JP2015121628A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to prevent misregistration of a primarily transferred toner image, due to vibration generated when a medium is nipped at a transfer nip.SOLUTION: An image forming apparatus 10 includes: an endless transfer body 36 circularly moved by a driving body 32D in contact with an inner circumferential surface, to secondarily transfer a primarily transferred toner image to a medium P; first transfer sections 22M, 22C, 22K each rotating around its own axial center and primarily transferring a toner image to the transfer body 36; and a second transfer section 22Y which is arranged upstream of the first transfer sections 22M, 22C, 22K in a circulation direction A of the transfer body 36 and downstream of a section 72, where the driving body 32D comes into contact with an inner circumferential surface of the transfer body 36, in the circulation direction A, has an inertial mass larger than those of the first transfer sections 22M, 22C, 22K, rotates around its own axial center, and primarily transfers the toner image to the transfer body 36.

Description

  The present invention relates to an image forming apparatus.

  In Patent Document 1, a flywheel is provided at the ends of the rotation shafts of a plurality of image carriers corresponding to relatively high-visibility color materials, and the image carrier corresponding to a relatively low-visibility color material is used as a flywheel. A configuration in which a wheel is not provided or a flywheel having a different diameter or weight is provided is disclosed.

  Patent Document 2 includes a second flywheel provided to be connectable to the first flywheel and a contact / separation mechanism for connecting and disconnecting the first and second flywheels in the photoreceptor unit. A configuration is disclosed in which the inertial mass applied to the drum is variable.

JP 2000-242055 A JP 2001-166633 A

  The image forming apparatus of the present invention is to suppress the deviation of the primary transferred toner image caused by vibration generated when the medium is sandwiched between the transfer nips.

  An image forming apparatus according to a first aspect of the present invention includes an endless transfer body that secondarily transfers a toner image that has been primarily transferred onto a medium while being driven to rotate by a driving body that contacts the inner peripheral surface. A first transfer section that rotates about its own axis and primarily transfers a toner image to the transfer body; an upstream side of the transfer body in the circumferential movement direction from the first transfer section; Arranged on the downstream side in the circumferential movement direction from the portion in contact with the inner peripheral surface of the body, the inertial mass is larger than that of the first transfer portion, and the toner image rotates about its own axis to primarily transfer the toner image to the transfer body. A second transfer portion.

  The image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the second transfer unit is a toner having less visibility than the toner of the first transfer unit, or less frequently used. The toner image formed with the toner is primarily transferred.

  An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the transfer body rotates around in a state where tension is applied in the rotation movement direction. The toner image is secondarily transferred to the medium on the upstream side in the circumferential movement direction from the portion around which the driving body is wound and on the downstream side in the circumferential movement direction from the first transfer unit.

  An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to any one of the first to third aspects, wherein the first transfer portion and the second transfer portion are cylindrical shapes that hold the toner image. And a rotating body that rotates together with the image holding body, and the number of the rotating bodies that constitute the second transfer portion is the rotation that constitutes the first transfer body. More than the number of bodies.

According to the image forming apparatus of the first aspect of the present invention, compared to the case where the inertial mass of the second transfer unit is the same as the inertial mass of the first transfer unit, it is caused by the vibration generated when the medium is pinched in the transfer nip. Deviation of the toner image that is primarily transferred can be suppressed.

  According to the image forming apparatus of the second aspect of the present invention, the second transfer unit primarily transfers a toner image formed with a toner having better visibility than the first transfer unit or a frequently used toner. Compared to the case, the shift of the toner image primarily transferred by the first transfer portion is made inconspicuous.

  According to the image forming apparatus of the third aspect of the present invention, the transfer body is primarily transferred by the first transfer unit as compared with the case where the toner image is secondarily transferred to the medium at the portion around which the driving body is wound. The deviation of the toner image can be suppressed.

  According to the image forming apparatus of the fourth aspect of the present invention, the number of rotating bodies constituting the second transfer unit is simpler than that in the case where the number of rotating bodies constituting the first transfer body is equal. The inertial mass of the second transfer part can be made larger than the inertial mass of the first transfer part.

1 is a schematic view illustrating an entire configuration of an image forming apparatus according to an embodiment as viewed from the front side (front side) in the apparatus depth direction. 1 is a schematic view of an image forming unit constituting an image forming apparatus according to an embodiment as viewed from the front side. FIG. 3 is a schematic view of a part of the image forming unit according to the embodiment when viewed from the upper side in the apparatus height direction. It is a graph which shows the relationship between the rotational frequency of a photoreceptor drum, and the amplification factor of an amplitude. FIG. 6 is a schematic view of a part of a modified image forming apparatus as viewed from the upper side in the apparatus height direction.

<< First Embodiment >>
<Overview>
An example of this embodiment will be described with reference to the drawings. First, an overview of the overall configuration and operation (image forming process and post-processing process) of the image forming apparatus 10 will be described, and then the configuration and operation of the photosensitive drum unit 22 and related members, which are the main parts of the present embodiment. explain in detail. Next, a modification of the first embodiment, a second embodiment, and a third embodiment will be described. In the following description, the direction indicated by the arrow Y in the drawings is the device height direction, and the direction indicated by the arrow X is the device width direction. In addition, a direction perpendicular to each of the apparatus height direction and the apparatus width direction (shown by an arrow Z as appropriate) is defined as an apparatus depth direction. In FIG. 1, the front side of the image forming apparatus 10 is the front side in the apparatus depth direction.

<Configuration of image forming apparatus>
As shown in FIG. 1, the image forming apparatus 10 includes an image forming unit 12 that forms an image on a medium P by an electrophotographic method, a fixing device 40 that fixes a toner image transferred to the medium P to the medium P, A medium transport unit 50 that transports the medium P and a post-processing unit 60 that performs post-processing and the like on the medium P on which an image is formed are configured. Further, the image forming apparatus 10 includes a control unit 70 that controls the above-described units and a toner replenishing device 80 that replenishes the toner image forming unit 20 with toner.

(Image forming part)
As shown in FIG. 2, the image forming unit 12 includes a toner image forming unit 20 that forms a toner image, and a transfer device 30 that transfers the image formed by the toner image forming unit 20 to the medium P. It is configured.

<Toner image forming section>
A plurality of toner image forming units 20 are provided so as to form a toner image for each color. In the present embodiment, toner image forming units 20Y, 20M, 20C, and 20K having a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are provided. In addition, Y, M, C, and K shown in FIGS. 1 and 2 indicate the colors described above. In the above description, the toner image forming units 20Y, 20M, 20C, and 20K are described as the toner image forming unit 20.

