JP2003076204A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the staining of the edge of transfer material by the fixing separation pawl of a fixing device and to reduce jamming by the pawl. SOLUTION: By setting the temperature of the fixing separation pawl to be higher than the surface temperature of a fixing roller, toner adhering to the fixing pawl is transferred to the fixing roller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer and a fax machine which form an image on a transfer material by using electrophotographic technology.
And other image forming apparatuses.

[0002]

2. Description of the Related Art It is known to use an electrostatic transfer process as one type of image forming means in an image forming apparatus. In this type of image forming apparatus, an electrostatic transfer process is performed on a transfer material such as paper. A fixing device is used to fix and fix the formed toner image on the transfer material.

This fixing device is provided with a fixing roller heated by a heater and a pressure roller pressed against the fixing roller which is also heated, and a toner image is formed in a pressing nip portion formed by these rollers. There is a type of fixing and fixing the toner image on the transfer material by passing the electrostatically formed transfer material. This type of fixing device has advantages such as high thermal efficiency, excellent safety, and miniaturization, and is widely put into practical use.

However, in this type of fixing device, since the toner image on the transfer material comes into direct contact with the fixing roller, a part of the toner adheres to the fixing roller during fixing, and this adhered toner arrives next. There is a case where a so-called offset phenomenon occurs that adheres to the surface and causes deterioration of image quality.

Therefore, in order to avoid the offset phenomenon, the surface of the fixing roller is made of a material having a good releasability for the toner and the like, and a means such as applying silicone oil is adopted. However, since it is difficult to completely eliminate the offset phenomenon even if such means is adopted, a type of cleaning the toner adhering to the fixing roller has been proposed.

As one type of this cleaning means,
A cleaning web (strip-shaped cleaning member) made of a non-woven fabric impregnated with silicon oil is always brought into contact with and pressed against a rotationally driven fixing roller, and the web is successively wound up while the fixing roller is being wound up. In some cases, the oil is applied to the surface and the surface of the fixing roller is cleaned at the same time.

In the above-mentioned cleaning means, the fresh cleaning web surface which is successively fed is always in sliding contact with the fixing roller surface, and the offset toner wiped when the web is wound is successively collected. It has excellent functionality. In addition, the fixing device is relatively simple, small,
It can be made lightweight.

An example of such an image forming apparatus will be described as a conventional example.

First, an outline of the entire image forming apparatus will be described with reference to FIG. The surface of the image carrier 1 uniformly charged by the charging device 3 is irradiated with a laser or the like according to image information to form an electrostatic latent image. After the electrostatic latent image is developed into a toner image by the developing device 4, the toner image on the image carrier 1 is transferred onto the transfer material 51 by the transfer device 7. The unfixed toner image on the transfer material 51 in this state is heated and pressure-fixed by the fixing device 9 to obtain an electrophotographic image.

Next, the outline of the fixing device 9 will be described with reference to FIG. The fixing device 9 includes a fixing roller 10 including a halogen heater 12a therein, a pressure roller 11 including a halogen heater 12b, a cleaning web 18 for cleaning the fixing roller 10, a fixing upper separation claw 16 and the like. The roller 10 has a fluororesin formed on its surface. The pressure roller 11 has a silicon rubber layer of about 5 mm on a SUS core metal, and the top layer is also covered with a fluororesin such as a PFA tube. Fixing roller 1
The outer diameters of both 0 and the pressure roller 11 are 50 mm.

The thermistors 13a and 13b for detecting the temperature of the rollers are in contact with the sheet passing area of the transfer material 51 on the surfaces of the fixing roller 10 and the pressure roller 11, and the fixing heater is detected depending on the detected temperature. 12 outputs are controlled. The maximum output of the fixing heater 12 during image formation is
Each is 500 w, and 60 sheets of A4 size transfer material 51 can be passed per minute. The fixing roller 10 is controlled by the control device 14 so as to be maintained at 200 degrees.

The cleaning web 18 is a nonwoven fabric such as polyamide impregnated with silicon oil, and is pressed against the fixing roller 10 by a web pressure roller 19 and wound in a direction counter to the rotation of the fixing roller 10. In order to reduce the frequency of replacement of the cleaning web 18 (reduction of running cost), the winding speed of the web is extremely slowed down to about 0.05 mm per one transfer material, but it is sufficient for normal copying. A cleaning effect can be exhibited. The silicone oil supplied from the cleaning web 18 forms a film on the fixing roller 10, but since a part of the oil is absorbed by the transfer material 51, the oil on the fixing roller 10 is kept at a substantially constant amount. There is.

