JP5337629B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus including the developing device, and more particularly to a developing device using a two-component developer composed of a magnetic carrier and toner. Is.

  Conventionally, as a developing method using dry toner in an image forming apparatus using an electrophotographic process, a one-component developing method using no carrier and a non-magnetic toner using a magnetic carrier (hereinafter also simply referred to as a carrier) are used. There is known a two-component developing system that uses a two-component developer to be charged and develops an electrostatic latent image on a photosensitive member with a magnetic brush composed of toner and a carrier formed on a developing roller.

  In an image forming apparatus using a two-component developing system, in order to reduce packing materials and cushioning materials as much as possible in consideration of environmental burdens, a developing device filled with a developer is mounted in the image forming apparatus main body. They are often shipped from factories. In view of this, a design has been made to improve the hermeticity of the developing device so that the developer does not leak due to an impact such as a fall or drop during conveyance.

  On the other hand, as a result of the recent increase in image processing speed, the driving speed of the developing device has increased, and as a result, the developer moving speed inside the developing device has also increased. When the seal of the developing device is increased to prevent the developer from leaking, the pressure inside the developing device also rises, so the toner that has fallen from the replenishing device into the developing device rises above the developer surface of the developing device due to air pressure. In some cases, the toner stays in the space and toner replenishment becomes unstable. In particular, near the end of the service life and in a state where the charging ability of the carrier is reduced, the toner is temporarily charged poorly due to the staying toner dropping at one time, and fogging occurs.

  Therefore, a method for alleviating the pressure increase inside the developing device has been proposed. For example, Patent Documents 1 and 2 provide a pressure relief hole at the top of the housing of the development device, and further covers the pressure relief hole with a filter. A developing device that suppresses an increase in pressure and leakage of developer is disclosed.

Japanese Patent Laid-Open No. 2-139487 JP 2006-250973 A

  However, in the methods of Patent Documents 1 and 2, in the case of a developing device having a long service life, the pressure reduction effect is reduced due to clogging of the filter. Further, when a developing device filled with a developer is shipped in a state where it is mounted in the main body of the image forming apparatus, the developer may leak out of the developing device through a filter and contaminate the inside of the image forming apparatus. It was.

  In view of the above problems, the present invention is a two-component development in which the internal pressure does not increase even when the image processing speed is increased, and the leakage of the developer from the inside of the developing device due to the impact of falling or dropping can be suppressed. An object of the present invention is to provide a developing device of the type and an image forming apparatus having the same.

  In order to achieve the above object, the present invention provides a developer container that contains a two-component developer containing toner and a magnetic carrier, an agitating and conveying member that agitates and conveys the developer contained in the developer container, and the agitation A developer carrying member that is rotatably provided above the carrying member and carries and conveys the developer, and a peeling electrode that is fixed inside the developer carrying member and peels the developer from the surface of the developer carrying member. A developing magnet comprising a fixed magnet body having a plurality of magnetic poles, and a panning blade disposed opposite to the developer carrier on the downstream side in the rotational direction of the developer carrier as viewed from the peeling pole, A sheet-like backflow prevention member is fixed to the inner surface of the developer container on the upstream side in the rotation direction of the developer carrier as viewed from the peeling pole, over the entire longitudinal direction of the developer carrier. The tip is developed It is arranged such that the contact or close proximity toward the downstream side in the rotational direction of the bearing member, the distal end portion of the backflow preventing member is characterized by notches are formed.

  According to the present invention, in the developing device configured as described above, the backflow prevention member is configured by stacking a plurality of sheet materials made of different materials.

  According to the present invention, in the developing device configured as described above, the backflow preventing member includes a first sheet disposed such that a base end portion is fixed to the developing container and a leading end portion is in contact with or close to the developer carrying member. And a second sheet material having an elastic modulus larger than that of the first sheet material, which overlaps with a base end side of the first sheet material.

  According to the present invention, in the developing device configured as described above, the depth of the notch is 1 mm or more and 2 mm or less.

  According to the present invention, in the developing device configured as described above, the notch is formed at a substantially central portion in the longitudinal direction of the backflow preventing member.

  The present invention also provides an image forming apparatus equipped with the developing device having the above-described configuration.

