JP2000075666A - Developing device and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize an amount of carried developer, which is moved from a carrying roll to a developing roll. SOLUTION: The developing device employs a so-called purge system in which the developer on the developing roll 1 is temporarily removed and recovered. In this developing device, the developer supply area 11 of the carrying roll 4 is disposed opposite a receiving magnetic pole 3, one of the magnetic poles of the magnet member 2 of the developing roll 1, which receives the developer from the carrying roll 4 first, and within a receiving magnetic flux density stable area 10 where the component, in the direction of the normal line, of the receiving magnetic flux density formed at the receiving magnetic pole 3 is stable in the axial line of the developing roll 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, and more particularly to a developing device using a two-component developer composed of a toner and a carrier. The present invention relates to a so-called purging type developing device for temporarily collecting and retracting a developer on a developing roll, and an improvement in an image forming apparatus using the developing device.

[0002]

2. Description of the Related Art Conventionally, for example, among electrophotographic image forming apparatuses, an apparatus for forming a multicolor image includes a plurality of color component developers around a latent image carrier such as a photosensitive drum. There is an apparatus in which a housed developing device is disposed to selectively form a toner image of each color component on a latent image carrier. In this type of image forming apparatus, in order to prevent color mixture with other color component toners when forming each color component toner image on the latent image carrier, the color component development of a developing device to be developed is performed. It is necessary to devise a method in which only the developer is rubbed against the electrostatic latent image on the latent image carrier to perform development, so that a color component developer of a developing device which is not a development target is not brought into contact with the latent image carrier.

Conventionally, for example, a developing device for each color component is arranged in parallel on a latent image carrier, and only a developing device to be developed is set at a position close to the latent image carrier, and the other developing devices are not developed. The developing device is retracted to a standby position separated from the set position, or a so-called retract system, in which a plurality of color component developing units are mounted on a rotating holder, and only the developing unit to be developed is latent by rotating the rotating holder appropriately. The so-called rotary method, which is set at a set position close to the image carrier, or the supply of the developer to the developing roll is stopped at the end of the development, and the developer remaining on the developing roll is temporarily collected. There is known a so-called purge method for retreating. Here, the purging method does not require the use of a retracting mechanism of a developing device such as a retracting method or a rotating mechanism such as a rotary method, and thus simplifies the device configuration, particularly the configuration related to holding the developing device. Also, it is preferable in that vibration generated when the developing device is moved is small.

A developing device using this type of purge system has a developing housing facing a latent image carrier such as a photosensitive drum, for example, and a so-called magnet roll (a plurality of magnet rolls inside the developing housing) is provided at an opening of the developing housing. A developing roller having a structure in which a magnet member having magnetic poles arranged thereon is fixedly disposed and a non-magnetic sleeve is rotatably disposed around the developing roller; Further, a layer thickness regulating blade that regulates the thickness of the developer to a predetermined thickness is disposed close to the transport roll, and further, the developer is stirred and transported to the back side of the transport roll. A device equipped with a stirring and conveying auger is already known (for example, Japanese Patent Application Laid-Open No. 63-2294).
No. 66, JP-A-8-248771).

[0005] In this type of purging type developing device, during the developing operation, the developer is supplied to the transport roll after being agitated and transported by the agitated and transported auger, and is supplied to the transport roll by the layer forming blade to have an appropriate layer thickness. To the developing roll, thereby supplying the developing agent to the developing area between the latent image carrier and the developing roll, and further transferring the residual developer on the developing roll to the agitating / conveying auger via the supply roll. I am going to put it back. On the other hand, at the end of the development, the transport roll is stopped first, the supply of the developer to the development roll is stopped, and the developer on the development roll is stopped after collecting the developer on the development roll into the development housing. Collect developer temporarily,
It is designed to be evacuated.

[0006]

However, in such a purging type developing apparatus, when the developer is transferred from the transport roll to the developing roll, the developer carried on both ends of the transport roll is charged with the developer. It does not move in the vertical direction of the axis, but moves slightly inside (toward the center) from both ends of the developing roll, and the amount of developer transported near both ends of the developer transport area of the developing roll is compared with that in the center. There was a technical problem that the resulting non-uniformity was significant. When such a phenomenon occurs, the transport amount increases in the region slightly closer to the center from both ends of the developing roll by the amount of the developer moved from both ends. In the developer concentration region where the transport amount of the developer is increased, the developer is easily fixed on the developing roll and the latent image carrier because the layer thickness of the developer is increased in the developing region, Further, there is a possibility that the developing roll and the latent image carrier are scraped. At this time,
In the region closer to the end than the developer concentration region, the amount of the developer transported is drastically reduced, so that the image density is significantly reduced. Such a phenomenon is particularly remarkable when the developer transport amount at the end of the transport roll is large.

