Image forming apparatus with holding unit that holds a recording medium

Provided is an image forming apparatus including: an annular transfer belt having an outer surface on which an image is transferred; a transferring unit including a transfer cylinder having a transfer area that sandwiches a recording medium with the outer surface of the transfer belt to transfer the image from the outer surface of the transfer belt to the recording medium, and a pair of first rotating bodies disposed on both axial end sides of the transfer cylinder; a pair of circulating members each being wound around the first rotating body and being circulated by rotation of the first rotating bodies; and a holding unit attached to the circulating members, the holding unit configured to hold the recording medium, transport the recording medium with circulation of the circulating members, and pass the recording medium through the transfer area.

BACKGROUND

Technical Field

Related Art

Patent Literature 1 discloses a configuration in which a leading portion of paper is gripped by a gripper provided on a circumferential surface of a transport drum to transport the paper.

CITATION LIST

Patent Literature

SUMMARY

In a configuration in which a circulating member to which a holding unit holding the recording medium is attached is circulated by rotation of a rotating member to transport a recording medium, and a transfer unit transfers an image to the recording medium, when a rotating body is provided as a member separate from the transfer unit, a large space is required.

Aspect of non-limiting embodiments of the present disclosure relates to save space as compared with a configuration in which a rotating body is provided as a member separate from a transfer unit.

According to an aspect of the present disclosure, there is provided an image forming apparatus including: an annular transfer belt having an outer surface on which an image is transferred; a transferring unit including a transfer cylinder having a transfer area that sandwiches a recording medium with the outer surface of the transfer belt to transfer the image from the outer surface of the transfer belt to the recording medium, and a pair of first rotating bodies disposed on both axial end sides of the transfer cylinder; a pair of circulating members each being wound around the first rotating body and being circulated by rotation of the first rotating bodies; and a holding unit attached to the circulating members, the holding unit configured to hold the recording medium, transport the recording medium with circulation of the circulating members, and pass the recording medium through the transfer area.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment according to the present invention is described based on the drawings.

The configuration of an image forming apparatus10according to the exemplary embodiment is described.FIG. 1is a schematic diagram showing the configuration of the image forming apparatus10according to the exemplary embodiment.

The image forming apparatus10shown inFIG. 1is an example of an image forming apparatus which forms an image on a recording medium. Specifically, the image forming apparatus10is an electrophotographic image forming apparatus which forms a toner image (an example of an image) on a recording medium P. More specifically, the image forming apparatus10includes an image forming unit14, a transport unit15, and a fixing device16. Hereinafter, each portion (the image forming unit14, the transport unit15, and the fixing device16) of the image forming apparatus10is described.

The image forming unit14has a function of forming a toner image (an example of an image) on the recording medium P. Specifically, the image forming unit14includes toner image forming units22and a transfer device17.

A plurality of toner image forming units22shown inFIG. 1are provided to form a toner image for respective color. In the exemplary embodiment, toner image forming units22for a total of four colors of yellow (Y), magenta (M), cyan (C) and black (K) are provided. (Y), (M), (C) and (K) shown inFIG. 1indicate components corresponding to the respective colors.

In the image forming apparatus10, when it is necessary to distinguish among yellow (Y), magenta (M), cyan (C) and black (K), (Y), (M), (C), and (K) are added after the reference sign of each member; when it is not necessary to distinguish among the above colors, (Y), (M), (C) and (K) may be omitted. Since the toner image forming units22of respective colors are configured in the same manner except for the toner to be used, as a representative of the toner image forming units22of respective colors, each portions of the toner image forming unit22(Y) are denoted by reference signs inFIG. 1.

Specifically, the toner image forming unit22of each color includes a photoreceptor drum32(photoreceptor) which rotates in one direction (for example, a counterclockwise direction inFIG. 1). Further, the toner image forming unit22of each color includes a charger23, an exposurer36, a developer38, and a remover40.

In the toner image forming unit22of each color, the charger23charges the photoreceptor drum32. Further, the exposurer36exposes the photoreceptor drum32charged by the charger23to form an electrostatic latent image on the photoreceptor drum32. In addition, the developer38develops the electrostatic latent image formed on the photoreceptor drum32by the exposurer36to form a toner image. Then, the remover40removes the toner remaining on the photoreceptor drum32after the transfer of the toner image to a transfer belt24to be described later.

The transfer device17shown inFIG. 1is a device for transferring the toner image formed by the toner image forming unit22to the recording medium P. Specifically, the transfer device17superimposes and primarily transfers the toner images of the photoreceptor drums32of respective colors on the transfer belt24as an intermediate transfer body, and secondarily transfers the superimposed toner image to the recording medium P at a secondary transfer position T2(a nip area28A to be described later). More specifically, as shown in FIG.1, the transfer device17includes the transfer belt24, a primary transfer roller26, a secondary transfer body27, and a charger60.

