JP5455048B2 - Developing device, and process cartridge and image forming apparatus including the same - Google Patents

Description

  The present invention relates to a developing device that uses a two-component developer including toner and a carrier, a process cartridge including the developing device, and an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  This type of developing device is generally a two-component developer (hereinafter simply referred to as “developer”) that is transported in a developer supply transport path extending in the direction of the rotation axis of the developer support along the developer support. ) Is carried on the surface of the rotating developer carrying member, and the developer is supplied to the developing region by the rotation of the developer carrying member. Some conventional developing devices employ a supply and recovery integrated system in which the developed developer that has consumed toner in the development region is returned to the developer supply and conveyance path. In this supply / collection-integrated developing device, the toner density of the developer flowing in the developer supply / conveyance path becomes lower toward the downstream side in the developer conveyance direction (hereinafter, simply referred to as “downstream”), and thus is supplied to the development region. In the developer, there is a drawback that unevenness of toner density occurs in the direction of the rotation axis of the developer carrier. Such toner density unevenness is likely to appear as density unevenness in the image formed on the recording material, and is therefore desired to be eliminated.

  As a developing device that can eliminate this drawback, a supply / recovery separation system that collects the developed developer that has consumed toner in the development area to a developer recovery transport path that is different from the developer supply transport path is adopted. (For example, Patent Document 1). In the supply / separation type developing device, the toner concentration of the developer flowing in the developer supply / conveyance path is maintained constant over the developer conveyance direction. Therefore, in the developer supplied to the development area, toner density unevenness does not occur in the direction of the rotation axis of the developer carrying member, and the above-described drawbacks are solved.

  For recent image forming apparatuses, increasing the image forming speed is strongly desired. In order to cope with an increase in the image forming speed, it is necessary to increase the rotation speed of the developer carrier of the developing device. The higher the rotation speed of the developer carrier, the more difficult it is to supply the developer to the developer carrier without a shortage. Therefore, the image density due to insufficient developer supply to the developer carrier is reduced. It tends to cause image quality degradation such as degradation. In particular, since there is a strong demand for downsizing of image forming apparatuses in recent years, downsizing of a developing device mounted on the image forming apparatus is also strongly desired. For this reason, the amount of developer that can be accommodated in the developing device Tend to be limited. Therefore, it is necessary to effectively utilize a limited amount of developer in the developing device and continue to supply the developer stably to the developer carrying member without shortage. Therefore, in order to achieve both a reduction in the size of the image forming apparatus and an increase in the image forming speed, there is no shortage of developer relative to the developer carrier that rotates at a high speed with a limited amount of developer in the developing apparatus. It is desired to keep supplying stably.

  However, in the developing device that employs the above-described supply / recovery separation method, the developer in the developer supply transport path is drawn to the developer carrier disposed along the developer supply transport path, and the downstream end portion It is conveyed to. For this reason, the amount of developer flowing in the developer supply / conveyance path decreases toward the downstream side. Therefore, when the rotation speed of the developer carrier is increased as described above, the pumping amount per unit time increases, and the amount of developer that can reach the downstream end of the developer supply conveyance path decreases. There may be a situation where the amount of developer is insufficient on the downstream side of the developer supply conveyance path.

  Conventionally, the situation where the amount of developer is insufficient on the downstream side of the developer supply transport path has been dealt with by increasing the developer transport speed in the developer supply transport path. According to this, since the unit amount of developer started to be transported from the upstream end is less pumped up to the developer carrier before being transported to the downstream end, the developer supply transport path It is difficult to cause a situation where the amount of developer is insufficient on the downstream side. However, since there is a limit to increasing the developer conveyance speed in the developer supply conveyance path, the method of increasing the developer conveyance speed in the developer supply conveyance path can cope with further increase in the speed of the developer carrier. There was a problem that I could not.

  The present invention has been made in view of the above problems, and the object of the present invention is to stabilize the developer without deficiency with respect to the developer carrier that rotates at high speed with a limited amount of developer in the developing device. A supply / recovery separation type developing device that can continue to be supplied, and a process cartridge and an image forming apparatus including the same.

In order to achieve the above-mentioned object, the invention according to claim 1 is directed to the toner and the carrier conveyed by the conveyance member in the developer supply conveyance path extending in the developer carrier rotation axis direction along the developer carrier. By carrying the contained two-component developer on the surface of the rotating developer carrier, the two-component developer carried on the surface of the developer carrier is transported to the development area, The toner in the two-component developer is adhered to the latent image on the surface of the latent image carrier to develop the latent image, and the two-component developer that has passed through the development area is supplied from the developer carrier to the developer. In the developing device that collects in the developer recovery transport path that is a transport path different from the transport path, the two-component developer transported to the downstream end of the developer supply transport path in the developer transport direction is used as the developer. Via the recovery transport path or separate from the developer recovery transport path A transport member that transports the two-component developer in the direction of the rotation axis of the developer carrying member, having a circulation transport mechanism that transports the developer supply transport path to the upstream end of the developer transport direction via the transport path. Among the transport paths provided in the developer supply transport path, the average transport speed of the two-component developer by the transport member inside the developer supply transport path is configured to be the slowest, and the circulation transport mechanism includes the developer The transport speed of the two-component developer in the collection transport path is configured so that the upstream side is slower than the downstream side in the developer transport direction .
Also, the second aspect of the present invention, in the developing apparatus of claim 1, the circulating conveying mechanism includes a helical blade portion to the rotation axis, and conveys the two-component developer along the axial direction A conveyance screw is provided in the developer collecting conveyance path, and the conveyance screw is a portion where the replenishment toner is supplied from a toner replenishing port for supplying replenishment toner, or a developer conveyance direction from the portion. The upstream blade portion provided in the downstream portion has a higher dispersion performance of the two-component developer than the downstream blade portion provided downstream in the developer transport direction than the portion, and the two-component developer The lead angle is increased so that the conveyance performance is lowered.
According to a third aspect of the present invention, in the developing device of the second aspect , the lead angle of the upstream blade portion of the conveying screw is set in a range of 55 ° to 70 °. Is.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the circulating transport mechanism is configured such that the transport speed of the two-component developer in the developer supply transport path is a developer. It is configured so that the downstream side is slower than the upstream side in the transport direction.
According to a fifth aspect of the present invention, there is provided a two-component developer including a toner and a carrier which are conveyed by a conveying member in a developer supply conveying path extending along the developer carrying member in the direction of the rotation axis of the developer carrying member. Is carried on the surface of the rotating developer carrying member, thereby transporting the two-component developer carried on the surface of the developer carrying member to the developing region, and in the two-component developer in the developing region. The toner is attached to the latent image on the surface of the latent image carrier to develop the latent image, and the two-component developer that has passed through the development area is separated from the developer carrier by a different path from the developer supply path. In the developing device that collects in the developer collection conveyance path that is a conveyance path, the two-component developer conveyed to the downstream end of the developer supply conveyance path in the developer conveyance direction is passed through the developer collection conveyance path. Or, via a transport path different from the developer recovery transport path, A conveyance path that has a circulation conveyance mechanism that conveys the upstream side of the developer supply direction of the image agent supply conveyance path to the developer conveyance direction, and that includes a conveyance member that conveys the two-component developer in the direction of the rotation axis of the developer carrier The average transport speed of the two-component developer by the transport member inside the developer supply transport path is configured to be the slowest, and the circulation transport mechanism includes the two-component developer in the developer supply transport path. The developer conveyance speed is configured to be slower on the downstream side than on the upstream side in the developer conveyance direction.
According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the circulation transport mechanism is transported to a downstream end portion in the developer transport direction of the developer supply transport path. The two-component developer is transferred to the developer recovery transport path, and the two-component developer transported to the downstream end of the developer recovery transport path in the developer transport direction is transferred to the developer supply transport path. The two-component developer is circulated and conveyed.
According to a seventh aspect of the present invention, there is provided a process in which the latent image carrier and the developing device for developing the latent image on the latent image carrier are integrally supported and detachably attached to the image forming apparatus main body. In the cartridge, the developing device according to any one of claims 1 to 6 is used as the developing device.
Further, the invention of claim 8 provides a latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, and a two-component developer containing a toner and a carrier. An image forming apparatus including: a developing device that develops a latent image; and a toner image formed on the latent image carrier by the developing device is finally transferred to a recording material to form an image on the recording material In the apparatus, the developing device according to any one of claims 1 to 6 is used as the developing device.

