JP2008122428A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device of a non-contact development system suitable to color superposition on a photoconductor, which can stably supply toner to a latent image and does not occure background contamination, and to provide a process cartridge and image forming apparatus. <P>SOLUTION: The developing device 61 includes: a toner replenishing opening 92 for replenishing with toner consumed by development; a developer storage part 100 storing two-component developer composed of toner and carrier; an agitating and charging means for agitating and charging the developer in the developer storage part 100; and a developer bearer 69 for bearing the developer by a magnetic force and conveying the developer to an area opposite an electrostatic toner bearing roller. The process cartridge and an image forming apparatus have this developing device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like. Specifically, the electrostatic toner is conveyed by rotating and moving the surface itself while floating the toner on the roller surface with respect to the surface by electrostatic force. The present invention relates to a developing device using a carrying roller.
The present invention also relates to a process cartridge having a developing device and an image forming apparatus.

Conventionally, there are known image forming apparatuses such as copying machines, facsimile machines, and printers described in Patent Document 1 and Patent Document 2. In these image forming apparatuses, the toner carried on the developer carrying member such as a developer carrying roller that moves on the surface is transported to a developing position that is opposite to the latent image carrying member such as a photosensitive member to carry the latent image. Develop an electrostatic latent image on the body. In such a configuration, the toner rubs between the developer carrying member whose surface moves and the latent image carrying member, and adheres to one of the surfaces, which may adversely affect the image. In addition, in an apparatus for forming a full-color image, considering a configuration in which toners of a plurality of colors are continuously developed on one photoconductor, the magnetic brush is in contact with the photoconductor for development. The toner image is disturbed by scavenging, and other color toners scraped by the magnetic brush are mixed into the developing unit. Therefore, a tandem configuration in which a photoconductor is provided for each color is required, or in the case of one photoconductor, the toner of the next color is transferred after being transferred to an intermediate transfer belt or the like for each color and cleaned. A configuration such as development is required, causing problems such as an increase in the number of parts and an increase in image formation time. Therefore, in order to develop the next color toner without disturbing the already developed toner image on the photoreceptor, it has been desired that the surface of the photoreceptor and the developing unit of the developing device are not in contact with each other.

In addition, if a normal two-component magnetic brush is merely brought into non-contact with a wide gap, a high bias must be applied in order to secure a developing amount, and there is a problem of damage to the photoreceptor due to discharge. . Further, even in the case of the one-component development method, if the toner is not contacted, the toner must overcome the mirror image force adhering to the surface of the developing roller and be developed, so that a high bias is required. In general, the one-component development method is shorter in durability than the two-component development method, and it is considered desirable to use the two-component development method for a highly durable image forming apparatus.
Therefore, methods described in Patent Document 3 and Patent Document 4 are known as non-contact development and a method in which toner easily flies to a latent image. The developing device of this image forming apparatus causes an EH (Electrostatic Transport & Hopping) phenomenon on the surface of the electrostatic toner transport substrate having a plurality of electrodes arranged at a predetermined pitch, and transports the toner to the developing position. The EH phenomenon is a phenomenon in which the energy of the phase-shift electric field acting on the powder is converted into mechanical energy and the powder itself dynamically changes. The toner in which the EH phenomenon has occurred jumps on the surface of the electrostatic transport substrate with a component in the traveling direction due to the phase-shift electric field, and moves in the direction of the substrate surface (transport) and moves in the direction perpendicular to the substrate surface ( Hopping).
However, since the electrostatic transport substrate itself does not rotate in EH development, there is a phenomenon that if the charge amount of the toner is reduced, the responsiveness to the electric field deteriorates and adheres to the electrostatic transport substrate. Means need to be provided. Further, when the charge amount of the toner is changed, there is a problem that the transport amount moving on the electrostatic transport substrate is affected.

JP-A-9-197781 JP-A-9-329947 JP 2002-341656 A Japanese Patent Laid-Open No. 2005-62808

Accordingly, the present invention has been made in view of the above-described problems, and the problem is that a stable toner supply to a latent image is possible in a non-contact developing type developing device suitable for color superimposition on a photoreceptor. Another object of the present invention is to provide a developing device, a process cartridge, and an image forming apparatus that are free from soiling.
Further, as a result of diligent research, the present inventors have invented a system in which toner is floated on the roller surface and the roller itself is rotated and conveyed to the development area. Furthermore, since toner floating depends on electrostatic force, the toner supplied to the electrostatic toner carrying roller must be normally charged. As a result of repeated research on means for quickly raising the charge of the replenishing toner The inventors have invented a method of compacting the developer in the replenishing side stirring chamber to promote the sliding of the developer.

