JP2016200665A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device including a heat source that can maintain temperature uniformity and prevent the occurrence of current leakage.SOLUTION: There is provided a fixing device 150 comprising: an endless belt member 80 that has flexibility; a pressure member 84 that is arranged opposite to the belt member 80; a nip forming member 88 that is pressed by the pressure member 84 with the belt member 80 therebetween to form a nip; first heat sources 82a, 82b that heat an area smaller than the maximum sheet size in an axial direction of the belt member 80; and a second heat source 112 that heats an area corresponding to the maximum sheet size in the axial direction of the belt member 80, wherein the nip forming member 88 includes a heat uniformizing member 110 that uniforms heat from the second heat source 112, and an insulating member 115 that is disposed between the second heat source 112 and the heat uniformizing member 110.SELECTED DRAWING: Figure 7

Description

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

  Image forming apparatuses such as copying machines and printers include a fixing device having a heater, and various sizes of paper are used for image formation. For this reason, if the heater length of the fixing device is set to a length corresponding to the maximum size paper, the temperature rise at the end, which is a non-sheet passing portion, will increase when a small size paper is passed. Need to slow down and reduce productivity. In order to cope with this problem, a first halogen heater having a dense light distribution at the center and a second halogen heater having a dense light distribution near the end are disposed inside the fixing roller. There is known a fixing device that turns on only a first halogen heater when a sheet of a size is used.

  In addition, although the frequency of use of the entire paper is very low, special large size paper such as A3 Nobi or 13 inches that is slightly larger than the A3 size may be used. Even if a halogen heater having a light distribution corresponding to such a large size paper is separately provided, there is a problem that the diameter size of the fixing roller based on downsizing is restricted, which is difficult.

  Therefore, a nip forming unit is provided inside a thin and flexible endless belt member that quickly rises to the fixing temperature, and a contact pressure between the belt member, a pressure roller that pressurizes the belt member, and the nip forming unit. A fixing device that forms a nip is known (see, for example, “Patent Document 1”). In this fixing device, a plurality of halogen heaters having different light distributions are arranged inside the belt member, and a large size is provided at both ends of the belt member in the width direction and upstream of the nip in the rotation direction of the belt member. The end heat source that can handle the paper is arranged in contact with the inner surface or the outer surface of the belt member. By arranging this end heat source, it is possible to cope with a large size paper with a simple configuration without adding a halogen heater dedicated to the large size.

In the configuration described in “Patent Document 1”, since the end heat source is disposed only at the end as the name suggests, temperature uniformity is maintained when the end heat source is driven together with other halogen heaters. In other words, the fixing temperature varies in the width direction of the paper. There is also a problem that current leakage from the end heat source occurs.
SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device having a heat source that can solve the above-described problems and can maintain temperature uniformity and prevent occurrence of current leakage.

  According to the present invention, an endless belt member having flexibility, a pressure member disposed to face the belt member, and a pressure member pressed through the belt member form a nip. A nip forming member; a first heat source that heats an area narrower than a maximum sheet size in the axial direction of the belt member; and a second heat source that heats an area corresponding to the maximum sheet size in the axial direction of the belt member. The nip forming member includes a heat equalizing member for uniformizing heat from the second heat source, and an insulating member disposed between the second heat source and the heat equalizing member. Features.

  According to the present invention, since large-size paper that is used infrequently is heated via the heat equalizing member, temperature uniformity and temperature followability can be improved, and variation in fixing temperature is suppressed in the width direction of the paper. A good image can be provided. Moreover, since the insulating member is provided between the soaking member and the second heat source, current leakage from the second heat source can be reliably prevented.

1 is a schematic view of an image forming apparatus to which an embodiment of the present invention can be applied. 1 is a schematic view of a fixing device used in an embodiment of the present invention. FIG. 3 is a schematic view in the vicinity of a nip portion of a fixing device used in an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a support structure for a fixing belt used in an embodiment of the present invention. It is the schematic which shows the light distribution distribution of the halogen heater used for one Embodiment of this invention, and the positional relationship of a heater. It is the schematic which shows the nip formation unit used for the 1st Embodiment of this invention. It is the schematic explaining the nip formation member used for the 1st Embodiment of this invention. It is a diagram explaining the heating characteristic of the heater which has the PTC characteristic used for the 1st Embodiment of this invention. It is a circuit block diagram of the halogen heater and edge part heater which are used for the 1st Embodiment of this invention. It is the schematic explaining the nip formation member used for the 2nd Embodiment of this invention. It is the schematic explaining the nip formation member used for the modification of the 2nd Embodiment of this invention. It is the schematic explaining the nip formation member used for the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, before explaining the present embodiment, the background of the proposal of the technique described in “Patent Document 1” will be described. If the recording medium is small, turn on a halogen heater with a dense light distribution in the center. If the recording medium is large, turn on a halogen heater with a dense light distribution near the edge together with appropriate on / off distribution. By doing so, it supports paper of various sizes.

