Image forming apparatus

Abstract

To prevent dew condensation on a roller surface.SOLUTION: A fixing portion disposed downstream of the transfer portion in a sheet conveyance direction and configured to fix the image by heating the sheet; A first guide surface configured to guide the sheet from the fixing unit to the first roller pair, and a second guide surface configured to guide the sheet reversed by the first roller pair to the transfer unit, the image forming apparatus includes a guide member configured to form a space between a first guide surface and a second guide surface, a second roller pair disposed above the fixing unit and on the guide member and configured to convey the sheet, at least one vent provided in the guide member and communicating with the space between the first guide surface and the second guide surface, and an air blowing unit configured to blow air into the space between the first guide surface and the second guide surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus having a fixing unit that heats a sheet to fix an image thereon. [Background technology]

[0002] In image forming devices such as copiers, when the maximum basis weight of sheets that can be passed through is increased to accommodate larger media, the amount of moisture that the sheets can contain also increases. In this case, the sheets release more water vapor than before after fixing. If the released water vapor diffuses into the transport path, it condenses on the surfaces of the transport guides that make up the transport path, causing paper jams and transfer failures. This requires dedicated moisture exhaust paths and ducts to exhaust the water vapor, which increases the size of the image forming device.

[0003] To address this issue, the technology disclosed in Patent Document 1 prevents the diffusion of water vapor by arranging a pair of wide rollers whose contact area extends across almost the entire width in the width direction perpendicular to the conveying direction immediately after fixing. Furthermore, a moisture exhaust path is provided inside the conveying guide that constitutes the conveying path to suppress the diffusion of water vapor into the conveying path near the outside of the device, and the device can be made smaller by not using a dedicated exhaust duct. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-172943 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the interior of the conveying guide is used as a moisture exhaust path as disclosed in Patent Document 1, as the device speed increases, the amount of water vapor released from the sheet increases, and the amount of water vapor contained in the air flowing inside the conveying guide increases. When the amount of water vapor contained in the air flowing inside the conveying guide increases, the dew point temperature decreases, making the inside of the conveying guide more susceptible to condensation. The conveying guide has holes that expose the conveying rollers supported inside to the conveying path, and there is a risk of water vapor leaking into the conveying path through these holes. In this case, the temperature is likely to drop depending on the ambient temperature, especially in the re-conveying path located near the exterior cover of the device, which may cause condensation on the roller surfaces and in the re-conveying path itself.

[0006] An object of the present invention is to prevent condensation on the roller surfaces and along the conveying path. [Means for solving the problem]

[0007] A typical configuration of the present invention includes a transfer unit that transfers an image onto a sheet, a fixing unit that is arranged downstream of the transfer unit in the sheet conveying direction and heats the sheet to fix the image, a first roller pair that is arranged downstream of the fixing unit in the sheet conveying direction and is capable of conveying the sheet by reversing in the direction opposite to the sheet conveying direction, a first guide surface that guides the sheet from the fixing unit to the first roller pair, and a second guide surface that guides the sheet reversed by the first roller pair to the transfer unit, and is arranged above the fixing unit and is disposed between the first guide surface and the second guide surface. The sheet transport device comprises a guide member that forms a space for air circulation, a second pair of rollers that are arranged above the fixing unit and are arranged on the guide member and that transport a sheet, at least one air vent that is provided on the guide member and that communicates with the space between the first guide surface and the second guide surface, and an air blowing section that blows air into the space between the first guide surface and the second guide surface, wherein the guide member supports one of the rollers of the second pair of rollers, and the guide member has a cover section that covers the one roller inside the space. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the leakage of water vapor from the space inside the guide member, and to prevent condensation on the roller surface and the guide surface of the guide member. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic cross-sectional view showing the entire image forming apparatus [Figure 2] 1 is a schematic cross-sectional view showing a portion from a fixing device to a re-conveying path of an image forming apparatus; [Figure 3] FIG. 10 is a perspective view showing the blower and the conveying guide; [Figure 4] Schematic diagram showing the suction part [Figure 5] FIG. 10 is a perspective view showing a first guide member; [Figure 6] FIG. 10 is a perspective view showing a first guide member and a roller cover portion; DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and are not intended to limit the scope of the present invention to these alone.

[0011] The configuration of an image forming apparatus according to this embodiment will be described below with reference to Fig. 1. Image forming apparatuses include printers, copiers, facsimiles, and multifunction peripherals, and form images on sheets used as recording media based on image information input from an external PC or image information read from an original. Sheets used as recording media include paper such as plain paper and cardboard, plastic film such as sheets for overhead projectors, sheets of special shapes such as envelopes and index paper, and cloth.

