JP2006251250A - Fixing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device where a recording medium which has passed through a nip part is peeled from a fixing roller even when a member coming into contact with the fixing roller is not provided, and also to provide an image forming apparatus equipped with the fixing device. <P>SOLUTION: In the fixing device 90, the recording medium on which an unfixed image is carried is made to pass through the nip part N formed by the press-contact of the fixing roller 91 with a pressure roller 92, and is heated and pressured, so that the unfixed image is fixed on the recording medium. The pressure roller 92 has a base part 92A and a pressuring-side elastic layer 92B provided on the outer periphery side of the base part, and the hardness at the end of the pressuring-side elastic layer 92B in the axial direction of the pressure roller 92 is made lower than that at the center part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device and an image forming apparatus including the same.

In an image forming apparatus such as a printer, a copy, or a facsimile employing an electrophotographic method, a toner image formed by toner is heated while pressing a recording medium such as paper carrying a toner image in an unfixed state. A fixing device for fixing to a recording medium is provided (for example, see Patent Document 1).
Such a fixing device has, for example, a fixing roller and a pressure roller that are pressed against each other, a heater that heats the fixing roller, and a separation claw that abuts on the outer peripheral surface of the fixing roller. During the fixing operation, the recording medium is heated and pressed by passing the recording medium through a nip portion formed by pressing the fixing roller and the pressure roller with the toner image on the recording medium facing the fixing roller. Then, the toner image formed on the recording medium is fixed on the recording medium. At that time, the toner image on the recording medium is melted by the heat from the fixing roller, and the recording medium tends to stick to the outer peripheral surface of the fixing roller. However, the recording medium after passing through the nip portion is separated from the fixing roller by the separation claw. (Peeling) and brought to a normal transport position.

However, in Patent Document 1, since the separation claw is in contact with the fixing roller, if the contact pressure is high, the fixing roller may be damaged, and as a result, the quality of the fixed image may be deteriorated. If the pressure at which the separation claw contacts the fixing roller is reduced, or if the separation claw is brought close to the fixing roller and is not in contact with the fixing roller, the recording medium after passing through the nip portion may not be separated from the fixing roller. .
Further, when the recording medium after passing through the nip portion is peeled off from the fixing roller, the image after fixing on the recording medium may come into contact with the separation claw and image quality may be deteriorated.

Japanese Patent Publication No.59-7390

  An object of the present invention is to provide a fixing device that can peel a recording medium after passing through a nip portion from a fixing roller without providing a member that contacts the fixing roller, and an image forming apparatus including the fixing device.

Such an object is achieved by the present invention described below.
The fixing device of the present invention includes a fixing roller and a pressure roller that are pressed against each other, and
A heater for heating the fixing roller,
By passing a recording medium carrying an unfixed image through a nip formed by the pressure contact between the fixing roller and the pressure roller, the recording medium is heated and pressed to record the unfixed image on the recording medium. A fixing device for fixing to a medium,
The pressure roller has a base and a pressure-side elastic layer provided on the outer periphery thereof, and the hardness at the end of the pressure-side elastic layer in the axial direction of the pressure roller is the hardness at the center. It is characterized by being smaller than.

  As a result, the width of the end portion in the longitudinal direction of the nip portion (direction parallel to the axis of the pressure roller) becomes larger than the width of the central portion. As a result, in a range where the recording medium passes through the nip portion, the end side in the width direction (longitudinal direction of the nip portion N) is wound around the fixing roller side rather than the center side, that is, the width. It becomes a state curved in the direction. Thereby, the stiffness of the recording medium after passing through the nip portion is increased, and the recording medium after fixing can be more reliably peeled off from the fixing roller.

In the fixing device of the present invention, the pressure-side elastic layer is formed of an elastic porous body, and the porosity at the end of the pressure-side elastic layer in the axial direction of the pressure roller is the pressure side in the same direction. The porosity is preferably larger than the porosity at the center of the elastic layer.
Thereby, the hardness at the end of the pressure-side elastic layer in the axial direction of the pressure roller can be made smaller than the hardness at the center with a relatively simple configuration.

In the fixing device of the present invention, an end portion of the pressure-side elastic layer in the axial direction of the pressure roller extends in a direction parallel to the axial direction of the pressure roller inside the pressure-side elastic layer. It is preferable to have an easily deformable portion that deforms more easily than other portions.
Thereby, the hardness at the end of the pressure-side elastic layer in the axial direction of the pressure roller can be made smaller than the hardness at the center with a relatively simple configuration.

