JP2016070993A - Imaging device, image forming apparatus, and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that can stabilize image density while suppressing scattering of developer on the downstream side of a developing area, and an image forming apparatus and a process cartridge including the developing device.SOLUTION: There is provided a developing device 40 including a developing roller 45, a casing body 121 and a gap forming member 112 that have a developing roller 45 exposed from an opening 51, and a developing bias power source 141. A casing gap area in which the developing roller 45 on the downstream side in a surface movement direction of the developing roller 45 with respect to the developing area is in proximity with a developing casing is configured so that a developer carried on the developing roller 45 makes contact with an opposing surface of the developing casing. The gap forming member 112 in the developing casing is formed of a conductive material and includes an insulating layer 123 on an opposing surface of the gap forming member 112 in a portion with which the developer on the surface of the developing roller 45 makes contact in the casing gap area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a developing device, and an image forming apparatus and a process cartridge provided with the developing device.

  Conventionally, in a developing device, it is known that an air flow (hereinafter referred to as “suction air flow”) is generated toward the inside of the casing at the casing entrance where the surface of the developer carrying member exposed from the casing in the developing region returns to the inside of the casing. It has been.

  In general, it is composed of a casing for containing a developer, an agitating and conveying member for agitating and conveying the developer in the casing, a developer carrying member for carrying and conveying the developer in the casing on the surface, and the like. The developer carried on the surface of the developer carrying member is transported to the downstream side in the surface movement direction along with the surface movement of the developer carrying member, and passes through a region (developing region) facing the latent image carrying member. When the developer on the surface of the developer carrying member passes through the developing area, the developer is developed by attaching toner to the electrostatic latent image on the latent image carrying member, and then collected again in the casing.

  Patent Document 1 describes a developing device that sets a gap between a developer carrier and a casing at a casing inlet so that the developer carried on the developer carrier contacts the casing. In this developing device, the developer moves into the casing while being in contact with the casing, so that the sealability between the developer carrier and the casing is maintained and a suction air flow into the casing is generated.

  In the configuration in which the suction airflow is generated, the developer that has been released from the developer carrier in the vicinity of the development region can be collected in the suction airflow and can be collected in the casing, thereby suppressing the scattering of the developer. it can.

  Further, if there is a gap between the developer carried on the surface of the developer carrying member and the casing at the inlet of the casing, an air flow from the inside of the casing to the outside through the gap (hereinafter referred to as “discharge air flow”). ) Occurs. If the discharge airflow occurs, the developer in the casing may leak on the airflow, or the developer may get in the suction airflow and go into the casing, which may cause the developer to scatter. is there. On the other hand, in the configuration in which the developer carried on the surface of the developer carrier is in contact with the casing at the casing entrance, there is no gap between the developer carried on the surface of the developer carrier and the casing. Therefore, it is possible to prevent the discharge airflow from occurring. Thereby, scattering of the developer can be further suppressed.

  However, when the configuration in which the developer carried on the surface of the developer carrying member is in contact with the casing at the casing entrance portion, there is a problem that the image density is lowered when a solid image is output.

  In order to solve the above-mentioned problems, the invention of claim 1 is directed to a developing region facing a surface of a latent image carrier by carrying a two-component developer comprising a toner and a carrier on the surface and moving the surface. Forming a developer carrying body for transporting the developer and a developer containing section for containing the developer to be supplied to the surface of the developer carrying body, and the developer carrying body arranged in the surface moving direction in the surface moving direction; Development comprising: a developing casing provided with an opening for allowing a part of the surface of the developer carrying member to face the latent image carrying member; and a developing bias applying means for applying a developing bias to the developer carrying member. In the apparatus, a casing gap portion in which the surface of the developer carrying member on the downstream side in the surface movement direction of the developer carrying member with respect to the developing region and the opposed surface of the developing casing are close to each other is formed on the developer carrying member. Supported development Is set to be in contact with the opposite surface of the developing casing, and a portion of the developing casing that forms the casing gap portion is formed of a conductive material, and development on the surface of the developer carrier is performed in the casing gap portion. An insulating layer is provided on the opposing surface of the developing casing at a portion in contact with the agent.

  According to the present invention, there is an excellent effect that image density can be stabilized while suppressing scattering of the developer on the downstream side of the development region.

FIG. 3 is an enlarged view of the vicinity of the developing roller of the developing device according to the embodiment. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. The schematic block diagram of a liquid cooling device. FIG. 2 is an enlarged configuration diagram illustrating a developing device and a photoreceptor. The perspective view which looked at the image development apparatus from diagonally upward. FIG. 6 is a perspective view of a state where a developing roller upper cover is removed from the developing device illustrated in FIG. 5. FIG. 3 is a schematic diagram of a developer flow in a developing device. FIG. 5 is a cross-sectional view showing only a casing forming three developer transport paths that are developer accommodating portions in the developing device shown in FIG. 4. FIG. 5 is an enlarged sectional view in the vicinity of a casing gap region in the sectional view of the developing device shown in FIG. 4. FIG. 6 is a schematic diagram of the vicinity of a casing gap region when the casing gap in the developing device is wide and when the casing gap is narrow. Explanatory drawing of the remodeling machine of the developing apparatus used in Experimental example 2. FIG. FIG. 3 is an explanatory diagram of a developing device showing a location where a toner adhesion amount is measured. FIG. 6 is an explanatory diagram illustrating a state where toner adheres to a surface of a gap forming member facing a photoreceptor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a configuration diagram illustrating a schematic configuration of a copier 500 as an image forming apparatus to which the present invention can be applied.
A copying machine 500 shown in FIG. 2 has an image forming unit 1 in which four image forming units 11 (Y, M, C, K) are arranged in parallel. The image forming unit 11 (Y, M, C, K) includes a drum-shaped photosensitive member 18 (Y, M, C, K) serving as a latent image carrier, a drum cleaning unit 12 (Y, M, C, K), The charging unit 13 (Y, M, C, K), the developing device 40 (Y, M, C, K) and the like are housed in a frame (not shown). The developing device 40 (Y, M, C, K) is a two-component developing system that uses a two-component developer composed of toner and carrier.

  These image forming units 11 (Y, M, C, K) are detachable from the main body of the copying machine 500 so that consumable parts can be replaced at a time. Further, the developing device 40 of the present embodiment employs a two-component developing system for using a two-component developer composed of toner and carrier.

  Above the image forming unit 1, an exposure unit 9 is provided as a latent image forming unit. In addition, a reading device 10 that scans and reads a document placed on a contact glass is provided at the top of the device. Below the image forming unit 1, a transfer unit 2 including an intermediate transfer belt 15 as an intermediate transfer member is provided. The intermediate transfer belt 15 is stretched around a plurality of support rollers, and rotates in the clockwise direction in FIG. A secondary transfer device 4 is provided below the transfer unit 2.

  The secondary transfer device 4 includes a secondary transfer roller 17, and the secondary transfer roller 17 is applied from a front surface of the intermediate transfer belt 15 to a place where the intermediate transfer belt 15 is wound around the transfer counter roller 16. A secondary transfer nip is formed in contact therewith.

  A secondary transfer bias is applied to the secondary transfer roller 17 by a power source (not shown). The transfer counter roller 16 is electrically grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip. On the left side of the secondary transfer device 4 in FIG. 2, a fixing unit 7 for fixing the toner image transferred onto the paper is provided. The fixing unit 7 has a heating roller provided with a heating element inside.

  In addition, a conveyance belt 6 is provided between the secondary transfer device 4 and the fixing unit 7 to convey the sheet after transfer of the toner image to the fixing unit 7. In the lower right part of the copier 500 in FIG. 2, a paper feed unit 3 is provided that feeds paper fed separately from a paper feed storage unit (not shown) to the secondary transfer device 4. . In addition, a double-sided unit 5 is provided at the lower right portion of the copying machine 500 in FIG. Further, on the left side of the fixing unit 7 in FIG. 2, a paper discharge unit 8 that discharges the paper that has passed through the fixing unit 7 to the outside of the apparatus or conveys it to the duplex unit 5 is provided.

  When copying with the copying machine 500, the document is read by the reading device 10. In parallel with this document reading, the surface of the intermediate transfer belt 15 moves so as to rotate in the clockwise direction in FIG. At the same time, in the image forming unit 1, the surface of the photosensitive member 18 (Y, M, C, K) whose surface is charged by the charging unit 13 (Y, M, C, K) is based on the content of the document read. Exposure is performed by the exposure unit 9 using information for each color of yellow, magenta, cyan, and black. Thereby, a latent image is formed on the surface of each photoconductor 18 (Y, M, C, K).

  Next, the latent image on each photoconductor 18 (Y, M, C, K) is developed by the developing device 40 (Y, M, C, K) to form a single color toner image (a visible image). Then, the toner images on the photoconductors 18 (Y, M, C, K) are sequentially transferred onto the intermediate transfer belt 15 so as to overlap each other, thereby forming a composite toner image on the intermediate transfer belt 15.

  The photosensitive members 18 (Y, M, C, K) after the toner image transfer remain on the photosensitive members 18 (Y, M, C, K) by the drum cleaning unit 12 (Y, M, C, K). The residual toner is removed to prepare for another image formation.

  In parallel with such toner image formation, the paper is fed out one by one from a paper feed accommodating portion (not shown), and abutted against the resist roller pair 14 and stopped. Then, the registration roller pair 14 is rotated in synchronization with the formation of the synthetic toner image on the intermediate transfer belt 15, and the sheet is fed to the secondary transfer nip formed by the intermediate transfer belt 15 and the secondary transfer device 4. The toner image is transferred onto the paper by being transferred by the secondary transfer device 4. The sheet on which the toner image has been transferred is conveyed by the conveying belt 6 and sent to the fixing unit 7. The fixing unit 7 applies heat and pressure to fix the toner image, and then the sheet is sent to the paper discharge unit 8.

In the paper discharge unit 8, the paper transport destination is switched by a switching claw and guided to a paper discharge tray (not shown) outside the apparatus (on the left side of the apparatus) or the lower duplex unit 5. In the duplex unit 5, the sheet is reversed and guided again to the secondary transfer nip, and an image is recorded on the back side, and then the sheet is discharged onto the sheet discharge tray by the sheet discharge unit 8.
On the other hand, after the toner image is transferred at the secondary transfer nip, the residual toner remaining on the intermediate transfer belt 15 is removed by the intermediate transfer belt cleaning unit 90 to prepare for the image formation again.

  Here, in the copying machine 500, from the viewpoint of reducing the size of the machine, the arrangement is such that the fixing unit 7 is also pulled down to the lower side of the transfer unit 2 along with the higher density inside the machine. Therefore, in the copying machine 500, as shown in FIG. 2, the intermediate transfer belt 15 is bent so as to cover the upper surface and the right side surface of the fixing unit 7. With this configuration, the height direction and the width direction of the apparatus are made compact.

