JP6763284B2 - Fixing device and image forming device - Google Patents

Description

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

An image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction device thereof is provided with a fixing device for fixing a toner image carried on a recording medium such as paper.

Generally, the fixing device includes a fixing member heated from a heat source such as a heater, and an opposing member that abuts on the fixing member to form a nip portion. When the image forming operation is started by the image forming apparatus and the toner image is transferred to the recording medium (for example, paper), the recording medium is placed between the fixing member and the facing member heated to a predetermined temperature. By passing through the nip portion, the toner supported on the recording medium is heated and melted, and the image is fixed.

In the fixing device configured as described above, there is a problem that the temperature rises excessively in the non-paper-passing region of the fixing member.

On the other hand, there is known a configuration in which a shielding member that shields heat from the heat source is provided between the heat source and the fixing member so as to be movable in the circumferential direction of the fixing member (for example, Patent Documents 1 and 2). reference).

In the fixing device described in Patent Documents 1 and 2, the shielding member can be moved between the retracted position and the shielding position to prevent excessive temperature rise in the non-paper-passing region of the fixing member.

However, the fixing device having such a configuration requires a space for retracting the shielding member, and there is a problem that the device cannot be miniaturized. Further, there is a problem that the configuration for driving the shielding member becomes complicated.

On the other hand, the shielding member fixed at the position between the fixing member and the heat source and the shielding member provided so as to be movable between the fixing member and the heat source are combined to overrise the non-passing area of the fixing member. A configuration for preventing temperature is known (see, for example, Patent Document 3).

The fixing device described in Patent Document 3 has a cylindrical rotatable first blocking member arranged so as to surround the heat source and a non-rotating non-rotating first blocking member arranged so as to cover the stay on the outer peripheral side of the first blocking member. A second blocking member is provided to prevent excessive temperature rise in the non-paper-passing region of the fixing member.

However, the fixing device described in Patent Document 3 has a configuration in which the temperature of the first blocking member itself is raised to heat the fixing member, and the heat of the heat source cannot be efficiently transferred to the fixing member when the fixing device starts up. There's a problem.

An object of the present invention is to provide a fixing device having a simple structure with good heating efficiency at the start of the device while preventing excessive temperature rise in the non-paper-passing region of the fixing member.

In order to solve the above-mentioned problems, the fixing device according to claim 1 of the present invention is used.
With a rotatable fixing member,
A heat source for heating the fixing member and
An opposing member that abuts on the outer peripheral surface of the fixing member to form a fixing nip,
A shielding member arranged between the fixing member and the heat source and shielding heat from the heat source is provided.
In a fixing device for transporting a recording medium carrying a toner image to the fixing nip and fixing the toner image on the recording medium.
The shielding member is provided so as to cover the outer periphery of the heat source.
The shielding member has at least one opening inside at least the maximum passage area of the recording medium.
It has a shielding member holding member which is provided so as to cover a part of the outer periphery of the shielding member and holds the shielding member.
A protrusion is provided on the outer periphery of the shielding member, and a heat insulating layer is formed between the shielding member and the shielding member holding member by the protrusion .

According to the present invention, it is possible to provide a fixing device having a simple structure with good heating efficiency at the start of the device while preventing excessive temperature rise in the non-paper-passing region of the fixing member.

It is a block diagram which shows schematic structure of the image forming apparatus which concerns on embodiment of this invention. It is a block diagram which shows the structure of the fixing device which concerns on embodiment of this invention in a partially cross-sectional view. It is a perspective view which shows the shielding structure which concerns on 1st Embodiment in a partially cross-sectional view. It is a perspective view which shows the shielding structure which concerns on 1st Embodiment in a partially cross-sectional view. It is explanatory drawing explaining the shielding structure which concerns on 1st Embodiment. It is explanatory drawing explaining the shielding structure which concerns on 2nd Embodiment. It is explanatory drawing explaining the shielding structure which concerns on 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the overall configuration of the image forming apparatus according to the embodiment of the present invention will be described. FIG. 1 is a configuration diagram schematically showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 is a color laser printer, and four image forming portions 4Y, 4C, 4M, and 4K are arranged side by side in the center of the printer body along the spreading direction of the intermediate transfer belt 30. Each image forming unit 4Y, 4C, 4M, 4K accommodates 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, it has the same configuration.

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 for charging the surface of the photoconductor 5. A developing device 7 that supplies toner to the surface of the photoconductor 5 and a cleaning device 8 that cleans the surface of the photoconductor 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 4K are assigned color codes, and the other image forming units 4Y, 4C, and 4M have a color code. The code is omitted.

