetic field does not occur, so that it is possible to suppress unevenness in the amount of heat generated in the axial direction of the first roller.
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 figure which shows the result of the temperature rising test of the fixing belt of embodiment of this invention. It is a figure which shows the result of the endurance test of the fixing belt of embodiment of this 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 disposed around the photosensitive drum 31Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like. 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 the electrostatic force acting on the primary transfer rollers 34Y to 34K to form a full-color toner image, and further move toward the secondary transfer position 46.
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 flux 170 a 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 163 is 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 a release layer 158, an elastic layer 157, a first metal heating layer 156, and a second metal heating layer 155 are laminated in this order from the outside.
The first metal heating layer 156 is an endless belt made of a diamagnetic material such as copper, and has a thickness smaller than the skin depth of the eddy current generated due to the magnetic field generated from the induction coil 173.

More specifically, the thickness is set to be about 5 μm to 40 μm (more preferably 10 μm to 15 μm), depending on the alternating frequency of the induction coil 173, and is about 280 MPa. It has a tensile strength of
The first metal heat generating layer 156 has a specific resistance of about 1.7 × 10 ⁻⁸ Ω · m, and has a tensile strength of about 280 MPa.

The second metal heat generating layer 155 is an endless belt made of a ferromagnetic material such as nickel, and has a thickness set to 10 μm or more and 100 μm or less (preferably 15 μm or more and 40 μm or less), and has a tensile strength of about 1150 MPa. Have.
Further, the second metal heat generating layer 155 has a specific resistance of about 6.8 × 10 ⁻⁸ Ω · m.

The alternating magnetic flux 170 a that has entered the second metal heating layer 155 travels in the second metal heating layer 155 in the axial direction of the roller shaft 151.
At this time, if the thickness of the second metal heat generating layer 155 is small, magnetic flux saturation occurs and the alternating magnetic flux 170a leaks to the outside, reducing the heat generation efficiency. Therefore, the thickness of the second metal heat generating layer 155 is sufficient. It is set large.

For this reason, the thickness of the second metal heating layer 155 is set to be thicker than that of the first metal heating layer 156.
The elastic layer 157 is, for example, a cylindrical body of silicone rubber 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 second metal 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 second metal heat generating layer 155 does not easily reach 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 has a thickness of 5 μm or more and 100 μm or less (desirably, 10 μm or more and 50 μm or less) to improve the release property on the surface of the fixing roller. Yes.

Here, the heat insulating layer 152, the second metal heating layer 155, the elastic layer 157, and the release layer 158 all have the same length in the Y-axis direction.
On the other hand, the first metal heat generating layer 156 has a shorter length in the Y-axis direction than these layers, and the edge of the first metal heat generating layer 156 recedes toward the center of the fixing belt 153.
More specifically, at both ends of the fixing roller 150, the edge of the first metal heat generation layer 156 recedes by a length L1 (3 mm ≦ L1 ≦ 10 mm) from the edge of the second metal heat generation layer 155, A second metal heat generating layer 155 is further formed in the portion where the first metal heat generating layer 156 is not formed by the retreat, and the flange member 159 and the first metal heat generating layer 156 are configured not to be in direct contact with each other. ing.

This is to reduce stress concentration on the edge of the first metal heating layer 156, which has a mechanical strength lower than that of the second metal heating layer 155, and to prevent the first metal heating layer 156 from being damaged.
In addition, the edge portion of the first metal heating layer 156 is configured to protrude outward from the both ends in the width direction (YY ′ direction) of the induction coil 173 by a length L2.
Here, L2 is a value in the range of 2 mm or more and 3 mm or less.

  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 outer sides of both edges of the first metal heating layer 156 and the second metal heating layer 155. , The ratio of the current density of the eddy current generated in the first metal heat generating layer 156 and the second metal heat generating layer 155 changes, and the amount of heat generated may be different from the central portion. Because.

