JP2021121838A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

To provide a fixing device that can adjust separability in a width direction of a recording medium from a rotating body to be heated or a pressure rotating body having an elastic layer, and an image forming apparatus including the same.SOLUTION: A fixing device comprises: a rotating body to be heated; a pressure rotating body; a heating unit; separation pawls; and a peeling assisting member, and fuses and fixes an unfixed toner image on a recording medium passing through a fixing nip part. The pressure rotating body is brought into pressure contact with the rotating body to be heated to form the fixing nip part. At least one of the rotating body to be heated and the pressure rotating body is an elastic roller having an elastic layer laminated on its surface. The separation pawls are arranged in proximity to the elastic roller and separate the recording medium from the elastic roller. The peeling assisting member has a roller shape, is brought into pressure contact with the elastic roller at a predetermined pressure, and elastically deforms a surface of the elastic roller to form concave parts. The peeling assisting member has a large diameter part having an outer diameter larger than that of the other part at least at one portion in an axial direction.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fixing device used for an image forming device such as a copying machine, a printer, a facsimile, and a multifunction device thereof, and an image forming device provided with the fixing device, and more particularly to a method for suppressing wrapping of a recording medium around a fixing member. Is.

In order to fix a toner image on paper in an image forming apparatus, a fixing device provided with a fixing member in which a fixing roller or a fixing belt (rotating body to be heated) and a pressure roller (pressurizing rotating body) are pressed against each other is widely used. It is used. In this fixing device, paper is passed through a fixing nip portion formed by a heating roller and a pressure roller, and heat and pressure are applied to the toner image to melt and fix the toner image on the paper.

In such a fixing device, especially when printing an image having a high image occupancy (printing rate), the molten toner causes the paper to adhere to a fixing roller, a fixing belt, or a pressure roller (hereinafter referred to as a fixing roller). And it may wrap around as it is. In particular, in a belt heating type fixing device using a fixing belt, it is preferable to increase the outer diameter of the pressure roller in order to secure the nip width of the fixing nip portion. In that case, the effect of separating the paper due to the curvature of the pressure roller is reduced, and the paper is easily wrapped around the pressure roller.

Therefore, a configuration is widely adopted in which a separation claw that comes into contact with a fixing roller or the like is provided to peel off the paper. In the configuration in which the separating claws are brought into contact with the fixing roller or the like, the amount of wear on the roller surface at the portion where the separating claws abut is larger than that of the other portions. As a result, the roller surface (belt surface) becomes rough, and there is a risk that the image quality may deteriorate. Further, since the release layer is worn and the releasability of the paper is lowered, there is a problem that the replacement cycle of the fixing roller or the like is shortened.

Therefore, a method of preventing paper from wrapping around a fixing member without using a separating claw has been proposed, and Patent Document 1 includes an external heating roller that abuts on a fixing roller having an elastic layer to supply heat. A fixing device is disclosed in which an external heating roller is brought into contact with the fixing roller in a state of being elastically deformed at a position downstream of the contact portion between the fixing roller and the pressure roller.

In the fixing device of Patent Document 1, the elastic layer of the fixing roller is elastically deformed at the contact portion of the external heating roller, so that the radius of curvature is partially reduced, and the paper on which a large amount of toner is placed is conveyed while being in close contact with the fixing roller. Even if it is done, it is separated from the fixing roller at the portion where the radius of curvature is small.

Japanese Unexamined Patent Publication No. 2003-5551

When the image occupancy in the width direction of the paper is different in one image, the adhesive force due to the toner becomes large in the portion where the printing rate is high. Further, in order to suppress the folding (ear folding) of the edge portion of the paper that has passed through the fixing nip portion, it may be desired to give priority to the separation of both ends of the paper in the width direction. In the configuration of Patent Document 1, since the outer diameter of the external heating roller pressed against the fixing roller is uniform, a portion having a small radius of curvature is also formed to be constant in the axial direction of the fixing roller. Therefore, the separability in the width direction of the paper could not be adjusted.

In view of the above problems, the present invention provides a fixing device capable of adjusting the separability of the recording medium in the width direction from the rotating body to be heated or the rotating body under pressure having an elastic layer, and an image forming device including the fixing device. The purpose is.

