Image forming apparatus including photoconductor drum

A drum unit of an image forming apparatus including a flange that is integrally provided with the photoconductor drum. A frame rotatably supports the photoconductor drum and covers its side. A gear portion is integrally formed with an outer circumferential surface of the flange. An outer diameter of the gear portion is larger than a diameter size of the photoconductor drum. A guide member is provided on an upper surface of the frame and guides the edge portion upward when the drum unit is pulled out of the apparatus main body. An upper surface of the guide member includes first and second guide surfaces. The first guide surface is located more on a side of a center of the photoconductor drum than the edge position, and the second guide surface is located more on the side of the insertion direction than the edge position.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2015-241834 filed on Dec. 11, 2015, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an image forming apparatus such as a copier or a multifunction peripheral, and in particular relates to an image forming apparatus including a photoconductor drum used in a process of forming an image on a sheet.

An image forming apparatus of an electrophotographic system includes a photoconductor drum on which a toner image is formed by a developing device. The toner image formed on the photoconductor drum is transferred to a transfer belt by a primary transfer device, and is further transferred from the transfer belt to a sheet by a secondary transfer device. The photoconductor drum is unitized into a drum unit together with a frame and the like, wherein the frame rotatably supports the photoconductor drum. The drum unit including the photoconductor drum is attached to the image forming apparatus in a detachable manner. There is known, as one example of conventional image forming apparatuses, an image forming apparatus to/from which the drum unit is inserted and pulled out horizontally.

As one example of such drum units, there is known a drum unit that includes a flange fixed to an end portion of the photoconductor drum in the axial direction. The flange is integrally formed with a gear portion that transmits a rotational driving force to another driven body.

SUMMARY

An image forming apparatus according to an aspect of the present disclosure includes an apparatus main body, a drum unit, and a transfer belt. The drum unit is attached, in a detachable manner, to a predetermined attachment position inside the apparatus main body. The drum unit includes a cylindrical photoconductor drum and is configured to be inserted and pulled out horizontally with respect to the apparatus main body. The transfer belt is disposed above the photoconductor drum in such a way as to face and contact an outer circumferential surface of the photoconductor drum in a state where the drum unit is disposed at the attachment position. The drum unit includes a flange, a frame, a gear, and a guide member. The flange is integrally provided with the photoconductor drum by being fixed to an inner hole of a side end portion of the photoconductor drum, the side end portion being on a side of an insertion direction of the drum unit opposite to a pulling out direction. The frame is configured to rotatably support the photoconductor drum and cover a side of the photoconductor drum. The gear portion is integrally formed with an outer circumferential surface of the flange, wherein an outer diameter of the gear portion is larger than a diameter size of the photoconductor drum. The guide member is provided on an upper surface of the frame and extends in the insertion direction and the pulling out direction on both sides of an edge position, wherein the edge position is a position at which an edge portion, on the side of the insertion direction, of a surface of the transfer belt facing the photoconductor drum, is disposed in the state where the drum unit is disposed at the attachment position, and the guide member is configured to guide the edge portion upward when the drum unit is pulled out of the apparatus main body. An upper surface of the guide member includes a first guide surface and a second guide surface, wherein the first guide surface is located more on a side of a center of the photoconductor drum than the edge position, and the second guide surface is located more on the side of the insertion direction than the edge position. The first guide surface is lower than a height position of a lower end of the edge portion, and the second guide surface is higher than an upper-end position of the gear portion.

DETAILED DESCRIPTION

The following describes an embodiment of the present disclosure with reference to the attached drawings. It should be noted that the following embodiment is an example of a specific embodiment of the present disclosure and should not limit the technical scope of the present disclosure. It is noted that, for the sake of explanation, a vertical direction in an installed state of an image forming apparatus10where the image forming apparatus10is usable (the state shown inFIG. 1) is defined as an up-down direction7. In addition, a front-rear direction8is defined on a supposition that a side to/from which a sheet feed cassette24shown inFIG. 1is inserted and pulled out in the installed state is a front side. Furthermore, a left-right direction9is defined based on the front side of the image forming apparatus10in the installed state.

The image forming apparatus10according to the present embodiment has at least a print function. The image forming apparatus10is a so-called tandem-type color printer.

As shown inFIG. 1andFIG. 2, the image forming apparatus10includes a housing10A (an example of the apparatus main body). The housing10A has an approximately rectangular parallelepiped shape as a whole. Some of the components constituting the image forming apparatus10are stored in the housing10A.

