JP2009093075A - Developing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently assure an image density and to suppress environmental degradation or degradation with time while using a conductive toner to which charges are injected by a charge injection electric field. <P>SOLUTION: A developing device is equipped with a toner holding body 3 holding and conveying a charged conductive toner 2, a development electric field forming means 6 forming a development electric field in a developing zone, and a charge injecting means 7 injecting charges to the uncharged conductive toner by causing a charge injection electric field to effect between a charge injecting member 8 and the toner holding body 3. The toner holding body 3 includes a developing toner holding body 4 that develops an electrostatic latent image on an image holding body 1 with the conductive toner 2, and an intermediate toner holding body 5 that is provided opposing to the developing toner holding body 4 and as rotatable at a rotational speed faster than that of the developing toner holding body 4 and that holds and conveys the conductive toner 2. A moving electric field is activated, which transfers the conductive toner 2 from the intermediate toner holding body 5 toward the developing toner holding body 4, by a transfer electric field forming means provided between the developing toner holding body 4 and the intermediate toner holding body 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus using the developing device.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a method in which an insulating toner is triboelectrically charged to give an electric charge and the triboelectrically charged toner is applied to development is generally used. However, the triboelectrically charged toner often includes a low-charged toner whose charge amount distribution is easy to spread and a low charge amount, and a reverse polarity toner charged to a polarity different from the original charge polarity of the toner. For this reason, the toner is separated from the toner holding body that holds and conveys the toner (so-called toner cloud), and image quality defects such as fogging may occur.

  On the other hand, as a method for charging toner, a method different from the above-described friction charging method is known (see Patent Document 1). In this patent document, a conductive toner is used, and the toner is injected into the toner layer regulated to a single layer or less while sliding the conductive toner between the charge injection member and the toner holder. A system for giving a predetermined charge amount is described.

Japanese Patent Laying-Open No. 2005-331780 (Embodiment 1, FIG. 11)

  A technical problem of the present invention is to provide a developing device capable of ensuring sufficient image density and suppressing environmental deterioration and deterioration over time while using conductive toner charged by an electric charge injection field, and image formation using the same. To provide an apparatus.

  According to a first aspect of the present invention, there is provided a developing device for visualizing an electrostatic latent image held on the surface of an image carrier with a conductive toner, the conductive device disposed opposite to the image carrier and charged. The toner holding body for holding and transporting the photosensitive toner, the developing electric field forming means for forming a developing electric field in the developing region between the toner holding body and the image holding body, and the image holding body of the toner holding body are different. And a charge injection member for injecting charges into uncharged conductive toner by applying a charge injection electric field between the charge injection member and the toner holder. The toner holder is rotatably provided to face the image holder, holds and conveys conductive toner to the development area, and applies a development electric field by a development electric field forming unit to the development area. Electrostatic latent on the holder A developing toner holder that develops the toner with a conductive toner, and an intermediate portion of the developing toner holder that is opposed to the developing toner holder and is rotatable at a higher rotational speed than the developing toner holder A moving electric field forming unit provided between the developing toner holding member and the intermediate toner holding member, the intermediate toner holding member holding and transporting the conductive toner charged by the charge injection member until reaching the point Thus, the developing device is configured to apply a moving electric field for moving the conductive toner from the intermediate toner holding member toward the developing toner holding member.

According to a second aspect of the present invention, in the developing device according to the first aspect, the charge injection unit injects the charge into the conductive toner by rubbing the conductive toner while applying a charge injection electric field. This is the developing device.
According to a third aspect of the present invention, in the developing device according to the first aspect, the toner holding member is set such that the developing toner holding member and the intermediate toner holding member are set to rotate in different directions at opposite portions. Device.
According to a fourth aspect of the present invention, in the developing device according to the first aspect, the conductive toner changes to a high resistance so as to maintain the charge retaining property of the conductive toner in the development region, and the charge injection field application range. In the developing device, the resistance is changed to a low resistance so as to facilitate the charge injection of the conductive toner.
The invention according to claim 5 is the developing device according to claim 4, wherein the conductive toner is coated with an insulating or semiconductive coating layer around the conductive toner substrate.
The invention according to claim 6 is the developing device according to claim 1, wherein the intermediate toner holding member is coated with a surface layer having a larger volume resistivity than the developing toner holding member.
The invention according to claim 7 is the developing device according to claim 1 or 6, wherein the intermediate toner holding member is coated with a surface layer having a volume resistivity of 10 ¹¹ Ω · cm or more in a charge injection electric field. Device.

According to an eighth aspect of the present invention, in the developing device according to the first aspect, the developing device further includes a neutralizing member that is provided in contact with the intermediate toner holding member and neutralizes the surface of the intermediate toner holding member.
According to a ninth aspect of the present invention, in the developing device according to the eighth aspect, the charge eliminating member also serves as a toner supply member for supplying conductive toner to the intermediate toner holding member.
According to a tenth aspect of the present invention, there is provided an image carrier that forms and holds an electrostatic latent image, and the electrostatic latent image on the image carrier that is provided opposite to the image carrier and develops the image carrier. And a developing device according to any one of the above.
According to an eleventh aspect of the present invention, there is provided an image carrier having a movable support body and a pixel electrode group supported by the support body and arranged vertically and horizontally in pixel units, and each of the pixel electrodes of the pixel electrode group. 10. A latent image forming unit that forms a latent image according to an image signal, and a latent image on the image holding member that is provided opposite to the image holding member and that is developed with toner. An image forming apparatus including the developing device.

According to the first aspect of the present invention, while using the conductive toner injected with a charge injection electric field, a sufficient image density can be secured, environmental degradation and deterioration over time can be suppressed, and further downsizing can be achieved. Development apparatus can be provided.
According to the second aspect of the invention, uniform and stable charge injection into the conductive toner can be performed.
According to the third aspect of the present invention, the conductive toner moves more favorably from the intermediate toner holding member to the developing toner holding member than the one not having this configuration. The amount of toner can be increased.
According to the fourth aspect of the present invention, good charge retention is maintained in the development region, and charge injection is efficiently performed in the charge injection field effect region.
According to the fifth aspect of the present invention, by providing the insulating or semiconductive coating layer around the base of the conductive toner, the resistance change due to the electric field of the conductive toner can be easily realized.
According to the sixth aspect of the present invention, by making the resistance of the intermediate toner holding member larger than that of the developing toner holding member as compared with the case without this configuration, the charge injection electric field can be effectively applied and the developing electric field can be applied. Does not increase
According to the seventh aspect of the present invention, the charge injection efficiency can be increased by making the intermediate toner holding member have a high resistance compared to the case where this configuration is not provided.

According to the eighth aspect of the present invention, the surface of the intermediate toner holding member can be easily neutralized, and the charge injection electric field and the moving electric field can be effectively applied as compared with the case where this configuration is not provided. .
According to the invention which concerns on Claim 9, compared with the case where it does not have this structure, it becomes possible to reduce a number of members.
According to the tenth aspect of the present invention, there is provided an image forming apparatus capable of ensuring a sufficient image density and suppressing environmental deterioration and deterioration over time while using conductive toner injected by a charge injection electric field. Will be able to.
According to the eleventh aspect of the invention, particularly for the method of forming a latent image for each pixel electrode, it is easy to reduce the developing electric field, and the conductive toner injected by the electric charge injection electric field is used. However, sufficient image density is ensured, and environmental degradation and deterioration over time can be more easily suppressed.

First, an outline of an embodiment model to which the present invention is applied will be described.
Outline of Embodiment Model FIG. 1 shows an outline of an image forming apparatus including an embodiment model of a developing apparatus that embodies the present invention. In FIG. 1, an image forming apparatus includes an image carrier 1 that forms and holds an electrostatic latent image, and a developing device that is provided opposite to the image carrier 1 and develops the electrostatic latent image on the image carrier 1. It consists of and.
A typical model of the developing device is a developing device that visualizes the electrostatic latent image held on the surface of the image carrier 1 with the conductive toner 2, and is disposed opposite to the image carrier 1. A toner holding body 3 that holds and conveys the charged conductive toner 2, a developing electric field forming means 6 that forms a developing electric field in a developing region between the toner holding body 3 and the image holding body 1, and the toner holding body 3. A charge injection member 8 disposed opposite to the image holding member 1 and an electric charge injection electric field acting between the charge injection member 8 and the toner holding member 3 to thereby cause uncharged conductive toner. And a toner injecting means 7 for injecting electric charge into the toner holding body 3. The toner holding body 3 is rotatably provided to face the image holding body 1 and holds and conveys the conductive toner 2 to the developing area and forms a developing electric field in the developing area. By applying a developing electric field by means 6, the image A developing toner holding body 4 that develops the electrostatic latent image on the holder 1 with the conductive toner 2 and a rotation speed faster than that of the developing toner holding body 4 are provided opposite to the developing toner holding body 4. And an intermediate toner holder 5 that holds and conveys the conductive toner 2 charged by the charge injection means 7 up to an intermediate point away from the development area of the development toner holder 4. The moving electric field forming means provided between the intermediate toner holding member 5 and the intermediate toner holding member 5 causes a moving electric field to move the conductive toner 2 from the intermediate toner holding member 5 toward the developing toner holding member 4. It is.

