Image forming apparatus

Abstract

The present invention provides an image forming apparatus that can simultaneously reduce ultrafine particles generated by heating the release agent contained in the toner, and discharge heat and water vapor. [Solution] The first duct unit comprises a first duct, a first duct fan 62, an intake port, and an exhaust port. The first duct constitutes a first ventilation path that guides air sucked in from the intake port to the exhaust port. The first duct fan 62 generates an airflow from the intake port to the exhaust port. The intake port is provided on the fixing belt side with respect to the sheet transport path between the secondary transfer roller and the fuser. The exhaust port exhausts the air that has been sucked into the first duct through the intake port to the outside of the image forming apparatus 200. When a continuous job is started, the image forming apparatus 200 starts operating the first duct fan 62 when the transport distance of the sheet passing through the fixing nip reaches 9450 mm.

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus using electrophotography, such as a printer, a copying machine, a facsimile machine, or a multifunction peripheral having a plurality of these functions. [Background Art]

[0002] Conventionally, an image forming apparatus includes a fixing device that fixes a toner image onto a recording material by applying heat and pressure to the recording material on which the toner image has been formed. Such a fixing device includes an endless heated fixing belt and a pressure roller that abuts against and presses the fixing belt. The fixing device fixes the toner image onto the recording material by nipping and conveying the recording material with the toner image formed thereon while heating and pressing the recording material in a fixing nip portion formed by the fixing belt and the pressure roller.

[0003] Further, a filter unit and an exhaust duct independent of the filter unit are disposed in the vicinity of the fixing device (for example, Patent Document 1). The filter unit includes a filter, and collects UFPs (Ultra Fine Particles), which are ultrafine particles of several nm to several hundreds of nm generated by vaporization of wax, which is a release agent contained in toner, due to heat, from air through the filter. Further, the exhaust duct is used for discharging exhaust heat and water vapor generated by heating the recording material, and does not include a ventilation resistor such as a filter for securing an air volume. As described above, a conventional image forming apparatus includes the filter unit and the exhaust duct respectively to achieve reduction of UFPs, discharge of exhaust heat, and discharge of water vapor. [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2020-134935 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, conventionally, with the increasing processing speed of modern image forming machines, the amount of water vapor and heat generated from the recording material tends to increase, making it difficult to adequately discharge the water vapor and heat. On the other hand, if the airflow of the exhaust duct is increased to discharge the water vapor and heat, the amount of UFP (Ultraviolet Flux) directed to the filter decreases. Therefore, conventionally, there is a challenge in achieving both UFP reduction and the discharge of water vapor and heat.

[0006] The object of the present invention is to provide an image forming apparatus that can achieve both a reduction in ultrafine particles generated by heating the release agent contained in the toner and the discharge of heat and water vapor. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention is an image forming apparatus capable of performing a continuous job of forming images on a plurality of recording materials, and comprises: an image forming means for forming a toner image using toner containing a release agent; a transfer means for performing a transfer operation to transfer the toner image formed by the image forming means to a recording material; a first rotating body heated by a heating means; a second rotating body that abuts against the first rotating body and together with the first rotating body forms a fixing nip portion; a fixing means for fixing the toner image to the recording material by clamping and conveying the recording material onto which the toner image has been transferred by the transfer means at the fixing nip portion; a first duct unit comprising: a first intake port for drawing in air between the fixing means and the transfer means; a first exhaust port for exhausting the air drawn in from the first intake port to the outside; and a first duct forming a first ventilation path between the first intake port and the first exhaust port; and provided in the first ventilation path. The second duct unit comprises a first duct fan that generates an airflow from the first intake port toward the first exhaust port, a second intake port that sucks in air between the fixing means and the transfer means, a second exhaust port that exhausts the air sucked in from the second intake port to the outside, and a second duct that forms a second ventilation path between the second intake port and the second exhaust port. The second duct unit comprises a second duct fan provided in the second ventilation path and generating an airflow from the second intake port toward the second exhaust port, a filter provided in the second ventilation path and removing fine particles, and control means for controlling the operation of the first duct fan and the second duct fan, wherein the control means starts the operation of the first duct fan when the transport distance of the recording material passing through the fixing nip section reaches a first predetermined value when the continuous job is started. [Effects of the Invention]

[0008] According to the present invention, it is possible to reduce ultrafine particles generated by heating the release agent contained in the toner, while simultaneously discharging heat and water vapor. [Brief explanation of the drawing]

[0009] [Figure 1]This is a schematic diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 2] This is a block diagram showing the configuration of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 3] This is a schematic diagram of a part of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 4] This is a partial perspective view of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 5] This figure shows the airflow of the duct unit of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 6] This figure shows the UFP generation mechanism in an image forming apparatus according to Embodiment 1 of the present invention, and the relationship between UFP generation, wax vapor concentration, and the temperature of the internal space of the apparatus. [Figure 7] This figure shows the relationship between time and UFP dispersion velocity in the operating and non-operating states of the second fan of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 8] This figure shows the operating time of the second fan of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 9] This figure shows the relationship between the time when the second fan of the image forming apparatus according to Embodiment 1 of the present invention is operated and the emission rate of UFP, compared with the case when the second fan is operated continuously. [Figure 10] This figure shows a modified example of the operating time of the second fan of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 11] This figure shows a further modified example of the operating time of the second fan of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 12] This is a block diagram showing the configuration of an image forming apparatus according to Embodiment 2 of the present invention. [Figure 13] This is a schematic diagram of a part of an image forming apparatus according to Embodiment 2 of the present invention. [Figure 14] This is a partial perspective view of an image forming apparatus according to Embodiment 2 of the present invention. [Figure 15]It is a diagram illustrating the airflow of a duct unit of an image forming apparatus according to Embodiment 2 of the present invention. [Figure 16] It is a diagram showing the operating times of a first fan, a first duct fan and a second duct fan of the image forming apparatus according to Embodiment 2 of the present invention. [Figure 17] It is a diagram showing the relationship between time and UFP emission rate when the first duct fan of the image forming apparatus according to Embodiment 2 of the present invention is operated, in comparison with the case where the first duct fan is continuously operated. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0011] (Embodiment 1) <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 1 to 3.

[0012] The image forming apparatus 100 is exemplified herein as a 4-color full-color laser printer of tandem-intermediate transfer type using an electrophotographic process. The image forming apparatus 100 forms an image on a sheet S as a recording material based on image information input to a control circuit unit A from an input device B such as a personal computer. The image forming apparatus 100 is a color electrophotographic apparatus such as a color copying machine including a plurality of photosensitive drums, but is not limited thereto, and may be a monochrome electrophotographic apparatus such as a monochrome copying machine or a printer including one photosensitive drum.

[0013] Specifically, the image forming apparatus 100 includes an image forming section 1, a belt suspension roller 10, a sheet feeding roller 13, a registration roller 14a, a registration roller 14b, a guide member 15, and a secondary transfer roller 16. The image forming apparatus 100 further includes a guide member 18, a fixing device 19, a guide member 20, a pair of discharge rollers 21, a discharge tray 22, toner bottles 23Y, 23M, 23C, 23K, a detection sensor 25, and a pair of discharge rollers 26. Furthermore, the image forming apparatus 100 includes a duct unit 50, a first fan 55, a sheet member 59, an internal temperature sensor 65, and a control circuit section A.

[0014] The image forming section 1 serving as image forming means forms a toner image using toner containing a release agent. The image forming section 1 includes a first image forming unit UY, a second image forming unit UM, a third image forming unit UC, a fourth image forming unit UK, an intermediate transfer belt unit 8, and a sheet cassette 11.

[0015] The first image forming unit UY forms a yellow (Y) toner image.

[0016] The second image forming unit UM forms a magenta (M) toner image.

[0017] The third image forming unit UC forms a cyan (C) toner image.

[0018] The fourth image forming unit UK forms a black (K) toner image.

[0019] Each of the first image forming unit UY, the second image forming unit UM, the third image forming unit UC, and the fourth image forming unit UK includes a drum 2, a charging roller 3, a laser scanner 4, a developing device 5, a primary transfer roller 6, and a drum cleaner 7.

[0020] The drum 2 is rotated by being driven by a drive device (not shown).

[0021] The charging roller 3 uniformly charges the surface of the drum 2.

[0022] The laser scanner 4 forms an electrostatic latent image on the drum 2 by irradiating the drum 2, which has been charged by the charging roller 3, with a laser based on the image information input from the input device B.

[0023] The developing unit 5 forms a toner image on the drum 2 by supplying toner to the drum 2 on which an electrostatic latent image has been formed by the laser scanner 4.

[0024] The primary transfer roller 6 is located inside the intermediate transfer belt 9 of the intermediate transfer belt unit 8 and is in pressure contact with the drum 2 via the intermediate transfer belt 9. The primary transfer roller 6 sequentially transfers the toner image formed on the drum 2 to the intermediate transfer belt 9.

