JP6025383B2 - Development device - Google Patents

Description

  The present invention relates to a developing device that replenishes a developer containing a carrier into a developer circulation path and causes excess developer to overflow from a discharge port, and more specifically, in a region along a discharge port of a developer conveying screw. For partial structure.

  The toner image formed on the image carrier by the developing device is transferred to a recording material directly or via an intermediate transfer member, and the recording material onto which the toner image has been transferred is heated and pressed by a fixing device to fix the image on the recording material. Image forming apparatuses are widely used.

  In a developing device that replenishes only toner that is consumed in association with image formation, the charging performance of the carrier that continues to be circulated through the developing device and continues to receive friction gradually decreases. For this reason, there has been put to practical use a developing device that discharges the developer that has become excessive due to the replenishment of the carrier while replenishing the replenishment developer including the carrier to the developer circulation path (Patent Document 1).

  In the developing device of Patent Document 2, a discharge port is provided in the developer circulation path, and a part of the developer conveyed by the conveying screw is caused to overflow from the discharge port. In this case, when the deterioration of the developer progresses or in a high humidity environment, if the developer fluidity decreases, the amount of the developer overflowed from the discharge port becomes unstable. Therefore, in Patent Document 2, the screw blades are removed or the diameter of the developer along the discharge port of the developer conveying screw is reduced.

JP 59-1000047 A JP 2000-112238 A

  When the blade blade is removed or the diameter of the developer along the discharge port of the developer conveying screw is reduced, the developer fluidity decreases when the deterioration of the developer progresses or in a high humidity environment. It has been found that the developer in the developing device tends to increase. This is because the developer that progresses along the discharge port without being agitated is less likely to collapse into the discharge port, so that it is easy to pass through the front of the discharge port while the developer surface is higher than the discharge port.

  The present invention stabilizes the developer discharging performance in the portion along the discharge port of the conveying screw, and the developer amount in the developing device is excessive even when the developer is deteriorated or in a high humidity environment. An object of the present invention is to provide an image forming apparatus that does not easily occur.

  The developing device of the present invention includes a rotating developer carrying member, a circulation path through which a developer including toner and a carrier circulates along the developer carrying body, and a replenishing unit that replenishes at least the carrier to the circulation path; A discharge port provided on a side wall of the circulation path, through which a part of the circulating developer overflows and is discharged, and a conveying member disposed in the circulation path and provided with screw blades around a central axis It is. And the area | region along the said discharge port of the said conveyance member has a cross-sectional area of the axial direction of the said central axis larger than the area | region which provided the said screw blade, without providing the said screw blade.

  In the developing device of the present invention, the rotation axis of the region along the discharge port of the conveying member has a larger cross-sectional area in the direction perpendicular to the front and rear regions, so that the developer surface when passing through the region As a result, the developer easily overflows from the discharge port.

  Therefore, the developer discharge performance in the portion along the discharge port of the conveying screw is stabilized, and the amount of developer in the developing device is unlikely to be excessive even when the deterioration of the developer progresses or in a high humidity environment.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of a developing device. It is explanatory drawing of the circulation path of the developer in a developing device. It is explanatory drawing of the partial structure of the image development screw in a comparative example. It is explanatory drawing of a structure of the image development apparatus of a comparative example. 2 is an explanatory diagram of a partial configuration of a developing screw in Embodiment 1. FIG. 2 is an explanatory diagram of a configuration of a developing device according to Embodiment 1. FIG. 6 is an explanatory diagram of a partial configuration of a developing screw in Embodiment 2. FIG. FIG. 10 is an explanatory diagram of a configuration of a developing device according to Embodiment 2. FIG. 10 is an explanatory diagram of a configuration of a developing device according to Embodiment 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention replaces part or all of the configuration of the embodiment as long as the central axis of the screw member is formed thick in the region along the discharge port of the conveying member and the developer discharge performance is enhanced. Other embodiments replaced with a typical configuration can also be implemented.

  Therefore, in the case of a developing device using a two-component developer, not only a vertical developing device in which the developing chamber and the stirring chamber are arranged in the vertical direction but also a horizontal type in which the developing chamber and the stirring chamber are arranged in the horizontal direction can be implemented. . The present invention can be carried out not only with a developing device using one developer carrier but also with two or three developing devices.

  Image forming apparatus is tandem type / 1 drum type, intermediate transfer type / recording material transport type / direct transfer type, electrostatic image forming method, charging / exposure method, transfer method, fixing device type, monochrome / full color distinction It can be implemented without. In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full color printer in which image forming portions SY, SM, SC, and SK of yellow, magenta, cyan, and black are arranged along an intermediate transfer belt 121. is there.

