JP2014074887A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of suppressing heating of a shield member.SOLUTION: A fixing device includes: a rotatable endless fixing belt 21; a heat source 23 that heats the fixing belt 21; a nip forming member 24 disposed on the inner peripheral side of the fixing belt 21; an opposing member 22 that comes into contact with the nip forming member 24 from the outer peripheral side of the fixing belt 21 to form a nip part N with the fixing belt 21; and a shield member 27 that shields heat from the heat source 23. The shield member 27 is disposed to surround the heat source 23 and formed over the entire width direction of a recording medium passing area in a circumferential direction with ends on both sides, and is configured to be movable between a shield position where at least a part of the shield member 27 faces directly to the heat source 23 to shield the heat, and a retreat position where the portion facing directly to the heat source 23 is retreated from the shield position and heating suppression members 25 and 26 are disposed to be interposed between the heat source 23 and the shield member 27.

Description

  The present invention relates to a fixing device that fixes an image on a recording medium, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Image forming apparatuses such as copiers, printers, facsimiles, and multifunction peripherals thereof are provided with a fixing device that fixes a toner image carried on a recording medium such as paper. Generally, a fixing device includes a fixing member that is heated by a heating source such as a heater, and an opposing member that forms a nip portion in contact with the fixing member. When the image forming operation is started in the image forming apparatus and the toner image is transferred to the sheet, the sheet passes through the nip portion between the fixing member heated to a predetermined temperature and the opposing member. The toner carried on the paper is heated and melted to fix the image.

  In the fixing device, since the heat of the fixing member is taken away by the sheet passing through the nip portion, the fixing member is managed to be maintained at an appropriate temperature by a temperature sensor or the like. On the other hand, in the non-sheet passing area where the sheet does not pass, the heat of the fixing member tends not to be taken away. For this reason, there is a problem that the fixing member overheats in the non-sheet passing region, particularly when the sheet is continuously passed.

  Therefore, conventionally, in order to solve this problem, there has been proposed a fixing device provided with a shielding member that shields heat from a heat source in a non-sheet passing region of the fixing member (see Patent Documents 1, 2, and 3).

  However, in the configuration in which the heat from the heating source is shielded by the shielding member, the shielding member itself is heated by the heating source, so that the shielding member may be deformed by the heat depending on the use situation or the like. If the shielding member is deformed, the function of the shielding member may be deteriorated, or the deformed portion may interfere with other members, and measures to suppress this are necessary.

  In view of such circumstances, the present invention intends to provide a fixing device capable of suppressing the heating of the shielding member, and an image forming apparatus including the fixing device.

  In order to solve the above-described problems, the present invention provides a rotatable endless fixing belt, a heating source for heating the fixing belt, a nip forming member disposed on an inner peripheral side of the fixing belt, and the fixing In the fixing device, comprising: a facing member that contacts the nip forming member from the outer peripheral side of the belt to form a nip portion with the fixing belt; and a shielding member that shields heat from the heating source. The shield member is disposed around the heat source, and is formed to have a circumferential end over the entire width direction of the recording medium passage region. At least a part of the shielding member directly faces the heat source. Between the shielding position where the heat is shielded and the retreat position where the portion directly facing the heating source is retracted from the shielding position and the heating suppression member is interposed between the heating source and the heat source. It was configured to be possible To.

  According to the present invention, by moving the shielding member to the retracted position, the portion directly opposed to the heating source at the shielding position before the movement is heated between the heating source at the retracted position after the movement. It arrange | positions so that a suppression member may interpose. Thereby, in the part in which a heating suppression member interposes, since a shielding member becomes difficult to receive the influence of the heat from a heating source, the temperature rise of a shielding member can be suppressed.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a fixing device mounted on the image forming apparatus. It is a figure which shows the state which moved the shielding member to the retracted position. It is a perspective view of the fixing device. It is a figure which shows the support structure of a shielding member. It is a figure which shows the drive means of a shielding member. It is a figure which shows the relationship between the shape of a shielding member, the heat generating part of a halogen heater, and paper size. It is a figure which shows the state which moved the shielding member to the shielding position. It is a figure which shows other embodiment of a shielding member. It is a figure which shows the state which moved the shielding member to the shielding position. It is a figure for demonstrating the characteristic part of this invention. It is a figure which shows the state which moved the shielding member to the shielding position for small sizes. It is a figure which shows the state which moved the shielding member to the shielding position for large sizes. It is a figure which shows the state which moved the shielding member to the retracted position. It is the figure which showed the temperature rise of a shielding member and a reflection member in the case where the heat capacity of a shielding member is large, and the case where it is small. It is a figure which shows the structure which made the shielding member contact a stay when a shielding member was moved to a retracted position. It is a perspective view which shows the structure which provided the heat transport member over the pressure roller from the stay. It is sectional drawing of FIG. It is the schematic of the structure which provided the heat transport member over the paper feed part from the stay.

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

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

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

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

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, A cleaning 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, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source (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 come to be.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. . A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Although not shown, a manual paper feed mechanism may be provided.

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

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

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

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

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

  In the lower part of the printer, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent to the transport path R is temporarily stopped by the registration rollers 12.

  Thereafter, rotation of the registration roller 12 is started at a predetermined timing, and the paper P is conveyed to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. 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, thereby forming a transfer electric field in the secondary transfer nip. . Then, the toner images on the intermediate transfer belt 30 are collectively transferred onto the paper P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

FIG. 2 is a cross-sectional view of the fixing device of this embodiment.
Hereinafter, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a pressure roller 22 as an opposing member that contacts the outer peripheral surface of the fixing belt 21, and a heating source that heats the fixing belt 21. Halogen heater 23, nip forming member 24 that contacts pressure roller 22 from the inner peripheral side of fixing belt 21 to form nip portion N, stay 25 as a support member that supports nip forming member 24, halogen heater A reflection member 26 that reflects heat from the fixing belt 21 to the fixing belt 21, a shielding member 27 that shields heat from the halogen heater 23, a temperature sensor 28 as temperature detecting means for detecting the temperature of the fixing belt 21, and the like.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes 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). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  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 uneven glossiness is formed on the solid portion of the image. It can happen. 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, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided.

