JP2011133596A - Developing apparatus, and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing apparatus that can achieve excellent circulation balance between a developer supply collection part on an upper side of the developing apparatus and a developer stirring part on a lower side thereof, can prevent an image from being deteriorated even if printing with a high coverage rate is successively performed, and can contribute to the long service life in a bearing part and the compactification of an image forming apparatus; and to provide the image forming apparatus including the same. <P>SOLUTION: A second communication opening 120 is formed on an upper side facing a first stirring screw 21 or a second stirring screw 22 and further in the vicinity of an end part of a downstream of the one stirring screw. A vertical wall part of a second developing tank 20, which supports an edge of a shaft provided downstream of the other stirring screw, is positioned upstream of the vertical wall supporting an edge of a shaft provided downstream of the one stirring screw in a conveying direction of a developer and further in front of the second communication opening 120. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developing device installed in a monochrome / color, stand-alone / network connection, such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof, and an image forming apparatus provided with the developing device. .

2. Description of the Related Art Conventionally, an electrophotographic developing device that records and forms a toner image using a known electrophotographic process such as a laser printer or a copying machine, and an image forming apparatus including the developing device are well known. In this type of developing device, a one-component developing system using only toner as a developer and a two-component developing system using toner and a carrier are used.

  The one-component developing type developing device includes a roller-shaped toner image carrying member that carries and conveys toner, and a friction charging member that contacts the toner carrying surface of the toner image carrying member. When the toner carried on the toner carrying member passes through the contact position of the friction charging member, the toner is brought into frictional contact with the friction charging member to be thinned and charged to a predetermined polarity.

  As described above, in the developing device of the one-component developing system, the toner is charged by frictional contact with the frictional charging member, so that a burden is imposed on the toner. A thermoplastic resin is used for the toner, and inorganic fine particles are attached to the surface as a fluidity modifier. Therefore, the surface of the toner undergoes a thermal change or inorganic fine particles are embedded due to the load. If a high-speed machine is used, the number of rotations of each member also increases, so that a higher load is applied to the toner.

  Further, in recent years, the diameter of toner has been remarkably reduced with an increase in image quality. For example, it is not uncommon to set the toner to 6 μm or less. Since such a small-diameter toner deteriorates in fluidity, a larger amount of post-treatment agent is added. As a result, toner aggregation and post-treatment agent embedding due to the load become significant. In addition, as an environmental measure, there is a significant tendency for low-temperature fixing. For this reason, the thermal resistance is lowered, and the load is further disadvantageous.

  In the two-component developing system, a toner charged by frictional charging with toner and carrier is attached to an electrostatic latent image formed on a developer carrying member for development. In the developing device, the charged state of the toner is maintained by keeping the ratio of the toner and the carrier constant. However, since the toner is consumed by developing the electrostatic latent image formed on the developer carrying member with toner, the toner is replenished by the replenishing means. The toner replenished by the replenishing means is uncharged and charged while being agitated and conveyed with the developer in the developing apparatus by the agitating / conveying means in the developing apparatus. In this method, since charging is performed by mixing particles, the load on the toner is small. Therefore, the toner has a longer life than the one-component development method and has a feature of excellent high-speed compatibility.

  On the other hand, in recent years, electrophotographic products have been introduced into the field of high production areas, and a system corresponding to high speed and long life has been proposed. In the developing device, a device having a plurality of developing rollers, a device having a trickle mechanism for gradually replacing the developer, a two-component developer in the supply roller portion, a hybrid developing device using one-component toner in the developing roller portion, these Combined development devices are available on the market. In any of the developing devices, the toner is replenished, and the toner is charged while being stirred and transported with the developer in the developing device by the stirring and transporting means in the developing device.

  In a toner supply type developing device, when printing with a high printing rate is continuously performed, a large amount of toner is consumed and uncharged toner is replenished repeatedly. When the replenished toner is transported in a state where the charge amount is low without being sufficiently stirred and supplied onto the developing roller, image deterioration such as toner scattering and fogging occurs.

  Further, since the speed of the apparatus in recent years has shortened the time for the replenished toner to be carried onto the developing roller, the problem of the image deterioration becomes more serious. Therefore, as a technique for solving such a problem, a first developer conveying screw that is provided at the rear of the developing sleeve and that conveys the developer in the axial direction of the developing sleeve and a rear portion of the first developer conveying screw are provided. A developing device has been proposed in which a developer is circulated and conveyed by a second developer conveying screw that conveys the developer in the opposite direction to the one conveying screw, while developing is performed by supplying the developer to a developing sleeve ( For example, see Patent Document 1.)

  In addition, the developer supply / recovery unit and the developer agitation unit that form the developer circulation transport path are arranged in the horizontal direction, and the developer is provided by two opposing agitating members provided in the developer agitation unit. By stirring in the circumferential direction while transporting in the direction of the rotation axis, the replenished developer is prevented from being transported onto the developing roller without being sufficiently stirred, and fogging, scattering, etc. are suppressed. A developing device that can be used has been proposed (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 9-152774 Japanese Patent No. 4155089

  However, in the developing device disclosed in Patent Document 1, due to the structure, sufficient mixing and agitation is not performed until the developer reaches the developing sleeve after the developer is replenished. Is supplied to the developing sleeve without sufficiently rising, and image degradation such as toner scattering and fog cannot be solved yet.

  Further, in the developing device disclosed in Patent Document 2, as a result of securing a sufficient mixing and stirring time in the developer stirring unit without reducing the transport speed of the developer, development in the developer stirring unit is achieved. In a state in which the toner is charged to a state having a predetermined charge (charge amount) by the mixing and stirring operation of the agent, the developer is supplied to the developer carrier at a uniform toner concentration in the axial direction by the developer supply / recovery unit. As a result, it is possible to prevent the occurrence of fogging and toner scattering due to defective charging of the toner, and to cope with higher speed.

