JP6859994B2 - Fixing device and image forming device - Google Patents

Description

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

In image forming devices such as printers, copiers, and facsimiles, unfixed toner images are transferred to recording medium sheets, printing paper, and photosensitive by the image transfer method or the direct method by the image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. It is formed on a recording medium such as paper or electrostatic recording paper. As a fixing device for fixing an unfixed toner image, a contact heating type fixing device such as a thermal roller method, a film heating method, and an electromagnetic induction heating method is widely adopted.

In these fixing devices, when the fixing member is heated to a predetermined temperature by a heating source, if the heating time to the predetermined temperature can be shortened, the energy consumption can be significantly reduced. In order to achieve this, it has been proposed to use a thin-walled belt having a low heat capacity composed of a metal base material and an elastic rubber layer as a fixing member (see Patent Document 1).

As shown in FIG. 8, this fixing device includes an endless belt 100, a pipe-shaped metal heat conductor 200 arranged inside the endless belt 100, and a heat source 300 arranged inside the metal heat conductor 200. A pressure roller 400 is provided which comes into contact with the metal heat conductor 200 via the endless belt 100 to form a nip portion N. The endless belt 100 is rotated by the rotation of the pressure roller 400, and at this time, the metal thermal conductor 200 guides the movement of the endless belt 100. Further, the endless belt 100 is heated by the heat source 300 in the metal heat conductor 200 via the metal heat conductor 200, so that the entire endless belt 100 can be heated. As a result, the first print time from the heating standby can be shortened, and the shortage of heat amount at the time of high-speed rotation can be solved.

However, in order to further save energy and improve the first print time, it is necessary to further improve the thermal efficiency. Therefore, a configuration has been proposed in which the endless belt is directly heated (without using the metal heat conductor) instead of indirectly heating the endless belt via the metal heat conductor (see Patent Document 2).

In this configuration, as shown in FIG. 9, the pipe-shaped metal thermal conductor is removed from the inside of the endless belt 100, and instead, a plate-shaped nip forming member 500 is provided at a position facing the pressure roller 400. There is. In the case of this configuration, since the endless belt 100 can be directly heated by the heat source 300 except for the portion where the nip forming member 500 is arranged, the heat transfer efficiency is significantly improved and the power consumption is reduced. This makes it possible to further shorten the first print time from the time of waiting for heating. In addition, cost reduction can be expected by not providing a metal thermal conductor.

In the configuration in which the endless belt is directly heated as shown in FIG. 9, various stresses act on the endless belt 100. For example, as shown in FIG. 10A, the belt 100 passing through the nip portion N has a shearing force (white outline) due to the rotational driving force of the pressure roller 400 and the frictional force generated between the nip forming member 500. (Indicated by the arrow) works. Further, as shown in FIG. 3B, the rotating belt is displaced to either one in the axial direction, and at that time, the end face of the belt 100 is in sliding contact with the belt holding member 600 that regulates the displacement of the belt 100. Shear force acts on. Further, as shown in FIG. 6C, in order to improve the separability when separating the paper from the belt surface, it is desired that the cross-sectional shape of the belt 100 be a shape other than a perfect circle. Due to the change in curvature between the X and Y parts, a repeated bending force acts on the belt 100.

In the configuration in which the endless belt is directly heated (FIG. 9), the stress generated by these forces tends to be concentrated on the end of the belt. Therefore, the end portion of the belt is easily damaged, and the durability of the belt is difficult.

Therefore, an object of the present invention is to provide a fixing device having improved durability of the fixing belt, and further to provide an image forming device provided with the fixing device.

In order to solve the above problems, the fixing device according to the present invention includes a rotatable endless fixing belt, a belt holding member that holds the fixing belt at both ends in the axial direction, and a heating source for heating the fixing belt. And a fixing having a nip forming member arranged inside the fixing belt and an opposed rotating body forming a nip portion between the nip forming member and the fixing belt by abutting with the nip forming member via the fixing belt. The apparatus is characterized in that the opposed rotating body and the belt holding member are arranged in a state of being displaced in the axial direction without overlapping in the axial direction.

According to the present invention, since the opposed rotating body and the belt holding member are arranged in a state of being displaced in the axial direction without overlapping in the axial direction, stress concentration around the end portion of the fixing belt is relaxed. To. Therefore, it is possible to prevent damage to the end of the belt during long-term use and improve the durability of the fixing belt, and it is possible to improve the durability of the fixing device and the image forming device.

It is sectional drawing which shows the schematic structure of the image forming apparatus which concerns on one Embodiment of this invention. It is sectional drawing which shows the schematic structure of the fixing device mounted on the image forming apparatus. It is a figure which shows the support structure of the end part of a fixing belt, (a) is a perspective view, (b) is a plan view, (c) is (b) a sectional view taken along the line AA. It is a top view which shows the other embodiment of the belt holding member. It is sectional drawing in the radial direction which shows the modification of the belt holding member. It is sectional drawing which shows the other embodiment of the fixing device. FIG. 6 is an enlarged cross-sectional view showing a nip forming member of the fixing device shown in FIG. It is sectional drawing which shows the schematic structure of the conventional fixing device. It is sectional drawing which shows the schematic structure of another conventional fixing apparatus. It is a figure explaining the stress generated in a belt, (a) is a cross-sectional view in a radial direction, (b) is a perspective view, and (c) is a cross-sectional view in a radial direction.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing for explaining the embodiment of the present invention, components such as members and components having the same function or shape are once described by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, with reference to FIG. 1, the overall configuration and operation of the image forming apparatus according to the embodiment of the present invention will be described.
The image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming portions 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each image forming unit 4Y, 4M, 4C, 4K accommodates developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. It has the same configuration except that it is.

