JP2000081788A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent a ghost phenomenon in consequence of a development history, in a developing device of the hybrid developing system. SOLUTION: In this developing device so called the hybrid developing system performing development by adopting the two component developer consisting of magnetic carriers and toner, and feeding only the toner on the developing roll, by independently providing the toner feed developer carrier 3 for feeding the toner to the toner carrier 2 carrying the two component developer, and the toner recovery developer carrier 5 for recovering the toner from the toner carrier 2 carrying the two component developer, the device is allowed to statically recover the toner permitted to pass being carried by the toner carrier 2, in the two component developer carried by the toner recovering developer carrier 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic copying machine or a laser printer, and more particularly to a developing device using a two-component developer comprising a magnetic carrier and a toner. The present invention relates to an improvement in a developing device called a so-called hybrid development system in which development is performed by supplying only toner onto a roll.

[0002]

2. Description of the Related Art As a conventional image forming apparatus, for example, an electrostatic latent image is formed on an electrostatic latent image carrier such as a photoreceptor by a charging / exposure process, and then a developer containing toner is used by a developing device. The electrostatic latent image is developed, and the developed toner image is transferred to a recording material by a transfer device. Then, the toner image transferred to the recording material by a fixing device is fused by heat and fixed to form an image on the recording material. Is known. As a developing device used in such an image forming apparatus, for example, a two-component developing system in which a two-component developer including a magnetic carrier and a toner is opposed to the surface of an electrostatic latent image carrier to develop an electrostatic latent image is used. A one-component developing method of developing an electrostatic latent image by using a used one or a one-component developer consisting of only a toner is widely used.

In such a developing device, in order to develop an electrostatic latent image formed on an electrostatic latent image carrier with toner, the toner is charged to a predetermined charge amount, and the charged toner is charged. Although it is necessary to transport the magnetic carrier to a developing position where it can be transferred onto the electrostatic latent image, in the case of the two-component developing method, the magnetic carrier is also transported and passes through the developing position. There is a possibility that the toner may adhere to the latent image carrier and cause transfer failure, or a load may be applied to the fixing device. Also, in the one-component developing method, the toner is often charged by friction with the layer forming blade.However, it is difficult to obtain a sufficient charge amount by the charging due to the friction. The opposite polarity toner that is charged may be generated, and the opposite polarity toner may be transferred to an area where the electrostatic latent image is not present on the electrostatic latent image carrier, causing fog.

[0004] Therefore, as a developing method for solving the problems in each of these developing methods, a developing method for obtaining desirable characteristics of both by combining the advantages of a non-magnetic one-component developing method and a two-component developing method using a donor roll. (Hereinafter referred to as a hybrid development system) has been proposed.
This is a developing method using a two-component developer as a developer. For example, as shown in FIG. 15, a developing housing 101 having an opening at a portion facing the photosensitive drum 11 rotating in the direction of arrow a, A donor roll 102 rotatably disposed facing the opening of the developing housing 101 and carrying only the toner of the two-component developer, and a two-component rotatably disposed on the rear side of the donor roll 102 so as to be rotatable. A transport supply roll 103 that carries and transports the developer and supplies only the toner of the two-component developer to the donor roll 102, and regulates a layer thickness of the two-component developer formed on the transport supply roll 103. The trimmer 104 is disposed at a predetermined interval between the trimmer 104 and the transport and supply roll 103, and transports the two-component developer to be supplied to the transport and supply roll 103 with stirring. Consists 105 and 106.,
Further, between these augers 105 and 106, there is provided a partition plate 101a for partitioning between the augers except at both ends. Further, the donor roll 102 and the transport supply roll 103
A bias applying device (not shown) for forming an electric field for transferring the toner on the transport and supply roll 103 onto the donor roll 102 is provided between them.

Here, a metal roll such as aluminum is used as the donor roll 102, and a plurality of magnetic poles are provided inside a rotatable sleeve made of a non-magnetic material such as aluminum as the transport and supply roll 103. Are fixedly included in a magnet roll in which are arranged.

In this developing device, the two-component developer is:
First, the two-component developer is sufficiently stirred and charged by the augers 105 and 106, and then the stirred two-component developer is transported by the magnetic force acting between the magnetic carrier of the two-component developer and the transport supply roll 103. Carried on the
It is transported with the rotation of the sleeve. At this time, the layer thickness of the two-component developer is regulated to be constant at the opposing portion between the transport supply roll 103 and the trimmer 104. Then, the two-component developer whose layer thickness is regulated is transported to a portion where the transport supply roll 103 and the donor roll 102 are opposed to each other, and an electric field formed by a bias applying device (not shown) causes the two-component developer to be out of the two-component developer. Only the toner is transferred from the transport supply roll 103 to the donor roll 102. Thereafter, the toner transferred to the donor roll 102 is
Is transported to a portion facing the photoconductor drum 11 with the rotation of the photoconductor drum 11 to develop the electrostatic latent image on the photoconductor drum.

In this hybrid developing system, the toner is charged by stirring the two-component developer, so that it is easy to secure a sufficient charge amount. Further, the supply of the toner from the transport supply roll 103 to the donor roll 102 is performed by electrostatic force. Therefore, the toner charged to the opposite polarity is not supplied to the donor roll 102. Accordingly, the toner does not adhere to the non-image area of the photosensitive drum 11, and the occurrence of fog is prevented. Further, since only the toner is supplied to the donor roll 102, the adhesion of the magnetic carrier to the photosensitive drum 11 is also prevented.

[0008]

However, in the hybrid developing method, the donor roll 10 is not developed without being developed.
2, there may be a difference in toner amount and toner particle size between the area where the toner remains on the area 2 and the area where new toner has been supplied after development, that is, there is a possibility that a problem of developing history may occur. . The occurrence of such a development history causes a difference in the development amount. As a result, for example, a density difference occurs in a developed image between a case where solid development is performed continuously and a case where solid development is performed after passing a blank sheet. When there is an area where the toner is consumed by the solid development and an area adjacent to the area where the toner is not consumed without the development, the area of the donor roll 102 is reduced. When solid or halftone is developed after one rotation, there is a technical problem that a density difference occurs in a developed image, that is, a so-called ghost phenomenon occurs.

Therefore, as a first means for solving this technical problem, a toner on a donor roll after development is mechanically scraped with a scraper or a roll as in a developing device using a one-component developer, for example. It is possible to take. In this case, the undeveloped toner is always separated from the donor roll once, so that the development history on the donor roll is eliminated.

However, in order to uniformly charge the scraped toner and use it again for development, it is necessary to uniformly mix the scraped toner again into the two-component developer. Since the area ratio of an image is generally about 5 to 30%, a large amount of toner is scraped off by a scraper without being developed, and it is difficult to uniformly remix the two-component developer. If the scraped toner is not uniformly remixed in the two-component developer, a toner having a higher charge than an appropriate value or a toner having a lower charge or opposite polarity is generated, that is, a toner is generated. May cause uneven charging, which may result in poor image quality. Further, in such an embodiment, stress is applied to the toner during scraping, so that the toner may be deteriorated.

As a second means, the voltage applied between the donor roll and the transport supply roll is switched at a high frequency, and the electric field for supplying the toner from the transport supply roll to the donor roll and the toner supplied from the donor roll to the transport supply roll are used. A technique for alternately forming an electric field to be peeled off has been proposed (see Japanese Patent Application Laid-Open No. 6-67546). In this prior art, by setting the formation time of the electric field for supplying the toner to the donor roll to be longer than the formation time of the electric field for separating the toner from the donor roll, the undeveloped toner is always separated from the donor roll once. And the development history on the donor roll is eliminated.

However, since the amount of toner supplied to the donor roll is reduced by the time required for removing the toner from the donor roll, sufficient toner cannot be supplied to the developing position, and it is difficult to obtain a required image density. A technical challenge arises.

