Patent Publication Number: US-10331067-B2

Title: Image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus of an electrophotographic type, and particularly relates to an image forming apparatus using a liquid developer in which toner particles are dispersed in a carrier liquid. 
     Conventionally, the image forming apparatus of the electrophotographic type has been widely used as a copying machine, a printer, a plotter, a facsimile machine, a multi-function machine having a plurality of functions of these machines, or the like. As the image forming apparatus of the electrophotographic type, an image forming apparatus in which a toner image is formed on an image bearing member with the liquid developer containing the toner particles and the carrier liquid and then is transferred onto a recording material such as recording paper has been known. 
     In the image forming apparatus using such a liquid developer, it has been known that a proportion (ratio) of the toner contained in the liquid developer largely influences an image quality. In the following, the proportion of the toner contained in the liquid developer is referred to as T/D (ratio) and is represented by a mass fraction (%). In general, viscosity of the liquid developer increases with T/D, and a toner migration speed in the liquid developer under application of a bias is strongly influenced by a viscosity resistance. For this reason, by the influence of the viscosity resistance, the toner migration speed in a liquid developer with a high T/D is slower than the toner migration speed in a liquid developer with a low T/D. For this reason, in the liquid developer with the high T/D in which the viscosity is high, there is a possibility of causing a problem of a lowering in image density or the like due to an insufficient movement amount of the toner particles. On the other hand, in the liquid developer with the low T/D in which the viscosity is low, due to a positional deviation of the toner generated by a flow of the liquid developer in which the toner particles are moved, there is a possibility of generation of an image defect such as a flow of the toner image. 
     In the image forming apparatus using such a liquid developer, the image defect generates in some cases due to a value of a penetration speed of the carrier liquid into the recording material. For example, as regards the recording material high in carrier liquid penetration speed, carrier liquid penetration generates to a high degree at a transfer portion onto the recording material, so that a so-called transfer void such that the toner is not completely transferred onto the recording material is liable to generate due to a lowering in toner movement amount with the increased T/D. On the other hand, as regards the recording material low in carrier liquid penetration speed, an excessive carrier liquid remains on the recording material while being in a state in which T/D is a low value, so that the image defect such as a flow, a blur, spreading, thickening of a thin line, or the like of the toner image occurs. That is, an optimum T/D for transfer varies depending on the kind of the recording material, and therefore, there is a need to optimize a liquid amount of the carrier liquid at the transfer portion onto the recording material. 
     In the image forming apparatus using such a liquid developer, as disclosed in Japanese Laid-Open Patent Application (JP-A) 2003-91161, a technique such that not only a means for adjusting T/D is provided but also a removal amount of the excessive carrier liquid is adjusted so as not to disturb the toner image formed on the image bearing member has been known. In this image forming apparatus, a layer (film) thickness of the liquid developer deposited on the surface of a photosensitive drum is appropriately regulated by adjusting a contact pressure of a sweep roller contactable to the photosensitive drum, so that the removal amount of the carrier liquid can be adjusted. 
     However, in the image forming apparatus disclosed in JP-A 2003-91161, the excessive carrier liquid can only be removed for adjusting the liquid amount of the carrier liquid of the liquid developer at the transfer portion onto the recording material. That is, the carrier liquid does not increase, and therefore, for example, even when shortage of the carrier liquid generates at the transfer portion for the recording material high in carrier liquid penetration speed, the image forming apparatus cannot deal with the carrier liquid shortage. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image bearing member movable in a predetermined movement direction and configured to bear a toner image formed at an image forming position by using a liquid developer containing toner particles and a carrier liquid; a transfer member configured to transfer the toner image onto a recording material at a transfer portion formed between itself and the image bearing member; an input portion into which information on a kind of the recording material onto which the toner image is transferred is inputted; an adjusting device configured to adjust an amount of the carrier liquid of the toner image on the image bearing member, wherein the adjusting device is provided at an adjusting position opposing a position of the image bearing member upstream of the transfer portion and downstream of the image forming position with respect to the movement direction and includes a carrier liquid container configured to store the carrier liquid, a rotatable adjusting roller configured to carry the carrier liquid stored in the carrier liquid container, and a contacting-and-spacing mechanism movable between a contact position where the adjusting roller is contacted to the image bearing member and a spaced position where the adjusting roller is spaced from the image bearing member; and an executing portion configured to execute an operation of the adjusting device depending on the information inputted in the input portion when the toner image on the image bearing member is in the adjusting position, wherein the executing portion executes either of a plurality of operations including a first operation in which the amount of the carrier liquid of the toner image on the image bearing member is increased by the adjusting device, a second operation in which the amount of the carrier liquid is decreased by the adjusting device, and a third operation in which the amount of the carrier liquid is not adjusted by the adjusting 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 sectional view of an image forming apparatus according to an embodiment of the present invention. 
         FIG. 2  is a schematic sectional view of a principal part of the image forming apparatus in the embodiment. 
         FIG. 3  is a schematic black diagram showing a connection relationship of a controller of the image forming apparatus in the embodiment. 
       In  FIG. 4 , ( a ) to ( c ) are schematic sectional views each showing an operation mode of an adjusting device of the image forming apparatus in the embodiment, in which (a) shows a normal mode, (b) shows a carrier impartation mode, and (c) shows a carrier removal mode. 
         FIG. 5  is a flowchart showing a procedure such that in the image forming apparatus in the embodiment, an operation mode for adjusting a liquid amount of a carrier liquid is set depending on a sheet kind and then an image is formed. 
         FIG. 6  is a graph showing, for each sheet kind, a relationship between T/D before secondary transfer and a secondary transfer efficiency in the image forming apparatus in the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, an embodiment of the present invention will be described with reference to  FIGS. 1-6 . An image forming apparatus  1  in this embodiment is a digital printer of an electrophotographic type in which a toner image formed with a liquid developer containing toner particles and a carrier liquid C is formed (transferred) on a recording material. 
