Patent Publication Number: US-7717551-B2

Title: Image forming method and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming method and an image forming apparatus, and more particularly to image formation technology in an image forming apparatus for forming a desired image on a medium by reacting an image forming liquid such as ink with a treatment liquid and fixing the image forming liquid onto the medium. 
     2. Description of the Related Art 
     In recent years, inkjet recording apparatuses have become common as image forming apparatuses which form images, such as photographic images, documents, or the like, on a medium. An inkjet recording apparatus forms a desired image on a medium by ejecting droplets of ink from nozzles, by driving ejection elements provided in the print head in accordance with data. 
     Depending on the type of medium and the type of ink, when the ejected ink droplets permeate into the media, bleeding or spreading of the formed dots may occur, thus leading to a marked decline in the quality of the image formed. In order to prevent image deterioration caused by bleeding or spreading of dots in this way, a system has been proposed which uses a radiation-curable ink whose curing (fixing) is promoted by the irradiation of radiation, such as ultraviolet light or an electron beam, onto the ink droplets ejected onto the media. 
     Japanese Patent Application Publication No. 10-287035 discloses an inkjet recording method, a recorded object, and an inkjet recording apparatus where printing is carried out by depositing a reactive solution containing a photopolymerization initiator, and an ink composition containing an acrylate monomer and an oligomer, onto a recording medium, and thereby print bleeding and print non-uniformities are suppressed so as to prevent color bleeding, which is uneven color mixing occurring at the boundary regions between the different colors used in the color inkjet recording method. 
     Japanese Patent Application Publication No. 2003-12971 discloses an inkjet recording method whereby printing is carried out by depositing an ink composition containing 30% to 98% (wt %: weight percentage) of a polymer compound and a coloring material, and a reactive liquid containing a polymer compound and a polymerization initiator, onto a recording medium, and thereby print bleeding and print non-uniformities are suppressed so as to prevent color bleeding, which is uneven color mixing at the boundary regions between the different colors in the color inkjet recording method. 
     Furthermore, Japanese Patent Application Publication No. 2000-135781 discloses an inkjet recording apparatus, an image forming method, and ink composition where at least a portion of the image is formed by mixing and curing a first ink composition and a second ink composition, in such a manner that a clear and highly detailed image can be recorded, even onto normal paper which has not received special processing. 
     However, according to a method whereby an ink droplet is ejected onto a treatment liquid deposited onto the media, the surface of the treatment liquid on the media onto which the ink droplets are ejected is not a completely flat surface, but rather the perimeter sections thereof in particular have a gradient, and hence the ink droplets deposited onto the treatment liquid may move due to this gradient. In this way, the dots are not formed at the prescribed positions, due to the movement of the ink arising at the perimeter sections of the treatment liquid, and this affects the quality of the image formed on the media. 
     Furthermore, if an organic solvent having the high boiling point is used for the solvent of the treatment liquid, then the unreacted treatment liquid which is not incorporated into the polymer compound (monomer, oligomer, or the like) in the ink, does not cure and remains on the surface of the media. Moreover, if the treatment liquid is deposited over a broader range than the ink droplet ejection range in such a manner that an ink droplet is not ejected onto the perimeter sections of the treatment liquid, then the amount of unreacted treatment liquid remaining on the surface of the media increases. 
     Japanese Patent Application Publications No. 10-287035, No. 2003-12971, and No. 2000-135781 do not disclose or suggest a concrete method for preventing landing interference in the case of high-speed printing. Landing interference means, for example, a phenomenon that a liquid droplet of ink moves and becomes fixed at a position different from its originally intended landing position or a phenomenon that the shape of the liquid ink droplet is deformed and disrupted, due to combination between liquid ink droplets on the surface of the recording medium, before fixing, and immediately after the ink droplets have landing on the recording medium. If landing interference occurs on the recording medium, in the cases of ink droplets of the same color, a density non-uniformity may become visible, and the line quality may decline. Furthermore, in the cases of inks of different colors, color bleeding may occur. 
     SUMMARY OF THE INVENTION 
     The present invention is conceived in view of the aforementioned circumstances, an object thereof being to provide an image forming method and an image forming apparatus, in order that a desirable image can be formed on a medium, by preventing the occurrence of image degradation due to landing interference on the medium, especially in the case of high-speed printing. 
     In order to attain the aforementioned object, the present invention is directed to an image forming method comprising the steps of: depositing a first liquid containing at least a dispersion inhibitor, a polymerization initiator, and a high-boiling-point organic solvent, onto an image forming region of a recording medium where an image is to be formed according to image data, and onto a peripheral region of the image forming region; ejecting a second liquid containing at least a radiation-curable polymer compound and a coloring material, onto the recording medium according to the image data after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region; ejecting a third liquid containing at least a radiation-curable polymer compound, onto at least the peripheral region of the image forming region after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region, the third liquid having a transparent color, the same color as the recording medium, or a similar color to the recording medium; and irradiating radiation onto the first liquid, the second liquid and the third liquid on the recording medium. 
     According to this aspect of the present invention, the second liquid ejected on the basis of the image data is deposited onto the first liquid, and consequently it is possible to prevent landing interference of the second liquid by means of the high-boiling-point organic solvent and the dispersion inhibitor which are components of the first liquid. If the deposition region of the first liquid corresponds to the droplet ejection region of the second liquid and the peripheral region of the droplet ejection region of the second liquid, then the second liquid lands on an area where the surface of the first liquid is flat, thus preventing displacement of the second liquid. Accordingly, it is possible to obtain a desirable image without the occurrence of displacement of the dot formed by the second liquid. 
     Here, the displacement of the landing position of the second liquid means a phenomenon which, rather than being caused by the variation in the flight direction of the second liquid, is caused by the second liquid moving over an inclined section of the first liquid, when the second liquid lands on the section having an incline at a boundary section of the first liquid, for example. 
     Furthermore, a third liquid, which is transparent, of the same color type as the recording medium, or of the similar color type to the recording medium, is ejected onto the peripheral region of the image forming region where the second liquid is not present, of the region where the first liquid has been deposited, and this liquid is cured reliably by being irradiated with radiation. Hence it is possible to prevent the remnant of surplus liquid on the recording medium. 
     A first liquid deposition region onto which the first liquid is deposited includes the image forming region onto which a second liquid are ejected, and the peripheral region of this image forming region. For example, if there is a cutaway section in the image to be formed, then there is a first liquid deposition region in this cutaway section as well. 
     Here, an “image” indicates an image in a broad sense, including a text character, a symbol, a figure, a pattern, or the like. 
     The recording medium is a medium which receives the deposited first liquid in the first liquid deposition step, the second liquid ejected in the second liquid droplet ejection step, and the third liquid ejected in the third liquid droplet ejection step. The recording medium may include various types of media, such as continuous paper, cut paper, sealed paper, a resin sheet such as a PHP sheet, film, cloth, or the like, irrespective of material or shape. 
     Preferably, the third liquid contains a polymerization initiator. 
     According to this aspect of the present invention, a polymerization initiator is included in the third liquid, and thereby it is possible to cure the first liquid and the third liquid reliably by irradiating radiation onto the mixed liquid of the first liquid and the third liquid. 
     In order to attain the aforementioned object, the present invention is also directed to an image forming method comprising the steps of: depositing a first liquid containing at least a dispersion inhibitor and a high-boiling-point organic solvent, onto an image forming region of a recording medium where an image is to be formed according to image data, and onto a peripheral region of the image forming region; ejecting a second liquid containing at least a radiation-curable polymer compound, a polymerization initiator, and a coloring material, onto the recording medium according to the image data after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region; ejecting a third liquid containing at least a radiation-curable polymer compound and a polymerization initiator, onto at least the peripheral region of the image forming region after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region, the third liquid having a transparent color, the same color as the recording medium, or a similar color to the recording medium; and irradiating radiation onto the first liquid, the second liquid and the third liquid on the recording medium. 
     According to this aspect of the present invention, each of the second liquid and the third liquid includes a polymerization initiator. Thereby it is possible to cure the second liquid and the third liquid reliably, even if the first liquid does not contain a polymerization initiator. 
     Preferably, a timing of ejecting the third liquid onto at least the peripheral region of the image forming region is substantially the same as a timing of ejecting the second liquid onto the recording medium, or is after the timing of ejecting the second liquid onto the recording medium. 
     “Being substantially the same as a timing of ejecting the second liquid” include a state where the second liquid ejection step is being carried out on any part of the recording medium while the second liquid ejection step has been completed and the third liquid droplet ejection step is being carried out in another part of the recording medium. Of course, it also includes an embodiment in which the third liquid ejection step is carried out simultaneously with respect to the region subject to the second droplet ejection step. 
     Preferably, a timing of ejecting the second liquid onto the recording medium is substantially the same as a timing of ejecting the third liquid onto at least the peripheral region of the image forming region, or is after the timing of ejecting the third liquid onto at least the peripheral region of the image forming region. 
     According to these aspects of the present invention, when the second liquid is ejected onto the image forming region after the third liquid have been ejected onto the peripheral region of the image forming region, then it is possible to surround the periphery of the image forming region with a reactive product of the first liquid and the third liquid, and hence spreading of the second liquid deposited onto the first liquid can be prevented. 