  In the present invention, in the conveyance path in which the two-component developer is circulated and conveyed by the circulation conveyance mechanism and includes a conveyance member for conveying the two-component developer in the direction of the rotation axis of the developer carrier. The average transport speed of the two-component developer in the developer supply transport path is the slowest. As a result, when the developer is circulated and conveyed in the developing device, the distribution of the developer amount on the circulation path becomes the largest at the upstream end of the developer supply and conveyance path. As a result, at the upstream end of the developer supply transport path, the maximum amount of the limited amount of developer can be sent to the downstream side of the developer supply transport path. As a result, even if the developer transport speed in the developer supply transport path is set slower than before, the developer in the developer supply transport path can reach the downstream end, and the developer rotates at high speed. The developer can be stably supplied to the carrier. Therefore, it is possible to stably supply the developer even to a high-speed developer carrier that cannot be handled by the method of increasing the developer conveyance speed in the developer supply conveyance path.

  According to the present invention, the developer can be continuously supplied stably and without deficiency to the developer carrier that rotates at a high speed with a limited amount of developer in the supply / recovery separation type developing device. Excellent effect is obtained.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is an explanatory diagram illustrating a schematic configuration of an image forming unit of the printer. FIG. 3 is a schematic view when the inside of the developing device is viewed from the side in order to explain the flow of the developer by the developer circulation conveyance mechanism in the developing device of the printer. FIG. 6 is an explanatory view showing a cross section at a downstream end portion of a developer recovery conveyance path of the developing device. It is explanatory drawing which displayed the magnetic flux density distribution on the developing roller surface of the developing device superimposed on the schematic configuration of the developing device. It is sectional drawing which shows the structure of the developing roller of the developing device. It is a perspective view for demonstrating the structure of the developer circulation conveyance mechanism provided in the developing device. FIG. 3 is an exploded view of the developer circulation conveyance mechanism. FIG. 6 is a schematic diagram illustrating a state where a developer shortage occurs at a downstream end portion in a developer supply conveyance path of the developing device. FIG. 4 is an explanatory diagram when a part of a developer recovery conveyance path of the developing device is cut out and a recovery path cell that is the cut-out portion is viewed from a horizontal direction orthogonal to the developer conveyance direction. It is a graph which shows an example of the relationship between the lead angle of the blade | wing part of a conveyance screw, and a developer conveyance speed. It is a graph which shows an example of the relationship between the lead angle of the blade | wing part of the conveyance screw, and the dispersibility of a developer. It is explanatory drawing which shows schematic structure of the developer circulation conveyance mechanism in a modification.

Hereinafter, an embodiment in which the present invention is applied to a color printer as an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment.
This printer is a so-called tandem type image forming apparatus in which a plurality of image forming units 17K, 17M, 17Y, and 17C are arranged along a conveying belt 15 that conveys a transfer sheet 8 as a recording material. The arrangement order of the image forming units is not limited to this. For example, the black image forming unit 17K is arranged on the most downstream side in the conveyance direction of the transfer paper 8, and magenta (M), cyan (C), yellow (Y ) And black (K) in this order.

  Each of these image forming units 17K, 17M, 17Y, and 17C has a photoreceptor as a latent image carrier, and forms a toner image of each color on each photoreceptor. Each of the image forming units 17K, 17M, 17Y, and 17C is not necessarily configured as a unit. However, in this embodiment, the image forming units 17K, 17M, 17Y, and 17C are unitized and are process cartridges that are detachable from the printer main body. These image forming units 17K, 17M, 17Y, and 17C have substantially the same configuration except that the color of the toner to be used is different.

FIG. 2 is an explanatory diagram showing a schematic configuration of the image forming units 17K, 17M, 17Y, and 17C of the printer according to the present embodiment.
The photoreceptor 1 is rotationally driven in the clockwise direction in the figure. A charging device 2 is disposed above the photoreceptor 1. In this embodiment, the charging device 2 employs a contact charging method in which a charging roller to which a charging bias is applied is brought into contact with the surface of the photoconductor to uniformly charge the photoconductor surface to a predetermined potential. A non-contact charging method may be adopted. The surface portion of the photoreceptor 1 uniformly charged by the charging device 2 is irradiated with the writing light L from the corresponding exposure devices 16K, 16M, 16Y, and 16C shown in FIG. It is formed. In this embodiment, the charging device 2 and the exposure devices 16K, 16M, 16Y, and 16C constitute a latent image forming unit.

  The electrostatic latent image on the photoconductor 1 moves to a developing area facing the developing device 3 as the photoconductor 1 rotates. The developing device 3 includes a toner and a carrier that are transported in a developer supply transport path that extends in a developing roller rotation axis direction (perpendicular to the paper surface in FIG. 2) along a developing roller 302 as a developer carrier. By carrying the two-component developer 320 on the surface of the rotating developing roller 302, the developer 320 carried on the surface of the developing roller 302 is conveyed to the developing area, and the toner in the developer in the developing area. Is attached to the electrostatic latent image on the photosensitive member 1 and developed.

  A part of the casing 301 of the developing device 3 is opened to expose the developing roller 302. The portion of the developing roller 302 exposed from the casing 301 is opposed to the photosensitive member 1 in the lateral direction (left and right direction in FIG. 2). As a result, a developing area A is formed in the area where the developing roller 302 and the photosensitive member 1 face each other. The developer 320 in the casing 301 is carried on the developing roller 302 and conveyed to the developing area A. The toner in the developer 320 adheres to the electrostatic latent image formed on the surface of the photoreceptor 1 in the development area A, and is visualized as a toner image.

  This toner image is conveyed to a region facing the conveying belt 15 (transfer region B) as the photosensitive member 1 rotates. A transfer device 5 is disposed on the opposite side of the photoreceptor 1 (the inner peripheral surface side of the conveyor belt 15) with the conveyor belt 15 in between. The transfer device 5 uses a transfer roller to which a transfer bias is applied, but may be of a corona discharge type. The conveyor belt 15 is stretched around two support rollers 18 and 19. One of these support rollers 18 and 19 is a drive roller, and the other is a driven roller. When the drive roller is driven to rotate, the conveyor belt 15 travels in the direction of the arrow in the figure.

  Below the transport belt 15, three paper feed trays 20, 21, and 22 that store the transfer paper 8 are provided. For example, the transfer paper 8 at the uppermost position among the transfer papers 8 stored in the paper feed tray 20 is sent out at the time of image formation and is temporarily kept on standby by the registration roller 23, and is synchronized with the image formation in the image forming unit 17K. It is fed out and is attracted to the conveyor belt 15 by electrostatic attraction. The transfer paper 8 adsorbed on the conveyance belt 15 is conveyed to the first image forming unit 17K, where a black image is transferred.

  When forming a color image, in each of the image forming units 17K, 17M, 17Y, and 17C, the peripheral surface of each photoconductor 1 is uniformly charged by each charging device 2 in the dark, and then from each exposure device 16. It is exposed by the writing light L, and each electrostatic latent image is formed. These electrostatic latent images are visualized by the respective color toners by the respective developing devices 3, and the respective color toner images are formed on the respective photoreceptors 1.

  These toner images are sequentially transferred to the transfer paper 8 on the conveyor belt 15 so as to overlap each other by each transfer device 5. The transfer paper 8 on which the full-color superimposed image is formed in this manner is peeled off from the conveyance belt 15 and fixed by the fixing device 24 while passing between the pair of fixing rollers, and then discharged onto the paper discharge tray 25. .