  In the fixing device of the present invention, the fixing roller has a base portion and a fixing side elastic layer provided on the outer peripheral side thereof, and the cross section of the easily deformable portion is from the inner peripheral side of the pressure side elastic layer. A longitudinal shape extending toward the outer peripheral side is formed, the longitudinal direction thereof is inclined with respect to the radial direction of the pressure roller, and an end portion on the outer peripheral side of the pressure-side elastic layer having the longitudinal shape is formed on the pressure roller. It is preferable to face upstream in the rotational direction.

  Accordingly, the outer peripheral surface of the fixing roller on the downstream side of the nip portion in the recording medium passing direction becomes a curved surface having a relatively small radius of curvature. When the recording medium reaches such a curved surface, the stiffness of the recording medium (that is, the force to return to the original state when the recording medium is curved) is larger than the force that the recording medium tries to adhere to the fixing roller. The recording medium peels off from the fixing roller. Therefore, the recording medium after passing the nip portion can be more reliably peeled from the fixing roller without providing a member such as a peeling member that contacts the fixing roller and peels the recording medium after passing the nip portion from the fixing roller. Can do.

  In the fixing device of the present invention, the fixing roller has a base portion and a fixing side elastic layer provided on the outer peripheral side thereof, and the cross section of the easily deformable portion is from the inner peripheral side of the pressure side elastic layer. A longitudinal shape extending toward the outer peripheral side is formed, the longitudinal direction thereof is inclined with respect to the radial direction of the pressure roller, and an end portion on the outer peripheral side of the pressure-side elastic layer having the longitudinal shape is formed on the pressure roller. It is preferable to face the downstream side in the rotation direction.

  Thus, the outer peripheral surface of the fixing roller on the upstream side of the nip portion in the recording medium passing direction becomes a curved surface with the pressure roller side as a convex surface. Such a curved surface brings the recording medium to the position on the pressure roller side upstream of the nip portion in the passing direction of the recording medium. Therefore, even when the distance from the transfer position of the toner image to the recording medium to the nip is short and the passing speed of the recording medium at the nip is slower than the passing speed of the recording medium at the transfer position, The recording medium bends to the pressure roller side between the position and the nip portion. As a result, when the recording medium receives toner transfer from a toner image carrier such as an intermediate transfer member, the area of the recording medium after passing through the transfer position approaches the toner image carrier and the toner image on the recording medium. Can be prevented from being retransferred to the toner image carrier.

In the fixing device according to the aspect of the invention, it is preferable that the easily deformable portion is a hole formed in the pressure-side elastic layer.
Thereby, an easily deformable part can be formed in the pressure side elastic layer with a simpler configuration.
In the fixing device of the present invention, it is preferable that a cross-sectional shape of the easily deformable portion is a rectangle or an ellipse.
Thereby, an easily deformable part can be formed in the pressure side elastic layer with a simpler configuration.

In the fixing device according to the aspect of the invention, it is preferable that an end portion of the easily deformable portion in the axial direction of the pressure roller is tapered.
Thus, the deformation amount of the pressure side elastic layer between the end portion of the easily deformable portion and the adjacent portion is gradually changed from the end portion of the easily deformable portion to the adjacent portion thereof. Can be prevented, and the durability of the pressure-side elastic layer can be improved.

In the fixing device according to the aspect of the invention, it is preferable that a plurality of the easily deformable portions are scattered in the circumferential direction of the pressure roller.
Thereby, the deformation amount of the pressure side elastic layer can be adjusted over the circumferential direction of the pressure roller.
In the fixing device according to the aspect of the invention, it is preferable that the easily deformable portion is unevenly distributed on the outer peripheral surface side of the pressure roller.
Thereby, the shape effect of an easily deformable part can be expressed more effectively, and the deformation amount of a pressurization side elastic layer can be adjusted.

In the fixing device of the present invention, the length in the longitudinal direction of the cross section of the easily deformable portion is L ₁ [mm], and the length in the direction perpendicular to the longitudinal direction of the cross section of the easily deformable portion is L _2. when a _{[mm], L 2 / L} 1 is preferably a 0.2 to 0.8.
Thereby, the deformation amount of the pressure side elastic layer can be adjusted more reliably.
In the fixing device of the present invention, a line extending in the longitudinal direction in the cross section of the easily deformable portion and a line extending in the radial direction of the pressure roller through the other end of the cross section of the easily deformable portion. When the angle is θ [°], θ is preferably 0 to 45 [°].
Thereby, the deformation amount of the pressure side elastic layer can be adjusted more reliably.