     In order to attain the aforementioned object, an apparatus for achieving the above methods is also conceived. The present invention is also directed to an image forming apparatus comprising: a first liquid deposition device depositing a first liquid containing at least a dispersion inhibitor and a high-boiling-point organic solvent, onto an image forming region of a recording medium where an image is to be formed according to image data, and onto a peripheral region of the image forming region; a second liquid ejection device ejecting a second liquid containing at least a radiation-curable polymer compound, a polymerization initiator, and a coloring material, onto the recording medium according to the image data after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region; a third liquid ejection device ejecting a third liquid containing at least a radiation-curable polymer compound and a polymerization initiator, onto at least the peripheral region of the image forming region after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region, the third liquid having a transparent color, the same color as the recording medium, or a similar color to the recording medium; and a radiation irradiation device irradiating radiation onto the first liquid, the second liquid and the third liquid on the recording medium. 
     According to this aspect of the invention, a polymerization initiator is included only in the first liquid. Hence, even if a portion of the radiation from the radiation irradiation device reaches the second liquid ejection device and the third liquid ejection device, a curing reaction of the second liquid in the second liquid ejection device and a curing reaction of the third liquid in the third liquid ejection device do not occur, and therefore liquid blockages in the second liquid ejection device and the third liquid ejection device can be prevented. 
     For the first liquid deposition device, it is possible to use an application device which applies the first liquid onto the recording medium, a liquid droplet device which ejects a droplet of the first liquid from a nozzle, or the like. Furthermore, for the second liquid ejection device and the third liquid ejection device, it is possible to use an inkjet head which ejects ink onto the recording medium. Of course, it is also possible to use the aforementioned inkjet head as the first liquid deposition device. 
     Examples of an inkjet head include a head having an ejection hole (nozzle) from which a liquid droplet is ejected, a liquid chamber (pressure chamber) accommodating liquid to be ejected in the form of a droplet from the ejection hole, and an actuator provided on the liquid chamber for pressurizing the liquid inside the liquid chamber. 
     The inkjet head may be a line type head having a row of nozzles of a length corresponding to the full width of the recording medium (the width of the possible ink droplet ejection region of the recording medium), or a serial type head which uses a short head having an ejection hole row of a length that does not reach the full width of the recording medium. The serial type head may scan in the breadthways direction of the recording medium. 
     A line type inkjet head may be formed to a length corresponding to the full width of the recording medium by combining short heads having rows of ejection holes which do not reach a length corresponding to the full width of the recording medium, these short heads being joined together in a staggered matrix fashion. 
     Preferably, the third liquid contains a polymerization initiator. 
     According to this aspect of the present invention, a polymerization initiator is included in the third liquid, and hence the first liquid and the third liquid react together reliably. Consequently, when radiation is irradiated onto this reaction product, the third liquid can be cured reliably. 
     In order to attain the aforementioned object, the present invention is also directed to an image forming apparatus, comprising: a first liquid deposition device depositing a first liquid containing at least a dispersion inhibitor and a high-boiling-point organic solvent, onto an image forming region of a recording medium where an image is to be formed according to image data, and onto a peripheral region of the image forming region; a second liquid ejection device ejecting a second liquid containing at least a radiation-curable polymer compound, a polymerization initiator, and a coloring material, onto the recording medium according to the image data after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region; a third liquid ejection device ejecting a third liquid containing at least a radiation-curable polymer compound and a polymerization initiator, onto at least the peripheral region of the image forming region after the first liquid is deposited onto the image forming region and the peripheral region of the image forming region, the third liquid having a transparent color, the same color as the recording medium, or a similar color to the recording medium; and a radiation irradiation device irradiating radiation onto the first liquid, the second liquid and the third liquid on the recording medium. 
     According to this aspect of the present invention, a polymerization initiator is included in the second liquid and the third liquid, and hence it is possible to cure the second liquid and the third liquid reliably even if the first liquid does not contain a polymerization initiator. 
     According to the present invention, by taking the deposition region of the first liquid to be the ejection region of the second liquid where second liquid is ejected on the basis of the image data, and the peripheral region of the ejection region of the second liquid, then the second liquid lands on an area where the surface of the first liquid is flat. Hence displacement of the landing position of the second liquid is prevented, and a desirable image can be obtained. Furthermore, by ejecting a third liquid which is transparent, of the same color type as the recording medium, or similar color type to the recording medium, onto the part where the second liquid is not present in the region where the first liquid has been deposited, and by irradiating radiation on the first liquid, the second liquid and the third liquid, it is possible to cure these liquids reliably, and therefore surplus liquid does not remain on the recording medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, wherein: 
         FIG. 1  is a general schematic drawing of an inkjet recording apparatus according to an embodiment of the present invention; 
         FIG. 2  is an enlarged drawing showing the composition of the print unit shown in  FIG. 1 ; 
         FIG. 3  is a principal plan diagram of the peripheral area of a print unit in the inkjet recording apparatus illustrated in  FIG. 1 ; 
         FIGS. 4A to 4C  are plan view perspective diagrams showing an embodiment of the composition of a print head; 
         FIG. 5  is a cross-sectional diagram along line  5 - 5  in  FIGS. 4A and 4B ; 
         FIG. 6  is a principal block diagram showing the system configuration of the inkjet recording apparatus shown in  FIG. 1 ; 
         FIGS. 7A and 7B  are diagrams showing a treatment liquid deposition region in the droplet ejection control according to an embodiment of the present invention; 
         FIGS. 8A and 8B  are diagrams showing an image forming region in the droplet ejection control according to an embodiment of the present invention; 
         FIGS. 9A and 9B  are diagrams showing a transparent ink droplet ejection region in the droplet ejection control according to an embodiment of the present invention; 
         FIG. 10  is a diagram showing an image formed by the image forming method according to an embodiment of the present invention; and 
         FIG. 11  is a block diagram showing the composition of a droplet ejection control block in the inkjet recording apparatus shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     General Composition of Inkjet Recording Apparatus 
       FIG. 1  is a diagram of the general composition of an inkjet recording apparatus relating to an embodiment of the present invention. As shown in  FIG. 1 , the inkjet recording apparatus  10  comprises: a print unit  12  having a plurality of inkjet heads (indicated by reference numerals  12 K,  12 C,  12 M, and  12 Y in  FIG. 2 ) provided for ink colors of black (K), cyan (C), magenta (M), and yellow (Y), respectively, a treatment liquid head (indicated by reference numeral  12 S in  FIG. 2 ) corresponding to the treatment liquid (S) for avoiding landing interference between the inks of the respective colors, and a transparent ink head (indicated by reference numeral  12 T in  FIG. 2 ) corresponding to a transparent ink (T) which does not contain coloring material; an ink storing and loading unit  14  for storing inks to be supplied to the print heads; a paper supply unit  18  for supplying a recording medium (recording paper)  16 ; a decurling unit  20  removing curl in the recording medium  16 , such as recording paper; a suction belt conveyance unit  22  disposed facing the nozzle surface (ink ejection surface) of the print unit  12 , for conveying the recording medium  16  while keeping the recording medium  16  flat; a print determination unit  24  for reading the printed result produced by the print unit  12 ; and a paper output unit  26  for outputting recorded recording paper (printed matter) to the exterior. 
     The ink storing and loading unit  14  comprises a treatment liquid supply tank  14 S which stores a treatment liquid (first liquid) to be ejected from the treatment liquid head, and ink supply tanks  14 K,  14 C,  14 M,  14 Y and  14 T which stores color inks (second liquids) and a transparent ink (third liquid) respectively. These tanks are connected to the treatment liquid head and the ink heads of the colors via required channels, respectively. The ink storing and loading unit  14  also comprises a warning device (for example, a display device or an alarm sound generator) for warning when the remaining amount of any ink is low, and has a mechanism for preventing loading errors between different colors. 
     In  FIG. 1 , a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit  18 ; however, more magazines with paper differences such as paper width and quality may be jointly provided. Moreover, papers may be supplied with cassettes that contain cut papers loaded in layers and that are used jointly or in lieu of the magazine for rolled paper. 
     In the case of a configuration in which a plurality of types of recording medium can be used, it is preferable that an information recording medium such as a bar code and a wireless tag containing information about the type of media is attached to the magazine, and by reading the information contained in the information recording medium with a predetermined reading device, the type of recording medium to be used (type of medium) is automatically determined, and ink-droplet ejection is controlled so that the ink-droplets are ejected in an appropriate manner in accordance with the type of medium. 
     The recording medium  16  delivered from the paper supply unit  18  retains curl due to having been loaded in the magazine. In order to remove the curl, heat is applied to the recording paper  16  in the decurling unit  20  by a heating drum  30  in the direction opposite from the curl direction in the magazine. The heating temperature at this time is preferably controlled so that the recording medium  16  has a curl in which the surface on which the print is to be made is slightly round outward. 