The primary transfer roller26shown inFIG. 1is a roller for transferring the toner image of the photoreceptor drum32of each color to the transfer belt24at a primary transfer position T1between the photoreceptor drum32and the primary transfer roller26. In the exemplary embodiment, the toner image formed on the photoreceptor drum32is transferred to the transfer belt24at the primary transfer position T1by applying a primary transfer electric field between the primary transfer roller26and the photoreceptor drum32.

The transfer belt24shown inFIG. 1is an example of an annular transfer belt on which an image is transferred to an outer surface thereof. Specifically, on the transfer belt24, the toner image is transferred from the photoreceptor drum32of each color to an outer circumferential surface (an example of the outer surface) thereof. More specifically, the transfer belt24is configured as follows. As shown inFIG. 1, the transfer belt24has an annular shape. The transfer belt24is wound around a plurality of rollers42including a driving roller42D and winding rollers42E and42F to determine the posture thereof. The transfer belt24circulates, for example, in a direction of an arrow A (hereinafter, referred to as belt circulating direction A), which is predetermined, by the driving roller42D of the plurality of rolls42being rotationally driven by a drive unit (not shown). The specific configuration of the winding rollers42E and42F is to be described later.

The secondary transfer body27is an example of a transfer unit. Specifically, as shown inFIG. 2, the secondary transfer body27includes a transfer cylinder28and a pair of sprockets29. The transfer cylinder28is an example of a transfer cylinder having a transfer area which sandwiches the recording medium with the outer surface of the transfer belt to transfer an image from the transfer belt to the recording medium. Specifically, as shown inFIG. 3, the transfer cylinder28has the nip area28A (an example of the transfer area) which sandwiches the recording medium P with the outer circumferential surface of the transfer belt24. The nip area28A can be said to be a sandwiching area since it is an area sandwiching the recording medium P. The transfer cylinder28can be said to be a sandwiching portion since it sandwiches the recording medium P with the transfer belt24. InFIG. 3, the recording medium P is simplified and a part thereof is shown.

The nip area28A is formed by winding the transfer belt24around the transfer cylinder28. In other words, the nip area28A can be said to be a contact area where the transfer belt24and the transfer cylinder28come into contact with each other. The nip area28A is the secondary transfer position T2where the toner image is transferred from the transfer belt24to the recording medium P. In addition, the transfer cylinder28sandwiches the recording medium P with the transfer belt24in the nip area28A to transport the recording medium P.

The pair of sprockets29is an example of a rotating body, and is an example of a first rotating body. As shown inFIG. 2, the pair of sprockets29is disposed on both axial end sides of the transfer cylinder28. In other words, the transfer cylinder28is provided between the pair of sprockets29. Further, the pair of sprockets29is disposed coaxially with the transfer cylinder28and configured to rotate integrally with the transfer cylinder28. The secondary transfer body27is rotationally driven by a drive unit (not shown).

As shown inFIG. 4, an outer diameter of each of the pair of sprockets29is smaller than an outer diameter of the transfer cylinder28. The outer diameter of the sprocket29is an outer diameter including a teeth29A (i.e., including the diameter of the tooth tip).

The transfer cylinder28includes a base member28E and a surface layer28F which is wound around an outer circumference of the base member28E and exchangeable with respect to the base member28E. As the base member28E, a metal material such as stainless steel is used. As the surface layer28F, a resin material such as urethane rubber, ethylene-propylene rubber (EPM), silicone rubber, fluororubber (FKM), and epichlorohydrin-butadiene rubber is used. The surface layer28F is detachably fixed to the base member28E. Therefore, the surface layer28F can be detached from the base member28E, and an unused surface layer28F can be attached thereto.

Further, on the outer circumference of the transfer cylinder28, two recessed portions28D are formed, in which a gripper54and an attaching member55of the transport unit15, which are to be described later, are accommodated. The number of the recessed portions28D may be one, or three or more.

The charger60is an example of a facing portion which faces the sandwiching portion and is on the inner side of the transfer belt. As shown inFIG. 3, the charger60is disposed on the inner side of the transfer belt24so as to face the transfer cylinder28. Specifically, the charger60faces the transfer cylinder28in an area including a center28S in the transport direction of the transport unit15in the nip area28A.

The charger60is a charger (so-called corotron charger) for transferring the toner image of the transfer belt24by corona discharge. Specifically, the charger60includes a discharge wire60A and a case62(housing). The discharge wire60A is linear having a length along the axial direction of the transfer cylinder28. The discharge wire60A is not in contact with the inner surface of the transfer belt24. That is, the discharge wire60A has a gap with the inner surface of the transfer belt24.

The case62is an example of a surrounding portion surrounding the discharge wire. The case62is formed in a box shape, and has an opening portion62C on the transfer cylinder28side (i.e., the lower side).

Specifically, the case62has a first wall62A disposed on a side opposite to the transfer cylinder28with respect to the discharge wire60A, and a pair of second walls62B respectively disposed on an upstream side and a downstream side of the belt circulating direction A with respect to the discharge wire60A. Furthermore, the case62has third walls (not shown) disposed on both ends in a length direction of the discharge wire60A.