  In the image forming unit SY, a yellow toner image is formed on the photosensitive drum 101 </ b> Y and is primarily transferred to the intermediate transfer belt 121. In the image forming unit SM, a magenta toner image is formed on the photosensitive drum 101M and is primarily transferred to the intermediate transfer belt 121. In the image forming sections SC and SK, a cyan toner image and a black toner image are formed on the photosensitive drums 101C and 101K, respectively, and are primarily transferred to the intermediate transfer belt 121. The four color toner images carried on the intermediate transfer belt 121 are conveyed to the secondary transfer portion T2 and secondarily transferred to the recording material P.

  The recording material P drawn from the recording material cassette 135 is separated one by one by the separation roller 136 and sent to the registration roller 137. The registration roller 137 sends the recording material P to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 121. In the process in which the recording material P is nipped and conveyed by the secondary transfer portion T2, a full color toner image is secondarily transferred from the intermediate transfer belt 121 to the recording material P by applying a voltage to the secondary transfer roller 125. The recording material P on which the four-color toner images are secondarily transferred is separated from the intermediate transfer belt 121 by the curvature, and sent to the fixing device 130. Is discharged. The transfer residual toner remaining on the surface of the intermediate transfer belt 121 is collected by the belt cleaning device 114.

  The image forming units SY, SM, SC, and SK are configured substantially the same except that the colors of toner used in the developing devices 104Y, 104M, 104C, and 104K are different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit SY will be described, and the image forming units SM, SC, and SK will be described by replacing Y at the end of the reference numerals attached to the constituent members being described as M, C, and K. .

  In the image forming unit SY, a corona charger 102Y, an exposure device 103Y, a developing device 104Y, a transfer blade 105Y, and a drum cleaning device 109Y are arranged around the photosensitive drum 101Y. The photosensitive drum 101Y is formed by forming a negatively charged photosensitive layer on the base of an aluminum cylinder, and rotates in the direction of arrow a. The corona charger 102Y irradiates charged particles accompanying corona discharge to uniformly charge the surface of the photosensitive drum 101Y to the negative dark portion potential VD.

  The exposure device 103Y scans the scanning line image data obtained by developing the yellow separated color image with a rotating mirror, and writes an electrostatic image of the image on the surface of the photosensitive drum 101Y. When the surface potential of the photosensitive drum 101Y charged to the dark portion potential VD is exposed to light and decreases to the light portion potential VL, the negatively charged toner can be attached. As will be described later, the developing device 104Y develops an electrostatic image formed on the photosensitive drum 101Y to form a toner image.

  The transfer blade 105 </ b> Y presses the inner surface of the intermediate transfer belt 121 to form a primary transfer portion between the photosensitive drum 101 </ b> Y and the intermediate transfer belt 121. By applying a voltage to the transfer blade 105Y, the toner image carried on the photosensitive drum 101Y is primarily transferred to the intermediate transfer belt 121. The drum cleaning device 109Y slides a cleaning blade on the photosensitive drum 101Y to recover the transfer residual toner remaining on the photosensitive drum 101Y by escaping from the primary transfer to the intermediate transfer belt 121.

  The intermediate transfer belt 121 is supported around a tension roller 123, a driving roller 122, and a counter roller 124, and is driven by the driving roller 122 to rotate in the direction of arrow R2. The secondary transfer roller 125 abuts on the intermediate transfer belt 121 whose inner surface is supported by the counter roller 124 to form a secondary transfer portion T2.

<Developer>
The developing device 104Y visualizes the electrostatic image on the photosensitive drum 101Y as a toner image using a developer (two-component developer) in which yellow toner (non-magnetic) and carrier (magnetic) are mixed.

  The toner has a binder resin such as a negatively chargeable polyester-based resin, a colorant, and, if necessary, an additive such as silica. The toner contains a wax to improve separation after fixing. There is also a case to let you. In recent years, a binder resin having a low melting point or a low glass transition point Tg (for example, Tg ≦ 70 ° C.) is used for improving the fixability. The average volume particle size of the toner is preferably 4 μm or more and 10 μm or less. Here, the average volume particle size is 7 μm. If the toner particle size is too small, it will be difficult to rub against the carrier, making it difficult to control the toner charge amount. If it is too large, a fine toner image cannot be formed.

  As the carrier, surface oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals, and alloys thereof, or magnetic particles such as oxide ferrite can be used. The method for producing magnetic particles is not particularly limited. The average volume particle size of the carrier is preferably 20 to 60 μm, and here, the average volume particle size is 40 μm. If the particle size of the carrier is too small, there will be a problem that the carrier adheres to the developing sleeve 6 during development, and if it is too large, there will be a problem that the carrier disturbs the toner image during development.

<Developing device>
FIG. 2 is an explanatory diagram of the configuration of the developing device. FIG. 3 is an explanatory diagram of a developer circulation path in the developing device.

