Patent Grant
11131944
This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-216503, filed on Nov. 29, 2019, in the Japan Patent Office, the entire disclosure of which is incorporated by reference herein.
Aspects of the present disclosure relate to a developing device, a process cartridge, and an image forming apparatus.
Generally, there is known an electrophotographic image forming apparatus that includes a developing device of a two-component developing system. In such a developing device, a doctor member is disposed so that a projecting end surface maintains a predetermined doctor gap with respect to a developing roller, and the amount of developer supplied onto the developing roller is adjusted by the function of the doctor member.
In an aspect of the present disclosure, there is provided a developing device that includes a developer container, a developing roller, and a doctor member. The developer container contains a developer including a toner and a developer. The developing roller includes a developing sleeve bearing the developer, a magnet roller in the developing sleeve. The doctor member includes a regulating portion regulating an amount of the developer home on the developing sleeve to be a predetermined amount. The regulating portion is disposed with a first distance from the developing sleeve. The developing sleeve is disposed with a second distance from an image bearer, and when the developing sleeve bearing the predetermined amount of developer passes a vicinity of the image bearer, a value obtained by dividing the predetermined amount by the second distance is less than a threshold of occurrence of adherence of the developer to the developing sleeve.
In another aspect of the present disclosure, there is provided a process cartridge that includes the developing device.
In still another aspect of the present disclosure, there is provided an image forming apparatus that includes the process cartridge.
In still yet another aspect of the present disclosure, there is provided an image forming apparatus that includes the developing device.
The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results.
Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable.
Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below.
Above the process cartridges 3Y, 3C, 3M, and 3K, there is disposed an intermediate transfer unit 10 including an intermediate transfer belt 9 to transfer toner images formed by the process cartridges 3. The intermediate transfer unit 10 has a plurality of rollers supporting the intermediate transfer belt 9. As any one of the rollers is driven to rotate, the intermediate transfer belt 9 is driven counterclockwise in
A secondary transfer roller 12 that secondarily transfers the toner images, which have been primarily transferred onto the intermediate transfer belt 9, onto a transfer sheet S is disposed downstream of the primary transfer roller 11K in a traveling direction of the intermediate transfer belt 9. Further, a belt cleaner 13 that removes residual toner remaining on the intermediate transfer belt 9 after image transfer is disposed on the upstream side of the primary transfer roller 11Y in the traveling direction of the intermediate transfer belt 9. Above the secondary transfer roller 12, a fixing device 14 includes a heating roller 40 and a pressure roller 41 to fix the toner image transferred on the transfer sheet S.
A sheet feeder 15 is disposed at the bottom of the apparatus body 2. The sheet feeder 15 includes a sheet feeding cassette 16, a feed roller 17, and a registration roller pair 18, and feeds a transfer sheet S stored in a sheet feeding cassette 16 toward the registration roller pair 18 by the feed roller 17. The registration roller pair 18 feeds the transfer sheet S toward a secondary transfer nip at which the secondary transfer roller 12 and the intermediate transfer belt 9 come into contact at a predetermined timing when the toner image formed on the intermediate transfer belt 9 matches a predetermined position of the transfer sheet S. Toner bottles 19Y 19C, 19M, and 19K containing toner of corresponding colors are disposed on an upper portion of the apparatus body 2 to supply to the respective developing device 6.
Next, each process cartridge 3 is described. Each of the process cartridges 3 is similarly configured except for the colors of toner contained therein. As illustrated in
Here, an example of the operation of the process of obtaining a color image using the color copying machine 1 is briefly described. First, in each process cartridge 3, the photoconductive drum 4 is uniformly charged by the charging device 5. After that, an optical unit 8 is operated to expose and scan the surface of the photoconductive drum 4 with laser light, and an electrostatic latent image based on image data is formed on the surface of the photoconductive drum 4. The formed electrostatic latent image is developed with toner of the corresponding color by the operation of the developing device 6, and the toner image of the corresponding color is formed on the surface of the photoconductive drum 4. The toner image on the photoconductive drum 4 is superimposed and transferred onto the intermediate transfer belt 9 by the operation of the corresponding primary transfer roller 11. The photoconductive drum 4, which has the toner image transferred thereon, is cleaned by the photoconductor cleaning device 7 and prepares for the next image forming process.