  The toner image forming units 20Y, 20M, 20C, and 20K have substantially the same configuration except for the toner to be used. In the following description, the subscripts Y, M, C, and K are omitted for the toner image forming units 20Y, 20M, 20C, and 20K and the members constituting the toner image forming portions when the toner colors need not be distinguished.

  The toner image forming unit 20 includes a photosensitive drum unit 22, a charging device 24, an exposure device 26, and a developing device 28.

(Photosensitive drum unit)
The photoconductor drum unit 22 includes a photoconductor drum 90. The photosensitive drum 90 is a cylindrical member, and is driven to rotate around its own axis by a driving device 100 (see FIG. 3) described later. As an example, a photosensitive layer having a negative charging polarity is formed on the outer peripheral surface of the photosensitive drum 90. An electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 90 by an exposure device 26 described later. The electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 90 is developed as a toner image by a developing device 28 described later. In other words, the photosensitive drum 90 is configured to hold a toner image. Here, the photosensitive drum 90 is an example of an image carrier.

  The photosensitive drums 90 (or photosensitive drum units 22) of the respective colors are arranged in a straight line along the apparatus width direction when viewed from the front side (see FIGS. 1 and 2). Further, the photosensitive drums 90 (or the photosensitive drum units 22) of the respective colors are arranged along the apparatus depth direction when viewed from the apparatus height direction (see FIG. 3). The photosensitive drum unit 22 is a main part of the present embodiment, and will be described in detail later.

(Charging device)
The charging device 24 charges the outer peripheral surface (photosensitive layer) of the photosensitive drum 90 to a negative polarity. In the present embodiment, the charging device 24 is a charging roll that is performed by bringing a roll into contact with the outer peripheral surface of the photosensitive drum 90. The charging device 24 for each color is disposed on the upper side in the device height direction of the photosensitive drum 90 for each color.

(Exposure equipment)
The exposure device 26 forms an electrostatic latent image on the outer peripheral surface of the photosensitive drum 90 charged by the charging device 24. Specifically, in accordance with image data received from an image signal processing unit (not shown) constituting the control unit 70, the exposure light that has been modulated is irradiated onto the outer peripheral surface of the photosensitive drum 90 that is charged by the charging device 24. It is like that. An electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 90 by irradiation of exposure light from the exposure device 26. In this embodiment, the exposure device 26 uses a light beam (arrow not shown) irradiated from a light source (an arrow pointing from the exposure device 26 in FIG. 1 to the photosensitive drum 90) to an optical scanning unit (not shown) including a polygon mirror. ), The surface of the photosensitive drum 90 is exposed while scanning. Further, the exposure devices 26 for the respective colors are arranged on the upper side in the apparatus height direction of the photosensitive drums 90 for the respective colors.

(Developer)
The developing device 28 develops the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 90 with a developer including toner and carrier as a toner image. The developing device 28 includes an accommodating portion 28A (see FIG. 2) for accommodating the developer, a developing roll 28B (see FIG. 2) for supplying the developer accommodated in the accommodating portion 28A to the photosensitive drum 90 while rotating. It is comprised including. The developing devices 28 for the respective colors are disposed on the right side in the apparatus width direction when viewed from the front side with respect to the photosensitive drums 90 for the respective colors.

  In the developing device 28, the toner inside the developing device 28 is consumed as the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 90 is developed as a toner image. Then, the toner contained in the toner replenishing device 80 is replenished to the developing device 28.

  The developing device 28 is provided with a toner concentration sensor (not shown) that measures the amount (remaining amount) of toner accommodated therein based on the relationship with the amount of carrier accommodated. The toner density sensor measures the amount (remaining amount) of toner inside the developing device 28 at a predetermined timing, and the control unit 70 to which the result is transmitted causes the toner to be supplied from the toner replenishing device 80 to the developing device 28. It is to be replenished.

<Transfer device>
As shown in FIGS. 1 and 2, the transfer device 30 performs primary transfer by superimposing the toner images formed on the photosensitive drums 90 of the respective colors on the transfer belt 36, and further, transferring the superimposed toner images to the medium. Secondary transfer to P is performed. As shown in FIGS. 1 to 3, the transfer device 30 includes a transfer belt 36, a plurality of rolls 32, 32 </ b> B, 32 </ b> D, and 32 </ b> T, a motor 32 </ b> M, and a secondary transfer roll 34. .

  The transfer belt 36 has an endless shape and is wound around a plurality of rolls 32, 32B, 32D, and 32T to determine the posture. The transfer belt 36 has an inverted obtuse triangular posture that is long in the apparatus width direction when viewed from the front side. The roll 32D functions as a drive roll that drives the transfer belt 36 so that the transfer belt 36 rotates in the direction of arrow A by the power of the motor 32M (see FIG. 3). The roll 32T functions as a tension applying roll that applies tension to the transfer belt. The roll 32 </ b> B functions as a counter roll of the secondary transfer roll 34.

  The transfer belt 36 is in contact with the photosensitive drum 90 of each color from the lower side in the apparatus height direction at the upper side extending in the apparatus width direction with the above-described posture. Then, the toner image held on each photosensitive drum 90 is primarily transferred to the transfer belt 36 by an electric field between the primary transfer roll 38 to which the primary transfer bias voltage is applied and the outer peripheral surface of the photosensitive drum 90. It has become so.

  Further, the transfer belt 36 is configured such that a transfer nip NT is formed by contacting the secondary transfer roll 34 at the apex on the lower side in the apparatus height direction that forms an obtuse angle. The transfer belt 36 passes through the transfer nip NT by the electric field between the roll 32 </ b> B to which the secondary transfer bias voltage is applied and the secondary transfer roll 34 after the toner image that has been primarily transferred while being superimposed on the transfer belt 36. Is transferred to the medium P. From another point of view, the transfer belt 36 is transferred from the portion 72 (see FIG. 2) wound around the roll 32D of the transfer belt 36 on the upstream side in the circumferential movement direction of the transfer belt 36 and from the photosensitive drum unit 22K. The toner image is secondarily transferred to the medium P on the downstream side in the circumferential movement direction of the belt 36.

  Here, the transfer belt 36 is an example of a transfer body. The roll 32D is an example of a driving body. The direction of arrow A is an example of the circumferential movement direction of the transfer belt 36. The portion 72 wound around the roll 32D in the transfer belt 36 is an example of a portion around which the driving body is wound. The portion 72 of the transfer belt 36 wound around the roll 32D is a portion where the roll 32D contacts the inner peripheral surface of the transfer belt 36.

[Fixing device]
The fixing device 40 fixes the toner image onto the medium P on which the toner image has been transferred by the transfer device 30 (see FIG. 1). In the present embodiment, the fixing device 40 is configured to fix the toner image on the medium P by applying pressure while heating the toner image in the fixing nip NF.