The features of the present invention, which is a means for solving the above problems, are listed below.
The present invention relates to a developing device having an electrostatic toner carrying roller that floats toner on a roller surface by electrostatic force and conveys the toner to a developing region as the roller rotates. The developing device is consumed by development. A toner replenishing port for replenishing the toner, a developer accommodating portion for accommodating a two-component developer composed of toner and carrier, an agitation / charging means for agitating / charging the developer in the developer accommodating portion, and the developer And a developer carrying body that carries the toner to a portion facing the toner electrostatic carrying roller.
In the present invention, the surface of the electrostatic toner carrying roller is formed by alternately arranging two-phase fine electrodes extending in the axial direction in the circumferential direction. The phase is shifted by 180 degrees to the electrodes and the frequency is 1 to 5 kHz. The developing device is characterized in that a rectangular driving pulse voltage is applied.
Further, the present invention applies an alternating voltage to the developer carrying member to generate an alternating electric field between the developer carrying member and the toner carrying member from the developer carrying member to the electrostatic toner carrying roller. It is characterized by making it. Thus, the toner can be efficiently moved from the developer carrying member to the electrostatic toner carrying roller, and a sufficient amount of toner can be held on the electrostatic toner carrying member.
The present invention is characterized in that the plurality of fixed magnetic poles arranged inside the developer carrying member are present only at positions from the downstream of the developer regulating member to the upstream of the developer guide with respect to the developing sleeve rotation direction. (See FIG. 1).

In the present invention, a section in which the cross-sectional shape of the replenishing side stirring chamber is circular along the outer periphery of the screw is downstream in the developer transport direction, and the developer is 360 ° on the wall surface of the stirring chamber only within the section. The developing device is in contact with each other. In the present invention, the developer accommodating portion on the side where toner is replenished is the replenishing side stirring chamber, and the developer accommodating portion on the side facing the developer carrying member is the developing side agitating chamber. Moreover, in FIG. 2, the cross-sectional shape of the sections C and D has shown the circular shape where the cross-sectional shape of the replenishment side stirring chamber followed the outer periphery of the screw.
According to the present invention, in the section where the cross-sectional shape of the replenishing side stirring chamber is a circular shape along the outer periphery of the screw, the portion where the developer is in contact with the wall surface of the replenishing side stirring chamber is 360 °. It is a continuous section including the downstream end of the side agitating chamber, and the section length is 10 to 40% of the total length of the developer carrying portion of the developer carrying member. Here, the portion carrying the developer of the developer carrying member is a portion excluding the shaft (see FIG. 3). In FIG. 3, 0.1L <x <0.4L.
In the present invention, the section in which the cross-sectional shape of the replenishment-side stirring chamber is a circular shape along the outer periphery of the screw is a continuous section including the downstream end portion of the replenishment-side stirring chamber, and the length of the section is developer Is longer than the section length in contact with the wall surface of the replenishing side stirring chamber 360 ° (see FIG. 3). In FIG. 3, x <d.
According to the present invention, the opening area where the developer is transferred from the replenishing side stirring chamber to the developing side stirring chamber is 30 times the area of the opening where the developer is transferred from the developing side stirring chamber to the replenishing side stirring chamber. It is characterized by being less than%.

According to the present invention, the screw shape of the replenishing side agitating chamber is characterized in that the conveying force in the longitudinal direction is large in the upstream and the agitating force in the circumferential direction is relatively large toward the downstream. It is a developing device. Here, the stirring force in the circumferential direction is a shearing force in the vertical direction.
In the present invention, the screw shape of the replenishment side stirring chamber is characterized in that a plate-like member connected in the longitudinal direction to the outermost periphery of the screw is provided in the downstream portion in the developer conveying direction (see FIG. 4). ).
The present invention is characterized in that the screw shape of the replenishing side stirring chamber has a screw pitch longer in the upstream in the developer conveying direction than in the downstream.

The present invention is a process cartridge in which the developing device described above is integrated with at least one or more of a latent image carrier, a charging device, and a latent image carrier cleaning device.
The present invention is an image forming apparatus having the developing device described above.
The present invention is an image forming apparatus having the process cartridge described above.

According to the present invention, in the non-contact developing type developing device suitable for color superimposition on the photosensitive member by the means for solving the above, a developing device capable of supplying stable toner to the latent image and not causing background staining, It has become possible to provide a process cartridge and an image forming apparatus.
In addition, it is possible to provide a developing device, a process cartridge, and an image forming apparatus in which toner is floated on the roller surface and the roller itself is rotated and conveyed to the developing region.
Furthermore, it has become possible to provide a developing device, a process cartridge, and an image forming apparatus of a type in which the developer is compacted in the replenishing side stirring chamber to promote the sliding of the developer.

The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

FIG. 5 is an internal configuration diagram around the photosensitive member of the color image forming apparatus to which the developing device according to the embodiment of the invention is applied.
A plurality of charging devices 60 and developing devices 61 are alternately arranged around the photoreceptor 40. The developing device 61 develops using four different colors of yellow (Y), magenta (M), cyan (C), and black (Bk) toner. The photosensitive member 40 charged to a constant potential by the charging device 60 is lowered in potential only by being exposed to the laser beam according to the original to form an electrostatic latent image. Then, after the toner is developed in a non-contact manner from the surface of the electrostatic toner carrying roller 68 of the developing device 61 and the electrostatic latent image is visualized, the photosensitive member 40 is charged again from above the toner image by the charging device 60. The By repeating this process, a full-color toner image is formed on the photoreceptor 40. Note that a neutralization device may be provided between the developing device 61 and the next charging device 60, and after developing each color, the photosensitive member 40 may be neutralized and then the next charging may be performed. The exposure apparatus may use an LED or the like.
The full-color toner image developed on the photoreceptor 40 is transferred directly to a sheet or to an intermediate transfer member (not shown) and then transferred to the sheet. The sheet after the image transfer is conveyed to a fixing device (not shown), heat and pressure are applied to fix the transferred image, and then the sheet is stacked on a paper discharge tray.

