JP5717362B2 - Development device - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system.

2. Description of the Related Art An image forming apparatus that forms a toner image on a sheet by an image forming principle such as an electrophotographic method or an electrostatic recording method or a process unit, fixes the toner image on the sheet by a fixing unit, and outputs an image formed product is known. . Examples of the image forming apparatus include a copying machine, a printer, a facsimile machine, or a multifunction machine having a plurality of these functions. As an image forming apparatus, there is a developing apparatus that develops an electrostatic latent image formed on an image carrier by transporting a developing sleeve coated with a developer to a position facing the image carrier. In such a case, the developer coated on the developing sleeve may be scattered outside the developing device. In order to prevent this, in a region where the developer is coated on the developing sleeve and then transported to the developing region, a developing sleeve cover formed on a curved surface maintaining a certain distance from the surface of the developing sleeve is attached. A scattering prevention sheet member for preventing toner scattering is attached to the tip of the developing sleeve cover without damaging the image carrier, and the sheet member is in contact with the image carrier. (See Patent Document 1)
Further, in Patent Document 2, when the developer on the developing sleeve that has passed through the developing region is collected in the developing container, the developer may flow backward from the intake port in the gap between the developing container and the developing sleeve. In order to prevent this, a configuration is disclosed in which an air discharge hole is provided in the upper lid of the developing container facing the downstream side in the developing sleeve rotation direction from the intake port so that air can be taken into the developing device.

JP-A-8-62978 JP-A-6-27795

  However, when a cover and a scattering prevention sheet are provided to prevent the developer from scattering as in Patent Document 1, there are the following problems. That is, the space covering the developing sleeve with the developing sleeve cover and the sheet is a closed space in a state close to a hermetically sealed state by the regulating member on the upstream side and the developing portion on the downstream side. Then, the space generated by the air flow generated by the drum and the developing sleeve becomes unstable due to a negative pressure, and a portion where air easily flows and a portion where it is difficult to flow may be generated in the longitudinal direction of the developing region. In particular, at the end of the developing sleeve where air can be taken in from the outside of the developing device, air flows more easily from the central portion of the developing sleeve, causing a difference in wind speed in the longitudinal direction of the developing region. As a result, the flowability of the developer in the development region changes between the end portion and the center portion with respect to the axial direction of the development sleeve, and there is a possibility that image density unevenness occurs.

  Further, even in the configuration of Patent Document 2, since the air discharge hole is provided after the development point, when the cover for preventing scattering is provided as described above, A similar problem may occur due to the difference in the wind speed distribution in the axial direction.

  Accordingly, an object of the present invention is caused by the instability of the airflow flowing from the space facing the sheet member to the developing region while suppressing the scattering of the developer from the upstream side of the developing region to the outside of the apparatus by the sheet member. An object of the present invention is to provide a developing device capable of suppressing image unevenness.

A developer container containing a developer;
A developer carrier that is rotatably provided so as to be partially exposed from an opening provided in the developer container, and that conveys the developer to a development region facing the image carrier;
A regulating member for regulating the developer coated on the developer carrying member;
A cover portion that is provided along the developer carrier from a position facing the regulating member toward the development region, and covers the developer carrier;
A sheet member covering a gap between the cover portion and the image carrier;
At least one of the cover portion or said seat member, said provided at a position opposite to the developer carrying member, have a, a vent for supplying air to the developing device, the vent developer In the axial direction of the carrier, the vent hole occupies a larger area per unit area at the center than at the end .

  According to the present invention, image unevenness caused by the instability of the airflow flowing from the space facing the sheet member to the developing region while suppressing the scattering of the developer from the upstream side of the developing region to the outside of the apparatus by the sheet member. It is possible to provide a developing device capable of suppressing the above.

Image forming unit between developing unit and photosensitive drum Image forming apparatus of this embodiment Developing roller cover diagram of the first embodiment Flow of wind around the developing roller and photosensitive drum in the comparative example (without vents) The flow of air around the developing roller and the photosensitive drum with the air holes of Example 1 Comparison of wind speed at developing point with and without vents Developing roller cover diagram of the second embodiment

[First embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the dimensions, materials, shapes, relative positions, and the like of the components of the image forming apparatus are not intended to limit the scope of the present invention only to those unless otherwise specified. Moreover, what attached | subjected the same code | symbol in each drawing has the same structure or effect | action, The duplication description about these was abbreviate | omitted suitably.