An image forming apparatus according to the present invention is an image forming apparatus that records an image on a recording medium through a series of image forming processes, and includes the fixing device according to claim 1. .
Accordingly, the recording medium after passing through the nip portion can be peeled from the fixing roller without providing a member such as a peeling member that contacts the fixing roller.

Preferred embodiments of a fixing device and an image forming apparatus having the same according to the present invention will be described below with reference to the accompanying drawings.
<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic cross-sectional view of an overall configuration showing an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a schematic view showing a preferred embodiment of a fixing device provided in the image forming apparatus shown in FIG. FIG. 3 is a sectional view taken along line AA in FIG. 2, FIG. 4 is a partially enlarged view of the fixing device shown in FIG. 2, and FIG. 5 illustrates another embodiment of the fixing device shown in FIG. FIG.

§Image forming device§
Prior to the fixing device of the present invention, an image forming apparatus including the fixing device of the present invention will be briefly described.
The image forming apparatus 10 according to the present embodiment records an image on a recording medium through a series of image forming processes. As shown in FIG. 1, the image forming apparatus 10 bears an electrostatic latent image and rotates in a direction indicated by an arrow. The charging unit 30, the exposure unit 40, the development unit 50, the primary transfer unit 60, and the cleaning unit 75 are sequentially arranged along the rotation direction. In addition, the image forming apparatus 10 has a paper feed tray 82 that accommodates a recording medium P such as paper at the bottom in FIG. 1, and two downstream of the paper feeding tray 82 in the conveyance direction of the recording medium P. A next transfer unit 80 and a fixing device 90 are sequentially arranged along the conveyance direction of the recording medium P. Further, a conveyance guide 87 is disposed between the secondary transfer unit 80 and the fixing device 90.

The photoconductor 20 has a cylindrical conductive substrate (not shown) and a photosensitive layer (not shown) formed on the outer peripheral surface thereof, and can rotate around the axis in the direction of the arrow in FIG. It has become.
The charging unit 30 is a device for uniformly charging the surface of the photoconductor 20 by corona charging or the like.
The exposure unit 40 receives image information from a host computer such as a personal computer (not shown) and irradiates a laser on the uniformly charged photoreceptor 20 to form an electrostatic latent image. It is a device to do.

  The developing unit 50 has four developing devices, a black developing device 51, a magenta developing device 52, a cyan developing device 53, and a yellow developing device 54. These developing devices are converted into latent images on the photosensitive member 20. It is an apparatus that visualizes a latent image as a toner image, selectively used correspondingly. The black developing device 51 uses black (K) toner, the magenta developing device 52 uses magenta (M) toner, the cyan developing device 53 uses cyan (C) toner, and the yellow developing device 54 uses yellow (Y) toner.

  The developing unit 50 in the present embodiment is rotatable so that the above-described four developing devices 51, 52, 53, 54 are selectively opposed to the photoconductor 20. Specifically, in the developing unit 50, four developing devices 51, 52, 53, and 54 are held by four holding portions 55a, 55b, 55c, and 55d of a holding body 55 that can rotate around a shaft 50a. The four developing devices 51, 52, 53, and 54 are selectively opposed to the photoconductor 20 while maintaining the relative positional relationship by the rotation of the holding body 55.

The primary transfer unit 60 is a device for transferring a single color toner image formed on the photoconductor 20 to the intermediate transfer body 70.
The intermediate transfer member 70 is an endless belt, and is driven to rotate in the direction of the arrow shown in FIG. On the intermediate transfer member 70, a toner image of at least one of black, magenta, cyan, and yellow is carried. For example, when a full-color image is formed, four color toner images of black, magenta, cyan, and yellow are sequentially formed. The toner images are transferred to form a full-color toner image.

The secondary transfer unit 80 is a device for transferring a single color or full color toner image formed on the intermediate transfer body 70 to a recording medium P such as paper, film, or cloth.
The conveyance guide 87 slides the recording medium P to the fixing device 90 while being in sliding contact with the back surface of the recording medium P to which the toner image has been transferred by the secondary transfer unit 80 (the surface opposite to the surface carrying the toner image). It is a guide.

As described above, the fixing device 90 heats and pressurizes the recording medium P that has received the transfer of the toner image, thereby fusing the toner image on the recording medium P to the recording medium P and fixing it as a permanent image. Device. The fixing device 90 will be described in detail later.
The cleaning unit 75 includes a cleaning blade 76 made of, for example, rubber that is in contact with the surface of the photoreceptor 20 between the primary transfer unit 60 and the charging unit 30, and a toner image is formed on the intermediate transfer body 70 by the primary transfer unit 60. This is a device for removing toner remaining on the photoreceptor 20 after being transferred by scraping it off with a cleaning blade 76.
Next, the operation of the image forming apparatus 10 configured as described above will be described.

