Image forming device

Abstract

To reduce dew condensation on a third conveyance path while reducing dew condensation between a fixing unit and a first rotating body pair.SOLUTION: An image forming apparatus comprises: a conveyance guide G1 and a conveyance guide G2 that form a guide surface of a conveyance path 4b and a guide surface of a re-conveyance path 4c; and a conveyance guide G3 that has an upper guide G3A arranged above the conveyance guide G2 and forms the guide surface of the re-conveyance path 4c. The image forming apparatus comprises a ventilation unit that sends air toward the conveyance path 3a. The conveyance guide G1 and the conveyance guide G2 have an opening D1 that communicates with the conveyance path 3a and an opening F2 that is arranged above the opening D1 and communicates with the re-conveyance path 4c. The conveyance guide G3 has an opening H that is opposite to the opening F2 and communicates with the re-conveyance path 4c.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] For example, in laser beam image forming devices such as printers, FAX machines, and multifunction machines, after a toner image is transferred to a sheet, the image is fixed to the sheet by heating and pressurizing it with a fixing device. The sheet heated by the fixing device may generate water vapor, which is cooled by the guide surface that forms the transport path, and condensation may occur on the guide surface. If the condensed water droplets on the guide surface adhere to the sheet being transported, the transport resistance increases, causing paper jams, and when double-sided printing is performed, localized transfer failures may occur, or unevenness in the image may occur due to wrinkles in the sheet.

[0003] In view of this, a proposal has been made to provide a roller pair (so-called through rollers) that contacts the fixing device across its entire width downstream in the sheet conveying direction, and to suck in the air between the fixing device and the roller pair (see Patent Document 1). By providing a roller pair that contacts the fixing device across its entire width in this manner, it is possible to prevent water vapor from condensing on the guide plate downstream in the conveying direction of the roller pair. In addition, by sucking in the air between the fixing device and the roller pair, it is possible to prevent the guide plate from condensing due to water vapor between them. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-174682 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when sucking air between the fixing device and the roller pair as in Patent Document 1, even if air flows in from the gap between the guide member and the roller, the amount of air sucked in may be insufficient. Therefore, it is possible to blow air between the fixing device and the roller pair to expel water vapor. However, blowing air between the fixing device and the roller pair in this way tends to cause high humidity air to diffuse inside the device. In particular, the temperature of the re-conveying path that re-conveys the sheet during double-sided printing may be low depending on the environmental temperature in the part close to the outside of the device, and when the high humidity air passes through, condensation is likely to occur, which may cause paper jams and image unevenness.

[0006] SUMMARY OF THE PRESENT DISCLOSURE In view of the above, an object of the present invention is to provide an image forming apparatus capable of reducing condensation between the fixing unit and the first pair of rotating bodies, while also reducing condensation in the third transport path. [Means for solving the problem]

[0007] One aspect of the present invention includes a transfer unit that transfers an image onto a sheet, a fixing unit that heats the sheet to fix the image transferred by the transfer unit, a first pair of rotating bodies that are arranged downstream of the fixing unit in a sheet transport direction and capable of transporting a sheet, and that are in contact with the sheet across the entire width in a width direction perpendicular to the sheet transport direction when the sheet is not being transported, a second pair of rotating bodies that are arranged downstream of the first pair of rotating bodies in the sheet transport direction and are capable of inverting the sheet with respect to the sheet transport direction and transporting it, a first transport path that guides the sheet from the fixing unit to the first pair of rotating bodies, a second transport path that guides the sheet from the first pair of rotating bodies to the second pair of rotating bodies, and a conveying path that conveys the sheet inverted by the second pair of rotating bodies toward the transfer unit. the first guide member has a first opening communicating with the first transport path, and a second opening disposed above the first opening, communicating with the first opening and communicating with the third transport path; and the second guide member has a third opening facing the second opening, disposed in the upper portion, and communicating with the third transport path. Effect of the Invention

