JP2010191208A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for suppressing a change with time in image quality caused by the fact that a developing electric field is changed with time even if a developing device for bringing a toner into a flare state on the insulative circumferential surface of a toner carrier is used. <P>SOLUTION: The developing device carries the toner on the insulative circumferential surface of the toner carrying roller provided with an inner electrode and an outer electrode and applies voltages different from each other to the inner electrode and the outer electrode to form an electric field (flare electric field) for hopping the toner in the circumferential surface portion of the toner carrying roller facing the inner electrode and the outer electrode outside the circumferential surface of the toner carrying roller. In the developing device, such a voltage that a potential difference between the surface of a toner supply roller supplying the toner to the circumferential surface of the toner carrying roller and the circumferential surface of the toner carrying roller is an electric discharge start voltage or higher is applied to the toner supply roller. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a copying machine that forms an image by finally transferring an image obtained by developing a latent image onto a recording material by feeding toner carried on an outer peripheral surface of a toner carrying member into a developing region. The present invention relates to an image forming apparatus such as a printer or a facsimile.

2. Description of the Related Art Conventionally, developing devices having a toner carrier having a plurality of electrodes to which different voltages are applied are known.
For example, there is a developing device that performs development by supplying toner to a latent image on a latent image carrier without directly contacting the toner on the toner carrier with a latent image carrier such as a photoconductor. As an example of this developing device, there is one that employs a system that supplies toner onto a latent image carrier by clouding the toner on the toner carrier. In the toner carrier used in this method, a plurality of types of electrodes are arranged at a predetermined pitch along the outer peripheral surface, and the outer peripheral surface side of the plurality of types of electrodes is covered with a protective layer. When different voltages that change with time are applied to the plurality of types of electrodes, respectively, and a time-changing electric field is formed between the plurality of types of electrodes that are close to each other, the electric field causes the toner on the toner carrier. Can be made to fly (hopping) between a plurality of types of electrodes close to each other (this phenomenon of toner flying is hereinafter referred to as “flare”). As a result, the toner is clouded in a space near the outer peripheral surface of the toner carrier.

  In this type of developing device, in order for the toner to hop without adhering to the outer peripheral surface of the toner carrier, an electric field (hereinafter referred to as “hereinafter referred to as“ electric field ”) formed between a plurality of types of electrodes adjacent to each other on the outer peripheral surface of the toner carrier. The magnitude relationship between the force F1 received by the toner from the “flare electric field” and the adhesion force F2 between the toner and the outer peripheral surface of the toner carrier becomes important. If F2 is larger than F1, the toner cannot escape from the adhesive force with the outer peripheral surface of the toner carrier and does not hop. If F1 is larger than F2, the toner can be hopped. The larger the difference between F2 and F1, the more stable the flare state can be realized. If F1 is increased, this difference can be increased so that a stable flare state can be realized. However, in order to increase F1, it is necessary to increase the flare electric field formed on the outer peripheral surface of the toner carrier.

  Patent Document 1 discloses a developing device in which two types of electrodes for forming a flare electric field are provided concentrically on a roller-shaped toner carrier. The toner carrier used in this developing device is one in which two types of comb-shaped electrodes are arranged along the outer peripheral surface so that the respective comb-tooth portions enter between the mating comb-tooth portions. Then, by applying the voltage described above to each type of electrode, the toner can fly between the comb teeth portions, and a flare state can be realized.

  Patent Document 2 discloses a roller-shaped toner carrier including three types of electrodes for forming a flare electric field. In this toner carrier, two of the three types of electrodes are provided on a concentric circle, but the remaining one type of electrode is arranged on the outer peripheral surface side of the two types of electrodes. Even in the developing device using the toner carrier, by applying three-phase voltages having different phases to the respective types of electrodes, the toner can fly between the various electrodes, and a flare state can be realized.

Thus, the outer peripheral surface of the toner carrier for hopping the toner generally needs to be an insulating surface by coating an insulating layer. The main reason is that some conductive member (such as a regulating blade for regulating the toner layer thickness) comes into contact with the electrode for forming the flare electric field formed along the outer peripheral surface of the toner carrier, This is to prevent leakage through the conductive member.
However, as a result of research by the present inventors, it has been found that the following problem arises because the outer peripheral surface of the toner carrier must be an insulating surface.

That is, when the outer peripheral surface of the toner carrier is insulative, the toner hops and repeatedly comes into contact with the outer peripheral surface of the toner carrier, so that the insulating outer peripheral surface of the toner carrier is charged by frictional charging with the toner. It is charged up to a polarity opposite to the charged polarity. For this reason, the absolute value of the surface potential of the toner carrier gradually increases with repeated development. As a result, there arises a problem that the image quality changes with time due to the gradual change in the magnitude of the developing electric field formed in the developing region.
This problem may occur even in a general one-component development method in which toner is not hopped. However, in the general one-component development method, the outer peripheral surface of the toner carrier does not necessarily have to be insulative. . Therefore, the surface layer of the toner carrying member can be constituted by, for example, a medium resistance layer lower than the resistance value of the insulating layer. According to this configuration, the surface layer is generated by charge-up without causing any problem. The electric charge on the outer peripheral surface of the toner carrying member can be released to some conductive member (such as a regulating blade for regulating the toner layer thickness) in contact therewith. That is, in the case of a general one-component developing method, the above-described problem due to charge-up can be solved by a simple method in which the surface layer of the toner carrier is formed of a medium resistance layer.
However, in the development method in which the toner is in a flare state, if the surface layer of the toner carrier is composed of a medium resistance layer, the flare electric field generated on the outer peripheral surface of the toner carrier is less than when the surface layer is composed of an insulating layer. The size becomes small, and it becomes difficult to hop toner. This is presumably because when the surface layer of the toner carrier is formed of a medium resistance layer, the electric field moves in the surface layer, and the flare electric field strength is weakened by the moved electric charge. In addition, when a larger bias is applied to a plurality of types of electrodes of a toner carrier having a surface layer formed of a medium resistance layer in an attempt to form a large flare electric field, the insulation between the electrodes is destroyed and leakage between the electrodes occurs. May occur, and the flare electric field itself may not be formed.

  The present invention has been made in view of the above problems, and an object of the present invention is to develop a developing electric field over time even when a developing device that flares toner on the insulating outer peripheral surface of the toner carrier is used. An object of the present invention is to provide an image forming apparatus capable of suppressing a change in image quality over time due to a change.

In order to achieve the above object, the invention according to claim 1, the toner is carried on the insulating outer peripheral surface of the latent image carrier and the toner carrier comprising a plurality of types of electrode members to which different voltages are applied. By applying different voltages to the plurality of types of electrode members, an electric field for hopping the toner at the outer peripheral surface portion of the toner support facing each of the plurality of types of electrode members is applied to the outer periphery of the toner support The outer surface of the toner carrier is formed on the outer surface of the toner carrier, and the toner in a hopped state is fed into the development area by moving the toner carrier, and the latent image on the latent image carrier is supplied with toner. An image forming apparatus for forming an image on the recording material by finally transferring the image obtained by developing the latent image onto the recording material. the above A toner supply member for supplying toner to the outer peripheral surface of the toner carrier, and a voltage at which a potential difference between the surface of the toner supply member and the outer peripheral surface of the toner carrier is equal to or higher than a discharge start voltage; A voltage supply means for applying to the toner supply member is provided.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the outer peripheral surface of the toner carrier is formed of an insulating material that imparts a charge having a normal charge polarity to the toner by friction with the toner. It is characterized by.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the surface layer of the toner supply member is a sponge layer in which a large number of micropores are dispersed on the surface. It is.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, a speed difference occurs at a contact portion between the surface of the toner supply member and the outer peripheral surface of the toner carrier. Thus, the toner supply member has a driving means for moving the surface.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the toner carrier has the plurality of types of electrode members parallel to the normal direction of the outer peripheral surface of the toner carrier. It is characterized by being arranged at different positions in different directions and having an insulating layer interposed between the plurality of types of electrode members.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, a plurality of the developing devices are provided, and latent images corresponding to the respective colors with different color toners by the respective developing devices. Each color image is developed, and each color image obtained thereby forms a color image overlapping each other.

