JP2010058980A - Sheet discharging device and image forming device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve rigidity in a discharge direction of a discharged sheet, stabilize a posture at the time of discharge, and improve stackability of discharged sheets.
In a sheet discharge unit including a pair of sheet discharge rollers for discharging a sheet, an outer diameter of a sheet discharge drive roller of the pair of sheet discharge rollers is a width orthogonal to a discharge direction of the discharged sheet. The outer diameter of the straight portion 61, which is the central portion in the direction, is set larger than the outer diameter of the end portions 62a on both sides in the width direction, and the sheet discharge roller pair includes metal shafts 51b and 52b extending in the width direction, respectively. Elastic layers 51a and 52a that are continuously formed to be longer than the width of the maximum size sheet P wound around the metal shafts 51b and 52b, and at least of the elastic layers 51a and 51b. The sheet discharge unit 50 is characterized in that one is made of foam.
[Selection] Figure 2

Description

  The present invention relates to a sheet discharging apparatus of an image forming apparatus that employs an electrostatic recording system, an electrophotographic recording system, and the like, and an image forming apparatus including the same.

  2. Description of the Related Art In recent years, image forming apparatuses have been reduced in size and performance, and an intermediate transfer type full-color image forming apparatus having a configuration as described in Patent Document 1 (particularly, FIG. 1) has been developed. The invention described in Patent Document 1 will be described with reference to FIG.

  As shown in FIG. 5, the image forming apparatus 200 forms a latent image on the photosensitive drum 11 as an image carrier using light, magnetism, electric charge, etc., and exposes the latent image with a developer such as toner. A plurality of image forming units 10 that form visible images by imaging. The image forming apparatus 200 is positioned above the image forming unit 10, and visible images are sequentially transferred from the image forming units 10 to form a plurality of color images, and a plurality of images on the intermediate transfer unit 30. And a secondary transfer roller 36 for transferring the color image to the sheet P. Further, the image forming apparatus 200 fixes a plurality of color images transferred onto the sheet P on the sheet P, and discharges the fixed sheet P out of the image forming apparatus 200. Sheet discharge means 250. Further, below the secondary transfer roller 36 of the image forming apparatus 200, a feeding unit 20 for transporting the sheet P to the secondary transfer unit Te, and a manual feed tray for feeding the sheet P to the feeding unit 20 are provided. 71 and the feeding cassette 21 are arranged.

  The intermediate transfer unit 30 uses an endless belt-shaped intermediate transfer belt 31 that is stretched and rotated by a plurality of rollers, and is close to the plurality of image forming units 10. The intermediate transfer unit 30 is a primary transfer charging device 35 disposed on a position facing the image forming unit 10 with the intermediate transfer unit 30 sandwiched between a visible image formed on the photosensitive drum 11 by the exposure device 6. Primary transfer is performed on the intermediate transfer unit 30. The visible images primarily transferred from the plurality of photosensitive drums 11 are superimposed on the intermediate transfer unit 30 and conveyed to the position of the secondary transfer portion Te to be transferred to the sheet P when the intermediate transfer unit 30 rotates. The

  The visible image on the intermediate transfer unit 30 is secondarily transferred by the secondary transfer roller 36 on the sheet P selected and fed from the manual feed tray 71 or the feeding cassette 21 at the position of the secondary transfer portion Te. Further, fixing is performed in the fixing unit 40. The sheet P on which the image is fixed is discharged out of the image forming apparatus 200 by the sheet discharge unit 250, whereby a full color image is obtained. Further, a sheet discharge tray 60 is disposed downstream of the sheet discharge unit 250 in the sheet conveyance direction, and the sheets P discharged by the sheet discharge unit 250 can be stacked.

  Regarding the sheet discharge means 250, as described in Patent Document 2, a plurality of rollers 502 having a narrow width are arranged side by side in a width direction orthogonal to the discharge direction of the sheet P with respect to a plurality of uneven rollers 501. There is something. The invention described in Patent Document 2 will be described with reference to FIG.

  As shown in FIG. 6, the sheet discharge unit 250 includes a roller 501 having a plurality of irregularities. According to such a sheet discharge means 250, the sheet P can be discharged while the curl of the sheet P is removed and the posture during discharge is always stabilized while the sheet P is seated. The leading end of the discharged sheet P does not push out the already stacked sheet P, and the sheet P is discharged in a well-aligned state.