Specifically, each image forming unit 4Y, 4M, 4C, 4K is formed on a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 for charging the surface of the photoconductor 5, and the surface of the photoconductor 5. A developing device 7 for supplying toner, a cleaning device 8 for cleaning the surface of the photoconductor 5, and the like 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 4K are designated by reference numerals, and the other image forming units 4Y, 4M, and 4C have reference numerals. The code is omitted.

Below each of the image forming portions 4Y, 4M, 4C, and 4K, an exposure device 9 for exposing the surface of the photoconductor 5 is arranged. The exposure device 9 has 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 the image data.

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

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, the secondary transfer backup roller 32 is rotationally driven so that the intermediate transfer belt 30 orbits (rotates) in the direction indicated by the arrow in the figure.

Each of the four primary transfer rollers 31 forms an intermediate transfer nip by sandwiching an intermediate transfer belt 30 with each photoconductor 5. Further, a power supply (not shown) is connected to each primary transfer roller 31, 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. Further, similarly to the primary transfer roller 31, a power supply (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

The belt cleaning device 35 has a cleaning brush and a cleaning blade arranged so as to come into contact with the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an inlet of a waste toner container (not shown).

A bottle accommodating portion 2 is provided on the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K accommodating replenishing toner are detachably attached to the bottle accommodating portion 2. A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each of the developing devices 7, and each development is performed from each toner bottle 2Y, 2M, 2C, 2K via this replenishment path. Toner is replenished to the device 7.

On the other hand, at the lower part of the printer main body, a paper feed tray 10 containing the paper P as a recording medium, a paper feed roller 11 for carrying out the paper P from the paper feed tray 10, and the like are provided. Here, the recording medium includes, in addition to plain paper, thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, and the like. Further, although not shown, a manual paper feed mechanism may be provided.

A transport path R for passing the paper P from the paper feed tray 10 through the secondary transfer nip and discharging the paper P to the outside of the apparatus is provided in the printer main body. In the transport path R, a pair of resist rollers 12 as transport means for transporting the paper P to the secondary transfer nip are arranged on the upstream side in the paper transport direction from the position of the secondary transfer roller 36.

Further, a fixing device 20 for fixing the unfixed image transferred to the paper P is arranged on the downstream side in the paper transport direction from the position of the secondary transfer roller 36. Further, a pair of paper ejection rollers 13 for ejecting the paper to the outside of the apparatus are provided on the downstream side of the transport path R in the paper transport direction with respect to the fixing device 20. Further, on the upper surface of the printer main body, a paper discharge tray 14 for stocking the paper discharged to the outside of the device is provided.

Subsequently, with reference to FIG. 1, the basic operation of the printer according to the present embodiment will be described.
When the image-drawing operation is started, each of the photoconductors 5 in each of the image-forming units 4Y, 4M, 4C, and 4K is rotationally driven clockwise by a drive device (not shown), and the surface of each photoconductor 5 is driven by the charging device 6. Is uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9, and an electrostatic latent image is formed on the surface of each photoconductor 5. At this time, the image information to be exposed to each photoconductor 5 is monochromatic image information obtained by decomposing a desired full-color image into yellow, magenta, cyan, and black color information. By supplying toner to the electrostatic latent image formed on each photoconductor 5 in this way by each developing device 7, the electrostatic latent image is visualized (visualized) as a toner image. ..

Further, when the image-drawing operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the drawing to rotate the intermediate transfer belt 30 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 at the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

After that, when the toner image of each color on the photoconductor 5 reaches the primary transfer nip as the photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Is sequentially superposed on the intermediate transfer belt 30 and transferred. Thus, a full-color toner image is supported on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be completely transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. After that, the surface of each photoconductor 5 is statically eliminated by a static elimination device (not shown), and the surface potential is initialized.

At the lower part of the image forming apparatus, the paper feed roller 11 starts rotational driving, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent out to the transport path R is timed by the resist roller 12 and 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 charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip.

After that, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 goes around, the transfer electric field formed in the secondary transfer nip causes the intermediate transfer belt 30 to move on the intermediate transfer belt 30. Toner images are collectively transferred onto the paper P. Further, the residual toner on the intermediate transfer belt 30 that could not be transferred to the paper P at this time is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

After that, 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 to the outside of the device by the paper ejection roller 13 and is stocked on the paper ejection tray 14.

The above description is an image forming operation when forming a full-color image on paper, but a single-color image can be formed by using any one of four image forming units 4Y, 4M, 4C, and 4K. It is also possible to form a two-color or three-color image using two or three image-forming sections.

