JP2008246763A - Method for discharging liquid and liquid discharging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for discharging liquid capable of reducing a consumption amount of an anti-curling agent, and a liquid discharging device. <P>SOLUTION: This method for discharging liquid comprises a step of coating a unit region on one face of a medium with a colored liquid, and a step of coating a region on the other face thereof corresponding the unit region with an achromatic liquid which tends to spread in the facial direction more than the colored liquid applied on the one face when the achromatic liquid is applied thereto such that the amount of the achromatic liquid is smaller than that of the colored liquid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid ejection method and a liquid ejection apparatus.

  As one of liquid ejecting apparatuses, an ink jet printer that performs printing by ejecting ink from nozzles onto various media such as paper, cloth, and film is known. When moisture in the ink used in the ink jet printer penetrates into the fibers constituting the printing paper, the printing paper swells. When the ink dries, the printing paper contracts. Therefore, when the difference between the swelling rate and the shrinkage rate on the front and back sides of the printing paper is large, the printing paper is curled.

  Therefore, when ink is applied only to the surface of printing paper as in single-sided printing, a colorless liquid or vapor (anti-curl agent) equivalent to the amount of ink on the surface is applied to the back surface to curl. Methods for preventing it have been proposed.

Hei 4-197637

  However, in the above-described method, although it is not related to printing, the same amount of colorless liquid (anti-curl agent) as the amount of ink used for printing is consumed.

  Therefore, an object of the present invention is to reduce the consumption of the anti-curl agent.

  The invention for achieving the above object includes a step of applying a colored liquid to a unit region on one side of a medium, and on the other side rather than the colored liquid applied on the one side. Applying a colorless liquid that easily spreads in the surface direction of the medium when applied to a region corresponding to the unit region on the other surface, less than the colored liquid. It is.

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

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, a step of applying a colored liquid to a unit region on one surface of the medium, and the medium of the medium when applied on the other surface rather than the colored liquid applied on the one surface. Applying a colorless liquid that is likely to spread in a surface direction to a region corresponding to the unit region on the other surface to be less than the colored liquid.
According to such a liquid discharge method, curling of the medium can be prevented with a less amount of colorless liquid than the colored liquid used for image formation. As a result, the consumption of colorless liquid can be reduced.

In this liquid ejection method, the colorless liquid is more likely to spread in the surface direction on the surface of the medium than the colored liquid.
According to such a liquid ejection method, it is possible to reduce the consumption of the colorless liquid used for preventing curling of the medium.

In this liquid discharge method, the surface tension of the colorless liquid is smaller than the surface tension of the colored liquid.
According to such a liquid ejection method, the colorless liquid is more easily spread in the surface direction than the colored liquid on the surface of the medium.

In this liquid ejection method, the colored liquid and the colorless liquid are more likely to spread in the surface direction on the other surface than on the one surface.
According to such a liquid ejection method, it is possible to reduce the consumption of the colorless liquid used for preventing curling of the medium.

In this liquid discharge method, the area where the colored liquid spreads in the plane direction in the unit area is equal to the area where the colorless liquid spreads in the plane direction in the corresponding area.
According to such a liquid ejection method, it is possible to reliably prevent curling of the medium.

In this liquid ejection method, the number of colorless liquid droplets ejected toward the corresponding region is smaller than the number of colored liquid droplets ejected toward the unit region.
According to such a liquid ejection method, it is possible to apply less colorless liquid than colored liquid to the corresponding region. In addition, since the number of ejections is small, data creation time and liquid ejection time can be shortened.

In this liquid ejection method, the colorless liquid droplet ejected toward the corresponding region is smaller than the colored liquid droplet ejected toward the unit region.
According to such a liquid ejection method, it is possible to apply less colorless liquid than colored liquid to the corresponding region.

In this liquid ejection method, the colored nozzles that eject the colored liquid are arranged at a predetermined interval in a predetermined direction, and the colorless nozzles that eject the colorless liquid are arranged at an interval wider than the predetermined interval in the predetermined direction. To be done.
According to such a liquid discharge method, the number of nozzles of colorless liquid is smaller than the number of nozzles of colored liquid, and the cost is reduced. Further, the colorless liquid can be discharged so that the number of nozzles of the colorless liquid is at least prevented from curling the medium.

In this liquid ejection method, the medium includes a transport mechanism that transports the medium in a direction intersecting the predetermined direction with respect to the colored nozzle and the colorless nozzle.
According to such a liquid ejection method, when the medium is transported without stopping in the transport direction and the liquid is ejected at high speed (eg, a line head printer), the liquid ejection process is performed before the colored liquid is dried. Since the medium is easily curled, the effect of the present invention can be further obtained.

Further, when a colored nozzle that discharges a colored liquid, a colorless nozzle that discharges a colorless liquid, and a colored liquid that is applied to a unit region on one surface of the medium, A colorless liquid that spreads more easily in the surface direction of the medium when applied on the other surface than a colored liquid, in a region corresponding to the unit region on the other surface, than the colored liquid. A liquid ejecting apparatus having a control unit that applies a small amount of liquid is realized.
According to such a liquid ejecting apparatus, curling of the medium can be prevented and consumption of the colorless liquid can be reduced.