  On the other hand, in recent years, with the increasing demand for compactness and space saving of image forming apparatuses, it has become an urgent task to introduce image forming apparatuses that are further compact and space-saving. However, in the developing device described in Patent Document 2, in addition to the configuration in which the developer supply / recovery unit and the developer agitation unit are arranged in the horizontal direction, a large-sized drive transmission mechanism for executing high-speed processing is provided. Therefore, it is necessary to secure a space for installing the image forming apparatus and hinder downsizing of the entire image forming apparatus. Therefore, there is a problem that it is impossible to meet a demand for downsizing and space saving of the entire image forming apparatus.

  Therefore, as an example of a developing device that can achieve compactness and space saving of the image forming apparatus, the developer supply / recovery unit and the developer agitation unit are arranged in the vertical direction, and one supply conveyance with the same screw diameter is performed. A configuration is conceivable in which the developer is circulated and conveyed in the vertical direction on two axes composed of a member and one stirring and conveying member. However, the developing device having such a configuration requires a vertical space even if the horizontal space can be made compact. In addition, since the developer transported in the axial direction is fed in the vertical direction, the stir transporting member lifts the developer in the developer stirring unit as the developer stays in the lifting unit, and as a result, the developer stays in the lifting unit. As the developer approaches, the inclined developer pool is formed in the developer agitating section and the developer supply / recovery section, resulting in a new problem of image unevenness.

Accordingly, the present invention has been made to solve the above-mentioned problems, and the object of the present invention is to provide a three-shaft having one supply conveyance member at the top and two agitation conveyance members at the bottom. In the developing device configured to circulate and convey the developer in the vertical direction, it is possible to ensure a good circulation balance of the developer between the upper developer supply and recovery unit and the lower developer agitation unit, and printing with a high printing rate. An object of the present invention is to provide a developing device and an image forming apparatus including the developing device, which can prevent image deterioration even when continuously performed.
Another object of the present invention is to provide a developing device that can contribute to extending the life of the bearing portion and reducing the size of the image forming apparatus, and an image forming apparatus including the developing device.

  The developing device according to the present invention includes a first developing tank and a second developing tank disposed immediately below the first developing tank. The first developing tank includes a magnetic field generating unit, and includes toner. And a developer carrying member that carries and conveys the developer composed of two components of the carrier to a developing region facing the photoreceptor, and the developer is disposed in the first developing tank, and the developer is disposed adjacent to the developer carrying member. And a supply and transport means including a screw member that supplies the developer carrier while transporting in the axial direction of the developer carrier, and the second developer tank is disposed in the second developer tank, The developer is stirred and dispersed, and has a stirring and conveying means including a screw member that conveys the developer in a direction opposite to the supply and conveying means, and the first developing tank and the second developing tank include the developer. The opening through which the gas flows is connected through a partition formed at both ends, so that the front A circulation transport path for the developer is formed developing apparatus. Openings formed at both ends of the partition wall are a first communication port for delivering the developer from the vicinity of the downstream end of the supply transport means to the vicinity of the upstream end of the stirring transport means, and the downstream of the stirring transport means And a second communication port for delivering the developer from the vicinity of the side end portion to the vicinity of the upstream end portion of the supply conveyance means, and the agitation conveyance means are arranged in parallel to each other along the conveyance direction of the developer. Each of the first agitation transport member and the second agitation transport member conveys the developer in the same direction, and the second communication port Is formed in a position in the vicinity of the downstream end of the one stirring / conveying member above the one stirring / conveying member of the first stirring / conveying member, The second developing tank supporting the downstream shaft end of the other agitating and conveying member; Straight wall, with a developer conveyance direction upstream side of the vertical wall portion for supporting the shaft end on the downstream side of the one agitating and conveying member, and is located on the front side of the second communication port.

  It is preferable that the screw diameters of the first agitation conveyance member and the second agitation conveyance member are smaller than the screw diameter of the supply conveyance means.

  It is preferable that the number of rotations of each of the first stirring and conveying member and the second stirring and conveying member is controllable.

  The developer conveying direction of one of the first agitating and conveying member or the second agitating and conveying member facing the second communication port is from the upstream end of the one agitating and conveying member. The conveyance direction from the second communication port to the upstream vicinity position and the conveyance direction from the second communication port to the upstream vicinity position to the downstream end of the one agitation conveyance member may be opposite directions. preferable.

  At the downstream end of the other stirring / conveying member that does not face the second communication port, there is a regulating means for regulating the conveyance of the developer in the axial direction and feeding the developer into the second communication port. Preferably it is formed.

  The regulating means may be a reverse winding part.

  The restricting means may be a paddle part.

  An image forming apparatus including the developing device according to the present invention includes the developing device according to any one of claims 1 to 7.

  As is apparent from the above description, according to the developing device of the present invention, the supply conveyance unit located above the vicinity of the downstream end of the agitation conveyance unit (the first agitation conveyance member and the second agitation conveyance member). A second communication port that delivers the developer to the vicinity of the upstream side of the first upper side of the first agitating / conveying member or the second agitating / conveying member; The vertical wall portion of the second developing tank, which is formed in the vicinity of the downstream end portion of the stirring and conveying member and supports the shaft end on the downstream side of the other stirring and conveying member, Since the configuration is located upstream of the vertical wall portion supporting the end in the developer transport direction and on the front side of the second communication port, the developer between the first developer tank and the second developer tank As a result of ensuring a good circulation balance, the first agitating and conveying member and the second agitating and conveying Even when it is necessary to increase the rotation speed of the material, it is not necessary to increase the rotation speed, and the bearings supporting the shaft ends of the first agitation transport member and the second agitation transport member can be provided at an early stage. Damage can be prevented.