  As shown in FIG. 2, the developing device 104Y is a vertical stirring type in which a developing chamber 401 and a stirring chamber 403 are arranged side by side in the height direction. However, the present invention can also be implemented in a horizontal stirring type developing device in which the developing chamber 401 and the stirring chamber 403 that are often used conventionally are arranged horizontally.

  The inside of the developing container 2 is divided into a developing chamber 401 and a stirring chamber 403 by a partition wall 300 at the center in the height direction. A developing screw 3 a is disposed in the developing chamber 401, and a stirring screw 3 b is disposed in the stirring chamber 403.

  As shown in FIG. 3, the developing chamber 401 and the stirring chamber 403 arranged above and below are communicated with each other by a scooping section 402 and a scooping section 404 at both ends of the partition wall 300. The scooping section 402 is an opening through which the developer that has passed through the developing chamber 401 without being supplied from the developing chamber 401 to the developing sleeve 6 is scooped into the stirring chamber 403. The pumping unit 404 is an opening through which the developer collected from the developing sleeve 6 in the stirring chamber 403 and the developer pumped off from the developing chamber 401 are pumped into the developing chamber 401.

  The developing screw 3a is disposed along the developing sleeve 6 at the bottom of the developing chamber 401, and rotates to supply the developer to the developing sleeve 6 while transporting the developer in the developing chamber 401 in the axial direction c. The agitating screw 3b is disposed at the bottom of the agitating chamber 403 in parallel with the developing sleeve 6, and conveys the developer in the agitating chamber 403 in the axial direction d opposite to the developing screw 3a.

  The developer is conveyed to the developing screw 3a and the agitating screw 3b in which screw blades are spirally attached at predetermined intervals in the circumferential direction, and the developer passes through the assembling unit 404 and the assembling unit 402, and the developing chamber 401 and the agitating chamber 403 Circulate between. The developer is conveyed while being stirred by the developing screw 3 a and the stirring screw 3 b and circulates in the developing container 2. When the developer is agitated, the toner and the carrier are rubbed against each other, and the toner is negatively charged and the carrier is positively charged.

  The developer circulation path in the developing device 104Y has a first path that contributes to development and a second path that does not contribute to development. The first path is a path that circulates through the developing chamber 401 → the developing sleeve 6 → the stirring chamber 403 → the assembly unit 404 → the developing chamber 401 and contributes to development. The second path is a path that circulates through the developing chamber 401 → the assembling unit 402 → the stirring chamber 403 → the assembling unit 404 → the developing chamber 401 and completes in the developing container 2 that does not contribute to development.

  As shown in FIG. 2, the developing device 104Y carries the charged developer on the rotating developing sleeve 6, forms a magnetic brush by the magnetic force of the magnet roller 6m, and rubs the photosensitive drum 101 with the tip of the magnetic brush. To do. The diameter of the developing sleeve 6 is 20 mm, and the diameter of the photosensitive drum 101 is 80 mm. The facing distance between the developing sleeve 6 and the photosensitive drum 101 is set to 400 μm. In the developing area A, a 700 μm magnetic brush is formed and the tip is brought into contact with the photosensitive drum 101. In the developing area A, the developing sleeve 6 moves in the forward direction and the moving direction of the photosensitive drum 101, and the circumferential speed of the developing sleeve 6 is 2.0 times the photosensitive drum ratio.

  The developing container 2 has an opening 2 h at a position corresponding to the developing area A facing the photosensitive drum 101. The developing sleeve 6 is rotatably disposed in the developing container 2 so as to be partially exposed in the direction of the photosensitive drum 101 through the opening 2h. The ratio of the peripheral speed of the developing sleeve 6 to the photosensitive drum is usually set to a value between 1.0 and 3.0. The higher the peripheral speed ratio, the better the developability. However, if the peripheral speed ratio is too large, toner scattering, developer deterioration, and the like occur.

  The developing sleeve 6 is made of non-magnetic aluminum, and has moderate unevenness on the surface. By the unevenness, friction between the developer and the surface of the developing sleeve 6 is intentionally created, and the transport amount of the developer is ensured. . This is because, when the surface of the developing sleeve 6 is smooth, the friction between the developer and the surface of the developing sleeve 6 is insufficient, and the transportability of the developer cannot be ensured sufficiently.

  The surface of the developing sleeve 6 has moderate unevenness using blasting. Blasting is a processing method in which particles such as abrasive powder and glass beads having a predetermined particle size distribution are sprayed at high pressure. The central area of the developing sleeve 6 that has been blasted is called a blast area, and the end area that is not blasted is called a non-blast area. In the central region of the developing sleeve 6, a blast region is formed by blasting an area slightly wider than the image formable region. Since the end regions at both ends of the developing sleeve 6 are non-blasted regions that are not blasted, the developer conveying ability is low.

