Patent Publication Number: US-8118401-B2

Title: Printing apparatus

Description:
This application claims priority to Japanese Patent Application No. 2008-219055, filed Aug. 28, 2008, the entirety of which is incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a printing technology for superposedly forming an image layer representing an image and a specific glossy layer that is different from the image layer on a printing medium. 
     2. Related Art 
     A method in which a primer coating layer is firstly formed on a printing medium and printing is performed on the primer coating layer is known (for example, Patent Document JP-T-2002-530229). The method can be adapted to various printing methods. For example, the method can be used to reproduce metallic colors having various tones. In order to reproduce the metallic color, for example, a metallic ink layer may be formed on a printing medium, and color inks are superposedly printed on the metallic ink layer. 
     However, in order to perform the metallic color printing in the an ink jet printer, a print head needs to have separate nozzles that eject metallic inks as well as nozzles that eject color inks for forming an image. Therefore, there is a problem in that cost for the printing apparatus is increased. Particularly, the printing apparatus is relatively expensive for a user who does not frequently use the metallic color printing. The problem is not limited to the metallic color printing, but it commonly occurs in cases where an image layer representing an image and another layer are superposedly printed on the printing medium. 
     SUMMARY 
     An advantage of some aspects of the invention is to suppress an increase in cost of a printing apparatus and to efficiently print a plurality of ink layers. 
     The invention is to provide at least a portion of the aforementioned problems. Therefore, the invention can be implemented by the following embodiments or application examples. 
     According to an aspect of the invention, there is provided a printing apparatus that superposedly forms an image layer representing an image and a specific glossy layer that is different from the image layer on a printing medium, including: a first connection unit that can be connected to a basic color ink container containing three primary color inks of which combination is used for performing color representation; a second connection unit that can be connected to a specific color ink container containing a specific color ink other than the three primary color inks; a reception unit that receives a kind of print available ink; a print head where nozzle columns in which a plurality of nozzles are aligned in a predetermined direction are arrayed in a direction intersecting an alignment direction of the nozzles in the nozzle columns, and at least one of specific color nozzle columns ejecting the specific color ink among the nozzle columns is disposed as an end-portion specific color nozzle column to at least one of end portions of the print head in the array direction of the nozzle columns; and a printing unit that performs printing by moving the print head relative to the printing medium and ejecting the three primary color inks and/or the specific color ink on the printing medium from the nozzle columns. At least the connection unit that can supply the ink to the end-portion specific color nozzle column inside the second connection unit can be connected to a specific gloss agent container containing a specific gloss agent that is used to form the specific glossy layer instead of the specific color ink container. When the specific gloss agent container is connected to the second connection unit and the reception unit receives the specific gloss agent as the available ink, the printing unit ejects the specific gloss agent from the end-portion specific color nozzle column to form the specific glossy layer. 
     In the printing apparatus having the configuration, a specific gloss agent instead of the specific color ink can be ejected from the end-portion specific color nozzle column disposed to at least one end portion in the alignment direction of the nozzle columns. Since the end-portion specific color nozzle column is disposed at the end portion in the alignment direction, the specific gloss agent can be ejected before any one of the three primary color inks and the specific color ink or after any one thereof according to the direction of the relative movement of the print head with respect to the printing medium. In other words, the specific glossy layer and the image layer can be superposedly printed on the printing medium in the order of the specific glossy layer and the image layer or in the order of the image layer and the specific glossy layer. In addition, since specific gloss agent is ejected by using the specific color nozzle column, the print head needs not to have any nozzle column dedicated to the specific gloss agent, so that it is possible to implement an economical printing apparatus. 
     In the printing apparatus according to the invention, the end-portion specific color nozzle columns may be disposed at both end portions of the print head in the array direction of the nozzle columns, and printing unit may eject the specific gloss agent from one of the end-portion specific color nozzle columns disposed at both end portions according to the direction of the relative movement of the print head to form the specific glossy layer. 
     In the printing apparatus having the configuration, since the specific gloss agent is ejected from any one of the end-portion specific color nozzle columns disposed at the two end portions in the alignment direction of the nozzle columns of the print head, the ejecting order of the specific gloss agent, the three primary color inks, and the specific color inks can be changed. In other words, the specific glossy layer and the image layer can be superposedly printed in a desired order. In addition, in a case where the printing apparatus is a serial type printing apparatus, even in bi-directional printing where the ink or the like is ejected from any one of the directions of the relative movements, the image layer and the specific glossy layer can be superposedly printed in a desired order by changing the end-portion specific color nozzle columns ejecting the specific gloss agent according to the directions of the relative movement of the print head. 
