JP2005003812A - Developing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a developing device which ensures stable developing properties free of occurrence of image unevenness and image fog by a structure using a recovery roll in a hybrid developing system, and to provide an image forming apparatus using the developing device. <P>SOLUTION: The developing device comprises a toner carrier 2 which is opposed to an image carrier 1 and carries toner on its surface, a developer carrier 3 for supply which is disposed in a position opposite to the toner carrier 2 at a prescribed interval and supplies toner to the toner carrier 2, a developer carrier 4 for recovery which recovers toner from the toner carrier 2, and a conveyance member 5 which is disposed opposite to the two developer carriers 3, 4 and the toner carrier 2 and transfers a two-component developer between the two developer carriers 3, 4, wherein the surface roughness of the conveyance member 5 is set so that it is made larger than the surface roughness of the developer carrier 3 for supply. The image forming apparatus using the developing device is also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer, and in particular, uses a two-component developer including a toner and a magnetic carrier to develop an electrostatic latent image on an image carrier with toner. The present invention relates to a developing device configured as described above and an improvement of an image forming apparatus using the developing device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a developing device used in an image forming apparatus such as a copying machine or a printer, a device adopting a so-called hybrid developing method is known.
This includes a donor roll that faces an image carrier such as a photoconductor and carries toner, and a toner transport roll that carries a two-component developer that contains the toner and a magnetic carrier and that faces this donor roll. A large amount of developer is supplied from a toner conveying roll by a magnetic brush to form a toner layer on a donor roll (see, for example, Patent Document 1).
In this hybrid development system, since the toner is normally charged by stirring the two-component developer, it is easy to ensure a sufficient charge amount, and the toner is supplied from the toner transport roll to the donor roll by electrostatic force. Therefore, the toner charged with the reverse polarity is not supplied to the donor roll. Therefore, there is no adhesion of toner to the non-image area of the image carrier and the occurrence of fog is prevented. Further, since only the toner is supplied to the donor roll, there is an advantage that adhesion of the magnetic carrier to the image carrier is prevented.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-21970 (column of embodiment of the invention, FIG. 1)
[Patent Document 2]
JP-A-9-251237 (column of embodiment of the invention, FIG. 1)
[Patent Document 3]
JP-A-10-319708 (column of embodiment of the invention, FIG. 1)
[0004]
[Problems to be solved by the invention]
However, in this type of hybrid development method, a method of replenishing toner in the toner supply area with respect to a portion where the toner is consumed on the donor roll is adopted. However, not only the portion where the toner is consumed but also the toner However, there is a problem in the development history that toner is supplied to the remaining non-consumed portion, and the previous toner consumption pattern appears on the developed image.
[0005]
In addition, when toner supply and scraping are repeated on the donor roll, the difference in physical adhesion between the large particle size toner and the small particle size toner (the large particle size toner is physically attached to the donor roll). Because the adhesion force is small, it can be easily scraped against the scraping force received in the nip area, but the toner with a small particle size is difficult to be scraped.) It will turn.
This change in particle diameter on the donor roll brings about a change in development characteristics and transfer characteristics. The toner remains on the donor roll without being developed, and a new toner is supplied to the area. There is a toner density difference between the supplied area and this may cause an image defect (development history).
[0006]
Therefore, a method is known in which all the toner is once removed from the donor roll that has passed through the development area, and then the toner is again carried on the donor roll at a portion (toner supply area) between the donor roll and the toner supply roll. .
For example, there is a system that uses a scraper as the toner removing means, but in this case, there is a problem that the toner is fused to each other at the contact portion between the scraper and the donor roll.
Therefore, a method of adding a toner collection roll separately from the toner supply roll and scraping off the toner on the donor roll with the toner collection roll is also disclosed (for example, see Patent Document 2).
[0007]
However, in this new method of adding a toner collection roll, if the amount of developer supplied to the toner supply roll and the toner collection roll is unstable, the amount of toner on the donor roll becomes unstable. , Uneven density occurs in the image.
In particular, it becomes more prominent when the developer is easily stressed between the toner supply roll and the toner collection roll, and the flowability of the developer decreases.
[0008]
For this reason, there has been proposed a method of stabilizing the developer conveyance amount by rotating the toner supply roll and the toner collection roll in the same direction and further bringing them close to each other (see, for example, Patent Document 3).
However, in this case, the problem of bias leakage between the two rolls is likely to occur, and is particularly noticeable when the toner concentration is lowered and the operating environment is in a high humidity state.
Furthermore, there is a problem that the developer entering between the two rolls is stressed, the developer is likely to be deteriorated, image fogging occurs, and stable development characteristics cannot be obtained over a long period of time. .