     In the case of the configuration in which roll paper is used as the recording medium  16 , a cutter (first cutter)  28  is provided as shown in  FIG. 1 , and the continuous paper is cut into a desired size by the cutter  28 . The cutter  28  has a stationary blade  28 A, whose length is not less than the width of the conveyor pathway of the recording medium  16 , and a round blade  28 B, which moves along the stationary blade  28 A. The stationary blade  28 A is disposed on the reverse side of the printed surface of the recording medium  16 , and the round blade  28 B is disposed on the printed surface side across the conveyor pathway. When cut papers are used, the cutter  28  is not required. 
     The decurled and cut recording medium  16  is delivered to the suction belt conveyance unit  22 . The suction belt conveyance unit  22  has a configuration in which an endless belt  33  is set around rollers  31  and  32  so that the portion of the endless belt  33  facing at least the nozzle face of the printing unit  12  and the sensor installation face of the print determination unit  24  forms a horizontal plane (flat plane). 
     The belt  33  has a width that is greater than the width of the recording medium  16 , and a plurality of suction apertures (not shown) are formed on the belt surface. A suction chamber  34  is disposed in a position facing the sensor installation surface of the print determination unit  24  and the nozzle surface of the printing unit  12  on the interior side of the belt  33 , which is set around the rollers  31  and  32 , as shown in  FIG. 1 . The suction chamber  34  provides suction with a fan  35  to generate a negative pressure, and the recording medium  16  is held on the belt  33  by suction. 
     The belt  33  is driven in the anti-clockwise direction in  FIG. 1  by the motive force of a motor  88  (shown in  FIG. 6 ) being transmitted to at least one of the rollers  31  and  32 , which the belt  33  is set around, and the recording medium  16  held on the belt  33  is conveyed from right to left in  FIG. 1 . 
     Since ink adheres to the belt  33  when a marginless print job or the like is performed, a belt-cleaning unit  36  is disposed in a predetermined position (a suitable position outside the printing area) on the exterior side of the belt  33 . Although the details of the configuration of the belt-cleaning unit  36  are not shown, examples thereof include a configuration in which the belt  33  is nipped with cleaning rollers such as a brush roller and a water absorbent roller, an air blow configuration in which clean air is blown onto the belt  33 , or a combination of these. In the case of the configuration in which the belt  33  is nipped with the cleaning rollers, it is preferable to make the line velocity of the cleaning rollers different than that of the belt  33  to improve the cleaning effect. 
     The inkjet recording apparatus  10  can comprise a roller nip conveyance mechanism, in which the recording paper  16  is pinched and conveyed with nip rollers, instead of the suction belt conveyance unit  22 . However, there is a drawback in the roller nip conveyance mechanism that the print tends to be smeared when the printing area is conveyed by the roller nip action because the nip roller makes contact with the printed surface of the paper immediately after printing. Therefore, the suction belt conveyance in which nothing comes into contact with the image surface in the printing area is preferable. 
     Each of the color inks and the transparent ink used in the inkjet recording apparatus  10  according to the present embodiment contains at least one polymer compound of an ultraviolet-curable monomer, an ultraviolet-curable oligomer, and a combination of these which have properties that the curing reaction of an aggregate in the polymer compounds is promoted by being mixed with a polymerization initiator containing a treatment liquid and being given energy, such as irradiation of ultraviolet light. 
     In other words, if ultraviolet light is irradiated from an ultraviolet light source  41  provided on the downstream side of the print unit  12  (i.e., after the print unit  12 ) in a state where the polymer compound contained in the ink is mixed with the polymerization initiator contained in the treatment liquid, then radicals are generated from the polymerization initiator, a polymerization reaction occurs, and the mixed liquid of ink and treatment liquid cures. The details of the inks used in the present embodiment, and the details of the ultraviolet light source  41  are described hereinafter. 
     The print determination unit  24  provided on the downstream side of the ultraviolet light source  41  (i.e., after the ultraviolet light source  41 ) has an image sensor for capturing the ink droplet deposition result of the print unit  12 , and functions as a device to check for ejection abnormalities, such as blocking of the nozzles in the print unit  12  from the recorded image read in by the image sensor. 
     The print determination unit  24  of the present embodiment is configured with at least a line sensor having photoelectric transducing elements with a width that is greater than the ink-droplet ejection width (image recording width) of the heads  12 K,  12 C,  12 M, and  12 Y. This line sensor has a color separation line CCD sensor including a R (red) light receiving element row composed of photoelectric transducing elements (pixels) arranged in a line provided with an R filter, a G (green) light receiving element row with a G filter, and a B (blue) light receiving element row with a B filter. Instead of a line sensor, it is possible to use an area sensor composed of light receiving elements which are arranged two-dimensionally. 
     The print determination unit  24  reads a test pattern image (or an actual image) printed by the heads  12 K,  12 C,  12 M, and  12 Y for the respective colors, and the ejection of each head is determined. The ejection determination includes the presence of the ejection, measurement of the dot size, and measurement of the dot deposition position. 
     The printed matter generated in this manner is output from the paper output unit  26 . The target print (i.e., the result of printing the target image) and the test print are preferably output separately. In the inkjet recording apparatus  10 , a sorting device (not shown) is provided for switching the outputting pathways in order to sort the printed matter with the target print and the printed matter with the test print, and to send them to paper output units  26 A and  26 B, respectively. When the target print and the test print are simultaneously formed in parallel on the same large sheet of paper, the test print portion is cut and separated by a cutter (second cutter)  48 . The cutter  48  is disposed directly in front of the paper output unit  26 , and is used for cutting the test print portion from the target print portion when a test print has been performed in the blank portion of the target print. The structure of the cutter  48  is the same as the first cutter  28  described above, and has a stationary blade  48 A and a round blade  48 B. 
     Although not shown in  FIG. 1 , the paper output unit  26 A for the target prints is provided with a sorter for collecting prints according to print orders. 
     Compositional Example of the Print Unit 
       FIG. 2  shows the details of the composition of the print unit  12 . The print unit  12  comprises the treatment liquid head  12 S corresponding to the treatment liquid, inkjet heads  12 K,  12 C,  12 M and  12 Y corresponding to inks of respective colors of black, cyan, magenta and yellow, and the inkjet head  12 T corresponding to transparent ink (T). Below, the treatment liquid head  12 S, the inkjet head  12 K,  12 C,  12 M,  12 Y and the inkjet head  12 T may be described simply as a “head”, such as the head  12 S. 
     The heads  12 S,  12 K,  12 C,  12 M,  12 Y and  12 T of the print unit  12  are full line heads having a length corresponding to the maximum width of the recording medium  16  used with the inkjet recording apparatus  10 , and comprising a plurality of nozzles for ejecting ink arranged on a nozzle face through a length exceeding at least one edge of the maximum-size recording medium (namely, the full width of the printable range) (see  FIG. 3 ). 
     The heads  12 S,  12 K,  12 C,  12 M,  12 Y and  12 T are disposed in sequence in the order corresponding to treatment liquid (S), black (K), cyan (C), magenta (M), yellow (Y) and transparent ink (T), from the upstream side, following the direction of conveyance of the recording medium  16  (the paper feed direction shown in  FIGS. 2 and 3 ), and the respective heads  12 S,  12 K,  12 C,  12 M,  12 Y and  12 T are fixed so as to extend in line with a direction substantially perpendicular to the paper feed direction. 
     A color image can be formed on the recording medium  16  by ejecting inks of different colors from the heads  12 S,  12 K,  12 C,  12 M,  12 Y and  12 T, respectively, onto the recording medium  16  while the recording medium  16  is conveyed by the suction belt conveyance unit  22 . 
     By adopting a configuration in which full line heads  12 S,  12 K,  12 C,  12 M,  12 Y and  12 T having nozzle rows covering the full paper width are separately provided according to liquids in this way, it is possible to record an image on the full surface of the recording medium  16  by performing just one operation of relative movement between the recording medium  16  and the print unit  12 , in the paper conveyance direction (the sub-scanning direction), (in other words, by means of one sub-scanning action). Higher-speed printing is thereby made possible and productivity can be improved in comparison with a shuttle type head configuration in which a recording head moves back and forth reciprocally in the direction which is perpendicular to the paper conveyance direction. 
     After droplets of the treatment liquid  100 S have been ejected onto a prescribed region of the recording medium  16  from the head  12 S on the furthest upstream side in terms of the paper feed direction, droplets of K ink  100 K, C ink  100 C, M ink  100 M, and Y ink  100 Y are ejected in sequence from the respective color heads  12 K,  12 C,  12 M,  12 Y, onto the treatment liquid deposition region (not shown in  FIG. 2 ; and indicated by reference numeral  200  in  FIGS. 7A and 7B  and the like) where treatment liquid  102 S has been deposited on the recording medium  16 . Moreover, after droplets of the K, C, M and Y inks have been ejected, droplets of transparent ink  100 T are ejected from the transparent ink head  12 T onto at least the sections of the treatment liquid deposition region where droplets the K, C, M and Y inks have not been ejected. In  FIG. 2 , the treatment liquid deposited on the recording medium is indicated by reference numeral  102 S. 
     In this way, when droplets of K, C, M, Y inks  102 K,  102 C,  102 M,  102 Y and transparent ink  100 T are ejected onto the treatment liquid  102 S deposited on the recording medium  16 , then landing interference between the K, C, M, Y inks  102 K,  102 C,  102 M and  102 Y, is prevented, due to the effects of the treatment liquid  102 S. 