The case62is not in contact with the inner surface of the transfer belt24. That is, the case62has a gap with the inner surface of the transfer belt24.

The case62may have a configuration which may have an opening portion in the third walls (not shown) disposed on both ends in the length direction of the discharge wire60A, and may have an opening portion62C at least on the transfer cylinder28side (i.e., the lower side).

The recording medium P is electrostatically attracted to the transfer belt24and the transfer cylinder28by applying a voltage to the discharge wire60A and discharging the voltage in the charger60. In addition, the transfer belt24is charged by the discharge of the discharge wire60A in the charger60, and the toner image superimposed on the transfer belt24is transferred from the transfer belt24to the recording medium P at the nip area28A (secondary transfer position T2).

The winding rollers42E and42F shown inFIGS. 1 and 3are examples of a pair of winding rollers around which the transfer belt is wound on the inner side of the transfer belt. The winding rollers42E and42F are respectively disposed on the upstream side and the downstream side of the belt circulating direction A with respect to the charger60.

As shown inFIG. 3, the winding rollers42E and42F are disposed such that a common circumscribed line XA of the winding rollers42E and42F passes above the transfer cylinder28when viewed in the axial direction of the winding rollers42E and42F.

Here, the common circumscribed line XA is a circumscribed line on which the winding rollers42E and42F are disposed on the same side of the circumscribed line (i.e., common circumscribed line) in contact with both the winding rollers42E and42F. More specifically, the common circumscribed line XA according to the exemplary embodiment is a circumscribed line in contact with a portion of the winding rollers42E and42F around which the transfer belt24is wound. In other words, the common circumscribed line XA according to the exemplary embodiment is a circumscribed line in contact with the winding rollers42E and42F on the transfer cylinder28side with respect to the charger60.

Further, both winding portions43E and43F wound around the winding rollers42E and42F on the transfer belt24are separated from the transfer cylinder28. The winding portion43E is a winding portion on the upstream side in the transport direction of the recording medium P with respect to the winding portion43F.

The transport unit15shown inFIG. 1toFIG. 3has a function of transporting the recording medium P. Specifically, the transport unit15has a function of transporting the recording medium P to pass through the nip area28A (seeFIG. 3). More specifically, as shown inFIGS. 1 and 2, the transport unit15includes a pair of sprockets19, a pair of chains52, the gripper54, and an attracting roller59. The pair of chains52is an example of a circulating member. The gripper54is an example of a holding unit which holds a recording medium. InFIG. 1, the sprockets19, the chains52and the gripper54are shown in a simplified manner. InFIG. 3, the chains52and the gripper54are shown in a simplified manner.

As shown inFIG. 1, the pair of sprockets19is disposed at an interval in a front-rear direction of the apparatus on the fixing device16side (left side inFIG. 1) with respect to the pair of sprockets29included in the secondary transfer body27. The pair of sprockets19is coaxially supported on a main body (not shown) of the image forming apparatus10so as to be integrally rotatable.

As shown inFIG. 1, the pair of chains52is annularly formed. As shown inFIG. 2, the pair of chains52is disposed at an interval in the front-rear direction (direction D inFIG. 2) of the apparatus. The pair of chains52is respectively wound around the pair of sprockets29of the secondary transfer body27and the pair of sprockets19(seeFIG. 1). Then, when the transfer cylinder28including the pair of sprockets29rotates, the chains52circulate in a circulating direction C (a direction of an arrow C inFIG. 1). Here, in the circulating direction C, the chains52are wound to straddle at least an area facing the charger60in the nip area28A. Accordingly, since the recording medium P is transported by the chains52during the secondary transfer, the speed fluctuation of the recording medium P is prevented at the secondary transfer position T2. Further, the chains52are wound to straddle the entire nip area28A. Accordingly, the speed fluctuation of the recording medium P is prevented more reliably at the secondary transfer position T2. In the exemplary embodiment, a winding angle at which the chains52are wound around the sprockets29is 180 degrees or more. Thus, the recording medium P can be easily transported along a surface of the transfer cylinder28. In order to facilitate transport of the recording medium P along the surface of the transfer cylinder28, it is desirable to set the winding angle to 90 degrees or more. In addition, in the exemplary embodiment, in the circulating direction C, the winding angle between the start of winding of the chains52and the arrival at the secondary transfer position T2is 90 degrees or more. Thus, the recording medium P is likely to be transported along the surface of the transfer cylinder28before arriving at the secondary transfer position T2.

In the exemplary embodiment, the chains52travel between the transfer belt24and the transfer cylinder28on the downstream side in the transport direction with respect to the nip area28A in a side view. In other words, the chain52has a gap with respect to the winding portion43F in the side view, and has a gap with respect to the transfer cylinder28on the side opposite to the winding portion43F with respect to the chain52.

