JP2011156763A - Printing apparatus and printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of a printing image due to formation of ink dots of magenta and cyan on positions deviated from each other in an ink jet printing apparatus which carries out printing by using ink of cyan, magenta and yellow. <P>SOLUTION: The printing apparatus includes (A) a head part which carries out printing by jetting the cyan ink, magenta ink and yellow ink arranged in a direction orthogonal to a transfer direction of a medium, and (B) a control part which specifies pixels to which the yellow ink is to be jetted on the medium and pixels to which the yellow ink is not to be jetted, makes the yellow ink jetted from the head part to the pixels to which the yellow ink is to be jetted and makes an undercoat ink jetted from the head part to the pixels to which the yellow ink is not to be jetted, and makes the cyan ink and magenta ink jetted from the head part to the medium after the yellow ink and undercoat ink are jetted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printing apparatus and a printing method.

  In an inkjet printing apparatus that prints an image or the like by ejecting ink from nozzles and landing ink dots on the medium, the medium may expand due to the ink dots soaking into the medium after landing. On the other hand, the ink ejection position and timing are controlled with reference to a normal medium that is not expanded. Therefore, when ink is ejected to the expanded medium, the ink dots land at points deviating from the initial landing positions, which causes image deterioration.

  Therefore, by configuring the nozzle arrangement so that ink is ejected in order from the nozzle with the smallest ink ejection amount during the conveyance of the medium, the timing of expansion of the medium during conveyance (during printing of an image or the like) is delayed as much as possible. A method of maintaining good image quality by reducing the deviation of the landing positions of ink dots has been proposed (for example, Patent Document 1).

JP 2002-079696 A

  Even if the expansion timing of the medium is delayed, the expansion of the medium itself cannot be stopped after all. Therefore, the ink dots ejected after the expansion of the medium in the downstream area of the conveyance of the medium must also land out of the expected landing position. Therefore, it is difficult to completely prevent image deterioration. In particular, dots formed with cyan ink and magenta ink are visually noticeable, and when cyan and magenta ink dots are formed out of alignment with each other, image deterioration is also noticeable.

  According to the present invention, in an inkjet printing apparatus that performs printing using cyan, magenta, and yellow ink, deterioration of a printed image due to formation of magenta ink dots and cyan ink dots at positions shifted from each other is prevented. The purpose is that.

  A main invention for achieving the above object is: A) A nozzle array arranged in a direction orthogonal to the medium conveyance direction, and printing by ejecting cyan ink, magenta ink, and yellow ink onto the medium And B) a control unit for controlling the head unit, which identifies a pixel from which the yellow ink is ejected on the medium and a pixel from which the yellow ink is not ejected, and ejects the yellow ink The yellow ink is ejected from the head portion to the pixels to be applied, and the undercoat ink is ejected from the head portion to the pixels to which the yellow ink is not ejected, and the yellow ink and the undercoat ink are ejected from the head portion. Control of ejecting the cyan ink and the magenta ink from the head unit onto the medium When a printing apparatus comprising a.

  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 illustrating an overall configuration of a printing apparatus. FIG. 2 is a schematic diagram illustrating a configuration around a printing area of the printer. It is explanatory drawing of the arrangement | sequence of a head. FIG. 4A is a conceptual diagram showing the structure of paper in a normal state. FIG. 4B is a conceptual diagram showing the paper structure when moisture is contained. It is a figure showing a mode that paper expands by absorption of ink. FIG. 6 is a diagram illustrating a relationship between an ink ejection amount and a paper expansion / contraction amount. It is a figure showing the arrangement of dots actually formed on a medium based on predetermined pixel data. FIG. 8 is a diagram illustrating the arrangement of dots formed on an expanded medium using the same pixel data as in FIG. 7. FIG. 9 is a diagram illustrating a dot arrangement in a state where the medium of FIG. FIG. 6 is a diagram illustrating a relationship between ink injection timings of CMY colors and the expansion amount of a medium. It is a figure showing the mode of dot formation when C ink is struck. It is a figure showing the mode of dot formation at the time of having struck M ink. FIG. 6 is a diagram illustrating a state of dot formation when Y ink is ejected. FIG. 6 is a diagram illustrating a relationship between ink ejection timing of each color and the expansion amount of the medium when the medium is completely expanded and M ink and C ink are printed. FIG. 13 is a diagram illustrating an arrangement of each color ink dot formed on a medium when printing is performed at the timing of FIG. 12. It is a figure showing arrangement of each color head in a 1st embodiment. It is a figure showing the relationship between the timing of ink ejection of each color and the expansion amount of the medium in the first embodiment. It is a figure showing the mode of each color dot actually formed on a medium in a 1st embodiment. It is a figure showing arrangement of each color head in a 2nd embodiment. It is a figure showing the relationship between the timing of ink ejection of each color and the expansion amount of the medium in the second embodiment. It is a figure showing the mode of each color dot actually formed on a medium in a 2nd embodiment.

