JP2010274484A - Liquid jetting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image quality of an image printed when liquid is switched to first liquid from second liquid. <P>SOLUTION: The liquid jetting apparatus includes: a nozzle train that jets liquid to a medium; a switching part that switches the liquid to be supplied to the nozzle train to either the first liquid for recording or the second liquid for preventing clogging; and a controller that performs dot forming operation for forming dots on pixels arranged in a moving direction of the medium by allowing the nozzle train to jet the liquid therefrom while moving the nozzle train in a moving direction crossing with a conveying direction of the medium, and controls, when the liquid to be supplied to the nozzle train is switched to the first liquid from the second liquid by controlling the switching part, to form the dots every predetermined pixels in the moving direction of the medium by succeeding some dot forming operation, and to form the dot between the dots formed by some dot forming operation by another dot forming operation after performing some dot forming operation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus.

  A liquid ejecting apparatus including a head for ejecting a plurality of colors of liquid onto a medium is already well known. As such a liquid ejecting apparatus, an ink jet printer that performs monochrome printing and color printing by ejecting ink (a kind of liquid) onto various media such as paper, cloth, and film is known.

  In addition, some ink jet printers include a nozzle array that selectively supplies recording ink (for example, white ink) and clogging prevention ink (for example, clear ink) (see, for example, Patent Document 1). ).

JP 2008-162023 A

In such a liquid ejecting apparatus, when white ink is not used (for example, when the power is turned off), clear ink is supplied to the nozzle row in order to prevent nozzle clogging. For example, when the power is turned on, switching from clear ink to white ink is performed. At this time, if an attempt is made to completely switch from clear ink to white ink, there is a lot of wasted ink as will be described later. Therefore, light white ink is used for printing. However, in this case, there is a problem that the density of ink gradually increases and density unevenness occurs.
Therefore, an object of the present invention is to improve the image quality of an image.

The main invention for achieving the above object is:
(A) a nozzle array for injecting liquid onto the medium;
(B) a switching unit that switches the liquid supplied to the nozzle row to either the first liquid for recording or the second liquid for preventing clogging;
(C) A dot forming operation for forming dots on pixels arranged in the moving direction of the medium by ejecting liquid from the nozzle row while moving the nozzle array in a moving direction that intersects the transport direction of the medium. A controller that performs
When the liquid supplied to the nozzle row is switched from the second liquid to the first liquid by controlling the switching unit, a dot is formed every predetermined pixel in the moving direction of the medium in a certain dot forming operation thereafter. A controller for forming dots between the dots formed by the certain dot forming operation in another dot forming operation after the certain dot forming operation;
A liquid ejecting apparatus including (D).

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram of a printer 1 according to an embodiment. 1 is a perspective view illustrating an outline of a printer. 1 is a perspective view illustrating an outline of a printer. FIG. 4 is a conceptual diagram illustrating nozzle rows formed on a head 41. 3 is a conceptual diagram showing a head 41 and an ink cartridge 34. FIG. 4 is an exploded perspective view for explaining a configuration of a head 41. FIG. 4 is a sectional view of a head 41. FIG. 4 is a conceptual diagram illustrating an ink suction unit 72. FIG. 9A to 9D are explanatory diagrams of the first embodiment. 10A to 10D are explanatory diagrams of the second embodiment. FIG. 11A and FIG. 11B are conceptual diagrams of the state of ink flow in the ink flow path. FIG. 11A is a diagram when the ink flow is fast. FIG. 11B is a diagram when the flow of ink is slow. 12A to 12D are explanatory diagrams of the third embodiment. It is explanatory drawing of 4th Embodiment. It is explanatory drawing of the example of improvement of 4th Embodiment.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

(A) a nozzle array for injecting liquid onto the medium;
(B) a switching unit that switches the liquid supplied to the nozzle row to either the first liquid for recording or the second liquid for preventing clogging;
(C) A dot forming operation for forming dots on pixels arranged in the moving direction of the medium by ejecting liquid from the nozzle row while moving the nozzle array in a moving direction that intersects the transport direction of the medium. A controller that performs
When the liquid supplied to the nozzle row is switched from the second liquid to the first liquid by controlling the switching unit, a dot is formed every predetermined pixel in the moving direction of the medium in a certain dot forming operation thereafter. A controller for forming dots between the dots formed by the certain dot forming operation in another dot forming operation after the certain dot forming operation;
The liquid ejecting apparatus including (D) is clarified.
According to such a liquid ejecting apparatus, it is possible to improve the image quality of an image to be printed after switching from the second liquid to the first liquid.

In this liquid ejecting apparatus, it is preferable that the moving direction of the nozzle row in the certain dot forming operation is opposite to the moving direction of the nozzle row in the other dot forming operation.
According to such a liquid ejecting apparatus, the image quality can be made more uniform.

  The dots formed by the certain dot forming operation may be smaller than the dots formed by the other dot forming operation. In this case, the remaining second liquid can be reduced quickly, and the dots that contain a large amount of the second liquid are small and are not noticeable.

