JP2010139537A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device compatibly achieving shortening of warm-up time and prolongation of service life of a fixing sleeve, and to provide an image forming apparatus. <P>SOLUTION: The fixing sleeve 201 receives alternating current magnetic flux generated by an exciting coil 213, and generates Joule heat. A fixing roller 202 includes a foaming rubber layer which is expanded and contracted in accordance with temperature. A heat insulation air layer is formed between the fixing sleeve 201 and the fixing roller 202 at ordinary temperature, whereby the warm-up time is shortened. When fixing, the fixing sleeve 201 is tightly fit to the fixing roller 202 by expansion pressure of the foaming rubber layer, whereby the meandering of the fixing sleeve 201 is reduced or suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a technique for preventing meandering of a fixing sleeve loosely fitted to a fixing roller.

In a thermal fixing type image forming apparatus in which a toner image is melted and pressed onto a recording sheet, it is required to shorten the warm-up time of the fixing apparatus in order to start image formation sooner after receiving a print instruction from a user. ing.
For this reason, for example, an induction heating method in which the fixing sleeve is heated by electromagnetic induction has been adopted. In the induction heating method, the fixing sleeve is wound around a single fixing roller to minimize the diameter of the fixing sleeve and reduce the heat capacity thereof, thereby achieving a significant reduction in warm-up time.

In order to further shorten the warm-up time in such an induction heating type fixing device, a technique of providing an air layer between the fixing sleeve and the fixing roller has been developed (see Patent Document 1).
By doing so, the heat insulation effect of the air layer between the fixing sleeve and the fixing roller prevents heat from escaping from the electromagnetic induction heated fixing sleeve to the fixing roller, so that the temperature of the fixing sleeve can be increased more quickly. can do.
Japanese Patent Laid-Open No. 10-074007

However, when an air layer is provided between the fixing sleeve and the fixing roller, the frictional force between the fixing sleeve and the fixing roller is reduced, and therefore the meandering of the fixing sleeve sliding in the direction of the rotation axis of the fixing roller becomes remarkable. .
Conventionally, a meandering restriction collar that restricts the meandering of the fixing sleeve has been provided at both ends in the rotation axis direction of the fixing roller. When the fixing sleeve comes into contact with the meandering restriction collar, the fixing sleeve cannot meander further. .

However, when the meandering becomes prominent and the fixing sleeve continues to hit the meandering restriction collar, there arises a problem that the fixing sleeve is worn or damaged due to friction with the meandering restriction collar.
SUMMARY An advantage of some aspects of the invention is that it provides a fixing device and an image forming apparatus that achieve both a reduction in warm-up time and a longer life of a fixing sleeve. .

  In order to achieve the above object, a fixing device according to the present invention is a fixing device that heats an endless belt-like fixing sleeve, melts a toner image, and fuses it to a recording sheet. A fixing roller that expands in diameter as the temperature of the fixing sleeve increases, a pressure roller that is in contact with the outer peripheral surface of the fixing sleeve and sandwiches the fixing sleeve between the fixing roller, and a temperature raising means that raises the temperature of the fixing sleeve; The fixing sleeve is loosely fitted to the fixing roller at normal temperature, while the fixing sleeve is in a state of being closely fitted to the fixing roller when the fixing sleeve is at the fixing temperature. To do.

In this way, when the fixing sleeve is at room temperature, the fixing sleeve is loosely fitted to the fixing roller, so that the warm-up time can be shortened, and when the fixing sleeve is at the fixing temperature, the fixing sleeve is closely fitted to the fixing roller. The meandering of the sleeve can be suppressed.
In this case, in the fixing roller, the outer peripheral surface of the cored bar is covered with a heat-expandable member, and the heat-expandable member is preferably expanded by heat from the fixing sleeve. If it is a porous elastic member with gas sealed inside, it is more preferable.

