Abstract:
A wet type image forming apparatus includes a photoconductive drum, a toner supplying roller that supplies toner to the photoconductive drum, a developing solution applying roller uniformly applying the developing solution onto the toner supplying roller, a developing solution supplying roller supplying the developing solution to the developing solution applying roller, and two sidewall members respectively arranged on both sides of the pair of developing solution applying roller and the developing solution supplying roller. The two sidewall members closely contact side faces of the pair of developing solution applying roller and the developing solution supplying roller at both sides thereof, respectively. The circumferential surfaces of the developing solution applying roller and the developing solution supplying roller and the two sidewall members define a deposition space for depositing the developing solution, which is configured such that the developing solution is allowed to overflow only in the developing solution supplying roller side.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a wet type image forming apparatus that forms an image with a developing solution containing a toner in a carrier solution.  
         [0002]     Apparatuses that transfer a toner to a recording paper to thereby form an image include, for example, a dry type image forming apparatus, which applies a powder toner to a surface of a developing roller to form an image, and a wet type image forming apparatus, which applies a developing solution containing a toner in a carrier solution to a surface of a developing roller to form an image, as disclosed in Japanese Patent Provisional Publication No. P2002-214920A. The toner employed in the latter apparatus is finer than that employed in the former. Accordingly, the latter provides an image of a higher quality.  
         [0003]      FIGS. 1 and 2  show an example of the conventional wet type image forming apparatus around an anilox roller  302  which serves to uniformly apply a developing solution DS onto the surface of a developing roller.  FIG. 1  is a perspective view from an upper direction showing the structure, and  FIG. 2  is a cross-sectional view taken along an axial direction of the structure shown in  FIG. 1 .  
         [0004]     The developing solution DS is picked up by a pickup roller  306  from a developing solution tank, and is applied to an add roller  304 . Then, the ink is deposited in a space defined by the anilox roller  302  and the add roller  304  which is configured to rotate while contacting the anilox roller. The amount of the developing solution DS that has adhered to the surface of the anilox roller  302  is, after passing through the contacted interface, accurately adjusted by a blade which contacts the surface, thereby the ink being uniformly applied onto the surface of the developing roller.  
         [0005]     When the developing solution DS is more than fully deposited in the space, the developing solution DS overflows beyond the end portions of the anilox roller  302  and the add roller  304 , and drops on a region around the developing solution tank. Since the developing solution DS has a relatively higher viscosity and hence a lower fluidity, a majority of the developing solution DS remains where it has dropped (i.e. in the periphery of the developing solution tank) as shown in  FIG. 2 , and barely flows toward the central portion of the developing solution tank. Therefore, the axial distribution of the developing solution DS lifted by the pickup roller  306 , as well as the axial distribution of the developing solution DS applied to the anilox roller  302  become uneven because of the uneven distribution of the developing solution DS in the developing solution tank. Consequently, on the surface of the developing roller, the developing solution DS is thickly distributed in a peripheral portion and thinly distributed in a central portion. Such uneven application of the developing solution DS to the surface of the developing roller results in uneven development of a latent image on the photoconductive drum. A solution of such a problem has been proposed, for example, in a wet type image forming apparatus disclosed in Japanese Patent Provisional Publication No. P2000-250318A.  
         [0006]     However, the wet type image forming apparatus according to Publication No. P2000-22250318A requires a space in which the developing solution is substantially enclosed, and further a control device for controlling the amount of the developing solution to be supplied to the space, which results in upsizing of the apparatus and increase of the manufacturing cost.  
       SUMMARY OF THE INVENTION  
       [0007]     In view of the foregoing situation, the present invention is advantageous in that an improved wet type image forming apparatus is provided, which apparatus is capable of preventing uneven development without incurring upsizing of the apparatus and increase of the manufacturing cost.  