As shown inFIG. 2, the attaching member55to which the gripper54is attached is across the pair of chains52along the front-rear direction of the apparatus. A plurality of attaching members55are fixed to the pair of chains52at predetermined intervals along the circumferential direction (the circulating direction C) of the chain52.

As shown inFIG. 2, a plurality of grippers54are attached to the attaching member55at predetermined intervals along the front-rear direction of the apparatus. In other words, the gripper54is attached to the chain52via the attaching member55. The gripper54has a function of holding a leading end portion of the recording medium P. Specifically, the gripper54includes a claw54A and a claw base54B as shown inFIG. 5. The gripper54holds the recording medium P by sandwiching the leading end portion of the recording medium P between the claw54A and the claw base54B. In other words, the gripper54can be said to be an example of a holding unit which holds the recording medium P in a thickness direction.

More specifically, the gripper54holds the leading end portion of the recording medium P outside an image area of the recording medium P. The image area of the recording medium P is an area on the recording medium P to which the toner image is transferred. In the gripper54, for example, the claw54A is pressed against the claw base54B by a spring or the like, and the claw54A is opened and closed relative to the claw base54B by the action of a cam or the like.

In the transport unit15, as shown inFIG. 5, the gripper54holds the leading end portion of the recording medium P sent from an accommodating portion (not shown) in which the recording medium P is accommodated. Further, when the chain52circulates in the circulating direction C in a state where the gripper54holds the front end of the recording medium P, the transport unit15transports the recording medium P by moving the gripper54, and the recording medium P passes through the nip area28A together with the gripper54while being held by the gripper54. Furthermore, the transport unit15transports the recording medium P to the fixing device16after passing through the nip area28A.

The attracting roller59is in contact with the transfer cylinder28on the upstream side in the transport direction with respect to the nip area28A. The attracting roller59presses the recording medium P against the transfer cylinder28and charges the recording medium P by supplying power from a power source57. Accordingly, the recording medium P is electrostatically attracted to the outer circumferential surface of the transfer cylinder28.

The fixing device16shown inFIG. 1is a device for fixing the toner image transferred to the recording medium P by the transfer cylinder28to the recording medium P. More specifically, as shown inFIG. 1, the fixing device16includes a heating roller68as a heating member and a pressure roller69as a pressure member. The fixing device16fixes the toner image formed on the recording medium P to the recording medium P by heating and pressing the recording medium P with the heating roller68and the pressure roller69.

(Effects According to Exemplary Embodiment)

Next, effects according to the exemplary embodiment are described.

According to the image forming apparatus of the exemplary embodiment, as shown inFIG. 5, the gripper54holds the leading end portion of the recording medium P sent from the accommodating portion (not shown) in which the recording medium P is accommodated. Further, when the chain52circulates in the circulating direction C in a state where the gripper54holds the front end of the recording medium P, the recording medium P is transported by moving the gripper54, and passes through the nip area28A together with the gripper54while the recording medium P is held by the gripper54(seeFIG. 3). The recording medium P is electrostatically attracted to the transfer cylinder28by the attracting roller59on the upstream side in the transport direction with respect to the nip area28A.

When the recording medium P passes through the nip area28A, the recording medium P is electrostatically attracted to the transfer belt24and the transfer cylinder28by the discharge of the discharge wire60A in the charger60. In addition, due to the discharge of the discharge wire60A in the charger60, the toner image superimposed on the transfer belt24is transferred from the transfer belt24to the recording medium P at the nip area28A (secondary transfer position T2).

In the exemplary embodiment, accordingly, the recording medium P is transported by circulating the chains52to which the gripper54is attached. Here, even when the sprockets29rotate at a constant speed, as the sprockets29and the sprockets19rotate, meshing positions of the teeth of the sprockets29and the teeth of the sprockets19with the chains52may change, causing the speed fluctuation of the chains52to occur.

Here, when viewed in a width direction of the transfer belt24(in a depth direction of the sheet ofFIG. 6), in the configuration in which the outer surface of the transfer belt24is in point contact with the transfer cylinder28as shown inFIG. 6, the speed fluctuation of the chain52may cause the speed fluctuation of the recording medium P in speed in the nip area28A. When the speed fluctuation of the recording medium P occurs in the nip area28A, a transfer failure of the toner image may occur.

In contrast, in the exemplary embodiment, as shown inFIG. 3, the nip area28A is formed by winding the transfer belt24around the transfer cylinder28. Thus, as compared with the configuration in which the outer surface of the transfer belt24is in point contact with the transfer cylinder28as shown inFIG. 6, the nip area28A sandwiching the recording medium P between the transfer belt24and the transfer cylinder28is wider in the belt circulating direction A. Therefore, as compared with the configuration in which the outer surface of the transfer belt24is in point contact with the transfer cylinder28as shown inFIG. 6, the speed fluctuation of the recording medium P in the nip area28A is prevented, and the transfer failure of the toner image is prevented. The configuration in which the outer surface of the transfer belt24is in point contact with the transfer cylinder28as shown inFIG. 6can also be said to have a configuration in which the common circumscribed line XA displaces from the transfer cylinder28.

