JP2014044371A - Image forming apparatus, and image forming unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the entire image formation area of a photoreceptor chargeable to prevent the occurrence of printing failure.SOLUTION: An image forming apparatus has a plurality of image forming units 10 each including a photoreceptor (photoreceptor drum 11) having a photosensitive layer, arranged adjacent with each other and shifted in an axial direction of the photoreceptor, so as to form an image by the plurality of adjacent image forming units in cooperation with each other. The plurality of adjacent image forming units 10A and 10B have an overlapping area PD where image formation areas PR and PL of the photoreceptor overlap with each other in the axial direction of the photoreceptor. The photoreceptor has a level difference part 93 at an end part on the overlapping area side in the axial direction. The level difference part is formed of a large diameter part 91 and a small diameter part 92 having a smaller diameter than that of the large diameter part.

Description

  The present invention relates to an image forming apparatus that forms an image using an electrophotographic process, and in particular, by arranging a plurality of image forming units in a plurality of rows with their positions shifted in the main scanning direction. The present invention relates to an image forming apparatus that forms an image wider than the width of a single printing area. The present invention also relates to an image forming unit used in the image forming apparatus.

  Conventionally, an image forming apparatus that forms an image using an electrophotographic process has been widely used. This type of image forming apparatus includes an image forming unit, an exposure head, a transfer mechanism, and a fixing mechanism.

The image forming unit is a unit that forms an image called a “developer image (toner image)” using a developer (toner).
The exposure head is an exposure unit that partially exposes a photosensitive drum provided in the image forming unit based on print data received from an external device.
The transfer mechanism is a mechanism for transferring a developer image formed on the surface of the photosensitive drum to a transfer target (or intermediate transfer member).
The fixing mechanism is a mechanism that heats and pressurizes the transfer target body onto which the developer image has been transferred, melts the developer image, and fixes it to the transfer target body.

  In the following description, the “transfer object” means a print medium such as a sheet on which a developer image is transferred and fixed. The “intermediate transfer member” is interposed between the photosensitive drum and the transfer target member, and after the developer image formed on the surface of the photosensitive drum is transferred, the developer image is transferred to the transfer target member. Description will be made assuming that the member to be retransferred is meant.

  The image forming unit is configured as a unit that can be freely attached to and detached from (attached to and removed from) the image forming apparatus. The image forming unit usually includes a photosensitive drum therein, and further includes a charging roller, a developing roller, and a cleaning mechanism around the photosensitive drum.

The photosensitive drum is a photosensitive member on which a developer image is formed. The photosensitive drum is formed in a cylindrical shape.
The charging roller is a charging member that uniformly charges the surface of the photosensitive drum.
The developing roller is a developing member that develops (visualizes) the electrostatic latent image as a developer image by supplying the developer to the photosensitive drum and attaching the developer onto the electrostatic latent image. . When the developer is supplied from the developing roller to the photosensitive drum, a developer image is formed on the surface thereof.
The cleaning mechanism removes the developer remaining on the surface of the photosensitive drum after the transfer process (that is, after the developer image is transferred from the photosensitive drum to the transfer target (or intermediate transfer member) by the transfer mechanism). It is.

  In the image forming apparatus, the exposure head is provided between the charging roller and the developing roller so as to face the photosensitive drum. In the image forming apparatus, the transfer roller of the transfer mechanism is provided between the developing roller and the cleaning mechanism. The transfer roller is a member that draws the developer image formed on the surface of the photosensitive drum and transfers the developer image from the photosensitive drum to the transfer target (or intermediate transfer member).

  In such a configuration, in the image forming apparatus, first, the charging roller uniformly charges the surface of the photosensitive drum. Next, in the image forming apparatus, the exposure head partially exposes the surface of the photosensitive drum based on the print data. As a result, the image forming apparatus forms an electrostatic latent image on the surface of the photosensitive drum.

  Thereafter, in the image forming apparatus, the developing roller supplies the developer to the photosensitive drum. As a result, the image forming apparatus attaches the developer onto the electrostatic latent image, and develops (visualizes) the electrostatic latent image as a developer image. As a result, a developer image is formed on the surface of the photosensitive drum.

  Next, in the image forming apparatus, the transfer roller of the transfer mechanism draws the developer image formed on the surface of the photosensitive drum, and transfers the developer image from the photosensitive drum to the transfer target (or intermediate transfer member). In the image forming apparatus, when the developer image is transferred to the intermediate transfer member, another transfer roller transfers the developer image from the intermediate transfer member to the transfer target.

  In the image forming apparatus, when the developer image is transferred to the transfer target, the fixing mechanism heats and pressurizes the transfer target to melt the developer image. As a result, the image forming apparatus fixes the developer image on the transfer target.

  In the image forming apparatus, when the developer image is transferred to the transfer target, the cleaning mechanism removes the developer remaining on the surface of the photosensitive drum.

  By the way, in recent years, a single image forming unit using a plurality of small image forming units (for example, an image forming unit whose length in the longitudinal direction is the same as the A3 size or A4 size). An image forming apparatus for forming (printing) an image on a medium (for example, a medium of A2 size or larger) wider than the width of the image forming area (hereinafter also referred to as “printing area”) has been proposed. (For example, refer to Patent Document 1). Here, “image forming area (printing area)” means an area for forming a developer image of the image forming unit.

  In this image forming apparatus, a plurality of small image forming units are arranged in a plurality of rows with their positions being shifted in the main scanning direction, and end portions of image forming regions (printing regions) of two adjacent image forming units An image is formed (printed) by overlapping the portions in the sub-scanning direction. Hereinafter, this image forming apparatus is referred to as a “conventional image forming apparatus”.

JP 2004-145285 A

  Normally, this type of image forming apparatus needs to charge the entire image forming area of the photosensitive drum with a charging member. However, in the conventional image forming apparatus, the end portion of the image forming area of the photosensitive drum is not coated with a liquid constituting the photosensitive layer (hereinafter referred to as “photosensitive liquid”) (hereinafter referred to as “photosensitive layer unexposed”). An area where the photosensitive solution is accumulated (hereinafter referred to as a “photosensitive layer liquid accumulation portion”) is generated. The photosensitive layer non-coated portion and the photosensitive layer liquid reservoir portion become a poorly charged region that is not charged by the charging member.

  For this reason, in the conventional image forming apparatus, when charging failure occurs at the end portion of the image forming area of the photosensitive drum, printing failure occurs that stains the developer image transferred onto the transfer medium or intermediate transfer body. was there.

  The present invention has been made to solve the above-described problems, and provides an image forming apparatus capable of charging the entire image forming area of a photosensitive drum (photoconductor) and preventing occurrence of printing defects. Is the main purpose.

  In order to achieve the above object, the first invention provides a plurality of adjacent images by disposing a plurality of image forming units each including a photosensitive member having a photosensitive layer while being shifted in the axial direction of the photosensitive member. An image forming apparatus for jointly forming an image by a forming unit, wherein the plurality of adjacent image forming units have an overlapping region in which an image forming region of the photoconductor overlaps in an axial direction of the photoconductor. The photosensitive member has a step portion at an end portion on the overlapping region side in the axial direction, and the step portion is formed by a large diameter portion and a small diameter portion having a smaller diameter than the large diameter portion. The configuration is as follows.

  This image forming apparatus has a plurality of image forming units each including a photoconductor having a photosensitive layer. In this image forming apparatus, a plurality of image forming units are arranged adjacent to each other while being shifted in the axial direction of the photosensitive member, so that an image is jointly formed by the plurality of adjacent image forming units.

  A plurality of adjacent image forming units have overlapping areas in which the image forming areas of the photoconductor overlap in the axial direction of the photoconductor. The photoreceptor has a stepped portion at the end on the overlapping region side in the axial direction. The step portion is formed by a large diameter portion and a small diameter portion having a smaller diameter than the large diameter portion.

  Therefore, in this image forming apparatus, the photoreceptor of each image forming unit is divided into a large diameter portion and a small diameter portion by the step portion. In this image forming apparatus, the image forming area can be formed as a large-diameter portion separated from the small-diameter portion by the step portion. Therefore, in this image forming apparatus, the charging member can be brought into good contact with the entire area of the image forming area. As a result, in this image forming apparatus, the charging member can charge the entire image forming area of the photoreceptor.

  For this reason, this image forming apparatus prevents the charging failure from occurring at the end portion of the image forming area of the photoreceptor, and the printing failure that stains the developer image transferred onto the transfer medium or intermediate transfer body. Can be prevented.