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

A) a head unit configured by nozzle rows arranged in a direction orthogonal to the medium transport direction, and performing printing by ejecting cyan ink, magenta ink, and yellow ink onto the medium; and B) the head unit. A control unit that controls a pixel from which the yellow ink is ejected and a pixel from which the yellow ink is not ejected from the medium. A yellow ink is ejected, and an undercoat ink is ejected from the head portion to pixels where the yellow ink is not ejected. After the yellow ink and the undercoat ink are ejected, the head portion onto the medium. And a control unit that ejects the cyan ink and the magenta ink.
According to such a printing apparatus, it is possible to prevent the print image from being deteriorated by forming magenta ink dots and cyan ink dots at positions shifted from each other during printing.

In this liquid ejecting apparatus, it is preferable that the yellow ink is ejected after ejecting the undercoat ink.
According to such a printing apparatus, the deviation between the yellow ink dots formed on the medium and the magenta ink dots (or cyan ink dots) can be further reduced.

In the liquid ejecting apparatus, the yellow ink ejecting head and the undercoat ink are ejected from an interval in a transport direction between the head ejecting the yellow ink and the head ejecting the undercoat ink. Among the heads to be transported, among the heads that are installed on the downstream side in the transport direction, the heads that eject the magenta ink, and the heads that eject the cyan ink, the heads that are installed on the upstream side in the transport direction It is desirable that the interval of is larger.
According to such a printing apparatus, after the yellow ink and the undercoat ink are applied to the medium, a sufficient time is ensured until the magenta ink (or cyan ink) is applied, and the medium can be expanded to the maximum. Therefore, the deviation between the magenta ink dots and the cyan ink dots can be further reduced.

In such a liquid ejection device, it is desirable that the undercoat ink is a clear ink or a white ink.
According to such a printing apparatus, even if a large amount of the undercoat ink is applied to the medium, it is possible to print the clear ink or the white ink as the background color, so that the printed image itself is hardly deteriorated.

  Further, a pixel on which the yellow ink is ejected on the medium and a pixel on which the yellow ink is not ejected are identified, and the identified pixel on which the yellow ink is ejected is arranged in a direction orthogonal to the conveyance direction of the medium. Ejecting yellow ink from a head portion constituted by nozzle rows, ejecting undercoat ink from the head portion to pixels to which the specified yellow ink is not ejected, and the yellow ink and the undercoat After the ink is ejected, a printing method including ejecting cyan ink and magenta ink from the head portion onto the medium becomes apparent.

=== Basic Configuration of Printing Apparatus ===
As a form of a printing apparatus for carrying out the invention, an ink jet printer (printer 1) will be described as an example.

<Printer configuration>
FIG. 1 is a block diagram illustrating the overall configuration of the printer 1.
The printer 1 is a liquid ejection device that records (prints) characters and images on a medium such as paper, cloth, and film, and is connected to a computer 110 that is an external device so as to be communicable.
A printer driver is installed in the computer 110. The printer driver is a program for displaying a user interface on a display device (not shown) and converting image data output from an application program into print data. This printer driver is recorded on a recording medium (computer-readable recording medium) such as a flexible disk FD or a CD-ROM. Also, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.
The computer 110 outputs print data corresponding to the image to be printed to the printer 1 in order to cause the printer 1 to print an image.

  The printer 1 includes a transport unit 20, a head unit 40, a detector group 50, and a controller 60. The controller 60 controls each unit based on print data received from the computer 110 that is an external device, and prints an image on a medium. 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 such as the transport unit 20 based on the detection result output from the detector group 50.

<Transport unit>
FIG. 2 is a schematic view around the print area of the printer 1.
The transport unit 20 is for transporting a medium (for example, paper S) in a predetermined direction (hereinafter referred to as a transport direction). The transport unit 20 includes an upstream transport roller 23A, a downstream transport roller 23B, and a belt 24 (FIG. 2). When a transport motor (not shown) rotates, the upstream transport roller 23A and the downstream transport roller 23B rotate, and the belt 24 rotates. The medium fed by a feed roller (not shown) is conveyed to a printable area (area facing the head) by the belt 24. The paper S on which an image is printed after passing through the printable area is discharged to the outside by the belt 24. The paper S being conveyed is electrostatically attracted or vacuum attracted to the belt 24.

<Head unit 40>
The head unit 40 is for ejecting ink onto the medium. The head unit 40 forms dots by ejecting each color ink onto the medium being transported, and prints an image on the medium. The printer 1 of this embodiment is a line printer, the head unit 40 is provided above the belt 24 of the transport unit 20 (FIG. 2), and each head can form dots corresponding to the medium width at a time.