First, in response to a command from a host computer (not shown), the photosensitive member 20, the developing roller (not shown) provided in the developing unit 50, and the intermediate transfer member 70 start to rotate. The photoreceptor 20 is sequentially charged by the charging unit 30 while rotating.
The charged region of the photoconductor 20 reaches the exposure position as the photoconductor 20 rotates, and is subjected to exposure processing according to image information of the first color, for example, yellow Y, by the exposure unit 40. As a result, a latent image corresponding to the image information of the first color is formed on the photoconductor 20.

The latent image formed on the photoconductor 20 reaches the development position as the photoconductor 20 rotates, and is developed with yellow toner by the yellow developing device 54. As a result, a yellow toner image is formed on the photoreceptor 20. At this time, in the developing unit 50, the yellow developing device 54 faces the photoconductor 20 at the developing position.
The yellow toner image formed on the photoconductor 20 reaches the primary transfer position as the photoconductor 20 rotates, and is transferred to the intermediate transfer body 70 by the primary transfer unit 60. At this time, a primary transfer voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner is applied to the primary transfer unit 60. During this time, the secondary transfer unit 80 is separated from the intermediate transfer member 70.

On the other hand, after the primary transfer position has elapsed, the toner adhering to the surface of the photoconductor 20 is scraped off by the cleaning blade 76 of the cleaning unit 75 to prepare for charging for forming the next latent image. The toner that has been scraped off is collected by a residual toner collecting section in the cleaning unit 75.
The same processing as described above is repeatedly executed for the second color, the third color, and the fourth color, so that the toner images of the respective colors corresponding to the respective image signals are transferred onto the intermediate transfer body 70 in an overlapping manner. The As a result, a full color toner image is formed on the intermediate transfer member 70.

On the other hand, the recording medium P is conveyed from the paper feed tray 82 to the secondary transfer unit 80 by a paper feed roller 84 and a registration roller 86.
The full-color toner image formed on the intermediate transfer body 70 reaches the secondary transfer position as the intermediate transfer body 70 rotates, and is transferred to the recording medium P by the secondary transfer unit 80. At this time, the secondary transfer unit 80 is pressed against the intermediate transfer body 70 and a secondary transfer voltage (secondary transfer bias) is applied.
The full-color toner image transferred to the recording medium P is heated and pressurized by the fixing device 90 and fused to the recording medium P.

§Fusing device§
Here, the fixing device 90 will be described in detail with reference to FIGS.
As shown in FIG. 2, the fixing device 90 includes a fixing roller 91 and a pressure roller 92 that are pressed against each other, a heater 93 for heating the fixing roller 91, and a temperature detection for detecting the temperature of the fixing roller 91. The body 94 and a cover 95 that covers a part of the peripheral surfaces of the fixing roller 91 and the pressure roller 92 are provided.

  In the fixing device 90, a recording medium carrying an unfixed image is conveyed from below in FIG. 2 to the nip portion N formed by pressure contact between the fixing roller 91 and the pressure roller 92. The unfixed image is fixed on the recording medium by heating and pressurizing the recording medium. In the present embodiment, the recording medium conveyed to the nip portion N carries an unfixed image on the fixing roller 91 side.

The fixing roller 91 has a cylindrical shape and is rotatable around its axis.
2 and 3, the fixing roller 91 includes a cylindrical metal base (core metal) 91A, a fixing-side elastic layer 91B covering the outer peripheral surface of the base 91A, and a fixing-side elastic layer. And a release layer 91C covering the outer peripheral surface of 91B.
In addition, the thickness of the release layer 91C is preferably 10 to 80 μm, and more preferably 20 to 50 μm. Thereby, the elasticity of the fixing-side elastic layer 91B can be sufficiently exhibited while maintaining the strength necessary for the release layer 91C.

Moreover, as a constituent material of the release layer 91C, for example, PTFE, PFA, or the like can be suitably used.
Further, the thickness of the fixing-side elastic layer 91B is preferably 0.3 to 5 mm, and more preferably 0.3 to 3 mm. Thus, the curved surface R as described later is formed on the outer peripheral surface of the fixing roller 91 while the durability of the fixing-side elastic layer 91B and the heat conductivity from the heater 93 to the outer peripheral surface of the fixing roller 91 are improved. can do.

