JP2017120392A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that is designed for a recording material in a special size, such as extended A3, without impairing reliability and quality, and can reduce starting torque even in a cold state.SOLUTION: A fixing device of the present invention comprises: an endless belt with flexibility; a pressure member that is provided on the outside of the belt and faces the belt; radiation type heat sources that are provided inside the belt; a nip forming member that is provided on the inside of the belt and forms a fixing nip between the belt and pressure member; a plurality of contact heat transfer type heat sources that are provided on the respective ends of the nip forming member and respectively heat the ends in the longitudinal direction of the belt; and a heat transfer auxiliary member that covers the respective surfaces of the nip forming member and plurality of contact heat transfer type heat sources that face the belt and transfers heat in its longitudinal direction. A lubricant is applied on the inside of the belt, and operation is performed in the order of heat generation by the plurality of contact heat transfer type heat sources, rotation of the belt, and heat generation by the radiation type heat sources.SELECTED DRAWING: Figure 11

Description

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

  In recent years, there has been a strong market demand for energy saving and high speed for image forming apparatuses such as copiers, printers, facsimiles, and multifunction machines having at least two of these functions.

  Among image forming devices, the fixing device consumes a lot of power and has a lot of room for energy saving.Therefore, various proposals have been made.For example, a thin endless belt with a low heat capacity and a metal heat that also serves as a support. There has been known a fixing device that can directly heat without using a conductor and can obtain good fixing performance even when mounted on a high-production image forming apparatus (see, for example, Patent Document 1). In this fixing device, a pressure roller disposed on the outer peripheral side of an endless fixing belt and a nip forming member fixedly disposed inside the fixing belt (in the loop) are brought into pressure contact with each other via the fixing belt, thereby fixing the fixing nip. Is forming.

  On the other hand, recording materials of various sizes are used in the image forming apparatus. In order to handle recording materials of various sizes, the fixing belt, which is a non-sheet-passing part, is used when fixing a small size recording material when the length of the fixing heat source (heater) of the fixing device is adjusted to the maximum size of the recording material. / The temperature of the roller end rises. Since the end is excessively heated during continuous paper feeding, it is necessary to reduce the productivity by, for example, slowing the recording material conveyance speed.

  In order to cope with this problem, there is known a fixing device including a halogen heater having a dense light distribution at the center and a halogen heater having a dense light distribution near the end inside the fixing belt / roller. . In the case of a recording material of a small size, this fixing device performs fixing by turning on only a halogen heater having a dense light distribution in the center, and in the case of a recording material larger than a small size, turning on both halogen heaters. .

  However, unlike the inkjet recording method, in image formation using toner, printing is performed with a non-printing area, so when image formation is performed on the full standard paper size although it is used infrequently, A recording material that is slightly larger than the standard paper size may be used (for example, an A3 novi size that is slightly larger than the A3 size), or a 13-inch size may be used. Therefore, further improvement has been desired to cope with these special-size recording materials.

  In order to solve such a problem, Patent Document 2 provides a plurality of halogen heaters having different light distributions in the belt width direction (paper width direction) inside the endless belt, and the longitudinal direction of the belt member. It has been proposed to provide an end heater in contact with the inner surface or outer surface of the belt at both ends and upstream of the nip in the belt rotation direction.

  However, in the fixing device disclosed in Patent Document 2, in order to increase the heat transfer efficiency from the end heater to the fixing belt, if the contact pressure of the end heater with respect to the fixing belt is increased, the gap between the end heater and the fixing belt is increased. The frictional force increases. This may lead to poor running of the fixing belt, resulting in a decrease in reliability.

  On the other hand, if the contact pressure of the end heater with respect to the fixing belt is reduced in order to avoid poor running of the fixing belt, heat transfer to the fixing belt is insufficient. This may lead to an excessive temperature rise of the end heater, resulting in a decrease in reliability.

  Also, there is a problem of quality deterioration that the residual toner on the fixing belt that has not been fixed to the recording material at the fixing nip is remelted at the position of the end heater and remains as a fixed toner.

  Furthermore, recent fixing devices are required to further shorten the first print time, and the following problems have become apparent.

  Since the nip forming member slides with the inner surface of the belt member, a lubricant such as fluorine grease or silicone oil is applied to the sliding surface to reduce the sliding torque. In particular, fluorine grease is advantageous for increasing the torque of the fixing device over time because it has good retention at the nip forming member.

  However, fluorine grease has a property that its viscosity changes with temperature. In order to shorten the first print time, it is necessary to speed up the start-up of the fixing device. However, the viscosity increases particularly during cold weather, and the starting torque of the fixing device increases. Therefore, a drive motor with a high torque output is required, leading to an increase in cost.

  Further, when the fixing belt is rotated with such a high torque, a large load is applied not only to the fixing belt but also to a gear for driving the fixing device. As a result, the mechanical life of the fixing belt, the fixing device, and the image forming apparatus may be shortened.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that can cope with a recording material of a special size such as A3 Nobi without impairing reliability and quality, and can reduce a starting torque even in a cold state.

