JP2008122794A - Developing device, process unit, and image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of suppressing deterioration in image quality due to charging of a surface of a toner carrying roller 16M.
M toner carried on a rotating surface of a toner carrying roller 16M having a pair of a plurality of A phase electrodes 17A and B phase electrodes 17B repeatedly arranged in a predetermined direction is applied to an A phase electrode 17A and a B phase electrode 17B. In an image forming apparatus that develops a latent image by adhering to a latent image carried on a photosensitive belt (not shown) while hopping on the surface of the toner carrying roller 16M by an electric field formed by applying a pulse voltage, respectively. A neutralizing unit was provided for neutralizing the surface of the carrying roller 16M at a predetermined position in the roller rotation direction. This neutralizing means includes a regulating member 28M that regulates the amount of toner supplied on the toner carrying roller 16M on the roller surface, a neutralizing power source 26M that applies a neutralizing bias to the regulating member 28M, and the like.
[Selection] Figure 2

Description

  The present invention relates to a developing device for developing a latent image on a latent image carrier with toner hopped on an endlessly moving surface of a toner carrier, and a process unit and an image forming apparatus using the same.

  Conventionally, as a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., toner that has been hopped on the surface of a toner carrier is not used for development but toner that is adsorbed on a developing roller or a magnetic carrier. Is used for development.

  For example, the developing device described in Patent Document 1 includes a cylindrical toner carrier including a plurality of electrodes arranged at a predetermined pitch in the circumferential direction. These electrodes are formed by repeatedly arranging electrode pairs composed of two adjacent electrodes. An alternating electric field is formed between the two electrodes in each electrode pair. Then, the toner located on one electrode in the electrode pair floats and landes on the other electrode, or floats on the other electrode and landes on one electrode. Then, while repeating the hopping in this manner, the toner is conveyed to the developing region by the surface movement accompanying the rotational driving of the cylindrical toner carrier. In the developing region, the toner that has floated to the vicinity of the latent image on the latent image carrier is attracted to the electric field by the latent image and does not descend toward the electrode of the toner carrier, and adheres to the latent image. In such a configuration, not the toner adsorbed on the developing roller or the magnetic carrier but the toner that does not exhibit the adsorbing force by hopping is used for the development. As a result, it is possible to realize low-potential development that cannot be realized by the conventional one-component development method or two-component development method. For example, toner can be selectively attached to an electrostatic latent image having a potential difference of only a few tens [V] with respect to surrounding non-image portions.

JP-A-3-21967 JP 2002-341656 A

  However, it has been found through experiments by the present inventors that such a configuration tends to cause image quality deterioration due to charging of the surface layer of the toner carrier. Specifically, when the plurality of electrodes described above are exposed on the surface of the toner carrier, the charge of the toner in contact with the electrodes leaks to the electrodes, and toner hopping is not performed. For this reason, it is common to use a toner carrier having an electrode coated with a surface layer to prevent charge leakage from the toner to the electrode. However, in the toner carrier having such a configuration, the potential difference between the latent image carrier and the toner carrier varies due to charging of the surface layer accompanying the rubbing with the toner to be hopped. It has been found by experiments by the present inventors that image quality is likely to be deteriorated. Furthermore, if a configuration in which a member to which a high voltage is applied, such as a toner supply roller, is opposed to the surface layer of the toner carrying member, a charge is induced in the surface layer by the high voltage. It was found that the potential difference between the latent image carrier and the toner carrier was varied.

  As a developing device that performs development with toner hopped on the surface of the toner carrier, a device described in Patent Document 2 is known in addition to the one described in Patent Document 1. This developing device has a toner transport substrate as a toner carrier having a plurality of electrodes arranged at a predetermined pitch on an insulating support plate. These electrodes are formed by repeatedly arranging electrode sets composed of three or more electrodes arranged continuously. A pulse voltage that is out of phase with each other is applied to each electrode in an electrode set including three or more electrodes. As a result, a traveling electric field is formed on the transport substrate, in which the toner is sequentially moved from one end side to the other end side while hopping the toner. The toner on the surface of the transport substrate is repeatedly hopped from above one electrode toward the adjacent electrode in a direction from one end side to the other end side of the substrate. And a latent image carrier such as a photosensitive member are conveyed to a developing region facing each other with a predetermined gap. Even in such a configuration, the same problem due to charging of the surface layer may occur.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a developing device capable of suppressing image quality deterioration caused by charging of the surface of the toner carrier, and a process unit and an image using the developing device. A forming apparatus is provided.

In order to achieve the above object, according to the first aspect of the present invention, a voltage is applied to the plurality of electrodes, the toner carried on the endlessly moving surface of the toner carrier having a plurality of electrodes arranged in a predetermined direction. In the developing device for developing the latent image by causing it to adhere to the latent image carried on the latent image carrier while being hopped on the surface by the electric field formed in Step 1, the surface of the toner carrier is made to adhere to the surface of the toner carrier. The present invention is characterized in that a charge eliminating means for eliminating charges at a predetermined position in the endless moving direction is provided.
According to a second aspect of the present invention, there is provided the developing device according to the first aspect, comprising: a counter member that faces the surface of the toner carrier; and a voltage applying unit that applies a voltage to the counter member. It is characterized by being used as.
According to a third aspect of the present invention, in the developing device of the second aspect, as the opposing member, a regulating member that regulates the amount of toner supplied on the surface of the toner carrier by the toner supply means on the surface. It is characterized by being used.
According to a fourth aspect of the present invention, in the developing device of the second aspect, a recovery member that transfers and collects toner on the surface of the toner carrier onto the surface of the toner carrier is used as the counter member. To do.
According to a fifth aspect of the present invention, there is provided the developing device according to the second aspect, wherein a seal member that closes a space between the endlessly moving surface of the toner carrier and the developing device housing is used as the facing member. To do.
According to a sixth aspect of the present invention, in the developing device according to any of the second to fifth aspects, an elastic layer made of an elastic material is brought into contact with the surface as a toner supply member that supplies toner to the surface of the toner carrier. And a toner supply roller that is rotated while supplying toner carried on the elastic layer to the surface.
According to a seventh aspect of the present invention, in the developing device according to any one of the second to fifth aspects, the toner supply member that supplies toner to the surface of the toner carrier is erected on the peripheral surface of the rotating shaft member. The present invention is characterized in that a toner supply brush roller is used which rotates a brush roller portion made of a plurality of raised brushes in contact with the surface and supplies toner trapped in the brush roller portion to the surface. .
According to an eighth aspect of the present invention, in the developing device according to any one of the second to seventh aspects, the surface potential detecting means for detecting the surface potential of the toner carrier, and the detection result by the surface potential detecting means. Voltage determining means for determining the value of the voltage applied by the voltage applying means is provided.
According to a ninth aspect of the present invention, in the developing device according to any of the second to seventh aspects, the charge amount estimating means for estimating the charge amount of the toner on the toner carrier, and the estimation result by the charge amount estimating means, Voltage determining means for determining the value of the voltage applied by the voltage applying means based on the voltages applied to the plurality of electrodes is provided.
According to a tenth aspect of the present invention, in the developing device according to the ninth aspect, a toner carrying amount detecting means for detecting a toner carrying amount per unit area on the surface of the toner carrying member is provided, in addition to the estimation result and the voltage. Thus, the voltage determining means is configured to determine the value of the applied voltage based on the detection result of the toner carrying amount detecting means.
According to an eleventh aspect of the present invention, in the developing device according to any one of the second to tenth aspects, the voltage applying unit applies a DC voltage to the facing member.
According to a twelfth aspect of the present invention, in the developing device according to any one of the second to tenth aspects of the present invention, the voltage applying unit applies an AC / DC superimposed voltage to the facing member. is there.
According to a thirteenth aspect of the present invention, at least a latent image carrier that bears a latent image and a developing unit that develops the latent image on the latent image carrier are held by a common holder, so that one unit is provided. In the process unit which is detachably attached to the image forming apparatus main body, the developing device according to any one of claims 1 to 12 is used as the developing means.
According to a fourteenth aspect of the present invention, there is provided an image forming apparatus having a latent image carrier for carrying a latent image and a developing means for developing the latent image on the latent image carrier. The developing device is characterized in that any one of the developing devices 1 to 12 is used.
The invention of claim 15 is characterized in that, in the image forming apparatus of claim 14, a plurality of the developing devices are provided, and the latent image carrier is superposed and developed by these developing devices. To do.