  Further, the dots formed by the certain dot forming operation may be larger than the dots formed by the other dot forming operation. In this case, the amount of pigment contained in the dots formed in each pixel can be made uniform, and density unevenness can be reduced.

In the liquid ejecting apparatus, the controller, after the another dot forming operation, causes the medium to be transported in the transport direction by a transport amount according to the length of the nozzle row, and in the subsequent dot forming operation, It is desirable that dots be formed in each pixel arranged in the moving direction of the medium by the nozzle row.
According to such a liquid ejecting apparatus, it is possible to make the density uniform for each region (band to be described later) corresponding to the length of the nozzle row.

  In the following embodiments, an ink jet printer (hereinafter also referred to as a printer 1) will be described as an example of the liquid ejecting apparatus.

=== About printer configuration ===
FIG. 1 is a block diagram of the overall configuration of the printer 1. 2 and 3 are perspective views showing an outline of the printer 1. FIG. FIG. 4 is a conceptual diagram showing nozzle rows formed on the head 41.

  The printer 1 corresponds to, for example, roll paper or large-sized printing paper (these correspond to media). In the example shown in FIGS. 2 and 3, the printer 1 includes roll paper S. The printer 1 is communicably connected to a computer 110 that is an external device.

  As shown in FIG. 1, the printer 1 according to the present embodiment includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, a controller 60, and a cleaning unit 70. The printer 1 that has received print data from the computer 110 that is an external device controls each unit (the transport unit 20, the head unit 40, etc.) by the controller 60. For example, the controller 60 receives print data from the computer 110, controls each unit based on the received print data, and prints an image on the roll paper S. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

  The transport unit 20 is for transporting the roll paper S in the transport direction. The transport unit 20 includes a paper feed motor 21, a transport roller 24 that is driven by the paper feed motor 21 to feed the roll paper S in the transport direction (hereinafter also referred to as sub-scanning direction), and a roll for setting the roll paper S. A paper holder 27, a paper pressing roller 29 for pressing the roll paper S against the transport roller 24, and a platen 26 that supports the roll paper S are provided.

  The roll paper S is set in the roll paper holder 27. The roll paper S is pressed against the transport roller 24 by the paper pressing roller 29, and is fed in the transport direction on the surface of the platen 26 as the transport roller 24 rotates.

  The carriage unit 30 supports the head 41 and is driven by a carriage 38, a carriage motor 39, and a carriage motor 39 to move the head 41 in a moving direction (hereinafter also referred to as a main scanning direction) intersecting the transport direction. And a guide rail 37 for guiding the carriage 38. The carriage 38 is pulled by the pulling belt 36 driven by the carriage motor 39 and moves along the guide rail 37 in the main scanning direction. Further, the carriage 38 detachably holds an ink cartridge 34 that stores ink to be supplied to the head 41.

  The head unit 40 is for ejecting ink (the ink is a concept including both water-based ink and oil-based ink. In this embodiment, water-based ink) onto the roll paper S. The head unit 40 includes a head 41 having a plurality of nozzles. Since the head 41 is provided on the carriage 38, when the carriage 38 moves in the main scanning direction, the head 41 also moves in the main scanning direction. The operation of intermittently ejecting ink from the nozzles while the head 41 is moving in the main scanning direction (dot forming operation) and the operation of the transport unit 20 sending the roll paper S in the transport direction (transport operation) are repeated. As a result, dots are formed on the roll paper S and an image is printed on the roll paper S. Hereinafter, the dot forming operation is also referred to as a pass. The nth pass is also referred to as pass n.

On the lower surface of the head 41, as shown in FIG. 4, 360 nozzles are provided for each of the five colors of ink (for each color). That is, in this embodiment, the nozzle from which white ink is ejected, the nozzle from which cyan ink is ejected, the nozzle from which magenta ink is ejected, the nozzle from which yellow ink is ejected, and the nozzle from which black ink is ejected are respectively 360 (360 × 5 = 1800 in total) are provided. The 360 nozzles are arranged in a row along the sub-scanning direction, and form a white nozzle row W, a cyan nozzle row C, a magenta nozzle row M, a yellow nozzle row Y, and a black nozzle row K. ing.
Details of the configuration of the head 41 will be described later.

  The cleaning unit 70 is for maintaining the state of the nozzles of the head 41, and includes an ink suction unit 72 and a flushing unit 76. Details of the cleaning unit 70 will be described later.

  The controller 60 is a control unit (control unit) for controlling the printer 1. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM as a volatile memory and an EEPROM as a nonvolatile memory. The CPU 62 controls each unit via the unit control circuit 64 in accordance with a program stored in the memory 63.

=== About the ink flow path ===
FIG. 5 is a conceptual diagram showing the head 41 and the ink cartridge 34.
In the printer 1 of the present embodiment, white printing (recording with white ink) can be executed in addition to normal monochrome printing and color printing. That is, the printer 1 includes a print mode for performing white printing (a print mode using white ink) in addition to a print mode for performing monochrome printing / color printing (a print mode not using white ink) as a print mode. Yes.