         [0008]     According to aspects of the invention, there is provided a wet type image forming apparatus that forms an image with a developing solution containing toner in a carrier solution. The image forming apparatus includes a photoconductive drum on which a latent image is formed, a toner supplying roller that supplies toner to a circumferential surface of the photoconductive drum, a pair of a developing solution applying roller and a developing solution supplying roller, the developing solution applying roller uniformly applying the developing solution onto a circumferential surface of the toner supplying roller, the developing solution supplying roller contacting the circumferential surface of the developing solution applying roller to supply the developing solution to a circumferential surface of the developing solution applying roller, and two sidewall members respectively arranged on both sides of the pair of developing solution applying roller and the developing solution supplying roller, the two sidewall members closely contacting side faces of the pair of developing solution applying roller and the developing solution supplying roller at both sides thereof, respectively. The circumferential surface of the developing solution applying roller, the circumferential surface of the developing solution supplying roller, and the two sidewall members define a deposition space for depositing the developing solution, the deposition space being configured such that the developing solution is allowed to overflow only in the developing solution supplying roller side.  
         [0009]     Optionally, the developing solution supplying roller and the developing solution applying roller may be arranged such that an uppermost portion of the developing solution supplying roller is lower than an uppermost portion of the developing solution applying roller.  
         [0010]     Further, the position of the upper ends of the sidewall members may be higher than the uppermost portion of the developing solution applying roller.  
         [0011]     The wet type image forming apparatus may further include a developing solution collecting tank configured to collect therein the developing solution that has not been consumed, and a developing solution pickup device that supplies the developing solution collected in the developing solution collecting tank into the space defined by the circumferential surface of the developing solution applying roller, the circumferential surface of the developing solution supplying roller, and the two sidewall members.  
         [0012]     The developing solution applying roller and the developing solution supplying roller may have a substantially same axial length, and are disposed such that the end faces on each axial side are flush with each other.  
         [0013]     Optionally, the wet type image forming apparatus may further include a casing accommodating at least the developing solution applying roller and the developing solution supplying roller, the housing having a pair of walls respectively facing the end faces of the pair of developing solution applying roller and the developing solution supplying roller, respectively. Further, the sidewall members may include elastic members arranged between the pair of walls and the end faces, respectively, the sidewall members being elastically deformed so as to closely contact the respective end faces of the pair of developing solution applying roller and the developing solution supplying roller.  
         [0014]     In this case, the elastic members may include rubber members. The rubber members may be made of urethane rubber or silicon rubber.  
         [0015]     Optionally, the sidewall members may include metal plates arranged to closely contact the respective end faces of the pair of developing solution applying roller and the developing solution supplying roller.  
         [0016]     Further, the wet type image forming apparatus may include a housing accommodating at least the pair of developing solution applying roller and the developing solution supplying roller, the housing having a pair of walls respectively facing the end faces of the pair of developing solution applying roller and the developing solution supplying roller, respectively, and biasing members provided between the metal plates and the end faces of the pair of developing solution applying roller and the developing solution supplying roller to urge the metal plates toward the end faces the pair of developing solution applying roller and the developing solution supplying roller. 
     
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0017]      FIG. 1  is a perspective view showing a structure around an anilox roller in a conventional wet type image forming apparatus;  
         [0018]      FIG. 2  is a cross-sectional view showing a structure around the anilox roller in the conventional wet type image forming apparatus;  
         [0019]      FIG. 3  is a cross-sectional side view showing a structure of a wet type printer according to an embodiment of the present invention;  
         [0020]      FIG. 4  is a cross-sectional side view showing a structure around a measuring roller in the wet type printer according to the embodiment of the present invention;  
         [0021]      FIG. 5  is a perspective view showing a structure around the measuring roller in the wet type printer according to the embodiment of the present invention;  
         [0022]      FIG. 6  is a cross-sectional view showing a structure around the measuring roller in the wet type printer according to the embodiment of the present invention; and  
         [0023]      FIG. 7  is a fragmentary perspective view showing a structure around a sealing device of a space S in a wet type printer according to another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0024]     Referring to the accompanying drawings, a wet type printer according to an embodiment of the present invention will be described in detail.  
       First Embodiment  
       [0025]      FIG. 3  is a cross-sectional side view showing a structure of a wet type printer  100  according to an embodiment of the present invention. The wet type printer  100  is an apparatus that forms an image with a developing roller that carries, on its surface, a developing solution DS containing a toner in a carrier solution, and more specifically an apparatus that receives print information (i.e., character and/or image information) from an external apparatus such as a computer, and prints out the letter or image on a recording paper P in accordance with a so-called electrophotographic imaging process.  
