JP4164331B2 - Development device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device having a screw for conveying a developer to a developing carrier .
[0002]
[Prior art]
2. Description of the Related Art As a developing device for an image forming apparatus that performs electrophotographic development, a two-component developing device that has very good chargeability to toner has been widely used. FIG. 13 is a top view of the developing device, and FIG. 14 is a cross-sectional view showing an example of the two-component developing device.
[0003]
As shown in the figure, reference numeral 10 denotes a developer container, which stores developer D composed of toner and carrier. An opening is provided in a portion of the developer container 10 that is in close proximity to the photosensitive drum 1, and a developing sleeve 2 that is a developer carrying member is provided in the opening. The developing sleeve 2 is a hollow non-magnetic metal sleeve and includes a magnet roller 3 as a magnetic field generating means.
[0004]
Reference numerals 5 and 6 denote developer conveying members (A screw 5 and B screw 6), which are screws in which blade members are spirally wound around a cylindrical central shaft member at a constant pitch. The A screw 5 and the B screw 6 are arranged substantially in parallel, and an inner wall 7 is provided between the A screw and the B screw for partitioning the developer so as not to come and go. There are no inner walls at both longitudinal ends, and the developer can move between the A and B screws. Since the A screw and the B screw convey the developer in opposite directions, when each screw rotates, the developer circulates through the inside without interruption as indicated by arrows.
[0005]
The developer supplied by the A screw 5 is supplied to the developing sleeve 2 by the magnetic force of the magnet roller 3 and is conveyed along with the rotation. Reference numeral 4 denotes a developer regulating member. When the developer on the developing sleeve 2 is regulated to an appropriate amount, a uniform developer coat is formed on the developing sleeve 2. The developer magnetic brush carried on the developing sleeve 2 comes into contact with the photosensitive drum 1 rotating in the developing portion, and the electrostatic latent image on the photosensitive drum 1 is developed.
[0006]
FIG. 15 is an external view of a conventional screw, and FIG. 16 is a cross-sectional view taken along a plane passing through the rotation center line of the conventional screw. In this figure, the developer transport direction is leftward. 13 is a rotation center line, 14 is a central shaft member, and 15 is a blade wound spirally. As shown in the figure, the angle formed by the blade surface in the transport direction (shown by hatching in the figure) with respect to the rotation center line is referred to as an angle θ. The angle θ is generally set to about 70 to 80 ° in consideration of the draft of the molding die and the like because the developer conveying force increases as the angle becomes closer to the vertical.
[0007]
[Problems to be solved by the invention]
However, the conventional configuration sometimes has problems as described below.
[0008]
FIG. 17 is an explanatory view schematically showing a state in which developer is conveyed by a conventional screw. As the screw rotates, the developer receives a force pushed in the advancing direction by the blade, so that the developer is shifted toward the conveyance direction surface side of the blade. Since the amount decreases as the distance from the blade decreases, each blade portion is transported in the state shown in FIG.
[0009]
Therefore, when looking at the distribution in the longitudinal direction of the developer, a large portion and a small portion (so-called unevenness) are formed according to the blade pitch. Then, as the screw rotates, the developer is conveyed in the longitudinal direction, so that the presence unevenness of the developer becomes a shading unevenness in the oblique direction and appears on the image. This image defect is hereinafter referred to as screw pitch unevenness. Screw pitch unevenness is extremely likely to occur in a two-component developing device in which a developing sleeve and a developer conveying screw are arranged close to each other.
[0010]
Therefore, the configuration of the developing sleeve 2 and each screw, the magnetic pole relationship of the magnet roller 3 in the developing sleeve 2, the compressed state of the developer in the restricting portion, and the like are optimized to prevent screw pitch unevenness. In the first place, it has been difficult to completely prevent the developer conveyed by the screw from being unevenly distributed at the screw blade pitch.
[0011]
Furthermore, in the two-component developing device, the toner density of the developer varies depending on the balance between toner consumption and replenishment, so the amount of developer may increase or decrease accordingly, and the amount of developer in the developing device decreases. However, it has been difficult to completely prevent screw pitch unevenness, no matter how the configuration is optimized.