  On the other hand, unnecessary toner remaining on the peripheral surface of the photoconductor 1 is removed by the cleaning device 6 from each photoconductor 1 after the transfer, and is prepared for the next image formation. The cleaning device 6 uses a cleaning blade 601 to remove toner remaining on the surface of the photoreceptor 1 without being transferred to the transfer paper 8. The surface of the photoreceptor 1 that has passed through the cleaning device 6 is then uniformly charged by the charging device 2 and the next image forming process is repeated.

  It can also be applied to an intermediate transfer belt system in which a toner image on a photosensitive member is temporarily transferred to an intermediate transfer member (such as an intermediate transfer belt) and then multicolor toners are transferred to a transfer paper in a batch. In the transfer area B, the toner on the photosensitive member is transferred to an intermediate transfer member (intermediate transfer belt).

Next, the developing device 3 will be described in detail.
As illustrated in FIG. 2, the developing device 3 according to the present embodiment collects the developer 320 that has passed through the developing region from the developing roller 302 to a developer recovery conveyance path that is a conveyance path different from the developer supply conveyance path. The so-called supply recovery separation system is adopted. The developing device 3 includes a first transport screw 304 for transporting the developer in the developer supply transport path and a second transport screw 305 for transporting the developer in the developer recovery transport path. . The developer supply transport path and the developer recovery transport path are formed by partitioning the casing 301 by a partition plate 306.

FIG. 3 is a schematic view when the inside of the developing device is viewed from the side in order to explain the flow of the developer by the developer circulation transport mechanism in the developing device 3 of the present embodiment.
The developing device 3 of the present embodiment has a vertical stirring configuration in which a developer recovery transport path is disposed below the developer supply transport path. The developer transported to the downstream end of the developer supply transport path by the first transport screw 304 reaches the upstream end of the developer recovery transport path through a communication hole 309 opened at the bottom surface of the downstream end of the developer supply transport path. As shown in FIG. 4, the developer moved and transported to the downstream end of the developer recovery transport path by the second transport screw 305 has an opening 307 opened at the bottom surface of the upstream end of the developer supply transport path. To the upstream end of the developer supply transport path.

FIG. 5 is an explanatory diagram in which the magnetic flux density distribution on the surface of the developing roller 302 is displayed superimposed on the schematic configuration of the developing device.
In the developing roller 302, a magnet roller 302d in which a plurality of magnets MG (only one is indicated by a symbol for preventing complication of the drawing) is arranged in the circumferential direction is fixedly arranged inside, and the periphery thereof is a cylindrical sleeve. 302c rotates integrally with the rotating shaft 302e. The sleeve 302c is formed of a nonmagnetic metal such as aluminum. The magnet roller 302d is fixed to the casing 301, for example, so that each magnet MG faces a predetermined direction. The developing roller 302 carries the developer 320 attracted to the surface of the sleeve 302c by the magnetic force of the magnet MG, and conveys this in the circumferential direction as the sleeve 302c rotates.

FIG. 6 is a cross-sectional view showing the structure of the developing roller 302.
The developing roller 302 mainly includes a fixed shaft 302a fixed to the casing 301, a columnar magnet roller 302d integrated with the fixed shaft 302a, and a sleeve 302c covering the periphery of the magnet roller 302d with a gap. And a rotating shaft 302e integrated with the sleeve 302c. The rotation shaft 302e is rotatable with respect to the fixed shaft 302a via a bearing 302f, and the rotation shaft 302e is driven to rotate by receiving power from a rotation driving means (not shown).

  As shown in FIG. 6, a plurality of magnets MG are fixed to the outer periphery of the magnet roller 302d with a predetermined interval. The sleeve 302c is rotated around these magnets MG. These magnets MG are for forming a magnetic field so that the developer can be spiked on the surface of the sleeve 302c, and can be cut off. In the present embodiment, as shown in FIG. 5, the sleeve 302c has five magnets MG, and five magnetic poles (magnetic force distribution) are generated. A magnetic pole disposed on an imaginary line connecting the center O-1 of the developing roller 302 and the center O-2 of the photosensitive member is defined as a P1 pole. Hereinafter, each magnetic pole is defined as a P2 pole and a P3 along the rotation direction of the developing roller 302. Pole, P4 pole, P5 pole.

  The polarities of the magnetic poles are the N pole, S pole, N pole, N pole, and S pole in order from the P1 pole, but these magnetic poles may have opposite polarities. On the developing roller 302, each magnetic pole is centered in FIG. 5 with the P1 pole at 8 o'clock on the watch dial, the P2 pole at 7 o'clock, the P3 pole at 5 o'clock, and the P4 pole at 1 o'clock. It is approximately located.

  The developing roller 302 and the photosensitive member 1 are not in direct contact with each other in the developing area A but are opposed to each other while maintaining a developing gap GP1 at a certain interval suitable for development. On the developing roller 302, the developer 320 is caused to rise at the P1 pole, and the developer 320 is brought into contact with the photosensitive member 1, whereby toner is attached to the electrostatic latent image on the surface of the photosensitive member 1 to be visualized.

  In the developing device 3, as shown in FIG. 5, a grounded developing bias power source VP is connected to the fixed shaft 302a. The voltage of the power source VP connected to the fixed shaft 302a is applied to the sleeve 302c via a conductive bearing and a conductive rotating shaft 302e. On the other hand, as shown in FIG. 5, the lowermost conductive support 31 constituting the photoreceptor 1 is grounded. Thus, an electric field is formed in the development area A to move the toner separated from the carrier to the photosensitive member 1 side, and the toner is removed by the potential difference between the sleeve 302c and the electrostatic latent image formed on the surface of the photosensitive member 1. This is used for moving toward the photoreceptor 1 side.

  Note that the developing apparatus of this example is combined with an image forming apparatus of a method of writing with exposure light L. The charging device 2 uniformly applies negative charges on the photosensitive member 1 and exposes the image portion with the exposure light L in order to reduce the writing amount. A so-called reversal development method is employed in which the latent image is developed with negative polarity toner. This is merely an example, and the polarity of the charged charge placed on the photoreceptor 1 is not a major problem in the developing method of the present invention.

  The developer 320 that has been developed in the development area A is conveyed to the inside of the casing 301 as the developing roller 302 rotates while being carried on the developing roller 302 by the magnetic force of the P2 pole. There is a part of the casing 301 at a position corresponding to the P2 pole, and a part of the casing 301 has a curved shape close to the peripheral surface of the sleeve 302c, and performs a so-called toner scattering prevention function by a sealing effect. Yes.

  The P3 pole and the P4 pole that are located downstream of the P2 pole in the developing roller rotation direction have the same polarity. For this reason, the magnetic force that has been attracted to the surface of the developing roller 302 until then is reduced between the P3 pole and the P4 pole, and thereby, the action of “agent separation” that separates the developer 320 from the developing roller 302 works. The agent separation area where the developer 320 is separated from the developing roller 302 is indicated by reference numeral 9 in FIGS. Since the developer 320 after development with the toner adhered to the photoreceptor 1 has a lower toner concentration in the developer, it is assumed that the developer having the lowered toner concentration does not leave the developing roller 302 and is again in the development region. If it is transported to A and used for development, there arises a problem that a target image density cannot be obtained. In order to prevent this, in the present embodiment, the developer is separated from the developing roller 302 in the agent separation area 9 and the separated developer is collected in a developer collection conveyance path different from the developer supply conveyance path. I have to.

  In this way, the surface of the developing roller 302 from which the developer has been separated moves to a position facing the developer supply / conveyance path as the developing roller 302 rotates. The P4 pole is present at this location, and the developer flowing through the developer supply / conveying path is pumped and carried in the agent pumping area 10 on the developing roller by the magnetic force of the P4 pole. The developer pumped up to the developing roller 302 by the magnetic force of the P4 pole passes through the developing doctor 303 which is a developer regulating member, is adjusted to a predetermined thickness, and is conveyed to the developing area A. The P5 pole located between the P4 pole and the P1 pole functions as a transport pole for carrying the developer on the surface of the developing roller 302 from the time when it passes through the developing doctor 303 to the developing area. ing.