[0012] <Configuration of image forming device> 1 is a schematic cross-sectional view showing the entire image forming apparatus 1 according to this embodiment. Image forming apparatus 1, which is a full-color laser copier, is configured to include, inside an apparatus main body 1A, an image forming section 150, a sheet feeding section 2, a fixing device 3 which is a fixing section, a toner storage section T (TY, TM, TC, TK), and a reversing and discharging section 4. Image forming apparatus 1 also includes a sheet stacking section 5 on the top surface of apparatus main body 1A, and further includes a control section 6 and an original reading device 7 which are arranged above apparatus main body 1A.

[0013] The image forming apparatus 1 is equipped with an electrophotographic image forming unit 150. The image forming unit 150 forms toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (Bk). That is, the image forming unit 150 is a so-called intermediate transfer tandem electrophotographic unit in which four drum units 11 (11Y, 11M, 11C, 11K) are arranged along an intermediate transfer belt 13a of an intermediate transfer unit 13. The toner storage units T (TY, TM, TC, TK) store toner of yellow (Y), magenta (M), cyan (C), and black (K), respectively.

[0014] The image forming section 150 includes drum units 11 (11Y, 11M, 11C, 11K), an intermediate transfer unit 13, and a secondary transfer roller 24 as a transfer section. Each drum unit 11 (11Y, 11M, 11C, 11K) has a photosensitive drum 110 (110Y, 110M, 110C, 110K) as a photosensitive member. Developing units 10 (10Y, 10M, 10C, 10K) that develop toner images are arranged around the photosensitive drums 110 (110Y, 110M, 110C, 110K).

[0015] Each photosensitive drum 110 is configured to be irradiated with laser light from an exposure device 12 provided below it. When the image formation process starts, the photosensitive drum 110, whose surface has been uniformly charged in advance by a charger (not shown), is irradiated with laser light from the exposure device 12, exposing the photosensitive drum 110. At this time, the exposure device 12 receives a signal (video signal) corresponding to the image data to be printed, and irradiates the photosensitive drum 110 with laser light modulated in accordance with the video signal via a scanning optical system including a polygon mirror. As a result, an electrostatic latent image corresponding to the image data is formed on the drum surface.

[0016] The developing unit 10 supplies toner to the electrostatic latent image formed on the photosensitive drum 110 to visualize (develop) the latent image into a toner image. Thereafter, a predetermined pressure force and electrostatic load bias are applied by primary transfer rollers 14 (14Y, 14M, 14C, 14K), thereby performing primary transfer of the toner image from the photosensitive drum 110 to the intermediate transfer belt 13a. Note that residual toner remaining on the photosensitive drum 110 after primary transfer is collected by a cleaning device (not shown), and the drum surface of the photosensitive drum 110 is cleaned.

[0017] The above-described toner image forming operation is carried out in parallel in each drum unit 11. Furthermore, primary transfer is performed onto the rotating intermediate transfer belt 13a so that the toner image formed by the upstream drum unit 11 is superimposed on the toner image formed by the downstream drum unit 11. As a result, a full-color toner image is finally formed on the intermediate transfer belt 13a, and is carried by the intermediate transfer belt 13a and transported to the secondary transfer roller 24 serving as a transfer section. The secondary transfer roller 24 transfers the toner image from the intermediate transfer belt 13a to the sheet S while nipping and transporting the sheet S.

[0018] The sheet S is then transported to a fixing device 3, which serves as a fixing section that applies heat and pressure to the toner image to fix it. The fixing device 3 has a pair of fixing rollers 31. The pair of fixing rollers 31 is composed of a heater roller 31a, which serves as a heating rotor with a built-in heater (not shown), and a pressure roller 31b that presses against the heater roller 31a. The heater roller 31a and pressure roller 31b apply heat and pressure to the toner image while sandwiching and transporting the sheet S. This melts the toner, which then solidifies and adheres to the sheet S, thereby fixing the image to the sheet S.