         [0026]     The wet type printer  100  generally includes a control unit  20  that controls a printing process, sheet feeding operation and so on, a driving unit  30  that drives various mechanisms, a laser scanning unit (hereinafter, abbreviated as “LSU”)  40  that outputs a laser beam modulated according to print information, a developing unit  50  that develops a latent image formed according to print information with a developing solution DS, a transfer unit  70  that transfers a toner image developed by the developing unit  50  at a transfer position onto the recording paper P, a feeding mechanism that feeds the recording paper P, and a fixing unit  80  that permanently fixes the toner image which has been transferred on the recording paper P.  
         [0027]     The driving unit  30  serving as a driving source of the mechanisms in the wet type printer  100  includes a plurality of actuators that drive the respective mechanisms. All of these actuators are connected to the control unit  20 , to be driven under the control of the control unit  20 . The driving unit  30  can cause a rotation of, for example, a developing roller  55  and photoconductive drum  61  included in the developing unit  50 , and a heat roller  81  included in the fixing unit  80 .  
         [0028]     On a side face of a housing of the wet type printer  100 , a paper inlet  12  is formed, through which the recording paper P is introduced into the printer  100 , and a paper tray  11  for storing the recording paper P is attached at the paper inlet  12 . On the opposite side face of the housing, a paper outlet  15  and a receiver tray  16  are provided. The recording paper P, upon being introduced into the wet type printer  100  through the paper inlet  12 , is fed along a paper path  13  to reach the transfer position defined by the transfer unit  70 , where the toner image is transferred onto the surface of the recording paper P. Thereafter the recording paper P is fed along a paper path  14  to reach a fixing position defined by the fixing unit  80  for fixation of the toner image. Then, the recording paper P is discharged from the wet type printer  100  through the paper outlet  15 .  
         [0029]     The toner image corresponding to the print information to be transferred to the recording paper P at the transfer unit  70  is initially generated by the control unit  20  and the LSU  40 . The LSU  40  includes a laser diode  41  serving as a light source, a collimating lens  42 , a cylindrical lens  43 , a polygon mirror  44 , an imaging lens  45  and a deflecting mirror  46 . Instead of the LSU  40 , an LED (Light Emitting Diode) and a reducing optical system may be employed as the exposure method.  
         [0030]     The laser diode  41  is driven under the control of the control unit  20 . That is, the laser diode  41  is turned on and off (i.e. modulated) according to the print information, thereby emitting a laser beam modulated carrying the image information. The laser beam irradiated by the laser diode  41  enters the collimating lens  42 , which converts the laser beam from a diffused luminous flux into a parallel luminous flux.  
         [0031]     The laser beam converted into a parallel luminous flux (i.e., collimated) is converged by the cylindrical lens  43  solely in a sub-scanning direction so that the laser beam is converged on a plane, in the sub-scanning direction, close to a reflecting surface of the polygon mirror  44 . It is to be noted that the sub-scanning direction herein referred to designates a direction parallel to a plane of  FIG. 1  (a direction orthogonal to the rotating shaft of the photoconductive drum  61 , i.e. a tangent on a circumferential surface thereof), while a direction orthogonal to the sub-scanning direction, i.e. a direction in which the laser beam is scanned on the photoconductive drum  61  (an axial direction on the photoconductive drum  61 ) is herein defined as a main scanning direction.  
         [0032]     The polygon mirror  44  is rotated by a motor (not shown), and hence the laser beam linearly converged (converged only in a sub-scanning direction) by the cylindrical lens  43  substantially at a section of the reflecting surface of the polygon mirror  44  is deflected so as to be scanned in a main scanning direction, and enters the imaging lens  45 . The laser beam passed through the image forming lens  45  scans in a main scanning direction at a predetermined speed on the photoconductive drum  61 . The laser beam thus converted is deflected by the deflecting mirror  46  toward the photoconductive drum  61 , to thereby form an image on the photoconductive drum  61 . At this stage, since the laser beam is modulated with the progress of the main scanning, a scanning line according to the print information is formed on the photoconductive drum  61 . Also, since the photoconductive drum  61  rotates in a sub-scanning direction, a plurality of scanning lines are formed in a sub-scanning direction on the photoconductive drum  61 . As a result, a two-dimensional latent image corresponding to the print information is formed on the photoconductive drum  61 . It should be noted that the reflecting surface of the polygon mirror  44  and the photoconductive drum  61  have a conjugate relationship with respect to the sub-scanning direction. Accordingly, the scanning line spacing is not shifted in a sub-scanning direction, even when the polygon mirror  44  incurs a facet error.  
