JP2008040067A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus which can solve problems such as toner splashing and scumming caused by toner separated from a carrier at the transfer of a developer and can obtain stable images. <P>SOLUTION: The developing device 1 includes a plurality of developer carriers opposed to a latent image carrier 2, arranged in parallel along the rotational direction of the latent image carrier 2 and having a plurality of magnetic poles in their insides. In the device, on the downstream part in the rotational direction of an upstream developer carrier 13 from the nearest portion C1 connecting the center of the upstream developer carrier 13 arranged on the upstream side in the rotational direction of the latent image carrier 2 and the center of the downstream developer carrier 14 arranged on the downstream side, the developer is transferred from the upstream developer carrier 13 to the downstream developer carrier 14. The image forming apparatus 100 includes the developing device 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing apparatus and an image forming apparatus using a dry two-component developer composed of a magnetic carrier and a non-magnetic toner in an image forming apparatus using electrophotography such as a copying machine and a printer.

In general, in a developing device used in various image forming apparatuses such as a copying machine, an electrostatic latent image corresponding to an image is formed on a latent image carrier made of a photoconductor and the like, and is provided in the developing device. A two-component developer consisting of a carrier and a toner is spiked and held on the developer carrying member, and the magnetic brush developer on the developer carrying member is carried into the development area by the transporting action of the developer carrying member. A developing operation is performed by supplying toner to the electrostatic latent image, and a visible image is obtained.
The developer carrying body includes a developing sleeve that is generally formed in a cylindrical shape, and a magnet body that forms a magnetic field in the developing sleeve so as to cause the developer to stand on the surface of the developing sleeve. Is provided. At this time, the carrier constituting the developer is spiked on the developing sleeve so as to follow the lines of magnetic force emitted from the magnet body, and the charged toner is attached to the spiked carrier become. The magnet body is formed in a roller shape having a plurality of magnetic poles, etc., and at least one of the developing sleeve and the magnet body is transported, whereby the developer spiked as a magnetic brush on the surface of the developing sleeve However, it has been moved. The developer carried into the development area is brought into contact with the surface of the latent image carrier so that the magnetic brush of the developer is bent, and the magnetic brush of the contact developer has a relative linear velocity difference from the latent image carrier. Based on this, toner is supplied while rubbing against the electrostatic latent image.

However, if the same developer magnetic spike in the development area is kept in contact with the latent image carrier for a long time and rubbed, the carrier spike will scrape off the toner already supplied and adhered to the electrostatic latent image. An abnormal image such as a solid cross-over occurs, and the rear end portion of the halftone tends to be faint. In order to solve this problem, the nip width of the magnetic brush with respect to the latent image carrier, i.e., the width of the development area has been reduced by reducing the magnetic pole width of the magnetic body that causes the magnetic brush developer to rise. It is thought from. However, when such a narrow nip configuration is adopted, the developing ability for a so-called line image can be improved, but the toner supply ability is lowered, so the image density of a so-called solid image may be lowered. .
In order to prevent such a decrease in image density in a solid image, a developing device has been proposed in which a plurality of developer carriers are installed in multiple stages as described in Patent Document 1. In the multi-stage developing device, each magnetic brush is formed such that a plurality of magnetic brushes in contact with the latent image carrier are arranged in parallel in the transport direction of the latent image carrier, and a developing operation for one electrostatic latent image is performed. By being applied a plurality of times, sufficient toner is supplied to the solid image.