A heater 93 is disposed in the internal space of the fixing roller 91, and the fixing roller 91 is heated by the heater 93. As a result, the pressure roller 92 sufficiently exhibits the elasticity of the pressure-side elastic layer 92B described later, and the fixing roller 91 is efficiently heated while obtaining a sufficient nip width, so that the temperature of the nip portion N is increased. It can be stable.
Such a temperature detector 94 for detecting the temperature of the fixing roller 91 is, for example, a thermistor, and is provided in contact with or in proximity to the peripheral surface of the fixing roller 91. Based on the temperature detected by the temperature detector 94, the driving of the heater 93 described above is controlled by a control unit (not shown) so that the outer surface of the fixing roller 91 becomes the target temperature.

The pressure roller 92 has a cylindrical shape or a columnar shape, is rotatable about its axis, and is in pressure contact with the fixing roller 91.
As shown in FIGS. 2 and 3, the pressure roller 92 includes a columnar metal base (core metal) 92A, a pressure-side elastic layer 92B covering the outer peripheral surface of the base 92A, and a pressure-side elasticity. A release layer 92C covering the outer peripheral surface of the layer 92B.
As a constituent material of the pressure side elastic layer 92B, for example, Si rubber, EPDM, fluorine rubber, or the like can be suitably used.

Further, at the end of the pressure side elastic layer 92B in the axial direction of the pressure roller 92, as shown in FIG. 3, it extends in a direction parallel to the axial direction of the pressure roller 92, and the pressure side elastic layer It has a deformable part 92B1 that is more easily deformed than the other parts of 92B.
A method for forming such an easily deformable portion 92B1 is not particularly limited. For example, after forming a uniform elastic layer on the base portion 92A, a method of drilling it with a drill or a laser or the like, Examples thereof include a method of placing on 92A and applying an elastic material thereon, and a method of extruding into a shape provided with holes in advance when the elastic layer is extruded.

  Since such an easily deformable portion 92B1 is provided at the end of the pressure side elastic layer 92B in the axial direction of the pressure roller 92, the hardness at the end of the pressure side elastic layer 92B in the axial direction of the pressure roller 92. Is smaller than the hardness at the center. Thereby, the width of the end portion in the longitudinal direction of the nip portion N (the direction parallel to the axis of the pressure roller 92) becomes larger than the width of the central portion. As a result, in a range where the recording medium passes through the nip portion N, the end side in the width direction (longitudinal direction of the nip portion N) is wound around the fixing roller 91 side rather than the central side. That is, the recording medium is curved in the width direction, the stiffness of the recording medium after passing through the nip portion N is increased, and the recording medium after fixing can be peeled off from the fixing roller 91.

  The pressure-side elastic layer 92B is made of an elastic porous body, and the porosity at the end of the pressure-side elastic layer 92B in the axial direction of the pressure roller 92 is such that the porosity at the center of the pressure-side elastic layer 92B is empty. It is preferable that it is larger than the porosity. Thereby, the effect mentioned above can be made more remarkable. In this case, even if the easily deformable portion 92B1 as described above is not provided in the pressure side elastic layer 92B, the end portion of the pressure side elastic layer 92B in the axial direction of the pressure roller 92 has a relatively simple configuration. Can be made smaller than the hardness at the center.

  As shown in FIG. 4, the easily deformable portion 92 </ b> B <b> 1 has a longitudinal shape (an elliptical shape in the present embodiment) whose cross section extends from the inner peripheral side to the outer peripheral side of the pressure side elastic layer 92 </ b> B. The transverse section of the easily deformable portion 92B1 is inclined in the longitudinal direction with respect to the radial direction of the pressure roller 92, and the end on the outer peripheral side of the longitudinal pressure-side elastic layer 92B is the rotation of the pressure roller 92. The direction is downstream.

Such an easily deformable portion 92B1 has a relatively high rigidity with respect to an external force in the longitudinal direction of its transverse section, and therefore has a small amount of deformation and is a direction perpendicular to the longitudinal direction of the transverse section (that is, the width direction). ), The amount of deformation increases because the rigidity is relatively low. Accordingly, as shown in FIG. 4, the easily deformable portion 92B1 has a nip portion in the recording medium passing direction because the longitudinal outer peripheral end of the cross section faces the upstream side in the rotation direction of the pressure roller 92. The amount of deformation is large on the upstream side of N (hereinafter referred to as the upstream side of the nip portion N), and the amount of deformation is small on the downstream side of the nip portion N in the recording medium passing direction (hereinafter referred to as the downstream side of the nip portion N). . As a result, the pressure contact force on the downstream side of the nip portion N becomes larger than the pressure contact force on the upstream side of the nip portion N.
That is, the easily deformable portion 92B1 adjusts the amount of deformation of the pressure side elastic layer 92B so that the pressure contact force on the downstream side of the nip portion N is larger than the pressure contact force on the upstream side of the nip portion N. Configure the means.

