JP6036032B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

  In image forming apparatuses such as copying machines, printers, facsimiles, etc., heat fixing that fixes an unfixed toner image formed on a recording medium (hereinafter referred to as paper) such as transfer paper or OHP sheet onto the paper by heat and pressure. The device is well known. In such a thermal fixing device, a belt fixing device using an endless fixing belt is known as a fixing method with a short warm-up time and low power consumption.

  For example, Japanese Patent Laying-Open No. 2011-59247 (Patent Document 1) discloses a belt fixing device that can adjust the state of a fixing nip portion to a state suitable for fixing.

  In the conventional belt fixing device, if the heater continues to be lit from room temperature or standby state, the heating plate and the fixing belt are deformed, or the adhesiveness between the heating plate and the fixing belt is changed, resulting in a gap. There has been a problem that the temperature of the fixing belt to be heated does not increase as expected, or temperature unevenness occurs in the belt.

Even in the fixing device described in Patent Document 1, the uniformity of the fixing belt when the heater is turned on or when the temperature is raised is not described, and the above problem is not solved.
SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus that can uniformly melt a toner without temperature unevenness in a belt and can stably obtain a good fixed image.

In order to solve the above problems, the present invention provides a fixing belt stretched between a heating roller heated by a heating source and a nip forming member, and presses the pressure member against the nip forming member with the fixing belt interposed therebetween. Forming a fixing nip and passing the recording material carrying the toner image through the fixing nip to fix the toner image onto the recording material. The belt is elastically deformed from the initial state by the tension of the belt to apply tension to the fixing belt, and is deformed so as to return to the initial state in response to the expansion of the fixing belt, so that the fixing belt is always stretched. to comprise a belt stretching state maintaining means, said belt stretching state maintaining means and said Rukoto provided the nip forming member integrally.

  In order to solve the above-described problem, the present invention provides a fixing belt stretched between a heating roller heated by a heating source and a nip forming member, and a pressure member is attached to the nip forming member across the fixing belt. A fixing device that forms a fixing nip by pressing, and fixes the toner image to the recording material by passing the recording material carrying the toner image through the fixing nip, and is movable by being urged by an elastic member The fixing belt is moved from the initial position by the tension of the fixing belt to apply tension to the fixing belt, and is moved back to the initial position according to the expansion of the fixing belt, so that the fixing belt is always stretched. It is characterized by comprising belt tension state maintaining means for maintaining the state in a closed state.

  According to the fixing device of the present invention, the fixing device is formed of a flexible member, and elastically deforms from an initial state by the tension of the fixing belt to apply tension to the fixing belt, and according to expansion of the fixing belt. A belt tension state maintaining unit that deforms to return to the initial state and maintains the fixing belt in a constantly stretched state, or is movably provided by an elastic member, and is provided by the tension of the fixing belt. A belt tension state in which tension is applied to the fixing belt by moving from an initial position, and the belt is moved back to the initial position in response to expansion of the fixing belt, so that the fixing belt is always stretched. Since the maintenance means is provided, even if the fixing belt is thermally expanded, the tension state maintenance means is deformed or returned to the initial state as much as the belt is extended. For imparting tension the fixing belt moves back to location, fixing belt, regardless of the degree of thermal expansion is maintained in an extended state at all times. Therefore, the fixing belt can be kept in close contact with the heating roller without any gap at all times. Therefore, there is no temperature unevenness in the fixing belt, the toner can be melted uniformly, and a good fixed image can be obtained stably.

1 is a configuration diagram schematically illustrating an outline of a laser printer including a fixing device according to the present invention. FIG. 2 is a cross-sectional view illustrating a main configuration of the fixing device. FIG. 3 is a cross-sectional view illustrating a fixing device during a fixing operation. It is a figure explaining the belt tension state maintenance means formed of the elastic member. It is a figure explaining the angle of the corner | angular part of the fixing belt formed by a tension state maintenance means. It is a figure explaining the width | variety which a tension state maintenance means stretches a fixing belt. It is a cross-sectional block diagram which shows the fixing device of 2nd Embodiment. The comparative example which does not have a tension state maintenance means is shown.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram schematically showing an outline of a laser printer which is an example of an image forming apparatus having a fixing device according to the present invention. A laser printer 100 shown in FIG. 1 includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging unit 2, a developing device 3, a transfer unit 4, a cleaning unit 5, and a discharging unit. 6 etc. are arranged. An exposure position is provided between the charging unit 2 and the developing device 3, and writing light from a laser writing device 7 disposed above is irradiated onto the photosensitive drum 1.

