Patent Publication Number: US-8967753-B2

Title: Image forming apparatus using a pre-processing liquid and drying a printing medium, and image forming method using a pre-processing liquid and drying the printing medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2013-091159, filed Apr. 24, 2013 and Japanese Patent Application No. 2012-104792, filed May 1, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments disclosed herein relate to an image forming apparatus and an image forming method. 
     2. Description of the Related Art 
     An inkjet image forming method has rapidly been adopted in recent years owing to an advantageous property that the method is easily enhanced for a method of forming color images, as well as properties that the method is noiseless and has a low running cost. 
     JP-A No. 2004-330568 discloses a pretreatment process of forming an ink receiving layer that aggregates colorant on paper of ink by applying the precoating liquid, an image forming process of jetting ink to the ink receiving layer, and a drying process of drying the precoating liquid by heating the paper near the ink receiving layer. 
     The most appropriate amount of the pre-processing liquid (precoating liquid) changes according to a printing condition, for example, the resolution of an image. 
     Using the technology disclosed in the above-described document, bleeding of the formed image or the contraction of the printing medium can occur. 
     SUMMARY 
     The embodiments disclosed herein have been developed in view of the above-described problems of conventional techniques. 
     An objective of the disclosed embodiments is to provide an image forming apparatus and an image formation method that can improve the quality of an image formed on a printing medium. 
     In one aspect, there is provided an image forming apparatus including an image forming device configured to eject droplets onto a printing medium, and to form an image on a surface of the printing medium; a pre-processing device configured to apply a pre-processing liquid to the surface of the printing medium before the image forming device forms the image; and a dryer configured to dry the printing medium on which the pre-processing liquid was applied, wherein the pre-processing device is configured to apply an amount of the pre-processing liquid that is determined based on a resolution of the image formed on the printing medium, and the dryer is configured to dry the printing medium using a drying strength that is determined based on the resolution of the image formed on the printing medium. 
     In another aspect, there is provided an image forming method including the steps of applying a pre-processing liquid to a surface of a printing medium; forming an image on the surface of the printing medium on which the pre-processing liquid was applied; and drying the printing medium on which the pre-processing liquid was applied, wherein the applying step includes applying an amount of the pre-processing liquid that is determined based on a resolution of the image formed on the printing medium, and drying the printing medium using a drying strength that is determined based on the resolution of the image formed on the printing medium. 
     According to the embodiments of the present invention, there are provided an image forming apparatus and an image formation method that can improve the quality of the printing medium on which the image is formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view showing an example of an image forming apparatus; 
         FIG. 2  is a schematic configuration view showing an example of a pre-processing unit of an image forming apparatus; 
         FIG. 3  is a schematic plan view showing an example of an image forming unit and a post-processing unit of an image forming apparatus; 
         FIG. 4  is a schematic plan view showing an example of a head unit of an ejecting head for ejecting the black color ink of an image forming unit; 
         FIG. 5  is a cross sectional view showing an example of a cross section shown along a longitudinal direction of a liquid chamber. 
         FIG. 6  is a cross sectional view showing an example of a cross section shown along a lateral directions of the liquid chamber. 
         FIG. 7  is an illustration showing of an example of the printing medium on which the image is formed by an image forming apparatus; 
         FIG. 8  is a schematic configuration view showing an example of a controlling unit of an image forming apparatus; 
         FIG. 9  is a schematic configuration view showing of an example of a superordinate apparatus of a controlling unit; 
         FIG. 10  is a functional block diagram showing an example of functions of the controlling unit; 
         FIG. 11  is a functional block diagram showing an example of functions of a data management unit in the controlling unit; 
         FIG. 12  is a functional block diagram showing an example of functions of an image output unit in the controlling unit; 
         FIG. 13  is a schematic configuration view showing an example of a drying unit of an image forming apparatus; 
         FIG. 14  is a flowchart showing an image forming method; 
         FIG. 15  is an illustration showing a relationship between the granularity of an image and the coating amount of pre-processing liquid; 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one embodiment will be explained for an inkjet image forming apparatus. However, the present advancements can be also applied to any image forming apparatus having an ejecting unit (ejecting head, ink head, recording head, or the like) that forms (e.g., prints) an image on a printing medium by ejecting recording liquid droplets (e.g., ink) such as a facsimile device, a copier device, a multi-function peripheral, etc., otherwise than as specifically described herein. 
     A Configuration of an Image Forming Apparatus 
     The outline of an image forming apparatus  100  according to one embodiment is explained with reference to  FIGS. 1 to 5 . 
     Although this embodiment has been described using an image forming apparatus having ejecting heads (recording head, print heads, ink heads) of the four colors of black (K), cyan (C), magenta (M), and yellow (Y), the scope of the present advancements is not limited to the described image forming apparatus having these ejecting heads. The scope of the present advancements includes the image forming apparatus also having the ejecting heads of green (G) red (R), light cyan (LC), and/or other colors, and the image forming apparatus only having an ejecting head of black (K). In the following explanation, Y, C, M, and K represent colors of yellow, cyan, magenta, and black, respectively. 
     Although the present advancements have been described using a continuous form sheet in the form of a roll (hereinafter referred to as “roll sheet Md”) as the printing medium, the printing medium that can be formed by the printing apparatus is not limited to the roll sheet. The printing medium that can be formed by the printing apparatus may also be a cut sheet. The scope of the printing medium that can be formed by the printing apparatus includes a medium that can form an image by liquid droplets on a surface such as standard paper, high quality paper, thick paper, thin paper, cut sheet, roll sheet, a OHP sheet, synthetic resin film, and metal thin film. The continuous form sheet includes perforated box paper or unperforated roll paper. A page of the box paper is, for example, between a first perforation and the next perforation. 
     As shown in  FIG. 1 , an image forming apparatus  100  according to an embodiment includes a sheet feeding unit  10  for feeding the roll sheet Md (printing medium), a pre-processing unit  20  for pre-processing the roll sheet Md that is fed by the sheet feeding unit  10 , and a drying unit  31  for drying the roll sheet Md that was treated by the pre-processing unit  20 . The image forming apparatus  100  includes an image forming unit  40  for forming an image on a surface of the roll sheet Md. Furthermore, as shown in  FIG. 1  the image forming apparatus  100  may include a post-processing unit  50  for treating a post-processing to the roll sheet Md that formed an image by the image forming unit  40 . Then, in some instances, the image forming apparatus  100  can include a drying unit  32  for drying the roll sheet Md that was treated by the post-processing unit  50 . The image forming apparatus  100  includes a sheet discharging unit  60  for discharging the roll sheet Md on which the image was formed. (In some instances the roll sheet Md may be further treated by the post-processing unit  50 .) Furthermore, the image forming apparatus  100  includes a controlling unit for controlling the action of the image forming apparatus  100 . 
     The image forming apparatus  100  according to an embodiment feeds the roll sheet Md by the sheet feeding unit  10 , treats pre-processing to the surface of the roll sheet Md by the pre-processing unit  20 , and dries the surface of the roll sheet Md by the drying unit  31 . The image forming apparatus  100  forms an image by the image forming unit  40  on the surface of the roll sheet Md that was treated by the pre-processing unit and dried. Furthermore, in some instances, the image forming apparatus  100  can perform post-processing by the post-processing unit  50  to the roll sheet Md on which an image is formed, and perform drying by the drying unit  32 . Then, the image forming apparatus  100  rolls up (discharges) the roll sheet Md by the sheet discharging unit  60 . 
     Hereinafter, each component of the image forming apparatus  100  will be concretely described. 
     A Configuration of the Sheet Feeding Unit 
     The sheet feeding unit  10  feeds a printing medium to the pre-processing unit  20 . In this embodiment, the sheet feeding unit  10  includes a sheet holder  11  and plural conveyance rollers  12 . The sheet feeding unit  10  conveys a roll sheet Md, which is held by the sheet holder  11 , to the pre-processing unit  20  by the conveyance rollers  12 . 
     Additionally, this embodiment is described with an example of using the roll sheet as a printing medium, but the present advancements can use other printing media, and in case of using other printing media, the sheet feeding unit  10  can include other configurations. 
     A Configuration of the Pre-Processing Unit 
     The pre-processing unit  20  treats a printing medium before the image processing unit  40  will form an image on the printing medium. In this embodiment, the pre-processing unit  20  treats a surface of the roll sheet Md that is conveyed by the feeding unit  10 . The pre-processing unit  20  treats the surface by a pre-processing liquid. 
     The pre-processing process is a process of uniformly applying the pre-processing liquid to a surface of the roll sheet Md (printing medium). The pre-processing liquid has a function of aggregating a droplet of ink. 