  On the other hand, regarding the sheet discharging means 250, the sheet discharging roller in which the rubber layer wound around the roller shaft has a length equal to or larger than the width of the sheet P, instead of the roller 501 having the plurality of projections and depressions of Patent Document 2 and FIG. A configuration of Patent Document 3 using a pair is proposed. The invention described in Patent Document 3 will be described with reference to FIG.

  As shown in FIG. 7, according to the sheet discharge means 350, the entire width of the elastic layers of the sheet discharge driving roller 503 and the sheet discharge driven roller 504 are in uniform contact with the sheet P, and the heat is taken away. Therefore, the occurrence of uneven glossiness of the image is prevented. Further, since the edge portion of the roller of the sheet P does not contact, it is possible to prevent the sheet P from being left with a roller mark.

JP 2004-151389 A JP 2006-117365 A JP 2007-223774 A

  However, when a roller 501 having a plurality of irregularities as shown in FIG. 6 is used, the contact of the roller surface with the sheet P becomes non-uniform. In this case, the portion of the sheet P that has passed through the fixing unit 40 is in contact with the surface of the roller and the portion of the sheet P that is not in contact with the sheet P is fixed on the sheet P because the amount of heat of the sheet P taken by the roller surface is different. A difference occurs in the cooling state of the toner image. For this reason, uneven glossiness of the image on the sheet P occurs between the portion where the roller surface is in contact and the portion where the roller surface is not in contact. In particular, in the case of a stiff sheet P such as thick paper, the contact surface and non-contact surface between the sheet P and the roller surface appear clearly, and thus uneven glossiness occurs more remarkably.

  In addition, a plurality of rollers 502 are connected in the width direction, and the sheet P is seated at the edge portion of each roller 502. Therefore, a roller trace is formed at the corner portion of each roller 502 on the sheet P softened by the fixing heat. I will put it on.

  Further, in the sheet discharge means 350 described in Patent Document 3 and FIG. 7 described above, the following problems occur.

  As shown in FIG. 7, the sheet discharge means 350 has a uniform diameter, and includes a sheet discharge roller pair of a sheet discharge driving roller 503 and a sheet discharge driven roller 504 that are continuous rollers in the width direction of the sheet P. . A sheet discharge tray 60 is disposed on the downstream side of the sheet discharge unit 50.

As shown in FIG. 7, the sheet discharge roller pair 505 is a straight roller pair having a uniform outer diameter over the entire length in the width direction, and the sheet discharge roller pair 505 does not have a function of sitting on the sheet P. Therefore, the sheet P1 is discharged onto the sheet discharge tray 60 with the front end portion Pa being substantially linear with the sheet discharge roller pair 505 and curling in the sheet discharge direction. At this time, the sheet P1 is discharged in the direction of the arrow A in such a manner that the entire front end portion Pa (dotted line circle portion) is pressed against the sheet P0 with respect to the sheet P0 already discharged and stacked on the sheet discharge tray 60. Is done. Therefore, the sliding resistance between the sheet P1 and the sheet P0 increases, and the sheet P0 may be pushed out in the direction of the arrow B. Further, the leading edge Pa of the sheet P1 may be caught by the surface property of the sheet P or a minute burr generated at the end when the sheet P is cut, and the sheet P1 may be rounded on the sheet discharge tray 60. As a result, the next discharged sheet cannot be discharged normally, and the possibility that the sheet P1 is pushed out of the sheet discharge tray 60 or jammed becomes extremely high, and the sheet discharge performance is significantly impaired.

  Furthermore, due to the difference in the material of the sheet discharge roller pair 505, the amount of heat taken by the sheet discharge roller pair 505 from the sheet P1 is different between the front surface and the back surface. As a result, the sheet may be easily curled.

  The present invention has been made in view of the above circumstances, and provides a sheet discharge apparatus that has increased rigidity in the sheet discharge direction, a stable posture during discharge, and improved stackability of discharged sheets. Is an issue.

  In order to achieve the above object, the present invention provides a sheet stacking unit for stacking sheets, and a sheet on which a toner image is heated and fixed, sandwiched in a convex shape in a width direction orthogonal to the discharge direction and discharged to the sheet stacking unit. A pair of sheet discharge rollers, and each of the sheet discharge roller pairs includes a rotation shaft extending in a width direction and a width of a maximum size sheet provided on the rotation shaft and passing in the width direction. And an elastic layer formed continuously, and at least one elastic layer is made of a foam.

