JP4869191B2 - Fixing device - Google Patents

Description

The present invention is an electrophotographic copying machine, about the constant wearing location that is mounted in an image forming apparatus such as an electrophotographic printer.

As a constant Chakusochi (fuser) you mounted in an image forming apparatus of a copying machine or a printer of an electrophotographic system, there is a belt type. A belt-type fixing device uses an endless belt to form a nip portion for heating while nipping and conveying a recording material such as a recording paper or an OHP sheet carrying a toner image. The width of the nip portion can be increased in the transport direction. For this reason, even if the conveying speed of the recording material is increased, the toner image can be heated for a sufficient time, and the printing speed can be increased. As a belt-type fixing device, a configuration in which a belt and a roller are combined and a configuration in which two belts are combined are proposed.

  As an example of a configuration in which a belt and a roller are combined, there is a fixing device disclosed in Patent Document 1. In this fixing device, an endless fixing belt is stretched between two rollers, a fixing roller and a heating roller having a heat source therein, and the outer peripheral surface (front surface) of the fixing belt is stretched between the fixing roller and the heating roller. The nip portion is formed by contacting the pressure roller.

  An example of a configuration in which two belts are combined is the fixing device disclosed in Patent Document 2. In the fixing device of Patent Document 2, a roller and a belt guide are arranged inside each belt, and a nip portion is formed by pressing the rollers inside each belt and the belt guides through the belt. Yes.

  As another example of a configuration in which a belt and a roller are combined, there are fixing devices disclosed in Patent Document 3 and Patent Document 4. Each of the fixing devices of Patent Document 3 and Patent Document 4 has a configuration in which a slackened belt and a roller are combined. In the fixing device of Patent Document 3, the nip is formed by bringing the outer peripheral surface (surface) of the fixing roller into contact with the slack portion (slack portion) of the seamless belt. In the fixing device disclosed in Patent Document 4, the slackened belt is brought into contact with the outer peripheral surface (surface) of the fixing roller facing the belt on the downstream side in the recording material conveyance direction to form a nip portion.

  In recent years, in order to enable high-speed printing, the recording material and the toner image are preheated by preheating means so that the toner image and the recording paper can be heated for a sufficient time even if the recording paper conveyance speed is increased. A fixing device having such a configuration has been proposed.

  For example, in Patent Document 5, in a fixing device that combines a fixing belt and a roller, the fixing belt and the recording paper are brought closer to each other on the upstream side of the fixing pressure nip portion with respect to the conveyance direction of the recording material. The toner image is preheated in a non-contact manner.

Further, in Patent Document 6, in a fixing device in which a lower belt supporting a recording material and a roller are combined, a fixing pressure nip portion is formed in pressure contact with the roller and the lower belt, and the toner is placed before the fixing pressure nip portion. In this configuration, the recording medium carrying the image is preheated from the back surface in contact with the lower belt.
JP-A-10-30796 JP 2005-173058 A JP-A-8-16008 JP 2002-207380 A JP-A-6-31801 JP-A-10-228190

  However, in the fixing device having the preheating means as described above, when the recording material type (recording material type) such as thin paper, plain paper, and thick paper is changed, the recording material and the toner image are changed depending on the thickness of the paper and the heat capacity. The heat transfer changes, and the effect of preheating changes.

  When the thick paper is passed through the fixing device like the plain paper by the method shown in the above-mentioned patent document 5, the preheated area is heated from the upper surface of the toner image in a non-contact manner by the radiant heat from the fixing belt. However, heat is not transferred to the inside of the cardboard. Therefore, even if the toner image is pressurized at the fixing pressure nip, it does not melt and spread inside the thick paper, reducing the adhesion between the toner image and the thick paper, resulting in a decrease in glossiness of the toner image, cold offset, etc. To do. On the other hand, when thin paper is passed through the fixing device in the same way as plain paper, the distance between the recording material surface and the fixing belt surface is small in the pre-heated area. Rubs with the fixing belt, and “image shift” occurs.

  When the thick paper is passed through the fixing device in the same manner as in the above-mentioned Patent Document 6 in the same manner as plain paper, it is heated from the back side of the thick paper carrying the toner image in the preheating area. Heat is not transferred to the toner image. For this reason, even if the toner image is pressurized at the fixing pressure nip portion, the toner image does not melt and spread so much that the glossiness of the toner image is reduced, a cold offset or the like occurs. On the other hand, when thin paper is passed through the fixing device in the same way as plain paper, heat is rapidly transferred from the back side to the front side of the thin paper carrying the toner image in the pre-heated area, and the toner image is excessively heated, and fixing is applied. The toner image is excessively melted and spreads at the pressure nip portion. As a result, the toner image on the recording paper after fixing has a high glossiness and cannot be maintained at the target optimum glossiness.

  In addition, a configuration has been proposed in which the pressure applied to the nip portion of the fixing device is variable in accordance with the recording material type (recording material type). With such a configuration, if the pressing force at the nip portion of the fixing device is variable, not only the nip width in the recording material conveyance direction of the nip portion changes, but also the pressing force at the nip portion changes. Therefore, the melt deformation of the toner on the recording paper cannot be kept constant corresponding to the paper type, and the target glossiness on the recording paper cannot be maintained at the optimum glossiness.

An object of the present invention is to prevent the toner from penetrating excessively into the fibers of the recording material during the fixing process, to suppress the deviation of the toner image during the fixing process, and to perform the fixing process according to the type of the recording material. It is an object of the present invention to provide a fixing device that can perform the above operation.

In order to achieve the above object, a first endless belt, a second endless belt that contacts an outer peripheral surface of the first endless belt, at least the first endless belt, and the second endless belt are provided. A heating member that heats one of the first endless belt, a first pressure member that contacts the inner peripheral surface of the first endless belt, and a second pressure that contacts the inner peripheral surface of the second endless belt. And the first endless belt and the second endless belt are sandwiched between the first pressure member and the second pressure member, and the first endless belt and the second endless belt are sandwiched between the first endless belt and the second endless belt. In a fixing device for fixing a non-fixed toner image on a recording material by heating while nipping and conveying a recording material carrying an unfixed toner image at a nip portion formed between two endless belts,
Of the first and second endless belts, at least one endless belt is disposed in a slack state, and the nip portion is formed between one endless belt and the other endless belt. A first nip region, a region of the first endless belt having a backup by the first pressure member, and a region of the second endless belt having a backup by the second pressure member are in contact with each other. The nip portion starts from the first nip region in the recording material conveyance direction, and immediately after the first nip region, the second nip region Have
Further, the first nip region has a mechanism for displacing the length in the recording material conveyance direction.