  In these inventions, the surface of the toner carrying member is neutralized at a predetermined position in the endless movement direction, whereby image quality deterioration due to charging of the surface of the toner carrying member can be suppressed.

An embodiment of an electrophotographic printer will be described below as an image forming apparatus to which the present invention is applied.
FIG. 1 is a schematic configuration diagram showing a printer according to the present embodiment. This printer can form a full color image by superposing toner images of magenta, cyan, yellow, and black (hereinafter referred to as M, C, Y, and K). The belt unit 1 includes four developing devices 10M, C, Y, and K, a registration roller pair 30, a transfer roller 31, a fixing device 32, a paper feeding cassette (not shown), a paper feeding path, and the like.

  The belt unit 1 moves the endless photosensitive belt 2 as a latent image carrier endlessly in the clockwise direction in the drawing while stretching in a vertically long posture that takes a space in the vertical direction rather than the horizontal direction. More specifically, the photosensitive belt 2 is stretched while being supported from the back side by a driving roller 3, a tension roller 4, a transfer upstream roller 5, a transfer backup roller 6, and four development counter rollers 7M, C, Y, and K. Yes. Then, the photosensitive belt 2 is moved endlessly by the rotation of the driving roller 3 that is rotated in the clockwise direction in the drawing by a driving means (not shown). The left tension surface (hereinafter referred to as the left tension surface) in the drawing of the photosensitive belt 2 is in a posture extending substantially in the vertical direction.

  Developing devices 10M, C, Y, and K for M, C, Y, and K are arranged in the vertical direction on the left side of the left-side stretched surface of the photosensitive belt 2, and are respectively arranged in the photosensitive belt. 2 facing the left-hand stretched surface.

  Among the four developing devices 10M, C, Y, and K, an M charging device 29M is provided on the left side of the photosensitive belt 2 further below the M developing device 10M that is positioned at the lowest in the vertical direction. It is arrange | positioned so that it may oppose. A C charging device 29C is disposed between the M developing device 10M and the C developing device 10C so as to face the left-side stretched surface of the photosensitive belt 2. A Y charging device 29Y is disposed between the C developing device 10C and the Y developing device 10Y so as to face the left-side stretched surface of the photosensitive belt 2. Further, a charging device 29K for K is disposed between the developing device 10Y for Y and the developing device 10K for K so as to face the left-side stretched surface of the photosensitive belt 2.

  On the left side of the four developing devices 10M, C, Y, and K arranged in the vertical direction, an optical writing unit (not shown) is disposed. This optical writing unit drives four semiconductor lasers (not shown) based on image information sent from an external personal computer or scanner (not shown) to provide four writing lights for M, C, Y, and K. Lm, Lc, Ly, and Lk are emitted. While these are deflected by a polygon mirror (not shown), they are reflected by a reflection mirror (not shown) or passed through an optical lens, thereby performing optical scanning on the photosensitive belt 2. Instead of such a configuration, an LED array that performs optical scanning may be used. The optical scanning is performed in the dark.

  The photosensitive belt 2 extends from the lower side to the upper side in the vertical direction between the lowermost transfer backup roller 6 and the uppermost driving roller 3 among the plurality of stretching rollers that stretch the photosensitive belt 2. Move almost straight toward you. Then, after passing through the place where the driving roller 3 is wound, it moves relatively from the upper side to the lower side in the vertical direction. The belt portion that has passed through the portion of the drive roller 3 and moved from the lower side to the upper side in the vertical direction has a negative polarity, for example, when passing the position facing the M charging device 29M. It is charged like this. Then, after the electrostatic latent image for M is carried by optical scanning with the M writing light Lm, it passes through a position facing the developing device 10M for M. At this time, the electrostatic latent image for M written on the photosensitive belt 2 is developed by the developing device 10M for M to become an M toner image.

  The photosensitive belt 2 on which the M toner image is formed is uniformly charged again by the C charging device 29C in accordance with the movement from the lower side to the upper side in the vertical direction, and then is written by the C writing light Lc. An electrostatic latent image for C is carried by optical scanning. The C electrostatic latent image is developed by the C developing device 10C to become a C toner image. At this time, the entire region or a partial region of the C toner image is developed in a state of being superimposed on the M toner image already formed on the photosensitive belt 2. And the superposition location becomes the secondary color by M and C.

  The photosensitive belt 2 on which the C toner image is formed is uniformly charged again by the Y charging device 29Y as it moves from the lower side to the upper side in the vertical direction, and then is written by the Y writing light Ly. An electrostatic latent image for Y is carried by optical scanning. The Y electrostatic latent image is developed by the Y developing device 10Y to become a Y toner image. At this time, the entire area or a partial area of the Y toner image is developed while being superimposed on the M toner image or the C toner image already formed on the photosensitive belt 2. Then, the overlapping portion becomes a secondary color by M and Y, a secondary color by C and Y, or a tertiary color by M, C and Y.

  The photosensitive belt 2 on which the Y toner image is formed is uniformly charged again by the K charging device 29K in accordance with the movement from the lower side to the upper side in the vertical direction, and then the K writing light Lk. An electrostatic latent image for K is carried by optical scanning. The K electrostatic latent image is developed by the K developing device 10K to become a K toner image. By superimposing and developing such M, C, Y, and K toner images, a four-color superimposed toner image is formed on the front surface (loop outer surface) of the photosensitive belt 2.

  A transfer roller 31 is in contact with the transfer backup roller 6 on the photosensitive belt 2 from the front surface side to form a transfer nip. While the transfer backup roller 6 is grounded, a transfer bias is applied to the conductive transfer roller 31 by a bias applying means (not shown). Thus, a transfer electric field for electrostatically moving the toner image on the photosensitive belt 2 from the transfer backup roller 6 side to the transfer roller 31 side between the transfer backup roller 6 and the transfer roller 31 sandwiching the transfer nip therebetween. Is formed.

  On the other hand, the recording paper P sent out from a paper feeding cassette (not shown) of the printer to a paper feeding path (not shown) at a predetermined timing is sandwiched between rollers of a registration roller pair 30 disposed on the right side of the transfer nip in the drawing. It is. As soon as the registration roller pair 30 sandwiches the leading end of the recording paper P, the rotation of the registration roller 30 temporarily stops. Then, the rotational driving is resumed at a timing at which the recording paper P can be synchronized with the four-color superimposed toner image on the photosensitive belt 2, and the recording paper P is sent to the transfer nip.

  The four-color superimposed toner image brought into intimate contact with the recording paper P at the transfer nip is collectively transferred from the belt to the recording paper P by the action of the nip pressure and the transfer electric field, and becomes a full color image combined with the white color of the recording paper P.

  The recording paper P on which a full-color image has been formed in this way is sent to the fixing device 32 from the transfer nip. The fixing device 32 forms a fixing nip by contact between a fixing roller 32a including a heat source such as a halogen lamp and a pressure roller 32b pressed against the fixing roller 32a. Is inserted into the fixing nip. Then, the full color image is fixed on the recording paper P by the action of the heating by the fixing roller 32a and the nip pressure.

  The recording paper P on which the full color image has been fixed in the fixing device 32 passes through a pair of paper discharge rollers (not shown) and is then discharged outside the apparatus. The transfer residual toner adhering to the front surface of the photosensitive belt 2 after passing through the transfer nip is removed from the belt by a belt cleaning unit (not shown).

  FIG. 2 is an enlarged configuration diagram showing the M developing device 10M. In the drawing, the developing device 10M stores M toner in a toner storage portion 12M formed in a casing 11M. The M toner is conveyed from the left side to the right side in the drawing while being agitated by the first agitation paddle 13M and the second agitation paddle 14M that are rotationally driven in the toner accommodation unit 12M. A toner supply roller 15M having a roller portion made of sponge or the like is disposed on the right side of the toner storage portion 12M in the drawing, and is driven to rotate counterclockwise in the drawing. The M toner discharged from the toner container 12M by the second stirring paddle 14M is pumped up by the toner supply roller 15M.

  A toner carrying roller 16M is disposed at the upper right of the toner supply roller 15M in the drawing, and is driven to rotate counterclockwise in the drawing while being in contact with the toner supply roller 15M. At the contact portion of both rollers, M toner on the toner supply roller 15M is supplied to the toner carrying roller 16M. For the purpose of increasing the efficiency of toner supply from the toner supply roller 15M to the toner carrying roller 16M, a supply bias having the same polarity as the toner is applied to the toner supply roller 15M by a supply bias power source (not shown).