FIG. 1 is a diagram illustrating a developing device inside the image forming apparatus. As shown in FIG. 1, in a developer accommodating portion (hereinafter referred to as “developer container”) 100, a toner replenishing side agitating screw 66, a developer carrying roller side agitating screw 67 as a developer agitating / conveying means, a developer carrying A body (hereinafter, “developer carrying roller”) 69 and an electrostatic toner carrying roller 68 are provided.
A supply port (not shown) is provided on the outer wall of the supply side stirring chamber 86, and toner is supplied from a toner supply device (not shown). The agitation screw 66 on the toner replenishment side agitates and conveys the two-component developer having the toner replenished from the toner replenishing device, the magnetic particles in the developer container 100, and the toner. Further, the stirring screw 67 of the developing side stirring chamber 87 on the developer carrying roller 69 side stirs and conveys the developer in the developer container 100. Note that the cross-sectional view of the replenishment-side stirring chamber in FIG. 1 shows the cross-sectional shape of the downstream end in the developer transport direction.
In the present invention, color overlap development on the photoreceptor 40 without color mixture can be performed by non-contact development. In addition, since the two-component system is used, it is possible to obtain an image in which toner charging is stable for a long period of time and there is no background stain and the density is stable.

For example, the electrostatic toner carrying roller 68 is manufactured as follows. That is, first, after a conductive layer made of aluminum or the like is vapor-deposited on the entire surface of a cylindrical resin base material made of polyimide or the like, each conductive electrode or bus line (common electrode) is formed by a photolithography method. To be patterned. Then, an insulating layer is coated on each patterned electrode or resin base material. As the insulating layer, a thin layer of an inorganic material such as SiO ₂ by a sputtering method or an organic film having a thickness of about 1 to 2 μm formed by spin coating may be pasted on each transport electrode. . The electrostatic toner carrying roller 68 having such a configuration is rotationally driven by a driving means (not shown).

FIG. 6 is a perspective view showing an electrostatic toner carrying roller. In the drawing, the illustration of the insulating layer coated on the drum surface is omitted. A plurality of strip-shaped electrodes extending in the roller axial direction are provided on the front surface of the electrostatic toner carrying roller 68 so as to be arranged at predetermined intervals over the entire circumference in the circumferential direction. These electrodes have a width of 30 μm and are arranged with a gap of 30 μm between them. The A phase electrode 68a and the B phase electrode 68b are alternately arranged in this order, and the A phase and B phase drive pulse voltages shown in FIG. 7 are output during development.

The cross-sectional shape of sections C and D in FIG. 2 is a circular shape in which the cross-sectional shape of the stirring chamber is along the outer periphery of the screw on the downstream side in the developer conveying direction of the replenishment-side stirring chamber 86, and development is performed only within the section A portion where the agent is in contact with the wall surface of the stirring chamber at 360 ° is provided. As a result, it is possible to provide a portion where the developer is in a consolidated state only in a part of the sections C and D. In sections C and D, the ceiling is shaped along the outer diameter of the screw, so there is no immobile layer where the driving force of the screw is not transmitted even when the developer is in a compacted state, and good developer dispersion and conveyance Capability can be secured.
In the compacted region, the rubbing force of the developer is increased, and the dispersion of the replenishing toner is promoted and the charging of the toner is promoted. Therefore, when the replenished toner is conveyed to the development side stirring chamber 87 and used for development, the toner is sufficiently charged, and good image formation without toner scattering and background contamination is performed.
Further, when the developing device 61 having such a configuration is used, since the replenishment-side stirring chamber 86 has a toner charging function, it is not charged by being rubbed intensively with a doctor blade as in the conventional developing device. It's okay. Therefore, the mechanical force in the vicinity of the doctor blade can be designed to be weak, and the life of the developer can be extended by reducing the stress of the entire unit.

Further, in the present invention, the length of the section where the developer contacts the 360 ° wall surface in the supply side stirring chamber 86 is defined. As shown in FIG. 3, the total length of the supply side stirring chamber is L (assuming that the length of the developing sleeve and the length of the supply side stirring chamber are substantially the same), and the total length of the sections C and D is d. , Where x is the length of the section where the developer is in a compacted state and in contact with the surrounding wall surface at 360 °,
0.1L <x <0.4L (1)
It can be expressed.
If the compacted area where the developer is in contact with the 360 ° wall surface is too larger than 40% of the total length L of the stirring chamber, the area with a low agent level suitable for replenishing toner replenishment will be 60% or less. Dispersibility will deteriorate. On the other hand, if it is 10% or less, sufficient rubbing cannot be obtained, and the toner is carried to the development area without sufficiently rising the charge. Therefore, by making it within the scope of the present invention, it is possible to achieve both high-level dispersion of replenishment toner and charging.
Furthermore, the length of the section where the cross-sectional shape of the replenishment side stirring chamber 86 is a circular shape along the screw shape is defined. When the present invention is expressed by a mathematical formula,
x <d (2)
It can be expressed.
The section in which the cross-sectional shape of the replenishment side stirring chamber 86 is circular along the outer periphery of the screw is a continuous section including the downstream end of the replenishment side stirring chamber 86, and is a section having a cross-sectional shape of section C in FIG. . The section length is longer than the section length in which the developer is in contact with the wall surface of the stirring chamber at 360 °. The total length of the sections C and D is d, which is 50% or less, preferably 40% or less, of the total length L of the developer carrying roller 69 carrying the developer. As a result, since the area where the developer is in a compacted state is a 360 ° circular wall surface, the developer is smoothly conveyed without generating a non-moving layer. In addition, the developer and the wall surface, the developer and the screw member, and the developer are sufficiently rubbed with each other, and the charging of the toner is promoted. Therefore, charging can be performed before the replenished toner is supplied to the developing sleeve, and an image can be formed without toner scattering and background contamination.