     This enables the image forming apparatus  100  to apply a pre-processing liquid, which has a function of aggregating a droplet of ink to a surface of the printing medium before the image processing unit  40  will form an image on the printing medium, in case the image forming apparatus  100  forms an image on a printing medium different from a sheet for inkjet. This enables the image forming apparatus  100  to reduce problems, such as bleeding of the image, a problem of image density, a problem of image tone, an ink strike-through problem, a problem of water resistance, or a problem of environment resistance. That is, the image forming apparatus  100  can improve the quality of an image that is formed on the printing medium, by applying the pre-processing liquid, which has a function of aggregating a droplet of ink to the printing medium by the pre-processing unit  20  before the image forming unit  40  will form the image on the printing medium. 
     Additionally, the image forming apparatus  100  may apply the pre-processing liquid, which has a function of aggregating a droplet of ink to the sheet for inkjet by the pre-processing unit  20 , before the image forming unit  40  will form the image on the sheet for inkjet. 
     The pre-processing method by the pre-processing unit  20  according to one embodiment is not restricted, and can be selected appropriately according to the object, and examples of the method for applying include a blade coating method, a gravure coating method, a gravure offset coating method, a bar coating method, a roll coating method, a knife coating method, an air knife coating method, a comma coating method, a U-comma coating method, an AKKU coating method, a smoothing coating method, a micro gravure coating method, a reverse roll coating method, a 4-roll or 5-roll coating method, a dip coating method, a curtain coating method, a slide coating method, and a die coating method. 
     The pre-processing unit  20  according to one embodiment can use a treating liquid that includes water-soluble aliphatic amino acids as the pre-processing liquid. The treating liquid that includes water-soluble aliphatic amino acids has a behavior of aggregating a water-dispersible colorant, which means converging each of the water-dispersible colorant particles. 
     Furthermore, the pre-processing unit  20  can adsorb ions onto the surface of the water-dispersible colorant by adding an ionic object, such as water-soluble aliphatic amino acids, in the pre-processing liquid. This enables the pre-processing unit  20  to neutralize the surface charge of the water-dispersible colorant. This also enables the pre-processing unit  20  to aggregate more of the water-dispersible colorant by increasing the aggregate by the force between the molecules. 
     An embodiment of a pre-processing unit  20  using a roll coating method will be described with reference to  FIG. 2 . 
     As shown in  FIG. 2 , the pre-processing unit  20  applies a pre-processing liquid  20 L, which is stored in the pre-processing unit  20 , to a surface of the roll sheet Md that is conveyed (fed) to the pre-processing unit  20  by the feeding unit  10  ( FIG. 1 ). 
     Specifically, a stirring roller  21  and a transferring roller  22  form the pre-processing liquid  20 L as a thin film to a surface of an applying roller first. Next, the pre-processing unit  20  presses the applying roller  23  onto a platen roller  24 , and rotates the applying roller  23 . In this state, the pre-processing unit  20  conveys the roll sheet Md between the applying roller  23  and the platen roller  24 . This enables the pre-processing liquid not to be applied to a surface of the roll sheet Md. 
     A pressure controller  25  of the pre-processing unit  20  controls the nip pressure between the applying roller  23  and the platen roller  24  at a time that the pre-processing unit applies the pre-processing liquid  20 L. The nip pressure is a force acting on a position of contact between the applying roller  23  and the platen roller  24 . The pre-processing unit  20  can control (change) the amount of the pre-processing liquid applied to the roll sheet Md by controlling (changing) the nip pressure by the pressure controller  25 . The applied amount of the pre-processing liquid includes the amount of liquid, the amount of applying, the amount of liquid after drying, and the thickness of the liquid film. 
     Furthermore, the pre-processing unit  20  controls the rotation speed of the applying roller  23  and the platen roller  24 . The pre-processing unit can control (change) the applied amount of the pre-processing liquid by controlling (changing) the rotation speed of the applying roller  23  and the platen roller  24 . Additionally, the pre-processing unit  20  may control the applying unit  23  and/or the platen roller  24  by controlling the power source (motor or the like) to drive the applying unit  23  and/or the platen roller  24 . 
     Accordingly, the pre-processing unit  20  of the image forming apparatus according to an embodiment using the roll coating method can more uniformly apply the pre-processing liquid to a surface of the roll sheet Md (printing medium) than using the spray coating method. The pre-processing unit  20  of this embodiment can uniformly and thinly apply the pre-processing liquid  20 L to a surface of the roll sheet Md when the pre-processing liquid  20 L has a high viscosity. The pre-processing unit  20  enables the image that will form after the pre-processing method to have reduced image bleeding by uniformly and thinly applying the pre-processing liquid  20 L to the roll sheet Md. This enables improved image quality. 
     The pre-processing unit  20  of the image forming apparatus according to this embodiment can apply an amount of the pre-processing liquid  20 L suitable for the image forming method and post-processing method to the roll sheet Md (printing medium) by controlling the amount of the pre-processing liquid by the applying roller  23  and/or the platen roller  24 . 
     A Configuration of the Drying Unit 
     The drying unit  30  is the unit to dry the printing medium by heating, etc. The drying unit  30  in this embodiment includes the pre-processing liquid drying unit  31 , which dries the roll sheet Md that was treated by the pre-processing unit  20 . The drying unit  30  can include the post-processing liquid drying unit  32 , which dries the roll sheet Md that was treated by the post-processing unit  50 . The post-processing liquid drying unit  32  may not be needed in some embodiments. 
     As shown in  FIG. 1 , the pre-processing liquid drying unit  31  of this embodiment uses plural heating rollers  31   h . Specifically, the heating roller  31   h  is heated from 40 degree C. to 80 degrees C., and a surface of the roll sheet Md to which the pre-processing liquid  20 L was applied contacts the heating roller  31   h . This enables the pre-processing liquid drying unit  31  to dry the roll sheet Md (the pre-processing liquid on the roll sheet Md) by evaporating the water in the pre-processing liquid by heating the surface of the roll sheet Md by the heating roller  31   h.    
     Additionally, the number of the heating rollers  31  in the drying unit  30  is not limited to that shown in  FIG. 1 , and can be changed as needed. 
     The pre-processing liquid drying unit  31  is not limited to include the heating roller as a drying method. That is, the pre-processing liquid drying unit  31  can use any drying method, such as an infrared ray drying method, a microwave drying method, or a hot-air drying method. The pre-processing liquid drying unit  31  can also use plural methods in combination. 
     A description of the configuration of the post-processing liquid drying unit will be omitted because it is similar to the pre-processing liquid drying unit. 
     A Configuration of the Image Forming Unit 
     The image forming unit  40  is a unit for forming an image on a printing medium. The image forming unit  40  of this embodiment forms an image on a surface of the roll sheet Md by ejecting the recording liquid droplets (e.g., ink) on the roll sheet Md that was dried by the drying unit  30 . 
     An example of an external shape of the image forming unit  40  will be described with reference to  FIGS. 3 and 4 .  FIG. 3  is a schematic plan view showing an example of the image forming unit  40  and a post-processing unit  50  of the image forming apparatus  100  according to this embodiment.  FIG. 4  is a schematic plan view showing an example of a head unit of an ejecting head for ejecting the black color ink of the image forming unit  40 . 
     As shown in  FIG. 3 , the image forming unit  40  can use full-line heads. That is, the image forming unit  40  includes four ejecting heads  40 K,  40 C,  40 M, and  40 Y for different colors, black (K), cyan (C), magenta (M), and yellow (Y), in this order from the upstream to the downstream in a printing medium conveyance direction Xm. 
     The ejecting head  40 K for ejecting the black (K) color ink includes four head units  40 K- 1 ,  40 K- 2 ,  40 K- 3 , and  40 K- 4 , which are arranged in a staggered manner in the direction perpendicular to the printing medium conveyance direction Xm. This enables the image forming apparatus  40  to form an image in the whole width of the image forming range (printing range) of the roll sheet Md (printing medium). A description of the configuration of the other ejecting heads  40 C,  40 M, and  40 Y will be omitted since they are similar to the ejecting head  40 K. 
       FIG. 4  is an enlarged plan view showing a head unit  40 K- 1  of the ejecting head  40 K for ejecting the black color ink of the image forming unit  40 . 
     As shown in  FIG. 4 , the head unit  40 K- 1  has plural eject openings  40 N (nozzles, printing nozzles) on the nozzle face. The plural eject openings  40 N are arranged along a longitudinal direction of the head unit  40 K- 1 , and form the nozzle array. Additionally, the head unit  40 K- 1  may have plural nozzle arrays. 
     A cross-sectional view showing the ejecting head of the image forming unit  40  will be described with reference to  FIGS. 5 and 6 .  FIG. 5  is a cross-sectional view showing an example of the ejecting head in the longitudinal direction of a liquid chamber  40 F of the image forming unit  40 .  FIG. 6  is a cross-sectional view showing the ejecting head in the lateral direction (nozzle sequence direction) of the liquid chamber  40 F of the image forming unit  40 .  FIG. 6  is a cross-sectional view when viewed along a line SC 1  in  FIG. 5 . 