  The M toner supplied to the toner carrying roller 16M rotates counterclockwise in the figure as the toner carrying roller 16M rotates while hopping on the surface of the toner carrying roller 16M. Then, the toner carrying roller 16M rotates and enters a contact portion between the regulating member 28M fixed to the casing 11M, and the carrying amount on the surface of the toner carrying roller 16M is regulated.

  The toner carrying roller 16M exposes a part of its peripheral surface from an opening provided in the casing 11M, and the exposed portion is opposed to the photosensitive belt (2) via a predetermined gap. The M toner whose carrying amount on the surface of the toner carrying roller 16M is regulated by the regulating member 28M reaches the developing region facing the photosensitive belt as the toner carrying roller 16M is driven to rotate. A part of the toner adheres to the electrostatic latent image for M on the photosensitive belt and contributes to development. The M toner that has not contributed to the development returns into the casing 11M as the toner carrying roller 16M is driven to rotate.

  FIG. 3 is a perspective view showing the toner carrying roller 16M. The toner carrying roller 16M includes a plurality of electrodes that extend in the roller axial direction and are arranged at a predetermined pitch in the roller circumferential direction on the circumferential surface of the roller portion. More specifically, as shown in FIG. 4, the plurality of electrodes are formed by alternately arranging A-phase electrodes 17A and B-phase electrodes 17B in the roller circumferential direction.

  In FIG. 3, the A-phase common electrode 18A is provided at one end in the axial direction of the roller portion of the toner carrying roller 16M so as to extend over the entire circumference of the roller portion. Is connected to one end of each of the plurality of A-phase electrodes 17A. In addition, a B-phase common electrode 18B is provided at the other end in the axial direction of the roller portion so as to extend over the entire circumference of the roller portion, and this includes the other ends of the plurality of B-phase electrodes 17B. Each part is connected.

  Although not shown in FIGS. 3 and 4 for convenience, a surface layer 19M made of a non-conductive material is coated on the plurality of A-phase electrodes 17A and B-phase electrodes 17B as shown in FIG. The surface layer 19M avoids contact between the electrodes and the toner. However, the surface layer is not provided on the A-phase common electrode 18A and the B-phase common electrode 18B shown in FIG. 3, and these common electrodes are exposed. An A-phase brush contact member (not shown) fixed to the casing (11M) rubs against the A-phase common electrode 18A that moves endlessly as the toner carrying roller 16M rotates. The A-phase pulse voltage output from the A-phase pulse power supply 27A is applied to each A-phase electrode 17A via the A-phase brush contact member and the A-phase common electrode 18A. Further, a B-phase brush contact member (not shown) fixed to the casing rubs against the B-phase common electrode 18B that moves endlessly as the toner carrying roller 16M rotates. The B-phase pulse voltage output from the B-phase pulse power supply 27B is applied to each B-phase electrode 17B via the B-phase brush contact member and the B-phase common electrode 18B.

  Hereinafter, a set of a plurality of A-phase electrodes 17A to which the A-phase pulse voltage is applied is referred to as an A-phase electrode group. A set of a plurality of B phase electrodes 17B to which a B phase pulse voltage is applied is referred to as a B phase electrode group. Since the A-phase electrodes 17A and the B-phase electrodes 17B are alternately arranged, the order of arrangement of the plurality of A-phase electrodes 17A from the predetermined position in the roller circumferential direction is odd or even. The arrangement order of the plurality of B-phase electrodes 17B is an even number when the arrangement order of the A-phase electrodes 17A is an odd number, and an even number when the arrangement order of the A-phase electrodes 17A is an even number. .

  For example, a rectangular wave A-phase pulse voltage Va that repeats rising and falling at a predetermined cycle as shown in FIG. 6 is applied to the A-phase electrode group. On the other hand, a rectangular wave B-phase pulse voltage Vb whose rising and falling phases are opposite to the A-phase pulse voltage Vb is applied to the B-phase electrode group, for example, as shown in FIG. When such a pulse voltage is applied, the M toner on the toner carrying roller (16M) floats right above the A-phase electrode 17A and forms a parabola so that it is directly above the adjacent B-phase electrode 17B. After landing, this time the reciprocating movement by hopping is repeated such that it floats right above the B-phase electrode 17B and returns to the adjacent A-phase electrode 17B so as to draw a parabola.

  The M toner that has been reciprocated by hopping in this way is conveyed to the development area by the rotational driving of the toner carrying roller (16M). Then, in the development area, when it is located near the apex of the parabolic hopping trajectory and in the vicinity of the electrostatic latent image of the photosensitive belt (2), it deviates from the hopping trajectory while being pulled by the electrostatic force of the electrostatic latent image, Adhere to the electrostatic latent image. On the other hand, when it is located near the background portion (uniformly charged portion) of the photosensitive belt (2) in the vicinity of the apex of the parabolic hopping locus, it descends without deviating from the hopping locus, and the toner carrying roller (16M). Land on the surface.

  In such a configuration, the M toner in which the adsorbing force with the toner carrying roller (16M) is released by hopping is used for development, so that the conventional one-component development method or two-component development method could not be realized. Low potential development can be realized. Hereinafter, a method in which development is performed by transporting the toner to the development region by moving the surface of the toner carrier while reciprocating the toner between the electrodes of the toner carrier by hopping as in the present printer is referred to as a flare development method. .

  By the way, in the conventional two-component development system, development is performed while rubbing the toner adhering to the surface of the magnetic carrier magnetically attracted to the developer carrier with the magnetic carrier together with the latent image carrier. Further, in the conventional one-component development method, the toner carried on the surface of the developer carrying member is rubbed against the latent image carrying member, or the toner on the developer carrying member arranged in non-contact with the latent image carrying member. The image is reciprocated between the developer carrying member and the latent image carrying member by an alternating electric field. In these methods, when overlay development is performed as in this printer, the toner in the toner image previously developed on the latent image carrier is transferred to the subsequent color developing device during the subsequent development. Cause color mixing.

  On the other hand, in this printer, development is performed without causing the toner on the toner carrying roller (16M) to rub against the photosensitive belt (2). Further, the toner is not reciprocated between the surface of the photosensitive belt and the surface of the toner carrying roller by an alternating electric field. Among the hopped toners, the toner carrying roller that does not contribute to the development is not brought into contact with the photosensitive belt. Return to the top. In addition, the toner contributing to the electrostatic latent image on the photosensitive belt is not re-transferred onto the toner carrying roller. As a result, it is possible to avoid color mixing in the developing device for subsequent colors.

  Unlike the so-called tandem type image forming apparatus that transfers toner images developed on a plurality of latent image carriers on a transfer body, the respective latent image carriers are optically written on the same latent image carrier. In addition, since the process of superimposing and transferring the toner images of the respective colors is not performed, a high-quality full-color image with little color misregistration can be obtained.

  The pulse voltage applied to the A-phase electrode group and the B-phase electrode group includes an A-phase pulse voltage Va composed of a rectangular wave as shown in FIG. 7 and a DC voltage Vb or 0 [V] that is the center value of the amplitude of the A-phase pulse voltage Va. ] May be adopted. Further, the relationship between the A phase and the B phase in this combination may be reversed. Further, as the waveform of the pulse voltage, other than a rectangular wave, for example, a sine wave, a triangular wave having a time constant, a sine wave corresponding to the time constant, or the like may be employed.

  In FIG. 2, the M toner that has not contributed to the development in the development area returns to the developing device 10M as the toner carrying roller 16M rotates, and then enters the contact position with the toner supply roller 15M. To do. At this time, since the M toner on the toner carrying roller 16M does not exhibit adhesion to the roller surface by hopping, the toner supply roller 15M that rotates so as to move the surface in the counter direction with respect to the toner carrying roller 16M is easy. It is scraped or leveled. At the same time, new toner is supplied from the toner supply roller 15M to the toner carrying roller 16M. Due to the synergistic action of scraping, collecting, leveling, and supply, a uniform amount of toner hops on the surface of the toner carrying roller 16M after passing through the toner supply region.