In the present invention, a discharge can be generated between the surface of the toner supply member and the outer peripheral surface of the toner carrier. This discharge can remove (or erase or neutralize) the charge on the insulating outer peripheral surface of the toner carrier that has been charged up by the toner hopping and repeatedly contacting the outer peripheral surface of the toner carrier.
Therefore, according to the present invention, even when a developing device that flares toner on the insulating outer peripheral surface of the toner carrier is used, it is possible to suppress changes in image quality over time due to changes in the developing electric field over time. The excellent effect that it becomes possible is obtained.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment. 2 is a schematic configuration diagram illustrating a developing device in the image forming apparatus. FIG. FIG. 6 is a schematic diagram when the toner carrying roller is viewed from a direction orthogonal to the rotation axis in order to explain the electrode arrangement of the toner carrying roller of the developing device. FIG. 4 is a partial cross-sectional view schematically showing a cross section of the toner carrying roller when cut along a plane orthogonal to the rotation axis. 4 is a graph showing an example of an inner voltage and an outer voltage applied to an inner electrode and an outer electrode of the toner carrying roller, respectively. It is a graph which shows the other example of the inner side voltage applied to an inner side electrode and an outer side electrode, and an outer side voltage. It is a graph which shows the further another example of the inner side voltage applied to an inner side electrode and an outer side electrode, and an outer side voltage. It is a schematic diagram when the electric power feeding structure to an inner side electrode and an outer side electrode is cut | disconnected along a roller axis | shaft. It is a perspective view which shows the same electric power feeding structure typically. In the first embodiment, in the charged state, the potential V1 ′ of the surface portion of the toner carrying roller facing the inner electrode, the potential V2 ′ of the surface portion of the toner carrying roller facing the outer electrode, and the supply applied to the toner supply roller It is a graph which shows the voltage VK. 6 is a graph of an example in which the supply voltage applied to the toner supply roller is an AC voltage in Example 1. In Example 2, in the charged state, the potential V1 ′ of the surface of the toner carrying roller facing the inner electrode, the potential V2 ′ of the surface of the toner carrying roller facing the outer electrode, and the supply applied to the toner supply roller It is a graph which shows the voltage VK. FIG. 10 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller in Modification 1 is cut along a plane orthogonal to the rotation axis thereof. FIG. 3 is an explanatory diagram illustrating an outline of electric lines of force in the toner carrying roller. FIG. 10 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller in Modification 2 is cut along a plane orthogonal to the rotation axis thereof. FIG. 3 is an explanatory diagram illustrating an outline of electric lines of force in the toner carrying roller. FIG. 4 is a schematic diagram when an outer electrode layer in the toner carrying roller is viewed from an outer peripheral surface side of the toner carrying roller. FIG. 10 is a partial cross-sectional view schematically showing a cross section when a toner carrying roller in Modification 3 is cut along a plane orthogonal to the rotation axis thereof. FIG. 4 is a schematic diagram when an outer electrode layer in the toner carrying roller is viewed from an outer peripheral surface side of the toner carrying roller. (A)-(c) is explanatory drawing which shows the manufacture procedure of a toner carrying roller. FIG. 10 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller in Modification 4 is cut along a plane orthogonal to the rotation axis thereof. FIG. 4 is a schematic diagram when an outer electrode layer in the toner carrying roller is viewed from an outer peripheral surface side of the toner carrying roller.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic image forming apparatus will be described.
First, the configuration and operation of the image forming apparatus according to the present embodiment will be described.
FIG. 1 is a schematic configuration diagram showing a main part of the image forming apparatus according to the present embodiment.
This image forming apparatus is an image forming apparatus that has a plurality of developing devices and forms a multicolor image by superimposing toner images of respective colors on a belt-like photoreceptor 1 as a latent image carrier. The belt-like photoreceptor 1 is rotationally driven in a clockwise direction in the figure by a driving unit (not shown) while being stretched around a plurality of rollers in a vertically long posture with a space in the vertical direction rather than the horizontal direction. The left tension surface (hereinafter referred to as “left tension surface”) of the photosensitive member 1 in the drawing has a posture extending substantially in the vertical direction.

  On the left side of the left-side stretched surface of the photoreceptor 1, images of a plurality of colors, for example, magenta (M), cyan (C), yellow (Y), and black (K) are provided so as to face the photoreceptor 1. Four process units 6M, 6C, 6Y, and 6K are arranged in the vertical direction as a plurality of image forming units for forming each. These four process units 6M, 6C, 6Y, and 6K include developing devices 4M, 4C, 4Y, and 4K, charging devices 2M, 2C, 2Y, and 2K that uniformly charge the photosensitive member 1, and a static eliminator (not shown). Are held in a common holding body (not shown) as one unit. The developing devices 4M, 4C, 4Y, and 4K, the charging devices 2M, 2C, 2Y, and 2K and the static eliminator are integrally attached to and detached from the housing of the image forming apparatus as process units 6M, 6C, 6Y, and 6K, respectively. Can be exchanged by the user.

  Exposure of each color by an optical writing device (not shown) as a latent image forming means from between the charging devices 2M, C, Y, K and the developing devices 4M, 4C, 4Y, 4K in the process units 6M, 6C, 6Y, 6K. Beams 3M, 3C, 3Y, and 3K are irradiated onto the photosensitive member 1. The image forming apparatus further includes a transfer unit, a cleaning unit, a paper feeding device, a fixing device, and the like (not shown).

The photosensitive member 1 is rotationally driven in the direction of the arrow in FIG. 1, uniformly charged by the magenta charging unit 2M in the magenta process unit 6M, and then modulated with magenta image data by an optical writing device (not shown). An electrostatic latent image is formed by exposure with the exposure beam 3M. The electrostatic latent image is developed by the magenta developing device 4M to become a magenta toner image. Thereafter, the photoreceptor 1 is neutralized by a neutralizer (not shown).
Next, the photoreceptor 1 is uniformly charged by a cyan charging unit 2C in a cyan process unit 6C, and then exposed by an exposure beam 3C modulated by cyan image data by an optical writing device (not shown). Thus, a cyan electrostatic latent image is formed. The electrostatic latent image is developed by the cyan developing device 4C to become a cyan toner image overlapping the magenta toner image. Thereafter, the photoreceptor 1 is neutralized by a neutralizer (not shown).
Further, the photoreceptor 1 is uniformly charged by the yellow charging unit 2Y in the yellow process unit 6Y, and then exposed by the exposure beam 3Y modulated by the yellow image data by an optical writing device (not shown). As a result, a yellow electrostatic latent image is formed. The electrostatic latent image is developed by the yellow developing device 4Y to become a yellow toner image overlapping the magenta toner image and the cyan toner image. Thereafter, the photoreceptor 1 is neutralized by a neutralizer (not shown).
Finally, the photoreceptor 1 is uniformly charged by the black charging device 2K in the black process unit 6K, and then exposed by the exposure beam 3K modulated by the black image data by an optical writing device (not shown). As a result, a black electrostatic latent image is formed. The electrostatic latent image is developed by the black developing device 4K to form a black toner image overlapping the magenta toner image, the cyan toner image, and the yellow toner image, thereby forming a full color image.

  On the other hand, a recording material such as recording paper is fed from a paper feeding device (not shown), and a full color image on the photoreceptor 1 is transferred to the recording material by a transfer roller as a transfer means to which a transfer bias is applied. The The recording material onto which the full color image has been transferred is fixed to the full color image by a fixing device (not shown) and discharged to the outside. Residual toner and the like are removed from the photoreceptor 1 by a cleaning unit (not shown) after the transfer of the full-color image.

In the image forming apparatus having such a configuration, four colors are written on the same photoconductor 1, so that a general tandem system in which toner images on each photoconductor are superposed by transfer using four photoconductors. Compared with the image forming apparatus, there is almost no positional deviation between the toner images, and a high-quality full-color image can be obtained.
The present invention can be applied to a general tandem type image forming apparatus, and can also be applied to other image forming apparatuses.

Next, the developing device employed in the image forming apparatus of the present embodiment will be described.
Since the developing devices 4M, 4C, 4Y, and 4K have the same configuration and operation except that the toner to be stored is different, the subscripts M, C, Y, and K will be omitted below.

FIG. 2 is a schematic configuration diagram of the developing device 4 according to the present embodiment.
The developing device 4 includes a toner carrier roller 41 as a toner carrier, a toner supply roller 42 as a toner supply member that supplies toner to the toner carrier roller 41, and a regulation blade as a toner regulation member that regulates the toner layer thickness. 43, an inlet seal 44, a first conveying screw 45 that is driven to rotate clockwise in the figure, and a second conveying screw 46 that is driven to rotate counterclockwise in the figure. The second conveying screw 46 conveys the toner from the near side in the figure to the far side in the figure by its rotational driving. The toner transported to the vicinity of the end on the back side in the figure enters the first transport screw 45 side, and is transported from the back side in the figure to the near side in the figure by the rotational drive of the first transport screw 45 this time. . Part of the toner being conveyed by the first conveying screw 45 moves toward the toner supply roller 42 and is carried on the surface of the toner supply roller 42. The toner carried on the surface of the toner supply roller 42 is brought into contact with the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 as the toner supply roller 42 rotates in the counterclockwise direction in FIG. Hereinafter, the toner is conveyed to a “toner supply position”.

