Abstract:
A recording method is for recording on a recording medium with a photocuring liquid substance by discharging droplets from a discharge head onto the recording medium while displacing the discharge head and the recording medium relative to each other. While the discharge head and the recording medium are displaced relative to each other, a droplet discharge step of discharging the droplets from the discharge head toward a predetermined section of the recording medium, and a radiation step of radiating the light toward the droplets discharged on the recording medium, are performed n (n being an integer of 2 or greater) times on the predetermined section to complete recording on the predetermined section, and the recording rate in the nth discharge step is lowered below 100%/n.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Japanese Patent Application No. 2011-021457 filed on Feb. 3, 2011. The entire disclosure of Japanese Patent Application No. 2011-021457 is hereby incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to recording method or the like. 
         [0004]    2. Related Art 
         [0005]    An inkjet device is one known example of a liquid discharge device that can discharge a liquid substance as droplets. An inkjet device can form dots on a recording medium by discharging ink or another liquid substance as droplets from a discharge head. Various images can be recorded by using such an inkjet device. 
         [0006]    In the field of recording using an inkjet device, a method for recording with ink that hardens from exposure to ultraviolet light (hereinbelow referred to as UV ink) has been known in the past (see Japanese Laid-Open Patent Publication No. 2008-188984, for example). 
       SUMMARY 
       [0007]    In the field of recording using UV ink, the dots formed on the recording medium sometimes solidify in a state of protruding from the surface of the recording medium. Furthermore, in cases in which tone or color is expressed, a plurality of dots will sometimes become superimposed. As a result of these things, bumps sometimes form in the image. The bumps forming in the image are sometimes visible as an unintended striped pattern. Therefore, bumps forming in the image readily lower the quality of the image. 
         [0008]    Thus, a problem with conventional recording methods is that it is difficult to improve the image quality. 
         [0009]    The present invention was devised in order to resolve at least some of the problems described above, and the present invention can be implemented as the following embodiments or applied examples. 
         [0010]    A recording method according to a first aspect of the present invention is a method for recording a liquid substance on a recording medium by discharging droplets from a discharge head onto the recording medium while displacing the discharge head and the recording medium relative to each other, the discharge head discharging the liquid substance as the droplets, the liquid substance having a photocuring property that is hardened by exposure to light radiation. The recording method includes a droplet discharge step of discharging the droplets from the discharge head toward a predetermined section of the recording medium, and a radiation step of radiating the light toward the droplets discharged on the recording medium. The droplet discharge step and the radiation step are performed n times, with n being an integer of 2 or greater, on the predetermined section to complete recording on the predetermined section while the discharge head and the recording medium are displaced relative to each other. A recording rate in the nth discharge step is lowered below 100%/n. 
         [0011]    The recording method of this applied example is a recording method for recording with a liquid substance on a recording medium by discharging droplets from a discharge head onto the recording medium while displacing the discharge head and the recording medium relative to each other, the discharge head discharging a photocuring liquid substance as droplets. Photocuring is the property of being hardened by exposure to light radiation. 
         [0012]    In this recording method, a crossing step and a radiation step are performed n times on the same section of the recording medium, whereby recording is completed on the same section. The same section is a section of the recording medium and is within a range that overlaps the discharge head. 
         [0013]    In the crossing step, the discharge head is made to cross the same section while droplets are discharged from the discharge head onto the same section of the recording medium. 
         [0014]    In the radiation step following the crossing step, light is radiated onto the same section. Hardening of the liquid substance in the same section is thereby facilitated. 
         [0015]    In this recording method, the crossing step and the radiation step are performed n times on the same section of the recording medium, whereby recording on the same section is completed. At this time, the recording rate in the n th  crossing step is lowered below 100%/n. Thereby, it becomes easy to reduce the occurrence of striped patterns in the image. 
         [0016]    The term “recording rate” refers to the percentage of dots formed during recording when the number of dots that represent one completed image is 100. 
         [0017]    In the recording method described above preferably, in the n droplet discharge steps, with a recording rate of a first droplet discharge step being denoted by a %, the recording rate of a final droplet discharge step being denoted by b %, and a recording rate of one of the n droplet discharge steps other than the first or final droplet discharge step being denoted by c %: a≧c≧b (and a&gt;b). 
         [0018]    Thereby, it becomes easy to reduce the occurrence of striped patterns in the image. 
         [0019]    In the recording method described above, in all of the n droplet discharge steps, an amount of droplets discharged per dot is preferably equal for the same recording data. 
         [0020]    Thereby, it becomes easy to reduce the occurrence of striped patterns in the image. 
         [0021]    In the recording method described above, an amount of light radiated is preferably equal in all the n radiation steps. 
         [0022]    Thereby, it becomes easy to reduce the occurrence of striped patterns in the image. 