[Toner replenisher]
The toner replenishing device 80 has a function of replenishing toner to the developing device 28. The toner replenishing device 80 replenishes the toner contained in the toner containing portion 82 to the developing device 28 via the reserve tank 84 and the toner transporting portion 86.

  The toner replenishment is performed under the control of the control unit 70 when the toner amount (remaining amount) inside the developing device 28 measured by the toner density sensor is less than a predetermined toner amount (remaining amount). It is like that.

[Media transport section]
The medium transport unit 50 includes a medium supply unit 52 that supplies the medium P to the image forming unit 12 and a medium discharge unit 54 that discharges the medium P on which the image is formed. Further, the medium transport unit 50 includes a medium return unit 58 that is used when images are formed on both sides of the medium P, and an intermediate transport unit 56 that transports the medium P from the transfer device 30 to the fixing device 40. Has been.

  The medium supply unit 52 supplies the medium P one by one to the transfer nip NT of the image forming unit 12 in accordance with the transfer timing of the secondary transfer. The medium discharge unit 54 discharges the medium P on which the toner image has been fixed by the fixing device 40 and formed an image from the medium discharge unit 56 to the outside of the apparatus. When an image is formed on the other side of the medium P on which an image is formed on one side, the medium return unit 58 reverses the front and back of the medium P and conveys it again to the image forming unit 12 (medium supply unit 52). It is supposed to let you.

[Post-processing section]
The post-processing unit 60 includes a medium cooling unit 62, a correction device 64, and an image inspection unit 66. The medium cooling unit 62 cools the medium P on which the image is formed by the image forming unit 12. The correcting device 64 corrects the curvature of the medium P cooled by the medium cooling unit 62. The image inspection unit 66 inspects the image formed on the medium P after the correction device 64 forces the curvature of the medium P.

<Operation of Image Forming Apparatus>
An outline of an image forming process on the medium P by the image forming apparatus 10 and a post-processing process performed thereafter will be described.

  Upon receiving the image formation command, the control unit 70 operates the toner image forming unit 20, the transfer device 30, and the fixing device 40. As a result, the photosensitive drum 90 and the developing roll 28B of the developing device 28 are rotated, and the transfer belt 36 is moved around. Further, the pressure roll 40A is rotated and the fixing belt 40B is rotated (see FIG. 1). Further, in synchronization with these operations, the control unit 70 operates the medium conveyance unit 50 and the like.

  As a result, the photosensitive drum 90 for each color is charged by the charging device 24 while being rotated. Further, the control unit 70 sends the image data subjected to the image processing by the image signal processing unit to the exposure device 26 for each color. The exposure device 26 emits exposure light L according to the image data, and exposes the charged photosensitive drum 90. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 90. The electrostatic latent image formed on the photosensitive drum 90 is developed as a toner image by the developer supplied from the developing device 28. As a result, toner images of corresponding colors among yellow (Y), magenta (M), cyan (C), and black (K) are formed on the photosensitive drums 90 of the respective colors.

  The toner images of the respective colors formed on the photoconductive drums 90 of the respective colors are sequentially primary-transferred sequentially to the transfer belt 36 that moves around by the application of the primary transfer bias voltage through the primary transfer rolls 38 of the respective colors. As a result, a toner image in which toner images for four colors are superimposed is formed on the transfer belt 36. This toner image is conveyed to the transfer nip NT by the circular movement of the transfer belt 36. A medium P is supplied to the transfer nip NT by the medium supply unit 52 so as to synchronize the timing of the toner image conveyance. By applying a secondary transfer bias voltage at the transfer nip NT, the toner image is secondarily transferred from the transfer belt 36 to the medium P.

  The medium P on which the toner image has been secondarily transferred is conveyed by the intermediate conveyance unit 56 from the transfer nip NT of the transfer device 30 toward the fixing nip NF of the fixing device 40 while being sucked with negative pressure. Thereafter, heat and pressure (fixing energy) are applied to the medium P on which the toner image has been transferred while passing through the fixing nip NF of the fixing device 40. As a result, the toner image secondarily transferred to the medium P is fixed to the medium P.

  The medium P discharged from the fixing device 40 is processed by the post-processing unit 60 while being conveyed by the medium discharge unit 54 toward the discharge medium receiving unit outside the apparatus. The medium P heated in the fixing process is first cooled in the medium cooling unit 62. Next, the curvature of the medium P is corrected by the correction device 64. Further, the toner image fixed on the medium P is detected by the image inspection unit 66 for the presence or absence of toner density defects, image defects, image position defects, and the like. Then, the medium P is discharged to the medium discharge unit 54.

  On the other hand, when an image is formed on the non-image surface of the medium P on which no image is formed (in the case of double-sided printing), the control unit 70 uses the medium discharge path to the transport path of the medium P after passing through the image inspection unit 66. The unit 54 is switched to the medium return unit 58. As a result, the medium P is returned to the medium supply unit 52 with its front and back reversed. An image is formed on the back surface of the medium P in the same process as the image forming process on the front surface. The medium P is discharged from the medium discharge unit 54 to the outside through the same process as the post-processing process after the image formation on the surface described above.

<Configuration of main parts>
Next, the configuration of the photosensitive drum unit 22 and related members, which are the main parts of the present embodiment, will be described with reference to the drawings.

[Photosensitive drum unit]
As shown in FIG. 3, each color photosensitive drum unit 22 includes a photosensitive drum 90, a flange 92, a shaft 94, a gear 96, and a flywheel 98.

  At both ends of the photosensitive drum 90, flanges 92 having through holes are fixed. A shaft 94 is fixed to the through hole so as to protrude from both ends of the photosensitive drum 90. A gear 96 is fixed to a portion of the shaft 94 on the near side in the apparatus depth direction. Further, a disk-like flywheel 98 is fixed to a portion of the shaft 94 that is closer to the device depth direction than the gear 96. The flywheels 98 of the photosensitive drum units 22 of the respective colors are formed of the same shape and the same material. Here, the flywheel 98 is an example of a rotating body.

  The number of flywheels 98 constituting the photosensitive drum units 22M, 22C, and 22K is one (one), whereas the number of flywheels 98 constituting the photosensitive drum unit 22Y is two (two). In other words, the number of flywheels 98 constituting the photosensitive drum unit 22Y is larger than the number of flywheels 98 constituting the photosensitive drum units 22M, 22C, and 22K of the respective colors. The configurations of the photosensitive drum units 22M, 22C, and 22K and the photosensitive drum unit 22Y differ only in this point. As a result, the inertial mass of the photosensitive drum unit 22Y is larger than the inertial mass of the photosensitive drum units 22M, 22C, and 22K.