  Further, in this image forming apparatus, the photosensitive layer non-coated portion and the photosensitive layer liquid reservoir portion can be provided in the small diameter portion. The small diameter portion has a smaller diameter than the image forming region formed as the large diameter portion. Therefore, this image forming apparatus prevents the photosensitive layer liquid reservoir from coming into contact with the transfer medium or the intermediate transfer body by forming the stepped portion higher than the standard thickness of the photosensitive layer liquid reservoir. Can do. Also by this, this image forming apparatus can prevent the occurrence of printing defects that contaminate the developer image transferred onto the transfer medium or intermediate transfer body.

The second invention is an image forming unit including a photosensitive member having a photosensitive layer, the photosensitive member including an image forming region in which a developer image is formed, and adjacent in the axial direction. The image forming area has an overlapping area that overlaps with the image forming area of the photoconductor of another image forming unit that is arranged in the image forming unit, and the photoconductor is at the end of the overlapping area in the axial direction. A step portion is provided, and the step portion is formed by a large diameter portion and a small diameter portion having a smaller diameter than the large diameter portion.
This image forming unit can be used in the image forming apparatus according to the first invention.

  According to the present invention, it is possible to provide an image forming apparatus capable of charging the entire image forming area of the photosensitive member and preventing the occurrence of printing defects, and an image forming unit used in the image forming apparatus.

1 is a diagram (1) illustrating a configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a diagram (2) illustrating the configuration of the image forming apparatus according to the first embodiment. 2 is a diagram illustrating a configuration of an image forming unit used in Embodiment 1. FIG. FIG. 3 is a diagram illustrating an arrangement relationship of image forming units used in the first embodiment. 2 is a diagram illustrating a configuration of a main part of an image forming unit used in Embodiment 1. FIG. 2 is a diagram illustrating a configuration of a photosensitive drum used in Embodiment 1. FIG. 2 is an explanatory diagram (1) of a photosensitive drum used in Embodiment 1. FIG. FIG. 3 is an explanatory diagram (2) of the photosensitive drum used in the first embodiment. 1 is a diagram illustrating a functional configuration of an image forming apparatus according to Embodiment 1. FIG. FIG. 4 is a diagram illustrating a configuration of a main part of an image forming unit used in Embodiment 2. 6 is a diagram illustrating a configuration of a photosensitive drum used in Embodiment 2. FIG.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. Each figure is only schematically shown so that the present invention can be fully understood. Therefore, the present invention is not limited to the illustrated example. Moreover, in each figure, the same code | symbol is attached | subjected about the common component and the same component, and those overlapping description is abbreviate | omitted.

[Embodiment 1]
<Configuration of image forming apparatus>
The image forming apparatus 1 according to the first exemplary embodiment is an apparatus that forms an image using an electrophotographic process. Here, the case where the image forming apparatus 1 is configured as a tandem type intermediate transfer color printer will be described.

  Hereinafter, the configuration of the image forming apparatus 1 according to the first embodiment will be described with reference to FIGS. 1 and 2. 1 and 2 are diagrams each showing a configuration of the image forming apparatus 1 according to the first embodiment. FIG. 1 shows the configuration of the image forming apparatus 1 in a state where the upper cover 3 is opened as viewed obliquely from above. 2 shows a cross-sectional configuration of the image forming apparatus 1 cut along the line AA shown in FIG.

  As shown in FIG. 1, the image forming apparatus 1 includes a housing 2 and an upper cover 3, and the upper cover 3 is openable and closable around a rotation axis provided in advance with respect to the housing 2. It is configured. The image forming apparatus 1 includes a plurality (eight in the illustrated example) of image forming units 10 inside the housing 2. In addition, the image forming apparatus 1 includes a plurality (eight in the illustrated example) of exposure heads 20 on the inner surface side of the upper cover 3.

  The image forming unit 10 is a unit that forms a developer image (hereinafter referred to as “toner image”) using a developer (hereinafter referred to as “toner”). The image forming unit 10 is configured as a unit that can be attached to and detached from (attached to and removed from) the housing 2 of the image forming apparatus 1.

  The exposure head 20 is an exposure unit that partially exposes the photosensitive drum 11 (see FIG. 2) provided in the image forming unit 10 based on print data received from an external device. Here, the case where the exposure head 20 is configured as an LED (Light Emitting Diode) head will be described. However, the image forming apparatus 1 may be configured to use a laser exposure device or other light emitting means instead of the exposure head 20 as the exposure unit.

  The image forming unit 10 forms a set of several units (two in the illustrated example) for each color of the toner image to be formed, and the main scanning direction (in the example shown in FIG. 1, the vertical direction) for each set. ) Are arranged in a plurality of rows (two rows in the illustrated example) with their positions shifted.

  In the first embodiment, two image forming units 10 form a set. Hereinafter, when distinguishing the two image forming units 10 constituting each group, the front image forming unit 10 shown in FIG. 1 is referred to as an “image forming unit 10A”, and the rear image forming unit shown in FIG. The unit 10 is referred to as an “image forming unit 10B”. The image forming unit 10 </ b> A and the image forming unit 10 </ b> B have the left and right (up and down in the example shown in FIG. 1) configurations reversed.

  In the first exemplary embodiment, the image forming apparatus 1 has four colors, yellow (Y), magenta (M), cyan (C), and black (K). Correspondingly, four image forming units 10A and four image forming units 10B are provided. Hereinafter, when distinguishing components corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K), an alphabetic character is added at the end of the code given to each component. The description will be provided with “(Y)”, “(M)”, “(C)”, and “(K)”.

  Therefore, in the first exemplary embodiment, the image forming apparatus 1 forms image forming units 10A (Y) and 10B (Y) that form Y (yellow) color toner images, and M (magenta) color toner images. Image forming units 10A (M) and 10B (M), image forming units 10A (C) and 10B (C) for forming C (cyan) toner images, and K (black) toner images are formed. The image forming units 10A (K) and 10B (K) are provided.

  The four image forming units 10A (that is, the image forming units 10A (Y), 10A (M), 10A (C), and 10A (K)) have the same configuration except that the color of the toner accommodated therein is different. It has become. Similarly, the four image forming units 10B (that is, the image forming units 10B (Y), 10B (M), 10B (C), and 10B (K)) also differ in the color of the toner accommodated therein. It has the same configuration.

  The exposure head 20 is disposed to face the upper side of the image forming unit 10. Therefore, as with the image forming unit 10, the exposure head 20 is composed of several sets for each color of the toner image to be formed, and a plurality of rows are arranged with the positions shifted in the main scanning direction for each set. It is divided and arranged.

  In the first embodiment, two exposure heads 20 constitute a set. Hereinafter, when distinguishing the two exposure heads 20 constituting each set, the exposure head 20 facing the image forming unit 10A shown in FIG. 1 is referred to as an “exposure head 20A”, and the image forming unit 10B shown in FIG. The exposure head 20 that faces is called “exposure head 20B”. The exposure head 20A and the exposure head 20B have the same configuration.

  In the first embodiment, the exposure head 20A and the exposure head 20B are provided corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K).

  Therefore, in the first exemplary embodiment, the image forming apparatus 1 includes the exposure heads 20A (Y) and 20B (Y) corresponding to Y (yellow) color and the exposure heads 20A (M) and M corresponding to M (magenta) color. 20B (M), exposure heads 20A (C) and 20B (C) corresponding to C (cyan) color, and exposure heads 20A (K) and 20B (K) corresponding to K (black) color It has become.

  As shown in FIG. 2, the image forming apparatus 1 is provided with a photosensitive drum 11 inside each image forming unit 10. The photosensitive drum 11 is a photosensitive member formed in a cylindrical shape. The photosensitive drum 11 has a configuration in which a photosensitive layer 72 (see FIG. 6) is applied on a base tube 71 (see FIG. 6) which is a cylindrical conductive support. The photosensitive drum 11 functions as an image carrier that carries an electrostatic latent image and a developer image (toner image) on the surface.

The image forming apparatus 1 includes an intermediate transfer unit 30 in addition to the image forming unit 10 and the exposure head 20.
The intermediate transfer unit 30 is a unit that functions as a transfer mechanism.

  Here, the intermediate transfer unit 30 includes an intermediate transfer belt 31 as an intermediate transfer member, and the intermediate transfer belt 31 is interposed between the photosensitive drum 11 of the image forming unit 10 and the medium 9 as a transfer target. In the following description, the toner image formed on the surface of the photosensitive drum 11 is transferred from the photosensitive drum 11 to the medium 9.

  That is, here, the intermediate transfer unit 30 once transfers the toner image formed on the surface of the photosensitive drum 11 of the image forming unit 10 to the intermediate transfer belt 31, and then transfers the transferred toner image to the intermediate transfer belt 31. Will be described as being re-transferred to the medium 9.

