Patent Grant
8346137
The present application is based on Japanese Patent Application No. 2009-194976 filed on Aug. 26, 2009, and Japanese Patent Application No. 2009-194978, filed on Aug. 26, 2009, the contents of which are hereby incorporated by reference.
The present disclosure relates to a developing device installed in an image-forming apparatus such as a photocopier, a facsimile machine, and a printer, and to an image-forming apparatus that is provided with the developing device. In particular, the present disclosure relates to a developing device that uses a two-component developer composed of a magnetic carrier and a toner.
Conventionally known developing methods involving the use of a dry toner in an image-forming apparatus in which an electrophotographic process are used include one-component developing methods in which a carrier is not used, and two-component developing methods in which a two-component developer composed of a magnetic carrier (also referred to simply as a carrier) and a toner that is electrostatically charged by the magnetic carrier is used to develop an electrostatic latent image on a photoreceptor through the use of magnetic brushes composed of toner and carrier formed on a developing roller.
In image-forming apparatus that use a two-component developing method, the developing device filled with the developer is often shipped from the factory already installed in the main body of the image-forming apparatus in order to minimize the amount of packaging materials or paddings in light of the environmental burden. Measures are therefore taken to enhance the sealing properties of the developing device so that overturning, dropping, and other adverse events during transport do not cause the developer to leak out.
As a result of the increased drive speed of stirring mixers and other devices rotating inside the developing device in concert with the recent increase in image processing speeds, the movement speed of the developer inside the developing device has also increased. If the sealing properties of the developing device are enhanced in order to prevent leakage of the developer, the fact that the air pressure of the space inside the developing device also increases when the developing device is driven means that toner that has fallen into the developing device from a supply device will be retained in a space higher than the developer surface in the developing device by the air pressure, and this leads to the problem of unstable feeding of toner. Particularly near the end of the service life of the developing device, in a state in which the ability to charge the toner by the carrier has declined, temporary defects in the charging of the toner occur due to such causes as the retained toner falling all at once into the developing device, and fogging can occur in the image that is formed on the paper.
Methods have been proposed for reducing the increase in pressure inside the developing device, and there have been disclosed developing devices, for example, in which pressure increase and developer leakage are suppressed by providing a pressure relief hole at the top of the housing of the developing device and also covering the pressure relief hole with a filter.
However, in the method described above, the effects for reducing the pressure inside the developing device are reduced by clogging of the filter in cases in which the developing device has a long service life. In cases in which the developing device filled with the developer is shipped already installed in the main body of the image-forming apparatus, there is a risk of the developer leaking out of the developing device through the filter and contaminating the inside of the image-forming apparatus when the image-forming apparatus is overturned or dropped during transport.
In view of the problems described above, an object of the present disclosure is to provide a two-component developing-type developing device and an image-forming apparatus provided therewith, whereby there is no increase in the air pressure of the space inside the developing device even in cases in which the image processing speed is increased, and it is possible to suppress leakage of the developer from within the developing device due to impact from overturning or dropping during transport.
The developing device according to a first aspect of the present disclosure for achieving the abovementioned objects includes a developing container configured to accommodate a two-component developer that includes a toner and a magnetic carrier; a stirring/conveyance member configured to stir and convey the developer accommodated in the developing container; a developer bearing member configured to bear and convey the developer, the developer bearing member being disposed so as to be able to rotate above the stirring/conveyance member; a fixed magnet configured to have a plurality of magnetic poles that includes a release pole for releasing the developer from a surface of the developer bearing member, the fixed magnet being fixed in the inside of the developer bearing member; a regulating blade configured to be disposed facing the developer bearing member so as to be downstream side in the direction of rotation of the developer bearing member as viewed from the release pole; and a backflow prevention member that is a sheet-shaped member configured to be disposed along the entire length in the longitudinal direction of the developer bearing member so as to be upstream side in the direction of rotation of the developer bearing member as viewed from the release pole, being disposed so that a proximal end portion thereof is fixed to an inside surface of the developing container, and a distal end portion thereof is in contact with or adjacent to the developer bearing member and facing downstream side in the direction of rotation of the developer bearing member.
Other objects of the present disclosure and specific advantages gained by the present disclosure will become clear from the following description of embodiments of the present disclosure.
Embodiments will next be described with reference to the drawings.