     As shown in  FIG. 5 , the ejecting head is configured with a nozzle communication channel  40 R that is a flow channel communicating with a nozzle  40 N for ejecting a recording liquid droplet (ink droplet) and provided by jointing and stacking a flow channel plate  41  that is formed, for example, by anisotropically etching a single crystal silicon substrate, a vibrating plate  42 , which is jointed to the lower surface of the channel plate  41  and formed by means of, for example, nickel electroforming, and a nozzle plate  43  jointed to the top surface of the flow channel plate  41 , a liquid chamber  40 F that is a pressure generating chamber, an ink supplying port  40 S that is provided for supplying ink to the liquid chamber  40 F through a fluid resistance part (supplying channel) and communicating with a common liquid chamber  40 C, and the like. 
     Also, there are provided two lines of laminated-type piezoelectric elements  45 P as electromechanical elements that are pressure generating devices  45  (actuator devices) for pressurizing ink in the liquid chamber  40 F by deforming the vibrating plate  42 , and a base substrate  45 B for jointing and fixing the piezoelectric elements  45 P. 
     Additionally, supporting pillar parts are provided between the piezoelectric elements  45 P. 
     The supporting pillar parts are parts that are formed together with the piezoelectric elements  45 P by dividing and processing a piezoelectric member, but are simple supporting pillars since no driving voltage is applied thereon. 
     Also, FPC cables  45 C on which a driving circuit (driving IC) is mounted are connected to the piezoelectric elements  45 P. 
     Then, the peripheral portion of the vibrating plate  42  is connected to a frame member  44 , and recesses provided for a perforation part for accommodating an actuator unit composed of the piezoelectric elements  45 P, the base substrate  45 B and the like and the common liquid chamber  40 C and an ink supply port  40 IN for supplying ink from the outside to the common liquid chamber  40 C are formed on the frame member  44 . 
     The frame member  44  is formed by means of injection molding of, for example, a thermosetting resin, such as epoxy-type resins or a poly(phenylene sulphite). 
     Herein, the flow channel plate  41  is provided by forming recesses and holes that are provided for the nozzle communication channel  40 R and the liquid chamber  40 F by, for example, anisotropically etching a single crystal silicon substrate with a crystallographic orientation ( 110 ) using an alkaline etching liquid such as an aqueous solution of potassium hydroxide (KOH). However, it is not limited to the single crystal silicon substrate and others, such as a stainless substrate and photosensitive resins, may also be used. 
     The vibrating plate  42  is formed from a metal plate of nickel and fabricated by, for example, an electroforming method (electrocasting method), although other metal plates, jointing members of a metal and resin plates, and the like may also be used. The piezoelectric elements  45 P and the supporting pillar parts are jointed to the vibrating plate  42  with a bonding material and the frame member  44  is further jointed with a bonding material. 
     The nozzle plate  43  includes a nozzle with a diameter of 10-30 μm, which is formed so as to correspond to each liquid chamber  40 F, and is jointed to the flow channel plate  41  with a bonding material. 
     The nozzle plate  43  includes a water-repellent layer formed on the top surface of a desired layer on the surface of a nozzle forming member made of a metal member. 
     As shown in  FIG. 6 , the piezoelectric element  45 P is a laminated-type piezoelectric element (herein, a PZT) provided by laminating piezoelectric materials  45 Pp and internal electrodes  45 Pe alternately. 
     A separate electrode  45 Pei and a common electrode  45 Pec are connected to each of internal electrodes  45 Pe, which are alternately led to the different end faces of the piezoelectric element  45 P. 
     Additionally, in this embodiment, there is provided a configuration such that ink in the liquid chamber  40 F is pressurized by using a deformation of the piezoelectric element  45 P in directions of d 33  as directions of piezoelectricity, but there may also be provided a configuration such that ink in the pressurized liquid chamber  40 F is pressurized by using a deformation of the piezoelectric element  45 P in directions of d 31  as directions of piezoelectricity. 
     Also, there may also be provided a configuration such that one line of piezoelectric elements  45 P is provided on one substrate  45 B. 
     In a thus-configured liquid ejecting head, for example, when a voltage applied to the piezoelectric element  45 P is lower relative to a reference electric potential, the piezoelectric element  45 P is contracted and the vibrating plate  42  is lowered so as to increase the volume of the liquid chamber  40 F, whereby ink flows into the liquid chamber  40 F. Subsequently, the voltage applied to the piezoelectric element  45 P is increased so that the piezoelectric element  45 P extends in the directions of lamination, and the vibrating plate  42  is deformed toward the direction of the nozzle  40 N so as to decrease the volume of the liquid chamber  40 F. Thereby, recording liquid (ink) in the liquid chamber  40 F is pressurized so as to eject (jet) a drop of recording liquid (ink) from the nozzle  40 N. 
     Then, when the voltage applied to the piezoelectric element  45 P is set back to the reference electric potential, the vibrating plate  42  is restored to the initial state and the liquid chamber  40 F expands so as to generate a negative pressure. Then, the inside of the liquid chamber  40 F is filled with recording liquid (ink) from the common liquid chamber  40 C. 
     Then, after the vibration of a meniscus surface at the nozzle  40 N damps and is stabilized, transition to an operation for the next liquid drop ejection is made. 
     Additionally, the method for driving the head is not limited to the above example (pull-push-ejection), but pull-ejection or push-ejection may also be conducted depending on a method for providing a driving wave pattern. 
     Accordingly, the image forming apparatus  100  accordingly to this embodiment can form a full-color image or a monochrome image along the whole width of the image-forming range by the image forming unit  40  (the ejecting units  40 K,  40 C,  40 M, and  40 Y) during a single conveyance of the printing medium (roll sheet Md). 
     Additionally, the pressure generating device  45  is not limited to the above example (the piezoelectric element  45 P). That is, the pressure generating device  45  may include, for example, a thermal actuator including an electrothermal converter element, such as a heating resistor or the like applying a phase change in a liquid by film boiling, a shape memory alloy actuator applying metallic phase change by a temperature variation, and an electrostatic actuator applying electrostatic force generating a pressure for jetting a liquid droplet. 
     A Configuration of the Post-Processing Apparatus 
     The post-processing unit  50  is a unit for treating the printing medium on which an image was formed. The post-processing unit  50  may not be needed in some embodiments. 
     In this embodiment, the post-processing unit  50  treats a surface of the roll sheet Md on which an image was formed by the image forming unit  40 . The post-processing unit  50  treats the surface by a post-processing liquid. 
     As shown in  FIG. 3 , the post-processing unit  50  in this embodiment is arranged downstream from the image forming unit  40  in a printing medium conveyance direction Xm. The post-processing unit  50  includes post-processing head units  50 H, which are arranged in a staggered manner in the direction perpendicular to the printing medium conveyance direction. Furthermore, the post-processing unit  50  controls the amount of ejecting (applying) of the post-processing liquid by controlling a driving wave pattern inputting to the post-processing head units  50 H. This enables the post-processing unit  50  to eject (apply) the post-processing liquid to the whole width of the image forming range (printing range) of the roll sheet Md (printing medium). A description of the configuration of post-processing head unit  50 H will be omitted as it is similar to the configuration of the image forming unit  40  ( FIGS. 3 to 6 ). 
     The post-processing is a process of ejecting (depositing) the post-processing liquid onto the roll sheet Md (printing medium). The post-processing liquid is deposited in the shape of dots or stripes. This enables improvement of the abrasion resistance, glossiness, and preservation stability (the environment resistance, the water resistance, and the gas resistance, or the like) of the printing medium on which the image was formed. As shown in  FIG. 7 , when the post-processing unit starts the post-processing, a surface of the roll sheet Md was applied with the pre-processing liquid  20 L and the ink  40 Ink for forming an image was ejected onto the surface. The post-processing unit  50  of the image forming apparatus  100  according to this embodiment performs the process of ejecting (depositing) the post-processing liquid  50 L onto the roll sheet Md on which the image was formed. 
     Furthermore, the post-processing unit  50  of the image forming apparatus  100  according to this embodiment can eject the post-processing liquid  50 L to a smaller area than the surface area on which the pre-processing liquid  20 L was applied. The post-processing unit  50  of the image forming apparatus  100  according to this embodiment can eject the post-processing liquid  50 L to a smaller area than the surface area on which the image is formed. 
     That is, the post-processing liquid  50 L is ejected (deposited) to a smaller area than the surface area of applying of the pre-processing liquid  20 L. In  FIG. 7 , the ink  40 Ink is ejected to the entire area, and the post-processing liquid  50 L is ejected (deposited) to a smaller area than the entire area. 
     Additionally,  FIG. 7  shows that the post-processing liquid  50 L is formed in the shape of dots. However, the post-processing liquid may be formed in the shape of stripes in a direction perpendicular to the cross section. 