  In the printer 1 of this embodiment, in order to realize these printing modes, white ink for white printing is prepared in addition to black ink, cyan ink, magenta ink, and yellow ink for monochrome / color printing. Has been. Furthermore, clear ink is prepared in the printer 1 of the present embodiment.

  The white ink is an ink for printing (recording) a background color (white color) of a color image, for example, when printing on a transparent medium. Thus, by making the background white, it becomes easier to see the color image. The white ink is described in, for example, Japanese Patent Laid-Open No. 2003-313481, and white titanium oxide (titanium dioxide) is a pigment-based aqueous ink. White ink tends to thicken and solidify when left for a long time. Moreover, it will settle easily when left for a long time.

  The clear ink is a colorless and transparent ink. Clear ink does not have any solid components, and the amount of moisturizing components (such as glycerin) is increased, and the water content is increased. Moreover, it is hard to settle even if left for a long time. In this embodiment, clear ink is used as ink for preventing clogging.

  As shown in FIG. 5, the ink cartridge 34 is detachably connected to the head 41, and the ink in the ink cartridge 34 is supplied to the head 41.

  As described above, in this embodiment, white ink and clear ink are prepared in addition to black ink, cyan ink, magenta ink, and yellow ink. Therefore, in this embodiment, as the ink cartridge 34, the ink cartridge 34W for white ink, the ink cartridge 34CL for clear ink, the ink cartridge 34M for magenta ink, the ink cartridge 34Y for yellow ink, and the ink cartridge for black ink 34K is connected to the head 41.

Next, the configuration of the head 41 will be described.
FIG. 6 is an exploded perspective view for explaining the configuration of the head 41, and FIG. 7 is a cross-sectional view of the head 41. The head 41 includes a drive unit 42, a case 43 for housing the drive unit 42, and a flow path unit 44 attached to the case.

  The drive unit 42 includes a piezo element group PZT composed of a plurality of piezo elements 421, a fixing plate 423 to which the piezo element group PZT is fixed, and a flexible cable 424 for supplying power to each piezo element 421. Is done. Each piezo element 421 is attached to the fixed plate 423 in a so-called cantilever state. The fixed plate 423 is a plate-like member having rigidity capable of receiving a reaction force from the piezo element 421. The flexible cable 424 is a flexible sheet-like wiring board, and is electrically connected to the piezo element 421 on the side surface of the fixed end opposite to the fixed plate 423. On the surface of the flexible cable 424, a head controller HC, which is a control IC for controlling the driving of the piezo element 421 and the like, is mounted.

  The case 43 has a rectangular parallelepiped block-like outer shape having a storage empty portion 431 in which the drive unit 42 can be stored. The flow path unit 44 is joined to the front end surface of the case 43. The housing empty portion 431 has a size that allows the drive unit 42 to be fitted exactly. The case 43 is also formed with an ink supply pipe 432 for supplying ink from the corresponding ink cartridge 34 to the flow path unit 44.

  The flow path unit 44 includes a flow path forming substrate 45, a nozzle plate 46, and an elastic plate 47. The flow path forming substrate 45 is laminated and integrated so that the flow path forming substrate 45 is sandwiched between the nozzle plate 46 and the elastic plate 47. Constructed. The nozzle plate 46 is a thin plate made of stainless steel on which the nozzles Nz are formed.

  In the flow path forming substrate 45, a plurality of vacant portions serving as pressure chambers 451 and ink supply ports 452 are formed corresponding to the respective nozzles Nz. The reservoir 453 is a liquid storage chamber for supplying the ink stored in the ink cartridge 34 to each pressure chamber 451 and communicates with the other end of the corresponding pressure chamber 451 through the ink supply port 452. The ink supplied from the ink cartridge 34 is introduced into the reservoir 453 through the ink supply pipe 432.

  The drive unit 42 is inserted into the housing empty portion 431 with the free end portion of the piezo element 421 facing the flow path unit 44 side, and the distal end surface of the free end portion is bonded to the corresponding island portion 473. Further, the back surface of the fixing plate 423 is bonded to the inner wall surface of the case 43 that partitions the housing empty portion 431. When a drive signal is supplied to the piezo element 421 via the flexible cable 424 in this stored state, the piezo element 421 expands and contracts to expand and contract the volume of the pressure chamber 451. Due to such a change in the volume of the pressure chamber 451, pressure fluctuation occurs in the ink in the pressure chamber 451. Then, ink droplets can be ejected from the corresponding nozzle Nz by utilizing the variation in the ink pressure.

As apparent from FIG. 5, for each of cyan, magenta, yellow, and black, only one ink cartridge 34 (that is, ink cartridge 34C, ink cartridge 34M, ink cartridge 34Y, ink cartridge 34K) is provided for each head 41. Each color is connected to a reservoir 453.
On the other hand, for the white ink, the two ink cartridges 34, that is, the white ink cartridge 34 </ b> W and the clear ink cartridge 34 </ b> CL are connected to the white ink reservoir 453 via the changeover switch 80.
Hereinafter, the reservoir 453 of the head 41, the pressure chamber 451, the nozzle Nz, and the like are also referred to as a filling chamber 450 for convenience.