  The problems include a flexible endless belt, a pressure member provided outside the belt, facing the belt, a radiant heat source provided inside the belt, and an inner side of the belt. A nip forming member that forms a fixing nip between the belt and the pressure member; and a plurality of nip forming members that are provided at respective ends of the nip forming member and that respectively heat the longitudinal ends of the belt. A contact heat transfer type heat source, and a heat transfer auxiliary member that covers each surface of the nip forming member and the plurality of contact heat transfer type heat sources facing the belt and moves heat in the longitudinal direction of the belt. And a lubricant is applied to the inside of the belt, and is solved by a fixing device that operates in the order of heat generation of the plurality of contact heat transfer type heat sources, rotation of the belt, and heat generation of the radiation type heat source. .

  The fixing device according to the present invention includes a plurality of contact heat transfer type heat sources for heating the longitudinal ends of the belt at the respective ends of the nip forming member, so that the reliability and quality of a special-size recording material are impaired. It can respond without. Further, since the operation is started in the order of heat generation from the contact heat transfer type heat source, rotation of the belt, and heat generation from the radiation type heat source, the starting torque can be reduced even in a cold state.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional configuration diagram illustrating an embodiment of a fixing device. It is a perspective view which shows the basic composition of a nip formation unit. It is a perspective view which shows the structure of a nip formation unit and a halogen heater. It is a schematic diagram which shows arrangement | positioning of the heat-emitting part of a halogen heater and an edge part heater. It is a schematic diagram which shows the positional relationship of each heat-emitting part of a halogen heater and an edge part heater. It is a graph (1st pattern) which shows the heating output of a 2nd halogen heater. It is a graph which shows the state of each heating output of the halogen heater which has a heat generating part near the center, and the halogen heater which has a heat generating part near the end. It is a graph (2nd pattern) which shows the heating output of a 1st, 2nd halogen heater. It is a graph (3rd pattern) which shows another example of the heating output of a 1st, 2nd halogen heater. It is a figure explaining the position of the temperature detection part provided for an edge part heater. 6 is a flowchart illustrating an operation of a fixing device according to an embodiment of the present invention. 6 is a graph showing a relationship between a temperature near a fixing nip portion and a unit torque in the fixing device.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 is a color laser printer. In the center of the printer body, four image forming units 4Y, 4C, 4M, and 4K are provided side by side along the extending direction of the intermediate transfer belt 30. Yes. Each of the image forming units 4Y, 4C, 4M, and 4K stores developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and A developing device 7 for supplying toner to the surface of the photoreceptor 5 and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are assigned color codes, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M The reference numerals are omitted.

  Below the image forming units 4Y, 4C, 4M, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. In addition, each primary transfer roller 31 is connected to a power source of a printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. .

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, the secondary transfer roller 36 is also connected to the power source of the printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30.
A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K containing replenishing toner are detachably attached to the bottle container 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development from each toner bottle 2Y, 2C, 2M, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, a lower portion of the printer main body is provided with a paper feed tray 10 that stores paper P as a recording material, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like. Here, in addition to plain paper, the recording material includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

  The basic operation of the printer according to this embodiment is as follows. When the image forming operation is started, the photoconductors 5 in the image forming units 4Y, 4C, 4M, and 4K are rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is set to a predetermined polarity by the charging device 6. Uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is formed by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized, and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed in the nip. Are collectively transferred onto the paper P. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container placed in the printer body. To be recovered.

Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.
The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4C, 4M, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

  FIG. 2 is a schematic cross-sectional configuration diagram showing an embodiment of the fixing device 20. The fixing device 20 includes an endless fixing belt 21 that is a thin and flexible cylindrical fixing member, and a pressure roller 22 that is a pressure member that abuts from the outer peripheral side of the fixing belt 21. ing. The fixing belt 21 is heated by radiant heat of halogen heaters 23A and 23B (hereinafter also referred to as first halogen heater 23A and second halogen heater 23B) as a plurality of fixing heat sources arranged inside (in the loop). The halogen heater represents a radiant heat source as a fixing heat source which is a main heat source.

  Further, a nip forming member 24 that forms a fixing nip N with the pressure roller 22 via the fixing belt 21 and a stay member 25 (support member) that supports the nip forming member 24 are arranged inside the fixing belt 21. Has been. The nip forming member 24 arranged across the width direction of the fixing belt 21 is fixedly supported by the stay member 25, thereby preventing the nip forming member 24 from being bent by the pressure from the pressure roller 22, A uniform nip width is obtained over the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly heat-resistant resins such as polyimide (PI) resin, polyether ether ketone (PEEK) resin, and reinforced them with glass fiber. Is made up of. This prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature range, ensures a stable fixing nip state, and stabilizes the output image quality. The stay member 25 and the halogen heaters 23A and 23B are fixedly held at both ends in the longitudinal direction by a side plate of the fixing device 20 or a separately provided holder. End heaters 26 a and 26 b as end heat sources different from the main heat source (fixing heat source) are integrally attached to both ends in the longitudinal direction of the nip forming member 24. As the end heater, a contact heat transfer type heat source that is a resistance heating element such as a ceramic saver is generally used.