  When the pressure contact force on the downstream side of the nip portion N becomes larger than the pressure contact force on the upstream side of the nip portion N, the outer peripheral surface of the fixing roller 91 on the downstream side of the nip portion N is a curved surface R having a relatively small radius of curvature. Become. When the recording medium reaches such a curved surface R, the original state when the recording medium is curved toward the fixing roller 91 than the force that the recording medium tries to adhere to the fixing roller 91 is obtained. The recording medium is peeled off from the fixing roller 91. As described above, the recording after passing through the nip portion N can be performed more reliably without providing a separate member such as a peeling member that contacts the fixing roller 91 and separates the recording medium after passing through the nip portion N from the fixing roller 91. The medium can be peeled from the fixing roller 91.

In the present embodiment, since the easily deformable portion 92B1 is a hole formed in the pressure side elastic layer 92B, the easily deformable portion 92B1 can be formed in the pressure side elastic layer 92B with a simpler configuration.
In addition, since the easily deformable portion 92B1 has an elliptical cross-sectional shape, the easily deformable portion 92B1 can be formed on the pressure-side elastic layer 92B with a simpler configuration. The cross-sectional shape of the easily deformable portion 92B1 may be rectangular as shown in FIG. 5, and in this case, the same effect as that obtained when the cross-sectional shape of the easily deformable portion 92B1 is elliptical is obtained. be able to.

  Further, as shown in FIG. 2, a plurality of easily deformable portions 92 </ b> B <b> 1 are scattered in the circumferential direction of the pressure roller 92. Thereby, the deformation amount of the pressure side elastic layer 92 </ b> B can be adjusted over the circumferential direction of the pressure roller 92. Therefore, in this embodiment, the deformation amount of the pressure side elastic layer 92B can be adjusted so that the pressure contact force on the downstream side of the nip portion N is always larger than the pressure contact force on the upstream side of the nip portion N. . Therefore, the recording medium after passing through the nip portion N can be peeled off from the fixing roller 91 without synchronizing the timing at which the recording medium enters the nip portion N with the rotation state of the pressure roller 92.

Moreover, as shown in FIGS. 2 and 4, the easily deformable portion 92B1 is unevenly distributed on the outer peripheral surface side of the pressure-side elastic layer 92B. Thereby, the shape effect of easily deformable part 92B1 can be expressed more effectively. Therefore, in this embodiment, the deformation amount of the pressure-side elastic layer 92B is adjusted more reliably so that the pressure contact force on the downstream side of the nip portion N is larger than the pressure contact force on the upstream side of the nip portion N. Can do.
In addition, the thickness of the pressure side elastic layer 92B is preferably 0.3 to 10 mm, and more preferably 0.6 to 8 mm. Thereby, the width of the nip portion N can be made sufficient while the durability of the pressure-side elastic layer 92B is excellent.

Further, the length in the longitudinal direction in the transverse section of the easily deformable portion 92B1 is L ₁ [mm], and the length in the direction perpendicular to the longitudinal direction in the transverse section of the easily deformable portion 92B1 is L ₂ [mm]. _{Occasionally,} it is preferable L 2 / _{L 1} is 0.2 to 0.8, and more preferably 0.3 to 0.6. Thereby, the deformation amount of the pressure side elastic layer 92B can be adjusted more reliably. Therefore, in this embodiment, the deformation amount of the pressure side elastic layer 92B can be adjusted so that the pressure contact force on the downstream side of the nip portion N is larger than the pressure contact force on the upstream side of the nip portion N.

  When the angle formed by the line extending in the longitudinal direction of the cross section of the easily deformable portion 92B1 and the line extending through the center of the cross section of the easily deformable portion 92B1 and extending in the radial direction of the pressure roller 92 is θ [°]. In addition, θ is preferably 0 to 45 [°], and more preferably 10 to 30 [°]. Thereby, the deformation amount of the pressure side elastic layer 92B can be adjusted more reliably. Therefore, in this embodiment, the deformation amount of the pressure side elastic layer 92B can be adjusted so that the pressure contact force on the downstream side of the nip portion N is larger than the pressure contact force on the upstream side of the nip portion N.