=== Configuration of Line Head Printer ===
In this embodiment, a line head printer in an ink jet printer will be described as a liquid ejecting apparatus.

  FIG. 1 is a block diagram showing the overall configuration of the printer 1 according to this embodiment. FIG. 2A is a cross-sectional view of the printer 1. FIG. 2B is a diagram illustrating a state in which the printer 1 transports the paper S (medium). The printer 1 that has received print data from the computer 60, which is an external device, controls each unit (conveyance unit 20, head unit 30, paper reversing unit 40) by the controller 10, and forms an image on the paper S. Further, the detector group 50 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The controller 10 (corresponding to a control unit) is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 60 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing the program of the CPU 12 and a work area. The CPU 12 controls each unit by a unit control circuit 14 according to a program stored in the memory 13.

  The transport unit 20 feeds the paper S to a printable position, and transports the paper S at a predetermined transport speed in the transport direction during printing. The paper S stacked on the paper feed unit 23 is automatically fed onto the transport belt 22 by a paper feed roller (not shown). Then, the ring-shaped transport belt 22 is rotated by the transport rollers 21A and 21B, and the sheet S on the transport belt 22 is transported. The paper S is electrostatically adsorbed or vacuum adsorbed to the transport belt 22 (not shown).

The head unit 30 is for ejecting ink onto the paper S, and has a plurality of heads 31. The lower surface of the head 31 has a plurality of nozzles that are ink ejection portions. Therefore, the sheet S is conveyed so as to face the lower surface (nozzle surface) of the head unit 30 (head 31), whereby an image is formed. Each nozzle is provided with a pressure chamber (not shown) containing ink and a drive element (piezo element PZT) for changing the volume of the pressure chamber to eject ink.
In addition, the printer 1 of the present embodiment has two head units 30. The upstream head unit 30 in the transport direction is referred to as an upstream head unit 30A, and the downstream head unit 30 is referred to as a downstream head unit 30B.

The paper reversing unit 40 reverses the paper S and switches the surface of the paper S facing the nozzle surface.
The detector group 50 includes a rotary encoder, a paper detection sensor, an optical sensor, and the like.

=== Regarding Curling of Sheet S and Countermeasures ===
FIG. 3 is a diagram showing the state of ink ejected from the nozzles onto the paper S. FIG. FIG. 4 is a diagram illustrating curling of the paper S during single-sided printing. As shown in FIG. 3, the ink ejected from the nozzles lands on the paper S, and then spreads wet on the surface of the paper S (surface). Then, the ink penetrates into the fibers constituting the paper S, and the ink is fixed on the paper S (drying) as the water in the ink evaporates.

  For example, when an image is printed only on one side of the paper S, moisture in the ink penetrates into the fibers of the paper S, and only the fibers on the printing surface side swell. As a result, the sheet S is curled so that the printing surface side is raised (curled, FIG. 4). Such curl immediately after printing is referred to as “sheet discharge curl”.

  After a while after printing, the moisture in the ink that has penetrated into the fibers of the paper S evaporates, and the fibers on the printing surface side contract more than before printing. As a result, the sheet S curls in the direction opposite to the sheet discharge curl (FIG. 4). Such curling after ink drying is referred to as “permanent curling”.

  For this reason, when a large amount of ink is applied to one side of the sheet S, the sheet S is discharged to the sheet discharge unit 24 in a curled state, and the sheets S are not correctly stacked in the sheet discharge unit 24. End up. In particular, as compared to a “serial printer” that discharges ink while one head moves, the “line head printer” exemplified in this embodiment transports the paper S without stopping, Since printing is performed at high speed, noticeable paper discharge curl occurs. Therefore, it is necessary to take measures to prevent curling of the paper S.

  The paper discharge curl occurs because the magnitude (swelling rate) of the force to swell (extend) the fibers on the surface of the paper S due to moisture in the ink differs between the front and back sides of the paper S. Similarly, the permanent curl occurs because the magnitude of the force (shrinkage rate) for shrinking the fibers on the surface of the paper S due to moisture in the ink differs between the front and back sides of the paper S. Therefore, curling of the paper S can be prevented by making the swelling rate and shrinkage rate on the front and back surfaces of the paper S equal. Ink (moisture) permeates not only on the surface (surface direction) of the paper S but also in the thickness direction of the paper S. Therefore, not only the fibers on the surface of the paper S but also the fibers inside the paper S. Swelling and shrinkage occur. However, since the deformation of the fiber on the surface of the paper S most affects the curl of the paper S, attention is paid to the swelling rate and the shrinkage rate on the surface of the paper S below.

  In the present embodiment, in order to equalize the swelling rate and the shrinkage rate on the front and back surfaces of the paper S, the area of the ink (moisture) that spreads wet on the surface on the surface side of the paper S, and the paper S The area of the ink (moisture) that spreads on the surface on the back side is made equal. Therefore, for example, in the case of single-sided printing, an anti-curl agent is applied to the surface opposite to the printing surface. Since the anti-curl agent is not related to the printed image, it needs to be a colorless and transparent liquid (corresponding to colorless ink) as much as possible (details will be described later).