  According to the present invention, since the sheet is sandwiched and discharged in a convex shape in the width direction by the sheet discharge roller pair, the rigidity in the sheet discharge direction is increased, and the posture during discharge is stabilized and discharged. Improvement of sheet stackability is realized. Further, by forming at least one of the elastic layers of the sheet discharge roller pair as a foam, contact between the sheet and the roller surface becomes uniform, and gloss unevenness can be prevented when an image is fixed on the sheet. Furthermore, since the corners of the rollers do not contact the sheet, there are no roller marks.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 6 is an enlarged side view illustrating a configuration of a sheet discharge unit viewed from the downstream side in the sheet conveyance direction. It is a schematic perspective view which shows the structure of a sheet discharge unit and a sheet discharge tray. FIG. 6 is an enlarged side view illustrating a configuration of a sheet discharge unit used in an image forming apparatus according to a second embodiment of the present invention as viewed from the downstream side in the sheet conveyance direction. It is sectional drawing which shows the structure of the conventional image forming apparatus. FIG. 10 is an enlarged side view illustrating a configuration of a conventional sheet discharge unit. It is a schematic perspective view which shows the structure of the conventional sheet discharge unit and a sheet discharge tray.

(First embodiment)
FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus 100 according to the first embodiment of the present invention. The image forming apparatus 100 is a color image forming apparatus using an electrophotographic image forming process.

  As shown in FIG. 1, the image forming apparatus 100 includes an image forming unit 1a that forms a yellow image and an image forming unit 1b that forms a magenta image. Further, the image forming apparatus 100 includes an image forming unit 1c that forms a cyan image and an image forming unit 1d that forms a black image. The image forming apparatus 100 includes these four image forming units (image forming units). These four image forming units 1a, 1b, 1c, and 1d are arranged in a line at regular intervals. In each of the image forming units 1a, 1b, 1c, and 1d, drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums) 2a, 2b, 2c, and 2d are installed as image carriers that form visible images. ing. Around each of the photosensitive drums 2a, 2b, 2c, and 2d, chargers 3a, 3b, 3c, and 3d, developing devices 4a, 4b, 4c, and 4d, and drum cleaning devices 5a, 5b, 5c, and 5d are installed, respectively. ing. An exposure device 6 is installed below the image forming units 1a, 1b, 1c, and 1d. Each developing device 4a, 4b, 4c, 4d contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is a negatively charged OPC photosensitive member having a photoconductive layer on an aluminum drum base, and is driven in a direction indicated by an arrow (clockwise) by a driving device (not shown). It is rotationally driven at a predetermined process speed. The chargers 3a, 3b, 3c, and 3d as charging means make the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d uniform to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). Charge. The developing devices 4a, 4b, 4c, and 4d develop toner images by attaching toners of respective colors to the electrostatic latent images formed on the photosensitive drums 2a, 2b, 2c, and 2d, respectively (visualization). To do. As a developing method using the developing devices 4a, 4b, 4c, and 4d, for example, toner particles mixed with a magnetic carrier are used as a developer and conveyed by magnetic force, and the photosensitive drums 2a, 2b, 2c, and 2d are used. In contrast, there is a two-component contact development method in which development is performed in contact.

  The primary transfer rollers 34a, 34b, 34c, and 34d as transfer means are constituted by elastic members, and the photosensitive drums 2a, 2b, and the like are respectively connected to each transfer nip portion via an endless belt-shaped intermediate transfer belt 31. 2c and 2d. Here, the primary transfer rollers 34 a, 34 b, 34 c, and 34 d are used as the transfer unit, but a high pressure is applied when the toner image is transferred to the transfer material, and the intermediate transfer belt 31 is in contact with the toner image. A transfer blade may be used.

  The drum cleaning devices 5a, 5b, 5c, and 5d remove and collect the transfer residual toner remaining on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively.

  In the exposure device 6, laser light modulated in accordance with the time series electric digital pixel signal of the image information is output from a laser output unit (not shown). The exposure device 6 exposes the surface of each photosensitive drum 2a, 2b, 2c, 2d via a polygon mirror (not shown) that rotates at high speed. As a result, electrostatic latent images of respective colors corresponding to the image information are formed on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d charged by the chargers 3a, 3b, 3c, and 3d.

  The feeding unit 20 includes a feeding cassette 21, a cassette feeding roller 22 that is a transport unit, registration rollers 23 a and 23 b that are transport units, a manual tray feeding roller 24, and a manual tray 71. The feeding unit 20 selects and feeds the sheet P in the feeding cassette 21 or on the manual feed tray 71 and transports the sheet P to the secondary transfer unit Te that is a transfer unit. The secondary transfer unit Te transfers the visible image formed by the image forming units 1a, 1b, 1c, and 1d to the sheet P.