  In FIG. 5 shown above, the A-phase electrode 17A and the B-phase electrode 17B have a thickness of 0.1 to 10 [μm], preferably 0.5 to 2.0 [μm] on the insulating support substrate 20M. A conductive layer made of a conductive material such as Al or Ni—Cr formed to a thickness of 2 is processed into a required electrode shape by a photolithography method or the like. As the support substrate 20M, a substrate made of an insulating material such as a glass substrate, a resin substrate, a ceramic substrate, or a polyimide substrate, or a substrate formed of an insulating film such as SiO2 on a substrate made of a conductive material such as SUS is used. It is possible.

  As a method of manufacturing the toner carrying roller 16M having such a configuration, various methods using conventionally known techniques can be cited. As an example, there is a method of winding a flexible support substrate on which an electrode pattern or a surface layer is formed around a support drum.

  Specifically, a polyimide base film (thickness 20 to 100 μm) is used as a supporting substrate, and a thickness 0.1 to 0.3 [μm] made of Cu, Al, Ni—Cr or the like is formed thereon by vapor deposition. A conductive film is obtained. Examples of the vapor deposition method include a sputtering method, an ion plating method, a CVD method, and an ion beam method. When the sputtering method is employed, a Cr film may be interposed, or plasma treatment or primer treatment may be performed in order to improve adhesion to a support substrate made of polyimide or the like. Further, the conductive film may be formed by a method different from the evaporation method. For example, an electrodeposition method may be employed. In this case, the support substrate is sequentially immersed in Sn chloride, Pd chloride, and Ni chloride to form a base on the substrate surface, and then electroless plating is performed in a Ni electrolyte solution to form a 1 to 3 [μm] Ni film. May be formed.

  After the conductive film is formed on the support substrate, an electrode pattern is obtained by applying resist coating, patterning, etching or the like to the conductive film. If the conductive film has a thickness of 0.1 to 3 [μm], a pattern having a width and interval of 5 to several tens [μm] can be formed with high accuracy by a photolithography method or an etching process.

  In the case of a conductive film having a width of 30 to 60 [cm], a roll-to-roll method (after printing a circuit pattern on a substrate wound in a roll shape and pasting it with a sealing film wound in a roll shape, etc. It is possible to easily form a combination of a support substrate, an electrode pattern, and a surface layer with an apparatus of a method of winding again on a roll. When forming the electrode pattern, the A-phase common electrode and the B-phase common electrode are also formed together with the A-phase electrode and the B-phase electrode. The width of the common electrode is preferably about 1 to 5 [mm].

Once the electrode pattern is obtained, next, a surface layer of 0.5 to 2 [μm] thickness made of SiO ₂ , BaTiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _5, etc. is sputtered, etc. Formed by. After a film of 2 to 5 [μm] made of PI (polyimide) is applied by a roll coater or other coating apparatus, it may be baked and finished as a surface layer. When trouble occurs with PI, an insulating film made of SiO ₂ or other inorganic material is further formed on the upper surface by sputtering or the like to a thickness of 0.1 to 0.5 [μm]. It is good also as a layer. Furthermore, an organic material such as polycarbonate may be coated on SiO ₂ or the like, and this may be used as the final surface layer. Zirconia or a material generally used as a coating material for a carrier of a two-component developer, such as a silicone resin, can also be selected. The thickness of the surface layer is 0.5 to 10 [μm], preferably 0.5 to 3 [μm]. Further, the material is preferably selected in consideration of the insulating properties, durability, roller manufacturing method, charge train with the toner to be used, and the like.

  The toner carrying roller can be manufactured by sticking the flexible substrate obtained as described above to a cylindrical drum or by partially forming a curved surface.

  As another method for producing a flexible substrate, a method of forming a conductive film made of Cu, SUS, or the like having a thickness of 10 to 20 [μm] on a polyimide base film (thickness 20 to 100 μm) as a base material. Is mentioned. In this method, for example, polyimide is applied on a metal material with a thickness of 20 to 100 [μm] by a roll coater and baked. Thereafter, a metal material may be patterned into an electrode by a photolithography method or an etching process, and polyimide may be coated thereon to form a surface layer. If there is an unevenness of about 10 to 20 [μm] due to a step between a place where the electrode pattern exists and a place where the electrode pattern does not exist, flattening is performed. For example, when a polyimide material or a polyurethane material having a viscosity of 50 to 10,000 [cps], more preferably 100 to 300 [cps] is spin-coated and left standing, unevenness is smoothed by the surface tension of the material.

Moreover, the following manufacturing method is mentioned as another manufacturing method of a flexible board | substrate. That is, a conductive film made of SUS, Al or the like is formed on a base material having a thickness of 20 to 30 [μm], and a diluted polyimide material of about 5 [μm] is coated thereon by a roll coater. Then, this polyimide is pre-baked for 30 minutes in an environment of 150 [° C.] or post-baked for 60 minutes in an environment of 350 ° C. to form a thin-layer polyimide film. Thereafter, after performing plasma treatment and primer treatment for improving adhesion, Ni—Cr is deposited as a conductive film to a thickness of 0.1 to 0.2 [μm], and several tens [ An electrode pattern with a fine pitch of μm] is formed. Furthermore, a flexible substrate can be obtained by forming a surface layer made of SiO ₂ , BaTiO ₂ , TiO ₂ or the like with a thickness of 0.5 to 1 [μm] thereon by sputtering. As the surface layer, an organic material such as polycarbonate may be coated on SiO ₂ or the like. It is also possible to select zirconia or a material generally used as a coating material for a carrier of a two-component developer, for example, a silicone resin.

As another method for manufacturing the toner carrying roller, there is a method in which an electrode pattern or a surface layer is directly formed on a cylindrical drum or a cylindrical roller. For example, the surface of the drum-like substrate is smoothly finished by peripheral turning to obtain a support substrate 20M on the drum as shown in FIG. Next, as shown in FIG. 8B, a plurality of grooves having a width of 50 [μm] are formed on the surface of the support substrate 20M at a pitch of 100 [μm] by cutting. Then, as shown in FIG. 8C, after electroless nickel plating is applied to the surface of the support substrate 20M on which a plurality of grooves are formed, as shown in FIG. A plurality of electrodes (17A, 17B, etc.) made of a plating material accommodated in each groove are obtained by turning a portion existing outside the groove. Next, as shown in FIG. 8 (e), a silicone resin is smoothly coated to obtain a surface layer 19M that exhibits a volume resistivity of about 10 ¹⁰ [Ω · cm] with a thickness of about 5 [μm]. .

  Electrodes can also be applied to the curved surface of the support substrate by screen-printing the conductive ink on the support substrate, pattern-printing the conductive ink by inkjet, or removing the conductive film obtained by plating by laser processing. A pattern can be formed.

  As materials for the support substrate, the electrodes, and the surface layer, materials other than those described so far can be used. For example, silver or copper may be used as the electrode material.

  In FIG. 3 described above, R indicates a gap between the A-phase electrode 17A and the B-phase electrode 17B. Moreover, L has shown the width | variety which is the length of the transversal direction of these electrodes. The electrode arrangement pitch P can be represented by a gap R + width L. On the roller surface, M toner (not shown) located between the electrodes moves along the electric lines of force extending in the direction in which the electrodes are arranged so as to lick the roller surface. On the other hand, the M toner located on the electrodes (17A, 17B) hops along the electric lines of force formed so as to draw a parabola between the electrodes, so that it contacts and separates from the roller surface. . In addition, the M toner located near the end in the width direction of the electrode may hop so as to jump over the adjacent electrode. For this reason, when the width L is relatively large, the number of M toner particles on the vicinity of the electrode end portion is relatively large, so that the toner having a large moving distance is relatively large. However, if the width L is too large, the electric field strength in the vicinity of the center of the electrode becomes relatively weak, resulting in poor hopping efficiency. There is an appropriate width L value for efficiently hopping M toner at a low voltage.

  The gap R is an element that affects the electric field strength between the electrodes. When the magnitude (amplitude) of the pulse voltage applied to the electrodes is constant, the electric field strength between the electrodes increases as the gap R decreases. Hopping speed increases. However, with the M toner that hops from right above the electrode to right above the adjacent electrode, the moving distance per hopping is relatively short. For this reason, if the frequency f of the pulse voltage is not set high, the landing time becomes longer than the floating time, resulting in poor efficiency. Therefore, there is also an appropriate gap R value for efficiently hopping M toner at a low voltage.

