JP7087658B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to a method for stabilizing a transport state of a recording medium on the upstream side of an image carrier and a transfer member.

In an image forming apparatus using an electrophotographic method, toner is adhered to an electrostatic latent image formed on an image carrier such as a photoconductor drum to form a toner image, and the toner image is recorded on a sheet-like recording medium such as paper. After transferring to, the toner image on the paper is fixed by the fixing device (fixing portion).

In such an image forming apparatus, since units such as a photoconductor drum and a developer are densely packed from the viewpoint of space saving, the airtightness around the photoconductor drum is high. In the above configuration, for example, the timing at which the front end of the paper enters the nip (transfer nip) between the photoconductor drum and the transfer roller from the resist roller pair, and the rear end of the paper is separated from the resist roller pair nip and the intermediate roller. At the timing and the like, a change in the transport state of the paper (fluttering of the paper or a sudden change in posture) causes a change in the volume of the transport space, and a change in air pressure caused by the change causes an air flow.

When this air flow passes through the gap (development nip) between the photoconductor drum and the developing roller, the toner particles flying from the developing roller to the photoconductor drum are scattered by the developing electric field. As a result, it may adhere to a position deviated from the original adhesion position on the photoconductor drum, and horizontal streaks may occur in a halftone image or a solid image.

On the other hand, if the space between the upper and lower pre-transfer guides arranged on the upstream side of the transfer nip in the paper transport direction is narrowed to suppress the fluttering of the paper, the transport load when transporting strong paper such as thick paper is large. Therefore, there is a possibility that transfer defects such as a decrease in transfer magnification and transfer deviation may occur.

Therefore, regardless of whether plain paper or thick paper is used, a method of suppressing transfer defects by smoothly guiding the paper to the transfer nip has been proposed. For example, Patent Document 1 describes a flexible film. A process cartridge and an image forming apparatus that reduce the load on thick paper while maintaining the state of entry of plain paper into the photoconductor by providing the first guide member and the second guide member made of the member on the upstream side of the transfer position are disclosed. Has been done.

Further, in Patent Document 2, a flexible guide plate that supports the paper conveyed by a paper feed roller or the like on one side and guides the paper toward the photoconductor drum, and a flexible guide plate provided on the other side of the guide plate. It has a sponge that is softer than the guide plate, and the sponge is formed so as to protrude from the edge of the guide plate on the photoconductor drum side toward the photoconductor drum side, so that the guide plate vibrates and the rear edge of the paper flutters. Disclosed is a configuration that suppresses the popping sound of the guide plate while suppressing the noise.

Japanese Unexamined Patent Publication No. 2006-208840 Japanese Unexamined Patent Publication No. 2008-26810

In the configuration of Patent Document 1, since the gap between the paper and the upper guide changes due to the elastic deformation of the first guide member which is a film member, it is not possible to prevent the generation of airflow due to the change in the posture of the paper, and the toner at the developing nip due to the airflow cannot be prevented. It was not possible to suppress the scattering of the paper. Further, in the configuration of Patent Document 2, when the upper transport guide facing the guide plate is present, the guide plate is pressed downward by the transport load of thick paper, the sponge is compressed, and the distance between the guide plate and the upper transport guide is increased. It will spread. Therefore, there is a problem that the fluttering of the rear end when the thick paper is conveyed cannot be sufficiently suppressed.

Further, since the transfer roller is pressed against the photoconductor drum in the bearings at both ends in the longitudinal direction, the transport force in the central portion in the longitudinal direction of the transfer roller is weakened. Therefore, when a thick paper having a small size in the width direction such as a postcard is conveyed, the transfer speed tends to be slowed down due to the influence of the transfer load by the pre-transfer guide. As a result, the transfer magnification is more likely to decrease and the transfer shift is more likely to occur than when the size in the width direction is large. Therefore, it is necessary to further reduce the transport load for thick paper having a small size in the width direction.

In view of the above problems, the present invention can effectively suppress the fluttering of the recording medium on the upstream side of the transfer nip, and also reduces the transport load when transporting the recording medium having a small width direction and strong stiffness. It is an object of the present invention to provide a possible image forming apparatus.