  In the intermediate transfer unit 30, the intermediate transfer belt 31 is stretched between the driving roller 32 and the tension roller 33, and is rotated (moved) in the direction of the arrow (counterclockwise) by driving the driving roller 32. The intermediate transfer belt 31 is made of a dielectric resin such as a polycarbonate, a polyethylene terephthalate resin film, a polyvinylidene fluoride resin film, or the like. Further, an intermediate transfer belt cleaning device 80 is installed at a position facing the tension roller 33 via the intermediate transfer belt 31. The intermediate transfer belt cleaning device 80 includes a cleaning blade 81 made of an elastic body that comes into contact with the intermediate transfer belt 31 with a predetermined pressure, and a conveyance screw 82 that conveys residual toner removed from the intermediate transfer belt 31 by the cleaning blade 81. With. The residual toner is conveyed by a conveying screw 82 to a toner collecting container (not shown).

  Further, a fixing unit 40 that is a fixing unit including a fixing roller 42 that includes a heat source and a pressure roller 41 is installed on the downstream side of the secondary transfer unit Te. The fixing unit 40 fixes the visible image on the sheet P transferred by the secondary transfer unit Te to the sheet P. Furthermore, a sheet discharge unit 50 that is a sheet discharge device is installed on the downstream side in the conveyance direction of the sheet P. A sheet discharge tray 60 as a sheet stacking unit for stacking sheets P discharged by the sheet discharge unit 50 is disposed further downstream of the sheet discharge unit 50 in the sheet passing direction and above the intermediate transfer unit 30. Yes.

  Next, an image forming operation by the image forming apparatus 100 described above will be described. When an image formation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1a, 1b, 1c, and 1d, which are rotationally driven at a predetermined process speed, are respectively charged by the chargers 3a, 3b, 3c and 3d are uniformly charged to negative polarity. Then, the exposure device 6 converts the image signal of the output image into an optical signal by a laser output unit (not shown), and the laser beam that is the converted optical signal is charged to each of the photosensitive drums 2a, 2b, Electrostatic latent images are formed by scanning exposure on 2c and 2d, respectively.

  First, yellow toner is attached to the electrostatic latent image formed on the photosensitive drum 2a by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied. The toner image is visualized. Then, a yellow toner image is transferred onto the intermediate transfer belt 31 by the primary transfer roller 34a to which a transfer bias (opposite polarity (positive polarity) with respect to toner) is applied in the primary transfer portion Ta.

  The intermediate transfer belt 31 onto which the yellow toner image has been transferred is moved to the image forming unit 1b by the drive roller 32. Also in the primary transfer portion Tb constituted by the image forming portion 1b and the primary transfer roller 34b, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is converted into the yellow toner image on the sheet P. Overlaid on top and transferred. In the same manner, cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1c and 1d on the yellow and magenta toner images superimposed and transferred onto the intermediate transfer belt 31 in the same manner. The images are sequentially overlapped at the next transfer portions Tc and Td. In this way, a full color toner image is formed on the intermediate transfer belt 31.

  Then, the sheet P fed from the feeding cassette 21 or the manual feed tray 71 is transferred by the registration rollers 23a and 23b to 2 by the timing at which the leading edge of the toner image on the intermediate transfer belt 31 is moved to the secondary transfer portion Te. It is conveyed to the next transfer portion Te. Then, a full-color toner image is transferred onto the sheet P by the secondary transfer roller 36 to which a transfer bias (polarity opposite to the toner (positive polarity)) is applied to the sheet P conveyed to the secondary transfer unit Te.

  The sheet P on which the full-color toner image is formed is conveyed to a fixing unit 40 as a fixing unit which is an image heating device. The sheet P is heated and pressed at the fixing nip between the fixing roller 42 and the pressure roller 41 to heat and fix the full color toner image on the surface of the sheet P. Then, the sheet P is placed on the sheet discharge tray 60 outside the apparatus by the sheet discharge unit 50. The sheet is discharged, and a series of image forming operations is completed.