         [0033]     The developing unit  50  includes a developing solution tank  51  that stores the developing solution DS and also serves as a housing that accommodates each component of the developing unit  50 , a pickup roller  52   a  that picks up the developing solution DS from the developing solution tank  51 , an add roller  52   b  that deposits the developing solution DS supplied by the pick up roller  52   a , a measuring roller  53  to which the deposited developing solution DS is supplied, an adjusting blade  54  that adjusts an amount of the developing solution DS supplied to the measuring roller  53 , a developing roller  55  that carries the adjusted developing solution DS, a developing roller charger (hereinafter, referred to as a corona charger)  56  that charges the developing roller  55 , and a developing roller cleaning blade  58  the scrapes off the developing solution from the surface of the developing roller  55 , for removal. On the surface of the photoconductive drum  61 , a latent image is formed by the LSU  40  based on the print information. A photoconductive drum charger (hereinafter, referred to as a corona charger)  62  charges the photoconductive drum  61  for adhering the toner according to the latent image onto the surface of the photoconductive drum  61 . The photoconductive drum  61  and the corona charger  62  are located close to the developing unit  50 . A photoconductive drum cleaning blade  63  is located close to the developing unit  50 , for scraping off the toner remaining on the surface of the photoconductive drum  61  without being transferred to an intermediate transfer roll  71 , to be later described, included in the transfer unit  70 .  
         [0034]     Next, a flow of the developing solution DS inside the developing unit  50  as well as a developing process performed therein will be described. FIGS.  4  to  6  show a structure around the measuring roller  53 .  FIG. 4  is a cross-sectional side view of the structure taken along a plane perpendicular to a rotational axis of the measuring roller  53 ,  FIG. 5  is a perspective view of the structure viewed from an upper direction, and  FIG. 6  is a cross-sectional view of the structure taken alone a plane parallel with the axis of the measuring roller  53 .  
         [0035]     The developing solution tank  51  serving also as a housing includes a wall portion  51   a  disposed, when the assembled, to cover the respective end faces of the rollers. Rotary shafts of the rollers are supported by openings formed on the wall portion  51   a , respectively.  
         [0036]     Most of the portion of the pickup roller  52   a  is dipped in the developing solution DS deposited in the developing solution tank  51 . When the pickup roller  52   a  is driven to rotate clockwise as shown in  FIGS. 3 and 4 , the developing solution DS that has adhered to the surface of the pickup roller  52   a  is lifted up and supplied to the add roller  52   b , upon reaching a region close to the interface between the pickup roller  52   a  and the add roller  52   b . The add roller  52   b  rotates clockwise as shown in  FIGS. 3 and 4 , so as to supply the developing solution DS that has adhered on its surface to the measuring roller  53 . It is to be noted that the developing solution DS stored in the developing solution tank  51  is agitated by an agitating mechanism (not shown). Further, the temperature of the developing solution DS is controlled by a temperature control system (not shown).  
         [0037]     The measuring roller  53  is driven to rotate counterclockwise as shown in  FIGS. 3 and 4 , and provided with a plurality of grooves formed at a predetermined interval on its surface. The adjusting blade  54  contacts the surface of the measuring roller  53  for scraping off an excessive portion of the developing solution DS stuck thereto.  