  Further, as shown in FIG. 3, a driving device 100 is disposed at a portion between the gear 96 and the flywheel 98. The driving device 100 includes a motor 102 and a gear 104 fixed to the rotation shaft of the motor 102. The gear 104 is engaged with the gear 96 of the photosensitive drum unit 22. When the torque generated by the motor 102 is transmitted from the gear 104 to the gear 96, the photosensitive drum unit 22 rotates around the shaft 94.

  Here, the graph of FIG. 4 shows the relationship between the rotational frequency of the photosensitive drum unit and the amplification factor of the amplitude when the inertial mass is changed in the driving system constituted by the photosensitive drum unit 22 and the driving device 100. . The rotational frequency of the photosensitive drum unit indicates the number of rotations of the photosensitive drum unit per unit time. The amplitude amplification factor refers to the amplitude in the apparatus width direction on the output side (the amplitude of vibration of the gear 104) generated when the photosensitive drum unit 22 rotates (the amplitude of the vibration of the gear 104) (photosensitive drum 90). The ratio of the vibration amplitude). In this graph, the spectrum of L1 is an example when the inertial mass is the smallest, the spectrum of L2 is an example when the inertial mass is the second largest after L1, and L3 is an example when the inertial mass is the largest. As shown in this graph, when the inertial mass is increased, the resonance frequency of the photosensitive drum unit is shifted to a lower frequency side, and the intensity value (peak value) at the resonance frequency is increased. In the graph of FIG. 4, the larger the amplitude amplification factor, the greater the vibration caused by the rotation of the photosensitive drum unit 22.

  In the case of the present embodiment, the relationship between the rotational frequency and the amplification factor of the amplitude of the photosensitive drum unit 22Y including two flywheels 98 is L2 spectrum, and the relationship between the photosensitive drum units 22M, 22C, and 22K including one flywheel 98 is illustrated. The relationship between the rotation frequency and the amplification factor of the amplitude is represented by the spectrum of L1. The photosensitive drum unit 22 is configured to perform an image forming operation while rotating around the shaft 94 at the rotation frequency C.

  Then, as shown in the graph of FIG. 4, the rotational frequency C of the photosensitive drum units 22M, 22C, and 22K is lower than the resonance frequency of the spectrum L1. Further, the rotational frequency C of the photosensitive drum 22Y is lower than the resonance frequency of the spectrum L2. Thus, in this embodiment, the rotation frequency C of all the photosensitive drum units 22 is set lower than the resonance frequency of each photosensitive drum unit 22. In other words, all the photosensitive drum units 22 according to the present exemplary embodiment have a period from when the image forming operation is started to when the photosensitive drum unit 22 is rotated from the stopped state to the rotating state rotating at the rotation frequency C (the frequency corresponding to the fastest speed in the image forming operation). (Hereinafter referred to as an image forming operation rising period), it does not rotate at the resonance frequency. For this reason, the photosensitive drum unit 22 does not vibrate at the resonance frequency during the image forming operation rising period.

  Further, the photosensitive drum unit 22Y is transferred from the photosensitive drum unit 22M on the upstream side in the circumferential movement direction of the transfer belt 36 (in the direction of arrow A in FIGS. 1 and 2) and from a portion of the transfer belt 36 wound around the roll 32D. The belt 36 is disposed on the downstream side in the circumferential movement direction. Here, the photosensitive drum units 22M, 22C, and 22K are examples of the first transfer unit. The photosensitive drum unit 22Y is an example of a second transfer unit.

[Configuration of related members]
Next, the configuration of members and the like related to the main part of the present embodiment will be supplementarily described below.

<Characteristic configuration of transfer device>
As described above, the transfer belt 36 has an inverted triangular shape that is long in the apparatus width direction when viewed from the front side. When viewed from the front side, the transfer belt 36 has a roll 32D that functions as a driving roll at the right end portion in the apparatus width direction, a roll 32T that functions as a tension applying roll at the left end portion in the apparatus width direction, and the apparatus height direction. It is wound around the roll 32B at the lower top.

  Here, in the transfer belt 36 that circulates, the transfer belt 36 rotates in the circumferential direction of the transfer belt 36 upstream of the portion 72 wound around the roll 32D and from the portion wound around the roll 32B. The downstream region is referred to as an upstream region 74 (see FIG. 2). Further, in the circumferentially moving transfer belt 36, the transfer belt 36 is disposed downstream of the portion 72 wound around the roll 32 </ b> D in the circumferential movement direction of the transfer belt 36 and from the portion wound around the roll 32 </ b> T in the circumferential movement direction. The upstream area is referred to as a downstream area 76 (see FIG. 2). A portion wound around the roll 32B corresponds to the transfer nip NT.

  For this reason, the tension in the upstream region 74 is larger than the tension in the downstream region 76 in a state where the transfer belt 36 is rotating.

<toner>
As described above, in the image forming apparatus 10, the yellow photosensitive drum unit 22 </ b> Y is arranged at the most upstream in the circumferential movement direction of the transfer belt 36 in the downstream region 76 (see FIGS. 1 to 3). The photosensitive drum units 22M, 22C, and 22K other than yellow are arranged in the order of the photosensitive drum unit 22M, the photosensitive drum unit 22C, and the photosensitive drum unit 22K from the upstream side in the circumferential movement direction of the transfer belt 36 ( 1 to 3).

  Generally, yellow toner is a toner that is difficult for humans to visually recognize when it is formed as an image on a medium compared to other color toners (magenta, cyan, and black). It is known that the toner has poor properties. Here, yellow toner is an example of toner with poor visibility. In the present embodiment, the photosensitive drum unit 22Y disposed at the most upstream in the circumferential movement direction of the transfer belt 36 holds a toner image formed of yellow toner that is less visible than magenta, cyan, and black. Primary transfer is performed on the transfer belt 36.

<Operation of First Embodiment>
Hereinafter, the operation of the present embodiment will be described with reference to the drawings. First, this embodiment will be described in comparison with comparative examples (Comparative Examples 1 to 6). In the following description, when using the components used in this embodiment, the description will be made using the reference numerals of the components as they are.

[Comparison with Comparative Example 1]
First, a comparative example 1 described below is assumed as a comparative example of the present embodiment, and then compared with the present embodiment.

  In the image forming apparatus of Comparative Example 1, the flywheel 98 of the yellow photosensitive drum unit is a single sheet. In other words, there is one flywheel 98 for each color photosensitive drum unit. Except for this point, the configuration is the same as that of the image forming apparatus 10 of the present embodiment.

  Here, when the toner image held on the photosensitive drum 90 is primarily transferred to the transfer belt 36, the toner image primarily transferred to the transfer belt 36 may be shifted due to vibration of the transfer belt 36 or the like. . The toner image shift here refers to a local area shift in the circumferential movement direction of the transfer belt 36, not the entire toner image primarily transferred to the transfer belt 36. , Banding spots.