Photoconductive drums 1a, 1b, 1c, and 1d on which visible images (toner images) of each color are formed on the surfaces thereof are provided to the image forming units Pa, Pb, Pc, and Pd, respectively, and an intermediate transfer belt 8 that is caused to rotate clockwise in
The transfer paper P onto which the toner images are transferred is accommodated in a paper cassette 16 disposed in the lower part of the color image-forming apparatus. During image formation, the transfer paper P is conveyed through a pair of resist rollers 12b toward a nip between the secondary transfer roller 9 and a drive roller 11 of the intermediate transfer belt 8 described hereinafter. A dielectric resin sheet is used as the intermediate transfer belt 8. A blade-shaped belt cleaner 19 for removing the toner that remains on the surface of the intermediate transfer belt 8 is disposed downstream side in the movement direction of the intermediate transfer belt 8 as viewed from the secondary transfer roller 9.
The image forming units Pa, Pb, Pc, and Pd will next be described. Charging devices 2a, 2b, 2c, and 2d for electrostatically charging the photoconductive drums 1a, 1b, 1c, and 1d respectively; an exposure unit 4 for exposing the photoconductive drums 1a, 1b, 1c, and 1d with image information and forming electrostatic latent images on the photoconductive drums 1a, 1b, 1c, and 1d; developing devices 3a, 3b, 3c, and 3d for forming toner images on the photoconductive drums 1a, 1b, 1c, and 1d by developing the electrostatic latent images formed on the photoconductive drums 1a, 1b, 1c, and 1d, respectively; and cleaning devices 5a, 5b, 5c, and 5d for respectively removing the developer (toner) that remains on the photoconductive drums 1a, 1b, 1c, and 1d are provided on the periphery of and below the photoconductive drums 1a, 1b, 1c, and 1d, which are provided so as to be able to rotate.
When image data are inputted from a PC or other upper-level device connected to the color image-forming apparatus 100, the surfaces of the photoconductive drums 1a, 1b, 1c, and 1d are first uniformly charged by the charging devices 2a, 2b, 2c, and 2d, respectively, then irradiated with light corresponding to the image data by the exposure unit 4; and an electrostatic latent image corresponding to the image data is formed on each of the photoconductive drums 1a, 1b, 1c, and 1d, respectively. The developing devices 3a, 3b, 3c, and 3d are each filled with a predetermined quantity of a two-component developer that includes toner in each of the colors of cyan, magenta, yellow, and black, respectively. The developing devices 3a, 3b, 3c, and 3d are replenished with toner from a toner replenishing device (not shown) in a case in which the ratio of toner in the two-component developer stored in the developing devices 3a, 3b, 3c, and 3d decreases below a specified value as a result of the forming of the toner images described hereinafter, respectively. The toners in the developers are fed onto the photoconductive drums 1a, 1b, 1c, and 1d by the developing devices 3a, 3b, 3c, and 3d and electrostatically absorbed, thereby forming toner images that corresponds to the electrostatic latent images formed by exposure by the exposure unit 4.
Electric fields are created by a predetermined transfer voltage between primary transfer rollers 6a, 6b, 6c, and 6d and the photoconductive drums 1a, 1b, 1c, and 1d by the primary transfer rollers 6a, 6b, 6c, and 6d, respectively; and the yellow, cyan, magenta, and black toner images on the photoconductive drums 1a, 1b, 1c, and 1d undergo a primary transfer onto the intermediate transfer belt 8, respectively. These four color toner images are formed with a corresponding positional relationship that is determined in advance in order to form a full-color image. The toner remaining on the surfaces of the photoconductive drums 1a, 1b, 1c, and 1d is then removed by the cleaning devices 5a, 5b, 5c, and 5d, respectively in preparation for subsequent formation of new electrostatic latent images.
The intermediate transfer belt 8 is extended across a driven roller 10 on the upstream side and a drive roller 11 on the downstream side, and when the intermediate transfer belt 8 begins to rotate clockwise as the drive roller 11 is caused to rotate by a drive motor (not shown), the transfer paper P is conveyed at a predetermined timing from the pair of resist rollers 12b toward the nip between the drive roller 11 and the secondary transfer roller 9 adjoining to the intermediate transfer belt 8; and the full-color image is transferred onto the transfer paper P. The transfer paper P onto which the full-color toner image is transferred is conveyed toward the fixing unit 7.
