JP2002148978A - Belt fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly fix toner on a recording medium by uniformly heating, pressurizing the toner on the recording medium even without using a belt for fixation in which an elastic layer is provided in belt fixing device to pressurize the flexible belt for fixation provided on the outer peripherals of a heat roller on the recording medium to which the toner is supplied by heating the belt by the heat roller and to fix the toner on the recording medium. SOLUTION: In the belt fixing device to pressurize the flexible belt 10 for fixation provided on the outer peripherals of the heat roller 12 on the recording medium 1 to which the toner t is supplied by heating the belt by the heat roller and to fix the toner o the recoding medium, the heat roller in which the elastic layer 12b with the thickness of >=100 μm is provided on the outer peripherals of a cylindrical core bar 12a and the belt for fixation consisting of a resin belt with the thickness of <=70 μm are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used for fixing a toner supplied to a recording medium to the recording medium in an image forming apparatus such as a copying machine or a printer, and more particularly, to an outer periphery of a heating roller. A belt fixing device that heats a flexible fixing belt provided in the printer with a heating roller and presses the fixing belt onto a recording medium supplied with toner to fix the toner on the recording medium. It is about.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, toner is supplied onto a recording medium, and the toner is fixed on the recording medium by a fixing device.

Here, as such a fixing device, conventionally, as shown in FIG. 1, a recording medium 1 to which toner t is supplied is guided between a pair of fixing rollers 2 and 3, and the pair of fixing rollers 2 and 3 is used. Toner t between fixing rollers 2 and 3
Is fixed on the recording medium 1.

Further, a pair of fixing rollers 2,
In fixing the toner t to the recording medium 1 during the interval 3, the toner t is sufficiently fixed to the recording medium 1 so that
Heating devices 4 and 5 are provided in the fixing rollers 2 and 3, and the fixing rollers 2 and 3 are made of an elastic material such as rubber on the outer peripheral surfaces of metal cores 2a and 3a. Each of the fixing rollers 2 and 3 is heated by the above-mentioned heating devices 4 and 5, and the fixing rollers 2 and 3 are pressed against each other. The length of the nip between the elastic layers 2b and 3b provided on the outer peripheral portions of the recording medium 1 and the toner t is sufficiently heated and pressed so that the toner t is fixed to the recording medium 1.

On the other hand, in recent years, the speed of the image forming apparatus as described above has been increased, and it is necessary to sufficiently fix the toner t to the recording medium 1 at a high speed. In a full-color image forming apparatus, In addition, the toner t of a plurality of colors is supplied onto the recording medium 1 and the layer of the toner t becomes thick, and it is necessary to sufficiently fix the toner t having such a thick layer on the recording medium 1.

Here, in the above fixing device,
In order to sufficiently fix the toner t to the recording medium 1 at a high speed, or to sufficiently fix the thick toner t to the recording medium 1, the toner t is applied between the fixing rollers 2 and 3. It became necessary to further increase the length of the nip portion to be heated and pressed.

In order to increase the length of the nip portion between the fixing rollers 2 and 3 as described above, the diameter of each of the fixing rollers 2 and 3 may be increased, or each of the fixing rollers 2 and 3 may be increased. For example, a method of increasing the thickness of the elastic layers 2b and 3b provided on the outer peripheral portion of the base 3 can be considered.

However, as described above, the fixing rollers 2, 3
When the diameter of the fixing device is increased, the fixing device becomes larger,
There is a problem that the recording medium 1 is likely to be wound around the fixing roller 2 that comes into contact with the toner t. Further, when the elastic layers 2b and 3b provided on the outer peripheral portions of the fixing rollers 2 and 3 are thickened, It becomes difficult to transfer heat to the outer peripheral surfaces of the fixing rollers 2 and 3, so that the toner t cannot be sufficiently heated, the toner t cannot be sufficiently fixed on the recording medium 1, and the outer circumference of each of the fixing rollers 2 and 3. In order to sufficiently heat the surface, a large amount of electric power is required, and there has been a problem that the running cost is high.

For this reason, in recent years, a flexible fixing belt is provided on the outer periphery of the heating roller, and the fixing belt is heated by the heating roller and pressed against the recording medium to which the toner has been supplied. A belt fixing device adapted to fix the toner to the toner has been used.

