JP5709454B2 - Development device - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a laser beam printer, a facsimile apparatus, and a printing apparatus using an electrophotographic system.

  Conventionally, a two-component development method using a two-component developer of a non-magnetic toner and a magnetic carrier has been widely used to reveal an electrostatic latent image formed on an image carrier. In this two-component development method, the developer stirred by the stirring means in the developing device is carried on a developer carrying body having a magnet as a magnetic field generating means, and this developer is used to face the image carrying body. The electrostatic latent image is visualized by the part.

  In a two-component developing apparatus employing such a two-component developing method, the toner particles in the developer are consumed during development, so the toner concentration in the developing apparatus always changes. For this reason, the developer concentration control device (ATR: Auto Toner Replenisher) is used to accurately detect the toner concentration of the developer in a timely manner, and the toner is replenished according to the change in the toner concentration. Then, it is necessary to sufficiently stir and maintain the image quality by always controlling the toner density constant.

  A typical two-component developing device has a developing container for containing a developer and a developing sleeve as a developer carrying member that is a rotating hollow cylinder. The developing roller includes a magnet roller that is a magnetic field generating unit fixedly arranged with respect to the rotation of the developing sleeve, and a screw member that is a developer agitating and conveying unit installed in the developing container. And it has a regulating blade which is a developer layer thickness regulating member arranged to form a thin layer of developer on the surface of the developing sleeve.

  Here, the following conventional examples have been proposed as the configuration of the screw member for satisfactorily stirring and conveying the toner and the magnetic carrier in the developing device.

  In Patent Document 1, a large number of fin members are provided in a second region after a position a predetermined distance away from the first region in the vicinity of the toner supply port on the downstream side in the developer transport direction. Thus, a configuration of a screw member that promotes stirring and mixing of the toner of the two-component developer and the magnetic carrier has been proposed.

  Further, in Patent Document 2, in a developing device including two stirring shafts that circulate and convey the developer, the rotational speed of the screw member closer to the developing sleeve is higher than the rotational speed of the screw member farther from the developing sleeve. Make it faster. Further, the screw member near the developing sleeve is a continuous screw blade, and the shape of the screw blade of the screw member far from the developing sleeve is cut out into an elliptical plate shape. Further, a configuration has been proposed in which the screw blade thickness of the screw member near the developing sleeve is thinner than the screw blade thickness of the screw member far from the developing sleeve.

JP 2004-272017 A JP 09-114209 A

  However, recently, it has been desired to further increase the image forming process speed, and the conventional screw member configuration has caused a problem that the image forming process speed cannot be sufficiently increased.

  For example, in the configuration of Patent Document 1, a large number of fin members are provided on the downstream side in the developer conveyance direction. However, in the portion where a large number of fin members are provided, the developer conveyance speed decreases. With the conventional image forming process speed, it is possible to suppress the stagnation of the developer flow even when the developer conveyance speed is low. However, when the image forming process speed is further increased, if a portion where the circulation of the developer is delayed occurs, the amount of the developer becomes extremely large in the portion, which causes the developer overflow or the developer clogging. . Also, if the number of fin members is reduced or the spacing between the screw blades of the screw member is increased in order to ensure developer circulation, sufficient stirring performance cannot be obtained and the toner charge amount is insufficient. .

  Further, in the configuration of Patent Document 2, it is possible to adjust the developer conveyance speed so that the screw member near the developing sleeve and the screw member far from the developing sleeve have the same speed. For example, it is possible to adjust the spacing between the screw blades, the shape of the screw blades, or the rotational speed of the screw member. If the spacing between the screw blades is reduced uniformly, the volume of the screw member itself increases extremely, the height of the developer surface in the developer container becomes too high, and poor stirring due to insufficient uptake of replenished toner. Will occur. Also, if the agitating chamber is widened to suppress the height of the developer surface, the developer container will be enlarged, or if the amount of developer circulating in the developer container will be reduced, the density fluctuation will increase. . In addition, a configuration in which only the toner replenishment portion is configured to increase the separation pitch of the screw blades is considered, but in the case of a high-speed machine, when a portion where the developer circulation is delayed occurs, the amount of developer in that portion becomes extremely large, This may cause developer overflow or developer clogging. It is also possible to increase the developer conveying speed by adjusting the spacing pitch of the screw blades so that the height of the developer surface does not become too high and increasing the rotational speed of the screw member. When the rotational speed of the screw member in the vicinity of the toner supply port is increased, toner scattering is likely to occur in the vicinity of the toner supply port. In particular, when the toner supply amount is large, the scattered toner moves to the developing chamber side as it is. As a result, the toner is transferred to the white background portion of the sheet that should not be printed, causing the white background to become so-called “image fogging”, or the scattered toner moves to the downstream side of the stirring chamber and is sufficiently It moves to the developing chamber without stirring and causes image fogging.

  Further, the replenished toner does not concentrate at the same point in the stirring chamber, but is replenished with a predetermined distribution in the longitudinal direction of the stirring chamber. When the toner replenishment amount is large, the distribution further spreads in the longitudinal direction of the stirring chamber. In this case, since the position where the newly supplied toner begins to be stirred, that is, the position where the toner is stirred and mixed with the magnetic carrier and the charge starts to be applied is different, the charge amount of the toner coming to the development position varies. Accordingly, it is preferable that the toner intake performance be emphasized in the vicinity of the toner replenishing port, and a configuration having sufficient stirring performance and charge imparting performance in the latter half of the developer conveying direction in the stirring chamber is required.

  It is an object of the present invention to provide a developer overflow or developer clogging due to a deterioration in developer circulation or a developer scattering or image fogging even when the developer circulation speed increases as the image forming process speed increases. Is not generated. Another object of the present invention is to propose a developing device capable of suppressing the variation in the charge amount of the toner and stably improving the stirring and conveying ability of the developer.

In order to solve the above problems, a typical configuration of a developing device according to the present invention is a developing unit that develops an electrostatic latent image formed on an image carrier using a developer containing toner and a magnetic carrier. A stirring chamber in which toner is replenished through a toner replenishing port, a screw member that stirs and conveys the developer in the stirring chamber, and a space between the developing chamber and the stirring chamber. A developing device comprising a developing chamber in which toner is circulated and a screw member that stirs and conveys the developer in the developing chamber, wherein the screw members in the stirring chamber have first and second screws having different shapes. member is from the configuration arranged coaxially, the stirring conveyance distance of the developer conveyance direction upstream side and the developer per unit rotational speed of the first screw member provided in the toner supply port side, the First Developer that is longer than the stirring and conveying distance of the developer per unit rotation number of the second screw member provided downstream of the screw member in the developer conveying direction, and that rotates in the circumferential direction by the second screw member The rotation speed of the developer is higher than the rotation speed of the developer rotated in the circumferential direction by the first screw member.