  However, if the fixing unit 7 is brought close to the intermediate transfer belt 15, the intermediate transfer belt 15 may be deformed due to thermal influence by the fixing unit 7 serving as a heating element, and image defects such as color misregistration may occur. . This has become more prominent due to an increase in the amount of heat generated inside the apparatus as the speed of the apparatus increases.

  Further, during double-sided printing, the paper heated by the fixing unit 7 passes through the double-sided unit 5 and again contacts the intermediate transfer belt 15 at the secondary transfer position. Therefore, the intermediate transfer belt is further transferred by heat transfer from the paper. The temperature of 15 rises and becomes a more severe condition. In addition, heat is transmitted to the photosensitive member 18 (Y, M, C, K) in contact with the intermediate transfer belt 15 and further to the developing device 40 (Y, M, C, K), and image defects due to belt deformation, In addition, problems such as solidification of toner are more likely to occur.

  Therefore, a heat insulating device 20 is provided between the fixing unit 7 that is a heat source and the intermediate transfer belt 15 that is disposed in the vicinity of the fixing unit 7. Although the heat insulating device 20 is often composed of an air flow by a duct, here, a heat insulating device using a heat pipe will be described. This is mainly composed of a heat receiving plate 21, a heat pipe 22, a heat radiating plate 23, a duct 24 and an exhaust fan (not shown).

  The heat receiving plate 21 that is a heat receiving member is formed of a material that easily absorbs heat, and is disposed between the fixing unit 7 that is a heat generation source and the transfer unit 2 that is a protection target portion to be protected from the influence of the heat. . The heat pipe 22 as a heat transfer means (heat transport means) is attached to the lower surface of the heat receiving plate 21, and one end portion (lower end portion) side thereof is a heat receiving portion. The other end side of the heat pipe 22 is a heat radiating portion, and is mounted on the heat radiating plate 23 at a position higher than the heat receiving portion. The heat radiating plate 23 that is a heat radiating member is formed of a material that easily releases heat, and a heat sink may be provided as necessary.

  In the copying machine 500 shown in FIG. 2, the duct 24 extends from the front surface to the back surface of the main body, and the heat radiating plate 23 is located inside the duct 24. An air inflow port is provided at the front side end of the duct 24, an exhaust port is provided at the back side end, and an exhaust fan (not shown) is provided at the exhaust port.

  The heat insulating device 20 configured as described above receives heat from the heat generating portion (the fixing unit 7 in this example) by the heat receiving plate 21, and the heat is transferred to the heat radiating portion (heat radiating plate 23) by the heat pipe 22 serving as heat transfer means. Transported up to. Then, heat is released from the heat radiating plate 23 in the duct 24, and the released heat is discharged outside the apparatus by an exhaust fan (not shown). Note that it is possible to perform natural cooling without providing an exhaust fan.

  In this way, the color due to the deformation of the intermediate transfer belt 15 is obtained by blocking the influence of the fixing heat and effectively protecting the image forming unit 11 (Y, M, C, K) and the transfer unit 2 to be protected. Prevents problems such as misalignment and problems due to toner solidification.

  Further, in each of the developing devices 40 (Y, M, C, K), when the developer agitating and conveying member that agitates and conveys the developer is driven, the friction caused by the friction between the developer agitating and conveying member and the developer is generated. The temperature in the developing device 40 is increased by heat or frictional heat generated by rubbing between the developers.

  Furthermore, the friction heat generated by the friction between the developer regulating member and the developer that regulates the layer thickness of the developer carried on the developer carrying body before the developer is conveyed to the developing region, and the developer regulating member. The temperature in the developing device 40 is raised by frictional heat due to rubbing between the developers at the time of regulation.

  When the temperature in the developing device 40 rises, the charge amount of the toner decreases, the toner adhesion amount increases, and a predetermined image density cannot be obtained. Further, the toner may melt due to the temperature rise and adhere to the developer regulating member, the developer carrying member, the photosensitive member, etc., and a streaky abnormal image may be generated in the image.

  In recent years, when a toner having a low melting temperature is used in order to reduce the fixing energy, an abnormal image or the like is likely to occur due to toner fixation. In addition, the development device 40 is likely to become hot due to the increase in printing speed.

  Therefore, the developing device 40 (Y, M, C, K) is a very important cooling part for achieving high image quality and high reliability. Conventionally, an air flow is generated around the developing device 40 by an air cooling fan or the like to cool the developing device 40 (Y, M, C, K), which is a temperature rise point, to the air of the developing device 40 (Y, M, C, K). The temperature is prevented from rising excessively.

  However, along with a demand for miniaturization, it is necessary to reduce a duct for forming a flow path around the developing device 40. If the duct becomes small, the flow rate of the gas flowing around the developing device 40 decreases, and the developing device 40 cannot be sufficiently cooled. Therefore, in the copying machine 500 of this embodiment, the developing device 40 (Y, M, C, K) is cooled by the liquid cooling device 30 shown in FIG.

  FIG. 3 is a schematic configuration diagram of the liquid cooling device 30. As shown in FIG. 3, the liquid cooling device 30 is pressed against the wall surface of the developing device 40 (Y, M, C, K), which is a temperature rise portion, and the cooling liquid is supplied to the developing device 40 (Y, M, C, K). ) Are provided with four heat receiving portions 32 (Y, M, C, K). Furthermore, the liquid cooling device 30 includes three cooling units 35 that cool the cooling liquid, a circulation pipe 34 that contains the cooling liquid, a cooling pump 31 that is a conveying means for circulating the cooling liquid in the circulation pipe 34, excess cooling A reserve tank 33 for storing the liquid is provided. Each cooling unit 35 includes a radiator 35b as a heat radiating unit, a cooling fan 35a, and the like.

  The heat receiving part 32 is provided with a flow path 32b inside a case 32a formed of a member having high thermal conductivity (see FIG. 4 described later). Usually, the case 32a of the heat receiving portion 32 is configured based on copper having a thermal conductivity of about 400 [W / mK] or aluminum of about 200 [W / mK]. Further, a material having higher thermal conductivity (for example, copper, silver, or gold) may be used.

  In addition, since the side surface of the developing device 40 is also made of aluminum in order to improve the thermal conductivity, if the heat receiving portion 32 is to be brought into close contact with the side surface of the developing device 40, an air layer is formed. If an air layer is formed, the efficiency of heat exchange falls.

  Therefore, in the present embodiment, a heat conductive sheet 130 (see FIG. 4) is attached to a surface (hereinafter referred to as a pressure contact surface) facing the developing device 40 of the heat receiving unit 32. The heat conductive sheet 130 is required to have high heat conductivity and at the same time, hardness (easiness to deform) that can crush the surface accuracy between the developing device 40 and the heat receiving unit 32. However, since the heat conductive sheet 130 is hard when it has high heat conductivity and soft when it has low heat conductivity, the heat conductive sheet 130 becomes hard to some extent in order to obtain high heat conductivity.

  Therefore, in the present embodiment, the heat receiving unit 32 is pressed with a large pressing force so that the heat receiving unit 32 is pressed against the side surface of the developing device 40. Thereby, even if the heat conductive sheet 130 that is hard to some extent is used, the heat conductive sheet 130 is deformed, and the surface accuracy between the developing device 40 and the heat receiving unit 32 is crushed. Thereby, it is possible to suppress the formation of an air layer between the developing device 40 and the heat receiving unit 32 and to conduct heat of the developing device 40 to the heat receiving unit satisfactorily. Further, the heat conductive sheet 130 may be attached to the side surface of the developing device 40.

  As shown in FIG. 3, each cooling unit 35 is a heat radiating unit that transfers and dissipates the cooling liquid through a housing (containing aluminum having high thermal conductivity) containing the cooling medium from the circulation pipe 34. A certain radiator 35b is provided. Then, forced air cooling by the cooling fan 35a or natural air cooling is performed in accordance with the amount of heat released from the radiator 35b. Moreover, the cooling part 35 may be one and may be four or more. Moreover, although the cooling fan 35a is provided for every cooling part 35, you may comprise so that external air may be supplied to the radiator 35b of the several cooling part 35 with one cooling fan 35a.

  By providing a plurality of cooling units 35, even if the cooling efficiency of each cooling unit 35 is low, it is possible to satisfactorily suppress the temperature rise of all the developing devices 40 (Y, M, C, K). As a result, a small radiator having a small heat radiation area and a very low cooling efficiency is used as compared with one cooling unit 35 that suppresses the temperature rise of all the developing devices 40 (Y, M, C, K). Thus, the cooling unit 35 can be reduced in size.

  The cooling pump 31 is a drive source that circulates the cooling liquid between the heat receiving section 32 (Y, M, C, K) and the cooling section 35, and circulates the cooling liquid as shown by arrows in FIG. The reserve tank 33 is a tank for storing a coolant. The coolant is a heat transport medium that transports heat received by the heat receiving unit 32 (Y, M, C, K) to the radiator 35b. The coolant is mainly composed of water, and propylene glycol or ethylene glycol is added to lower the freezing temperature, or a rust inhibitor (for example, phosphate-based material: potassium phosphate to prevent rusting of metal components). Salt, inorganic potassium salt, etc.).

  When the coolant is water, the constant heat capacity is 3000 times or more that of air, and a large amount of heat can be transferred with a small flow rate, so that cooling can be performed more efficiently than forced air cooling.

  FIG. 4 is an enlarged configuration diagram illustrating the developing device 40 and the photoconductor 18 included in one of the four image forming units 11 (Y, M, C, and K). The four image forming units 11 (Y, M, C, and K) have substantially the same configuration except that each of the handled toner colors is different. Therefore, the four image forming units 11 (Y, M, C, and K) are used in the drawings in FIG. The suffix “Y, M, C, K” indicating the color of the toner is omitted. 5 is a perspective view of the developing device 40 as viewed obliquely from above. FIG. 6 is a perspective view of the developing device 40 shown in FIG. 5 with the developing roller upper cover 220 removed.

  As shown in FIG. 4, the surface of the photosensitive member 18 is charged by a charging device (not shown) while rotating in the direction of arrow G in the drawing. An electrostatic latent image is formed on the surface of the charged photoreceptor 18 by the laser light emitted from the exposure unit 9. Thereafter, toner is supplied from the developing device 40 to the formed electrostatic latent image to form a toner image.

  The developing device 40 supplies the developer contained in the developer containing container formed by the casing body 121 and the like to the electrostatic latent image on the surface of the photoreceptor 18 while moving in the direction of arrow I in FIG. And a developing roller 45 as a developer carrier to be developed. The developing roller 45 includes a rotatable developing sleeve 45a, and a magnet roller 45b serving as a magnetic field generating unit having a plurality of magnetic poles is disposed therein.