  Here, referring to the paper size and frequency of use, most of the normally used paper is up to A3 size, and A3 size paper is passed in the vertical direction. In particular, A4 or LT size paper, which is frequently used, is often passed in the horizontal direction in order to increase productivity. Therefore, if a heating width of about 300 mm is secured as the fixing device, in most cases, 99% or more of the recording medium can be covered depending on the model. On the other hand, although the frequency of use for the whole is very low, it is required to support paper having a size larger than the A3 width, such as A3 Nobi or 13 inches.

  In the case of a heating method using a halogen heater, a plurality of heaters corresponding to small size paper are provided inside a fixing roller having a diameter of about 30 mm, so the number of heaters cannot be easily increased. For this reason, it is necessary to lengthen the halogen heater having a dense end portion light distribution according to the paper width larger than the A3 width. As described above, when the frequency of use is considered, the heating of about 300 mm width is overwhelmingly large. However, when the above-described long halogen heater is used, it is heated to the vicinity of 330 mm width, and the difference energy consumption is wasted. . Furthermore, when the paper is passed in A3 or A4 horizontal (A4Y) size, the temperature near the end of the 330 mm width rises, and in order to cool this, it is necessary to reduce productivity or install a fan. It was. In the case where the reflector is provided, there is a problem that the temperature at the heater end abnormally increases. In order to deal with such a problem, the device described in Patent Document 1 has been proposed.

  Hereinafter, a first embodiment of the present invention capable of solving the above-described problems of the prior art will be described. First, an outline of the configuration of an image forming apparatus to which this embodiment can be applied will be described with reference to FIG. The image forming apparatus 100 is a tandem color printer in which image forming units that form a plurality of color images are arranged in parallel along the moving direction of the intermediate transfer belt.

  The image forming apparatus 100 includes a photosensitive drum 20Y as an image carrier that can form images corresponding to colors separated into yellow (Y), cyan (C), magenta (M), and black (Bk). , 20C, 20M, 20Bk. A visible toner image formed on each photoconductive drum 20 is superimposed on an intermediate transfer belt 11 as an intermediate transfer member that is movable in the direction of arrow A1 while facing each photoconductive drum 20, and is primary. Transcribed. Thereafter, the sheet S as a recording medium is collectively transferred by the secondary transfer process. Around each photosensitive drum 20, an apparatus for performing an image forming process according to the rotation of each photosensitive drum 20 is disposed.

  A device for performing image forming processing will be described on behalf of the photosensitive drum 20Bk that forms a black image. Around the photosensitive drum 20Bk, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk that perform image forming processing are sequentially arranged along the rotation direction of the photosensitive drum 20Bk. After charging by the charging device 30Bk, the optical writing device 8 performs optical writing on the surface of the photosensitive drum 20Bk based on the image information to form an electrostatic latent image. The electrostatic latent image is visualized as a toner image by the developing device 40Bk.

  The toner images formed on the respective photoconductive drums 20 are primarily transferred to the same position on the intermediate transfer belt 11 while the intermediate transfer belt 11 moves in the A1 direction. In this primary transfer, the timing is shifted from the upstream side toward the downstream side in the A1 direction by applying a voltage from each primary transfer roller 12 disposed opposite to each photoconductor drum 20 with the intermediate transfer belt 11 interposed therebetween. Done. The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this color order from the upstream side in the moving direction of the intermediate transfer belt 11. Each of the photosensitive drums 20Y, 20C, 20M, and 20Bk is provided in an image station for forming yellow, cyan, magenta, and black images, respectively.