  In this embodiment, 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 a range 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, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. Note that the fixing member and the facing member are not limited to being in pressure contact with each other, and may be configured to simply contact without pressing.

  The pressure 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 pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at 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 may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. 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 heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  The halogen heater 23 is disposed on the inner peripheral side of the fixing belt 21 and on the upstream side of the nip portion N in the sheet conveyance direction. Specifically, in FIG. 2, assuming that a virtual straight line passing through the center Q of the nip portion N in the paper transport direction and the rotation center O of the pressure roller 22 is L, the halogen heater 23 is closer to the paper transport direction than the virtual straight line L. It is arranged on the upstream side (lower side in FIG. 2). The halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 28. Is called. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. A temperature sensor (not shown) for detecting the temperature of the pressure roller 22 is provided in place of the temperature sensor for detecting the temperature of the fixing belt 21, and the temperature of the fixing belt 21 is predicted based on the temperature detected by the temperature sensor. You may make it do.

  In this embodiment, two halogen heaters 23 are provided, but the number of halogen heaters 23 may be one or three or more according to the size of the paper used in the printer. In addition to the halogen heater, a resistance heating element, a carbon heater, or the like can be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 includes a base pad 241 and a low friction sliding sheet 240 provided on a surface of the base pad 241 facing the fixing belt 21. The base pad 241 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22. The shape of the nip portion N is determined by the base pad 241 receiving the pressure applied by the pressure roller 22. In the present embodiment, the shape of the nip portion N is flat, but may be a concave shape or other shapes. The sliding sheet 240 is provided to reduce sliding friction when the fixing belt 21 rotates. Note that when the base pad 241 itself is formed of a low-friction member, the sliding sheet 240 may not be provided.

  The base pad 241 is made of a heat-resistant member having a heat-resistant temperature of 200 ° C. or more, prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature region, and ensures a stable state of the nip portion N for output. Stabilizes image quality. Examples of the material of the base pad 241 include polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), and polyether ether ketone (PEEK). A general heat resistant resin can be used.

  The base pad 241 is fixedly supported by the stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending. The base pad 241 is also preferably made of a material that is hard to some extent to ensure strength. As a material for the base pad 241, a resin such as a liquid crystal polymer (LCP), a metal, a ceramic, or the like can be used.

  The reflection member 26 is fixedly supported by the stay 25 so as to face the halogen heater 23. By reflecting the heat (or light) radiated from the halogen heater 23 to the fixing belt 21 by the reflecting member 26, the heat is suppressed from being transmitted to the stay 25 and the like, and the fixing belt 21 is efficiently heated. At the same time, we are trying to save energy. As the material of the reflecting member 26, aluminum, stainless steel or the like is used. In particular, in the case of using a material obtained by vapor-depositing silver having a low emissivity (high reflectivity) on an aluminum base material, the heating efficiency of the fixing belt 21 can be improved.

  The shielding member 27 is configured by forming a metal plate having a thickness of 0.1 mm to 1.0 mm into an arc-shaped cross-sectional shape along the inner peripheral surface of the fixing belt 21. The shielding member 27 is movable in the circumferential direction of the fixing belt 21 as necessary. In the present embodiment, in the circumferential region of the fixing belt 21, a direct heating region in which the halogen heater 23 directly heats the fixing belt 21 is heated, and other than the shielding member 27 between the halogen heater 23 and the fixing belt 21. There are non-direct heating regions where members (reflecting member 26, stay 25, nip forming member 24, etc.) intervene, but when it is necessary to shield heat, shield member 27 is directly heated region as shown in FIG. It is arranged at the shielding position on the side. On the other hand, when there is no need for heat shielding, as shown in FIG. 3, the shielding member 27 is moved to the retracted position on the non-direct heating region side, and the shielding member 27 is retracted to the back side of the reflecting member 26 and the stay 25. Is possible. Moreover, since the shielding member 27 requires heat resistance, it is preferable to use a metal material such as aluminum, iron, stainless steel, or ceramic as the material.

FIG. 4 is a perspective view of the fixing device of this embodiment.
As shown in FIG. 4, flange members 40 as belt holding members are inserted into both ends of the fixing belt 21, and the fixing belt 21 is rotatably held by the flange members 40. Each flange member 40, halogen heater 23 and stay 25 are fixedly supported by a pair of side plates (not shown) of the fixing device 20.

FIG. 5 is a diagram illustrating a support structure of the shielding member.
As shown in FIG. 5, the shielding member 27 is supported via an arcuate slide member 41 attached to the flange member 40. Specifically, the projection 27 a provided at the end of the shielding member 27 is inserted into the hole 41 a provided in the slide member 41, so that the shielding member 27 is attached to the slide member 41. Also, the slide member 41 is provided with a convex portion 41b, and when the convex portion 41b is inserted into an arcuate groove portion 40a provided in the flange member 40, the slide member 41 slides along the groove portion 40a. It is possible. Thereby, the shielding member 27 can rotate and move integrally with the slide member 41 in the circumferential direction of the flange member 40. In the present embodiment, the flange member 40 and the slide member 41 are made of resin.

  In FIG. 5, only the support structure of one end portion is shown, but the other end portion is similarly held rotatably via the slide member 41.

