JP2011174992A - Transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image, transferred to a transfer body from an image holding body not separated, from being disarranged. <P>SOLUTION: A transfer device includes: the endless belt-like transfer body performing circling move; a plurality of first transfer means, which are arranged on the inner circumferential side of the transfer body so as to respectively face a plurality of image holding bodies respectively holding images formed by charged developer through the transfer body, and which electrify the transfer body to a polarity opposite to that of the developer, to respectively transfer the images from the image holding bodies to the transfer body; and a separation means separating one or more of the plurality of image holding bodies from the transfer body. The transfer device is configured so that at least one of the first transfer means facing the image holding bodies separated from the transfer body by the separation means electrifies the transfer body to the polarity opposite to that of the developer, before the images are transferred to the transfer body from the image holding bodies not separated from the transfer body by the separation means, and the transfer device is used. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transfer device and an image forming apparatus.

  The electrophotographic image forming apparatus includes a primary transfer for transferring an image formed on an image carrier to an intermediate transfer belt, and a secondary transfer for transferring the image transferred to the intermediate transfer belt to a recording medium such as paper. There is something to do. In such an image forming apparatus, for the purpose of reducing power consumption, for example, a monochrome mode for forming an image using only a single color toner such as black and a color mode for forming an image using a plurality of color toners are used. In some cases, it is necessary to adjust the potential of the intermediate transfer belt in accordance with the switching. Patent Document 1 discloses that a member for removing the charge of the intermediate transfer belt is separately provided upstream of the primary transfer. In Patent Document 2, when the mode is switched from the full color mode to the black single color mode, a regulating roller that is at a position separated from the intermediate transfer belt and is connected to the ground potential is brought into contact with the intermediate transfer belt to be in a charged state. It is disclosed to have an impact.

JP 2004-117389 A JP 2008-107506 A

  An object of the present invention is to suppress disturbance of an image transferred from a non-separated image carrier to a transfer member in an image forming apparatus that separates some of the plurality of image carriers from a transfer member. is there.

  In order to solve the above-described problem, a transfer apparatus according to claim 1 of the present application includes an endless belt-like transfer member that moves around and a plurality of image carriers that respectively hold images formed by a charged developer. A plurality of first transfer means arranged on the inner peripheral side of the transfer body so as to face each other via the transfer body, and charging the transfer body with a polarity opposite to that of the developer, A plurality of first transfer means for respectively transferring the image from the image holding body to the transfer body; and a separation means for separating one or a plurality of image holding bodies and the transfer body among the plurality of image holding bodies. And holding the image separated from the transfer body by the separation means before the image is transferred to the transfer body from the image holding body which is not separated from the transfer body by the separation means. Face to face At least one first transfer means of the serial first transfer means, characterized in that charging the transfer member to the developer and opposite polarity.

  According to a second aspect of the present invention, in the transfer device according to the first aspect, the separation unit has a narrow area in which the transfer body and the image carrier that is not separated from the transfer body are in contact with each other. As described above, the shape or posture of the transfer member is changed to separate the one or more image holding members from the transfer member.

  The transfer device according to claim 3 of the present application is the transfer device according to claim 1 or 2, wherein the transfer body is one of the first transfer means arranged at a position facing the image carrier separated from the transfer body. Power is supplied from a common power source to the first transfer means for charging the first transfer means and the first transfer means arranged at a position facing the image carrier not separated from the transfer body by the separation means. Features.

  A transfer device according to a fourth aspect of the present invention is the transfer device according to any one of the first to third aspects, wherein the first transfer unit faces the image carrier separated from the transfer member by the separation unit. The potential difference generated between the transfer member and the developer when the transfer member is charged is such that the first transfer unit charges the transfer member when the image holding member is not separated from the transfer member. It is smaller than a potential difference generated between the transfer member and the developer.

  According to a fifth aspect of the present invention, in the transfer device according to any one of the first to fourth aspects, the recording medium is conveyed to a certain position on the outer peripheral side of the transfer body by a conveying unit that conveys the recording medium. Before transfer, the transfer member is charged to the same polarity as the developer, and the second transfer unit transfers the image transferred to the transfer member to the recording medium transported to the certain position by the transport unit. Among the first transfer means arranged at positions facing the image carrier separated from the transfer body, the first transfer means for charging the transfer body is transferred by the second transfer means to the transfer body. The amount of charge for charging the transfer body is adjusted according to the amount of charge charged to the surface.