  According to the present invention, the developer agitation transport distance per unit rotation number of the first screw member provided on the toner supply port side is the unit rotation of the second screw member provided on the downstream side. It is larger than the stirring and conveying distance of the developer per number. For this reason, it is possible to prevent the developer from overflowing, clogging the developer, or scattering of the toner when the toner is replenished, and no image fog is generated. Further, since the rotation speed of the developer rotated in the circumferential direction by the second screw member is higher than the rotation speed of the developer rotated in the circumferential direction by the first screw member, the developer is stirred by the second screw member. Performance is improved. As a result, variations in the charge amount of the toner can be suppressed. The developer agitating and conveying ability can be stably improved in response to further increase in the image forming process speed.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including a developing device according to the present invention. (A) is sectional explanatory drawing which shows the structure of 1st Embodiment of the developing device which concerns on this invention, (b) is plane explanatory drawing which shows the structure of 1st Embodiment of the developing device which concerns on this invention. (A) is a schematic explanatory view showing an example of the developing bias voltage of the developing device according to the present invention, (b) is a diagram showing the relationship between the agitating / conveying path length of the developer and the toner scattering amount, and (c) is the developer. It is a graph which shows the relationship between the stirring conveyance path | route length of this, and image fogging. FIG. 7A is a diagram illustrating an example of toner charge amount distribution in the developing container of the first embodiment, and FIG. 9B is a diagram illustrating an example of toner charge amount distribution in the developing container of Comparative Example 2. It is a schematic explanatory drawing which shows the structure of the screw member in the developing device of 1st Embodiment. (A) is a schematic explanatory drawing which shows the structure of the screw member in the developing device of the comparative example 1, (b) is a schematic explanatory drawing which shows the structure of the screw member in the developing device of the comparative example 2. (A) is a figure which shows the change of the stirring state in the developer conveyance direction in the developing device in the comparative example 1, (b) is a figure which shows the change in the stirring state in the developer conveyance direction in the developing device in the first embodiment. It is. (A) is a schematic explanatory drawing which shows the structure of the screw member in the developing device in 2nd Embodiment of the developing device based on this invention, (b), (c) is a fin member provided in the screw member of 2nd Embodiment. It is the front view and sectional drawing which show an example.

  Hereinafter, an embodiment of an image forming apparatus including a developing device according to the present invention will be specifically described with reference to the drawings. In addition, although these embodiment is an example of the best embodiment in this invention, this invention is not limited by these embodiment.

  A configuration of a first embodiment of an electrophotographic image forming apparatus including a developing device according to the present invention will be described below with reference to FIGS.

(Image forming device)
A first embodiment of an image forming apparatus including a developing device according to the present invention will be described with reference to FIG. In the image forming apparatus main body 17 shown in FIG. 1, image forming portions Pa, Pb, Pc, and Pd serving as image forming means are arranged in parallel, and toner images of different colors pass through the latent image, development, and transfer processes. It is formed on a recording material 18 such as a recording sheet. Hereinafter, in order to prevent the description from becoming complicated, the four image forming portions Pa, Pb, Pc, and Pd of yellow, magenta, cyan, and black will be described as the representative of the image forming portion P, and each of the following related processes The same applies to the means.

  The image forming unit P includes photosensitive drums 30a, 30b, 30c, and 30d, which are dedicated image carriers, and toner images of the respective colors are formed on the photosensitive drums 30a to 30d. An intermediate transfer member 130 including an intermediate transfer belt is installed adjacent to each of the photosensitive drums 30a to 30d. The toner images of the respective colors formed on the photosensitive drums 30a to 30d are primarily transferred onto the intermediate transfer body 130, and transferred onto the recording material 18 at the secondary transfer portion provided with the secondary transfer roller 11. Further, the recording material 18 to which the toner image has been transferred is heated and pressed by the fixing unit 9 to fix the toner image on the recording material 18 and then discharged out of the apparatus as a recorded image.

  Drum chargers 20a, 20b, 20c, and 20d, developing devices 100a, 100b, 100c, and 100d, primary transfer chargers 24a, 24b, 24c, and 24d and cleaners 40a, 40b, and 40c are disposed on the outer periphery of the photosensitive drums 30a to 30d, respectively. , 40d are provided. Light source devices 13a, 13b, 13c, 13d and a polygon mirror are further installed above the image forming apparatus main body 17.

  The laser beam emitted from the light source devices 13a to 13d is scanned by rotating the polygon mirror. The light beam of the scanning light is deflected by a reflection mirror, and the beam scanned at an equal angle by a rotating polygon mirror is condensed on the buses of the photosensitive drums 30a to 30d by an fθ lens having a function of scanning the imaging surface at a constant speed. To expose. As a result, electrostatic latent images corresponding to the image signals are formed on the photosensitive drums 30a to 30d.

  The developing devices 100a to 100d are filled with a predetermined amount of cyan, magenta, yellow, and black toners as developers, respectively, by a supply device (not shown). The developing devices 100a to 100d develop the electrostatic latent images on the photosensitive drums 30a to 30d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images, and black toner images.

  The intermediate transfer member 130 is driven to rotate in the direction of arrow A in FIG. 1 at the same peripheral speed as that of the photosensitive drum 30. The yellow toner image formed and supported on the photosensitive drum 30a passes through the nip portion between the photosensitive drum 30a and the intermediate transfer member 130. In the process, the intermediate transfer is performed on the outer peripheral surface of the intermediate transfer body 130 by the electric field and pressure formed by the primary transfer bias voltage applied to the intermediate transfer body 130.

  A secondary transfer roller 11 is arranged in parallel with the intermediate transfer member 130 so as to be in contact with the lower surface portion of the intermediate transfer member 130. A desired secondary transfer bias voltage is applied to the secondary transfer roller 11 by a secondary transfer bias power source. Transfer of the composite color toner image superimposed and transferred onto the intermediate transfer member 130 to the recording material 18 passes from the feeding cassette 10 through a registration roller 12 and a pre-transfer guide (not shown). Then, the recording material 18 is fed to the contact nip portion between the intermediate transfer member 130 and the secondary transfer roller 11 at a predetermined timing. At the same time, a secondary transfer bias voltage is applied from a bias power source. The composite color toner image is transferred from the intermediate transfer member 130 to the recording material 18 by the secondary transfer bias voltage.

  Thereafter, similarly, a magenta toner image, a cyan toner image, and a black toner image are sequentially superimposed and transferred onto the intermediate transfer body 130 to form a composite color toner image corresponding to the target color image.

  After the primary transfer, the photosensitive drums 30a to 30d are removed by cleaning the transfer residual toner by the respective cleaners 40a to 40d, and are subsequently prepared for forming the next electrostatic latent image. The toner and other foreign matters remaining on the intermediate transfer body 130 are wiped off by bringing a cleaning web 19 made of a nonwoven fabric into contact with the surface of the intermediate transfer body 130.

  The recording material 18 that has received the transfer of the toner image passes through the recording material conveyance unit provided between the secondary transfer unit provided with the secondary transfer roller 11 and the fixing unit 9 and is introduced into the fixing unit 9. . Then, the toner image is fixed on the recording material 18 by applying heat and pressure, and is discharged to the discharge tray 63 as a full color print.

  The configuration of the image forming apparatus according to the present embodiment is an example, and various methods can be applied. Basically, as described above, an image is formed in the charging, exposure, development, transfer, and fixing processes. Is done.

(Schematic configuration of developing device)
Next, the developing device 100 according to this embodiment installed in the above-described image forming apparatus will be described with reference to FIG. 2 taking one developing device 100a among the four developing devices 100a to 100d as an example. Note that the configurations of the other developing devices 100b to 100d are the same as the configuration of the developing device 100a except for the developer used, and the description thereof is omitted.

  FIG. 2A is a cross-sectional view showing the developing device 100 according to this embodiment, and is a view of the developing device 100 as viewed from the back. FIG. 2B is a cross-sectional view seen from above. The developing device 100 includes a developing container 21. The developing container 21 contains a two-component developer containing a non-magnetic toner (hereinafter simply referred to as “toner”) and a magnetic carrier. The developer will be described in detail later.

  The inside of the developing container 21 is divided into a developing chamber 4 and a stirring chamber 5 by a partition wall 7. A toner storage chamber 50 separate from the developing device 100 is provided above the stirring chamber 5. The toner 50 contains replenishment toner (non-magnetic toner). A toner replenishing port 8 is provided in the upper portion of the agitating chamber 5 of the developing container 21, and an amount of replenishing toner commensurate with the toner consumed for toner image formation through the toner replenishing port 8 is contained in the agitating chamber 5. Dropped replenishment. Here, the two-component developing method in the developing device 100 will be described.