[0009]
Accordingly, the inventors of the present invention previously added a transport member for transferring the developer between the toner supply roll and the toner collection roll in order to ensure the transport stability of the developer. Thus, a developing device configured to stabilize the developer conveyance amount has been proposed (see Japanese Patent Application No. 2003-157592).
However, in such a type, when the developer transportability on the transport member is insufficient, there is a concern that the toner recoverability may be non-uniform and density unevenness may occur. In particular, this phenomenon becomes prominent when a so-called spherical toner (toner with a high sphericity having a toner shape factor of 125 or less) that is excellent in developability and transferability is used to obtain a high-quality image.
Further, when the surface roughness of the toner supply roll is rough, pattern noise caused by the roughness of the roll surface when the toner is supplied to the donor roll (on the donor roll, the toner density along the roll surface shape of the toner supply roll) However, there is a concern that a new problem is superimposed on the image.
The present invention has been made in order to solve the above technical problems, and a developing device having a stable developer supply amount, preventing uneven density, and stable development characteristics over a long period of time. An image forming apparatus used is provided.
[0010]
[Means for Solving the Problems]
That is, according to the present invention, as shown in FIG. 1, a toner carrier 2 that bears toner on its surface facing an image carrier 1 that carries an electrostatic latent image, and a predetermined interval between the toner carrier 2 and the toner carrier 2. And a supply developer carrier 3 for carrying and transporting a two-component developer containing toner and a magnetic carrier and supplying the toner to the toner carrier 2, and a predetermined amount to the toner carrier 2. A collecting developer carrier 4 that is disposed at opposed positions and carries a two-component developer and collects toner from the toner carrier 2, and the two developer carriers 3, 4 A conveying member 5 disposed opposite to the toner carrier 2 and delivering the two-component developer between the two developer carriers 3 and 4, and the surface roughness of the conveying member 5 is for supply It is characterized by being set so as to be rougher than the surface roughness of the developer carrier 3 It is.
[0011]
In such technical means, since the developing device according to the present application is of a type using a two-component developer, toner having various color components can be used, and a single-color developing device is provided. The present invention can be applied to, for example, a full-color image forming apparatus including a plurality of developing devices.
[0012]
The supply developer carrier 3, the recovery developer carrier 4 and the transport member 5 in the present invention may be appropriately selected as long as they carry and transport a two-component developer. There is a mode in which a sleeve and a magnet member fixedly disposed in the non-magnetic sleeve and provided with magnetic field generating means are provided.
Further, the magnetic field generation means may be any means having a plurality of magnetic poles. For example, as a configuration example of the magnetic poles, a toner supply magnetic pole for contributing to development and a function of capturing a developer are provided. Examples include a pickup magnetic pole and a conveyance magnetic pole that conveys the developer, but are not limited thereto, and may be appropriately selected.
[0013]
The supply developer carrier 3 and the recovery developer carrier 4 are provided with a predetermined electric field for supplying or collecting toner to the toner carrier 2 between the toner carrier 2 and the toner carrier 2. It is desirable. Accordingly, a developing bias (VB) 6 for developing the electrostatic latent image on the image carrier 1 is supplied to the toner carrier 2, and a supply for supplying toner to the toner carrier 2 is supplied to the developer carrier 3 for supply. A bias (VS) 7 is applied, and a recovery bias (VR) 8 for recovering the toner from the toner carrier 2 is applied to the recovery developer carrier 4. The supply bias (VS) 7 and the recovery bias (VR) 8 are normally DC voltages, but may be AC superimposed DC voltages.
[0014]
In the present invention, it is preferable that the rotation direction of the conveying member 5 is the same direction from the viewpoint of reducing the stress of the developer at a portion facing the supply developer carrier 3 and the recovery developer carrier 4. Even if it is in a different direction, there is no problem as long as the developer stress is reduced.
In the present invention, the developer flows in two ways: the direction in which the developer flows from the supply developer carrier 3 through the transport member 5 to the recovery developer carrier 4, and the direction from the recovery developer carrier 4 to the transport member 5. There is a direction in which the developer flows through the supply developer carrier 3.
When the conveying member 5 delivers the two-component developer between the two developer carriers 3 and 4, the upstream developer between the two developer carriers 3 and 4. A mode of passing through the conveying member 5 instead of a mode of passing directly from the carrier to the developer carrier on the downstream side is shown.
Since the developer flow is in a bi-directional manner, there is an embodiment in which both of the two developer carriers 3 and 4 are on the upstream side of the developer flow.
[0015]
Further, the transport member 5 may be in contact with the toner carrier 2 as long as it is separated from the supply developer carrier 3 and the recovery developer carrier 4 by a predetermined distance. (In this case, the conveying member 5 is rotated so as not to hinder the rotation of the toner carrier 2).