  The magnet roller 6m is disposed inside the developing sleeve 6 and both ends thereof are fixed to the developing container 2 in a non-rotating manner. The magnet roller 6 m is a roller-shaped magnetic field generating means included in the developing sleeve 6. The magnet roller 6m has a developing magnetic pole S1 at a position facing the developing area A. The developer in the development area A forms a magnetic brush by the magnetic field of the S1 pole.

  In addition to the S1 pole, the magnet roller 6m has a total of 5 poles of N1, N2, N3, and S2. The developer bounced up by the developing screw 3a is restrained by the developing sleeve 6 by the magnetic field of the N2 pole. The developer is applied to the developing sleeve 6 by a magnetic field between the N2 pole and the S2 pole, a magnetic field between the S2 pole and the N1 pole, a magnetic field between the N1 pole and the S1 pole, and a magnetic field between the S1 pole and the N3 pole. Supported. The developer rises due to the magnetic field of the S2 pole, and the amount of developer carried is regulated to an appropriate amount by the regulating blade 5. The repulsive magnetic field between the N3 pole and the N2 pole releases the magnetic binding force.

  The regulating blade 5 is disposed in the developing container 2 so that the leading end thereof faces the center of the developing sleeve 6 and faces the developing sleeve 6 with a predetermined gap, upstream of the developing region A in the rotation direction of the developing sleeve 6. The The regulating blade 5 is a plate-like member that extends along the longitudinal axis of the developing sleeve 6. The material of the regulating blade 5 is a nonmagnetic material such as aluminum or stainless steel, a magnetic low carbon steel material such as SPCC, a laminated material of a nonmagnetic material and a magnetic material, or the like.

  The regulating blade 5 defines an interval at which the developer on the developing sleeve 6 can pass from the inside of the developing container 2 to the photosensitive drum 101 side, and an appropriate amount of developer supplied to the electrostatic image on the photosensitive drum 101 in the developing area A. To. With the rotation of the developing sleeve 6, the developer on the developing sleeve 6 passes through the gap between the tip of the regulating blade 5 and the developing sleeve 6 and is sent to the developing area A.

By adjusting the gap between the regulating blade 5 and the developing sleeve 6, the amount of the developer carried on the developing sleeve 6 and conveyed to the developing area A is adjusted. The distance between the regulating blade 5 and the developing sleeve 6 was set to 400 μm, and the mass per unit area of the developer in the developing sleeve 6 was adjusted to 30 mg / cm ² .

  If the gap between the regulating blade 5 and the developing sleeve 6 is too narrow, toner agglomerates are likely to be clogged in the gap, and a desired toner amount cannot be secured, resulting in a decrease in image density. If the gap between the regulating blade 5 and the developing sleeve 6 is too wide, the mass per unit area of the developer in the developing sleeve 6 increases, which is not preferable because the developer is clogged in the developing region A and carrier transfer increases.

  As the developing screw 3 a rotates, the developer jumps up and is supplied to the developing sleeve 6. Since the developer carrier is a magnetic material, the surface of the developing sleeve 6 is coated by being restrained by the magnetic force generated by the magnet roller 6 m in the developing sleeve 6. Since the carrier is positively charged, it is coated with a negatively charged toner. As the developing sleeve 6 rotates, the developer on the developing sleeve 6 passes through the regulating blade 5 and its layer thickness is regulated to adjust the coating amount. Thereafter, the developer on the developing sleeve 6 is conveyed to the developing area A facing the photosensitive drum 101, forms a magnetic brush, rubs the photosensitive drum 101, and charges the charged toner by electrostatic force. 101 is transferred to the electrostatic image.

  The power source D6 applies an oscillating voltage obtained by superimposing the AC voltage Vac to the negative DC voltage Vdc to the developing sleeve 6 and has an electric quantity of toner corresponding to the development contrast that is the difference potential between the bright portion potential VL and the DC voltage Vdc. Is transferred from the developing sleeve 6 to the photosensitive drum 101. The developer that has passed through the developing region A is separated from the developing sleeve 6 in the developing container 2 and collected by the stirring screw 3b.

  The power source D6 applies to the developing sleeve 6 an oscillating voltage obtained by superimposing an AC voltage Vac having a peak-to-peak voltage Vpp of 1800 V and a frequency f of 12 kHz on a DC voltage Vdc of −500 V. However, the DC voltage and the AC voltage are not limited to this.

<Replenishment and discharge of developer>
As shown in FIG. 3, since the toner is charged by friction with the carrier, the toner charge amount Q / M changes when the ratio of the toner to the carrier in the developer changes. The toner and the carrier in the developing device 104Y are charged with opposite polarities, and the total charge amount becomes zero. Therefore, the toner charge amount Q / M decreases as the toner ratio of the developer increases. When toner is consumed by image formation, the toner ratio of the developer decreases and the toner charge amount Q / M increases. When the toner charge amount Q / M is increased, the amount of toner developed by offsetting the charge of the same electrostatic image is reduced and the image density is lowered. Therefore, almost the same amount of toner as consumed toner is supplied to the developing device 104Y. To be replenished. As a result, the toner ratio of the developer is maintained within a certain range, and the toner charge amount Q / M is controlled to be substantially constant.