         [0023]    In the recording method described above, the light is preferably ultraviolet light. 
         [0024]    In this applied example, recording can be performed on a recording medium with a liquid substance that is hardened by being exposed to radiation of ultraviolet light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Referring now to the attached drawings which form a part of this original disclosure: 
           [0026]      FIG. 1  is a perspective view showing the schematic configuration of a liquid discharge device in the present embodiment; 
           [0027]      FIG. 2  is a front view of the carriage in the present embodiment as seen from the direction A in  FIG. 1 ; 
           [0028]      FIG. 3  is a bottom view of the discharge head in the present embodiment; 
           [0029]      FIG. 4  is a cross-sectional view along line B-B in  FIG. 2 ; 
           [0030]      FIG. 5  is a block diagram showing the schematic configuration of the liquid discharge device in the present embodiment; and 
           [0031]      FIG. 6  is a chart showing the flow of the recording process in the present embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0032]    With reference to the drawings, a liquid discharge device is used as an example of a recording device to describe the embodiment. The configurations and members are sometimes scaled differently in the drawings in order to present the configurations in recognizable sizes. 
         [0033]    A liquid discharge device  1  in the present embodiment has a workpiece conveying device  3 , a carriage  7 , and a carriage conveying device  11 , as shown in  FIG. 1  which is a perspective view showing the schematic configuration. 
         [0034]    The carriage  7  is provided with a head unit  13  and two radiation devices  15 . 
         [0035]    With the liquid discharge device  1 , a desired pattern can be drawn (recorded) on a substrate or other workpiece W with a liquid substance by discharging the liquid substance as droplets from the head unit  13  while varying the relative positions of the head unit  13  and the workpiece W in a plan view. The Y direction in the drawing shows the movement direction of the workpiece W, and the X direction shows a direction orthogonal to the Y direction in a plan view. The direction orthogonal to the XY plane is defined by the X direction and the Y direction is defined as the Z direction. 
         [0036]    Such a liquid discharge device  1  is applicable to drawing (recording) on a workpiece W not readily permeable by the liquid substance, such as a resin film or the like, for example. 
         [0037]    The liquid discharge device  1  is also applicable to, e.g., the manufacture of color filters used in liquid crystal display panels and the like, the manufacture of organic EL devices, and other applications. 
         [0038]    In the case of a color filter having the three filter elements red, green, and blue, the liquid discharge device  1  can be suitably used in the process of forming colored layers of red, green, and blue on a substrate, for example. In this case, liquids corresponding to the colored layers are discharged as droplets from the head unit  13  onto the workpiece W, whereby a pattern of the filter elements red, green, and blue is drawn on the workpiece W. 
         [0039]    In the manufacture of organic EL devices, the liquid discharge device  1  can also be suitably used in the process of forming functional layers (organic layers) corresponding to the colors for each red, green, and blue pixel, for example. In this case, liquid substances corresponding to functional layers of the colors are discharged as droplets from the head unit  13  onto the workpiece W, whereby a pattern of the functional layers of red, green, and blue is drawn on the workpiece W. 
         [0040]    The configurations of the liquid discharge device  1  are described herein in detail. 
         [0041]    The workpiece conveying device  3  has a press platen  21 , a guide rail  23   a,  a guide rail  23   b,  and a workpiece table  25 , as shown in  FIG. 1 . 
         [0042]    The press platen  21  is made of stone, for example, or another material having a low thermal expansion coefficient, and is set up so as to extend along the Y direction. The guide rail  23   a  and the guide rail  23   b  are placed on a top surface  21   a  of the press platen  21 . The guide rail  23   a  and the guide rail  23   b  both extend along the Y direction. The guide rail  23   a  and the guide rail  23   b  are aligned separated from each other by a space in the X direction. 
         [0043]    The workpiece table  25  is provided in a state of facing the top surface  21   a  of the press platen  21  with the guide rail  23   a  and the guide rail  23   b  in between. The workpiece table  25  is placed on the guide rail  23   a  and the guide rail  23   b  in a state of being raised above the press platen  21 . The workpiece table  25  has a placement surface  25   a  which is a surface on which the workpiece W is placed. The placement surface  25   a  is made to face in the direction (upward) opposite the press platen  21 . The workpiece table  25  is guided along the Y direction by the guide rail  23   a  and the guide rail  23   b,  and is capable of reciprocating along the Y direction over the press platen  21 . 
         [0044]    The workpiece table  25  can be reciprocated in the Y direction by a movement mechanism and a motive power source (neither shown). The movement mechanism can be a mechanism that combines a ball screw and a ball nut, a linear guide mechanism, or the like, for example. In the present embodiment, a workpiece conveying motor (described hereinafter) is used as a motive power source for moving the workpiece table  25  along the Y direction. Various motors can be used as the workpiece conveying motor, including a stepping motor, a servo motor, a linear motor, and the like. 