[0025] The drum cleaner 7 removes and recovers the toner that remains on the drum 2 without being transferred to the intermediate transfer belt 9 by the primary transfer roller 6.

[0026] The intermediate transfer belt unit 8 is located above the first imaging unit UY, the second imaging unit UM, the third imaging unit UC, and the fourth imaging unit UK, and includes an intermediate transfer belt 9.

[0027] The intermediate transfer belt 9 rotates counterclockwise in Figures 1 and 3 by a drive mechanism (not shown). The four toner images of Y, M, C, and K from the first imaging unit UY, the second imaging unit UM, the third imaging unit UC, and the fourth imaging unit UK are superimposed onto the intermediate transfer belt 9 by the primary transfer roller 6. The intermediate transfer belt 9 conveys the primary transferred toner images by rotating.

[0028] The sheet cassette 11 is located below the first imaging unit UY, the second imaging unit UM, the third imaging unit UC, and the fourth imaging unit UK.

[0029] An intermediate transfer belt 9 is suspended from the belt suspension roller 10.

[0030] The sheet dispensing roller 13 is driven at a predetermined control timing to separate the sheets S contained in the sheet cassette 11 one by one and feed them to the register roller 14a and register roller 14b via the transport path 12.

[0031] The resist rollers 14a and 14b constitute a resist roller pair. The resist rollers 14a and 14b temporarily stop the transport of the sheet S fed by the sheet feed roller 13, and then transport the sheet S to the secondary transfer nip section 17 at a predetermined control timing.

[0032] The guide member 15 is provided between the resist rollers 14a and 14b and the secondary transfer roller 16. The guide member 15 guides the transport of the sheet S being transported between the resist rollers 14a and 14b and the secondary transfer roller 16 in the transport path 12.

[0033] The secondary transfer roller 16, acting as a transfer means, contacts the belt suspension roller 10 via the intermediate transfer belt 9 with a predetermined pressing force, and together with the intermediate transfer belt 9, forms a secondary transfer nip section 17. At the secondary transfer nip section 17, the secondary transfer roller 16 performs a transfer operation to transfer the superimposed toner images of the four colors that were primary transferred onto the intermediate transfer belt 9 to the sheet S being transported by the register rollers 14a and 14b. The secondary transfer roller 16 then transports the sheet S, on which the toner images have been secondary transferred, to the fuser 19.

[0034] The guide member 18 is provided between the secondary transfer roller 16 and the fuser 19. The guide member 18 guides the transport of the sheet S being transported between the secondary transfer roller 16 and the fuser 19 in the transport path 12.

[0035] The fuser 19 is a belt-heating type on-demand fuser and has a vertical path configuration that transports the sheet S from bottom to top in the direction of gravity. However, the fuser 19 is not limited to a vertical path configuration and may also have a horizontal path configuration that transports the sheet S in a horizontal direction.

[0036] The fuser unit 19 performs a thermal fixing process in which it applies heat and pressure to the toner image that has been secondarily transferred to the sheet S, which is transported from the secondary transfer nip section 17 by the secondary transfer roller 16, in the fixing nip section N to fix the toner image to the sheet S. The fuser unit 19 then transports the sheet S with the fixed toner image to the discharge roller pair 26. Details of the configuration of the fuser unit 19 will be described later.

[0037] The guide member 20 is provided between the fuser 19 and the discharge roller pair 21. The guide member 20 guides the transport of the sheet S being transported between the fuser 19 and the discharge roller pair 21 in the transport path 12.

[0038] The discharge roller pair 21 discharges the sheet S, which is being conveyed by the discharge roller pair 26, into the discharge tray 22.

[0039] The sheet S is discharged into the discharge tray 22 by the discharge roller pair 21.

[0040] Toner bottles 23Y, 23M, 23C, and 23K are removable and replaceable, and contain replenishment toner for the developer unit 5. Each of the toner bottles 23Y, 23M, 23C, and 23K replenishes the developer unit 5 of each imaging unit UY, UM, UC, and UK with the appropriate amount of toner at the appropriate time via a toner replenishment mechanism (not shown).

[0041] The detection sensor 25, which serves as a means for detecting recording material, is located downstream of the discharge roller pair 26 in the direction of conveying the sheet S (hereinafter simply referred to as the "conveying direction"). The detection sensor 25 detects the sheet S being conveyed from the discharge roller pair 26 to the discharge roller pair 21 and outputs an electrical signal to the control circuit unit A according to the detection result.

[0042] The discharge roller pair 26 is located downstream of the fuser 19 in the conveying direction and conveys the sheet S conveyed by the fuser 19 to the discharge roller pair 21.

[0043] The duct unit 50 sucks in the air between the fuser 19 and the intermediate transfer belt 9, and the air between the fuser 19 and the secondary transfer roller 16, and discharges it to the outside of the image forming apparatus 100. Details of the configuration of the duct unit 50 will be described later.

[0044] The first fan 55 is positioned downstream of the fuser 19 in the transport direction. The first fan 55 is operated by the control circuit unit A to collect and discharge water vapor floating downstream of the fuser 19 in the transport direction.

[0045] The sheet member 59 is provided in the duct unit 50 to help prevent the advection of water vapor contained in the sheet S to the intermediate transfer belt unit 8. The sheet member 59 extends from the duct unit 50 toward the intermediate transfer belt 9 downstream of the secondary transfer nip section 17 in the direction of toner image transport by the intermediate transfer belt 9 (see Figure 3).

[0046] The in-machine temperature sensor 65, which serves as a temperature detection means, measures the ambient temperature (hereinafter simply referred to as "ambient temperature") near the sheet inlet 35 of the fuser unit 19 housing 34 described later and around the fuser unit 19, and outputs an electrical signal corresponding to the measured ambient temperature to the control circuit unit A.

[0047] The control circuit unit A, acting as a control means, controls the operation of the entire image forming apparatus 100 based on image information input from the input device B. The control circuit unit A is capable of executing continuous jobs that perform image forming on multiple sheets S in succession. The control circuit unit A controls the power supplied to the fixing heater 39 of the fuser 19 (described later) so as to maintain the temperature indicated by the electrical signal input from the thermistor TH of the fuser 19 at a target temperature, thereby adjusting the temperature detected by the thermistor TH to a predetermined target temperature. The control circuit unit A controls the operation of the second fan 56 of the duct unit 50 (described later) based on the detection result of the sheet S indicated by the electrical signal input from the detection sensor 25 and the ambient temperature indicated by the electrical signal input from the in-machine temperature sensor 65.

[0048] In Figure 1, which shows the interior of the image forming apparatus 100 having the above configuration, a transport path 12 for transporting the sheet S from bottom to top is provided on the right side. From the bottom to the top of the transport path 12, a sheet feeding roller 13, a resist roller 14a and a resist roller 14b, a secondary transfer roller 16, a fuser 19, a pair of discharge rollers 26 and a pair of discharge rollers 21 are provided in this order.

[0049] <Fuser Unit Configuration> The configuration of the fuser 19 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 1, 3, and 4.

[0050] The fuser unit 19 includes a fuser belt 27, a pressure roller 28, a housing 34, a fuser heater 39, a heater holder 40, a rigid stay 41, and a thermistor TH.

[0051] The fixing belt 27, acting as the first rotating body, is in contact with the pressure roller 28 at the fixing nip portion N. When the pressure roller 28 is rotationally driven, the frictional force between the belt and the pressure roller 28 transmits a driving force from the pressure roller 28, causing the belt to rotate in a counterclockwise direction as shown in Figure 3.

[0052] The pressure roller 28, acting as the second rotating body, is an elastic roller equipped with a core metal 28a (see Figure 4). As shown in Figure 4, the pressure roller 28 is rotatably held at both longitudinal ends of the core metal 28a by bearings (not shown). One end of the core metal 28a of the pressure roller 28 is connected to a drive mechanism including a motor (not shown), which is a drive source, and the pressure roller 28 is rotated at a predetermined peripheral speed in a clockwise direction in Figure 3 via the core metal 28a by the drive of the motor. When the fixing belt 27 is pressed against the pressure roller 28, the elastic rubber layer on its surface elastically deforms to conform to the shape of the fixing heater 39, thereby forming a fixing nip portion N of a predetermined width between the pressure roller 28 and the fixing belt 27.

[0053] The fixing belt 27 and the pressure roller 28 grip and transport the sheet S, which is carrying the unfixed toner image, at the fixing nip section N, fixing the toner image to the sheet S using heat and pressure.

[0054] The housing 34 houses the fixing belt 27 and the pressure roller 28. The housing 34 includes a sheet inlet 35, a first guide member 36, a second guide member 37, and a sheet outlet 38.

[0055] The sheet inlet 35 is formed by a first guide member 36 and a second guide member 37. The sheet inlet 35 is located below the sheet outlet 38 in the direction of gravity. The sheet inlet 35 is the entrance to the fuser 19 when the sheet S is transported from the secondary transfer roller 16 to the fuser 19.