  In addition to single-sided printing as well as double-sided printing, the amount of ink applied to the front and back surfaces differs greatly, and curling of the paper S occurs when the area of ink that spreads wet on the front and back surfaces is different. Therefore, an anti-curl agent is applied to the side of the surface with the smaller area where the ink spreads.

FIG. 5A shows a cross-sectional view of the paper S that has been curled. FIG. 5B is a diagram illustrating a surface opposite to the printing surface of the paper S on which the curl prevention measure is taken. When the colored ink (YMCK) and the anti-curl agent for forming an image land on the paper S and spread wet, circular dots as shown in FIG. 5B are formed. Here, on the surface of the colored ink sheet S, the dot diameter (diameter) and spreads the positive yen form a D, wetting area of the color ink becomes [pi] D ^2/4. In this case, in the present embodiment, for preventing curling of the sheet S, anti-curl agents on the surface of the surface opposite to such spreads in an area of [pi] D ^2/4 and the printing surface. For example, if the dot diameter (diameter) formed of a positive yen shaped anti-curl agents dots (area [pi] D ^2/4) of the opposite surface is D, the ink spreads on respective surfaces of the front and back of the sheet S (colored The areas of the ink and the anti-curl agent) become equal, and the curling of the paper S is prevented.

  Usually, the ink droplets ejected toward the paper S wet and spread on the surface of the paper S in a circular shape (dot shape). Therefore, as shown by arrows in FIG. 5B, the force (swelling force) for swelling the fibers of the paper S and the force (shrinking force) for shrinking are applied to the dots formed on the paper S. Therefore, it occurs in any direction on the surface of the paper S. However, the paper has a fiber direction (paper eyes). For example, if the paper S is composed of a fiber flow along the paper width direction, the paper S is wrinkled along the transport direction intersecting the paper width direction. It becomes easy to approach. In such a case, the swelling force and contraction force in the conveying direction with respect to the fibers of the paper S greatly affect the curl of the paper S.

=== Regarding the nozzle surface ===
In this embodiment, not only a colored ink nozzle (YMCK) for image formation but also an anti-curl agent nozzle for discharging an anti-curl agent. Hereinafter, the arrangement of nozzles formed on the lower surface of the head unit will be described.

  FIG. 6 is a diagram illustrating the arrangement of the heads 31 on the lower surfaces of the upstream head unit 30A and the downstream head unit 30B. Each head unit 30 has a plurality (n) of heads 31. The plurality of heads 31 are arranged in a staggered manner in the paper width direction. The head 31 belonging to the upstream head unit 30A is referred to as an upstream head 31A, and the head 31 belonging to the downstream head unit is referred to as a downstream head 31B. Then, the head 31 on the left side in the paper width direction is given a younger number in parentheses.

  FIG. 7A is a diagram showing a nozzle arrangement on the lower surface of the upstream head 31A. A yellow ink nozzle row Y, a magenta ink nozzle row M, a cyan ink nozzle row C, and a black ink nozzle row K are formed on the lower surface of the upstream head 31A, and each nozzle row includes 180 nozzles. ing. Of the 180 nozzles, the left nozzle is assigned a smaller number (# i = 1 to 180). Then, in the head 31A arranged in a staggered manner, the nozzle # 1 and the left head of the right head 31A (3) of the two heads (for example, 31A (2) and 31A (3)) adjacent in the paper width direction. The interval between the nozzles # 180 of 31A (2) is 180 dpi. That is, the yellow, magenta, black, and cyan nozzles are aligned at a constant interval of 180 dpi in the paper width direction.

  FIG. 7B is a diagram illustrating an arrangement of nozzles on the lower surface of the downstream head 31B. A yellow ink nozzle row Y, a magenta ink nozzle row M, a cyan ink nozzle row C, a black ink nozzle row K, and an anti-curl agent nozzle row P are formed on the lower surface of the downstream head 31B. That is, the downstream head 31B has more nozzle rows than the upstream head 31A by the amount of the anti-curl agent nozzle row. Each nozzle row of the downstream head unit 30B also includes 180 nozzles, and the nozzles are aligned at a constant interval of 180 dpi in the paper width direction.

  Further, the ink nozzle (YMCK) of the upstream head 31A is shifted to the right in the paper width direction by 360 dpi, which is a half interval of 180 dpi, with respect to the ink nozzle (YMCK) of the downstream head 31B. For example, the nozzle # 180 of the upstream head 31A (2) is disposed on the right side by 360 dpi in the paper width direction from the nozzle # 180 of the downstream head 31B (2).

  That is, when the nozzles of the upstream head unit 30A and the nozzles of the downstream head unit 30B are combined, the nozzles of yellow Y, magenta M, cyan C, and black K are arranged at an interval of 360 dpi (corresponding to a predetermined interval) in the paper width direction. Will be. That is, the paper S is first conveyed so as to face the upstream head unit 30A, an image is printed at a resolution of 180 dpi in the paper width direction, and then the paper S is conveyed so as to face the downstream head unit 30B. The image is printed at a resolution of 180 dpi in the paper width direction with a shift of 360 dpi from the image printed by the upstream head unit 30A. In other words, each nozzle row of yellow Y, magenta M, cyan C, and black K can be printed at a resolution of 360 dpi in the paper width direction.