  Further, the upstream side end of the one agitating and conveying member indicates the developer conveying direction of one of the first agitating and conveying member or the second agitating and conveying member facing the second communication port. The conveyance direction from the second communication port to the upstream vicinity position from the second communication port and the conveyance direction from the second communication port to the upstream vicinity position to the downstream end of the one agitation conveyance member are opposite directions. . Thereby, when it is necessary to increase the rotation speeds of the first agitation transport member and the second agitation transport member, the pressure due to the concentration of the developer at the downstream end of each agitation transport member is relieved. In addition, as a result of the developer being smoothly fed to the first communication port, the load applied to the bearing portions that support the shaft ends of the first agitation transport member and the second agitation transport member is reduced, and the wear and seal of the bearing portions are reduced. Sexual deterioration can be prevented. Further, a restriction for restricting conveyance of the developer in the axial direction and feeding the developer to the second communication port at the downstream end of the other stirring and conveying member that does not face the second communication port. Means were provided. As a result, it is possible to prevent the developer from staying at the second communication port. As a result, it is possible to prevent the occurrence of problems such as density unevenness, fogging, toner scattering, and vertical white stripes.

  Further, the first developing tank and the second developing tank disposed immediately below the first developing tank, the stirring and conveying means including the screw member disposed in the second developing tank (the first stirring and conveying member and Since the screw diameter of the second agitating and conveying member) is smaller than the screw diameter of the supply and conveying means including the screw member disposed in the first developing tank, the space required in the vertical direction and the horizontal direction is reduced. The developing device main body can be made compact.

  Further, according to the image forming apparatus provided with the developing device according to the present invention, there is an effect that it is possible to provide an image forming apparatus that is compact and can cope with high-speed processing.

1 is a schematic configuration diagram of an image forming apparatus including a developing device according to an embodiment of the present invention. 1 is a perspective view showing a developing device according to an embodiment of the present invention. 1 is a side view showing a developing device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view taken along line AA of the developing device in FIG. 3. FIG. 4 is a cross-sectional view taken along line DD of the developing device in FIG. 3. FIG. 4 is a cross-sectional view of the developing device in FIG. 3 taken along the line BB and the line CC. It is a figure which shows the example which provided the reverse winding part in the downstream edge part of a 1st stirring conveyance member, and the downstream edge part from the upstream vicinity position from the 2nd communicating port in a 2nd stirring conveyance member. 6 is a data table showing the result of visual recognition of an image printed by the image forming apparatus.

  Hereinafter, a developing device according to an embodiment of the present invention and an image forming apparatus including the developing device will be described with reference to the accompanying drawings. In the following description, “upper part”, “lower part” and terms including those terms, “clockwise direction”, and “counterclockwise direction” are used for convenience, but these are for ease of understanding of the invention. The terms should not be construed as limiting the technical scope of the present invention.

1. Configuration of Image Forming Apparatus Next, the image forming apparatus T according to the present embodiment will be described with reference to FIGS. The image forming apparatus T generally includes a developing device 1, an exposure unit 2, a primary transfer unit 3, a secondary transfer unit 4 and a fixing unit 5, and a series of operations including driving of these components is not shown. Controlled by the unit. The image forming apparatus T can be applied to, for example, a so-called four-cycle color image forming apparatus or a monochrome output image forming apparatus. Further, the present invention can also be applied to a copying machine, a printer, a facsimile machine, or a multi-function machine having a combination of these functions.

  The image forming units 60 are arranged at four locations along the intermediate transfer belt 32 of the primary transfer unit 3, and yellow (Y), magenta (M), cyan (C), and cyan (C) from the upstream side in the transport direction (X direction), respectively. By forming a black (Bk) image, a color image is formed on the surface of the intermediate transfer belt 32. Each image forming unit 60 includes a developing device 1, a charging device 8, and a cleaning device 9 around the photosensitive drum 7.

  The charging device 8 forms a predetermined surface potential on the surface of the photosensitive drum 7. This surface potential becomes an electrostatic latent image when exposed by the exposure unit 2.

  The exposure unit 2 irradiates the photosensitive drum 7 with laser light, and forms an electrostatic latent image corresponding to image data read by scanner means (not shown).

  The developing device 1 includes a first developing tank 10 and a second developing tank 20 disposed immediately below the first developing tank 10. A developing roller (developer carrying member) 11 and a conveying screw (supply / conveying means) 12 are disposed in the first developing tank 10, and a first agitating screw (first conveying screw) is provided in the second developing tank 20. An agitating and conveying means comprising an agitating and conveying member 21 and a second agitating screw (second agitating and conveying member) 22 is provided. A detailed description of the developing device 1 will be described later.

  The developer carrier may be a roller-shaped photosensitive member as in the present embodiment, or a belt-shaped photosensitive member.

  In the primary transfer unit 3 and the secondary transfer unit 4, the intermediate transfer belt 32 is laid over support rollers 31 arranged at three locations, and the support roller 31 is driven by a driving unit (not shown), so that the intermediate transfer belt 32 is yellow (Y ) From the developing device 1 to the black (Bk) developing device 1, and the toner image formed on the intermediate transfer belt 32 by the voltage applied to the secondary transfer roller 40 is recorded on the recording medium. Transfer to P. The primary transfer unit 3 and the secondary transfer unit 4 may be a direct transfer method using a transfer charger, a transfer belt, or the like, instead of the transfer method using a transfer roller.

  After the transfer to the surface of the photosensitive drum 7, the cleaning device 9 collects and cleans toner remaining on the surface of the photosensitive drum 7 with a cleaning blade (not shown), for example. The cleaning device 9 is not limited to the cleaning blade type, and may be, for example, a complex cleaning type mechanism using a cleaning brush, a cleaning roller, or a combination of these means. A cleanerless system that collects toner remaining on the surface of the body drum 7 may be used.