[0016]
Further, the surface roughness of the supply developer carrier 3 is preferably not set from the viewpoint of supplying the toner to the toner carrier 2 and is preferably 35 μm or less if possible. If the surface of the developer carrying member 3 for supply is too rough, the toner layer supplied onto the toner carrying member 2 is kept in a shaded state, and this appears as pattern noise in the image as it is. Become.
Furthermore, from the viewpoint of improving developer transportability, the surface roughness of the transport member 5 is preferably set to be greater than the surface roughness of the developer carrier 3 for supply, and this roughness is the magnetic carrier used. More preferably, the average particle size is set to be equal to or larger than the average particle size. As a result, the developer from the supply developer carrier 3 does not convey the developer distribution on the supply developer carrier 3 as it is by the conveyance member 5, but the conveyance member 5 has axial stability. Secured.
From the viewpoint of further improving the developer transportability and axial stability of the transport member 5, at least a pattern parallel to the axial direction (by a method such as cutting or etching) is formed on the transport member 5. It is preferable that
[0017]
The surface roughness of the collecting developer carrier 4 prevents the pattern when the toner is collected from the toner carrier 2, so that the surface roughness of the collecting developer carrier 4 is less than 35 μm. preferable.
Further, in a mode in which the developer flow is on the upstream side of the collecting developer carrier 4, the developer distribution on the collecting developer carrier 4 is reduced, and the distribution is transferred to the conveying member 5 as it is. The surface roughness of the conveying member 5 is preferably larger than the surface roughness of the recovery developer carrier 4.
[0018]
The toner carrier 2 in the present invention is preferably an elastic member at least on the surface from the viewpoint of finely developing the toner on the image carrier 1, but may be a metal. In the case of an elastic member, the elastic member is preferably disposed in contact with the image carrier 1.
Further, the toner in the present invention may be magnetic or non-magnetic as long as it adheres to the magnetic carrier. In particular, from the viewpoint of obtaining a high-quality image, a so-called spherical toner (toner shape factor) having excellent developability and transferability. It is preferable to use a toner having a sphericity of 125 or less.
Note that the present invention is not limited to the above-described developing device, but also targets an image forming apparatus using these developing devices.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows Embodiment 1 of an image forming apparatus including a developing device to which the present invention is applied.
In the figure, reference numeral 21 denotes a photoconductor that carries an electrostatic latent image made of an organic photoconductor that rotates in the direction of an arrow. The photoconductor 21 is charged by a charging device 22 such as a scorotron, and a laser writing device or LED. An electrostatic latent image is written by the exposure device 23 having an array. The electrostatic latent image is formed as a potential image based on contrast with a high potential portion not exposed to light because the surface potential of the photoreceptor 21 in the portion exposed to light is lowered.
[0020]
Further, the developing device 30 contains a two-component developer composed of toner and a magnetic carrier in a developing housing 31, a donor roll 32 that carries the toner, a toner supply roll 33 for supplying toner, and a toner for collecting toner. A collection roll 34 and a transport roll 35 for transporting the developer are provided.
In the present embodiment, the toner image on the photoreceptor 21 is visualized by the developing device 30 and then transferred onto the recording material 28 by the transfer roll 26, and the transferred recording material 28 is fixed. The toner image on the recording material 28 is fixed by the fixing device 50. The fixing device 50 has, for example, a heat roll method, and includes a heating roll 51 and a pressure roll 52. By passing the recording material 28 between the heating roll 51 and the pressure roll 52, a toner image is obtained. Is fixed to the recording material 28.
The toner remaining on the photoreceptor 21 is removed by, for example, a doctor blade type cleaning device 29.
[0021]
Here, the developing device 30 which is a feature of the present invention will be described in detail with reference to FIG.
In the drawing, the developing device 30 has a developing housing 31 that opens toward the photosensitive member 21, and a donor roll 32 is placed at a position facing the opening of the developing housing 31 and facing the photosensitive member 21. It is housed so as to be rotatable in the A direction. A bias power source 37 is connected to the donor roll 32 so that a predetermined developing bias VB is applied.
In the present embodiment, the outer peripheral portion of the donor roll 32 is configured to be covered with an elastic member. However, for example, a metal roll made of aluminum or stainless steel may be used.
Further, the donor roll 32 and the photoconductor 21 are in contact with each other, but they may be non-contact.
