JP4646298B2 - Developing device, developing method, and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device for developing an image by an electrophotographic method, a developing method, and an image forming apparatus incorporating the developing device.

Patent Document 1 discloses a developing device that performs development using electrostatic conveyance means. This apparatus performs development using an endless loop electrostatic transfer means. Further, Patent Document 2 discloses a developing device that combines a two-component developing system including an electrostatic conveying unit and an axial stirring unit. The two-component developing system in Patent Document 2 is provided with an axial stirrer that can function sufficiently even if the electrostatic transfer unit is omitted, and cannot be reduced in size. Only larger and heavier.
JP 2002-99423 A JP-A-3-21967

  In a developing device (EH developing device) that moves toner particles by a phase-shift electric field that is a traveling wave electric field, unlike the developing sleeve in the conventional two-component development, the electrostatic conveying member itself does not move. When attached to a member, it is difficult to peel it off with physical force. For this reason, it is desirable to remove the adhering toner particles from the electrostatic conveying member by a phase-shift electric field, but when weakly charged toner or uncharged toner adheres, it is difficult to remove it by the phase-shift electric field. Even if the toner is sufficiently charged, if the non-electrostatic adhesion force of the toner is large, the toner adhered to the electrostatic transport member cannot be transported by an electric field. Becomes conspicuous, and stable image formation cannot be achieved.

  In order to suppress the non-electrostatic adhesion force of the toner, it is necessary that the external additive is dispersed on the toner surface layer. However, the external additive loses its effect due to the embedding in the toner base during the stirring and dispersing process with the carrier. There's a problem. The most effective way to suppress the burying of the external additive is to not apply excessive force to the toner.

  As a means for combining the toner supply means to the electrostatic conveying member and the contaminant removal means, a toner supply / contaminant removal means by a magnetic brush developing system is used. Since excessive force is applied to the toner and damage to the conveyance base of the magnetic brush contact portion is large, there is a problem that stability over time is impaired as a result.

  The present invention has been made in consideration of such problems, and it is possible to suppress an increase in non-electrostatic adhesion force of toner and to remove contamination of the electrostatic transport member, thereby stabilizing the toner. An object of the present invention is to provide a developing device, a developing method, and an image forming apparatus capable of maintaining electrostatic transportability, that is, stable image formation.

In the developing device according to the first aspect of the present invention, an electrostatic conveying member using a traveling wave electric field is disposed in a section from a mixed region of toner and carrier to a developing region for developing the image carrier, In a developing device that selectively transports toner to a development area and performs development, toner supply to the electrostatic transport member is performed by a cascade development system, and a developer recovery unit is placed below the toner supply unit of the electrostatic transport member. A toner collecting unit and a toner replenishing unit for used toner are arranged, and a mixing agitating unit for mixing and agitating the collected developer with the collected toner and the replenishing toner, and a circulation unit for circulating the developer, and the circulation unit from the mixing agitation unit The path to is the lowermost surface of the mixing and stirring unit, and the carrier specific gravity / toner specific gravity is 2 or more and 8 or less .

According to a second aspect of the invention, in the developing apparatus according to claim 1, wherein said toner replenishing portion and the toner collector is characterized in that it is arranged in the developer recovery section.

According to a third aspect of the present invention, in the developing device according to the first or second aspect , the circulating means is a monopump.

According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the toner collecting unit, the circulation unit, and the electrostatic conveyance member are integrally incorporated. It is characterized by.

According to a fifth aspect of the present invention, there is provided a developing method in which an electrostatic conveyance member using a traveling wave electric field is arranged in a section from a mixed area of toner and carrier to a developing area where development is performed on the image carrier. In this method, the toner is selectively conveyed to the development area and developed, and the toner is supplied to the electrostatic conveyance member by a cascade method, and the collected developer is mixed with the collected toner and the replenishment toner below the electrostatic conveyance member. The developer stirred and circulated is supplied to the electrostatic conveying member by circulating the developer, and the developer is circulated from the lowest part of the mixing and stirring, and the carrier specific gravity / toner specific gravity is set to 2 or more and 8 or less. It is characterized by.

