JP2018066834A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a phenomenon in which a lubrication function is damaged due to an increase in viscosity caused by mixing of abrasion powder generated through rubbing between a fixing belt and a nip forming member, and torque generated when the fixing belt is driven to rotate is increased.SOLUTION: A fixing device comprises: an endless belt having flexibility; a pressure member that is provided outside the belt and faces the belt; a heat source that heats the belt; a nip forming member that is provided inside the belt and forms a fixing nip between the belt and the pressure member; and a heat transfer auxiliary member that covers a surface of the nip forming member facing the belt. The fixing device arranges first lubricant attached to an inner peripheral surface of the belt and second lubricant obtained by combining at least various types of base oil between the nip forming member and the heat transfer auxiliary member, and the base oil contained in the second lubricant is dropped onto the belt by heating.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device that fixes an image on a recording material, 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 the image forming devices, the fixing device consumes a lot of power and has a lot of room for energy saving, so various proposals have been made. However, in order to save energy and improve the first print time, lower the heat capacity of the members. As we proceeded, further problems occurred. In the fixing device, when a recording material (small size paper) having a width smaller than the heating width of a heat source (heater) for heating the fixing belt is passed, the temperature in the width direction of the fixing belt (direction perpendicular to the paper conveyance direction) , A so-called edge temperature rise occurs in which the temperature rise in a region outside the sheet passing range becomes significant. This is because the heat transfer in the width direction of the fixing belt is hindered by the thinning of the fixing belt. In addition, a member constituting the fixing device such as a pressure roller / belt may reach a temperature higher than the heat resistance temperature, and the temperature outside the sheet passing range must be suppressed to protect the member. There was a problem (CPM down) that the productivity of passing paper had to be reduced. Furthermore, there is another problem that the toner is hot-offset near the end of the recording material (near the end in the width direction) due to the rise in the end temperature. In order to deal with these problems, for example, Patent Document 1 proposes a configuration in which a good heat conducting member is arranged in the fixing nip so as to reduce the temperature gradient in the axial direction at the fixing nip.

  In order to increase the axial temperature uniformity at the fixing nip, it is preferable to use a good heat conduction member such as copper or aluminum as a heat transfer auxiliary member. However, because of the good heat conductivity when warming up from room temperature, There is a problem that the heat of the fixing belt is absorbed by the entire moving auxiliary member, the temperature rise of the fixing belt is delayed, and the warm-up time is delayed. Since the above-mentioned temperature rise at the end is longer than the warm-up time as a time axis, if a thin thermal resistance layer is provided on the surface of the heat transfer assisting member, a significant delay in the warm-up time can be prevented. This is a negative factor in ensuring the uniformity of the axial temperature.

  The fixing nip is a part for fixing the toner to the recording material by the applied pressure, and a sliding resistance is generated between the fixing belt and the heat transfer assisting member, so it is necessary to reduce the friction. Conventionally, a sliding contact sheet made of a material such as fluorine is provided on the surface of the heat transfer auxiliary member. Such means can lower the sliding resistance, but if the adhesion to the heat transfer auxiliary member is poor, the temperature gradient relaxation function may be impaired. Furthermore, as a thin-film sliding contact sheet, it is known that a low-torque can be maintained over a long period of time by holding a lubricant in a porous or fibrous sliding contact material. Because of the high heat conductivity. On the other hand, the non-porous material has a problem that the retention of the lubricant is poor and the lubricant flows out from the end face of the fixing belt and the torque increases with time.

  Among these problems, the adhesion problem can be solved by coating the heat transfer auxiliary member with a low friction material, but for the retention of the lubricant, it is necessary to provide a lubricant supply member separately, Further, there is a problem that a low-viscosity lubricant tends to flow out from the end face of the fixing belt, and a high-viscosity lubricant does not stabilize the outflow from the lubricant supply member. Also, the sliding contact surface at the fixing nip tends to generate wear powder over time, and there is a problem in that the viscosity increases and the torque increases when the lubricant and the wear powder are mixed.

  In view of the above-described conventional problems, the present invention is to increase the viscosity due to mixing of wear powder generated by rubbing between the fixing belt and a nip forming member fixedly disposed inside the fixing belt (in the loop). An object of the present invention is to suppress the phenomenon that the lubrication function is impaired and the torque generated when the fixing belt is driven to rotate is increased.