     Although a configuration with the four standard colors of K, C, M and Y is described in the present embodiment, the combination of the ink colors and the number of colors are not limited to those. Light and/or dark inks, and special color inks can be added as required. For example, a configuration is possible in which inkjet heads for ejecting light-colored inks, such as light cyan and light magenta, and dark inks such as dark yellow, are added. Furthermore, there are no particular restrictions of the sequence in which the heads of respective colors are arranged. 
     Moreover, it is also possible to provide a plurality of treatment liquid heads corresponding to a plurality of treatment liquids of different types (for example, treatment liquids having different physical properties, such as viscosity, or treatment liquids having different compositions), and it is also possible to adopt a composition in which a plurality of treatment liquids can be ejected from one head. 
     Structure of the Head 
     Next, the structure of a head is described below. The heads  12 K,  12 C,  12 M and  12 Y of the respective ink colors have the same structure, and a reference numeral  50  is hereinafter designated to any of the heads. 
       FIG. 4A  is a plan view perspective diagram showing an example of the structure of a head  50 , and  FIG. 4B  is an enlarged diagram of a portion of same. Furthermore,  FIG. 4C  is a plan view perspective diagram showing a further example of the composition of a print head  50 , and  FIG. 5  is a cross-sectional diagram showing a three-dimensional composition of an ink chamber unit (being a cross-sectional view along line  5 - 5  in  FIGS. 4A and 4B ). In order to achieve a high density of the dot pitch printed onto the surface of the recording medium  16 , it is necessary to achieve a high density of the nozzle pitch in the head  50 . As shown in  FIGS. 4A and 4B , the head  50  according to the present embodiment has a structure in which a plurality of ink chamber units  53 , each including a nozzle  51  forming an ink droplet ejection hole, a pressure chamber  52  corresponding to the nozzle  51 , and the like, are disposed two-dimensionally in the form of a staggered matrix, and hence the effective nozzle interval (the projected nozzle pitch) as projected in the lengthwise direction of the head (the main scanning direction, which is perpendicular to the paper conveyance direction) is reduced (high nozzle density is achieved). 
     Embodiments of one or more nozzle rows covering a length corresponding to the full width of the recording medium  16  is not limited to the present embodiment. For instance, instead of the composition in  FIG. 4A , as shown in  FIG. 4C , a line head having nozzle rows of a length corresponding to the entire length of the recording medium  16  can be formed by arranging and combining, in a staggered matrix, short head blocks  50 ′ having a plurality of nozzles  51  arrayed in a two-dimensional fashion. 
     The pressure chamber  52  provided corresponding to each of the nozzles  51  is approximately square-shaped in plan view, and a nozzle  51  and a supply port  54  are provided respectively at either corner of a diagonal of the pressure chamber  52 . Each pressure chamber  52  is connected via a supply port  54  to a common flow channel  55 . The common liquid chamber  55  is connected to an ink supply tank forming an ink source (not shown in  FIGS. 4A to 4C , corresponding to the ink storing and loading unit shown by the reference numeral  14  in  FIG. 1 ), and the ink supplied from the ink supply tank is distributed and supplied to the respective pressure chambers  52  via the common liquid chamber  55  shown in  FIG. 5 . 
     An actuator  58  provided with an individual electrode  57  is bonded to a pressure plate  56  which forms the upper face of the pressure chamber  52  and also serves as a common electrode, and the actuator  58  is deformed when a drive voltage is supplied to the individual electrode  57 , thereby causing ink to be ejected from the nozzle  51 . When ink is ejected, new ink is supplied to the pressure chamber  52  from the common flow passage  55 , via the supply port  54 . 
     For the actuator  58  shown in  FIG. 5 , it is suitable to use a piezoelectric element based on a ceramic material, such as PZT (Pb(Zr.Ti)O 3 , lead titanate zirconate), and the like. Of course, it is also possible to use piezoelectric elements based on a fluoride resin material, such as PVDF (polyvinylidene fluoride) or PVDF-TrFE (a polyvinylidene fluoride/trifluoride ethylene copolymer). 
     As shown in  FIG. 4B , the high-density nozzle head according to the present embodiment is achieved by arranging a plurality of ink chamber units  53  having the above-described structure in a lattice fashion based on a fixed arrangement pattern, in a row direction which coincides with the main scanning direction, and a column direction which is inclined at a fixed angle of θ with respect to the main scanning direction, rather than being perpendicular to the main scanning direction. 
     More specifically, by adopting a structure in which a plurality of ink chamber units  53  are arranged at a uniform pitch d in line with a column direction forming an angle of θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to align in the main scanning direction satisfies “P=d×cos θ, and hence, in terms of the main scanning direction, the nozzles  51  can be regarded to be equivalent to those arranged linearly at a fixed pitch P. Such configuration makes it possible to achieve a nozzle row having a high nozzle density. 
     In a full-line head comprising rows of nozzles that have a length corresponding to the entire width of the image recordable width, the “main scanning” is defined as printing one line (a line formed of a row of dots, or a line formed of a plurality of rows of dots) in the width direction of the recording medium (main-scanning direction) by driving the nozzles in one of the following ways: (1) simultaneously driving all the nozzles; (2) sequentially driving the nozzles from one side toward the other; and (3) dividing the nozzles into blocks and sequentially driving the nozzles from one side toward the other in each of the blocks. 
     In particular, when the nozzles  51  arranged in a matrix such as that shown in  FIGS. 4A and 4B  are driven, it is desirable that the “main scanning” is performed in accordance with (3) described above. 
     On the other hand, the “sub-scanning” is defined as to repeatedly perform printing of one line (a line formed of a row of dots, or a line formed of a plurality of rows of dots) formed by the main scanning, while the full-line head and the recording medium  16  are moved relatively to each other. 
     In other words, the nozzles  51  which eject ink droplets that are to form dots which are adjacently formed in a mutually overlapping fashion on the recording medium  16 , are arranged following a column direction forming an angle of θ with respect to the main scanning direction. However, when embodiments of the present invention are implemented, the arrangement of the nozzles is not limited to that of the example illustrated. 
     Description of the Control System 
       FIG. 6  is a principal block diagram showing the system configuration of the inkjet recording apparatus  10 . The inkjet recording apparatus  10  comprises a communication interface  70 , a system controller  72 , a memory  74 , a motor driver  76 , a heater driver  78 , a print controller  80 , an image buffer memory  82 , a head driver  84 , a light source driver  85 , and the like. 
     The communication interface  70  is an interface unit for receiving image data sent from a host computer  86 . A serial interface such as USB, IEEE1394, Ethernet, wireless network, and a parallel interface such as a Centronics interface can be used as the communication interface  70 . A buffer memory (not shown) may be mounted in this portion in order to increase the communication speed. The image data sent from the host computer  86  is received by the inkjet recording apparatus  10  through the communication interface  70 , and is temporarily stored in the memory  74 . 
     The memory  74  is a storage device for temporarily storing images inputted through the communication interface  70 , and data is written and read to and from the image memory  74  through the system controller  72 . The memory  74  is not limited to a memory composed of semiconductor elements, and a hard disk drive or another magnetic medium may be used. 
     The system controller  72  is constituted by a central processing unit (CPU) and peripheral circuits thereof, and the like, and it functions as a control device for controlling the whole of the inkjet recording apparatus  10  in accordance with a prescribed program, as well as a calculation device for performing various calculations. More specifically, the system controller  72  controls the various sections, such as the communication interface  70 , memory  74 , motor driver  76 , heater driver  78 , and the like, and controls communications with the host computer  86  and writing and reading to and from the memory  74 , and it also generates control signals for controlling the motor  88  such as a motor in the conveyance system and the heater  89  such as a heater in the post drying unit  42 . 
     The program executed by the CPU of the system controller  72  and the various types of data which are required for control procedures are stored in the memory  74 . The memory  74  may be a non-writeable storage device, or it may be a rewriteable storage device, such as an EEPROM. The memory  74  is used as a temporary storage region for the image data, and it is also used as a program development region and a calculation work region for the CPU. 
     The motor driver  76  is a driver (drive circuit) which drives the motor  88  in accordance with commands from the system controller  72 . The heater driver  78  is a driver which drives the post drying unit  42 , and the heater  89  such as the temperature adjustment heater in the inkjet recording apparatus  10  and in the head  50 , in accordance with commands from the system controller  72 . 
     The print controller  80  has a signal processing function for performing various tasks, compensations, and other types of processing for generating print control signals on the basis of the image data stored in the memory  74  in accordance with commands from the system controller  72  so as to supply the generated print data (dot data) to the head driver  84 . Required signal processing is carried out in the print controller  80 , and the ejection amount and the ejection timing of the ink droplets from the respective print heads  50  are controlled via the head driver  84 , on the basis of the print data. By this means, desired dot size and dot positions can be achieved. 
     The print controller  80  is provided with the image buffer memory  82 ; and image data, parameters, and other data are temporarily stored in the image buffer memory  82  when image data is processed in the print controller  80 . Also possible is an aspect in which the print controller  80  and the system controller  72  are integrated to form a single processor. 