In the exemplary embodiment, as shown inFIG. 3, the winding rollers42E and42F are disposed such that a common circumscribed line XA of the winding rollers42E and42F passes above the transfer cylinder28when viewed in the axial direction of the winding rollers42E and42F. Thus, as compared with the configuration in which the common circumscribed line XA displaces from the transfer cylinder28(seeFIG. 6), the nip area28A is wider in the belt circulating direction A. Therefore, as compared with the configuration in which the outer surface of the transfer belt24is in point contact with the transfer cylinder28as shown inFIG. 6, the speed fluctuation of the recording medium P in the nip area28A is prevented, and the transfer failure of the toner image is prevented.

The recording medium P is attached to the transfer cylinder28and the transfer belt24by being sandwiched between the transfer belt24and the transfer cylinder28in the nip area28A. For example, when the transfer belt24is separated from the recording medium P, the recording medium P is peeled off from the transfer belt24.

Here, in the configuration in which the recording medium P is transported by only a pair of transport rollers and passed through the nip area28A (hereinafter, this configuration is referred to as a comparative example), the recording medium P attached to the transfer cylinder28is less likely to be pulled in a direction away from the transfer cylinder28and is less likely to be peeled off from the transfer cylinder28. The comparative example in which the recording medium P is transported by only the pair of transport rollers can be said to be a configuration in which the recording medium P is transported without being held.

In contrast, in the exemplary embodiment, as described above, the gripper54is moved to transport the recording medium P, and the recording medium P passes through the nip area28A together with the gripper54while being held by the gripper54.

Thus, as compared with the comparative example, the recording medium P attached to the transfer cylinder28is likely to be pulled in the direction away from the transfer cylinder28and is likely to be peeled off from the transfer cylinder28. Therefore, the peeling defect in peeling the recording medium P on which the toner image is transferred from the transfer cylinder28is prevented.

In addition, in the exemplary embodiment, as shown inFIG. 3, the winding portion43E of the transfer belt24is separated from the transfer cylinder28. Thus, as compared with a configuration in which the winding portion43E of the transfer belt24is in contact with the transfer cylinder28, the recording medium P can be easily introduced into the nip area28A.

Further, in the exemplary embodiment, both the winding portion43E and the winding portion43F of the transfer belt24are separated from the transfer cylinder28. Thus, as compared to a configuration in which either the winding portion43E or the winding portion43F is in contact with the transfer cylinder28, the load (nip load) sandwiching the recording medium P between the transfer belt24and the transfer cylinder28is reduced.

Furthermore, in the exemplary embodiment, the pair of sprockets29is provided on the secondary transfer body27. Thus, space is saved as compared with a configuration in which the pair of sprockets29is provided as a member separate from the secondary transfer body27. Examples of the configuration in which the pair of sprockets29is provided as a separate member include a configuration in which the sprockets29are disposed at positions displacing from the axis of the transfer cylinder28. Other examples of the configuration in which the pair of sprockets29is provided as a separate member include a configuration in which the sprockets29rotate by a drive different from the transfer cylinder28

In addition, in the exemplary embodiment, as shown inFIG. 4, the outer diameter of each of the pair of sprockets29is smaller than the outer diameter of the transfer cylinder28. Here, in a configuration in which the outer diameter of each of the pair of sprockets29is equal to or larger than the outer diameter of the transfer cylinder28, the circumferential speed of the sprockets29is larger than the circumferential speed of the transfer cylinder28. Accordingly, the transport speed of the recording medium P held by the gripper54attached to the chain52wound around the sprocket29may be larger than the circumferential speed of the transfer cylinder28. Accordingly, in the nip area28A, the recording medium P may be pulled and displaced to the downstream side in the transport direction with respect to the transfer cylinder28and the transfer belt24.

In contrast, in the exemplary embodiment, as described above, since the outer diameter of each of the pair of sprockets29is smaller than the outer diameter of the transfer cylinder28, the recording medium P is prevented from being displaced to the downstream side in the transport direction with respect to the transfer cylinder28and the transfer belt24, as compared with the configuration in which the outer diameter of each of the pair of sprockets29is equal to or larger than the outer diameter of the transfer cylinder28.

Further, in the exemplary embodiment, the transfer cylinder28includes the base member28E and the surface layer28F which is wound around the outer circumference of the base member28E and exchangeable with respect to the base member28E.

Thus, when the surface layer28F is deteriorated, it is sufficient to replace only the surface layer28F, and it is not necessary to replace the secondary transfer body27including the pair of sprockets29.

(Modification Relating to Winding Portion43E and Winding Portion43F of Transfer Belt24)

In the exemplary embodiment, both the winding portion43E and the winding portion43F of the transfer belt24are separated from the transfer cylinder28, but the present invention is not limited thereto. For example, as shown inFIG. 7, the winding portion43E may be in contact with the transfer cylinder28, and the winding portion43F may be separated from the transfer cylinder28.