  An opening is formed in a portion of the developing container 21 on the photosensitive drum 30 side, and a hollow cylindrical developing sleeve 1 serving as a developer carrying member is configured to protrude outside from the opening. The developing sleeve 1 is rotatably incorporated in the vicinity of the opening of the developing container 21. The developing sleeve 1 is configured as developing means for developing the electrostatic latent image formed on the photosensitive drum 30 (on the image carrier) using a developer containing toner and a magnetic carrier.

  In the present embodiment, the developing sleeve 1 having a diameter of 20 (mm) is used. The developing sleeve 1 is made of a non-magnetic material such as stainless steel (SUS305AC), for example, and a magnet 2 serving as magnetism generating means is fixedly disposed inside the developing sleeve 1.

  The magnet 2 fixedly arranged inside the developing sleeve 1 has a magnetic pole S1 that is a developing magnetic pole disposed in the vicinity of a developing region that is a facing portion between the photosensitive drum 30 and the developing sleeve 1. Furthermore, it has a magnetic pole N1 that is a developer layer thickness regulating magnetic pole that faces a regulating blade 3 that is a developer layer thickness regulating member that regulates the layer thickness of the developer carried on the developing sleeve 1. Further, magnetic poles N2, S2, and N3 are provided for transporting the developer while being carried on the developing sleeve 1.

  Further, the magnet 2 is disposed in the developing sleeve 1 so that the magnetic pole S1, which is a developing magnetic pole, is 5 ° upstream of the photosensitive drum 30 in the drum rotation direction.

  The magnetic pole S1 forms a magnetic field in the vicinity of the developing portion between the developing sleeve 1 and the photosensitive drum 30, and a magnetic brush is formed by the magnetic field. In the developing section, as the developing sleeve 1 rotates, the developer conveyed in the direction of arrow B shown in FIG. 2B contacts the photosensitive drum 30, and the electrostatic latent image on the photosensitive drum 30 is developed. The Rukoto. At this time, in the present embodiment, the developing sleeve 1 and the photosensitive drum 30 are moved in opposite directions in the developing portion that is in the proximity of the developing sleeve 1 and the photosensitive drum 30.

  The developer that has been developed at the magnetic pole S1 is peeled off from the developing sleeve 1 by the repulsive magnetic field formed by the magnetic pole N1 and the magnetic pole N2, and falls into the developing chamber 4.

  Incidentally, a vibration bias voltage obtained by superimposing a direct current voltage on an alternating current voltage is applied to the development sleeve 1 as a development bias voltage from a development bias power source. The dark portion potential (non-exposed portion potential) and the bright portion potential (exposed portion potential) of the electrostatic latent image on the photosensitive drum 30 are located between the maximum value and the minimum value of the vibration bias potential. As a result, an alternating electric field whose direction changes alternately is formed in the developing portion. In this alternating electric field, the toner and the magnetic carrier are vigorously vibrated, and the toner shakes off the electrostatic restraint on the developing sleeve 1 and the magnetic carrier, and an amount of toner corresponding to the latent image potential adheres to the photosensitive drum 30.

  In the present embodiment, the dark portion potential on the photosensitive drum 30 is set to −600 V, and the bright portion potential is set to −200 V. A DC voltage of −450 V is applied to the developing sleeve 1 as a DC bias voltage. An AC voltage having a voltage Vpp = 1.8 kV and a frequency F = 2 kHz is applied as the AC bias voltage. The duty ratio, which is the ratio between the period and the pulse width when a periodic pulse wave is emitted, is 35% on the development flying side. As shown in FIG. 3A, the vibration bias voltage, which is the development bias voltage, is a bias voltage that can be applied alternately at time T1 at the minimum voltage side and at time T2 at the maximum voltage side. , T1: T2 is 65:35.

(Developer circulation configuration)
A developing chamber 4 closer to the developing sleeve 1 in the developing container 21 is provided with a screw member 4a that is disposed substantially parallel to the developing sleeve 1 and stirs and conveys the developer. The agitating chamber 5 far from the developing sleeve 1 is provided with screw members 5a and 5b for agitating and conveying the developer. The screw member 5a is configured as a first screw member, and the screw member 5b is configured as a second screw member. Then, the developer is conveyed and stirred by the screw member 4a and the screw members 5a and 5b, and circulates in the developing container 21 in the direction of arrow B shown in FIG. A partition wall 7 is provided between the screw member 4a and the screw members 5a and 5b. The partition wall 7 is provided with openings 7a and 7b that can communicate with the developing chamber 4 and the stirring chamber 5 at both ends.

  Next, the configuration of the developing device 100 will be described with reference to FIG. As shown in FIG. 2 (b), the screw member 4a and the screw members 5b and 5b are disposed substantially in parallel in the developing container 21, and the space between them is developed between the screw member 4a and the screw members 5a and 5b. It is partitioned by a partition wall 7 so that the agent does not come and go. There are no partition walls 7 at both ends in the longitudinal direction of the developing container 21, and openings 7a and 7b are provided so that the developer can move between the screw member 4a and the screw members 5a and 5b. As shown in FIG. 2B, the screw member 4a and the screw members 5a and 5b are designed to circulate and convey the developer in opposite directions when viewed from above. A circulation path is formed that turns without interruption.

(Configuration of screw member and drive configuration)
Here, the configuration and driving method of the screw member will be described.

  The screw member 4a and the screw members 5a and 5b have continuous spiral screw blades 4a2, 5a2 and 5b2, respectively. As shown in FIG. 5, the screw members 5a and 5b are set so that the spacing pitches of the screw blades 5a2 and 5b2 in the directions of the screw shafts 5a1 and 5b1 are different from each other. In the present embodiment, the spacing pitch of the screw blades 5a2 of the screw member 5a is set to be larger than the spacing pitch of the screw blades 5b2 of the screw member 5b. The screw member 5a is provided on the upstream side in the developer conveyance direction (left side in FIG. 2B) and on the toner supply port 8 side (toner supply port side). The screw member 5b is provided downstream of the screw member 5a in the developer transport direction (the right side in FIG. 2B). In the present embodiment, both ends of the screw shafts 5a1 and 5b1 of the screw member 4a and the screw member 5b are rotatably supported through the developing container 21. The screw member 5a is arranged coaxially with the screw member 5b, and the screw member 5b is configured to be shorter in the direction of the screw shafts 5a1 and 5b1 than the screw member 5a.

  The screw shaft 5a1 of the screw member 5a is configured by a cylindrical member that is rotatably mounted on the screw shaft 5b1 of the screw member 5b. One end thereof penetrates the developing container 21 and is rotatably supported with respect to the screw shaft 5b1 of the screw member 5b via a bearing member (not shown) attached to both ends. In the present embodiment, the outer diameter of the screw shaft 5a1 of the screw member 5a is set to be larger than the outer diameter of the screw shaft 5b1 of the screw member 5b. As another configuration, the outer diameter of the screw shaft 5a1 of the screw member 5a and the outer diameter of the screw shaft 5b1 of the screw member 5b may be the same diameter. The screw shaft 5a1 of the screw member 5a and the screw shaft 5b1 of the screw member 5b may be coaxially connected to each other so as to be rotatable. That is, the outer diameter of the screw shaft 5a1 of the screw member 5a is set to be equal to or larger than the outer diameter of the screw shaft 5b1 of the screw member 5b. The spiral screw blade 5b2 provided on the screw shaft 5b1 of the screw member 5b is disposed at a portion that does not overlap the screw shaft 5a1 of the screw member 5a. Thus, the screw members 5a and 5b are configured to have different shapes.