Further, in Japanese Patent Application Laid-Open No. 6-67546, as a third means, a toner peeling member is provided separately from the transport and supply rolls, and the toner on the donor roll is electrically peeled and collected. A technique has also been proposed in which the separated and recovered toner is electrically transferred to a transport supply roll and collected by the transport supply roll. Here, the toner peeling member is constituted by a rotatable cylindrical member provided with three or more electrodes divided in the circumferential direction, and is disposed so as to face both the donor roll and the transport supply roll. You. Then, a voltage that forms an electric field in a direction in which the toner is separated from the donor roll and the toner is collected on the electrode is applied to the electrode at the position facing the donor roll,
In addition, a voltage is applied to the electrode at a position facing the transport supply roller so as to form an electric field in a direction in which toner is separated from the electrode and toner is collected on the transport supply roller. In this developing device, the toner is collected from the donor roll at a position facing the donor roll with the rotation of the toner peeling member, and the toner is transferred to the transport supply roll at a position facing the transport supply roll.

However, in order to prevent discharge between a plurality of electrodes provided on the toner peeling member, it is necessary to arrange the electrodes at a certain distance, and an electric field cannot be formed between these electrodes. An area is formed, and in the area, the toner cannot be peeled off from the donor roll, but remains, and a striped history may be generated.

Furthermore, as a fourth means, the rotational direction of the donor roll is located downstream of the position where the transport / supply roll and the donor roll face each other in the rotational direction of the donor roll and the direction of rotation of the donor roll relative to the position where the donor roll and the photosensitive drum face. There has been proposed a technique in which a toner layer regulating member which is arranged close to or in contact with a donor roll is provided on the upstream side (Japanese Patent Laid-Open Publication No. Hei 6 (1994)).
-130798). According to this prior art, the amount of toner supplied from the transport supply roll to the donor roll is set to be larger than the amount of toner carried on the donor roll and passing through the toner layer regulating member, thereby passing through the toner layer regulating member. The development history on the donor roll is prevented by keeping the amount of toner to be constant.

In the prior art, for example, when a rigid blade is used as a toner layer regulating member and is disposed at a constant interval with respect to the donor roll, it is necessary to set the setting gap with the donor roll to 10 to 80 μm. There is. However, the donor roll is not suitable for manufacturing accuracy.
Since the eccentricity of about 0 to 50 μm occurs, it is very difficult to prevent the set gap from swinging when the donor roll rotates. For this reason, there is a technical problem that unevenness occurs in the toner transport amount for each rotation cycle of the donor roll, and image unevenness is likely to occur.

Further, when an elastic blade is used as a toner layer regulating member and is disposed in pressure contact with a donor roll, it is difficult to equalize the amount of toner passing through, and unevenness in the amount of transported toner may occur. There is a technical problem that the development history on the donor roll cannot be sufficiently prevented.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problem. By improving means for collecting the toner after development, the ghost phenomenon caused by the development history of the toner carrier is improved. An object of the present invention is to provide a developing device that can surely prevent the developing device.

[0019]

That is, as shown in FIG. 1, the present invention is arranged so as to be rotatable in opposition to an electrostatic latent image carrier 1, and a toner is carried and conveyed on the surface thereof to carry the electrostatic latent image. A toner carrier 2 for developing an electrostatic latent image formed on an image carrier 1, and a rotation direction upstream of the toner carrier 2 from a developing position where the electrostatic latent image carrier 1 and the toner carrier 2 are opposed to each other. A toner supply developer carrier 3 that is disposed opposite to the toner carrier 2 and has a two-component developer composed of a magnetic carrier and toner carried and conveyed on the surface thereof and supplies toner to the toner carrier 2; Supply bias applying means 4 for applying a bias between the toner carrier 2 and the developer carrier 3 for supplying toner to transfer the toner on the developer carrier 3 for toner supply to the toner carrier 2; Electrostatic latent image carrier 1
Downstream of the developing position where the toner carrier 2 and the toner carrier 2 are opposed to each other, and upstream of the toner carrier 2 in the rotational direction of the toner carrier 2 and the developer carrier 3 for supplying toner. Between the toner carrier 2 and the toner carrier 2, the toner carrier 2 being disposed opposite to the toner carrier 2 and carrying the two-component developer on its surface. And a recovery bias applying means 6 for applying a bias for transferring the toner on the toner carrier 2 to the developer carrier 5 for toner recovery.

In such technical means, since the developing device according to the present invention uses a two-component developer, a toner having various color components can be used. The present invention can be applied to an image forming apparatus having a plurality of developing devices, such as a full-color image forming apparatus, as well as an image forming apparatus having the apparatus.

The toner carrier 2 may be appropriately selected as long as it is rotatably disposed and can carry and convey toner around the toner carrier. Further, the developer carrier 3 for toner supply and the developer carrier 5 for toner collection may be any as long as it can carry and transport a two-component developer.
The number of such arrangements may be appropriately selected. As this specific mode, for example, a mode in which a magnetic field generating means is installed inside a non-magnetic sleeve is usually used.

The supply bias applying means 4 includes:
The two-component developer carried on the toner supply developer carrier 3 may be appropriately selected as long as it can form an electric field in which the toner is transferred to the toner carrier 2. Further, the collection bias applying means 6 may be appropriately selected as long as it can form an electric field in which the toner carried on the toner carrier 2 is transferred to the supply developer carrier 3.

Here, from the viewpoint of improving the toner collecting ability of the toner collecting developer carrier 5 and preventing the charging characteristics from becoming non-uniform due to agglomeration of the collected toners, the toner adhering is not considered. It is preferable that the collected toner is adhered to the small amount of the magnetic carrier, and from this viewpoint, the collected toner is carried by the toner supply developer carrier 3 and passed through the position facing the toner carrier 2. It is preferable that the two-component developer is configured to be moved to the developer carrier 5 for collecting toner. From the viewpoint of simply and surely realizing such a configuration, for example, the movement of the two-component developer from the toner supply developer carrier 3 to the toner recovery developer carrier 5 is the It is preferably performed by a magnetic field formed between the developer carrier 3 for toner and the developer carrier 5 for toner recovery.

In the present application, the two-component developer may be appropriately selected as long as it is composed of a magnetic carrier and a toner, and the color of the toner may be appropriately selected. .

In the present invention, an electric field is formed by the supply bias applying means 4 so that the toner of the two-component developer carried on the developer carrier 3 for toner supply is transferred to the toner carrier 2 and the electric field is collected. Since an electric field for transferring the toner carried on the toner carrier 2 to the supply developer carrier 3 by the bias applying means 6 is formed, the toner supply developer carrier 3 and the toner recovery developer carrier are formed. 5, a large potential difference occurs. In this case, in a type in which a magnetic carrier having a volume resistivity of 10 ⁸ Ω · cm or less is used as the magnetic carrier of the two-component developer, the magnetic carrier is connected to the toner supply developer carrier 3 and the toner. If a path is formed between the toner carrier 5 and the collecting developer carrier 5, a short circuit may occur between the toner supplying developer carrier 3 and the toner collecting developer carrier 5. From the viewpoint of reliably preventing such inconveniences, the toner supply developer carrier 3 and the toner recovery developer carrier 5 should be arranged at an interval capable of preventing a short circuit therebetween. preferable.