         [0045]    The motive power from the workpiece conveying motor is transmitted through the movement mechanism to the workpiece table  25 . The workpiece table  25  can thereby reciprocate along the guide rail  23   a  and the guide rail  23   b,  i.e., along the Y direction. In other words, the workpiece conveying device  3  can cause the workpiece W placed on the placement surface  25   a  of the workpiece table  25  to reciprocate along the Y direction. 
         [0046]    The head unit  13  has a head plate  31  and a discharge head  33  as shown in  FIG. 2 , which is a front view of the carriage  7  as seen from the direction A in  FIG. 1 . 
         [0047]    The discharge head  33  has a nozzle surface  35  as shown in  FIG. 3 , which is a bottom view. The nozzle surface  35  has a plurality of nozzles  37  formed therein. In  FIG. 3 , the nozzles  37  are exaggerated and the number of nozzles  37  is reduced in order to make the nozzles  37  easier to understand. 
         [0048]    In the discharge head  33 , the nozzles  37  constitute four nozzle rows  39  aligned along the Y direction. The four nozzle rows  39  are aligned separated from each other by spaces in the X direction. In the nozzle rows  39 , the nozzles  37  are formed at a predetermined nozzle pitch P along the Y direction. 
         [0049]    Hereinbelow, the terms nozzle row  39   a,  nozzle row  39   b,  nozzle row  39   c,  and nozzle row  39   d  are used when distinguishing the four nozzle rows  39 . 
         [0050]    In the discharge head  33 , the nozzle row  39   a  and the nozzle row  39   b  are misaligned from each other in the Y direction by a distance P/ 2 . The nozzle row  39   c  and the nozzle row  39   d  are also misaligned from each other in the Y direction by a distance P/ 2 . 
         [0051]    The two radiation devices  15  are provided at positions facing each other with the head unit  13  in between in the X direction, as shown in  FIG. 2 . Hereinbelow, the terms radiation device  15   a  and radiation device  15   b  are used when distinguishing between the two radiation devices  15 . 
         [0052]    The radiation device  15   a  and radiation device  15   b  each have a light source  43  for emitting ultraviolet light  41 . The ultraviolet light  41  from the light sources  43  promote hardening of the functional liquid  53  (liquid substance) discharged from the discharge head  33 . The functional liquid  53  begins to harden upon being irradiated by the ultraviolet light  41 . 
         [0053]    Various light sources  43  can be used as the light sources  43 , such as LEDs, LDs, mercury lamps, metal halide lamps, xenon lamps, excimer lamps, and the like, for example. 
         [0054]    In the present embodiment, the lengths of the radiation devices  15  in the Y direction are set to the length that encompasses the nozzle rows  39  of the discharge head  33 . 
         [0055]    The light source  43  of the radiation device  15   a  and the light source  43  of the radiation device  15   b  overlap in a plan view in the movement path of the nozzle surface  35  of the discharge head  33  along the X direction. 
         [0056]    The discharge head  33  has a nozzle plate  46 , a cavity plate  47 , a vibrating plate  48 , and a plurality of piezoelectric elements  49  as shown in  FIG. 4 , which is a cross-sectional view along line B-B of  FIG. 2 . 
         [0057]    The nozzle plate  46  includes the nozzle surface  35 . The nozzles  37  are provided to the nozzle plate  46 . 
         [0058]    The cavity plate  47  is provided on the side of the nozzle plate  46  opposite the nozzle surface  35 . A plurality of cavities  51  are formed in the cavity plate  47 . The cavities  51  are provided in correspondence to the nozzles  37  and are communicated with their corresponding nozzles  37 . The functional liquid  53  is supplied to the cavities  51  from a tank (not shown). 
         [0059]    The vibrating plate  48  is provided to the cavity plate  47  on the side opposite the nozzle plate  46 . The vibrating plate  48  vibrates in the Z direction (longitudinal vibration), thereby enlarging and reducing the internal volumes of the cavities  51 . 
         [0060]    The piezoelectric elements  49  are provided to the vibrating plate  48  on the side opposite the cavity plate  47 . The piezoelectric elements  49  are provided in correspondence to the cavities  51 , and are made to face the cavities  51  with the vibrating plate  48  in between. The piezoelectric elements  49  stretch based on a drive signal. The vibrating plate  48  thereby reduces the internal volumes of the cavities  51 . At this time, pressure is applied to the functional liquid  53  inside the cavities  51 . As a result, the functional liquid  53  is discharged as droplets  55  from the nozzles  37 . The method of discharging droplets  55  from the discharge head  33  is an example of the inkjet method. The inkjet method is an example of a coating method. 
         [0061]    The discharge head  33  having the configuration described above is supported on the head plate  31  in a state in which the nozzle surface  35  protrudes from the head plate  31 , as shown in  FIG. 2 . 