In FIG. 5, on the upstream side of the changeover switch 80 (on the ink cartridge 34 side), there are a flow path from the ink cartridge 34W and two flow paths from the ink cartridge 34CL. On the other hand, there is only one flow path communicating with the reservoir 453 of the head 41 on the downstream side (head 41 side) of the changeover switch 80. That is, the changeover switch 80 switches the ink supplied to the reservoir 453 corresponding to each white nozzle Nz (white nozzle row W) of the head 41 to either the white ink of the ink cartridge 34W or the clear ink of the ink cartridge 34CL. . For example, when the white ink reservoir 453 communicates with the white ink cartridge 34W by the changeover switch 80, white ink is supplied to the white ink reservoir 453, and the white ink reservoir 453 and the clear ink cartridge 34CL are supplied. Is communicated with the white ink reservoir 453. The changeover switch 80 is controlled by the controller 60.
A specific method for switching from white ink to clear ink (clear ink to white ink) by the switch 80 and an example of switching timing will be described in detail later.

=== About the cleaning unit ===
As described above, the cleaning unit 70 of the printer 1 of the present embodiment includes the ink suction unit 72 and the flushing unit 76. Hereinafter, the ink suction unit 72 and the flushing unit 76 will be described.

<Ink suction unit>
The ink suction unit 72 is for sucking ink. As shown in FIGS. 2 and 3, the ink suction unit 72 is provided at a position where the head 41 faces when the carriage 38 is located at the home position at the end portion in the main scanning direction. The ink suction unit 72 performs a cleaning process for eliminating the ejection failure of the head 41 and a switching process from white ink to clear ink (clear ink to white ink) (details of the switching process will be described later). Ink the ink.

  FIG. 8 is a conceptual diagram showing the ink suction unit 72. As shown in FIG. 8, the ink suction unit 72 includes a head cap 73, a hose 74, and a suction pump 75.

  In the head cap 73, the internal space is partitioned into five suction chambers 73a. When the head cap 73 is raised, the head cap 73 comes into close contact with the lower surface of the head 41. At this time, each of the five suction chambers 73a has a closed space covering the corresponding nozzle row of the five nozzle rows. Form. That is, the head cap 73 is raised so as to seal the lower surface (nozzle surface) of the head 41.

  The suction pump 75 has two small rollers 75a in the vicinity of the peripheral edge thereof, and a hose 74 is wound around the two small rollers 75a. Then, when the suction pump 75 is driven by a motor (not shown) and rotates in the direction of the arrow, the air in the hose 74 is pushed by the small roller 75a, thereby exhausting in the closed space in the head cap 73. ing. When exhaust is performed in the closed space, the closed space becomes negative pressure, and ink is sucked from the nozzles Nz (filling chamber 450) of the head 41. The sucked ink is discharged through a hose 74 to a waste ink discharge unit (not shown).

  The head cap 73 exhibits the following functions without the suction pump 75 being operated. That is, when the printer 1 does not perform printing (and when the carriage 38 is positioned at the home position), the head cap 73 is raised and is in close contact with the lower surface of the head 41. This suppresses ink evaporation from the nozzles 72 (in other words, ink drying). That is, the head cap 73 functions as a lid that seals the lower surface (nozzle surface) of the head 41 during printing suspension and suppresses ink evaporation.

<Flushing unit>
As shown in FIG. 3, a flushing unit 76 is provided at a position adjacent to the ink suction unit 72 in the main scanning direction (a position located inside the ink suction unit 72).

  In the present embodiment, a flushing box 77 is provided as the flushing unit 76. In the printer 1, while the printing process is being executed (that is, from when the controller 60 receives a print command until the printer 1 shifts to a standby state), the head 41 ejects ink for printing an image. When the operation is not performed, the flushing is performed on all the nozzles Nz (including the nozzles Nz that are not used for printing the image).

  When flushing is performed, the carriage 38 moves to a position where the head 41 faces the flushing box 77. At this position, when the above-described piezo element 421 performs the expansion / contraction operation based on the drive pulse included in the drive signal output from the unit control circuit 64, the capacity of the pressure chamber 451 changes, and the nozzle Nz Ink is ejected toward the flushing box 77. The ink ejected toward the flushing box 77 is discharged to a waste ink discharge unit (not shown).

=== About the process of switching to clear ink when the power is turned off ===
First, the purpose of selectively supplying white ink and clear ink to the white ink filling chamber 450 will be described.

  The purpose is to prevent clogging in the white nozzle row W of the head 41. That is, when comparing the white ink and the clear ink, as described above, the white ink is more likely to cause the clogging, and the white ink is filled in the white ink filling chamber 450. If the ink is left for a long time, the thickening of the white ink is promoted, and there is a high possibility that the head 41 (particularly, the nozzle Nz) is clogged. Therefore, in view of this, when the ink is left for a long time, the white ink filling chamber 450 is filled with clear ink which is not easily clogged but is not clogged with white ink.