  To achieve the above object, according to the present invention, an endless belt having flexibility, a pressure member provided outside the belt and facing the belt, a heat source for heating the belt, and the belt A nip forming member that forms a fixing nip between the belt and the pressure member, and a heat transfer auxiliary member that covers a surface of the nip forming member that faces the belt. In the apparatus, a first lubricant adhering to the inner peripheral surface of the belt and a second lubricant having at least a base oil type are arranged between the nip forming member and the heat transfer assisting member, The base oil of the second lubricant is configured to drop onto the belt by heating.

  According to the present invention, the first lubricant adhering to the inner peripheral surface of the belt and the second lubricant at least of the base oil type are arranged between the nip forming member and the heat transfer assisting member, Since the base oil of the second lubricant is dripped onto the belt by heating, the base oil contained in the second lubricant can be removed by heating with a heat source and replenished onto the inner peripheral surface of the belt. It is possible to suppress an increase in viscosity due to the mixing of wear powder generated by rubbing the nip forming member, and to maintain a low torque generated when the belt is driven and rotated.

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 two halogen heaters. 6 is a graph showing the relationship between the weight ratio (wt%) of wear powder contained in the second lubricant and the driving rotational torque of the fixing belt. It is a rough section lineblock diagram showing the concrete composition which arranges the 2nd lubricant between a heat transfer auxiliary member and a nip formation member. It is a schematic diagram which shows the modification which arrange | positions a 2nd lubricant between a heat transfer auxiliary member and a nip formation member. It is a schematic diagram explaining the structure which forms a bulge in the longitudinal center part vicinity of a nip formation member in order to cope with bending. It is a cross-sectional schematic diagram which shows the further modification which arrange | positions a 2nd lubricant between a heat transfer auxiliary member and a nip formation member. It is a figure which shows the modification of a heat transfer auxiliary member, (a) is sectional drawing, (b) is a longitudinal direction schematic front view.

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 denoted by reference numerals, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M are denoted by reference numerals. 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 the 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 The halogen heater represents a radiant heat source as a fixing 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.

  A heat transfer assisting member 27, which is also referred to as a soaking member, for relaxing the temperature gradient in the width direction (longitudinal direction) of the fixing belt is disposed so as to cover the surface of the nip forming member 24 that faces the inner peripheral surface of the belt. Further, it is possible to prevent heat from staying in the end region of the fixing belt 21 when passing small-size paper, and to positively move the heat in the width direction of the fixing belt 21, that is, in the longitudinal direction of the heat transfer auxiliary member 27. , To eliminate the temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer auxiliary member 27 is formed of a material having high thermal conductivity that enables heat transfer in a short time, such as copper or aluminum. 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 substantially L-shaped cross section and composed of a first member 25A and a second member 25B and having a T-shaped cross section as a whole has an upright portion 25a that stands upright on the side opposite to the fixing nip N side. The halogen heaters 23A and 23B as fixing heat sources are arranged so as to be separated by the standing portion 25a, and also function as a partition member. 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. As is well known, the elastic layer of the pressure roller 22 is crushed at a location where the pressure roller 22 is pressed against the fixing belt 21 by the spring of the pressure means and is in pressure contact with the fixing belt 21, thereby fixing the fixing nip having a predetermined width. N is formed. 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 (illustration of a portion accommodating the second lubricant is omitted). As shown in FIG. 3, the nip forming unit includes a nip forming member 24, a stay member 25, and a heat transfer assisting member 27. 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 integral structure of the heat transfer assisting member 27 and the nip forming member 24 may be provided by engaging a claw or the like. A second lubricant 241 is disposed between the nip forming member 24 and the heat transfer assisting member 27 as shown in FIG. 2, which 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.

  FIG. 4 is a perspective view showing configurations of the nip forming unit and the halogen heater. As shown in FIG. 4 and as described above with reference to FIG. 2, 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 23A and a second halogen heater 23B are disposed on both sides of the standing portion 25a in the short direction. That is, the first halogen heater 23A and the second halogen heater 23B are shielded from each other by the standing portion 25a. Further, the first halogen heater 23A and the second halogen heater 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). Irradiation angles α and β (see FIG. 2) become 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 halogen heaters 23A and 23B may be arranged so as to be partitioned from each other with the upright portion 25a interposed therebetween, and the first member 25A and the second member 25B may be curvedly extended in the longitudinal direction of the halogen heater. 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.