In order to achieve the above object, the first configuration of the present invention includes a rotating body to be heated, a pressurized rotating body, a heating portion, a separation claw, and a peeling auxiliary member, and passes through a fixing nip portion. This is a fixing device that melts and fixes an unfixed toner image on a recording medium by heating and pressurizing the recording medium. The pressurized rotating body is pressed against the heated rotating body to form a fixing nip portion. At least one of the heated rotating body and the pressurized rotating body is an elastic roller in which an elastic layer is laminated on the surface. The heating unit heats the rotating body to be heated. The separation claw is arranged close to the elastic roller on the downstream side of the fixing nip portion with respect to the insertion direction of the recording medium, and separates the recording medium from the elastic roller. The peeling auxiliary member has a roller shape and is pressed against the elastic roller at a predetermined pressure on the downstream side of the fixing nip portion with respect to the insertion direction of the recording medium to elastically deform the surface of the elastic roller to form a recess. The peeling auxiliary member has a large diameter portion having a larger outer diameter than the other portion at at least one position in the axial direction.

According to the first configuration of the present invention, the radius of curvature of the surface of the elastic roller is smaller than that of other portions at the edge of the recess formed on the surface of the elastic roller by the large diameter portion of the peeling auxiliary member. Therefore, the tip of the recording medium that passes through the fixing nip portion and is conveyed while being in close contact with the elastic roller is separated from the surface of the elastic roller at the edge portion, and is smoothly peeled off from the surface of the elastic roller by the separation claw. Therefore, the separability of the recording medium from the elastic roller in the width direction can be adjusted by the position of the large diameter portion formed on the peeling auxiliary member.

Schematic cross-sectional view showing the internal structure of the image forming apparatus 100 on which the fixing apparatus 13 according to the embodiment of the present invention is mounted. Side sectional view of the fixing device 13 according to the first embodiment of the present invention. A plan view of the periphery of the contact portion between the pressure roller 22 and the peeling auxiliary member 33 in FIG. 2 as viewed from the downstream side in the insertion direction of the paper S. Front view of the peeling auxiliary member 33 used in the fixing device 13 according to the second embodiment of the present invention as viewed from a direction perpendicular to the axial direction. A plan view of the periphery of the contact portion between the pressure roller 22 and the peeling auxiliary member 33 in the fixing device 13 according to the third embodiment of the present invention as viewed from the downstream side in the insertion direction of the paper S.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an internal structure of an image forming apparatus 100 on which the fixing apparatus 13 according to the embodiment of the present invention is mounted. In the main body of the image forming apparatus 100 (here, a color printer), four image forming portions Pa, Pb, Pc and Pd are arranged in order from the upstream side in the transport direction (right side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and are cyan, magenta, and yellow, respectively, depending on each step of charging, exposure, development, and transfer. And black images are formed sequentially.

Photoreceptor drums (image carriers) 1a, 1b, 1c and 1d that carry visible images (toner images) of each color are arranged on these image forming portions Pa to Pd. Further, in FIG. 1, an intermediate transfer belt 8 rotating in the clockwise direction is provided adjacent to each image forming portion Pa to Pd. The toner images formed on the photoconductor drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while abutting on the photoconductor drums 1a to 1d. After that, the toner image primaryly transferred onto the intermediate transfer belt 8 is secondarily transferred by the secondary transfer roller 9 onto the paper S as an example of the recording medium. Further, the paper S on which the toner image is secondarily transferred is discharged from the image forming apparatus 100 main body after the toner image is fixed in the fixing device 13. An image forming process for each of the photoconductor drums 1a to 1d is executed while the photoconductor drums 1a to 1d are rotated counterclockwise in FIG. 1 by a main motor (not shown).

The paper S on which the toner image is secondarily transferred is housed in a paper cassette 16 arranged in the lower part of the main body of the image forming apparatus 100, and is housed in the second transfer roller 9 via the paper feed roller 12a and the resist roller pair 12b. And the nip portion of the intermediate transfer belt 8 with the drive roller 11. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless (seamless) belt is mainly used. Further, a blade-shaped belt cleaner 19 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is arranged on the downstream side of the secondary transfer roller 9.

Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photoconductor drums 1a to 1d, charging devices 2a, 2b, 2c and 2d for charging the photoconductor drums 1a to 1d, and image information on each of the photoconductor drums 1a to 1d. The exposure apparatus 5 for exposing the above, the developing apparatus 3a, 3b, 3c and 3d for forming a toner image on the photoconductor drums 1a to 1d, and the developer (toner) remaining on the photoconductor drums 1a to 1d are removed. Cleaning devices 7a, 7b, 7c and 7d are provided.