Hereinafter, as necessary, the arrangement of each member will be described with reference to FIG. 7 showing the internal configuration of the developing device in an assembled state, FIG. 8 showing the exploded state, and the like.
As shown in FIGS. 7 and 8, the first conveying screw 304 disposed in the developer supply conveying path has a screw shape with a spiral blade portion around its rotation axis, and the developing roller 302. Is driven to rotate in a clockwise direction indicated by an arrow in the figure around a center line O-304a parallel to the center line O-302a passing through the center O-302. As a result, the developer is conveyed while stirring as indicated by the arrow 11 from the back side of the center line O-304a in the drawing toward the front side in the drawing. That is, the first conveying screw 304 conveys the developer in the direction of the rotation axis from the rear side in the drawing toward the front side in the drawing by the rotation of the rotation shaft.

  As shown in FIG. 7, the second conveying screw 305 disposed in the developer collecting and conveying path has a screw shape with a spiral blade portion around the rotation axis, and the center O of the developing roller 302. It is driven to rotate in the counterclockwise direction indicated by the arrow in the figure around a center line O-305a parallel to the center line O-302a passing through -302. As a result, the developer is conveyed while being stirred as indicated by an arrow 12 from the near side of the center line O-305a in the figure toward the far side in the figure. That is, the second conveying screw 305 conveys the developer from the near side in the figure in the direction opposite to the conveying direction by the first conveying screw 304 to the far side in the figure by the rotation of the rotation shaft.

  The developer supply conveyance path and the second conveyance between the first conveyance screw 304 and the second conveyance screw 305 and in the central portion excluding both ends in the longitudinal direction of the developing roller 302 and the second conveyance screw. A partition plate 306 that divides the developer collection conveyance path in which the screw 305 is disposed is formed in a cantilevered manner integrally with the inner wall of the casing 301 on the side away from the developing roller 302. The partition plate 306 is located at the center of the developing roller 302 except for both ends in the longitudinal direction, and is not located at the portion corresponding to both ends in the longitudinal direction of the developing roller 302. On the other hand, each longitudinal end portion of the first transport screw 304 and the second transport screw 305 extends to both longitudinal end portions of the developing roller 302.

  The developer transported in the developer recovery transport path in the direction of arrow 12 by the second transport screw 305 is cut off on the side wall of the casing 301 at the downstream end in the transport direction, and therefore rises along the side wall and opens. It moves along the arrow 13 via the section 307 to the developer supply and conveyance path where the first conveyance screw 304 is arranged. On the other hand, the developer transported in the developer supply transport path in the direction of the arrow 11 by the first transport screw 304 is transferred to the arrow 14 from the communication hole 309 provided on the bottom surface of the downstream end portion of the developer supply transport path. And descends to the developer recovery transport path.

  The partition plate 306 is positioned at the center of the developing roller 302 except for both ends in the longitudinal direction. As a result, the flow of the developer indicated by the arrows 13 and 14 at the end portions in the longitudinal direction is made possible, and a developer circulation conveyance path along the arrows 11, 14, 12 and 13 is formed as a whole. it can. Further, the partition plate 306 supports the developer 320 agitated and conveyed by the first conveying screw 304 from below to form a developer supply conveyance path, and is separated from the developing roller 302 in the agent separation area 9 to collect and convey the developer. The developer recovered to the path is prevented from moving to the developer supply and conveyance path. In order to ensure such a function, the distance between the outer peripheral portion of the developing roller 302 and the partition plate 306 and the partition plate gap GP2 are preferably maintained at about 0.2 to 1 mm. If it is less than 0.2 mm, the partition plate 306 may come into contact with the developing roller due to eccentricity when the developing roller 302 rotates. If it exceeds 1 mm, the function of preventing the collected developer from moving to the developer supply / conveyance path. This is because it becomes insufficient.

  Furthermore, it is possible to obtain a function as a partition plate even if the arrangement is shifted from the agent separation region 9. However, when the arrangement is shifted from the agent separation area 9, there is a possibility that the partition plate restricts a large amount of developer, which is not preferable because the stress received by the developer becomes large. Therefore, the agent separation region 9 is located in the lower part around the developing roller 302 on the opposite side of the photosensitive member 1 with the developing roller 302 therebetween, and the agent is pumped up adjacent to the downstream side of the upper agent separation region 9 in the rotation direction of the developing roller. A position where the position 10 is located, and a space around the first conveying screw 304 at a position where the amount of developer adhering around the developing roller 302 is the smallest between the agent separating area 9 and the agent pumping position 10; The partition plate 306 is provided so as to shield the space around the second conveying screw 305, and the end of the partition plate 306 on the developing roller 302 side is opposed to the developing roller 302. According to this configuration, even if the partition plate gap GP2 is not set to 0.2 to 1 mm, the portion where the partition plate is provided is the position where the amount of developer adhering around the developing roller 302 is the smallest. Therefore, the function of the partition plate 306 can be exhibited, and the stress applied to the developer can be minimized by being regulated by the partition plate. That is, gap management at the time of setting the partition plate can be relaxed. However, if the configuration is further added with the condition that the partition plate gap GP2 is set to 0.2 to 1 mm, stress applied to the developer can be further reduced.

  In this embodiment, the closest position between the developing roller 302 and the partition plate 306 is between the first conveying screw 304 and the second conveying screw 305, and the amount of developer attached to the developing roller 302 is the smallest. The magnetic flux density on the surface of the developing roller is set within the agent separation area 9 of 10 mT or less between the areas, that is, the P3 pole and the P4 pole.

  In this embodiment, as shown in FIG. 8, in the downstream portion of the developer conveying direction by the second conveying screw 305, an impeller 308 is replaced with a spiral blade portion in a range corresponding to the opening 307. Is formed. The impeller 308 is a plurality of plate members extending radially from the axial center (center line O-305a) with respect to the shaft portion 305J of the second conveying screw 305, and the developer 320 is accompanied by the rotation of the second conveying screw 305. Has a function of jumping upward.

  As shown in FIG. 4, the center O-304 of the first conveying screw 304 and the center O-305 of the second conveying screw 305 are on substantially the same vertical line, and the impeller 308 rotates counterclockwise. The developer 320 is flipped up along the inner wall of the casing 301. The opening 307 does not disturb the path of the developer due to the jumping up, and the center O-304 and the center O-305 are prevented so that the developer jumped up does not fall into the second conveying screw 305. Is formed so as to extend from a position slightly closer to the casing inner wall to a casing inner wall portion than a substantially vertical line connecting the two. That is, since the opening 307 is formed in a state where a hole is formed in a part of the partition plate 306, the upper and lower spaces are connected to the portion where the developer is lifted from the second conveying screw 305 to the first conveying screw 304. Although there is an opening 307, a partition plate is present at a position on the developing roller side corresponding to the opening 307 as in the central portion in the developing roller axial direction. By the remaining partition plate portion, the developer that has moved from the bottom to the top through the opening portion 307 is attracted to the developing roller 302 without falling again, and is transported to the second transport screw 305 by the developing roller 302. Alternatively, since the toner is conveyed by the first conveying screw 304, efficient developer circulation can be performed.

  The rotation direction of the first conveying screw 304 is a clockwise direction opposite to the developing roller 302 that rotates counterclockwise. In general, since the screw has an action of moving the conveyed object in the axial direction while moving it in the axial direction, the first conveying screw 304 conveys the developer 320 while moving it toward the developing roller 302 in the developer supply conveyance path. become. Therefore, a large amount of developer that contacts the developing roller 302 can be secured, and a stable developer supply to the developing roller 302 can be achieved.

  The second conveying screw 305 is rotated in the same direction as the developing roller 302. In this embodiment, it is counterclockwise. As a result, the second conveying screw 305 conveys the developer 320 while moving it away from the developing roller 302. Therefore, the developer once separated from the developing roller 302 by the magnetic force, the partition plate 306, or the like in the agent separating area 9 is suppressed from adhering to the developing roller 302 again. Therefore, it is possible to prevent the developer whose toner density after development has been lowered from moving to the region of the first conveying screw 304.