  The image forming apparatus 100 is disposed so as to face four image stations that perform image forming processing for each color and above each photosensitive drum 20, and includes an intermediate transfer belt 11 and primary transfer rollers 12Y, 12C, and 12M. , 12Bk, and an intermediate transfer belt unit 10. In addition, the image forming apparatus 100 includes a secondary transfer roller 5 that is disposed to face the intermediate transfer belt 11 and serves as a secondary transfer unit that is driven by the intermediate transfer belt 11. The image forming apparatus 100 includes an intermediate transfer belt cleaning device 13 that is disposed to face the intermediate transfer belt 11 and cleans the upper surface of the intermediate transfer belt 11. The optical writing device 8 is disposed below the four image stations so as to face them.

  The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, a rotating polygon mirror as a deflecting means, and the like. The optical writing device 8 emits writing light Lb corresponding to each color to each photoconductor drum 20 to form an electrostatic latent image on each photoconductor drum 20. In FIG. 1, for the sake of convenience, the writing light is labeled Lb for only the black image station, but the same applies to other image stations.

  Below the image forming apparatus 100, a sheet feeding device 61 is provided as a sheet feeding cassette on which sheets S transported between the photosensitive drums 20 and the intermediate transfer belt 11 are stacked. The sheet S conveyed from the sheet feeding device 61 is transferred between the intermediate transfer belt 11 and the secondary transfer roller 5 by the registration roller pair 4 at a predetermined timing in accordance with the toner image formation timing by the image station. It is fed out toward the secondary transfer part. The fact that the leading edge of the paper S has reached the registration roller pair 4 is detected by a sensor (not shown).

  The sheet S on which the toner image is transferred is sent to the fixing device 150 where heat and pressure are applied to fix the toner image on the sheet S. The fixed sheet S is discharged onto the upper surface of the main body of the image forming apparatus as a discharge tray by the discharge roller pair 7. Below the upper surface of the main body of the image forming apparatus, toner bottles 9Y, 9C, 9M, and 9Bk filled with toners of yellow, cyan, magenta, and black are provided.

In addition to the intermediate transfer belt 11 and each primary transfer roller 12, the intermediate transfer belt unit 10 includes a driving roller 72 and a driven roller 73 around which the intermediate transfer belt 11 is wound. The driven roller 73 also has a function as a tension applying unit for the intermediate transfer belt 11. For this reason, the driven roller 73 is provided with a biasing unit using a spring or the like. The intermediate transfer belt unit 10, each primary transfer roller 12, the secondary transfer roller 5, and the intermediate transfer belt cleaning device 13 constitute a transfer device 71.
The sheet feeding device 61 includes a feeding roller 3 that abuts on the upper surface of the uppermost sheet S, and the uppermost sheet S is moved by rotating the feeding roller 3 counterclockwise. The sheet is fed toward the registration roller pair 4.

  The intermediate transfer belt cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade arranged to face and contact the intermediate transfer belt 11. The intermediate transfer belt cleaning device 13 scrapes and removes foreign matters such as residual toner on the intermediate transfer belt 11 with a cleaning brush and a cleaning blade. The intermediate transfer belt cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

  As shown in FIG. 2, the fixing device 150 includes a fixing belt 80 as an endless belt member that is thin and flexible, and a pressure roller 84 as a pressure member disposed to face the fixing belt 80. have. Inside the fixing belt 80, a nip forming unit 86 is provided for forming a nip portion N that sandwiches and conveys the sheet S as a recording medium between the fixing belt 80 and the pressure roller 84. The nip forming unit 86 includes a nip forming member 88 disposed inside the fixing belt 80 so as to face the pressure roller 84, and a stay member that holds the nip forming member 88 against the pressure applied from the pressure roller 84. 90. The nip forming member 88 slides on the inner surface of the fixing belt 80 via a low friction sheet as a sliding sheet. In addition, the sliding torque can be reduced by applying a lubricant such as fluorine grease or silicone oil to the sliding sheet. Further, the nip forming member 88 may be in direct contact with the inner surface of the fixing belt 80. A more detailed configuration of the nip forming member 88 will be described later.