  The head unit 40 includes a head 41 having a plurality of nozzles. FIG. 3 is an explanatory diagram of an arrangement of a plurality of heads on the lower surface of the head unit 40. As shown in the figure, a plurality of heads 41 are arranged in a staggered pattern along the paper width direction. In each head, a C (cyan) ink nozzle row, an M (magenta) ink nozzle row, a Y (yellow) ink nozzle row, a CL (clear) ink nozzle row, and the like are formed. In addition, CL (clear) ink means a colorless and transparent ink. Each nozzle row includes a plurality of nozzles that eject ink. The plurality of nozzles in each nozzle row are arranged at a constant nozzle pitch along the paper width direction. Then, ink droplets are intermittently ejected from each nozzle to the medium being transported, whereby each nozzle forms a dot line (raster line) along the medium transport direction.

<Detector group 50>
The detector group 50 includes a rotary encoder (not shown), a paper detection sensor (not shown), and the like. The rotary encoder detects the rotation amount of the upstream side conveyance roller 23A and the downstream side conveyance roller 23B. The transport amount of the medium can be detected based on the detection result of the rotary encoder. The paper detection sensor detects the position of the leading edge of the medium being fed.

<Controller 60>
The controller 60 is a control unit (control unit) for controlling the printer. 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 device for performing overall control of the printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and is configured by a storage element such as a RAM or an EEPROM. Then, the CPU 62 controls each unit such as the transport unit 20 via the unit control circuit 64 in accordance with a program stored in the memory 63.

<Printer operation>
The printing operation of the printer 1 will be briefly described. The controller 60 receives a print command from the computer 110 via the interface unit 61, and performs printing by controlling each unit.

  When the printer 1 receives print data from the computer 110, the controller 60 rotates a paper feed roller (not shown), supplies the paper S to be printed into the printer, and sends the paper S to be printed to the transport belt 24. Subsequently, the belt 24 is rotated by the upstream and downstream transport rollers 23A and 23B, and the paper S sent from the paper feed roller is transported to the printing start position. The paper S is conveyed on the belt 24 without stopping at a constant speed, and passes under the head unit 40.

  While the paper S moves along the transport direction, the controller 60 intermittently ejects ink from the head 41 based on the print data. When the ejected ink droplets land on the paper S, dots are formed on the paper S, and a dot line (raster line) including a plurality of dots along the transport direction is formed on the paper S. The controller 60 ejects ink from the head 41 until there is no more data to be printed, and gradually prints an image composed of dot lines on the paper S. When there is no more data to be printed, the paper is discharged by belt conveyance. The same processing is repeated when printing on the next paper, and the printing operation is terminated when not printing.

=== About Expansion of Medium (Paper) ===
In the printing apparatus according to the present embodiment, it is assumed that “paper” is mainly used as a medium for printing an image. At the time of printing, ink droplets ejected from the head land on paper, which is a medium, and penetrate and fix to form dots on the paper surface, and the dots gather to form an image.

<Properties of paper>
In general, “paper” is composed of cellulose fibers, and a large number of cellulose fibers are entangled to form a planar paper. Cellulose fiber is a polymer compound in which carbohydrates are linearly polymerized, and is used for clothing fibers as well as paper.
FIG. 4A is a diagram conceptually showing the structure of paper in a normal state. FIG. 4B is a diagram conceptually showing the paper structure when water is included.
As described above, paper has a structure in which straight-chain cellulose fibers are entangled in a complicated manner, and each cellulose fiber is bound to each other by hydrogen bonding (FIG. 4A). In a normal state, the shape of the paper (paper as a printing medium is a flat shape) is maintained by the bonding force of hydrogen bonds.

Here, when moisture is added to the paper, water molecules are dispersed between the cellulose fibers constituting the paper, and hydrogen bonds between the cellulose fibers are broken. The fibers that have lost the bonding force due to hydrogen bonding are weakened in each other, so that the distance between the intertwined fibers is widened and swollen. As a result, the planar paper is expanded (FIG. 4B).
Thereafter, when the absorbed moisture is dried, the state again becomes as shown in FIG. 4A, and the paper returns to the original size (the one that has been expanded contracts to the original size). Note that the hydrogen bonds between cellulose fibers do not return completely to the same bonding state as the original, so they do not always have a clean flat shape. There is.

<How to expand the paper>
I explained that the expansion of paper is caused by changes in the bonding force between cellulose fibers, but actually figure out how much of what part of the bond is cut between the fibers that make up the paper as a print medium. It is impossible to do. Therefore, in the present embodiment, the description will be simplified by assuming that the paper that has absorbed ink expands uniformly.

  FIG. 5 is a diagram for explaining how paper expands due to ink absorption in the present embodiment. What is drawn with a solid line represents the outline of the paper in the normal state, and what is drawn with a broken line represents the outline of the paper expanded by absorbing moisture (ink). The expansion is performed evenly in the horizontal direction (X direction) and the vertical direction (Y direction) in FIG. 5 with the center of the paper as a reference point. For example, when one dot of ink droplet is formed in the center of the paper, by absorbing the moisture contained in the ink droplet, the paper spreads by ± n micrometers (μm) in the X direction, and similarly in the Y direction. It shall spread by ± n micrometers (μm).