FIG. 6 is a diagram illustrating a driving unit of the shielding member.
As shown in FIG. 6, in the present embodiment, as a driving unit for the shielding member 27, a motor 42 that is a driving source and a gear train including a plurality of transmission gears 43, 44, and 45 are provided. In the gear train, the gear 43 on one end side is connected to the motor 42, and the gear 45 on the other end side is connected to a gear portion 41 c provided in the circumferential direction of the slide member 41. Thus, when the motor 42 is driven, the driving force is transmitted to the slide member 41 via the gear train, and the shielding member 27 is rotated.

FIG. 7 is a diagram showing the relationship between the shape of the shielding member, the heat generating portion of the halogen heater, and the paper size.
First, the shape of the shielding member 27 will be described in detail with reference to FIG.
As shown in FIG. 7, the shielding member 27 according to the present embodiment includes a pair of shielding portions 48 provided at both ends for shielding heat from the halogen heater 23 and a connecting portion 49 that connects the shielding portions 48 to each other. And have. In addition, between the shielding portions 48, there is an opening 50 for releasing heat from the halogen heater 23 without shielding it.

  Moreover, the straight part 51 parallel to the rotation direction of the shielding member 27 and the inclination part 52 which inclines with respect to the rotation direction are formed in the inner edge which each shielding part 48 mutually opposes. In FIG. 7, when the side on which the shielding member 27 is rotationally moved to the shielding position is defined as the shielding side Y, each inclined portion 52 is continuously provided on the shielding portion side Y of the straight portion 51 and faces toward the shielding side Y. Tilted away. Thereby, the opening part 50 is formed in the same width | variety between the straight parts 51 toward the shielding side Y, and is formed so that a width | variety may spread between the inclination parts 52. FIG.

Next, the relationship between the heat generating part of the halogen heater and the paper size will be described.
As shown in FIG. 7, in the present embodiment, the length and the arrangement position of the heat generating portions of the halogen heaters 23 are varied in order to change the heating area according to the paper size. Of the two halogen heaters 23, the heat generating part 23a of one (lower side in the figure) of the halogen heater 23 is disposed on the central part in the longitudinal direction, and the heat generating part 23b of the other halogen heater 23 (upper side in the figure). Are disposed on both ends in the longitudinal direction. In this example, the heat generating part 23a on the center side is disposed in a range corresponding to the medium-size sheet passing width W2, and the heat generating part 23b on both ends is larger than the medium-sized sheet passing width W2 and has a large size. And an extra large size sheet passing width W3, W4.

  In addition, in the relationship between the shape of the shielding member 27 and the paper size, each straight portion 51 is disposed in the width direction inner side with respect to the end portion of the large size paper passing width W3, and each inclined portion 52 is the large size. Is disposed at a position straddling the end of the sheet passing width W3.

  As an example of the paper size in the present embodiment, for example, the medium size is letter size (paper passing width 215.9 mm) or A4 size (paper passing width 210 mm), and the large size is double letter size (paper passing width 279.4 mm) or A3 size (sheet passing width 297 mm), extra large size A3 Nobi (sheet passing width 329 mm), and the like. However, the paper size example is not limited to this. The medium size, large size, and extra large size referred to here indicate the relative relationship between the sizes, and may be a small size, a medium size, a large size, or the like.

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, power is supplied to the halogen heater 23 and the pressure roller 22 starts to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the paper P carrying the unfixed toner image T in the above-described image forming process is conveyed in the direction of the arrow A1 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 in the pressure contact state and It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper P on which the toner image T is fixed is carried out from the nip portion N in the direction of the arrow A2 in FIG. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of a separation member (not shown). Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

  In particular, in the present embodiment, the fixing belt 21 has a low heat capacity as described above, and the pressure roller 22 has a configuration in which the thin release layer 22c is effectively warmed by the heat insulating effect of the elastic layer 22b. Therefore, it is possible to fix the toner on the sheet with the minimum amount of heat.

Next, the control of the halogen heater and the control of the shielding member for each paper size will be described.
First, when passing the medium-size paper P2 shown in FIG. 7, only the range corresponding to the medium-size paper passing width W2 is heated by heating only the heat generating portion 23a on the center side. When passing oversized paper P4, in addition to the heat generating portion 23a on the center side, the heat generating portions 23b on both ends are also heated, and the range corresponding to the oversized paper passing width W4 is heated.

  However, in the present embodiment, the heating range of the halogen heater 23 corresponds only to the medium-size sheet passing width W2 and the extra-large-size sheet passing width W4. For this reason, when passing large size paper P3, if only the heat generating part 23a on the center side is heated, the necessary range is not heated, and the heat generating parts 23a, 23b on the center side and both ends are heated. As a result, the heated range exceeds the large sheet passing width W3. If the large-size sheet P3 is passed as it is in a state in which the heat generating portions 23a and 23b on the both ends on the center side are heated, the fixing belt in the non-sheet-passing area outside the large-size sheet passing width W3. There is a problem that the temperature of 21 rises excessively.

  Therefore, in the present embodiment, when passing the large size paper P3, as shown in FIG. 8, the shielding member 27 is moved to the shielding position. As a result, the shield 48 on both ends can cover the outer area from the vicinity of the end of the large sheet passing width W3, so that the temperature rise of the fixing belt 21 can be suppressed in the non-sheet passing area.

  Further, when it is no longer necessary to shield the heat, such as when the fixing process is completed, or when the temperature of the non-sheet passing area of the fixing belt 21 is equal to or lower than a predetermined threshold, the shielding member 27 is returned to the retracted position. . In this way, by moving the shielding member 27 to the shielding position as necessary, good fixing can be performed without reducing the sheet passing speed.