As shown inFIG. 2, the image forming apparatus10includes four image forming units4, an intermediate transfer unit5, a laser scanning device13, a secondary transfer roller20, a fixing device16, a sheet discharge tray18, the sheet feed cassette24, an operation/display portion25(seeFIG. 1), a belt cleaning device6, and a control portion2.

Each of the image forming units4includes a developing device31, a primary transfer roller32, and a drum unit50including a photoconductor drum51, and forms an image by the electrophotography system. The image forming units4are arranged in alignment along the front-rear direction8in the housing10A, and form a color image based on a so-called tandem system. The image forming units4form a color toner image on a transfer belt46by transferring toner images of different colors from the photoconductor drums51to the transfer belt46such that the toner images are overlaid with each other. The toner image on the transfer belt46is transferred by the secondary transfer roller20to a printing sheet fed from the sheet feed cassette24.

The intermediate transfer unit5is provided above the four image forming units4. That is, the intermediate transfer unit5is provided above the four drum units50. As shown inFIG. 3, the intermediate transfer unit5includes a main body frame45and a transfer belt46. In addition, a driving pulley5A and a driven pulley5B are provided at opposite ends of the main body frame45in the front-rear direction8. The transfer belt46is supported by the driving pulley5A and the driven pulley5B by being suspended therebetween. This enables the belt surface of the transfer belt46to extend horizontally in the front-rear direction8. The transfer belt46can move in a direction indicated by the arrow19while the surface thereof is in contact with the surfaces of the photoconductor drums51. In the present embodiment, the transfer belt46is supported in such a way as to face and contact the outer circumferential surfaces of the photoconductor drums51in a state where the drum units50are disposed at predetermined attachment positions in the housing10A.

Specifically, the transfer belt46is an annular belt member. The width of the transfer belt46is equal to the longitudinal length of the photoconductor drums51. The transfer belt46includes a base layer portion and a surface layer portion that is formed on the surface of the base layer portion. The base layer portion is formed from a thermoplastic resin. For example, the thermoplastic resin is PC (polycarbonate), PVDF (polyvinylidene fluoride), PA (nylon), or PBT (polybutylene terephthalate). The surface layer portion is formed by coating the base layer portion with a thermosetting resin. For example, the thermosetting resin is PI (polyimide), PAI (polyamideimide), or AC (acrylic).

Each drum unit50includes a photoconductor drum51. The photoconductor drum51is formed in a cylindrical shape, and is made by forming a thin photoconductive layer of an amorphous silicon (a-Si) photoconductive material on the surface of a blank pipe made of aluminum. That is, the photoconductive layer is formed on the surface of the photoconductor drum51. An electrostatic latent image is formed on the photoconductive layer. The photoconductor drums51are disposed under the primary transfer rollers32respectively, and the transfer belt46is held at nip portions between the photoconductor drums51and the primary transfer rollers32. It is noted that the drum unit50is described below.

The laser scanning device13is provided below the four image forming units4. The laser scanning device13generates laser beams based on image data of respective colors input thereto, and irradiates the laser beams to the surfaces of the photoconductor drums51of the drum units50. This allows electrostatic latent images to be formed on the surfaces of the photoconductive layers of the photoconductor drums51.

The sheet feed cassette24is provided in a bottom portion (the lowest portion) of the housing10A. Printing sheets of a predetermined size are stored in the sheet feed cassette24. The sheet feed cassette24is supported in the housing10A in a detachable manner. The sheet feed cassette24is attached to a predetermined attachment position in the housing10A. A vertical conveyance path26is formed in a rear side inside the housing10A, wherein the vertical conveyance path26extends from the sheet feed cassette24to the fixing device16via the secondary transfer roller20. In addition, a sheet feed unit24A is provided in proximity to a rear-end portion of the sheet feed cassette24. In a state where the sheet feed cassette24is attached to the attachment position, the sheet feed unit24A picks up, one by one, the printing sheets stacked on the sheet feed cassette24, and feeds the printing sheet toward the vertical conveyance path26.

The secondary transfer roller20is provided in the rear side inside the housing10A at a position facing the driving pulley5A. The toner image is transferred from the transfer belt46to the printing sheet by the secondary transfer roller20.

The fixing device16is provided above the secondary transfer roller20. The fixing device16fixes the toner image to the printing sheet by adding heat to the printing sheet. The fixing device16includes a pair of rollers: a heating roller16A and a pressure roller16B. In the fixing device16, the printing sheet conveyed thereto from the secondary transfer roller20is conveyed while being nipped between the heating roller16A and the pressure roller16B. At this time, heat is transmitted from the heating roller16A to the printing sheet, and the toner on the printing sheet is fused and fixed to the printing sheet. This allows a color image to be formed on the printing sheet.