  An image forming apparatus according to claim 6 of the present application is arranged along the circumferential direction on the outer peripheral side of the transfer body of the transfer device according to any one of claims 1 to 5 and the transfer device, A plurality of image holders for holding an image formed by a developer having a color, an image forming unit for forming an image on the image holder using the developer according to image data indicating an image, and A transfer unit configured to transfer a recording medium onto which an image is transferred by the transfer body of the transfer device.

According to the transfer device according to claim 1 of the present application, compared to the case where all the first transfer means facing the image carrier separated from the transfer member do not charge the transfer member, the image is not separated. It is possible to prevent the image transferred from the holding body to the transfer body from being disturbed.
According to the transfer apparatus according to claim 2 of the present application, it is possible to reduce a load that the image carrier receives due to contact with the transfer body.
According to the transfer apparatus according to claim 3 of the present application, the number of power supplies can be reduced.
According to the transfer device according to claim 4 of the present application, the effect of suppressing the disturbance of the image transferred from the image carrier not separated to the transfer member is improved.
According to the transfer device according to claim 5 of the present application, for example, even if the charge charged to the transfer body and the recording medium is changed according to the environment such as temperature and humidity, the type of the recording medium, etc., they are not separated. It is possible to prevent the image transferred from the image carrier to the transfer body from being disturbed.
According to the image forming apparatus of claim 6 of the present application, all the first transfer units facing the image carrier separated from the transfer member are not separated from each other as compared with the case where the charge is not charged to the transfer member. It is possible to prevent the image transferred from the image carrier to the transfer body from being disturbed.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a diagram illustrating a configuration of a transfer unit in a color mode. FIG. 3 is a diagram illustrating a configuration of a transfer unit in a monochrome mode. FIG. 4 is an enlarged view of the photosensitive drum and its periphery in FIG. 3. FIG. 6 is a diagram illustrating a state of toner on a photosensitive drum (black) when power supply to all primary transfer rolls upstream of the primary transfer roll (black) is cut off in the circumferential direction of the intermediate transfer belt. FIG. 6 is a diagram illustrating a state of toner on a photosensitive drum (black) when neutralization is performed by a primary transfer roll (yellow) upstream from the primary transfer roll (black) in the circumferential direction of the intermediate transfer belt.

Embodiments of the present invention will be described below.
1. Overall Configuration of Image Forming Apparatus FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a recording medium supply unit 11, an optical scanning unit 12, developing units 13Y, 13M, 13C, and 13K, a transfer unit 14, a fixing unit 15, and a recording medium discharge. A unit 16 and a control unit 19 are provided. The recording medium supply unit 11, the optical scanning unit 12, the developing units 13Y, 13M, 13C, and 13K, the transfer unit 14, the fixing unit 15, and the recording medium discharge unit 16 are controlled by the control unit 19. Note that the symbols Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. Each of the developing units 13Y, 13M, 13C, and 13K is different only in the toner used, and there is no significant difference in the configuration. Hereinafter, when it is not necessary to particularly distinguish each of the developing units 13Y, 13M, 13C, and 13K, the alphabet at the end of the code indicating the color of the toner is omitted and referred to as “developing unit 13”.

The recording medium supply unit 11 accommodates a sheet P serving as a recording medium that has been cut to a predetermined size. The sheets P stored in the recording medium supply unit 11 are taken out one by one in accordance with an instruction from the control unit 19 and conveyed to the transfer unit 14 via a sheet conveyance path. The recording medium is not limited to paper, and may be, for example, a resin sheet.
The optical scanning unit 12 includes an irradiation device that generates beam light according to image data of each color.

  The transfer unit 14 includes an intermediate transfer belt 141, a belt transport roll 142, a secondary transfer roll 143, a cleaner backup roll 144, a steering roll 145, a stretching roll 146, a primary transfer roll 147, and a chamfering roll 148. And a belt cleaner 149, and a transfer device that transfers the image formed by the developing unit 13 onto the paper P. The intermediate transfer belt 141 is an endless belt-like member that circulates and is hung by a belt conveyance roll 142, a cleaner backup roll 144, a steering roll 145, a stretching roll 146, a primary transfer roll 147, and a chamfering roll 148. Passed.