[0008] According to the present invention, it is possible to reduce condensation between the fixing unit and the first rotating body pair, and also to reduce condensation on the third transport path. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an entire image forming apparatus according to an embodiment of the present invention. [Diagram 2] (a) is a schematic diagram showing the state of moisture in the sheet before fixing. (b) is a schematic diagram showing the state of moisture in the sheet during fixing. (c) is a schematic diagram showing the state of moisture in the sheet immediately after fixing. (d) is a schematic diagram showing the state of moisture released from the sheet after fixing. [Diagram 3] 2 is a schematic cross-sectional view showing a portion from the fixing device to a pair of reverse discharge rollers according to the embodiment; [Figure 4] FIG. 2 is a cross-sectional view showing the fixing device and each transport guide according to the embodiment. [Diagram 5] FIG. 4 is a perspective view showing each transport guide and a blower according to the embodiment. [Figure 6] FIG. 2 is a perspective view showing the fixing device, each transport guide, and a blower according to the embodiment. [Figure 7] FIG. 2 is a perspective view showing a conveying guide G1 according to the embodiment. [Figure 8] FIG. 4 is a bottom perspective view showing the conveying guide G2 according to the embodiment. [Figure 9] FIG. 4 is a top perspective view showing a conveying guide G2 according to the embodiment. [Figure 10] FIG. 4 is a bottom perspective view showing the upper guide G3A according to the embodiment. [Figure 11] FIG. 4 is a schematic diagram showing a duct GD3 and a suction fan according to the embodiment as viewed from above. [Figure 12] FIG. 4 is a schematic cross-sectional view showing a portion from a fixing device to a pair of reverse discharge rollers in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an image forming apparatus according to the present embodiment will be described with reference to the drawings. The image forming apparatus includes a printer, a copier, a facsimile, and a multifunction machine, and forms an image on a sheet used as a recording medium based on image information input from an external PC or image information read from an original. The sheets used as recording media include paper such as plain paper and cardboard, plastic films such as sheets for overhead projectors, sheets of special shapes such as envelopes and index paper, and cloth.

[0011] <Configuration of Image Forming Apparatus> 1 is a schematic cross-sectional view showing the entire image forming apparatus 1 according to the present 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 arranged on the upper part of apparatus main body 1A.

[0012] The image forming apparatus 1 is equipped with an electrophotographic image forming section 150. The image forming section 150 forms toner images of four colors, yellow (Y), magenta (M), cyan (C) and black (Bk). That is, the image forming section 150 is a so-called intermediate transfer tandem type electrophotographic unit in which four drum units 11 (11Y, 11M, 11C, 11K) are arranged along the intermediate transfer belt 13a of the intermediate transfer unit 13. The toner storage sections T (TY, TM, TC, TK) store toners of yellow (Y), magenta (M), cyan (C) and black (K), respectively.

[0013] 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. Around the photosensitive drum 110 (110Y, 110M, 110C, 110K), a developing unit 10 (10Y, 10M, 10C, 10K) that develops a toner image is disposed.

[0014] 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 is started, the photosensitive drum 110, the surface of which has been uniformly charged in advance by a charger (not shown), is irradiated with laser light from the exposure device 12 to expose the photosensitive drum 110. At this time, the exposure device 12 receives a signal (video signal) corresponding to image data to be printed, and irradiates the photosensitive drum 110 with laser light modulated in response to 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.

[0015] A developing unit (not shown) 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 primary transfer device (not shown) applies a predetermined pressure force and an electrostatic load bias, thereby performing primary transfer of the toner image from the photosensitive drum 110 to the intermediate transfer belt 13a. Residual toner remaining on the photosensitive drum 110 after the primary transfer is collected by a cleaning device (not shown), and the drum surface of the photosensitive drum 110 is cleaned.

[0016] The above-mentioned toner image forming operation is performed in parallel in each drum unit 11. In addition, primary transfer is performed on 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 for transfer. 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.

[0017] Thereafter, the sheet S is conveyed to a fixing device 3 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 as a pair of fixing rotors. The pair of fixing rollers 31 is composed of a heater roller 31a 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 the pressure roller 31b apply heat and pressure to the toner image while sandwiching and conveying the sheet S. This melts the toner, which then solidifies and adheres to the sheet S, thereby fixing the image on the sheet S.