When image data is input from a higher-level device such as a personal computer, first, the surfaces of the photoconductor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the exposure apparatus 5 irradiates light according to the image data to form an electrostatic latent image corresponding to the image data on the photoconductor drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer containing toners of cyan, magenta, yellow, and black, respectively. When the ratio of toner in the two-component developer filled in the developing devices 3a to 3d falls below the specified value due to the formation of the toner image described later, the toner containers 4a to 4d to the developing devices 3a to 3d are used. Toner is replenished. The toner in the developer is supplied onto the photoconductor drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. As a result, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure apparatus 5 is formed.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photoconductor drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and cyan, magenta, yellow, and cyan, magenta, yellow, and cyanide, magenta, and yellow on the photoconductor drums 1a to 1d are applied. The black toner image is primarily transferred onto the intermediate transfer belt 8. These four-color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. After that, in preparation for the subsequent formation of a new electrostatic latent image, the toner and the like remaining on the surfaces of the photoconductor drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

The intermediate transfer belt 8 is hung between the driven roller 10 on the upstream side and the drive roller 11 on the downstream side, and the intermediate transfer belt 8 watches as the drive roller 11 is rotated by the belt drive motor (not shown). When the rotation is started in the clockwise direction, the paper S is conveyed from the resist roller pair 12b to the nip portion (secondary transfer nip portion) between the drive roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. Then, the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the paper S. The paper S on which the toner image is secondarily transferred is conveyed to the fixing device 13.

The paper S conveyed to the fixing device 13 is heated and pressurized by the fixing belt 21 and the pressure roller 22 (see FIG. 2), and the toner image is fixed on the surface of the paper S to form a predetermined full-color image. .. The paper S on which the full-color image is formed is divided into transport directions by the branching portions 14 branched in a plurality of directions, and is sent to the double-sided transport path 18 as it is (or after the images are formed on both sides), and the discharge roller pair It is discharged to the discharge tray 17 by 15.

FIG. 2 is a side sectional view of the fixing device 13 according to the first embodiment of the present invention. The upper side of FIG. 2 is the downstream side of the paper insertion direction (conveyance direction) with respect to the fixing device 13, and the lower side is the upstream side of the paper insertion direction with respect to the fixing device 13. As shown in FIG. 2, the fixing device 13 includes a fixing belt 21 (heated rotating body), a pressure roller 22 (pressurized rotating body), a heating unit 23, a nip forming member 24, a belt guide 25, and a frame member 26. Be prepared.

The fixing belt 21 is rotatably supported around a horizontal shaft core by a housing portion (not shown) of the fixing device 13. The fixing belt 21 has an endless shape, for example, has a cylindrical shape with an outer diameter of 20 mm to 50 mm, and has an axial length (length in the width direction of the paper S) substantially the same as that of the pressure roller 22. The fixing belt 21 rotates in the clockwise direction of FIG. 2 along the insertion direction of the paper S which is a recording medium.

The fixing belt 21 has a laminated structure in which an elastic layer and a release layer are laminated on the outer peripheral side of a heat generating layer which is a base material layer. The heat generating layer is composed of, for example, a metal film having a thickness of 30 μm to 50 μm such as nickel, or a polyimide film having a thickness of 50 μm to 100 μm mixed with a metal powder such as copper, silver, or aluminum. The elastic layer is made of, for example, silicon rubber having a thickness of 100 μm to 500 μm. The release layer is composed of a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) having a thickness of 30 μm to 50 μm, for example.

The pressure roller 22 is rotatably supported by the housing portion of the fixing device 13 around a horizontal axis. The pressure roller 22 has a cylindrical shape and has substantially the same axial length (the width direction length of the paper S) as the fixing belt 21. A predetermined pressure is applied to the pressure roller 22 toward the fixing belt 21 by a pressure mechanism (not shown). The outer peripheral surface of the pressure roller 22 is pressed against the outer peripheral surface of the fixing belt 21 by pressing the nip forming member 24 via the fixing belt 21 to form the fixing nip portion N.

The pressurizing roller 22 is connected to a drive source including a motor (not shown), receives power from the motor, and rotates counterclockwise in FIG. The pressure roller 22 comes into contact with the outer peripheral surface of the fixing belt 21 and applies a rotational driving force in the clockwise direction to the fixing belt 21.