  Next, the relationship between the amount of moisture absorbed and the amount of paper expansion will be examined. Even when moisture is absorbed by the paper and hydrogen bonds between the cellulose fibers are broken, the state in which the fibers are entangled with each other is maintained, and the individual fibers do not fall apart. Therefore, paper does not expand indefinitely according to the amount of moisture absorbed, but the amount of expansion is always limited.

FIG. 6 shows a relationship between the amount of ink ejected onto the paper (hereinafter also referred to as ink ejection amount) and the amount of paper that expands and contracts by absorbing the ink. Note that the data in FIG. 6 is obtained when the black ink is ejected while changing the ejection amount onto an A4 size (210 mm × 297 mm) medium (paper) using the printing apparatus of the present embodiment. This is based on the result of measuring the amount of expansion and contraction of the paper after 2 seconds. In addition, when solid printing is performed on the entire surface of A4 (when the ink dots having the maximum diameter are formed for all the pixels of the A4 paper), the ink shot amount is 3.6 mg / inch ² .

The amount of expansion / contraction of the paper increases as the amount of ink applied increases, but it can be seen that the amount of expansion / contraction becomes constant when the amount of ink injection exceeds 2 mg / inch ² . That is, the paper expands in proportion to the amount of ink (moisture) absorbed. When a certain amount or more of ink (moisture) is absorbed, the ink is saturated, and even when a larger amount of ink is applied, the paper does not expand. Note that the amount of expansion of the paper is considered to vary depending on the type and properties of the paper, the ink component (water content), and the like.

=== Generation of printing misalignment due to expansion ===
A description will be given of how the printed image is affected by the expansion of the paper.

<Dot formation when paper does not expand>
First, the formation of ink dots when the medium (paper) does not expand at all will be described. FIG. 7 is a diagram showing the arrangement of dots actually formed on a medium when printing is performed on the medium using certain print data. Data used for printing are pixels for forming dots on predetermined pixels (6 pixels P1, 3, 4, 5, 8, and 9 in FIG. 7) among the 3 × 3 grid-like pixels P1 to P9. Data. Ink is ejected from the head toward the corresponding pixel on the medium according to the pixel data, thereby forming a dot at the pixel specified by the pixel data. Note that the pixel data is simplified data for convenience, and the pixel data used for actual printing is larger than this. Here, it is assumed that the dots formed on the P5 pixel land on the (paper) center position of the medium, and that the dot landing position is not shifted due to an operation error of the head unit or the transport unit.
If the medium (paper) is not in an expanded state, the print data can be printed without causing a shift between the position of the dot represented by the pixel data and the position of the dot actually formed on the medium. You can print the exact image.

<Dot formation when paper expands>
Next, how dots are formed when ink is ejected onto a medium (paper) that has expanded by absorbing moisture will be described. FIG. 8 is a diagram showing the arrangement of dots actually formed on a medium when printing is performed on the expanded medium using the same pixel data as the pixel data used in FIG. FIG. 9 is a diagram showing a state in which the medium on which dots are formed in FIG. 8 is shrunk by drying. Note that, as described above, the medium expands uniformly in the X direction and the Y direction with reference to the center position of the medium.

  The pixels P1 ′ to P9 ′ on the medium after expansion are wider than the pixels P1 to P9 before expansion, and the pixels other than the central pixel P5 ′ serving as the expansion reference position are also displaced. In order to print an image according to the original print data, it is necessary to form dots in accordance with the expanded pixels P1 ′ to P9 ′. That is, the ink dots ejected from the head unit must land at the center positions of the respective pixels P1 ′ to P9 ′, and the dots are originally formed at the positions indicated by ○ in FIG. Should. However, due to the expansion of the medium, the pixels (P1 to P9) on the pixel data and the pixels (P1 ′ to P9 ′) on the actual medium are displaced. Dots are formed at the represented positions. The deviation of the relative position generated between ◯ and ● is the printing deviation.

  When the medium is dried after a predetermined time has elapsed, the size of the medium returns to the original state (the size of the medium in FIG. 7). When the medium is reduced, similarly to the case of expansion, if the center of the medium (pixel P5 ′) is reduced as a reference, the expanded pixels (P1 ′ to P9 ′) also become (P1 ″ to P9 ″), and again. The shape returns to the pixel data (P1 to P9). Then, the ink dots formed in FIG. 8 also move to the position represented by ● in FIG. 9 as the medium is reduced.

  When the images printed in FIG. 7 and FIG. 9 are compared, even when printing is performed using the same pixel data, the ink dots formed after the expansion of the medium are larger than the ink dots formed before the expansion of the medium. Is also formed to be displaced inward (close to the reference point) as a whole.