  The intermediate transfer unit 30 includes an intermediate transfer belt 31, and a drive roller 32, idle rollers 33, and a plurality of (here, eight) belt transfer rollers so as to contact the inner peripheral surface of the intermediate transfer belt 31. 34 is provided.

  The drive roller 32 and the idle roller 33 are rollers that stretch the intermediate transfer belt 31. The drive roller 32 is driven to rotate by a drive source (not shown) and causes the intermediate transfer belt 31 to travel.

  The intermediate transfer belt 31 is interposed between the photosensitive drum 11 of the image forming unit 10 and the medium 9 as a transfer target, and after the toner image formed on the surface of the photosensitive drum 11 is transferred, the toner image is transferred. Is a belt-like intermediate transfer member that re-transfers the toner to the medium 9. The intermediate transfer belt 31 is disposed immediately below the eight image forming units 10 so that the outer peripheral surface thereof is in contact with the photosensitive drums 11 of the eight image forming units 10.

  The belt transfer roller 34 is a transfer member that draws the toner image formed on the surface of the photosensitive drum 11 of the image forming unit 10 and transfers the toner image from the photosensitive drum 11 to an intermediate transfer belt 31 as an intermediate transfer member. The belt transfer roller 34 is disposed so as to face the photosensitive drum 11 with the intermediate transfer belt 31 interposed therebetween. In the first embodiment, eight belt transfer rollers 34A (Y), 34B (Y), 34A (M), 34B (M), 34A (C), 34B (C), 34A (K), 34B (K) Are eight photosensitive drums 11A (Y), 11B (Y), 11A (M), 11B (M), 11A (C), 11B (C), 11A (K), and 11B (K), respectively. It arrange | positions so that it may oppose.

As shown in FIG. 2, the image forming apparatus 1 includes a medium tray 4 provided inside the housing 2, a stacker 5 provided on the upper surface of the upper cover 3, and a conveyance path. 6 is provided from the medium tray 4 to the stacker 5.
The medium tray 4 is a component that houses a print medium (hereinafter referred to as “medium 9”) used as a transfer medium, such as paper.
The stacker 5 is a portion where the media 9 on which the toner images are fixed are stacked.
The conveyance path 6 is a path through which the medium 9 is conveyed.

  In the image forming apparatus 1, a separation roller 61 is provided on the outlet side of the medium tray 4. The separation roller 61 separates the media 9 stored inside the media tray 4 one by one and feeds the media 9 to the transport path 6.

  In the image forming apparatus 1, the conveyance roller 62, the medium transfer roller 63, the fixing unit 40, and the discharge roller 64 are provided on the conveyance path 6.

  The conveyance roller 62 is a roller that conveys the medium 9 fed to the conveyance path 6 by the separation roller 61 to the downstream side. In the example illustrated in FIG. 2, the image forming apparatus 1 includes a pair of conveyance rollers 62 a provided directly above the separation roller 61 as a conveyance roller 62, and a pair provided between the conveyance roller 62 a and the medium transfer roller 63. The conveyance roller 62b is provided. The medium 9 is fed between the intermediate transfer belt 31 of the intermediate transfer unit 30 and the medium transfer roller 63 by the conveyance roller 62.

  The medium transfer roller 63 is a transfer member that draws the toner image transferred to the intermediate transfer belt 31 of the intermediate transfer unit 30 and transfers the toner image from the intermediate transfer belt 31 to the medium 9 as a transfer target.

  The fixing unit 40 is a unit that functions as a fixing mechanism that heats and pressurizes the medium 9 onto which the toner image has been transferred by the medium transfer roller 63 to melt the toner image and fix it on the medium 9.

  The discharge roller 64 is a transport member that transports the medium 9 on which the toner image is fixed by the fixing unit 40 to the stacker 5 and discharges the medium 9 onto the stacker 5. The image forming apparatus 1 discharges and holds the printed medium 9 (the medium 9 on which the toner image is fixed) on the stacker 5.

<Configuration of image forming unit>
Hereinafter, the configuration of the image forming unit 10 will be described with reference to FIG. FIG. 3 is a diagram illustrating a configuration of the image forming unit 10 used in the first embodiment. FIG. 3 shows a cross-sectional configuration of the image forming unit 10 cut along the line AA shown in FIG.

  As shown in FIG. 3, the image forming unit 10 includes a detachable toner storage container 51 in an upper portion of the unit. The image forming unit 10 stores the toner TN inside the toner storage container 51.

  The image forming unit 10 includes a stirring member 53 inside the toner storage container 51. The image forming unit 10 stirs the toner TN stored in the toner storage container 51 by the stirring member 53.

  Further, the image forming unit 10 includes a toner hopper 52 below the toner storage container 51. The image forming unit 10 discharges the toner TN from the toner storage container 51 to the toner hopper 52 and stores the toner TN inside the toner hopper 52.

  The image forming unit 10 includes a stirring member 54 inside the toner hopper 52. The image forming unit 10 stirs the toner TN stored in the toner hopper 52 by the stirring member 54.

  The image forming unit 10 includes a photosensitive drum 11 inside, and further includes a charging roller 12, a developing roller 13, and a cleaning blade 16 around the photosensitive drum 11 so as to contact the photosensitive drum 11. ing.

  The photosensitive drum 11 is a photosensitive member on which a toner image is formed. The photosensitive drum 11 functions as an image carrier that carries an electrostatic latent image and a toner image on the surface. The photosensitive drum 11 is formed in a cylindrical shape.

  The charging roller 12 is a charging member that uniformly charges the surface of the photosensitive drum 11. When the surface of the photosensitive drum 11 is uniformly charged by the charging roller 12, it is partially exposed by the exposure head 20. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 11.

  The developing roller 13 is a developer carrying member that carries the toner TN on its surface. The developing roller 13 supplies toner TN to the photosensitive drum 11 and adheres the toner TN onto the electrostatic latent image, thereby developing the electrostatic latent image as a toner image (visualization). Function. When the toner TN is supplied from the developing roller 13 to the photosensitive drum 11, a toner image is formed on the surface thereof.

  The cleaning blade 16 removes the toner TN remaining on the surface of the photosensitive drum 11 after the toner image is transferred from the photosensitive drum 11 to the intermediate transfer belt 31 (see FIG. 2) by the intermediate transfer unit 30 (see FIG. 2). It is a member.

  In addition, the image forming apparatus 1 includes a supply roller 14 and a developing blade 15 around the developing roller 13 so as to contact the developing roller 13.

  The supply roller 14 is a supply member that supplies the toner TN stored in the toner hopper 52 to the developing roller 13. When the toner TN is supplied to the developing roller 13 by the supply roller 14, it adheres to the surface of the developing roller 13.

  The developing blade 15 is a layer thickness regulating member that regulates the layer thickness of the toner TN adhering to the surface of the developing roller 13 to be constant. When the toner TN adheres to the surface of the developing roller 13, the toner TN is regulated to a constant layer thickness by the developing blade 15, and then moves from the developing roller 13 to the photosensitive drum 11 by contacting the photosensitive drum 11. As a result, the electrostatic latent image formed on the surface of the photosensitive drum 11 by the exposure head 20 is developed as a toner image.

  In addition, the image forming apparatus 1 includes a waste toner storage chamber 55 and a waste toner transport member 56 around the cleaning blade 16.

The waste toner storage chamber 55 is a storage unit that temporarily stores toner TN to be discarded (hereinafter referred to as “waste toner”).
The waste toner transport member 56 is a transport member that transports waste toner to a predetermined part. Here, description will be made assuming that the predetermined part is provided outside the image forming unit 10.

<Disposition relationship of image forming units>
Hereinafter, the arrangement relationship of the image forming units 10 will be described with reference to FIG. FIG. 4 is a diagram illustrating an arrangement relationship of the image forming units 10 used in the first embodiment. 4 shows the positional relationship of the image forming units 10A and 10B with respect to the intermediate transfer belt 31 of the intermediate transfer unit 30 as viewed from above.

  FIG. 4 shows only the arrangement relationship of the pair of image forming units 10A and 10B closest to the idle roller 33 (that is, the image forming units 10A (Y) and 10B (Y) (see FIGS. 1 and 2)). ing. However, the arrangement relationship of the other sets of image forming units 10A and 10B is the same.

  Each image forming unit 10 has a configuration in which the width of a print area (hereinafter also referred to as “image forming area”) P is shorter than the width of the maximum width medium 9 used in the image forming apparatus 1. Yes. Here, “printing area (image forming area) P” means an area for forming a toner image of the image forming unit 10. Here, the length in the longitudinal direction of each image forming unit 10 that is a printing area (image forming area) P is the same as the vertical width of A3 size or A4 size, and is used in the image forming apparatus 1. Description will be made assuming that the maximum width of the medium 9 is A2 size or larger.