  Further, in the present embodiment, since the inclined portion 52 is provided in the shielding portion 48, it is possible to adjust the range in which the heat generating portion 23b is covered by the shielding portion 48 by changing the rotational position of the shielding member 27. . For example, the temperature of the fixing belt 21 in the non-sheet passing area tends to increase as the number of sheets passed and the sheet passing time increase. Therefore, when the number of sheets passed reaches a predetermined number or when the sheet passing time reaches a predetermined time. The temperature rise can be suppressed to a higher degree by rotating the shielding member 27 in such a direction as to cover the heat generating portions 23b on both ends.

The temperature sensor 28 that detects the temperature of the fixing belt 21 is preferably disposed in a region where the temperature increase in the axial direction of the fixing belt 21 is significant.
In the case of the present embodiment, the temperature is likely to rise particularly in a region outside the large-size sheet passing width W3. Therefore, it is desirable to dispose the temperature sensor 28 outside the large-sized sheet passing width W3 (FIG. 7). reference). Further, in the present embodiment, of the two halogen heaters 23, it is the halogen heater 23 having the heat generating portions 23 b on both end sides that is largely caused by the temperature rise, and therefore the heat generating portion 23 b of the halogen heater 23. It is desirable to dispose the temperature sensor 28 at a position opposite to.

FIG. 9 shows another embodiment of the shielding member.
In the shielding member 27 shown in FIG. 9, the shielding portions 48 on both ends are each formed in a shape having two step portions. That is, each shielding part 48 is comprised by the small shielding part 48a with a small longitudinal direction width | variety, and the large shielding part with a large longitudinal direction width | variety. The large shielding parts 48b are connected to each other via a connecting part 49, and the small shielding part 48a is provided continuously on the shielding side Y of the large shielding part 48b. Further, the inner edges of the small shielding part 48a facing each other and the inner edges of the large shielding part 48 facing each other are inclined parts 52a and 52b that are inclined away from each other toward the shielding side Y. The straight part 51 like the shielding member 27 shown in FIG. 7 is not formed.

  In the embodiment shown in FIG. 9, at least four types of paper are used: small size paper P1, medium size paper P2, large size paper P3, and extra large size paper P4. As an example of the paper size in this embodiment, for example, a small size is a postcard size (paper passing width 100 mm), a medium size is A4 size (paper passing width 210 mm), a large size is A3 size (paper passing width 297 mm), and an extra large size is A3. Nobi (sheet passing width 329 mm). However, the paper size example is not limited to this.

  Here, the paper passing width W1 of the small size paper P1 is in a range smaller than the length of the heat generating portion 23a on the center side. Further, in relation to the shape of the shielding member 27, each inclined portion 52b of the large shielding portion 48b is disposed at a position straddling the end of the small size sheet passing width W1, and each inclined portion 52a of the small shielding portion 48a is The sheet is disposed at a position straddling the end of the large sheet passing width W3. Note that the positional relationship between the paper sizes other than the small size (medium, large, extra large) and each of the heat generating portions 23a, 23b is the same as in the above embodiment, and thus the description thereof is omitted.

  When the small size paper P1 is passed, only the heat generating portion 23a on the center side is heated. However, in this case, since the range heated by the heat generating part 23a on the center side exceeds the small sheet passing width W1, the shielding member 27 is moved to the shielding position as shown in FIG. As a result, the large shielding portion 48b can cover the outer area from the vicinity of the end portion of the small sheet passing width W1, so that the temperature rise of the fixing belt 21 can be suppressed in the non-sheet passing area.

  Note that the control of the halogen heater 23 and the shielding member 27 when passing other size sheets (medium, large, extra large) is basically the same as in the above embodiment. In this case, the function as the shielding part 48 in the embodiment is performed by the small shielding part 48a.

  In the case of the embodiment shown in FIG. 9 as well, since the inclined portions 52a and 52b are provided in the small shielding portion 48a and the large shielding portion 48b, respectively, similarly to the shielding portion 48 of the above embodiment, the rotation of the shielding member 27 is performed. By changing the position, it is possible to adjust the range in which the heat generating portions 23a and 23b are covered by the shielding portions 52a and 52b.

  By the way, in the configuration in which the nip forming member 24 is provided inside the fixing belt 21 as described above, the shielding member 27 is arranged in the entire width direction of the recording medium passage region (a plurality of types) in order to avoid interference with the nip forming member 24. If there is a sheet passing width, it is necessary to form an endless shape that is not annular in the circumferential direction over the maximum sheet passing range including all of them. However, if the shielding member 27 is formed in a shape having a circumferential end, when the shielding member 27 is excessively heated, the circumferential end portion of the shielding member 27 falls on the outer peripheral side or the inner peripheral side. There is a risk of thermal deformation.

  Moreover, when the shielding member 27 is configured to be rotatable and movable as in the above-described embodiment, the drivability between the members that support the shielding member 27 (between the flange member 40 and the slide member 41) is ensured. There is a need. Therefore, it is necessary to provide a certain amount of play (gap) between the support members. In that case, heat of the shielding member 27 is radiated through the support member as compared with the case where the shielding member 27 is fixed to a side plate or the like. The effect is low. This is not limited to the configuration of the above embodiment. Therefore, in general, in the case of a movable shielding member, heat tends to be stored more easily than a stationary shielding member, and the possibility of thermal deformation increases.

  Further, in the above embodiment, the surface of the reflecting member 26 facing the halogen heater 23 is formed so as to spread toward the inner peripheral surface of the fixing belt 21 (see FIG. 2). The area where the shielding member 27 is irradiated increases, and the shielding member 27 is easily heated. In the reflecting member 26 shown in FIG. 2, the portion facing the lower side of the halogen heater 23 is provided to shield the heat at both ends of the halogen heater 23, and extends along the entire longitudinal direction of the reflecting member 26. It is not provided across.

