Patent Publication Number: US-10310419-B2

Title: Image forming apparatus and carrier separating device

Description:
TECHNICAL FIELD 
     The present invention relates to an electrophotographic image forming apparatus, including a separating device, for forming an image with the liquid developer, and relates to the separating device for separating a toner and a carrier liquid from a liquid developer. 
     BACKGROUND ART 
     Conventionally, the image forming apparatus for forming the image with the liquid developer containing the toner and the liquid developer has been known. In the image forming apparatus, the liquid developer which is not used in an image forming step is collected and recycled. In such a recycling process of the liquid developer, toner particles which are a dispersoid in the liquid developer (liquid material) and the carrier liquid which is a dispersion medium in the liquid developer are separated, and then the carrier liquid is used again (for example, Japanese Laid-Open Patent Application 2008-242436). 
     However, by repeating recycling, in the carrier liquid, a substance having a low volume resistivity accumulates. Thus, a resistance of an entirety of the liquid developer lowers, so that there is a liability that an image defect generates. By periodically exchanging (replacing) a container accommodating the liquid developer, the generation of the image defect can be suppressed, but in this case, a running cost increases, as does a load of maintenance by a user or a service person. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in view of the above-described circumstances and a principal object of the present invention is to replace a constitution capable of suppressing a lowering in volume resistivity of a collect to be reused. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image forming portion configured to form a toner image on a recording material with a liquid developer containing a toner and a carrier liquid, wherein the carrier liquid contains a first substance for imparting an electrical polarity to the toner and a second substance, higher in volume resistivity than the first substance, as a dispersion medium for dispersing the toner; and a carrier separating device configured to separate the carrier liquid into the first substance charged to an opposite polarity to a charge polarity of the toner and the second substance by applying an electric field to the liquid developer collected from the image forming portion so as to collect each of the first substance and the second substance. 
     According to another aspect of the present invention, there is provided a separating device comprising: a supplying portion configured to supply a liquid developer carrier tanking a toner, a first substance for imparting an electrical polarity to the toner and a second substance, higher in volume resistivity than the first substance, as a dispersion medium for dispersing the toner; a separating portion configured to separate the liquid developer into the first substance charged to an opposite polarity to a charge polarity of the toner and the second substance by applying an electric field to the liquid developer supplied to the supplying portion; and a collecting portion configured to collect each of the first substance and the second substance which are separated by the separating portion. 
     According to a further aspect of the present invention, there is provided an image forming apparatus comprising: a photosensitive member configured to form a latent image thereto; a developing device configured to develop the latent image, formed on the photosensitive member, into a toner image using a liquid developer containing a toner and a collect; a transfer device configured to transfer the toner image from the photosensitive member onto a recording material; a collecting device configured to collect the liquid developer remaining on the photosensitive member, wherein the carrier liquid contains a first substance for imparting an electrical polarity to the toner and a second substance, higher in volume resistivity than the first substance, as a dispersion medium for dispersing the toner; and a separating device configured to separate the carrier liquid into the first substance charged to an opposite polarity to a charge polarity of the toner and the second substance by applying an electric field to the liquid developer collected from the collecting device so as to collect each of the first substance and the second substance, wherein the second substance collected from the separating device is supplyable to the developing device. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an image forming apparatus according to a First Embodiment of the present invention. 
         FIG. 2  is a schematic illustration showing a feeding path of a liquid developer in the image forming apparatus in the First Embodiment. 
         FIG. 3  is a control block diagram of a feeding operation of the liquid developer in the image forming apparatus in the First Embodiment. 
         FIG. 4  is a flowchart showing control of the feeding operation of the liquid developer in the image forming apparatus in the First Embodiment. 
         FIG. 5  is a perspective view of a separation and extraction device in the First Embodiment. 
         FIG. 6  is a partially cut perspective view showing the separation and extraction device in the First Embodiment. 
         FIG. 7  is a sectional view showing a part of the separation and extraction device in the First Embodiment. 
         FIG. 9  is a perspective view showing a part of the separation and extraction device in the First Embodiment. 
         FIG. 10  is a perspective view showing the part of the separation and extraction device in the First Embodiment as seen from an angle different from an angle in  FIG. 9 . 
         FIG. 11  is a flowchart showing control of a separation and extraction operation of the liquid developer in the First Embodiment. 
         FIG. 12  is a schematic illustration showing a feeding path of a liquid developer in an image forming apparatus according to another example of the First Embodiment. 
         FIG. 13  is a schematic illustration of an image forming apparatus according to a Second Embodiment. 
         FIG. 14  is a schematic illustration showing a feeding path of a liquid developer in the image forming apparatus in the Second Embodiment. 
         FIG. 15  is a flowchart showing control of a feeding and extracting operation of the liquid developer in the Second Embodiment. 
         FIG. 16  is a flowchart showing control of a supplying operation of the liquid developer to a carrier tank in the Second Embodiment. 
         FIG. 17  is a flowchart showing control of a feeding operation of the liquid developer in the image forming apparatus in the Second Embodiment. 
         FIG. 18  is a schematic illustration showing a feeding path of a liquid developer in an image forming apparatus according to another example of the First Embodiment. 
         FIG. 19  is a schematic illustration showing a feeding path of a liquid developer in the image forming apparatus in another second example of the Second Embodiment. 
         FIG. 20  is a flowchart showing control of a supplying operation of the liquid developer to a carrier tank in another second example of the Second Embodiment. 
         FIG. 21  is a flowchart showing a feeding path of the liquid developer in an image forming apparatus in another third example of the Second Embodiment. 
         FIG. 22  is a schematic illustration showing a relation of carrier tanks with mixers in a Third Embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     The First embodiment of the present invention will be described using  FIGS. 1-14 . First, a general structure of an image forming apparatus in this embodiment will be described using  FIG. 1 . 
     (Image Forming Apparatus) 
     An image forming apparatus  100  in this embodiment is a digital printer of an electrophotographic type in which a toner image is formed on a recording material (a sheet, a sheet material such as an OHP sheet and so on). The image forming apparatus  100  is operated on the basis of an image signal, and a toner image formed by an image forming portion  12  is transferred onto a sheet as the recording material is successively fed from each of cassettes  11   a ,  11   b  and then is fixed on the sheet S, so that an image is obtained. The image signal is sent from an external terminal such as an unshown scanner or an unshown personal computer. 
     The image forming portion  12  includes a photosensitive drum as an image bearing member, a charger  14 , a laser exposure device  15 , a developing device  16  and a drum cleaner  19 . A surface of the photosensitive drum  13  electrically charged by the charger  14  is irradiated with laser light E from the laser exposure device  15  depending on the first signal, so that an electrostatic latent image is formed on the photosensitive drum  13 . This electrostatic latent image is developed as a toner image by the developing device  16 . In this embodiment, in the developing device  16 , a liquid developer D as a liquid material in which a powdery toner which is a dispersoid is dispersed in a carrier liquid which is a dispersion medium is accommodated, and development is effected using this liquid developer D. 
     The liquid developer D is generated by mixing and dispersing a toner T in a carrier liquid C in a predetermined ratio in a mixer  31  as a mixing device, and then is supplied to the developing device  16 . The carrier liquid C is accommodated in a carrier tank  32  as a carrier container (collecting container), and the toner T is accommodated in a toner tank  33  as a toner container. Then, depending on a mixed state of the carrier liquid C and the toner T in the mixer  31 , the carrier liquid C or the toner T is supplied from an associated tank. In the mixer  31 , a stirring blade driven by an unshown motor is accommodated, and the developer liquid D is mixed with the carrier liquid C or the toner T by being stirred, so that the toner is dispersed in the carrier liquid. 
     The liquid developer supplied from the mixer  31  to the developing device  16  is coated (supplied) on a developing roller  18  as a developer carrying member and is used for development. The developing roller  18  carries and feeds the liquid developer D on a surface thereof, and develops with the toner the electrostatic latent image formed on the photosensitive drum  13  (first bearing member). The carrier liquid C and the toner T which remain on the developing roller  18  after the development is collected in a collecting section  16   b  of the developing device  16 . Here, each of coating of the liquid developer from a coating roller  17  onto the developing roller  18  and the development of the electrostatic latent image on the photosensitive drum  13  by the developing roller  18  is made using an electric field. 
     The toner image formed on the photosensitive drum  13  is transferred onto an intermediary transfer roller  20  using the electric field, and then is fed to a nip formed by the intermediary transfer roller  20  and a transfer roller  21 . The toner T and the carrier liquid C which remain on the photosensitive drum  13  after the toner image transfer onto the intermediary transfer roller  20  are collected by the drum cleaner  19 . Incidentally, at least one of the intermediary transfer roller  20  and the transfer roller  21  may also be an endless belt. 
     The sheet S accommodated in each of the cassettes  11   a ,  11   b  is fed toward a registration feeding portion  23  by an associated feeding portion  22   a  or  22   b  constituted by feeding rollers. The registration feeding portion  23  feeds the sheet S to the nip between the intermediary transfer roller  20  and the transfer roller  21  by being timed to the toner image transferred on the intermediary transfer roller  20 . 
     In the nip between the intermediary transfer roller  20  and the transfer roller  21 , the toner image is transferred onto the sheet S passing through the nip, and the sheet S on which the toner image is transferred is fed to a fixing device  25  by a feeding belt  24 , so that the toner image transferred on the sheet S is fixed. The sheet S on which the toner image is fixed is discharged to an outside of the image forming apparatus, so that an image forming step is completed. 
     The intermediary transfer roller  20  and the transfer roller  21  are provided with an intermediary transfer roller cleaner  26  and a transfer roller cleaner  27 , respectively, for collecting the toner T and the carrier liquid C which remain on the associated roller. 
     (Liquid Developer) 
     Next, the liquid developer D will be described. As the liquid developer D, a conventionally used liquid developer may also be used, but in this embodiment, an ultraviolet-curable liquid developer D is used and will be described below. 
     The liquid developer D is an ultraviolet-curable liquid developer which contains a cation-polymerizable liquid monomer, a photo-polymerization initiator and toner particles insoluble in the cation-polymerizable liquid monomer. The cation-polymerizable liquid monomer is vinyl ether compound, and the photo-polymerization initiator is a compound represented by the following formula (1). 
     