Next, the operation of the above technical means will be described. In FIG. 1, a developer carrier 3 for supplying toner is provided.
The two-component developer supplied and carried to the toner carrier is conveyed to a position facing the toner carrier. Then, at the opposing position, the toner of the two-component developer carried on the developer carrier 3 for toner supply is transferred and supplied to the toner carrier 2 by the electric field formed by the voltage applied by the supply bias applying unit 4. You. Next, the toner supplied to the toner carrier 2 is transported to a developing position where the electrostatic latent image carrier 1 and the toner carrier 2 face each other as the toner carrier 2 rotates, and The electrostatic latent image formed on the body 1 is developed. Then, the toner on the toner carrier 2 that has passed through the developing position is transported to a position where the toner carrier 2 and the toner recovery developer carrier 5 are opposed to each other as the toner carrier 2 rotates. On the other hand, the two-component developer supplied to and carried by the toner recovery developer carrier 5 is also transported to a position facing the toner carrier. Then, at the opposed position, the toner carried on the toner carrier 2 is collected by the collection bias applying unit 6.
Is transferred to and collected by the developer carrier 5 for toner collection by an electric field formed by the applied voltage of. At this time, since the two-component developer is carried on the developer carrier 5 for toner collection, the collected toner adheres to the two-component developer and is collected.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of an electrophotographic image forming apparatus incorporating a first embodiment of a hybrid developing type developing apparatus to which the present invention is applied. In the figure, reference numeral 11 denotes a photoconductor drum rotating in the direction of arrow a, and 12 denotes a photoconductor 11
Charger 13 for charging the photosensitive drum 11
A laser exposure device for writing an electrostatic latent image on the photosensitive drum 11; a developing device 14; a transfer charger 15 for collectively transferring a toner image developed on the photosensitive drum 11 onto recording paper 17; A cleaner for removing the residual toner on the photosensitive drum 11; and a removing lamp 19 for removing the residual charge on the photosensitive drum 11.

In the present embodiment, the photosensitive drum 11
Has a surface layer made of a negatively charged organic photoreceptor on the surface. Further, the laser exposure device 13 includes the charger 1
2 is irradiated with light corresponding to an image on the photoreceptor drum 11 charged by 2. In the case of reversal development, the image portion potential is Vl, and the non-image portion potential is Vh (= charged by the charger 12. Potential), the contrast | Vh-Vl
An electrostatic latent image of | is formed.

As shown in FIG. 3, the developing device 14 has a development opening 22
And a developing housing 21 in which a two-component developer G is accommodated. The developing housing 21 faces the developing opening 22 of the developing housing 21 at a predetermined distance from the photosensitive drum 11. A developing roll (donor roll) 23 is provided. In the present embodiment, as the two-component developer G, the magnetic carrier C is positive,
In addition, a toner that negatively charges the toner T is used, and a conductive carrier having a volume resistivity of 10 ⁸ Ω · cm or less is used as the magnetic carrier C from the viewpoint of increasing the supply amount of the developer. .

The donor roll 23 is made of, for example, aluminum or the like, and has a smooth pipe or columnar surface. 11 is rotated in the opposite direction (against direction).

Further, as shown in FIG. 4, a developing bias Vd is applied between the photosensitive drum 11 and the donor roll 23 to develop the electrostatic latent image on the photosensitive drum 11 as shown in FIG. A developing bias applying device 20 to be applied is connected. Here, the developing bias Vd is set between the image portion potential Vl and the non-image portion potential Vh, and is applied to the donor roll 23 by an electric field formed by a potential difference (development potential) from the image portion potential Vl. The toner T develops the image portion of the photoconductor drum 11, and the toner T adheres to the non-image portion on the photoconductor drum 11 by an electric field formed by a potential difference (cleaning potential) from the non-image portion potential Vh. Is prevented. Note that an AC component may be superimposed on the developing bias Vd as necessary.

A toner supply roll 24 for carrying and transporting the two-component developer G and supplying the toner T to the donor roll 23 is disposed in proximity to a lower portion of the developing housing 21 on the back side of the donor roll 23. A toner collecting roll 25 that carries and transports the two-component developer G and collects the toner T remaining on the donor roll 23 after passing through the developing area is disposed in proximity to the upper rear side of the roll 23.

As shown in FIG. 4, the toner supply roll 24 has a plurality of magnetic poles (N11, S1) inside a rotatable sleeve 241 made of a non-magnetic material such as aluminum.
Magnet roll 242 on which 2, N13, S14, N15) are arranged
Is fixedly included, and is rotationally driven in a direction opposite to the donor roll 23 (against direction) at a position facing the donor roll 23 while maintaining a predetermined distance from the donor roll 23. The surface of the sleeve 241 is roughened or grooved so that the two-component developer G can be easily carried and transported.
Further, the toner supply roll 24 includes the toner supply roll 2.
A trimmer 24 a that regulates the layer thickness of the two-component developer G supplied to the toner supply roll 4 is provided at a predetermined distance from the toner supply roll 24. Here, the trimmer 24a is generally formed of a non-magnetic metal plate, and if necessary, a trimmer 24a having a magnetic plate adhered to the upstream surface in the transport direction of the two-component developer G is also used.

Further, between the donor roll 23 and the toner supply roll 24, a supply bias power supply 26 to which a supply bias Vs for forming an electric field for transferring the toner T from the toner supply roll 24 to the donor roll 23 is connected. Have been. In this embodiment, since the negatively charged toner T is used, the setting is performed such that the potential of the donor roll 23 is higher than the potential of the toner supply roll 24. Note that an AC component may be superimposed on the supply bias Vs as necessary.

On the other hand, the toner collecting roll 25 is a rotatable sleeve 251 made of a non-magnetic material such as aluminum.
Multiple magnetic poles (N21, S22, N23, S24, N25) inside
Are fixedly included, and are rotatably driven in a direction opposite to the donor roll 23 (against direction) at a position facing the donor roll 23 while maintaining a predetermined interval with the donor roll 23. It has become. The surface of the sleeve 251 is roughened or grooved so that the two-component developer G can be easily carried and transported. Also, the toner collection roll 2
5, a trimmer 25 a that regulates the layer thickness of the two-component developer G supplied to the toner collection roll 25 is provided at a predetermined distance from the toner collection roll 25. Here, the trimmer 25a is generally made of a non-magnetic metal plate, and if necessary, a magnetic plate attached to the surface on the upstream side in the transport direction of the two-component developer G is also used.

Further, between the donor roll 23 and the toner collecting roll 25, a collecting bias power supply 27 to which a collecting bias Vr for forming an electric field for transferring the toner T from the donor roll 23 to the toner collecting roll 25 is applied is connected. Have been. In this embodiment, since the negatively charged toner T is used, the setting is performed such that the potential of the toner supply roll 24 is higher than the potential of the donor roll 23. Note that an AC component may be superimposed on the recovery bias Vr as necessary.

In the present embodiment, since a conductive carrier having a volume resistivity of 10 ⁸ Ω · cm or less is used as the magnetic carrier C, the donor roll 23 and the toner are transferred through the magnetic carrier C. Supply roll 24
Alternatively, the donor roll 23 and the toner collection roll 25 may be short-circuited. Therefore, in the present embodiment, a material in which the surface of the donor roll 23 has been subjected to an insulating treatment or a high resistance treatment is used to prevent a short circuit therebetween. As a specific method, for example, as an insulation treatment method, a method of alumite treatment (alumite: trade name) on the surface of the donor roll 23, a method of resin coating or ceramic coating, and the like, and a method of increasing resistance are used. Examples include coating a conductive resin or a conductive ceramic having a controlled resistance value. Further, for the same reason, the toner supply roll 24 and the toner recovery roll 25 may be short-circuited via the magnetic carrier C. To prevent this, the donor roll 2
As in the case of 3, the surface of at least one of the toner supply roll 24 and the toner recovery roll 25 may be subjected to an insulation treatment or a high resistance treatment. In the present embodiment, the occurrence of a short circuit is prevented by setting an interval at which a short circuit does not occur between the toner supply roll 24 and the toner recovery roll 25, for example, an interval at the nearest portion between the two to 5 mm. are doing. The reason for this will be described later.

Further, on the back side of the toner supply roll 24 and the toner recovery roll 25, a partition member 21a along the axial direction of the toner supply roll 24 and the toner recovery roll 25 is provided.
Communication ports (not shown) are formed at both ends of the partition member 21a.
And a pair of augers 28 and 29 for conveying the two-component developer G to be supplied to the toner recovery roll 25 while stirring the two-component developer G.
Are arranged. Here, the augers 28 and 29 are both rotating members having a screw structure in which spiral blades are formed, and the two-component developer G is moved in the opposite axial direction by the thrust of the screw rotating in the opposite direction. Transported to One auger 28 transports the two-component developer G from the in side to the out side of the developing device 14, and the other auger 29 transports the two-component developer G from the out side to the in side. Then, the two-component developer G is passed from the communication ports formed at both ends to the other auger and circulated. Further, a toner replenishing device (not shown) is provided above the passage in which the two-component developer G circulates, and replenishes the developing device 14 with the toner T corresponding to the amount consumed in the developing area. ing.

