JP2014174311A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid, in providing a nip forming member and its support member on an inner peripheral side of a fixing belt in addition to a heat source, a reduction in strength and thermal deformation of the members due to the application of heat thereto, and a reduction in energy saving performance.SOLUTION: A fixing device includes an endless belt, a pressure member that is brought into contact with an outer peripheral surface of the belt, a nip forming member that is arranged inside the belt and forms a fixing nip part with the pressure member with the belt therebetween, a support member that is arranged inside the belt and supports the nip forming member, and a heat source that is arranged inside the belt. The fixing device is further provided with a heat transfer member that is attached to the support member to be in contact with the belt.

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.

  In image forming apparatuses such as copiers, printers, facsimiles, or multi-function machines having these functions, image fixing methods such as electrophotographic recording, electrostatic recording, magnetic recording, etc. are not fixed by image transfer method or direct method. A toner image is formed on a recording medium such as paper. A copy or recorded matter can be obtained by heating and fixing the unfixed toner image transferred and carried on the recording medium. During fixing, the unfixed image is heated while the recording medium carrying the unfixed image is sandwiched and conveyed by the fixing member and the pressure member, so that the toner of the unfixed image is melted and softened and penetrates into the recording medium. As a result, the toner is fixed to the recording medium.

  In recent years, market demands for energy saving and high speed are increasing for image forming apparatuses. Among them, a fixing device for fixing an unfixed toner image consumes a large amount of energy, so that many proposals have been made from the viewpoint of energy saving. As such a fixing device, a heat roller method, a belt method, a film heating method (surf fixing) using a ceramic heater, a contact heating method fixing device such as an electromagnetic induction heating method, etc. are widely adopted.

  In the belt-type fixing device, in recent years, further reduction in warm-up time and first print time has been desired (Problem 1). The warm-up time is the time required from a normal temperature state to a predetermined printable temperature (reload temperature), such as when the power is turned on, and the first print time is the print operation after receiving a print request and preparing for printing. This is the time until the paper discharge is completed. Further, as the speed of the image forming apparatus increases, the number of sheets to be passed per unit time increases and the required heat amount increases, so that there is a problem that the heat amount is insufficient at the beginning of continuous printing (so-called temperature drop). (Problem 2).

  As a method for solving the problem of problem 1, surf fixing using a very thin film as a fixing member has been proposed. Compared to the belt method, this method can be reduced in heat capacity and reduced in size, but it is difficult to endure, and since only the nip part is heated locally, other parts are not heated, and the nip part is not heated. There is a problem that the belt is in the coldest state at the entrance, and fixing failure tends to occur. In particular, in a high-speed machine, there is a problem that fixing failure is more likely to occur because the belt rotates fast and the heat radiation of the belt outside the nip increases (problem 3).

  In order to solve the above problems 1 to 3, the present applicant has made a proposal in Patent Document 1. This makes it possible to heat the entire belt in a configuration that uses an endless belt, shortens the first print time from the standby time of heating, and eliminates the lack of heat during high-speed rotation, resulting in high production. Even if it is mounted on a compatible image forming apparatus, good fixability is obtained.

  FIG. 10 schematically shows the fixing device proposed in Patent Document 1. A pipe-shaped metal heat conductor 22 is fixed inside the endless fixing belt 21 so as to be able to guide the movement of the fixing belt 21, and metal heat is generated by a halogen heater 23 in the metal heat conductor 22. The fixing belt 21 is heated via the conductor 22. Further, a pressure roller 24 as a pressure member that forms a nip portion N in contact with the metal heat conductor 22 through the fixing belt 21 is provided, and the fixing belt 21 is rotated so as to rotate as the pressure roller 24 rotates. Move in the circumferential direction. With such a configuration, the entire endless belt constituting the fixing device can be warmed, the first print time from the heating standby time can be shortened, and the shortage of heat at the time of high-speed rotation can be solved.

  However, in order to further save energy and improve the first print time, it is necessary to further improve the thermal efficiency, and the applicant further describes a configuration in which an endless belt is directly heated without using a metal heat conductor, for example, in Patent Document 2 Proposed. In this configuration, it is possible to reduce the power consumption by greatly improving the heat transfer efficiency and to further shorten the first print time from the heating standby time. In addition, the cost can be reduced without using a metal heat conductor.

