JP2010160185A - Image forming apparatus and cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to suppress an increase in local shaving of an electrostatic latent image at each end portion of a charging device, thereby suppress the occurrence of a leak image. <P>SOLUTION: The local shaving of the electrostatic latent image carrier at each end portion of the charging device is mainly caused by a discharge. Then, an area influenced by the charging device which promotes the discharge and the pre-exposure in the longitudinal direction is set to be between an image area and the end portion of the charging device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that forms an image by an electrophotographic method or an electrostatic recording method, and more particularly, an electrostatic latent image carrier, a charging device, an exposure device, a transfer device, a pre-exposure. It relates to the longitudinal arrangement of the device.

  The present invention also relates to a cartridge that is detachably attached to the main body of the image forming apparatus.

  Conventionally, in electrophotographic technology such as copying machines and printers, a contact charging method in which a charging member is charged by bringing a conductive member into contact with an electrostatic latent image carrier has been widely used from the viewpoint of ozone suppression.

  As the configuration of the contact charging method, the following configuration is common. That is, the electrostatic latent image carrier and the charging member are in close contact with each other in the rotation direction (hereinafter referred to as the longitudinal direction) of the charging member orthogonal to the moving direction of the electrostatic latent image carrier and the electrostatic latent image carrier. As described above, one is an elastic body (including a brush or a sheet backed up by an elastic body), and the other is a rigid body.

  The simplest configuration is a configuration in which the electrostatic latent image carrier is a rigid body and the charging member is an elastic body. Generally, the charging member uses conductive rubber as an elastic layer around the cored bar, and the end is cut substantially perpendicular to the cored bar. In particular, as an exchange unit or cartridge configured to be detachable from the apparatus main body of the image forming apparatus, when it is configured to include an electrostatic latent image carrier or a charging member, it is often used in the above combination.

  Exposure devices can be broadly classified into single light sources and multiple light sources. From the viewpoint of the amount of irradiation light and the uniformity of the shape of each dot, a single light source is used, the polygon mirror is rotated, the lens is corrected, and the electrostatic latent A method of scanning the surface of an image carrier is widely used.

  The developing device is generally a reversal developing system. In addition, a contact development method in which development is performed by bringing an electrostatic latent image carrier into contact with a developer carrier is widely used because of advantages such as halftone reproducibility and suppression of excessive edge effects.

  The transfer device applies a positive voltage to transfer the reversal-developed developer image, and performs transfer from the electrostatic latent image carrier to the intermediate transfer member or the final transfer material. At this time, in the system for transferring from the electrostatic latent image carrier to the final transfer material, the longitudinal width of the electrostatic latent image carrier, the exposure width of the exposure device, the longitudinal width of the transfer material, and the effective charging width of the charging device And the effective transfer width of the transfer member. Otherwise, black streaks on the paper edge and toner on the transfer device will occur.

  An effective configuration for avoiding this problem is disclosed in Patent Document 1. That is, the width of the photosensitive layer of the electrostatic latent image carrier is Ws. The width of the transfer material is Wp. A longitudinal width (hereinafter referred to as an effective charge width) that allows the surface of the electrostatic latent image carrier to be uniformly charged by causing a discharge phenomenon in the charging device, and a length in which the developer image is uniformly transferred in the transfer device. A longitudinal width in which the widths (hereinafter referred to as effective transfer widths) overlap is defined as Wt. And let the relationship of the longitudinal arrangement of each apparatus be Ws> Wt> Wp> We.

  The pre-exposure device is installed for the purpose of controlling the surface potential of the electrostatic latent image carrier after transfer in order to achieve both suppression of positive ghost images in the period of the electrostatic latent image carrier and transferability of the developer image. Yes. Conventionally, in order to increase the amount of light on the irradiated surface and increase the irradiation efficiency, the electrostatic latent image carrier is irradiated almost perpendicularly by using a WED array, a light guide, or the like.