  Each image forming unit 10 constitutes a group of several units (here, two units), and is divided into a plurality of columns (here, two columns) with the positions shifted in the main scanning direction for each group. It is an arranged configuration.

  For example, in the first exemplary embodiment, each image forming unit 10 has a staggered shape (a shape in which the positions are shifted in the vertical direction alternately at regular intervals for each row) for each color of the toner image to be formed. Are arranged in two columns. Specifically, the image forming units 10A (Y) and 10B (Y) that form (print) Y (yellow) toner images are arranged in two rows in a staggered manner. . Similarly, two image forming units 10A (M) and 10B (M) for forming (printing) M (magenta) toner images are arranged in a staggered manner in two rows. Further, two image forming units 10A (C) and 10B (C) for forming (printing) C (cyan) toner images are arranged in a staggered manner in two rows. Also, two image forming units 10A (K) and 10B (K) for forming (printing) K (black) toner images are arranged in a staggered manner in two rows.

  For each color of the toner image to be formed, the image forming apparatus 1 arranges each image forming unit 10 in a plurality of rows (here, two) in a zigzag manner in a plurality of rows (here, two rows). By forming an image together with the image forming unit 10, an image is formed (printed) on a medium 9 (for example, a medium 9 having an A2 size or larger) wider than the width of the printing area of the image forming unit 10 alone. be able to.

  However, in the first exemplary embodiment, the image forming apparatus 1 is configured to use two image forming units 10 for each color. However, the image forming apparatus 1 may be configured to use three or more image forming units 10 for each color, and the number of columns may be arbitrarily set, such as two rows for three, three rows for three, etc. Can be changed to a number.

  Each exposure head 20 is disposed so as to face the corresponding photosensitive drum 11 of the image forming unit 10. Therefore, in the first exemplary embodiment, as with each image forming unit 10, the exposure heads 20 are arranged in two rows in a staggered manner in pairs for each color of the toner image to be formed.

  Each image forming unit 10 (here, the image forming units 10A and 10B) that forms (prints) the same color toner image is the sum of the print areas of the individual photosensitive drums 11 (here, the print area PR of the photosensitive drum 11A). And the print area PL of the photosensitive drum 11B) together form the entire print area P of the image forming apparatus 1.

  That is, in the image forming units 10A and 10B for forming (printing) toner images of the same color, the total of the width of the printing area PR of the photosensitive drum 11A and the width of the printing area PL of the photosensitive drum 11B is the entire image forming apparatus 1. Are arranged in a zigzag pattern so as to satisfy the width of the print area P.

  Therefore, the printing area P of the photosensitive drums 11A and 11B includes an overlapping area PD where the printing area PR of the photosensitive drum 11A and the printing area PL of the photosensitive drum 11B overlap, and the printing area PR of the photosensitive drum 11A and the printing area of the photosensitive drum 11B. Non-overlapping areas PN1 and PN2 that do not overlap with PL are included.

  Therefore, the photosensitive drums 11A and 11B of each image forming unit 10 have the end portions of the print areas PR and PL between the two adjacent image forming units 10A and 10B in each set, in the sub-scanning direction (see FIG. 4). In the example shown, the overlapping region PD overlaps in the vertical direction. The print area PR is composed of an overlapping area PD and a non-overlapping area PN1, and the print area PL is composed of an overlapping area PD and a non-overlapping area PN2.

  The reason for providing the “overlapping area PD” is that when the photosensitive drums 11A and 11B are arranged without providing the overlapping area PD, an area where image formation (printing) cannot be performed in the main scanning direction occurs due to variation in arrangement accuracy. This is to prevent the occurrence of an area where the image cannot be formed (printed).

  The photosensitive drum 11 </ b> A is provided with a drive gear 83 </ b> A at an end portion outside the region of the intermediate transfer belt 31. Similarly, the photosensitive drum 11 </ b> B is provided with a drive gear 83 </ b> B at an end portion outside the region of the intermediate transfer belt 31. The photosensitive drums 11A and 11B are rotationally driven by a driving source (not shown).

<Configuration of main part of image forming unit>
Hereinafter, the configuration of the main part of the image forming unit 10 will be described with reference to FIG. FIG. 5 is a diagram illustrating a configuration of a main part of the image forming unit 10 used in the first embodiment. FIG. 5A shows a configuration in the vicinity of the overlapping region PD of the photosensitive drum 11A as seen from the direction of the arrow C shown in FIG. FIG. 5B shows a configuration in the vicinity of the overlapping region PD of the photosensitive drum 11B as seen from the direction of the arrow C shown in FIG.

  As shown in FIG. 5A, in the photosensitive drum 11A of the image forming unit 10A, the printing area PR including the overlapping area PD is formed as a large diameter portion 91A having a large diameter. Further, in the photosensitive drum 11A of the image forming unit 10A, a small-diameter portion 92A having a diameter smaller than that of the large-diameter portion 91A is adjacent to the overlapping region PD side of the large-diameter portion 91A, and is axially (mainly). (In the scanning direction). As a result, the stepped portion 93A is formed at the end of the overlapping region PD in the axial direction of the photosensitive drum 11A. The small-diameter portion 92A is provided with a flange 81A at its end for supporting a shaft 82A serving as the axis of the photosensitive drum 11A. Further, the photosensitive drum 11A of the image forming unit 10A has a large diameter portion 91A and a small diameter portion 92A separated by a step portion 93A.

  Similarly, as shown in FIG. 5B, in the photosensitive drum 11B of the image forming unit 10B, the printing area PL including the overlapping area PD is formed as a large diameter portion 91B having a large diameter. Further, in the photosensitive drum 11B of the image forming unit 10B, a small-diameter portion 92B having a diameter smaller than that of the large-diameter portion 91B is adjacent to the overlapping region PD side of the large-diameter portion 91B and is axially (mainly). (In the scanning direction). Thereby, the stepped portion 93B is formed at the end portion on the overlapping region PD side in the axial direction of the photosensitive drum 11B. The small-diameter portion 92B is provided with a flange 81B at its end for supporting a shaft 82B serving as the axis of the photosensitive drum 11B. Further, in the photosensitive drum 11B of the image forming unit 10B, a large diameter portion 91B and a small diameter portion 92B are separated by a step portion 93B.

  Hereinafter, the large-diameter portion 91A and the large-diameter portion 91B are collectively referred to as “large-diameter portion 91”. Hereinafter, the small diameter portion 92 </ b> A and the small diameter portion 92 </ b> B are collectively referred to as “small diameter portion 92”. Hereinafter, the stepped portion 93A and the stepped portion 93B are collectively referred to as “stepped portion 93”. The step portion 93 is formed by the large diameter portion 91 and the small diameter portion 92.

  In the first embodiment, the outer diameter of the large diameter portion 91 is “φE”, the outer diameter of the small diameter portion 92 is “φF”, and the outer diameter φE of the large diameter portion 91 and the small diameter portion 92 are The description will be made assuming that the outer diameter φF satisfies the relationship “φF <φE”.

  As shown in FIG. 5A, the charging roller 12A of the image forming unit 10A has a large diameter portion of the photosensitive drum 11A so as to straddle (over) the stepped portion 93A with respect to the photosensitive drum 11A. 91A and the small diameter portion 92A are arranged to face each other. The outer diameter φE of the large diameter portion 91A and the outer diameter φF of the small diameter portion 92A satisfy the relationship “φF <φE”. Accordingly, the charging roller 12A is in contact with the photosensitive drum 11A at the large diameter portion 91A and is separated from the photosensitive drum 11A by the gap ΔT1 at the small diameter portion 92A.

  Further, as shown in FIG. 5B, the charging roller 12B of the image forming unit 10B has a large size of the photosensitive drum 11B so as to straddle (over) the stepped portion 93B with respect to the photosensitive drum 11B. It arrange | positions facing the diameter part 91B and the small diameter part 92B. The outer diameter φE of the large diameter portion 91B and the outer diameter φF of the small diameter portion 92B satisfy the relationship “φF <φE”. Accordingly, the charging roller 12B is in contact with the photosensitive drum 11B at the large diameter portion 91B and is separated from the photosensitive drum 11B by the gap ΔT1 at the small diameter portion 92B.

  Further, as shown in FIGS. 5A and 5B, the intermediate transfer belt 31 is used for all image forming units 10 (image forming units 10A (Y), 10B (Y), 10A (M), 10B). (M), 10A (C), 10B (C), 10A (K), and 10B (K) (see FIGS. 1 and 2)) across the stepped portion 93 (over). The large-diameter portion 91 and the small-diameter portion 92 of the photosensitive drum 11 are disposed to face each other. As a result, the intermediate transfer belt 31 contacts the photosensitive drum 11 at the large diameter portion 91 with respect to each photosensitive drum 11 of all the image forming units 10 and is separated from the photosensitive drum 11 by the gap ΔT2 at the small diameter portion 92. It is in a state.

