Abstract:
A liquid-developer drying device includes a covering wall which has a facing surface covering and facing to part of an image-carrying body with a drying air passage between them. The image-carrying body carries developed image in a first direction along the drying air passage. The developed image includes liquid developer having toner particles and carrier liquid,. The covering wall has a plurality of slits formed therein. The slits are distributed in a region with substantially less than half length along the facing surface covering the image-carrying body so as to blow dry air to the drying air passage in a second direction parallel to the first direction. Each of the slits extends across the drying air passage. The liquid-developer drying device also includes an air source supplying drying air to the slits.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a device for drying excess liquid developer and an apparatus for forming an image utilizing the drying device.  
           [0002]    The liquid-process type image-forming apparatus, which produces a developed image by using liquid developer, has some important advantages. Firstly, it is able to realize high quality images owing to fine toner particles of sub-microns in diameter. Secondly, it is economical and is able to realize a quality comparable to that of printing (including offset printing), because sufficient image density can be obtained with a small amount of toner. Thirdly, it is able to accomplish energy saving because the toner can be fixed to a paper at a relatively low temperature, etc.  
           [0003]    As part of an image forming process with the above-mentioned liquid-process, pressure transfer method can be used to transfer the toner image formed on a photosensitive member to a medium (such as paper) to be transferred to. In this method, adherence of the toner particles is utilized and the photosensitive member is brought into contact under pressure with the medium to be transferred to. With regard to the pressure transfer method, it has been confirmed that transferring can be effectively carried out if the liquid carrier on the surface of the developed image is sufficiently removed. On the other hand, transferring efficiency deteriorates if the surface of the photosensitive member is dampened with the liquid carrier when transferring process is carried out. Therefore, to improve transferring efficiency, excess liquid carrier on the image should be removed sufficiently before transferring process is carried out.  
           [0004]    Recently, cutting down the time for removing the excess liquid carrier is required to reduce the time for the image forming process. To remove the excess liquid carrier on the developed image rapidly, a nozzle block  7  has been proposed as shown in FIG. 10. The nozzle block  7  has plural steps of nozzles  7   b  blowing drying air into a covering wall  7   a  along the surface of the photosensitive member  6 , and faces to the photosensitive member  6  between the developing device  8  and the pressure-transferring device  9 . In the gap between the covering wall  7   a  and the photosensitive member  6 , the nozzle block  7  forms a drying passage  7   c  for the drying air to flow through. High speed drying air is blown from the plural steps of the nozzles  7   b . The excess liquid carrier on the developed image is, therefore, rapidly removed by blowing the high speed drying air into the drying passage  7   c.    
           [0005]    However, further cut-down of the time for removing the excess carrier is required for further speedup of the image forming apparatus and improvement of the image quality today. Therefore, in spite of using the above-mentioned nozzle block, transfer efficiency by the pressure transfer method could be deteriorated because the excess liquid carrier might not be sufficiently removed before the developed image had reached the pressure transferring device.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    An object of the present invention is to solve the problem mentioned above and is intended to provide a drying device for a liquid developer and an image forming apparatus to obtain high quality images at a high speed. According to the present invention, the excess liquid carrier remaining on the developed image may be removed rapidly and securely before it is transferred, and transferring efficiency by the pressure transfer method may be improved in spite of speedup of the image forming process. Thereby, high quality transferred images can be obtained by avoiding occurrence of transfer defects.  
           [0007]    According to an aspect of the present invention, there has been provided a liquid-developer drying device. The device includes a covering wall which has a facing surface covering and facing to part of an image-carrying body with a drying air passage between them. The image-carrying body carries developed image in a first direction along the drying air passage. The developed image includes liquid developer having toner particles and carrier liquid. The covering wall has a plurality of slits formed therein. The slits are distributed in a region with substantially less than half length along the facing surface covering the image-carrying body so as to blow dry air to the drying air passage in a second direction parallel to the first direction. Each of the slits extends across the drying air passage. The liquid-developer drying device also includes an air source which supplies drying air to the slits.  