The web pressure roller 19 is a single foam roller having an outer diameter of 24 mm and having a single foam sponge layer formed by foaming a silicon rubber material having a thickness of 8 mm on a solid core metal made of stainless steel having a diameter of 8 mm. The web is pressed against the fixing roller 10 in the direction of the fixing roller 10 by a pressure mechanism (not shown) at both ends in the longitudinal direction perpendicular to the direction. The contact Nip between the cleaning web 18 and the fixing roller 10 is about 6 mm.

A fixing upper separation claw 16 is provided on the downstream side of the Nip portion between the fixing roller 10 and the pressure roller.
It is abutted against 0 with a pressing force of about 20 gf. The upper fixing separation claw 16 has a width of 2.5 mm at the tip end which is in contact with the fixing roller 10, and the entire width is in stable contact with the fixing roller 10. The melted toner of the transfer material 51 that has passed through the fixing Nip serves as an adhesive agent, and is easily wound around the fixing roller 10. Therefore, the transfer material 51 is separated by the fixing upper separation claw 16. Further, the curl of the transfer material 51 itself also causes winding around the fixing roller 10 depending on its direction.

The fixing upper separating claw 16 is symmetrical in the longitudinal direction, and the front and rear 1 at the positions of about 40 mm and 120 mm from the center, respectively.
Each one has a total of four. The minimum width of the transfer material 51 on which an image can be formed by the image forming apparatus is 100 m.
m, the maximum is 296 mm, and the paper is passed through the center.

[0016]

However, in the image forming apparatus as in the conventional example, there is a problem that the transfer material 51 is edge-dirty by the upper fixing separation claw 16. The fixing upper separation claw 16 does not have a mechanism for removing dirt on the leading end thereof, and since the contact with the fixing roller 10 is secured, toner adheres to the fixing upper separation claw 16. As described above, the cleaning of the surface of the fixing roller 10 is achieved by the cleaning web 18, but the upper fixing separation claw 16 is located on the upstream side in the rotation direction of the fixing roller 10 and has toner. A surface which is in contact with the transfer material 51 but not in contact with the cleaning web 18 comes into contact with the tip of the fixing separation claw 16. From this, the toner is deposited on the tip of the upper fixing claw 16. Further, since the transfer material 51 tends to adhere to the fixing roller 10, the transfer material 51 is generally separated from the fixing roller 10 by the upper fixing separation claw 16. Under these conditions, the toner deposited on the upper fixing separation claw 16 adheres to the leading end of the transfer material 51, leading to edge contamination.

[0017]

In order to solve the above problems, in the invention described in the present specification, the temperature of the fixing upper separation claw is set higher than that of the fixing roller so that the fixing upper separation claw moves from the fixing upper separation claw to the fixing roller. The deposited toner is transferred to remove the toner deposited on the tip of the separation claw for fixing, thereby preventing the edge of the transfer material from being smeared. The toner transferred to the fixing roller is
Finally, it is cleaned by the cleaning web.

Further, in more detail, the present invention can solve the above problems by the following constitution.

(1) After the toner image formed on the image bearing member is transferred onto the transfer material, the transfer material is sandwiched between a pair of heated rotating members and the unfixed toner image is heated and fixed onto the transfer material. In the image forming apparatus having a device, the fixing device is a fixing device in which a cleaning member is provided on a fixing roller, which is a rotating body on a side where an unfixed toner image comes into contact, of the rotating pair.
An image forming apparatus characterized in that the temperature of a transfer material separating member facing the fixing roller is made higher than that of the fixing roller, and the fixing roller is rotated when the transfer material is not sandwiched.

(2) The temperature of the separating member of the transfer material is raised by raising the temperature of the roller (hereinafter referred to as "pressure roller") facing the fixing roller to be higher than that of the fixing roller. The image forming apparatus according to (1) above.

(3) In making the temperature of the separating member higher than that of the fixing roller, the radiant heat from the pressure roller is utilized, according to the above (1) or (2). Image forming apparatus.