  A paper feed cassette 8 is provided below the apparatus, and a paper feed roller 9, a transport roller pair 10, a registration roller pair 11, and the like are provided for feeding paper. A fixing device 70 is disposed on the side of the transfer portion where the photosensitive drum 1 and the transfer unit 4 face each other. The fixing device 70 will be described later.

An image forming operation in the laser printer 100 configured as described above will be briefly described.
When the image forming operation is started, the photosensitive drum 1 is driven to rotate clockwise in the drawing by a driving unit (not shown), and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity by the charging unit 2. . In the laser writing device 7, an LD (laser diode) (not shown) is driven based on image data sent from a host machine such as a personal computer, and irradiates the photosensitive drum 1 with laser light as writing light. As a result, an electrostatic latent image is formed on the photosensitive drum 1. Toner is applied to the electrostatic latent image from the developing device 3 and visualized as a toner image.

  On the other hand, the recording paper is fed from the paper feed cassette 8 by the paper feed roller 9 and conveyed by the conveyance roller pair 10. The sheet is once abutted against the registration roller 11 and then sent out in synchronization with the visible image. The toner image is transferred onto the sheet at a transfer portion where the photosensitive drum 1 and the transfer unit 4 face each other. Transcribed. When the paper on which the toner image is transferred passes through the fixing device 20, the toner image is fixed on the paper by heat and pressure. The paper on which the toner image has been fixed is discharged onto the paper discharge tray 12 by a paper discharge roller (not shown) and stacked.

  After the transfer of the toner image onto the paper, the adhering matter such as residual toner adhering to the surface of the photosensitive drum 1 is cleaned by the cleaning means 5, and the residual charge on the surface of the photosensitive drum 1 is removed by the charge eliminating means 6. In preparation for the next image formation.

2 and 3 are cross-sectional views showing the configuration of the main part of the fixing device 70. FIG. 2 shows a state during standby and FIG. 3 shows a state during a fixing operation.
As shown in these drawings, the fixing device 70 has a fixing belt 21 formed of an endless belt member as a fixing member, and a function of a holding member that is provided in the fixing belt 21 and holds the fixing belt, as well as the fixing belt 21. A heating roller 22 that performs a function of applying heat, a halogen heater 23 that is a heating means, a thermistor (not shown) that is a temperature sensor that detects a surface temperature in contact with or close to the fixing belt 21, and a contact with the heating roller 22. A fixing pad 24 for holding the fixing belt in the fixing belt, a pressure roller 31 as a pressure member for forming a fixing nip in contact with the fixing belt 21, and the like.

  The fixing pad 24 is made of an elastic body such as silicone rubber or fluorine rubber, or a heat-resistant resin, and these members are in contact with the inner surface of the fixing belt 21 via a sliding sheet. Further, it slides indirectly on the inner surface of the fixing belt 21 through a lubricant such as a sliding sheet or grease. Further, the fixing pad 24 is also a nip forming member that presses against the pressure roller 31 across the fixing belt 21 to form a fixing nip.

  Here, the fixing pad 24 is brought into pressure contact with the pressure roller 31 via the sliding sheet or the fixing belt 21, and the load from the pressure roller and the pressure of the fixing pad 24 constitute a fixing nip. The toner image can be fixed by pressure and heat.

  In the pressure roller 31, a silicone rubber layer 31a is provided on a hollow metal roller 31b, and a release layer (PFA resin layer or PTFE resin layer) is provided on the outer surface to obtain releasability. The pressure roller 31 is rotationally driven by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus via a gear train.

  Further, the pressure roller 31 is pressed against the fixing belt side by a pressure mechanism (not shown), and a predetermined nip width is formed in the fixing nip when the rubber layer 31a of the pressure roller is crushed and deformed. The The pressure roller may be formed of a solid roller, but a hollow roller is preferable because it has a smaller heat capacity.