[0022]
A toner supply roll 33 and a toner recovery roll 34 are disposed at a predetermined distance from the donor roll 32 at the rear part (the side opposite to the photoreceptor 21) of the donor roll 32. The surface of the rotary sleeve 33a of the toner supply roll 33 and the surface of the rotary sleeve 34a of the toner recovery roll 34 are both adjusted to have a surface roughness of 30 μm.
Further, bias power sources 38 and 39 are connected to the toner supply roll 33 and the toner recovery roll 34, respectively, and a supply bias VS and a recovery bias VR are applied thereto.
Further, on the rear part of the toner supply roll 33 and the toner collection roll 34, a conveyance roll 35 for carrying and conveying the developer G so as to deliver the developer G on the outer periphery of the toner supply roll 33 to the toner collection roll 34 is arranged. It is installed. At this time, the toner supply roll 33, the toner collection roll 34, and the transport roll 35 are arranged to be separated by about 3 to 5 mm. Further, the transport roll 35 may be the same size as the toner supply roll 33 and the toner collection roll 34.
The donor roll 32, the toner supply roll 33, and the toner collection roll 34 have an angle formed by a straight line connecting the center of the donor roll 32 and the center of the toner supply roll 33 and the toner collection roll 34 is 90 degrees or less. Also, the center of the toner collection roll 34 is arranged so as to be the lowest in the vertical direction among the toner supply roll 33, the toner collection roll 34, and the conveyance roll 35.
[0023]
In the present embodiment, the toner supply roll 33, the toner collection roll 34, and the transport roll 35 are fixedly disposed inside the rotatable sleeves 33 a to 35 a and the rotatable sleeves 33 a to 35 a, and have a plurality of magnetic poles. Magnet bodies 33b to 35b having
The magnet body 33b of the toner supply roll 33 is provided with a plurality of magnetic poles (S2, N1, S1, N2, N3) on the outer periphery thereof, the magnetic pole S1 is provided at a position facing the donor roll 32, and the magnetic pole N2 and the magnetic pole Arranged so that a substantially middle part of N3 is opposed to the transport roll 35, magnetic poles N2 and N3 having the same polarity act as repelling magnetic poles.
Further, the magnet body 34b of the toner recovery roll 34 includes a plurality of magnetic poles (S4, N4, S3, N5, N6) on the outer periphery thereof, and a magnetic pole S3 is provided at a position facing the donor roll 32, and the magnetic pole S4. Are arranged so as to face the transport roll 35, and S5 and S6 of the same polarity act as repulsive magnetic poles.
Further, the magnet body 35 b of the transport roll 35 is arranged so that the magnetic pole S 5 is positioned opposite the toner supply roll 33 among the plurality of magnetic poles (S 5, N 7, S 6).
In the present embodiment, the arrangement and number of magnetic poles are not limited to this embodiment, and may be appropriately selected.
In this embodiment, the rotation direction of the toner supply roll 33 and the toner recovery roll 34 is the same as that of the donor roll 32 (the direction of arrow A in FIG. 3), and the rotation direction of the transport roll 35 is opposite to these. ing.
[0024]
The surface shape of the transport roll 35 according to the present embodiment (the surface of the rotating sleeve 35a) is the one shown in FIG. That is, a slit pattern parallel to the axial direction is engraved on the surface of the transport roll 35 by cutting with a bite so that the surface roughness is 50 μm.
2B and 2C show other examples of the surface shape of the transport roll 35, and FIG. 3B intersects the axis direction of the transport roll 35 at an inclination of about 45 degrees. The slit pattern to be cut is provided by cutting, and (c) is a blast process along the axial direction of the transport roll 35.
Therefore, in these aspects, the transportability of the developer G and the axial stability are improved during the transport of the developer.
[0025]
In addition, a stirring member 41 is disposed at the rear portion of the transport roll 35 via a partition plate 40. The agitating member 41 is composed of, for example, a spiral auger, and is configured to supply the developer G to the toner supply roll 33 after the two-component developer (developer) G is agitated and charged.
In addition, in this Embodiment, although it is set as the aspect provided with two stirring members 41, it is not limited to two, One may be sufficient and there may be three or more. In addition to the auger, a magnetic or non-magnetic roll may be used.
[0026]
Furthermore, a first guide piece 43 that is substantially concentric with the transport roll 35 and guides the developer transport is provided at the rear of the transport roll 35 in front of the partition plate 40. Is efficiently transported on the outer periphery of the transport roll 35. A second guide piece 44 for suppressing the flow of the developer G is provided at a position facing the toner recovery roll 34, and at a position facing the toner supply roll 33 with a predetermined interval, A trimmer 42 for controlling the layer thickness of the developer on the toner supply roll 33 is provided.
[0027]
Here, the developing bias VB, the supply bias VS, and the recovery bias VR will be described.