     The liquid developer used in this embodiment is a liquid developer in which the toner particles are dispersed in the carrier liquid. The toner particles are negatively chargeable resin particles of 0.1-2.0 nm in average diameter, in which a colorant and a binder are a main component and a charge-assisting agent or the like is added. The carrier liquid C is a non-volatile liquid having a high resistance and low dielectric constant, and is 1.0×10 Ω·cm or more in volume resistivity, 10 or less in relative dielectric constant, and 1-100 cP in viscosity. As the carrier liquid C, a carrier liquid prepared by adding a charge control agent or the like into an insulative carrier such as silicone oil, mineral oil, Isopar M (registered trademark, manufactured by Exxon Mobil Corp.) is usable. Further, also a photo-curable liquid monomer is usable when the liquid monomer satisfies the above-described physical properties. In this embodiment, the above-described toner particles and carrier liquid are mixed and adjusted to provide a T/D (mass fraction of the toner contained in the liquid developer) of 1-15%, and a resultant mixture is used as the liquid developer. Incidentally, also a liquid developer having viscosity exceeding 100 cP is usable in principle, but a load of liquid feeding increases, and therefore, in this embodiment, a liquid developer having relatively low viscosity is used, and the viscosity of the liquid developer is increased together with T/D in a concentration step described later. 
     As shown in  FIG. 1 , the image forming apparatus  1  includes a sheet feeding portion  30 , an image forming portion  40 , an adjusting device (adjusting means)  20 , a controller  50  and an operating portion  11 . Incidentally, on a sheet S which is a recording material, a toner image is to be formed, and specific examples of the sheet S include plain paper, coated paper coated with a coating agent at a surface thereof, thick paper, a sheet for an overhead projector (OHT (overhead transparency) sheet), and the like. 
     The image forming apparatus  1  operates on the basis of an image signal, and transfers the toner image formed on the image forming portion  40  onto the sheet S as the recording material successively fed (conveyed) from a sheet cassette  31 , and thereafter the toner image is fixed on the sheet S and thus an image is obtained. The image signal is sent to the image forming apparatus  1  from an unshown external terminal such as a scanner or a personal computer. 
     The sheet feeding portion  30  includes the sheet cassette  31  for stacking and accommodating sheets such as recording paper and includes a feeding roller  32 , and feeds the accommodated sheet S to the image forming portion  40 . 
     The image forming portion  40  includes a photosensitive drum (photosensitive member)  41 , a charger  42 , a laser exposure device  43 , a developing device  60 , an intermediary transfer unit  44 , a secondary transfer portion  45 , a fixing device  46  and a cleaning device  48 . The image forming portion  40  is capable of forming the image on the sheet S on the basis of image information. Incidentally, the image forming apparatus  1  in this embodiment is capable of forming a full-color image and includes the photosensitive drums  41   y  for yellow (y),  41   m  for magenta (m),  41   c  for cyan (c) and  41   k  for black (k), which have the same constitution and which are provided separately. This is true for the chargers  42   y ,  42   m ,  42   c  and  42   k , the laser exposure devices  43   y ,  43   m ,  43   c  and  43   k , the developing devices  60   y ,  60   m ,  60   c  and  60   k , primary transfer rollers  47   y ,  47   m ,  47   c  and  47   k , and the cleaning devices  48   y ,  48   m ,  48   c  and  48   k . For this reason, in  FIG. 1 , respective constituent elements for four colors are shown by adding associated color identifiers to associated reference numerals, but in  FIG. 2  and in the specification, the constituent elements are described using only the reference numerals without adding the color identifier in some cases. 
     As shown in  FIG. 2 , the photosensitive drum  41  is a drum-shaped electrophotographic photosensitive member, and is rotated in an arrow R 1  direction in  FIG. 1  by an unshown drum motor, so that the photosensitive drum  41  is circulated and moved while carrying an electrostatic latent image formed on the basis of image information during image formation. The photosensitive drum  41  is movable while carrying the toner image formed with the liquid developer at a developing portion  41   d  through development of the electrostatic latent image. 
     The charger  42  is disposed substantially parallel to a center axis of the photosensitive drum  41  and electrically charges uniformly a surface of the photosensitive drum  41  to a dark-portion potential Vd of the same polarity as a charge polarity of the toner. In this embodiment, as the toner, a negatively chargeable toner is used, and therefore, the dark-portion potential Vd has a negative value. Further, as the charger  42 , a corona charger is used. However, the charger  42  is not limited to the corona charger, but a charging roller or the like may also be used as the charger  42 . 
     The laser exposure device  43  exposes the surface of the photosensitive drum  41  charged to the dark-portion potential to laser light emitted in a side downstream of the charger  42  with respect to the R 1  direction and thus causes potential drop at an exposure portion, so that the electrostatic latent image is formed on the surface of the photosensitive drum  41 . The potential at the exposure portion when the voltage drop is caused at the exposure portion is a light-portion potential V 1 . 
     The developing device  60  is disposed downstream of the laser exposure device  43  with respect to the R 1  direction, and is provided in contact with the photosensitive drum  41 . The developing device  60  includes a developing container  61 , a developing roller (developer carrying member)  62 , a developing electrode  63 , a squeeze roller ((liquid) amount-reducing means)  64 , and a cleaning roller  65 . The developing container  61  accommodates the developing roller  62 , the developing electrode  63 , the squeeze roller  64 , and the cleaning roller  65 , and the liquid developer is supplied from an unshown mixer. 
     The developing roller  62  includes a metal shaft and an elastic layer of an electroconductive rubber formed around the metal shaft, and contacts the photosensitive drum  41  at a contact portion with predetermined pressure, so that a developing portion  41   d  is formed. The developing roller  62  is supplied with a predetermined developing bias by an unshown voltage source and is rotationally driven in an arrow R 2  direction by an unshown driving means so that a surface speed thereof is substantially equal to a surface speed of the photosensitive drum  41 . The developing roller  62  is capable of supplying the liquid developer to the photosensitive drum  41 , and develops the electrostatic latent image, on the surface of the photosensitive drum  41 , with the toner at the developing portion  41   d . To a gap between the developing roller  62  and the developing electrode  63 , the liquid developer in which T/D is adjusted in advance by an unshown mixer is supplied by an unshown supplying means, so that the liquid developer in the neighborhood of the surface of the developing roller  62  is fed by rotation of the developing roller  62  while being carried on the surface of the developing roller  62 . 
     The developing electrode  63  is disposed opposed to the developing roller  62  and is provided so that a bias of the same polarity as the charge polarity of the toner is applicable to the developing roller  62 . By the rotation of the developing roller  62  in the R 2  direction, the liquid developer carried on the developing roller  62  passes through between the developing electrode  63  and the developing roller  62 . At this time, by the application of the bias to the developing electrode  63 , the toner in the liquid developer between the developing electrode  63  and the developing roller  62  electrophoretically moves toward the surface of the developing roller  62  and is fed to a contact region, between the developing roller  62  and the squeeze roller  64 , downstream of the developing electrode  63  with respect to the R 2  direction. Incidentally, by adjusting a magnitude of the bias applied from the developing electrode  63  to the developing roller  62 , T/D at the developing portion can be adjusted, and in addition, T/D at a secondary transfer portion  45  can be adjusted. 