In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image carrier, a transfer member, a resist roller pair, and a transport guide. The transfer member transfers the toner image formed on the image carrier to the recording medium. The resist roller pair conveys the recording medium to the transfer nip between the transfer member and the image carrier at a predetermined timing. The transfer guide is composed of a first transfer guide facing the surface of the recording medium on the image carrier side and a second transfer guide facing the surface of the recording medium on the transfer member side, which is transferred from the resist roller pair to the transfer nip. Will be done. The second transport guide has a main body portion, an elastic member, and a film member. The main body has a convex portion that protrudes most toward the first transport guide side in the recording medium transport path from the resist roller pair to the transfer nip, and a stepped portion formed adjacent to the downstream side of the convex portion with respect to the recording medium transport direction. And have. The elastic member projects toward the first transport guide side from the plane passing through the downstream end of the convex portion and the downstream end of the step portion. The film member covers the surface of the main body facing the first transport guide together with the elastic member over the entire width direction orthogonal to the recording medium transport direction. The ridgeline on the downstream side of the elastic member is linear with respect to the recording medium transport direction, and the elastic member is more elastic in a part in the width direction through which the recording medium having the smallest size in the width direction passes. An easily deformable portion that is easily deformed is provided.

According to the first configuration of the present invention, the elastic member is provided so as to project toward the first transport guide side from the plane passing through the downstream end portion of the convex portion of the second transport guide and the downstream end portion of the stepped portion. By arranging the recording medium, the recording medium can be conveyed along the first transfer guide when the recording medium having a weak elasticity is conveyed, and the fluttering of the recording medium can be suppressed. On the other hand, when the recording medium having a strong stiffness is conveyed, the elastic member is elastically deformed and the transfer load is reduced. Further, since the distance between the second transport guide and the first transport guide is maintained constant, the fluttering of the recording medium can be suppressed as much as possible. Therefore, since the fluttering of the recording medium is suppressed regardless of the strength of the conveyed recording medium, it is possible to suppress the toner scattering at the developing nip due to the generation of the air flow. In addition, it is possible to suppress a decrease in the transfer magnification and the occurrence of transfer deviation due to an increase in the transport load of the recording medium.

Further, by providing an easily deformable portion in a part of the elastic member in the width direction through which the recording medium having the minimum width direction passes, a recording medium having a small width direction and a strong stiffness may be conveyed. The elastic member can be sufficiently elastically deformed. Therefore, the transport load can be reduced regardless of the size of the transport recording medium, and the decrease in transfer magnification and the transfer shift can be effectively suppressed.

Side sectional view showing the internal structure of the image forming apparatus 100 according to the first embodiment of the present invention. A partially enlarged view showing a paper transport path from the resist roller pair 13 to the fixing device 15 in FIG. Side sectional view of the lower transport guide 32 constituting the transport guide 30 used in the image forming apparatus 100 of the first embodiment cut along the transport direction. Top view of the lower transport guide 32 of FIG. 3 as viewed from above. It is a side sectional view which shows the transport state of the paper S from the resist roller pair 13 to the transfer nip N, and is the figure which shows the case where the paper S is plain paper S1. Enlarged view of the lower transport guide 32 in FIG. It is a side sectional view which shows the transport state of the paper from the resist roller pair 13 to the transfer nip N, and is the figure which shows the case where the paper S is thick paper S2. Enlarged view of the lower transport guide 32 in FIG. Side sectional view of the lower transport guide 32 in which the small-sized thick paper S2'is conveyed and the central portion of the elastic sheet 41 is bent in the width direction is cut along the transport direction. Side sectional view of the lower transport guide 32 in which the small-sized thick paper S2'is conveyed and the central portion of the elastic sheet 41 is bent in the width direction is cut along the paper width direction. Side sectional view of the lower transport guide 32 used in the image forming apparatus 100 according to the second embodiment of the present invention cut along the transport direction. Top view of the lower transport guide 32 of FIG. 11 as viewed from above. Side sectional view of the lower transport guide 32 in which the thick paper S2 is transported and the elastic sheet 41 is bent along the transport direction. Side sectional view of the lower transport guide 32 in which the small-sized thick paper S2'is conveyed and the central portion of the elastic sheet 41 is bent in the width direction is cut along the transport direction. Side sectional view of the lower transport guide 32 in which the small-sized thick paper S2'is conveyed and the central portion of the elastic sheet 41 is bent in the width direction is cut along the paper width direction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention. FIG. 2 is a partially enlarged view showing a paper transport path from the resist roller pair 13 to the fixing device 15 in FIG. 1. As shown in FIG. 1, an image forming unit P that forms a monochrome image by each step of charging, exposure, development, and transfer is provided in an image forming apparatus (for example, a monochrome printer) 100. The image forming unit P includes a charging device 4, an exposure device (laser scanning unit, etc.) 7, a developing device 8, a transfer roller 14, and cleaning along the rotation direction of the photoconductor drum 5 (counterclockwise direction in FIG. 1). A device 19 and a static elimination device (not shown) are arranged.