Next, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 is fixed by a fixing belt 21 as a rotatable fixing rotating body, a pressurizing roller 22 as an opposed rotating body rotatably provided facing the fixing belt 21, and fixing. Radiation from the halogen heater 23 as a heating source for heating the belt 21, the nip forming member 24 arranged inside the fixing belt 21, the stay 25 as a support member for supporting the nip forming member 24, and the halogen heater 23. A reflective member 26 that reflects the light to be reflected onto the fixing belt 21, a temperature sensor 27 as a temperature detecting means for detecting the temperature of the fixing belt 21, a separating member 28 that separates paper from the fixing belt 21, and a fixing belt 21. A belt holding member 40 (see FIGS. 3A to 3C) for holding both ends, a pressurizing means (not shown) for pressurizing the pressurizing roller 22 onto the fixing belt 21 and the like are provided.

The fixing belt 21 is made of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 is formed of a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Alternatively, it is composed of a release layer on the outer peripheral side formed of polytetrafluoroethylene (PTFE) or the like. Further, an elastic layer made of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the base material and the release layer.

The pressure roller 22 includes a core metal 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, fluororubber, or the like provided on the surface of the core metal 22a, and PFA provided on the surface of the elastic layer 22. Alternatively, it is composed of a release layer 22c made of PTFE or the like. The pressurizing roller 22 is pressurized to the fixing belt 21 side by a pressing means (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the position where the pressure roller 22 and the fixing belt 21 are in pressure contact with each other, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. Further, the pressurizing roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer main body. When the pressurizing roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 by the nip portion N, and the fixing belt 21 is driven to rotate.

In the present embodiment, the pressure roller 22 is a solid roller, but it may be a hollow roller. In that case, a heating source such as a halogen heater may be arranged inside the pressurizing roller 22. If there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image and the solid part of the image becomes unevenly glossy. It can occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, it is possible to absorb minute irregularities due to elastic deformation of the elastic layer, so that it is possible to avoid the occurrence of uneven gloss. The elastic layer 22b may be solid rubber, but if there is no heating source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because it has higher heat insulating properties and is less likely to take away heat from the fixing belt 21. Further, the fixing belt 21 and the pressure roller 22 are not limited to the case where they are in pressure contact with each other, and the fixing belt 21 and the pressure roller 22 may be configured to simply contact each other without applying pressure.

Both ends of each of the halogen heaters 23 are fixed to the side plates (not shown) of the fixing device 20. Each halogen heater 23 is configured to generate heat by controlling the output by a power supply unit provided in the printer main body, and the output control is based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. Will be done. By controlling the output of the heater 23 in this way, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. Further, as a heating source for heating the fixing belt 21, an IH, a resistance heating element, a carbon heater or the like may be used in addition to the halogen heater.

The nip forming member 24 has a base pad 241 and a sliding sheet (low friction sheet) 240 provided on the surface of the base pad 241. The base pad 241 is arranged longitudinally along the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and determines the shape of the nip portion N by receiving the pressing force of the pressure roller 22. is there. Further, the base pad 241 is fixedly supported by the stay 25. As a result, the nip forming member 24 is prevented from bending due to the pressure of the pressure roller 22, and a uniform nip width can be obtained in the axial direction of the pressure roller 22. The stay 25 is preferably made of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the bending prevention function of the nip forming member 24. In the present embodiment, the surface of the base pad 241 facing the pressure roller 22 is formed in a flat surface shape, and therefore the nip portion N has a straight shape. By forming the nip portion N into a straight shape, the pressing force by the pressurizing roller 22 can be reduced.

Further, the base pad 241 is made of a heat-resistant material having a heat-resistant temperature of 200 ° C. or higher, which is hard to some extent to ensure strength. As a result, deformation of the nip forming member 24 due to heat is prevented in the toner fixing temperature range, a stable state of the nip portion N is ensured, and the output image quality is stabilized. Materials of the base pad 241 include polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), and polyetheretherketone (PEEK). In addition to general heat-resistant resins, metals, ceramics, etc. can be used.

The sliding sheet 240 is arranged on the surface of the base pad 241 facing at least the fixing belt 21. As a result, the base pad 241 indirectly contacts the fixing belt 21 via the sliding sheet 240. Since the fixing belt 21 slides with respect to the sliding sheet 240 during the rotation of the fixing belt 21, the frictional force generated in the fixing belt 21 is reduced, and the driving torque of the fixing belt 21 is reduced. It is also possible to have a configuration that does not have the sliding sheet 240.

The reflection member 26 is arranged between the stay 25 and the halogen heater 23. In this embodiment, the reflective member 26 is fixed to the stay 25. As the material of the reflective member 26, aluminum, stainless steel, or the like can be used. By arranging the reflecting member 26 in this way, the light radiated from the halogen heater 23 to the stay 25 side is reflected to the fixing belt 21. As a result, the amount of light emitted to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the transfer of radiant heat from the halogen heater 23 to the stay 25 and the like, energy saving can be achieved.

Although not shown, shielding members for shielding heat from the halogen heater 23 are provided between the fixing belt 21 and the halogen heater 23 at both ends in the axial direction of the fixing belt 21. As a result, in particular, it is possible to suppress an excessive temperature rise in the non-passing region of the fixing belt during continuous paper passing, and it is possible to prevent deterioration and damage due to heat of the fixing belt.

Further, the fixing device 20 according to the present embodiment has been devised in various configurations in order to further improve energy saving and first print time.