  The fixing unit 5 fixes the toner image on the recording medium P by applying heat and pressure to the recording medium P to which the toner image conveyed in the X ′ direction is transferred. The fixing unit 5 may be a fixing method using a fixing belt or a non-contact fixing method instead of a fixing method using a fixing roller.

  A control unit (not shown) executes developer replenishment processing based on the detection voltage input from the toner density sensor 200 of the developing device 1.

2. Structure of the developing apparatus Next, the developing apparatus 1 according to this embodiment will be described with reference to Figures 2-7. As shown in FIGS. 2, 3, 4, and 6, the developing device 1 is formed in a substantially inverted L shape extending from one end side to the other end side of the photosensitive drum 7. The first developing tank 10 and the second developing tank 20 disposed immediately below the first developing tank 10 are configured. The interior of the developing device 1 divides the first developing tank 10 and the second developing tank 20 by a partition wall 100 extending in the longitudinal direction.

  However, the first developing tank 10 and the second developing tank 20 communicate with each other through a first communication port 110 and a second communication port 120 formed at both ends of the partition wall 100, respectively. The developer can be circulated and moved between the first developing tank 10 and the second developing tank 20. That is, the first developing tank 10 and the second developing tank 20 are connected to each other via the first communication port 110 and the second communication port 120 formed at both ends of the partition wall 100. . As a result, the first developing tank 10 and the second developing tank 20 form a developer conveying path through the first communication port 110 and the second communication port 120. In addition, a discharge port 19 for discharging excess developer fed from the second developing tank 20 is provided on the bottom surface of the downstream end of the first developing tank 10 at the upstream end of the second developing tank. A developer supply port 29 is formed on the upper surface of the toner.

  Further, at the bottom surface position facing the upstream side of the second communication port 120 in the vicinity of the downstream end portion in the second developing tank 20, the toner that detects the toner concentration and transmits the voltage signal to a control unit (not shown). A density sensor 200 is provided.

  As shown in FIG. 4, a developing roller (developer carrier) 11 disposed in the first developing tank 10 includes a magnet roller 11a that is fixedly disposed and a rotatable sleeve roller 11b that includes the magnet roller 11a. This is a so-called magnet roller. Below the sleeve roller 11b of the developing roller 11, a regulating plate 15 is fixed to the first developing tank 10 and extends in parallel with the central axis of the developing roller 11 to regulate the thickness of the developer layer. It is arranged opposite to the developing roller 11 through a gap.

  The magnet roller 11a has five magnetic poles N1, S1, N3, N2, and S2 along the circumferential direction of the sleeve roller 11b. Of these magnetic poles, the main magnetic pole N1 is disposed at the position of the developing region facing the photosensitive drum 7, and has the same polarity for generating a repulsive magnetic field for peeling off the developer on the sleeve roller 11b. N3 and N2 are arranged at positions facing the inside of the first developing tank 10. The sleeve roller 11b of the developing roller 11 rotates in the opposite direction to the rotation direction of the photosensitive drum 7 at the facing portion.

  The conveying screw 12 extends in the first developing tank 10 along the rotation axis direction of the developing roller 11. The conveying screw 12 includes a spiral blade 12b around the rotating shaft 12a. The blades 12b are formed in a direction in which the developer is conveyed from the second communication port 120 side to the first communication port 110 side when the conveyance screw 12 is rotated. With such a configuration, the conveying screw 12 supplies the developer directly or indirectly to the developing roller 11 and conveys the developer in the longitudinal direction (from the second communication port 120 side to the first communication port 110 side). Then, the developer is fed into the second developing tank 20 through the first communication port 110. Therefore, a conveyance path for conveying the developer from the second communication port 120 side to the first communication port 110 side is formed in the first developing tank 10 provided with the conveyance screw 12.

  In the present embodiment, the conveyance screw 12 has been described with an example in which the spiral blade 12b that is a forward winding blade is provided around the rotation shaft 12a. You may provide a reverse winding part and a disk-shaped member. In this way, the excess developer that cannot circulate through the first developing tank 10 climbs over the reverse winding portion and the disk-shaped member, and passes them over the upstream end (right end) of the first developing tank 10 in the transport direction. Can be discharged from the discharge port 19 provided in the section).

  As shown in FIGS. 4 and 6, the first agitation screw 21 and the second agitation screw 22 (agitating and conveying means) disposed in the second developing tank 20 are provided in the second developing tank 20. Are arranged immediately below the partition wall 100 and extend in parallel with each other along the rotation axis direction of the conveying screw 12. It is preferable that the rotation directions of the first stirring screw 21 and the second stirring screw 22 rotate in directions in which the respective circumferential surfaces are separated from the lower direction to the upper direction at positions facing each other. In addition, the rotation direction of the 1st stirring screw 21 and the 2nd stirring screw 22 is not restricted to this, A various change is possible.

  Here, a characteristic configuration of the developing device 1 of the present embodiment will be described with reference to FIG. In the developing device 1, one of the first stirring screw 21 and the second stirring screw 22 disposed in the second developing tank 20 is opposed to the second communication port 120, The other stirring screw is configured not to face the second communication port 120. Specifically, as shown in FIG. 5, the stirring screw facing the second communication port 120 is, for example, only the second stirring screw 22, and the upper part of the first stirring screw 21 is separated by the partition wall 100. Covered.

  With such a configuration, the feeding of the developer from the conveyance path of the first stirring screw 21 over the guide 25 to the conveyance path of the second stirring screw 22 is promoted, and the developer is smoothly supplied to the second communication port 120. Can be sent to.

  Returning to FIG. 6, the vertical wall portion of the second developing tank that supports the downstream shaft end of the first stirring screw 21 is the vertical wall portion that supports the downstream shaft end of the second stirring screw 22. It is located on the upstream side of the developer conveying direction and on the front side of the second communication port 120.