The charging device 4 has a charging roller 4a that contacts the photoconductor drum 5 and applies a charging bias to the drum surface. The charging roller 4a is made of conductive rubber and is arranged so as to come into contact with the photoconductor drum 5. When the photoconductor drum 5 rotates in the counterclockwise direction of FIG. 2, the charging roller 4a in contact with the surface of the photoconductor drum 5 rotates in the clockwise direction of FIG. At this time, by applying a predetermined voltage to the charging roller 4a, the surface of the photoconductor drum 5 is uniformly charged.

The developing apparatus 8 includes a developing roller 8a, and develops an electrostatic latent image formed on the photoconductor drum 5 by the developing roller 8a into a toner image. The developing roller 8a is arranged with a predetermined gap (development nip) between the photoconductor drum 5 and rotates clockwise in FIG. 2. A one-component developer (hereinafter, also simply referred to as toner) composed of only magnetic toner components is housed in the developing device 8. Toner supply to the developing device 8 is performed from the toner container 9.

The transfer roller 14 forms a transfer nip N by coming into contact with the photoconductor drum 5, and transfers the toner image formed on the surface of the photoconductor drum 5 to the paper S passing through the transfer nip N. A transfer bias power supply and a bias control circuit (none of which are shown) for applying a transfer bias having the opposite polarity to the toner are connected to the transfer roller 14. A static elimination needle 21 is arranged in the immediate vicinity of the downstream side of the transfer roller 14 with respect to the paper transport direction. The static elimination needle 21 removes the residual charge (negative charge) of the paper S that has passed through the transfer nip N by applying a bias (transfer reverse bias) having the same polarity (positive electrode property) as the toner, and removes the residual charge (negative charge) of the paper S from the photoconductor drum 5. It facilitates the separation of the paper S of.

The transfer roller 14 is installed offset to the upstream side (left side in FIG. 2) of the lower end portion of the photoconductor drum 5 with respect to the paper transport direction. As a result, the transport direction of the paper S that has passed through the transfer nip is directed downward, so that the paper S is less likely to wind up. Therefore, it is possible to satisfactorily eliminate the static electricity of the paper S by the static elimination needle 21 after passing through the transfer nip N. Further, it is possible to suppress the wrapping of the paper S around the photoconductor drum 5 when the curvature of the paper S is separated from the photoconductor drum 5.

The cleaning device 19 has a rubbing roller 19a and a cleaning blade 19b, and removes residual toner on the surface of the photoconductor drum 5 and polishes the surface of the photoconductor drum 5. Further, a static elimination device (not shown) for removing the residual charge on the surface of the photoconductor drum 5 is provided on the downstream side of the cleaning device 19.

A transport guide 30 is arranged in the first paper transport path 16a between the resist roller pair 13 and the transfer roller 14. The transport guide 30 extends along the paper width direction (direction perpendicular to the paper surface in FIG. 2), and includes an upper transport guide 31 facing the upper surface of the paper S and a lower transport guide 32 facing the lower surface of the paper S. It is composed of.

The resist roller pair 13 is arranged below the tangential direction of the photoconductor drum 5 on the approach side of the transfer nip N. As a result, the resist roller pair 13 is separated from the attachment / detachment path of the drum unit including the developing device 8, the toner container 9, and the photoconductor drum 5, so that the maintainability of the developing device 8, the toner container 9, and the photoconductor drum 5 is improved.

Further, the entry path of the paper S to the transfer nip N may be previously conveyed along the photoconductor drum 5 before coming into contact with the transfer roller 14 in order to suppress the scattering of toner on the upstream side of the transfer nip N. preferable. Therefore, the first paper transport path (pre-transfer transport path) 16a from the resist roller pair 13 to the transfer nip N is once inclined upward from the resist roller pair 13 by the upper transport guide 31 and the lower transport guide 32, and then is then tilted upward. It is configured in an inverted V shape so as to incline downward toward the transfer nip N.

When performing the image forming operation, the photoconductor drum 5 rotating in the counterclockwise direction is uniformly charged by the charging device 4. Next, an electrostatic latent image is formed on the photoconductor drum 5 by a laser beam from the exposure device 7 based on image data transmitted from a personal computer (not shown) or the like, and the electrostatic latent image is developed by the developing device 8. An agent (hereinafter referred to as toner) is adhered to form a toner image.

The paper S is conveyed from the paper feed cassette 10 to the photoconductor drum 5 on which the toner image is formed as described above via the resist roller pair 13 and the first paper transport path 16a, and the photoconductor is conveyed by the transfer roller 14. The toner image formed on the surface of the drum 5 is transferred to the paper S. The paper S on which the toner image is transferred is separated from the photoconductor drum 5 and conveyed to the fixing device 15 via the second paper transport path 16b to fix the toner image.