         [0038]     The elastic members  521  may be, for example, molded components constituted of urethane rubber or silicone rubber, which are resistant against a developing solution, and each includes a shaft hole  521   a  for receiving the rotary shaft of the add roller  52   b , as well as a shaft hole  521   b  for receiving the rotary shaft of the measuring roller  53 . The elastic members  521  are elastically deformed at positions adjacent to the respective end faces of the add roller  52   b  and the measuring roller  53 , and between the wall portion  51   a  and the respective end faces of these two rollers  52   b  and  53 , with the rotary shafts of the same rollers inserted through the respective shaft holes  521   a  and  521   b . Since the elastically deformed elastic members  521  generate a force to restore the initial state, the elastic members  521  apply such force to the respective end faces and the wall portion  51   a , so as to be closely pressed-contacted with the wall portion  51   a  and end faces of the rollers  52   b  and  53 . It should be noted that, according to the embodiment, the add roller  52   b  and the measuring roller  53  are formed to have the same axial length, and disposed such that the respective end faces become flush with each other when assembled in the developing solution tank  51 .  
         [0039]     When the add roller  52   b , the measuring roller  53  and the two elastic members  521 , are assembled in the developing solution tank  51 , a space S is formed. The space S has a bottom portion delimited by the contact interface between the two rollers  52   b  and  53 , and is surrounded by a part of the surfaces of the two rollers and by the two elastic members  521 . It should be noted that the add roller  52   b  is arranged such that the uppermost portion h 2  thereof is located lower than the uppermost portion h 1  of the measuring roller  53 , so as to prevent the developing solution DS deposited in the space S from overflowing beyond the measuring roller  53  and from sticking to the developing roller  55  and the photoconductive drum  61  and, as will be subsequently described, to apply the developing solution DS uniformly to the surface of the developing roller  55 . Accordingly, the space S is closed at the front portion (more precisely on the measuring roller  53  side) and both side portions, while open at the top, and a part of the rear portion (corresponding to the height gap between the uppermost portions h 1  and h 2 , on the add roller  52   b  side) over the entire width (i.e., the entire width of the add roller  52   b  or the measuring roller  53 ). In order to have the area of the surface of the measuring roller  53  dipped in the developing solutions as much as possible, the position of the uppermost portion h 2 , in the height direction, is close to the position of the uppermost portion h 1 .  
         [0040]     Since both lateral (side) portions of the space S are closed by the elastic members  521 , the developing solution DS can only overflow beyond the front portion of the space S, and drops into the developing solution tank  51 . Whereas, the uppermost portion h 2  of the add roller  52   b  is lower than the uppermost portion h 1  of the measuring roller  53  as described above. Further, the upper end of the elastic members are higher than the uppermost portion h 1  of the measuring roller  53 . Accordingly, a portion of the developing solution DS that has exceeded the capacity of the space S flows over the entire axial length of the add roller  52   b , by which the developing solution DS naturally drops over the entire width of the developing solution tank  51 . Consequently, the developing solution DS is deposited relatively uniformly in the peripheral portion as well as in the central portion of the developing solution tank  51 , instead of concentrating in the peripheral portion as in the conventional structure. It should be noted that, although  FIG. 6  includes upwardly and downwardly oriented arrows to indicate the flow of the developing solution DS, two stacked layers of the developing solution DS are present on the surface of the add roller  52   b  (and the pickup roller  52   a ), namely a layer of the developing solution DS which is picked up from the developing solution tank  51  (a layer contacting the surface) and another layer of the developing solution DS overflowing out of the space S (a layer separate from the surface) are stacked.  
         [0041]     The uniform distribution of the developing solution DS deposited in the developing solution tank  51  over the entire width provides uniform distribution of the developing solution DS picked up onto the pickup roller  52   a  (and the add roller  52   b ) over the entire width thereof. As a result, the developing solution DS supplied to the measuring roller  53  is also uniformly distributed over the entire width, and thus uneven application of the developing solution DS to the developing roller  55  will not occur.  
         [0042]     In the space S, the developing solution DS is adhered to the entire surface of the measuring roller  53 . Then a portion of the developing solution DS that has reached the contact interface between the add roller  52   b  and the measuring roller  53  is scraped (i.e. adjusted) by the adjusting blade  54 . Another portion of the developing solution DS which is supplied to the measuring roller  53  will not be scraped, since such portion is retained in the grooves. Accordingly, only the portion retained in the grooves, i.e. the accurately adjusted portion of the developing solution DS remains on the surface of the measuring roller  53 , and consequently the developing solution DS can be uniformly applied to the developing roller  55 , which is in rotational contact with the measuring roller  53 .  