  At the toner supply position, the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 are moved in opposite directions (counter direction). Therefore, the toner on the toner supply roller 42 conveyed to the toner supply position is rubbed against the outer peripheral surface of the toner carrying roller 41 and moves to the outer peripheral surface of the toner carrying roller 41. At this time, the toner is charged to the normal polarity (negative polarity in this embodiment) side by friction with the outer peripheral surface of the toner carrying roller 41.

  The toner carrying roller 41 supplied with the toner exposes a part of the outer peripheral surface from an opening provided in the casing of the developing device 4. This exposed portion is opposed to the photoreceptor 1 with a gap of several tens to several hundreds [μm]. In this way, the region where the toner carrying roller 41 and the photosensitive member 1 face each other is a development region in the image forming apparatus.

  The toner supplied on the surface of the toner carrying roller 41 is hopped on the surface of the toner carrying roller 41 for the reason described later, and moves from the toner supply position toward the developing position as the toner carrying roller 41 rotates. Be transported. The toner conveyed to the development area adheres to the electrostatic latent image portion on the surface of the photosensitive member due to the developing electric field between the toner carrying roller 41 and the electrostatic latent image on the photosensitive member 1, thereby developing the toner. Is called. The toner that has not contributed to the development is further conveyed by the rotation of the toner carrying roller 41 while hopping, and is carried to the toner supply position. Then, when entering the toner supply position, the toner supply roller 42 scrapes off the toner carrying roller 41 so that the toner is returned to the inside of the casing of the developing device 4 and reused.

Next, a specific configuration of the toner carrying roller 41 in the present embodiment will be described.
FIG. 3 is a schematic diagram when the toner carrying roller 41 is viewed from a direction orthogonal to the rotation axis in order to explain the electrode arrangement of the toner carrying roller 41 in the present embodiment. For convenience of explanation, the surface layer 56 and the insulating layer 55 are not shown.
FIG. 4 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller 41 according to the present embodiment is cut along a plane orthogonal to the rotation axis thereof.
The toner carrying roller 41 of the present embodiment is configured by a hollow roller member, and is provided with an innermost electrode member located on the innermost periphery or an inner electrode 53a as an innermost electrode member, and on the outermost periphery side. A comb-like outer electrode 54a is provided as an outermost peripheral electrode member that is positioned and to which a voltage (outer voltage) different from a voltage (inner voltage) applied to the inner electrode 53a is applied. Further, an insulating layer 55 is provided between the inner electrode 53a and the outer electrode 54a to insulate them. A surface layer 56 that covers the outer peripheral surface side of the outer electrode 54a is also provided. That is, the toner carrying roller 41 of the present embodiment has a four-layer structure of the inner electrode 53a, the insulating layer 55, the outer electrode 54a, and the surface layer 56 in order from the inner peripheral side.

  The inner electrode 53a also functions as a base of the toner carrying roller 41, and is a metal roller obtained by molding a conductive material such as SUS or aluminum into a cylindrical shape. In addition, as a configuration of the inner electrode 53a, a structure in which a conductive layer made of a metal layer such as aluminum or copper is formed on the surface of a resin roller made of polyacetal (POM), polycarbonate (PC), or the like. As a method of forming this conductive layer, a method of forming by metal plating, vapor deposition, or the like, a method of adhering a metal film to the roller surface, or the like can be considered.

  The outer peripheral surface side of the inner electrode 53 a is covered with an insulating layer 55. In the present embodiment, the insulating layer 55 is made of polycarbonate, alkyd melamine, or the like. In the present embodiment, the thickness of the insulating layer 55 is preferably in the range of 3 [μm] to 50 [μm]. If it is smaller than 3 [μm], the insulation between the inner electrode 53a and the outer electrode 54a cannot be sufficiently maintained, and there is a high possibility that leakage occurs between the inner electrode 53a and the outer electrode 54a. Become. On the other hand, if it is larger than 50 [μm], the electric field created between the inner electrode 53a and the outer electrode 54a becomes difficult to form outside the surface layer 56, and a strong flare electric field (external electric field) is formed outside the surface layer 56. ) Is difficult to form. In the present embodiment, the thickness of the insulating layer 55 made of melamine resin is 20 [μm]. The insulating layer 55 can be formed with a uniform film thickness on the inner electrode 53a by a spray method, a dip method or the like.

  An outer electrode 54 a is formed on the insulating layer 55. In the present embodiment, the outer electrode 54a is formed of a metal such as aluminum, copper, or silver. Various methods are conceivable as a method for forming the comb-shaped outer electrode 54a. For example, there is a method in which a metal film is formed on the insulating layer 55 by plating or vapor deposition, and a comb-like electrode is formed by photoresist etching. A method of forming a comb-like electrode by attaching a conductive paste on the insulating layer 55 by an ink jet method or screen printing is also conceivable.

  The outer peripheral surfaces of the outer electrode 54 a and the insulating layer 55 are covered with an insulating surface layer 56. When the hopping is repeated on the surface layer 56, the toner is charged by contact friction with the surface layer 56. In this embodiment, silicone, nylon (registered trademark), urethane, alkyd melamine, polycarbonate, or the like is used as a material for the surface layer 56 in order to give the toner a normal charging polarity (negative polarity in the present embodiment). In this embodiment, polycarbonate is employed. Further, since the surface layer 56 also has a role of protecting the outer electrode 54a, the film thickness of the surface layer 56 is preferably in the range of 3 [μm] or more and 40 [μm] or less. If it is smaller than 3 [μm], the outer electrode 54a may be exposed due to film scraping or the like due to use over time, and may leak through the toner carried on the toner carrying roller 41 or other members contacting the toner carrying roller 41. There is. On the other hand, if it is larger than 40 [μm], the electric field generated between the inner electrode 53a and the outer electrode 54a is hardly formed outside the surface layer 56, and a strong flare electric field is formed outside the surface layer 56. It becomes difficult. In this embodiment, the film thickness of the surface layer is 20 [μm]. The surface layer 56 can be formed by a spray method, a dipping method, or the like, similarly to the insulating layer 55.

  In the present embodiment, the electric field created between the inner electrode 53a and the outer electrode 54a, more specifically, the portion of the inner electrode 53a that does not face the outer electrode 54a (the inner side located between the comb teeth of the outer electrode 54a). The electric field created between the electrode 53a portion and the comb-teeth portion of the outer electrode 54a is formed outside the surface layer 56, thereby hopping the toner on the toner carrying roller 41, thereby clouding the toner. Make it. At this time, the toner on the toner carrying roller 41 flies between the surface layer portion facing the inner electrode 53a via the insulating layer 55 and the surface layer portion facing the outer electrode 54a adjacent thereto. Hopping is performed so as to reciprocate.

  In order to stably make the toner cloud, it is important to form a flare electric field of a corresponding magnitude. To form such a large flare electric field, the inner electrode 53a and the outer electrode 54a It is necessary to form a large potential difference between them. However, in order to stably form such a large potential difference, it is important to stably and effectively insulate between the inner electrode 53a and the outer electrode 54a to prevent leakage.

  Here, when two types of electrodes for forming a flare electric field are each formed in a comb-like shape and arranged concentrically, and each comb-tooth portion is configured to enter between the other comb teeth, the comb If the formation quality of the tooth-like electrode is poor, the insulation between the two kinds of electrodes is remarkably lowered, and leakage is likely to occur. Specifically, for example, when an electrode is formed by etching, a part of the metal film to be removed remains, or when an electrode is formed by an ink jet method or a screen printing method, a conductive paste adheres between the electrodes. Can happen. When such a situation occurs, leakage easily occurs between the two types of electrodes, and an appropriate flare electric field cannot be formed. In this configuration, even if the comb-like electrodes are formed with high quality on the resin surface of the roller, the outer peripheral surface side is covered with an insulating material after the two types of comb-like electrodes are formed. In order to obtain insulation between the electrodes by filling the insulating material, the interface between the resin surface of the roller and the insulating material is formed between the electrodes, and leakage through this interface is likely to occur, and a relatively large voltage is applied. The insulation between the electrodes is significantly reduced.

According to the present embodiment, since the insulating layer 55 is provided on the inner electrode 53a and the comb-shaped outer electrode 54a is formed on the insulating layer, it may cause a leak between these electrodes. There is no such interface. Further, in the manufacturing stage of the toner carrying roller 41, the possibility that a conductive material that may cause a leak is interposed between the electrodes can be extremely reduced. Therefore, according to the present embodiment, the inner electrode 53a and the outer electrode 54a can be stably and effectively insulated, and leakage can be effectively prevented even when a relatively large voltage is applied.
The present invention is an example in which two kinds of electrodes for forming a flare electric field are each formed in a comb-like shape and arranged concentrically so that each comb-tooth portion enters between the other comb-tooth. It is also applicable to.