An image forming apparatus according to a sixth aspect of the invention is characterized by using at least one developing device according to any one of the first to fourth aspects.

  According to the present invention, since toner damage due to toner charging and supply means is greatly reduced, the electrostatic transport member is contaminated with toner particles due to an increase in non-electrostatic adhesion of the toner and charging failure. Can be suppressed. For this reason, it is possible to suppress the deterioration of the development characteristics in the temporal operation including maintenance.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. In each embodiment, the same members are assigned the same reference numerals.

[Embodiment 1]
1 to 8 show Embodiment 1 of the present invention, and FIG. 1 shows an image forming apparatus according to Embodiment 1 of the present invention.

  In the image forming apparatus shown in FIG. 1, in a normal image forming operation mode, a transfer material such as a recording sheet supplied from the paper supply device 5 is conveyed by applying a predetermined voltage to the suction roller 2a. Adsorbed to the belt 2. The transfer material is moved along with the conveyance belt 2 while being carried on the conveyance belt 2, and toner images are transferred from the process cartridges 1K, 1M, 1C, and 1Y as image forming means during the movement. When the transfer material passes through the conveying belt 2 and reaches the fixing device 3, the toner image on the transfer material is heated while being sandwiched between the heating roller 3a and the pressure roller 3b, whereby the image is fixed on the transfer material. A visible image is formed on the transfer material.

  On the other hand, in a mode in which the color misregistration and toner density of each color toner image are adjusted, a toner image having a predetermined pattern is directly formed on the transfer material conveying belt 2 from the process cartridges 1K, 1M, 1C, and 1Y. The toner pattern is detected by 2b, and the writing timing and the development bias are changed based on the detection result, so that an optimum color image can be obtained. The toner pattern on the transfer belt 2 is adjusted in charge polarity by a bias applied to the suction roller 2a, and then the process cartridges 1K, 1M, and 1C are applied by voltages applied to the transfer rollers 2bk, 2bm, 2bc, and 2by. 1Y is collected.

  Process cartridges 1K, 1M, 1C, and 1Y are cartridges for forming toner images of black, magenta, cyan, and yellow, respectively. This process cartridge is constituted integrally including at least a developing device and an image carrier, and is detachable from the main body of the image forming apparatus. As shown in FIG. 3, the process cartridge can be detached from the space opened by the transfer material transport belt 2 being retracted from the main body of the image forming apparatus, and can be replaced by the user. During image formation, writing devices 4K, 4M, 4C, and 4Y irradiate process cartridges 1K, 1M, 1C, and 1Y with writing light corresponding to image information of black, magenta, cyan, and yellow, respectively. The cartridges 1K, 1M, 1C, and 1Y form toner images corresponding to the writing light and transfer them to a transfer material.

  The writing devices 4K, 4M, 4C, and 4Y write latent images on the charged image carrier 11 according to image information. As the writing devices 4K, 4M, 4C, and 4Y, various devices such as an optical scanning device using a polygon and an LED array can be selected.

The transfer rollers 2bk, 2bm, 2bc, and 2by are opposed to the image carrier 11 via the transfer material conveying belt 2. The transfer rollers 2bk, 2bm, 2bc, 2by have at least a cored bar and a conductive elastic layer that covers the cored bar. The conductive elastic layer is made of an elastic material such as polyurethane rubber, ethylene-propylene-diene polyethylene (EPDM), etc., and mixed with a conductivity-imparting agent such as carbon black, zinc oxide, tin oxide, and the like. Is an elastic body adjusted to a medium resistance of 10 ⁶ to 10 ¹⁰ Ω · cm.

  FIG. 2 shows the process cartridge of this embodiment. Since the process cartridges 1K, 1M, 1C, and 1Y have the same structure, only one process cartridge will be described.

