JP2012128250A - Image forming device - Google Patents

Abstract

An image forming apparatus capable of effectively suppressing, with a simple configuration, shaving of a photosensitive layer caused by foreign matter staying between a cleaning blade and an image carrier and generation of vertical streaks in an output image associated therewith. I will provide a.
A cleaning blade 31 is fixed in a housing 35 of a cleaning device 5a at a position where the toner is scraped from below the photosensitive drum 1a. A toner discharge screw 33 is rotatably supported on the side of the cleaning blade 31. The rotation center 33a of the toner discharge screw 33 is below the pressure contact position R where the cleaning blade 31 and the photosensitive drum 1a are in contact, and the uppermost surface 33b of the toner discharge screw 33 is positioned above the pressure contact position R. Further, the developing device 3a can execute a toner discharging operation for supplying the toner on the developing roller 29 to the photosensitive drum 1a side.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus having a mechanism for removing residual toner on the surface of an image carrier using a cleaning blade, and more particularly to an image forming apparatus configured to scrape off toner on the surface of an image carrier from below. The present invention relates to a method for extending the life by suppressing damage to the body surface.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, or a FAX, a powder developer is mainly used, and an electrostatic latent image formed on an image carrier such as a photosensitive drum using the developing apparatus. A general process is to make an image visible, transfer the visible image (toner image) onto a recording medium, and perform a fixing process. The toner remaining on the surface of the image carrier is removed by a cleaning device, and a new toner image is formed.

  The cleaning device includes a cleaning member such as a cleaning blade and a cleaning roller pressed against the surface of the image carrier in the housing, and a toner discharge screw that discharges residual toner scraped off by the cleaning member to the outside of the cleaning device. . In particular, when an OPC photosensitive drum whose surface photosensitive layer is easily scraped is used as the image carrier, the toner on the surface of the photosensitive drum is scraped off using only a cleaning blade made of an elastic material, and the scraped waste toner is removed from the toner discharge screw. The structure which discharges by is used.

  Normally, the toner discharge screw is placed with a priority on space saving. However, in the configuration where the cleaning device is placed on the side of the photoconductor drum and the toner on the surface of the photoconductor drum is scraped off from below by the cleaning blade, it is discarded. In many cases, the toner discharge screw is arranged significantly below the position where the cleaning blade and the photosensitive drum are in contact with each other so that the toner can be collected to some extent in the housing of the cleaning device.

  For example, Patent Document 1 discloses a cleaning device that removes residual toner on an intermediate transfer belt. However, a conveying screw that conveys residual toner from the cleaning device is disposed below a contact position between the cleaning blade and the intermediate transfer belt. The configuration is disclosed.

JP-A-2005-241724

  By the way, in the configuration in which the toner on the surface of the photosensitive drum is scraped off from the lower side using the cleaning blade, foreign matters such as paper dust and toner external additive aggregates stay between the cleaning blade and the photosensitive drum. For this reason, when the OPC photosensitive drum is used, the photosensitive layer in the portion where the foreign matter stays is scraped in a streak shape in the drum circumferential direction, and vertical streaks may occur in the output image. In recent years, there are an increasing number of products aimed at extending the service life of replacement units from the viewpoint of environmental considerations. However, the occurrence of vertical stripes due to the removal of the photosensitive layer is a serious problem for extending the service life of drum units including photosensitive drums. It was.

  In view of the above problems, the present invention effectively removes the photosensitive layer due to the retention of foreign matter between the cleaning blade and the image carrier, and the occurrence of vertical stripes in the output image associated therewith with a simple configuration. It is an object of the present invention to provide a cleaning device that can be suppressed and an image forming apparatus including the same.

  To achieve the above object, the present invention provides an image carrier having a photosensitive layer formed on the surface, a charging device for uniformly charging the surface of the image carrier, and the image carrier charged by the charging device. A developing device that forms a toner image corresponding to the electrostatic latent image by attaching toner to the electrostatic latent image formed on the surface, and is pressed against the surface of the image carrier at a predetermined pressure, A cleaning blade for scraping residual toner from below, a housing for temporarily storing waste toner scraped off by the cleaning blade, and a housing disposed in a side of the cleaning blade in the housing. And a cleaning device having a toner discharge screw for discharging to the outside of the image forming apparatus. The toner discharge screw is positioned below the pressure contact position between the pressing blade and the image carrier, and the uppermost surface of the toner discharge screw is positioned above the pressure contact position, and at a predetermined timing during non-image formation. The image forming apparatus executes a toner discharging operation for supplying toner from the developing device to the image carrier.