  However, when the endless belt, which is a fixing member, is heated directly from the inside, the radiant heat from the heat source also heats the components inside the endless belt. There is a risk of malfunction. Further, the amount of heat taken away by these internal components increases, leading to a reduction in energy saving performance. The applicant of the present application has devised a structure in which a fixed nip forming member is used to abut the flexible endless belt against the pressure rotating body, and the nip forming member is supported by the supporting member inside the endless belt. In general, a metal material is used for the support member in order to ensure rigidity. Therefore, the increase in the amount of heat absorption becomes remarkable due to the high thermal conductivity of the support member. In addition, since the nip forming member and the support member are exposed to high temperatures, there is a problem in that they are damaged due to thermal deformation or the like and the life of the parts is reduced.

  The object of the present invention is to avoid a decrease in strength, thermal deformation, and further reduction in energy savings due to heating of a nip forming member and its supporting member in addition to a heat source on the inner peripheral side of the fixing belt. There is to do.

  The above-described problem is that an endless belt, a pressure member that abuts on the outer peripheral surface of the belt, and a nip formation that is disposed inside the belt and forms a fixing nip portion with the pressure member via the belt. In a fixing device having a member, a support member disposed inside the belt and supporting the nip forming member, and a heat source disposed inside the belt, the fixing device is attached to the support member and contacts the belt This is solved by providing a heat transfer member.

  According to the present invention, the heat transfer member is attached to the support member that is disposed inside the fixing belt and supports the nip forming member, and the heat transfer member is in contact with the belt, so that the heat applied to the nip forming member and the support member is heat. Not only is the overheating of the nip forming member and the support member avoided by being transferred to the fixing belt via the transmission member, but the heat applied to these members can be used for the original fixing.

1 is a front view showing an entire image forming apparatus. 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of a fixing device according to another embodiment. It is sectional drawing of the fixing device which concerns on another embodiment provided with the light-shielding member. It is an expanded view of the light shielding member which has the light-shielding width match | combined with each paper width. It is a figure explaining the operation position of the light-shielding member with respect to different paper widths. It is a fragmentary perspective view explaining the shape which can respond to the different paper size of the heat transfer member characteristic of this invention. It is a conceptual front view of the heat transfer member corresponding to FIG. It is a figure explaining contact / separation control of the heat transfer member with respect to a fixing belt. It is a schematic sectional drawing which shows the basic composition of the fixing device which concerns on a prior art.

  First, the overall configuration and operation of an image forming apparatus equipped with a fixing device according to the present invention will be described with reference to FIG. The image forming apparatus 1 is a tandem color laser printer. As a matter of course, the image forming apparatus according to the present invention is not limited to this method, and is also included in an object such as a copying machine or a facsimile.

  In FIG. 1, four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the printer 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. Since the configuration is the same except for the configuration, only the configuration of the black image forming unit 4K will be described. The other image forming units 4Y, 4M, and 4C omit the symbol display.

  The image forming unit 4K includes a drum-shaped photosensitive member 5 as a latent image carrier, a charging device 6 that charges the surface of the photosensitive member 5, a developing device 7 that supplies toner to the surface of the photosensitive member 5, and a photosensitive member. And a cleaning device 8 for cleaning the surface of 5.

  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 a transfer body, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, and a secondary transfer backup roller 32. ing. Further, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are also 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 connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 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 main body, and four toner bottles 2Y, 2M, 2C, and 2K containing 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 developing device is connected from each toner bottle 2Y, 2M, 2C, 2K via this replenishment path. 7 is supplied with toner.

  On the other hand, at the bottom 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. Here, the concept of the recording medium includes, in addition to plain paper, thick paper, 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, on the upstream side of the secondary transfer roller 36 in the paper transport direction, a timing adjusting roller 12 called a pair of registration rollers is disposed as a transport means for transporting the paper P to the secondary transfer nip. ing.

  Further, the fixing device 20 is disposed downstream of the secondary transfer roller 36 in the sheet conveyance 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. The fixing motor M1 that drives the fixing device 20 and the paper discharge motor M2 that drives the paper discharge roller 13 can be driven independently of each other. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

  Next, the basic operation of the printer according to this example will be described. When the image forming operation is started, each photoconductor 5 in each of the image forming units 4Y, 4M, 4C, and 4K is rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by a charging device. 6 is uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 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. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  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 successively 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. The toner on each photoconductor 5 that has not been transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, 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 image forming apparatus, 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 sheet P sent to the transport path R is timed by the registration roller 12 and sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. .