  Gears 41 and 42 are fixed to both ends of the screw shaft 4a1 of the screw member 4a protruding from the developing container 21, respectively. Gears 51 and 52 are fixed to one end portions of the screw shafts 5a1 and 5b1 of the screw members 5a and 5b protruding from the developing container 21, respectively. A rotational drive shaft of a motor 23 serving as a rotational drive source is connected to an end of the screw member 4a where the gear 41 of the screw shaft 4a1 is provided. When the motor 23 is driven to rotate, the screw shaft 4a1 and the gears 41 and 42 of the screw member 4a rotate integrally. Then, the screw shaft 5a1 of the screw member 5a rotates through the gear 52 that meshes with the gear 42, and the screw shaft 5b1 of the screw member 5b rotates through the gear 51 that meshes with the gear 41, respectively. The gear ratio between the gear 42 and the gear 52 and the gear ratio between the gear 41 and the gear 51 are set as appropriate. Accordingly, the rotational speed of the screw shaft 5a1 of the screw member 5a and the rotational speed of the screw shaft 5b1 of the screw member 5b can be set to the same rotational speed or different rotational speeds using one motor 23 as a rotational drive source. Easy to do.

  In this embodiment, the gear 42 fixed to the screw shaft 4a1 of the screw member 4a transmits the rotational driving force to the screw shaft 5a1 of the screw member 5a via the gear 52 that meshes with the gear 42. By adjusting the gear ratio between the gear 52 fixed to the screw shaft 5a1 of the screw member 5a and the gear 42, the rotational speeds of the screw member 4a and the screw member 5a are set to be the same. The gear 41 fixed to the screw shaft 4a1 of the screw member 4a transmits the rotational driving force to the screw shaft 5b1 of the screw member 5b via the gear 51 meshing with the gear 41. By adjusting the gear ratio between the gear 51 and the gear 41 fixed to the screw shaft 5b1 of the screw member 5b, the rotational speed of the screw member 5b is set to be higher than the rotational speed of the screw member 4a and the screw member 5a. ing. Thereby, the rotation speed of the developer rotating in the circumferential direction of the screw shaft 5b1 is set to be larger than the rotation speed of the developer rotating in the circumferential direction of the screw shaft 5a1.

  In the present embodiment, the agitating and conveying distances in the traveling direction of the developer per unit rotation speed of the screw members 5a and 5b (the direction of arrow B in FIG. 2B) are La and Lb, respectively. Further, the rotational speeds per unit time of the screw members 5a and 5b are Ra and Rb, respectively. Also, Va and Vb are transport speeds in the developer traveling direction (direction of arrow B in FIG. 2B) by the screw members 5a and 5b. At this time, the relationship shown by the following formula 1 was set.

[Equation 1]
Va = La × Ra
Vb = Lb × Rb
La> Lb
Ra <Rb

  In the following description, the configuration of the screw members 5a and 5b provided on the stirring chamber 5 side of the developing container 21 will be mainly described, but the screw member 4a provided on the developing chamber 4 side is also configured similarly. I can do it.

(Schematic configuration of toner density detection and toner supply)
A toner concentration sensor 6 is provided on the upstream side in the developer conveyance direction (left side in FIG. 2B), which is the wall surface behind the screw member 5a. In this embodiment, the toner concentration sensor 6 uses an inductance detection method that detects an apparent permeability change as a mixing ratio of the toner and the magnetic carrier. If the developer stays on the sensor surface of the toner concentration sensor 6, the toner concentration of the developer cannot be detected accurately. For this reason, the toner concentration sensor 6 is arranged so that the sensor surface is perpendicular to the developer surface in the vicinity of the screw member 5a so that the developer does not stay on the sensor surface of the toner concentration sensor 6. Yes. Here, the toner concentration is a mixing ratio of the toner and the magnetic carrier, and is referred to as a T / D ratio.

  Thus, in the stirring chamber 5, the toner concentration sensor 6 is provided on the upstream side in the developer conveying direction of the screw member 5a (left side in FIG. 2B) because the toner is used for image formation and the toner concentration. This is because the toner density is immediately detected with respect to the developer having decreased.

  The developer that is present on the screw member 4 a side of the developing chamber 4 and is used for image formation is sent to the screw member 5 a side through the circulation path described above, and the toner concentration sensor 6 detects the toner concentration. Based on the detection result, an appropriate amount of toner is supplied from the toner storage chambers 50a, 50b, 50c, and 50d through the toner replenishing port 8 provided on the downstream side of the toner concentration sensor 6 in the developer conveyance direction (right side in FIG. 2B). Is replenished. As a result, the toner density of the developer is always kept constant.

(Developer transport speed balance)
Next, in order to be able to smoothly stir and convey the developer and to form a better image, the following points must be noted.

  First, in FIG. 2B, it is necessary to keep the balance of the developer conveyance speed between the screw member 5a and the screw member 5b constant. This is because if the difference in developer conveyance speed between the screw member 5a and the screw member 5b becomes too large, the developer circulation performance is greatly impaired at the connecting portion between the screw member 5a and the screw member 5b, and the developer clogging or the developer occurs. This is because it causes overflow.

  For example, when the developer transport speed of the screw member 5a is high and the developer transport speed of the screw member 5b is slow, the developer stagnation occurs in the screw member 5b, and as a result, the developer circulation transport balance cannot be achieved. End up. As in Patent Document 1, in the configuration in which the fin member is raised on the downstream side in the developer conveying direction of the stirring chamber 5 to improve the stirring property, the structure is designed so that the above problem does not occur. However, when the image forming process speed is increased, the difference in developer conveyance speed between the upstream side and the downstream side in the developer conveyance direction of the agitating chamber 5 becomes too large, and the developer circulation conveyance balance becomes difficult. End up. If the spacing between the screw blades is increased or the number of fin members is decreased in order to balance the developer circulation and transport, the developer stirring performance will drop and the sufficient stirring and transport function will not be satisfied.

  The above description has been made by taking the connecting portion between the screw member 5a and the screw member 5b as an example. However, the circulation and conveyance balance of the developer is required to have the same stirring and conveying function throughout the entire area of the developing device 100. Therefore, the developer conveyance speed balance is maintained so that the developer conveyance circulation does not collapse in the entire area of the screw members 5a and 5b, the developer delivery section between the screw members 5a and 5b and the screw member 4a, and the entire area of the screw member 4a. Become important.

(Developer surface height)
Second, in FIG. 2A, the developer surface height in the developing chamber 4 provided with the screw member 4a and the stirring chamber 5 provided with the screw members 5a and 5b needs to be maintained at a predetermined height. There is.

  In the developing chamber 4, if the height of the developer surface is too low, the amount of developer conveyed by the screw member 4a is too small as a whole. In this case, the amount of the developer supplied to the developing sleeve 1 stays at the restriction portion of the restriction blade 3 is reduced, and it becomes easy to cause uneven supply of the developer from the screw member 4a in this portion. As a result, so-called screw pitch unevenness is generated, in which density unevenness occurs in the image at the spacing pitch of the screw blades 4a2.

  Conversely, when the developer surface is too high and the developer completely covers the portion of the developing sleeve 1 where the developer is peeled off, the peeled developer is pressed down by the covered developer and the developing sleeve is covered. It will return to 1 above. In this case, the developer is peeled off relatively well in the vicinity of the screw blade 4a2 of the screw member 4a, while the other parts are not peeled off, so that the screw pitch at the time of printing a solid image It will cause unevenness. Therefore, it is desirable that the developer surface height be a height that sufficiently covers the regulating portion of the regulating blade 3 without completely covering the repulsion poles of the portion of the developing sleeve 1 where the developer is peeled off.

