JP2016218434A - Fixation device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device which has a second heat source for generating heat in a sheet nip part and can prevent the occurrence of malfunction like fixation defect and image quality reduction.SOLUTION: A fixation device 150 comprises: an endless belt member 80 which has flexibility; a pressure member 84 which is arranged so as to face the belt member 80 and forms a nip part N with pressure; first heat sources 82a, 82b which heat the spot closer to the center in the axial direction of the belt member 80 with a portion other than the nip part N; second heat sources 112a, 112b which heat the spots in the vicinity of both ends in the axial direction of the belt member 80 with the nip part N. The belt member 80 includes both-heating region heated by both first heat sources 82a, 82b and second heat sources 112a, 112b, and the calorific power of the second heat sources 112a, 112b is set to be smaller in both-heating region in comparison to the single-heating region heated only by the second heat sources 112a, 112b.SELECTED DRAWING: Figure 11

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.

  At the same time as paper handling, due to the recent increase in energy-saving demands, preheating the fixing heat source during the standby state of the apparatus has hardly been performed because of an increase in power consumption. For this reason, in recent years, a technique for shortening the return time from the energy saving mode has been considered, and as a directionality, the basic technique is to reduce the heat capacity of a heated member such as a fixing belt, that is, to reduce the thickness. However, there is a problem that the amount of heat transfer per unit time in the axial direction of the fixing belt decreases due to the thinning. In other words, in the non-sheet passing portion in the fixing belt, heat is not taken away by the sheet during the sheet passing in the non-sheet passing portion. In the paper passing portion where the paper is taken away, the amount of heat transfer between the non-paper passing portion is reduced. As a result, the temperature in the axial direction in the fixing belt cannot be kept uniform, and an excessive temperature rise is likely to occur in the non-sheet passing portion, and the temperature is increased by reducing the production speed and reducing the input energy of the heating source. It must be prevented and the user's request could not be satisfied.

  Therefore, in order to solve such problems, a sheet heating element having a plurality of halogen heaters as the first heat source and a second heat source at a position corresponding to the large-size sheet end of the sheet nip portion. The structure which provides is proposed. However, this configuration has a characteristic that the heat generation output is reduced at the end of the halogen heater, whereas the planar heating element does not have such a property. Therefore, when these are combined, unevenness is generated in the amount of heat supplied to the fixing belt in the double heating region where the heating regions of the halogen heater and the planar heating element overlap. As a result, there is a problem that fixing defects such as cold offset and hot offset, and image quality deterioration such as uneven gloss occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that solves the above-described problems, has a second heat source that generates heat at the paper nip portion, and can prevent occurrence of problems such as fixing failure and image quality degradation. To do.

  The present invention relates to an endless belt member having flexibility, a pressurizing member that is disposed opposite to the belt member and forms a nip portion by pressurization, and an axially central portion of the belt member other than the nip portion. A first heat source for heating and a second heat source for heating the vicinity of both axial ends of the belt member at the nip portion, and the belt member is heated by both the first heat source and the second heat source. The heat generation amount of the second heat source is set to be smaller in the double heating region than in the single heating region heated only by the second heat source. To do.

  According to the present invention, the temperature of the belt member can be made uniform by providing the calorific value distribution of the second heat source so as to complement the end sagging of the first heat source. Due to this uniformization, the occurrence of unevenness in the axial direction of the belt member can be reduced, and the occurrence of fixing failure can be prevented and stable quality image formation can be performed.

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 an edge part heater. It is the schematic which shows the nip formation unit used for one Embodiment of this invention. It is the schematic explaining the edge part heater applicable to the 1st Embodiment of this invention. It is the schematic explaining the contact state of the edge part heater and nip formation member used for one Embodiment of this invention, and a fixing belt. It is a circuit block diagram of the halogen heater and end part heater in one Embodiment of this invention. It is the schematic explaining the resistive heating element used for the 1st Embodiment of this invention. It is a diagram which shows the relationship between the emitted-heat amount of each heater in one Embodiment of this invention, and a longitudinal direction position. It is the schematic explaining the edge part heater used for the 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to describing this embodiment, a conventional configuration and problems 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.

  Below, the 1st Embodiment of this invention which can eliminate the problem of the patent document 1 mentioned above is 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 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 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. 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 uneven fixing (glossy) This causes a problem that unevenness remains.