[0019] Meanwhile, a sheet S used as a recording medium is supplied to the image forming unit 150 by a sheet feeding unit 2. The sheet feeding unit 2 includes a cassette 21 having a lift-up device that moves up and down while the sheets S are stacked thereon, and the sheets S are fed out one by one from the cassette 21. The sheet S fed from the cassette 21 is conveyed to a pre-registration roller pair 22 via a conveyance path 2a formed by a conveyance guide (not shown), and is then conveyed to a registration roller pair 23 via a conveyance path 2b. The registration roller pair 23 corrects skew of the sheet S and conveys the sheet S to a secondary transfer roller 24 via a conveyance path 2c at a timing determined in accordance with the formation of a toner image by the image forming unit 150.

[0020] The sheet S, onto which the toner image has been transferred by the secondary transfer roller 24, is transported to the fixing device 3 via the transport path 2d. The sheet S, onto which the fixed image has been fixed by the fixing device 3, is transported by the fixing discharge roller pair 42 through the transport path 3a formed by a transport guide, and reaches a branching section where the first switching flap FL1 is disposed. The first switching flap FL1 guides the sheet S to either the transport path 4a toward the discharge roller pair 44 or the transport path 4b toward the reversing discharge roller pair 45, which serves as the first roller pair. The sheet S toward the transport path 4a is transported to the discharge roller pair 44 by the fixing discharge roller pair 42. The sheet S that has reached the discharge roller pair 44 is discharged onto the sheet stacking section 5 by the discharge roller pair 44.

[0021] Meanwhile, the sheet S heading toward the conveying path 4b is conveyed along the conveying path 4b by a branch conveying roller pair 43 serving as a third roller pair, and is conveyed to a reversing discharge roller pair 45 serving as a first roller pair arranged above the discharge roller pair 44. The reversing discharge roller pair 45 is a first roller pair that can convey the sheet by reversing in the direction opposite to the sheet conveying direction.

[0022] When the sheet S reaches the pair of reversing and discharging rollers 45, in the case of single-sided printing, it is conveyed directly in the sheet conveying direction by the pair of reversing and discharging rollers 45 and discharged to the sheet stacking unit 5. On the other hand, when double-sided printing is performed, the sheet S is reversed and conveyed in the opposite direction to the sheet conveying direction by the reversing operation of the pair of reversing and discharging rollers 45. The reversed sheet S is guided to the re-conveying path 4c by the second switching flap FL2. The sheet S guided to the re-conveying path 4c is reversed, conveyed to the double-sided joining conveying path 4d by the pairs of double-sided conveying rollers 46 and 47 and the pair of double-sided pre-registration rollers 48, and re-conveyed to the pair of registration rollers 23. When the sheet S reaches the pair of registration rollers 23, an image is formed on the second side in the same process as on the first side, and then the sheet is discharged to the sheet stacking unit 5.

[0023] <Configuration of the fixing device and the guide member that forms the transport path> Next, the configuration of the fixing device 3 and the guide members that form the conveying paths 3a, 4a, and 4b on the downstream side in the sheet conveying direction and the re-conveying path 4c will be described with reference to Figures 2 and 3. Figure 2 is a schematic cross-sectional view showing the portion from the fixing device 3 to the re-conveying path 4c of the image forming apparatus shown in Figure 1. Figure 3 is a perspective view showing the air blowing unit and the conveying guide.

[0024] The secondary transfer roller 24 is a transfer unit that transfers an image onto the sheet. The fixing device 3 is disposed downstream of the secondary transfer roller 24 in the sheet conveyance direction, and is a fixing unit that heats the sheet to fix the image.

[0025] As shown in FIG. 2, the fixing device 3 includes a case 30 that houses the fixing roller pair 31, which includes the heater roller 31a and pressure roller 31b. The heater roller 31a and pressure roller 31b are in contact with each other across a width that is larger than the width of the sheet transport path in the width direction perpendicular to the sheet transport direction. In other words, the heater roller 31a and pressure roller 31b are configured to be in contact with each other across the entire width, which is larger than the width of the largest sheet that can be transported by the image forming apparatus 1. Therefore, the nip formed by the contact between the heater roller 31a and pressure roller 31b blocks the flow of air in the sheet transport direction.

[0026] The fixing discharge roller pair 42 is a third roller pair disposed between the fixing device 3 and the reverse discharge roller pair 45, and is disposed in the conveyance guide G1 to convey the sheet. The fixing discharge roller pair 42 is a roller pair disposed immediately after the fixing roller pair 31 in the sheet conveyance direction. The fixing discharge roller pair 42 includes a drive roller 42a and a driven roller 42b. The drive roller 42a and the driven roller 42b are each formed into a single cylindrical shape made of, for example, rubber, and are disposed so that their ends nip across substantially the entire width of the conveyance path in the width direction. In other words, the drive roller 42a and the driven roller 42b are in contact across substantially the entire width of the sheet conveyance path in the width direction perpendicular to the sheet conveyance direction. Therefore, the nip formed by the contact between the drive roller 42a and the driven roller 42b blocks the air flow in the sheet conveyance direction.