Here, in such a belt fixing device, when the fixing belt is pressed onto the recording medium to which the toner is supplied to fix the toner on the recording medium, the toner is appropriately fixed on the recording medium. In order to achieve this, a belt provided with an elastic layer made of an elastic material such as rubber on a flexible belt base made of metal or resin is used as the fixing belt. Has been brought into close contact with the toner on the recording medium, and the toner on the recording medium is heated and pressed by the fixing belt.

However, the provision of the elastic layer of rubber or the like on the flexible belt base made of metal or resin as described above requires the elastic layer of rubber or the like on the outer peripheral surface of the metal core. Is very troublesome as compared with the case of providing the elastic layer, the area for providing the elastic layer is also large, the manufacturing cost is high, and it is very difficult to provide a uniform elastic layer. There has been a problem that it is not possible to heat and press uniformly.

Further, when the fixing belt in which the flexible belt base material is provided with the elastic layer such as rubber is provided on the outer periphery of the heating roller and is moved, the fixing belt is composed of the belt base material and rubber. There is also a problem that a load is applied between the elastic layer and the elastic layer provided on the belt base material and the elastic layer peels off.

[0013]

SUMMARY OF THE INVENTION According to the present invention, a flexible fixing belt provided on the outer periphery of a heating roller is heated by a heating roller, and the fixing belt is placed on a recording medium supplied with toner. It is an object of the present invention to solve the above-described problem in a belt fixing device that presses and fixes a toner on a recording medium.

That is, according to the present invention, in the above-described belt fixing device, even if a fixing belt provided with an elastic layer made of an elastic material such as rubber is not used, the fixing device can be used.
The toner on the recording medium is uniformly heated and pressed,
It is an object of the present invention to appropriately fix toner on a recording medium.

[0015]

In the first belt fixing device according to the present invention, in order to solve the above-mentioned problems, a flexible fixing belt provided on the outer periphery of the heating roller is heated by the heating roller. In a belt fixing device that heats and presses the fixing belt onto a recording medium to which toner is supplied to fix the toner on the recording medium, an elastic layer having a thickness of 100 μm or more is formed around a cylindrical cored bar. Is used, and a fixing belt made of a resin belt having a thickness of 70 μm or less is used.

Further, as in the first belt fixing device, a heating roller having an elastic layer having a thickness of 100 μm or more provided on the outer periphery of a cylindrical core is used, and a resin belt having a thickness of 70 μm or less is used. When the fixing belt is heated by a heating roller and pressed against a recording medium supplied with toner, an elastic layer provided on the heating roller is deformed, and the fixing belt is The toner adheres to the toner on the recording medium, and the toner on the recording medium is uniformly heated and pressed by the fixing belt, so that the toner is appropriately fixed on the recording medium.

Further, in the second belt fixing device according to the present invention, in order to solve the above-mentioned problem, a flexible fixing belt provided on the outer periphery of the heating roller is heated by the heating roller. In a belt fixing device in which the fixing belt is pressed onto a recording medium to which toner is supplied to fix the toner on the recording medium, a heating roller having an elastic layer provided on an outer periphery of a cylindrical core is used. A fixing belt made of a resin belt was used, and the rubber hardness at a portion where the fixing belt was in contact with the outer periphery of the heating roller was set to be less than 50 degrees. The rubber hardness is a JIS-A rubber hardness measured according to JIS K6301.

Then, as in the second belt fixing device, the fixing is performed by using a heating roller in which an elastic layer having a thickness is provided on the outer periphery of a cylindrical metal core and a fixing belt made of a resin belt. When the fixing belt is heated by the heating roller and pressed on the recording medium to which the toner is supplied, the fixing belt is heated by the heating roller so that the rubber hardness at the portion where the belt contacts the outer periphery of the heating roller is less than 50 degrees. The elastic layer provided is appropriately deformed, and the fixing belt adheres to the toner on the recording medium, and the toner on the recording medium is uniformly heated and pressed by the fixing belt, so that the toner is applied to the recording medium. It will be properly established.