  A heat transfer auxiliary member 27, also referred to as a soaking member, that facilitates heat transfer in the longitudinal direction of the fixing belt, has each surface facing the inner peripheral surface of the fixing belt 21 of each of the nip forming member 24 and the end heater 26. The cover belt is arranged so as to prevent heat from staying in the end region of the fixing belt 21 when passing small-size paper or when the end heater 26 is turned on, and thus positively in the width direction of the fixing belt 21, that is, The heat is transferred in the longitudinal direction of the heat transfer assisting member 27 to eliminate the temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer auxiliary member 27 is made of a material having high thermal conductivity that enables heat transfer in a short time, such as copper (398 W / mk) or aluminum (236 W / mk). In the depiction in FIG. 2, the surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21 and is a nip forming surface that is formed flat. However, it may be a concave shape or other shapes. When the nip forming surface has a concave shape, the discharge direction at the front end of the sheet is closer to the pressure roller, the separation is improved, and jamming is suppressed.

  As is well known, a temperature sensor 29 for detecting the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 21, for example, upstream of the fixing nip in the belt rotation direction, and downstream of the fixing device 20 in the sheet conveyance direction. On the side, a separating member 41 for separating the paper P from the fixing belt 21 is disposed. Further, releasable pressure means for pressing the pressure roller 22 to the fixing belt 21 is also provided.

  In order to achieve a low heat capacity, the endless fixing belt 21 which is thin and small in diameter like a film is composed of a base material on the inner peripheral side made of a metal material such as nickel or SUS, or a resin material such as polyimide, and a PFA. It is constituted by a release layer on the outer peripheral side formed of (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene). An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. When the thickness of the elastic layer is about 100 μm, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface can be absorbed by the elastic deformation of the elastic layer, and uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to a thickness of 1 mm or less and a diameter of 20 to 40 mm as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, more preferably 0.16 mm or less, and the diameter is 30 mm. The following is desirable.

  The stay member 25 having a T-shaped cross section has an upright portion 25a that is upright on the side opposite to the fixing nip N side, and is arranged so that halogen heaters 23A and 23B as main heat sources are separated by the upright portion 25a. One of the halogen heaters 23A and 23B has a heat generating portion at a longitudinal center portion corresponding to a small size paper, and the other has a heat generating portion at both longitudinal end portions corresponding to a large size paper. The halogen heaters 23 </ b> A and 23 </ b> B are configured to generate heat by being output controlled by a power supply unit provided in the printer body. The output control is performed on the belt surface by a temperature sensor 29 provided on the outer periphery of the fixing belt 21. This is performed based on the temperature detection result. By such heater output control, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  Reflecting members 28A and 28B are disposed between the stay member 25 and the halogen heaters 23A and 23B. Accordingly, the heating efficiency of the halogen heaters 23A and 23B with respect to the fixing belt 21 can be increased, and wasteful energy consumption due to the stay member 25 being heated by the radiant heat from the halogen heaters 23A and 23B can be suppressed. The same effect can be obtained by performing heat insulation or mirror treatment on the surface of the stay member 25 instead of providing the reflecting members 28A and 28B.

  The pressure roller 22 includes a cored bar, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the cored bar, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. It is configured. At a location where the pressure roller 22 is pressed against the fixing belt 21 by a pressing means such as a spring and is pressed against the fixing belt 21, the elastic layer of the pressure roller 22 is crushed to form a fixing nip N having a predetermined width. The The pressure roller 22 is rotationally driven by a driving source such as a motor provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 through the fixing nip N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched and rotated at the fixing nip N, and travels while being guided by side plate flanges disposed at both ends except for the fixing nip N.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  FIG. 3 is a perspective view showing a basic configuration of the nip forming unit. As shown in FIG. 3, the nip forming unit includes a nip forming member 24, a stay member 25, a heat transfer assisting member 27, and end heaters 26a and 26b. In the nip forming unit, the surface of the nip forming member 24 opposite to the fixing nip N side is integrated with the plane of the stay member 25 on the fixing nip N side. At this time, uneven shapes such as bosses and pins may be formed on the respective surfaces, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. The heat transfer assisting member 27 and the nip forming member 24 may be integrated with each other by providing a claw or the like, but may be bonded or the like. Concave portions 24a and 24b as stepped portions are formed at both ends in the longitudinal direction of the nip forming member 24, and end heaters 26a and 26b are accommodated and fixed at these portions. The positional relationship between the end heaters 26a and 26b and the halogen heaters 23A and 23B will be described later.

  The surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is configured as a belt sliding contact surface 27a. However, in terms of mechanical strength, the nip forming surface is substantially the addition of the nip forming member 24. This is a surface 24 c facing the pressure roller 22.

  As described above, in the present embodiment, the end heaters 26 a and 26 b are integrally provided on the nip forming member 24 necessary for forming the fixing nip, so that the end heaters 26 a and 26 b are provided on the fixing belt 21. It can be placed inside with space saving.