     In the printing apparatus according to the invention, each of the basic color ink container, the specific color ink container, and the specific gloss agent container may include a storage unit storing the kind of the contained ink and a communication unit communicating with the printing apparatus, and the reception unit may perform the reception by receiving a signal indicating the kind of ink through the communication unit from the container that is connected to the first connection unit or the second connection unit. 
     Since the printing apparatus having the configuration receives signals from the connected container to receive the kinds of the available inks, that is, to receive the kinds of the inks contained in the connected container, the printing apparatus can be easily manipulated. 
     In the printing apparatus according to the invention, the end-portion specific color nozzle column may be a nozzle column that ejects the specific color ink other than a black ink. 
     Since the specific color inks except for the black ink generally has a low use frequency in comparison with the black ink, in the printing apparatus having the configuration, influence of connection of the specific gloss agent container to at least a portion of the second connection unit to the image quality of the image layer can be suppressed in a low level. 
     In the printing apparatus according to the invention, the end-portion specific color nozzle column may be a nozzle column that ejects a light ink where coloring ingredients of the three primary color inks have low concentrations. 
     Since the printing apparatus having the configuration can be adapted to a printing apparatus using light inks, the printing apparatus can be used with high general versatility. 
     The aforementioned printing apparatuses can be applied to specific gloss agents of Application Example 6 or 7. 
     In the printing apparatus according to the invention, the specific gloss agent may be an ink of which optical property has a reflection angle dependency when the ink is printed on a surface of the printing medium. 
     In the printing apparatus according to the invention, the specific gloss agent may be an ink that includes a pigment expressing a metallic sensation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description will be clarified by the specification and the accompanying drawings. 
         FIG. 1  is a schematic view showing a configuration of a printing system  10  according to an embodiment of the invention. 
         FIG. 2  is a view showing a configuration of a computer  100  as a printing control apparatus. 
         FIG. 3  is a view showing a configuration of a printer  200 . 
         FIG. 4  is a view for explaining details of a print head  250 . 
         FIG. 5  is a flowchart showing a procedure of a printing process. 
         FIGS. 6A and 6B  are views for explaining situation of ink change and printing in a printing process. 
         FIGS. 7A and 7B  are views for explaining situation of ink change and printing according to a modified example. 
         FIG. 8  is a flowchart showing details of a step S 430  of a printing process according to another modified example. 
         FIGS. 9A and 9B  are views for explaining situation of ink change and bi-directional printing according to another modified example. 
         FIG. 10  is a view for explaining details of a print head  250   b  and situation of ink change according to another modified example. 
         FIG. 11  is a view for explaining details of a print head  250   c  and situation of ink change according to another modified example. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A. Printing System 
       FIG. 1  is a schematic view showing a configuration of a printing system  10  according to an embodiment of the invention. As shown in the figure, the printing system  10  according to the embodiment includes a computer  100  that is used as a printing control apparatus and a printer  200  that actually prints an image under the control of the computer  100 . The printing system  10  integrally functions as a printing apparatus in a wide sense. 
     In the printer  200  according to the embodiment, a cyan ink C, a magenta ink M, a yellow ink Y, a black ink K, a light cyan ink Lc, and a light magenta ink Lm are provided as color inks. In addition, instead of the inks, a metallic ink S may be provided. In addition, in the invention, “color ink” may also include a black ink. In the embodiment, the color ink is a dye ink. However, the kind of the color inks is not particularly limited. Therefore, for example, the color ink may be a pigment ink. In addition, in the embodiment, among the color inks, the cyan ink C, the magenta ink M, and the yellow ink Y that are used for color representation using subtractive color mixture are referred to as “three primary color inks”, and except for the three primary color inks, the black ink K, the light cyan ink Lc, and the light magenta ink Lm are referred to as “specific color inks”. 
