JP2016133782A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that has stabilized an electrification potential of a photoreceptor at the ends of a developer coating width and can suppress acceleration of chipping of the photoreceptor at the ends of an effective electrification width.SOLUTION: When the width of an area where a toner image on a photoreceptor can be formed in the rotation axis direction of the photoreceptor is an image area width A, the width of the photoreceptor irradiated with electricity eliminating light by an electricity eliminating device is a pre-exposure width B, the width in which a developing member carries a developer is a developer coating width C, and the width of the photoreceptor electrified by an electrification member is an effective electrification width D, an image forming apparatus 100 satisfies the relationship A≤C≤B≤D, where in the rotation axis direction of the photoreceptor, an area with a smaller width is included inside an area with a larger width, and both ends of areas with the same width are the same positions.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile machine.

  Conventionally, in an image forming apparatus using an electrophotographic method, as a method of charging an electrophotographic photosensitive member (photosensitive member), a charging process is performed by applying a voltage to a charging member that is in contact with or close to the photosensitive member. Alternatively, there is a proximity charging method (hereinafter referred to as “contact charging method” as a representative). In the contact charging method, the surface of the photoconductor is charged by discharge in a minute gap between the surface of the photoconductor and the surface of the charging member. According to the contact charging method, it is possible to suppress the generation of ozone, NOx, SOx, and the like as compared with the corona charging method using a corona discharger.

  Further, the contact charging method includes a “DC charging method” in which only a DC voltage is applied to the charging member, and an “AC charging method” in which a superimposed voltage of the DC voltage and the AC voltage is applied to the charging member. The AC charging method has an advantage that the surface of the photoreceptor can be uniformly charged by applying an oscillating voltage and alternately causing positive and negative discharges. On the other hand, the DC charging method has an advantage that the life of the photosensitive member can be extended because the amount of discharge to the photosensitive member is smaller than that of the AC charging method. Further, since no AC power source is required, there is an advantage that the initial cost of the image forming apparatus can be suppressed. However, the DC charging method is inferior to the surface potential uniformity (charging uniformity) of the photoreceptor compared to the AC charging method. That is, in the case of the DC charging method, discharge occurs due to a potential difference between the surface potential of the photoreceptor before charging and the surface potential of the charging member. For this reason, if the surface potential of the photoconductor before charging is different, the discharge amount is also different, and the surface potential unevenness of the photoconductor after charging may occur.

  As a method for adjusting the surface potential of the photoreceptor before charging, as a charge eliminating means for eliminating the charge on the surface of the photoreceptor after transfer and before charging, a charge eliminating device that irradiates the photoreceptor with a charge eliminating light (photo charge eliminating device, front There is a method of providing an exposure apparatus.

  Here, Patent Document 1 defines the relationship between the irradiation width of the neutralizing light by the neutralizing device, the contact width of the cleaning roller for cleaning the photosensitive member, and the effective charging width by the charging device in the axial direction of the photosensitive member. The invention is disclosed. That is, Patent Document 1 discloses that A ≦ B ≦ C is satisfied, where A is the irradiation width of the neutralizing light, B is the contact width of the cleaning roller, and C is the effective charging width by the charging device. In the invention of Patent Document 1, by adopting such a configuration, the cleaning roller is brought into contact with all areas where charging and discharging are performed, and the surface of the photosensitive member is not expanded beyond the effective charging width. An attempt is made to effectively suppress the adhesion of discharge products.

JP 2010-8625 A

  By the way, particularly in the case of a two-component development method using a two-component developer containing toner and carrier as a developer, it is important to stabilize the fog removal potential difference Vback in a certain region. The fog removal potential difference Vback is a charge potential (dark portion potential) Vd, which is the surface potential of the photoreceptor after charging, and a DC component (development DC bias) Vdc of the development bias applied to the developer carrier of the developing device. It is a potential difference. This is because when Vback is small, fog occurs where the toner adheres to a non-image portion where the toner should not adhere, and when Vback is large, carrier adhesion occurs where the carrier adheres to the photoconductor. In particular, in the DC charging method, when the relationship between the developer coat width on which the developer carrying member carries the developer and the irradiation width of the charge removal light by the charge removal device is not appropriate, the photosensitive member is at the end of the developer coat width. In some cases, the charging potential is not stable, and fogging and carrier adhesion occur.