[0056] The first guide member 36 faces the back surface of the sheet S, which is the non-toner image-bearing surface of the sheet S.

[0057] The second guide member 37 faces the surface of the sheet S, which is the toner image-bearing surface of the sheet S.

[0058] The sheet outlet section 38 is the outlet of the fuser 19 when the sheet S is conveyed to the discharge roller pair 26 by the fixing belt 27 and the pressure roller 28.

[0059] The fixing heater 39, which serves as a heating means, is located inside the fixing belt 27. The fixing heater 39 is both a heating source that heats the fixing belt 27 and a pressing member that presses the fixing belt 27 toward the pressure roller 28. The fixing heater 39 is, for example, a ceramic heater. The fixing heater 39 is positioned along the rotation axis of the fixing belt 27, with the rotation axis of the fixing belt 27 as the longitudinal direction, and is in slidable contact with the inner surface of the fixing belt 27. The fixing heater 39 generates heat and its temperature rises rapidly when power is supplied from a power supply unit (not shown) under the control of the control circuit unit A.

[0060] The heater holder 40 is located inside the fixing belt 27. The heater holder 40 is a member that holds the fixing heater 39 along its longitudinal direction. The heater holder 40 fixes the fixing heater 39 toward the pressure roller 28 side such that the fixing heater 39 and the inner surface of the fixing belt 27 are in contact. The heater holder 40 also acts as a guide member that guides the formation of the circumferential curvature shape of the fixing belt 27 in order to facilitate the separation of the sheet S from the fixing belt 27. The heater holder 40 preferably has excellent heat resistance, and for example, liquid crystal polymer resin can be used.

[0061] The rigid stay 41 is located inside the fixing belt 27. The rigid stay 41 is provided along the longitudinal direction of the heater holder 40 and the fixing heater 39, and is a support member that supports the heater holder 40 and the fixing heater 39. Both ends of the rigid stay 41 in the longitudinal direction are pressurized toward the pressure roller 28 by a pressurizing mechanism (not shown).

[0062] The thermistor TH is located inside the fixing belt 27. The thermistor TH detects the temperature of the fixing belt 27 and outputs an electrical signal corresponding to the detected temperature to the control circuit unit A.

[0063] In the fuser 19 having the above configuration, the pressure roller 28 is driven to rotate, and the temperature detected by the thermistor TH is controlled by the control circuit A to a predetermined target temperature. In this state, the sheet S onto which the unfixed toner image has been transferred by the secondary transfer nip section 17 is transported to the fuser 19 via the sheet inlet section 35. The toner image is fixed to the sheet S transported to the fuser 19. The sheet S with the fixed toner image is then discharged from the sheet outlet section 38.

[0064] <Duct unit configuration> The configuration of the duct unit 50 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 1 and 3 to 5.

[0065] The duct unit 50 comprises a plate member 51, an intake port 52, an exhaust port 53, a base member 54, a second fan 56, and a duct 57.

[0066] The plate member 51 is flat and attached to the base member 54.

[0067] The air intake port 52 is located near the center of the plate member 51 in the longitudinal direction parallel to the rotation axis direction of the fixing belt 27 (the direction perpendicular to the plane of the paper in Figure 3). The air intake port 52 is located on the fixing belt 27 side of the sheet S transport path 12 between the secondary transfer roller 16 and the fuser 19. The air intake port 52 draws air between the fuser 19 and the intermediate transfer belt 9, which is sucked in by the second fan 56, and air between the fuser 19 and the secondary transfer roller 16 into the duct 57.

[0068] The exhaust port 53 exhausts the air that has been drawn into the duct 57 via the intake port 52 by the second fan 56 to the outside of the image forming apparatus 100.

[0069] The length Wd of the base member 54 in the width direction perpendicular to the conveying direction is greater than the maximum width W of the sheet S in the width direction (Wd > W) (see Figure 4) in order to prevent water vapor contained in the sheet S from advection across the entire upper surface of the intermediate transfer belt unit 8.

[0070] The second fan 56 is operated by the control circuit unit A, generating an airflow from the intake port 52 to the exhaust port 53.

[0071] The duct 57 is formed by a base member 54 and a plate member 51, and connects an intake port 52 and an exhaust port 53. The duct 57 constitutes an air passage that guides air drawn in from the intake port 52 to the exhaust port 53. The duct 57 does not have any air resistance elements such as filters on the air passage.

[0072] In the duct unit 50 having the above configuration, the air taken in from the intake port 52 is exhausted from the exhaust port 53 via the path indicated by the arrows in Figure 5. The second fan 56 is positioned on the air path indicated by the arrows in Figure 5. The duct unit 50 is required to generate a certain amount of airflow to prevent condensation on the intermediate transfer belt 9, therefore, no airflow resistance material such as a filter is provided on the path indicated by the arrows in Figure 5.

[0073] <Operation of the image forming apparatus> The operation of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 1 and 2.

[0074] The image forming apparatus 100 starts operating when image information is input to the control circuit unit A from an input device B such as a personal computer.

[0075] First, the control circuit unit A, using a paper feeding mechanism including a feed roller 13, takes one sheet S from the sheet cassette 11 and transports it to the image forming unit 1.

[0076] An unfixed toner image is formed on the sheet S transported to the image forming unit 1 by the toner image formation operation in the image forming unit 1.

[0077] The sheet S, on which an unfixed toner image has been formed by the image forming unit 1, passes through the discharge roller pair 26 after the toner image has been fixed in the fuser unit 19.

[0078] As the sheet S passes through the discharge roller pair 26, the passage of the leading edge in the transport direction is detected by a detection sensor 25 located downstream of the discharge roller pair 26 in the transport direction.

[0079] When the leading edge of the sheet S in the transport direction is detected by the detection sensor 25, the sheet S is discharged to the discharge tray 22 via the discharge roller pair 21, and the passage of the trailing edge in the transport direction is detected by the detection sensor 25.

[0080] The control circuit unit A counts the transport distance of the sheet S based on the detection timing of the leading edge of the sheet S in the transport direction indicated by the electrical signal input from the detection sensor 25, the transport speed of the sheet S, and the distance from the fixing nip section N to the detection sensor 25. Information regarding the transport speed of the sheet S and information regarding the transport distance from the fixing nip section N to the detection sensor 25 are stored in advance in a storage means (not shown) and read from the storage means by the control circuit unit A. Then, the control circuit unit A controls the operation of the second fan 56 based on the counted transport distance of the sheet S.

[0081] In the image forming operation described above, the generation of UFP and water vapor becomes a challenge. UFP is formed when volatile wax, a release agent contained in the toner, condenses into particulate matter in the air. In order to keep the particle concentration in the exhaust from the image forming apparatus 100 below the standard values ​​stipulated in environmental standards such as the Blue Angel standard, it is necessary to suppress the generation of UFP.

[0082] Furthermore, when the sheet S is heated in the fixing nip section N, moisture contained in the sheet S is released as water vapor. This water vapor causes condensation on surrounding components, negatively affecting the quality of the image formed on the sheet S. In addition, much of the water vapor is generated downstream of the fuser 19 in the transport direction (upward in Figure 1), causing condensation on components along the transport path, such as the guide member 20. The moisture that adheres to the components in this way then transfers to the sheet S, causing wrinkles and other defects on the sheet S.

[0083] Furthermore, some of the water vapor generated downstream of the fixing nip section N in the transport direction is transferred to the upstream side (downward in Figure 1) of the fixing nip section N in the transport direction by the airflow generated by the rotation of the fixing belt 27 and the pressure roller 28. Although the amount is small, this water vapor transferred upstream condenses slightly on the intermediate transfer belt 9. The moisture condensed on the intermediate transfer belt 9 reacts with the filler and other materials contained in the sheet S, and the reaction products of the condensed moisture and filler and other materials may accumulate on the intermediate transfer belt 9. Such deposits degrade the image quality of the unfixed toner image formed in the secondary transfer nip section 17.

[0084] Therefore, the control circuit unit A operates the first fan 55 to collect and discharge water vapor floating downstream in the transport direction of the fuser 19. Furthermore, the control circuit unit A operates the second fan 56 after the secondary transfer operation has started in the secondary transfer nip section 17 by the secondary transfer roller 16. When the second fan 56 is operated, the air containing water vapor between the fuser 19 and the intermediate transfer belt 9 is taken into the duct 57 through the intake port 52 and discharged outside the image forming apparatus 100 through the exhaust port 53. This makes it possible to suppress condensation on components on the transport path such as the guide member 20 and on the intermediate transfer belt 9.

[0085] Furthermore, the duct unit 50's air intake and exhaust also serve to dissipate the heat generated from the fuser unit 19. This allows the temperature of the intermediate transfer belt unit 8 to be maintained at an appropriate level.