  According to the first configuration of the present invention, the sheet-like backflow preventing member has the base end fixed to the inner surface of the developing container, and the tip end directed toward the downstream side in the rotation direction of the developer supporting body. By arranging the notch at the tip of the backflow prevention member, the increase in pressure in the developing container is suppressed by the air passage formed by the notch, and toner replenishment is possible. As a result, the occurrence of fog due to poor charging of the toner can be reduced. Further, when the backflow preventing member is pushed by the developer in the developing container, the air passage is narrowed, so that leakage of the developer from the developing container can be suppressed.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, the backflow prevention member formed by superposing a plurality of sheet materials made of different materials is used, whereby the elasticity of the backflow prevention member is obtained. And resilience can be easily adjusted.

  According to the third configuration of the present invention, in the developing device of the second configuration, the backflow preventing member is fixed at the base end portion to the developing container and the tip end portion contacts the developer carrying member. By configuring the first sheet material arranged in this manner and the second sheet material that overlaps the base end side of the first sheet and has a larger elastic modulus than the first sheet material, the restoring force of the second sheet material The contact or proximity state between the backflow preventing member and the developer carrying member can be reliably maintained.

  According to the fourth configuration of the present invention, in the developing device having any one of the first to third configurations, the depth of the notch is set to 1 mm or more and 2 mm or less, whereby the pressure in the developing container is increased. It is possible to stabilize the toner supply by reliably suppressing the rise, and to effectively suppress the leakage of the developer when an impact is applied to the developing device.

  According to the fifth configuration of the present invention, in the developing device having any one of the first to fourth configurations, the notch is formed in the substantially central portion in the longitudinal direction of the backflow prevention member. It is possible to suppress leakage of the developer from both ends in the longitudinal direction of the developing device, which is particularly likely to occur when the forming device falls or falls.

  Further, according to the sixth configuration of the present invention, by mounting the developing device having any one of the first to fifth configurations, the pressure in the developing device is increased even when the image processing speed is increased. Therefore, stable toner replenishment is performed, so that charging failure and fogging of toner are suppressed, and further, an image forming apparatus capable of suppressing leakage of developer during transportation.

Schematic showing the overall configuration of an image forming apparatus equipped with the developing device of the present invention Side surface sectional drawing which shows the example of 1 structure of the image development apparatus of this invention The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller Side view of a backflow prevention member mounted on the developing device of the present invention A plan view of the backflow preventing member viewed from the auxiliary sheet side Enlarged side view of the backflow prevention member when the developing device is driven The side enlarged view which shows the state by which the backflow prevention member was pushed by the internal developer Side view showing a configuration in which the backflow preventing member is in contact with the magnetic roller Side surface sectional drawing which shows the other structural example of the image development apparatus of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with the developing device of the present invention. Here, a tandem color image forming apparatus is shown. In the color image forming apparatus 100 main body, four image forming portions Pa, Pb, Pc and Pd are arranged in order from the right side in FIG. These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and are further driven by a driving unit (not shown). The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller 9. Is transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip between the rollers 11. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. Further, a blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side in the moving direction of the intermediate transfer belt 8 when viewed from the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d, which are rotatably arranged. The exposure unit 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning devices 5a, 5b, 5c and 5d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then light is irradiated according to the image data by the exposure unit 4. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d is less than a predetermined value due to the formation of a toner image, which will be described later, each developing device 3a to The toner is replenished in 3d. The toner in the developer is supplied onto the photosensitive drums 1 a to 1 d by the developing devices 3 a to 3 d and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure unit 4. A toner image is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and yellow, cyan, magenta, and yellow on the photosensitive drums 1a to 1d are applied. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller pair 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, the image is directly discharged onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer paper P is distributed to the paper conveyance path 18 by the branching section 14 by rotating the discharge roller pair 15 in the reverse direction, and is re-conveyed to the registration roller pair 12b with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. The paper is discharged from the discharge roller pair 15 to the discharge tray 17.