The transfer paper P conveyed to the fixing unit 7 is heated and pressed by a pair of fixing rollers 13, the toner image is fixed to the surface of the transfer paper P, and a full-color image is formed. The direction of conveyance of the transfer paper P on which the full-color image is formed is divided by a branching unit 14 that is branched in a plurality of directions. In cases in which an image is formed on only one side of the transfer paper P, the transfer paper P is directly discharged to a discharge tray 17 by a pair of discharge rollers 15.
On the other hand, when images are formed on both sides of the transfer paper P, a portion of the transfer paper P having passed through the fixing unit 7 is caused to temporarily protrude to the outside of the image-forming apparatus 100 from the pair of discharge rollers 15. The transfer paper P is then sent to a paper conveyance path 18 by the branching unit 14 by causing the pair of discharge rollers 15 to rotate in the opposite direction, and the transfer paper P is conveyed back to the pair of resist rollers 12b in a state in which the image surface is reversed. A subsequent image formed on the intermediate transfer belt 8 is then transferred by the secondary transfer roller 9 onto the surface of the transfer paper P on which an image were not yet formed, and the transfer paper P is conveyed to the fixing unit 7 to fix the toner image, thereafter the transfer paper P is discharged to the discharge tray 17 from the pair of discharge rollers 15.
As shown in
The developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and second stirring screw 21b, and is circulated between the first and second stirring chambers 20b, 20c through developer passages (not shown) that is formed in the partition wall 20a. In the example shown in the drawing, the developing container 20 extends to the top left side, inside the developing container 20, a magnetic roller 22 is disposed above the second stirring screw 21b, and a developing roller 23 is disposed in a top left side of the magnetic roller 22 so as to face the magnetic roller 22. The developing roller 23 faces the photoconductive drum 1a on the open side (left side in
A toner concentration sensor (not shown) is provided on the developing container 20 so as to face the first stirring screw 21a, and the developing container 20 is replenished with toner through a toner replenishment port 20d from a replenishing device (not shown) according to the toner concentration detected by the toner concentration sensor.
The magnetic roller 22 is composed of a non-magnetic rotary sleeve 22a (developer bearing member) and a fixed magnet 22b, having a plurality of magnetic poles, that is disposed within the rotary sleeve 22a. In the present embodiment, the fixed magnet 22b has five magnetic poles; namely a main pole 35, a regulating pole (magnetic pole for recovery) 36, a conveyance pole 37, a release pole 38, and an uptake pole 39.
A regulating blade 25 is attached to the developing container 20 along the longitudinal direction (the direction perpendicular to the plane of the page on which
The developing roller 23 is composed of a cylindrical developing sleeve 23a and a developing-roller-side magnetic pole 23b that is fixed inside the developing sleeve 23a, and the magnetic roller 22 and the developing roller 23 face each other having a predetermined gap in the facing position (opposing position) thereof. The developing-roller-side magnetic pole 23b has a different polarity from the magnetic pole (main pole) 35 of the fixed magnet 22b that faces the developing roller-side magnetic pole 23b.
A first bias circuit 30 for applying a direct current (hereinafter referred to as Vslv (DC)) and an alternating current (hereinafter referred to as Vslv (AC)) to the developing roller 23, is connected to the developing roller 23, and a second bias circuit 31 for applying a direct current (hereinafter referred to as Vmag (DC)) and an alternating current (hereinafter referred to as Vmag (AC)) to the magnetic roller 22, is connected to the magnetic roller 22. The first bias circuit 30 and the second bias circuit 31 are connected to a common ground.
A voltage-variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31 and configured so as to be able to vary the Vslv (DC), Vslv (AC) applied to the developing roller 23 and the Vmag (DC), Vmag (AC) applied to the magnetic roller 22, respectively.
As previously described, the developer is circulated through the developing container 20 while being stirred by the first stirring screw 21a and second stirring screw 21b with the toner being electrostatically charged, and conveyed to the magnetic roller 22 by the second stirring screw 21b. Since the regulating pole 36 of the fixed magnet 22b faces the regulating blade 25, by using a non-magnetic body or a magnetic body having a different polarity from the regulating pole 36 as the regulating blade 25, a magnetic field is formed whereby the rotary sleeve 22a and the distal end of the regulating blade 25 attract each other in the gap therebetween.
