JP2007017904A - Developing unit, process cartridge, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in an image forming device that uses a two-component developer, wherein processing cartridges are commonly used even in a small developing unit for agitating the toner with magnetic carriers to statically charge the toner insufficiently resulting in the stained surface of the transfer paper, then conventionally for this reason the toner is statically charged by the friction in the developer near the developer regulating blade receiving a large load to the toner in the developer reservoir thus degrading the developer. <P>SOLUTION: Agitating screws 66, 67 are provided respectively in the agitating chamber 86, close to the toner replenishing hole and in the agitating chamber 87 close to the developing sleeve 68. The two-component developer circulates through both agitating chambers, connected to each other at their ends. The developer is compressed and quickly static charged, by providing a stagnation path to delay its flow, during the time it is making a single round in the developer container 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus using a two-component developer.

In recent years, along with demands for downsizing and personalization of image forming apparatuses using electrophotographic technology such as copying machines and printers, downsizing of developing devices has been attempted. Further, in response to such a request, when the toner runs out, the disposable developing device that is replaced with the developing device, or a latent image carrier (on which an electrostatic latent image of the original image is formed) in addition to the developing device. A so-called process cartridge in which a photosensitive member) and a cleaning unit that removes toner remaining on the photosensitive member are integrated is also widely used.
However, such a miniaturized developing device has a small amount of developer containing the toner and the magnetic carrier. In addition, since the space for the developer agitation unit is also inevitably reduced, the time required for the replenished toner to reach the development area is short, and the agitation between the toner and the magnetic carrier becomes insufficient, resulting in a charge amount of the toner. Becomes smaller, and floating toner is likely to be generated. When floating toner is generated, the background of the transfer paper becomes very dirty, which is not preferable. Such a phenomenon occurs remarkably when the amount of toner replenishment increases, such as when the amount of toner replenishment increases, as in the case of continuously printing a document with a high image area ratio.
In addition, as the machine speed increases, the developer agitating / conveying member rotates at high speed, and the toner is 3 to 12 μm fine particles, so a part of the replenished toner is scattered without being well agitated with the developer. , Float or move on the developer surface. When such toner is transported to the development roller and transported to the development area, uncharged, reversely charged, and weakly charged poorly charged toner may cause non-image area background contamination, density unevenness, or toner scattering. Arise.

In order to solve such a problem, a scattering prevention member that prevents the toner replenished from the toner replenishing portion from sliding on the surface of the agent and being conveyed to the screw portion on the developing roller side without being charged is provided. It has been proposed (see, for example, Patent Document 1).
However, these means emphasize the uniform dispersion of the toner among the two conditions that must be satisfied before the toner is transported to the developing unit. In other words, the screw portion is provided with a function to uniformly distribute the replenishment toner to the developer, and the toner charging is covered by the rubbing of the developer in the vicinity of the developer regulating blade as before. In such a development system, there is a problem in that the toner is subjected to a large load in the developer reservoir on the back side of the developer regulating blade and the developer deteriorates. Deteriorated toner tends to be weakly charged / reversely charged toner, and after a long-time image forming process, the charge amount distribution is broadened, leading to background contamination and toner scattering. However, if the stress on the back of the developer regulating blade is easily reduced, insufficient charging of the toner may occur, and on the contrary, background stains and toner scattering may increase.

  In addition, it has been proposed to increase the charge amount by operating the agent passage amount regulating member in the developing device so as to approach the developing roller (see, for example, Patent Document 2). However, in this configuration, although the rubbing force applied to the agent is increased, the location where the agent is regulated is in the vicinity of the doctor blade. There is also a concern that density unevenness may occur.

JP-A-9-106161 JP-A-11-202573

In view of the above problems, the present invention can prevent the replenished toner from reaching the developing sleeve directly in a low-charged or uncharged state, and when the image forming process is repeated over a long period of time, or consumes less toner. It is an object of the present invention to provide a developing device and an image forming apparatus in which the developer is hardly deteriorated even in a special use state for a long period of time and there is no background contamination or toner scattering over a long period of time.
The basic idea is that the charging function of the toner is shared by the agitating / conveying screw, thereby reducing the burden on the developer as a whole of the developing device and extending the life of the developer.