  On the other hand, in recent years, a configuration advantageous in terms of downsizing and cost is considered by directly irradiating without using a light guide or the like from the longitudinal side surface of the electrostatic latent image carrier.

Japanese Patent No. 2925432

  However, in addition to the longitudinal configuration proposed in the embodiment of Patent Document 1, when a pre-exposure device is mounted so as to irradiate from the outside in the longitudinal direction of the electrostatic latent image carrier, a leak image may occur. It was.

  The longitudinal width of the charging roller is Wc. Let Wp be the longitudinal width of the surface irradiation region of the electrostatic latent image carrier surface of the pre-exposure device that irradiates from the outside in the longitudinal direction of the electrostatic latent image carrier. The longitudinal width of the transfer roller is Wt. In the longitudinal relationship in Table 1, the photosensitive layer of the electrostatic latent image carrier is locally sharply scraped at the longitudinal end portion of the contact area between the electrostatic latent image carrier and the charging roller. A leak image may occur.

  The inventors of the present invention have found that the cause of local scraping of the latent electrostatic image bearing member is a difference in discharge amount between the central portion and the end portion in the longitudinal direction of the charging roller. A leak image is generated when the electrostatic latent image bearing member has insufficient pressure resistance. In general, the withstand voltage reduction mechanism is caused by the discharge of the electrostatic latent image carrier, the photosensitive layer of the electrostatic latent image carrier is deteriorated, the amount of abrasion of the photosensitive layer is increased, and the thickness of the photosensitive layer as an insulator is increased. Becomes thinner and the pressure resistance decreases.

  The main factors that increase the discharge amount locally at the end in the longitudinal direction of the contact area between the electrostatic latent image carrier and the charging roller are 1) the shape factor of the charging roller and 2) the longitudinal direction of the potential before charging inrush. This is an interaction with the non-uniformity factor.

  First, the shape factor of the charging roller is cut almost perpendicularly to the longitudinal direction at the end of the charging roller. Is configured to increase locally.

  Next, the cause of the non-uniformity in the longitudinal direction of the electric potential before charging inrush is that the pre-exposure is applied to the electrostatic latent image carrier from the side surface direction of the electrostatic latent image carrier. For this reason, the photosensitive layer transmittance at the longitudinal center of the electrostatic latent image carrier may be about 30% with respect to the end. Therefore, if the pre-exposure light quantity is set in order to achieve both positive ghost in the rotation center of the electrostatic latent image carrier in the longitudinal center and transferability, the light quantity at the end becomes excessive, and the potential before charging inrush is at the central part. However, the end portion is in a low state, and the discharge amount at the end portion increases. Further, as a factor for increasing the discharge amount at the end of the charging roller, a decrease in potential before charging inrush at the end of the charging roller due to transfer is raised. When the effective transfer width is longer than the effective charging width, the potential before charging charging at the end of the charging roller is lowered, so that the amount of discharge at the end of the charging roller is locally increased as compared with the central portion.

  The present invention has been proposed in view of the above, and an object of the present invention is to propose a configuration that suppresses the occurrence of a leak image by suppressing an increase in local scraping of the electrostatic latent image carrier at the end of the charging device. And

In order to achieve the above object, the image forming apparatus according to the present invention includes a movable electrostatic latent image carrier, a charging device that contacts the electrostatic latent image carrier and uniformly charges the surface, An exposure device that forms an electrostatic latent image on the surface of the electrostatic latent image carrier that is uniformly charged; and a transfer device that transfers an image developed on the surface of the electrostatic latent image carrier to a transfer medium; A pre-exposure device for irradiating the surface of the electrostatic latent image carrier with light from the outside in the longitudinal direction of the electrostatic latent image carrier in order to neutralize the surface potential of the electrostatic latent image carrier before charging after transfer And an optical path from the pre-exposure device to the surface of the electrostatic latent image carrier so that the end of the discharge region of the charging device and the irradiation region of the surface of the electrostatic latent image carrier of the pre-exposure device do not overlap. A discharge member in the longitudinal direction of the charging device Wc, and a length of the exposure device Wl direction of the electrostatic latent image formation width, a longitudinal width of the transfer device Wt, the longitudinal direction of the exposure width by the pre-exposure device after the shield in the shielding member Wp, and when,
Wc>Wt> Wl and Wc>Wp> Wl
It is characterized by becoming.