       
         
         
             
             
         
       
     
     Specifically, first, the toner particles include a colorant and a toner resin material in which the colorant is incorporated. Together with the toner resin material and the colorant, another material such as a charge control agent may also be contained. As a manufacturing method of the toner particles, a well-known technique such as a coacervation in which the colorant is dispersed and a resin material is gradually polymerized so that the colorant is incorporated in the polymer or an internal pulverization method in which a resin material or the like is melted and the colorant is incorporated in the melted resin material may also be used. As the toner resin material, epoxy resin, styrene-acrylic resin or the like is used. The colorant may be a general-purpose organic or inorganic colorant. In the manufacturing method, in order to enhance a toner dispersing property, a dispersant is used but a synergist can also be used. 
     Next, a curable liquid which is the carrier liquid is constituted by the charge control agent for imparting electric charges to the toner surface, a photo-polymerization agent (initiator) for generating acid by ultraviolet (UV) irradiation and a monomer bondable by the acid. The monomer is a vinyl ether compound which is polymerizable by a cationic polymerization reaction. Separately from the photo-polymerization initiator, a sensitizer may also be contained. By photo-polymerization, a storage property lowers, and therefore a cationic polymerization inhibitor may also be added in an amount of 10-5000 ppm. In addition, a charge control aid, another additive or the like may also be used in some cases. 
     The UV curing agent (monomer) of the developer is a mixture of about 10% (weight %) of a monofunctional monomer having one vinyl ether group (formula 2 below) and about 90% (weight %) of difunctional monomer having two vinyl ether groups (formula 3 below). 
     
       
         
         
             
             
         
       
     
     As the photo-polymerization initiator, 0.1% of a compound represented by formula 4 below is mixed. By using this photo-polymerization initiator, different from the case where an ionic photo-acid generator, a high-resistance liquid developer is obtained while enabling satisfactory fixing. 
     
       
         
         
             
             
         
       
     