     The head driver  84  drives the actuators  58  of the treatment liquid head  12 S, the heads of the respective colors,  12 K,  12 C,  12 M,  12 Y, and the transparent ink head  12 T, on the basis of print data supplied by the print controller  80 . A feedback control system for maintaining constant drive conditions in the head may be included in the head driver  84 . 
     The light source driver  85  functions as a control block which controls the on and off switching of the ultraviolet light source  41  shown in  FIGS. 1 and 2  (the illumination timing, illumination time), the irradiation light quantity, and the like. In other words, the on/off switching of the ultraviolet light source  41 , and the amount of light irradiated by the ultraviolet light source  41 , are set on the basis of the control signal supplied by the print controller  80 . 
     The image data to be printed is externally inputted through the communications interface  70 , and is stored in the memory  74 . At this stage, RGB image data is stored in the memory  74 . 
     The image data stored in the memory  74  is sent to the print controller  80  via the system controller  72 , and in the print controller  80 , the droplet ejection region (deposition region) for the treatment liquid, the droplet ejection region for the K, C, M and Y inks, and the droplet ejection region for the transparent ink are determined, and the image data is converted into dot data for each of the K, C, M and Y inks and the transparent ink. In other words, the print controller  80  carries out processing for converting the input RGB image data into dot data of the four colors, K, C, M and Y, processing for converting the image data into dot data for the transparent ink, processing for converting into dot data for the treatment liquid. The respective sets of dot data generated by the print controller  80  are stored in the image buffer memory  82 . The details of the droplet ejection control in the inkjet recording apparatus  10  are described hereinafter. 
     The head driver  84  generates drive control signals for the head  50  on the basis of the dot data stored in the image buffer memory  82 . By supplying the drive control signals generated by the head driver  84  to the head  50 , droplets of the treatment liquid, the K, C, M and Y inks, and the transparent ink are ejected from the head  50 . By controlling droplet ejections from the print heads  50  in synchronization with the conveyance speed of the recording medium  16 , an image is formed on the recording medium  16 . 
     Various control programs are stored in the program storage unit  90  shown in  FIG. 6 , and a control program is read out and executed in accordance with commands from the system controller  72 . A semiconductor memory, such as a ROM, EEPROM, a magnetic disk, or the like may be used as the program storage unit  90 . An external interface may be provided, and a memory card or PC card may also be used. Naturally, a plurality of these storage media may also be provided. The program storage unit  90  may also serve as a storage device (not illustrated) for storing operational parameters, and the like. 
     In the present embodiment, the system controller  72 , the memory  74 , and the print controller  80 , and the like, are described as separate functional blocks; however, they may be also integrated to form one single processor. Furthermore, it is also possible to achieve a portion of the functions of the system controller  72  and a portion of the functions of the print controller  80 , in one processor. 
     Description of the Droplet Ejection Control 
     Next, the droplet ejection control (image forming method) according to an embodiment of the present invention is described.  FIG. 7A  is a plan diagram showing a treatment liquid deposition region  200  and an image forming region  202  set on a recording medium  16  (viewed from the image forming surface  16 A side shown in  FIG. 7B ), and  FIG. 7B  is a diagram viewed in the direction indicated by an arrow A in  FIG. 7A . Reference numeral  200  indicated by the solid line in  FIG. 7A  indicates a treatment liquid deposition region onto which treatment liquid is deposited. The treatment liquid deposition region  200  is determined so as to be larger than the image forming region  202  (indicated by the broken line) in which printing is carried out by depositing droplets of K, C, M and Y inks (indicated by reference numeral  206  in  FIGS. 8A and 8B ), the image forming region  202  being specified on the image forming surface of the recording medium  16 . The treatment liquid  204  shown in  FIG. 7B  corresponds to the treatment liquid  102 S deposited on the recording medium  16  indicated by reference numeral  102 S in  FIG. 2 . 
       FIGS. 8A and 8B  show a state where droplets of K, M, C, and Y inks  206  have been ejected onto the treatment liquid  204  deposited on the recording medium  16 . If the treatment liquid  204  has been deposited onto the image forming surface  16 A of the recording medium  16  as shown in  FIGS. 7A and 7B , then printing is carried out using K, C, M and Y inks  206 , on top of the treatment liquid  204  deposited on the recording medium  16 , as shown in  FIGS. 8A and 8B . In the droplet ejection control shown in the present embodiment, by making the treatment liquid deposition region  200  in which printing is carried out using the treatment liquid  204 , as shown in  FIG. 8B , larger than the image forming region  202  where printing is carried out using the K, C, M and Y inks, then the K, C, M and Y inks land on a flat region  204 A of treatment liquid  204  as shown in  FIGS. 8A and 8B  (in other words, the K, C, M and Y inks  206  do not land on the peripheral sections  204 B of the treatment liquid  204 ), thereby preventing displacement of the dot formation position caused by movement of the K, C, M and Y inks  206  upon landing (immediately after landing) due to the gradient of the peripheral sections  204 B of the treatment liquid  204 . 
       FIGS. 9A and 9B  show a state where, after the ejection of droplets of K, C, M and Y inks, droplets of transparent ink  212  have been ejected onto a transparent ink droplet ejection regions  210  (shown in  FIG. 9B ) which are set, in the treatment liquid deposition region  200 , in the peripheral sections of the image forming region  202  where droplets of K, C, M and Y inks have been ejected. In the transparent ink droplet ejection regions shown in  FIGS. 9A and 9B , treatment liquid  204  has been applied. 
     As shown in  FIG. 9B , droplets of transparent ink  212  are ejected onto the transparent ink droplet ejection regions  210 , which include a region of the treatment liquid deposition region  200  where droplets of K, C, M and Y inks  206  have not been ejected. More specifically, droplets of transparent ink  212  are ejected in such a manner that the treatment liquid deposition region  200 , which is set to a broader region than the image forming region  202 , is covered completely by at least one of either the K, C, M and Y inks  206 , and the transparent ink  212 . In other words, droplets of transparent ink  212  are ejected in such a manner that they completely cover at least the non-image forming regions (not shown) which are the regions apart from the image forming region  202 , in the treatment liquid deposition region  200 . 
     If droplets of at least one of the K, C, M and Y inks  206  and the transparent ink  212  are ejected onto the treatment liquid  204  deposited on the treatment liquid deposition region  200 , then the polymer compound (for example, a monomer, an oligomer, or a compound containing a monomer and an oligomer) contained in the K, C, M and Y inks and the transparent ink, and the polymerization initiator contained in the treatment liquid  204  mix together. 
     When ultraviolet light is irradiated by the ultraviolet light source  41  shown in  FIG. 1 , and other drawings, onto this mixed liquid, then a polymerization reaction starts, and the treatment liquid  204 , the K, C, M and Y inks  206  and the transparent ink  212  cure and become fixed on the recording medium  16 . 
       FIG. 10  shows a recording medium  16  on which the character “A” (image  220 ) has been printed. The treatment liquid deposition region  200  (indicated by the diagonal hatching) onto which droplets of treatment liquid  204  have been ejected with respect to the image  220  shown in  FIG. 10  is set to the outer edge sections  224  of the “A” character, and the inner side of the central cutaway section  226 . In this way, in the example shown in  FIG. 10 , the treatment liquid deposition region  200  is also set appropriately in the central cutaway section of the “A”. In other words, in the present example, the peripheral sections of the image forming region  202  for which a treatment liquid deposition region  200  is set may include the central cutaway section of the image, and the like, as shown in  FIG. 10 . 
     Droplets of the K, C, M and Y inks  206  which are required to form the image  220  are ejected appropriately onto the image forming region  202  (indicated by the blacked-out area) shown in  FIG. 10 . A transparent ink droplet ejection region  210  is determined in such a manner that the whole of the treatment liquid deposition region  200  is covered by the K, C, M and Y inks  206  and the transparent ink  212 , and thus droplets of the transparent ink  212  are ejected onto this transparent ink droplet ejection region  210 .  FIG. 10  shows a portion of the transparent ink  212  which has landed on the transparent ink droplet ejection region  210 . 
     Description of the Droplet Ejection Control Unit 
       FIG. 11  is a block diagram showing the composition of a droplet ejection control unit which implements the droplet ejection control described above. According to the droplet ejection control shown in the present embodiment, when image data  300  as shown in  FIG. 11  is obtained from the host computer  86 , or the like, via the communications interface shown in  FIG. 6 , the treatment liquid deposition region calculation unit  302  determines a treatment liquid deposition region  200  shown in  FIG. 7A , and the like, on the basis of the image data  300 . Furthermore, the image forming region calculation unit  304  in  FIG. 11  determines an image forming region (KCMY droplet ejection region)  202  shown in  FIGS. 7A and 8A , and the like. Moreover, the transparent ink droplet ejection region calculation unit  306  in  FIG. 11  determines transparent ink droplet ejection regions  210  shown in  FIGS. 9A and 9B , and the like. 
     Desirably, the transparent ink droplet ejection regions  210  shown in  FIGS. 9A and 9B  and the like are determined so as not to overlap with the image forming region  202 . Furthermore, it may also include sections to the outer side of the outer edge of the treatment liquid deposition region  200  shown in  FIGS. 7A and 7B , or the like, and sections to the inner side of the inner edge of same. 