When a fixing belt made of a resin belt is used as in the first and second belt fixing devices, a flexible belt base made of metal, resin, or the like is used as a base material. Compared to a conventional fixing belt provided with an elastic layer made of an elastic material, the production is easier and the cost is lower, and the elastic layer provided on the belt base material like the conventional fixing belt is peeled off. Without doing so, the fixing belt can be used stably for a long time.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a belt fixing device according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings.

In the belt fixing device of this embodiment, as shown in FIG. 2, a fixing belt 10 is attached to the outer periphery of a heating roller 12 and a supporting roller 13 in which a heating device 11 such as a heater lamp is provided. Along with
The heating roller 12 presses the fixing belt 10 against a pressure roller 15 in which a heating device 14 such as a heater lamp is provided.

With the rotation of the heating roller 12, the supporting roller 13 and the pressing roller 15, the fixing belt 10 is moved between the heating roller 12 and the supporting roller 13, and Heating devices 11, 14
Heats the heating roller 12 and the pressure roller 15, and heats the fixing belt 10 with the heating roller 12 and the pressure roller 15, so that the toner t supplied to the recording medium 1 comes into contact with the fixing belt 10. Thus, the recording medium 1 to which the toner t has been supplied is fixed to the fixing belt 10 and the pressing roller 15.
Then, the toner t supplied to the recording medium 1 is heated and pressed between the fixing belt 10 and the pressure roller 15 so as to be fixed on the recording medium 1.

In the belt fixing device of this embodiment, the heating roller 12 is such that a cylindrical cored bar 12a provided with an elastic layer 12b having a thickness of 100 μm or more on the outer periphery thereof is used. In addition, as shown in FIG. 3, a belt 10a made of resin and a release layer 10b made of resin is provided on the surface of the belt 10 for fixing. When the belt 10 is wound around the outer periphery of the heating roller 12 and the supporting roller 13, the fixing belt 1
0 is such that the rubber hardness at the portion in contact with the outer periphery of the heating roller 12 is less than 50 degrees.

The material of the elastic layer 12b provided on the outer periphery of the cored bar 12a in the heating roller 12 is as follows.
A known elastic material can be used, and for example, silicone rubber, fluorine rubber, or the like can be used. However, it is preferable to use silicone rubber having a small surface tension and excellent elasticity and thermal stability. As such silicone rubber, RTV silicone rubber, HT
V silicone rubber or the like can be used. Specifically,
Polydimethyl silicone rubber (MQ), methyl phenyl silicone rubber (PMQ), methyl vinyl silicone rubber (VMQ), fluorosilicone rubber (FVMQ), or the like can be used.

As in the belt fixing device shown in this embodiment, a heating device 11 such as a heater lamp is provided inside a heating roller 12, and the heating device 11 heats the heating roller 12 and the fixing belt 10. In order to ensure that the heating roller 12 and the fixing belt 10 are quickly heated, the thickness of the elastic layer 12b provided on the heating roller 12 is preferably set to 700 μm or less, and more preferably, the thickness of the elastic layer 12b is reduced. 200 to 5 thickness
It should be within the range of 00 μm.

Here, like the heating roller 12 described above,
In providing the elastic layer 12b on the outer periphery of the cored bar 12a, for example, a coating liquid using a material such as rubber used for the elastic layer 12b is prepared, and the coating liquid is applied to the outer peripheral surface of the cored bar 12a by a known coating method. It can be applied and dried. As the coating method, for example, a kneader coating method, a bar coating method, a curtain coating method, a spin coating method, a dip coating method, and the like can be used.From the viewpoint of productivity and the like, a dip coating method is used. Is preferred.

On the other hand, as a material of the belt substrate 10a in the fixing belt 10, for example, a resin such as thermosetting polyimide, thermoplastic polyimide, polyamide, or polyamideimide can be used.
In order to enhance the heat resistance, abrasion resistance, chemical resistance, etc., it is preferable to use the belt base material 13a made of thermosetting polyimide.

As a material of the release layer 10b provided on the surface of the belt base material 10a, it is preferable to use a resin having low adhesion of the toner t, for example, a perfluoroalkoxy fluororesin (PFA), Fluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), polyethylene / tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polychloroethylene trifluoride (PCTFE), vinyl fluoride (PVF) ) Is preferably used.