  Further, at the end of the charging member in the axial direction of the photoconductor, the discharge amount is larger than that at the center due to the wraparound of the axial discharge, and the surface of the photoconductor at the end is larger than the surface of the photoconductor at the center. Is easier to cut. In particular, in the DC charging method, as described above, the amount of discharge varies depending on the potential difference between the surface potential of the photoreceptor before charging and the surface potential of the charging member. For this reason, in the configuration in which the surface of the photoconductor is neutralized by the static eliminator before charging, if the irradiation width of the neutralizing light is made larger than the effective charging width, the surface of the photoconductor is scraped by discharge at the end of the charging member. Will be promoted. As a result, fogging due to insufficient potential retention due to a decrease in the film thickness of the photosensitive layer tends to occur at the end of the photosensitive member at the end of the durability of the photosensitive member, and as a result, there is a concern that the photosensitive member may have a short life. Therefore, it is desirable to make the relationship between the effective charge width and the irradiation width of the static elimination light appropriate.

  Note that, as described above, in Patent Document 1, the irradiation width of the neutralizing light by the neutralizing device, the contact width of the cleaning roller for cleaning the photosensitive member, and the effective charging width by the charging device in the axial direction of the photosensitive member. It is disclosed that the relationship is defined. However, in the invention of Patent Document 1, the problem of fogging and carrier adhesion when the relationship between the developer coat width and the irradiation width of the charge removal light is not appropriate, and the relationship between the effective charge width and the discharge width of the discharge light are appropriate. The problem due to acceleration of photoconductor scraping is not recognized. Therefore, the invention of Patent Document 1 cannot cope with these.

  Accordingly, an object of the present invention is to stabilize the charging potential of the photoconductor at the end of the developer coat width, and to suppress the acceleration of the photoconductor at the end of the effective charge width. A forming apparatus is provided.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a rotatable photosensitive member, a charging member that is disposed in contact with or close to the surface of the photosensitive member, and a voltage is applied to charge the surface of the photosensitive member at a charging position, and a developer. A developing member that forms a toner image on the surface of the photoconductor, a transfer device that transfers the toner image from the photoconductor to the transfer target at the transfer position, and the transfer in the rotation direction of the photoconductor An image forming apparatus including: a discharge device that irradiates the photoconductor with discharge light downstream of the charging position and upstream of the charging position; and forming a toner image on the photoconductor in a rotation axis direction of the photoconductor The width of the possible area is the image area width A, the width of the discharger to irradiate the photoreceptor with the discharge light is the pre-exposure width B, the width of the developing member carrying the developer is the developer coat width C, and the charging The member is the photoconductor Assuming that the width to be charged is the effective charge width D, the following formula, A ≦ C ≦ B ≦ D [where the smaller width region is included inside the larger width region in the rotation axis direction of the photoconductor. Both end portions between regions having the same width are at the same position. ] Is satisfied.

  According to the present invention, it is possible to further stabilize the charging potential of the photoconductor at the end portion of the developer coat width and to suppress the abrasion of the photoconductor at the end portion of the effective charge width.

