JP2009237520A - Image forming apparatus and process unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents an electrostatic charge product from depositing on an image carrier. <P>SOLUTION: The image forming apparatus includes a charging body 3 disposed close to an image carrier 2 and electrostatically charging the image carrier 2 by corona discharge. The apparatus includes: a charging body moving means that moves the charging body 3 between a charging position close to the image carrier 2 and a stand-by position separated from the image carrier 2; a shielding member 20 that prevents an electrostatic charge product generated on the charging body 3 from depositing on the image carrier 2; and a shielding member moving means that moves the shielding member 20 between a shielding position present in the middle of the charging body 3 at the stand-by position and the image carrier 2, and a retraction position retracting from the shielding position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine of these, and a process unit provided in the image forming apparatus.

  An image forming apparatus using an electrophotographic image forming process such as a copying machine, a facsimile machine, or a printer exposes a photosensitive member as an image carrier, a charging member that charges the surface of the photosensitive member, and a charged surface of the photosensitive member. An exposure device for forming an electrostatic latent image, developing means for supplying toner to the electrostatic latent image on the surface of the photoreceptor to form a toner image, and removing residual toner adhering to the surface of the photoreceptor Cleaning means, and static elimination means for removing residual charges on the photosensitive member.

  The operation of the image forming apparatus will be described. First, the surface of the photosensitive member is uniformly charged by a charging member, and the charged surface is exposed by an exposure device to form an electrostatic latent image. Then, toner is supplied to the electrostatic latent image on the photosensitive member by a developing unit to form a toner image, and the toner image is transferred to a transfer paper or the like. Thereafter, the toner remaining on the surface of the photoconductor is removed by a cleaning unit, and the residual charge on the photoconductor is removed by a charge eliminating unit.

  When the charged body is a corona discharger that charges using corona discharge, ozone is generated during the corona discharge. Ozone generation generates nitrogen oxides and charged products such as nitrates from the nitrogen oxides. Therefore, when the above image forming operation is repeated, the charged products are accumulated on the grid electrode of the charged body. The Then, the charged product accumulated on the grid electrode of the charged body gasifies over time, and it falls onto the photoreceptor and adheres. When the charged product adheres to the photoconductor and the photoconductor deteriorates, electrostatic charges are not easily formed in the deteriorated portion. For this reason, there is a problem that problems such as image blur and image density unevenness occur.

The image forming apparatus disclosed in Patent Document 1 changes the direction of the charged body after the image forming operation is completed, and disposes the grid electrode so as not to face the photoconductor, thereby moving the charged product from the grid electrode to the photoconductor. You can prevent it.
JP 2001-109240 A

  However, as described in Patent Document 1, even if the grid electrode is moved to a position not facing the photoconductor, the charged product may gradually drop and accumulate on the photoconductor from the charged body. The occurrence of abnormal images cannot be reliably prevented.

  In view of such circumstances, an object of the present invention is to provide an image forming apparatus for preventing a charged product from adhering to an image carrier (photosensitive member) and a process unit provided thereon.

  According to a first aspect of the present invention, there is provided an image forming apparatus including a charging member that is disposed in the vicinity of the image carrier and charges the image carrier by corona discharge. The charging member is disposed in proximity to the image carrier. A charging member moving means for moving between the charged position and a standby position separated from the image carrier, a shielding member for preventing the charged product generated on the charger from adhering to the image carrier, Shield member moving means for moving the shield member between a shield position interposed between the charged body moved to the standby position and the image carrier and a retracted position retracted from the shield position It is.

  After the charging of the image carrier with the charged body, the charged body is moved from the charging position to the standby position by the charging body moving means, and the shielding member is moved from the retracted position to the shielding position by the shielding member moving means. Between the body and the image carrier. As a result, even if the charged product generated on the charged body moves to the image carrier side, the charged product can be received by the shielding member, and the charged product can be prevented from adhering to the image carrier. it can.

  Further, when charging the image carrier, the shielding member is moved from the shielding position to the retracted position by the shielding member moving means, and the charged body is moved from the standby position to the charging position by the charging body moving means.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the charged body is provided so as to be rotatable about a support shaft extending in the axial direction of the image carrier, and the charged body moving means The charged body is rotated and moved between the charging position and the standby position.

  Thereby, the charged body can be stably moved between the charging position and the standby position, and the reliability is improved. In addition, the configuration of the charged body moving means can be simplified, and the cost can be reduced and the space can be saved.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the charging body moving means includes a cam receiving portion provided on the charging body, and the charging body in sliding contact with the cam receiving portion and the charging position. It has a cam part which carries out rotation operation between the said standby positions.

  Thus, the charged body can be moved between the charging position and the standby position by a simple mechanism.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the shielding member moving means includes a guide mechanism for guiding the shielding member between the shielding position and the retracted position, and a shielding member. It has a moving engagement part that engages with the provided engaging part and moves the shielding member from the retracted position to the shielding position, and an urging means that urges the shielding member in the direction of moving the shielding member to the retracted position. is there.

  Thereby, the shielding member can be moved between the shielding position and the retracted position by a simple mechanism.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the cam portion of the charged body moving means and the moving engagement portion of the shielding member moving means are arranged at a first position and a second position. And is integrally disposed on a moving member that reciprocates between them, and when the moving member is moved to the first position, the cam portion is moved to a position corresponding to the charging position of the charging body. The moving engagement portion is moved to a position corresponding to the retracted position of the shielding member, and the cam portion is moved to the standby position of the charged body when the moving member is moved to the second position. In addition to being moved to a position corresponding to the position, the moving engagement portion is moved to a position corresponding to the shielding position of the shielding member.

  By moving the moving member, the cam portion for moving the charged body and the moving engagement portion for moving the shielding member can be moved integrally. As a result, the drive source for the charged body moving means and the drive source for the shielding member moving means can be used as a common drive source, and the apparatus can be made compact and the manufacturing cost can be reduced.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the moving engagement portion is moved from the engagement portion of the shielding member in a state where the moving member is disposed at the first position. When the moving member is moved from the first position to the second position by disposing the member at a predetermined distance in a direction opposite to the direction in which the member is moved to the second position, the movement is performed. When the engaging portion engages with the engaging portion of the shielding member, the start of movement of the shielding member to the shielding position is started. To the standby position of the charged body due to the cam portion slidingly contacting the cam receiving portion. This is configured to be delayed for a predetermined time from the start of the movement.

