Image forming device

Abstract

To provide an image forming apparatus that, with a simple configuration, can prevent dew condensation and can reduce waiting time until the start of printing.SOLUTION: A fixing device 300 accommodates a fixing belt 310 and a pressure roller 320 in a housing 301, and a paper ejection unit ejecting a sheet member and a branch unit branching the sheet member during double-sided printing are disposed above the fixing device 300. The housing 301 has a cross-sectional shape in which two arcs are arranged to face each other in the horizontal direction, and an inlet 302 and an outlet 303 for the sheet member are formed in upper and lower plane parts of the housing 301. Openings 304 opening in a rectangular shape are formed from the middle to an upper end in a height direction of the arc shape cross section of the housing 301. The openings 304 are formed as a pair on both ends in a longitudinal direction of the housing 301 and open toward both ends in a longitudinal direction of the fixing belt 310. Forming at least part of the opening 304 above the fixing belt 310 can actively send heat of the fixing device 300 to a dew condensation part above.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus in which a cooling opening is formed in the housing of a fixing device, and is provided in the upper part of the housing. [Background technology]

[0002] When the power supply of the image forming apparatus is turned from OFF to ON and single-sided printing is performed, the post-fixing transport path and the double-sided transport path located above the fixing device are still cold. For this reason, when the paper is heated in the nip of the fixing device during single-sided printing, the moisture contained in the paper evaporates and becomes steam, which rises from the fixing device and comes into contact with the switching members of the post-fixing transport path and the double-sided transport path located above, causing condensation. If the paper printed on one side becomes wet with condensed water, image defects may occur during double-sided printing, or a jam may occur due to wrinkles caused by the condensed water. For this reason, when the power supply of the image forming apparatus is turned ON, the image forming apparatus is controlled to run idle (warm-up operation) until each transport path warms up to above the dew point. Summary of the Invention [Problem to be solved by the invention]

[0003] However, if warm-up operation is performed until each transport path is heated above the dew point, the waiting time before printing becomes long. A fixing device equipped with a dedicated fan for eliminating condensation to shorten the waiting time is also known, but this has the problem of making the device complicated, large, and expensive. Therefore, the object of the present invention is to provide an image forming device that can prevent condensation with a simple configuration and shorten the waiting time before printing can begin. [Means for solving the problem]

[0004] In order to solve the above problem, the image forming apparatus of the present invention contains a heating member and a pressure member that have a longitudinal direction and form a nip portion within a housing, and has a fixing device that transfers heat from the heating member to a sheet member by passing the sheet member through the nip portion, and above the fixing device is disposed a paper discharge path for discharging the sheet member, and a branch portion that branches from the paper discharge path to an inversion transport path that inverts and transports the sheet member when double-sided printing, and is characterized in that the housing has a pair of openings that open toward both longitudinal ends of the heating member inside the housing and open upward on the outside of the housing. Effect of the Invention

[0005] According to the present invention, condensation can be prevented with a simple configuration, and the waiting time until printing can be started can be shortened. [Brief description of the drawings]

[0006] [Figure 1A] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; [Figure 1B] 1 is a diagram illustrating the principle of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] 2 is a cross-sectional view of a fixing device used in the image forming apparatus. [Figure 3A] 1A is a perspective view of a fixing device according to an embodiment of the present invention with a shutter member in an open state, FIG. 1B is a cross-sectional view thereof, and FIG. [Figure 3B] 1A is a perspective view of a fixing device according to an embodiment of the present invention in which a shutter member is in a closed state, FIG. 1B is a cross-sectional view, and FIG. 1C is a perspective view of a modified example. [Figure 3C] 1 is a cross-sectional view of a fixing device as a comparative example having a lateral opening that is disadvantageous for exhausting heat. [Figure 3D] 4 is a cross-sectional view of the fixing device according to the embodiment of the present invention when the shutter member is in a half-open state. [Figure 3E] 11 is a cross-sectional view of a fixing device according to a modified embodiment of the present invention in which a blower fan is provided on the inlet side of an air duct. [Figure 3F]13 is a cross-sectional view of a fixing device according to a modified embodiment of the present invention in which a blower fan is provided on the outlet side of an air duct. [Figure 4] 1A is a perspective view of a fixing device having a different drive system for a shutter member, in which FIG. 1A is a perspective view of the shutter member in an open state, FIG. 1B is a perspective view of the shutter member in a closed state, and FIG. [Diagram 5] 13(a) and 13(b) are plan views of a heater connected in parallel to two electrodes at both ends. [Figure 6] FIG. 1 is a plan view of a heater connected in parallel to three electrodes. [Figure 7] 4(a) to 4(c) are plan views of the heater, showing the state in which the resistance heating element is energized to generate heat. [Figure 8] 1A is a perspective view of a fixing device according to a modified embodiment of the present invention having left and right independent shutter members, and FIG. 1B is a plan view of a state in which air ducts are connected to the left and right openings of the housing. [Figure 9] 11 is a front view of a fixing device showing an embodiment in which guide ribs for diffusing air are formed in a post-fixing transport path. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, a fixing device and an image forming apparatus (laser printer) according to an embodiment of the present invention will be described with reference to the drawings. A laser printer is an example of an image forming apparatus, and the image forming apparatus is of course not limited to a laser printer. In other words, the image forming apparatus can be configured as any one of a copier, a facsimile, a printer, a printing machine, and an inkjet recording apparatus, or as a multifunction machine that combines at least two or more of these.

[0008] In addition, the same or corresponding parts in each drawing are given the same reference numerals, and duplicated explanations are appropriately simplified or omitted. Furthermore, the dimensions, materials, shapes, relative positions, etc. in the explanations of each component are examples, and unless otherwise specified, the scope of this invention is not limited to them.

[0009] In the following embodiments, the sheet member (recording medium) will be described as "paper", but the "recording medium" is not limited to paper. The "recording medium" includes not only paper but also overhead projector sheets, fabrics, metal sheets, plastic films, and prepreg sheets made of carbon fibers pre-impregnated with resin.

[0010] All media to which developer or ink can be attached, recording paper, and recording sheets are included in the "recording media." In addition to plain paper, "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, etc.

[0011] Furthermore, the term "image formation" used in the following description refers not only to applying images such as characters and figures to a medium, but also to applying a pattern or other design to a medium.

[0012] (● Laser printer configuration) Fig. 1A is a schematic diagram showing the configuration of a color laser printer as one embodiment of an image forming apparatus 100 equipped with a fixing device 300. Fig. 1B shows a simplified diagram of the principle of the color laser printer.

[0013] The image forming apparatus 100 includes four process units 1K, 1Y, 1M, and 1C as image forming means. These process units form images using developers of the colors black (K), yellow (Y), magenta (M), and cyan (C) that correspond to the color separation components of a color image. The image forming means may be of an indirect transfer type that uses an intermediate transfer belt 16 described below, or may be of a direct transfer type that does not use the intermediate transfer belt 16 and directly transfers toner images formed by the process units 1K, 1Y, 1M, and 1C onto paper.

[0014] Each process unit 1K, 1Y, 1M, and 1C has the same configuration, except that it has toner bottles 6K, 6Y, 6M, and 6C that contain unused toner of different colors. Therefore, the configuration of one process unit 1K will be described below, and descriptions of the other process units 1Y, 1M, and 1C will be omitted.