Further, the pressure roller 31 may be provided with a heating source such as a halogen heater.
The silicone rubber layer 31a in the pressure roller may be solid rubber, but if there is no heating source such as a heater inside the pressure roller, sponge rubber may be used. Use of sponge rubber is desirable because heat insulation is enhanced and heat of the fixing belt is hardly transmitted to the pressure roller.

  The fixing belt 21 can be a metal belt such as nickel or stainless steel, or a resin material such as polyimide, polyamide, or fluorine resin, and is an endless belt (or film). In this example, a polyimide belt was used.

  The surface layer of the fixing belt 21 has a release layer such as a PFA resin layer or a PTFE resin, and has a release property so that the toner on the recording medium does not adhere. Further, an elastic layer such as a silicone rubber layer may be formed between the base material of the fixing belt 21 and the PFA resin layer (or PTFE resin).

  In the absence of a silicone rubber layer, the heat capacity is reduced and the fixability is improved, but the unfixed toner image is crushed, and the subtle irregularities on the surface of the fixing belt are transferred to the image during fixing, and the image There is a problem in that a crusty skin-like mark remains on the solid portion. In order to improve this, it is necessary to provide a silicone rubber layer of 100 μm or more. Due to the deformation of the silicone rubber layer, subtle irregularities are absorbed and the skin image is improved.

  The hollow heating roller 22 uses a pipe-shaped metal such as aluminum, iron, and stainless steel as the material of the cored bar 22a. The heating roller 22 of this embodiment has a circular shape with a diameter of 4 mm smaller than the diameter of the fixing belt 21. Inside the heating roller 22, a black coating is applied to the inner surface in order to easily absorb radiant heat from a halogen heater or the like.

  The heating roller 22 is provided in contact with the fixing pad 24. Note that the pressure applied by the pressure roller 31 to the fixing belt 21 is transmitted to the fixing belt 21, a sliding sheet (not shown), and the fixing pad 24, and is received by the heating roller 22. In the present embodiment, the heating roller 22 is rotationally driven by a driving mechanism (not shown). The speed is substantially the same as that of the fixing belt 21 so that the rotation direction is the same as that of the fixing belt 21. Further, as the heat source for raising the temperature of the heating roller 22, the illustrated halogen heater may be used, but an IH (induction heating) method as described later may be used. Furthermore, a resistance heating element, a carbon heater, or the like can be used.

  The fixing belt 21 rotates along with the pressure roller 31. That is, the pressure roller 31 is driven to rotate by a driving source (not shown), and the driving force is transmitted to the fixing belt 21 through the fixing nip, whereby the fixing belt 21 rotates. The fixing belt 21 is sandwiched between the fixing pad 24 and the pressure roller 31 and rotates at the fixing nip, but is guided to the fixing pad 24 except for the fixing nip.

  A lubricant such as silicone oil or fluorine grease is interposed at the interface between the fixing belt 21 and the heating roller 22. Then, the surface roughness of the surface of the heating roller 22 is set to be equal to or larger than the particle diameter of the lubricant, so that the lubricant can be easily held. As a method of roughening the surface of the heating roller 22, a method of physically roughing such as sand blasting, a method of chemically roughing such as etching, or a method of applying a paint mixed with small diameter beads However, any method can be adopted.

  By the way, in the conventional belt fixing device, the fixing heater is turned on, and when the temperature of the fixing belt rises from room temperature to the fixing set temperature, the belt itself expands due to thermal expansion. Since the contact between the fixing belt and the heating roller is reduced by the extension, the surface temperature of the fixing belt varies. The temperature variation depends on the contact time, but when the temperature varies from 5 ° C., a difference of 30 ° C. or more occurs. Depending on the conditions of the fixing nip and the melting characteristics of the toner, if the fixing temperature is different by 10 ° C. or more, the toner melting degree is different and the color of the color toner is different (for example, La * b * coordinate space: JIS Z 8729 In the defined uniform color space, ΔE is 5 or more). Further, when the variation occurs at 30 ° C. or more, it is not a difference in color and the toner is not melted. In addition, a high temperature portion also appears, exceeding the heat resistance of the fixing belt, causing a problem that the silicone rubber is deteriorated and a part of the belt material emits smoke.

