JP5610920B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention uses a developing device for making a visible image by attaching a developer to a latent image formed on an image carrier, and an electrophotographic method or an electrostatic recording method provided with the developing device. The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, and a composite machine of these.

  2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic method generally charges the surface of a drum-shaped photoconductor, which is an image carrier, uniformly by a charger, and the charged photoconductor is converted into image information by an exposure device. In response to the exposure, an electrostatic latent image is formed on the photoreceptor. The electrostatic latent image formed on the photosensitive member is visualized as a toner image by a toner as a developer using a developing device. The visualized image is transferred to a recording material by a transfer device. Thereafter, the toner image transferred onto the recording material is melted and fixed onto the recording material with heat and pressure by a fixing device.

  As such a developing apparatus, there is one that uses a two-component developer including non-magnetic toner particles (toner) as a developer and magnetic carrier particles (carrier). In the developing device using the two-component developer, the toner and the carrier are conveyed in the developing container while being agitated, and the developer is carried on the developing sleeve which is a developer carrying member. The carrying amount of the developer carried on the developing sleeve is regulated by a regulating blade that is a developer regulating member. Thereafter, by applying a developing bias between the developing sleeve and the photosensitive member, only the toner is transferred to the electrostatic latent image formed on the surface of the photosensitive member, and a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive member. Is formed.

  As shown in FIG. 14, the developing device using the two-component developer as described above includes a developing chamber 102 that supplies the developer to the developing sleeve 101, and a stirring chamber 103 that is arranged in parallel with the developing chamber 102. Have. The developing chamber 102 and the stirring chamber 103 are partitioned by a partition wall 104 having both ends opened. Further, a conveying screw as a conveying member is disposed in each of the developing chamber 102 and the stirring chamber 103. Then, as indicated by an arrow in the figure, the developer is supplied to the developing sleeve 101 while the developer is circulated between the developing chamber 102 and the stirring chamber 103 by the conveying screw. The developer carried on the developing sleeve 101 and having passed through the developing area of the photosensitive member is peeled off from the developing sleeve 101 and collected in the developing chamber 102 as indicated by the broken arrow in the drawing.

  Therefore, in the developing chamber 102, the developer is supplied to the developing sleeve 101 while being conveyed by the conveying screw, and the developer peeled off from the developing sleeve 101 is collected. For this reason, the number of times the developer in the developing chamber 102 is carried on the developing sleeve 101 increases as it goes downstream in the conveying direction by the conveying screw. That is, the developer that passes through the developing region and consumes the toner more downstream in the developing chamber 102. As a result, the developer in the developing chamber 102 has a toner concentration that decreases toward the downstream in the transport direction, causing unevenness in the toner concentration of the developer supplied to the developing sleeve 101. If image formation is performed in such a state, density unevenness occurs in the output product.

  On the other hand, a structure in which a developing chamber and a stirring chamber are arranged side by side in the direction of gravity is also known as a developing device (see Patent Documents 1 and 2). In the case of this structure, the developer peeled off from the developing sleeve is collected in the lower stirring chamber. For this reason, the developer having a low toner concentration is sufficiently stirred in the stirring chamber and then conveyed to the developing chamber and supplied to the developing sleeve. Therefore, the density unevenness hardly occurs in the output product.

  However, in such a configuration, since the developer peeled off from the developing sleeve is collected in the stirring chamber, as shown in FIG. 15, the developer amount decreases toward the downstream of the developing chamber 102 in the transport direction. To go. For this reason, it is necessary to increase the speed of the conveying screw so that the supply of the developer to the developing sleeve 101 is not insufficient.

  In addition, as shown in FIG. 16, there is a developing device in which the developing chamber 102 and the stirring chamber 103 are arranged in the horizontal direction, and has a structure in which the partition 104 a is extended to be close to the developing sleeve 101 (see Patent Document 3). Patent Document 3 does not describe how the developer is sent to the developing chamber 102 and the stirring chamber 103, respectively.

JP 2003-295602 A JP-A-5-333691 JP-A-11-190942

  As shown in FIG. 15 described above, in the structure in which the developing chamber 102 and the stirring chamber 103 are arranged in the direction of gravity and the developer peeled off from the developing sleeve 101 is sent to the stirring chamber 103, the conveying screw is operated at a high speed. It is necessary to make it. For this reason, for example, when the process speed of the image forming apparatus is increased, it is necessary to further increase the conveying screw. In order to increase the speed of the conveying screw, the motor for driving the conveying screw becomes expensive, and further, the temperature rises easily. An increase in temperature is not preferable because it affects the state of the developer.

  In the case of the structure shown in FIG. 16, it can be considered that all the developer peeled off at the tip of the partition wall 104 a is sent to the stirring chamber 103. However, it is considered that the developer peeled off at the tip of the partition wall 104 a is sent to the stirring chamber 103, and the developer that has passed through the gap between the partition wall 104 a and the developing sleeve 101 is sent to the development chamber 102. Here, if all the removed developer is sent to the stirring chamber 103, the same problem as the structure shown in FIG. 15 may occur.

  On the other hand, if the developer peeled off at the tip of the partition wall 104a is sent to the stirring chamber 103 and the developer that has passed through the gap between the partition wall 104a and the developing sleeve 101 is sent to the development chamber 102, the following problem occurs. Arise. That is, unless the gap between the partition wall 104a and the developing sleeve 101 is strictly regulated, it is difficult to properly feed the developer into the stirring chamber 103. That is, it is necessary to make it close to the partition wall 104a so as to be smaller than the height (coat amount) at which the developer is carried on the surface of the developing sleeve 101. Here, if the tip of the partition wall 104 a is too close to the surface of the developing sleeve 101, most of the developer is fed into the stirring chamber 103, and if too far, most of the developer is fed into the developing chamber 102.