  According to the present invention, in the image forming apparatus configured as described above, the photosensitive layer is an organic photosensitive layer.

  According to the present invention, in the image forming apparatus configured as described above, the charging device charges the surface of the image carrier by applying a DC voltage to a charging member that contacts the surface of the image carrier. .

  According to the first configuration of the present invention, the positional relationship between the cleaning blade and the toner discharge screw in the cleaning device is defined, and the toner at the edge portion of the cleaning blade is replaced by periodically performing the toner discharge operation. New toner always stays at the edge. For this reason, the toner on the edge portion functions as a buffer to prevent the foreign matter staying in the edge portion from rubbing against the image carrier, and the foreign matter is removed from the edge portion by the replacement of the toner. It is possible to suppress the occurrence of vertical stripes in the output image due to attachment.

  In addition, according to the second configuration of the present invention, in the image forming apparatus having the first configuration described above, the organic photosensitive layer is used as the photosensitive layer on the surface of the image carrier. The life of the image bearing member can be extended by suppressing the shaving and scratching of the photosensitive layer.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the surface of the image carrier is applied by applying a DC voltage to the charging member that contacts the surface of the image carrier. By using a charging device for charging, an image forming apparatus that can effectively suppress charging unevenness due to scratches on the surface of the image carrier, which is particularly problematic in the contact charging method, is obtained.

Schematic sectional view showing the configuration of the image forming apparatus of the present invention Partial enlarged view of the image forming portion Pa in FIG. Partial enlarged view of the cleaning device 5a in FIG. Side sectional view showing the configuration of the cleaning device of Comparative Example 1 in which the toner discharge screw 33 is located below the scope of the present invention. Side sectional view showing the configuration of the cleaning device of Comparative Example 2 in which the toner discharge screw 33 is above the range of the present invention. When a continuous printing is performed using the color printer (invention) equipped with the cleaning device shown in FIG. 3 and the color printer (comparative example) equipped with the cleaning device of Comparative Example 1 shown in FIG. A graph showing the relationship between the number of printed sheets and the drum surface roughness Rz

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus equipped with a cleaning device of the present invention. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of the respective colors. Here, an organic photosensitive layer is provided on the outer peripheral surface of the aluminum drum. An OPC photoreceptor on which (OPC) is formed is used. Further, an intermediate transfer belt 8 that rotates clockwise in FIG. 1 by a driving means (not shown) is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. Further, a blade-like belt cleaner 19 for removing the toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. Around and below the photosensitive drums 1a to 1d having organic photosensitive layers (OPC) rotatably disposed, charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d, and respective photosensitive drums Remaining on the photosensitive drums 1a to 1d, the exposure unit 4 that exposes image information to the photosensitive drums 1a to 1d, the developing devices 3a, 3b, 3c, and 3d that form toner images on the photosensitive drums 1a to 1d. Cleaning devices 5a to 5d for removing the developer (toner) are provided.

  When an image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d includes a developing roller disposed so as to face the photosensitive drums 1a to 1d, and each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer including yellow, cyan, magenta, and black toners. This toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing devices 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure unit 4. A toner image is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and yellow, cyan, magenta, and the like on the photosensitive drums 1a to 1d. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched around a plurality of suspension rollers including a driven roller 10 and a drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). Is started, the transfer paper P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the nip portion (secondary transfer nip portion) with the intermediate transfer belt 8 is transferred. ), The full color image is secondarily transferred onto the transfer paper P. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13, and the toner image is fixed on the surface of the transfer paper P, so that a predetermined full color is obtained. An image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the transfer paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the registration roller pair 12b with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed, and conveyed to the fixing unit 7 to fix the toner image. , And discharged to the discharge tray 17.

  FIG. 2 is an enlarged view of the vicinity of the image forming portion Pa in FIG. Since the image forming units Pb to Pd have basically the same configuration, description thereof is omitted. Around the photosensitive drum 1a, a charging device 2a, a developing device 3a, a cleaning device 5a, and a charge eliminating lamp 20 are disposed along the drum rotation direction (counterclockwise in FIG. 2), and the intermediate transfer belt 8 is interposed therebetween. The primary transfer roller 6a is arranged.