According to the present invention, it is possible to prevent the toner from penetrating excessively into the recording material fiber during the fixing process, to suppress the deviation of the toner image during the fixing process, and to perform the fixing process according to the type of the recording material. It is possible to provide a fixing device that can perform the above operation.

  The present invention will be described with reference to the drawings.

[Example 1]
(1) Example of Image Forming Apparatus Figure 14 is a block schematic drawing of an example of an image forming apparatus equipped with the engagement shall be specified wearing location to the invention. This image forming apparatus is a laser beam printer that forms an image on a recording material (for example, recording paper, OHP sheet, etc.) using an electrophotographic image forming system.

  An image forming apparatus A shown in this embodiment includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 101 as an image carrier. The photosensitive drum 101 is rotatably supported by an image forming apparatus main body B that constitutes a casing of the image forming apparatus A, and is rotationally driven in a direction of an arrow at a predetermined process speed by a driving unit (not shown). Around the photosensitive drum 101, a charging roller (charging means) 102, a laser exposure device (exposure means) 103, a developing device (developing means) 105, a transfer roller (transfer means) 106, and a cleaning device are arranged along the rotation direction. (Cleaning means) 107 are arranged in that order.

  During the rotation operation, the outer peripheral surface (surface) of the photosensitive drum 101 is uniformly charged to a predetermined potential and polarity by the charging roller 102. Then, the surface of the photosensitive drum 101 is scanned and exposed from the laser exposure device 103 to the laser L based on target image information through the mirror 104 and the like. As a result, the charge at the exposed portion is removed, and an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 101. The electrostatic latent image is developed using toner (developer) by a developing device 105 having a developing roller 105a. In other words, the developing device 105 applies a developing bias to the developing roller 105 a and attaches toner to the electrostatic latent image on the surface of the photosensitive drum 101. Thereby, the electrostatic latent image is visualized (visualized) as a toner image (developed image).

  On the other hand, the recording material P is fed from the feeding cassette 108 by the feeding roller 109 at a predetermined timing, and the recording material P is transferred to the transfer nip Tn between the photosensitive drum 101 and the transfer roller 106 by the transport roller 110. Be transported. The recording material P is nipped and conveyed by the transfer nip Tn, and a transfer bias is applied to the transfer roller 106 in the conveyance process. As a result, the toner images on the surface of the photosensitive drum 101 are sequentially transferred onto the recording material P.

Recording material P bearing the unfixed toner image at the transfer nip portion Tn is conveyed along the conveying guide 111 is separated from the photosensitive drum 101 surface to the constant Chakusochi 112. The fixing device 112 applies heat and pressure to the unfixed toner image on the recording material P to heat and fix the unfixed toner image on the recording material P. The recording material P that has exited the fixing device 112 is transported to the discharge roller 114 by the transport roller 113, and is discharged to the discharge tray 115 on the apparatus main body B by the discharge roller 114.

  The surface of the photosensitive drum 101 after the transfer of the toner image is subjected to removal of adhering matter such as transfer residual toner by a cleaning blade 107a of the cleaning device 107, and used for the next image formation.

(2) Fixing Device In the following description, with respect to the fixing device or the members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the short direction.

  FIG. 1 is a schematic cross-sectional view of an example of the fixing device 112. 2 is a cross-sectional view of the fixing device 112 taken along the line II-II shown in FIG. 3 is a cross-sectional view of the fixing device 112 taken along line III-III shown in FIG.

The fixing device 112 shown in this embodiment includes a fixing belt 11 and a pressure belt 12 as endless belts, a fixing roller 13 and a pressure roller 14 as pressure members, and a heating roller (first support) as a support member. Member) 16 and a tension roller (second support member) 17. The fixing device 112 includes a halogen heater 15 as a heating member , a temperature detection element 18 such as a thermistor as a temperature detection unit, and first frames 21L and 21R and second frames 22L and 22R as support members. Have. The fixing belt 11, the fixing roller 13, the heating roller 16, the heater 15, the temperature detecting element 18, and the first frames 21L and 21R constitute a fixing belt unit U1. The pressure belt unit U2 includes the pressure belt 12, the pressure roller 14, the tension roller 17, and the second frames 22L and 22R.

  In the fixing device 112 of this embodiment, in the fixing belt unit U1, the fixing roller 13 and the heating roller 16 are provided inside the fixing belt 11 arranged along the longitudinal direction of the fixing device 112, and the fixing roller 13 and the heating roller 16 are provided. Thus, the fixing belt 11 is supported. Further, in the pressure belt unit U 2, a pressure roller 14 and a tension roller 17 are provided inside the pressure belt 12 disposed along the longitudinal direction of the fixing device 112, and the pressure roller 14 and the tension roller 17 apply pressure. The pressure belt 12 is supported.

  The layer configuration of the fixing belt 11 and the pressure belt 12 will be described with reference to FIG.

  4A is a cross-sectional view illustrating an example of the layer configuration of the fixing belt 11, and FIG. 4B is a cross-sectional view illustrating an example of the layer configuration of the pressure belt 12.

  Each of the fixing belt 11 and the pressure belt 12 has endless base layers 11a and 12a on the inner side, elastic layers 11b and 12b on outer peripheries of the base layers 11a and 12a, and outer peripheries of the elastic layers 11b and 12b. The release layers 11c and 12c are provided (FIGS. 4A and 4B). The base layers 11a and 12a are electroless belts made of metal such as nickel and SUS, or endless belts made of a heat resistant resin such as polyimide. The thickness of the base layers 11a and 12a is about 50 to 150 μm in the case of a metal electroformed belt, and about 50 to 300 μm in the case of a heat resistant resin. The belt itself has appropriate rigidity and flexibility. It is preferable to have. The elastic layers 11b and 12b are silicon rubber layers having a thickness of about 50 to 300 μm formed on the base layers 11a and 12a. The release layers 11c and 12c are fluororesin layers such as PFA and PTFE having a thickness of about 10 to 50 μm formed on the elastic layers 11b and 12b. The elastic layers 11b and 12c are formed by covering or coating the tube. 12b is formed.