Here, as a developing method for handling the conductive toner 2, any developing method such as a one-component developing method or a two-component developing method may be used as long as the conductive toner 2 is supplied to the electric charge injection field action region. May be.
The developing toner holding body 4 and the intermediate toner holding body 5 are not limited as long as the conductive toner 2 can be held and conveyed, and any shape such as a roll shape or a belt shape may be used. In the embodiment using the above, the magnetic pole arrangement and the like may be arbitrarily set. The intermediate toner holder 5 "holds and conveys the conductive toner 2 injected by the charge injection means 7 up to an intermediate point away from the development area of the development toner holder 4" The position at which the conductive toner 2 held and conveyed by the toner holder 5 moves to the developing toner holder 4 is not particularly limited, and may be any position between the area where the charge injection electric field acts and the developing area. That means.
Further, the developing electric field forming means 6 includes a wide range of devices that form a developing electric field between the image holding member 1 and the toner holding member 3, and the developing electric field here is a direct current electric field or an alternating electric field superimposed. You may select DC electric fields suitably.

  Further, the conductive toner 2 maintains the charge retaining property of the conductive toner 2 in the development region from the viewpoint of efficiently performing the charge injection action at the time of charge injection and good development action at the time of development. Thus, it is preferable to change to a high resistance and to change to a low resistance so as to facilitate the charge injection of the conductive toner 2 in the electric field region of charge injection. Furthermore, it is preferable that the resistance change to a high resistance so as to maintain the charge holding property of the conductive toner 2 even in the moving electric field action region moving from the intermediate toner holding member 5 to the developing toner holding member 4.

  Therefore, as the conductive toner 2 used in the present embodiment model, a conductive toner base is used as a base, and an insulating or semiconductive coating layer is provided on the surface, for example, an insulating toner base is used. There are various modes such as embedding conductive fine particles on the surface of the base, but from the viewpoint of facilitating the production, the conductive toner 2 is coated with an insulating or semiconductive coating around the conductive toner substrate. It is preferred that the layer is coated. Here, the conductive toner substrate may be a toner substrate having conductivity as a result. For example, conductive fine particles may be mixed in the insulating toner substrate, or conductive fine particles may be mixed in the vicinity of the outer surface of the insulating toner substrate. It may be selected as appropriate, for example, to adhere. Further, the coating layer is not limited to a mode in which the conductive toner substrate is completely coated, but includes a mode in which the conductive toner substrate is completely coated. In this case, in order to adjust the electrical conductivity of the toner, the coating layer may be provided with a recess or by adjusting the layer thickness of the coating layer itself.

The charge injection means 7 injects charges into the conductive toner 2 by applying a charge injection electric field between the charge injection member 8 and the toner holder 3 (specifically, the intermediate toner holder 5). I just need it. At this time, the shape of the charge injection member 8 is not particularly limited as long as it has a function of injecting charges into the conductive toner 2. For example, a roll shape, a plate shape, a blade shape or the like may be appropriately selected. A typical example is a metal roll.
The charge injection field of the charge injection means 7 may be selected as appropriate, such as a direct current electric field alone or a direct current electric field superimposed with an alternating electric field.

  Further, the charge injection member 8 may have only a function of performing charge injection with the intermediate toner holding member 5 or may have a function of supplying a toner. In this case, in the former case, the charge injection member 8 has an advantage of pursuing only a function for charge injection, but on the other hand, a member that realizes toner supply for supplying the conductive toner 2 to the charge injection field effect region. Is required separately. On the other hand, the latter needs to satisfy both functions.

  From the viewpoint of performing stable charge injection to the conductive toner 2, the charge injection unit 7 includes a charge injection electric field between the charge injection member 8 and the toner holder 3 (specifically, the intermediate toner holder 5). It is preferable to inject the charge by rubbing and rubbing the conductive toner 2 while acting. According to this method, it is possible to reduce the generation rate of toner that is not normally charged (WST: abbreviation of Wrong Sign Toner) compared to the case where this method is not used.

  Further, as a typical mode in which the conductive toner 2 is rubbed between the charge injection member 8 and the intermediate toner holding member 5, the charge injection unit 7 rotates between the charge injection member 8 and the intermediate toner holding member 5. Any device that has a speed difference may be used. More specifically, the charge injection means 7 includes a rotatable charge injection member 8, and the charge injection member 8 can be rotated faster than the intermediate toner holder 5. In this embodiment, the rotation direction of the charge injection member 8 is arbitrary, but considering the chargeability of the conductive toner 2, the speed ratio between the charge injection member 8 and the intermediate toner holding member 5 is 1.5 to 2.5. It is preferable that it is double.

  Further, as a preferable mode in which the charge injection member 8 also functions as a toner supply function, it is sufficient if the charge injection member 8 rotates in the same direction and with a speed difference at a portion facing the intermediate toner holding member 5. That is, in the method (With method) in which the rotation direction of the charge injection member 8 is the same direction at the portion facing the intermediate toner holder 5, stable charging is possible, but the rotation direction of the charge injection member 8 is reverse. In the method (Against method), since the toner moves to the intermediate toner holding body 5 before the conductive toner 2 is sandwiched between the charge injection member 8 and the intermediate toner holding body 5, stable charging is performed. There is a risk that it will be difficult to perform.

Further, as another charge injection means 7 for giving the speed difference, a charge injection member 8 is fixedly disposed so as to face the intermediate toner holding body 5 so as to give a speed difference to the intermediate toner holding body 5. The embodiment made into is mentioned. The charge injection member 8 of this embodiment is preferably a blade-like member.
Further, as a preferred embodiment of the charge injection means 7, it is important to sandwich the conductive toner 2 between the charge injection member 8 and the intermediate toner holding body 5 in a single layer state, thereby enabling uniform charging. As a result, it is possible to effectively prevent the occurrence of reverse polarity toner.

In addition, the charge injection means 7 applies a charge injection electric field between the charge injection member 8 and the intermediate toner holding member 5. However, in a preferred aspect of this embodiment model, the charge injection means 7. In the charge injection method, the conductive toner 2 is sandwiched and rubbed between the charge injection member 8 and the intermediate toner holder 5, so that the charge injection is performed with the apparent resistance of the conductive toner 2 lowered. Therefore, even if the charge injection electric field is set to a certain extent, the charging performance of the conductive toner 2 after charge injection can be kept good. For this reason, it is possible to inject the charge into the conductive toner 2 without necessarily setting the charge injection electric field to be larger than the development electric field and the moving electric field.
Therefore, the conductive toner 2 can realize a behavior of changing to a high resistance in the developing region and the moving electric field application region and changing to a low resistance in the charge injection electric field application region.

However, since the conductive toner 2 exhibits a behavior in which the resistance changes depending on the magnitude of the electric field acting on the toner, the conductive toner 2 is more effective in the charge injection electric field application region than in the development region and the moving electric field application region. In order to reduce the resistance, it is preferable to apply a charge injection electric field larger than the developing electric field and the moving electric field.
Thus, in the charge injection means 7 satisfying the relationship of charge injection electric field> development electric field (moving electric field), it becomes easy to switch the electric resistance of the conductive toner 2 between a high resistance and a low resistance. . The conductive toner 2 in this embodiment preferably has a volume resistivity of 10 ¹⁰ Ω · cm or less in a charge injection electric field and 10 ¹¹ Ω · cm or more in a development electric field (or moving electric field). This is because if the electric charge injection electric field is 10 ¹⁰ Ω · cm or less, it is easy to inject electric charges, while if the developing electric field is 10 ¹¹ Ω · cm or more, electric charges are easily held.

In order to inject the charge into the conductive toner 2 with such a charge injection electric field, the intermediate toner holder 5 is covered with a surface layer having a volume resistivity of 10 ¹¹ Ω · cm or more with the charge injection electric field. It is preferable that

Further, in order to perform good development in the development region, it is necessary to hold a sufficient amount of the conductive toner 2 on the toner holder 3 (specifically, the development toner holder 4). Therefore, it is necessary to increase the amount of movement of the conductive toner 2 from the intermediate toner holder 5 to the developing toner holder 4. Therefore, in order to favorably move the conductive toner 2 from the intermediate toner holding body 5 to the developing toner holding body 4, the intermediate toner holding body 5 is interposed between the intermediate toner holding body 5 and the developing toner holding body 4. It is necessary to apply a moving electric field that causes the proper conductive toner 2 to move to the developing toner holder 4 and to have a speed difference between the two.
Further, in order to effectively move the conductive toner 2 between the intermediate toner holding member 5 and the developing toner holding member 4, the developing toner holding member 4 and the intermediate toner holding member 5 are arranged at the opposite portions. It is preferable to set so as to rotate in different directions.