[0018] On the other hand, 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 with the sheets S stacked thereon, and the sheets S are sent 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 conveying path 2a, and is conveyed to a registration roller pair 23 via a conveying 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 conveying path 2c at a timing determined in accordance with the formation of a toner image by the image forming unit 150.

[0019] The sheet S onto which the toner image has been transferred by the secondary transfer roller 24 is conveyed to the fixing device 3 via the conveying path 2d. The sheet S on which the fixed image has been fixed by the fixing device 3 is conveyed by the fixing discharge roller pair 42 as the first rotating body pair through the conveying path 3a, and reaches a branching portion where the first switching flap FL1 (see FIG. 3) is disposed. The first switching flap FL1 guides the sheet S to either the conveying path 4a toward the discharge roller pair 44 or the conveying path 4b toward the reverse discharge roller pair 45 as the second rotating body pair. The sheet S toward the conveying path 4a is conveyed 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 portion 5 by the discharge roller pair 44.

[0020] On the other hand, the sheet S heading toward the conveying path 4b is conveyed along the conveying path 4b by the branch conveying roller pair 43, and conveyed to the reverse discharge roller pair 45 arranged above the discharge roller pair 44. The sheet S that has reached the reverse discharge roller pair 45 is directly discharged to the sheet stacking section 5 by the reverse discharge roller pair 45, or, in the case of double-sided printing, the sheet conveying direction is reversed by the reversing operation of the reverse discharge roller pair 45 and conveyed. In the case of double-sided printing, the reversed sheet S is guided to the re-conveying path 4c by the second switching flap FL2 (see FIG. 3). The sheet S guided to the re-conveying path 4c is reversed, conveyed to the double-sided junction conveying path 4d by the double-sided conveying roller pairs 46, 47 and the double-sided pre-registration roller pair 48, and conveyed again to the registration roller pair 23. The sheet S that has reached the registration roller pair 23 has an image formed on its second side in the same process as that on the first side on which an image has already been formed, and then discharged to the sheet stacking section 5.

[0021] [Movement of moisture inside the sheet due to heating of the fixing device] Next, the movement of moisture inside the sheet S due to heating by the fixing device 3 will be described with reference to Fig. 2. Fig. 2(a) is a schematic diagram showing the state of moisture in the sheet before fixing, and Fig. 2(b) is a schematic diagram showing the state of moisture in the sheet during fixing. Fig. 2(c) is a schematic diagram showing the state of moisture in the sheet immediately after fixing, and Fig. 2(d) is a schematic diagram showing the state of moisture released from the sheet after fixing.

[0022] 2(a), the sheet S has a first side A and a second side B, which is the reverse side of the first side A, and in single-sided printing, for example, a toner image Tim is transferred to the first side A. Moisture Wa is contained inside the sheet S. Before being heated by the fixing device 3, the moisture Wa inside the sheet S is uniformly distributed in the thickness direction.

[0023] 2(b), the toner image Tim is fixed onto the first side A of the sheet S by applying heat from the heater roller 31a of the fixing device 3 and pressure from the pressure roller 31b. At that time, the moisture Wa inside the sheet S moves from the first side A to the second side B due to the heat applied from the heater roller 31a. The moisture Wa that has moved to the second side B is prevented from being released into the air by the pressure roller 31b, so that the moisture Wa inside the sheet S is biased toward the second side B.

[0024] 2(c), the sheet S immediately after passing through the fixing device 3 contains more moisture Wa on the second surface B side than on the first surface A side. Therefore, as shown in FIG. 2(d), more moisture Wa is released from the sheet S into the air from the second surface B side than from the first surface A side.

[0025] [Configuration of the fixing device and the transport path downstream in the transport direction] Next, the configurations of the fixing device 3, and the conveying paths 3a, 4a, and 4b on the downstream side in the sheet conveying direction, and the guide members forming the re-conveying path 4c will be described with reference to FIGS.

[0026] As shown in Fig. 3, the fixing device 3 includes a case 30, and the fixing roller pair 31, which is composed of the heater roller 31a and pressure roller 31b, is housed inside the case 30. The heater roller 31a and pressure roller 31b are in contact with each other over 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, these rollers are configured to be in contact with each other over the entire width that is larger than the width of the maximum size 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 air flow in the sheet transport direction.