Further, the configuration of the cartridge according to the present invention for achieving the above object is as follows.
A movable electrostatic latent image carrier, a charging device that abuts the electrostatic latent image carrier and uniformly charges the surface, and electrostatically adheres to the surface of the uniformly charged electrostatic latent image carrier. An exposure device for forming a latent image, a transfer device for transferring an image developed on the surface of the electrostatic latent image carrier to a transfer medium, and removing the surface potential of the electrostatic latent image carrier before charging after transfer. For this purpose, a pre-exposure device for irradiating the surface of the electrostatic latent image carrier with light from the outside in the longitudinal direction of the electrostatic latent image carrier, a discharge region end of the charging device, and the static of the pre-exposure device A shielding member that shields an optical path from the pre-exposure device to the surface of the electrostatic latent image carrier so that irradiation areas on the surface of the electrostatic latent image carrier do not overlap, and in the longitudinal direction of the charging device The discharge width is Wc, the electrostatic latent image formation width in the longitudinal direction of the exposure device is Wl, and the longitudinal width of the transfer device is W. When the longitudinal direction of the exposure width by the pre-exposure device after the shield in the shielding member Wp, that,
Wc>Wt> Wl and Wc>Wp> Wl
The cartridge is detachably attached to the apparatus main body of the image forming apparatus, and has at least the shielding member.

  According to the present invention, it is possible to suppress the occurrence of a leak image by suppressing an increase in local scraping of the electrostatic latent image carrier at the end of the charging device.

Schematic sectional view of the image forming apparatus of the embodiment Explanatory drawing of longitudinal arrangement of charging roller, exposure area, transfer roller and pre-exposure irradiation area for electrostatic latent image carrier Vd-Charge before charging rush and photosensitive layer abrasion Comparison of wear amount at the end of the charging roller between the conventional configuration and the embodiment

  A preferred embodiment of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

[Example 1]
(1) Description of Overall Configuration of Example Image Forming Apparatus FIG. 1 is an overall configuration model diagram of an example of an image forming apparatus 100 according to the present invention. The image forming apparatus 100 is a tandem type full-color laser beam printer (multicolor image forming apparatus) using a transfer type electrophotographic process.

  Y, M, C, and Bk are first to fourth image forming stations that form toner images of yellow, magenta, cyan, and black corresponding to the color separation component colors of the full color image, respectively. In the apparatus main body, they are arranged in the vertical direction in order from the bottom to the top.

  Each of the image forming stations Y, M, C, and Bk has a movable (rotatable) drum-type electrophotographic photosensitive member 1 (ad) as an electrostatic latent image carrier. The electrophotographic photoreceptor 1 is hereinafter referred to as a drum. Moreover, it has the charging device 2 (ad) which contacts the drum 1 and charges the surface uniformly. Further, the exposure apparatus 3 (a to d) that forms an electrostatic latent image by exposing the surface of the uniformly charged drum 1 to an image. The image forming apparatus further includes developing devices 4 (a to d) that develop the electrostatic latent image formed on the surface of the drum 1 as a toner image (image) with a developer (hereinafter referred to as toner). Further, a cleaning device 6 (ad) that cleans the surface of the drum after the toner image is transferred to the transfer medium (recording medium, transfer material) S is provided.

  The charging device 2 is a charging roller as a contact charging member (conductive member) disposed in contact with the drum 1. The exposure apparatus 3 is a laser scanner unit. The unit 3 outputs a laser beam modulated in accordance with electrical image information input from an external host device (not shown) such as a personal computer to a control circuit unit (not shown) of the image forming apparatus to output the drum 1. The uniformly charged surface is subjected to scanning exposure. Thereby, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the drum. The exposure device 3 is disposed in the horizontal direction of the drum 1 and includes a laser diode (not shown), a scanner motor (not shown), a polygon mirror 9 (ad), an imaging lens 10 (ad), and the like. ing.