           [0008]    According to another aspect of the present invention, there has been provided an image forming apparatus. The apparatus includes an image-carrying body which carries latent electrostatic image in a first direction. The apparatus also includes a developing device which supplies liquid developer having toner particles and carrier liquid to the latent electrostatic image to form a developed image on the image-carrying body. The apparatus also includes a transferring device which transfers the developed image on the image-carrying body to a medium disposed outside of the image-carrying body. The apparatus also includes a covering wall which has a facing surface covering and facing to part of the image-carrying body with a drying air passage between them. The covering wall is disposed between the developing device and the transferring device. The covering wall has a plurality of slits formed therein. The slits are distributed in a region with substantially less than half length along the facing surface covering the image-carrying body so as to blow dry air to the drying air passage in a second direction parallel to the first direction. Each of the slits extends across the drying air passage. The apparatus also includes an air source which supplies drying air to the slits.  
           [0009]    According to the construction mentioned above, high-speed air is blown along the conveying passage of the developed image in order to dry and remove securely the excess liquid carrier before it is transferred. In spite of speedup of the image forming process, the transferring efficiency by the pressure transfer method is improved, and furthermore high quality images can be obtained at a high speed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The above and other features and advantages of the present invention will become apparent from the discussion hereinbelow of specific, illustrative embodiments thereof presented in conjunction with the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 is a schematic diagram explaining the principle of the present invention by using a two-step nozzle block;  
         [0012]    [0012]FIG. 2 is a schematic diagram explaining the principle of the present invention by using a four-step nozzle block;  
         [0013]    [0013]FIG. 3 is a schematic cross-sectional diagram showing an image-forming portion of a full-color electro-photographic apparatus of a first embodiment according to the present invention;  
         [0014]    [0014]FIG. 4 is an enlarged schematic cross-sectional diagram showing the nozzles in the nozzle block and their vicinity shown in FIG. 3;  
         [0015]    [0015]FIG. 5 is a schematic cross-sectional diagram showing the measuring points for the drying air in the drying passage shown in FIG. 4;  
         [0016]    [0016]FIG. 6 is a schematic cross-sectional diagram showing the measuring points for the drying air of a reference case;  
         [0017]    [0017]FIG. 7 is a table showing the speed of the drying air and the drying efficiency by the nozzle block of the first embodiment according to the present invention and a nozzle block of the reference case;  
         [0018]    [0018]FIG. 8 is a schematic cross-sectional diagram showing the drying device of a second embodiment according to the present invention;  
         [0019]    [0019]FIG. 9 is a schematic cross-sectional diagram showing the nozzle block of a modification of the second embodiment according to the present invention; and  
         [0020]    [0020]FIG. 10 is a schematic cross-sectional diagram showing a conventional nozzle block. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    First of all, the principle of the present invention will be described. Actual air speed and pressure were measure using a prior-art image forming apparatus. As shown in FIG. 1, a nozzle block  13  having first and second nozzles  12   a ,  12   b  located on a covering wall  11  along the surface of photosensitive member  10  was used. Measured speed of drying air generated in the drying passage  14  between the photosensitive member  10  and the nozzle block  13  is shown as a line (α).  
         [0022]    Namely, the air speed in region (A) between the first nozzle  12   a  and the second nozzle  12   b  in the drying passage  14  decreased as compared with the air speeds in the other regions (B) and (C). The reason was that both the drying airs blown from the first nozzle  12   a  and the second nozzle  12   b  impinged each other and generated a high pressure at the position facing the first nozzle  12   a  and the second nozzle  12   b  in the drying passage  14  as represented by the line (β) of FIG. 1. Therefore, the air speed in the region (A) between the nozzle  12   a  and the nozzle  12   b  decreased relatively.  
