Patent Publication Number: US-11042113-B2

Title: Image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus including a fixing means for fixing an image on a sheet by heating the sheet. 
     In an image forming apparatuses of a laser beam type, such as a printer, a facsimile machine or a multi-function machine, a toner image is transferred onto a sheet and thereafter is heated and pressed by a fixing device, so that the image is fixed on the sheet. From the sheet heated by the fixing device, water vapor generates in some instances, and this water vapor is cooled by a guiding surface forming a feeding passage, so that dew condensation occurs on the guiding surface in some instances. Then, when a water droplet generated by the dew condensation on the guiding surface is deposited on the sheet fed, a feeding resistance increases and causes a sheet (paper) jam, and in the case where double-side printing, improper transfer occurs locally in some instances, and image non-uniformity occurs due to generation of creases of the sheet in some instances. 
     Therefore, a constitution in which a pair of rollers contacting each other over a full width is provided on a side downstream of the fixing device with respect to a sheet feeding direction and air between the fixing device and the roller pair is discharged and thus dew condensation of water vapor on a guiding plate provided on a side downstream of the roller pair with respect to the sheet feeding direction is intended to be suppressed has been proposed (Japanese Laid-Open Patent Application (JP-A) 2007-86509). Further, a constitution in which a pair of rollers contacting each other over a full width is provided onto a side downstream of the fixing device with respect to the sheet feeding direction similarly as in the above-described constitution and air blowing and air discharging are carried out on a side downstream of the roller pair with respect to the sheet feeding direction and thus the dew condensation on a guiding plate provided on the side downstream of the roller pair with respect to the sheet feeding direction is intended to be suppressed has also been proposed (JP-A 2012-194462). 
     Incidentally, in recent years, diversification of sheet materials capable of being used in the image forming apparatus has been required. Particularly, when the sheet material with a large basis weight is intended to be used in the image forming apparatus, water content of the sheet material increases, so that water vapor in a large amount is given off of the sheet material heated by the fixing device. For that reason, it has been desired that a degree of the dew condensation on the guiding plate is efficiently reduced. 
     SUMMARY OF THE INVENTION 
     A principal object of the present invention is to provide an image forming apparatus capable of efficiently reducing a degree of dew condensation occurring on a side downstream of a fixing means with respect to a sheet feeding direction. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: a fixing portion configured to fix an image on a sheet by heating the sheet; a first guiding portion provided downstream of the fixing portion with respect to a sheet feeding direction and configured to form a first feeding passage along which the sheet is fed; a second guiding portion provided downstream of the first feeding passage with respect to the sheet feeding direction and configured to form a second feeding passage along which the sheet is fed; a first rotatable member pair provided between the first guiding portion and the second guiding portion with respect to the sheet feeding direction and configured to feed the sheet, wherein the first rotatable member pair includes one rotatable member and the other rotatable member which are in contact with each other over a full width of the first feeding passage with respect to a widthwise direction perpendicular to the sheet feeding direction in a state in which the first rotatable member pair does not feed the sheet; an air discharging portion configured to discharge air from the first feeding passage to an outside of a main assembly of the image forming apparatus; and a second rotatable member pair provided downstream of the second guiding portion with respect to the sheet feeding direction, wherein the second rotatable member pair includes one rotatable member and the other rotatable member which are in contact with each other over a full width of the second feeding passage with respect to the widthwise direction in a state in which the second rotatable member pair does not feed the sheet. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view showing entirety of an image forming apparatus according to a first embodiment. 
         FIG. 2  is a schematic perspective view showing from a fixing device to a discharging roller pair in the first embodiment. 
         FIG. 3  is a schematic perspective view showing from a fixing device to a discharging roller pair in a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     In the following, an image forming apparatus according to a first embodiment of the present invention will be described with reference to the drawings. The image forming apparatus includes a printer, a copying machine, a facsimile machine and a multi-function machine and forms an image on a sheet used as a recording medium on the basis of image information inputted from an external PC (personal computer) or image information read from an original. The sheet used as the recording medium includes papers such as plain paper and thick paper, plastic films such as a sheet for an overhead projector, sheets having particular shapes, such as an envelope and index paper, and a cloth. 
       FIG. 1  is a schematic sectional view showing entirety of an image forming apparatus  100  according to the first embodiment. In an apparatus main assembly  101  of the image forming apparatus  100 , as an example of an image forming means, an image forming portion  102  of an electrophotographic type is mounted. The image forming portion  102  is an electrophotographic unit of a so-called intermediary transfer tandem type in which four image forming units  140  for forming toner images of four colors of yellow (Y), magenta (M), cyan (C) and black (Bk) are provided along an intermediary transfer belt  145 . 