  In the process in which the developer is agitated and conveyed in the developing device 104Y, the carrier in the developer receives friction from the toner, other carriers, the regulating blade 5, and the like. The charging performance of the carrier gradually decreases. The material on the surface of the carrier is peeled off due to friction, or a foreign substance adheres to the surface of the carrier, so that the surface property of the carrier is changed and the charging performance of the carrier is lowered. This is called carrier deterioration. When the charging performance of the carrier is lowered, the toner charge amount Q / M is lowered, and problems such as white background fogging where the toner adheres to the white background portion of the image are not preferable.

  Therefore, in the developing device 104Y, the replenishment developer in which the carrier is mixed with the toner in a certain ratio is replenished along with the image formation, while the developer that has become excessive in the development device 104Y due to the replenishment of the replenishment developer Is overflowing from the discharge port 40. The developing device 104Y has a discharge port 40 outside the blast region of the developing sleeve 6 in the longitudinal direction of the developing device 104Y.

  The developing device 104Y replenishes the carrier with the image formation, and mixes the replenished carrier and the developer that circulates with the developing screw 3a and the agitating screw 3b, while discharging the excess developer in the developing container 2 to the discharge port 40. To the outside of the developing device 104Y. The carrier in the developing container 2 is continuously replaced with a new one little by little to maintain the average charging performance of the entire carrier.

  Above the developing device 104Y, a hopper 12 that contains a replenishment developer in which 90% by weight toner and 10% by weight carrier are mixed is disposed. In FIG. 3, the hopper 12 is shown exaggerated so that a path for supplying the developer to the stirring chamber 403 can be seen. The hopper 12 includes a screw-like replenisher transport member 13 at the lower portion, and one end of the replenisher transport member 13 extends to the position of the replenishment port 11 provided at the end of the developing device 104Y. The replenishment developer containing the amount of toner consumed by the image formation is cut out from the hopper 12 by the rotation of the replenishment screw 14, passes through the replenishment port 11, and is replenished to the developing container 2. The replenishment developer is conveyed from the hopper 12 in the direction of arrow g and enters the developing container 2. In order to prevent the replenished developer from being supplied to the developing sleeve 6 before being stirred, the replenishing port 11 is provided downstream of the end of the developing chamber 401. A discharge port 40 for discharging the developer is provided on the wall surface in the downstream region of the developing chamber 401. In order to prevent the replenished developer from being immediately discharged from the discharge port 40, the discharge port 40 is provided upstream of the supply port 11.

  As shown in FIG. 2, when the developer for replenishment is replenished from the hopper 12 and the developer in the developing container 2 is increased, the excess developer corresponding to the increased amount overflows from the discharge port 40 in the direction of arrow i. To be discharged. The developer overflowed from the discharge port 40 falls into the discharge chamber 405 and is returned to a collection container (not shown) disposed at one end portion in the longitudinal direction of the developing container 2 by the collection screw 3 c disposed on the bottom surface of the discharge chamber 405. Collected.

<Comparative Example 1>
FIG. 4 is an explanatory diagram of a partial configuration of the developing screw in the comparative example. FIG. 5 is an explanatory diagram of a configuration of a developing device of a comparative example.

  As shown in FIG. 4, when the screw blades 3p are continuously formed on the entire developing screw 3a, the developing screw 3a jumps up to the discharge port 40 and discharges the developer that is not excessive. As shown in FIG. 5, with the rotation of the developing screw 3a, the screw blade 3p jumps up and discharges the developer at a position lower than the discharge port 40. When more developer than necessary is discharged through the discharge port 40, the developer in the developing container 2 is reduced, and in the worst case, the developer cannot be supplied to the developing sleeve 6.

  Therefore, as shown in FIG. 4, in the developing device 104H of the comparative example, the discharge port 40 is provided on the surface of the side wall perpendicular to the transport direction c. In the region SQ that is the position facing the discharge port 40 along the discharge port 40 of the developing screw 3a, the screw blade 3p of the developing screw 3a is omitted to form a thin cylindrical shaft 200. By omitting the screw blades 3p, the force applied to the developer in the direction of the discharge port 40 is reduced, so that the discharge of the developer due to the splashing with the rotation of the development screw 3a is reduced, and only the excess developer is discharged. be able to. The developer is prevented from jumping to the discharge port 40 by the rotation of the developing screw 3a, and the developer discharge through the discharge port 40 due to the jump is reduced. A developer that is not excessive is prevented from being discharged by the developer jumping up by the developing screw 3a.