  In order to improve the above problems, it is necessary to provide a silicone rubber layer of 100 μm or more. As a result, deformation of the silicone rubber layer absorbs subtle irregularities and improves fixing unevenness. 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. 2 and 3. However, the shape of the nip N may be a concave shape or other shape that is convex 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 of end heaters 112a and 112b, which will be described later, is a second heat source provided integrally with the nip forming member 88. The surface may also have a shape along the nip forming surface.

  Due to the action of the stay member 90, it is possible to prevent the nip forming member 88 that receives pressure from the pressure roller 84 from being bent and to obtain a uniform nip width in the axial 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 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 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.

  The difference between the A3 size width, the A4Y width with the A4 size turned sideways, and A3 nobi (329 mm) and 13 inches (330 mm) is 32 to 33 mm. Therefore, if only the both ends in the axial direction of the fixing belt 80 are heated, both ends can be heated by a width of 16 to 16.5 mm, which is half of the above, as shown in FIG. The width of paper can be expanded to nobi. In other words, if the portions where the light distribution distribution at both ends of the halogen heater 82b is not dense can be heated, it is possible to cope with a large size paper S such as A3 Nobi. Therefore, as the end heaters 112a and 112b used as the end heat source, a small heater having an axial length of about 20 mm is sufficient.

  When passing a large size paper S such as A3 Nobi or 13 inches, the halogen heaters 82a and 82b and the end heaters 112a and 112b are energized. When passing paper of A3 size or smaller, only the halogen heaters 82a and 82b or the halogen heater 82a are energized, and the end heaters 112a and 112b are 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 above problem can be solved by adding a simple configuration in which end heaters 112a and 112b are added to both ends of the fixing belt 80 or in the vicinity of both ends.

  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. At both ends in the longitudinal direction of the nip forming member 88, concave portions 88a and 88b as stepped portions are formed, and end heaters 112a and 112b are respectively accommodated and fixed by means such as adhesion. A surface of the nip forming member 88 facing the pressure roller 84 forms a nip forming surface 88c.

  On the nip portion N side of the nip forming member 88, a metal plate 89 as a heat transfer assisting unit is provided so as to cover the nip forming member 88. The metal plate 89 is preferably a material capable of heat transfer in a short time in order to reduce temperature non-uniformity in the longitudinal direction of the fixing belt 80, and has a high thermal conductivity such as copper, aluminum, silver, etc. Is desirable. Among these, copper is most preferable from the viewpoint of cost, availability, thermal conductivity characteristics, and workability. The metal plate 89 slides on the inner surface of the fixing belt 80 through a low friction sheet as a sliding sheet (not shown), and a sliding torque is applied by applying a lubricant such as fluorine grease or silicone oil to the sliding sheet. Can be reduced. Note that the metal plate 89 may be in direct contact with the inner surface of the fixing belt 80 without using a sliding sheet. In that case, it is desirable to coat the surface of the metal plate 89 with a resin or the like that reduces the frictional force with the fixing belt 80.

  In the above-described embodiment, the configuration in which the metal plate 89 is provided is shown. However, in order to reduce the heat capacity of the fixing device and improve the warm-up time and the power consumption, the metal plate 89 may be omitted. In this case, the nip forming member 88 and the fixing belt 80 slide. In the case of this configuration, a sliding sheet may be interposed as in the case where the metal plate 89 is provided, or the surface of the nip forming member 88 may be coated without interposing the sliding sheet. Good.

  FIG. 7 shows the end heaters 112a and 112b used in the first embodiment of the present invention. In the figure, the end heaters 112a and 112b are configured by laminating a resistance heating element 114 and an insulating layer 115 made of a thin glass layer on a ceramic base 113 having an outer shape of about 10 mm × 20 mm. Here, by adopting a configuration in which the resistance heating element 114 is not provided to the outer peripheral portion of the ceramic base 113, the heat generation amount of the outer peripheral portion is configured to be lower than that of the central portion. And it has the structure which prevents heat dissipation as much as possible by making the recessed part 88a (88b) contact | abut to an outer peripheral part. The contact surface with each of the recesses 88a and 88b may be on the ceramic base 113 side or the insulating layer 115 side. However, when contacting the recesses 88a and 88b on the insulating layer 115 side composed of a thin film glass layer, the temperature rise rate is increased. Fast and efficient. In FIG. 7A, the side where the circuit of the resistance heating element 114 turns back (left side in the figure) is the center side in the longitudinal direction, and the side where power is input to the resistance heating element 114 (right side in the figure) is the end in the longitudinal direction. On the side.

