JP4325426B2 - Developing device and image forming apparatus using the same - Google Patents

Description

  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.

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.

Japanese Patent Laid-Open No. 9-21970 (column of embodiment of the invention, FIG. 1) JP-A-9-251237 (column of embodiment of the invention, FIG. 1) JP-A-10-319708 (column of embodiment of the invention, FIG. 1)

  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.

  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 the particle size on the donor roll causes a change in development characteristics and transfer characteristics, and a region where new toner is supplied without developing and the toner remains on the donor roll, and the toner is developed and developed. There is a possibility that a toner density difference occurs between the area where new toner is supplied in a state where the toner is consumed, and this may cause an image defect (development history).

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 new toner collecting roll separately from the toner supplying roll and scraping off the toner on the donor roll with the toner collecting roll is also disclosed (for example, see Patent Document 2).

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.

For this reason, the toner supply roll and the toner collection roll are rotated in the same direction (rotated in different directions at the opposite portions of the rolls), and further arranged close to each other to stabilize the developer transport amount. Proposals have been made (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. Further, the developer entering between the two rolls is stressed, the developer is likely to be deteriorated, and there is a problem that fog occurs, and there is a problem that stable development characteristics cannot be obtained over a long period of time.
The present invention has been made in order to solve the above technical problems, and a developing device having a stable developer supply amount, capable of suppressing uneven density, and stable development characteristics over a long period of time. An image forming apparatus used is provided.

  That is, as shown in FIGS. 1A and 1B, the basic configuration of the present invention includes a toner carrier 2 that is disposed opposite to an image carrier 1 that carries an electrostatic latent image, and that carries toner on its surface, A two-component developer G (hereinafter referred to as “developer G” as appropriate) is disposed at a position facing the toner carrier 2 and contains toner and a magnetic carrier, and supplies the toner to the toner carrier 2. A developer carrier 3 for supply, a developer carrier 4 for collection which is disposed at a position facing the toner carrier 2 to carry and transport the developer G and collect toner from the toner carrier 2; A conveying member 5 disposed opposite to the two developer carriers 3 and 4 and the toner carrier 2 to deliver the developer G between the two developer carriers 3 and 4; Guide member which surrounds a part of the sheet and forms a developer conveyance path around the conveyance member 5 It is those with a door.

In such technical means, the developing device according to the present application is of the type using the two-component developer G, and therefore, toner having various color components can be used. Needless to say, the present invention can be applied to an image forming apparatus including a plurality of developing devices, for example, a full-color image forming apparatus.
The toner carrier 2 is preferably an elastic member at least on the surface. However, the toner carrier 2 may be a metal, and may be in contact with the image carrier 1 in the case of an elastic member.
The two developer carriers 3 and 4 may be appropriately selected as long as the developer carriers 3 and 4 are provided with a magnetic field generating means and carry and transport the developer G. For example, a rotatable nonmagnetic sleeve, There is an aspect including a magnet member fixedly disposed in the non-magnetic sleeve and provided with a magnetic field generating means.
Further, the magnetic field generating means may be any means having a plurality of magnetic poles. For example, as a configuration example of the magnetic poles, a development magnetic pole for contributing to development and a function of capturing the developer G are provided. Examples include a pickup magnetic pole, a conveyance magnetic pole for conveying the developer G, and the like, but are not limited thereto, and may be appropriately selected.
Furthermore, from the viewpoint of effectively transferring the toner between the two developer carriers 3 and 4 and the toner carrier 2, and between the developer carrier 3 for supply and the toner carrier 2 and the recovery. It is preferable that a predetermined electric field for supplying or collecting the toner to the toner carrier 2 is formed between the developer carrier 4 and the toner carrier 2, and at this time, the developer carrier The bias applied to 3 and 4 may be a DC voltage, or may be an AC voltage superimposed on a DC voltage.