According to the first aspect of the present invention, the two-component developer having toner particles and carrier particles is stirred and dispersed by two rotatable screws disposed in the developer container and conveyed to a predetermined position. And a toner supply means for replenishing toner consumed by development, the developer storage portion on the side where the toner is stored is a supply side agitation chamber and faces the developer carrier. When the developer accommodating portion on the side is a development side stirring chamber, the average advection speed at which the developer makes a round in the developer container is Vverage, and the local advection speed at which the developer moves in the developer container is Vlocal.
0.6 <Vlocal / Vaverage <0.9
A delay path satisfying the above relationship exists in the developing container.
According to a second aspect of the present invention, in the developing device according to the first aspect, the delay path occupies 10 to 50% of the entire conveyance path in the developer developing apparatus.

According to a third aspect of the present invention, in the developing device according to the first or second aspect, the delay path exists in the supply side stirring chamber.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the replenishment path includes an opening for passing the developer to the developing side stirring chamber. It exists in the developer conveyance direction downstream of a side stirring chamber, It is characterized by the above-mentioned.

According to a fifth aspect of the present invention, in the developing device according to the first aspect, by locally changing the screw pitch of the screw, the local advection speed Vlocal where the developer moves in the developing container is
0.6 <Vlocal / Vaverage <0.9
It is characterized by changing so as to satisfy the relationship.
According to a sixth aspect of the present invention, in the developing device according to the first aspect, the local advection speed Vlocal where the developer moves in the developing container is changed by locally changing the thickness of the shaft portion of the screw. ,
0.6 <Vlocal / Vaverage <0.9
It is characterized by changing so as to satisfy the relationship.

According to a seventh aspect of the present invention, in the developing device according to the first aspect, the local advection speed Vlocal where the developer moves in the developing container by locally changing the number of blades constituting the screw. 0.6 <Vlocal / Vaverage <0.9
It is characterized by changing so as to satisfy the relationship.
According to an eighth aspect of the present invention, in the developing device according to any one of the first to seventh aspects, the dynamic torque when the developer carrier alone is driven is Tsleeve, and the dynamic torque when the entire developing device is driven is Tall. When
0.4 <Tsleeve / Tall <0.7
It is characterized by satisfying the relationship.
According to a ninth aspect of the present invention, the developing device according to any one of the first to eighth aspects and at least two of the latent image carrier, the charging device, and the latent image carrier cleaning device are integrated. The process cartridge is characterized.
According to a tenth aspect of the present invention, there is provided an image forming apparatus for recording an image formed by a series of image processes on a recording medium, wherein the image forming apparatus includes the developing device according to any one of the first to ninth aspects. Features the device.

According to the present invention, when the average advection speed in which the developer makes one round in the developer container is Vaverage, and the local advection speed in which the developer moves in the developer container is Vlocal,
0.6 <Vlocal / Vaverage <0.9
By satisfying the above relationship, the developer stays at a location where the advection speed is slow, and the developer is brought into a compacted state, and there is an effect of promoting the charge rising.
When printing is performed in a state satisfying this relationship, good image formation without toner scattering and background stains can be performed.

FIG. 1 is an internal configuration diagram of a color image forming apparatus to which a developing device according to an embodiment of the present invention is applied.
In the figure, reference numeral 100 is a copying apparatus main body, 200 is a paper feed table on which the copying apparatus main body 100 is placed, 300 is a scanner (reading optical system) mounted on the copying apparatus main body 100, and 400 is an automatic document feeder (400) further mounted thereon. ADF) is shown respectively. Other symbols are directly cited in the detailed description.
Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. The image forming apparatus shown in the figure is specifically a tandem indirect transfer type electrophotographic copying apparatus. An endless belt-like intermediate transfer member 10 extending in the lateral direction is provided at the center position of the copying apparatus main body 100. In the illustrated example, the intermediate transfer member is wound around three support rollers 14, 15, and 16 so as to be able to rotate and convey clockwise in the drawing. In this illustrated example, an intermediate transfer body cleaning device 17 that removes residual toner remaining on the intermediate transfer body 10 after image transfer is provided to the left of the second support roller 15 among the three support rollers. Further, among the three support rollers, the intermediate transfer member 10 stretched between the first support roller 14 and the second support roller 15 has black, yellow, magenta, and cyan along the transport direction. The tandem image forming unit 20 is configured by arranging the four image forming units 18 side by side. An exposure device 21 is further provided immediately above the tandem image forming unit 20 as shown in FIG. On the other hand, a secondary transfer device 22 is provided on the opposite side of the intermediate transfer body 10 from the tandem image forming unit 20. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer body 10 is transferred to a sheet. A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt. The secondary transfer device 22 described above also has a sheet transport function for transporting the image-transferred sheet to the fixing device 25. In the illustrated example, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet is provided below the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming unit 20 described above. Is provided.