  A driving unit (not shown) such as a motor is connected to the belt conveying roll 142 via a gear or the like, and moves the intermediate transfer belt 141 in the direction of arrow D14 in the drawing. The other rolls that are not connected to the drive unit rotate following the circumferential movement of the intermediate transfer belt 141. As the intermediate transfer belt 141 rotates and rotates in the direction of arrow D14 in the drawing, the image transferred by the transfer unit 14 is moved to a region where the belt conveyance roll 142 and the secondary transfer roll 143 are in contact with each other. The secondary transfer roll 143 is provided at a position facing the belt conveyance roll 142 outside the intermediate transfer belt 141, and sandwiches the intermediate transfer belt 141 together with the belt conveyance roll 142. The secondary transfer roll 143 is maintained at a predetermined potential by being grounded, for example.

  The belt conveyance roll 142 pushes a portion in contact with the intermediate transfer belt 141 from the inside to the outside, and charges the contact portion with the same polarity as the toner. As a result, a predetermined potential difference is generated between the contact portion of the intermediate transfer belt 141 and the secondary transfer roll 143, so that the image on the intermediate transfer belt 141 is transferred from the recording medium supply unit 11 by this potential difference. It is transferred to the conveyed paper P.

The belt cleaner 149 removes untransferred toner remaining on the surface of the intermediate transfer belt 141. The cleaner backup roll 144 supports the intermediate transfer belt 141 from the inside at a position facing the belt cleaner 149, and supports toner cleaning by the belt cleaner 149.
The steering roll 145 moves together with the primary transfer rolls 147C, 147M, and 147Y, the chamfering roll 148, the cleaner backup roll 144, and the belt cleaner 149 under the control of the control unit 19 when the mode is switched. Accordingly, the tension for pulling the intermediate transfer belt 141 is adjusted so that the intermediate transfer belt 141 does not sag.

Here, the “mode” is a method for forming an image on a recording medium, and forms a monochrome mode for forming an image using only a single color toner such as black and an image using a plurality of color toners. There is a color mode. “Mode switching” means switching the selected mode to another mode.
The chamfering roll 148 supports the intermediate transfer belt 141 from the inside so as to ensure a contact area between the photosensitive drum 131Y of the developing unit 13 and the intermediate transfer belt 141 at a certain width or more.
The tension roll 146 supports the intermediate transfer belt 141 from the primary transfer roll 147K to the belt conveyance roll 142 from the inside. Then, the transfer unit 14 conveys the paper P on which the image is transferred to the fixing unit 15.

  Each developing unit 13 includes a photosensitive drum 131 as an example of an image holding body that holds an image. Each photoconductor drum 131 holds a latent image corresponding to the light emitted from the optical scanning unit 12. Each developing unit 13 forms an image corresponding to the image data of each color from the latent image held by the photosensitive drum 131 using the corresponding color toner. Specifically, the charge of the same polarity as the toner is held on the surface of the photosensitive drum 131, and the toner is attached to the portion where the charge has been lost by irradiating the surface with light by the optical scanning unit 12. The developing unit 13 forms an image.

As described above, the primary transfer roll 147 is provided inside the intermediate transfer belt 141 at a position facing each photosensitive drum 131. The primary transfer roll 147 pushes a portion in contact with the intermediate transfer belt 141 from the inside to the outside, and charges the contact portion with a polarity opposite to that of a predetermined toner. As a result, a potential difference is generated between the contact portion of the intermediate transfer belt 141 and the photosensitive drum 131 facing the primary transfer roll 147, so that an image is transferred to the intermediate transfer belt 141. That is, the intermediate transfer belt 141 is an example of an endless belt-like transfer body that moves around. Further, the primary transfer roll 147 is arranged on the outer peripheral side of the transfer body along the circumferential direction so as to face a plurality of image holding bodies that respectively hold images formed by the charged developer. A plurality of first transfer means arranged on the inner peripheral side of the transfer body, each of the image holding bodies facing each other is charged with a charge having a polarity opposite to that of the developer, and an image is transferred from the image holding body to the transfer body. It is an example of a plurality of first transfer means to transfer each. Further, the belt conveyance roll 142 is disposed at a certain position on the inner peripheral side of the transfer body, and when the recording medium is conveyed to a position facing a certain position on the outer peripheral side of the transfer body by the conveying means for conveying the recording medium. In addition, the recording medium is an example of a second transfer unit that charges the recording medium and transfers the image transferred to the transfer body to the recording medium.
After the image is transferred, the surface of the photosensitive drum 131 is neutralized by a cleaner and the remaining untransferred toner is removed.