Similarly to the developer carriers 3 and 4, the conveying member 5 in the present invention includes a magnetic field generating means inside, and is spaced a predetermined distance from the supply developer carrier 3 and the recovery developer carrier 4. In other words, a mode in which the toner carrier 2 is in contact with the toner carrier 2 is also possible.
Here, “delivering the two-component developer G between the two developer carriers 3 and 4” means that the developer G is transferred between the two developer carriers 3 and 4 on the upstream side. This is not a mode in which the developer is conveyed directly from the body to the downstream developer carrier, but a mode in which the material is delivered through the conveying member 5.
Further, the conveying member 5 is preferably rotated in the same direction at a portion facing the two developer carriers 3, 4, whereby the conveying member 5 and the two developer carriers 3, 4 are rotated. In the opposite part, the stress of the developer G conveyed is reduced.
Furthermore, in the present invention, the developer G transported on the transport member 5 is smoothly transported by the guide member 6 provided in the direction opposite to the toner carrier 2 in the vicinity of the transport member 5. Become.
The toner used in the present invention may be magnetic or non-magnetic as long as it adheres to a magnetic carrier (carrier).

In the above-described aspect, in order to reduce the size of the developing device, it is necessary to reduce the size of each component of the device. Here, in particular, in order to reduce the size while arranging a large number of magnetic poles on the conveying member 5, there is a problem in the manufacturing method, and it is difficult to reduce the size at a low cost.
This is because, when magnetizing a small-diameter magnet body after molding, the magnetic poles interfere with each other, so it is difficult to magnetize with, for example, 5 poles. This is because magnetization is difficult. For this reason, when manufacturing the small-diameter conveying member 5, it is necessary to use a high-cost manufacturing method in which, for example, a rare earth metal or the like of a ferromagnetic material is embedded.

Therefore, as one aspect of the present invention, as shown in FIG. 1 (a), the conveying member 5 has only a pair of magnetic poles α and β having different polarities. Of the plurality of magnetic poles of each of the two developer carriers 3 and 4, the characteristic feature is that they are arranged at positions corresponding to the magnetic poles m and n closest to the conveying member 5.
Furthermore, in this embodiment, in particular, the configuration in which the developer G flows from the supply developer carrier 3 to the recovery developer carrier 4 via the conveying member 5 (Against configuration) It is preferable since the effect of gravity can be added to the transportability of the developer G on the transport member 5 and the flow of the developer G can be secured by the developer transport path by the guide member 6. As a result, even if the conveying member 5 is downsized, the magnetic pole arrangement is composed of only two poles.

On the other hand, as another aspect of the present invention, as shown in FIG. 1B, the conveying member 5 is provided with a pair of magnetic poles α and β having different polarities. The two developer carriers 3 and 4 are disposed at positions corresponding to the magnetic poles closest to the conveying member 5 among the plurality of magnetic poles of each of the two developer carriers 3 and 4, and the pair of magnetic poles α, It is characterized in that at least a pair of auxiliary magnetic poles αm, βm having a magnetic force smaller than β is disposed between the pair of magnetic poles α, β having different polarities and closer to the guide member 6.
Further, in this embodiment, in particular, in the case of a configuration (With configuration) in which the developer G is allowed to flow from the recovery developer carrier 4 to the supply developer carrier 3 via the conveyance member 5. Even if the transportability of the developer G upward in the member 5 is weakened by gravity, it is preferable because the transportability of the developer G is secured by the auxiliary magnetic poles αm and βm. In the aspect including the auxiliary magnetic poles αm and βm, the magnetic force of the auxiliary magnetic poles αm and βm is preferably small so as not to affect the magnetization of the pair of magnetic poles α and β having different polarities. Thereby, the conveying member 5 can be collectively magnetized, and the conveying member 5 can be made small and inexpensive.