     The squeeze roller  64  is pressed against the developing roller  62  by an unshown pressing means under application of a bias of the same polarity as the toner charge polarity to the developing roller  62 , and is rotated by rotation of the developing roller  62 . As a result, the layer thickness of the liquid developer on the surface of the developing roller  62  is regulated so as to be substantially uniform and T/D of the liquid developer increases up to 25-40%, so that the liquid developer is concentrated (concentration step). In this embodiment, the layer thickness of the liquid developer passing through between the developing roller  62  and the squeeze roller  64  is determined on the basis of Young&#39;s modulus, liquid developer viscosity and a process concentration. For this reason, by adjusting pressure at which the squeeze roller  64  is pressed against the developing roller  62 , the layer thickness of the liquid developer reaching the developing portion  41   d  can be adjusted. Incidentally, a toner amount per unit area can be adjusted depending on a magnitude of a bias from the developing electrode  63 . 
     The liquid developer which cannot pass through between the developing roller  62  and the squeeze roller  64  and which is pushed back passes through an upper portion of the developing electrode  63  and is returned to the mixer by an unshown discharging means. That is, the squeeze roller  64  is capable of decreasing the liquid amount of the carrier liquid C deposited on the developing roller  62 . 
     The liquid developer concentrated through the concentration step is supplied to the electrostatic latent image on the photosensitive drum  41  by the rotation of the developing roller  62 , so that the electrostatic latent image is developed into the toner image (developing step). At this time, T/D of the toner image on the photosensitive drum  41  at an image portion increases compared with T/D of the liquid developer immediately after the concentration step, and is 30-45%. This is because in the developing step, in order to develop the electrostatic latent image at the image portion by the developing roller  62 , most of the toner and a part of the carrier liquid C move to the photosensitive drum  41 , but the carrier liquid C in a certain amount remains on the developing roller  62 . A similar phenomenon can generate also in a primary transfer step, a secondary transfer step and T/D control which are described later. 
     The cleaning roller  65  is disposed downstream of the developing portion  41   d  with respect to the R 2  direction, and is provided by being pressed against the developing roller  62  by an unshown pressing means. The cleaning roller  65  removes the liquid developer remaining on the surface of the developing roller  62  after the development by applying the bias of the opposite polarity to the toner charge polarity to the developing roller  62 . The removed liquid developer is returned to the mixer by the discharging means. 
     As shown in  FIG. 1 , the intermediary transfer unit  44  includes a plurality of rollers including a driving roller  44   a , a tension roller  44   t  and the primary transfer rollers  47   y ,  47   m ,  47   c  and  47   k  and includes the intermediary transfer belt (image bearing member)  55   b  wound around these rollers. The primary transfer rollers  47   y ,  47   m ,  47   c  and  47   k  are disposed opposed to the photosensitive drums  41   y ,  41   m ,  41   c  and  41   k , respectively. The respective primary transfer rollers  47  are urged toward the respective photosensitive drums  41  so as to sandwich the intermediary transfer belt  44   b  therebetween by an unshown pressing (urging) means, so that primary transfer portions  49   y ,  49   m ,  49   c  and  49   k  are formed. 
     The cleaning device  48  is disposed downstream of the primary transfer portion of the photosensitive drum  41  with respect to the R 1  direction, and removes the liquid developer remaining on the surface of the photosensitive drum  41  after the primary transfer. The removed liquid developer is fed to an unshown separating means by an unshown feeding means and is separated into the carrier liquid C and a high-density (concentration) liquid developer, and thereafter the carrier liquid C is fed to a recycling carrier tank (container) and the high-density liquid developer is fed to a residual (waste) liquid tank (container). 
     The intermediary transfer belt  44   b  is constituted by adding therein a resistance-adjusting agent such as carbon black and is 1.0×10 9 -1.0×10 13  Ω·cm in volume resistivity. On the intermediary transfer belt  44   b , a certain tension or more is exerted also when the intermediary transfer belt  44   b  is not driven, and the intermediary transfer belt  44   b  is not spaced from the photosensitive drums  41   y ,  41   m ,  41   c  and  41   k  but always contacts these photosensitive drums. By applying a positive transfer bias to the intermediary transfer belt  44   b  through the primary transfer rollers  47   y ,  47   m ,  47   c  and  47   k , negative toner images on the photosensitive drums  41   y ,  41   m ,  41   c  and  41   k  are multiple-transferred successively onto the intermediary transfer belt  44   b . As a result, the intermediary transfer belt  44   b  on which a full-color toner image obtained by developing the electrostatic latent images on the surfaces of the photosensitive drums  41   y ,  41   m ,  41   c  and  41   k  is transferred moves. By applying the bias of the opposite polarity to the toner charge polarity to the primary transfer rollers  41 , the toner images are transferred from the photosensitive drums  41  onto the intermediary transfer belt  44   b  (primary transfer step). At this time, T/D of the toner image on the intermediary transfer belt  44   b  at the image portion increases compared with T/D of the liquid developer immediately after the developing step and is 35-50%. That is, under application of the transfer bias, the toner images formed on the photosensitive drums  41  are transferred onto the intermediary transfer belt  44   b  at the primary transfer portions  49 , and the intermediary transfer belt  44   b  is movable while carrying the toner images. 
     The toner images transferred superposedly onto the intermediary transfer belt  44   b  at the primary transfer portions  49   y ,  49   m ,  49   c  and  49   k  pass through the adjusting device and are fed to the secondary transfer portion  45 . That is, the adjusting device  20  is disposed in a liquid developer feeding path from the primary transfer portions  49  to the secondary transfer portion  45 . Details of the adjusting device  20  will be described later. 
     The secondary transfer portion  45  includes an inner secondary transfer roller  45   a  and an outer secondary transfer roller (secondary transfer means)  45   b  which contacts contact the intermediary transfer belt  44   b  while opposing each other. Between the outer secondary transfer roller  45   b  and the intermediary transfer belt  44   b , the sheet S fed from a registration roller pair  12  is nipped and fed. By applying a positive secondary transfer bias to the outer secondary transfer roller  45   b , the full-color image formed on the intermediary transfer belt  44   b  is transferred onto the sheet S. At this time, T/D of the toner image on the sheet S as the image portion increases compared with T/D of the liquid developer immediately after the primary transfer step, and is 40-55%. That is, the outer secondary transfer roller  45   b  forms the secondary transfer portion  45  where the toner images are transferred from the intermediary transfer belt  44   b  onto the sheet S under application of the transfer bias. 