  FIG. 2 is an enlarged side view illustrating the configuration of the sheet discharge unit 50 as viewed from the downstream side in the conveyance direction of the sheet P. As shown in FIG. 2, the sheet discharge unit 50 that is a sheet discharge device includes a sheet discharge drive roller 51 that is one sheet discharge roller of the pair of sheet discharge rollers and a sheet discharge driven roller 52 that is the other sheet discharge roller. . The sheet discharge driving roller 51 is a roller that transmits a driving force of a driving source (not shown). The sheet discharge driven roller 52 faces the sheet discharge drive roller 51 and is pressed and biased to the sheet discharge drive roller 51. The sheet discharge unit 50 is a unit that discharges the sheet P on which the toner image that has passed through the fixing unit 40 is heated and fixed to the outside of the image forming apparatus main body 100a by the rotation of the sheet discharge driving roller 51 and the sheet discharge driven roller 52. .

  The sheet discharge driving roller 51 includes a metal shaft 51b that is a rotating shaft, and an elastic layer 51a wound around the metal shaft 51b. The elastic layer 51a is made of a foam, that is, a resin material such as a foaming rubber material or an elastomer. For example, urethane, NBR, EPDM, or the like is used. The hardness of the rubber material at this time is preferably 20 to 60 (when measured with an Asker C hardness meter) in order to securely grip and convey the sheet. The sheet discharge driving roller 51 is connected to a driving source (not shown) and is configured to be rotatable as a driving roller. The elastic layer 51a is continuously formed in the direction along the metal shaft 51b.

  On the other hand, the sheet discharge driven roller 52 includes a metal shaft 52b, which is a rotation shaft, and an elastic layer 52a wound around the metal shaft 52b. Similarly to the sheet discharge driving roller 51, the elastic layer 52a of the sheet discharge driven roller 52 is made of a foamed material, that is, a resin material such as a foaming rubber material or an elastomer, and for example, urethane, NBR, EPDM, or the like is used. If at least one of the elastic layers of the sheet discharge driving roller 51 and the sheet discharge driven roller 52 is formed of a foam material, the total amount of heat taken from the sheet P is reduced, and the sheet P is discharged while maintaining flexibility. So curling is suppressed. Further, in order to reduce curling, it is desirable that the sheet discharge driving roller 51 is made of the same material or a material having the same thermal conductivity. Also, the hardness of the rubber material is desirably 20 to 60 (when measured with an Asker C hardness meter) in order to securely grip and convey the sheet, similarly to the sheet discharge driving roller 51. The elastic layer 52a is formed continuously in the direction along the metal shaft 52b. Further, the sheet discharge driven roller 52 has pressure springs 54 disposed at both ends of the metal shaft 52b via bearings 53, and is pressed against the sheet discharge drive roller 51 with a predetermined pressure. The spring pressure of the pressure spring 54 at this time is preferably set to about 0.1 to 1 kg so that the transportability of the sheet P can be secured.

  Further, the elastic layer 51 a of the sheet discharge driving roller 51 has a substantially symmetric shape with respect to the center line a which is the center in the width direction of the sheet P. The elastic layer 51a includes a straight portion 61 which is a cylindrical portion having no change in outer diameter, and a tapered portion 62 having a taper amount d1 from both ends of the straight portion 61b to both ends of the elastic layer 51a. Here, the part of the center line a is called at least the central part of the sheet discharge driving roller 51. Here, the portion of the straight portion 61 also corresponds to the central portion of the sheet discharge driving roller 51. Further, in the elastic layer 52a of the sheet discharge driving roller 51, the outer diameter D1 of the central portion is set larger than the outer diameter D2 of both end portions 62a that are both end portions in the width direction.

  If the length L in the axial direction of the straight portion 61 is too long, the effect of the outer diameter difference D1-D2 between the straight portion 61 of the elastic layer 51a and both end portions 62a may be reduced. On the other hand, if it is too short, the balance for holding the sheet P tends to collapse in the axial direction, and the sheet P may be skewed or may not be discharged normally. Therefore, it is desirable that the axial length L of the straight portion 61 is greater than 0 and equal to or less than 1/3 of the width direction length L1 (see FIG. 3) of the maximum size sheet P that can pass. That is, it is desirable that there is a relationship of 0 <L ≦ 1 / 3L1.

  FIG. 3 is a schematic perspective view showing the configuration of the sheet discharge unit 50 and the sheet discharge tray 60. As shown in FIG. 3, the sheet discharge tray 60 is disposed downstream of the sheet discharge unit 50 in the sheet P passing direction. In discharging the sheet P, it is assumed that the sheet P is conveyed based on the central reference regardless of the size of the sheet P.