[Image forming apparatus]
FIG. 2 is an explanatory diagram of the image forming apparatus in the present embodiment. As shown in FIG. 2, the image forming apparatus 100 according to the first embodiment includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a corona charger 9 as a charging unit, an exposure device 3, a developing unit 2 as a developing device, a primary transfer roller 17 as a transfer unit, and a toner recovery device 8 as a cleaning device are arranged. Yes. The photosensitive drum 1 is composed of a metal cylinder having a negatively charged photosensitive layer formed on the surface thereof, and rotates in the arrow R1 direction. (Figure 1)
The toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 5 at a primary transfer portion where the photosensitive drum 1 and the intermediate transfer belt 5 face each other. Thereafter, the image transferred onto the intermediate transfer belt 5 is secondarily transferred to the recording material P at the secondary transfer portion facing the intermediate transfer belt 5 and the secondary transfer roller 11. Further, the recording material P is pulled out from the recording material deck 7 one by one and sent out to the secondary transfer portion. The recording material P on which the image has been transferred in the secondary transfer portion is transferred from the secondary transfer portion to the fixing device 4 by the pre-fixing conveyance belt unit 18. The fixing device 4 receives heat and pressure to fix the toner image on the surface, and then is discharged outside the image forming apparatus.

[Developer]
With reference to FIG. 1, the developing device 2 of the present embodiment will be described in detail. The developing device 2 includes a developing roller 31 and a developing roller 32 as developer carriers. As a result, the developer T accommodated in the developing container can be supplied to the photosensitive drum 1. The developing roller 31 and the developing roller 32 are rotatably provided so as to be partially exposed from the opening of the developing container so as to be partially exposed from the developing container. A coating regulating member 33 is attached to the upper part of the developing roller 31, and thereby the amount of developer T coated on the developing roller 31 is regulated. The developer T coated on the surface of the developing roller 31 by the coating amount regulating member 33 is carried to a developing region facing the photosensitive drum 1 by the rotation of the developing roller 31. At the development point P2 where the developing roller 31 and the photosensitive drum 1 are closest to each other, the clearance is about 300 μm. Further, the developing roller 31 is rotated at a peripheral speed of 140% with respect to the photosensitive drum 1 to maintain the supply of the developer. Similarly, the developing roller 32 forms a coat of the developer T by a gap with the developing roller 31 and supplies the developer T to the photosensitive drum 1.

  In addition, if the point where the coating amount regulating member 33 that regulates the coating amount of the developer T is closest to the developing roller 31 is defined as the coating amount regulating point P1, the coating point regulating point P1 is moved to the development point P2 on the surface of the developing roller 31. Is coated with developer T. In order to prevent the coating portion from being exposed and the developer T from being scattered into the image forming apparatus 100, the upper portion of the developing roller 31 is a cover portion having a curved surface provided with a space of about 2 mm along the outer periphery of the developing roller 31. A developing roller cover 34 is attached. Further, a scattering prevention cover (sheet member) 35 is attached from the tip of the developing roller cover 34 toward the photosensitive drum 1. The scattering prevention cover 35 is made of a urethane material, fills the gap between the developing roller cover 34 and the photosensitive drum 1 without damaging the photosensitive drum 1, and prevents the developer T from scattering due to the rotation of the developing roller 31. doing.

Further, a space K is formed by the developing roller 31 and the developing roller cover 34, the coating amount regulating member 33, and the photosensitive drum 1 between the coating amount regulating point P1 and the developing point P2. In the space K, wind is generated by the rotation of the developing roller 31 and the photosensitive drum 1 as shown in FIG.
In the present embodiment, as shown in FIG. 3, a plurality of vent holes 36 are provided in the developing roller cover 34 above the space K in the axial direction of the developing roller 31. Thereby, it is possible to prevent the airflow in the closed space K from being blocked by the developing roller cover 34 due to the rotation of the developing roller 31 and the photosensitive drum 1, and the airflow flowing through the developing region becomes unstable in the longitudinal direction. Is suppressed. Further, a ventilating filter 37 that blocks the vent hole 36 is attached to the vent hole 36 so that the developer T does not scatter from the space K through the vent hole 36. From the viewpoint of equalizing the wind speed passing through the development region, the vent holes 36 are preferably provided over the axial direction, but a plurality of vent holes 36 are provided from the viewpoint of the strength of the developing container.

