JP5089083B2 - Image heating device - Google Patents

Description

  The present invention relates to an image heating apparatus for heating an image formed on a recording material. This image heating apparatus is used in, for example, a copying machine, a printer, and a FAX.

  In a fixing device of an electrophotographic image forming apparatus, a toner image formed on a sheet is fixed on the sheet by heating and pressing. As such a fixing device, a roller fixing method in which a pressure roller is brought into pressure contact with a fixing roller to form a fixing nip has been conventionally employed.

  By the way, in order to increase the glossiness of the image and increase the speed of image formation, it is preferable to lengthen the sheet nip passage time and sufficiently melt the toner. In order to achieve this with the conventional roller fixing method, the diameters of the fixing roller and the pressure roller must be increased, and the fixing device is increased in size.

Therefore, Patent Document 1 proposes a belt fixing method capable of obtaining a sufficient nip width (length in the sheet conveying direction) while achieving a reduction in size and speed of the apparatus as compared with the roller fixing method. Has been. In such a belt fixing system, a sufficiently long fixing nip is formed in the sheet conveying direction by the fixing belt and the pressure belt.
JP 2004-341346 A

  However, the fixing device described in Patent Document 1 has the following problems. That is, in the fixing nip formed between both belts, a high pressure portion pressed by the suspension rollers of both belts, a low pressure portion pressed only by the fixing pad, There is a part where the belt is not pressurized and the pressure is released.

  For this reason, a difference occurs in the sheet conveyance speed between the high pressure portion and the pressure release portion. Therefore, when an unfixed toner image is to be fixed, the belt has a certain degree of flexibility. Therefore, the belt expands and contracts due to the above-described difference in the conveyance speed, and the image on the sheet shifts.

  Further, in the portion where the pressure is released, water vapor generated during heating cannot be suppressed. For this reason, in the part where the pressure is released, there are a part where air or water vapor is accumulated in the width direction of the sheet (a direction perpendicular to the sheet conveying direction) and a part where the pressure is not. The uneven glossiness of the image due to the different contact state occurs. In particular, it tends to occur in a sheet having low air permeability such as coated paper.

  Accordingly, an object of the present invention is to provide an image heating apparatus capable of suppressing the occurrence of image heating failure in a configuration in which a nip portion is formed using a first belt and a second belt.

  Another object of the present invention is to provide an image heating apparatus capable of preventing the occurrence of a large pressure loss portion in the nip portion in the configuration in which the nip portion is formed using the first belt and the second belt. Is to provide.

  Further objects of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings.

  According to the present invention, the above object can be achieved.

The present invention relates to an image heating apparatus having a first belt and a second belt for forming a nip portion for heating an image on a recording material, wherein the first belt pressurizing the first belt at the nip portion. A pressure pad, a first roller provided downstream of the first pressure pad in the recording material conveyance direction, and pressurizing the first belt at the nip portion; and the first pressure A second pressure pad provided to face the pad and presses the second belt at the nip portion , and the first pressure pad on the downstream side of the second pressure pad in the recording material conveyance direction. provided so as to face the roller, the second belt and a second roller friction coefficient is smaller than the first roller for pressing in the nip, the first pressure The pressure pad is arranged in non-contact with the first roller; Serial second pressure pad is characterized by placing in contact with the second roller.

  According to the present invention, it is possible to suppress occurrence of defective image heating in a configuration in which the nip portion is formed using the first belt and the second belt. Further, in the configuration in which the nip portion is formed using the first belt and the second belt, it is possible to prevent a large pressure loss portion from being generated in the nip portion. Therefore, the occurrence of image defects such as uneven gloss can be suppressed.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of embodiments to which the present invention can be applied, the present invention is not limited to these examples, and various modifications are possible within the scope of the idea of the present invention.

(First embodiment)
First, the overall configuration of the image forming apparatus will be described with reference to FIG.
The image forming apparatus shown in FIG. 6 is an image forming apparatus (so-called printer) that employs an electrophotographic system.

  The image forming apparatus 1 is roughly divided into an image forming unit for forming a toner image on a sheet as a recording material, and a fixing device as an image heating apparatus for fixing the toner image formed on the sheet by heating and pressing. It has been.