[0027] The pair of fixing and discharging rollers 42 includes a driving roller 42a and a driven roller 42b. The driving roller 42a and the driven roller 42b are each formed of, for example, a rubber cylinder, and are arranged so that both ends are located outside both ends of the conveying path 182 in the width direction. That is, the driving roller 42a and the driven roller 42b are in contact with each other over a width larger than the width of the sheet conveying path in the width direction perpendicular to the sheet conveying direction. That is, these rollers are also configured to be in contact with each other over a full width larger than the width of the maximum size sheet that can be conveyed by the image forming apparatus 1. Therefore, the nip formed by the contact between the driving roller 42a and the driven roller 42b blocks the air flow in the sheet conveying direction.

[0028] On the downstream side of the fixing device 3 in the sheet conveying direction, there are arranged a conveying path 3a as a first conveying path, a fixing discharge roller pair 42 as a first rotating body pair, a conveying path 4b as a second conveying path, and a reverse discharge roller pair 45 as a second rotating body pair. A conveying path 4a is arranged from the fixing discharge roller pair 42 to the discharge roller pair 44. Furthermore, a re-conveying path 4c as a third conveying path is arranged from the reverse discharge roller pair 45 to the secondary transfer roller 24.

[0029] Between the transport path 4b and the re-conveying path 4c, transport guides G1 and G2 are disposed as first guide members. The transport guide G1, which is a lower guide member, is disposed above the fixing device 3 so as to have a gap da therebetween. The transport guide G2, which is an upper guide member, is disposed above the transport guide G1 so as to have a gap db therebetween. An elastic plate Pa is attached to the lower portion of the transport guide G1 on the re-conveying path 4c side as a partition member that separates the gap da and the re-conveying path 4c. That is, the elastic plate Pa is made of an elastic member such as rubber, and is disposed so that the upper end abuts against the transport guide G1 and the lower end abuts against the case 30 of the fixing device 3 to substantially close the gap da. The elastic plate Pa may be attached to the case 30 of the fixing device 3.

[0030] On the other hand, 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 guide G1 and the transport guide G2 across the re-transport path 4c. As shown in FIG. 4, the transport guide G3 has an upper guide G3A disposed above the transport guide G2 serving as the upper part, 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, is disposed in the lower guide G3B of the transport guide G3.

[0031] Further, a conveying guide G4 is disposed on the sheet stacking section 5 side of the conveying guide G3 in the horizontal direction. Further, a conveying guide G5 and a conveying guide G6 are disposed below the conveying guide G4. The conveying guide G5 and the conveying guide G6 are disposed at positions facing the conveying guide G1, the conveying guide G2, and the conveying guide G4 with the conveying path 3a and the conveying path 4b interposed therebetween, and on the sheet stacking section 5 side in the horizontal direction of the conveying guide G1 and the conveying guide G2. The conveying guide G5 is disposed below the conveying guide G4 so as to have the conveying path 4b therebetween. And the conveying guide G6 is disposed below the conveying guide G5 so as to have the conveying path 4a therebetween.

[0032] A guide surface G1a, which is the surface on the sheet stacking section 5 side at one side of the conveying guide G1, forms one guide surface of the conveying path 3a on the upstream side in the sheet conveying direction of the fixing discharge roller pair 42. The guide surface G1a also forms one guide surface of the conveying path 4b on the downstream side in the sheet conveying direction of the fixing discharge roller pair 42. Furthermore, a guide surface G2a, which is the surface on the sheet stacking section 5 side at one side of the conveying guide G2, forms one guide surface of the conveying path 4b. And a guide surface G4a, which is the lower surface at one side of the conveying guide G4, forms one guide surface of the conveying path 4b.