     In a side downstream of the secondary transfer portion  45  on the intermediary transfer belt  44   b  with respect to an R 3  direction, an unshown intermediary transfer belt cleaning device is provided and removes the developer remaining on the surface of the intermediary transfer belt  44   b  after the secondary transfer. The removed liquid developer is fed to a separating means by an unshown feeding means. 
     The fixing device  46  includes a fixing roller  46   a  and a pressing roller  46   b . The sheet S is nipped and fed between the fixing roller  46   a  and the pressing roller  46   b , whereby the toner image transferred on the sheet S is heated and pressed and is fixed on the sheet S. 
     The operating portion  11  is an operating panel including operating buttons and a display portion and is connected to the controller  50 . Through the operating portion  11 , by an operation by a user, for example, in addition to the sheet kind, a copying sheet number, enlargement, reduction, both-side/one-side printing, color/monochromatic printing, a cassette for feeding the sheet, a sheet size and the like are settable for the controller  50 . 
     As shown in  FIG. 3 , the controller  50  is constituted by a computer and includes, for example, a CPU  51 , a ROM  52  for storing a program for controlling the respective portions, a RAM  53  for temporarily storing data, and an input/output circuit (I/F)  54  through which signals are inputted from and outputted into an external device. The controller  50  is connected with the operating portion  11 , the adjusting device  20 , the sheet feeding portion  30  and the image forming portion  40  via the input/output circuit  54  and not only transfers signals with the respective portions but also controls operations of the respective portions. Details of an operation of the controller  50  will be described later. 
     Next, the image forming operation of the image forming apparatus  1  constituted as described above will be described. 
     When an image forming job signal is inputted into the controller  50 , the image forming operation is started, and the photosensitive drum  41  is rotated and the surface thereof is electrically charged by the charger  42 . Then, on the basis of the image information, the laser light is emitted from the laser exposure device  43  to the photosensitive drum  41 , so that the electrostatic latent image is formed on the surface of the photosensitive drum  41 . The toner is deposited on this electrostatic latent image, whereby the electrostatic latent image is developed and visualized as the toner image and then the toner image is primary-transferred onto the intermediary transfer belt  44   b.    
     On the other hand, the feeding roller  32  rotates in parallel to such a toner image forming operation and feeds an uppermost sheet S on the sheet cassette  31  to the registration roller pair  12  while separating the sheet S and the sheet S is once stopped at the registration roller pair  12 . Then, the sheet S is conveyed to the secondary transfer portion  45  by being timed to the toner image on the intermediary transfer belt  44   b . The sheet S supplied to the secondary transfer portion  45  is nipped and conveyed by the intermediary transfer belt  44   b  and the outer secondary transfer roller  45   b . The sheet S on which the toner image is transferred at the secondary transfer portion  45  is conveyed to the fixing device  46 , in which the unfixed toner image is heated and pressed and thus is fixed on the surface of the sheet S, and then the sheet S is discharged. 
     Next, a constitution of the adjusting device  20  of the image forming apparatus  1  in this embodiment will be described specifically with reference to  FIG. 4 . 
     The adjusting device  20  is provided at a position opposing a position of the intermediary transfer belt  44   b  between the primary transfer portion  49  and the secondary transfer portion  45  ( FIG. 1 ). The adjusting device  20  includes a carrier liquid container (tank)  21 , a supplying roller (second roller)  22 , a supplying roller regulating blade  23 , an adjusting roller (first roller)  24 , an adjusting roller regulating blade  25 , a high-voltage source  26  and an opposite roller  27 . 
     The carrier liquid container  21  is a storing container (tank) which opens upwardly, and is positioned under the supplying roller  22  and the adjusting roller  24 . Inside the carrier liquid container  21 , the carrier liquid C is stored. The carrier liquid container  21  is connected to the recycling carrier tank and is supplied with the carrier liquid C as desired from the recycling carrier tank. Above a liquid surface of the stored carrier liquid C, a liquid surface sensor  21   s  is provided. The liquid surface sensor  21   s  is connected to the controller  50 , and on the basis of a detection result of the liquid surface sensor  21   s , the controller  50  controls supply of the carrier liquid C from the recycling carrier tank so that a detected liquid surface height of the carrier liquid C falls within a predetermined range. In this embodiment, as the liquid surface sensor  21   s , an ultrasonic sensor is used, and the liquid surface height is detected by a reflection time of ultrasonic wave with which the liquid surface of the carrier liquid C is irradiated. However, the liquid surface sensor  21   s  is not limited to the ultrasonic sensor. 
     The supplying roller  22  is positioned above the carrier liquid container  21  and under the adjusting roller  24 , and is rotationally driven in an arrow direction shown in (b) of  FIG. 4  by an unshown driving means. That is, the supplying roller  22  is interposed between the adjusting roller  24  and the carrier liquid C stored in the carrier liquid container  21 . Further, the carrier  22  is capable of being raised and lowered in a vertical (up-down) direction by an unshown raising and lowering means, and a contact and spaced state thereof relative to the adjusting roller  24  can be switched depending on an operating mode. That is, the supplying roller  22  is relatively placeable between a contact state in which the supplying roller  22  simultaneously contacts the carrier liquid C and the adjusting roller  24  and a spaced state in which the supplying roller  22  is spaced from at least one of the carrier liquid C and the adjusting roller  24 . In this embodiment, the supplying roller  22  is rotatably supported at the same position relative to the carrier liquid container  21  so as to always contact the carrier liquid C stored in the carrier liquid container  21 . 
     The supplying roller  22  includes a core metal and an elastic layer formed at a periphery of the core metal. In this embodiment, a material of the elastic layer is an urethane rubber and has a volume resistivity of 1.0×10 11  Ω·cm or more, a JIS-A hardness of 30-50 degrees and a surface roughness Rz of 2 μm or less. Incidentally, in the case where there is no liability of generation of swelling by the carrier liquid C, a fluctuation in physical values described above, a fluctuation in physical values of the carrier liquid C and another deterioration, it is also possible to use materials other than the above-described material. 
     The supplying roller regulating blade  23  is supported at a fixed position relative to the supplying roller  22  so as to contact the surface of the supplying roller  22  with predetermined contact pressure. As a result, a thickness of the carrier liquid C on the supplying roller  22  is regulated uniformly to a predetermined value, so that an excessive carrier liquid C drops into the carrier liquid container  21 . Incidentally, the contact pressure of the supplying roller regulating blade  23  is set so that the thickness of the carrier liquid C on the supplying roller  22  after being regulated by the supplying roller regulating blade  23  is 6-20 μm. Further, as shown in (a) and (b) of  FIG. 4 , in a state in which the supplying roller  22  also contacts the adjusting roller  24 , in a nip formed by the supplying roller  22  and the adjusting roller  24 , about ½ of an amount of the carrier C on the supplying roller  22  is transferred from the supplying roller  22  onto the adjusting roller  24 . As a result, a thickness of the carrier liquid C on the adjusting roller  24  is 3-10 μm. 