[0027] On the downstream side of the fixing device 3 in the sheet conveying direction, there are arranged conveying paths 3a and 4b as a first conveying path, a fixing discharge roller pair 42, and a reversing discharge roller pair 45 as a first roller pair. Further, there is arranged a conveying path 4a from the fixing discharge roller pair 42 to the discharge roller pair 44. Furthermore, there are arranged a re-conveying path 4c as a second conveying path and a double-sided merging conveying path 4d from the reversing discharge roller pair 45 to the secondary transfer roller 24.

[0028] A guide member is arranged between the transport path 4b and the re-transport path 4c. The guide member is made up of at least one or more guide members. Here, the guide members arranged are a transport guide G1 (first transport guide) and a transport guide G2 (second transport guide). The transport guide G1 is arranged above the fixing device 3 with a gap da therebetween. The transport guide G2 is also arranged above the transport guide G1 with a gap db therebetween.

[0029] Each guide member includes a first guide surface that guides the sheet from the fixing device 3 to the pair of reversing and discharging rollers 45, and a second guide surface that guides the sheet that has been reversed by the pair of reversing and discharging rollers 45 to the secondary transfer roller 24. Each guide member is disposed above the fixing device 3, and forms a space between the first guide surface and the second guide surface that allows air to circulate.

[0030] Specifically, the conveying guide G1 includes a guide surface G1a as a first guide surface that guides the sheet from the fixing device 3 to the pair of reverse discharge rollers 45, and a guide surface G1b as a second guide surface that guides the sheet reversed by the pair of reverse discharge rollers 45 to the secondary transfer roller 24. The conveying guide G1 is disposed above the fixing device 3, and forms a space for air circulation between the guide surface G1a and the guide surface G1b.

[0031] Similarly, the conveying guide G2 includes a guide surface G2a as a first guide surface that guides the sheet from the fixing device 3 to the pair of reverse discharge rollers 45, and a guide surface G2b as a second guide surface that guides the sheet reversed by the pair of reverse discharge rollers 45 to the secondary transfer roller 24. The conveying guide G2 is disposed above the fixing device 3, and forms a space for air circulation between the guide surface G2a and the guide surface G2b.

[0032] Although the example described here is one in which the guide member is made up of two guide members, the present invention is not limited to this. The guide member may be made up of one guide member, or may be made up of three or more guide members.

[0033] Furthermore, an elastic plate Pa is attached to the lower portion of the conveying guide G1 on the re-conveying path 4c side as a partition member that separates the gap da between the conveying guide G1 and the fixing device 3 from the re-conveying path 4c formed by the guide surface G1b of the conveying guide G1. That is, the elastic plate Pa is made of an elastic material such as rubber. Note that the elastic plate as a partition member is an example, and the partition member is not limited to an elastic material. The elastic plate Pa is arranged so that its upper end (one end) abuts against the guide surface G1b of the conveying guide G1 and its lower end (the other end) abuts against the case 30 of the fixing device 3, thereby substantially closing the gap da. Note that the elastic plate Pa may be attached to the case 30 of the fixing device 3.

[0034] Meanwhile, a transport guide G3 serving as a second guide member is disposed inside the exterior cover 49 of the apparatus main body 1A at a position facing the transport guides G1 and G2 across the re-transport path 4c. As shown in FIG. 4, the transport guide G3 has an upper guide G3A (upper portion) disposed above the transport guide G2 and a lower guide G3B disposed below the upper guide G3A. The upper guide G3A and the lower guide G3B are integrally assembled to form the transport guide G3. In addition, a transport guide G7, which is integrally formed with the exterior cover 49 that forms the exterior of the image forming apparatus 1, is disposed in the lower guide G3B of the transport guide G3.

[0035] Furthermore, a transport guide G4 is disposed on the sheet stacking unit 5 side of the transport guide G3 in the horizontal direction. Furthermore, transport guides G5 and G6 are disposed below the transport guide G4. The transport guides G5 and G6 are disposed in positions facing the transport guides G1, G2, and G4 with the transport paths 3a and 4b between them, and on the sheet stacking unit 5 side in the horizontal direction of the transport guides G1 and G2. The transport guide G5 is disposed below the transport guide G4 so as to have the transport path 4b therebetween. The transport guide G6 is disposed below the transport guide G5 so as to have the transport path 4a therebetween.