  Each of the first stirring screw 21 and the second stirring screw 22 includes spiral blades 21b and 22b around the rotation shafts 21a and 22a. The blades 21b and 22b rotate the first stirring screw 21 and the second stirring screw 22 in the direction in which the developer is conveyed from the first communication port 110 side to the second communication port 120 side (FIG. 6 ( a) shown in a).

  In other words, the first stirring screw 21 and the second stirring screw 22 convey the developer in the longitudinal direction (from the first communication port 110 side to the second communication port 120 side), and the second communication port 120 passes through the second communication port 120. Then, the developer is fed into the first developing tank 10. In other words, the second developing tank 20 in which the first stirring screw 21 and the second stirring screw 22 are disposed has a transport path a for transporting the developer in the direction opposite to that of the first developing tank 10. Has been. In addition, it is preferable that the rotation speeds of the first stirring screw 21 and the second stirring screw 22 are different from each other in order to improve the stirring ability of the developer. For example, the units of the first stirring screw 21 and the second stirring screw 22 may be configured such that the number of rotations of each screw can be controlled by a control unit (not shown). In addition, for example, by changing the gear ratio of the gear that drives each screw, it is also possible to make each rotation speed different.

  Further, in each of the first stirring screw 21 and the second stirring screw 22, the developer conveyed in the rotation axis direction (a direction shown in FIG. 6A) is stirred in the radial direction of the blades 21b and 22b. The rectangular ribs 21 c and 22 c that are dispersed and uniformly distribute a predetermined amount of developer in the axial direction of the second developing tank 20 are fixed. Specifically, the rib 21c is positioned upstream of the blade 21b and fixed to the outer peripheral surface of the rotating shaft 21a, and is disposed on the same plane parallel to the rotating shaft direction of the first stirring screw 21. ing. Similarly, the rib 21c is also fixed on the outer peripheral surface of the rotating shaft 22a at the upstream side of the blade 22b, and is disposed on the same plane parallel to the rotating shaft direction of the second stirring screw 22. .

  At the bottom of the second developing tank 20 located between the first stirring screw 21 and the second stirring screw 22, one end of the first stirring screw 21 and the second stirring screw 22 in the rotational axis direction is provided. A protruding guide 25 is formed from the side to the other end side. The cross-sectional shape orthogonal to the axial direction of the rotation shafts 21a, 22a of the first stirring screw 21 and the second stirring screw 22 in the guide 25 is a mountain shape with the skirt extending outwardly, and the first stirring screw 21 And the clearance gap between the outermost part of each 2nd stirring screw 22 and the said bottom part is formed so that it may become predetermined distance.

  As is apparent from a comparison of the first stirring screw 21 and the second stirring screw 22 and the conveying screw 12, the first stirring screw 21 and the second stirring screw 22 arranged in parallel to each other. The screw diameter is smaller than the screw diameter of the conveying screw 12. Thereby, the space required for the vertical direction and the horizontal direction of the main body of the developing device 1 can be reduced.

  Of the first stirring screw 21 or the second stirring screw 22, the conveying direction of one stirring screw facing the second communication port 120 is the second from the upstream end of the one stirring screw. The conveyance direction to the upstream vicinity region of the communication port 120 and the conveyance direction from the upstream vicinity region of the second communication port 120 to the downstream end of the one stirring screw are configured to be opposite to each other. Also good. Specifically, as shown in FIG. 7, the second stirring screw 22 facing the downstream region S including the upstream vicinity region of the second communication port 120 is moved in the direction opposite to the developer conveying direction a. A blade 22d (in the direction b) may be provided, and the mounting pitch of the blade 22d may be smaller than that of the blades 21b and 22b to apply a braking force in the developer transport direction.

  By adopting such a configuration, the conveying force in the direction opposite to the a direction is applied to the developer that is conveyed in the a direction in the second developing tank 20 and is present in the vicinity of the second communication port 120 and its vicinity. By imparting, it is possible to prevent the developer from staying at the second communication port 120. As described above, it is possible to prevent the developer from staying at the second communication port 120. As a result, it is possible to prevent problems such as density unevenness, fogging, toner scattering, and vertical white stripes.

  Further, a regulating means for regulating the movement of the developer conveyed from the upstream side to the second communicating port 120 at the downstream end of the other stirring screw that does not face the second communicating port 120. May be provided. Specifically, as shown in FIG. 7, the downstream end portion of the first agitating and conveying screw 21 that does not face the second communication port 120 is in a direction opposite to the developer conveying direction a (direction b). A blade 21d may be provided.

  With such a configuration, the developer can be smoothly fed into the second communication port 120, and the force received by the vertical wall portion supporting the downstream shaft end portion of the first agitating and conveying screw 21 can be reduced. Thus, the torque required to drive the first stirring and conveying screw 21 and the second stirring screw 22 can be reduced. Note that the same effects as described above can be obtained by providing a disk-shaped member or paddle instead of the blade 21d.

3. Developer Used in Developing Device In the present embodiment, the developer comprises toner, a carrier for charging the toner, and reverse polarity particles. The toner may be a known toner that is generally used, and is not particularly limited. It is possible to use a binder resin containing a colorant and, if necessary, a charge control agent, a release agent, or the like and treating an external additive. The toner particle diameter is not limited to this, but is preferably about 3 to 15 μm, for example. In manufacturing such a toner, it can be manufactured by a publicly known method, for example, a pulverization method, an emulsion polymerization method, a suspension polymerization method, or the like.

  The binder resin used in the toner is not limited to this. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene-substituted product), polyester resin, epoxy resin, vinyl chloride Resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins and the like can be mentioned. It is preferable to use those having a softening temperature in the range of 80 to 160 ° C. and those having a glass transition point in the range of 50 to 75 ° C., depending on the resin alone or the composite.

