JP2014056007A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device with a heat insulation member, having substantially the same size as a device having no heat insulation member, and configured to properly insulate various sizes of recording media from heat to prevent heat deterioration of a fixing member or hot offset.SOLUTION: A fixing device 20 includes: a flexible fixing member 21 which can be endlessly rotated; a heat source 25 for heating the fixing member inside the fixing member, and a pressure member 31 which is brought into pressure contact with the fixing member. A recording medium S with an unfixed image carried thereon passes through a nip part N between the fixing member and the pressure member to fix the image. A heat insulation member 50 is arranged between an inner surface of the fixing member and the heat source, and moves in a peripheral direction of the fixing member according to a width of the recording medium to block radiation heat emitted from the heat source to the fixing member.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system, and a fixing device used therefor.

  Conventionally, an image forming apparatus using an electrophotographic method has been used. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. This process consists of a process in which the transferred image is transferred onto a recording paper by a transfer device to carry the image, and a toner image on the recording paper is fixed by a fixing device using pressure or heat.

  The fixing device is provided with a fixing rotator configured by opposing rollers or belts or a combination thereof, and sandwiches the recording paper and applies heat and pressure to fix the toner image on the recording paper.

FIG. 15 shows an example of a belt fixing type fixing device 100. A heating belt 103 having a heater 101 as a heat source, a fixing belt (fixing body) 107 including a fixing roller 105 having a rubber layer on the surface layer, and a pressure roller (pressure body) in contact with the fixing belt Reference numeral 109 denotes a fixing rotator. The recording paper 115 transferred with toner, which has reached the fixing device, enters the nip between the fixing belt and the pressure roller, and the transferred toner image is heated and pressurized to be fixed in the process of passing the recording paper through the fixing nip. . A separation claw 117 is provided downstream of the nip, and separates the recording paper stuck to the fixing roller.
Patent Document 1 discloses a film fixing type fixing device.

  Further, a fixing device having a fixing member that is in sliding contact with the inner surface of a rotating body is known (Patent Document 2). In this fixing device, since the fixing member and the metal heat conductor are thin, the heat conductivity in the main scanning direction is not good. Therefore, when a recording medium having a short length in the main scanning direction is continuously passed, the temperature at the end of the fixing member, which is a portion through which the recording medium does not pass, rises, causing thermal degradation and hot offset. was there. For this reason, when the temperature of the fixing member rises, it is necessary to restrict the sheet passing, and there is a problem that productivity is lowered.

  Also, with respect to the same problem, Patent Document 3 makes it possible to introduce a shielding member into the irradiation path of radiant heat from the heat source direction toward the fixing roller, and in the fixing roller longitudinal direction according to the paper width of the recording medium to be passed. Discloses a configuration in which the irradiation area of the radiant heat is changed and the radiant heat is not irradiated to the fixing roller non-sheet passing portion. However, this configuration requires a large space such as an external heating source or a shielding member, which increases the size of the apparatus.

  Therefore, the present invention has an apparatus size that is substantially the same as when there is no heat insulating member while having a heat insulating member, and performs optimal heat insulation for recording media of various sizes, so that heat deterioration and hot offset of the fixing member are prevented. It is an object of the present invention to provide a fixing device that can be prevented.

  In order to solve this problem, the present invention provides a flexible endless rotatable fixing member, a heating source for heating the fixing member inside the fixing member, and a pressurizing pressure against the fixing member. A fixing device for fixing an image by passing a recording medium carrying an unfixed image through a nip portion between the fixing member and the pressure member, and an inner surface of the fixing member and the heating source. A heat insulating member that is disposed between and capable of moving in the circumferential direction of the fixing member in accordance with the width of the recording medium to be passed to shield the radiant heat radiated from the heating source to the fixing member. A fixing device is proposed.

  A recording medium of various sizes with a device size that is substantially the same as a device without a heat insulating member by providing a movable heat insulating member inside the fixing member and moving it according to the width of the recording medium to insulate the fixing member. Therefore, the heat insulation and hot offset of the fixing member can be prevented.