  In the stirring chamber 5, the screw members 5a and 5b have a purpose of stirring and mixing the new toner supplied and the developer in the developer container 21, but if the height of the developer surface is too high, the screw The developer at a position higher than the members 5a and 5b is hardly stirred. In particular, when the toner is replenished, if the developer surface is located higher than the screw member 5a, the toner having a specific gravity smaller than the magnetic carrier in the developer may remain floating on the developer surface. is there. In this case, the replenished toner is not easily mixed with the developer in the stirring chamber 5, and almost uncharged toner is supplied to the developing sleeve 1 as it is, and problems such as image fog and poor density occur. .

  On the other hand, if the height of the developer surface at the screw members 5a and 5b is too low, the amount of the replenished toner that directly contacts the rotating screw members 5a and 5b increases. In this case, scattering of the toner increases, and the toner is directly scattered to the developing chamber 4 side, which causes a problem that image fog is likely to occur. Or it will scatter to the developer conveyance direction downstream side (right side of FIG.2 (b)) of the stirring chamber 5. FIG. As a result, the agitating and conveying path length, which is the distance that the developer rotates and moves in the circumferential direction around the screw shafts 5a1 and 5b1 of the screw members 5a and 5b, is too short, resulting in poor agitation. It will cause fogging.

  That is, on the stirring chamber 5 side, it is important to have a configuration in which new toner replenished from the toner replenishing port 8 is efficiently taken into the developer, and then efficiently stirred, mixed, and finely dispersed.

(Agitating and conveying path length and toner chargeability)
Next, the agitating / conveying path length, which is the distance that the developer rotates while moving in the circumferential direction around the screw shafts 4a1, 5a1, 5b1 of the screw members 4a, 5a, 5b, and the toner charge imparting property. explain. FIG. 3B shows the relationship between the developer agitation transport path length and the toner scattering amount. FIG. 3C qualitatively shows the relationship between the developer conveyance path length and the image fog. Here, the developer agitation transport path length is a moving distance in which the developer moves while being stirred and mixed by the screw members 4a, 5a, and 5b.

  As shown in FIGS. 3B and 3C, the shorter the developer conveyance path length, the greater the amount of toner scattering and the greater the image fog. That is, a long developer conveyance path length means that the developer conveyance ability is low and the stirring ability is high. This is because, when the developer agitating / conveying path length is long, the apparent conveyance in which the developer advances in the traveling direction (the direction of arrow B in FIG. 2B) per unit rotation number of the screw members 4a, 5a, and 5b. Speed V becomes slower. Conversely, the opportunity and frequency of stirring by the screw members 4a, 5a, 5b increases. As described above, the toner scatters in the vicinity of the toner supply port 8. Then, for the toner that has started stirring and mixing from the downstream side of the stirring chamber 5 in the developer transport direction (right side in FIG. 2B), the stirring transport path length of the developer is shortened. It can be seen that the amount of toner scattering increases and the image fog increases.

  Here, the charge imparting property of the toner will be described with reference to FIG. FIG. 4A shows a toner charge amount distribution with respect to a toner particle distribution accommodated in the developing device 100 having the configuration shown in FIG. In FIG. 4A, the vertical axis represents the number of toner particle distributions, the horizontal axis represents the charge amount, the right side is positive, and the left side is negative. As shown in FIG. 2 (b), a measurement point C is a portion where the developer is transferred from the screw member 5 b to the screw member 4 a through the opening 7 a provided at one end of the partition wall 7 of the developing container 21. In the case of this embodiment, the developer agitating / conveying path length is long and the agitation and mixing are sufficiently performed. Therefore, as shown in FIG. I understand that. Since the toner of the present exemplary embodiment has a negative polarity, it is preferable that the toner is charged to the minus side of 0. Since the amount of toner having a charge amount near 0 is very small, the amount of scattered toner is extremely small, and image fogging is unlikely to occur.

  On the other hand, FIG. 4B shows the toner charge amount distribution when the developer transport path length is short and stirring and mixing are not sufficiently performed. In this case, it can be seen that the amount of toner whose charge amount is in the vicinity of 0 increases due to poor charging. That is, there are many toners that are not sufficiently charged. That is, since the charging is not sufficiently performed, the amount of scattered toner is large and image fogging occurs.

  In this embodiment, as described above, (1) the developer transport speed balance is optimized so that the developer circulation speed balance does not collapse even if the image forming process speed is increased. (2) To optimize the developer surface height and improve the stirring and mixing performance. (3) A sufficient agitating / conveying path length of the developer is secured, and the toner charging performance is improved. These three points were solved. Hereinafter, the configuration of the screw members 5a and 5b on the stirring chamber 5 side will be mainly described, but the same configuration can be used for the screw member 4a on the developing chamber 4 side.

  In this embodiment, as shown in FIG. 5, the spacing pitch of the screw blades 5a2 of the screw member 5a is 16 (mm), and the spacing pitch of the screw blades 5b2 of the screw member 5b is 8 (mm). The outer diameters of the screw blades 5a2 and 5b2 at this time are set to 20 (mm) for both the screw members 5a and 5b, and the outer diameters of the screw shafts 5a1 and 5b1 are 10 (mm) for the screw member 5a and the screw member 5b. 8 (mm). The total length of the screw members 5a and 5b in the stirring chamber 5 is 340 (mm) in total, and the length of the screw member 5a is 170 (mm) and the length of the screw member 5b is 170 (mm). It was. Regarding the lengths of the screw members 5a and 5b, the position of the toner replenishing port 8 on the screw member 5a side needs to be configured so as to place importance on toner intake. It is also important that the screw member 5b is provided on the downstream side of the toner supply port 8 in the developer conveyance direction (the right side in FIG. 2B). Further, it is important to obtain sufficient toner charge imparting property by improving the stirring and mixing ability of the developer in the screw member 5b. In the present embodiment, at least the length of the screw member 5b is 80 ( mm) to 100 (mm) is required. However, the required lengths of the screw members 4a, 5a, and 5b vary depending on the configuration of the developing device 100 and the developer amount, and are not limited to the above-described numerical values.

  At this time, the outer diameters of the screw shafts 5a1 and 5b1 of the screw members 5a and 5b are larger than the outer diameter of the screw shaft 5b1. Alternatively, it is desirable that the outer diameters of the screw shafts 5a1 and 5b1 are the same. The developer is transported from the upstream side to the downstream side in the developer transport direction (from the left side to the right side in FIG. 2B). When the outer diameter of the screw shaft 5b1 of the screw member 5b is larger than the outer diameter of the screw shaft 5a1 of the screw member 5a, the developer is compressed at the connecting portion of the screw members 5a and 5b, and toner aggregation occurs. It becomes easy to do.

  Here, the agitating and conveying ability of the developer means the agitating and conveying distance L in which the developer is conveyed in the traveling direction (the direction of arrow B in FIG. 2B) while the screw members 4a, 5a, and 5b rotate unit. Say. Further, since the developer is stirred and mixed as the distance that the developer is transported in the traveling direction (the direction of arrow B in FIG. 2B) while the screw members 4a, 5a, and 5b rotate unit, the stirring ability is increased. Becomes higher. This is because the screw members 4a, 5a and 5b are rotated and stirred and mixed while being sheared in the circumferential direction around the screw shafts 4a1, 5a1 and 5b1.