Next, an image forming process of the image forming apparatus according to the present embodiment will be described. First, the surface of the photosensitive drum 11 is uniformly charged to a negative polarity by the charger 12, and is then exposed to the image by the laser exposure device 13, and the surface of the photosensitive drum 11 is exposed to the image. An electrostatic latent image is formed. And the photosensitive drum 1
The electrostatic latent image formed on the photosensitive drum 11 is reversely developed by the developing device 14, and a toner image corresponding to the electrostatic latent image is formed on the photosensitive drum 11. After the toner image is transferred onto the recording paper 17 by the transfer charger 15, the toner image is separated from the photosensitive drum 11 by the separation charger 16, and the image is fixed by a fixing device (not shown). On the other hand, after the transfer, the residual toner on the photosensitive drum 11 is removed by the cleaner 18, and the residual charge on the photosensitive drum 11 is removed by the removing lamp 19.

The operation of the developing device 14 in such an image forming process will be described in detail. In FIG. 3, the two-component developer G that is agitated by the augers 28 and 29 and circulated and transported in the developing housing 21 is sufficiently charged by the agitation and then transported from the auger 28 to the toner supply roll 24. At this time, as shown in FIG.
The two-component developer G conveyed from the auger 28 is carried on the toner supply roll 24 by the magnetic force acting between the magnetic carrier C of the two-component developer G and the magnetic pole N11 of the toner supply roll 24, and thereafter the toner supply roll 24 rotation and magnetic pole N
While being moved in the same direction as the rotation direction of the toner supply roll 24 by the magnetic force acting between the magnetic pole 11 and the magnetic pole S12, the layer thickness is adjusted appropriately by the trimmer 24a disposed near the magnetic pole N11. The donor roll 23 passes over the magnetic pole N13.
Is transported to the vicinity of the magnetic pole S14 opposite to.

Next, the magnetic pole S14 on the toner supply roll 24
The toner T of the two-component developer G transported to the vicinity is supplied to the toner supply roll 24 by an electric field Es formed by the supply bias Vs applied between the donor roll 23 and the toner supply roll 24 by the supply bias power supply 26. To the donor roll 23 and is electrostatically carried on the donor roll 23. Then, the toner T is applied to the donor roll 23.
And the two-component developer G in which the ratio of the magnetic carrier C has increased becomes magnetic pole S with rotation of the toner supply roll 24.
14 and is transported to the magnetic pole N15.
In this case, the magnetic pole N15 and the magnetic pole N11 cannot move because the magnetic poles N15 and N11 have the same polarity and form a repulsive magnetic field. The material is agitated and transported by the auger 28.

On the other hand, the toner T carried on the donor roll 23 reaches a developing area facing the photosensitive drum 11 as the donor roll 23 rotates. Photoconductor drum 11
On the upper surface, an electrostatic latent image is formed by the image portion potential Vl and the non-image portion potential Vh by the charger 12 and the laser exposure device 13, and the photosensitive drum 11 and the donor roll 2
3, a developing bias applying device 20 in which a developing electric field Ed is formed by applying a developing bias Vd.
Thus, the electrostatic latent image on the photosensitive drum 11 is developed by the toner T on the donor roll 23, and the toner T on the donor roll is consumed by that amount. Thereafter, the toner T having passed through the developing area m is transported to a position facing the toner collecting roll 25 with the rotation of the donor roll 23.

The two-component developer G, which has been agitated by the augers 28 and 29 and is circulated and transported in the developing housing 21 and transported from the auger 28, not only to the toner supply roll 24 but also to the toner collection roll 25. Being transported. Then, the transported two-component developer G includes the magnetic carrier C of the two-component developer G and the magnetic pole N of the toner collection roll 25.
21 and is carried on the toner collecting roll 25 by the magnetic force acting between the toner collecting roll 25 and the rotation of the toner collecting roll 25 and the magnetic pole N
While being moved in the same direction as the rotation direction of the toner collecting roll 25 by the magnetic force acting between the magnetic pole 21 and the magnetic pole S22, the layer thickness is adjusted appropriately by the trimmer 25a disposed near the magnetic pole N21. It is transported to the vicinity of the magnetic pole N23 facing the donor roll 23.

Next, the toner T transported to the position where the donor roll 23 and the toner collecting roll 25 face each other is subjected to a collecting bias Vr applied between the donor roll 23 and the toner collecting roll 24 by the collecting bias power supply 27. Due to the formed electric field Er, it moves from above the donor roll 23 to above the toner collecting roll 25. At this time, since the two-component developer G is carried on the toner collection roll 25,
The collected toner T is electrostatically attached together with the other toner T originally attached on the magnetic carrier C of the two-component developer G. Then, the toner T is supplied from the donor roll 23, and the two-component developer G in which the ratio of the toner T is increased.
Is transported to the magnetic pole N25 after passing over the magnetic pole S24 with the rotation of the toner collecting roll 25, and further attempts to move toward the magnetic pole N21. Here, the magnetic pole N25 and the magnetic pole N21 have the same polarity. Therefore, the toner cannot be moved due to the formation of the repulsive magnetic field, and is separated from the surface of the toner recovery roll 25 and is again stirred and transported by the auger 28.
FIG. 5 is a diagram schematically showing the developing process, and is different from the actual one.

In the present embodiment, since the toner T supplied to the donor roll 23 and not used for development is collected by the two-component developer G, the charging at the time of recharging accompanying the aggregation of the toner T is performed. The occurrence of unevenness and image defects due to uneven charging can be prevented.

Here, the reason why the surface of the toner supply roll 24 and the toner collection roll 25 is not subjected to the insulation treatment or the resistance increase treatment will be described. The inventor of the present invention carried out an experiment by attaching a toner supply roll 24 having a surface insulated or a toner recovery roll 25 having a surface insulated to the developing device shown in FIG.

As a result, first, when the toner supply roll 24 whose surface is insulated is used, it becomes difficult to supply the toner T onto the donor roll 23, and a necessary toner layer is formed on the donor roll 23. It turned out to be impossible. This is because, due to the presence of the insulating layer on the surface of the toner supply roll 24, charge is not injected from the toner supply roll 24 side to the two-component developer G carried on the toner supply roll 24, and the two-component developer G Donor roll 2
It is considered that the cause is that the electric field required for supplying the toner is not formed between the first and third toner cells.

When the surface of the toner collecting roll 25 is insulated, the toner collecting roll 25 may be used.
The toner T adheres and accumulates on the surface, and the toner collection roll 2
It was found that the toner recovery capacity of No. 5 was lost after one or two rotations. The possible causes are as follows.
Due to the presence of the insulating layer on the surface of the toner collecting roll 25, the toner collecting roll 25
No electric charge is injected into the two-component developer G carried thereon, and a strong electric field is formed between the two-component developer G and the toner collecting roll 25. For this reason, the toner T on the donor roll 23 adheres below the two-component developer layer on the toner collection roll 25, that is, on the surface of the toner collection roll 25. At this time, the toner T is non-magnetic and has the magnetic poles N25 and N25.
Since the toner cannot be removed by the repulsive magnetic field formed between the rollers 21, the toner is accumulated on the toner collecting roll 25. Since the toner T is negatively charged, the electric charge of the toner T accumulated on the toner collecting roll 25 cancels the potential for collecting the toner T, and the electric field Er for collecting the toner T.
Are not formed.

For this reason, in the present embodiment, the surfaces of the toner supply roll 24 and the toner collection roll 25 are not subjected to insulation treatment or high resistance treatment, and the two are appropriately separated from each other as described below. It was done.