  First, the image forming means is provided with a device described below. A charger 3 as a charging unit is provided around the photosensitive drum 2 as an image carrier, and the surface of the photosensitive drum 2 is uniformly charged by the charger 3. Then, an electrostatic latent image is formed on the photosensitive drum 2 by irradiating light 5 corresponding to the image from an exposure device 4 as an exposure unit. This electrostatic latent image is developed by a developing device 6 as developing means to form a toner image. On the other hand, the sheet S is stored in a feeding cassette 9 at the lower part of the apparatus and fed by a feeding roller 10. The sheet is conveyed in synchronism with the toner image on the photosensitive drum 2 by a pair of registration rollers 11 as conveying means. The toner image on the photosensitive drum is electrostatically transferred onto a sheet by a transfer roller 7 as a transfer unit, and is conveyed to the fixing device A. Thereafter, the toner remaining on the photosensitive drum 2 is removed by a cleaning device 8 as a cleaning unit.

  Then, the toner image formed on the sheet S by the image forming means is fixed on the sheet by being heated and pressed in the fixing device A as an image heating device. Thereafter, the sheet S on which the toner image is fixed is conveyed and discharged by the discharge roller pair 12 to the discharge tray 13 at the upper part of the apparatus.

  FIG. 1 is a cross-sectional view of the fixing device A, and FIG. 2 is a cross-sectional view illustrating a comparative example. As shown in the figure, the fixing device A includes a fixing belt (fixing means) 20 as an example of a first belt and a pressure belt (pressure means) 21 as an example of a second belt. . The toner image is heated and pressurized while the sheet is nipped and conveyed in a fixing nip (image heating nip) formed between the fixing belt 20 and the pressure belt 21. As a result, the toner image is fixed on the sheet that has passed through the fixing nip.

  The fixing belt 20 has an inner diameter of 40 mm and a thickness of 75 μm as a base layer, and an elastic layer is provided on the outer periphery of the base layer with a thickness of 300 μm. As a material of the elastic layer, a known elastic material can be used, and for example, silicone rubber, fluorine rubber, or the like can be used. In this embodiment, silicone rubber is used, the hardness is JIS-A 20 degrees, and the thermal conductivity is 0.8 W / mK. Due to the deformation of the elastic layer, it is possible to prevent the sheet from being wound around the fixing belt 20 and to obtain good separation performance from the belt. Further, on the outer periphery of the elastic layer, a fluororesin layer (for example, PFA or PTFE) is provided with a thickness of 30 μm as a surface release layer.

  The pressure belt 21 has an inner diameter of 40 mm and a polyimide layer with a thickness of 75 μm as a base layer, and a PFA tube which is a fluororesin as a release layer is provided on the surface with a thickness of 30 μm.

  The fixing belt 20 is stretched by a heating roller 22 as a suspension roller and a fixing roller 23. The heating roller 22 is a 1 mm-thick iron hollow roller having an outer diameter of 20 mm and an inner diameter of 18 mm, and a halogen heater 22a as a heating means is disposed inside. The heating roller also has a function as a tension roller. Fixing of the fixing roller 23 also functions as a driving roller for driving the belt 20.

  A temperature sensor is installed on the outer surface of the fixing belt 20 at a position facing the heating roller 22. A signal indicating the temperature of the fixing belt 20 is input to the controller (CPU) from the temperature sensor. The controller that receives this signal controls the energization of the halogen heater (on / off) to control the fixing belt so as to maintain a predetermined fixing temperature (190 degrees in this example). Has been.

  The fixing roller 23 as a first roller (high friction roller) has a high friction property in which a silicone rubber layer as a surface elastic layer is provided on a cored bar made of an iron alloy having an outer diameter of 20 mm and a diameter of 18 mm. This is a rubber roller. By providing the elastic layer in this manner, the driving force input from the driving source (motor) via the driving gear train can be transmitted satisfactorily without slipping to the fixing belt. Further, at the time of fixing, a pressure roller 26, which will be described later, is pressed toward the fixing roller 23 via the fixing belt 20 and the pressure belt 21, so that the rubber layer of the fixing roller 23 has a shape recessed by a predetermined amount. . As a result, it is possible to form a fixing nip for ensuring separation of the sheet from the fixing belt. As will be described later, the pressure of the fixing nip is set to a maximum value in the region suspended by the fixing roller 23.