         [0023]    On the contrary, outlet ends of drying air were free in the regions (B) and (C), and the pressure was lower. Therefore, the air speed was very high, and thereby, drying efficiency became very high at the regions (B) and (C) where the drying air flew at a high speed.  
         [0024]    As shown in FIG. 2, a nozzle block  18  having first to fourth nozzles  17   a ,  17   b ,  17   c  and  17   d  located on a covering wall  16  along the surface of photosensitive member  10  was used next. Measured speed of drying air generated in the drying passage  20  between the photosensitive member  10  and the nozzle block  18  is shown by a line (γ).  
         [0025]    Namely, the air speed in the region (D) between the first and the fourth nozzles  17   a  and  17   d  decreased as compared with the air speeds in the both side regions thereof (E) and (F), when steps of nozzles located on the covering wall  16  were increased to heighten density of the air blowing into the drying passage  20 . The reason was that air pressure increases much more at the position facing to the first to the fourth nozzles  17   a ,  17   b ,  17   c  and  17   d  in the drying passage  20  due to the drying air blown from the nozzles  17   a  to  17   d  as denoted by the line (δ) of FIG. 2. Therefore, the air speed in the region (D) between the nozzles  17   a  and  17   b  further decreased relatively.  
         [0026]    On the contrary, increase of the air speed in response to the increase of nozzle steps was observed in the regions (E) and (F) where outlet ends of drying air were free. Therefore, drying efficiency became higher at the regions (E) and (F) where drying air flew at a very high speed.  
         [0027]    As mentioned above, speed of the drying air, which passes between neighboring nozzles of the nozzle block having plural steps of nozzles, is generally suppressed relatively low by intervention of pressure, caused by the air blown from the neighboring nozzles. Thus, in the conventional nozzle block, which has plural steps of nozzles located uniformly on the whole region of the covering wall, speed of the drying air is suppressed low over quite a wide region in the drying passage. Consequently, drying-efficiency is suppressed low in spite of the increased flow rate of the air from the nozzles.  
         [0028]    The present invention has been accomplished according to the principle mentioned above. Now a first embodiment according to the present invention is explained in detail referring to FIGS.  3  to  5 . FIG. 3 shows an image forming portion  30  of a liquid-process type full-color electro-photographic apparatus i.e. the image forming apparatus of the present invention. The image forming portion  30  has a photosensitive drum  31  including a photosensitive layer of organic system or amorphous silicon system formed on an image-supporting member of an electric conductive substrate such as an aluminum substrate. On the periphery of the photosensitive drum  31 , first to fourth image-forming units  32 Y,  32 M,  32 C and  32 BK are arranged along the rotation of the photosensitive drum  31  in the direction of an arrow h shown in FIG. 3. The image-forming units  32 Y,  32 M,  32 C and  32 BK form images on the photosensitive drum  31  sequentially with liquid developers of yellow (Y), magenta (M), cyan (C), and black (BK), respectively.  
         [0029]    Although colors of the liquid developers to be used for the image-forming units  32 Y to  32 BK are different from each other, the units have basically the same construction except for the colors. Explanation will be, therefore, carried out referring to the image-forming unit  32 Y of yellow (Y) positioned upstream. With regard to the other image-forming units  32 M,  32 C and  32 BK, explanation will be omitted by giving the same mark and a suffix denoting each color to the same part as that of the unit  32 Y.  
         [0030]    The image-forming unit  32 Y of yellow (Y) has a charger  34 Y which may include a well-known corona charger or scorotron charger. The image forming unit  32 Y also has an exposing portion  37 Y, which selectively irradiates a laser beam Y corresponding to the light signal of yellow (Y) emitted from a laser irradiation device (not shown).  