  When the moving member is moved from the first position to the second position, the moving engaging portion is separated from the engaging portion of the shielding member by a predetermined distance in the direction opposite to the moving direction. It takes a predetermined time to engage with the engaging portion of the shielding member. Thereby, the start of the movement of the shielding member to the shielding position can be delayed for a predetermined time from the start of the movement of the charged body to the standby position. That is, since the shielding member waits for the start of movement of the charged body to the standby position and then starts moving to the shield position, interference with the charged body can be avoided. Further, the retracting position of the shielding member can be disposed at a position close to or near the charging position of the charged body, and the apparatus can be made compact.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the shielding member disposed at the shielding position is an image carrier that faces the charged body disposed at the charging position. It is arranged so as to be inclined in a direction away from the image carrier with respect to a tangent line at a circumferential intermediate point of the opposing surface.

  When the shielding member is arranged at the shielding position, if the vibration generated by the cover opening / closing operation of the image forming apparatus is transmitted to the shielding member, the shielding member may come into contact with the surface of the image carrier. However, since the shielding member is disposed so as to be inclined with respect to the tangent at the intermediate point in the circumferential direction of the opposing surface of the image carrier, the shielding member contacts the image carrier. It becomes difficult.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the charging member is moved from the retracted position of the shielding member before reaching the standby position from the charged position. The movement to the shield position is started.

  This can reduce the possibility that the shielding member does not reach the shielding position even if the image forming apparatus is turned off immediately after the image formation is completed.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the charged body is moved from the retracted position to the shielded position before the charged body reaches the standby position from the charged position. In this configuration, at least a part of the shielding member moved toward the surface is interposed between the image carrier and the charged body.

  This can reduce the possibility that the shielding member does not reach the shielding position even if the image forming apparatus is turned off immediately after the image formation is completed.

  A tenth aspect of the present invention is the image forming apparatus according to any one of the first to ninth aspects, wherein the charging member is moved from the standby position before the shielding member reaches the retracted position from the shielding position. It is configured to start moving to the charging position.

  As a result, the preparation time from the standby of the charged body to the start of image formation can be shortened.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, when a stop instruction for stopping the driving of the image carrier during the image forming operation is given, or the stop thereof After the instruction is given and before the driving of the image carrier is stopped, the charging body starts to move from the charging position to the standby position, and the shielding member is moved from the retracted position to the standby position. It is configured to start moving to the shielding position.

  By starting the movement of the charged body to the standby position and the movement of the shielding member to the shielding position before the driving of the image carrier stops, the movement of the charged body and the shielding member can be completed at an early stage. . Thereby, the possibility that the charged product adheres to the image carrier can be reduced.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, when the image forming condition is input or after the image forming condition is input. Before the start of the image forming operation is instructed, the charging body starts to move from the standby position to the charging position, and the shielding member starts to move from the shielding position to the retracted position. It is comprised as follows.

  The movement of the charged body and the shielding member is completed at an early stage by starting the movement of the charged body to the charging position and the movement of the shielding member to the retracted position before an instruction to start the image forming operation is given. Can do. Thereby, the waiting time until the first printing is performed can be shortened.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the image forming operation is started when the image forming preparation operation is started or after the image forming preparation operation is started. Before the start instruction is performed, the charging body starts to move from the standby position to the charging position, and the shielding member starts to move from the shielding position to the retracted position. Is.

  The movement of the charged body and the shielding member is completed at an early stage by starting the movement of the charged body to the charging position and the movement of the shielding member to the retracted position before an instruction to start the image forming operation is given. Can do. Thereby, the waiting time until the first printing is performed can be shortened.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, a human body detection sensor that detects the presence of a user is provided, and an image forming preparation operation is performed based on a detection signal of the human body detection sensor. The image forming apparatus is configured to start an image forming operation when the human body detection sensor detects the presence of a user or after the human body detection sensor detects the presence of a user. The structure in which the charging member starts to move from the standby position to the charging position and starts moving from the shielding position to the retracted position before the start instruction is given. It is.

  The movement of the charged body and the shielding member is completed at an early stage by starting the movement of the charged body to the charging position and the movement of the shielding member to the retracted position before an instruction to start the image forming operation is given. Can do. Thereby, the waiting time until the first printing is performed can be shortened.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fourteenth aspects, at least a part of the shielding member is formed of a soft member.

  Since at least a part of the shielding member is formed of a soft member, it is possible to suppress or prevent the image carrier from being damaged even if the shielding member contacts the image carrier.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fourteenth aspects, at least a part of the shielding member is formed of a flexible member.

  Since at least a part of the shielding member is formed of a flexible member, it is possible to suppress or prevent the image carrier from being damaged even if the shielding member contacts the image carrier.

  According to a seventeenth aspect of the present invention, in the image forming apparatus according to any one of the first to sixteenth aspects, the toner for forming a visible image on the image carrier has a volume average particle diameter of 3 μm to 8 μm. The ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) is in the range of 1.00 to 1.40.

  Thereby, it is possible to obtain a high-definition and high-quality image with little background fog.

  The invention according to claim 18 is the image forming apparatus according to any one of claims 1 to 16, wherein the toner for forming a visible image on the image carrier has a shape factor SF-1 of 100 to 100. It was in the range of 180, and the shape factor SF-2 was in the range of 100 to 180.

  When the values of the shape factors SF-1 and SF-2 approach 100, the shape of the toner becomes nearly spherical. In this case, since the contact state between the toner and the toner or the toner image carrier is point contact, the attractive force between the toners becomes weak. Accordingly, the fluidity is increased, and the attracting force between the toner and the photoreceptor is weakened, and the transfer rate is increased. On the other hand, if any of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

  According to a nineteenth aspect of the present invention, in the image forming apparatus according to any one of the first to sixteenth aspects, the toner for forming a visible image on the image carrier has at least a functional group containing a nitrogen atom. A toner material liquid in which the polyester prepolymer, polyester, colorant, and release agent having the dispersion were dispersed in an organic solvent was formed by crosslinking and / or elongation reaction in an aqueous medium.

  Thereby, a high-quality image can be formed.

  According to a twentieth aspect of the present invention, in the image forming apparatus according to any one of the first to sixteenth aspects, the toner for forming a visible image is formed in a substantially spherical shape on the image carrier.

  Thereby, a high-quality image can be formed.

  According to a twenty-first aspect of the present invention, in the image forming apparatus according to any one of the first to sixteenth aspects, the shape of the toner for forming a visible image on the image carrier is defined by a major axis r1, a minor axis r2, When defined by the thickness r3 (however, r1 ≧ r2 ≧ r3), the ratio (r2 / r1) of the major axis r1 to the minor axis r2 is in the range of 0.5 to 1.0, and the thickness r3 And the minor axis r2 (r3 / r2) were in the range of 0.7 to 1.0.