  Further, as the silicone rubber of the fixing roller 23, a rubber having a hardness of JIS-A 15 degrees and a thermal conductivity of 0.8 W / mK is used. Therefore, the heat conduction to the inside by the silicone rubber layer is reduced, and the warm-up time is shortened.

  Since the friction coefficient of the silicone rubber layer on the surface of the fixing roller 23 to which rotational force is input from the motor via the drive gear train is large, the silicone rubber layer and the polyimide layer on the inner surface of the fixing belt 20 are fixed without slipping. The belt 20 rotates properly.

  A fixing pad 24 as a first pressure pad that presses the fixing belt 20 toward the pressure belt 21 is juxtaposed with the fixing roller 23 in a non-contact manner. In this example, the minute gap between the fixing roller 23 and the fixing pad 24 is set to 3 mm.

  The fixing pad 24 is made of heat-resistant silicone rubber as an elastic body having a thickness of 3 mm and a width of 12 mm.

  The fixing pad 24 has a cover as a low-sliding sheet in which a glass fiber cloth is coated with a fluororesin in order to reduce frictional resistance with the inner surface of the sliding fixing belt 20. This cover is provided so as to cover the high friction silicone rubber surface of the fixing pad. Therefore, since the cover slides on the inner surface of the fixing belt, the driving torque of the fixing roller 23 is suppressed, and the fixing belt can be rotated stably without increasing the size of the motor.

  The pressure belt 21 is stretched by a tension roller 25 and a pressure roller 26 as suspension rollers. The tension roller 25 is provided with a silicone sponge layer for reducing heat conduction from the pressure belt 21 on an iron alloy cored bar having an outer diameter of 20 mm and a diameter of 16 mm. The pressure roller 26 as a second roller (low friction roller) is a low-sliding metal roller made of an iron alloy having an outer diameter of 20 mm and an inner diameter of 16 mm and a thickness of 2 mm. The degree of unevenness of the metal surface is set so that the pressure roller has improved slipperiness. Specifically, the friction coefficient between the pressure roller and the pressure belt is set to be in the range of 0.005 to 0.3.

  The tension roller 25 and the pressure roller 26 are configured to rotate by transmitting a rotational force from the fixing belt 20 to the pressure belt 21 when at least a fixing nip is formed and a fixing process is possible. Has been.

  Note that the pressure unit including the pressure belt 21 may be brought into and out of contact with the fixing unit including the fixing belt 20 by a contact / separation mechanism during non-fixing processing (standby). In such a configuration, when the pressure belt is separated from the fixing belt, the pressure roller has a function as a driving roller, and the pressure belt 21 is driven by the pressure roller 26 to which the driving force is input from the driving mechanism. It is also possible to adopt a configuration in which the is driven to rotate.

  A pressure pad 27 as a second pressure pad (elastic pad) that pressurizes the pressure belt 21 toward the fixing belt 20 (fixing pad 24) is juxtaposed so as to contact the pressure roller 26.

  The pressure pad 27 is made of heat-resistant silicone rubber as an elastic body having a thickness of 3 mm and a width of 15 mm.

  Further, like the fixing pad 24, the pressure pad 27 is made of a glass fiber cloth as a low-sliding sheet that is fluorinated in order to reduce sliding resistance between the inner surface of the pressure belt 21 and the peripheral surface of the pressure roller 26. It has a resin-coated cover. That is, this cover is provided so as to cover the heat-resistant silicone rubber.

  Here, in order to form a fixing nip also between the fixing pad 24 and the pressure pad 27, the pressure pad 27 has a holding plate holding silicone rubber in a predetermined direction by a pressure mechanism in the direction of the arrow in FIG. Pressurized by pressure. At this time, the fixing pad 24 is fixed to the frame of the fixing device so that the fixing pad 24 does not move up and down.

  Further, the pressure roller 26 of the pressure belt 21 is pressed toward the fixing roller 23 with a predetermined pressure by a pressure mechanism in the direction of the arrow in FIG. At this time, the fixing roller 23 is fixed to the frame of the fixing device so that the fixing roller 23 does not move up and down. Of course, the fixing roller 23 is fixed to the frame of the fixing device via a bearing so as to be rotatable.