[0033] 3, a guide surface G6a, which is the surface on the exterior cover 49 side on the other side of the conveying guide G6, forms the other 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 G6a also forms one guide surface of the conveying path 4a on the downstream side of the fixing discharge roller pair 42 in the sheet conveying direction. Furthermore, a guide surface G5b, which is the lower surface on one side of the conveying guide G5, forms the other guide surface of the conveying path 4a. And a guide surface G5a, which is the surface on the other side of the conveying guide G5 from the exterior cover 49 side to the upper side, forms the other guide surface of the conveying path 4b.

[0034] Furthermore, the guide surface G3a, which is the surface from the lower side to the sheet stacking unit 5 side on one side of the conveying guide G3, forms the other guide surface of the re-conveying path 4c. The guide surface G2b, which is the surface on the outer cover 49 side on the other side of the conveying guide G2, forms one guide surface of the re-conveying path 4c. The guide surface G1b, which is the surface on the outer cover 49 side on the other side of the conveying guide G1, forms one guide surface of the re-conveying path 4c. The guide surface G7a, which is the surface on the sheet stacking unit 5 side on one side of the conveying guide G7, forms the other guide surface of the re-conveying path 4c. 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 irregularities, but refer to a surface that the sheet S comes into contact with and is guided, such as a surface connecting the apexes of a plurality of ribs.

[0035] [Air flow in an image forming apparatus according to a comparative example] Here, the air flow in the image forming apparatus according to the comparative example will be described with reference to FIG. 12. Inside the conveying guide G1, a duct GD1 is formed as an air duct for the blower 25, and the duct GD1 is arranged to extend in the width direction. The duct GD1 communicates with a blower fan not shown in FIG. 12, and air from outside the image forming apparatus is blown into the duct GD1. Inside the duct GD1 of the conveying guide G1, a driving roller 42a of the fixing discharge roller pair 42 is arranged so that a part of the driving roller 42a protrudes from the guide surface G1a. Between the driving roller 42a and the guide surface G1a of the conveying guide G1, there is a gap so that they do not come into contact with each other, and the gap is formed as an opening C, particularly on the upstream side of the driving roller 42a in the sheet conveying direction.

[0036] Therefore, when air is blown into the duct GD1, the air is blown from the opening C toward the conveying path 3a between the drive roller 42a and the fixing device 3. As described above, the sheet S heated by the fixing device 3 releases moisture toward the pressure roller 31b side, and the moisture is released as water vapor toward the conveying guide G1 side of the conveying path 3a. As described above, the pair of fixing rollers 31 is in close contact with each other over the entire width, and the pair of fixing discharge rollers 42 is also in close contact with each other over the entire width. Therefore, as shown by the arrow in FIG. 12, the air blown from the opening C causes the water vapor to pass through the gap between the case 30 of the fixing device 3 and the conveying guide G1 and flow into the re-conveying path 4c.

[0037] Since the re-conveying path 4c is closer to the exterior cover 49 than the conveying path 3a, it is closer to the outside of the device main body 1A and is more susceptible to the influence of the outside air temperature. Therefore, the air flowing into the re-conveying path 4c is high in humidity as described above, and is cooled by the guide surfaces G3a and G7a of the conveying guides G3 and G7 that form the re-conveying path 4c due to the influence of the outside air temperature. When the temperature of the air that has flowed in decreases in this way, the relative humidity of the air increases, and when the relative humidity exceeds 100%, condensation occurs on the guide surfaces G3a and G7a. The condensed water that has adhered to the guide surfaces G3a and G7a due to condensation adheres to the sheet S that passes through during double-sided printing, and may cause transfer failure at the secondary transfer roller 24 or wrinkles on the sheet at the fixing device 3.

[0038] [Air flow in the image forming apparatus according to the present embodiment] Next, the air flow in the image forming apparatus according to the present embodiment will be described using FIG. 3 with reference to FIGS.

[0039] As shown in Fig. 3 and Fig. 4, in the same manner as the comparative example, inside the conveying guide G1, a duct GD1 of the blower 25 is formed, and the duct GD1 is arranged to extend in the width direction. As shown in Fig. 5 and Fig. 6, the blower 25 has a fan case 26 having an opening 26A, a blower fan 27 housed in the fan case 26, and the duct GD1. The outlet of the blower path of the fan case 26, not shown, is connected to one end of the duct GD1 in the width direction via a connecting duct 28. When the blower fan 27 is driven, air is sucked in from the outside of the image forming apparatus 1 through the opening 26A of the fan case 26, and the air is blown to the duct GD1 through the connecting duct 28.