According to this configuration, the nip area28A is wider in the belt circulating direction A as compared with the configuration in which both the winding portions43E and43F are separated from the transfer cylinder28.

In addition, as shown inFIG. 8, the winding portion43E may be separated from the transfer cylinder28, and the winding portion43F may be in contact with the transfer cylinder28.

According to this configuration, the nip area28A is wider in the belt circulating direction A as compared with the configuration in which both the winding portions43E and43F are separated from the transfer cylinder28. In addition, as compared with a configuration in which the winding portion43E of the winding roller42E is in contact with the transfer cylinder28, the recording medium P can be easily introduced into the nip area28A.

Further, as shown inFIG. 9, both the winding portion43E and the winding portion43F may be in contact with the transfer cylinder28.

According to this configuration, the nip area28A is wider in the belt circulating direction A as compared with the configuration in which either one the winding portions43E and43F is separated from the transfer cylinder28.

In the exemplary embodiment, as shown inFIG. 3, the charger60faces the transfer cylinder28in an area including the center28S in the transport direction of the transport unit15in the nip area28A, but the present invention is not limited thereto.

Examples of the facing portion include, as shown inFIG. 10, a facing portion170including a charger160disposed on the upstream side of the center28S in the nip area28A. The charger160is configured in the same manner as the charger60described above. The charger160is an example of the facing portion on the upstream side.

According to this configuration, a range in which the recording medium P is electrostatically attracted to the transfer belt24and the transfer cylinder28is wider, as compared with a configuration including only a charger disposed in a range from the center28S of the nip area28A to the downstream side.

Further, as shown inFIG. 11, the facing portion170may include a charger180which is disposed on the downstream side of the charger160in the transport direction and to which a voltage larger than that of the charger160is applied. Here, a transfer voltage value optimal for transferring the toner image to the recording medium P is larger than an electrostatic attraction voltage value optimum for electrostatically attracting the recording medium P to the transfer belt24and the transfer cylinder28. Then, for example, the electrostatic attraction voltage value is applied to the charger160, and the transfer voltage value is applied to the charger180. The charger180is an example of the facing portion on the downstream side.

In the configuration shown inFIG. 11, the charger160has a function of electrostatically attracting the recording medium P to the transfer belt24and the transfer cylinder28as a main function, and the charger180has a function of transferring the toner image to the recording medium P as a main function, as compared with a configuration in which the voltages applied to the charger160and the charger180are the same. Thus, in the configuration shown inFIG. 11, the charger160and the charger180are functionally separated.

In the exemplary embodiment, as shown inFIG. 3, the chains52travel between the transfer belt24and the transfer cylinder28on the downstream side in the transport direction with respect to the nip area28A in a side view, but the present invention is not limited thereto.

For example, as shown inFIG. 12, the chains52may travel along the transfer belt24on the downstream side in the transport direction with respect to the nip area28A in a side view. Specifically, the chains52travel along the transfer belt24to the winding portion43F on the downstream side in the transport direction with respect to the nip area28A in a side view.

Accordingly, the recording medium P transported in a state of being held by the gripper54moves along the transfer belt24to the winding portion43F on the downstream side in the transport direction with respect to the nip area28A, and the recording medium P is peeled off from the transfer cylinder28before being peeled off from the transfer belt24.

In other words, the configuration shown inFIG. 12is a configuration in which the recording medium P is peeled off from the transfer cylinder28before being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A.

The configuration shown inFIG. 12is realized, for example, by supporting a portion of the chain52travelling from the sprockets29to the sprockets19with a sprocket202disposed on the inner side of the chain52, as shown inFIG. 13.

According to the configuration shown inFIG. 12, the peeling discharge between the transfer belt24and the recording medium P is prevented, as compared with a configuration in which the recording medium P is peeled off from the transfer cylinder28after being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A (hereinafter, this configuration is referred to as a configuration in which the recording medium P is peeled off from the transfer cylinder28after being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A). As a result, the scattering of the toner of the toner image transferred to the recording medium P is prevented, as compared with the configuration in which the recording medium P is peeled off from the transfer cylinder28after being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A.

Further, instead of the configuration shown inFIG. 3, as shown inFIG. 14, the chains52may travel along the transfer cylinder28on the downstream side in the transport direction with respect to the nip area28A in a side view. Specifically, the chains52travel along the transfer cylinder28at least to a facing position28X facing the winding portion43F on the downstream side in the transport direction with respect to the nip area28A in a side view.

Accordingly, the recording medium P transported in a state of being held by the gripper54moves along the transfer cylinder28to the winding portion43F on the downstream side in the transport direction with respect to the nip area28A, and the recording medium P is peeled off from the transfer cylinder28after being peeled off from the transfer belt24.

In other words, the configuration shown inFIG. 14is a configuration in which the recording medium P is peeled off from the transfer cylinder28after being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A.

