JP2003307954A - Fixing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing apparatus capable of coping with a high speed image formation and a full-color image formation and free from the occurrence of an image noise and paper wrinkles, as for the fixing apparatus used for an electrophotographic image forming apparatus. <P>SOLUTION: The fixing apparatus is provided with a fixing roller, an endless belt which circularly moves a 1st press contact roller coming into press contact with the fixing roller from the inside of the belt so as to form a 1st nip part at the upstream part in the recording medium carrying direction, a 2nd press contact roller coming into press contact with the fixing roller from the inside of the belt so as to form a 2nd nip part at the downstream part in the recording medium carrying direction, a belt supporting means for supporting the belt while separating the belt from the fixing roller between the 1st nip part and the 2nd nip part, and a belt heating means for heating the belt between the 1st nip part and the 2nd nip part. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique of a fixing device used in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus such as an electrophotographic printer or a copying machine is provided with a fixing device for fixing an unfixed toner image held on a recording medium such as a recording paper or an OHP sheet. The so-called heat roller method has been widely used as the fixing method in this fixing device. This heat roller type fixing device has a heating roller having a heat source and a pressure roller that is in pressure contact with the heating roller. At least one of the heating roller and the pressure roller has a structure in which an elastic layer made of rubber or the like is provided around a cored bar, and an unfixed toner image is formed in the nip portion which is a deformation region due to the pressure contact of the elastic layer. The toner image is fixed on the recording medium by applying heat and pressure through the recording medium holding the toner.

In recent years, there has been a demand for higher printing speeds and full-color printing in image forming apparatuses, and it has become necessary for the fixing apparatus, which is a component of the image forming apparatus, to support them. For example, when the printing speed is increased, it is necessary to supply the amount of heat for fixing the toner in a shorter time. Further, in forming a full-color image, the toner layer thickness is 3 to 4 times that in the case of a monochrome image, and the amount of toner is large. Therefore, it is necessary to supply a larger amount of heat.

In order to supply a large amount of heat in such a short time, the nip width, which is the length of the nip portion in the conveying direction, is secured as wide as possible, and an unfixed toner image formed on the recording medium is possible. It is desirable to heat it for a long span as long as possible and fix it on the recording medium.

Since the nip portion is formed by pressing a pair of rollers into contact with each other to deform the elastic layer of the rollers,
The nip width in the heat roller method depends on the outer diameter of each roller and the thickness of the elastic layer. Therefore, in order to widen the nip width, it is necessary to increase the diameter of the heating roller and the pressure roller or to increase the thickness of the elastic layer. However, when the diameter of the roller is increased, there are problems that the fixing device becomes large and the recording medium is wound around the roller. When the elastic layer of the heating roller is thickened,
The heat transfer performance to the surface of the roller deteriorates, and it takes time to supply a sufficient amount of heat for fixing the toner, which makes it difficult to support high-speed printing. In addition, power consumption for sufficiently heating the surface of the heating roller increases, which causes a problem of high cost.

In order to solve the above problems, as a fixing device capable of widening the width of a nip portion, an endless belt or a sheet belt is supported by a plurality of rollers, and a thermal belt is pressed against the other rollers. System fixing devices have been proposed. In this belt-type fixing device, since the belt has a low heat capacity, the time required to raise the temperature is short and the amount of radiant heat is small, so that low power consumption and high-speed printing can be realized. Further, it is possible to make the device compact as compared with a heat roller type fixing device having the same nip width.

For example, in the structure of the fixing device disclosed in Japanese Patent Application Laid-Open No. 10-115990, an endless belt is wound around two pressure contact rollers, and these pressure contact rollers are interposed between the opposing fixing rollers via the belt. It is configured to be pressed. As a result, a wide nip width can be secured, making it possible to support high-speed printing and full-color machines.

[0008]

However, in the fixing device described in Japanese Patent Laid-Open No. 10-115990, it is sandwiched only by the fixing roller and the belt rather than the two nip portions sandwiched by the fixing roller and the pressure contact roller. The pressure at the nip portion is low, and the recording medium conveyance speed is different between the high pressure nip portion and the low pressure nip portion. Therefore, there is a problem that image noise such as color misregistration or bleeding of an image in the fixing step and wrinkles occur when paper is used as a recording medium.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device which is compatible with high-speed and full-color image formation and which is free from image noise and wrinkles on the recording medium.