  In addition, the surface of the end heaters 26a and 26b that faces the inner surface of the fixing belt 21 and the surface of the nip forming member 24 that faces the fixing belt 21 are positioned at the same height (on the same plane). Sufficient pressure is applied through the heat transfer assisting member 27.

  As a result, the fixing belt 21 is in a state of being in intimate contact with the end heaters 26a and 26b, so that stable belt traveling can be performed. Further, the fixing belt 21 and the end heaters 26a and 26b are in contact with each other with a sufficient contact pressure, and good heating is maintained. With these configurations, the reliability of the fixing device 20 is improved.

  Further, the heating portion of the fixing belt 21 by the end heaters 26a and 26b is in the nip region. For this reason, the problem of re-melting of unfixed residual toner due to heating at a site different from the fixing nip N as in Patent Document 1 does not occur.

  FIG. 4 is a perspective view showing configurations of the nip forming unit and the halogen heater. As shown in FIG. 4, the stay member 25 includes a first member 25 </ b> A and a second member 25 </ b> B having a substantially L-shaped section, and has a substantially T-shaped section. Therefore, the rigidity is high and the nip forming member 24 can be prevented from being bent by the stress from the pressure roller 22. The stay members 25 (the first member 25 </ b> A and the second member 25 </ b> B) extend linearly in the longitudinal direction of the nip forming member 24 and are fixed to the nip forming member 24. Therefore, a good nip forming surface can be maintained over the entire longitudinal direction of the fixing nip N.

  A first halogen heater 23 </ b> A and a second halogen heater 23 </ b> B are disposed on both sides of the standing portion 25 a in the short direction. That is, the first and second halogen heaters 23A and 23B are shielded from each other by the standing portion 25a. Therefore, unlike the fixing device shown in FIG. 11, the glass tubes are not heated when the heater is turned on, so that the heating efficiency is not lowered. Further, since the first and second halogen heaters 23A and 23B are not surrounded by the stay member 25 (the center of each halogen heater 23 is outside the space surrounded by the stay member 25), the irradiation angles α and β (see FIG. 2) becomes obtuse and heating efficiency can be improved.

  The cross-sectional shape of the stay member 25 is not limited to a substantially T shape. The first and second halogen heaters 23A and 23B may be arranged so as to partition each other with the upright portion 25a interposed therebetween, and the first member 25A and the second member 25B extend in the longitudinal direction of the halogen heater in a curved manner. May be. Further, the first member 25A and the second member 25B may be raised in an oblique direction with respect to the nip forming surface of the nip forming member 24.

  Next, the arrangement of heat sources that can be used for recording materials of special sizes such as A3 Novi will be described. FIG. 5 is a schematic diagram showing the arrangement of the heating portions of the halogen heater and the end heater. As shown in FIG. 5, a first halogen heater 23A having a dense light distribution at the center in the longitudinal direction and a second halogen heater 23B having a dense light distribution at both ends in the longitudinal direction are arranged. Yes. That is, the first halogen heater 23 </ b> A heats the central range of the fixing belt 21, and the second halogen heater 23 </ b> B heats the side range of the fixing belt 21.

  The heat generating part 40A of the first halogen heater 23A corresponds to a recording material of a small size such as A4 vertical size, for example, and the heat generating part 40B of the second halogen heater 23B has an A3 vertical size that cannot be covered by the first halogen heater 23A. Covers the edge range of the largest standard size recording material that can be used. That is, the heat generating unit 40 including the heat generating units 40A and 40B of both halogen heaters corresponds to the maximum standard size paper width and does not cover the nobi size paper width larger than the maximum standard size.

  On the other hand, the end heaters 26a and 26b have heating portions 42a and 42b that are located at positions corresponding to both ends in the longitudinal direction of the second halogen heater 23B and heat both ends of the nobi size paper width larger than the maximum regular size. Further, part of the heat generating portions 42a and 42b of the end heaters 26a and 26b overlaps the heat generating portion 40B of the halogen heater 23B. As a result, the fixing device 20 can cope with both ends of the nobi size paper width larger than the maximum standard size.

  Here, the amount of heat (heating output) actually output from the halogen heater and the end heater will be described. FIG. 6 is a schematic diagram showing the positional relationship between the heat generating portions of the second halogen heater 23B and the end heater 26b and the heating output of each heater. The upper part of FIG. 6 shows the state of the right end of the heat generating part of the second halogen heater 23B, and the lower part of FIG. 6 shows the state of the left side of the heat generating part of the end heater 26b.

  Generally, in the halogen heater, the heating output is reduced at the longitudinal end portion of the heat generating portion (portion where the filament is spirally wound). This also changes depending on the winding density of the filament, and is more likely to decrease if the winding density is sparse. As shown in the upper part of FIG. 6, the heat generating part 40B of the second halogen heater 23B ranges from a part that outputs a predetermined heating output of 100 (%) to a part where the heat output is reduced and the heating output becomes 50%. For example, it can be defined.

  Further, as shown in the lower part of FIG. 6, the end heater 26 b also has a reduced heating output at the end in the longitudinal direction of the heat generating part 42 b (the part where the heat generating pattern 37 is provided). In other words, 100% of the predetermined heating output is not output at the end, and the heating output is sag.