Next, toner supply will be described.
Since the developer 320 in the developing device 3 consumes toner while the developing operation is repeated, it is necessary to replenish the toner in the device from the outside of the developing device. In the present embodiment, as shown in FIG. 8, the toner replenishing port 310 is located above the downstream end (the front end of the developing device) of the developer supply conveyance path in which the communication hole 309 is provided. Is provided. The toner replenishing port 310 is formed in the casing 301 above the end on the near side without the partition plate 306. The toner replenished from the toner replenishing port 310 descends through the communication hole 309 together with the developer 320 from the downstream end of the developer supply / conveyance path that is out of the developing region facing portion of the developing roller 302, and collects and conveys the developer. The developer moves to the upstream end of the path and is transported through the developer recovery transport path by the second transport screw 305 while being agitated with the developer.

  In this embodiment, the supply / recovery separation system is employed, and the developer flowing through the developer recovery / conveying path is not supplied to the developing roller 302. Therefore, the developer whose toner charge amount is insufficient and the toner density is not uniform due to the newly replenished toner from the toner replenishing port 310 is not supplied to the developing roller 302 for development. The replenished toner is conveyed to the downstream end (the end on the back side of the developing device 3) while being agitated and mixed with the developer 320 having a low toner concentration collected from the developing roller 302 in the developer collecting conveyance path. Until the toner is sufficiently frictionally charged, the toner density is normalized. Then, such developer is lifted from the opening 307 to the developer supply conveyance path by the action of the impeller 308 and the like, and is supplied to the developing roller 302 while being conveyed to the front side by the first conveyance screw 304 and used for development. Is done.

  Here, the configuration in which circulation conveyance is performed in two conveyance paths in which the developer recovery conveyance path is disposed below the developer supply conveyance path has been described. However, in the case of the supply recovery separation method, the developer supply conveyance path It may be configured such that circulation conveyance is performed by two conveyance paths arranged in a substantially horizontal direction and developer collection conveyance path, or may be configured such that circulation conveyance is performed by three or more conveyance paths.

Next, the developer circulation transport mechanism, which is a feature of the present invention, will be described.
FIG. 9 is a schematic diagram illustrating a state where the developer shortage occurs at the downstream end in the developer supply conveyance path.
Since the developing device of the present embodiment employs a supply / recovery separation system, the amount of developer is shown in FIG. 3 if the transport speed in the developer supply transport path is constant in the developer transport direction. As shown in FIG. As the rotational speed of the developing roller 302 increases, the amount of the developer in the developer supply / conveyance path pumped up to the developing roller 302 per unit time increases. Therefore, there is a shortage of developer at the downstream end portion in the developer supply conveyance path, and as shown in FIG. 9, a situation where the developer is exhausted easily occurs at the downstream end portion in the developer supply conveyance path. When such a shortage of developer occurs, the amount of developer supplied to the developing roller 302 is insufficient at the downstream end portion in the developer supply transport path, and the image density is lowered at that portion.

Here, the minimum condition for preventing the depletion of the developer on the downstream side of the developer supply conveyance path is to satisfy the following formula (1) in the equilibrium state. Note that “Mku” in the formula (1) is the development per unit time from the developer recovery conveyance path provided with the second conveyance screw 305 to the developer supply conveyance path provided with the first conveyance screw 304. The amount of agent movement is indicated (arrow indicated by reference numeral 13 in the figure). Further, “Mzs” in the equation (1) indicates the developer transport amount per unit time transported with the rotation of the developing roller 302 (arrow indicated by reference numeral 7 in the figure).
Mku> Mzs (1)

  When Expression (1) is satisfied in the equilibrium state, the amount of developer flowing into the developer supply transport path per unit time always exceeds the amount of developer flowing out per unit time from the developer supply transport path. Therefore, the developer is not depleted on the downstream side of the developer supply conveyance path. The larger the developer movement amount Mku from the developer recovery conveyance path to the developer supply conveyance path with respect to the developer conveyance amount Mzs by the developing roller 302, the higher the margin that satisfies the above equation (1). The developer depletion on the downstream side of the developer supply conveyance path can be prevented more stably.

  However, in a small-sized developing device, the amount of developer that can be accommodated in the developing device is limited. Therefore, in the conventional developing device, the developer supply transport path from the developer recovery transport path with respect to the developer transport amount Mzs by the developing roller 302. It has been difficult to sufficiently increase the amount of developer movement Mku to the road. For this reason, when the developing device is downsized, the margin satisfying the above formula (1) becomes low, and it becomes difficult to stably prevent the developer depletion on the downstream side of the developer supply conveyance path. In particular, when the developing roller 302 is rotated at a high speed in order to increase the image forming speed, the developer transport amount Mzs by the developing roller 302 increases, so that the margin is further reduced, and the downstream of the developer supply transport path. It is extremely difficult to stably prevent the developer depletion on the side.

  Therefore, in this embodiment, the average transport speed of the developer in the developer supply transport path is the slowest among the two transport paths of the developer supply transport path and the developer recovery transport path through which the developer is circulated. It is set to be. As a result, the distribution of the developer amount in an equilibrium state on the developer circulation path has the largest developer amount at the upstream end of the developer supply conveyance path. That is, a limited small amount of developer in the developing device when the developing device is downsized can be unevenly distributed at the upstream end of the developer supply conveyance path in an equilibrium state. As a result, the developer movement amount Mku from the developer recovery transport path to the developer supply transport path can be maximized with a limited developer amount in the developing device, and satisfies the above formula (1). The margin can be increased as much as possible.

  Further, since the margin satisfying the above formula (1) is increased, the developer depletion on the downstream side of the developer supply transport path can be stabilized even if the average transport speed in the developer supply transport path is decreased. It becomes possible to prevent. That is, an increase in the degree of margin satisfying the above formula (1) means that the amount of developer existing at the upstream end of the developer supply conveyance path increases. Therefore, the amount of developer that can be sent out from the upstream end of the developer supply conveyance path toward the downstream side increases. If the amount of developer sent from the upstream end of the developer supply transport path toward the downstream increases, even if the developer transport speed in the developer supply transport path is slow, the downstream end of the developer supply transport path It is possible to prevent the developer from remaining and causing depletion.

  In this embodiment, the developer transport speed in the developer recovery transport path is not constant over the entire developer transport direction, and is set so that the upstream side is slower than the downstream side in the developer transport direction. Yes. This is because, as described above, while setting the average transport speed of the developer in the developer supply transport path to be the slowest, the developer revolving and developer that can occur on the downstream side of the developer recovery transport path This is to suppress leakage.

  Since the developing device of the present embodiment employs a supply / recovery separation method, the amount of developer is as shown in FIG. 3 if the transport speed in the developer recovery transport path is constant in the developer transport direction. As shown in FIG. Therefore, a situation may occur in which the developer stays on the downstream side of the developer recovery transport path and the developer in the developer recovery transport path contacts the surface of the developing roller 302. When such a situation occurs, it becomes difficult to peel off the developed developer transported from the development area as the developing roller 302 rotates from the surface of the developing roller 302. As a result, as the developed developer is carried on the developing roller 302 along with the rotation of the developing roller 302, the developer is transported to the developing area again. In addition, the developed developer once peeled off from the surface of the developing roller 302 may adhere to the surface of the developing roller 302 again. When the rotation of the developer occurs, the developed developer having a low toner concentration contributes to the development, and the image density is lowered at that portion.

  In addition, a pressing force is applied to the developer existing downstream from the developer recovery transport path by the developer transported later in the developer recovery transport path. This pressing force promotes the movement of the developer existing downstream of the developer recovery transport path to the developer supply transport path, but there is a situation where the developer stays downstream of the developer recovery transport path. When this occurs, a situation occurs in which a part of the staying developer cannot move to the developer supply conveyance path side. Such developer moves through a gap between the developing roller 302 and the inner wall of the developing casing, and causes developer leakage that flows out of the developing device.