In the present embodiment, the closest distance between the toner supply roll 24 and the toner collection roll 25 is 5
The reason for setting mm is as follows. The present inventor investigated the relationship between the distance between electrodes and the leak start voltage under the condition where the two-component developer G was present. Here, as shown in FIG. 6A, the experimental device has a thickness D (m) having a notch 51a having a width of 50 (mm) and a depth of 20 (mm).
m), an aluminum plate 5 as an electrode is provided on both end surfaces of the rubber plate 51.
2 and 53 are adhered to each other to form a developer retaining member 50 for retaining the two-component developer G in the notch 51a. The aluminum plates 52 and 53 of the developer retaining member 50
As shown in (b), a device connected to a bias power supply 70 for applying a bias voltage _VAP was used. At this time, a DC voltage and an AC (rectangular wave) voltage were independently used as the bias voltage _VAP . The experimental conditions are as follows. Bias voltage V _AP 0~500V (DC) 0~500V (AC: square wave amplitude value of 4 kHz), two component toner concentration TC 1.7% of the developer G, 2.3
%, 5.5%, as shown in FIG. 6B, the case where the magnet 60 extending in the width direction of the developer retaining member 50 is disposed close to the aluminum plate 53, that is, the two-component developer The difference between the case where G ears were formed and the case where G ears were not formed was also investigated. Here, the thickness of the magnet 60 is 2 m
m, the width is 4 mm, and the density of the generated magnetic flux is 150 mT inside the aluminum plate 53.

FIG. 7 shows the relationship between the thickness D (gap between electrodes) D of the rubber plate 51 and the DC leakage start voltage when DC is applied as the bias voltage _VAP . In addition, 500V in the figure
The mark at the position indicates that the bias voltage _VAP is 5
This shows that no leakage occurred even when the voltage became 00V. The following items can be understood from FIG. 1. The larger the gap D, the higher the leak start voltage. The larger the gap D, the greater the number of conductive carriers C interposed in the gap direction and the number of contact points, so that it is difficult to form an electric path and the resistance increases. It is believed that there is. In particular, when the gap D is 5 mm, the leakage start voltage is 300 V at any toner concentration TC.
It was confirmed that this was the case. 2. The higher the toner concentration TC, the higher the leak start voltage. The higher the toner concentration TC, the more toner T is present around the conductive carrier C, and the toner T is insulating. Therefore, it is considered that the reason is that the probability that the conductive carriers C come into contact with each other decreases and the resistance increases. 3. Comparing the two components using the two-component developer G having the same toner concentration TC, the leakage start voltage is higher when the magnet 60 is not disposed in proximity than in the case where the magnet 60 is disposed in proximity. It is considered that the cause is that the probability of contact between the conductive carriers C is increased due to the formation of the ears of the developer G and the resistance is reduced.

FIG. 8 shows the relationship between the rubber plate thickness (gap) D and the leak start voltage when an alternating current is applied as the bias voltage _VAP . In the drawing, the reference numeral at the position of 500 V indicates that no leakage occurred even when the bias voltage _VAP was 500 V, as in the case of the direct current. From the figure, it is understood that the result is almost equal to the DC leak start voltage. In particular, the AC leak start voltage (amplitude value) is almost equal to the DC leak start voltage, and the gap D = 5 mm In any case, the leak start voltage is 300 V
It was confirmed that this was the case. Therefore, in the present embodiment, the closest distance between the toner supply roll 24 and the toner collection roll 25 is set to 5 mm, and leakage between the two rolls is reliably prevented. However, this does not mean that the closest distance between the toner supply roll 24 and the toner collection roll 25 is required to be at least 5 mm or more, and the toner concentration TC, the toner diameter, and the carrier C of the two-component developer G to be used. May be appropriately set in consideration of the resistance value, the carrier diameter and the shape of the carrier C, the presence or absence of the influence of the magnetic field, the magnitude of the magnetic field, the shape of the magnetic field pattern, the applied bias voltage, and the like. For example, when the toner concentration TC is 2.3% and the applied bias is 100 V
In the following cases, the leak can be prevented even if the closest distance is set to about 4 mm.

Embodiment 2 This embodiment is almost the same as Embodiment 1, but is different from Embodiment 1 in that the toner is carried and conveyed by a toner supply roll and passed through a position facing a donor roll. The component developer is configured to be moved to the toner collection roll. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the present embodiment, the developing device 14
As shown in FIG. 9, a portion facing the photosensitive drum 11 is opened as a developing opening 32, and a two-component developer G
A developing roll (donor roll) 33 disposed at a predetermined distance from the photosensitive drum 11 is disposed at a portion facing the developing opening 32 of the developing housing 31. It was established.

The donor roll 33 is made of, for example, aluminum or the like, and has a smooth surface in the shape of a pipe or a cylinder. 11 (wi)
(th direction).

Further, as shown in FIG. 10, a developing bias Vd is applied between the photosensitive drum 11 and the donor roll 33 to develop the electrostatic latent image on the photosensitive drum 11 as shown in FIG. A developing bias applying device 20 to be applied is connected.

A toner supply roll 34 for carrying and transporting the two-component developer G and supplying the toner T to the donor roll 33 is disposed in proximity to the upper portion of the developing housing 31 on the rear side of the donor roll 33. A toner collecting roll 35 that carries and conveys the two-component developer G and collects the toner T remaining on the donor roll 33 after passing through the developing area is disposed close to the lower rear side of the roll 33.

Here, the toner supply roll 34 is
As shown in FIG. 7, a plurality of magnetic poles (N31, S31) are provided inside a rotatable sleeve 341 made of a nonmagnetic material such as aluminum.
32, N33, S34, N35) are arranged in a magnet roll 342
Is fixedly included, and is rotationally driven in a direction opposite to the donor roll 33 (against direction) at a position facing the donor roll 33 while maintaining a predetermined distance from the donor roll 33. The surface of the sleeve 341 is subjected to a surface roughening process or a groove process so that the carrying and transport of the two-component developer G is facilitated.
Further, the toner supply roll 34 includes the toner supply roll 3.
A trimmer 34 a that regulates the layer thickness of the two-component developer G supplied to the toner supply roll 4 is provided at a predetermined distance from the toner supply roll 34. Here, the trimmer 34a is generally formed of a non-magnetic metal plate, and if necessary, a magnetic plate attached to the upstream surface of the two-component developer G in the transport direction is also used.

Further, between the donor roll 33 and the toner supply roll 34, a supply bias power supply 26 to which a supply bias Vs for forming an electric field for transferring the toner T from the toner supply roll 34 to the donor roll 33 is connected. Have been.

On the other hand, the toner collecting roll 35 is a rotatable sleeve 351 made of a non-magnetic material such as aluminum.
A plurality of magnetic poles (N41, S42, N43, S44, S45) inside
Are fixedly included therein, and are rotationally driven in a direction opposite to the donor roll 33 (against direction) at a position facing the donor roll 33 while maintaining a predetermined interval with the donor roll 33. It has become. The surface of the sleeve 351 is roughened or grooved so that the two-component developer G can be easily carried and transported.

Further, between the donor roll 33 and the toner collecting roll 35, a collecting bias power supply 27 to which a collecting bias Vr for forming an electric field for transferring the toner T from the donor roll 33 to the toner collecting roll 35 is connected. Have been.

Further, in the present embodiment, similarly to the first embodiment, a donor roll 33 whose surface is subjected to insulation treatment or high resistance treatment is used, and a toner supply roll 34 and a toner collection roll 35 are used. Is also set to 5 mm at the closest part.