  In the first embodiment, for example, the outer diameter φE of the large diameter portion 91 is “40 mm”, the outer diameter φF of the small diameter portion 92 is “39 mm”, and the height H (see FIG. (Not shown) is “0.5 mm”, and the gap ΔT1 between the small diameter portion 92 and the charging roller 12 is “0.4 mm”. The case where the gap ΔT2 is “0.3 mm” and the width PDW (not shown) of the overlapping region PD is “5 to 20 mm” will be described.

<Configuration of photosensitive drum>
Hereinafter, the configuration of the photosensitive drum 11 will be described with reference to FIG. FIG. 6 is a diagram illustrating a configuration of the photosensitive drum 11 used in the first embodiment. FIG. 6 shows an enlarged configuration around the stepped portion 93 of the photosensitive drum 11 </ b> A as the photosensitive drum 11.

  As shown in FIG. 6, the photosensitive drum 11 includes a blocking layer (not shown) and a charge generation (not shown) from the lower layer side on the peripheral surface of the raw tube 71 as a conductive support made of, for example, an aluminum alloy. A layer and a charge transport layer (not shown) are sequentially formed. Hereinafter, the layers from the blocking layer to the charge transport layer are collectively referred to as “photosensitive layer 72”.

The blocking layer is, for example, a layer obtained by subjecting the surface of an aluminum alloy to an anodic oxidation (alumite) treatment and then performing a pore sealing treatment containing nickel acetate as a main component (sealing treatment of micropores generated by the alumite treatment). .
The charge generation layer is prepared by adding polyvinyl butyral 5 to 160 parts of a pigment dispersion prepared by adding 10 parts (mass part) of oxotitanium phthalocyanine to 150 parts of 1,2-dimethoxyethane and pulverizing and dispersing with a sand grind mill. 100 parts of a binder solution having a solid content of 5% dissolved in 95 parts of 1,2-dimethoxyethane was mixed, and finally 1,2-dimethoxyethane and 4-methoxy-4- This is a layer coated with a liquid prepared and adjusted so that the mass ratio of methylpentanone-2 is 9: 1.
The charge transport layer is, for example, a layer coated with a transparent polycarbonate resin liquid.

As shown in FIG. 6, the photosensitive drum 11 has a configuration in which a photosensitive layer 72 is applied on the peripheral surface of the raw tube 71.
In the photosensitive drum 11, the base tube 71 is immersed in a liquid tank filled with a liquid constituting the photosensitive layer 72 (hereinafter referred to as “photosensitive solution”), and the photosensitive solution is placed on the peripheral surface of the base tube 71. The photosensitive layer 72 is formed by applying to the photosensitive layer 72. The photosensitive layer 72 is formed over the entire area of the large diameter portion 91 and the small diameter portion 92 of the photosensitive drum 11 including the stepped portion 93.

  At this time, a region where the small amount of the photosensitive liquid is accumulated (hereinafter referred to as “photosensitive layer liquid reservoir portion 79”) is a portion (hereinafter referred to as “corner portion 71b”) which becomes the lower end of the stepped portion 93 of the base tube 71. ) Around.

  However, the raw tube 71 is formed in a portion where the chamfer of about 0.1 mm for removing burrs and the like during processing is the upper end of the stepped portion 93 (hereinafter referred to as “edge portion 71a”). . As a result, the photosensitive layer 72 has a shape in which a portion above the edge portion 71a of the tube 71 (hereinafter referred to as “edge portion 72a”) is chamfered in the same manner as the edge portion 71a of the tube 71. . Therefore, even if the photosensitive layer liquid reservoir 79 is generated around the corner portion 71b, the photosensitive layer 72 does not protrude in a protruding shape at the edge portion 72a.

  Here, the features of the photosensitive drum 11 used in the first exemplary embodiment will be described with reference to FIGS. 7 and 8 are explanatory diagrams of the photosensitive drum 11 used in the first embodiment, respectively.

  In the photosensitive drum 11, a region where the photosensitive solution is not applied (hereinafter referred to as “photosensitive layer non-applied portion 78”) and a photosensitive layer liquid reservoir portion 79 are formed on the peripheral surface according to the manufacturing process. .

The photosensitive layer uncoated portion 78 and the photosensitive layer liquid reservoir portion 79 are formed as follows.
As described above, in the photosensitive drum 11, the photosensitive tube 72 is formed by immersing the base tube 71 in a liquid tank filled with the photosensitive solution and applying the photosensitive solution onto the peripheral surface of the base tube 71. . At this time, a chuck member (not shown) for fastening and fixing the photosensitive drum 11 is attached to the end of the photosensitive drum 11. Therefore, the photosensitive drum 11 is formed with the photosensitive layer uncoated portion 78 at the end where the chuck member is attached.

  Further, when the photosensitive drum 11 is taken out from the liquid tank, a photosensitive layer liquid reservoir portion 79 is formed at an end portion vertically below the photosensitive drum 11. In the photosensitive layer liquid reservoir 79, the thickness of the photosensitive layer 72 does not become a predetermined thickness. For this reason, the photosensitive layer liquid reservoir 79 is a poorly charged region.

  FIG. 7 shows an example in which the photosensitive layer uncoated portion 78 is formed on the peripheral surface of the small diameter portion 92 and the photosensitive layer liquid reservoir portion 79 is formed on the peripheral surface of the large diameter portion 91. The photosensitive drum 11 is configured as shown in FIG. 7 when a chuck member (not shown) is attached to the end of the small diameter portion 92.

  FIG. 8 shows an example in which the photosensitive layer liquid reservoir 79 is formed on the peripheral surface of the small diameter portion 92 and the photosensitive layer uncoated portion 78 is formed on the peripheral surface of the large diameter portion 91. The photosensitive drum 11 is configured as shown in FIG. 8 when a chuck member (not shown) is attached to the end of the large diameter portion 91.

  The photosensitive layer liquid reservoir 79 has a thickness of about 50 μm while the thickness of the photosensitive layer 72 is generally about 10 to 30 μm. The photosensitive layer liquid reservoir 79 has a thickness H (not shown) (for example, 0.5 mm) of the stepped portion 93 of the photosensitive drum 11 or a large diameter portion 91 of the photosensitive drum 11. A gap ΔT1 between the charging roller 12 (see FIG. 5) (for example, 0.4 mm) and a gap ΔT2 between the large diameter portion 91 of the photosensitive drum 11 and the intermediate transfer belt 31 (see FIG. 5) (for example, 0.3 mm). Therefore, the photosensitive layer liquid reservoir 79 does not contact the charging roller 12 </ b> A and the intermediate transfer belt 31.

<Functional configuration of image forming apparatus>
Hereinafter, the functional configuration of the image forming apparatus 1 will be described with reference to FIG. FIG. 9 is a diagram illustrating a functional configuration of the image forming apparatus 1 according to the first embodiment.

  As shown in FIG. 9, the image forming apparatus 1 includes an external I / F unit 1001, a data analysis unit 1002, an image data creation unit 1003, an image data division unit 1004, a development control unit 1005, a first development unit 1006A, and The second developing unit 1006B is included.

The external I / F unit 1001 is a component that transmits and receives data.
The data analysis unit 1002 is a component that analyzes paper size information, color information, and the like from received print data.
The image data creation unit 1003 is a component that creates image data based on the received print data.
The image data dividing unit 1004 is a component that divides the image data created by the image data creating unit 1003 into data output by the first developing unit 1006A and the second developing unit 1006B.

The development control unit 1005 is a component that controls the transfer timing of image data to the first development unit 1006A and the second development unit 1006B and controls the driving of the first development unit 1006A and the second development unit 1006B.
Each of the first developing unit 1006A and the second developing unit 1006B is a component that forms an image based on the image data. The first developing unit 1006A includes an image forming unit 10A and an exposure head 20A. Similarly, the second developing unit 1006B includes an image forming unit 10B and an exposure head 20B.

<Operation of Image Forming Apparatus>
Hereinafter, the operation of the image forming apparatus 1 will be described with reference to FIG.
The image forming apparatus 1 receives print data from an external device (not shown) such as a host computer or a facsimile by an external I / F unit 1001 (see FIG. 9). The external I / F unit 1001 outputs the received print data to the data analysis unit 1002 (see FIG. 9).

  Based on the received print data, the data analysis unit 1002 analyzes the designation information (for example, paper size information, color information, etc.) designated by the external device, and the analysis result of the designation information is an image data creation unit 1003. (See FIG. 9).