Specifically, the halogen heater 23 allows the fixing belt 21 to be directly heated at a location other than the nip portion N (direct heating method). In the present embodiment, nothing is interposed between the halogen heater 23 and the left side portion of FIG. 2 of the fixing belt 21, and radiant heat from the halogen heater 23 is directly applied to the fixing belt 21 at that portion.

Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in the ranges of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, it is desirable that the thickness of the entire fixing belt 21 is 0.2 mm or less, and more preferably 0.16 mm or less. Further, it is desirable that the diameter of the fixing belt 21 is 30 mm or less.

In the present embodiment, the diameter of the pressurizing roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressurizing roller 22 are made equal to each other. However, the configuration is not limited to this. For example, the diameter of the fixing belt 21 may be formed to be smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressurizing roller 22, the paper P discharged from the nip portion N is easily separated from the fixing belt 21.

Further, as described above, as a result of reducing the diameter of the fixing belt 21, the space inside the fixing belt 21 becomes smaller, but the stay 25 is formed in a concave shape bent at both ends, and the inside of the concave portion is formed. By accommodating the halogen heater 23 in the space, the stay 25 and the halogen heater 23 can be arranged even in a small space.

Further, in order to arrange the stay 25 as large as possible even in a small space, the nip forming member 24 is formed compactly on the contrary. Specifically, the width of the base pad 241 in the paper transport direction is formed to be smaller than the width of the stay 25 in the paper transport direction. Further, in FIG. 2, the heights of the base pads 241 at the upstream end 24a and the downstream end 24b of the base pad 241 with respect to the respective nip portions N or their virtual extension lines E are set to h1 and h2, and the upstream end portions 24a. When the maximum height of the nip portion N or its virtual extension line E in the portion of the base pad 241 other than the downstream end portion 24b is h3, h1 ≦ h3 and h2 ≦ h3. With this configuration, the upstream end 24a and the downstream end 24b of the base pad 241 do not intervene between the bent portions of the stay 25 on the upstream and downstream sides in the paper transport direction and the fixing belt 21. Therefore, each bent portion can be arranged close to the inner peripheral surface of the fixing belt 21. As a result, the stay 25 can be arranged as large as possible within the limited space in the fixing belt 21, and the strength of the stay 25 can be ensured. As a result, the nip forming member 24 can be prevented from bending due to the pressure roller 22, and the fixability can be improved.

Further, in order to secure the strength of the stay 25, in the present embodiment, the stay 25 comes into contact with the nip forming member 24 and extends in the paper transport direction (vertical direction in FIG. 2), and the base portion 25a and the base portion 25a. It is configured to have a rising portion 25b extending from each end on the upstream side and the downstream side in the paper transport direction toward the contact direction (left side in FIG. 2) of the pressure roller 22. That is, by providing the stay 25 with the rising portion 25b, the stay 25 has a horizontally long cross section extending in the pressurizing direction of the pressurizing roller 22, the cross section coefficient becomes large, and the mechanical strength of the stay 25 becomes large. Can be improved.

The strength of the stay 25 is improved by forming the rising portion 25b longer in the contact direction of the pressure roller 22. Therefore, it is desirable that the tip of the rising portion 25b is as close as possible to the inner peripheral surface of the fixing belt 21. However, during rotation, the fixing belt 21 is shaken (disturbed in behavior) to a greater or lesser extent. Therefore, if the tip of the rising portion 25b is brought too close to the inner peripheral surface of the fixing belt 21, the fixing belt 21 will move to the tip of the rising portion 25b. May come into contact with. In particular, in the configuration using the thin fixing belt 21 as in the present embodiment, since the swing width of the fixing belt 21 is large, it is necessary to pay attention to the position setting of the tip of the rising portion 25b.

Specifically, in the case of the present embodiment, the distance d in the contact direction of the pressure roller 22 between the tip of the rising portion 25b and the inner peripheral surface of the fixing belt 21 is at least 2.0 mm, preferably 3.0 mm or more. It is preferable to set it. On the other hand, when the fixing belt 21 is thick to some extent and there is almost no runout, the distance d can be set to 0.02 mm. When the reflective member 26 is attached to the tip of the rising portion 25b as in the present embodiment, it is necessary to set the distance d so that the reflective member 26 does not come into contact with the fixing belt 21.

In this way, by arranging the tip of the rising portion 25b as close as possible to the inner peripheral surface of the fixing belt 21, the rising portion 25b is arranged long in the contact direction of the pressure roller 22. Can be done. This makes it possible to improve the mechanical strength of the stay 25 even in a configuration using a small-diameter fixing belt 21.

Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG.
When the power switch of the printer main body is turned on, electric power is supplied to the halogen heater 23, and the pressurizing roller 22 starts rotationally driving clockwise in FIG. As a result, the fixing belt 21 is driven and rotated counterclockwise in FIG. 2 due to the frictional force with the pressure roller 22.

After that, the paper P on which the unfixed toner image T is supported by the above-mentioned image forming step is conveyed in the direction of arrow A1 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 and the fixing belt 21 in the pressure welding state. It is fed to the nip portion N of the pressure roller 22. The fixing roller 21 heats the side of the paper P on which the unfixed image T is supported, and the heat generated by the halogen heater 23 and the pressing force between the fixing belt 21 and the pressurizing roller 22 cause toner on the surface of the paper P. The image T is fixed.