         [0031]    The image-forming units  32 Y to  32 BK also have developing rollers  40 Y to  40 BK accommodating liquid developers  38 Y to  38 BK for respective colors and feeding the liquid developers  38 Y to  38 BK to the photosensitive roller  31  to form a developed image. The image-forming units  32 Y to  32 BK also have developing devices  42 Y to  42 BK which include squeezing rollers  41 Y to  41 BK located apart from the photosensitive drum  31  with a slight clearance of 20 to 50 micrometers and removing simultaneously fogs and liquid carriers from the developed image after development.  
         [0032]    The liquid developers  38 Y to  38 BK may have toner particles of 0.1 to 0.2 micrometer in diameter having different colors from each other, and liquid carriers to disperse the toner particles. As the liquid carriers, non-polar solvent of petroleum system such as ISOBAR L (Product of Exxon Inc.) may be utilized, for example.  
         [0033]    A porous elastic roller  46  or a liquid-removing member to remove excess liquid carriers remaining in the photosensitive drum  31  after development is provided at the downstream side of the image-forming units  32 Y to  32 BK on the periphery of the photosensitive drum  31 . Furthermore, a drying device  47  is provided in the region between the porous elastic roller  46  and a transferring device  48  transferring the developed image under pressure. The drying device  47  dries and removes the excess liquid carriers remaining on the photosensitive drum  31  by the aid of drying air.  
         [0034]    The porous elastic roller  46  has a fine porous elastic surface having electric conductivity for preventing the toner particles from sticking, and accelerates sucking rate of the liquid carrier by the aid of the capillary phenomenon. Preferably, a rubber system material with elasticity such as polyurethane sponge may be used for the porous elastic material, for example. The liquid-removing member is not limited to the porous elastic roller but may be used with the photosensitive member being in contact with a roller formed of oleophilic material such as silicon rubber.  
         [0035]    The transferring device  48  has a pressing roller  48   a  and an intermediate transfer roller  48   b  pressed against the photosensitive drum  31  by the pressing roller  48   a  with a pressure force of approximately 0.5to 50 kgf/cm 2  (or 0.049 to 4.9 MPa). The transferring device  48  transfers primarily the toner image of toner particles formed on the photosensitive drum  31  to the intermediate transfer roller  48   b  by utilizing adherence of the toner particles, and then transfers the image secondarily to a paper P or a member to be finally transferred to. Additionally, a cleaner  50  removing the toner particles remaining on the photosensitive drum  31  and an erasing lamp  51  erasing charges remaining on the photosensitive drum  31  are disposed at the downstream side of the transferring device  48  along the periphery of the photosensitive drum  31 .  
         [0036]    The drying device  47  for drying and removing excess liquid carrier remaining on the photosensitive drum  31  is now described in detail. The drying device  47  has a nozzle block  52  and a blower  53  that is an air source sending air to the nozzle block  52 . The nozzle block  52  has a covering wall  52   a , which covers the surface of the photosensitive drum  31  between the porous elastic roller  46  and the intermediate transfer roller  48   b . A drying passage  52   b  of approximately 2 mm in width is formed between the covering wall  52   a  and the photosensitive drum  31 .  
         [0037]    Drying air flows in the direction of arrow h, which is the same direction as the rotation direction of the photosensitive drum  31 , and flows near the surface of the photosensitive drum  31  in the drying passage  52   b . The surface of the covering wall  52   a  is formed in a smooth shape without roughness so that the drying air may pass the drying passage  52   a  without generating turbulence. The covering wall  52   a  may be made of aluminum or stainless steel buffed with a file of fineness JIS (Japanese Industrial Standard) No. 600 or so, and formed in a cylindrical concave surface to fit substantially coaxially with the surface of the photosensitive drum  31 .  
         [0038]    On the covering wall  52   a , nozzles  52   c  or openings to blow the drying air onto the surface of the photosensitive drum  31  are formed in four steps. The nozzles  52   c  have the shape of slits extending in the axial direction of the photosensitive drum  31  or perpendicular to the circumferential direction of the photosensitive drum  31 . The nozzles  52   c  are supplied with airflow from the blower  53  through a pipe  53   a . The four step nozzles  52   c  are distributed only in the upstream side (or the side closer to the porous elastic roller  46 ) in the drying passage  52   b , preferably within approximately a quarter of the total length L of the covering wall  52   a.    