  The fixing unit 15 includes a heating roll and a support roll, and fixes the image transferred to the paper P to the paper P by heating and pressurization using these. The recording medium discharge unit 16 discharges the paper P that has undergone the fixing process by the fixing unit 15 to a paper storage place provided in the upper part of the image forming apparatus 1. The control unit 19 sets the mode for forming an image in accordance with a user operation or the like by an operation unit (not shown), the “monochrome mode” for forming an image using only black toner, or yellow, magenta, cyan, black Is switched to one of “color modes” in which an image is formed using the toner. Then, the control unit 19 changes the shape or posture of the transfer unit 14 in accordance with the switched mode, and controls each component of the image forming apparatus 1 such as the developing unit 13 to form an image on a recording medium. Note that the posture of the transfer unit 14 is the direction of the intermediate transfer belt 141 and the like, for example, in which direction the longitudinal direction of the intermediate transfer belt 141 is directed with respect to the direction in which the photosensitive drums 131 are arranged. Is it etc.

2. FIG. 2 is a diagram showing the shape of the transfer portion 14 in the color mode. In the color mode, the intermediate transfer belt 141 is in contact with all the photosensitive drums 131, and an image is transferred from each photosensitive drum 131 to the intermediate transfer belt 141. In the color mode, all the primary transfer rolls 147 charge the intermediate transfer belt 141 with a charge having a polarity opposite to that of the toner. Therefore, the portion of the intermediate transfer belt 141 that has been charged is the corresponding photosensitive drum. The toner of 131 is attracted. For example, when the toner is charged with a negative polarity, the primary transfer roll 147 charges the portion of the intermediate transfer belt 141 so that the contacted portion is charged with a positive polarity. The portion charged to the negative polarity attracts the toner charged to the negative polarity. As a result, the toner is transferred to the intermediate transfer belt 141. The portion of the intermediate transfer belt 141 to which the toner has been transferred moves to a region sandwiched between the belt conveyance roll 142 and the secondary transfer roll 143 via the stretching roll 146. In this region, the belt conveyance roll 142 charges the intermediate transfer belt 141 to a negative polarity that is the same polarity as the toner, so that the toner image transferred to the intermediate transfer belt 141 is recorded in the direction of arrow D11. Transferred to the medium.

3. Shape and Operation of Transfer Section in Monochrome Mode FIG. 3 is a diagram showing the shape of the transfer section 14 in the monochrome mode. In the monochrome mode, the steering roll 145, the primary transfer rolls 147C, 147M, 147Y, the chamfering roll 148, the cleaner backup roll 144, and the intermediate transfer belt 141 are separated from the photosensitive drums 131C, 131M, 131Y. A belt cleaner 149 (hereinafter referred to as a movable roll group) moves. In this monochrome mode, the primary transfer roll 147K charges the intermediate transfer belt 141 with a charge opposite in polarity to the toner, but the primary transfer rolls 147C and 147M are cut off from the power supply by the control unit 19, so The portion in contact with the transfer belt 141 is not charged with a polarity opposite to that of the toner. In such a case, for example, if the power supply to the primary transfer roll 147Y is cut off, the intermediate transfer belt 141 is charged with the same polarity as the toner by the belt transport roll 142, and the intermediate backup belt 141 is cleaned with the cleaner backup roll 144 → the steering roll 145 → the chamfer. The roll 148 → the primary transfer roll 147Y → the primary transfer roll 147M → the primary transfer roll 147C is sequentially passed to reach the primary transfer roll 147K. As a result, the intermediate transfer belt 141 charged with the same polarity as the toner and the toner on the photosensitive drum 131K facing the primary transfer roll 147K come close to each other and electrically repel, so that the surface of the photosensitive drum 131K May disturb the image formed.