     As shown in  FIG. 7 , this embodiment requires that the post-processing liquid  50 L be ejected (deposited) to a smaller area than the surface area on which an image is formed. The post-processing liquid  50 L may be ejected (deposited) to the area on which an image is not formed or may not be ejected (deposited) to the area on which an image is not formed. 
     In case that the printing medium that is formed to the shape in  FIG. 7  is scraped against an object, a surface part of a layer of the post-processing liquid  50 L is scraped against the object. The post-processing liquid  50 L prevents not only the ink  40 Ink of the area on which the post-processing liquid  50 L is ejected from peeling off, but also the ink  40 Ink of the area on which the post-processing liquid  50 L is not ejected from peeling off, because the layer of the post-processing liquid  50 L has a certain thickness. 
     Accordingly, the image forming apparatus  100  according to an embodiment can eject (deposit) the post-processing liquid  50 L by the post-processing unit  50  to the printing apparatus (roll sheet Md) on which an image was formed. This enables the image forming apparatus  100  according to this embodiment to prevent the image (ink) printed on the printing medium (roll sheet Md) from peeling off by being scraped against an object (e.g., another printing medium), compared to when the post-processing liquid is not ejected (not deposited). That is, the image forming apparatus  100  can improve the abrasion resistance of the image to be formed on the printing medium by using the post-processing unit  50 . 
     Then, the image forming apparatus  100  can improve the quality of an image to be formed on the printing medium, because the post-processing unit  50  can deposit (eject) the post-processing liquid  50 L onto the printing medium (roll sheet Md) on which an image was formed. That is, the image forming apparatus  100  can reduce problems such as bleeding of the image, a problem of image density, a problem of image tone, an ink strike-through problem, a problem of water resistance, or a problem of environment resistance, because the post-processing unit  50  can deposit (eject) the post-processing liquid  50 L onto the printing medium on which an image was formed. 
     The post-processing unit  50  of the image forming apparatus  100  according to this embodiment preferably ejects (deposits) onto an area of the roll sheet Md on which an image was formed, as the post-processing method. Furthermore, the post-processing unit  50  preferably changes the amount of ejecting of the post-processing liquid  50 L and/or the method of ejecting, based on the type and/or the penetrability and/or the glossiness of the printing medium, and/or the type of the printing medium, and/or the amount of applied pre-processing liquid by the pre-processing unit  20 . 
     The post-processing unit  50  according to this embodiment can eject the post-processing liquid in a desired amount, to the shape of dots as desired, or to the shape of stripes as desired, to a desired area. 
     Specifically, the post-processing unit  50  can eject any area described as follows. The post processing unit  50  can eject to the area available for image forming. The post processing unit  50  can eject to the area on which an image was formed. The post processing unit  50  can eject to the area on which the ink droplets were ejected. The post-processing unit  50  can also eject to a slightly (1 dot or 2 dots) larger area than the area of the roll sheet Md (printing medium) on which an image was formed. Furthermore, the post-processing unit can eject to a percentage N of the selected area (as the shape of dots or stripes). 
     The percentage N may be from 5 percent to 50 percent. The percentage N may be decided by experiment or numerical calculations. 
     The post-processing unit  50  can decide the area of ejecting by using any decision method described as follows. The post-processing unit  50  can decide based on the coverage rate of printing. The post-processing unit  50  can decide based on the amount of ejecting of the post-processing liquid  50 L. The post-processing unit  50  may also decide that first the post-processing unit calculate the amount of ejecting of the post-processing liquid or the coverage rate of printing based on inputted information (printing image data or the like), and then the post-processing unit  50  decide based on the amount of the post-processing liquid ejected or the coverage rate of printing. 
     Accordingly, the post-processing unit  50  of the image forming apparatus according to an embodiment can eject (deposit) to an area related to the area on which an image was formed. This enables the image forming apparatus  100  according to this embodiment to shorten the time of post-processing and drying of the post-processing liquid. The image forming apparatus  100  according to this embodiment can reduce the amount of post-processing liquid compared to when the post-processing liquid is applied (ejected) to the entire surface of the printing medium. Furthermore, the image forming apparatus  100  according to this embodiment can reduce the cost of post-processing by reducing the amount of post-processing liquid compared to when the post-processing liquid is applied (ejected) to the entire surface of the printing medium. 
     Additionally, the post-processing method of the post-processing unit  50  is not particularly limited, and can be appropriately selected according to the type of post-processing liquid. The post-processing method of the post-processing unit  50  can be the pre-processing method of the pre-processing unit  20  or the ink ejecting method of the image processing unit  40 . Furthermore, from the viewpoint of downsizing of the image forming apparatus and the viewpoint of the storage stability of the post-processing liquid, the post-processing method of the post-processing unit  50  is preferably the same method of the ink ejecting method of the image forming unit. In case of ejecting the post-processing liquid, the post-processing liquid preferably includes a water-soluble organic solvent. The water-soluble organic solvent may include a wetting agent. The wetting agent is added for the purpose of preventing clogging in a nozzle of an ejecting head, which is caused by the drying of the recording liquid (ink) in the ink ejecting method of the image forming unit  40 . 
     The amount of the post-processing liquid on the roll sheet Md after drying is preferably from 0.5 g/m2 to 10 g/m2. The amount of the post-processing liquid on the roll sheet Md after drying is more preferably from 2 g/m2 to 10 g/m2. Additionally, in case that the amount of the post-processing liquid on the roll sheet Md after drying is less than 0.5 g/m2, the quality of the image (the abrasion resistance, glossiness, and preservation stability (the environment resistance, the water resistance, and the gas resistance, or the like)) may be reduced. In case that the amount of the post-processing liquid on the roll sheet Md after drying is more than 10 g/m2, the drying characteristics of the layer of the post-processing liquid (a protective layer) may be reduced because it may take a long time to dry. Furthermore, in case that the amount of the post-processing liquid on the roll sheet Md after drying is more than 10 g/m2, the quality of the image may be not improved any further, which may be economically unfavorable. 
     The post-processing unit  50  according to this embodiment can use a treating liquid that includes a material forming a clear protective layer on the roll sheet Md (printing medium) as the post-processing liquid. The treating liquid that includes a material forming a clear protective layer includes a water-based resin (a water-soluble resin or a water-dispersible resin), the water-soluble organic solvent (a wetting agent), a penetrating agent, a surfactant, water, and/or other components. The post-processing liquid may be an ultraviolet curing resin composition and/or a thermoplastic resin composition. Furthermore, for improving the glossiness and the fixability, the post-processing liquid is preferably a thermoplastic resin emulsion. This enables the post-processing unit  50  to improve the glossiness of a surface of the roll sheet Md on which an image was formed, or to protect the surface of the roll sheet Md by the resin layer, based on the method of the ejecting (applying). 
     Any type of water-based resin may be used depending on the desired purpose. For example, the following water-based resins may be used: acrylic resin, styrene-acrylic resin, urethane resin, acrylic silicone resin, and a fluorine resin. The contained amount of the water-based resin in the protective layer is preferably from 1% by mass to 50% by mass. Furthermore, in case of ejecting the post-processing liquid from the ejecting head, the contained amount of the water-based resin in the protective layer is preferably from 1% by mass to 30% by mass. Additionally, in case that the contained amount of the water-based resin is greater than the 50% by mass, viscosity of the post-processing liquid may be too high. In case that the contained amount of the water-based resin is less than the 1% by mass, the energy of the post-processing unit for drying the water in the post-processing liquid may increase. 
     The average particle diameter of the water-based resin in the post-processing liquid relates to the viscosity of the post-processing liquid. In case of the same composition, the average particle is smaller and the viscosity is greater. Accordingly, for preventing too great a viscosity of the post-processing liquid, the average particle diameter of the water-based resin is preferably larger than the 50 nm. 
     In case that the average particle diameter of the water-based resin in the post-processing liquid is tens of nanometers, the average particle diameter may be larger than the nozzle diameter. The average particle diameter is preferably smaller than the nozzle diameter (a diameter of the eject opening  40 N in  FIG. 3 ). Even though the average particle diameter of the water-based resin in the post-processing liquid is smaller than the diameter of the nozzle, in case of including the large diameter particle, the ability of ejecting may be deteriorated. 
     Accordingly, the average particle diameter of the water-based resin in the post-processing liquid is preferably smaller than 200 nm, more preferably smaller than 150 nm. 
     In case of using the water-soluble organic solvent (a wetting agent), the contained amount of the water-soluble organic solvent in the post-processing liquid is not particularly limited. The contained amount of the water-soluble organic solvent may be from 10% by mass to 80% by mass. The contained amount of the water soluble organic solvent is preferably from 15% by mass to 60% by mass. The water-soluble organic solvent (a wetting agent) is for example, 1,3-butadiene, glycerin, or the like. 