1 is a schematic configuration diagram of a color printer which is an embodiment of an image forming apparatus according to the present invention. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device according to the present invention. It is a schematic sectional drawing which shows the rotation position of a heat insulation member. It is the schematic which shows the shape of a heat insulation member. It is a figure which shows the relationship between a heater and paper size seen in the arrow direction of FIG. It is a figure which shows the relationship between a heater and paper size when the heat insulation member exists in the heat insulation state seen in the arrow direction of FIG. It is a figure which shows a pressing member. It is a figure which shows the movement state of the heat insulation member by a pressing member. It is a figure which shows the movement state of the heat insulation member by a pressing member. It is a figure which shows the flange for hold | maintaining a heat insulation member. It is a figure which shows the flange for hold | maintaining a heat insulation member. It is the schematic which shows the position fixing method of a heat insulation member. It is a figure which shows the modification of a heat insulation member. It is a figure which shows the modification of a heat insulation member. It is sectional drawing which shows schematic structure of a well-known fixing device (belt fixing system).

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view showing an example of an image forming apparatus 100 such as a color printer provided with a fixing device of the present invention. The image forming unit is provided with a plurality (four in the illustrated example) of image forming units 1Y, 1C, 1M and 1K. Although the first to fourth image forming units 1Y, 1C, 1M and 1K have the same configuration, only the corresponding toner colors are different. In these image forming units, for example, a yellow toner image and a cyan toner image A magenta toner image and a black toner image are respectively formed. Since these image forming units have the same configuration except for the difference in developer (toner) color, in the following description, the Y, C, M, and K subscripts in the reference numerals are omitted as appropriate.

  The image forming unit 1 is provided with a drum-shaped photoconductor 2 which is an electrostatic latent image carrier, and a charging member 3, a developing device 4 and a cleaning unit 5 are provided around the photoconductor 2. . The photosensitive member 2 is driven to rotate clockwise, and a charging member 3 is pressed against the surface of the photosensitive member 2, and the charging member 3 is driven to rotate as the photosensitive member 2 is driven to rotate. In addition, a predetermined bias voltage is applied to the charging member 3 from a high voltage power source (not shown) so that the surface of the photoconductor 2 to be rotationally driven can be uniformly charged. The charging member 3 shown here employs a roller-like member that contacts the photoreceptor 2, but a non-contact type utilizing corona discharge or the like can also be employed.

  In addition, an exposure device 6 is provided in parallel with the four image forming units 1 obliquely below. The exposure device 6 has appropriate and appropriate components such as a light source, a polygon mirror, an f-θ lens, and a reflection mirror, and a charging member based on image information formed according to image data of each color toner. Each photoconductor 2 charged by 3 is exposed to create an electrostatic latent image on each photoconductor 2. The electrostatic latent image formed on the photosensitive member 2 using the exposure device 6 is developed and visualized by applying each color toner when passing through the developing device 4 by the rotation of the photosensitive member 2. . In addition, toner bottles 11Y, 11C, 11M, and 11K filled with yellow, cyan, magenta, and black toners are disposed above the image forming apparatus, and the toner bottles 11Y, 11C, 11M, and 11K are disposed. A predetermined replenishment amount of toner is replenished to each of the color developing devices 4Y, 4C, 4M and 4K through a conveyance path (not shown).