The pressure roller 22 has a laminated structure in which an elastic layer 22b is laminated on the outer peripheral side of the core metal 22a, and a release layer (not shown) is laminated on the surface of the elastic layer 22b. The core metal 22a is made of a metal such as aluminum having a diameter of about 20 mm, for example. The elastic layer 22b is made of, for example, silicon rubber having a thickness of about 8 mm. The release layer is made of a fluorine-based resin such as PFA having a thickness of, for example, about 10 μm to 50 μm.

The heating unit 23 is arranged in a region opposite to the side where the pressure roller 22 is arranged with respect to the fixing belt 21 so as to face the outer peripheral surface of the fixing belt 21 with a predetermined gap. The heating portion 23 extends slightly longer than the fixing belt 21 along the axial direction of the fixing belt 21 (the width direction of the paper S, the direction perpendicular to the paper surface of FIG. 2). The heating unit 23 heats the fixing belt 21 by generating heat in the heat generating layer of the fixing belt 21 by induction heating.

The heating unit 23 includes an exciting coil 23a, a holding member (not shown), a core, and the like. The exciting coil 23a and the core are held in place by the holding member. The exciting coil 23a is composed of a litz wire in which a plurality of conducting wires are bundled, and is wound so as to extend along the axial direction of the fixing belt 21. The exciting coil 23a is formed in an arc shape along the outer peripheral surface of the fixing belt 21 in the circumferential direction of the fixing belt 21.

The nip forming member 24 is arranged inside the fixing belt 21 so as to face the pressure roller 22 across the fixing belt 21. The nip forming member 24 comes into contact with the inner peripheral surface of the fixing belt 21 and forms a fixing nip portion N between the fixing belt 21 and the pressure roller 22.

The nip forming member 24 has a substantially rectangular parallelepiped shape extending along the axial direction of the fixing belt 21 (direction perpendicular to the paper surface of FIG. 2) with substantially the same length as the fixing belt 21. The nip forming member 24 has a base material made of a metal such as aluminum or a heat-resistant resin such as a liquid crystal polymer. The nip forming member 24 may have an elastic layer made of, for example, an elastomer or silicon rubber on the side facing the fixing belt 21 of the base material. Further, the nip forming member 24 has a sheet material (release layer) made of a fluorine-based resin such as PFA in a region facing the fixing belt 21. The sheet material comes into contact with the inner peripheral surface of the fixing belt 21 at the fixing nip portion N, and extends to a region on the upstream side and the downstream side of the fixing nip portion N in the rotation direction of the fixing belt 21 so as not to contact the fixing belt 21.

The belt guide 25 is arranged inside the fixing belt 21 so as to face the heating portion 23 across the fixing belt 21. The belt guide 25 contacts the inner peripheral surface of the fixing belt 21 other than the fixing nip portion N, and supports the fixing belt 21 from the inside. The belt guide 25 is composed of a sheet metal extending along the axial direction of the fixing belt 21 with a length substantially the same as that of the fixing belt 21. The belt guide 25 is made of an elastic magnetic metal such as SUS430 having a thickness of 0.1 mm to 0.5 mm, for example. The belt guide 25 includes a contact portion 25a and a connection portion 25b.

The contact portion 25a is arranged on the opposite side of the fixing nip portion N with the radial center portion of the fixing belt 21 separated from the contact portion 25a. The contact portion 25a is curved in an arc shape along the inner peripheral surface of the fixing belt 21. The contact portion 25a contacts the inner peripheral surface of the fixing belt 21 over almost the entire outer peripheral surface. The contact portion 25a faces the exciting coil 23a with the fixing belt 21 interposed therebetween.

The connecting portion 25b is arranged on the downstream side of the contact portion 25a with respect to the rotation direction of the fixing belt 21. The connecting portion 25b is connected to one end in the circumferential direction of the contact portion 25a. The connecting portion 25b bends and extends inward in the radial direction of the fixing belt 21 from one end in the circumferential direction of the contact portion 25a, and further bends toward the fixing nip portion N adjacent to the frame member 26. The connecting portion 25b does not come into contact with the fixing belt 21.

The frame member 26 is a substantially central portion in the radial direction of the fixing belt 21, and is arranged between the contact portion 25a of the belt guide 25 and the nip forming member 24. The frame member 26 extends slightly longer than the fixing belt 21 along the axial direction of the fixing belt 21.