[0012]
Conventionally, there have been devices that devise the shape and number of strips of the developer conveying member (for example, JP-A-10-221937 and JP-A-2002-31940), but the developer agitation is improved, There was no object to solve the screw pitch unevenness.
[0013]
Accordingly, an object of the present invention is to provide a developing device having a developer conveying member that can effectively prevent the occurrence of screw pitch unevenness.
[0014]
[Means for Solving the Problems]
To achieve the above object, a typical configuration of the present invention is a developing device used in an image forming apparatus for forming an image on a recording medium, in which a developer is supplied from a developer supplying device. A developer carrying member that develops the latent image formed on the toner using a developer, and a developer housing that contains a developer for developing the latent image of the electrophotographic photosensitive member replenished from the developer replenishing device. A developer accommodating portion partitioned by an inner wall provided along the longitudinal direction of the developer carrying member except for both end portions in the longitudinal direction, and the developer accommodating portion from the developer supply device When the developer is replenished, the replenishment port through which the developer passes and the developer replenished from the replenishment port provided at a position farther from the developer carrier than the inner wall are stirred while the developer is being stirred. First screw transported in the longitudinal direction When, than the inner wall is provided at a position closer to said developer carrying member, the developer that has passed through the portion having no inner wall by the first screw into the developer carrying member while conveying in the longitudinal direction A second screw for supplying developer, a central shaft member rotatably provided, and a first blade surface in the developer transport direction provided in a spiral shape around the central shaft member And a plurality of bulging blade portions having a second blade surface in the developer conveyance direction provided spirally around the central shaft member separately from the conveyance blade portion. And when the second screw is viewed in a section cut by a plane passing through the rotation center line of the second screw, the second screw is formed with respect to the rotation center line of the center shaft member. The angle of the second blade surface is determined by the rotation of the central shaft member. Rather smaller than the angle of the first blade surface which forms with respect to the center line, the center axis member is characterized by being covered without exposing by the conveying blade portion and the plurality of bulking blade portion Development device.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
( Reference example )
FIG. 5 is an explanatory diagram of an image forming apparatus in the present reference example and an embodiment described later . 1 is a photosensitive drum as an image carrier, 20 is a charging device, 21 is an exposure device for forming a latent image on the photosensitive drum, 11 is a developing device for visualizing the latent image with toner, and 9 is a developing device. A developer replenishing device for replenishing toner, 22 is a transfer device for transferring a visualized toner image onto a transfer material, 23 is a fixing device for fixing the toner image transferred onto the transfer material, and 24 is a photosensitive drum. It is a cleaning device for removing the transfer residual toner remaining on the top.
[0016]
The developing device includes a developer container 10 that stores a developer, and stores a developer D in which toner particles and magnetic carrier particles are mixed. As the toner, a known toner in which a colorant, a charge control agent, etc. are added to a binder resin can be used. In this reference example and the embodiments described later , those having a volume average particle diameter of 5 to 15 μm were used. On the other hand, as the magnetic carrier, a ferrite carrier, a resin-coated one or the like is preferably used, and an average particle size of 15 to 70 μm is preferable. A developer replenishing device 9 is provided above the developer conveying member 6, and an amount of toner corresponding to the consumed toner is dropped and replenished into the developer container 10 through the replenishing port 8. The developer is always kept at a constant toner concentration.
[0017]
Next, the screw which is the developer conveying member according to this reference example will be described. 1 and 2 are cross-sectional views taken along a plane passing through the rotation center line of the screw of this reference example , and are diagrams for explaining the angle of blades and the length of each blade. In this figure, the developer transport direction is leftward.
[0018]
In the configuration of the present invention, in addition to the spiral spiral blade 15 serving as the conveyor blade portion being spirally wound around the shaft of the screw, a bulky spiral blade 16 serving as a blade portion is additionally provided immediately after the spiral spiral blade 15. It is characterized by that.