  Here, a wedge-shaped space Z between the inner surface of the pressure belt 21 and the pressure roller 26 (FIG. 1) so that a large pressure loss portion does not occur in the fixing nip that is sufficiently long along the sheet conveyance direction. The end of the pressure pad 27 is incorporated without any gap. That is, the pressure pad 27 (cover described later) is arranged so as to contact the pressure roller together with the pressure belt in order to create such a situation.

  A structure in which a wire as a pressure assisting member is provided in a substantially entire region along the longitudinal direction of the pressure pad (the sheet width direction orthogonal to the sheet conveying direction) in the portion of the pressure pad positioned in the wedge-shaped space Z described above. It does not matter. Specifically, the wire is fixed to the heat resistant silicone rubber. As a result, the drop of the nip pressure in the space Z can be further suppressed. In this case, the wire is covered with the above-described silicone rubber by a low-sliding cover described later.

  In this way, as shown in FIG. 1, the recording material conveyance in the area pressurized by the fixing roller and the pressure roller from the point P (the upstream end in the recording material conveyance direction of the area pressurized by both pads). A wide fixing nip is formed up to the downstream end in the direction). A pressure pad 27 is disposed in contact with the pressure roller 26 having a small sliding load (friction coefficient), while the fixing pad 24 is disposed on the fixing roller 23 having a large sliding load (friction coefficient). They are arranged so as to be separated from each other by a small gap without contact. That is, the friction coefficient of the pressure roller 26 is smaller than that of the fixing roller 23. Specifically, the friction coefficient (dynamic friction coefficient) of the pressure roller 26 and the fixing roller 23 can be measured by a method described later. In this example, when the friction coefficient of the pressure roller 26 and the fixing roller 23 is measured, a sliding medium (in this example, a test piece described later) that is slid on each of the pressure roller 26 and the fixing roller 23 is commonly used. By doing so, the magnitude relationship of the friction coefficient is obtained.

  As a result, it is possible to satisfactorily form a fixing nip not only between the fixing roller 23 and the pressure roller 26 but also between the fixing pad 24 and the pressure pad 27 while suppressing an increase in the driving torque of the fixing belt. Thus, it is possible to prevent the occurrence of a portion where the pressure is largely removed in the fixing nip that is sufficiently long along the sheet conveyance direction.

  Note that the friction coefficient (dynamic friction coefficient) of the pressure roller 26 with respect to the pressure pad 27 (the state with the cover described above) can be measured as follows. First, in this example, since the pressure roller is made of SUS, this test piece (3 cm × 4 cm) is prepared. Then, a single pad cover for the pressure pad 27 (a material made of the same material as the pad cover may be used for testing) is prepared. Next, a predetermined load (210 g in this example) is applied to the pressure pad cover by a test piece made of SUS and a weight placed thereon. In such a state, the test piece made of SUS is pulled at a predetermined pulling speed (200 mm / sec in this example) with respect to the pad cover whose position is fixed. Then, when the SUS test piece starts to move and is in a stable state, the force required to pull the SUS test piece is measured several times with a digital force gauge. In this example, the force required to pull the SUS test piece was obtained by averaging the plurality of measurement results. Finally, the friction coefficient (μ) is obtained from the relationship (F = μN) between “force (F) required to pull the SUS test piece” and “load (N)”. In addition, the atmospheric temperature at the time of measurement is 23 degree | times. As a result, the friction coefficient of the pressure roller 26 against the pressure pad 27 (pad cover) was 0.15.

  By reducing the friction coefficient of the pressure roller 26 in this way, it contributes to the formation of a fixing nip without a large pressure missing part while preventing the conveyance load of the pressure belt from becoming too large.

  On the other hand, as described above, the fixing roller 23 is an elastic roller having a large friction coefficient in order to satisfy the function as a driving roller. Therefore, by disposing the fixing pad 24 close to the fixing roller 23 in a non-contact manner, the conveyance torque required for driving the fixing roller 23 is prevented from becoming too large, and the conveyance performance of the fixing belt is stabilized. It contributes to making it.

  As described above, the fixing pad 24, the fixing roller 23, the pressure pad 27, and the pressure roller 26 as means for forming the fixing nip are continuously provided between the fixing belt 20 and the pressure belt 21 in the sheet conveying direction. The fixing nip thus formed can be formed.