Further, on the back side of the toner supply roll 34 and the toner recovery roll 35, a partition member 31a along the axial direction of the toner supply roll 34 and the toner recovery roll 35 is provided.
, And a two-tiered developer transport path is formed in which communication ports (not shown) are formed at both ends of the partition member 31a. A pair of augers 38 and 39 in which the transport directions of the two-component developer G are opposite to each other are arranged in the upper and lower stages of the developer circulation path. Here, the augers 38 and 39 are both rotating members having a screw structure in which spiral blades are formed,
The two-component developer G is stirred and conveyed in opposite axial directions by the thrust of the screws rotating in opposite directions. For this reason, the two-component developer G conveyed to the side wall of the developing housing 31 by the lower auger 38 loses its place to go up and rises, and when it becomes higher than the position of the partition member 31a through the communication port, the upper auger 39 reverses the direction. Transported to Thereafter, the two-component developer G transported to the opposite side wall of the developing housing 31 by the upper auger 39 drops to the lower auger 38 side from the opposite communication port by gravity. As described above, the two-component developer G is circulated in the developing device 14 by the two upper and lower augers 38 and 39. Further, a toner replenishing device (not shown) is provided above the passage in which the two-component developer G circulates, and replenishes the developing device 14 with the toner T corresponding to the amount consumed in the developing area. ing.

Next, the developing process according to the present embodiment will be described. In FIG. 9, the two-component developer G stirred and agitated by the augers 38 and 39 and circulated and transported in the developing housing 31 is sufficiently charged by the agitation and then transported from the upper auger 39 to the toner supply roll 34. . At this time, as shown in FIG. 11, the two-component developer G transported from the auger 39 is supplied by the magnetic force acting between the magnetic carrier C of the two-component developer G and the magnetic pole N31 of the toner supply roll 34. After being carried on the roll 34, the toner supply roll 34 is disposed near the magnetic pole S 32 while moving in the same direction as the rotation of the toner supply roll 34 by the rotation of the toner supply roll 34 and the magnetic force acting between the magnetic pole N 31 and the magnetic pole S 32. The trimmer 34a makes the layer thickness appropriate, and then
After passing over the magnetic pole N33, it is transported to the vicinity of the magnetic pole S34 facing the donor roll 33.

Next, the magnetic pole S34 on the toner supply roll 34
The toner T of the two-component developer G transported to the vicinity is supplied to the toner supply roll 34 by the electric field Es formed by the supply bias Vs applied between the donor roll 33 and the toner supply roll 34 by the supply bias power supply 26. , And is electrostatically carried on the donor roll 33. Then, the toner T is supplied to the donor roll 33, and the two-component developer G having the increased ratio of the magnetic carrier C passes over the magnetic pole S 34 with the rotation of the toner supply roll 34 and faces the toner collection roll 35. To the magnetic pole N35.

On the other hand, the toner T carried on the donor roll 33 reaches the developing area m facing the photosensitive drum 11 as the donor roll 33 rotates. Photoconductor drum 1
1, an electrostatic latent image is formed by an image portion potential Vl and a non-image portion potential Vh by a charger 12 and a laser exposure device 13.
3 is provided with a developing bias applying device 20 for forming a developing electric field Ed by applying a developing bias Vd, whereby the electrostatic latent image on the photosensitive drum 11 is And the toner T on the donor roll is consumed by that amount. Thereafter, the toner T having passed through the developing area m is transported to a position facing the toner collecting roll 35 with the rotation of the donor roll 33.

The two-component developer G conveyed by the auger 38 tends to transfer to the toner collecting roll 35. In the present embodiment, the magnetic pole S45 of the toner collecting roll 35 facing the auger 38 is Since the developer is provided above the height of the developer supplied from the developer 38, the developer cannot be transferred.

On the other hand, the two-component developer G in which the ratio of the magnetic carrier C conveyed to the magnetic pole N35 of the toner supply roll 34 is increased tends to move further in the direction of the magnetic pole N31. Since the magnetic pole N31 and the magnetic pole N31 have the same polarity and form a repulsive magnetic field, they cannot move, and the two-component developer G tends to peel off from the surface of the toner supply roll 34. At this time, the magnetic poles N41 and S42 of the toner collecting roll 35 are arranged at positions facing the magnetic pole N35 carrying the two-component developer G to be separated. Therefore, the magnetic poles N41 and S42 and the toner supply roll 34
Magnetic field formed by the magnetic pole N35 of the two-component developer G
Is transferred onto the magnetic pole S42 of the toner collecting roll 35. Here, in the present embodiment, since the toner collecting roll 35 is disposed substantially below the toner supply roll 34 in the vertical direction, the drop due to gravity also contributes to the transfer of the two-component developer G. Then, the supported two-component developer G collected by the toner collecting roll 35 is thereafter transferred to the toner collecting roll 35.
And the magnetic force acting between the magnetic pole S42 and the magnetic pole N43, the toner collecting roll 35 is moved in the same direction as the rotation direction of the toner collecting roll 35, and is conveyed to the vicinity of the magnetic pole N43 facing the donor roll 33.

Next, the toner T transported to the position where the donor roll 33 and the toner collecting roll 35 face each other is subjected to a collecting bias Vr applied between the donor roll 33 and the toner collecting roll 35 by the collecting bias power supply 27. The generated electric field Er moves from above the donor roll 33 to above the toner collecting roll 35. At this time, the two-component developer G in which the toner T is supplied to the donor roll 33 and the ratio of the magnetic carrier C is increased is transferred to the toner collecting roll 35 and is carried and conveyed.
Is electrostatically attached to the magnetic carrier C having a small toner attachment amount of the two-component developer G. Then, the toner T is supplied from the donor roll 33, and the two-component developer G in which the ratio of the toner T approaches the normal value passes over the magnetic pole N43 with the rotation of the toner collecting roll 35 and is transported to the magnetic pole S44. Further, the magnetic pole S45 attempts to move in the direction of the magnetic pole S45, but cannot move because the magnetic pole S44 and the magnetic pole S45 have the same polarity and form a repulsive magnetic field. Then, the toner is separated from the surface of the toner collecting roll 35 and is agitated and transported by the auger 38 at the lower portion. Note that FIG. 11 is a diagram schematically illustrating the developing process, and is different from an actual one.

In the present embodiment, the toner T supplied to the donor roll 33 and not used for development is replaced by the two-component developer G supplied with the toner T to the donor roll 33 and the ratio of the magnetic carrier C is increased. Since the toner is collected, a high collecting ability of the toner T is secured, and the difference in toner concentration in the two-component developer G is suppressed to be small. The occurrence of accompanying image defects and the like is prevented.

In the present embodiment, the transfer of the two-component developer G from the toner supply roll 34 to the toner collection roll 35 is performed using a magnetic field formed by magnetic poles built in both. However, the present invention is not limited to this. For example, a scraper may be disposed in contact with the lower side of the toner supply roll 34 and mechanically peeled off and transferred to the toner collection roll 35 by gravity.
A magnet roll may be provided to transfer the toner to and from the toner collecting roll 35.

Further, in the first and second embodiments, the non-contact developing system in which the donor roll 23 (33) is spaced apart from the photosensitive drum 11 is used. However, the present invention is not limited to this. Donor roll 2 for drum 11
3 (33) is also applicable to a contact development system in which contact arrangement is performed. In such an embodiment, from the viewpoint of preventing the leakage of the electrostatic latent image formed on the photosensitive drum 11, the surface of the donor roll 23 (33) is insulated or the resistance is increased. Processing is required. Further, in the contact developing method, from the viewpoint of stabilizing the contact state between the photosensitive drum 11 and the donor roll 23 (33), it is preferable to use a conductive rubber as the material of the donor roll 23 (33). .

[0073]

Embodiment 1 FIG. 3 is a configuration diagram also showing Embodiment 1 of the developing device according to the present invention. In the figure, as the photoconductor drum 11,
A negatively charged OPC having a drum diameter of 84 mm was used. In addition, the donor roll 23 was obtained by insulating the surface of an aluminum roll having an outer diameter of 24 mm with alumite (trade name). The sleeves 241 and 251 of the toner supply roll 24 and the toner recovery roll 25 were made of aluminum having an outer diameter of 16 mm and had a surface roughness Rz of 15 μm.

