JP5049526B2 - Fixing device, image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile machine using the fixing device.

  A heating unit having an elastic layer and a heat source; and a pressing unit having an endless member and a pressing member. The recording medium is transported with an unfixed toner image attached to the endless member by the heating unit. Various proposals have been made regarding a fixing device that passes through a nip portion to be formed and fixes an unfixed toner image on the recording medium. However, the conventional technology is a rotatable fixing device whose surface is elastically deformed. This is a belt nip method in which a pressure member that locally elastically deforms the outlet portion is pressed against a heating roller, a nip portion is formed, and a toner image on the recording medium fed therebetween is pressed and heated to be fixed. . However, this belt nip type fixing device has a problem that image misalignment is likely to occur due to a speed difference due to local deformation of the exit portion. Furthermore, the elastic layer of the heating roller is pressed with a hard member to locally strain the elastic layer and create a nip shape with a small curvature, which increases the load on the paper (paper damage and curl amount). .

  Therefore, in Patent Document 1, the pressing means of the fixing pressure belt is configured by an entrance pad, a center pad, and an exit pressure roller, each of which is independently pressurized, and the center pad is more in the load direction than the entrance pad. A thicker one is disclosed.

  In Patent Document 2, a pressure roll that stretches a pressure belt is pressed against the fixing roll near the exit of the nip portion, and an elastic body layer is provided on the surface of the fixing roll so that the pressure roll is pressed. Discloses that the peeling of the recording sheet is promoted. In this case, an auxiliary roll having a flexible elastic layer is pressed against the upstream portion of the nip portion to prevent the entire recording sheet from being conveyed at a speed higher than the surface speed of the fixing roll, thereby preventing image displacement. To do. The sum of the pressure contact force P3 of the auxiliary roll and the pressure contact force P2 due to the tension of the pressure belt is set larger than the pressure contact force P1 of the pressure roll, thereby effectively preventing image displacement.

  Patent Document 3 includes a heating roll, a pressure belt that presses the heating roll, and the pressure roll that presses the pressure belt from behind, and a nip region formed by the heating roll and the pressure belt. Discloses a heat and pressure type fixing device that passes an unfixed toner image and fixes the toner image by heat and pressure.

  Patent Document 4 discloses a heat-fixing roller in which a silicon rubber layer having a hardness JIS A of 35 degrees or less, a compression set of 10% or less, and a rubber thickness of 1.5 to 4 mm is formed on a core metal of a heat fixing roller.

Patent Document 5 discloses an image forming apparatus, which includes a pressure belt that presses a transfer sheet against a heat fixing roller, and a pressure belt support unit that includes a plurality of belt support members that are stretched over the pressure belt. And a pressing means for pressing the transfer paper between the heat fixing roller and the outer peripheral surface of the pressure belt, and the pressing means is disposed on the inner peripheral surface of the heat fixing roller and the inner peripheral surface of the pressure belt. Further, there is disclosed one having at least one set of pressing members.
Japanese Patent Laid-Open No. 2005-164721 JP 08-166734 A JP-A-11-212389 JP-A 63-036283 JP 2002-207388

  In view of the above-described conventional example, the present invention is a fixing device including at least a heating unit, a pressure member, and an endless member, which simplifies the configuration of the device and does not apply a large load to the recording medium. It is an object of the present invention to provide a fixing device, an image forming apparatus, and an image forming method that improve the separation of the recording medium from the recording medium and improve the image quality formed on the recording medium.

The invention of claim 1
Heating means formed as one member having an elastic layer and a heat source;
A pressure means having an endless member arranged in a tension-free state and a pressure member fixedly held;
In a fixing device that transports a recording medium with an unfixed toner image attached thereto, passes the endless member through a nip formed by the heating means, and fixes the unfixed toner image on the recording medium.
The pressure member has an elastic layer, and the surface of the elastic layer of the pressure member is formed flat across the entire nip portion;
A support member that supports the pressure member supports a surface of the pressure member opposite to the surface of the elastic layer;
The load direction thickness of the nip portion central region of the support member is set to be a convex shape by making it thicker than the load direction thickness of the nip portion entrance region and the exit region,
The fixing device is characterized in that.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the width of the pressure member in the recording medium conveyance direction is the same as the nip width formed when the heating unit is pressed using an infinite flat plate or The pressure member is less than that.