  A transfer unit 5 transfers the toner image formed on the drum 1 (a to d) onto the transfer medium S. The unit 5 includes an endless transfer belt 11 that circulates and moves so as to face and be in contact with all the drums 1 (a to d). The drive roller 13, the two driven rollers 14 a and 14 b, and the tension roller 15 are four. Between the two rollers and arranged in the vertical direction. Reference numerals 12 (a to d) denote transfer rollers as transfer devices, which are arranged side by side in contact with the inner peripheral surface of the transfer belt so as to sandwich the transfer belt 11 between the drums 1 (a to d). . That is, high-resistance sponge rollers 12 (a to d) as transfer devices are arranged in parallel at positions facing the inside of the transfer belt 11 and facing the four drums 1a, 1b, 1c, and 1d.

  Reference numeral 16 denotes a transfer medium feeding unit disposed in the lower part of the apparatus main body of the image forming apparatus, which feeds the transfer medium S to the transfer belt 11 of the transfer unit 5. In the feeding unit 16, 17 is a feeding cassette in which a plurality of transfer media S are stored. Reference numeral 18 denotes a feeding roller (half-moon roller), 19 denotes a registration roller, and 22 denotes an electrostatic attraction roller.

  Reference numeral 20 denotes a fixing unit disposed in the upper part of the main body of the image forming apparatus, and fixes a plurality of color toner images transferred to the transfer medium S. A heating roller 21a that rotates, a pressure roller 21b that applies pressure to the transfer medium S in contact therewith, a discharge roller pair 23, a discharge port 24, and the like are included. Reference numeral 25 denotes a discharge tray provided in the upper part of the image forming apparatus main body.

  The operation for forming a full-color image is as follows. The image forming stations Y, M, C, and Bk are sequentially driven in accordance with a predetermined control timing of the image forming sequence, and the drum 1 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined speed. Further, the transfer belt 11 is circulated and driven by the drive roller 13 in a clockwise direction indicated by an arrow at a speed corresponding to the rotational speed of the drum 1.

  The outer peripheral surface (surface) of the drum 1 is subjected to a primary charging process uniformly to a predetermined polarity (negative polarity in this embodiment) and potential by the charging roller 2 during the rotation of the drum. Image scanning exposure with laser light modulated in accordance with image information output from the exposure device 3 is performed on the charged surface, and an electrostatic latent image of image information is formed on the drum surface. That is, image light corresponding to an image signal is output by a laser diode (not shown) of the exposure device 3, and the image light is applied to a polygon mirror 9 that is rotated at high speed by a scanner motor (not shown). The image light reflected by the polygon mirror selectively exposes the charged drum surface via the imaging lens 10. As a result, an electrostatic latent image is formed on the drum surface.

  The electrostatic latent image is developed as a toner image by the developing means 4. In this embodiment, reversal development using negative polarity toner is performed. As a result, each of the colors of yellow, magenta, cyan, and black, which are color separation component color images of a full-color image, is formed on the surfaces of the drums 1 (a to d) of the image forming stations Y, M, C, and Bk by an electrophotographic process. A toner image is formed at a predetermined sequence control timing.