The frame member 26 is supported by the housing portion of the fixing device 13 and holds the nip forming member 24 and the belt guide 25. The nip forming member 24 is fixed to the nip side wall portion 26a of the frame member 26 facing the fixing nip portion N. The connecting portion 25b of the belt guide 25 is fixed to the side wall portion 26b of the frame member 26 on the upstream side in the rotational direction of the fixing belt 21 of the fixing nip portion N.

A fixing entry guide 27 is arranged on the upstream side (lower side of FIG. 2) of the fixing nip portion N with respect to the paper insertion direction. The fixing entry guide 27 guides the paper S that has passed through the secondary transfer nip portion (see FIG. 1) to the fixing nip portion N.

A fixing side separating claw 30, a pressure side separating claw 31, and a peeling assisting member 33 are arranged on the downstream side (upper side in FIG. 2) of the fixing nip portion N with respect to the paper insertion direction. The fixing side separation claw 30 is a member that separates the paper S after the fixing process from the surface of the fixing belt 21. The fixing side separation claw 30 is arranged at a predetermined angle so that the tip portion is directed toward the upstream side (counter direction) with respect to the rotation direction of the fixing belt 21 and the tip portion is close to the outer peripheral surface of the fixing belt 21. There is.

The pressure side separation claw 31 is a member that separates the paper S after the fixing process from the surface of the pressure roller 22. The pressure side separation claw 31 is arranged at a predetermined angle so that the tip portion is directed toward the upstream side (counter direction) with respect to the rotation direction of the pressure roller 22 and the tip portion is close to the outer peripheral surface of the pressure roller 22. Has been done.

The peeling auxiliary member 33 is a roller-shaped member that is pressed against the surface of the pressure roller 22 at a predetermined pressure. The peeling assisting member 33 assists the peeling of the paper S from the surface of the pressure roller 22 by elastically deforming the surface of the pressure roller 22 to form recesses 40a to 40c (see FIG. 3).

FIG. 3 is a plan view of the periphery of the contact portion between the pressure roller 22 and the peeling auxiliary member 33 in FIG. 2 as viewed from the downstream side (upper side of FIG. 2) of the paper S in the insertion direction. As shown in FIG. 3, the pressurizing side separation claws 31 are arranged at a plurality of locations (here, 5 locations) along the axial direction (left-right direction in FIG. 3) of the pressurizing roller 22. Although not shown here, the fixing side separation claws 30 (see FIG. 2) are also arranged at a plurality of locations along the axial direction of the fixing belt 21 (left-right direction in FIG. 3).

The peeling auxiliary member 33 has a roller shape that extends slightly longer than the elastic layer 22b along the axial direction of the pressure roller 22. The peeling auxiliary member 33 is made of a metal such as aluminum or a heat-resistant resin. The outer peripheral surface of the peeling auxiliary member 33 is coated with a coating material of a fluororesin such as PFA in order to improve the mold releasability.

Both ends of the peeling auxiliary member 33 are rotatably supported by one end of the bearing portion 35, respectively. The other end of the bearing portion 35 is urged to the pressure roller 22 side by the compression spring 37, and the peeling auxiliary member 33 is pressed against the pressure roller 22 at a predetermined pressure by the urging force of the compression spring 37. An eccentric cam 38 is arranged above the compression spring 37. By rotating the eccentric cam 38, the compression length of the compression spring 37 is changed to adjust the balance of the pressure contact force of the peeling auxiliary member 33 with respect to the pressure roller 22 in the axial direction.

As shown in FIG. 3, the peeling auxiliary member 33 has a large diameter portion 33a at the central portion in the axial direction, which has a larger outer diameter than the other portions. As a result, when the peeling auxiliary member 33 is pressed against the pressure roller 22, three recesses 40a to 40c are formed in the axial direction.

At this time, as shown in FIG. 2, of the peripheral edges of the recesses 40a to 40c, the edge E on the upstream side with respect to the rotation direction of the pressure roller 22 is formed near the tip of the pressure side separation claw 31. In addition, the position of the peeling auxiliary member 33 is determined with respect to the circumferential direction of the pressure roller 22.