  As a comparative example, a case where there is no vent 36 as shown in FIG. 4 will be described. In the comparative example, since the side of the developing roller cover 34 is open only at the end of the developing roller 31, air can be taken in from the outside. However, as shown in FIG. 6, (1) in the case without the air vent 36, the wind speed V that escapes at the developing point P2 is V = 1.3 mm / s at the end of the developing roller, but at the center in the axial direction of the developing roller. It falls about 60% with V = 0.8 mm / s. This is because the developing roller cover 34 forms a closed space at the center in the axial direction of the developing roller, so that air does not flow easily. The difference in wind speed at the development point P2 changes the fluidity of the developer T supplied to the photosensitive drum 1 at the development point P2 between the end portion and the shaft center portion, thereby causing image density unevenness.

  In contrast, the presence of the air vent 36 allows air to be taken in from the air vent 36 along the developing roller cover as shown in FIG. As a result, as shown in FIG. 6, (2) when the air hole 36 is provided, the wind speed V at the developing point P2 at the axial center can be increased to V = 1.3 mm / s, which is the same as that at the end of the developing roller. It becomes possible. As a result, the wind speed at the developing point in the axial direction can be made uniform, and image density unevenness occurring at the developing point P2 can be reduced.

  In this embodiment, the developing roller cover 34 is provided with a vent hole. However, the present invention is not limited to this. For example, a vent hole may be provided in the sheet member. The same effect can be obtained by making the sheet member itself a breathable filter that does not allow the developer to scatter.

[Second Embodiment]
In the first embodiment, the size of the air holes 36 is uniform in the longitudinal direction. In this embodiment, as shown in FIG. 7, the opening of the vent hole in the circumferential direction of the developing roller is larger in the central portion than in the end portion with respect to the axial direction of the developing roller. Is different.
In the developing roller cover, if a vent hole is provided on the entire surface, the strength may be lowered. On the other hand, when the vent hole 36 is not provided as shown in FIG. 6, the wind speed at the developer point P tends to be lower in the central portion in the developing roller axial direction than in the end portion of the developing roller. Therefore, in this embodiment, the vent hole is configured such that the area of the vent hole per unit area is larger in the central portion than in the end portion in the axial direction of the developing roller. Specifically, a wide hole is provided in the central portion of the developing roller 31 where it is difficult to take in outside air with respect to the end of the developing roller 31 that can take in outside air from the side of the developing device. By doing so, it is possible to make the image uniform while maintaining the strength.

  In this embodiment, the twin roller configuration of the developing rollers 31 and 32 is adopted. However, the present invention is not limited to the twin roller configuration, and a single roller configuration with one developing roller is within the range of the effect.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 1 Photoconductor drum 2 Developing device 3 Exposure apparatus 7 Paper feeding unit 8 Developer recovery unit 31, 32 Developing roller 33 Coat amount regulating member 34 Developing roller cover 35 Splash prevention sheet 36 Vent hole 37 Filter

Claims (4)

A developer container containing a developer;
A developer carrier that is rotatably provided so as to be partially exposed from an opening provided in the developer container, and that conveys the developer to a development region facing the image carrier;
A regulating member for regulating the developer coated on the developer carrying member;
A cover portion that is provided along the developer carrier from a position facing the regulating member toward the development region, and covers the developer carrier;
A sheet member covering a gap between the cover portion and the image carrier;
At least one of the cover portion or said seat member, said provided at a position opposite to the developer carrying member, have a, a vent for supplying air to the developing device, the vent developer A developing device characterized in that, in the axial direction of the carrier, the area of the vent hole occupied by the central portion per unit area is larger than the end portion .   The image forming apparatus according to claim 1, further comprising a breathable filter that covers the vent hole.   The image forming apparatus according to claim 1, wherein a plurality of the air holes are provided in the axial direction of the developer carrier.   The image forming apparatus according to claim 1, wherein the air hole is provided in the cover portion.

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