According to a third aspect of the present invention, in the fixing device of the second aspect , the permanent deformation of the elastic layer of the heat fixing roller is 4% or less .

According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the thickness in the load direction of the central region of the nip portion of the support member is set to the thickness in the load direction of the inlet region and the outlet region of the nip portion. It is characterized by being thicker than that and set to a curved shape.

According to a fifth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the thickness in the load direction of the central region of the nip portion of the support member is set to the thickness in the load direction of the inlet region and the outlet region of the nip portion. It is characterized by being thicker than that and set in a step shape.

According to a sixth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the thickness in the load direction of the center region of the nip portion of the support member is set to the thickness in the load direction of the entrance region and the exit region of the nip portion. It is thicker than that, and has a mountain shape.

According to a seventh aspect of the present invention, in the fixing device according to any one of the first to sixth aspects, the heat-fixing roller has an outer diameter of 27 mm or less, a rubber hardness of the elastic layer of 8 Hs (JIS-A) or less, and a rubber thickness. Is 0.8 mm or more .

The invention of claim 8 comprises a plurality of developing means for forming toner images of different colors, a photosensitive means for attaching the toner image of the developing means to the surface, an intermediate transfer means for transferring the toner image of the photosensitive means, 8. An image forming apparatus comprising: a transfer unit that transfers a toner image of the intermediate transfer unit to a recording medium, and comprising the fixing device according to claim 1 .

  The present invention sets the elastic coefficient K of the elastic layer of the pressure member in the central region in the nip portion formed by the heating means to be higher than that in the nip portion entrance region and the exit region, and supports the pressure member By making the thickness in the load direction in the center area in the nip larger than the thickness in the load direction in the nip entrance area and the exit area, and setting the convex shape, local deformation of the heating roller elastic layer in this area occurs, By optimizing the paper protruding posture at the nip outlet, it is possible to efficiently improve the peeling performance while reducing image shift and paper load.

  Embodiments as the best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 100 includes a photoconductor 110 that rotates in the direction of arrow A, a scorotron charging device 112 that charges the surface of the photoconductor 110, and an exposure light R that modulates the surface of the charged photoconductor 110 with image information. A ROS (laser output unit) 113 that forms an electrostatic latent image on the photosensitive member 110 by exposure, and a developing device that develops the electrostatic latent image on the photosensitive member 110 with toner to form a toner image on the photosensitive member 110 114, a transfer device 115 that transfers the toner image on the photoconductor 110 to the paper P, a fixing device 116 that fixes the toner image transferred to the paper P, a paper tray 117 that stores the paper P, and the surface of the photoconductor 110. A cleaner 118 for removing residual charges on the surface of the photoconductor 110, and a charge eliminating device 119 for removing residual charges on the surface of the photoconductor 110.

Next, an image forming operation in the image forming apparatus will be described with reference to FIG.
First, an original image signal read from an original by an image reading unit (not shown) or an original image signal created by an external computer (not shown) or the like is input to an image processing unit (not shown). Appropriate image processing is performed. The input image signal obtained in this way is input to a ROS (laser output unit) 113 to modulate the laser beam R. The laser beam R modulated by the input image signal is irradiated on the surface of the photoreceptor 110 uniformly charged by the scorotron charging device 112 as a raster. When the surface of the photoconductor 110 is irradiated with the laser beam R, an electrostatic latent image corresponding to the input image signal is formed on the photoconductor 110.

  The electrostatic latent image formed on the photoconductor 110 is developed with toner by the developing device 114 to form a toner image on the photoconductor 110. The toner image formed on the photoconductor 110 is conveyed toward the transfer device 115 disposed opposite to the photoconductor 110 as the photoconductor 110 rotates in the direction of arrow A.

  On the other hand, the paper P stored in the paper tray 117 is supplied toward the nip portion between the photoconductor 110 and the transfer device 115, and the toner image on the photoconductor 110 is transferred onto the paper P by the transfer device 115. The The toner image transferred onto the paper P is conveyed and fixed by the fixing device 116 to obtain a desired image.

  Adhered matter such as residual toner adhering to the surface of the photoconductor 110 after the transfer of the toner image onto the paper P is cleaned by the cleaner 118, and the residual charge on the surface of the photoconductor 110 is removed by the static eliminator 119. Thus, one image forming operation is completed.