     The metallic ink is an ink that allows a printed material to express a metallic sensation. For example, as the metallic ink, an oil ink composition of a metallic pigment expressing the metallic sensation, an inorganic solvent, and a resin may be used. In order to effectively form visually-metallic sensation, the aforementioned metallic pigment is preferably constructed with tabular particles. In a case where a planar long diameter, a planar short diameter, and a thickness of the tabular particle are X, Y, and Z, respectively, it is preferable that an average particle diameter R 50  which is 50% of a circle-equivalent diameter obtained from an area of an X-Y plane of a tabular particle is in a range of 0.5 to 3 μm, and a condition of R 50 /Z&gt;50 is satisfied. For example, the metallic pigment may be formed from aluminum or an aluminum alloy. In addition, the metallic pigment may be prepared by crushing a metal vaporizing layer. A concentration of the metallic pigment included in the metallic ink may be, for example, in a range of 0.1 to 10.0 wt %. The composition of the metallic ink is not limited thereto. Other compositions that can create a metallic sensation may be suitably employed. 
     In the embodiment, the composition of the metallic ink S is 1.5 wt % of aluminum pigment, 20 wt % of glycerin, 40 wt % of triethylene glycol monobuthyl ether, and 0.1 wt % of BYK-UV3500 (manufactured by BYK Chemie Japan). 
     A predetermined operating system is installed in the computer  100 , and an application program  20  is operated under the operating system. In the operating system, a video driver  22  or a printer driver  24  is assembled. For example, the application program  20  inputs image data ORG from a digital camera  120  through a peripheral-apparatus interface  108 . Next, the application program  20  displays an image represented by the image data ORG on a display  114  by using the video driver  22 . In addition, the application program  20  outputs the image data ORG to the printer  200  by using the printer driver  24 . The image data ORG that the application program  20  inputs from the digital camera  120  are data constructed with three color components, that is, red (R), green (G), and blue (B). 
     The application program  20  can designate, with respect to an arbitrary area within the image data ORG, an area (hereinafter, referred to as a “metallic area”) constructed with a metallic color as well as an area (hereinafter, referred to as a “color area”) constructed with R, G, and B color components. The metallic area and the color area may be superposedly disposed. In other words, these areas may be designated so that a color image is formed on a background of which color is a metallic color. 
     The printer driver  24  includes a color conversion module  42 , a halftone module  44 , and a printing control module  46 . 
     The color conversion module  42  converts the color components R, G, and B of the color area in the image data ORG to color components (cyan (C), magenta (M), yellow (Y), black (K), light cyan (Lc), and light magenta (Lm) colors) that can be represented by the printer  200  according to a prepared color conversion table LUT. 
     The halftone module  44  performs a halftone process that can represent gradation of the image data color-converted by the color conversion module  42  by using a distribution of dots. In the embodiment, a well-known ordered dither method is used as the halftone process. In addition to the ordered dither method, an error diffusion method, a concentration pattern method, or other halftone techniques may be used as the halftone process. 
     The printing control module  46  performs controlling the printer  200  by aligning data sequence of the halftone-processed image data in the order for transmission to the printer  200 , outputting the data sequence as printing data to the printer  200 , and outputting various commands such as a printing start command and a printing end command to the printer  200 . In addition, the printing control module  46  forms dots with the metallic ink on the metallic area designated by the application program  20 . 
     B. Configuration of Apparatus 
       FIG. 2  is a view showing a configuration of the computer  100  as the printing control apparatus. The computer  100  is a well-known computer where a CPU  102 , a ROM  104 , a RAM  106 , and the like are connected to each other through a bus  1   16 . 
     A disk controller  109  that is used to read data from a flexible disk  124 , a compact disk  126 , or the like, a peripheral-apparatus interface  108  that is used to receive/transmit data from/to peripheral apparatuses, and a video interface  112  that is used to drive the display  114  are connected to the computer  100 . The printer  200  and the hard disk  118  are connected to the peripheral-apparatus interface  108 . In addition, if a digital camera  120  or a color scanner  122  is connected to the peripheral-apparatus interface  108 , an imaging process can be performed on an image acquired by the digital camera  120  or the color scanner  122 . In addition, if a network interface card  110  is installed, the computer  100  is connected thereto through a communication line  300 , and thus, data stored in a storage unit  310  connected to the communication line can be acquired. If the computer  100  acquires to-be-printed image data, the computer  100  performs printing of the image data by controlling the printer  200  through the function of the aforementioned printer driver  24 . 
     Next, a configuration of the printer  200  is described with reference to  FIG. 3 . As shown in  FIG. 3  the printer  200  includes a mechanism for transporting a printing medium P by using a sheet transporting motor  235 , a mechanism for reciprocatingly moving a carriage  240  in a shaft direction of a platen  236  by using a carriage motor  230 , a mechanism for ejecting ink and forming dots by driving a print head  250  mounted in the carriage  240 , and a control circuit  260  that controls signal communication with the sheet transporting motor  235 , the carriage motor  230 , the print head  250 , and a manipulation panel  266 . 