  In this embodiment, the fixing belt 11 and the pressure belt 12 are configured as follows. That is, an endless belt made of a nickel layer having a thickness of 75 μm is used as the base layers 11a and 12a, and a silicon rubber layer having a thickness of 300 μm is formed as elastic layers 11b and 12b on the outer periphery of the base layers 11a and 12a. Further, the elastic layers 11b and 12b are covered with 50 μm PFA tubes as the release layers 11b and 12b. The outer diameter of both the fixing belt 11 and the pressure belt 12 is 60 mm.

  The fixing roller 13 and the pressure roller 14 are each an elastic roller having an outer diameter of φ30 mm in which elastic layers 13 b and 14 b made of a silicon sponge rubber layer having a thickness of 5 mm are provided on the outer periphery of a SUS core metal 13 a and 14 a of φ20. It is. The Asker C hardness at this time is about 50 ° when 9.8 N (1 kgf) is applied. The outer diameter of the fixing roller 13 is smaller than the inner diameter of the fixing belt 11. Accordingly, the fixing belt 11 is loosely fitted on the fixing roller 13. The outer diameter of the pressure roller 14 is smaller than the inner diameter of the pressure belt 12. Accordingly, the pressure belt 12 is loosely fitted on the pressure roller 14. The longitudinal dimensions of the elastic layers 13b and 14b of the fixing roller 13 and the pressure roller 14 are set to be slightly larger than the longitudinal dimensions of the fixing belt 11 and the pressure belt 12 (FIG. 2). Alternatively, the longitudinal dimensions of the elastic layers 13 b and 14 b of the fixing roller 13 and the pressure roller 14 are set to be approximately the same as the longitudinal dimensions of the fixing belt 11 and the pressure belt 12.

  The fixing roller 13 is rotatably supported by the first frames 31L and 31R through the bearings 32L and 32R at both ends of the cored bar 13a (FIG. 2). The pressure roller 14 is disposed below the fixing roller 13 in parallel with the fixing roller 13, and both ends of the cored bar 13a are rotatably supported by the second frames 33L and 33R via bearings 34L and 34R.

  FIG. 5 is an explanatory diagram showing the relationship among the fixing roller 13, the heating roller 16, and the fixing belt 11. 5A is a view showing a state in which the fixing belt 11 is wound around the fixing roller 13 and the heating roller 16 by the shortest path length of the fixing belt 11. FIG. FIG. 2B is a diagram illustrating a state in which the fixing belt 11 is wound around the fixing roller 13 and the heating roller 16 with a margin longer than the shortest path length of the fixing belt 11.

  The heating roller 16 is an aluminum hollow cylindrical body having a thickness of 1 mm and an outer diameter of 18 mm. The heating roller 16 is provided at a position where the fixing belt 11 wound around the fixing roller 13 protrudes obliquely upward on the upstream side in the recording material conveyance direction from the fixing roller 13. That is, the circumferential length of the fixing belt 11 is longer with a margin than the shortest path length of the fixing belt 11 when the fixing belt 11 is wound around the fixing roller 13 and the heating roller 16. Such a position is intentionally arranged. That is, the fixing belt 11 is not stretched around the fixing roller 13 and the heating roller 16 as shown in FIG. 5A, but is fixed around the fixing roller 13 as shown in FIG. Loosely hung around the heating roller 16. Accordingly, the fixing belt 11 has a slack portion 11 d formed between the fixing roller 13 and the heating roller 16 in the circumferential direction of the fixing belt 11. At that position, the heating roller 16 is supported by the first frames 31L and 31R so as to be displaced along an imaginary straight line L1 connecting the rotation center of the fixing roller 13 and the rotation center of the heating roller 16. That is, bearings 35L and 35R (FIG. 3) for rotatably supporting the heating roller 16 are provided at both ends of the heating roller 16. Then, both ends of the heating roller 16 are attached to the bearings 35L, 31 as sliders SL1, SR1, which are movably provided in the first frames 31L, 31R so as to approach or separate from the fixing roller 13 along the virtual straight line L1. It is supported via 35R.

  Both ends of the halogen heater 15 provided inside the heating roller 16 are supported by heater support portions 31L1 and 31R1 provided on the sliders SL1 and SR1. The inner surface of the heating roller 16 is painted black so that the radiant heat of the halogen heater 15 is easily absorbed.

  The heating roller 16 contacts a part of the outer peripheral surface (front surface) of the heating roller 16 with the inner peripheral surface (inner surface) of the fixing belt 11, and transmits heat from the halogen heater 15 to the fixing belt 11 from the contact region. Thus, the fixing belt 11 is heated. That is, the fixing belt 11 is heated by the halogen heater 15 through the heating roller 16. Further, the change of the travel position in the longitudinal direction due to the rotation of the fixing belt 11 (the deviation of the fixing belt 11) is regulated by the contact area of the surface of the heating roller 16 that contacts the inner surface of the fixing belt 11.

  FIG. 6 is an explanatory diagram showing the relationship among the pressure roller 14, the tension roller 17, and the pressure belt 12. 6A is a diagram showing a state in which the pressure belt 12 is wound around the pressure roller 14 and the tension roller 17 by the shortest path length of the pressure belt 12. (B) is a diagram showing a state in which the pressure belt 12 and the tension roller 17 are wound around the pressure belt 12 with a margin longer than the shortest path length of the pressure belt 12.

The tension roller 17 is a roller having an outer diameter of φ18 mm, and has an elastic layer 17b made of a silicon sponge rubber layer having a thickness of 2 mm on the outer periphery of a SUS φ14 mm cored bar 17a. The longitudinal dimension of the elastic layer 17 b is equal to the longitudinal dimension of the elastic layers 13 b and 14 b of the fixing roller 13 and the pressure roller 14. The tension roller 17 is provided at a position where the pressure belt 12 wound around the pressure roller 14 protrudes obliquely downward from the pressure roller 14 on the upstream side in the recording material conveyance direction. In other words, the tension roller 17 has a margin in the circumferential length of the pressure belt 12 than the shortest path length of the pressure belt 12 when the pressure belt 12 is wound around the pressure roller 14 and the tension roller 17. It is intentionally placed at a position where it can be long. That is, the pressure belt 12 is not wound around a state where the pressure roller 14 and the tension roller 17 are tensioned as shown in FIG. 6A, but is pressed as shown in FIG. 6B. The roller 14 and the tension roller 17 are loosely wound around. Therefore, a slack portion 12 d is formed on the pressure belt 12 between the pressure roller 14 and the tension roller 17 in the circumferential direction of the pressure belt 12.
At that position, the tension roller 17 is supported by the second frames 33L and 33R so as to be displaced along an imaginary straight line L2 connecting the rotation center of the pressure roller 14 and the rotation center of the tension roller 17. That is, bearings 36L and 36R (FIG. 3) for rotatably supporting the tension roller 17 are provided at both ends of the tension roller 17. Then, both ends of the tension roller 17 are attached to the bearings 36L on the sliders SL2 and SR2 as moving members provided movably on the second frames 33L and 33R so as to approach or separate from the pressure roller 14 along the virtual straight line L2. -It is supported via 36R.