Therefore, in the present invention, measures are taken to prevent thermal deformation of the shielding member as described above.
Hereinafter, the characteristic part of the present invention will be described by taking as an example an embodiment in which each of the shielding portions has one step portion.

  As shown in FIG. 11, when the shielding member 27 is retracted from the shielding position (the position indicated by the solid line in the figure) to the retracted position (the position indicated by the two-dot chain line in the figure), the shielding member 27 is reflected by the reflecting member 26 or the stay 25. It moves so that it may approach into the back side (opposite side of the halogen heater 23, or the non-direct heating area | region side). At this time, a part of the portion directly opposed to the halogen heater 23 in the shielding position before the movement is disposed on the back side of the reflecting member 26 or the stay 25 in the retracted position after the movement. Specifically, in FIG. 11, assuming that the portion where the shielding member 27 directly faces the halogen heater 23 at the shielding position is H1, when the shielding member 27 moves to the retracted position, a part H2 of the directly facing portion H1 is reflected. It moves to the position indicated by H3 on the back side of the member 26 or the stay 25.

  Thus, by moving the shielding member 27 to the retracted position, a portion H2 of the portion H1 directly facing the halogen heater 23 is hidden from the halogen heater 23 (the reflecting member 26 or the stay 25 between the halogen heater 23). Can be disposed at a position where the Thereby, since the shielding member 27 becomes difficult to receive the influence of the heat from the halogen heater 23, the temperature rise of the shielding member 27 itself is suppressed, and the thermal deformation of the shielding member can be prevented.

  Further, when the shielding member 27 is retracted, the moving stroke S of the shielding member 27 needs to be ensured as large as possible so that more portions can be hidden from the halogen heater 23. However, as shown in FIG. 11, in the configuration in which the nip forming member 24 is provided in the fixing belt 21, there is a limitation that it is difficult to retract the shielding member 27 to the nip portion N side.

  Therefore, here, the halogen heater 23 is disposed on the upstream side of the nip portion N in the sheet conveyance direction (below the imaginary straight line L), and the shielding member 27 is disposed at the upstream shielding position and the downstream retracted position. It is configured to be movable between. As a result, the shielding member 27 can be retracted without interfering with the nip forming member 24, and a large movement stroke S of the shielding member 27 can be ensured.

  As shown in FIG. 11, in this embodiment, the stay 25 is formed so as to extend from the downstream side of the nip forming member 24 in the sheet conveyance direction to the side opposite to the pressure roller 22, and the stay 25 is extended. A retraction space U into which the shielding member 27 can enter is provided between the portion 250 and the inner peripheral surface of the fixing belt 21. In other words, by extending the stay 25 to the side opposite to the pressure roller 22, a large retreat space U is secured in a limited space in the fixing belt 21.

  As described above, in the present embodiment, since the retreat space U and the movement stroke S are configured to be large, the shielding member 27 is hidden from the halogen heater 23 during retraction, so that the temperature rises further. A suppressive effect can be expected. In addition, the configuration in which the moving stroke S and the retreat space U of the shielding member 27 can be ensured to be large as described above, particularly in the configuration in which the diameter of the fixing belt 21 is reduced to reduce the heat capacity, as described above. This is preferable because the inner space of the is small.

12-14 is a figure which shows the shielding position or retraction | saving position of a shielding member in embodiment which each said shielding part has two level | step-difference parts.
Specifically, FIG. 12 is a diagram illustrating a state in which the shielding member 27 is moved to a small size shielding position (first shielding position) when the small size paper P1 is passed, and FIG. FIG. 14 shows a state in which the shielding member 27 is moved to the large-size shielding position (second shielding position) when passing the size paper P3. FIG. 14 shows the state in which the shielding member 27 is moved to the retracted position. FIG. In each figure, (a) is a perspective view of the fixing device in each state, (b) is a sectional view taken along line DD in (a), (c) is a sectional view taken along line EE in (a), and (d). FIG. 6 is a sectional view taken along line FF in FIG.

  First, when the small-size paper P1 shown in FIG. 12 is passed, it is necessary to shield the heat of the halogen heater 23 mainly by the large shielding portion 48b of the shielding member 27. Therefore, the large shielding portion 48b is connected to the halogen heater 23. Move to the opposite position. Therefore, particularly in this case, the shielding member 27 is most exposed to the halogen heater 23 side.

  Next, when the medium-size paper P2 shown in FIG. 13 is passed, the large shielding portion 48b is not exposed to the halogen heater 23 side, and the heat of the halogen heater 23 is mainly shielded by the small shielding portion 48a. In this case, compared to the case shown in FIG. 12, the exposure of the shielding member 27 to the halogen heater 23 side is reduced, and a part of the large shielding portion 48b is disposed on the back side of the reflecting member 26 or the stay 25. The shielding member 27 is not easily heated.

  Further, as shown in FIG. 14, when the shielding member 27 is moved to the retracted position, the exposure of the shielding member 27 to the halogen heater 23 side is the least. As described above, even in the embodiment in which each shielding portion has two stepped portions, the portion where the shielding member 27 is hidden from the halogen heater 23 by the reflecting member 26 or the stay 25 by moving the shielding member 27 to the retracted position. As a result, the temperature rise of the shielding member 27 itself is suppressed. Further, particularly in this case, as shown in FIG. 14C, the entire wide large shielding portion 48b is completely hidden from the halogen heater 23 (so that the reflecting member 26 or the stay 25 is interposed between the halogen heater 23). Therefore, the heat suppression effect of the shielding member 27 is enhanced.

  In addition, in the said description, although the case where the shielding member of the type in which each shielding part has a level | step-difference part and the type which has two each about the effect | action and effect of this invention was demonstrated, Even in a shielding member of a type having three or more step portions, it is possible to suppress heating of the shielding member by retracting the shielding member to the back side of a stay or the like.