  As described above, in the developing device 100, the developer agitating and conveying by the screw members 4a, 5a, and 5b includes a force that conveys the developer in the traveling direction (the direction of arrow B in FIG. 2B). Furthermore, it consists of the force rotated while shearing in the circumferential direction (vertical direction) around the screw shafts 4a1, 5a1, 5b1 of the screw members 4a, 5a, 5b. The agitation transport distance L transported in the traveling direction of the developer per unit rotational speed of the screw members 4a, 5a, 5b (in the direction of arrow B in FIG. 2B) is short. This means that the opportunity and frequency of shearing in the circumferential direction (longitudinal direction) around the screw shafts 4a1, 5a1, and 5b1 by the screw members 4a, 5a, and 5b are increased. This means that the stirring ability is high. In order to increase the developer stirring ability by the screw members 4a, 5a, 5b, for example, the spacing pitch of the screw blades 4a2, 5a2, 5b2 is set small. Then, the distance that the developer moves in the circumferential direction around the screw shafts 4a1, 5a1, and 5b1 is lengthened. As a result, the agitation transport distance L transported in the developer traveling direction (in the direction of arrow B in FIG. 2B) per unit rotation speed of the screw members 4a, 5a, 5b is shortened. Further, fin members 16 shown in FIG. 8 and described later are provided on the screw shafts 4a1, 5a1, and 5b1 of the screw members 4a, 5a, and 5b. Then, the developer is stirred by increasing the shearing force in the circumferential direction (longitudinal direction) around the screw shafts 4a1, 5a1, and 5b1. Then, the agitation transport distance L transported in the developer traveling direction (in the direction of arrow B in FIG. 2B) per unit rotational speed of the screw members 4a, 5a, 5b is shortened.

  In this embodiment, the developer stirring ability is improved. Therefore, the spacing pitch of the screw blades 5b2 of the screw member 5b is set to be smaller than the spacing pitch of the screw blades 5a2 of the screw member 5a. Thereby, the stirring conveyance distance La of the screw member 5a is set to be larger than the stirring conveyance distance Lb of the screw member 5b. The agitation transport distance La is a distance in which the developer is transported in the direction of travel of the developer per unit rotational speed of the screw member 5a (the arrow B direction in FIG. 2B). The agitation transport distance Lb is a distance transported in the developer traveling direction (in the direction of arrow B in FIG. 2B) per unit rotation number of the screw member 5b. Further, in the screw member 5b, the length of the agitating and conveying path, which is the distance that the developer rotates and moves while being sheared in the circumferential direction around the screw shaft 5b1, can be increased, and the stirring and mixing ability of the developer is improved. I can do it. In addition, the structure of the screw members 4a, 5a, and 5b is an example, and is not limited to this.

  In this embodiment, the screw members 4a, 5a, and 5b are configured as described above with reference to FIGS. 2 and 5. Here, the developer agitation in each of the screw members 4a, 5a, and 5b is performed. Verify the transport capability. Here, the agitating and conveying ability of the developer is the agitating and conveying distance L that is conveyed in the advancing direction of the developer per unit rotational speed of the screw members 4a, 5a, and 5b (the direction of arrow B in FIG. 2B). . In the verification in this embodiment, toner of a color different from that of the original developer is supplied from the toner supply port 8, and the toner of that color moves in the direction of the developer (in the direction of arrow B in FIG. 2B) after a unit time. ) Was measured. In this verification, the rotation speed per unit time of the screw members 4a, 5a, and 5b is 4 (rps) (revolution per second), and the developer traveling direction after 1 second (FIG. 2B). The agitating and conveying distance L in the direction of arrow B) was measured. The agitating and conveying distance La in the developer traveling direction (in the direction of arrow B in FIG. 2B) after 1 second by the screw member 5a was about 60 (mm) on average. The agitating and conveying distance Lb in the developer traveling direction (in the direction of arrow B in FIG. 2B) after 1 second by the screw member 5b was about 30 (mm) on average. In addition, the measured value of the stirring and conveying distance L was an average value of values measured five times including variations. Therefore, the agitation and conveyance of the developer per unit rotation speed of the screw members 5a and 5b (the direction of arrow B in FIG. 2B) that provides the agitation and conveyance ability of the developer by the screw members 5a and 5b. The distances La and Lb are La≈60 (mm) and Lb≈30 (mm).

  Next, the rotation speeds (rps) per unit time of the screw members 5a and 5b are Ra and Rb, respectively. The screw members 5a and 5b are set to have different stirring and conveying path lengths, which are distances by which the developer rotates and moves while being sheared in the circumferential direction around the screw shafts 5a1 and 5b1. For this reason, the rotational speeds Ra and Rb per unit time of the screw members 5a and 5b are adjusted to optimize the circulation and conveyance balance of the developer. Here, the apparent transport speeds Va and Vb of the respective developers that are stirred and transported by the screw members 5a and 5b in the developer traveling direction (in the direction of arrow B in FIG. 2B) are determined. The screw members 5a and 5b are the same. Thus, the rotation speeds Ra and Rb per unit time of the screw members 5a and 5b were set to Ra = 8.0 (rps) and Rb = 16.0 (rps), respectively.

  In the above setting, the apparent transport speeds Va and Vb in the developing direction (the direction of arrow B in FIG. 2B) are measured. Although there is a slight difference depending on the height of the developer surface of the developing device 100, both the screw member 5a and the screw member 5b have an apparent transport speed Va in the developer traveling direction (the direction of arrow B in FIG. 2B). , Vb is about 120 (mm / sec) on average. As shown in FIG. 5, the spacing pitch of the screw blades 5a2 of the screw member 5a is 16 (mm). Furthermore, the rotation speed Ra per unit time of the screw member 5a was set to 8.0 (rps). Furthermore, the spacing pitch of the screw blades 5b2 of the screw member 5b was 8 (mm). Furthermore, the rotation speed Rb per unit time of the screw member 5b was set to 16.0 (rps). In this case, the speed is approximately equal to or slightly smaller than the speed 128 (mm / sec) (= 16 (mm) × 8.0 (rps) = 8 (mm) × 16.0 (rps)) obtained by calculation. This is considered to be a reasonable value considering that the developer is made of powder.

  In the present embodiment, the outer diameter of the screw blade 4a2 of the screw member 4a provided in the developing chamber 4 is the screw member 5a provided on the upstream side in the developer conveying direction of the stirring chamber 5 (left side in FIG. 2B). The same diameter as the outer diameter of the screw blade 5a2. Further, the outer diameter of the screw shaft 4a1 is also the same as the outer diameter of the screw shaft 5a1. Moreover, the rotation speed R per unit time of the screw member 4a was also set to the same rotation speed as the rotation speed R per unit time of the screw member 5a.

  The developer was circulated and transported in a well-balanced manner without causing developer retention, developer overflow, and developer clogging when the developer circulation and transport balance was confirmed. I was able to confirm.

  Further, the intake performance, stirring and mixing performance, and toner charging performance of the new toner replenished from the toner replenishing port 8 were confirmed. As a result, sufficient toner intake performance could be secured on the screw member 5a side in the vicinity of the toner supply port 8 on the upstream side in the developer conveying direction of the stirring chamber 5 (left side in FIG. 2B). Further, it was confirmed that sufficient stirring and mixing performance of the toner can be secured on the screw member 5b side on the downstream side in the developer conveying direction (right side in FIG. 2B).

  In addition, it was confirmed that toner scattering during toner replenishment was kept low, and movement of uncharged toner to the downstream side in the developer transport direction was also kept low. Further, the toner charging performance when the portion of the opening 7a provided at one end of the partition wall 7 for transferring the developer from the screw member 5b to the screw member 4a shown in FIG. It was also confirmed that the toner was sufficiently charged. The above can be confirmed from the fact that the charge amount distribution of the toner is measured at the measurement point C where the developer is transferred, as shown in FIG. .