At the edges E of the recesses 40a to 40c, the radius of curvature of the surface of the pressure roller 22 is partially reduced. Therefore, the tip of the paper S that passes through the fixing nip portion N and is conveyed while being in close contact with the pressure roller 22 rises from the surface of the pressure roller 22 at the edge portion E (curvature separation). Then, the tip of the pressurizing side separation claw 31 located near the edge E enters between the tip of the paper S and the pressurizing roller 22, and the paper S is smoothly peeled off from the surface of the pressurizing roller 22.

By the way, the image occupancy rate on the paper S is generally large at the central portion in the width direction of the paper S and small at the edge portion. Further, when the heating portion 23 starts heating the fixing belt 21, the central portion of the fixing belt 21 in the width direction tends to retain heat and rise in temperature as compared with both end portions. The temperature distribution in the width direction of the fixing belt 21 becomes uniform as the paper S is inserted, but at the start of inserting the paper S, the toner is likely to be melted in the central portion of the paper S in the width direction. Therefore, the separability of the paper S is lowered at both ends of the axially central portion of the pressure roller 22.

Therefore, in the present embodiment, by forming the large-diameter portion 33a in the axially central portion of the peeling auxiliary member 33, the recess 40b formed in the axially central portion of the pressure roller 22 is compared with the recesses 40a and 40c. I try to get deeper. As a result, the radius of curvature of the edge E of the recess 40b is smaller than that of the edges P of the recesses 40a and 40c, so that the peelability (separability) of the paper S at the axial center of the pressure roller 22 is further improved. Can be made to.

Further, if there is a step at the boundary between the large diameter portion 33a and the other portion, the elastic layer 22b of the pressure roller 22 may be damaged by the step. Therefore, it is preferable that the large diameter portion 33a has a shape without a step in which the outer diameter becomes continuously (smoothly) toward the axial end portion of the peeling auxiliary member 33.

In the present embodiment, the large-diameter portion 33a is formed at one location in the axially central portion of the peeling auxiliary member 33, but for example, the large-diameter portion 33a may be formed at two or more locations in the axial direction of the peeling auxiliary member 33. good. The number and outer diameter of the large diameter portion 33a, the forming range in the axial direction, and the like can be arbitrarily set according to the size of the paper S to be passed, the output range of the heating portion 23, and the like.

FIG. 4 is a plan view of the periphery of the contact portion between the pressure roller 22 and the peeling auxiliary member 33 in the fixing device 13 according to the second embodiment of the present invention as viewed from the downstream side in the insertion direction of the paper S. In the present embodiment, large diameter portions 33a are formed at both ends of the peeling auxiliary member 33 in the axial direction. The outer diameter of the large diameter portion 33a is continuously (gentlely) increased toward the end in the axial direction. The configuration of the other parts of the fixing device 13 is the same as that of the first embodiment.

According to the present embodiment, by forming the large diameter portions 33a at both ends of the peeling auxiliary member 33 in the axial direction, the recesses 40a and 40c formed at both ends of the pressure roller 22 are formed at the central portion in the axial direction. It is deeper than the recess 40b.

By adopting the configuration of the present embodiment, the peelability (separability) of the paper S at both ends in the axial direction of the pressure roller 22 is improved. Therefore, this is a particularly effective embodiment when it is desired to prioritize the separation of both ends of the paper S in the width direction in order to suppress the folding (ear folding) of the edge portion of the paper S that has passed through the fixing nip portion N.

FIG. 5 is a plan view of the periphery of the contact portion between the pressure roller 22 and the peeling auxiliary member 33 in the fixing device 13 according to the third embodiment of the present invention as viewed from the downstream side in the insertion direction of the paper S. In the present embodiment, the separation claws 31a are arranged at three positions in the axial direction of the pressure roller 22 at equal intervals. The peeling auxiliary member 33 has a large diameter portion 33a formed at two positions between the separation claws 31. The configuration of the other parts of the fixing device 13 is the same as that of the first embodiment.

According to the present embodiment, by arranging the large diameter portion 33a of the peeling auxiliary member 33 between the separating claws 31 arranged at a plurality of positions in the axial direction of the pressure roller 22, it is formed between the separating claws 31. The recesses 40a and 40b to be formed are deeper than the other portions. Therefore, it is possible to improve the separability of the paper S between the separation claws 31 on which the separation claws 31 are not arranged and the separation effect is not sufficient.