As shown inFIG. 2, a discharge path28is formed to extend from the fixing device16to a sheet discharge port27. In the discharge path28, a pair of discharge rollers23is provided near the sheet discharge port27. The pair of discharge rollers23is composed of a driving roller23A and a driven roller23B, wherein the driven roller23B is pressed in contact by the driving roller23A. The printing sheet that has passed through the fixing device16is conveyed in the discharge path28, and then discharged to the sheet discharge tray18from the sheet discharge port27by the pair of discharge rollers23.

The following describes the photoconductor drum51and the configuration of the drum unit50that includes the photoconductor drum51, with reference toFIG. 3toFIG. 7B.

As described above, the image forming apparatus10includes the drum unit50. The drum unit50rotatably supports the photoconductor drum51, and as shown inFIG. 4, includes the photoconductor drum51, a charging roller52(an example of the transmitted portion of the present disclosure), a cleaning portion53, and a frame54that supports these portions. In addition, the drum unit50includes a rotation shaft62that rotatably supports the photoconductor drum51. The rotation shaft62is supported by the frame54. That is, the photoconductor drum51is unitized by being attached to the frame54, together with the charging roller52, the cleaning portion53, the rotation shaft62and the like.

The charging roller52is configured to uniformly charge the surface of the photoconductor drum51to a certain potential, and is a roller-like rotator. The charging roller52is provided below the photoconductor drum51. A support shaft is provided on each of opposite ends of the charging roller52in the longitudinal direction. The support shafts are rotatably supported by the frame54. The cleaning portion53is configured to remove toner that has remained on the surface of the photoconductor drum51, and includes, in an inside thereof, cleaning members such as a brush roller and a cleaning blade. The cleaning portion53is integrally attached to the frame54.

FIG. 4andFIG. 5are diagrams showing a configuration of the drum unit50.FIG. 4is a perspective view showing an outer appearance of the drum unit50.FIG. 5is a cross-sectional view of the drum unit50taken along a vertical plane that passes through the center of the rotation shaft62. As shown inFIG. 4andFIG. 5, the drum unit50is elongated in one direction. As shown inFIG. 4, the drum unit50is provided in the housing10A such that its longitudinal direction matches the left-right direction9of the image forming apparatus10. It is noted that in the following description, the up-down direction7, the front-rear direction8, and the left-right direction9are defined for the drum unit50based on the state where the drum unit50is attached to the inside of the housing10A.

The drum units50are disposed at predetermined attachment positions in the housing10A. The drum units50are slidably supported by an inner frame or the like of the housing10A such that they can be inserted and pulled out horizontally with respect to the housing10A. In the present embodiment, the drum units50can be horizontally inserted along the left-right direction9from the right side of the housing10A, and pulled out in a direction reverse to the insertion direction. When the drum units50are inserted into the innermost portion of the housing10A and attached to the attachment positions, the image formation becomes available.

Here, as the image formation is repeatedly performed, the photoconductive layers on the surfaces of the photoconductor drums51of the drum units50are gradually deteriorated or worn. When the photoconductive layers are deteriorated, chargeability is reduced; and when the photoconductive layers are worn out, the surfaces of the photoconductor drums51are not charged to a certain potential, both resulting in reduction of image quality. As a result, the photoconductor drums51need to be replaced at a predetermined replacement timing. In the present embodiment, the photoconductor drums51are respectively provided in the drum units50. As a result, when the photoconductor drums51are replaced, the drum units50need to be pulled out from the housing10A. In addition, when maintenance is performed to the inside of the image forming apparatus10, the drum units50need to be pulled out as necessary.

The frame54is a housing of the drum unit50. The frame54is elongated in one direction. The frame54is detachably attached to the inner frame or the like of the housing10A in a state where its longitudinal direction matches the left-right direction9. The frame54supports opposite ends of the rotation shaft62. The rotation shaft62supports the photoconductor drum51such that the photoconductor drum51can rotate around the rotation shaft62. The frame54includes support portions63and64that are separated from each other in the left-right direction9. The rotation shaft62is rotatably supported by the support portions63and64. In addition, the frame54includes a side cover portion61that covers a rear-side part of the circumferential surface of the photoconductor drum51. The side cover portion61extends along the left-right direction9, connecting the support portion63and the support portion64. The cleaning member is provided inside the side cover portion61.