  As Comparative Example 1, as shown in FIG. 6A, the screw members 5a and 5b have a conventional screw member configuration that is not divided on the upstream side and the downstream side in the developer conveyance direction on the same axis. The spacing pitch of the screw blades 5a2 of the screw member 5a on the upstream side in the developer conveyance direction (left side in FIG. 6A) was set to 16 (mm). Furthermore, the spacing pitch of the screw blades 5b2 of the screw member 5b on the downstream side in the developer conveyance direction (right side in FIG. 6A) was set to 8 (mm). In this case, the developer circulation balance was confirmed.

  First, the agitating and conveying distance La, which is conveyed in the traveling direction of the developer per unit rotation speed by the screw members 5a and 5b of Comparative Example 1 shown in FIG. 6A (from the left to the right in FIG. 6A), The measurement results of Lb were La≈60 (mm) and Lb≈30 (mm).

  Here, in Comparative Example 1, the screw members 5a and 5b are not divided on the upstream side and the downstream side in the developer transport direction, and thus rotate on the same axis and at the same rotation speed R per unit time. The rotational speed R per unit time of the screw members 5a and 5b was changed from 4 (rps) to 16 (rps). The difference between the apparent conveying speeds Va and Vb in the developing direction of the developer between the screw member 5a and the screw member 5b (left to right in FIG. 6A), and the circulation of the developer at that time The results of confirming the conveyance balance are shown in Table 1 below. In Table 1 below, “◯” indicates a state where the developer circulation balance is good, “Δ” indicates a state where the developer is partially circulated, and “×” indicates that the developer is circulated. It cannot be taken.

  As shown in Table 1 above, as in Comparative Example 1 shown in FIG. 6A, the screw members 5a and 5b provided in the stirring chamber 5 are coaxially arranged on the upstream side and the downstream side in the developer conveying direction. The conventional screw member is not divided. When the image forming process speed is increased, as the rotational speed R per unit time of the screw members 5a and 5b increases, the circulation and conveyance balance of the developer is lost. It was. As a result, developer stagnation, developer overflow and developer clogging are likely to occur.

  Actually, as in the above-described embodiment, the values at which the apparent transport speeds Va and Vb in the developer traveling direction (from left to right in FIG. 6A) are 128 (mm / sec) are set. To get. For this purpose, in the configuration of Comparative Example 1 shown in FIG. 6A, the screw member 5b has a rotational speed per unit time between 8 (rps) and 12 (rps) as shown in Table 1 above. Adjust with. In this case, as shown in Table 1 above, it becomes difficult to achieve a developer circulation / balance, or a developer circulation / balance cannot be achieved.

  On the other hand, as Comparative Example 2, as shown in FIG. 6B, the screw members 5a and 5b are configured to have a conventional screw member that is coaxially divided between the upstream side and the downstream side in the developer transport direction. Both the screw members 5a and 5b were checked for the developer conveyance speed balance, stirring and mixing performance, and toner charge imparting performance when the spacing pitch of the screw blades 5a2 and 5b2 was 12 (mm).

  First, the agitation transport distance La, which is transported in the advancing direction of developer per unit rotation speed by the screw members 5a, 5b of Comparative Example 2 shown in FIG. 6B (from the left to the right in FIG. 6B), The measurement result of Lb was La≈Lb≈45 (mm).

  Here, in Comparative Example 2, since the screw members 5a and 5b are not divided on the upstream side and the downstream side in the developer transport direction, they rotate on the same axis and at the same rotation speed R per unit time. The rotational speed R per unit time of the screw members 5a and 5b is adjusted, and the apparent conveyance in the developer traveling direction (from left to right in FIG. 6B) as in the above-described embodiment. A value at which the speeds Va and Vb are 128 (mm / sec) was obtained. Therefore, the number of rotations Ra / Rb = 10.7 (rps) per unit time of the screw members 5a and 5b (= conveyance speed 128 (mm / sec) / separation pitch 12 (mm)). In the above setting, when the apparent transport speeds Va and Vb in the developer traveling direction (from left to right in FIG. 6B) were measured, the average was about 120 (mm / sec).

  When the above settings were made and the developer circulation and transport balance was actually confirmed, the developer circulation and transport balance was well maintained without causing developer retention, developer overflow, and developer clogging. I was able to confirm.

  However, the taking-in performance of the toner supplied from the toner supply port 8 is confirmed. Consider the number of rotations Ra per unit time of the screw member 5a in the vicinity of the toner supply port 8. The rotational speed Ra per unit time of the screw member 5a of the present embodiment is increased from 8.0 (rps) to the rotational speed Ra of the screw member 5a of Comparative Example 2 per unit time of Ra = 10.7 (rps). It was. For this reason, in Comparative Example 2 shown in FIG. 6B, the amount of scattered toner that directly contacts the screw member 5a is large. As shown in FIG. 4B, the charge imparting performance is also increased in the comparative example 2 shown in FIG. It can be seen that the amount of defective toner has increased.

  Since the toner of the present embodiment has a negative polarity, it is preferable that the toner particles are distributed on the minus side of the charge amount from zero. Toner with a charge amount near 0 tends to scatter and fog. This can be explained as follows.

  Regarding toner replenishment, the toner replenishment port 8 is opened with a predetermined width in the developer transport direction (left-right direction in FIG. 2B). For this reason, the toner replenished from the toner replenishing port 8 to the stirring chamber 5 is not replenished in a concentrated manner. The stirring chamber 5 is replenished in a state of being distributed and spread with a predetermined width in the developer transport direction (left and right direction in FIG. 2B). On the other hand, as in Comparative Example 2 shown in FIG. 6B, the spacing pitch of the screw blades 5a2 and 5b2 was set to be constant in the developer transport direction (left and right direction in FIG. 6B). In this case, as shown in FIG. 7A, the stirring and mixing performance of the developer or the toner charging performance is uniformly increased from the upstream side to the downstream side in the developer transport direction. This is the stirring and mixing performance, or the toner charging performance as the stirring and conveying path length becomes longer, which is the distance that the developer rotates while moving in the circumferential direction around the screw shafts 5a1 and 5b1 of the screw members 5a and 5b. This is because it improves. Accordingly, the toner replenished from the toner replenishing port 8 is replenished to the agitating chamber 5 in a state of being distributed and spread with a predetermined width in the developer transport direction (left and right direction in FIG. 2B). Then, the toner that has dropped to the upstream side in the developer conveyance direction and the toner that has fallen to the downstream side move and rotate while being sheared in the circumferential direction around the screw shafts 5a1 and 5b1 of the screw members 5a and 5b. A difference can be made in the agitating and conveying path length which is the distance to be moved. For this reason, the chargeability at the position where the toner conveyed to the developing chamber 4 is developed is greatly different. Further, as in Comparative Example 2 shown in FIG. 6B and described above, when the rotation number Ra per unit time of the screw member 5a in the vicinity of the toner supply port 8 is large (the rotation speed is high), the toner Is easily scattered downstream in the developer conveying direction. And it appears as a more remarkable difference regarding chargeability.

  On the other hand, as in the present embodiment described above with reference to FIGS. 2B and 5, in the vicinity of the toner replenishing port 8, the rotation speed Ra per unit time of the screw member 5 a is set with emphasis on the toner intake. Do not raise. Further, the separation pitch of the screw blades 5b2 of the screw member 5b provided coaxially on the downstream side in the developer transport direction with respect to the screw member 5a was set to be smaller than the separation pitch of the screw blades 5a2 of the screw member 5a. At the same time, the rotational speed Rb per unit time of the screw member 5b was set to be larger than the rotational speed Ra per unit time of the screw member 5a. In the case of this configuration, as shown in FIG. 7B, the developer agitation and mixing performance or the toner charge imparting performance gradually increases at the site where the screw member 5a on the upstream side in the developer transport direction is provided. . The region where the screw member 5b on the downstream side in the developer conveying direction is provided exhibits such a characteristic that it rapidly rises.