Due to such a configuration, the width of the first metal heating 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. Yes.
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 the above configuration, when the alternating magnetic flux 170a is generated from the magnetic flux generator 170, the portion of the second metal heating layer 155, which is a ferromagnetic material, mainly facing the magnetic flux generator 170 tries to draw the alternating magnetic flux 170a. . At this time, since the first metal heat generating layer 156 exists between the magnetic flux generator 170 and the second metal heat generating layer 155, when the magnetic flux passes through the first metal heat generating layer 156, the first metal heat generating layer 156 is swung. An electric current is generated.

Here, since the first metal heat generating layer 156 has a lower specific resistance than the second metal heat generating layer 155, an eddy current is concentrated on the first metal heat generating layer 156.
Further, the first metal heat generating layer 156 is thinner than the skin depth of the eddy current, and the current density of the eddy current is increased, so that heat is efficiently generated.
Further, since the alternating magnetic flux 170a that penetrates through the first metal heat generating layer 156 and enters the second metal heat generating layer 155 generates an eddy current in the second metal heat generating layer 155, the second metal heat generating layer 155 is also heated. The

As described above, the first metal heat generating layer 156 and the second metal heat generating layer 155 having different magnetism are combined as heat generating layers, and conditions such as thicknesses are appropriately selected in each layer so that the total heat generation amount of both layers is maximized. Thus, the heat generation efficiency can be increased.
The inventor conducted a temperature increase rate test for confirming the temperature increase rate when the thicknesses of the second metal heat generation layer 155 and the first metal heat generation layer 156 were changed.
(Temperature increase rate test)
FIG. 4 is a diagram illustrating a change in the heating rate when the thickness of the second metal heating layer 155 is fixed to 30 μm and the thickness of the first metal heating layer 156 is changed.

As a result, as shown in the figure, it was found that when the thickness of the first metal heating layer 156 was 15 μm, the temperature rising rate peaked, and the peak value was 9.9 (° C./s·W).
In addition to this, the same test was performed on the second metal heat generating layer 155 with the thickness slightly changed, but none of the above peak values were found.
The fixing unit 5 according to the present embodiment is configured so that the flange member 159 and the first metal heat generating layer 156 having low strength do not come into direct contact with each other, and therefore, the first metal heat generating with relatively low mechanical strength. Breakage of the edge of the layer 156 can be made difficult.

In order to confirm this effect, the inventor uses a fixing belt 153 (hereinafter referred to as “example product”) and a conventional fixing belt (hereinafter referred to as “conventional product”) in the present embodiment. Each of the sections 5 was continuously driven for a long time, and an endurance test was performed to check the time until each fixing belt was damaged.
(Example product specifications)
About the first metal heating layer Thickness: 10 μm
Material: Copper For the second metal heating layer Thickness: 30 μm
Material: Nickel Retraction amount L1 from the side edge of the fixing belt of the first metal heating layer L1: 7 mm
Fixing roller rotation speed: 130 rpm
(Conventional product specifications)
About the first metal heating layer Thickness: 10 μm
Material: Copper For the second metal heating layer Thickness: 30 μm
Material: Nickel The retraction amount L1 of the first metal heat generating layer from the side end of the fixing belt 0 mm
(Similar to the laminated state shown in FIG. 9)
Fixing roller rotation speed: 130 rpm
(Endurance test results)
As shown in FIG. 5, in the conventional product, the fixing belt was damaged when the fixing unit 5 was driven for 25 hours.