The paper P on which the toner image T is fixed is carried out from the nip portion N in the direction of arrow A2 in FIG. The tip 28a of the separating member 28 arranged near the outlet of the nip portion N is not in contact with the surface of the fixing belt 21, and forms a separation gap g with the surface. When the tip of the paper P carried out from the nip portion N comes into contact with the tip 28a of the separating member 28, the paper P is separated from the fixing belt 21. After that, the separated paper P is discharged to the outside of the machine by the paper ejection roller and stocked in the paper ejection tray as described above.

Next, a support structure for supporting both ends in the axial direction of the fixing belt 21 will be described with reference to FIGS. 3A to 3C. In this support structure, both ends of the fixing belt 21 are rotatably supported by the belt holding member 40 inserted in the inner circumference thereof. By attaching the belt holding member 40 to a side plate (not shown), the fixing device 20 is incorporated into the image forming device. In addition, in FIGS. 3A to 3C, only the belt holding member 40 on one side is shown, but since the belt holding member on the opposite side has the same configuration, the belt on one side is described below. Only the holding member 40 will be described.

As shown in FIGS. 3A and 3B, the belt holding member 40 projects toward the outer diameter side of the tubular portion 40a having a cylindrical outer peripheral surface and the tubular portion 40a, and moves the fixing belt 21 in the axial direction. It has a flange portion 40b to be regulated. The belt holding member 40 is integrally formed by, for example, injection molding of resin. As shown in FIG. 3C, the tubular portion 40a of the belt holding member 40 is formed in a C-shaped cross section having an axial notch at the position of the nip portion N (the position where the nip forming member 24 is arranged). ing. The tubular portion 40a of the belt holding member 40 is loosely fitted to the inner peripheral surface of the fixing belt 21, and the end portion of the fixing belt 21 is rotatably held by the cylindrical portion 40a. The end of the stay 25 is fixed and positioned on the belt holding member 40.

As shown in FIGS. 3A and 3B, the end of the fixing belt 21 is between the axial end surface of the fixing belt 21 and the facing surface of the belt holding member 40 facing the axial end surface (end surface 401 of the flange portion 40b). A slip ring 41 is arranged as a protective member for protecting the portion. As a result, when the fixing belt 21 is displaced in the axial direction, it is possible to prevent the end portion of the fixing belt 21 from directly contacting the end surface 401 of the flange portion 40b of the belt holding member 40, and the end portion of the fixing belt 21 can be prevented from coming into direct contact with the end surface 401. It can prevent wear and damage. Since the slip ring 41 is fitted on the outer periphery of the cylindrical portion 40a of the belt holding member 40 with a margin, when the end portion of the fixing belt 21 comes into contact with the slip ring 41, the slip ring 41 becomes the fixing belt 21. It is possible to take around. At this time, it is not always necessary to rotate the slip ring 41, and the slip ring 41 may be stationary. As the material of the slip ring 41, it is preferable to apply a so-called super engineering plastic having excellent heat resistance, for example, PEEK, PPS, PAI, PTFE or the like.

In the above support structure, since only both ends of the fixing belt 21 are held by the belt holding member 40, the fixing belt 21 is in a state of being freely deformable except for the nip portion N between both ends. Further, as the nip portion N is made into a straight shape, a force always acts on the fixing belt 21 to deform it into an elliptical shape. Therefore, the rotating fixing belt 21 has a substantially circular cross section in the radial direction at both ends thereof, and has an elliptical shape in the region between both ends having a short axis in the normal direction of the nip portion N in the radial cross section. It transforms so that it becomes.

In the fixing device 20 having such a configuration, when the axial length of the pressure roller 22 is about the same as that of the fixing belt 21 and the pressure roller 22 is arranged so as to overlap with the belt holding member 40 in the axial direction, during long-term use. It was revealed that the end portion of the fixing belt 21 was damaged. Specifically, at the boundary between the portion of the fixing belt 21 that contacts the tubular portion 40a of the belt holding member 40 and the portion that does not contact the tubular portion 40a (the tip edge 403 of the vicinity of the tip of the tubular portion 40a excluding the outer peripheral chamfer 402). It was found to cause circumferential cracks and streaks along the line. As described above, the fixing belt 21 is damaged by the action of the shearing force (FIG. 10 (a)) at the nip portion N, the action of the shearing force (FIG. 10 (b)) at the end of the belt, and further deformation into an elliptical shape. It is considered that this is caused by the fluctuation of the bending force ((c) in the figure) due to the shearing force, and the stress concentration is generated in the region of the fixing belt 21 along the tip edge 403 of the tubular portion 40a.