In this embodiment, a two-component developer composed of a toner and a magnetic carrier is used, and the toner is charged with a negative polarity and the magnetic carrier is charged with a positive polarity by frictional contact with each other.
Further, the outer peripheral surface of the photosensitive member 21 is negatively charged (for example, −600 V), and toner is attached to a portion where the potential is attenuated by exposure (for example, −100 V) for development. In this case, the developing bias VB is set to -400V, the supply bias VS is set to -420 to -750V, and the recovery bias VR is set to -350 to 0V.
A DC voltage is used for the bias power supplies 37 to 39 for supplying the developing bias VB, the supply bias VS, and the recovery bias VR. However, for example, an AC superimposed DC voltage may be used as the power supply.
[0028]
The two-component developer G used in the present embodiment is a developer composed of a toner and a magnetic carrier. For example, a non-magnetic toner is used as the toner. Toner can be used.
Further, the toner is a polymerized toner of a styrene acrylic resin and is a so-called spherical toner having a shape factor of 125 or less, and the carrier is a ferrite carrier having an average particle diameter of 50 μm.
Here, the shape factor (SF) of toner is quantified by performing image analysis mainly based on a microscope image or an electron microscope image, and is defined by the following equation.
SF = (ML ² / A) × (π / 4) × 100
In the above equation, ML represents the absolute maximum length of the toner particles, and A represents the projected area of the toner particles.
[0029]
Next, the operation of the image forming apparatus according to the present embodiment will be described focusing on the developing device 30.
In FIG. 3, the two-component developer (developer) G is stirred by the stirring member 41, and after the toner is negatively charged and the magnetic carrier is positively charged, the magnetic pole of the magnet body 33 b of the toner supply roll 33 is charged. The toner is supplied to the toner supply roll 33 in the developer supply area upstream of the developer flow in S2.
When the developer G reaches the vicinity of the trimmer 42, it forms a spike by the magnetic pole S2. Further, the rising of the developer G is controlled by the trimmer 42 so that the developer layer is held on the outer periphery of the toner supply roll 33 and is conveyed in the A direction along with the rotation of the rotating sleeve 33a. At this time, the developer G constitutes a magnetic brush along the lines of magnetic force formed by the magnet body 33b.
[0030]
Next, when the developer G enters an area (toner supply area) where the toner supply roll 33 and the donor roll 32 face each other, a magnetic brush is formed by the magnetic attractive force of the magnetic pole S1, and the development in which the magnetic brush is formed. Only the toner in the agent G is electrostatically attracted from the toner supply roll 33 to the donor roll 32 by the influence of the electric field formed between the toner supply roll 33 and the donor roll 32, and adheres to the donor roll 32.
At this time, in this embodiment, since spherical toner is used as the toner, it is easy to be surely electrostatically attracted to the donor roll 32 side.
On the other hand, the magnetic carrier that has lost the toner and the developer G that has passed through the toner supply region are attracted by the magnetic field 33b of the toner supply roll 33 and the magnet body 35b of the transfer roll 35, and are supplied to the toner supply roll 33 and the transfer roll 35. Are delivered to the transport roll 35 in a region facing each other.
[0031]
The developer G delivered to the transport roll 35 is held on the transport roll 35 by the magnetic field attracted by the magnet body 35b, transported on the outer periphery thereof, and then the magnet body 35b of the transport roll 35 and the magnet of the toner recovery roll 34. Due to the attraction magnetic field with the body 34b, the toner is transferred to the toner collecting roll 34 in a region where the conveying roll 35 and the toner collecting roll 34 face each other. In addition, by providing the slit pattern on the surface of the transport roll 35, the transportability is improved, and the developer G is transported reliably.
The developer G transported on the outer periphery of the toner recovery roll 34 recovers the toner on the donor roll 32 in the toner recovery region near the magnetic pole S3, and is then transported on the outer periphery of the toner recovery roll 34, so that the magnetic pole N5 Due to the repulsive magnetic field with the magnetic pole N 6, the toner is separated from the toner collecting roll 34 and is supplied to the stirring member 41 along the second guide piece 44.
[0032]
On the other hand, the toner supplied to the donor roll 32 is conveyed in the A direction according to the rotation of the donor roll 32 and is used for developing the electrostatic latent image formed on the photoconductor 21 in the development region. Further, the toner that has passed through the development area without being used for development is sent to the toner collection area.
The toner conveyed to the toner collection area is affected by the electric field formed between the donor roll 32 and the toner collection roll 34, and in the toner collection area, the negatively charged toner is transferred from the donor roll 32. While being attracted by the high potential toner collecting roll 34, it is scraped off by a magnetic brush formed on the toner collecting roll 34 and collected to the toner collecting roll 34 side. At this time, since the spherical toner is used, the physical adsorption force of the toner to the donor roll 32 is reduced and the effect of scraping off the developer G is increased, so that the toner can be reliably collected. become.
