Abstract:
A wet type image forming apparatus having a developing solution container a preparatory developing solution container, which is adapted to store developing solution to be supplied to the developing solution container, and an attachment unit to which the preparatory developing solution container is attached, is provided. The preparatory developing solution container includes a coupling portion removably coupled to the attachment unit, a developing solution path being formed in the coupling portion to allow the developing solution to flow therein, a blocking system blocking the developing solution path, and a stirring unit stirring the developing solution in the preparatory developing solution container. The attachment unit includes a releasing system to open the developing solution path blocked by the blocking system when the coupling portion of the preparatory developing solution container is coupled to the attachment unit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a wet type image forming apparatus equipped with a preparatory developing solution container for storing developing solution that is to be supplied to another developing solution container.  
         [0002]     Apparatuses to form an image on a recording sheet by employing an electrophotographic technique include, for example, a dry type image forming apparatus, which applies powder toner to a surface of a developing roller to form an image, and a wet type image forming apparatus, which applies developing solution containing toner in carrier solution to a surface of a developing roller to form an image. The toner used in the latter apparatus is generally finer than that employed in the former. Accordingly, the latter provides an image of a higher quality.  
         [0003]     A conventional wet type image forming apparatus is generally equipped with a developing solution container, and developing solution therein is supplied to a developing device during an image forming operation. In such a wet type image forming apparatus, color density of an image being formed depends on density of the toner in the developing solution. As the image is formed, quantity of the developing solution in the container decreases. Therefore, as disclosed in Japanese Patent Provisional Publication No. P2002-278294A, the wet type image forming apparatus is provided with a preparatory solution container so that developing solution therein is supplied to the developing solution container when the quantity of the developing solution in the developing solution container decreases.  
         [0004]     When the image forming apparatus with the preparatory solution container is left unused for a long period of time, the developing solution in the preparatory solution container tends to be separated into a layer containing only carrier solution and a layer containing high-density toner, which may affect the color density of the image to be formed. In order to avoid the separation of the developing solution, the image forming apparatus in the above-referenced publication is provided with a stirrer in the preparatory solution container, and the preparatory solution container is fixed to a body of the image forming apparatus so that the stirrer is securely positioned in the preparatory solution container. With this configuration, the preparatory solution container is exchangeable even when the developing solution therein is used up, and new developing solution must be refilled in the preparatory solution container. Therefore, during such a refilling operation, the body of the image forming apparatus and/or hands of an operator are often contaminated by the developing solution. Further, when a new kind of developing solution is used in the image forming apparatus, the developing solution remaining in the preparatory solution container is required to be completely removed, so that the different kinds of developing solutions may not be mixed. However, removing the remaining developing solution from the fixed preparatory solution container is difficult.  
       SUMMARY OF THE INVENTION  
       [0005]     In view of the foregoing situation, the present invention is advantageous in that an improved wet type image forming apparatus with a preparatory solution container, in which an operation to remove residual developing solution is not required, is provided. Further, the improved wet type image forming apparatus, wherein the body thereof and/or hands of the operator are not contaminated by the developing solution, during an replacing operation of the preparatory solution container, is provided.  
         [0006]     According to an aspect of the invention, there is provided a wet type image forming apparatus having a developing solution container a preparatory developing solution container, which is adapted to store developing solution to be supplied to the developing solution container, and an attachment unit to which the preparatory developing solution container is attached, is provided. The preparatory developing solution container includes a coupling portion removably coupled to the attachment unit, a developing solution path being formed in the coupling portion to allow the developing solution to flow therein, a blocking system blocking the developing solution path, and a stirring unit stirring the developing solution in the preparatory developing solution container. The attachment unit includes a releasing system to open the developing solution path blocked by the blocking system when the coupling portion of the preparatory developing solution container is coupled to the attachment unit.  
         [0007]     Optionally, the blocking system may include a movable sealing member being adapted to block the developing solution path, and an expansive member being adapted to apply expanding force to the movable sealing member so that the movable sealing member with the expanding force blocks the developing solution path.  
         [0008]     Optionally, the releasing system may be adapted to shift the movable sealing member against the expanding force of the expansive member so that the developing solution path is opened.  