  In order to suppress the rotation of the developer and the leakage of the developer as described above, the amount of the developer existing on the downstream side of the developer recovery conveyance path may be reduced. To that end, it is conceivable to slow down the developer transport speed in the developer recovery transport path. However, if the developer transport speed is uniformly decreased throughout the developer transport direction in the developer recovery transport path, the developer supply It may be difficult to realize the above-described setting that the average transport speed of the developer in the transport path is the slowest.

  Therefore, in the present embodiment, the developer conveyance speed on the upstream side of the developer collection conveyance path is set slower than that on the downstream side. As a result, the average transport speed of the developer in the developer recovery transport path is maintained on the downstream side of the developer recovery transport path while maintaining a state higher than the average transport speed of the developer in the developer supply transport path. The amount of developer present can be reduced.

FIG. 10 is an explanatory diagram when a part of the developer recovery transport path is cut out and the cut-out portion (hereinafter referred to as “collection path cell”) is viewed from a horizontal direction orthogonal to the developer transport direction.
At an arbitrary point (collection path cell) of the developer recovery conveyance path, the developer amount Mu flows in from the upstream side, the developer amount Mk flows out downstream, and the developer amount Ms flows in from the developing roller 302. There are three types of developer streams. If the developer amount in the recovery path cell is in an equilibrium state during circulation of the developer, the following equation (2) is established for the three developer amounts. That is, the amount of developer flowing into the recovery path cell is equal to the amount of developer flowing out of the recovery path cell.
Mk = Mu + Ms (2)

Note that the developer inflow amount Ms is equal to the area of the developer portion (upstream cross-sectional area of the developer) Su on the upstream side surface of the recovery path cell and the recovery path cell as shown in the following formula (3). It is determined by the product of the developer conveyance speed Vu passing through the upstream side surface.
Ms = Su × Vu (3)
Similarly, as shown in the following formula (4), the developer outflow amount Mk is equal to the area of the developer portion (downstream cross-sectional area of the developer) Sk on the downstream side surface of the recovery path cell, It is determined by the product of the developer conveyance speed Vk passing through the downstream side surface.
Mk = Sk × Vk (4)

When Vu and Vk have the same speed, the downstream sectional area Sk of the developer is larger than the upstream sectional area Su of the developer by the amount of developer collected from the developing roller 302. Therefore, when Vk = Vu = V, the following equation (5) is obtained.
Sk × V = Su × V + Ms (5)
When this equation (5) is modified, the following equation (6) is obtained.
Sk = Su + Ms / V (6)
From this equation (6), the downstream cross-sectional area Sk of the developer is larger by Ms / V than the upstream cross-sectional area Su of the developer.
As can be seen from the above, in the developing device according to the present embodiment adopting the supply / recovery separation method, the amount of developer is as long as the transport speed in the developer recovery transport path is constant in the developer transport direction. As shown in Fig. 4, the number increases on the downstream side.

Here, the following formula (7) can be derived from the above formula (2), the above formula (3), and the above formula (4).
Sk × Vk = Su × Vu + Ms (7)
From the above equation (7), for example, when it is desired to have the same area as Sk = Su = S, that is, when it is desired to keep the volume of the developer in the developer collection conveyance path constant, the following equation (8) is satisfied. In addition, the developer transport speed Vu passing through the upstream side surface of the recovery path cell and the developer transport speed Vk passing through the downstream side surface of the recovery path cell may be set.
Vk = Vu + Ms / S (8)

  The above formula (8) is obtained by increasing the developer transport speed Vk on the downstream side surface of the recovery path cell at an arbitrary point in the developer recovery transport path by Ms / S with respect to the developer transport speed Vu on the upstream side surface. Means good. Therefore, if the developer transport speed is increased toward the downstream side of the developer recovery transport path, the change in the bulk of the developer in the developer recovery transport path can be reduced. As a result, it is possible to avoid a situation where the developer stays on the downstream side of the developer collection conveyance path.

  Note that the principle of the developer recovery transport path described above is that the developer recovery amount Ms recovered from the developing roller 302 is replaced with the developer pumping amount (-Ms) pumped up to the developing roller 302, thereby supplying and supplying the developer. The same applies to the road. Therefore, if the developer transport speed is reduced toward the downstream side of the developer supply transport path, the change in the bulk of the developer in the developer supply transport path can be reduced. As a result, the depletion of the developer on the downstream side of the developer supply conveyance path can be prevented more stably.

Next, a specific configuration in which the developer conveyance speed on the upstream side of the developer recovery conveyance path is made slower than that on the downstream side will be described.
As a method of making the developer transport speed on the upstream side of the developer recovery transport path slower than that on the downstream side, the pitch of the blades is made different in the axial direction of the second transport screw 305 or the lead angle of the blades (screw A known method can be used, such as making the angle between the surface perpendicular to the axial direction and the surface of the blade portion different. Generally, the developer transport speed in the developer recovery transport path is often made different in the developer transport direction by a method in which the pitch of the blade section is varied in the axial direction. Adopt a technique that makes the difference.

FIG. 11 is a graph showing an example of the relationship between the lead angle of the blade and the developer conveyance speed.
When the second conveying screw 305 having the characteristics of this graph is used and the lead angle of the blade portion is set to 45 ° on the downstream side, for example, when the developer conveying speed on the upstream side is slower than that on the downstream side, In general, the blade portion on the upstream side with respect to the screw shaft is set up. That is, it is common to employ a method of slowing the upstream developer conveyance speed by reducing the lead angle of the upstream blade portion (for example, in the range of 20 ° to 35 °). However, as shown in the graph of FIG. 11, even if the lead angle of the upstream blade portion is increased (for example, in the range of 55 ° to 70 °), the upstream developer conveyance speed can be slowed.

FIG. 12 is a graph showing an example of the relationship between the lead angle of the blade and the dispersibility of the developer.
The dispersibility of the developer indicates the stirring performance of the developer by the screw. After adding a new toner to the developer having a uniform toner concentration or a developer containing no toner, this is fixed by the screw. The toner density distribution in the developer when transported by a distance is measured, and a value obtained by dividing the dispersion σ of the toner density distribution by the toner density average value is used.
The conventional idea is that the smaller the lead angle of the blade portion (that is, the higher the blade portion is raised with respect to the screw shaft), the higher the dispersibility of the developer. According to the research by the present inventors, the developer dispersibility increases even when the lead angle exceeds 35 °, even if the lead angle is large (that is, the blade is laid down with respect to the screw shaft). It has been found. The results are shown in FIG. Moreover, it has been found that increasing the lead angle of the blade portion to a range of 55 ° or more exhibits high dispersibility that cannot be obtained when the lead angle of the blade portion is reduced. Therefore, when it is desired to increase the dispersibility of the developer, the inventors' idea of increasing the lead angle of the blade part is more advantageous than the conventional idea of reducing the lead angle of the blade part.

Here, in the developer collection conveyance path, the toner replenished from the toner replenishing port 310 is taken into the developer and stirred, and the developer in a state where the toner is sufficiently mixed is delivered to the developer collection conveyance path. Is important. In general, the stirring of the developer in the developer collecting / conveying path can be explained by the following stirring model.
That is, the inside of the developer recovery conveyance path is divided into three areas in the developer conveyance direction, and the agitation process in the area located on the most upstream side is referred to as phase 1, and the agitation process in the area located in the center is referred to as phase 2. The stirring process in the region located on the most downstream side is referred to as phase 3. Phase 1 is the place where the highest developer dispersibility is required, and the overlap of the developers and the movement of the developer in the direction of the developer depth are dominant, and the replenishment toner is increased in the developer. Achieving agitation that incorporates. In phase 2, the developer slippage and the agitation caused by the collision at the contact portion with the blade portion of the second conveying screw 305 become dominant, and the toner dispersion in the developer is promoted. In phase 3, position exchange between neighboring particles occurs due to a local conveyance speed difference, and dispersion in the developer conveyance direction is promoted.
In particular, in the present embodiment, since the developer that has reached the downstream end of the developer recovery conveyance path is transferred to the developer supply conveyance path, the developer slip or collision in phase 2 or development is performed. Since the local replacement of the developer at the location where the developer is transferred from the developer recovery conveyance path to the developer supply conveyance path (location where the developer is lifted) occurs effectively, the replenishment toner is good in the developer in phase 1. If it can be taken in, efficient dispersibility can be obtained.