<When printing with multiple colors of ink>
In the printing apparatus of the present embodiment, printing is performed using a plurality of inks such as Y (yellow), M (magenta), and C (cyan). The inks of the respective colors are ejected on the medium in order from the respective color heads arranged in the medium transport direction (see FIG. 2). Here, since there is no expansion of the medium at the initial stage of conveyance in which no ink is ejected on the medium, the ink dots formed at the beginning of the conveyance process have a problem of printing misalignment as shown in FIG. Does not occur. However, in the last stage of the conveyance, a large number of ink dots are ejected on the medium in the conveyance process so far, so that the medium expands by absorbing the moisture of the ink, as shown in FIGS. In this way, the dots are formed out of alignment. In other words, during the medium transport process, there may be a deviation in the landing position of the formed dots due to the difference in the timing of ink ejection.

  For example, when printing is performed by ejecting ink in the order of Y, M, and C on the medium, how the expansion of the medium affects the printed image is considered. FIG. 10 shows the relationship between the ink ejection timing of each color and the expansion amount of the medium when the same amount of ink is ejected onto the medium based on the same pixel data using the three colors of YMC. FIG. FIG. 11A is a diagram showing how dots are formed when Y ink is applied. FIG. 11B is a diagram showing how dots are formed when M ink is ejected. FIG. 11C is a diagram showing how dots are formed when C ink is applied. As in the case described above, it is assumed that the medium expands evenly with respect to the central portion.

  Before Y ink is first jetted, the expansion amount is zero because the medium does not absorb moisture (FIG. 10). Therefore, the Y ink dots are formed without shifting to the positions specified by the pixel data on the medium. FIG. 11A shows a case where printing is performed based on pixel data for forming dots in 3 × 3 pixels.

  Subsequently, M ink is ejected onto the medium. When the M ink is ejected, the medium is in an expanded state by the amount of the Y ink that has been previously ejected (this is the first stage expansion). Note that the M ink is fired after the medium has absorbed Y ink and the first stage of expansion has been completed and the size of the medium has become constant, as shown in FIG.

  As described with reference to FIGS. 7 to 9, when ink is ejected to the expanded medium based on the same pixel data, dots are formed at positions shifted before and after the expansion of the medium. Also in FIG. 11B, the M ink dots are formed at positions shifted from the Y ink dots formed before the medium expansion. For example, the M ink dot formed in the upper right pixel in FIG. 11B is formed at a position shifted by x1 in the −X direction and y1 in the −Y direction from the Y ink dot formed first.

  Finally, C ink is ejected onto the medium. When C ink is ejected, the medium absorbs the Y ink and M ink that have been previously ejected and is further expanded (referred to as expansion in the second stage). The timing of ink ejection of C ink is after the medium has absorbed M ink and the second stage of expansion has been completed and the size of the medium has become constant (see FIG. 10). Since the medium is further expanded, as shown in FIG. 11C, the C ink dot is formed at a position further shifted from the M ink dot. For example, the C ink dot formed in the upper right pixel in FIG. 11C is shifted by x2 (x2> x1) in the −X direction and y2 (y2> y1) in the −Y direction from the Y ink dot formed first. Formed.

  In other words, in the process of transporting the medium, when each color ink is ejected in order from the head located on the upstream side of the transport, the deviation of the landing positions of the ink dots gradually increases as the transport proceeds. That is, the later the ink dots are formed, the larger the amount of deviation from the ink dots formed first, and the deterioration of the image due to printing deviation becomes conspicuous.

=== Method for Preventing Image Degradation Due to Printing Misalignment ===
As described above, when paper is used as a printing medium, the size of the medium changes by absorbing ink in the middle of printing, so it is difficult to land the ink dots at the planned positions. There are many cases where deviation occurs. Therefore, it is necessary to study a method that makes it difficult to notice the deterioration of the printed image even if the dot landing position is deviated.

  The problem here is when the “deviation” between ink dots formed on the medium is noticeable. The fact that the dot misalignment is conspicuous means that the visibility between the dots is high, and therefore the color scheme of the ink used for printing (in this embodiment, at least three colors of C, M, and Y) has a great influence. To do. This is because, generally, the greater the difference in brightness between different colors, the higher the visibility.

  In this embodiment, printing is often performed using “white paper” as a medium, and the background color of the printed image is white. When the background color is “white”, M (magenta) and C (cyan) are colors having a greater brightness difference than “white”. Therefore, the M ink dots formed on the white medium are easily noticeable, and similarly, the C ink dots formed on the white medium are easily noticeable. On the other hand, since Y (yellow) has a small brightness difference with respect to the background color “white”, Y ink dots formed on a white medium are less noticeable than M ink dots and C ink dots.

  From the above, when the formation positions of the M ink dots and C ink dots formed on the “white paper” are misaligned, the misalignment between the two dots is easy to see and is a direct cause of print image deterioration. It becomes.