  Further, as shown in FIG. 3, the end of the easily deformable portion 92B1 in the axial direction of the pressure roller 92 is tapered. Thereby, the deformation amount of the pressure side elastic layer 92B is gradually changed from the end portion of the easily deformable portion 92B1 to the adjacent portion thereof, and the pressure side elastic layer between the end portion of the easily deformable portion 92B1 and the adjacent portion thereof. It is possible to prevent an abrupt change in the amount of deformation of 92B (generation of stress) and improve the durability of the pressure side elastic layer 92B.

In addition, the thickness of the release layer 92C is preferably 10 to 80 μm, and more preferably 20 to 50 μm. Thereby, the elasticity of the pressure side elastic layer 92B can be sufficiently exhibited while maintaining the strength required for the release layer 92C.
Moreover, as a constituent material of the release layer 92C, for example, PTFE, PFA, or the like can be suitably used.
As described above, the fixing device 90 according to the present exemplary embodiment does not require a member such as a peeling member that peels the recording medium after passing the nip portion N from the fixing roller 91 while being in contact with the fixing roller 91. The recording medium after passing through the portion N can be peeled off from the fixing roller 91.

Second Embodiment
A second embodiment of the present invention will be described with reference to FIG. Hereinafter, the second embodiment will be described with a focus on differences from the first embodiment described above, and description of similar matters will be omitted.
FIG. 6 is a diagram for explaining the fixing device of the present embodiment.
The fixing device 90 ′ of the present embodiment is the same as the fixing device 90 of the first embodiment except that the configuration of the pressure-side elastic layer of the pressure roller is different.
As shown in FIG. 6, the pressure roller 92 ′ provided in the fixing device 90 ′ has a longitudinal direction of the transverse section of the easily deformable portion 92′B1 inclined with respect to the radial direction of the pressure roller. An end portion on the outer peripheral side of the pressure-side elastic layer 92′B having a longitudinal shape of the easy portion 92′B1 faces the downstream side in the rotation direction of the pressure roller 92 ′.

Thereby, the outer peripheral surface of the fixing roller 91 on the upstream side of the nip portion N becomes a curved surface with the pressure roller 92 ′ side as a convex surface. Such a curved surface brings the recording medium upstream of the nip portion N to a position on the pressure roller 92 ′ side (that is, the conveyance guide 87 side). Therefore, the distance from the transfer position of the toner image to the recording medium (that is, the portion where the intermediate transfer body 70 and the secondary transfer unit 80 face) to the nip portion N is shorter than the length in the recording medium conveyance direction, and Even when the passing speed of the recording medium at the nip portion N is slower than the passing speed of the recording medium at the transfer position, the recording medium bends toward the pressure roller 92 ′ between the transfer position and the nip portion. It will be. As a result, when the recording medium receives the transfer of toner from the intermediate transfer body 70, the area of the recording medium that has passed the transfer position approaches the intermediate transfer body 70, and the toner image on the recording medium reappears on the intermediate transfer body 70. Transfer can be prevented.
As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to this.

For example, each unit constituting the fixing device and the image forming apparatus of the present invention can be replaced with an arbitrary one that exhibits the same function, or another configuration can be added.
The pressure-side elastic layer in the present invention is the same as that of the above-described embodiment as long as the hardness at the end of the pressure-side elastic layer in the axial direction of the pressure roller is smaller than the hardness at the center. It is not limited. For example, in the central part of the pressure side elastic layer in the axial direction of the pressure roller, it extends in a direction parallel to the axial direction of the pressure roller and is hard to be deformed more easily than other parts of the pressure side elastic layer. It may have a part.

In the above-described embodiment, the description has been given of the case where the easily deformable portion is formed as a hole formed in the pressure-side elastic layer. However, the easily deformable portion deforms more easily than other portions of the pressure-side elastic layer. Anything is acceptable. For example, a hole formed in the pressure-side elastic layer may be filled with a material that is more easily deformed than other portions of the pressure-side elastic layer.
Further, the shape, position, and size of the easily deformable portion are not limited to those of the above-described embodiment, and are arbitrary.