In the prior art, for example, a technique for suppressing the spread of the developer conveyed on the magnet roll to the end side by devising the shape and configuration of the layer regulating blade (Japanese Patent Laid-Open Publication No. Hei.
333677, JP-A-9-204100,
JP-A-8-202153, JP-A-6-14907
No. 0, JP-A-6-35314, etc.) or a technique for reducing the amount of developer supply to the end of the magnet roll by devising the shape of the stirring and conveying paddle for supplying the developer to the magnet roll. (See Japanese Unexamined Patent Publication No. Hei 6-35314). However, in the purge type developing device, since the layer regulating blade is provided on the transport roll side, even if the above configuration is adopted, the spread of the developer layer on the transport roll is only suppressed, When transferring the developer from the transport roll to the developing roll, there is still a technical problem that the developer transport amount near both ends of the developer transport region of the developer roll is significantly non-uniform as compared with the central portion. I can't solve it.

In order to solve such a technical problem, a layer regulating blade has to be adjusted to balance the amount of developer transported at the end of the transport roll and the amount of developer transported in the developer concentrated portion of the developer roll. And the shape of the stirring and transport paddle should be designed, but this optimization design is very difficult, and even if it could be designed, the shape of the layer regulating blade and the stirring and transport paddle would be complicated. There's a problem.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 7-219354, if a layer regulating blade is also provided on the developing roll side to regulate the amount of developer transport, the developer is transferred from the transport roll to the developing roll. In this case, even if the transport amount of the developer becomes non-uniform, it can be said that it is possible to make the transport amount of the developer uniform again after transferring to the developing roll. However, in such an aspect, there is a technical problem that the number of components is increased or the size of the device for securing the installation space is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problem. In a so-called purging type developing device, the structure of a transport roll and a developing roll is improved by changing the configuration of the transport roll and the developing roll. The present invention provides a developing device capable of equalizing the amount of developer transported to the image forming apparatus and an image forming apparatus using the developing device.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above-mentioned technical problems, and have found that the magnetic flux density distribution due to the magnetic field for transferring the developer from the transport roll to the developing roll and the amount of developer transported Paying attention to the fact that there is a correlation between the present invention and the present invention.

That is, as shown in FIGS. 1 (a) and 1 (b), the present invention has a developing housing 8 which is open to face the latent image carrier 9 and has a plurality of Developing member 1 in which a magnet member 2 having a magnetic pole is fixedly disposed inside and a two-component developer is carried and transported.
And a transport roll for supplying a developer to the developing roll 1 and collecting the developed developer carried on the developing roll 1, and a magnet member 5 having a plurality of magnetic poles formed therein is fixedly disposed therein. And a stirring and conveying member 6 for conveying the developer to be conveyed while being conveyed to the conveying rolls 4.
And a layer thickness regulating member 7 that regulates the layer thickness of the developer supplied to the transport roll 4, wherein, among the plurality of magnetic poles of the magnet member 2 of the developing roll 1, With respect to the receiving magnetic pole 3 which receives the developer from the transport roll 4 first, the receiving magnetic flux in which the component of the received magnetic flux density formed by the receiving magnetic pole 3 in the direction normal to the surface of the developing roll 1 is stable in the axial direction of the developing roll 1 It is characterized in that the developer supply region 11 of the transport roll 4 is arranged to face the density stable region 10.

In such technical means, the present invention can be applied to any type of developing apparatus of a so-called purge system. Furthermore, an image forming apparatus provided with the developing device according to the present invention is also an object of the present invention.

If the magnet members 2 and 5 have a plurality of magnetic poles formed around them, the structure is such that permanent magnets, electromagnets or other magnets are buried, or a corresponding portion is attached to a magnetic body. A magnetized one may be selected as appropriate. Here, the polarity of the magnetic poles formed on each of the magnet members 2, 5 is such that, at least in the region where the developer is conveyed, between the adjacent magnetic poles and the magnet members 2 and 5 in each of the magnet members 2, 5. It is necessary to configure the magnetic poles adjacent to each other at the position where the developer is delivered to have different polarities. Then, a region where the developer is not conveyed within the same magnet members 2 and 5 (for example, the magnet members 2 and 5).
And the magnetic poles adjacent to the magnet members 2 and 5 formed at both ends of the closest part between the magnetic poles 5 and 5, the polarity relationship between the adjacent magnetic poles is appropriately determined as long as the transport of the developer in this area is prevented. You can choose it.

Further, in the present invention, among the plurality of magnetic poles of the magnet member 2 of the developing roll 1, the receiving magnetic pole 3 which first receives the developer from the transporting roll 4 relates to the receiving magnetic flux formed by the receiving magnetic pole 3. It is necessary to dispose the developer supply area 11 of the transport roll in a receiving magnetic flux density stable area 10 where the component of the density in the normal direction of the surface of the development roll 1 is stable in the axial direction of the development roll 1. This is related to the receiving magnetic pole 3 which first receives the developer from the transport roll 4 among the plurality of magnetic poles of the magnet member 2 of the developing roll 1, and the surface of the developing roll 1 having the receiving magnetic flux density formed by the receiving magnetic pole 3. In other words, the region where the received magnetic flux density is unstable in which the component of the normal direction fluctuates in the axial direction of the developing roll is not made to face the developer supply region 11 of the transport roll. Kill. Here, the received magnetic flux density stable area 10 in the present invention refers to an area having the same magnetic flux density as the received magnetic flux density near the center of the developing roll 1, while the received magnetic flux density unstable area refers to the developing roll 1 A region having a magnetic flux density significantly lower than the received magnetic flux density near the center.