[0086] However, while the discharge of air by the duct unit 50 suppresses dew condensation on components on the conveyance path such as the guide member 20 and the intermediate transfer belt 9, it may promote the generation of UFP. Therefore, conventionally, it has been difficult to achieve both dew condensation prevention and UFP reduction only with an exhaust duct not provided with a filter.

[0087] In contrast, the image forming apparatus 100 according to the present embodiment can achieve both dew condensation prevention and UFP reduction only with the duct unit 50. Next, the mechanism of UFP generation will be described, and the operation and processing of the image forming apparatus 100 according to the present embodiment for achieving both dew condensation prevention and UFP reduction only with the duct unit 50 will be described.

[0088] <Mechanism of UFP Generation> The mechanism of UFP generation in the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to FIG. 6.

[0089] In FIG. 6, FIG. 6(a) schematically illustrates the UFP generation mechanism, and FIG. 6(b) shows the relationship among UFP generation, the concentration C of wax vapor, and the space temperature T.

[0090] The fixing device 19 fixes a toner image onto a sheet S by bringing the high-temperature fixing belt 27 into contact with the sheet S at the fixing nip portion N. At this time, an offset phenomenon or the like, in which a part of the toner on the sheet S adheres to the fixing belt 27, may occur. Such toner adhering to the fixing belt 27 causes image defects.

[0091] Therefore, in order to suppress the adhesion of toner to the fixing belt 27, a toner containing a release agent, such as paraffin wax, is used. When such a wax-containing toner is heated, the melted wax seeps out from the surface, and the seeped-out wax migrates to the fixing belt 27 during the fixing process. By covering the surface of the fixing belt 27 with wax, the release effect of the wax can suppress the adhesion of toner to the fixing belt 27.

[0092] The above-mentioned waxes include not only pure waxes but also compounds containing wax molecular structures, such as compounds formed by the reaction of toner resin molecules with wax molecular structures such as hydrocarbon chains. Furthermore, the release agent is not limited to wax; substances with release properties such as silicone oil may also be used.

[0093] On the other hand, some of the wax adhering to the fixing belt 27 vaporizes (gasifies) when the surface temperature of the fixing belt 27 exceeds a predetermined temperature. The vaporized wax components then solidify when cooled in the air, becoming UFPs (Ultra-Fiber Powders) with a particle size of several nanometers to several hundred nanometers.

[0094] Such UFPs are generated by the process shown in Figure 6(a). Specifically, when the surface 46 of an object such as a fixing belt 27 to which wax is attached is heated to a degree that causes the wax to volatilize, wax vapor 45a is generated from the surface 46. The wax vapor 45a generated from the surface 46 cools and begins to condense when it moves away from the surface 46. As a result, nuclei 45b are formed, which are clusters of molecules that make up the vapor 45a. This phenomenon of generating such nuclei 45b is called nucleation. Then, the nuclei 45b collide with each other and combine to form a large clump that becomes UFP 45c. It should be noted that the nucleation phenomenon also occurs in the formation of fog in the atmosphere.

[0095] This nucleation phenomenon is the one that governs the number of UFPs produced. Therefore, controlling the nucleation phenomenon is important in order to reduce UFPs.

[0096] Next, the conditions for the formation of nucleus 45b will be explained in detail with reference to Figure 6(b). In Figure 6(b), the horizontal axis represents the wax vapor concentration C, and the vertical axis represents the ambient temperature T. The curve UC shown in Figure 6(b) represents the combination of ambient temperature T and wax vapor concentration C at which the nucleation rate is constant, based on classical nucleation theory.

[0097] The rate of nucleus 45b formation can be determined by the nucleation rate equation derived from classical nucleation theory. The nucleation rate equation uses the physical properties of the wax vapor molecules, ambient temperature T, and wax vapor concentration C as parameters. When the physical properties of the wax vapor molecules are fixed, the rate of nucleus 45b formation becomes a function of the wax vapor concentration C and ambient temperature T. Since the formation of nucleus 45b is a condensation phenomenon, it becomes less likely to occur as the ambient temperature T is higher and the wax vapor concentration C is lower, similar to the formation of fog.

[0098] Specifically, in Figure 6(b), moving to the upper left of the curve UC (the arrow in the UFP Low direction in Figure 6(b)) indicates a decrease in UFP because the ambient temperature T is high and the wax vapor concentration C is low. On the other hand, moving to the lower right of the curve UC (the arrow in the UFP High direction in Figure 6(b)) indicates an increase in UFP because the ambient temperature T is low and the wax vapor concentration C is high.

[0099] Furthermore, the formation of nuclei 45b occurs around the fixing belt 27 where wax vapor is generated. The wax vapor volatilized from the fixing belt 27 is carried upstream in the conveying direction of the fixing nip section N by the airflow generated as the fixing belt 27 rotates counterclockwise in Figure 3. Therefore, the formation of nuclei 45b is predominantly carried near the sheet inlet 35, which is upstream in the conveying direction of the fixing nip section N.

[0100] The airflow generated at the intake port 52 of the duct unit 50 changes the ambient temperature T and the wax vapor concentration C, thereby influencing the formation of nuclei 45b near the sheet inlet 35, and consequently, the formation of UFPs. Thus, the duct unit 50 is involved not only in preventing condensation on the intermediate transfer belt 9, but also in the generation of UFPs.

[0101] <Effects of the second fan's operation> The effects of the operation of the second fan 56 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 6 and 7.

[0102] Figure 7 shows the time course of the UFP emission rate generated in the image forming apparatus 100 when the second fan 56 is activated (Fan On) and when the second fan 56 is not activated (Fan Off). In Figure 7, the UFP emission rate on the vertical axis increases as you move upwards on the vertical axis. Also, the higher the UFP emission rate, the greater the amount of UFP generated. The time domain Ra in Figure 7 corresponds to the time domain A in Figure 6(b), and the time domain Rb in Figure 7 corresponds to the time domain B in Figure 6(b).

[0103] The operation of the second fan 56 prevents condensation on the intermediate transfer belt 9 and, depending on the state of the image forming apparatus 100, may amplify or reduce the generation of UFP.

[0104] The area A enclosed by the dashed line in Figure 6(b) shows the relationship between the ambient temperature T and the wax vapor concentration C immediately after the image forming apparatus 100 starts operating after it has cooled down and become accustomed to room temperature (hereinafter referred to as "cold operation"). Plot P1 in area A shows the relationship between the ambient temperature T and the wax vapor concentration C when the second fan 56 is stopped (Fan Off). Plot P2 in area A shows the relationship between the ambient temperature T and the wax vapor concentration C when the second fan 56 is operating (Fan On).

[0105] Furthermore, the area B enclosed by the dashed line in Figure 6(b) shows the relationship between the ambient temperature T and the wax vapor concentration C near the sheet inlet 35 when the image forming apparatus 100 is in continuous operation for several minutes (hereinafter referred to as "warm-up operation"). Plot P3 in area B shows the relationship between the ambient temperature T and the wax vapor concentration C when the second fan 56 is operating (Fan On). Plot P4 in area B shows the relationship between the ambient temperature T and the wax vapor concentration C when the second fan 56 is stopped (Fan Off).

[0106] In region A, when the second fan 56 is deactivated, the wax vapor concentration C is low because it is immediately after the start of paper feeding. Also, in region A, when the second fan 56 is deactivated, the ambient temperature T is somewhat high because, in addition to the heat generated by paper feeding, heat generated from the fixing belt 27 before the start of paper feeding is also accumulated.

[0107] From this, plot P1, where the second fan 56 is stopped in region A, is on the lower side of UFP. On the other hand, plot P2, where the second fan 56 is activated in region A, is on the higher side of UFP because the ambient temperature T drops sharply due to heat dissipation. In other words, the amount of UFP generated when the second fan 56 is activated in region A exceeds the amount of UFP generated when the second fan 56 is not activated in region A, as shown in the time domain Ra of Figure 7.

[0108] Furthermore, the wax vapor concentration C in region B when the second fan 56 is deactivated is high because it is filled with a large amount of wax vapor generated by the continuous operation of the image forming apparatus 100. Also, the temperature T in region B when the second fan 56 is deactivated is high due to the continuous operation of the image forming apparatus 100.

[0109] Therefore, in region B, plot P4, where the second fan 56 is stopped, is on the high UFP side. On the other hand, in region B, plot P3, where the second fan 56 is activated, the accumulated wax vapor is discharged and the concentration C drops sharply, and the heat emitted from the fixing belt 27 spreads around the fixing unit 19, so the temperature T does not drop easily and is on the low UFP side. In other words, the amount of UFP generated when the second fan 56 is activated in region B is lower than the amount of UFP generated when the second fan 56 is not activated, as shown in the time domain Rb of Figure 7.