Further, in the present invention, the opening area where the developer is transferred from the replenishment side stirring chamber 86 to the development side stirring chamber 87 is the opening area where the developer is transferred from the development side stirring chamber 87 to the replenishment side stirring chamber 86. By being less than 30% of the area, it becomes difficult to transfer to the development side stirring chamber 87. At this time, a compacted state is easily created in the downstream portion of the replenishment side stirring chamber 86. Therefore, the developer and the wall surface, the developer and the screw member, and the developer are sufficiently rubbed with each other, and the charging of the toner is promoted. Therefore, charging can be performed before the replenished toner is supplied to the developing sleeve, and an image can be formed without toner scattering and background contamination.

Furthermore, in the present invention, the screw shape of the replenishment side stirring chamber 86 has a shape in which the conveying force in the longitudinal direction is large in the upstream and the stirring force in the circumferential direction increases in the downstream, so in the upstream, The developer level of the developer is lowered, the agent level is increased in the downstream, and in some sections, an area that contacts the ceiling of the wall surface, that is, 360 ° around is created. In such an agent level state, there are three effects.
The first effect is that the low agent level in the vicinity of the toner supply port means that the supplied toner is likely to be caught in the developer that moves as the screw rotates, and the supplied toner is immediately dispersed with the carrier. . Conversely, when toner is replenished to a position where the agent level is high, a so-called upslip phenomenon occurs in which the replenished toner is conveyed while being layered on the surface of the original developer. Since the toner that has slipped does not have an opportunity to come into contact with the carrier, it is not charged and causes toner scattering.
The second effect is that the agent level increases in the middle of the stirring chamber. Even if the upslip of the replenishment toner cannot be eliminated 100% on the upstream side, the replenishment toner blocks at the position where the agent level is high. This is to prevent the undispersed toner from being transported as it is downstream.
The third effect is that the agent level on the downstream side is high, and the developer is in a compacted state, so that the developer and the wall surface, the developer and the screw member, and the developer are sufficiently rubbed with each other, and toner charging is promoted. That is. Therefore, charging can be performed before the replenished toner is supplied to the developing sleeve, and an image can be formed without toner scattering and background contamination.

(Example 1)
In the 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. A prescribed amount of this developer was put in a developing device, and an image forming experiment was conducted. Here, the toner is negatively charged.
The pitch of the replenishing side stirring screw was 12.5 mm, and the pitch of the developing side stirring screw was 12.5 mm. The surface of the developer carrying roller 69 is made of an aluminum sleeve and is sandblasted. FIG. 8A shows the normal direction magnetic flux density of the developer carrying roller 69 used in this embodiment. The gap between the developer carrying roller 69 and the electrostatic toner carrying roller 68 was 0.5 mm, and a pulse voltage having a DC component of −500 V, Vpp of 800 V, and a frequency of 4 kHz was applied.
The gap between the electrostatic toner carrying roller 68 and the photosensitive member 40 is 0.2 mm, and the two-phase electrode of the electrostatic toner carrying roller 68 has a DC component of −150 V, Vpp of 300 V, and a frequency of 1 kHz. A pulse voltage was applied to the A-phase electrode and the B-phase electrode by shifting the phase by 180 degrees.
In order to evaluate the color overlap on the photoconductor, a cyan developing unit was set on the uppermost stream of the photoconductor 40, and a yellow developing unit was set second. An experiment was conducted in which a thin line (600 dpi, 2 dot lines) was developed with cyan for the first color, and then a yellow solid was developed for the second color.
First, when it was confirmed that the toner image of the first color on the photoreceptor 40 was not disturbed during the development of the second color, yellow of the second color could be developed without disturbing the fine line developed with cyan. Further, a sufficient amount of yellow was secured.
Next, it was confirmed that the first color toner was not mixed into the second color developing unit. As a method for confirming the color mixture on the unit, the developer was sampled from the development unit after printing 1000 sheets, and it was confirmed by visual observation with an optical microscope that there was no color mixture toner. As a result, it was confirmed that the cyan toner of the first color was not mixed in the yellow unit of the second color, and no reverse development from the photosensitive member to the electrostatic toner carrying roller 68 occurred.
When an experiment was conducted by changing the frequency of the voltage applied to the electrostatic toner carrying roller 68, a frequency of 1 to 5 kHz was suitable for the floating of the toner. That is, if the frequency is too low, the toner adheres to the electrostatic toner carrying roller 68 and the movement becomes slow and development is difficult, and if the frequency is too high, the toner becomes difficult to respond to the electric field and the movement becomes slow. It was. The optimum frequency depends on the charge amount of the toner and the mass of the toner. If the toner particle size becomes smaller and the mass becomes lighter, it floats actively even at a high frequency.
Further, the surface of the electrostatic toner carrying roller 68 is formed by alternately arranging two-phase fine electrodes extending in the axial direction in the circumferential direction, and a rectangular shape having a frequency of 1 to 5 kHz by shifting the phase by 180 degrees to the electrodes. By applying the drive pulse voltage, the toner floating on the surface of the electrostatic toner carrying roller 68 actively vibrates between the electrodes. Therefore, when the toner is transported to the development area facing the photoconductor 40, the toner flies to the latent image and is developed in accordance with the electric field formed by the electrostatic latent image. On the other hand, the toner does not fly to the background portion, and good development is performed with no background stain. Further, since the surfaces of the photosensitive member 68 and the electrostatic toner carrying roller 68 are not in contact with each other, the toner images of other colors already developed on the photosensitive member 40 are disturbed or scraped, and the developer storage portion. No color mixing at 100.