[0019]
As shown in FIGS. 1 and 2, the angle between the blade surface in the transport direction of the transport spiral blade 15 and the center line of the shaft is (θ1), the height of the blade is (H1), and the length of the blade in the axial direction. Is (L1), the angle formed between the blade surface in the conveying direction of the spiral blade and the shaft center line is (θ2), the blade height is (H2), and the blade axial length is (L2). It was. The outer diameter including the blades of the screw was 14 mm, the diameter of the central shaft member was 6 mm, the longitudinal pitch of the blades was 15 mm, θ1 = 70 °, H1 = 4 mm, L1 = 3 mm, and L2 = 5 mm.
[0020]
In a state where the conditions of the conveying spiral blade 15 are fixed, the image forming test was performed by increasing the height and shaking the height H2 of the spiral blade 16 to some level. The result is shown in FIG. From this result, it was confirmed that the screw pitch unevenness was improved by increasing the volume of the conveying spiral blade 15 and adding the spiral blade 16. The reason for this will be described with reference to FIG.
[0021]
In the configuration of only the conveying spiral blade 15 as in the prior art, the position immediately after the conveying spiral blade 15 is less likely to have a gap due to less developer. On the other hand, in the present reference example , the bulk of the developer D is increased by applying a force exerted on the developer D in a direction substantially perpendicular to the central shaft member 14 by adding the bulky spiral blade 16. By increasing the volume of the developer D in this way, the gap immediately after the conveying spiral blade 15 can be filled. For this reason, it seems that screw pitch nonuniformity can be prevented effectively.
[0022]
Further, as shown in FIG. 3, there is a suitable range for the height H2 of the bulking spiral blade 16 and it can be seen that the effect is small if it is too large or too small. If H2 is too small, the effect of increasing the pitch of the developer is reduced, so that the effect of preventing screw pitch unevenness is reduced. Further, if H2 is too large, it will increase in volume and a gap with little developer will be formed immediately after the spiral blade 16, and even if the gap immediately after the conveying spiral blade 15 is filled, a new developer gap will be generated. Because it will end up.
[0023]
Taking these into consideration, it is desirable that the upper limit of the height of the bulked spiral blade 16 is within H2 <H1 × 0.7. Further, the optimum angle of θ2 at this time is 5 ° <θ2 <40 °, 60 ° <θ1, and more preferably 10 ° <θ2 <30 ° and 60 ° <θ1.
[0024]
In the study of this reference example, the above results were obtained because the screw diameter and pitch were fixed. However, if these shapes were changed, the preferred value of the angle θ slightly fluctuated. However, by providing the increased spiral blade 16, the gap immediately after the transport spiral blade can be filled, and the original function and effect that screw pitch unevenness can be effectively prevented does not change.
[0025]
As described above, in this reference example , by increasing the volume immediately after the conveying spiral blade 15 and providing the spiral blade 16, the conveying state of the developer to be conveyed is improved substantially horizontally. As a result, the supply unevenness of the developer D to the developing sleeve 2 and the accompanying compression unevenness in the restricted portion, and consequently the toner concentration of the developer D conveyed by the screw and the developed developer returning from the developing sleeve 2. Such as the difference in the number of image unevenness caused by the screw pitch can be reduced. Thus, the screw pitch unevenness image can be improved.
[0026]
( First embodiment)
In the above-described reference example , the configuration in which one spiral blade 16 is provided separately from the spiral spiral blade 15 immediately after the transport spiral blade 15 has been described. The provided structure will be described. FIG. 6 is an external view of the screw according to the present embodiment, and FIGS. 7 and 8 are cross-sectional views taken along a plane passing through the rotational center line of the screw according to the present embodiment. It is a figure for doing. In this figure, the developer transport direction is leftward.
[0027]
The outer diameter including the blades of the screw was 14 mm, the diameter of the central shaft member was 6 mm, the longitudinal pitch of the blades was 15 mm, θ1 = 70 °, H1 = 4 mm, and L1 = 3 mm. As described in the reference example , the bulking spiral blades were H2 = 2 mm and L2 = 5 mm.