  The charging device 2 a includes a charging roller 21 that contacts the photosensitive drum 1 a and applies a charging bias (DC voltage) to the drum surface, and a charging cleaning roller 23 for cleaning the charging roller 21. In the present invention, in order to reduce the amount of ozone generated and to reduce the cost of the charging bias power source, a charging bias consisting of only a DC voltage is applied to the charging roller 21, but an AC bias is superimposed on the DC bias. Alternatively, a bias application method may be used.

  The developing device 3a is a two-component developing type having two stirring and conveying screws 25, a magnetic roller 27, and a developing roller 29, and a toner thin film is applied to the developing roller 29 using a magnetic brush that stands on the surface of the magnetic roller 27. A layer is formed, and a developing bias having the same polarity (positive) as the toner is applied to the developing roller 29 to cause the toner to fly on the drum surface.

  Further, the developing device 3a can execute a toner discharging operation (refresh mode) for supplying (discharging) the toner on the developing roller 29 to the photosensitive drum 1a side. As a result, the deteriorated toner (overcharged toner) on the developing roller 29 is discharged to the photosensitive drum 1a side to prevent image defects such as fogging, and to the toner supplied to the photosensitive drum 1a side, the photosensitive drum 1a. Foreign matter such as surface moisture, paper powder, and toner external additive aggregates can be adsorbed and removed together with the toner.

  This toner discharging operation is periodically performed at a predetermined timing, for example, after printing a predetermined number of sheets, after a predetermined driving time has elapsed, or at the end of the continuous printing operation. The toner supplied to the photosensitive drum 1a is scraped off by the cleaning blade 31 of the cleaning device 5a.

  The cleaning device 5 a has a cleaning blade 31 and a toner discharge screw 33. The detailed configuration of the cleaning device 5a will be described later.

  A neutralizing lamp 20 is disposed between the cleaning device 5a and the charging device 2a. The neutralization lamp 20 removes residual charges on the surface of the drum by irradiating the surface of the photosensitive drum 1a with light.

  FIG. 3 is a side sectional view of a cleaning device mounted on the image forming apparatus of the present invention. In FIG. 3, the cleaning device 5a disposed in the image forming portion Pa will be described as an example, but the cleaning devices 5b to 5d disposed in the image forming portions Pb to Pd have the same configuration. In the housing 35 of the cleaning device 5a, the cleaning blade 31 is disposed in the longitudinal direction of the photosensitive drum 1a on the downstream side of the contact surface (see FIG. 2) with the intermediate transfer belt 8 with respect to the rotational direction of the photosensitive drum 1a. It is fixed in a state where it is pressed along (the front and back direction in FIG. 3).

  As the cleaning blade 31, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive member at the contact point. That is, the cleaning blade 31 is disposed at a position where the toner is scraped from the counter direction (downward) with respect to the rotation direction of the photosensitive drum 1a. The material, hardness and dimensions of the cleaning blade 31, the amount of biting into the photosensitive drum 1a, the pressure contact force, and the like are appropriately set according to the specifications of the photosensitive drum 1a.

  A toner discharge screw 33 is rotatably supported on the side of the cleaning blade 31. Residual toner removed from the surface of the photosensitive drum 1a by the cleaning blade 31 is transported in the longitudinal direction of the housing 35 (front and back in FIG. 3) as the toner discharge screw 33 rotates, and is discharged outside the cleaning device 5a. And stored in a waste toner collecting container (not shown).

  In addition, a toner shielding member 37 that is in pressure contact with the photosensitive drum 1a at a predetermined pressure is provided at the end of the housing 35 adjacent to the photosensitive drum 1a on the upstream side of the cleaning blade 31 with respect to the rotation direction of the photosensitive drum 1a. Has been placed. The toner shielding member 37 is a flexible film member that extends in the longitudinal direction of the housing 35, and allows the untransferred toner, paper powder, toner external additive aggregates, and the like on the surface of the photosensitive drum 1 a to pass therethrough. It has a function of shielding the waste toner in the housing 35 from leaking outside while allowing the toner to enter.