  Further, the developing device 40 supplies a developer to the developing roller 45 and supplies a developer screw 48 as a supply conveying member that conveys the developer from the back side to the near side in FIG. 4 along the axial direction of the developing roller 45. have. Further, on the downstream side in the direction of surface movement of the developing roller 45 with respect to the facing portion between the surface of the developing roller 45 and the supply screw 48, the developer that regulates the developer supplied to the developing roller 45 to a thickness suitable for development. A doctor blade 42 is provided as an agent regulating means.

  On the downstream side in the surface movement direction of the developing roller 45 with respect to the developing area, which is the facing portion between the developing roller 45 and the photoreceptor 18, the developed developer that has passed through the developing area and separated from the surface of the developing roller 45 is collected. The collection conveyance path 47 faces the developing roller 45. The collection conveyance path 47 is a collection conveyance member for conveying the collected developer collected in the same direction as the supply screw 48 along the axial direction of the developing roller 45, and a screw-shaped collection screw 46 arranged parallel to the axial direction. I have. A supply conveyance path 49 in which the supply screw 48 is arranged is arranged in the lateral direction of the developing roller 45, and a collection conveyance path 47 in which the collection screw 46 is arranged is arranged in parallel below the developing roller 45.

  Note that the developer is detached from the developing roller 45 by setting the magnet roller 45b provided in the developing sleeve 45a described above to a state where there is no magnetic pole only at a position where it is desired to be separated. The developer can be separated and separated. Alternatively, a magnet roller 45b having a magnetic pole arrangement in which a repulsive magnetic field is formed at a location (separation portion) to be separated may be used.

  The developing device 40 is provided with a stirring conveyance path 44 in parallel with the collection conveyance path 47 below the supply conveyance path 49. In the stirring and conveying path 44, a screw-shaped stirring screw 43 that conveys the developer while stirring the developer along the axial direction of the developing roller 45 is disposed. The agitating screw 43 is an agitating and conveying member that conveys the developer in the agitating and conveying path 44 from the near side to the far side in FIG. 4, which is the opposite direction to the supply screw 48, and is arranged in parallel to the axial direction. ing. The stirring screw 43 has a helical stirring blade 43b fixed to a stirring shaft 43a.

The supply conveyance path 49 and the stirring conveyance path 44 are partitioned by a first partition wall 133 that is a partition wall. Of the portion of the first partition wall 133 that partitions the supply conveyance path 49 and the agitation conveyance path 44, both ends of the front end and the rear end in FIG. 4 are openings, and the supply conveyance The path 49 and the stirring and conveying path 44 communicate with each other.
The supply conveyance path 49 and the recovery conveyance path 47 are also partitioned by the first partition wall 133, but an opening is provided in a portion of the first partition wall 133 that partitions the supply conveyance path 49 and the recovery conveyance path 47. Not provided.

  In addition, the two developer conveyance paths of the stirring conveyance path 44 and the collection conveyance path 47 are partitioned by a second partition wall 134 as a partition member. The second partition wall 134 has an opening at the front side end in FIG. 4, and the stirring conveyance path 44 and the collection conveyance path 47 communicate with each other.

  The supply screw 48, the recovery screw 46, and the stirring screw 43, which are developer conveying members, are made of resin or metal screw members. The screw diameter of each screw member is φ22 [mm]. The screw pitch is a double winding of 50 [mm] for the supply screw, and a single winding of 25 [mm] for the recovery screw 46 and the stirring screw 43. The number of rotations is set to about 600 [rpm] for all screw members. Further, in the developing device 40 of the present embodiment, the total length of the agitation transport path 44 is 410 [mm], and the total length of the supply transport path 49 is 320 [mm].

  The developer on the developing roller 45 thinned by the doctor blade 42 made of a metal such as stainless steel disposed above the developing roller 45 is opposed to the photosensitive member 18 by the surface movement of the developing roller 45. It is transported to the development area and developed. The surface of the developing roller 45 is subjected to a V-groove forming process or a sand blasting process, and is made of a base tube of aluminum (Al) or stainless steel (SUS) having a diameter of 25 [mm]. The doctor gap, which is the gap between the developing roller 45 and the doctor blade 42, and the developing gap, which is the gap between the developing roller 45 and the photosensitive member 18, are both about 0.3 mm.

  The developer on the surface of the developing roller 45 after passing through the developing area is collected by the collecting and conveying path 47, conveyed to the front side of the cross section in FIG. 4, and the second partition wall 134 provided in the non-image area portion. The developer is transferred to the stirring and conveying path 44 through the opening.

  A toner concentration detection sensor (not shown) that detects the toner concentration of the developer is provided below the stirring conveyance path 44. Then, by operating a toner replenishing device (not shown) based on the detection result of the toner density detection sensor, the toner supply device is provided above the stirring conveyance path 44 in the vicinity of the opening of the second partition wall 134 in the stirring conveyance path 44. Toner is replenished from the toner replenishing port 201 to the agitation transport path 44.

  The casing main body 121 of the developing device 40 is formed of wall members that form the agitation conveyance path 44, the recovery conveyance path 47, the supply conveyance path 49, and the like. In addition, the casing body 121 is provided with an opening 51 for allowing a part of the surface of the developing roller 45 in the moving direction of the surface of the developing roller 45 disposed therein to face the photoreceptor 18.

FIG. 7 is a schematic diagram of the flow of the developer in the developing device 40, and each arrow in FIG. 7 indicates the moving direction of the developer.
In the supply conveyance path 49 that receives the developer supplied from the agitation conveyance path 44, the developer is conveyed downstream in the developer conveyance direction of the supply screw 48 while supplying the developer to the developing roller 45. The surplus developer that has been transported to the downstream end of the supply transport path 49 without being supplied to the developing roller 45 is supplied to the stirring transport path 44 from the surplus opening 92 of the first partition wall 133. (Arrow E in FIG. 7).

  On the other hand, the developer supplied to the developing roller 45 is used for development in the developing region, and then separated / separated from the developing roller 45 and transferred to the collection conveyance path 47. The collected developer transferred from the developing roller 45 to the collection conveyance path 47 and conveyed to the downstream end of the collection conveyance path 47 in the developer conveyance direction by the collection screw 46 is agitated from the collection opening 93 of the second partition wall 134. It is supplied to the conveyance path 44 (arrow F in FIG. 7).

  In the agitation conveyance path 44, the supplied surplus developer and recovered developer are conveyed while being agitated by the agitation screw 43, and are supplied to the supply conveyance path 49 from the supply opening 91 of the first partition wall 133 (FIG. 7). Middle arrow D).

  In the agitation transport path 44, the collected developer, the surplus developer, and the toner replenished from the toner replenishing port 201 as necessary by the transfer unit are fed into the recovery transport path 47 and the supply transport path 49 by the stirring screw 43. Agitated and conveyed in the opposite direction to the developer. Then, the agitated developer is transferred to the upstream side in the developer conveyance direction of the supply conveyance path 49 communicated by the supply opening 91 on the downstream side in the developer conveyance direction.

  In the developing device 40 shown in FIG. 7, a supply conveyance path 49 and a collection conveyance path 47 are provided, and developer supply and collection are performed in different developer conveyance paths, so that the developed developer is supplied to the supply conveyance path 49. There is no contamination. For this reason, it is possible to prevent the toner concentration of the developer supplied to the developing roller 45 from decreasing toward the downstream side of the supply conveyance path 49 in the developer conveyance direction.

  In addition, since the recovery conveyance path 47 and the agitation conveyance path 44 are provided, and the developer recovery and agitation are performed in different developer conveyance paths, the developed developer does not fall during the agitation. Thereby, since the sufficiently stirred developer is supplied to the supply conveyance path 49, it is possible to prevent the developer supplied to the supply conveyance path 49 from being insufficiently stirred. In this way, the toner density of the developer in the supply conveyance path 49 can be prevented from decreasing, and the developer in the supply conveyance path 49 can be prevented from being insufficiently stirred, so the image density during development can be reduced. Can be constant.

In the developing device 40, the developer carried on the developing roller 45 and passed through the developing region is transported by the recovery screw 46 and the stirring screw 43, and the supply transport path on the upper stage from the stirring transport path 44 in which the stirring screw 43 is disposed. To 49.
As shown in FIG. 7, the movement of the developer from the lower stage to the upper stage of the developing device 40 is only the arrow D. The movement of the developer indicated by an arrow D is to push the developer downstream of the agitation transport path 44 by the rotation of the agitation screw 43, so that the developer is raised and supplied to the supply transport path 49. .

  In the developing device 40, a fin member may be provided on the shaft of the stirring screw 43 in the vicinity of the downstream end of the developer transport path of the stirring transport path 44 where the stirring transport path 44 and the supply transport path 49 communicate with each other. good. This fin member is a plate-like member constituted by a side parallel to the axial direction of the stirring screw 43 and a side perpendicular to the axial direction of the stirring screw 43. By scooping up the developer with this fin member, it is possible to more efficiently deliver the developer from the stirring conveyance path 44 to the supply conveyance path 49.

  Further, a developer discharge port (not shown) is formed in the vicinity of the upstream end in the transport direction (end in the axial direction) of the supply transport path 49 so that the supply transport path 49 and the discharge transport path 41 communicate with each other. To do. When the amount of the developer reaching the upstream end of the supply conveyance path 49 exceeds a predetermined amount, the developer reaches the height of the developer discharge port, passes through the developer discharge port, and goes to the discharge conveyance path 41. And the developer is handed over.

  The developer delivered to the discharge conveyance path 41 is collected by a discharge developer collecting unit (not shown) provided outside the developing device 40 by a discharge screw 41a. By providing the configuration for discharging the developer as described above, the amount of the developer in the developing device 40 can be kept constant.

  Further, when a premix toner containing a carrier is replenished as the toner to be replenished to the developing device 40, the deteriorated carrier is discharged together with the toner to the discharge conveyance path 41, and the carrier is replaced. The deterioration of the agent can be suppressed.

  FIG. 8 is a cross-sectional view showing only the casing main body 121 that forms three developer transport paths that are developer accommodating portions of the developing device 40 shown in FIG.

  As shown in FIGS. 4, 5, and 6, the developing device 40 includes a casing main body 121, a transport path upper cover 230, a developing roller upper cover 220, a rear end side plate 250, and a front end. The side plate 240 forms a developing casing that houses the developer. This developing casing is a developer container.

  The developing device 40 includes three developer conveying screws for stirring and conveying the developer in the three developer conveying paths formed by the developing casing. Further, a developing roller 45 that carries the developer supplied from the supply conveyance path 49 out of the three developer conveyance paths and conveys the developer to the development area that is the closest to the photoreceptor 18 is provided. Further, when the developing roller 45 carries and conveys the developer, the doctor is a developer regulating member for uniformly regulating and leveling the layer thickness of the developer on the developing roller 45 in the longitudinal direction (axial direction). A blade 42 is provided.