On the other hand, in the sheet feeder 15, the transfer sheet S in the sheet feeding cassette 16 is separated and fed by the operation of the feed roller 17, and the transfer sheet S is fed to the secondary transfer nip at a predetermined timing by the operation of the registration roller pair 18. The transfer sheet S, on which a full color toner image formed on the intermediate transfer belt 9 at the secondary transfer nip, is conveyed to the fixing device 14 to fix the transferred image. After the transferred image is fixed on the transfer sheet S by the fixing device 14, the transfer sheet S is ejected onto an output tray 28 on the upper portion of the apparatus body 2 by an ejection roller pair 27. The ejection roller pair 27 is disposed on the downstream side of the fixing device 14 in a sheet conveyance direction. Similarly to the photoconductive drum 4, residual toner remaining on the intermediate transfer belt 9 is cleaned by the belt cleaner 13. Each color toner contained in each toner bottle 19 is replenished in a predetermined amount to the corresponding developing device 6 via a toner conveyance path, as needed.
Next, the developing device 6 is described. The developing device 6 is a developing device using two-component developer consisting of toner and carrier, and includes the developing roller 23 and a doctor blade 29 serving as a doctor member in the developing case 22. The developing roller 23 opposed to the photoconductive drum 4 includes a magnet roller 30 provided inside the developing roller 23 and a developing sleeve 31 provided around the magnet roller 30. The doctor blade 29 regulates the amount of developer borne on the developing sleeve 31.
The developing sleeve 31, which has a cylindrical shape made of aluminum, is disposed at a position to maintain a predetermined developing gap Gp (illustrated in
The magnet roller 30 has a P1 pole (main pole) that is arranged so that the peak of the magnetic force is directed toward the center of the photoconductive drum 4. The magnet roller 30 also has P2, P3, P4, and P5 poles that are arranged in turn from the P1 pole in the rotational direction of the developing sleeve 31. A thin layer of the developer formed on the developing sleeve 31 by the P1 pole is formed in contact with the photoconductive drum 4, and the toner is provided for the developing process from the developer layer placed in a developing area opposite the photoconductive drum 4. Thereafter, as the developing sleeve 31 rotates, the developer is moved and returned into the developing case 22 by the magnetic force from the P2 pole along with the rotation of the developing sleeve 31, and then the developer is released from the developing sleeve 31 by the repulsive magnetic force of the P3 pole and the P4 pole and falls into the developing case 22.
In the developing case 22, a first stirring screw 32 is rotatably disposed so as to be parallel to the developing roller 23. The first stirring screw 32 rotates counterclockwise in
As illustrated in
The technique disclosed in JP-2007-121964-A described above proposes a convex shape as the shape of the regulating portion 29a in order to prevent an increase in the scooping amount ρ at the center of the doctor blade 29, for example, the shape may be as illustrated in
Further, since both ends of the developing sleeve 31 are fixed as compared with the center and the developing gap Gp does not fluctuate easily, a value obtained by dividing the scooping amount ρ by the developing gap Gp, i.e., ρ/Gp, that is, an adjustment amount of the scooping amount ρ is greater at both ends than at the center. In other words, since more developer passes through the developing gap Gp that remains narrow at both ends, both ends of the developing sleeve 31 are more likely to receive a large pressure from the developer. When a large pressure acts on the developer in this way, the toner using a charge adjusting material made of titanium oxide as developer does not cause any particular problem, but in the case of a toner having a high adhesion force such as a toner (i.e., titanium-less toner) in which titanium oxide is replaced by alumina, adherence of toner to the developing sleeve 31, that is, so-called developing sleeve adherence may be worsen, thus causing background stains. In order to prevent the occurrence of developing sleeve adherence, it is necessary to devise the shape of the regulating portion 29a so that the adjustment amount ρ/Gp is lower than the adherence threshold of the developing sleeve 31 at a point where the adjustment amount ρ/Gp tends to become large, especially at both ends of the developing sleeve 31 in the present embodiment. According to a first embodiment of the present disclosure, there is provided a doctor blade 29 capable of preventing the developing sleeve adherence.