  The image carrier 11 is a negatively charged organic photoreceptor, and is provided so as to be rotated in the direction of the arrow, that is, in the counterclockwise direction by a rotation driving mechanism (not shown). A cleaning device 14, a contact charging member 12, and a developing device 13 are disposed on the image carrier 11.

  As shown in FIG. 2, a cleaning device 14, a charging roller 12 as a contact charging member, and a developing device 13 are disposed in the vicinity of the image carrier 11.

  The cleaning device 14 includes a cleaning blade 14a that is brought into contact with the rotation direction of the image carrier 11 by a counter, and a waste toner storage portion 14b that stores the cleaned toner particles as waste toner.

  The charging roller 12 as a contact charging member is formed in a flexible roller shape in which a foamed urethane layer 12b is coated on a core metal 12a. The urethane foam layer 12b is composed of a medium resistance layer in which carbon black as a conductive particle, a sulfurizing agent, a foaming agent, and the like are formulated with respect to the urethane resin. The material of the medium resistance layer formed on the cored bar 12a is not limited to the above, but includes urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, and the like. In order to adjust the resistance, a rubber material in which a conductive material such as carbon black or a metal oxide is dispersed, or a foamed material of these resins can be used.

  The developing device 13 of the present embodiment includes a roller-shaped electrostatic transport member 13a having a plurality of electrodes for generating an electric field for transporting, developing, and collecting powder toner particles. The electrostatic transport member 13a faces the image carrier 11 in a non-contact manner with a gap of 50 to 1000 μm, preferably 150 to 400 μm, at the time of image formation.

  The configuration of the electrostatic transfer member 13a is shown in FIG. FIG. 4 is an enlarged cross-sectional view of the surface of the electrostatic transport member 13a on the image carrier 11 side. The electrostatic transfer member 13a includes a plurality of electrodes 102, 102, 102... On the support substrate 101 as a set, arranged at a predetermined interval along the toner moving direction, and the surface protective layer 103 thereon. It is the structure which laminated | stacked. The surface protective layer 103 serves as a protective film that covers the surface of the electrode 102 and serves as an insulating conveyance surface forming member that forms a conveyance surface, and is formed of an inorganic or organic insulating material.

As the support substrate 101 in this embodiment, an insulating film such as SiO ₂ is formed on a substrate made of an insulating material such as a glass substrate, a resin substrate or a ceramic substrate, or a substrate made of a conductive material such as SUS (stainless steel). And a substrate made of a flexible and deformable material such as a polyimide film can be used.

  The electrode 102 is formed by depositing a conductive material such as Al or Ni—Cr on the support substrate 101 with a thickness of 0.1 to 10 μm, preferably 0.5 to 2.0 μm. Is formed into a desired electrode shape by patterning. The width L of the plurality of electrodes 102 in the powder traveling direction is 1 to 20 times the average particle size of the moving powder, and the distance R in the powder traveling direction of the electrodes 102 and 12 is also moved. The average particle size of the body is 1 to 20 times.

As the surface protective layer 103, for example, SiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _{5 and the} like are formed to a thickness of 0.5 to 10 μm, preferably 0.5 to 3 μm. Is formed.

  In FIG. 4, lines extending from the respective electrodes 102 represent conductive lines for applying a voltage to the respective electrodes 102. Of the overlapping portions of the respective lines, only the portions indicated by black circles are electrically connected, and the other portions are Electrically insulated. Different driving voltages of n phases are applied to the electrodes 102 from the power source on the main body side. In the present embodiment, a case where a three-phase drive voltage is applied (n = 3) will be described. However, the present invention can be applied to any natural number n satisfying n> 2 as long as toner particles are conveyed. In the present embodiment, each electrode 102 is connected to one of the contact points S11, S12, S13, S21, S22, and S23 on the process cartridge side, and each contact point is in a state where the process cartridge is mounted on the image forming apparatus main body. Are connected to the main body side power supply for providing drive waveforms V11, V12, V13, V21, V22, and V23, respectively. Here, the contact points S11, S12, S13, S21, S22, and S23 on the process cartridge side are exposed to the outside of the process cartridge as shown in FIG. 8, and are connected to the contact points on the main body side when the process cartridge is mounted. Electric power is supplied from the main body side power source.