  A magnet roller 45b is provided inside the developing sleeve 45a constituting the developing roller 45, and the developer can be carried by the magnetic force of the magnet roller 45b. In addition, the magnetic carrier and the toner are charged with opposite polarities by being agitated, and are adhered to each other by the electrostatic force due to this charging. A magnetic carrier is carried on the surface of the developing roller 45 by magnetic force, and toner adheres to the magnetic carrier by electrostatic force, whereby a magnetic brush-like developer layer is formed on the surface of the developing roller 45.

  The developer layer carried on the developing roller 45 and uniformly leveled by the doctor blade 42 is conveyed to the developing area as the surface of the developing roller 45 moves. The toner moves onto the photoconductor 18 and is developed by an electric field (development electric field) generated by a potential difference between the developing roller 45 to which the developing bias is applied and the surface of the photoconductor 18 on which the electrostatic latent image is formed. The

  After that, the developer that has passed through the development area is collected again in the developer conveyance path formed by the development casing, and new toner is supplied from the toner replenishing port 201 while circulating in the developer conveyance path. And used again for development.

  As described above, when the electrostatic latent image on the photoconductor 18 is developed with toner by the developing device 40, a toner image corresponding to the electrostatic latent image is formed on the photoconductor 18. This toner image is transferred to an intermediate transfer belt 15 provided in the transfer unit 2 as an intermediate transfer device, and then transferred onto a print medium such as paper by the secondary transfer device 4. Then, an image is formed on the print medium by passing through a fixing device 25 that melts and fixes the toner by applying heat or pressure to the toner image transferred onto the print medium.

  The developing casing of the developing device 40 has a length in the longitudinal direction (axial direction) that is equal to or greater than the printing width on the printing medium. The casing main body 121, which is a part of the developing casing, is recovered by a supply conveyance path 49 that supplies the developer to the developing roller 45, a collection conveyance path 47 that collects and conveys the developer used for development, and a collected conveyance path 47. An agitation conveyance path 44 for agitating the developer and newly supplied toner is formed.

  As shown in FIGS. 5 and 6, the rear side end side plate 250 and the front side end side plate 240, which are a part of the developing casing, are axially opposite ends of the casing body 121, the developing roller 45, and the three developers. It is a member which supports the both ends of the rotating shaft of a conveyance screw. Further, the transport path upper cover 230 is a member that is fixed to the casing body 121 so as to cover the upper portion of the casing body 121 to form a supply transport path 49 and to which the doctor blade 42 is fixed. The developing roller upper cover 220 is a member that covers the surface of the developing roller 45 closer to the developing region than the doctor blade 42.

  With respect to the casing main body 121, the supply conveyance path 49, the recovery conveyance path 47, and the agitation conveyance path 44 described above need to be partitioned in spaces other than the openings that deliver the developer therebetween. Considering that the length of the developer transport path is equal to or greater than the width of the printing medium, for example, in the case of the developing device 40 used in the image forming apparatus for A3 size paper, the axial direction of the casing body 121 The length of 297 is required to be 297 [mm] or longer.

  Thus, the casing main body 121 is a member having a certain size in the axial direction, and needs to have the same cross-sectional shape (the cross-sectional shape shown in FIG. 8) in the axial direction. Furthermore, in the developing device 40 of the present embodiment, a portion that becomes the stirring conveyance path 44 that is one of the three developer conveyance paths has a cylindrical shape that is surrounded by a wall surface to accommodate the developer. It has a shape. It is difficult to produce the casing body 121 having such a shape as a single injection molded product of a general plastic material.

  It is also conceivable to produce the shape of the casing main body 121 described above by welding two parts of a plastic molded product to a shape that is difficult to produce by a single product. However, the following problems may occur in a high-speed high-speed machine with a high speed and high image quality that exceeds 60 sheets of A4 size paper output per minute.

  That is, in such a high-end machine, it is necessary to store 400 to 800 [g] of two-component developer in one developing device 40. When the casing main body 121 containing this amount of developer is made of plastic, the charge of the charged developer charges up the casing main body 121, which may cause a problem on the image.

  For example, there is a case where toner circulating inside is attracted by charging up of the casing main body 121 itself to cause the toner to adhere to the wall surface. If the adhered toner is peeled off and used for development, abnormal images such as black spots or white spots on the image are generated.

  Further, in the configuration in which the intermediate transfer belt 15 is positioned below the developing device 40 as in the copying machine 500, the charged casing body 121 is between the toner image transferred onto the intermediate transfer belt 15. There is a risk of electrical force working. When such an electric force is applied, an electrical phenomenon such as electric discharge occurs, which may disturb the toner increase and appear as dust or blur on the image.

  As a configuration for preventing such a problem, in the developing device 40 of this embodiment, an extruded aluminum material is used as the material of the casing main body 121. By using the extruded material, a casing body 121 having a cylindrical portion having a certain length can be manufactured having the same cross-sectional shape in the longitudinal direction. Further, a metal material such as aluminum is used as the material of the casing main body 121, which is electrically connected to the copying machine 500 main body and electrically grounded, whereby the casing main body 121 is charged up. It is possible to prevent the occurrence of malfunctions.

  Further, by making the casing body 121 from a metal such as aluminum, the heat of the developer can be efficiently transmitted to the heat receiving part 32 of the liquid cooling device 30 via the casing body 121.

  In the developing area of the developing device 40, the surface of the developing roller 45 is exposed outside the developing casing, and the developer carried on the surface of the developing roller 45 is temporarily conveyed to the outside of the developing device 40. Become. The developer is carried on the surface of the developing roller 45 by magnetic force and electrostatic force, and is collected again in the developing device 40 after passing through the developing region. However, since the developing sleeve 45a of the developing roller 45 is rotating, it is inevitable that a part of the developer (weakly charged toner) on the surface of the developing roller 45 is released and scattered by the centrifugal force. is there.

  If the amount of developer scattered in this way increases, it may cause dirt inside and outside the copier 500, or may cause failure of other parts in the copier 500. Further, if the scattered developer accumulates around the area indicated by “α” in FIG. 4 on the downstream side in the rotation direction of the developing sleeve 45a with respect to the developing area in the developing device 40, it falls on the image. This causes abnormal images such as black spots and white spots.

In order to suppress the scattering of the developer as much as possible, the developer that has passed through the developing region is collected in the developing device 40 on the downstream side in the rotation direction of the developing sleeve 45a with respect to the developing region. It is effective to generate an airflow that goes. This air flow causes the developing roller 45 and the developing casing to face each other with a predetermined gap in a predetermined range so as to face each other, and the developer conveyed while rotating together with the developing sleeve 45a together with the air in the developing device 40. It occurs when heading to.
By generating such an air flow, the developer that has been released from the holding force of the developing roller 45 is also carried on the air flow toward the inside of the developing device 40, so that the developing device is not scattered outside the developing device 40. It becomes possible to collect within 40.

At this time, in order to optimize the airflow for suppressing the scattering of the developer, the surface of the developing sleeve 45a that has passed through the developing region is the closest portion between the developing casing and the developing roller 45 where the surface enters the developing casing. A certain casing gap area needs to be optimally designed.
The above-described airflow toward the developing device 40 (hereinafter referred to as “suction airflow”) is generated by the movement of the magnetic brush of the developer held and conveyed by the developing roller 45. However, if the space between the developing roller 45 and the developing casing is too wide, a suction airflow cannot be generated in the entire casing gap region, and the effect of suppressing the scattering of the developer cannot be sufficiently obtained.

This is due to the following reason. That is, if the space between the developing roller 45 and the developing casing is too wide, a gap is generated between the tip of the magnetic brush and the developing casing. Due to the movement of the developer, an air flow in the same direction as the movement direction of the developer is generated in the vicinity of the surface of the magnetic brush, and the pressure inside the developing device 40 is increased by this air flow. At this time, if there is a gap between the tip of the magnetic brush and the developing casing, the increased pressure escapes from the gap between the magnetic brush and the developing casing. Therefore, if the space between the developing roller 45 and the developing casing is too wide, a suction airflow cannot be generated in the entire casing gap region, and the effect of suppressing the scattering of the developer cannot be sufficiently obtained.
For this reason, it is desirable that the developer magnetic brush and the developing casing are in contact with each other in order to obtain the effect of suppressing the scattering of the developer by the suction airflow.

  On the other hand, if the gap in the casing gap region is too narrow, the entire amount of developer conveyed cannot pass through the casing gap region, and the developer overflows on the downstream side in the surface movement direction of the developing sleeve 45a with respect to the developing region. The circulation of is no longer established.

  Accordingly, the gap in the casing gap region is within a range in which the developer magnetic brush and the developing casing can be in contact with each other while ensuring a minimum width that does not hinder the circulation of the developer, and according to various conditions of the developing device 40. It is required to design optimally. In the range in which the magnetic brush and the developing casing can contact, the optimum casing gap varies depending on the characteristics of the developer used, the number of rotations of the developing sleeve 45a, and the internal configuration of the developing device 40. Therefore, it is desirable to tune the optimum gap value and the casing gap region shape in the configuration of the developing device 40.

  At this time, when considering the mass productivity of the product, the casing gap area has a certain length or more in the longitudinal direction (axial direction), so the gap size in the casing gap area is guaranteed with high accuracy in all mass production machines. It is difficult to do. When the inventors conducted an evaluation experiment using a development device of “ProC750” manufactured by Ricoh Co., Ltd., by adjusting the gap of the casing gap region to a range of 0.7 to 0.8 [mm], The result was that the amount of developer scattering could be reduced most.

However, if the casing gap region is formed by the casing body 121, which is an aluminum extrusion material, and the surface of the developing roller 45, it is difficult to ensure that the adjustment range of the gap is ± 0.05 [mm]. It is. This is due to the following reason. That is, both ends of the developing roller 45 in the axial direction are held by the back side end side plate 250 and the front side end side plate 240, and the casing body 121 is also held by these two end side plates. Therefore, the accuracy of the gap in the casing gap region is determined by the accumulation of the dimensional tolerance between the developing roller 45 and the two end side plates and the dimensional tolerance between the two end side plates and the casing main body 121. Since dimensional tolerances accumulate in this way, it is difficult to ensure that the adjustment range of the gap is ± 0.05 [mm].
Further, in the developing device 40 of the present embodiment, an aluminum extruded material is used for the casing main body 121, but there is a problem that it is difficult to determine the dimensions of the aluminum extruded material in terms of processing accuracy.

  As a configuration in which the gap in the casing gap region is set to a desired range, a configuration in which the assembly position of the casing main body 121 with respect to the back side end side plate 250 and the front side end side plate 240 can be adjusted is conceivable. In this configuration, the casing body 121 can be moved in one direction with respect to the rear end side plate 250 and the front end side plate 240 holding the developing roller 45. Then, the accuracy of the gap in the casing gap region is guaranteed by assembling and fixing the size of the gap in the casing gap region, which is the closest part to the developing roller 45, by a predetermined abutting method. is there.