  On the other hand, the anti-curl agent nozzle row P is formed only on the downstream side head 31B, and the anti-curl agent nozzles are arranged at intervals of 180 dpi in the paper width direction. Therefore, the maximum resolution in the paper width direction that can be printed by the anti-curl agent nozzle row P is 180 dpi.

=== About the printing procedure ===
In this embodiment, in order to prevent curling of the paper S, in the case of single-sided printing, an anti-curling agent is applied to the surface opposite to the surface on which an image is formed. Also, in the case of double-sided printing, when the areas of ink that spreads on the surface of the paper S are different between the front and back sides, an anti-curl agent is applied to the side of the smaller surface where the ink spreads. Hereinafter, the printing procedure will be described by taking single-sided printing as an example.

  When the controller 10 in the printer 1 receives print data or the like, first, the controller 10 sends the paper S to be printed onto the transport belt 22. Then, the controller 10 rotates the transport rollers 21A and 21B to position the fed paper S at the print start position. At this time, the surface (printing surface) of the paper S faces at least some of the nozzles.

  Next, the sheet S is conveyed on the conveyor belt 22 without stopping at a constant speed, and passes under the upstream head unit 30A and the downstream head unit 30B. While the paper S passes under the two head units 30, ink is intermittently ejected from the colored ink nozzles (YMCK) based on the print data. As a result, an image designated by the user is printed on the surface of the paper S with YMCK ink. At this time, the sheet S passes under the anti-curl agent nozzle, but the anti-curl agent is not discharged from the anti-curl agent nozzle.

  When printing on the front surface of the sheet S is completed, the sheet S is conveyed upward by the switching guide 41A (FIG. 2A). At this time, the sheet S is fed to the reversing unit 42 while being pressed by the conveying roller 21 and the like so as not to curl (discharge curl). For example, in the case of printing with a border, the border portion (margin portion) along the transport direction of the paper S is always transported while being pressed by a transport roller or the like. Then, the sheet S is sent to the reversing unit 42 by the upper switching guide 41B. At this time, the paper S is detected by a paper detection sensor (not shown). Note that the switching guide 41 is variable in the direction of the arrow in the figure, and changes the direction in which the paper S is guided according to the situation. The detected sheet S is sent to the reversing unit 42 by a predetermined amount by the reversing roller 43, and then the reversing roller 43 rotates in the reverse direction, and the sheet S returns to the fed side again. The returned paper S is guided to the switching guide 41B, passes over the head unit 30, and is conveyed to the paper feeding unit 23 side.

  Then, the paper S is fed again so that the back surface (opposite surface) of the paper S faces the anti-curl agent nozzle, and the anti-curl agent is discharged from the anti-curl agent nozzle. At this time, the sheet S passes under the colored ink nozzles, but no ink is ejected from the colored ink nozzles.

  Thus, when printing on both sides of the paper S is completed, the paper S is guided to the switching guide 41A and discharged to the paper discharge unit 24. At this time, in this embodiment, since the anti-curl agent is applied so that the swelling rate and the shrinkage rate of the front and back sides of the paper S are equal, the paper S is not curled and is correctly stacked on the paper discharge unit 24.

=== About the anti-curl agent ===
First, after describing the “anti-curl agent of the comparative example” different from the present embodiment, the “anti-curl agent of the present embodiment” will be described.

<Regarding the anti-curl agent of the comparative example>
FIG. 8A is a diagram illustrating a state where the colored ink and the anti-curl agent of the comparative example are discharged onto the paper S. FIG. FIG. 8B is a diagram showing an application example of the anti-curl agent of the comparative example. As shown in FIG. 8A, when “Ypl (picoliter) ink” is ejected from the colored ink nozzle (YMCK) toward the paper S, “dots having a diameter of X (round circles) on the paper S Is formed. That is, "colored ink Ypl" is on the surface of the sheet S, it spreads in the range of "area πX ^2/4".

When the “Ypl comparative anti-curl agent” is ejected from the nozzle for anti-curl toward the paper S, “dots having a diameter of X (perfect circle) on the paper S, like the colored ink,” Is formed. In other words, "anti-curl agents of the comparative example Ypl" is on the surface of the sheet S, it spreads in the range of "area πX ^2/4".

In other words, the area of the colored ink and anti-curl agents of the same amount (YPL) wets and spreads over the surface of each sheet S (πX ^2/4) is equal, and the colored ink and the anti-curl agents, wetting with respect to the surface direction of the sheet S It can be said that the spread is equal. Therefore, for example, if Ypl colored ink is ejected to the printing surface side of the paper S, in order to prevent curling of the paper S, the same amount (Ypl) of anti-curling agent as the colored ink is applied to the side opposite to the printing surface. Must be discharged onto the surface.