  When most of the developer is fed into the stirring chamber 103, the same situation as that shown in FIG. On the other hand, when most of the developer is fed into the developing chamber 102, the density unevenness described with reference to FIG. 14 may occur. Therefore, in the case of the structure shown in FIG. 16, the relationship between the amount of developer that is peeled off by the tip of the partition wall 104a and sent to the stirring chamber 103 and the amount of developer that passes through this tip and sent to the developing chamber 102 is appropriate. Must be. For this purpose, it is necessary to strictly regulate the distance between the partition wall 104a and the developing sleeve 101. On the other hand, if the interval between the partition wall 104a and the developing sleeve 101 is strictly regulated in this way, the manufacturing cost increases.

  Specifically, since the thickness of the developer on the developing sleeve 101 is about 2 mm at most, the amount of developer supplied to the developing chamber 102 greatly depends on the distance (gap amount) between the partition wall 104a and the sleeve 101. To do. Therefore, in order to stabilize the ratio at which the developer is distributed between the developing chamber 102 and the stirring chamber 103, it is necessary to appropriately adjust the above-described gap amount, which is not preferable in terms of cost increase. Even if the adjustment is properly performed, considering the fluctuation of the distribution ratio according to the adjustment tolerance (for example, about ± 0.5 mm), it is very difficult to realize the stable developer distribution with the configuration of FIG. is there.

  In view of such circumstances, the present invention was invented to realize a structure capable of reducing density unevenness of an output product at low cost.

The present invention includes a developer carrying member that carries and conveys a developer containing toner and a carrier and supplies the developer to a developing region of the image carrier, and a first chamber that supplies the developer to the developer carrying member. A second chamber that forms a circulation path with the first chamber; a conveying means that is provided in the first chamber along a direction in which the developer carrier is disposed; and conveys the developer in the circulation path; Distributing means for stripping off the developer that has passed through the development area from among the developer carried and transported by the developer carrier, and distributing the stripped developer to the first chamber and the second chamber; , have a developer amount per the unit is stripped from the developer carrying member is sent to the first chamber times, there are more upstream than the conveying direction downstream by the conveying means, characterized in that It is in the developing device.

  According to the present invention, the developer peeled off from the developer carrying member is distributed and sent to the stirring chamber and the developing chamber by the distributing unit, so that the positional relationship between the distributing unit and the developer carrying member is strictly regulated. It is not necessary to reduce the density unevenness of the output material at low cost.

1 is a schematic cross-sectional view of a main part of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic cross-sectional view of a developing device according to a first embodiment. FIG. 3 is a schematic diagram illustrating a flow of an agent of the developing device according to the first embodiment. The perspective view which takes out and shows a distribution member. The test chart used for the experiment for demonstrating the effect which concerns on 1st Embodiment. The graph which shows the in-plane density difference with respect to the number of image formation in the experimental result for demonstrating the effect which concerns on 1st Embodiment. The figure which shows the determination result of the in-plane density nonuniformity with respect to screw rotation speed by the experimental result for demonstrating the effect which concerns on 1st Embodiment. The perspective view of the distribution member which concerns on the 2nd Embodiment of this invention. FIG. 10 is a schematic diagram illustrating a flow of an agent in a developing device according to a second embodiment. The figure which shows the determination result of the in-plane density nonuniformity with respect to screw rotation speed by the experimental result for demonstrating the effect which concerns on 2nd Embodiment. The perspective view of the distribution member which concerns on the 3rd Embodiment of this invention. FIG. 10 is a perspective view schematically showing a schematic configuration of a developing device according to a third embodiment. FIG. 10 is a schematic diagram illustrating a flow of an agent in a developing device according to a third embodiment. The schematic diagram which shows the flow of the agent of the developing device which concerns on the prior art which has arrange | positioned the developing chamber and the stirring chamber in the horizontal direction. Sectional drawing of the developing device which concerns on the prior art which has arrange | positioned the developing chamber and the stirring chamber in the gravity direction. Sectional drawing of the developing device which concerns on the prior art which made the partition close to the image development sleeve.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent. In the following description, a tandem type image forming apparatus that forms a full-color image will be described as an example of an image forming apparatus. However, an image forming apparatus to which the developing device according to the present embodiment is applied is described below. Needless to say, it is not limited to such a device.

[Image forming apparatus]
First, the image forming apparatus of this embodiment will be described with reference to FIG. In FIG. 1, only the main part of the image forming apparatus is shown, but the other parts are the same as those of conventionally known image forming apparatuses. The full-color image forming apparatus according to this embodiment includes stations for yellow (Y), magenta (M), cyan (C), and black (K). The Y, M, C, and K stations have almost the same configuration, and a full-color image forms yellow, magenta, cyan, and black images, respectively.

  In the following description, if the developing device 1 is used, the developing device 1Y, the developing device 1M, the developing device 1C, and the developing device 1K in each of the Y, M, C, and K stations are commonly referred to. In FIG. 1, Y, M, C, and K are added to the reference numerals of the respective components, but they are omitted in the description.

  The photosensitive drum 10 that is an image carrier is rotatably provided, and the surface of the photosensitive drum 10 is uniformly charged by the primary charger 21. Thereafter, the surface of the uniformly charged photosensitive drum 10 is exposed to light modulated in accordance with an information signal by a light emitting element 22 as a latent image means such as a laser to form an electrostatic latent image. . The electrostatic latent image formed in this way is visualized as a toner image by the developing device 1.

  Next, the visible image is transferred to the recording material 27 conveyed by the recording material conveying sheet 24 by the transfer charger 23 and further fixed to the recording material 27 by the fixing device 25. Further, the transfer residual toner on the photosensitive drum 10 is removed by the cleaning device 26. Further, the toner consumed in the image formation is supplied from the toner supply tank 20 (FIG. 2).