     In this embodiment, the thickness of the carrier liquid C supplied to the adjusting roller  24  is controlled using the supplying roller  22  and the supplying roller regulating blade  23 , but the control means is not limited thereto. For example, if the thickness of the carrier liquid C is uniformly controllable, means such as a roller pair or anilox roller may also be used. 
     The adjusting roller  24  is positioned on the supplying roller  22  and is rotationally driven in an arrow direction shown in (b) of  FIG. 4  by an unshown driving means, and a bias of the same polarity as the toner charge polarity is applicable to the adjusting roller  24  by the high-voltage source  26  connected to the adjusting roller  24 . In this embodiment, as the adjusting roller  24 , a roller formed of SUS alloy and having the surface roughness Rz of 0.2-2.0 μm is used. The adjusting roller  24  is capable of being raised and lowered in the vertical direction by an unshown raising and lowering means, and depending on an operating mode, a contact and spaced state thereof relative to the supplying roller  22  or the intermediary transfer belt  44   b  is switched. As a result, an impartation and removal operation of the carrier liquid C relative to the toner image on the intermediary transfer belt  44   b  is switched. That is, the adjusting roller  24  not only contacts the liquid developer feeding path but also is capable of carrying the carrier liquid C stored in the carrier liquid container  21 . Incidentally, the adjusting roller regulating blade  25  is provided in contact with the adjusting roller  24  and removes the carrier liquid C remaining on the surface of the adjusting roller  24 . 
     Next, respective operation modes in operations of the adjusting device  20  of the image forming apparatus  1  in this embodiment will be described specifically with reference to  FIG. 4 . As shown in (a), (b) and (c) of  FIG. 4 , the operation mode of the adjusting device  20  is switchable among three operation modes including a normal mode ((a) of  FIG. 4 ), a carrier impartation mode ((b) of  FIG. 4 ) and a carrier removal mode ((c) of  FIG. 4 ). 
     As shown in (a) of  FIG. 4 , in the operation in the normal mode, the adjusting roller  24  is spaced from the intermediary transfer belt  44   b , so that not only supply of the carrier liquid C to the intermediary transfer belt  44   b  but also removal of the carrier liquid C from the intermediary transfer belt  44   b  are not carried out. 
     For this reason, T/D of the toner image on the intermediary transfer belt  44   b  at the image portion is substantially unchanged from T/D immediately after the primary transfer step, and is 35-50%. 
     As shown in (b) of  FIG. 4 , in the operation in the carrier impartation mode, the adjusting roller  24  simultaneously contacts the intermediary transfer belt  44   b  and the supplying roller  22 , and the supplying roller  22  simultaneously contacts the adjusting roller  24  and the carrier liquid C. The carrier liquid C is drawn up from the carrier liquid container  21  by the supplying roller  22 , is supplied to the adjusting roller  24 , and then is supplied from the adjusting roller  24  to the intermediary transfer belt  44   b . At this time, by the bias, of the same polarity as the toner charge polarity, applied to the adjusting roller  24 , the toner on the intermediary transfer belt  44   b  is not moved to the adjusting roller  24  but is still carried on the intermediary transfer belt  44   b , so that only the carrier liquid C is increased in amount. That is, the adjusting device  20  is capable of at least increasing the liquid amount of the carrier liquid C of the liquid developer fed in the liquid developer feeding path from the developing portion  41   d  to the secondary transfer portion  45 . As a result, T/D of the toner image on the intermediary transfer belt  44   b  at the image portion decreases compared with T/D immediately after the primary transfer step, and is 30-45%. The carrier liquid C remaining on the adjusting roller  24  after being supplied to the intermediary transfer belt  44   b  is removed by the adjusting roller regulating blade  25  and drops into the carrier liquid container  21 . 
     As shown in (c) of  FIG. 4 , in the operation in the carrier removal mode, the adjusting roller  24  contacts the intermediary transfer belt  44   b  and is spaced from the supplying roller  22 . At a nip formed by the adjusting roller  24  and the intermediary transfer belt  44   b , a part of the carrier liquid C on the intermediary transfer belt  44   b  is transferred (moved) from the intermediary transfer belt  44   b  onto the adjusting roller  24 . At this time, by the bias, of the same polarity as the toner charge polarity, applied to the adjusting roller  24 , the toner on the intermediary transfer belt  44   b  is not moved to the adjusting roller  24  but is still carried on the intermediary transfer belt  44   b , so that only the carrier liquid C is decreased in amount. That is, the adjusting device  20  is capable of decreasing the liquid amount of the carrier liquid C of the fed liquid developer. As a result, T/D of the toner image on the intermediary transfer belt  44   b  at the image portion increases compared with T/D immediately after the primary transfer step, and is 40-55%. The carrier liquid C remaining on the adjusting roller  24  after being removed from the intermediary transfer belt  44   b  is removed by the adjusting roller regulating blade  25  and drops into the carrier liquid container  21 . 
     Here, control of T/D at the image portion of the toner image on the intermediary transfer belt  44   b  before secondary transfer for each of sheets different in kind will be described on the basis of  FIG. 6 . Incidentally, in this case, T/D before secondary transfer is T/D when the toner image is fed to the secondary transfer portion  45 , and means T/D at a portion from the primary transfer portions to the secondary transfer portion and does not contain T/D at a portion upstream of the primary transfer portions. In  FIG. 6 , a relationship between T/D (T/D before secondary transfer) at the portion from the primary transfer portions to the secondary transfer portion and second transfer efficiency. Here, the second transfer efficiency means a proportion of the toner, of the toner on the intermediary transfer belt  44   b  after the primary transfer step and before the secondary transfer step, moved on the sheet by the secondary transfer. Further, in  FIG. 6 , not only plain paper as an example of high-penetration media having a penetration speed higher than that of coated paper but also an OHT surface as an example of non-penetrative media having a penetration speed lower than that of the coated paper are shown together with the coated paper, but the sheet kind is not limited thereto. 
     As shown in  FIG. 6 , in the case where comparison is made at the same T/D, the second transfer efficiency of the plain paper is lower than the second transfer efficiency of the coated paper. Further, at a relatively low T/D (about 45% or less), the second transfer efficiency of the OHT sheet is lower than the second transfer efficiency of the coated paper and the second transfer efficiency of the plain paper, but when T/D is increased (about 50% or more), this relationship is reversed. Further, in the case of the coated paper and the OHT sheet, although the second transfer efficiency does not lower at a low T/D, an image defect such as a flow of the toner can generate in some cases (broken line portions). The flow of the toner is more noticeable in the case of the OHT sheet than in the case of the coated paper, and there is a tendency that the flow of the toner generates also at a higher T/D. 