  FIG. 2 is a configuration diagram of the fixing device 116 employed in the image forming apparatus 100 shown in FIG. The fixing device shown in FIG. 2 corresponds to an embodiment of the fixing device of the present invention.

  In FIG. 2, reference numeral 1 denotes a heat fixing roller. The heat fixing roller 1 includes a surface coating layer 2, an elastic layer 3, a cored bar 4, and a heat source 6, and is integrally configured to drive and rotate. Yes. Reference numeral 32 denotes a recording medium, and 31 denotes unfixed toner attached to the surface of the recording medium 32. The recording medium 32 is conveyed in the direction of the arrow in FIG. A pressing unit is provided with the recording medium 32 interposed therebetween. The pressurizing means includes a pressurizing member 21, a support member 22 that supports the pressurizing member 21, and a pressurizing spring 11 that pressurizes the pressurizing member 21 and the support member 22 toward the recording medium 32. Has been placed. Further, an endless member 23 is locked to the pressurizing means, and the endless member 23 is driven by the heat fixing roller 1. A low-friction member 25 for reducing the friction between the endless member 23 and the pressure member 21 and a guide 24 for defining the transport path of the endless member 23 are provided, and the endless member 23 is not tensioned. In this state, the heat fixing roller 1 is driven.

  The surface of the pressure member 21 is flat, and the support member 22 has a curved shape in the transport direction. When the surface of the elastic layer is flat and the center of the support member is convex, the elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = load) of the central area in the nip of the elastic layer of the pressure member (Direction thickness) becomes higher than the elastic modulus of the nip entrance region and the exit region. Reference numeral 27 in the figure denotes a lubricating oil supply member that supplies lubricating oil for further reducing friction between the endless member 23 and the pressure member 21. Generally, lubricating oil containing silicon oil or fluorine oil is used. Reference numeral 33 denotes a fixed image on the recording medium 32 after passing through the nip portion between the heat fixing roller 1 and the endless member 23. As the surface coating layer 2 of the heat fixing roller 1, a PFA layer or the like is used so that the unfixed toner 31 does not easily adhere. Moreover, as the elastic layer 3, silicon rubber, fluororubber, or the like is generally used. When silicon rubber is used, a fluorine layer or the like may be coated to improve swelling resistance. The endless member 23 is made of PFA and polyimide. The pressure member 21 is a pressure pad having a flat surface in the pressure direction, and has a rubber layer of silicon rubber or fluoro rubber. Here, examples of the recording medium 32 include sheets such as cut sheets.

  FIG. 3 is a diagram showing a modification of the configuration of FIG. In this example, the surface of the pressure member 21 is flat and the support member 22 is convex. Other configurations are the same as those shown in FIG.

  FIG. 4 is also a diagram showing a modification of the configuration of FIG. In this example, the surface of the pressure member 21 is flat and the support member 22 has a mountain shape. Other configurations are the same as those in FIG.

  FIG. 5 is a graph showing an example of the pressure distribution in the sheet conveyance direction of the heat fixing roller at the nip portion and the pressure distribution in the comparative example, which are obtained when the pressure member is brought into pressure contact with the heat fixing roller. In the graph of FIG. 5, the vertical axis indicates the pressure, and the horizontal axis indicates the paper conveyance direction (circumferential direction) of the heat fixing roller. From the left side (the side on which the vertical axis is written), the recording medium 32 enters the nip portion between the heat fixing roller and the pressure member. Hereinafter, the left side of the distribution line will be described as the entrance to the nip portion, and the right side will be described as the exit from the nip region. The nip width is the conveyance direction of the recording medium 32.

  In FIG. 5, a curve 81 is a comparative example, and is an example of a pressure distribution obtained with a configuration in which the rubber hardness and the thickness in the load direction of the elastic layer of the pressure member are constant. It is simply shown for comparison. The curve 61 shows the elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = thickness in the load direction) in the center region in the nip of the elastic layer of the pressure member, and the elasticity of the nip entrance region and the exit region. This is an example of pressure distribution obtained by setting the thickness in the load direction of the center region in the nip of the support member supporting the pressure member to be thicker than the load direction thickness of the nip entrance region and the exit region. is there. Both pressure distributions are examples of pressure distributions obtained under the same conditions of the heating and fixing roller configuration, load value, and nip width (variable pad width). As shown in FIG. 5, the curve 81, which is a comparative example, has a lower peak pressure than the curve 61 and is distributed in a gentle curve from the nip inlet to the outlet.