     Additionally, in case that the contained amount of the water-soluble organic solvent is greater than 80% by mass, the drying characteristics of the post-processing liquid on the printing medium may be deteriorated. In case that the contained amount of the water-soluble organic solvent is less than 10% by mass, the components of the post-processing liquid may be changed by mixing with the pre-processing liquid. 
     Penetrating agent and surfactant is not limited. The penetrating agent is, for example, 2-ethyl-1,3-hexanediol or the like. The surfactant is, for example, polyethylene oxide end-capped with perfluoroalkyl or the like. As the penetrating agent and the surfactant by using the post-processing unit  50 , penetrating agent and surfactant of including the pre-processing liquid using by the pre-processing unit  20  or the ink using by the image forming unit  40  can be arbitrarily selected. 
     Additionally, the post-processing liquid may include other components. The post-processing liquid may include, for example, wax, pH adjuster, antimicrobial agent, surface modifier, or antiforming agent. 
     The wax is for example, polyethylene wax or the like. The pH adjuster is for example, 2-amino-2-ethyl-1,3-propanediol or the like. The antimicrobial agent is for example, 1,2-benzothiazolyl-3-one or the like. The surface modifier is, for example, polyether modified poly-dimethyl-siloxane (BYK-Chemie) or the like. The antiforming agent is for example, 2,4,7,9-Tetramethyl-4,7-decanediol or the like. 
     A Configuration of the Sheet Discharging Unit 
     The sheet discharging unit  60  is a unit of discharging the printing medium on which an image was formed. As shown in  FIG. 1 , the sheet discharging unit  60  of this embodiment includes a sheet holder  61  and plural conveyance rollers  62 . The sheet discharging unit  60  using the conveyance rollers rolls up the roll sheet Md in the roller of the sheet holder. 
     Additionally, this embodiment has been described with an example of using the roll sheet as a printing medium, but other embodiments can use other printing media, and in case of using other printing media, the sheet discharging unit  60  can include other configurations. 
     Additionally, in case that the pressure to the roll sheet Md is high when the roll sheet Md is rolled up in the roller of the sheet holder  62 , a drying unit for drying the roll sheet Md may be disposed adjacent to the entrance of the sheet holder  62 , for preventing transfer of an image to the reverse side of the sheet. 
     A Configuration of the Controlling Unit 
     The controlling unit  70  is a unit for controlling the action of the image forming apparatus  100 . The controlling unit of this embodiment instructs each component in the image forming apparatus  100 , and controls the action of each component. The controlling unit  70  according to this embodiment will be described with reference to  FIGS. 8 to 12 . 
     Additionally, the image processing unit  100  may be a production printing system. The production printing system is a printing system able to print (form of image) a large volume of printing matter (document) in a short period of time, by efficiently controlling the job or the printing image data. Specifically, the image forming apparatus  100  (the controlling unit) according to this embodiment includes plural apparatuses. An apparatus controls the order of the printing job data, or transforms the printing job data to the raster image data (RIP process). The other apparatus performs printing based on the raster image data. 
     The image forming apparatus  100  (controlling unit  70 ) constructs a workflow system for managing production of printing job data to distribute the printing matter. That is, the image forming apparatus  100  (controlling unit  70 ) can more quickly process the workflow by distributing the process among the plural apparatuses. 
     As shown in  FIG. 8 , the controlling unit  70  of the image forming apparatus  100  according to this embodiment includes a superordinate apparatus  71  (DFE, Digital Front End, RIP apparatus, raster image processor, or the like) and a printer control apparatus  72 . The superordinate apparatus  71  produces the raster image data (RIP process), for example. The printer control apparatus  72  is included in a printing apparatus for printing. The superordinate apparatus  71  and the printer control apparatus  72  are connected via plural data lines  7 OLD and plural control lines  70 LC. 
     The superordinate apparatus  71  and the printer control apparatus  72  of the controlling unit  70  according to this embodiment will be explained below. 
     The Superordinate Apparatus 
     The superordinate apparatus  71  is an apparatus that produces the raster image data (RIP process) based on the printing job data (printing data, job data, or the like) that is received from the host apparatus. That is, the superordinate apparatus  71  produces the raster image data (hereinafter referred to as printing image data) corresponding to the ink colors, based on the printing data. The printing image data includes the data relating to ejecting of the post-processing liquid by the post-processing unit  50  (hereinafter referred to as the post-processing liquid image data). 
     The superordinate apparatus  71  produces the data for controlling the printing action (hereinafter referred to as control information data), based on the printing job data or the information of the host apparatus. The control information data include the type of printing, the form of printing, the information of the feeding and discharging of the sheet, the order of a surface of the printing, the size of the sheet for printing, the size of the data of the printing image data, the resolution, the type of the sheet, the tonal range, the information of the color, the number of the page, etc. The control information data includes the data of the ejecting of the post-processing liquid that is ejected by the post-processing unit  50  (hereinafter referred to as the post-processing control data). 
     As shown in  FIG. 9 , the superordinate apparatus of this embodiment includes the CPU (Central Processing Unit)  71   a , ROM (Read Only Memory)  71   b , RAM (Random Access Memory)  71   c , and HDD (Hard Disk Drive)  71   d . The superordinate apparatus  71  also includes an external interface  71   e , a control information interface  71   f , and an image data interface  71   g . Moreover, the superordinate apparatus  71  includes a bus  71   h  that connects to the CPU  71   a , etc. That is, the CPU  71   a , etc. in the superordinate apparatus  71  can communicate via the bus  71   h.    
     The CPU  71   a  controls the entire superordinate apparatus  51 . The CPU  71   a  controls the action of the superordinate apparatus  71  by using the control program in the ROM  71   b  and/or the HDD  71   d.    
     The ROM  71   b , the RAM  71   c , and the HDD  71   d  store data. The ROM  71   b  and/or the HDD  71   d  previously store the control program for controlling the CPU  71   a . The RAM  71   c  is used as the work memory of the CPU  71   a.    
     The external interface  71   e  controls communication with devices external to the image forming apparatus  100 . The external interface  71   e  can control the communication using TCP/IP (Transmission Control Protocol/Internet Protocol). 
     The control information interface  71   f  controls the communication of the control information data. The control information interface  71   f  can control communication corresponding to the PCI Express (Peripheral Component Interconnect Bus Express). 
     The imaged data interface  71   g  controls the communication of the printing image data. The image data interface  71   g  can control the communication corresponding to the PCI Express in case that high-speed transfer is required. The image data interface  71   g  includes plural channels corresponding to each color of the printing image data. 
     The superordinate apparatus  71  of the controlling unit  70  according to this embodiment receives the printing job data from the host apparatus by the external interface  71   e , then the superordinate apparatus  71  stores the printing job data to the HDD  71   d  using the CPU  71   a . The superordinate apparatus  71  reads the printing job data from the HDD  71   d  using the CPU  71   a . Furthermore, the superordinate apparatus  71  produces the plural raster image data of each color (Yellow (Y), Cyan (C), Magenta (M), and Black (B)), then the superorinate apparatus  71  stores each color of the raster image data to the RAM  71   c . At this time, the superordinate apparatus  71  (controlling unit  70 ) can produce each color raster image data by rendering the PDL (Page Description Language) as the RIP processing, then the superordinate apparatus  71  stores the data to the RAM  71   c.    
     Next, the superordinaete apparatus compresses and encodes the each color raster image data and the superordinate apparatus  71  stores the data to the HDD  71   d.    
     When the print controlling apparatus starts the print action, the superordinate apparatus  71  (CPU  71   a ) reads each raster image data from the HDD  71   d , then the superordinate apparatus  71  decodes each raster image data and stores, to the RAM  71   c , each raster image data which is decoded. Next, the superordinate apparatus  71  reads each color raster image data from the RAM  71   c , then the superordinate apparatus  71  outputs each color raster image data to the printer control apparatus  72  via each channel of the image data interface  71   g . The superordinate apparatus  71  can output the printing image data to the printer control apparatus  72  via plural data lines  7 OLD ( 7 OLD-Y,  7 OLD-C,  7 OLD-M, and  7 OLD-K) in  FIG. 8 , corresponding to the colors. 
     The superordinate apparatus  71  receives and sends the control information data to the printer control apparatus  72  via the control information interface  71   f  (control lines  70 LC) corresponding to the progression of the printing action. 
     Furthermore, when the printer control apparatus starts the post processing, the superordinate apparatus  71  according to this embodiment reads the encoded post-processing liquid image data from the HDD by the CPU  71   a . The superordinate apparatus  71  outputs to the printer control apparatus  72  via the data line  70 LD-P ( FIG. 10 ) 
     The Printer Control Apparatus 
     The printer control apparatus  72  of the controlling unit  70  according an embodiment is an apparatus for controlling the action of forming an image on the printing medium based on the printing image data and the control information data. 
     As shown in  FIG. 10 , the printer control apparatus  72  of this embodiment includes the printer controller  72 C and the printer engine  72 E. 