From the viewpoint of realizing the above conditions with a simple configuration, of the plurality of magnetic poles of the magnet member 5 of the transport roll 4, the axial direction of the transfer magnetic pole that transfers the developer to the developing roll 1 is used. It is preferable that the length is set to be less than the axial length of the receiving magnetic pole 3, and both ends of the receiving magnetic pole 3 in the axial direction are disposed at or outside the axial ends of the delivered magnetic pole.

Further, when the developer carried near the end of the transport roll 4 moves to the developing roll 1, the developer moves to a region slightly inside the end of the developing roll 1 and the developer is moved to the region. From the viewpoint of reliably preventing concentration, from among the plurality of magnetic poles of the magnet member of the transport roll 4, regarding the transfer magnetic pole that transfers the developer to the developing roll 1,
In the received magnetic flux density stable area 10, a delivered magnetic flux density stable area in which the component of the delivered magnetic flux density formed by the delivered magnetic pole in the normal direction of the surface of the transport roll 4 is stable in the axial direction of the transport roll 4 is arranged to face each other. Is preferred.

Further, from the viewpoint of increasing the amount of the developer transported in the developer supply area 11 of the transport roll 4 and decreasing the amount of the developer transported near the end portion, the developer of the transport roll 4 It is preferable that the surface roughness of the supply region 11 is set to be larger than the non-developer supply regions at both ends of the transport roll 4.

Similarly, the developer supply area 1 of the transport roll 4
From the viewpoint of increasing the amount of the developer conveyed through the conveying roller 1 and decreasing the amount of the developer conveyed in the vicinity of the end, the developing roller 1 of the plurality of magnetic poles of the magnet member 5 of the conveying roll 4 With respect to the delivery magnetic poles to be delivered and received, the components of the delivery magnetic flux density formed by the delivery magnetic poles in the direction of the normal to the surface of the transport roll 4 are stable with respect to the transport roll 4 axis direction, It is preferable to dispose a sealing member having magnetism outward from the inside.

Next, the operation of the above technical means will be described. 1A and 1B, the stirring and conveying member 6
The developer stirred and transported by the transport roll 4 is carried on the developer supply area 11 of the transport roll 4, transported on the transport roll 4 with the rotation of the transport roll 4, and moved to a position facing the layer thickness regulating member 7. The layer thickness of the developer is regulated, and the developer that has passed through the layer thickness regulating member 7 is transported to the vicinity of a portion facing the developing roll 1. Here, the developer supply area 1 on the transport roll 4
The developer carried on the transfer roller 1 moves from the transfer roll 4 onto the development roll 1. At this time, the developer is transferred from the transfer roll 4 among the plurality of magnetic poles of the magnet member 2 of the development roll 1. Regarding the receiving magnetic pole 3 received first, the developing roll 1 of the receiving magnetic flux density formed by the receiving magnetic pole 3
Since the developer supply area 11 of the transport roll 4 is disposed opposite to the magnetic flux density stable area 10 in which the normal component of the surface is stable in the axial direction of the developing roll, as shown in FIG. Not only the developer transported in the center of the developer supply area 11 of the transport roll 4 but also the developer transported slightly at the inner end and the developer transported at the edge are perpendicular to the axis of the transport roll 4. Move in the direction. In this way, a substantially uniform developer layer G is formed on the developing roll 1 in the axial direction of the developing roll 1.

On the other hand, when this point is set to a mode other than the above, as shown in FIG. 3, the developer conveyed in the central portion of the developer supply area 11 of the transport roll 4 While moving in the direction perpendicular to the axis to form a region A having a substantially uniform layer thickness on the developing roll 1, the developer conveyed at the end slightly inside or the developer conveyed at the end is transported by the conveying roll 4. The developing roll 1 does not move in the direction perpendicular to the axis of
Because it moves slightly inward (toward the center) from both ends of,
It is experimentally confirmed that a developer increasing area B is formed in the area, a developer decreasing area C is formed outside the area, and a non-uniform area is formed at an end of the developer layer G. Was done.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. FIG. 4 shows an outline of an embodiment of a color image forming apparatus to which the present invention is applied. In the figure, the color image forming apparatus according to the present embodiment has a plurality of image forming units 81 and 82 arranged on a conveyor belt 90. Here, as the image forming units 81 and 82, for example, a uniform charging device 22 such as a scorotron for uniformly charging the photosensitive drum 21 to the negative polarity around the photosensitive drum 21 of the negative polarity, and a two-color image An exposure device 23 such as a laser scanning device for writing a corresponding electrostatic latent image, a two-component developing device 24 (24K, 24M or 24Y, 24
C), a grid collecting device 25 for collecting the carrier and the fog toner (toner transferred to the background) transferred to the photosensitive drum 21 side, and transferring the toner image formed on the photosensitive drum 21 to facilitate transfer. A pre-transfer processing device 26 such as a corotron for pre-processing, a transfer device 27 such as a corotron for transferring a toner image on the photosensitive drum 21 to a transfer material 30 such as paper or a transparent sheet, and the photosensitive drum 2
1 is provided with a static eliminator 28 such as a static elimination lamp for neutralizing the residual toner on the photosensitive drum 21 before the cleaning process, a cleaning device 29 for collecting the residual toner on the photosensitive drum 21 and the like. Then, each image forming unit 8
1, 82 developing devices (24K, 24M or 24
Y, 24C) include predetermined four colors (black in this example,
Magenta, yellow, cyan) developer is stored therein, and the photoconductor drums of the image forming units 81 and 82 are respectively rotated twice to form the respective color component toner images on the photoconductor drums 21 and on the transport belt 90. Are sequentially superimposed and transferred onto a transfer material 30 such as a sheet of paper held in the printer.