  As shown in FIG. 4, since the developing device 104H of the comparative example omits the screw blade 3p, the developer near the discharge port 40 does not receive force from the developing screw 3a. The developer in the vicinity of the discharge port 40 is conveyed while being lifted up by being pushed in the circulation direction by the developer conveyed from the upstream side, and the developer at a height higher than the lower end of the discharge port 40 is discharged. It is discharged from 40.

  In the developing device 104H of the comparative example, since the screw blade 3p in the region along the discharge port 40 is omitted, the force that the developer receives in the direction of the discharge port 40 tends to be too small. If the screw blade 3p at the position facing the discharge port 40 of the developing screw 3a is omitted, the developer receives insufficient force from the screw 3a toward the discharge port 40, so that the developer is positioned higher than the lower end of the discharge port 40. Even if it exists, it will pass through the discharge port 40. In this case, the tendency for the developer to pass in front of the discharge port 40 increases, and it becomes difficult for the excess developer to be discharged.

  If the excess developer is not discharged, the function of replacing the carrier of the developing device 104H is weakened, and the effect of maintaining the charging performance of the carrier is reduced. Further, if the carrier is continuously supplied from the hopper 12 under the situation where the developer is not sufficiently discharged through the discharge port 40, the developer in the developing container 2 increases too much and the power consumption of the developing device 104H increases. As the developer increases, the load on the developing screw 3a becomes too large. It has been confirmed that the same problem as in the comparative example occurs even when the outer diameter of the screw blade in the region along the discharge port 40 of the developing screw 3a is made smaller than the other parts.

  Therefore, in the following embodiment, the central axis of the region SQ where the screw blades along the discharge port 40 of the developing screw 3a are omitted is made thicker than the central axis 3g of the region before and after the screw blades 3p are provided. Yes.

<Example 1>
FIG. 6 is an explanatory diagram of a partial configuration of the developing screw in the first embodiment. FIG. 7 is an explanatory diagram of a configuration of the developing device according to the first embodiment. Among the configurations of the developing device in the first embodiment, the same configurations as those in the comparative example are denoted by the same reference numerals as those in FIGS. 4 and 5, and redundant description is omitted.

  As shown in FIG. 3, in the first embodiment, the developing chamber 401, which is an example of a circulation path, circulates along the developing sleeve 6, which is an example of a developer carrying member on which a developer including toner and a carrier rotates. The hopper 12 that is an example of a supply unit supplies at least the carrier to the stirring chamber 403 that is an example of a circulation path. The discharge port 40 is provided on the side wall of the developing chamber 401, and a part of the circulating developer overflows and is discharged. The developing screw 3a, which is an example of a conveying member, is disposed in the developing chamber 401, and screw blades 3p are provided around the central axis.

  As shown in FIG. 6, in the first embodiment, the region along the discharge port 40 of the developing screw 3a is not provided with the screw blade 3p, but is cut off in the direction perpendicular to the axis of the central axis more than the region provided with the screw blade 3p. The area is large. The outer peripheral surface of the central axis in the region where the screw blades 3p are provided and the outer peripheral surface of the central axis in the region along the discharge port 40 are connected by a tapered surface 3q. The area along the discharge port 40 of the developing screw 3a has an elliptical shape in which the cross-sectional shape of the central axis in the direction perpendicular to the central axis is smaller than the diameter of the screw blade 3p. The region along the discharge port 40 of the developing screw 3a is an ellipse having a cross-sectional shape in the direction perpendicular to the central axis of the central axis smaller than the diameter of the screw blade 3p without providing the screw blade 3p. The area along the discharge port 40 of the developing screw 3a has a larger cross-sectional area in the direction perpendicular to the central axis than the outside in a range wider than the discharge port 40 in the axial direction of the developing screw 3a.

  In the first embodiment, the developing screw 3a in the region along the discharge port 40 is provided with the axial blade cross-sectional area of the central axis of the developing screw 3a and the screw blades 3p before and after the screw screw 3p, instead of omitting the screw blade 3p. It is larger than the area. As a result, the developer surface of the developer conveyed through the developing chamber 401 rises high along the center line of the developing chamber 401 and forms an inclined surface of the developer that decreases toward the discharge port 40. Therefore, since the developer flows on the inclined surface and overflows to the discharge port 40, the variation in the overflow amount accompanying the change in fluidity is reduced.

  In the first embodiment, the developing screw 3 a in the region along the discharge port 40 has a flat elliptical axis 201 with a central axis from which the screw blade 3 p is omitted. Thereby, the developer surface of the developer shakes with the rotation of the developing screw 3a, and the developer that is lifted to a position higher than the lower end of the discharge port 40 increases periodically. For this reason, the inclination of the inclined surface of the developer that decreases toward the discharge port 40 periodically becomes steep, so that the developer flows through the inclined surface and more easily overflows into the discharge port 40. Therefore, the variation in the overflow amount accompanying the change in the fluidity of the developer is further reduced, and the discharge of excess developer is further promoted.