  Further, as the colorant, known ones that are generally used can be used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultra Marine blue, rose bengal, lake red or the like can be used, and it is generally preferable to use 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  Also, known charge control agents can be used, and examples of charge control agents for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazoles. System compounds and polyamine resins. Examples of the charge control agent for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curlyx arene compounds. In general, the charge control agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  Also, as the above-mentioned mold release agent, known ones that are generally used can be used. For example, polyethylene, polypropylene, carnauba wax, sazol wax and the like can be used alone or in combination of two or more. In general, it is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  In addition, as the external additive, known ones that are generally used can be used, and fluidity improvement, for example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin, etc. In addition, resin fine particles such as a fluororesin can be used, and it is particularly preferable to use a resin that has been hydrophobized with a silane coupling agent, a titanium coupling agent, silicon oil, or the like. Then, such a fluidizing agent is added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The number average primary particle size of the external additive is preferably 10 to 100 nm.

  The carrier is not particularly limited, and a commonly used carrier can be used, and a binder type carrier, a coat type carrier, and the like can be used. Although it is not limited to this as a carrier particle size, 15-100 micrometers is preferable.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and positive or negative chargeable fine particles can be fixed on the carrier surface, or a surface coating layer can be provided. Charging characteristics such as polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, and the type of the surface coating layer. Examples of the binder resin used for the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, and curable resins such as phenol resins. .

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape may be granular, spherical, or needle-shaped. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added in an amount of 50 to 90% by weight in the magnetic resin carrier.

  Silicone resin, acrylic resin, epoxy resin, fluorine-based resin, etc. are used as the surface coating agent for the binder type carrier, and these resins are coated on the surface and cured to form a coat layer. Can be improved. For example, the charging fine particles or the conductive fine particles can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly and adhering the fine particles to the surface of the magnetic resin carrier. By applying a strong impact force and fixing the fine particles so as to be driven into the magnetic resin carrier. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier. As the chargeable fine particles, organic or inorganic insulating materials are used.

  Specifically, organic insulating fine particles such as polystyrene, styrene-based copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof may be used as the organic type. Regarding the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, a surface treatment, and the like. Further, as the inorganic type, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and also in a coated carrier, positively or negatively chargeable fine particles are fixed on the surface of a carrier in the same manner as a binder carrier. You can. Charging characteristics such as polarity of the coat type carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, the same resin as the binder resin of the binder type carrier can be used as the coating resin.

4). Operation of Image Forming Apparatus Next, the operation of the image forming apparatus T having the above configuration will be described. At the time of image formation, color print data obtained by reading an image or image data output from a personal computer or the like is subjected to predetermined signal processing, and then yellow (Y), magenta (M), cyan ( C) and image signals of black (Bk) are transmitted to the respective image forming units 60.

  In each image forming unit 60, a laser beam modulated by an image signal is projected onto each photosensitive drum 7 to form an image latent image. Then, toner is supplied from the developing device 1 to the photosensitive drum 7. In the developing device 1, by rotating the first stirring screw 21 and the second stirring screw 22, the developer stored in the second developing tank 20 is circulated while stirring. Then, the developer is supplied from the conveying screw 12 to the developing roller 11, scraped off by the regulating member 15 to a constant amount, and then conveyed to the photosensitive drum 7.

  As a result, yellow, magenta, cyan, and black toner images are formed on the respective photosensitive drums 7. The formed yellow, magenta, cyan, and black toner images are primary-transferred by the primary transfer unit 3 while being sequentially superimposed on the moving intermediate transfer belt 32. The superimposed toner image formed on the intermediate transfer belt 32 in this way moves to the secondary transfer unit 4 according to the movement of the intermediate transfer belt 6, and the intermediate transfer belt is applied by the voltage applied to the secondary transfer roller 40. The toner image formed on the recording medium P is transferred to the recording medium P.

  Then, the fixing unit 5 fixes the toner image on the recording medium P by applying heat and pressure to the recording medium P to which the toner image conveyed in the X ′ direction is transferred. The untransferred toner remaining on the intermediate transfer belt 32 is scraped off from the intermediate transfer belt 32 by a cleaning unit (not shown).

  Next, agitation / circulation of the developing device 1 of the present embodiment will be described with reference to FIGS. 2, 4, 5, and 6. The toner supplied from the supply port 29 is supplied to the second developing tank 20 of the developing device 1. For example, when the first stirring screw 21 rotates counterclockwise when viewed from the upstream side in the screw conveying direction and the second stirring screw 22 rotates clockwise when viewed from the upstream side in the screw conveying direction, replenishment The developed developer is conveyed from the top to the bottom by the second stirring screw 22 along the vertical wall portion opposite to the first stirring screw 21.

  Thereafter, the developer is agitated in the conveying path of the first agitating screw 21, is sent to the conveying path of the second agitating screw 22 over the guide 25, and at the same time in the longitudinal direction (arrow shown in FIG. 5A). a direction). Further, the developer is agitated in the conveyance path of the second agitating screw 22, is sent to the conveyance path of the first agitating screw 21 over the guide 25, and is also longitudinally (arrow shown in FIG. 5A). a direction). In this way, the developer in the conveyance path of each of the stirring screws 21 and 22 is stirred and transported by the first stirring screw 21 and the second stirring screw 22.

  Here, the guide 25 between the first agitating screw 21 and the second agitating screw 22 assists in improving the speed when feeding the developer in the longitudinal direction, while the first agitating screw 21. Is also provided with an auxiliary function for feeding the developer from the conveying path to the conveying path of the second stirring screw 22 and vice versa. The first agitating screw 21 and the second agitating screw 22 rotate, for example, from the bottom to the top in portions facing each other, and a developer is obtained along the guide 25 by obtaining a propulsive force by the rotational movement of the ribs 21c and 22c. Since the toner is fed in the rotating direction, the developer can be well stirred.