     In the image forming apparatus  1  in this embodiment, the T/D before secondary transfer in the case where the liquid amount adjustment control is not carried out is 35-50%. As shown in  FIG. 6 , in a range of T/D=35-50%, as regards the coated paper, the second transfer efficiency of 90% or more can be obtained. On the other hand, as regards the plain paper, in the range of T/D=35-50%, the second transfer efficiency lowers when compared with the coated paper and is below 90% in the neighborhood of T/D=50%. Further, as regards the OHT sheet, in the range of T/D=35-50%, although the second transfer efficiency of 90% or more is obtained, the image defect such as the flow of the toner generates in the neighborhood of T/D=35%. 
     The above-described tendency can be explained on the basis of a magnitude of the carrier penetration speed into the sheet. That is, the penetration speed of the carrier liquid C into the plain paper is higher than that into the coated paper, and therefore, at the secondary transfer portion  45 , an increase degree of T/D of the image portion of the toner image is large, so that a transfer void due to a lowering in toner mobility is liable to generate. On the other hand, as regards the OHT sheet, the penetration of the carrier liquid C into the sheet generates little, and therefore, due to a flow of an excessive carrier liquid C, a positional deviation of toner particles on the sheet is liable to generate, so that the image defect such as the flow of the toner is liable to generate. 
     In this embodiment, in order to optimize the secondary transfer step depending on the carrier penetration speed for each of the above-described sheets, adjustment of T/D is carried out depending on the sheet by the adjusting device  20 . That is, as regards the sheet such as the plain paper having the carrier penetration speed higher than that of the coated paper, in order to avoid the lowering in second transfer efficiency at the high T/D, the T/D before secondary transfer may preferably be decreased compared with the case of the coated paper. Further, as regards the sheet such as the OHT sheet into which the carrier liquid little penetrates, in order to avoid the toner image flow at the low T/D, the T/D before secondary transfer may preferably be increased compared with the case of the coated paper. Specifically, the controller  50  sets the operation mode of the adjusting device  20  at the normal mode for the coated paper, the carrier impartation mode for the plain paper and the carrier removal mode for the OHT sheet. Incidentally, in this embodiment, the three operation modes are employed, but the number of the operation modes is not limited to three. For example, in the case where a plurality of adjusting devices are used or in the like case, the operation mode may also be classified more specifically. 
     The controller  50  adjusts the liquid amount of the carrier liquid C at the secondary transfer portion on the basis of the kind of the sheet S, onto which the toner image is to be transferred, by using the adjusting device  20  and the squeeze roller  64 . In the case where the liquid amount of the carrier liquid is increased in the liquid developer fed in the feeding path, the controller  50  causes the adjusting roller  24  to carry, on the surface of the adjusting roller  24 , the carrier liquid C stored in the carrier liquid container  21 , and is capable of executing the operation in the carrier impartation mode in which the carrier liquid C is supplied to the liquid developer fed in the feeding path. In the operation in the carrier impartation mode, the controller  50  places the supplying roller  22  in a contact state, so that the carrier liquid C stored in the carrier liquid container  21  is supplied to the surface of the adjusting roller  24  via the supplying roller  22  and is carried on the surface of the adjusting roller  24 . 
     Further, in the case where the liquid amount of the carrier liquid is decreased in the liquid developer fed in the feeding path, the controller  50  does not cause the adjusting roller  24  to carry, on the surface of the adjusting roller  24 , the carrier liquid C stored in the carrier liquid container  21 . In this case, the controller  50  is capable of executing the operation in the carrier removal mode in which the carrier liquid C is removed by the adjusting roller  24  from the liquid developer fed in the feeding path. In the operation in the carrier removal mode, the controller  50  places the supplying roller  22  in a spaced state, so that the carrier liquid C stored in the carrier liquid container  21  is not carried on the surface of the adjusting roller  24 . Incidentally, information on the operation modes corresponding to the respective sheet kinds and setting of states of the adjusting device  20  in the operations in the respective operation modes are stored in storing devices such as the ROM  52  and the RAM  53 . 
     Next, a procedure in which the operation mode for adjusting the liquid amount of the carrier liquid C at the secondary transfer portion  45  is set depending the sheet kind and then image formation is effected by the image forming apparatus  1  in this embodiment will be described along a flow chart shown in  FIG. 5 . 
     The user inputs the kind of the sheet, subjected to the image formation, through the operating portion  11  or the like in advance, and the inputted sheet kind is stored in the RAM  53 . In this embodiment, the sheet kind is set by the user through the operating portion  11 , but the present invention is not limited thereto. For example, the kind of the sheet staked in the sheet cassette  31  may also be detected using a sheet sensor for detecting surface roughness or the like of the sheet. 
     When the CPU  51  receives a print job start signal (step S 1 ), the CPU  51  makes reference to the RAM  53  and reads the sheet kind (step S 2 ). The CPU  51  sets the operation mode of the adjusting device  20  depending on the read sheet kind (step S 3 ). In this embodiment, the CPU  51  sets the operation mode so that the operation mode is the normal mode when the sheet kind is the coated paper, the carrier impartation mode when the sheet kind is the plain paper, and the carrier removal mode when the sheet kind is the OHT sheet. 
     The CPU  51  sets a state of respective portions of the adjusting device  20  correspondingly to the operation mode (step S 4 ). In this step, when the CPU  51  sets the normal mode, as shown in (a) of  FIG. 4 , the CPU  51  causes the adjusting roller  24  to be spaced from the intermediary transfer belt  44   b . Further, when the CPU  51  set the carrier impartation mode, as shown in (b) of  FIG. 4 , the CPU  51  places the supplying roller  22 , the adjusting roller  24  and the intermediary transfer belt  44   b  in a contact state. Further, when the CPU  51  sets the carrier removal mode, as shown in (c) of  FIG. 4 , the CPU  51  causes the supplying roller  22  to be spaced from the adjusting roller  24  while keeping contact between the adjusting roller  24  and the intermediary transfer belt  44   b . Then, the CPU  51  starts an image forming operation after completion of the setting of the state of the respective portions of the adjusting device  20  (step S 5 ). 
     As described above, according to the image forming apparatus  1  in this embodiment, the controller  50  adjusts the liquid amount of the carrier liquid C at the secondary transfer portion  45  on the basis of the kind of the sheet S, onto which the toner image is to be transferred, by using the adjusting device  20  capable of increasing and decreasing the liquid amount of the carrier liquid C. For this reason, the adjusting device  20  can increase and decrease the liquid amount of the carrier liquid C, and therefore, as desired, the liquid amount of the carrier liquid C at the secondary transfer portion  45  can be increased and decreased. As a result, at the secondary transfer portion  45  to the sheet S, the liquid amount of the carrier liquid C can be adjusted to an appropriate amount, so that it becomes possible to compatibly realize suppression of the transfer void and the toner flow. 