Furthermore, in the present invention, the distance D between the guide member 6 and the conveyance member 5 provided substantially concentrically on the conveyance member 5 is set from the viewpoint of ensuring the conveyance property of the developer G on the conveyance member 5. It is preferable to set as follows.
Therefore, in order to quantify the influence of the magnetic force of the conveying member 5, a magnetic flux density index is set.
Now, as shown in FIG. 2, the conveying member 5 is assumed to be a cylindrical body 7 having a plurality of magnetic poles (magnetic poles 1 to 3), and attention is paid to one of the magnetic poles (magnetic pole 2). It is assumed that the magnetic lines of force on the surface of the surface extend radially from the center of the cylindrical body 7 and are not distorted.
Therefore, the magnetic flux density at the point P on the magnetic pole surface of the cylindrical body 7 is B ₀ (mT), the radius of the cylindrical body 7 is R (mm), and the point extended from the center of the cylindrical body 7 in the radial direction through the P point. When the distance to Q is L (mm), the number of magnetic lines of force per unit length φ (Wb / m) passing through the range for the angle θ between the position of the radius R and the position of the distance L is constant. Therefore, the relational expression as shown in the expression (2) in FIG. 3 is established.
Thereby, the magnetic flux density index B at the point Q is expressed by the equation (1) in FIG. 3 using the magnetic flux density B ₀ on the outer peripheral surface of the cylindrical body 7.
The magnetic flux density index B is calculated on the assumption that the direction of the magnetic field lines is radial from the center of the cylindrical body 7. Strictly speaking, the magnetic flux density index B is influenced by other magnetic poles of the cylindrical body 7, and the angle of the magnetic poles. The number of lines of magnetic force crossing the area occupied by θ decreases as the distance L from the center of the cylindrical body 7 increases. However, in the present invention, since it is assumed that the developer G is within the range where the magnetic poles are affected, it has been determined that the number of lines of magnetic force due to the distance L does not change.
Thus, the above assumption is valid if the point P is at the magnetic pole position of the cylindrical body 7 and the position in the vicinity thereof. When the point P is different from the position of the magnetic pole, the magnetic lines of force are not radial, but the number of magnetic lines that cross the area occupied by the angle θ from the center of the cylindrical body 7 is such that the point P as described above It is considered that the relationship is the same as in the case of the position. Therefore, from the relationship of the magnetic flux density between an arbitrary point P on the surface of the cylindrical body 7 and a point Q extending radially through this point P, generally the magnetic flux density index at the point Q is shown in FIG. It becomes possible to make it into a formula.

By using this magnetic flux density index B, the distance D between the guide member 6 and the conveying member 5 is such that the magnetic flux density index on the developer guide surface on the side of the recovery developer carrier 4 from the lowest end of the guide member 6. Is set to be 40 or more, in particular, the flow of the developer G in the Against configuration can be regulated within the range covered by the magnetic force of the transport member 5, and the developer G in the guide member 6 due to the influence of gravity. The generation | occurrence | production of the accumulation of can be suppressed. This also has the same effect in the flow of the developer G in the With configuration.
The present invention is also directed to an image forming apparatus including the developing device described above.

According to the present invention, a toner carrier and two developer carriers for supplying and recovering toner to the toner carrier are provided, and further, between the two developer carriers at positions opposed to these. Since the conveying member for delivering the developer is provided, the flow of the developer becomes smooth and the stress received by the developer is reduced, so that a developing device free from development history, density unevenness and fogging can be provided.
In particular, the transport member has only a pair of magnetic poles of different polarities, and each magnetic pole corresponds to each of the magnetic poles closest to the transport member among the plurality of magnetic poles of each of the two developer carriers. Since it is arranged at the position, a small and inexpensive developing device is possible.
On the other hand, the conveying member is provided with a pair of magnetic poles having different polarities, and the pair of magnetic poles having different polarities correspond to the magnetic poles closest to the conveying member among the plurality of magnetic poles of the two developer carriers. Further, even if the at least one pair of auxiliary magnetic poles having a magnetic force smaller than that of the pair of different polarity magnetic poles is arranged between the pair of different polarity magnetic poles and closer to the guide member, the small size, An inexpensive developing device becomes possible.
Further, by using this developing device, an image forming apparatus having stable development characteristics can be provided.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 4 shows Embodiment 1 of an image forming apparatus 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.

Further, the developing device 30 includes toner and a magnetic carrier (carrier) in the developing housing 31.
A donor roll 32 that contains a two-component developer (developer) and that carries toner, a toner supply roll 33 for supplying toner, a toner collection roll 34 for collecting toner, and a transport roll that transports the developer 35.
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.

Here, the developing device 30 which is a feature of the present invention will be described in detail with reference to FIG. In the present embodiment, the developer G is configured to flow from the toner supply roll 33 to the transport roll 35 and the toner collection roll 34 (Against system).
In the drawing, the developing device 30 has a developing housing 31 (see FIG. 4) that opens toward the photosensitive member 21, and faces the opening of the developing housing 31 and faces the photosensitive member 21. The donor roll 32 is accommodated so as to be rotatable in the direction of the arrow. 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 covered with a polyurethane resin-based elastic member having a predetermined volume resistivity. For example, the donor roll 32 is a metal roll made of aluminum or stainless steel. There is no problem. Further, the donor roll 32 and the photoconductor 21 are in contact with each other, but they may be non-contact.