  Next, an example of switching timing from white ink to clear ink will be described. In the present embodiment, when the printer 1 is turned off, the white ink filling chamber 450 is filled with clear ink. Therefore, when the power is turned off, the controller 60 executes switching from white ink to clear ink.

  When switching from white ink to clear ink, first, the controller 60 controls the head unit 40 and switches the changeover switch 80 described above. That is, by switching the changeover switch 80, the controller 60 clears the white ink filling chamber 450 from the state where the white ink filling chamber 450 (more specifically, the reservoir 453) communicates with the white ink cartridge 34W. The ink cartridge 34CL for ink is shifted to a communication state.

  Next, in a state where the white ink filling chamber 450 and the ink cartridge 34CL communicate with each other, the controller 60 controls the ink suction unit 72 to perform ink suction. As a result, the white ink filled in the white ink filling chamber 450 is discharged to the waste ink discharge portion and replaced with the white ink, so that the clear ink is replaced with the white ink filling chamber 450 from the clear ink cartridge 34CL. To be supplied.

  Note that flushing may be performed by the flushing unit 76 instead of ink suction. Also in this case, the clear ink is supplied from the ink cartridge 34CL to the white ink filling chamber 450 so that the white ink filled in the white ink filling chamber 450 is ejected to the waste ink discharge portion and replaced with the white ink. .

=== Processing for switching to white ink when the power is turned on ===
First, an example of switching timing from clear ink to white ink will be described. In this embodiment, when the printer 1 is turned on, the white ink filling chamber 450 is filled with white ink. For this reason, when the power is turned on, the controller 60 executes switching from clear ink to white ink. However, the present invention is not limited to this. For example, when the printer is in a standby state even after the power is turned on, or when executing a printing mode that does not use white ink, printing using white ink is not performed. When the mode is executed, the clear ink may be switched to the white ink.

  When switching from clear ink to white ink, first, the controller 60 controls the head unit 40 and switches the changeover switch 80 described above. That is, the controller 60 switches the white ink filling chamber 450 and the white ink ink cartridge 34W from the state where the white ink filling chamber 450 and the clear ink ink cartridge 34CL communicate with each other by switching the changeover switch 80. Shift to a state in which the.

  Next, in a state where the white ink filling chamber 450 and the ink cartridge 34 </ b> W communicate with each other, the controller 60 controls the ink suction unit 32 to perform ink suction. Thus, the white ink is filled from the white ink cartridge 34 </ b> W so that the clear ink filled in the white ink filling chamber 450 is discharged to the waste ink discharge portion and replaced with the clear ink. To be supplied.

  Note that flushing may be performed by the flushing unit 76 instead of ink suction. Also in this case, the white ink is supplied from the ink cartridge 34 </ b> W to the white ink filling chamber 450 so that the clear ink filled in the white ink filling chamber 450 is ejected to the waste ink discharge portion and replaced with the clear ink.

=== Printing operation immediately after switching to white ink ===
<Issues>
Immediately after switching from clear ink to white ink, even if suction or flushing is performed, the clear ink may remain in the filling chamber 450 and the ink supply pipe 432. The white ink ejected from each white nozzle Nz (white nozzle row W) may become light. As a result, the brightness (L value) of white may be lowered. However, if suction or flushing is added and light white ink is thrown away, waste is increased. For this reason, in this embodiment, light white ink is used for printing. This suppresses wasteful consumption of white ink.

  However, even if the white ink is light immediately after switching from the clear ink to the white ink, if the white ink is continuously ejected, the white ink gradually becomes darker. That is, the white L value gradually increases. This is because the remaining clear ink in the filling chamber 450 of the head 41 and the supply pipe 432 gradually decreases. For this reason, if dots are formed in order on each pixel arranged in the moving direction of the medium by one pass, the difference in density (density unevenness) increases on one side and the other side in the moving direction.

  Therefore, in this embodiment, dots (relatively light dots) are formed every predetermined pixel of the medium moving method in a pass after switching from clear ink to white ink, and between dots that have already been formed in subsequent passes. A dot (a relatively dark dot) is formed. Thereby, density unevenness can be reduced and image quality can be improved.

<First Embodiment>
In this embodiment, overlap printing is performed when switching from clear ink to white ink. Overlap printing is a method in which dot rows (raster lines) arranged in the moving direction of a medium are formed by a plurality of passes. Furthermore, bidirectional printing is performed in the first embodiment.

  9A to 9D are explanatory diagrams of the first embodiment. In the figure, a state of dot formation on the roll paper S is shown. Here, dot formation by the nozzles Nz of the white nozzle row W after switching from clear ink to white ink is shown. Also, the numbers in the dots shown in the figure indicate the number of passes in which each dot is formed.

  First, after performing the switching process from the clear ink to the white ink described above, the controller 60 performs the first dot formation operation (pass 1) as shown in FIG. White ink is ejected from each nozzle of the white nozzle row W while moving 41 in the movement direction (rightward direction in the figure: forward path). In this pass 1, the controller 60 ejects white ink from the nozzles Nz every other pixel for the pixels arranged in the moving direction of the roll paper S. Thereby, as shown in FIG. 9B, dots are formed on the roll paper S every other pixel.

