JP4869186B2 - 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 are the fixing devices disclosed in Patent Document 1 and Patent Document 2. In these fixing devices, an endless fixing belt is stretched between two rollers, a fixing roller and a heating roller having a heat source therein. A fixing nip portion is formed by bringing a pressure roller into contact with the outer peripheral surface (front surface) of the fixing belt between the fixing roller and the heating roller.

Examples of a configuration in which two belts are combined include the fixing devices disclosed in Patent Document 3 and Patent Document 4. In these fixing devices, a fixing belt applied to a plurality of rollers and a pressure belt applied to the plurality of rollers come into contact with each other and are pressed to form a fixing nip portion.
JP-A-10-30796 JP-A-6-31801 JP-A-3-133871 JP 2004-341346 A

  However, with the above-mentioned fixing device that combines a belt and a roller, a configuration in which a roller is wound around the belt to widen the nip width can increase the time for transferring heat to the recording material in the nip, but pressurizes in the nip. The time that is being also lengthens. Therefore, in the case of plain paper (hereinafter simply referred to as paper) among the recording materials, the toner image carried on the fiber on the paper surface tends to penetrate into the paper fiber.

  When the toner penetrates into the paper fiber in this way, the unevenness (texture) originally possessed by the paper appears on the surface of the fixed image surface. That is, the paper fiber is exposed to the fixed image surface without being covered with toner.

  Thus, when the texture of the paper fiber is visible on the surface of the fixed image surface, the fiber on the paper surface cannot be uniformly covered with the toner image, and it is difficult to achieve a high image density. At the same time, since the smoothness of the fixed image surface is impaired, it is difficult to achieve high glossiness.

  In the fixing device in which the belt and the roller are combined, the pre-fixing heating unit is disposed upstream of the nip portion with respect to the conveyance direction of the recording material, and the recording material and the toner image are heated in a non-contact manner. When printing at high speed, the recording material and the toner image cannot be heated sufficiently. In addition, since the nip is narrow, a fixing failure occurs due to insufficient heat.

  In the fixing device combining the above two belts, the recording material and the toner image can be heated in a non-contact manner by the radiant heat from the fixing belt upstream of the nip in the recording material conveyance direction. When fixing, the recording material and the toner image cannot be heated sufficiently. In addition, since the nip is narrow, fixing failure occurs due to insufficient heat.

  In the fixing device that combines two belts, the belt is brought into contact with the recording material and the toner image by making use of the flexibility of the belt to form a long nip width and sandwiching the recording material in a long region of the belt. Some of them try to actively transfer the heat of the belt.

  However, in this case, it is difficult to obtain a pressure distribution that maintains the adhesion between the belt and the recording material carrying the toner image over the entire fixing nip. If there is a region where the pressure is once increased and then the pressure is weakened, the toner image fixed halfway in the region where the pressure is high is shifted in the region where the pressure is weakened. There is a problem that the image is easily fixed in a shifted state.

  Such a state in which a region with a higher pressure force continues after passing through a region with a higher pressure force at the beginning of the fixing nip is generally called “pressure loss”. Such “pressure loss” is caused by “image displacement” in which the toner image T is fixed due to the inability to maintain the adhesion between the belt and the recording paper, or the contact state between the belt and the recording paper. It tends to cause abnormal images, such as uneven glossiness due to instability.

An object of the present invention is to provide a fixing device capable of preventing toner from penetrating excessively into recording material fibers during the fixing process and suppressing a deviation of the toner image during the fixing process .

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 the fixing device for fixing the unfixed toner image on the recording material by sandwiching and conveying the recording material carrying the unfixed toner image at the nip portion formed between the two endless belts, the first and second At least one of the endless belts The first nip region formed between the endless belt and the other endless belt due to the slack of one endless belt, and the backup by the first pressure member. A region of the endless belt and a second nip region formed by contacting the regions of the second endless belt with backup by the second pressure member, and the nip portion includes: The first nip region starts from the first nip region in the recording material conveyance direction, and the second nip region is provided immediately after the first nip region.

According to the present invention, it is possible to provide a fixing device that can prevent the toner from soaking into the fibers of the recording material during the fixing process and can suppress the deviation of the toner image during the fixing process .

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

[Example 1]
(1) Example of Image Forming Apparatus Figure 27 is a block schematic drawing of an example of an image forming apparatus equipped with constant Chakusochi engagement Ru in the present invention. This image forming apparatus is a laser beam printer that forms an image on a recording material (for example, a recording material, an 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.

The recording material P bearing the 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 toner image on the recording material P to heat and fix the 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 (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. 4 is a cross-sectional view of the fixing device 112 taken along the line IV-IV shown in FIG.

The fixing device 112 shown in this embodiment includes a fixing belt (first endless belt) 11 and a pressure belt (second endless belt) 12 as an endless belt, and a fixing roller (first addition belt) as a pressure member. Pressure member) 13 and a pressure roller (second pressure member) 14, and a heating roller 16 and a tension roller 17 as rotating bodies. The fixing device 112 includes a halogen heater 15 as a heating member and a temperature detection element 19 such as a thermistor as a temperature detection unit. In addition, the fixing device 112 includes first frames 31L and 31R as support members that support the fixing roller 13, and second frames 33L and 33R as support members that support the pressure roller 14. The fixing device 112 includes third frames 35L and 35R as support members that support the heating roller 16, and fourth frames 37L and 37R as support members that support the tension roller 17.

  The fixing belt 11, the fixing roller 13, the heating roller 16, the heater 15, the temperature detection element 19, the first frames 31 </ b> L and 31 </ b> R that support the fixing roller 13, and the third frames 35 </ b> L and 35 </ b> R that support the heating roller 16. The fixing belt unit U1 is configured.

  The pressure belt unit U2 is configured by the pressure belt 12, the pressure roller 14, the tension roller 17, the second frames 33L and 33R that support the pressure roller 14, and the fourth frames 37L and 37R that support the tension roller. It is composed.

  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. FIG. 5A is a cross-sectional view illustrating an example of a layer configuration of the fixing belt 11, and FIG. 5B is a cross-sectional view illustrating an example of a 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 55 mm.

  The fixing roller 13 and the pressure roller 14 are elastic rollers having an outer diameter of φ28 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 having a diameter of 18 mm, respectively. It is. The Asker C hardness at this time is about 40 ° when 9.8 N (1 kgf) is applied.

  In this embodiment, 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 ( Figure 2). The longitudinal dimensions of the elastic layers 13b and 14b of the fixing roller 13 and the pressure roller 14 are substantially the same as the longitudinal dimensions of the fixing belt 11 and the pressure belt 12, or the longitudinal dimensions of the fixing belt 11 and the pressure belt 12. There is no problem even if the dimension is set shorter than the dimension in the direction.

  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. 6 is an explanatory diagram showing the relationship among the fixing roller 13, the heating roller 16, and the fixing belt 11. 6A shows 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. 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.

  At that position, both ends of the heating roller 16 are rotatably supported by the third frames 35L and 35R via bearings 36L and 36R (FIG. 4). Alternatively, the bearings 35L and 35R at both ends of the heating roller 16 are attached by a spring or the like in a direction P1 (FIG. 1) away from the fixing roller 13 on an imaginary straight line L1 connecting the rotation center of the heating roller 16 and the rotation center of the fixing roller 13. It is supported by the third frames 35L and 35R in a biased state. That is, the fixing belt 11 is not stretched around the fixing roller 13 and the heating roller 16 as shown in FIG. 6A, but is fixed around the fixing roller 13 as shown in FIG. Loosely hung around the heating roller 16. Accordingly, the fixing belt 11 is formed with a slack portion 11 a between the fixing roller 13 and the heating roller 16 in the circumferential direction of the fixing belt 11. In this embodiment, the distance between the axial center position of the fixing roller 13 and the central position of the heating roller 16 is set to 23 [mm] to form the slack portion 11d.

  Both ends of the halogen heater 15 provided inside the heating roller 16 are supported by heater support portions 35L1 and 35R1 provided on the third frames 35L and 35R. 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.