The paper S that has passed through the fixing device 15 is conveyed to the upper part of the image forming apparatus 100 via the third paper transport path 16c, and when an image is formed on only one side of the paper S (during single-sided printing), the ejection roller It is discharged to the discharge tray 18 via the pair 17.

On the other hand, when an image is formed on both sides of the paper S (during double-sided printing), after the rear end of the paper S passes through the branch portion 20 of the paper transport path 16, the discharge roller pair 17 is rotated in the reverse direction to reverse the transport direction. Let me. As a result, the paper S is distributed from the branch portion 20 to the reversing transport path 21, and is re-conveyed to the resist roller pair 13 with the image plane inverted. Then, the next toner image formed on the photoconductor drum 5 is transferred by the transfer roller 14 to the surface on which the image of the paper S is not formed. The paper S on which the toner image is transferred is conveyed to the fixing device 15, the toner image is fixed, and then the paper S is discharged to the discharge tray 18 via the discharge roller pair 17.

FIG. 3 is a side sectional view of the lower transport guide 32 constituting the transport guide 30 cut along the transport direction. The lower transport guide 32 has a main body portion 35, an elastic member 37, and a film member 40. The main body 35 is made of a conductive resin material. The main body portion 35 is formed so as to be adjacent to a convex portion 35a that protrudes most upward in the first paper transport path 16a from the resist roller pair 13 to the transfer nip N and a downstream side of the convex portion 35a with respect to the paper transport direction. It has a stepped portion 35b and a tip portion 35c extending downstream of the stepped portion 35b and close to the transfer nip N (see FIG. 2).

The elastic member 37 is fixed to the stepped portion 35b of the main body portion 35 over the entire area in the paper width direction (direction perpendicular to the paper surface in FIG. 3, hereinafter also simply referred to as width direction). In this embodiment, a sponge is used as the elastic member 37. The elastic member 37 has a rectangular parallelepiped shape (rectangular cross section), and the upper corner portion (upper right portion in FIG. 3) on the downstream side with respect to the paper transport direction is the downstream side of the edge portion E1 and the step portion 35b on the downstream side of the convex portion 35a. It is arranged so as to project toward the upper transport guide 31 from the plane L passing through the edge portion E2 of the above.

The film member 40 passes through the elastic member 37 from the convex portion 35a of the main body portion 35 over the entire area in the paper width direction to the tip portion 35c so as to cover the facing surface with the upper transport guide 31. It is wrapped around and fixed. The film member 40 is fixed with a tension (tension) to such an extent that the elastic member 37 is not elastically deformed. As the material of the film member 40, a resin film having high wear resistance and good slidability is preferable. Further, in order to prevent the toner from adhering due to charging due to friction with the paper S, the film member 40 is preferably conductive. In this embodiment, a conductive ultra-high molecular weight polyethylene sheet is used as the film member 40.

Further, it is preferable that the film member 40 is grounded in order to release the electric charge accumulated in the film member 40 due to friction with the paper S. The film member 40 may be directly connected to the frame (not shown) of the image forming apparatus 100 and grounded, or if the main body 35 is conductive, the film member 40 may be grounded via the main body 35. May be good. If the resistance of the paper S is low due to water content or the like, the transfer bias leaks to the ground via the paper S and the lower transfer guide 32. Therefore, when the film member 40 is grounded, a resistor having a resistance value in megaohm units ( It is preferable to ground via a high Meg resistor).

FIG. 4 is a plan view of the lower transport guide 32 of FIG. 3 as viewed from above. Note that FIG. 3 shows a state in which the film member 40 is removed for convenience of explanation. As shown in FIG. 4, the elastic member 37 has a linear ridge line 37a on the downstream side (lower side of FIG. 4) with respect to the paper transport direction. On the other hand, the ridge line 37b on the upstream side (upper side in FIG. 4) with respect to the paper transport direction is formed with a recess 37c in which the central portion in the paper width direction (left-right direction in FIG. 4) is recessed on the downstream side. That is, the thickness of the central portion of the elastic member 37 in the width direction is smaller than that of the other portions.

Next, the transfer of the paper S from the resist roller pair 13 to the transfer nip N in the image forming apparatus 100 of the present embodiment will be described. FIG. 5 is a side sectional view showing a state in which the plain paper S1 is conveyed from the resist roller pair 13 to the transfer nip N, and FIG. 6 is an enlarged view of the vicinity of the lower transfer guide 32 in FIG. Since the plain paper S1 is weak, the amount of deformation of the elastic member 37 during transportation of the plain paper S1 is small.