Here, a case where one-side printing is performed with the black ink nozzle row K (monochrome printing) at a resolution of “360 dpi × 360 dpi” in the “conveyance direction × paper width direction” will be described as an example. That is, the size of the black ink pixel is “conveyance direction × paper width direction = 360 dpi × 360 dpi”. Further, when Ypl ink (anti-curl agent) is ejected from the black ink nozzle and the anti-curl agent nozzle each time, one dot having a dot diameter X of 360 dpi (area 4πX ² ) is formed. To do.

Then, as shown in FIG. 8B, 16 black ink dots (black circles) are printed in the unit area (6 × 6 pixels) on the printing surface side of the paper S. In this case, toward the black ink nozzle unit region "black ink 16Ypl" is discharged, ^{"(16 = πX 2/4 ×) 4πX} 2 " black area ink wets and spreads on the surface of the unit area It becomes.

Therefore, in order to prevent the curling of the paper S, the anti-curl agent is discharged to the opposite surface so that the wetting and spreading area of the anti-curl agent on the surface opposite to the printing surface becomes “4πX ² ”. There is a need to. In addition to equalizing the area of the ink (anti-curl agent) spreading on the surface of the paper S on the front and back sides of the paper S, the positions of the inks (anti-curl agent) applied to the front and back sides of the paper S overlap each other. The more the position is, the more the paper S can be prevented from curling. Therefore, in this comparative example, by forming 16 anti-curl dots (dotted circles) at the position (pixel) on the opposite side corresponding to the position (pixel) of the dot formed on the printing surface side, The areas (4πX ² ) where the ink and the anti-curl agent spread on the front and back surfaces of the paper S are made equal to prevent the paper S from curling.

  By the way, in order to form 16 dots of the anti-curl agent on the opposite surface of the paper S, it is necessary to discharge “16 Ypl anti-curl agent” from the nozzle for the anti-curl agent. That is, in order to prevent curling of the paper S, the black ink amount (16 Ypl) applied to the unit area on the printing surface side of the paper S and the anti-curling agent amount (16 Ypl) applied to the unit area on the opposite surface side of the paper S ( 16Ypl) are equal.

  That is, in this comparative example, the ease of wetting and spreading on the surface of the paper S is the same for the colored ink and the anti-curl agent, so in the case of single-sided printing, to prevent the paper S from curling, The same amount of anti-curl agent as the amount of colored ink used for printing must be applied to the surface. Since the anti-curl agent is an ink (colorless) that has nothing to do with image formation, the consumption of the anti-curl agent should be minimized as much as possible. Therefore, an object of the present embodiment is to reduce the consumption of the anti-curl agent.

<About the anti-curl agent of this embodiment>
FIG. 9 is a diagram illustrating a state where the colored ink and the anti-curl agent of the present embodiment are ejected onto the paper S. As described above, when “Ypl ink” is ejected from the colored ink nozzle (YMCK) toward the paper S, “dots with a diameter of X (perfect circle)” are formed on the paper S, and the paper wetting area of the colored ink on the surface of S is "πX ^2/4".

In contrast, when the anti-curl agent of this embodiment is ejected from the nozzle for anti-curl agent toward the paper S, “dots having a diameter of 2 × ( A perfect circle) ”, and the wetting and spreading area of the anti-curl agent on the surface of the paper S is“ πX ² ”.

That is, the area of anti-curl agents of Ypl wets and spreads on the surface of the sheet S (πX ²⁾ is four times the area (πX ^2/4) where colored ink Ypl wets and spreads on the surface of the sheet S. In other words, the area that spreads on the surface of the paper S by the same amount (Ypl) of colored ink and the anti-curl agent is larger for the anti-curl agent than for the colored ink, and the anti-curl agent of this embodiment is more than the colored ink. It can be said that the sheet S tends to be wet and spread easily.

FIG. 10A is a diagram illustrating an application example of the anti-curl agent of the present embodiment. FIG. 10B is an image diagram of the application method of the anti-curl agent of the present embodiment. Similarly to the previous case, it is assumed that the resolution in the “conveyance direction × paper width direction” is “360 dpi × 360 dpi” and single-sided printing is performed by the black ink nozzle row K (black and white printing). ink is ejected for, and dot dot diameter X is 360 dpi (area πX ^2/4) is one form. And the anti-curl agent of this embodiment is apply | coated to the surface on the opposite side to a printing surface. In FIG. 10A, the black ink dots (white circles) and the anti-curl dots (dotted lines) are shown on the same surface for the sake of explanation.

As shown in FIG. 10A, 16 black ink dots (white circles) are formed in the unit area (6 × 6 pixels) on the printing surface side of the paper S. In this case, the black ink nozzle "black ink 16Ypl" is ejected, the area where the black ink wets and spreads on the surface of the unit area is "4πX 2 ⁽¹⁶ pieces ^{= πX 2/4} ×)". In order to prevent curling of the paper S, an anti-curling agent is applied to the opposite surface of the paper S so that the area of the anti-curling agent spreading on the surface opposite to the printing surface becomes “4πX ² ”. It is necessary to discharge.