[0110] Thus, UFP levels are high immediately after the start of operation when the temperature inside the image forming apparatus 100 is low, and decrease as time passes after the start of operation, as nucleation is suppressed as the temperature inside the image forming apparatus 100 rises. From this, it can be seen that in order to reduce the generation of UFP, the second fan 56 should be stopped immediately after the start of operation of the image forming apparatus 100, and the second fan 56 should be operated during continuous operation of the image forming apparatus 100. On the other hand, in order to prevent condensation, it is advantageous to keep the second fan 56 running at all times. Therefore, in order to achieve both the reduction of UFP and the prevention of condensation, ingenuity is required in the operation of the second fan 56.

[0111] <Second fan operation> The operation of the second fan 56 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 8 and 9.

[0112] In Figure 8, Figure 8(a) shows the case where the second fan 56 is operated continuously in comparison with this embodiment, and Figure 8(b) shows the time progression of the operating state of the second fan 56 of the image forming apparatus 100 according to this embodiment. In Figures 8(a) and 8(b), the horizontal axis represents time, and the vertical axis represents the power P of the second fan 56.

[0113] The dashed line in Figure 9, representing Fan ON, shows the change in UFP dissipation velocity when the second fan 56 operates as shown in Figure 8(a). The solid line in Figure 9, representing Fan OFF→ON, shows the change in UFP dissipation velocity when the second fan 56 operates as shown in Figure 8(b). In Figure 9, the UFP dissipation velocity on the vertical axis increases as you move upwards on the vertical axis.

[0114] In Figures 8 and 9, time t0 is the time when temperature control was started, and time t1 is the time when paper feeding was started.

[0115] When the secondary transfer operation is started in the secondary transfer nip section 17 by the secondary transfer roller 16, the control circuit A starts operating the second fan 56 when the transport distance of the sheet S passing through the fixing nip section N reaches a predetermined value. Specifically, when the secondary transfer operation is started, as shown in Figure 8(b), the control circuit A keeps the second fan 56 in a non-operating (OFF) state from time t0 to time t2, and operates the second fan 56 at full power from time t2 onward. In this case, the UFP dissipation speed is kept lower than the UFP dissipation speed when the second fan 56 is constantly operating, as shown in Figure 9.

[0116] In this case, if the second fan 56 starts operating too early, it will lead to an increase in UFP, and if the second fan 56 starts operating too late, it will cause condensation on the intermediate transfer belt 9.

[0117] Here, the wax vapor concentration C that governs the generation of UFP increases as the sheet S passes through the fixing nip N more times, and as the transport distance of the sheet S increases, assuming a constant amount of toner on the sheet S. Also, the generation of water vapor that governs condensation increases as the sheet S passes through the fixing nip N more times, and as the transport distance of the sheet S increases.

[0118] Therefore, the control circuit unit A starts operating the second fan 56 at time t2 within the time range R from time t_min to time t_max, which allows for both reduction of UFP generation and prevention of condensation. In other words, time t_min is the shortest time from which the reduction in UFP generation can be achieved by operating the fan. Also, time t_max is the maximum time by which condensation will occur if the fan is not operated by this time. Time t_min and time t_max are set according to the transport distance of the sheet S passing through the fixing nip section N.

[0119] Specifically, the desired UFP reduction effect was achieved by activating the second fan 56 from time t_min, when the transport distance of the sheet S, at which the leading edge of the sheet S in the transport direction passes through the fixing nip section N, reaches 660 mm. Furthermore, the desired condensation prevention effect was achieved by starting the operation of the second fan 56 by time t_max, when the transport distance of the sheet S, at which the leading edge of the sheet S in the transport direction passes through the fixing nip section N, reaches 12600 mm. Thus, in order to achieve both UFP reduction and condensation prevention, the control circuit A activates the second fan 56 when the transport distance of the sheet S is 660 mm or more and 12600 mm or less.

[0120] When the conveying speed of sheet S is 264 mm / s, the time required to convey a distance of 660 mm is 2.5 seconds. Furthermore, in this case, as can be seen from Figure 7, in order to obtain the desired UFP reduction effect, the second fan 56 should be activated within 105 seconds. Moreover, in this case, the time required to convey a distance of 12,600 mm is 67 seconds. Therefore, in order to achieve both UFP reduction and condensation prevention, the control circuit unit A activates the second fan 56 2.5 seconds after the sheet S passes the fixing nip portion N at the leading edge in the conveying direction and 67 seconds after the sheet S passes the fixing nip portion N at the leading edge in the conveying direction.

[0121] The timing for starting the operation of the second fan 56 is, in this example, 17 seconds after the sheet S passes the fixing nip section N at the leading edge in the conveying direction, which is necessary to convey the sheet S by 2100 mm.

[0122] For example, an A4-sized sheet S (with a length of 210 mm in the transport direction) is transported at intervals of approximately 0.2 seconds during continuous feeding. Therefore, the t_min for an A4-sized sheet S is 10.1 seconds, which is the sum of the 0.2 seconds between the first and second sheets, the 0.2 seconds between the second and third sheets, and the 0.5 seconds between the third and fourth sheets, plus the 2.5 seconds mentioned above, and the 7 seconds from time t=0 to time t1.

[0123] The timing for starting the operation of the second fan 56 described above is fundamentally set based on the transport distance of the sheet S, regardless of whether a portion of the sheet S remains at the fixing nip section N, because the transport distance of the sheet S directly affects the generation of UFP and the generation of water vapor. On the other hand, it is preferable from the viewpoint of ease of creating a control program to start the operation of the second fan 56 when the leading edge of the sheet S in the transport direction is detected by the detection sensor 25.

[0124] However, when this type of control is performed, the timing of the start of operation of the second fan 56 will be slightly delayed compared to when the second fan 56 is started when the leading edge of the sheet S in the transport direction passes the fixing nip section N. In response to this, the control circuit A calculates the transport distance of the sheet S by adding the distance from the fixing nip section N to the detection sensor 25 and the transport distance of the sheet S after the detection sensor 25 detects the leading edge of the sheet S in the transport direction. Then, the control circuit A activates the second fan 56 when the calculated transport distance of the sheet S is 660 mm or more and 12600 mm or less.

[0125] Alternatively, a control program may be created to control the operation of the second fan 56 only according to the transport distance of the sheet S after the detection sensor 25 detects the leading edge of the sheet S in the transport direction. Even in this case, by ensuring that the transport distance of the sheet S until the leading edge of the sheet S passes through the fixing nip section N does not exceed 12,600 mm, it is possible to achieve both reduction of UFP and prevention of condensation. For example, the operation of the second fan 56 can be started 17 seconds after the detection sensor 25 detects the leading edge of the sheet S in the transport direction, which is necessary to transport the sheet S 2,100 mm.

[0126] Furthermore, UFP and condensation are more likely to occur at lower ambient temperatures. Therefore, it is preferable that the control circuit A performs the above control of the second fan 56 when the ambient temperature indicated by the electrical signal input from the in-machine temperature sensor 65 before the start of the secondary transfer operation by the secondary transfer roller 16 is 10°C or higher and 30°C or lower. This ensures that the occurrence of UFP and condensation is reliably suppressed. Alternatively, the control circuit A may perform the above control of the second fan 56 when the temperature indicated by the electrical signal input from the thermistor TH before the start of the secondary transfer operation by the secondary transfer roller 16 is 10°C or higher and 30°C or lower.

[0127] Furthermore, the air intake port 52 is located on the fixing belt 27 side of the sheet S transport path between the secondary transfer roller 16 and the fixing unit 19. This allows the air intake port 52 to be located near the intermediate transfer belt 9, which is the target of condensation prevention, and the fixing belt 27, which generates wax vapor.

[0128] Furthermore, by providing the air intake port 52 near the approximate center of the longitudinal direction of the plate member 51, the area of ​​the air intake port 52 can be reduced compared to the case where the air intake port 52 is provided along the entire longitudinal direction of the plate member 51. This allows for a faster intake velocity at the air intake port 52, enabling rapid control of the wax vapor concentration C and ambient temperature T around the fixing belt 27.

[0129] The control circuit unit A may operate the second fan 56 not only as shown in Figure 8(b), but also as shown in Figure 10. In the case of Figure 10, the control circuit unit A starts operating the second fan 56 at time t_min when condensation is likely to occur, such as when the sheet S is made of cardboard or the like that which contains a lot of moisture, or when the ambient temperature of the image forming apparatus 100 is low. This makes it possible to effectively prevent condensation even under conditions where condensation is likely to occur.

[0130] Furthermore, the control circuit unit A may operate the second fan 56 as shown in Figure 11. In the case of Figure 11, the control circuit unit A starts operating the second fan 56 at time t_max when condensation is unlikely to occur, such as when the sheet S is thin paper that does not contain much moisture, or when the ambient temperature of the image forming apparatus 100 is high. This ensures a condensation prevention effect and reduces noise caused by the operation of the second fan 56 by delaying its operation.