In such a color image forming apparatus,
First, in the first image forming unit 81, the uniform charging device 2
The photosensitive drum 21 whose surface is uniformly charged to negative polarity by the exposure device 23 is exposed by the exposure device 23 to the upper developing device 24.
An electrostatic latent image corresponding to the color (black) developed with K is formed. At this time, the lower developing device 24M is in a non-developing state, and the electrostatic latent image is developed into a toner image by the upper developing device 24K. This toner image is transferred to the pre-transfer processing device 2
6 and transported to the transfer unit. here,
The transfer material 30 is sent out at a predetermined timing by a registration roll 91, is adsorbed and held on a conveyor belt 90 by an adsorbing device 92 such as a corotron, and is conveyed along α in the drawing, and is transferred to a transfer unit at a predetermined timing. The toner image is supplied and transferred by the transfer device 27. The transfer material 30 that has passed through the transfer section is a second image forming unit 82
To the transfer section of the photosensitive drum 21. here,
A toner image is formed on the photosensitive drum 21 by the upper developing device 24Y at a predetermined timing, and is transferred to the transfer material 30 by the transfer device 27. Further, the transfer material 30 is transported along β and γ in the drawing, and is again transported to the transfer section of the photosensitive drum 21 of each of the image forming units 81 and 82. At this time, the toner image developed by the lower developing device 24M on the photosensitive drum 21 of the first image forming unit 81, and the lower toner image on the photosensitive drum 21 of the second image forming unit 82. A toner image developed by the developing device 24C is formed, and a full-color toner image is formed on the transfer material 30 after the transfer by the transfer device 27 is completed. Thereafter, the transfer material 30 is transported by the transport belt 90, processed by the peeling device 93, and then transported to a fixing device (not shown) along δ.
A full-color fixed image is obtained. Reference numerals 94 and 95 denote a static eliminator such as a corotron that neutralizes the conveyance belt 90 when the suction and holding operation of the transfer material 30 is completed.

Next, the developing device 24 (24K, 24M or 24Y, 24C) used in the present embodiment will be described in detail with reference to FIGS. 5 and 6, taking the developing device (24K, 24M) as an example. In the present embodiment, the basic configuration of the black developing device 24 </ b> K has a developing housing 41 that opens to face the photoconductor drum 21, and the developing housing 41 faces the opening 42 of the developing housing 41. A developing roll 43 is provided, and a transport roll 44 is provided on the back of the developing roll 43.
A pair of agitating and conveying augers 45 are formed on the back side of the agitating and conveying auger 45 in which spiral blades are continuously formed around the rotating shaft and the developer is agitated and transported from the back to the front in the rotating shaft direction or from the front to the back. , 46, a layer thickness regulating plate 47 for regulating the layer thickness of the developer supplied to the transport roll 44 is provided in the vicinity of the transport roll 44. Between the agitating / conveying auger 45, an agitating / conveying auxiliary paddle 48 composed of a plurality of plate-like blades for scraping up the developer around the rotation axis is provided. On the other hand, the basic configuration of the lower developing device 24M is similar to that of the black developing device 24K, in which the developing roll 53 is disposed at a position facing the opening 52 of the developing housing 51, and
A transport roll 54 is disposed on the back side, and a pair of agitated transport augers 55 are further provided via an agitated transport auxiliary paddle 58.
56, and a layer thickness regulating plate 57 is arranged near the transport roll 54.

Here, the difference between the black developing device 24K and the magenta developing device 24M will be described. First, the black developing device 24K will be described. As shown in FIG. 5, the developing roll 43 includes, for example, S, N, S, N, S
Magnet roll 4 around which five magnetic poles are arranged
31 is fixedly arranged, and a non-magnetic sleeve 432 is rotatably arranged around this. On the other hand, the transport roll 44
Is fixedly installed, for example, a magnet roll 441 around which six magnetic poles indicated by N, S, S, N, S, N are arranged,
A non-magnetic sleeve 442 is rotatably disposed around this, and the rotation center of the transport roll 44 is deviated above the rotation center of the developing roll 43.