     The printer controller  72 C controls the action of the printer engine  72 E. The printer controller  72 C receives and sends the control information data, etc. to the superordinate apparatus  71  via the control line  70 LC. The printer controller  72 C receives and sends the control information data, etc. to the printer engine  72 E via the control line  72 LC. This enables the printer controller  72 C to write the various printing conditions that are included the control information data to the register of a print control unit  72 Cc, and store the printing conditions. The printer controller  72 C can control the printer engine  72 E based on the control information data, and print corresponding to the printing job data (control information data). 
     As shown in  FIG. 10 , the printer controller  72 C of this embodiment includes a CPU  72 Cp and a print control unit  72 Cc. The CPU  72 Cp and the print control unit  72 Cc are connected via a bus  72 Cb in the printer controller  72 C. The bus  72 Cb is connected to the control lines  70 LC via a communication interface. 
     The CPU  72 Cp controls the action of the entire printer control apparatus  72  using a control program stored in a ROM. The print control unit  72 Cc receives and sends the command or the status information to the printer engine  72 E based on the control information data that is received from the superordinate apparatus  71 . This enables print control unit  72 Cc to control the action of the printer engine  72 E. 
     The printer engine  72 E controls the action of forming an image on the printing medium based on the printing image data that is received from the superordinate apparatus  71  and the control information data that is received from the printer controller  72 C. The printer engine  72 E controls the action of the post-processing based on the printing image data (post-processing liquid image data) that is received from the superordinate apparatus  71  and the control information data (post-processing control data) that is received from the printer controller  72 C. 
     As shown in  FIG. 10 , the printer engine  72 E is connected to the plural data lines  7 OLD ( 7 OLD-Y,  7 OLD-C,  7 OLD-M,  70 LD-K, and  70 LP-P). The printer engine  72 E receives the printing image data from the superordinate apparatus  71  via the plural data lines ( 7 OLD-C) or the like. This enables the printer engine  72 E to control the action of forming image data and performing the post-processing based on the printing image data that is received. 
     As shown in  FIG. 10 , the printer engine  72 E of this embodiment includes plural data storing units  72 EC,  72 EM,  72 EY,  72 EK, and  72 EP. The printer engine  72 E includes an image output unit  72 Ei which receives data from the data storing unit  72 C etc., and a conveyance control unit  72 EC that controls the conveying of the printing medium. Furthermore, the printer engine  72 E of this embodiment includes a post-processing liquid output unit  72 Ep, which receives the post-processing liquid image data from the data storing unit  72 EP, and a post-processing drying control unit  72 Epb, which controls the drying unit  30  ( FIG. 1 ). 
     Additionally, the printer engine  72 E may include a pre-processing control unit  72 Epc, a pre-processing drying control unit  72 Epd, and pre-roll-up drying control unit  72 Epe. 
     The configuration of the data storing unit  72 EC will be explained with reference to  FIG. 10 . Additionally, the configuration of the other data storing units  72 EM,  72 EY,  72 EK, and  72 EP will be omitted since they are similar to the configuration of the data storing unit  72 EC. 
     As shown in  FIG. 11 , the data storing unit  72 EC includes a logic circuit  72 EC 1  and a memory unit  72 ECm. The data storing unit  72 EC (the logic circuit  72 ECI) is connected to the superordinate apparatus  71  via the data line  70 LD-C. The data storing unit  72 EC (the logic circuit  72 ECI) is connected to the printer controller  72 C (print control unit  72 Cc) via the control line  72 LC. 
     The logic circuit  72 EC 1  stores the printing image data to the memory unit  72 ECm, which is outputted from the superordinate apparatus  71 , based on the control signal, which is outputted from the printer controller  72 C (print control unit  72 Cc). Based on the control signal that is outputted from the printer controller (print control unit  72 Cc), the logic circuit  72 EC 1  reads the printing image data Ic ( FIG. 7 ) from the memory unit  72 ECm corresponding to cyan (C), and outputs to the image output unit  72 Ei. Additionally, the logic circuit  72 EC 1  (data storing unit  72 EP) outputs the post-processing liquid image data Ip ( FIG. 7 ) to the post-processing liquid output unit  72 Ep. 
     The memory unit  72 ECm can have a capacity that is able to store the image data of three pages or more. The three pages printing image data includes printing image data corresponding to the page that is receiving from the superordinate apparatus  71 , and printing image data corresponding to the page that is sending to the image output unit  72 Ei, and printing image data corresponding to the next sending page. 
     Additionally, the data storing unit  72 EC may use a hardware logical circuit that is configured by the combination of plural logical circuits. This enables the data storing unit  72 EC to perform the process at a higher speed. The data storing unit  72 EC may decide a process to perform by logical determination based on the control signal of the bit sequence, for example. 
     The configuration of the image output unit  72 Ei will be described with reference to  FIG. 12 . Additionally, the configuration of the post-processing liquid output unit  72 Ep will be omitted as it is similar to the configuration of the image output unit  72 Ei. 
     As shown in  FIG. 12  the image output unit  72 Ei includes the output control unit  72 Eic. The output control unit  72 Eic outputs each printing image data to each ejecting head  40 C,  40 M,  40 Y, and  40 K ( FIG. 3 ) corresponding to the color of the printing image data. This enables the output control unit  72 Eic to control the action of the ejecting head  40 C etc., based on the printing image data. 
     Specifically, the output control unit  72 Eic individually controls the plural ejecting heads  40 C,  40 M,  40 Y, and  40 K. The output control unit  72 Eic may simultaneously control the plural ejecting heads  40 C,  40 M,  40 Y, and  40 K, based on the printing image data (for example, Ic in  FIG. 12 ). Furthermore, the output control unit  72 Eic may control the ejecting head  40 C, etc. based on the control signal that is inputted from a control apparatus. The output control unit  72 Eic may control the ejecting head  40 C, etc. based on the operation input of the user. 
     Accordingly, the printer control apparatus  72  inputs to the plural ejecting heads  40 C, etc. the printing image data that is outputted from the superordinate apparatus, by using the data storing unit  72 EC and the output control unit  72 Eic. At this time, the printer control apparatus  72  can individually control each color printing image data. The printer control apparatus  72  can change the configuration of the printer engine  72 E corresponding to the number of colors of the printing image data (C, M, Y, and K or K only) or the number of ejecting heads. That is, the printer control apparatus  72  in the image forming apparatus  100  according to this embodiment can reduce the cost and downsize the apparatus by mounting only the data storing unit  72 EC that is needed and the ejecting head  40 C that is needed. 
     For example, in case of forming the full-color image using C, M, Y, and K, the printer control apparatus  72  in the image forming apparatus  100  according to this embodiment can have all of the data storing units  72 EC, etc. This enables the printer control apparatus  72  in the image forming apparatus  100  to connect to the ejecting heads  40 C, etc. each output from the data storing units  72 EC, etc. by the output control unit  72 Eic. 
     For example, in case of forming the image using K only, the printer control apparatus  72  in the image forming apparatus  100  can have one data storing unit  72 EK and one ejecting head  40 K, giving priority to the cost. This enables the printer control apparatus in the image forming apparatus  100  to connect to the ejecting head  40 K the output from the data storing unit  72 EK by the output control unit  72 Eic. 
     Furthermore, for example, in case of forming the image by K only, the printer control apparatus  72  in the image forming apparatus  100  can have one data storing unit  72 EK and four ejecting heads giving priority to the speed of printing. 
     This enables the printer control apparatus  72  in the image forming apparatus  100  to connect the output from the data storing unit  72 EK to each of the four ejecting heads by the output control unit  72 Eic. 
     In this case, the printer control apparatus  72  in the image forming apparatus  100  can form an image at a speed four times the speed of using one ejecting head, by forming one color (K) using four ejecting heads. 
     Controlling the Amount of Applying of the Pre-Processing Liquid, Controlling the Dry Strength 
     In this embodiment, the pre-processing control unit  72 Epc of the controlling unit controls the applied amount of the pre-processing liquid based on the resolution of an image formed on the printing medium, and the pre-processing dry control unit  72 Epd of the controlling unit controls the dry strength based on the resolution of an image formed on the printing medium. 
     The diameter of ink and the ease of drying change based on the resolution of an image formed on the printing medium. For example, when a low resolution image is formed, the diameter of an ink dot is large compared to when a high-resolution image is formed, and ink dots are difficult to dry because an ink dot has a large volume relative to surface area. Because the printing speed is high compared to when the high-resolution image is formed and ink dots are difficult to dry and penetrate, the bleeding of the image can easily occur. 
     Because of changing the necessary applied amount of the pre-processing liquid based on the resolution of an image formed on the printing medium, the controlling unit  70  of the image forming apparatus  100  improves quality of an image and reduces the bleeding by applying the right amount of the pre-processing liquid corresponding to the resolution. 