  According to the sheet discharge unit 50 of the present embodiment, since the sheet discharge drive roller 51 has an outer diameter difference D1-D2 between the straight portion 61 and the end portion 62a, the peripheral speed of the sheet discharge drive roller 51 is different. The straight portion 61 is fast, and the end portion 62a has a slower speed. Accordingly, the sheet discharge speed of the discharged sheet P is also different between the central portion Pb and both end portions Pc, and the central portion Pb at the front end of the sheet is compared with both end portions Pc at the front end of the sheet as shown by an arrow C in FIG. Is discharged at a high speed. Accordingly, the central portion Pb at the leading end of the sheet is in a leading state, and both end portions Pc of the leading end of the sheet are pulled toward the central portion Pb side of the leading end of the sheet, and as a result, slightly lifted along the shape of the tapered portion 62. Will be discharged. Therefore, when the sheet P1 is discharged, the leading end portion of the sheet P1 is discharged while only the central portion Pb of the sheet leading end is in contact with the sheet P0 that has already been discharged onto the sheet discharge tray 60. Yes.

  As described above, according to the image forming apparatus 100 of the first embodiment, the outer diameter of the elastic layer 51 a of the sheet discharge driving roller 51 is formed substantially symmetrically about the center in the width direction of the sheet P, and the straight portion 61. The outer diameter D1 is set larger than the outer diameter D2 of both end portions 62a. And it is formed in a gentle taper shape from the straight part 61 toward the end part 62a. Accordingly, the discharge speed of the sheet P is set to be faster at the straight portion 61 and slower than that at both end portions 62a. Therefore, the sheet P is ejected while being sandwiched in a convex shape in which the central portion Pb is lowered and both end portions Pc are slightly lifted by the sheet ejection roller pair in the width direction orthogonal to the sheet ejection direction. As a result, the rigidity of the sheet in the sheet discharge direction is increased, and the front end of the discharged sheet P1 and the contact area of the already discharged sheet P0 are minimized. As a result, the situation where the discharged sheet P1 is caught by the already discharged sheet P0 and pushed out is suppressed. Also, jamming is suppressed. Furthermore, the dischargeability and stackability of the discharged sheets P are improved. Further, the front end portion of the discharged sheet P is caught and rounded by the surface property of the sheet P already discharged onto the sheet discharge tray 60 or the minute burrs generated at the end portion when the sheet P is cut. It is possible to suppress the phenomenon that occurs. Since the rigidity of the sheet in the sheet discharge direction increases, the sheet may be sandwiched and discharged in a reverse convex shape by the sheet discharge roller pair.

  Both the sheet discharge driving roller 51 and the sheet discharge driven roller 52 have an elastic layer on the outer peripheral side. As a result, when the sheet P passes while the sheet discharge driving roller 51 and the sheet discharge driven roller 52 are pressed against each other, the straight portion 61 of the sheet discharge driving roller 51 is elastically recessed according to the thickness of the sheet P. it can. The elastic layer 51a can contact the sheet P uniformly. As a result, there is no difference in the amount of heat that the surfaces of the sheet discharge driving roller 51 and the sheet discharge driven roller 52 take away from the toner image on the sheet P, and therefore it is possible to prevent the occurrence of uneven glossiness of the image.

  The elastic layer 51a is continuous in the direction along the metal shaft 51b. The edge portion of the elastic layer 51a is not pressed against the softened sheet, and no roller marks are generated, and a high-quality print image is output.

  Both the sheet discharge driving roller 51 and the sheet discharge driven roller 52 have foaming elastic layers 51a and 52a. As a result, since the heat capacities of the sheet discharge driving roller 51 and the sheet discharge driven roller 52 are set small, the total amount of heat taken from the sheet P is reduced, so that the discharged sheet P is cooled and solidified more than necessary. There is no end to it. Since the sheet P is stacked on the sheet discharge tray 60 while maintaining flexibility, the sheet P is cooled in a state following the smooth stacking surface, thereby reducing the occurrence of curling. Since the amount of heat taken away from the sheet P is made uniform between the front and back of the sheet P, undulation and curling of the discharged sheet P are suppressed.

  A sheet discharge driving roller 51 in which the outer diameter of the straight portion 61 is larger than the outer diameter of the end portion 62 a is disposed above the sheet discharge driven roller 52. Accordingly, the sheet P is pressed and discharged from the center position in the width direction on the upper surface of the sheet P. As a result, when the sheet P passes between the sheet discharge driving roller 51 and the sheet discharge driven roller 52, the sheet P is easily discharged in a reverse U-shape. The central position in the width direction of the discharged sheet P1 is not easily caught by the already discharged sheet P0. On the contrary, if the straight portion 61 and the tapered portion 62 are formed on the sheet discharge driven roller 52, the sheet P may be discharged in a U-shape, which is not good.