     Incidentally, a cationic polymerizable liquid monomer may desirably be a compound selected from the group consisting of dichloropendadiene vinyl ether, cyclohexanedimethanol divinyl ether, tricyclodecane vinyl ether, trimethylolpropane trivinyl ether, 2-ethyl-1,3-hexanediol divinyl ether, 2,4-diethyl-1,5-pentanediol divinyl ether, 2-butyl-2-ethyl-1,3-propanediol divinyl ether, neopentylglycol divinyl ether, pentaerythritol tetravinyl ether, and 1,2-decanediol divinyl ether. 
     As the charge control agent, a well-known compound can be used. As a specific example, it is possible to use fats and oils such as linseed oil and soybean oil; alkyd resin; halogen polymer; oxidative condensates such as aromatic polycarboxylic acid, acidic group-containing water-soluble dye and aromatic polyamine; metallic soaps such as cobalt naphthenate, nickel naphthenate, iron naphthenate, zinc naphthenate, cobalt octylate, nickel octylate, zinc octylate, cobalt dodecylate, nickel dodecylate, zinc dodecylate, aluminum stearate, and cobalt 2-ethylhexylate; sulfonic acid metal salts such as petroleum acid metal salt and metal salt of sulfosuccinic acid; phospholipid such as lectithin; salicylic acid metal salt such as t-butylsalicylic acid metal complex; polyvinyl pyrrolidone resin; polyamide resin; sulfonic acid-containing resin; and hydroxybenzoic acid derivative. 
     (Feeding of Liquid Developer) 
     Next, feeding of the liquid developer D in this embodiment will be described using  FIGS. 2 to 4 . First, as described above, the developer collected at the image forming portion  12  including the drum cleaner  19 , the intermediary transfer roller cleaner  26  and the transfer roller cleaner  27  is sent to a first separation and extraction device (first separating device)  37  and a second separation and extraction device (second separating device)  34 . Incidentally, the developer which remains on the developing roller  18  after development and which is collected into the collecting section  16   b  of the developing device is returned to the mixer  31 , but may also be fed to the first and second separation and extraction devices  37 ,  34 . 
     Although details will be described later, the first separation and extraction device  37  separates a reusable carrier liquid and a waste liquid W containing the toner and an impurity such as paper powder when the carrier liquid and the toner are separated from each other, so that the separated waste liquid W is collected in a waste liquid collecting container  35 . 
     Although details will be described later, the second separation and extraction device  34  separates the carrier liquid, separated and extracted by the first separation and extraction device  37 , into a first substance having an opposite polarity to a charge polarity of the toner and a second substance having an intermediary charge amount between those of the toner and the first substance. The waste liquid W containing the first substance separated from the second substance and the impurity is collected in the waste liquid collecting container. 
     Here, as the first substance, for example, a substance (low-resistance carrier) which is contained in the carrier liquid and which has a low volume resistivity is used. As described above, in the substances forming the carrier liquid, the charge control agent is contained, so that the first substance in this embodiment is principally the charge control agent. On the other hand, the second substance is a substance other than the charge control agent and is a substance (high-resistance carrier) having a volume resistivity higher than the volume resistivity of the charge control agent. The volume resistivity of the second substance from which the first substance is separated is 1.0×10 12  Ω·cm, and the volume resistivity of the first substance is, for example, 1.0×10 9  Ω·cm. 
     In the case where an electric field is applied to the liquid developer containing the toner and the carrier liquid, for example, the toner has a negative charge amount (e.g., −4 μC), the first substance has a positive charge amount (e.g., +3 μC), and the first substance has a charge amount of substantially 0 (e.g., ±0 μC). That is, the first substance has the charge amount of the opposite polarity to the toner charge polarity, and the second substance has the intermediary charge amount between the charge amounts of the toner and the first substance. Here, the intermediary charge amount refers to the charge amount between a maximum (+3 in this embodiment) of the charge amount and a minimum (−4 in this embodiment) of the charge amount also in consideration of a sign (+ or −) of the charge polarity. In this embodiment, although details will be described later, using a difference in such a charge amount, each of the toner, the first substance and the second substance is separated and extracted. 
     Specifically, feeding of the liquid developer will be described. A transporting pipe from the carrier tank  32  to the mixer  31  and a transporting pipe from the toner tank  33  to the mixer  31  are provided with electromagnetic valves  41  and  42 , respectively, and a supply amount of the carrier liquid C to the mixer  31  and a supply amount of the toner T to the mixer  31  are adjusted. From the mixer  31 , the liquid developer D necessary for the development is supplied using a pump  44  as a liquid developer supplying means. 
     The developer collected in the collecting container  16   b  of the developing device  16  is returned to the mixer  31  by a pump  43 . This is because the developer collected in the collecting container  16   b  is little used for the development or the like and therefore is little deteriorated. 
     The residual carrier liquid and the residual toner which are collected by the drum cleaner  19 , the intermediary transfer roller cleaner  26  and the transfer roller cleaner  27  are fed to the first separation and extraction device  37  by pumps  48 ,  49  and  50 , respectively. The liquid developer (carrier liquid) separated and extracted by the first separation and extraction device  37  is sent to the second separation and extraction device  34  by an electromagnetic valve  51 . 
     The reusable carrier liquid separated by the first and second separation and extraction devices  37 ,  34  is fed to the carrier tank  32  by an electromagnetic valve  45 . On the other hand, the waste liquid separated by the separation and extraction device  34  is appropriately fed to the waste liquid collecting container  35  by an electromagnetic valve  47  provided to a transporting pipe through self-weight fall. 
     As shown in  FIG. 3 , the above-described pumps  43 ,  44 ,  48 ,  49 ,  50  and electromagnetic valves  41 ,  42 ,  45 ,  47 ,  52  are controlled by a CPU  200  as a controller through a pump driver  201  and an electromagnetic valve driver  202 , respectively. The CPU  200  controls the respective pumps and the like on the basis of detection values of a developer amount detecting device  160 , a solid component content detecting device  310  and a carrier liquid resistance detecting device  34   a.    
     A feeding operation of the liquid developer will be described using  FIG. 4  while making reference to  FIGS. 2 and 3 . First, as shown in  FIGS. 2 and 3 , the developing device  16  is provided with the developer amount detecting device  160 , so that an amount of the liquid developer in the developing device  16  is detected by the developer amount detecting device  160 . Further, the mixer  31  is provided with the solid component content detecting device  310 , so that a content of a solid component such as the toner in the mixer  31  is detected. The solid component content detecting device  310  is, for example, provided with a light-emitting portion and a light-receiving portion, and a portion where the liquid in the mixer  31  passes is irradiated with light from the light-emitting portion and then the light passing through the portion is received by the light-receiving portion. Depending on the amount of the solid component at this portion, a light quantity of the light received by the light-receiving portion changes, and therefore depending on the change in light quantity, the content of the solid component in the mixer  31  can be detected. 
     As shown in  FIG. 4 , a developer amount in the developing device  16  is detected by the developer amount detecting device  160  (S 1 ). Then, in the case where the developer amount in the developing device  16  is not more than a predetermined amount (e.g., 200±10 cc), the CPU  200  drives the pump  44  (S 2 ), so that adjustment of the liquid developer amount in the developing device  16  is made. After the adjustment, the drive of the pump  44  is stopped (S 3 ). 
     Then, the content of the solid component in the mixer  31  is detected by the solid component content detecting device  310  (S 4 ). In the case where the content of the solid component in the mixer  31  is out of a predetermined range (e.g., 10±0.5%), the CPU  200  discriminates whether or not the solid component content is 10.5% or more (S 5 ). In the case where the solid component content is 10.5% or more, the electromagnetic valve  41  is opened, so that the carrier liquid is supplied from the carrier tank  32  into the mixer  31  (S 6 ). On the other hand, in the case where the solid component content is not 10.5% or more, i.e., in the case where the solid component content is 9.5% or less, the electromagnetic valve  42  is opened, so that the toner is supplied from the toner tank  33  into the mixer  31  (S 7 ). As a result, content adjustment of the liquid developer in the mixer  31  is made. 
     That is, in the case where a toner content (solid component content) is high, the carrier liquid is supplied from the carrier tank  32  to the mixer  31  through the electromagnetic valve  41 . Further, in the case where the toner content is low, the liquid developer higher in toner content than the liquid developer used in the mixer  31  is supplied from the toner tank  33  to the mixer  31  through the electromagnetic valve  42 . 
     When the solid component content in the mixer  31  falls within the predetermined range, the pump  44  is driven as desired, and then the liquid developer subjected to the content adjustment is supplied from the mixer  31  to the developing device  16  (S 8 ). Then, image formation is started (S 9 ), and at the same time, drive of the pumps  43 ,  48 ,  49 ,  50  is also started (S 10 ), and also drive of the separation and extraction device  34  is started (S 11 ). 
     (Second Separation and Extraction Device) 
     The first separation and extraction device  37  and the second separation and extraction device  34  have the same constitution. Accordingly, in the following description, the second separation and extraction device  37  as the separating device will be described using  FIGS. 5 to 11 , and as regards the first separation and extraction device  34 , the same constitution is represented by an associated reference numeral or symbol in parentheses and a portion different in action (function) from an associated portion will be described supplementarily. 
     First, the first separation and extraction device  34  is a device for separating the liquid developer into the toner and the carrier liquid using the electric field and for separately extracting the carrier liquid and the toner. The second separation and extraction device  34  is, as described above, a device for separating and extracting the low-resistance carrier (principally the charge control agent) as the first substance from the carrier liquid separated and extracted by the first separation and extraction device  37 , by using the electric field. 
     The reason why the second separation and extraction device  34  is provided will be described. The carrier liquid is repetitively subjected to recycling, so that the substance (low-resistance carrier) having the low volume resistivity accumulates in the carrier liquid. Thus, the resistance of the entirety of the liquid developer lowers, so that there is a liability that the image defect generates. Particularly, in the case where a high-density image such as a solid image (which is a toner image formed on an entire surface of an image formable region of the photosensitive drum and which refers to the case where an image ratio (print ratio is 100%), a proportion of the carrier liquid in an output image is small, and therefore particularly the resistance is liable to lower. In this embodiment, in order to suppress such a lowering in volume resistivity of the carrier liquid, the second separation and extraction device  34  is provided. 