[0131] Furthermore, the control circuit unit A may vary the timing of the start of operation of the second fan 56 within the time range R, depending on the type of sheet S or the ambient temperature. Specifically, if the sheet S is a type that contains a lot of moisture, such as cardboard, or if the ambient temperature is low, the control circuit unit A advances the start timing of the second fan 56 to prevent condensation. On the other hand, if the sheet S is a type that does not contain a lot of moisture, such as thin paper, or if the ambient temperature is high, the control circuit unit A delays the start timing of the second fan 56 to reduce UFP and also reduce the noise caused by the operation of the second fan 56.

[0132] In this case, the image forming apparatus 100 has a storage means (not shown) that stores a table associating the type of sheet S with the start time of operation of the second fan 56. The control circuit unit A activates the second fan 56 when the leading edge of the sheet S in the transport direction has passed through the fixing nip section N, and the start time corresponding to the type of sheet S indicated by the electrical signal input from the input device B in the table has been reached. This allows the control circuit unit A to vary the operating timing of the second fan 56.

[0133] Furthermore, the image forming apparatus 100 has a storage means (not shown) that stores a table that associates ambient temperature with the start time of operation of the second fan 56. The control circuit unit A activates the second fan 56 when the leading edge of the sheet S in the transport direction has passed through the fixing nip section N, and the start time, which is associated with the ambient temperature indicated by the electrical signal input from the in-machine temperature sensor 65 in the table, has been reached. This allows the control circuit unit A to vary the operating timing of the second fan 56.

[0134] In this embodiment, when the transfer operation is started, the second fan 56 is activated when the transport distance of the sheet S passing through the fixing nip section N reaches a predetermined value. This allows for miniaturization because the reduction of ultrafine particles generated by the heating of the release agent contained in the toner, as well as heat dissipation and water vapor discharge, can be achieved solely through the duct 57.

[0135] In this embodiment, the distance from the fixing nip section N to the detection sensor 25 and the transport distance of the sheet S detected by the detection sensor 25 (= length of paper) were added together to calculate the transport distance of the sheet S (length of the sheet S that passed through the fixing nip section N). In other words, the transport distance of the sheet S that passed through the fixing nip section N = distance from the fixing nip section N to the detection sensor 25 + (length of one sheet S in the transport direction that passed through the detection sensor 25) × (number of sheets S that were transported).

[0136] The reason for adding the distance from the fixing nip section N to the detection sensor 25 in the above is that even during transport of the first sheet S after it has passed through the fixing nip section N until it reaches the detection sensor 25, UFP and moisture evaporate from the fixed sheet S. The distance from the fixing nip section N to the detection sensor 25 is approximately 30 mm, for example. The second fan 56 was activated when the calculated transport distance of the sheet S was 660 mm or more and 12600 mm or less.

[0137] However, the operation of the second fan 56 may be started when the transport distance of the sheet S reaches less than 12,600 mm, for example, 2,100 mm. In this case, the second predetermined value is set so that the value obtained by adding the distance from the fixing nip section N to the detection sensor 25 to the second predetermined value does not exceed 12,600 mm.

[0138] (Embodiment 2) <Configuration of an image forming apparatus> The configuration of the image forming apparatus 200 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 12 and 13.

[0139] In Figures 12 and 13, parts that have the same configuration as those in Figures 1 to 3 are denoted by the same reference numerals, and their descriptions are omitted.

[0140] The image forming apparatus 200 is exemplified here as a four-color full-color laser printer using a tandem-intermediate transfer method with an electrophotographic process. The image forming apparatus 200 forms an image on a recording material sheet S based on image information input to the control circuit unit A from an input device B such as a personal computer. The image forming apparatus 200 is a color electrophotographic device such as a color copier equipped with multiple photoreceptor drums, but is not limited to this, and may also be a monochrome electrophotographic device such as a monochrome copier or printer equipped with one photoreceptor drum.

[0141] Specifically, the image forming apparatus 200 includes an image forming unit 1, a belt suspension roller 10, a sheet feeding roller 13, a resist roller 14a, a resist roller 14b, a guide member 15, and a secondary transfer roller 16. The image forming apparatus 200 also includes a guide member 18, a guide member 20, a pair of discharge rollers 21, and a discharge tray 22 which includes toner bottles 23Y, 23M, 23C, and 23K, and a detection sensor 25. Furthermore, the image forming apparatus 200 includes a first fan 55, a sheet member 59, a second duct unit 63, an internal temperature sensor 65, a first duct unit 66, a fuser 119, and a control circuit unit A.

[0142] The sheet member 59 is provided in the second duct unit 63 to help prevent the advection of water vapor contained in the sheet S to the intermediate transfer belt unit 8. The sheet member 59 extends from the second duct unit 63 toward the intermediate transfer belt 9 on the downstream side of the toner image transport direction by the intermediate transfer belt 9 in the secondary transfer nip section 17.

[0143] The fuser 119, used as a fixing means, is a belt-heating type on-demand fuser and has a vertical path configuration that transports the sheet S from bottom to top in the direction of gravity. However, the fuser 119 is not limited to a vertical path configuration and may also have a horizontal path configuration that transports the sheet S in a horizontal direction.

[0144] The fuser 119 performs a thermal fixing process in the fixing nip section N, applying heat and pressure to the toner image that has been secondarily transferred to the sheet S, which is transported from the secondary transfer nip section 17 by the secondary transfer roller 16, to fix the toner image to the sheet S. The fuser 119 then transports the sheet S with the fixed toner image to the discharge roller pair 21. Details of the configuration of the fuser 119 will be described later.

[0145] The guide member 20 is provided between the fuser 119 and the discharge roller pair 21. The guide member 20 guides the transport of the sheet S being transported between the fuser 119 and the discharge roller pair 21 in the transport path 12.

[0146] The first fan 55 is positioned downstream of the fuser 119 in the transport direction. The first fan 55 is operated by the control circuit unit A to collect and discharge water vapor floating downstream of the fuser 119 in the transport direction.

[0147] The second duct unit 63 sucks in the air between the fuser 119 and the intermediate transfer belt 9, and the air between the fuser 119 and the secondary transfer roller 16, and discharges it to the outside of the image forming apparatus 200. Details of the configuration of the second duct unit 63 will be described later.

[0148] The first duct unit 66 sucks in the air between the fuser 119 and the intermediate transfer belt 9, and the air between the fuser 119 and the secondary transfer roller 16, and discharges it to the outside of the image forming apparatus 200. Details of the configuration of the first duct unit 66 will be described later.

[0149] Control circuit unit A controls the operation of the entire image forming apparatus 200 based on image information input from input device B. Control circuit unit A is capable of executing a continuous job of forming images on multiple sheets S in succession. Control circuit unit A controls the operation of the first duct fan 62 of the first duct unit 66, described later, based on the detection result of the sheet S indicated by the electrical signal input from detection sensor 25 and the ambient temperature indicated by the electrical signal input from in-machine temperature sensor 65. Control circuit unit A controls the operation of the second duct fan 61 of the second duct unit 63, described later, based on the detection result of the sheet S indicated by the electrical signal input from detection sensor 25 and the ambient temperature indicated by the electrical signal input from in-machine temperature sensor 65.

[0150] In the image forming apparatus 200 having the above configuration, the sheet feeding roller 13, the resist roller 14a and resist roller 14b, the secondary transfer roller 16, the fuser 119, and the discharge roller pair 21 are arranged in this order from the bottom to the top of the transport path 12.

[0151] <Fuser Unit Configuration> The configuration of the fuser 119 of the image forming apparatus 200 according to Embodiment 2 of the present invention will be described in detail with reference to Figures 12 and 13.

[0152] The fuser 119 comprises a pair of discharge rollers 26, a fuser belt 27, a pressure roller 28, a fuser heater 39, a heater holder 40, a rigid stay 41, a housing 134, and a thermistor TH.

[0153] The discharge roller pair 26 is located downstream of the fixing belt 27 and the pressure roller 28 in the conveying direction, and conveys the sheet S, which is being conveyed by the fixing belt 27 and the pressure roller 28, to the discharge roller pair 21.

[0154] The housing 134 houses the discharge roller pair 26, the fixing belt 27, and the pressure roller 28. The housing 134 includes a sheet inlet 35, a first guide member 36, and a sheet outlet 38.

[0155] The sheet inlet 35 is the inlet of the fuser 119 when the sheet S is transported from the secondary transfer roller 16 to the fuser 119.

[0156] The sheet outlet section 38 is the outlet of the fuser 119 when the sheet is transported to the discharge roller pair 21 by the discharge roller pair 26.

[0157] In the fuser 119 having the above configuration, the pressure roller 28 is driven to rotate, and the temperature detected by the thermistor TH is controlled by the control circuit A to a predetermined target temperature. In this state, the sheet S onto which the unfixed toner image has been transferred by the secondary transfer nip section 17 is transported to the fuser 119 via the sheet inlet section 35. The toner image is fixed to the sheet S transported to the fuser 119. The sheet S with the fixed toner image is then discharged from the sheet outlet section 38.