Further, if the intermediate toner holding member 5 is covered with a surface layer having a larger volume resistivity than that of the developing toner holding member 4, a charge injection electric field is effectively applied at the time of charge injection in the intermediate toner holding member 5. It is possible to increase the developing electric field.
Further, from the viewpoint of applying an effective electric field at the time of charge injection electric field action or moving electric field action, it is necessary to keep the potential of the surface of the intermediate toner holder 5 stable, and the surface of the intermediate toner holder 5 is neutralized. It is preferable to provide a static elimination member. As an aspect including the charge eliminating member, it is preferable that the charge removing member also serves as a toner supply member that supplies the conductive toner 2 to the intermediate toner holding member 5.

Further, as a preferable aspect of the resistance change of the conductive toner 2, there is an aspect in which switching is performed from a high resistance to a low resistance with an electric field larger than a transfer electric field formed at the time of transfer and smaller than a charge injection electric field.
According to this aspect, since the conductive toner 2 switches from high resistance to low resistance in the intermediate electric field between the transfer electric field and the charge injection electric field, the conductive toner 2 is kept at high resistance in the transfer electric field application region. Therefore, during transfer, there is no movement of electric charge between the conductive toner 2 and the transfer medium (recording material, etc.), and the conductive toner is also applied to a transfer medium such as highly water-containing paper. 2 is maintained, and good transfer performance can be obtained.

Next, the operation of the developing device of this embodiment model will be described.
As shown in FIG. 2, by applying a charge injection electric field between the charge injection member 8 and the intermediate toner holding member 5, the conductive toner 2 is injected in this charge injection electric field action region, and the intermediate toner toner Move to the holding body 5 side. At this time, if the electric charge is injected so as to be sandwiched between the electric charge injection member 8 and the intermediate toner holding member 5 and rubbed with the conductive toner 2, the intermediate toner holding is performed in the electric charge injection electric field application region. More uniform charge injection can be performed on the conductive toner 2 having a toner layer of a single layer or less on the body 5.

Then, the conductive toner 2 held on the intermediate toner holding member 5 in a state of a single layer or less reaches a moving electric field action region between the intermediate toner holding member 5 and the developing toner holding member 4, and the intermediate toner holding member. 5 to the developing toner holder 4 side. At this time, by making the speed of the intermediate toner holder 5 faster than the speed of the developer toner holder 4, the amount of movement of the conductive toner 2 to the developer toner holder 4 can be increased, and the developer toner hold The conductive toner 2 on the body 4 can have a toner amount density larger than the toner amount density on the intermediate toner holding member 5.
Further, at this time, if the intermediate toner holding member 5 and the developing toner holding member 4 are rotated in different directions (Against) at the opposite portions, the conductive toner 2 can pass through the nip region between the two. Therefore, there is no change in the toner charge amount, and the amount of movement to the developing toner holder 4 can be increased. That is, a toner layer having a high toner amount density and a stable charge amount is formed on the developing toner holder 4.

The conductive toner 2 that has moved onto the developing toner holder 4 is transported to the development area between the image carrier 1 and the developing toner holder 4, moves to the image carrier 1, and moves onto the image carrier 1. The electrostatic latent image is developed to make a visible image.
At this time, since the conductive toner 2 changes to a high resistance in the development region, the conductive toner 2 maintains a state of holding a charge, and the movement of the charge between the conductive toners 2 is not As a result, the generation of reverse polarity toner can be suppressed.
Here, since the toner amount density on the developing toner holding member 4 is high, it is not necessary to increase the speed of the developing toner holding member 4, and a sufficient image density can be secured, and the fine line reproducibility is ensured. And image formation with excellent graininess.

  On the other hand, such a developing device is used as an image carrier 1 having a movable support and a pixel electrode group supported by the support and arranged in pixels in the vertical and horizontal directions. The present invention can also be applied to an image forming apparatus having latent image forming means for forming a latent image corresponding to an image signal. In this case, there is an effect due to the elimination of the charging process, and it is possible to prevent the occurrence of image quality defects due to, for example, contamination due to charging.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 3 shows Embodiment 1 of an image forming apparatus including a developing device to which the present invention is applied.
In FIG. 1, the image forming apparatus according to the present embodiment has a photoconductor 20 as an image carrier that rotates in a predetermined direction, and a charging device 21 that charges the photoconductor 20 around the photoconductor 20. For example, an exposure device 22 as a latent image writing device for forming a latent image on the charged photoconductor 20, and a developing device 30 for visualizing the electrostatic latent image formed on the photoconductor 20. And a transfer device 24 for transferring the toner image visualized on the photoconductor 20 to the recording material 28 and a cleaning device 25 for cleaning the residual toner on the photoconductor 20 are sequentially arranged.

As shown in FIG. 4, the developing device 30 in the present embodiment has a developing housing 31 in which conductive toner (hereinafter, abbreviated as toner as appropriate) is accommodated. The developing housing 31 faces the photoreceptor 20. The developing opening 32 is opened, and a developing roll (corresponding to a developing toner holding member) 33 is disposed so as to face the developing opening 32 and rotate in the same direction (With) at a portion facing the photosensitive member 20. A predetermined developing bias is applied between the photosensitive member 20 and the developing roll 33 by a bias power source 42, so that a developing electric field is applied to a developing region where the photosensitive member 20 and the developing roll 33 face each other. . And the developing roll 33 of this Embodiment is comprised by the elastic roll member whose outer diameter is 14-30 mm, for example, and the volume resistivity of the surface is 10 < ¹¹ > ohm * cm or less. Further, the rotation speed is set to be 1 to 2 times the peripheral speed of the photoconductor 20, and the amount of interference with the photoconductor 20 (corresponding to the gap) is -0.5 to +0.5 (the biting side is indicated by +). ).

Further, on the side of the developing roll 33 different from the photoreceptor 20, an intermediate roll 34 is provided as an intermediate toner holding body that holds and conveys charged conductive toner, facing the developing roll 33.
The intermediate roll 34 in the present embodiment is formed of an elastic roll member of, for example, 14 to 30 mm, substantially the same as the outer diameter of the developing roll 33, and rotates in mutually different directions (Against) at portions facing the developing roll 33. In addition, the peripheral speed is set to be 1.2 to 2 times the peripheral speed of the developing roll 33. The amount of interference between the intermediate roll 34 and the developing roll 33 is −0.5 to +0.5, and a predetermined moving bias (0) is provided between the intermediate roll 34 and the developing roll 33 by the bias power source 43. (Approx. 50V) is applied to the moving region where the intermediate roll 34 and the developing roll 33 face each other. The intermediate roll 34 of the present embodiment has a surface volume resistivity of 10 ¹¹ Ω · cm or more.

Further, a charge injection roll 35 as a charge injection member capable of injecting charges into uncharged toner is provided at a position facing substantially above the intermediate roll 34.
The charge injection roll 35 of the present embodiment is constituted by a roll member made of metal such as aluminum or stainless steel having an outer diameter of 10 to 20 mm, for example, and the amount of interference with the intermediate roll 34 is adjusted to 0 to 0.5. Yes. Further, by applying a predetermined charge injection bias (50 to 300V) between the intermediate roll 34 and the intermediate roll 34, a charge injection electric field acts on the charge injection region where the charge injection roll 35 and the intermediate roll 34 face each other. It is supposed to let you. Further, the charge injection roll 35 rotates in the same direction (With) at a portion facing the intermediate roll 34, and its peripheral speed is 1.5 to 2.5 times the peripheral speed of the intermediate roll 34. It has become. In addition, as the charge injection roll 35, the surface may be subjected to, for example, sandblasting so as to have an appropriate rough surface.

  Further, in the developing device 30 of the present embodiment, in order to supply toner to the intermediate roll 34, a toner supply roll 36 having a conductive foam roll configuration made of polyurethane resin having an outer diameter of 12 to 30 mm, for example, is charged. It is disposed opposite to the intermediate roll 34 at a position upstream of the roll 35 in the rotation direction of the intermediate roll 34, and is provided to rotate in different directions (Against) at a portion facing the intermediate roll 34. The amount of interference between the toner supply roll 36 and the intermediate roll 34 is +0.5 to +2.0 (the biting side is indicated by +), and the peripheral speed of the intermediate roll 34 is 0.3 to 1.0. It is set to rotate at twice the peripheral speed. In this embodiment, the toner supply roll 36 and the intermediate roll 34 are electrically short-circuited. Therefore, even if the surface of the intermediate roll 34 is charged between the charge injection roll 35 and the intermediate roll 34, the action of making the potentials of the toner supply roll 36 and the intermediate roll 34 uniform works, and the surface of the intermediate roll 34 is charged. The effect of suppressing, that is, the effect of removing electricity, is activated, the toner adhering to the intermediate roll 34 can be cleaned, and the toner supply roll 36 performs the refresh function of the intermediate roll 34.

  Further, an agitator 41 that stirs and supplies toner to the toner supply roll 36 is provided behind the toner supply roll 36 so that the toner contained in this portion can be supplied to the toner supply roll 36 side.