FIG. 15 is a diagram illustrating the temperature rise of the shielding member and the reflecting member when the heat capacity of the shielding member is large and when the heat capacity is small.
In FIG. 15, the vertical axis represents temperature, and the horizontal axis represents continuous paper passing time. A dotted line Ta1 is a temperature rise of the shielding member when a shielding member having a small heat capacity is used, and a dotted line Ta2 is a temperature rise of the reflecting member when a shielding member having a small heat capacity is used. On the other hand, the solid line Tb1 is the temperature rise of the shielding member when the shielding member having a large heat capacity is used, and the solid line Tb2 is the temperature rise of the reflecting member when the shielding member having the same heat capacity is used. Also, the alternate long and short dash line G1 indicates the heat resistant temperature of the shielding member, and the alternate long and short dash line G2 indicates the heat resistant temperature of the reflecting member.

  As shown in FIG. 15, the temperature rise of the shielding member is more gradual when the heat capacity is large (Tb1) than when the heat capacity is small (Ta1). Therefore, when the heat capacity is large, the time until the heat resistant temperature is reached becomes longer, so that it is possible to make the shielding member less likely to be thermally deformed, and as a result, the number of sheets that can be continuously fed can be increased.

  Further, as shown in FIG. 15, the temperature rise of the reflecting member is more gradual when the shielding member has a large heat capacity (Tb2) than when the shielding member has a small heat capacity (Ta2). This is considered to be because when the heat capacity of the shielding member is large, the amount of heat (heat storage amount) that the shielding member can absorb increases, and as a result of absorbing ambient heat, the heat imparted to the reflecting member decreases. Thus, by increasing the heat capacity of the shielding member, the amount of heat that can be absorbed by the shielding member is increased, and as a result, there is a secondary effect that the temperature rise of the peripheral members can be suppressed.

  For example, resin members (flange member 40, slide member 41, etc.) in the above embodiment have a heat-resistant temperature of about 250 ° C., which is lower than iron-based metal members, and thus tend to be easily damaged by heat. is there. In addition, since the reflecting member 26 is formed in a material and shape having a low heat capacity, the temperature easily rises and the distance from the halogen heater 23 is short and the heat-resistant temperature is low (about 200 ° C.). Is the most concerned member. Therefore, as described above, by increasing the heat capacity of the shielding member, a part of the heat applied to the peripheral member such as the reflecting member 26 and the resin member can be absorbed, and the temperature rise of these peripheral members is suppressed. can do. Thereby, it becomes possible to prevent damage and deterioration of the peripheral members due to heat. In particular, it is desirable that the heat capacity of the shielding member 27 is larger than the heat capacity of the reflecting member 26 in order to effectively suppress the temperature rise of the reflecting member 26 that is likely to be damaged by heat.

  In order to increase the heat capacity of the shielding member 27, the width size, circumferential size, or thickness of the shielding member 27 may be increased. Moreover, you may change into the shape like the shielding member 27 shown in FIG. 9 from the shape like the shielding member 27 shown in FIG. The shielding member 27 shown in FIG. 9 has a larger heat capacity than the shielding member 27 shown in FIG. Therefore, the heat capacity of the shielding member 27 can be increased by using the shielding member 27 shown in FIG. 9 instead of the shielding member 27 shown in FIG.

  In addition, as shown in FIG. 16, when the shielding member 27 is moved to the retracted position, the distal end portion 27 b in the retracting direction of the shielding member 27 is brought into contact with the stay 25, so that it is stored in the shielding member 27. Heat can be released to the stay 25. Thereby, the temperature rise of the shielding member 27 can be suppressed, and the thermal deformation of the shielding member 27 can be more reliably prevented. Further, by releasing the heat stored in the shielding member 27 to the stay 25, the effect of absorbing the peripheral heat by the shielding member 27 is also improved, so that it is possible to further suppress the temperature rise of the peripheral members such as the reflecting member 26. Become.

  Further, as shown in FIGS. 17 and 18, a heat transport member 55 such as a heat pipe is provided from the stay 25 to the pressure roller 22, and the heat of the stay 25 is supplied to the pressure roller 22 through the heat transport member 55. You may make it transmit to. Thereby, since the heat stored in the stay 25 can be effectively used for heating or preheating of the pressure roller 22, energy saving performance is improved. Here, the heat transport member 55 is brought into contact with the outer peripheral surface of the pressure roller 22, but may be brought into contact with the cored bar 22 a of the pressure roller 22.

  Further, as shown in FIG. 19, the heat transport member 55 may be provided from the stay 25 to the paper feed unit (paper feed cassette) including the paper feed tray 10. In this case, since the paper P accommodated in the paper feed tray 10 can be preheated, the heat energy required for fixing can be saved. In addition, in this case, by applying heat to the paper P, prevention of paper wrinkles and curling due to moisture absorption of the paper P can be expected.

  In the above description, the suppression of excessive temperature rise from the viewpoint of heat resistance has been described, but on the other hand, improvement of fixing property and energy saving property, shortening of startup time (hereinafter referred to as “improvement of fixing property, etc.”) ), The fixing belt and the like should be preferentially heated. In other words, when the power switch is turned on or when returning from the energy saving mode or standby mode, the halogen heater starts to generate heat and heats up until the temperature of the fixing belt reaches a predetermined temperature required for fixing. It is desirable to preferentially heat in order from a member having a large contribution to improvement of fixing property.

  Therefore, for example, in the fixing device having the configuration shown in FIG. 2, when the temperature of the fixing belt 21 is heated to a predetermined temperature, the temperature increase rate of the halogen heater 23 is Vt1, the temperature increase rate of the fixing belt 21 is Vt2, Assuming that the temperature increase rate of the pressure roller 22 is Vt3, the temperature increase rate of the nip forming member 24 is Vt4, the temperature increase rate of the stay 25 is Vt5, and the temperature increase rate of the shielding member 27 is Vt6, Vt1> Vt2> Vt3> Vt4. It is desirable to have a relationship of> Vt5> Vt6.