  Further, an endless belt-like intermediate transfer belt 7 configured as an intermediate transfer member is disposed opposite to the photosensitive member 2 of each image forming unit, and each photosensitive member 2 contacts the surface of the intermediate transfer belt 7. ing. The intermediate transfer belt 7 shown in FIG. 1 is configured by being wound around a plurality of support rollers (for example, support rollers 9a and 9b). In the illustrated example, the support roller 9a is connected to a drive motor as a drive source (not shown), and the intermediate transfer belt 7 is rotated counterclockwise in the figure by the drive of the drive motor. The rotatable support roller 9b also rotates. A primary transfer roller 8 is disposed inside the intermediate transfer belt 7 so as to be opposed to the photoreceptor 2 with the belt interposed therebetween. A primary transfer bias is applied to the primary transfer roller 8 from a high voltage power source (not shown), and the toner image visualized by the developing device 4 is primarily transferred to the intermediate transfer belt 7. The primary transfer residual toner left on the photoconductor 2 without being primarily transferred is removed by the cleaning device 5 in preparation for the next image forming operation by the photoconductor 2, and the toner on the photoconductor 2 is completely removed. Removed.

  Further, a secondary transfer roller 10 as a secondary transfer device is provided on the downstream side in the driving direction of the intermediate transfer belt 7. The secondary transfer roller 10 faces the support roller 9b with the intermediate transfer belt 7 interposed therebetween, and the secondary transfer roller 10 and the support roller 9b form a secondary transfer nip portion via the intermediate transfer belt 7. ing. The image forming apparatus also includes a pair of registration rollers 14 and the like in addition to a paper feed cassette 12 and a feed roller 13 as a stacking unit for paper S that is a recording medium, and also includes a pair of registration rollers 14 and the like. A fixing device 20 and a paper discharge roller pair 15 are provided on the downstream side in the transport direction.

Next, an image forming operation will be described.
First, the photosensitive member 2 is driven to rotate clockwise by a driving source (not shown). At this time, the surface of the photosensitive member 2 is irradiated with light from a static eliminator (not shown) to initialize the surface potential. Next, the surface of the photoreceptor 2 is uniformly charged to a predetermined polarity by the charging member 3. Next, the surface of the photoreceptor 2 is irradiated with laser light from the exposure device 6, thereby forming an electrostatic latent image on the surface of the photoreceptor 2. The image information exposed to each photoreceptor 2 at this time is single-color image information obtained by separating a desired full-color image into yellow, cyan, magenta, and black toner color information. The electrostatic latent image formed on the photoreceptor 2 is visualized as a visualized toner image by being supplied with toner (developer) of each color from the developing device 4 when passing through the developing device 4.

  The intermediate transfer belt 7 is driven to run counterclockwise in the figure, while a primary transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photoreceptor 1 is applied to the primary transfer roller 8. Is done. As a result, a transfer electric field is formed between the photosensitive member 2 and the intermediate transfer belt 7, and the toner image on the photosensitive member 2 is electrostatically transferred onto the intermediate transfer belt 7 that is driven to rotate in synchronization with the photosensitive member 2. Primary transfer. In this way, the respective color toner images that are primarily transferred are superimposed on the intermediate transfer belt 7 at sequential timing from the upstream side in the transport direction of the intermediate transfer belt 7 to form a desired full-color image.

  On the other hand, the sheet S on which an image is formed is separated and fed one by one from a bundle of sheets stacked on the sheet feeding cassette 12 to the registration roller pair 14 by a conveying member such as a feeding roller 13. At that time, the leading edge of the conveyed paper S hits the nip portion of the registration roller pair 14 that has not started to rotate, forms a loop, and registration of the paper S is performed. After that, at the timing of the full color toner image carried on the intermediate transfer belt 7, the rotational drive of the registration roller pair 14 is started, and the secondary transfer nip portion constituted by the support roller 9 b and the secondary transfer roller 10. The sheet S is sent out toward. In the present embodiment, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the surface of the intermediate transfer belt 7 is applied to the secondary transfer roller 10, whereby the full color toner image formed on the surface of the intermediate transfer belt 7 is transferred to the sheet S. It is transcribed at the same time. Next, the sheet S to which the toner image has been transferred is conveyed to the fixing device 20, and heat and pressure are applied when passing through the fixing device 20, and the toner image is fixed on the sheet S as a permanent image. Next, the paper S is discharged to a paper discharge portion such as a discharge tray via the paper discharge roller pair 15, and the image forming operation is completed. The residual toner remaining on the intermediate transfer belt 7 without being transferred at the secondary transfer nip is removed and collected by the intermediate transfer belt cleaning means 16.