[0040] 3 to 7, inside the duct GD1 of the conveying guide G1, the driving roller 42a of the pair of fixing and discharging rollers 42 is disposed so that a part of it protrudes from the guide surface G1a. Between the driving roller 42a and the guide surface G1a of the conveying guide G1, there is a gap so that they do not come into contact with each other, and particularly, an opening C (fourth opening) is formed on the upstream side of the driving roller 42a in the sheet conveying direction.

[0041] On the other hand, as shown in FIG. 3, FIG. 4, and FIG. 7, below the conveying guide G1, an opening D1 (first opening) is formed, which faces the case 30 of the fixing device 3 and communicates with the gap da, and thereby communicates with the conveying path 3a. This opening D1 is composed of a plurality of slit-shaped openings in the width direction. Furthermore, above the opening D1 of the conveying guide G1, an opening D2 (fifth opening) is formed, which faces the conveying guide G2 and communicates with the gap db. This opening D2 is also composed of a plurality of slit-shaped openings in the width direction. Therefore, the inside of the conveying guide G1 is formed to have the duct GD1 and a ventilation section GW1 that communicates with the openings D1 and D2 to ventilate.

[0042] As shown in Figs. 3, 4, and 8, an opening F1 (sixth opening) is formed below the conveying guide G2, facing the opening D2 of the conveying guide G1 and communicating with the gap db. This opening F1 is formed of a single slit-shaped opening that is wide in the width direction. Furthermore, as shown in Figs. 3, 4, and 9, an opening F2 (second opening) is formed above the conveying guide G2, facing the upper guide G3A of the conveying guide G3 and communicating with the re-conveying path 4c. This opening F2 is also formed of a plurality of slit-shaped openings in the width direction. As shown in Figs. 3 and 4, a second switching flap FL2 is disposed in the conveying guide G2, and a gap is formed between the conveying guide G2 and the second switching flap FL2, and this gap is formed as an opening F3. Therefore, the inside of the conveying guide G2 is formed to have a ventilation section GW2 that communicates with the opening F1, the opening F2, and the opening F3 to ventilate.

[0043] Further, as shown in FIG. 3, FIG. 4, and FIG. 10, an opening H (third opening) is formed below the conveying guide G3 so as to face the opening F2 of the conveying guide G2 and communicate with the re-conveying path 4c. This opening H is also formed of a plurality of slit-shaped openings in the width direction. Also, as shown in FIG. 3 and FIG. 4, a gap is formed between the conveying guide G3 and the conveying guide G4, and this gap is formed as an opening J. Furthermore, as shown in FIG. 3, FIG. 4, and FIG. 11, the space in the upper part inside the conveying guide G3 is formed as a duct GD3 extending in the width direction, and the opening H and the opening J communicate with the duct GD3. And, a suction fan 29 is arranged as a suction part so as to communicate with the duct GD3.

[0044] In the image forming apparatus 1 according to the present embodiment configured as described above, when the toner image Tim is fixed to the sheet S by the fixing device 3 (see FIG. 2), as shown in FIG. 3, a large amount of water vapor is released from the sheet S to the conveying path 3a. As described above, since the pair of fixing rollers 31 are in close contact over the entire width and are so-called through rollers, air containing water vapor does not almost flow from the conveying path 3a to the upstream side in the sheet conveying direction. In addition, since the pair of fixing discharge rollers 42 are also in close contact over the entire width and are so-called through rollers, air containing water vapor does not almost flow from the conveying path 3a to the conveying paths 4a and 4b located downstream in the sheet conveying direction.

[0045] 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 is then blown into the transport path 3a from the opening C. 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 into 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 into the ventilation section DW2 of the transport guide G2.

[0046] 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, and then flows from opening F2 through opening H or from opening F3 through opening J into duct GD3 of conveyance guide G3. Then, the air containing water vapor that has flowed into duct GD3 is discharged to the outside of image forming apparatus 1 through suction fan 29 (see FIG. 11).