[Developer]
Next, the developing device 1 will be described with reference to FIGS. The developing device 1 includes a developing container 2, a cylindrical developing sleeve 8 that is a developer carrier, a panning member 9, a first conveying screw 5 and a second conveying screw 6 that constitute conveying means, Distribution means 30. Among these, the developing container 2 accommodates a two-component developer containing a non-magnetic toner and a magnetic carrier. In addition, a partition wall 7 extending in a direction perpendicular to the paper surface in FIG. 2 is disposed at a substantially central portion in the developing container 2, and the developing container 2 is stirred by the partition wall 7, which is a first chamber and a developing chamber 3. The chamber 4 is partitioned in a direction (horizontal (left and right) direction in the illustrated example) that intersects the direction of gravity. That is, the developing chamber 3 and the stirring chamber 4 are arranged side by side in a direction that intersects the direction of gravity. The developer is accommodated in the developing chamber 3 and the stirring chamber 4. The two-component developer is prepared with a weight ratio of 8% (toner weight / developer weight), for example, and the developer amount is 400 g.

  In the developing chamber 3 and the agitating chamber 4, a first conveying screw 5 and a second conveying screw 6 are arranged as developer agitating / conveying members, respectively. The first conveying screw 5 is disposed substantially parallel to the bottom of the developing chamber 3 along the axial direction of the developing sleeve 8 (the arrangement direction, the direction perpendicular to the paper surface of FIG. 2). The second conveying screw 6 is disposed at the bottom of the stirring chamber 4 substantially in parallel with the first conveying screw 5. Each of the first conveying screw 5 and the second conveying screw 6 has a screw structure in which blade members made of a nonmagnetic material are provided in a spiral shape around a rotating shaft made of a ferromagnetic material. It rotates synchronously through a power transmission mechanism such as a gear. The first conveying screw 5 rotates to convey the developer in the developing chamber 3 in one direction along the axial direction. On the other hand, the developer in the stirring chamber 4 is transported in the direction opposite to the transport direction of the first transport screw 5 by rotating the second transport screw 6.

  Openings 11 and 12 (FIG. 3) for communicating between the developing chamber 3 and the stirring chamber 4 are formed at both ends of the partition wall 7 in the axial direction. In other words, the developing chamber 3 and the stirring chamber 4 are partially communicated. Therefore, as described above, by the rotation of the first conveying screw 5 and the second conveying screw 6, the developer is provided with openings 11 and 12 provided at both ends of the partition wall 7 as indicated by arrows in FIG. 3. Through the developing chamber 3 and the stirring chamber 4. That is, the developing chamber 3 and the stirring chamber 4 form a circulation path. Then, the developer is conveyed in the circulation path.

  In addition, an opening is provided at a position corresponding to the developing region F of the developing container 2 facing the photosensitive drum 10, and the developing sleeve 8 is rotatably arranged in the opening so that the developing sleeve 8 is partially exposed in the direction of the photosensitive drum 10. It is installed. In the present embodiment, the developing sleeve 8 is disposed substantially parallel to the photosensitive drum 10 above the developing chamber 3. Therefore, the developer is supplied from the developing chamber 3 to the developing sleeve 8. Such a developing sleeve 8 supplies developer to the developing area F of the photosensitive drum 10 in the developing container 2 to develop the electrostatic latent image formed on the photosensitive drum 10. Further, according to the amount of toner used for development, toner (which may include a carrier or the like) is supplied from the toner supply tank 20 to the stirring chamber 4.

  The developing sleeve 8 is formed in a cylindrical shape with a nonmagnetic material in order to transport the developer to the developing region F as described above, and a cylindrical magnet 80 as a magnetic field means is installed in a non-rotating state inside the developing sleeve 8. Has been. The magnet 80 has a plurality of magnetic poles in the circumferential direction and magnetically attracts the developer to be carried on the surface of the developing sleeve 8. The developer carried on the surface of the developing sleeve 8 by the magnet 80 is conveyed while being carried by the rotation of the developing sleeve 8.

  The plurality of magnetic poles are formed by sequentially arranging magnetic poles N2, S2, S3, and N1 for conveying the developer from the developing pole S1 in the clockwise direction in FIG. Of these, a region (a repulsion pole, between the S2 and S3 poles) where the same-polarity magnetic poles are adjacent to each other is a stripping portion 81. The stripping portion 81 constitutes stripping means for stripping off the developer carried on the developing sleeve 8 by repelling the magnetic force because adjacent magnetic poles are the same pole. Due to this action, the developer present on the developing sleeve 8 is once carried and then peeled off by the stripping portion 81, so that the developing sleeve 8 is not brought along.

  Further, the ear cutting member 9 regulates the ears of the developer carried on the developing sleeve 8. The ear cutting member 9 is made of a nonmagnetic member such as aluminum, and is disposed upstream of the photosensitive drum 10 in the rotation direction of the developing sleeve 8. The developer (both non-magnetic toner and magnetic carrier) carried on the developing sleeve 8 passes between the tip of the ear cutting member 9 and the developing sleeve 8, thereby reducing the length of the developer ear. It is sent to the development area in a regulated state. Therefore, by adjusting the gap between the ear cutting member 9 and the surface of the developing sleeve 8, the amount of the developer magnetic brush carried on the developing sleeve 8 is regulated and the amount of developer conveyed to the developing region is reduced. Adjusted.

  Such a developing device 1 rotates the developing sleeve 8 in the direction of the arrow in the drawing and carries a two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the cutting member 9, The toner is conveyed to a development area facing the photosensitive drum 10. Then, a developer is supplied to the latent image formed on the photosensitive drum 10 to develop the latent image. At this time, in order to improve the developing efficiency (that is, the toner application rate to the latent image), a developing bias voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 8 from a power source.

[Distribution means]
In the case of this embodiment, the developer carried and transported to the developing sleeve 8 that has passed (exceeded) the development area without being used for development is peeled off by the distribution means 30, and the stirring chamber 4 and the development chamber 3. To be distributed and sent. For this purpose, the distribution means 30 is arranged at the position facing the above-described stripping portion 81 and the stripping portion 81, and a distribution member that sends a part of the developer stripped by the stripping portion to the stirring chamber 4. 31.