  FIG. 7 is an explanatory diagram showing the relationship among the pressure roller 14, the tension roller 17, and the pressure belt 12. 7A shows 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 a configuration in which an elastic layer 17b made of a silicon sponge rubber layer having a thickness of 4 mm is provided on the outer periphery of a SUS φ10 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. At that position, both ends of the cored bar 17a of the tension roller 17 are rotatably supported by the fourth frames 37L and 37R via bearings 38L and 38R (FIG. 4). Alternatively, the bearings 38L and 38R at both ends of the cored bar 17a are on a virtual straight line L2 connecting the rotation center of the pressure roller 14 and the rotation center of the tension roller 17 in the direction P2 (FIG. 1) away from the pressure roller 14 Is supported by the fourth frames 37L and 37R. 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. 7A, but is pressed as shown in FIG. 7B. 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. In this embodiment, the distance between the axial center position of the pressure roller 14 and the central position of the tension roller 17 is set to 23 [mm] to form the slack portion 12d.

  Therefore, in this embodiment, the slack portions 11d and 12d are formed on both the fixing belt 11 and the pressure belt 12 which are two endless belts.

  Next, details of a 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.

  Hereinafter, in the configuration of the fixing device of the present embodiment, for convenience of explanation, the nip portion is described with the names “pre-nip portion” and “pressure nip portion” according to the functional role. The “pre-nip portion” is a nip portion formed by belt regions where the fixing belt 11 and the pressure belt 12 are not in contact with the fixing roller 13 and the pressure roller 14, respectively (FIG. 1). The “pressure nip portion” is a nip portion formed by regions where the backup of the fixing roller 13 and the pressure roller 14 disposed on the inner surfaces of the fixing belt 11 and the pressure belt 12, respectively, is present (FIG. 1). Further, a nip region including the “pre-nip portion N1” and the “pressure nip portion N2” is defined as a “total nip”. The total nip that is a nip portion is formed by bringing the outer peripheral surfaces of the fixing belt 11 and the pressure belt 12 that are two endless belts into contact with each other.

  In the fixing belt unit U1 and the pressure belt unit U2, the first frame that supports the fixing roller 13 and the second frame that supports the pressure roller are respectively provided with pressure springs 41L, 41R, and 42L. 42R is disposed (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 11 by pressing the fixing belt 11 and the pressure belt 12 between the elastic layers 13b and 14b. The outer peripheral surface (surface) of the belt 12 comes into contact. As a result, a pressure nip portion N2 is formed by contact between the surface of the fixing belt 11 and the surface of the pressure belt 12 (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.

  FIG. 8 is an explanatory diagram of the pre-nip portion N1 formed by the slack portions 11d and 12d of the fixing belt 11 and the pressure belt 12 when the pressure nip portion N2 is formed.

  As described above, the fixing belt unit U1 in the non-pressurized state has the slack portion 11d as shown in FIG. Further, the pressure belt unit U2 in the non-pressurized state has a slack portion 12d as shown in FIG.

The fixing roller 13 and the pressure roller 14 are urged toward each other, and a pressure nip portion N <b> 2 is formed by contact between the fixing belt 11 and the pressure belt 12. Then, from the upper end of the pressure nip portion N2 in the recording material conveyance direction, a region that overlaps the slack portions 11d and 12d of the fixing belt 11 and the pressure belt 12 within a predetermined range, and an overlapping region (dotted line portion in FIG. 8). ) Occurs. Each of the slack portions 11d and 12d is in contact with the surface of the fixing belt 11 and the surface of the pressure belt 12 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 (first nip region) N1 is formed in the overlapping region (FIG. 1). Accordingly, the nip pressure in the pre-nip portion N1 tries to return the contact state of the fixing belt 11 and the pressure belt 12 from the contact state shown in FIG. 1 to the non-contact state shown in FIGS. 6B and 7B, respectively. This is due to the elastic force of the fixing belt 11 and the pressure belt 12.

  That is, the nip pressure in the pre-nip portion N1 mainly returns to the shape in the non-contact state depending on the rigidity and flexibility of the respective base layers 11a and 12a of the fixing belt 11 and the pressure belt 12. This is due to the resilience of 11 · 12 itself. The width of the pre-nip portion N1 formed in this way is approximately 15 mm.

  The pre-nip portion N1 formed in this way is formed by contact between the fixing belt 11 and the pressure belt 12 which are flexible and deformable. Therefore, the pressure distribution is substantially uniform within the range of the pre-nip portion N1, and it is possible to maintain a stable contact state.

  Further, the pre-nip portion N1 is formed continuously with the pressure nip portion N2 formed by urging the fixing roller 13 included in the fixing belt 11 and the pressure roller 14 included in the pressure belt 12. Is done. Therefore, when the recording material is sandwiched and conveyed, the adhesion between the recording material P and the fixing belt 11 and the pressure belt 12 is maintained in the total nip including the pre-nip portion N1 and the pressure nip portion N2. .

  FIG. 9 shows a contact state between the pre-nip portion and the pressure nip portion formed at this time.

In this embodiment, the fixing belt 11 and the pressure belt 12 have the same specifications, and the fixing roller 13 and the pressure roller 14 are both elastic rollers having the same specifications. It will be the same. The same deformation amount means that the length of the fixing roller 13 disposed in the fixing belt 11 is in contact with the inner surface of the fixing belt 11 and the pressure roller 14 disposed in the pressure belt 12 is the pressure belt. 12 The length in contact with the inner surface is substantially equal. That is, the length that the fixing roller 13 backs up the fixing belt 11 is substantially equal to the length that the pressure roller 14 backs up the pressure belt 12. Accordingly, in the region of the pressure nip portion N2, the endless belt regions that are backed up by the fixing roller 13 and the pressure roller 14 as pressure members, that is, the regions of the fixing belt 11 and the pressure belt 12 are formed. It has the part which was made. In this embodiment, that portion is the entire pressure N2 (second nip region) N2. Accordingly, as shown in FIG. 9, the state at this time includes a pre-nip portion N1 formed by contact of the belts from the upstream side in the recording material conveyance direction. Then, following the pre-nip portion N1, a pressure nip portion N2 formed by contact between the belts backed up by each roller is continuously formed. That is, the total nip (nip portion) starts from the pre-nip portion N1, and the fixing belt 11 and the pressure belt, which are two endless belts, are formed so that the pressure nip portion N2 is continuously formed downstream in the recording material conveyance direction. 12 is supported.

The pressure distribution of the total nip formed in the present embodiment formed by the pre-nip portion N1 and the pressure nip portion N2 was measured using a pressure distribution measurement system PINCH manufactured by Nitta Corporation. FIG. 10 shows the measured pressure distribution.

  As shown in FIG. 10, since the fixing roller 13 and the pressure roller 14 are urged toward each other, the fixing belt 11 and the pressure belt 12 are formed in contact with each other at a position corresponding to this portion. The applied pressure is highest at the pressure nip portion N2.

  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) Heating and fixing operation of the fixing device When the driving gear G (FIG. 2) provided at the end of the core bar 14a of the pressure roller 14 is driven to rotate by the fixing motor M, the pressure roller 14 is It is rotated in the direction of the arrow at the peripheral speed (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 in the state in which the fixing belt 11 and the pressure belt 12 are intentionally loosened as in this embodiment (FIGS. 6B and 7B), the fixing belt 11 and the pressure belt 12 are respectively The base layers 11a and 12a have rigidity and flexibility. Therefore, the fixing belt 11 and the pressure belt 12 rotate while maintaining the slackened state.

  Even during the heat fixing operation, the fixing belt 11 and the pressure belt 12 rotate while maintaining a slack shape. Therefore, undulation (swelling in the longitudinal direction of the belt) is less likely to occur than when the fixing belt 11 and the pressure belt 12 are rotated in a tensioned state (FIGS. 6A and 7A). Therefore, there is an advantage that the surface of the fixing belt 11 can be brought into uniform contact with the recording material P.

  The heater 15 is energized by an energization control unit 41 (FIG. 4) serving 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 19 (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 19 so that the heater 15 Perform temperature control. That is, the energization control unit 41 outputs an output signal from the temperature detection element 19 so as to maintain a predetermined set temperature (target temperature) at which the toner image T is heated to a temperature approximately equal to or higher than the outflow start temperature in the flow tester in the prenip portion N1. The energization to the heater 15 is controlled based on S1.