  On the other hand, the feeding roller 18 of the feeding unit 16 is rotationally driven at a predetermined control timing. Thereby, the transfer medium S in the cassette 17 is separated and fed one by one. The leading edge of the transfer medium S abuts against the nip portion of the registration roller pair 19 which is in a rotation stop state at that time, and is temporarily stopped. Then, the registration roller pair 19 is rotationally driven in synchronization with the rotation of the transfer belt 11 and the toner image formed on the drum 1. As a result, the transfer medium S is fed between the electrostatic attraction roller 22 and the transfer belt 11. The feeding unit 16 feeds the transfer medium S to the image forming unit, and a plurality of transfer media S are stored in the cassette 17. At the time of image formation, the feeding roller 18 and the registration roller pair 19 are driven and rotated in accordance with the image forming operation to separate and feed the transfer medium S in the cassette 17 one by one. The leading edge of the fed transfer medium S abuts against the registration roller pair 19 and temporarily stops to form a loop. Then, the rotation of the transfer belt 11 and the image writing position are synchronized, and the registration roller pair 19 moves to the transfer belt 11. The paper is fed. The transfer medium S is sandwiched between the electrostatic attraction roller 22 and the transfer belt 11 and contacts the outer peripheral surface of the transfer belt 11. When a voltage is applied between the transfer belt 11 and the electrostatic attraction roller 22, electric charges are induced in the transfer medium S that is a dielectric and the dielectric layer of the transfer belt 11. Then, the transfer medium S is electrostatically attracted to the surface of the electrostatic transfer belt 11. As a result, the transfer medium S is stably adsorbed to the transfer belt 11 and conveyed from the most upstream transfer portion to the most downstream transfer portion by the movement of the transfer belt 11 in the transfer belt moving direction.

While being conveyed in this manner, the transfer medium S sequentially superimposes and transfers the toner image on the drum 1 by the electric field formed between the drum 1 and the transfer roller 12 at each of the image forming stations Y, M, C, and Bk. receive. In this embodiment, a positive charge is applied from the transfer roller 12 to the transfer medium S via the transfer belt 11. Due to the electric field due to the electric charge, the negative toner image on the drum 1 is transferred to the transfer medium S in contact with the drum 1. That is, the transfer medium S is electrostatically adsorbed and held on the surface of the transfer belt 11. The belt 11 is conveyed from the bottom to the top by the rotation of the belt 11. In the conveying process, the toner images of yellow, magenta, cyan, and black formed on the surface of the drum 1 are sequentially transferred at the transfer portions of the image forming stations Y, M, C, and Bk. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the transfer medium S.

  The transfer medium S that has received the superimposed transfer of the four color toner images is separated from the transfer belt 11 at the position of the driving roller 13 and is conveyed to the fixing unit 20. The transfer medium S is nipped and conveyed by a nip portion (fixing nip portion) formed by a rotating heating roller 21a and a pressure roller 21b in contact therewith. As a result, heat and pressure are applied to the transfer medium S by the roller pairs 21a and 21b, and the toner images of a plurality of colors are heated and fixed on the surface of the transfer medium S. The transfer medium S is discharged from the discharge port 24 to the discharge tray 25 by the discharge roller pair 23 after the toner image is fixed by the fixing unit 20.

  At each of the image forming stations Y, M, C, and Bk, the surface of the drum 1 after the transfer of the toner image onto the transfer medium S is freed of residual deposits such as transfer residual toner by the cleaning member 6, and is repeatedly used for image formation. Is done.

  FIG. 2 is a relationship diagram of the longitudinal arrangement of the charging roller 2 with respect to the drum 1, the exposure area of the exposure device 3, the transfer roller 12, and the pre-exposure irradiation area of the pre-exposure device 8 in each image forming station Y, M, C, and Bk. It is.

  In each of the image forming stations Y, M, C, and Bk, a pre-exposure device 8 that irradiates the drum surface with light from the outside in the longitudinal direction of the drum 1 in order to remove the surface potential of the drum 1 before charging after transfer. (A to d) are arranged. In FIG. 2, the pre-exposure device 8 is disposed on both sides in the longitudinal direction of the drum 1. In the present embodiment, the pre-exposure device 8 uses a red diode. The pre-exposure device 8 controls the potential of the drum surface by exposing the entire drum surface after transfer. In addition, shielding members 81 (a to d) are disposed on the irradiation light path from the pre-exposure device 8 to the drum 1 and shield the pre-exposure from hitting the end portion of the charging roller. In other words, the shielding member 81 shields the optical path from the pre-exposure device 8 to the drum surface so that the discharge region end of the charging roller 2 and the irradiation region of the drum surface of the pre-exposure device 8 do not overlap. The transfer residual toner remaining on the drum surface after the pre-exposure transfer is removed by the cleaning device 6.