Example 2
The magnetic flux density in the normal direction of the developer carrying roller 69 used in the next embodiment is shown in FIG. The normal direction magnetic flux density of the agent separating pole 11 is almost 0, and the normal direction magnetic flux density of the pumping pole 12 is also made smaller on the upstream side in the developer conveying direction than the doctor blade. The developer after supplying the toner to the electrostatic toner carrying roller 68 is pushed out along with the rotation of the sleeve along the developer guide 88 provided close to the developer carrying roller 69. The toner is separated from the carrying roller 69 and is stirred by the stirring screw 87 together with the toner-rich developer (see FIG. 5). That is, even if there is no agent separation pole 11, the developer does not rotate as it is, so there is no problem that the toner supplied to the electrostatic toner carrying roller 68 is exhausted. Further, the amount of developer restrained by the normal direction magnetic flux density in the vicinity of the doctor blade is reduced, and the stress is reduced. By using the developer carrying roller 69 containing a mag roller having such a normal direction magnetic flux density distribution, the life of the developer can be extended, and stable toner charging can be maintained over a long period of time.

Example 3
In the next embodiment, in order to compensate for the decrease in toner charging ability caused by changing the normal direction magnetic flux density distribution around the developer carrying roller 69 to weaken the stress, the toner charging acceleration function is further provided in the supply side stirring chamber 86. Made improvements. Further, the series of measures here not only promote charging, but also improve the dispersibility of the replenished toner, so that the toner supply amount to the electrostatic toner carrying roller 68 can be further stabilized.
Conventionally, if the stress is reduced too much, toner fine powder will be spent on the carrier surface, or the toner will be transported to the development area with insufficient charge amount due to insufficient rubbing between the replenishment toner and the carrier, causing toner scattering and background contamination. It was a cause.
However, according to the present invention, since the toner is charged in the replenishing-side stirring chamber 86, it is not necessary to apply excessive stress with the doctor blade, and it is only necessary to play the role of regulating the amount of developer. Thereby, the stress applied to the developer is reduced, and the life of the developer can be extended.

Here, a method for examining the charge rising property of the toner will be described. The developing device 61 in which the toner electrostatic carrying roller 68 was removed from the developing device 61 was used for the evaluation of toner charge rising. A predetermined amount of developer is put into the developing device 61. Further, the screw rotation speed of the replenishment side stirring chamber 86 was appropriately changed so that the flow rate to the developing side stirring chamber 87 became a predetermined amount. Next, 1 g of toner was supplied to the toner supply port (point A in FIG. 9). At the time when the peak of the replenished toner is conveyed to the developer carrying roller 69, the developer on the developer carrying roller 69 is sampled, and the toner charge amount distribution is measured using an E-spart analyzer manufactured by Hosokawa Micron. . The time at which the replenishment toner reaches the developer carrying roller 69 is measured in advance in a prior experiment by frequently measuring the toner concentration of the developer on the developer carrying roller 69 after the toner replenishment, and checking the time when the toner density becomes the highest in advance. Use the one you have left.
From the charge amount distribution measured by such a procedure, the number frequency of the toner on the plus side of −0.1 [fC / μm] was evaluated as a WST rate (Wong Sign Toner). In this embodiment, a negatively charged toner is used.
Further, in an actual developing device, the amount replenished at one time is 0.2 g / s or less, and the replenishment amount 1 g in this experiment is an extreme condition for evaluating the charging performance of the stirring unit. It is noted.
As a result of intensive studies by the present inventors, it has been found that good image formation without toner scattering and scumming can be performed under the condition that the WST rate is 10% or less in this evaluation. Therefore, whether or not the condition is acceptable was determined using this index.