[0010]

The present inventors have found that the above problems can be solved by using a fixing device having the following structure.

In a fixing device for fixing an unfixed toner image on a recording medium, a fixing roller, an endless belt which circulates, and a first nip portion which is pressed against the fixing roller from the inside of the belt. A first pressure contact roller,
A second pressure roller that presses against the fixing roller from the inside of the belt to form a second nip portion downstream of the nip portion in the recording medium conveyance direction; and the belt between the first nip portion and the second nip portion. And a belt heating unit configured to heat the belt between the first nip portion and the second nip portion.

In the present invention, in order to prevent the occurrence of image noise, the toner image is fixed through a two-step process. First,
As a first step, the toner image is lightly fixed at the first nip portion between the first pressure contact roller and the fixing roller. After that, as a second step, complete fixing is performed in the second nip portion formed by the second pressure contact roller and the fixing roller. By using such a method, it is possible to obtain an image without color shift or blurring.

When fixing the toner by the fixing device, whether the toner stays in the light fixing or complete fixing occurs,
It depends on the amount of heat applied to the toner, and the amount of heat applied is related to the temperature of the heat source, the heating time, and the nip pressure. In order to perform light fixing at the first nip portion and complete fixing at the second nip portion as described above, at least one of the temperature, the nip width, and the nip pressure of the second nip portion is set to the first nip portion. It is necessary to make the value larger than.

Therefore, in the fixing device of the present invention, a belt heating means is provided between the first nip portion and the second nip portion in order to adjust the fixing conditions. The fixing belt heated by the belt heating means first heats the lightly fixed toner in the second nip portion to completely fix the toner. After that, the fixing belt returns to the first nip portion while leaving the residual heat, and heats the unfixed toner for light fixing. As described above, the temperature of the second nip portion is set higher than that of the first nip portion.

In this fixing device, the fixing belt having a smaller heat capacity than the roller is heated. Moreover, as described above, the residual heat is also utilized in the first nip portion, which is effective in reducing the power consumption of the image forming apparatus.

As the belt heating means, those conventionally used as a heat source for a heat fixing device such as a heating roller, a sheet heater, a heater lamp, and an electromagnetic induction heating device can be used. Further, the belt supporting means may also serve as the belt heating means.

The nip width of the first nip portion and the nip width of the second nip portion can be different. Thereby, the heating time in each of the first stage and the second stage can be optimized.

Further, the nip pressure of the first nip portion and the nip pressure of the second nip portion can be set to different magnitudes. The larger the nip pressure is, the more efficiently the heat quantity is transferred to the toner. Therefore, by setting the nip pressure of the second nip portion higher than the nip pressure of the first nip portion,
Fixing conditions suitable for the above-described two-step fixing method can be provided.

Further, the hardness of the first pressing roller and the hardness of the second pressing roller can be different. By independently setting the hardness of each roller, it is possible to adjust the above nip pressure and nip width to more optimal conditions.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A fixing device according to an embodiment of the present invention will be specifically described below with reference to the accompanying drawings.

As an embodiment, an example in which the present invention is applied to a fixing device of a full-color copying machine is shown in FIG. Figure 1
Is an example of a tandem type full color copying machine, but the present invention can be applied to a copying machine using other image forming system such as a 4-cycle type full color copying machine or a monochrome copying machine. Further, the use of the present invention is not limited to a copying machine, but can be applied to any electrophotographic image forming apparatus such as a printer, a facsimile, or a microfilm reader printer.

The copying machine shown in FIG. 1 will be described below. This copying machine includes an image reader unit IR for reading a document image and a print unit PR for reproducing the read image on a recording sheet S as a recording medium.

The image reader unit IR separates an original image into three primary colors of R, G and B by an image sensor such as CCD and reads it. The structure and operation are well known, and the description thereof is omitted.

The printing section PR includes the recording sheet conveyance path 20 formed along the surface of the conveyance belt 27 and the conveyance section 2.
And an image forming unit 3C (cyan), 3M (magenta), 3Y (yellow), 3K (black) for forming images of four colors on the recording paper S in an overlapping manner. Image forming unit 3C, 3
M, 3Y, and 3K are process units 4C, 4M, 4Y, and 4K arranged along the conveyance path 20, and a laser scanning optical system 5.
It is composed of C, 5M, 5Y, and 5K.