As a result, since the film member 40 is supported in a convex shape by the ridge line 37a of the elastic member 37 formed in a straight line, the transport trajectory of the plain paper S1 (indicated by the broken lines in FIGS. 5 and 6) as shown in FIG. ) Is a trajectory that approaches the upper transport guide 31 over the entire width direction, the gap between the plain paper S1 and the upper transport guide 31 does not widen, and the fluttering of the plain paper S1 is suppressed. Therefore, toner scattering at the developing nip due to the generation of airflow is suppressed.

FIG. 7 is a side sectional view showing a state in which the thick paper S2 is transported from the resist roller pair 13 to the transfer nip N, and FIG. 8 is an enlarged view of the vicinity of the lower transport guide 32 in FIG. Since the thick paper S2 has a strong elasticity, it is conveyed to the transfer nip N while elastically deforming by pressing the convex portion (ridge line 37a) of the elastic member 37. As a result, the friction between the thick paper S2 and the lower transport guide 32 is reduced, and the transport load during transport of the thick paper S2 is reduced.

Further, as shown in FIG. 7, the transport track of the thick paper S2 (indicated by the broken line in FIGS. 7 and 8) is a track that approaches the lower transport guide 32 over the entire width direction. Since the convex portion 35a is provided, the gap between the convex portion 35a and the upper transport guide 31 is maintained at a constant width even if the elastic member 37 is elastically deformed. Therefore, even when the thick paper S2 is conveyed, the transfer load can be reduced while minimizing the fluttering width of the thick paper S2.

As described above, since the transport force of the central portion of the transfer roller 14 in the longitudinal direction is weaker than that of both ends, when a thick paper having a small size in the width direction such as a postcard is transported, the transport load by the lower transport guide 32 is transferred. The transport speed tends to slow down due to the influence. As a result, the transfer magnification is more likely to decrease and the transfer shift is more likely to occur than when the size in the width direction is large. Therefore, in the present embodiment, by providing the recess 37c in the central portion in the width direction of the elastic member 37 through which the paper S having a small size in the width direction passes, it is possible to reduce the transport load on the thick paper having a small size in the width direction. There is.

FIG. 9 is a side sectional view of the lower transport guide 32 in which the small-sized thick paper S2'is conveyed and the central portion in the width direction of the film member 40 is bent, and the lower transport guide 32 is cut along the transport direction. FIG. 10 is a small size. It is a side sectional view (AA'arrow-view cross-sectional view of FIG. 9) in which the thick paper S2'is conveyed and the lower transport guide 32 in which the central portion in the width direction of the film member 40 is bent is cut along the paper width direction. When the small-sized thick paper S2'is conveyed, it is conveyed while elastically deforming by pressing the central portion in the width direction of the elastic member 37. Here, since the concave portion 37c is formed in the central portion in the width direction of the elastic member 37, the elastic member 37 is more easily elastically deformed than the other portions.

As a result, only the dotted line in FIG. 9 and the central portion in the width direction of the film member 40 bend downward, and the transport trajectory of the thick paper S2'(indicated by the broken line in FIG. 9) becomes the lower transport guide 32. It will be a closer trajectory. As a result, the transport load on the thick paper S2'can be effectively reduced.

According to the configuration of the present embodiment, it protrudes upward from the plane L passing through the edge portion E1 on the downstream side of the convex portion 35a of the lower transport guide 32 and the edge portion E2 on the downstream side of the stepped portion 35b in the paper transport direction. By arranging the elastic member 37 in such a manner, the paper S can be transported along the upper transport guide 31 at the time of transporting the plain paper S1 having a weak stiffness, and the fluttering of the rear end of the paper S is suppressed. On the other hand, when the thick paper S2 having strong elasticity is conveyed, the elastic member 37 is elastically deformed and the transfer load is reduced. Further, since the distance between the lower transport guide 32 and the upper transport guide 31 is kept constant by the convex portion 35a, the fluttering of the rear end of the thick paper S2 during transport can be suppressed as much as possible.

Therefore, since the fluttering of the rear end of the paper S is suppressed regardless of the stiffness of the paper S to be conveyed, it is possible to suppress the toner scattering at the developing nip due to the generation of the air flow. Further, it is possible to suppress a decrease in the transfer magnification and the occurrence of transfer deviation due to an increase in the transport load of the paper S.