         [0009]     Optionally, the stirring unit may include at least one paddle to stir the developing solution in the preparatory developing solution container, and a rotary shaft to which the at least one paddle is attached. The at least one paddle may be adapted to be unfolded according a rotation of the rotary shaft in one direction, and folded according to a rotation of the rotary shaft in an opposite direction.  
         [0010]     Optionally, an outer diameter of a circular area in a plane perpendicular to an axis of the rotary shaft, within which the stirring unit with the paddles folded fit, may be configured to be smaller than an inner diameter of the coupling portion.  
         [0011]     Optionally, the stirring unit may include at least one paddle to stir the developing solution in the preparatory developing solution container, and a rotary shaft to which the at least one paddle is attached. The attachment unit may include a drive force transmitting system to transmit drive force generated in the wet type image forming apparatus to the rotary shaft.  
         [0012]     Optionally, the rotary shaft may include a first shaft having the at least one paddle attached thereto, a second shaft, of which an end portion is exposed from an opening formed in the coupling portion, being slidable in an axial direction of the first shaft, and an expansive member applying an expanding force to the second shaft toward the opening. The drive force transmitting system may be adapted to engage with the second shaft and to press the second shaft in an axial direction of the second shaft against the expanding force from the expansive member when the preparatory developing solution container is attached to the attachment unit so that the drive force via the drive force transmitting system is transmitted to the rotary shaft.  
         [0013]     Optionally, the second shaft may be provided with a sealing member that is applied the expanding force by the expansive member to block the developing solution path. The second shaft may be shifted to open the developing solution path when the drive force transmitting system is engaged with the second shaft.  
         [0014]     According to aspects of the invention, there is provided a developing solution container to store developing solution therein for a wet type image forming apparatus, having a coupling portion, which is removably coupled to an attachment unit of the wet type image forming apparatus, a developing solution path, which is formed in the coupling portion to allow the developing solution to flow therein, a blocking system, which is adapted to block the developing solution path, and a stirring unit, which is adapted to stir the developing solution in the developing solution container. The developing solution path is blocked when the developing solution container is attached to the attachment unit of the wet type image forming apparatus, and is opened when the developing solution container is removed from the attachment unit of the wet type image forming apparatus. 
     
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0015]      FIG. 1  is a cross-sectional side view showing a structure of a wet type printer according to an embodiment of the present invention.  
         [0016]      FIG. 2  is another cross-sectional side view of the wet type printer taken from a rear side thereof according to the embodiment of the present invention.  
         [0017]      FIG. 3  is an illustrative diagram of a preparatory solution container of the wet type printer according to the embodiment of the present invention.  
         [0018]      FIG. 4  is an enlarged side view showing a rotary shaft of the preparatory solution container of the wet type printer according to the embodiment of the present invention.  
         [0019]      FIG. 5  is a cross-sectional side view showing a structure of a receiver unit of the wet type printer according to the embodiment of the present invention.  
         [0020]      FIG. 6A  is an enlarged perspective view of a lower end portion of a drive force transmitting shaft, and  FIG. 6B  is an enlarged perspective view of an upper end portion of a drive shaft according to the embodiment of the present invention.  
         [0021]      FIG. 7  is a cross-sectional side view showing a structure of the preparatory solution container mounted to the receiver unit according to the embodiment of the present invention.  
         [0022]      FIGS. 8A and 8B  are cross-sectional top views showing an internal structure of the preparatory container with a paddle unit therein according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0023]     Referring to the accompanying drawings, a wet type printer according to an embodiment of the present invention will be described in detail.  
         [0024]      FIG. 1  is a cross-sectional side view showing a structure of a wet type printer according to an embodiment of the present invention. The wet type printer  100  is an apparatus for forming an image using developing solution that contains toner in 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 characters or the images on a sheet of recording paper P 1  in accordance with a so-called electrophotographic imaging process.  FIG. 2  is another cross-sectional side view of the wet type printer  100  taken from a rear side thereof according to the embodiment of the present invention.  