(4) The image forming apparatus as described in any one of (1) to (3) above, wherein a cleaning member provided on the fixing roller is made to function when the fixing roller and the pressure roller are rotated.

(5) A step of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. The image forming apparatus according to any one of (1) to (4) above, which is performed after power is turned on once in the morning and before image formation.

(6) A step of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. The image forming apparatus according to any one of (1) to (5) above, which is performed during standby.

(7) A step of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. The image forming apparatus as described in any one of (1) to (6) above, wherein the step is limited in the standby state by the number of image forming sheets.

(8) After the heating and fixing process of the fixing device is completed, the heating of the fixing roller and the pressure roller is interrupted, so that the surface temperature of the fixing roller is higher than the surface temperature of the pressure roller. The image forming apparatus according to any one of (1) to (7), wherein the image forming apparatus rapidly decreases.

(9) The image forming apparatus as described in (8) above, wherein the heat capacity of the fixing roller is smaller than that of the pressure roller.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) As a structure of a fixing upper separating claw 16, a large amount of width radiant heat emitted from a pressure roller 11 is received, and the received width radiating heat is a tip of the fixing upper separating claw 16. In order to efficiently transfer heat to Al, Al is used, which is partially excellent in thermal conductivity.

FIG. 3 shows the structure of the upper fixing separation claw 16.
This will be described with reference to (a), (b) and FIGS. 4 (a), (b).

FIGS. 3A and 3B show a conventional structure of the conventional fixing upper separation claw 16, and 16a uses PPS which is a flame retardant material, and is provided at a position corresponding to the tip of the fixing claw. In order to reduce friction with the fixing roller 10, a Teflon (R) coat is applied. Similarly, the fixing claw support 16b also employs PPS, and for convenience of manufacturing, two objects are united to form the fixing upper separation claw 16.

The upper fixing separation claw is axially supported by the support shaft 16c, and the tip of the upper fixing separation claw 16 is pressed against the fixing roller 10 by a spring member (not shown).

On the other hand, the constitution of the upper fixing separation claw 16 shown in this embodiment is as shown in FIGS. 4 (a) and 4 (b).
Two items 16d and 16e are added. In addition, 16
As the material of a, Al having excellent thermal conductivity is adopted, and a tip portion contacting the fixing roller 10 is coated with Teflon (R) like the fixing upper separation claw 16 used conventionally.
Two similar articles are also attached to the lower fixing claw 17.

Reference numeral 16e is a radiant heat receiving portion which is a layer made of the same carbon as the thick layer of the lamp black so that the radiant heat from the pressure roller 11 can be efficiently received. Instead, a matte black oil-based paint has almost the same effect. The layer of the radiant heat receiving portion 16e is made to adhere to the Al (aluminum) base material 16d having excellent thermal conductivity.

With this structure, the radiant heat of the pressure roller 11 can be efficiently received, and further, the heat can be efficiently transmitted to the tip end portion of the upper fixing claw 16 which is in contact with the fixing roller 10. With this separation claw, as shown below, the surface temperature of the pressure roller 11 is made higher than the surface temperature of the fixing roller 10, and as a result, the temperature at the tip of the fixing upper separation claw 16 is higher than the surface temperature of the fixing roller 10. Also decided to raise.

The temperature at the tip of the fixing upper separation claw 16 is
When the surface temperature of the fixing roller 10 is 100 ° C. and the surface temperature of the pressure roller 11 is 150 ° C., it is 140 ° C.,
In this embodiment, even when the temperature of the fixing roller 10 is lower than that of the pressure roller 11, the temperature of the pressure roller is not lower than 15 ° C.

Hereinafter, by lowering the temperature of the pressure roller 11 below the temperature of the fixing roller 10 and rotating the fixing roller 10 and the pressure roller 11, the toner adhering to the tip of the upper fixing claw 16 is removed. Will be described (see FIG. 5).

When the main body of the image forming apparatus is operated (hereinafter referred to as "morning first"), the temperature control of the fixing roller 10 is delayed. As a result, the fixing roller 10 and the upper fixing claw 16 are fixed.
A temperature difference is created between the fixing upper separation claw 16 and the fixing roller 10 during the previous rotation in the morning, the toner attached to the fixing upper separation claw 16 is moved to the fixing roller 10, and finally the toner on the fixing roller 10 is cleaned by the cleaning web 18. Wipe with.