  In the configuration of the present embodiment, toner is supplied from the toner supply port 8 to the stirring chamber 5 in a state of being distributed and spread with a predetermined width in the developer transport direction (left and right direction in FIG. 2B). Even so, the dispersion of the stirring and mixing performance or the toner charging performance due to the spread of the distribution can be kept low. Further, in the vicinity of the toner replenishing port 8, the rotational speed Ra per unit time of the screw member 5a is made small (rotational speed is slow), so that when toner is replenished, the toner moves in the developer transport direction (left and right in FIG. 2B). (Distributed in the direction) is also suppressed. Accordingly, as shown in FIG. 4A, the toner charge performance can be kept in a good state with a very small amount of toner having a charge amount near zero.

  As described above, according to the configuration of the present embodiment, (1) it is possible to optimize the developer transport speed balance so that the developer transport speed balance is not lost even if the image forming process speed is increased. I can do it. (2) The height of the developer surface in the developing device 100 can be optimized and the stirring and mixing performance can be improved. (3) A sufficient agitation transport path length, which is the distance that the developer rotates and moves while being sheared in the circumferential direction around the screw shafts 5a1 and 5b1 of the screw members 5a and 5b, and improves the toner charging performance. I can do it. As a result, even when the developer circulation speed increases with the increase in the image forming process speed, the developer overflows and the developer clogs due to the decrease in developer circulation and transport balance, or toner scattering and image fogging occur. Is not generated. Furthermore, it is possible to suppress the variation in the toner charge amount and to stably improve the developer agitating and conveying ability.

  In the present embodiment, as shown in FIG. 8, the developer agitating / conveying capacity is increased so that the screw shaft 5b1 (on the screw shaft) of the screw member 5b avoids the screw blades 5b2. A fin member 16 erected in the radial direction from the surface was provided. Then, the developer is agitated by increasing the shearing force in the circumferential direction (longitudinal direction) around the screw shaft 5b1. The stirring conveyance distance Lb of the screw member 5b is set smaller than the stirring conveyance distance La of the screw member 5a. The agitation conveyance distance Lb is a distance in which the developer is conveyed in the traveling direction (from left to right in FIG. 8A) per unit rotation number of the screw member 5b. The agitation transport distance La is a distance in which the developer per unit rotation speed of the screw member 5a is transported in the traveling direction (from left to right in FIG. 8A).

  In the present embodiment, the configuration shown in FIG. 8A is used as the configuration of the screw members 5a and 5b described in the first embodiment. That is, the spacing pitch of the screw blades 5a2 of the screw member 5a was 16 (mm). Further, the spacing pitch of the screw blades 5b2 of the screw member 5b was set to 12 (mm). Further, a fin member 16 made of a plate-like member for promoting the stirring and mixing performance is provided on the screw shaft 5b1 side of the screw member 5b. Two fin members 16 were attached at a spacing pitch 12 (mm) of the screw blades 5b2. As shown in FIGS. 8B and 8C, the fin member 16 is a plate-like member having a width of 4 (mm), a height of 6 (mm), and a thickness of 1 (mm). The other screw members 4a, 5a, and 5b, the development conditions, the image forming process, and the like are configured in the same manner as in the first embodiment.

  First, the agitation transport distance La, which is transported in the traveling direction of the developer per unit rotation speed by the screw members 5a, 5b of the present embodiment shown in FIG. 8A (from the left to the right in FIG. 8A), The measurement results of Lb were La≈60 (mm) and Lb≈30 (mm). The spacing pitch of the screw blades 5b2 of the screw member 5b is 12 (mm). It is longer than 8 (mm) of the separation pitch of the screw blades 5b2 of the screw member 5b of the first embodiment shown in FIG. By providing the fin member 16, the shearing force in the circumferential direction (longitudinal direction) about the screw shaft 5b1 increases, and as a result, the above measured value is obtained.

  On the other hand, since the fin member 16 is provided, the apparent conveyance speed Vb in the developer traveling direction (left to right in FIG. 8A) by the screw member 5b is slow. Actually, in order to obtain the developer conveyance speed Va comparable to that of the screw member 5a, it is necessary to increase the rotational speed Rb per unit time as compared with the state where the fin member 16 is not provided. Therefore, the actual conveying speeds Va and Vb in the developer traveling direction (from left to right in FIG. 8A) on average are actually 120 (mm / sec) for both the screw member 5a and the screw member 5b. To get the value For this purpose, the rotational speeds Ra and Rb per unit time of the screw members 5a and 5b are Ra = 8 (rps) and Rb = 14.2 (rps), respectively. At this time, the rotation speed of the developer rotated in the circumferential direction by the screw member 5b is larger than the rotation speed of the developer rotated in the circumferential direction by the screw member 5a. Note that the rotational speeds Ra and Rb per unit time of the screw members 5a and 5b in the present embodiment are the values described above, but this varies depending on the shape, size, number, etc. of the fin members 16, It is not limited to this.

  When the above settings were made and the developer circulation and transport balance was actually confirmed, the developer circulation and transport balance was well maintained without causing developer retention, developer overflow, and developer clogging. I was able to confirm.

  Further, the intake performance, stirring and mixing performance, and toner charging performance of the toner replenished from the toner replenishing port 8 were confirmed. As a result, as in the first embodiment, sufficient toner intake performance can be secured on the screw member 5a side in the vicinity of the toner supply port 8 on the upstream side in the developer conveyance direction (left side in FIG. 8A). It was. Further, it was confirmed that sufficient stirring and mixing performance of the developer can be secured on the screw member 5b side provided on the downstream side in the developer transport direction (the right side in FIG. 8A). In addition, it was confirmed that toner scattering during toner replenishment was suppressed to a low level, and that the movement of uncharged toner downstream in the developer transport direction was also suppressed to a low level. As for the charge imparting property of the toner, it was confirmed that the charge imparting substantially equivalent to the characteristics of the first embodiment shown in FIG.

5a, 5b ... Screw member 8 ... Toner supply port

Claims (5)

Developing means for developing the electrostatic latent image formed on the image carrier using a developer containing toner and magnetic carrier;
A stirring chamber in which toner is supplied through a toner supply port;
A screw member for stirring and conveying the developer in the stirring chamber ;
A developing chamber disposed between the developing means and the stirring chamber, in which toner is circulated and conveyed between the stirring chamber,
A screw member for stirring and conveying the developer in the developing chamber;
A developing device comprising:
The screw member of the stirring chamber has a configuration in which first and second screw members having different shapes are arranged coaxially,
Agitation conveyance distance of the developer conveyance direction upstream side and the developer per unit rotational speed of the first screw member provided in the toner supply port side, the developer transport direction downstream of the first screw member Greater than the agitating and conveying distance of the developer per unit rotational speed of the second screw member provided on the side,
The developing device according to claim 1, wherein a rotation speed of the developer rotated in the circumferential direction by the second screw member is larger than a rotation speed of the developer rotated in the circumferential direction by the first screw member.   2. The developing device according to claim 1, wherein the developing speed of each developer that is stirred and conveyed in the developer conveying direction by the first and second screw members is set to be the same.   3. The development according to claim 1, wherein a separation pitch of the screw blades of the first screw member is set to be larger than a separation pitch of the screw blades of the second screw member. 4. apparatus.   The developing device according to claim 1, wherein a fin member is provided on a screw shaft of the second screw member.   The developing device according to claim 1, wherein an outer diameter of the screw shaft of the first screw member is set to be equal to or larger than an outer diameter of the screw shaft of the second screw member. .

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