[0028]
In this state, immediately after the bulking spiral blade 16 of the reference example , another bulking spiral blade 17 as another bulking blade part was installed. Since the blade surface in the transport direction of the bulking spiral blade 17 newly provided in the present embodiment is located very close to the blade surface in the transport direction of the transport spiral blade 15, the blade surface in the transport direction of both the points P ( 8) and connected to each other at a different angle. Under these conditions, in order to increase the volume of the spiral blade 17 and increase the angle of the spiral blade 17, the height H3 was swung to some level, and the effects on screw-pitch unevenness and developer transportability were examined. The result is shown in FIG. From this result, it was confirmed that the screw pitch unevenness was improved by increasing the bulk and adding the spiral blade 17. The reason for this will be described with reference to FIG.
[0029]
As shown in FIG. 10, in the present embodiment, by providing the increased spiral blade 17, not only can the gap between the developer immediately after the transport spiral blade 15 be filled as in the reference example , but also the developer height is increased. A force exerted on the developer in a direction substantially perpendicular to the rotation center line can be applied to an intermediate point between the conveying spiral blade 15 and the conveying spiral blade 15 that tends to be lowered. This makes it possible to achieve a very uniform developer height as a whole. Moreover, since the apparent amount of the developer is merely increased and the transport amount is not reduced, the developer transportability is not hindered if used within a suitable range.
[0030]
As shown in FIG. 9, the height H3 of the spiral blade 17, that is, the angle θ3 has a suitable range, and it has been found that the effect is small if it is too large or too small. If H3 is too small, the effect of increasing the pitch of the developer is reduced, so that the effect of preventing screw pitch unevenness is reduced. On the other hand, if H3 is too large, the bulk increases and the effective area of the conveying spiral blade 15 located immediately after the spiral blade 17 becomes small, so that the developer conveying property is deteriorated, and the density is easily lowered.
[0031]
Considering these facts, the preferred range of the bulking spiral blade 17 is H3 <H1 × 0.5. In this case, the optimum angle of θ3 is 5 ° <θ3 <40 °, and more preferably 10 ° <θ3 <30 °.
[0032]
As described above, in the present embodiment, the two bulky spiral blades are provided, so that it is possible not only to fill the gap immediately after the transport spiral blades as in the reference example , but also the developer height tends to decrease. By applying a force in the direction perpendicular to the rotation center line to the developer at the intermediate point between the conveying spiral blade and the conveying spiral blade, it becomes possible to achieve a very uniform developer height as a whole. It was.
[0033]
As a result, uneven supply of the developer to the developing sleeve, and accompanying compression unevenness in the restricting portion, as well as a difference in toner concentration between the developer conveyed by the screw and the developer returned from the developing sleeve, etc. Since it is possible to reduce the cause of any image unevenness due to screw pitch, it is possible to improve the screw pitch unevenness image.
[0034]
Up to this point, the description has been given with respect to the case where the number of the spiral blades is increased to two. However, as shown in FIG. It may be configured as described above. In this way, by arranging a plurality of increased spiral blades in addition to the transport spiral blade, the central shaft member is covered with the transport spiral blade and the increased spiral blade, and the screw is not exposed to the central shaft member. Most of these are constituted by surfaces inclined in the transport direction. As a result, the force in the conveying direction and the force exerted in the direction perpendicular to the rotation center line can be applied to the developer present at any location of the screw, and the developer height can be kept more uniform.
[0035]
Note that the above results were obtained because the screw diameter and pitch were fixed in the study of the present embodiment, but the preferred value of the angle θ varies slightly if these shapes change. However, by providing the increased spiral blade, which is a feature of the present invention, it is possible to fill the gap immediately after the transport spiral blade and the intermediate point between the transport spiral blade and the transport spiral blade. It does not change the original effect that can be prevented.