Since the outline of the entire image forming apparatus is almost the same as the conventional example, it will be omitted.

The fixing device 9 also has the same hardware structure as that of the conventional example, and therefore will be described with reference to FIG.

The fixing device 9 includes a fixing roller 10 including a fixing heater (halogen heater) 12, a pressure roller 11, a cleaning web 18 for cleaning the fixing roller 10, a fixing upper separation claw 16 and the like. The roller 10 has a hollow 12 mm thick Al cored bar having a Si rubber layer of about 12 mm as an intermediate layer, and a fluorine resin such as PTFE is coated on the Si rubber layer of about 20 μm to form a surface layer. The pressure roller 11 has a silicon rubber layer having a thickness of 25 μm on an Al cored bar having a thickness of 12 mm and a top layer covering a PFA tube having a thickness of about 50 μm. Both the fixing roller 10 and the pressure roller 11 have an outer diameter of 50 m.
m. The cleaning web 18 is made of a nonwoven fabric such as polyamide having a thickness of 50 μm, is impregnated with silicone oil having a viscosity of 10,000 cs, is pressed against the fixing roller 10, and is wound in a direction against the rotation of the fixing roller 10. The winding speed is 0.0 per image.
It is 5 mm. (When continuously feeding, 0.0
5 mm).

Regarding the feeding of the web, the rotation of the winding roller is supported by a one-way clutch, an arm is provided for the clutch, and one end of the arm is operated by a solenoid magnet, whereby a small amount of stable web is fed. A feed operation has been achieved. The maximum output of the fixing heater 12 during image formation is 1000 W in total, and
60 sheets of 4-size transfer material can be passed per minute. The rotation speed of the fixing roller 10 is controlled to 300 mm / s.

The fixing roller 10 and the pressure roller 11 are controlled by the controller 14 so as to be maintained at 200 ° C. during the image forming process. A fixing upper separation claw 16 is in contact with the fixing roller 10 at a pressure of about 20 gf on the downstream side of the Nip portion between the fixing roller 10 and the pressure roller. The fixing upper separation claw 16 has a width of 2.5 mm at the tip end which is in contact with the fixing roller 10, and the entire width of the tip end is the fixing roller 1.
Stable contact with 0. Four fixing upper separation claws 16 are attached to the longitudinal direction, one at the front and one at the positions of 40 mm and 120 mm from the center, in total.

Next, the fixing roller 10 and the pressure roller 11
The temperature adjustment and the rotation timing will be described.

Regarding the temperature adjustment of the fixing roller 10 and the pressure roller 11, first, until the temperature detected by the thermistor 13a contacting the surface of the fixing roller 10 rises to 100.degree. The halogen heaters 12a and 12b are turned on until the temperature detected by the thermistor 13b rises to 150 ° C. When both of the rollers have reached the temperature, the fixing roller 10 and the pressure roller 11 are rotated. In addition, the feeding of the cleaning web 18 is started 10 seconds after the rotation of the fixing roller 10 is started, and is performed until 25 seconds after the rotation of the fixing roller 10 is started (the 0.75 mm cleaning web 18 is fed over 15 seconds). It will be.). The cleaning web 18 is fed in synchronization with the rotation of the fixing roller 10.

The halogen heaters 12a and 12b are turned on again when both the fixing roller 10 and the pressure roller 11 are started to rotate, and both the fixing roller 10 and the pressure roller 11 have a target temperature of 200.degree. According to the temperature detection of the thermistors 13a and 13b, the temperature is adjusted depending on whether or not the halogen heaters 12a and 12b are turned on,
When both rollers reach the target temperature, they enter a standby state and accept an image forming command. The fixing device 9 in the present embodiment has a configuration of 0.75 m of the cleaning web 18 in view of the relationship between the heat capacity of both rollers and the output wattage of the fixing heater (halogen heater) 12.
It does not enter the standby state until the feeding of m is completed.

In the present embodiment, 5,000 sheets of image were formed per day, and when the edges of the transfer materials that were passed during the durability of 500,000 were confirmed, the transfer materials were piled up to clean the edges of the edges. When measured using a density meter, the amount of toner adhering to the edge was reduced to 1/10.