In using the fixing belt 10 in which the release layer 10b made of resin is provided on the surface of the belt base material 10a made of resin, the thickness of the fixing belt 10 is reduced. If the thickness of the fixing belt 10 is too thin, the strength of the fixing belt 10 becomes weak, and the fixing belt 10 is gradually deformed and damaged, and stable fixing cannot be performed for a long time. It is preferable to set it as above, and it is more preferable to set it in the range of 30 to 50 μm.

Further, in the belt fixing device of this embodiment, the above-mentioned pressure roller 15 is also configured such that an elastic layer 15b is provided on the outer periphery of a cylindrical cored bar 15a. Further, the elastic layer 15b
A release layer (not shown) may be provided on the substrate.

Using the heating roller 12 and the fixing belt 10 as described above, the fixing belt 10 is heated by the heating roller 12 as described above, and is pressed against the recording medium 1 to which the toner t is supplied. Is heated and pressed between the fixing belt 10 and the pressure roller 15, the elastic layer 12b provided on the heating roller 12 is appropriately deformed, and the fixing belt 10
To the toner t by the fixing belt 10.
Is uniformly heated and pressurized, and is appropriately fixed to the recording medium 1.

In the belt fixing device of this embodiment, the fixing belt 10 is wound around the outer periphery of the heating roller 12 and the supporting roller 13 as described above, and the fixing belt 10 is connected to the heating roller 12 and the supporting roller. 13, but as shown in FIG. 4,
The fixing belt 10 is provided on the outer periphery of the heating roller 12, and the heating roller 12 and the pressing roller 15 are brought into pressure contact with each other via the fixing belt 10 to form a nip portion, and the holding member 16 having a columnar shape is used. The fixing belt 10 is pressed against the outer peripheral surface of the heating roller 12 along the axial direction thereof, and the fixing belt 10 is separated from the outer peripheral surface of the heating roller 12 on the downstream side of the nip portion in the feeding direction of the recording medium 1. It is also possible to form a slack portion and bring the slack portion into contact with the outer peripheral surface of the pressure roller 15.

Then, the toner t supplied to the recording medium 1 by the belt fixing device as shown in FIG.
When the fixing belt 10 is heated by the heating roller 12 and the pressure roller 15, the fixing belt 10 is heated by the rotation of the heating roller 12 and the pressure roller 15. The recording medium 1 is moved to the outer peripheral side so that the surface of the recording medium 1 to which the toner t is supplied comes into contact with the fixing belt 10, and the recording medium 1 is guided between the fixing belt 10 and the pressure roller 15. The toner t supplied to the recording medium 1 between the fixing belt 10 and the pressure roller 15 heated at the nip portion
Is heated and pressed to fix the recording medium 1, and further downstream of the nip portion in the feed direction of the recording medium 1, the contact portion where the slack portion of the fixing belt 10 and the other fixing roller 12 contact each other. The recording medium 1 is nipped so that the toner t is fixed on the recording medium 1.

In this case, the heating roller 1
The elastic layer 12b provided on the recording medium 1 is appropriately deformed, so that the fixing belt 10 properly adheres to the toner t on the recording medium 1, and the toner t is uniformly heated and pressed by the fixing belt 10. The image is appropriately fixed on the recording medium 1.

Next, in the belt fixing device shown in FIG. 2, the thickness of the belt base 10a and the release layer 10b of the fixing belt 10 is changed, and the thickness of the elastic layer 12b provided on the heating roller 12 is changed. In the belt fixing device of the embodiment satisfying the conditions of the present invention, a modified experiment was conducted, and the toner t
Clarify that can be properly established.

In this experiment, the fixing belt 10 was a belt base 10 made of polyimide resin.
a surface of perfluoroalkoxy fluororesin (PF
A) provided with a release layer 10b made of A), and as shown in Table 1 below, the belt base material 10a
And the thickness of the release layer 10b is set to 5 μm and 10 μm, and the thickness of the entire resin fixing belt 10 is changed within the range of 20 to 80 μm. The fixing belt 10 was used.

[0037]

[Table 1]

The heating roller 12 has a thickness of 2 mm.
elastic layer 1 made of silicone rubber having a rubber hardness of 20 degrees around the outer periphery of an iron core bar 12a having an outer diameter of 60 mm and an outer diameter of 60 mm.
2b, and as shown in Table 2 below, five types of heating rollers 12 in which the thickness of the elastic layer 12b is changed in the range of 50 to 700 μm are used. A heater lamp was provided as the heating device 14 inside.