  The electrostatic transport member 13a transports toner particles to the vicinity of the image carrier 11 and also transports toner particles to the latent image on the image carrier 11 for transporting the toner particles that have not contributed to development after passing through the development region. It is divided into a developing region for forming particles by adhering particles. The development area exists only in the area close to the image carrier 11, and the conveyance area exists in the entire area other than the development area on the periphery of the electrostatic conveyance member 13a. Hereinafter, an area where the toner particles can move by the phase electric field is referred to as an “electrostatic transfer surface”. In this embodiment, the entire surface of the electrostatic transport member 13a is an electrostatic transport surface. Drive waveforms V11, V12, and V13 are applied to each electrode 102 in the transport region, and drive waveforms V21, V22, and V23 are applied to each electrode 102 in the development region.

  Next, the principle of electrostatic conveyance of toner in the electrostatic conveyance member 13a will be described with reference to FIG. By applying an n-phase driving waveform to the plurality of electrodes 102 of the electrostatic transfer member 13a, a phase-shift electric field (traveling wave electric field) is generated by the plurality of electrodes 102 and charged on the electrostatic transfer member 13a. The toner particles move in the transport direction in response to a repulsive force and / or suction force.

For example, for a plurality of electrodes 102 of the electrostatic transfer member 13a, the timing of the three-phase pulse drive waveform that changes between the ground G (0V) and the positive voltage + as shown in FIG. Apply by shifting. At this time, as shown in FIG. 5B, the negatively charged toner T is present on the electrostatic conveyance member 13a, and “G”, “G”, “ In the state of reference numeral 131 to which “+”, “G”, and “G” are applied, the negatively charged toner T is positioned on the “+” electrode 102. At the next timing, “+”, “G”, “G”, “+”, and “G” are respectively applied to the plurality of electrodes 102 to be in the state of reference numeral 132. The repulsive force acts between the electrode 102 and the “+” electrode 102 on the right side. For this reason, the negatively charged toner T moves to the “+” electrode 102 side on the right side. Further, at the next timing indicated by reference numeral 133, “G”, “+”, “G”, “G”, “+” are respectively applied to the plurality of electrodes 102, and the same applies to the negatively charged toner T. Repulsive force and suction force act on each. Therefore, the negatively charged toner T further moves to the right “+” electrode 102 side.
In this way, by applying a multi-phase driving waveform whose voltage changes to the plurality of electrodes 102, a traveling wave electric field is generated on the electrostatic conveyance member 13a, and the negatively charged toner is moved in the traveling direction of the traveling wave electric field. Moving. In the case of positively charged toner, the drive waveform changes in the same direction by reversing the drive waveform change pattern.

  In the present embodiment, in the transport region of the electrostatic transport member 13a, the application time ta of +100 V for each phase is set to about 33%, which is 1/3 of the repetition period tf, as shown in FIG. The three-phase drive waveforms (drive pulses) V11, V12, and V13, which are the patterns (carrier voltage pattern), are applied. It has been found from the inventor's research that this driving waveform is a waveform suitable for high-speed conveyance of toner particles in the conveyance region.

  Further, in the development region, a pattern (development voltage pattern) in which the application time ta of +100 V or 0 V of each phase is set to about 67% which is 2/3 of the repetition period tf as shown in FIG. The three-phase drive waveforms (drive pulses) V21, V22, and V23 are applied. In the development region, it is preferable that toner particles are positively launched toward the image carrier, and it has been found from the inventor's research that the drive waveform in FIG. 7 is suitable for launching toner particles.