  The outflow start temperature Tfb in the flow tester used in this example is determined under the following conditions.

  Using a flow tester CFT-500D (manufactured by Shimadzu Corporation), die hole diameter: 1 [mm], load value: 405 [kgf], temperature increase rate: 4 [° C./min. The toner pellets are heated and melted out under the conditions of At this time, the temperature at the time when the toner started to flow out of the hole of the die was defined as “flowing start temperature Tfb”.

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 heating and fixing the 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 toner image T is introduced into the prenip portion N1 with the toner image carrying surface facing upward. Is done.

  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. Since the pre-nip portion N1 is formed only by contact between the fixing belt 11 and the pressure belt 12 as shown in FIG. 3, the fixing belt 11 and the pressure belt are respectively recorded in a state where the recording material P is sandwiched. It is an area that is in contact with only the material.

  That is, the fixing belt 11 in the pre-nip portion N1 comes into contact only with the toner image carrying surface of the recording material P and does not come into contact with the fixing roller 13 or other components.

Further, the pressure belt 12 in the prenip portion N1 is in contact only with the toner image non-carrying surface of the recording material P, and is not in contact with the pressure roller 14 or other components.
Accordingly, the heat held by the fixing belt 11 and the pressure belt 12 can be efficiently transmitted to the recording material P.

  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 toner image T carried on the recording material P is sufficiently heated above the substantially outflow start temperature 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 in the pressure nip portion N2. Pressurized.

  As a result, the toner image T carried on the recording material P is heat-fixed on the surface of the recording material P as a fixed image having sufficient fixability and gloss (gloss).

  That is, a temperature distribution and a pressure distribution for pressurizing and fixing the toner image T onto the recording material P at the pressure nip portion N2 after securing a time for the toner image T to sufficiently melt at the prenip portion N1 are pressurized with the prenip portion N1. It can be obtained by the nip portion N2. As a result, the occurrence of fixing failure, blistering, offset and the like of the toner image T can be greatly reduced. Then, the recording material P is discharged from the pressure nip portion N2.

  Through the heating and fixing process passing through the pre-nip portion N1 and the pressure nip portion N2, the temperature change of the toner image T at each point in the total nip of the toner image T carried on the recording material P was measured.

  The temperature profile was measured as follows. A thermocouple (for example, K-type thermocouple wire diameter 50 μm manufactured by Anritsu Keiki Co., Ltd.) having a small heat capacity of the temperature detection unit is attached on the recording material P, and the prenip portion of the fixing device 112 in which the recording material P is temperature-controlled. N1 and the pressure nip N2 were nipped and conveyed. And the electric potential difference signal was measured with Hioki Electric Co., Ltd. memory high coder (8842) from the thermocouple at that time.

  In this way, it is possible to measure the temperature change with respect to time when passing through the nip portion. By multiplying this by the conveyance speed of the recording material, it is possible to obtain a temperature profile at each position in the total nip. it can.

  FIG. 11 shows temperature profiles in the pre-nip portion N1 and the pressure nip portion N2 of the fixing device 112 of the present embodiment measured in this way. In this figure, the distribution of the applied pressure shown in FIG. 10 is overlapped with the temperature profile after the positions at each point of the total nip are aligned in the horizontal axis direction.

  In order to explain the melting and fixing process, a model diagram showing the state of the recording material P and the toner image T in the fixing process is shown in FIG.

  In the toner layer model diagrams of FIG. 12 and subsequent figures, the state of the toner is expressed by color distribution as shown in the legend.

  12A is a diagram showing the state of the recording material P and the toner image T before entering the prenip portion N1, and similarly, FIG. 12B is a state immediately after passing through the prenip portion N1, and FIG. 12C is a pressure nip portion. It is a model figure which shows the state immediately after N2 passage.

  Hereinafter, the process of fixing the toner image T with the fixing device of this embodiment will be described with reference to the temperature profile in FIG. 11, the distribution of the applied pressure, and the model diagram showing the state of the recording material P and the toner image T in FIG. .

  First, the recording material (recording paper) P carrying the toner image T is introduced into the pre-nip portion N1.

  In the pre-nip portion N1, as shown in FIG. 11, the toner image T is gradually preheated and its temperature rises. At this time, the temperature profile at the pre-nip portion N1 rises, and the inclination gradually becomes gentler toward the second half of the pre-nip portion N1, and shows a tendency to be saturated.

  At this time, as shown in FIG. 11, the temperature reaches substantially equal to or higher than the outflow start temperature in the flow tester within the range of the pre-nip portion N1.

  First, it is preferable that the temperature is approximately equal to or higher than the outflow start temperature in the flow tester for the following reason.

  In order for the toner image T to be actually fixed to the recording paper P with sufficient strength, it must be fixed with an anchor effect that penetrates at least the paper fibers and is fixed between the fibers. In order to penetrate into the paper fiber in this way, the toner must first be melted and deformed.

  From the measurement principle, the outflow start temperature Tfb in the flow tester indicates the temperature at which the toner starts to melt and deform.

  That is, the temperature at which the toner begins to flow out of the die hole when the temperature is gradually increased with respect to the toner pellet in a state where a constant load is applied in the flow tester indicates the temperature at which the toner starts to melt and deform. Yes.

  This was confirmed experimentally as follows.

  When the recording paper P carrying the toner image T was left unpressed and left in an environment at or below the outflow start temperature Tfb, the toner image T carried on the recording paper did not change at all.

  On the other hand, when left in an environment at or above the outflow start temperature Tfb, the toner image T carried on the recording paper has started to melt, and it was clearly recognized that adhesion to the recording paper was improved.

  Next, the reason why it is desirable to set the temperature of the toner image T to Tfb or more, particularly in the pre-nip portion N1, is to make a sufficiently melted state before reaching the pressure nip portion N2 where pressure is applied. It is.

  The recording paper P carrying the toner image T is continuously subjected to pressure at the pressure nip portion N2 to which pressure is applied, and the toner image T is appropriately permeated into the paper fibers of the recording paper to obtain a fixed image.

  At this time, if the temperature in the pre-nip portion N1 has already reached a temperature equal to or higher than Tfb, the toner image T has a temperature that is substantially equal to or higher than the outflow start temperature over the entire pressure nip portion N2 to which the applied pressure is applied. It can be maintained. That is, since the toner image T is in a state of being melted and deformed throughout the entire area of the pressure nip portion N2, the pressure applied by the pressure nip N2 allows the toner image T to penetrate the recording paper P without waste. Used for

  On the other hand, if there is a portion in the pressure nip N2 where the toner has not reached the temperature equal to or higher than the outflow start temperature Tfb, the toner image T is not deformed. For this reason, the applied pressure applied at that portion is wasted as a force for pressing the particulate toner against the recording paper, and the force for effectively penetrating the recording paper P is reduced.

  As described above, in order to effectively use the applied pressure and fix the toner image T with the minimum necessary pressure, the toner image is spread over the entire pressure nip portion N2 where the pressure is applied. T is set to a temperature equal to or higher than Tfb. That is, it is preferable that the temperature of the toner image T is equal to or higher than the outflow start temperature Tfb in the flow tester in the pre-nip portion N1.

  Needless to say, the effect of the temperature of the toner image T not reaching Tfb in the pre-nip portion N1 does not mean that the effect is not lost. Even in this case, the temperature can be brought close to the most effective state by raising the temperature of the toner image T as much as possible in the pre-nip portion N1.

  By being preheated over time in this way, the toner image T is melted almost uniformly even in the thickness direction, and is in a good melted state from the upper layer to the lower layer of the toner layer. . At the same time, almost no pressure is applied in the pre-nip portion N1, so that the toner image T on the recording paper P exists in a molten state without much penetration into the recording paper P as shown in FIG.

  As described above, after the pre-nip portion N1 is sufficiently melted, the recording paper P reaches the pressure nip portion N2 and receives a pressure as shown in FIG.

At this time, the toner image T has reached or exceeded the outflow start temperature Tfb in the pre-nip portion N1, and the toner image T is sufficiently melted in the thickness direction.
The applied pressure can be effectively applied to allow the toner image T to permeate the recording paper P appropriately. That is, since the toner image T is sufficiently melted, it is possible to appropriately permeate the paper fiber and secure the fixing property without applying a high pressure. At this time, since a high pressing force is not required, the toner image T does not excessively penetrate into the paper fiber.