     The mechanism for reciprocatingly moving the carriage  240  in the shaft direction of the platen  236  includes a sliding shaft  233  that is disposed in parallel to the shaft of the platen  236  to slidably support the carriage  240 , a pulley  232  that longitudinally provides an endless driving belt  231  in a space between the pulley  232  and the carriage motor  230 , and a position detecting senor  234  that detects an original position of the carriage  240 . 
     Color ink cartridges  242  to  247  that contain color inks, that is, a cyan ink C, a magenta ink M, a yellow ink Y, a black ink K, a light cyan ink Lc, and a light magenta ink Lm, respectively, are mounted in the carriage  240 . Six kinds of nozzle columns  252  to  257  corresponding to the aforementioned color inks are formed in the print head  250  in a lower portion of the carriage  240 . When the ink cartridges  242  to  247  are mounted in the carriage  240  from the upper side, the inks can be supplied from the cartridges to the nozzle columns  252  to  257 . In addition, in the embodiment, the ink cartridges  242  to  247  have IC chips in which kinds of contained inks are recorded. Therefore, although not shown, if the ink cartridges  242  to  247  are mounted in the carriage  240 , the IC chips are designed to be electrically connected to the control circuit  260 . The aforementioned nozzle columns  252  to  257  correspond to the specific color nozzle columns in Claims. The aforementioned nozzle columns  256  and  257  correspond to the end-portion specific color nozzle column in Claims. In addition, the carriage  240  corresponds to the first connection unit and the second connection unit in claims. Although the first and second connection units in claims may be separately constructed, the first and second connection units may be integrally constructed like the connection unit of the embodiment. 
     In the control circuit  260  of the printer  200 , a CPU, a ROM, a RAM, a PIF (peripheral-apparatus interface), and the like are connected through a bus. The control circuit  260  controls main and sub scan movements of the carriage  240  by controlling operations of the carriage motor  230  and the sheet transporting motor  235 . In addition, if the control circuit  260  receives the printing data output from the computer  100  through the PIF, the control circuit  260  can drive the print head  250  for each color by applying a driving signal corresponding to the printing data to the print head  250  in accordance with the main or sub scan movement of the carriage  240 . In addition, the control circuit  260  corresponds to a printing unit in Claims and also has a function as a reception unit. 
     In the printer  200  having the aforementioned configuration, the print head  250  (nozzle columns  252  to  257  corresponding to the colors) is reciprocatingly moved in a main scan direction with respect to the printing medium P by driving the carriage motor  230 , and the printing medium P is moved in a sub scan direction by driving the sheet transporting motor  235 . The control circuit  260  forms ink dots having suitable colors at suitable position on the printing medium P by driving nozzles at suitable timings based on the printing data in accordance with the reciprocating movement (main scan) of the carriage  240  or the sheet transporting movement (sub scan) of the printing medium P. As a result, the printer  200  can print a color image on the printing medium P. In addition, in the aforementioned configuration, the ink for each color is contained in a detachable cartridge that is mounted in the printer  200 . Alternatively, the ink may be contained in an ink containing tank that is constructed in separation from the printer  200 , and the ink containing tank and the printer  200  can be connected. In addition, alternatively, the three primary color inks may be contained in a non-detachable container that is integrally provided to the printer  200 . 
     In addition, in the printer  200  according to the embodiment, the ink is ejected only in the forward movement path among the reciprocating movement of the print head  250  in the main scan direction, and one-directional printing that can implement high quality printing is used as default setting. In addition, in the printer  200 , a transparent printing medium such as an OHP film as well as an opaque printing medium such as normal paper and coat paper can be used as the printing medium P. 
     C. Details of Printing Head 
       FIG. 4  shows details of the aforementioned print head  250 . In the figure, a lower surface of the print head  250  (that is, a surface facing the printing medium P) is schematically shown. As shown in the figure, the print head  250  includes a plurality of the nozzle columns  252  to  257  that are aligned in the sub scan direction. In the embodiment, each nozzle column is constructed with 180 nozzles. The nozzle columns  252  to  257  correspond to ink colors of the cartridges mounted in the carriage  240 , so that the nozzle column  252  to  257  can eject the cyan ink C, the magenta ink M, the yellow ink Y, the black ink K, the light cyan ink Lc, and the light magenta ink Lm, respectively. In addition, in the embodiment, in each nozzle column corresponding to each ink color, the nozzles are aligned in one column, but the alignment of nozzles in one nozzle column is not particularly limited. For example, the nozzles may be aligned in multiple columns. Alternatively, the nozzles in the multiple columns may be disposed in a zigzag manner. 