  For this reason, it is desirable that the heating roller and the fixing belt are always in contact with each other regardless of the thermal expansion of the belt. In the present invention, in order to bring the fixing belt into contact with the heating roller regardless of the thermal expansion of the fixing belt, tension is always applied to the fixing belt (always maintaining the fixing belt in a tensioned state), and the fixing belt 21 The heating roller 22 is configured to be kept in close contact stably.

  Furthermore, by rotating the heating roller, the heating roller temperature can be made uniform, and as a result, the belt temperature can be stabilized. There is a method of applying tension to the fixing belt from the outside to the inside of the fixing belt or from the inside to the outside.

  In the present embodiment, the fixing belt 21 is stretched from the inside to the outside by the stretch state maintaining means 25, 25 provided on the fixing pad 24. In the present embodiment, members (stretching state maintaining means 25, 25) for stretching the fixing belt are provided as a part of the fixing pad 24. The portion where the fixing belt 21 is stretched is provided as a portion different from the portion where the pressure roller and the fixing nip are formed. The position where the tension is applied may be either upstream or downstream of the fixing nip, or may be upstream or downstream. In this embodiment, the tension is applied both upstream and downstream of the fixing nip.

  In the present embodiment, the stretched state maintaining means 25, 25 are configured to stretch the fixing belt 21 using elastic force. As a configuration in which tension is applied to the fixing belt 21 by an elastic force, a tension is applied by the elasticity of the tension state maintaining unit itself (the elastic force of the member itself) and an elastic member such as a spring. There is a method of applying tension by urging the state maintaining means.

  When the former method is employed, the stretched state maintaining means 25, 25 are formed of elastic members. The tension state maintaining means 25, 25 may be provided as a separate member from the fixing pad 24 and fixed to the fixing pad 24, or the tension state maintaining means 25, 25 may be provided integrally with the fixing pad 24. (As described above, the fixing pad 24 can be provided as an elastic body).

  As shown in FIG. 4A, the stretched state maintaining means 25 formed of an elastic member is provided in a state of being greatly opened outward in an initial state (a state where the tension of the fixing belt 21 does not act). When the fixing belt 21 is stretched between the fixing pad 24 and the heating roller 22 and the tension of the fixing belt 21 acts on the tension state maintaining means 25, 25, as shown in FIG. The tension state maintaining means 25 pushed by the belt tension is elastically deformed inward (so that the opening angle of the tension state maintaining means 25 becomes small). Then, when the fixing belt 21 is heated by the heating roller 22 and the fixing belt 21 is thermally expanded at the time of fixing (temperature increase), the fixing belt 21 is expanded due to thermal expansion as shown in FIG. 4C. The stretched state maintaining means 25 is elastically deformed outward (so that the opening angle of the stretched state maintaining means 25 is increased). Although only the upstream side of the nip is shown in FIG. 4, the same applies to the downstream side of the nip.

  That is, the stretched state maintaining means 25 (having flexibility) formed of an elastic member elastically deforms from the initial state by the tension of the fixing belt 21 to apply tension to the fixing belt 21, and the fixing belt 21 In the case of thermal expansion, the tension state maintaining means 25 is deformed so as to return to the initial state as much as the belt is extended, and tension is applied to the fixing belt 21. Therefore, the fixing belt 21 is always kept in tension regardless of the degree of thermal expansion.

  When adopting a method of applying tension by urging the tension state maintaining means with an elastic member such as a spring, the tension state maintaining means 25, 25 may be rigid members. The stretched state maintaining means 25, 25 are attached (supported) to the fixing pad 24 so as to be able to rotate (swing). The tension state maintaining means 25, 25 pivotally supported on the fixing pad 24 is urged by an elastic member (not shown) such as a spring. In that case, an appropriate member such as a coil spring, a leaf spring, or a torsion spring can be used as the elastic member.

  As shown in FIG. 4A, the stretched state maintaining means 25 urged by the elastic member is provided in a state of being largely opened outward in an initial state (a state where the tension of the fixing belt 21 does not act). When the fixing belt 21 is stretched between the fixing pad 24 and the heating roller 22 and the tension of the fixing belt 21 acts on the tension state maintaining means 25, 25, as shown in FIG. Then, the tension state maintaining means 25 pushed by the belt tension is turned inward (so that the opening angle of the tension state maintaining means 25 becomes small). Then, when the fixing belt 21 is heated by the heating roller 22 and the fixing belt 21 is thermally expanded at the time of fixing (temperature increase), the fixing belt 21 is expanded due to thermal expansion as shown in FIG. 4C. The tension state maintaining means 25 is rotated outward by an amount (so that the opening angle of the tension state maintaining means 25 is increased). Although only the upstream side of the nip is shown in FIG. 4, the same applies to the downstream side of the nip.