  The tension roller 17 travels in the longitudinal direction due to the rotation of the pressure belt 12 by the contact area of the outer peripheral surface (surface of the tension roller 17) of the elastic layer 17b that contacts the inner peripheral surface (inner surface) of the pressure belt 12. A change in position (a deviation of the pressure belt 12) is regulated.

  Next, the nip portion formed by the fixing belt 11 of the fixing belt unit U1 and the pressure belt 12 of the pressure belt unit U2 will be described.

In the fixing belt unit U1 and the pressure belt unit U2, both ends of the core metal 13a of the fixing roller 13 and both ends of the core metal 14a of the pressure roller 14 are respectively provided with pressure springs 41L. 41R, 42L and 42R are arranged (FIG. 2). The fixing roller 13 and the pressure roller 14 are urged toward each other by the pressure springs 41L / 41R, 42L / 42R. The fixing roller 13 and the pressure roller 14 are pressed against the outer peripheral surface (surface) of the fixing belt 13 by pressing the fixing belt 13 and the pressure belt 14 between the elastic layers 13b and 14b. The outer peripheral surface (surface) of the belt 14 comes into contact. Its fixing belt 13 surface (fixing roller 13 is a backup by area) and the pressure belt 14 surface (the pressure roller 14 is a backup by area) good to the Ri pressure nip portion (second nip region) N2 is formed (FIG. 1). In this embodiment, the total pressure applied to the fixing roller 13 and the pressure roller 14 by the pressure springs 41L, 41R, 42L, and 42R is 196 N (20 kgf), whereby the width of the pressure nip portion N2 is 5 mm. It is said. That is, the fixing roller 13 and the pressure roller 14 as pressure members are fixed so that the outer peripheral surfaces of the two endless belts 13 and 14 are in contact with each other to form the pressure nip portion N2. The belt 13 and the pressure belt 14 are supported.

FIG. 7 shows a pre-nip portion (first nip region) N2 as a second nip portion formed by the slack portions 11d and 12d of the fixing belt 11 and the pressure belt 12 with the formation of the pressure nip portion N2. It is explanatory drawing of.

  As described above, the fixing belt 11 and the pressure belt 12 have the slack portions 11d and 12d, respectively. When the pressure nip portion N2 is formed by the fixing belt 11 and the pressure belt 12, the slack portions 11d and 12d of the fixing belt 11 and the pressure belt 12 from the upper end of the pressure nip portion N2 in the recording material conveyance direction. An area (dotted line portion in FIG. 7) that overlaps within a predetermined range is generated. In each of the slack portions 11d and 12d, the surface of the fixing belt 11 and the surface of the pressure belt 12 are in linear contact with each other in the overlapping region. As a result, the fixing belt 11 and the pressure belt 12 are appropriately deformed so as to be balanced in the circumferential direction. As a result, a pre-nip portion N1 is formed in the overlapping region (FIG. 1). Accordingly, the nip pressure in the pre-nip portion N1 is such that the fixing belt 11 and the pressure belt 12 return from the contact state shown in FIG. 1 to the non-contact state shown in FIGS. 5B and 6B. This is due to the elastic force of the belt 11 and the pressure belt 12. In other words, the nip pressure in the pre-nip portion N1 depends on the rigidity and flexibility of the base layers 11a and 12a of the fixing belt 11 and the pressure belt 12, respectively, and the belts 11 and 12 themselves trying to return to the non-contact state. This is due to resilience. The width of the pre-nip portion N1 formed in this way is approximately 15 mm. The pre-nip portion N1 does not have to be linear, and may be curved in an arc.

  The pressure distribution in the pre-nip portion N1 and the pressure nip portion N2 was measured using a pressure distribution measurement system PINCH manufactured by Nita Corporation. FIG. 8 shows the pressure distribution in the pre-nip portion N1 and the pressure nip portion N2.

  As shown in FIG. 8, in the pressure nip portion N2, the surface of the fixing belt 11 and the surface of the pressure belt 12 are brought into contact with each other by the fixing roller 13 and the pressure roller 14; The pressing force reaches a peak at the contact position between the surface 11 and the surface of the pressure belt 12. In contrast, in the pre-nip portion N1, the surface of the fixing belt 11 and the surface of the pressure belt 12 are in contact with each other only by the elastic force (restoring force) between the fixing belt 11 and the pressure belt 12. It is very low compared to the applied pressure at the nip portion N2. Further, in the pre-nip portion N1, since the fixing belt 11 provided with a rigid endless belt as the base layers 11a and 12a is in contact with the pressure belt 12, the pressure distribution is uniform.

(3) Heat Fixing Operation of Fixing Device When the driving gear (FIG. 2) provided at the end of the cored bar 14a of the pressure roller 14 is rotationally driven by the fixing motor M, the pressure roller 14 has a predetermined peripheral speed. Is rotated in the direction of the arrow (FIG. 1). When the pressure roller 14 rotates, the rotation of the pressure roller 14 is transmitted to the pressure belt 12 in the pressure nip portion N2, and the pressure belt 12 and the tension roller 14 are rotated along with the rotation of the pressure roller 14. Move around 17 in the direction of the arrow. The rotation of the pressure belt 12 is transmitted to the tension roller 17, and the tension roller 17 is driven to rotate in the direction of the arrow as the pressure belt 12 rotates. In addition, the rotation of the pressure belt 12 is transmitted to the surface of the fixing belt 11 at the pressure nip portion N2, and the fixing belt 11 rotates around the fixing roller 13 and the heating roller 16 along with the rotation of the pressure belt 12. 12 and move in the direction of the arrow at the same speed. The rotation of the fixing belt 11 is transmitted to the heating roller 16, and the heating roller 16 is driven to rotate in the direction of the arrow as the fixing belt 11 rotates. In this embodiment, the circumferential movement speed (traveling speed) of the pressure belt 12 and the fixing belt 11 is 200 mm / s.