  As can be seen from FIGS. 4 and 5, the first halogen heater 23A has a heat generating portion (a portion in which the filament is spirally wound and the light distribution is dense) at the center in the longitudinal direction, and is fixed. The central range of the belt 21 is heated and corresponds to a small size paper such as A4 vertical size. On the other hand, the second halogen heater 23B has heat generating portions at both ends in the longitudinal direction, and heats the side region of the fixing belt 21. For example, when passing a large size paper such as A3 vertical size, not only the first halogen heater 23A but also the second halogen heater 23B is turned on to correspond to the 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.

  In this way, the two halogen heaters 23A and 23B correspond to different sizes of paper. However, when using different sizes of paper, heat is absorbed by the paper in the paper passing area, while heat is lost in the non-paper passing area. In this embodiment, the width of the fixing belt 21 is positively increased by the heat transfer auxiliary member 27 formed of a material having high thermal conductivity. The heat is moved in the direction, that is, the longitudinal direction of the heat transfer assisting member 27 to eliminate the temperature non-uniformity in the longitudinal direction.

  However, since the heat transfer assisting member 27 is in sliding contact with the inner peripheral surface of the fixing belt 21, a friction coefficient is increased when a material having high thermal conductivity such as copper or aluminum is brought into sliding contact with the inner peripheral surface of the fixing belt 21 as it is. There are problems such as a large unit torque and a shortened device life. Therefore, the belt sliding contact surface 27a (see FIG. 3) facing (contacting) the fixing belt 21 of the heat transfer assisting member 27 is made as smooth as possible (excluding the space for accommodating the second lubricant 241), and is low. It is also desirable to apply a friction treatment. Specifically, fluorine-based paint or coating such as PFA or PTFE is applied.

  In this embodiment, the sliding resistance is further reduced by interposing a lubricant between the heat transfer assisting member 27 and the inner peripheral surface of the fixing belt 21. At this time, a second lubricant 241 that is a further lubricant is added to suppress problems caused by wear powder generated over time between the heat transfer assisting member 27 and the inner peripheral surface of the fixing belt 21. ing. That is, as shown in FIG. 2, first, the first lubricant 240 is attached to the inner peripheral surface of the fixing belt 21, and the heat transfer is caused by the fixing belt 21 being rotated by the rotation of the pressure roller 22. It also adheres to the surface of the auxiliary member 27. As the lubricant, fluorine oil or silicone oil can be used as the base oil, a thickener as the additive, and grease containing PTFE or the like as the solid lubricant. In this example, the base oil is fluorine oil. . Low torque is maintained by using semi-fluid or extremely soft grease having a consistency of about 0 to 0. Since the structure using fluorine oil as the base oil has higher heat resistance and is chemically stable than when silicone oil is used, even if there is a heat source in the fixing belt 21, volatilization loss and alteration can be suppressed. it can.

  On the other hand, in accordance with the type of the base oil of the first lubricant 240, in the present embodiment, the second lubricant 241 whose base oil is a fluorine oil is attached in advance between the heat transfer assisting member 27 and the nip forming member 24. Is arranged. The second lubricant 241 is accommodated in at least one recess provided in the nip forming member 24 as long as the pressure of the fixing nip N does not decrease. The holding volume of the second lubricant 241 may be increased by increasing the depth of the concave portion of the nip forming member 24. Further, a recess may be formed on the heat transfer auxiliary member 27 side, and the holding volume of the second lubricant 241 may be increased by forming a recess on both the nip forming member 24 and the heat transfer auxiliary member 27. . The temperature of the fixing nip N is controlled so that the temperature is maintained within a predetermined range in terms of its function, whereby the second lubricant 241 held by the heat transfer from the heated fixing belt 21 is performed. Therefore, oil separation is stably promoted, and only the fluorine oil in the grease is transferred to the fixing belt 21. Further, by disposing the second lubricant 241 on the heat transfer assisting member 27 located in the temperature-controlled fixing nip N, the lubricant is excessively heated and the base oil is abnormally evaporated and reduced. It is also possible to suppress generation of substances that may impair environmental performance such as TVOC (total volatile organic compounds) and UFP (ultrafine particle dust).