This magnetic field forms a magnetic brush between the regulating blade 25 and the rotary sleeve 22a. After the thickness of the magnetic brush on the magnetic roller 22 is restricted by the regulating blade 25, when the rotation of the rotary sleeve 22a moves the magnetic brush to the position opposite the developing roller 23, an attracting magnetic field created by the developing-roller-side magnetic pole 23b and the main pole 35 of the fixed magnet 22b is given to the magnet brush, and the magnetic brush therefore makes contact with the surface of the developing roller 23. A thin layer of toner is then formed on the developing roller 23 by the magnetic field and the potential difference ΔV between Vmag (DC) applied to the magnetic roller 22 and Vslv (DC) applied to the developing roller 23.
The thickness of the toner layer on the developing roller 23 varies according to factors such as the resistance of the developer, the difference in rotation speed between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. The bigger ΔV is, the thicker the thickness of the toner layer on the developing roller 23 is. And the smaller ΔV is, the thinner the thickness of the toner layer on the developing roller 23 is. The appropriate range of ΔV at the time of development is usually about 100V to 350V.
Consequently, the voltage applied to the gap between the magnetic roller 22 and the developing roller 23 (referred to as MS hereinafter) is a synthetic waveform Vmag-Vslv having a Vpp (max) and Vpp (min) as shown in
The thin layer of toner formed on the developing roller 23 by the magnetic brush is conveyed with the rotation of the developing roller 23 to the portion at which the photoconductive drum 1a and the developing roller 23 face each other. Since the Vslv (DC) and the Vslv (AC) are applied to the developing roller 23, the toner flies to the photoconductive drum 1a with a potential difference between the developing roller 23 and the electrostatic latent image formed on the photoconductive drum 1a and the electrostatic latent image on the photoconductive drum 1a is developed.
When the rotary sleeve 22a is further caused to rotate clockwise, the magnetic brush is then withdrawn from the surface of the developing roller 23 by the magnetic field in the horizontal direction (roller peripheral direction) that is generated by the conveyance pole 37 having different polarity from the main pale 35 and being adjacent to the main pole 35, and the remaining toner on the developing roller 23 being not used for development is recovered onto the rotary sleeve 22a from the developing roller 23. When the rotary sleeve 22a is further rotated, since a repulsive magnetic field created by the release pole 38 (developer separation part) and the uptake pole 39 having the same polarity with the release pole 38 of the fixed magnet 22b, the developer separates from the rotary sleeve 22a inside the developing container 20. After being stirred and conveyed by the second stirring screw 21b, the two-component developer is restored to the proper toner concentration and uniformly charged, the magnetic brush is re-formed on the rotary sleeve 22a with the uptake pole 39, and the developer is conveyed to the position facing the regulating blade 25.
A sheet-shaped backflow prevention member 40 is provided along the entire length in the longitudinal direction (direction perpendicular to the plane of the page on which
If the regulating blade 25 and the backflow prevention sheet 40a cause the first and second stirring chambers 20b, 20c positioned below the magnetic roller 22 to become nearly closed spaces, there is a possibility that the toner supply may become unstable with risk of the pressure increasing during driving of the first stirring screw 21a, second stirring screw 21b, and other components. A ventilation path must therefore be provided between the backflow prevention sheet 40a and the rotary sleeve 22a.
In cases in which the developing device 3a is subjected to impact through overturning or dropping of the image-forming apparatus 100 during transport, the backflow prevention sheet 40a is pushed by the developer inside the second stirring chamber 20c and pushed toward the magnetic roller 22. There is a possibility that the developer may leak from the opening (on the periphery of the developing roller 23) of the developing container 20 at this time when there is a ventilation passage between the backflow prevention sheet 40a and the rotary sleeve 22a.