  Further, the thickness of the surface layer 19M is one factor that influences the electric field strength on the roller surface. In particular, the influence of the vertical component on the electric field lines is large, which greatly affects the efficiency of hopping. That is, setting the width L, the gap R, and the surface layer thickness appropriately is an important factor for performing efficient hopping at a low voltage. In this printer, both the width L and the gap R are set to 1 to 20 times the average particle diameter of the toner. The length in the axial direction of the roller portion of the toner carrying roller 16M is set to a length of 21 [cm] or more, preferably 30 [cm] or more, which is the A4 vertical width.

  Although the developing device 10M for M has been described in detail, the developing devices for other colors (10C, Y, K) have the same configuration as that for M.

Next, a characteristic configuration of the printer will be described.
The present inventors prepared a test device for a developing device for K having the same configuration as the developing device 10M for M shown in FIG. The electrostatic capacity measured between the A phase electrode and the B phase electrode of the toner carrying roller in this test machine was 1000 to 2000 [pF].

As the toner supply roller of the test machine, a sponge roller having a volume resistivity of 10 ⁸ [Ω · cm] was used. The toner supply roller having such a configuration was brought into contact with the toner carrying roller with a biting amount of 0.5 [mm]. With the rotation of the toner carrying roller, the toner that has passed through the developing region and returned to the contact position (toner supply position) with the toner supply roller has weakened the adhesive force with the toner carrying roller by hopping. Even a biting amount as small as about 5 mm can be sufficiently collected by the toner supply roller.

  An insulating rubber blade was used as a regulating member for regulating the toner carrying amount on the toner carrying roller. In addition, a toner having an average particle diameter in the range of 3 to 12 [μm] was used as a toner to be mounted on the testing machine. When the average particle diameter is in this range and the silica addition amount is 1 to 5 parts by weight with respect to 100 parts by weight of the toner base resin, charging is performed with a normal charge amount in the test machine, resulting in poor charging. It was confirmed that hopping failure due to toner and sticking to the surface of the toner carrying roller due to excessive charging were not caused.

  Next, negatively chargeable (minus chargeable) K toner having a volume average particle diameter of 6 [μm] was set in the test machine, and the toner carrying roller was rotated at a linear speed of 300 [mm / sec]. At this time, the toner supply roller was rotated at a linear velocity of 200 [mm / sec] so that the toner supply roller was rubbed against the toner carrying roller in the counter direction. Further, as shown in FIG. 6, the A phase pulse voltage and the B phase pulse voltage having opposite phases were applied to the A phase electrode group and the B phase electrode group of the toner carrying roller. As the frequency f of these pulse voltages, 1 [kHz] was adopted, and 200 [V] was adopted as Vpp (peak-to-peak voltage). Further, −200 [V] was adopted as the offset voltage which is the center of the amplitude. That is, the A-phase pulse voltage and the B-phase pulse voltage repeat rising and lowering between a Max value of −100 [V] and a Min value of −300 [V], centering on −200 [V]. A DC supply bias of −450 [V] was applied to the toner supply roller. In all experiments described below, a negatively chargeable toner was used.

  Under such conditions, the surface potential of the toner carrying roller was measured with a non-contact surface potential sensor while idling (running without developing), and the measured value increased with time. (It became larger on the plus side). Note that pulse voltages are applied to the A-phase electrode group and the B-phase electrode group, respectively, and they repeatedly rise and fall within an extremely short time around the offset potential Vo of −200 [V]. Therefore, when a pulse voltage is applied and no toner is placed on the roller, -200 [V] which is the center potential of the pulse voltage is detected by the surface potential sensor.

  Next, the surface potential of the toner carrying roller in the initial state in which no pulse voltage is applied to the A-phase electrode group and the B-phase electrode group (GND connection) and no toner is placed on the surface is measured, and the result is It was confirmed that the voltage was 0 [V]. Then, after negatively charged toner was supplied to the surface of the toner carrying roller, an idle operation for 90 seconds was performed in the same manner as before. Then, after stopping the application of the pulse voltage (electrode connected to GND), the surface potential of the toner carrying roller was measured, and a measurement result of about -250 [V] was obtained. This is a value equal to the absolute value of the potential difference between the toner supply bias and the offset potential Vo, and it can be seen that the surface potential changes so that the supply electric field is zero.

  Next, in an initial state tester in which K toner is not mounted in the toner container, the idling operation was started while applying the pulse voltage shown in FIG. 6 to each electrode. Then, the idle operation was temporarily stopped every 30 seconds, and the surface potential of the toner carrying roller was measured in a state where no pulse voltage was applied. Under the conditions in which the toner supply bias was set to +50 “V”, −200 “V”, −450 “V”, and −750 “V”, the above-described empty driving experiments were performed. Note that the offset potential Vo in the pulse voltage during idling is all −200 [V].

  The results are shown as a graph in FIG. From this graph, when the toner supply bias Vc is equal to the offset potential Vo of the pulse voltage (Vc = −200 V), the surface potential of the toner carrying roller does not change much even if the idle operation for 90 seconds is performed. I understand. On the other hand, when a potential difference is provided between the toner supply bias Vc and the offset potential Vo (−200 V), the toner carrying roller has a polarity that is opposite to the supply potential (Vo−Vc) and has the same absolute value. It can be seen that the surface potential (including the toner potential) is changed. From these results, it is considered that charges are induced in the surface layer of the toner carrying roller at the position facing the toner supply roller to which the supply bias is applied, due to the influence of the supply electric field. As shown in FIG. 10, the surface layer of the toner carrying roller functions like a capacitor of an RC series circuit, and charges are accumulated on the surface layer.

  If charges are accumulated in the surface layer in this way, the development potential (difference between the offset potential and the latent image potential) or the background potential (offset potential and background portion) in the development region where the toner carrying roller and the photosensitive belt face each other. The difference between the image density and the image density may be changed, resulting in insufficient image density or background contamination. In the continuous print mode in which images are continuously formed on a plurality of recording sheets, the operation time of the developing device becomes long, so that such an image density shortage and background stain are particularly likely to occur. Further, even if the supply bias is stopped, the electric charge accumulated in the surface layer does not disappear easily, so even if it is a single print, if the time has not passed since the previous print, Insufficient concentration or soiling will occur.

  Although there is an example in which the toner supply bias Vc has a polarity opposite to that of the toner, even with such a bias, a certain amount of the toner supply bias Vc is caused by the mechanical contact between the toner supply roller and the toner carrying roller. Low charge amount toner could be supplied from the toner supply roller to the toner carrying roller.

  Next, the inventors continuously rotated the toner carrying roller while applying +50 [V] to the toner supply roller as the toner supply bias Vc. Then, 90 seconds after the start of rotation, the application of the pulse voltage to each electrode of the toner carrying roller was stopped, and the surface potential of the toner carrying roller was measured after each electrode was grounded. Then, the measurement result became about 250 [V].

  Summarizing these results, the following can be said. That is, immediately after the rotation of the toner carrying roller, even if the surface potential is 0 [V] and an intended image is obtained, the surface potential gradually changes with the passage of the rotation time thereafter. End up. When the surface potential of the toner carrying roller increases to the plus side, the developing potential (potential difference between the latent image and the toner carrying roller) decreases accordingly, and the image density gradually decreases. To go. On the contrary, when the surface potential of the toner carrying roller increases to the minus side, the developing potential increases accordingly, and the image density gradually increases.

  Next, the inventors of the present invention tested the surface of the toner carrying roller while performing idling without applying a pulse voltage and a supply bias (grounding) in a test machine in an initial state in which K toner is not mounted in the toner container. The potential was measured. In such a test, the only factor that charges the surface layer of the toner carrying roller is the friction between the toner supply roller and the regulating member and the surface layer. As a result of this test, as shown in FIG. 11, the surface potential of the toner carrying roller gradually decreased immediately after the idling operation was started, and stabilized at about −40 [V] after 30 seconds. As a result, it has been found that the surface layer of the toner carrying roller is charged by friction with the toner supply roller and the regulating member. In this test, the potential of the surface layer after frictional charging was stabilized at about −40 [V]. However, depending on the relationship between the toner supply roller, the regulating member, and the material of the surface layer, the potential was stabilized at a different potential value. I think that. In addition, depending on the material relation, the amount of biting of the toner supply roller, and the contact pressure of the regulating member, the surface layer may be triboelectrically charged positively, or the time for stabilizing the potential may be faster or slower than 30 seconds. .