[0158] <Configuration of the first and second duct units> The configurations of the first duct unit 66 and the second duct unit 63 of the image forming apparatus 200 according to Embodiment 2 of the present invention will be described in detail with reference to Figures 13 to 15.

[0159] In Figure 14, Figure 14(a) is a perspective view of the first duct unit 66 and the second duct unit 63, and Figure 14(b) is a perspective view of the filter 64. Also, in Figure 15, Figure 15(a) shows the airflow of the first duct unit 66, and Figure 15(b) shows the airflow of the second duct unit 63.

[0160] The surface temperature of the fixing belt 27 of the fuser 119 of the image forming apparatus 200 is set higher than the surface temperature of the fixing belt 27 of the fuser 19 of the image forming apparatus 100 in order to improve the fixing performance of the toner image. As a result, the amount of wax vapor generated from the fixing belt 27 of the image forming apparatus 200 and the amount of UFP generated from the wax vapor are greater than the amount of wax vapor and UFP generated from the fixing belt 27 of the image forming apparatus 100. In contrast, the image forming apparatus 200 of this embodiment is equipped with a second duct unit 63 with a filter 64 for removing UFP, in addition to a first duct unit 66 whose main purpose is to discharge water vapor, in order to improve the UFP reduction capability.

[0161] First, the configuration of the first duct unit 66 will be described in detail.

[0162] The first duct unit 66 includes a first duct 60, a fan 62 for the first duct, an intake port 67, and an exhaust port 68.

[0163] The first air intake port 67 is provided in the first duct 60. The air intake port 67 is located on the fixing belt 27 side of the sheet S transport path 12 between the secondary transfer roller 16 and the fuser 119. The air intake port 67 is located in the center of the rotation axis direction of the fixing belt 27 (the direction perpendicular to the plane of the paper in Figure 13). The air intake port 67 is located adjacent to the air intake port 72. The air intake port 67 takes in air between the fuser 119 and the intermediate transfer belt 9 and air between the fuser 119 and the secondary transfer roller 16 (air A) that is sucked in by the first duct fan 62 into the first duct 60.

[0164] The exhaust port 68, which serves as the first exhaust port, exhausts the air drawn into the first duct 60 via the intake port 67 by the first duct fan 62 to the outside of the image forming apparatus 200.

[0165] The first duct fan 62 is operated by the control circuit unit A to generate an airflow from the intake port 67 to the exhaust port 68. The first duct fan 62 is provided to discharge water vapor.

[0166] The first duct 60 connects the intake port 67 and the exhaust port 68. The first duct 60 constitutes a first ventilation path that guides the air drawn in from the intake port 67 to the exhaust port 68.

[0167] In the first duct unit 66 having the above configuration, air taken in from the intake port 67 is exhausted from the exhaust port 68 through the first ventilation path shown by the dashed arrow in Figure 15(a). The first duct fan 62 is located in the first ventilation path. The first duct unit 66 is required to generate a certain amount of airflow to prevent condensation on the intermediate transfer belt 9, so no ventilation resistor such as a filter is provided in the first ventilation path.

[0168] Next, we will explain in detail the configuration of the second duct unit 63.

[0169] The second duct unit 63 includes a second duct fan 61, a filter 64, an exhaust port 69, a frame member 70, a second duct 71, and an intake port 72.

[0170] The second duct fan 61 is operated by the control circuit unit A to generate airflow from the intake port 72 to the exhaust port 69. The second duct fan 61 is provided to remove UFP (Ultraviolet Fluid).

[0171] The filter 64 has an elongated shape that conforms to the shape of the frame member 70. The filter 64 is provided with a notch 64a for providing an air intake port 67. The filter 64 is a nonwoven fabric made of electrostatically treated polypropylene fibers, and captures UFP guided to the filter 64 by the electrical adsorption force due to the electrostatic charge applied to the fibers and the physical barrier force of the fibers. The higher the fiber density of the filter 64, the greater the UFP reduction ability of the filter 64.

[0172] The exhaust port 69, which serves as the second exhaust port, exhausts the air drawn into the second duct 71 via the intake port 72 by the second duct fan 61 to the outside of the image forming apparatus 200.

[0173] The frame member 70 is provided around the air intake ports 67 and 72. A filter 64 is attached to the frame member 70.

[0174] The second duct 71 connects the intake port 72 and the exhaust port 69. The second duct 71 constitutes a second ventilation path that guides the air drawn in from the intake port 72 to the exhaust port 69.

[0175] The intake port 72, which serves as a second air intake, is covered by a filter 64 attached to the frame member 70. The intake port 72 is located on the fixing belt 27 side of the sheet S transport path 12 between the secondary transfer roller 16 and the fixing unit 119. The intake port 72 is located adjacent to the intake port 67. The intake port 72 draws in air between the fixing unit 119 and the intermediate transfer belt 9, and air (air B) between the fixing unit 119 and the secondary transfer roller 16, which are drawn in by the second duct fan 61, into the second duct 71.

[0176] In the second duct unit 63 having the above configuration, air taken in from the intake port 72 via the filter 64 is exhausted from the exhaust port 69 through the second ventilation path shown by the dashed arrow in Figure 15(b). The second duct fan 61 and filter 64 are located in the second ventilation path.

[0177] <Operation of the first fan, the first duct fan, and the second duct fan> The operation of the first fan 55, the first duct fan 62, and the second duct fan 61 of the image forming apparatus 200 according to Embodiment 2 of the present invention will be described in detail with reference to Figures 12 to 17.

[0178] In Figure 16, Figure 16(a) shows the operating time of the first fan 55, Figure 16(b) shows the operating time of the second duct fan 61, and Figure 16(c) shows the operating time of the first duct fan 62. In Figures 16(a) to 16(c), the horizontal axis, "time," represents time, and the vertical axis, "P," represents the power used to operate each fan.

[0179] The first duct fan 62 is provided to discharge water vapor, and the second duct fan 61 is provided to remove UFP; therefore, both the first duct fan 62 and the second duct fan 61 must be operated. In addition, the first duct unit 66 does not have a ventilation resistor such as a filter in order to ensure airflow. As a result, the airflow of the first duct unit 66 is approximately three times that of the second duct unit 63, which has a filter 64.

[0180] Most of the UFP inside the image forming apparatus 200 is discharged to the outside of the image forming apparatus 200 by the first duct unit 66 without passing through the filter 64 while the first duct unit 66 is operating. Therefore, in this embodiment, in order to ensure that the filter 64 removes UFP, the timing at which the first duct fan 62 starts operating is delayed compared to the timing at which the second duct fan 61 starts operating.

[0181] Specifically, at time t0, when temperature control of the fixing belt 27 is initiated before the sheet S is transported, the first fan 55 and the second duct fan 61 start operating at full power. The first fan 55 operates to collect and discharge water vapor floating downstream in the transport direction of the fuser 119. The second duct fan 61 operates to collect UFP generated by the fuser 119 in the filter 64.

[0182] The first duct fan 62 stops operating from time t1 to time t2 when a continuous job is started, and operates at full power from time t2 onward. Here, time t2 is the time when, after the start of temperature control, the transport distance of the sheet S from the time the leading edge of the sheet S in the transport direction passes the fixing nip section N reaches a first predetermined value of 9450 mm. The timing for starting the operation of the first duct fan 62 is later than in the above embodiment 1, in which the second fan 56 is activated when the transport distance of the sheet S from the time the leading edge of the sheet S in the transport direction passes the fixing nip section N reaches 2100 mm. As a result, the effect of reducing UFP by the filter 64 can be improved compared to the above embodiment 1.

[0183] Note that the timing for operating the first duct fan 62 is not limited to the above; any timing other than the above is acceptable as long as it is within the time R from time t_min to time t_max in Figure 16(c). Even in this case, sufficient UFP reduction and condensation prevention effects can be obtained. Here, time t_min is the time when the transport distance of the sheet S reaches 660 mm from the time the leading edge of the sheet S in the transport direction passes the fixing nip N. Also, time t_max is the time when the transport distance of the sheet S reaches 12600 mm from the time the leading edge of the sheet S in the transport direction passes the fixing nip N.

[0184] Figure 17 compares the changes in UFP emission rate when the first duct fan 62 is activated from time t0 and when it is activated from time t2. Here, time t2 is exemplified as approximately 52 seconds. In Figure 17, the dashed line shows the change in UFP emission rate when the first duct fan 62 is activated from time t0, and the solid line shows the change in UFP emission rate when the first duct fan 62 is activated from time t2.

[0185] Figure 17 shows that the UFP emission rate when the first duct fan 62 is operated from time t2 is lower than the UFP emission rate when the first duct fan 62 is operated from time t0. Furthermore, in the Rb region of Figure 17, which occurs after a certain amount of time has elapsed, the area around the fuser 119 is heated, so operating the first duct fan 62 can reduce UFP. In this way, immediately after the start of paper feeding, when a large amount of UFP is generated, the filter 64 stably removes UFP. After that, the synergistic effect of the UFP reduction effect by operating the first duct fan 62 and the UFP removal effect by the filter 64 can significantly reduce UFP.