  The recording paper P pressurized at the pressure nip portion N2 is discharged from the pressure nip portion N2 after the toner image T has permeated appropriately, thereby obtaining a fixed image having sufficient fixability (FIG. 12). (C)).

  The fixing process realized by the fixing device of the present embodiment that is fixed through the above-described process has the following three features.

  The first feature of the fixing process using the fixing device of this embodiment is that almost no pressure is applied until the temperature of the toner image T is sufficiently increased.

  When the pressure is applied in a state where the toner is not melted, the applied pressure only presses the powdery toner against the recording paper P, and thus does not contribute to fixing at all. The pressure applied at this time is wasted. That is, in order to perform the fixing efficiently, it is necessary to apply a pressing force in a state where the toner image T is sufficiently melted.

  As shown in FIG. 11, no pressure is applied in the range of the pre-nip portion N1, which is a process in which the toner image T is heated and heated.

  In this embodiment, the fixing belt 11 and the pressure belt 12 sandwich a configuration in which preheating is performed without positively applying pressure to the recording paper P carrying the toner image T in the region of the pre-nip portion N1. This is realized by forming the pre-nip portion N1.

  The second feature of the fixing device of the present embodiment is that the temperature of the toner image T is maintained at or above the outflow start temperature Tfb in the flow tester over the pressure nip portion N2 region where the pressure is applied. There is.

  As shown in FIG. 11, the temperature of the toner image T is maintained at a temperature equal to or higher than the outflow start temperature Tfb in the flow tester in the region of the pressure nip portion N2 where pressure is applied.

  As a result, the temperature of the toner image T reaches Tfb or higher, and the toner image T is pressed in a sufficiently melted state, whereby the fixing to the recording material P can be performed with the minimum necessary pressure.

  The reason why it is particularly preferable to set the pressure nip portion N2 to be equal to or higher than the “flow start temperature Tfb in the flow tester” is as described above.

  As described above, when the toner is sufficiently melted and pressed, the melted toner can be appropriately permeated into the paper fiber and efficiently fixed without wasting the applied pressure.

  The third feature of the fixing device of this embodiment is that the difference between the temperature of the upper layer of the toner image T and the temperature of the lower layer of the toner image T is small, that is, the toner melted almost uniformly in the thickness direction of the toner image T. It is a point to pressurize when it becomes.

  As shown in FIG. 11, in the temperature profile of the fixing device of this embodiment, the temperature of the toner image T rises in the pre-nip N1 and reaches Tfb or more. The inclination of the temperature change of the toner image T gradually becomes gentle toward the second half of the pre-nip portion N1, and shows a tendency to be saturated.

  The fact that the temperature change tends to saturate in this way indicates that the temperature gradient in the vicinity thereof has decreased.

  That is, the heat of the fixing belt 11 is sufficiently transmitted to the recording paper P side, and the temperature difference between the fixing belt 11 and the recording paper P is becoming smaller.

  This also applies to the thickness layer direction of the recording paper P.

  That is, at this time, the temperature distribution in the thickness layer direction of the recording paper P, that is, if the toner image T is actually carried, indicates that the temperature distribution in the thickness direction of the toner image T is small. ing.

  The fact that the temperature distribution in the thickness direction of the toner image T is small, that is, the melting state of the toner in the upper and lower layers of the toner image T is close, and the toner image T can be melted almost uniformly in the thickness direction. (FIG. 12B).

  When the toner image T is melted in the same way in the upper layer and the lower layer as described above, it is pressurized in the pressure nip N2, so that the melted toner is appropriately permeated into the paper and at the same time sufficient gloss is realized. Yes.

  As described above, the fixing device of this embodiment sufficiently preheats the recording paper P carrying the toner image T in the pre-nip portion N1, and the difference between the temperature of the upper layer of the toner image T and the temperature of the lower layer of the toner image T. The state with less That is, the toner is almost uniformly melted in the thickness direction of the toner image T. Then, after the toner is in a molten state, pressurization is performed at the pressure nip portion N2, so that the melted toner is appropriately permeated into the paper and fixed, and sufficient gloss is produced.

  The above effects could actually be obtained even within a range of about ± 5 ° C. with respect to the outflow start temperature Tfb in the flow tester.

  Therefore, if the “substantially outflow start temperature” is about the outflow start temperature Tfb ± 5 ° C., the same effect can be obtained.

  Cross-sectional views of the fixing devices (fixing devices) of Comparative Example 1, Comparative Example 2, and Comparative Example 3 prepared for comparison with the fixing device (fixing device) 112 of this embodiment are shown in FIGS. Here, the same members / portions as those of the fixing device 112 of the present embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  As a comparative example 1, the fixing device shown in FIG. 13 has a nip portion N1a formed by a fixing belt unit U1 wound around a belt as shown in FIG. 6A and a roller 50 having a release layer on the surface layer. It is. At this time, the fixing inlet guide 51 for guiding the recording material P is disposed along the fixing belt 11, and the toner image T and the recording material P are preheated by radiant heat from the fixing belt 11.

  As a comparative example 2, the fixing device shown in FIG. 14 is similar to the fixing device of the present embodiment. Two endless belts are wound around two rollers 13, 16, 14, 17, and the unsupported belts 11, 12 are mutually connected. The nip portions N1b, N2b, and N3b are formed by pressure contact. The rollers corresponding to the heating roller 16 and the tension roller 17 are urged in the direction in which they contact each other, and are wound around the heating roller 16 and the tension roller 17. Further, the fixing device of this embodiment is different in that the surfaces of the belts 11 and 12 are in contact with each other.

  A fixing device shown in FIG. 15 as Comparative Example 3 uses a roller 50 having a release layer as a surface layer instead of the pressure belt unit U2 of the fixing device of this embodiment, and the fixing belt 11 of the fixing belt unit U1 is a roller. A comparatively long nip width is formed with respect to the heat roller fixing device of Comparative Example 1 so as to be wound around 50 circumferences.

  For each of the fixing devices of Comparative Examples 1 to 3, the pressure distribution and the temperature profile were measured in the same manner as the fixing device of this example.

  16 to 18 show the measurement results of the pressure distribution and the temperature profile in Comparative Examples 1 to 3, respectively. FIGS. 19 to 21 are model diagrams showing the melted state of the recording material P and the toner image T in Comparative Examples 1 to 3, respectively.

  First, the result of performing the fixing operation in the fixing device of Comparative Example 1 shown in FIG. 13 will be described.

  FIG. 19A is a diagram illustrating a state of the recording paper P and the toner image T immediately before entering the nip portion N1a in the fixing device of the comparative example 1. Similarly, FIG. 19B illustrates the nip portion N1a. It is a model figure which shows the state after going out.

  In the fixing device of the comparative example 1, the recording paper P carrying the toner image T is first conveyed along the fixing inlet guide 51. At this time, the temperature of the recording paper P is heated from the toner image T carrying surface side by radiant heat, but since the heat transfer by radiation is slight, the temperature of the recording paper P hardly increases. Subsequently, the recording paper P carrying the toner image T enters the nip portion N1a, contacts the fixing belt 11, receives heat, is simultaneously pressurized and discharged.

  The same toner image T as that used in this embodiment was fixed by the fixing device of Comparative Example 1, but a fixed image having a gloss equal to or higher than that of the fixed image obtained by the fixing device of this embodiment is obtained. I couldn't.

  The fixed image obtained with the fixing device of Comparative Example 1 was observed. Then, the toner located on the convex and concave portions of the recording paper P penetrates the recording paper P, and it becomes easy to see the texture of the paper fiber, and the fixed toner image T and the texture of the paper appear to be mixed. It was a non-uniform fixed image. As a result, the glossiness (gloss) equivalent to that of the fixed image by the fixing device of the present embodiment cannot be realized.

  This is presumably due to the following mechanism.

  FIG. 16 shows the measurement results of the pressure distribution and temperature profile in the fixing device of Comparative Example 1. The difference between the fixing device of Comparative Example 1 and the fixing device of this embodiment is that the nip where the pressing force is applied. This is the temperature within the part N1a region.