[0033]
In the developing device 30 configured as described above, the toner that has not been used for development in the development area is collected by the toner collection roll 34 in the toner collection area. Further, new toner is uniformly supplied from the toner supply roll 33 to the donor roll 32 from which the toner has been collected.
Accordingly, the donor roll 32 that has passed through the toner collection area has no toner consumption pattern, and this toner consumption pattern does not appear in a toner image developed thereafter.
Further, when the developer G is transferred from the toner supply roll 33 to the transport roll 35 and from the transport roll 35 to the toner recovery roll 34, the moving direction of the opposite roll surface is the same (specifically, the toner supply roll). Since the movement direction of the surface of each roll is the same in the part where the roll 33 and the conveyance roll 35 face each other and the part where the conveyance roll 35 and the toner collection roll 34 face each other, the amount of movement of the developer G is Since it is stable in the respective roll axis directions, the toner collection performance in the toner collection area is stabilized, and the developer supply amount is also stabilized, so that it is possible to suppress development history and density unevenness.
[0034]
In the present embodiment, the surface of the transport roll 35 is made equal to the average particle diameter of the magnetic carrier, and the slit shape of the transport roll 35 is parallel to the axial direction. The developer G can be conveyed and improved, and the conveyance stability in the axial direction on the conveyance roll 35 is ensured.
Incidentally, since the surface roughness of the surfaces of the toner supply roll 33 and the toner collection roll 34 is set to 30 μm, there is no generation of pattern noise particularly for the image, and no pattern is generated at the time of toner collection.
[0035]
In addition, by disposing the transport roll 35 between the toner supply roll 33 and the toner collection roll 34, the distance between the toner supply roll 33 and the toner collection roll 34 that causes a bias difference can be equivalently increased. In addition to ensuring the stability of the conveyance of the developer G, the flow of the developer G between the rolls can be made in one direction, so that the stress received by the developer G can be reduced, such as image fogging. It is possible to satisfy the suppression of bias leakage and the suppression of bias leakage.
[0036]
Embodiment 2
FIG. 5 shows a second embodiment of a developing device used in an image forming apparatus to which the present invention is applied.
In this figure, the present embodiment is configured in substantially the same manner as the developing device 30 in the first embodiment, but the flow of the developer G is different from that in the first embodiment, and the transport roll 35, toner supply from the toner recovery roll 34 It is configured to flow to the roll 33.
In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.
[0037]
In the present embodiment, the magnet body 33b of the toner supply roll 33 has magnetic poles (N2, S1, N1, S2, S3) on the outer periphery thereof, and the magnetic pole S1 is provided at a position facing the donor roll 32. It arrange | positions so that the conveyance roll 35 may be opposed in the vicinity of the magnetic pole N2.
Further, the magnet body 34b of the toner recovery roll 34 has a plurality of magnetic poles (S5, N3, S4, N4, N5) on the outer periphery thereof, and a magnetic pole S4 is provided at a position facing the donor roll 32, so that the magnetic pole N4 is provided. And the magnetic pole N5 are arranged so that the middle of the magnetic pole N5 faces the transport roll 35.
Further, the magnet body 35 b of the transport roll 35 is disposed so that the magnetic pole S 7 is positioned opposite the toner recovery roll 34 among the plurality of magnetic poles (S 7, N 6, S 6).
[0038]
Further, a stirring member 41 is disposed at the rear of the transport roll 35 via a partition plate 40. The stirring member 41 stirs and charges the two-component developer (developer) G, and then collects the toner collection roll 34. The developer G is supplied to the printer.
Further, a first guide piece 43 that is semi-circular and substantially concentric with the conveyance roll 35 is provided at the rear of the conveyance roll 35 in front of the partition plate 40 so that the developer G The outer periphery of the transport roll 35 is efficiently transported. A second guide piece 44 for suppressing the flow of the developer G is provided at a position facing the toner supply roll 33, and at a position facing the toner recovery roll 34 with a predetermined interval, A trimmer 42 for controlling the layer thickness of the developer on the toner collecting roll 34 is provided.
[0039]
Next, the operation of the developing device according to the present embodiment will be described.
In FIG. 5, the two-component developer (developer) G is agitated by the agitating member 41, and after the toner is negatively charged and the magnetic carrier is positively charged, it is in the magnet body 34 b of the toner recovery roll 34. The toner is supplied to the toner collection roll 34 in the developer supply area on the upstream side of the magnetic pole S5.