  For this reason, when a drop in heating output occurs at the ends of the second halogen heater 23B and the end heater 26b, good fixing is performed particularly at the end of a recording material having a larger size than the maximum standard size. There is a risk of not.

  Therefore, in this embodiment, as shown in FIG. 6, the boundary Bh at which the heating output at the heat generating portion 40B of the second halogen heater 23B begins to decrease and the boundary Bc at which the heating output at the heat generating portion 42b of the end heater 26b begins to decrease. To match. In an actual apparatus, the halogen heater 23B and the end heater 26b are arranged apart from each other in the space, and therefore, the boundaries Bh and Bc coincide with each other in the longitudinal direction in a projected state. The same applies to the other end heater 26a.

  Thereby, in the area | region where the halogen heater 23B and the both-ends heaters 26a and 26b overlap, the heating output does not decrease and 100% of the predetermined heating output can be maintained. Therefore, it is possible to guarantee good fixing particularly at both ends of a recording material having a nobi size larger than the maximum standard size.

  As described above, in the present embodiment, the boundary Bh of the second halogen heater 23B and the boundary Bc of the end heater 26b are matched. However, as described above, since the nip forming unit has the heat transfer assisting member 27 with good thermal conductivity, it is possible to level out a certain decrease in heating output. Therefore, a predetermined allowable range may be provided in the arrangement of the boundary where the heating output of the both end heaters 26a and 26b starts to decrease.

  Next, how to set the end portion near the center of the end heater (the boundary Bc at which the heating output begins to decrease) will be described in three patterns using a graph of the heating output. The position where the boundary Bc is set has a predetermined allowable range.

(First pattern)
FIG. 7 is a graph showing the heating output of the second halogen heater. The depiction of the graph shows the output at one end for convenience of explanation. In FIG. 7, the vertical axis represents the output ratio (%) with respect to a predetermined heating output, and the horizontal axis represents the position in the longitudinal direction of the halogen heater 23. The graph of the heating output draws a curve having a convex peak in the longitudinal direction.

  In the case of the heating output shown in FIG. 7, the boundary Bc of the end heater 26 (the boundary where the heating output near the center in the longitudinal direction in the heat generating part 42b starts to decrease) is closer to the end in the longitudinal direction in the second halogen heater. It is set to a range (a range indicated by A in the figure) from a location where the peak heating output is 40% to a location where the peak heating output is located 80% of the peak heating output. If the boundary Bc of the end heater 26 is set in such a range, the heating output at the end portions of the end heater 26 and the second halogen heater 23B can be within an allowable range.

(Second pattern)
FIG. 8 is a graph showing the heating output states of a halogen heater having a heat generating part in the central range and a halogen heater having a heat generating part in the side range. The heating output of the halogen heater having the heat generating portion in the central range corresponding to the first halogen heater 23A is shown by a broken line graph, and the heating output of the halogen heater having the heat generating portion in the side range corresponding to the second halogen heater 23B is shown by a solid line. It shows with. A plurality of halogen heaters having different light distributions in the longitudinal direction and thus having different heating output patterns can have different patterns of total heating output.

  FIG. 9 is a graph showing the heating output of the first and second halogen heaters. As shown in FIG. 9, in the graph of the heating output, the output ratio rises to 100% in the vicinity of both end portions, and is gentle at almost 100% in the central region in the longitudinal direction.

  Here, the range where the heating output is approximately 100% is defined as length (B), and the range where the output ratio is approximately 100% to 40% is defined as length (C). At this time, the boundary Bc of the end heater 26 is arranged in a range from a position where the output ratio is 40% of the heating output to a length D that satisfies (C + B × 1/10) toward the center in the longitudinal direction. . If the boundary Bc of the end heater 26 is arranged in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

(Third pattern)
FIG. 10 is a graph showing another example of the heating output of the first and second halogen heaters. As shown in FIG. 10, the central area of the graph is gentle, but both ends thereof are higher than the central area. When the filament of the heat generating part of the second halogen heater 23B is wound more densely than the filament of the heat generating part of the first halogen heater 23A, such a shape is obtained.

  Here, a range sandwiched between both ends where the heating output is approximately 100% is defined as length (B '), and a range where the output ratio is approximately 100% to 40% is defined as length (C). At this time, the boundary Bc of the end heater 26 is within a range from a position where the output ratio is 40% of the heating output to a length D ′ that satisfies (C + B ′ × 1/10) toward the center in the longitudinal direction. Be placed. If the boundary Bc of the end heater 26 is arranged in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

Next, an advantageous configuration of the fixing device of the present invention will be described.
Since the heat transfer assisting member 27 is in sliding contact with the inner surface of the fixing belt 21, if a metal material such as copper or aluminum is used as it is, the friction coefficient increases. If the friction coefficient is large, the unit torque becomes large, causing problems such as shortening the life of the apparatus.