  Such a distribution member 31 is formed in a plate shape as shown in FIG. 4 and, as shown in FIG. 2, the developer chamber 3 moves from the developing chamber 3 to the photosensitive drum 10 with respect to the developer conveying direction (rotational direction). It is arranged so as to cover the developing chamber 3 upstream of the position where the developer is supplied. The length C of the distribution member 31 in the longitudinal direction (the direction along the developing sleeve 8) is the same as or slightly larger than the axial length of the magnet 80 disposed in the developing sleeve 8. Further, the width of the distribution member 31 is slightly smaller than the distance between the tip of the partition wall 7 and the peeling portion 81 of the developing sleeve 8. In addition, the distribution member 31 has one end (base end) in the width direction fixed to the tip of the partition wall 7 and is arranged from the tip of the partition wall 7 toward the stripping portion 81. Then, the other end portion (tip portion) in the width direction of the distribution member 31 comes close to the surface of the peeling portion 81 of the developing sleeve 8. The distribution member 31 may be formed integrally with the partition wall 7 or may be fixed to the partition wall 7 as a separate body.

  The distance between the distal end portion of the distribution member 31 and the developing sleeve 8 may be a distance such that most of the developer peeled off by the peeling portion 81 moves onto the distribution member 31. In other words, since the distance is such that the distribution member 31 and the developing sleeve 8 do not come into contact with each other, most of the developer removed by the peeling portion 81 does not pass through the gap between the distribution member 31 and the developing sleeve 8. It may be between about a certain distance. In the stripping portion 81, the developer is stripped by the repulsion pole. Therefore, if the gap between the distribution member 31 and the developing sleeve 8 is not very large, the stripped developer hardly passes through the gap. For this reason, in the present embodiment, it is not necessary to strictly regulate the distance between the distal end portion of the distribution member 31 and the developing sleeve 8.

  The distribution member 31 may be brought into contact with the developing sleeve 8 or may be brought into contact through a seal member. In this case, it is preferable to seal between the distribution member 31 and the developing sleeve 8 using, for example, a light pressure contact member such as a urethane sheet.

  Further, as shown in FIG. 4, the distribution member 31 has a plurality (three in the present embodiment) of openings 32 a, 32 b, and 32 c. As described above, since the distribution member 31 is disposed so as to cover the developing chamber 3, the upper portion (outside) of the distribution member 31 and the developing chamber 3 communicate with each other through the openings 32a, 32b, and 32c. Therefore, the developer peeled off from the developing sleeve 8 partially enters the agitating chamber 4 along the portions 33a, 33b, 33c, 33d removed from the openings 32a, 32b, 32c of the distribution member 31, and the rest opens 32a. , 32b, and 32c to the developing chamber 3, respectively.

  In other words, in the case of this embodiment, the developer peeled off from the developing sleeve 8 by the repulsive pole passes through the distribution member 31 after being peeled off, and basically returns to the stirring chamber 4. ing. However, a part of the developer that passes over the distribution member 31 passes through the openings 32 a, 32 b, and 32 c and returns to the developing chamber 3 without reaching the stirring chamber 4. This can be schematically represented as arrows a, b, c, and d in FIG. First, the developer is supplied from the developing chamber 3 to the developing sleeve 8 as indicated by a solid arrow a. Next, a part of the developer that has passed through the developing region and has been peeled off from the developing sleeve 8 is sent to the stirring chamber 4 along the portions 33a to 33d that are out of the opening, as indicated by solid arrows b and c. The remainder is sent to the developing chamber 3 through the openings 32a to 32c, as indicated by broken line arrows D.

  Here, the lengths of the openings 32a, 32b, and 32c in the longitudinal direction are A1, A2, and A3, respectively, and the total of these is A (= A1 + A2 + A3). Further, the lengths of the portions 33a, 33b, 33c, and 33d that are out of the openings are defined as B1, B2, B3, and B4, and the sum of these is B (= B1 + B2 + B3 + B4). The sum of A and B is the length C of the distribution member 31 in the longitudinal direction (C = A + B).

  The width E of each of the openings 32a to 32c is preferably 2/3 or less of D in order to ensure the rigidity of the distribution member 31 when the width of the distribution member 31 is D. On the other hand, the lower limit value of the width E only needs to have a width through which the developer can pass, and is preferably set to 1 mm or more, for example. Specifically, when the width D of the distribution member 31 is 15 mm, the width E is preferably 1 to 10 mm. In the case of this embodiment, the width E is set to 1/3 of the width D (E is 5 mm when D is 15 mm).

  In the case of this embodiment, among the developers peeled off from the developing sleeve 8, the developer amount per unit time sent to the stirring chamber 4 is larger than the developer amount per unit time sent to the developing chamber 3. There are also many. For this reason, the total length B of the portions 33a to 33d deviated from the opening is made larger than the total length A of the openings 32a to 32c (B> A). As a result, the amount of the developer that is peeled off from the developing sleeve 8 and moved onto the distribution member 31 through the portions 33a to 33d that are out of the opening into the stirring chamber 4 is the amount of the developer 32a to 32c. The amount of the developer sent to the developing chamber 3 through is increased. The ratio of A to B (A: B) is preferably 1: 1 to 1: 4. That is, A / C = 1/2 to 1/5 (C = A + B) is preferable.

  In the case of this embodiment configured as described above, the developer can be appropriately distributed and sent to the developing chamber 3 and the agitating chamber 4 by the distribution member 31. First, the developer carried on the developing sleeve 8 and peeled off by the peeling portion 81 moves onto the distribution member 31 and moves toward the stirring chamber 4 on the distribution member 31. Then, a part of the developer is sent to the stirring chamber 4 along the portions 33a to 33d that are out of the opening, and the rest is sent to the developing chamber 3 through the openings 32a to 32c. For this reason, even if the distance between the distribution member 31 and the developing sleeve 8 is not strictly regulated, the developing chamber 3 is only regulated by restricting the size relationship between the openings 32a to 32c and the portions 33a to 33d outside the opening. Thus, the relationship between the amount of developer sent to the developer and the amount of developer sent to the stirring chamber 4 can be appropriately regulated.

  As described above, if the developer can be properly distributed to the developing chamber 3 and the stirring chamber 4, the developer that has passed the developing region in the developing chamber 3 and consumed the toner frequently increases, resulting in uneven density of the output product. Can be reduced. At the same time, it is possible to reduce the amount of the developer that is excessively sent to the agitating chamber 4 and go downstream in the conveying direction of the developing chamber, and it is not necessary to increase the speed of the conveying screw. As a result, according to the present embodiment, the density unevenness of the output product can be reduced at low cost.

