JPH0721680B2 - Fixing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fixing device of a system in which heat energy is applied to an image carrier (recording material) through a film.

This fixing device is used in image forming devices such as copiers, laser beam printers, facsimiles, microfilm reader printers, image display (display) devices, recorders, etc. to form appropriate images such as electrophotography, electrostatic recording, magnetic recording, etc. The target image is directly or indirectly (transferred) on the surface of the recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) by using a toner made of heat-meltable resin by the process means. It can be utilized as an image fixing device which forms and carries an unfixed sheet image corresponding to information, and heats and fixes the unfixed toner image as a permanently fixed image on the surface of the recording material carrying the image.

Further, it is not limited to the image fixing device, and can be widely used as a device for heating the image carrier, such as a device for heating a recording material carrying an image to modify the surface property.

(Prior Art) Conventionally, for example, a heating device for a recording material for heating and fixing an image includes a heating roller that is maintained at a predetermined temperature and a heating roller that has an elastic layer and is in pressure contact with the heating roller. ,
A heat roller method is widely used in which a recording material is nipped and conveyed and heated.

As disclosed in U.S. Pat. No. 3,578,797, a belt fixing method is also known as an image fixing means. This is because the toner image is brought into contact with the heating element web and is heated to its melting point to be melted, and after the melting, the toner is cooled to have a relatively high viscosity, and the toner adhesion tendency is weakened from the heating element web. It is a method of fixing without causing offset by going through the process of peeling.

There are also flash fixing method and oven fixing method.

Recently, a heating device (film heating system) having a constitution including a fixedly-supported heating body, a film which is pressed against the heating body, and a pressing member which heats a recording material through the film has been devised. . The system device disclosed in Japanese Patent Application Laid-Open No. 63-313182 proposed by the present applicant belongs to this system, and an unfixed sheet image is formed through a thin heat-resistant film (sheet) that is pressed and slid on a fixed heating element. It is a heating means / apparatus based on the fact that the film and the recording material are separated from each other by applying heat energy to the film to soften / melt it, or after the toner is cooled / solidified.

(Problems to be Solved by the Invention) However, the conventional heat roller system as described above, the belt fixing system described in US Pat. No. 3,578,797, and other systems have the following problems.

Heat roller method It takes a long time to rise to a predetermined temperature,
During that time, the image forming operation is prohibited. That is, there is a so-called wait time.

 A large amount of electric power is required because a heat capacity is required.

A rotating roller with a high roller temperature requires a heat resistant special bearing.

The roller comes into direct contact with the hands, which is dangerous and requires a protective member.

Depending on the fixing temperature and the curvature of the roller, the recording material may wind around the roller, and it is easy to see jams of the recording material.

Since the temperature at the fixing point for fixing the toner on the recording material is equal to the temperature at the separation point between the recording material and the heat roller, high-temperature offset depending on the separation temperature is likely to occur, and the degree of image gloss depending on the separation temperature. Can't control.

Flash, oven fixing system The device becomes larger.

There is a risk of ignition if the sharpness of the image deteriorates or the recording paper stays in the fixing device.

Belt fixing method This method also has the same problems as the above heat roller method, such as the weight time and the large power consumption.

The film heating method is effective because it has a small heat capacity and a short wait time due to the increase in heat capacity, and the fixing point and the separation point can be set separately, so that offset is also prevented. However, regarding the perimeter of the film used in this film heating system, the conventional one has the same perimeter both at the center and the end of the film in the film axial direction (film width direction). Therefore, there is a drawback that wrinkles are likely to occur in the recording material, which is the material to be heated, that passes through the heating portion of the apparatus. This wrinkle of the recording material is due to uneven distribution in the longitudinal direction which occurs when the recording material passes through the heating portion of the heating device under pressure.

The present invention relates to a heating device in which a heating body is arranged on one surface side of a film (sheet) and an image carrying body is closely adhered to the other surface side, and heat energy is applied to the image carrying body through the film, which is an endless film. The purpose is to prevent the occurrence of wrinkles on the recording material when a belt type one is used.

(Means for Solving Problems) In the present invention, a heating body is arranged on one side of a film, and an image carrier is brought into close contact with the other side of the film, and heat energy is applied to the image carrier via the film. The fixing device is characterized in that the film is an endless film, and the peripheral length of the film increases from one point other than the end portion in the axial direction of the film toward the end portion of the film.