  FIG. 2 is a side sectional view showing the structure of the developing device of the present invention. Hereinafter, the developing device 3a disposed in the image forming unit Pa in FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus description thereof is omitted. To do.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter also simply referred to as a developer) is accommodated. The developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into agitating chambers 20b and 20c, and a toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and is supplied to the first and second via a developer passage (not shown) formed in the partition wall 20a. It circulates between the stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side of the developing container 20 (left side in FIG. 2), and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing with respect to the respective rotation axes. .

  The developing container 20 is provided with a toner concentration sensor (not shown) facing the first stirring screw 21a, and a replenishing device (not shown) according to the toner concentration detected by the toner concentration sensor. Then, toner is supplied into the developing container 20 through the toner supply port 20d.

  The magnetic roller 22 includes a non-magnetic rotating sleeve 22a and a fixed magnet body 22b having a plurality of magnetic poles contained in the rotating sleeve. In the present embodiment, the magnetic poles of the fixed magnet body 22 b have a five-pole configuration including a main pole 35, a regulation pole (head cutting pole) 36, a transport pole 37, a separation pole 38, and a pumping pole 39.

  Further, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the spike cutting blade 25 rotates in the rotational direction of the magnetic roller 22 (clockwise in the figure). Around the opposite position between the developing roller 23 and the magnetic roller 22. A slight gap (gap) is formed between the front end of the spike cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 includes a cylindrical developing sleeve 23a and a developing roller-side magnetic pole 23b fixed in the developing sleeve 23a. The magnetic roller 22 and the developing roller 23 are predetermined at a facing position (opposed position). It is facing with a gap of. The developing roller side magnetic pole 23b is different in polarity from the opposing magnetic pole (main pole) 35 of the fixed magnet body 22b.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected. The first bias circuit 30 and the second bias circuit 31 are grounded to a common ground.

  A voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC), Vslv (AC) applied to the developing roller 23 and Vmag (DC) applied to the magnetic roller 22. ), Vmag (AC) can be varied.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Since the regulation pole 36 of the fixed magnet body 22 b faces the ear cutting blade 25, a nonmagnetic material or a magnetic body having a polarity different from that of the regulation pole 36 is used as the ear cutting blade 25. A magnetic field is generated in a direction attracting the gap with the sleeve 22a.

  Due to this magnetic field, a magnetic brush is formed between the ear cutting blade 25 and the rotating sleeve 22a. Then, after the thickness of the magnetic brush on the magnetic roller 22 is regulated by the cutting blade 25, when the magnetic brush moves to a position facing the developing roller 23 as the rotating sleeve 22a rotates, the main pole 35 and the developing of the fixed magnet body 22b are developed. Since the magnetic field attracted by the roller-side magnetic pole 23 b is applied, the magnetic brush contacts the surface of the developing roller 23. Then, a toner thin layer is formed on the developing roller 23 by a potential difference ΔV between Vmag (DC) applied to the magnetic roller 22 and Vslv (DC) applied to the developing roller 23 and a magnetic field.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 23 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 3 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. Further, the magnetic roller 22 has a second combined waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a rectangular wave Vmag (AC) having a phase different from Vslv (AC). Applied from the bias circuit 31.

  Accordingly, the voltage applied between the magnetic roller 22 and the developing roller 23 (hereinafter referred to as MS) is a composite waveform Vmag-Vslv having Vpp (max) and Vpp (min) as shown in FIG. Become. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to a facing portion between the photosensitive drum 1 a and the developing roller 23 by the rotation of the developing roller 23. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  When the rotating sleeve 22a further rotates clockwise, the magnetic brush is now separated from the surface of the developing roller 23 by the horizontal (roller circumferential direction) magnetic field generated by the opposite polarity transport pole 37 adjacent to the main pole 35, and the developing roller 23a develops. The remaining toner that is not used for is collected from the developing roller 23 onto the rotating sleeve 22a. When the rotating sleeve 22a further rotates, a magnetic field repelling is applied by the peeling pole 38 (developer separating portion) of the magnetic roller side magnetic pole 22b and the scooping pole 39 having the same polarity as that, so that the developer is contained in the developing container 20. Detach from the rotating sleeve 22a. Then, after being stirred and conveyed by the second agitating screw 21b, a magnetic brush is again formed on the rotating sleeve 22a by the scooping pole 39 as a two-component developer uniformly charged with an appropriate toner concentration, It is conveyed to 25.