An exposure device 9 that exposes the surface of the photoconductor 5 is arranged below the image forming portions 4Y, 4C, 4M, and 4K. The exposure apparatus 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 arranged above the image forming portions 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, by rotating the secondary transfer backup roller 32, 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 has an intermediate transfer belt 30 sandwiched between the four primary transfer rollers 31 and the photoconductors 5 to form a primary transfer nip. Further, a power supply of the printer main body 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, the power supply of the printer main body 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 is supposed to be done.

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 bottle accommodating portion 2 is provided on the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K accommodating replenishing toner are detachably attached to the bottle accommodating portion 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 is performed from each toner bottle 2Y, 2C, 2M, 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, as is well known, 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 (alignment 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. ing.

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 body, a paper ejection tray 14 for stocking the paper ejected outside the apparatus is provided.

Next, the basic operation of the image forming apparatus will be described. When the image-drawing operation is started, each of the photoconductors 5 in each image-forming unit 4Y, 4C, 4M, and 4K is rotationally driven clockwise in the figure, and the surface of each photoconductor 5 is brought to a predetermined polarity by the charging device 6. It is uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure apparatus 9, and an electrostatic latent image is formed on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is monochromatic image information obtained by decomposing a desired full-color image into yellow, cyan, magenta, 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. ..

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. The intermediate transfer belt 30 is sequentially superposed 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. The surface of each photoconductor 5 is then statically eliminated to initialize the surface potential.

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 toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed at the nip. Is 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 the waste toner container placed in the printer main body. , Will be recovered.

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 monochromatic image can be formed by using any one of four image forming units 4Y, 4C, 4M, 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 will be described. FIG. 2 is a configuration diagram showing a partially cross-sectional view of the configuration of the fixing device according to the embodiment of the present invention.

As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a rotatable fixing member, a pressure roller 22 as an opposing member rotatably provided facing the fixing belt 21, and a fixing belt 21. A halogen heater 23 as a heat source for heating the fixing belt 21, a nip forming member 24 arranged inside the fixing belt 21, and a stay 25 as a supporting member for supporting the nip forming member 24. A shielding member 26 that shields the light radiated from the halogen heater 23, a known pressurizing means that pressurizes the pressurizing roller 22 onto the fixing belt 21, and the like are provided.

The fixing belt 21 heats the side on which the unfixed image of the paper P is supported, and is composed 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.

Both ends of the fixing belt 21 in the axial direction are held by the belt holding member 29 inserted in the inner circumference thereof. In this way, by holding only both ends of the fixing belt 21 by the belt holding member 29, the fixing belt 21 is in a state where it can be freely deformed except for the fixing nip N between both ends. Further, as the fixing nip 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 perfect circular cross section in the radial direction at both ends thereof, and the radial cross section in the region between both ends has an elliptical shape having the normal direction of the fixing nip N as the short axis. Transform so that

In order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is thin and has a small 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 fixing nip N is smaller than the curvature of the pressurizing roller 22, the paper P discharged from the fixing nip N is easily separated from the fixing belt 21.

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 or PFA provided on the surface of the elastic layer 22. 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 known pressurizing means 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 fixing nip N having a predetermined width. Further, the pressurizing roller 22 is configured to be rotationally driven by a known motor. When the pressurizing roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 by the fixing nip 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 heat source such as a halogen heater may be arranged inside the pressurizing roller 22. In addition, when 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. To prevent this, it is desirable to provide an elastic layer with 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 heat 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.

The central axis of the halogen heater 23 is slightly offset from the rotation axis of the fixing belt 21 in a direction away from the fixing nip N, and both ends thereof are fixed to the side plates of the fixing device 20. The halogen heater 23 is configured to generate heat by controlling the output, and the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by controlling the output of the halogen heater 23. Further, as a heat 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. In this embodiment, one halogen heater is provided, but a plurality of halogen heaters may be provided. Further, the position of the central axis of the halogen heater 23 is not limited to this embodiment, and may coincide with the rotation axis of the fixing belt 21.

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 fixing nip 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 fixing nip N has a straight shape. By forming the fixing nip N into a straight shape, the pressing force by the pressurizing roller 22 can be reduced.

The base pad 241 is made of a material that is hard to some extent to ensure strength and has a heat resistant temperature of 200 ° C. or higher. As a result, deformation of the nip forming member 24 due to heat is prevented in the toner fixing temperature range, a stable fixing nip N state is ensured, and 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 may be disposed on the surface of the base pad 241 facing at least the fixing belt 21. As a result, when the fixing belt 21 rotates, the fixing belt 21 slides with respect to the sliding sheet 240, so that the driving torque generated in the fixing belt 21 is reduced and the load due to the frictional force on the fixing belt 21 is reduced. To. It is also possible to have a configuration that does not have the sliding sheet 240.