     In other words, by ejecting droplets of transparent ink  212  onto sections to the outer side of the outer edge of the treatment liquid deposition region  200 , and to the inner side of the inner edge of same, it is possible to prevent the existence of unreacted treatment liquid  204  in the vicinity of the outer edge or the vicinity of the inner edge of the treatment liquid deposition region  200 . Furthermore, it is also possible to set the treatment liquid deposition region  200  so as to be the whole of the possible image forming region of the recording medium  16 . In this case, the consumption of treatment liquid  204  and transparent ink  212  increases, and hence a desirable mode is one in which the treatment liquid deposition region  200  is set to the vicinity of the image forming region  202  (namely a range of several dots to the outer side of the outer edge sections and to the inner side of the inner edges of the image forming region  202 ). 
     Furthermore, more desirably, the treatment liquid deposition region  200  is determined by taking account of error in the landing positions of the treatment liquid  204  and the transparent ink  212 . 
     When the treatment liquid deposition region  200 , the image forming region  202 , and the transparent ink droplet ejection region  210  have been determined in this way, then the treatment liquid dot data generation unit  312 , the KCMY ink dot data generation unit  314  and the transparent ink dot data generation unit  316  shown in  FIG. 11  calculate dot data for the treatment liquid  204 , the K, C, M and Y inks  206 , and the transparent ink  212  respectively. 
     To give an example of the treatment liquid deposition region  200 , the image forming region  202  and the transparent ink droplet ejection region  210 , as shown in  FIGS. 9A and 9B , the treatment liquid deposition region  200  is set to a range of 1.5 dots about the periphery of the image forming region  202 , and the transparent ink droplet ejection region  210  is set to a range of 2 dots about the periphery of the image forming region  202 . 
     The relationship among the treatment liquid deposition region  200 , the image forming region  202  and the transparent ink droplet ejection region  210  is changed appropriately in accordance with the type of the recording medium  16 , and the physical properties values of the treatment liquid  204 , the K, C, M and Y inks  206 , and the transparent ink  212 . For example, if the surface tensions of the K, C, M and Y inks  206  and the transparent ink are large with respect to the treatment liquid, then the treatment liquid deposition region  200  is desirably determined to be a broader area. 
     On the basis of the dot data for the treatment liquid  204 , the K, C, M and Y inks  206  and the transparent ink  212  generated in this way, drive signals are generated by a treatment liquid head drive signal generation unit  322 , a K, C, M and Y ink head drive signal generation unit  324 , and a transparent ink head drive signal generation unit  326 . The respective drive signals are subjected to prescribed signal processing by a treatment liquid head drive unit  332 , a KCMY ink drive unit  344  and a transparent ink head drive unit  336 , and are then supplied to the actuators  58  (shown in  FIG. 5 ) provided in the heads  12 S,  12 K,  12 C,  12 M,  12 Y and  12 T shown in  FIG. 6 . 
     For example, there is a mode in which drive signals of digital data are generated in the treatment liquid head drive signal generation unit  322  and the K, C, M and Y ink head drive signal generation unit  324 , and processing such as A/D conversion, amplification, and the like, is carried out on these digital data drive signals, in the treatment liquid head drive unit  332 , the K, C, M and Y ink head drive unit  334 , and the transparent ink head drive unit  336 . 
     In the present embodiment, the treatment liquid deposition region calculation unit  302 , the image forming region calculation unit  304 , the transparent ink droplet ejection region calculation region  306 , the treatment liquid dot data generation unit  312 , the K, C, M and Y ink dot data generation unit  314 , and the transparent ink dot data generation unit  316  shown in  FIG. 11  are incorporated into the print controller  80  shown in  FIG. 6 , and the treatment liquid head drive signal generation unit  322 , the K, C, M and Y ink head drive signal generation unit  324 , the transparent ink head drive signal generation unit  326 , the treatment liquid head drive unit  332 , the K, C, M and Y ink head drive unit  334 , and the transparent ink head drive unit  336  are incorporated into the head driver  84  shown in  FIG. 6 . 
     Of course, the composition of the droplet ejection control unit described above is merely an example, and it may be changed appropriately (or a function may be added or removed), in accordance with the composition of the print controller  80  and the head driver  84  shown in  FIG. 6 . 
     Description of the Treatment Liquid, K, C, M and Y Inks, and Transparent Ink 
     Next, an ink set used in the inkjet recording apparatus  10  according to the present embodiment is described below. The ink set used in the present embodiment includes the treatment liquid (reference numeral  202  in  FIG. 7A , and the like), the K, C, M and Y inks (reference numeral  206  in  FIG. 8A , and the like), and the transparent ink (reference numeral  212  in  FIG. 9A ), each of which are described above. 
     More specifically, in the present embodiment, liquids of various types including the treatment liquid  204 , the K, C, M and Y inks  206 , and the transparent ink  212  are used as the ink set, and an image is formed by depositing the treatment liquid  204 , the K, C, M and Y inks  206  and the transparent ink  212  on the recording medium  16 , simultaneously, or by depositing one of these liquids first and depositing another subsequently, in such a manner that the liquids make contact with each other. By depositing the treatment liquid  204  which contains a polymerization initiator, K, C, M and Y inks  206  which contains ink coloring material and a polymer compound, and the transparent ink  212  which contains a polymer compound but does not contain ink coloring material, it is possible to effectively suppress bleeding or landing interference. 
     From the viewpoint of further suppressing the occurrence of bleeding and landing interference, the treatment liquid used in the present embodiment contains a high-boiling-point organic solvent which has a viscosity at 25° C. of 100 mPa·s or below and a viscosity at 60° C. of 30 mPa·s or below (Condition 1), and has a boiling point exceeding 100° C. (Condition 2). The treatment liquid also contains a dispersion inhibitor and a polymerization initiator, which prevent the spreading of the K, C, M and Y inks (the dots formed by the K, C, M and Y inks) after K, C, M and Y inks have landed on the treatment liquid. 
     In the case of a high-boiling-point organic solvent which does not satisfy either of the viscosity conditions stated in the above Condition 1, the viscosity is high and the solvent may inhibit the deposition of liquid onto the recording medium. On the other hand, in the case of a high-boiling-point organic solvent which does not satisfy the boiling-point conditions stated in the above Condition 2, the boiling point is too low, and hence the solvent evaporates during image formation and this may impede the effects of preventing landing interference according to the present embodiment. Furthermore, the evaporation and dispersion into the atmosphere of this solvent is undesirable from an environmental point of view. 
     With regard to the conditions stated in the above Condition (1), more desirably, the viscosity at 25° C. is 70 mPa·s or below, even more desirably, it is 40 mPa·s or below, and especially desirably, it is 20 mPa·s or below. Desirably, the viscosity at 60° C. is 20 mPa·s or below, and especially desirably, it is 10 mPa·s or below. Here, the “viscosity” according to embodiments of the present invention is the viscosity found by using a RE80 type viscometer manufactured by Toki Sangyo Co., Ltd. The RE80 viscometer is based on a conical rotor/flat plate measurement system equivalent to an E type, and measurement is carried out on the basis of a Code No. 1 rotor, at a rotational speed of 10 rpm. In the cases of material having a viscosity greater than 60 mPa·s, according to requirements, measurement is carried out by changing the rotational speed to 5 rpm, 2.5 rpm, 1 rpm, 0.5 rpm, and the like. 
     Furthermore, with regard to the boiling point in the above Condition (2), more desirably, the boiling point is 150° C. or above, and especially desirably, 170° C. or above. Moreover, desirably, the high-boiling-point organic solvent has a melting point of 80° C. or below, and a water solubility (at 25° C.) is 4 g or less. More desirably, the water solubility is 3 g or less, even more desirably, it is 2 g or less, and especially desirably, 1 g or less. Here, the “water solubility” according to the present embodiment is the saturated density of water in the high-boiling point organic solvent at 25° C., and it means the mass (g) of water that can be dissolved per 100 g of the high-boiling-point organic solvent at 25° C. 
     In the present embodiment, desirable physical properties for liquid (inks) ejected as droplets onto the recording medium  16  are a viscosity of 5 to 100 mPa·s in each liquid, and more desirably, a viscosity of 10 to 80 mPa·s. Desirably, the surface tension of the ink composition is 20 to 60 mN/m, and more desirably, 30 to 50 mN/m. 
     With regard to even more desirable properties, desirably, each of a viscosity difference between the treatment liquid  204  and the K, C, M and Y inks  206 , and a viscosity difference between the treatment liquid  204  and the transparent ink  212 , is 25 mPa·s or less. Desirably, each of a surface tension difference between the treatment liquid  204  and the K, C, M and Y inks  206 , and a surface tension difference between the treatment liquid  204  and the transparent ink  212 , is 20 mN/m or less. Furthermore, there are no particular restrictions on the mass of the liquid droplets, which is selected in accordance with the sharpness of the image to be formed, but in general, desirably, the mass per droplet of one liquid is approximately 0.5 pl to 10 pl. 
     When droplets of the treatment liquid  204  are ejected from the treatment liquid head  12 S prior to the K, C, M and Y inks  206  and the transparent ink  212 , then landing interference occurs due to the fact that the treatment liquid  204  itself makes direct contact with the recording medium  16 , and the peripheral sections of the ejected liquid droplets have a ragged shape. However, since the treatment liquid does not contain any coloring material, this occurrence of landing interference does not cause problems. 