  In the present embodiment, the electrode width of the outer electrode 54a (the width of each comb tooth portion) is preferably 10 [μm] or more and 120 [μm] or less. If it is smaller than 10 [μm], the electrode may be too thin and the electrode may be disconnected in the middle. On the other hand, if it is larger than 120 [μm], the voltage at a location where the distance from the power-supplied portion 54b of the outer electrode 54a is low, and it becomes difficult to hop toner stably and effectively at that location. As shown in FIG. 3, the power-supplied portions 54 b of this embodiment are provided at both ends in the axial direction on the outer peripheral surface of the toner carrying roller 41. Therefore, in the present embodiment, when the electrode width of the outer electrode 54a is larger than 120 [μm], the flare electric field at the central portion in the axial direction of the toner carrying roller 41 is relatively lower than the flare electric fields at both axial end portions, It becomes difficult to hop the toner carried in the central portion in the axial direction stably and effectively.

In the present embodiment, it is preferable that the electrode pitch (distance between the comb teeth portions) of the outer electrode 54a is equal to or wider than the electrode width. If it is smaller than the electrode width, most of the lines of electric force from the inner electrode 53a converge on the outer electrode 54a before coming out of the outer surface layer 56, and the flare electric field formed outside the outer surface layer 56 becomes weaker. Because it will end up. On the other hand, if the electrode pitch is large, the flare electric field at the center between the electrodes becomes weak. In the present embodiment, the electrode pitch is preferably within the range of not less than the electrode width and not more than 5 times the electrode width.
In this embodiment, both the electrode width and the electrode pitch are set to 80 [μm].

  In the present embodiment, the electrode pitch of the outer electrode 54 a is set to be constant over the circumferential direction of the toner carrying roller 41. By making the electrode pitch constant, the flare electric field created between the inner electrode 53 a and the outer electrode 54 a becomes substantially uniform over the circumferential direction on the toner carrying roller 41. Therefore, it is possible to achieve uniform toner hopping in the circumferential direction at the development position, and uniform development is possible.

Next, the voltage applied to the inner electrode 53a and the outer electrode 54a will be described.
An inner voltage as a first voltage and an outer voltage as a second voltage are applied to the inner electrode 53a and the outer electrode 54a on the toner carrying roller 41 from pulse power sources 51A and 51B, respectively. A rectangular wave is most suitable for the inner voltage and the outer voltage applied by the pulse power supplies 51A and 51B. However, not limited to this, for example, a sine wave or a triangular wave may be used. In this embodiment, the electrodes for forming the flare electrode have a two-phase configuration of the inner electrode 53a and the outer electrode 54a, and voltages having a phase difference π are applied to the electrodes 53a and 54a, respectively. The

FIG. 5 is a graph showing an example of the inner voltage and the outer voltage applied to the inner electrode 53a and the outer electrode 54a, respectively.
In the present embodiment, each voltage is a rectangular wave, and the inner voltage and the outer voltage applied to the inner electrode 53a and the outer electrode 54a, respectively, have the same magnitude (peak-to-peak voltage Vpp) that are out of phase with each other by π. Voltage. Therefore, there is always a potential difference of Vpp between the inner electrode 53a and the outer electrode 54a. Due to this potential difference, an electric field is generated between the electrodes, and the toner hops on the surface layer 56 by a flare electric field formed outside the surface layer 56 of the electric field. In the present embodiment, Vpp is preferably in the range of 100 [V] to 2000 [V]. When Vpp is smaller than 100 [V], a sufficient flare electric field cannot be formed on the surface layer 56, and it becomes difficult to stably hop the toner. On the other hand, if Vpp is larger than 2000 [V], there is a high possibility that leakage occurs between the electrodes due to use over time. In this embodiment, Vpp is set to 500 [V].
In the present embodiment, the center value V0 of the inner voltage and the outer voltage is set between the image portion potential (the potential of the electrostatic latent image portion) and the non-image portion potential (the potential of the background portion), and the development condition Depending on the situation.

  In the present embodiment, the frequency f of the inner voltage and the outer voltage is preferably 0.1 [kHz] or more and 10 [kHz] or less. If it is less than 0.1 [kHz], toner hopping may not be able to keep up with the development speed. On the other hand, if it is larger than 10 [kHz], the movement of the toner cannot follow the switching of the electric field, and it becomes difficult to stably hop the toner. In the present embodiment, the frequency f is set to 500 [Hz].

FIG. 6 is a graph showing another example of the inner voltage and the outer voltage applied to the inner electrode 53a and the outer electrode 54a.
In this example, an inner voltage similar to that shown in FIG. 5 is applied to the inner electrode 53a, but a DC voltage is applied to the outer electrode 54a. In this case, the potential difference between the electrodes is Vpp / 2. Therefore, a suitable range of Vpp in this example is 200 [V] or more and 4000 [V] or less. According to this example, it is not necessary to consider the phase difference between the inner electrode 53a and the outer electrode 54a, and the power supply cost is reduced.

FIG. 7 is a graph showing still another example of the inner voltage and the outer voltage applied to the inner electrode 53a and the outer electrode 54a.
In this example, an inner voltage similar to that shown in FIG. 5 is applied to the outer electrode 54a, but a DC voltage is applied to the inner electrode 53a. Also in this case, the potential difference between the electrodes is Vpp / 2. Therefore, a suitable range of Vpp in this example is 200 [V] or more and 4000 [V] or less. Also in this example, it is not necessary to consider the phase difference between the inner electrode 53a and the outer electrode 54a, and the power supply cost is reduced.

FIG. 8 is a schematic diagram when the power supply configuration to the inner electrode 53a and the outer electrode 54a in this embodiment is cut along the roller axis.
FIG. 9 is a perspective view schematically showing the power supply configuration.
In the power supply configuration to the inner electrode 53a and the outer electrode 54a in the present embodiment, the inner electrode 53a is integrated with the roller shaft of the toner carrying roller 41, and the end surface of the roller shaft serves as the power supplied portion 53b. A power supply brush 57 connected to the pulse power source 51A is in contact with the power-supplied portion 53b configured by the end surface of the roller shaft. On the other hand, the surface layer 56 is not provided at both end portions of the outer peripheral surface of the toner carrying roller 41, and both end portions of the outer electrode 54a on the outer peripheral surface of the toner carrying roller 41 are exposed. 54b. A power feeding roller 58 connected to the pulse power source 51B is in contact with the power-supplied portion 54b constituted by the exposed surface. The power supply roller 58 is rotatably supported, and rotates along with the rotation of the toner carrying roller 41 while being in contact with the power supplied portion 54b.

  In the present embodiment, two power supply rollers 58 for applying an external voltage to the outer electrode 54a are provided, but may be one or three or more. If there are a plurality of power supply rollers for applying an external voltage to the outer electrode 54a, even if a power supply failure due to contact failure occurs in some power supply rollers, power can be supplied by other power supply rollers, so stable power supply Can be performed.

  Further, as in the present embodiment, a part of the outer electrode 54a is exposed on the outer peripheral surface of the toner carrying roller 41, and the exposed portion is used as a power-supplied portion 54b to supply power by bringing a power supply roller 58 into contact therewith. When employed, the power-supplied portion 54b is located on the outer side in the axial direction than the developing width on the toner carrying roller 41 (region width on which the electrostatic latent image can be formed on the photosensitive member). desired. This is because when the power-supplied portion 54b is positioned within the development width, the toner crushed between the toner carrying roller 41 and the power-supplied portion 54b contributes to development, and a development failure occurs in that portion. is there. More preferably, the power-supplied portion 54b is desirably positioned on the outer side in the axial direction with respect to the toner supply width on the toner carrying roller 41 (region width where the toner is supplied from the toner supply roller 42). This is because when the power-supplied portion 54b is positioned within the toner supply width, a large amount of toner is interposed between the toner carrying roller 41 and the power-supplied portion 54b, and power supply failure is likely to occur. In the present embodiment, the power-supplied portion 54 b is configured to be positioned on the outer side in the axial direction than the toner supply width on the toner carrying roller 41. Furthermore, in this embodiment, a toner seal (not shown) is provided on the axially central side of each power-supplied portion 54b located at both ends of the roller so that the toner within the toner supply width does not adhere to the power-supplied portion 54b. .

In the present embodiment, the power supply roller 58 that rotates along with the power-supplied portion 54b is used as the power supply member. However, the present invention is not limited thereto, and for example, a conductive brush or a conductive leaf spring may be used. . When using a power supply member that slides against the power-supplied portion 54b, such as a conductive brush or a conductive leaf spring, conductive grease or the like is used to suppress wear of the contact portion with the power-supplied portion 54b. It is good to fill.
In the present embodiment, the case where the power-supplied portion of the inner electrode 53a is the end surface of the roller shaft has been described. However, the present invention is not limited thereto. For example, the peripheral surface of the roller shaft or the end surface of the roller main body may be used. .