  However, in this configuration, it is required that the casing main body 121, which is a main member that forms the developer accommodating portion, be movable with respect to the rear side end side plate 250 and the front side end side plate 240 of the developing device 40. . On the other hand, the rear end side plate 250 and the front end side plate 240 hold a developer conveying screw in addition to the developing roller 45. For this reason, when positioning the casing main body 121 with priority given only to the dimension of the gap in the casing gap region, the clearance between the inner wall surface of the casing main body 121 and the outer peripheral portion of the developer conveying screw is ensured with the required accuracy. Difficult to do.

If the clearance is too wide, the circulation of the developer in the developing device 40 is deteriorated, the uniformity of the toner density is impaired, and the image density becomes unstable. Further, the developer staying in the developing device 40 aggregates or adheres, and when such developer is peeled off and used for development, an abnormal image such as black spots or gaps on the image appears.
On the other hand, when the clearance is too narrow, the developer is sandwiched between the rotating developer conveying screw and the inner wall surface of the casing main body 121 and is pressurized, thereby causing aggregation and fixation. Further, when there is no clearance at all, that is, when the developer conveying screw comes into contact with the inner wall surface of the casing main body 121, the rotating developer conveying screw rubs the inner wall surface of the casing main body 121 and causes various damage such as damage. It is self-evident to cause a malfunction.

In this configuration, the positional relationship between the casing main body 121, which is a main member forming the developer accommodating portion, and the rear side end side plate 250 and the front side end side plate 240 is determined as follows. That is, it is determined only by screwing after adjusting the dimension of the gap in the casing gap region, not the positioning reference. This causes a problem that the relative positional relationship between the rear end side plate 250 and the front end side plate 240 is slightly different for each developing device 40. As a result, axial misalignment of the bearing members at both ends in the axial direction that supports the developing sleeve 45a and the developer conveying screw occurs, causing problems such as an increase in load torque at the bearing portion and toner fixation due to heat generation.
In particular, as energy savings are demanded in recent image forming apparatuses, in order to reduce the amount of heat necessary for the fixing process that consumes the most energy in the image forming apparatuses, the melting point of toner is being lowered. As a result, if heat is generated at the bearing portion of the developing device 40, toner aggregation and sticking are likely to occur. Therefore, it is required to suppress the load torque at the bearing portion as much as possible.

  In the developing device 40 of the present embodiment, as illustrated in FIG. 4, a gap between the casing main body 121 and the developing sleeve 45 a is formed in a portion where the surface of the developing sleeve 45 a that has passed through the developing region enters the inside of the casing main body 121. A gap forming member 112 for adjusting the size is provided. The gap forming member 112 is made of aluminum like the casing main body 121, but is a separate member from the casing main body 121, and the assembly position with respect to the casing main body 121 can be arbitrarily adjusted within a predetermined range. By this adjustment, it is possible to arbitrarily adjust the width of the gap in the casing gap region where the surface of the developing sleeve 45a that has passed through the developing region enters the inside of the casing main body 121. Further, by replacing the gap forming member 112 with a different shape, the facing surface on the developing casing side facing the developing roller 45 in the casing gap region can be arbitrarily adjusted.

  FIG. 9 is an enlarged sectional view of the vicinity of the casing gap region in the sectional view of the developing device 40 shown in FIG. The gap forming member 112 is a separate member from the casing main body 121 and is configured to fix the gap forming member 112 to the gap forming member fixing portion 113 that is a part of the casing main body 121. As shown in FIG. 9, the surface of the gap forming member 112 that faces the developing roller 45 is a curved surface that follows the surface of the developing roller 45. In the vicinity of the casing gap region, the surface of the developing sleeve 45a moves as indicated by an arrow A in FIG. 9, and the surface moves toward the inside from the outside of the casing body 121.

  The gap forming member 112 is configured to be movable in the direction toward the center of the developing roller 45 along the slope of the gap forming member fixing portion 113. Then, the casing gap G1 that is a gap between the gap forming member 112 and the developing roller 45 is adjusted to a predetermined value (0.75 mm in this embodiment). After this adjustment, the gap forming member 112 is fixed to the gap forming member fixing portion 113 by gap adjusting screws 501 that are screw members at three positions in the axial direction.

Further, if the head of the gap adjusting screw 501 made of a metal magnetic material such as iron is exposed, the gap adjusting screw 501 may be magnetized and the carrier may adhere. If the carrier adheres to the head of the gap adjusting screw 501 located on the surface of the gap forming member 112 facing the photoreceptor 18, the surface of the photoreceptor 18 may be damaged.
In the developing device 40, an inlet seal 50 that functions as a cover member is provided so as to cover the head of the gap adjusting screw 501 on the surface of the gap forming member 112 that faces the photoreceptor 18. Thereby, it is possible to prevent the carrier from adhering to the surface of the gap forming member 112 facing the photoreceptor 18.

In order to suppress problems due to toner scattering even when the developer is lowly charged in a high temperature and high humidity environment or the like, the gap in the casing gap region is reduced (narrowed), and a sufficient air flow into the developing device 40 is provided. It is necessary to secure.
However, as described above, the gap forming member 112 and the casing main body 121 are made of aluminum, and the gap forming member 112 fixed to the casing main body 121 is grounded via the casing main body 121. For this reason, there is a potential difference between the developing roller 45 to which the developing bias is applied and the gap forming member 112, and an electric field is formed in which the toner moves from the developing roller 45 side to the gap forming member 112 side. When the gap in the casing gap region is made small so as to secure a sufficient suction airflow, the toner contained in the developer carried on the surface of the developing roller 45 is electrostatically attached to the gap forming member 112. Sometimes occurred.

  In the developing device 40, a developing bias is applied to the developing roller 45, and toner is applied to the photosensitive member 18 by a potential difference from the electrostatic latent image on the photosensitive member 18 for development. In the conventional developing device, the casing gap is set wider than the developing gap, which is the gap between the developing roller 45 and the photoconductor 18, so that the toner adheres electrostatically to the gap forming member 112 in a normal environment. The phenomenon is unlikely to occur. However, when the casing gap is narrow as in the developing device 40 of the present embodiment or when the developing bias is high, the toner concentration of the developer is decreased under a high temperature and high humidity environment, and the resistance of the developer is decreased. In some cases, toner adheres electrostatically to the gap forming member 112.

  A separation portion where the magnetic force of the magnet roller 45 b hardly acts on the surface of the developing roller 45 is provided at a position facing the collection conveyance path 47 on the downstream side in the surface movement direction of the developing roller 45 with respect to the casing gap region. . Normally, the developer is collected in the collection chamber by separating the developer from the developing roller 45 in this separation section. However, when toner (toner charged in negative polarity in this embodiment) electrostatically adheres to the gap forming member 112, the developer (carrier) carried on the surface of the developing roller 45 is counter-charged (this embodiment). Then, a positive polarity charge) is generated.

  The developer in which the counter charge has occurred has an increased electrostatic adhesion to the developing roller 45, making it difficult for the developing roller 45 to be separated at the separation portion. As a result, the developer whose toner has been consumed when it passes through the development area reaches the supply section as it is, and is transported to the development area again together with the developer pumped up from the supply transport path 49 by the supply section. As a result, the developer having a lowered toner density is supplied to the development area, and the image density is lowered.

  FIG. 10 is a schematic diagram of the vicinity of the casing gap region when the casing gap G1 in the developing device 40 is wide and when it is narrow. FIG. 10A is an explanatory diagram showing that the casing gap G1 is wide, and FIG. 10B is an explanatory diagram showing that the casing gap G1 is narrow.

  FIG. 10A shows a case where the casing gap is wide enough that the toner T contained in the developer carried on the surface of the developing roller 45 does not electrostatically adhere to the gap forming member 112. In this case, the developer composed of the toner T and the carrier C is separated from the developing roller 45 at the separation portion where the magnetic force acting on the surface of the developing roller 45 becomes small, and moves into the collection conveyance path 47.

On the other hand, FIG. 10B shows a case where the casing gap is so narrow that the toner T contained in the developer carried on the surface of the developing roller 45 is electrostatically attached to the gap forming member 112.
In the developing device 40, since the developing casing including the gap forming member 112 is grounded, an electric field for electrostatically moving the toner T from the developing roller 45 side to the gap forming member 112 side is formed. For this reason, as shown in FIG. 10, when the casing gap G <b> 1 is narrow, a large amount of toner T is electrostatically attached to the gap forming member 112 in the casing gap region.

  The developer (carrier C) from which the toner T has moved to the gap forming member 112 side is charged with a positive polarity, and has an electrostatic adhesion force to the developing roller 45 to which a negative polarity developing bias is applied. Becomes larger. As a result, even when the magnetic force acting on the surface of the developing roller 45 reaches a separating portion where the magnetic force is small, the developer is not separated from the developing roller 45 and is re-pumped as it is into the developing region. Hereinafter, this phenomenon is referred to as “developer accompanying the developer”. When the developer is accompanied, the image density is lowered as described above.

FIG. 1 is an enlarged view of the vicinity of the developing roller 45 of the developing device 40 according to the embodiment.
As shown in FIG. 1, the developing device 40 includes a developing roller 45 that conveys the developer to a developing region facing the surface of the photoreceptor 18 by carrying the developer on the surface and moving the surface. Further, it is composed of a casing main body 121 and a gap forming member 112 which form a developer accommodating portion such as a supply conveyance path 49 that accommodates the developer supplied to the surface of the developing roller 45, a collection conveyance path 47, and a stirring conveyance path 44. A developing casing. Further, a developing bias power supply 141 that is a developing bias applying unit that applies a developing bias to the developing roller 45 is provided.

  Further, as shown in FIG. 1, the developing device 40 is configured such that the developer carried on the developing roller 45 forms a developing casing in the casing gap region downstream of the developing region in the surface movement direction of the developing roller 45. The opposing surface of the forming member 112 is contacted. Further, the casing main body 121 and the gap forming member 112 are formed of a conductive material, aluminum, and include an insulating layer 123 at a portion of the surface of the gap forming member 112 that contacts the developer on the surface of the developing roller 45.

  As shown in FIG. 1, when the insulating layer 123 was provided, the occurrence of a decrease in image density could be suppressed. Further, at this time, toner adhesion to the gap forming member 112 is suppressed, and the occurrence of the accompanying developer can be suppressed. In the configuration in which the insulating layer 123 is provided, the casing gap G <b> 1 is set to have the same value by moving the gap forming member 112 away from the surface of the developing roller 45 by the thickness of the insulating layer 123.