  The stay member 90 has a box shape with an opening opposite to the nip portion N side, and halogen heaters 82a and 82b as first heat sources are disposed therein. The fixing belt 80 is directly heated by radiant heat from the inner surface side by the halogen heaters 82 a and 82 b on the opening side of the stay member 90. In order to increase the heating efficiency of the halogen heaters 82 a and 82 b, a plate-like reflection member 94 that reflects light emitted from the halogen heaters 82 a and 82 b to the fixing belt 80 is provided on the inner surface of the stay member 90. The reflection member 94 is provided to suppress wasteful energy consumption due to the stay member 90 being heated by radiation heat from the halogen heaters 82a and 82b. The same effect can be obtained by performing heat insulation or mirror treatment on the inner surface of the stay member 90 instead of the reflecting member 94.

  As shown in FIG. 3, the pressure roller 84 has a structure in which a silicone rubber layer 84b is provided on a hollow metal roller 84a. In order to obtain releasability, a release layer having a layer thickness of 5 to 50 μm made of PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene) is provided on the surface of the rubber layer 84b. The pressure roller 84 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus 100 via a gear. The pressure roller 84 is pressed toward the fixing belt 80 by a spring or the like, and the rubber layer 84b is crushed and deformed to form a predetermined nip width Nw in the sheet conveyance direction. The pressure roller 84 may be a solid roller, but a hollow roller is more preferable because it has a smaller heat capacity. The pressure roller 84 may have a heating source such as a halogen heater inside. The rubber layer 84b may be solid rubber, but sponge rubber may be used when there is no heater inside the pressure roller. Sponge rubber is more preferred because it increases heat insulation and makes it difficult for heat of the fixing belt 80 to be taken away.

  The fixing belt 80 is an endless belt or a film using a metal belt such as nickel or SUS having a layer thickness of 30 to 50 μm, or a resin material such as polyimide. In the case of induction heating, a heating layer such as copper or silver is provided on these substrates. The surface layer of the belt has a release layer such as a PFA or PTFE layer, and has a release property so that toner does not adhere. In addition, an elastic layer formed of a silicone rubber layer or the like may be provided between the belt substrate and the PFA or PTFE layer. When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, subtle irregularities on the belt surface are transferred to the image, and the solid part of the image is crusty. There is a problem that marks remain.

  In order to improve the above problems, it is necessary to provide a silicone rubber layer of 100 μm or more. Thereby, a delicate unevenness | corrugation is absorbed because a silicone rubber layer deform | transforms, and a yuzu skin image is improved. The fixing belt 80 is rotated by contact friction by the rotation of the pressure roller 84. The fixing belt 80 is sandwiched and rotated at the nip portion N, but both ends are held in a cylindrical shape except for the nip portion N, and the cross-sectional shape of the fixing belt 80 is stably maintained in a circular shape. As shown in FIG. 2, a separation member 32 that separates the sheet S from the fixing belt 80 is provided on the downstream side of the nip portion N in the sheet conveyance direction.

  In the present embodiment, the shape of the nip portion N is flat as shown in FIGS. 1 and 3. However, the shape of the nip portion N may be a concave shape or other shape that protrudes toward the fixing belt 80 when viewed from the pressure roller 84 side. There may be. As for the shape of the nip portion N, the discharge direction at the front end of the sheet is closer to the pressure roller 84 in the concave shape, and the separation is improved, so that the occurrence of jam is suppressed. In this case, the nip forming surface of the nip forming member 88 is formed in a concave shape. In this case, the contact surface of the heating heater 112, which is a second heat source to be described later, provided integrally with the nip forming member 88 is also nip. It is good also as a shape along a formation surface. Further, when the shape of the nip portion N is straight, the paper passing property of the envelope is improved.

  The stay member 90 prevents the nip forming member 88 that receives pressure from the pressure roller 84 from being bent, and a uniform nip width can be obtained in the axial direction of the fixing belt 80 that is the paper width direction. In the present embodiment, the pressure roller 84 is pressed toward the fixing belt 80 to form the nip portion N. However, the nip forming unit 86 is pressed toward the pressure roller 84 to form the nip portion N. It is good. The stay member 90 has a sufficient bending strength to support the nip forming member 88. Examples of the material include metal materials such as stainless steel and iron, and metal oxides such as ceramics.