  Further, a sheet-like backflow prevention member 40 is provided over the entire longitudinal direction (paper surface direction in FIG. 2) of the magnetic roller 22 on the upstream side in the rotation direction of the rotation sleeve 22a when viewed from the separation pole 38. The base end portion of the backflow preventing member 40 is fixed to the inside of the developing container 20, and the front end portion is disposed toward the downstream side in the rotation direction of the rotary sleeve 22a.

  FIG. 4 is an enlarged side view showing the relationship between the backflow preventing member and the magnetic roller. The backflow prevention member 40 includes a backflow prevention sheet (first sheet material) 40a that prevents backflow of the developer in the second stirring chamber 20c, and a reinforcing auxiliary layer that is superimposed on the base end 41 side of the backflow prevention sheet 40a. It is composed of a sheet (second sheet material) 40b. Here, a PET film having a thickness of 0.1 mm is overlapped as an auxiliary sheet 40b on a backflow prevention sheet 40a made of a urethane sheet having a thickness of 0.2 mm. Further, the base part 41 of the backflow prevention sheet 40a and the auxiliary sheet 40b is extended to form an affixing part 42 that is fixed inside the developing container 20.

  When the first and second stirring chambers 20b and 20c located below the magnetic roller 22 are brought into a closed space by the spike cutting blade 25 and the backflow prevention sheet 40a, the pressure increases during driving and toner replenishment becomes unstable. There is a risk. Therefore, it is necessary to provide an air passage between the backflow prevention sheet 40a and the rotating sleeve 22a.

  On the other hand, when an impact is applied to the developing device 3a because the image forming apparatus 100 falls or falls, the backflow prevention sheet 40a is pressed by the developer in the second stirring chamber 20c and pressed against the magnetic roller 22 side. It will be in such a state. At this time, if an air passage exists between the backflow prevention sheet 40a and the rotating sleeve 22a, the developer may leak from the opening of the developing container 20 (around the developing roller 23).

  FIG. 5 is a plan view of the backflow preventing member 40 as viewed from the auxiliary sheet 40b side. In the present invention, a gap A is provided between the backflow prevention member 40 and the rotating sleeve 22a, and a rectangular cutout 50 is formed at the tip 43 of the backflow prevention sheet 40a.

  With this configuration, as shown in FIG. 6, when the developing device 3a is driven, the compressed air in the first and second stirring chambers 20b and 20c is formed by the gap A and the notch 50. Since it passes through 51 and escapes to the outside, an increase in pressure in the first and second stirring chambers 20b and 20c can be suppressed. Although not shown in FIG. 6, a developer layer (magnetic brush layer) is formed on the rotating sleeve 22a when the developing device 3a is driven.

  Further, as shown in FIG. 7, when the backflow prevention sheet 40a is pushed by the developer in the second stirring chamber 20c due to an impact during conveyance of the image forming apparatus 100, the leading end 43 of the backflow prevention sheet 40a rotates. The gap A is closed in close contact with the sleeve 22a, but the cutout portion 50 remains partly closed (hatched area) without being closed.

  Here, when the developer is biased to both end portions in the longitudinal direction of the developing device 3 a due to the overturning or dropping of the image forming apparatus 100, the developer is likely to leak from the gap between the developing container 20 and the magnetic roller 22. Therefore, as shown in FIG. 5, if the notch 50 is provided in the substantially central portion in the longitudinal direction of the backflow preventing sheet 40a, the notch 50 may not be completely closed as shown in FIG. The leakage of the developer from both ends in the longitudinal direction can be suppressed.

  As the depth B of the notch 50 is reduced, the developer leakage prevention effect is improved, but the pressure reducing effect in the first and second agitating chambers 20b and 20c is reduced, and toner replenishment becomes unstable. There is a risk of fogging. On the other hand, as the depth B increases, the effect of reducing the pressure in the first and second stirring chambers 20b and 20c is improved. On the other hand, when an impact is applied to the developing device 3a, the developer tends to leak. Therefore, it is preferable to set the depth B of the notch 50 to 1 mm or more and 2 mm or less.