  When the analysis result of the designation information is input from the data analysis unit 1002, the image data creation unit 1003 creates image data based on the received print data and the analysis result of the designation information, and the image data division unit 1004. (See FIG. 9).

  At this time, when the print data is data for a color image, the image data creation unit 1003 creates image data for each color based on the color information, and creates image data based on the paper size information. Determine the size.

  When the image data is input from the image data creation unit 1003, the image data dividing unit 1004 converts the image data into a portion corresponding to the print region PR (see FIGS. 4 and 5) and the print region PL (see FIGS. 4 and 5). ).

  At this time, the image data dividing unit 1004 divides each image data created for each color when the print data is data for a color image. Hereinafter, the divided image data is referred to as “divided image data”.

  When the image data dividing unit 1004 creates divided image data for one page, it outputs the divided image data for one page to the development control unit 1005 (see FIG. 9).

  When the divided image data for one page is input from the image data dividing unit 1004, the development control unit 1005 receives the image forming unit 10A and the second developing unit 1006B (see FIG. 9) of the first developing unit 1006A (see FIG. 9). ) Is started, and the transport position of the medium 9 transported by the transport rollers 62a and 62b is monitored.

  As a result, in the image forming apparatus 1, the separation roller 61 separates the medium 9 stored in the medium tray 4 one by one and feeds it to the conveyance path 6, and the conveyance rollers 62 a and 62 b transfer the medium 9 to the medium transfer roller 63. Transport toward.

  At this time, each image forming unit 10 receives a control signal from the development control unit 1005 (see FIG. 9), and the stirring members 53 and 54 start to rotate. As a result, each image forming unit 10 agitates the toner TN stored in the toner storage container 51 (see FIG. 3) and the toner hopper 52 (see FIG. 3).

  At the same time, in each image forming unit 10, a drive source (not shown) rotates the supply roller 14 in the direction of arrow A14 (see FIG. 3). As a result, each image forming unit 10 supplies the toner TN stored in the toner hopper 52 (see FIG. 3) to the developing roller 13.

  At the same time, in each image forming unit 10, a driving source (not shown) rotates the developing roller 13 in the direction of arrow A13 (see FIG. 3). At this time, the supply roller 14 supplies the toner TN to the developing roller 13. As a result, the toner TN adheres to the surface of the developing roller 13.

  The toner TN attached to the surface of the developing roller 13 contacts the developing blade 15 as the developing roller 13 rotates. As a result, the toner TN adhering to the surface of the developing roller 13 is formed into a thin layer having a constant layer thickness by the developing blade 15 and is charged.

  In each image forming unit 10, a driving source (not shown) rotates the photosensitive drum 11 in the direction of arrow A11 (see FIG. 3). At this time, the charging roller 12 uniformly charges the surface of the photosensitive drum 11. At that time, as shown in FIG. 5, the charging roller 12 is in contact with only the large-diameter portion 91 having the outer diameter φE because the gap ΔT1 is present between the photosensitive drum 11 and the small-diameter portion 92. It does not contact the small diameter portion 92 having the outer diameter φF. Therefore, the charging roller 12 charges only the large diameter portion 91 of the photosensitive drum 11 and does not charge the small diameter portion 92 of the photosensitive drum 11.

  When the development control unit 1005 (see FIG. 9) of the image forming apparatus 1 detects that the conveyance position of the medium 9 has reached a predetermined position, the divided image data is divided into the first development unit 1006A and the second development unit 1006B. And output.

  As a result, in the image forming apparatus 1, the exposure head 20 partially exposes the surface of the photosensitive drum 11 based on the print data in accordance with the conveyance timing of the medium 9 by the conveyance rollers 62a and 62b. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 11.

  At this time, the exposure head 20A partially exposes a portion corresponding to the print region PR (see FIGS. 4 and 5) on the surface of the photosensitive drum 11. The exposure head 20B partially exposes a portion corresponding to the print area PL (see FIGS. 4 and 5) on the surface of the photosensitive drum 11. As a result, an electrostatic latent image for the entire print area P of the image forming apparatus 1 is formed.

  In each image forming unit 10, the toner TN attached to the surface of the developing roller 13 moves from the developing roller 13 to the photosensitive drum 11 by contacting the photosensitive drum 11. As a result, each image forming unit 10 develops the electrostatic latent image formed on the surface of the photosensitive drum 11 as a toner image.

  In the image forming apparatus 1, a drive source (not shown) causes the intermediate transfer belt 31 of the intermediate transfer unit 30 to travel in the direction of arrow A31 (see FIG. 4) in accordance with the conveyance timing of the medium 9 by the conveyance rollers 62a and 62b. At this time, in the intermediate transfer unit 30, the belt transfer roller 34 draws the toner image formed on the surface of the photosensitive drum 11 and transfers the toner image from the photosensitive drum 11 to the intermediate transfer belt 31. At this time, as shown in FIG. 5, the intermediate transfer belt 31 is in contact with only the large-diameter portion 91 having the outer diameter φE because the gap ΔT1 exists between the small-diameter portion 92 and the photosensitive drum 11. , Does not contact the small diameter portion 92 of the outer diameter φF. Therefore, the belt transfer roller 34 transfers the toner existing only on the surface of the large diameter portion 91 of the photosensitive drum 11 to the intermediate transfer belt 31.

  Thereafter, in the image forming apparatus 1, the medium transfer roller 63 attracts the toner image transferred to the intermediate transfer belt 31, and transfers the toner image from the intermediate transfer belt 31 to the medium 9. In the image forming apparatus 1, the medium transfer roller 63 and the conveyance rollers 62 a and 62 b convey the medium 9 toward the fixing unit 40.

  Thereafter, in the image forming apparatus 1, the fixing unit 40 heats and pressurizes the medium 9 to melt the toner image transferred to the medium 9 and fix the toner image on the medium 9. In the image forming apparatus 1, the discharge rollers 64 a and 64 b transport the medium 9 toward the stacker 5 and discharge the medium 9 onto the stacker 5.

  In each image forming unit 10, when the toner image is transferred from the photosensitive drum 11 to the intermediate transfer belt 31, the cleaning blade 16 scrapes off the residual toner remaining on the surface of the photosensitive drum 11. As a result, waste toner is stored in the waste toner storage chamber 55. In each image forming unit 10, the waste toner conveying member 56 discharges the waste toner stored in the waste toner storage chamber 55 to a predetermined part at an arbitrary timing.

  The image forming apparatus 1 creates and divides image data for each color. For this reason, when the print data is data for color images, the image forming apparatus 1 uses all the image forming units 10A (Y), 10B (Y), 10A (M), 10B (M), and 10A (C). , 10B (C), 10A (K), 10B (K), the same operation is performed.

  In such a configuration, the image forming apparatus 1 according to the first embodiment arranges the plurality of image forming units 10 for each color in a plurality of rows in a state where the positions are shifted in the main scanning direction. It is configured to form an image wider than the width of 10 single print areas.

  The photosensitive drum 11 of each image forming unit 10 is an overlapping region PD in which the end portions of the printing regions PR and PL overlap in the sub-scanning direction between two adjacent image forming units 10A and 10B in each set. Yes. In each photosensitive drum 11, the print regions PR and PL including the overlapping region PD are formed as the large-diameter portion 91 having a large diameter, and the small-diameter portion 92 having a smaller diameter than the large-diameter portion 91 is the large-diameter portion 91. The large-diameter portion 91 and the small-diameter portion 92 are separated from each other by a step portion 93.

  In the image forming apparatus 1, the print regions PR and PL are formed as a large-diameter portion 91 that is separated from the small-diameter portion 92 by a step portion 93. Therefore, the image forming apparatus 1 can satisfactorily abut the charging rollers 12A and 12B on all the printing areas PR and PL. As a result, in the image forming apparatus 1, the charging rollers 12 </ b> A and 12 </ b> B can charge all the print areas PR and PL that are in contact with the intermediate transfer belt 31 of the photosensitive drums 11 </ b> A and 1 </ b> B without excess or deficiency. it can.

  Therefore, the image forming apparatus 1 prevents the charging failure from occurring at the end portion of the image forming region (printing region PR, PL) of the photosensitive member (photosensitive drum 11), and the transferred object (medium 9) or It is possible to prevent the occurrence of printing defects that contaminate the developer image (toner image) transferred onto the intermediate transfer member (intermediate transfer belt 31).