     The carrier liquid (liquid developer) separated by the first separation and extraction device  37  is fed from an inlet  34   b  of the separation and extraction device  34  into a liquid accommodating container  346  as show by arrows in  FIGS. 5 and 6 . Then, the liquid developer is supplied to a buffer container  348  in the liquid accommodating container  346 . In this embodiment, the buffer container  348  is provided in the second separation and extraction device  34 , but may also be provided separately as a single member. The collect carrier liquid supplied to the buffer container  348  is fed by a pump  34   c  and passes through a filter  34   d.    
     The carrier liquid passed through the filter  34   d  is poured on a supply tray  346   a  as a supplying portion as shown in  FIG. 6 . Incidentally, in the second separation and extraction device  34 , the filter  34   d  may also be omitted, so that the carrier liquid separated and extracted by the first separation and extraction device  37  may be directly poured on the supply tray  346   a . As described later specifically, the carrier liquid poured on the supply tray  346   a  is separated into the low-resistance carrier (first substance, charge control agent) and the high-resistance carrier (second substance) by the second separation and extraction device  34 . Then, the extracted low-resistance carrier is sent to the waste liquid collecting container  35 , and the extracted high-resistance carrier (carrier liquid) is fed to the carrier tank  32 . 
     Next, a constitution of separation and extraction of the low-resistance carrier and the high-resistance carrier in the second separation and extraction device  34  will be described. As shown in  FIGS. 6 and 7 , in the liquid accommodating container  346 , a coating electrode member  341  as a second external electrode member, an electrode roller  342  as an electroconductive second roller, a collecting device  350  and the like are provided. A pair of second electrodes, between which the liquid developer is passable, is constituted by the coating electrode member  341  and the electrode roller  342 , and the electrode roller  342  includes a second electrode  342   a  as one of the second electrodes, and the coating electrode member  341  includes a second electrode  341   a  as the other second electrode. The liquid accommodating container  346  is a container capable of accommodating the carrier liquid and includes the above-described supply tray  346   a , a discharge portion  346   b  as a second discharge portion through which a reusable carrier liquid is to be discharged as described later, and a collecting portion  354  for collecting the developer which is the waste liquid. 
     The electrode roller  342  is an electroconductive roller which is, for example, formed by integrally molding a core metal, formed with a solid stainless steel material in an outer diameter of 40 mm, with a urethane rubber elastic layer formed on a surface of the core metal. As shown in  FIG. 3 , a driving force is externally inputted into the electrode roller  342  by a driving motor  205 , so that the electrode roller  342  is rotated in a predetermined direction (arrow directions of  FIGS. 6 and 7 ). In this embodiment, a rotational speed of the driving motor  205  is 2000 rpm. Then, the electrode roller  342  is rotated at a rotational speed of, e.g., 400 rpm by reducing the rotational speed of the driving motor  205  by a speed reducer. Incidentally, a voltage applying device  345  is controlled by the CPU  200  through a high-voltage driver  204 , and the driving motor  205  is controlled by the CPU  200  through a motor driver  203 . 
     The coating electrode member  341  is disposed with a gap  347  as a second gap with a part of the electrode roller  342  as shown in  FIGS. 7 and 8 . With an upstream end portion  347   a  of the gap  347  with respect to a rotational direction of the electrode roller  342 , the supply tray  346   a  is connected. Further, the carrier liquid poured in the supply tray  346   a  as described above is supplied into the gap  347  through the upstream end portion  347   a . The gap  347  is sealed at both end portions thereof with respect to a rotational axis direction of the electrode roller  342 , so that the carrier liquid supplied into the gap  347  is fed through the gap  347  toward a downstream side of the gap  347  with respect to the rotational direction of the electrode roller  342  with rotation of the electrode roller  342 . With a downstream end portion  347   a  of the gap  347  with respect to the rotational direction of the electrode roller  342 , the discharge portion  346   b  is connected ( FIG. 6 ). Further, the carrier liquid passed through the gap  347  is sent to the carrier tank  32  through the discharge portion  346   b  via a transporting pipe  346   c  ( FIGS. 2 and 6 ). 
     Incidentally, the transporting pipe  346   c  is connected with also a path through which the discharged carrier liquid is returned to the separation and extraction device  34  again. The discharge portion  346   b  is provided with the carrier liquid resistance detecting device  34   a , so that the volume resistivity of the carrier liquid sent into the discharge portion  346   b  is detected. The carrier liquid resistance detecting device  34   a  detects the volume resistivity of the carrier liquid by detecting the resistance of the carrier liquid when a current is caused to flow through a pair of electrodes provided in the carrier liquid. Further, in the case where the volume resistivity of the carrier liquid sent to the discharge portion  346   b  is less than a predetermined value (e.g., 1.0×10 11  Ω·cm), the carrier liquid is returned to the second separation and extraction device  34  again, so that the separation of the carrier liquid into the low-resistance carrier and the high-resistance carrier is effected. 
     This is because, for example, the case where an abnormal situation such that a power source is shut down during an operation of the second separation and extraction device  34  generates and thus the low-resistance carrier and the high-resistance carrier cannot be sufficiently separated from each other by the second separation and extraction device  34  is assumed. In such a case, the volume resistivity of the carrier liquid sent to the discharge portion  346   b  is less than the predetermined value, and therefore in this case, the carrier liquid is returned to the second separation and extraction device  34 . Ordinarily, as described later, the carrier liquid passes through the gap  347 , so that the low-resistance carrier and the high-resistance carrier are separated from each other and then the extracted high-resistance carrier is sent to the discharge portion  346   b . Accordingly, the volume resistivity of the carrier liquid sent to the discharge portion  346   b  is not less than the predetermined value, so that the carrier liquid is sent to the carrier tank  32  without being returned to the second separation and extraction device  34 . Incidentally, such a path for returning the carrier liquid to the second separation and extraction device  34  may also be omitted. 
     As described above, the coating electrode member  341  disposed opposite to the electrode roller  342  with the gap  347  is formed of an electroconductive material at least at a surface of a portion  341   x  on which the liquid passes through the gap  347 . The coating electrode member  341  is formed of, e.g., a solid stainless steel material in width of 400 mm. The portion  341   x  on which the liquid passes has a shape of accommodating a part of the electrode roller  342 , and an opposing surface of the portion  341   x  to the electrode roller  342  has a curved shape such that a predetermined distance (i.e., the gap  347 ) is maintained between the opposing surface and the surface of the electrode roller  342 . This predetermined distance is, e.g., 0.2 mm. 
     As shown in  FIG. 3 , with the coating electrode member  341  and the electrode roller  342 , the voltage applying device  345  as a second voltage applying means is connected. Further, between the coating electrode member  341  and the electrode roller  342 , a voltage is applied by the voltage applying device  345  so that an electric field moves the low-resistance carrier (first substance, charge control agent) toward the electrode roller  342  side (side of one of the second electrodes). That is, to the gap  347 , a voltage such that an electric field for attracting the low-resistance carrier to the electrode roller  342  is generated is applied. 
     In this embodiment, the charge control agent is positively charged, and therefore for example, a voltage of −300 V is applied to the electrode roller  342 , and a voltage of −200 V is applied to the coating electrode member  341 . Thus, the low-resistance carrier in the carrier liquid passing through the gap  347  is moved from the coating electrode member  341  to the electrode roller  342 . As a result, during the passing of the carrier liquid through the gap  347 , the low-resistance carrier is carried on the electrode roller  342 , so that the low-resistance carrier and the high-resistance carrier are separated from each other. The separated high-resistance carrier (carrier liquid) is discharged to the discharge portion  346   b  connected with the downstream end portion  347   b  of the gap  347 , and then is sent to the carrier tank  32  as a collecting container as described above. 
     The collecting device  350  is positioned downstream of the coating electrode member  341  with respect to the rotational direction of the electrode roller  342 , and collects the low-resistance carrier carried on the electrode roller  342 . The collecting device  350  includes collecting roller  351 , the voltage applying device  345  as a collecting voltage applying means, and a blade member  352  as a scraping member. 
     The collecting roller  351  is an electroconductive roller formed of, e.g., a solid stainless steel material in an outer diameter of 20 mm, and is provided in contact with the electrode roller  342 . Further, the collecting roller  351  contacts the electrode roller  342  and is rotated by the electrode roller  342  in arrow directions of  FIGS. 6 and 7 . Incidentally, a rotational speed of the collecting roller  351  is, e.g., 800 rpm. 
     As shown in  FIGS. 9 and 10 , the electrode roller  342  and the collecting roller  351  are disposed in substantially parallel to each other, and both end portions of these rollers  342  and  351  with respect to a rotational axis direction are rotatably supported by frames  346   e  constituting the liquid accommodating container  346 . At both end portions of the collecting roller  351 , urging mechanisms  353  such as springs are provided. The collecting roller  351  is urged toward the electrode roller  342  by the urging mechanisms  353 , so that the electrode roller  342  is elastically deformed. An urging force for urging the collecting roller  351  toward the electrode roller  342  by the urging mechanisms  353  is, e.g., 3 kgf (29.4 N). 
     The coating electrode member  341  and the collecting roller  351  are positioned on the basis of the electrode roller  342 , so that the electrode roller  342  is a positional basis for these members  341  and  351 . 
     The voltage applying device  345  is connected with the electrode roller  342  and the collecting roller  351  as shown in  FIG. 3 , and applies a voltage between the collecting roller  351  and the electrode roller  342  so that an electric field for moving the toner toward the collecting roller  351  is generated. In this embodiment, the voltage applying device connected with the electrode roller  342  and the collecting roller  351  and the voltage applying device connected with the electrode roller  342  and the coating electrode member  341  are used in common, but may also be separately provided. In this embodiment, for example, a voltage of −300 V is applied to the electrode roller  342 , and a voltage of −400 V is applied to the collecting roller  351 . Thus, the low-resistance carrier which is carried on the electrode roller  342  and which is fed toward the collecting roller  351  is moved from the electrode roller  342  to the collecting roller  351 . 