     In addition, as shown in the figure, in the print head  250 , among the nozzle columns  252  to  257  that eject specific color inks, the nozzle column  256  corresponding to the light cyan ink Lc is disposed at the one end portion in the alignment direction of the nozzle columns  252  to  257 . In addition, the nozzle column  257  corresponding to the light magenta ink Lm is disposed at the other end portion in the alignment direction of the nozzle columns  252  to  257 . If the ink cartridges  246  and  247  containing the light cyan ink Lc and the light magenta ink Lm which are mounted in the carriage  240  are detached from the carriage  240  and if the ink cartridges  246  and  247  are replaced with the ink cartridge containing the metallic ink S, the nozzle columns  256  and  257  can eject the metallic ink S. Hereinafter, the replacement of the ink cartridges is referred to as “ink change”. 
     D. Printing Process 
     Now, the metallic color printing process that the computer  100  performs by using the functions of the printer driver  24  is described.  FIG. 5  is a flowchart showing the printing process according to the embodiment. In the embodiment, after a user performs the ink change from the light cyan ink Lc to the metallic ink S, the user instructs printing execution by manipulating the computer  100 , so that the printing process starts. When the printing process starts, the computer  100  firstly receives kinds of available inks (Step S 400 ). More specifically, the computer  100  periodically transmits signals to the IC chips provided to the ink cartridges  242  to  247 . In response to the received signal, the IC chips transmit signals indicating the kinds of inks recorded in the storage area to the computer  100 . The computer  100  analyzes the response signals to receive the kind of the ink cartridges  242  to  247  mounted in the carriage  240 , that is, the kinds of the available inks. In the embodiment, the metallic ink S, the cyan ink C, the magenta ink M, the yellow ink Y, the black ink K, and the light magenta ink Lm are received as the available inks. In addition, the method for receiving the available inks is not limited to the aforementioned method. For example, in a configuration, the kinds of the ink cartridges mounted in the carriage  240  may be input by user&#39;s manipulating the computer  100 , and the computer  100  may receive the kinds of the ink cartridges. 
     If the computer  100  receives the available inks, the computer  100  inputs image data designating the metallic area and the color area from the application program  20  by the printer driver  24  (Step S 410 ). 
     If the image data is input, the computer  100  converts RGB-format image data to CMYKLcLm-format image data in the color area of the image data (Step S 420 ). The conversion is performed by using a color conversion table LUT corresponding to the kinds of the available inks received in the Step S 400  among a plurality of stored color conversion tables LUT. When the CMYKLcLm-format image data is obtained, the computer  100  performs a halftone process by using the halftone module  44  to generate data that can be transmitted to the printer  200  (Step S 430 ). 
     After the halftone process, the computer  100  controls the printer  200  to print the metallic area by using the metallic ink S and to print the halftone-processed color area by using the color ink (Step S 440 ). In addition, the printing medium P 1  used in the embodiment is an opaque printing medium. In addition, in the embodiment, the computer  100  performs the one-directional printing by ejecting inks only in the forward movement path among the reciprocating movement of the print head  250  in the main scan direction. 
     The aforementioned Step S 440  is described in detail with reference to  FIGS. 6A and 6B . The scan direction of the print head  250  shown in  FIG. 6A  is the direction of the forward movement among the reciprocating movement in the main scan direction, that is, the scan direction in which the ink ejecting is performed. As shown in the figure, in the print head  250  according to the embodiment, since the ink change from the preceding light cyan ink Lc to the metallic ink S is performed, the nozzle column  256  disposed at the front end portion in the scan direction in which the ink ejecting is performed ejects the metallic ink S. Herein, the nozzle column  256  ejecting the metallic ink S firstly reaches a predetermined printing position on the printing medium P 1  prior to the other nozzle columns, so that the metallic ink S prior to the color inks is ejected. Next, according to the movement of the print head  250 , the nozzle columns  252  to  255  and  257  reach predetermined positions, so that color inks are ejected. 