  In the case of Comparative Example 1, when the medium P is transported toward the transfer nip NT and the medium P is sandwiched between the transfer nip NT, vibration is generated in the transfer nip NT (see FIGS. 1 and 2). This vibration is transmitted to the most upstream photosensitive drum unit (hereinafter referred to as the most upstream unit) in the circumferential movement direction of the transfer belt 36 via the transfer belt 36. As a result, the yellow toner image primarily transferred by the most upstream unit is shifted. Furthermore, although some of the vibrations generated in the transfer nip NT are absorbed (damped) by the most upstream unit, vibrations that are not absorbed by the most upstream unit are transferred to a plurality of downstream side via the transfer belt 36. The signals are sequentially transmitted to the photosensitive drum units 22M, 22C, and 22K. Therefore, the toner images primarily transferred by these photosensitive drum units 22M, 22C, and 22K are shifted. The vibration generated in the transfer nip NT increases as the thickness of the medium P increases. Therefore, the deviation of the primary-transferred toner image increases as the vibration generated in the transfer nip NT increases. In other words, the amount of deviation of the primary transferred toner (easiness of banding spots) becomes remarkable.

  In contrast to this, in the image forming apparatus 10 of the present embodiment, unlike the image forming apparatus of Comparative Example 1, there are two flywheels 98 of the photosensitive drum unit 22Y at the most upstream in the circumferential movement direction of the transfer belt 36. (See FIG. 3). In other words, the inertial mass of the photosensitive drum unit 22Y of this embodiment is larger than the inertial mass of the yellow photosensitive drum unit of Comparative Example 1. For this reason, the rotational speed (angular speed) of the photosensitive drum unit 22Y of the present embodiment is less likely to change compared to the yellow photosensitive drum unit of Comparative Example 1, even if vibration generated in the transfer nip NT is propagated.

  Therefore, according to the image forming apparatus 10 of the present embodiment, it is possible to suppress the deviation of the toner image of the yellow toner primarily transferred from the photosensitive drum unit 22Y as compared with the case of the comparative example 1.

  Further, the photosensitive drum unit 22Y of the present embodiment has a larger inertial mass of the photosensitive drum unit 22Y than the case of the comparative example 1, and therefore easily absorbs vibrations generated in the transfer nip NT. As a result, in the image forming apparatus 10 of the present embodiment, the vibration generated in the transfer nip NT is propagated to the photosensitive drum units 22M, 22C, and 22K other than the uppermost stream of the transfer belt 36 as compared with the case of the comparative example 1. hard. In other words, the photosensitive drum units 22M, 22C, and 22K of the present embodiment are less likely to vibrate compared to the case of the first comparative example.

  Therefore, according to the image forming apparatus 10 of the present embodiment, it is possible to suppress the deviation of the toner image primarily transferred from the photosensitive drum units 22M, 22C, and 22K as compared with the case of the comparative example 1.

  As described above, all the photosensitive drum units 22Y, 22M, 22C, and 22K of the image forming apparatus 10 according to the present embodiment can suppress the deviation of the toner image that has been primarily transferred as compared with the case of the first comparative example. . Therefore, according to the image forming apparatus 10 of the present embodiment, as compared with the case of the comparative example 1, it is possible to suppress the deviation of the toner images of all the colors that are primarily transferred.

[Comparison with Comparative Example 2]
Next, a comparative example 2 described below is assumed as a comparative example of the present embodiment, and then compared with the present embodiment.

  The image forming apparatus of Comparative Example 2 has two flywheels 98 of magenta, cyan, and black photosensitive drum units. In other words, there are two flywheels 98 for each color photosensitive drum unit. Except for this point, the configuration is the same as that of the image forming apparatus 10 of the present embodiment.

  In the case of Comparative Example 2, the number of flywheels 98 of the photosensitive drum unit at the most upstream in the circumferential movement direction of the transfer belt 36 is two as in the case of this embodiment. For this reason, in the most upstream unit of Comparative Example 2, even if the vibration generated in the transfer nip NT is propagated, the rotational speed (angular speed) is less likely to change compared to the case where the number of flywheels 98 is one. As a result, in the most upstream unit of Comparative Example 2, as in the case of the present embodiment, it is possible to suppress the deviation of the toner image of the yellow toner that has been primarily transferred.

  However, in the case of the comparative example 2, all the photosensitive drum units other than the most upstream unit have two flywheels 98. Therefore, all the photosensitive drum units other than the most upstream unit have a larger vibration due to the rotation of each photosensitive drum unit than in the case where the number of flywheels is one (see L1 in FIG. 4) (see FIG. 4). See L1 and L2 in C). As a result, in the case of the comparative example 2, the deviation of the toner image primarily transferred by all the photosensitive drum units other than the most upstream unit becomes large.

  On the other hand, in the image forming apparatus 10 of the present embodiment, unlike the image forming apparatus of Comparative Example 1, only the flywheel 98 of the photosensitive drum unit 22Y is two, and the other photosensitive drum units 22M, 22C, There is one 22K flywheel 98 (see FIG. 3). For this reason, in the case of the image forming apparatus 10 according to the present embodiment, the photosensitive drum units 22M, 22C, and 22K themselves have less vibration due to their own rotation than in the case of the comparative example 2.

  Therefore, according to the image forming apparatus 10 of the present embodiment, it is possible to suppress the primary transfer deviation caused by the vibration of the photosensitive drum units 22M, 22C, and 22K itself, as compared with the case of the comparative example 2.

  As described above, the photosensitive drum units 22M, 22C, and 22K of the image forming apparatus 10 according to the present embodiment can suppress the deviation of the primarily transferred toner image as compared with the case of the comparative example 2. Therefore, according to the image forming apparatus 10 of the present embodiment, as compared with the case of the comparative example 2, it is possible to suppress the deviation of the primary transferred magenta, cyan, and black toner images.

  In the image forming apparatus 10, on the premise of the above configuration, the toner that is primarily transferred by the most upstream photosensitive drum unit 22 </ b> Y in the circumferential movement direction of the transfer belt 36 is yellow toner. The yellow toner is a toner having poor visibility as compared with other toners (magenta, cyan, and black).

  Therefore, according to the image forming apparatus 10 of the present embodiment, compared to the case of the comparative example 2, the transfer belt 36 can be moved in the circumferential movement direction while suppressing the deviation of the magenta, cyan, and black toner images that have been primarily transferred. Deviation of the toner image primarily transferred by the upstream photosensitive drum 22Y is made inconspicuous.