When the toner adhesion on the tip of the fixing upper separation claw 16 is reduced, the separability of the transfer material from the fixing roller 10 is ensured, so that the frequency of jams in the fixing portion can be reduced. .

(Embodiment 2) Next, assuming that the temperature of the fixing roller 10 and the pressure roller 11 is not adjusted independently at the time of start-up in the morning, and the rise in the morning is achieved in a minimum time. A structure capable of obtaining the same effect as that of the first embodiment is shown.

In the present embodiment, the fixing roller 10 has an inner layer of 1.
A structure having a 0 mm Si rubber layer and a so-called thin roller structure is selected. In such a configuration, in the present exemplary embodiment, after the standby state after the image formation, the temperature of the thermistor 13a that is in contact with the surface of the fixing roller 10 becomes 120 ° C., and then the fixing roller 10
Then, the pressure roller 11 is rotated (the temperature controlled temperature in the standby state is 100 ° C.). The rotation time is 30 seconds,
Additionally, the cleaning web 18 is fed by the fixing roller 1.
It starts 15 seconds after the rotation of 0 starts and continues for 15 seconds after the rotation of the fixing roller 10 (the 0.75 mm cleaning web 18 is fed over 15 seconds). In this embodiment, the fixing roller 10 has a smaller heat capacity than the pressure roller 11, and even when the surface temperature of the fixing roller 10 is lowered to 120 ° C., the surface temperature of the pressure roller 11 is 170. The surface temperature of the fixing roller 10 is maintained at around 0 ° C., and the surface temperature of the fixing roller 10 is lower than the surface temperature of the pressure roller 11. The surface temperature of the fixing roller 10 and the pressure roller 11 during image formation is adjusted to 200 ° C.

The roller rotation at the time of standby described in this embodiment is performed when the cumulative number of images formed from the previous standby reaches 1000 or more, so that the feeding amount of the cleaning web 18 is reduced. It was confirmed that the effect can be suppressed and the same level of effect as in Example 1 can be obtained.

(Embodiment 3) In this embodiment, in order to improve the degree of freedom in selecting the thickness of the fixing roller 10, the temperature difference between the fixing roller 10 and the pressure roller 11 is achieved at a controlled temperature. Enter. The temperature of the pressure roller 11 has two stages of temperature during standby, the first temperature is 150 ° C, and the second temperature is 100 ° C. As shown in the second embodiment, the standby fixing roller 10 is used at the time of standby when the cumulative number of formed images exceeds 1000.
The standby temperature on the surface of the pressure roller 11 is 100 ° C., and the standby temperature on the surface of the pressure roller 11 is the first temperature, as in the second embodiment. And the thermistor 1
When both the sensors 3a and 13b can sense that the temperature has been reached, the fixing roller 10 and the pressure roller 11 are rotated at that time (the temperature control temperature in the standby state is 100 ° C.). The rotation time is 30 seconds, and in addition, the feeding of the cleaning web 18 is started 15 seconds after the rotation of the fixing roller 10 and the pressure roller 11 is started and 15 seconds after the rotation of the fixing roller 10 is started (15 0.75mm cleaning web 18 over a second
Will be sent. ). Then, after this step is completed, the standby temperature of the pressure roller 11 is set to 100 ° C. which is the second temperature.

As a result, the pressure roller 11 can be cleaned after a fixed number of images have been formed, and the standby temperature is maintained at 100 ° C. when the pressure roller 11 is not cleaned, and the power consumption is the minimum required. Can be suppressed to.

The present embodiment is different from the second embodiment only in the method of making the temperature difference between the fixing roller 10 and the pressure roller 11, and the effect is not significantly changed.

(Embodiment 4) In this embodiment, the temperature of the pressure roller 11 during image formation is controlled by the fixing roller 10.
30 degrees higher than the controlled temperature of
It is set so that the toner is transferred from the upper fixing separation claw 16 to the fixing roller 10. In this embodiment, the toner adhering to the tip of the fixing claw can be removed during image formation, and it is not necessary to separately provide a sequence, but the temperature control temperature of the pressure roller 11 is set higher than that of the fixing roller 10. It is subject to the restrictions that it must have. The effect of this example was equivalent to that shown in Example 1.