[0036] A guide surface G1a, which is the surface on one side of the conveying guide G1 facing the sheet stacking unit 5, forms one guide surface of the conveying path 3a on the upstream side of the fixing discharge roller pair 42 in the sheet conveying direction. The guide surface G1a also forms one guide surface of the conveying path 4b on the downstream side of the fixing discharge roller pair 42 in the sheet conveying direction. Furthermore, a guide surface G2a, which is the surface on one side of the conveying guide G2 facing the sheet stacking unit 5, forms one guide surface of the conveying path 4b. And a guide surface G4a, which is the lower surface on one side of the conveying guide G4, forms one guide surface of the conveying path 4b.

[0037] 2, guide surface G6a, which is the surface on the exterior cover 49 side on the other side of conveying guide G6, forms the other guide surface of conveying path 3a on the upstream side of the fixing discharge roller pair 42 in the sheet conveying direction. Also, guide surface G6a forms one guide surface of conveying path 4a on the downstream side of the fixing discharge roller pair 42 in the sheet conveying direction. Furthermore, guide surface G5b, which is the lower surface on one side of conveying guide G5, forms the other guide surface of conveying path 4a. And guide surface G5a, which is the surface on the other side of conveying guide G5 from the exterior cover 49 side to the upper side, forms the other guide surface of conveying path 4b.

[0038] Furthermore, guide surfaces G3Aa and G3Ba, which are surfaces on one side of the conveying guide G3 (G3A and G3B) from the lower side toward the sheet stacking unit 5, form the other guide surface of the re-conveyance path 4c. Also, guide surface G2b, which is the surface on the other side of the conveying guide G2 facing the exterior cover 49, forms one guide surface of the re-conveyance path 4c. Also, guide surface G1b, which is the surface on the other side of the conveying guide G1 facing the exterior cover 49, forms one guide surface of the re-conveyance path 4c. And guide surface G7a, which is the surface on one side of the conveying guide G7 facing the sheet stacking unit 5, forms the other guide surface of the re-conveyance path 4c.

[0039] Note that the guide surfaces forming each of the conveying paths of the conveying guides G1 to G7 described above are not necessarily formed in a surface shape without any irregularities, but refer to the surfaces that the sheet S comes into contact with and is guided through, such as the surfaces connecting the vertices of multiple ribs.

[0040] The upper guide G3A of the conveying guide G3 serving as the second guide member includes a guide surface G3Aa, and the lower guide G3B includes a guide surface G3Ba. The guide surface G3Aa is disposed opposite the guide surface G2b of the conveying guide G2, and is a third guide surface that guides the sheet reversed by the reverse discharge roller pair 45 to the secondary transfer roller 24.

[0041] <Air flow in image forming devices> Next, the air flow in the image forming apparatus according to this embodiment will be described with reference to Figures 2, 3 and 4. Figure 4 is a schematic diagram showing the suction unit.

[0042] The conveying guide G1 is disposed above the fixing device 3, and forms a duct GD1, which is a space for circulating air, between the guide surface G1a and the guide surface G1b. That is, inside the conveying guide G1, a duct GD1 (see FIG. 2) to which the blower 25 is connected is formed, and this duct GD1 is extended in the width direction.

[0043] The blower unit 25 blows air into the duct GD1 between the guide surfaces G1a and G1b. As shown in FIG. 3, the blower unit 25 has a fan case 26 having an intake opening 26A, a blower fan 27 housed in the fan case 26, and a connecting duct 28. The fan case 26 is connected to the duct GD1 via the connecting duct 28, which is connected to one end of the duct GD1 in the width direction. When the blower fan 27 is driven, it draws in air from outside the image forming apparatus 1 through the intake opening 26A of the fan case 26 and blows the air into the duct GD1 via the connecting duct 28.

[0044] The drive roller 42a of the fixing / discharge roller pair 42 is disposed inside the duct GD1 of the conveying guide G1, with a portion of the drive roller 42a protruding from the guide surface G1a. A gap is provided between the drive roller 42a and the guide surface G1a of the conveying guide G1 to prevent them from contacting each other, and this gap is formed as an opening C, particularly on the upstream side of the drive roller 42a in the sheet conveying direction.