Next, a configuration for supplying toner to the toner carrying roller 41, which is a feature of the present invention, will be described.
If the contact pressure between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 is set high at the toner supply position, the force for rubbing the toner against the outer peripheral surface of the toner carrying roller 41 is increased, and the toner charge amount is increased. The absolute value can be increased. However, if the contact pressure is set high, the mechanical stress on the toner increases and the life of the toner is shortened. On the other hand, if the contact pressure is set low, the mechanical stress on the toner is reduced and a sufficient toner life can be obtained. However, the toner charge amount is insufficient and the toner carrying roller 41 is stable. It becomes difficult to make a flare state. Further, it is difficult to achieve both the securing of the toner charge amount necessary for stable flare and the securing of a sufficient toner life only by adjusting the contact pressure.

In the present embodiment, the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 are brought into contact with each other with a contact pressure that is low enough to ensure a sufficient toner life. It is supposed to be supplemented by the configuration of
That is, as shown in FIG. 2, a power supply 47 as a voltage supply means is connected to the toner supply roller 42, and the potential difference between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 is equal to or higher than the discharge start voltage. A configuration in which such a voltage is applied to the toner supply roller 42 is employed. With this configuration, between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41, more specifically, in a minute gap adjacent to the toner supply position on the downstream side in the movement direction of the outer peripheral surface of the toner carrying roller 41, A discharge can be generated. By this discharge, the charge of the normal charge polarity of the toner carried on the toner carrying roller 41 can be efficiently applied, and the toner charge amount necessary for stably flaring can be secured stably. .

  Here, even when a voltage is applied to the toner supply roller 42 such that the potential difference between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 is less than the discharge start voltage, Compared with the case where no voltage is applied, the toner charge amount can be increased. This is considered to be mainly due to the charge injection by the voltage applied to the toner supply roller 42 with respect to the toner contacting the toner supply roller 42. However, as a result of studies by the present inventors, when the potential difference between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 is greater than or equal to the discharge start voltage, this is not the case. In particular, it has been found that the charging efficiency of the toner changes significantly. This is considered due to the fact that charging by discharging is higher in charging efficiency than charging by charge injection.

Further, as in the present embodiment, when a configuration is adopted in which a voltage is applied to the toner supply roller 42 such that the potential difference between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 is equal to or higher than the discharge start voltage, The effect of can also be obtained.
That is, the insulating outer peripheral surface of the toner carrying roller 41 is charged up to a polarity opposite to the normal charging polarity (minus polarity) of the toner due to frictional charging with the toner, and the absolute value of the surface potential of the toner carrying roller 41. Increases with time. For this reason, the magnitude of the developing electric field changes between the initial time point and the time point, and the image quality may change with time. In the developing method in which the toner is flared as in the present embodiment, as described above, the surface layer of the toner carrying roller 41 is configured by the middle resistance layer, and the charge up on the toner carrying roller 41 (positive polarity charge). ) Cannot be released through the regulating blade 43 or the like. According to the configuration of the present embodiment, between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41, more specifically, adjacent to the toner supply position on the upstream side in the movement direction of the outer peripheral surface of the toner carrying roller 41. A discharge can be generated in the minute gap. This discharge removes (or erases or neutralizes) the charge (positive charge) on the toner carrying roller 41 that has been charged up while passing from the toner supply position through the development region to the toner supply position again. Is done. Therefore, according to the present embodiment, the development electric field can be prevented from changing with time, and the change in image quality over time can also be suppressed.

  In particular, the toner supply roller 42 of the present embodiment is configured by a sponge roller having a surface layer of a sponge layer having a large number of fine holes dispersed on the surface. When such a sponge roller is employed as the toner supply roller 42, there are microscopic voids due to a large number of fine holes over the entire contact portion between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41. . As a result, electric discharge can be generated over the entire contact area even at the toner supply position. As a result, compared to the case where a roller having a flat surface is adopted as the toner supply roller 42, the charging efficiency of the toner can be improved, and the charge removal efficiency on the charged toner carrying roller 41 can also be improved. it can.

  In this embodiment, the toner supply roller 42 is rotationally driven so that a speed difference is generated at a contact portion (toner supply position) between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41. In this embodiment, a speed difference is provided so that the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 move in opposite directions (counter direction) at the toner supply position. You may make it provide a speed difference in the structure which moves to a revolving direction. In any case, such a speed difference causes problems caused by discharge unevenness, that is, uneven toner charge amount distribution on the toner carrying roller 41, charge removal unevenness of charge-up charge on the toner carrying roller 41, and the like. The image density non-uniformity due to can be reduced.

[Example 1]
Next, an example of the image forming apparatus according to the above-described embodiment (hereinafter, this example is referred to as “Example 1”) will be described.
FIG. 10 shows the potential V1 ′ on the surface portion of the toner carrying roller facing the inner electrode 53a and the outer electrode 54a in a state where the toner is charged up while passing through the development area from the toner supply position and reaching the toner supply position again. 6 is a graph showing a potential V2 ′ of the surface portion of the toner carrying roller facing and a supply voltage VK applied to the toner supply roller.
In the first embodiment, the outer shape of the inner voltage V1 applied to the inner electrode 53a and the outer voltage V2 applied to the outer electrode 54a are as shown in FIG. 300 V, Vpp is 500 V (−50 V, −550 V), frequency f is 1 kHz, and phases are shifted from each other by π. However, since it is charged up by about +100 V while passing through the development region from the toner supply position and reaching the toner supply position again, the potential V1 ′ of the surface of the toner carrying roller facing the inner electrode 53a and the outer electrode The potential V2 ′ at the surface of the toner carrying roller facing 54a is as shown in FIG.
Note that the voltage applied to the toner supply roller 42 is a DC voltage of −1000V.

Other preconditions in the first embodiment are mainly as follows.
-Photoconductor diameter φ: 60 [mm]
-Photoconductor linear velocity: 300 [mm / s]
-Toner carrying roller diameter φ: 16 [mm]
-Toner carrying roller linear speed: 300 [mm / s]
-Toner-carrying roller rotation direction: Rotating direction with respect to photoreceptor rotation direction-Development gap: 300 [μm]
Toner supply roller diameter φ: 14 [mm]
Toner supply roller linear speed: 195 [mm / s]
-Toner supply roller rotation direction: counter direction with respect to toner carrying roller rotation direction-Toner supply roller material: urethane sponge-Encroachment amount of toner supply roller into toner carrying roller: 0.5 [mm]
・ Regulation blade material: Phosphor bronze ・ Contact pressure of regulation blade: 6 [gf / cm]

  In the case of developing under the above conditions, a potential difference of at least about 550 V is present between the inner electrode 53a and the outer electrode 54a and the toner supply roller 42 in consideration of the charge-up charge (about +100 V at most) on the toner carrying roller 41. Therefore, a potential difference equal to or higher than the discharge start voltage is always generated. As a result, between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41, more specifically, a minute gap adjacent to the toner supply position on the downstream side in the movement direction of the outer peripheral surface of the toner carrying roller 41, or toner Electric discharge can be generated in minute gaps formed by a large number of fine holes formed on the surface of the supply roller 42. By this discharge, the charge of the normal charge polarity of the toner carried on the toner carrying roller 41 can be efficiently applied, and the toner charge amount necessary for stable flare can be secured stably. Further, the toner is generated by a discharge generated in a minute gap adjacent to the toner supply position on the upstream side in the movement direction of the outer peripheral surface of the toner carrying roller 41 or in a minute gap formed by a number of minute holes formed on the surface of the toner supply roller 42. The charge-up charge on the carrier roller 41 is removed, the development electric field can be prevented from changing over time, and the change in image quality over time can also be suppressed.

According to the experiments by the present inventors, according to the conditions of the first embodiment, the toner charge amount is remarkably increased as compared with the conditions of the comparative example, and the charge-up charge on the toner carrying roller 41 is removed. It has been confirmed that
The conditions used as the comparative example are the same as those in the first embodiment except that the voltage applied to the toner supply roller 42 is a DC voltage of −300V. Under these conditions, the potential difference between the inner electrode 53a and outer electrode 54a and the toner supply roller 42 is always less than the discharge start voltage, and no discharge occurs.

In this experiment, as a method for confirming the toner charge amount, after printing 100 solid images continuously, the toner existing in the development area on the toner carrying roller 41 is sucked, and the charge amount of the sucked toner is measured by an electrometer. A method of measuring and calculating an average charge amount (Q / M) was used. When the average charge amount (Q / M) in Example 1 and the comparative example were compared, it was confirmed that the absolute value of the toner charge amount in Example 1 was higher than that in the comparative example.
Further, as a method for confirming the charge-up charge amount on the toner carrying roller 41, the surface potential of the developing region on the toner carrying roller 41 in which 100 solid images are continuously printed and all the toner is not developed. Was measured with a surface potential meter. When the potential increase from the first sheet to the 100th sheet was monitored, it was confirmed that the surface potential gradually increased in the comparative example, whereas the surface potential did not increase in the first example.