The reason why the decrease in image density can be suppressed by providing the insulating layer 123 is considered to be as follows.
That is, by separating the gap forming member 112 from the surface of the developing roller 45 by the layer thickness of the insulating layer 123, the distance between the surface of the developing roller 45 and the gap forming member 112 made of a conductive material is equal to the layer thickness of the insulating layer 123. Just get far away. Even if the potential difference between the two electrodes is the same, the electric field becomes weaker as the distance increases. Therefore, by providing the insulating layer 123, the electric field becomes weaker, and the electrostatic force moves the toner toward the gap forming member 112. Power is weakened. As a result, electrostatic toner adhesion to the gap forming member 112 is suppressed, occurrence of counter-charge in the developer carried on the developing roller 45 is also suppressed, and electrostatic attachment of the developer to the developing roller 45 is suppressed. An increase in wearing force is suppressed. Therefore, the separation of the developer from the developing roller 45 in the separation unit is promoted, the occurrence of the accompanying developer is suppressed, and the occurrence of a decrease in image density can be suppressed.

  At this time, since the value of the casing gap G1 is the same as that before the insulating layer 123 is provided, the developer carried on the developing roller 45 comes into contact with the surface of the insulating layer 123 provided on the gap forming member 112, and is sufficient. A suction airflow can be secured. As a result, the developer released by the developing roller 45 can be sucked into the developing device 40 by the suction airflow, and the scattering of the developer on the downstream side of the developing region can be suppressed. Further, it is possible to stabilize the image density by suppressing the occurrence of a decrease in the image density.

Moreover, the following reasons can be considered that the accompanying rotation of the developer can be suppressed by providing the insulating layer 123.
That is, in the configuration without the insulating layer 123, an electric field is formed between the gap forming member 112 and the developing roller 45, and the toner on the surface of the developing roller 45 moves electrostatically to the gap forming member 112. Charge flows into the gap forming member 112. As a result, the toner layer on the surface of the gap forming member 112 has the same potential (0 [V]) as the ground, and does not hinder further electrostatic movement of the toner.

  On the other hand, even in the configuration including the insulating layer 123, an electric field is formed between the gap forming member 112 and the developing roller 45. However, even if the toner on the surface of the developing roller 45 electrostatically moves to the gap forming member 112, the toner charge is blocked by the insulating layer 123 and does not flow into the gap forming member 112. As a result, the toner layer on the surface of the gap forming member 112 is charged to the same polarity as the toner contained in the developer carried on the developing roller 45, preventing further electrostatic movement of the toner. It becomes.

Thereby, electrostatic toner adhesion to the gap forming member 112 is suppressed as compared with a configuration in which the insulating layer 123 is not provided, and the occurrence of counter charge in the developer carried on the developing roller 45 is also suppressed. Accordingly, an increase in electrostatic adhesion force of the developer to the developing roller 45 is suppressed, separation of the developer from the developing roller 45 in the separation unit is promoted, and occurrence of the accompanying developer is suppressed. I think.
Further, by suppressing the occurrence of the accompanying developer, it is possible to suppress the occurrence of a decrease in image density.

[Experimental Example 1]
The inventors of the present invention have used the developing device 40 in which the gap in the casing gap region is made small so as to ensure a sufficient suction airflow, and the developing device 40 in which the image density of the black solid image is reduced is as follows. Experiments were conducted.

  First, a sheet material that is in contact with a part in the width direction of the separation portion of the developing roller 45 was arranged to output a black solid image. With respect to the width direction of the image, no decrease in image density occurred in the portion where the sheet material was in contact with the developing roller 45, and a decrease in image density occurred in other portions. In the portion where the sheet material comes into contact, the developer on the surface of the developing roller 45 is forcibly removed by the sheet material, thereby reliably preventing the accompanying rotation of the developer. Since the image density is reduced except at the portion in contact with the sheet material, it is assumed that in the developing device 40 in which the gap in the casing gap region is reduced, the developer density is accompanied and the image density is lowered. Conceivable.

Next, the developing device 40 in which the gap forming member 112 of the developing device 40 shown in FIG. 4 is floated and the developing device 40 in which the insulating layer 123 is provided on the surface facing the developing roller 45 of the gap forming member 112 are used. A black solid image was output.
As a configuration in which the gap forming member 112 is floated, an insulating member is sandwiched between the gap forming member 112 and the casing main body 121 so that no current flows between the gap forming member 112 and the casing main body 121. did.
The insulating layer 123 is provided with a PTFE (polytetrafluoroethylene) tape attached to the surface of the gap forming member 112 facing the developing roller 45.

  In the conventional developing device 40 in which the gap forming member 112 is grounded via the casing main body 121, when a black solid image is output, the image density is lowered. On the other hand, in the configuration in which the gap forming member 112 is floated or in the configuration in which the insulating layer 123 is provided on the gap forming member 112, a decrease in image density can be suppressed.

From Experimental Example 1, the following can be considered.
That is, in the conventional developing device 40, the toner contained in the developer carried on the developing roller 45 in the casing gap region is electrostatically gapd by the electric field formed between the developing roller 45 and the gap forming member 112. Move to forming member 112. Then, the counter charge is generated in the developer (carrier) remaining on the developing roller 45 side, whereby the adhesive force of the developer to the developing roller 45 is increased, and the developer is accompanied. When the developer is rotated, the developer whose toner density has decreased after passing through the developing area is supplied to the developing area again while being carried on the developing roller 45, so that when the black solid image is output, It is thought that a decrease in concentration occurred.

  In the developing device 40, the width of the insulating layer 123 is set wider than the width of the developing region so that both ends in the longitudinal direction of the developing region are within the range of the width of the insulating layer 123 in the longitudinal direction. Thereby, it is possible to suppress the occurrence of the accompanying rotation of the developer over the entire width direction of the development area where the toner of the developer can be consumed, and the occurrence of the decrease in image density due to this.

[Experimental example 2]
A developing bias is applied to the developing roller 45 using a developing device 40 that has been modified to open a window for visualization around the separation portion in the developing casing, and the developer is applied to the surface of the developing roller 45 after passing through the casing gap region. It was confirmed whether there was a companion.

FIG. 11 is an explanatory diagram of a modified machine of the developing device 40 used in Experimental Example 2. “P1” to “P5” in FIG. 11 indicate the method of the magnetic field formed by each magnetic pole on the surface of the developing roller 45. The distribution of linear magnetic flux density (absolute value) is shown.
In the developing device 40 used in Experimental Example 2, a hole is formed in the casing main body 121 in a range to be the observation window 401, three screw members are removed, and confirmation from the direction indicated by an arrow H in FIG. The surface which becomes the separation part of the developing roller 45 is made visible. A high-speed camera (not shown) was installed outside the observation window 401, and the surface of the developing roller 45 near the separation portion was photographed from the observation window 401.
Further, as a configuration for supplying the developer to the supply portion on the surface of the developing roller 45, a configuration in which the developer 403 is disposed on the inclined plate 402 and the developer 403 is continuously supplied to the surface of the developing roller 45 for a certain period of time. It was.
The experimental conditions are shown below.

・ Developing device: Ricoh ProC750 development unit remodeling machine (the development casing is grounded)
Casing gap: 0.70 [mm]
-Developer pumping amount: 40 [mg / cm ² ]
・ Developing roller linear velocity: 529.2 [mm / s]
・ Developer: Black developer for ProC750 manufactured by Ricoh (toner concentration: 4 [wt%])
Development bias: -400 [V], -500 [V], -600 [V], -700 [V], -800 [V]
・ High speed camera: EXILIM EX-FH20 made by Casio
・ Shooting conditions: Frame rate 210 [fps]

In Experimental Example 2, a configuration in which the insulating layer 123 is provided on the gap forming member 112 and a configuration in which the insulating layer 123 is not provided are compared.
In the configuration in which the insulating layer 123 is not provided, the gap forming member 112 is developed so that the casing gap G1 becomes 0.70 [mm] without performing insulation treatment on the surface of the gap forming member 112 facing the developing roller 45. The position relative to the roller 45 was adjusted.
Moreover, as a structure which provides the insulating layer 123, the PTFE tape (Sumitomo 3M PTFE tape model number 5490) was affixed on the surface facing the developing roller 45 of the gap formation member 112 as an insulation process. Then, the position of the gap forming member 112 with respect to the developing roller 45 was adjusted so that the casing gap G1 from the surface of the PTFE tape to the surface of the developing roller 45 was 0.70 [mm].
The experimental results of Experimental Example 2 are shown in Table 1.

As shown in Table 1, when the PTFE tape was affixed to the surface of the gap forming member 112 facing the developing roller 45, the developer was not rotated. Thereby, it is possible to suppress the occurrence of a decrease in image density caused by the accompanying developer.
In Experimental Example 2, PTFE tape is applied to the insulating process for the surface of the gap forming member 112 facing the developing roller 45. The insulating process of the gap forming member 112 may be a general anodizing process as an insulating process of aluminum, or may be applied with another insulating tape or a coating process of an insulating material.

[Experimental Example 3]
In Experimental Example 2, PTFE tape is also applied to the surface of the gap forming member 112 facing the developing roller 45 as an insulating process. However, in a long-life developing device in which the number of printed sheets exceeds, for example, 10 [10,000 sheets], a member having an adhesive layer such as an insulating tape is used as an insulating process for the surface of the gap forming member 112 facing the developing roller 45. The configuration of attaching is not preferable. This is due to the following reason.
That is, when the adhesive layer is exposed due to wear of the contact portion with the developer on the surface of the insulating tape, the developer adheres to the gap forming member 112, and the developer clogs or adheres to the casing gap region. This is because the developer may become an aggregate.
Therefore, in Experimental Example 3, as an insulating method without an adhesive layer, an ETFE (tetrafluoroethylene / ethylene copolymer) resin coating treatment was used as an insulating resin material, and a configuration in which no insulation treatment was applied. It was confirmed whether the developer was accompanied.

In Experimental Example 3, the modified machine shown in FIG. 11 was used as the experimental developing device 40 as in Experimental Example 2.
The experimental conditions are shown below.

・ Developing device: Ricoh ProC750 development unit remodeling machine (the development casing is grounded)
Casing gap: 0.70 [mm]
-Developer pumping amount: 40 [mg / cm ² ]
・ Developing roller linear velocity: 529.2 [mm / s]
・ Developer: Black developer for ProC750 manufactured by Ricoh (toner concentration: 4 [wt%])
Development bias: -400 [V], -500 [V], -600 [V], -700 [V], -800 [V]
・ High speed camera: EXILIM EX-FH20 made by Casio
・ Shooting conditions: Frame rate 210 [fps]
Insulating layer: ETFE resin (TC-820 manufactured by Ashiya Co., Ltd.) coating (film thickness: 20 [μm])

In the configuration in which the insulating layer 123 is not provided, as in Experimental Example 2, the casing gap G1 is set to 0.70 [mm] without performing insulation treatment on the surface of the gap forming member 112 facing the developing roller 45. The position of the gap forming member 112 with respect to the developing roller 45 was adjusted.
In addition, as a configuration in which the insulating layer 123 is provided, the insulating layer 123 is formed by performing an ETFE resin coating process on the surface of the gap forming member 112 facing the developing roller 45 as an insulating process. The layer thickness (coating thickness) of the insulating layer 123 at this time is 20 [μm]. Then, the position of the gap forming member 112 relative to the developing roller 45 was adjusted so that the casing gap G1 from the surface of the coating layer of ETFE resin to the surface of the developing roller 45 was 0.70 [mm].
The experimental results of Experimental Example 3 are shown in Table 2.