The stirring unit of the developing device 61 used in the experiment in this embodiment will be described in more detail.
FIG. 2 is a longitudinal sectional view of the partition plate 80 that separates the replenishment side stirring chamber 86 and the development side stirring chamber 87. At both ends of the partition plate 80, a developer delivery section 78 from the replenishment side stirring chamber 86 to the development side stirring chamber 87 and a delivery section 79 from the development side stirring chamber 87 to the replenishment side stirring chamber 86 are provided. . In this embodiment, the transfer opening area from the developing side stirring chamber 87 to the replenishing side stirring chamber 86 is 800 mm ² , and the opening area from the replenishing side stirring chamber 86 to the developing side stirring chamber 87 is 180 mm ² .
The shape of the opening 78 from the replenishing side stirring chamber 86 to the developing side stirring chamber 87 is not limited to a rectangle, and a plurality of circles or polygons arranged in a mesh shape may be used. Further, the opening position does not need to be at the lower part of the partition plate as shown in FIG. 2, and it is sufficient if the opening is at a height where the developer exists. Further, a variable shutter having a mechanism capable of controlling the opening area may be used.
The screw of the replenishing side stirring chamber 86 was 320 mm in total length and as shown in FIG. 10 (c), a screw with spiral screw blades having a pitch of 25 mm was used.

Next, the wall surface of the supply side stirring chamber 86 will be described in detail. A cross-sectional view of the agitation chamber in each of the sections A to D is shown on the lower side of FIG. In the section A, an opening is provided for the developer to return from the development side stirring chamber 87 to the replenishment side stirring chamber 86. In the middle of the section B, there is a toner supply port, and toner is supplied from the outside. Therefore, in the section B, it is an important function to uniformly distribute the supplied toner in the developer. Next, section C is a feature of the present invention, and the ceiling portion of the stirring chamber is circular so as to follow the outer peripheral surface of the screw. In the last section D, the wall surface of the stirring chamber is the same as that of section C, but an opening for delivering the developer to the developing side stirring chamber 87 is provided. The area of the opening is smaller than the opening from the development side stirring chamber 87 to the replenishment side stirring chamber 86.
In this example, the gap between the screw blade and the stirring chamber wall surface in the sections C and D was 1 mm. Further, as shown in Condition 1 of Table 1, the opening area was 180 mm ^2, and the section length d obtained by adding the sections C and D was 0.4 L.

By reducing the area of the opening from the supply side stirring chamber 86 to the development side stirring chamber 87, the developer is consolidated in the downstream portion of the supply side stirring chamber 86. At this time, if the shape of the wall surface is such that the upper half of the screw is open as in the section B, even if the screw rotates, the force in the transport direction is not transmitted to the developer at the corner of the upper part of the stirring chamber. , Will form an immobile layer. On the other hand, in the present invention, the region where the developer is brought into a compacted state is always a region of a circular wall surface. Therefore, even if the developer is brought into a compacted state, the developer is not generated without generating a stationary layer. Is smoothly transported.
In the configuration of this embodiment, of the total section length d of the sections C and D is 128 mm (= 0.4 L), the section length where the developer is in contact with the ceiling is 110 mm from the most downstream side of the replenishment side stirring chamber 86. (= 0.33L). The axial torque of the replenishing side stirring screw 66 was measured and found to be 0.35 kgf · cm.
When charging start-up evaluation of the replenishing toner was performed under these conditions, a sufficient level of both toner dispersion and charge start-up could be secured.
When image output is performed using the developing device 61 to which the electrostatic toner carrying roller 68 is attached under these conditions, the replenished toner is required to reach the developing side stirring chamber 87 even under a severe toner replenishment condition (during solid image development). In the meantime, the image was sufficiently dispersed and charged, and good image formation without background stains and toner scattering could be performed.

On the other hand, the same evaluation was performed under conditions 2 to 7 in Table 1 as a comparative example.
Under condition 2, when the opening area of the transfer portion 78 from the supply side stirring chamber 86 to the development side stirring chamber 87 is 800 mm ² , the developer does not become compact, and the developer is 360 on the wall surface of the supply side stirring chamber 86. ° Could not make contact section. The WST rate after toner replenishment was as poor as 30%, and toner scattering occurred.

Under Condition 3, when the opening area was narrowed to 140 mm ² , the compacted area where the developer contacts the wall of the stirring chamber at 360 ° becomes as long as 192 mm (= 0.6 L), which is sufficient after the toner is replenished. Soon after being dispersed, it entered the consolidation area. At this time, the toner is transported to the development area without the toner density being made uniform. Therefore, when the image is actually output by the developing device 61 to which the developer carrying roller 69 is attached under this condition, density unevenness appears. .

In condition 4, the section length d for making the wall surface of the replenishing side stirring chamber 86 circular is as long as 0.8L. As shown in FIG. 11, the developer level in the section B immediately after replenishment includes a portion where the developer 90 protrudes from the screw projection surface at the left and right ends of the stirring chamber. Such a developer 96 at the end is hardly subjected to a force in the conveying direction even if the screw 95 is rotated, so that a difference in conveying speed occurs between the developer in the screw projection surface and the developer 96 at the end. When the toner is replenished, this speed difference promotes dispersion of the toner in the longitudinal direction. On the other hand, since all the developer is present in the screw projection surface on the wall surfaces in the sections C and D, a speed difference in the transport direction is unlikely to occur. Therefore, as in Condition 4, if the section length d for making the wall surface of the replenishing side stirring chamber 86 circular is too long, 0.8 L, the dispersion of the replenishing toner is slightly insufficient.