[0015] The process unit 1K has an image carrier 2K (e.g., a photosensitive drum), a drum cleaning device 3K, and a charge removal device. The process unit 1K further has a charging device 4K as a charging means for uniformly charging the surface of the image carrier, and a developing device 5K as a developing means for performing visible image processing of the electrostatic latent image formed on the image carrier. The process unit 1K is detachably mounted on the main body of the image forming apparatus 100, and consumable parts can be replaced at the same time.

[0016] The exposure unit 7 is disposed above each of the process units 1K, 1Y, 1M, and 1C installed in the image forming apparatus 100. The exposure unit 7 is configured to perform writing scanning according to image information, that is, to reflect laser light L from a laser diode by a mirror 7a based on image data and irradiate the image carrier 2K.

[0017] In this embodiment, the transfer device 15 is disposed below each of the process units 1K, 1Y, 1M, and 1C. This transfer device 15 corresponds to the transfer section TM in Fig. 1B. Primary transfer rollers 19K, 19Y, 19M, and 19C are disposed in contact with the intermediate transfer belt 16 and facing the image carriers 2K, 2Y, 2M, and 2C, respectively.

[0018] The intermediate transfer belt 16 circulates around the primary transfer rollers 19K, 19Y, 19M, and 19C, the drive roller 18, and the driven roller 17. The secondary transfer roller 20 is disposed opposite the drive roller 18 and in contact with the intermediate transfer belt 16. If the image carriers 2K, 2Y, 2M, and 2C are the first image carriers for the respective colors, then the intermediate transfer belt 16 is the second image carrier that combines these images.

[0019] The belt cleaning device 21 is disposed downstream of the secondary transfer roller 20 in the running direction of the intermediate transfer belt 16. In addition, a cleaning backup roller is disposed on the opposite side of the intermediate transfer belt 16 to the belt cleaning device 21.

[0020] A paper feeder 200 having a tray for stacking paper P is installed below the image forming apparatus 100. This paper feeder 200 constitutes a recording medium supply section, and is capable of storing a large number of sheets of paper P as recording media in a bundle. The paper feeder 200 is unitized with a paper feed roller 60 and a roller pair 210 as a means for transporting paper P.

[0021] The paper feed device 200 can be inserted into and removed from the main body of the image forming apparatus 100 for the purpose of replenishing paper, etc. The paper feed roller 60 and the roller pair 210 are disposed above the paper feed device 200, and are configured to transport the topmost paper P of the paper feed device 200 toward the paper feed path 32.

[0022] The pair of registration rollers 250 as a separation conveying means are disposed immediately upstream of the secondary transfer roller 20 in the conveying direction, and can temporarily stop the paper P fed from the paper feeding device 200. This temporary stop creates slack in the leading edge of the paper P, and corrects the skew of the paper P.

[0023] A registration sensor 31 is disposed immediately upstream of the registration roller pair 250 in the conveying direction, and the passage of the leading edge of the paper is detected by this registration sensor 31. When a predetermined time has elapsed after the registration sensor 31 detects the passage of the leading edge of the paper, the paper is abutted against the registration roller pair 250 and temporarily stops.

[0024] A transport roller 240 is disposed at the downstream end of the paper feed device 200 to transport the paper upward, the paper having been transported to the right from the roller pair 210. As shown in FIG 1A, the transport roller 240 transports the paper upward toward the registration roller pair 250.

[0025] The roller pair 210 is composed of a pair of upper and lower rollers. The roller pair 210 may be of an FRR separation type or an FR separation type.

[0026] In the FRR separation method, a separation roller (return roller) to which a fixed amount of torque is applied in the counter-feed direction by the drive shaft via a torque limiter is pressed against the feed roller to separate the paper in the nip between the rollers.In the FR separation method, a separation roller (friction roller) supported on a fixed shaft is pressed against the feed roller via a torque limiter to separate the paper in the nip between the rollers.

[0027] In this embodiment, the roller pair 210 is configured using the FRR separation method. That is, the roller pair 210 is configured with an upper feed roller 220 that transports the paper into the machine, and a lower separation roller 230 that is given a driving force by a drive shaft via a torque limiter in the opposite direction to the feed roller 220.

[0028] The separation roller 230 is biased by a biasing means such as a spring toward the feed roller 220. The feed roller 60 rotates counterclockwise in FIG. 1A by transmitting the driving force of the feed roller 220 via a clutch means.

[0029] The paper P, which has been struck against the pair of registration rollers 250 and has a slack formed at its leading edge, is sent to the secondary transfer nip (transfer nip N in FIG. 1B) between the secondary transfer roller 20 and the drive roller 18 in time for the toner image formed on the intermediate transfer belt 16 to be suitably transferred. The toner image formed on the intermediate transfer belt 16 is then electrostatically transferred to the desired transfer position with high precision by a bias applied to the secondary transfer nip of the sent-out paper P.

[0030] The post-transfer conveying path 33 is disposed above the secondary transfer nip between the secondary transfer roller 20 and the drive roller 18. The fixing device 300 is installed near the upper end of the post-transfer conveying path 33. The fixing device 300 includes a fixing belt 310 as a heating member containing a heat-generating member, and a pressure roller 320 as a pressure member that rotates while contacting the fixing belt 310 with a predetermined pressure.

[0031] The post-fixing transport path 35 is disposed above the fixing device 300, and branches into a paper discharge path 36 and a reversing transport path 41 at the upper end of the post-fixing transport path 35. A switching member 42 is disposed at this branching point, and the switching member 42 is adapted to swing about its swing shaft 42a. A pair of paper discharge rollers 37 is disposed near the open end of the paper discharge path 36.

[0032] The reverse conveying path 41 merges with the paper feed path 32 at the other end opposite to the branching portion. A pair of reverse conveying rollers 43 is disposed midway along the reverse conveying path 41. The paper output tray 44 is disposed on the upper portion of the image forming apparatus 100, forming a concave shape facing inward of the image forming apparatus 100.

[0033] The powder container 10 (for example, a toner container) is disposed between the transfer device 15 and the paper feed device 200. The powder container 10 is detachably attached to the main body of the image forming apparatus 100.

[0034] In the image forming apparatus 100 of this embodiment, a certain distance is necessary between the paper feed roller 60 and the secondary transfer roller 20 due to the relationship with the transfer paper transport. The powder container 10 is installed in the dead space generated in this distance, thereby making the entire laser printer smaller.

[0035] The transfer cover 8 is installed on the top of the paper feed device 200, in front of the paper feed device 200 in the pull-out direction. By opening the transfer cover 8, it is possible to inspect the inside of the image forming apparatus 100. The transfer cover 8 is provided with a manual feed roller 45 for manual paper feed and a manual feed tray 46 for manual paper feed.

[0036] (● Principles of image forming devices) 1B, a principle diagram of the image forming apparatus 100 described above will be described. The image forming apparatus 100 has an image carrier 2 (e.g., a photoconductor drum) and a drum cleaning device 3. It also has a charging device 4 as a charging means for uniformly charging the surface of the image carrier, a developing device 5 for visualizing the electrostatic latent image formed on the image carrier, a transfer means TM disposed below the image carrier 2, and a charge removing device.