  Further, a layer forming blade 37 that regulates the toner supplied from the toner supply roll 36 to the intermediate roll 34 to be layered is provided between the toner supply roll 36 and the charge injection roll 35 of the intermediate roll 34. . The layer forming blade 37 is made of a plate spring member such as stainless steel or phosphor bronze having a thickness of 0.05 to 0.2 mm, for example, and is fixed to the free end side of a support member 37a whose one end side is fixed to the developing housing 31. It has come to be supported. In particular, the layer forming blade 37 is provided so that the surface on the free end side is pressed against the intermediate roll 34 with a predetermined pressing force, and the layer forming blade 37 is layered without excessively scraping off the toner on the intermediate roll 34. The effect of arranging can be further demonstrated. The layer forming blade 37 is not particularly limited as long as the toner can be layered, and an elastic body may be provided on the surface of the plate spring member.

  On the other hand, a refresh roll 38 made of a metal roll made of aluminum, for example, is brought into contact with the developing roll 33 at a position facing the developing roll 33 between the intermediate roll 34 on the downstream side of the developing area of the developing roll 33. Is provided. Then, by grounding the refresh roll 38, the residual toner on the developing roll 33 is electrostatically removed, and the surface of the developing roll 33 is neutralized. The refresh roll 38 is provided with a metal blade (not shown) so as to collect the toner adhering to the refresh roll 38. The refresh roll 38 is not limited to a metal roll, and for example, a brush using conductive fibers may be used.

  Each device other than the developing device 30 used in this embodiment may be appropriately selected. As the transfer device 24, for example, a transfer roll (not shown) is disposed facing the photoconductor 20, and a transfer electric field is applied between the photoconductor 20 and the transfer roll by applying a transfer bias to the transfer roll. The toner image on the photosensitive member 20 may be appropriately selected on the recording material 28, or the like.

Here, the conductive toner in the present embodiment will be described. For example, as shown in FIG. 5A, the conductive toner has a conductive toner base (conductive core) made of a conductive material, and an insulating coating layer (for example, around the conductive core). Insulating resin layer) is used, and the insulating coating layer is provided with an appropriate number of recesses so that a part of the conductive core is exposed.
In this embodiment, the toner can be produced by a polymerization method or various known encapsulation techniques. At this time, the conductive core disperses a conductive agent such as conductive carbon or ITO in a polyester resin or a styrene acrylic resin, or a particle surface made of a polyester resin or a styrene acrylic resin. It is produced by coating with a conductive agent.

  When a high electric field is applied to such a toner, the toner tends to have a low resistance. The magnitude of the electric field that lowers the resistance depends mainly on the occupation ratio of the concave portion of the toner or the thickness of the insulating coating layer. About this mechanism, since the conductive core is covered with the insulating coating layer, the conductive core itself does not contact the cores or directly contact the electrode member, etc. As a result, it is presumed that when a high electric field is applied, for example, the tunnel effect or the like is conducted.

  As another embodiment of the conductive toner, for example, as shown in FIG. 5B, the conductive core is covered with an insulating or semiconductive coating layer, and the thickness h of the coating layer is adjusted appropriately. By doing so, it is possible to appropriately select a mode in which the resistance of the toner can be adjusted. At this time, for the semiconductive coating layer, a semiconductive material itself may be used. For example, a trace amount of metal oxide such as titanium oxide or tin oxide or conductive carbon may be added to the insulating resin. You may make it use the semiconductive resin contained. As the conductive core, for example, a mode in which conductive fine particles adhere to the vicinity of the outer surface of an insulating toner base (insulating core) made of a normal insulating toner, or conductive fine particles are mixed inside the insulating core. You can choose what you want.

Next, the method for producing the conductive toner may be appropriately selected, such as a wet production method, a dry production method, or a combination method of both.
First, the insulating core may be manufactured by any method such as a kneading pulverization method that is a dry manufacturing method, an emulsion aggregation method that is a wet manufacturing method, or a dissolution suspension method, but the toner particle size distribution is sharpened. The emulsion aggregation method is preferable from the viewpoint of the degree of freedom in controlling the shape of the produced toner. In the emulsion aggregation method, a resin fine particle dispersion is prepared by emulsion polymerization, and a colorant dispersion in which a colorant is dispersed in a solvent and, if necessary, a release agent dispersion are prepared, and then these are mixed to prepare a toner. In this method, agglomerated particles corresponding to the particle diameter are formed and heated to fuse / unify the agglomerated particles to produce a toner. This manufacturing process may be mixed and agglomerated in a lump, or the aggregation process may be performed in a plurality of stages, and after the formation of the first stage of the matrix aggregation, the particles added in the second stage of the agglomeration formation are the first stage. You may make it adhere to the surface of the parent | base aggregate particle.
Further, at the time of toner preparation by such an emulsion aggregation method, conductive fine particles may be attached to the surface of the insulating core, and a coating layer may be formed. In the above-described manufacturing method, conductive fine particles are adhered to the surface of the insulating core. However, the conductive fine particles may be mixed in the insulating core during toner preparation by the emulsion aggregation method. .

Further, as a dry production method of conductive toner, for example, after drying an insulating core produced by an emulsion aggregation method, conductive fine particles are adhered to the surface, and further, resin fine particles as a coating layer are formed into a film. The thing which was done is mentioned.
In this manufacturing method, for example, after mixing an insulating core and conductive fine particles in a stirring mixer, the mixture is stirred and mixed for a predetermined time, and the conductive fine particles are adhered to the insulating core to form a conductive core (stirring and mixing step ( I)). After that, after mixing the conductive core and resin fine particles made of polyester, styrene acrylic, etc. into the stirring mixer, the mixture is stirred for a predetermined time to form a coating layer (insulating layer) around the conductive core. (Stirring and mixing step (II)).
Here, specific examples of the conductive toner dry manufacturing method include, for example, a predetermined amount (for example, 15 wt%) of ITO fine particles (manufactured by Sumitomo Metal Mining Co., Ltd.) in an insulating core having an average particle diameter of 6.5 μm, and a sample. The mixture is stirred and mixed for a predetermined time (for example, 12000 rpm, 30 seconds) by a mill (model: SK-M10 type, manufactured by Kyoritsu Riko Co., Ltd.), and ITO fine particles are adhered to the surface of the insulating core. Thereafter, a predetermined amount (eg, 10 wt%) of resin fine particles such as polyester is added to the insulating core (conductive core) to which the ITO fine particles are adhered, and the mixture is stirred and mixed in the sample mill for a predetermined time (eg, 12000 rpm, 30 minutes). ), And the like that form a predetermined insulating layer.

Next, the operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
When the image forming process is started, first, the surface of the photoconductor 20 is charged by the charging device 21, and the exposure device 22 writes an electrostatic latent image on the charged photoconductor 20. The electrostatic latent image is developed to make a visible image. Thereafter, the toner image on the photoconductor 20 is conveyed to a transfer site, and the transfer device 24 electrostatically transfers the toner image on the photoconductor 20 onto the recording material 28. The residual toner on the photoconductor 20 is cleaned by the cleaning device 25.

Here, an outline of the operation of the developing device 30 in the present embodiment will be described for each process based on FIG.
-Toner supply-
In the drawing, in the developing device 30 according to the present embodiment, the toner stirred by the agitator 41 is supplied to the toner supply roll 36 side. The toner supplied to the toner supply roll 36 is transported to a position facing the intermediate roll 34 by the rotation of the toner supply roll 36 and supplied to the intermediate roll 34 side of the Against rotation.

-Layer formation-
The layer thickness of the toner supplied onto the intermediate roll 34 is regulated by the layer forming blade 37, and a substantially uniform toner layer is formed.

-Charge injection-
Next, the uniformly formed toner layer on the intermediate roll 34 is charged between the intermediate roll 34 and the charge injection roll 35 while being sandwiched and rubbed between the two while being charged by the bias power supply 44. Charges are injected by the injection electric field.
In such a state, since the toner sandwiched between them is arranged to be equal to or less than a single layer, the contact probability between the toner and the charge injection roll 35 is increased, and the contact resistance of the toner can be reduced. Accordingly, the apparent resistance of the toner is reduced, and the toner is injected with a low resistance. For this reason, even when the electric charge injection field is relatively low, the electric charge is efficiently injected into the toner. In particular, the present embodiment has a feature that the charge injection function can be stably performed because the charge injection roll 35 can exclusively perform the charge injection function to the toner.
In this way, by performing charge injection on the toner having a single layer or less, charge injection into the toner is effectively performed, and generation of WST can be suppressed.
Then, on the intermediate roll 34 that has passed through the portion facing the charge injection roll 35, a toner layer of a single layer or less in which uniform charge injection is performed is held and conveyed by the intermediate roll 34.