[Comparison with Comparative Examples 3 to 5]
As comparative examples of the present embodiment, comparison examples 3 to 5 described below are assumed and compared with the present embodiment.

  In the image forming apparatuses of Comparative Examples 3 to 5, the inertial mass of the most upstream unit is the same as that of the present embodiment, but the shape of the flywheel is different. Except this point, it is the same as the case of this embodiment. In other words, any of the configurations of Comparative Examples 3 to 5 described below aims to make the inertial mass of the most upstream unit larger than the inertial masses of the other photosensitive drum units 22M, 22C, and 22K.

In Comparative Example 3, instead of the two flywheels 98 of the photosensitive drum unit 22Y, the thickness of the flywheel is increased to one.
In Comparative Example 4, instead of the two flywheels 98 of the photosensitive drum unit 22Y, the flywheel diameter is increased to one.
In Comparative Example 5, instead of the two flywheels 98 of the photoconductor drum unit 22Y, the flywheel 98 is used as one and an inertia for increasing the inertial mass is provided inside the photoconductor drum 90Y.
Note that Comparative Examples 3 to 5 are one embodiment of the present invention.

  In the case of Comparative Example 3 and Comparative Example 4, since the shape of the flyhole is different between the most upstream unit and the other photosensitive drum units 22M, 22C, and 22K, two types of flywheels are prepared when manufacturing the photosensitive drum unit. Must. For example, when manufacturing a flywheel by pressing, at least two types of molds must be prepared. Therefore, there is a risk of increasing the manufacturing cost of the flywheel. In the case of Comparative Example 3 and Comparative Example 4, two types of photosensitive drum units must be managed in the manufacturing process of the photosensitive drum unit. For this reason, there is a risk of increasing the manufacturing time of the photosensitive drum unit, increasing the manufacturing cost associated with component management, and the like.

  On the other hand, in the case of this embodiment, compared with the comparative example 3 and the comparative example 4, since the metal mold | die for manufacturing a flywheel may be one type, the manufacturing cost of a flywheel can be reduced. In the case of the present embodiment, all the photosensitive drum units 22 of the respective colors have the same structure, so that parts management in the manufacturing process of the photosensitive drum unit 22 is easier than in the comparative example 3 and the comparative example 4. In addition, the manufacturing time can be reduced accordingly. Further, the inertial mass of the photosensitive drum unit 22Y can be made larger than the inertial masses of the other photosensitive drum units 22M, 22C, and 22K with a simple configuration.

  In the case of Comparative Example 4, the diameter of the flywheel of the most upstream unit is larger than the diameter of the flywheel 98. Therefore, it is necessary to fix the flywheel to the shaft 94Y so that the flywheel does not interfere with the flywheel 98 of the photosensitive drum unit 22M. Then, since there is a possibility of interfering with each device, each component, etc. constituting the image forming apparatus, there is a possibility that the size of the image forming apparatus is increased.

  On the other hand, in the case of the present embodiment, since two flywheels 98 are fixed to the shaft 98Y, each of the image forming apparatuses according to the increase in the diameter of the flywheel as in the case of the comparative example 4. Difficult to interfere with devices and parts. Therefore, according to the image forming apparatus 10 of the present embodiment, the image forming apparatus can be downsized as compared with the image forming apparatus of Comparative Example 4.

  Moreover, in the case of the comparative example 5, the flywheel 98 of the most upstream unit is one piece. In addition, an inertia for increasing the inertial mass is provided inside the photosensitive drum 90Y in order to supplement the inertial mass corresponding to the reduction of one flywheel 98. Therefore, in the case of the comparative example 5, there is no interference with each device, each component, etc. of the image forming apparatus accompanying the increase in the diameter of the flywheel as in the comparative example 5.

  However, in the case of Comparative Example 5, charging, electrostatic latent image formation, development, etc. performed on the outer peripheral surface of the photosensitive drum 90Y by providing an inertia for increasing the inertial mass inside the photosensitive drum 90Y. There is a possibility that a new problem may occur in each process. For example, when the charging process is performed by applying an AC voltage to the charging device 24, there is a possibility that vibration noise caused by the frequency of the AC voltage of the charging device 24, the shape of the photosensitive drum 90Y, and the like may occur. In addition, when the developing process is performed by applying an AC voltage to the developing roll 28B of the developing device 28, there is a possibility that vibration noise caused by the frequency of the AC voltage of the developing roll 28B, the shape of the photosensitive drum 90Y, and the like may occur. is there. Therefore, according to the image forming apparatus 10 of the present embodiment, compared to the image forming apparatus of Comparative Example 6, when an AC voltage is used in the charging process or the developing process, vibration noise is less likely to occur.

  Moreover, in the case of the comparative example 5, since it is necessary to prepare the inertia for enlarging inertial mass, there exists a possibility of causing the increase in the manufacturing cost of this inertia. In the case of Comparative Example 5, two types of photosensitive drum units must be managed in the manufacturing process of the photosensitive drum unit. For this reason, there is a risk of increasing the manufacturing time of the photosensitive drum unit, increasing the manufacturing cost associated with component management, and the like. Therefore, according to the present embodiment, the manufacturing time is shortened as compared with the case of the comparative example 5. In addition, the manufacturing cost is reduced accordingly.

[Comparison with Comparative Example 6]
Next, a comparative example 6 described below is assumed as a comparative example of the present embodiment, and then compared with the present embodiment.

  In the image forming apparatus of Comparative Example 6, the secondary transfer roll 34 is disposed on the opposite side of the roll 32D that functions as a drive roll for the transfer belt 36 with the transfer belt 36 interposed therebetween. It also has a function as an opposing roll (see FIG. 2). That is, the transfer nip NT is formed by a portion of the transfer belt 36 wound around the roll 32D and the secondary transfer roll 34. Except for this point, the configuration is the same as that of the image forming apparatus 10 of the present embodiment. Note that Comparative Example 6 is one embodiment of the present invention.

  In the case of Comparative Example 6, when the medium P is sandwiched by the transfer nip NT, vibration is generated in the transfer nip NT (see FIGS. 1 and 2). This vibration is propagated to the most upstream unit via the transfer belt 36, but unlike the case of the present embodiment, it is propagated via the downstream region 76 without passing through the upstream region 74 of the transfer belt 36. . Therefore, a part of the vibration generated in the transfer nip NT is not absorbed by the upstream region 74 of the transfer belt 36 and then propagated to the most upstream unit.

  In contrast, in the image forming apparatus 10 according to the present embodiment, a part of the vibration generated in the transfer nip NT is absorbed by the upstream region 74 of the transfer belt 36 and then further the downstream region of the transfer belt 36. 76 is propagated to. For this reason, in the image forming apparatus 10 of the present embodiment, the vibration propagated to the photosensitive drum unit 22Y is smaller than in the case of the comparative example 6.