     Further, according to the image forming apparatus  1  in this embodiment, the adjusting device  20  is disposed in the liquid developer feeding path from the primary transfer portions  49  to the secondary transfer portion  45 . For this reason, the adjusting device  20  can replenish the carrier liquid C, decreased in amount at the developing portion  41   d  and the primary transfer portions  49 , by increasing the carrier liquid C as desired. Further, the liquid amount of the carrier liquid C can be adjusted immediately in front of the secondary transfer portion  45 , and therefore, for example, compared with the case where the adjusting device  20  is provided in the feeding path in a side upstream of the primary transfer portions  49 , the liquid amount of the carrier liquid C can be adjusted with high accuracy. 
     Further, according to the image forming apparatus  1  in this embodiment, the developing device  60  includes the developing electrode  63  and the squeeze roller  64 , and therefore, can decrease the liquid amount of the carrier liquid C, i.e., can concentrate the toner in the liquid developer, in a side upstream of the developing portion  41   d . For this reason, the developing electrode  63  and the squeeze roller  64  can be effectively used in the case where T/D before secondary transfer is enhanced. 
     Further, according to the image forming apparatus  1  in this embodiment, the adjusting device  20  includes the supplying roller  22  and the adjusting roller  24 , and the carrier liquid C carried on the supplying roller  22  is regulated by the supplying roller regulating blade  23  and the regulated carrier liquid C is carried on the adjusting roller  24 . As a result, a layer having the layer (film) thickness of the carrier liquid C carried on the adjusting roller  24  can be formed as a very thin film of about 3-10 μm in thickness with high accuracy, for example. For this reason, compared with the case where the carrier liquid C is directly supplied to the adjusting roller  24  without using the supplying roller  22  and the layer thickness of the carrier liquid C is regulated by the supplying roller regulating blade, it is possible to easily realize the film formation with high accuracy. 
     Incidentally, in the image forming apparatus  1  in this embodiment, the case where the supplying roller regulating blade  23  is supported by the supplying roller  22  at a fixed relative position so as to contact the surface of the supplying roller  22  with predetermined contact pressure was described, but the present invention is not limited thereto. For example, the contact pressure of the supplying roller regulating blade  23  to the supplying roller  22  may also be made variable. In this case, the thickness of the carrier liquid C on the supplying roller  22  can be adjusted, so that the amount of the carrier liquid C supplied from the adjusting roller  24  to the intermediary transfer belt  44   b  is varied. For this reason, compared with the case where the contact pressure of the supplying roller regulating blade  23  is fixed, the amount of the carrier liquid C supplied to the toner image on the intermediary transfer belt  44   b  can be controlled. As a result, T/D before secondary transfer can be controlled for more sheet kinds. 
     In the image forming apparatus  1  in this embodiment, the case where only one adjusting device  20  is provided was described, but the present invention is not limited thereto. For example, two or more adjusting devices  20  may also be provided. In this case, compared with the case where only one adjusting device  20  is provided, the carrier liquid C in a larger amount can be removed from the toner image on the intermediary transfer belt  44   b , so that the toner flow in the case of using a low-viscosity liquid developer can be effectively suppressed, for example. 
     In the image forming apparatus  1  in this embodiment, the case where the adjusting device  20  is disposed in the liquid developer feeding path from the primary transfer portions  49  to the secondary transfer portion  45  was described, but the present invention is not limited thereto. For example, the adjusting device  20  may also be disposed in the liquid developer feeding path from the developing portion  41   d  to the primary transfer portion  49 . 
     In the image forming apparatus  1  in this embodiment, the case where the adjusting device  20  includes the supplying roller  22  and the adjusting roller  24  was described, but the present invention is not limited thereto. For example, without using the supplying roller  22 , the carrier liquid C may also be directly supplied to the adjusting roller  24  and then may be regulated by the supplying roller regulating blade. Also in this case, at the secondary transfer portion  45  to the sheet S, the amount of the carrier liquid C can be adjusted to an appropriate amount in the case where excess and deficiency of the carrier liquid C generates, so that suppression of the transfer void and the toner flow can be realized compatibly. 
     In the image forming apparatus  1  in this embodiment, the case where the type in which the intermediary transfer belt  44   b  which is an intermediary transfer member is employed was described, but the present invention is not limited thereto. For example, a type in which the toner image is directly transferred from the photosensitive drum onto the sheet material may also be employed. In this case, the image forming apparatus includes the photosensitive drum (image bearing member), a transfer means, the adjusting device (adjusting means) and the controller. Further, the photosensitive drum is movable while carrying the toner image formed by developing the electrostatic latent image with the liquid developer at the developing portion. The transfer means forms a transfer portion where the toner image is transferred from the photosensitive drum onto the sheet under application of the transfer bias. The adjusting device is capable of at least increasing the liquid amount of the carrier liquid C of the liquid developer fed in the liquid developer feeding path in a region from the developing portion to the transfer portion. The controller adjusts the liquid amount of the carrier liquid C at the transfer portion on the basis of the kind of the sheet, onto which the toner image is transferred, by using the adjusting device. Also in this case, at the transfer portion where the toner image is transferred onto the sheet, the amount of the carrier liquid C can be adjusted to an appropriate amount in the case where excess and deficiency of the carrier liquid C generates, so that it becomes possible to compatibly realize the transfer void and the toner flow. 
     Embodiment 
     Using the image forming apparatus  1  in the above-described embodiment, images were formed on the plain paper, the coated paper and the OHT sheet. As the operation mode of the adjusting device  20 , the carrier impartation mode was applied to the plain paper (T/D before secondary transfer: 30-45%), the normal mode was applied to the coated paper (T/D before secondary transfer: 35-50%), and the carrier removal mode was applied to the OHT sheet (T/D before secondary transfer: 40-50%). After the image formation, with respect to the formed images, degrees of the transfer void and the toner flow were checked. A result is shown in Table 1. As shown in Table 1, in this embodiment, with regards to the sheets of the three kinds, the second transfer efficiency was 90% or more, and no toner flow generated. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 EMB. 
                 CE1* 1   
                 CE* 2   
                 CE 3   
               