         [0062]    The carriage  7  supports the head unit  13  as shown in  FIG. 2 . The head unit  13  herein is supported on the carriage  7  in a state in which the nozzle surface  35  faces downward in the Z direction. 
         [0063]    The workpiece W can be coated with the functional liquid  53  by the discharge head  33  as described above. 
         [0064]    In the present embodiment, longitudinally vibrating piezoelectric elements  49  are used, but the pressurizing means for applying pressure to the functional liquid  53  is not limited to these elements, and flexibly deforming piezoelectric elements made of a stacked bottom electrode, piezoelectric layer, and top electrode can also be used, for example. The pressurizing means can also be a so-called electrostatic actuator, wherein static electricity is generated between a vibrating plate and an electrode and the vibrating plate is deformed by the electrostatic force to discharge liquid droplets from nozzles. Another configuration that can be used is one in which a heating element is used to form bubbles in the nozzles and pressure is applied to the functional liquid by the bubbles. 
         [0065]    In the present embodiment, a functional liquid  53  that begins to harden by being irradiated with light is used as the functional liquid  53 . In the present embodiment, the ultraviolet light  41  is used as the light that causes the functional liquid  53  to harden. 
         [0066]    The functional liquid  53  includes a resin material, a photoinitiator, and a solvent as components. By adding to these components a pigment, dye, or other colorant; and a surface-modifying material or other functional material having a property such as lyophilicity or liquid repellency; a functional liquid  53  having a unique function can be created. A functional liquid  53  containing a pigment, dye, or other colorant can be used as the functional liquid  53  for forming an image to be recorded on the workpiece W, for example. Hereinbelow, the functional liquid  53  for forming an image to be recorded on the workpiece W is referred to as an image coating. 
         [0067]    By using an acrylic resin material or another phototransparent resin material, for example, as the resin material component of the functional liquid  53 , a phototransparent functional liquid  53  can be created. A possible application for a phototransparent functional liquid  53  is clear ink, for example. The phototransparent functional liquid  53  is hereinbelow referred to as a translucent material. 
         [0068]    Possible applications of the clear ink include application as an overcoat layer for covering the image, application as a base layer before the image is formed, and other applications, for example. The functional liquid  53  applied as a base layer is hereinbelow referred to as a base coating. 
         [0069]    Not only can the translucent coating be used as the base coating, but a functional liquid  53  having various pigments added to the translucent coating can be used as well. For example, a functional liquid  53  white in color, a functional liquid  53  exhibiting a metallic luster, and the like can be used as the base coating. 
         [0070]    The resin material in the functional liquid  53  is a material for forming a resin film. Such a resin material is a liquid at room temperature, and is not particularly limited as long as it is a material that becomes a polymer by being polymerized. The resin material preferably has low viscosity, and the resin material is preferably in the form of an oligomer. It is even more preferable that the resin material be in the form of a monomer. 
         [0071]    The photoinitiator is an additive that acts on the cross-linking groups of polymers and promotes a cross-linking reaction. Benzyl dimethyl ketal or the like, for example, can be used as the photoinitiator. In the present embodiment, a radical photoinitiator is used as the photoinitiator. IRGACURE 819 made by Ciba Japan®, for example, can be used as the radical photoinitiator. 
         [0072]    The solvent is for adjusting the viscosity of the resin material. 
         [0073]    The carriage conveying device  11  has a mounting  101  and a guide rail  103 , as shown in  FIG. 1 . 
         [0074]    The mounting  101  extends in the X direction and reaches beyond the workpiece conveying device  3  in the X direction. The mounting  101  faces the workpiece conveying device  3  from the side of the workpiece table  25  opposite the press platen  21 . The mounting  101  is supported by a pair of supports  107 . The two supports  107  are provided to positions where they face each other in the X direction with the press platen  21  in between. 
         [0075]    Hereinbelow, the terms support  107   a  and support  107   b  are used when distinguishing between the two supports  107 . The support  107   a  and support  107   b  both protrude above the workpiece table  25  in the Z direction. Space is thereby maintained between the mounting  101  and the workpiece table  25 . 
         [0076]    The guide rail  103  is provided to the side of the mounting  101  that faces the press platen  21 . The guide rail  103 , which extends along the X direction, is provided along the entire width of the mounting  101  in the X direction. 
         [0077]    The previously described carriage  7  is supported on the guide rail  103 . With the carriage  7  being supported on the guide rail  103 , the nozzle surface  35  of the discharge head  33  faces toward the workpiece table  25  in the Z direction. The carriage  7  is guided along the X direction by the guide rail  103 , and is supported on the guide rail  103  so as to be capable of reciprocating in the X direction. The nozzle surface  35  and the placement surface  25   a  of the workpiece table  25  face each other with a space thereinbetween in a state in which the carriage  7  overlaps the workpiece table  25  in a plan view. 