A toner supply roll 33 and a toner collection roll 34 are arranged at a predetermined distance (interval) from the donor roll 32 at the rear part (the side opposite to the photoreceptor 21) of the donor roll 32.
The toner supply roll 33 and the toner collection roll 34 are connected to bias power supplies 38 and 39, respectively, and supply bias VS for supplying toner from the toner supply roll 33 to the donor roll 32. A collection bias VR for collecting the toner is applied to the collection roll 34.
Further, at the rear 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.

In the present embodiment, the toner supply roll 33, the toner recovery roll 34, and the transport roll 35 are fixedly disposed inside the rotatable sleeves 33a to 35a and the rotatable sleeves 33a to 35a, 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 It is arranged so as to face the transport roll 35 in the vicinity of the middle of N3. In addition, the codes N and S of the magnetic poles indicate the N pole and the S pole, respectively.
In addition, the magnet body 34b of the toner recovery roll 34 includes a plurality of magnetic poles (S4, S5, N4, S3, N5) on the outer peripheral portion thereof, the magnetic pole S3 is provided at a position facing the donor roll 32, and the magnetic pole S5. Is disposed so as to face the transport roll 35.
Further, the magnet body 35 b of the transport roll 35 has a pair of magnetic poles (S 6, N 6) disposed at substantially opposite positions, the magnetic pole S 6 is the magnetic pole N 2 of the toner supply roll 33, and the magnetic pole N 6 is the toner recovery roll 34. They are arranged at positions corresponding to the magnetic poles S5, respectively.

In addition, a conveyance guide 43 is provided at the rear of the conveyance roll 35 so as to guide the developer conveyance in a semicircular shape substantially concentric with the conveyance roll 35, and the developer G efficiently conveys the outer periphery of the conveyance roll 35. To be.
In particular, in the present embodiment, the distance D between the transport roll 35 and the transport guide 43 is set by using the magnetic flux density index B described above, and the toner collection roll 34 side (δ region) from the lowest end of the transport guide 43. The magnetic flux density index B is set to be 40 or more.
Here, as a specific measurement method, Gauss meter MODEL HGM-8300-5 manufactured by ADS Co., Ltd. was used, and measurement was performed in a state in which the probe was vertically close to the surface of the transport roll 35.

Further, in the present embodiment, as shown in FIG. 5, a trimmer 42 for regulating the layer thickness of the developer G is provided at a position facing the magnetic pole S <b> 2 of the toner supply roll 33.
In addition, a release guide 44 that guides the developer G peeled from the toner recovery roll 34 is provided in the vicinity of the toner recovery roll 34.
Two augers 41 as stirring members are disposed behind the conveyance guide 43, and the developer G recovered from the toner recovery roll 34 is stirred and charged, and then the developer G is applied to the toner supply roll 33. It is configured to supply. In the present embodiment, two augers 41 are provided. However, the present invention is not limited to this, and any number of augers 41 may be used.

Here, in this embodiment, the diameter of the magnet body 35b of the transport roll 35 is 10 mm, the diameter of the rotating sleeve 35a is 12 mm, and the magnetic flux density on the surface of the rotating sleeve 35a is 80 mT for both the magnetic pole S6 and the magnetic pole N6.
The magnet body 35b of the transport roll 35 is made of a bonded magnet containing ferrite-based powder, and is formed by forming a cylindrical magnet body 35b and then magnetizing it in a lump.
FIG. 6 shows a state in which the magnet body 35b is magnetized in a lump. FIG. 6A shows a method of forming two magnetic poles N and S in the magnet body 35b (corresponding to the present embodiment). (B) shows a method of forming two magnetic poles N and S and weaker magnetic poles Nm and Sm (corresponding to the method shown in the second embodiment to be described later), and (c) shows three or more magnetic poles having a large magnetic force. 1 shows a method of forming five magnetic poles S, N, N, S, N like the toner supply roll 33, for example.
In order to form these magnetic poles, magnetized yokes 51 to 55 for forming predetermined magnetic poles are installed in the molded magnet body 35b, and the coils of the magnetized yokes 51 to 55 are arranged in a predetermined direction. This is done by passing a current.
When the diameter of the magnet body 35b is reduced to reduce the size of the developing device, the volume of the magnet body decreases in proportion to the square of the diameter. For this reason, when the diameter is reduced while keeping the five magnetic poles as shown in (c), the volume of the magnet body per magnetic pole becomes smaller than the large diameter, and a desired magnetic force cannot be obtained at each magnetic pole. Increasing the current flowing through the magnetizing yoke to increase the magnetic force saturates the magnetization of the ferrite, making it difficult to increase the magnetic force.
Therefore, as shown in (a), when it is configured to have only two poles having a large magnetic force, a sufficient volume of the magnet body can be secured to obtain a desired magnetic force at each magnetic pole, so the diameter of the magnet body 35b is small. Even in this case, it is possible to perform magnetization with a stable desired magnetic force. In addition, as shown in (b), even when it is configured to include two poles with a large magnetic force and a small two poles, the volume of the magnet body sufficient to obtain a desired magnetic force at each magnetic pole can be secured in the same manner. It can be magnetized to a stable desired magnetic force.
Therefore, in the magnetic pole arrangement (two poles) as in the present embodiment, normal collective magnetization is possible, and an inexpensive magnet body 35b is possible.