[0045] On the other hand, as shown in FIG. 2, an opening D1 (first ventilation port) is formed below the transport guide G1, facing the case 30 of the fixing device 3 and communicating with the gap da and thus with the transport path 3a. The opening D1 is the first ventilation port provided in the transport guide G1 as a guide member and communicating with the duct GD1. This opening D1 is composed of multiple slit-shaped openings in the width direction. Furthermore, above the opening D1 of the transport guide G1, an opening D2 is formed facing the transport guide G2 and communicating with the gap db. This opening D2 also consists of multiple slit-shaped openings in the width direction. Therefore, the interior of the transport guide G1 is formed to have the duct GD1 extending in the width direction and a ventilation section GW1 that ventilates in the vertical direction through the openings D1 and D2 that communicate with the top and bottom of the duct GD1, respectively.

[0046] An opening F1 is formed below the transport guide G2, facing the opening D2 of the transport guide G1 and communicating with the gap db. This opening F1 is configured as a single slit-shaped opening that is wide in the width direction. Furthermore, an opening F2 (second ventilation port) is formed above the transport guide G2, facing the upper guide G3A of the transport guide G3 and communicating with the re-conveyance path 4c. The opening F2 is provided in the transport guide G2 as a guide member, and is located above the opening D1 across the space of the transport guide G2, as a second ventilation port that communicates with the space of the transport guide G2. This opening F2 is also configured as a plurality of slit-shaped openings in the width direction. A second switching flap FL2 is also arranged in the transport guide G2, and a gap is formed between the transport guide G2 and the second switching flap FL2, and this gap is configured as an opening F3. Therefore, the interior of the conveying guide G2 is formed to have a ventilation section GW2 through which ventilation occurs in the vertical direction via the opening F1, the opening F2 and the opening F3.

[0047] Furthermore, below the conveying guide G3, an opening H (third ventilation port) is formed opposite the opening F2 of the conveying guide G2 and communicating with the re-conveying path 4c. The opening H is provided in the conveying guide G3 as the second guide member, is positioned opposite the opening F2, and is the third ventilation port communicating with the space of the conveying guide G3. This opening H is also composed of multiple slit-shaped openings in the width direction.

[0048] 3 and 4, a gap is formed between the conveying guide G3 and the conveying guide G4, and this gap forms an opening J. Furthermore, as shown in FIG. 4, the space in the upper part inside the conveying guide G3 is formed as a duct GD3 extending in the width direction, and the openings H and J communicate with this duct GD3. That is, the upper guide G3A forms the duct GD3, which is a space for circulating air. A suction fan 29 serving as a suction unit is arranged so as to communicate with this duct GD3.

[0049] In the image forming apparatus 1 according to the present embodiment configured as described above, when a toner image is fixed to the sheet S by the fixing device 3, a large amount of water vapor is released from the sheet S into the conveying path 3a. As described above, the pair of fixing rollers 31 are in close contact across the entire width, i.e., so-called through rollers, and therefore air containing water vapor does not substantially flow from the conveying path 3a to the upstream side in the sheet conveying direction. In addition, the pair of fixing discharge rollers 42 are also in close contact across the entire width, i.e., so-called through rollers, and therefore air containing water vapor does not substantially flow from the conveying path 3a to the conveying paths 4a and 4b located downstream in the sheet conveying direction.

[0050] Meanwhile, by driving the blower fan 27, air from outside the image forming apparatus 1 is blown into the duct GD1 of the transport guide G1 and sent to the transport path 3a. Then, the air containing water vapor in the transport path 3a flows into the gap da between the transport guide G1 and the case 30 of the fixing device 3. The air containing water vapor that has flowed into the gap da is blocked by the elastic plate Pa and flows from the opening D1 to the ventilation section GW1 of the transport guide G1. Most of the air containing water vapor that has flowed into the ventilation section GW1 of the transport guide G1 flows from the opening D2 through the opening F1 to the ventilation section GW2 of the transport guide G2.

[0051] The air containing water vapor that has flowed into ventilation section GW2 of conveyance guide G2 first flows from openings F2 and F3 to the upper portion of re-conveyance path 4c, then flows from opening F2 to opening H, or from opening F3 to opening J, and into duct GD3 of conveyance guide G3. The air containing water vapor that has flowed into duct GD3 is then discharged to the outside of image forming apparatus 1 by suction fan 29.