         [0078]    The carriage  7  can be reciprocated in the X direction by a movement mechanism and a motive power source (neither shown). The movement mechanism can be a mechanism that combines a ball screw and a ball nut, a linear guide mechanism, or the like, for example. In the present embodiment, a carriage conveying motor (not shown) is used as a motive power source for moving the carriage  7  along the X direction. Various motors can be used as the carriage conveying motor, including a stepping motor, a servo motor, a linear motor, and the like. 
         [0079]    The motive power from the carriage conveying motor is transmitted through the movement mechanism to the carriage  7 . The carriage  7  can thereby reciprocate along the guide rail  103 , i.e., along the X direction. In other words, the carriage conveying device  11  can cause the head unit  13  supported on the carriage  7  to reciprocate along the X direction. 
         [0080]    With the liquid discharge device  1  having the configuration described above, a pattern is recorded (drawn) on the workpiece W by discharging droplets  55  from the discharge head  33  while the discharge head  33  and the workpiece W are relatively reciprocated in a state in which the discharge head  33  faces the workpiece W. 
         [0081]    The liquid discharge device  1  has a controller  111  for controlling the actions of the configurations described above, as shown in  FIG. 5 . The controller  111  has a CPU (Central Processing Unit)  113 , a drive controller  115 , and a memory  117 . The drive controller  115  and the memory  117  are connected to the CPU  113  via a bus  119 . 
         [0082]    The liquid discharge device  1  also has a carriage conveying motor  121 , a workpiece conveying motor  123 , an input device  129 , and a display device  131 . 
         [0083]    The carriage conveying motor  121  and the workpiece conveying motor  123  are both connected to the controller  111  via an input/output interface  133  and the bus  119 . The input device  129  and the display device  131  are also both connected to the controller  111  via the input/output interface  133  and the bus  119 . 
         [0084]    The carriage conveying motor  121  generates drive force for driving the carriage  7 . The workpiece conveying motor  123  generates drive force for driving the workpiece table  25 . 
         [0085]    The input device  129  is a device for inputting various working conditions. The display device  131  is a device for displaying working conditions and operating conditions. The operator who operates the liquid discharge device  1  can input various information via the input device  129  while confirming the information displayed on the display device  131 . 
         [0086]    The discharge head  33 , the radiation device  15   a,  and the radiation device  15   b  are both connected to the controller  111  via the input/output interface  133  and the bus  119 . 
         [0087]    The input device  129  is a device for inputting various working conditions. Various information can be inputted via the input device  129 . 
         [0088]    The CPU  113  performs various calculation processes as a processor. The drive controller  115  controls the driving of the configurations. The memory  117  includes RAM (Random Access Memory), ROM (Read Only Memory), and the like. The memory  117  is provided with a section for storing program software  135  on which procedures for controlling the actions of the liquid discharge device  1  are written, a data decompressor  137  which is a section for temporarily decompressing various data, and the like. Examples of data decompressed in the data decompressor  137  include recording data showing a pattern to be recorded, program data of recording processes and the like, etc. 
         [0089]    The drive controller  115  has a motor controller  141 , a discharge controller  145 , a radiation controller  147 , and a display controller  151 . 
         [0090]    The motor controller  141  separately controls the driving of the carriage conveying motor  121  and the driving of the workpiece conveying motor  123  on the basis of commands from the CPU  113 . 
         [0091]    The discharge controller  145  controls the driving of the discharge head  33  on the basis of commands from the CPU  113 . 
         [0092]    The radiation controller  147  separately controls the light-emitting states of the respective light sources  43  of the radiation device  15   a  and radiation device  15   b  on the basis of commands from the CPU  113 . 
         [0093]    The display controller  151  controls the driving of the display device  131  on the basis of commands from the CPU  113 . 
         [0094]    The recording process in the liquid discharge device  1  is described here. 
         [0095]    In the liquid discharge device  1 , when the controller  111  receives recording data from the input device  129  via the input/output interface  133  and the bus  119 , the recording process shown in  FIG. 6  is started by the CPU  113 . 
         [0096]    The recording data indicates a pattern to be recorded on the workpiece W with the functional liquid  53  (liquid substance), and dots to be formed by droplets  55  are expressed in bitmap format. The pattern recorded on the workpiece W is expressed as a collection of a plurality of dots formed by droplets  55 . The pattern is recorded on the workpiece W by discharging droplets  55  from the discharge head  33  in predetermined cycles while relatively reciprocating the discharge head  33  and the workpiece W in a state in which the discharge head  33  faces the workpiece W. 
         [0097]    In the recording process, the CPU  113  first outputs a carriage convey command to the motor controller  141  ( FIG. 5 ). At this time, the motor controller  141  controls the driving of the carriage conveying motor  121 , causing the carriage  7  to move to an advancing start position of the drawing area. 