  Even when the fixing belt 11 and the pressure belt 12 are intentionally loosened as in this embodiment (FIGS. 3b and 4b), the fixing belt 11 and the pressure belt 12 have base layers 11a and 12a, respectively. Since it has rigidity and flexibility, it rotates while maintaining its relaxed state. For this reason, the fixing belt 11 and the pressure belt 12 shown in this embodiment are wavy in the belt itself as compared with the case where the fixing belt 11 and the pressure belt 12 rotate in a tensioned state (FIGS. 3a and 4a). Less likely to occur. Therefore, there is an advantage that the surface of the fixing belt 11 can be brought into uniform contact with the carrying surface of the unfixed toner image T of the recording material P. Therefore, image distortion or the like hardly occurs in the unfixed toner image T on the recording material P.

  The heater 15 is energized by an energization control unit 41 (FIG. 3) as an energization control means before or after the rotational driving of the pressure roller 14 or simultaneously. As a result, the heater 15 generates heat, the heating roller 16 heats the heating roller 16 that is rotating, and the heating roller 16 heats the fixing belt 11 that is rotating. The heat of the fixing belt 11 is transmitted to the pressure belt 12 that is rotating through the pressure nip portion N2 and the pre-nip portion N1, and the pressure belt 12 is heated. The temperature of the heating roller 16 is detected by the temperature detection element 18 (FIG. 1), and the power supply control unit 41 controls the electric power supplied to the heater 15 based on the output signal S1 from the temperature detection element 18 so that the heater 15 Perform temperature control. In other words, the energization control unit 41 starts from the temperature detection element 18 so as to maintain a predetermined set temperature (target temperature) for heating the unfixed toner image T to a temperature equal to or higher than the glass transition point Tg (FIG. 9) in the prenip portion N1. The energization to the heater 15 is controlled based on the output signal S1.

  In the fixing roller 13, the pressure roller 14, and the tension roller 17, the elastic layers 13b, 14b, and 17b are formed of a silicon sponge rubber layer having heat insulation. Therefore, the heat capacities of the members 13, 14, and 17 necessary for heating the fixing belt 11 and the pressure belt 12 for heat-fixing the unfixed toner image T on the recording material P can be reduced. Therefore, the image forming apparatus A equipped with the fixing device 112 according to the present embodiment can shorten the time (FPOT: First Print Out Time) until the first image is output after the printer command is input. That is, the warm-up time can be shortened. In addition, the fixing device 112 according to the present exemplary embodiment can reduce power consumption during standby waiting for a printer command.

  In the state where the pressure belt 12 and the fixing belt 11 are rotated and the heater 15 is energized as described above, the recording material P carrying the unfixed toner image faces the prenip portion N1 with the toner image carrying surface facing upward. be introduced. The recording material P is weakly and uniformly held by the elasticity (restoring force) of the fixing belt 11 and the pressure belt 12 by the fixing belt 11 and the pressure belt 12 in the pre-nip portion N1, and is conveyed to the state. At the same time, the recording material P is preheated from both the toner image carrying surface on the fixing belt 11 side and the toner image non-carrying surface on the pressure belt 12 side by the preheated fixing belt 11 and pressure belt 12. As described above, the recording material P is sandwiched between the surface of the fixing belt 11 and the pressure belt 12 by the elasticity of the fixing belt 11 and the pressure belt 12, so that the surface of the recording material P is uniformly weakly pressed over the entire area. And preheated uniformly.

  The unfixed toner image T carried on the recording material P is sufficiently heated above the glass transition point Tg in the pre-nip portion N1, and is then nipped and conveyed by the surface of the fixing belt 11 and the surface of the pressure belt 12 at the pressure nip portion N2. While being pressed, it is pressurized.

(4) Displacement Control of Heating Roller 16 and Tension Roller 17 The fixing device 112 of this embodiment performs recording when various types of recording paper such as thin paper, plain paper, and thick paper having different thicknesses are used as the recording material P. The nip width in the recording material conveyance direction of the pre-nip portion N1 can be changed according to the type of paper. Hereinafter, displacement control of the heating roller 16 and the tension roller 17 for changing the width of the pre-nip portion N1 will be described.

  A predetermined driving mechanism M1 as a driving unit is coupled to the sliders SL1 and SR1 that support the heating roller 16, and a predetermined driving mechanism M2 as a driving unit is coupled to the sliders SL2 and SR2 that support the tension roller 17. ing. The drive mechanisms M1 and M2 are each driven and controlled by an MPU (microprocessor unit) as a control unit that controls the entire image forming apparatus A.

When the MPU forms an image based on a print signal output from an operation panel of the image forming apparatus A or a personal computer, the designated recording is performed based on a designation signal of the recording material P corresponding to the print signal. The basis weight of the material P is obtained. That is, based on the designation signal of the recording material P, the basis weight of the recording material P corresponding to the type of the designated recording material P is obtained using a predetermined table or the like. Then, the MPU executes a mode for forming an image on the designated recording material P based on the basis weight. For example, when plain paper is designated as the recording material P, the basis weight of the plain paper is obtained based on the plain paper designation signal, and the plain paper mode for performing image formation on the plain paper based on the basis weight is set. Execute. When thick paper is designated as the recording material P, the basis weight of the thick paper is obtained based on the thick paper designation signal, and the thick paper mode for forming an image on the thick paper is executed based on the basis weight. When thin paper is designated as the recording material P, the basis weight of the thin paper is obtained based on the thin paper designation signal, and the thin paper mode for forming an image on the thin paper is executed based on the basis weight. In the plain paper mode, an image is formed on the recording material P having a basis weight of 70 to 150 g / m ² . In the thick paper mode, an image is formed on the recording material P having a basis weight of greater than 150 g / m ² as the recording material P. In the thin paper mode, an image is formed on the recording material P having a basis weight of less than 70 g / m ² as the recording material P. When executing the plain paper mode, the thick paper mode, and the thin paper mode, the MPU drives the drive mechanisms M1 and M2 and moves the sliders SL1 and SR1, SL2 and SR2 along the virtual straight lines L1 and L2 according to the respective modes. Control to move a predetermined amount in a predetermined direction is performed. In accordance with the movement of the sliders SL1, SR1, SL2, SR2, the heating roller 16 and the tension roller 17 are displaced by a predetermined amount in a predetermined direction along the virtual straight lines L1, L2.

As described above, the tension applied to the fixing belt 11 and the pressure belt 12 can be changed by displacing the heating roller 16 and the tension roller 17 along the virtual straight lines L1 and L2. Accordingly, the slackness of the slack portions 11d and 12d of the fixing belt 11 and the pressure belt 12 is adjusted according to the type of the recording material P, thereby changing the pressure of the prenip portion N1 without changing the pressure applied to the pressure nip portion N2. Only the nip width (length) in the recording material conveyance direction is changed.