  In other words, the pressure portion of the fixing belt 20 is formed from the fixing pad 24 to the fixing roller 23, and the pressure portion of the pressure belt 21 is formed from the pressure pad 27 to the pressure roller 26. Further, it is possible to prevent a large pressure loss portion from being generated between the nip portion between the fixing roller and the pressure roller and the nip portion between the fixing pad and the pressure pad. As a result, in this example, a sufficiently long fixing nip is obtained without a large pressure missing portion.

  In this example, the width of the fixing nip between the fixing belt 20 and the pressure belt 21 in the sheet conveyance direction is about 18 mm. Since the nip width is wide as described above, the image can be sufficiently fixed even if the image formation speed is increased. In addition, the use of endless belts on the fixing side and the pressure side as members related to fixing makes it possible to achieve a lower heat capacity than before. As a result, it contributes to shortening the warm-up time (the time required from when the main power of the image forming apparatus is turned on until it can be fixed).

  The fixing belt 20 is rotationally driven in the direction of arrow X in FIG. 1 by rotating the fixing roller 23 by a motor at least during execution of image formation. The peripheral speed of the fixing belt 20 is slightly lower than the transport speed of the sheet S transported from the image forming unit side to form a loop on the sheet.

  The pressure belt 21 rotates in the arrow Y direction following the fixing belt 20. Here, the configuration is such that the most downstream part of the fixing nip (the part where the pressure distribution (sheet conveying direction) in the fixing nip is maximum) is conveyed with the fixing belt 20 and the pressure belt 21 sandwiched by a pair of rollers. Belt slip can be prevented. In this embodiment, the peripheral speed of the fixing belt 20 is 300 mm / sec, and it is possible to form 70 full-color images on an A4 size sheet per minute.

  In such a fixing device, after the fixing belt 20 rises to a predetermined fixing temperature (190 degrees in this example), the sheet S having the unfixed toner image T is conveyed to the fixing nip. At this time, the sheet S is introduced with the surface carrying the unfixed toner image facing the fixing belt 20 side. The unfixed toner image T on the sheet S is nipped and conveyed while being in close contact with the outer peripheral surface of the fixing belt 20, so that heat is mainly applied from the fixing belt 20 and the surface of the sheet S is subjected to pressure. To be established.

  Further, since the fixing roller 23 in the fixing belt 20 is an elastic roller having a rubber layer, and the pressure roller 26 in the pressure belt 21 is a metal rigid roller, the fixing roller 23 has an outlet at the fixing nip. Deformation (dent) is large. As a result, the fixing belt is also greatly deformed, and the sheet S carrying the toner image is separated from the fixing belt 20 by the curvature thereof by its own strain.

  By adopting such a configuration, it is possible to prevent the occurrence of a large pressure loss portion in the fixing nip while stably securing the driving of the fixing belt and the sheet separation.

  Next, FIG. 3 shows the pressure distribution in the sheet conveyance direction of the fixing nip. In this figure, the vertical axis indicates pressure, and the horizontal axis indicates the position in the sheet conveying direction. “Upstream” on the horizontal axis means an inlet portion of the fixing nip, and “downstream” means an outlet portion of the fixing nip. As can be seen from this, in this example, there is no large pressure-removal portion in the fixing nip, and the pressure gradually increases from the upstream side and reaches the maximum at the sheet separation position. Therefore, while forming a wide fixing nip in the sheet conveyance direction, there is no difference in sheet conveyance speed, and no image misalignment occurs. Further, since no air or water vapor stays in the fixing nip, gloss unevenness does not occur in the image.

  Table 1 below shows the results of evaluating the relationship between the gap along the sheet conveyance direction between the fixing roller 23 and the fixing pad 24 arranged in non-contact with the fixing roller 23 in the configuration of this embodiment, and the state of occurrence of image defects. .

  As the sheet, plain paper and coated paper were used. As a result, coated paper is less air permeable and image defects are more likely to occur. By setting the gap between the fixing roller and the fixing pad to 5 mm or less, image defects such as image misalignment and uneven glossiness do not occur. Was confirmed. On the other hand, the minute gap between the fixing roller and the fixing pad is preferably set to 0.1 mm or more in order to prevent the two from accidentally contacting when forming the fixing nip (pressurization).