         [0039]    Operation of the first embodiment is now described. The photosensitive drum  31  rotates in the direction of arrow h after image-forming process starts. The photosensitive drum  31  is charged by the charger  34 Y at the image-forming unit  32 Y, and then is selectively irradiated by a laser beam  36 Y emitted from a laser device (not shown) corresponding to the image information of yellow. Thus, an electrostatic latent image corresponding to yellow (Y) image is formed.  
         [0040]    Toner particles of the liquid developer  38 Y of yellow (Y) are fed into the clearance between the photosensitive drum  31  and the developing roller  40 Y located in non-contact manner with the photosensitive drum  31 . Then the toner particles are adsorbed by electrophoresis, and the toner image of yellow (Y) is formed on the photosensitive drum  31 .  
         [0041]    Thereafter, the squeeze roller  41 Y removes extended toner particles. The squeeze roller  41 Y may scrape liquid carrier in the liquid developer, which remains on the photosensitive drum  31  when the developing process is carried out, to reduce the quantity of excess carrier liquid in advance.  
         [0042]    Similarly, toner images of magenta (M), cyan (C), and black (BK) are sequentially superimposed by succeeding image-forming units  32 M to  32 BK, and a full-color developed image is formed on the photosensitive drum  31 .  
         [0043]    After development has finished, excess liquid carrier of the full-color developed image on the photosensitive drum  31  is absorbed by the surface of the porous elastic roller  46  by the aid of capillary phenomenon of the porous elastic roller  46 . The porous elastic roller  46  rotates such that the peripheral velocity of the porous elastic roller  46  in the direction of arrow i is the same as that of the photosensitive drum  31 . Thus, disturbance of the developed image on the photosensitive drum  31  is suppressed.  
         [0044]    A bias voltage with the polarity reverses to that of the toner particles is then applied to the porous elastic roller  46 . Thereby, the toner particles are prevented from being exfoliated from the surface of the photosensitive drum  31 , and deterioration of the image is suppressed. In addition, the surface of the porous elastic roller  46  is prevented from being clogged by absorption of the toner particles when excess liquid carrier is absorbed and removed.  
         [0045]    After excess liquid carrier is absorbed and removed by the porous elastic roller  46 , the developed image on the photosensitive drum  31  passes the drying passage  52   b  for the drying air, which is formed by the covering wall  52   a  of the nozzle block  52 . The nozzle block  52  blows airflow fed by the blower  53  onto the surface of the photosensitive drum  31  through the four step nozzles  52   c  as the drying air.  
         [0046]    Thereafter, the drying air passes the region where the nozzles  52   c  are not formed in the drying passage  52   b , where the drying air is not adversely affected by the air pressure from the nozzles  52   c . Thus, the drying airflow remains at high speed. Moreover, the drying airflow is not affected by the turbulence caused by unevenness of the surface of the covering wall  52   a , so that it is kept at high speed.  
         [0047]    Consequently, because the developed image on the photosensitive drum  31  is continuously blown by the high speed drying air while it is conveyed in the drying passage  52   b  after the region where the nozzles  53   c  are formed, remaining excess liquid carrier can be sufficiently dried and removed rapidly.  