  Here, in order to confirm the charge injection effect of the present embodiment, the charge injection action on the toner will be described with reference to FIGS. 6 to 10. Now, the charge injection roll 35 (corresponding to the injection electrode) and the intermediate roll are now described. 34 (corresponding to the intermediate electrode) simply by interposing the toner (conductive toner) and applying a charge injection electric field (however, the conductive toner is sandwiched between the injection electrode and the intermediate electrode and rubbed. As shown in FIG. 6, for example, the generation rate of WST changes according to the magnitude of a charge injection electric field (corresponding to an electric field applied to a particle layer of conductive toner).

That is, when the electric charge injection electric field as shown by the arrow A in FIG. 6 is in a low electric field region, the charging efficiency is deteriorated, and as shown in FIG. 7, unchargeable toner (neutralized toner) adheres to the charged toner. Or move to the intermediate electrode side by non-electrostatic adhesion with the intermediate electrode. Therefore, as the charge injection electric field is increased, the charging efficiency is increased and WST is reduced.
On the other hand, when the electric charge injection electric field is a high electric field region as indicated by an arrow B in FIG. 6, the charged toner moves to the intermediate electrode as shown in FIG. Then, charge exchange is performed and polarization occurs, and the upper layer toner becomes WST. Therefore, the WST due to polarization tends to increase as the charge injection electric field is increased. Further, when the electric charge injection electric field is a high electric field, abnormal discharge is likely to occur, and there is a concern that the generation rate of WST increases correspondingly.

  Therefore, as a solution for reducing the incidence of WST, for example, as shown in FIG. 9A, a high injection efficiency is realized with a low electric field, or as shown in FIG. It is conceivable to prevent from moving to the intermediate electrode. Further, as shown in FIG. 10 (a), it is necessary not to polarize between toner layers even at a high electric field, or as shown in FIGS. 10 (b) and 10 (c), the toner does not become multi-layered, in other words, heavy. A policy of preventing it from happening can be considered.

  The present embodiment has been devised based on such a policy. The toner is sandwiched between the charge injection roll 35 (injection electrode) and the intermediate roll 34 (intermediate electrode), and in particular, rubbing. However, if the charge injection is performed, the probability of contact of the toner with the charge injection roll 35 can be increased and the contact resistance can be reduced, so that the toner can be efficiently in a single layer state with a low charge injection electric field. It becomes possible to inject charges into the. At this time, since a shearing force is applied between the toner layers, it is possible to prevent the toners from overlapping in a polarized state, and it is possible to prevent the occurrence of WST even if the charge injection electric field is a high electric field.

-Movement (improvement of toner density)-
Next, the toner charged by the charge injection is conveyed to a portion where the intermediate roll 34 and the developing roll 33 are opposed to each other. Here, since the intermediate roll 34 and the developing roll 33 are rotated against each other and a moving electric field is applied by the bias power source 43, the toner does not pass through the nip between the intermediate roll 34 and the developing roll 33. The toner is electrostatically moved to the developing roll 33, and the toner charge amount is not changed at all. Further, since the peripheral speed of the intermediate roll 34 is increased by 1.2 to 2 times the peripheral speed of the developing roll 33, the amount of toner moving from the intermediate roll 34 to the developing roll 33 can be increased. Thus, the toner amount density on the developing roll 33 can be approximately 1.2 to 2 times the toner amount density on the intermediate roll 34, and the toner amount density on the developing roll 33 can be set on the intermediate roll 34. The toner amount density can be increased.
At this time, the intermediate roll 34 and the developing roll 33 do not necessarily have to rotate Against, and may be rotated with. This is because the moving electric field is set to be smaller than the electric charge injection electric field, so that there is less possibility of changing the charged state of the toner during the movement.

-Development-
Then, the toner that has moved onto the developing roll 33 is conveyed on the developing roll 33 as it is, and proceeds to a portion where the developing roll 33 and the photoconductor 20 face each other. Here, the developing electric field by the bias power source 42 acts, so that the toner on the developing roll 33 develops the electrostatic latent image to become a visible image. At this time, since the toner amount density on the developing roll 33 is high, it is possible to realize an image density according to the electrostatic latent image. Further, since it is not necessary to increase the peripheral speed of the developing roll 33, the toner on the photoconductor 20 is not scraped off by the rotation of the developing roll 33. A sufficient image density can be obtained without image quality deterioration. Since the development electric field is lower than the electric charge injection electric field, the electric charge injected into the conductive toner by the electric charge injection electric field does not escape from the electric development electric field, and good development is performed.

-Transcription-
Further, the toner image visualized on the photoconductor 20 is transferred onto the recording material 28 at a portion where the photoconductor 20 and the transfer device 24 face each other as shown in FIG.
At this time, if the transfer electric field formed by the photoconductor 20 and the transfer device 24 is lower than the electric charge injection electric field in this transfer step, the electric charge injected into the conductive toner by the electric charge injection electric field. However, good transfer is performed without escape by the transfer electric field. Needless to say, the recording material 28 to which the toner has been transferred is transported to a fixing device (not shown) to fix the toner.

Here, among the above-described steps, the toner movement in the steps from the toner supply to the movement will be described in more detail below with reference to FIG.
-Toner supply-
As shown in (a), the toner supply roll 36 and the intermediate roll 34 rotate Against, the peripheral speed V1 of the toner supply roll 36 is equal to or less than the peripheral speed V2 of the intermediate roll 34, and the toner supply roll 36 further Since the toner has bite into the intermediate roll 34, the toner conveyed by the toner supply roll 36 is rubbed in the nip area with the intermediate roll 34 and transferred onto the intermediate roll 34.

-Layer formation-
Next, as shown in (b), the toner on the intermediate roll 34 is regulated by the layer forming blade 37, so that a substantially uniform toner layer is formed on the intermediate roll 34 after passing through the layer forming blade 37. Is formed and used for the next charge injection.

-Charge injection-
As shown in (c), the charge injection roll 35 and the intermediate roll 34 rotate with With, and the peripheral speed V3 of the charge injection roll 35 is 1.5 to 2.5 times the peripheral speed V2 of the intermediate roll 34. Therefore, in the electric charge injection electric field action region which is the opposite portion between the two, the toner is sandwiched and rubbed between both, so that a toner layer of a single layer or less is formed. At this time, since the peripheral speed V3 of the charge injection roll 35 is larger than the peripheral speed V2 of the intermediate roll 34, a toner layer aligned with a single layer or less is formed on the intermediate roll 34 that has passed through the charge injection field effect region. Will come to be. Further, since the contact probability between the toner and the charge injection roll 35 is increased in the charge injection electric field action region, the toner is favorably injected by the action of the charge injection electric field.

-Movement-
As shown in (d), the toner layer on the intermediate roll 34 into which the charge has been injected moves to the developing roll 33 side at a position facing the developing roll 33. Here, the developing roll 33 and the intermediate roll 34 are Against rotated so that the peripheral speed V2 of the intermediate roll 34 is 1.2 to 2.0 times the peripheral speed V4 of the developing roll 33. The toner conveyed by the toner moves to the developing roll 33 side with a toner amount density higher than the toner amount density on the intermediate roll 34, with the help of a moving electric field acting between them.
That is, as shown in FIG. 12, when the displacement amount per unit time of the intermediate roll 34 is 1 and the displacement amount per unit time of the developing roll 33 is m, the intermediate roll 34 adheres on the length l of the surface of the intermediate roll 34. The toner that has been moved moves to m within the developing roll 33 as it is, and the toner layer on the developing roll 33 has a higher toner amount density than the toner layer on the intermediate roll 34. Therefore, it is possible to prevent the occurrence of a situation where the toner supplied to the development site is insufficient, and to realize a developed image density with a high density.

  In the present embodiment, as a charge injection method to the conductive toner, a charge injection electric field is applied between the charge injection roll 35 and the intermediate roll 34, and the charge is injected while being rubbed with the conductive toner interposed therebetween. As a result, by increasing the contact probability between the conductive toner and the charge injection roll 35 and reducing the contact resistance of the conductive toner, the apparent toner resistance can be reduced correspondingly and is relatively low. Charges can be uniformly injected into the conductive toner by a charge injection electric field. Further, in the electric charge injection field application region, it becomes easy to control the toner layer on the intermediate roll 34 to a single layer or less, so that the toner can be uniformly charged and the generation rate of the reverse polarity toner is effectively suppressed. be able to. Furthermore, since charge can be injected into the conductive toner with a relatively low charge injection electric field, the risk of occurrence of abnormal discharge is low, and the generation rate of reverse polarity toner can be effectively suppressed accordingly. .

The conductive toner is changed to a low resistance in the electric charge injection field application region to facilitate charge injection, and changed to a high resistance in the moving electric field application region and the development region (development electric field application region). In particular, it is possible to effectively avoid a situation where unnecessary charge injection is performed in the development region while maintaining good charge injection performance. Therefore, low-charge toner and reverse polarity toner are rarely generated in the development area, and fog and toner cloud can be effectively prevented.
In particular, the toner density on the developing roll can be increased, and the image density can be increased accordingly, so that fine line reproducibility and the like can be formed and an image with sufficient image density can be formed. become able to.