In addition, the present invention is not limited to each of the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, a belt heating type fixing device 13 provided with an endless fixing belt 21 as a rotating body to be heated has been exemplified, but for example, a rotating body to be heated other than the fixing belt 21 such as a fixing roller. Of course, it can be applied to the fixing device provided with the above in exactly the same way. Further, the heating unit 23 is not limited to the induction heating method including the exciting coil and the core, and may be, for example, a halogen heater.

Further, if the fixing roller has an elastic layer on the surface, the peeling auxiliary member 33 is pressed against the fixing roller to form a recess on the surface of the fixing roller, so that the paper S can be peeled off (separated) from the fixing roller. Sex) can also be improved.

Further, in the vertical transport type fixing device 13 in which the paper S passes through the fixing nip portion N from the lower side to the upper side as shown in each of the above embodiments, the direction of gravity applied to the paper S is different from the peeling direction. , The action of gravity cannot be expected when the paper S is peeled from the pressure roller 22. Therefore, it is particularly effective to assist the peeling with the peeling assisting member 33. However, the present invention can be similarly applied to a horizontal transfer type fixing device in which the paper S passes horizontally through the fixing nip portion N.

Further, the image forming apparatus 100 is not limited to the tandem type color printer as shown in FIG. 1, and can be applied to various image forming apparatus provided with a fixing device such as a monochrome copier, a digital multifunction device, a facsimile and a laser printer. Is.

The present invention is used in a fixing device in which a recording medium is inserted through a fixing nip portion formed of a rotating body to be heated and a pressure member, and heat and pressure are applied to the toner image to melt and fix the toner image on the recording medium. It is possible. By utilizing the present invention, a fixing device capable of reliably separating the recording medium from the rotating body to be heated or the rotating body under pressure and suppressing deterioration of image quality, and an image forming device provided with the fixing device can be provided. Can be provided.

13 Fixing device 21 Fixing belt (rotating body to be heated)
22 Pressurized roller (pressurized rotating body, elastic roller)
22a Core metal 22b Elastic layer 23 Heating part 24 Nip forming member 25 Belt guide 26 Frame member 30 Fixing side separation claw 31 Pressurizing side separation claw 33 Peeling auxiliary member 33a Large diameter part 35 Bearing part 37 Compression spring 40a to 40c Recess 100 Image formation Equipment N Fixing nip part E Edge (concave)
S paper (recording medium)

Claims (9)

The rotating body to be heated and
A pressurized rotating body that is pressed against the heated rotating body to form a fixing nip portion, and a pressurized rotating body.
A heating unit that heats the rotating body to be heated,
In a fixing device that melts and fixes an unfixed toner image on the recording medium by heating and pressurizing the recording medium that passes through the fixing nip portion.
At least one of the heated rotating body and the pressurized rotating body is an elastic roller having an elastic layer laminated on its surface.
On the downstream side of the fixing nip portion with respect to the insertion direction of the recording medium,
A separation claw that is placed close to the elastic roller and separates the recording medium from the elastic roller.
A roller-shaped peeling auxiliary member that is pressed against the elastic roller at a predetermined pressure and elastically deforms the surface of the elastic roller to form a recess.
Is placed,
The peeling auxiliary member is a fixing device having a large diameter portion having an outer diameter larger than that of the other portion at at least one position in the axial direction. The fixing device according to claim 1, wherein the peeling auxiliary member has the large diameter portion at a central portion in the axial direction. The fixing device according to claim 1, wherein the peeling auxiliary member has the large diameter portions at both ends in the axial direction. The separation claws are arranged at a plurality of locations along the axial direction of the elastic roller, and the peeling auxiliary member is characterized in that the large diameter portion is arranged between the plurality of separation claws in the axial direction. The fixing device according to claim 1. The fixing device according to any one of claims 1 to 4, wherein the large diameter portion continuously changes in outer diameter along the axial direction of the peeling auxiliary member. The peeling assisting member is provided so that the edge portion of the peripheral edge portion of the recess formed by the peeling assisting member on the upstream side with respect to the rotation direction of the elastic roller is located near the tip end portion of the separating claw. The fixing device according to any one of claims 1 to 5, wherein the fixing device is positioned with respect to the circumferential direction of the elastic roller. The fixing device according to any one of claims 1 to 6, wherein the peeling auxiliary member has an outer peripheral surface coated with a fluorine-based resin material. The fixing device according to any one of claims 1 to 7, wherein the insertion direction is a vertical transport type from the lower side to the upper side of the fixing nip portion. An image forming apparatus including the fixing device according to any one of claims 1 to 8.

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