  In the case of the present embodiment, among the developer peeled off from the developing sleeve 8, the amount of developer per unit time sent to the stirring chamber 4 is calculated from the amount of developer per unit time sent to the developing chamber 3. Therefore, it is possible to further reduce the occurrence of density unevenness in the output product. That is, when the amount of the developer sent to the developing chamber 3 is larger, the developer that consumes a lot of toner (that is, the developer having a low toner concentration) increases in the developing chamber 3 and density unevenness is likely to occur. Become. On the other hand, if a large amount of developer is sent to the stirring chamber 4, the developer having a low toner concentration is sent to the developing chamber 3 after being stirred with a developer having a sufficient toner concentration in the stirring chamber 4. Unevenness can be reduced.

<Example 1>
Next, an experiment conducted for confirming the effect of the present embodiment will be described with reference to FIGS. FIG. 5 is a schematic diagram of the chart (1) and the chart (2) used for the study in this example. Chart (1) is a chart adjusted so as to have a dark halftone (image density of 1.2, measured by X-rite Model: 504), and solid patches were provided at five locations. Chart (2) is a solid image. Similarly to (1), the chart (2) also has five solid patch portions, but since it is the same as the background, it appears that there is nothing on the image.

  Compared to the chart (1), the image of the chart (2) has a higher printing rate and therefore consumes more toner. Therefore, the toner density unevenness inside the developing device 1 is a more severe test in the chart (2) in which the toner replacement is increased. When two types of charts (1) and (2) are examined and the results are compared, the image density unevenness due to the toner density unevenness in the developing device 1 is worse than the result of the chart (2) than the chart (1). It should be. For this reason, it is effective to examine the difference between the two types of charts when interpreting the examination result and determining whether or not there is an influence due to image density unevenness due to other factors. In other words, in the case where the result of examining the chart (1) shows better density unevenness than when the chart (2) is examined, the presence of unevenness other than the density unevenness due to the toner replacement described above. Can be doubted. On the other hand, if the result of the chart (2) is worse than the result of the chart (1) as expected, it can be considered that the image density unevenness due to the toner replacement is accurately extracted.

  In the experiment, with the configuration of the developing device 1 shown in this embodiment and the developing device shown in FIGS. 14 and 15, the chart (2) is continuously imaged in A3 size, and an image forming sample is obtained every 500 sheets. Was taken out, and the density of the five patch portions was measured. This concentration measurement was performed using Model: 504 manufactured by X-rite. The result of this experiment is shown in FIG. FIG. 6 is a graph showing the relationship between the number of formed images and the difference (in-plane density difference) Δ between the maximum and minimum densities of the five measured patches.

  14 and 15, the screw configurations of the developing chamber and the stirring chamber used in the present embodiment are unified in a spiral shape with a screw diameter of 20 mm, a shaft diameter of 8 mm, and a pitch of 25 mm. Also, the developer conditions were unified (weight ratio 8%, developer amount 400 g). Further, the screw rotation speeds of the developing chamber and the stirring chamber were 500 rpm in the configuration of FIG. 14, 900 rpm in the configuration of FIG. 15, and 650 rpm in the configuration of this embodiment. In addition, the minimum number of rotations was set for each screw so that the developer circulated from the stirring chamber through the developing chamber to the developing sleeve without delay.

  In the configuration of the present embodiment, the distribution member 31 has C = 300 mm, A: B = 1: 2 = 33 mm: 66 mm, and thickness 2 mm. The developing sleeve is unified in each configuration, and the outer diameter of the sleeve is 20 mm / linear velocity = photosensitive linear velocity × 2 (in this embodiment, the photosensitive linear velocity = 400 mm / s), and the length in the longitudinal direction is 300 mm. . Further, the amount of developer per unit area on the developing sleeve was 40 mg / cm 2, and examination was performed under conditions for high-speed image formation.

  The minimum screw rotation speed in the configuration shown in FIG. 14 is based on the premise that supply unevenness is not generated at least in the developing sleeve, and 500 rpm is an appropriate value. That is, when the speed is less than 500 rpm, the developer amount on the sleeve gradually becomes uneven. In other words, if the rotation speed is 500 rpm, at least uneven supply of the agent to the developing sleeve can be prevented, so that it is not necessary to increase the screw rotation speed further. On the other hand, the temperature rises from the end of the screw due to the increase in the number of rotations, and the heat spreads throughout the developing device using the developer circulating in the developing container as a medium, resulting in an increase in the temperature of the entire developing device. To trigger. When the developer temperature rises, the deterioration of the developer such as fluidity deterioration and toner spent on the carrier becomes remarkable, which is not preferable. For this reason, it is desirable to keep the screw speed as low as possible. In view of the above, in the configuration shown in FIG.

  As apparent from FIG. 6, in the configuration shown in FIG. 14, the occurrence of uneven density in the surface becomes more prominent as the image formation proceeds. At this time, if the in-plane density unevenness is 0.2 or less, it can be seen that the target value is interrupted by image formation of about 2500 sheets even though the variation in color for the solid image is at an acceptable level. On the other hand, in the configuration of FIG. 15 and the present embodiment, it can be seen that the in-plane density unevenness is suppressed to a target value or less even after 3000 images have been formed, and is excellent.

  Next, in the configuration of the present embodiment, the relationship between the total length A of the openings 32a to 32c of the distribution member 31 and the total length B of the portions 33a to 33d deviated from the openings and the in-plane density unevenness is examined. The experiment will be described. In this experiment, the ratio of A: B was changed, the number of rotations of the screw in the developing chamber and the stirring chamber was optimized for each ratio, and in-plane density unevenness was determined when images were continuously formed. Specifically, for each of the chart (1) and chart (2) shown in FIG. 5, the same examination as described above was performed, and in-plane density unevenness after 300 sheets were imaged was determined. This density | concentration was measured by Model-504 by X-rite. The result is shown in FIG. Further, FIG. 7 shows the ratio of A: B of a plurality of conditions and the rotation speeds of the screws respectively arranged in the developing chamber 3 and the stirring chamber 4 optimized for those conditions. In addition, the circles in FIG. 7 indicate that the density unevenness is within the allowable range, and the triangles indicate that the density unevenness is slightly out of the allowable range, but the level is practically no problem. Indicates that the density unevenness is a problem level.