  Conversely, even if the relative positions of the Y ink dots formed on the “white paper” and the M ink dots are deviated, the Y ink dots themselves are not noticeable, and the deviation from the M ink dots is also not noticeable. . Similarly, the deviation between the Y ink dots formed on the “white paper” and the C ink dots is hardly noticeable. Therefore, even if the Y ink dot formation position is misaligned, it is difficult to cause deterioration of the printed image.

  Therefore, the printing image is prevented from deteriorating by performing printing so that the formation positions of the M ink dots and the C ink dots are not shifted.

  FIG. 12 shows the relationship between the ink ejection timing of each color and the expansion amount of the medium when printing is performed so that the formation positions of the M ink dots and the C ink dots are not shifted. FIG. 13 shows the state of each color dot formed on the medium in that case.

  As described above, the deterioration of the image due to the expansion of the medium absorbs the moisture of the ink while the medium is transported and gradually expands, whereas each color ink is driven in during the expansion of the medium. As a result, the landing positions of the respective color ink dots are shifted (FIGS. 11A to 11C). On the contrary, if the M ink and C ink are driven after the medium sufficiently absorbs moisture and expands to the maximum and does not expand any more, the formation positions of the M ink dot and the C ink dot shift. There is nothing.

  For this purpose, as shown in FIG. 12, first, Y ink and CL (clear) ink are applied to the entire surface of the medium, so that a sufficient amount of moisture is absorbed in the medium and the ink is completely expanded. By printing the M ink and the C ink after the medium is not expanded any more, the M ink dot and the C ink dot can be printed without being affected by the medium expansion. Details regarding the CL ink ejection and the like will be described later.

  In the actually printed image, as shown in FIG. 13, the displacement of the formation positions of the Y ink dots that are first ejected on the medium and the M ink dots and C ink dots that are ejected after the expansion of the medium is large. . However, since the misalignment of the Y ink dots is not noticeable as described above, the image does not deteriorate. Since the displacement between the formation positions of the M ink dots and the C ink dots is reduced, it is possible to prevent the deterioration of the printed image as a whole.

=== First Embodiment ===
In the first embodiment, printing is performed using CL (clear) ink as an undercoat ink for causing the medium to absorb moisture in addition to the inks of the three colors Y, M, and C. However, the CL ink is not an ink for constituting an image, but an ink serving as a background or a base. Therefore, it is also possible to use W (white) ink as a background color instead of CL ink. Hereinafter, a case where printing is performed using CL ink will be described.

  FIG. 14 shows the arrangement of each color head in the first embodiment. As apparent from FIG. 14, in this embodiment, ink is ejected onto the medium in the order of Y → CL → M → C from the upstream side in the transport direction. Note that the order of ejection of M ink and C ink may be reversed. However, in this embodiment, as will be described later, it is necessary to eject the M ink and the C ink after the Y ink and the CL ink are sufficiently absorbed by the medium. Therefore, in FIG. 14, the distance between the CL ink head and the M ink head (or C ink head) should be as wide as possible, and it is desirable to keep at least a distance between the Y ink head and the CL ink head.

  Printing can also be performed using K (black) ink in addition to M and C inks. This is because when the medium reaches the fully expanded state by hitting the Y ink and the CL ink, the dot landing position will not be displaced no matter what order the ink is hit thereafter. That is, it is only necessary that the medium is expanded to the maximum extent by ejecting ink in the order of Y → CL.

  FIG. 15 shows the relationship between the ink ejection timing of each color ink and the expansion amount of the medium (paper) in the present embodiment. FIG. 16 shows the state of each color dot actually formed on 3 × 3 pixels (P1 to P9) on the medium.

  First, Y ink dots are ejected from the Y ink head to the medium according to the print data. By absorbing the landed Y ink dots, the medium expands slightly (first-stage expansion in FIG. 15). In normal image printing, the ratio of pixels on which Y ink dots are formed to all the pixels on the medium is not so large in most cases. For example, in FIG. 16, Y ink dots are formed only in three pixels (P3, P4, P8) among nine pixels (P1 to P9). The medium cannot be expanded to a saturated state with only such a small amount of Y ink dots.

  Therefore, CL ink dots are ejected to all remaining pixels on which Y ink is not formed on the medium. For example, in FIG. 16, CL ink dots are formed for 6 pixels of (P1, P2, P5, P6, P7, P9). As a result, the medium absorbs the CL ink dots and further expands (second stage expansion in FIG. 15). Since the CL ink is transparent, the printed image does not deteriorate even when a large amount is applied to the medium. Eventually, all pixels on the medium (P1 to P9 in FIG. 16) are completely filled with Y ink dots and CL ink dots, so that the medium expands by absorbing moisture until saturation. Thereafter, a sufficient time is taken for the medium to expand, and the M ink and the C ink are ejected after the medium is completely expanded.