When the developer G reaches the vicinity of the trimmer 42, it forms a spike by the magnetic pole N3. Further, the rising of the developer G is controlled by the trimmer 42 so that the developer layer is held on the outer periphery of the toner collecting roll 34 and is conveyed in the B direction along with the rotation of the rotating sleeve 34a. At this time, the developer G constitutes a magnetic brush along the lines of magnetic force formed by the magnet body 34b.
[0040]
Next, when the developer G enters the toner recovery area where the toner recovery roll 34 and the donor roll 32 face each other, a magnetic brush is formed by the magnetic attractive force of the magnetic pole S4, and the toner on the donor roll 32 is scraped off. take. At this time, an electrostatic force that attracts toner from the donor roll 32 to the toner collection roll 34 is activated by the electric field between the donor roll 32 and the toner collection roll 34, and toner collection from the donor roll 32 to the toner collection roll 34 is ensured. Yes.
[0041]
The developer G from which the toner has been collected is transferred to the transporting roll 35 in the vicinity of the region where the toner collecting roll 34 and the transporting roll 35 face each other due to the attractive magnetic field of the magnet body 34b of the toner collecting roll 34 and the magnet body 35b of the transporting roll 35. Delivered.
The developer G transferred to the transport roll 35 is held on the transport roll 35 by the magnetic field attracted by the magnet body 35 b and transported on the outer periphery thereof, and the magnet body 35 b of the transport roll 35 and the magnet body 33 b of the toner supply roll 33. Is transferred to the toner supply roll 33 in a region where the transport roll 35 and the toner supply roll 33 face each other.
[0042]
The developer G conveyed on the outer periphery of the toner supply roll 33 forms a magnetic brush by the magnetic attraction force of the magnetic pole S1 in the toner supply area near the magnetic pole S1, and only the toner in the developer G forming the magnetic brush is used. Due to the influence of an electric field formed between the toner supply roll 33 and the donor roll 32, the toner supply roll 33 is electrostatically attracted to the donor roll 32 and adheres to the donor roll 32.
Thereafter, the developer G transported on the outer periphery of the toner supply roll 33 is separated from the toner supply roll 33 by the repulsive magnetic field between the magnetic pole S2 and the magnetic pole S3, and is applied to the stirring member 41 along the second guide piece 44. Supplied.
[0043]
In this embodiment as well, the surface roughness of the transport roll 35 is made rougher than the surface roughness of the toner collection roll 34 and the toner supply roll 33, so that the toner collection performance and developer supply amount in the toner collection area are set. Is stable, no pattern noise is generated in the toner supply area, no stress is applied to the developer G, and there is no bias leak.
Therefore, also in this embodiment, a small-sized developing device that does not have development history, density unevenness, and image fogging can be realized.
[0044]
【Example】
Example 1
In this embodiment, the correlation between the average particle diameter of the magnetic carrier and the toner shape factor with respect to the surface roughness of the transport roll is evaluated and confirmed. The surface roughness of the toner supply roll and toner recovery roll was 30 μm.
As for the surface roughness of the transport roll, samples of 20 μm and 35 μm were prepared by blasting, and samples of 50 μm and 100 μm were prepared by cutting with a cutting tool.
As the magnetic carrier, a known ferrite system having an average particle diameter of 35 μm and 50 μm was used.
As the toners having the shape factors 115 and 125, styrene acrylic resin toner prepared by a known emulsion polymerization method was used.
[0045]
The evaluation method was a modified machine of DocuColor 1250 manufactured by Fuji Xerox Co., Ltd. under the following conditions.
Surface potential of photoconductor: -650V
Development bias applied to donor roll: −450 V
Supply bias applied to toner supply roll: -575V
Recovery bias applied to toner recovery roll: -250V
Photoconductor peripheral speed: 220 mm / s
Donor roll peripheral speed: 280 mm / s
Toner supply roll peripheral speed: 450 mm / s
Toner recovery roll peripheral speed: 450 mm / s
Conveying roll peripheral speed: 450 mm / s
Distance between trimmer and rotating sleeve: 0.7mm
Distance between donor roll and toner supply roll: 0.5 mm
Note that a rectangular wave AC electric field of 9 kHz and a maximum amplitude of 500 V was superimposed on the supply bias.
[0046]
The evaluation was performed by outputting a halftone image with an image density of 30% on the entire surface of the paper and visually judging the density unevenness.
As shown in FIG. 6, the evaluation result is such that the surface roughness of the transport roll is equal to or greater than the average particle diameter of the magnetic carrier to be used, so that density unevenness does not occur when the toner shape factor is 115 or 125. It was confirmed.