The anti-curl agent of this embodiment has a dot diameter 2X (= 720 dpi) that is twice the dot diameter X of black ink when Ypl anti-curl agent is ejected from the anti-curl agent nozzle at a time. One dot of “πX ² ” is formed. Therefore, curling of the paper S can be prevented by forming four anti-curl dots on the opposite side of the surface corresponding to the position where the black ink dots are formed. In order to form four dots, “4Ypl anti-curling agent” may be ejected from the anti-curling agent nozzle.

  Summarizing the above, in this embodiment, as shown in FIG. 10B, if Ypl anti-curling agent is applied to 4Ypl colored ink, the ink (anti-curling agent) on the front and back surfaces of the paper S is applied. ) Wet spreading area can be made equal. That is, the anti-curl agent of the present embodiment is more likely to be wet and spread in the surface direction of the paper S than the black ink (colored ink), and therefore the amount of black ink applied in the unit area on the printing surface side of the paper S is larger. The amount of anti-curling agent applied in the unit region on the surface opposite to the printing surface can be reduced. In the comparative example, the same amount of 16 Ypl anti-curling agent as that of the colored ink is applied to the opposite surface side, whereas in this embodiment, 16 Ypl of black ink applied to the printing surface side is applied. The anti-curling agent of 4Ypl, which is 1/4, may be applied on the opposite surface side, and this embodiment can reduce the consumption of the anti-curling agent compared to the comparative example.

  Further, as shown in FIG. 10A, in order to prevent curling of the paper S, anti-curl dots are formed at a rate of one for every four black ink dots. That is, one anti-curl dot is formed in an area of “180 dpi × 180 dpi (conveying direction × paper width direction)” of four black ink pixels (360 dpi × 360 dpi). That is, the anti-curl agent is ejected at a resolution (180 dpi × 180 dpi) lower than that of the colored ink. However, since the anti-curl agent is not related to the image quality of printing, there is no problem even if the resolution is lowered.

  Since the anti-curl agent dots are formed at an interval of 180 dpi in the paper width direction, the nozzle interval of the anti-curl agent nozzle row can be set to 180 dpi. Therefore, in the present embodiment, as described above (FIG. 7), the interval (180 dpi) in the paper width direction of the nozzle row P for anti-curl agent is set to twice the interval (360 dpi) in the paper width direction of the nozzle row for colored ink YMCK. . On the other hand, in the comparative example (FIG. 8B), the anti-curl dots are formed at intervals of 360 dpi in the paper width direction, similar to the colored ink dots, and the nozzle interval of the anti-curl agent nozzle row P ′ in the comparative example is 360 dpi. . That is, this embodiment can reduce the number of anti-curl agent nozzle rows as compared with the comparative example, thereby reducing the cost.

  As shown in FIGS. 7 and 10A, the anti-curl agent nozzle row P of this embodiment is displaced by 720 dpi in the paper width direction with respect to the colored ink nozzle row (YMCK). By doing so, an anti-curl agent dot can be formed at the center of the four pixels, which are the two black ink pixels aligned in the paper width direction and the two black ink pixels aligned in the transport direction. As a result, the anti-curl dots are formed without being biased toward any of the black ink pixels, and the positions where the colored ink and the anti-curl agent are applied are substantially the same on the front and back of the paper S. Further, curling of the paper S can be further prevented.

  Furthermore, while the length of the black ink pixels in the transport direction is 360 dpi, the anti-curl dots are formed at intervals of 180 dpi in the transport direction. Therefore, when only the anti-curl agent is applied to one side of the paper S, the conveyance time (printing time) can be shortened. This is because if the discharge interval T at which the ink is discharged from the black ink nozzle and the anti-curl agent nozzle is constant, the paper S is transported only 360 dpi during the discharge interval T when the black ink is applied. On the other hand, when the anti-curl agent is applied, the sheet S is conveyed by 180 dpi during the discharge interval T. That is, the transport speed of the paper S when the anti-curl agent is applied is twice the transport speed of the paper S when an image is formed with colored ink.

  Further, one anti-curl dot is formed for four black ink dots. Since one dot is formed by applying Ypl ink (anti-curl agent) at a time from the black ink nozzle and the anti-curl agent nozzle each time, the number of black ink ejections (colored liquid droplets) The number of discharges of the anti-curl agent (corresponding to the number of colorless liquid droplets) can be reduced. That is, the number of data for ejecting the anti-curl agent can be made smaller than the number of data for ejecting the black ink. As a result, the data creation time is shortened and the printing time is also shortened.

In summary, in this embodiment, a colored liquid (YMCK) is applied to a unit area on one side (printing surface) of a medium (paper S), and the colored liquid applied on the one side is applied. A colorless liquid (anti-curl agent) that spreads more easily in the surface direction of the medium when applied on the other surface (opposite surface) than the liquid is applied to a region corresponding to the unit region on the other surface. The curling of the paper S is prevented by applying less than the colored liquid.
By doing so, curling of the paper S can be prevented by an amount of the anti-curling agent that is smaller than the amount of the colored ink applied, so that the consumption of the anti-curling agent can be suppressed.