  The fluorine oil that is the base oil of the second lubricant 241 may have a lower viscosity than the fluorine oil of the first lubricant 240. Since the first lubricant 240 is directly irradiated by the halogen heaters 23A and 23B for a long time, the first lubricant 240 evaporates from a low molecular weight and becomes highly viscous. By reducing the viscosity of the second lubricant 241 that is not directly irradiated to the halogen heaters 23A and 23B, the viscosity of the entire lubricant that adheres to the inner peripheral surface of the fixing belt 21 when mixed with the first lubricant 240 increases. Can be suppressed.

  FIG. 6 shows the relationship between the weight ratio (wt%) of wear powder contained in the second lubricant and the driving torque of the fixing belt 21. As the wear powder mixing ratio increases, the viscosity increases and the driving rotational torque increases. This is because the viscosity is increased by adding abrasion powder in addition to the liquid base oil and the solid thickening component.

  Further, when transferring the fluorine oil from the second lubricant 241 to the fixing belt 21, it is not switched to the high temperature heating rotation mode at the time of printing operation, but is switched to the oil separation promotion mode in which the heat source is further increased to promote oil separation. It is conceivable to execute. In the oil separation promotion mode, even when the first lubricant 240 deteriorates and decreases over time and the torque increases due to thickening, the base oil movement from the second lubricant 241 is forcibly promoted, Low torque is maintained. The switching control to the oil separation promotion mode may be performed every regular number of sheets or may be performed at regular time intervals. In general, when the number of sheets passed is increased, the abrasion powder generated from the fixing belt 21 and the abrasion powder from the portion coated on the heat transfer assisting member 27 are mixed with the lubricant to increase the viscosity. A low torque can be maintained by periodically performing the oil separation promotion mode.

  FIG. 7 shows a specific configuration in which the second lubricant 241 is disposed between the heat transfer assisting member 27 and the nip forming member 24 in the fixing nip N. In the fixing device of FIG. 7, a plurality of grooves 242 are formed in the longitudinal direction on the side of the nip forming member 24 facing the heat transfer assisting member 27 to form a second lubricant recess. On the other hand, in the fixing device shown in FIG. 2, it should be understood that the second lubricant is accommodated in one groove. The second lubricant stored in this manner is sealed when the heat transfer assisting member 27 and the nip forming member 24 are brought into close contact with each other by the pressure from the pressure roller 22 when the apparatus is in operation, and the lubricant flows between the grooves. Is blocked. However, when the apparatus is not in operation, the pressure roller releases pressure in order to prevent compression set of rubber, and has a known mechanism for that purpose. In this pressure release state, the pressure between the heat transfer auxiliary member 27 and the nip forming member 24 is also reduced, a lubricant flow path is generated, and the base oil gradually moves downward from the groove in the vertical direction to move the heat. It flows out between the auxiliary member 27 and the nip forming member 24 and drops onto the inner peripheral surface of the fixing belt 21. When the pressure is released, the heat source is not heated. Therefore, the temperature decreases with time, and the outflow of the lubricant is gradually suppressed and does not continue to flow out. With such a configuration, it is possible to prevent the second lubricant 241 from flowing out to the fixing belt 21 in a short time.