     The blade member  352  solid components off the low-resistance carrier on the collecting roller  351  in contact with the collecting roller  351 . The blade member  352  is disposed at a position downstream of a position of contact between the electrode roller  342  and the collecting roller  351  with respect to a rotational direction of the collecting roller  351  so that the blade member  352  contacts the collecting roller  351  with respect to a counter direction to the rotational direction of the collecting roller  351 . Incidentally, the counter direction is a direction such that a direction in which the free end portion  352   a  contacting the surface of the collecting roller  351  extends is opposite to a tangential direction along the rotational direction of the collecting roller  351 . Further, the blade member  352  is a plate(-like) member extending along a longitudinal direction (rotational axis direction) of the collecting roller  351  and for example, a stainless steel material is used as a material of the collecting roller  351 . 
     As described above, the low-resistance carrier moved from the electrode roller  342  to the collecting roller  351  is scraped off by the blade member  352  and then is sent to the collecting portion  354 . The low-resistance carrier collected in the collecting portion  354  is sent to the waste liquid collecting container  35  as described above. Incidentally, a scraping member for scraping the low-resistance carrier off the collecting roller  351  is not limited to the blade member. For example, the blade member may also be formed in a brush shape other than the blade shape. 
     (Positional Relation Between End Portions of Gap) 
     In the case of this embodiment, as described above, the carrier liquid which is collected at the image forming portion  12  and which is supplied from the supply tray  346   a  to the gap  347  passes through the gap  347 , so that the liquid developer is separated into the low-resistance carrier and the high-resistance carrier. Here, the liquid flows from above to below along a direction of gravitation. 
     Therefore, in this embodiment, as shown in  FIG. 7 , in the case where a line α passing through a center O of the electrode roller  342  and a top of the electrode roller  342  with respect to the direction of gravitation is 0°, the upstream end portion  347   a  of the gap  347  is positioned in a range of 0° or more and less than 180° with respect to the rotational direction of the electrode roller  342 . In other words, an angle formed between the line α and a line β passing through the upstream end portion  347   a  of the gap  347  and the center O is θ, the upstream end portion  347   a  is positioned so that the angle θ is 0° or more and less than 180°. In a preferred example, the upstream end portion  347   a  of the gap  347  is positioned in a range of 60° or more and 120° or less with respect to the rotational direction of the electrode roller  342 . In this embodiment, the upstream end portion  347   a  is positioned in a range from 90° to 120° with respect to the rotational direction of the electrode roller  342 . 
     The downstream end portion  347   b  of the gap  347  is positioned below the upstream end portion  347   a  with respect to the direction of gravitation. In a preferred example, the downstream end portion  347   b  of the gap  347  is positioned in a range of 180° or less with respect to the rotational direction of the electrode roller  342 . That is, it is preferable that the downstream end portion  347   b  is positioned in a range which includes the position of 180° and in which the downstream end portion  347   b  is positioned upstream of the position of 180° with respect to the rotational direction of the electrode roller  342 . As a result, the liquid developer passing through the gap  347  is prevented from being fed against gravitation, so that the reuse efficiency can be further enhanced. In this embodiment, the downstream end portion  347   b  is in the position of 180° with respect to the rotational direction of the electrode roller  342 . 
     Incidentally, a length of the gap  347 , i.e., a length from the upstream end portion  347   a  to the downstream end portion  347   b  along the electrode roller  342  may preferably be not less than ⅕ of a peripheral length of an outer peripheral surface of the electrode roller  342 . This length of the gap  347  may also be set depending on the rotational speed of the electrode roller  342 . For example, in the case where the rotational speed of the electrode roller  342  is slow, the length of the gap  347  can be shortened. In summary, it is only required that a length in which the low-resistance carrier and the high-resistance carrier are separated from each other is ensured during the passing of the liquid developer through the gap  347 . 
     [Supplemental Description of First Separation and Extraction Device) 
     As described above, the liquid developer collected by the image forming portion  12  such as the drum cleaner  19  is fed from an inlet  37   b  of the first separation and extraction device  37  into a liquid accommodating container  376  as shown by arrows in  FIGS. 5 and 6 . Then, the liquid developer is supplied to a buffer container  378  in the liquid accommodating container  376 . The liquid developer supplied to the buffer container  378  is fed by a pump  37   c  and passes through a filter  37   d.    
     The liquid developer passed through the filter  37   d  is poured on a supply tray  376   a  as a supplying portion as shown in  FIG. 6 . As described later specifically, the liquid developer poured on the supply tray  376   a  is separated into the toner and the carrier liquid by the first separation and extraction device  37 . Then, the extracted toner is sent to the waste liquid collecting container  35 , and the extracted carrier liquid is fed to the second separation and extraction device  34  as described above. 
     As shown in  FIGS. 6 and 7 , in the liquid accommodating container  376 , a coating electrode member  371  as a first external electrode member, an electrode roller  372  as an electroconductive first roller, a toner collecting device  380  and the like are provided. A pair of first electrodes, between which the liquid developer is passable, is constituted by the coating electrode member  371  and the electrode roller  372 , and the electrode roller  372  includes a first electrode  372   a  as one of the second electrodes, and the coating electrode member  371  includes a first electrode  371   a  as the other second electrode. The liquid accommodating container  376  is a container capable of accommodating the liquid developer and includes the above-described supply tray  376   a , a discharge portion  376   b  as a first discharge portion through which the carrier liquid is to be discharged, and a collecting portion  384  for collecting the developer which is the waste liquid. 
     As shown in  FIG. 3 , a driving force is externally inputted into the electrode roller  372  by a driving motor  205 , so that the electrode roller  342  is rotated in a predetermined direction (arrow directions of  FIGS. 6 and 7 ). In this embodiment, a rotational speed of the driving motor  205  is 2000 rpm. Incidentally, the driving motor  205  for driving the electrode roller  342  of the second separation and extraction device  34  and the electrode roller  372  of the first separation and extraction device  37  may be the same or may also be separately provided for each of the electrode rollers  342 ,  372 . 
     The coating electrode member  371  is disposed with a gap  377  as a first gap with a part of the electrode roller  372  as shown in  FIGS. 7 and 8 . With an upstream end portion  377   a  of the gap  377  with respect to a rotational direction of the electrode roller  372 , the supply tray  376   a  is connected. Further, the liquid developer poured in the supply tray  376   a  as described above is supplied into the gap  377  through the upstream end portion  377   a . The liquid developer supplied into the gap  377  is fed through the gap  377  toward a downstream side of the gap  377  with respect to the rotational direction of the electrode roller  372  with rotation of the end portion  372 . With a downstream end portion  377   a  of the gap  377  with respect to the rotational direction of the electrode roller  372 , the discharge portion  376   b  is connected ( FIG. 6 ). Further, the liquid developer passed through the gap  377  is sent to the second separation and extraction device  34  through the discharge portion  376   b  via a transporting pipe  376   c  ( FIGS. 2 and 6 ). 
     Incidentally, the transporting pipe  376   c  is connected with also a path through which the discharged liquid developer is returned to the separation and extraction device  34  again. The discharge portion  376   b  is provided with an unshown carrier liquid content detecting device, so that the toner content in the liquid developer sent into the discharge portion  376   b  is detected. Further, in the case where the toner content of the liquid developer sent to the discharge portion  376   b  is larger than a predetermined value (e.g., 0.02%), the liquid developer is returned to the first separation and extraction device  37  again, so that the separation of the liquid developer into the toner and the carrier liquid is effected. This is because, for example, the case where an abnormal situation such that a power source is shut down during an operation of the first separation and extraction device  37  generates and thus the carrier liquid and the toner cannot be sufficiently separated from each other by the second separation and extraction device  34  is assumed. 
     As described above, the coating electrode member  371  disposed opposite to the electrode roller  372  with the gap  377  is formed of an electroconductive material at least at a surface of a portion  371   x  on which the liquid passes through the gap  377 . As shown in  FIG. 3 , with the coating electrode member  371  and the electrode roller  372 , the voltage applying device  375  as a first voltage applying means is connected. Further, between the coating electrode member  371  and the electrode roller  372 , a voltage is applied by the voltage applying device  375  so that an electric field moves the toner toward the electrode roller  372  side (side of one of the first electrodes). That is, to the gap  377 , a voltage such that an electric field for attracting the toner to the electrode roller  372  is generated is applied. 
     In this embodiment, the toner is negatively charged by the charge control agent, and therefore for example, a voltage of −300 V is applied to the electrode roller  372 , and a voltage of −1000 V is applied to the coating electrode member  371 . As a result, during the passing of the liquid developer through the gap  377 , the toner is carried on the electrode roller  372 , so that the toner and the collect are separated from each other. The separated carrier liquid is discharged to the discharge portion  376   b  connected with the downstream end portion  377   b  of the gap  377 . 
     The toner collecting device  380  is positioned downstream of the coating electrode member  371  with respect to the rotational direction of the electrode roller  372 , and collects the toner carried on the electrode roller  372 . The collecting device  380  including a collecting roller  381 , the voltage applying device  375  as a collecting voltage applying means, and a blade member  382  as a scraping member. The voltage applying device  375  and the above-described voltage applying device  345  can be the same or different from each other. 
     The collecting roller  381  is provided in contact with the electrode roller  372 . Further, the collecting roller  381  contacts the electrode roller  372  and is rotated by the electrode roller  342  in arrow directions of  FIGS. 6 and 7 . As shown in  FIGS. 9 and 10 , the electrode roller  372  and the collecting roller  371  are disposed substantially parallel to each other, and both end portions of these rollers  372  and  381  with respect to a rotational axis direction are rotatably supported by frames  376   e  constituting the liquid accommodating container  376 . At both end portions of the collecting roller  381 , urging mechanisms  383  such as springs are provided. The collecting roller  381  is urged toward the electrode roller  372  by the urging mechanisms  383 , so that the electrode roller  372  is elastically deformed. 
     The voltage applying device  375  is connected with the electrode roller  372  and the collecting roller  381  as shown in  FIG. 3 , and applies a voltage between the collecting roller  381  and the electrode roller  372  so that an electric field for moving the toner toward the collecting roller  381  is generated. In this embodiment, for example, a voltage of −300 V is applied to the electrode roller  372 , and a voltage of −200 V is applied to the collecting roller  381 . Thus, the toner which is carried on the electrode roller  372  and which is fed toward the collecting roller  381  is moved from the electrode roller  372  to the collecting roller  381 . 