The parameters of the developing device 14 in this embodiment are as follows. 1.5 mm between the trimmer 24a and the sleeve 241 (the same applies to the gap between the trimmer 25a and the sleeve 251). The rotational speed of the donor roll 23 is 240 mm / s. The rotational direction of the donor roll 23 Against (the direction opposite to the photoconductor). Rotation speed 320 mm / s ・ Sleeve 241 rotation direction Against (in the opposite direction to the donor roll) ・ Donor roll 23-sleeve 241 gap 1.5 mm ・ Sleeve 251 (for recovery) rotation speed 320 mm / s ・ Sleeve 251 rotation direction Against (donor roll)・ The distance between the donor roll 23 and the sleeve 251 is 1.5 mm. ・ The distance between the sleeve 241 and the sleeve 251 is 5.0 mm.

The following developers were used. -Magnetic carrier (positive charge) Iron-based carrier with an average particle size of 50 μm, volume resistivity 10 ⁹ Ω
・ Cm ・ Black toner (negatively charged) Polyester resin with an average particle diameter of 9 μm ・ Toner concentration TC Mixing ratio of toner and carrier 4.0 wt.%

The process conditions and the development conditions were set as follows. 1. Photoconductor drum 11 rotation speed 160 mm / s-Photoconductor drum 11-donor roll 23 gap 0.3 mm-Non-image portion potential Vh -500 V-Image portion potential Vl -300 V-Development bias Vd DC component -400 V AC component 0 kV (peak to peak value) Frequency 2.4 kHz square wave ・ Supply bias Vs DC component -80 V AC component 0.2 kV (peak to peak value) Frequency 4.0 kHz square wave ・ Recovery bias Vr DC component +80 V AC component 0.2 kV (Peak to peak value) Frequency 4.0kHz square wave

Embodiment 2 FIG. 9 is a block diagram also showing Embodiment 2 of the developing device according to the present invention. In this embodiment, the outer diameter of the donor roll 33 was 20 mm, and the outer diameters of the toner supply roll 34 and the toner recovery roll 35 were 18 mm. In this example, the donor roll 33 was obtained by insulating the surface of an aluminum roll having an outer diameter of 18 mm with alumite (trade name). The outer diameter of the sleeve 341 of the toner supply roll 34 is 18 mm, and the sleeve 351 of the toner collection roll 35 is
Is made of aluminum having an outer diameter of 16 mm, and both have a surface roughness Rz of 20 to 30 μm.

Among the magnetic poles of the toner supply roll 34, the magnetic flux density in the radial direction of the N35 pole related to the transfer of the two-component developer G to the toner collection roll 35 is 80 mT.
The magnetic flux density of the N31 pole is 60 mT, and the opening angle of both poles is 10
0 °. Further, among the magnetic poles of the toner collecting roll 35, the magnetic flux density in the radial direction of the S42 pole related to the transfer of the two-component developer G from the toner supply roll 34 is 80.
The magnetic flux density of the mT and N41 poles was 60 mT, and the opening angle of both poles was 30 °. Further, the gap between the toner supply roll 34 and the toner collection roll 35 is set to 5.0 mm, and the opposed position of the toner supply roll 34 is 20 ° downstream of the N35 pole.
The opposing position of the toner collection roll 35 is the upstream side 20 of the S42 pole.
゜

The parameters of the developing device 14 in this embodiment are as follows. -Trimmer 34a-Sleeve 341 gap 1.5mm-Donor roll 33 rotation speed 108mm / s-Donor roll 33 rotation direction With (same direction as photoconductor)-Sleeve 341 (for supply) rotation speed 200mm / s-Sleeve 341 rotation direction Against (the direction opposite to the donor roll)-Donor roll 33-sleeve 341 gap 1.5 mm-Sleeve 351 (for collection) rotation speed 208 mm / s-Sleeve 351 rotation direction Against (the direction opposite to the donor roll)-Donor roll 33-sleeve 351 gap 1.5mm ・ Sleeve 341-sleeve 351 gap 5.0mm

The following developers were used. -Magnetic carrier (positive charge) Iron-based carrier with an average particle size of 50 μm, volume resistivity 10 ⁹ Ω
・ Cm ・ Black toner (negatively charged) Polyester resin with an average particle size of 9 μm ・ Toner concentration TC Mixing ratio of toner and carrier 5.2 wt.%

The process conditions and the development conditions were set as follows. 1. Photoconductor drum 11 rotation speed 160 mm / s ・ Photoconductor drum 11-donor roll 33 gap 0.3 mm ・ Non-image part potential Vh -500 V ・ Image part potential Vl -300 V ・ Development bias Vd DC component -400 V AC component 0kV (peak to peak value) Frequency 2.4kHz square wave ・ Supply bias Vs DC component -80V AC component 0.15kV (peak to peak value) Frequency 4.0kHz square wave ・ Recovery bias Vr DC component + 80V AC component 0.15kV (Peak to peak value) Frequency 4.0kHz square wave

Comparative Example 1 FIG. 15 shows Comparative Example 1 (conventional example) of the developing device according to the present invention.
FIG. In Comparative Example 1, the outer diameter of the donor roll 102 was 24 mm, and the other conditions were the same as those of the donor roll 23 of Example 1. The outer diameter of the transport supply roll 103 is also set to 24 mm, and the other conditions are the same as those of the toner supply roll 24 of the first embodiment.
The same conditions were used.

Using the developing devices shown in Examples 1 and 2 and Comparative Example 1, first, the presence or absence of development history was investigated. Investigation was conducted after developing a cross-shaped electrostatic latent image with a width of 4 mm and a length of 20 mm at an image density of 100%, forming a halftone image with a constant image density, printing the image, and printing the printed halftone image. This was performed by checking whether or not the cross-shaped development history was found in the position of the first rotation of the donor roll in the image. Here, the halftone image density is 30, 50, 70,
The electrostatic latent image was formed by writing 400 lines in a laser beam. The evaluation was performed by visually confirming the printed image and measuring the density difference.

As a result, as shown in FIG.
In the (conventional example), when printing halftones having image densities of 30 and 50%, a density difference of 0.03 or more appears and a ghost occurs due to development history, and halftones having an image density of 70% are printed. Although ghosts were observed to the extent that they could be visually confirmed even when printed, in Examples 1 and 2, it was confirmed that no development history was observed when halftones of any image density were printed. .

Example 3 Using the developing device shown in FIG. 9, an experiment for confirming the toner collecting ability of the toner collecting roll 35 was performed. In this experiment, the bias Vd applied to the donor roll 33 was set to 0 V, and the other conditions were the same as during development. Therefore, the toner on the donor roll 33 is collected in the developing housing without performing the developing. Then, the toner amount, the toner charge amount, and the average toner particle size on the donor roll 33 were compared between the first round and the 40th round of the donor roll 33. Also, the toner collection bias V
The difference due to the presence or absence of the application of r was also investigated. The results are shown in FIGS. In the figure, the result of the first round is indicated by a solid line, and the result of the 40th round is indicated by a triangle. According to this, when the collection bias Vr is not applied, the toner amount and the toner charge amount on the donor roll 33 increase in the 40th lap, while the average toner particle diameter decreases, whereas the collection bias Vr is increased. When the voltage was applied, it was confirmed that the toner amount, the toner charge amount, and the average toner particle diameter on the donor roll 33 did not change in the first round and the 40th round. It was also confirmed that when the closest distance between the toner supply roll 34 and the toner collection roll 35 was set to 5 mm, no leak occurred between the two.

Example 4 Using the developing device shown in FIG. 3, a comparative experiment was conducted on the ability to supply the toner T to the donor roll 33 and the ability to collect the toner T from the donor roll 33 due to the difference in the conductivity of the carrier C. Was. Here, the carrier C used in the experiment was a conductive one (volume resistivity of 10 ⁶ Ω · cm) and a semi-conductive one (volume resistivity of 10 ¹⁰ Ω · cm). In this experiment, the bias Vd applied to the donor roll 33 was 0 V
Other conditions were the same as those for development. Therefore, the toner on the donor roll 33 is collected in the developing housing without performing the developing. Then, the toner amount and the toner charge amount on the donor roll 33 are compared with the first rotation of the
It was compared with the lap.