The shielding member 26 is arranged on the inner peripheral side of the fixing belt 21 so as to cover the outer periphery of the halogen heater 23.

Next, the basic operation of the fixing device will be described.
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 to rotate 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 along the transport path R while being guided by a known guide plate, and the fixing belt 21 and the pressure roller 22 in a pressure-welded state are conveyed. It is sent to the fixing nip N of. Then, the toner image is fixed on the surface of the paper P by the heat generated by the fixing belt 21 heated by the halogen heater 23 and the pressing force between the fixing belt 21 and the pressurizing roller 22.

The paper P on which the toner image is fixed is carried out to the downstream side of the fixing nip N of the transport path R. 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.

[First Embodiment]
Next, the shielding configuration of the first embodiment will be described. FIG. 3 is a perspective view showing a partially cross-sectional view of the shielding configuration according to the first embodiment. FIG. 4 is a perspective view showing a partially cross-sectional view of the shielding configuration according to the first embodiment. FIG. 5 is an explanatory diagram illustrating a shielding configuration according to the first embodiment.

As shown in FIG. 2, the shielding member 26 has a cylindrical shape, is arranged so as to surround the halogen heater 23, and is configured to rotate around the halogen heater 23. The shielding member 26 is composed of a resin material having heat resistance and low friction, or a member obtained by coating a metal plate with a resin having heat resistance and low friction.

At least one opening is provided on the outer periphery of the shielding member 26 other than the longitudinal end of the fixing belt 21. That is, the shielding member 26 has at least one opening inside the maximum passage area of the paper. In the region other than the opening width (paper passage width) of the opening, the radiant heat from the halogen heater 23 is shielded to prevent deterioration of the fixing belt 21 due to excessive temperature rise in the non-paper passing region of the fixing belt 21.

Specifically, as shown in FIG. 3, the shielding member 26 is provided with three openings 26a, 26b, 26c in the circumferential direction of the shielding member 26. Here, for example, the paper size such as A3 portrait and A4 landscape, which is often used in the market, is defined as the paper size A, the paper size such as A4 portrait, which is often used in the market, is defined as the paper size B, and the small size such as a postcard is defined. Paper size C. The opening 26a has an opening width Wa corresponding to the paper size A. The opening 26b has an opening width Wb corresponding to the paper size B. The opening 26b has an opening width Wc corresponding to the paper size C.

The inner peripheral surface of the shielding member 26 may be mirror-treated to be a reflective surface.

As a result, the shielding member 26 can have both a function of shielding radiant heat from the halogen heater 23 and a function of reflecting radiant heat from the halogen heater 23. Further, the absorption rate and the transmittance of the radiant heat of the shielding member 26 can be lowered, and the radiant heat from the halogen heater 23 toward the stay 25 can be reflected toward the fixing belt 21. As a result, the heating efficiency of the fixing belt can be improved.

The method of giving the shielding member 26 a reflective function is not limited to the method of applying a mirror surface treatment to the inner peripheral surface of the shielding member 26, and the material of the shielding member 26 is a material having high reflectance such as aluminum or stainless steel. It may be a method using.

As shown in FIGS. 2 and 4, the shielding member 26 is rotatably held by the shielding member holding member 27 fixed to the bracket 28 holding the halogen heater 23 with screws or the like.

As shown in FIGS. 2, 4 and 5, the shielding member holding member 27 has a semi-cylindrical shape, covers the fixing nip N side of the outer periphery of the shielding member 26, and the shielding member 26 is on the opposite side of the fixing nip N. Has an opening larger than the openings 26a, 26b, 26c of. Then, the shielding member holding member 27 transmits the radiant heat from the halogen heater 23 to the inner peripheral surface of the fixing belt 21 on the opposite side of the fixing nip N through any of the openings 26a, 26b, 26c of the shielding member.

It is preferable to provide a protrusion on the outer periphery of the shielding member 26. Specifically, as shown in FIG. 3, ring-shaped protrusions 26d are provided along the outer peripheral surface at both ends of the shielding member 26 in the longitudinal direction.

As a result, an air layer as a heat insulating layer can be provided between the shielding member holding member 27 and the shielding member 26 so that the heat of the shielding member 26 is not directly transferred to the shielding member holding member 27. Therefore, it is possible to prevent the heat of the shielding member 26 from being transferred to the stay 25 and lowering the heating efficiency. As a result, the heat of the halogen heater 23 can be efficiently transferred to the fixing belt 21 when the fixing device is started up.