  First, in the fixing device of Comparative Example 1, the temperature of the toner image T hardly rises until it reaches N1a. Therefore, heat is applied in the nip portion N1a region shorter than the total nip width in the fixing device of this embodiment. There is a need to do. In order to transfer heat with a short nip width, it is necessary to increase the temperature gradient with respect to the recording paper, that is, to set the temperature higher than the fixing belt 11 temperature of the fixing device of this embodiment.

  However, it is clear that a temperature difference in the layer direction of the object to be heated tends to occur when heat is suddenly transmitted in this way. That is, the difference between the temperature of the upper layer of the toner image T and the temperature of the lower layer of the toner image T is large. This means that the melting state of the upper layer and the lower layer of the toner image T is greatly different.

  19A and 19B are model diagrams showing the melting state of the toner layer at this time.

  FIG. 19A shows the state of the toner image T in the nip portion N1a, and FIG. 19B shows the state of the toner image T immediately after exiting the nip portion N1a.

  As shown in FIG. 19A, in the nip portion N1a region, when the toner lower layer temperature is in an optimum state for penetrating appropriate paper, the upper layer of the toner image T is already in an overmelted state. I'm stuck. For this reason, the toner in the upper layer of the toner image excessively penetrates into the paper fibers, and the texture of the paper fibers is exposed on the surface of the fixed image.

  When the texture of the paper fiber is visible on the surface of the fixed image surface, the convex portion of the paper fiber is not covered with the toner image, and “transparency” occurs, and at the same time, the fiber image on the paper surface is uniformly covered with the toner image. It is difficult to achieve a high image density.

  In addition, since the smoothness of the fixed image surface is impaired, it is difficult to achieve high glossiness (gloss).

  On the other hand, in order to suppress such over-melting of the upper layer of the toner image T, fixing was attempted by lowering the temperature of the fixing belt so that the temperature of the upper layer of the toner image T is lower than this.

  FIGS. 19C and 19D are model diagrams showing the melting state of the toner layer at this time. Similarly, FIG. 19C shows the state of the toner image T in the nip portion N1a region, and FIG. 19D shows the state of the toner image T immediately after leaving the nip portion N1a region.

  In this case, the toner in the upper layer of the toner image T did not reach a temperature at which it was overmelted and did not pass through. However, at the same time, since the temperature of the paper fiber lower layer is lowered, the toner of the paper fiber lower layer is not sufficiently melted, and a cold offset occurs (FIGS. 19C and 19D).

  As described above, in the fixing device of Comparative Example 1, even when the temperature of the fixing belt 11 is changed, the glossiness decreases due to the penetration of the toner image T due to the overmelting of the toner image T, and the toner melts on the other hand. There is a problem of cold offset due to shortage. Therefore, in the fixing device of Comparative Example 1, a fixed image having sufficient glossiness (gloss) could not be obtained between the two problems.

  Next, the result of fixing in the fixing device of Comparative Example 2 will be described.

  In the fixing device of Comparative Example 2, in addition to the nip portion (pre-nip portion N1 and pressure nip portion N2) in the fixing device of this embodiment, the belt portion wound around the heating roller 16 and the tension roller 17 is brought into contact. It has a nip area that is formed.

  In the fixing device of Comparative Example 2 shown in FIG. 14, the nip formed by the belts 11 and 12 wound around the heating roller 16 and the tension roller 17 in order from the upstream side in the recording material conveyance direction is N1b, and the belts 11 and 12. A nip portion where the portions are in contact with each other is designated as N2b. A nip portion where the belts 11 and 12 wound around the fixing roller 13 and the pressure roller 14 are in contact with each other is defined as N3b.

  20A is a diagram showing the state of the recording paper P and the toner image T immediately before entering the nip portion. FIGS. 20B, 20C, and 20D are diagrams showing the nip portions N1b, N2b, and N3b, respectively. FIG. 6 is a model diagram illustrating a state of the recording paper P and the toner image T immediately after passing through.

  The steps when fixing is performed using the fixing device of Comparative Example 2 will be described in order.

  First, the recording paper P carrying the toner image T is introduced into the nip portion N1b formed by the belts 11 and 12 wound around the heating roller 16 and the tension roller 17, and is given heat as shown in FIG. receive. At the same time, the toner image T starts to melt to some extent and begins to penetrate into the recording paper P by being pressed by the heating roller 16 and the tension roller 17 urged through the belts 11 and 12 (FIG. 20 ( b)). When the recording paper P subsequently reaches the nip portion N2b, the force for sandwiching the recording paper P is weakened in the nip portion N2b region, so that the pressure is reduced with respect to the nip portion N1b. That is, the adhesion between the belts 11 and 12 and the recording paper P is insufficient, so-called pressure loss occurs (FIG. 20C). When such pressure loss occurs, image displacement occurs regardless of the temperature of the toner image T.

  Once the fixing belt 11 is pressed against the recording paper P and separated again, the toner image T carried on the recording paper P adheres to the recording paper P side and to the belt 11 side. Divided into things. This is the same even if the toner is not melted and is on the particles, or it is in a melted state.

  In the nip portion N2b, since the recording paper P is constantly applied with heat, the recording paper P is subjected to a force to shrink. In this state, when the force with which the fixing belt 11 presses the paper is weakened, a positional shift occurs between the fixing belt 11 and the paper having different degrees of contraction.

  In this disturbed image state, the image is pressed and fixed at the nip portion N3b (FIG. 20D). For this reason, the image after fixing becomes an abnormal image called “image shift” and becomes a non-uniform fixed image.

  As described above, in the fixing device having the configuration of the comparative example 2, although a long nip width can be realized, a valley is generated in the distribution of the applied pressure in the nip, so that a pressure drop occurs, and it is very important to prevent image displacement. It was difficult.

  Next, the result of fixing in the fixing device of Comparative Example 3 will be described.

  In the fixing device of Comparative Example 3 shown in FIG. 15, a roller 50 having a release layer on the surface is brought into contact with the fixing belt unit U1 in the fixing device of this embodiment in the same manner as in the fixing device of Comparative Example 1 to The part is formed. At this time, the fixing belt 11 of the fixing belt unit U1 is arranged to be wound around the roller 50. As a result, the contact between the surface of the fixing belt 11 and the surface of the roller 50 on the upstream side of the nip portion N2c formed in the pressure contact region between the fixing roller 13 and the roller 50 included in the fixing belt 11 in the recording material conveyance direction. A nip portion N1c is formed.

  As described above, in the fixing device of Comparative Example 3, the nip portion N1c is formed on the upstream side in the recording material conveyance direction of the nip portion N2c, thereby securing a wide nip width as the entire fixing device.

  In the fixing device of Comparative Example 3, when the fixing belt 11 is wound, the nip portion N1c is formed more closely, so that the fixing belt 11 is properly stretched between the fixing roller 13 and the heating roller 16. Is held in. The fixing roller 13 included in the fixing belt 11 is urged against the roller 50 so as to apply a pressing force necessary for fixing.

  FIG. 21A is a diagram illustrating a state of the recording paper P and the toner image T in the nip portion N1c. FIGS. 21B and 21C are models showing the state of the recording paper P and the toner image T in each of the nip portions N1c and N2c, and the state of the recording paper P and the toner image T immediately after passing through the nip portion N2c. FIG.

  The fixing process when fixing is performed using the fixing device of Comparative Example 3, and the characteristics of the fixed image obtained in the fixing process will be described in order.

  First, the recording paper P carrying the toner image T is introduced into a nip portion N1c formed by the fixing belt 11 and the roller 50. Here, the recording paper P carrying the toner image T receives heat from the belt 11. At the same time, as shown in FIG. 18, a certain amount of pressure is also applied to the nip portion N1c, which is the winding portion of the belt 11, so that the toner is pressed onto the recording paper P at the same time as the melting starts. Subsequently, the toner enters the nip portion N2c and receives the applied pressure appearing in the applied pressure distribution in FIG. 18 and at the same time the temperature of the toner rises, so that the toner gradually melts and penetrates into the recording paper P and is fixed. Will be.