     Furthermore, since the droplets of K, C, M and Y inks  206  are ejected so as to make contact with the treatment liquid  204  on the recording medium  16  onto which the treatment liquid  204  has already been deposited, then landing interference does not occur between the droplets of the K, C, M and Y inks (either between inks of the same color or between inks of different colors), and hence the dot shapes formed by the ink droplets are preserved. 
     The K, C, M and Y inks  206  including ink coloring material, and the transparent ink  212  which does not contain coloring material, contain at least one polymer compound of an ultraviolet-curable monomer, an ultraviolet-curable oligomer, and a combination of these. 
     When the K, C, M and Y inks  206  and the transparent ink  212  land on the treatment liquid  204 , and the K, C, M and Y inks  206  and the transparent ink  212  make contact with the treatment liquid  204 , then landing interference of the K, C, M and Y inks  206  is prevented and the polymerization initiator in the treatment liquid  204  mixes with the K, C, M and Y inks  206  and the transparent ink  212 . When ultraviolet light is irradiated onto this mixed liquid, the mixed liquid (namely, the treatment liquid  204 , the K, C, M and Y inks  206 , and the transparent ink  212 ) cures and becomes fixed onto the recording medium  16 . 
     In an embodiment where only the treatment liquid  204  contains a polymerization initiator, even if leaked light of ultraviolet light irradiated from the ultraviolet light source  41  reaches the heads  12 K,  12 C,  12 M,  12 Y and  12 T which eject droplets of K, C, M and Y inks  206  and transparent ink  212 , the ink in the nozzles  51  (shown in  FIG. 5 ) of the heads  12 K,  12 C,  12 M,  12 Y and  12 T is not cured, and therefore it is possible to prevent blocking of the nozzles of the heads  12 K,  12 C,  12 M,  12 Y and  12 T. 
     In the ink set used in the present example, a polymerization initiator may also be included in the K, C, M and Y inks  206  and the transparent ink  212 . In a two-liquid system where inks (in the present embodiment, the K, C, M and Y inks  206  containing ink coloring material, and the transparent ink  212  which does not contain coloring material) and a treatment liquid  204  which does not contain a polymerization initiator are used, desirably, the balance in the amount of liquid deposited per droplet onto the image forming region (indicated by reference numeral  202  in  FIGS. 7A and 7B ) of the recording medium  16  is such that, taking the deposition amount of the K, C, M and Y inks  206  and the deposition amount of the transparent ink to be 1, the deposition amount (mass ratio) of the treatment liquid is in the range of 0.05 to 5, more desirably, the range of 0.07 to 1, and even more desirably, the range of 0.1 to 1. By setting the ratio of the transparent ink  212  with respect to the K, C, M and Y inks  206  to be 5 or less, superior image quality can be obtained from the viewpoint of relief effects, and furthermore, by setting the ratio to be 0.05 or above, then a suitable effect in preventing landing interference, which is the beneficial effect of the present embodiment, can be obtained. 
     Furthermore, if each of the K, C, M and Y inks  206  and the transparent ink  212  contains a polymerization initiator, then if leaked light of ultraviolet light irradiated from the ultraviolet light source  41  shown in  FIG. 1  reaches the nozzle forming surface (ejection surface) of the heads  12 K,  12 C,  12 M,  12 Y and  12 T, the ink inside the nozzles  51  undergoes a polymerization reaction and becomes cured inside the nozzles  51  of the heads  12 K,  12 C,  12 M,  12 Y and  12 T, thus giving rise to ink blockages in the nozzles  51 . In particular, in the case of the transparent ink head  12 T which is closest to the ultraviolet light source  41 , the leaked light of the ultraviolet light irradiated from the ultraviolet light source  41  is more likely to reach the head  12 T than the other heads, and hence there is a greater probability that the ink inside the nozzles  51  cures due to leaked light of this kind. Therefore, in a mode where the K, C, M and Y inks  206  and the transparent ink  212  contain a polymerization initiator, it is desirable to provide a shielding member which shuts out the leaked ultraviolet light, between the ultraviolet light source  41 , and the heads  12 K,  12 C,  12 M,  12 Y and  12 T. 
     To give examples of the shielding member described above, it is possible to install a shielding plate between the ultraviolet light source  41  and the transparent ink head  12 T, and it is also possible to provide shutter mechanisms on the nozzle forming surfaces of the heads  12 K,  12 C,  12 M,  12 Y and  12 T, the opening and shutting of the shutter mechanisms being controlled in accordance with the irradiation timing of the ultraviolet light source  41  and the droplet ejection timing of the heads  12 K,  12 C,  12 M,  12 Y and  12 T. 
     Furthermore, it is possible to adopt a composition in which a polymerization initiator is included in the treatment liquid  204  and the transparent ink  212 . By including a polymerization initiator in the transparent ink, it is possible to ensure that the transparent ink  212  cures reliably, and furthermore, it is also possible to prevent nozzle blockages caused by leaked light of ultraviolet light irradiated from the ultraviolet light source  41 , in the heads  12 K,  12 C,  12 M and  12 Y corresponding to the K, C, M and Y inks  206 . 
     It is also possible to adopt a composition in which, instead of transparent ink  212 , an ink of the same color (or the similar color type) as the recording medium  16  is used, in such a manner that it completely covers at least the non-image forming region. Here, the “similar color type” includes light inks, dark inks, and the like, and for example, if the color of the recording medium  16  is cyan, then a composition can be adopted in which a cyan or light cyan ink is used instead of the transparent ink  212 . 
     Description of Curing Energy 
     In the inkjet recording apparatus  10  according to the present embodiment, with a view to obtaining excellent fixing properties, a process is implemented for fixing an image on the recording medium  16  by applying energy after image formation. 
     In other words, by applying energy to the mixed liquid combining treatment liquid  204 , the K, C, M and Y inks  206 , and the transparent ink  212  deposited on the recording medium  16 , it is possible to form a strongly fixed and resilient image, efficiently, by means of polymerization and curing reactions. In the present embodiment, this application of energy is performed by irradiating radiation, such as ultraviolet light. 
     In other words, the generation of active material (active species) caused by the decomposition of the polymerization initiator in the mixed liquid is promoted by the energy (ultraviolet light) given by the ultraviolet light source  41 , and furthermore, the polymerization and curing reaction of the polymer compound caused by the active material is promoted, by increase in the active material and increase in the temperature. 
     In the present embodiment, an ultraviolet light source is described as one example of an exposure light source for promoting the polymerization of the polymer compound. Besides this embodiment, it is also possible to apply energy by irradiating visible light, α rays, γ rays, X rays, an electron beam, or the like, and of these, ultraviolet light and visible light are desirable from the viewpoint of cost and safety, and ultraviolet light is particularly desirable. The amount of energy required for the curing reaction varies depending on the type and the contained amount of the polymerization initiator, and in general, it is about 1 to 500 mJ/cm 2 . 
     Description of the Recording Medium 
     In embodiments of the present invention, it is possible to use an ink-permeable type of recording medium and an non-ink-permeable type of recording medium. Examples of ink-permeable recording media include: normal paper, paper for inkjet printing, coated paper, electronic photographic paper, cloth, non-woven cloth, porous film, high-polymer absorbing body, and the like. These are described as “recording media” in Japanese Patent Application Publication No. 2001-1891549, and the like. 
     The outstanding beneficial effects of embodiments of the present invention are notably seen in the cases of recording media which have slow ink permeability or zero ink permeability. Examples of recording media which have slow or zero permeability for ink include art paper, synthetic resin, rubber, resin-coated paper, glass, metal, ceramic, wood, and the like. In order to add other functions, it is also possible to use a composite base material in which some or all of these materials are combined. 
     For the synthetic resin, it is possible to use any type of synthetic resin, and typical examples include: polyethylene terephthalate, polybutadiene terephthalate or other polyesters, polyvinyl chloride, polystyrene, polyethylene, polyurethane, polypropylene or other polyolefins, acrylic resins, polycarbonate, acrylonitrile-butadiene styrene copolymer, diacetate, triacetate, polyimide, cellophane, celluloid, and the like. There are no restrictions on the thickness and shape of these synthetic resin base materials, and they may have a film shape, a card shape, or a block shape, or the like. Furthermore, the synthetic resin may be transparent or it may be opaque. 
     For the mode of using synthetic resin, it is desirable to use the resin in the form of a film as used in so-called soft packages, and it is possible to use various types of non-absorbent plastics or non-absorbent plastic films. Examples of such plastic films include PET film, OPS film, OPP film, PNy film, PVC film, PE film, TAC film, and the like. Other plastics may also be used, such as polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubber, or the like. 
     As a resin-coated paper, for example, it is possible to use papers, such as a transparent polyester film, an opaque polyester film, an opaque polyolefin resin film, a paper support body having polyolefin resin covering both surfaces of the paper, or the like, and the paper support body having polyolefin resin covering both surfaces of the paper is especially desirable. 