  Furthermore, the present inventors removed the regulating member from the testing machine. Then, the test machine was idled while applying a pulse voltage including the offset potential Vo to each electrode of −200 [V]. Such idling was performed under the conditions of toner supply bias Vc of +50 [V], -200 [V], and -450 [V], respectively. After starting the idling operation under each condition, the application of the pulse voltage is stopped at an arbitrary timing, the K toner on the toner carrying roller is sucked and removed, and then the surface of the toner carrying roller under the condition that each electrode is grounded The potential was measured.

  The result is shown in FIG. At each measurement point in the figure, since no toner is present on the surface of the toner carrying roller, the measured value should be 0 [V] if the surface layer is not charged. However, as shown in the figure, the measured value changed with the elapsed time. This change is caused by induction of charge on the surface layer of the toner carrying roller due to the toner supply bias, charging of the surface layer of the toner carrying roller due to friction with the toner supply roller, and induction of reverse charge on the surface layer due to friction with the toner. This is the result of all three phenomena. When 150 [V] is subtracted from each measured value 90 seconds after the start of idling, the respective data become +250 [V], 0 [V], −250 [V], and the experimental results shown in FIG. Matches. From this, under any condition, it can be said that the amount of change in the surface potential of the toner carrying roller due to the toner inducing charge in the surface layer is about 150 [V].

As described above, it has been found that the surface layer of the toner carrying roller is charged due to the following three factors as the developing device operates.
(A) A charge is induced by a high voltage applied to a member facing itself (capacitor model).
(B) Friction charging occurs in accordance with the rubbing with the toner supply roller and the regulating member.
(C) A charge having a polarity opposite to that of the toner is induced on the surface layer in accordance with the rubbing with the toner to be hopped.

  If only the above-mentioned factor (A) is to charge the surface layer, it is possible to avoid fluctuations in the surface potential of the toner-carrying roller by supplying the toner only by mechanical action without applying a supply bias to the toner supply roller. be able to. However, since the factors (B) and (C) are also involved, it is difficult to avoid charging of the toner carrying roller.

  Therefore, in the printer according to the present embodiment, each of the developing devices 10M, C, Y, and K for each color is provided with a discharging unit that discharges the surface of the toner carrying roller at a predetermined position in the endless movement direction (rotation direction). Yes. In such a configuration, the surface potential fluctuation of the toner carrying roller in the developing region can be suppressed by removing the surface layer of the toner carrying roller by the charge removing unit. As a result, it is possible to suppress the occurrence of uneven image density and background stains due to surface potential fluctuations.

  In the present embodiment, as the charge eliminating means, a regulating member (for example, 28M in FIG. 2) which is a facing member facing the surface of the toner carrying roller, and a charge removing power source (for example, a voltage applying means for applying a charge eliminating bias) to the regulating member. 26M) in FIG. 2 is used.

The present inventors prepared a test device for a developing device for K having the same configuration as the developing device 10M for M shown in FIG. The conditions of this testing machine are as listed below.
Toner supply roller: Sponge roller with a volume resistance of 10 ⁸ [Ω · cm] Biting amount of toner supply roller with respect to the toner carrying roller: 0.5 [mm]
・ Regulator: Conductive stainless steel blade ・ Supply bias: AC / DC bias bias ・ DC component of supply bias: Same as offset potential Vo of A-phase pulse voltage Va and B-phase pulse voltage Vb ・ Frequency of AC component of supply bias: 300 [Hz]
-Peak-to-peak voltage (Vpp) of AC component of supply bias: 400 to 800 [V]
-Volume average particle size of K toner: 6 [μm]
-Addition amount of silica in K toner: 2 parts by weight with respect to 100 parts by weight of toner base resin-Linear speed of toner carrying roller: 300 [mm / sec]
-Linear speed of toner supply roller: 200 [mm / sec]
The rubbing direction between the toner supply roller and the toner carrying roller: counter direction. Pulse voltage to the electrodes: A-phase pulse voltage Va and B-phase pulse voltage Vb shown in FIG.
-Frequency of pulse voltage f: 1 [kHz]
・ Vpp of pulse voltage is 200 [V]
・ Offset potential Vo of the pulse voltage: -200 [V]

  In the testing machine having such a configuration, the surface layer of the toner carrying roller is discharged through the toner layer by applying a discharging bias to the regulating member. When the idling was actually performed, as shown in FIG. 13, the potential increase of the surface layer over time could be avoided.

  Note that the surface potential shown in FIG. 13 is measured in a state where the application of the pulse voltage is stopped. Moreover, you may use as a control member what coat | covered the surface of the metallic base | substrate with the insulating layer. In addition to the DC voltage, an AC voltage or an AC / DC superimposed voltage can be employed as the charge eliminating bias. However, when an AC / DC superposed voltage is employed, it is necessary to remove electricity by discharging from the regulating member to the toner carrying roller, and therefore, it is necessary to use a bare conductive surface as the regulating member. Furthermore, it is necessary to employ a DC component having the same value as the offset potential Vo of the pulse voltage.

  FIG. 14 is an enlarged configuration diagram illustrating the M developing device 10M in the first modified example of the printer according to the embodiment. The developing device 10M includes an area (hereinafter referred to as a collection area) before passing through the developing area with rotation and before entering the contact position with the toner supply roller 15M among all the areas in the circumferential direction of the toner carrying roller 16M. A recovery means for recovering the M toner. This collecting means is composed of a collecting roller 21M that comes into contact with the aforementioned area, a flicker member 22M that comes into contact with this, a collecting power source 25M, and the like.

  The collection roller 21M has a metal rotating shaft member that is rotatably supported and a roller portion made of an elastic material coated on the peripheral surface thereof. Then, the roller portion is driven to rotate while contacting the collection area of the toner carrying roller 16M.

  The collection power source 25M applies a collection bias having a polarity opposite to the toner charging polarity (positive polarity in this example) to the rotating shaft member of the collection roller 21M. By this application, the negatively chargeable M toner hopping on the surface of the toner carrying roller 16M is electrostatically attracted toward the collection roller 21M.

  When the M toner on the toner carrying roller 16M enters the position facing the collection brush roller 21M as the roller rotates, it is transferred to the collection roller 21M while being scraped off by the collection roller 21M. At this time, the transfer of the M toner is promoted by attracting the M toner by the electrostatic force due to the recovery bias.

  The flicker member 22M is cantilevered by the casing 11, and its free end is in contact with the collection roller 21M. Then, in accordance with the rubbing with the collection roller 21M, the free end side is swung around the fixed end side, and the M toner on the collection roller 21M is screened off.

  In such a configuration, a combination of the collection roller 21M, which is a facing member facing the surface of the toner carrying roller, and the collection power source 25M that applies a collection bias to the recovery roller 21M functions as a charge removing unit that removes the surface layer of the toner carrying roller. ing. The surface layer in which a charge having a polarity opposite to that of the toner (positive in this example) is induced by the influence of the supply bias is neutralized by the charge having the same polarity as that of the toner due to the influence of the recovery bias having a polarity opposite to that of the toner. Because.

The present inventors prepared a test device for a developing device for K having the same configuration as the developing device 10M for M shown in FIG. Various conditions in this testing machine are listed below.
Toner supply roller: Sponge roller with a volume resistance of 10 ⁸ [Ω · cm] Biting amount of toner supply roller with respect to the toner carrying roller: 0.5 [mm]
・ Regulator: Insulating rubber blade ・ Recovery roller: Sponge roller ・ Rubbing direction between the recovery roller and the toner carrying roller: Counter direction ・ Intrusion amount of the collection roller with respect to the toner carrying roller: 0.5 [mm]
Pulse voltage: A phase pulse voltage Va and B phase pulse voltage Vb shown in FIG.
・ Offset potential Vo of the pulse voltage: -200 [V]
・ Supply bias: DC voltage of −400 [V] ・ Recovery bias: DC voltage of +400 [V]

  When the test machine having such a configuration was idled, a positive charge of +400 [V] induced in the surface layer by the supply bias was a negative charge of +400 [V] induced in the surface layer by the recovery bias. By canceling out, the surface layer could be neutralized.