[0055]

According to the present invention, by making the surface temperature of the upper fixing claw 16 higher than the surface temperature of the fixing roller 10, the toner attached on the upper fixing claw 16 adheres to the fixing roller 10 side. Let When the toner is in a molten state, the toner of the fixing upper separation claw 16 tends to adhere to the lower temperature side when it exists at the contact position of the fixing upper separation claw 16 and the fixing roller 10, so that the toner of the fixing upper separation claw 16 is removed. By transferring to the fixing roller 10, the upper fixing separation claw 16 is cleaned. At the same time, the lower fixing claw 17 can be made to act on the pressure roller 11 in the same manner as the upper fixing claw 16.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of an entire conventional image forming apparatus.

FIG. 2 is a cross-sectional view schematically showing a fixing device of a conventional image forming apparatus.

3A and 3B schematically show fixing upper separation claws of an image forming apparatus of a conventional example, FIG. 3A is a plan view and FIG. 3B is a side view.

4A and 4B are schematic views of a fixing upper separation claw of an image forming apparatus of the present invention, in which FIG. 4A is a plan view and FIG. 4B is a side view.

FIG. 5 is a graph showing the correlation among fixing roller surface temperature control, pressure roller surface temperature control, pressure / fixing roller rotation temperature control, and cleaning web feed.

[Explanation of symbols]

1 Image carrier 2 Pre-exposure device 3 charging device 4 Developing device 7 Transfer device 8 cleaning device 9 Fixing device 10 fixing roller 11 Pressure roller 12 Fixing heater 13a Temperature detection device (thermistor) 13b Temperature detection device (thermistor) 14 Control device 15 Fixing entrance guide 16 Separation nail on fixing 16a Separation claw contact part 16b Separation claw support 16c support shaft 16d Al (aluminum) base material 16e Width heat receiving part 17 Separation under fixing nail 18 cleaning web 19 Web pressure roller 30 manuscripts 31 Original illumination lamp 32 CCD 33 laser 34 polygons 35 Laser exposure 36 image memory 41 Transfer material cassette 42 Paper feeder 43 Registration roller 45 conveyor belt 46 Output tray 47 Double-sided switchback device 48 hand tray 51 Transfer material 52 Unfixed toner image

Claims (9)

[Claims] 1. A fixing device for transferring a toner image formed on an image carrier onto a transfer material, and then sandwiching the transfer material between a pair of heated rotating bodies to heat and fix an unfixed toner image on the transfer material. In the image forming apparatus having the above-mentioned fixing device, the fixing device has a cleaning member provided on a fixing roller which is a rotating body on a side of an unfixed toner image that comes into contact with the fixing device. An image forming apparatus characterized in that the temperature of a separating member for a transfer material is set higher than that of the fixing roller, and the fixing roller is rotated when the transfer material is not sandwiched. 2. The temperature of a separation member for the transfer material is increased by increasing the temperature of a roller (referred to as a “pressure roller”) facing the fixing roller higher than that of the fixing roller. The image forming apparatus according to claim 1. 3. The image forming according to claim 1, wherein the temperature of the separating member is set higher than that of the fixing roller by utilizing the radiant heat from the pressure roller. apparatus. 4. The image forming apparatus according to claim 1, wherein a cleaning member provided on the fixing roller functions when the fixing roller and the pressure roller rotate. 5. The process of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. The image forming apparatus according to any one of claims 1 to 4, which is performed after power is turned on in the morning and before image formation. 6. The process of rotating the fixing roller and the pressure roller when the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing, and when the transfer material is not sandwiched. The image forming apparatus according to claim 1, wherein the image forming apparatus is performed in a standby mode. 7. The step of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. The image forming apparatus according to any one of claims 1 to 6, wherein the interval between the steps is limited by the number of image forming sheets when the process is performed in the standby mode. 8. The surface temperature of the fixing roller is lower than the surface temperature of the pressure roller as a result of interrupting the heating of the fixing roller and the pressure roller after the heating and fixing process of the fixing device is completed. 8. The image forming apparatus according to claim 1, wherein the image forming apparatus is fast. 9. The image forming apparatus according to claim 8, wherein the heat capacity of the fixing roller is smaller than the heat capacity of the pressure roller.