  As shown in FIG. 8A, the surfaces of the end heaters 112a and 112b that contact the inner surface of the fixing belt 80 and the nip forming surface 88c are in the direction of the arrow F (the drag direction) that is the direction of pushing the inner surface of the fixing belt 80. ) Have the same height. In other words, the surfaces of the end heaters 112a and 112b that are in contact with the inner surface of the fixing belt 80 are configured to be extended surfaces in the longitudinal direction of the nip forming surface 88c. In the present embodiment, the end heaters 112a and 112b are integrally provided with respect to the nip forming member 88 necessary for forming the nip, so that the end heaters 112a and 112b are provided inside the fixing belt 80. It can be arranged and space can be saved.

  Further, since the surfaces of the end heaters 112a and 112b that are in contact with the inner surface of the fixing belt 80 and the nip forming surface 88c are located at the same height (on the same plane), sufficient pressing force by the pressure roller 84 is applied to the fixing belt. 80 and the end heaters 112a and 112b. Thereby, belt running can be realized in a state where the fixing belt 80 and the end heaters 112a and 112b are in close contact with each other, and good heating efficiency by the end heaters 112a and 112b can be maintained by improving heat transfer. In addition, since the heating part for the fixing belt 80 by the end heaters 112a and 112b exists in the nip region, there is a problem of re-melting of the untransferred toner due to heating at a part different from the nip part N as in Patent Document 1. Does not occur. Furthermore, since the pressure roller 84 also serves as an urging means for bringing the end heaters 112a and 112b and the fixing belt 80 into close contact with each other in order to improve heat transfer, it is not necessary to press only the end heaters 112a and 112b. Thus, the configuration can be simplified as compared with the conventional case. In other words, since the end heaters 112a and 112b and the fixing belt 80 are brought into close contact with each other by using a pressing force for forming the nip portion N, the running performance and heat transfer in the configuration disclosed in Patent Document 1 are described. There is no trade-off problem with defects.

  In the present embodiment, the shape of the recess formed in the nip forming member 88 is a shape in which the end portion in the axial direction is opened. However, as shown in FIG. 8B, the recesses 88a and 88b are surrounded by four sides. Also good. Moreover, it is good also as a structure by which the front and back of the axial direction were block | closed and the both sides orthogonal to an axial direction were open | released. In the present embodiment, the stay member 90 and the halogen heaters 82a and 82b are integrally provided as the nip forming unit 86. However, a single product having an integrated structure of the nip forming member 88 and the end heaters 112a and 112b is also provided. It is a nip forming unit according to the invention.

  In the first certain period of time immediately after the warm-up when the fixing belt 80 and the pressure roller 84 are not yet sufficiently warm, the halogen heaters 82a and 82b and the end heaters 112a and 112b are energized and then the paper is passed. Sometimes the amount of power is controlled by temperature control. In order to avoid a decrease in heat generation output (end sagging) at the extreme end of the halogen heater 82b, it is necessary to increase the length of the heat generation portion of the halogen heater 82b. This is a rise in the temperature of the non-sheet passing portion during continuous sheet passing. Cause the problem. Moreover, since it is necessary to heat even an unnecessary part, useless energy will be consumed.

  In the present embodiment, both the end heaters 112a and 112b may have PTC characteristics. If it has a PTC characteristic, the resistance value increases above the set temperature, so that the temperature does not rise above the set temperature, and a safe fixing device without the risk of combustion or belt breakage can be realized. Further, in this embodiment, the end heaters 112a and 112b are provided inside the fixing belt 80, so that the belt end can be heated from the inside without obstructing the traveling movement of the fixing belt 80.

  Further, since the recesses 88a and 88b for holding the end heaters 112a and 112b are formed integrally with the nip forming member 88, the end heaters 112a and 112b can be disposed inside the fixing belt 80 in a space-saving manner. Further, since the end heaters 112a and 112b are disposed at the same height as the nip forming member 88 and the metal plate 89 is disposed thereon, the high thermal conductivity characteristics of the metal plate 89 are utilized to fix the fixing belt 80. The temperature can be kept more uniform.

  In the present embodiment, a configuration having two halogen heaters as fixing heat sources 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. Moreover, it is good also as a structure which has only one halogen heater and serves as the function of the halogen heater 82b in which an edge part heater heats an edge part.

  FIG. 9 shows an electrical connection configuration of the halogen heaters 82a and 82b and the end heaters 112a and 112b in the above embodiments. When transporting the sheet S based on the center, the end heaters 112a and 112b are always driven at the same time, so that the end heaters 112a and 112b are electrically connected in series to the power source 120, respectively. By adopting such a connection configuration, electric control can be simplified as compared with a configuration in which the end heaters 112a and 112b are individually turned on and off. Further, when one end heater 112a or 112b breaks down, the electrical connection between them can be cut off at the same time, so safety can be ensured. The halogen heater 82a is turned on and off by the switch 120a, the halogen heater 82b is turned on by the switch 120b, and the end heaters 112a and 112b are turned on and off by the switch 120c.