  FIG. 6 is an example of a deformed shape in the transport direction of the heat-fixing roller elastic layer from the center of the nip to the exit. In FIG. 6, a curve 70 is the surface shape of the heat-fixing roller before deformation, and a curve 82 is an example of the deformation shape (nip shape) of the heat-fixing roller elastic layer after deformation obtained by the pressure distribution of the curve 81 in FIG. The straight line 83 is a straight line simulating the paper protruding state derived from the nip shape, and the clearance 84 indicates the distance until the curve 70 intersects the line drawn in the direction perpendicular to the straight line 83.

  Further, a curve 62 is an example of a deformed shape (nip shape) of the heat-fixing roller elastic layer after deformation obtained by the pressure distribution of the curve 61 in FIG. 5, and a straight line 63 indicates a sheet protruding state derived from the nip shape. In the simulated straight line, the clearance 64 indicates the distance until the curve 70 intersects the line drawn in the direction perpendicular to the straight line 63. This large clearance is considered to facilitate the separation of the sheet from the surface of the heat fixing roller. It can be seen that the clearance formed between the paper surface and the heat fixing roller surface formed after the nip outlet portion paper protrudes greatly affects the load direction deformation amount of the heat fixing roller elastic layer and the heat fixing roller outer diameter. Therefore, it is considered that the peeling characteristics can be improved by increasing the amount of deformation in the load direction of the heat-fixing roller elastic layer.

  7 shows the fixing device shown in FIGS. 2 to 4 (Showa Electric Wire Heating and Fixing Roller: Outer Diameter φ27, Elastic Layer Rubber Thickness 1.0 mm, Elastic Layer Rubber Hardness 8 Hs (JIS-A), Rubber Permanent Strain This is a result of evaluating the sheet peeling characteristics by applying a load of 40 kgf to 4% and a rubber axial length of 230 mm, changing the configuration of the pressure member. The settings of the experiment described below are all the same, and the nip width is made constant by finely adjusting the width in the conveyance direction of the pressure member (the pressure member conveyance direction width in FIG. 7 is a reference value). Peeling experiments were conducted with only the configuration changed. Cut paper was used as the recording medium. In this experiment, a full-color image was deposited on a general paper having a basis weight of 55 g / cm ^ 2, and the experiment was conducted with the fixing device shown in FIG.

  As a result, the shapes of the pressure member and the support member are shown in FIGS. 2 to 4 as compared with a fixing device using a pressure member having a rubber hardness of 8 Hs (JIS-A), a rubber permanent strain of 4%, and a rubber load direction thickness of 4 mm. It was confirmed that the peeling performance was improved by changing to As shown by the straight line in FIG. 6 (a line simulating the paper posture), the elastic modulus difference between the inlet and the center of the pressurizing member, and the outlet and the center is set to an appropriate value or more. The thickness difference in the load direction between the center part and the center part, and the outlet part and the center part is set to an appropriate value or more, and the convex shape is used. . Further, when the rubber permanent set of the elastic layer on the heat fixing roller side is large, the surface shape of the heat fixing roller is locally deformed, which causes image deterioration such as uneven gloss of the image. From this experiment, it was found that when the rubber permanent strain is 5% or more, gloss unevenness is conspicuous and the rubber permanent strain is preferably 4% or less.

  Further, it is understood that the outer diameter of the heat-fixing roller is one of the parameters for determining the clearance from the idea that if the clearance between the surface of the heat-fixing roller after the nip exit and the surface of the paper is large, the paper is easily peeled off. In this experiment, it was confirmed that when the outer diameter of the heat fixing roller is φ27 or more, the peeling performance is lowered. Therefore, the outer diameter of the heat fixing roller is preferably φ27 or less. Further, it can be seen that the thickness of the elastic layer of the heat fixing roller is one of the parameters that determine the clearance between the surface of the heat fixing roller and the paper surface.

  From this experiment, it was found that when the rubber thickness is 0.8 mm or less, the peeling performance decreases. This is considered to be because the amount of deformation becomes smaller as the thickness of the heat-fixing roller elastic layer becomes thinner, and the sheet projecting posture at the nip exit portion cannot be brought into an appropriate state. Therefore, the thickness of the elastic layer of the heat fixing roller is desirably 0.8 mm or more. Similarly, it can be seen that the rubber hardness of the elastic layer of the heat fixing roller is one of the parameters for determining the clearance. From this experiment, it was found that when the rubber hardness is 8Hs (JIS-A) or more, the peeling performance is lowered. This is because the amount of deformation decreases as the hardness of the heat-fixing roller elastic layer increases, and the sheet protruding posture at the nip exit portion cannot be brought into an appropriate state.