         [0098]    A recording area is set in the liquid discharge device  1 . The recording area is a section of overlap between the path along the Y direction through which the workpiece table  25  shown in  FIG. 1  moves, and the path along the X direction through which the discharge head  33  moves. 
         [0099]    The advancing start position is a position where the carriage  7  begins to advance during its reciprocating movement. In the present embodiment, the advancing start position is positioned outside of the recording area in a plan view. 
         [0100]    In the present embodiment, the advancing start position is positioned to the side of the recording area in the direction of the support  107   a  in a plan view. 
         [0101]    Next, in step S 2 , the CPU  113  outputs a workpiece convey command to the motor controller  141  ( FIG. 5 ). At this time, the motor controller  141  controls the driving of the workpiece conveying motor  123 , causing the workpiece W to move to the recording area. 
         [0102]    Next, in step S 3 , the CPU  113  outputs a carriage scan command to the motor controller  141  ( FIG. 5 ). At this time, the motor controller  141  controls the driving of the carriage conveying motor  121 , starting the reciprocating movement of the carriage  7 . 
         [0103]    During the reciprocating movement of the carriage  7 , the carriage  7  reciprocates between the aforementioned advancing start position and a retreating start position. In other words, the route of moving from the advancing start position to the retreating start position and then back to the advancing start position is one reciprocation of the carriage  7 . Therefore, in the present embodiment, the route from the advancing start position to the retreating start position is the advancing of the carriage  7 . The route from the retreating start position to the advancing start position is the retreating of the carriage  7 . 
         [0104]    The retreating start position is a position that faces the advancing start position with the recording area in between in the X direction. The retreating start position is positioned outside of the recording area in a plan view. Therefore, the advancing start position and the retreating start position face each other across the recording area in the X direction in a plan view. 
         [0105]    In the present embodiment, the retreating start position is positioned to the side of the recording area in the direction of the support  107   b  in a plan view. 
         [0106]    Next, in step S 4 , the CPU  113  outputs a radiation command for the radiation device  15   a  to the radiation controller  147  ( FIG. 5 ). At this time, the radiation controller  147  controls the driving of the light source  43  of the radiation device  15   a,  causing the light source  43  of the radiation device  15   a  to turn on. 
         [0107]    Next, in step S 5 , the CPU  113  determines whether or not the position of the discharge head  33  has reached a recording start position while advancing. 
         [0108]    The recording start position is a position where the discharge of droplets  55  from the discharge head  33  is started within the recording area. 
         [0109]    At this time, when it is determined that the position of the discharge head  33  has reached the recording start position (Yes), the process transitions to step S 6 . When it is determined that the position of the discharge head  33  has not reached the recording start position (No), the process waits until the position of the discharge head  33  reaches the recording start position. 
         [0110]    Next, in step S 6 , the CPU  113  outputs a discharge command to the discharge controller  145  ( FIG. 5 ). At this time, the discharge controller  145  controls the driving of the discharge head  33 , causing droplets  55  to be discharged from the nozzles  37  on the basis of the recording data. Recording during advancing is thereby started. 
         [0111]    Next, in step S 7 , the CPU  113  determines whether or not the position of the discharge head  33  has reached a recording stop position during advancing. 
         [0112]    The recording stop position is a position where the discharge of droplets  55  from the discharge head  33  is stopped within the recording area. 
         [0113]    At this time, when it is determined that the position of the discharge head  33  has reached a recording stop position (Yes), the process transitions to step S 8 . When it is determined that the position of the discharge head  33  has not reached the recording stop position (No), the process waits until the position of the discharge head  33  reaches the recording stop position. 
         [0114]    Next, in step S 8 , the CPU  113  outputs a discharge stop command to the discharge controller  145  ( FIG. 5 ). At this time, the discharge controller  145  stops the driving of the discharge head  33 , causing the discharge of droplets  55  from the nozzles  37  to stop. Recording during advancing thereby ends. 
         [0115]    Next, in step S 9 , the CPU  113  outputs a radiation stop command for the radiation device  15   a  to the radiation controller  147  ( FIG. 5 ). At this time, the radiation controller  147  controls the driving of the light source  43  of the radiation device  15   a,  causing the light source  43  of the radiation device  15   a  to turn off 
         [0116]    Next, in step S 10 , the CPU  113  determines whether or not the position of the carriage  7  has reached the retreating start position. At this time, when it is determined that the position of the carriage  7  has reached the retreating start position (Yes), the process transitions to step S 11 . When it is determined that the position of the carriage  7  has not reached the retreating start position (No), the process waits until the position of the carriage  7  reaches the retreating start position. 