  In the first embodiment, an example in which a DC voltage is applied to the toner supply roller 42 has been described. However, there is always a potential difference equal to or greater than the discharge start voltage between the inner electrode 53a and the outer electrode 54a and the toner supply roller 42. The same effect can be obtained by applying such an alternating voltage. However, when an AC voltage is applied, if the surface potential of the toner supply roller 42 is on the plus side with respect to the surface potential of the toner carrying roller 42 and the potential difference therebetween becomes equal to or higher than the discharge start voltage, In the generated discharge, a charge having a polarity opposite to the normal charging polarity (negative polarity) is imparted to the toner, resulting in a decrease in charging efficiency of the toner. Therefore, there is no state where the surface potential of the toner supply roller 42 is on the plus side with respect to the surface potential of the toner carrying roller 42, or even if the state exists, the potential difference in that state is equal to or greater than the discharge start voltage. It is preferable to set an AC voltage to be applied to the toner supply roller 42 so as not to occur. For example, as shown in FIG. 11, if an AC voltage having a maximum value of −100 V and a minimum value of −1000 V is applied to the toner supply roller 42, the toner is supplied to the surface potential of the toner carrying roller 42. Although there is a state in which the surface potential of the roller 42 is located on the plus side, the potential difference in that state does not become equal to or higher than the discharge start voltage, so the same effect as in the first embodiment can be obtained.

[Example 2]
Next, another example of the image forming apparatus in the above embodiment (hereinafter, this example is referred to as “Example 2”) will be described.
FIG. 12 shows the potential V1 ′ of the surface of the toner carrying roller facing the inner electrode 53a and the outer electrode 54a in a state of being charged up while passing through the developing region from the toner supply position and reaching the toner supply position again. 7 is a graph showing a potential V2 ′ of the surface portion of the toner carrying roller facing and a supply voltage VK ″ applied to the toner supply roller.
The second embodiment is the same as the first embodiment except that the same AC voltage (supply voltage VK ″) as the inner voltage V 1 is applied to the toner supply roller 42. In the second exemplary embodiment, an AC voltage having a maximum value of −50 V and a minimum value of −550 V is applied to the toner supply roller 42.

  In the second exemplary embodiment, the surface potential of the toner supply roller 42 is on the negative side with respect to the surface potential of the toner carrying roller 41, and the surface potential of the toner supply roller 42 with respect to the surface potential of the toner carrying roller 41 is There is a state located on the plus side. In the former state, the potential difference (about 600 V) between the surface potential (+50 V) of the toner carrying roller 41 and the surface potential (−550 V) of the toner supply roller 42 is equal to or higher than the discharge start voltage. A discharge occurs. On the other hand, in the latter state, the potential difference (about 400 V) between the surface potential (−450 V) of the toner carrying roller 41 and the surface potential (−50 V) of the toner supply roller 42 is less than the discharge start voltage. There is no discharge between them.

As described above, also in the second exemplary embodiment, since no discharge occurs when the surface potential of the toner supply roller 42 is on the plus side with respect to the surface potential of the toner carrying roller 42, the charging efficiency of the toner is reduced. There is no such thing, and the same effect as the first embodiment can be obtained.
In addition, according to the second embodiment, the pulse power sources 51A and 51B for the inner electrode or the outer electrode can be used as the power source of the toner supply roller 42, and the configuration is simplified as compared with the case where the independent power source 47 is used. This is advantageous in terms of space saving.

[Modification 1]
Next, a modified example of the outer electrode 54a (hereinafter, this modified example is referred to as “modified example 1”) will be described.
Usually, most of the toner on each outer electrode 54a is caused by a flare electric field between two outer electrodes adjacent to each outer electrode 54a (a portion where the inner electrode 53a not facing the outer electrode 54a faces). (Hereinafter, referred to as “inner electrode facing portion”), and most of the toner on each inner electrode facing portion is caused by flare electric field to be adjacent to each inner electrode facing portion. The width of the outer electrode 54a (the length in the direction of movement of the toner carrying roller surface) and the width of the inner electrode facing portion are set according to the strength of the flare electric field so that it can move to any of the above.

Here, the width of the outer electrode 54a and the width of the inner electrode facing portion are uniform (strictly, some non-uniformity occurs due to manufacturing errors), and the inner electrode 53a and the outer electrode 54a have equal potentials. If so, a flare electric field with little unevenness can be formed on the toner carrying roller 41. In such a case, as long as no other external force acts on the toner hopping on the toner carrying roller 41, the toner on the toner carrying roller 41 is distributed almost uniformly over the entire outer peripheral surface where the inner electrode 53a and the outer electrode 54a face each other. In this state, you can hop.
However, the inner electrode 53a and the outer electrode 54a are not equal in potential, and the toner carrying roller 41 is caused by a potential gradient caused by a manufacturing error in the surface moving direction of the toner carrying roller 41 in each of the electrodes 53a and 54a. In some cases, a flare electric field that is biased in the direction of surface movement is formed. In this case, the toner hopping on the toner carrying roller 41 moves so as to be biased in the surface moving direction of the toner carrying roller 41 so as to move while hopping the outer electrode 54a and the inner electrode facing portion according to the potential gradient. . As a result, a large amount of toner is unevenly distributed on the toner carrying roller 41, and a large amount of toner unevenness (low frequency unevenness) occurs on the toner carrying roller 41.
In addition, an air flow generated near the surface of the toner carrying roller 41 may act on the toner to generate an external force that moves the toner upstream or downstream in the surface movement direction of the toner carrying roller 41. For example, when an external force is generated downstream in the direction of surface movement of the toner carrying roller 41, most of the toner hopping on the toner carrying roller 41 is affected by the flare electric field and the external force in the direction of movement of the toner carrying roller during hopping. Move downstream in the direction. Therefore, a large amount of toner moves so as to be biased in the surface movement direction of the toner carrying roller 41 so as to walk downstream in the toner carrying roller surface movement direction direction while hopping the outer electrode 54a and the inner electrode facing portion. As a result, a large amount of toner is unevenly distributed on the toner carrying roller 41, and a large amount of toner unevenness (low frequency unevenness) occurs on the toner carrying roller 41.
Such unevenness causes image density unevenness.

FIG. 13 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller 41 according to the first modification is cut along a plane orthogonal to the rotation axis thereof.
FIG. 14 is an explanatory diagram illustrating an outline of the lines of electric force.
In the first modification, the width X of the outer electrode 54a is manufactured to be equal, but the width of the inner electrode facing portion is alternately a short width Y1 and a long width Y2 in the surface movement direction of the toner carrying roller 41. Is manufactured to exist. In the width of the inner electrode facing portion, the difference (Y2−Y1) between the short width Y1 and the long width Y2 is a difference that exceeds the range of the manufacturing error when attempting to uniformly manufacture the width of the inner electrode facing portion. In such a configuration, even when a force for moving the toner to the upstream side or the downstream side in the direction of movement of the surface of the toner carrying roller is generated due to a potential gradient or an air current, as described below, the toner carrying roller 41 is used. It is possible to suppress the toner from being unevenly distributed.

  That is, when such a force is generated, most of the toner hopping on the toner carrying roller 41 tends to move along the toner carrying roller surface moving direction in the direction of the force. Here, when attention is paid to one outer electrode 54a, as shown in FIG. 14, each flare electric field (an electric field formed outside the surface layer 56) formed between two adjacent inner electrode facing portions as shown in FIG. ) Varies relatively depending on the width of the inner electrode facing portion. In other words, the flare electric field formed between the long electrode Y2 and the inner electrode facing part with the long width Y2 is stronger than the flare electric field formed between the inner electrode facing part with the short width Y1. And the flare electric field formed between the inner electrode facing part of the long width Y2 is the case where the width of the inner electrode facing part is made equal if the voltage applied to the inner electrode 53a and the outer electrode 54a is the same. The electric field is stronger than Therefore, even when the above-described force is generated, a large amount of toner hopped from the outer electrode 54a to the inner electrode facing portion having the long width Y2 adjacent in the direction of the force is returned to the original outer electrode 54a again. It becomes possible. As a result, the toner that has moved from the outer electrode 54a to the inner electrode facing portion of the long width Y2 adjacent in the direction of the force is less likely to travel to the outer electrode 54a adjacent in the direction of the force.