  Even when a drive waveform of the development voltage pattern is applied, since the toner is also subjected to a lateral force other than the toner positioned at the center of the 0V electrode, not all the toners are launched at the same time, but move in the horizontal direction. Conversely, even when a drive waveform of a carrier voltage pattern is applied, depending on the position of the toner, there is a toner whose ascending distance is larger than that of being obliquely launched at a large angle and moving horizontally. Therefore, the drive waveform pattern applied to each electrode 102 in the transport region is not limited to the transport voltage pattern shown in FIG. 6 described above, and the drive waveform pattern applied to each electrode 102 in the development region 12 is also described above. The development voltage pattern shown in FIG.

  Up to this point, the drive waveform has been described for the case of three layers. However, when this is generalized to n-phase, the drive waveform is as follows. When a traveling wave electric field is generated by applying an n-phase (n is an integer of 3 or more) pulsed voltage (driving waveform) to each electrode, the voltage application time per phase {repetition cycle time × (n -1) / n}, the efficiency of conveyance and development can be increased by setting the voltage application duty to be less than 1 / n}. For example, when a three-phase drive waveform is used, the voltage application time ta of each phase is set to less than about 67%, which is 2/3 of the repetitive cycle time tf, and when a four-phase drive waveform is used, It is preferable to set the voltage application time of each phase to less than 75%, which is 3/4 of the repetition cycle time.

  On the other hand, the voltage application duty is preferably set to {repetition cycle time / n} or more. For example, when a three-phase driving waveform is used, it is preferable to set the voltage application time ta of each phase to about 33% or more, which is 1/3 of the repetition cycle time tf. That is, between the voltage applied to the electrode of interest and the voltages applied to the upstream adjacent electrode and downstream adjacent electrode in the traveling direction, the upstream adjacent electrode repels and the downstream adjacent electrode sucks. The efficiency can be improved by setting. In particular, when the drive frequency is high, the initial speed for the toner on the electrode of interest is set by setting it within the range of {repeat cycle time / n} or more and less than {repeat cycle time × (n−1) / n}. It becomes easy to obtain.

  In the above electrostatic transport member, the best mode is described. However, if desired transport / development performance can be obtained, the interval between the electrodes 102 is made different between the development region and the transport region. The direction of the electric field may be adjusted, or the distance between the electrodes and the drive waveform may be the same in the development area and the conveyance area.

  As shown in FIG. 2, the developing device 13 is provided with a cascade base 13b for supplying toner to the electrostatic transport member 13a, and a developer recovery unit 13c is provided downstream of the cascade base 13b. Below the developer recovery unit 13c, there is disposed a mixing agitation unit 13d that mixes and stirs the developer dropped from the cascade base 13b with the collected toner and the replenishment toner. Further, the developer is placed on the lowermost surface of the mixing / mixing agitation unit 13d. A path to the circulation means 13e to be circulated is arranged, and the developer in the developing device 13 falls from the upstream side of the cascade base 13b in the order of the conveying member 13a and the developer recovery part 13c, and passes through the mixing and stirring part 13d to circulate means. 13e circulates upstream of the cascade base 13b. Thus, the path to the circulation means 13e for circulating the developer is arranged on the lowermost surface of the mixing and stirring unit 13d, so that the uncharged toner separated from the carrier (not electrostatically adsorbed) is separated from the carrier. Due to the difference in specific gravity, the toner remains on the mixing stirrer 13d and is not supplied to the circulation unit 13e. Therefore, only the stably charged toner passes through the developer circulation unit 13e and is supplied to the electrostatic conveyance unit. This effect is particularly remarkable with spherical toners with poor dispersibility and with small particle diameters of 5 μm or less.

  A blade 13f for regulating the amount of developer is installed in the developer transport direction in the toner supply section of the cascade substrate 13b, and the gap with the cascade substrate 13b is set to 1 to 5 mm. If it is 1 mm or less, developer clogging occurs in the gap portion, and if it is 5 mm or more, the supply is excessive and an appropriate toner supply amount to the conveying member 13a cannot be obtained.