In condition 5, the area of the compacted state became as long as 0.6 L by reducing the opening area to 140 mm ² , but this is a condition where the section of the circular wall surface is only 0.3 L. In this case, the developer is in contact with the 360 ° wall surface on the wall surface of the section B, but the developer stays in the corner portion of the stirring chamber where the force of the screw does not reach and a non-moving layer is formed.

In condition 6, the screw shape was changed. When a member extending in the longitudinal direction is provided on the outer periphery of the screw, the stirring force in the circumferential direction, which is the longitudinal direction, increases. However, in the screw of type (d) in FIG. Is provided. Therefore, although it is once in a consolidated state, the pressure is released at the most downstream portion of the stirring chamber, and efficient sliding cannot be performed. The object of the present invention is to provide a lot of sections with low agent level in the upstream part of the replenishing side agitating chamber 86 to improve toner dispersion, and to efficiently create a compacted part in the downstream part to promote developer rubbing. Therefore, a configuration in which the compaction part is moved upstream as in Condition 6 and the pressure is relaxed again at the most downstream part as in Condition 6 can be obtained from both the dispersion surface and the toner charge surface. It is not preferable.

Under condition 7, when the opening area of the transfer section 78 from the supply side stirring chamber 86 to the development side stirring chamber 87 is set to 400 mm ² , the developer does not become compact, and the developer is 360 on the wall surface of the supply side stirring chamber 86. ° Could not make contact section. The WST rate after toner replenishment was as poor as 30%, and toner scattering occurred.

Example 4
In the next example, as shown in Conditions 8 to 12, the area of the transfer opening was 180 mm ² , the section of the circular wall surface was fixed to 0.4 L, and the screw shape of the supply side stirring chamber 86 was changed.

In condition 8, as shown in (a-1) of FIG. 10, out of the total length of 320 mm with spiral screw blades, the upstream side 160 mm was 50 mm pitch, and the downstream part was 25 mm pitch. When this screw is used, the conveyance speed on the upstream side is faster than that on the downstream side, so that the developer is in a compacted state on the downstream side. Accordingly, the sliding of the developer is promoted, the toner is charged, and good image formation without toner scattering can be performed.

In condition 9, as shown in FIG. 10 (b-1), out of the total length of 320 mm with a helical screw blade having a pitch of 25 mm, it is connected in the longitudinal direction to the outer periphery of the screw blade by 3 pitches from the most downstream portion. A screw provided with a plate-like member was used. When this screw is used, the advection speed becomes slow at the portion where the plate-like stirring member is attached. Further, since the plate-like member is attached, the circumferential stirring direction, which is the vertical direction, is strong, so that the developer can be further compressed to create a strong compacted state. Accordingly, the sliding of the developer is promoted, the toner is charged, and good image formation without toner scattering can be performed.

The condition 10 is the same as the condition 9 except that, as shown in FIG. Even under these conditions, the compacted portion is formed, the sliding of the developer is promoted, the toner is charged, and good image formation without toner scattering can be performed.

In condition 11, as shown in (a-2) of FIG. 10, among the total length of 320 mm with the helical screw blades, the upstream side 160 mm was 50 mm pitch and the downstream part was 25 mm pitch. Of the portions with spiral screw blades with a pitch of 25 mm, a screw provided with a plate-like member connected in the longitudinal direction to the outer periphery of the screw blades by 3 pitches from the most downstream portion was used. When this screw is used, since the pitch is large in the upstream, the conveyance speed is faster than that on the downstream side, and the advection speed is further reduced in the portion where the plate-like stirring member is attached. Further, since the plate-like member is attached, the circumferential stirring direction, which is the vertical direction, is strong, so that the developer can be further compressed to create a strong compacted state. Accordingly, the sliding of the developer is promoted, the toner is charged, and good image formation without toner scattering can be performed.

The condition 12 is the same as the condition 11 except that the stirring member provided in the most downstream portion is set to 5 pitches as shown in (a-3) of FIG. Even under these conditions, the compacted portion is formed, the sliding of the developer is promoted, the toner is charged, and good image formation without toner scattering can be performed.
As a result of the examination by the inventors, in the state where the agent level shown in the present invention is maintained, there is no problem that the stress is too strong and the deterioration of the developer is accelerated, and the developer in the developing side stirring chamber 87 is insufficient. As a result, good image formation could be performed without causing poor pumping to the developer carrying roller 69.

As described above, by promoting the dispersion and charging of the replenishment toner in the replenishment-side stirring chamber 86, it is not necessary to apply a strong load to the developer in order to charge the toner near the doctor blade as in the prior art. If an excessive load on the developer can be reduced, deterioration of the developer can be suppressed. Therefore, not only initial background contamination and toner scattering but also good image formation without background contamination and toner scattering over a long period of time can be achieved.