  The above description is an image forming operation when a full-color image is formed on the paper S. A single-color image is formed by using any one of the image forming means, or a two-color or three-color image is formed. It can also be formed. When monochrome printing is performed using the printer of the present embodiment, an electrostatic latent image is formed only on the photosensitive drum 2K of the image forming unit 1K, developed by the unit, transferred to the paper S, Fixing may be performed by the fixing device 20.

FIG. 2 is a schematic configuration diagram of the fixing device according to the present invention.
The fixing device has a pressure roller 31 as a pressure member and a fixing belt 21 as a fixing member, and the fixing belt 21 is directly heated by radiant heat from the inner peripheral side by a halogen heater 25 as a heating source. Further, in the fixing belt 21, there is a nip forming member 26 that forms a nip N with a pressure roller 31 opposed via the fixing belt, and directly on the inner surface of the fixing belt or indirectly through a sliding sheet (not shown). It comes to slide.

  In the illustrated example, the shape of the nip N formed by the pressure roller 31 and the fixing belt 21 is the concave shape 26a, but may be a flat shape or other shapes. However, if the shape of the nip N is concave, the discharge direction at the front end of the sheet is closer to the pressure roller 31 and the separation is improved, so that the occurrence of jam is suppressed.

  The pressure roller 31 has a silicone rubber layer on a hollow metal roller, and a release layer (PFA or PTFE layer) is provided on the surface to obtain releasability. The pressure roller 31 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus via a gear. The pressure roller is pressed against the fixing belt 21 by a spring or the like, and has a predetermined nip width as a result of the rubber layer being crushed and deformed. The pressure roller may be a solid roller, but a hollow roller may have a smaller heat capacity. Further, a heating source such as a halogen heater may be provided in the pressure roller.

  The silicone rubber layer may be solid rubber, but if there is no heater inside the pressure roller 31, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt 21 to lose heat.

  The fixing belt 21 is an endless belt or film using a metal belt such as nickel or SUS or a resin material such as polyimide. The surface layer of the belt has a release layer such as a PFA or PTFE layer, and has a release property so that toner does not adhere. There may be an elastic layer formed of a silicone rubber layer or the like between the belt substrate and the PFA or PTFE layer. When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, the subtle irregularities on the belt surface are transferred to the image and the image has a crusty skin shape. This causes a problem that the trace remains. In order to improve this, it is necessary to provide a silicone rubber layer of 100 μm or more. Due to the deformation of the silicone rubber layer, subtle irregularities are absorbed and the skin image is improved.

  A reinforcing member (support) 23 for supporting the nip N may be provided inside the fixing belt 21. The reinforcing member 23 is made of a metal such as stainless steel, iron, or aluminum. The reinforcing members are held and fixed at both ends by a fixing device frame, a fixing belt holding member (flange), and the like. At this time, if the reinforcing member 23 is heated by radiant heat from a halogen heater or the like, the surface of the reinforcing member is thermally insulated or mirror-finished to prevent heating, thereby suppressing wasteful energy consumption. Can do.

The heat source for raising the temperature of the fixing belt may be induction heating instead of the illustrated halogen heater, or may be a resistance heating element, a carbon heater, or the like.
In addition, a temperature sensor 40 is provided on the outer peripheral surface of the fixing belt 21 to monitor that the temperature of the fixing belt 21 is a predetermined temperature necessary for fixing.

  The fixing belt 21 is rotated by an external pressure roller 31. In the case of FIG. 2, the pressure roller 31 is rotated by a driving source (not shown), and the driving force is transmitted to the fixing belt 21 at the nip N to rotate the belt. The belt is sandwiched and rotated at the nip portion, but is guided by the metal body except at the nip portion, and is guided so that the position of the belt is not separated from the heat conductor more than a certain distance.