         [0048]    When the developed image from which excess liquid carrier has been removed as mentioned above reaches the transferring device  48 , the developed image on the photosensitive drum  31  is transferred primarily to the intermediate transfer roller  48   b . The intermediate transfer roller  48   b  is pressed against the photosensitive drum  31  by the load of the pressing roller  48   a . Then, the transferred image is further transferred secondarily to the paper P conveyed from the intermediate transfer roller  48   b  in the direction of arrow j. Thus, a full-color image is formed on the paper P. Excess liquid carrier is sufficiently dried and removed from the developed image on the photosensitive drum  31  before the pressure transferring is carried out by the transferring device  48 , as described above. Therefore, adhesive force of the toner particles does not deteriorate and the developed image is transferred to the intermediate transfer roller  48   b  and then to the paper P with a high transferring efficiency. After the transferring is finished, the cleaner  50  removes the remaining toner particles on the photosensitive drum  31 , and the erasing lamp  51  erases the remaining charge. Thus, a series of image-forming process finishes and the photosensitive drum  31  gets ready for the next image-forming process.  
         [0049]    The nozzle block  52  of this embodiment was installed in an experimental electro-photographic apparatus for performance tests. Then, speed of the drying airflow at the first measuring point (S 1 ) and at the second measuring point (S 2 ) in the drying passage  52   c  formed by the photosensitive drum  31  and the nozzle block  52  was measured. Drying efficiency of the developed image was also measured after it has passed the drying passage  52   c . FIG. 7 shows the results obtained from the measurement.  
         [0050]    In comparison to the above, a conventional nozzle block  60  having four step nozzles  60   c  arranged with an equal interval was installed in the experimental electro-photographic apparatus mentioned above, as shown in FIG. 6. Then, speed of the drying air at the third measuring point (S 3 ) and at the fourth measuring point (S 4 ) in the drying passage  60   b  formed by the photosensitive drum  31  and the nozzle block  60  was measured. Drying efficiency of the developed image after it has passed the drying passage  60   b  was also measured. FIG. 7 also shows the results obtained from the measurement of this reference case. Blowing speeds of the drying air from the nozzles  52   c  and the nozzles  60   c  were set to be the same in the tests.  
         [0051]    In the case of the nozzle block  52  of this embodiment, the nozzles  52   c  are formed only-in the region of a length of about L/4 on the upstream side of the whole length (L) of the nozzle block  52 . The drying air speeds up at the first measuring point (S 1 ) shortly after it has passed the region where the nozzles  52   c  are formed. Thereafter, the drying air can maintain its high speed without being affected by air pressure caused by blowing from the nozzles in the remaining region of the length of 3 L/4 on the downstream side of the nozzle block  52 . On the other hand, in the case of the prior-art nozzle block  60  (reference case), the drying air cannot get a high speed at the third measuring point (S 3 ), because it is adversely affected by air pressure caused by blowing from the downstream nozzle  60   c . The drying air can finally get a high speed at the fourth measuring point (S 4 ) in the vicinity of the outlet of the drying passage  60   b  at the downstream end of the nozzle block  60 .  
         [0052]    Thus, the drying passage  52   b  in the nozzle block  52  of this embodiment provides higher speed of drying air in a larger area than the drying passage  60   b  in the nozzle block  60  of the reference case to the developed image. Therefore, the drying efficiency of the developed image for the nozzle block  52  of this embodiment can be improved compared to the reference case. Then, the image can be dried in a short time, and speedup of the apparatus and downsizing of the blower can be achieved.  
         [0053]    In the structure mentioned above, sufficient quantity of air to speed up the drying air can be obtained by locating the four step nozzles  52   c  at the upstream side of the whole length of the nozzle block  52 . The drying air merely passes through in the downstream side of the nozzle block  52 . The upstream region into which the drying air is blown and the downstream region where the drying air passes are divided from each other, so that the drying air in the drying passage  52   b  can keep its high speed for a long time. Consequently, because the drying efficiency is improved, the developed image can be sufficiently dried in spite of speedup of image-forming process. When pressure transferring is carried out, transferring defect due to insufficient removing of excess liquid carrier can be prevented or suppressed, so that a high quality transferred image can be obtained with a high transferring efficiency. Then, a high-speed image-forming apparatus can be realized.  
