JP4780651B2 - Development device - Google Patents

Description

  The present invention relates to a developing device that repeatedly forms a large number of images in an electrophotographic method, an image forming method, and the like.

  A conventional developing device will be described with reference to FIG. A developing device in a conventional electrophotographic image forming apparatus has a first developing roll 4 that rotates in the clockwise direction on the upstream side in the rotational direction of the image carrier 1, and a first developing roller 4 that rotates in the counterclockwise direction on the downstream side. There is a doctor member 6 between the two developing rolls 3 and the first developing roll 4 and between the scraper 7 and the two developing rolls 3 and 4, and a paddle 5 of a stirring impeller that can rotate opposite to the second developing roll 3. Further, there is a carrier supplement roll 8 so as to face the image carrier 1, and a bottom plate 2 is installed below the second developing roll 3. Development is performed by supplying toner onto the image carrier 1 by means of both developing rollers 3 and 4.

  Next, the flow of the developer in the developing device will be described. The developer lifted upward by the paddle 5 is delivered to the second developing roll 3. The developer conveyed by the developing roll 3 is distributed to the second developing roll 3 and the first developing roll 4 by the doctor member 6, and is conveyed to the developing area by each developing roll and developed. After the development is completed, the developer remaining on the first developing roll 4 is scraped off by the scraper 7, passes through the stirring and mixing area, and is returned to the paddle 5. On the other hand, after the development is completed, the developer remaining on the second developing roll 3 is not adjacent to the second developing roll 3 because a separating member such as the scraper 7 cannot be installed due to the space of the developing device. By disposing the same magnetic pole, the developer is peeled off from the second developing roll 3 and returned to the paddle 5. Such a developing device is well known.

  In this case, when the developer fluidity or the like deteriorates, a developer pool is generated at a portion indicated by A in the figure, and the developer that has completed development is mixed with the developer into which new toner is introduced. In the worst case, the developer that has just been developed is transported again to the development area, which adversely affects image quality.

  In addition, a developer peeling developing machine having a magnetic pole arrangement in which an internal magnet of a developing roll adjacent to the image carrier is provided adjacent to each other with the same polarity, and the developer starts to fall from the developing roll from this location. (For example, refer to Patent Document 1).

  The developing device has a configuration in which a non-magnetized portion is provided from the developer peeling portion to the re-magnetization portion by the same-pole magnetic pole arrangement. Further, since the developing machine is placed vertically, there is no problem in conveying the developer even if it is a non-magnetized part from the developer peeling part to the re-magnetization part.

  However, when it is employed in a horizontal developing device, there is a problem in that the developer transport becomes unstable because the developer does not flow smoothly due to the deterioration of the fluidity of the developer.

  Further, in order to make the gap formed between the lower part of the developing roll and the casing and between the stirring impeller and the casing uniform, a member made of a flexible member is used on the casing bottom plate so that the casing bottom plate is developed. There is a developing device that flexibly corresponds to the shape of the developer under the roll and the stirring impeller (see, for example, Patent Document 2).

  In this case, since the member made of the flexible member provided on the housing bottom plate corresponds to the shape of the developer under the developing roll and the stirring impeller, the adhesion is improved, but the flow of the developer is deteriorated. Inevitably, the developer whose fluidity has deteriorated over time has a problem in that poor conveyance occurs.

Japanese Patent Publication No. 02-022384

Japanese Patent Laid-Open No. 04-107485

  The flow of the developer in the developing machine will be described in more detail. The developer mixed and stirred with the replenished new toner is lifted upward by the paddle 5, transferred to the second developing roll 3 that rotates counterclockwise, and distributed by the doctor 6, one of which is clockwise. The other developer is transported to the rotating first developing roll 4, and the developer that has been developed is peeled off from the first developer opening electrode provided under the second developing roll 3, There is no problem if it is returned to the lower part of the paddle 5, mixed and stirred with a developer containing new toner, and conveyed again to the development area.

  However, when the flowability of the developer deteriorates with time, the flow of the developer is not smooth in the developing machine, and in particular, the flow becomes worse at a position A shown in FIG. It becomes like this. The developer pool gradually increases, and the developer that has completed the development adheres again to the second developer opening electrode provided to peel off the developer and is transported to the development area. In this case, the developer that has completed the development has a reduced toner concentration, which is the ratio of the toner in the developer, due to the development. When the toner is not mixed with new toner and is transported to the development area again, there is a problem that the image density becomes thin. Further, since this phenomenon is repeated, there is a problem that the image is not recovered.

