JP2017142541A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can reduce energy loss due to an increase in temperature of a reflection member.SOLUTION: A blocking member 27 is arranged between a halogen heater 23 and a fixing belt 21 of a fixing device, and blocks heat directed from the halogen heater 23 to the fixing belt 21 with a blocking part 48 of the blocking member 27. The heat reflection ratio of at least a surface of the blocking part 48 of the blocking member 27 facing the halogen heater 23 is made smaller than the heat reflection ratio of a surface of a reflection member 26 facing the halogen heater 23.SELECTED DRAWING: Figure 13

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.

  In order to solve this problem, there has been proposed a fixing device provided with a shielding member that shields heat from a heating source in a non-sheet passing region of the fixing member (Patent Document 1). In this fixing device, a reflecting member having an opening directed to the fixing member is disposed around the halogen heater, and the shielding member is put in and out of the irradiation path of heat irradiated from the opening of the reflecting member toward the fixing roller. Thus, an excessive temperature rise of the fixing member in the non-sheet passing region is prevented.

  However, the fixing device of Patent Document 1 has a problem in that heat is reflected even by the shielding member arranged in the irradiation path, and a part of the reflected heat returns to the reflecting member to raise the temperature of the reflecting member. Since the reflecting member is not a member that should be heated originally, such a temperature rise of the reflecting member causes energy loss.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device capable of reducing energy loss and an image forming apparatus including the fixing device.

  In order to achieve the above object, the present invention provides a rotatable fixing member, a heating source for heating the fixing member, an opposing member that abuts on the outer peripheral surface of the fixing member to form a nip portion, and around the heating source. In a fixing apparatus, comprising: a reflecting member disposed; and a shielding member disposed between a heating source and a fixing member, wherein the shielding member is provided with a shielding portion that shields heat from the heating source toward the fixing member. Among the members, at least the shielding part has a thermal reflectance of a surface facing the heating source, which is smaller than a thermal reflectance of the surface of the reflecting member facing the heating source.

  According to the present invention, heat reflection at the shielding portion is suppressed, and thereby the amount of heat absorbed by the shielding portion increases, and therefore, the amount of heat absorbed by the reflecting member can be reduced accordingly. In this case, the temperature of the shielding member rises due to the heat absorbed by the shielding part, but the fixing member is located closer to the fixing member than the reflecting member, so that the fixing member can be heated by the heat absorbed by the shielding member. it can. Therefore, the energy loss due to the temperature rise of the reflecting member can be reduced.

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 which shows the relationship between the shape of a shielding member, and the heat generating part of a halogen heater. It is a figure which shows the relationship between the shape of a shielding member, and the heat generating part of a halogen heater. It is sectional drawing of a shielding member. It is sectional drawing of a shielding member. It is sectional drawing of a shielding member. It is sectional drawing which shows schematic structure around a halogen heater.

  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 80 μm or more. By providing an elastic layer having a thickness of 80 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, 80 to 300 μm, and 3 to 50 μm, and the total 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 22. 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 material having a heat resistant temperature of 200 ° C. or higher. With such a configuration, it is possible to prevent the nip forming member 24 from being deformed by heat in the toner fixing temperature range, to secure a stable state of the nip portion N, and to stabilize the output image quality. In addition, the base pad 241 is required to have appropriate rigidity to ensure strength. The material of the base pad 241 that satisfies the above conditions includes polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone. Resins such as (PEEK) and liquid crystal polymer (LCP) can be used. In addition, the base pad 241 can be formed of metal or ceramic.

  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 steel in order to satisfy the function of preventing the nip forming member 24 from bending.

  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.

  The shielding member 27 is made of, for example, a thin metal plate having a thickness of 0.1 mm to 1.0 mm, and the whole is formed in a partial cylindrical surface shape having a cross section orthogonal to the longitudinal direction as an end. The shielding member 27 is close to the inner peripheral surface of the belt inside the fixing belt 21 and rotates substantially coaxially with the fixing belt 21 in a non-contact state with the inner peripheral surface. 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 is a non-direct heating region in which members (reflection member 26, stay 25, nip forming member 24, etc.) are interposed. When it is necessary to perform heat shielding, as shown in FIG. 2, the shielding member 27 is directly arranged at the shielding position on the heating region side. On the other hand, when there is no need for heat shielding, as shown in FIG. 3, the shielding member 27 is rotated and moved to the retracted position on the non-direct heating region side, and the shielding member 27 is moved to the back side of the reflecting member 26 and the stay 25. It is possible to evacuate. By rotating the shielding member 27 in this manner, the amount of heat supplied from the halogen heater 23 to the fixing belt 21 is adjusted by increasing or decreasing (including the case where the shielding area 27 is set to 0). Yes. The shielding member 27 is formed of a material having heat resistance of 350 ° C. or higher, and the shielding member 27 can be formed of a material other than metal, such as resin or ceramic, as long as this condition is satisfied.