  FIG. 10A is an explanatory diagram illustrating the width of the pre-nip portion N1 in the fixing device 112 in the plain paper mode. FIG. 10B is an explanatory diagram showing the width of the pre-nip portion N1 in the fixing device 112 in the thick paper mode. FIG. 10C is an explanatory diagram illustrating the width of the pre-nip portion N1 in the fixing device 112 in the thin paper mode. In the fixing device 112 of the present embodiment, for example, the positions of the heating roller 16 and the tension roller 17 in the plain paper mode that is relatively frequently used are set to the home position (FIG. 1). Then, the heating roller 16 and the tension roller 17 are displaced from that position in accordance with the thick paper mode and the thin paper mode. The width of the pre-nip portion N1 in the plain paper mode is about 15 mm. In the thick paper mode, the heating roller 16 and the tension roller 17 are displaced along the imaginary straight lines L1 and L2 by the sliders SL1 and SR1, SL2 and SR2 in a direction approaching the fixing roller 11 and the pressure roller 14, and the width of the pre-nip portion N1. Is set to about 20 mm. In the thin paper mode, the heating roller 16 and the tension roller 17 are displaced along the imaginary straight lines L1 and L2 by the sliders SL1, SR1, SL2, and SR2 in a direction away from the fixing roller 11 and the pressure roller 14, and the width of the pre-nip portion N1. Is set to about 5 mm. The nip width in the recording material conveyance direction of the pressure nip portion N2 is about 5 mm. This nip width is common in each of the plain paper mode, the thick paper mode, and the thin paper mode.

  FIG. 9A is a diagram showing a temperature change on the recording material P in the pre-nip portion N1 and the pressure nip portion N2 in the heating and fixing process in the plain paper mode. FIG. 9B is a diagram showing the temperature change and the applied pressure distribution on the recording material P in the pre-nip portion N1 and the pressure nip portion N2 in the heating and fixing process in the thick paper mode. FIG. 9C is a diagram showing a temperature change and pressure distribution on the recording material P in the pre-nip portion N1 and the pressure nip portion N2 in the heat fixing process in the thin paper mode. In these drawings, the distribution of the applied pressure as shown in FIG. 8 is overlapped with the temperature profile after the position at each point of the nip is matched in the horizontal axis direction.

  Tfb in FIG. 9 is a toner outflow start temperature in the flow tester. Flow tester CFT-500D (manufactured by Shimadzu Corporation) was used, die hole diameter: 1 [mm], load value: 3969 N (405 [kgf]), temperature increase rate 4 [° C./min. The toner pellets were heated and melted out. At that time, the temperature at the time when the toner started to flow out from the hole of the die was defined as “flowing start temperature Tfb”.

  The temperature on the recording material P in FIG. 9 was measured as follows.

  A thermocouple (for example, K-type thermocouple wire diameter 50 μm manufactured by Anri Keiki Co., Ltd.) having a small heat capacity of the temperature detection unit is attached on the recording material, and the recording material is pre-nip portion N1 of the fixing device 112 that is temperature-controlled. It was nipped and conveyed by the pressure nip N2. The potential difference signal from the thermocouple was measured with a Hioki Electric Memory HiCorder (8842). As a result, as shown in FIG. 9, it can be seen that the temperature on the recording material has risen above the toner outflow start temperature in the flow tester before entering the pressure nip portion N2.

  When the recording material P passes through the pre-nip portion N1 and the pressure nip portion N2, the unfixed toner image T is heat-fixed on the recording material P surface as a fixed image having sufficient fixability and gloss (gloss). The In other words, the temperature distribution and the pressure distribution at which the unfixed toner image T is pressure-fixed on the recording material P at the pressure nip portion N2 after securing the time for the unfixed toner image T to sufficiently melt at the prenip portion N1 are pre-nip portion N1 and the pressure nip N2 can be obtained. Thereby, the occurrence of fixing failure, blistering, offset and the like of the unfixed toner image T can be greatly reduced. Then, the recording material P is discharged from the pressure nip portion N2.

  In the thick paper mode, as shown in FIG. 9B, the temperature on the thick paper gradually rises compared to the plain paper, but the paper heating distance at the pre-nip portion N1 is lengthened and the time for heating the toner image T is lengthened. By doing so, it is possible to obtain an appropriate toner image gloss that is the same target as that of plain paper. On the other hand, in the thin paper mode, as shown in FIG. 9C, the temperature on the thin paper rises more rapidly than the plain paper. However, by shortening the heating distance of the paper at the pre-nip portion N1 and shortening the time for heating the toner image T, the toner image T does not melt excessively, and an appropriate toner image having the same target as that of the plain paper can be obtained. Gloss can be obtained. Therefore, even if the type of the recording material P changes, it is not necessary to change the conveyance speed of the recording material P or a predetermined set temperature for heating the unfixed toner image T, and the heating roller 16 and the tension roller 17 are displaced. The pre-nip portion N1 width is changed. As a result, the target glossiness of the toner image T carried by the recording material P can be maintained at an optimum gloss level.

  As described above, according to the fixing device 112 of this embodiment, the following operational effects can be obtained. In other words, the heating roller 16 and the tension roller 17 are displaced along the virtual straight lines L1 and L2 according to the type of the recording material P, so that the recording material of the prenip portion N1 is not changed without changing the pressure applied to the pressure nip portion N2. Only the nip width in the transport direction can be changed. As a result, the target gloss of the toner image T carried by the recording material P can be maintained at an optimum gloss level.

[Example 2]
Another example of the fixing device will be described.

  In the present embodiment, members and portions that are common to the fixing device 112 of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 11 is a schematic cross-sectional view of an example of the fixing device 112 according to the present embodiment.

The fixing device 112 shown in the present embodiment is the fixing device according to the first embodiment except that the heating roller 16 and the tension roller 17 are configured to be displaced along a direction orthogonal to (intersect) the virtual straight lines L1 and L2. 112 has the same configuration. Therefore, the bearings 35L and 35R at both ends of the heating roller 16 are mounted on the sliders SL1 and SR1 that are movably provided in the first frames 31L and 31R (not shown) along a direction orthogonal (crossing) the virtual straight lines L1 and L2. (Not shown) is supported. Further, bearings 36L and 36R at both ends of the tension roller 17 are mounted on sliders SL2 and SR2 which are movably provided in second frames 33L and 33R (not shown) along a direction orthogonal (crossing) to the virtual straight lines L1 and L2. (Not shown) is supported.