As shown inFIG. 5, a flange65(seeFIG. 5) is provided on a left end portion51A, which is one of opposite end portions of the photoconductor drum51, located on the left side. Specifically, the flange65is provided on the left end portion51A on the side of an insertion direction D1when the drum unit50is inserted in the housing10A. The flange65is integrally fixed to (coupled with) the photoconductor drum51by being fitted in an inner hole of the left end portion51A of the photoconductor drum51. A flange71(seeFIG. 5) is provided on a right end portion51B, which is the other of the opposite end portions of the photoconductor drum51, located on the right side. The flange71is integrally fixed to (coupled with) the photoconductor drum51by being fitted in an inner hole of the right end portion51B of the photoconductor drum51.

A shaft hole66(seeFIG. 6) is formed at a central portion of the flange65, and a shaft hole (not shown) is formed at a central portion of the flange71. The rotation shaft62is rotatably inserted in the shaft hole66of the flange65and the shaft hole of the flange71.

The rotation shaft62passes through the support portion63and protrudes to the left side. On the other hand, an input gear69is provided on the inner frame of the housing10A, wherein the input gear69is configured to receive a rotational driving force transmitted from a driving source such as a motor (not shown). When the drum unit50is attached to the housing10A, a left end portion62A of the rotation shaft62is inserted in a shaft hole formed at the center of the input gear69. The rotational driving force is transmitted from the input gear69to the flange65via a joint74that is described below, and is further transmitted from the flange65to the photoconductor drum51. Upon receiving the rotational driving force, the photoconductor drum51rotates around the rotation shaft62in a predetermined rotation direction.

As shown inFIG. 6, the flange65is attached to the left end portion51A of the photoconductor drum51. The flange65is a resin member formed from a crystalline resin, such as polyacetal (POM) that has small friction coefficient and good slidability. The flange65is engaged and coupled with a cylindrical portion74A of the joint74in a circumferential direction, wherein the cylindrical portion74A and the joint74are described below. This enables the flange65to receive the rotational driving force from the joint74.

Specifically, the flange65includes a pressure input portion65A, a gear portion65B, and a shaft portion65C, and these portions are integrally formed by a metal molding. The flange65is formed from a resin member.

The pressure input portion65A is a cylindrical portion protruding from the right side surface of the gear portion65B outward (rightward) in the axial direction. The pressure input portion65A is inserted and fitted in the inner hole of the photoconductor drum51by pressure. This allows the pressure input portion65A to be fixed to the photoconductor drum51. It is noted that the shaft hole66is formed at the central portion of the flange65, more specifically at the central portion of the pressure input portion65A. The rotation shaft62is inserted in the shaft hole66.

The gear portion65B is integrally formed on the outer circumferential surface of the flange65. The outer diameter of the gear portion65B is larger than the diameter size of the photoconductor drum51. The gear portion65B is coupled with a cleaning roller (not shown) for cleaning the charging roller52so that drive can be transmitted. During a rotation of the photoconductor drum51, the rotational driving force is transmitted from the gear portion65B to the input gear of the cleaning roller, and the cleaning roller for the charging roller52is rotated. To provide excellent transmission of the rotational driving force and reduce the driving sound and wear during the connection driving, lubricant such as silicone grease is applied to the gear portion65B. It is noted that in the present embodiment, the gear portion65B is a helical gear that has teeth inclined in the axial direction. Of course, the gear portion65B may be a spur gear or a bevel gear.

The shaft portion65C protrudes from the left side surface of the gear portion65B outward (leftward) in the axial direction. In a state where the pressure input portion65A of the flange65is fixed to the left end portion51A of the photoconductor drum51, the shaft portion65C protrudes outward in the axial direction from the center of the left side surface of the gear portion65B. The shaft portion65C is smaller in diameter than the gear portion65B and the pressure input portion65A. The shaft portion65C is formed in the shape of a cylinder whose inside is hollow. The inner diameter of the shaft portion65C is larger than the outer diameter of the cylindrical portion74A of the joint74. As a result, the cylindrical portion74A can be inserted in an inner hole of the shaft portion65C. In the present embodiment, the cylindrical portion74A is inserted in the inner hole of the shaft portion65C, and the flange65and the joint74are engaged and coupled with each other in the circumferential direction. For example, an engaging rib (not shown) extending in the axial direction is provided on the outer circumferential surface of the cylindrical portion74A, an engaging groove (not shown) extending in the axial direction is provided on the inner surface of the shaft portion65C, and when the cylindrical portion74A is inserted in the inner hole of the shaft portion65C, the engaging rib is inserted in the engaging groove. This makes it possible for the shaft portion65C and the cylindrical portion74A to be coupled with each other in the circumferential direction, and move relative to each other in the axial direction.