         [0025]     The wet type printer  100  includes a laser scanning unit (hereinafter abbreviated as “LSU”)  30  that outputs a laser beam modulated according to print information, a developing unit  50  that develops a latent image formed on a photoconductive drum  55  according to the print information with the developing solution in the electrophotographic method, a feeding unit  90  that feed the recording paper P 1 , a transfer unit  70  that transfers a toner image developed by the developing unit  50  at a transfer position onto the recording paper P 1 , and a fixing unit  80  that permanently fixes the toner image that has been transferred on the recording paper P 1 .  
         [0026]     The developing unit  50  includes an add roller  51 , a measuring roller  52 , an adjusting blade  52   a , a developing roller  53 , a developing roller cleaning blade  53   a , a developing roller corona charger  54 , the photoconductive drum  55 , a photoconductive drum corona charger  57 , a squeeze roller  58 , and a screw  59 . The measuring roller  52  is provided to measure amount of the developing solution on a surface thereof. The adjusting blade  52   a  evenly adjusts thickness of the developing solution on the surface of the measuring roller  52 . The developing roller  53  carries the developing solution supplied from the measuring roller  52 . The developing roller cleaning blade  53   a  scrapes off excessive amount of the developing solution from the surface of the developing roller  53 . The developing roller corona charger  54  charges the surface of the developing roller  53 . A surface of the photoconductive drum  55  is formed the latent image by the laser beam from the LSU  30 . The photoconductive drum corona charger  57  uniformly charges the surface of the photoconductive drum  55 . The squeeze roller  58  collects used developing solution from the surface of the photoconductive drum  55 . And a screw  59  transmits residual developing solution collected in the developing unit  50  to the solution container  3  (see  FIG. 2 ). All of rotation axes of the respective rollers are in parallel with each other and are perpendicular to a direction parallel to a plane of  FIG. 1 , although rotating directions of the respective rollers may vary.  
         [0027]     When the image is formed, the developing solution stored in the solution container  3  is injected and the injected developing solution is transitionally pooled in a pit portion formed by the add roller  51  that rotates in a clockwise direction in  FIG. 1  and the measuring roller  52  that rotates in a counterclockwise direction in  FIG. 1 . Thereafter, the developing solution is supplied to a surface of the measuring roller  52  by the rotation of the measuring roller  52 . The supplied developing solution is partially scraped off and thereby adjusted by the adjusting blade  52   a  of which an edge is in contact with the surface of the measuring roller  52  so that excessive amount of the developing solution is removed. Thus, the remaining developing solution on the surface of the measuring roller  52  is transferred evenly to a surface of the developing roller  53 , which is in contact with the measuring roller  52 .  
         [0028]     The photoconductive drum  55  has the surface constituted of a conductive material, so that such surface is uniformly charged by a corona charging effect of the developing roller corona charger  57 . On the surface of the photoconductive drum  55 , a latent image corresponding to the print information is formed, by the laser beam emitted from the LSU  30 . The photoconductive drum  55  is charged so as to gain a higher potential than that of the developing roller  53 , by the photoconductive drum corona charger  57 . However, the region where the latent image is formed gains a lower potential than the developing roller  53 , due to an effect of the laser beam. Accordingly, between the region excluding the latent image on the photoconductive drum  55  and the surface of the developing roller  53 , the toner remains closely stuck to the lower-potential region, i.e. the surface of the developing roller  53 , without being transferred to the region where no latent image exists. Consequently, the region excluding the latent image is not developed. By contrast, between the latent image region on the surface of the photoconductive drum  55  and the surface of the developing roller  53 , the toner performs electrophoresis toward the lower-potential region, i.e. the latent image region on the surface of the photoconductive drum  55 , thus to adhere thereto. That is how the latent image on the photoconductive drum  55  is developed, to turn into a toner image.  
         [0029]     The toner image developed on the surface of the photoconductive drum  55  is transferred to the recording paper P 1  by the transfer unit  70 . The transfer unit  70  includes an intermediate transfer roller  71  and a secondary transfer roller  73 .  
         [0030]     To the intermediate transfer roller  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  55  is transferred as a primary step to the intermediate transfer roller  71 , at the interface between the photoconductive drum  55  and the intermediate transfer roller  71 .  