         [0043]     The developing solution contains the toner in a uniform concentration, immediately after the application to the developing roller  55  from the measuring roller  53 . Accordingly, the toner is uniformly distributed in the carrier solution, in a region close to the interface between the measuring roller  53  and the developing roller  55 . The developing roller  55  rotates in the clockwise direction, according to the orientation of  FIGS. 3 and 4 . Therefore, the developing solution having a uniform concentration is carried by the surface of the developing roller  55 , to thereby pass under the corona charger  56 .  
         [0044]     The developing roller  55  has a surface constituted of a conductive material, so that such surface is uniformly charged by a corona charging effect of the corona charger  56 . The charging effect generates an electric field between the surfaces of the developing roller  55  and the developing solution DS, thereby causing the toner, which has been uniformly distributed in the carrier solution DS, to move toward the surface of the developing roller  55  and to closely stick thereto. In other words, the developing solution DS is split into two layers, namely a layer containing only the carrier solution and the other layer containing the toner in a higher concentration than the initial state in the carrier solution. Obviously it is the latter layer that contacts the surface of the developing roller  55 .  
         [0045]     The developing solution DS split into two layers then reaches the position to contact the photoconductive drum  61 . On the surface of the photoconductive drum  61 , the latent image corresponding to the print information is formed, by the beam emitted from the LSU  40 . The photoconductive drum  61  is charged so as to gain a higher potential than that of the developing roller  55 , by corona charger  62 . However, the region where the latent image is formed gains a lower potential than the developing roller  55 , because of an effect of the laser beam. Accordingly, between the region excluding the latent image on the photoconductive drum  61  and the surface of the developing roller  55 , the toner remains closely stuck to the lower-potential region, i.e. the surface of the developing roller  55 , without being transferred to the region where the latent image is not provided. Consequently, the region excluding the latent image is not developed. By contrast, between the latent image region on the surface of the photoconductive drum  61  and the surface of the developing roller  55 , the toner performs electrophoresis toward the lower-potential region, i.e. the latent image region on the surface of the photoconductive drum  61 , thus to adhere thereto. That is how the latent image on the photoconductive drum  61  is developed, to turn into a toner image.  
         [0046]     The developing solution DS containing the toner, which has not been utilized in the developing process, is scraped off by the developing roller cleaning blade  58  disposed in contact with the surface of the developing roller  55 , and collected into the developing solution tank  51 .  
         [0047]     The toner image developed on the surface of the photoconductive drum  61  is transferred to the recording paper P by the transfer unit  70 . The transfer unit  70  includes an intermediate transfer roll  71 , a carrier solution squeeze roll  72 , a carrier solution cleaning blade  73 , a secondary transfer roll  74 , and an intermediate transfer roll cleaning unit  75 .  
         [0048]     To the intermediate transfer roll  71 , a transfer bias of a reverse polarity to the toner is applied, so that the toner image developed on the surface of the photoconductive drum  61  is transferred as a primary step to the intermediate transfer roll  71 , at the interface between the photoconductive drum  61  and the intermediate transfer roll  71 . At this stage, the portion of the toner remaining on the surface of the photoconductive drum  61  without being transferred at the interface is scraped from the surface, by the photoconductive drum cleaning blade  63 . Also, the carrier solution that has adhered to the surface of the intermediate transfer roll  71  together with the toner image is squeezed off from the surface by the carrier solution squeeze roll  72 . Such residual carrier solution is then removed from the surface of the carrier solution squeeze roll  72  by the carrier solution cleaning blade  73 , and collected in a waste toner box (not shown), to be disposed of as a waste toner.  