  Thereby, a high-quality image can be formed.

  According to a twenty-second aspect of the present invention, in the process unit integrally including at least the image carrier and the charged body, the image forming apparatus according to any one of the first to twenty-first aspects is configured to be detachable from the image forming apparatus. It is.

  By adopting a detachable process unit in the image forming apparatus, maintenance such as replacement, repair, and replenishment becomes easy.

  According to the image forming apparatus of the present invention, after the charging operation is completed, the charged product is moved from the charged body to the image carrier side by interposing the shielding member between the charged body and the image carrier. This can be received by the shielding member. This prevents the charged product from adhering to the surface of the image carrier, and thus it is possible to prevent the occurrence of abnormal images such as image blurring and image density unevenness.

  The process unit provided in the image forming apparatus can achieve the same effects as described above.

  FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. The image forming apparatus of the present invention shown in FIG. 1 has four process units 1Y, 1C, 1M for forming an image with developers of different colors of yellow, cyan, magenta and black corresponding to color separation components of a color image. , 1Bk.

  The process units 1Y, 1C, 1M, and 1Bk have the same configuration except that they store different color toners. Therefore, the configuration of one process unit 1Y will be described as an example.

  The process unit 1Y includes a photosensitive member 2 as an image carrier for holding an electrostatic latent image, a charging member 3 for charging the surface of the photosensitive member 2, and a toner for the electrostatic latent image on the surface of the photosensitive member 2. A developing unit 4 that forms a toner image by supplying, a cleaning unit 5 that removes residual toner adhering to the surface of the photoreceptor 2, and a neutralizing unit 6 such as a neutralizing lamp that removes residual charges on the photoreceptor 2 are provided. ing. As the cleaning means 5, a cleaning blade, a cleaning roller, a cleaning brush, or the like can be applied. Or you may use these together.

  Above each of the process units 1Y, 1C, 1M, and 1Bk, an exposure device 7 that forms an electrostatic latent image on the surface of the photoreceptor 2 is disposed. An intermediate transfer unit 8 is disposed below each process unit 1Y, 1C, 1M, 1Bk. The intermediate transfer unit 8 includes a plurality of rollers 9, 10, and 11 including a driving roller and a driven roller, and an endless belt-shaped intermediate transfer belt 12 that is stretched over the plurality of rollers 9, 10, and 11.

  Four primary transfer rollers 13Y, 13C, 13M, and 13Bk as transfer means are disposed to face the respective photoreceptors 2 of the four process units 1Y, 1C, 1M, and 1Bk. The four primary transfer rollers 13Y, 13C, 13M, 13Bk and the respective photoreceptors 2 sandwich the intermediate transfer belt 12 to form a primary transfer nip.

  A secondary transfer roller 14 is disposed opposite to the roller 10 at the bottom of the intermediate transfer unit 8 in the figure. The intermediate transfer belt 12 is sandwiched between the secondary transfer roller 14 and the roller 10 to form a secondary transfer nip.

  A paper feeding unit 15 is disposed at the lower part of the image forming apparatus. The paper feed unit 15 includes a paper feed cassette that can store a plurality of recording papers P and a paper feed roller that carries the recording paper P out of the paper feed cassette (not shown).

  Between the sheet feeding unit 15 and the intermediate transfer unit 8, a pair of registration rollers 16a and 16b, a transfer sheet conveyance unit 17 including a conveyance belt stretched between a driving roller and a driven roller, and a fixing device 18 are disposed. ing.

  The fixing device 18 includes, for example, a fixing belt 18c stretched between a fixing roller 18a and an auxiliary roller 18b, and a pressure roller 18d, and has a heating source such as a heater in at least one of the fixing roller 18a and the auxiliary roller 18b. .

  Reference numeral 19 in the figure denotes a paper discharge tray for stocking the transfer paper P discharged to the outside of the image forming apparatus main body.

The basic operation of the image forming apparatus will be described below with reference to FIG.
First, the image forming operation will be described using one process unit 1Y as an example. The surface of the photosensitive member 2 is charged to a uniform high potential by the charging member 3. Based on the image data, the surface of the photosensitive member 2 is irradiated with a laser beam from the exposure device 7, and the potential of the irradiated portion is lowered to form an electrostatic latent image. The toner charged by the developing means 4 is electrostatically transferred to the portion of the surface of the photoreceptor 2 where the electrostatic latent image is formed, and a yellow toner image is formed (visualized).

  The primary transfer roller 13Y is applied with a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner. As a result, an electric field (transfer electric field) is formed in the primary transfer nip between the primary transfer roller 13Y and the photoreceptor 2. Then, in the primary transfer nip, the toner image on the rotating photoreceptor 2 is transferred to the intermediate transfer belt 12 running in the direction of the arrow in the figure.

  In each of the other process units 1C, 1M, and 1Bk, toner images are similarly formed on the photoreceptor 2, and the four color toner images are transferred to the intermediate transfer belt 12 so as to overlap each other.

  In addition, each cleaning unit 5 removes residual toner adhering to the surface of the photoreceptor 2 after the primary transfer process. Thereafter, the residual charge of the photoreceptor 2 is neutralized by the neutralizing means 6.

  On the other hand, a paper feed roller (not shown) of the paper feed unit 15 is rotated to feed the recording paper P from the paper feed cassette. The recording paper P delivered from the paper feed cassette is temporarily stopped by the registration rollers 16a and 16b.

  By the above image forming operation, a composite toner image is formed by superimposing the toner images of the respective colors on the intermediate transfer belt 12, and then the driving of the registration rollers 16a and 16b is resumed. In synchronization, the recording paper P is fed to the secondary transfer nip between the secondary transfer roller 14 and the roller 10. Then, the composite toner image on the intermediate transfer belt 12 is transferred to the recording paper P sent to the secondary transfer nip.

  The recording paper P to which the synthesized toner image has been transferred is conveyed to the fixing device 18. The recording paper P sent to the fixing device 18 is sandwiched between the fixing roller 18a and the pressure roller 18d and heated and pressurized, and the composite toner image is fixed on the recording paper P. Thereafter, the recording paper P is discharged to the paper discharge tray 19 and stocked.