[0037] The exposure unit 7 is disposed above the image carrier 2. The exposure unit 7 performs writing scanning according to image information, that is, irradiates the image carrier 2 with laser light Lb from a laser diode, which is reflected by a mirror 7a, based on image data.

[0038] A paper feeder 200 having a tray for stacking paper P is installed below the image forming apparatus 100. This paper feeder 200 can accommodate a large number of sheets of paper P as recording media in a bundle, and is unitized with a paper feed roller 60 as a means for transporting the paper P.

[0039] A pair of registration rollers 250 serving as a separation and conveyance means is disposed downstream of the paper feed roller 60. The paper P fed from the paper feed device 200 is temporarily stopped by the pair of registration rollers 250. This temporary stop causes slack to form on the leading edge side of the paper P, and the skew of the paper P is corrected.

[0040] The paper P, which has been struck against the pair of registration rollers 250 and has a slack formed at its leading edge, is sent to the transfer nip N of the transfer means TM in time with the toner image on the image carrier 2 being suitably transferred to the paper P. The toner image on the image carrier 2 is then electrostatically transferred to the desired transfer position of the sent paper P by a bias applied to the transfer nip N.

[0041] A fixing device 300 is disposed downstream of the transfer nip N. The fixing device 300 includes a fixing roller 310 that is heated by a heater, and a pressure roller 320 that rotates while contacting the fixing roller 310 with a predetermined pressure.

[0042] (● Laser printer operation) Next, the basic operation of the laser printer according to this embodiment will be described below with reference to Fig. 1A. First, single-sided printing will be described.

[0043] 1A, the paper feed roller 60 rotates in response to a paper feed signal from the control unit of the image forming apparatus 100. Then, the paper feed roller 60 separates only the topmost sheet of the stack of sheets P stacked in the paper feed device 200, and sends it to the paper feed path 32.

[0044] When the leading edge of the paper P sent out by the paper feed roller 60 and the roller pair 210 reaches the nip of the registration roller pair 250, it forms a slack and waits in that state. Then, the toner image formed on the intermediate transfer belt 16 is transferred to the paper P at the optimal timing (synchronization), and the leading edge skew of the paper P is corrected.

[0045] In the case of manual paper feeding, a stack of papers stacked on manual feed tray 46 is conveyed one by one, starting from the topmost paper, through a part of reverse conveyance path 41 by manual paper feed roller 45 to the nip of registration roller pair 250. The subsequent operation is the same as that of paper feeding from paper feeder 200.

[0046] Here, the image forming operation will be described for one process unit 1K, and the description of the other process units 1Y, 1M, and 1C will be omitted. First, the charging device 4K uniformly charges the surface of the image carrier 2K to a high potential. Then, the exposure device 7 irradiates the surface of the image carrier 2K with laser light L based on image data.

[0047] The potential of the irradiated portion of the surface of the image carrier 2K is reduced, forming an electrostatic latent image. The developing device 5K has a developer carrier that carries a developer containing toner, and transfers unused black toner supplied from a toner bottle 6K, via the developer carrier, to the surface portion of the image carrier 2K on which the electrostatic latent image is formed.

[0048] The image carrier 2K to which the toner has been transferred forms (develops) a black toner image on its surface. Then, the toner image formed on the image carrier 2K is transferred to the intermediate transfer belt 16.

[0049] The drum cleaning device 3K removes the residual toner adhering to the surface of the image carrier 2K after the intermediate transfer process. The removed residual toner is sent by a waste toner transport means to a waste toner storage section in the process unit 1K and collected. In addition, the charge removing device removes the residual charge of the image carrier 2K from which the residual toner has been removed by the cleaning device 3K.

[0050] Similarly, in the process units 1Y, 1M, and 1C of the respective colors, toner images are formed on the image carriers 2Y, 2M, and 2C, and the toner images of the respective colors are transferred onto the intermediate transfer belt 16 so as to be superimposed on each other.

[0051] The intermediate transfer belt 16, onto which the toner images of each color have been transferred so as to be superimposed, travels to the secondary transfer nip between the secondary transfer roller 20 and the drive roller 18. Meanwhile, the pair of registration rollers 250 rotates while nipping the paper that has been abutted against them at a predetermined timing, and transports the paper to the secondary transfer nip of the secondary transfer roller 20 in accordance with the timing at which the toner images formed by superimposing and transferring onto the intermediate transfer belt 16 are suitably transferred. In this way, the toner image on the intermediate transfer belt 16 is transferred to the paper P sent out by the pair of registration rollers 250.

[0052] The paper P onto which the toner image has been transferred is transported to the fixing device 300 via a post-transfer transport path 33. The paper P transported to the fixing device 300 is then sandwiched between a fixing belt 310 and a pressure roller 320, and the unfixed toner image is fixed to the paper P by applying heat and pressure. The paper P onto which the toner image has been fixed is sent from the fixing device 300 to a post-fixing transport path 35.

[0053] 1A, at the timing when the paper P is sent out from the fixing device 300, the switching member 42 is in a position that opens the vicinity of the upper end of the post-fixing transport path 35. Then, the paper P sent out from the fixing device 300 is sent out to the paper discharge path 36 via the post-fixing transport path 35. The paper discharge roller pair 37 pinches the paper P sent out to the paper discharge path 36 and rotates to discharge the paper P onto the paper discharge tray 44, thereby completing the single-sided printing.

[0054] Next, a case where double-sided printing is performed will be described. As in the case of single-sided printing, the fixing device 300 sends the paper P to the paper discharge path 36. When double-sided printing is performed, the pair of paper discharge rollers 37 are driven to rotate to transport a part of the paper P outside the image forming apparatus 100.

[0055] 1A, the switching member 42 swings about the swing shaft 42a, and closes the upper end of the post-fixing transport path 35. Almost simultaneously with the closing of the upper end of the post-fixing transport path 35, the pair of paper discharge rollers 37 rotates in the direction opposite to the direction in which the paper P is transported out of the image forming apparatus 100, and sends the paper P to the reverse transport path 41.

[0056] The paper P sent to the reversing conveying path 41 passes through a pair of reversing conveying rollers 43 and reaches a pair of registration rollers 250. The pair of registration rollers 250 then determines the optimal timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the non-transferred surface of the paper P, and sends the paper P to the secondary transfer nip.

[0057] Then, when the paper P passes through the secondary transfer nip, the secondary transfer roller 20 and the drive roller 18 transfer the toner image onto the non-transferred surface (rear surface) of the paper P. Then, the paper P onto which the toner image has been transferred is transported to the fixing device 300 via the post-transfer transport path 33.

[0058] The fixing device 300 sandwiches the conveyed paper P between a fixing belt 310 and a pressure roller 320, and applies heat and pressure to fix the unfixed toner image to the back surface of the paper P. The paper P with the toner images fixed on both sides in this manner is sent from the fixing device 300 to a post-fixing conveyance path 35.

[0059] 1A, the switching member 42 is in a position that opens the vicinity of the upper end of the post-fixing transport path 35. The paper P sent out from the fixing device 300 is then sent to the paper discharge path 36 via the fixing transport path. The paper discharge roller pair 37 pinches the paper P sent out to the paper discharge path 36, and rotates to discharge the paper to the paper discharge tray 44, thereby completing double-sided printing.