  In addition, since the toner can be moved in a low electric field without rubbing the toner at the time of transfer, the toner has high resistance and charge retention is improved, and the toner charge between the recording material 28 and the toner is reduced. The electrostatic attraction force to the toner is maintained without causing the movement. Accordingly, the toner image can be transferred onto the recording material that has absorbed moisture even in the electrostatic transfer system.

Embodiment 2
FIG. 13 shows a developing device according to the second embodiment. In the figure, the developing device 30 in the present embodiment is configured in substantially the same manner as the developing device in the first embodiment, but unlike the first embodiment, the charge injection roll is not a dedicated member for charge injection, and is an intermediate member. It is arranged so as to also function as a toner supply to the roll 34. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.

  The developing device 30 in the present embodiment is provided with an intermediate roll 34 facing the developing roll 33, and a charge injection roll 35 provided on the substantially opposite side of the intermediate roll 34 to the developing roll 33. Further, a developing electric field acts between the developing roll 33 and the photosensitive member 20 in a developing region where the two are opposed by a bias power source 42. Further, the developing roll 33 and the intermediate roll 34 rotate against each other, and a moving electric field is applied between them by a bias power source 43. Even in this embodiment, the peripheral speed of the intermediate roll 34 is 1.2 to 2 times the peripheral speed of the developing roll 33.

Further, the intermediate roll 34 and the charge injection roll 35 rotate with With, and a charge injection electric field acts between the intermediate roll 34 and the charge injection roll 35 by a bias power supply 44.
In the present embodiment, the charge injection roll 35 is provided with a layer forming blade 37, one end of the layer formation blade 37 is fixedly supported by the support member 37 a, and the free end side of the charge injection roll 35 has a predetermined amount with respect to the charge injection roll 35. It comes to come in pressure contact with the pressing force. A toner supply roll 36 that rotates Against the charge injection roll 35 is provided on the upstream side of the mounting position of the layer forming blade 37 in the rotation direction of the charge injection roll 35, and is supplied to the toner supply roll 36 by the agitator 41. The toner thus supplied is supplied to the charge injection roll 35.

  Further, in the present embodiment, a refresh roll 38 is provided at a position facing the intermediate roll 34 between the developing electric field action area and the downstream side of the developing area of the developing roll 33, and the developing roll of the intermediate roll 34 is also provided. A refresh roll 39 is provided between a portion facing the charge injection roll 35 on a downstream side of a portion facing the 33. In addition, the refresh rolls 38 and 39 are grounded so that the toner on the developing roll 33 and the intermediate roll 34 can be removed, and the surface of the developing roll 33 and the intermediate roll 34 is neutralized. It has become. The refresh rolls 38 and 39 are provided with metal blades (not shown) so that the toner on the refresh rolls 38 and 39 is scraped off and the performance of the refresh rolls 38 and 39 can be maintained.

Next, the operation of the developing device 30 in the present embodiment will be described with reference to FIG.
In the developing device 30, the conductive toner is stirred by the agitator 41 in the developing housing 31, and the stirred toner is supplied to the toner supply roll 36 side. Since the toner supply roll 36 and the charge injection roll 35 rotate against each other, the toner supplied to the toner supply roll 36 moves toward the charge injection roll 35 at a portion facing the charge injection roll 35. The toner moved onto the charge injection roll 35 is regulated in layer thickness by the layer forming blade 37, and the toner conveyed by the charge injection roll 35 forms a predetermined toner layer.

  The toner layer formed by the layer forming blade 37 is charged by injecting electric charge by the electric charge injection electric field acting between the electric charge injection roll 35 and the intermediate roll 34 at an opposite portion. At this time, the toner is sandwiched between the charge injection roll 35 and the intermediate roll 34, and is charged into a single layer or less while being rubbed by the difference in peripheral speed between the two. Contact probability between the toner and the charge injection roll 35 and the contact resistance of the toner can be reduced, and the apparent resistance of the toner is reduced accordingly, and the toner is injected in a low resistance state. Is done.

  The charged and charged toner is held as a single or lower toner layer on the intermediate roll 34 and is conveyed as it is, and reaches a position where the intermediate roll 34 and the developing roll 33 face each other. Here, a moving electric field in a direction that facilitates the movement of the toner acts between the two, and further, Against rotation is performed so that the peripheral speed of the intermediate roll 34 is faster than the peripheral speed of the developing roll 33. A toner layer having a toner amount density higher than the toner amount density on the intermediate roll 34 is formed on the developing roll 33 and is held and conveyed on the developing roll 33. The toner conveyed by the developing roll 33 is developed into a visible image by developing a latent image on the photoconductor 20 by a developing electric field in a developing area that is a portion facing the photoconductor 20.

  As described above, also in this embodiment, the toner amount density on the developing roll 33 can be made larger than the toner amount density on the intermediate roll 34, and the image density can be increased accordingly. . In addition, low-charge toner and reverse polarity toner are rarely generated in the development region, and the same effect as in the first embodiment can be obtained in that fog and toner cloud can be effectively prevented.

Embodiment 3
The present embodiment is configured in substantially the same manner as the image forming apparatus of the first embodiment, and the developing apparatus has the same configuration, but uses an image holding body including pixel electrodes instead of the photosensitive body. Different from the first embodiment. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the description is abbreviate | omitted here.

  As shown in FIG. 14, the image carrier 50 according to the present embodiment winds a matrix panel 60 in which a large number of pixels are formed in a so-called matrix form on a film on a rigid drum 51 that is a rotatable support. It is fixed and supported. The matrix panel 60 is manufactured using, for example, a thin film technique used in a so-called IC manufacturing process for a heat-resistant PET (polyester resin) film, and pixels are arranged in a matrix in the vertical and horizontal directions. Yes. For example, the pixels arranged in a matrix form have a data line (main scanning direction) as a direction along the rotation axis direction of the rigid drum 51 and a scanning line (sub-scanning direction) as the direction along the rotation direction. It is said. Therefore, an appropriate number of data drivers 61 and scanning drivers 62 connected to each pixel are provided on the data lines and scanning lines of the matrix panel 60, and the input lines to these drivers 61 and 62 are further summarized. When the number is reduced, the wiring is made through the matrix panel 60 to the inner surface side of the rigid drum 51.

The rigid drum 51 is provided with a groove 51a along the rotation axis direction at a part of the outer periphery thereof, and a so-called slip for electrical connection between the matrix panel 60 and the outside is provided at the axial center of the rigid drum 51. A ring 54 is provided for insertion, and the rigid drum 51 rotates around the slip ring 54.
Further, as shown in FIGS. 15A and 15B, an appropriate number of terminals 52 are provided along the rotation axis direction of the rigid drum 51 on the inner surface side of the rigid drum 51. Each is connected to a data driver 61 and a scanning driver 62 of the matrix panel 60. Further, these terminals 52 are provided with sliders 53 extending in the direction of the center of the rotation axis and in the direction in which the respective end portions are separated from each other, and are connected to the terminals 52. A current collecting ring 54a is attached. The current collecting ring 54a portion of the slip ring 54 is smaller in diameter than the insulating rings 54b on both sides, and the slider 53 is always kept in contact with the opposite current collecting ring 54a by the rotation of the rigid drum 51. It is like that. The groove 51a of the rigid drum 51 is closed by, for example, a seal tape, so that the resistance of the air current when the image carrier 50 rotates is reduced and the influence at the time of development is also prevented. .

  Therefore, transmission / reception of signals between the matrix panel 60 and the outside is performed from the lead wire 55 wired in the slip ring 54 corresponding to the current collection ring 54 a of the slip ring 54 via the current collection ring 54 a and the slider 53. It is performed with the panel 60, and even when the rigid drum 51 rotates, signals can be exchanged with the matrix panel 60 appropriately. The rotation method of the rigid drum 51 is not particularly limited. For example, the rigid drum 51 may be rotated by being applied to a rotating roll on the outer peripheral surface end side of the rigid drum 51, or may be different from the insertion side of the slip ring 54. However, it is possible to provide a rotating shaft for rotating the rigid drum 51 itself.

Next, the pixels of the matrix panel 60 will be described.
As shown in FIG. 16A, the matrix panel 60 of the present embodiment has pixels arranged vertically and horizontally, and each pixel is configured in a so-called active matrix system as shown in FIG. A TFT 63, a pixel electrode 64, a storage capacitor 65, and wiring (source line, gate line, etc.) as elements are formed. Each pixel and the connection between the pixels are collected as a source line to which the source of the TFT 63 is connected for each data line, and a gate line to which the gate of the TFT 63 is connected for each scanning line. Further, the pixel electrode 64 and the storage capacitor 65 are connected in parallel to the drain of the TFT 63, and one of the storage capacitors 65 is grouped for each scanning line (not shown), and is configured as shown in (c).