  Note that it is not always necessary to use a collection roller as the collection member to which the collection bias is applied. For example, a recovery brush roller having a rotating shaft member and a brush roller portion formed of a plurality of raised brushes standing on the peripheral surface of the rotation shaft member may be used as the recovery member. Further, an electrode plate provided with toner cleaning means may be used as the recovery member. Further, a rubber roller may be used as the collecting member as long as it is disposed in a non-contact manner with respect to the toner carrying roller.

  FIG. 15 is an enlarged configuration diagram illustrating the M developing device 10M in the second modified example of the printer according to the embodiment. A casing 11M, which is a developing device casing of the developing device 10M, cantilever-supports a seal member 23M that closes the space between the endlessly moving surface of the toner carrying roller 16M and the casing 11M. The seal member 23M is made of a conductive material, and seals between the casing 11M and the toner carrying roller 16M by sliding the free end side against the toner carrying roller 16M. And the static elimination bias which consists of an alternating current direct current superposition voltage is applied to this sealing member 23M by the static elimination power supply 24M.

  In such a configuration, a combination of a seal member 23M, which is a facing member facing the surface of the toner carrying roller, and a static elimination power source 24M that applies a static elimination bias to the seal member 23M functions as a static elimination means for eliminating the surface layer of the toner carrying roller. ing. This is because the surface layer in which a charge having a polarity opposite to that of the toner (positive in this example) is induced by the influence of the supply bias is removed by discharging from the seal member 23M.

The present inventors prepared a test device for a developing device for K having the same configuration as the developing device 10M for M shown in FIG. Various conditions in this testing machine are listed below.
-Seal member: Conductive mylar sheet-Frequency of AC component of static elimination bias: 300 [Hz]
-Peak-to-peak voltage (Vpp) of the AC component: 400 to 800 [V]
-DC component of static elimination bias: Same value as offset potential Vo of pulse voltage

  When the idling operation was performed with the test machine having such a configuration, the positive charge induced in the surface layer by the supply bias could be eliminated by the discharge from the seal member. Note that a DC voltage having a polarity opposite to that of the supply bias may be adopted as the charge eliminating bias. In this case, the absolute value is set to be the same as the absolute value of the supply bias.

Next, printers according to the respective examples in which a more characteristic configuration is added to the printer according to the embodiment will be described. Note that the configuration of the printer according to each example is the same as that of the embodiment unless otherwise specified.
[First embodiment]
As described above, when a toner supply bias is applied to the toner supply roller, the surface potential of the toner carrying roller has a polarity opposite to that of the toner supply bias and an absolute value equal to the absolute value (hereinafter referred to as supply bias) due to charge induction in the surface layer. Polarity inversion value). In such a case, basically, the neutralization bias may be set to a value that can cancel the supply bias polarity reversal value determined from the toner supply bias. However, the surface potential of the toner carrying roller does not immediately become the supply bias polarity inversion value immediately after the start of the image forming operation as shown in FIG. For this reason, if a static elimination bias having a value corresponding to the supply bias polarity inversion value is applied immediately after the start of the image forming operation, the surface layer is reversely charged due to excessive static elimination immediately after the start of the image forming operation.

  Therefore, in the printer according to the first embodiment, a surface potential sensor (not shown) for detecting the surface potential of the toner carrying roller by a known technique is provided in each color developing device (10M, C, Y, K). These surface potential sensors are areas before passing into the contact position with the regulating member (28M, C, Y, K) after passing through the toner supply position in the entire area in the rotation direction of the toner carrying roller. Are arranged so as to face all or a part of each of them with a predetermined gap.

  On the other hand, the static elimination power source (26M, C, Y, K) that applies the static elimination bias to the regulating member (28M, C, Y, K) has the static elimination bias based on the detection result by the surface potential sensor as the surface potential detection means. Voltage determining means for determining an output value (value of applied voltage) is included. This voltage determination means is composed of a CPU (Central Processing Unit) as a calculation means, a RAM (Random Access Memory) as a data storage means, a ROM (Read Only Memory) as a data storage means, and the like. A function expression of the detection result of the surface potential and the appropriate neutralization bias corresponding thereto is stored in the ROM. Based on this relational expression and the detection result by the surface potential sensor, an appropriate neutralization bias value is stored. Then, the neutralization bias having the same value as that of the identification is output from the neutralization power source.

  In such a configuration, it is possible to avoid the occurrence of reverse charging of the surface layer of the toner carrying roller due to improper application of the neutralizing bias immediately after the start of the image forming operation.

[Second Embodiment]
In the printer according to the second embodiment, toner is supplied without applying a toner supply bias to the toner supply rollers (15M, C, Y, K) in the developing devices (10M, C, Y, K) of the respective colors. Toner is supplied from the rollers (15M, C, Y, K) to the toner carrying rollers 16 (M, C, Y, K). Even if a toner supply bias is not applied to the toner supply roller, the toner can be supplied to the toner support roller by mechanical contact between the toner supply roller and the toner support roller.

  In such a configuration, the surface potential fluctuation amount due to the charge amount fluctuation of the surface layer of the toner carrying roller is not controlled by the toner supply bias, but is affected by the toner amount on the toner carrying roller, the triboelectric charge amount of the surface layer, and the like. It becomes difficult to grasp the surface potential.

  Therefore, in the printer according to the second embodiment, as in the first embodiment, the surface potential sensor is provided in the developing device for each color, and the output value of the static elimination bias (the value of the applied voltage) is determined based on the detection result. ) Is provided in each color neutralizing power source.

  With this configuration, the toner carrying roller can be appropriately discharged while accurately grasping the surface potential fluctuation of the toner carrying roller that is not affected by the toner supply bias.

[Third embodiment]
In this printer, each color toner carrying roller (16M, C, Y, K) is coated with a surface layer made of, for example, a silver material that exhibits good light reflectivity, and the surface layer is mirror-finished. Have. In addition, a reflection type photosensor facing the toner carrying roller via a predetermined gap is provided. The reflection type photosensor includes all or part of the entire region in the rotation direction of the toner carrying roller, after passing through the toner supply position and before entering the contact position with the regulating member. A voltage corresponding to the light reflectance is output. As the toner carrying amount per unit area of the toner carrying roller increases, the light reflectance of the surface layer decreases. Therefore, the toner carrying amount increases as the output voltage from the reflective photosensor decreases. In other words, the reflection type photosensor functions as a toner carrying amount detection unit that detects the toner carrying amount per unit area on the surface of the toner carrying roller.

  The printer also includes a reflective photosensor for a belt that detects a developing density as a toner adhesion amount per unit area with respect to a predetermined reference toner image formed on the photosensitive belt 2. Then, a reference toner image of each color is formed on the photosensitive belt 2 at a predetermined timing, and each developing density is detected by a belt reflective photosensor.

  The printer also includes a humidity sensor that detects humidity using a known technique, and a charge amount estimation unit that estimates the charge amount on the toner carrying roller based on the detection result. This charge amount estimation means is composed of a CPU (Central Processing Unit) as a calculation means, a RAM (Random Access Memory) as a data storage means, a ROM (Read Only Memory) as a data storage means, and the like. A data table indicating the relationship between the toner charge amount and the humidity constructed based on the result of the experiment in advance is stored in the ROM. Based on the data table and the detection result by the humidity sensor, the data on the toner carrying roller is stored. The charge amount of the toner is estimated.

  The neutralizing power source (26M, C, Y, K) for applying a neutralizing bias to the regulating members (28M, C, Y, K) of the respective colors has an estimation result by the charge amount estimating means, an offset potential Vo of the pulse voltage, and reflection. The static elimination bias is determined on the basis of the detection result by the mold photosensor and the above-described development density detection result.

  Even in such a configuration, it is possible to avoid the occurrence of reverse charging of the surface layer of the toner carrying roller due to improper application of the neutralizing bias immediately after the start of the image forming operation. Further, when no toner supply bias is applied to the toner supply roller, the toner carrying roller can be appropriately discharged while accurately grasping the surface potential fluctuation of the toner carrying roller that is not affected by the toner supply bias.

  As described above, in the printer according to the embodiment, each modification device, and the printer according to each example, the opposing member that faces the surface of the toner carrying roller that is the toner carrying member, and the power source that is the voltage applying unit that applies a voltage to the opposing member. Are used as static elimination means. In this configuration, the surface layer of the toner carrying roller can be neutralized by the action of the voltage applied to the opposing member.