  At the time of printing, the controller 60 specifies, from the pixel data used for printing, a pixel from which Y ink is ejected and a pixel from which Y ink is not ejected among all the pixels on the medium. Y ink is ejected to the pixels from which Y ink is ejected (P3, P4, P8 in FIG. 16), and CL is applied to the pixels from which Y ink is not ejected (P1, P2, P5, P6, P7, P9 in FIG. 16). Ink is ejected. Then, after the Y ink and the CL ink are ejected, the M ink and the C ink are ejected from the M ink head and the C ink head on the transport downstream side.

  By the method of the present embodiment, as shown in FIG. 16, Y ink dots, CL ink dots, M ink dots, and C ink dots are formed at positions shifted on the medium. In FIG. 16, for the sake of explanation, it is assumed that M and C dots are formed for each 3 × 3 pixel.

  As described above, the displacement of the Y ink dot formation position is not conspicuous, and the displacement of the CL ink dot formation position can be ignored because the dot itself is transparent. On the other hand, regarding the M ink dots and the C ink dots that greatly affect the visibility, no deviation occurs in the relative positions of each other. Thereby, deterioration of the image is prevented.

  It should be noted that the CL ink ejection amount may be determined in accordance with properties such as the moisture absorption amount of the medium (paper). For example, by specifying the size of the CL dot as the gradation value, the driving amount is adjusted according to the printing conditions. In addition, in consideration of the influence of atmospheric humidity, it is possible to make adjustments such as reducing the amount of CL ink applied when the humidity is high, and conversely increasing the amount of CL ink applied when the humidity is low.

=== Second Embodiment ===
The basic configuration of the second embodiment is the same as that of the first embodiment, and printing is performed using CL as an undercoat ink in addition to the three colors Y, M, and C. However, the ejection order of Y ink and CL ink is different from that of the first embodiment.

  FIG. 17 shows the arrangement of each color head in the second embodiment. As is apparent from FIG. 17, in this embodiment, ink is ejected onto the medium in the order of CL → Y → M → C from the upstream side in the transport direction. As in the first embodiment, the order of the M ink and the C ink may be reversed. That is, in the second embodiment, it is only necessary that the medium is expanded to the maximum by ejecting ink in the order of CL → Y.

  FIG. 18 shows the relationship between the ink ejection timing of each color ink and the expansion amount of the medium (paper) in the second embodiment. FIG. 19 shows the state of each color dot actually formed on 3 × 3 pixels (P1 to P9) on the medium.

  Also in this embodiment, first, the controller 60 identifies pixels that eject Y ink and pixels that do not eject. Then, CL ink dots are ejected from the CL ink head to pixels on which Y ink is not ejected on the medium. The medium expands by absorbing the landed CL ink dots (first-stage expansion in FIG. 18). The CL ink dots are ejected to all pixels in the print data where Y ink dots are not to be formed on the medium. For this reason, the ejection amount of the CL ink dots is relatively larger than the ejection amount of the Y ink dots ejected thereafter. For example, in FIG. 19, CL ink dots are formed for 6 pixels (P1, P2, P5, P6, P7, P9) of 9 pixels (P1 to P9). Therefore, the ink absorption amount of the medium in the first stage increases, and the expansion amount of the medium also increases. That is, the first stage medium expansion amount in the second embodiment is larger than the first stage medium expansion amount in the first embodiment.

  After the CL ink dots are ejected, Y ink dots are ejected to predetermined pixels according to the print data. For example, in FIG. 19, Y ink dots are formed on three pixels (P3, P4, P8). As a result, the medium absorbs Y ink dots and expands further (second stage expansion in FIG. 18). Eventually, all the pixels on the medium (P1 to P9 in FIG. 19) are completely filled with Y ink dots and CL ink dots, so that the medium absorbs moisture until it is saturated and completely expands. Thereafter, the M ink and the C ink are ejected onto the completely expanded medium.

  As shown in FIG. 19, in the second embodiment, the Y ink dots, the CL ink dots, the C ink dots, and the M ink dots are formed so as to be shifted on the medium. On the other hand, regarding the M ink dots and the C ink dots that greatly affect the visibility, no deviation occurs in the relative position between them.

  Furthermore, in the present embodiment, the medium expansion amount in the first stage is larger than that in the first embodiment (see FIGS. 15 and 18), and the medium from the expanded state in the first stage to the fully expanded state is reached. The amount of expansion is reduced. That is, when the medium is inflated in the first stage, Y ink dots are ejected, and after the Y ink dots are ejected, M ink dots and C ink dots are ejected without causing the medium to expand greatly. Therefore, it is possible to further reduce the deviation of the relative positions of the Y ink dots formed on the medium and the M ink dots and the C ink dots (see FIGS. 16 and 19). Thereby, the further image degradation prevention effect can be acquired.