Further, by providing the recess 37c in the central portion in the width direction of the elastic member 37, the elastic member 37 can be sufficiently elastically deformed even when the thick paper S2', which has a small size in the width direction, is conveyed. Therefore, the transport load can be reduced regardless of the size of the thick paper to be conveyed, and the decrease in the transfer magnification and the transfer deviation can be effectively suppressed. On the other hand, when the plain paper S1 is conveyed, the central portion in the width direction of the film member 40 is supported without bending by the ridge line 37a of the elastic member 37 formed in a straight line, so that the plain paper S1 is spread over the entire width direction. It can be transported on a track closer to the upper transport guide 31.

The forming width w1 (see FIG. 4) of the recess 37c in the paper width direction has a minimum width so that the elastic member 37 is sufficiently deformed when the minimum width paper S used in the image forming apparatus 100 is conveyed. It is preferable that the width of the paper S is equal to or larger than the paper width of the paper S. The depth of the recess 37c (dimension in the paper transport direction) can be appropriately set according to the stiffness (basis weight) of the thick paper S2'to be transported.

Further, in the image forming apparatus 100 of the present embodiment, the first paper transport path 16a from the resist roller pair 13 to the transfer nip N is once inclined upward from the resist roller pair 13 and then downward toward the transfer nip N. It is configured in an inverted V shape so as to incline in the direction. In this case, it is particularly preferable to use the lower transfer guide 32 of the present embodiment because the transfer load when the strong paper S such as thick paper S2 and S2'is conveyed becomes large.

FIG. 11 is a side sectional view of the lower transport guide 32 used in the image forming apparatus 100 according to the second embodiment of the present invention cut along the transport direction. In the lower transport guide 32 shown in FIG. 11, an elastic sheet 41 is provided in place of the elastic member 37. The configuration of the other parts of the lower transport guide 32 is the same as that of the first embodiment.

One end of the elastic sheet 41 is fixed to the convex portion 35a, and the other end of the elastic sheet 41 projects upward from the convex portion 35a toward the downstream side in the paper transport direction toward the stepped portion 35b. The elastic sheet 41 is formed from a plane L on which the ridge line 41a on the downstream side (right end portion in FIG. 11) passes through the edge portion E1 on the downstream side of the convex portion 35a and the edge portion E2 on the downstream side of the step portion 35b in the paper transport direction. Is also arranged so as to project toward the upper transport guide 31 side. As the material of the elastic sheet 41, a polyethylene terephthalate (PET) sheet is used.

FIG. 12 is a plan view of the lower transport guide 32 of FIG. 11 as viewed from above. Note that FIG. 12 shows a state in which the film member 40 is removed for convenience of explanation. As shown in FIG. 12, the elastic sheet 41 has a linear ridge line 41a on the downstream side (lower side of FIG. 12) with respect to the paper transport direction. Further, a thin wall portion 41b is formed in the central portion of the elastic sheet 41 in the paper width direction. In the thin portion 41b, the thickness of the polyethylene terephthalate sheet constituting the elastic sheet 41 is thinner than that of the other portions, and the elastic modulus (Young's modulus) is small. In the present embodiment, as shown in FIG. 15 described later, a thin portion 41b is formed by stacking a plurality of (two) sheets at both ends of the elastic sheet 41 and forming the central portion with one sheet. ing.

When the plain paper S1 is conveyed using the lower transfer guide 32 having the configuration of the present embodiment, the elasticity of the plain paper S1 is weak, so that the amount of deformation of the elastic sheet 41 is small. As a result, as shown in FIG. 11, the elastic sheet 41 maintains the protruding state, and the film member 40 is supported in a convex shape by the ridge line 41a of the elastic sheet 41 formed in a straight line, so that the paper transport trajectory is shown in FIG. Similarly, the trajectory is along the film member 40 supported by the elastic sheet 41. Therefore, the gap between the plain paper S1 and the upper transport guide 31 does not widen, and the fluttering of the rear end of the plain paper S1 is suppressed, so that the toner scattering at the developing nip due to the generation of the air flow is suppressed.

FIG. 13 is a side sectional view taken along the transport direction of the lower transport guide 32 in which the thick paper S2 is transported and the elastic sheet 41 is bent. As shown in FIG. 13, when the thick paper S2 having a strong elasticity is conveyed, it is conveyed to the transfer nip N while elastically deforming by pressing the convex portion (ridge line 41a) of the elastic sheet 41. As a result, the transport load during transport of the thick paper S2 is reduced. Further, the paper transport trajectory is a trajectory along the elastically deformed elastic sheet 41 as in FIG. 8, but since the lower transport guide 32 is provided with the convex portion 35a, even if the elastic sheet 41 is elastically deformed. The gap between the convex portion 35a and the upper transport guide 31 is maintained at a constant width. Therefore, even during the transfer of the thick paper S2, the transfer load can be reduced while minimizing the fluttering at the rear end.