Through this configuration, the air compressed inside the first and second stirring chambers 20b, 20c during driving of the developing device 3a escapes to the outside through a ventilation path 51 formed by the gap A and the notch 50, as shown in
In a case in which the backflow prevention sheet 40a is pushed by the developer inside the second stirring chamber 20c due to impact during transport of the image-forming apparatus 100, as shown in
When overturning or dropping of the image-forming apparatus 100 causes the developer to clustered on the ends of the developing device 3a in the longitudinal direction thereof, the developer readily leaks from the gap between the developing container 20 and the magnetic roller 22. Therefore, by providing the notch 50 substantially at the center in the longitudinal direction of the backflow prevention sheet 40a as shown in
Although the effects whereby developer leakage is prevented are enhanced as the depth (dimension in the direction orthogonal to the longitudinal direction) B of the notch 50 decreases, the effects whereby the pressure inside the first and second stirring chambers 20b, 20c is reduced are diminished, the toner supply becomes unstable, and fogging is prone to occur. On the other hand, the effects whereby the pressure inside the first and second stirring chambers 20b, 20c is reduced are enhanced as the depth B increases, but the developer is more prone to leak in cases in which the developing device 3a is subjected to impact. The depth B of the notch 50 is therefore preferably set to 1 mm or greater and 2 mm or less.
The amount of protrusion of the distal end portion 43 of the backflow prevention sheet 40a from the point N of closest approach is not particularly limited, but when there is too little protrusion, the distal end portion 43 of the backflow prevention sheet 40a is not adequately pressed against the magnetic roller 22 in cases in which the developing device 3a is subjected to impact, and there is a possibility of the developer leaking in cases in which the image-forming apparatus 100 is overturned or dropped and the developing device 3a is subjected to impact. The amount of protrusion is therefore preferably 0.5 mm or greater.
A configuration may also be adopted in which a gap A is not provided, and the distal end portion 43 of the backflow prevention sheet 40a is brought into contact with the magnetic roller 22. In this case, the ventilation path 51 is formed between the backflow prevention sheet 40a and the rotary sleeve 22a by the notch 50, as shown in
The backflow prevention member 40 may also be formed by only the backflow prevention sheet 40a, without the use of the auxiliary sheet 40b. However, it is preferred that the proximal end portion of the backflow prevention sheet 40a is overlapped by the auxiliary sheet 40b having a greater elastic modulus than the backflow prevention sheet 40a, as in the present embodiment, because the resilience (body) of the backflow prevention member 40 is thereby enhanced, the backflow prevention sheet 40a is not readily deformed by the compression force of the developer, and the effects for preventing developer leakage are enhanced.
In a case in which the backflow prevention sheet 40a is brought into contact with the rotary sleeve 22a as shown in
The term “elastic modulus” used in the present specification is a physical property that indicates resistance to deformation, and is a proportionality constant between stress and distortion in elastic deformation. In other words, a material having a higher elastic modulus less readily deforms and has superior resilience.
As shown in
In a case in which the backflow prevention sheet 40a and the rotary sleeve 22a are placed in contact with each other, the spaces inside the first and second stirring chambers 20b, 20c positioned below the magnetic roller 22 are nearly closed by the regulating blade 25 and the backflow prevention member 40, the pressure increases during driving of the developing device 3a, and the toner supply may become unstable. Therefore, by forming the first openings 50a in the backflow prevention sheet 40a and forming the second openings 50b in the auxiliary sheet 40b in the present embodiment, the increase in pressure inside the first and second stirring chambers 20b, 20c is suppressed during driving of the developing device 3a.
As a result, a gap is formed in the overlapping portion of the backflow prevention sheet 40a and auxiliary sheet 40b, and a ventilation path 51 (indicated by the dashed-line arrow in
The developer layer G is not formed on the rotary sleeve 22a before the developing device 3a is driven, and the backflow prevention sheet 40a and auxiliary sheet 40b overlap with no gap. Accordingly, there is no possibility of the developer leaking through the first and second openings 50a, 50b during transport of the image-forming apparatus 100.
An auxiliary sheet 40b formed from a material (PET sheet) having a larger elastic modulus than the backflow prevention sheet 40a is preferably superposed on the backflow prevention sheet 40a, as in the present embodiment, because the resilience (body) of the backflow prevention member 40 is thereby enhanced, the backflow prevention sheet 40a is not readily deformed by the pressure of the developer, and the effects for preventing leakage of the developer are enhanced.
Since there is a possibility of damage to the surface of the rotary sleeve 22a when the backflow prevention sheet 40a in contact with the rotary sleeve 22a has high rigidity, a low-elastic modulus member made of urethane or the like is preferably used as the backflow prevention sheet 40a.