  Further, the amount of protrusion of the front end portion 43 of the backflow prevention sheet 40a from the nearest contact point N is not particularly limited, but if the amount of protrusion is too small, the front end portion 43 of the backflow prevention sheet 40a when an impact is applied to the developing device 3a. May not sufficiently adhere to the magnetic roller 22, and the developer may leak out when an impact is applied to the developing device 3a due to the image forming apparatus 100 falling or dropping. Therefore, the protrusion amount is preferably 0.5 mm or more.

  In addition, it is good also as a structure which makes the front-end | tip part 43 of the backflow prevention sheet 40a contact the magnetic roller 22, without providing the clearance gap A. FIG. In this case, as shown in FIG. 8, an air passage 51 is formed between the backflow prevention sheet 40a and the rotating sleeve 22a by the notch 50, and the first and second stirring chambers 20b and 20c are driven when the developing device 3a is driven. The compressed air inside passes through the air passage 51 to the outside. On the other hand, when the backflow prevention sheet 40a is pushed by the developer in the second stirring chamber 20c, the notch 50 is closed leaving a part of the upper end (shaded area) as in FIG. Leakage is suppressed. Since the portion in contact with the backflow prevention sheet 40a is on the downstream side in the rotation direction of the rotary sleeve 22a when viewed from the main pole 35, there is no possibility of affecting the formation of the toner thin layer on the developing roller 23.

  Furthermore, the backflow prevention member 40 can be configured only by the backflow prevention sheet 40a without using the auxiliary sheet 40b. However, when the auxiliary sheet 40b having a larger elastic modulus than the backflow prevention sheet 40a is superposed on the base end portion of the backflow prevention sheet 40a as in the present embodiment, the restoring force (koshi) of the backflow prevention member 40 becomes stronger, and development is performed. This is preferable because the backflow preventing sheet 40a is hardly deformed by the pressing force of the developer and the effect of preventing the developer leakage is improved.

  On the other hand, when the backflow prevention sheet 40a is brought into contact with the rotary sleeve 22a as shown in FIG. 8, if the rigidity of the backflow prevention sheet 40a is large, the surface of the rotary sleeve 22a may be damaged. It is preferable to use a low elastic modulus material such as urethane.

  Here, the elastic modulus is a physical property value indicating difficulty of deformation, and is a proportional constant between stress and strain in elastic deformation. In other words, a material having a higher elastic modulus is less likely to be deformed and has better resilience.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the material and dimensions of the backflow prevention member 40 shown in the above embodiment are merely examples, and can be appropriately designed according to the specifications of the developing device. Moreover, you may comprise the backflow prevention member 40 with the sheet material of 3 or more from which a material differs.

  Further, the present invention is not limited to the developing device having the magnetic roller 22 and the developing roller 23 as shown in FIG. 2, but as shown in FIG. 9, the magnetic roller having the fixed magnet body 22b therein. A magnetic brush composed of a toner component and a magnetic carrier is formed on 22 and the developer leaks from the developing device 3 that develops the electrostatic latent image on the photosensitive drum 1 by bringing the magnetic brush into contact with the photosensitive drum 1. The prevention mechanism can be applied in exactly the same manner.

  The present invention is not limited to the tandem type color printer shown in FIG. 1, but a two-component developing device such as a digital or analog type monochrome copying machine, a monochrome printer, a rotary developing type color printer, a color copying machine, a facsimile, or the like. The present invention can be applied to various image forming apparatuses provided. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

  In the test machine as shown in FIG. 1 in which the developing device of the present invention shown in FIG. 2 is mounted, the relationship between the size of the notch 50 formed in the backflow prevention member 40 and the occurrence of fog and developer leakage. Was investigated. The test was performed in a cyan image forming portion Pa including the photosensitive drum 1a and the developing device 3a.