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the transfer electric field formed in the secondary transfer nip causes the toner image on the intermediate transfer belt 30 to move. The toner images are transferred onto the paper P all at once. At this time, the residual toner on the intermediate transfer belt 30 that has not been transferred to 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. Of course, it is possible to form a two-color or three-color image using two or three image forming units.

  Next, the fixing device according to this embodiment will be described with reference to FIG. The fixing device 20 includes a pressure roller 24 that is a pressure rotator (pressure member), a fixing belt 21 that is a flexible endless belt, and halogen heaters 23A, 23B, and 23C that are heat sources. The fixing belt 21 is directly heated from the inner peripheral side by these halogen heaters. The heat source is composed of three halogen heaters 23A, 23B, and 23C to support various paper widths, and by providing a plurality of heaters corresponding to the paper widths, excessive heat supply can be suppressed and energy saving can be achieved. It leads to improvement.

  A nip forming member 26 that forms a fixing nip portion N and a pressure roller 24 that is opposed to each other via the fixing belt 21 is disposed on the inner peripheral side of the fixing belt 21, and directly on the inner surface of the fixing belt or a low friction (not shown). The sheet is rubbed indirectly through the sheet. The nip forming member 26 is made of a heat-resistant member, and is arranged in a long length in the axial direction of the fixing belt 21 or the axial direction of the pressure roller 24.

  In FIG. 2, the shape of the fixing nip portion N is flat, but may be a concave shape in which the nip forming member 26 or the pressure roller 24 side is depressed or other shapes. If the nip forming member 26 has a concave shape, the discharge direction at the front end of the paper is closer to the pressure roller, so that the separation property is improved and the occurrence of jam can be suppressed.

  The fixing belt 21 is composed of a thin and flexible endless belt or film using a metal material such as nickel or SUS or a resin material such as polyimide. The outer peripheral surface of the belt has a release layer such as PFA, PTFE, etc., and has a release property so that toner does not adhere. There may be an elastic layer formed of silicone rubber or the like between the base material of the fixing belt 21 and the release layer. When there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, the minute irregularities on the belt surface are transferred to the image and the image has a crusty skin shape. There is a possibility of causing a defect in which gloss unevenness (zudder skin image) remains. In order to improve this, it is preferable to provide an elastic layer of silicone rubber of 100 [μm] or more. Due to the deformation of the silicone rubber, minute irregularities are absorbed.

  A support member 27 (stay) for supporting the nip forming member 26 is provided inside the fixing belt 21 to prevent the nip forming member 26 that receives pressure from the pressure roller 24 from being bent and uniform in the axial direction. The nip width can be obtained. The support member 27 is positioned by being held and fixed to the holding member 28 (flange) at both ends (both ends in a direction perpendicular to the paper surface). In addition, a reflection member 29 is provided between the halogen heaters 23A, 23B, and 23C and the support member 27, and wasteful energy consumption that the support member 27 is heated by radiant heat from the halogen heaters 23A, 23B, and 23C is suppressed. doing. Here, instead of providing the reflecting member 29, the same effect can be obtained even if the surface of the support member 27 is subjected to heat insulation or mirror treatment. The heat source may be the illustrated halogen heater, but may be IH, a resistance heating element, a carbon heater, or the like.

  In the pressure roller 24, an elastic rubber layer 24b is provided on the core metal 24a, and a release layer (PFA or PTFE layer) is provided on the surface in order to obtain releasability. The pressure roller 24 is rotated by a driving force transmitted through a gear from a driving source such as a motor provided in the image forming apparatus. The pressure roller 24 is pressed against the fixing belt 21 by a spring (not shown) and the elastic rubber layer is crushed and deformed to secure a predetermined nip width. The pressure roller 24 may be a hollow roller or a solid roller. In the case of a hollow roller, the pressure roller 24 may have a heat source such as a halogen heater. The elastic rubber layer may be solid rubber, but if there is no heat source in the pressure roller 24, sponge rubber may be used. Sponge rubber is more desirable because it improves heat insulation and makes it difficult for the fixing belt to lose heat.

  The fixing belt 21 rotates along with the pressure roller 24. As described above, the pressure roller 24 is rotated by a driving source (not shown), and the driving force is transmitted to the belt 21 at the fixing nip portion N, whereby the fixing belt 21 is rotated. The fixing belt 21 is nipped and rotated by the pressure roller 24 and the nip forming member 26 at the fixing nip portion N, and travels while being guided by the holding member 28 (flange) at both ends other than the fixing nip portion.