Particularly, in the present embodiment, the developing roll 43
As shown in FIG. 6, the magnetic pole 43b for receiving the developer from the transport roll 44 and the magnetic pole 43a for delivering the developer to the transport roll 44 have the same polarity (S pole in this example). It has become. On the other hand, with respect to the magnetic poles of the transport rolls 44, the magnetic poles 44a (N poles in this example) which first receive the developer from the developing rolls 43 and the downstream side in the rotation direction (corresponding to the developer transport direction) of the transport rolls 44 adjacent thereto. And the magnetic pole 44b (S pole in this example) has a different pole configuration.
Further, the magnetic pole 44b and the magnetic pole 44c adjacent to the magnetic roll 44b on the downstream side in the rotation direction of the transport roll 44 have the same repulsive magnetic pole configuration. Furthermore, a magnetic pole 44a that receives the developer first from the developing roll 43 and a transport roll 44 adjacent to the magnetic pole 44a
And the magnetic pole 44d (corresponding to the magnetic pole that transfers the developer to the developing roll 43 in this example) 44d in the rotational direction has the same polarity configuration (N pole in this example).

In this embodiment, the transport rolls 44
The range of the magnetic field formed by the magnetic pole pairs 44a and 44b of
The seal / collection portion 49 having a narrower gap than the front and rear portions is formed between the bottom wall protrusion 41b and the transport roll 44. Further, as shown in FIG. 6, the rotational direction of the stirring and transporting auxiliary paddle 48 and the transporting roll 44 is set to a rotating direction in which the stirring and transporting auxiliary paddle 48 and the transporting roll 44 move in opposite directions at the closest point. In this configuration, the developer dropped from the transport roll 44 is quickly stirred and transported by the auger 45.
As the ability to take in the inside, it has a superior ability to directly oppose the stirring and conveying auger 45 having the spiral blade directly to the conveying roll 44.

Next, the lower developing device 24M will be described. As shown in FIG. 5, the developing roll 53 has, for example, six magnetic poles indicated by S, N, S, N, S, and N around it. The magnet roll 531 is fixedly arranged, and a non-magnetic sleeve 532 is rotatably arranged around the magnet roll 531. On the other hand, the transport rolls 54 are, for example, S, N, S,
A magnet roll 541 around which five magnetic poles indicated by S and N are arranged is fixedly arranged, and a non-magnetic sleeve 5
The rotation center of the transport roll 54 is deviated below the rotation center of the developing roll 53. Further, the developing housing 5
The first bottom wall 51a is disposed below the developing roll 53 and the transporting roll 54 as close as possible to the extent that the magnetic field of the two rolls 53 and 54 can reach.
In the passage between the bottom wall 51a and the bottom wall 51a, the collected developer
a. The configuration of the agitating and transporting assist paddle 58 is substantially the same as that of the upper developing device 24K. The developing device 24Y of the image forming unit 82 has the same configuration as the developing device 24K, and the developing device 24C has the same configuration as the developing device 24M.

Next, the developing device 24 (24K, 24M, 2
4Y, 24C), the relationship between the developing roll 43, the transport roll 44, and the layer thickness regulating plate 47 will be described using the black developing device 24K as an example. FIG. 7 shows the developing device 24 viewed from the direction A in FIG.
K is shown. In the present embodiment, the thickness regulating plate 47 is
Both ends are attached to side projections 41c provided on the side wall of the developing housing 41, and the end surface 41d of the side projection 41c is set to be 10 mm central from both ends 441a of the magnet roll 441 of the transport roll 44. ing.

The non-magnetic sleeve 4 of the transport roll 44
A blast surface 443 as a developer supply area is formed at the center of the 42 peripheral surface. In the present embodiment, both ends 443a of the blast surface 443 are set to be 2 mm closer to the center than both ends 441a of the magnet roll 441. This is for the following reasons. That is, regarding the transfer magnetic flux density formed in the direction normal to the surface of the transport roll 44 by the magnetic pole 44d that transfers the developer to the developing roll 43 among the magnet rolls 441 of the transport roll 44, the transfer magnetic flux density is determined in the axial direction of the transport roll 44. 8 (a) and 8 (b) were obtained as a result of examining the distribution of the magnetic poles (however, the figure shows only the results near the end of the magnetic pole 44d). In addition, when the amount of change in the delivered magnetic flux density distribution according to the position was determined in correspondence with FIGS. 8A and 8B, the results shown in FIGS. 8C and 8D were obtained. Thus, not only the region outside the both ends 441a of the magnet roll 441 but also these four ends
It has been found that there is also a region where the received magnetic flux density and the delivered magnetic flux density change in the region closer to the center than 31a and 441a. In such a region where the magnetic flux density changes, the amount of developer that can be carried may change. Therefore, in the present embodiment, both ends 443a of the blast surface 443 are disposed at a center 2 mm from both ends 441a of the magnet roll 441 in which the delivered magnetic flux density is stable, so that the carrier is supported on the blast surface 443 of the transport roll 44. The amount of the developer to be applied is made substantially uniform in the axial direction.