     The image forming portion  102  includes the image forming units  140 , the intermediary transfer belt  145 , an inner secondary transfer roller  131  and an outer secondary transfer roller  132 . Each of the image forming units  140  includes a photosensitive drum  141  as a photosensitive member, a developing device  143 , a primary transfer device  144 , a charging device  146 , and a cleaning device  147 . The photosensitive drum  141  of each of the image forming units  140  is constituted so as to be irradiated with laser light emitted from an exposure device  142  provided at a lower portion of the apparatus main assembly  101 . When the image forming process is started, the photosensitive drum  141  electrically charged uniformly in advance by the charging device  146  is irradiated with the laser light emitted from the exposure device  142 , so that the photosensitive drum  141  is exposed to the laser light. At this time, the exposure device  142  has already received a signal (video signal) corresponding to data of an image to be printed and emits laser light modulated depending on the video signal, and the photosensitive drum  141  is irradiated with the laser light through an optical system including a polygon mirror. As a result, an electrostatic latent image corresponding to the image data is formed on a surface of the photosensitive drum  141 . 
     The developing device  143  supplies toner to the electrostatic latent image formed on the photosensitive drum  141 , so that the latent image is visualized (developed) into a toner image. Thereafter, a predetermined pressing force and a predetermined electrostatic load bias are applied by the primary transfer device  144 , so that the toner image is primary-transferred from the photosensitive drum  141  onto the intermediary transfer belt  145 . Incidentally, residual toner remaining on the photosensitive drum  141  after primary transfer is collected by the cleaning device  147 , so that a drum surface of the photosensitive drum  141  is cleaned. 
     The intermediary transfer belt  145  is rotationally driven in an arrow R 1  direction of  FIG. 1 . A toner image forming operation described above is performed in parallel in the respective image forming units  140 . Further, primary transfer of the toner images onto the intermediary transfer belt  145  is carried out so that the toner image formed by the image forming unit  140  on a downstream side is superposed on the toner image formed by the image forming unit  140  on an upstream side. As a result, consequently, a full-color toner image is formed on the intermediary transfer belt  145  and is carried by the intermediary transfer belt  145 , and thus is fed toward a secondary transfer portion  130  as a transfer portion. 
     The secondary transfer portion  130  is a nip formed by the inner secondary transfer roller  131  and the outer secondary transfer roller  132  which oppose each other, and the toner image is transferred from the intermediary transfer belt  145  onto a sheet S while the sheet S is nipped and fed. That is, a predetermined pressing force and an electrostatic load bias are applied by the outer secondary transfer roller  132 , so that the toner images are transferred from the intermediary transfer belt  145  onto the sheet S. 
     Thereafter, the sheet S is fed toward a fixing device  150  as a fixing means for heating the toner image under application of heat and pressure. The fixing device  150  includes a heating belt  151  as a rotatable heating member in which an unshown heater is incorporated and a pressing roller  152  as a rotatable pressing member pressed against the heating belt  151 . The fixing device  150  applies heat and pressure to the toner images while nipping and feeding the sheet S by these heating belt  151  and pressing roller  152 . As a result, the toner is melted and thereafter is solidified, so that the toner is fixed on the sheet S and thus the image is fixed on the sheet S. 
     On the other hand, the sheet used as the recording medium is supplied to the image forming portion  102  by a sheet feeding device  110 . The sheet feeding device  110  includes a cassette  111  including a lift-up device moving upward and downward in a state in which the sheets S are stacked and includes a feeding roller pair  112  for feeding the sheets S one by one from the cassette  111 . The sheet S fed by the feeding roller pair  112  is fed toward a registration roller pair  121  through a feeding passage. The registration roller pair  121  corrects oblique movement of the sheet S and then feeds the sheet S toward the secondary transfer portion  130  at timing determined in synchronism with the toner image forming operation by the image forming portion  102 . 
     The sheet S on which the toner image is transferred at the secondary transfer portion  130  and then is fixed as a fixed image by the fixing device  150  passes through a feeding passage  181  and is fed by a fixing discharging roller pair  122 , and then reaches a branch portion where a first switching flap F 1  is provided. The first switching flap F 1  guides the sheet S to either one of a feeding passage  182  toward a first discharging roller pair  160  which is a first rotatable discharging member pair and a feeding passage  183  toward a second discharging roller pair  161  which is a second rotatable discharging member pair (another rotatable discharging member pair). The sheet S fed toward the feeding passage  182  is fed to the first discharging roller pair  160  by the fixing discharging roller pair  122 . The sheet S reached the first discharging roller pair  160  is discharged by the first discharging roller pair  160  onto a first discharge tray  170  provided at an upper portion of the apparatus main assembly  101 . 
     On the other hand, the sheet S fed toward the feeding passage  183  is fed along the feeding passage  184  by a branch feeding roller pair  124  as a branch rotatable member pair and is fed to the second discharging roller pair  161  disposed at a position above (different from) a position of the first discharging roller pair  160 . 