The support roller 13 has an outer diameter of 1
The pressure roller 15 is made of an aluminum core having a thickness of 2 mm and the outer circumference of an iron core bar 15 a having an outer diameter of 60 mm. The elastic layer 15b is provided, and a release layer made of perfluoroalkoxy fluororesin (PFA) having a thickness of 50 μm is provided on the elastic layer 15b.

Then, as described above, the fixing belt 10 is wrapped around the outer periphery of the heating roller 12 and the supporting roller 13,
In this state, a force of 80 N is applied to the support roller 13 so as to separate from the heating roller 12 to apply tension to the fixing belt 10, and the fixing belt 10 is applied to the pressing roller 15 by the heating roller 12 at 400 N. Pressed by force.

Here, as described above, each fixing belt 10
Is applied to the outer periphery of each heating roller 12 and the supporting roller 13 to apply a tension, and the rubber hardness at a portion where each fixing belt 10 contacts the outer periphery of each heating roller 12 is measured by a commercially available rubber hardness tester. (Micro rubber hardness meter MD-1 manufactured by Kobunshi Keiki Co., Ltd.), and the results are shown in Table 2.

Then, while using a commercially available color printer (ColorPageProL manufactured by Minolta),
A yellow toner and a magenta toner obtained by adding a polyethylene wax to each of the yellow toner and the magenta toner used in this commercially available color printer are used. A red solid image is formed on the entire surface of the recording medium 1 made of A4 size recording paper at an amount of ² mg / cm ² , and this is combined with each of the fixing belts 10 and each of the heating rollers 12. The fixing was performed by each of the belt fixing devices used, and the obtained image was examined for gloss unevenness, temperature fluctuation and durability of each fixing belt 10, and the results are shown in Table 2.

Here, regarding the gloss unevenness of the image, the fixing is performed so that the temperature of the surface of the fixing belt 10 becomes 170 ° C. in each belt fixing device, and the gloss unevenness in the obtained image is visually evaluated. ◎, a case where there was no gloss unevenness and very good, ○ when no gloss unevenness was a problem, and x when a gloss unevenness occurred and became a problem.

As for the temperature fluctuation in the fixing belt 10, the surface temperature of the fixing belt 10 is 170 ° C.
Each of the heating devices 11 and 14 provided on the heating roller 12 and the pressure roller 15 is controlled so as to perform continuous fixing at a speed of 40 sheets per minute by each belt fixing device. The temperature fluctuation on the surface of the belt 10 is measured,
The case where the temperature variation was 30 ° C. or less was indicated by “○”, and the case where the temperature exceeded 30 ° C. was indicated by “X”. Here, when the temperature fluctuation on the surface of the fixing belt 10 exceeds 30 degrees, a difference in gloss occurs between the images obtained under the respective temperature conditions.

With respect to the durability of the fixing belt 10, fixing is performed for 1000 hours continuously by each belt fixing device so that the surface temperature of the fixing belt 10 becomes 170 ° C. The deformation due to the elongation of the end of the sample was examined, and the case where there was no deformation was indicated by ○, and the case where it was slightly deformed was indicated by Δ.

[0046]

[Table 2]

As is apparent from the result, the elastic layer 12
b, a heating roller 12 having a thickness of 100 μm or more, and a fixing belt 1 comprising a resin belt having a thickness of 70 μm or less.
In the belt fixing device in which the rubber hardness at the portion where the fixing belt 10 is brought into contact with the outer periphery of the heating roller 12 is less than 50 degrees, a good image with less gloss unevenness can be obtained. .

Further, when the heating roller 12 having the thickness of the elastic layer 12b of 500 μm or less is used, the temperature fluctuation in the fixing belt 10 is reduced, and
When the fixing belt 10 made of a resin belt of 0 μm or more was used, the durability of the fixing belt 10 was also increased. In particular, while using the heating roller 12 in which the thickness of the elastic layer 12b is in the range of 200 to 500 μm,
When the fixing belt 10 made of a resin belt having a thickness in the range of 0 to 50 μm is used, a very good image can be obtained without any gloss unevenness, and the temperature on the surface of the fixing belt 10 can be improved. , The difference in gloss between images is reduced, and the deformation of the fixing belt 10 is also reduced, so that proper fixing can be performed for a long period of time.