In this case, specifically, the thermally expandable member may be foamed rubber. In particular, it is preferable that the core metal has an outer peripheral surface that is substantially cylindrical, and the foamed rubber covers the outer peripheral surface so as to have a thickness of 12.5 mm or more.
Further, when the fixing roller is heated to the fixing temperature with the fixing sleeve removed, it is preferable to select a fixing roller whose outer diameter is larger than the inner diameter of the fixing sleeve to prevent meandering. The outer diameter of the fixing roller at the fixing temperature is 1.4 mm or more smaller than the inner diameter of the fixing sleeve at normal temperature, and the outer diameter of the fixing roller at the fixing temperature is 0 than the inner diameter of the fixing sleeve at the fixing temperature in the state of being extracted from the fixing sleeve. If the fixing roller and the fixing sleeve having a relationship of 8 mm or more are used, the warm-up time can be further shortened.

Further, if a regulating member is provided at both ends of the fixing roller in the rotational axis direction and regulates the displacement of the fixing sleeve beyond the predetermined direction in the rotational axis direction, it effectively prevents meandering during warm-up. Can do.
In this case, when the fixing roller is disposed at both ends in the rotation axis direction of the fixing roller and at normal temperature, the displacement of the fixing sleeve in the rotation axis direction is restricted more than a predetermined amount, and the restriction is released at the time of fixing. In particular, if the regulation member is reversibly thermally deformed to perform the regulation and release thereof, the wear of the fixing sleeve at the time of fixing can be suppressed, and the service life thereof can be extended.

  An image forming apparatus according to the present invention is characterized by the fixing device according to the present invention. In this way, both shortening the warm-up time and preventing the fixing sleeve from meandering can be achieved.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings, taking an induction heating type image forming apparatus as an example.
[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.
FIG. 1 is a diagram illustrating a main configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes an imaging unit 100Y to 100K, an exposure device 101, an intermediate transfer belt 102, a secondary transfer roller 103, a cleaner 104, a paper feed cassette 105, a pickup roller 106, and a fixing device 107. , A discharge roller 108 and a discharge tray 109, and toner bottles 110Y to 110K are mounted.

The imaging units 100Y to 100K develop the electrostatic latent image formed by the exposure device 101 to form toner images of colors of yellow (Y), magenta (M), cyan (C), and black (K). Primary transfer is performed on the transfer belt 102. Residual toner on the intermediate transfer belt 102 is removed by a cleaner 104.
The paper feed cassette 105 stores recording sheets P therein. The recording sheets P are taken out one by one by the pickup roller 106 and sent out to the conveyance path. The secondary transfer roller 103 electrostatically transfers the toner image on the intermediate transfer belt 102 onto the recording sheet.

The fixing device 107 melts the toner image and presses it on the recording sheet. Thereafter, the recording sheet is discharged onto the discharge tray 108 by the discharge roller 107. The toner bottles 110Y to 110K are detachably mounted, and supply toner of each color to the imaging units 100Y to 100K, respectively.
[2] Configuration of Fixing Device 107 Next, the configuration of the fixing device 107 will be described.

As shown in FIG. 2, the fixing device 107 is a so-called induction heating type fixing device, and includes a fixing sleeve 201, a fixing roller 202, a pressure roller 203, a coil bobbin 210, a skirt core 211, a main core 212, and an excitation coil. 213 and an end core 214.
The AC magnetic flux generated by the exciting coil 213 wound around the coil bobbin 210 is guided to the fixing sleeve 201 by the bottom core 211, the main core 212, and the end core 214.