     As shown in  FIG. 6B , in the printed material, a metallic ink layer MR where dots are formed by using the metallic ink S is firstly positioned on the printing medium P 1 , and color ink layer CR where dots are formed by using the color inks is superposedly positioned on the metallic ink layer MR. When the printed material is observed in the direction from the color ink layer CR to the printing medium P 1 , the metallic color of the printed material can be observed. 
     In this manner, in the printing system  10  according to the invention, the nozzle column  256  for the light cyan ink Lc that is a specific color ink is disposed, the front end portion in the scan direction in which the ink ejecting is performed among the end portions in the alignment direction of the nozzle columns of the print head  250 . Therefore, when the ink change from the light cyan ink Lc to the metallic ink S is performed, the metallic ink layer MR and the color ink layer CR are superposedly printed on the printing medium P 1  in the order. 
     In addition, since the nozzle column that is diverted to the nozzle column ejecting the metallic ink S is the nozzle column corresponding to a specific color ink, color representation can be performed to some extent by using the three primary color inks without using the ink color corresponding to the diverting nozzle column. Particularly, in a case where the metallic color printing is performed by superposing the color ink layer CR and metallic ink layer MR, brightness of the image is generally decreased in comparison with a case where only the color ink layer CR is performed. However, according to the embodiment, if the ink change from the light ink where a concentration of coloring ingredient (in the embodiment, a dye compound) of the three primary color inks is lowered to the metallic ink S is performed, the deterioration in image quality that is caused from the decrease in the number of kinds of the color inks used for the printing can be suppressed. In addition, since the nozzle column  256  that originally corresponds to the light cyan ink Lc is diverted to the metallic ink S, the print head  250  needs not to have any nozzle column dedicated to the metallic ink S, so that it is possible to implement an economical printing system. 
     E. MODIFIED EXAMPLE 
     Modified examples of the aforementioned embodiment are described. 
     E-1. Modified Example 1 
     In the embodiment, a metallic ink layer MR and a color ink layer CR are formed on an opaque printing medium P 1  in this order, and metallic color printing is performed. However, the order of forming the ink layers may be reversed. For example, as shown in  FIG. 7B , in a case where printing is performed on a transparent printing medium P 2 , the color ink layer CR and the metallic ink layer MR may be formed on the printing medium P 2  in this order. As a result, when a printed material is observed in the direction from printing medium P 2  to the metallic ink layer MR, the metallic color of the printed material can be observed. 
     In this case, since the order of forming the metallic ink layer MR and the color ink layer CR may be reversed with respect to the order of the example, the metallic ink S may be designed to be ejected from the nozzle column that is disposed at the rear end portion in the scan direction in which the ink ejecting is performed among the end portions in the alignment direction of the nozzle columns of the print head  250 . Therefore, as shown in  FIG. 7A , if the ink change from the light magenta ink Lm that is a specific color ink corresponding to the nozzle column  257  disposed at the rear end in the scan direction to the metallic ink S is performed, the color ink layer CR and the metallic ink layer MR can be superposedly printed on the printing medium P 1  in this order. 
     E-2. Modified Example 2 
     In the embodiment and Modified Example 1, the one-directional printing is exemplified as the metallic color printing. However, the printer  200  may be configured for bi-directional printing. More specifically, for example, the ink change from light inks corresponding to the nozzle columns  256  and  257  that are disposed at the two end portions in the alignment direction of the nozzle columns of the print head  250  to the metallic inks S may be performed. 
     In this case, since the bi-directional printing is performed, the Step  430  shown in  FIG. 5  can be replaced with, for example, a process shown in  FIG. 8 . More specifically, after a halftone process, the computer  100  determines whether or not a raster of a to-be-printed object includes a metallic area (Step S 431 ). As the result of determination, if the metallic area is not included (Step S 431 : NO), only the nozzle columns  252  to  255  ejecting the color inks among the nozzle columns  252  to  257  provided to the print head  250  are determined to be used, but the nozzle columns  256  and  257  ejecting the metallic inks S are determined not to be used (Step S 435 ). 
     On the other hand, if the metallic area is included in the raster of the to-be-printed object (Step S 431 : YES), the computer  100  determines whether or not the currently-performed scan operation of the print head  250  is a movement in the forward movement path among the reciprocating movement in the main scan direction (Step S 432 ). As the result of determination, if the currently-performed scan operation is the movement of the path of the forward movement (Step S 432 : YES), as shown in  FIG. 9A , the computer  100  determines that the nozzle column  256  disposed at the front end portion in the scan direction of the print head  250  among the nozzle columns  252  to  255  ejecting the color inks and the nozzle columns  256  and  257  ejecting the metallic inks S is used (the nozzle column  257  disposed at the rear end portion in the scan direction is not used) (Step S 433 ). 