FIG. 14 is a side sectional view of the lower transport guide 32 in which the small-sized thick paper S2'is conveyed and the central portion in the width direction of the film member 40 is bent, and the lower transport guide 32 is cut along the transport direction. FIG. 15 is a small size. It is a side sectional view (BB'view cross-sectional view of FIG. 14) in which the thick paper S2'of the above is conveyed and the lower transport guide 32 in which the central portion in the width direction of the film member 40 is bent is cut along the paper width direction. When the small-sized thick paper S2'is conveyed, the thin-walled portion 41b provided at the center in the width direction of the elastic sheet 41 is pressed and elastically deformed while being conveyed. Since the thin portion 41b is more easily elastically deformed than the other portions of the elastic sheet 41, only the dotted line in FIG. 14 and the central portion in the width direction bend downward in the film member 40, and the thick paper S2' The transport track (indicated by the broken line in FIG. 14) is a track closer to the lower transport guide 32. As a result, the transport load on the thick paper S2'can be effectively reduced.

According to the configuration of the present embodiment, as in the first embodiment, the fluttering of the rear end of the paper S is suppressed regardless of the stiffness of the paper S to be conveyed, so that the development nip due to the generation of airflow can be suppressed. Toner scattering can be suppressed. Further, it is possible to suppress a decrease in the transfer magnification and the occurrence of transfer deviation due to an increase in the transport load of the paper S.

Further, by providing the thin wall portion 41b at the center portion in the width direction of the elastic sheet 41, the elastic sheet 41 can be sufficiently elastically deformed even when the thick paper S2', which has a small size in the width direction, is conveyed. Therefore, the transport load can be reduced regardless of the size of the thick paper to be conveyed, and the decrease in the transfer magnification and the transfer deviation can be effectively suppressed. On the other hand, when the plain paper S1 is conveyed, the central portion in the width direction of the film member 40 is supported without bending by the ridge line 41a of the elastic sheet 41 formed in a straight line, so that the plain paper S1 is spread over the entire width direction. It can be transported on a track closer to the upper transport guide 31.

The forming width w2 (see FIG. 12) of the thin-walled portion 41b in the paper width direction is the minimum width so that the elastic sheet 41 is sufficiently deformed when the minimum width paper S used in the image forming apparatus 100 is conveyed. It is preferable that the width of the paper S is equal to or larger than the paper width of the paper S. The thickness of the thin portion 41b can be appropriately set according to the strength (basis weight) of the thick paper S2'to be conveyed.

In the present embodiment, the thin-walled portion 41b is formed by reducing the number of sheets constituting the elastic sheet 41, and the elastic modulus of the central portion in the width direction of the elastic sheet 41 is lowered, but the present invention is not limited to this. do not have. For example, the elastic sheet 41 may be divided into three regions, a central portion in the width direction and both ends, and the central portion in the width direction may be formed of a material having a lower elastic modulus (Young's modulus) than the other portions. Specifically, there is a configuration in which both ends of the elastic sheet 41 are formed of a stainless steel sheet and the central portion is formed of a polyethylene terephthalate sheet.

Others The present invention is not limited to each of the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the distance between the convex portion 35a and the upper transport guide 31, the elastic member 37, the amount of protrusion of the elastic sheet 41, the thickness of the elastic sheet 41, and the like can be appropriately set according to the type of the paper S to be transported and the like. ..

Further, in each of the above embodiments, the so-called central reference paper passing system in which the paper S is always conveyed along the center in the width direction of the paper transport path has been described, but the paper S is aligned with the widthwise end of the paper transport path. It can be applied in exactly the same way to the so-called one-sided standard paper passing system. In that case, since the small-sized paper S is transported along one side in the width direction of the lower transport guide 32, the recess 37c and the thin-walled portion 41b are provided in the portions of the elastic member 37 and the elastic sheet 41 through which the paper S passes, respectively. It should be formed.

Further, the present invention is not limited to the monochrome printer as shown in FIG. 1, and is connected to other types of image forming devices such as color printers, monochrome and color copiers, digital multifunction devices, facsimiles, and image forming devices. Of course, it can also be applied to paper post-processing equipment.

INDUSTRIAL APPLICABILITY The present invention can be used for an image forming apparatus such as a copying machine, a printer, and a facsimile provided with a transfer guide on the upstream side of a transfer nip. By utilizing the present invention, it is possible to provide an image forming apparatus capable of effectively suppressing fluttering of a recording medium on the upstream side of a transfer nip and reducing a transport load when transporting a recording medium having a strong stiffness. can.