     The sheet S reached the second discharging roller pair  161  is discharged as it is by the second discharging roller pair  161  onto a second discharge tray  171  provided over the first discharge tray  170  or is reversed and fed by a reversing operation of the second discharging roller pair  161  in the case where double-side printing is carried out. In the case where the double-side printing is carried out, the reversed sheet S is guided by a second switching flap F 2  to a double-side (printing) feeding passage  185  as a re-feeding passage formed by a re-feeding guiding means  250 . The sheet S guided to the double-side feeding passage  185  is turned upside down and is fed again to the registration roller pair  121  by double-side (printing) feeding roller pairs  172 ,  173  and  174 . The sheet S reached the registration roller pair  121  is discharged onto either one of the discharge trays  170  and  171  after an image is formed on a second surface in a step similar to the step for a first surface on which the image has already been formed. 
     [Feeding Path from Fixing Device to a First Discharging Roller Pair and Structure of Air Discharging Device] 
     Then, a feeding path from the fixing device  150  to the first discharging roller pair  160  and a structure of an air discharging device  300  will be described with reference to  FIG. 2 . As shown in  FIG. 2 , from the fixing device  150  toward a downstream side with respect to the sheet feeding direction, the feeding passage  181  as a first feeding passage, the fixing discharging roller pair  122  as a first rotatable member pair, the feeding passage  182  as a second feeding passage, and the first discharging roller pair  160  as a second rotatable member pair are disposed. 
     The feeding passage  181  is formed as a feeding passage along which the sheet is fed by a first guiding means  200  including a pair of guiding members  201  and  202  which oppose each other and which are formed in a plate-like shape. The guiding member  201  is disposed on a side where the heating belt  151  of the fixing device  150  is disposed relative to the feeding passage  181 . Further, the guiding member  201  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the heating belt  151  with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. Further, the guiding member  201  is disposed so that a downstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of a driving roller  122 A of the image form discharging roller pair  122  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. 
     On the other hand, the guiding member  202  is disposed on a side where the pressing roller  152  of the fixing device  150  is disposed relative to the feeding passage  181 . Further, the guiding member  202  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the pressing roller  152  with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. Further, the guiding member  202  is disposed so that a downstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of a follower roller  122 B of the image form discharging roller pair  122  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. Further, on a side opposite from the feeding passage  181  of the guiding member  202 , not only an air discharging duct  301  of the air discharging device  300  as an air discharging means described later is provided, but also the guiding member  202  is provided with a plurality of through holes, so that an inside of the feeding passage  181  and an inside of the air discharging duct  301  communicate with each other. 
     The above-described fixing discharging roller pair  122  includes the driving roller  122 A and the follower roller  122 B as a pair of rotatable members. Each of these driving roller  122 A and follower roller  122 B is formed with, for example, a single cylindrical-shaped member made of a rubber, and those rollers are disposed so that opposite ends thereof are positioned outside opposite ends of the feeding passage  181  with respect to a widthwise direction perpendicular to the sheet feeding direction. That is, the driving roller  122 A and the follower roller  122 B form a nip in which entire portions (full widths) thereof with respect to the widthwise direction are in a contact state in a state in which the sheet is not fed through the nip and are disposed over a full width of the feeding passage  181  ranging between the opposite ends of the feeding passage  181 . By this, the feeding passage  181  and the feeding passage  182  are blocked by the fixing discharging roller pair  122  and are constituted so as to be in a blocked state in which the air does not directly flow through the nip therebetween although the air leaks through a gap formed due to a component tolerance or the like. 
     The feeding passage  182  is formed as a feeding passage along which the sheet is fed by a second guiding means  210  including a pair of guiding members  211  and  212  and a pair of guiding members  211  and  213  which oppose each other and which are formed in a plate-like shape. The guiding member  211  is disposed on a side where the heating belt  151  of the fixing device  150 , the guiding member  201  and the driving roller  122 A of the fixing discharging roller pair  122  are disposed relative to the feeding passage  182 . Further, the guiding member  211  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the driving roller  122 A with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. Further, the guiding member  211  is disposed so that a downstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of a driving roller  160 A of the first discharging roller pair  160  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. 
     On the other hand, the guiding member  212  is disposed on a side where the pressing roller  152  of the fixing device  150 , the guiding member  202  and the follower roller  122 B of the fixing discharging roller pair  122  are disposed relative to the feeding passage  182 . Further, the guiding member  212  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the follower roller  122 B with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. Further, the guiding member  212  is continuously connected to a guiding member forming the feeding passage  183  ( FIG. 1 ) as the branch feeding passage at an end portion thereof positioned on a downstream side with respect to the sheet feeding direction. 
     Further, the guiding member  213  is disposed on a side where the pressing roller  152  of the fixing device  150 , the guiding member  202 , the follower roller  122 B of the fixing discharging roller pair  122 , the guiding member  212  and the first switching flap F 1  are disposed relative to the feeding passage  182 . Further, the guiding member  213  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the first switching flap F 1  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. Further, the guiding member  213  is disposed so that a downstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of a follower roller  160 B of the first discharging roller pair  160  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. 