The joint74is provided on the left side of the flange65. The joint74receives the rotational driving force input to the input gear69, and transmits the rotational driving force to the flange65. As shown inFIG. 6, the joint74includes a cylindrical portion74A and a cylindrical portion74B that are different in outer diameter. The cylindrical portion74A is smaller than the cylindrical portion74B in outer diameter. In the joint74, the cylindrical portion74A is provided on the flange65side, and the cylindrical portion74B is provided on the opposite side (on the input gear69side). In addition, a shaft hole75is formed at the center of the joint74, wherein the shaft hole75is common to the cylindrical portion74A and the cylindrical portion74B. The rotation shaft62is inserted in the shaft hole75. The cylindrical portion74B has an engaging groove (not shown) that can be coupled with the input gear69. When the joint74is biased by a coil spring67that is described below, the input gear69and the cylindrical portion74B are engaged in the rotation direction, and the joint74and the input gear69are coupled with each other.

As shown inFIG. 6, the coil spring67is provided between the flange65and the joint74. The coil spring67biases the joint74outward (leftward) in the axial direction by a predetermined spring force (elastic force). In the present embodiment, the coil spring67acts as a compression spring, and is attached to the hollow portion of the shaft portion65C of the flange65. In this state, the cylindrical portion74A is inserted in the inner hole of the shaft portion65C. This makes it possible for the coil spring67to elastically bias the joint74outward (leftward) in the axial direction.

A cylindrical protection cover77is provided to cover the cylindrical portion74A of the joint74and the shaft portion65C of the flange65. The protection cover77is inserted in an opening63A formed in the support portion63such that a part of the protection cover77is exposed to outside. An inclined surface63B is formed on an upper end portion of the support portion63on the side of the insertion direction D1. The inclined surface63B plays a role of a guide surface that, when the drum unit50is inserted in the housing10A, abuts on an edge portion of the transfer belt46and guides the edge portion to rise upward.

Here, in the drum unit50, in a case where the outer diameter (addendum circle diameter) of the gear portion65B of the flange65is larger than the outer diameter of the photoconductor drum51, when the drum unit50is pulled out of the housing10A during replacement or maintenance, the gear portion65B may be caught by an edge portion46A of the transfer belt46, and the edge portion46A may be damaged. As a result, conventionally, a well-known retreating mechanism is provided in the image forming apparatus10, such as a mechanism that, when the drum unit50is pulled out, lowers the drum unit50in a direction (downward) away from the transfer belt46, or a mechanism that moves the transfer belt46upward before the drum unit50is pulled out. However, since, as described above, the transfer belt46is formed from a resin member and suspended between the driving pulley5A and the driven pulley5B with a predetermined tension, slack would be generated on the transfer belt46. As a result, when the transfer belt46and the photoconductor drum51are relatively separated from each other by the retreating mechanism, the transfer belt46may be in a state of being in contact with the photoconductor drum51. When the drum unit50is pulled out in such a state, the gear portion65B would be caught by the edge portion46A of the transfer belt46that is located on the side of the insertion direction D1. Even if the gear portion65B is not caught by the edge portion46A, if the gear portion65B contacts the surface of the edge portion46A during the pulling out, the lubricant applied to the gear portion65B adheres to the surface of the transfer belt46. This may reduce adhesion or transferability of the toner image on the surface of the transfer belt46, and cause reduction in image quality.

In view of the above-described problem, in the drum unit50of the present embodiment, a guide member80is provided on the upper surface of the side cover portion61of the frame54. Furthermore, a film member90(an example of the cover member of the present disclosure) is provided so as to cover the gear portion65B of the flange65. The provision of the guide member80and the film member90prevents the gear portion65B of the flange65from contacting the transfer belt46when the drum unit50is pulled out.

The guide member80guides the edge portion46A (seeFIG. 6) of the transfer belt46upward when the drum unit50is pulled out of the housing10A. As shown inFIG. 4, the guide member80is provided on the frame54. Specifically, the guide member80is provided on the upper surface of the side cover portion61. The guide member80may be integrally formed with the frame54. In addition, the guide member80may be a member provided independently of the frame54. In a case where the guide member80is provided independently of the frame54, the guide member80is attached to the upper surface of the side cover portion61by adhesive, double-sided tape or the like.