The fixing sleeve 201 has an inner diameter of 46.4 mm and a thickness of 40 μm on a nickel base outer peripheral surface, a 200 μm thick silicon rubber elastic layer, and a 20 μm thick PFA (Tetrafluoroethylene-perfluoroalkylvinyl ether copolymer) mold release. Layers are sequentially stacked. The fixing sleeve 201 receives AC magnetic flux from a nickel base and generates Joule heat.
The fixing roller 202 has a foamed rubber layer made of silicon formed on the peripheral surface of a core metal of φ20 mm, and has an outer diameter of 45.0 mm at room temperature (15 ° C.). For this reason, a gap (insulating air layer) is formed between the fixing sleeve 201 and the fixing roller 202 at room temperature (FIG. 2A). The maximum layer thickness of the insulating air layer is 1.4 mm. For this reason, at the time of warm-up, heat is prevented from escaping from the fixing sleeve 201 to the fixing roller 202, so that the warm-up time can be shortened.

  Further, the fixing roller 202 expands as the temperature rises, and in a state where the fixing roller 202 is taken out from the fixing sleeve 201, the outer diameter is increased to 200.degree. C. to 47.2 mm. For this reason, the fixing sleeve 201 is closely fitted to the fixing roller 202 by this expansion pressure during fixing (FIG. 2B). Accordingly, since the frictional force between the fixing roller 202 and the fixing sleeve 201 is increased, the meandering of the fixing sleeve 201 is reduced and suppressed.

  In FIG. 2B, a broken line 202a is shown to compare the outer diameter of the fixing roller 202 at room temperature with the outer diameter at the time of expansion. It can be seen that as the fixing roller 202 expands, the NIP width that is a contact point with the pressure roller 203 increases. On the contrary, when the temperature of the fixing roller 202 is low, the NIP width is reduced, and accordingly, the contact area between the fixing sleeve 201 and the fixing roller 202 is also reduced, so that the warm-up time is shortened.

  FIG. 3 is a perspective view showing an end portion of the fixing roller 202. When the temperature of the fixing roller 202 is low, the contact area between the fixing roller 202 and the fixing sleeve 201 is small and the frictional force is small, so that the fixing sleeve 201 may meander. Therefore, at the end of the fixing roller 202, the meandering restriction collar 301 is fitted on the cored bar 202a protruding from the foamed rubber layer 202b.

The meandering restriction collar 301 is made of a heat-resistant resin material such as PPS (polyphenylene sulfide), and is fixed to the core metal 202 a with a retaining ring 302. This prevents the fixing sleeve 201 from meandering beyond the meandering restriction collar 301 even when the fixing sleeve 201 is not fitted to the fixing roller 202 during warm-up.
[3] Experiments Several experiments were conducted to confirm the effectiveness of the present invention, and the results will be described.

(1) Insulating Air Layer and Warm-up Time First, the relationship between the size of the gap (insulating air layer) between the fixing sleeve and the fixing roller and the length of the warm-up time will be described.
FIG. 4 is a graph showing the relationship between the warm-up time for raising the temperature of the fixing sleeve from 20 ° C. to the fixing temperature (target temperature 170 ° C.) and the size of the heat insulating air layer.

In FIG. 4, a graph 401 shows a temperature change when the fixing sleeve 201 is warmed up. On the other hand, the graph 402 shows the temperature change during warm-up when the fixing sleeve and the fixing roller are brought into close contact with each other.
As shown in FIG. 4, when the insulating air layer is provided, it takes about 31.5 seconds for the fixing sleeve to reach 170 ° C., whereas when the insulating air layer is not provided, it is about 48. It takes 2 seconds. Therefore, the warm-up time can be shortened by about 35% by providing the insulating air layer.

When the warm-up time is shortened, energy saving can be achieved as follows. FIG. 5 is a graph showing the transition of the fixing temperature. Conventionally, since the rate of temperature rise is not so fast, for example, the warm-up time is shortened by setting the preheating temperature to 120 ° C. during standby and the preheating temperature during sleep to 50 ° C. (FIG. 5 (a)).
On the other hand, in the case of the present invention, the rate of temperature rise can be increased, so that the warm-up time can be sufficiently shortened without performing preheating during standby or sleep (FIG. 5 ( b)).