(Operation) FIGS. 1 (a), (b), and (c) respectively show schematic views of a form example of the endless film 24 according to the present invention.

FIG. 1A shows the axial center portion A of the endless film 24.
Is shorter than the peripheral lengths of both end portions B and C, and the peripheral length is increased from the central portion A toward both end portions B and C.

FIG. 2B shows a form in which the circumferential length of the endless film 24 is directly and largely changed along the axial center portion A of the film toward both end portions B and C.

In FIG. 6C, the shortest portion A _x of the film perimeter is not the central portion A in the film axial direction.

Thus, by making the perimeter of the film such that the perimeter of the film is increased from one point other than the end in the axial direction of the film toward the end of the film, the movement of the recording material to be closely conveyed to the film surface is moved. The speed becomes higher at the end portion than at the central portion, so that both end portions are stretched and wrinkling of the recording material is suppressed.

The film 24 having the configuration as shown in FIG. 1C is effective when a recording material having a small recording material width is passed, for example, on the basis of one side end portion.

(Example) (1) Example of image fixing device (Fig. 2) Fig. 2 shows an example of the image fixing device 11 according to the present invention.

Reference numeral 24 denotes an endless fixing film, which has a driving roller 25 on the left side, a driven roller 26 on the right side, and a low heat capacity linear heating element 20 as a heating element disposed below the rollers 25, 26.
The three members 25, 26 and 20 are suspended and stretched.

The driven roller 26 also serves as a tension roller for the endless belt-shaped fixing film 24.
Is an image carrier (recording material) having an unfixed toner image Ta conveyed from the image forming unit 8 side on the upper surface at a predetermined peripheral speed in the clockwise direction with the clockwise rotation of the drive roller 25. The transfer material sheet P is rotationally driven at the same peripheral speed as the conveying speed of the transfer material sheet P without wrinkles, meandering, or speed delay.

Reference numeral 28 denotes a pressure roller having a rubber elastic layer having a good releasability such as silicon rubber as a pressure member, and sandwiching the film portion on the descending side of the endless belt-shaped fixing film 24 of the heating body 20. The lower surface is brought into counter-pressure contact with an urging means (not shown) with a total pressure of 4 to 7 kg, and rotates counterclockwise in the forward direction of the transfer material sheet P conveyance direction.

The low heat capacity linear heating element 20 as a heating element is of this example,
A heater support 27 that has laterally long rigidity, high heat resistance, and heat insulation with the fixing film transverse direction (film width direction) as the longitudinal direction.
And a heater substrate 21 provided with a heating element 22, a temperature measuring element 23 and the like integrally attached and held along the length on the lower surface side of the support.

The heater support 27 heat-insulates and supports the heating body 20 with respect to the fixing device 11 and the entire image forming apparatus, and includes, for example, PPS (polyphenylene sulfide) / PAI (polyamide imide) / PAI.
It can be composed of high heat resistant resins such as I (polyimide), PEEK (polyetheretherketone), liquid crystal polymer, and composite materials of these resins and ceramics, metal, glass, etc.

As an example, the heater substrate 21 has a thickness of 1.0 mm, a width of 10 mm, and a length of 240.
It is a mm alumina substrate.

The heating element 22 is formed by applying an electric resistance material such as Ag / Pd (silver-palladium) to a thickness of about 10 μm and a width of 1 to 3 mm by screen printing or the like along the length substantially in the center of the lower surface of the substrate 21. Heat-resistant glass 21a as a surface protection layer on top of it
It is m-coated.

As an example, the temperature measuring element 23 has a low heat capacity such as a Pt film coated by screen printing on a substantially central portion of the upper surface of the substrate 21 (the surface opposite to the surface on which the heating element 22 is provided) and has a low heat capacity. It is a resistor. As the temperature measuring element, a thermistor having a low heat capacity may be arranged in contact with the substrate 21.

In the case of the heating element 20 of this example, a linear or band-shaped heating element 22
On the other hand, electricity is applied from both ends in the longitudinal direction to heat the heating element 22 over substantially the entire length. The energization is AC 100 V, and the energization power is controlled by controlling the energizing phase angle by an energization control circuit (not shown) including a triac according to the temperature detected by the temperature detecting element 23.