[0047] As described above, in the image forming apparatus 1 according to the present embodiment, the air containing water vapor in the conveying path 3a between the fixing device 3 and the pair of fixing and discharging rollers 42 can be expelled by the blowing fan 27. This can reduce condensation in the conveying path 3a. Then, the air containing water vapor can be made to flow to the conveying guide G3 through the insides of the conveying guide G1 and the conveying guide G2 between the conveying path 4b and the re-conveying path 4c in the vertical direction. Therefore, the air containing water vapor does not basically pass through the portion of the re-conveying path 4c that is close to the exterior cover 49 and extends in the vertical direction, making it difficult for the air containing water vapor to flow in, thereby reducing condensation in the re-conveying path 4c.

[0048] In particular, the opening F2 of the transport guide G2 and the opening H of the transport guide G3 are arranged at a position where they at least partially overlap in the vertical direction, so that the warm air that contains water vapor and is heated by the fixing device 3 can flow upward as it is, making it difficult for the re-transport path 4c to fill up.

[0049] In addition, since the conveying guide G1 has a duct GD1 and a ventilation section GW1 inside, it is possible to blow air to the conveying path 3a while allowing air containing water vapor to flow to the conveying guide G3 between the conveying path 4b and the re-conveying path 4c.

[0050] In particular, the duct GD1 of the transport guide G1 has an opening C that opens between the drive roller 42a and below the fixing and discharging roller pair 42, so that air containing water vapor in the transport path 3a can be efficiently expelled.

[0051] In addition, the transport guide G1 is disposed above the case 30 of the fixing device 3 so as to have a gap da between it and the case 30, and the opening D1 is disposed opposite the case 30, so that air containing water vapor from the transport path 3a can be taken in through the gap da.

[0052] In addition, since an elastic plate Pa is provided to separate the gap da between the transport guide G1 and the case 30 of the fixing device 3 from the re-transport path 4c, it is possible to prevent air containing water vapor from flowing into the re-transport path 4c through the gap da.

[0053] In addition, the transport guide G1 and the transport guide G2 are arranged vertically between the transport path 4b and the re-transport path 4c, but the opening D2 of the transport guide G1 faces the opening F1 of the transport guide G2. Therefore, most of the air containing water vapor can flow from the transport guide G1 to the transport guide G2.

[0054] Since a suction fan 29 is provided in communication with the opening H of the conveying guide G3 to draw in air, the air containing water vapor can be drawn in through the conveying guide G3 and discharged to the outside of the image forming apparatus 1.

[0055] [Possibility of other embodiments] In the above embodiment, the transport guide G1 and the transport guide G2 are separated into two, but these transport guides may be integrally formed as a first transport guide member. Conversely, the first transport guide member may be separated into three or more transport guides.

[0056] In the present embodiment, the transport guide G3 is divided into two guides, an upper guide G3A and a lower guide G3B, and the upper guide G3A is disposed above the transport guide G2. However, this is not limiting, and the upper guide G3A and the lower guide G3B may be integrated as a second transport guide member. When the guide members are integrated in this manner, the portion located above the transport guide G2 is the upper portion of the second transport guide member. Conversely, the second transport guide member may be divided into three or more transport guides.

[0057] In the present embodiment, the duct GD1 and the ventilation section GW1 are provided inside the transport guide G1, but these may be separate.

[0058] In the present embodiment, the printer is described as being provided with the discharge roller pair 44 and the reverse discharge roller pair 45. However, the printer may not be provided with the discharge roller pair 44, that is, may discharge the sheet from one location, or may be provided with multiple discharge rollers and discharge the sheet from three or more locations. In these cases, the structure of the conveying path downstream of the fixing discharge roller pair 42 in the sheet conveying direction is different, and therefore the number and arrangement of the conveying guides will change accordingly.