  Further, according to the study of the present inventor, when the friction coefficient of the pressure roller with respect to the pressure pad 27 is set to 0.5 or less, the load increases as the pressure pad comes into contact with the pressure belt. It was found that it does not affect the rotation. When the pressure is 0.5 or more, the cover of the pressure pad 27 is pulled between the pressure roller 26 and the pressure belt 21 and is damaged. The method for measuring the friction coefficient is as described above.

  On the other hand, FIG. 2 shows a comparative example in which the pressure pad 27 is arranged in non-contact with the pressure roller 26.

  In the configuration of the fixing device shown in FIG. 2, the gap between the pressure roller and the pressure pad and the gap between the fixing roller and the fixing pad are opposed to each other.

  FIG. 4 shows the pressure distribution at the fixing nip in this comparative example, similar to FIG. As shown in FIG. 4, it can be seen that a large pressure-removal portion is generated at a portion where the gap between the pressure roller and the pressure pad and the gap between the fixing roller and the fixing pad face each other.

  In this comparative example, the gap between the pressure roller and the pressure pad was set to 3 mm, and the unfixed toner image was fixed using plain paper and coated paper. The occurrence of uneven gloss was confirmed.

  As another comparative example, a configuration in which the fixing roller 23 and the fixing pad 24 are placed in contact with each other was verified. In such a configuration, the driving torque is increased by the frictional force between the fixing roller 23 and the cover of the fixing pad 24. As a result, when the fixing belt is rotated in such a situation, the cover of the fixing pad 24 is pulled between the fixing roller 23 and the fixing belt 20 and damaged.

  As described above, in this example, the fixing pad is arranged in a non-contact manner close to the elastic fixing roller, and the pressure pad is arranged in contact with the rigid pressure roller. Therefore, it is possible to suppress the occurrence of a large pressure drop portion in the fixing nip while the configuration is such that a long fixing nip is formed in the sheet conveying direction. In other words, since there is no such large pressure-out portion, it is possible to prevent image defects such as image misalignment and gloss unevenness.

(Second embodiment)
A second embodiment of the fixing device and the image forming apparatus according to the present invention will be described. Since the sectional view is the same as that of the first embodiment, FIG. 1 is used for the description.

  The fixing pad 24 of this embodiment is made of resin, specifically, PPS (polyphenylene sulfide resin). However, the fixing pad 24 is not limited to a resin and may be a rigid body such as a metal as long as it does not have a rubber elastic layer and has a high rigidity. Other configurations are the same as those of the first embodiment.

  When the rubber fixing pad as in the first embodiment is used, the fixing pad may be elastically deformed and contact the fixing roller when the fixing nip is formed (pressurization). Further, when the fixing pad is made of rubber, there is a limit in improving the pressure value of the “drop portion” in FIG.

  Therefore, in this example, the fixing pad is made of a highly rigid resin or metal. That is, the hardness of the fixing pad is larger than the hardness of the pressure pad. Therefore, with the configuration of this example, it is possible to prevent the fixing pad from erroneously contacting the fixing roller when the fixing nip is formed (pressurization). Further, when the fixing pad is made of resin or metal having high rigidity, the pressure value of the “drop portion” in FIG. 3 can be increased. In particular, when the fixing pad is made of metal, it can be said that the dimensional management / dimensional accuracy of the gap between the fixing roller 23 and the fixing pad 24 can be easily improved, which is a more preferable configuration.

  As described above, since the fixing pad installed side by side with a small gap with respect to the fixing roller is a highly rigid pad, it is possible to stably maintain the small gap between the fixing roller 23 and the fixing pad 24. It is. In this example as well, this minute gap is set to 3 mm.

  As described above, in this example, the fixing pads installed side by side with a slight gap with respect to the fixing roller are rigid bodies with little or no deformation within the usage range of the apparatus, and are arranged in contact with the pressure roller. The pressure pad is an elastic body. Accordingly, it is possible to increase the pressure of the “dropping portion” (FIG. 3) at the fixing nip while maintaining the gap between the fixing roller 23 and the fixing pad 24 for a long period of time.

  Needless to say, as in the first embodiment, a long fixing nip is formed in the sheet conveyance direction, but since there is no large pressure missing portion, it is possible to prevent image defects such as image misalignment and gloss unevenness. .

(Third embodiment)
FIG. 5 is a diagram schematically showing another example of the fixing device according to the present invention. This example is an example in which the configurations of the fixing side and the pressure side in Example 1 are substantially reversed.