Japanese Patent No. 3552010

However, in the conventional multi-stage developing device, since the developer is transferred up and down immediately before the closest portion (photoconductor side) between the upstream developing sleeve and the downstream developing sleeve, several problems occur.
Since the developing sleeve in the developing device rotates at high speed, the developer itself on the developing sleeve also has high kinetic energy. Therefore, when the developer is transferred from the upstream developing sleeve to the downstream developing sleeve, if the impact force when the developer is transferred to the downstream sleeve becomes larger than the adhesion force between the toner and the carrier, the toner is removed from the carrier. I will leave. Further, since the developing sleeve in the developing device rotates at a high speed, an air flow is generated, and when the toner that has flowed in the air flow gets on, the toner is scattered outside the developing container, so-called toner scattering occurs.
Further, if the scattered toner adheres to the non-image part of the latent image carrier, so-called background stain on the photoreceptor is caused, and if this background stain moves to the paper in the transfer portion, the background stain on the paper occurs. Further, if the toner remains on the photosensitive member, the toner recovered by cleaning and discarded is increased, and the toner yield is deteriorated. Passing through the cleaning causes problems such as charging stains and photoconductor filming, resulting in poor images.
Further, in the conventional system, there is a case where unevenness of toner density exists in the developer conveyed to the downstream developing sleeve, and thus there is a problem that the image becomes unstable. That is, when the developer passes through the developing area of the upstream developing sleeve, if a latent image exists on the photoconductor, the toner moves to the photoconductor side, and if there is no latent image on the photoconductor, the toner is Move to the developing sleeve side. For this reason, the developer that has passed through the upstream development region may have uneven toner density in the circumferential direction and tangential direction. In the conventional method, the unevenness of the toner density is transferred to the downstream developing sleeve as it is, causing a problem that the image becomes unstable.

  Accordingly, the present invention has been made in view of the above-mentioned problems, and its problem is to improve the problems such as toner scattering and background smear caused by the toner separated from the carrier during delivery of the developer, and to produce a stable image. A developing device and an image forming apparatus are provided.

The features of the present invention, which is a means for solving the above problems, are listed below.
The present invention relates to a developing device including a plurality of developer carriers that are opposed to a latent image carrier and are arranged in parallel along a rotation direction of the latent image carrier and have a plurality of magnetic poles therein. Direction of rotation of the upstream developer carrier from the closest portion connecting the center of the upstream developer carrier disposed upstream with respect to the rotational direction of the body and the center of the downstream developer carrier disposed downstream. In the developing device, the developer is transferred from the upstream developer carrier to the downstream developer carrier at a downstream portion. Here, the upstream developer carrying body and the downstream developer carrying body are the developer carrying bodies that are the nearest developer carrying bodies among the plurality of developer carrying bodies and that have the closest portion.
The present invention provides a first magnetic pole and a second magnetic pole from the downstream portion among the magnetic poles of the upstream developer carrier at the downstream portion relative to the rotation direction of the upstream developer carrier from the closest portion, The magnetic poles at the transfer portion of the downstream developer carrying member have the same polarity.
The present invention is characterized in that there are two developer carriers.
The present invention is characterized in that the developer is supplied only to the upstream developer carrier disposed on the most upstream side with respect to the rotation direction of the latent image carrier.
The present invention is characterized in that the developer delivery section has a member for assisting the delivery of the developer.
The present invention is an image forming apparatus having the developing device described above.

  According to the present invention, there is provided a developing device and an image forming apparatus for improving a problem such as toner scattering and background smear caused by toner separated from a carrier at the time of developer delivery, and providing a stable image. It became possible to provide.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

FIG. 1 is a cross-sectional view showing an example of a developing device according to the present invention. First, the entire configuration will be clarified. The developing device 1 is disposed opposite to a drum-shaped photoconductor 2 which is an example of a latent image carrier, and the photoconductor 2 is rotationally driven in a clockwise direction in the drawing as indicated by an arrow A in FIG. A developing container 3 of the developing device 1 contains a powdery two-component developer 4 having a magnetic carrier and magnetic or non-magnetic toner.
In the developing container, first to third stirring screws 5, 6, and 7 as developer stirring means are provided in parallel to the developing sleeve. First to third conveyance paths 10, 11, 12 that are partitioned by the first and second partition walls 8, 9 are formed.
An opening (not shown) is provided at one end of the first partition 8, and conducts between the second transport path 11 and the third transport path 12. At both ends of the second partition 9, Openings (not shown) are provided, respectively, to conduct between the first transport path 10 and the third transport path 12.

In the second transport path 11, the developer collected by the stirring screw 6 is transported from the second transport path 11 to the third transport path 12 while being stirred. In the third transport path 12, the third transport is performed by the stirring screw 7. The developer is transported to the end of the path 12, and the developer is lifted from the third transport path 12 to the first transport path 10 through the opening and circulated and supplied from the third transport path 12 to the first transport path 10.
In the first conveyance path 10, the excess developer that is supplied to the first developing sleeve 13 while being agitated and conveyed by the agitating screw 5 and is not applied to the first developing sleeve 13 of the first conveyance path 10 falls to the third conveyance path 12. Supplied.
When the toner concentration in the developer decreases, the toner is replenished from the toner container (not shown) into the developer 4 in the third conveyance path 12 and stirred by the third stirring screw 7.
The developing device 1 shown in FIG. 1 includes a first developing sleeve 13 and a second developing sleeve 14 arranged in a positional relationship upstream and downstream, as viewed from the rotation direction of the latent image carrier, and the inside of each developing sleeve. It has a plurality of magnets 13a and 14a fixedly arranged along the circumferential direction.