  Further, the image forming apparatus 1 can provide the photosensitive layer uncoated portion 78 and the photosensitive layer liquid reservoir portion 79 in the small-diameter portion 92 outside the image forming region (printing regions PR and PL). The small diameter portion 92 has a smaller diameter than the image forming region (printing regions PR and PL) formed as the large diameter portion 91. Therefore, the image forming apparatus 1 forms the stepped portion 93 higher than the standard thickness of the photosensitive layer liquid reservoir 79, so that the photosensitive layer liquid reservoir 79 is transferred to the transfer target (medium 9) or the intermediate transfer member ( Contact with the intermediate transfer belt 31) can be prevented. Also by this, the image forming apparatus 1 can prevent a printing defect from occurring.

  In the image forming apparatus 1, the belt transfer rollers 34 </ b> A and 34 </ b> B prevent the intermediate transfer belt 31 from wavy or stagnation. Therefore, the image forming apparatus 1 can prevent the intermediate transfer belt 31 from coming into contact with the small diameter portions 92A and 92B of the photosensitive drums 11A and 1B. Also by this, the image forming apparatus 1 can prevent a printing defect from occurring.

  As described above, according to the image forming apparatus 1 according to the first embodiment, it is possible to charge all the image forming areas (print areas PR and PL) of the photoconductors (photosensitive drums 11A and 11B), and occurrence of printing defects. Therefore, it is possible to provide the image forming apparatus 1 that prevents the above.

[Embodiment 2]
The image forming apparatus 1 according to the first embodiment has a configuration in which the stepped portion 93 of the photosensitive drum 11 is vertically cut. Therefore, in the image forming apparatus 1 according to the first embodiment, when the charging roller 12 comes into contact with the photosensitive drum 11, the load may locally increase around the stepped portion 93. Thereby, in the image forming apparatus 1 according to the first embodiment, the charging roller 12 may be easily worn. In the image forming apparatus 1 according to the first embodiment, the photosensitive layer 72 (see FIG. 6) of the photosensitive drum 11 may be peeled off.

  Therefore, in the second embodiment, the load is locally prevented from increasing around the stepped portion, the wear of the charging roller 12 is suppressed, and the photosensitive drum according to the second embodiment (hereinafter, referred to as “photosensitive drum”) Provided is an image forming apparatus 201 that prevents peeling of a photosensitive layer (hereinafter referred to as “photosensitive layer 272”) of a “photosensitive drum 211”.

  Hereinafter, the configuration of the image forming apparatus 201 according to the second embodiment will be described with reference to FIGS. 10 and 11. FIG. 10 is a diagram illustrating a configuration of a main part of the image forming unit 210 used in the second embodiment. FIG. 11 is a diagram illustrating a configuration of the photosensitive drum 211 used in the second embodiment.

  The image forming apparatus 201 according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in that an image forming unit 210 is used instead of the image forming unit 10. In the second embodiment, the image forming unit 210 includes an image forming unit 210A (see FIG. 10A) that replaces the front image forming unit 10A shown in FIG. 1, and a back image forming unit 10B shown in FIG. The description will be made assuming that the image forming unit 210B (see FIG. 10B) is replaced with the image forming unit 210B.

  As shown in FIG. 10A, the image forming unit 210A is different from the image forming unit 10A (see FIG. 5A) in that a photosensitive drum 211A is provided instead of the photosensitive drum 11. ing. 10B, the image forming unit 210B is different from the image forming unit 10B (see FIG. 5B) in that a photosensitive drum 211B is provided instead of the photosensitive drum 11. ing.

  As shown in FIG. 10A, in the photosensitive drum 211A, the stepped portion between the large diameter portion 91A and the small diameter portion 92A has a taper angle θ, and the diameter decreases from the large diameter portion 91A toward the small diameter portion 92A. It is formed as an inclined portion (hereinafter referred to as “taper portion 294 </ b> A”) that is inclined in the direction to be moved. Similarly, as shown in FIG. 10B, in the photosensitive drum 211B, the step portion between the large-diameter portion 91B and the small-diameter portion 92B has a taper angle θ toward the small-diameter portion 92B from the large-diameter portion 91B. It is formed as an inclined portion (hereinafter referred to as “taper portion 294B”) that is inclined in the direction of decreasing the diameter.

  Hereinafter, the photosensitive drum 211A and the photosensitive drum 211B are collectively referred to as “photosensitive drum 211”. Further, when the taper portion 294A and the taper portion 294B are collectively referred to as “taper portion 294”.

  As shown in FIG. 10A, the charging roller 12A of the image forming unit 210A has a large-diameter portion 91A and a small-diameter portion of the photosensitive drum 211A so as to straddle the taper portion 294A with respect to the photosensitive drum 211A. It is arranged to face 92A. The outer diameter φE of the large diameter portion 91A and the outer diameter φF of the small diameter portion 92A satisfy the relationship “φF <φE”. Therefore, the charging roller 12A is in contact with the photosensitive drum 211A at the large diameter portion 91A with respect to the photosensitive drum 211A, and is separated from the photosensitive drum 211A by the gap ΔT1 at the small diameter portion 92A.

  Similarly, as shown in FIG. 10B, the charging roller 12B of the image forming unit 210B has a large diameter portion 91B of the photosensitive drum 211B so as to straddle the taper portion 294B with respect to the photosensitive drum 211B. And the small-diameter portion 92B. The outer diameter φE of the large diameter portion 91B and the outer diameter φF of the small diameter portion 92B satisfy the relationship “φF <φE”. Therefore, the charging roller 12B contacts the photosensitive drum 211B at the large diameter portion 91B with respect to the photosensitive drum 211B, and is separated from the photosensitive drum 211B by the gap ΔT1 at the small diameter portion 92B.

  In the second embodiment, for example, the outer diameter φE of the large diameter portion 91 is “40 mm”, the outer diameter φF of the small diameter portion 92 is “39 mm”, and the height H of the tapered portion 294 (see FIG. (Not shown) is “0.5 mm”, and the gap ΔT1 between the small diameter portion 92 and the charging roller 12 is “0.4 mm”. The gap ΔT2 is “0.3 mm”, the taper angle θ is “30 to 60 °”, and the width PDW (not shown) of the overlapping region PD is “5 to 20 mm”. A description will be given assuming that

  As shown in FIG. 11, the photosensitive drum 211 includes a blocking layer (not shown) and a charge generation (not shown) from the lower layer side on the peripheral surface of the raw tube 271 as a conductive support made of, for example, an aluminum alloy. A layer and a charge transport layer (not shown) are sequentially formed. Hereinafter, the layers from the blocking layer to the charge transport layer are collectively referred to as “photosensitive layer 272”.

  The base tube 271 of the photosensitive drum 211 is formed with a step portion (taper portion 294) as a taper portion 271T. The photosensitive drum 211 is configured such that a photosensitive layer 272 is applied on the peripheral surface of the raw tube 271.

  In the photosensitive layer 272, the step portion of the tube 271 is formed as a tapered portion 271T. Therefore, the photosensitive layer 272 has a configuration in which a tapered portion 272T having the same shape as the tapered portion 271T is formed in the stepped portion.

  In the photosensitive drum 211, a step portion of the photosensitive layer 272 is formed as a tapered portion 272T. Therefore, the photosensitive drum 211 can suppress the generation of the photosensitive layer liquid reservoir 79 in the stepped portion. As a result, the photosensitive drum 211 has a configuration in which the photosensitive layer 272 is uniformly applied, and a part of the photosensitive layer 272 does not protrude in a protruding shape.

  In the image forming apparatus 201 using such a photosensitive drum 211, as shown in FIGS. 10 and 11, the photosensitive drum 211 comes into contact with the charging roller 12 at a tapered portion 294. Therefore, the image forming apparatus 201 can suppress a local increase in load around the tapered portion 294 that is a stepped portion. As a result, the image forming apparatus 201 can suppress the charging roller 12 from being worn, and can prevent the photosensitive layer 272 of the photosensitive drum 211 from being peeled off.

  As described above, according to the image forming apparatus 201 according to the second embodiment, similarly to the image forming apparatus 1 according to the first embodiment, the image forming areas (printing areas PR and PL) of the photoconductors (photosensitive drums 11A and 11B). ) Can be charged, and the image forming apparatus 1 that prevents the occurrence of printing defects can be provided.

  In addition, according to the image forming apparatus 201, since the step portion is configured as the tapered portion 294, it is possible to suppress the load from locally rising around the tapered portion 294 having the step portion. As a result, according to the image forming apparatus 201, the charging roller 12 can be prevented from being worn, and the photosensitive layer 272 of the photosensitive drum 211 can be prevented from peeling off.

The present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the gist of the present invention.
For example, the present invention can be applied not only to LED printers but also to laser beam printers.
Further, for example, the present invention can be used not only in a printer but also in an image forming apparatus such as a facsimile machine, a copying machine, and an MFP. “MFP” means a Multi Function Printer in which a facsimile function, a scanner function, a copy function, and the like are added to a printer.