  As shown in FIG. 7, in Example 1, the flat part was made into an ellipse. The major axis of the ellipse is half that of the screw blade 3p, and the minor axis of the ellipse is made equal to the central axis 3g so that the developer is not splashed up and discharged from the outlet 40 by the ellipse portion. The length of the elliptical axis 201 in the longitudinal direction is wider than the range of the discharge port 40.

  The movement of the developer near the discharge port 40 in the first embodiment will be described. In the sectional view of the vicinity of the discharge port 40, the major axis of the ellipse repeats horizontal and vertical as the screw rotates. As shown in FIG. 7, the agent surface when the major axis of the ellipse axis 201 is vertical is higher than that when the major axis of the ellipse axis 201 is horizontal, and is higher than the lower end of the discharge port 40. The developer amount increases and the discharge amount increases.

  The developer near the discharge port 40 is pushed in the circulation direction by the developer conveyed from the upstream side, and is conveyed while being raised to the discharge port 40 while being discharged. The developer overflowed from the discharge port 40 falls into the discharge chamber 405 and is returned to a collection container (not shown) disposed at one end portion in the longitudinal direction of the developing container 2 by the collection screw 3 c disposed on the bottom surface of the discharge chamber 405. Collected. Further, when the amount of the developer passing through the vicinity of the discharge port 40 is small, the developer does not come into contact with the elliptical axis, so that the problem of jumping up the developer and discharging it to the discharge port 40 does not occur.

  In the developing device of Example 1, the developer rises high without being agitated at the central portion along the central axis formed thick, and the surface of the agent is inclined toward the discharge port. For this reason, even if the developer is at the height of the edge of the discharge port, the developer overflows from the discharge port so as to collapse the inclined surface. For this reason, the problem of discharging due to splashing and excessive developer is not solved at the same time. Further, by shaking the agent surface and increasing the developer passing through a position higher than the lower end of the discharge port 40, the sensitivity of the discharge amount with respect to the developer amount in the developer container 2 increases, and the developer amount in the developer container 2 increases. Is stable.

  In the developing device of Example 1, the change in the developer amount in the developing device 104Y is about half that of the comparative example, and the carrier can be replaced and the charging ability of the carrier can be accurately maintained. Further, there is no problem that the excess developer is not discharged and the developer in the developing container 2 becomes excessive.

  In electrophotography, since toner is controlled using electrostatic force even in the transfer process, it is important to maintain the toner charge amount Q / M at a desired value. According to the configuration of the first embodiment, the fluctuation range of the toner charge amount Q / M is reduced by reducing the fluctuation of the developer amount in the developing device 104Y. For this reason, it becomes easy to maintain the toner charge amount Q / M at a desired value, and the transfer performance, image density, and the like are also stabilized.

<Example 2>
In the first embodiment, the screw blade 3p in the region along the discharge port 40 is completely omitted. However, the present invention is also effective when the screw blades 3p in the region along the discharge port 40 are reduced in size and omitted incompletely. In the developing device in which the discharge port 40 is provided on a side surface perpendicular to the developer transport direction and the screw blade 3p of the developing screw 3a at the position facing the developer discharge port 40 is made smaller in diameter than the front and rear regions, excessive development is performed. The discharge of the agent can be promoted and the charging ability of the carrier can be maintained. The predetermined area including the area facing the discharge port 40 in the axial direction of the developing screw 3a is smaller in the diameter of the screw blade 3p than the outside thereof, and in the axis-perpendicular direction of the central axis than the area where the screw blade 3p is provided. Large cross-sectional area.

<Example 3>
FIG. 8 is an explanatory diagram of a partial configuration of the developing screw in the second embodiment. FIG. 9 is an explanatory diagram of a configuration of the developing device according to the second embodiment. Among the configurations of the developing device in the third embodiment, the same configurations as those in the comparative example are denoted by the same reference numerals as those in FIGS. 4 and 5 and redundant description is omitted.

  As shown in FIG. 8, in the developing device of Example 3, the region along the discharge port 40 of the developing screw 3 a is not provided with the screw blade 3 p, and is axially perpendicular to the center axis than the region where the screw blade 3 p is provided. Large cross-sectional area.

  In the screw 3a in the vicinity of the discharge port 40, by increasing the central axis in which the screw blade 3p is omitted, the developer surface in the vicinity of the discharge port 40 is increased, and the developer passing through a position higher than the lower end of the discharge port 40 is increased. This facilitates the discharge of excess developer.

  In Example 3, the diameter of the large-diameter shaft 202 having a circular cross section was made half the diameter of the screw blade 3p. Further, the length of the large diameter shaft 202 in the longitudinal direction is made wider than the range of the discharge port 40.