Further, the transport roll 4 of the layer thickness regulating plate 47
(4) A rubber magnet 471 as a developer sealant for removing the developer carried on the non-blasted surface of the transport roll 44 is attached to a surface facing the region where the blast surface 443 is not formed at both ends. It is attached.

On the other hand, the non-magnetic sleeve 4 of the developing roll 43
The blast surface 4 of the transport roll 44
A blast surface 433 that has been subjected to blast processing is formed to both ends 433a outside the both ends 443a of the 43. In the present embodiment, both ends 4 of the blast surface 433
33a is 2 mm larger than both ends 431a of the magnet roll 431
It is set to be on the center side. This is for the following reasons. That is, the magnet roll 4 of the developing roll 43
The magnetic flux 43b, which first receives the developer from the transport rolls 44, forms the reception magnetic flux density formed in the normal direction of the surface of the development roll 43.
Fig. 9 (a) shows the result of investigation of the distribution in the axial direction of No. 3.
The result shown in (b) was obtained (however, the magnetic pole 43b is shown in the figure).
The results are shown only near the end of.) FIG.
When the amount of change in the received magnetic flux density distribution according to the position corresponding to (a) and (b) was obtained, the results shown in FIGS. 9 (c) and (d) were obtained. Thus, similarly to the transport roll 44, there is a region where the received magnetic flux density and the delivered magnetic flux density change in a region outside the both ends 431a of the magnet roll 431 as well as in a region on the center side of the both ends 431a. I understood. In such a region where the magnetic flux density changes, the amount of developer that can be carried may change. Therefore, in the present embodiment, by forming both ends 433a of the blast surface 433 at the center side of 2 mm from both ends 431a of the magnet roll 431 in which the received magnetic flux density is stable, the magnet 431 is supported on the blast surface 433 of the developing roll 43. The amount of the developer to be applied is made substantially uniform in the axial direction.

Further, in the present embodiment, the developing roll 43
The two ends 431a of the magnet roll 431 are disposed outside the both ends 441a of the magnet roll 441 of the transport roll 44 by 4 mm. By doing so, FIG.
As shown in FIG. 5, the magnetic poles 43 are located outward from both ends 443a of the blast surface 443 (= both ends of the stable area of the transferred magnetic flux density by the magnetic poles 44d), which are the developer supply areas of the transport rolls 44.
It is possible to dispose both ends of the stable region of the received magnetic flux density by b.

The developing conditions in the present embodiment are as follows. The closest distance between the photosensitive drum 21 and the developing roll 43 or 53: 0.3 to 0.4 mm Photoconductor drum rotation speed: 220 mm / sec Toner image forming section potential: -300 V Background section potential: -700 V Development bias (DC): -550 V Development bias (AC, peak to peak): 1.5 kV Development bias (AC, Duty): 0.5 Development bias (AC, frequency): 4.0 kHz Development roll 43 (53), transport roll Outer diameter of 44 (54): 18 mm Rotation speed of developing roll 43 (53), transport roll 44 (54): Sleeve rotation speed 385 mm / sec Outer diameter of transport agitator augers 45, 46 (55, 56): 20 mm Transport agitator Number of rotations of augers 45 and 46 (55, 56): 273 rpm Outer diameter of auxiliary paddle 48 (58) for stirring and transporting: 16 mm Stirring and transporting Revolution of auxiliary paddle 48 (58): 670 rpm

In this embodiment, the average particle diameter is 35 μm.
m of a ferrite carrier and a toner having an average particle diameter of 7 μm. Here, the developer in the developing device 24 had a toner concentration of 8.0 wt% per 500 g.
Further, in the present embodiment, the transport amount of the developer transported on the transport roll 44 is set to 300 to 400 g / m ² . Thereby, the blast surface 44 of the transport roll 44
The developer conveyed at the three ends can be suppressed, and the developer can be uniformly conveyed on the conveyance roll 44 in the axial direction of the conveyance roll 44.

Here, the developing device 2 in the present embodiment
4 (24K, 24M, 24Y, 24C) will be described using the developing device 24K above the image forming unit 81 as an example. In the developing device 24K, as shown in FIGS. 5 and 6 (thick dotted arrows in the drawings indicate the transport path of the developer), a pair of agitating and transporting augers 45 and 46 are a two-component developer including a toner and a carrier. The stirring and conveying augers 45, 4
The developer transported by the agitating and transporting augers 45 and 46 is sent to the agitating and transporting auxiliary paddle 48, and is closest to the agitating and transporting auxiliary paddle 48 of the transport roll 44. Attracted to the pole (44c),
Sequentially in the counterclockwise direction, N-pole → S-pole → N-pole (44d). During this time, the developer passing amount is regulated by the layer thickness regulating plate 47 so that a desired amount passes, and the development carried on the non-blast surface of the transport roll 44 by the rubber magnet 471 attached to the layer regulating plate 47. The agent is removed.