The process sections 4C, 4M, 4Y, and 4K are for forming an image by the electrostatic copying method, and the conveyor belt 2 is used.
7, the photosensitive drums 11C, 11M, 1 arranged in parallel above
It is configured around 1Y and 11K. The cleaners 12C, 12M, 12Y, 12K and the charger 1 are provided around the photoconductor drums 11C, 11M, 11Y, 11K.
4C, 14M, 14Y, 14K, developing units 15C, 15
M, 15Y, 15K, etc. are arranged. Further, transfer chargers 16C, 16M, 1 are provided directly below the respective photoconductor drums 11C, 11M, 11Y, 11K via a conveyor belt 27.
6Y and 16K are arranged.

The transport unit 2 is constructed around an endless transport belt 27 stretched via a drive roller 24, a driven roller 25 and a tension roller 26, and the recording paper S is fixed on the transport belt 27. It is designed to be transported at a speed.

Upstream side of the conveyor belt 27 (right side in FIG. 1)
Includes a paper feed cassette 21 for accommodating and storing recording paper S of a predetermined size, a paper feed roller 22 for feeding the recording paper S one by one from the paper feed cassette 21, and the fed recording paper S on a conveyor belt 27. A timing roller 23 that sends out at a predetermined timing is provided.

On the other hand, on the downstream side of the conveyor belt 27, a fixing device 2 for fixing the toner transferred to the recording paper S.
8 and a paper discharge tray 29 for accommodating and storing the recording paper S after completion of fixing. Further, sensors SE1 and SE2 are arranged on the upstream side and the downstream side of the transport belt 27, respectively, to detect the timing of paper feeding, paper jam, and the like.

The operation of the copying machine will be described below.
First, with respect to the image data for each of the R, G, and B color components obtained by the image reader unit IR, the control unit 8
Necessary data processing such as shading correction, density conversion, and edge enhancement are performed. Further, the image data of each reproduction color of C (cyan), M (magenta), Y (yellow), and K (black) is converted, and the image data after the conversion is temporarily stored in the image memory of the control unit 8. .

Then, based on the image data stored in the image memory, laser scanning optical systems 5C, 5M, 5
In Y and 5K, laser light corresponding to each reproduced color is modulated and emitted. Photoconductor drums 11C, 11M, 1
1Y and 11K are rotating clockwise in FIG. 1, and the chargers 14C, 14M, 14Y, and 14K are rotated.
After the surface is uniformly charged by the laser beam, it is exposed and scanned by the laser beam.

By this exposure, each photosensitive drum 11
The electrostatic latent images corresponding to the reproduced colors formed on C, 11M, 11Y, and 11K are the developing devices 15C, 15M, and 15Y,
Each color is developed by 15K to obtain a toner image of each color.

These toner images are transferred to the photosensitive drum 11
Transfer chargers 16C, 16M, 16 are provided at the respective facing portions of C, 11M, 11Y, 11K and the conveyor belt 27.
By Y and 16K, they are sequentially transferred onto the recording paper S fed from the paper feeding cassette 21. After that, the recording paper S on which the four color toner images have been transferred is heated in the fixing device 28, whereby each toner image is fixed on the recording paper S. After the image is fixed, the recording paper S is discharged to the paper discharge tray 29.

(Fixing Device) FIG. 2 is a schematic view of the first embodiment of the fixing device 28 in the present invention. As shown in FIG. 2, the fixing device 28 includes an endless fixing belt 36. The fixing belt 36 is made of carbon steel, stainless steel,
A thin, preferably seamless belt formed of nickel, a heat resistant resin or the like, and having a heat resistant elastic body layer (for example, silicone rubber) and / or a heat resistant release layer (for example, fluorine resin) on the surface.

A first pressure contact roller 31 and a second pressure contact roller 32 are arranged inside the fixing belt 36 to support the fixing belt 36.

First pressure contact roller 31 and second pressure contact roller 32
Has a structure in which an elastic layer having a low hardness is provided around the core metal from the viewpoint of ensuring a predetermined nip width. Porous rubber is preferable as the material of the elastic layer, and foamed silicone rubber is used in this embodiment.