Next, the operation of the developing device 30 according to this embodiment will be described.
In FIG. 5, the developer G is stirred by the auger 41 so that the toner is charged with a negative polarity and the carrier is charged with a positive polarity, and then the developer on the upstream side of the magnetic pole S <b> 2 in the magnet body 33 b of the toner supply roll 33. In the supply region, the toner is supplied to the toner supply roll 33. Then, when the developer G reaches the vicinity of the trimmer 42, a spike is formed by the magnetic pole S2. Further, the rise 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 direction of the arrow along with the rotation of the rotary sleeve 33a. At this time, the developer G constitutes a magnetic brush along the lines of magnetic force formed by the magnet body 33b.

  Next, when the developer G enters the 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 developer that has formed this magnetic brush is formed. Only the toner of 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. On the other hand, the carrier that has lost the toner and the developer G that has passed through the toner supply region are attracted to the toner supply roll 33 and the transport roll 35 by the attractive magnetic field between the magnet body 33b of the toner supply roll 33 and the magnet body 35b of the transport roll 35. Are delivered to the transport roll 35 in the opposite area.

  The developer G transferred to the transport roll 35 is held by the transport roll 35 due to the magnetic field of the magnet body 35b and the effects of gravity and the transport guide 43, and is transported on the outer periphery thereof, and then the magnet body of the transport roll 35. Due to the attraction magnetic field between 35 b and the magnet body 34 b of the toner recovery roll 34, the toner is transferred to the toner recovery roll 34 in a region where the transport roll 35 and the toner recovery roll 34 face each other.

On the other hand, the toner supplied to the donor roll 32 is transported on the donor roll 32 according to the rotation of the donor roll 32, and is formed on the photoconductor 21 in a developing region at a portion facing the donor roll 32 and the photoconductor 21. Used for developing an electrostatic latent image. Further, the toner that has passed through the development area without being used for development is sent to the toner collection area near the magnetic pole S3 of the toner collection roll 34.
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.
Further, the developer G that has finished collecting the toner is further conveyed on the outer periphery of the toner collecting roll 34 and is peeled off from the toner collecting roll 34 along the release guide 44.
Then, the developer G peeled off from the toner collecting roll 34 is returned to the auger 41 by a conveyance assisting means such as a paddle (not shown).

In the present embodiment, the distance D in the downstream δ region between the transport roll 35 and the transport guide 43 is such that the magnetic flux density index B is 40 or more. Therefore, the developer G that flows along the transport roll 35. However, it remains within the range covered by the magnetic force of the transport roll 35 and does not stay in the transport guide 43 due to the influence of gravity. Further, since the magnetic pole of the transport roll 35 is only the pair of magnetic poles S6 and N6, the magnetic force is weak in the vicinity of the center of the transport guide 43 (γ region), and the back surface side of this transport guide 43 (facing the auger 41). Adhesion of developer G to the side) can be reduced. Therefore, the flow of the developer G becomes smooth, and image defects such as density unevenness are prevented.
Further, by using this developing device 30, an image forming apparatus capable of obtaining a stable image over a long period of time becomes possible.

Embodiment 2
FIG. 7 shows a second embodiment of a developing device 30 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 (With method). In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.