When the photosensitive member 2 is rotationally driven in the direction of arrow A, an electrostatic latent image is formed on the surface thereof. In this example, the electrostatic latent image moves from upstream to downstream at a portion facing the developing device 1.
As described above, the developer supplied to the first developing sleeve 13 by the first stirring screw 5 is applied to the first developing sleeve 13 by the rotation of the developing sleeve 13 and the magnetic force of the magnet 13a provided therein. While being carried, it is conveyed in the direction of arrow B1. That is, first, the developer supplied and carried on the first developing sleeve 13 passes through the doctor blade 15 as indicated by an arrow B3 while being carried on the developing sleeve 13, and at this time, an excess developer as indicated by an arrow B2. Is scraped off. The appropriate amount of developer that has passed through the doctor blade 15 passes through the upstream developing region D1 between the first developing sleeve 13 and the photosensitive member 2 as indicated by an arrow B3, and the first and second developing sleeves 13 and 14 are passed. Passes through the closest portion C1 and moves to a position where the action of the magnetic force on the first developing sleeve 13 side is weakened, the second developing sleeve 14 is caused by the magnetic force on the second developing sleeve 14 side as indicated by an arrow B4. The surface moves to the surface, passes through the second developing region D2 between the second developing sleeve 14 and the photosensitive member 2 as indicated by an arrow B5, continues away from the lower developing sleeve 14, flows to the bottom of the developing container 3, and flows to the bottom. The mixture is again stirred by the two stirring screws 6.
When the developer 4 is conveyed and stirred as described above, the toner and the carrier are triboelectrically charged with opposite polarities, and when the developer passes through the development regions D1 and D2 as described above, the developer The toner inside is electrostatically transferred to the electrostatic latent image formed on the photosensitive member 2, and the latent image is visualized.
As described above, the developing device 1 rotationally drives the first developing sleeve 13 and the second developing sleeve 14 in the same direction, and the two-component developer supplied to the first developing sleeve 13 is supplied to each of the magnets described above. After passing through the developing region D1 between the first developing sleeve 13 and the latent image carrier 2 by the magnetic force and the rotation of the developing sleeves 13 and 14, the second developing sleeve 14 is moved to the second developing sleeve 14 The electrostatic latent image formed on the latent image carrier 2 is visible by the toner in the developer that passes through the development region D2 between the toner image 14 and the latent image carrier 2 and passes through the development regions D1 and D2. It is configured to image.

FIG. 2 is an explanatory view showing the arrangement state of the developing sleeves 13 and 14 shown in FIG. 1 and the magnets 13a and 14a therein. Here, the magnet 13a provided in the first developing sleeve 13 is shown here. Reference numerals P1 to P5 are assigned to the individual magnets, and reference numerals Q1 to Q5 are assigned to the individual magnets 13a provided in the lower developing sleeve 13, respectively. The arrangement of the magnetic poles of the magnets 13a and 14a provided in the sleeves 13 and 14 is P1 (N pole), P2 (S pole), P3 (N pole), P4 (N pole), and P5 (S pole), respectively. , Q1 (N pole), Q2 (S pole), Q3 (S pole), Q4 (N pole), and Q5 (S pole).
When the flow of the developer is described in detail, the developer pumped up from P4 is transported from P5 to P1 to P2 after the amount of the agent is regulated by the doctor blade 15. As shown in FIG. 3, the developer transported to P2 is caused by the rotation of the first developing sleeve 13, the magnetic repulsive force from Q5, and the magnetic attraction force from P3, and the closest region C1 of both developing sleeves. And is transported to P3. Since the developer conveyed to P3 receives a magnetic repulsive force from P4, the developer that can no longer be held by P3 is transferred to Q4, and the rotation of the second developing sleeve 14 and the magnetic attractive force from Q5 As a result, the paper passes again through the closest region C1 and is conveyed from Q5 to Q1 to Q2.