     The blade member  382  solid components off the toner on the collecting roller  381  in contact with the collecting roller  381 . The blade member  382  is disposed at a position downstream of a position of contact between the electrode roller  372  and the collecting roller  381  with respect to a rotational direction of the collecting roller  381  so that the blade member  382  contacts the collecting roller  381  with respect to a counter direction to the rotational direction of the collecting roller  381 . As described above, the toner moved from the electrode roller  372  to the collecting roller  381  is scraped off by the blade member  382  and then is sent to the collecting portion  384 . The toner collected in the collecting portion  384  is sent to the waste liquid collecting container  35  as described above. 
     Further, also a positional relation between upstream and downstream end portions of the gap  377  of the first separation and extraction device  37  is the same as that in the case of the above-described second separation and extraction device  34 . That is, as shown in  FIG. 7 , in the case where a line α passing through a center O of the electrode roller  372  and a top of the electrode roller  342  with respect to the direction of gravitation is 0°, an upstream end portion  377   a  of the gap  377  is positioned in a range of 0° or more and less than 180° with respect to the rotational direction of the electrode roller  372 . In a preferred example, the upstream end portion  377   a  of the gap  377  is positioned in a range of 60° or more and 120° or less with respect to the rotational direction of the electrode roller  372 . In this embodiment, the upstream end portion  377   a  is positioned in a range from 90° to 120° with respect to the rotational direction of the electrode roller  372 . 
     A downstream end portion  377   b  of the gap  377  is positioned below the upstream end portion  377   a  with respect to the direction of gravitation. In a preferred example, the downstream end portion  377   b  of the gap  377  is positioned in a range of 180° or less with respect to the rotational direction of the electrode roller  372 . Further, a length of the gap  377 , i.e., a length from the upstream end portion  377   a  to the downstream end portion  377   b  along the electrode roller  372  may preferably be not less than ⅕ of a peripheral length of an outer peripheral surface of the electrode roller  372 . 
     Incidentally, the first separation and extraction device  37  may also have a constitution different from the constitution of the second separation and extraction device  34  if the separation and extraction process of the toner and the carrier liquid is performed. 
     (Control Flow of Separation and Extraction Operation of Liquid Developer) 
     Next, a control flow of a separation and extraction operation of the liquid developer in the second separation and extraction device  34  constituted as described above in this embodiment will be described using  FIGS. 11 and 12 . First, the electromagnetic valve  51  provided to the transporting pipe  376   c  is opened, so that the carrier liquid, in a predetermined amount, separated by the first separation and extraction device  37  is sent to the second separation and extraction device  34 , and then the electromagnetic valve  51  is closed (S 21 ). 
     Then, the drive of the driving motor  205  is started, so that the electrode roller  342  is rotated (S 22 ). As a result, the carrier liquid (liquid developer) is fed with rotation of the electrode roller  342 . At this time, the collecting roller  351  is rotated by the electrode roller  342 . Further, the voltage applying device  345  is turned on (S 23 ). As a result, a voltage is applied between the coating electrode member  341  and the electrode roller  342  so that an electric field for moving the low-resistance carrier toward the electrode roller  342  is generated, and a voltage is applied between the collecting roller  351  and the electrode roller  342  so that an electric field for moving the low-resistance carrier toward the collecting roller  351  is generated. For this reason, the low-resistance carrier in the carrier liquid is first moved toward the electrode roller  342  and then is moved toward the collecting roller  351 . The carrier liquid (high-resistance carrier) from which the low-resistance carrier is removed remains on the coating electrode member  341  side. 
     That is, the toner low-resistance carrier in the liquid developer passing through the gap  347  not only is electrically attracted to the electrode roller  342  but also receives an electrically repelling force from the coating electrode member  341 . As a result, the low-resistance carrier is electrically urged toward the electrode roller  342 . Further, the low-resistance carrier, in the carrier liquid, which passed through the gap  347  and which was then fed to the collecting roller  351  by the electrode roller  342  not only is electrically attracted to the collecting roller  351  but also receives an electrically repelling force from the electrode roller  342 . As a result, the low-resistance carrier is electrically urged in a direction of being spaced from the electrode roller  342 , i.e., toward the collecting roller  351 . 
     The low-resistance carrier electrically deposited on the collecting roller  351  is scraped off by the blade member  352 . Here, the electromagnetic valve  52  is opened (S 24 ). As a result, the low-resistance carrier scraped by the blade member  352  falls by its own weight and then is collected into the waste liquid collecting container  35  through the collecting portion  354 . Incidentally, the low-resistance carrier may be disposed of or reused. 
     Further, the high-resistance carrier (carrier liquid) discharged to the discharge portion  346   b  through the downstream end portion  347   b  of the gap  347  is subjected to detection of the volume resistivity by the carrier liquid resistance detecting device  34   a . Then, whether or not the detected volume resistivity is a predetermined value (e.g., 1.0×10 11  Ω·cm) or more is discriminated (S 25 ). When the volume resistivity is the predetermined value or more, the electromagnetic valve  45  is opened, so that the carrier liquid is sent to the carrier tank  32  (S 26 ). 
     Then, when the separation and extraction of the carrier liquid from the second separation and extraction device  34  is completed (S 27 ), the electromagnetic valves  45 ,  51  and  52  are closed (S 28 ), and the voltage applying device  345  and the driving motor  205  are successively stopped (S 29 , S 30 ). 
     Then, the carrier liquid, in a predetermined amount, separated by the first separation and extraction device  37  is fed again into the second separation and extraction device  34  by the electromagnetic valve  51 , and a subsequent separation process is performed. Thereafter, such an operation is repeated. 
     In the first and second separation and extraction devices  37  and  34  in this embodiment, from 100.0 cc of the liquid developer (containing 90.0 cc of the carrier liquid and 10.0 cc of the toner), 88.0 cc of the carrier liquid can be extracted. A required time in one separation process is 30 seconds, for example, and in this case, it is possible to meet a process speed up to 800 mm/s. 
     As described above, in the case of this embodiment, the carrier liquid, of the high-resistance carrier, from which the low-resistance carrier such as the charge control agent is removed is extracted by the second separation and extraction device  34 . For this reason, a lowering in volume resistivity of the carrier liquid to be reused can be suppressed, and also the generation of the image defect can be suppressed. 
     That is, in the case of this embodiment, from the liquid developer collected at the image forming portion  12 , first, the toner is separated by the first separation and extraction device  37 . Next, the liquid developer from which the toner is separated is sent to the second separation and extraction device  34 . Then, by the second separation and extraction device  34 , the low-resistance carrier such as the charge control agent which is the first substance having the opposite polarity to the toner charge polarity is separated from the liquid developer, and then the carrier liquid from which the low-resistance carrier is separated is sent to the carrier tank  32  and then is used again. For this reason, it is possible to increase the volume resistivity of the carrier liquid which is sent to the carrier tank  32  and which is then reused. 
     Incidentally, in the above description, from the liquid developer collected at the image forming portion  12 , first, the toner is separated and then the low-resistance carrier is separated, but the order of separation of these substances may also be reversed. However, from the following reason, the above-described order is preferred. For example, in the case where the negative charge amount of the toner is larger than the positive charge amount (in absolute value), a negative charge component of the toner and a positive charge component are rarely electrostatically attracted to each other in some instances. In such a case, when the low-resistance carrier is removed first and then the toner is intended to be removed, in a step of separating the low-resistance carrier, the positive charge component, of the low-resistance carrier, attracted to the toner remains in the carrier liquid in some instances. Thus, also in a subsequent step of separating the toner, there is a possibility that the low-resistance carrier remains in the carrier liquid and thus the volume resistivity of the carrier liquid intended to be reused cannot be sufficiently lowered. For this reason, as described above, it is preferable that the toner is separated first and then the low-resistance carrier is separated. Particularly, in this embodiment, the charge amount of the toner is larger than the charge amount of the low-resistance carrier, and therefore this order is preferred. 
     Further, other than the use of the pump, in the case where the feeding of the liquid developer or the like can be made by, e.g., self-weight fall, such as a feeding type using the self-weight without providing the pump may also be used. 
     Another Example of First Embodiment 
     Another example of the First Embodiment will be described using  FIG. 12 . In this example, a supplying device  38 A for supplying a carrier liquid for supply to the carrier tank  32  is provided. The supplying device  38 A includes a supply carrier tank  38  and an electromagnetic valve  53  provided to a communication pipe for establishing communication between the supply carrier tank  38  and the carrier tank  32 . 
     In the carrier tank  32 , a float sensor  320  as a liquid amount detecting means detects a liquid amount of the carrier liquid in the carrier tank  32 . The float sensor  320  detects the liquid amount in the carrier tank  32  by detecting a position (liquid level) of a float floated on a liquid surface. As the float sensor  320 , for example, a float sensor in which a float provided with a magnet and a reed switch are provided and a position of the float is detected by the reed switch is used. The liquid amount detecting means may also have a constitution other than the float sensor described above. 
     The supplying device  38 A supplies the carrier liquid for supply into the carrier tank (carrier container)  32  on the basis of the float sensor  320 . Specifically, when detection that the liquid level of the carrier liquid in the carrier tank  32  is not more than a predetermined position (level) is made by the float sensor  320 , the electromagnetic valve  53  is opened, so that the carrier liquid for supply is supplied from the supply carrier tank  38  to the carrier tank  32 . Such control is effected by the CPU  200  ( FIG. 3 ). That is, a detection result of the float sensor  320  is sent to the CPU  200 , and then on the basis of this detection result, the CPU  200  controls the electromagnetic valve  53 . 
     The carrier liquid for supply accommodated in the supply carrier tank  38  is a fresh carrier liquid or a carrier liquid having a high volume resistivity. Such a carrier liquid for supply may preferably be higher in volume resistivity than the carrier liquid which is separated and extracted by the second separation and extraction device  34  and which is then sent to the carrier tank  32 . In the case where the carrier liquid for supply is the fresh carrier liquid, the volume resistivity thereof may preferably be, e.g., 1.0×10 14  Ω·cm or more. Further, the carrier liquid having the high volume resistivity may preferably have the volume resistivity of 1.0×10 12  Ω·cm or more. 