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 includes a plurality of magnetic poles (S6, N3, S4, N4, S5) on the outer periphery thereof, the magnetic pole S4 is provided at a position facing the donor roll 32, and the magnetic pole S5. Is disposed so as to face the transport roll 35.

In particular, in the present embodiment, the magnet body 35b of the transport roll 35 is disposed such that, of the pair of magnetic poles N5 and S7, the vicinity of the magnetic pole N5 is at a position facing the toner recovery roll 34. Further, a pair of auxiliary magnetic poles Sm and Nm having a magnetic force smaller than those of the magnetic poles N5 and S7 are arranged between the pair of magnetic poles N5 and S7 on the side facing the developer G conveyance path side.
Furthermore, in the present embodiment, the auger 41 as a stirring member is disposed below the transport roll 35.
Also in the present embodiment, similarly to the first embodiment, the diameter of the magnet body 35b of the transport roll 35 is 10 mm, the diameter of the rotating sleeve 35a is 12 mm, and the magnetic flux density on the surface of the rotating sleeve 35a is the magnetic pole N5 and the magnetic pole S7. And 80 mT, and the auxiliary magnetic pole Sm and the auxiliary magnetic pole Nm are 40 mT. Therefore, when magnetizing the magnet body 35b in this case, since the auxiliary magnetic poles Sm and Nm are sufficiently smaller than the magnetic poles N5 and S7, collective magnetization is possible and the manufacturing cost is reduced (see FIG. 6).
In the present embodiment as well, as in the first embodiment, the distance D on the toner collection roll 34 side (δ region) of the conveyance guide 43 is arranged so that the magnetic flux density index is 40 or more. Therefore, the accumulation of the developer G in this region is prevented.

Next, the operation of the developing device 30 according to this embodiment will be described.
In FIG. 7, the developer G stirred and charged by the auger 41 is supplied to the toner collecting roll 34.
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 conveyed along with the rotation of the rotating sleeve 34a.

  Next, when the developer G enters the toner collection area where the toner collection 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 to collect the toner from the donor roll 32. 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. .

The developer G from which the toner has been collected is transferred to the conveyance roll 35 in the vicinity of a region where the toner collection roll 34 and the conveyance roll 35 face each other.
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.

The developer G conveyed on the outer periphery of the toner supply roll 33 forms a magnetic brush by the magnetic attractive force of the magnetic pole S1 in the toner supply region near the magnetic pole S1, and is formed between the toner supply roll 33 and the donor roll 32. Under the influence of the applied electric field, the toner on the toner supply roll 33 is supplied to the donor roll 32.
After the toner supply, the developer G is separated from the toner supply roll 33 by the repulsive magnetic field of the magnetic pole S2 and the magnetic pole S3 of the toner supply roll 33, and returned to the auger 41 along the release guide 44.

In the present embodiment, the magnetic pole arrangement of the transport roll 35 is provided with a pair of magnetic poles N5 and S7 having a strong magnetic force and a pair of auxiliary magnetic poles Sm and Nm having a weak magnetic force. In the portion where Nm is arranged, the magnetic force in the γ region on the back side of the conveyance guide 43 is weak, so when the developer G recovered from the release guide 44 returns to the auger 41, the γ of the conveyance guide 43 The adhesion of the developer G to the region can be reduced. Therefore, the developer G does not accumulate and the developer G flows smoothly. Furthermore, there is no accumulation of the developer G in the conveyance guide 43.
Therefore, also in this embodiment, a small and inexpensive developing device that does not have development history, density unevenness, and fogging can be realized.

In this example, the relationship between the distance D (distance on the downstream side in the developer conveyance direction) between the conveyance roll and the conveyance guide in Embodiment 1 (see FIG. 5) and the magnetic flux density index is changed from the conveyance roll to the toner collection roll. Evaluation and confirmation of developer transport characteristics to
In this embodiment, the diameter of the magnet body of the transport roll is 10 mm, the diameter of the rotating sleeve is 12 mm, and the magnetic flux density on the surface of the rotating sleeve is 80 mT for both poles (corresponding to the magnetic pole S6 and magnetic pole N6 in FIG. 5). It was. In this embodiment, the magnetic flux density index at the magnetic pole N6 is used as a factor.
As shown in FIG. 8, as the distance D is increased, the magnetic flux density index gradually decreases. As a result, if the distance D is 6 mm or less (the magnetic flux density index is 40 or more), the transport roll Good developer transportability was confirmed from the downstream side to the toner collecting roll. On the other hand, when the distance D is 7 mm or more, a developer pool is generated on the downstream side of the transport roll.
Therefore, it was confirmed that the developer flow was kept good if the position of the conveyance guide was 40 or more as the magnetic flux density index.