In particular, when the shape of the intermediate transfer belt 141 is deformed when switching from the color mode to the monochrome mode, it is not necessary to move each photosensitive drum 131, but an image formed on the surface of the photosensitive drum 131K. Is often disturbed.
FIG. 4 is an enlarged view of the photosensitive drum 131K and its periphery in FIG. The photosensitive drum 131 rotates in the direction of arrow D13 shown in FIG. Points P0, P1, and P2 shown in the figure all indicate points on the surface of the photosensitive drum 131, and are arranged in the order of point P2 → point P1 → point P0 from upstream to downstream in the direction of the arrow D13. It is out. Point P0 is a point indicating the end on the primary transfer roll 147K side, which is the downstream side in the direction of the arrow D13, in the contact region where the intermediate transfer belt 141 contacts the photosensitive drum 131K. Point P1 is a point indicating the end of primary transfer roll 147C on the upstream side in the direction of arrow D13 in the contact area described above in the monochrome mode. Point P2 is a point indicating the end of primary transfer roll 147C on the upstream side in the direction of arrow D13 in the above-described contact region in the color mode. That is, the contact area in the monochrome mode is between point P0 and point P1, and the contact area in the color mode is between point P0 and point P2, so the contact area is narrower in the monochrome mode than in the color mode. . In other words, the movable roll group described above has a plurality of images by changing the shape or posture of the transfer body so that the area where the transfer body and the image holding body that is not separated from the transfer body are in contact with each other is narrowed. It is an example of a separation unit that separates one of the holding members from the transfer member. As described above, when the contact area is narrowed, a load such as tension or wear applied to the photosensitive drum 131K from the intermediate transfer belt 141 is reduced, but there is a high possibility that the transferred image is disturbed. This reason is considered as follows, for example.

  If the rotating speed of the intermediate transfer belt 141 is constant, the narrow contact area as described above means that the time during which the intermediate transfer belt 141 is in contact with the photosensitive drum 131K is short. For example, a current is generated due to a potential difference between the intermediate transfer belt 141 and the photosensitive drum 131K, and the toner moves. However, if the contact time is short, the intermediate transfer belt 141 and the photosensitive member are not stabilized before the toner position is stabilized. Since the drum 131K is physically peeled off, the toner is considered to be easily scattered. Further, when the contact area is wide, the intermediate transfer belt 141 physically holds the toner to be scattered for a long time, so that toner scattering can be suppressed. However, in the monochrome mode where the contact area is narrow, Compared to the case of the color mode, since the period for pressing the toner on the surface of the photosensitive drum 131K by the intermediate transfer belt 141 immediately ends, it is considered that the toner is likely to be scattered.

  FIG. 5 is a diagram illustrating a state of toner on the photosensitive drum 131K when power supply to all the primary transfer rolls 147 upstream of the primary transfer roll 147K in the circumferential direction of the intermediate transfer belt 141 is cut off. As shown in the drawing, the intermediate transfer belt 141 moves in the direction of arrow D14, and the photosensitive drum 131K moves in the direction of arrow D13. At this time, the intermediate transfer belt 141 is conveyed to the photosensitive drum 131K by the belt conveyance roll 142 while being charged with “negative polarity” which is the same polarity as the toner. Therefore, the toner on the surface of the photosensitive drum 131K may be electrically repelled and scattered on the surface of the photosensitive drum 131K when the surface of the intermediate transfer belt 141 approaches as shown in FIG.

  Therefore, the transfer unit 14 supplies power to the primary transfer roll 147Y in the monochrome mode. Then, the primary transfer roll 147Y charges a portion in contact with the intermediate transfer belt 141 with a polarity opposite to that of the toner so that the potential of the same polarity as that of the toner generated on the intermediate transfer belt 141 is removed by the belt conveyance roll 142. Accordingly, since the intermediate transfer belt 141 that has passed through the primary transfer roll 147Y has been neutralized, the electric repulsive force generated between the intermediate transfer belt 141 and the toner on the photosensitive drum 131K is reduced, and the photosensitive drum is reduced. The possibility of disturbing the image formed on the surface of 131K is suppressed.

  FIG. 6 is a diagram illustrating the state of toner on the photosensitive drum 131K when the charge is removed by the primary transfer roll 147Y upstream of the primary transfer roll 147K in the circumferential direction of the intermediate transfer belt 141. At this time, since the intermediate transfer belt 141 has been neutralized by the primary transfer roll 147Y, the intermediate transfer belt 141 is conveyed to the photosensitive drum 131K in a state of being charged with “positive polarity” that is opposite in polarity to the toner. Therefore, the toner on the surface of the photosensitive drum 131K is less likely to be electrically repelled and scattered even when the surface of the intermediate transfer belt 141 approaches as shown in FIG.