(2) Fixing Execution Operation In response to the image formation start signal, the image forming apparatus conveys the transfer material sheet P having the unfixed toner image Ta carried on the upper surface, which is conveyed from the transfer portion (8) to the fixing device 11 as an image forming operation. The non-fixed toner image surface enters the pressure contact portion N between the heating body 20 and the pressure roller 28 between the fixing film 24 and the pressure roller 28 by being guided by 29, and has the same speed as the sheet P conveyance speed. Between the heating member 20 and the pressure roller 28 in the overlapping contact state N in close contact with the lower surface of the fixing film 24 that is rotated in the same direction without causing surface misalignment or wrinkling. Pass through while receiving the clamping pressure.

Since the heating body 20 is electrically heated at a predetermined timing by the image formation start signal, the toner image Ta is heated at the press contact portion N and becomes the softened / melted image Tb.

The fixing film 24 is turned at a steep angle (the bending angle θ is about 45 °) at the edge portion S where the support 27 has a large curvature (the radius of curvature is about 2 mm). Therefore, the fixing film
The sheet P conveyed by passing through the pressure contact portion N in a state of being overlapped with 24 is separated from the fixing film 24 by the curvature at the edge portion S, and is discharged to the discharge tray (12). By the time the paper is ejected, the toner has been sufficiently cooled and solidified and is completely fixed on the sheet P (toner image Tc).

Since the toner used in this example has a sufficiently high viscosity when heated and melted, even if the toner temperature at the time of separation from the fixing film 24 is equal to or higher than the melting point of the toner, the adhesion force between the toners causes the toner to adhere to the fixing film 24. The force is much larger than the force, and therefore, when the fixing film 24 and the sheet P are separated from each other, toner offset to the fixing film 24 does not substantially occur.

Further, in this example, the heating element 22 and the substrate 21 of the heating element 20 are used.
Has a small heat capacity and is heat-insulated and supported by the support body 27, the surface temperature of the heating body 20 at the press contact portion N is sufficient for the melting point of toner (or the fixing temperature on the sheet P) in a short time. Since the temperature rises to a very high temperature, the temperature of the heating element 20 is raised in advance (so-called standby temperature control).
There is no need, energy can be saved, and the temperature rise inside the machine can be prevented.

(3) Fixing Film 24 The fixing film 24 has a form as illustrated in FIGS. 1 (a) to 1 (c), that is, the peripheral length of the film goes from one point to the end other than the end in the axial direction of the film. Accordingly, by increasing the film circumference, the moving speed of the recording material conveyed in close contact becomes higher at the end portion than at the central portion, and wrinkling of the recording material is suppressed by pulling both end portions.

For example, as a disassembled film as shown in FIG. 1 (a),
By using the film 24 having a circumference of 100φ · 314.16mm perimeter at the end portions B and C, and a 99.5φ · 312.59mm perimeter at the central portion A, the peripheral speed difference of the film can be obtained and both end portions of the recording material can be obtained. Was pulled and the wrinkles of the recording material were suppressed.

Even in the case of the film having the form as shown in FIG. 1 (b), good results were obtained for preventing wrinkles of the recording material.

The configuration as shown in FIG. 1 (c) is effective for preventing wrinkles when a recording material having a small recording material width is passed, for example, on the basis of one side end portion.

As the fixing film 24, a composite layer film having heat resistance, releasability, durability and the like, which is generally 100 μm or less, preferably 40 μm or less, can be used.

FIG. 3 is a cross-sectional film structure diagram of an example of a composite layer film, in which 24a is a heat-resistant layer as a base layer (base film) of the fixing film, and 24b is an outer surface of the heat-resistant layer 24a (on the side facing the toner image). It is a release layer laminated on the surface).

The heat-resistant layer 24a is made of, for example, polyimide, polyetheretherketone (PEEK), polyethersulfone (PES), polyetherimide (PEI), polyparabanic acid (PPA), PFA.
High heat resistant resin film such as, and metal such as Ni, SUS, Al, etc., which have excellent strength and heat resistance can be used.