         [0054]    Now a second embodiment according to the present invention is explained referring to FIG. 8. The second embodiment has a collecting mechanism for the drying air at the downstream side of the nozzle block, added to the structure of the above-mentioned first embodiment. Because the other portions are the same as the first embodiment, the portions of the same structure as the structure explained in the first embodiment will be denoted by the same marks and detailed explanation thereof will be omitted.  
         [0055]    The drying device  70  of this embodiment is provided with a collecting mechanism  72  for collecting the drying air blown out to the drying passage  71   b  by a nozzle block  71 . Four step nozzles  71   c  are formed only on the region of the upstream side of about ¼ of the covering wall  71   a  of the nozzle block  71  facing the photosensitive drum  31  interposed by the drying passage  71   b.    
         [0056]    A suction port  72   a  or a collecting member is formed at the downstream side of the covering wall  71   a  to collect the drying air. The suction port  72   a  is communicated to a compressor  73  through a pipe  73   a  and sucks the drying air containing vaporized liquid carrier in the direction of arrow k shown in FIG. 8, while it passes the drying passage  71   b . The drying air sucked from the suction port  72   a  is sent to a filter (not shown) to collect liquid carrier. Then, the drying air is fed again to the nozzles  71   c  via a blower  53  via. Thus, the drying air circulates inside the drying device  70  without being exhausted.  
         [0057]    In accordance with the construction of the second embodiment described above, the developed image can be sufficiently dried in spite of speedup of image-forming process, as the first embodiment. Then, a high quality transferred image can be obtained with a high transferring efficiency, and a high-speed image-forming apparatus can be realized. Furthermore, evaporated liquid carrier can be prevented from diffusing to the environment, by circulating the drying air inside the drying device  70 , which result in environment conservation.  
         [0058]    The present invention is not limited to the embodiments described above, but any modification thereof can be available within the scope of the invention where the purpose of the invention does not change. For example, the image-supporting member may be a photosensitive belt where the photosensitive layer is formed on the surface of a rotatable annular elastic belt. The transferring device may transfer an image directly from the photosensitive drum to the paper without the intermediate transfer roller intervening between them. The pressure force is also not limited.  
         [0059]    Step number of the nozzles or openings to blow the drying air onto the image-supporting member is not restricted. Locations of the nozzles are not restricted, so long as they are distributed mainly on the upstream side of the covering wall. The openings are preferably located within the region of a half length of the covering wall on the upstream side in order to secure a long high-speed region of the drying air.  
         [0060]    Although the width of the drying passage is arbitrary so long as speedup of the drying air can be maintained, the width of the drying passage is preferably narrowed down to about 0.5 to 5 mm, to increase the speed of the drying air. The width of the slit-like openings is also preferably narrowed in order to blow the drying air with a higher speed. The cross section of the drying passage must be narrowed as compared to the area of the openings to raise the speed of the drying air in the drying passage. Therefore, the cross section of the drying passage is preferably set smaller in comparison with the total area of plural steps of the openings.  
         [0061]    Blowing direction of the drying air by the drying device is not restricted. For instance, as a modification of the second embodiment, the upstream side and the downstream side of the nozzle block  71  may be reversed as shown in FIG. 9. Namely, the region where the nozzles  71   c  are located may be positioned at the side of the transferring device  48 , and the suction port  72   a  sucking the drying air may be positioned at the side of the porous elastic roller  46 . Thus, the drying air blown from the nozzles  71   c  flows in the direction of arrow m which is in the reverse direction of the rotation direction h of the photosensitive drum  31 . Then, the drying air is sucked into the suction port  72   a  side. This structure may be preferable especially when the transferring device  48  is heated up to enhance transferring efficiency, because the drying air is prevented from blowing to the transferring device  48  and cooling of the transferring device  48  is avoided.  
         [0062]    Furthermore, the liquid carrier collected by the filter etc. may be recycled and reused in the second embodiment.