[0060] After the toner image on the intermediate transfer belt 16 is transferred to the paper P, residual toner remains on the intermediate transfer belt 16. The belt cleaning device 21 removes this residual toner from the intermediate transfer belt 16. The toner removed from the intermediate transfer belt 16 is transported by the waste toner transport means to the powder container 10 and collected in the powder container 10.

[0061] (●About condensation) When the image forming apparatus body is powered on and printing is being performed at all times, heat from the fixing device 300 moves upward, so the paper discharge path 36, reverse transport path 41, and switching member 42 are relatively warm and condensation rarely occurs. However, when the image forming apparatus body is turned from OFF to ON, these are still in a cold state. When single-sided printing is performed in this state, paper containing moisture is heated in the nip of the fixing device, and the moisture is vaporized and sent above the fixing nip, causing condensation around the cold paper discharge path 36, reverse transport path 41, and switching member 42.

[0062] Moisture that condenses on the discharge path 36, which discharges recording materials during single-sided printing, adheres to the paper being printed on one side and evaporates while being discharged to the discharge tray 44, and does not cause a problem. However, during single-sided printing, the discharge path 36, reversal transport path 41, and switching member 42, which transport the recording material for double-sided printing, do not come into contact with the paper being printed on one side, so moisture condenses and gradually accumulates there.

[0063] If double-sided printing is performed in this state, the moisture accumulated in the discharge path 36, the reversing transport path 41, and the switching member 42 will adhere to the paper when the paper performs the switchback operation, and if the paper is then used for image formation again, this can result in poor image quality, wrinkles on the paper, or a jam.

[0064] To deal with this condensation, conventionally, when the image forming apparatus is turned on, the image forming apparatus is operated at idle (warm-up operation) until each transport path warms up, so that condensation does not occur during subsequent printing. Also, when the image forming apparatus is turned on and an instruction to perform duplex printing for the first time is input, the image forming apparatus is operated at idle (warm-up operation) until the condensation disappears, so that moisture adhering to the duplex transport path evaporates.

[0065] However, either control method has a problem of a long waiting time before printing can be performed. In the image forming apparatus of this embodiment, at least a part of the opening 304 of the housing (cover) 301 of the fixing device 300 is provided above the fixing belt 310, so that the heat of the fixing device 300 can be actively sent to the condensation part, and the problem of a long waiting time before printing can be solved by shortening the waiting time as much as possible.

[0066] (● Fixing device) Next, the fixing device 300 according to the embodiment of the present invention will be further described below. The fixing device 300 is a surf fixing device, and as shown in Fig. 2, is composed of a thin fixing belt 310 with low heat capacity and a pressure roller 320. The fixing belt 310 has a cylindrical body made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 µm, for example.

[0067] Fixing device 300 may be of a type that uses fixing belt 310 as shown in Fig. 2, or may be of a roller fixing type or belt fixing type. In any fixing type, when a toner image formed on small size paper P is heated and fixed, the heat of the heater is absorbed by the paper P in the area where paper P passes, but the heat of the heater is not absorbed by the paper P in the area where paper P does not pass, so that the temperature may rise excessively.

[0068] Since such end overheating is prominent in the SURF fixing device, the fixing devices of Patent Document 1 (JP Patent No. 5907594) and Patent Document 2 (JP Patent Publication No. 2013-007777) use fans to cool the non-paper passing portions at both ends of the fixing belt. However, these fixing devices do not take into consideration the elimination of condensation in the paper discharge path, etc., as described above. In this embodiment, the heat of the fixing device 300 can be actively sent to the condensation portions of the paper discharge path, etc., and problems such as longer waiting times before printing, complicated device mechanisms, and larger and more expensive devices can be eliminated.

[0069] In order to enhance durability and ensure releasability, a release layer made of fluorine-based resin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 310. An elastic layer made of rubber or the like and having a thickness of 50 to 500 μm may be provided between the base and the release layer.

[0070] The base material of the fixing belt 310 is not limited to polyimide, but may be a heat-resistant resin such as PEEK, or a metal base material such as nickel (Ni) or SUS. The inner circumferential surface of the fixing belt 310 may be coated with polyimide, PTFE, or the like as a sliding layer.

[0071] Pressure roller 320 has an outer diameter of, for example, 25 mm, and is composed of a solid iron core 321, an elastic layer 322 formed on the surface of this core 321, and a release layer 323 formed on the outside of elastic layer 322. Elastic layer 322 is made of silicone rubber, and has a thickness of, for example, 3.5 mm.

[0072] In order to improve releasability, it is desirable to form a release layer 323 made of a fluororesin layer having a thickness of, for example, about 40 μm on the surface of the elastic layer 322. A pressure roller 320 is pressed against the fixing belt 310 by a biasing means.

[0073] A stay 350 and a heater holder 340 are disposed in the axial direction inside the fixing belt 310. The stay 350 is made of a metal channel material, and both ends thereof are supported by both side plates of the fixing device 300. The stay 350 reliably receives the pressing force of the pressure roller 320 to stably form the fixing nip SN.

[0074] The heater holder 340 is for holding a base material 341 of the heater 330 of the fixing device 300, and is supported by a stay 350. The heater holder 340 can be preferably formed of a heat-resistant resin with low thermal conductivity, such as LCP, which reduces heat transfer to the heater holder 340 and enables the fixing belt 310 to be heated efficiently.

[0075] The heater holder 340 is shaped to support only two points near both ends of the substrate 341 in the short side direction in order to avoid contact with the high temperature portion of the substrate 341. This further reduces the amount of heat flowing to the heater holder 340, making it possible to efficiently heat the fixing belt 310.

[0076] Thermistors TH1 and TH2 serving as temperature detection means for detecting the temperature of a resistance member 370 of a heater 330 (described later) are disposed on the rear surface of the base material 341. Thermistors TH1 and TH2 are pressed against the rear surface of the base material 341 by a spring 387, thereby enabling the accurate temperature of the resistance member 370 to be detected.

[0077] One thermistor, TH1, is located in the center of the small size paper width direction. The other thermistor, TH2, is located on the outside of the large size paper width direction in a non-paper passing portion. Based on the temperature information from both thermistors TH1 and TH2, the power supplied to the resistance member 370 and the drive mechanism of the shutter member 305, which will be described later, are controlled, making it possible to effectively suppress temperature rise in the non-paper passing portion.

[0078] The thermistor TH1 or TH2 can be replaced with a thermistor disposed facing the outer circumferential surface of the pressure roller 320. By disposing the thermistor on the pressure roller 320 side on the outside of the fixing belt 310, maintenance of the thermistor becomes easier. Various types of fixing device 300 are possible, and the fixing device in FIG. 2 described above is merely one example.

[0079] (● Fixing device having a shutter member) 3A and 3B, a fixing device 300 according to an embodiment of the present invention having a shutter member 305 will be described. In this fixing device 300, the fixing belt 310 as the heating member and the pressure roller 320 as the pressure member are housed in a housing (cover) 301 for thermal insulation and heat retention as shown in FIG. 3A(b).

[0080] The shape of the housing 301 is a compact cross-sectional shape with two arcs facing each other horizontally so as to eliminate any wasted space outside the fixing belt 310 and pressure roller 320 housed inside. An inlet 302 and an outlet 303 are formed on the upper and lower flat parts of the housing 301.