     On the other hand, if the currently-performed scan operation of the print head  250  is not the movement in the forward movement path among the reciprocating movement in the main scan direction, that is, if the currently-performed scan operation is a movement in the backward movement path (Step S 432 : NO), as shown in  FIG. 9B , the computer  100  determines that the nozzle column  257  disposed at the front end in the scan direction of the print head  250  among the nozzle columns  252  to  255  ejecting the color inks and the nozzle columns  256  and  257  ejecting the metallic inks S is used (the nozzle column  256  disposed at the rear end portion in the scan direction is not used) (Step S 434 ). 
     If the to-be-used nozzle column is determined, the computer  100  controls the printer  200  to perform the printing by ejecting the metallic ink or the color ink from the to-be-used nozzle column determined in the Steps S 433  to S 435  during one-time scanning of the print head  250  (Step S 436 ). 
     During the one-time scanning of the print head  250   b , the computer  100  determines whether or not the printing for all the rasters is ended (Step S 437 ). As the result of determination, if the printing is determined not to be ended (Step S 437 : NO), the computer  100  returns the process to the Step S 431  to continue to perform the printing process on the raster where the printing is not performed. On the other hand, if the printing is determined to be ended (Step S 437 : YES), the computer  100  ends the printing process. 
     Even in a case where the printing is performed, the metallic color printing can be performed by forming the metallic ink layer MR and the color ink layer CR on the opaque printing medium P 1  in this order. In addition, since the metallic ink S and the color ink are simultaneously ejected on the same raster by one-time main scan, the decrease in the printing speed can be suppressed. In addition, in a case where the metallic ink layer MR and the color ink layer CR are formed in the reverse order, the used and not-used nozzle columns among the nozzle columns  256  and  257  in each scan direction may be exchanged. 
     E-3. Modified Example 3 
       FIG. 10  shows details of a print head  250   b  according to Modified Example 3. The print head  250   b  is different from the print head  250  shown in  FIG. 6A  in terms of the alignment of nozzle columns. More specifically, the example is different from the embodiment in that the nozzle column  257   b  and  255   b  corresponding to the specific color inks are disposed between the nozzle column  256   b  disposed at the front end portion in the scan direction of the print head and the nozzle columns  252   b  to  255   b  corresponding to the three primary colors. 
     In a case where the same metallic color printing as that of the embodiment is performed by using the print head  250   b , if the to-be-printed image of the metallic area is to be formed with no use of the light magenta ink Lm and/or the black ink K or with almost no use thereof, and if the printing is performed by performing the conversion process in the Step S 420 , a time interval from the time when the metallic ink S is landed at a position on the printing medium to the time when the three primary color inks are landed at the same position can be secured as a time for drying the landed metallic ink S. Therefore, mixing of the metallic ink S and the three primary color inks can be suppressed, so that deterioration in image quality can be suppressed. If the nozzle column corresponding to the specific color ink is disposed between the nozzle columns where the ink change is performed and the nozzle columns corresponding to the primary colors, the above effect can be obtained irrespective of the alignment order of nozzle columns. 
     E-4. Modified Example 4 
     In the aforementioned embodiment and Modified Examples, the metallic color printing is performed through the ink change from the light cyan ink Lc and/or the light magenta ink Lm corresponding to the nozzle columns disposed at the end portions in the alignment direction of the nozzle columns of the print head  250  to the metallic ink S. However, the nozzle columns disposed at the end portions of the print head  250  are not limited to the nozzle columns corresponding to the light cyan ink Lc or the light magenta ink Lm, but the nozzle columns may correspond to the specific color inks other than the three primary color inks. For example, the nozzle column corresponding to the black ink K may be disposed at the end portion, and the ink change from the black ink K to the metallic ink S may be performed. Alternatively, in a case where the printer  200  has a configuration capable of using specific color inks such as a blue ink, a red ink, a green ink, an orange ink, and a clear ink, the nozzle column corresponding to the specific color inks may be disposed at the end portion of the print head  250 , and the ink change from the specific color inks to the metallic ink S may be performed. 