  In other words, the stretched state maintaining means 25 urged by the elastic member (having mobility) moves from the initial position by the tension of the fixing belt 21 to apply tension to the fixing belt 21, and the fixing belt 21 is heated. When the belt expands, the tension state maintaining means 25 moves so as to return to the initial position as much as the belt extends, and tension is applied to the fixing belt 21. Therefore, the fixing belt 21 is always kept in tension regardless of the degree of thermal expansion.

  As described above, the tension state maintaining units 25 and 25 always apply tension to the fixing belt 21 regardless of the thermal expansion of the fixing belt 21. At this time, if the fixing belt is stretched at an acute angle, the rotation of the fixing belt is hindered. That is, as shown in FIG. 5, both the angle α and β of the belt corner formed by the stretched state maintaining means 25 (shown only on the upstream side of the nip in FIG. 5) are both obtuse during both standby and fixing. It is provided to become. The tension state maintaining means 25, 25 are movable or flexible, but are set so as not to contact the heating roller 22 in any case.

The tension state maintaining means 25, 25 are heated to a certain degree by receiving heat from the fixing belt 21. Therefore, it is desirable to reduce the heat capacity as much as possible from the viewpoint of energy saving.
Further, the tension state maintaining means 25 and 25 always apply tension to the fixing belt 21 when the fixing belt 21 is extended regardless of standby, JAM processing, or printing. The stretched state maintaining means 25, 25 have sufficient heat resistance at least with respect to the belt temperature.

  Also, as shown in FIG. 6, the width W2 over which the tension state maintaining means 25, 25 stretch the fixing belt 21 is set to be equal to or less than the outer diameter W1 of the heating roller. This is because at least the fixing belt 21 is brought into contact with the half circumference portion of the heating roller 22. In addition, if the distance of the outermost part of the both-side-stretched state maintaining means 25, 25 in the initial state described in FIG. 4A is set to W1 or less, W2 will be W1 or less at the maximum.

  The toner used in this embodiment may be either a pulverized toner or a polymerized toner. To 100 parts of toner, 2 parts of hydrophobic silica RY50 (manufactured by Aerosil) is added, and a peripheral speed of 40 m / sec for 5 minutes with a 20 L Henschel mixer. A mixing process was performed. Thereafter, a toner was obtained using a sieve having an opening of 75 microns.

Next, a second embodiment of the fixing device will be described with reference to FIG.
A fixing device 70B according to the second embodiment shown in FIG. 7 is configured to always apply tension to the fixing belt from the outside of the fixing belt to maintain the belt in a constantly tensioned state. In the fixing device 70B shown in this figure, the fixing belt 21, the heating roller 22, the fixing pad 24, and the pressure roller 31 are the same as those of the fixing device 70 of the first embodiment. The tension state maintaining means 25B is disposed outside the fixing belt 21 (outside the belt loop). In this example, a stretched state maintaining unit 25B is provided so as to contact the heating roller 22 with the fixing belt 21 interposed therebetween.

  As shown in FIG. 7A, the tension state maintaining unit 25 </ b> B is provided so as to be movable along the outer peripheral portion of the heating roller 22. And it is urged | biased by biasing members which are not shown in figure, such as a spring, and is located in the initial position shown as a continuous line. When moving from the initial position indicated by the solid line in the direction indicated by the dotted line, it moves against the urging force of the urging member. FIG. 7B shows a standby state (room temperature state), and the tension state maintaining means 25B is moved from the initial position by the tension of the fixing belt 21 acting on the tension state maintaining means 25B. From this state, when the halogen heater 23 is turned on during the fixing operation and the fixing belt 21 is thermally expanded, as shown in FIG. 7C, the stretched state maintaining means 25B is moved from the standby position indicated by the dotted line to the initial position. Move in the direction.