  Therefore, it is desirable that the belt sliding contact surface 27a (see FIG. 3) facing (contacting) the fixing belt 21 of the heat transfer assisting member 27 is smooth and further subjected to a low friction process. Specifically, the friction between the heat transfer assisting member 27 and the inner surface of the fixing belt 21 is reduced by applying fluorine-based paint or coating such as PFA or PTFE. It is also desirable to apply a lubricant such as fluorine grease or silicone oil between the heat transfer assisting member 27 and the inner surface of the fixing belt 21, and the friction can be further reduced.

  Next, a temperature detection unit different from the temperature sensor 29 shown in FIG. 2 for detecting the temperature of the fixing belt 21 heated by the end heater 26 will be described. Using a contact-type sensor (for example, a thermistor) for detecting the temperature of the fixing belt 21 has the advantage of being inexpensive and highly accurate. However, there is a possibility that a minute sliding contact mark may be generated at the contact position, or a minute gloss unevenness may occur in the image at the corresponding position. For this reason, especially in color image output machines, it is the mainstream not to use a contact type sensor within a standard size paper width.

  By the way, in the Nobi size recording material, the Novi part is the ear part when forming an image up to the edge of the maximum standard size paper edge, a line image called a register mark used for printing alignment, or a small area for color confirmation The solid patch is used as the part to be imaged. And it is often cut finally. Therefore, even if a contact mark is generated by the contact-type temperature detection unit, it can be said that minute gloss unevenness does not appear as an abnormal image.

  Therefore, in this embodiment, as shown in FIG. 11, temperature detectors 45 a and 45 b (45 a is provided at the opposite end portion) that detects the temperature of the portion heated by the end heaters 26 a and 26 b of the fixing belt 21. Therefore, it is provided outside the fixing belt 21 and outside the maximum standard size paper width and inside the nobi size paper width larger than the maximum standard size in the longitudinal direction of the fixing belt 21. . Thereby, the temperature can be detected with high accuracy at low cost without revealing an abnormal image such as minute uneven gloss. Of course, a non-contact type temperature detection unit may be used in order to prevent an abnormal image such as minute uneven glossiness from occurring even in the image range of the nobby portion.

  Although the configuration for detecting the temperature of the portion heated by the end heaters 26a and 26b of the fixing belt 21 has been described, a sensor for detecting the temperature of a part of the end heater itself is provided, and the end heater is based on the detection result. It is also possible to apply a method for controlling the above.

Next, a configuration capable of fixing quickly without increasing the operating load even in a cold state will be described.
As described above, the heat transfer assisting member 27 is in sliding contact with the inner surface of the fixing belt 21. By applying a lubricant such as fluorine grease or silicone oil between the heat transfer assisting member 27 and the inner surface of the fixing belt 21, the friction coefficient can be reduced.

  Here, the heat transfer assisting member 27 does not actively absorb the lubricant on the sliding surface. Therefore, the use of fluorine grease or the like having good retention as the lubricant has an effect of suppressing the unit torque from increasing with time.

  However, fluorine grease, in particular, has a property that its viscosity changes with temperature. In particular, when the fixing device 20 is started in a cold time, the unit torque increases, and the load on the fixing device 20 and the image forming apparatus 1 increases.

  In order to cope with this problem, this embodiment proposes a fixing device that operates in the order of heat generation of the end heaters 26a and 26b, rotation of the fixing belt 21, and heat generation of the halogen heater 23 at the start of operation.

  That is, when the operation of the fixing device 20 is started, first, energization to the end heaters 26a and 26b is started. Next, the detected temperatures of the temperature detectors 45a and 45b are both a predetermined temperature T1 (° C.) (a first temperature at which the starting torque of the fixing device 20 has a predetermined magnitude; a temperature at which the fixing belt 21 may start rotating). At this point, the fixing belt 21 starts to rotate. Alternatively, the rotation of the fixing belt 21 is started when it is determined (estimated) by a thermometer provided inside the image forming apparatus 1. Then, after the fixing belt 21 starts to rotate, the halogen heater 23 is energized. These series of operations are for the following reason.

  Since the surface of the fixing belt 21 facing the halogen heater 23 is directly heated by the heater, the temperature becomes high. On the other hand, the surface of the fixing belt 21 that does not face the halogen heater 23 is not directly heated by the heater, so the temperature is low. As a result, a temperature difference may occur in the circumferential direction or the longitudinal direction of the fixing belt 21.

  Such a temperature difference becomes a “temperature spot” in the circumferential direction of the fixing belt 21 and often does not disappear completely even if the fixing belt 21 is idled for a while. In particular, when starting up an apparatus in a cold state, a large amount of heat moves from the fixing belt 21 toward the pressure roller having a large heat capacity. Therefore, even if the fixing belt 21 is idled for a long time, temperature spots are generated. It becomes difficult to disappear.

  If temperature spots with a large temperature difference are generated, the surface of the fixing belt 21 may be distorted due to a local thermal expansion difference of the fixing belt 21. When the surface of the fixing belt 21 is thus distorted, a good fixing nip portion is not formed, and an image with deteriorated quality is formed.