In the present embodiment, the first pressure contact roller 31 has an elastic layer hardness (Asker C) of 30 °, and the second pressure contact roller 32 has an elastic layer hardness (Asker C) of 40. The thing of ° was used. The suitable value of the hardness (Asker C) of the elastic layer of the first pressure contact roller 31 is 10 ° to 50 °, preferably 20 ° to 40 °.
Further, the preferable value of the second pressure contact roller 32 is 20 ° to 60 °,
It is preferably 30 ° to 50 °.

The first pressure contact roller 31 and the second pressure contact roller 32 are biased toward the fixing roller 33 by springs (not shown). As a result, the first pressing roller 3
The first and second pressing rollers 32 are pressed against the fixing roller 33 via the fixing belt 36 to form a first nip portion 41 and a second nip portion 42, respectively.

The pressure of each nip portion can be adjusted independently. In this embodiment, the pressure of the first nip portion 41 is 50 kPa and the pressure of the second nip portion 42 is 200 kPa.
It was Pa. In addition, as a suitable range of each nip pressure, the first nip portion 41 is 10 k to 150 kPa, preferably 30 k to 70 kPa, and the second nip portion 42.
Is 100 k to 250 kPa, preferably 170 k to 23
It is 0 kPa. It is desirable to set the second nip portion 42 to a higher pressure than the first nip portion 41, and the fixing conditions suitable for the above-described two-step fixing method can be obtained.

The nip width of the first nip portion 41 and the second nip portion 42 formed by the first pressure contact roller, the second pressure contact roller and the fixing roller is a condition for determining the heating time of the toner during fixing. . In the present embodiment, by setting the hardness of the first and second pressing rollers and the pressure of the nip portion as described above, the width of the first nip portion was 3 mm and the width of the second nip portion was 7 mm. The preferred range is
The first nip portion is 1 to 7 mm, preferably 2 to 4 mm, and the second nip portion is 2 to 15 mm, preferably 5 to 9 m.
m. It is desirable to make the width of the second nip portion larger than the width of the first nip portion.

The fixing roller 33 has a cored bar, an elastic layer provided on the outer surface of the cored bar, and a release layer for imparting releasability of the toner. The core metal may be made of aluminum or copper, and silicone rubber is preferable as the material of the elastic layer. Further, the release layer is preferably formed by using fluorine rubber or fluorine resin.

The fixing roller 33 is connected to a motor (not shown) and is driven to rotate in the direction of arrow 45.
A halogen heater lamp 38 as a heat source is provided at the center of the fixing roller. In addition to the heater lamp, a resistance heating element, an electromagnetic induction heating device, or the like may be used as the heat source.

Further, as described above, in the present invention, the endless fixing belt which circulates and moves is used, and not only the second nip portion immediately after the fixing belt is heated by the belt heating means but also the second nip portion at the first nip portion. Since the high temperature can be maintained by the residual heat after passing through the part, the effect of the present invention can be obtained without providing a heat source in the fixing roller.

Between the first pressure contact roller and the second pressure contact roller, there is provided a belt support means for retracting the fixing belt 36 from the fixing roller 33 between the first nip portion 41 and the second nip portion 42. There is. In this embodiment, the heating roller 3
4a serves both as a belt supporting means and a belt heating means.
The heating roller 34 a is provided at a position where it does not contact the fixing roller, and is in contact with the outer surface of the fixing belt 36. From the viewpoint of supplying heat to the fixing belt 36, the heating roller 34a is preferably a member having high thermal conductivity, and for example, a member made of aluminum or copper is preferably used.
Further, it is desirable to form a surface layer using fluorine rubber or fluorine resin on the surface.

Further, the heating roller 34a is provided with a halogen heater lamp 39a which is a heat source in the center thereof. A resistance heating element, an electromagnetic induction heating device, or the like may be used as the heat source.

The heating roller 34a is provided with a thermistor (not shown), and the detected temperature is fed back to a control device of a heat source (not shown) so that the heating roller 34a can be heated.
The temperature is adjusted.

From the second pressure contact roller 32 to the first pressure contact roller 3
The fixing belt 36 returning to 1 is supported from the inside by the idle roller 35.