[0186] Furthermore, since the second duct fan 61 is operated before the first duct fan 62 is operated, the water vapor between the fuser 119 and the intermediate transfer belt 9 is drawn in through the intake port 72 of the second duct unit 63 and discharged through the exhaust port 69. Therefore, although the water vapor concentration rises before the first duct fan 62 is operated, it is gradual, and condensation on the intermediate transfer belt 9 can be suppressed.

[0187] Furthermore, in addition to the operation of the second duct fan 61, the first duct fan 62 is activated when the conveying distance of the sheet S reaches 9450 mm, thereby reliably suppressing condensation on the intermediate transfer belt 9.

[0188] Furthermore, the first duct fan 62 may be configured to perform the above operation when the temperature detected by the internal temperature sensor 65 is 10°C or higher and 30°C or lower. On the other hand, if the temperature detected by the internal temperature sensor 65 is higher than 30°C, the amount of UFP generated is small and condensation is less likely to occur, so the operation of both the first duct fan 62 and the second duct fan 61 can be stopped. This allows for power saving. On the other hand, if the temperature detected by the internal temperature sensor 65 is less than 10°C, it is preferable to operate both the first duct fan 62 and the second duct fan 61 from time t0 in order to prioritize preventing condensation, which affects image quality.

[0189] Furthermore, the transport distance of the sheet S from the moment the leading edge of the sheet S in the transport direction passes the fixing nip section N is reset when predetermined conditions are met. For example, if the image forming operation is interrupted for a certain period of time and the temperature detected by the in-machine temperature sensor 65 drops below a predetermined temperature, the amount of UFP generated increases. In such a case, if the transport distance of the sheet S is not reset, the stopping time of the first duct fan 62 will be shortened. Therefore, in such a case, the control circuit unit A resets the count value that was counted as the transport distance of the sheet S from the moment the leading edge of the sheet S in the transport direction passed the fixing nip section N.

[0190] Furthermore, the transport distance of the sheet S from the time the leading edge of the sheet S in the transport direction passes the fixing nip section N when the first duct fan 62 starts operating may be changed depending on the type of sheet S and productivity. For example, the transport distance of the sheet S from the time the leading edge of the sheet S in the transport direction passes the fixing nip section N is set to a smaller value when the sheet S is made of cardboard containing a lot of moisture or when the productivity of the sheet S is high, as this generates more water vapor.

[0191] Thus, in this embodiment, UFP can be stably removed by the operation of the first duct fan 62 and the second duct fan 61, and condensation on the intermediate transfer belt 9 can be suppressed. Therefore, the image forming apparatus 200 of this embodiment is suitable when the temperature of the fixing belt 27 is high, resulting in a large amount of UFP generation, and when it is desired to suppress condensation on the intermediate transfer belt 9.

[0192] Furthermore, since the second duct unit 63 is equipped with a filter 64 that can stably reduce UFP regardless of temperature and concentration, the second duct unit 63 can stably reduce UFP.

[0193] Since the operation of the image forming apparatus 200 is identical to that of the image forming apparatus 100, its explanation will be omitted.

[0194] In this embodiment, when a continuous job is started, the first duct fan 62 is activated when the transport distance of the sheet S passing through the fixing nip section N reaches 9450 mm. This makes it possible to reduce UFP, dissipate heat, and discharge water vapor.

[0195] Furthermore, by providing the air intake ports 67 and 72 adjacent to each other, the image forming apparatus 200 can be miniaturized.

[0196] In this embodiment, the first duct fan 62 was operated according to the distance traveled by the sheet S from the moment the leading edge of the sheet S in the transport direction passed through the fixing nip section N. However, the first duct fan 62 may also be operated according to the total area of ​​the sheet S that has passed through the fixing nip section N. In this case, the calculation process becomes somewhat more complex, but since the amount of water vapor generated from the sheet S is correlated with the total area of ​​the sheet S, it is reasonable from the standpoint of preventing condensation.

[0197] Furthermore, in this embodiment, the second duct fan 61 is operated from time t0, but the second duct fan 61 may be operated at time t1, which is the paper feeding start time, or a few seconds later than time t1. Even in this case, the amount of UFP generated is not very large before or immediately after paper feeding starts, so a sufficient UFP reduction effect can be obtained.

[0198] In this embodiment, the operation of the first duct fan 62 may also be controlled solely according to the transport distance of the sheet S after the detection sensor 25 detects the leading edge of the sheet S in the transport direction. For example, after the detection sensor 25 detects the leading edge of the sheet S in the transport direction, the operation of the first duct fan 62 is started when the transport distance of the sheet S reaches a second predetermined value of 2100 mm, which is less than 9450 mm. In this case, by setting the second predetermined value such that the value obtained by adding the distance from the fixing nip portion N to the detection sensor 25 is 660 mm or more and 12600 mm or less, it is possible to achieve both reduction of UFP and prevention of condensation.

[0199] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0200] A Control circuit section 1 Image forming unit 8. Intermediate Transfer Belt Unit 9. Intermediate transfer belt 12. Transport Route 16. Secondary transfer roller 17 Secondary transfer nip section 19 Fuser 25 detection sensors 27 Fixing belt 28 Pressure roller 39. Fuser Heater 55 First Fan 60 First Duct 61 Fan for the second duct 62 Fan for the first duct 63 Second duct unit 64 filters 65. In-flight temperature sensor 66 First Duct Unit 67 First air intake 68 First exhaust port 69 Second exhaust port 71 Second duct 72 Second air intake 100 Image forming apparatus 119 Fuser 200 Image forming apparatus

Claims

1. An image forming apparatus capable of performing a continuous job of forming images on multiple recording materials, Image forming means for forming a toner image using toner containing a release agent, A transfer means that performs a transfer operation to transfer the toner image formed by the image forming means onto a recording material, A fixing means comprising a first rotating body heated by a heating means, and a second rotating body that contacts the first rotating body and together with the first rotating body forms a fixing nip portion, wherein the fixing means fixes the toner image to the recording material by clamping and transporting the recording material onto which the toner image has been transferred by the transfer means at the fixing nip portion, A first duct unit comprising: a first air intake port for drawing in air between the fixing means and the transfer means; a first exhaust port for exhausting the air drawn in from the first air intake port to the outside; and a first duct that forms a first ventilation path between the first air intake port and the first exhaust port; A first duct fan is provided in the first ventilation path and generates an airflow from the first intake port to the first exhaust port, A second duct unit comprising: a second air intake port for drawing in air between the fixing means and the transfer means; a second exhaust port for exhausting the air drawn in from the second air intake port to the outside; and a second duct that forms a second ventilation path between the second air intake port and the second exhaust port, A second duct fan is provided in the second ventilation path and generates an airflow from the second intake port toward the second exhaust port, A filter provided in the second ventilation path for removing fine particles, Control means for controlling the operation of the first duct fan and the second duct fan, It has, The control means is When the continuous job is started, the operation of the first duct fan is started when the transport distance of the recording material passing through the fixing nip section reaches a first predetermined value. An image forming apparatus characterized by the following features.

2. The control means is The second duct fan is activated before the transport of the recording material begins. The image forming apparatus according to feature 1.

3. The first air intake port is, Located adjacent to the second air intake port, The image forming apparatus according to feature 1.

4. The first air intake port is, The first rotating body is provided at the central part in the direction of its rotation axis, The image forming apparatus according to feature 3.

5. The fixing means has a temperature detection means for detecting the temperature around it, The control means is When the temperature detected by the temperature detection means is 10°C or higher and 30°C or lower, the operation of the fan is started when the transport distance of the recording material passing through the fixing nip reaches the first predetermined value. The image forming apparatus according to feature 1.

6. The first predetermined value is, It is 660 mm or more and 12,600 mm or less. The image forming apparatus according to any one of claims 1 to 4.

7. The fixing nip section has a recording material detection means for detecting the recording material downstream in the direction of transport of the recording material, The control means is The operation of the first duct fan is started when the transport distance of the recording material after it has been detected by the recording material detection means reaches a second predetermined value that is less than the first predetermined value. The image forming apparatus according to any one of claims 1 to 4.

8. The first air intake port is, The transport path of the recording material from the transfer means to the fixing means is provided on the first rotating body side, The image forming apparatus according to any one of claims 1 to 4.

9. The aforementioned first duct is, The first ventilation path does not include a ventilation resistor. The image forming apparatus according to any one of claims 1 to 4.

10. The control means is The first predetermined value is made variable depending on the type of recording material. The image forming apparatus according to any one of claims 1 to 4.

11. The fixing means has a temperature detection means for detecting the temperature around it, The control means is The first predetermined value is varied according to the temperature detected by the temperature detection means. The image forming apparatus according to any one of claims 1 to 3.

Images