     According to this example, in the case where the carrier amount in the carrier tank  32  is not more than the predetermined amount, it is possible to automatically supply the carrier liquid for supply. During a period of existence of the carrier liquid in an amount not less than the predetermined amount in the carrier tank  32 , the carrier liquid for supply is not supplied. During this period, a carrier liquid for recycling separated and extracted by the second separation and extraction device  34  can be used preferentially, so that a supplying cycle of the carrier liquid for supply can be prolonged. 
     Incidentally, a constitution in which the supply carrier tank  38  exclusively for supplying the carrier liquid for supply is not provided and the carrier liquid for supply is directly supplied to the carrier tank  32  may also be employed. Other constitutions and actions are similar to those in the First Embodiment. 
     Second Embodiment 
     The Second Embodiment of the present invention will be described using  FIGS. 13 to 17 . In the First Embodiment described above, the high-resistance carrier (carrier liquid) separated and extracted by the second separation and extraction device  34  was supplied to the carrier tank  32 . On the other hand, in an image forming apparatus  100 A in this embodiment, the low-resistance carrier separated and extracted by a second separation and extraction device  34  is supplied to a carrier tank  32 . Further, the high-resistance carrier separated and extracted by the second separation and extraction device  34  is supplied to a mixer  31  via a second carrier tank  39  as a second carrier container. Other basis constitutions and actions are similar to those in the above-described First Embodiment, and therefore in the following, the similar constitutions will be omitted from description and illustration or briefly described, and a portion different from the First Embodiment will be principally described. 
     As shown in  FIG. 14 , transporting pipes from the carrier tank  32 , the second carrier tank  39  and a toner tank  33  to the mixer  31  are provided with electromagnetic valves  41 ,  55  and  42 , respectively, so that a supply amount of the carrier liquid C or the toner T to the mixer  31  is adjusted. From the mixer  31 , using a pump  44 , a developer D necessary for development is supplied to the developing device  16 . 
     The liquid developer collected at the image forming portion  12  is fed to the first separation and extraction device  37  by the pumps  48 ,  49  and  50 , and then is separated into the toner and the carrier liquid. Then, the carrier liquid (liquid developer) separated and extracted by the first separation and extraction device  37  is fed to the second separation and extraction device  34  by the electromagnetic valve  51 . On the other hand, the waste liquid W containing the toner and the impurity is appropriately fed by the self-weight fall to the waste liquid collecting container  35  by the electromagnetic valve  47  provided to the transporting pipe. 
     In the second separation and extraction device  34 , the first substance (low-resistance carrier) having the opposite polarity to the toner charge polarity and the second substance (high-resistance carrier) having the intermediary charge amount between the charge amounts of the toner and the first substance are separated from the carrier liquid separated and extracted by the first separation and extraction device  37 . Then, a liquid containing the first substance (principally the charge control agent), separated from the second substance, and the impurity is supplied to the carrier tank  32  by the electromagnetic valve  45 , as a first gap means. On the other hand, the high-resistance carrier (carrier liquid) from which the first substance is separated by the second separation and extraction device  34  is fed to the second carrier tank  39  by the electromagnetic valve  54 . 
     A control flow of a separation and extraction operation of the liquid developer in the second separation and extraction device  34  in this embodiment is as shown in  FIG. 15 . Also in the case of this embodiment, the discharge portion  346   b  of the second separation and extraction device  34  is provided with the carrier liquid resistance detecting device  34   a , so that the volume resistivity of the high-resistance carrier (carrier liquid) separated and extracted by the second separation and extraction device  34  is detected.  FIG. 15  is substantially similar to  FIG. 11  described in the First Embodiment except for the following points. The points different from  FIG. 11  is that the second separation and extraction device  34  is operated and the electromagnetic valve  45  is opened (S 241 ), that when the volume resistivity is not less than a predetermined value in S 25 , the electromagnetic valve  54  is opened and thus the carrier liquid is sent to the second carrier tank  39  (S 261 ), and that when the separation and extraction is completed in S 27 , the electromagnetic valves  45 ,  51  and  54  are closed (S 281 ). 
     The high-resistance carrier fed to the second carrier tank  39  is appropriately fed to the mixer  31  by the electromagnetic valve  55  as the second supplying means. That is, the high-resistance carrier obtained by separating the low-resistance carrier from the liquid developer by the second separation and extraction device  34  is supplied to the mixer  31  via the second carrier tank  39  by the electromagnetic valve  55 . 
     In the case of this embodiment, similarly as in another example of the First Embodiment described with reference to  FIG. 12 , the supplying device  38 A for supplying the carrier liquid for supply to the carrier tank  32  is provided. The supplying device  38 A includes the supply carrier tank  38  and the electromagnetic valve  53  provided to the communication pipe for establishing communication between the supply carrier tank  38  and the carrier tank  32 . In the supply carrier tank  38 , as the carrier liquid for supply, similarly as in another example of the First Embodiment, the fresh carrier liquid or the carrier liquid having the high volume resistivity (e.g., 1.0×10 12  Ω·cm or more is accommodated. 
     In this embodiment, similarly as in another example of First Embodiment, in the carrier tank  32 , the float sensor  320  as the liquid amount detecting means for detecting the liquid amount of the carrier liquid in the carrier tank  32  is provided. Further, in this embodiment, in the carrier tank  32 , a carrier liquid resistance detecting device  321  as a resistance detecting mean for detecting the volume resistivity of the carrier liquid in the carrier tank  32  is provided. A constitution of the carrier liquid resistance detecting device  321  is the same as the constitution of the above-described carrier liquid resistance detecting device  34   a.    
     The supplying device  38 A supplies the carrier liquid for supply into the carrier tank (carrier container)  32  on the basis of detection results of the float sensor  320  and the carrier liquid resistance detecting device  321 . This operation will be described using  FIG. 16 . First, the volume resistivity of the carrier liquid in the carrier tank  32  is detected by the carrier liquid resistance detecting device  321  (S 101 ). In the case where a detection result is less than a predetermined value (e.g., 1.0×10 11  Ω·cm), the electromagnetic valve  53  is opened and then the carrier liquid for supply is supplied from the supply carrier tank  38  to the carrier tank  32  (S 102 ). 
     Then, when by the float sensor  320 , detection that the liquid level (position) of the carrier liquid in the carrier tank  32  is not more than a predetermined position (e.g., not more than 5000 cc) is made (S 103 ), the electromagnetic valve  53  is opened. Then, the carrier liquid for supplying is supplied from the supply carrier tank  38  to the carrier tank  32  (S 102 ). In the case where the volume resistivity of the carrier liquid in the carrier tank  32  is not less than the predetermined value and the liquid level is higher than the predetermined position, the electromagnetic valve  53  is closed (S 104 ), so that the control is ended. Such control is effected by the CPU  200  ( FIG. 3 ). That is, the detection results of the float sensor  320  and the carrier liquid resistance detecting device  321  are sent to the CPU  200 , and then the CPU  200  controls the electromagnetic valve  53  on the basis of the detection results. 
     As a result, in the case where the carrier liquid amount in the carrier tank  32  is not more than the predetermined amount or the volume resistivity of the carrier liquid is not more than the predetermined value, it is possible to automatically supply the fresh carrier liquid or the carrier liquid having the high volume resistivity. 
     Such a feeding operation of the liquid developer in this embodiment is as shown in  FIG. 17 . Also in the case of this embodiment, the developing device  16  is provided with a developer amount detecting device  160  and the developer amount detecting device  160  detects an amount of the liquid developer in the developing device  16 . Further, the mixer  31  is provided with a solid component content detecting device  310  and the solid component content detecting device  310  detects the content of the solid component such as the toner in the mixer  31 .  FIG. 17  is substantially similar to  FIG. 4  described in the First Embodiment except for the following point. The point different from  FIG. 4  is that in S 5 , in the case where the solid component content is 10.5% or more, the electromagnetic valve  41  or  55  opened and thus the carrier liquid is supplied from the carrier tank  32  or the second carrier tank  39  into the mixer  31  (S 61 ). 
     Incidentally, either one of the electromagnetic valves  41  and  55  may be opened preferentially, and the electromagnetic valves  41  and  55  may also be alternately opened or simultaneously opened. However, it is preferable that the carrier liquid to be reused is used preferentially, and in this case, the electromagnetic valve  55  is opened preferentially and thus the carrier liquid is supplied from the second carrier tank  39  to the mixer  31 . Then, in the case where the liquid amount in the second carrier tank  39  is not more than the predetermined amount, the electromagnetic valve  41  is opened and thus the carrier liquid is supplied from the carrier tank  32  to the mixer  31 . 
     In the case of this embodiment described above, it is possible to suppress a lowering in volume resistivity of the carrier liquid to be reused while effectively using the low-resistance carrier separated and extracted by the second separation and extraction device  34 . That is, in this embodiment, the carrier liquid separated and extracted by the second separation and extraction device  34  is supplied to the carrier tank  32 . Into the carrier tank  32 , from the supply carrier tank  38 , the fresh carrier liquid or the carrier liquid having the high volume resistivity is supplied, and therefore even when the low-resistance carrier is supplied, the volume resistivity of the carrier liquid in the carrier tank  32  can be increased. Further, each of the low-resistance carrier from the second separation and extraction device  34  and the carrier liquid for supply from the supply carrier tank  38  is made supplyable into the carrier tank  32 , and therefore it is easy to adjust the volume resistivity of the carrier liquid in the carrier tank  32 . 
     Accordingly, as the carrier liquid to be reused, the liquid carrier properly adjusted in volume resistivity can be supplied from the carrier tank  32  to the mixer  31 . Thus, in this embodiment, it is possible to suppress the lowering in volume resistivity of the carrier liquid to be reused while effectively using the low-resistance carrier separated and extracted by the second separation and extraction device  34 . Incidentally, the high-resistance carrier separated and extracted by the separation and extraction device  34  can be reused by being directly supplied to the mixer  31 . Other constitutions and actions are similar to those in the First Embodiment. 
     Another First Example of the Second Embodiment 
     Another first example of the Second Embodiment will be described using  FIG. 18 . In this example, a second supplying device  400  for supplying a carrier liquid for supply (fresh carrier liquid or carrier liquid having high volume resistivity) to the second carrier tank  39  is provided. As the fresh carrier liquid, for example, the volume resistivity thereof may preferably be 1.0×10 14  Ω·cm or more, and as the carrier liquid having the high volume resistivity, for example, the volume resistivity thereof may preferably be 1.0×10 12  Ω·cm or more. 