  FIG. 12A is an explanatory diagram showing the width of the pre-nip portion N1 in the fixing device 112 in the plain paper mode. FIG. 12B is an explanatory diagram showing the width of the pre-nip portion N1 in the fixing device 112 in the thick paper mode. FIG. 12C is an explanatory diagram illustrating the width of the pre-nip portion N1 in the fixing device 112 in the thin paper mode.

  In the fixing device 112 of this embodiment, for example, the positions of the heating roller 16 and the tension roller 17 in the plain paper mode with relatively high use frequency are set to the home position (FIG. 11). Then, the heating roller 16 and the tension roller 17 are displaced from that position in accordance with the thick paper mode and the thin paper mode. The width of the pre-nip portion N1 in the plain paper mode is about 15 mm. In the thick paper mode, the heating roller 16 and the tension roller 17 are displaced in the direction approaching each other by the sliders SL1, SR1, SL2, and SR2 along the direction orthogonal to the virtual straight lines L1 and L2, and the width of the pre-nip portion N1 is set to about 20 mm. Set. In the thin paper mode, the heating roller 16 and the tension roller 17 are displaced in the direction away from each other by the sliders SL1, SR1, SL2, and SR2 along the direction orthogonal to the virtual straight lines L1 and L2, and the width of the pre-nip portion N1 is set to about 5 mm. Set. The nip width in the recording material conveyance direction of the pressure nip portion N2 is about 5 mm. This nip width is common in each of the plain paper mode, the thick paper mode, and the thin paper mode.

  The fixing device 112 of this embodiment displaces the heating roller 16 and the tension roller 17 along the direction orthogonal to the virtual straight lines L1 and L2 according to the type of the recording material P. Thus, only the nip width in the recording material conveyance direction of the pre-nip portion N1 can be changed without changing the pressure applied to the pressure nip portion N2.

  Further, the fixing device 112 according to the present embodiment does not need to change the conveyance speed of the recording material P or the predetermined set temperature for heating the unfixed toner image T, and only displaces the heating roller 16 and the tension roller 17. The width of the pre-nip portion N1 can be changed. Therefore, even if the type of the recording material P changes, the target optimum gloss of the toner image can be obtained.

  Therefore, the fixing device 112 according to the present embodiment can obtain the same effects as the fixing device 112 according to the first embodiment.

[Experimental example]
In order to confirm the gloss of the toner image heat-fixed on the recording material P by the fixing devices 112 of the first and second embodiments, the fixing device 112 and the fixing device of the comparative example are used as follows. Experiments were conducted.

  The fixing device of the comparative example does not have the function of displacing the heating roller 16 and the tension roller 17 in the fixing device 112 of the first embodiment, and the widths of the pre-nip portion N1 and the pressure nip portion N2 are set to the widths of the plain paper mode, respectively. It is configured to be held. Other configurations are the same as those of the fixing device of the first embodiment.

[Evaluation]
Evaluation of Toner Image Fixability For each of the fixing devices described above, the following toner image fixability was evaluated.

The evaluation condition was that the surface temperature of the fixing belt was adjusted to 170 ° C. As the recording material, A4-size plain paper having a basis weight of 40 g / m ² , 64 g / m ² , 80 g / m ² , 105 g / m ² , 160 g / m ² , and 200 g / m ² was used. Then, an output was made on the recording material so that the amount of the color toner was 1.0 mg / cm ^2, and it was formed as a color patch having an image length of 2 cm and width of 5 cm. The toner image was introduced into each of the fixing devices described above at a process speed of 300 mm / s, and the toner image fixability was evaluated.

  For the evaluation of the fixing property, the glossiness of the toner image portion after fixing was measured with a Nippon Denshoku gloss meter PG-1M (75 °). The glossiness of the preferred image varies depending on the type of image and the way people see it. However, business documents and technical reports that include diagrams that are output on plain paper generally have low glossiness on the toner image. There is no sense of quality and it is not preferable. Even if the glossiness of the toner image is too high, the difference in glossiness between the toner image portion and the paper surface is large and dull, which is not preferable. Therefore, in this experimental example, the fixing property was evaluated according to the following criteria. ○ or more is practically preferable.

〔Evaluation criteria〕
A: The glossiness is 10 or more and less than 30.

    (Triangle | delta): Glossiness is less than 10 or 30 or more.

    X: High temperature offset or low temperature offset occurs.

  The results in Table 1 are obtained by evaluating the glossiness of the 10 toner images after 10 sheets of unfixed toner recording material are continuously introduced into the fixing device after the fixing belt rises to the target temperature. .

* 1: Output in the thin paper mode * 2: Output in the plain paper mode * 3: Output in the thick paper mode From the results of the thin paper in Table 1, in the comparative example, a high temperature offset occurs at the thin paper 40 g / m ² and the thin paper 64 g / m ^A toner image with a glossiness of ² is too high. However, in the thin paper mode of Example 1 and Example 2, since the width of the pre-nip portion N1 is as small as about 5 mm as compared with the comparative example, the toner of the thin paper 40 g / m ² and the thin paper 64 g / m ² is heated. Never too much. Therefore, the high temperature offset is improved, and the toner image is moderately glossy.

From the results of the thick paper in Table 1, in the comparative example, a low temperature offset occurs when the thick paper is 200 g / m ² , and the toner image is too low in gloss when the thick paper is 160 g / m ² . However, in the thick paper mode of Example 1 and Example 2, the width of the pre-nip portion N1 is as large as about 20 mm as compared with the comparative example. Therefore, the toner of the thick paper 160 g / m ² and the thick paper 200 g / m ² has a heating time. Is enough. For this reason, the low temperature offset is improved, and the toner image is moderately glossy.

[Example 3]
Another example of the fixing device will be described.

  FIG. 13 is a schematic cross-sectional view of an example of a fixing device according to this embodiment.

  In the fixing device 112 of the first and second embodiments, the slack portions 11d and 12d are formed on both the fixing belt 11 and the pressure belt 12 in order to form the pre-nip portion N1. It may be formed on either one of the pressure belts 12. That is, one of the belts is wound around as shown in FIGS. 5A and 6A, and the other belt has a slack portion as shown in FIGS. 5B and 6B. Even when it is wound around, the pre-nip portion N1 can be formed upstream of the pressure nip portion N2 in the recording material conveyance direction.