[0081] The entrance 302 and the exit 303 face each other in a direction (vertical direction in FIG. 3A(b)) transverse to the longitudinal direction (axial direction perpendicular to the paper surface in FIG. 3A(b)) of the fixing belt 310. A sheet carrying a toner image enters from the entrance 302, passes through the fixing nip SN, and exits from the exit 303.

[0082] 3A(a), rectangular openings 304 are formed from halfway up the height direction of one of the arcuate sides of the housing 301 to the top end. A pair of openings 304 are formed at both longitudinal ends of the housing 301, and open toward both longitudinal ends (non-paper passing portions) of the fixing belt 310. By forming at least a portion of the openings 304 of the housing 301 above the fixing belt 310, heat from the fixing device 300 can be actively sent to the condensation portion above.

[0083] 3E and 3F, an air duct 510 can be connected to the opening 304. Here, "connection" means that an air flow is formed, and a gap may be present between the opening 304 and the air duct 510.

[0084] A blower fan 520 is disposed in air duct 510 on the outside of opening 304. This blower fan 520 supplies cooling air to opening 304. The combination of air duct 510 and blower fan 520 can more efficiently suppress the temperature rise in the non-paper passing area, and can actively send the heat of fixing device 300 to the condensation area above.

[0085] (Rotary shutter parts) 3A(a), the amount of cooling air supplied can be adjusted by the opening degree of a pair of shutter members 305 disposed on the left and right sides outside the opening 304. The pair of left and right shutter members 305 are interconnected by a connecting portion 305a extending in the longitudinal direction of the housing 301. The connecting portion 305a makes it possible to configure the shutter members 305 from a single member, realizing a lower-cost shutter mechanism.

[0086] 3A(b), the shutter member 305 has an arc-shaped cross section, and a sector-shaped arm portion 305b is connected to the outer end portion in the longitudinal direction. A shaft portion 305c formed at the tip of the arm portion 305b is supported on the end face of the housing 301 so as to be freely rotatable.

[0087] 3A(b), the shaft portion 305c is disposed inside (almost at the center) the fixing belt 310. This allows the shutter member 305 to rotate about an axis extending in the longitudinal direction of the fixing belt 310. This makes it possible to minimize the rotation locus about the shaft portion 305c when the fixing belt 310 is in the open and closed states, thereby enabling the image forming apparatus as a whole to be made more compact.

[0088] The shutter member 305 has a curved shape so as to cover the fixing belt 310. In this embodiment, the shutter member 305 has a curved shape with the axis portion 305c as the center of curvature as a whole, but as shown in Fig. 3B(c), the shutter member 305 may include partially linear flat portions 305d and 305e, or may include a partially curved shape. The curvature of the shutter member 305 can be measured using, for example, a laser microscope (VK-X100) made by Keyence.

[0089] In short, there is no problem as long as the shutter member 305 can be opened and closed by compactly rotating about the shaft portion 305c in a shape that substantially covers the fixing belt 310. By having such a curved shape, it is possible to reduce the rotational locus of the shutter member 305, and it is possible to reduce the size of the entire image forming apparatus.

[0090] A rotating shaft of a motor with a reducer is connected coaxially to the shaft portion 305c on the outer surface of the arm portion 305b. The shutter member 305 is opened and closed by rotating the motor forward and backward. The motor can be disposed on the longitudinal end side of the fixing device 300, so that a simple and space-saving drive system can be achieved.

[0091] (●Sliding shutter parts) The shutter member 305 described above is of a rotating type, but it is also possible to use a sliding shutter member 307 as shown in Fig. 4. This shutter member 307 slides by a rack-and-pinion mechanism provided in the center of the longitudinal direction of the housing 301. Fig. 4(a) shows the shutter member 307 in an open state, and Fig. 4(b) shows the shutter member 307 in a closed state.

[0092] A pair of left and right shutter members 307 are disposed so as to be slidable in the longitudinal direction of the housing of the fixing device 300, and a pinion 308 disposed in the longitudinal center meshes with a rack 307a extending from the shutter members 307 toward the longitudinal center. Rotation of the pinion 308 moves the left and right shutter members 307 toward and away from each other, thereby opening and closing the opening 304.

[0093] 4(c) is a cross-sectional view of the shutter member 307 in a closed state. The shutter member 307 opens and closes by sliding in the longitudinal direction, so when it is half-open, heated air rises from a limited area in the longitudinal direction of the opening 304. For this reason, the range of the dew condensation prevention effect of the branching portion described above is limited, but it is still effective.

[0094] In contrast, in this embodiment, even in the half-open state of Fig. 3D, heated air rises from the entire longitudinal width of the opening 304. This makes it possible to maximize the range of the dew condensation prevention effect of the branching portion.

[0095] The shutter member 305 may be a press-molded product of a heat-resistant metal plate. By forming the shutter member 305 as a press-molded product, the dimensional accuracy of the shutter member can be improved.

[0096] To improve heat insulation, a heat retaining material (insulating material) such as felt or sponge may be attached to the inner surface of the shutter member 305. Even if the shutter member 305 is made of a heat-resistant resin, a heat retaining material (insulating material) can be attached to the back surface thereof.

[0097] 3A(b), the region of the opening 304 is a region (upper portion) extending from the center of the arcuate side surface of the housing 301 in the height direction to the ceiling of the housing 301 when the paper is being heated. In addition, in the longitudinal direction of the housing 301, the region faces both longitudinal ends of the fixing belt 310, as shown in FIG. 3A(c).

[0098] 3A(b), opening 304 opens obliquely upward when paper is being heated. Opening 304 is almost entirely visible when viewed from directly above housing 301, but is not visible from directly below housing 301. By opening upward or obliquely upward, excess heat that would cause an excessive rise in temperature at the end of fixing belt 310 can be efficiently discharged from opening 304 to the outside of housing 301.

[0099] That is, it is sufficient that the opening 304 is formed in a position where it is at least slightly visible when viewed from directly above the fixing device 300, and where the fixing belt 310 is at least slightly visible through the opening 304. Specifically, it is sufficient that the dimension A in Fig. 3A(b) is equal to or greater than 0 (zero). Therefore, as shown in Fig. 3C, a horizontal opening 306 where the fixing belt 310 is completely invisible from directly above the housing 301 cannot efficiently discharge excess heat that causes an excessive rise in temperature of the end portion of the fixing belt 310 to the outside of the housing 301.

[0100] 3D, the shutter member 305 preferably closes the opening 304 by rotating upward so that heat can be efficiently discharged from the opening 304 to the outside of the housing 301 even in the half-open state. If the opening 304 is opened at about 45° in the vertical direction around the shaft portion 305c, the central angle of the shutter member 305 may also be about 45°, so that the opening 304 can be closed without any gaps as shown in FIG. 3B(b).

[0101] Even when the shutter member 305 is only half-open or fully open, the opening 304 can discharge excess heat upward, which would cause an excessive rise in temperature at the end of the fixing belt 310. In order to enhance the cooling effect at the end of the fixing belt 310, an air duct 510 may be connected horizontally to the opening 304 as shown in FIG. 3E, and a blower fan 520 may be provided in the air duct 510.