FIG. 2 is a diagram illustrating a developing device inside the image forming apparatus. It is the figure which showed sectional drawing of the longitudinal direction of the partition plate which separates the replenishment side stirring chamber and the image development side stirring chamber. It is a figure which shows the full length L, the section length d, and the section length x of a replenishment side stirring chamber. It is a figure which shows the plate-shaped member connected to the outermost periphery of the screw in the longitudinal direction. 1 is an internal configuration diagram around a photoconductor of a color image forming apparatus to which a developing device according to an embodiment of the present invention is applied. It is a perspective view showing a toner electrostatic carrying roller. It is the figure which showed A phase and B phase drive pulse voltage output. It is a figure which shows the normal direction magnetic flux density of a developer carrying roller. It is a figure which shows the replenishment side stirring chamber and the image development side stirring chamber. It is a figure which shows a screw shape. It is a figure which shows the developer level of the area B immediately after replenishment.

Explanation of symbols

11 Electrode separating electrode 12 Pumping electrode 40 Latent image carrier (photoconductor)
60 charging device 61 developing device 66 replenishment side stirring screw 67 developer carrying roller side stirring screw 68 electrostatic toner carrying roller 68a A phase electrode 68b B phase electrode 69 developer carrying body (developer carrying roller)
75 Toner concentration sensor 77 Developer regulating member 78 Developer delivery section 79 from the replenishment side stirring chamber to the development side stirrer chamber 79 Developer delivery section 80 from the development side stirring chamber to the replenishment side stirring chamber 80 Partition plate 86 Replenishment side stirring chamber 87 Development side stirring chamber 88 Developer guide 90 Developer 91 Developer transport direction 92 Toner replenishment port 93 Plate member 94 Longitudinal direction 95 Screw 96 Developer 100 outside screw projection surface Developer container (developer container)
Point A Toner supply point Point B Delivery section

Claims (14)

In the developing device having a toner electrostatic carrying roller that floats the toner on the roller surface by electrostatic force and conveys the toner to the developing area as the roller rotates.
The developing device includes:
A toner replenishing port for replenishing toner consumed by development;
A developer accommodating portion for accommodating a two-component developer composed of toner and carrier;
Stirring and charging means for stirring and charging the developer in the developer container;
A developer carrying member that carries the developer by a magnetic force and conveys the developer to a portion facing the electrostatic toner carrying roller;
A developing device comprising: The developing device according to claim 1,
In the developing device, the surface of the electrostatic toner carrying roller is alternately arranged in the circumferential direction with two-phase fine electrodes extending in the axial direction.
A developing device characterized in that a rectangular driving pulse voltage having a frequency of 1 to 5 kHz is applied to the electrode by shifting the phase by 180 degrees. The developing device according to claim 2,
The developing device applies an alternating voltage to the developer carrying member to generate an alternating electric field between the toner electrostatic carrying roller,
A developing device that moves toner from the developer carrying member to the electrostatic toner carrying roller. In the developing device according to any one of claims 1 to 3,
In the developing device, a plurality of fixed magnetic poles arranged inside the developer carrier are present only at positions from the downstream of the developer regulating member to the upstream of the developer guide with respect to the rotation direction of the developing sleeve. A developing device. The developing device according to any one of claims 1 to 4,
In the developing device, a section in which the cross-sectional shape of the replenishment side stirring chamber is a circular shape along the outer periphery of the screw is downstream in the developer transport direction,
The developing device is characterized in that the developer is in contact with the wall surface of the stirring chamber at 360 ° only within the section. The developing device according to claim 5,
In the developing device, in the section where the cross-sectional shape of the replenishing side stirring chamber is a circular shape along the outer periphery of the screw, the portion where the developer is in contact with the wall surface of the replenishing side stirring chamber is 360 °. It is a continuous section including the downstream end of the replenishment side stirring chamber,
The section length is 10 to 40% of the total length of the portion of the developer carrying member carrying the developer. The developing device according to claim 5 or 6,
In the developing device, a section in which the cross-sectional shape of the replenishing side stirring chamber is a circular shape along the outer periphery of the screw is a continuous section including a downstream end portion of the replenishing side stirring chamber.
The section length is longer than the section length where the developer is in contact with the wall surface of the replenishing side stirring chamber 360 °,
A developing device. The developing device according to any one of claims 5 to 7,
The developing device has an opening area where the developer is transferred from the replenishing side agitating chamber to the developing side agitating chamber, and an opening area where the developer is transferred from the developing side agitating chamber to the replenishing side agitating chamber. A developing device characterized by being less than 30%. The developing device according to any one of claims 5 to 8,
The developing device is characterized in that the screw shape of the replenishing side stirring chamber is such that the upstream conveying force is large in the longitudinal direction and the circumferential stirring force is relatively large toward the downstream. Developing device. The developing device according to claim 9, wherein
The developing device is characterized in that the screw shape of the replenishing-side stirring chamber is provided with a plate-like member connected to the outermost periphery of the screw in the longitudinal direction at the downstream portion in the developer transport direction. The developing device according to claim 9 or 10,
In the developing device, the screw shape of the replenishment side stirring chamber has a screw pitch longer in the upstream in the developer transport direction than in the downstream,
A developing device. Process cartridge
A developing device according to any one of claims 5 to 11,
At least one of a latent image carrier, a charging device, and a latent image carrier cleaning device; and
Is a process cartridge that is integrated. An image forming apparatus comprising the developing device according to claim 5. An image forming apparatus comprising the process cartridge according to claim 12.

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