As described above, in the first modification, the inner electrode facing portion having the long width Y2 functions as a barrier that prevents the movement of the toner that moves in the direction of the force under the action of the force as described above. Further, it is possible to suppress the toner from being unevenly distributed on the toner carrying roller 41. Therefore, it is possible to suppress the occurrence of a large amount of toner unevenness (low frequency unevenness) on the toner carrying roller 41 and to suppress image density unevenness.
In the first modification, the inner electrode facing portion having the longer width Y2 is adjacent to the inner electrode facing portion having the longer width Y2 than the amount of toner existing in the vicinity between the inner electrode facing portion having the shorter width Y1 and the outer electrode 54a adjacent thereto. Since the amount of toner existing near the outer electrode 54a is larger, the amount of toner is uneven on the toner carrying roller 41 when viewed microscopically. However, such unevenness is a high-frequency unevenness with a very short period, so that it is difficult to affect the image density, and even if the image density is affected, it does not become an unevenness that can be detected by humans. Does not affect the image quality.

In the first modification, the long width Y2 of the inner electrode facing portion is preferably set to 2 to 5 times the short width Y1 of the inner electrode facing portion. If it is less than 2 times, the flare electric field formed between the inner electrode facing part having the long width Y2 cannot be made sufficiently strong, and the role as the barrier cannot be sufficiently achieved. The effect of suppressing density unevenness is low. On the other hand, when it exceeds 5 times, the toner existing in the center of the inner electrode facing portion of the long width Y2 cannot move onto the adjacent outer electrode 54a, and it becomes difficult to efficiently cloud the toner. In addition, it is preferable that the short width Y1 of the inner electrode facing portion is approximately the same as the electrode width of the outer electrode 54a.
In the first modification, the electrode width of the outer electrode 54a is set to 40 [μm], the short width Y1 of the inner electrode facing portion is set to 40 [μm], and the long width Y2 of the inner electrode facing portion is set to 120 [μm]. Yes.

In the first modification, the case has been described in which the width X of the outer electrode 54a is made uniform and the width of the inner electrode facing portion is made unequal, but conversely, the width X of the outer electrode 54a is made unequal, The same effect can be obtained even when the widths of the inner electrode facing portions are made uniform.
In the first modification, the width of the inner electrode facing portion is not uniform so that the short width Y1 and the long width Y2 exist alternately in the surface movement direction of the toner carrying roller 41. The method is not limited. For example, it may be unequal such that one long width Y2 exists after two or more short widths Y1 continue. Moreover, you may make it become three or more types of widths.

[Modification 2]
Next, another modified example of the outer electrode 54a (hereinafter, this modified example is referred to as “modified example 2”) will be described.
FIG. 15 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller 41 according to the second modification is cut along a plane orthogonal to the rotation axis thereof.
FIG. 16 is an explanatory diagram illustrating an outline of electric lines of force.
In the second modification, after the insulating layer 55 is provided on the outer peripheral surface side of the inner electrode 53a, the outer electrode layer mainly composed of aluminum, copper, silver or the like is provided on the entire insulating layer 55. This outer electrode layer is obtained by dispersing insulating particles 54c in aluminum, copper, silver or the like, and the metal portion thereof becomes the outer electrode 54a. The average particle diameter of the insulating particles 54c is larger than the layer thickness of the outer electrode layer. As a result, as shown in FIG. 16, the lines of electric force from the inner electrode 53a come out of the surface layer 56 through the insulating particles 54c, and a flare electric field can be efficiently formed outside the surface layer 56. Examples of the insulating particles 54c include resins such as polyester and epoxy, and electrical insulators such as glass beads. Further, the method for forming the outer electrode layer on the insulating layer 55 is not particularly limited. For example, there is a method in which a conductive paste in which insulating particles 54c are dispersed is directly formed on the insulating layer 55 by screen printing. Can be mentioned. The layer thickness of the outer electrode layer is preferably several [μm] to several tens [μm]. In the second modification, it is set to 5 [μm].

FIG. 17 is a schematic diagram when the outer electrode layer is viewed from the outer peripheral surface side of the toner carrying roller 41.
In the second modification, the surface area of the formed outer electrode 54a can be controlled by changing the volume ratio of the insulating particles 54c to the entire outer electrode layer, and the strength of the flare electric field can be controlled. . In the second modification, if the volume ratio of the insulating particles 54c to the entire outer electrode layer is in the range of 0.2 to 0.8, the toner can be sufficiently clouded. When the volume ratio of the insulating particles 54c to the entire outer electrode layer is larger than 0.8, a large number of float electrodes exist because the insulating particles 54c occupy most of the outer electrode layer. That is, the voltage applied to the outer electrode layer is distributed throughout the outer electrode layer through the outer electrode 54a that is not divided by the insulating particles 54c, but when the insulating particles 54c occupy most of the outer electrode layer, Many parts of the outer electrode 54a are divided by the insulating particles 54c to be in an electrically floating state. Although the float electrode may be present even if the volume ratio of the insulating particles 54c to the entire outer electrode layer is 0.8 or less, the formation of the flare electric field is not greatly affected if the number is small. On the other hand, when the volume ratio of the insulating particles 54c to the entire outer electrode layer is smaller than 0.2, most of the electric lines of force from the inner electrode 53a converge on the outer electrode 54a before coming out of the surface layer 56. As a result, the flare electric field formed outside the surface layer 56 is weakened. In the second modification, the volume ratio of the insulating particles 54c to the entire outer electrode layer is set to 0.4.

  According to the second modification, the width of the outer electrode 54a becomes uneven, and the inter-particle distance of the insulating particles 54c (corresponding to the width of the inner electrode facing portion in the first modification) also becomes uneven. As a result, as in the first modification, a locally strong flare electric field can be dispersedly formed on the toner carrying roller 41. Thereby, even when a force for moving the toner in a specific direction is generated due to a potential gradient or an air flow, it is possible to suppress the toner from being unevenly distributed on the toner carrying roller 41. Moreover, in the first modification, only the force in the direction along the surface movement direction of the toner carrying roller 41 can be dealt with, but according to the second modification, the direction along the axial direction of the toner carrying roller 41, etc. This is more advantageous than Modification 1 in that it can cope with forces in other directions.

[Modification 3]
Next, still another modified example of the outer electrode 54a (hereinafter, this modified example is referred to as “modified example 3”) will be described.
FIG. 18 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller 41 according to the third modification is cut along a plane orthogonal to the rotation axis thereof.
FIG. 19 is a schematic diagram when the outer electrode layer is viewed from the outer peripheral surface side of the toner carrying roller 41.
Also in the third modification, after providing the insulating layer 55 on the outer peripheral surface side of the inner electrode 53a (FIG. 20A), the outer electrode layer is provided on the entire insulating layer 55 as in the second modification. . However, the outer electrode layer in Modification 3 is a layer made of a conductive urethane resin 54a and an insulating melamine resin 54d. Specifically, after preparing a conductive urethane resin foam raw material, pouring it into a mold and heat-curing and foaming (FIG. 20 (b)), a melamine resin is placed in the cell (hole) formed by foaming. Coating is performed using a roller coater (FIG. 20C). Thereby, the outer electrode layer in a state where the conductive urethane resin 54a and the insulating melamine resin 54d are randomly dispersed on the insulating layer 55 is formed. The conductive urethane resin portion 54a serves as an outer electrode. In place of melamine resin, urethane, polyimide, polyamide, bakelite, polycarbonate, PET, POM, PPE and the like can also be used. The layer thickness of the outer electrode layer is preferably in the range of 0.01 [mm] to 0.3 [mm]. If it is less than 0.01 [mm], the accuracy of the mold becomes a problem, and if it is greater than 0.3 [mm], an air layer generated by foaming is confined in the outer electrode layer. In the third modification, the thickness of the outer electrode layer was set to 0.1 [mm]. Note that the cell diameter after foaming needs to be equal to or greater than the thickness of the outer electrode layer, as in the case of the insulating particles 54c in Modification 2.

  Also in the third modification, the width of the conductive urethane resin 54a (outer electrode) becomes uneven, and the width of the melamine resin portion 54d (corresponding to the inner electrode facing portion in the first modification) also becomes uneven. As a result, similarly to the first modification and the second modification, a locally strong flare electric field can be distributed and formed on the toner carrying roller 41. Thereby, even when a force for moving the toner in a specific direction is generated due to a potential gradient or an air flow, it is possible to suppress the toner from being unevenly distributed on the toner carrying roller 41. In addition, as in the second modification, the second embodiment is more advantageous than the first modification in that it can cope with forces in other directions such as the direction along the axial direction of the toner carrying roller 41.