  With the above-described configuration, it is possible to realize a fixing device that is inexpensive, has a fast warm-up, and stabilizes the temperature of the entire belt.

  Further, a heat insulating member 50 that shields radiant heat radiated from the heater 25 to the fixing belt 21 is provided in the fixing belt 21. The heat insulating member 50 is disposed along the inner peripheral surface of the fixing belt 21, and the amount of radiant heat to be shielded can be adjusted by rotating in the circumferential direction according to the paper size to be fixed. In terms of strength, thermal conductivity, and space, the heat insulating member is preferably a metal plate, but is not limited thereto.

FIG. 3 is a schematic cross-sectional view showing the rotational position of the heat insulating member.
FIG. 3A is a normal position of the heat insulating member 50. In this position, the heating position 60 of the fixing belt 21 facing the heater is not covered with the heat insulating member 50, and heat insulation is not performed. Accordingly, the fixing belt 21 is heated substantially corresponding to the axial width of the heater 25. FIG.3 (b) shows the heat insulation state 1 when the heat insulation member 50 act | operates and moves to the heat insulation position of illustration from a normal position. FIG.3 (c) shows the heat insulation state 2 when the heat insulation member 50 further operates and moves to the heat insulation position of illustration. In the heat insulation position of the heat insulation states 1 and 2, since the heat insulation member 50 covers a part of the heater 25, a part of the radiant heat from the heater 25 is blocked.

FIG. 4 is a schematic view showing the shape of the heat insulating member of the present embodiment.
The heat insulation state by the heat insulation member 50 depends on the shape and position of the heat insulation member, the arrangement of the heater, and the like. The heat insulating member spreads stepwise from its axial center to its end, and its surface area is increased. As will be described later, since the shielding plate can cope with various paper sizes by adjusting the position of the shielding plate as described later, the shielding effect of the heater by the rotated shielding plate is optimized, and the fixing belt outside the paper width Is not heated more than necessary, and an increase in end temperature can be prevented. In the figure, a region 52 is a portion at the heating position 60 in the heat insulation state 1, and a region 54 is a portion at the heating position 60 in the heat insulation state 2.

FIG. 5 is a diagram showing the relationship between the heater and the paper size when viewed in the direction of the arrow in FIG.
As shown in the figure, the heater includes two heaters, a central heater 25a disposed above and an end heater 25b disposed below. The central heater 25a serving as the first heating unit heats only the axial central portion of the fixing belt 21, and the end heater 25b serving as the second heating unit heats both axial end portions of the fixing belt 21. . In FIG. 5A, the central heater 25a and the end heater 25b are lit, and the entire length of the heater substantially corresponds to the width of the paper A. The paper A corresponds to, for example, A3 Nobi. Here, the heat insulating member 50 is in the normal position, so that the radiant heat radiated from the heater to the fixing belt 21 is not shielded, and the fixing belt 21 is heated at the heating position 60. As shown in the figure, the fixing belt temperature rises substantially corresponding to the length of the heater, so that the end temperature of the fixing belt does not rise after the sheet A is fixed.

  In FIG. 5B, only the central heater 25a is turned on, the end heater 25b is turned off, and the entire heater length (central heater 25a) substantially corresponds to the width of the paper C. The paper C corresponds to, for example, A4 portrait. Also in this case, the heat insulating member 50 is in the normal position, and therefore the radiant heat radiated from the heater to the fixing belt 21 is not shielded, and the fixing belt 21 is heated at the heating position 60. Since the fixing belt temperature rises substantially corresponding to the length of the heater, the end temperature of the fixing belt does not rise after the sheet C is fixed.