  The end heaters 112 are not limited to a configuration in which one pair is provided at both left and right ends as shown in the above embodiment, and for example, a plurality of pairs may be provided according to various paper sizes, and further outside the halogen heater 82b. It may be arranged. In such a case, it is possible to cope with a larger number of sheets, and more accurate heating is possible, which is more desirable.

  The heating operation based on the circuit configuration shown in the above embodiment is temperature-controlled by a temperature sensor 125 (see FIG. 2) disposed near the outside of the fixing belt 80. Therefore, a safety device such as a thermostat 126 (see FIG. 2) needs to be provided in the vicinity of the outside of the fixing belt 80 in order to prevent the temperature sensor 125 from running away when it fails.

  As described above, according to the present invention, even if the heating power of the end heater 112 is inferior to the heating power of the halogen heater 82, only the end heater 112 can be independently heated and driven. Thereby, the heating temperature by the end heater 112 can be controlled to the same temperature as the heating temperature by the halogen heater 82, and the degree of freedom of heater selection can be improved.

  Next, the heat generation distribution of the end heater 112, which is a feature of the present invention, will be described. FIG. 10 shows a portion where the circuit of the resistance heating element 114 of the end heater 112 is folded, that is, the center side in the longitudinal direction. The resistance heating element 114 has a U-shaped folded portion 114b with respect to the straight portion 114a, and is formed so that the sectional area Sb of the folded portion 114b is larger than the sectional area Sa of the linear portion 114a. . With this configuration, the resistance value of the conducting wire is inversely proportional to the cross-sectional area. Therefore, when power is supplied to the resistance heating element 114, the amount of heat generated per unit length in the longitudinal direction of the folded portion 114b compared to the straight portion 114a. Can be reduced.

  In this embodiment, the amount of power is adjusted by changing the resistance value by changing the cross-sectional area of the resistance heating element 114, but by changing the resistance value by connecting the conductors with materials having different electrical resistivity. Alternatively, the adjustment may be performed by changing the circuit to a parallel circuit or the like. Moreover, in the said embodiment, although the cross-sectional area was formed large in the folding | turning part 114b, you may adjust calorific value by changing a cross-sectional area in the linear part 114a.

  The effect by the structure mentioned above is demonstrated. FIG. 11 shows the distribution of each heat generation amount with respect to the fixing belt 80 in the halogen heater 82 and the end heater 112 in the longitudinal direction. 11A shows a conventional configuration where the resistance heating element has a uniform cross-sectional area, and FIG. 11B shows the case where the end heater 112 having the resistance heating element 114 shown in FIG. 10 is used. Each is shown.

  Due to the heat generation characteristics of the halogen heater 82, a so-called end sag occurs in which the heat output at both ends is lower than that at the center. For this reason, in FIG. 11A, in the region where the heat generation of the end halogen heater 82b and the heat generation of the end heater 112 overlap (hereinafter referred to as a double heating region), the amount of heat is excessive compared to other regions. . On the other hand, in the region that is not heated by the end heater 112, there is a region where the amount of heat is insufficient due to end sagging. Therefore, in the conventional configuration, when all the heaters are turned on to pass a large size paper such as A3 Novi size, the belt temperature becomes non-uniform in the vicinity of the double heating region, and image defects such as uneven gloss and low temperature portions Quality degradation such as insufficient fixing strength occurs.

  On the other hand, in the end heater 112 shown in the present embodiment, the resistance value of the double heating region is made smaller than the region heated only by the end heater 112 (hereinafter referred to as a single heating region), so that The amount of heat generated in the double heating region is smaller than that in the heating region. As a result, the inclination of the heat generation amount in the longitudinal direction can be moderated, and the temperature of the fixing belt 80 can be made uniform by providing the heat generation amount distribution of the end heater 112 so as to complement the end sag of the halogen heater 82b. Can be made. Due to this uniformization, the occurrence of unevenness in the axial direction of the fixing belt 80 can be reduced, and the occurrence of fixing failure can be prevented and stable quality image formation can be performed.

  Further, in the present embodiment, the resistance value of the resistance heating element 114 is made smaller in the double heating region than in the single heating region, so that the above-described configuration can be easily achieved. In the present embodiment, the sectional area of the resistance heating element 114 is smaller in the double heating region than in the single heating region, so that the above configuration can be achieved without greatly changing the conventional circuit configuration. it can.