[0052] In the image forming apparatus 1 according to this embodiment, the air containing water vapor along the transport path 3a can be expelled from the ventilation section GW1 to the ventilation section GW2 by the airflow from the blower fan 27. At this time, the opening of the gap da to the re-conveyance path 4c is blocked by the elastic plate Pa, preventing the air from flowing into the re-conveyance path 4c. Furthermore, the air containing water vapor moves upward due to natural convection caused by the heat of the fixing device 3, making it difficult for the air to move to the transport path below the fixing device 3. Therefore, at the duplex transport roller pair 47 located below the fixing device 3 on the re-conveyance path 4c, water vapor is prevented from flowing in due to the blocking of the opening to the re-conveyance path 4c by the elastic plate Pa and natural convection caused by the heat of the fixing device 3, making it difficult for condensation to form.

[0053] <Roller cover> Next, the roller cover portion, which is a feature of the present invention, will be described with reference to Figures 2, 5, and 6. Figure 5 is a perspective view of the portion of the conveying guide G2 having the guide surface G2b, with the cover member RC removed. Figure 6 is a perspective view of the portion of the conveying guide G2 having the guide surface G2b, with the cover member RC added.

[0054] 5, the conveying guide G2 is provided with a driven roller 46b, which is one of the pair of double-sided conveying rollers 46. An opening W is provided in the guide surface G2b of the conveying guide G2 to allow the driven roller 46b of the pair of double-sided conveying rollers 46 to protrude from the guide surface G2b. The driven roller 46b is supported by the conveying guide G2 in a manner that protrudes into the guide surface G2b.

[0055] As shown in FIG. 6, the transport guide G2 has a cover member RC that serves as a roller cover that covers the driven roller 46b inside the space between the guide surfaces G2a and G2b. The cover member RC is supported inside the transport guide G2. The cover member RC is disposed inside the transport guide G2 so as to cover the opening W and the driven roller 46b. The cover member RC is fastened to the transport guide G2 with screws BS, thereby coming into close contact with the transport guide G2 and sealing off the driven roller 46b and the opening W from the inside of the transport guide G2.

[0056] The driven roller 46b contacts the drive roller 46a, which is the other roller of the duplex conveying roller pair 46 and is located near the exterior cover 49, to form a nip. The drive roller 46a is close to the outside air and is susceptible to the effects of the outside air, so it is prone to becoming cold. In addition, the driven roller 46b is also prone to becoming cold due to heat conduction through the nip with the drive roller 46a. Therefore, the driven roller 46b is particularly prone to condensation among the rollers in the re-conveyance path 4c.

[0057] Therefore, by isolating the driven roller 46b from the ventilation section GW2 with the cover member RC, the air containing water vapor flowing through the ventilation section GW2 does not come into contact with the driven roller 46b, thereby suppressing condensation on the roller surface. Furthermore, by covering the driven roller 46b inside the space of the conveying guide G2 with the cover member RC, the opening W for projecting the driven roller 46b onto the guide surface G2b of the conveying guide G2 is also covered, which prevents air containing water vapor from leaking from the opening W into the re-conveyance path 4c and causing condensation inside the re-conveyance path 4c.

[0058] As described above, according to this embodiment, it is possible to suppress the leakage of water vapor from the space inside the conveying guide G2, and to prevent condensation on the roller surfaces and the guide surface G2b of the conveying guide G2.

[0059] In the above-described embodiment, the cover member RC and the conveying guide G2 are separate members, but this is not limiting. The cover member RC may be configured as a single member as part of the shape of the conveying guide G2, as long as it has a shape that isolates the rollers supported by the guide members that form the ventilation sections GW1 and GW2 from the ventilating air inside.

[0060] In the above-described embodiment, a cover member is not provided for the branch conveying roller pair 43 supported by the conveying guide G2. However, a cover member may be provided for the branch conveying roller pair 43 to isolate it from the air circulating inside. The branch conveying roller pair 43 is disposed between the fixing device 3 and the reverse discharge roller pair 45, and is disposed in the conveying guide G2 to convey a sheet. One of the branch conveying roller pair 43 is supported on the guide surface G2a of the conveying guide G2. Covering this one roller supported on the guide surface G2a with a roller cover suppresses condensation on the roller surface. Covering this one roller also covers an opening (not shown) that protrudes into the guide surface G2a of the conveying guide G2. This prevents air containing water vapor from leaking from the opening into the conveying path 4b and causing condensation within the conveying path 4b.

[0061] In the above-described embodiment, a suction unit that sucks from the transport guide G3, which is the second guide member, is provided, but this is not limiting. For example, a suction unit that sucks from the transport guide G2, which is the guide member, may be provided.