     The above-described first discharging roller pair  160  includes the driving roller  122 A and the follower roller  160 B as a pair of rotatable members. Each of these driving roller  160 A and follower roller  160 B is formed with, for example, a single cylindrical-shaped member made of a rubber, and those rollers are disposed so that opposite ends thereof are positioned outside opposite ends of the feeding passage  182  with respect to the widthwise direction. That is, the driving roller  160 A and the follower roller  160 B form a nip in which entire portions (full widths) thereof with respect to the widthwise direction are in a contact state in a state in which the sheet is not fed through the nip and are disposed over a full width of the feeding passage  182  ranging between the opposite ends of the feeding passage  181 . By this, the feeding passage  182  and the outside of the apparatus main assembly  101  are blocked by the first discharging roller pair  160  and are constituted so as to be in a blocked state in which the air does not directly flow through the nip therebetween although the air leaks through a gap formed due to a component tolerance or the like. Incidentally, the driving roller  160 A and the follower roller  160 B are disposed in the neighborhood of a main assembly cover  101 C constituting an outer casing of the apparatus main assembly  101  with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. By this, the blocked state between the feeding passage  182  and the outside of the apparatus main assembly  101  is enhanced. 
     Incidentally, as shown in  FIG. 1 , the branch feeding roller pair  124  is disposed on a side downstream of the feeding passage  183  with respect to the sheet feeding direction and on a side upstream of the feeding passage  184  with respect to the sheet feeding direction. Also as regards this branch feeding roller pair  124 . Each of these driving roller  124 A and follower roller  124 B as a pair of rotatable members is formed with, for example, a single cylindrical-shaped member made of a rubber, and those rollers are disposed so that opposite ends thereof are positioned outside opposite ends of the feeding passage  182  with respect to the widthwise direction. That is, the branch feeding roller pair  124  forms a nip in which entire portions (full widths) thereof with respect to the widthwise direction are in a contact state in a state in which the sheet is not fed through the nip and are disposed over full widths ranging between the opposite ends of the feeding passages  183  and  184 . By this, the feeding passage  183  and the feeding passage  184  are blocked by the branch feeding roller pair  124  and are constituted so as to be in a blocked state in which the air does not directly flow through the nip therebetween although the air leaks through a gap formed due to a component tolerance or the like. 
     In summary, the feeding passage  182  and the feeding passage  183  are put in the blocked state by the fixing discharging roller pair  122 , the first discharging roller pair  160  and the branch feeding roller pair  124 , and are particularly constituted so that the air does not readily flow (more) to the feeding passage  181  and the outside of the apparatus main assembly  101 . 
     Incidentally, in this embodiment, the air is blocked by the branch feeding roller pair  124 , but the branch feeding roller pair  124  may also be constituted by a plurality of comb-(teeth) shaped rollers provided at a plurality of positions with respect to an axial direction. In this case, irrespective of the branch feeding roller pair  124 , the feeding passage  183  and the feeding passage  184  are in a communication state with each other in terms of a flow of the air. However, the second discharging roller pair  161  can be constituted by the driving roller  161 A and the follower roller  161 B which are a pair of rotatable members forming a nip in which these rollers are in a contact state over full widths thereof in a state in which the sheet is not fed through the nip. By this, the feeding passages  182 ,  183  and  184  are put in the blocked state by the fixing discharging roller pair  122 , the first discharging roller pair  160  and the second discharging roller pair  161  and are particularly constituted so that the air does not readily flow to the feeding passage  181  and the outside of the apparatus main assembly  101 . 
     Then, the structure of the air discharging device  300  will be described. As shown in  FIG. 2 , the air discharging device  300  discharging the air of the feeding passage  181  to the outside includes the air discharging duct  301  and an air discharging fan device  302  connected to an opening  301   e  of the air discharging duct  301 . The air discharging duct  301  includes a lower wall  301   a , a side wall  301   b , an upper wall  301   c  and a side end wall  301   d . The air discharging duct  301  is formed in a cylindrical shape with respect to the widthwise direction by the guiding member  202 , the lower wall  301   a , the side wall  301   b  and the upper wall  301   c , and a font-side end which is one of opposite ends of the air discharging duct  301  with respect to the widthwise direction is closed by the side end wall  301   d . For this reason, a rear-side end which is the other one of the opposite ends with respect to the widthwise direction constitutes an opening  301   e  through which the air discharging fan device  302  is connected to the air discharging duct  301 . The air discharging fan device  302  includes a fan  303 , and the fan  303  discharges the air of the feeding passage  181  to the outside of the apparatus main assembly  101 , i.e., toward the rear surface side of the apparatus main assembly  101  at an air velocity Vo through the inside of the air discharging duct  301 . 