  In the fixing device 20, a heat transfer member 42 is further attached to the support member 27. A state in which the transmission member 42 is in contact with the fixing belt 21 is indicated by reference numeral 42a, and a state in which the transmission member 42 is separated from the fixing belt 21 is indicated by reference numeral 42b. The heat transfer member 42 is attached with one end in contact with the support member 27 in order to transmit the heat of the support member 27 to the fixing belt 21, and is disposed so as to be able to contact and separate from the inner peripheral surface of the fixing belt 21. Due to the contact from the inner peripheral surface side, it is possible to avoid the damage of the surface layer of the fixing belt 21 and the occurrence of abnormal images. A soft sheet material is used for the heat transfer member 42 so that the sliding load of the fixing belt 21 is increased and the parts are not damaged. In order to further suppress the sliding load, the surface layer of the heat transfer member 42 may be covered with a fluororesin such as PFA, PTFE, ETFE to about 5 to 50 μm. Alternatively, holes may be formed in the contact area of the heat transfer member 42 to reduce the contact area with the fixing belt 21 and reduce the sliding load. In FIG. 2, the heat transfer member 42 is fixed in the vicinity of the fixing nip portion of the support member 27, in particular, at a location on the downstream side in the sheet conveyance direction, which is a low temperature region of the fixing nip portion. The upstream side in the paper transport direction is an area where the temperature has been adjusted appropriately for fixing, and heat is not transferred to this side, but is transferred to the downstream side where the heat is absorbed by the paper and becomes low temperature. Does not affect. Further, in order to avoid an overheating state, it is reasonable to transfer the heat of the support member or the like to the fixing belt 21 that should be heated, and thus it is rational to move to a low temperature range, and energy saving is improved.

  Here, the contact and separation of the heat transfer member 42 with respect to the fixing belt 21 will be described. The amount of heat stored in the support member 27 differs depending on the sheet passing conditions, as in the case where several sheets are printed from a state in which the apparatus is cold or the case where continuous printing is performed. If the fixing belt 21 is brought into contact with the fixing belt 21 at a higher temperature than the supporting member 27, the supporting member 27 may take heat from the fixing belt 21 via the heat transfer member 42 and cause fixing failure. Therefore, a mechanism for bringing the heat transfer member 42 into and out of contact with the fixing belt 21 is provided so as to switch the contact and separation of the heat transfer member 42 according to the sheet passing conditions and the temperature difference between the fixing belt 21 and the support member 27. That is, when the support member 27 is hotter than the fixing belt 21, the heat transfer member 42 is brought into contact with the fixing belt 21 to suppress the occurrence of fixing failure and optimize energy saving. The contact / separation mechanism itself that contacts and separates two members is well known, and the description of the configuration of the contact / separation mechanism is omitted here, but the contact when the heat transfer member 42 can handle a plurality of paper widths is omitted. The separation control will be described with reference to FIG. The heat transfer member 42 is separated from the fixing belt 21 before the rotation of the fixing belt 21 is stopped in order to avoid local heating of the fixing belt 21.

  The contact and separation of the heat transfer member 42 may be switched according to the sheet passing condition based on the temperature difference between the fixing belt 21 and the support member 27 obtained in advance from experiments. Such a method does not require a temperature detection sensor or a circuit and can improve energy saving at low cost. On the other hand, when the sensors for detecting the temperature of the inner peripheral surface of the fixing belt 21 and the support member 27 are provided, the heat transfer member 42 can be controlled with high accuracy, and energy saving can be improved in that respect. it can.

Moreover, as a material of the heat transfer member 42, for example, a material having the following heat resistance and good thermal conductivity is preferable.
Material Thermal conductivity (W / mK)
Carbon nanotube 3000-5500
Silver 420
Copper 398
Aluminum 236

  In this example, a thermopile 45 as a temperature detecting means is arranged with a temperature control point at a position a in the figure where only the fixing belt 21 is interposed with respect to the halogen heaters 23A, 23B and 23C as heat sources.