[0036]
( Second Embodiment)
The present embodiment is an example when the first embodiment is mounted on a color image forming apparatus including a plurality of developing devices. FIG. 12 shows a four-drum type (in-line) printer in which images developed on four image carriers are once continuously transferred to an intermediate transfer belt 40 as an intermediate transfer member to obtain a full-color print image.
[0037]
In FIG. 12, an endless intermediate transfer belt 40 is suspended from a drive roller 41, a tension roller 42, and a secondary transfer counter roller 43, and is rotated in the direction of the arrow in the figure.
[0038]
The photosensitive drum 1 that develops yellow toner is uniformly charged to a predetermined polarity and potential by a primary charging roller as a charging device 20 in the course of rotation, and then image exposure means (not shown) (color of a color original image) Yellow of the target color image by receiving image exposure by a separation / imaging exposure optical system, a scanning exposure system by laser scanning that outputs a laser beam modulated in accordance with a time-series electric digital pixel signal of image information, etc. An electrostatic latent image corresponding to the component image is formed. Next, the electrostatic latent image is developed by the first developing device 11 (yellow developing device), and the bias is transferred onto the transfer belt. In this way, yellow, magenta, cyan, and black images are sequentially superimposed on the intermediate transfer body 40 to form a full-color image.
[0039]
The four-color full-color image formed on the intermediate transfer belt 40 is then collectively transferred to a transfer material by the secondary transfer roller 44 and melted and fixed by a fixing device (not shown) to obtain a color print image. The secondary transfer residual toner remaining on the intermediate transfer belt 40 is subjected to blade cleaning by the intermediate transfer belt cleaner 45 to prepare for the next image forming process.
[0040]
In such a color image forming apparatus, unevenness of fixed pitch such as screw pitch unevenness tends to be amplified and deteriorated due to color overlap. However, the configuration of the first embodiment according to the present invention is very high. It is effective and exhibits a great effect even in such a color image forming apparatus.
[0041]
(Other embodiments)
In the above-described embodiment, the example in which the photosensitive drum 1 and the process unit acting on the photosensitive drum 1 are separately provided has been described. However, the present invention is not limited to this. As the process means that acts, at least the developing device 11 may be integrated into a cartridge so that the process cartridge is configured to be detachable from the image forming apparatus. As the process cartridge, for example, in addition to the photosensitive drum 1 and the developing device 11, any or all of the charging device 20, the exposure device 21, and the cleaning device 24 may be arranged in one frame to form a process cartridge. This process cartridge can be attached to and detached from the apparatus main body by the user himself. As a result, the maintenance of the apparatus main body can be performed by the user himself.
[0042]
In addition to the printer described above, the image forming apparatus according to the present invention may take the form of a copying machine, a facsimile machine, or the like.
[0043]
【The invention's effect】
As described above, in the present invention, the center shaft member is covered with the transport blade portion and the plurality of increased blade portions, and the center shaft member is not exposed, and most of the second screw is in the developer transport direction. It is constituted by an inclined surface. As a result, the developer height can be kept more uniform everywhere on the second screw. For this reason, it is possible to prevent a portion where the amount of developer supplied in the longitudinal direction of the developer carrier is large and a portion where the amount is small, and it is possible to effectively prevent the occurrence of screw pitch unevenness.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view taken along a plane passing through a rotation center line of a screw of a reference example .
FIG. 2 is a cross-sectional view taken along a plane passing through the rotation center line of the screw of the reference example .
FIG. 3 is a diagram showing a result of an image formation test using the height of the bulked spiral blade 16 as a parameter.
FIG. 4 is a diagram for explaining the effect of a reference example .
FIG. 5 is an explanatory diagram of a reference example and an image forming apparatus according to the first embodiment.
FIG. 6 is an external view of a screw according to the first embodiment.
FIG. 7 is a cross-sectional view taken along a plane passing through the rotation center line of the screw of the first embodiment.
FIG. 8 is a cross-sectional view taken along a plane passing through the rotation center line of the screw of the first embodiment.