In the present embodiment, the donor roll 33
Was obtained by insulating the surface of an aluminum roll having an outer diameter of 25 mm with alumite (trade name). The outer diameter of the sleeve 341 of the toner supply roll 34 is 22 mm,
The outer diameter of the sleeve 351 of the toner collecting roll 35 is 18 mm.
And both of which were subjected to groove processing on the surface.

The parameters of the developing device 14 in this experiment are as follows. Type of carrier C Semi-conductive Conductive ・ Trimmer 34a-sleeve 341 gap 0.5mm 1.5mm ・ Donor roll 33 rotation speed 204mm / s ← ・ Donor roll 33 rotation direction Against assumed ← ・ Sleeve 341 (supply) rotation Speed 204 mm / s 408 mm / s • Sleeve 341 rotation direction Against ← • Donor roll 33-sleeve 341 gap 0.35 mm 1.5 mm • Sleeve 351 (for collection) rotation speed 204 mm / s ← Sleeve 351 rotation direction Against ← • Donor Roll 33-sleeve 351 gap 0.35 mm 1.5 mm ・ Sleeve 341-sleeve 351 gap 5.0 mm ← ・ Toner concentration TC 7.3 wt.% 5.8 wt.% ・ Supply bias Vs DC component -175 V -90 V AC component 1 0.2 kV 0.2 kV ・ Recovery bias Vr D Components + 150 V + 100 V AC component 1.2 kV 0.2 kV Note, AC components of the supply bias Vs and retrieving bias Vr is a rectangular wave having a frequency 4.0kHz a both peak to peak value.

FIG. 14A shows the change over time in the amount of toner on the donor roll 33 due to the difference in the conductivity of the carrier C, and FIG.
(B). Note that, in the figure, reference symbol S-CMB indicates a semiconductive carrier, and reference symbol CMB indicates a conductive carrier. According to this, when the semiconductive carrier C is used, the toner collecting ability is already reduced in the forty lap (specifically, the first and second laps), and the toner amount and the toner charge on the donor roll 33 are reduced. Although the amount increased, the conductive carrier C
In the case of using the donor roll 33 for both the first lap and the 40th lap,
It was confirmed that the toner amount and the toner charge amount did not change. This is because the toner collection roll 25
For the same reason as in the case of insulating. By using the semiconductive carrier C, the charge is not injected from the toner recovery roll 35 side to the two-component developer G carried on the toner recovery roll 35, and the two-component developer G and the donor roll 33 A stronger electric field is formed between the two-component developer G and the toner collection roll 35 than between them. For this reason, the toner T on the donor roll 33 adheres below the two-component developer layer on the toner collection roll 35, that is, on the surface of the toner collection roll 35. At this time, since the toner T is non-magnetic and cannot be removed by the repulsive magnetic field formed between the magnetic poles S44 and S45, the toner collection roll 35
Accumulate on top. Since the toner T is negatively charged, the charge of the toner T accumulated on the toner collecting roll 35 cancels the potential for collecting the toner T, and the electric field Er for collecting the toner T is not formed. .

[0090]

As described above, according to the present invention,
Using a two-component developer consisting of a magnetic carrier and a toner,
In a so-called hybrid developing type developing device in which only toner is supplied onto a developing roll to perform development, a toner supply developer carrier for carrying a two-component developer and supplying toner to the toner carrier is provided. A toner recovery developer carrier for supporting the toner and recovering the toner from the toner carrier is provided separately, and the two-component developer carried on the toner recovery developer carrier is supported on the toner carrier. Since the toner passing through the developing position is electrostatically collected, it is possible to continuously collect the toner, and as a result, it is possible to prevent the development history and the occurrence of a striped history due to uneven collection. it can. Further, since the collected toner is electrostatically attached to the two-component developer, it is possible to prevent aggregation of the toner in the two-component developer, that is, to make the toner concentration uniform.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a developing device according to the present invention.

FIG. 2 is an explanatory diagram illustrating a schematic configuration of an image forming apparatus incorporating the developing device according to the first embodiment of the present invention.

FIG. 3 is an explanatory sectional view showing a specific configuration of a developing device used in the first embodiment.

FIG. 4 is an enlarged view of a developer delivery section of the developing device shown in the first embodiment.

FIG. 5 is a schematic diagram illustrating a state of transport of the developer according to the first embodiment.

FIGS. 6A and 6B are explanatory diagrams showing an outline of an experimental apparatus relating to an optimum separation distance between a donor roll and a toner supply roll (toner recovery roll).

FIG. 7 is a graph showing a leak start voltage when a DC bias is applied.

FIG. 8 is a graph showing a leak start voltage when an AC bias is applied.

FIG. 9 is an explanatory sectional view showing a specific configuration of a developing device used in the second embodiment.

FIG. 10 is an enlarged view of a developer delivery section of the developing device shown in the second embodiment.

FIG. 11 is a schematic diagram illustrating a state of transport of a developer according to the second embodiment.

FIG. 12 is an explanatory diagram showing the presence or absence of a development history between Examples 1 and 2 and a comparative example. FIG.

FIGS. 13A and 13B are graphs showing the change over time in (a) the amount of toner on the donor roll, (b) the amount of charge on the donor roll, and (c) the average toner particle size on the donor roll. FIG.

FIGS. 14A and 14B are graphs showing a change over time in a toner amount on a donor roll, and FIG.

FIG. 15 is an explanatory view showing an example of a conventional developing device of a hybrid developing system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... electrostatic latent image carrier, 2 ... toner carrier, 3 ... toner supply developer carrier, 4 ... supply bias application means, 5 ... toner collection developer carrier, 6 ... collection bias application means,
DESCRIPTION OF SYMBOLS 11 ... Photoreceptor drum, 12 ... Charger, 13 ... Laser exposure device, 14 ... Developing device, 15 ... Transfer charger, 16 ... Peeling charger, 17 ... Recording paper, 18 ... Cleaner, 19 ... Removal lamp, 23 ... Developing roll (donor roll), 24: toner supply roll, 25: toner recovery roll, 26: supply bias power supply, 27: recovery bias power supply, G: two-component developer, C: magnetic carrier, T: toner

Claims (4)

[Claims] 1. A toner carrier that is rotatably arranged opposite to an electrostatic latent image carrier, and that carries toner on the surface thereof to develop an electrostatic latent image formed on the electrostatic latent image carrier. A two-component comprising a magnetic carrier and a toner disposed on the surface of the toner carrier at a position upstream of the developing position where the electrostatic latent image carrier and the toner carrier face each other in the rotational direction of the toner carrier; A developer-supplying developer carrier on which developer is carried and supplying toner to the toner carrier; and a toner-supplying developer carrier between the toner carrier and the toner-supplying developer carrier. Supply bias applying means for applying a bias to transfer the toner to the toner carrier; and a rotation direction downstream of the toner carrier from the developing position where the electrostatic latent image carrier and the toner carrier are opposed to each other. Supply A toner recovery developer carrier that is disposed opposite to the toner carrier on the upstream side in the rotation direction of the toner carrier from the position facing the image agent carrier, and the two-component developer is carried and conveyed on the surface thereof; Developing means for applying a bias for transferring a toner on the toner carrier to the developer carrier for toner recovery between the toner carrier and the developer carrier for toner recovery. apparatus. 2. The developing device according to claim 1, wherein the two-component developer carried and conveyed by the toner supply developer carrier and passing through a position facing the toner carrier is transferred to the toner recovery developer carrier. A developing device characterized by being moved. 3. The developing device according to claim 2, wherein the movement of the two-component developer from the toner supply developer carrier to the toner recovery developer carrier is performed by a magnetic field. Developing device. 4. The developing device according to claim 1, wherein
^{In a} type in which a magnetic carrier having a volume resistivity of ⁸ Ωcm or less is used, the toner-supplying developer carrier and the toner-collecting developer carrier are arranged at an interval capable of preventing a short circuit therebetween. A developing device, which is provided.