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. The slide member 41 is provided with a convex portion 41b, and the convex portion 41b is inserted into an arcuate groove portion 40a provided in the flange member 40, whereby the guide 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, the drive means for the shielding member 27 includes a motor 42 that is a drive source and a gear train that includes a plurality of transmission gears 43, 44, and 45. 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 27, the heat generating portion of the halogen heater 23, 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. Further, an opening 50 is provided between the shielding portions 48 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.

  In this embodiment, for example, the medium size is letter size (sheet passing width 215.9 mm) or A4 size (sheet feeding width 210 mm), and the large size is double letter size (sheet feeding width 279.4 mm) or A3 size ( The paper passing width is 297 mm), and the extra large size is A3 Nobi (paper passing width 329 mm). However, the paper size example is not limited to this. Further, the medium size, large size, and extra large size referred to here indicate the relative size relationship of each size, and the specific numerical value of the sheet passing width is not limited to the above example.

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.

Next, the control of the halogen heater and the control of the shielding member 27 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.

  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.

  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 halogen heater 23 b 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. Is reached, the shielding member 27 is rotated in a direction to cover the heat generating portion 23b on both ends. Thereby, it is possible to reliably suppress an abnormal temperature rise of the fixing belt 21.

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 configuration example of the shielding member.
In the shielding member 27 shown in FIG. 9, the shielding portions 48 on both ends are integrally 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 48b with a large longitudinal direction width | variety. The small shielding parts 48a are located at both ends in the longitudinal direction of the shielding member 27, and protrude to the shielding side Y from the large shielding part 48b. The two shielding parts 48 are connected via a connecting part 49. 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 so as to be separated from each other toward the shielding side Y. In this type of shielding member 27, the straight portion 51 as in 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. In this embodiment, for example, the small size is a postcard size (sheet feeding width 100 mm), the middle size is A4 size (sheet feeding width 210 mm), the large size is A3 size (sheet feeding width 297 mm), and the extra large size is A3 nobi (Paper 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.

  As shown in FIGS. 2 and 3, in the present invention, the shielding member 27 is disposed inside the fixing belt 21, and the shielding member 27 is moved between the shielding position and the retracted position. In particular, when the shielding member 27 is at the shielding position, a part of the heat irradiated from the heating source 23 is reflected by the shielding portion 48 of the shielding member 27 and returned to the reflecting member 26. This heat is reflected again by the reflecting member 26, so that the heat goes back and forth between the shielding member 27 and the reflecting member 26. Therefore, as a result, the reflection member 26 is heated and the reflection member 26 is heated. Alternatively, since heat applied to the reflecting member 26 escapes to the stay 25, the heat capacity in the reflecting member 26 and its peripheral structure increases. These factors result in increased energy loss.

  As a countermeasure against this, in the present invention, as shown in FIG. 11, the thermal reflectance of at least the surface of the shielding member 48 facing the heating source 23 (region with a dotted pattern in the drawing) of the shielding member 27. Is made smaller than the heat reflectance of the surface of the reflecting member 26 facing the heating source 23.

  As a result, even when the shielding member 27 is in the shielding position, the amount of heat absorbed by the shielding portion 48 is increased, so that the heat absorption by the reflecting member 26 is reduced and the reflecting member 26 is excessively heated (particularly its non-sheet passing state). Overheat in the region) and increase in energy loss due to the large heat capacity inside the fixing belt 21 can be suppressed. In this case, the temperature of the shielding part 48 rises, but the shielding member 48 is disposed between the heating source 23 and the fixing belt 21 and is located close to the inner peripheral surface of the fixing belt 21. The fixing belt 21 can be heated by the heat absorbed by the toner. Accordingly, energy loss in the entire fixing device 20 can be reduced.