Since the matrix panel 60 has a configuration in which a large number of pixels are arranged in this manner, the drive method is performed as follows.
That is, in the matrix panel 60, as shown in FIG. 17, a predetermined number of pixels are grouped for each data line and scanning line, and the source side of the TFT 63 is connected to the data driver 61 for each data line. The gate side is connected to the scanning driver 62 for each scanning line, and the data driver 61 and the scanning driver 62 are controlled by a control device 70 provided on the panel. Therefore, by controlling the data driver 61 and the scanning driver 62, a predetermined pixel can be selected. In FIG. 17, the pixel electrode 64 is omitted, but it goes without saying that the pixel electrode 64 connected between the TFT 63 and the storage capacitor 65 is provided.

For such an image carrier 50, as the developing device, the developing device 30 of the first embodiment (see FIG. 4) or the developing device 30 of the second embodiment (see FIG. 13) is applied. Become. Therefore, development is performed between the pixel electrode 64 and the developing roll 33, and toner adhesion is performed according to each pixel electrode 64 of the image carrier 50. Even at this time, since the amount of toner on the developing roll 33 is increased by the intermediate roll 34, it is possible to secure a sufficient image density and prevent image quality deterioration such as fogging.
Then, the toner image developed on the image carrier 50 is transferred to the recording material 28 by the transfer device 24. At the time of transfer, the pixel electrode 64 side may be set to the same potential, or a potential corresponding to the image signal may be applied to each pixel electrode 64. In the latter case, the control is slightly complicated. However, even if the amount of toner differs from pixel to pixel, it can be transferred onto the recording material 28 as it is.

Here, an image forming process in the image carrier 50 will be described.
-Latent image formation-
As shown in FIG. 18A, the latent image potential formed on the pixel electrode 64 of this example is a voltage corresponding to the image signal for each pixel of the image carrier 50 (here, V, 2V / 3). , V / 3 (showing three stages) is applied, and is not easily affected by adjacent pixels. Further, there is no need to worry about the rotation unevenness of the image holding member 50. For example, when the photoconductor is used, there is no possibility that the rotation unevenness of the photoconductor may result in a dark and light stripe pattern (banding) of the image formed as it is. Further, since the potential difference between the pixels can be easily realized, the image density can be easily changed. Needless to say, the latent image potential may be binarized without gradation.

-Development-
As shown in FIG. 18B, in the developing process itself, the amount of toner adhering to each pixel electrode 64 changes due to the difference in the formed latent image potential, and it is easy to represent the density of the image. Further, since the developing electric field is easily concentrated between the respective pixels and the developing roll 33, the sharpness of the image is also increased.

-Transcription-
As shown in FIGS. 18C and 18D, a voltage corresponding to the image signal (with a polarity opposite to that of the latent image potential) is applied to the pixels, whereby the image carrier 50 and the recording material 28 (specifically, the recording material 28). A transfer electric field is selectively formed between the image carrier 50 and the toner on the image carrier 50 as it is.
In particular, here, by using the same gradation method as in the latent image formation, a transfer electric field corresponding to the toner adhesion amount on the pixel electrode 64 can be formed, and transfer according to the image density can be performed. Can be easily realized.

−Cleaning−
As shown in FIG. 18E, at the time of cleaning, a voltage corresponding to an image signal is applied to the pixel electrode 64, so that both a pixel with a large amount of residual toner and a pixel with a small amount of toner can be efficiently cleaned. .

In particular, when the pixel electrode 64 is used, a low developing bias can be used and it is preferable to use the conductive toner into which such charge is injected for the low breakdown voltage of the TFT 63.
Further, in the present embodiment, the image carrier 50 in which the two-dimensional matrix is formed in a cylindrical shape is shown. However, for example, the two-dimensional matrix can be left as it is in a flat plate shape. In this case, the flat panel may be moved in accordance with the rotation of the developing roll 33, and at the time of transfer, at least one of the transfer device 24 or the flat panel may be moved, and the recording material 28 moves around the transfer device 24. It only needs to be able to move. Alternatively, the toner image on the flat panel may be temporarily transferred to the intermediate transfer member, and the transferred toner image may be transferred onto the recording material 28. Needless to say, it is possible to apply a voltage corresponding to the image signal to the pixel electrode 64 during transfer or cleaning.

As described above, also in this embodiment, the toner amount density on the developing roll 33 can be made larger than the toner amount density on the intermediate roll 34, and the image density can be increased accordingly. . In addition, low-charge toner and reverse polarity toner are rarely generated in the development region, and the same effect as in the first embodiment can be obtained in that fog and toner cloud can be effectively prevented.
In addition, since the charging step is not required by using the matrix panel 60, it is not necessary to consider the adverse effect due to the charging device itself being contaminated with toner and causing a charging failure or the discharging of the charging device. Furthermore, since the position of the image is determined by the pixel electrode 64, the occurrence of image defects such as density unevenness, color unevenness, and streaks can be suppressed, and the image quality can be improved.

As described above, in the first to third embodiments, a so-called single-color image forming apparatus has been described. For example, an image forming apparatus capable of forming a color image by arranging such image forming units in parallel. It is also possible to do. In this case, the photosensitive member and the image holding member may be arranged in parallel to the belt-shaped or drum-shaped intermediate transfer member, or the photosensitive member and the image holding member are arranged in parallel to the recording material conveyance member. However, the toner image may be directly transferred onto the recording material.
Furthermore, a plurality of developing devices may be arranged in parallel for one photoconductor (image holding member).

Example 1
In order to confirm the effect of the resistance of the intermediate roll on the generation of WST during charge injection, the following experiment was performed.
In the combination of the charge injection roll and the intermediate roll of the first embodiment, the relationship between the electric field applied to the conductive toner (particle layer applied electric field: equivalent to the charge injection electric field) and the WST occurrence rate was evaluated.
As the injection electrode (charge injection roll), aluminum (untreated) was used as it was and rotated at a peripheral speed of 210 mm / s. On the other hand, as an intermediate electrode (intermediate roll), a roll having a 20 μm thick high-resistance elastic layer (hardness: Asker C hardness = 50 degrees) on the surface was rotated at a peripheral speed of 120 mm / s.
The conductive toner was coated with 15 wt% ITO fine particles on the surface of the insulating toner, and further provided with a latex coating layer to obtain particles having a particle diameter of 6.5 μm.
The volume resistivity of the high resistance layer of the intermediate roll was obtained as shown in FIG.

As a result, as shown in FIG. 20, it was found that when the volume resistivity is 9.5 (Log Ωcm), the WST generation rate is large, and when the volume resistivity is 11 (Log Ωcm) or more, the WST generation rate is small. The electric field applied to the particle layer is 1. It was also found that in the vicinity of E + 04 (V / cm), the volume resistivity is 11 (Log Ωcm) or more and the WST generation rate is within about 5%.
Thereafter, evaluation was performed by further increasing the number of samples, and it was confirmed that the WST generation rate could be kept at a practically satisfactory level if the volume resistivity of the intermediate roll was 11 (Log Ωcm) or more.

The performance required for the intermediate roll and the developing roll is such that the potential applied to the roll itself is low, easily self-discharge, easy to control against overcurrent, and does not adversely affect toner charging control. And so on. Therefore, if the volume resistivity is set within the range of 10 ⁹ to 10 ¹¹ Ω · cm, the self-discharge property and the overcurrent control can be satisfied. However, from the result of FIG. The charge controllability of the toner is poor and reverse polarity toner is likely to be generated.
Accordingly, the intermediate roll that contributes to charge injection has a volume resistivity of 10 ¹¹ Ω · cm or more, and in this case, complete self-discharge becomes difficult. Therefore, it is preferable to provide a static elimination mechanism. A developing roll that does not participate in toner charge control can obtain a good effect by setting the volume resistivity to 10 ⁹ to 10 ¹¹ Ω · cm.

◎ Comparative Example 1
This comparative example assumes a mode in which charge is injected between a development roll and a charge injection roll without using an intermediate roll, and a toner layer of a single layer or less is held on the development roll as a comparative configuration. As a measure for ensuring the image density of the toner, it was evaluated how the toner amount (development toner amount) on the photoreceptor changes by changing the peripheral speed of the developing roll.
FIG. 21 shows the dependency of the peripheral speed when the potential on the photosensitive member side is 25 V, the developing bias applied to the developing roll is 15 V, and the toner amount on the developing roll is 3 g / m ² .

  According to this, it was found that when the peripheral speed ratio exceeds 2, no increase in the developing toner amount is observed. This is thought to be because the toner is scraped off by the rubbing between the developing roll and the photoconductor, and this measure not only provides the desired image density but also reduces the image quality such as fine line reproducibility and graininess. To come. Therefore, the usefulness of the intermediate roll of the present invention was understood.

◎ Comparative Example 2
This comparative example evaluates the change in the toner amount on the photosensitive member when the toner amount on the developing roller is changed when the peripheral speed of the developing roller is twice that of the photosensitive member, based on the result of Comparative Example 1. It is a thing.
The toner amount (development toner amount) on the photoconductor when the potential on the photoconductor side is 25 V, the development bias applied to the development roll is 15 V, and the toner amount on the development roll is changed is as shown in FIG. .
According to this, it was found that even when the peripheral speed ratio is 2, the amount of developing toner increases.