  From FIG. 7, the higher the ratio of B of A: B, that is, the higher the ratio at which the agent peeled from the developing sleeve is returned to the stirring chamber 4, the more the chart (1) and the chart (2) were continuously imaged. It can be seen that the density unevenness that occurs at the time is difficult to occur. On the other hand, the number of rotations of the screw tends to increase in order to supply the developer onto the developing sleeve 8 without any problem. Further, chart (1) consumes less toner than chart (2), and toner density unevenness on the developing sleeve 8 is less likely to occur, so even if the ratio of A: B is 1: 1. There is no problem level. FIG. 7 also shows that when the A: B ratio is 1: 2, the screw rotation speed can be reduced to about 70% of the configuration of FIG. 15 while maintaining the same level of image performance as the configuration of FIG. .

  As described above, by providing a distribution member that distributes the developer on the developing sleeve after passing through the developing region to the developing chamber and the transport chamber, it becomes easy to always supply a uniform concentration of developer to the developing sleeve. It was. In addition, a uniform image without image unevenness (image unevenness caused by insufficient stirring) and density difference (density difference caused by insufficient stirring) in the screw conveyance direction (thrust direction) was obtained. Further, it is possible to minimize the strengthening of the developing chamber conveying force due to the increase in speed, and to provide a developing device with little apparatus deterioration and temperature rise.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIGS. In the case of this embodiment, the amount of developer per unit time peeled off from the developing sleeve 8 and sent to the developing chamber 3 is higher than the downstream in the conveying direction by the first conveying screw 5 (see FIG. 2) of the developing chamber 3. Is trying to be more. For this reason, the lengths of the openings 32a to 32c of the distribution member 31a are made smaller toward the upstream in the transport direction. That is, the openings 32a, 32b, and 32c are formed in order from the upstream, and when the lengths are A1, A2, and A3 in order, A1>A2> A3. In the present embodiment, among the portions 33a to 33d deviated from the openings, the lengths B1 and B4 of the portions 33a and 33d located at both ends in the transport direction are the same (B1 = B4), and between the openings. The lengths B2 and B3 of the positioned portions 33b and 33c are the same (B2 = B3). That is, the openings 32a, 32b, and 32c are equally arranged in the length direction.

  As a result, among the openings 32a, 32b, and 32c of the distribution member 31a, the amount of developer that passes through the opening in the upstream of the screw conveyance direction increases, so the amount of developer sent to the developing chamber 3 through the openings 32a to 32c. Is more upstream in the transport direction. FIG. 9 shows the developer flow in this embodiment.

  According to the present embodiment, it is possible to further reduce the occurrence of uneven density in the output product while securing the amount of developer sent to the developing chamber 3. That is, the developer having a lower toner concentration tends to be returned to the stirring chamber 4 as it goes downstream in the transport direction of the developing chamber 3. In the present embodiment, more developer is sent to the agitating chamber 4 on the downstream side where the toner concentration becomes lower, and more developer enters the developing chamber 3 on the upstream side where the toner concentration is not lowered. I am trying to send it. For this reason, a developer whose toner concentration is not low can be sent to the developing chamber 3, and the amount of developer in the developing chamber 3 can be secured by a developer that does not easily cause density unevenness, and the developer whose toner concentration is low is sent to the stirring chamber 4. After stirring in the stirring chamber 4, it can be sent to the developing chamber 3, and density unevenness can be further reduced.

  This will be described more specifically. In the conventional developing device shown in FIG. 14 described above, the developer in the developing chamber is conveyed while being repeatedly pumped up to the developing sleeve and taken in from the sleeve. It has a lot of history that has been pumped up by the sleeve and passed through the development area. Therefore, when an image with a large amount of toner consumption like the chart (2) used in Example 1 is flowed, the developer that has passed through the developing area consumes a large amount of toner for image formation and is returned to the developing chamber again. For this reason, there is a developer who has experienced a greater number of toner consumptions as the developing chamber becomes downstream. Therefore, toner density unevenness occurs upstream and downstream of the developing chamber, and as a result, in-plane density unevenness on the image is easily induced. On the other hand, with the same concept, the developer on the upstream side of the developing chamber has a smaller history of passing through the developing region than the downstream side, so that the decrease in toner density is relatively small compared to the downstream side of the developing chamber. Therefore, in this embodiment, the developer peeled off from the developing sleeve corresponding to the upstream side of the developing chamber, which has a relatively small toner density reduction, is preferentially returned to the developing chamber to prevent a decrease in the developer amount in the developing chamber. To do. On the other hand, the agent peeled off from the developing sleeve corresponding to the downstream side of the developing chamber where the toner density is significantly lowered is preferentially returned to the stirring chamber and stirred with new toner. Thereby, the occurrence of uneven toner density in the developing chamber can be prevented, and as a result, in-plane density unevenness on the image can be prevented, and the phenomenon of the developer in the developing chamber accompanying the increase in speed can be prevented.

  In the above description, the lengths of the openings 32a, 32b, and 32c are made different. However, the lengths of these openings are the same (A1 = A2 = A3), and the portions 33b and 33c located between the openings are used. The lengths B2 and B3 may be different. That is, the length B2 of the portion 33b located upstream in the transport direction is made smaller than the length B3 of the portion 33c also located downstream (B2 <B3). As a result, the interval between the openings 32a and 32b is reduced upstream in the screw conveyance direction of the distribution member 31, and the interval between the openings 32b and 32c is increased downstream in the conveyance direction, so that the development sent to the developing chamber 3 through the openings 32a to 32c. The amount of the agent is greater upstream in the transport direction.