         [0031]     The intermediate transfer roller  71  and the secondary transfer roller  73  are disposed so as to oppose to each other across a paper path for the recording paper P 1 , and mutually abut at a predetermined nip pressure. The toner image transferred to the surface of the intermediate transfer roller  71  is transferred to the recording paper P 1  being carried along the paper path at the interface with the secondary transfer roller  73 , by the effect of a transfer electric field, the nip pressure and so on.  
         [0032]     The recording paper P 1  on which the toner image has been transferred is carried to the fixing unit  80  along the paper path. The fixing unit  80  serves to apply heat and pressure to the recording paper P 1 , so as to fix the toner image onto the recording paper P 1 , and includes a heat roller  81  that heats up the recording paper P 1 , and a press roller  82  located opposing to the heat roller  81  across the paper path, so as to hold the recording paper P 1  in cooperation with the heat roller  81 , thus to apply a pressure to the recording paper P 1 .  
         [0033]     The feeding unit  90  includes a core roller  91 , around which the recording paper P 1  as a continuous form recording sheet is rolled, a feed roller  93 , which carries the recording paper P 1 , a subsidiary feed roller  94 , which is rolled accordingly to rotation of the feed roller  93  to carry the recording paper P 1 , and a drive motor  95 , which supplies rotating force to the feed roller  93 .  
         [0034]     Next, referring to  FIG. 2 , the solution container  3 , to store the developing solution therein, will be described. The wet type printer  100  in the present embodiment includes a solution container  3 , wherein developing solution is stored, a preparatory solution container  5 , a preparatory carrier solution container  7 , a supplier pump unit  9 , and a conveyer pump unit  11 . The preparatory solution container  5  stores therein preparatory developing solution, which is supplied to the solution container. Carrier solution is stored in the preparatory carrier solution container  7 , and is supplied to the solution container  3 . The supplier pump unit  9  is used to transmit the preparatory developing solution in the preparatory solution container  5  to the solution container  3 .  
         [0035]     During a printing operation of the wet type printer  100 , the developing solution in the solution container  3  is conveyed to the developing unit  50  by the conveyer pump unit  11 . An outlet of the conveyer pump unit  11  is connected to a solution pipe  49 . When the level of the developing solution in the solution container  3  becomes too low, the developing solution is not supplied to the developing unit. Therefore, in the present embodiment, the preparatory developing solution stored in the preparatory solution container  3  is supplied to the solution container  3  when the level of the developing solution in the solution container becomes as low as a predetermined lower limit. Further, toner density of the developing solution in the solution container  3  tends to be concentrated over image forming operations. Therefore, the toner density is monitored by a density sensor (not shown) so that the carrier solution is supplied from the preparatory carrier solution container  7  if necessary.  
         [0036]     As mentioned above, color density of an image to be formed depends on toner density of the developing solution. That is, the image is printed in higher density when the toner density of the developing solution is high, and in lower density when the toner density is low. In the wet type printer  100  in the present embodiment, the toner density in the developing solution in the solution container  3  is adjusted with the supplemental carrier solution from the preparatory carrier solution container  7  so that the toner density (i.e., the color density of the image) is maintained constant. More specifically, the developing solution in the solution container  3 , as well as the developing solution in the preparatory solution container, is composed in a weight ratio of approximately 30% as toner and the remaining 70% as carrier solution.  
         [0037]     The solution container  3  is provided with a stirring unit  4 , which stirs the stored developing solution, and a lateral opening  6 . The lateral opening  6  is connected to a pipe (not shown), which is further connected to an opening (not shown) provided on an extended line (not shown) of an axis of the screw  59  (see  FIG. 1 ). The developing solution carried by the screw  59  is returned to the solution container  3  via the lateral opening  6 .  