FIG. 6 is a diagram illustrating the relationship between the heater and the paper size when the heat insulating member 50 is in a heat insulating state when viewed in the direction of the arrow in FIG. 3.
In FIG. 6A, the heat insulating member 50 is in a heat insulating state 1, the central heater 25 a and the end heater 25 b are lit, and both outer end portions of the end heater are covered with the heat insulating member 50. At this time, the region 52 is at the heating position 60 in the heat insulating state 1, and the entire length of the heater not covered with the heat insulating member 50 in the region 52 substantially corresponds to the width of the paper B. The paper B corresponds to, for example, A3 portrait and A4 landscape. Since the fixing belt temperature increases substantially corresponding to the length of the heater not covered with the heat insulating member, the fixing belt end temperature does not increase after the sheet B is fixed.

  In FIG. 6B, the heat insulating member 50 is in the heat insulating state 2, and only the central heater 25 a is lit, and both outer ends of the central heater are covered with the heat insulating member 50. At this time, the region 54 is at the heating position 60 in the heat insulating state 2, and the entire length of the heater not covered with the heat insulating member 50 in the region 54 substantially corresponds to the width of the paper D. The paper D corresponds to, for example, a postcard. Since the fixing belt temperature increases substantially corresponding to the length of the heater not covered with the heat insulating member, the fixing belt end temperature does not increase after the sheet D is fixed.

  As described above, the heat insulating member 50 has a stepped shape including a portion covering the central heater 25a and a portion covering the end heater 25b, and switching between turning on / off of the central heater 25a and the end heater 25b, Four sizes of paper can be passed without causing an increase in the temperature at the end of the fixing belt.

  Table 1 shows the relationship between the paper size to be passed and the heater on / off state. The paper size is an example and is not limited to the description.

FIG. 7 is a view showing the pressing member 56.
The heat insulating member 50 disposed inside the fixing belt is pressed against the fixing belt by a pressing member 56 attached to the frame of the fixing device. The pressing member 56 can be moved in the arrow direction by means (not shown). The pressing member 56 is preferably a roller made of a material such as rubber and is provided at both ends of the fixing belt 21. Accordingly, a frictional force is generated between the heat insulating member 50 and the fixing belt 21, and the heat insulating member 50 moves in the belt rotation direction. By utilizing the friction with the fixing belt, a new power source is not required for the operation of the heat insulating member, and the heat insulating member can be provided while maintaining the same device volume as the device without the heat insulating member.

FIGS. 8 and 9 are views showing a moving state of the heat insulating member 50 by the pressing member 56.
FIG. 8 shows the rotation of the fixing belt 21 in the forward rotation direction. First, the heat insulating member 50 is in the normal position. Next, when the pressing member 56 presses the heat insulating member 50 against the fixing belt 21, the heat insulating member also rotates together with the forward rotation of the fixing belt, and finally the heat insulating member is in a heat insulating state. At the 1 or 2 position.

FIG. 9 shows the rotation of the fixing belt 21 in the reverse direction.
First, the heat insulating member 50 is in the heat insulating state 1 or 2, and the heat insulating member also rotates with the reverse rotation of the fixing belt, and the heat insulating member comes to the normal position. However, the stop position of the heat insulating member is not limited to these positions. As described above, the position of the heat insulating member can be freely changed according to various sizes of paper by using the forward and reverse operations of the fixing belt.

10 and 11 are external views showing a flange 61 for holding the heat insulating member 50.
A circular flange 61 is fixed to the frame of the fixing device so as not to rotate, and an end portion of the fixing belt 21 is supported on an outer peripheral surface of a small diameter portion of the flange 61. When the fixing belt 21 rotates along with the pressure roller 31, the fixing belt 21 slides on the outer peripheral surface of the small diameter portion of the flange 61. A groove 63 is preferably formed at the edge of the small diameter portion of the flange 61 at 360 °, and the heat insulating member 50 is accommodated in the groove 63. The heat insulating member 50 can move in the direction of the arrow in the groove 63 by a frictional force when pressed against the fixing belt 21 by the pressing member 56. In this way, the heat insulating member 50, the fixing belt 21, and the reinforcing member 23 are held so as not to contact each other, and the fixing device can be operated stably.