With this configuration, the developer can pass the developer in the region C2 after passing through the closest region C1 of the developing sleeves 13 and 14. In the conventional method, since the developer is transferred in the region C3, the toner scattered during the developer transfer may adhere to the photosensitive member 2 or jump out of the developing container 3. Even if the toner is scattered during the delivery of the developer, the scattered toner is shielded by the closest portion C1 between the developing rollers, and thus is confined on the stirring roller side and does not jump out of the developing container 3. Further, the toner can adhere to the photoreceptor 2 and the paper surface, and the developer can be conveyed without causing background staining.
When the toner scattering amount of the present invention and the conventional method was measured, the toner scattering amount increased as the developer deteriorated in the conventional method, but the toner scattering amount can be suppressed even when the developer deteriorates. The result was obtained.
Further, when the toner density unevenness in the second developing roller was compared between the present invention and the conventional method, the present invention showed that the toner density unevenness was suppressed and a stable image was obtained.
Further, as shown in FIG. 4, by providing a member 16 for assisting the delivery of the developer in the vicinity of the region C2 for delivering the developer from the first developing sleeve 13 to the second developing sleeve 14, the toner scattering can be further suppressed. We were able to deliver the developer.

As described above, in the present invention, since the developer is transferred in the region C2, even if the toner is detached from the carrier when the developer is transferred from the upstream developing sleeve to the downstream developing sleeve, the toner adheres to the photoreceptor 2. Or the possibility of going out of the developing container 3 can be reduced. Further, since the developer is rubbed at the closest portion C1 between the developing sleeves 13 and 14, a stable toner density can be obtained even in the stable downstream developing region D2, and the image is also stabilized.
In the above embodiment, the case where there are two developing sleeves is shown, but three or more developing sleeves may be provided.

FIG. 5 is a diagram showing the configuration of the image forming apparatus of the present invention. In the figure, reference numeral 100 denotes an image forming apparatus main body, 200 denotes a paper feed table on which the image forming apparatus is mounted, 300 denotes a scanner attached to the image forming apparatus main body 100, and 400 denotes an automatic document feeder (ADF) attached thereon.
The image forming apparatus main body 100 is provided with an endless belt-shaped intermediate transfer member 104 at the center. As shown in FIG. 5, in the illustrated example, it is wound around three support rollers 114, 115, and 116 so as to be able to rotate and convey clockwise in the figure.
In this illustrated example, an intermediate transfer body cleaning device 117 that removes residual toner remaining on the intermediate transfer body 104 after image transfer is provided to the left of the second support roller 115 among the three.
Further, four images of black, cyan, magenta, and yellow are formed on the intermediate transfer member 104 stretched between the first support roller 114 and the second support roller 115 of the three along the conveyance direction. The tandem image forming apparatus 20 is configured by arranging the forming units 18 side by side. The image forming unit 18 includes the developing device 1 of the present invention (not shown).
Further, an exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.

On the other hand, a secondary transfer device 22 is provided on the side opposite to the tandem image forming apparatus 20 with the intermediate transfer member 104 interposed therebetween. In the illustrated example, the secondary transfer device 22 includes a secondary transfer belt 24, which is an endless belt, spanned between two rollers 23, and is pressed against the third support roller 116 via the intermediate transfer body 104. The image on the intermediate transfer member 104 is transferred to a sheet.
A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.
The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the image-transferred sheet to the fixing device 25. Of course, a non-contact charger may be arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this sheet conveyance function together.
In the illustrated example, under such a secondary transfer device 22 and a fixing device 25, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet in parallel with the tandem image forming device 20 described above. Is provided.

When making a copy using this color image forming apparatus, the document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it.
When a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. At that time, the scanner 300 is immediately driven to travel the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.

When a start switch (not shown) is pressed, one of the support rollers 114, 115, and 116 is rotated by a drive motor (not shown) and the other two support rollers are driven to rotate, and the intermediate transfer member 104 is rotated and conveyed. To do. At the same time, the individual image forming means 18 rotate the photoconductor 2 to form black, yellow, magenta, and cyan monochrome images on each photoconductor 2. Then, along with the conveyance of the intermediate transfer member 104, those single color images are sequentially transferred to form a composite color image on the intermediate transfer member 104.
On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43, and the separation roller 45. Are separated one by one into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the image forming apparatus main body 100, and abutted against the registration roller 49 and stopped.
Alternatively, the sheet feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.
Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer member 104, the sheet is fed between the intermediate transfer member 104 and the secondary transfer device 22, and is transferred by the secondary transfer device 22. A color image is recorded on the sheet.