  Therefore, the rubber hardness of the elastic layer of the heat fixing roller is desirably 8 Hs (JIS-A) or less. Furthermore, when the rubber permanent set of the pressure member is large, the nip shape may be deformed with time, and the fixing characteristics and the peeling characteristics may become unstable. From this experiment, it was confirmed that when the rubber permanent set of the pressure member is 5% or more, the peeling property after heating idling for 100 hours or more is lowered. Therefore, it was found that the rubber permanent strain of the pressure member is preferably 4% or less.

  FIG. 8 shows a second embodiment of the present invention. Parts that are the same as or similar to those in the first embodiment will be described with the same reference numerals. A member denoted by reference numeral 5 provided on the image surface side of the recording medium 32 to which the unfixed toner 31 is attached is an endless heating member. In the figure, reference numeral 8 denotes a heating member having an elastic layer, reference numeral 9 denotes a pressure support member that supports the heating member 8, reference numeral 6 denotes a heat source, and reference numeral 7 denotes a heating roller that stretches or heats the endless heating member 5 at the same time. Is shown. When the amount of heat is insufficient, the endless heating member 5 can be heated by contacting the heating roller 7b from the outside.

  Reference numeral 7a in the figure is a driven roller that rotates without having a heat source therein. Although the driving source for driving the endless heating member is in the heating roller 7, it may be provided in the driven roller 7a. Compared to the configuration using the heat fixing roller 1 as shown in FIG. 2, this configuration uses an endless heating member, so the overall size of the apparatus is not affected so much, and the nip width and the deformed shape of the nip exit portion are not affected. Have the advantage of being able to adjust. The surface of the pressure member 21 is flat, and the support member 22 has a curved shape in the transport direction. In the case of this configuration, the width of the pressure member 21 needs to be set equal to or smaller than the width of the heating member 8.

  FIG. 9 is a diagram showing a modification of the configuration of FIG. In this example, the surface of the pressure member 21 is flat, and the support member 22 has a step shape. Other configurations are the same as those in FIG.

  FIG. 10 is also a diagram showing a modification of FIG. In this example, the surface of the pressure member 21 is flat and the support member 22 has a mountain shape. Other configurations are the same as those in FIG.

  In the present invention as described above, the elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = thickness in the load direction) of the central region in the nip of the elastic layer of the pressure member is defined as the nip entrance region. Make it higher than the elastic modulus of the exit area, and set the thickness in the load direction of the center area in the nip of the support member that supports the pressure member to be thicker than the thickness in the load direction of the nip entrance area and the exit area, and set it in a convex shape Thus, by causing local deformation of the heating roller elastic layer in this region and optimizing the paper projecting posture of the nip exit portion, it is possible to efficiently improve the peeling performance while reducing image misalignment and paper load. I was able to.

  Further, in the present invention, by optimizing the rubber width, local deformation of the heating roller elastic layer is generated, and by optimizing the paper projecting posture of the nip exit portion, while reducing image shift and paper load, The stripping performance could be improved efficiently.

  In the present invention, the elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = thickness in the load direction) of the central region in the nip of the elastic layer of the pressure member is set between the nip inlet region and the outlet region. It is also possible to set a step shape by making the load direction thickness in the center region in the nip of the support member supporting the pressure member higher than the elastic modulus and thicker than the load direction thickness in the nip entrance region and the exit region. Street.

  In the present invention, the elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = thickness in the load direction) of the central region in the nip of the elastic layer of the pressure member is set between the nip inlet region and the outlet region. It is possible to set a curved surface shape by making the thickness in the load direction of the center region in the nip of the support member supporting the pressure member thicker than the load direction thickness of the nip entrance region and the exit region. It was.

  In the present invention, the elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = thickness in the load direction) of the central region in the nip of the elastic layer of the pressure member is set between the nip inlet region and the outlet region. It is higher than the elastic modulus, and the thickness in the load direction of the center region in the nip of the support member that supports the pressure member can be made thicker than the thickness in the load direction of the nip entrance region and the exit region, and can be set in a mountain shape. . Moreover, in this invention, it was able to be made low price by using a heating roller.