     Furthermore, the controlling unit  70  of the image processing unit  100  according to this embodiment can prevent the contraction of the printing medium by preventing over drying of the pre-processing liquid, and can prevent the degrading of quality of the image by preventing under drying of the pre-processing liquid, by controlling the dry strength of the pre-processing liquid drying unit  31  based on the resolution of an image to be printed. That is, the image forming apparatus  100  according to this embodiment can improve the image quality (printing quality). 
     The speed of conveying the printing medium is set to slow by the controlling unit  70  of the image forming apparatus  100 , because a number of the dots that are formed by the image forming unit  40  is increased when a high resolution image is formed. As shown in  FIG. 1 , the time of passing through the drying unit is long when the speed of conveying the printing medium is slow, because the drying unit  30  and the image forming apparatus  40  are arranged in the same conveyance line. Accordingly, the drying unit  30  of the image processing unit  100  according to this embodiment can prevent the contraction of the printing medium by preventing over drying of the pre-processing liquid, by controlling the dry strength of the pre-processing liquid drying unit  31  based on the resolution of an image to be printed. 
     The print control unit  72 Cc receives the resolution of the image from the superordinate apparatus  71 . 
     The amount to be applied of the pre-processing liquid may be stored in association with the resolution, and the amount to be applied of the pre-processing liquid may be read when printing. The amount to be applied of the pre-processing liquid may be determined based on the operation input of the user. 
     The pre-processing liquid  20  using the roll coating method can adjust (control) the amount to be applied of the pre-processing liquid by changing (controlling) the nip pressure or the rotation speed of the applying roller  23  and/or the platen roller  24 . 
     The drying strength may be stored in association with the resolution, and the drying strength may be read when printing. The drying strength may be determined based on the operation input of the user. 
     The drying unit  30  according to present embodiment is not limited to the above example. 
     As shown in  FIG. 13 , the drying unit  30  of this embodiment uses plural heating rollers  311 ,  312 ,  313 ,  314 ,  315 , and  316 . 
     The drying unit lowers the temperature of the heating roller  311  ( 312 , etc), when the drying unit lowers the drying strength. For example, the drying unit  30  lowers the temperature when using ink that has a low penetrability, and raises the temperature when using ink that has a high penetrability. The drying unit  30  heats the heating unit  311  (or  312 , or the like) from 40 degree C. to 80 degrees C., for example. 
     Furthermore, the drying unit  31  may control the drying strength by controlling the number of heating rollers that are used, so that the heating roller  311  and the heating roller  312  are heated, and the other heating rollers are not heated. Additionally, the drying unit  30  can control the drying strength by controlling both the temperature of the heating rollers and the number of rollers that are used, and can control the temperature of the heating rollers or the number of the heating rollers that are used separately. 
     Accordingly, the controlling unit  70  can increase the applied amount of the pre-processing liquid and the drying strength according to a decrease in the resolution of an image. 
     The controlling unit  70  can decrease the applied amount of the pre-processing liquid and the drying strength according to an increase in the resolution of an image. 
     This enables the controlling unit  70  of the image forming apparatus  100  to improve quality of an image and reduces the bleeding by applying the right amount of the pre-processing liquid corresponding to the resolution. Furthermore, the controlling unit  70  can prevent the contraction of the printing medium by preventing over drying of the pre-processing liquid, and can prevent the degrading of quality of the image by preventing under drying of the pre-processing liquid. 
     The controlling unit  70  can control further based on type of the printing medium. 
     The type of the printing medium includes the penetrability and/or the glossiness and/or the thickness of the printing medium. The type of the printing medium is not only the class, such as recycled paper, good quality paper, and heavy paper, but may be a trade name and/or a manufacturer&#39;s name. 
     In case that the type of the printing medium is heavy paper, the controlling unit  70  can increase the applied amount of the pre-processing liquid and the drying strength. In case of heavy paper, the absorbed amount is high. In case that the absorbed amount is high, the controlling unit  70  increases the applied amount of the pre-processing liquid. So, when the amount is increased, the controlling unit  70  raises the drying strength because of the difficulty in drying. 
     In case the type of the printing medium is high penetrability paper, the controlling unit  70  can increase the applied amount of the pre-processing liquid and the drying strength. In case the penetrability is high, the controlling unit  70  increases the applied amount of the pre-processing liquid. So, when the amount is increased, the controlling unit  70  increases the drying strength because of the difficulty in drying. 
     Accordingly, the image forming apparatus  100  can apply the appropriate amount of the pre-processing liquid, and can use the most appropriate drying condition of the printing medium before the image forming process, by controlling the pre-processing unit and the drying unit based on the resolution and type of the printing medium. This further enables the controlling unit  70  of the image forming apparatus  100  to improve the quality of an image and reduces the bleeding by applying the right amount of the pre-processing liquid corresponding to the resolution. Furthermore, the controlling unit  70  can further prevent the contraction of the printing medium by preventing over drying of the pre-processing liquid, and can prevent the degrading of quality of the image by preventing under drying of the pre-processing liquid. 
     The controlling unit  70  can store an amount to be applied of the pre-processing liquid and the drying strength corresponding to the resolution and the type of the printing medium. The controlling unit  70  can refer to the amount to be applied of the pre-processing liquid and the drying strength corresponding to the inputted resolution and the inputted type of the printing medium. Then, the controlling unit  70  can control the amount to be applied of the pre-processing and the drying strength based on input data. 
     The type of the printing medium can be inputted to the image forming apparatus  100  by a user. Specifically, the image forming apparatus  100  may receive the type of the printing medium from the operation input of the user using the UI (User Interface) or the like. In that case, the superordinate apparatus  71  can send control information data to the printer control apparatus  72  corresponding to the inputted information, and the printer control apparatus  72  can control the pre-processing control unit  72 Epc and the pre-processing dry control unit  72 Epd based on the control information data. The printer control unit  72  may have an external input device. In that case, the printer control unit  72  may receive the type of printing medium from the external input device. 
     The controlling unit  70  can increase the drying strength of the drying unit  30  by increasing the applied amount of the pre-processing liquid. The controlling unit  70  can decrease the drying strength of the drying unit  30  by decreasing the applied amount of the pre-processing liquid. This enables the controlling unit  70  of the image forming apparatus  100  to improve the quality of an image and reduces the bleeding and the contraction of the printing medium by preventing over drying of the pre-processing liquid, and can prevent the degrading of quality of the image, by controlling the most appropriate drying condition of the printing medium on which the pre-processing liquid was applied. This enables the image forming unit  40  to stably form an image. In some instances, this enables the post-processing unit  50  to stably apply (eject) the post-processing liquid. 
     In another embodiment, an image forming method of an image forming apparatus according will be explained. 
     The image forming apparatus of this embodiment can use the image forming apparatus  100  described above. 
     A configuration of the image forming apparatus of this embodiment is shown in  FIGS. 1 to 6 . 
     As shown in  FIGS. 1 to 6 , a description of the configuration of the image forming apparatus will be omitted because it is similar to the image forming apparatus described above. 
     A configuration of a controlling unit  70  of the image forming apparatus  100  according to this embodiment is shown in  FIGS. 7 to 12 . 
     As shown in  FIGS. 7 to 12 , a description of the configuration of the controlling unit  70  of the image forming apparatus  100  according to this embodiment will be omitted because it is similar to the controlling unit  70  described above. 
     The operation of forming an image by the image forming apparatus  100  according to this embodiment will be described with reference to  FIGS. 14 and 15 . 
     As shown in  FIG. 14 , the image forming apparatus  100  according to this embodiment, in step S 1401 , initiates forming an image, based on printing job data that is inputted from a device external to the image forming apparatus  100 . The image forming apparatus  100  stores the printing job data, which is inputted to the HDD  71   d  of the superordinate apparatus  71 . 
     Then, in step S 1402 , the image forming apparatus  100  determines the type of the printing medium by the controlling unit  70 , and stores (sets) the determined type of printing medium to the HDD  71   d  of the superordinate apparatus  71 . 
     At this time, the controlling unit  70  may store the information of the printing medium, including (a physical property value of the printing medium (a material, a thickness, a basis weight of the paper, or the like). The controlling unit  70  may store the type of the printing medium related to the pre-stored type of the printing medium in the HDD  71   d  of the superordinate apparatus  71 . This enables the controlling unit  70  to read the type of the printing medium by using the related type. Additionally, the image forming apparatus  100  can pre-store the type of the printing medium to the HDD  71   d  of the superordinate apparatus based on the operation input of the user. Additionally, when the image forming apparatus  100  does not use the type of the printing apparatus as a parameter of control, the image forming apparatus  100  does not need to perform step S 1402 . 
     Then, in step S 1403 , the image forming apparatus  100  produces the printing image data and the control information data, or the like by the superordinate apparatus  71  of the controlling unit  70 . Specifically, the superordinate apparatus  71  of the controlling unit  70  produces the printing job data and the control information data based on at least the resolution of the image in the printing job data, which is stored in the HDD  71   d , or the like. 