         [0049]     The intermediate transfer roll  71  and the secondary transfer roll  74  are disposed so as to oppose each other across the paper path for the recording paper P, and mutually abut at a predetermined nip pressure. The toner image transferred to the surface of the intermediate transfer roll  71  is transferred to the recording paper P being carried along the paper path at the interface with the secondary transfer roll  74 , by the effect of a transfer electric field, the nip pressure and so on. The intermediate transfer roll  71 , interposed between the secondary transfer roll  74  and the photoconductive drum  61 , also serves to prevent the nip pressure of the secondary transfer roll  74  from being directly applied to the photoconductive drum  61 . Further, the toner that remains on the surface of the intermediate transfer roll  71  after the transference to the recording paper P is removed by the intermediate transfer roll cleaning unit  75 , and collected in a waste toner box (not shown), to be disposed of as a waste toner.  
         [0050]     The recording paper P on which the toner image has been transferred is carried to the fixing unit  80  along the paper path  14 . The fixing unit  80  serves to apply heat and pressure to the recording paper P, so as to fix the toner image (i.e. the printing information) onto the recording paper P, and includes a heat roller  81  that heats up the recording paper P, and a press roller  82  opposing the heat roller  81  across the paper path, so as to hold the recording paper P in cooperation with the heat roller  81 , thus to apply a pressure to the recording paper P. The recording paper P, on which the image according to the printing information has been fixed by the fixing unit  80 , is discharged through the paper outlet  15 .  
         [0051]     Although the present invention has been described based on the foregoing embodiment, it is to be understood that the present invention is not limited thereto, but various modifications may be made without departing from the scope of the present invention.  
       Second Embodiment  
       [0052]      FIG. 7  shows a region around a sealing device for the lateral portions of the space S (i.e. a device corresponding to the elastic members  521  of the first embodiment), in a wet type printer according to a second embodiment. With respect to the wet type printer shown in  FIG. 7 , the same components as those in the wet type printer  100  according to the first embodiment shown in FIGS.  3  to  6  are given an identical numeral, and detailed description thereof will be omitted.  
         [0053]     In the wet type printer according to the second embodiment, a metal plate  522  and two compression coil springs  523  are employed for sealing each of the lateral portions of the space S, and provided adjacent to end faces of the add roller  52   b  and the measuring roller  53  (the structure at only one end faces being shown in  FIG. 7 ). The metal plate  522  includes, like the elastic member  521 , two shaft holes through which the rotary shafts of the two rollers  52   b  and  53  are inserted.  
         [0054]     To achieve a closely sealed state in the lateral portions of the space S in the second embodiment, firstly, the respective rotary shafts of the add roller  52   b  and the measuring roller  53  are inserted in the shaft holes of the metal plate  522 . Then the compression coil springs  523  are attached to the rotary shafts of the rollers  52   b  and  53 . Next, the two rollers  52   b  and  53  are assembled to the developing solution tank  51 . With this structure, the respective compression coil springs  523  are compressed between the wall portion  51   a  and the metal plate  522 . Since the compression coil springs  523 , which are compressed, generate a force to reinstate the initial state, acting against the metal plate  522  and the wall portion  51   a . As a result, each metal plate  522  is pressed to closely contact the end faces of the two rollers  52   b  and  53 , thus achieving a closely sealed state in the lateral portions of the space S. In the second embodiment, the upper ends of the metal plates  522  are higher than the uppermost portion h 1  of the measuring roller  53 .  
         [0055]     In the first and second embodiments, the elastic members  521  or the metal plates  522  are provided with the shaft holes for allowing the rotary shafts  52   b  and  53  to be inserted therein. It may be possible to form cut-away portions such as a D-shaped cut instead of the shaft holes. In this case, the add roller  52   b  and the measuring roller  53  may be assembled to the developing solution tank  51 , and then, the elastic members  521  or the metal plates  522  may be attached adjacent to the end faces of the rollers  52   b  and  53 .  
         [0056]     While the add roller  52   b  and the measuring roller  53  are formed to have the same axial length in the first and second embodiments, these rollers may be configured to have different lengths. In such a case, by forming each of the elastic members  521  or the metal plates  522  to have a stepped portion according to the lengths of the rollers, it is possible to make the elastic members  521  or the metal plates  522  closely fit to the end faces of the rollers  52   b  and  53 .  
         [0057]     The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2004-175555, filed on Jun. 14, 2004, which is expressly incorporated herein by reference in its entirety.