  Further, in the present embodiment, the number of openings that lead to the developing chamber 3 of the distribution member 31 is three, but the number of openings can be more than three, or one or two. You can also When one opening or two openings of the same length are used, the position of the opening is biased upstream in the transport direction, and the amount of developer sent to the developing chamber 3 through the opening is set upstream in the transport direction. To be more. In short, if the amount of developer sent to the developing chamber 3 is increased upstream in the transport direction, the relationship between the number of openings, the length of each opening, and the length of the portion outside each opening can be set as appropriate. Other structures and operations are the same as those in the first embodiment.

<Example 2>
FIG. 10 shows the result of examination in this example. In this embodiment, the configuration of Example 1 and the configuration of Example 2 are used with the screw rotation speed of the developing chamber and the stirring chamber as a parameter, and the chart (2) shown in Example 1 is made with 3000 sheets of A3 size paper. In-plane density unevenness after imaging was examined. This density | concentration was measured by Model-504 by X-rite. FIG. 10 shows the determination result of the in-plane density unevenness measured in this way. Note that C = 300 mm and A: B = 1: 2, and each aperture is set as A1 = A2 = A3 = 33 mm in Example 1, A1 = 60 mm, A2 = 30 mm, and A3 = 10 mm in Example 2. Were arranged almost evenly in the longitudinal direction. Other conditions are the same as in the first embodiment. Further, the meanings of the circle, triangle, and cross marks in FIG. 10 are the same as those in FIG.

  According to FIG. 10, in the configuration of Example 1, the in-plane density unevenness gradually deteriorates when the screw rotation speed becomes less than 650 rpm, whereas in the configuration of Example 2, the in-plane density even at 600 rpm. Unevenness is a problem. This is considered to be because density unevenness was prevented as a result by increasing the ratio of returning the developer on the developing sleeve corresponding to the downstream side of the developing chamber that most induces in-plane density unevenness to the stirring chamber. By adopting the configuration of Example 2, it was possible to further reduce the number of rotations of the conveying screw at 50 rpm compared to Example 1.

<Third Embodiment>
A second embodiment of the present invention will be described with reference to FIGS. Also in this embodiment, as in each of the above-described embodiments, the distribution member 31b is moved from the developing chamber 3 to the photosensitive drum 10 (see FIGS. 1 and 2) with respect to the developer transport direction (rotation direction) by the developing sleeve 8. It is arranged upstream of the position where the developer is supplied to. However, in this embodiment, the distribution member 31b is made shorter than the distribution member of each of the above-described embodiments as shown in FIG. 11, and as shown in FIG. 12, the first conveying screw 5 ( It is configured so as to cover a part of the transport direction (a part of the first chamber) according to FIG. That is, in each of the above-described embodiments, the length C of the distribution member is the same as or slightly larger than the axial length of the magnet 80 disposed in the developing sleeve 8, but in this embodiment, the distribution member The length C ′ of 31 b is shorter than the length of the magnet 80. Specifically, the length C ′ of the distribution member 31 b is half the length of the magnet 80. This length can be set as appropriate.

  Further, the installation position of the distribution member 31b is downstream in the conveyance direction of the developing chamber 3 by the conveyance screw 5. In the present embodiment, the half on the downstream side in the transport direction of the developing chamber 3 is covered with the distribution member 31b, and the half on the upstream side is open. In the present embodiment, the developer is conveyed as shown by arrows in FIG. That is, a part of the developer peeled off from the developing sleeve 8 is sent to the agitating chamber 4 along the distributing member 31b, and the remaining part is sent to the developing chamber 3 through a portion removed from the distributing member 31b. In other words, the distribution member 31b conveys a part of the developing sleeve 8 in the axial direction to the developing chamber 3 out of the developer that has passed through the developing region with the developer on the developer carrying member (on the developing sleeve 8). The remaining developer is distributed to the stirring chamber 4. In particular, in the case of this embodiment, since the distribution member 31b is arranged so as to cover the half part on the downstream side of the developing chamber 3, the developer per unit time peeled off from the developing sleeve 8 and sent to the developing chamber 3 The amount is higher upstream than the downstream of the developing chamber 3 in the transport direction. In the case of this embodiment as well, the distribution member 31b and the stripping portion constitute a distribution means.

  In the case of this embodiment, by arranging the distribution member 31b so as to cover the half on the downstream side of the developing chamber 3, the same effect as the second embodiment can be obtained with a simple configuration. . That is, in the case of the present embodiment, it is not necessary to provide an opening as in the distribution member of each of the above-described embodiments, so that the distribution member 31b can have a simple configuration. Further, by disposing the distribution member 31b as described above, the developer peeled off from the developing sleeve 8 can be distributed and sent to the stirring chamber 4 and the developing chamber 3. Similar effects can be obtained at a lower cost. Other structures and operations are the same as those in the first embodiment or the second embodiment described above.

  From each of the embodiments described above, the ratio of distributing the stripped developer to the developing chamber and the stirring chamber is the ratio of the length of the opening provided in the distributing member and the portion outside the opening, or the distribution member Depends on the length. Therefore, there is no major factor that affects the distribution ratio other than the component accuracy of the distribution member. On the other hand, considering the accuracy of the mold when mass-producing mold parts, the dimensional tolerances for each part are very small if they are parts from the same mold. Therefore, the present invention has the advantage that the latitude is very wide and the cost of adjustment and the like is not required as compared with a configuration in which the distribution ratio is determined by managing and adjusting the gap, for example.

<Other embodiments>
In each of the above-described embodiments, the case where the present invention is applied to a structure in which a developing chamber and a stirring chamber are arranged side by side in a direction intersecting the direction of gravity has been described as a developing device. However, the present invention is not limited to such a structure, and can also be applied to a structure in which a developing chamber and a stirring chamber are arranged side by side in the direction of gravity as shown in FIG. In this case, for example, the distribution member is disposed so as to cover the stirring chamber, and an opening is provided in the distribution member, or the length of the distribution member is shortened. As a result, a part of the developer peeled off from the developing sleeve is sent to the stirring chamber through the opening of the distributing member or the part removed from the distributing member, and the rest is sent to the developing chamber through the distributing member.