[0102] The upper end outlet of air duct 510 is preferably extended a predetermined distance upward from opening 304 to create a chimney effect. The "chimney effect" refers to the phenomenon in which, when there is air in a chimney that is hotter than the outside air, the hot air has a lower density than the cold air, so that buoyancy occurs in the air inside the chimney, causing the warm air to rise while drawing in cold air from the outside into the chimney through the air intake at the bottom of the chimney. Air duct 510 and blower fan 520 are positioned near opening 304, making effective use of the space in the image forming apparatus body as needed.

[0103] By forcibly blowing cooling air into the housing 301 toward the end of the fixing belt 310 using the blower fan 520, it is possible to effectively cool the end of the fixing belt 310 and prevent the end from overheating. The air blown into the housing 301 is heated by the end of the fixing belt 310 and is naturally exhausted upward.

[0104] At this time, exhaust is promoted by the chimney effect of air duct 510. Note that a part of the air blown into housing 301 is also exhausted upward from outlet 303. Therefore, it is possible to prevent condensation from adhering to paper P transported upward from outlet 303.

[0105] The warm air exhausted upward in this way can be effectively used to prevent condensation from forming at the branching portion. That is, as shown in Fig. 1A, by disposing the switching member 42, which branches into the paper reversing transport path 41 during double-sided printing, above the fixing device 300, it is possible to prevent condensation from forming on the switching member 42. In order to effectively prevent condensation from forming, it is advisable to dispose the switching member 42 vertically above the opening 304.

[0106] Conventionally, the countermeasures against condensation on the paper transport path have been to run the image forming device at idle (warm-up operation) until the condensation disappears, or to install a separate fan to remove the condensation. The former has the problem of increasing the waiting time before printing, while the latter has the problem of complicating the mechanism with the fan, which makes the device larger and more expensive.

[0107] Also, as in Patent Document 3 (JP Patent Publication 2017-215385 A), a device is known in which an exhaust shielding member that can be opened and closed is provided at the paper discharge port following the paper discharge tray, and the exhaust shielding member is closed except when paper is being discharged to enhance the heat retention effect and prevent condensation. However, the problem of the mechanism becoming complicated, the device becoming larger and the cost becoming higher, is the same as with the independent fan described above.

[0108] Also, as shown in Patent Document 4 (JP Patent Publication 2006-106030 A, Figs. 2-4), a structure is known in which the air inside the cover member of the fixing device is sucked in and exhausted by a suction fan through multiple openings formed in the cover member to prevent condensation inside the cover member. However, even this structure does not take into consideration preventing condensation that occurs above the fixing device. The above-mentioned problem can be solved by effectively utilizing the exhaust heat from the end of the fixing belt 310 and actively sending it to the condensation area above the fixing device as in this embodiment.

[0109] Blower fan 520 may be disposed on the inlet side of air duct 510 as shown in Fig. 3E, or on the upper end outlet side as shown in Fig. 3F. By disposing blower fan (suction fan) 520 as shown in Fig. 3F, the heating and ventilation effects on switching member 42 can be enhanced, so that the above-mentioned dew condensation prevention effect can be more reliably achieved.

[0110] (●Heater) The fixing device 300 described above has a heater 330 held by a heater holder 340 as shown in Fig. 2. This heater 330 has a resistance member 370 configured of a resistance heating element (planar heater) on a base material 341. The resistance member 370 can be formed in a variety of types, such as the heater 330 whose examples are shown in Figs. 5(a) and (b) described later.

[0111] In either type, the resistance member 370 is formed on a base material 341 made of a long and narrow metal thin plate member covered with an insulating material. In a fixing method in which the fixing nip SN is heated by a planar heater, the resistance member, which is a heating element, is divided into multiple parts in the paper width direction and the heating is controlled individually, thereby making it possible to heat multiple types of paper widths uniformly.

[0112] Low-cost aluminum, stainless steel, etc. are preferable as materials for the base material 341. The base material 341 is not limited to being made of metal, and can be made of ceramics such as alumina and aluminum nitride, or non-metallic materials with excellent heat resistance and insulation properties such as glass and mica.

[0113] In order to improve the uniformity of the heater 330 and enhance the image quality, the base material 341 may be made of a material with high thermal conductivity such as copper, graphite, graphene, etc. In this embodiment, an alumina base material with a short side width of 8 mm, a long side width of 270 mm, and a thickness of 1.0 mm is used.

[0114] 5(a) and 5(b), the heater 330 can be configured as a multi-type heater in which resistance heating elements 371 to 378 are electrically connected in parallel. The heater 330 has two electrodes 370c, 370d, and if the resistance between the electrodes 370c, 370d at both ends is 10Ω, the resistance of each of the heating elements 371 to 378 becomes as large as 80Ω due to the parallel connection.

[0115] A PTC element can be used for the resistance heating elements 371 to 378. The PTC element is made of a material having a positive temperature coefficient of resistance, and has the characteristic that the resistance value increases as the temperature T increases (the current I decreases and the heater output decreases). The temperature coefficient of resistance (TCR) can be, for example, 1500 PPM (parts per million).

[0116] 5(a) and (b) are arranged linearly and at equal intervals in the longitudinal direction of the base material 341. Low-resistance conductors 370a, 370b are linearly arranged parallel to each other on both sides of the short sides of each of the heating elements 371-378, and both ends of each of the heating elements 371-378 are connected to the conductors 370a, 370b. AC power is supplied to electrodes 370c, 370d formed on one end of each of the conductors 370a, 370b.

[0117] Heat generating elements 371-378 and conductors 370a, 370b are covered with a thin insulating layer 385. This insulating layer 385 can be made of heat-resistant glass having a thickness of 75 μm, for example. Insulating layer 385 insulates and protects heat generating elements 371-378 and conductors 370a, 370b, and maintains sliding ability with fixing belt 310.

[0118] The heating elements 371-378 can be formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the base material 341 by screen printing or the like, and then firing the base material 341. In this embodiment, the resistance value of each of the heating elements 371-378 is set to 80Ω at room temperature (the total resistance value is 10Ω).

[0119] In addition to the above, the materials of the heating elements 371 to 378 include silver alloy (AgPt) and ruthenium oxide (RuO 2 The conductors 370a, 370b and the electrodes 370c, 370d may be made of silver (Ag) or silver palladium (AgPd) by screen printing or the like.

[0120] The insulating layer 385 side of the heating elements 371-378 comes into contact with the fixing belt 310 and heats up, increasing the temperature of the fixing belt 310 through heat transfer, and heating and fixing the unfixed image conveyed to the fixing nip SN. When PTC elements are used as the heating elements 371-378, when the temperature of the heating elements in the non-paper passing area increases due to the passage of small-sized paper, the amount of heat generated by the PTC elements decreases due to their temperature resistance dependency, and the temperature increase can be suppressed.

[0121] Due to this feature, for example, when printing on paper narrower than the overall width of the heating elements 371-378 (for example, within the width of the heating elements 373-376), the temperature of the heating elements 371, 372, 377, 378 outside the paper width rises because the heat is not absorbed by the paper. Then, the resistance value of the heating elements 371, 372, 377, 378 due to the PTC element increases.