  Here, the temperature distribution in the circumferential direction of the fixing belt 21 will be described. First, the surface temperature of the fixing belt 21 is detected at the temperature control point a by the thermopile 45 and heated by the heaters 23A to 23C so as to reach the target temperature. The reflection member 29 is provided in order to efficiently supply the radiant heat of the heater to the fixing belt 21, but the reflectance of the reflection member 29 is around 90%, and the support member 27 is also gradually heated. Further, the support member 27 is further heated as the ambient temperature rises. Next, the fixing belt 21 heated at “a” in the drawing rotates along with the pressure roller 24 and rotates in the conveying direction. When the fixing belt 21 rotates, an area that is not sufficiently heated reaches the position a in the figure, and the halogen heater continues to heat. The fixing belt 21 heated at the temperature control point is further heated by the residual heat of the halogen heater until it reaches the fixing nip portion while rotating in the conveying direction. The portion of the fixing belt 21 that has reached the fixing nip is deprived of heat by the pressure roller 24 or the toner T and the paper P, and reaches the temperature control point a in FIG.

  In this example, in order to suppress an increase in cost and a decrease in energy saving due to an increase in the size of the apparatus, each component is reduced in size, and a nip forming mechanism and a heat source are integrated inside the fixing belt 21. Therefore, a member close to the halogen heater as a heat source is easily affected by the reflectance of the reflecting member 29 and the ambient temperature, and is likely to become high temperature. In particular, the support member 27 generally uses a metal material in order to ensure rigidity, and the heat absorption is significant. On the other hand, regarding the fixing property, the temperature of the surface (outer peripheral surface) of the fixing belt 21 and the pressure at the fixing nip portion are dominant, and the heat of the support member 27 does not particularly affect the fixing property. That is, as the support member 27 is heated, energy saving is reduced. Further, since the nip forming member 26 and the support member 27 are exposed to a high temperature, there are problems that cause damage due to thermal deformation or the like and a reduction in the life of the parts. As a result of providing the heat transfer member 42 and transferring the heat of the support member 27 to the fixing belt 21 via the heat transfer member 42, it is possible to suppress a reduction in energy saving and a shortened life of components.

  FIG. 3 shows another example of the fixing device. In the example of FIG. 2, the heat source is composed of three halogen heaters 23 </ b> A, 23 </ b> B, and 23 </ b> C, whereas in this example, the heat source is composed of one halogen heater 23. The same members as those in the example of FIG. Even in the fixing device having such a simple configuration, the heat transfer member 42 transmits heat of the support member 27 to the fixing belt 21, thereby avoiding a problem due to overheating of the support member 27.

  FIG. 4 shows still another example of the fixing device. In this example, in addition to the heat transfer member 42 and a plurality of heat sources (two) for accommodating a plurality of paper widths, a light shielding member 25 is provided. As shown in FIG. 5, the light shielding member 25 has a stepped shape having a plurality of light shielding widths in accordance with the respective paper widths. The light shielding member 25 is configured to rotate in a non-contact manner along the inner side of the fixing belt 21, and moves to a position corresponding to each paper width to shield an area unnecessary for heating. FIG. 6 shows the position of the light shielding member 25 when the A3 paper is passed and when the postcard is passed. With such a configuration, even when narrow paper is continuously passed, it is possible to prevent the non-sheet passing area from becoming overheated, and control such as reducing productivity to cancel the overheated area. There is no need to do. Further, by using the light shielding member in combination, it is possible to reduce the number of heat sources required for dealing with a plurality of paper widths. Even in the fixing device configured as in this example, the heat of the support member 27 is transmitted to the fixing belt 21 by the heat transfer member 42 to avoid the problem due to overheating of the support member 27.

  Next, an improved modification regarding the heat transfer member will be described. FIG. 7 is a conceptual diagram showing the relationship between the heat transfer member 42 and the sheet passing width. P1 and P2 represent sheet passing widths on different sheets. In this example, the positional relationship in the case of adopting the central sheet feeding method in which the longitudinal center position of the fixing belt 21 and the longitudinal center position of the sheet are conveyed is shown, and the component configuration inside the fixing belt 21 is the longitudinal center. The shape is symmetrical.

  If the heat of the support member 27 is transmitted to the entire longitudinal direction of the fixing belt 21 via the heat transfer member 42, the heat is also transmitted to a non-sheet passing area that does not require heat supply, and the effect of suppressing reduction in energy saving is reduced. On the other hand, assuming that heat is transferred only to an arbitrary sheet passing area, if the paper size is changed, heat transfer in the longitudinal direction becomes non-uniform, which may cause abnormal images such as uneven gloss and poor fixing. Therefore, a plurality of heat transfer regions of the heat transfer member 42 are provided so that they can be changed according to the sheet passing width. Then, by bringing the heat transfer area corresponding to the paper passing area where heat supply is required into contact with the inner peripheral surface of the fixing belt 21, only the paper passing area where heat supply is required is uniformly transferred to the abnormality. Reduces image generation and energy savings. For example, when the P1 width paper is passed, the x region in the drawing of the heat transfer member 42 abuts the fixing belt 21, and when the P2 width paper is passed, the y region in the drawing of the heat transfer member 42 is fixed. It abuts on the belt 21. Note that the width of each region of the heat transfer member 42 is preferably about 5 to 20 mm wider than the sheet passing widths P <b> 1 and P <b> 2 in order to surely and uniformly supply heat to the end of the sheet.