[Modification 4]
Next, still another modified example of the outer electrode 54a (hereinafter, this modified example is referred to as “modified example 4”) will be described.
FIG. 21 is a partial cross-sectional view schematically showing a cross section when the toner carrying roller 41 according to the fourth modification is cut along a plane orthogonal to the rotation axis thereof.
FIG. 22 is a schematic diagram when the outer electrode layer is viewed from the outer peripheral surface side of the toner carrying roller 41.
Also in the fourth modification, as in the second modification and the third modification, the insulating layer 55 is provided on the outer peripheral surface side of the inner electrode 53a, and then the outer electrode layer is provided on the entire insulating layer 55. However, the outer electrode layer in the fourth modification is a layer in which the metal filler 54a is dispersed in the resin binder 54e. The metal fillers 54a are fused to each other. Specifically, the paste material in which the metal filler is dispersed in the resin binder is applied onto the insulating layer 55 by spraying, so that the metal filler 54a is randomly dispersed in the resin binder 54e on the insulating layer 55. An outer electrode layer is formed. In addition, this metal filler part becomes an outer electrode. The paste material to be coated on the insulating layer 55 can be used as long as it is obtained by dispersing metal particles made of one or more of gold, silver, platinum, palladium, lead, tungsten, nickel, etc. as fillers in an organic resin solution. Is possible. Further, as the metal filler 54a, a metal oxide such as lead oxide, zinc oxide, silicon oxide, boron oxide, aluminum oxide, yttrium oxide, or titanium oxide may be used. As the binder resin, an epoxy resin, a phenol resin, or the like is preferable. Moreover, isopropyl alcohol etc. are used as a solvent. As a thickener, cellulose or the like may be contained. The amount of the binder resin 54e in the paste material is preferably 40% to 60%. If the amount is too large, the metal filler will not be fused and the electrical resistance will be too large. If the amount is too small, the area occupied by the binder resin 54e will be too small, and the flare electric field formed outside the surface layer 56 will be weak. End up. In this modification 4, it was set to 50%. The layer thickness of the outer electrode layer is preferably in the range of 0.01 [mm] or more and 0.3 [mm] or less as in the third modification. In the fourth modification, the layer thickness of the outer electrode layer was set to 0.1 [mm].

  Also in the fourth modification, the width of the metal filler 54a (outer electrode) becomes uneven, and the width of the resin binder 54e (corresponding to the inner electrode facing portion in the first modification) also becomes uneven. As a result, similarly to the first to eighth modifications, a locally strong flare electric field can be distributed and formed on the toner carrying roller 41. Thereby, even when a force for moving the toner in a specific direction is generated due to a potential gradient or an air flow, it is possible to suppress the toner from being unevenly distributed on the toner carrying roller 41. In addition, as in Modification 2 and Modification 3, it is more advantageous than Modification 1 in that it can cope with forces in other directions such as the direction along the axial direction of the toner carrying roller 41.

  In the second to fourth modifications, the same effect can be obtained even when the insulating material portion and the conductive material portion are reversed.

As described above, the image forming apparatus according to the present embodiment (including each modified example; the same applies hereinafter) includes the photoreceptor 1 as a latent image carrier and inner electrodes that are a plurality of types of electrode members to which different voltages are applied. The toner is carried on the insulating outer peripheral surface of the toner carrying roller 41 as the toner carrying member having the 53a and the outer electrode 54a, and different voltages (inner voltage and outer voltage) are applied to the inner electrode 53a and the outer electrode 54a. By applying the electric field, an electric field (flare electric field) for hopping the toner is formed outside the outer peripheral surface of the toner carrying roller at the outer peripheral surface portion of the toner carrying roller facing the inner electrode 53a and the outer electrode 54a. The toner in the hopped state is fed into the development area by moving the outer peripheral surface of the toner, and the toner is transferred to the electrostatic latent image on the photoreceptor 1. And developing devices 4M, 4C, 4Y, and 4K for developing the electrostatic latent image, and finally transferring the image obtained by developing the electrostatic latent image onto the recording material. An image forming apparatus for forming an image on the screen. The developing devices 4M, 4C, 4Y, and 4K of this image forming apparatus move as the toner is carried on the surface, and serve as toner supply members that supply toner to the outer peripheral surface of the toner carrying roller 41 that contacts the surface. Voltage supply means for applying a voltage to the toner supply roller 42 such that the potential difference between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 is equal to or greater than the discharge start voltage. A power supply 47 or power supplies 51A and 52A are provided. As a result, the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41 are brought into contact with a contact pressure that is low enough to ensure a sufficient toner life. It is possible to stably secure the toner charge amount necessary to compensate for the toner charge amount and achieve a stable flare state. Further, by causing discharge, the charge-up charge on the toner carrying roller 41 can be efficiently removed, the development electric field can be prevented from changing over time, and the change in image quality over time can also be suppressed.
In addition, according to the present embodiment, since the charge-up charge on the toner carrying roller 41 can be efficiently removed, the outer peripheral surface of the toner carrying roller 41 is given a charge of normal charging polarity to the toner by friction with the toner. It can be formed of an insulating material. Therefore, the triboelectric charging efficiency of the toner is also increased, and the toner charge amount necessary for stably flaring can be secured more stably.
Further, according to the present embodiment, the surface layer of the toner supply roller 42 is a sponge layer in which a large number of micropores are dispersed on the surface. Therefore, when a roller having a flat surface is adopted as the toner supply roller 42. In comparison, the charging efficiency of the toner can be improved, and the charge removal efficiency on the charged toner carrying roller 41 can also be improved.
Further, according to the present embodiment, the driving means for moving the surface of the toner supply roller 42 so that a speed difference is generated at a contact portion (toner supply position) between the surface of the toner supply roller 42 and the outer peripheral surface of the toner carrying roller 41. Have. As a result, it is possible to reduce defects caused by uneven discharge, that is, uneven image density due to uneven distribution of toner charge amount on the toner carrying roller 41, uneven discharge of charge-up charge on the toner carrying roller 41, and the like.
Further, according to the present embodiment, as the configuration of the toner carrying roller 41, the inner electrode 53a and the outer electrode 54a are arranged at different positions in a direction parallel to the normal direction of the outer peripheral surface of the toner carrying roller, and between these electrodes. A configuration in which the insulating layer 55 is interposed is employed. As a result, the electrodes 53a and 54a provided on the toner carrying roller 41 are separated from each other by the insulating layer 55, so that there is an interface connecting these electrodes, or toner is interposed between these electrodes. There is nothing to do. Therefore, there is no leakage through the interface or toner between the electrodes 53a and 54a provided on the toner carrying roller 41, and a stable flare electric field can be formed.

4M, 4C, 4Y, 4K Developing device 41 Toner carrying roller 42 Toner supply roller 43 Regulating blade 47 Power supply 51A, 51B Pulse power supply 53a Inner electrode 53b Powered part 54a Outer electrode 54b Powered part 54c Insulating particles 55 Insulating layer 56 Surface layer 57 Power supply brush 58 Power supply roller

JP 2007-133388 A JP 2008-116599 A

Claims (6)

A latent image carrier;
By carrying toner on the insulating outer peripheral surface of a toner carrier having a plurality of types of electrode members to which different voltages are applied, and applying different voltages to the plurality of types of electrode members, An electric field for hopping the toner is formed outside the outer peripheral surface of the toner carrier at the outer peripheral surface portion of the toner carrier facing each of the types of electrode members, and the developing region is moved by moving the outer peripheral surface of the toner carrier A developing device that feeds toner in a hopped state into the latent image and supplies the toner to the latent image on the latent image carrier to develop the latent image;
In an image forming apparatus for finally transferring an image obtained by developing the latent image onto a recording material and forming an image on the recording material,
The developing device includes a toner supply member that supplies toner to the outer peripheral surface of the toner carrier,
An image forming apparatus comprising voltage supply means for applying a voltage to the toner supply member such that a potential difference between the surface of the toner supply member and the outer peripheral surface of the toner carrier is equal to or higher than a discharge start voltage. . The image forming apparatus according to claim 1.
An image forming apparatus, wherein an outer peripheral surface of the toner carrying member is formed of an insulating material that gives a charge of a normal charging polarity to the toner by friction with the toner. The image forming apparatus according to claim 1 or 2,
The image forming apparatus according to claim 1, wherein the surface layer of the toner supply member is a sponge layer in which a large number of micropores are dispersed on the surface. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus comprising drive means for moving the surface of the toner supply member so that a speed difference is generated at a contact portion between the surface of the toner supply member and the outer peripheral surface of the toner carrier. The image forming apparatus according to any one of claims 1 to 4, wherein:
The toner carrier has a configuration in which the plurality of types of electrode members are arranged at different positions in a direction parallel to the normal direction of the outer peripheral surface of the toner carrier, and an insulating layer is interposed between the plurality of types of electrode members. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
A plurality of the developing devices are provided, each developing device develops a latent image corresponding to each color with different color toners, and each color image obtained thereby forms a color image overlapping each other. Image forming apparatus.

Images