[0049]

As described in detail above, the first belt fixing device according to the present invention uses a heating roller in which a cylindrical core is provided with an elastic layer having a thickness of 100 μm or more on the outer periphery thereof. Since a fixing belt made of a resin belt having a thickness of 70 μm or less is used, when the fixing belt is heated by a heating roller and pressed onto a recording medium to which toner is supplied, the fixing belt is provided on the heating roller. The elastic layer is deformed and the fixing belt adheres to the toner on the recording medium, and the toner on the recording medium is uniformly heated and pressed by the fixing belt, so that the toner is appropriately fixed on the recording medium. It became so.

In the second belt fixing device according to the present invention, a fixing roller made of a resin belt and a heating roller provided with an elastic layer on the outer periphery of a cylindrical cored bar are used for fixing. Since the rubber hardness at the portion where the belt was in contact with the outer periphery of the heating roller was set to 50 degrees or less, when the fixing roller was heated by the heating roller and pressed against the recording medium to which the toner was supplied, the heating was performed. The elastic layer provided on the roller is appropriately deformed,
The fixing belt properly adheres to the toner on the recording medium, and the toner on the recording medium is uniformly heated and pressed by the fixing belt, so that the toner is appropriately fixed on the recording medium.

Further, in the first and second belt fixing devices of the present invention, since the fixing belt composed of the resin belt is used as described above, the flexible belt made of metal or resin is used. Compared with conventional fixing belts that have an elastic layer made of an elastic material such as rubber on the base material, the production is easier and the cost is lower, and the belt base material is similar to the conventional fixing belt. The fixing belt can be used stably for a long time without the provided elastic layer peeling off.

[Brief description of the drawings]

FIG. 1 is a schematic illustration of a conventional fixing device in which a recording medium supplied with toner is guided between a pair of fixing rollers to fix the toner on the recording medium.

FIG. 2 is a schematic explanatory diagram of a belt fixing device according to an embodiment of the present invention.

FIG. 3 is an explanatory sectional view of a fixing belt used in the belt fixing device of the embodiment.

FIG. 4 is a schematic explanatory view of a belt fixing device according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording medium 10 Fixing belt 11 Heating device 12 Heating roller 12a Core 12b Elastic layer t Toner

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ken Satoshi 2-3-13 Azuchicho, Chuo-ku, Osaka City Osaka International Building Minolta Co., Ltd. (72) Inventor Shozo Miyazaki 2-3-3 Azuchicho, Chuo-ku, Osaka City No. 13 Osaka International Building Minolta Co., Ltd. (72) Inventor Yasuhiro Ono 2-3-1 Azuchicho, Chuo-ku, Osaka City Osaka International Building Minolta Co., Ltd. (72) Inventor Toshiya Natsuhara 2-chome Azuchicho, Chuo-ku, Osaka-shi No. 3-13 Osaka International Building Minolta Co., Ltd. F-term (reference) 2H033 AA03 AA06 AA23 AA31 BA11 BA12 BB05 BB06 BB15 BB28 BE03

Claims (2)

[Claims] 1. A fixing belt provided on the outer periphery of a heating roller is heated by a heating roller, and the fixing belt is pressed onto a recording medium to which the toner is supplied, so that the toner is applied to the recording medium. In the belt fixing device for fixing, a thickness of 100 μm is applied to the outer periphery of the cylindrical cored bar.
A belt fixing device using a heating roller provided with an elastic layer having a thickness of not less than m and a fixing belt made of a resin belt having a thickness of not more than 70 μm. 2. A heating device for heating a flexible fixing belt provided on an outer periphery of a heating roller, and pressing the fixing belt onto a recording medium to which toner has been supplied, thereby applying toner to the recording medium. In a belt fixing device for fixing, a heating roller having an elastic layer provided on the outer periphery of a cylindrical core is used, and a fixing belt made of a resin belt is used, and the fixing belt is brought into contact with the outer periphery of the heating roller. A belt fixing device, wherein a rubber hardness at a part where the belt is made is less than 50 degrees.