The release layer 24b is preferably made of a fluororesin such as PTFE (polytetrafluoroethylene) / PFA / FEP, a silicone resin, or the like. The release layer 24b is laminated on the heat-resistant layer 24a by adhesive lamination of the release layer film, lamination of the release layer material by film forming technology such as electrostatic coating (coating), vapor deposition, and CVD, heat-resistant layer material and release It can be performed by forming a two-layer film by co-extruding the layer materials.

The resistance value of the surface of the fixing film 24 may be lowered by a method of mixing a conductive agent such as carbon black, graphite, conductive whiskers or the like into the release layer 24b. Accordingly, the toner contact surface of the fixing film 24 can be prevented from being charged. When the toner contact surface of the fixing film 24 is insulative, the surface of the fixing film is charged and disturbs the toner image on the sheet P which is a recording material, or the toner image is fixed on the fixing film 24.
However, these problems can be avoided by the measures described above.

(4) Example of image forming apparatus (FIG. 4) FIG. 4 shows an example of an image forming apparatus in which the heating device 11 shown in FIG. 2 according to the present invention is incorporated and used as an image fixing device.

The image forming apparatus of this example is a reciprocating type / rotating drum type / transfer type electrophotographic copying apparatus.

Reference numeral 100 is a device casing. Reference numeral 1 denotes a reciprocating type document placing table composed of a transparent plate member such as a glass plate disposed on the upper surface plate 100a of the machine housing. The upper surface plate 100a of the machine housing is placed on the right side a and the left side a'in the drawing. Each of them is driven to reciprocate at a predetermined speed.

Reference numeral G denotes a document, which is placed by placing the document surface of the document table 1 on the upper surface of the document table 1 according to a predetermined mounting standard with the image surface side to be copied facing downward, and by pressing the document pressure plate 1a onto the document platen 1a. .

Reference numeral 100b denotes a slit opening serving as a document illuminating section which is opened on the surface of the machine housing upper surface plate 100a with a direction perpendicular to the reciprocating direction of the document placing table 1 (direction perpendicular to the paper surface) as a longitudinal direction. The downward image surface of the document G placed and set on the document placing table 1 sequentially passes through the position of the slit opening 100b from the right side to the left side in the process of reciprocating to the right a of the document placing table 1. , Slit L opening the light L of the lamp 7 in the course of its passage
100b is received through the transparent document placing table 1 and is illuminated and scanned. The light reflected from the document surface of the illumination scanning light is image-wise exposed on the surface of the photosensitive drum 3 by the short-focus small-diameter image-forming element array 2.

The photosensitive drum 3 is coated with a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer, and is rotated in a clockwise direction indicated by an arrow b at a predetermined peripheral speed around the central support shaft 3a. A uniform charging process of positive or negative polarity is performed by the charger 4, and the uniformly charged surface is subjected to imagewise exposure (slit exposure) of the original image, so that the surface of the photosensitive drum 3 is imagewise exposed. An electrostatic latent image corresponding to the changed image is sequentially formed.

The electrostatic latent image is sequentially visualized by the developing device 5 with toner made of resin or the like which is softened and melted by heating, and the toner image as the visualized image is transferred to a portion where the transfer discharger 8 as a transfer portion is provided. I will do it.

Reference numeral S denotes a cassette in which transfer material sheets P as recording materials are stacked and housed, the sheets in the cassette are fed out and fed one by one by the rotation of the feeding roller 6, and then the toner on the drum 3 is fed by the registration roller 9. When the leading edge of the image forming portion reaches the portion of the transfer discharger 8, the leading edge of the transfer material sheet P also reaches the position between the transfer discharger 8 and the photosensitive drum 3 and is timed and synchronized so as to coincide with each other. Be delivered. Then, the toner images on the photosensitive drum 3 side are sequentially transferred to the surface of the fed sheet by the transfer discharger 8.

The sheet that has received the toner image transfer at the transfer unit 8 is sequentially separated from the surface of the photosensitive drum 3 by a separation unit (not shown), and is conveyed by a conveying device.
The unfixed toner image carried to the fixing device 11 by the fixing device 11 is subjected to the heat fixing process as described in the above section (action), and the image is formed as a copy on the discharge tray 12 outside the machine. Is discharged to.

On the other hand, the surface of the photosensitive drum 3 after the transfer of the toner image is repeatedly used for image formation after the adhering contaminants such as the transfer residual toner are removed by the cleaning device 13.