The image-transferred sheet is conveyed by the secondary transfer device 22 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transferred image. Are discharged and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and the image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.
On the other hand, the intermediate transfer member 104 after image transfer is removed by the intermediate transfer member cleaning device 117 to remove residual toner remaining on the intermediate transfer member 104 after image transfer, and is prepared for re-image formation by the tandem image forming device 20.
Further, it can be used in the image forming apparatus and can be a process cartridge having the developing device, which has an advantage of facilitating replacement work and the like.

1 is a cross-sectional view showing the overall configuration of a developing device according to the present invention. It is a figure explaining the positional relationship of an upstream developing sleeve, a downstream developing sleeve, and a magnet provided therein. FIG. 10 is a diagram illustrating the movement of the agent in the vicinity of the developing sleeve. FIG. 6 is a diagram illustrating a positional relationship between a delivery assisting member and a developing sleeve. 1 is a diagram illustrating a configuration of an image forming apparatus according to the present invention.

Explanation of symbols

1 Developing Device 2 Photoconductor (Latent Image Carrier)
3 Developing container 4 Two-component developer 5 Stir screw 6 Stir screw 7 Stir screw 8 Partition 9 Partition 10 First transport path 11 Second transport path 12 Third transport path 13 First developer sleeve (upstream developer carrier)
13a Magnet 14 Second developing sleeve (downstream developer carrier)
14a Magnet 15 Doctor blade 16 Auxiliary member 18 Image forming means 20 Tandem image forming device 21 Exposure device 22 Secondary transfer device 23 Roller 24 Secondary transfer belt 25 Fixing device 26 Fixing belt 27 Pressure roller 28 Sheet reversing device 30 Document table 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 42 Paper feed roller 43 Paper bank 44 Paper feed cassette 45 Separating roller 46 Paper feed path 47 Transport roller 48 Paper feed path 49 Registration roller 50 Feed Paper roller 51 Manual feed tray 52 Separating roller 53 Manual feed path 55 Switching claw 56 Discharge roller 57 Paper discharge tray 100 Image forming apparatus 104 Intermediate transfer body 114 Support roller 115 Support roller 116 Support roller 117 Intermediate transfer body cleaning apparatus 200 Paper feed table 300 Su Turbocharger Na 400 automatic document feeder (ADF)
C1 Nearest part C2 Developer delivery area C3 Conventional developer delivery area D1 First development area D2 Second development area P1 (N pole)
P2 (S pole)
P3 (N pole)
P4 (N pole)
P5 (S pole)
Q1 (N pole)
Q2 (S pole)
Q3 (S pole)
Q4 (N pole)
Q5 (S pole)

Claims (6)

Facing the latent image carrier,
Aligned along the rotational direction of the latent image carrier,
In a developing device including a plurality of developer carriers having a plurality of magnetic poles therein,
The developing device includes:
The upstream developer carrying from the closest portion connecting the center of the upstream developer carrying body arranged upstream with respect to the rotation direction of the latent image carrying body and the center of the downstream developer carrying body arranged downstream. Downstream of the direction of body rotation,
A developing device, wherein a developer is delivered from the upstream developer carrier to the downstream developer carrier. The developing device according to claim 1,
The developing device includes:
From the closest portion to the downstream portion with respect to the rotation direction of the upstream developer carrier,
2. A developing device according to claim 1, wherein the first magnetic pole and the second magnetic pole from the downstream portion among the magnetic poles of the upstream developer carrier and the magnetic poles at the transfer portion of the downstream developer carrier have the same polarity. The developing device according to claim 1 or 2,
The developing device includes:
2. A developing device according to claim 1, wherein there are two developer carriers. In the developing device according to any one of claims 1 to 3,
The developing device includes:
2. A developing device that supplies a developer only to an upstream developer carrying member disposed on the most upstream side with respect to a rotation direction of the latent image carrying member. The developing device according to any one of claims 1 to 4,
The developing device includes:
A developing device having a developer transfer member in the developer transfer portion. The image forming apparatus
An image forming apparatus comprising the developing device according to claim 1.

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