         [0117]    Next, in step S 11 , the CPU  113  determines whether or not there is any superimposed data. Superimposed data is data showing a new recording pattern that will be superimposed over the recording pattern in the recording during advancing that had just ended. At this time, when it is determined that there is superimposed data (Yes), the process transitions to step S 13 . When it is determined that there is no superimposed data (No), the process transitions to step S 12 . 
         [0118]    In step S 12 , the CPU  113  outputs a line break command to the motor controller  141  ( FIG. 5 ). At this time, the motor controller  141 , having received the line break command, controls the driving of the workpiece conveying motor  123 , moving the workpiece W in the Y direction (line break) and moving a new section in the workpiece W on which a pattern is to be recorded to the recording area. 
         [0119]    In step S 13 , the CPU  113  outputs a radiation command for the radiation device  15   b  to the radiation controller  147  ( FIG. 5 ). At this time, the radiation controller  147  controls the driving of the light source  43  of the radiation device  15   b,  causing the light source  43  of the radiation device  15   b  to turn on. 
         [0120]    Next, in step S 14 , the CPU  113  determines whether or not the position of the discharge head  33  has reached the recording start position during retreating. At this time, when it is determined that the position of the discharge head  33  has reached the recording start position (Yes), the process transitions to step S 15 . When it is determined that the position of the discharge head  33  has not reached the recording start position (No), the process waits until the position of the discharge head  33  reaches the recording start position. 
         [0121]    Next, in step S 15 , the CPU  113  outputs a discharge command to the discharge controller  145  ( FIG. 5 ). At this time, the discharge controller  145  controls the driving of the discharge head  33 , causing droplets  55  to be discharged from the nozzles  37  on the basis of the recording data. Recording during retreating is thereby started. 
         [0122]    When a transition is made from step S 11  to step S 13  omitting step S 12 , recording during retreating is performed on the workpiece W without a line break. A recording pattern from retreating can thereby be superimposed over the recording pattern from advancing. Hereinbelow, recording involving the superimposing of a plurality of recording patterns is referred to as superimposed recording. 
         [0123]    Following step S 15 , in step S 16 , the CPU  113  determines whether or not the position of the discharge head  33  has reached the recording stop position during retreating. At this time, when it is determined that the position of the discharge head  33  has reached the recording stop position (Yes), the process transitions to step S 17 . When it is determined that the position of the discharge head  33  has not reached the recording stop position (No), the process waits until the position of the discharge head  33  reaches the recording stop position. 
         [0124]    Next, in step S 17 , the CPU  113  outputs a discharge stop command to the discharge controller  145  ( FIG. 5 ). At this time, the discharge controller  145  stops the driving of the discharge head  33 , causing the discharge of droplets  55  from the nozzles  37  to stop. Recording during retreating thereby ends. 
         [0125]    Next, in step S 18 , the CPU  113  outputs a radiation stop command for the radiation device  15   b  to the radiation controller  147  ( FIG. 5 ). At this time, the radiation controller  147  controls the driving of the light source  43  of the radiation device  15   b,  causing the light source  43  of the radiation device  15   b  to turn off. 
         [0126]    Next, in step S 19 , the CPU  113  determines whether or not the position of the carriage  7  has reached the advancing start position. At this time, when it is determined that the position of the carriage  7  has reached the advancing start position (Yes), the process transitions to step S 20 . When it is determined that the position of the carriage  7  has not reached the advancing start position (No), the process waits until the position of the carriage  7  reaches the advancing start position. 
         [0127]    Next, in step S 20 , the CPU  113  determines whether or not there is any superimposed data. Superimposed data is data showing a new recording pattern that will be superimposed over the recording pattern in the recording during advancing that had just ended. At this time, when it is determined that there is superimposed data (Yes), the process transitions to step S 4 . When it is determined that there is no superimposed data (No), the process transitions to step S 21 . 
         [0128]    In step S 21 , the CPU  113  outputs a line break command to the motor controller  141  ( FIG. 5 ). At this time, the motor controller  141 , having received the line break command, controls the driving of the workpiece conveying motor  123 , moving the workpiece W in the Y direction (line break) and moving a new section in the workpiece W on which a pattern is to be recorded to the recording area. 
         [0129]    Next, in step S 22 , the CPU  113  determines whether or not recording data has ended. At this time, when it is determined that recording data has ended (Yes), the process ends. When it is determined that recording data has not ended (No), the process transitions to step S 4 . 
         [0130]    When a transition is made from step S 20  to step S 4 , recording during advancing is performed on the workpiece W without a line break. In other words, when a transition is made from step S 20  to step S 4 , superimposed recording will be performed. 
         [0131]    In step S 11  or step S 20  in this example, the next recording is performed without a line break when there is superimposed data, but a line break may be used. In this case, a different nozzle group may be used to perform recording on predetermined sections before and after the line break. 
         [0132]    When a predetermined section of the recording section is reached, the predetermined section being within a range overlapping the discharge head  33  in a plan view, the predetermined section and the discharge head  33  cross each other multiple times during superimposed recording. 