(5) Other Configuration Example 1 of Fixing Device (FIG. 5) FIG. 5 shows another configuration example of the fixing device 11.

Reference numeral 32 denotes a heating roller as a heating body, which has a built-in heater 33 and causes the heater 33 to appropriately generate heat in accordance with the heating roller surface temperature detected by the temperature detecting element 41, thereby bringing the surface of the heating roller 32 to a predetermined temperature. Can be maintained.

Reference numeral 34 denotes a small-diameter separation upper roller arranged downstream of the heating roller 32 in the sheet P transport direction. 25 is a fixing film 24
Is a driving roller for rotating and rotating, and 26 is a fixing film.
It is a driven roller that always applies an appropriate tension to 24. The driving roller 25 and the heating roller 32 are both the sheet P.
It is rotationally driven in the clockwise direction at the same speed as the transport speed of.

The fixing film 34 has a structure according to the present invention and is stretched around the four members 32, 34, 25 and 26.

36 is a pressure roller disposed below the heating roller 32, 35 is a separation lower roller disposed below the separation upper roller 34, and 37 is a pressure roller 36 and a separation lower roller. An endless belt-shaped transport belt (backup belt) stretched between 35.

The pressure roller 36 is a roller whose surface layer is made of an elastic material such as silicon rubber. The lower side film portion of the endless belt-shaped fixing film 24 is sandwiched between the pressure roller 36 and the heating roller 32, and a contact pressure of, for example, a total pressure of 4 to 7 kg is obtained by urging means (not shown). There is.

The pressure roller 36 is driven to rotate by the rotational driving of the heating roller 32, and the transport belt 37 also rotates in the counterclockwise direction at the same speed as the transport speed of the sheet P while pressing the sheet P against the fixing film 34.

In the transfer material sheet P having the unfixed toner image Ta carried on the upper surface thereof, which is conveyed from the transfer portion 8 to the fixing device 11 by the image forming start signal in response to the image forming start signal, the heating roller 32 is rotationally driven. Therefore, while the fixing film 24 and the conveyor belt 37 are rotating, the fixing film 24 and the conveyor belt 37 are guided by the guide 29 and enter between the fixing film 24 and the conveyor belt 37 at the pressure contact portion N between the heating roller 32 and the pressure roller 36. Then, the unfixed toner image surface comes into close contact with the lower surface of the fixing film 24 which is rotated at the same speed as the sheet P in the same direction in the same direction, and overlaps with the fixing film 24 without causing surface misalignment or wrinkling. In this state, the heating roller 32 and the pressure roller 36 pass between the mutual pressure contact portions N while receiving a sandwiching pressure.

In the process of passing through the mutual pressure contact portion N, the toner image Ta on the sheet P is heated and becomes a softened / melted image Tb.

The sheet portion passing through the mutual pressure contact portion N between the heating roller 32 and the pressure roller 36 is spread between the heating roller 32 and the separation upper roller 34 until it reaches the position of the separation upper roller 34. The fixing film that is running continues to be conveyed in close contact. The conveyor belt 37 supports the back surface of the sheet P and maintains the close contact between the sheet P and the fixing film 24. In the carrying process C, the heat of the softened / melted toner image Tb is dissipated and becomes a cooled / solidified toner image Tc.

The heat radiation of the toner in this heat radiation / cooling process is natural heat radiation cooling in this example, but it may be forcibly performed by heat radiation cooling by disposing heat radiation fins or blowing means.

When the fixing film 24 is conveyed to the position S of the separation upper roller 34, the running direction of the fixing film 24 is turned away from the surface of the sheet P along the surface of the separation upper roller 34 having a large curvature. Are separated from each other and are discharged to the sheet P discharge tray 12. By the time of this separation, the toner has sufficiently cooled and solidified Tc, and the adhesion and fixing force of the toner with respect to the sheet P is sufficiently large and that with respect to the fixing film 24 has become extremely small. The separation is easily performed sequentially without causing toner offset to the fixing film 24.

In the present embodiment, it is possible to set the temperature of the heating roller 32, which is the heating element, higher than the temperature that causes high temperature offset in the conventional heating roller fixing method, and the fixability is improved. Further, the allowable temperature range of the heating element is wide on the high temperature side, and the temperature control can be simplified.