  As described above, according to the present invention, the developer stripped from the developing sleeve is agitated by appropriately setting the length and installation position of the distribution member or the position and size of the opening formed in the distribution member. It is characterized by being distributed to the chamber and the developing chamber. Therefore, the distribution means referred to in the present invention is a total of such relationships as the length of the distribution member.

  Further, in each of the above-described embodiments, the distribution member is disposed at a position facing the peeling portion 81 of the developing sleeve 8, but the position of the distribution member is not limited to this position. For example, the distribution member may be brought into contact with the position removed from the peeling portion 81 of the developing sleeve 8 so that the developer carried on the surface of the developing sleeve 8 is peeled off. That is, the stripping means is constituted by the tip of the distribution member. In this case, the magnetic attraction force may be weakened at the position where the distribution member abuts, for example, by not providing a magnetic pole. In any case, by providing an opening in the distribution member as in the first or second embodiment, the developer peeled off by the distribution member is distributed to the developing chamber and the agitation chamber by the distribution member.

  Further, as in the third embodiment, a short distribution member is used, and this distribution member is disposed in contact with a part of the developing sleeve in the axial direction, so that it is supported on a part of the developing sleeve in the axial direction. The developed developer may be peeled off. In this case, the distribution member functions as a contact / separation member. That is, a part of the developer carried and transported to the developing sleeve beyond the developing region and peeled off from the developing sleeve by the contact separation member (distribution member) is part of the developing chamber or the stirring chamber along the contact separation member. Sent to one of the rooms. On the other hand, the remainder of the developer carried and transported to the developing sleeve is sent to the other chamber through a portion removed from the contact separation member, and is stripped off by, for example, a stripping portion.

  In this way, even when the contact separating member is brought into contact with the developing sleeve and the developer is peeled off, it is not necessary to strictly regulate the gap between the contacting and separating member and the developing sleeve, and the cost can be reduced. Further, such a configuration is the same as the above-described configuration in which the developer peeled off by the stripping unit 81 is distributed, except that the method for stripping off the developer is different.

  DESCRIPTION OF SYMBOLS 1 ... Developing device, 2 ... Developing container, 3 ... Developing chamber, 4 ... Stirring chamber, 5 ... 1st conveyance screw (conveyance member), 6 ... 2nd conveyance Screw (conveying member), 7 ... partition wall, 8 ... developing sleeve (developer carrier), 10 ... photosensitive drum (image carrier), 30 ... separating means, 31, 31a, 31b ..Separating members, 32a, 32b, 32c ... openings, 33a, 33b, 33c, 33d ... parts removed from the openings, 80 ... magnets, 81 ... peeling parts

Claims (7)

A developer carrying member that carries and conveys a developer containing toner and a carrier, and supplies the developer to the development region of the image carrier;
A first chamber for supplying a developer to the developer carrier;
A second chamber forming a circulation path with the first chamber;
A conveying means provided in the first chamber along a direction in which the developer carrying member is disposed , and conveying the developer in the circulation path;
Distributing means for stripping off the developer that has passed through the development area from among the developer carried and transported by the developer carrier, and distributing the stripped developer to the first chamber and the second chamber; ,
I have a,
The developing device characterized in that the amount of developer per unit time peeled off from the developer carrying member and sent to the first chamber is higher in the upstream than in the transport direction downstream by the transport means . Of the developer peeled off from the developer carrier, the developer amount per unit time sent to the second chamber is larger than the developer amount per unit time sent to the first chamber.
The developing device according to claim 1, wherein: The developer carrying member has a cylindrical developing sleeve and a developing sleeve that is disposed inside the developing sleeve and has a plurality of magnetic poles in a circumferential direction to attract the developer magnetically so as to surface the developing sleeve. A magnet to be carried on the magnet, a magnetic pole of the same polarity arranged adjacent to a part of the magnet in the circumferential direction, and a peeling portion for peeling off the developer carried on the developing sleeve from the developing sleeve; Have
The distribution means is disposed at a position facing the stripping section and the stripping section, and distributes a part of the developer stripped by the stripping section to the first chamber or the second chamber. A member,
The developing device according to claim 1, wherein The first chamber and the second chamber are arranged side by side in a direction intersecting the direction of gravity,
The distribution member is disposed so as to cover the first chamber upstream of a position where the developer is supplied from the first chamber to the image carrier in the transport direction of the developer by the developer carrier. An opening communicating with the first chamber;
Part of the developer peeled off from the developer carrying member is sent to the second chamber along the part of the distribution member that is off the opening, and the rest is sent to the first chamber through the opening. ,
The developing device according to claim 3 , wherein: The first chamber and the second chamber are arranged side by side in a direction intersecting the direction of gravity,
The distribution member covers a part of the first chamber upstream of a position where the developer is supplied from the first chamber to the image carrier with respect to a developer transport direction by the developer carrier. Configured,
Part of the developer peeled off from the developer carrying member is sent to the second chamber along the distribution member, and the other part is sent to the first chamber through a portion removed from the distribution member.
The developing device according to claim 3 , wherein: A developer carrying member that carries and conveys a developer containing toner and a carrier, and supplies the developer to the development region of the image carrier;
A first chamber for supplying a developer to the developer carrier;
A second chamber forming a circulation path with the first chamber;
A conveying means provided in the first chamber along a direction in which the developer carrying member is disposed , and conveying the developer in the circulation path;
Of the developer that has passed through the development area with the developer on the developer carrier, a part of the developer carrier in the axial direction is transported to the first chamber, and the remaining developer is transferred to the second chamber. possess a distribution means for distributing to the chamber, the,
The developing device characterized in that the amount of developer per unit time peeled off from the developer carrying member and sent to the first chamber is higher in the upstream than in the transport direction downstream by the transport means . In an image forming apparatus comprising: an image carrier; and a developing device that develops an electrostatic latent image formed on the image carrier.
The developing device is the developing device according to any one of claims 1 to 6 .
An image forming apparatus.

Images