Hereinafter, the structure of the characteristic part of the present invention will be described with reference to FIGS.
The charging member 3 applied to the image forming apparatus of the present invention charges the photosensitive member 2 using corona discharge. As shown in FIG. 2, the charged body 3 is disposed in a non-contact state in proximity to the photosensitive body 2. The charged body 3 includes a discharge electrode (not shown) and a grid electrode 3 a that regulates the charge flowing from the discharge electrode to the photosensitive member 2. In this embodiment, the grid electrode 3 a is disposed in a curved shape so as to face the surface of the photoreceptor 2.

  The charging body 3 is configured to be movable between a charging position where the charging body 3 is close to the photosensitive body 2 (see FIG. 2) and a standby position where the charging body 3 is separated from the photosensitive body 2 (see FIG. 4). Hereinafter, the configuration of the charged body 3 and the configuration of the charged body moving means for moving the charged body 3 will be described in detail.

  The charging member 3 is provided so as to be rotatable about a support shaft 21 extending in the axial direction of the photosensitive member 2. The support shaft 21 is attached to a holding member 27 that holds the charging body 3 and is rotatably attached to a fixing member 22 that is fixed to the main body of the image forming apparatus.

  The charging body moving means includes a cam portion 26a and a cam receiving portion 28a for rotating the charging body 3 between a charging position and a standby position. The cam portion 26 a is formed on the inner peripheral surface of the long hole 26 formed in the moving member 23. On the other hand, the cam receiving portion 28 a is formed on the outer peripheral surface of the slide pin 28 attached to the upper portion of the holding member 27. The slide pin 28 is movably inserted into the long hole 26.

  The moving member 23 is attached to the fixed member 22 so as to slide in the horizontal direction. A concave and convex gear portion 24 is formed on the lower surface of the moving member 23 in the longitudinal direction, and a gear member 25 such as a pinion gear that meshes with the gear portion 24 is rotatably provided on the fixed member 22. . By rotating the gear member 25 in the forward or reverse direction, the moving member 23 is moved between a first position disposed on the left side of FIG. 2 and a second position disposed on the right side of FIG. It is configured to reciprocate.

  The image forming apparatus of the present invention includes a shielding member 20. The shielding member 20 is configured to be movable between a shielding position (see FIG. 4) interposed between the charging body 3 and the photosensitive member 2 and a retreat position (see FIG. 2) retreated from the shielding position. ing. Hereinafter, the configuration of the shielding member 20 and the configuration of the shielding member moving means for moving the shielding member 20 will be described in detail.

  The shielding member moving means includes a guide mechanism 29 for guiding the shielding member 20 between the shielding position and the retracted position, a moving engagement portion 34 for moving the shielding member 20 from the retracted position to the shielding position, and a shielding member. There is urging means 36 that urges 20 in a direction to move 20 to the retracted position.

  The shielding member 20 is composed of a plate-like member extending corresponding to the longitudinal direction of the charged body 3. At least a part of the shielding member 20 is formed of a soft member or a flexible member. In this embodiment, a sheet made of urethane rubber is disposed at the distal end portion 20 a of the shielding member 20. An attachment member 37 for attaching the shielding member 20 to the fixing member 22 is integrally provided at the base end portion of the shielding member 20.

  The guide mechanism 29 includes two guide grooves 30 and 31 formed in the fixing member 22 and two guide pins 32 and 33 inserted through the guide grooves 30 and 31. The two guide pins 32, 33 are attached to the attachment member 37, whereby the shielding member 20 is supported by the fixing member 22.

  The moving engagement portion 34 is formed on the moving member 23. Specifically, as shown in FIG. 2, the left end edge of the rectangular hole 35 formed in the moving member 23 is a moving engagement portion 34. Further, one of the two guide pins 32 and 33 on the right side in FIG. 2 serves as an engaging portion that engages with the moving engaging portion 34. The guide pin 33 is inserted into the rectangular hole 35, so that the moving member 23 moves from the first position in FIG. 2 to the direction indicated by the arrow A in FIG. The moving engagement portion 34 is configured to come into contact with the guide pin 33 when moving in the direction 2).

  As shown in FIG. 2, when the moving member 23 is disposed at the first position, the moving engagement portion 34 is moved away from the guide pin 33 engaged therewith in the direction opposite to the direction of the arrow A in FIG. Further, they are arranged at positions separated by a predetermined distance L.

  The biasing means 36 is constituted by an elastic member such as a spring, for example. One end of the urging means 36 is attached to the mounting member 37 of the shielding member 20, and the other end is attached to the image forming apparatus main body (not shown). A tensile force acts on the urging means 36, and the urging force is applied to the urging means 36 in the direction of moving the shielding member 20 to the retracted position (toward the left side in FIG. 2). Further, a compression spring may be used as the urging means 36, and the shielding member 20 may be urged in the same direction as described above by the pressing force of the compression spring.

  Further, in FIG. 5, when the circumferential intermediate point of the opposing surface of the photosensitive member 2 facing the charging member 3 disposed at the charging position is Q and the tangent at the circumferential intermediate point Q is X, the charging member 3 is disposed at the shielding position. The shielding member 20 is disposed so as to be inclined with respect to the tangent line X in a direction away from the photoreceptor 2.

Hereinafter, operations of the charging body 3 and the shielding member 20 will be described.
When the photosensitive member 2 is charged by the charging member 3, the charging member 3 is disposed at the charging position as shown in FIG. At this time, the shielding member 20 is disposed at the retracted position. Moreover, the moving member 23 is arrange | positioned in the 1st position of the left side of FIG.

  After the charging operation is completed by the charging body 3, the gear member 25 is rotated clockwise in FIG. Accordingly, the moving member 23 moves to the right side (second position side) in FIG.

  When the moving member 23 moves, the slide pin 28 slides in the long hole 26. At this time, as shown in FIG. 3, the slide pin 28 is pushed upward by the cam portion 26 a of the long hole 26, and accordingly, the charged body 3 rotates upward about the support shaft 21. On the other hand, the moving engagement portion 34 approaches the guide pin 33 as the engagement portion, but has not yet contacted the guide pin 33.

  In FIG. 3, when the moving member 23 is further moved to the right side of the drawing, the moving engagement portion 34 comes into contact with the guide pin 33 and moves the guide pin 33 to the right side of the drawing against the urging force of the urging means 36. Let Thereby, the shielding member 20 moves to the right side of the figure.

  Then, as shown in FIG. 4, when the moving member 23 moves to the second position on the right side of the drawing, the rotation of the gear member 25 is stopped. In this state, the slide pin 28 is positioned at the left end portion of the long hole 26 in the figure, and the charged body 3 is held at the standby position. Each guide pin 32, 33 is positioned at the right end of the corresponding guide groove 30, 31 in the figure, and the shielding member 20 is held at the shielding position.