In FIG. 8, the shape of the heat transfer member 42 that contacts the inner peripheral surface of the fixing belt 21 will be described.
The portion of the heat transfer member 42 that comes into contact with the inner peripheral surface of the fixing belt 21 has a step shape corresponding to a plurality of paper passing widths so as to be compatible with a plurality of types of paper having different widths. When passing P1 width paper, heat is transferred in the x region, and when passing P2 width paper, heat is transferred in the y region. The reason why the step shape is not a trapezoidal shape is that it is easy to manage the dimensions of the parts. In other words, in the case of an inclined shape, two-point management of the X axis and the Y axis is necessary. By using the heat transfer member having such a shape, an increase in the number of parts can be suppressed, and an increase in cost can be suppressed. In order to cope with a plurality of types of sheets having different widths, a configuration in which the heat transfer member is divided in accordance with the sheet widths P1 and P2 is conceivable. However, when supporting a wide sheet, the heat transfer in the longitudinal direction is interrupted. There is also a problem that a mechanism for driving each of the divided portions is required.

  Switching between the contact positions of the x region and the y region that are in contact with the inner peripheral surface of the fixing belt 21 will be described with reference to FIG. The contact of the heat transfer member 42 to the inner peripheral surface of the fixing belt 21 is performed by the contact control member 43. The change of the contact area between the heat transfer member 42 and the fixing belt 21 is realized by changing the standing position of the contact control member 43. That is, when the x region is brought into contact with the fixing belt 21 to correspond to the P1 width, the contact control member 43 is in the maximum standing state as shown in FIG. 9A, and the y region is brought into contact with the fixing belt 21 to correspond to the P2 width. In this case, an intermediate standing state is obtained as shown in FIG. 9b. As described above, since the heat transfer member 42 is a soft sheet material, when the contact control member 43 is in an intermediate standing state, the tip of the heat transfer member 42 hangs down by its own weight, and the contact area is switched. 9C, the heat transfer member 42 is separated from the fixing belt 21.

  As mentioned above, although this invention was demonstrated based on preferred embodiment, this invention is not limited to the demonstrated structure, In the range which does not deviate from the summary, it can change variously.

20 Fixing device 21 Fixing belt 23 Halogen heater (heat source)
24 Pressure roller 26 Nip forming member 27 Support member 28 Holding member 29 Reflecting member 42 Heat transfer member 45 Thermopile

JP 2007-334205 A JP 2009-42305 A

Claims (11)

  An endless belt, a pressure member abutting on the outer peripheral surface of the belt, a nip forming member disposed inside the belt and forming a fixing nip portion with the pressure member via the belt, In a fixing device that is disposed inside a belt and supports the nip forming member, and a heat source that is disposed inside the belt, a heat transfer member that is attached to the support member and contacts the belt A fixing device is provided.   The fixing device according to claim 1, wherein the heat transfer member contacts an inner peripheral surface of the belt.   The fixing device according to claim 1, wherein the heat transfer member is disposed on a downstream side of the fixing nip portion in a sheet conveying direction.   The fixing device according to claim 1, wherein a mechanism for bringing the heat transfer member into contact with and separating from the belt is provided.   The fixing device according to claim 4, wherein the heat transfer member contacts the belt when the support member is hotter than the belt.   The fixing device according to claim 4, wherein there are a plurality of regions of the heat transfer member in contact with the belt according to a sheet width passing through the fixing nip portion.   The fixing device according to claim 6, wherein the region has a step shape corresponding to a plurality of paper widths.   The contact / separation mechanism includes a contact control member that changes a contact position of the heat transfer member with respect to the belt in accordance with a sheet width. Fixing device.   The fixing device according to claim 1, wherein a surface of the heat transfer member that contacts the belt has a release layer.   The fixing device according to claim 4, wherein the heat transfer member is separated from the belt before the rotation of the belt stops.   An image forming apparatus comprising the fixing device according to claim 1.

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