  The circulating means 13e described above is not limited as long as the developer can circulate the developer upstream of the cascade base 13e, but a monopump is preferably used. By using the monopump, an appropriate rubbing force is applied between the toner and the carrier, and the toner charging stability is improved. In this case, it is preferable that the monopump part passage time is set to 3 seconds or more and 10 seconds or less. If it is 3 seconds or less, a sufficient effect of the rubbing force in the monopump cannot be obtained, and if it is 10 seconds or more, stable toner charging can be obtained, but the embedding of the external additive tends to proceed. As described above, when the monopump is used as the circulation unit 13e, the minimum rubbing force necessary for toner charging can be uniformly applied to the developer supplied to the toner supply unit.

  In the developing means 13, toner particles and carriers (not shown) are stored. In carrying out this embodiment, it is not necessary to specifically limit carrier particles and toner particles, but the toner particles in this embodiment are composed of a styrene or acrylic polymerizable monomer as a binder resin together with a polymerization initiator. Use a polymer that has been radically polymerized while dispersed in water, or a polyester resin that has been polymerized by a polyaddition reaction by dispersing the polyester resin in water. Non-magnetic toner particles having a weight average particle diameter of about 5 μm obtained by the above process.

  Further, glass beads are used as the carrier, but the carrier is not limited to this as long as the carrier can give an appropriate charge by mixing with the toner. The carrier specific gravity / toner specific gravity is preferably 2 or more and 8 or less. When the carrier specific gravity / toner specific gravity is 2 or less, the free toner is taken into the circulation means, and toner scattering is likely to occur. On the other hand, when the carrier specific gravity / toner specific gravity is 8 or more, even when the cascade system is used, the impact when the developer drops is large, and the external additive embedding of the toner and the deterioration of the charging performance become remarkable. For example, when the surface of the toner in which the developer is circulated for 8 hours only in the developing device is observed with an SEM, the external additive is completely buried.

  The toner that is electrostatically transported and is not used in the development area is collected by the developer collection unit 13c by the toner collection unit 13g. The collected toner is remixed with the developer dropped from the cascade substrate 13b and circulated. The replenishing toner replenishing port 13h is arranged in the developer circulation path upstream of the mixing and stirring unit 13d.

  Next, the operation of the above process cartridge will be described. As the image forming apparatus of the present embodiment, an image forming apparatus that can function as a copying machine and a printer can be used. When functioning as a copier, the image information read from the scanner is subjected to various image processing such as A / D conversion, MTF correction, gradation processing, etc., and converted into writing data. When functioning as a printer, image information in a format such as a page description language or a bitmap transferred from a computer or the like is subjected to image processing and converted into write data.

  Prior to image formation, the image carrier 11 starts to rotate in the direction of the arrow in FIG. 2, that is, in the counterclockwise direction so that the moving speed of the surface becomes a predetermined measure. Further, the charging roller 12 rotates by being entangled with the image carrier 11. At this time, a DC voltage of −100 V and an AC voltage with an amplitude of 1200 V and a frequency of 2 kHz are applied to the cored bar 12 a of the charging roller 12 from the charging bias application power source, whereby the surface of the image carrier 11 is charged to about −100 V.

  The writing device 4 (4C, 4M, 4Y, 4K) performs exposure according to the writing data on the charged image carrier 11. That is, by changing the potential of the image portion by light irradiation, a difference from the potential of the non-image portion not irradiated with light is generated, and an electrostatic latent image is formed by this potential contrast.

  The electrostatic latent image formed on the image carrier by the writing device 4 is developed by the developing device 13 and is visualized on the image carrier 11 as a toner image by attaching toner particles to the image portion. In the development by the phase-shifting electric field, the toner particles move while jumping on the surface of the electrostatic conveyance member 13a, and are attached so as to be attracted to the image portion when approaching the image carrier 11 for development. In the present embodiment, a voltage of −50 V is applied to the electrostatic transport substrate 13 a and a voltage of −250 V is applied to the supply roller 13 b, so that the electrostatic transport substrate 13 a from the supply roller 13 b and the image transport body 11 from the electrostatic transport substrate 13 a are applied. An electric field is formed that guides the toner particles to the image area.