In the first embodiment of the present disclosure, the inventors first investigated the effect of the adjustment amount ρ/GP on developing sleeve adherence by varying the scooping amount ρ and the development gap Gp, which affect the pressure acting on the developer in the developing area, in order to explore the characteristic values that effectively act on the developing sleeve adherence. A toner with high adhesion that was likely to cause developing sleeve adherence was used in the investigation, and the scooping amount ρ and the developing gap Gp were adjusted so that the adjustment amounts ρ/GP were 120, 220-1, 220-2, and 240. Here, the adjustment amount 220-1 was investigated when the developing gap Gp was narrowed and the scooping amount ρ was increased, and the adjustment amount 220-2 was investigated when the developing gap Gp was widened and the scooping amount ρ was decreased, respectively. The image formation was performed on 50,000 sheets in an actual machine, and the presence or absence of the developing sleeve adherence on the developing sleeve 31 and the presence or absence of the background stains on the formed image were checked. The results of the investigation are illustrated in
According to the results of the investigation illustrated in
According to the first embodiment of the disclosure, as described above, the doctor blade 29 including the regulating portion 29a is used in which the adjustment amount ρ/Gp is lower than the adherence threshold of the developing sleeve 31 determined by an investigation in an area where the developing gap Gp does not vary as the developer passes through. In other words, the shape of the regulating portion 29a is determined so that the adjustment amount ρ/Gp is lower than the adherence threshold of the developing sleeve 31. Thus, the occurrence of the developing sleeve adherence can be prevented even more than the conventional case and an output material with stable image quality with less background stains can be obtained.
Next, a second embodiment of the present disclosure is described. When a photoconductor with low rigidity, such as a belt-shaped photoconductor without a core metal, is used, the photoconductor is likely to be more deformed by the pressure of the developer. For example, even if the layer thickness of developer on the developing sleeve 31 is equalized, the developing gap Gp near the center of the longitudinal direction at the doctor blade 29 may be widened and the amount of toner adhered to the photoconductor may be reduced. In other words, in the vicinity of both ends fixed to the developing case 22, the developing gap Gp does not change and accordingly the image density is appropriately obtained. However, near the center that is easily deformed due to the low rigidity of the photoconductive drum 4, the image density may become low and uneven density may occur.
Hence, in the second embodiment, a doctor blade 37 is used as a doctor member including a linearly formed regulating portion 37a, as illustrated by the long-dashed and short-dashed line in
In the second embodiment, the regulating portion 37a was formed in a linear shape, but when the straightness of the regulating portion 37a was changed to change the scooping amount ρ, it was found that it was effective in preventing image unevenness when the straightness was set to 0.05 (mm) or less. From this result, setting the straightness of the regulating portion 37a to 0.05 or less can prevent the occurrence of image unevenness. When a tolerance of the straightness of 0.05 is expressed in the drawing, the straightness of 0.05 is satisfied even if the regulating portion 37a has a shape as illustrated in
Next, a third embodiment of the present disclosure is described. If the straightness of the regulating portion 37a cannot be reduced due to the limit of processing and the adjustment amount ρ/Gp at the ends of the doctor blade cannot be reduced below the adherence threshold of the developing sleeve 31, a plurality of grooves 38 extending in the axial direction as illustrated in
Next, a fourth embodiment of the present disclosure will be described. As a method of reducing the scooping amount ρ, there is a method of changing a magnetic waveform of the developing roller 23. In the magnetic waveform of the magnet roller 30 illustrated in
In the above-described embodiments and modified examples, the example using the full-color copying machine 1 as an image forming apparatus is described. However, an image forming apparatus according to an embodiment of the present disclosure is not limited to such a full-color copying machine, and may be a printer, a facsimile, a multifunction peripheral, a monochrome machine, and the like. In the above-described embodiments, the configuration of using a transfer sheet S as a recording medium on which an image is formed is described. However, examples of the recording medium include thick paper, postcards, envelopes, plain paper, thick paper, coated paper (coated paper, art paper, etc.), tracing paper, overhead projector (OHP) sheet, OHP film, and resin film, and any material may be used as long as the material has a sheet shape and image formation and folding processing can be performed on the material.
Although several embodiments of the present disclosure have been described above, embodiments of the present disclosure are not limited to the above-described embodiments, and unless specifically limited in the description above, the above-described embodiments can be variously transformed and modified within the scope of the present disclosure as described in the claims. The effects described in the embodiments of the present disclosure are examples of the most suitable effects arising from the embodiments, the effects according to embodiments of the present disclosure are not limited to the above-described effects.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2019-216503 | Nov 2019 | JP | national |
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| 20120093543 | Ikeda | Apr 2012 | A1 |
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| Number | Date | Country |
|---|---|---|
| 2007-121964 | May 2007 | JP |
| 2012-177847 | Sep 2012 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20210165344 A1 | Jun 2021 | US |