     [Flow of Water Vapor and Reduction of Dew Condensation] 
     Then, in the image forming apparatus  100  according to the first embodiment, a flow of water vapor generating from the sheet S heated by the fixing device  150  and reduction in degree of dew condensation in a second guiding means  210  will be described. It has been known that from the sheet S heated and pressed by the heating belt  151  and the pressing roller  152  of the fixing device  150 , the water vapor is liable to generate from a surface opposite from a surface on a side where the sheet S is pressed by the heating belt  151 , i.e., from a side where the pressing roller  152  is disposed. 
     As shown in  FIG. 2 , when the sheet S heated by the fixing device  150 , the water vapor generates (is emitted) from the side where the pressing roller  152  in the feeding passage  181  is disposed, but the water vapor is sucked by the air discharging device  300  and is discharged to the outside of the pressing roller  152 . That is, the water vapor in the feeding passage  181  is discharged, whereby the water vapor does not readily diffuse into the feeding passage  182 . Incidentally, when the air is discharged by the air discharging device  300 , a constitution in which the air is easily sucked from a side upstream of the feeding passage  181  with respect to the sheet feeding direction, i.e., from the fixing device  150  side is employed, and thus a constitution in which a flow of the air in the feeding passage  182  does not readily generate is employed. 
     Thereafter, the heated sheet S is fed to the feeding passage  182  by the fixing discharging roller pair  122  or is fed from the feeding passage  182  to the feeding passage  183  by switching of the first switching flap F 1 . These feeding passages  182  and  183  are constituted so as not to readily cause the flow of the air by the fixing discharging roller pair  122 , the first discharging roller pair  160  and the branch feeding roller pair  124  as described above. For that reason, these feeding passages  182  and  183  are increased in temperature by the heated sheet S, but the feeding passages are in the blocked state and a lowering in temperature due to cooling by the air from the outside of the apparatus main assembly  101  or from another portion of the inside of the apparatus main assembly  101  is intended to be prevented. Accordingly, even when the water vapor is continuously emitted from the sheet S, prevention of cooling of the water vapor in the feeding passage  182  or in the feeding passage  183  is realized, so that a degree of occurrence of the dew condensation on the guiding members  211 ,  212  and  213  is reduced. 
     Incidentally, although the feeding passages  182  and  183  are in the blocked state, as described above, there are slight gaps between the guiding members  211 ,  212  and  213  and the associated roller pair consisting of the fixing discharging roller pair  122 , the first discharging roller pair  160  and the branch feeding roller pair  124 . For that reason, the water vapor emitted to the feeding passage  182  and the feeding passage  183  does not cause dew condensation but is gradually discharged to the outside of these feeding passages  182  and  183 . 
     As described above, according to the image forming apparatus  100  of the first embodiment, the lowering in temperature of the feeding passage  182  is suppressed, and in combination with the discharge of the water vapor in the feeding passage  181  by the air discharging device  300 , it is possible to reduce the degree of the occurrence of the dew condensation particularly in the feeding passage  182 . 
     Second Embodiment 
     Then, a second embodiment in which the above-described first embodiment is partly changed will be described. Incidentally, in description of the second embodiment, portions similar to those in the above-described first embodiment are represented by the same reference numerals or symbols and will be omitted from description. 
     Compared with the first embodiment, an image forming apparatus  100  according to the second embodiment roughly further includes a pre-discharging roller pair  123  which is a rotatable feeding roller pair and an air blowing device  400 . Further, between the air discharging device  300  and the air blowing device  400 , a blocking portion  500  is provided. By this, with respect to the sheet feeding direction, the feeding passage  181  as the first feeding passage is provided on a side downstream of the fixing device  150  and upstream of the fixing discharging roller pair  122 . Further, with respect to the sheet feeding direction, a feeding passage  186  as a second feeding passage is provided on a side downstream of the fixing discharging roller pair  122  and upstream of the pre-discharging roller pair  123 , and a feeding passage  187  as a third feeding passage is provided on a side downstream of the pre-discharging roller pair  123  and upstream of the first discharging roller pair  160 . 
     As described above, the feeding passage  181  is formed by a pair of guiding members  201  and  202 , of a first guiding means  200 , opposed to each other and formed in a plate-like shape. Further, the feeding passage  186  is formed by a pair of guiding members  221  and  222 , of a second guiding means  220 , opposed to each other and formed in a plate-like shape. Further, the feeding passage  187  is formed by a pair of guiding members  231  and  233  and a pair of guiding members  231  and  232 , of a third guiding means  230 , opposed to each other and formed in a plate-like shape. Incidentally, similarly as in the first embodiment, the feeding passage  187  is connected to the feeding passage  183  ( FIG. 1 ) which is the branch feeding passage, and a part of the guiding member  233  opposes the guiding member  231  and a remaining part of the guiding member  233  forms the feeding passage  183 . 
     Specifically, the guiding member  221  is disposed on a side where the heating belt  151  of the fixing device  150 , the guiding member  201  and the driving roller  122 A of the fixing discharging roller pair  122  are disposed relative to the feeding passage  186 . Further, the guiding member  221  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the driving roller  122 A with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. Further, the guiding member  221  is disposed so that a downstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of a driving roller  123 A of the pre-discharging roller pair  123  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. 