1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus. FIG. 2 is a longitudinal sectional view showing a schematic configuration around a photosensitive drum. FIG. 6 is a schematic diagram illustrating an example of a relationship among an image area width A, a pre-exposure width B, a developer coat width C, and an effective charging width D. FIG. 4 is a schematic diagram showing a region R1 on the photosensitive drum where the charging process and pre-exposure processing are performed, and a region R2 which is charged and not pre-exposed. It is a graph for demonstrating the pre-exposure width. FIG. 6 is an enlarged view of FIG. 5. FIG. 4 is a schematic cross-sectional view in the vicinity of a charging roller for explaining an effective charging width. 6 is a schematic diagram illustrating an example of a relationship among an image area width A, a pre-exposure width B, a developer coat width C, an effective charging width D, and a transfer portion width E. FIG.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. FIG. 1 is a schematic longitudinal sectional view of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type color image forming apparatus that employs an intermediate transfer method and can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd as a plurality of image forming units. These four image forming portions Pa, Pb, Pc, and Pd form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) in this order. FIG. 2 is a schematic longitudinal sectional view showing the configuration of the first image forming portion Pa as a representative in more detail.

  In this embodiment, the configurations and operations of the first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are substantially the same except that the color of toner used for development is different. Are identical. Therefore, in the following, unless there is a particular distinction, a suffix “a”, “b”, “c”, “d” in the figure indicating an element provided for any color is omitted, and the element is summarized. Explained.

  The image forming portion P is provided with a photosensitive drum 1 which is a rotatable drum type (cylindrical) electrophotographic photosensitive member as an image carrier. In this embodiment, the photosensitive drum 1 is rotationally driven at a process speed (circumferential speed) of 100 mm / sec in the direction of arrow R1 in the figure by a driving means (not shown).

  Around the photosensitive drum 1, the following units are arranged almost in order along the rotation direction. First, a charging roller 2 that is a roller-type charging member (contact charging member) as a charging unit is disposed. The charging roller 2 is disposed in contact with the photosensitive drum 1. A cleaning roller 9 is disposed in contact with the charging roller 2. Next, an image exposure device 3 is disposed as image exposure means (electrostatic latent image forming means). Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-type primary transfer member (transfer device) as a primary transfer unit is disposed. Next, a drum cleaning device 6 as a photosensitive member cleaning unit is disposed. Next, a static elimination device (pre-exposure device) 11 as a static elimination means is arranged.

  The surface of the photosensitive drum 1 that is rotationally driven is uniformly charged by a charging roller 2 to a predetermined potential having a predetermined polarity (negative polarity in this embodiment). At this time, a negative DC voltage is applied to the charging roller 2 as a charging voltage (charging bias) from a charging power source (high voltage power source) as a charging voltage application unit (not shown). The charging voltage may be an oscillating voltage in which an AC voltage and a DC voltage are superimposed. The surface of the photosensitive drum 1 after charging is irradiated with light according to image information by the image exposure device 3 to form an electrostatic latent image (electrostatic image) on the photosensitive member.

  The electrostatic latent image formed on the photosensitive drum is developed (visualized) by the developing device 4. In this embodiment, the developing device 4 uses a two-component developer containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as the developer. The developing device 4 has a developing roller 41 as a developer carrying member (developing member) that incorporates a magnet roller as a magnetic field generating means. The developing roller 41 is rotationally driven in the direction of arrow R4 in the figure so that the surface of the developing roller 41 and the surface of the photosensitive drum 1 move in the same direction at the portion facing the photosensitive drum 1. The developing device 4 conveys the developer carried on the developing roller 41 to a portion facing the photosensitive drum 1 by a magnetic field generated by the magnet roller. The developer on the developing roller 41 rises at a portion facing the photosensitive drum 1 to form a magnetic brush, and the magnetic brush contacts or approaches the photosensitive drum 1. The developing roller 41 is applied with an oscillating voltage in which a DC voltage and an AC voltage are superimposed as a developing voltage (developing bias) from a developing power source (not shown) as a developing voltage applying unit. Thus, toner is transferred from the magnetic brush to the photosensitive drum 1 in accordance with the electrostatic latent image on the photosensitive drum 1, and the electrostatic latent image is developed as a toner image. The potential of the DC component of the development voltage is a predetermined negative potential between the charging potential (dark portion potential) of the photosensitive drum 1 and the exposure portion potential (bright portion potential). In this embodiment, a toner image is formed by image portion exposure and reversal development. That is, the toner charged to the same polarity as the charged polarity of the photosensitive drum 1 adheres to the exposed portion on the photosensitive drum 1 where the absolute value of the potential is lowered by being exposed after being uniformly charged. The charging polarity of the toner used in this example is negative.