  Further, when the distortion exceeds the yield stress of the fixing belt 21, buckling failure (kink) may occur in the fixing belt 21. When the fixing belt 21 is kinked, it develops into an abnormal image and further leads to destruction of the fixing belt 21. Such a problem is conspicuous in a fixing device having improved start-up characteristics (temperature rise characteristics) such as the present fixing device.

  Therefore, in order to prevent temperature spots and buckling failure (kink), it is necessary to energize the halogen heater 23 after the fixing belt 21 starts rotating.

  As described above, by starting the operation in the order of energization to the end heaters 26a and 26b, rotation of the fixing belt 21, and energization to the halogen heater 23, the load on the fixing device 20 and the image forming apparatus 1 can be reduced. Durability can be improved (long life).

Next, the operation of the fixing device according to the embodiment will be described using a flowchart.
FIG. 12 is a flowchart illustrating the operation of the fixing device according to the embodiment. Here, the temperature T2 (° C.) is a second temperature (T2> T1) at which the starting torque of the fixing device 20 becomes sufficiently small (a temperature at which the fixing device 20 may be started immediately).

  First, in step S1, the fixing device 20 determines whether the detected temperatures of the temperature detectors 45a and 45b are both higher than the temperature T2 (° C.).

  If the detected temperatures of the temperature detectors 45a and 45b are both higher than the temperature T2 (° C.) (in the case of YES), the starting torque of the fixing device 20 is sufficiently small. In step S <b> 2, the fixing device 20 starts rotating the fixing belt 21. In this case, it is not necessary to energize the end heaters 26a and 26b.

  On the other hand, if at least one of the detected temperatures of the temperature detectors 45a and 45b is equal to or lower than the temperature T2 (° C.) in step S1 (NO), the process proceeds to step S4.

  In step S4, the fixing device 20 determines whether the detected temperatures of the temperature detectors 45a and 45b are both higher than the predetermined temperature T1 (° C.) and lower than the predetermined temperature T2 (° C.).

  That is, at the start of the operation of the fixing device 20, the detected temperatures of the temperature detectors 45a and 45b may show different values (different courses) depending on the content of the previous operation and the time left since the previous operation. If the detected temperatures of the temperature detectors 45a and 45b are both higher than a predetermined temperature T1 (° C.), the starting torque of the fixing device 20 is not more than a predetermined value. From the viewpoint of shortening the first print time, it is desirable to start energization of the end heaters 26a and 26b and rotation of the fixing belt 21 simultaneously. Accordingly, the process proceeds to step S5, and energization of the end heaters 26a and 26b and rotation of the fixing belt 21 are started.

  On the other hand, in step S4, when the detected temperature of at least one of the temperature detectors 45a and 45b is lower than the predetermined temperature T1 (° C.) (in the case of NO), the process proceeds to step S6 and to the end heaters 26a and 26b. Start energizing.

  Next, the process proceeds from step S6 to step S7, and the fixing device 20 waits until the detected temperatures of the temperature detection units 45a and 45b are equal to or higher than a predetermined temperature T1 (° C.) (in the case of NO).

  In step S7, when the detected temperature becomes equal to or higher than a predetermined temperature T1 (° C.) (in the case of YES), the process proceeds to step S8, and the fixing device 20 starts rotating the fixing belt 21.

  As described above, when the detected temperature of either of the temperature detecting units 45a and 45b is lower than the predetermined temperature T1 (° C.), the end heaters 26a and 26b heat the nip forming unit, and the respective detected temperatures are predetermined. When the temperature becomes equal to or higher than T1 (° C.), the fixing belt 21 is rotated. As a result, the difference in starting torque at both ends of the fixing belt 21 can be reduced.

  Next, the process proceeds to step S <b> 3, and the fixing device 20 energizes the halogen heater 23. Next, the process proceeds to step S9, and the image forming preparation of the fixing device 20 is completed. Then, an image forming operation by the entire image forming apparatus is started.

  FIG. 13 is a graph showing the relationship between the temperature near the fixing nip portion and the unit torque in the fixing device. In FIG. 13, the vertical axis represents unit torque (Nm), and the horizontal axis represents the temperature (° C.) near the fixing nip. Plots marked with ○ are unit torques when the rotational linear velocity is 100 (mm / sec), and plots marked with × are unit torques when the rotational linear velocity is 300 (mm / sec).

  As can be seen from the graph, even when the temperature in the vicinity of the fixing nip is the same, the unit torque decreases as the rotational linear velocity decreases.

  If the temperature is the same, a lower rotational linear velocity is advantageous because the starting torque is reduced. In order to shorten the first print time, the rotation should be started early. In a fixing device having a plurality of linear rotation speeds, it is desirable to select a low rotation speed at least until the halogen heater 23 is turned on.

  In this case, the timing for switching the low rotation linear velocity to the high rotation linear velocity may be synchronized with the timing when the halogen heater 23 is turned on. Alternatively, if the temperature in the longitudinal direction and the circumferential direction of the fixing belt 21 is within the temperature deviation that does not cause the above-described temperature spots and buckling failure (kinks), the timing is not necessarily synchronized with the timing when the halogen heater 23 is turned on. Also good. Therefore, the timing may be selected under conditions that are advantageous for increasing the temperature of the fixing belt 21.