  FIG. 11A is a diagram illustrating an application example of an anti-curl agent when four colors of ink (YMCK) are overprinted on one colored ink pixel. FIG. 11B is an image diagram of a method of applying an anti-curl agent when colored ink is overprinted. So far, the case where one dot is formed in one pixel from the black ink nozzle has been described. Next, the case where four dots are overprinted in one pixel will be described.

  For example, it is assumed that four colors of ink (YMCK) are overprinted on one color ink pixel (360 dpi × 360 dpi). At this time, if Ypl ink is ejected from each nozzle of YMCK, “4 Ypl ink” is ejected to one colored ink pixel.

Incidentally, in FIGS. 10A and 10B described above, "ink 4Ypl" is ejected on the printing surface of the sheet S, 4 pieces area of ink spreads on the print surface of the sheet S is ^{"πX 2 (= πX 2/4} × ) ”. However, this is because 4Ypl is divided into four times and ink is ejected to different pixels, so that the ink wetting spread area is also increased in proportion to the amount of ink ejected. Therefore, when 4 Ypl of ink is ejected to the same pixel and overprinted, the wetting and spreading area of the ink does not increase in proportion to the amount of ejected ink, and when Ypl of ink is ejected than the wet-spreading area "πX ^2/4" of, is the degree to which slightly larger.

For example, as shown in FIG. 11A, when the dot diameter formed by overprinting 4Ypl ink is 1.2 times the dot diameter formed by Ypl ink, wetting of 4Ypl ink by overstrike spread area is "9πX ^2/25". Even if four overprinted dots are formed in the unit area (2 pixels × 2 pixels) and “16 Ypl of ink” is ejected on the printing surface, the wet spread area on the printing surface is “36πX ^{2/25 (= 4 × (} 9πX 2/25)) is "not much different" wetting area with the black ink "in 4Ypl" PaiX ² "in FIG. 10B described above (1.44 times). Therefore, in order to prevent curling of the paper S, dots (36 / 25πX ² ) slightly larger than the area “πX ² ” of dots formed when the “Ypl anti-curling agent” is discharged are formed. Thus, an anti-curl agent may be applied. That is, the curling of the paper S can be prevented by applying an amount of anti-curl agent smaller than the amount of colored ink (16 Ypl) applied in the unit area (2 pixels × 2 pixels). In FIG. 11A, one dot is formed so that the area “36 / 25πX ² ” where the colored ink spreads on the printing surface and the dot area of the anti-curl agent (the area where the curl spreads) are equal. However, the present invention is not limited to this, and a plurality of dots may be formed or an anti-curl agent may be struck repeatedly so as to be equal to the area where the colored ink is spread.

=== Composition of colored ink and anti-curl agent ===
FIG. 12A is a diagram illustrating an example of black ink and an anti-curl agent of the present embodiment. FIG. 12B is a diagram illustrating a relationship between surface tension and liquid wetting. Here, the “surface tension” is a force for reducing the surface area of the liquid. Therefore, as shown in FIG. 12B, when the surface tension of the ink (anti-curl agent) is increased, the contact angle θ between the paper S and the ink increases (θ> 90 °), and the ink (anti-curl agent) is applied to the paper S. On the other hand, it becomes difficult to spread. On the other hand, when the surface tension of the ink (anti-curl agent) is reduced, the contact angle between the paper S and the ink is reduced (θ <90 °), and the ink (anti-curl agent) is likely to be wet and spread with respect to the paper S.

  In the present embodiment, the curling agent consumption is reduced by making the curling agent spread more easily on the paper S than the colored ink. For this reason, if the surface tension of the anti-curl agent is made smaller than the surface tension of the colored ink, the anti-curl agent is more likely to spread on the surface of the paper S than the colored ink. The surface tension of the ink is usually preferably 20 to 55 mN / m. If the surface tension is excessively larger than this range, the drying property of the ink is poor, and color bleeding (bleeding between inks of different colors) occurs. On the other hand, if the surface tension is too small, the nozzle surface of the head 31 tends to get wet and ink may not be stably ejected from the nozzle.

  As shown in FIG. 12A, the black ink (colored ink) of this embodiment is mainly composed of a color material (coloring), a solvent (dissolution of the color material), a wetting agent (preventing drying of the nozzle surface), a surfactant ( = Penetrant, acceleration of drying of ink on medium), and surface tension is about 30 to 35 mN / m. In order to make the surface tension of the anti-curl agent smaller than that of the black ink (for example, −5 mN / m), the anti-curl agent of this embodiment contains more surfactant (Olfin E1010) than the black ink. ing. Further, since the anti-curl agent is preferably colorless and transparent, it is assumed that it does not contain a coloring material.

  Note that the black ink and the anti-curl agent illustrated in FIG. 12A are examples, and the present invention is not limited thereto. For example, in addition to or instead of containing more surfactant than colored ink, the anti-curl agent contains more organic solvent having a lower surface tension than the organic solvent used in colored ink. Also good. Or it is good also as what added the surfactant for making it low surface tension into the pure water for curl prevention. In this case, it is possible to reduce the cost of the anti-curl agent. However, in order to enable the anti-curl agent to be ejected by the same ejection device and ejection control as the colored ink, the anti-curl agent component is as close as possible to the colored ink component except that it does not contain a color material. It is preferable. That is, since the anti-curl agent of this embodiment is colorless and transparent and needs only a surface tension smaller than that of the colored ink, it is not always necessary to match the physical properties of the colored ink (YMCK) and the anti-curl agent. The selection range is expanded.