  Here, in this embodiment, the photosensitive drum 1, the charging roller 2, the cleaning roller 9, the developing device 4, and the drum cleaning device 6 are integrally incorporated in the cartridge container 8 (dotted line in FIG. 2). A process cartridge 10 is configured. The process cartridge 10 is detachable from the main body of the image forming apparatus 100.

  Opposite to the photosensitive drum 1, an intermediate transfer belt 7 formed by an endless belt as an intermediate transfer member is disposed. The intermediate transfer belt 7 is an example of a transfer target body onto which a toner image is transferred from the photosensitive drum 1. The intermediate transfer belt 7 is formed endlessly with a dielectric resin such as polyimide, and is stretched around a driving roller 11, a tension roller 12, and a secondary transfer counter roller 13 as a plurality of stretching rollers. The intermediate transfer belt 7 is rotationally driven by a driving roller 11 in the direction of arrow R7 in the figure. The primary transfer roller 5 is disposed on the inner peripheral surface side of the intermediate transfer belt 7, is brought into contact with the photosensitive drum 1 through the intermediate transfer belt 7, and the primary transfer in which the intermediate transfer belt 7 and the photosensitive drum 1 are in contact with each other. Part (primary transfer nip) N1 is formed. The primary transfer roller 5 rotates in the direction of the arrow R5 in the figure following the movement of the intermediate transfer belt 7. Connected to the primary transfer roller 5 are a primary transfer power supply (high voltage power supply) 82 as a primary transfer voltage application means and a control device 83 as a control means for controlling the primary transfer power supply 82. The toner image formed on the surface of the photosensitive drum 1 is electrostatically transferred (primary transfer) to the surface of the intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer nip portion N1. At this time, a primary transfer voltage (primary transfer bias) is applied from the primary transfer power source 82 to the primary transfer roller 5. In this embodiment, the primary transfer voltage is a DC voltage having a polarity (positive polarity in this embodiment) opposite to the toner charging characteristics (normal charging polarity) during development.

  For example, when forming a color image, yellow, magenta, cyan, and black toner images are respectively formed in the first, second, third, and fourth image forming portions Pa, Pb, Pc, and Pd by the above-described process. It is formed on the photosensitive drums 1a, 1b, 1c and 1d. These four color toner images are primary-transferred so as to be sequentially superimposed on the intermediate transfer belt 7 in each primary transfer portion N1 as described above.

  At a position corresponding to the secondary transfer counter roller 13 on the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 14 that is a roller-type secondary transfer member as a secondary transfer unit is disposed. The secondary transfer roller 14 is in contact with the secondary transfer counter roller 13 via the intermediate transfer belt 7, and a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 7 and the secondary transfer roller 14 are in contact with each other. Is forming. The toner image on the intermediate transfer belt 7 is recorded on a recording material such as a recording sheet which is conveyed by being sandwiched between the intermediate transfer belt 7 and the secondary transfer roller 14 by the action of the secondary transfer roller 14 in the secondary transfer portion N2. It is electrostatically transferred (secondary transfer) onto S. When the recording material S passes through the secondary transfer portion N2, the secondary transfer roller 14 is supplied with a secondary transfer voltage (secondary transfer bias) from a secondary transfer power source (high voltage power source) as a secondary transfer voltage application unit. Is applied. In this embodiment, the secondary transfer bias is a DC voltage having a polarity (positive in this embodiment) opposite to the charging characteristics (normal charging polarity) of the toner during development. For example, at the time of forming a color image, a multiple toner image formed with four color toners on the intermediate transfer belt 7 is secondarily transferred onto the recording material S all at once.