As shown in Table 2, the ETFE resin coating was applied to the surface of the gap forming member 112 facing the developing roller 45, so that the developer was not rotated. Examples of the resin material used for other coatings include PTFE, polyimide (PI), polyamideimide (PAI), acrylic resin, and epoxy resin. These resin materials are coated on the surface of the gap forming member 112 facing the developing roller 45, and, as in Experimental Example 3, a developing bias is applied to the developing roller 45 to rotate the developer after passing through the casing gap region. The occurrence of was confirmed. As a result, in any case, the rotation of the developer did not occur. In addition to these resins, if an insulating resin material is used, it is possible to suppress the accompanying rotation of the developer by coating.
The method of coating the resin material on the surface of the gap forming member 112 facing the developing roller 45 includes spraying, electrodeposition coating, electrostatic coating, and the like. However, any method can be used as long as it can be applied to the surface of the aluminum material. is not.

  The inventors confirmed the durability of the insulating layer 123 using the developing device 40 including the gap forming member 112 in which the insulating layer 123 used in Experimental Example 3 is a coating layer of ETFE resin. Specifically, the developing device 40 for 594K sheets is driven, the amount of reduction in the thickness of the insulating layer 123 at that time (the amount of wear due to the rubbing of the developer) is measured, and 5400K is determined from the measurement result. The amount of decrease in the layer thickness when the developing device 40 for one sheet was driven was estimated. The amount of decrease in the layer thickness varies between the vicinity of the front side end, the vicinity of the center, and the vicinity of the back side end in the direction orthogonal to the cross section shown in FIG. The estimated amount of decrease in the vicinity of the portion was 24.6 [μm]. Accordingly, by setting the thickness of the insulating layer 123 to 30 [μm] or more, the insulating layer 123 can be maintained even after the driving of the developing device 40 for 5400K sheets. It is possible to suppress the occurrence of a decrease in image density due to the above.

[Experimental Example 4]
In Experimental Example 4, the difference in the adhesion state of the toner to the surface of the gap forming member 112 facing the photoreceptor 18 due to the difference in the surface property of the resin material was confirmed in the configuration in which the insulating layer 123 was formed by coating the resin material. . In Experimental Example 3, an insulating layer 123 was provided on the surface of the gap forming member 112 facing the developing roller 45 with respect to the developing unit used in the ProC750, which is an image forming apparatus manufactured by Ricoh, as the experimental developing device 40. A modified machine was used.
The experimental conditions are shown below.

Apparatus conditions-Image forming apparatus: ProC750 manufactured by Ricoh
・ Developing device: Ricoh ProC750 development unit remodeling machine (the development casing is grounded)
・ Coating material for insulating layer: “PI”, “ETFE” or “PTFE” coated ・ Case gap: 0.8 [mm]
Printing conditions-Image area ratio: 0.5 [%]
-Number of printed sheets: 10,000 [sheets]

  Table 3 shows the contact angle of each coating material with water and the amount of toner adhering to the surface of the gap forming member 112 facing the photoreceptor 18 when the developing roller 45 is rotated. FIG. 12 is an explanatory diagram of the developing device 40 showing the locations where the toner adhesion amount is measured. In Experimental Example 4, after printing the number of printed sheets (10000 [sheets]), the toner in the area indicated by α in FIG. 12 was collected, and the “toner adhesion speed” was calculated from the amount of adhered toner.

The toner adhered to PI as a whole, but the toner hardly adhered to ETFE and PTFE. From this result, the toner is less likely to adhere to the resin material having a larger contact angle with water.
In Experimental Example 4, toner adheres to the surface of the gap forming member 112 facing the photoreceptor 18. If the adhesion speed is 3 [mg / km] or less, the toner is applied to the intermediate transfer belt 15. It is possible to prevent the toner from dropping to a place where it is not. Then, it is possible to prevent the occurrence of abnormal images such as toner stains and black spots due to toner falling on the intermediate transfer belt 15.
Here, the “toner adhesion speed” is the image forming condition of the image area ratio (0.5 [%]) where toner adhesion is most likely to occur, and the photosensitive member 18 of the gap forming member 112 when 10000 [sheets] are printed. The amount of toner adhering to the opposite surface is divided by the travel distance of the photoreceptor 18.

  As shown in Table 3, by selecting a resin material on which the toner hardly adheres to the surface of the insulating layer 123, toner contamination (attachment) on the surface of the gap forming member 112 facing the photoreceptor 18 can be reduced. .

  FIG. 13 is an explanatory diagram showing the state where the toner T adheres to the surface (“112f” in FIG. 13) of the gap forming member 112 that faces the photoconductor 18. By providing the insulating layer 123, it is possible to suppress toner from adhering electrostatically to the surface of the gap forming member 112 facing the developing roller 45, but it is not possible to suppress adhesion of weakly charged toner. If the weakly charged toner adheres to the surface of the gap forming member 112 facing the developing roller 45 and remains attached without being scraped off by the developer carried on the surface of the developing roller 45, the development of the gap forming member 112 is performed. Toner accumulates on the surface facing the roller 45. Then, the new toner adheres and the position where the toner accumulates gradually moves to the outlet side (upstream side in the surface movement direction of the developing roller 45), and as shown in FIG. Toner adheres to the opposing surface (112f).

On the other hand, if a resin material that does not easily adhere to the surface of the insulating layer 123 is selected, the weakly charged toner that adheres to the surface of the insulating layer 123 can be easily scratched by the developer carried on the surface of the developing roller 45. It is possible to prevent toner from being deposited. As a result, it is considered that toner contamination (attachment) on the surface of the gap forming member 112 facing the photoreceptor 18 can be reduced.
When the toner adhering to the surface (112f) facing the photoreceptor 18 accumulates and forms an aggregate of a certain size and peels off from the gap forming member 112, it falls to an unintended location on the intermediate transfer belt 15, Abnormal images such as toner stains and black spots occur.
In contrast, the occurrence of such an abnormal image can be suppressed by reducing toner contamination (attachment) on the surface of the gap forming member 112 facing the photoreceptor 18.

  As shown in Table 3, the contact angle between the coating material forming the insulating layer 123 and water is desirably 95 [°] or more. By using ETFE or PTFE as the coating material for forming the insulating layer 123 than the result of Experimental Example 4, toner contamination (adhesion) on the surface of the gap forming member 112 facing the photoconductor 18 can be reduced. Generation of images can be suppressed.

  Table 4 is a list of evaluations of the functions (insulation, contact angle with water, surface properties) and effects (toner adhesion, rotation) of the insulating layer 123 when the insulation treatment is performed. Content that has not been evaluated is blank (“/”).

From Table 4, it can be seen that the number of falling insulation treatments improves the follow-up compared to the configuration in which the insulating layer 123 is not provided (no treatment). Among the coating treatments, the epoxy coating has an accompany evaluation of “Δ”, while the PAI coating has “◎”. Therefore, it is considered desirable for the insulating property of the resin material to be coated to have a volume resistance of 1 × 10 ¹⁴ [Ω / cm] or more.

  The embodiment described above is an example of the best mode of the present invention, and does not limit the scope of the claims of the present application. In the above-described embodiment, the configuration in which the image forming apparatus including the developing device 40 having the configuration of the present invention is a copying machine has been described. However, the present invention can also be applied to other image forming apparatuses such as a facsimile and a printer.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A developer comprising toner and carrier is carried on the surface and moved to move the developer to the developing region facing the surface of the latent image carrier such as the photosensitive member 18 to carry the developer such as the developing roller 45. And a developer carrying member disposed inside the developer carrying part such as a supply carrying path 49, a collection carrying path 47, and a stirring carrying path 44 for containing the developer to be supplied to the surface of the developer carrying body. Development casings such as a casing main body 121 provided with an opening such as an opening 51 for making a part of the surface of the developer carrier in the surface movement direction of the surface opposite the latent image carrier, and a gap forming member 112, and the like. In a developing device such as a developing device 40 including a developing bias power source 141 and the like for applying a developing bias to the developer carrying member, the surface movement direction of the developer carrying member with respect to the developing region A casing gap portion such as a casing gap region where the surface of the developer carrier on the flow side and the opposing surface of the developing casing are close to each other so that the developer carried on the developer carrier contacts the opposing surface of the developing casing. A portion of the developing casing that forms the casing gap, such as the gap forming member 112, is formed of a conductive material, and a portion of the casing gap that is in contact with the developer on the surface of the developer carrying member is opposed to the developing casing. Are provided with an insulating layer such as an insulating layer 123.
According to this, as described in the above embodiment, it is possible to stabilize the image density while suppressing the scattering of the developer on the downstream side of the development region. This is due to the following reason.
That is, the developer carried on the developer carrying member in the casing gap is brought into contact with the opposite surface of the developing casing, thereby preventing the generation of the discharge airflow and generating a stable suction airflow downstream of the development region. Can do. Therefore, the scattering of the developer on the downstream side of the development region can be suppressed.
However, when a configuration in which the developer carried on the surface of the developer carrying member is brought into contact with the casing at the casing gap portion, there is a problem that the image density is lowered when a solid image is output. As a result of extensive research by the present inventors, the developer on the surface of the developer carrying member that has passed through the developing region is not separated at the separation portion to be separated from the developer carrying member. It has been found that a phenomenon of reaching the supply portion where the developer is supplied to the surface of the toner occurs. The developer that has passed through the development area consumes toner and has a low toner concentration. When the developer reaches the supply unit without being separated, the developer having a lowered toner density is supplied to the development area. Therefore, it is considered that the above-described problem that the image density is lowered occurs.
When the developer that has passed through the developing region reaches the supply unit without being separated by the separation unit, the developer is accompanied by an insulating layer on the opposite surface of the developing casing at the part where the developer contacts on the surface of the developer carrying member. The present inventors have found through experimentation that it can be suppressed by providing.
By suppressing the accompanying rotation of the developer, it is possible to suppress the developer having a lowered toner density from being supplied to the development area and to suppress the image density from being lowered, thereby stabilizing the image density. be able to.
As described above, in the aspect A, it is possible to stabilize the image density while suppressing the scattering of the developer on the downstream side of the developing region.
Note that the reason why the developer can be prevented from being rotated by providing an insulating layer on the surface of the developer carrier on the opposite surface of the developer casing where the developer contacts is considered to be as follows.
That is, in the casing gap portion, an electric field is formed between the developer carrying member to which the developing bias is applied and the opposing surface of the conductive developing casing, and the toner contained in the developer carried on the developer carrying member. In contrast, an electrostatic force directed to the opposite surface of the developing casing acts. When the toner electrostatically adheres to the opposite surface of the developing casing due to the action of this force, a counter charge having a polarity opposite to that of the toner is generated on the carrier in the developer remaining on the developer carrying member. Adhesive force between the toner and the developer carrying member increases. As a result, the developer cannot be separated at the separation portion, and the developer is accompanied.
In the aspect A, when the casing gap portion is set to have a desired gap, the distance between the facing surface of the developing casing made of the conductive material and the surface of the developer carrier is set such that the casing gap portion becomes the desired gap. It is farther than the conventional structure set to the thickness of the insulating layer. Even if the potential difference between the opposing surface of the developing casing and the surface of the developer carrying member is the same, the electric field becomes weaker as the distance increases, and the electrostatic force that moves the toner toward the opposing surface of the developing casing becomes weaker. Become. As a result, electrostatic toner adhesion to the opposing surface of the developing casing is suppressed, occurrence of counter charge in the developer carried on the developer carrying member is also suppressed, and the electrostatic charge of the developer on the developing carrier is suppressed. Increase in the adhesive force can be suppressed. Therefore, it is considered that the separation of the developer from the developer carrying member in the separation unit is promoted, and the occurrence of the accompanying developer is suppressed.