On the other hand, in the example product, no damage was observed on the fixing belt even when the fixing unit 5 was driven for 600 hours.
<Method for Producing Second Metal Heating Layer 155 and First Metal Heating Layer 156>
Here, a combination of the second metal heating layer 155 and the first metal heating 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 40 μm or less). To do.
2) Separately, using a diamagnetic material such as copper by drawing, such as spatula drawing (spinning) processing, iron drawing (DI) processing, or electroforming, etc., the thickness is 5 μm or more and 40 μm or less ( Preferably, an endless belt (hereinafter referred to as “diamagnetic metal belt”) having a cylindrical shape with a diameter of 10 μm or more and 15 μm or less is equal to the outer diameter of the nickel belt and shorter than the nickel belt. To do.
3) Press-fit the diamagnetic metal belt into the nickel belt with the core inserted.
4) Mask the surface of the diamagnetic metal belt with tape.
5) Again, by nickel electroforming, plating is performed until the thickness of the nickel layer at both ends of the belt is the same as the thickness of the diamagnetic metal belt 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. 6, a laminated metal layer 154a in which the first metal heating layer 156a is embedded in the second metal 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 diamagnetic metal belt 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.
<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 release layer 158, the elastic layer 157, the first metal heating layer 156, and the second metal heating layer 155 are laminated in this order from the outside. However, the present invention is not limited to this configuration, and it is sufficient that the fixing belt includes at least the first metal heating layer 156 and the second metal heating layer 155.
(2) In the above-described embodiment, the edge of the first metal heat generating layer 156 recedes from the edge of the second metal heat generating layer 155, and the second metal heat generating layer 155 is formed in the retracted portion. Although the flange member 159 and the first metal heat generation layer 156 are configured not to be in direct contact with each other, the present invention is not limited to this configuration. For example, as shown in FIG. The edge of the layer 156b may be configured to recede from the edge of the second metal heating layer 155b.

Even in this case, the first metal heat generation layer 156b and the second metal heat generation 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. The layer 156b does not move in the axial direction alone and does not come into contact with the flange member 159.
(3) In the above embodiment, the fixing roller 150 has the roller shaft 151 having the heat insulating layer 152 formed on the peripheral surface thereof inserted inside the cylindrical fixing belt 153. Although a gap of 0 μm or more and 200 μm or less is provided between the two metal heating layer 155, the present invention is not limited to this configuration.

For example, as shown in FIG. 8, the outer diameter of the fixing belt 153 is enlarged (hereinafter referred to as “fixing belt 253”), the gap is secured about several millimeters, and the gap 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) In the above embodiment, the first metal heating layer 156 is an endless belt made of copper, but may be a diamagnetic material such as aluminum, brass, gold, and silver.

In that case, since the skin depth of the eddy current generated due to the magnetic field generated from the induction coil 173 is also different, it is necessary to appropriately set the thickness of the first metal heating layer 156.
Aluminum, brass, gold, and silver have lower specific resistance than the second metal heating layer 155, and tensile strengths are about 108, 270, 225, and 220 MPa, respectively. The strength of the second metal heating layer 155 is similar to that of copper.
(5) In the above embodiment, the tandem type color printer has been described. However, the present invention is not limited to this, and can be applied 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 156, 156a, 156b First metal heat generating layer 155, 155a, 155b Second metal heat generating layer 157 Elastic layer 158 Release layer 159 Gutter member 160 Pressure roller 161 Roller shaft 162 Elastic Layer 163 Release layer 1 0 magnetic flux generating portion 173 induction coil 201 leakage flux 254 guide plate

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, 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 first metal heating layer made of a diamagnetic material;
A second metal heat generating layer made of a ferromagnetic material, having a mechanical strength higher than that of the first metal heat generating layer, a large specific resistance, and a thick thickness,
The width of the first metal heat generation layer in the axial direction of the first roller is narrower than that of the second metal heat generation layer, and the edge of the first metal heat generation layer recedes toward the belt center at both ends of the belt. A fixing device characterized. The first metal heating layer is made of any one of copper, aluminum, brass, gold and silver,
The fixing device according to claim 1, wherein the second metal heating layer is made of nickel.   The fixing device according to claim 1, wherein a width of the first metal heating layer in an axial direction of the first roller is larger than a maximum width of the recording sheet passing through the fixing nip. The induction coil is disposed at a position facing the second metal heating layer,
The width in the axial direction of the first roller in the first metal heating layer and the second metal heating layer is larger than the width in the axial direction of the first roller in the induction coil. The fixing device according to any one of the above.   An image forming apparatus having the fixing device according to claim 4.

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