Next, as shown in FIG. 9C, the controller 60 ejects white ink from the nozzles of the white nozzle row W while moving the head 41 in the direction opposite to the pass 1 (the left direction in the figure: the return path) ( Pass 2). In pass 2, the controller 60 ejects white ink from each nozzle Nz so that dots are formed between the dots formed in pass 1.
As a result, as shown in FIG. 9D, a dot row (raster line) in which the dots formed in pass 1 and the dots formed in pass 2 are alternately arranged along the moving direction of the roll paper S is formed.

  Thus, in this embodiment, dots are formed every other pixel in the moving direction of the roll paper S by overlap printing. For this reason, after the dots formed in pass 1 are dry, dots can be formed in pass 2, so that compared to the case where dots are formed in each pixel in a single pass (non-overlapping printing), The amount of white ink ejected can be increased. Therefore, even if light white ink is used, the amount of (white) pigment per unit area can be prevented from decreasing.

Also, if non-overlapping printing is performed, the density of the white ink ejected from the nozzles gradually increases, so the difference in density between the one side and the other side in the movement direction increases. On the other hand, in overlap printing, the relatively light dots formed in pass 1 and the relatively dark dots formed in pass 2 are alternately arranged. Therefore, the density difference is less noticeable than in non-overlapping printing.
Thus, in this embodiment, since overlap printing is performed after switching from clear ink to white ink, the image quality of the printed image can be improved.

In this embodiment, bidirectional printing is performed. That is, the direction of the movement direction of pass 1 and the movement direction of pass 2 are opposite. For this reason, for example, in FIG. 9D, the dots formed in pass 1 (dots with the number 1) gradually increase in density from the left side to the right side in the figure, while the dots formed in pass 2 ( The number of dots (2) gradually increases in density from the right side to the left side of the figure. As a result, even when the density of the ink gradually increases each time the white ink is ejected, the density unevenness in the printed image becomes inconspicuous.
By performing overlap printing and bidirectional printing in this way, the image quality can be made more uniform and the image quality can be further improved.

<Second Embodiment>
Also in the second embodiment, overlap printing is performed after switching from clear ink to white ink. However, in the second embodiment, during overlap printing, small dots are formed in the first pass (pass 1), and large dots are formed in the next pass (pass 2).
10A to 10D are explanatory diagrams of the second embodiment. The numbers in the dots shown in the figure indicate the number of passes in which each dot is formed.

  First, the controller 60 performs the switching process from the clear ink to the white ink, and then performs the first dot forming operation (pass 1) as shown in FIG. White ink is ejected from the nozzles of the white nozzle row W while moving in the movement direction (right side in the figure). In this pass 1, the controller 60 ejects white ink having an ink amount corresponding to a small dot from the nozzle Nz every other pixel for the pixels arranged in the moving direction of the roll paper S. As a result, as shown in FIG. 10B, small dots are formed on the roll paper S every other pixel in the moving direction. In the second embodiment, as illustrated in FIG. 10B, the controller 60 moves the head 41 to the original position after the pass 1.

Next, as shown in FIG. 10C, the controller 60 ejects white ink from the nozzles of the white nozzle row W while moving the head 41 in the movement direction (rightward direction in the figure) (pass 2). At this time, the controller 60 ejects white ink having an ink amount corresponding to a large dot from each nozzle Nz so as to form a dot between the dots formed in pass 1.
As a result, as shown in FIG. 10D, along the moving direction of the roll paper S, a dot row (raster line) in which small dots formed in pass 1 and large dots formed in pass 2 are alternately arranged is formed. Is done.

Hereinafter, the reason why a small dot is formed first and then a large dot is formed will be described.
FIG. 11A and FIG. 11B are conceptual diagrams of the state of ink flow in the ink flow path. FIG. 11A is a conceptual diagram when the ink flow is fast. FIG. 11B is a conceptual diagram when the ink flow is slow.
For example, when forming a large dot, the flow velocity in the ink flow path is fast. Therefore, the ink flow in the ink flow path is as shown in FIG. 11A. In this case, the ink flow is large in the central portion of the ink flow path, but the ink does not flow very much on the ink flow path wall.
On the other hand, when forming small dots, the flow velocity in the ink flow path is slow. Therefore, the ink flow in the ink flow path is as shown in FIG. 11B. In this case, the difference in the ink flow between the central portion of the ink flow path and the ink flow path wall is small.
Here, the clear ink tends to remain near the ink flow path wall. Therefore, as is apparent from the figure, the residual clear ink can be reduced more quickly when the small dots are formed (FIG. 11B) than when the large dots are formed (FIG. 11A).

As described above, in the second embodiment, when overlap printing is performed after switching from clear ink to white ink, small dots are formed in the first pass (pass 1) and large dots in the next pass (pass 2). Is forming. Thereby, the residual clear ink can be reduced quickly. In addition, since the dots (light dots) formed in pass 1 are small and the dots (dark dots) formed in pass 2 are large, the portion with a light density is hardly noticeable.
In the second embodiment, bi-directional printing may be performed as in the first embodiment.