[0122] Because the voltage applied to the heating elements 371-378 is constant, the output of the heating elements 371, 372, 377, 378 outside the paper width is relatively lower, suppressing the temperature rise at the ends. If the heating elements 371-378 are electrically connected in series, the only way to suppress the temperature rise of the heating elements 371, 372, 377, 378 outside the paper width during continuous printing is to slow down the printing speed. By electrically connecting the heating elements 371-378 in parallel, it is possible to suppress the temperature rise in non-paper passing areas while maintaining the printing speed.

[0123] If there are gaps between the heat generating elements 371-378 in the short direction, the amount of heat generated will decrease in the gaps, which will easily cause uneven fixing. Therefore, in Figures 5(a) and (b), the ends of the heat generating elements 371-378 are overlapped with each other in the long direction.

[0124] In Fig. 5(a), a step is formed by an L-shaped notch at the end of the heating elements 371-378, and the step is made to overlap the step of the adjacent element end. In Fig. 5(b), an inclined portion is formed by an oblique notch at the end of the heating elements 371-378, and the inclined portion is made to overlap the inclined portion of the adjacent element end. By overlapping the ends of the heating elements 371-378 with each other in this way, it is possible to suppress the effect of a decrease in the amount of heat generated in the gap between the elements.

[0125] Further, the electrodes 370c, 370d can be arranged on both ends of the heating elements 371 to 378, or on one side of the heating elements 371 to 378. By arranging the electrodes 370c, 370d on one side in this way, it is possible to save space in the longitudinal direction. Although each of the heating elements 371 to 378 in Fig. 5(a) and (b) is composed of a rectangular sheet heating element, in order to obtain a desired output (resistance value), it can also be composed of a plurality of heating elements formed in a meandering shape with a narrow line width electrically connected in parallel.

[0126] (● Heater modification) Next, a modified example of heater 330 is shown in Fig. 6. Heater 330 of this modified example has three electrodes 370h, 370i, 370j disposed on both ends of substrate 341, and seven heating elements 371-377 disposed between the electrodes in the longitudinal direction of substrate 341. As will be described later, three heating patterns shown in Fig. 7(a)-(c) can be selected.

[0127] Five heating elements 372-376 in the center of the heater 330 in the longitudinal direction are connected in parallel to a first electrode 370h and a second electrode 370i via conductors 370e and 370f having a lower resistance than the heating elements. Two resistive heating elements 371 and 377 at both ends in the longitudinal direction are connected in parallel to a second electrode 370i and a third electrode 370j via conductors 370f and 370g having a lower resistance than the heating elements 371 and 377.

[0128] Here, when the five heating elements 372 to 376 in the longitudinal center are referred to as first resistive heating elements, and the two resistive heating elements 371, 377 at both ends in the longitudinal direction are referred to as second resistive heating elements, the conductors 370e, 370f connected to the first resistive heating elements are referred to as first conductors, and the conductors 370f, 370g connected to the second resistive heating elements are referred to as second conductors.

[0129] The second electrode 370i on the right side is always connected to an AC power source, and the first electrode 370h and the third electrode 370j on the left side are selectively connected to the AC power source by switching the switch. This allows the selection of the three heating patterns shown in Figures 7(a) to 7(c).

[0130] In heater 330 having three selectable heating patterns, the longitudinal length of five consecutive heating elements 372-376 in the longitudinal center of heater 330 is set to the width of A4 paper, and the longitudinal length of all seven heating elements 371-377 including both ends is set to the width of A3 paper. By appropriately controlling the heating states in Figures 7(a) and (b), it is possible to uniformly heat A4 size paper in Figure 7(a) and A3 size paper in Figure 7(b).

[0131] In the heating state of Fig. 7(b), the heating elements 371 and 377 at both ends tend to conduct heat outward and become lower in temperature. Therefore, while the heating state of Fig. 7(b) is the main state, the heating state of Fig. 7(c) is occasionally mixed in to control the heater 330 so that it heats more uniformly in the longitudinal direction. Fig. 7(c) applies a voltage only to the second electrode 370i and the third electrode 370j, and current flows only through the heating elements 371 and 377 at both ends via the conductors 370f and 370g, so that only the heating elements 371 and 377 generate heat.

[0132] A common method for controlling the heating of the heating elements 371-377 is to vary the lighting time (lighting duty) of the heating elements within a specified control time to obtain an appropriate amount of heat. The lighting duty is adjusted by phase-controlling the AC power supply with a triac as a control means. The current is zero at a duty ratio of 0%, and the current is maximum at a duty ratio of 100%. The heating state in Figure 7(c) occurs momentarily and intermittently within this lighting duty.

[0133] In the above explanation, the longitudinal lengths and resistance values ​​of blocks 1 and 7 (called end blocks) and blocks 2 to 6 (center blocks) are made the same so that A4 and A3 can be heated uniformly. However, the lengths of the end blocks and center blocks may be changed so that different paper sizes (e.g. A4 and A3) can be heated uniformly. However, although changing the length also changes the resistance value, the problem of temperature being asymmetric in the longitudinal direction as shown in Figures 8C and 9B is not resolved.

[0134] (● Independent left and right shutter components) Therefore, as shown in Fig. 8(a), the pair of shutter members 305 are made independent of the left and right by eliminating the connecting portion 305a. This makes it possible to independently adjust the opening degree of the left and right shutter members 305, 305 so as to suppress the asymmetrical temperature that occurs in opposite directions when heating A4 paper and A3 paper as described above.

[0135] 8(b), a bifurcated air duct 511 can be connected to the left and right openings 304a, 304b of the housing 301 of the fixing device 300. Here, "connected" means that an air flow is formed, and there may be a gap between the openings 304a, 304b and the air duct 511. Then, a blower fan 520 is disposed upstream of the branch of the air duct 511.

[0136] By using air duct 511 that branches into two branches in this way, only one blower fan 520 is required. This makes it possible to reduce the size of the device. It is also possible to provide left and right air ducts 511 as independent types with blower fans 520 in each, in which case the wind force per opening 304a, 304b increases, improving the cooling effect.

[0137] In explaining the suppression of asymmetric temperatures in the opposite directions at A4 and A3, the left one of the left and right openings 304a, 304b will be called the first opening 304a and the right one the second opening 304b. One longitudinal end of the heater 330, on which the first electrode 370h and the third electrode 370j are provided, is disposed in the housing 301 so as to face the first opening 304a. The other longitudinal end of the heater 330, on which the opposite second electrode 370i is provided, is disposed in the housing 301 so as to face the second opening 304b.

[0138] Here, the opening area of ​​the first opening 304a is S1, and the opening area of ​​the second opening 304b is S2. When only the first resistance heating elements 372-376 are heated to heat A4 paper, the shutter members 305, 305 are rotated so that the relationship S1>S2 is satisfied in order to suppress the asymmetric heat generation amount distribution in FIG.

[0139] Also, when heating both the first resistance heating elements 372 to 376 and the second resistance heating elements 371 and 377 for A3 paper heating, the shutter members 305, 305 are rotated so that the relationship S1 < S2 is established in order to suppress the asymmetric heat generation amount distribution in FIG. 9B. Thereby, it is possible to more effectively prevent the excessive temperature rise at the ends of the fixing belt 310 during A4 heating and A3 heating, and image defects such as gloss unevenness due to the asymmetric heat generation amount distribution in FIGS. 8C and 9B.