  The pre-exposure device 8 has a red diode fixed to the base. The pre-exposure device 8 is arranged on both sides in the longitudinal direction of the drum 1 so as to increase the margin of the light amount at the drum longitudinal center.

  In FIG. 2, Wc is the discharge width in the longitudinal direction of the charging roller 2 as a charging device. Wl is an electrostatic latent image formation width (exposure region) in the longitudinal direction of the exposure apparatus 3. Wt is the width in the longitudinal direction of the transfer roller 12 as a transfer device. Wp is the exposure width in the longitudinal direction by the pre-exposure device 8 after being shielded by the shielding member 81. The shielding member 81 is disposed so as to shield the pre-exposure light so that Wc> Wt> Wl and Wc> Wp> Wl. The conveyance of the transfer medium S is based on the central reference, and the centers of the widths W1, Wp, Wt, and Wc coincide with the central reference line.

(2) Details of local photosensitive layer abrasion at the end of the charging roller Details of abrasion of the photosensitive layer of the drum 1 performed by the image forming apparatus 100 will be described. In order to improve the leak image, the mechanism of the local scraping of the photosensitive layer at the end of the charging roller and the solution were investigated.

  In the examination, an idling experiment was performed in the above-described image forming apparatus 100 in a 15 ° C./10% Rh environment. In the idling experiment, a voltage was applied to the charging roller 2 so that the drum surface was -500V. A voltage of −350 V was applied to the developing roller (developer carrier) of the developing device 4 so that the toner (developer) could be uniformly supported. A positive voltage was applied so that the applied voltage of the transfer roller 12 was 20 μA by constant current control.

  The amount of abrasion of the photosensitive layer of the drum 1 was calculated from the surface film thickness after initial rotation and idling. As the surface film thickness, a Fisher surface film thickness measuring device was used.

  FIG. 3 shows the relationship between the difference between the desired potential Vd and the potential before charging inrush in the center of the image of the drum 1 (the drum longitudinal center), and the abrasion of the photosensitive layer. At this time, the potential before charging rush was changed by changing the amount of pre-exposure light. From this result, the amount of abrasion of the photosensitive layer increases as the difference between the desired potential Vd and the potential before charging, that is, the amount of discharge increases. Therefore, an increase in local abrasion of the photosensitive layer at the end of the charging roller can be suppressed by reducing the amount of discharge at the end of the charging roller.

  Based on this result, the photosensitive layer abrasion amount of the conventional configuration (with pre-exposure irradiation at the end of the charging roller) and the configuration of Example 1 (pre-exposure shielding at the end of the charging roller) is compared. As shown in FIG. 4, in the conventional configuration, the photosensitive layer scraping amount at the end of the charging roller is about twice as large as that at the center of the image. This is considered to be the effect of the discharge effect from the end of the charging roller and the effect of pre-exposure irradiated from the side surface. Further, when the amount of abrasion of the photosensitive layer in the configuration shown in this embodiment and the conventional configuration is compared, the amount of abrasion of the photosensitive layer in the configuration shown in this embodiment is about half. In this way, the pre-exposure at the end of the charging roller is shielded, and the transfer roller 12 is made shorter than the charging roller 2, thereby reducing the discharge at the end of the charging roller, and even at the end of the life, due to the decrease in the film thickness of the photosensitive layer. The occurrence of a leak image can be suppressed.

In the first embodiment, the drum 1 has a base of an aluminum base tube having a diameter of 30 mm and a thickness of 0.7 mm. An organic photoconductive layer (photosensitive layer) is applied on the outer peripheral surface. In order to suppress the abrasion of the photosensitive layer, the photosensitive layer uses a photosensitive layer containing a polyarylate resin that is difficult to be scraped into a polycarbonate resin. The sensitivity of the photosensitive layer was set so that Vl would be -85 V when exposed to a surface light quantity of 0.37 μJ / cm ² when Vd was −420 V in a 23 ° C./50% environment.