  FIG. 8 shows a modification regarding the configuration in which the second lubricant 241 is disposed between the heat transfer assisting member 27 and the nip forming member 24. In this configuration example, the through groove 243 is provided so as to penetrate the plurality of grooves 242 formed in the nip forming member for accommodating the lubricant. As described above, when the pressure from the pressure roller 22 is released, the pressure between the heat transfer assisting member 27 and the nip forming member 24 is also reduced, so that the base oil of the lubricant is directed downward from above in the vertical direction. Flowing. However, the stay member 25 that supports the nip forming member 24 and the heat transfer auxiliary member 27 is fixed and held on the side plate of the fixing device 20 or a separately provided holder at both ends in the longitudinal direction. In order to cope with this, the nip forming member 24 has a stay contact portion 244 in the vicinity of its longitudinal center as shown in FIG. There is a case where it is configured to be higher by the amount of deflection that is assumed in advance. In such a configuration, even when the pressure roller 22 is depressurized when the apparatus is not in operation and the bending of the stay member 25 is eliminated, the pressure in the longitudinal center portion is hardly eliminated. That is, in the central portion in the longitudinal direction, the pressure between the heat transfer assisting member 27 and the nip forming portion 24 is high, and the flow of the second lubricant 241 is likely to be hindered. Therefore, a vertical through groove 243 is provided in the central portion in the longitudinal direction to promote the flow of the second lubricant 241. Although one groove is depicted in this example, a plurality of grooves may be used, and the shape is not limited as long as the second lubricant 241 is dropped downward in the vertical direction.

  Yet another modification is shown in FIG. In this configuration example, the plurality of grooves 242 ′ are provided in the nip forming member 24 as concave portions for the lubricant as in the examples according to FIGS. 7 and 8, but in the fixing nip N region, the upstream side in the belt rotation direction is vertical. In the case of the lower side in the direction, the width of the groove is narrower toward the lower side in the vertical direction. The temperature in the fixing nip is higher on the upstream side of the nip, and the temperature is lowered on the downstream side due to heat transfer to the paper and toner. By narrowing the width of the groove provided in the nip forming member 24 toward the upstream side, the base oil whose viscosity has been reduced can be uniformly diffused in the belt width direction by capillary action, and is dropped onto the fixing belt 21. Variations in the amount of lubricant 2 are less likely to occur.

  Further, the portion to be dripped onto the fixing belt 21 is formed by distributing a plurality of grooves cut in the vertical direction in the longitudinal direction of the nip forming member 24, thereby stabilizing the dripping of the lubricant onto the fixing belt. Also good.

  FIG. 11 shows a configuration for more appropriately dropping the lubricant across the width direction of the fixing belt 21 when the second lubricant 241 is dropped on the inner peripheral surface of the fixing belt 21 (for the sake of simplicity of depiction). The depiction of the nip forming member is omitted). As shown in FIG. 11, the heat transfer assisting member 127 is provided with a protruding portion 127 b having a sharp tip at the entire lower end surface in the vertical direction. The first lubricant 240 adhering to the nip forming surface 127a of the heat transfer assisting member 127 from the fixing belt 21 travels along the nip forming surface 127a in the vertical direction and simultaneously fuses with the second lubricant 241. The highly fluid base oil is concentrated on the convex protrusion 127b and dropped again on the fixing belt 21.

  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. In addition, various modifications can be made without departing from the scope of the present invention.

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 second member 25a standing portion 27 heat transfer assisting member 27a nip forming surface 28A, 28B, 70 reflecting 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 40A, 40B, 42a, 42b Heat generation part 41 Separating member 45a, 45b Temperature detection part 240 First lubricant 241 Second lubricant N Fixing nip P Paper α, β Irradiation Corner

JP2015-99352A

Claims (6)

An endless belt having flexibility;
A pressure member provided outside the belt and facing the belt;
A heat source for heating the belt;
A nip forming member provided inside the belt and forming a fixing nip between the belt and the pressure member;
A fixing device having a heat transfer auxiliary member that covers a surface of the nip forming member facing the belt;
A first lubricant adhering to the inner peripheral surface of the belt and a second lubricant at least of a base oil type are arranged between the nip forming member and the heat transfer assisting member, and the second lubricant A fixing device having a configuration in which a base oil of a lubricant is dropped onto the belt by heating.   The fixing device according to claim 1, wherein the second lubricant has a base oil having a viscosity lower than that of the base oil of the first lubricant.   The at least one groove for the second lubricant extending in the width direction of the belt is formed on a surface of the nip forming member facing the heat transfer assisting member. The fixing device according to 1 or 2.   The fixing device according to claim 1, wherein a plurality of the grooves are provided, and the plurality of grooves are connected by a groove that crosses the grooves.   The fixing device according to claim 3, wherein a plurality of the grooves are provided, and the width of the grooves is narrower toward the upstream side in the belt rotation direction.   An image forming apparatus comprising the fixing device according to claim 1.

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