     On the other hand, the guiding member  222  is disposed on a side where the pressing roller  152  of the fixing device  150 , the guiding member  202  and the follower roller  122 B of the fixing discharging roller pair  122  are disposed relative to the feeding passage  186 . Further, the guiding member  222  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the follower roller  123 B with a gap (for example, about 1 mm) formed in consideration of a component tolerance or the like. Further, on a side opposite from the feeding passage  186  of the guiding member  222 , the blocking portion  500  described later is disposed. 
     The pre-discharging roller pair  123  includes the driving roller  123 A and a follower roller  123 B as a pair of rotatable members. Each of the driving roller  123 A and the follower roller  123 B is formed with, for example, a single cylindrical-shaped member made of a rubber, and these rollers are disposed so that opposite ends thereof are positioned outside opposite ends of the feeding passages  186  and  187  with respect to the widthwise direction. That is, the driving roller  125 A and the follower roller  123 B from a nip in which entire portions (full widths) thereof with respect to the widthwise direction are in a contact state in a state in which the sheet S is not fed through the nip and are disposed over full widths ranging between the opposite ends of the feeding passage  186  and  187 . By this, the feeding passages  186  and  181  are blocked by the fixing discharging roller pair  122 , and the feeding passages  186  and  187  are blocked by the pre-discharging roller pair  123 . Accordingly, the feeding passage  186  is constituted so as to be in a blocked state in which the air does not directly flow through the nip although the air leaks through a gap formed due to a component tolerance or the like. 
     The above-described guiding member  231  is disposed on a side where the heating belt  151  of the fixing device  150 , the guiding member  201 , the driving roller  122 A of the fixing discharging roller pair  122 , the guiding member  221  and the driving roller  123 A of the pre-discharging roller pair  123  are disposed relative to the feeding passage  187 . Further, the guiding member  231  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the driving roller  123 A with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. Further, the guiding member  231  is disposed so that a downstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the driving roller  160 A of the first discharging roller pair  160  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. 
     Further, the guiding member  233  is disposed on a side where the pressing roller  152 , the guiding member  202 , the follower roller  122 B of the fixing discharging roller pair  122 , the guiding member  222 , the follower roller  123 B of the pre-discharging roller pair  123  and the first switching flap F 1  are disposed relative to the feeding passage  187 . Further, the guiding member  233  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the follower roller  123 B of the pre-discharging roller pair  123  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. Further, on a side opposite from the feeding passage  187  of the guiding member  233 , not only an air blowing duct  401  of the air blowing device  400  as an air blowing means described later is provided, but also the guiding member  233  is provided with a plurality of through holes, so that the feeding passage  187  and the inside of the air blowing duct  401  communicate with each other through the through holes. 
     On the other hand, the guiding member  232  is disposed on a side where the pressing roller  152  of the fixing device  150 , the guiding member  202 , the follower roller  122 B of the fixing discharging roller pair  122 , the guiding member  222  and the follower roller  123 B of the pre-discharging roller pair  123  are disposed relative to the feeding passage  187 . Further, the guiding member  232  is disposed so that an upstream end portion thereof with respect to the sheet feeding direction extends to the neighborhood of the first switching flap F 1  with a gap (for example, about 1 mm) formed in consideration of the component tolerance or the like. 
     Each of the driving roller  160 A and the follower roller  160 B of the first discharging roller pair  160  in the second embodiment is constituted by juxtaposing a plurality of rollers along an axial direction. For example, the follower roller  160 B is constituted in the form such that a plurality of rollers  160 Ba are supported on a shaft  160 Bb. Incidentally, although illustration is omitted, the plurality of rollers of the driving roller  160 A are provided at the same positions as the positions of the plurality of rollers  160 Ba of the follower roller  160 B and are in contact with the rollers  160 Ba of the follower roller  160 B, respectively, so that a plurality of nips are formed. That is, the driving roller  160 A and the follower roller  160 B form a plurality of gaps between the associated opposing rollers thereof, so that a structure such that the air flows through the gaps is formed. That is, the feeding passage  187  communicates with the outside of the apparatus main assembly  101  through the opening of the main assembly cover  101 C of the apparatus main assembly  101 . 
     In the second embodiment, the branch feeding roller pair  124  and the second discharging roller pair  161  ( FIG. 1 ) are also constituted so as to include a plurality of rollers similarly as in the case of the first discharging roller pair  160 . Accordingly, the feeding passage  183  and the feeding passage  184  also communicate with each other through the opening of the main assembly cover  101 C of the apparatus main assembly  101 . 