=== Summary ===
In the present embodiment, using a printer that performs printing by ejecting ink dots from nozzle rows arranged in a direction perpendicular to the medium conveyance direction, the formation positions are C (cyan) ink dots and M (magenta) ink dots. It is possible to perform printing that is less likely to cause misalignment.

First, Y (yellow) ink and CL (clear) ink as an overcoat ink are ejected from the head portion, and all pixels on the medium (paper) surface are filled with Y ink dots and CL ink dots. Thereafter, printing is performed by ejecting M (magenta) ink and C (cyan) ink.
As a result, the M (magenta) ink dot and the C (cyan) ink dot are formed without deviation, and the deterioration of the printed image caused by the expansion of the medium can be prevented.

Further, when printing, the CL ink is ejected to the medium first, and then the Y ink is ejected to all pixels other than the pixels on which the CL ink dots are formed, thereby removing the medium (paper). After sufficiently expanding, printing is performed by ejecting M ink and C ink.
Thereby, it is possible to reduce the displacement of the formation positions of the Y ink dots and the C and M ink dots compared to the case where the Y ink is ejected prior to the CL ink.

In the present embodiment, the transport direction interval between the head on the downstream side in the transport direction among the Y ink head and the CL ink head and the head on the upstream side in the transport direction among the M ink head and the C ink head is The distance between the Y ink head and the CL ink head is greater than the conveyance direction interval.
As a result, since the M / C ink can be swallowed after the medium has sufficiently expanded, the relative displacement between the formation positions of the M ink dot and the C ink dot is minimized, and the deterioration of the image quality is prevented. The effect to do becomes larger.

In this embodiment, CL (clear) ink or W (white) ink can be used as the overcoat ink.
By using these inks as the base ink, the medium can be sufficiently expanded without deteriorating the image formed by CMY.

=== Other Embodiments ===
Although the printer 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.

<Ink used>
In the above-described embodiment, an example of printing using four colors of inks of CMY and CL has been described. However, the present invention is not limited to this. For example, printing may be performed using inks of colors other than CMYCL, such as light cyan, light magenta, white, and black.
In the case of using inks of other colors, if the combination of colors having a large difference in brightness is applied to the medium as much as possible, the misalignment of dots becomes less conspicuous.

<About the printer driver>
The printer driver processing may be performed on the printer side. In that case, a printer is constituted by the printer and the PC on which the driver is installed.

<About other printing devices>
In the above-described embodiment, a so-called line printer having a head fixed as the printer 1 has been described as an example. However, if the order of ejecting ink can be controlled, a printer of a type that moves the head 41 together with the carriage is used. It may be used.

1 printer, 20 transport unit,
23A upstream transport roller, 23B downstream transport roller,
24 belts, 40 head units,
41 head, 411 case, 412 flow path unit,
412a flow path forming plate, 412b elastic plate, 412c nozzle plate,
412d pressure chamber, 412e nozzle communication port, 412f common ink chamber,
412g Ink supply path, 412h island part, 412i elastic film,
50 detector groups, 60 controllers, 61 interface units,
62 CPU, 63 memory, 64 unit control circuit,
110 computer

Claims (5)

A) a head unit configured by nozzle rows arranged in a direction orthogonal to the medium conveying direction, and performing printing by ejecting cyan ink, magenta ink, and yellow ink onto the medium;
B) A control unit for controlling the head unit,
A pixel on which the yellow ink is ejected on the medium and a pixel on which the yellow ink is not ejected;
The yellow ink is ejected from the head portion to the pixels from which the yellow ink is ejected,
Undercoat ink is ejected from the head portion to pixels where the yellow ink is not ejected,
A control unit that ejects the cyan ink and the magenta ink from the head unit onto the medium after the yellow ink and the undercoat ink are ejected;
A printing apparatus comprising: The printing apparatus according to claim 1,
A printing apparatus that ejects the yellow ink after ejecting the undercoat ink. The printing apparatus according to claim 1, wherein:
More than the distance in the transport direction between the head that ejects the yellow ink and the head that ejects the undercoat ink,
Of the head that ejects the yellow ink and the head that ejects the undercoat ink, a head installed on the downstream side in the transport direction; and
Of the head that ejects the magenta ink and the head that ejects the cyan ink, a head installed on the upstream side in the transport direction;
The printing apparatus is characterized in that the interval in the transport direction is larger. The printing apparatus according to any one of claims 1 to 3,
A printing apparatus, wherein the undercoat ink is a clear ink or a white ink. Identify pixels on the medium where yellow ink is ejected and pixels where yellow ink is not ejected,
Ejecting yellow ink from a head portion configured by nozzle rows arranged in a direction orthogonal to the medium transport direction to the identified pixels from which the yellow ink is ejected;
Jetting undercoat ink from the head portion to pixels where the identified yellow ink is not jetted;
After the yellow ink and the undercoat ink are ejected, ejecting cyan ink and magenta ink from the head portion to the medium;
A printing method comprising:

Images