    Now, when making a copy using this color electrophotographic apparatus, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. When a start switch (not shown) is pressed, when a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. Immediately, the scanner 300 is driven, and the first traveling body 33 and the second traveling body 34 travel. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read. When a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 is rotationally driven by a drive motor (not shown), and the other two support rollers are driven to rotate, so that the intermediate transfer body 10 is moved. Rotate and convey. At the same time, the individual image forming means 18 rotates the photoconductors 40 to form black, yellow, magenta, and cyan monochrome images on the photoconductors 40, respectively.

  Along with the conveyance of the intermediate transfer member 10, these single color images are sequentially transferred to form a composite color image on the intermediate transfer member 10. On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43, thereby separating rollers 45. Are separated one by one into the paper feed path 46, conveyed by the conveyance roller 47, guided to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer member 10, the sheet is fed between the intermediate transfer member 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. A color image is recorded on the sheet. The image-transferred sheet is conveyed by the secondary transfer device 22 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transferred image. Are discharged and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56. On the other hand, the intermediate transfer body 10 after the image transfer is removed by the intermediate transfer body cleaning device 17 to remove residual toner remaining on the intermediate transfer body 10 after the image transfer, so that the tandem image forming unit 20 can prepare for another image formation.

FIG. 2 is a view showing an embodiment of a developing device used in the image forming apparatus.
In the figure, reference numeral 61 denotes a developing device, 65 denotes a developer container, 66 denotes a toner replenishing side stirring screw, 67 denotes a developer carrying member side stirring screw, 68 denotes a developer carrying member (developing roller), 75 denotes a toner density sensor, Reference numeral 77 denotes a doctor blade, 86 denotes a supply side stirring chamber, and 87 denotes a development side stirring chamber.
FIG. 3 is a longitudinal sectional view of the developing device.
In the figure, reference numeral 78 denotes a developer passage amount regulating member, and 80 denotes a threshold plate.
In the tandem image forming unit 20 described above, each image forming unit 18 includes a charging device, a developing device, a primary transfer device, a photoconductor cleaning device, a static elimination device, and the like around a drum-shaped photoconductor 40. .
The developing device 61 includes a developer supply-side stirring screw 66 as a developer stirring / conveying means, a developer carrier-side stirring screw 67, and a developer carrier (developing roller) 68 in a developer container 65. A supply port (not shown) is provided on the outer wall of the container of the first developer stirring chamber 86, and toner is supplied from a toner supply device (not shown). (Hereinafter, the first developer stirring chamber is referred to as a replenishing side stirring chamber.) The toner replenishing side agitating screw 66 includes the toner replenished from the toner replenishing device and the developer (magnetic particles and toner in the developer container 65). And a two-component developer). Further, the stirring screw 67 in the second developer stirring chamber 87 (on the developer carrying member side) stirs and conveys the developer in the developer container 65. (Hereinafter, the second developer stirring chamber is referred to as a developing side stirring chamber.)
As shown in FIG. 3, the replenishment side stirring chamber and the development side stirring chamber are partitioned by a partition plate 80, and there are openings for delivering the developer at both ends.