  FIG. 12 shows end heaters 116a and 116b as second heat sources used in the second embodiment of the present invention, and the end heaters 116a and 116b are used in place of the end heaters 112a and 112b. . Compared with the end heater 112, the end heater 116 replaces the ceramic base material 113 and the insulating layer 115 having a rectangular shape, and the ceramic base material 117 having a shape in which the periphery of one vertex from the center side in the rectangle is cut off. An insulating layer 119 is used. Accordingly, instead of the resistance heating element 114, a resistance heating element 118 wired according to the above-described shape is used.

  With the above-described configuration, the portion 118a from which a part of the resistance heating element 118 is cut has a smaller wiring density per length in the longitudinal direction than the portion 118b that is not cut out, and the fixing belt 80 in the longitudinal direction. The contact area is reduced. As a result, the amount of generated heat can be reduced, so that the gradient of the amount of generated heat in the double heating region can be moderated as in the first embodiment. As a result, the temperature distribution of the fixing belt 80 can be made uniform by providing a distribution of the amount of heat generated so as to complement the end sagging of the halogen heater 82b.

  With the above-described configuration, it is possible to reduce the amount of heat generated by the resistance heating element 118 by reducing the wiring density of the resistance heating element 118 in the double heating region, and it is possible to easily obtain the same effects as those of the first embodiment. Can do. Further, by reducing the contact area of the resistance heating element 118 to the fixing belt 80 in the double heating region, the amount of heat generated by the resistance heating element 118 can be reduced, and the same effect as that of the first embodiment can be easily obtained. be able to.

  In the above embodiment, a halogen heater is used as the first heat source. However, the same effect can be obtained as long as the heat generation amount is a heat source whose end portion is lower than the center portion in the longitudinal direction. For example, even when the belt surface is heated in a non-contact manner by electromagnetic induction such as an IH coil, end sagging occurs due to the characteristics of the magnetic field caused by the electromagnetic induction, so that the same effect as the above embodiment can be expected. In this embodiment, the fixing belt is directly heated by the halogen heater. However, a sleeve member or the like may be provided between the halogen heater and the fixing belt, and the fixing belt may be heated via the sleeve member. Alternatively, a separate heating roller may be provided, and the fixing belt may be wound so that the halogen heater heats the heating roller, and the fixing belt is heated via this.

  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 89 Heat transfer auxiliary means (metal plate)
100 Image forming apparatus 112a, 112b, 116a, 116b Second heat source (end heater)
114, 118 Resistance heating element 150 Fixing device N Nip part

JP 2014-178370 A

Claims (10)

An endless belt member having flexibility;
A pressure member that is disposed opposite to the belt member and forms a nip portion by pressure;
A first heat source that heats the belt member near the center in the axial direction other than the nip portion;
A second heat source for heating the vicinity of both axial ends of the belt member at the nip portion;
The belt member has a double heating region heated by both the first heat source and the second heat source, and the heat generation amount of the second heat source is larger than that of the single heating region heated only by the second heat source. A fixing device in which the twin heating region is set smaller. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the second heat source includes a resistance heating element, and the resistance value of the resistance heating element is smaller in the double heating area than in the single heating area. The fixing device according to claim 2.
The fixing device according to claim 1, wherein a cross-sectional area of the resistance heating element is larger in the twin heating region than in the single heating region. The fixing device according to any one of claims 1 to 3,
The fixing device according to claim 1, wherein the second heat source includes a resistance heating element, and the wiring density in the axial direction of the resistance heating element is smaller in the twin heating area than in the single heating area. In the fixing device according to any one of claims 1 to 4,
The second heat source has a resistance heating element, and the contact area of the resistance heating element with the belt member in the axial direction is smaller in the twin heating area than in the single heating area. Fixing device. In the fixing device according to any one of claims 1 to 5,
A fixing device comprising heat transfer assisting means for equalizing the temperature of the belt member. The fixing device according to any one of claims 1 to 6,
The fixing device, wherein the second heat source is electrically connected in series. In the fixing device according to any one of claims 1 to 7,
The fixing device, wherein the second heat source is temperature-controlled independently of the first heat source. In the fixing device according to any one of claims 1 to 8,
It has a nip forming member that forms the nip portion by being pressed by the pressure member through the belt member, and the second heat source is provided on substantially the same plane as the nip forming member. A fixing device characterized.   An image forming apparatus comprising the fixing device according to claim 1.

Images