     As regards the metal, any type of metal can be used, and it is desirable to use metals such as aluminum, steel, gold, silver, copper, nickel, titanium, chromium, molybdenum, silicon, lead, zinc, and a composite material combining these with stainless steel, or the like. 
     For the recording medium used in embodiments of the present invention, it is possible to use read-only optical disks, such as a CD-ROM and DVD-ROM, a write-once type of optical disk, such as a CD-R or DVD-R, or a rewriteable optical disk. It is also possible to provide an ink accommodating layer and a gloss application layer onto the label surface of such disks. 
     Further Embodiments 
     The treatment liquid  204  does not necessarily have to be deposited on the recording medium  16  in the form of droplets ejected from a treatment liquid head  12 S, and it may also be deposited by another device. From the viewpoint of suppressing bleeding or landing interference, it is desirable that droplets of K, C, M and Y inks  206  and transparent ink  212  are ejected from the nozzles  51  of the heads  12 K,  12 C,  12 M,  12 Y,  12 T, simultaneously with or after the deposition of the treatment liquid  204  onto the recording medium  16 . 
     As modes of depositing the treatment liquid  204  on the recording medium  16 , an application member of simple composition which applies treatment liquid by making soft roller contact the recording medium  16 , may be provided, and an application apparatus may also be provided. There are no particular restrictions on the application apparatus, and a commonly known application apparatus may be appropriately selected in accordance with the desired objectives. Examples of application apparatuses include: an air doctor coater, a blade coater, a rod coater, a knife coater, a squeeze coater, an immersion coater, a reverse roll coater, a transfer roll coater, a gravure coater, a kiss roll coater, a cast coater, a spray coater, a curtain coater, an extrusion coater, and the like. For more details, we can refer to a document “Coating Engineering” attributed to Yuji Harazaki. Furthermore, a mode in which a treatment liquid head  12 S and an application device are jointly used, is also possible. 
     In the embodiments described above, one treatment liquid head  12 S is disposed on the furthest upstream side of the print unit  12  (see  FIG. 2 ); however, it is also possible to integrate the treatment liquid head  12 S with the furthest upstream side head of the heads  12 K,  12 C,  12 M,  12 Y and  12 T corresponding to the K, C, M and Y inks  206  and the transparent ink  212 . In other words, a composition is possible in which droplets of treatment liquid  204  are ejected from a portion of the nozzles  51  provided in one head, and droplets of K, C, M and Y inks  206  and transparent ink  212  are ejected from the remaining nozzles  51 . Moreover, it is also possible to adopt a composition in which the treatment liquid head  12 S, the K, C, M and Y ink heads  12 K,  12 C,  12 M,  12 Y, and the transparent ink head  12 T, are formed in an integrated fashion. 
     The treatment liquid  204  is deposited in a substantially uniform fashion (substantially evenly) on the prescribed region of the recording medium  16  (the treatment liquid deposition region shown in  FIGS. 7A and 7B ), and therefore, a high-density dot formation is not required for the treatment liquid in comparison with the K, C, M and Y inks  206  and the transparent ink  212 . Consequently, the treatment liquid head  12 S may also be composed with a reduced number of nozzles (a reduced nozzle density) in comparison with the K, C, M and Y ink heads  12 K,  12 M,  12 C and  12 Y, and the transparent ink head  12 T. 
     It is also possible to adopt a composition in which the nozzles of the treatment liquid head  12 S are larger in diameter than the nozzles of the KCMY ink heads  12 K,  12 C,  12 M,  12 Y, and the transparent ink head  12 T. By making the diameter of the nozzles of the treatment liquid head  12 S larger, it is possible to eject droplets of treatment liquid  204  having a higher consistency (viscosity). 
     Furthermore, the transparent ink  212  is ejected so as to cover completely the whole of the treatment liquid deposition region  200  (see  FIGS. 7A and 7B , or the like) where treatment liquid  204  has been deposited, and therefore, a high-density dot formation is not required for the transparent ink in comparison with the K, C, M and Y inks. Consequently, the transparent ink head  12 T may also have a smaller number of nozzles (a lower nozzle density) than the KCMY ink heads  12 K,  12 C,  12 M and  12 Y, and it may also have nozzles of larger diameter. 
     In this way, by increasing the nozzle diameter of the treatment liquid head  12 S which ejects droplets of treatment liquid  204 , and by increasing the nozzle diameter of the transparent ink head  12 T, in comparison with the heads  12 K,  12 C,  12 M and  12 Y which eject droplets of K, C, M and Y inks  206 , it can be expected to make manufacturing of the treatment liquid head  12 S and the transparent ink head  12 T more easy. 
     If the landing position error in the treatment liquids  204  and the transparent inks  212  is taken into account, then a desirable mode is one in which the nozzle densities of the treatment liquid head  12 S and the transparent ink head  12 T are substantially the same, and furthermore, it is also desirable that the treatment liquid head  12 S and the transparent ink head  12 T have substantially the same nozzle diameter. 
     If it is difficult to cover the treatment liquid deposition region completely with the K, C, M and Y inks  206  and the transparent ink  212 , due to landing variation in the treatment liquid  204  and the transparent ink  212 , then uncured treatment liquid can remain. Therefore, desirably, the treatment liquid deposition region  200  and the transparent ink droplet ejection region  210  are determined in such a manner that the outer edge section (inner edge section) of the transparent ink droplet ejection region  210  lies to the outer side of the outer edge section of the treatment liquid deposition region  200 . 
     Furthermore, embodiments are described above in which the K, C, M and Y ink heads  12 K,  12 C,  12 M and  12 Y are provided on the upstream side of the print unit  12 , and a transparent ink head  12 T is provided after the K, C, M and Y ink heads  12 K,  12 C,  12 M and  12 Y (on the downstream side); however, it is also possible to provide the transparent ink head  12 T on the upstream side of the K, C, M and Y ink heads  12 K,  12 C,  12 M and  12 Y (before the K, C, M and Y ink heads  12 K,  12 C,  12 M and  12 Y). 
     In other words, it is possible to adopt a composition in which droplets of transparent ink  212  are ejected so as to cover completely the non-image forming region (not illustrated), which is a region other than the image forming region  202  where droplets of the K, C, M and Y inks  206  are to be ejected, of the region of the treatment liquid deposition region  200  onto which treatment liquid  204  has been deposited on the recording medium  16 , whereupon droplets of the K, C, M and Y inks  206  are subsequently ejected onto the image forming region  202 . 
     According to the composition described above, by ejecting droplets of transparent ink  212  prior to the K, C, M and Y inks  206 , it is possible to suppress unwanted spreading of the K, C, M and Y inks  206  when they land, and hence degradation of image quality caused by dot spreading can be prevented. 
     The inkjet recording apparatuses  10  having the composition described above is inkjet recording apparatuses based on a two-liquid system in which an image is formed on a recording medium  16  by using a treatment liquid  204  containing a polymerization initiator, a dispersion inhibitor, and a high-boiling-point organic solvent, K, C, M and Y inks  206  containing an ink coloring material, and at least one of an ultraviolet-curable monomer, an ultraviolet-curable oligomer, and a combination of same, and a transparent ink  212 . In these inkjet recording apparatuses, the treatment liquid  204  is deposited onto a treatment liquid deposition region  200  which is set to be wider than the image forming region  202  where droplets of the K, C, M and Y inks  206  are ejected onto the recording medium  16 . Consequently, landing interference is prevented due to the fact that the K, C, M and Y inks  206  land on the treatment liquid, and it is also possible to prevent degradation of the image quality caused by displacement of the dot positions due to movement of the K, C, M and Y inks  206  arising when the inks  206  land on undulations (inclined sections) at the peripheral sections of the treatment liquid  204 . Furthermore, since droplets of transparent ink  212  are ejected in such a manner that the transparent ink  212  covers completely the region of the treatment liquid deposition region  200  onto which droplets of the K, C, M and Y inks have not been ejected, then it is possible to prevent an unreacted treatment liquid  204  remaining on the recording medium  16 . 
     Moreover, after ejecting droplets of the K, C, M and Y inks  206  and the transparent ink  212  so as to cover completely the treatment liquid deposition region  200 , the K, C, M and Y inks  206  and the transparent ink  212  are cured by being irradiated with ultraviolet light, thus fixing the image formed on the recording medium  16 . 
     In the foregoing embodiments, an inkjet recording apparatus  10  using page-wide full line type heads  50  ( 12 K,  12 C,  12 M and  12 Y) having nozzle rows of a length corresponding to the entire width of the recording medium  16  is described; however, the scope of application of the present invention is not limited to this. The present invention may also be applied to an inkjet recording apparatus using a shuttle head which performs image recording while a recording head of short dimensions is moved in a reciprocal fashion. 
     In the foregoing embodiments, an inkjet recording apparatus  10  for forming images on a recording medium  16  by ejecting ink from nozzles  51  provided in a head (inkjet head)  50  is described; however, the scope of application of the present invention is not limited to this. The present invention may also be applied broadly to image forming apparatuses which form images (three-dimensional shapes) by means of a liquid other than ink, such as resist, and to liquid ejection apparatuses, such as dispensers which eject liquid chemicals (drug solution), water, or the like, from nozzles (ejection holes). 
     It should be understood that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.