  Of the shielding member 27, the connecting portion 49 is always behind the reflecting member 26 regardless of the shielding state and retracted state of the shielding member 49, and therefore can directly receive heat from the heating source 23 and the reflecting member 26. Absent. Therefore, the heat reflectance of the connecting portion 49 is not particularly problematic. Further, since the amount of heat of irradiation is reduced outside the region of the heating source 23 that faces the heat generating portions 23b at both ends, the heat reflectance of the shielding portion 48 in this outer region is not so problematic. Therefore, the minimum effect can be obtained if the thermal reflectance of the region indicated by the dotted pattern in FIG.

  Of course, the heat reflectivity of the entire surface of the shielding member 27 on the heating source 23 side may be defined by the above relationship. For example, when a coating having a high thermal reflectance (for example, a silver alloy coating) is formed on the surface of the reflecting member 26 on the heating source side, or when the surface of the reflecting member 27 on the heating source side is an aluminum electrolytic polishing surface, the shielding member If the whole 27 is made of stainless steel, the relationship of the thermal reflectance of the shielding member 27 <the thermal reflectance of the reflecting member 26 can be obtained, so that the above effect can be obtained.

  FIG. 12 shows a case where the present invention is applied to the shielding member 27 shown in FIG. Even in this type of shielding member 27, the heat reflectance of at least the surface of the shielding portion 48 facing the heating source 23 (region with a dotted pattern in the drawing) of the shielding member 27 is determined by heating the reflecting member 26. The same effect can be obtained by making it smaller than the thermal reflectance of the surface facing the source.

  FIG. 13 shows a shielding member 27 having a composite structure composed of a base material 270 and a low heat reflectance layer 271 covering the surface of the base material 270. This shielding member 27 is particularly suitable when it is desired to use a material having a high thermal reflectance as a material but having other merits (for example, low cost). In this case, such a material is used for the base material 270, and the low heat reflectivity layer 271 is formed of a material having a lower heat reflectivity than the base material 270. As the low thermal reflectance layer 271, a film formed by a known film forming means such as plating or vapor deposition can be used. In addition, a composite structure shown in FIG. 13 can be obtained by laminating two kinds of thin plate materials.

  Also in this configuration, the above effect can be obtained by making the thermal reflectance of the low thermal reflectance layer 271 smaller than the thermal reflectance of the surface of the reflecting member 27 on the heating source 23 side. In addition to making the entire shielding member 27 have a composite structure, it is sufficient to make at least the area of the shielding part 48 facing the heating source 23 (the area with the dotted pattern in FIGS. 11 and 12) a composite structure. In addition, as a material of the base material 270, metal materials, such as aluminum and steel (a stainless steel is included), Furthermore, a ceramic etc. can be used.

  By the way, in the shielding member 27 in the shielding state, since the shielding part 48 is heated intensively, the temperature around the shielding part 48 of the shielding member 27 tends to be locally increased. In particular, when the reflectance of the shielding portion 48 is lowered as described above, this tendency is promoted. It is desirable to avoid the local temperature rise of the shielding member 27 because it causes heating unevenness and deformation of the shielding member 27.

  As a countermeasure for this problem, it is conceivable to increase the thermal conductivity of the shielding member 27. As described above, by increasing the thermal conductivity of the shielding member 27, it becomes possible to quickly diffuse the heat absorbed locally by the shielding portion 48 to the entire shielding member 27. Overheating can be prevented.

  FIG. 14 shows a specific example of this measure, and shows a composite structure shielding member 27 comprising a base material 270 and a high thermal conductivity layer 272 covering the surface of the base material 270. In this case, the thermal conductivity of the high thermal conductivity layer 272 is at least larger than the thermal conductivity of the base material 270. Specifically, the high thermal conductivity layer 272 is formed of a material having a thermal conductivity of 30 W / (m · K) or higher, preferably 80 W / (m · K) or higher at room temperature. Specific examples of such materials include copper-based materials, aluminum-based materials, and nickel-based materials. Note that the high thermal conductivity layer 272 can be formed of a film or a thin plate material in the same manner as the low thermal reflectance layer 271.

  The high thermal conductivity layer 272 is formed over the entire surface of either one of the surface on the heat source 23 side of the shielding member 27 and the opposite surface thereof. In the embodiment of FIG. 14, as an example, the high thermal conductivity layer 272 is formed on the surface of the base material 270 opposite to the surface facing the heating source 23. In this case, the surface of the base material 270 facing the heating source 23 needs to have a smaller thermal reflectance than the surface of the reflecting member 26 facing the heating source 23.