  Thereafter, when the photosensitive member 2 is charged again from the state shown in FIG. 4, the gear member 25 is rotated counterclockwise in the opposite direction. Thereby, the moving member 23 moves to the left side (first position side) in FIG. When the long hole 26 moves to the left in FIG. 4 along with the movement of the moving member 23, the slide pin 28 slides in the long hole 26. As a result, the charged body 3 rotates around the support shaft 21 downward in the figure. Move. On the other hand, the shielding member 20 moves to the left in FIG. 4 by the movement of the moving member 23 and the tensile force by the urging means 36.

  As shown in FIG. 3, the guide pins 32 and 33 are positioned at the left end portions of the corresponding guide grooves 30 and 31 in the drawing, and the shielding member 20 is held in the retracted position. In the state shown in FIG. 3, the rotation (movement) of the charging body 3 has not been completed yet.

  As shown in FIG. 2, when the moving member 23 is moved to the first position on the left side of the drawing, the slide pin 28 is positioned at the right end portion of the long hole 26 in the drawing, and the charging body 3 is held at the charging position. . In this way, the charging member 3 is returned from the standby position to the charging position, and the photosensitive member 2 is charged. Further, the moving engagement portion 34 is arranged in a state separated from the engaged guide pin 33 by a predetermined distance L.

  Thereafter, similarly, after the charging operation is completed, the charged body 3 is moved to the standby position, and the shielding member 20 is moved to the shielding position. When performing the charging operation, the shielding member 20 is moved to the retracted position. At the same time, the charged body 3 is moved to the charging position.

  As described above, according to the image forming apparatus of the present invention, after the charging operation is finished, the shielding member 20 is moved to the shielding position, and the shielding member 20 is interposed between the charging member 3 and the photosensitive member 2. As a result, it is possible to prevent the charged product adhering to the grid electrode 3 a and the like of the charged body 3 from adhering to the surface of the photoreceptor 2. That is, even if the charged product falls from the charged body 3, the shielding member 20 receives the charged product, so that it is possible to prevent the charged product from adhering to the photoreceptor 2. Moreover, since the shielding member 20 is configured to move in a substantially horizontal direction between the shielding position and the retracted position, the charged product received on the upper surface of the shielding member 20 is unlikely to fall. As a result, it is possible to prevent the occurrence of abnormal images such as image blur and image density unevenness. When performing the charging operation, the photosensitive member 2 can be charged by separating the shielding member 20 from between the charging member 3 and the photosensitive member 2 and setting the charging member 3 to the charging position. .

  A cam portion 26 a for moving the charging body 3 and a moving engagement portion 34 for moving the shielding member 20 are provided integrally with the moving member 23. For this reason, the drive source of the charged body moving means and the drive source of the shielding member moving means can be a common drive source (gear member 25). As a result, it is possible to reduce the size of the apparatus and reduce manufacturing costs.

  In the state shown in FIG. 2, since the movement engagement portion 34 and the guide pin 33 are separated by a predetermined distance L, the movement engagement portion 34 starts to move to the right side in the drawing until it engages with the guide pin 33. It takes a certain amount of time. Thereby, the start of the movement of the shielding member 20 to the shielding position can be delayed for a predetermined time from the start of the movement of the charging body 3 to the standby position. That is, since the shielding member 20 waits for the charging body 3 to start moving to the standby position and then starts moving to the shielding position, interference with the charging body 3 can be avoided. In addition, the retracting position of the shielding member 20 can be disposed at a position close to or near the charging position of the charging body 3, and the apparatus can be made compact.

  Further, by changing the length of the distance L between the moving engagement portion 34 and the guide pin 33, the timing of starting the movement of the shielding member 20 to the shielding position can be adjusted. When the distance L is shortened, the start of movement of the shielding member 20 to the shielding position can be accelerated, and conversely, when the distance L is increased, the movement start of the shielding member 20 to the shielding position can be delayed. is there.

  In the above embodiment, the charging body 3 is rotated to move between the charging position and the standby position. Thereby, compared with the case where the charging body 3 is moved in parallel such as horizontal movement or vertical movement, the charging body 3 can be moved stably, and the reliability is improved. In addition, the configuration of the charged body moving means can be simplified, and the cost can be reduced and the space can be saved.

  When the shielding member 20 is disposed at the shielding position, there is a possibility that the shielding member 20 may come into contact with the surface of the photoreceptor 2 when vibration generated by the cover opening / closing operation of the image forming apparatus is transmitted to the shielding member 20. However, since at least a part of the shielding member 20 is formed of a soft member or a flexible member, it is possible to suppress or prevent the photoreceptor 2 from being damaged even when the shielding member 20 contacts the photoreceptor 2. it can. In addition, as shown in FIG. 5, the shielding member 20 disposed at the shielding position is inclined with respect to the tangent line X of the photosensitive member 2 in a direction away from the photosensitive member 2. It can be made difficult to contact the body 2.

  Moreover, it is preferable to start the movement of the shielding member 20 to the shielding position as soon as possible. Specifically, the configuration is such that the movement of the shielding member 20 to the shielding position is started before the charged body 3 reaches the standby position. Alternatively, the charging member 3 is moved so that at least a part of the shielding member 20 is interposed between the charging member 3 and the photosensitive member 2 before reaching the standby position. This can reduce the possibility that the shielding member 20 does not reach the shielding position even if the image forming apparatus is turned off immediately after the image formation is completed.

  The movement of the charging body 3 to the charging position is preferably started before the shielding member 20 reaches the retracted position. Thereby, the preparation time from the standby time of the charged body 3 to the start of image formation can be shortened.

  Further, after the image formation is completed, the charging member 3 is moved to the standby position and the shielding member 20 is moved to the shielding position in order to reduce the possibility that the charged product of the charging member 3 adheres to the photosensitive member 2. It is preferable to do as soon as possible. Therefore, for example, as shown in the timing chart shown in FIG. 6, when a stop signal for stopping the rotation (drive) during the image forming operation of the photosensitive member 2 is issued, the charging member 3 and the shielding member 20 are generated by the stop signal. It is desirable to drive the drive motor for the (gear member 25). As a result, when the instruction to stop the rotation of the photosensitive member 2 is given, or after the instruction is given and before the rotation of the photosensitive member 2 is stopped, the charging member 3 is moved to the standby position. The movement of the shielding member 20 to the shielding position can be started. Therefore, the movement of the charging body 3 to the standby position and the movement of the shielding member 20 to the shielding position can be completed at an early stage, and the possibility that the charged product of the charging body 3 adheres to the photoreceptor 2 is reduced. It is possible.