[0062] In the above-described embodiment, an image forming apparatus is illustrated in which an intermediate transfer member is used, toner images of each color are transferred to the intermediate transfer member in a sequentially overlapping manner, and the toner images carried on the intermediate transfer member are then transferred all at once to a recording medium, but the present invention is not limited to this. For example, an image forming apparatus may be used in which a recording medium carrier is used, toner images of each color are transferred to a recording medium carried on the recording medium carrier in a sequentially overlapping manner, and similar effects can be obtained by applying the present invention to such an image forming apparatus.

[0063] In the above-described embodiment, the electrophotographic method is exemplified as the recording method of the image forming unit that forms the image, but this is not limited to this, and the image forming unit may also be of another recording method, such as an inkjet method. [Explanation of symbols]

[0064] C,D1,D2,F1,F2,F3,H,J,W...Opening FL1, FL2...Switching flaps G1, G2, G3, G4, G5, G6, G7 ...Transport guide G1a, G1b, G2a, G2b, G3Aa, G3Ba, G4a, G5a, G5b, G6a, G7a ... guide surface G3A...upper guide G3B...Downward guide GD1, GD3...Duct GW1…Ventilation section Pa...Elastic plate RC...Cover material S...Seat da,db...gap 1...Image forming device 3...Fusing device 3a...Transport path 4...Reverse discharge section 4a, 4b ...Transport path 4c...Re-transportation route 4d... Double-sided merging conveyor 24...Secondary transfer roller 26...Fan case 26A...Air intake opening 27...Ventilation fan 28...Connecting duct 29...Suction fan 30...cases 31...Fuser roller pair 31a...heated roller 31b...Pressure roller 42 ... Fixing discharge roller pair 43... Branching conveying roller pair 44...Discharge roller pair 45...Reverse discharge roller pair 49...Exterior cover 110...Photosensitive drum 150...Image forming unit

Claims

1. a transfer unit that transfers an image onto a sheet; a fixing unit disposed downstream of the transfer unit in a sheet conveying direction and configured to heat the sheet to fix an image; a first roller pair that is disposed downstream of the fixing unit in a sheet conveying direction and that is capable of conveying the sheet in a direction opposite to the sheet conveying direction; a guide member including a first guide surface that guides the sheet from the fixing unit to the first roller pair and a second guide surface that guides the sheet inverted by the first roller pair to the transfer unit, the guide member being disposed above the fixing unit and forming a space between the first guide surface and the second guide surface through which air can circulate; a second roller pair disposed above the fixing unit and on the guide member for conveying a sheet; at least one ventilation hole provided in the guide member and communicating with the space between the first guide surface and the second guide surface; a blower that blows air into the space between the first guide surface and the second guide surface, the guide member supports one roller of the second roller pair, The guide member has a cover portion that covers the one roller inside the space. An image forming apparatus characterized by:

2. The cover portion is a separate member from the guide member.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The guide member is composed of at least one guide member.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. a third roller pair disposed between the fixing unit and the first roller pair and disposed on the guide member to transport a sheet; the third roller pair forms a nip portion that holds the sheet across the entire width in a width direction perpendicular to the sheet conveying direction; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. the guide member is disposed above the fixing portion with a gap therebetween, a partition member having one end abutting the second guide surface of the guide member and the other end abutting the fixing unit across the gap, and separating the gap between the guide member and the fixing unit from a sheet conveyance path formed by the second guide surface of the guide member; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. a second guide member including a third guide surface that is disposed opposite the second guide surface and that guides the sheet that has been inverted by the first roller pair to the transfer unit, and that forms a space through which air flows; the guide member has, as the ventilation openings, a first ventilation opening that is arranged above the fixing portion and communicates with the space of the guide member, and a second ventilation opening that is arranged above the first ventilation opening across the space of the guide member and communicates with the space of the guide member, the second guide member has a third vent hole disposed opposite the second vent hole and communicating with a space in the second guide member; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. a suction portion that sucks air from the space of the second guide member; 7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. an exterior cover that forms the exterior of the image forming apparatus; The second roller pair is a roller pair in which one roller disposed on the guide member comes into contact with the other roller disposed on the outer cover to form a nip portion.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. the guide member has an opening for allowing one roller of the second roller pair to protrude from the second guide surface, the one roller of the second roller pair is supported by the guide member in a manner to protrude from the second guide surface, the cover portion covers the opening and the one roller inside the space; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images