  In this embodiment, the upstream developer transport speed in the developer recovery transport path is slower than the downstream developer transport speed, but phase 1 is executed on the upstream side in the developer recovery transport path. And high developer dispersibility is required. Therefore, in the present embodiment, in Phase 1, the lead angle of the blade portion is set in the range of 55 ° or more and 70 ° or less so that the developer conveyance speed is slow but high dispersibility can be exhibited. When the blade part lies down, the effect of the agent jumping up is enhanced, the movement of the agent in the developer depth direction is activated, and high developer dispersibility is obtained. In Phase 2 after the replenishment toner is mixed to some extent, the lead angle of the blade is set to about 45 °, which has a higher conveyance speed and better dispersibility than Phase 1. As a result, the developer conveyance speed is increased to effectively cause the developer to get over the blade portion, and to cause dispersion due to the sliding or collision of the agent in the gap between the second conveyance screw 305 and the casing inner wall. In phase 3, it is necessary to lift the developer at the downstream end portion of the developer recovery conveyance path to the upstream end portion of the developer supply conveyance path positioned above. In order to smoothly lift the developer and prevent the developer from staying at the downstream end of the developer recovery transport path, the lead angle of the blade is set to about 45 ° as in the case of Phase 2, and is high. The conveyance speed is realized.

[Experimental example]
Next, using the image forming apparatus according to the above-described embodiment, the developer supply is performed by changing the screw pitch (the distance between the blade portions in the screw axial direction) of the first conveying screw 304 and the second conveying screw 305 in the developing device. An experiment was conducted to evaluate the occurrence of developer depletion on the downstream side of the conveyance path and the occurrence of developer rotation on the downstream side of the developer recovery conveyance path.
Table 1 below shows the measurement results of the developer conveyance speed at each screw pitch when the screw diameter is 14 mm and the screw rotation speed is 1000 rpm. In this experimental example, the developer transport speed is measured using a toner density sensor, and the movement time of the developer is measured by monitoring the toner movement with a plurality of toner density sensors. Is calculated.

In Example 1, a 20 mm pitch screw was used as the first conveying screw 304 in the developer supply conveying path. On the other hand, as the second conveying screw 305 in the developer recovery conveying path, a screw that is divided into two in the axial direction, the upstream screw portion is 40 mm pitch, and the downstream screw portion is 28 mm pitch was used. . Since the screw diameter of each screw part is 14 mm, the lead angle of the upstream screw part is 55 °, and the lead angle of the downstream screw part is 45 °. As a result, the average transport speed of the developer in the developer supply transport path was about 14 cm / sec, and the average transport speed of the developer in the developer recovery transport path was about 17 cm / sec. Using the developing device according to Example 1, the amount of developer accommodated in the developing device and the screw rotation speed were changed, and the developer depletion and developer rotation were evaluated. The evaluation results are as shown in Table 2 below.
In Table 2 below, the black diamonds indicate the case where developer depletion occurs, “×” indicates the case where accompaniment occurs, and “◯” indicates that either accompaniment or exhaustion occurs. The case where it did not do is shown.

In the second embodiment, the first conveying screw 304 in the developer supply conveying path is divided into two screws in the axial direction, the screw portion on the upstream side has a pitch of 20 mm, and the screw portion on the downstream side has a pitch of 15 mm. Using. On the other hand, as the second conveying screw 305 in the developer recovery conveying path, a screw that is divided into two in the axial direction, the upstream screw portion is 40 mm pitch, and the downstream screw portion is 28 mm pitch was used. . Since the screw diameter of each screw part is 14 mm, the lead angle of the upstream screw part is 55 °, and the lead angle of the downstream screw part is 45 °. As a result, the average transport speed of the developer in the developer supply transport path was about 13 cm / sec, and the average transport speed of the developer in the developer recovery transport path was about 17 cm / sec. Using the developing device according to Example 2, the amount of developer accommodated in the developing device and the screw rotation speed were changed, and developer depletion and developer rotation were evaluated. The evaluation results are as shown in Table 3 below.

Moreover, the same evaluation was performed about the comparative example 1 which used the screw of 28 mm pitch for both the 1st conveyance screw 304 and the 2nd conveyance screw 305. FIG. The evaluation results are as shown in Table 4 below.

Also, a first conveying screw 304 having an upstream screw portion of 40 mm pitch and a downstream portion of 20 mm pitch, and a second conveying screw 305 having an upstream screw portion of 40 mm pitch and a downstream portion of 20 mm pitch are used. Comparative Example 2 was also evaluated in the same manner. The evaluation results are as shown in Table 5 below.

  Further, 100 g of the developer adjusted so that the toner density becomes 5% is put into the developing device of Example 2, and then 0.4 g of toner is replenished from the replenishing position, and the developer on the developing roller 302 The toner concentration was measured. Measurement of the toner density of the developer on the developing roller 302 was performed several times at different times and averaged. As a result, in Example 2, the maximum toner density increased by 5.3%, whereas in Comparative Example 2, it was 5.8%. It can be said that the stirring performance of Example 2 is higher than that of Comparative Example 2 because the smaller the increase in toner density on the developing roller 302, the faster the mixing.

[Modification]
Next, a modified example of the developer circulation conveyance mechanism in the embodiment will be described.
FIG. 13 is an explanatory diagram showing a schematic configuration of a developer circulation conveyance mechanism in the present modification.
In the above embodiment, the developer recovery conveyance path is disposed below the developer supply conveyance path, and the developer is circulated and conveyed on these two conveyance paths. However, in this modification, three conveyance paths are provided. In this configuration, the developer is circulated and conveyed. Note that the configuration in which the developer is circulated and transported through the three transport paths is not limited to the configuration of the present modification.

  In this modification, a developer supply transport path in which the first transport screw 304 is disposed, a developer recovery transport path in which the second transport screw 304 is disposed, and a downstream of the developer supply transport path and the developer recovery transport path. There are provided three transport paths called developer agitation transport paths for returning the developer transported to the end to the upstream end of the developer supply transport path. A third conveyance screw 315 is provided in the developer stirring conveyance path. In the present modification, the developer transport direction of the developer supply transport path and the developer recovery transport path is from the back side to the front side, and is in the same direction. On the other hand, the developer conveyance direction of the developer agitation conveyance path is from the near side to the back side, and is opposite to the developer conveyance direction of the developer supply conveyance path and the developer recovery conveyance path.

In the configuration of this modification, the developer circulation paths are as follows.
1st conveyance screw 304 (developer supply conveyance path)-> development roller 302-> 2nd conveyance screw 305 (developer collection conveyance path)-> 3rd conveyance screw 315 (developer stirring conveyance path)-> 1st conveyance This is the forward path of the screw 304 (developer supply conveyance path).
The second is the first path of the first transport screw 304 (developer supply transport path) → the third transport screw 315 (developer stirring transport path) → the first transport screw 304 (developer supply transport path).

  In this modification as well, the problem of developer depletion may occur on the downstream side of the developer supply conveyance path as in the configuration of the above-described embodiment in which the developer is circulated and conveyed by two conveyance paths. The average developer conveyance speed is set to be the slowest. Thus, as in the case of the above embodiment, the developer movement amount from the developer stirring and conveying path to the developer supply and conveying path is maximized with a limited amount of developer in the developing device. The margin that satisfies the minimum condition that does not cause depletion increases as much as possible.