  Further, it is preferable that the time from when the start button for instructing the start of the image forming operation to be initially printed is as short as possible. Therefore, for example, as shown in the timing chart of FIG. 7, when an image forming condition such as the number of copies is input, a driving motor for the charging body 3 and the shielding member 20 (gear member 25) is input by the input signal. To drive. As a result, when the image forming condition is input, or after the image forming condition is input and before the start of the image forming operation is performed, the charging position of the charging body 3 is set. The movement and the movement of the shielding member 20 to the retracted position can be started. Therefore, the movement of the charged body 3 to the charging position and the movement of the shielding member 20 to the retracted position can be completed at an early stage, and the waiting time until the first printing is performed can be shortened.

  In general, in an image forming apparatus such as a copying machine, before starting an image forming operation, image forming preparation such as detecting a document placed on a document table by a document detection sensor or canceling a residual heat mode is performed. Operation is performed. For example, as shown in the timing chart of FIG. 8, when the above-described image formation preparation operation is performed, the charging body 3 and the shielding member 20 (gears) are based on a signal transmitted with the start of the preparation operation. The driving motor of the member 25) may be driven. As a result, when the image forming condition is input, or after the image forming condition is input and before the start of the image forming operation is performed, the charging position of the charging body 3 is set. The movement and the movement of the shielding member 20 to the retracted position can be started. Therefore, the movement of the charged body 3 to the charging position and the movement of the shielding member 20 to the retracted position can be completed at an early stage, and the waiting time until the first printing is performed can be shortened.

  In some cases, the image forming apparatus includes a human body detection sensor that detects the presence of a user approaching the periphery of the image forming apparatus. In this case, for example, as shown in the timing chart of FIG. 9, the driving motor for the charging body 3 and the shielding member 20 (the gear member 25) may be driven based on the detection signal of the body detection sensor. Thereby, when the human body detection sensor detects the presence of the user, or after the human body detection sensor detects the presence of the user and before the start of the image forming operation is performed, the charging of the charged body 3 is performed. The movement to the position and the movement of the shielding member 20 to the retracted position can be started. Therefore, the movement of the charged body 3 to the charging position and the movement of the shielding member 20 to the retracted position can be completed at an early stage, and the waiting time until the first printing is performed can be shortened. .

Hereinafter, the toner used in the image forming apparatus of the present invention will be described.
As the volume average particle diameter Dv of the toner is smaller, the fine line reproducibility can be improved. However, since the developing property and the cleaning property are lowered when the particle size is small, at least 3 μm is preferable. Further, if the particle size is less than 3 μm, the toner having a small particle diameter that is difficult to be developed on the surface of the carrier or the developing roller increases. This is not preferable because abnormal images such as fogging are formed.

  The particle size distribution represented by the ratio (Dv / Dn) of the volume average particle size Dv to the number average particle size Dn is preferably in the range of 1.00 to 1.40. By sharpening the particle size distribution, the toner charge amount distribution can be made uniform. When Dv / Dn exceeds 1.40, the toner charge amount distribution is wide and the amount of reversely chargeable toner increases, making it difficult to obtain a high-quality image. If Dv / Dn is less than 1.00, it is difficult to produce and it is not practical.

FIG. 10 is a diagram schematically illustrating the shape of the toner. FIG. 10A is a diagram for explaining the shape factor SF-1, and FIG. 10B is a diagram for explaining the shape factor SF-2. . The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-2 = {(PERI) ² / AREA} × (100π / 4) (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  It is assumed that the toner used in the image forming apparatus of the present invention has the shape factor SF-1 in the range of 100 to 180 and the shape factor SF-2 in the range of 100 to 180. When the values of the shape factors SF-1 and SF-2 approach 100, the shape of the toner becomes nearly spherical. When the toner has a substantially spherical shape, the contact state between the toner and the toner or the toner and the photosensitive member is a point contact, so that the attractive force between the toners becomes weak. Accordingly, the fluidity is increased, and the attracting force between the toner and the photoreceptor is weakened, and the transfer rate is increased. On the other hand, if any of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

The shape of the toner suitable for the image forming apparatus of the present invention is a substantially spherical shape and can be represented by the following shape definition.
11A to 11C schematically show the shape of the toner.
In FIG. 11, when a substantially spherical toner is defined by a major axis r1, a minor axis r2, and a thickness r3 (where r1 ≧ r2 ≧ r3), the toner of the present invention has a major axis and a minor axis. The ratio (r2 / r1) (see FIG. 11 (b)) is 0.5 to 1.0, and the ratio of thickness to minor axis (r3 / r2) (see FIG. 11 (c)) is 0.7 to 1.0. It is preferable to be in the range of 1.0. When the ratio of the major axis to the minor axis (r2 / r1) is less than 0.5, the dot reproducibility and transfer efficiency are inferior because of being away from the true spherical shape, and high quality image quality cannot be obtained. On the other hand, if the ratio of thickness to minor axis (r3 / r2) is less than 0.7, the shape is close to a flat shape, and a high transfer rate like a spherical toner cannot be obtained. In particular, when the ratio of the thickness to the minor axis (r3 / r2) is 1.0, the rotating body has a major axis as a rotation axis, and the fluidity of the toner can be improved.

  Further, as the toner, at least a polyester prepolymer having a functional group containing a nitrogen atom, a polyester, a toner material liquid in which a colorant and a release agent are dispersed in an organic solvent are crosslinked and / or in an aqueous medium. It is preferable to employ a toner obtained by an extension reaction. Thereby, a high quality image can be obtained.

Hereinafter, the constituent material and the manufacturing method of the toner will be described. However, it is not limited to the following constituent materials and manufacturing methods.
The toner is manufactured through a toner composition forming step, an emulsification step, an aging step, a solvent removal step, an alkali washing / water washing step, a drying step, and an external additive treatment step.

  In the toner composition forming step, for example, a toner raw material composed of a resin, a colorant, a wax, a charge control agent, and a polyester resin (prepolymer) having an isocyanate group is dissolved in an organic solvent such as ethyl acetate, and this is dissolved in the toner. It is set as a composition. The prepolymer is a polymer having two or more reactive groups in one molecule of the base polymer.