1 is a schematic cross-sectional view illustrating an overall configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a fixing device provided in the image forming apparatus illustrated in FIG. 1. It is the sectional view on the AA line in FIG. FIG. 3 is a partial enlarged cross-sectional view of the fixing device shown in FIG. 2. FIG. 4 is a partial enlarged cross-sectional view for explaining another form of the fixing device shown in FIG. 2. It is a figure for demonstrating the fixing device in 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming device 20 ... Photoconductor 30 ... Charge unit 40 ... Exposure unit 50 ... Development unit 50a ... Shaft 51 ... Black development device 52 ... Magenta development device 53 ... Cyan developing device 54 ... Yellow developing device 55 ... Holding body 55a to 55d ... Holding section 60 ... Primary transfer unit 70 ... Intermediate transfer body 75 ... Cleaning unit 76 ... Cleaning blade 80 ... Secondary transfer unit 82 ... Paper feed tray 84 ... Paper feed roller 86 ... Registration roller 87 ... Transport guide 90, 90 '... Fixing device 91 ... Fixing roller (rotating body) 91A ... Base 91B ... Fixing side elastic layer 92, 92 '... Pressure roller (rotating body) 92A ... Base 92B ... Pressure side elastic layer 9 B1,92'B1 ‥‥‥ easily deformable portion 91C, 92C ‥‥‥ release layer 93 ‥‥‥ heater 94 ‥‥‥ temperature sensing element 95 ‥‥‥ cover N ‥‥‥ nip P ‥‥‥ recording medium

Claims (13)

A fixing roller and a pressure roller that are pressed against each other;
A heater for heating the fixing roller,
By passing a recording medium carrying an unfixed image through a nip formed by the pressure contact between the fixing roller and the pressure roller, the recording medium is heated and pressed to record the unfixed image on the recording medium. A fixing device for fixing to a medium,
The pressure roller has a base and a pressure-side elastic layer provided on the outer periphery thereof, and the hardness at the end of the pressure-side elastic layer in the axial direction of the pressure roller is the hardness at the center. A fixing device characterized in that the fixing device is smaller.   The pressure-side elastic layer is made of an elastic porous body, and the porosity at the end of the pressure-side elastic layer in the axial direction of the pressure roller is the center of the pressure-side elastic layer in the same direction. The fixing device according to claim 1, wherein the fixing device is larger than a porosity.   At the end of the pressure side elastic layer in the axial direction of the pressure roller, it extends in a direction parallel to the axial direction of the pressure roller, and is easier than other portions of the pressure side elastic layer. The fixing device according to claim 1, further comprising an easily deformable portion that deforms.   The fixing roller includes a base and a fixing-side elastic layer provided on an outer peripheral side thereof, and a transverse section of the easily deformable portion extends in a longitudinal direction from an inner peripheral side to an outer peripheral side of the pressure-side elastic layer. It has a shape, the longitudinal direction thereof is inclined with respect to the radial direction of the pressure roller, and the outer peripheral end of the pressure side elastic layer of the longitudinal shape is directed upstream in the rotation direction of the pressure roller. The fixing device according to claim 3.   The fixing roller includes a base and a fixing-side elastic layer provided on an outer peripheral side thereof, and a transverse section of the easily deformable portion extends in a longitudinal direction from an inner peripheral side to an outer peripheral side of the pressure-side elastic layer. It has a shape, the longitudinal direction thereof is inclined with respect to the radial direction of the pressure roller, and the end portion on the outer peripheral side of the pressure side elastic layer of the longitudinal shape is directed downstream in the rotation direction of the pressure roller. The fixing device according to claim 3.   The fixing device according to claim 3, wherein the easily deformable portion is a hole formed in the pressure-side elastic layer.   The fixing device according to claim 3, wherein a cross-sectional shape of the easily deformable portion is a rectangle or an ellipse.   The fixing device according to claim 3, wherein an end portion of the easily deformable portion in the axial direction of the pressure roller is tapered.   The fixing device according to claim 3, wherein a plurality of the easily deformable portions are scattered in a circumferential direction of the pressure roller.   The fixing device according to claim 3, wherein the easily deformable portion is unevenly distributed on an outer peripheral surface side of the pressure roller. When the length in the longitudinal direction in the transverse section of the easily deformable portion is L ₁ [mm], and the length in the direction perpendicular to the longitudinal direction in the transverse section of the easily deformable portion is L ₂ [mm]. The fixing device according to claim 3, wherein L ₂ / L ₁ is 0.2 to 0.8.   An angle between a line extending in the longitudinal direction of the cross section of the easily deformable portion and a line passing through the other end of the cross section of the easily deformable portion and extending in the radial direction of the pressure roller is θ [°]. 12. The fixing device according to claim 3, wherein θ is 0 to 45 °. An image forming apparatus for recording an image on a recording medium by a series of image forming processes, comprising the fixing device according to any one of claims 1 to 12.

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