     E-5. Modified Example 5 
     In the aforementioned embodiment and Modified Examples, a configuration where the metallic color printing is performed by superposedly forming a layer of metallic ink S and a layer of color ink on a printing medium is exemplified. However, the invention is not limited to a combination of the layer of metallic ink S and the layer of color ink, but the invention may be adapted to a configuration where an image layer representing an image and layers of various specific gloss agents are superposed. The specific gloss agent is an ink representing specific gloss on a printed surface of the printing medium. The specific gloss agent may be an ink of which optical property has a reflection angle dependency to express various hues according to a viewing angle when the ink is printed on a surface of the printing medium as well as a metallic ink including a pigment expressing a metallic sensation. More specifically, in addition to the metallic ink, a pearl glossy ink including a pigment expressing a pearl glossy sensation after the fixing on a surface of a printing medium or a lame ink or an earth ink including a pigment having micro-unevenness for expressing so-called lame sensation or earthy sensation that is caused from diffused reflection after the fixing on the surface of the printing medium may be used as the aforementioned ink. 
     In addition, the invention is not limited to the specific gloss agent, but it may be adapted to a case where an image layer and an auxiliary layer that assists the image layer are superposed. For example, a layer of assisting expression of the image layer can be used as the auxiliary layer. Herein, the phrase “assisting expression of the image layer” denotes expressing the color representation of the image layer, changing the color representation, and the like. For example, a white ink that is used as a base for expressing the color representation of the image layer and various inks that have a property of concealment may be used as an auxiliary material for forming the auxiliary layer. 
     In addition, for example, a layer of protecting or concealing the image layer may be used as the auxiliary layer. The auxiliary layer of protecting or concealing the image layer may be constructed with an overcoat agent for protecting the image layer by preventing the ink from peeling or deteriorating or an undercoat agent for improving a property of fixing of the image layer to the printing medium by forming a porous micro-particle layer. In addition, the auxiliary layer may be constructed with an ink having a low fixing force that is used to manufacture a scratch card. 
     In this manner, in a case where various layer and the image layer are superposedly printed, similarly to the aforementioned embodiment and Modified Examples, which one of the nozzle columns corresponding to the auxiliary layer which are disposed at the two end portions of the print head  250  is to be used may be determined by taking into consideration the order of forming the auxiliary layer and the image layer on the printing medium. In addition, the image layer is not limited to the plurality of the color inks like the embodiment. For example, a single color ink such as black ink K may be used. 
     E-6. Modified Example 6 
     In the aforementioned embodiment, the printing process shown in  FIG. 5  is performed by the printing system  10  (a printing apparatus in a wide sense) including the computer  100  and the printer  200 . However, a process equivalent to the printing process may be performed by a CPU in the control circuit  260  of the printer  200 . Accordingly, the image data can be input from a digital camera, various memory cards, or the like, so that suitable printing can be performed by the printer  200  without using the computer  100 . 
     E-7. Modified Example 7 
     In the aforementioned embodiment and Modified Examples, a configuration of a serial type ink jet printer where the print head performs printing by ejecting ink during the movement in the main scan direction is shown. However, the invention may be adapted to a line printer where a print head is non-movably fixed and the printing is performed in units of raster by nozzles aligned according to a width of a printing medium in a direction perpendicular to a transport direction of the printing medium. 
     More specifically, for example, as shown in  FIG. 11 , in the print head  250   c  of the line printer including nozzle columns corresponding to colors aligned according to the sheet width, the nozzle column  257   c  corresponding to a specific color ink (in the example, light magenta ink Lm) disposed at the rear end portion in the transport direction of the printing medium may be disposed at the end in the alignment direction of the nozzle columns, and the ink change from the light magenta ink Lm to a metallic ink S may be performed so that the printing can be performed. Accordingly, the metallic ink layer MR and the color ink layer CR may be superposedly printed on the printing medium in this order. In addition, in a case where the superposing order is reversed, the nozzle column corresponding to the specific color ink may be disposed at the front end portion of the print head  250   c  in the printing medium transport direction, and the ink change for the specific color ink may be performed. Next, the printing is performed. 
     Hereinbefore, while the exemplary embodiments of the invention are described, the invention is not limited thereto. Various modifications and changes can be made within the scope of the invention without departing from the spirit of the invention. For example, the invention can be implemented with a printing method, a printing program, or the like as well a configuration as a printing apparatus. 
     The disclosure of Japanese Patent Application No. 2008-219055 filed Aug. 28, 2008 including specification, drawings and claims is incorporated herein by reference in its entirety.