  In the emulsification step, the toner composition and amines are added to an aqueous medium containing a surfactant, a viscosity modifier, and resin fine particles, and dispersed by shearing force to form an emulsified state.

  In the aging step, the reaction system is heated in order to promote the elongation and / or crosslinking reaction due to the reaction between the isocyanate group and the amine.

  As an example of the solvent removal step, a method of gradually raising the temperature of the entire system and evaporating and removing the organic solvent in the droplets can be adopted.

  The alkali washing / water washing step is a step for removing foreign matters (surfactant, viscosity modifier, etc.) remaining on the surface of the obtained toner particles.

  In the drying step, the obtained toner particles are collected by filtration and dried.

  In the external additive treatment step, external additive particles (silica, titania, alumina, etc.) are externally added by a mixer in the range of 0.1 to 5.0 parts by weight, if necessary.

Hereinafter, an example of a method for producing toner used in the image forming apparatus of the present invention will be described. However, it is not limited to this manufacturing method.
In a reaction vessel equipped with a cooling pipe, a stirrer, and a nitrogen introduction pipe, 690 parts by weight of bisphenol A ethylene oxide 2-mol adduct and 256 parts by weight of terephthalic acid are placed, and polycondensed at 230 ° C. for 8 hours under normal pressure. Next, after reacting at a reduced pressure of 10 to 15 mmHg for 5 hours, the mixture is cooled to 160 ° C., 18 parts by weight of phthalic anhydride is added thereto and reacted for 2 hours to obtain an unmodified polyester.

  Further, in a reaction vessel equipped with a cooling pipe, a stirrer and a nitrogen introduction pipe, 800 parts by weight of bisphenol A ethylene oxide 2-mol adduct, 180 parts by weight of isophthalic acid, 60 parts by weight of terephthalic acid, and 2 parts by weight of dibutyltin oxide were added. The mixture is allowed to react at 230 ° C. for 8 hours under normal pressure. Furthermore, after reacting for 5 hours at a reduced pressure of 10 to 15 mmHg, the mixture is cooled to 160 ° C., and 32 parts by weight of phthalic anhydride is added thereto and reacted for 2 hours. Then, it cools to 80 degreeC and reacts with 170 weight part of isophorone diisocyanate in ethyl acetate for 2 hours, and an isocyanate group containing prepolymer is obtained.

  In addition, 30 parts by weight of isophoronediamine and 70 parts by weight of methyl ethyl ketone are charged into a reaction vessel equipped with a stir bar and a thermometer, and reacted at 50 ° C. for 5 hours to obtain a ketimine compound.

  In a beaker, 15.4 parts by weight of the prepolymer, 60 parts by weight of the polyester, and 78.6 parts by weight of ethyl acetate are stirred and dissolved. Next, 10 parts by weight of rice WAX (melting point 83 ° C.) as a release agent and 4 parts by weight of copper phthalocyanine blue pigment (cyan pigment) were added, and stirred at 12000 rpm with a TK homomixer at 60 ° C. to uniformly dissolve and disperse. Let Then, 2.7 parts by weight of the ketimine compound is added and dissolved. This is a toner material solution.

  In a beaker, 306 parts by weight of ion-exchanged water, 265 parts by weight of a 10% calcium phosphate suspension, 0.2 parts by weight of sodium dodecylbenzenesulfonate, and styrene / acrylic resin fine particles having an average particle diameter of 0.20 μm are placed uniformly. Dissolve. The temperature is raised to 60 ° C., and the toner material solution is added while stirring at 12000 rpm with a TK homomixer and stirred for 10 minutes. 500 g of this mixed solution is weighed and transferred to a Kolben equipped with a stir bar and a thermometer, heated to 45 ° C., and the solvent is removed over 0.5 hours while causing a urea reaction under reduced pressure. This is filtered, washed, and dried, followed by air classification to obtain a base resin.

  100 parts by weight of the base resin and 0.25 parts by weight of a charge control agent (Bontron E-84 manufactured by Orient Chemical Co., Ltd.) are introduced into a Q-type mixer (manufactured by Mitsui Mining Co., Ltd.). 2 cycles, 2 minutes of operation and 1 minute of rest for a total of 10 minutes. Further, 0.5 part by weight of hydrophobic silica (H2000, manufactured by Clariant Japan Co., Ltd.) is added, mixed for 30 seconds at a peripheral speed of 15 m / sec, and suspended for 1 minute for 5 cycles to obtain a cyan toner. Thereafter, 0.5 part by weight of hydrophobic silica and 0.5 part by weight of hydrophobic titanium oxide are mixed with 100 parts by weight of toner particles by a Henschel mixer to obtain the toner of the present invention.

  Further, by applying the following pigments in place of the “copper phthalocyanine blue pigment (cyan pigment) 4 parts by weight”, it is possible to produce toners of other colors. For example, in the case of yellow toner, 6 parts by weight of benzidine yellow pigment is applied. In the case of magenta toner, 6 parts by weight of rhodamine lake pigment is applied. In the case of black toner, 10 parts by weight of carbon black may be applied.

  The configuration of the present invention has been described by taking as an example the case where the configuration of the present invention is applied to a color image forming apparatus of a tandem type indirect transfer system having a plurality of photoconductors. The present invention can also be applied to an image forming apparatus, an intermediate transfer type color image forming apparatus having one photoconductor, or a direct transfer type monochrome image forming apparatus.

  Further, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

1 is an overall configuration diagram of an image forming apparatus of the present invention. FIG. 2 is an enlarged view of a main part of the image forming apparatus, and shows a state in which a charged body is disposed at a charging position and a shielding member is disposed at a retracted position. FIG. 2 is an enlarged view of a main part of the image forming apparatus, and shows a state in the middle of movement of a charged body and a shielding member. FIG. 2 is an enlarged view of a main part of the image forming apparatus, and shows a state in which a charged body is arranged at a standby position and a shielding member is arranged at a shielding position. It is a figure which shows the state which has arrange | positioned the said shielding member in the shielding position. It is a figure which shows an example of the timing chart for demonstrating the timing which starts the movement to the standby position of a charging body, and the movement to the shielding position of a shielding member. It is a figure which shows an example of the timing chart for demonstrating the timing which starts the movement to the charging position of a charging body, and the movement to the retracted position of a shielding member. It is a figure which shows the other example of the timing chart for demonstrating the timing which starts the movement to the charging position of a charging body, and the movement to the retracted position of a shielding member. It is a figure which shows another example of the timing chart for demonstrating the timing which starts the movement to the charging position of a charging body, and the movement to the retracted position of a shielding member. 4A and 4B are diagrams schematically illustrating the shape of a toner, where FIG. 5A is an explanatory diagram of a shape factor SF-1, and FIG. 5B is an explanatory diagram of a shape factor SF-2. 2A and 2B are schematic views illustrating an outer shape of the toner, in which FIG. 1A is an external view of the toner, and FIGS.