  The recording material S used for image formation is stored in a paper feed cassette (not shown), and a registration roller 15 is fed by a paper feed / conveyance device (not shown) having a paper feed roller, a transport roller, a transport guide, and the like. It is conveyed to. The recording material S is supplied to the secondary transfer nip N2 after the skew is corrected by the registration roller 15.

  The recording material S to which the toner image has been transferred is transported to the fixing device 22 along the transport guide 18. The recording material S is heated and pressed when passing through a fixing nip formed by the fixing roller 20 and the pressure roller 21 in the fixing device 22, and the toner image is fixed on the surface thereof. This completes the formation of, for example, a full-color image on one sheet of recording material S. Thereafter, the transfer material S is discharged outside the apparatus main body of the image forming apparatus 100.

  Toner remaining on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 7 during the primary transfer (residual toner) is removed from the surface of the photosensitive drum 1 by the cleaning blade 61 of the drum cleaning device 6. The removed toner is collected in a waste toner container (not shown) by the waste toner conveying screw 62.

  The surface of the photosensitive drum 1 cleaned by the drum cleaning device 6 is irradiated with static elimination light by the static elimination device 11, whereby the surface of the photosensitive drum 1 is neutralized. The neutralization device 11 irradiates the surface of the photosensitive drum 1 with neutralizing light downstream of the primary transfer position (more specifically, the cleaning position) and upstream of the charging position in the rotation direction of the photosensitive drum 11. In the present embodiment, the static eliminator 11 includes an LED as a light source disposed on the back side in FIG. 2 of the main body of the image forming apparatus 100 and an acrylic resin as a light guide attached to the process cartridge 10. And a light guide. The light guide is disposed so as to face the photosensitive drum 1. In detail, the light guide guides light from the LED over a predetermined irradiation range in the rotation axis direction (longitudinal direction) of the photosensitive drum 1, which will be described later, and removes it on the surface of the photosensitive drum 1. Irradiate lightning.

  Further, the toner remaining on the surface of the intermediate transfer belt 7 without being transferred to the recording material S during the secondary transfer (residual toner) is belt cleaning as an intermediate transfer belt cleaning unit disposed at a position facing the tension roller 12. It is removed by the device 17 and collected.

  Further, the surface of the charging roller 2 is cleaned by a cleaning roller 9 disposed in contact with the charging roller 2. In this embodiment, the charging roller 2 rotates following the rotation of the photosensitive drum 1, and the cleaning roller 9 rotates following the rotation of the charging roller 2.

  Here, in the rotation direction of the photosensitive drum 1, a position where the charging process is performed by the charging roller 2 on the photosensitive drum 1 is a charging position. The charging roller 2 is a minute gap between the surface of the photosensitive drum 1 and the surface of the charging roller 2 formed on the upstream side and downstream side of the contact portion (charging nip) with the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. The photosensitive drum 1 is charged by a discharge generated in at least one of the gaps. Further, in the rotational direction of the photosensitive drum 1, a position where light corresponding to image information is irradiated from the image exposure device 3 on the photosensitive drum 1 is an image exposure position. Further, in the rotation direction of the photosensitive drum 1, a development position is a position where toner is supplied from the developing roller 2 on the photosensitive drum 1 and development is performed. Further, in the rotation direction of the photosensitive drum 1, a position in contact with the intermediate transfer belt 7 on the photosensitive drum 1 is a primary transfer position (primary transfer portion). Further, the position where the cleaning blade 61 of the drum cleaning device 6 abuts in the rotation direction of the photosensitive drum 1 is the cleaning position. Further, in the rotation direction of the photosensitive drum 1, the position where the neutralization light is emitted from the neutralization device 11 is the neutralization position.