  In order to heat and melt and fix the toner carried on the paper, it is sufficient that at least the fixing belt 21 and the pressure roller 22 have a heat quantity sufficient to melt the toner. The roller 22 should be heated with particular priority. On the other hand, the nip forming member 24, the stay 25, and the shielding member 27 do not need to be heated so aggressively. Accordingly, heat transfer speeds Vt1 and Vt2 of the fixing belt 21 and the pressure roller 22 can be transferred so as to be faster than the temperature rising speeds Vt4, Vt5, and Vt6 of the nip forming member 24, the stay 25, and the shielding member 27. desirable. In the configuration shown in FIG. 2, the heat from the halogen heater 23 is first applied to the fixing belt 21, and a part of the heat amount of the fixing belt 21 is transmitted to the pressure roller 22. The temperature rising speeds of the three members of the halogen heater 23, the fixing belt 21, and the pressure roller 22 have a relationship of Vt1> Vt2> Vt3 as described above.

  Further, the fixing belt 21 is in contact with both the pressure roller 22 and the nip forming member 24. However, in order to improve the fixing property, the heat amount of the fixing belt 21 is higher than that of the pressure roller than the nip forming member 24. It is better to actively communicate to 22. Therefore, the heat transfer rate between the fixing belt 21 and the pressure roller 22 is preferably larger than the heat transfer rate between the fixing belt 21 and the nip forming member 24.

  However, a part of the heat of the fixing belt 21 is still taken away by the nip forming member 24. Therefore, for the purpose of making it difficult for heat to be removed from the fixing belt 21, it is desirable that the temperature of the nip forming member 24 be raised faster than that of the stay 25 and the shielding member 27 (temperature raising speed Vt 4 of the nip forming member 24> rise of the stay 25. Temperature rate Vt5> Temperature increase rate Vt6 of the shielding member 27).

  The stay 25 that does not need to be actively heated is desirably disposed at a position as far as possible from the halogen heater 23. In particular, as in the embodiment shown in FIG. 2, by interposing the reflecting member 26 between the halogen heater 23 and the stay 25, the heat from the halogen heater 23 is almost totally reflected by the reflecting member 26. The positive heat transfer to 25 can be suppressed. Furthermore, if the reflecting member 26 is disposed so as not to be in contact with each other via the air layer with respect to the stay 25, the heat of the reflecting member 26 can be more difficult to be transmitted to the stay 25. Further, the shielding member 27 that does not need to be actively heated is moved to the retracted position during the temperature raising operation, and is retracted to the back side of the reflecting member 26 and the stay 25, thereby reducing heat absorption by the shielding member 27. The heat applied to the fixing belt 21 can be increased.

  When the temperature increase rate of the reflecting member 26 shown in FIG. 2 is further added as Vt7 to the relationship between the temperature increase rates of the above members, the relationship Vt1> Vt2> Vt7> Vt3> Vt4> Vt5> Vt6 is established. It is desirable.

  The reflection member 26 is formed in a material and shape having a low heat capacity so as to eliminate wasteful energy consumption as much as possible. For this reason, the heating rate is the second highest after the fixing belt 21 (of the fixing belt 21). Temperature rising speed Vt2> temperature increasing speed Vt7 of the reflecting member 26).

  Further, when image fixing processing is performed continuously for a long time, heat is transmitted from the fixing belt 21 to the nip forming member 24, or heat from the halogen heater 23 is transmitted to the reflecting member 26, the stay 25, or the like. As a result, heat is gradually stored in each component of the fixing device. Thereafter, the temperature of each component is in an equilibrium state. In the situation where the temperature of each component member is in an equilibrium state, each component member in the equilibrium state is as follows in order to increase energy savings and achieve a long life and high durability of the component parts. It is desirable to set the temperature.

  For example, in the fixing device having the configuration shown in FIG. 2, when the temperature reaches an equilibrium state, the temperature of the halogen heater 23 is Et1, the temperature of the fixing belt 21 is Et2, the temperature of the pressure roller 22 is Et3, and the nip forming member 24 It is preferable that Et1> Et5> Et4> Et2> Et3 be satisfied, where Et4 is Et4 and the temperature of the stay 25 is Et5.

  As in the above relationship, in the equilibrium state, the temperature Et5 of the stay 25 becomes high, and a large amount of heat is stored in the stay 25, so that the stay 25 is a medium that applies the stored heat to the fixing belt 21 and the like. Can function. As a result, the halogen heater 23 can supply a sufficient amount of heat for fixing with a smaller amount of heat generation (heat generation amount per unit time) than during the temperature raising operation.

  In addition, by making the temperature Et4 of the nip forming member 24 higher after the stay 25, the amount of heat taken by the nip forming member 24 from the fixing belt 21 can be reduced. Thereby, it is possible to prevent the occurrence of fixing failure due to a drop in temperature at the nip portion N.

  However, when the nip forming member 24 is made of resin, heat resistance is lower than that of the metal stay 25, so care must be taken not to raise the temperature of the nip forming member 24 too much. In particular, it is preferable to prevent excessive heat transfer from the stay 25 where the temperature is high to the nip forming member 24. Therefore, the heat transfer coefficient between the nip forming member 24 and the stay 25 is preferably smaller than the heat transfer coefficient between the nip forming member 24 and the fixing belt 21. Accordingly, heat transfer from the stay 25 to the nip forming member 24 can be suppressed, and conversely, heat transfer from the nip forming member 24 to the fixing belt 21 can be promoted. It is possible to suppress deterioration and damage due to heat.