  Since the length of the straight portion 61 is 1/3 or less of the width direction length L1 of the maximum size sheet P that can pass, the grip force of the sheet P by the sheet discharge driving roller 51 and the sheet discharge driven roller 52 is increased. It is kept moderate. Even in the case of a stiff sheet P such as thick paper, it is possible to securely nip the entire width direction of the sheet P. Therefore, uneven gloss can be prevented. If the length of the straight portion 61 is larger than 1/3 of the maximum width of the sheet P that can be passed, the sheet P has a straight portion 61 in the width direction of the sheet P and both end portions 62a. It is difficult to make a difference in the discharge speed. In addition, when there is no straight portion 61, the balance for holding the sheet P is easily broken in the axial direction, and the sheet P may be skewed or cannot be discharged normally.

  As described above, it is possible to reduce the size and cost of the image forming apparatus 100 while improving the sheet discharge performance of the discharged sheet P while maintaining a high quality print image with a simple configuration. It becomes possible.

  Needless to say, the present embodiment is widely effective for the discharge unit of the image forming apparatus regardless of the developing method and transfer method of the image forming apparatus introduced in the present embodiment.

(Second Embodiment)
FIG. 4 is an enlarged side view showing a configuration of the sheet discharge unit 150 used in the image forming apparatus according to the second embodiment of the present invention as viewed from the downstream side in the sheet P conveyance direction. The sheet discharge unit 150 is different from the first embodiment in that a sheet discharge drive roller 151 is used instead of the sheet discharge drive roller 51. Of the configuration of the sheet discharge unit 150, the same configuration and effects as those of the sheet discharge unit 50 of the first embodiment are denoted by the same reference numerals, and description thereof is omitted as appropriate. In the second embodiment, the image forming apparatus can be employed in the same image forming apparatus as that in the first embodiment, and the description of the image forming apparatus is omitted.

  As shown in FIG. 4, the sheet discharge unit 150 includes a sheet discharge drive roller 151 and a sheet discharge driven roller 52. The sheet discharge driving roller 151 includes a metal shaft 51b and an elastic layer 151a wound around the metal shaft 51b. The elastic layer 151a has a crown shape in which the center in the width direction of the sheet P is the maximum outer diameter D1. The elastic layer 151a is made of a foam, that is, a foamable rubber material, and urethane, NBR, EPDM, or the like is used. The hardness of the rubber material at this time is preferably 20 to 60 (when measured with an Asker C hardness meter) in order to securely grip and convey the sheet P. The sheet discharge driving roller 151 is connected to a driving source (not shown) and is configured to be rotatable as a driving roller.

  On the other hand, the sheet discharge driven roller 52 includes a metal shaft 52b and an elastic layer 52a wound around the metal shaft 52b. The elastic layer 52a of the sheet discharge driven roller 52 is also made of a foaming rubber material like the sheet discharge drive roller 151, and urethane, NBR, EPDM, etc. are used, and the same material or the same heat as the sheet discharge drive roller 151. It is desirable that the material has conductivity. Also, the hardness of the rubber material is desirably 20 to 60 (when measured with an Asker C hardness meter), similarly to the sheet discharge driving roller 151. Further, the sheet discharge driven roller 52 has pressure springs 54 disposed at both ends of the metal shaft 52b via bearings 53, and is pressed against the sheet discharge drive roller 151 with a predetermined pressure. The spring pressure of the pressure spring 54 at this time is preferably set to about 0.1 to 1 kg so that the transportability of the sheet P can be secured.

  The elastic layer 151a of the sheet discharge driving roller 151 has a substantially symmetrical shape with respect to the center line a which is the center in the width direction of the sheet P, and the outer shape is a gentle crown shape with a crown amount d2.

  In the image forming apparatus of the second embodiment, the same effect as that of the image forming apparatus 100 of the first embodiment can be obtained. The elastic layer 151a of the sheet discharge driving roller 151 has a crown shape in which the center in the width direction of the sheet P is the maximum outer diameter D1. As a result, the elastic layer 151a of the sheet discharge driving roller 151 has an additional effect that it can be gently deformed in accordance with the shape of the sheet P in the width direction of the sheet P.