On the other hand, in the present invention, as shown in FIG. 3B, the pressure roller 22 and the belt holding member 40 are arranged in a state of being displaced in the axial direction without overlapping in the axial direction. In this case, the axial length of the pressurizing roller 22 is shorter than the axial length of the fixing belt 21, and the tip of the belt holding member 40 (the tip of the tubular portion 40a) and the end 22a of the pressurizing roller 22 are shafts. Separate in the direction. As a result, the fixing belt 21 is formed with an axial region L that is not in contact with both the pressure roller 22 and the belt holding member 40 (the tubular portion 40a axially outside the tip edge 403). According to the verification by the present inventors, it has been found that by adopting such a configuration, it is possible to prevent the generation of cracks and streaks at the end of the fixing belt 21. It is considered that this is because the stress concentration near the tip edge 403 of the fixing belt 21 can be relaxed. By preventing damage at the end of the fixing belt 21 in this way, it is possible to improve the durable life of the fixing device 20 and the image forming device.

In order to obtain the above effects, it is desirable that the axial separation distance L between the end portion 22a of the pressure roller 22 and the tip edge 403 of the belt holding member is 3 mm or more, preferably 5 mm or more. ..

FIG. 4 shows another embodiment of the fixing device 20 of the present invention. In the embodiments of FIGS. 3A to 3C, the tubular portion 40a of the belt holding member 40 is formed in a C-shaped cross section, and the nip forming member 24 is accommodated in the notch portion of the tubular portion 40a to accommodate the nip forming member. 24 is arranged over the entire length of the fixing belt 21 in the axial direction. On the other hand, in the embodiment shown in FIG. 4, the tubular portion 40a of the belt holding member 40 is formed into a cylindrical shape without a notch, and the nip forming member 24 is shortened to be between the tubular portions 40a of the belt holding members 40 on both sides. The nip forming member 24 is arranged. At this time, the end portion of the nip forming member 24 is on the central side in the axial direction with respect to the end portion 22a of the pressure roller 22.

Also in this embodiment, similarly to the embodiments shown in FIGS. 3A to 3C, the pressure roller 22 and the belt holding member 40 are arranged in a state of being displaced in the axial direction without overlapping in the axial direction. This makes it possible to prevent cracks and streaks from being generated at the end of the fixing belt 21. The axial separation distance L between the end portion 22a of the pressure roller 22 and the tip edge 403 of the belt holding member 40 is set to 3 mm or more (preferably 5 mm or more). In this case, the value obtained by subtracting the thickness α of the slip ring 41 from the axial distance W between the end surface 401 of the flange portion 40b of the belt holding member 40 and the end portion 22a of the pressure roller 22 is 10 mm or more. Set.

In this configuration, the fixing belt 21 is formed with an axial region L that does not come into contact with any of the pressure roller 22, the nip forming member 24, and the belt holding member 40. In this region, the shape of the fixing belt 21 is not constrained by the pressure roller 22, the nip forming member 24, or the belt holding member 40, and the fixing belt can be freely deformed. Therefore, the stress concentration in the vicinity of the tip edge 403 of the tubular portion 40a of the fixing belt 21 can be relaxed, and the durability of the fixing belt 21 can be improved.

FIG. 5 is a modified example of the tubular portion 40a of the belt holding member 40. In the embodiments of FIGS. 3 (a) to 3 (c) and FIG. 4, the cross-sectional shape of the tubular portion 40a is substantially circular, but in FIG. 5, the cross-sectional shape of the tubular portion 40a is close to a rectangle. With such a configuration, the curvature of the fixing belt 21 becomes large (the radius of curvature becomes small) near the outlet of the nip portion N, so that the separability of the paper P by the tip 28a of the separating member 28 is improved.

FIG. 6 shows another embodiment of the fixing device 20. The fixing device 20 of this embodiment includes three halogen heaters 23 as heating sources. In this case, by making the heat generating region different for each halogen heater 23, it is possible to heat the fixing belt 21 in a range corresponding to various widths of paper. Further, a sheet metal 250 is provided so as to surround the nip forming member 24, and the nip forming member 24 is supported by the stay 25 via the sheet metal 250.

Also in this embodiment, similarly to the embodiments shown in FIGS. 3 (a) to 3 (c) and FIG. 4, the pressure roller 22 and the belt holding member 40 are displaced in the axial direction without overlapping in the axial direction. By arranging with, it is possible to prevent the generation of cracks and streaks at the end of the fixing belt 21.

In the nip forming member 24 shown in FIG. 6, a protruding portion 241a projecting toward the pressure roller 22 is provided at the downstream end of the nip portion N. From such a configuration, as shown in FIG. 7, the outlet of the nip portion N faces the pressure roller 22 side, so that the separability of the paper P can be improved. The nip forming member 24 can also be used as a nip forming member of the fixing device 20 shown in FIG.

In the embodiment shown in FIG. 6, the configurations other than the above are basically the same as the configurations of the embodiment shown in FIG. 2, and therefore duplicate description will be omitted.

The features of the fixing device 20 according to the present invention described above are listed below.

A rotatable endless fixing belt 21, a belt holding member 40 for holding the fixing belt 21 at both ends in the axial direction, a heating source 23 for heating the fixing belt 40, and a nip arranged inside the fixing belt. In the fixing device 20 having the forming member 24 and the opposing rotating body 22 forming a nip portion N between the forming member 24 and the fixing belt 21 by abutting against the nip forming member 24 via the fixing belt 21, the opposed rotating body 22 and the opposing rotating body 22 By arranging the belt holding member 40 in a state of being displaced in the axial direction without overlapping in the axial direction, stress concentration on the fixing belt 21 is alleviated and damage to the end portion of the fixing belt 21 is prevented for a long period of time. It becomes possible to do.