4). Modification The above is the description of the embodiment, but the contents of this embodiment can be modified as follows. Further, the following modifications may be combined.
(1) In the above-described embodiment, the shape of the intermediate transfer belt 141 is changed by the movement of the steering roll 145 or the like in the transfer unit 14, and the intermediate transfer belt 141 and the photosensitive drums 131C, 131M, and 131Y However, the mechanism for separating the intermediate transfer belt 141 from the photosensitive drums 131C, 131M, and 131Y is not limited to this. For example, the transfer unit 14 may move without being moved or deformed, and the photosensitive drums 131C, 131M, and 131Y may move away from the intermediate transfer belt 141. In short, it is sufficient that the intermediate transfer belt 141 is in contact with all the primary transfer rolls 147 in both the monochrome mode and the color mode.

(2) In the above-described embodiment, the potential difference generated between the intermediate transfer belt 141 and the toner by the primary transfer roll 147Y charging the intermediate transfer belt 141 in the monochrome mode is the same as the potential difference between the primary transfer roll 147Y in the color mode. The potential difference generated between the intermediate transfer belt 141 and the toner may be made smaller by charging the transfer belt 141.

  In the color mode, the portion where the primary transfer roll 147Y is in contact with the intermediate transfer belt 141 is in contact with the photosensitive drum 131Y, and the toner adhering to the surface of the photosensitive drum 131Y or the surface thereof is transferred to the primary transfer roll 147Y. Since the electric charge having the opposite polarity to the electric charge charged to the intermediate transfer belt 141 is held, the electric charge charged to the intermediate transfer belt 141 changes in the direction to be canceled at that portion, but in the monochrome mode, The part is separated from the photosensitive drum 131Y. Therefore, in the monochrome mode, if the intermediate transfer belt 141 is neutralized as much as when the primary transfer roll 147Y is in the color mode, the above-described portion of the intermediate transfer belt 141 may be shaken too much in the opposite polarity to the toner. Then, for example, as indicated by a broken line in FIG. 6, before this portion contacts the photosensitive drum 131K, toner on the surface of the photosensitive drum 131K may be attracted to disturb the image. Therefore, in the monochrome mode, it is desirable to charge the intermediate transfer belt 141 so that the potential difference generated between the intermediate transfer belt 141 and the toner is smaller than in the color mode.

(3) Although the power supply of each primary transfer roll 147 has not been described in detail in the above-described embodiment, a power supply may be shared among those primary transfer rolls 147 that supply power in the monochrome mode. In the monochrome mode, the primary transfer rolls 147C and 147M are cut off from power supply, but the primary transfer rolls 147K and 147Y are supplied with power. Therefore, by using a common power source as a power source for supplying power to these primary transfer rolls 147K and 147Y, the number of parts can be suppressed.

(4) In the above-described embodiment, the primary transfer roll 147 used for static elimination in the monochrome mode is the primary transfer roll 147Y, but may be a primary transfer roll 147C or a primary transfer roll 147M. In the monochrome mode, two or more of these may be used for static elimination, or all three may be used for static elimination. In short, the first transfer means that faces the image carrier separated from the transfer body by the separation means before the image is transferred to the transfer body from the image carrier that is not separated from the transfer body by the separation means. It suffices that at least one first transfer unit charges the transfer body with a polarity opposite to that of the developer.

  However, in the monochrome mode, it is desirable that the primary transfer roll 147 used for static elimination is a color in which the toner color is not conspicuous with respect to the ground color (for example, white) of the recording medium. This is because the primary transfer roll 147 used for neutralization is separated from the opposing photosensitive drum 131, but the toner may be attracted to the intermediate transfer belt 141 by the neutralization. Even if the image is distorted due to the toner being attracted, if the toner color is inconspicuous with respect to the ground color of the recording medium, the image turbulence is inconspicuous, which affects the viewer of the recording medium. Less is. A color that is not conspicuous with respect to the ground color is a color that is close to the ground color in a color space such as the L * a * b * color space, or any one of hue, saturation, and brightness is close to the ground color. A color or a value evaluated by combining these means a color close to the ground color.