2. Arrangement of Each Member of Image Forming Unit Next, an arrangement relationship of each member in the image forming unit P in the rotation axis direction of the photosensitive drum 1 will be described. FIG. 3 is a schematic diagram showing the relationship among the image area width A, the pre-exposure width B, the developer coat width C, and the effective charging width D in the rotation axis direction of the photosensitive drum 1. The image area width A is the width of an image forming area (image guarantee area) that is an area in which a toner image on the photosensitive drum 1 can be formed in the rotation axis direction of the photosensitive drum 1. The pre-exposure width B is a width (an irradiation width of the static elimination light, a static elimination width) of a region in the photosensitive drum 1 where sufficient static elimination light is irradiated from the static elimination device 11 in the rotation axis direction of the photosensitive drum 1 (more specifically, (It will be described later.) The developer coat width C is the width of the region carrying the developer on the developing roller 41 in the rotation axis direction of the photosensitive drum 1. The effective charging width D is a width of an area to be charged by the charging roller 2 in the rotation axis direction of the photosensitive drum 1 (more details will be described later).

In the image forming apparatus 100 of the present embodiment, the image area width A, the pre-exposure width B, the developer coat width C, and the effective charging width D are expressed by the following equations:
A ≦ C ≦ B ≦ D
Is set to satisfy the relationship. In this embodiment, the image area width A, the pre-exposure width B, the developer coat width C, and the effective charging width D are arranged with respect to the center of the photosensitive drum 1 in the rotation axis direction. And the area | region of a smaller width | variety is contained inside the area | region of a larger width | variety, and the both ends between the areas | regions with the same width | variety become the same position, respectively.

  By making the pre-exposure width B the same as the developer coat width C or longer than the developer coat width C, the surface of the photosensitive drum 1 before charging is discharged even at the end of the developer coat width to charge the charging roller. 2 can be stabilized, and a stable charging potential of the photosensitive drum can be secured. Therefore, the fog removal potential difference Vback is stabilized in a desired constant region over the entire developer coat width, and the fogging and carrier adhesion can be continuously suppressed.

  Further, by making the pre-exposure width B the same as or shorter than the effective charging width D, the surface of the photosensitive drum 1 before charging is excessively discharged at the end of the effective charging width, and the photosensitive drum. It is possible to suppress the occurrence of excessive wraparound of the discharge in the direction of the rotation axis 1. That is, it is possible to suppress the scraping of the photosensitive drum 1 from being promoted at the end portion of the effective charge width as compared with the central portion. Therefore, the film thickness of the photosensitive layer (such as a charge transport layer) at the end portion and the central portion in the rotation axis direction of the photosensitive drum 1 can be made more uniform. As a result, when the photosensitive layer thickness of the photosensitive drum 1 becomes thinner than the central portion at the end at the end of the durability of the photosensitive drum 1, the charging potential (dark portion potential) decreases due to insufficient holding of the potential at the end. The resulting fog can be suppressed. As a result, the life of the photosensitive drum 1 can be extended.

From the above viewpoint, the image area width A, the pre-exposure width B, the developer coat width C, and the effective charging width D are expressed by the following equations:
A ≦ C <B <D
It is more preferable to set so as to satisfy the relationship.

In particular, in this embodiment, as shown in FIG.
A <C <B <D
It is set to satisfy the relationship. More specifically, in this embodiment, the image area width A is 305 mm, the pre-exposure width B is 315 mm, the developer coat width C is 314 mm, and the effective charging width D is 319 mm.

  Therefore, in this embodiment, as shown in FIG. 4, on the photosensitive drum 1, a region R <b> 1 that is charged by the charging roller 2 and discharged by the charge removing device 11, and charged by the charging roller 2. There is a region R2 where static elimination by the device 11 is not performed. In the region R1, the static elimination light is radiated by the static elimination device 11 more reliably over the entire area of the developer coat width. As a result, the surface potential of the photosensitive drum 1 before charging can be made more uniform throughout the developer coat width. Therefore, the charged potential of the photosensitive drum 1 after charging becomes more uniform throughout the developer coat width, and a stable charged potential of the photosensitive drum 1 can be secured over the entire developer coat width. As a result, it is possible to more reliably and continuously suppress fogging and carrier adhesion throughout the developer coat width. In the region R2, the surface potential of the photosensitive drum 1 at the end of the effective charging width is more reliably maintained. As a result, it is possible to more reliably suppress the potential difference between the surface potential of the charging roller 2 and the surface potential of the photosensitive drum 1 from exceeding the discharge threshold at the end portion of the effective charging width, and substantially prevent discharge. it can. Therefore, it is possible to suppress the abrasion of the photosensitive drum 1 at the end portion of the effective charging width. In addition, since the generation of discharge products can be suppressed, an increase in the coefficient of friction on the surface of the photosensitive drum 1 can be suppressed, and problems such as chatter and wobbling of the cleaning blade 61 can be suppressed.