         [0038]     Hereinafter, the preparatory solution container  5  in the present embodiment will be described. The preparatory solution container  5  is threadably mounted to the receiver unit  8 , which is fixedly mounted to a body of the wet type printer  100 . The preparatory solution container  5  is removable from the receiver unit  8  (see  FIGS. 2 and 3 ).  FIG. 3  is an illustrative diagram of the preparatory container  5  of the wet type printer  100  being removed from the receiver unit  8  according to the embodiment of the present invention. However, in  FIG. 3 , the preparatory solution container  5  is shown in a position when the preparatory solution container  5  is mounted to the receiver unit  8 . The preparatory solution container  5  includes a rotary shaft  13 , paddle unit  19  that are coupled to the rotary shaft  13 , an inlet  21 , a container-side stopper  23 . The inlet  21  is provided so that the air is introduced therethrough to the inside of the preparatory solution container  5  when the developing solution is aspirated by the supplier pump unit  9 . The preparatory solution container  5  is mounted to the receiver unit  8  with a coupling portion  16 . The rotary shaft  13  includes a drive force transmitting shaft  14 , which transmits drive force provided externally from the wet type printer  100 , and a hollow cylinder  15 , wherein a part of the drive force transmitting shaft  14  is slidably inserted at a lower end of the hollow cylinder  15 , and a spring  17 , which applies downward expanding force to the inserted portion of the drive force transmitting shaft  14 . An outer circumference of the coupling portion  16  is formed a threaded portion  25 . The coupling portion  16  is formed an opening therein, through which the developing solution is aspirated. (Detail of the opening will be described hereinbelow.)  
         [0039]      FIG. 4  is an enlarged side view showing the rotary shaft  13  of the preparatory container  5  according to the embodiment of the present invention. As mentioned above, a part of the drive force transmitting shaft  14  is slidably inserted into the hollow cylinder  15 , and is provided with downward expanding force by the spring  17 , which is in contact with the drive force transmitting shaft  14  at one end. The other end of the spring  17  provides the hollow cylinder  15  with upward expanding force. The drive force transmitting shat  14  includes a rotary shaft-side stopper  27 , engaging pins  101 , and a drive force transmitting pin  103 . The rotary shaft-side stopper  27  is adapted to be in contact with the container-side stopper  23  when the drive force transmitting shaft  14  is depressed by the spring  17 . The engaging pins  101  is adapted to engage with the receiver unit  8  when the preparatory solution container  5  is mounted to the receiver unit  8 . It should be noted that the container-side stopper  23  is formed to have a shape of a cylinder, and an outer diameter thereof is configured to fit an inner diameter of the coupling portion  16  (see  FIG. 3 ). Further, the container-side stopper  23  is provided with a through hole  23   a , which is at a center and in parallel with an axial direction of the cylinder. The rotary shaft-side stopper  27  is partially inserted to the drive force transmitting shaft  14 , and is formed as a circular cone with an axis corresponding to a rotation axis of the drive force transmitting shaft  14  with an apex portion thereof being removed, i.e., having a cross-sectional shape of an approximate circular truncated cone. A bevel surface  27   a  of the rotary shaft-side stopper  27  is in close contact with the container-side stopper  23 . As the rotary shaft-side stopper  27  is sealed to the container-side stopper  23 , the developing solution in the preparatory solution container  5  will not leak through the through hole  23   a  when the preparatory container  5  is not mounted to the receiver unit  8 . The hollow cylinder  15  is provided with an elongated opening  105 , through which a drive force transmitting pin  103  is inserted. The drive force transmitting pin  103  is adapted to be a spring pin, and is disposed in the elongated opening  105  when the drive force transmitting shaft  14  is inserted into the hollow cylinder  15 . As the drive force transmitting shaft  14  is rotated, the drive force transmitting pin  103  becomes in contact with an inner edge of the elongated opening  105 , and thereby the rotating force is transmitted to the hollow cylinder  15 . The drive force transmitting pin  103  is capable of shifting in a longitudinal direction of the elongated opening  105 .  