         [0133]    Every time the discharge head  33  crosses the predetermined section, droplets  55  are discharged and a recording pattern is recorded on the recording medium. 
         [0134]    Superimposed recording can thereby be performed on the predetermined section. 
         [0135]    Such superimposed recording can be applied at times such as when one recording pattern is completed by superimposing a plurality of patterns, for example. If the number of times the predetermined section and the discharge head  33  cross is n (n being an integer of 2 or greater) times, one pattern in the predetermined section is completed by recording on the predetermined section during each of the n crossings. Such superimposed recording can also be expressed as a method for recording one pattern in n passes. For example, a method for completing one pattern in two crossings is a method for recording one pattern in two passes. 
         [0136]    In the present embodiment, the phrase “completing one pattern in n crossings” means that in n crossings, the recording rate of the pattern is 100%. 
         [0137]    The recording rate is the percentage of the number of dots per unit surface area when the number of dots expressing a completed pattern is 100 per unit surface area. 
         [0138]    In the present embodiment, in superimposed recording in which one pattern is completed in n crossings, the 100% recording rate is distributed among the n crossings. The recording rate distributed among the n crossings is 100% when totaled. For example, when one pattern is completed in two crossings, if the recording rate in the first crossing is 50% and the recording rate in the second crossing is 50%, a pattern having a recording rate of 100% can be completed. 
         [0139]    In the present embodiment, if the variation in the discharge amount due to individual differences among the plurality of nozzles is dispelled, the amount of droplets discharged per dot in each of the crossings will be equal if the recording data is the same. The amount of radiation of the radiation devices in each of the crossings will also be the same. 
         [0140]    The following is a description of a working example in which superimposed recording, wherein one pattern is completed in two crossings, is performed using the liquid discharge device  1  described above. 
       WORKING EXAMPLE 1 
       [0141]    In Working Example 1, the recording rate in the first crossing is 80% and the recording rate in the second crossing is 20%. 
       COMPARATIVE EXAMPLE 1 
       [0142]    The following is a description of Comparative Example 1 in which superimposed recording, wherein one pattern is completed in two crossings, is performed using the liquid discharge device  1 . 
         [0143]    In Comparative Example 1, the recording rate in the first crossing is 20% and the recording rate in the second crossing is 80%. 
       COMPARATIVE EXAMPLE 2 
       [0144]    The following is a description of Comparative Example 2 in which superimposed recording, wherein one pattern is completed in two crossings, is performed using the liquid discharge device  1 . 
         [0145]    In Comparative Example 2, the recording rate in the first crossing is 100%. 
         [0146]    In the working example, Comparative Example 1, and Comparative Example 2, the same pattern is mutually used as the pattern to be completed. 
         [0147]    The image qualities of the recorded images were evaluated in the working example, Comparative Example 1, and Comparative Example 2. The evaluation results are shown in Table 1 below. 
         [0000]    
       
         
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Image Quality 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Working Example 1 
                 ∘ 
               
               
                   
                 Comparative Example 1 
                 Δ 
               
               
                   
                 Comparative Example 2 
                 x 
               
               
                   
               
             
          
         
       
     
         [0148]    In the image quality evaluation results of Table 1, the symbol “∘” indicates that stripes occurring due to bumps were not observed, i.e., that a high image quality was obtained throughout the entire image. 
         [0149]    The symbol “Δ” indicates that strips were more easily observed that the symbol “∘.” 
         [0150]    The symbol “×” indicates that strips were more easily observed that the symbol “Δ.” 
         [0151]    It is understood from the results shown in Table 1 that the image quality in the working example was more satisfactory than in Comparative Example 1 or Comparative Example 2. 
         [0152]    The dot density tends to be sparser as the recording rate decreases. In other words, the lower the recording rate, the less likely the dots are to overlap during the recording thereof, and bumps are therefore less likely to form in the image of the recording thereof. It is believed that by forming an image not prone to bumps in the n th  crossing step, the occurrence of bumps in the final image is reduced, and the occurrences of striped patterns are easily suppressed. 
         [0153]    Because of the above, it is easy to reduce the occurrences of striped patterns in the image in the superimposed recording of the present embodiment. In other words, during superimposed recording in which one pattern is completed in n crossings, the image quality can easily be improved by reducing the recording rate during the n th  crossing step below 100%/n. In the n crossings, with the recording rate during the first crossing denoted by a %, the recording rate during the final crossing denoted by b %, and the recording rate during a predetermined crossing other than the first and final crossings denoted by c %: a≧c≧b (and a&gt;b). 
       GENERAL INTERPRETATION OF TERMS 
       [0154]    In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. Finally, terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least±5% of the modified term if this deviation would not negate the meaning of the word it modifies. 
         [0155]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.