In particular, as in the above-described modification (3), when the primary transfer roll 147 is configured to use a common power source for the primary transfer roll 147K and the primary transfer roll 147K, the primary transfer used for the neutralization is used. When the primary transfer roll 147 (for example, the primary transfer roll 147Y in the above example) whose toner color is inconspicuous with respect to the background color of the recording medium is selected as the roll 147, the following effects are obtained.
That is, when power is supplied from a common power source to the primary transfer roll 147K that supplies black toner and the primary transfer roll 147Y that supplies yellow toner that is inconspicuous with respect to white (ground color of the recording medium), In conditions such as the amount of power supply, one of the conditions is matched with the other condition, and the condition of the primary transfer roll 147 that is matched may deviate from the original optimum condition. In this case, the conditions for the primary transfer roll 147Y may be set in accordance with the optimum conditions for the primary transfer roll 147K. As a result, even if a problem such as toner scattering occurs in the primary transfer roll 147Y in the color mode because the conditions set for the primary transfer roll 147Y deviate from the optimum conditions inherent to the primary transfer roll 147Y. Since the color of the toner supplied by the primary transfer roll 147Y is yellow, which is an inconspicuous color with respect to the ground color of the recording medium, this problem is not noticeable.

  When there is a photosensitive drum 131 for transferring toner that does not contain a color material such as transparent toner, a primary transfer roll 147 that faces the photosensitive drum 131 may be used for static elimination.

(5) In the above-described embodiment, the primary transfer roll 147 used for static elimination has the intermediate transfer belt 141 opposite to the toner regardless of the charge amount of the same polarity as the toner charged by the belt transfer roll 142 to the intermediate transfer belt 141. Although the polarity is charged, the charge amount for charging the intermediate transfer belt 141 may be adjusted according to the charge amount charged on the intermediate transfer belt 141 by the belt conveyance roll 142. Here, the charge amount is an amount of electric charge that is changed when a medium such as the intermediate transfer belt 141 is charged by a charging member such as the belt conveyance roll 142.

  For example, it may be desirable to adjust the amount of charge that the belt conveyance roll 142 charges the intermediate transfer belt 141 according to the environment such as temperature and humidity, the type of the recording medium, and the like. Specifically, a detection unit (not shown) such as an optical sensor or a pressure sensor provided in the recording medium supply unit 11 detects the thickness of the recording medium conveyed to the transfer unit 14 and controls the detection signal. Send to part 19. The control unit 19 specifies the thickness of the recording medium based on the sent detection signal, and controls the belt conveyance roll 142 so that the thicker the recording medium is, the higher the charging amount is. In some cases, the belt conveyance roll 142 is controlled such that the lower the temperature around the intermediate transfer belt 141 or the lower the humidity, the higher the charging amount. In this case, specifically, a detection unit (not shown) such as a temperature sensor and a humidity sensor around the intermediate transfer belt 141 detects the temperature and humidity around the intermediate transfer belt 141 and sends the detection signal to the control unit 19. The control unit 19 adjusts the charge amount according to the sent detection signal.

  In the monochrome mode, when such adjustment is made to the amount of charge charged on the intermediate transfer belt 141 by the belt conveyance roll 142, the electrical polarity of the intermediate transfer belt 141 when it approaches the primary transfer roll 147Y changes. In this case, the potential of the intermediate transfer belt 141 approaching the photosensitive drum 131K is changed by changing the electric power used by the primary transfer roll 147Y for charge removal in accordance with the amount of charge charged by the belt conveyance roll 142 to the intermediate transfer belt 141. Adjust it. In other words, the higher the charge amount charged on the recording medium by the belt conveyance roll 142 by the control unit 19, the larger the amount by which the primary transfer roll 147 Y neutralizes the intermediate transfer belt 141. As a result, even if the amount of charge that the belt transfer roll 142 charges the intermediate transfer belt 141 is adjusted according to the environment such as temperature and humidity, the type of the recording medium, and the like, this allows the photosensitive drum 131K to move from the photosensitive drum 131K in the monochrome mode. Disturbances in the image transferred to the intermediate transfer belt 141 are suppressed.

(6) In the above-described embodiment, a driving unit such as a motor is connected to the belt conveyance roll 142 via a gear or the like, and the intermediate transfer belt 141 is moved, but the roll moved by the driving unit is Other rolls may be used. For example, the steering roll 145 and the stretching roll 146 may be connected to the drive unit via a gear, and the intermediate transfer belt 141 may be moved. In this case, the belt conveying roll 142 rotates following the movement of the intermediate transfer belt 141.