In the present invention, a plurality of developing rolls are installed facing the image carrier, and at least one set of developing rolls having different rotation directions is included therein, and a doctor installed between the developing rolls. Therefore, the developer layer thickness of each developing roll is regulated by a doctor, and the rotatable developing roll located at the most downstream side in the image carrier moving direction is downstream in the rotational direction from the developing pole that develops in contact with the image carrier. A first developer open pole is provided on the side, a second developer open pole is provided adjacent to the first developer open pole in the direction of rotation of the developing roll, both developer open poles are set to the same pole, In a developing device in which a bottom plate is installed under a rotatable developing roll located at the most downstream side in the image carrier moving direction and a paddle for stirring the developer is installed, the developing roll rotation of the second developer opening electrode The transport pole of the direction Beauty and the second developer open pole the same polarity, the first developer open electrode is located beneath the developing roller, ± said first developer open pole center the vertical axis of the developing roll center and 0 ° 5 The second developer open pole is located at an angle of 30 ° to 60 ° from the center of the first developer open pole to the center of the second developer open pole. The first developer is disposed at 90 ° from the center of the open electrode.

  According to the present invention, a stable developer flow can be realized and high image quality can be maintained even when the developer fluidity is lowered in the developing machine.

  Embodiments of the present invention will be described below with reference to FIGS.

  FIG. 1 is a view showing a developing device according to the present invention. In FIG. 1, the image carrier 1 rotates in the direction of the arrow (clockwise) and is uniformly charged by a charger (not shown), and then is applied to the surface of the image carrier 1 by an optical system (not shown). A latent image is formed, and the latent image is developed by a developing machine to obtain an image. Opposite to the image carrier 1, there is a first developing roll 4 on the upstream side in the rotation direction of the image carrier 1, and a second developing roll 3 on the downstream side thereof, although not shown in the drawing, The inner magnet has a fixed and rotatable sleeve on the outer periphery, whereby the developer is conveyed, contacts the image carrier 1, and is supplied with toner and developed. Incidentally, a developing system called a fountain type in which the first developing roll 4 rotates clockwise and the second developing roll 3 rotates counterclockwise is adopted. This development system has a high development capability and is suitable for high-speed machines.

  The developer is composed of a toner and a carrier, and the carrier mistakenly attached to the image carrier 1 is captured by a carrier capturing roll 8 provided facing the image carrier 1.

  As the developer flow, the developer mixed and stirred with the replenished toner is lifted upward by the paddle 5 in the shape of an impeller. At this time, the developer is smoothly delivered from the second developing roll 3 by the shielding plate 9 provided between the second developing roll 3 and the paddle 5. The developer conveyed on the second developing roll 3 is regulated to be distributed to the first developing roll 4 and the second developing roll 3 by the doctor 6. The developer conveyed on the second developing roll 3 comes into contact with the image carrier 1 and develops. The developer that has been developed is returned to the bottom of the paddle 5. On the other hand, the developer conveyed on the first developing roll 4 comes into contact with the image carrier 1, and after development, is scraped off from the first developing roll 4 by the scraper 7 and returned to the lower part of the paddle 5.

  Next, the development electrode arrangement will be described with reference to FIG. The magnetizing arrangement shown in FIG. 3 is an arrangement that employs the top cutting at the doctor 6 part, and the polarity of the magnetic pole of the doctor 6 part of the corresponding first developing roll 4 is the polarity of the second developing roll 3. Different polar arrangements are employed, and a first developer opening electrode 31 and a second developer opening electrode 32 are installed at the lower part of the second developing roll 3, and the same as the second developer opening electrode 32. A pole transport pole 33 is also provided. The magnetization position of the first developer opening pole 31 is such that the angle between the vertical direction (Y axis) of the center line of the second developing roll 3 and the center portion of the first developer opening pole 31 is 0 ° ± 5 °. Further, the magnetized position of the adjacent second developer opening pole 32 is set so that the angle θ1 between the center of the first developer opening pole 31 and the center of the second developer opening pole 32 is 30. It is preferable that the angle is set to be greater than or equal to °, and the angle in the figure is when the angle is set to about 45 °. By setting the angle θ1 to 30 ° or more, an appropriate interval is generated between the first developer opening electrode 31 and the second developer opening electrode 32, thereby improving the releasability and further releasing the developer. Become smooth. Further, by extending the angle θ1 to 60 °, a certain interval is generated with respect to the transport pole that is the next magnetic pole of the second developer opening pole 32, and the peelability becomes perfect.

  Next, the relationship between the gap t0 between the doctor 6 and the first developing roll 4, the doctor gap t1 between the second developing roll 3, the distance t2 between the second developing roll 3 and the bottom plate 2, and the first developer opening electrode 31. The shape of the bottom plate 2 positioned on the central extension will be described with reference to FIG. When the gap between the doctor 6 and the first developing roll 4 is set to t0 and the gap between the second developing roll 3 is set to t1, t0 and t1 are adjusted to t0 ≦ t1. This setting is used to improve the image quality. Furthermore, it was confirmed that the flow of the developer becomes smoother by setting the interval t2 between the second developing roll 3 and the bottom plate 2 to be twice or more of t1. By setting this interval to be twice or more, the flow of the developer becomes smoother. However, since the size of the developing device itself is increased, t2 is preferably set to be twice t1. Further, a bottom plate inclined portion 21 is provided at a lower portion of the second developing roll 3 and is located on an extension of the central portion of the first developer opening pole 31, and the inclination angle θ2 is 45 ° to 90 °. Set by. As a result, the developer peeled off by the first developer opening electrode 31 flows more smoothly when the inclination of the bottom plate inclined portion 21 is set to 45 ° or more, and the flowability of the developer deteriorates. A smooth flow of the developer can be maintained between the second developing roll 3 and the bottom plate 2.