<Appendix>
The image forming apparatus according to the first aspect has the following features.
A first invention is an image forming apparatus for forming an image using an electrophotographic process, and a photosensitive member having a photosensitive layer formed on a conductive support, and a charging member for charging the surface of the photosensitive member. A plurality of image forming units each including a developing member that supplies a developer to the photoconductor and forms a developer image on the surface of the photoconductor; For each color of the agent image, a set is composed of several units, and each set is divided into a plurality of columns with the position being shifted in the main scanning direction, and the photosensitive member of each of the image forming units is arranged. The end portion of the image forming area where the developer image is formed is an overlapping area where two adjacent image forming units in each set overlap in the sub-scanning direction, and the overlapping area The image forming area containing a large diameter A small-diameter portion smaller in diameter than the large-diameter portion is provided on the outer side in the axial direction than the large-diameter portion, and the large-diameter portion and the small-diameter portion are further formed by a step portion. The structure is delimited.

  This image forming apparatus has a plurality of image forming units. The plurality of image forming units constitutes a set of several units for each color of the developer image to be formed, and each set is arranged in a plurality of rows with the positions being shifted in the main scanning direction. .

  The photosensitive member of each image forming unit is an overlapping region in which the end portion of the image forming region overlaps in the sub-scanning direction between two adjacent image forming units in each set. In each photoconductor, an image forming region including an overlapping region is formed as a large-diameter portion having a large diameter, and a small-diameter portion having a smaller diameter than the large-diameter portion is provided on the outer side in the axial direction than the large-diameter portion. The large diameter portion and the small diameter portion are separated by a step portion.

  Therefore, in this image forming apparatus, the photoreceptor of each image forming unit is divided into a large diameter portion and a small diameter portion by the step portion. In this image forming apparatus, the image forming area is formed as a large-diameter portion separated from the small-diameter portion by a step portion. Therefore, in this image forming apparatus, the charging member can be brought into good contact with the entire area of the image forming area. As a result, in this image forming apparatus, the charging member can charge the entire image forming area of the photoreceptor.

  For this reason, this image forming apparatus prevents the charging failure from occurring at the end portion of the image forming area of the photoreceptor, and the printing failure that stains the developer image transferred onto the transfer medium or intermediate transfer body. Can be prevented.

  Further, in this image forming apparatus, the photosensitive layer non-coated portion and the photosensitive layer liquid reservoir portion can be provided in the small diameter portion outside the image forming region. The small diameter portion has a smaller diameter than the image forming region formed as the large diameter portion. Therefore, this image forming apparatus prevents the photosensitive layer liquid reservoir from coming into contact with the transfer medium or the intermediate transfer body by forming the stepped portion higher than the standard thickness of the photosensitive layer liquid reservoir. Can do. Also by this, this image forming apparatus can prevent the occurrence of printing defects that contaminate the developer image transferred onto the transfer medium or intermediate transfer body.

The image forming unit according to the second invention has the following characteristics.
According to a second aspect of the present invention, a photosensitive member having a photosensitive layer formed on a conductive support, a charging member for charging the surface of the photosensitive member, a developer is supplied to the photosensitive member, and the surface of the photosensitive member is supplied. An image forming unit comprising a developing member for forming a developer image on the photosensitive member, wherein the image forming area on which the developer image is formed is formed as a large-diameter portion having a large diameter, A small-diameter portion having a smaller diameter than the large-diameter portion is provided on the outer side in the axial direction than the large-diameter portion, and the large-diameter portion and the small-diameter portion are separated by a step portion. .
This image forming unit can be used in the image forming apparatus according to the first invention.

1,201 Image forming device (printer)
2 Housing 3 Upper cover 4 Media tray 5 Stacker 6 Transport path 9 Printing medium (transferred material)
10 (10A, 10B), 210 (210A, 210B) Image forming unit 11 (11A, 11B), 211 (211A, 211B) Photosensitive drum (photoconductor)
12 (12A, 12B) Charging roller (charging member)
13 (13A, 13B) Developing roller (developing member)
14 Supply roller 15 Developing blade 16 Cleaning blade 20 (20A, 20B) Exposure head (exposure section)
30 Intermediate transfer unit 31 Intermediate transfer belt (intermediate transfer member)
32 Drive roller 33 Idle roller 34 (34A, 34B) Belt transfer roller 40 Fixing unit 51 Toner storage container 52 Toner hopper 53, 54 Stirring member 55 Waste toner storage chamber 56 Waste toner conveying member 61 Separating roller 62 (62a, 62b) Roller 63 Media transfer roller 64 (64a, 64b) Discharge roller 71,271 Base tube (conductive support)
71a Edge portion 71b Corner portion 72, 272 Photosensitive layer 72a Edge portion 78 Photosensitive layer uncoated portion 79 Photosensitive layer liquid reservoir portion 81 (81A, 81B) Flange 82 (82A, 82B) Shaft 83 (83A, 83B) Drive gear 91 ( 91A, 91B) Large diameter portion 92 (92A, 92B) Small diameter portion 93 (93A, 93B) Stepped portion 271T, 272T, 294 (294A, 294B) Tapered portion (inclined portion)
1001 External I / F unit 1002 Data analysis unit 1003 Image data creation unit 1004 Image data division unit 1005 Development control unit 1006A First development unit 1006B Second development unit P (PL, PR) Print area (image formation area)
PD Overlapping area PN1, PN2 Non-overlapping area TN Developer (toner)

Claims (9)

Image formation in which a plurality of image forming units each including a photosensitive member having a photosensitive layer are arranged adjacent to each other while being shifted in the axial direction of the photosensitive member, thereby forming an image jointly with the plurality of adjacent image forming units. In laying down
The plurality of adjacent image forming units have an overlapping area where the image forming areas of the photoconductor overlap in the axial direction of the photoconductor,
The photoreceptor has a stepped portion at an end portion on the overlapping region side in the axial direction,
The image forming apparatus according to claim 1, wherein the step portion is formed by a large diameter portion and a small diameter portion having a smaller diameter than the large diameter portion. The image forming apparatus according to claim 1.
The small-diameter portion of the photoreceptor is either a photosensitive layer non-coated portion where the liquid constituting the photosensitive layer is not applied or a photosensitive layer liquid reservoir where the liquid constituting the photosensitive layer is accumulated. An image forming apparatus characterized in that is formed. The image forming apparatus according to claim 2.
The image forming apparatus, wherein the step portion of the photoconductor is formed higher than a standard thickness of the photosensitive layer liquid reservoir. The image forming apparatus according to any one of claims 1 to 3,
Each of the plurality of image forming units includes a charging member that charges the surface of the photoreceptor.
The charging member is in contact with the photoconductor at the large diameter portion with respect to the photoconductor, and straddles the step portion so as to be separated from the photoconductor at the small diameter portion. An image forming apparatus, wherein the image forming apparatus is disposed to face a diameter portion and the small diameter portion. The image forming apparatus according to any one of claims 1 to 4,
Each of the photoconductors functions as an image carrier that carries a developer image formed by a developer on the surface,
Furthermore, after the developer image formed on the surface of the photoconductor is transferred, a belt-shaped intermediate transfer body that re-transfers the developer image to the transfer target,
The intermediate transfer member straddles the stepped portion so that the large-diameter portion contacts the photoconductor with the large-diameter portion and is spaced apart from the photoconductor by the small-diameter portion with respect to the photoconductors of all the image forming units. An image forming apparatus, wherein the image forming apparatus is disposed to face the large diameter portion and the small diameter portion of the photoconductor. The image forming apparatus according to any one of claims 1 to 5,
2. The image forming apparatus according to claim 1, wherein the photosensitive layer of the photoconductor is formed over the large diameter portion and the small diameter portion including the stepped portion. The image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus according to claim 1, wherein the step portion of the photoconductor is formed as an inclined portion that is inclined in a direction in which the diameter decreases from the large diameter portion toward the small diameter portion. In an image forming unit comprising a photoreceptor having a photosensitive layer,
The photoconductor includes an image forming area in which a developer image is formed, and an overlapping area overlapping with an image forming area of a photoconductor of another image forming unit arranged adjacently in the axial direction. In the image forming area,
Furthermore, the photoconductor has a step portion at an end portion on the overlapping region side in the axial direction,
The image forming unit, wherein the step portion is formed by a large diameter portion and a small diameter portion having a smaller diameter than the large diameter portion. The image forming unit according to claim 8.
The image forming unit according to claim 1, wherein the step portion of the photosensitive member is formed to be higher than a standard thickness of a photosensitive layer liquid reservoir portion formed by accumulation of a liquid constituting the photosensitive layer.

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