Explanation of symbols

1Y, 1C, 1M, 1Bk Process unit 2 Photoconductor 3 Charged body 20 Shield member 21 Support shaft 23 Moving member 26a Cam portion 28a Cam receiving portion 29 Guide mechanism 34 Moving engagement portion 36 Energizing means L Distance

Claims (22)

In an image forming apparatus provided with a charging member that is disposed in the vicinity of an image carrier and charges the image carrier by corona discharge,
Charged body moving means for moving the charged body between a charging position close to the image carrier and a standby position separated from the image carrier;
A shielding member for preventing the charged product generated on the charged body from adhering to the image carrier;
Shielding member moving means for moving the shielding member between a shielding position interposed between the charged body moved to the standby position and the image carrier and a retracted position retracted from the shielding position. An image forming apparatus.   The charging body is provided so as to be rotatable about a support shaft extending in the axial direction of the image carrier, and the charging body is rotated by the charging body moving means between the charging position and the standby position. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to be moved.   3. The charging body moving means includes a cam receiving portion provided on the charging body, and a cam portion that slides on the cam receiving portion to rotate the charging body between the charging position and the standby position. The image forming apparatus described in 1.   The shielding member moving means engages with a guide mechanism for guiding the shielding member between the shielding position and the retracted position, and an engaging portion provided on the shielding member, and moves the shielding member from the retracted position to the retracting position. The image forming apparatus according to claim 3, further comprising: a moving engagement portion that moves to a shielding position; and a biasing unit that biases the shielding member in a direction to move the shielding member to the retracted position. A cam portion of the charging body moving means and a moving engagement portion of the shielding member moving means are integrally disposed on a moving member that reciprocates between a first position and a second position;
When the moving member is moved to the first position, the cam portion is moved to a position corresponding to the charging position of the charging body, and the moving engagement portion is made to correspond to the retracted position of the shielding member. Configured to move to a position,
When the moving member is moved to the second position, the cam portion is moved to a position corresponding to the standby position of the charged body, and the moving engagement portion is made to correspond to the shielding position of the shielding member. The image forming apparatus according to claim 4, wherein the image forming apparatus is configured to be moved to a position. In a state where the moving member is disposed at the first position, the moving engagement portion is moved a predetermined distance from the engagement portion of the shielding member in a direction opposite to the direction in which the moving member is moved to the second position. Arranged at a distance of
When the moving member is moved from the first position to the second position, the movement engaging portion engages with the engaging portion of the shielding member, and thus the movement of the shielding member to the shielding position is started. The image forming apparatus according to claim 5, wherein the cam portion is delayed for a predetermined time from the start of movement of the charged body to the standby position when the cam portion is in sliding contact with the cam receiving portion.   The shielding member arranged at the shielding position is inclined with respect to the tangent at the intermediate point in the circumferential direction of the opposing surface of the image carrier facing the charged body arranged at the charging position in a direction away from the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.   8. The structure according to claim 1, wherein the charging member starts moving from the retracted position to the shielding position before the charging body reaches the standby position from the charging position. 9. Image forming apparatus.   Before the charged body reaches the standby position from the charging position, at least a part of the shielding member moved from the retracted position toward the shielding position is interposed between the image carrier and the charged body. The image forming apparatus according to claim 1, configured as described above.   10. The apparatus according to claim 1, wherein the charging member starts moving from the standby position to the charging position before the shielding member reaches the retracted position from the shielding position. 11. Image forming apparatus.   When the stop instruction for stopping the drive during the image forming operation of the image carrier is performed, or after the stop instruction is performed and before the drive of the image carrier is stopped, the charged body The movement from the charging position to the standby position is started, and the movement of the shielding member from the retracted position to the shielding position is started. Image forming apparatus.   When the image forming condition is input, or after the image forming condition is input and before the start of the image forming operation is performed, the charging position is changed from the standby position to the charged position. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to start moving to the retracted position from the shielding position of the shielding member.   When the image forming preparation operation is started or after the image forming preparation operation is started and before the image forming operation start instruction is given, the charged body is moved from the standby position to the charging position. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to start and move the shielding member from the shielding position to the retracted position. An image forming apparatus comprising a human body detection sensor for detecting the presence of a user, and configured to start an image forming preparation operation by a detection signal of the human body detection sensor,
When the human body detection sensor detects the presence of a user, or after the human body detection sensor detects the presence of a user and before an instruction to start an image forming operation is issued, the standby of the charged body is performed. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to start moving from a position to the charging position and start moving the shielding member from the shielding position to the retracted position. .   The image forming apparatus according to claim 1, wherein at least a part of the shielding member is formed of a soft member.   The image forming apparatus according to claim 1, wherein at least a part of the shielding member is formed of a flexible member.   The toner for forming a visible image on the image carrier has a volume average particle diameter in the range of 3 μm to 8 μm, and a ratio (Dv) of volume average particle diameter (Dv) to number average particle diameter (Dn). The image forming apparatus according to claim 1, wherein / Dn) is in a range of 1.00 to 1.40.   The toner for forming a visible image on the image carrier has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180. 17. The image forming apparatus according to any one of items 1 to 16.   Toner for forming a visible image on the image carrier, a toner material liquid in which at least a polyester prepolymer having a functional group containing a nitrogen atom, a polyester, a colorant, and a release agent are dispersed in an organic solvent The image forming apparatus according to claim 1, which is formed by crosslinking and / or elongation reaction in an aqueous medium.   The image forming apparatus according to claim 1, wherein the toner for forming a visible image on the image carrier is formed in a substantially spherical shape.   When the shape of the toner for forming a visible image on the image carrier is defined by a major axis r1, a minor axis r2, and a thickness r3 (provided that r1 ≧ r2 ≧ r3), the major axis r1 and the minor axis The ratio (r2 / r1) to r2 is in the range of 0.5 to 1.0, and the ratio (r3 / r2) of the thickness r3 to the minor axis r2 is in the range of 0.7 to 1.0. The image forming apparatus according to any one of claims 1 to 16. In a process unit integrally including at least the image carrier and the charged body,
A process unit configured to be detachable from the image forming apparatus according to any one of claims 1 to 21.

Images