FIG. 4 is a diagram showing another embodiment of the present invention.
FIG. 5 is a diagram showing a temporal change in toner density at a certain position.
FIG. 6 is a schematic diagram for explaining the developer advection speed.
FIG. 7 is a diagram showing experimental results. FIG. 4A shows the result of the comparative example, and FIG. 4B shows the result of the present example.
In this example, an experiment was performed under the condition of a toner concentration of 7 wt% using a carrier having a volume average particle diameter of 35 μm and a toner having a particle diameter of 6 μm. First, a method for measuring the developer advection speed will be described. As shown in FIGS. 3 and 4, the developing device used in the experiment is provided with a plurality of toner concentration sensors 75 in the replenishing side stirring chamber and the developing side stirring chamber. When the time transition of each toner density sensor output when a certain amount of toner is replenished and stirred, the time transition of the toner density at a certain position is obtained as schematically shown in FIG. The advection speed of the velocity component (waveform peak position) is obtained. This is defined as an average advection velocity Average.
The average advection speed V2 when the developer makes one round in the developing device is obtained by dividing the transport path length by the time from the first round to the second round peak.

On the other hand, the local advection velocity Vlocal is obtained from the time difference between waveform peaks of adjacent toner density sensors and the distance between the sensors.
In this example, the experiment was conducted by changing the screw pitch of the 50% downstream side of the replenishment side stirring chamber (25% with respect to the total developer transport path) to 12.5 mm (the screw pitch of the other part was 37 mm). went. At this time, the local advection speed in the developing unit is as shown in FIG. 6, and when the advection speed ratio Vlocal / Vaverage was measured under these conditions, it was 0.72. The behavior of the developer under these conditions will be described. Since the developer advancing speed is locally slow in the vicinity of the opening where the developer with the screw pitch shortened is delivered, the developer moves to the ceiling of the developer unit. The developer is in a compacted state. In the portion where the advection speed is slow, the developer stays, and the developer is brought into a compacted state, which has the effect of promoting the charge rising. An area in such a state in the transport path is referred to as a delay path.
When an appropriate value of the advection speed ratio Vlocal / Vaverage was examined, it was as follows.
0.6 <Vlocal / Vaverage <0.9
If this ratio exceeds the upper limit, the developer will not be in a compacted state, and the effect of promoting charge rise will not appear. On the other hand, if the lower limit is exceeded, the stress applied to the developer becomes excessive, resulting in an increase in the stirring torque of the developing device and toner deterioration, which is not appropriate.

  Next, a method for examining the charge rising property of the toner under the conditions of this embodiment will be described. 1 g of replenishment toner is replenished to the most upstream part of the replenishment side stirring chamber. The screw is rotated at a predetermined speed, and the charge amount distribution of the developer at the most downstream side of the developing side stirring chamber is measured at the time when the peak of the replenished toner makes a round of the developing device. The result is shown in FIG. This graph is measured with a simple stirring device (supply side stirring device, development side stirring device, screw) after removing the developing roller and doctor blade from the developer unit in order to verify the effect of improving the developer path. It is the result. The effect of improving the developer path portion is clear, and it can be confirmed that the charge rising is promoted and the amount of uncharged toner is small. Next, this condition was carried out in an actual developing unit, and a printing test was conducted. As a result, even under strict toner replenishment conditions (during solid image development), the replenished toner is sufficiently dispersed and charged before reaching the developing side stirring chamber, and good image formation with no background contamination or toner scattering is achieved. Was done.

In the present example, the same developer was used as in Example 1 except for the screw in the replenishment side stirring chamber, and the experiment was performed with the shaft diameter of the 50% downstream portion of the replenishment side stirring chamber being increased. Since the developer storage volume is reduced in the portion where the shaft diameter is increased, as a result, the developer is in a compacted state, and the rise of charging can be promoted. This area is a delay path.
With the configuration of this example, it was possible to perform good image formation without toner scattering and background stains.

In this example, the same developer is used as in Example 1 except for the screw in the replenishment side agitation chamber, and the experiment was performed with 3 threads (the other part is 2) in the 50% downstream side of the replenishment side agitation chamber. It was. By setting the number to three, the developer advancing speed becomes slow, and as a result, the developer becomes a compacted state, and it is possible to accelerate the charge rising. This area is a delay path. .
With the configuration of this example, it was possible to perform good image formation without toner scattering and background stains.
In these embodiments, since the developer before being supplied to the developing roller after being replenished with toner can be brought into a compacted state, the rise of charging can be promoted more reliably. Further, by slowing the advection speed on the downstream side of the replenishing side stirring chamber, it is possible to make it less susceptible to the effect of toner upslip during toner replenishment.