     The air discharging device  300  in the second embodiment is formed in an L-shape as seen in the widthwise direction. That is, the air discharging device  300  includes an upper wall  301   g  on a side upstream of the follower roller  122 B of the fixing discharging roller pair  122  with respect to the sheet feeding direction, and a side wall  301   f  connecting the upper wall  301   g  and an upper wall  301   c  and opposing the blocking portion  500  described later. The upper wall  301   c  is bonded to a lower wall  401   a  of the air blowing device  400  described later. Accordingly, the air discharging device  300  not only covers the blocking portion  500  described later from two directions but also is connected to the bottom of the air blowing device  400  described later. Incidentally, the upper wall  301   c  may also be omitted, so that the air discharging duct  301  may also be constituted by using the lower wall  401   a  of the air blowing device  400  described later. 
     The blocking portion  500  includes a lower wall  501   a , a side wall  501   b  and a side end wall  501   d  each formed in a wall shape. Incidentally, the blocking portion  500  also includes a side end wall (not shown) on a side opposite from the side end wall  501   d  with respect to the widthwise direction. The lower wall  501   a  of the blocking portion  500  is disposed on a side downstream of the follower roller  122 B of the fixing discharging roller pair  122  with respect to the sheet feeding direction and is connected to the guiding member  222 . Further, the side wall  501   b  is caused to stand so as to opposite the side wall  301   f  of the discharging device  300 , so that an upper end thereof extends to the neighborhood of the lower wall  401   a  of the air blowing device  400  described later. Accordingly, the blocking portion  500  blocks an inside space by a double structure in a region defined by the air discharging duct  301  of the air discharging device  300  and the air blowing duct  401  of the air blowing device  400 . 
     The air blowing device  400  blowing the air to the feeding passage  187  includes the air blowing duct  401  and an air blowing fan device  402  connected to an opening  401   e  of the air blowing duct  401 . The air blowing duct  401  includes a lower wall  401   a , a side wall  401   b , an upper wall  401   c  and a side end wall  401   d . The air blowing duct  401  is formed in a cylindrical shape with respect to the widthwise direction by the lower wall  401   a , the side wall  401   b , the upper wall  401   c  and the guiding member  233 , and a font-side end which is one of opposite ends of the air blowing duct  401  with respect to the widthwise direction is closed by the side end wall  401   d . For this reason, a rear-side end which is the other one of the opposite ends with respect to the widthwise direction constitutes an opening  401   e  through which the air blowing fan device  402  is connected to the air discharging duct  301 . The air blowing fan device  402  includes a fan  403 , and the fan  403  blows the air to the feeding passage  187  and then to the outside of the apparatus main assembly  101  at an air velocity V I  through the inside of the air blowing duct  401  and the plurality of through holes of the guiding member  233 , i.e., from the rear surface side of the apparatus main assembly  101 . [Flow of water vapor and reduction of dew condensation] 
     Then, in the image forming apparatus  100  according to the second embodiment, a flow of water vapor generating from the sheet S heated by the fixing device  150  and reduction in degree of dew condensation in the second guiding means  220  and a third guiding means  230  will be described. Similarly as in the first embodiment from the sheet S heated and pressed by the fixing device  150 , the water vapor is liable to generate from a side where the pressing roller  152  is disposed. 
     As shown in  FIG. 3 , when the sheet S heated by the fixing device  150  the water vapor generates (is emitted) from the side where the pressing roller  152  in the feeding passage  181  is disposed, but the water vapor is sucked by the air discharging device  300  and is discharged to the outside of the pressing roller  152 . That is, the water vapor in the feeding passage  181  is discharged, whereby the water vapor does not readily diffuse into the feeding passage  186 . Incidentally, when the air is discharged by the air discharging device  300 , a constitution in which the air is easily sucked from a side upstream of the feeding passage  181  with respect to the sheet feeding direction, i.e., from the fixing device  150  side is employed, and thus a constitution in which a flow of the air in the feeding passage  186  does not readily generate is employed. 
     Thereafter, the heated sheet S is fed to the feeding passage  186  by the fixing discharging roller pair  122 . The feeding passage  186  is are constituted so as not to readily cause the flow of the air by the fixing discharging roller pair  122  and the pre-discharging roller pair  123  as described above. Further, the blocking portion  500  is disposed outside the guiding member  222  relative to the feeding passage  186 , and in combination with the double structure thereof with the air discharging duct  301  and the air blowing duct  401 , heat transfer does not readily occur. Further, the blocking portion  500  blocks the flow of the air between the discharging roller pair  122  and the pre-discharging roller pair  123 , particularly between the guiding member  202  which is an air inlet portion of the air discharging device  300  and the guiding member  233  which is an air outlet portion of the air blowing device  400 . For that reason, the feeding passage  186  is increased in temperature by the heated sheet S, but the feeding passages are in the blocked state and a lowering in temperature due to cooling by the air from the outside of the apparatus main assembly  101  or from another portion of the inside of the apparatus main assembly  101  is intended to be prevented. Accordingly, even when the water vapor is continuously emitted from the sheet S, prevention of cooling of the water vapor in the feeding passage  186  is realized, so that a degree of occurrence of the dew condensation on the guiding members  221  and  222  is reduced. 