  Therefore, according to the image forming apparatus 10 of the present embodiment, the vibration generated at the transfer nip NT and propagated to the photosensitive drum unit 22Y can be reduced as compared with the case of the comparative example 6.

<< Modification of First Embodiment >>
Hereinafter, modified examples of the present embodiment will be described with reference to FIGS. In the following description, when using the components used in this embodiment, the description will be made using the reference numerals of the components as they are.

<Configuration of modification>
[Modification 1]
In the case of the first modification, the flywheel 98A of each photosensitive drum unit is fixed in the order of 4, 2, 2, and 1 from the most upstream to the most downstream in the circumferential movement direction of the transfer belt 36. . The flywheel 98A has the same shape as 98 of the present embodiment, but is lighter than the flywheel 98. Except this point, the configuration is the same as that of the present embodiment.

[Modification 2]
In the case of the first modification, the flywheel 98A of each photosensitive drum unit is fixed in the order of two sheets, two sheets, one sheet, and one sheet from the most upstream to the most downstream in the circumferential movement direction of the transfer belt 36. . Except this point, the configuration is the same as that of the present embodiment.

[Modification 3]
In the case of the first modification, the flywheel 98A of each photosensitive drum unit is fixed in the order of four, three, two, and one sheet from the most upstream to the most downstream in the circumferential movement direction of the transfer belt 36. . Except this point, the configuration is the same as that of the present embodiment.

<Operation of Modifications (Modifications 1 to 3)>
In any of Modifications 1 to 3, as in the case of the present embodiment, the number of flywheels 98A of the most upstream unit is the same as that of flywheels 98A of all the photosensitive drum units in the image forming apparatus of each modification. It is the most in the number of sheets. For this reason, in the case of the first to third modifications, the deviation of the primary transfer toner image due to the vibration generated in the transfer nip NT in the most upstream unit is suppressed as in the present embodiment. In the case of Modifications 1 to 3, as in the present embodiment, vibration generated in the transfer nip NT is difficult to propagate to the photosensitive drum unit other than the most upstream unit. The deviation of the primary transfer toner image is suppressed as in the case of the present embodiment. Other operations are the same as those in the present embodiment.

  In the third modification, the flywheel 98A of each photosensitive drum unit gradually decreases in the order from the most upstream to the most downstream in the circumferential movement direction of the transfer belt 36. Due to such a configuration, the vibration generated in the transfer nip NT and propagated through the transfer belt 36 is gradually applied to each photoconductive drum unit in the order from the most upstream in the circumferential movement direction of the transfer belt 36 to the most downstream. Absorbed. For this reason, the deviation of the toner image that is primarily transferred due to the vibration generated in the transfer nip NT is gradually alleviated in the arrangement order of the photosensitive drum units. Therefore, according to the image forming apparatus of Modification 3, the deviation of the toner image that is primarily transferred and superimposed is conspicuous as compared with the image forming apparatus of this embodiment and other modifications (Modifications 1 and 2). hard.

<< Second Embodiment >>
The second embodiment will be described below. In the following description, when using the components used in this embodiment, the description will be made using the reference numerals of the components as they are.

<Configuration of Second Embodiment>
In the second embodiment, unlike the image forming apparatus 10 of the first embodiment, a part upstream of the photosensitive drum unit 22Y in the circumferential movement direction of the transfer belt 36 and a part downstream of the part 72 around which the roll 32D is wound. In addition, a photosensitive drum unit (hereinafter referred to as the most upstream unit W) for primary transfer of white toner is disposed. Further, two flywheels 98 of the most upstream unit W and one flywheel of the other photosensitive drum units are used so that the inertial mass of the most upstream unit W is larger than the inertial mass of other photoreceptor drum units. Has been. Except for this point, the second embodiment is the same as the first embodiment.

  In this image forming apparatus, not only the image forming operation of the first embodiment (referring to a normal image forming operation) is possible, but when the medium P is a transparent medium, white toner is replaced with other colors (Y, An image forming operation (referred to as an image forming operation with white toner) using a toner image of M, C, K) as a base layer is also possible.

  Here, the underlayer refers to a layer formed so as to overlap at least a toner image of another color. Note that the image formed by the image forming operation using the white toner is not the image formed by the normal image forming operation from the surface side of the medium P, but the side on which the toner image is transferred onto the transparent medium (fixing) It can be visually recognized from the opposite side (back side). In this case, since the white toner image is used as a base layer for the toner layers of other colors, it is difficult to visually recognize the white toner image. Therefore, the white toner in this case is an example of a toner with poor visibility.

  In the present image forming apparatus, when a normal image forming operation is performed, the most upstream unit W rotates about its own axis together with other photosensitive drum units. For this reason, when the image forming apparatus performs a normal image forming operation, vibration generated in the transfer nip NT is propagated to and absorbed by the most upstream unit W that does not perform primary transfer.

  In general, an image forming operation using white toner on a medium transparent to medium P or colored paper is rarely performed. Therefore, an image forming operation using white toner is performed with other color toners (Y, M, C, K). This is considered to be executed less than the normal image forming operation using at least one or two or more toners. In other words, white toner is considered to be a toner that is used less frequently than other color toners (Y, M, C, K). Here, the white toner is an example of a toner that is not frequently used.

<Operation of Second Embodiment>
In the case of this image forming apparatus, even when a normal image forming operation is performed, the vibration generated in the transfer nip NT is propagated and absorbed by the most upstream unit W. For this reason, vibration generated in the transfer nip NT is reduced and propagated to the other photosensitive drum units to which the primary transfer is performed.

  Therefore, according to the image forming apparatus of the present embodiment, it is possible to suppress the primary transfer deviation of the toner of each color in the normal image forming operation as compared with the case where the most upstream unit W is not provided.

  When the image forming apparatus performs an image forming operation using white toner, the white toner is used as a base layer for toner images of other colors. For this reason, an image of a toner image of another color is formed on the white toner base layer. That is, when the medium P on which the image is formed is visually recognized, even if there is a deviation due to the primary transfer in the white toner layer which is the base layer, it is difficult to stand out. Other operations are the same as those in the first embodiment.

«Third embodiment»
Hereinafter, the third embodiment will be described with reference to FIG. In the following description, when using the components used in this embodiment, the description will be made using the reference numerals of the components as they are.

<Configuration of Third Embodiment>
In the third embodiment, instead of the uppermost stream unit W of the second embodiment, an uppermost stream unit for primary transfer of clear toner (hereinafter referred to as an uppermost stream unit CL) is disposed. The other color photosensitive drum units are arranged on the downstream side. Except this point, the second embodiment is the same as the second embodiment.