The charging roller 2 is a conductive elastic rubber roller formed in a roller shape. The roller is brought into contact with the drum surface at a weight of 500 g on one side, and a charging bias is applied to the roller by a voltage applying means (not shown). The charging roller 2 rotates following the rotation of the drum 1. The surface of the drum is uniformly charged by the charging roller 2. The volume resistance of the charging roller 2 is 10 ⁵ Ω when pressed against an Al cylinder with a weight of 500 g and applied with −200 V while rotating at 30 rpm. As for the hardness, MD1 hardness is 57 ° and Asker C hardness is 86 °. Since the end shape is cut off after molding, the end shape is perpendicular to the circumferential surface in contact with the drum 1.

The exposure device (scanner unit) 3 accurately scans the drum surface by irradiating the polygon mirror with red light from a single light source and rotating the polygon mirror. At this time, the amount of light per unit area of the drum 1 is 0.37 μJ / cm ² , but between 0.25 and 0.4 μJ / cm ² shows the same tendency as the results described later.

The transfer roller 12 is made of, for example, a metal core and a conductive sponge. The roller is brought into contact with the drum 1 with a weight of 400 g on one side, and is driven to rotate with respect to the drum 1. The volume resistance is 10 ⁷ Ω in a state where a pressure of −1000 V is applied to the Al cylinder while being pressed at a weight of 500 g and rotating at 30 rpm. The hardness is Asker C hardness of 24 °. The transfer belt 12 is made of polyimide. The volume resistance is 10 ¹⁰ Ω under the condition that a belt is placed on a metal plate and a -100 V is applied by a Mitsubishi Oil Chemical Highvester.

  The amount of light of the pre-exposure device (red diode) 8 may be such that the amount of decrease in drum surface potential after pre-exposure irradiation differs between the center of the image and the end of the charging roller. In the present embodiment, the pre-exposure device 8 emits light by energizing it with 40 mA. The drum surface potential after pre-exposure irradiation at the center of the image is set to -100V. The pre-exposure device 8 at the end of the charging roller is disposed at both lateral positions of 10 mm from the end of the drum 1 to the outside in the longitudinal direction, 16 mm from the top in the vertical direction in the longitudinal direction, and 5 mm downstream from the transfer roller contact position. Then, the surface of the drum 1 is discharged by irradiating the drum surface at an angle θ = 2 ° between the axial direction of the drum 1 and the optical axis. Even in the case of irradiation from one side, if the relationship with the shielding member 81 is maintained, it is effective in suppressing the abrasion of the photosensitive layer.

  As described above, the shielding member 81 is disposed so as to block the pre-exposure light so that Wc> Wt> Wl and Wc> Wp> Wl. Specifically, the shielding member 81 is longer in the longitudinal direction than the line connecting the light source of the pre-exposure device 8 and the charging roller end, and more outward in the longitudinal direction than the line connecting the light source of the pre-exposure device 8 and the image forming region end. Arrange so that In the present embodiment, a mold shielding member 81 is disposed on the vertical lower side of the pre-exposure device 8. When the shielding member 81 is not provided, the drum surface potential before charging rush in the center of the image of the drum 1 is about −100V, whereas the drum surface potential before charging rush at the end of the charging roller is −30 to −50V. It has become.

  Specifically, Wc: 228 mm, Wl: 209.5 mm, Wt: 227.4 mm, and Wp: 224 mm. With this longitudinal arrangement, it is possible to suppress an increase in local abrasion of the photosensitive layer at the end of the charging roller, to increase the pressure resistance of the drum surface at the end of its life, and to prevent the occurrence of a leak image.