In such a configuration, the belt holding member 40 is provided with a tubular portion 40a inserted into the inner circumference of the fixing belt 21 and a flange portion 40b overhanging on the outer diameter side of the tubular portion, and the tip of the tubular portion 40a and the tip thereof. It can be realized by separating the ends of the opposing rotating bodies 22 in the axial direction. At this time, it is desirable that the separation distance L in the axial direction is 5 mm or more.

By providing the fixing belt 21 with an axial region that does not come into contact with both the opposing rotating body 22 and the belt holding member 40 (see FIG. 3B), stress concentration on the fixing belt is alleviated and the fixing belt is damaged. It is possible to prevent it for a long period of time.

By providing the fixing belt 21 with an axial region that does not come into contact with any of the opposing rotating body 22, the belt holding member 40, and the nip forming member 24 (see FIG. 4), stress concentration in the fixing belt is alleviated and the fixing belt is provided. The durability of the belt can be improved.

It is desirable that the fixing belt 21 is driven to rotate with respect to the opposing rotating body 22.

If the outer peripheral surface shape of the tubular portion 40a of the belt holding member 40 is made non-circular, the separability of the paper P by the separating member 28 is enhanced. A similar effect can be obtained by projecting the nip forming member 24 toward the opposing rotating body 22 at the downstream end of the nip portion N.

Although the embodiment of the present invention has been described above, the present invention is not limited to the fixing device having a thin and small diameter fixing belt in order to improve energy saving and the like as in the above-described embodiment. Further, the fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, and can be mounted on a monochrome image forming device, other printers, copiers, facsimiles, or a combination machine thereof. .. In addition, it goes without saying that various changes can be made without departing from the gist of the present invention.

20 Fixing device 21 Fixing belt 22 Pressurized roller (opposite rotating body)
22a End 23 Halogen heater (heating source)
24 Nip forming member 25 Stay (support member)
28 Separation member 40 Belt holding member 40a Cylinder part 40b Flange part 403 Tip edge (tip)
N Nip part P Paper (recording medium)
g Separation gap

JP-A-2007-334205 Japanese Unexamined Patent Publication No. 2007-23301

Claims (24)