  As shown in FIG. 9, the cross-sectional area of the screw blade 3p in the vicinity of the discharge port 40 is larger than the central axis 3g in the front and rear regions where the screw blade 3p is provided, so compared with the surface of the comparative example of FIG. As the diameter is increased, the surface becomes higher. For this reason, the developer amount at a position higher than the lower end of the discharge port 40 increases, and the discharge amount increases. The developer in the vicinity of the discharge port 40 is pushed in the circulation direction by the developer conveyed from the upstream side, and is conveyed while being raised to the discharge port 40 while being discharged. The developer overflowed from the discharge port 40 falls into the discharge chamber 405 and is returned to a collection container (not shown) disposed at one end portion in the longitudinal direction of the developing container 2 by the collection screw 3 c disposed on the bottom surface of the discharge chamber 405. Collected.

  In addition, when the amount of developer passing through the vicinity of the discharge port 40 is small, the developer does not come into contact with the large-diameter shaft 202, and therefore, the developer is splashed up and discharged from the discharge port 40 so that the necessary developer is not satisfied. Will not happen. Therefore, the configuration according to the third embodiment can simultaneously solve the problem of discharging due to splashing and excessive developer being not discharged.

  According to the developing device 104Y of the third embodiment, the developer surface can be increased by reducing the volume through which the developer in the vicinity of the discharge port 40 can pass, and the developer passing through a position higher than the lower end of the discharge port 40 can be increased. it can. Therefore, the sensitivity of the discharge amount with respect to the developer amount in the developing container 2 is increased, and the developer amount in the developing device 104Y is stabilized. In the developing device 104Y of Example 3, the variation in the amount of developer in the developing device 104Y is about half that of the prior art, and the carrier can be replaced accurately. Further, there is no problem that the excess developer is not discharged and the developer in the developing container 2 becomes excessive.

<Example 4>
FIG. 10 is an explanatory diagram of the configuration of the developing device according to the fourth embodiment. As shown in FIG. 10, in Example 4, the center of the central axis having a large cross-sectional area in the direction perpendicular to the axis in the region along the discharge port 40 in Example 3 is eccentric from the center of the developing screw 3a. Thereby, the effect of shaking the developing surface with the rotation of the developing screw 3a similar to that of the first embodiment is realized.

1a, 1b, 1c, 1d photosensitive drums 2a, 2b, 2c, 2d corona chargers 3a, 3b, 3c, 3d exposure devices 4a, 4b, 4c, 4d developing devices 5a, 5b, 5c, 5d transfer rollers, 6 developing sleeves DESCRIPTION OF SYMBOLS 11 Supply port, 12 Hopper, 13 Supply agent conveyance member 22 Developing container, 23 Developing chamber, 24 Stirring chamber,
25 First conveying screw, 26 Second conveying screw 27 Bulkhead, 28 Developing sleeve, 28 m Magnet roller 29 Regulating blade, 32 Supply screw, 40 Developer discharge port 52 Screw shaft 53, 54, 55 Rib 56 Disk member 201 Elliptical shaft, 202 Large-diameter shaft 401 Development chamber, 403 Stir chamber

Claims (5)

A rotating developer carrier;
A circulation path through which a developer including toner and a carrier circulates along the developer carrier;
Supply means for supplying at least the carrier to the circulation path;
A discharge port provided on a side wall of the circulation path, and a part of the circulating developer overflows and is discharged;
A conveying member disposed in the circulation path and provided with screw blades around the central axis;
The developing device according to claim 1, wherein an area along the discharge port of the conveying member has a larger cross-sectional area in the direction perpendicular to the central axis than the area where the screw blades are provided without providing the screw blades.   The region along the discharge port of the transport member has a larger cross-sectional area in the axis-perpendicular direction of the central axis than the outside in a range wider than the discharge port in the axial direction of the transport member. Item 2. The developing device according to Item 1.   The region along the discharge port of the conveying member is an ellipse having a cross-sectional shape in a direction perpendicular to the axis of the central axis that is smaller in diameter than the diameter of the screw blade. Development device. A rotating developer carrier;
A circulation path through which a developer including toner and a carrier circulates along the developer carrier;
Supply means for supplying at least the carrier to the circulation path;
A discharge port provided on a side wall of the circulation path, and a part of the circulating developer overflows and is discharged;
A conveying member disposed in the circulation path and provided with screw blades around the central axis;
The region along the discharge port of the transport member is a predetermined region including a region facing the discharge port in the axial direction of the transport member, and the diameter of the screw blade is smaller than the outside thereof, and the screw blade is A developing device characterized in that a cross-sectional area in a direction perpendicular to the central axis of the central axis is larger than a provided area. The outer peripheral surface of the central axis of the region provided with the screw blades and the outer peripheral surface of the central shaft having a large cross-sectional area in the direction perpendicular to the axis of the region along the discharge port are connected by a tapered surface. The developing device according to any one of 1 to 4.

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