It is explanatory drawing which shows the outline | summary of the image development apparatus concerning this invention. It is explanatory drawing which shows a magnetic flux density parameter | index. It is explanatory drawing which shows the numerical formula which calculates | requires a magnetic flux density parameter | index. 1 is an explanatory diagram illustrating an image forming apparatus according to Embodiment 1. FIG. FIG. 2 is an explanatory diagram illustrating a developing device according to the first embodiment. It is a figure which shows the magnetizing method of a magnet body. FIG. 10 is an explanatory diagram illustrating a developing device according to a second embodiment. It is explanatory drawing which shows the result of an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Toner carrier, 3 ... Supply developer carrier, 4 ... Collecting developer carrier, 5 ... Conveyance member, 6 ... Guide member, G ... Two-component developer, (alpha) ... Magnetic pole , Β: magnetic pole, m: magnetic pole, n: magnetic pole, αm: auxiliary magnetic pole, βm: auxiliary magnetic pole

Claims (6)

A toner carrying member facing the image carrying member carrying the electrostatic latent image and carrying toner on the surface;
A developer carrying body for supply, which is disposed at a position facing the toner carrying body, carries and conveys a two-component developer containing toner and a magnetic carrier, and supplies the toner to the toner carrying body;
A collecting developer carrier that is disposed at a position facing the toner carrier, carries and conveys the two-component developer, and collects toner from the toner carrier;
A conveying 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 including a guide member that surrounds a part of the conveying member and forms a developer conveying path around the conveying member;
Each developer carrier has a plurality of magnetic poles,
The transport member is provided with only a pair of different polarity magnetic poles, and the pair of different polarity magnetic poles is connected to each of the magnetic poles closest to the transport member among the plurality of magnetic poles of each of the two developer carriers. A developing device arranged at a corresponding position. A toner carrying member facing the image carrying member carrying the electrostatic latent image and carrying toner on the surface;
A developer carrying body for supply, which is disposed at a position facing the toner carrying body, carries and conveys a two-component developer containing toner and a magnetic carrier, and supplies the toner to the toner carrying body;
A collecting developer carrier that is disposed at a position facing the toner carrier, carries and conveys the two-component developer, and collects toner from the toner carrier;
A conveying 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 including a guide member that surrounds a part of the conveying member and forms a developer conveying path around the conveying member;
Each developer carrier has a plurality of magnetic poles,
The conveying member is provided with a pair of magnetic poles having different polarities, and the pair of magnetic poles having different polarities correspond to the magnetic poles closest to the conveying member among the plurality of magnetic poles of each of the two developer carriers. Further, at least a pair of auxiliary magnetic poles having a magnetic force smaller than that of the pair of different polarity magnetic poles are arranged between the pair of different polarity magnetic poles and closer to the guide member. apparatus. The developing device according to claim 1 or 2,
The conveying member is a cylindrical body capable of conveying a two-component developer having a magnetic pole therein, wherein the magnetic flux density at an arbitrary point P on the surface of the cylindrical body is B ₀ (mT), and the radius of the cylindrical body is R ( mm), and when the distance from the center of the cylindrical body to the point Q extending radially through P is L (mm), the numerical value obtained by B (mT) = B ₀ R / L is the point Q If the magnetic flux density index of
The guide member is provided substantially concentrically with the conveying member. Further, the distance between the guide member and the conveying member is a magnetic flux density index on the developer guide surface extending from the lowest end of the guide member to the collecting developer carrier. A developing device characterized by being set as described above. The developing device according to claim 1,
A developing device characterized in that a two-component developer is allowed to flow from a supply developer carrier to a recovery developer carrier via a conveying member. The developing device according to claim 2, wherein
A developing device characterized in that a two-component developer is allowed to flow from a collecting developer carrier to a supply developer carrier via a conveying member. An image carrier for carrying an electrostatic latent image;
An image forming apparatus comprising the developing device according to claim 1, which develops an electrostatic latent image on the image carrier.

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