FIG. 9 is a diagram showing a result of an image forming test using the height of the bulked spiral blade 17 as a parameter.
FIG. 10 is a diagram for explaining the effect of the first embodiment.
FIG. 11 is a cross-sectional view showing a modification of the first embodiment.
FIG. 12 is an explanatory diagram of an image forming apparatus equipped with a plurality of developing devices according to the second embodiment.
FIG. 13 is a top view of a conventional developing device.
FIG. 14 is a cross-sectional view showing an example of a conventional two-component developing device.
FIG. 15 is an external view of a conventional screw.
FIG. 16 is a cross-sectional view taken along a plane passing through the rotation center line of a conventional screw.
FIG. 17 is an explanatory diagram schematically illustrating a developer conveyance state by a conventional screw.
[Explanation of symbols]
D: Developer, 1 ... Photosensitive drum, 2 ... Developing sleeve, 3 ... Magnet roller, 4 ... Developer regulating member, 5 ... Developer conveying member, 6 ... Developer conveying member, 7 ... Inner wall, 8 ... Supply port , 9 ... Developer supply device, 10 ... Developer container, 11 ... Development device, 13 ... Rotation center line, 14 ... Center shaft member, 15 ... Conveying spiral blade, 16 ... Bulking spiral blade, 17 ... Bulking spiral blade , 18 ... spiral blade, 20 ... charging device, 21 ... exposure device, 22 ... transfer device, 23 ... fixing device, 24 ... cleaning device, 40 ... intermediate transfer belt, 41 ... drive roller, 42 ... tension roller, 43 ... two Next transfer counter roller 44... Secondary transfer roller 45. Intermediate transfer belt cleaner

Claims (5)

In a developing device used in an image forming apparatus for forming an image on a recording medium, the developer is supplied from a developer supplying device .
A developer carrier that develops the latent image formed on the image carrier using a developer;
A developer accommodating portion for accommodating a developer for developing a latent image of the electrophotographic photosensitive member replenished from the developer replenishing device, and an inner wall provided along a longitudinal direction of the developer carrying member A developer storage section partitioned by excluding both ends in the longitudinal direction ,
A replenishment port through which the developer passes when the developer is replenished from the developer replenishing device to the developer accommodating portion;
A first screw that is provided at a position farther from the developer carrier than the inner wall and conveys the developer replenished from the replenishing port in the longitudinal direction while stirring;
Provided in a position closer to said developer carrying member than said wall, the developer of the developer that has passed through the portion having no inner wall by the first screw into the developer carrying member while conveying in the longitudinal direction a second screw for supplying, has a central shaft member which is rotatably provided, disposed helically around the central axis member, the first blade surface of the developer carrying direction A second blade having a plurality of increased blade portions having a second blade surface in the developer conveying direction, provided in a spiral shape around the central shaft member, separately from the conveying blade portion and the conveying blade portion . And the screw
Have
When the second screw is viewed in a cross section cut by a plane passing through the rotation center line of the second screw, the angle of the second blade surface made with respect to the rotation center line of the center shaft member is the central axis rotation center line the rather smaller than the angle of the first blade surface which forms with respect to the member, the central axis member is covered without being exposed by the conveying blade portion and the plurality of bulking blade unit developing apparatus is characterized in that there. The distance from the central shaft member to the tip of the outer diameter of the conveying blade is H1,
When the distance from the central shaft member to the tip of the outer diameter of the increased blade portion is Hn (n = 2, 3,...),
Hn <H1 × 0.7,
The developing device according to claim 1, wherein: An angle formed by the first blade surface with respect to the rotation center line is θ1,
When the angle formed by the second blade surface with respect to the rotation center line is θn (n = 2, 3,...),
5 ° <θn <40 °, 60 ° <θ1,
The developing device according to claim 1, wherein the developing device is a developing device.     4. The developing device according to claim 1, wherein in the developer transport direction, the increased blade portion is disposed immediately after the transport blade portion. 5.     The developing device according to claim 1, wherein the developer is a two-component developer including a toner and a carrier.

Images