The developer regulated and carried to an appropriate thickness on the blast surface 443 of the developing roll is transported to the N pole (44d) closest to the developing roll 43 on the transporting roll 44, and the opposite developing roll S pole on 43 (43b)
Passed to. At this time, in the present embodiment, FIG.
As shown in FIG. 0, the magnetic poles 4 are located outward of both ends 443a of the blast surface 443 (= both ends of the stable area of the transferred magnetic flux density by the magnetic poles 44d), which are the developer supply areas of the transport rolls 44.
3b, the developer carried on the blast surface 443 moves in the direction perpendicular to the axis of the transport roll 44 and the developing roll 43
Transfer to the top. In this manner, a substantially uniform developer layer is formed on the developing roll 43 in the axial direction of the developing roll 43.

The S pole (43) on the developing roll 43
The developer delivered to b) is sequentially carried in a counterclockwise direction on the developing roll 43 in the order of N pole → S pole → N pole → S pole (43a). And while developing the electrostatic latent image,
The developer transported to the S-pole (43a) on the developing roll 43 is transferred to the N-pole (44a) on the opposing transport roll 44, and then formed between the adjacent S-pole (44b). Magnetic field (magnetic field along the circumferential direction of the transport roll 44)
Is transported through the seal / collection passage 49, and is separated from the transport roll 44 based on the repulsive magnetic field generated by the repulsive magnetic poles S and S (44 b).
And is returned to the stirring and transporting augers 45 and 46 via.
In FIG. 6, each functional unit such as a developer peeling / adsorbing unit, a developer layer forming unit, and a developer supply transfer unit is surrounded by a dotted line.

On the other hand, when the development for one color of the electrostatic latent image is completed, as shown in FIG. 11A, the rotation of the transport roll 44 is stopped, and the supply of the developer to the development roll 43 is stopped. Thereafter, as shown in FIG.
3 rotates at least once and stops, so that the developer adhering to the developing roll 43 is transported to the S pole (43a) on the developing roll 43, and then is transferred to the opposing transport roll 4
4 to the north pole (44a). At this time, in the developer collecting region between the S pole (43a) of the developing roll 43 and the N pole (44a) of the transport roll 44, the amount of the developer increases rapidly. Since the pair of different polarity N poles (44a) and S poles (44b) are provided in the portion of the transport roll 44 that has received the developer from the developing roll 43, the transport roll 44 is provided even if the distance is short.
Is formed, and the developer in the developer collecting area flows along the circumferential magnetic field. As described above, once the circumferential flow of the developer is created, the attitude of the developer in contact with the bottom wall protrusion 41 b in the seal / collection passage 49 changes (the attitude along the circumferential magnetic field of the transport roll 44). ), The developer is smoothly collected in the direction of the agitating / conveying assist paddle 48.

Here, the magnet roll 43 of the developing roll 43
By changing the positional relationship between 1 and the magnet roll 441 of the transport roll 44, the transport amount ratio of the developer transported between the center and the end of the developing roll 43 was examined. The result is shown in FIG. According to this, if both ends of the area where the delivered magnetic flux density of the developing roll 43 is stable are outside the both ends of the area where the delivered magnetic flux density of the transport roll 44 is stable (see FIG. 10), the developing roll 43 is placed on the developing roll 43. It became clear that the formed developer layer was substantially uniform.

As described above, in the present embodiment, both ends of the region where the received magnetic flux density of the developing roll 43 is stable are disposed outside the both ends of the region where the delivered magnetic flux density of the transport roll 44 is stable. Transport roll 44
When the developer carried on the transfer roller 43 moves to the developing roll 43, the developer does not concentrate near the end portion, so that the developer is fixed to the transport roll 44 and the photosensitive drum 21 and is scraped off by rubbing of the developer. Etc. are prevented. In particular, even when the gap between the transport roll 44 and the photosensitive drum 21 is set to be as small as 0.3 mm to 0.4 mm as in the present embodiment, the fixation of the developer and the scraping by the developer are sufficiently prevented. It was confirmed that it would be.

In the present embodiment, the surface of the developing roll 43 and the surface of the transporting roll 44 which have been blasted are used. However, the present invention is not limited to this. Any material may be appropriately selected as long as the surface roughness is improved to improve the developer conveying force. In the present embodiment, the developing roll 4
Although the gap between the photoconductor drum 3 and the photosensitive drum 21 is set to be small, the present invention is not limited to this.

[0043]

As described above, according to the present invention,
In a so-called purge type developing device, a developer supply area of a transport roll is disposed opposite to a stable receiving magnetic flux density area of a developer roll, and when the developer is transferred from the transport roll to the developer roll, the developer is moved to the center side. Since the deviation is suppressed, the amount of the developer transported from the transport roll to the developing roll can be made uniform. Accordingly, it is possible to prevent the developer from sticking to the developing roll and the latent image carrier and to prevent the developer from being scraped off, and to form a good image without density unevenness.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram showing an outline of a developing device according to the present invention, and FIG. 1B is an explanatory diagram showing a relative relationship between a transport roll and a developing roll.