  The test machine conditions were a system speed of 35 sheets / min, a photosensitive drum peripheral speed of 240 mm / sec, and a drum surface potential of 300 V for the white background potential (V0) and 20 V for the image portion potential (VL). The developing roller and magnetic roller have a diameter of 20 mm, the developing roller has a peripheral speed ratio of 1.5 with respect to the photosensitive drum (forward rotation on the surface facing the photosensitive member), and the magnetic roller has a peripheral speed ratio of the developing roller. On the other hand, it was 1.5 (counter rotation on the surface facing the developing roller). The gap between the photosensitive drum and the developing roller was 0.15 mm, and the gap between the magnetic roller and the developing roller was 0.3 mm. Further, a fixed magnet body was fixed in the magnetic roller so that the main pole was disposed at a position of 10 ° downstream from the closest portion between the magnetic roller and the developing roller, and the magnetic force of the main pole was set to 70 mT.

  As the developer, a two-component developer comprising a positively charged toner having an average particle diameter of 6.8 μm and a specific gravity of 1.2 and a coated ferrite carrier having an average particle diameter of 35 μm and a specific gravity of 4.5 is used. The ratio (T / C) was 9% by weight.

  The voltage application conditions to the developing roller were Vslv (DC) = 50 V, Vpp of Vslv (AC) was 1.5 kV, frequency was 3 kHz, and Duty = 35%. The voltage application conditions for the magnetic roller were Vmag (DC) = 250 V, Vmag (AC) Vpp of 1.4 kV, frequency of 3 kHz, and Duty = 65%.

  As an evaluation method, as shown in FIG. 4, an auxiliary sheet 40b having a length L2 of 7 mm is superimposed on the base end 41 side of the backflow prevention sheet 40a having a length L1 of 10.5 mm, Using the backflow prevention member 40 in which the distance D to the tip of the auxiliary sheet 40b is 3.5 mm, the gap A between the backflow prevention member 40 and the rotating sleeve 22a and the depth of the notch 50 shown in FIG. Occurrence of fog after printing 250,000 sheets of white paper (white solid) image when the width B and width C are changed is visually observed. The case where there was no problem was indicated by Δ and the case where there was fogging and there was a practical problem was indicated by ×.

  For developer leakage, a tester equipped with a developing device was tested from a height of 60 cm to a corner (one location), a ridgeline (three locations in the vertical, horizontal, and height directions around the corner), upper surface, side surface ( 4 points), a drop test was performed in which the bottom surface was the landing point, and dropped 10 times each time. After that, remove the developing device from the testing machine and visually observe the developer leakage. If there is no developer leakage, ○, if there is a slight developer leakage but there is no practical problem. When there was a leak and there was a problem in practical use, it was set as x. The evaluation results are shown in Table 1 together with the values of gap A, depth B, and width C. Table 2 shows the results when using the backflow prevention member 40 composed only of the backflow prevention sheet 40a without using the auxiliary sheet 40b.

  As is clear from Tables 1 and 2, in the present inventions 1 to 10 in which the notch 50 is provided in the backflow preventing member 40, the fog cannot be confirmed, or even if fog occurs, there is no practical problem. It was. In particular, in the present inventions 2, 3, 5, 7, 8, and 10 in which the depth B of the notch 50 is 2 mm, the fog suppression effect is high. As for developer leakage after the drop test, the present invention 1 to 10 in which the depth B of the notch 50 is set to 1 mm and 2 mm is practical even if there is no developer leakage or developer leakage. It was the range without any problem.

  Furthermore, from the comparison between the present inventions 1 to 5 and the present inventions 6 to 10, the use of the auxiliary sheet 40b suppressed the leakage of the developer during the drop test. This is considered to be because the restoring force of the auxiliary sheet 40b is large, so that the backflow preventing member 40 is not easily deformed by the developer pressure, and a gap is not easily formed between the auxiliary sleeve 40b and the rotating sleeve 22a.

  On the other hand, in Comparative Examples 1 to 4 in which the backflow preventing member 40 was not provided with the notch 50, the developer leakage was not observed or was in a practically no problem range, but the fog was noticeably generated. did. Here, the test was performed using the cyan image forming portion Pa, but it has been confirmed that similar results can be obtained in the magenta, yellow, and black image forming portions Pb to Pd.

  The above embodiment is merely an example of the present invention, and the drum surface potential, conditions for applying voltage to the developing roller and the magnetic roller, and the like can be appropriately set according to the specifications of the apparatus and the usage environment.