  As shown in FIG. 4, the fixing belt 80 is rotatably supported at both ends in the axial direction described above by flanges 36 as support members protruding in the axial direction from the side plate 34. Although FIG. 4 shows a support structure on one side in the axial direction of the fixing belt 80, the other side has the same structure. The flange 36 that guides both ends of the fixing belt 80 has an outer diameter substantially equal to the inner diameter of the fixing belt 80, and has a length of 5 to 10 mm inward from both ends of the fixing belt 80. Since the fixing belt 80 is guided by the flange 36, the cross-sectional shape thereof is maintained in a circular shape even during traveling (during rotation). A portion corresponding to the nip portion N of the flange 36 is opened to place the nip forming unit 86 at a predetermined position. The stay member 90 has a length that extends over the entire axial direction of the fixing belt 80, and is supported in a state in which both sides thereof are fixed and positioned on the side plate 34.

  As shown in FIG. 5, the halogen heater 82 a is a halogen heater corresponding to a small-sized sheet S having a dense light distribution at the center in the longitudinal direction that is the axial direction of the fixing belt 80. The halogen heater 82b is a halogen heater corresponding to a sheet S of A3 size or the like having a light distribution distribution at both ends in the same longitudinal direction. When the paper S is a small size, only the halogen heater 28a is turned on, and the non-sheet passing portion is prevented from being excessively heated.

  In the vicinity of the outer peripheral surface of the fixing belt 80, sensors 125a and 125b for controlling the heat generation of the halogen heaters 82a and 82b and safety circuits 126a and 126b when the heaters run away are disposed. A non-contact thermopile is preferably used as the sensors 125a and 125b from the viewpoint of responsiveness, and the safety circuits 126a and 126b are preferably interrupted by using a thermostat from the viewpoint of cost. However, the sensor 125 and the safety circuit 126 are not limited to this. For example, a contact type sensor 125 may be used. Further, the temperature control method is performed in the same manner as in the prior art.

  As shown in FIG. 6, two protrusions 90 b and 90 c extending in the longitudinal direction of the fixing belt 80 are formed on the side surface 90 a on the pressure roller 84 side of the stay member 90. The rectangular parallelepiped nip forming member 88 is accommodated and positioned between the ridges 90b and 90c, and is fixed to the side surface 90a by means such as adhesion. As shown in FIG. 7, the nip forming member 88 is provided inside the fixing belt 80 so as to cover the nip forming pad 87, the heater 112 as the second heat source held by the nip forming pad 87, and the heater 112. And soaking member 110 and the like. An insulating member 115 is provided between the heater 112 and the heat equalizing member 110.

  The nip forming pad 87 is formed of a heat resistant resin such as PPS or liquid crystal polymer, and is formed such that the length in the paper width direction that is the axial direction of the fixing belt 80 is larger than the maximum paper size. Has been. At the center of the nip forming pad 87 in the running direction of the fixing belt 80, a recess into which the heater 112 is inserted is formed over the entire width. The heater 112 is a resistance heating element in which resistance is patterned on a ceramic heater or a glass substrate, and terminals (not shown) connected to a power source and a switch element are provided at both ends thereof. As shown in FIG. 5, the heater 112 is formed to have a length that can heat a maximum size paper region such as an A3 size or a 13-inch size.

  A copper plate having a thickness of about 0.5 mm is used as the soaking member 110, and the soaking member 110 is formed by bending so as to cover the nip forming pad 87. The insulating member 115 is made of tetrafluoroethylene resin, polyimide, or the like, but the insulating member 115 may be formed directly on the heat equalizing member 110 by coating. As shown in FIG. 7, when the insulating member 115 is formed of a sheet member, the nip forming pad 87, the heater 112, and the insulating member 115 fit into the recess of the heat equalizing member 110, thereby saving space and stabilizing the pressure. Is planned.

  When passing a large size paper S such as A3 Nobi or 13 inches, the halogen heaters 82a and 82b are not energized, and only the heater 112 is energized. When passing a sheet of A3 size or smaller, only the halogen heaters 82a and 82b or the halogen heater 82a are energized, and the heater 112 is not energized. If the halogen heater 82b is configured to be able to handle large-size paper S such as A3 Novi, even when the large-size paper S is not passed, that portion is heated and wasteful energy is consumed. become. According to the configuration of the present embodiment, the sheet-corresponding width is widened from the A3 size to the 13-inch size by adding a simple configuration in which the heater 112 corresponding to the maximum sheet size is added, so that the above problem can be solved. .