(Aspect B)
In the aspect A, the insulating layer such as the insulating layer 123 is obtained by coating the opposing surface of the developing casing such as the gap forming member 112 with an insulating resin material.
According to this, as described in the above embodiment, it is possible to realize a configuration in which the insulating layer is provided on the opposing surface of the developing casing. In addition, unlike the insulating tape, since the adhesive layer is not provided, even if the insulating layer 123 becomes thin due to wear over time, there is no problem that the adhesive and the developer are in contact with each other.

(Aspect C)
In either embodiment A or B, the surface of an insulating layer such as the insulating layer 123 has a contact angle with water of 95 [°] or more.
According to this, as described in the above embodiment, toner is prevented from accumulating on the facing surface of the developing casing such as the gap forming member 112 and the like, and the developing casing faces the latent image carrier such as the photosensitive member 18. It is possible to prevent toner from adhering to the surface.

(Aspect D)
In any one of the aspects A to C, the volume resistance of the insulating layer such as the insulating layer 123 is 1 × 10 ¹⁴ [Ω / cm] or more.
According to this, as described in the above embodiment, it is possible to more reliably prevent the occurrence of the accompanying developer.

(Aspect E)
In any of the aspects A to D, the layer thickness of the insulating layer such as the insulating layer 123 is 30 [μm] or more.
According to this, as described in the above embodiment, the insulating layer can be maintained over time, and the occurrence of the accompanying developer and the occurrence of the image density reduction due to this can be suppressed. Can do.

(Aspect F)
In any of the aspects A to E, when the direction perpendicular to the surface movement direction on the surface of the developer carrier such as the developing roller 45 is defined as the width direction, the end in the width direction of the insulating layer such as the insulating layer 123 The portion is located at the same position as the end portion in the width direction of the development region or outside the end portion in the width direction of the development region.
According to this, as described in the above-described embodiment, the occurrence of the accompanying rotation of the developer over the entire width direction of the developing area where the toner of the developer can be consumed, and the occurrence of the image density decrease due to this. Can be suppressed.

(Aspect G)
In any of the aspects A to F, the developing casings such as the casing main body 121 and the gap forming member 112 face the surface of the developer carrying member such as the developing roller 45 so that the casing gap portion such as the casing gap region is formed. Forming a gap forming member such as a gap forming member 112 made of a conductive material, such as a casing main body 121 such as a casing main body 121 that forms a developer containing portion such as a supply conveyance path 49, a collection conveyance path 47, and a stirring conveyance path 44. It is provided as a separate member from the section.
According to this, as described in the above embodiment, the width of the gap of the casing gap portion can be arbitrarily adjusted.

(Aspect H)
In the aspect G, the gap forming member such as the gap forming member 112 is fixed to the casing main body portion such as the casing main body 121 by a metal screw member such as the gap adjusting screw 501, and the screw member on the surface of the gap forming member The surface from which the head portion is exposed is covered with a nonmagnetic cover member such as the inlet seal 50.
According to this, as described in the above embodiment, the carrier is prevented from adhering to the surface where the head of the screw member such as the surface of the gap forming member facing the latent image carrier such as the photoreceptor 18 is exposed. it can.

(Aspect I)
At least a latent image carrier such as the photosensitive member 18, a charging means such as a charging device for charging the surface of the latent image carrier, and a latent image of the exposure unit 9 or the like that forms an electrostatic latent image on the surface of the latent image carrier. In an image forming apparatus such as a copying machine 500 having a forming unit and a developing unit that develops an electrostatic latent image, the developing unit includes a developing unit such as the developing unit 40 according to any one of modes A to H. .
According to this, as described in the above embodiment, it is possible to stabilize the image density while suppressing the scattering of the developer on the downstream side of the development region. Accordingly, it is possible to suppress the occurrence of an abnormal image due to the developer that has come out of the developing device, and it is possible to stabilize the image density, thereby improving the image quality. Further, the occurrence of dirt in the apparatus can be suppressed.

(Aspect J)
At least the latent image carrier and the developing means in an image forming apparatus such as a copying machine 500, which includes a latent image carrier such as the photosensitive member 18 that carries the latent image, and a developing unit that develops the latent image on the surface of the latent image carrier. In a process cartridge such as the image forming unit 11 that is held on a common holding body as a unit and detachable from the main body of the image forming apparatus, the developing unit according to any one of aspects A to H A developing device such as the developing device 40 is provided.
According to this, as described in the above embodiment, it is possible to improve the exchangeability of the developing device capable of stabilizing the image density while suppressing the scattering of the developer on the downstream side of the developing region. it can.

DESCRIPTION OF SYMBOLS 1 Image forming part 2 Transfer unit 3 Paper feed unit 4 Secondary transfer device 5 Duplex unit 6 Conveyor belt 7 Fixing unit 8 Paper discharge unit 9 Exposure unit 10 Reading device 11 Image forming unit 12 Drum cleaning unit 13 Charging unit 14 Registration roller pair DESCRIPTION OF SYMBOLS 15 Intermediate transfer belt 16 Transfer counter roller 17 Secondary transfer roller 18 Photoconductor 20 Heat insulation device 21 Heat receiving plate 22 Heat pipe 23 Heat radiating plate 24 Duct 25 Fixing device 30 Liquid cooling device 31 Cooling pump 32 Heat receiving portion 32a Case 32b Flow path 33 Reserve Tank 34 Circulating pipe 35 Cooling section 35a Cooling fan 35b Radiator 40 Developing device 41 Discharge transport path 41a Discharge screw 42 Doctor blade 43 Stirring screw 43a Stirring shaft section 43b Stirring blade section 44 Stirring transport path 45 Developing roller 45a Developing sleeve 45b Magnet roller 46 Collection screw 47 Collection conveyance path 48 Supply screw 49 Supply conveyance path 50 Inlet seal 90 Intermediate transfer belt cleaning unit 91 Supply opening 92 Surplus opening 93 Collection opening 112 Gap forming member 113 Gap formation Member fixing portion 121 Casing body portion 123 Insulating layer 130 Heat conduction sheet 133 First partition wall 134 Second partition wall 141 Development bias power supply 201 Toner supply port 220 Developing roller upper cover 230 Transport path upper cover 240 Front side end side plate 250 Back Side end side plate 401 Observation window 402 Inclined plate 403 Developer 500 Copying machine 501 Gap adjustment screw C Carrier G1 Casing gap T Toner

JP 2009-216848 A

Claims (10)

A developer carrying member for carrying the developer to a developing region facing the surface of the latent image carrying member by carrying a two-component developer comprising a toner and a carrier on the surface and moving the surface;
Forming a developer containing portion for containing a developer to be supplied to the surface of the developer carrying member, and a part of the surface of the developer carrying member in the direction of surface movement of the developer carrying member disposed inside the developer carrying member; A developing casing provided with an opening for facing the latent image carrier;
A developing bias applying means for applying a developing bias to the developer carrying member;
A casing gap portion in which the surface of the developer carrying member on the downstream side in the surface movement direction of the developer carrying member with respect to the developing region and the facing surface of the developing casing are close to each other is carried by the developer carrying member. The developer is set to contact the opposite surface of the developing casing;
A portion forming the casing gap portion in the developing casing is formed of a conductive material,
A developing apparatus comprising an insulating layer on an opposing surface of the developing casing at a portion where the developer on the surface of the developer carrying member is in contact with the casing gap. The developing device according to claim 1.
The developing device, wherein the insulating layer is a coating of an insulating resin material on an opposing surface of the developing casing. The developing device according to claim 1 or 2,
The developing device according to claim 1, wherein the surface of the insulating layer has a contact angle with water of 95 ° or more. In the developing device according to any one of claims 1 to 3,
The developing device characterized in that the volume resistance of the insulating layer is 1 × 10 ¹⁴ [Ω / cm] or more. In the developing device according to any one of claims 1 to 4,
2. A developing device according to claim 1, wherein the insulating layer has a thickness of 30 [μm] or more. The developing device according to any one of claims 1 to 5,
When the direction perpendicular to the surface movement direction on the surface of the developer carrier is a width direction,
The developing device according to claim 1, wherein an end portion in the width direction of the insulating layer is positioned at the same position as an end portion in the width direction of the developing region or outside an end portion in the width direction of the developing region. The developing device according to any one of claims 1 to 6,
The developing casing forms the casing gap portion so as to face the surface of the developer carrying member, and the gap forming member made of a conductive material is a separate member from the casing main body portion forming the developer containing portion. A developing device. The developing device according to claim 7,
The gap forming member is fixed to the casing main body by a metal screw member, and a surface of the surface of the gap forming member where the head of the screw member is exposed is covered with a nonmagnetic cover member. A developing device. At least a latent image carrier;
Charging means for charging the surface of the latent image carrier;
Latent image forming means for forming an electrostatic latent image on the surface of the latent image carrier;
In an image forming apparatus having developing means for developing the electrostatic latent image,
An image forming apparatus comprising the developing device according to claim 1 as the developing unit. In at least the latent image carrier and the developing means as a single unit in an image forming apparatus comprising a latent image carrier for carrying a latent image and a developing means for developing the latent image on the surface of the latent image carrier. In the process cartridge that is held by the holder and is detachable from the image forming apparatus main body,
A process cartridge comprising the developing device according to claim 1 as the developing unit.

Images