  In the printer according to the embodiment, a regulating member that regulates the carrying amount of the toner supplied onto the surface of the toner carrying roller by the toner supply roller serving as the toner supply unit is used as the facing member. Yes. In such a configuration, it is possible to reduce the size and cost of the apparatus by using the restricting member also as the opposing member to which the neutralizing bias is applied.

  In the first modified apparatus, a recovery roller that is a recovery member that transfers the toner on the surface of the toner carrying roller to its own surface and recovers it is used as the counter member. In such a configuration, the collection roller is also used as the counter member, and the recovery power source that applies the recovery bias to the recovery roller is also used as the power source that applies the neutralization bias to the counter member. Cost can be reduced.

  In the second modified apparatus, a sealing member that closes the space between the endlessly moving surface of the toner carrying roller and the casing that is the developing device housing is used as the facing member. In such a configuration, it is possible to reduce the size and cost of the apparatus by using the sealing member also as the opposing member to which the neutralizing bias is applied.

  In addition, in the printer according to the embodiment, each modification device, and the printer according to each example, an elastic layer (sponge) made of an elastic material is used as a toner supply member that supplies toner to the surface of the toner carrying roller. A toner supply roller that rotates while being in contact with the surface and supplies the toner carried on the elastic layer to the surface of the toner carrying roller is used. In such a configuration, since it is possible to supply toner to the toner carrying roller while the elastic layer that is flexibly deformed is brought into contact with the toner carrying roller with a relatively weak pressure, it is possible to extend the life of the toner carrying roller. .

  If an elastic layer having a plurality of recesses on the surface, such as foamed cells or sponges, is used, the toner is accommodated in the recesses, and the elastically deformable elastic layer is brought into contact with the toner carrying roller with a relatively weak pressure. Since the toner can be supplied to the toner carrying roller, the life of the toner carrying roller can be extended.

  Further, as the toner supply member, a toner that is trapped in the brush roller portion by rotating a brush roller portion made up of a plurality of raised portions standing on the peripheral surface of the rotating shaft member while contacting the surface of the toner carrying roller. A toner supply brush roller that supplies toner to the surface of the toner carrying roller may be used. In this case as well, it is possible to supply toner to the toner carrying roller while the brush roller portion that is flexibly deformed is brought into contact with the toner carrying roller with a relatively weak pressure, so that the life of the toner carrying roller can be extended. Can do. Furthermore, it is possible to supply toner to the toner carrying roller while capturing the toner between the brushes of the brush roller portion and bringing the elastically deformable elastic layer into contact with the toner carrying roller with a relatively weak pressure. The life of the toner carrying roller can be extended.

  In the printer according to the embodiment, as the voltage applying unit that applies a voltage to the facing member, a device that applies a neutralizing bias including a DC voltage to a regulating member that is the facing member is used. In such a configuration, the cost can be reduced as compared with the voltage applying means for applying the AC voltage.

  In the second modified apparatus, as the voltage applying means for applying a voltage to the facing member, a device for applying a static elimination bias composed of an AC / DC superposed voltage to the sealing member as the facing member is used. In such a configuration, the toner carrying roller can be discharged more reliably than in the case of using a discharging bias consisting of only a DC voltage.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a developing device for M in the printer. FIG. 3 is a perspective view showing a toner carrying roller in the developing device. FIG. 3 is a schematic plan view showing an electrode configuration of the toner carrying roller. FIG. 3 is a partial cross-sectional view showing the toner carrying roller. The graph which shows the characteristic of the pulse voltage applied to the electrode of the toner carrying roller. The graph which shows the characteristic in the other example of the same pulse voltage. FIGS. 4A to 4E are schematic views showing manufacturing steps of the toner carrying roller. The graph which shows the relationship between the surface potential of the toner carrying roller of a testing machine, and idle operation time. FIG. 4 is a schematic diagram for explaining a capacitor model of a toner carrying roller of the developing device. 6 is a graph showing the relationship between the surface potential of the toner carrying roller of the test machine in a state where no bias is applied to the toner supply roller to each electrode and the idle operation time. 3 is a graph showing a relationship between a surface potential of a toner carrying roller after toner suction and an idle operation time in the test machine. The graph which shows the relationship between the surface potential of the toner carrying | supporting roller of the test machine provided with the static elimination means, and idle operation time. The expanded block diagram which shows the image development apparatus for M in a 1st modification apparatus. The expansion block diagram which shows the image development apparatus for M in a 2nd modification apparatus.

Explanation of symbols

2: Sensitive belt (latent image carrier)
10M, C, Y, K: Developing device 15M: Toner supply roller (toner supply member)
16M: toner carrier roller (toner carrier)
17A: Phase A electrode (electrode)
17B: Phase B electrode (electrode)
21M: Recovery roller (a part of the static elimination means, opposing member)
23M: Sealing member (a part of the static elimination means, opposing member)
24M: Static elimination power source (part of static elimination means, voltage application means)
25M: Recovery power supply (a part of static elimination means, voltage application means)
26M: Static elimination power source (part of static elimination means, voltage application means)
28M: Restricting member (a part of the static eliminating means, opposing member)

Claims (15)

A toner carried on an endlessly moving surface of a toner carrier having a plurality of electrodes arranged in a predetermined direction is laid on the surface while being hopped on the surface by an electric field formed by applying a voltage to the plurality of electrodes. In a developing device for developing a latent image attached to a latent image carried on an image carrier,
A developing device, comprising: a discharging means for discharging the surface of the toner carrier at a predetermined position in the endless movement direction of the toner carrier. The developing device according to claim 1.
A developing device comprising: a member having a facing member facing the surface of the toner carrying member; and a voltage applying unit for applying a voltage to the facing member. The developing device according to claim 2.
2. A developing device according to claim 1, wherein the opposing member is a regulating member that regulates a carrying amount of the toner supplied to the surface of the toner carrier by a toner supply unit. The developing device according to claim 2.
2. A developing device according to claim 1, wherein a recovery member that transfers toner on the surface of the toner carrying member to the surface of the toner carrying member for recovery is used as the counter member. The developing device according to claim 2.
A developing device, wherein a seal member for closing a space between the endlessly moving surface of the toner carrier and the developing device housing is used as the facing member. The developing device according to any one of claims 2 to 5,
As a toner supply member for supplying toner to the surface of the toner carrier, a toner supply for supplying the toner carried on the elastic layer to the surface by rotating an elastic layer made of an elastic material in contact with the surface A developing device using a roller. The developing device according to any one of claims 2 to 5,
As a toner supply member for supplying toner to the surface of the toner carrying member, a brush roller portion composed of a plurality of raised brushes erected on the peripheral surface of the rotary shaft member is rotated while being in contact with the surface, and the brush roller A developing device using a toner supply brush roller for supplying toner trapped in the section to the surface. The developing device according to any one of claims 2 to 7,
A surface potential detecting means for detecting the surface potential of the toner carrier, and a voltage determining means for determining the value of the applied voltage by the voltage applying means based on the detection result by the surface potential detecting means, Developing device. The developing device according to any one of claims 2 to 7,
A charge amount estimating means for estimating a charge amount of the toner on the toner carrier, a value of an applied voltage by the voltage applying means based on an estimation result by the charge amount estimating means and a voltage applied to the plurality of electrodes; And a voltage determining means for determining a developing device. The developing device according to claim 9.
A toner carrying amount detecting unit for detecting a toner carrying amount per unit area on the surface of the toner carrying member is provided, and the application is performed based on a detection result by the toner carrying amount detecting unit in addition to the estimation result and the voltage. A developing device characterized in that the voltage determining means is configured to determine a voltage value. The developing device according to any one of claims 2 to 10,
A developing device using a means for applying a DC voltage to the opposing member as the voltage applying means. The developing device according to any one of claims 2 to 10,
2. A developing apparatus according to claim 1, wherein said voltage applying means applies an AC / DC superimposed voltage to said opposing member. At least a latent image carrier that carries a latent image and a developing unit that develops the latent image on the latent image carrier are held by a common holder so that the unit can be attached to and detached from the image forming apparatus main body as a single unit. Process unit
13. A process unit using the developing device according to claim 1 as the developing means. In an image forming apparatus having a latent image carrier that carries a latent image, and a developing unit that develops the latent image on the latent image carrier.
An image forming apparatus using the developing device according to claim 1 as the developing means. The image forming apparatus according to claim 14.
An image forming apparatus, comprising: a plurality of the developing devices, wherein the developing devices are superposed on the latent image carrier.

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