  When the fixed image obtained by the fixing device of Comparative Example 3 was observed, it was the same as that of the fixing device of Comparative Example 1. In other words, the toner on which the convex and concave portions of the recording paper P are located is excessively permeated into the recording paper P, and it becomes easy to see the texture of the paper fiber, and at the same time as the “through” occurs, the fixing is performed. As a result, the toner image T and the paper texture were mixed, resulting in a non-uniform fixed image. If the texture of the paper is exposed on the fixed image surface in this way, the smoothness of the fixed image surface is impaired, and naturally the glossiness (gloss) tends to be low.

  For this reason, the fixed image obtained by the fixing device of Comparative Example 3 could not achieve the same glossiness (gloss) as the fixed image obtained by the fixing device of the present embodiment.

  It is considered that the fixed image obtained by the fixing device of Comparative Example 3 has such a fixed image surface for the following reason.

  FIG. 18 shows the pressure distribution and the temperature profile in the fixing device of Comparative Example 3. The difference from the fixing device of this embodiment is that the nip width is different from the total nip width realized in this embodiment. The nip width formed by the portion N1c and the nip portion N2c is short.

  The nip portion N2c to which the pressure is applied can be formed to have a length equivalent to the pressure nip width N2 of the present embodiment by adjusting the pressure. However, in the fixing device of Comparative Example 3, it is difficult to form the nip portion N1c formed on the upstream side in the recording material conveyance direction of the nip portion N2c to be equal to or more than the pre-nip portion N1 of this embodiment.

  This is because the fixing device of Comparative Example 3 forms the nip portion N1c by winding the belt 11 around the roller 50, and the nip portion N1c cannot be easily elongated. As a means for lengthening the N1c, it is conceivable that the fixing belt 11 is further wound around the roller 50. However, in such a method, the recording paper is bent long in the fixing process, so that the paper after the fixing is fixed. The curl gets worse.

  As another means, a method of increasing N1c while keeping the curvature small by increasing the outer diameter of the roller 50 can be considered. However, in this case as well, the fixing device is enlarged, the heat capacity increases with the increase in the diameter of the roller 50, and the energy-saving performance of the fixing device is reduced due to an increase in warm-up time and an increase in the heat radiation area. Will occur.

  As described above, in the fixing device configuration of Comparative Example 3, it is difficult to form a nip width equal to or longer than that of the fixing device of this embodiment without inducing harmful effects.

  Therefore, in the fixing device configuration of Comparative Example 3, it is necessary to apply heat at the nip portions N1c and N2c that are shorter than the total nip width in the fixing device of this embodiment.

  In order to transfer heat with a short nip width, it is necessary to increase the temperature gradient with respect to the recording paper as in Comparative Example 1, that is, to set the temperature higher than the fixing belt 11 temperature of the fixing device of this embodiment. .

  However, in this way, when heat is suddenly transmitted, that is, when the temperature gradient between the fixing belt 11 and the recording paper P is increased, at the same time, the toner image T that is a heated material and the inside of the recording paper P in the layer direction. It is clear that the temperature difference is likely to occur. That is, as shown in FIGS. 21A and 21B, a temperature difference occurs between the upper layer and the lower layer of the toner image T in the nip portions N1c and N2c, and the entire thickness direction is sufficiently warmed. Not done.

  As shown in FIGS. 21 (a) and 21 (b), when the toner image T lower layer temperature is in an optimum state for penetrating appropriate paper, the upper layer of the toner image T is already in an overmelted state. Yes.

  As a result, the toner in the upper layer of the toner image T penetrates excessively into the paper fibers, and the texture of the paper fibers is exposed on the fixed image surface. At the same time as “transparency” occurs (FIG. 21C), the fiber on the paper surface cannot be uniformly covered with the toner image, so that a high image density cannot be achieved.

  At the same time, since the smoothness of the fixed image surface is impaired, a high glossiness (gloss) equivalent to that of the fixed image by the fixing device of this embodiment could not be achieved.

  On the other hand, in order to suppress such overmelting of the upper layer of the toner image T, fixing was attempted by lowering the temperature of the fixing belt 11 so that the temperature of the upper layer of the toner image T is lower than this. FIGS. 21D, 21E and 21F are model diagrams showing the melting state of the toner image layer at this time.

  FIG. 21D is a model diagram illustrating a state of the recording paper P and the toner image T in the nip portion N1c when the fixing is performed with the temperature of the fixing belt 11 lowered. FIG. 21E is a model diagram illustrating a state of the recording paper P and the toner image T in the nip portion N2c when the fixing is performed with the temperature of the fixing belt 11 lowered. FIG. 21F is a model diagram illustrating a state of the recording paper P and the toner image T immediately after passing through the nip portion N2c when fixing is performed with the temperature of the fixing belt 11 lowered.

  In this case, the toner in the upper layer of the toner image T did not reach a temperature at which it was overmelted (FIGS. 21D and 21E), and did not become transparent. However, at the same time, the temperature of the paper fiber lower layer was lowered, so that the toner of the paper fiber lower layer was not sufficiently melted and a cold offset occurred (FIG. 18 (f)).

  As described above, in the fixing device configuration of Comparative Example 3 as well, as in Comparative Example 1, pressure is applied in a state where a temperature difference occurs between the upper layer and the lower layer of the toner image T in the nip portion. For this reason, the fixing device of Comparative Example 3 also has sufficient gloss between the problems of a decrease in glossiness due to permeation of the recording paper P due to overmelting of the toner image T, and a cold offset due to insufficient melting of the toner. A fixed image having a degree (gross) cannot be obtained.

As described above, the fixing device 112 of this embodiment intentionally connects the fixing belt unit U1 (FIG. 6B) having the slack portion and the pressure belt unit U2 (FIG. 7B) to each other. By making the pre-nip portion N1 formed only by the elasticity of the belt by abutting, the fixing process using the fixing device of this embodiment is as follows:
(I) Almost no pressure is applied until the temperature of the toner image T rises sufficiently.
(Ii) The temperature of the toner image T is maintained at a temperature substantially equal to or higher than the outflow start temperature Tfb in the flow tester over the pressure nip portion N2 region where the applied pressure is applied.
(Iii) The pressure is applied when the difference between the temperature of the upper layer of the toner image T and the temperature of the lower layer of the toner image T is small, that is, when the toner is almost uniformly melted in the thickness direction of the toner image T.
It has become possible to realize a pressure distribution and temperature profile as shown in FIG.

  By realizing such a pressure distribution and temperature profile, it is possible to realize a wide nip width that can accommodate high speeds, and at the same time, there is no pressure loss that causes abnormal images such as image displacement and sufficient gloss A fixed image having a degree of gloss can be obtained.

  In the present embodiment, the fixing device configuration including the fixing belt unit U1 (FIG. 6B) and the pressure belt unit U2 (FIG. 7B) having the slack portions is described. Is not limited to this. That is, if the pre-nip portion N1 formed only by the elasticity of the belts 11 and 12 is a fixing device formed on the upstream side of the pressure nip portion N2 in the recording material conveyance direction, the same effect can be obtained. it can.

  In the fixing device 112 of the present embodiment, as shown in FIG. 9, the fixing belt 11 and the pressure belt 12 have the same specifications, and the fixing roller 13 and the pressure roller 14 both have the same specifications. explained.

  The fixing device 112 has a pre-nip portion N1 formed by contacting the fixing belt 11 and the pressure belt 12 without backing up the fixing roller 13 and the pressure roller 14 from the upstream side in the recording material conveyance direction. Then, following the pre-nip portion N1, the fixing belt 11 and the pressure belt 12 are in contact with each other while being backed up by the fixing roller 13 and the pressure roller 14, respectively, so that the pressure nip portion N2 is continuously provided with the pre-nip portion N1. It was a thing.

  On the other hand, even if the fixing belt 11 and the pressure belt 12 are in contact with each other as shown in FIG. 22, for example, the same effect can be obtained.

  FIG. 22 is an explanatory view showing another contact state between the fixing belt 11 and the pressure belt 12 of the fixing device 112 of this embodiment, and the contact between the fixing belt 11 and the pressure belt 12 in the total nip. It is the figure which showed the contact state. In FIG. 22, an elastic roller having an outer diameter of 28 mm and Asker C hardness (at 9.8 N load) of 40 ° is used as the pressure roller 14. As the fixing roller 13, an elastic roller having an outer diameter of 36 mm and an Asker C hardness (at 9.8 N load) of 40 ° is used.