[0140] (●Guide ribs in the post-fixing conveyance path) An embodiment in which a plurality of guide ribs 35a to 35d are formed in the post-fixing conveyance path 35 will be described with reference to FIG. 9. In this embodiment, the high-temperature air discharged from the openings 304 at both longitudinal ends of the housing 301 is evenly diffused in the width direction of the post-fixing conveyance path 35 by a plurality of guide ribs 35a to 35d serving as air flow guiding members. The plurality of guide ribs 35a to 35d are formed on the inner surface of the post-fixing conveyance path 35 so as to incline toward the center in the width direction of the post-fixing conveyance path 35. The number of guide ribs 35a to 35d is four on each of the left and right sides in the illustrated example, but may be appropriately increased or decreased according to the width of the opening 304, the length of the post-fixing conveyance path 35, etc.

[0141] When there are no guide ribs 35a to 35d, the high-temperature air discharged from the opening 304 tends to rise directly above the opening 304. Since dew condensation may occur in the width direction of the paper discharge path 36, in order to effectively eliminate the dew condensation at the center in the width direction of the paper discharge path 36, it is necessary to diffuse the high-temperature air rising above the opening 304 in the width direction of the paper discharge path 36.

[0142] Therefore, as shown in FIG. 9, a plurality of guide ribs 35a to 35d are formed on the inner surface of the post-fixing conveyance path 35. The high-temperature air rising above the opening 304 is diffused in the width direction of the paper discharge path 36 by the plurality of guide ribs 35a to 35d, and dew condensation occurring in the width direction of the paper discharge path 36 can be effectively eliminated.

[0143] Although the present invention has been described above based on the embodiment, it goes without saying that the present invention is not limited to the embodiment and can be modified in various ways within the scope of the technical ideas described in the claims. For example, the shutter member 305 is disposed outside the opening 304 so as to be openable and closable, but the shutter member 305 can also be disposed inside the opening 304 so as to be openable and closable.

[0144] The heating device of the present invention can be used in a paper drying device of an inkjet printer, in addition to being used in the fixing device 300 described above. As the heating element for heating the fixing belt 310, in addition to the heater 330 using a PTC element, other heating elements such as a ceramic heater can also be used. [Explanation of symbols]

[0145] 1K, 1Y, 1M, 1C: Process unit 2K, 2Y, 2M, 2C: Image carrier 3K, 3Y, 3M, 3C: Drum cleaning device 4K, 4Y, 4M, 4C: Charging device 5K, 5Y, 5M, 5C: Developing unit 6K, 6Y, 6M, 6C: Toner bottle 7: Exposure device 7a: Mirror 8: Transfer cover 10: Powder container 15: Transfer device 16: Intermediate transfer belt 17: driven roller 18: driving roller 19K, 19Y, 19M, 19C: Primary transfer rollers 20: Secondary transfer roller 21: Belt cleaning device 31: Resist sensor 32: Paper feed path 33: Post-transfer transport path 35: Post-fixing transport path 35a to 35d: Guide ribs 36: Paper discharge path 37: Paper discharge roller pair 41: Reversing conveying path 42: Switching member 42a: swing shaft 43: pair of reverse conveying rollers 44: Paper output tray 45: Paper feed roller 46: Tray 60: Paper feed roller 100: Image forming device 200: Paper feeding device 210: Roller pair 220: Feeding roller 230: Separation roller 240: Conveying roller 250: pair of registration rollers 300: fixing device 301: Housing (cover) 302: Entrance 303: Exit 304, 306: Opening 305: shutter member 305a: connecting portion 305b: Arm 305c: Shaft 305d: Plane part 305e: Plane part 306: Opening 307: Shutter member 307a: Rack 308: Pinion 310: Fixing belt 320: Pressure roller 321: Core metal 322: Elastic layer 323: Release layer 330: Resistance member 334: Pressure belt 340: Heater holder 341: Base material 350: Stay 370: Resistance member 370a, 370b: Conductors 370c, 370d: electrodes 370e to 370g: conductors 370h: first electrode 370i: second electrode 370j: third electrode 371-378: resistance heating element 385: Insulating layer 387: Spring 410, 420: shutter member 510, 511: air duct 520: Blower fan 401: Entrance 402: Exit L: Laser light N: Transfer nip P: Paper (sheet material) SN: Fixing nip TH1~TH3: Thermistor TM: Transcription section [Prior art documents] [Patent documents]

[0146] [Patent Document 1] Patent No. 5907594 [Patent Document 2] JP 2013-007777 A [Patent Document 3] JP 2017-215385 A [Patent Document 4] JP 2006-106030 A

Claims

1. An image forming apparatus having a fixing device that contains a heating member and a pressure member that form a nip portion having a longitudinal direction in a housing, and transfers heat from the heating member to a sheet member by passing the sheet member through the nip portion, and above the fixing device, a paper discharge path for discharging the sheet member, and a branching portion that branches from the paper discharge path to a reversing conveying path for reversing and conveying the sheet member during double-sided printing, the housing has a pair of openings that open toward both ends of the heating member in a longitudinal direction inside the housing and open upward outside the housing, an image forming apparatus, characterized in that a plurality of guide ribs inclined toward a center in a width direction of the post-fixing transport path are formed in the post-fixing transport path between the pair of openings and the paper discharge path.

2. An image forming apparatus having a fixing device that contains a heating member and a pressure member that form a nip portion having a longitudinal direction in a housing, and transfers heat from the heating member to a sheet member by passing the sheet member through the nip portion, and above the fixing device, a paper discharge path for discharging the sheet member, and a branching portion that branches from the paper discharge path to a reversing conveying path for reversing and conveying the sheet member during double-sided printing, the housing has a pair of openings that open toward both ends of the heating member in a longitudinal direction inside the housing and open upward outside the housing, the housing has a shutter member that opens and closes the opening, 4. An image forming apparatus, comprising: a shutter member that is curved along an outer circumferential surface of the heating member;

3. 3. The image forming apparatus according to claim 1, wherein the heating member is a resistance heating element that generates heat by applying a voltage to the resistance heating element, and the pressing member is brought into pressure contact with the heating element to form the nip portion.

4. 2. The image forming apparatus according to claim 1, wherein the housing has a shutter member for opening and closing the opening.

5. 5. An image forming apparatus according to claim 4, wherein said shutter member is curved along the outer circumferential surface of said heating member.

6. 6. The image forming apparatus according to claim 5, wherein the shutter member opens and closes the opening by rotating about an axis extending in a longitudinal direction of the heating member.

7. 7. An image forming apparatus according to claim 6, wherein an axis about which said shutter member rotates is disposed in an inner region of an outer circumferential surface of said heating member which contacts said pressure member.

8. 4. The image forming apparatus according to claim 3, wherein the temperature of the heating member is controllable by controlling the power supplied to the resistance heating element by a control means based on a detection result of a temperature detection means for detecting the temperature of the heating member.

9. 9. An image forming apparatus according to claim 8, wherein an air duct is connected to the opening, and a blower fan is provided in the air duct.

10. 10. The image forming apparatus according to claim 9, wherein the opening opens toward the upper part of the housing, and the air inside the housing is exhausted upward by the blower fan.

Images