         [0040]      FIG. 5  is a cross-sectional side view showing a structure of the receiver unit  8 , which is fixedly mounted to the body of the wet type printer  100  according to the embodiment of the present invention. The receiver unit  8  includes drive shafts  107 ,  111 , gears  109 ,  112 , and double-helical gears  110   a ,  110   b . The drive shaft  107  is adapted to be coupled to the drive force transmitting shaft  14  when the preparatory solution container  5  is mounted to the receiver unit  8 . The gear  109  is coupled to a drive source such as a drive motor (not shown) equipped in the developing unit  50  (see  FIG. 1 ). The double-helical gear  110   a  is coupled to a common rotation axis of the gear  109 , and is in engagement with the double-helical gear  110   b . Further, the double-helical gear  110   b  is coupled to the drive shaft  111 , which is coupled to the gear  112  in a vicinity to a lower end of the drive shaft  111 . The receiver unit  8  is provided with a threaded portion  28 , wherein the threaded portion  25  of the preparatory solution container  5  is screwed when the preparatory solution container  5  is mounted to the receiver unit  8 . The receiver unit  8  is further provided with a gear  114  in a vicinity to a lower end of the drive shaft  107 . As the gear  114  and the gear  112  are engaged with each other, rotating force of the drive shaft  111  is transmitted to the drive shaft  107  via the gears  114 ,  112 . It should be noted that an upper end of the drive shaft  107  is formed an approximately conic shaped pit  108 , which is coupled to a lower end portion of the drive force transmitting shaft  14  when the preparatory solution container  5  is mounted to the receiver unit  8 .  
         [0041]      FIG. 6A  is an enlarged perspective view of the lower end portion of the drive force transmitting shaft  14 , and  FIG. 6B  is an enlarged perspective view of an upper end portion of the drive shaft  107  according to the embodiment of the present invention. As shown in  FIG. 6A , four engaging pins  101  are provided at the lower end portion of the drive force transmitting shaft  14 , and are arranged at 90 degrees with respect to each other in a plane that is perpendicular to the rotation axis of the drive force transmitting shaft  14 . As shown in  FIG. 613 , four recessed portions  102  are formed on the upper end portion of the drive shaft  107 , at positions that correspond to the engaging pins  101  of the drive force transmitting shaft  14 . The engaging pins  101  are engaged with the recessed portions  102  respectively, so that the drive force transmitting shaft  14  and the drive shaft  107  are coupled, and the rotating force of the drive shaft  107  is securely transmitted to the drive force transmitting shaft  14 . It should be noted that the number of the engaging pins  101  and the recessed portions  102  is not limited to four. For example, one engaging pin  101  that penetrates through the drive force transmitting shaft  14  may be provided at the positions corresponding to two of the above-mentioned four engaging pins  101 , and two recessed portions  102  may be provided to the drive shaft  107  at positions corresponding to the one engaging pin  101 .  
         [0042]      FIG. 7  is a cross-sectional side view showing a structure of the preparatory solution container  5  mounted to the receiver unit  8  according to the embodiment of the present invention. When the preparatory solution container  5  is mounted to the receiver unit  8  and the lower end portion of the drive force transmitting shaft  14  is pressed against the receiver unit  8 , the spring  17  is contracted by the upper end portion of the drive force transmitting shaft  14 . Thus, the rotary shaft-side stopper  27  is uplifted, and the rotary shaft-side stopper  27  is unsealed from the container-side stopper  23 . A diameter of the through hole  23   a  of the container-side stopper  23  is configured to be greater than an outer diameter of the upper end portion of the drive shaft  107 . Therefore, as the shaft-side stopper  27  is uplifted, a clearance C is formed between the container-side stopper  23  and the drive shaft  107 , through which the developing solution exudes. The developing solution from the preparatory exuded from the preparatory solution container  5  thereafter reaches to an outlet portion  24 , which is at a bottom of the container-side stopper  23 , as the flow is indicated by a dotted arrow A. The receiver unit  8  is provided with a solution path  113  that leads the exuded developing solution to be aspirated by the supplier pump unit  9 , and thereby transmitted to the solution container  3  (see  FIG. 2 ).  
         [0043]     When the preparatory solution container  5  is mounted to the receiver  8 , the lower end portion of the drive force transmitting shaft  14  becomes in contact with the pit  108  of the drive shaft  107 . It should be noted that heights of the threaded portion  25  of the preparatory solution container  5  and the threaded portion  28  of the receiver unit  8  in the present embodiment are configured to be substantial to uplift the rotary shaft-side stopper  27  from the container-side stopper  23  as the threaded portion  25  and the threaded portion  28  are screwed together. Further, as the rotary shaft-side stopper  27  is uplifted from the container-side stopper  23 , the clearance C is formed between the rotary shaft-side stopper  27  and the container-side stopper  23 , so that the preparatory developing solution in the preparatory solution container  5  can be supplied to an external unit (i.e., the solution container  3 ).  