<Third Embodiment>
Also in the third embodiment, overlap printing is performed after switching from clear ink to white ink. However, in the third embodiment, during overlap printing, large dots are formed in the first pass (pass 1), and small dots are formed in the next pass (pass 2).
12A to 12D are explanatory diagrams of the third embodiment. The numbers in the dots shown in the figure indicate the number of passes in which each dot is formed.

  First, the controller 60 moves the head 41 in the first dot formation operation (pass 1) as shown in FIG. 12A when performing printing with white ink after performing processing for switching from clear ink to white ink. White ink is ejected from the nozzles of the white nozzle row W while moving in the direction (rightward direction in the figure). In pass 1, the controller 60 ejects white ink having an ink amount corresponding to a large dot from the nozzle Nz every other pixel for pixels arranged in the moving direction of the roll paper S. Thereby, as shown in FIG. 12B, large dots are formed on the roll paper S every other pixel in the moving direction. In the third embodiment, as shown in FIG. 12B, the controller 60 moves the head 41 to the original position after pass 1.

Next, as shown in FIG. 12C, the controller 60 ejects white ink from the nozzles of the white nozzle row W while moving the head 41 in the movement direction (rightward direction in the figure) (pass 2). At this time, the controller 60 ejects white ink having an ink amount corresponding to a small dot from the nozzle Nz so as to form a dot between the dots formed in pass 1.
Thereby, as shown in FIG. 12D, along the moving direction of the roll paper S, a dot row (raster line) in which large dots formed in pass 1 and small dots formed in pass 2 are alternately arranged is formed. Is done.

Thus, in the third embodiment, when overlap printing is performed after switching from clear ink to white ink, large dots are formed in the first pass and small dots are formed in the next pass. Note that the white ink ejected from the nozzle in the first pass is light (the white pigment content is small), and the white ink ejected from the nozzle in the next pass is dark (the white pigment content is large).
Thereby, the amount of the white pigment contained in the dots formed in each pixel can be made uniform. Therefore, density unevenness can be reduced.
In the third embodiment, bi-directional printing may be performed as in the first embodiment.

<Fourth embodiment>
In the fourth embodiment, overlap printing and non-overlap printing are performed according to the band printing band. Band printing is a printing method in which printing for the head width (nozzle row length) and conveyance of the roll paper S for the head width are repeated alternately. A band is a plurality of raster lines printed in a pass. That is, the width of the plurality of raster lines (hereinafter also referred to as band width) is equal to the length of the nozzle row.

FIG. 13 is an explanatory diagram of the fourth embodiment.
The left side in the figure shows the positions of the head 41 and nozzles (nozzles in the white nozzle row W) during the pass, and the right circle in the figure shows the dots formed by the pass. Here, for simplification of explanation, the number of nozzles in the white nozzle row is five (# 1 to # 5 nozzles). The numbers in the dots indicate the number of passes in which each dot is formed.

First, the controller 60 ejects ink every other pixel in the moving direction from each nozzle (# 1 to # 5 nozzle) of the head 41 in the first pass (pass 1) after the ink switching. Thereby, a dot row in which dots are arranged every other pixel in the movement direction is formed at a position corresponding to each nozzle.
Subsequently, in the pass 2, the controller 60 forms dots between the dots formed in the pass 1 (overlap printing). By this pass 1 and pass 2, five dot rows corresponding to the bandwidth are formed (# 1 to # 5 raster lines).
Thereafter, the controller 60 causes the roll paper S to be conveyed downstream in the conveyance direction by the bandwidth. As a result, the relative position of the head 41 with respect to the roll paper S moves upstream in the transport direction.
In the next pass (pass 3), the controller 60 ejects ink from the nozzles of the head 41 to the pixels arranged in the moving direction of the roll paper S (non-overlapping printing). As a result, five dot rows corresponding to the bandwidth are formed in one pass below the raster lines formed in pass 1 and pass 2 (upstream in the transport direction) (# 6 to # 10 rasters). line).
Thereafter, similarly, the controller 60 repeatedly performs a pass (non-overlap printing similar to pass 3) and a transport operation for the bandwidth of the paper S.

  Thus, overlap printing is performed in the first band (# 1 to # 5 raster lines) immediately after switching to white ink, and non-overlapping printing is performed in the second band (# 6 to # 10 raster lines) and thereafter. Is going. By doing this, printing after the density gradually increases can be returned to normal printing (printing without increasing the ink ejection amount per unit area), and the white L value can be made uniform regardless of the band. can do.

  Note that the printer 1 of the present embodiment performs non-overlapping printing as shown in pass 3 and pass 4 in FIG. 13 during normal printing (other than immediately after switching from clear ink to white ink). As described above, when the L value of the white ink ejected from the nozzle becomes sufficiently large, the overlap printing is switched to the normal non-overlap printing. In the case of the above-described embodiment, similarly, non-overlapping printing is performed during normal printing.