  In the present embodiment, a heater 112 having a PTC characteristic may be used. Thereby, since the resistance value increases above the set temperature, the temperature does not rise above the set temperature, and a safe fixing device free from the risk of combustion or belt damage can be realized. As shown in FIG. 8, the heater having the PTC characteristic has a heating characteristic that saturates at a certain constant temperature.

  When a heater having PTC characteristics is used as the heater 112, it usually takes longer to raise the temperature than a halogen heater. For this reason, if the heater 112 and the halogen heaters 82a and 82b are heated at the same timing, only the inner side of the central portion is heated first, and wasteful energy is consumed. Further, if the heat is taken away by the sheet passing, the heating time for the end heaters 112a and 112b to return to the target temperature is longer than the halogen heaters 82a and 82b due to the characteristics of PTC.

  For this reason, the heater 112 is not driven at the same time as the halogen heaters 82a and 82b, and it is possible to perform heating control without temperature variation by responding by reducing the productivity in accordance with the heating capacity of the heater 112. . Further, the transport speed when transporting the paper S of a size (for example, A3 size) using the heater 112 is made slower than the transport speed of the other standard size (for example, A3T) of the paper S. In this way, by reducing the productivity of the large-sized paper S that is not frequently used, the heater 112 can be simplified and reduced in cost, and the efficiency can be improved. In this embodiment, a configuration having two halogen heaters as the first heat source is shown, but the present invention is not limited to this, and a configuration having three or more halogen heaters for small-size paper may be used. .

  In the present embodiment, the drive circuits for the halogen heaters 82a and 82b and the heater 112 are configured as shown in FIG. In FIG. 9, the halogen heater 82b is turned on by the switch S1, the halogen heater 82a is turned on by the switch S2, and the heater 112 is turned on / off by the switch S3. According to this driving circuit, the driving of the heater 112 is separated from the halogen heaters 82a and 82b, and the temperature sensor 125 and the thermostat 126 can be shared with the halogen heater 82b having a close heat generation area at the end. Since the temperature sensor 125 and the thermostat 126 are shared by the halogen heater 82b and the heater 112, the cost of the drive circuit can be reduced.

  Further, in this embodiment, since the heater 112 is provided inside the fixing belt 80, an area corresponding to the maximum sheet size from the inside without interfering with the traveling movement of the fixing belt 80 is interposed via the heat equalizing member 110. Can be heated. Then, by configuring the belt contact surface of the heat equalizing member 110 with another member made of a smooth material, the sliding resistance can be reduced and the belt running can be stabilized. It is good also as a structure which affixes a sheet | seat with favorable slidability on the soaking | uniform-heating member 110. FIG.

  In addition, since the heating portion of the heater 112 with respect to the fixing belt 80 exists in the nip region, the problem of remelting of untransferred toner due to heating at a portion different from the nip portion N as in Patent Document 1 occurs. Absent. Further, since the pressure roller 84 also serves as an urging means for bringing the heater 112 and the fixing belt 80 into close contact with each other in order to improve heat transfer, a configuration for pressurizing only the heater 112 becomes unnecessary, and a configuration compared to the conventional configuration is required. It can be simplified. In other words, since the heater 112 and the fixing belt 80 are brought into close contact with each other using the applied pressure for forming the nip portion N, the trade between running performance and poor heat transfer in the configuration disclosed in Patent Document 1. There is no off problem.

  In this embodiment, since the heater 112 is formed integrally with the nip forming member 88, the heater 112 can be disposed inside the fixing belt 80, and space saving can be achieved. Further, since the heater 112 is disposed in the concave portion of the nip forming pad 87, a sufficient pressing force by the pressure roller 84 is applied among the fixing belt 80, the heat equalizing member 110, the heater 112, and the nip forming pad 87. . Accordingly, since the fixing belt 80 is driven to travel with respect to the heat equalizing member 110 without any gap, heat transfer from the surface of the heater 112 to the inner surface of the fixing belt 80 can be kept good, and optimum heating efficiency is maintained. be able to.

  According to the present invention from the configuration described above, since large-size paper that is used infrequently is heated via the heat equalizing member 110, temperature uniformity and temperature followability can be improved, and the fixing temperature in the width direction of the paper can be improved. It is possible to provide a good image while suppressing variations in the image quality. In addition, since an insulating member is provided between the heat equalizing member 110 and the heater 112, current leakage from the heater 112 can be reliably prevented.