     Further, the sheet S is fed to the feeding passage  187  by the pre-discharging roller pair  123  or is fed from the feeding passage  187  to the feeding passage  183  by switching of the first switching flap F 1 . To the feeding passage  187 , as described above, the air is blown from the air blowing device  400  and passes through the first discharging roller pair  160  and through the branch feeding roller pair  124  and the second discharging roller pair  161 , so that the air in the feeding passages  187 ,  183  and  184  is discharged to the outside of the apparatus main assembly  101 . For this reason, even when the sheet S continuously generates (emits) the water vapor in the feeding passage  187 , the air is discharged from the feeding passages  187 ,  183  and  184 , so that a degree of the occurrence of the dew condensation particularly at the guiding members  231 ,  232  and  233  is reduced. 
     Incidentally, although the feeding passage  186  is in the blocked state, as described above, there are slight gaps between the guiding members  221  and  222  and the associated roller pair consisting of the fixing discharging roller pair  122  and the pre-discharging roller pair  123 . For that reason, the water vapor emitted to the feeding passage  186  does not cause dew condensation but is gradually discharged to the outside of the feeding passage  186 . 
     As described above, also according to the image forming apparatus  100  of the second embodiment, the lowering in temperature of the feeding passage  186  is suppressed, and in combination with the discharge of the water vapor in the feeding passage  181  by the air discharging device  300 , it is possible to reduce the degree of the occurrence of the dew condensation particularly in the feeding passage  186 . Further, the air in the feeding passage  187  is discharged to the outside of the apparatus main assembly  101  by the air blowing device  400 , so that it is also possible to reduce the degree of the occurrence of the dew condensation in the feeding passage  187 . 
     Incidentally, in the above-described first and second embodiments, the constitution in which the air discharging device  300  was disposed only on the pressing roller  152  side relative to the feeding passage  181  was described. However, the present invention is not limited thereto, but a constitution in which the air discharging device is disposed only on the heating belt  151  side relative to the feeding passage  181  or a constitution in which two air discharging devices are disposed on both sides relative to the feeding passage  181 . That is, the air discharging device may only be required that at least one of the guiding members  201  and  202  which form the feeding passage  181  is provided with a through hole and the air discharging device is connected to the guiding member provided with the through hole. 
     Further, in the second embodiment, the constitution in which the air blowing device  400  was disposed only on one side (the pressing roller  152  side) relative to the feeding passage  187  was described. However, the present invention is not limited thereto, but a constitution in which the air blowing device is disposed only on the other side (the heating belt  151  side) relative to the feeding passage  187  or a constitution in which two air blowing devices are disposed on both sides relative to the feeding passage  187 . That is, the air blowing device may only be required that at least one of the guiding members  231  and  233  which form the feeding passage  187  is provided with a through hole and the air discharging device is connected to the guiding member provided with the through hole. 
     Further, in the first and second embodiments, the constitution in which the sheet S can be discharged selectively from the two portions consisting of the first discharging roller pair  160  and the second discharging roller pair  161  was described. However, the present invention is not limited thereto, but for example as in the case of a desk(-top) printer, when the image forming apparatus discharges the sheet from one portion, a constitution in which the feeding passages  183  and  184  and the first switching flap F 1  are not provided may also be employed. In this case, in the first embodiment, the feeding passage  182  is put in the blocked state only by the first discharging roller pair  122  and the first discharging roller pair  160 . Further, in the second embodiment, the air in the feeding passage  187  is discharged only from the first discharging roller pair  160 . 
     Further, in the first and second embodiments, the constitution in which the first switching flap F 1  switches the feeding passage of the sheet was described. However, the present invention is not limited thereto, but a constitution in which an elastic member such as a rubber is provided at a free end portion or a base portion of the first switching flap F 1  and blocks the flow of the air may also be employed. Further, in the second embodiment, a constitution in which the first switching flap F 1  may also be formed in a comb-shape and the air can pass through the comb-shaped portion may also be employed. 
     Further, in the second embodiment, the constitution in which the blocking portion  500  included the lower wall  501   a  and the side wall  501   b  and formed the double structure with the air discharging duct  301  and the air blowing duct  401  was described. However, the present invention is not limited thereto, but a constitution in which the blocking portion  500  is formed by the upper wall  301   g  and the side wall  301   f  of the air discharging duct  301  and the lower wall  401   a  of the air blowing duct  401 , i.e., a constitution of a single structure may also be employed. 
     According to the above-described embodiments, the temperature lowering of the second feeding passage is suppressed and in combination with the discharge of the water vapor in the first feeding passage by the discharging means, the degree of the occurrence of the dew condensation can be reduced. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2019-123256 filed on Jul. 1, 2019, which is hereby incorporated by reference herein in its entirety.