In the present embodiment, the guide member80is provided on the upper surface of the side cover portion61near an end of the side cover portion61on the side of the insertion direction D1. The guide member80extends on both sides of an edge position P1(seeFIG. 6) along the left-right direction9(insertion and pulling out direction of the photoconductor drum51), wherein the edge position P1is a position at which the edge portion46A of the transfer belt46is disposed in the state where the drum unit50is disposed at the attachment position in the housing10A.

As shown inFIG. 6, the upper surface of the guide member80includes a first guide surface81, a second guide surface82and an inclined guide surface83. The first guide surface81is a part of the upper surface of the guide member80, and located more on the side of the center of the photoconductor drum51than the edge position P1. The second guide surface82is another part of the upper surface of the guide member80, and located more on the side of the insertion direction D1than the edge position P1. The inclined guide surface83is formed in an area that extends on both sides of the edge position P1, between the first guide surface81and the second guide surface82. In the present embodiment, the first guide surface81is lower than a height position P2, which is a height position of a lower end of the edge portion46A in the up-down direction7(height direction). In addition, the second guide surface82is higher than the height position P2and an upper-end position P3, wherein the upper-end position P3is a height position of an upper end of the gear portion65B.

With the guide member80configured as described above being provided in the drum unit50, when the drum unit50is pulled out from the attachment position in the housing10A, first the guide member80abuts on the edge portion46A of the transfer belt46. Then, during the process of pulling out the drum unit50, the edge portion46A is guided from the first guide surface81to the inclined guide surface83, and then to the second guide surface82. This causes the edge portion46A to rise to at least the upper-end position P3of the gear portion65B. As a result, the gear portion65B does not contact the edge portion46A when the drum unit50is pulled out of the housing10A. This prevents the edge portion46A from being damaged by contact.

It is noted that in the case where the guide member80is provided independently of the frame54, the guide member80is not necessarily formed from the resin member as the frame54is, but may be formed from a material that is soft enough to absorb the impact of the contact with the edge portion46A, and rigid enough to raise the edge portion46A upward at the contact.

As shown inFIG. 4, the film member90is attached to the support portion63of the frame54to cover the gear portion65B of the flange65. The gear portion65B is coupled with the input gear of the charging roller52. As a result, in the present embodiment, the film member90is attached in such a way as to cover an area excluding a lower end portion of the gear portion65B where the gear portion65B is coupled with the input gear. Specifically, the film member90is attached in such a way as to cover an upper area of the outer circumferential surface of the gear portion65B. The film member90is formed in a curved shape along the outer circumferential surface of the gear portion65B. An end portion91(seeFIG. 7A), which is one of opposite end portions of the film member90, is fixed to the guide member80, and an end portion92(seeFIG. 7A), which is the other of the opposite end portions of the film member90, is fixed to the support portion63.

The film member90is a film made of, for example, polyester. As shown inFIG. 7AandFIG. 7B, the end portion92is approximately vertically bent, and the film member90is fixed when the end portion92is inserted in a slit-like groove formed in the support portion63. In addition, a slit-like groove extending horizontally is formed in a side surface of the guide member80, and the film member90is fixed when the end portion91is inserted in this groove.

As shown inFIG. 6, the film member90protrudes in the insertion direction D1from an end portion of the gear portion65B on the side of the insertion direction D1.

With the film member90configured as described above being provided, the gear portion65B does not directly contact the lower surface of the transfer belt46when the drum unit50is pulled out. As a result, the lubricant applied to the gear portion65B does not adhere to the lower surface of the transfer belt46. This prevents reduction of adhesion or transferability of the toner image on the lower surface of the transfer belt46.

In addition, with the configuration where the film member90protrudes in the insertion direction D1from an end portion of the gear portion65B on the side of the insertion direction D1, even if the lubricant moves in the insertion direction D1from the gear portion65B when the flange65is rotated, the lubricant is prevented from climbing over the film member90and moving to the transfer belt46located at a higher position. In particular, in a case where a helical gear is used as the gear portion65B, and the helical gear is inclined toward the upstream in the rotation direction of the flange65, the lubricant is apt to move in the insertion direction D1. According to the present embodiment, the film member90protrudes in the insertion direction D1from an end portion of the gear portion65B on the side of the insertion direction D1. This configuration effectively prevents the lubricant from adhering to the transfer belt46.