  FIG. 10 shows a second embodiment of the present invention. Compared with the first embodiment described above, the second embodiment replaces the nip forming pad 87 and the heat equalizing member 110 with the heat equalizing member 113 and the second member as the first member. It differs only in the point which uses the thermal member 114, and the other structure is the same. The heat equalizing member 113 is formed by bending a copper plate having a thickness of 2 mm. A heater 112 is disposed in a recess of the heat equalizing member 113, and the heat equalizing member 113 is sandwiched from the copper plate having a thickness of 2 mm so as to sandwich the heater 112. A soaking member 114 is provided. With this configuration, it is possible to ensure a larger soaking cross section than in the first embodiment, and it is possible to cope with high productivity.

  In the second embodiment, the concave portion of the heat equalizing member 113 may be configured to be shallower than the sum of the thickness of the heater 112, the thickness of the heat equalizing member 114, and the thickness of the insulating member 115. As a result, as shown in FIG. 11, the heat equalizing member 114 receives a load and transmits the load to the heat equalizing member 113 via the heater 112. As a result, the contact thermal resistance to the heat equalizing member 113 can be reduced, and the applied pressure can be applied to the nip portion N while keeping the load uniform. Furthermore, the heater 112 and the insulating member 115 can be reliably fixed by the bent portion while preventing pressure non-uniformity due to, for example, contact with the bent portion of the heat equalizing member 113.

  FIG. 12 shows a third embodiment of the present invention. Compared with the first embodiment described above, the third embodiment replaces the nip forming pad 87 and the soaking member 110 with the soaking member 116 as the first member and the soaking member as the second member. It differs only in the point which uses the thermal member 117, and the other structure is the same. The heat equalizing member 116 is formed by bending a copper plate having a thickness of 2 mm, and the heater 112 is disposed at a notch portion that is formed by bending the heat equalizing member 116 and appears as if it is notched. A soaking member 117 made of a copper plate having a thickness of 2 mm is provided so as to sandwich the heater 112 with the soaking member 116. With this configuration, the heat equalizing member 117 receives a load in a state in which the insulating member 115 is simply wound around the heater 112, and transmits the load to the heat equalizing member 116 via the heater 112. Thereby, the contact thermal resistance to the heat equalizing member 116 can be reduced, and the applied pressure can be applied to the nip portion N while keeping the load uniform. Furthermore, the configuration of the insulating member 115 that prevents the occurrence of current leakage from the heater 112 can be simplified.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to such specific embodiments, and unless specifically limited by the above description, the present invention described in the claims is not limited. Various modifications and changes are possible within the scope of the gist. The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

80 Belt member (fixing belt)
82a, 82b First heat source (halogen heater)
84 Pressure member (Pressure roller)
88 Nip forming member 100 Image forming apparatus 110 Heat equalizing member 112 Second heat source (heater)
113 First member (soaking member)
114 Second member (soaking member)
115 Insulating member 116 First member (heat equalizing member)
117 Second member (heat equalizing member)
150 Fixing device S Recording medium (paper)

JP 2014-178370 A

Claims (6)

An endless belt member having flexibility;
A pressure member disposed opposite to the belt member;
A nip forming member that forms a nip by being pressed by the pressure member through the belt member;
A first heat source for heating a region narrower than the maximum paper size in the axial direction of the belt member;
A second heat source for heating a region corresponding to the maximum paper size in the axial direction of the belt member;
The nip forming member includes a heat equalizing member that uniformizes heat from a second heat source, and an insulating member disposed between the second heat source and the heat equalizing member. The fixing device according to claim 1.
The fixing device, wherein the insulating member has a sheet shape. The fixing device according to claim 1 or 2,
The fixing device, wherein the heat equalizing member includes a first member and a second member, and a second heat source is sandwiched and held by the members. The fixing device according to claim 3.
The first member has a recess into which the second heat source is fitted, and the depth of the recess is shallower than the sum of the thickness of the second heat source, the thickness of the insulating member, and the thickness of the second member. A fixing device characterized in that the fixing device is formed. The fixing device according to claim 3.
The first member has a notch portion on which the second heat source is placed at a predetermined position, and the depth of the notch portion includes the thickness of the second heat source, the thickness of the insulating member, and the thickness of the second member. A fixing device formed so as to be shallower than the sum of the two.   An image forming apparatus comprising the fixing device according to claim 1.

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