  INDUSTRIAL APPLICABILITY The present invention can be used for a two-component developing type developing device that uses a developer carrier having a fixed magnet body therein, and includes a sheet-like backflow prevention member having a base end fixed to the inner surface of a developing container. The tip portion is arranged so as to be in contact with or close to the developer carrier so that the developer carrier is directed downstream in the rotation direction of the developer carrier, and a notch is provided at the tip of the backflow preventing member.

  As a result, the air flow path formed by the notch prevents the pressure in the developer container from increasing when the developing device is driven, stabilizes the toner supply, and when an impact is applied to the developing device, the backflow prevention member is provided. A developing device that is pressed by the developer in the developer container, the notch is pressed against the developer carrier, and at least a part of the air passage is closed, so that fog generation and developer leakage can be effectively suppressed; and Become.

1a to 1d Photosensitive drum 3a to 3d Developing device 20 Developing container 21a First stirring screw (stirring conveyance member)
21b Second stirring screw (stirring conveyance member)
22 Magnetic roller (developer carrier)
22a Rotating sleeve 22b Fixed magnet body 23 Developing roller 23a Developing sleeve 23b Developing roller side magnetic pole 25 Ear cutting blade 35 Main pole 36 Regulating pole 37 Conveying pole 38 Separating pole 40 Backflow preventing member 40a Backflow preventing sheet (first sheet material)
40b Auxiliary sheet (second sheet material)
41 Base end portion 43 Front end portion 50 Notch portion 51 Ventilation path 100 Image forming apparatus

Claims (6)

A developer container containing a two-component developer containing toner and a magnetic carrier;
An agitating and conveying member for agitating and conveying the developer contained in the developing container;
A developer carrying member that is rotatably provided above the stirring and conveying member and carries and conveys the developer; and
A fixed magnet body having a plurality of magnetic poles including a separation pole which is fixed inside the developer carrying body and peels off the developer from the surface of the developer carrying body;
A panning blade disposed opposite to the developer carrier on the downstream side in the rotational direction of the developer carrier as viewed from the peeling pole;
In a developing device having
On the upstream side in the rotation direction of the developer carrying member as viewed from the peeling pole, a sheet-like backflow constructed by stacking a plurality of sheet materials of different materials over the entire longitudinal direction of the developer carrying member. A preventing member is disposed such that the base end is fixed to the inner surface of the developer container, and the tip is in contact with or close to the downstream side in the rotation direction of the developer carrier, and the tip of the backflow preventing member Is a developing device in which a notch is formed. The backflow preventing member includes a first sheet material arranged such that a base end portion is fixed to the developing container and a front end portion is in contact with or close to the developer carrier, and a base end portion of the first sheet material 2. The developing device according to claim 1, wherein the developing device includes a second sheet material that overlaps with the first sheet material and has a higher elastic modulus than the first sheet material . The developing device according to claim 1, wherein a depth of the notch is 1 mm or more and 2 mm or less . The developing device according to claim 1 , wherein the notch is formed at a substantially central portion in a longitudinal direction of the backflow preventing member . A developer container containing a two-component developer containing toner and a magnetic carrier;
An agitating and conveying member for agitating and conveying the developer contained in the developing container;
A developer carrying member that is rotatably provided above the stirring and conveying member and carries and conveys the developer; and
A fixed magnet body having a plurality of magnetic poles including a separation pole which is fixed inside the developer carrying body and peels off the developer from the surface of the developer carrying body;
A panning blade disposed opposite to the developer carrier on the downstream side in the rotational direction of the developer carrier as viewed from the peeling pole;
In a developing device having
A sheet-like backflow prevention member is fixed to the inner surface of the developer container on the upstream side in the rotation direction of the developer carrier as viewed from the peeling pole, over the entire longitudinal direction of the developer carrier. The tip portion is arranged so as to contact or be close to the downstream side in the rotation direction of the developer carrying member, and the tip portion of the backflow prevention member is cut into a substantially central portion in the longitudinal direction of the backflow prevention member. current image device you characterized in that-out part is formed.   An image forming apparatus on which the developing device according to claim 1 is mounted.