  Further, when the temperature of the reflecting member 26 is further added as Et7 to the temperature relationship in the equilibrium state of each member, the temperature Et7 of the reflecting member 26 becomes the second highest after the temperature Et1 of the halogen heater 23, so Et1> Et7>. The relationship is Et5> Et4> Et2> Et3.

  As described above, according to the present invention, since heating of the shielding member can be suppressed, deformation of the shielding member due to heat can be prevented. As a result, it is possible to avoid degradation of the function due to thermal deformation of the shielding member and interference between the deformed portion and other members, and the reliability of the apparatus is improved.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, the shape of the shielding member is not limited to the above-described embodiment. In the above-described embodiment, the circumferential cross section of the shielding member is formed in an arc shape, but may be formed in a curved shape other than the arc shape, a shape having a straight portion, or the like.

  In the above-described embodiment, the reflecting member 26 and the stay 25 function as a heating suppression member that is interposed between the shielding member 27 and the halogen heater 23 and suppresses the heating of the shielding member 27. May be used as a heating suppression member. Further, a dedicated heating suppression member may be provided. In addition, when there is a gap between the heating suppression members, the shielding member can be hidden from the heating source by causing the shielding member to enter the gap. That is, the location where the shielding member is hidden from the heating source is not limited to the back side of the heating suppression member (the surface side facing the fixing belt 21).

  Further, the surface of the shielding member facing the heating source may be a mirror surface. In this case, the heat reflectivity of the shielding member can be increased, and heating of the shielding member can be further suppressed.

  Further, the image forming apparatus equipped with the fixing device according to the present invention is not limited to the printer as shown in FIG. 1, but can be a copying machine, a facsimile, or a complex machine thereof.

20 Fixing device 21 Fixing belt 22 Pressure roller (opposing member)
23 Halogen heater (heating source)
24 Nip forming member 25 Stay (heating suppression member)
26 Reflective member (heating suppression member)
27 shielding member 48 shielding portion 48a small shielding portion 48b large shielding portion 55 heat transport member U retreat space portion P paper (recording medium)

Japanese Patent No. 4130898 JP 2008-58833 A JP 2008-139779 A

Claims (13)

A rotatable endless fixing belt, a heating source for heating the fixing belt, a nip forming member disposed on the inner peripheral side of the fixing belt, and the nip forming member from the outer peripheral side of the fixing belt. In a fixing device comprising: a facing member that forms a nip portion in contact with the fixing belt; and a shielding member that shields heat from the heating source.
The shielding member is disposed around the heating source, and is formed in an end in the circumferential direction over the entire width direction of the recording medium passage region,
The shielding member has a shielding position where at least a part thereof directly faces the heating source and shields heat, and a portion directly opposed to the heating source retreats from the shielding position and suppresses heating between the heating source and the shielding source. A fixing device configured to be movable between a retracted position where members are interposed. The heating source is disposed on the inner peripheral side of the fixing belt and on the upstream side of the nip portion in the recording medium conveyance direction, and
The heating suppression member is disposed on the inner peripheral side of the fixing belt and on the downstream side of the nip portion in the recording medium conveyance direction,
2. The configuration according to claim 1, wherein the shielding member is configured to be movable between the shielding position on the upstream side of the nip portion in the recording medium conveyance direction and the retracted position on the downstream side of the nip portion in the recording medium conveyance direction. Fixing device. A support member for supporting the nip forming member;
The fixing device according to claim 1, wherein the support member is the heating suppression member. The support member is formed so as to extend from the downstream side of the nip forming member in the recording medium conveyance direction to the opposite side of the facing member,
The fixing device according to claim 3, wherein a retraction space portion into which the shielding member can enter is provided between a portion of the support member that extends to the opposite side of the facing member and an inner peripheral surface of the fixing belt. A reflection member that reflects heat from the heating source to the fixing member;
The fixing device according to claim 1, wherein the reflection member is the heating suppression member. The shielding member has a small shielding part having a small longitudinal width and a large shielding part having a large longitudinal width at both longitudinal ends thereof,
6. The device according to claim 1, wherein, when the shielding member is moved to the retracted position, at least the entire large shielding portion is disposed so that the heating suppressing member is interposed between the heating source and the heating source. The fixing device according to claim 1.   The fixing device according to claim 1, wherein a surface of the shielding member facing the heating source is a mirror surface. A reflection member that reflects heat from the heating source to the fixing member;
The fixing device according to claim 1, wherein a heat capacity of the shielding member is larger than a heat capacity of the reflecting member.   The fixing device according to claim 8, wherein when the shielding member moves to the retracted position, the shielding member contacts the heating suppression member.   The fixing device according to claim 9, further comprising a heat transport member that transmits heat from the heating suppression member to the opposing member. A support member for supporting the nip forming member;
When heating the fixing belt to a predetermined temperature,
The temperature rise rate of the heating source is Vt1, the temperature rise rate of the fixing belt is Vt2, the temperature rise rate of the counter member is Vt3, the temperature rise rate of the nip forming member is Vt4, and the temperature rise rate of the support member is Vt5. When the heating rate of the shielding member is Vt6,
The fixing device according to claim 1, wherein the fixing device is configured to satisfy a relationship of Vt 1> Vt 2> Vt 3> Vt 4> Vt 5> Vt 6. A reflection member that reflects heat from the heating source to the fixing member;
When heating the fixing belt to a predetermined temperature,
When the heating rate of the reflecting member is Vt7,
12. The fixing device according to claim 11, wherein the fixing device is configured to satisfy a relationship of Vt1>Vt2>Vt7>Vt3>Vt4>Vt5> Vt6.   An image forming apparatus comprising the fixing device according to claim 1.

Images