That is, according to the present invention, since the warm-up time can be sufficiently shortened by contracting the fixing roller and providing the heat insulating air layer at room temperature, preheating is not required and energy saving can be achieved.
(2) Fixing Roller Size Next, the fixing roller size will be described.

(A) Outer diameter during fixing The fixing roller according to the present invention expands and expands during fixing and is fitted to the fixing sleeve to prevent meandering of the fixing sleeve. Accordingly, the temperature of the fixing roller according to the present invention is raised to the fixing temperature in a state where the fixing roller is taken out from the fixing sleeve, and when the outer diameter (hereinafter referred to as “free expansion outer diameter”) becomes large, An experiment was conducted to see if meandering can be prevented.

The inner diameter of the fixing sleeve used in this experiment is approximately 40 mm at both normal temperature and fixing time. A fixing roller having an outer diameter of 39.8 mm at room temperature was used, and the free expansion outer diameter was changed by adjusting the temperature. As will be described later, the free expansion outer diameter of the fixing roller is proportional to the temperature (FIG. 8).
The system speed was 300 m / sec. Accordingly, the fixing sleeve is also fed at this speed. The nip load is 475N. Although the nip width differs depending on the temperature control temperature, it was set to 10.5 mm at 180 ° C.

Further, the rotational axis of the fixing roller and the rotational axis of the pressure roller are in a twisted positional relationship. This positional relationship of torsion is a positional relationship obtained when the tolerances of all parts are assembled in the worst state. Thus, an experiment was conducted in which the axial force applied to the fixing sleeve (hereinafter referred to as “meandering force”) was the largest within the tolerance range.
Under such conditions, the degree of meandering was determined visually. That is, the case where the movement of the fixing sleeve can be confirmed visually is determined as “meandering”. Further, even when it was not judged as “meandering”, it was judged as “slightly meandering” when the fixing sleeve, the fixing roller and the pressure roller were continuously rotated for 30 minutes and the meandering could be visually confirmed. Otherwise, it was determined as “no meandering”.

FIG. 6 is a table showing the experimental results. As shown in FIG. 6, when the difference between the free expansion outer diameter of the fixing roller and the inner diameter of the fixing sleeve (hereinafter referred to as “diameter difference”) is 0.2 mm or less, the fixing sleeve meanders. It was found that the meandering was slightly in the case of .4 mm, but not meandering in the case of 0.8 mm or more.
(B) Outer diameter during warm-up The fixing roller according to the present invention contracts at room temperature and has a heat insulating air layer between the fixing sleeve and the warm-up time. Therefore, using fixing rollers having different outer diameters at normal temperature, the average temperature increase rate is obtained from the time required for the temperature to rise from 25 ° C. to 100 ° C., and the outside of the fixing roller suitable for shortening the warm-up time is obtained. The diameter was examined.

The inner diameter of the fixing sleeve used in the experiment is 40 mm at room temperature, and a substantially constant inner diameter is maintained regardless of the temperature control temperature. Fixing rollers having different outer diameters from 37 mm to 40 mm by 0.2 mm were used.
The input power of the induction heating (IH) apparatus was 1050 W, the system speed was 300 mm / second, and the nip load was 475 N. The nip width varies depending on the outer diameter of the fixing roller, but is 10.5 mm if the outer diameter of the fixing roller is 40 mm.

FIG. 7 is a graph showing the relationship between the diameter difference between the fixing sleeve and the fixing roller at normal temperature and the heating rate. As shown in FIG. 7, when the diameter difference exceeds 1.4 mm, the rate of temperature increase increases, whereas when the diameter difference is less than 1.4 mm, the rate of temperature increase decreases.
(C) Expansion amount of fixing roller As described above, the outer diameter of the fixing roller must be 1.4 mm or more smaller than the inner diameter of the fixing sleeve at room temperature, and 0.8 mm or more larger than the inner diameter at the time of fixing. That is, the outer diameter of the fixing roller must be expanded by 2.2 mm or more from the outer diameter at room temperature to the outer diameter at the time of fixing.