  In the fixing device 112 of this embodiment, the surface of the slack portion 12d of the pressure belt 12 wound around as shown in FIG. 6B is used as the surface of the fixing belt 11 wrapped around as shown in FIG. And a pre-nip portion N1 is formed. Although not shown, on the contrary, the surface of the slack portion 11d of the fixing belt 11 that has been wound as shown in FIG. 5B is applied to the pressure belt that is wound as shown in FIG. 6A. The pre-nip portion N <b> 1 may be formed in contact with the 12 surfaces. Then, both the heating roller 16 and the tension roller 17 are displaced along the virtual straight lines L1 and L2 according to the type of the recording material P. Alternatively, both the heating roller 16 and the tension roller 17 are displaced along a direction orthogonal (intersect) with the virtual straight lines L1 and L2 according to the type of the recording material P. Thereby, it is possible to change only the nip width of the pre-nip portion N1 in the recording material conveyance direction without changing the pressure applied to the pressure nip portion N2.

  Also in the fixing device 112 of the present embodiment, the nip width in the recording material conveyance direction of the pre-nip portion N1 can be changed, so that the same effect as the fixing device 112 of the first embodiment can be obtained.

[Others]
In each of the fixing devices 112 described above, depending on the type of the recording material P, either the heating roller 16 or the tension roller 17 is moved along the virtual straight lines L1 and L2 or in a direction orthogonal to the virtual straight lines L1 and L2. May be configured to be displaced. Also in the fixing device 112 having such a configuration, the nip width in the recording material conveyance direction of the pre-nip portion N1 can be changed.

1 is a cross-sectional model diagram of an example of a fixing device according to Embodiment 1. FIG. FIG. 2 is a cross-sectional view taken along the line II-II of the fixing device illustrated in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III of the fixing device illustrated in FIG. 1. (A) is a sectional view showing an example of a layer configuration of a fixing belt, and (b) is a sectional view showing an example of a layer configuration of a pressure belt. (A) is a diagram showing a state in which a fixing belt is wound around a fixing roller and a heating roller by the shortest path length of the fixing belt, and (b) is a shortest length of the fixing belt between the fixing roller and the heating roller. It is a figure showing the state hung with allowance rather than the path length. (A) is a figure showing the state which wound the pressure belt on the pressure roller and the tension roller by the shortest path length of the pressure belt. (B) is a diagram showing a state where a pressure belt is wound around a pressure roller and a tension roller with a margin longer than the shortest path length of the pressure belt. It is explanatory drawing of the pre-nip part formed of each slack part of a fixing belt and a pressure belt with formation of a pressure nip part. It is explanatory drawing showing the pressure distribution in a pre-nip part and a press nip part. FIG. 6 is an explanatory diagram showing a temperature change and a pressure distribution on a recording sheet in a pre-nip portion and a pressure nip portion in a heat fixing process in a plain paper mode. FIG. 7 is an explanatory diagram showing temperature change and pressure distribution on a recording sheet in a pre-nip portion and a pressure nip portion in a heat fixing process in a thick paper mode. FIG. 5 is an explanatory diagram showing temperature change and pressure distribution on a recording sheet in a pre-nip portion and a pressure nip portion in a heat fixing process in a thin paper mode. FIG. 7 is an explanatory diagram showing a pre-nip portion width in the fixing device in a plain paper mode. FIG. 6 is an explanatory diagram illustrating a pre-nip portion width in the fixing device in a thick paper mode. FIG. 6 is an explanatory diagram showing a pre-nip portion width in the fixing device in a thin paper mode. FIG. 6 is a schematic cross-sectional view of an example of a fixing device according to a second embodiment. FIG. 7 is an explanatory diagram showing a pre-nip portion width in the fixing device in a plain paper mode. FIG. 6 is an explanatory diagram illustrating a pre-nip portion width in the fixing device in a thick paper mode. FIG. 6 is an explanatory diagram showing a pre-nip portion width in the fixing device in a thin paper mode. 10 is a schematic cross-sectional view of an example of a fixing device according to Embodiment 3. FIG. 1 is a configuration model diagram of an example of an image forming apparatus.

Explanation of symbols

11: fixing belt, 11d: slack portion, 12: pressure belt, 12d: slack portion, 13: fixing roller, 14: pressure roller, 15: halogen heater, 16: heating roller, 17: tension roller, N1: prenip , N2: Pressure nip, L1, L2: Virtual straight line

Claims (5)

A first endless belt; a second endless belt in contact with an outer peripheral surface of the first endless belt; and a heating member that heats at least one of the first endless belt and the second endless belt; And a first pressure member that contacts an inner peripheral surface of the first endless belt, and a second pressure member that contacts an inner peripheral surface of the second endless belt, The first endless belt and the second endless belt are sandwiched between the pressure member and the second pressure member, and are formed between the first endless belt and the second endless belt. In a fixing device for fixing a non-fixed toner image to a recording material by heating while nipping and conveying a recording material carrying an unfixed toner image at a nip portion,
Of the first and second endless belts, at least one endless belt is disposed in a slack state, and the nip portion is formed between one endless belt and the other endless belt. A first nip region, a region of the first endless belt having a backup by the first pressure member, and a region of the second endless belt having a backup by the second pressure member are in contact with each other. The nip portion starts from the first nip region in the recording material conveyance direction, and immediately after the first nip region, the second nip region Have
The fixing device further comprises a mechanism for displacing the length of the first nip region in the recording material conveyance direction. The fixing device according to claim 1, wherein at least the endless belt on the side in contact with the toner image is disposed in a slack state. The fixing device according to claim 1, wherein the mechanism displaces a length of the first nip region according to a type of the recording material. A first support member that contacts the inner peripheral surface of the first endless belt and supports the first endless belt; and a second support member that contacts the inner peripheral surface of the second endless belt and supports the second endless belt. A second support member, wherein at least one of the first and second support members has a center of the support member and a center of the pressure member in contact with the inner peripheral surface of the same belt. The fixing device according to claim 1, wherein the length of the first nip region is displaced by being displaced along an imaginary straight line.   A first support member that contacts the inner peripheral surface of the first endless belt and supports the first endless belt; and a second support member that contacts the inner peripheral surface of the second endless belt and supports the second endless belt. A second support member, wherein at least one of the first and second support members has a center of the support member and a center of the pressure member in contact with the inner peripheral surface of the same belt. The fixing device according to claim 1, wherein the length of the first nip region is displaced by being displaced along a direction intersecting with a virtual straight line to be connected.