  Therefore, it is possible to increase the amount of toner on the photosensitive member in this way, but increasing the amount of toner on the developing roll in the comparative configuration results in an increase in reverse polarity toner, and fogging and the like. The image quality is degraded. On the other hand, according to the present invention, it is possible to increase the amount of toner on the developing roll without generating reverse polarity toner, thereby preventing deterioration in image quality such as fogging and obtaining a sufficient image density. Is better understood.

◎ Comparative Example 3
In this comparative example, as in the third embodiment, a two-dimensional matrix panel using TFTs is used, and the relationship between the potential on the pixel electrode side and the toner amount is evaluated using a developing device model.
As a developing device model, as shown in FIG. 23, a two-dimensional matrix panel was used as an image carrier, and the potential of the pixel electrode was changed between 0 and 25 V in consideration of the breakdown voltage of the TFT. A 1 μm thick SiO ₂ layer was formed as a protective layer on the panel surface and moved at 130 mm / sec.

The developing roll was provided with an elastic layer having a thickness of 10 μm, a volume resistivity of 10 ¹¹ Ω · cm, and an Asker C hardness of 40 degrees on the surface.
Further, instead of the charge injection roll, an aluminum plate was used so that it could move at a speed 1.75 times the peripheral speed of the developing roll.
Further, 100 V was applied as a charge injection voltage between the developing roll and the aluminum plate, and 15 V was applied as a developing bias to the developing roll.
The toner used had a particle size of 6.5 μm, with an insulating coating layer around the conductive toner substrate.

FIG. 24 shows the result of evaluating the toner amount (developed toner amount) on the panel so that the same potential is applied to the entire pixel electrode. The broken line (comparative example) shows the pixel electrode when the developing bias is 15V. Shows the change in the amount of toner (development toner amount) adhering to the panel depending on the potential of. Therefore, even when the pixel electrode potential is 20 V, the developing toner amount is 4 g / m ² , and does not reach 5 g / m ² or more.
In other words, in order to set the developing bias to 15 V and the developing toner amount to 5 g / m ² or more, it is necessary to set conditions in a range above the solid line (target) in the figure, and the developing sensitivity is about 1 from the broken line part. It turns out that a 6-fold improvement is necessary.

In other words, in a two-dimensional matrix panel using TFTs, the breakdown voltage of the TFT is low and the output potential is about 25 V at maximum. However, considering reliability and the breakdown voltage of the control driver, about 15 V is practically the maximum. Become. Therefore, it is necessary to be able to develop at a low potential during development. In the method of charging by charge injection, the toner charge amount can be kept low and the toner can be uniformly charged. Therefore, it is suitable to use such toner for a two-dimensional matrix panel. However, in order to obtain a developing toner amount of 5 g / m ² or more which is generally required, a pixel electrode potential of 25 V is required. Therefore, it is necessary to improve the development sensitivity.

  On the other hand, in the present invention, since the toner amount on the developing roll can be increased by the intermediate roll, it is easy to increase the toner amount (developing toner amount) moved from the developing roll as in Comparative Example 2. Thus, the development sensitivity can be improved. For this reason, it is possible to provide a developing device suitable for those using a two-dimensional matrix panel.

1 is an explanatory diagram showing an overview of an image forming apparatus according to an embodiment model embodying the present invention. It is explanatory drawing which shows the effect | action of embodiment model. 1 is an explanatory diagram showing an overview of an image forming apparatus according to Embodiment 1. FIG. FIG. 2 is an explanatory diagram illustrating an outline of a developing device according to the first embodiment. (A) and (b) are explanatory views showing the structure of the conductive toner used in the first embodiment. It is explanatory drawing which shows the relationship between the electric field applied to the particle layer with respect to the conventional conductive toner, and a WST generation rate. It is explanatory drawing which shows typically the behavior at the time of charge injection (at the time of a low electric field effect | action) of the conventional conductive toner. It is explanatory drawing which shows typically the behavior at the time of charge injection (at the time of a high electric field effect | action) of the conventional conductive toner. (A) (b) is explanatory drawing which shows the solution with respect to the technical subject at the time of the charge injection of a conductive toner (at the time of a low electric field effect | action). (A)-(c) is explanatory drawing which shows the solution with respect to the technical subject at the time of the charge injection of a conductive toner (at the time of a high electric field effect | action). (A)-(d) is explanatory drawing which shows the motion of the toner in each process. FIG. 7 is an enlarged explanatory diagram illustrating toner movement in a moving process. FIG. 10 is an explanatory diagram illustrating an overview of a developing device according to a second embodiment. FIG. 6 is a perspective view illustrating an outline of a photoconductor according to a third embodiment. (A) and (b) are explanatory views showing the internal structure of the photoreceptor of the third embodiment. FIG. 4 is an explanatory diagram showing a pixel structure of Embodiment 3, where (a) shows a pixel group, (b) shows one pixel, and (c) shows a connection between the pixels. FIG. 10 is an explanatory diagram illustrating a configuration of a matrix panel of a photoreceptor according to a third embodiment. (A)-(e) is explanatory drawing which shows the effect | action of Embodiment 3. FIG. FIG. 3 is an explanatory diagram illustrating a method for calculating a volume resistivity of Example 1. 3 is a graph showing the results of Example 1. 6 is a graph showing the results of Comparative Example 1. 10 is a graph showing the results of Comparative Example 2. FIG. 10 is an explanatory diagram illustrating a developing device model of Comparative Example 3. 10 is a graph showing the results of Comparative Example 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image holding body, 2 ... Conductive toner, 3 ... Toner holding body, 4 ... Development toner holding body, 5 ... Intermediate toner holding body, 6 ... Development electric field formation means, 7 ... Charge injection means, 8 ... Charge injection member

Claims (11)

A developing device that visualizes an electrostatic latent image held on the surface of an image carrier with a conductive toner,
A toner holder that is disposed opposite to the image holder and holds and conveys charged conductive toner;
A developing electric field forming means for forming a developing electric field in a developing region between the toner holder and the image holder;
The toner holding member has a charge injection member disposed opposite to the side different from the image holding member, and an electric charge injection electric field is applied between the charge injection member and the toner holding member to cause uncharged conduction. Charge injection means for injecting charges into the conductive toner,
The toner holder is
An electrostatic latent image on the image carrier is provided so as to be rotatable in opposition to the image carrier, and holds and conveys conductive toner to the development region and applies a development electric field to the development region by a development electric field forming unit. A developing toner holder for developing the image with conductive toner;
Opposite to the developing toner holding member, the developing toner holding member is provided so as to be rotatable at a higher rotational speed than the developing toner holding member. An intermediate toner holder for holding and transporting conductive toner,
A moving electric field forming means provided between the developing toner holding member and the intermediate toner holding member causes a moving electric field to move the conductive toner from the intermediate toner holding member to the developing toner holding member. A developing device comprising: The developing device according to claim 1,
The developing device according to claim 1, wherein the charge injection unit injects the charge into the conductive toner by rubbing and rubbing the conductive toner while applying a charge injection electric field. The developing device according to claim 1,
The developing device according to claim 1, wherein the toner holding member is set so that the developing toner holding member and the intermediate toner holding member rotate in different directions from each other at the facing portion. The developing device according to claim 1,
The conductive toner changes to a high resistance so as to maintain the charge retention property of the conductive toner in the development region, and the resistance of the conductive toner decreases to facilitate the charge injection of the conductive toner in the electric field region where the electric charge is applied. A developing device that changes. The developing device according to claim 4.
The developing apparatus according to claim 1, wherein the conductive toner is a conductive toner base coated with an insulating or semiconductive coating layer. The developing device according to claim 1,
The developing device, wherein the intermediate toner holding member is coated with a surface layer having a larger volume resistivity than the developing toner holding member. The developing device according to claim 1 or 6,
The developing device, wherein the intermediate toner holding member is coated with a surface layer having a volume resistivity of 10 ¹¹ Ω · cm or more in a charge injection electric field. The developing device according to claim 1,
And a neutralizing member that is disposed in contact with the intermediate toner holding member and neutralizes the surface of the intermediate toner holding member. The developing device according to claim 8, wherein
The developing device according to claim 1, wherein the charge eliminating member also serves as a toner supply member that supplies conductive toner to the intermediate toner holding member. An image carrier for forming and holding an electrostatic latent image;
An image forming apparatus comprising: the developing device according to claim 1 provided to face the image holding member to develop an electrostatic latent image on the image holding member. An image carrier having a movable support and a pixel electrode group supported by the support and arranged vertically and horizontally in pixel units;
Latent image forming means for forming a latent image corresponding to an image signal for each of the pixel electrodes of the pixel electrode group;
An image forming apparatus comprising: the developing device according to claim 1, wherein the developing device is provided to face the image holding member and develops a latent image on the image holding member with toner.

Images