  In this case, since the outer diameter of the fixing roller 13 is larger than the outer diameter of the pressure roller 14, the length of the fixing roller 13 contacting the inner surface of the fixing belt 11 for backup is added by the pressure roller 14. It becomes slightly longer than the length of backing up the pressure belt 12.

  As a result, an intermediate nip portion N2-a is formed after the pre-nip portion N1 formed by the contact between the fixing belt 11 and the pressure belt 12 without back-up of the fixing roller 13 and the pressure roller 14, respectively. . The intermediate nip portion N2-a is in contact with the area of the pressure belt 12 that is not backed up by the pressure roller 14 from the back surface and the area of the fixing belt 11 that is backed up by the fixing roller 13 from the back surface. Is formed.

  Subsequently, the main nip portion N2- where the region of the pressure belt 12 backed up from the back surface to the pressure roller 14 and the region of the fixing belt 11 backed up from the back surface to the fixing roller 13 come into contact with each other. b is formed. Accordingly, in the area of the pressure nip portion N2, the endless belt areas that are backed up by the fixing roller 13 and the pressure roller 14 as pressure members are formed, that is, areas of the fixing belt 11 and the pressure belt 14 are formed. As a portion thus formed, the main nip portion N2-b is provided. That is, the intermediate nip portion N2-a and the main nip portion N2-b are formed as the pressure nip N2 formed subsequent to the pre-nip portion N1.

  In this case, there is a pre-nip portion N1 formed by the contact between the belts 11 and 12 without backup from the upstream side in the recording material conveyance direction, and then the contact between the fixing belt 11 with backup and the pressure belt 12 without backup. There is an intermediate nip N2-a formed in Subsequently to the intermediate nip N2-a, a pressure nip portion N2-b formed by contact between the belts 11 and 12 backed up by the rollers 13 and 14 is formed continuously with the intermediate nip N2-a. It becomes a state.

  The other contact states of the fixing belt 11 and the pressure belt 12 in the total nip shown in FIG. 22 may be applied to the fixing devices 112 shown in FIGS. 23, 24, 25, and 26.

  Even in such a contact state, in the fixing device 112 of the present embodiment, the pre-nip portion N1 is formed by the contact between the belts 11 and 12 without backup. As a result, the recording paper P carrying the toner image T can be sufficiently preheated so that the difference between the temperature of the upper layer of the toner image T and the temperature of the lower layer of the toner image T is small. That is, the toner can be melted almost uniformly in the thickness direction of the toner image T. Then, after the toner is in a molten state, pressure is applied at the pressure nip portion N2, whereby the molten toner is appropriately permeated into the paper and fixed. That is, it is essential that the recording paper P carrying the toner image T in the pre-nip portion N1 is sufficiently preheated to make the toner in a molten state, and the toner melted in the pressure nip portion N2 is appropriately permeated into the paper and fixed. Therefore, the same effects as those shown in FIG. 9 can be obtained.

  That is, it is possible to realize a wide nip width that can cope with high speed, and at the same time, to realize a fixed image having sufficient glossiness (gross) without causing pressure loss that causes an abnormal image such as image shift. The effect remains the same.

Further, here, the region of the pressure belt 12 where the intermediate nip portion N2-a is not backed up from the back surface to the pressure roller 14 and the region of the fixing belt 11 backed up from the back surface to the fixing roller 13 are matched. The case where it is formed by contact is described.
Conversely, the area of the pressure belt 12 backed up by the pressure roller 14 from the back surface and the area of the fixing belt 11 not backed up by the fixing roller 13 from the back surface are in contact with each other. Even if it exists, the prenip part N1 should just be formed. Even with such a fixing device configuration, the effect is essentially the same.

On the other hand, there is a pre-nip portion N1 formed by the contact state as shown in FIG. 22, that is, the contact between the belts 11 and 12 without backup, and the belt 11 with backup and the belt 12 without backup are next. There is an intermediate nip N2-a formed by contact. Subsequently to the intermediate nip portion N2-a, a main nip portion N2-b formed by contact between the belts 11 and 12 backed up by the rollers 13 and 14 is formed continuously with the intermediate nip portion N2-a. Examples include the following cases.
When the fixing roller 13 and the pressure roller 14 have different outer diameters When the fixing roller 13 and the pressure roller 14 have different hardnesses When the fixing belt 11 and the pressure belt 12 have different outer diameters The fixing belt 11 When the layer configuration is different between the pressure belt 12 and the rigidity thereof is different. When the outer diameter and arrangement of the tension roller 17 and the heating roller 16 are changed from the present embodiment. In either case, there is no backup. Since it is essential to form the pre-nip portion N1 by the contact between the belts 11 and 12, similar effects can be obtained as described above.

  For example, the fixing belt unit U1 in a state where the fixing belt 11 shown in FIG. 6A is stretched, and the pressure belt unit U2 in a state where the pressure belt 12 shown in FIG. Even when the belt is used, a region where the belts 11 and 12 overlap each other is formed. Therefore, the belts 11 and 12 come into contact with each other by elasticity, and a pre-nip portion N1 is formed.

  That is, it is a “slack contact portion” in which a slack portion is formed on at least one of the fixing belt 11 and the pressure belt 12 which are two endless belts, and the slack portion is in contact with the other belt. The pre-nip portion N1 is included in the total nip as the nip portion. The pre-nip portion N1 is formed on the most upstream side in the recording material conveyance direction of the total nip.

  Conversely, the fixing belt unit U1 in a state where the fixing belt 11 shown in FIG. 6B is slackened, and the pressure belt unit U2 in a state where the pressure belt 12 shown in FIG. 7A is stretched. The same applies to a combination of. In this case, of the fixing belt 11 and the pressure belt 12, a slack portion is formed on the fixing belt 11 facing the toner image carrying surface on the recording material.

  Further, even when the belts 11 and 12 are slightly curved over the entire contact area, the same effect can be obtained.

  For example, the fixing belt unit U1 in a state where the fixing belt 11 shown in FIG. 6B is loosened and the pressure belt 12 as shown in FIG. 23 are both loose in a concave shape in the same direction. The belt unit U2 and the belt unit U2 are installed so as to approach each other. If the pre-nip portion N1 is formed by the contact between the belts 11 and 12 without backup, the same effect can be obtained.

  In the fixing device of this embodiment, a halogen heater 15 is used as a heating source, and the heater 15 is disposed in the heating roller 16 of the fixing belt unit U1 to heat the fixing belt 11. It is not limited to this. For example, the heater 15 may be disposed at the position of the fixing roller 13. Further, there is no problem even if the heaters 15 are provided in a plurality of rollers (not shown) around which the fixing belt 11 is wound.

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

  The same members / portions as those of the fixing device 112 of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The same applies to Example 3 to Example 5.

  FIG. 24 is a schematic cross-sectional view of an example of a fixing device according to this embodiment.

  The fixing device 113 shown in the present embodiment is the same as the first embodiment except that a fixing member (pressure member) 20 that is elongated in the longitudinal direction is used in place of the rotatable fixing roller 13 in the fixing device 112 of the first embodiment. The fixing device 112 has the same configuration.

  The fixing roller 13 in the fixing device 112 according to the first embodiment rotates in contact with the fixing belt 11, but the fixing member 20 in the fixing device 112 according to this embodiment is configured to slide with the fixing belt 11. As a result, in the fixing device 112 of this embodiment, the heat capacity can be reduced, and the rise time as the fixing device can be shortened.

  Thus, even if the fixing roller 13 in the fixing device 112 of the first embodiment is used as the fixing member 20, the pre-nip portion N1 formed only by the elasticity of the belts is upstream of the pressure nip portion N2 in the recording material conveyance direction. If it is formed in the same manner, the same effect can be obtained.

  Further, the use of the fixing member 20 is not limited to the portion corresponding to the fixing roller 13 of the fixing device 112 of the first embodiment, and there is no problem even if another roller supporting the belt is changed to the fixing member. The same effects as those of the fixing device 112 of Example 1 can be obtained.

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

  FIG. 25 is a schematic cross-sectional view of an example of a fixing device according to this embodiment.