The configuration shown inFIG. 14is realized, for example, by supporting a portion of the chain52travelling from the sprockets29to the sprockets19with a sprocket204disposed on the outer side of the chain52, as shown inFIG. 15.

According to the configuration shown inFIG. 14, vibration of the recording medium P is prevented, as compared with a configuration in which the recording medium P is peeled off from the transfer cylinder28before being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A.

Further, as shown inFIGS. 16 and 17, the sprocket202and the sprocket204may be provided to switch the configuration between a state (the state shown inFIG. 12) where the recording medium P is peeled off from the transfer cylinder28before being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A and a state (the state shown inFIG. 14) where the recording medium P is peeled off from the transfer cylinder28after being peeled off from the transfer belt24on the downstream side in the transport direction with respect to the nip area28A.

According to the configuration shown inFIGS. 16 and 17, depending on a situation in which image formation is performed, such as the type of the recording medium P, switching is made between the state shown inFIG. 12and the state shown inFIG. 14. Specifically, for example, in the case of using a type of recording medium P (for example, thick paper) effective to prevent vibration, the configuration is switched to the state shown inFIG. 14, and in using a type of recording medium P (for example, thin paper) effective to prevent the peeling discharge with the transfer belt24, the configuration is switched to the state shown inFIG. 12.

(Modification Relating to Fixing Device16)

In the exemplary embodiment, as shown inFIG. 1, the fixing device16is provided on the downstream side of the sprocket19in the transport direction of the recording medium P, but the present invention is not limited thereto.

For example, as shown inFIG. 19, the fixing device16may include the heating roller68, the pressure roller69, and the pair of sprockets19. The fixing device16is an example of a fixing unit.

The pair of sprockets19is an example of a second rotating body. The pair of sprockets19is respectively disposed on both axial end sides of the pressure roller69. In other words, the pressure roller69is provided between the pair of sprockets19. Further, the pair of sprockets19is disposed coaxially with the pressure roller69and configured to rotate integrally with the pressure roller69. The pressure roller69is rotationally driven by a drive unit (not shown).FIG. 19shows, of the pair of sprockets19, one sprocket19disposed on one axial end side (the back side of the sheet ofFIG. 19) of the pressure roller69.

Further, on an outer circumference of the pressure roller69, a recessed portion69D is formed, in which the gripper54and the attaching member55of the transport unit15are accommodated. A plurality of recessed portions69D may be formed according to the disposition interval of the grippers54along the circulating direction C of the chain52.

With the transport unit15, the recording medium P passes through the nip area28A together with the gripper54while being held the by the gripper54. Further, with the transport unit15, the recording medium P passes through the nip area28A, and then passes through a nip area69A (an example of a fixing area) together with the gripper54while being held the by the gripper54.

According to this configuration, space is saved as compared with a configuration in which the sprocket19is provided as a member separate from the fixing device16.

In addition, after the nip area28A is passed through in the circulating direction C of the chain52, no sprocket is provided until the recording medium P arrives at the nip area69A.

According to this configuration, the chain52is wound in a straight line after the secondary transfer and before fixing, and the recording medium P on which the image is transferred is prevented from being bent and transported, as compared with a configuration in which the sprocket is provided before the recording medium P arrives at the nip area69A after the nip area28A is passed through in the circulating direction C of the chain52.

The outer diameter of each of the pair of sprockets19is smaller than the outer diameter of the pressure roller69. The outer diameter of the sprocket19is an outer diameter including the teeth (i.e., including the diameter of the tooth tip).

According to this configuration, in the nip area69A, the recording medium P is prevented from being displaced to the downstream side in the transport direction with respect to the heating roller68, as compared with a configuration in which the outer diameter of the sprocket19is equal to or larger than the outer diameter of the pressure roller69.

The pressure roller69includes a base member69E and a surface layer69F which is wound around an outer circumference of the base member69E and exchangeable with respect to the base member69E. As the base member69E, a metal material such as stainless steel is used. As the surface layer69F, an elastic material such as silicone rubber or one obtained by sequentially laminating a release layer made of PFA on an elastic material such as silicone rubber is used. The surface layer69F is detachably fixed to the base member69E. Therefore, the surface layer69F can be detached from the base member69E, and an unused surface layer69F can be attached thereto.

Thus, when the surface layer69F is deteriorated, it is sufficient to replace only the surface layer69F, and it is not necessary to replace the fixing device16including the pair of sprockets19.

Further, as shown inFIG. 19, a non-contact heating unit70may be provided between the secondary transfer body27and the fixing device16in the transport direction of the recording medium P, which heats the recording medium P without being in contact with the recording medium P. Here, the non-contact heating unit70includes a reflection plate72and a plurality of infrared heaters74(hereinafter referred to as “heaters74”).

The reflection plate72is formed using an aluminum plate, and has a shallow bottom box shape in which the transported recording medium P side (lower side inFIG. 19) is opened. In the exemplary embodiment, as viewed from above, the reflection plate72is configured to cover the transported recording medium P in the depth direction (the depth direction in the sheet ofFIG. 19) of the apparatus.