     The second supplying device  400  includes a second supply carrier tank  40  and an electromagnetic valve  56  provided to a communication pipe for establishing communication between the second supply carrier tank  40  and the second carrier tank  39 . In the second carrier tank  39 , a float sensor  390  as a liquid amount detecting means detects a liquid amount of the carrier liquid in the second carrier tank  39 . A constitution of the float sensor  390  is similar to the constitution of the above-described float sensor  320 . 
     The second supplying device  400  supplies the carrier liquid for supply into the second carrier tank  39  on the basis of the float sensor  390 . Specifically, when detection that the liquid level of the carrier liquid in the second carrier tank  39  is not more than a predetermined position (level) is made by the float sensor  390 , the electromagnetic valve  56  is opened, so that the carrier liquid for supply is supplied from the second supply carrier tank  40  to the second carrier tank  39 . Such control is effected by the CPU  200  ( FIG. 3 ). That is, a detection result of the float sensor  390  is sent to the CPU  200 , and then on the basis of this detection result, the CPU  200  controls the electromagnetic valve  56 . 
     According to this example, in the case where the carrier amount in the second carrier tank  39  is not more than the predetermined amount, it is possible to automatically supply the carrier liquid for supply. During a period of existence of the carrier liquid in a member not less than the predetermined amount in the second carrier tank  39 , the carrier liquid for supply is not supplied. During this period, a carrier liquid for recycling separated and extracted by the second separation and extraction device  34  can be used preferentially, so that a supplying cycle of the carrier liquid for supply can be prolonged. 
     Incidentally, a constitution in which the second supply carrier tank  40  exclusively for supplying the carrier liquid for supply is not provided and the carrier liquid for supply is directly supplied to the second carrier tank  39  may also be employed. Other constitutions and actions are similar to those in the Second Embodiment. 
     Another Second Example of the Second Embodiment 
     Another second example of the Second Embodiment will be described using  FIGS. 19 and 20 . In this example, with respect to the constitution of the Second Embodiment, as the supplying device for supplying the carrier liquid for supply (fresh carrier liquid or carrier liquid having high volume resistivity) to the carrier tank  32 , in addition to the supplying device  38 , another supplying device  38   a A is provided. 
     Another supplying device  38   a A includes another supply carrier tank  38   a  and an electromagnetic valve  53   a  provided to a communication pipe for establishing communication between another supply carrier tank  38   a  and the carrier tank  32 . Here, the carrier liquid for supply in another supplying device  38   a A is different in volume resistivity from the carrier liquid for supply in the supplying device  38 A. For example, the volume resistivity of the carrier liquid in the supply carrier tank  38  of the supplying device  38 A is made higher than the volume resistivity of the carrier liquid in another supply carrier tank  38   a  of another supplying device  38   a A. Specifically, in the supply carrier tank  38 , a fresh carrier liquid (e.g., having the volume resistivity of 1.0×10 14  Ω·cm or more) containing no charge control agent is accommodated. On the other hand, in another supply carrier tank  38   a , a carrier liquid which contains a small amount of the charge control agent but which has a high volume resistivity (e.g., 1.0×10 12  Ω·cm or more) is accommodated. 
     The supplying device  38 A and another supplying device  38   a A supply the carrier liquid for supply into the carrier tank (carrier container)  32  on the basis of detection results of the float sensor  320  and the carrier liquid resistance detecting device  321 . For example, on the basis of a detection result of the carrier liquid resistance detecting device  321 , the electromagnetic valve  53  of the supplying device  38 A is controlled, and on the basis of the detection result of the float sensor  320 , the electromagnetic valve  53   a  of another supplying device  38   a A is controlled. 
     This operation will be described using  FIG. 20 . First, the volume resistivity of the carrier liquid in the carrier tank  32  is detected by the carrier liquid resistance detecting device  321  (S 201 ). In the case where a detection result is less than a predetermined value (e.g., 1.0×10 11  Ω·cm), the electromagnetic valve  53  is opened and then the carrier liquid for supply is supplied from the supply carrier tank  38  to the carrier tank  32  (S 202 ). 
     Then, by the float sensor  320 , detection that the liquid level (position) of the carrier liquid in the carrier tank  32  is not more than a predetermined position (e.g., not more than 5000 cc) is made (S 203 ), the electromagnetic valve  53   a  is opened. Then, the carrier liquid for supplying is supplied from another supply carrier tank  38   a  to the carrier tank  32  (S 204 ). In the case where the volume resistivity of the carrier liquid in the carrier tank  32  is not less than the predetermined value and the liquid level is higher than the predetermined position, the electromagnetic valves  53  and  53   a  are closed (S 205 ), so that the control is ended. Such control is effected by the CPU  200  ( FIG. 3 ). That is, the detection results of the float sensor  320  and the carrier liquid resistance detecting device  321  are sent to the CPU  200 , and then the CPU  200  controls the electromagnetic valves  53  and  53   a  on the basis of the detection results. 
     As a result, in the case where the carrier liquid amount in the carrier tank  32  is not more than the predetermined amount or the volume resistivity of the carrier liquid is not more than the predetermined value, it is possible to automatically supply the fresh carrier liquid or the carrier liquid having the high volume resistivity. 
     Incidentally, the supplying operations of the carrier liquids from the supplying device  38 A and another supplying device  38   a A may also be those other than the above-described supplying operations. For example, on the basis of the detection result of the carrier liquid resistance detecting device  321 , the carrier liquid for supply is supplied from another supplying device  38   a A to the carrier tank  32 . Further, on the basis of the detection result of the float sensor  320 , the carrier liquid for supply may also be supplied from the supplying device  38 A to the carrier tank  32 . Or, the supplying operations of the carrier liquids from the supplying device  38 A and another supplying device  38   a A may also be performed simultaneously. That is, on the basis of the detection results of the float sensor  320  and the carrier liquid resistance detecting device  321 , both of the electromagnetic valves  53  and  53   a  may also be controlled. Other constitutions and actions are similar to the Second Embodiment. 
     Another Third Example of the Second Embodiment 
     Another third example of the Second Embodiment will be described using  FIG. 21 . In this example, another first example of the Second Embodiment and another second example of the Second Embodiment which are described above are combined with each other. That is, with respect to the constitution of the Second Embodiment, the second supplying device  400  and another supplying device  38   a A are added. Constitutions and actions are similar to those of another first example of the Second Embodiment and another second example of the Second Embodiment. 
     In the above-described the Second Embodiment and each of another first, second and third examples, the carrier liquid resistance detecting device is provided in the carrier tank  32  but may also be provided in the mixer  31 . In this case, the supply of the carrier liquid to the carrier tank is made on the basis of the detection result of the float sensor. On the other hand, the supply of the carrier liquid from the carrier tank  32  and the second carrier tank  39  to the mixer  31  is made on the basis of the detection result of the carrier liquid resistance detecting device. 
     Third Embodiment 
     The Third Embodiment of the present invention will be described using  FIG. 22 . In the above-described Embodiments, the constitution including the image forming portion  12  for a single color was described. On the other hand, in this embodiment, a plurality of unshown image forming portions are provided. In this embodiment, four image forming portions capable of forming toner images of colors of yellow (Y), magenta (M), cyan (C) and black (K) are provided, so that a full-color image is formable on a recording material. 
     The four image forming portions have the same constitution as the constitution of the image forming portion  12  as shown in  FIG. 1 , and includes images  31 Y,  31 M,  31 C and  31 K, respectively, as shown in  FIG. 22 . The respective mixers  31 Y,  31 M,  31 C and  31 K supply liquid developers of the respective colors to associated ones of developing devices of the respective image forming portions. To the mixers  31 Y,  31 M,  31 C and  31 K, toners of the respective colors can be supplied from toner tanks  33 Y,  33 M,  33 C and  33 K, respectively. In the respective mixers  31 Y,  31 M,  31 C and  31 K, associated solid component content detecting devices are provided, and on the basis of detection results thereof, electromagnetic valves  42 Y,  42 M,  42 C and  42 K are controlled, respectively. Thus, the toners are appropriately supplied from the toner tanks  33 Y,  33 M,  33 C and  33 K. 
     On the other hand, a single carrier tank  32  for supplying the carrier liquid to the respective mixers  31 Y,  31 M,  31 C and  31 K is provided. That is, the carrier liquid is supplied from the single carrier tank  32  to the respective mixers  31 Y,  31 M,  31 C and  31 K. Communication pipes for establishing communication of the single carrier tank  32  with the mixers  31 Y,  31 M,  31 C and  31 K are provided with electromagnetic valves  41 Y,  41 M,  41 C and  41 K. 
     The electromagnetic valves  41 Y,  41 M,  41 C and  41 K are controlled on the basis of detection results of the carrier liquid resistance detecting devices of the mixers  31 Y,  31 M,  31 C and  31 K. Thus, the carrier liquid is appropriately supplied from the single carrier tank  32  to the mixers  31 Y,  31 M,  31 C and  31 K. 
     In this embodiment, the single carrier tank (carrier container)  32 , the four mixers (mixing devices)  31 Y,  31 M,  31 C and  31 K and the four electromagnetic valves (carrier supplying devices for mixing)  41 Y,  41 M,  41 C and  41 K are provided. In other words, commonalty of carrier tanks for the respective image forming portions is achieved. This is because the carrier tanks can used in common to the respective image forming portions. 
     Also as regards the first and second separation and extraction devices for separating the liquid developers collected at the image forming portions for the respective colors, a single separation and extraction device is employed and is used in common to the image forming portions. Further, also the supply carrier tank  38  and the like described in the above-described embodiments are used in common. Incidentally, as in the Second Embodiment, in the case of a constitution including the second carrier tank  39 , a single second carrier tank  39  is employed and the carrier liquid is supplied from the single second carrier tank  39  to the mixers  31 Y,  31 M,  31 C,  31 K for the respective colors. 
     In the case of this embodiment, the carrier tank  32  is used in common for the respective colors, and therefore downsizing and cost reduction of the image forming apparatus can be realized. Further, commonality of the first and second separation and extraction devices and the like is also achieved, so that the downsizing and the cost reduction can be further effectively realized. Other constitutions and actions are similar to those of either one of the above-described embodiments. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, a lowering in volume resistivity of the collect to be reused can be suppressed.