  In the fixing device 112 shown in the present embodiment, the heating roller 16 is eliminated from the fixing device 112 of the first embodiment, and instead a heating roller 22 including a halogen heater 15 as a heating source is brought into contact with the outer peripheral surface of the fixing roller 13. It is arranged as follows.

  Since the heating roller 22 is in contact with the outer peripheral surface (surface) of the fixing belt 11 that directly contacts the recording material P carrying the toner image T, the heating roller 22 has a release layer on the outer peripheral surface (surface) of the heating roller 22. The heating roller 22 brings the inner peripheral surface of the fixing belt 11 into contact with the surface of the fixing roller 13 at a position in contact with the surface of the fixing belt 11. As a result, the rotation locus of the fixing belt 11 is restricted, and the rotation of the fixing belt 11 is stabilized.

  As described above, the heating roller 22 that heats the fixing belt 11 on the outer peripheral surface of the fixing roller 13 and restricts the rotation trajectory of the fixing belt 11 is also disposed in the same manner as the fixing device of the first embodiment. The pre-nip portion N1 can be formed only by the elasticity of the belts 11 and 12. Since the pre-nip portion is formed on the upstream side of the pressure nip portion in the recording material conveyance direction, the same effect as the fixing device 112 of the first embodiment can be obtained.

[Example 4]
Another example of the fixing device will be described.

  FIG. 26 is a schematic cross-sectional view of an example of a fixing device according to this embodiment.

  The fixing device 112 shown in the present embodiment is the same as the fixing device 112 of the first embodiment except that the heating means is an induction heating method.

  That is, the heating roller 16 in the fixing device 112 of the first embodiment is changed to the upper tension roller 17 in which an elastic layer 17b made of a silicon sponge rubber layer having a thickness of 4 mm is provided on the outer periphery of a SUS φ10 mm cored bar 17a. is there. In addition, an electromagnetic induction heating unit 80 serving as a magnetic flux generation unit is disposed along the outer peripheral surface of the fixing belt 11. Except for these two points, the configuration is the same as that of the fixing device 112 of the first embodiment.

  The upper tension roller 17 is rotatably supported by the third frames 35L and 35R, similarly to the heating roller 16 of the fixing device 112 of the first embodiment.

  Although not shown, the electromagnetic induction heating unit 80 is an induction heating unit casing formed of an electrically insulating resin, and a magnetic core (hereinafter abbreviated as a core) built in the induction heating unit casing. And an induction heating coil (hereinafter abbreviated as a coil). The core is formed from, for example, a ferrite core or a laminated core. The coil is configured, for example, by winding a copper wire having a fusion layer and an insulating layer on the surface a plurality of times.

  The electromagnetic induction heating unit 80 includes, for example, an induction heating unit housing in which a coil formed by winding a litz wire in a horizontally long and flat sheet-like spiral shape and a core covering the coil are formed of an electrically insulating resin. It is a horizontally long and thin plate member housed in the body. In the induction heating unit casing, the core is arranged so that the magnetic flux does not leak to the fixing belt 11 other than the facing area surface. The electromagnetic induction heating unit 80 is disposed close to the outer peripheral surface of the fixing belt 11 with a predetermined distance.

  In the induction heating method, the amount of heat generation is likely to vary depending on the distance between the electromagnetic induction heating unit that generates magnetic flux and the heated object that absorbs the magnetic flux and generates heat. Therefore, the electromagnetic induction heating unit 80 is fixed to the third frames 35L and 35R that support the upper tension roller 17 so that the distance of the electromagnetic induction heating unit 80 from the outer peripheral surface of the upper tension roller 17 does not vary. . At the same time, the fixing belt 11 wound around the upper tension roller 17 and the portion where the upper tension roller 17 contacts are arranged so as to overlap with a region where heat is generated by the magnetic flux generated from the electromagnetic induction heating unit 80.

  In the fixing device 112 of this embodiment, the base layer 11a of the metal fixing belt 11 is induction-heated by supplying an alternating current of 10 k to 1 MHz to a coil from an excitation circuit (not shown) during a fixing operation. That is, the magnetic flux supplied to the fixing belt 11 is generated by energizing the coil. This magnetic flux is absorbed by the base layer 11a, which is the heat generating layer of the fixing belt 11, in a region where the electromagnetic induction heating unit 80 and the fixing belt 11 are opposed to each other, and a vortex induced current is generated in the base layer 11a. It generates heat due to its specific resistance.

  As in this embodiment, even if the heating means is an induction heating method, the pre-nip portion N1 formed only by the elasticity of the belts 11 and 12 is formed upstream of the pressure nip portion N2 in the recording material conveyance direction. Therefore, the same effect as the fixing device 112 of the first embodiment can be obtained.

[Others]
1) The layer configuration, thickness, outer diameter, etc. of each member such as the fixing belt 11, the pressure belt 12, the fixing roller 13, the pressure roller 14, the heating roller 15, and the tension roller 17 are limited to those in this embodiment. Instead, it is appropriately set according to the fixing device that is actually commercialized.

  2) Heat supply to the surface of the fixing belt 11 may also be heating by radiant heat, heating by hot air, or heating by induction heating when the belt base layer is a metal.

  3) Regarding the configuration of the fixing roller 13 and the pressure roller 14, the outer diameter, the core metal diameter, the material of the elastic layer, the thickness, and the like are appropriately changed according to the requirements of the specifications of the fixing device that is actually commercialized. It goes without saying that the width of the pressure 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. FIG. 4 is a cross-sectional view taken along line IV-IV 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. 3 is an explanatory diagram illustrating a contact state between a fixing belt and a pressure belt at a pre-nip portion and a pressure nip portion according to Embodiment 1. FIG. It is explanatory drawing showing the pressure distribution in a pre-nip part and a press nip part. FIG. 6 is an explanatory diagram illustrating a change in toner temperature in a pre-nip portion and a pressure nip portion in a heat fixing process. FIG. 3 is a model diagram illustrating a molten state of a recording material and a toner image in a fixing process of Example 1. 3 is a schematic cross-sectional view of a fixing device of Comparative Example 1. FIG. 10 is a cross-sectional model view of a fixing device of Comparative Example 2. FIG. 10 is a cross-sectional model view of a fixing device of Comparative Example 3. FIG. 6 is an explanatory diagram showing a pressure distribution and a temperature profile of a fixing device of Comparative Example 1. FIG. FIG. 10 is an explanatory diagram illustrating a pressure distribution and a temperature profile of a fixing device of Comparative Example 2. FIG. 10 is an explanatory diagram showing a pressure distribution and a temperature profile of a fixing device of Comparative Example 3. FIG. 6 is a model diagram illustrating a melting state of a recording material P and a toner image in a fixing process of a fixing device of Comparative Example 1. FIG. 10 is a model diagram illustrating a melting state of a recording material P and a toner image in a fixing process of a fixing device of Comparative Example 2. FIG. 10 is a model diagram illustrating a melting state of a recording material P and a toner image in a fixing process of a fixing device of Comparative Example 3. FIG. 6 is an explanatory diagram illustrating another contact state of the fixing belt and the pressure belt of the fixing device according to the first exemplary embodiment. FIG. 6 is a schematic cross-sectional view of another belt configuration in the fixing device according to the first exemplary embodiment. 6 is a schematic cross-sectional view of an example of a fixing device according to Embodiment 2. FIG. 10 is a schematic cross-sectional view of an example of a fixing device according to Embodiment 3. FIG. 6 is a schematic cross-sectional view of an example of a fixing device according to Embodiment 4. FIG. 1 is a configuration model diagram of an example of an image forming apparatus.

Explanation of symbols

11: fixing belt, 12: pressure belt, 13: fixing roller, 14: pressure roller, 15: halogen heater, 16: heating roller, 17: tension roller, N1: pre-nip portion, N2: pressure nip portion

Claims (3)

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 A fixing device. 2. The fixing device according to claim 1, wherein at least the endless belt on the side in contact with the unfixed toner image is disposed in a slack state. The fixing device according to claim 1, wherein the unfixed toner image is heated to a temperature equal to or higher than a substantially outflow start temperature in a flow tester while the recording material passes through the first nip region.