  In the cleaning device 5a of the present invention, the rotation center 33a of the toner discharge screw 33 is below a position where the cleaning blade 31 and the photosensitive drum 1a are in contact (hereinafter referred to as a pressure contact position R). The upper surface 33b is located above the press contact position R.

  By disposing the toner discharge screw 33 in the above-described range, the upper surface (indicated by a one-dot chain line in FIG. 3) of the waste toner accumulated in the housing 35 is in the vicinity of the pressure contact position R. In this configuration, the transfer voltage applied to the primary transfer rollers 6a to 6d is turned off while rotating the photosensitive drum 1a at a timing when image printing is not performed, or a voltage having the same polarity as the toner (transfer reverse bias) is applied. When the toner is discharged from the developing roller 29 (see FIG. 2) to the photosensitive drum 1a without transferring the toner to the intermediate transfer belt 8 (primary transfer), the toner is always applied to the edge portion of the cleaning blade 31. While creating a state in which the toner stays, the toner supplied from the developing roller 29 promotes the replacement of the toner at the edge portion. When the staying toner is replaced, paper dust and foreign matter are removed together with the toner from the edge portion.

  FIG. 4 is a side cross-sectional view showing the configuration of the cleaning device of Comparative Example 1 in which the toner discharge screw 33 is below the range. The configuration of the other parts is the same as that in FIG. In the configuration of Comparative Example 1 shown in FIG. 4, the upper surface (indicated by the alternate long and short dash line in FIG. 4) of the waste toner accumulated in the housing 35 is below the pressure contact position R and below the edge portion 31 a of the cleaning blade 31. Toner is discharged.

  As a result, the toner does not always stay in the edge portion 31a, and the toner scraped off by the cleaning blade 31 spills downward immediately from the edge portion 31. Accordingly, paper dust and toner additive aggregates that cause damage to the photosensitive drum 1a at the edge portion 31a come into contact with the photosensitive drum 1a in an exposed state, and the life of the photosensitive drum 1a is remarkably shortened.

  Further, since the toner does not stay in the edge portion 31a, the supplied toner immediately spills from the edge portion 31a even if the toner discharging operation is periodically performed. Therefore, the buffering effect by the toner discharging operation as described above and the foreign matter removing effect by replacing the toner staying at the edge portion of the cleaning blade 31 are very short-term and insufficient.

  FIG. 5 is a side cross-sectional view showing the configuration of the cleaning device of Comparative Example 2 in which the toner discharge screw 33 is above the range. The configuration of the other parts is the same as that shown in FIGS. In the configuration of Comparative Example 2 shown in FIG. 5, the upper surface (indicated by the alternate long and short dash line in FIG. 5) of the waste toner accumulated in the housing 35 is above the pressure contact position R, and the edge portion 31 a of the cleaning blade 31 is completely discarded. It will be filled with toner.

  As a result, even if the toner discharging operation is performed, the toner in the edge portion 31 does not move, and the waste toner that has been subjected to mechanical stress due to the rotation of the toner discharging screw 33 causes aggregation in the edge portion 31, thereby causing the photosensitive drum 1a. Will be scratched and vertical stripes will occur.

  In other words, the positional relationship between the cleaning blade 31 and the toner discharge screw 33 in the cleaning device 5a is regulated within the range shown in FIG. 3, and the toner discharge operation is periodically performed, whereby the edge portion of the cleaning blade 31 is obtained. Although the toner 31a is in the toner rich state, the toner at the edge portion 31a is replaced by performing the toner discharging operation, and new toner always stays in the edge portion 31a. For this reason, the toner staying at the edge portion 31a serves as a buffer to prevent paper dust and toner external additive aggregates from rubbing strongly against the photosensitive drum 1a. Foreign matter such as agent agglomerates are removed from the edge portion 31a, generation of image vertical stripes in the output image due to scratches on the photosensitive drum 1a can be suppressed, and the life of the photosensitive drum 1a can be extended. Can do.

  Further, in the case of the contact charging method in which a charging bias is applied to the charging roller 21 (see FIG. 2) that is in contact with the photosensitive drum 1a, the surface of the photosensitive drum 1a is damaged compared to a non-contact charging method such as corona charging. Be susceptible. Even in the contact charging method, when an AC voltage is applied as a charging bias, a certain amount of charging unevenness can be absorbed, but when only a DC voltage is applied as in this embodiment, uniform charging becomes difficult. Therefore, the above configuration is particularly effective in the contact charging method in which a DC voltage is applied as the charging bias.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the materials, shapes, relative arrangements, and the like of the component parts described in the above embodiments are not intended to limit the scope of the present invention, but merely illustrative examples, unless otherwise specified. .

  Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, but various digital copiers, rotary or tandem type color copying machines, copying machines such as analog monochrome copying machines, facsimiles, etc. Of course, it can be applied to an image forming apparatus. Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

  The polishing effect on the surface of the photosensitive drum in the image forming apparatus equipped with the cleaning device of the present invention was evaluated. As an evaluation method, a test image using a color printer (invention) equipped with the cleaning device shown in FIG. 3 and a color printer (comparative example) equipped with the cleaning device of Comparative Example 1 shown in FIG. (Printing rate 1.5%) was continuously printed in a normal temperature and humidity environment (25 ° C., 45%), and the drum surface roughness Rz for each 50k (50,000) printing was measured. Further, during continuous printing, a toner discharging operation was executed every 20 minutes of driving time. The results are shown in FIG.

  As is apparent from FIG. 6, the rotation center 33a of the toner discharge screw 33 is disposed below the pressure contact position R, and the uppermost surface position 33b of the toner discharge screw 33 is disposed above the pressure contact position R. In the forming apparatus (data series of ● in FIG. 6), the drum surface roughness Rz after printing 200k sheets (200,000 sheets) changed to a low level of about 1.0 μm.

  On the other hand, in the image forming apparatus of the comparative example in which the uppermost surface 33b of the toner discharge screw 33 is disposed below the press contact position R (data series in FIG. 6), the drum surface after printing 200k sheets (200,000 sheets). The roughness Rz was as high as about 2.0 μm. From the above results, the toner discharge operation is performed with the configuration in which the rotation center 33a of the toner discharge screw 33 is disposed below the pressure contact position R and the uppermost surface 33b of the toner discharge screw 33 is disposed above the pressure contact position R. Thus, it was confirmed that the surface of the photosensitive drum was effectively suppressed from being damaged.

  INDUSTRIAL APPLICABILITY The present invention can be used in an image forming apparatus including a cleaning device that scrapes toner on the surface of an image carrier from below using a cleaning blade, and a rotation center of a toner discharge screw disposed on the side of the cleaning blade. Is positioned below the pressure contact position between the cleaning blade and the image carrier, the uppermost surface of the toner discharge screw is positioned above the pressure contact position, and at a predetermined timing during non-image formation A toner discharging operation for supplying toner from the toner to the image carrier is executed.

  By utilizing the present invention, it is possible to provide an image forming apparatus capable of effectively suppressing the occurrence of scratches on the surface of the image carrier and the occurrence of image vertical stripes resulting therefrom and extending the life of the image carrier.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
2a to 2d charging device 3a to 3d developing device 5a to 5d cleaning device 21 charging roller (charging member)
31 Cleaning blade 31a Edge portion 33 Toner discharge screw 33a Rotation center 33b Top surface 35 Housing 100 Color printer (image forming apparatus)
R Pressure contact position

Claims (3)

An image carrier having a photosensitive layer formed on the surface;
A charging device for uniformly charging the surface of the image carrier;
A developing device that forms a toner image corresponding to the electrostatic latent image by attaching toner to the electrostatic latent image formed on the surface of the image carrier charged by the charging device;
A cleaning blade that is pressed against the surface of the image carrier at a predetermined pressure and scrapes residual toner on the image carrier from below; a housing that temporarily stores waste toner scraped off by the cleaning blade; A cleaning device having a toner discharge screw disposed on the side of the cleaning blade in the housing and discharging the waste toner to the outside of the housing;
In an image forming apparatus comprising:
The rotation center of the toner discharge screw is positioned below the pressure contact position between the cleaning blade and the image carrier, and the uppermost surface of the toner discharge screw is positioned above the pressure contact position. An image forming apparatus that performs a toner discharge operation for supplying toner from the developing device to the image carrier at a predetermined timing during non-image formation.   The image forming apparatus according to claim 1, wherein the photosensitive layer is an organic photosensitive layer.   The image forming apparatus according to claim 1, wherein the charging device charges the surface of the image carrier by applying a DC voltage to a charging member that contacts the surface of the image carrier. .

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