  FIG. 14 is an explanatory diagram of an improved example of the fourth embodiment. FIG. 14 shows the dot formation state of the first band (# 1 to # 5 raster lines) in FIG.

  In FIG. 13, the ejection timing of the white ink from each nozzle of the head 41 is the same for the pixels arranged in the transport direction. However, in FIG. 14, the ejection timing is different between the odd nozzle and the even nozzle. As a result, as shown in FIG. 14, dots are formed on the roll paper S in a checkered pattern by pass 1. In pass 2, dots are formed (in a checkered pattern) on the pixels in which no dots are formed in pass 1. In this way, since the dots formed in each pass are not arranged in the transport direction as well as in the movement direction, the amount of white ink ejected can be increased as compared with the case of FIG.

  Further, the number of overlaps may be gradually decreased according to the band. For example, in the first band, each raster line is formed in 4 passes (overlap printing in which dots are formed every 3 pixels), and in the second band, each raster line is formed in 2 passes (dots are formed every other pixel). In the third band and thereafter, each raster line may be formed in one pass (non-overlapping printing).

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About the printer>
In the above-described embodiment, the printer is described as an example of the liquid ejecting apparatus, but the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, liquid vaporizer, organic EL manufacturing apparatus (particularly polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technology as that of the present embodiment may be applied to various devices to which inkjet technology is applied, such as a device and a DNA chip manufacturing device.

<About ink>
Since the above-described embodiment is an embodiment of a printer, ink is ejected from the nozzles, but the liquid ejected from the nozzles is not limited to ink. For example, liquids (including water) including metal materials, organic materials (especially polymer materials), magnetic materials, conductive materials, wiring materials, film forming materials, electronic ink, processing liquids, gene solutions, etc. are ejected from nozzles. May be.

  In the above-described embodiment, the white ink is used as the printing ink and the clear ink is used as the clogging prevention ink. However, the present invention is not limited to this. For example, L cyan (light cyan) may be used as the ink for preventing clogging of the cyan nozzle row C (cyan ink), and at this time, the same processing as in the above-described embodiment may be performed.

<About dot formation>
The printer may be capable of both the overlap printing of the second embodiment and the overlap printing of the third embodiment, and is formed in pass 1 based on the time interval between pass 1 and pass 2 in the overlap printing. The magnitude relationship between the size of the dot to be formed and the size of the dot formed in pass 2 may be determined.

1 printer, 20 transport unit, 21 paper feed motor,
24 transport rollers, 26 platens, 27 roll paper holders,
29 Paper pressing roller, 30 Carriage unit,
34 ink cartridge, 36 traction belt, 37 guide rail,
38 carriage, 39 carriage motor,
40 head units, 41 heads, 42 drive units,
43 cases, 44 flow path units, 45 flow path forming substrates,
46 nozzle plate, 47 elastic plate, 50 detector group,
60 controller, 61 interface part,
62 CPU, 63 memory, 64 unit control circuit,
70 cleaning unit, 72 ink suction unit,
73 head cap, 73a suction chamber, 74 hose,
75 suction pump, 75a small roller,
76 flushing units, 77 flushing boxes,
421 piezo element, 423 fixing plate, 424 flexible cable,
431 empty space, 432 ink supply pipe, 450 filling chamber,
451 pressure chamber, 452 ink supply port, 453 reservoir,
110 Computer, S roll paper, HC head controller

Claims (5)

(A) a nozzle array for injecting liquid onto the medium;
(B) a switching unit that switches the liquid supplied to the nozzle row to either the first liquid for recording or the second liquid for preventing clogging;
(C) A dot forming operation for forming dots on pixels arranged in the moving direction of the medium by ejecting liquid from the nozzle row while moving the nozzle array in a moving direction that intersects the transport direction of the medium. A controller that performs
When the liquid supplied to the nozzle row is switched from the second liquid to the first liquid by controlling the switching unit, a dot is formed every predetermined pixel in the moving direction of the medium in a certain dot forming operation thereafter. A controller for forming dots between the dots formed by the certain dot forming operation in another dot forming operation after the certain dot forming operation;
A liquid ejecting apparatus comprising (D). The liquid ejecting apparatus according to claim 1,
The moving direction of the nozzle row in the certain dot forming operation is opposite to the moving direction of the nozzle row in the other dot forming operation.
A liquid ejecting apparatus. The liquid ejecting apparatus according to claim 1 or 2,
The dots formed by the certain dot forming operation are smaller than the dots formed by the other dot forming operation,
A liquid ejecting apparatus. The liquid ejecting apparatus according to claim 1 or 2,
The dots formed by the certain dot forming operation are larger than the dots formed by the other dot forming operation.
A liquid ejecting apparatus. The liquid ejecting apparatus according to claim 1,
The controller is
After the another dot forming operation, the medium is transported in the transport direction by a transport amount according to the length of the nozzle row,
In the subsequent dot forming operation, a dot is formed on each pixel arranged in the moving direction of the medium by the nozzle row.