The arrangement of the first and second openings 50a, 50b is not limited to that of the embodiment described above; the first and second openings 50a, 50b may be in any positions that do not overlap each other. For example, the openings may be arranged in a zigzag pattern as shown in
However, when the first and second openings 50a, 50b are positioned too far away from the proximal end portions 41a, 41b, the overlapping portions of the backflow prevention sheet 40a and the auxiliary sheet 40b may separate in the event of impact to the developing device 3a, causing the developer to leak. Although depending on the rigidity and the dimensions of the overlapping portions of the backflow prevention sheet 40a or the auxiliary sheet 40b, the first and second openings 50a, 50b are preferably formed as close as possible to the proximal end portion 41a, 41b.
In this configuration as well, when the developing device 3a is driven, the backflow prevention sheet 40a is lifted toward the second stirring chamber 20c (in the direction of the arrow in
Consequently, since the air compressed inside the first and second stirring chambers 20b, 20c during driving of the developing device 3a escapes out through the ventilation path 51, the increase in air pressure inside the first and second stirring chambers 20b, 20c can be suppressed. Since the backflow prevention sheet 40a and auxiliary sheet 40b overlap with no gap before the developing device 3a is driven, there is also no possibility of the developer leaking through the first openings 50a during transport of the image-forming apparatus 100.
The first openings 50a are preferably formed in positions overlapping the vicinity of the distal end portion of the auxiliary sheet 40b so that the ventilation path 51 is easily formed by the lifting of the backflow prevention sheet 40a. The shape, size, and number of the first openings 50a may also be modified as desired.
Other aspects of the present disclosure are not limited to the embodiments described above; various modifications are possible within the intended scope of the present disclosure. For example, the material and dimensions of the backflow prevention member 40 described in the embodiments above are merely given by way of example, and may be designed as appropriate according to the specifications of the developing device. The backflow prevention member 40 may also be composed of three or more sheets of different materials.
The present disclosure is also not limited to a developing device provided with a magnetic roller 22 and a developing roller 23 such as shown in
The present disclosure is also not limited to the tandem-type color printer shown in
[Experiment 1]
An investigation was conducted into the relationship between the dimensions of the notch 50 formed in the backflow prevention member 40 and the occurrence of fogging and developer leakage in a test machine shown in
In the test machine, the image forming rate was 35 pages/minute, the peripheral speed of the photoconductive drum 1a was 240 mm/second, about the surface potential of the photoconductive drum 1a, a blank-portion potential (V0) was 300 V, and the image-portion potential (VL) was 20 V. The developing roller 23 and the magnetic roller 22 were 20 mm in diameter, the peripheral speed ratio of the developing roller 23 with respect to the photoconductive drum 1a was 1.5 (forward rotation of the surface opposite the photoreceptor), and the peripheral speed ratio of the magnetic roller 22 with respect to the developing roller 23 was 1.5 (counter-rotation of the surface opposite the developing roller). The gap between the photoconductive drum 1a and the developing roller 23 was 0.15 mm, and the gap between the magnetic roller 22 and the developing roller 23 was 0.3 mm. The fixed magnet 22b was fixed inside the magnetic roller 22 so that the main pole 35 was placed at a position 10° downstream side in the rotation direction of the rotary sleeve 22a from the point of closest approach between the magnetic roller 22 and the developing roller 23, and the magnetic attraction of the main pole 35 was 70 mT.
A two-component developer composed of 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 was used as the developer, and the mixture ratio (T/C) of toner to carrier was 9 wt %.
Voltage was applied to the developing roller under the following conditions: Vslv (DC)=50 V; Vpp of Vslv (AC): 1.5 kV; frequency: 3 kHz; and duty ratio=35%. Voltage was applied to the magnetic roller under the following conditions: Vmag (DC)=250 V; Vpp of Vmag (AC): 1.4 kV; frequency: 3 kHz; and duty ratio=65%.
Evaluation was carried out by the following method. Using a backflow prevention member 40 such as the one shown in
To evaluate developer leakage, a drop test was conducted in which a packaged test machine in which the developing device was installed was dropped a total of ten times from a height of 60 cm, with one drop each being at the landing sites of a corner (one location), edges (three locations in the length, width, and height directions with a corner at the center), a top surface, side surfaces (four locations), and a bottom surface. The developing device 3a was then removed from the test machine, and leakage of the developer was macroscopically observed. Cases of no developer leakage were designated as “◯,” cases in which some leakage was present but not to a practically problematic degree were designated as “Δ,” and cases in which there was a practically problematic degree of leakage were designated as “x.” The evaluation results are shown in Table 1 in conjunction with the values for the gap A, depth B, and width C. Table 2 shows the results obtained when using a backflow prevention member 40 that was composed only of the backflow prevention sheet 40a without the auxiliary sheet 40b.