  The transfer material is conveyed from the sheet feeding device 5 in synchronization with the timing at which the toner image formed on the image carrier 11 reaches the transfer portion which is the opposite portion between the transfer roller 2b and the image carrier 11 and the image is transferred. The toner image on the carrier 11 is transferred to the transfer material by the voltage applied to the transfer roller 2b. The transferred toner image is fixed on the transfer material by the fixing device 3 and an image is output. On the other hand, toner remaining on the image carrier 11 without being transferred (transfer residual toner) is cleaned by the cleaning device 14, and the surface of the image carrier after cleaning is used for the next image formation.

  In such an embodiment, the toner charging and the damage to the toner by the supply means are greatly reduced, so that the electrostatic transport member is contaminated with toner particles due to an increase in non-electrostatic adhesion of the toner and a charging failure. Therefore, it is possible to suppress the deterioration of the development characteristics in the temporal operation including maintenance.

[Embodiment 2]
9 to 11 show a second embodiment of the present invention.

  FIG. 9 shows an image forming apparatus according to this embodiment. Reference numeral 11 denotes an image carrier in which a negatively charged organic photoconductor is formed in a belt shape, and is rotated in the direction of an arrow by a rotation driving mechanism (not shown). Developing cartridges 13K, 13M, 13C, and 13Y and a charging device to be described later are opposed to the image carrier 11 for each color, and the toner images are sequentially superimposed on the image carrier 11 as the image carrier 11 moves. (1 pass color).

  In FIG. 9, reference numeral 5 denotes a paper feeding device that stores a transfer material such as a recording sheet and starts conveying the transfer material during image formation. Reference numeral 3 denotes a fixing device for fixing an unfixed toner image formed on the transfer material. At the time of image formation, the transfer material sent from the paper feeding device 5 is conveyed to the contact portion between the image carrier 11 and the transfer roller 2b, and the full color image formed on the image carrier 11 at the contact portion is transferred to the transfer roller 2b. The image is transferred onto the transfer material by the voltage applied to. Thereafter, when the transfer material reaches the fixing device 3, the toner image on the transfer material is heated while being sandwiched between the heating roller 3 a and the pressure roller 3 b, thereby being fixed on the transfer material and allowed to be transferred onto the transfer material. A visual image is formed.

  Reference numerals 13K, 13M, 13C, and 13Y denote developing cartridges for developing toner images of black, magenta, cyan, and yellow, respectively. As shown in FIG. 11, the developing cartridge can be detached from the space opened by the image carrier 11 being retracted, and can be replaced by the user. The writing devices 4K, 4M, 4C, and 4Y write latent images corresponding to black, magenta, cyan, and yellow, respectively, on the charged image carrier 11 according to image information. As the writing devices 4K, 4M, 4C, and 4Y, various devices such as an optical scanning device using a polygon and an LED array can be used.

  FIG. 10 shows a structure for forming a toner image on an image carrier such as a developing cartridge according to the second embodiment. In this case, since the developing cartridges for the respective colors have the same structure, only one will be described.

  In FIG. 10, reference numeral 22 denotes a charging device for uniformly charging the surface of the image carrier 11, and in this embodiment, corona charging is used. By using non-contact charging means such as corona charging, the image carrier 11 can be charged without disturbing the toner image formed by the upstream developing cartridge. Reference numeral 13 denotes a developing cartridge, that is, a developing device, which is the same as the developing device described in the first embodiment although the shape is slightly changed.

  In the operation of forming a toner image on the image carrier, first, the surface of the image carrier 11 is uniformly charged by the charging device 22. Even when a toner image has already been formed on the image carrier 11, the surface of the image carrier 11 including the toner image is uniformly charged. Next, a light beam corresponding to the image information is emitted from the writing device. Since the light beam passes between the charging device 22 and the developing cartridge 13, the light beam is irradiated onto the image carrier 11 that has already been uniformly charged, and the image is a negatively charged photoconductor. On the surface of the carrier 11, a region corresponding to the image portion is neutralized to form a latent image.