  In the transport path in the second developing tank 20, the first stirring screw 21 and the second stirring screw 22 facing the downstream region S including the upstream vicinity region of the second communication port 120 are provided with development. Since the blades 21d and 22d, which are in the opposite direction (b direction) to the agent conveyance direction a, are provided, the developer is braked in the vicinity of the upstream side of the second communication port 120 with respect to the conveyance direction. A part of the braked developer is pushed out by the developer continuously conveyed by the first agitating screw 21 and the second agitating screw 22 and merges with each other. Thus, the developer can be smoothly fed to the vicinity of the upstream side of the conveying screw 12 in the first developing tank 10 located immediately above. The forces received by the first developing tank 10 and the second developing tank 20 of the developing device 1 in the developer transport direction by the blades 21d and 22d, and consequently the forces received by the first stirring screw 21 and the second stirring screw 22 Therefore, the torque required for driving the developing device 1 can be reduced.

  A predetermined amount of developer fed into the first developing tank 10 through the second communication port 120 is conveyed toward the first communication port 110 as the conveyance screw 12 rotates. A predetermined amount of developer is blocked by a disc-like member (not shown) provided at the upstream end of the conveying screw 12 and is stored in a predetermined amount before the discharge port 19. However, when the developer is further fed thereafter, the developer gets over the disk-shaped member and enters the discharge port 19 and is discharged from the discharge port 19. In this way, it is not necessary to send the developer to the discharge port 19 until the developer exceeding a certain amount is sent, so that the developer is not reduced when it is not necessary. Therefore, it can be avoided that the amount of the developer becomes too small in the circulation conveyance path.

  The developer that has been sufficiently stirred and conveyed by the developing device 1 and has been normally charged is conveyed in the longitudinal direction while being supplied to the developing roller 11 in the first developing tank 10. The developer conveyed by the conveying screw 12 is sent from the first developing tank 10 to the second developing tank 20 through the first communication port 110 downstream in the developer conveying direction. Further, the first agitating screw 21 is fed from the conveying path over the guide 25 to the conveying path of the second agitating screw 22. At this time, the second stirring screw 22 is the only stirring screw facing the second communication port 120, and the upper portion of the first stirring screw 21 is covered with the partition wall 100. For this reason, the feeding of the developer from the conveying path of the first agitating screw 21 to the conveying path of the second agitating screw 22 over the guide 25 is promoted, and the developer is smoothly fed into the second communication port 120. be able to. Thus, a good circulation balance of the developer in the developing device 1 is ensured.

  On the other hand, in the developing device 1, the toner concentration is detected by the toner concentration sensor 200 on the downstream side of the second developing tank 20 in the developer transport direction. Then, a developer replenishment amount is determined based on the toner density and image information at the time of image formation, and developer replenishment is performed from a hopper (not shown) filled with the developer to the supply port 29.

5. Experimental Examples Hereinafter, in the developing device 1 according to the present invention and the image forming apparatus T including the same, even if the first stirring screw 21 and the second stirring screw 22 rotate at a low speed, the image quality is not deteriorated. An experimental example for confirming the effect of whether or not a good image can be obtained will be described. The experimental conditions are as shown in FIG. The image density unevenness was evaluated as “×” for those that could be clearly confirmed on the image, “Δ” for those that could be faintly confirmed, and “◯” for those that could not be confirmed. As an image output condition, 100 sheets of A4 printing rate 100% continuous and 10 sheets of printing rate 0% were confirmed by images when 1 set and 5 sets were continuous. The rotation speeds of the conveying screws are 200 rpm, 400 rpm, and 600 rpm, respectively, corresponding to 40, 80, and 120 output sheets per minute.

  The “reverse winding” in the end change column of the first stirring screw 21 and the second stirring screw 22 in the figure is one in which a reverse winding portion is provided at the downstream end of each of the stirring screws 21 and 22 ( (See FIG. 6). The “paddle” is a paddle portion provided at the downstream end of each of the agitating screws 21 and 22. “None” indicates a configuration in which a reverse winding portion or a paddle portion is not provided at the downstream end portion of each of the stirring screws 21 and 22. Furthermore, “short” indicates a stirring screw that does not face the second communication port 120.

  In the developing device 1 shown in FIG. 9, the rotational speeds of the first stirring screw 21 and the second stirring screw 22 are sequentially increased in order to eliminate uneven image density when the rotational speed of the conveying screw 12 is 600 rpm. As a result, the developer leaked between ˜1250 rpm.

  In the developing device 2 shown in FIG. 9, the axial length of the second stirring screw 22 that does not face the second communication port 120 is made 50 mm shorter than the first stirring screw 21, for example. The length of 120 in the axial direction was set to 40 mm, for example. According to this experimental example, good image quality can be obtained even if the rotation speed of the first stirring screw 21 and the second stirring screw 22 is low, and development is possible even when the rotation speed of the conveying screw 12 is 600 rpm. It was confirmed that there was no leakage of the agent.

  In the developing device 3 shown in FIG. 9, the rotational speed of the first stirring screw 21 is set to 1.2 times the rotational speed of the second stirring screw 22, and the length of the second communication port 120 in the axial direction is set. For example, it was set to 40 mm. The length of the second stirring screw 22 in the axial direction is the same as that of the developing device 2. According to this experimental example, good image quality could be obtained in the low rotation range, medium rotation range, and high rotation range excluding the first stirring screw 21 and the second stirring screw 22 extremely low rotation range.

  In the developing device 4 shown in FIG. 9, a reverse winding portion is provided at the downstream end of the first stirring screw 21, and the rotational speed of the first stirring screw 21 is set to 1.. The axial length of the second communication port 120 was set to 40 mm, for example. The length of the second stirring screw 22 in the axial direction is the same as that of the developing device 2. According to this experimental example, the image density unevenness was the same as that of the developing device 3, and the result of eliminating the leakage of the developer was obtained.