(7) In the above-described embodiment, the movable roll group is moved so that the intermediate transfer belt 141 is separated from the photosensitive drums 131C, 131M, and 131Y in the monochrome mode. However, the movable roll group is moved to the intermediate transfer belt 141 in the monochrome mode. This is not the case with the photosensitive drum separated from the photosensitive drum. For example, in an image forming apparatus that uses only two color materials of black and cyan, the movable roll group performs intermediate transfer of the photosensitive drum 131C that forms an image on the surface with toner containing cyan color material in the monochrome mode. It may be separated from the belt 141. In addition, the photosensitive drum 131 in which the movable roll group is not separated from the intermediate transfer belt 141 in the monochrome mode is not limited to the photosensitive drum 131K. For example, in an image forming apparatus using two types of black color materials, the two photoconductive drums 131 corresponding to the two types of toners containing the two types of color materials are not separated from each other, and the other photoconductive drums 131 are not separated. May be separated. In short, the movable roll group may be an example of a separation unit that separates one or a plurality of image carriers from the plurality of image carriers and the transfer member.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Recording medium supply part, 12 ... Optical scanning part, 13 ... Developing part, 131 ... Photoconductor drum, 14 ... Transfer part, 141 ... Intermediate transfer belt, 142 ... Belt conveyance roll, 143 ... Two Next transfer roll, 144 ... Cleaner backup roll, 145 ... Steering roll, 146 ... Stretch roll, 147 ... Primary transfer roll, 148 ... Chamfer roll, 149 ... Belt cleaner, 15 ... Fixing section, 16 ... Recording medium discharge section, 19 ... control unit, P ... paper.

Claims (6)

An endless belt-shaped transfer body that moves around,
A plurality of first transfers arranged on the inner peripheral side of the transfer body so as to face the plurality of image carriers that respectively hold images formed by the charged developer, through the transfer body. A plurality of first transfer means for charging the transfer member with a polarity opposite to that of the developer and transferring the image from the image holding member to the transfer member, respectively;
A separating unit that separates one or more of the plurality of image holding members from the transfer member;
Before the image is transferred from the image carrier that is not separated from the transfer member by the separation unit to the transfer member, the image carrier that is separated from the transfer member by the separation unit faces the image carrier. At least one first transfer unit among the first transfer units charges the transfer body with a polarity opposite to that of the developer. The separation means changes the shape or posture of the transfer body so as to narrow a contact area between the transfer body and the image carrier that is not separated from the transfer body. The transfer apparatus according to claim 1, wherein the image holding member and the transfer member are separated from each other. Of the first transfer means arranged at a position facing the image carrier separated from the transfer body, the first transfer means for charging the transfer body is not separated from the transfer body by the separation means. The transfer apparatus according to claim 1, wherein electric power is supplied from a common power source to the first transfer unit arranged at a position facing the image holding member. The potential difference generated between the transfer member and the developer when the transfer member is charged by the first transfer member facing the image carrier separated from the transfer member by the separation unit is the image difference. It is smaller than a potential difference generated between the transfer body and the developer when the transfer body is charged by the first transfer unit when the holding body is not separated from the transfer body. The transfer device according to claim 1. Before the recording medium is transported to a certain position on the outer peripheral side of the transfer body by the transport means for transporting the recording medium, the transfer body is charged to the same polarity as the developer and transferred to the transfer body. Second transfer means for transferring the transferred image to the recording medium transported to the certain position by the transport means;
Of the first transfer means arranged at a position facing the image carrier separated from the transfer body, the first transfer means for charging the transfer body is charged to the transfer body by the second transfer means. The transfer device according to claim 1, wherein the charge amount for charging the transfer body is adjusted according to the charged amount. A transfer device according to any one of claims 1 to 5;
A plurality of image carriers that are arranged along the circumferential direction on the outer peripheral side of the transfer member of the transfer device and hold an image formed by a charged developer;
Image forming means for forming an image on the image carrier using the developer according to image data representing an image;
An image forming apparatus comprising: a transport unit configured to transport a recording medium onto which an image is transferred by the transfer body of the transfer device.

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