[0059] In the present embodiment, the openings C and F1 are formed by one opening, and the openings D1, D2, F2, and H are formed by a plurality of openings arranged in parallel in a slit shape. However, the present invention is not limited to these, and any shape may be used as long as each opening is one or a plurality of openings that can correspond to the width direction length of the sheet. The positions of these openings are not limited to the positions in the present embodiment, and in particular, the positional relationship between the openings D2 and F1, and the openings F2 and H are not necessarily completely opposite to each other, and they may be arranged in a positional relationship with a slight offset. [Explanation of symbols]

[0060] 1...image forming apparatus / 3...fixing device (fixing section) / 3a...conveying path (first conveying path) / 4b...conveying path (second conveying path) / 4c...re-conveying path (third conveying path) / 25...air blowing section / 27...air blowing fan / 24...secondary transfer roller (transfer section) / 29...suction fan (suction section) / 30...case / 31...pair of fixing rollers (pair of fixing rotors) / 42...pair of fixing discharge rollers (pair of first rotors) / 45...pair of discharge reversing rollers (pair of second rotors) / C...opening (fourth opening) / D1...opening (first opening) / D2...opening (fifth opening) / F1...opening (sixth opening) / F 2...Opening (second opening) / G1...Transport guide (first guide member, lower guide member) / G1a, G2a...Guide surface (one guide surface of the second transport path) / GD1...Duct (air supply duct) / GW1...Ventilation section / G2...Transport guide (first guide member, upper guide member) / G2a, G1b...Guide surface (one guide surface of the third transport path) / G3...Transport guide (second guide member) / G3A...Upper section / G3a...Guide surface (the other guide surface of the third transport path) / H...Opening (third opening) / Pa...Elastic plate (partition member) / S...Sheet / da...Gap

Claims

1. A transfer unit that transfers an image onto a sheet; a fixing section for heating the sheet to fix the image transferred by the transfer section; a first rotor pair disposed downstream of the fixing unit in a sheet conveying direction, capable of conveying a sheet, and in a state of contact over an entire width in a width direction perpendicular to the sheet conveying direction when the sheet is not being conveyed; a second pair of rotors arranged downstream of the first pair of rotors in a sheet transport direction and capable of transporting a sheet by reversing the sheet with respect to the sheet transport direction; a first conveying path that guides a sheet from the fixing unit to the first pair of rotating bodies; a second conveying path that guides a sheet from the first pair of rotating bodies to the second pair of rotating bodies; a third conveying path that guides the sheet inverted by the second rotating body pair toward the transfer unit; a first guide member forming one guide surface of the second transport path and one guide surface of the third transport path; a second guide member having an upper portion disposed above the first guide member and forming the other guide surface of the third transport path; a blower that blows air toward the first transport path, the first guide member has a first opening communicating with the first transport path, and a second opening disposed above the first opening, communicating with the first opening and communicating with the third transport path; the second guide member is disposed in the upper portion and faces the second opening, and has a third opening communicating with the third transport path; 1. An image forming apparatus comprising:

2. The third opening is disposed at a position where it at least partially overlaps with the second opening in the up-down direction.

2. The image forming apparatus according to claim 1,

3. the air blowing section includes an air blowing fan that blows air, and an air blowing duct that guides the air from the air blowing fan in the width direction and discharges it toward the first transport path, The first guide member has therein a ventilation section that ventilates the ventilation duct and the first opening and the second opening.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

4. The air supply duct has a fourth opening portion that opens below the first pair of rotors and between the first pair of rotors and one of the rotors.

4. The image forming apparatus according to claim 3.

5. The fixing unit includes a pair of fixing rotors that heat a sheet to fix an image thereon, and a case that contains the pair of fixing rotors; the first guide member is disposed above the case with a gap therebetween, The first opening is disposed opposite the case.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus further comprises a first fixing unit.

6. a partition member that separates the gap between the first guide member and the case from the third transport path; 6. The image forming apparatus according to claim 5,

7. the first guide member includes a lower guide member having the first opening, and an upper guide member having the second opening and disposed above the lower guide member; the lower guide member has a fifth opening disposed above the first opening and communicating with the first opening, the upper guide member has a sixth opening disposed opposite the second opening and communicating with the second opening; 7. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

8. a suction section communicating with the third opening for suctioning air; 8. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises:

Images