FIG. 8 is a graph showing the relationship between the temperature adjustment temperature and the outer diameter of the fixing roller having a core metal diameter of 20 mm and different foam rubber layer thicknesses. In FIG. 8, graphs 801 to 805 indicate the degree of expansion of the fixing roller whose outer diameter at normal temperature is 46.0 mm, 45.0 mm, 44.0 mm, 39.8 mm, and 36.0 mm, respectively. This is indicated by an increase Δφ.
As shown in FIG. 8, the outer diameter of the fixing roller is directly proportional to the temperature adjustment temperature, and Δφ increases as the thickness of the foam rubber layer increases. Moreover, if FIG. 8 is used, the required dimension of a fixing roller can be estimated.

For example, when the temperature adjustment temperature at the time of fixing is 200 ° C., it can be seen from FIG. 8 that the outside diameter at normal temperature must be 45 mm or more. Since the core metal diameter is 20 mm, the thickness of the foam rubber layer may be 12.5 mm or more.
(D) Summary From the above discussion, in the present embodiment, the fixing roller has a core metal diameter of 20 mm, an outer diameter of 45 mm, and an inner diameter of the fixing sleeve of 46.4 mm. The fixing roller is fitted to the fixing sleeve at the time of fixing to suppress meandering of the fixing sleeve.

[4] Modifications As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .
(1) In the above embodiment, the case where the meandering prevention collar 301 is used to prevent meandering in the state where the fixing roller 202 is not fitted to the fixing sleeve 201 during warming up has been described. Needless to say, the present invention is not limited to this. Instead of the meandering prevention collar 301, the following may be adopted.

  FIG. 9 is a perspective view showing an end portion of the fixing roller 202 according to this modification. A meandering restriction collar 901 is fitted to the cored bar 202 a protruding from the foamed rubber layer 202 b at the end of the fixing roller 202. The meandering restriction collar 901 is fixed to the cored bar 202a by a retaining ring 902, and the fixing sleeve 201 is prevented from meandering beyond the meandering restriction collar 901 (FIG. 9A).

  The meandering restriction collar 901 is an annular member made of a heat-expandable material, for example, silicon rubber, and has a groove 901b along its peripheral edge 901a (FIG. 9B). When the fixing roller 202 is not fitted to the fixing sleeve 201 at normal temperature or warming up, the meandering fixing sleeve 201 is brought into contact with the peripheral portion 901a to prevent further meandering.

  In addition, when the fixing roller 202 is fitted to the fixing sleeve 201 at the time of fixing or the like, and the meandering of the fixing sleeve 201 is suppressed, the meandering prevention collar 901 also expands and a groove portion is formed at the fixing sleeve 201. 901b is arranged. As a result, the fixing sleeve 201 and the meandering prevention collar 901 do not rub against each other more than necessary, so that the consumption of the fixing sleeve 201 can be suppressed and the life can be extended.

Note that the material of the meandering restriction collar 901 is not limited to a thermally expandable material, and other materials such as a shape memory alloy may be used.
(2) In the above embodiment, the case where the outer diameter of the fixing roller 202 is changed by thermally expanding the foamed rubber layer of the fixing roller 202 has been described, but it is needless to say that the present invention is not limited to this. Other materials such as shape memory alloys may be used.

Foamed rubber expands by elastically expanding the rubber part by thermally expanding a large number of bubbles contained in the inside, but the present invention is not limited to this. A member that expands an elastic member that seals the gas by thermally expanding the gas sealed inside such as a body may be provided on the outer peripheral surface of the cored bar.
Further, the temperature of the fixing sleeve may be detected by a temperature sensor, and the fixing roller may be enlarged by mechanical means when the temperature reaches the fixing temperature or approaches the fixing temperature. The mechanical means is, for example, injecting a gas or a liquid into an elastic member provided on the outer peripheral surface of the core metal of the fixing roller and expanding the elastic member.