FIG. 2 is an explanatory diagram showing a state of movement of a developer in a developing device according to the present invention.

FIG. 3 is an explanatory diagram showing a state of movement of a developer in a developing device of a comparative model.

FIG. 4 is an explanatory diagram showing an outline of an embodiment of a color image forming apparatus to which the present invention is applied.

FIG. 5 is an explanatory diagram illustrating a configuration of a developing device used in the embodiment.

FIG. 6 is an explanatory diagram showing a peripheral structure of a developing roll and a supply roll of the upper developing device.

FIG. 7 is an explanatory diagram of the developing device used in the embodiment viewed from a direction A in FIG. 5;

FIGS. 8A and 8B are axial distributions of a magnetic flux density (normal component) near both ends of a transport roll of the developing device according to the embodiment, and FIGS. It is a graph which shows a rate.

FIGS. 9A and 9B are axial distributions of a received magnetic flux density (a component in a normal direction) near both ends of a developing roll of the developing device according to the embodiment, and FIGS. It is a graph which shows a rate.

FIG. 10 is an explanatory diagram illustrating an arrangement relationship between a transport roll and a developing roll in the developing device according to the embodiment.

FIGS. 11A and 11B are explanatory diagrams illustrating a process of collecting residual developer on a developing roll.

FIG. 12 is a graph illustrating a relationship between end positions of a transport roll and a developing roll and a developer transport amount ratio.

[Explanation of symbols]

1 ... Developing roll, 2 ... Magnet member, 3 ... Receiving magnetic pole,
DESCRIPTION OF SYMBOLS 4 ... Conveyance roll, 5 ... Magnet member, 6 ... Stirring conveyance member, 7 ... Layer thickness regulation member, 8 ... Development housing, 9 ... Latent image carrier, 10 ... Receiving magnetic flux density stable area, 11 ... Developer supply area, 21 photoconductor drum, 24 developing device, 41,
51: developing housing, 43, 53: developing roll, 4
4, 54 ... transport rolls, 45, 46, 55, 56 ... stirring transport augers, 47, 57 ... layer thickness regulating plates, 48, 58 ...
Stirring / conveyance assist paddle, 431: magnet roll, 433: blast surface, 441: magnet roll, 443: blast surface,
471 ... Rubber magnet

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tomio Onuki 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. Reference) 2H031 AB02 AB03 AC03 AC08 AC10 AC14 AC19 AC20 BA04 CA11 FA01 2H077 AB02 AB03 AB18 AC12 AD02 AD06 AD13 AD36 EA03 FA03 GA13

Claims (6)

[Claims] An image forming apparatus includes: a developing housing which is opened to face a latent image carrier; a magnet member having a plurality of magnetic poles formed around the developing housing; A developing roll to be carried and conveyed, and a magnet member having a plurality of magnetic poles formed around it are fixedly disposed inside, a developer is supplied to the developing roll, and the developed developer carried on the developing roll is collected. A transport roll, a stirring transport member that transports the developer to be transported to the transport roll while being stirred, and a layer thickness regulating member that regulates the layer thickness of the developer supplied to the transport roll. In the developing device housed, among the plurality of magnetic poles of the magnet member of the developing roll,
Regarding the receiving magnetic pole that first receives the developer from the transport roll, the component of the receiving magnetic flux density formed by the receiving magnetic pole in the normal direction of the developing roll surface is within the receiving magnetic flux density stable region where it is stable in the developing roll axial direction. And a developer supply area of a transport roll, which is opposed to the developer supply area. 2. The developing device according to claim 1, wherein, among the plurality of magnetic poles of the magnet member of the transport roll,
The axial length of the transfer magnetic pole that transfers the developer to the developing roll is set to be less than the axial length of the receiving magnetic pole of the developing roll,
Further, the developing device is characterized in that both ends in the axial direction of the receiving magnetic pole are arranged at or outside both axial positions of the receiving magnetic pole. 3. The developing device according to claim 1, wherein a plurality of magnetic poles of a magnet member of the transport roll are provided.
Regarding the transfer magnetic pole that transfers the developer to the developing roll, the component of the transfer magnetic flux density formed by the transfer magnetic pole in the normal direction of the transfer roll surface is stable in the transfer roll axial direction within the receive magnetic flux density stable region. A developing magnetic flux density stable region facing the developing device. 4. The developing device according to claim 1, wherein a surface roughness of a developer supply area of the transport roll is set to be larger than a non-developer supply area at both ends of the transport roll. . 5. The developing device according to claim 1, wherein, among the plurality of magnetic poles of the magnet member of the transport roll,
Regarding the delivery magnetic pole that delivers the developer to the developing roll, the component of the delivery magnetic flux density formed by the delivery magnetic pole in the direction normal to the surface of the delivery roll is stable in the delivery magnetic flux density stable area with respect to the delivery roll axial direction. A developing device characterized in that magnetic sealing members are disposed facing each other at both ends or outside from the inside. 6. An image forming apparatus comprising the developing device according to claim 1.