  Here, the pre-exposure width B and the effective charging width D in the rotation axis direction of the photosensitive drum 1 will be described in more detail.

  FIG. 5 is a graph showing the distribution of the irradiation light quantity per unit area of the surface of the photosensitive drum 1 of the static elimination light irradiated from the static elimination apparatus 11 to the photosensitive drum 1. The horizontal axis represents the position of the photosensitive drum 1 in the rotation axis direction, and the vertical axis represents the amount of irradiation light. This figure also shows the relationship between the lower limit value of the irradiation light amount used in this embodiment, the image area width, the effective charging width, and the developer coat width with the above distribution. FIG. 6 is an enlarged graph of one end side of the horizontal axis in FIG.

  5 and 6, in this embodiment, an average value is calculated from the amount of light irradiated to the image forming area on the photosensitive drum 1, and a light amount equal to or less than 30% of the average value is set as the lower limit value of the light amount. It was. Then, the position of this lower limit value is an end position that defines the pre-exposure width B, and the width between the end positions is the pre-exposure width B. This lower limit value is a value that can be evaluated that the surface of the photosensitive drum 1 is not substantially neutralized if the irradiation light quantity is less than that. It is possible to determine whether or not the effect of suppressing the promotion of shaving of the drum 1 is present.

  Next, FIG. 7 is a schematic cross-sectional view of the vicinity of the end portion of the charging roller 2 in the rotation axis direction of the photosensitive drum 1 in this embodiment. As shown in FIG. 7, the end position of the portion where the photosensitive drum 1 and the charging roller 2 are in contact is defined as the end position of the charging roller 2 that defines the effective charging width D, and the width between these end positions is defined as The effective charge width is D.

  In the present embodiment, as described above, the static eliminator 11 includes an LED disposed on the apparatus body side and an acrylic resin light guide provided on the process cartridge 10 side. . However, the present invention is not limited to such an embodiment. For example, a plurality of LEDs may be arranged in the direction of the rotation axis of the photosensitive drum. In this case, the static eliminator 11 composed of the plurality of LEDs may be provided on the process cartridge 10 side or on the apparatus main body side.

  Next, the width of the transfer portion in the rotation axis direction of the photosensitive drum 1 will be described.

  Conventionally, in the configuration in which no pre-exposure is performed, in order to make the surface potential of the photosensitive member before charging in the entire region of the developer coating width uniform, the transfer portion width in the rotation axis direction of the photosensitive member is longer than the developer coating width. To be done. However, in this case, the length of the transfer member such as a transfer roller in the direction of the rotation axis of the photosensitive member may increase, and the apparatus may increase in size. In addition, since the width of the transfer portion is longer than the developer coat width, the potential difference between the surface of the photoreceptor (dark portion potential portion) and the surface of the transfer member always increases outside the end of the developer coat width. . Therefore, outside the edge of the developer coat width, an increase in the coefficient of friction of the surface of the photosensitive member due to discharge at the transfer portion is promoted, and problems such as chattering and wobbling of the cleaning blade may occur. is there.