When the temperature of the fixing sleeve, which has been lowered to room temperature after fixing, is raised again, if the gas or liquid is discharged from the elastic member in advance, the fixing roller can be reduced in diameter to shorten the warm-up time.
[5] Others (1) Although not particularly mentioned in the above embodiment, when the outer diameter of the fixing roller does not reach the inner diameter of the fixing sleeve, the fixing roller and the pressure are increased as the fixing roller expands. The nip width formed by the roller is increased.

When the rotation axis of the fixing roller and the rotation axis of the pressure roller are in a torsional positional relationship, the force in the rotation axis direction applied to the fixing sleeve increases as the nip width increases. This is a factor that promotes meandering.
On the other hand, as the fixing roller expands, the contact area between the fixing roller and the fixing sleeve increases, so that the frictional force between the fixing roller and the fixing sleeve increases. This is a factor that suppresses meandering.

When the outer diameter of the fixing roller reaches the inner diameter of the fixing sleeve and the fixing roller is fitted to the fixing sleeve, the nip width does not increase any more, but the pressing force on the fixing sleeve by the fixing roller increases as the temperature rises. Become. For this reason, since the nip pressure increases, the frictional force between the fixing sleeve and the pressure roller increases. This is a factor that promotes meandering.
On the other hand, if the pressing force to the fixing sleeve by the fixing roller increases, the frictional force between the fixing roller and the fixing sleeve also increases. This is a factor that suppresses meandering.

(2) Factors affecting meandering include the inner diameter of the fixing sleeve in addition to temperature.
Generally, the nip width is proportional to 1/3 of the radius of the fixing roller. Therefore, the meandering force is proportional to 1/3 of the outer diameter of the fixing roller. Further, since the circumferential length of the contact portion between the fixing roller and the fixing sleeve is proportional to the circumferential length of the fixing sleeve, the force for suppressing meandering is proportional to the inner diameter of the fixing sleeve. Therefore, meandering is suppressed as the inner diameter of the fixing sleeve increases.

(3) When the outer diameter of the fixing roller is smaller than the inner diameter of the fixing sleeve, the nip area where the fixing sleeve contacts the pressure roller includes a pseudo nip area where the fixing sleeve does not contact the fixing roller.
That is, as shown in FIG. 10, in the configuration in which the fixing sleeve 1001 is sandwiched between the fixing roller 1002 and the pressure roller 1003, the fixing sleeve 1001 is in the nip region where the fixing sleeve 1001 contacts the pressure roller 1003. A pseudo nip region 1010 where 1001 does not contact the fixing roller 1002 is included.

  In the pseudo nip region 1010, since the fixing sleeve 1001 does not contact the fixing roller 1002, it is considered that the heat transfer from the fixing sleeve 1001 to the fixing roller 1002 is small. In particular, the smaller the outer diameter of the fixing roller 1002, the smaller the heat transfer from the fixing sleeve 1001 to the fixing roller 1002, so the warm-up time can be shortened.