With a rotatable endless fixing belt,
A heating member that heats the fixing belt and
With the nip forming member arranged inside the fixing belt,
An opposed rotating body that forms a nip portion between the fixing belt and the nip forming member by contacting the nip forming member via the fixing belt.
In a fixing device having a belt holding member that holds the fixing belt at both ends in the axial direction and does not hold the fixing belt between both ends in the axial direction.
A tubular portion in which at least a part of the belt holding member is arranged inside the axial end of the anchoring belt in a direction orthogonal to the axial direction of the anchoring belt, and a tubular portion of the tubular portion of the anchoring belt. It has a flange portion that projects outward in a direction orthogonal to the axial direction, and has a flange portion.
It has a slip ring rotatably fitted on the outer periphery of the tubular portion of the belt holding member on the axially outer side of the axial end of the fixing belt.
The entire outer peripheral surface and the entire inner peripheral surface of the slip ring are located between the end surface of the fixing belt and the flange portion, and are located outside the fixing belt in the axial direction.
A fixing device characterized in that the opposed rotating body and the tubular portion of the belt holding member are arranged in a state of being separated from each other in the axial direction. With a rotatable endless fixing belt,
A heating member that heats the fixing belt and
With the nip forming member arranged inside the fixing belt,
An opposed rotating body that forms a nip portion between the fixing belt and the nip forming member by contacting the nip forming member via the fixing belt.
In a fixing device having a belt holding member that holds the fixing belt at both ends in the axial direction and does not hold the fixing belt between both ends in the axial direction.
A tubular portion in which at least a part of the belt holding member is arranged inside the axial end of the anchoring belt in a direction orthogonal to the axial direction of the anchoring belt, and a tubular portion of the tubular portion of the anchoring belt. It has a flange portion that projects outward in a direction orthogonal to the axial direction, and has a flange portion.
It has a slip ring rotatably fitted on the outer periphery of the tubular portion of the belt holding member on the axially outer side of the axial end of the fixing belt.
The size of the total inner diameter of the slip ring is smaller than the outer diameter of the axial end portion of the fixing belt, and the slip ring is not located inside the axial end face of the fixing belt.
A fixing device characterized in that the opposed rotating body and the tubular portion of the belt holding member are arranged in a state of being separated from each other in the axial direction. With a rotatable endless fixing belt,
A heating member that heats the fixing belt and
With the nip forming member arranged inside the fixing belt,
An opposed rotating body that forms a nip portion between the fixing belt and the nip forming member by contacting the nip forming member via the fixing belt.
In a fixing device having a belt holding member that holds the fixing belt at both ends in the axial direction and does not hold the fixing belt between both ends in the axial direction.
A tubular portion in which at least a part of the belt holding member is arranged inside the axial end of the anchoring belt in a direction orthogonal to the axial direction of the anchoring belt, and a tubular portion of the tubular portion of the anchoring belt. It has a flange portion that projects outward in a direction orthogonal to the axial direction, and has a flange portion.
It has a slip ring rotatably fitted on the outer periphery of the tubular portion of the belt holding member on the axially outer side of the axial end of the fixing belt.
The slip ring is not provided inside the axial end surface of the fixing belt in the axial direction.
A fixing device characterized in that the opposed rotating body and the tubular portion of the belt holding member are arranged in a state of being separated from each other in the axial direction. With a rotatable endless fixing belt,
A heating member that heats the fixing belt and
With the nip forming member arranged inside the fixing belt,
An opposed rotating body that forms a nip portion between the fixing belt and the nip forming member by contacting the nip forming member via the fixing belt.
In a fixing device having a belt holding member that holds the fixing belt at both ends in the axial direction and does not hold the fixing belt between both ends in the axial direction.
A tubular portion in which at least a part of the belt holding member is arranged inside the axial end portion of the fixing belt in a direction orthogonal to the axial direction of the fixing belt, and a tubular portion of the fixing belt. It has a flange portion that projects outward in a direction orthogonal to the axial direction, and has a flange portion.
It has a slip ring rotatably fitted on the outer periphery of the tubular portion of the belt holding member on the axially outer side of the axial end of the fixing belt.
Of the fixing belt , the outer peripheral surface in the direction orthogonal to the axial direction does not come into contact with the slip ring, and the slip ring is not located inside the fixing belt in the axial direction from the end surface of the fixing belt.
A fixing device characterized in that the opposed rotating body and the tubular portion of the belt holding member are arranged in a state of being separated from each other in the axial direction. With a rotatable endless fixing belt,
A heating member that heats the fixing belt and
With the nip forming member arranged inside the fixing belt,
An opposed rotating body that forms a nip portion between the fixing belt and the nip forming member by contacting the nip forming member via the fixing belt.
In a fixing device having a belt holding member that holds the fixing belt at both ends in the axial direction and does not hold the fixing belt between both ends in the axial direction.
A tubular portion in which at least a part of the belt holding member is arranged inside the axial end of the anchoring belt in a direction orthogonal to the axial direction of the anchoring belt, and a tubular portion of the tubular portion of the anchoring belt. It has a flange portion that projects outward in a direction orthogonal to the axial direction, and has a flange portion.
It is rotatably fitted to the outer periphery of the tubular portion of the belt holding member on the axially outer side of the axial end of the fixing belt, and the entire surface on the fixing belt side has a slip ring which is a single flat surface.
The opposed rotating body and the tubular portion of the belt holding member are arranged in a state of being separated in the axial direction.
A fixing device characterized in that the fixing belt is provided with an axial region that does not come into contact with any of the opposed rotating body, the belt holding member, and the nip forming member. The fixing device according to any one of claims 1 to 5, wherein the heating member is a halogen heater. The fixing device according to claim 6, further comprising a support member that is arranged inside the fixing belt and supports the nip forming member by coming into contact with the nip forming member. The fixing device according to claim 7, wherein a reflecting member that reflects light radiated from the halogen heater is disposed between the support member and the halogen heater. The fixing device according to any one of claims 1 to 8, wherein the fixing belt and the cylinder portion are in contact with each other. The fixing device according to any one of claims 1 to 4, wherein the flange portion can regulate the axial movement of the fixing belt when the fixing belt moves in the axial direction. The fixing device according to any one of claims 1 to 10, wherein the slip ring can rotate with the fixing belt. The fixing device according to any one of claims 1 to 11, wherein the tip of the tubular portion of the belt holding member and the end of the opposed rotating body are arranged in a state of being separated from each other in the axial direction. The fixing device according to claim 12, wherein the separation distance in the axial direction is 5 mm or more. The fixing device according to any one of claims 1 to 4, wherein the fixing belt is provided with an axial region that does not come into contact with both the opposed rotating body and the belt holding member. The fixing device according to any one of claims 1 to 4, wherein the fixing belt is provided with an axial region that does not come into contact with any of the opposed rotating body, the belt holding member, and the nip forming member. The fixing device according to any one of claims 1 to 15, wherein the end portion of the nip forming member is on the central side in the axial direction with respect to the end portion of the opposed rotating body. The fixing device according to any one of claims 1 to 15, which has a support member that supports the nip forming member, and the end portion of the nip forming member is on the central side in the axial direction with respect to the end portion of the support member. .. The fixing device according to any one of claims 1 to 17, wherein the fixing belt is driven to rotate with respect to the opposed rotating body. The fixing device according to any one of claims 1 to 18, wherein the outer peripheral surface shape of the tubular portion is made into a non-perfect circular shape. The fixing device according to any one of claims 1 to 19, wherein the nip forming member is projected toward the opposed rotating body at the downstream end of the nip portion. The fixing device according to any one of claims 1 to 20, wherein the value obtained by subtracting the thickness of the slip ring from the axial distance between the end face of the flange portion and the end portion of the opposed rotating body is 10 mm or more. .. The fixing device according to any one of claims 1 to 21, wherein the fixing belt has a base material formed of a metal material. The fixing device according to any one of claims 1 to 22, wherein a part of the outer circumference of the slip ring when viewed from the axial direction is on the opposite rotating body side with respect to the surface of the nip forming member that comes into contact with the fixing belt. .. An image forming apparatus including the fixing device according to any one of claims 1 to 23.

Images