FIG. 12 is a schematic view showing a method for fixing the position of the heat insulating member.
The heat insulating member 50 moves as shown in FIGS. 3, 8, and 9, but is stopped at a desired position by a position fixing member 68 attached to the frame of the fixing device. The position fixing member 68 is configured to be movable in the axial direction of the fixing belt by means (not shown). In the present embodiment, at the end of the heat insulating member 50, three engaging portions 65, 67, and 69 that are shifted in the axial direction of the heat insulating member and extend away from the fixing belt are formed. The three engaging portions 65, 67, and 69 have different heights, and the stop position of the heat insulating member when the engaging portions 65, 67, and 69 are engaged with the position fixing member 68 is shown in FIG. It corresponds to the normal position, the heat insulation state 1 and the heat insulation state 2 of (c). In the illustrated example, the position fixing member 68 is engaged with the engaging portion 67, and the position of the heat insulating member at this time corresponds to the heat insulating state 1 in FIG.

13 and 14 are diagrams showing a modification of the heat insulating member 50.
Here, a protruding portion 71 is formed between the engaging portion 65 and the engaging portion 67. The protrusion 71 is a portion along the groove of the flange 61 and is accommodated in the groove 63 together with the end 72 to ensure movement along the groove of the heat insulating member.

  According to the present invention, an image forming apparatus with stable productivity and image quality can be obtained by using the above-described fixing device.

  Although the present invention has been described above with reference to the illustrated examples, the components of the present invention are not limited to this, and various modifications can be made. The configuration of each part of the image forming apparatus is arbitrary. For example, the image forming apparatus is not limited to the tandem type, and any image forming method can be adopted. Further, not only the intermediate transfer method but also a direct transfer method can be adopted. The present invention can also be applied to a full color machine using three color toners, a multicolor machine using two color toners, or a monochrome apparatus. Of course, the image forming apparatus is not limited to a copying machine, but may be a printer, a facsimile, or a multifunction machine having a plurality of functions.

20 Fixing device 21 Fixing belt (fixing member)
25 Halogen heater (heating source)
31 Pressure roller (Pressure member)
50 Thermal insulation material S Paper (recording medium)

Japanese Patent No. 2861280 JP 2007-334205 A JP 2008-139779 A

Claims (10)

A flexible endless rotatable fixing member; a heating source for heating the fixing member inside the fixing member; and a pressure member in pressure contact with the fixing member. In a fixing device for fixing an image by passing a recording medium carrying an unfixed image in a nip portion between pressure members,
Radiation heat that is disposed between the inner surface of the fixing member and the heating source, moves in the circumferential direction of the fixing member according to the width of the recording medium to be passed, and is radiated from the heating source to the fixing member. A fixing device comprising a heat insulating member capable of shielding.   The fixing device according to claim 1, wherein the heat insulating member moves by a frictional force with the fixing member.   The fixing device according to claim 1, wherein the heat insulating member moves in accordance with a forward rotation operation and a reverse rotation operation of the fixing member.   The fixing device according to claim 1, wherein the heat insulating member is accommodated in a groove formed in a flange that holds the fixing member, and moves in the groove.   The fixing device according to claim 1, wherein the heat insulating member includes at least one engaging portion for stopping the heat insulating member at a desired position.   The fixing device according to claim 5, further comprising a position fixing member that is movable in an axial direction of the fixing member and that engages with the engaging portion.   The heat insulating member is between a normal position where the heat insulating member does not cover the heating source and a heat insulating position where the heat insulating member covers at least a part of the heating source according to the width of the recording medium to be passed. The fixing device according to claim 1, wherein the fixing device moves.   In the normal position and the heat insulating position, the heating source is turned on or off so that the entire length of the heating source not covered by the heat insulating member substantially corresponds to the width of the recording medium to be passed. The fixing device according to claim 7.   9. The heating source according to claim 1, wherein the heating source includes at least a first heating unit that heats an axially central portion of the fixing member and a second heating unit that heats both axial ends of the fixing member. The fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1.

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