  In the developing device 5 shown in FIG. 9, a reverse winding portion is provided at the downstream end portions of the first stirring screw 21 and the second stirring screw 22, and the rotation speed of the first stirring screw 21 is set to the second stirring screw 22. The axial length of the second communication port 120 was set to 40 mm, for example, 1.2 times the rotational speed. The length of the second stirring screw 22 in the axial direction is the same as that of the developing device 2. According to this experimental example, a good image can be obtained without causing the image quality to deteriorate over the entire range from the low speed range to the high speed range when the conveying screw 12, the first stirring screw 21 and the second stirring screw 22 are rotated. Can do. In addition, leakage of the developer could be prevented.

  In the developing device 6 shown in FIG. 9, a paddle portion is provided instead of the reverse winding portion provided at the downstream end portion of the second stirring screw 22 of the developing device 5. Other conditions are the same as those of the developing device 5. According to this experimental example, similarly to the developing device 5, the rotation speed of the conveying screw 12, the first stirring screw 21 and the second stirring screw 22 causes the image quality to deteriorate over almost the entire range from the low speed range to the high speed range. And a good image can be obtained. In addition, leakage of the developer could be prevented.

  In the developing device 7 shown in FIG. 9, the screw diameter of the conveying screw 12 of the developing device 6 is changed from 30 mm to 40 mm, and the screw diameters of the first stirring screw 21 and the second stirring screw 22 are changed from 20 mm to 25 mm. . Other conditions are the same as those of the developing device 6. According to this experimental example, as with the developing devices 5 and 6, the rotation speed of the conveying screw 12, the first stirring screw 21, and the second stirring screw 22 deteriorates the image quality over almost the entire range from the low speed range to the high speed range. A good image can be obtained without inviting. In addition, leakage of the developer could be prevented.

  In the above experimental example, the rotation direction of the developing roller 11 may be a clockwise direction or a counterclockwise direction. Further, the developer transport amount may be the same or different, and the bias to be applied may be the same or different. The number of rotations of the developing roller 11 may be constant or controlled. Further, it has been confirmed that the same effect can be obtained even when a carrier having a particle size of 20 μm, 40 μm, and 60 μm is used, but the developer is not limited thereto.

  In this embodiment, the carrier is replenished from the hopper simultaneously with the toner, but may be replenished by a single carrier. Further, it may be replenished to the same level as the toner density in the developing device 1 or may be a system that does not replenish the carrier (in this case, no discharge means is provided).

  The embodiments disclosed herein are illustrative and not limiting. The present invention is defined by the scope of the claims, rather than the scope described above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

  The present invention is applicable not only to the trickle-type developing device described in the above embodiment, but also to an ordinary two-component type developing device.

DESCRIPTION OF SYMBOLS 1 Developing apparatus 2 Exposure unit 3 Primary transfer part 4 Secondary transfer part 5 Fixing unit 7 Photoconductor drum 10 1st developing tank 11 Developing roller 12 Conveying screw 15 Control member 20 2nd developing tank 21 1st stirring screw 22 Second stirring screw 25 Guide 100 Partition wall 110 First communication port 120 Second communication port 200 Density sensor T Image forming apparatus

Claims (8)

A first developing tank and a second developing tank disposed immediately below the first developing tank;
The first developing tank is
A developer carrier that contains magnetic field generating means and carries a developer composed of two components of toner and carrier to a development region facing the photoreceptor;
Supply conveyance including a screw member disposed in the first developer tank and supplying the developer to the developer carrier while conveying the developer in the axial direction of the developer carrier adjacent to the developer carrier. Means,
The second developing tank is
An agitating / conveying means including a screw member disposed in the second developing tank and agitating / dispersing the developer and conveying the developer in a direction opposite to the supply / conveying means;
The first developer tank and the second developer tank are connected to each other through a partition wall formed at both end portions through which the developer flows, thereby forming a circulation transport path for the developer. Development device,
Openings formed at both ends of the partition wall include a first communication port that delivers the developer from the vicinity of the downstream end of the supply transport unit to the vicinity of the upstream end of the stirring transport unit, A second communication port that delivers the developer from the vicinity of the downstream end of the agitation transport means to the vicinity of the upstream end of the supply transport means;
The agitating and conveying means comprises a first agitating and conveying member and a second agitating and conveying member disposed in parallel with each other along the developer conveying direction,
Each of the first stirring and conveying member and the second stirring and conveying member conveys the developer in the same direction,
The second communication port is an upper portion facing either one of the first stirring and conveying member or the second stirring and conveying member, and a downstream end portion of the one stirring and conveying member The vertical wall portion of the second developing tank that is formed in the vicinity and supports the downstream shaft end of the other stirring and conveying member is the vertical wall portion that supports the downstream shaft end of the one stirring and conveying member. A developing device, wherein the developing device is located on the upstream side in the developer conveying direction and on the near side of the second communication port.   2. The developing device according to claim 1, wherein screw diameters of the first agitation transport member and the second agitation transport member are smaller than a screw diameter of the supply transport unit.   The developing device according to claim 1, wherein the number of rotations of each of the first stirring and conveying member and the second stirring and conveying member is controllable.   The developer conveying direction of one of the first agitating and conveying member or the second agitating and conveying member facing the second communication port is the upstream end of the one agitating and conveying member. The conveyance direction from the second communication port to the upstream vicinity position from the second communication port is opposite to the conveyance direction from the second communication port to the upstream vicinity position to the downstream end of the one agitation conveyance member The developing device according to claim 1, wherein the developing device is a developing device.   At the downstream end of the other agitating / conveying member that is not opposed to the second communication port, a restricting means for restricting the conveyance of the developer in the axial direction and feeding the developer into the second communication port. The developing device according to claim 1, wherein the developing device is formed.   The developing device according to claim 5, wherein the restricting unit is a reverse winding portion.   The developing device according to claim 5, wherein the restricting unit is a paddle part.   An image forming apparatus comprising the developing device according to claim 1.

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