  The fixing device and the image forming apparatus according to the present invention are useful as a technique for preventing meandering of a fixing sleeve that is loosely fitted to a fixing roller.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 2A and 2B are cross-sectional views showing the main configuration of the fixing device 107, where FIG. 1A shows a state at normal temperature, and FIG. 2B shows a state at fixing. FIG. 5 is an assembly diagram showing the structure of the end portion of the fixing roller 202, and shows an appearance in which the fixing sleeve 201 is partially cut away. 6 is a graph showing the relationship between the warm-up time for raising the temperature of the fixing sleeve from 20 ° C. to 170 ° C. and the size of the insulating air layer. It is a graph which illustrates transition of temperature control temperature, (a) is a graph concerning a prior art, and (b) is a graph concerning the present invention. 4 is a table showing a relationship between a difference between an inner diameter of a fixing sleeve and an outer diameter of a fixing roller at a normal temperature and a meandering state of the fixing sleeve. 6 is a graph showing a relationship between a diameter difference between a fixing sleeve and a fixing roller at a normal temperature and a heating rate. 6 is a graph showing the relationship between the temperature adjustment temperature and the outer diameter for each of fixing rollers having a core metal diameter of 20 mm and different thicknesses of foamed rubber layers. FIG. 9 is an assembly diagram illustrating a configuration of an end portion of a fixing roller 202 according to a modified example of the present invention, where (a) is an external perspective view in which a fixing sleeve 201 is partially cut away, and (b) is a cross-sectional view. is there. FIG. 6 is a cross-sectional view illustrating the shape of a fixing sleeve in a nip region.

Explanation of symbols

1. Image forming apparatus 107... Fixing devices 201 and 1001... Fixing sleeves 202 and 1002... Fixing rollers 203 and 1003. ……………… Bottom core 212 ……………… Main core 213 ……………… Excitation coil 214 ……………… End core 202 b ……………… Foam rubber layer 202 a ………… Metal cores 301, 901 ...... Meandering control collars 302, 902 ...... Retaining ring 901a ......... Peripheral edge 901b ......... Groove 1010 ......... Pseudo nip region

Claims (11)

A fixing device that heats an endless belt-shaped fixing sleeve, melts a toner image, and fuses it to a recording sheet,
A fixing roller that is inserted into the fixing sleeve and expands as the temperature of the fixing sleeve increases;
A pressure roller that contacts the outer peripheral surface of the fixing sleeve and sandwiches the fixing sleeve with the fixing roller;
A temperature raising means for raising the temperature of the fixing sleeve,
At room temperature, while the fixing sleeve is loosely fitted to the fixing roller,
A fixing device, wherein when the fixing sleeve is at a fixing temperature, the fixing sleeve is in a state of being closely fitted to the fixing roller. The fixing roller is formed by coating the outer peripheral surface of the core metal with a thermally expandable member.
The fixing device according to claim 1, wherein the thermally expandable member is expanded by heat from the fixing sleeve. The fixing device according to claim 2, wherein the thermally expandable member is a porous elastic member in which a gas is sealed. The fixing device according to claim 3, wherein the thermally expandable member is foamed rubber. The metal core has a substantially cylindrical outer peripheral surface,
The fixing device according to claim 4, wherein the foamed rubber covers the outer peripheral surface to have a thickness of 12.5 mm or more. 6. The fixing roller according to claim 1, wherein when the fixing roller is heated to a fixing temperature with the fixing sleeve removed, the fixing roller is selected such that the outer diameter becomes larger than the inner diameter of the fixing sleeve. A fixing device according to claim 1. The outer diameter of the fixing roller at room temperature is 1.4 mm or more smaller than the inner diameter of the fixing sleeve at room temperature,
The fixing roller and the fixing sleeve having a relationship in which the outer diameter of the fixing roller at the fixing temperature is 0.8 mm or more larger than the inner diameter of the fixing sleeve at the fixing temperature in a state of being extracted from the fixing sleeve. The fixing device according to claim 6. The image fixing device according to claim 1, further comprising a regulating member that is disposed at both ends of the fixing roller in the rotational axis direction and regulates a displacement of the fixing sleeve in the rotational axis direction beyond a predetermined amount. Disposed at both ends of the fixing roller in the rotation axis direction;
When the fixing roller is at room temperature, restrict the displacement of the fixing sleeve beyond the predetermined direction in the direction of the rotation axis,
The image fixing device according to claim 1, further comprising a regulating member that cancels the regulation at the time of fixing. The fixing device according to claim 9, wherein the restriction member performs the restriction and the release thereof by reversibly thermally deforming. An image forming apparatus comprising the fixing device according to claim 1.

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