Next, the basic operation of the fixing device 28 will be briefly described. In this fixing device 28, when a motor (not shown) is driven, the fixing roller 33 rotates in the direction of arrow 45.
As a result, the fixing belt 36 moves in the direction of the arrow 46,
The first pressure contact roller 31 is driven to rotate in the direction of arrow 48, and the second pressure contact roller 32 is driven to rotate in the direction of arrow 47. The recording paper S conveyed along the paper feed side guide 52 and the unfixed toner adsorbed on the recording paper S are
The first nip portion 41 formed by the pressing roller 31 and the fixing roller 33 is heated and pressed. The first nip portion 41 is set so that the amount of heat and the pressure to completely fix the unfixed toner are not supplied, and the unfixed toner is lightly fixed on the recording paper S here. At this light fixing stage, the toner is melted and does not scatter, but it is in an incomplete fixing state.

The recording paper S that has passed through the first nip portion 41 moves in the direction of arrow 49 in FIG. 1 as the fixing roller 33 rotates, and is sent to the second nip portion 42. Since the first pressure contact roller 31 and the second pressure contact roller 32 have lower elasticity than the fixing roller 33, the first nip portion 41 and the second nip portion 42 mainly correspond to the first pressure contact roller 31 and the second pressure contact roller 32. It is formed by recessing the elastic layer. Therefore, the change in the curvature of the transport path from the inlet of the first nip portion 41 to the outlet of the second nip portion 42 is small, and the recording sheet S is easily transported along the outer shape of the fixing roller 33. Further, since the toner adhering surface of the recording paper S is in close contact with the fixing roller 33, the recording paper S at the exit of the first nip portion 41.
However, it is difficult for the fixing roller 33 to be easily peeled off.
Further, by providing a guide 54 below the fixing roller 33, the recording paper S is surely moved from the first nip portion 41 to the second nip portion 42.

After passing through the first nip portion 41, the fixing belt 36 is heated in the contact area (belt heating area 37) between the belt supporting means and the heating roller 34a which also serves as the belt heating means, and then is transferred to the second nip portion 42. Moving. Therefore, the second
The nip portion 42 supplies a larger amount of heat to the recording paper S than the first nip portion 41. The recording paper S is heated and pressed again at the second nip portion, and the toner is completely fixed on the recording paper S.

Thereafter, the recording paper S is peeled off from the fixing roller 33 by the separating claw 50 at the exit of the second nip portion 42,
It is guided to the paper discharge side guide 53.

By using the fixing device having the above structure, it is possible to form an image free from noise such as color misregistration and bleeding and prevent wrinkles on the recording paper.

FIG. 3 shows a second embodiment of the present invention. The heating roller 34b also functions as the idle roller 35 shown in FIG. 2 although it is substantially the same as the first embodiment. That is, the heating roller 34b also serves as a belt supporting unit, a belt heating unit, and an idle roller. By reducing the number of rollers in this way, it is possible to reduce image noise, prevent wrinkles on the recording paper, and downsize the fixing device.

FIGS. 4 and 5 show the third and fourth aspects of the present invention.
The above-mentioned embodiments are shown, and the effects similar to those of the first and second embodiments can be obtained in these embodiments. Here, unlike the first and second embodiments, a belt heating unit different from the heating roller is provided between the first pressure contact roller and the second pressure contact roller. Here, since the fixing belt 36 is directly heated, not through the heating roller, heating control of the belt becomes easy. As the heating means, for example, a heater element formed of a metal foil such as stainless steel, iron-nickel alloy, nickel-chromium alloy, copper-nickel alloy, or a planar heater using ceramics can be used. Also, an electromagnetic induction heating device can be used.

In the third embodiment shown in FIG. 4, a belt support roller 34c having no heating means is arranged between the first pressure contact roller 31 and the second pressure contact roller 32, and passes through the first nip portion. After that, the fixing belt 36 is once retracted from the fixing roller 33.

It is preferable to use, as the belt supporting roller 34c, a roller having a low hardness elastic layer such as foamable silicone rubber as in the above pressure contact roller, from the viewpoint of securing a heating area and heat insulating property of the roller. Further, it is also possible to use a roller in which the outer circumference of the core metal is coated or covered with a fluororesin. In this case, the fixing belt 36 is used.
It is possible to secure the transport stability of.

A ceramic heater 39c is arranged on the side opposite to the belt supporting roller 34c with respect to the fixing belt 36, and the fixing belt 36 is heated in the belt heating area 37.