     Then, in step S 1404 , the image forming apparatus  100  calculates the amount of the pre-processing liquid (the amount to be applied of the liquid in this embodiment), and the drying strength (pre-processing liquid drying strength) by the controlling unit  70 . 
     Specifically, the controlling unit  70  calculates the amount to be applied of the pre-processing liquid  20 L by the pre-processing unit  20  and the drying strength of the drying unit  30  based on at least the resolution of the image. The controlling unit  70  can calculate the amount to be applied of the pre-processing liquid  20 L and the drying strength by further using the type of printing medium. When the resolution of the forming image is high, the controlling unit  70  can reduce the amount to be applied of the pre-processing liquid  20 L. When the resolution of the forming image is low, the controlling unit  70  can raise the amount to be applied of the pre-processing liquid  20 L. 
     Furthermore, when the resolution of the forming image is high, the controlling unit  70  can reduce the drying strength by the drying unit  30 . When the resolution of the forming image is low, the controlling unit  70  can increase the drying strength by the drying unit  30 . 
     That is, the controlling unit  70  can calculate an amount to be applied of the pre-processing liquid  20 L based on the resolution of the formed image. This enables the controlling unit  70  of the image forming apparatus  100  to improve the quality of an image and reduce the bleeding and the contraction of the printing medium by preventing over drying of the pre-processing liquid, and can prevent the degrading of the quality of the image, by controlling the most appropriate drying condition of the printing medium on which the pre-processing liquid was apply applied. This enables the image forming unit  40  to stably form an image. 
     In case of ejecting the post-processing liquid, the controlling unit  70  can calculate an amount of ejecting (applying) of the post-processing liquid in step S 1404 . The controlling unit  70  can calculate the amount of ejecting (applying) of the post-processing liquid based on resolution of an image, type of the printing medium, and the amount of applying the pre-processing liquid. 
     This enables the image forming apparatus  100  to improve the abrasion resistance by controlling the amount of ejecting (applying) of the post-processing liquid  50 L. 
     Additionally, the controlling unit  70  can set the amount to be applied of the pre-processing liquid  20 L to 1.5 g/m2 or more, when increasing the amount to be applied of the pre-processing liquid  20 L. The controlling unit  70  can set the amount to be applied of the post-processing liquid  50 L to 1.2 g/m2 or more, when increasing the amount to be applied of the post-processing liquid  50 L. Alternatively, the controlling unit  70  can set the amount to be applied of the pre-processing liquid  20 L to less than 1.5 g/m2, when reducing the amount to be applied of the pre-processing liquid  20 L. The controlling unit  70  can set the amount to be applied of the post-processing liquid  50 L to less than 1.2 g/m2, when reducing the amount to be applied of the post-processing liquid  50 L. The controlling unit  70  doesn&#39;t need to apply and eject, when reducing the amount to be applied of the pre-processing  20 L and the amount of ejecting of the post-processing liquid  50 L. Furthermore, the controlling unit  70  may change the amount to be applied of the pre-processing liquid  20 L and the amount of ejecting of the post-processing liquid  50 L, corresponding to a physical property value of the printing medium or the like. 
     The image forming apparatus  100  performs step S 1405  after calculating the amount of the pre-processing liquid  20 L and the drying strength (and the amount of the post-processing liquid  50 L in some instances). 
     Then, in step S 1405 , the image forming apparatus  100  feeds the printing medium to the pre-processing unit  20  by using the sheet feeding unit  10  ( FIG. 1 ). Additionally, the image forming apparatus  100  may initiate step S 1405  soon after the initiation of step S 1401 . The image forming apparatus  100  performs step S 1406  after initiating the feeding. 
     In step S 1406 , the image forming apparatus  100  performs the pre-processing by using the pre-processing unit  20  ( FIG. 2 ). Specifically, the pre-processing unit  20  controls the nip pressure based on the amount to be applied of the pre-processing liquid  20 L, which is calculated in step S 1404  by using the pressure controller  25 , and controls (changes) the amount to be applied of the pre-processing liquid  20 L (the thickness of the liquid film, etc.). Additionally, the pre-processing unit  20  may control the amount to be applied of the pre-processing liquid  20 L by changing the rotation speed of the applying roller  23  ( FIG. 2 ). This enables the image forming apparatus  100  to reduce the bleeding of the formed image by controlling the amount to be applied of the pre-processing liquid  20 L. 
     As shown in  FIG. 15 , the image forming apparatus  100  can make the granularity of an ink dot to be small, by raising the amount to be applied of the pre-processing liquid  20 L. That is, in the image forming apparatus  100 , the granularity of ink dots can be less than a predetermined granularity Rs, by increasing the applied amount of the pre-processing liquid  20 L. The predetermined granularity Rs can be the granularity of the difficulty to bleed an ink on the printing medium. The predetermined granularity Rs can be determined in an experiment or by numerical calculations. Then, the image forming apparatus  100  feeds the printing medium to the drying unit  30  (the pre-processing liquid drying unit  31  in  FIG. 1 ). 
     In step S 1407 , the image forming apparatus  100  dries the printing medium by using the pre-processing liquid drying unit  31  ( FIG. 1 ). The pre-processing liquid drying unit  31  dries the printing medium based on the pre-processing liquid drying strength, which was determined in step S 1404 . Specifically, the pre-processing drying unit  31  dries the printing medium based on at least the resolution of an image that is formed on the printing medium. The pre-processing drying unit  31  can dry the printing medium further using the type of the printing medium. 
     As shown in  FIG. 13 , the drying unit  30  (the pre-processing drying unit  31 ) can control the drying strength by controlling both the temperature of the heating roller and the number of rollers that are used, and can control the temperature of the heating roller or the number of the heating rollers that are used separately. The method of drying of the drying unit  30  (the pre-processing drying unit  31 ) is not limited to this method. 
     Then, the image forming apparatus  100  feeds the printing medium to the image forming unit  40  ( FIGS. 1 ,  4 , and  5 ). 
     In step S 1408 , as an image forming step, the image forming apparatus  100  forms an image on a surface of the printing medium by using the image forming unit  40 , based on the printing image data that was produced (in step S 1403 ). The image forming unit  40  may form an image by further using the resolution of the forming image and the type of the printing medium. The image forming unit  40  can control the action of the image forming by controlling the voltage applied to the piezoelectric element  45 P (the pressure generating device  45  in  FIGS. 6 and 7 ) 
     Then, the image forming apparatus  100  feeds the printing medium to the post-processing unit  50  ( FIG. 1 ). Additionally, when the post-processing is not performed, the image forming apparatus does not perform step S 1409 , and performs step S 1410 . In this case, the image forming apparatus does not need to perform step S 1410 . 
     In step S 1409 , as a post-processing step, the image forming apparatus  100  treats the printing medium by using the post-processing unit  50 . 
     Specifically, the post-processing unit  50  ejects (deposits) the post-processing liquid  50 L onto a specify area in the area of forming an image of the printing medium, based on the post-processing liquid image data (in step S 1403 ) and the amount of ejecting of the post-processing liquid that was calculated (in step S 1404 ). The post-processing unit  50  can control the amount of ejecting of the post-processing liquid  50 L on the printing medium by using the post-processing liquid output unit  72 Ep of the controlling unit  70 , based on the post-processing liquid image data. 
     Then, the image forming apparatus  100  feeds the printing medium to the drying unit  30  (the post-processing liquid drying unit  32  in  FIG. 1 ). 
     Additionally, when the post-processing is not performed, the image forming apparatus performs step S 1410 , because the drying unit  30  (post-processing liquid, drying unit) dries not only the post-processing liquid but also dries the image that was formed in the image forming step. In this case, the image forming apparatus does not need to perform step S 1410 . 
     In step S 1410 , the image forming apparatus  100  dries the printing medium by using the post-processing liquid drying unit  32  (heating roller). The post-processing liquid drying unit  32  dries the printing medium based on the post-processing liquid drying strength, which was determined in step S 1406 . Specifically, the post-processing drying unit  31  dries the printing medium based on at least resolution of an image that is formed on the printing medium. The post-processing drying unit  31  can dry the printing medium further using the type of the printing medium, the amount to be applied of the pre-processing liquid (and the amount of ejecting (applying) of the post-processing liquid in some instances). 
     Then, in step S 1411 , the image forming apparatus  100  discharges the printing medium by using the sheet discharging unit  60  ( FIG. 1 ). 
     Then the image forming apparatus  100  completes the image forming operation. 
     Accordingly, the image forming apparatus  100  according to this embodiment can obtain the same effect as the image forming apparatus  100  in the above described embodiments. 
     The foregoing description of the embodiments has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the inventions to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teachings. It is therefore intended that the scope of the inventions be limited not by this detailed description, but rather by the claims appended hereto.