The following configuration changes are possible. Of the elastic layers 51a, 151a, 52a of the sheet discharge driving rollers 51, 151 and the sheet discharge driven roller 52 of the first and second embodiments, at least one of the elastic layers 51a, 151a, 52a located on the printing surface side of the sheet. A tube-shaped resin film may be wound around the outer periphery. According to such a configuration, even if the toner is not completely fused to the sheet P by the fixing unit 40, the toner is prevented from being taken by the elastic layers 51a, 151a, and 52a.

  Further, the elastic layers 51 a and 151 a of the sheet discharge driving rollers 51 and 151 of the first and second embodiments may be set higher in hardness than the elastic layer 52 a of the sheet discharge driven roller 52. According to such a configuration, the elastic layers 51 a and 151 a of the sheet discharge driving rollers 51 and 151 are higher in hardness than the elastic layer 52 a of the sheet discharge driven roller 52. Therefore, the phenomenon that the elastic layers 51a and 151a of the sheet discharge driving rollers 51 and 151 are scraped by the sheet discharge driven roller 52 is suppressed. As a result, the outer diameter difference D1-D2 between the straight portion 61 and the end portion 62a in the sheet discharge driving rollers 51 and 151 is maintained for a long period.

  Furthermore, in the first and second embodiments, the configuration in which the sheet discharging apparatus according to the present invention is incorporated in the image forming apparatus has been described. However, the sheet discharging apparatus may be a finisher that can be connected from the outside of the image forming apparatus. .

1a to 1d ··· Image forming unit 3a to 3d ··· Photoconductor drum (image carrier)
22 ·············· Cassette feeding roller (conveyance unit)
23a, 23b... Registration roller (conveying unit)
40 Fixing unit (fixing part)
50 Sheet discharge unit (sheet discharge section)
51 Sheet discharge drive roller (sheet discharge roller)
51a Elastic layer 51b Metal shaft 52 Sheet discharge driven roller (sheet discharge roller)
52a Elastic layer 52b Metal shaft 61 Straight part (cylindrical part)
62 Tapered portion 62a End portion 100 Image forming apparatus 100a Image forming apparatus main body

Claims (8)

A sheet discharge apparatus comprising: a sheet stacking unit that stacks sheets; and a sheet discharge roller pair that sandwiches a sheet on which a toner image is heated and fixed in a convex shape in a width direction orthogonal to the discharge direction and discharges the sheet onto the sheet stacking unit. In
Each of the sheet discharge roller pairs includes a rotation shaft extending in the width direction, and an elastic layer provided on the rotation shaft and continuously formed longer than the width of the maximum size sheet that can pass in the width direction. A sheet discharging apparatus comprising: at least one elastic layer made of a foam.   The outer diameter of one sheet discharge roller of the pair of sheet discharge rollers is such that the outer diameter of the central portion in the width direction orthogonal to the discharge direction of the discharged sheet is larger than the outer diameter of both end portions in the width direction. The sheet discharging apparatus according to claim 1.   The sheet discharge apparatus according to claim 2, wherein the one sheet discharge roller is disposed above the other sheet discharge roller.   The elastic layer of the one sheet discharge roller has a cylindrical portion whose outer diameter does not change at the center in the width direction, and the length L of the cylindrical portion is the maximum that can pass between the pair of sheet discharge rollers. 0 <L ≦ 1 / 3L1 with respect to the width L1 of the size sheet, and from both widthwise ends of the cylindrical portion toward both widthwise ends of the one sheet discharge roller The sheet discharging apparatus according to claim 2, wherein the sheet discharging apparatus has a tapered shape.   5. The sheet discharge according to claim 2, wherein the elastic layer of the one sheet discharge roller has a crown shape in which the center in the width direction of the sheet has a maximum outer diameter. apparatus.   6. The sheet discharge apparatus according to claim 2, wherein the elastic layer of the one sheet discharge roller has higher hardness than the elastic layer of the other sheet discharge roller.   The tube-shaped resin film is wound around the outer periphery of at least one elastic layer located on the printing surface side of the sheet among the elastic layers of the sheet discharge roller pair. The sheet discharging apparatus according to any one of the above. An image forming unit for forming a toner image;
A fixing unit that heats and fixes the toner image on the sheet formed by the image forming unit to the sheet;
The sheet discharge device according to any one of claims 1 to 7, wherein the sheet that has passed through the fixing unit is discharged.
An image forming apparatus comprising:

Images