5 Photoreceptor drum (image carrier)
13 Resist roller vs. 14 Transfer roller (transfer member)
16a First paper transport path (recording medium transport path)
30 Transport guide 31 Top transport guide (first transport guide)
32 Lower transport guide (second transport guide)
35 Main body 35a Convex 35b Step 35c Tip 37 Elastic members 37a, 37b Ridge 37c Recess (easily deformed)
40 Film member 41 Elastic sheet (elastic member)
41a Ridge line 41b Thin-walled part (easy deformation part)
100 Image forming device N Transfer nip S Paper (recording medium)
S1 plain paper S2, S2'thick paper

Claims (8)

With the image carrier,
A transfer member that transfers the toner image formed on the image carrier to a recording medium, and
A pair of resist rollers that convey a recording medium to the transfer nip between the transfer member and the image carrier at predetermined timings,
A first transport guide facing the image carrier side surface of the recording medium conveyed from the resist roller pair to the transfer nip, and a second transfer guide facing the transfer member side surface of the recording medium. Consists of a transport guide and
In an image forming apparatus equipped with
The second transport guide is
A convex portion that protrudes most toward the first transport guide side in the recording medium transport path from the resist roller pair to the transfer nip, and a stepped portion formed adjacent to the downstream side of the convex portion with respect to the recording medium transport direction. And, with the main body,
An elastic member projecting toward the first transport guide side from a plane passing through the downstream end portion of the convex portion and the downstream end portion of the step portion in the recording medium transport direction.
A film member that covers the surface of the main body facing the first transport guide together with the elastic member over the entire width direction orthogonal to the recording medium transport direction.
Have,
The ridgeline on the downstream side of the elastic member is linear with respect to the recording medium transport direction, and the elastic member having the smallest size in the width direction passes through a part of the elastic member in the width direction. An easily deformable part that is more easily elastically deformed than the part is provided ,
The elastic member is a rectangular parallelepiped sponge, and is fixed to the step portion along the width direction, and the corner portion on the downstream side of the elastic member with respect to the recording medium transport direction is the first of the planes. Protruding to the transport guide side,
The easily deformable portion is an image forming apparatus characterized in that the ridgeline on the upstream side of the elastic member is a concave portion recessed on the downstream side with respect to the recording medium transport direction . With the image carrier,
A transfer member that transfers the toner image formed on the image carrier to a recording medium, and
A pair of resist rollers that convey a recording medium to the transfer nip between the transfer member and the image carrier at predetermined timings,
A first transport guide facing the image carrier side surface of the recording medium conveyed from the resist roller pair to the transfer nip, and a second transfer guide facing the transfer member side surface of the recording medium. Consists of a transport guide and
In an image forming apparatus equipped with
The second transport guide is
A convex portion that protrudes most toward the first transport guide side in the recording medium transport path from the resist roller pair to the transfer nip, and a stepped portion formed adjacent to the downstream side of the convex portion with respect to the recording medium transport direction. And, with the main body,
An elastic member projecting toward the first transport guide side from a plane passing through the downstream end portion of the convex portion and the downstream end portion of the step portion in the recording medium transport direction.
A film member that covers the surface of the main body facing the first transport guide together with the elastic member over the entire width direction orthogonal to the recording medium transport direction.
Have,
The ridgeline on the downstream side of the elastic member is linear with respect to the recording medium transport direction, and the elastic member having the smallest size in the width direction passes through a part of the elastic member in the width direction. An easily deformable part that is more easily elastically deformed than the part is provided,
The elastic member is an elastic sheet, one end of which is fixed to the convex portion along the width direction, and the other end of the elastic member projects so as to overlap above the stepped portion.
The easily deformable portion is an image forming apparatus characterized in that the thickness of the elastic sheet is a thin portion thinner than other portions . The image according to claim 1 or 2 , wherein the dimension of the easily deformable portion in the width direction is equal to or larger than the dimension in the width direction of the recording medium having the minimum width passing through the recording medium transport path. Forming device. The image forming apparatus according to any one of claims 1 to 3, wherein the film member has conductivity . The image forming apparatus according to claim 4, wherein the film member is grounded via the main body portion . The image forming apparatus according to claim 5 , wherein the film member is grounded via a resistor having a resistance value in mega ohm units . The image forming apparatus according to any one of claims 1 to 6, wherein the film member is an ultrapolymer polyethylene sheet . Claims 1 to 7 , wherein the recording medium transport path has an inverted V shape that is once inclined upward from the resist roller pair and then inclined downward toward the transfer nip . The image forming apparatus according to any one.

Images