[0047]
Example 2
The present embodiment is a comparative example of the first embodiment, and confirms the correlation with the toner shape factor when the surface roughness of the transport roll is reduced.
In this embodiment, the surface roughness of the transport roll is 20 μm (produced by blasting), the magnetic carrier has an average particle diameter of 35 μm, and the toners having the shape factors of 115 and 125 are styrene acrylic resins prepared by a known emulsion polymerization method. As the toner having a shape factor of 140, so-called irregular toner (pulverized toner) was used.
[0048]
The evaluation method was performed in the same manner as in Example 1, and density unevenness and graininess were confirmed.
Here, the density unevenness is evaluated by the same evaluation as in Example 1. Regarding the graininess, an image of 30 mm square with an image density of 10% and an image of 30 mm square with an image density of 20% are output, and each image is visually observed. The smoothness of the image was evaluated. The case where the image was homogeneous and smooth was judged as ◯, and the case where the omission of the screen structure and the dispersion of toner was remarkable and the smoothness of the image was impaired was judged as x. The screen line number was evaluated at 200 lines.
As shown in FIG. 7, the evaluation results show that uneven density occurs with so-called spherical toners having shape factors 115 and 125 with good graininess, and nonuniform density does not occur with amorphous toner with poor graininess.
Therefore, it was confirmed that the toner whose surface roughness of the transport roll has a shape factor of 125 or less is greatly related to the occurrence of density unevenness.
[0049]
【The invention's effect】
As described above, according to the present invention, the toner carrier and the two developer carriers for supplying and collecting the toner to the toner carrier are provided, and two developing members are provided at positions facing these. By providing a transport member that delivers the developer to and from the developer carrier, and making the surface roughness of the transport member rougher than the surface roughness of the developer carrier, the developer transportability is further stabilized. Further, it is possible to reduce stress due to the collision between developers, and it is possible to provide a developing device free from development history, density unevenness and image fog.
Further, by using this developing device, it is possible to provide an image forming apparatus having stable development characteristics over a long period of time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of a developing device of an image forming apparatus according to the present invention.
FIG. 2 is an explanatory diagram showing Embodiment 1 of an image forming apparatus to which the present invention is applied.
FIG. 3 is an explanatory diagram illustrating details of the developing device according to the first embodiment.
FIGS. 4A, 4B, and 4C are views showing a form of a transport roll in Embodiment 1. FIGS.
FIG. 5 is an explanatory diagram showing a second embodiment of a developing device to which the invention is applied.
6 is an explanatory diagram showing the results of Example 1. FIG.
7 is an explanatory diagram showing the results of Example 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Toner carrier, 3 ... Supply developer carrier, 4 ... Collecting developer carrier, 5 ... Conveyance member, 6 ... Development bias (VB), 7 ... Supply bias (VS) , 8 ... Recovery bias (VR)

Claims (10)

A toner carrying member facing the image carrying member carrying the electrostatic latent image and carrying toner on the surface;
A supply developer carrier disposed at a position facing the toner carrier at a predetermined interval, carrying and transporting a two-component developer containing toner and a magnetic carrier, and supplying the toner to the toner carrier; ,
A collecting developer carrier disposed at a position facing the toner carrier at a predetermined interval, carrying and transporting the two-component developer, and collecting the toner from the toner carrier;
A transport member disposed opposite to the two developer carriers and the toner carrier, and delivering a two-component developer between the two developer carriers;
A developing device characterized in that a surface roughness of a conveying member is set to be rougher than a surface roughness of a developer carrying member for supply. The developing device according to claim 1,
A predetermined electric field for supplying or recovering toner to the toner carrier is formed between the supply developer carrier and the toner carrier and between the recovery developer carrier and the toner carrier. A developing device. The developing device according to claim 1,
The developing device according to claim 1, wherein the conveying member rotates in the same direction at a portion facing the two developer carriers. The developing device according to claim 1,
A developing device characterized in that the surface roughness of the conveying member is set to be equal to or greater than the average particle diameter of the magnetic carrier used. The developing device according to claim 1,
2. A developing device according to claim 1, wherein a pattern including at least a component parallel to the axial direction is formed on the surface of the conveying member. The developing device according to claim 1,
A developing device using a toner having a shape factor of 125 or less. The developing device according to claim 1,
A developing device characterized in that the developer carrying member for supply has a surface roughness of less than 35 μm. The developing device according to claim 1,
A developing device characterized in that a surface roughness of a conveying member is set to be rougher than a surface roughness of a collecting developer carrier. The developing device according to claim 1,
A developing device, wherein the recovery developer carrying member has a surface roughness of less than 35 μm. An image forming apparatus comprising the developing device according to claim 1.

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