  In the present invention, the heat fixing roller can have an outer diameter of φ27 or less, a rubber hardness of the heating roller elastic layer of 8 Hs (JIS-A) or less, and a rubber thickness of 0.8 mm or more.

  In the present invention, the permanent deformation of the heat-fixing roller elastic layer can be 4% or less.

  Further, in the present invention, it is possible to cope with high speed by using the heating belt.

  Further, in the present invention, by providing the fixing device, the configuration of the image forming apparatus is simplified, the separation property of the recording medium from the heating means is improved without imposing a large load on the recording medium, and the image forming apparatus is formed on the recording medium. The image quality can be improved.

  In the present invention, the image forming method as described above can improve the separation property of the recording medium from the heating means without imposing a large load on the recording medium, and can also improve the image quality formed on the recording medium. did it.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is a configuration diagram of a fixing device employed in the image forming apparatus illustrated in FIG. 1. It is a figure which shows the modification of the structure of FIG. It is a figure which shows the modification of the structure of FIG. It is a figure which shows the pressure distribution example of each example. It is a figure which shows the example of the conveyance direction deformation | transformation shape of the heat-fixing roller elastic layer from a nip center part to an exit part. It is a figure which shows the experimental result of the peeling characteristic of the fixing device shown in FIGS. It is a figure which shows Example 2 of this invention using a heating belt. It is a figure which shows the modification of the structure of FIG. It is a figure which shows the modification of the structure of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat-fixing roller 2 Surface coating layer 3 Elastic layer 4 Core metal 5 Endless heating member 6 Heat source 7 Heating roller 7a Follower roller 7b Heating roller 8 Heating member 11 Pressing spring 21 Pressing member 22 Supporting member 23 Endless member 24 Guide 25 Low friction member 27 Lubricating oil supply member 31 Unfixed toner 32 Recording medium 64 Clearance 84 Clearance 100 Image forming device 110 Photoconductor 112 Scorotron charging device 114 Developing device 115 Transfer device 116 Fixing device 117 Paper tray 118 Cleaner 119 Static elimination device P: Paper R: Exposure light

Claims (8)

Heating means formed as one member having an elastic layer and a heat source;
A pressure means having an endless member arranged in a tension-free state and a pressure member fixedly held;
In a fixing device that transports a recording medium with an unfixed toner image attached thereto, passes the endless member through a nip formed by the heating means, and fixes the unfixed toner image on the recording medium.
The pressure member has an elastic layer, and the surface of the elastic layer of the pressure member is formed flat across the entire nip portion;
A support member that supports the pressure member supports a surface of the pressure member opposite to the surface of the elastic layer;
The load direction thickness of the nip portion central region of the support member is set to be a convex shape by making it thicker than the load direction thickness of the nip portion entrance region and the exit region,
A fixing device.   The fixing device according to claim 1, wherein the heating unit is a rotatable heat-fixing roller having the elastic layer and the heat source therein.   3. A fixing device according to claim 2, wherein the elastic layer of said heat fixing roller has a permanent deformation of 4% or less. 4. The fixing device according to claim 1, wherein a thickness in a load direction of a central region of the nip portion of the support member is larger than a thickness in a load direction of an entrance region and an exit region of the nip portion, and a curved surface shape is formed. A fixing device characterized by being set to. 4. The fixing device according to claim 1, wherein a thickness in a load direction of a central region of the nip portion of the support member is made thicker than a thickness in a load direction of an entrance region and an exit region of the nip portion. A fixing device characterized by being set to. 4. The fixing device according to claim 1, wherein a thickness in a load direction of the central region of the nip portion of the support member is made thicker than a thickness in a load direction of an entrance region and an exit region of the nip portion, A fixing device characterized by being set to.   7. The fixing device according to claim 1, wherein the heat-fixing roller has an outer diameter of 27 mm or less, a rubber hardness of the elastic layer of 8 Hs (JIS-A) or less, and a rubber thickness of 0.8 mm or more. A fixing device. A plurality of developing means for forming toner images of different colors, a photosensitive means for attaching the toner image of the developing means to the surface, an intermediate transfer means for transferring the toner image of the photosensitive means, and a toner image of the intermediate transfer means An image forming apparatus comprising: a transfer unit that transfers the image to a recording medium, and comprising the fixing device according to claim 1.