The shape, number, and the like of the protrusions 26d are not limited to the above-described aspects, and an air layer may be provided between the shielding member holding member 27 and the shielding member 26. Further, the protrusion 26d is not limited to the mode provided on the outer circumference of the shielding member 26, and may be provided on the inner circumference of the shielding member holding member 27.

As shown in FIGS. 2 and 4, a drive gear 60 is press-fitted into one end of the shielding member 26. A gear 66 is provided on the rotating shaft of the drive motor 67. A gear 64 is provided on the support shaft 65 fixed to the bracket 28 by caulking or the like. Gears 61 and 63 are provided on the transmission shaft 62 fixed to the bracket 28 by caulking or the like. The drive gear 60 is connected to the gear 66 provided on the rotating shaft of the drive motor 67 via the gears 61, 62, 64.

When a signal (a signal for instructing the rotation of the shielding member 26) is sent to the drive motor 67 and the drive motor 67 starts rotating, this rotational force is applied to the drive gear 60 via the gears 66, 64, 63, 61. The shielding member 26 is rotated.

Next, the operation of the shielding configuration of the first embodiment will be described.
The shielding member 26 rotates and moves until the openings 26a, 26b, 26c corresponding to the width of each paper to be passed come to the overheated position (opposite the fixing nip N) closest to the fixing belt 21 and the paper is passed. The fixing belt 21 is heated according to each paper width.

Specifically, for example, when paper of paper size A is passed through, the opening 26a corresponding to the paper size A is shielded so as to be located on the opposite side of the fixing nip N as shown in FIG. The member 26 is rotationally moved by the drive motor 67. When the paper of the paper size B is passed, the shielding member 26 is rotationally moved by the drive motor 67 so that the opening 26b corresponding to the paper size B is located on the opposite side of the fixing nip N. When paper of paper size C is passed, the shielding member 26 is rotationally moved by the drive motor 67 so that the opening 26c corresponding to the paper size C is located on the opposite side of the fixing nip N.

When an abnormality such as paper clogging is detected, the shielding member 26 is rotationally moved by the drive motor 67 so that the gaps 26a, 26b, and 26c of the shielding member 26 are located on the opposite side of the fixing nip N. Shields between the halogen heater 23 and the fixing belt 21.

As a result, it is possible to shield the area unnecessary for heating the fixing belt 21 according to the paper size. Therefore, even when the transfer paper having a narrow paper width is continuously passed, the non-passing region of the fixing belt 21 does not become an overheated state, and the productivity is lowered in order to eliminate the overheated state. You don't even have to.

Further, by executing the switching operation of the openings 26a, 26b, 26c according to the paper size, the shielding area can be changed for each paper passing size, and the fixing efficiency can be improved.

Further, by having a rotatable cylindrical shielding member 26 having a plurality of openings 26a, 26b, 26c and a shielding member holding member 27 covering a part of the shielding member 26, the openings matched to the paper size. It is possible to perform the switching operation of 26a, 26b, 26c and the shielding operation (total shielding operation) at the time of abnormality such as jam in a short time.

Further, by mirror-treating the inner peripheral surface of the shielding member, the shielding member 26 can have both a function of shielding radiant heat from the halogen heater 23 and a function of reflecting radiant heat from the halogen heater 23. .. Further, the absorption rate and the transmittance of the radiant heat of the shielding member 26 can be lowered, and the radiant heat from the halogen heater 23 toward the stay 25 can be reflected toward the fixing belt 21. As a result, the heating efficiency of the fixing belt can be improved.

Further, by forming the shielding member 26 into a cylindrical shape, it is possible to save space without requiring a space for retracting the shielding member.

Further, since the shielding member 26 and the drive gear 60 are integrally formed, the drive mechanism can be simplified.

By making the shielding member 26 heat resistant and low friction, the halogen heater 23 including the shielding member 26 can be brought as close as possible to the fixing belt 21. Therefore, the fixing efficiency can be improved.

[Second embodiment]
Next, the shielding configuration of the second embodiment will be described.
FIG. 6 is an explanatory diagram illustrating a shielding configuration according to the second embodiment.

The second embodiment is different from the first embodiment in that a reflective surface is provided on the inner peripheral surface of the shielding member holding member 27.

The reflective surface 27b is formed by applying a mirror surface treatment to the inner peripheral surface of the shielding member holding member 27 corresponding to the openings 26a, 26b, 26c of the shielding member 26.

Specifically, for example, when the opening 26a corresponding to the paper size A is rotationally moved so as to be located on the opposite side of the fixing nip N as shown in FIG. 6, the shield corresponding to the openings 26b and 26c is shielded. The inner peripheral surface of the member holding member 27 is mirror-treated. The reflective surface may be provided over the entire inner peripheral surface of the shielding member holding member 27.