  Next, the relationship between the developer peeling operation performed under the second developing roll 3 and the shielding plate 9 will be described with reference to FIG.

  Conventionally, the first developer opening pole 31 and the second developer opening pole 32 provided at the lower part of the second developing roll 3 are the same pole (both are N poles in the figure), so the developer is not conveyed. After passing through the first developer opening electrode 31, it peels off from the second developing roll 3 and returns to the lower part of the paddle 5. However, when the flowability of the developer deteriorates, the developer pool is generated on the bottom plate 2 and the developer is reattached to the second developer opening electrode 32 for peeling the developer. There is a problem that the image quality is adversely affected.

  A shielding plate 9 is provided at the lower part of the second developing roll 3, and the upper part of the shielding plate 9 is installed between the first developer opening pole 31 and the second developer opening pole 32 magnetized at the lower part of the second developing roll 3. did. The developer peeled from the lower part of the second developing roll 3 advances on the bottom plate 2 by the shielding plate 9, is mixed and stirred with new developer at the lower part of the paddle 5, and is conveyed to the developing area. Even if the developer fluidity deteriorates and the developer is likely to accumulate, the movement of the developer is restricted by the shielding plate 9, so that there is no redeposition to the second developing roll 3 and stable image quality. Can be maintained. Further, in the example shown in the figure, since the transport pole 33 adjacent to the second developer opening pole 32 is also the same pole, there is no illegal developer transport from the lower part of the second developing roll 3, and only the paddle 5 is developed. As a result, the normal developer flow can be stably maintained.

1 is a diagram illustrating a developing device according to an embodiment of the present invention. Explanatory drawing which showed the prior art example. Explanatory drawing which showed magnetic pole arrangement | positioning in the developing device enlarged view of this invention. Explanatory drawing which showed the gap of a developing roll and each site | part with the developing device enlarged view of this invention.

Explanation of symbols

1 is an image carrier, 2 is a bottom plate, 21 is a bottom plate inclined portion, 3 is a second developing roll, 4 is a first developing roll, 5 is a paddle, 6 is a doctor, 7 is a scraper, 8 is a carrier supplement roll, 9 is a shielding plate, 31 is a first developer opening electrode, 32 is a second developer opening electrode, and 33 is a conveying electrode.

Claims (4)

A plurality of developing rolls are installed facing the image carrier, and at least one set of developing rolls having different rotation directions is included therein. Each developing roll is provided by a doctor installed between the developing rolls. The thickness of the developer layer is regulated by a doctor, and the rotatable developing roll located at the most downstream side in the image carrier moving direction is first on the downstream side in the rotational direction from the developing pole that contacts and develops the image carrier. A developer open pole is provided, a second developer open pole is provided adjacent to the first developer open pole in the rotation direction of the developing roll, the developer open poles are set to the same pole, and the image carrier is moved. In the developing device in which a bottom plate is installed at the lower part of the rotatable developing roll located at the most downstream in the direction and a paddle for stirring the developer is installed,
The transport pole of the second developer opening pole in the rotation direction of the developing roll is the same pole as the first and second developer opening poles ,
The first developer opening pole is located directly below the developing roll, the first developer opening pole center is set at 0 ° ± 5 ° with the vertical axis of the developing roll center, and the second developer opening pole The angle of the first developer open pole center to the second developer open pole center is 30 ° to 60 °, and the transport pole is 90 ° from the first developer open pole center. A developing device installed in The distance between the first developing roll, which is arranged upstream of the rotation direction of the image carrier and is rotated clockwise, and the doctor is t0, and is arranged downstream of the rotation direction of the image carrier and is rotated counterclockwise. When the distance between the second developing roll and the doctor is t1, t0 ≦ t1, and when the distance between the second developing roll and the bottom plate is t2, t2 ≧ t1 × 2. The developing device according to claim 1. 2. The development according to claim 1, wherein the bottom plate located under the second developing roll is inclined at 45 ° to 90 ° from a position located on an extension of the central portion of the first developer opening pole. apparatus. A shielding plate is provided between the first developing roll and the paddle, and the upper portion of the shielding plate is located between the first developer opening electrode and the second developer opening electrode. The developing device according to claim 1.

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