         [0044]      FIGS. 8A and 8B  are cross-sectional top views showing an internal structure of the preparatory solution container  5  with a paddle unit  19  therein according to the embodiment of the present invention. The paddle unit  19  includes paddles  190  and hinges  20 . As shown in  FIG. 5A , the paddles  190  are in initial folded positions thereof. Each of the paddles  190  includes pressure receiving portions  190   a  and tapered pressure receiving portions  190   c . From the folded position, each tapered pressure receiving portion  190   c  is adapted to receive pressure from the developing solution being stirred when the paddle unit  19  starts to rotate. Initially, the paddles  190  are folded to fit within an inner diameter of the coupling portion  16  of the preparatory solution container  5 . More specifically, an outer diameter of a circular area in a plane perpendicular to the axis of the rotary shaft  13 , wherein the folded paddles  190  fit, is configured to be smaller than the inner diameter of the coupling portion  16 . With this configuration, the paddle unit  19  can be easily installed in the preparatory solution container  5  through the coupling portion  16 . When each tapered pressure receiving portion  19   c  receives pressure from the developing solution to be stirred as the paddle unit  19  rotates in a counterclockwise direction in  FIG. 8A , each paddle  19  is opened accordingly. That is, as the paddle unit  19  rotates in the counterclockwise direction, the tapered pressure receiving portions  190   c  receive pressure from the developing solution that is transitioned in a clockwise direction (as indicated by an arrow in  FIG. 8A ) with respect to the paddles  190 . Further, as the pressure from the developing solution increases, the paddles  190  are rotated about the hinges  20  respectively and are fully opened as shown in  FIG. 8B .  
         [0045]      FIG. 8B  is a cross-sectional top view showing the internal structure of the preparatory solution container  5  with the paddles  190  opened therein according to the embodiment of the present invention. The paddles  190  are fully opened, i.e., at approximately 90 degrees with respect to the initial folded positions, as the rotary shaft  13  rotate in the counterclockwise direction as indicated by an arrow in  FIG. 8B . In the preparatory solution container  5  of the present embodiment, it is preferable that the paddles of the paddle unit  19  rotate in a greater circular area so that the developing solution in the preparatory solution container  5  is stirred substantially to have the toner therein to be evenly distributed and not to be deposited in the solution. Therefore, the paddle unit  19  with a greater outer diameter when the paddles  190  are fully opened is preferable. It should be noted that the paddle unit  19  in the present embodiment is adapted to have a greater outer diameter when in use, whilst the paddle unit  19  with the paddles  190  folded can be installed in the preparatory solution container  5  easily. It should be further noted that the paddles  190  can be folded when the rotary shaft  13  rotates in an opposite direction from the direction to unfold the paddles  190 , i.e., the clockwise direction as indicated by the arrow in  FIG. 8A , so that the paddle unit  19  can be taken out of the preparatory solution container  5  in case, for example, the paddle unit  19  requires to be replaced.  
         [0046]     With the above-described configuration, additional developing solution can be supplied to the wet type printer  100  by replacing the preparatory solution container  5  to a new preparatory solution container when the level of the developing solution in the preparatory solution container  5  becomes low. Further, as the clearance C between the rotary shaft-side stopper  27  and the container-side stopper  23  is sealed as the preparatory solution container  5  is unscrewed from the receiver unit  8 , the residual developing solution is not allowed to leak therethrough when the preparatory solution container  5  is removed from the receiver unit  8 . Therefore, the body of the wet type printer  100  and/or hands of the operator are not contaminated by the developing solution during the replacing operation of the preparatory solution container  5 . Furthermore, as the rotating force to stir the paddle unit  19  is provided from the drive motor equipped to one of the units of the wet type printer  100 , no specific drive force dedicated to the paddle unit  19  is required, so that the wet type printer  100  can be designed in a more simple configuration.  
         [0047]     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.  
         [0048]     The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2005-139300, filed on May 12, 2005, which is expressly incorporated herein by reference in its entirety.