On the other hand, in the present embodiment, the surface potential of the photosensitive drum 1 before charging can be made uniform by the static elimination device 11, and therefore the transfer portion width can be appropriately set so as to suppress the above problem. Here, the primary transfer roller 5, the intermediate transfer belt 7, and the photosensitive drum 1 are in contact with each other in the rotational axis direction of the photosensitive drum 1 (that is, the photosensitive drum 1 and the primary transfer roller 5 are connected via the intermediate transfer belt 7). The width of the contact area) is defined as a transfer portion width E. At this time, A, B, C, D and E are expressed by the following equations:
A ≦ E ≦ C ≦ B ≦ D
It is preferable to set so as to satisfy this relationship. In addition,
A ≦ E ≦ C <B <D
It is more preferable to set so as to satisfy the relationship. As shown in FIG. 8, in this embodiment,
A <E <C <B <D
It is set to satisfy the relationship. In this embodiment, the width E of the transfer portion is also arranged with respect to the center in the rotation axis direction of the photosensitive drum 1 as in A, B, C, and D. And the area | region of a smaller width | variety is contained inside the area | region of a larger width | variety, and the both ends between the areas | regions with the same width | variety become the same position, respectively.

  Thus, a stable charging potential of the photosensitive drum 1 can be secured even at the end portion of the developer coat width without making the width E of the transfer portion longer than the developer coat width. And the above-mentioned effect can be acquired by prescribing the relationship between the developer coat width, the pre-exposure width, and the effective charge width as described above.

  As described above, according to the present embodiment, the charging potential of the photosensitive drum 1 at the end portion of the developer coat width is further stabilized, and suppression of the abrasion of the photosensitive drum 1 at the end portion of the effective charging width is suppressed. Can do.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  For example, in the above-described embodiment, the case where the charging member is in contact with the photosensitive member has been described as an example. However, if the charging member can charge the photosensitive member by discharging between the charging member and the photosensitive member, the charging member is close to the photosensitive member. May be arranged.

  The image forming apparatus is not limited to a color image forming apparatus, and may be a single color image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Image exposure apparatus 4 Developing apparatus 5 Primary transfer roller 6 Drum cleaning apparatus 7 Intermediate transfer belt 11 Static elimination apparatus

Claims (6)

A rotatable photoreceptor,
A charging member that is disposed in contact with or close to the surface of the photoconductor, and a voltage is applied to charge the surface of the photoconductor at a charging position;
A developing member that carries and conveys a developer to form a toner image on the surface of the photoreceptor;
A transfer device for transferring a toner image from the photoconductor to a transfer target at a transfer position;
A static eliminator that irradiates the photosensitive member with static elimination light downstream of the transfer position and upstream of the charging position in the rotation direction of the photosensitive member;
In an image forming apparatus having
In the rotation axis direction of the photoconductor, the width of an area where a toner image can be formed on the photoconductor is an image area width A, the width of the photoconductor to be irradiated with static elimination light is the pre-exposure width B, and When the width of the developer member carrying the developer is the developer coat width C, and the width of the charging member to charge the photosensitive member is the effective charge width D,
A ≦ C ≦ B ≦ D
[However, in the direction of the rotation axis of the photosensitive member, a region having a smaller width is included inside a region having a larger width, and both end portions between regions having the same width are at the same position. ]
An image forming apparatus satisfying the relationship:   The image forming apparatus according to claim 1, wherein a relationship of A ≦ C <B <D is satisfied. The transfer device includes a transfer member that sandwiches the transfer target with the photoconductor, and the photoconductor and the transfer member are in contact with each other via the transfer target in the rotation axis direction of the photoconductor. When the width of the contact area is the transfer portion width E, the following equation:
A ≦ E ≦ C ≦ B ≦ D
[However, in the direction of the rotation axis of the photosensitive member, a region having a smaller width is included inside a region having a larger width, and both end portions between regions having the same width are at the same position. ]
The image forming apparatus according to claim 1, wherein the relationship is satisfied.   The image forming apparatus according to claim 3, wherein the relationship of A ≦ E ≦ C <B <D is satisfied.   The image forming apparatus according to claim 1, wherein the developing member carries a two-component developer including toner and a carrier.   The image forming apparatus according to claim 1, wherein only a DC voltage is applied to the charging member in order to charge the surface of the photoconductor.

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