  When the base material 270 having such heat reflectivity cannot be used, the low heat reflectivity layer 271 described in the embodiment of FIG. 13 is formed on the surface of the base material 270 on the heating source 23 side as shown in FIG. Form. Thereby, it is possible to prevent an excessive temperature rise of the reflecting member 26 and a large heat capacity inside the fixing belt 21 to reduce energy loss.

  13 to 15 exemplify the shielding member 27 having a composite structure of two or more layers, but each of the physical properties required for the shielding member 27 (predetermined thermal reflectance, 30 W / (m · K) or more. The shielding member 27 may be formed of the material itself as long as it is a material (for example, a copper-based material, an aluminum-based material, or a nickel-based material) that satisfies the above thermal conductivity, more preferably heat resistance of 350 ° C. or higher. Absent.

  In each of the embodiments described above, in order to reduce energy loss, the thermal reflectance of the shielding member 27 is defined as a predetermined condition. However, this purpose is not limited to the material physical properties, but the shape of the reflecting member 26. It can also be achieved with care.

  Specifically, as shown in FIG. 16A, among the reflecting members 26 arranged around the heating source 23, the interval W <b> 1 between the side walls 26 a arranged on both sides of the heating source 23 is set as the reflecting member 26. Enlarge the tip side of. If the interval W2 between the side walls 26a ′ is constant even on the tip side as in the reflecting member 26 ′ shown in FIG. 16B, heat tends to be trapped in the space between the heating source 23 and the reflecting member 26 ′. Although this contributes to excessive heating of the reflecting member 26 and an increase in the heat capacity inside the fixing belt 21, the configuration shown in FIG. 16A promotes heat dissipation. Can suppress energy loss. Further, as shown in FIG. 2, if the gap 29 between the reflecting member 26 and the stay 25 is locally increased, the heat of the reflecting member 26 becomes difficult to be transmitted to the stay 25, so that the energy loss can be further reduced. it can.

  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. In the above embodiment, the case where the present invention is applied to a fixing device using a fixing belt has been described as an example. However, a configuration in which a hollow (cylindrical) or solid fixing roller is used instead of the fixing belt. It is possible to apply the present invention. Further, the shape of the shielding member is not limited to the above-described embodiment. Depending on the paper size used, the shielding member may be formed in a shape having three or more step portions. 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 (fixing member)
22 Pressure roller (opposing member)
23 Halogen heater (heating source)
24 Nip forming member 25 Stay (support member)
26 Reflecting member 27 Shielding member 40 Belt holding member 41 Slide member 270 Base material 271 Low thermal reflectance layer 272 High thermal conductivity layer P Paper (recording medium)

JP 2008-139779 A

Claims (7)

A rotatable fixing member;
A heating source for heating the fixing member;
An opposing member that contacts the outer peripheral surface of the fixing member to form a nip portion;
A reflective member disposed around the heating source;
A shielding member disposed between the heating source and the fixing member;
In the fixing device in which the shielding member is provided with a shielding portion that shields heat from the heating source toward the fixing member.
The thermal reflectance of the surface of the shielding member inside the fixing member, the surface of the shielding part facing the heating source inside the fixing member,
Smaller than the thermal reflectance of the surface of the reflecting member inside the fixing member facing the heating source,
The fixing device, wherein the reflecting member is disposed between the heating source and a metal material supporting member inside the fixing member that supports the reflecting member. Of the shielding member, at least a region facing the heating source of the shielding part has a base material and a low thermal reflectance layer that covers the surface of the base material on the heating source side and has a lower thermal reflectance than the base material. The fixing device according to claim 1. The fixing device according to claim 1, wherein the shielding member includes a base material and a high thermal conductivity layer that covers the surface of the base material and has a higher thermal conductivity than the base material. The fixing device according to claim 1, wherein the shielding member is formed of a high thermal conductivity material having a thermal conductivity of 30 W / (m · K) or more. The fixing device according to claim 1, wherein the fixing member is a cylindrical member, and a heating source, a shielding member, and a reflecting member are disposed inside the fixing member. The fixing device according to claim 5, wherein the fixing member is an endless fixing belt, and a nip forming member that forms a nip portion and a support member that supports the nip forming member are disposed inside the fixing belt. An image forming apparatus comprising the fixing device according to claim 1.

Images