  As described above, the fixing device of the present embodiment operates in the order of heat generation of the end heaters 26a and 26b, rotation of the fixing belt 21, and heat generation of the halogen heater 23. Breaking can be avoided and the starting torque can be reduced.

  In the fixing device of the present embodiment, the rotation of the fixing belt 21 is started when the detected temperatures of the temperature detectors 45a and 45b each detect a predetermined temperature (T1). Therefore, the rotation of the fixing belt 21 can be started with the time when the temperature T1 at which the starting torque is reduced becomes a trigger.

  Furthermore, since the fixing device of the present embodiment has a plurality of linear rotation speeds and operates at a low linear rotation speed until at least the heat generation of the halogen heater 23, it is possible to achieve both reduction in starting torque and reduction in first print time.

(Modification)
As a modification, the temperature of the fixing belt 21 may be detected by a temperature sensor 29 provided on the outer peripheral side of the fixing belt 21 instead of the temperature detection units 45a and 45b. Alternatively, the temperature of the fixing belt 21 may be estimated by a temperature sensor provided inside the image forming apparatus 1. Also in these cases, the flowchart of FIG.

  The present invention has been described based on the embodiments. The present invention is not limited to the embodiments, and can be appropriately changed within the scope of the present invention. The image forming apparatus provided with the fixing device of the present invention is not limited to a copying machine or a printer, but may be a facsimile machine or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Bottle accommodating part 2C, 2K, 2M, 2Y Toner bottle 3 Transfer apparatus 4C, 4K, 4M, 4Y Image forming part 5 Photoconductor 6 Charging apparatus 7 Developing apparatus 8 Cleaning apparatus 9 Exposure apparatus 10 Paper feed tray 11 Paper feed roller 12 Registration roller 13 Paper discharge roller 14 Paper discharge tray 20 Fixing device 21, 60 Fixing belt 22 Pressure roller 23A, 23B, 50A, 50B Halogen heater 24 Nip forming member 24a, 24b Recess 24c Surface 25 Stay member 25A First 1 member 25B 2nd member 25a Standing portion 26a, 26b End heater 27 Heat transfer assisting member 27a Nip forming surface 28A, 28B, 70 Reflective member 29 Temperature sensor 30 Intermediate transfer belt 31 Primary transfer roller 32 Secondary transfer backup roller 33 Cleaning Backup roller 34 Tension roller 35 Belt cleaning device 36 Secondary transfer roller 37 Heat generation pattern 41 Separating member 40A, 40B, 42a, 42b Heat generation part 45a, 45b Temperature detection part Bc, Bh Boundary N Fixing nip P Paper α β Irradiation angle

JP 2010-32631 A JP 2014-178370 A

Claims (9)

An endless belt having flexibility;
A pressure member provided outside the belt and facing the belt;
A radiant heat source provided inside the belt;
A nip forming member provided inside the belt and forming a fixing nip between the belt and the pressure member;
A plurality of contact heat transfer type heat sources provided at respective ends of the nip forming member and respectively heating the longitudinal ends of the belt;
A heat transfer auxiliary member that covers each surface of the nip forming member and the plurality of contact heat transfer type heat sources facing the belt and moves heat in a longitudinal direction of the belt;
A fixing device in which a lubricant is applied to the inside of the belt and operates in the order of heat generation of the plurality of contact heat transfer type heat sources, rotation of the belt, and heat generation of the radiation type heat source. A temperature detector for detecting the temperature of the belt;
The fixing device according to claim 1, wherein the belt is rotated when the temperature detection unit detects a predetermined first temperature.   When the temperature detection unit detects a temperature that is higher than the first temperature, higher than the first temperature, and lower than a second temperature at which the starting torque is sufficiently small, the contact heat transfer type heat source is The fixing device according to claim 2, wherein the fixing device generates heat and rotates the belt.   4. The fixing device according to claim 3, wherein when the temperature detection unit detects a temperature higher than the second temperature, the belt rotates and the radiant heat source generates heat. 5. A plurality of temperature detection units for detecting the temperature of the belt heated by the plurality of contact heat transfer type heat sources;
The fixing device according to claim 1, wherein the belt is rotated when each of the plurality of temperature detection units detects a predetermined first temperature.   When the plurality of temperature detection units detect a temperature that is higher than the first temperature, higher than the first temperature, and lower than a second temperature at which the starting torque is sufficiently small, the plurality of contact transmissions. 6. The fixing device according to claim 5, wherein the fixing device generates heat from a heat source and rotates the belt.   7. The fixing device according to claim 6, wherein when the plurality of temperature detection units respectively detect temperatures higher than the second temperature, the belt rotates and the radiation heat source generates heat.   The fixing device according to claim 1, wherein the belt has a plurality of linear rotation speeds, and operates at a low rotation linear speed until at least heat generation of the radiation heat source.   An image forming apparatus comprising the fixing device according to claim 1.

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