The heater74is an infrared heater whose outer shape is a cylindrical shape, and a plurality of heaters74are accommodated in the reflection plate72and disposed to extend in the depth direction of the apparatus. In the exemplary embodiment, as viewed from above, the heaters74are configured to cover the recording medium P to be transported in the depth direction of the apparatus. In addition, the plurality of heaters74are arranged in the width direction (left-right direction inFIG. 19) of the apparatus. The heater74is an example of a non-contact heating unit.

According to this configuration, the image can be heated without being in contact with the recording medium P, as compared with a case where no non-contact heating unit70is provided between the secondary transfer body27and the fixing device16in the transport direction of the recording medium P, which heats the recording medium P without being in contact with the recording medium P. Further, the recording medium P is transported while being held by the gripper54from the nip area28A to the nip area69A, so that the registration displacement of the recording medium P is prevented as compared with a case where the recording medium P is not transported while being held from the nip area28A to the nip area69A.

Here, in a case of performing duplex printing, an image may be already formed on a surface (hereinafter, referred to as “back surface”) of the recording medium P opposite to the surface on which the image is transferred. When the recording medium P is heated in a non-contact manner, the transport unit which transports the recording medium P in contact with the back side of the recording medium P is heated by the heat received from the heater74and the image on the back side of the recording medium P in contact with the transport unit may be disturbed. However, in the exemplary embodiment, since the recording medium P is transported without the back surface thereof being contacted with the transport unit in the area facing the heater74, the disruption of the image on the back surface of the recording medium P is prevented.

Further, as shown inFIG. 19, a blowing unit76may be provided at a position facing the heater74with the chain52(specifically, a portion on the downstream side of the sprocket29and on the upstream side of the sprocket19in the circulating direction C of the chain52) sandwiched therebetween in a side view. The blowing unit76includes an air hole80directed to the back surface of the recording medium P and a fan78. The blowing unit76is an example of a blowing unit.

In this configuration, the fan78blows air toward the back surface of the recording medium P, so that the posture of the recording medium P is stabilized such that the sheet surface of the recording medium P transported between the blowing unit76and the heater74is directed in an upper-lower direction. That is, when the force of the air blown out from the fan78is controlled, the trailing end of the transported recording medium P is prevented from moving downward with respect to the leading end of the recording medium P. The air hole80does not face the surface of the recording medium P to which the image is transferred. Thus, cooling of the image transferred to the recording medium P is prevented.

In the exemplary embodiment, a so-called corotron is used as the charger60, but the present invention is not limited thereto. For example, a so-called scorotron having a grid may be used as the charger60.

In addition, in the exemplary embodiment, the gripper54as an example of the holding unit holds the leading end portion of the recording medium P, but the present invention is not limited thereto. For example, as shown inFIG. 18, grippers154,155and156which hold the side end portion of the recording medium P may be used as examples of the holding unit. In this configuration, the grippers154,155and156hold the recording medium P in an area outside an area GR to which the toner image of the recording medium P is transferred. Also in this configuration, when transporting the recording medium P, the grippers154,155and156pass through the nip area28A in a side view. InFIG. 18, the chains52are shown in a simplified manner. In addition,FIG. 18shows a state where the recording medium P is transported between the sprocket29and the sprocket19.

Further, the holding unit may be configured only by the gripper154which holds the leading end side of the recording medium P. The leading end side of the recording medium is a portion on the downstream side (front side) of the center of the recording medium in the transport direction.

Further, in the exemplary embodiment, the chain52is used as an example of the circulating member, but the present invention is not limited thereto. For example, a timing belt may be used as an example of the circulating member. In addition, in the exemplary embodiment, the sprocket29was used as an example of the rotating body, but the present invention is not limited thereto. For example, a timing pulley around which a timing belt is wound may be used as an example of the rotating body. When a timing pulley is used as an example of the rotating body, a timing pulley is also used instead of the sprocket19. In the configurations shown inFIG. 12toFIG. 17, when a timing pulley is used as an example of the rotating body, a timing pulley is used instead of the sprockets202and204.

In addition, in the exemplary embodiment, the charger60is used as an example of the facing portion, but the present invention is not limited thereto. For example, a facing roller in contact with the transfer belt24may be used as an example of the facing portion.

In addition, in the exemplary embodiment, the heating roller68is used as an example of the heating unit, but the present invention is not limited thereto. For example, a heating belt in contact with the pressure roller69may be used as an example of the heating unit.

In addition, in the exemplary embodiment, the heater74is used as an example of the non-contact heating unit, but the present invention is not limited thereto. For example, a halogen lamp may be used as an example of the non-contact heating unit.

The present invention is not limited to the above embodiment, and various modifications, changes, and improvements can be made without departing from the scope of the invention. For example, the modifications shown above may be combined with each other as appropriate.