In the fourth embodiment shown in FIG. 5, the fixing belt 3 is provided between the first nip portion 41 and the second nip portion 42.
6 is supported by the two belt supporting rollers 34d, and the fixing belt 36 is heated in the belt heating region 37 by using the ceramic heater 39d while the fixing belt 36 is extended. The fixing belt 36 is flat and is in contact with the planar ceramic heater 39d, and the amount of heat applied is the same as the fixing belt 36.
Since it is used only for heating, the heating efficiency can be improved.

Although not shown, the fixing belt 3
The surface of the belt heating region 37 on the fixing roller side of 6 may be heated.

[0059]

As described above, in the fixing device of the present invention, the heating means is arranged between the two fixing rollers forming the nip. After the toner adsorbed on the recording medium is heated and pressed in the first nip portion for light fixing, the pressure is once released and sent to the second nip portion, and heated and pressed at a higher temperature to completely fix the toner. Through these steps, the fixing device can be applied to high-speed or full-color image formation and does not generate image noise such as image bleeding or color misregistration.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus using a fixing device of the present invention.

FIG. 2 is a schematic view showing a first embodiment of a fixing device according to the present invention.

FIG. 3 is a schematic view showing a second embodiment of the fixing device according to the present invention.

FIG. 4 is a schematic view showing a third embodiment of the fixing device according to the present invention.

FIG. 5 is a schematic diagram showing a fixing device according to a fourth embodiment of the invention.

[Explanation of symbols]

IR; Image reader section PR; Print department S: Recording paper SE1, SE2; sensor 2; Transport section 3C, 3M, 3Y, 3K; image forming unit 4C, 4M, 4Y, 4K; process section 5C, 5M, 5Y, 5K; laser scanning optical system 8; Control unit 11C, 11M, 11Y, 11K; photoconductor drum 12C, 12M, 12Y, 12K; cleaner 14C, 14M, 14Y, 14K; Charger charger 15C, 15M, 15Y, 15K; developing device 16C, 16M, 16Y, 16K; Transfer charger 20: Recording paper conveyance path 21; Paper feed cassette 22; Paper feed roller 23; Timing roller 24; drive roller 25; driven roller 26; Tension roller 27; Conveyor belt 28: Fixing device 29; Paper output tray 31; First pressing roller 32; Second pressing roller 33; fixing roller 34a, 34b; heating roller 34c, 34d; belt support rollers 35; Idol Laura 36; fixing belt 37; Belt heating area 38; Heater lamp 39a, 39b; heater lamp 39c, 39d; ceramic heater 41; First nip portion 42; Second nip portion 43; heating area 45: An arrow indicating the rotation direction of the fixing roller 46; Arrow indicating the moving direction of the fixing belt 47; arrow indicating the direction in which the second pressure contact roller rotates 48; arrow indicating the direction in which the first pressure contact roller rotates 49; arrow indicating the passage of the recording paper 50; Separation claw 52; Paper feed side guide 53; Paper ejection side guide 54; Guide

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Yamada             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. (72) Inventor Norito Hagimoto             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. (72) Inventor Hiroyuki Maeda             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. F term (reference) 2H033 AA01 AA15 AA20 BA11 BA12                       BA26 BB29 BB30 BB33 BB34                       BB38

Claims (6)

[Claims] 1. A fixing device for fixing an unfixed toner image on a recording medium, a fixing roller, an endless belt that circulates, and a first nip portion that is pressed against the fixing roller from the inside of the belt. A first pressure contact roller for forming a
A second pressure roller that presses against the fixing roller from the inside of the belt to form a second nip portion downstream of the nip portion in the recording medium conveyance direction; and the belt between the first nip portion and the second nip portion. And a belt heating unit that heats the belt between the first nip portion and the second nip portion. 2. The fixing device according to claim 1, wherein the belt supporting means also serves as the belt heating means. 3. The nip width of the first nip portion and the second nip portion
The fixing device according to claim 1, wherein the nip width of the nip portion is different. 4. The nip pressure of the first nip portion and the second nip pressure.
The fixing device according to claim 3, wherein the nip pressure of the nip portion is different. 5. The nip pressure of the first nip portion is the second nip pressure.
The fixing device according to claim 4, wherein the fixing pressure is lower than the nip pressure of the nip portion. 6. The fixing device according to claim 3, wherein the hardness of the first pressure contact roller and the hardness of the second pressure contact roller are different from each other.