As is apparent from Tables 1 and 2, fogging either was not observed or was not present to a practically problematic degree in Example 1 to 10 in which the notch 50 was provided to the backflow prevention member 40. The fogging-suppression effects were particularly significant in Example 2, 3, 5, 7, 8, and 10, in which the depth B of the notch 50 was set to 2 mm. As for leakage of the developer after the drop test, developer either did not leak or leakage was not present to a problematic degree in Example 1 through 10, in which the depth B of the notch 50 was set to 1 mm or 2 mm.
It is furthermore apparent from comparison of Example 1 to 5 and Example 6 to 10 that use of the auxiliary sheet 40b further suppressed leakage of the developer during drop testing. The reason for this may be that because the auxiliary sheet 40b is highly resilient, the backflow prevention member 40 was not readily deformed by the pressure of the developer, and a gap was not readily formed between the backflow prevention member 40 and the rotary sleeve 22a.
In contrast, in Comparative Examples 1 to 4 in which the notch 50 was not provided to the backflow prevention member 40, although developer leakage was absent or not present to a practically problematic degree, severe fogging occurred. The image forming unit Pa for cyan was tested in this case, but the same effects were also confirmed for the magenta, yellow, and black image forming units Pb,Pc and Pd.
[Experiment 2]
An investigation was conducted into the relationship between the positioning of the first and second openings 50a, 50b formed in the backflow prevention member 40 and the occurrence of fogging and developer leakage in a test machine shown in
Evaluation was carried out by the following method. As shown in
To evaluate developer leakage, a drop test was conducted in which a packaged test machine in which the developing device was installed was dropped a total of ten times from a height of 60 cm, with one drop each being at the landing sites of a corner (one location), an edge (three locations in the length, width, and height directions with a corner at the center), the top surface, a side surface (four locations), and the bottom surface. The developing device 3a was then removed from the test machine, and leakage of the developer was macroscopically observed. Cases of no developer leakage were designated as “◯,” cases in which some leakage was present but not to a practically problematic degree were designated as “Δ,” and cases in which there was a practically problematic degree of leakage were designated as “x.” The evaluation results are shown in Table 3 in correlation with the values for the distances A, B, C, and D.
As is apparent from Table 3, fogging was not observed Example 11 and 12 in which first and second openings 50a, 50b having a width of 1 mm were provided 1 mm apart, or in Example 13 in which first and second openings 50a, 50b having a width of 1.5 mm were provided 0.5 mm apart. There was also no leakage of developer observed after the drop test.
In contrast, in Comparative Example 5 in which the first and second openings 50a, 50b were not formed, fogging was severe despite the absence of developer leakage. The image forming unit Pa for cyan was tested in this case, but the same effects were also confirmed for the magenta, yellow, and black image forming units Pb,Pc and Pd.
The examples described above represent only an example of the configuration of the present disclosure; the surface potential of the photoconductive drum 1a, the conditions of voltage application to the developing roller 23 and magnetic roller 22, and other characteristics may be set as appropriate according to device specifications or usage environment.
According to the present disclosure, since increases in pressure inside the developing container are suppressed by the ventilation path formed between the developer bearing member and the backflow prevention member, and the supply of toner is stabilized, it is possible to reduce the occurrence of fogging due to defects in toner charging.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-194976 | Aug 2009 | JP | national |
| 2009-194978 | Aug 2009 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4731632 | Fukushima et al. | Mar 1988 | A |
| 4963930 | Yoshimaru et al. | Oct 1990 | A |
| 7583916 | Ogata et al. | Sep 2009 | B2 |
| 7917046 | Kubo | Mar 2011 | B2 |
| Number | Date | Country |
|---|---|---|
| 1619434 | May 2005 | CN |
| 101334613 | Dec 2008 | CN |
| 2-139587 | May 1990 | JP |
| 2006-250973 | Sep 2006 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20110052270 A1 | Mar 2011 | US |