Further, when fixing a multi-color toner image, especially a three-color toner image, it can be sufficiently melted at a high temperature, so that color mixing is easy. Further, since the toner is once melted, cooled and solidified in a state of being in close contact with the fixing film 24, and then peeled from the fixing film 24, the surface property of the toner image can be made similar to the surface property of the fixing film. Therefore, for example, if the surface of the fixing film 24 is made smooth, it becomes possible to give the surface of the toner image Tc gloss like that of a silver salt photograph.

Further, by making the fixing film 24 thin as described above, heat accumulation in the fixing film is prevented and the cooling process of the toner image is made efficient. Further, when a resin thin film was used as the fixing film, the adhesion to the toner image was improved and the heat transfer efficiency was improved.

(6) Another fixing device configuration example 2 (FIG. 6) In the apparatus of FIG. 5, the heating body 34 is not limited to the heating roller, and as shown in FIG. 6, the fixed heating shown in the apparatus of FIG. The body 20 may be used. In this case, in addition to the above-described effects, the heat capacity of the heating element 22 and the substrate 21 is small, and since they are insulated, there is an advantage that the temperature rising speed is fast and the standby temperature control is not required.

Further, instead of the separation upper roller 34 of the apparatus shown in FIG. 5, a separation stay 38 having an end face having a larger curvature as in the apparatus shown in FIG. 6 is arranged, so that the sheet P is separated more reliably from the fixing film 24. It will be possible.

(7) Other Fixing Device Configuration Example 3 (FIG. 7) In the device of FIG. 7 in the device of FIG. 1, a transparent member 39 such as heat-resistant glass is arranged in place of the heating body 20, and the member 39 is used. The radiant heat source 40 such as a halogen lamp disposed inside the endless fixing film 24 is used to heat the toner image.

In this embodiment, the fixing film 24 is preferably transparent to the radiant heat wavelength. Therefore, in the present embodiment, as an example, a film 24 is used in which a heat-resistant layer 24a (FIG. 3) made of transparent polyimide containing fluororesin powder is formed with a release layer 24b made of transparent silicon resin.

In the case of the apparatus of this embodiment, since the heating is performed by radiation, the temperature of the toner can be instantly heated and melted. Therefore, the sheet P
Since it suffices to heat only when the pressure contact portion N is in the pressure contact portion N, power can be saved and the temperature rise inside the machine is small.

(Effects of the Invention) As described above, according to the present invention, a heating device is disposed on one surface side of a film, an image carrier is closely attached to the other surface side, and a thermal energy is applied to the image carrier through the film. With regard to the above, it is possible to solve the problem of wrinkling of the recording material in the case of using an endless belt type film as a film with a simple means configuration, and it is possible to obtain stable apparatus performance over a long period of time.

[Brief description of drawings]

1 (a), (b), and (c) are schematic views showing various forms of the film used in the present invention, FIG. 2 is a configuration diagram of an example of a fixing device according to the present invention, and FIG. 3 is a film. FIG. 4 is a schematic diagram of an example of an image forming apparatus incorporating the fixing device of FIG. 2, and FIGS. 5 to 7 are diagrams of other configuration examples of the fixing device. 24 is an endless film, 20, 32, 39 and 40 are heating elements, P
Is a transfer material sheet as an image carrier (recording material).

Front page continued (72) Inventor Shigeo Kimura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroyuki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-59-68766 (JP, A) JP-A-59-157678 (JP, A) JP-A 61-109083 (JP, A) JP-A 63-56662 (JP, A) Kaihei 1-144084 (JP, A) JP-A-2-157880 (JP, A) JP-A-2-157885 (JP, A) JP-A-47-13288 (JP, A) JP, U) Actual opening Sho 58-137042 (JP, U) Actual opening Sho 50-89339 (JP, U) Actual opening Sho 49-110644 (JP, U) Actual opening Flat 2-81551 (JP, U) Special public 51-29825 (JP, B1)

Claims (1)

[Claims] 1. A fixing device in which a heating body is disposed on one side of a film and an image carrier is closely attached to the other side of the film, and thermal energy is applied to the image carrier via the film, wherein the film is endless. A fixing device, which is a film, and has a film circumferential length that increases from one point other than the film axial end toward the film end.