  In this image forming apparatus, not only a normal image forming operation as in the first embodiment is possible, but also image formation using clear toner as a surface layer of toner images of other colors (Y, M, C, K). Operation (referred to as image forming operation using clear toner) is also possible. Here, the surface layer refers to a layer formed so as to overlap at least a toner image of another color. In this image forming apparatus, an image forming operation using clear toner is possible by setting of the control unit 70. Note that the image formed by the image forming operation using the clear toner is visible from the side (surface side) on which the toner image is transferred onto the medium P, similarly to the image formed by the normal image forming operation. It has become.

  In general, an image using clear has high added value such as producing a high-class feeling. Therefore, an image forming operation using clear toner can be performed with any of the other color toners (Y, M, C, K). This is considered to be performed less frequently than a normal image forming operation in which an image is formed with one or more toners. In other words, the clear toner is considered to be used less frequently than the other color toners (Y, M, C, K). Here, the clear toner is an example of a toner that is less frequently used.

  Further, clear has a characteristic that visible light is not easily reflected even when compared with yellow toner, which is an example of toner with poor visibility. That is, clear toner is an example of toner with poor visibility. From a different point of view, the clear toner is composed of a highly transparent resin similar to other color toners, but unlike other color toners, it is dispersed in this resin. The amount of pigment contained is smaller than that of other color toners, or toner in which the pigment is not dispersed in this resin.

<Operation of Third Embodiment>
Unlike other color toners, clear toner has poor visibility. Therefore, when looking at the medium P on which an image is formed, even if there is a primary transfer defect on the surface layer, it is difficult to stand out (it is difficult for humans to recognize through vision). Other operations are the same as those of the first embodiment and the second embodiment.

  As mentioned above, although this invention was demonstrated in detail about specific embodiment, this invention is not limited to embodiment mentioned above, Other embodiment is possible within the scope of the present invention.

  For example, in the embodiment, the first embodiment, the modified example of the first embodiment, the second embodiment, and the third embodiment have been described as different embodiments. However, an embodiment in which these are appropriately combined also falls within the scope of the present invention. Contained within. For example, the photosensitive drum unit according to the first modification of the first embodiment may be combined with the white toner according to the second embodiment. Further, the photosensitive drum unit according to the third modification of the first embodiment may be combined with the clear toner according to the third embodiment. Further, the image forming apparatus according to the second embodiment and the third embodiment may be combined.

  In the first embodiment, it has been described as if the magnitude of the inertial mass between the photosensitive drum unit 22Y and the other photosensitive drums 90M, 22C, and 22K is determined only by the number of flywheels 98. However, it is only necessary that the inertial mass of the photosensitive drum 90Y arranged at the most upstream in the circumferential movement direction of the transfer belt 36 is larger than the inertial masses of the other photosensitive drums 90M, 90C, and 90K. For example, the inertia may be determined by providing inertia inside the photosensitive drum 90. Alternatively, the number of flywheels of all the photosensitive drum units 22 may be one and may be determined by the thickness, shape, and the like.

  In the first embodiment, each photosensitive drum unit 22 has been described as being rotated by the drive device 100 provided separately. However, each photosensitive drum unit 22 may be rotated. For example, gears may be connected and rotated by one driving device 100 provided in the image forming apparatus 10 so that each photosensitive drum unit 22 can be rotated about its own axis.

  In the first embodiment, the photosensitive drum units 22 of the image forming apparatus 10 are described as having four colors. However, the image forming apparatus includes a plurality of photosensitive drum units 22 and a transfer belt 36. If it is. For example, the photosensitive drum unit 22 may be configured for two colors, three colors, or five colors or more. In the second and third embodiments, if the white toner and the clear toner can be primarily transferred to the most upstream unit, the photosensitive drum unit 22 is composed of 2 to 4 colors or 6 or more colors. May be.

  Further, in the first embodiment, the toner has been described on the premise that it constitutes a developer together with the carrier. Anything can be used. For example, the developer may be a so-called one-component developer including toner and an external additive.

  In the first embodiment, the toner is assumed to be powder (solid). However, the toner is primarily transferred from the photosensitive drum 90 constituting the plurality of photosensitive drum units 22 to the transfer belt 36. Anything can be used. For example, a toner in which toner (particles) is dispersed in a liquid (so-called liquid toner) may be used.

  In the first embodiment, the photosensitive drum 90 is assumed to be a cylindrical member and the transfer belt 36 is an endless belt. However, toner images held on a plurality of photosensitive members are transferred to the transfer member. Any structure may be used as long as the primary transfer is performed. For example, a belt-shaped photoconductor may be used instead of the photoconductor drum 90, or a transfer drum (cylindrical transfer body) may be used instead of the transfer belt.

10 Image forming apparatuses 22Y, 22M, 22C Photosensitive drum unit (an example of a first transfer unit)
22K photosensitive drum unit (example of second transfer unit)
32D roll (example of driving body)
36 Transfer belt (an example of a transfer body)
72 Part of the transfer belt wound around the roll 32D (an example of a part of the transfer body that contacts the driving body, an example of a part of the transfer body that contacts the inner peripheral surface)
90Y, 90M, 90C, 90K Photosensitive drum (an example of an image carrier)
98 Flywheel (an example of a rotating body)
A. Circumferential movement direction of the transfer belt (an example of the circular movement direction of the transfer body)
P Medium

Claims (4)

An endless transfer body that secondary-transfers the toner image that has been primarily transferred to the medium while being driven by a driving body that is in contact with the inner peripheral surface,
A first transfer portion that rotates about its own axis and primarily transfers a toner image to the transfer body;
The first transfer portion is disposed upstream of the transfer body in the circumferential movement direction, and further downstream of the drive body in contact with the inner peripheral surface of the transfer body, and downstream of the first transfer section. A second transfer unit that has a larger inertial mass than the unit, rotates about its own axis, and primarily transfers a toner image to the transfer body;
An image forming apparatus. The second transfer portion primarily transfers a toner image formed with a toner that is less visible than the toner of the first transfer portion or a toner that is less frequently used.
The image forming apparatus according to claim 1. The transfer body moves around in a state where tension is applied in the rotation movement direction,
The transfer body secondarily transfers a toner image to the medium on the upstream side in the circumferential movement direction from a portion around which the driving body is wound and on the downstream side in the circumferential movement direction from the first transfer unit.
The image forming apparatus according to claim 1. The first transfer unit and the second transfer unit include a cylindrical image holding body that holds the toner image, and a rotating body that rotates together with the image holding body,
The number of the rotators constituting the second transfer part is greater than the number of the rotators constituting the first transfer body,
The image forming apparatus according to claim 1.

Images