  The developing cartridge 13 attaches toner particles to the image portion of the latent image formed on the image carrier 11 as in the first embodiment, and visualizes the latent image as a toner image. The above-described charging, light beam irradiation, and development steps are repeated at the portion facing each developing cartridge as described above, and a full-color image in which four color toner images are superimposed on the image carrier 11 is formed.

  In the image forming apparatus of this embodiment, no cleaning member is provided for collecting the transfer residual toner particles on the surface of the image carrier 11. Accordingly, the transfer residual toner particles remain on the surface of the image carrier 11, but are charged by the four charging devices 22 and eventually transferred to a transfer material and removed from the image carrier 11. This is because, when the transfer residual toner particles are transferred to the transfer material, some image disturbance occurs, but if the transfer residual toner particles are slightly disturbed, they are not visually recognized.

1 is a cross-sectional view illustrating a structure of an image forming apparatus according to Embodiment 1 of the present invention. It is sectional drawing which shows the developing device in Embodiment 1 of this invention. It is sectional drawing which shows the exchange state of a developing device. It is sectional drawing of an electrostatic conveyance member. It is explanatory drawing explaining the principle of the electrostatic conveyance of an electrostatic conveyance member. It is a wave form diagram which shows the application pattern to the conveyance area | region in an electrostatic conveyance member. It is a wave form diagram which shows the application pattern to the image development area | region in an electrostatic conveyance member. It is a side view showing contact arrangement of a process cartridge. It is sectional drawing which shows the structure of the image forming apparatus in Embodiment 2 of this invention. It is sectional drawing which shows the image development apparatus in Embodiment 2 of this invention. It is sectional drawing which shows the replacement | exchange state of the image development apparatus in Embodiment 2 of this invention.

Explanation of symbols

1K, 1M, 1C, 1Y Process cartridge 2 Conveying belt 3 Fixing device 4K, 4M, 4C, 4Y Writing device 5 Paper feeding device 11 Image carrier 12 Charging roller 13 Developing device 13a Electrostatic conveying member 13b Cascade base 13c Developer Recovery part 13d Mixing and stirring part 13e Circulation means 13g Toner recovery part 13h Toner replenishing port 14 Cleaning device

Claims (6)

An electrostatic conveyance member using a traveling wave electric field is arranged in a section from a mixed area of toner and carrier to a development area where development is performed on the image carrier, and the charged toner is selectively conveyed to the development area. In the developing device for developing,
The toner is supplied to the electrostatic conveying member by a cascade development system, and a developer collecting unit, a toner collecting unit for unused toner, and a toner replenishing unit are arranged below the toner supplying unit of the electrostatic conveying member and collected. A mixing and agitation unit for mixing and agitating the developer with the collected toner and the replenishing toner, and a circulation means for circulating the developer ;
A developing device characterized in that a path from the mixing and stirring unit to the circulation means is a lowermost surface of the mixing and stirring unit, and a carrier specific gravity / toner specific gravity is 2 or more and 8 or less . The developing device according to claim 1, wherein the toner replenishing unit and the toner collecting unit are disposed in the developer collecting unit . 3. The developing device according to claim 1 , wherein the circulating means is a monopump . 4. The developing device according to claim 1 , wherein the toner collecting unit, the circulation unit, and the electrostatic conveyance member are integrated into a cartridge . 5. An electrostatic conveyance member using a traveling wave electric field is arranged in a section from a mixed area of toner and carrier to a development area where development is performed on the image carrier, and the charged toner is selectively conveyed to the development area. In the method of developing,
  The toner is supplied to the electrostatic conveying member by a cascade system, and the collected developer is mixed and stirred together with the collected toner and the replenishment toner below the electrostatic conveying member, and the mixed and stirred developer is circulated to electrostatically convey the member. To supply
  A developing method characterized in that the developer is circulated from the lowest part of the mixing and stirring, and the carrier specific gravity / toner specific gravity is set to 2 or more and 8 or less.   An image forming apparatus using at least one developing device according to claim 1.

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