As described above, the printer according to the present embodiment (including modifications) includes the photoreceptor 1 as a latent image carrier, the charging device 2 as a latent image forming unit that forms an electrostatic latent image on the photoreceptor 1, and An exposure device 16 and a developing device 3 that develops the electrostatic latent image on the photoconductor 1 with a two-component developer containing toner and a carrier, and a toner image formed on the photoconductor 1 by the developing device 3 This is an image forming apparatus that finally transfers to a transfer sheet 8 as a recording material and forms an image on the transfer sheet. The developing device 3 uses a developer 320 conveyed in a developer supply / conveying path extending in the direction of the developing roller rotation axis along a developing roller 302 as a developer carrying member, and the surface of the rotating developing roller 302. The developer 320 carried on the surface of the developing roller 302 is conveyed to the developing area A, and the toner in the developer is adhered to the electrostatic latent image on the surface of the photosensitive member in the developing area A. The developing device develops the electrostatic latent image and collects the developer that has passed through the development area A from the developing roller 302 to a developer collection conveyance path that is a conveyance path different from the developer supply conveyance path. In addition, the developing device transfers the developer conveyed to the downstream end portion in the developer conveyance direction of the developer supply conveyance path via a developer recovery conveyance path or a separate conveyance path ( For example, a circulation conveyance mechanism that conveys the developer supply conveyance path to the upstream end portion in the developer conveyance direction via the developer agitation conveyance path). The circulation conveyance mechanism is configured such that the average conveyance speed of the developer in the developer supply conveyance path is the slowest among the conveyance paths through which the developer is circulated. As a result, with a limited amount of developer in the developing device, the amount of developer movement from the developer stirring and conveying path to the developer supply and conveying path is maximized, and there is a margin that satisfies the minimum condition that does not cause developer depletion. The degree will be as large as possible. As a result, even if the average transport speed in the developer supply transport path is decreased, it is possible to stably prevent the developer from being depleted on the downstream side of the developer supply transport path.
In particular, in this embodiment (including modifications), the developer transported to the downstream end of the developer supply transport path in the developer transport direction is transferred to the developer recovery transport path, and the developer recovery transport path The developer is circulated and conveyed so that the developer conveyed to the downstream end portion in the developer conveyance direction is transferred to the developer supply conveyance path. Such circulating conveyance is advantageous for downsizing of the developing device.
In this embodiment (including modifications), the developer conveyance speed in the developer collection conveyance path is set to be slower on the upstream side than on the downstream side in the developer conveyance direction. Thereby, it is possible to effectively suppress the rotation of the developer and the developer leakage.
Further, in the present embodiment (including modifications), the second conveying screw 305 that has a spiral blade portion on the rotating shaft and conveys the developer along the rotating shaft direction is provided as a developer recovery conveying path. The second conveying screw 305 is provided at a location where the replenishing toner is supplied from the toner replenishing port 310 for supplying the replenishing toner, or at a location downstream of the relevant location in the developer conveying direction. The upstream blade portion (the portion corresponding to phase 1) is higher in developer dispersion performance (dispersibility) than the downstream blade portion provided downstream in the developer transport direction, and developer transport. The lead angle is increased so that the performance (developer transport speed) is lowered. Specifically, the lead angle is set within a range of 55 ° to 70 °. Thereby, a high dispersibility can be exhibited in a place where a high dispersibility of the developer is required.
In this embodiment (including modifications), the developer conveyance speed in the developer supply conveyance path may be configured to be slower on the downstream side than on the upstream side in the developer conveyance direction. . This is advantageous in suppressing the depletion of developer on the downstream side of the developer supply conveyance path.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Developing device 15 Conveying belt 16 Exposure device 17 Image forming unit 301 Casing 302 Developing roller 302c Sleeve 302d Magnet roller 303 Developing doctor 304 First conveying screw 305 Second conveying screw 306 Partition plate 307 Opening portion 308 Blade Car 309 communication hole 310 toner supply port 315 third conveying screw 320 developer

JP 11-84874 A

Claims (8)

A developer that rotates a two-component developer including a toner and a carrier that are transported by a transport member in a developer supply transport path that extends in the developer support rotational axis direction along the developer support. By carrying the toner on the surface of the carrier, the two-component developer carried on the surface of the developer carrier is transported to the development area, and the toner in the two-component developer is transferred onto the surface of the latent image carrier in the development area. A developer collecting transport path that is a transport path different from the developer supply transport path from the developer carrying member for developing the latent image by adhering to the latent image of the developer and developing the latent image. In the developing device to collect in
The two-component developer transported to the downstream end of the developer supply transport path in the developer transport direction passes through the developer recovery transport path or a transport path different from the developer recovery transport path. , And a circulation transport mechanism that transports the developer supply transport path to the upstream end of the developer transport direction,
Among the transport paths that internally include a transport member that transports the two-component developer in the direction of the rotation axis of the developer carrier, the average transport speed of the two-component developer by the transport member inside the developer supply transport path is the slowest. It is configured such that,
The development is characterized in that the circulation transport mechanism is configured such that the upstream side of the developer recovery transport path is slower than the downstream side in the developer transport direction with respect to the transport speed of the two-component developer. apparatus. The developing device according to claim 1 .
The circulation transport mechanism has a spiral blade portion on a rotation shaft, and includes a transport screw that transports the two-component developer along the rotation shaft direction in the developer collection transport path.
The conveying screw has an upstream blade portion provided at a location where the replenishing toner is supplied from a toner replenishing port for supplying the replenishing toner, or at a location downstream of the location in the developer conveying direction. Also, the lead angle is increased so that the dispersion performance of the two-component developer is higher than that of the downstream blade provided on the downstream side in the developer conveyance direction and the conveyance performance of the two-component developer is lowered. A developing device comprising: The developing device according to claim 2 .
The developing device according to claim 1, wherein a lead angle of the upstream blade portion of the conveying screw is set in a range of 55 ° to 70 °. The developing device according to any one of claims 1 to 3 ,
The developing device characterized in that the circulation transport mechanism is configured such that the transport speed of the two-component developer in the developer supply transport path is slower on the downstream side than on the upstream side in the developer transport direction. .   A developer that rotates a two-component developer including a toner and a carrier that are transported by a transport member in a developer supply transport path that extends in the developer support rotational axis direction along the developer support. By carrying the toner on the surface of the carrier, the two-component developer carried on the surface of the developer carrier is transported to the development area, and the toner in the two-component developer is transferred onto the surface of the latent image carrier in the development area. A developer collecting transport path that is a transport path different from the developer supply transport path from the developer carrying member for developing the latent image by adhering to the latent image of the developer and developing the latent image. In the developing device to collect in
  The two-component developer transported to the downstream end of the developer supply transport path in the developer transport direction passes through the developer recovery transport path or a transport path different from the developer recovery transport path. , And a circulation transport mechanism that transports the developer supply transport path to the upstream end of the developer transport direction,
  Among the transport paths that internally include a transport member that transports the two-component developer in the direction of the rotation axis of the developer carrier, the average transport speed of the two-component developer by the transport member inside the developer supply transport path is the slowest. Is configured to be
  The developing device characterized in that the circulation transport mechanism is configured such that the transport speed of the two-component developer in the developer supply transport path is slower on the downstream side than on the upstream side in the developer transport direction. .   The developing device according to any one of claims 1 to 5,
  The circulation transport mechanism transfers the two-component developer transported to the downstream end portion in the developer transport direction of the developer supply transport path to the developer recovery transport path, and the developer transport direction of the developer recovery transport path A developing device characterized in that the two-component developer is circulated and conveyed so that the two-component developer conveyed to the downstream end is transferred to the developer supply and conveyance path. In a process cartridge that integrally supports a latent image carrier and a developing device that develops a latent image on the latent image carrier and is configured to be detachable from the image forming apparatus main body,
7. A process cartridge using the developing device according to claim 1 as the developing device. A latent image carrier, a latent image forming unit that forms a latent image on the latent image carrier, and a developing device that develops the latent image on the latent image carrier using a two-component developer containing toner and a carrier. An image forming apparatus for forming an image on the recording material by finally transferring the toner image formed on the latent image carrier by the developing device to the recording material,
An image forming apparatus using the developing device according to claim 1 as the developing device.

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