As a result, the shielding member holding member 27 has a function of shielding radiant heat from the halogen heater 23 and a function of reflecting radiant heat from the halogen heater 23. Further, the absorption rate and the transmittance of the radiant heat of the shielding member holding member 27 can be lowered, and the radiant heat from the halogen heater 23 toward the stay 25 can be reflected toward the fixing belt 21. As a result, the heating efficiency of the fixing belt can be improved.

[Third embodiment]
Next, the shielding configuration of the third embodiment will be described.
FIG. 7 is an explanatory diagram illustrating a shielding configuration according to the third embodiment.

In the third embodiment, the position of the opening of the shielding member 26 is characteristic.

As shown in FIG. 7, when the shielding member 26 is in the shielding position for shielding between the halogen heater 23 and the fixing belt 21, the openings 26a, 26b, and 26c are provided at positions other than the shielding position.

This makes it possible to prevent the inside of the shielding member 26 from overheating.

The shielding member holding member 27 may be provided with an opening. As shown in FIG. 7, the opening 27a is provided with the same size as the openings 26a, 26b, 26c of the shielding member 26. The opening 27a is located between the openings 26a, 26b, 26c of the shielding member 26 on the opposite side of the fixing nip N, and when the radiant heat from the halogen heater 23 to the fixing belt 21 is shielded, the openings 26a, 26b, 26c It is provided at a position corresponding to any of the above. The shape of the opening 27a is not limited to the same size as the openings 26a, 26b, 26c of the shielding member 26, and may be smaller or larger than this. Further, a plurality of openings 27a may be provided. This makes it possible to further prevent the inside of the shielding member 26 from overheating.

The present invention has been described above based on the embodiments. The present invention is not limited to the embodiments, and it is possible to make appropriate changes within the scope of the present invention or to combine the above-described embodiments. Further, the image forming apparatus provided with the fixing apparatus of the present invention is not limited to a copying machine or a printer, but may be a facsimile or a multifunction device having a plurality of functions.

20 Fixing device 21 Fixing belt (an example of fixing member)
22 Pressurizing roller (example of facing member)
23 Halogen heater (an example of heat source)
26 Shielding member 26a, 26b, 26c Opening 27 Shielding member holding member 27a Opening N Fixing nip

Patent No. 5907358 Japanese Unexamined Patent Publication No. 2016-48332 Japanese Unexamined Patent Publication No. 2016-110014

Claims (12)

With a rotatable fixing member,
A heat source for heating the fixing member and
An opposing member that abuts on the outer peripheral surface of the fixing member to form a fixing nip,
A shielding member arranged between the fixing member and the heat source and shielding heat from the heat source is provided.
In a fixing device for transporting a recording medium carrying a toner image to the fixing nip and fixing the toner image on the recording medium.
The shielding member is provided so as to cover the outer periphery of the heat source.
The shielding member has at least one opening inside at least the maximum passage area of the recording medium.
It has a shielding member holding member which is provided so as to cover a part of the outer periphery of the shielding member and holds the shielding member.
A fixing device characterized in that a protrusion is provided on the outer periphery of the shielding member, and a heat insulating layer is formed between the shielding member and the shielding member holding member by the protrusion . The fixing device according to claim 1, wherein the inner peripheral surface of the shielding member is a reflecting surface that reflects radiant heat from the heat source. The fixing device according to claim 1 or 2, wherein the inner peripheral surface of the shielding member holding member is a reflecting surface that reflects radiant heat from the heat source. A plurality of the openings are provided in the circumferential direction of the shielding member.
The fixing device according to any one of claims 1 to 3, wherein each of the openings has a different width in the axial direction of the heat source. The fixing device according to any one of claims 1 to 4, wherein the shielding member has heat resistance and low friction. The fixing device according to any one of claims 1 to 5, wherein the shielding member has a cylindrical shape. The fixing device according to any one of claims 1 to 6, wherein the shielding member is rotatable around the outer periphery of the heat source. A gear is provided on the shielding member.
The fixing device according to any one of claims 1 to 7, wherein the shielding member and the gear are integrally formed. When the shielding member is in a shielding position that shields between the heat source and the fixing member,
The fixing device according to any one of claims 1 to 8, wherein the opening is provided at a position other than the shielding position. The fixing device according to claim 9, wherein the shielding member holding member has at least one opening at a position corresponding to the opening. The fixing device according to any one of claims 1 to 10, wherein when an abnormality is detected, the shielding member rotates to a shielding position that shields between the heat source and the fixing member. .. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 11.

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