  Specifically, in this example, the fixing roller 23 in the fixing belt 20 is a rigid roller, and the fixing pad 24 is an elastic body, and the fixing pad is disposed in contact with the fixing roller.

  On the other hand, the pressure roller 26 in the pressure belt 27 is an elastic roller (there is also a function of receiving drive input and driving transmission to the pressure belt), and pressurizing the pressure pad while making the pressure pad 27 a rigid body. It is arranged close to the roller in a non-contact manner.

  Further, the fixing belt 20 is not provided with an elastic layer and is the same as the pressure belt 21 of the first embodiment. The pressure roller 26 is driven by a motor, the pressure belt 21 is rotated, and the fixing belt is driven to rotate. In other words, except for the halogen heater 22a, the configuration on the fixing side and the pressure side is opposite to that in the second embodiment.

  Even with the configuration of this example, it is possible to achieve the same effects as those of the first and second embodiments. That is, since there is no large pressure missing portion in the fixing nip, it is possible to prevent image defects such as image misalignment and gloss unevenness.

  Further, the configuration of the second embodiment described above can be similarly applied to the fixing device of this example.

  In Examples 1 to 3 described above, the example of the fixing device has been described as the image heating device. However, the following configuration may be used. For example, the present invention can also be applied to a gloss applying device that improves the glossiness of an image by reheating a toner image that is supposedly attached to a sheet by a fixing device.

  In the first to third embodiments, an example in which a halogen heater is employed as a heating source for the fixing belt has been described. However, a heat source (excitation coil) with high energy efficiency may be employed. . In this case, the fixing belt has a configuration including a conductive layer that generates electromagnetic induction heat by the magnetic flux generated from the exciting coil.

1 is a cross-sectional view of a fixing device according to a first embodiment. It is sectional drawing explaining the comparative example of 1st Example. 1 is a diagram illustrating a fixing device according to a first embodiment. It is a figure explaining the comparative example of 1st Example. FIG. 10 is a diagram simply illustrating an example of another configuration of a fixing device. 1 is a diagram illustrating an overall configuration of an image forming apparatus.

Explanation of symbols

A Fixing device S Sheet 1 Image forming device 2 Photosensitive drum 3 Charger 4 Optical device 5 Light 6 Developer 7 Transfer roller 8 Cleaning device 9 Feed cassette 10 Feed roller 11 Registration roller pair 12 Discharge roller pair 13 Discharge tray 20 Fixing belt 21 Pressure belt 22 Heating roller 22a Halogen heater 23 Fixing roller 24 Fixing pad 25 Tension roller 26 Pressure roller 27 Pressure pad

Claims (8)

In an image heating apparatus having a first belt and a second belt forming a nip portion for heating an image on a recording material,
A first pressure pad that pressurizes the first belt at the nip portion;
A first roller provided downstream of the first pressure pad in the recording material conveyance direction and pressurizing the first belt at the nip portion;
A second pressure pad provided to face the first pressure pad and pressurizes the second belt at the nip portion;
The first belt is provided on the downstream side of the second pressure pad in the recording material conveyance direction so as to face the first roller, and pressurizes the second belt at the nip portion. A second roller having a smaller coefficient of friction than the roller,
The image heating apparatus according to claim 1, wherein the first pressure pad is disposed in contact with the first roller, and the second pressure pad is disposed in contact with the second roller .   The image heating apparatus according to claim 1, wherein a friction coefficient between the second roller and the second pressure pad is 0.5 or less. The image heating apparatus according to claim 1 or 2, wherein a distance between the first pressure pad and the first roller is 0.1 mm or greater and 5.0 mm or less.   The image heating apparatus according to claim 1, wherein the first roller is a driving roller that drives the first belt.   5. The image heating apparatus according to claim 1, wherein the surface of the first roller is made of rubber, and the surface of the second roller is made of metal.   6. The image heating apparatus according to claim 1, wherein the hardness of the first pressure pad is larger than that of the second pressure pad. Any of claims 1 to 6, characterized in that the pressure in this region is the largest such that the recording material is separated by the first roller and the second pressurized region by rollers Kano image heating apparatus.   The image heating apparatus according to claim 1, wherein the first belt is provided on a side in contact with an image on a recording material.

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