               
                   
                 AMS* 4   
                 NM* 5   
                 CIM* 6   
                 CRM* 7   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 TV* 8   
                 TF* 9   
                 TV* 8   
                 TF* 9   
                 TV* 8   
                 TF* 9   
                 TV* 8   
                 TF* 9   
               
               
                   
               
               
                 PP* 10   
                 ◯ 
                 ◯ 
                 X 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 ◯ 
               
               
                 CP* 11   
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
                 ◯ 
               
               
                 OHT* 12   
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 ◯ 
                 X 
                 ◯ 
                 ◯ 
               
               
                   
               
               
                 * 1 “CE1” is Comparison Example 1. 
               
               
                 * 2 “CE2” is Comparison Example 2. 
               
               
                 * 3 “CE3” is Comparison Example 3. 
               
               
                 * 4 “AMS” is all mode switching. 
               
               
                 * 5 “NM” is the normal mode only. 
               
               
                 * 6 “CIM” is the carrier impartation mode only. 
               
               
                 * 7 “CRM” is the carrier removal mode only. 
               
               
                 * 8 “TV” is the transfer void. 
               
               
                 * 9 “TF” is the toner flow. 
               
               
                 * 10 “PP” is the plain paper. 
               
               
                 * 11 “CP” is the coated paper. 
               
               
                 * 12 “OHT” is the OHT sheet. 
               
            
           
         
       
     
     In Table 1, “o” in evaluation of the transfer void represents the second transfer efficiency of 90% or more, and “x” in evaluation of the transfer void represents the second transfer efficiency of less than 90%. Further, “o” in evaluation of the toner flow represents that there was no image disturbance which can be recognized by visual observation, and “x” in evaluation of the toner flow represents that image disturbance which can be recognized by eye observation generated. 
     Comparison Example 1 
     In the image forming apparatus  1 , the image formation was carried out in the operation only in the normal mode as the operation mode of the adjusting device  20  irrespective of the sheet kinds. A result is shown in Table 1. As shown in Table 1, the second transfer efficiency on the plain paper was less than 90%, and the toner flow generated on the OHT sheet. 
     Comparison Example 2 
     In the image forming apparatus  1 , the image formation was carried out in the operation only in the carrier impartation mode as the operation mode of the adjusting device  20  irrespective of the sheet kinds. A result is shown in Table 1. As shown in Table 1, the toner flow generated on the coated paper and the OHT sheet. 
     Comparison Example 3 
     In the image forming apparatus  1 , the image formation was carried out in the operation only in the carrier removal mode as the operation mode of the adjusting device  20  irrespective of the sheet kinds. A result is shown in Table 1. As shown in Table 1, the second transfer efficiency on the plain paper and the second transfer efficiency on the coated paper were less than 90%. 
     Accordingly, according to the image forming apparatus  1  in Embodiment, by appropriately switching the operation mode of the adjusting device  20  depending on the sheet kind, it was confirmed that suppression of the transfer void and the toner flow can be realized for the respective sheets. 
     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. 
     This application is a divisional of U.S. patent application Ser. No. 15/622,565, filed Jun. 14, 2017, which claims the benefit of Japanese Patent Application No. 2016-121097 filed on Jun. 17, 2016, both of which are hereby incorporated by reference herein in their entirety.