  That is, the stretched state maintaining means 25B urged by the urging member (elastic member) (movable) moves from the initial position by the tension of the fixing belt 21 to apply tension to the fixing belt 21, and When the fixing belt 21 is thermally expanded, the tension state maintaining means 25B moves so as to return to the initial position by the amount of the belt extension, and tension is applied to the fixing belt 21. Therefore, the fixing belt 21 is always kept in tension regardless of the degree of thermal expansion.

  As described above, the stretched state maintaining unit 25B can keep the fixing belt 21 in close contact with the heating roller 22 without any gap regardless of the thermal expansion of the fixing belt during standby or during fixing. The tension state maintaining means 25B is preferably provided as a rotatable roller member.

FIG. 8 shows a configuration (comparative example) that does not have the stretched state maintaining means 25 or 25B for comparison with the present invention.
In this figure, when the fixing heater is turned on and the heating roller 122 heats the fixing belt 121, the fixing belt 121 is thermally expanded, so that a gap is formed between the fixing belt 121 and the heating roller 122 and does not adhere. Therefore, the temperature of the fixing belt does not increase as expected, or temperature unevenness occurs in the belt.

  On the other hand, in the fixing device according to the present invention, the fixing device 70 of the first embodiment and the fixing device 70B of the second embodiment are provided with the stretched state maintaining means 25 or 25B, so that the fixing device 70 can be used at the time of fixing even during standby. However, the fixing belt 21 can be kept in close contact with the heating roller 22 without any gaps regardless of the thermal expansion of the fixing belt. Therefore, there is no temperature unevenness in the fixing belt, the toner can be melted uniformly, and a good fixed image can be obtained stably. Further, low temperature offset and smoke generation due to non-uniform adhesion can be prevented.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. The fixing device can have an appropriate configuration, and is not limited to the one in which the heater is disposed in the roller, but may be one that is heated from the outside. Further, not only a heater such as a halogen heater but also an induction heating method can be adopted as a heating means. Appropriate materials can be used for the fixing pad and the flexible tension state maintaining means. The shape and size of the tension state maintaining means can be appropriately set within the scope of the present invention. Further, a pressure belt can be used instead of the pressure roller.

  The configuration of each part of the image forming apparatus is also arbitrary, and the image carrier is not limited to the drum, and a belt-like one can also be adopted. Further, the present invention can be applied not only to a monochrome apparatus but also to a full color machine or a multicolor machine. Further, the present invention is not limited to the direct transfer method and the intermediate transfer method. Of course, the image forming apparatus is not limited to a printer, and may be a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

1 Photosensitive drum (image carrier)
21 Fixing belt (fixing member)
22 Heating roller 23 Halogen heater (heating source)
24 Fixing pad (nip forming member)
25, 25B Tension state maintaining means 31 Pressure roller (pressure member)
70, 70B Fixing device 100 Image forming device

JP 2011-59247 A

Claims (9)

A fixing belt is stretched between a heating roller heated by a heating source and a nip forming member, a pressing member is pressed against the nip forming member across the fixing belt to form a fixing nip, and a toner image is supported. A fixing device for fixing the toner image to a recording material by passing the recording material through the fixing nip,
It is formed of a flexible member, elastically deforms from the initial state by the tension of the fixing belt to apply tension to the fixing belt, and deforms to return to the initial state according to the expansion of the fixing belt. Belt tension state maintaining means for maintaining the fixing belt in a state of being always tensioned ,
A fixing device wherein the belt stretching state maintaining means and said Rukoto provided the nip forming member integrally. The fixing device according to claim 1, wherein the belt tension state maintaining unit is provided on at least one of an upstream side and a downstream side of the fixing nip. The belt stretching state maintaining means, characterized in that it is arranged inside the loop of the fixing belt, a fixing device according to claim 1 or 2. Wherein wherein the stretching angle of the fixing belt by the belt stretching state maintaining means is configured to be obtuse, the fixing device according to any one of claims 1-3. Width for stretching the fixing belt by the belt stretching state maintaining means may be smaller than the outer diameter of the heating roller, a fixing device according to any one of claims 1-4. The fixing device according to claim 1, wherein the heating roller is rotationally driven. The fixing device according to claim 1, wherein the belt tension state maintaining unit is provided apart from the heating roller. An image forming apparatus comprising: a fixing device according to any one of claims 1-7. The image forming apparatus according to claim 8 , wherein a toner using oil-containing silica as an external additive is used.

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