In this embodiment, the experiment is performed with a dynamic torque of 100 kgf when the developer carrier alone is driven and a dynamic torque of 200 kgf when the entire developing device is driven. In the configuration of the present invention, the developer is charged when the developer is supplied to the developing roller and regulated by the doctor and at the compacted portion before being supplied to the roller. Since the stress on the developer during doctor regulation is very high, it is desirable to reduce the stress on the doctor part as much as possible.
When the dynamic torque when driving the developer carrier alone is Tsleeve, and the dynamic torque when driving the entire developing device is Tall,
0.4 <Tsleeve / Tall <0.7
There is an optimum value that achieves both stress and electrostatic start-up characteristics within the range of.
0.4> Tsleeve / Tall
In such a case, it is not possible to sufficiently start up the charge only by promoting the charge start-up at the compacted part.
Tsleeve / Tall> 0.7
In this case, an excessive stress is applied to the start-up of the charge, and the deterioration of the developer is accelerated.

1 is an internal configuration diagram of a color image forming apparatus to which a developing device according to an embodiment of the present invention is applied. It is a figure which shows one Embodiment of the image development apparatus used for the said image forming apparatus. It is longitudinal direction sectional drawing of a developing device. It is a figure which shows other embodiment of this invention. It is a figure which shows the time change of the toner density in a certain position. It is a schematic diagram for demonstrating the advection speed of a developing agent. It is a figure which shows an experimental result.

Explanation of symbols

66, 67 Agitating screw 75 Toner density sensor 78 Developer passage amount regulating member 80 Partition plate 86 Supply side agitating chamber 87 Developing side agitating chamber

Claims (10)

Agitating means for agitating and dispersing a two-component developer having toner particles and carrier particles with two rotatable screws disposed in a developer container and transporting them to a predetermined position, and toner consumed by development In the developing device having at least toner replenishing means for replenishing the toner, the developer accommodating portion on the side where the toner is accommodated is a replenishing side stirring chamber, and the developer accommodating portion on the side facing the developer carrying member is the developing side When the average advection speed at which the developer makes one round in the developing container is Vaverage and the local advection speed at which the developer moves within the developing container is Vlocal,
0.6 <Vlocal / Vaverage <0.9
A developing apparatus characterized in that a delay path satisfying the above relationship exists in the developing container.   2. The developing device according to claim 1, wherein the delay path occupies 10 to 50% of the entire conveyance path in the developer developing apparatus.   3. The developing device according to claim 1, wherein the delay path exists in a replenishment side stirring chamber. 4.   4. The developing device according to claim 1, wherein the delay path includes an opening that delivers the developer to the developing side stirring chamber, and is downstream of the replenishing side stirring chamber in the developer transport direction. A developing device that exists on the side. The developing device according to claim 1, wherein a local advection speed Vlocal where the developer moves in the developing container is changed by locally changing a screw pitch of the screw.
0.6 <Vlocal / Vaverage <0.9
The developing device is changed so as to satisfy the above relationship. In the developing device according to claim 1, by locally changing the thickness of the shaft portion of the screw, the local advection speed Vlocal where the developer moves in the developing container is
0.6 <Vlocal / Vaverage <0.9
The developing device is changed so as to satisfy the above relationship. 2. The developing device according to claim 1, wherein the local advection speed Vlocal at which the developer moves in the developing container is 0.6 <Vlocal / Vaverage <by changing locally the number of blades constituting the screw. 0.9
The developing device is changed so as to satisfy the above relationship. In the developing device according to any one of claims 1 to 7, when the dynamic torque when driving the developer carrier alone is Tsleeve, and the dynamic torque when driving the entire developing device is Tall,
0.4 <Tsleeve / Tall <0.7
A developing device satisfying the relationship:   9. A process cartridge comprising: the developing device according to claim 1; and at least two of a latent image carrier, a charging device, and a latent image carrier cleaning device.   An image forming apparatus for recording an image formed by a series of image processes on a recording medium, comprising the developing device according to claim 1.

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