Example 2
In this embodiment, the drum 1, the charging roller 2, the developing device 4, the cleaning device 6, the pre-exposure device 8, and the shielding member 81 in each of the image forming stations Y, M, C, and Bk of the image forming apparatus 100 of the first embodiment. Is a cartridge 7 (ad). That is, the above-described electrophotographic process equipment is a cartridge (process cartridge) that is detachably attached to the main body of the image forming apparatus 100.

  Also in this case, the longitudinal arrangement of Wc> Wt> Wl and Wc> Wp> Wl suppresses an increase in local abrasion of the photosensitive layer at the end of the charging roller, and the pressure resistance of the drum surface at the end of its life And the occurrence of leak images can be suppressed.

  The cartridge 7 (a-d) has at least a shielding member 81. In addition to the shielding member 81, the drum 1, the charging roller 2, the developing device 4, the cleaning device 6, and the pre-exposure device 8 are included.

  1 .... Drum (electrostatic latent image carrier) 2 .... Charging device 3 .... Laser scanner (exposure device) 4 .... Developing device 5 .... Transfer unit 11 .... Transfer belt 12 .... Transfer roller (transfer device) 6. Cleaning device 7. Cartridge 8. Pre-exposure device 81 Blocking member 9. Polygon mirror 10. Imaging lens 16. Feeding unit , 17 ·· Feed cassette, 18 ·· Feed roller, 19 ·· Registration roller pair, 20 ·· Fusing unit, 21 ·· Fixing roller pair, 21a ·· Heating roller, 21b ·· Pressure roller, 100 ·・ Image forming device, S ・ ・ Transfer media

Claims (3)

A movable electrostatic latent image carrier, a charging device that abuts the electrostatic latent image carrier and uniformly charges the surface, and electrostatically adheres to the surface of the uniformly charged electrostatic latent image carrier. An exposure device for forming a latent image, a transfer device for transferring an image developed on the surface of the electrostatic latent image carrier to a transfer medium, and removing the surface potential of the electrostatic latent image carrier before charging after transfer. For this purpose, a pre-exposure device for irradiating the surface of the electrostatic latent image carrier with light from the outside in the longitudinal direction of the electrostatic latent image carrier, a discharge region end of the charging device, and the static of the pre-exposure device A shielding member that shields an optical path from the pre-exposure device to the surface of the electrostatic latent image carrier so that irradiation areas on the surface of the electrostatic latent image carrier do not overlap, and in the longitudinal direction of the charging device The discharge width is Wc, the electrostatic latent image formation width in the longitudinal direction of the exposure device is Wl, and the longitudinal width of the transfer device is W. When the longitudinal direction of the exposure width by the pre-exposure device after the shield in the shielding member Wp, that,
Wc>Wt> Wl and Wc>Wp> Wl
An image forming apparatus, wherein A movable electrostatic latent image carrier, a charging device that abuts the electrostatic latent image carrier and uniformly charges the surface, and electrostatically adheres to the surface of the uniformly charged electrostatic latent image carrier. An exposure device for forming a latent image, a transfer device for transferring an image developed on the surface of the electrostatic latent image carrier to a transfer medium, and removing the surface potential of the electrostatic latent image carrier before charging after transfer. For this purpose, a pre-exposure device for irradiating the surface of the electrostatic latent image carrier with light from the outside in the longitudinal direction of the electrostatic latent image carrier, a discharge region end of the charging device, and the static of the pre-exposure device A shielding member that shields an optical path from the pre-exposure device to the surface of the electrostatic latent image carrier so that irradiation areas on the surface of the electrostatic latent image carrier do not overlap, and in the longitudinal direction of the charging device The discharge width is Wc, the electrostatic latent image formation width in the longitudinal direction of the exposure device is Wl, and the longitudinal width of the transfer device is W. When the longitudinal direction of the exposure width by the pre-exposure device after the shield in the shielding member Wp, that,
Wc>Wt> Wl and Wc>Wp> Wl
A cartridge that is detachably mounted on the main body of the image forming apparatus, and has at least the shielding member.   The cartridge according to claim 2, further comprising the electrostatic latent image carrier and a charging device in addition to the shielding member.