  Thus, as shown in FIG. 9, the anti-curl agent is more easily spread on the surface of the paper S than the colored ink so that the colored ink discharged toward the unit area on the printing surface side of the paper S can be obtained. In order to prevent curling of the paper S, the amount of anti-curl agent discharged toward the opposite side corresponding to the discharge position of the colored ink can be made smaller than the discharge amount. Consumption can be suppressed.

=== Second Embodiment ===
In the above-described embodiment, the surface tension of the anti-curl agent is made smaller than the surface tension of the colored ink so that the anti-curl agent spreads more easily on the surface of the medium than the colored ink, but the present invention is not limited to this. For example, in this second embodiment, the anti-curl agent is not changed by changing the properties of the surface of the medium to which the colored ink is applied and the surface of the medium to which the anti-curl agent is applied instead of the ink (anti-curl agent). It makes it easier to wet and spread on the surface of the medium than colored ink.

  By the way, normally, the smaller the dot diameter formed with colored ink, the higher the quality of the image. For this reason, it is possible to obtain a high-quality image when the ink landed on the medium does not spread as much as possible (does not spread). Thus, by using coated paper (eg, coated paper or art paper) obtained by coating plain paper with a coating material or the like, a high-quality image with little ink bleeding can be obtained.

FIG. 13 is an image diagram showing how the coated paper 70 is prevented from curling. The materials constituting the colored ink and the anti-curl agent in the figure are the same except for the color material, and when the colored ink and the anti-curl agent are applied to the plain paper, the material spreads on the surface of the plain paper. The area is assumed to be the same for the colored ink and the anti-curl agent. However, since the coated paper is processed so that a dot diameter with less bleeding is formed on the printing surface (coating layer side), “colored ink of Ypl” is ejected toward the coating layer side of the coated paper 70. color ink spreads wetted area (πX ^2/4) when the the area curl inhibitor spreads when the discharged toward the plain paper layer side of the coated paper 70 "anti-curl agents of Ypl" (PaiX ² ).

  That is, the anti-curl agent ejected toward the plain paper layer (corresponding to the other side) is different from the colored ink ejected toward the coat layer (corresponding to the one surface). It spreads much wetter than the spread area. Therefore, in order to prevent curling of the paper S, the application amount of the anti-curling agent discharged toward the region on the opposite side (plain paper layer) side corresponding to the region of the printing surface (coat layer) on which the colored ink is discharged ( Ypl) can be made smaller than the amount of colored ink applied (4 Ypl), and the consumption of the anti-curl agent can be reduced.

=== Other Embodiments ===
Each of the above embodiments has been described mainly for a printing system having an ink jet printer, but includes disclosure of a method for preventing curling of a medium and the like. The above-described embodiments are for facilitating understanding of the present invention, and are 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.

<Amount applied from nozzle>
In the above-described embodiment, the same amount of ink (Ypl) ejected from the colored ink nozzle and the anti-curl agent nozzle at the same time is applied to the surface opposite to the amount of colored ink applied to the printing surface. In order to reduce the amount of anti-curl agent (colorless ink), the number of discharges of the anti-curl agent is made smaller than the number of discharges of the colored ink, but this is not restrictive. For example, in order to apply less anti-curl agent (colorless ink) to the opposite surface than colored ink, the amount of anti-curl agent discharged at once from the nozzle for anti-curl agent (corresponding to colorless liquid droplets), It may be less than the amount of ink ejected from the colored ink nozzle at a time (corresponding to a colored liquid droplet).

<Application position of anti-curl agent>
In the previous embodiment, the anti-curl agent is applied to the area on the opposite side corresponding to the area where the colored ink is spread. In FIG. 10A, an anti-curl agent is applied so that each pixel overlaps with each other, and the anti-curl agent pixel corresponding to the four black ink pixels. However, the present invention is not limited to this. For example, in the unit region (6 × 6 pixels) in FIG. 10A, the anti-curl agent is not provided at the left end in the unit region, even if it is not the four central anti-curl pixels. Dots may be formed. Curling of the paper S can be prevented even if the black ink and the anti-curl dot do not overlap if the area where the colored ink spreads wet in the setting area (unit area) and the area where the colored ink spreads in the corresponding setting area are equal. be able to.

<About paper discharge curl and permanent curl>
In the above-described embodiment, the anti-curl agent is applied to prevent the paper discharge curl and the permanent curl that are generated due to the difference between the swelling rate and the shrinkage rate of the front and back fibers of the paper. However, the present invention is not limited to this. For example, even on the same side of the paper, if a location where a large amount of ink is applied and a location where no ink is applied are adjacent, the location where the paper swells / shrinks and the location where the paper does not change are adjacent, and the paper There are times when you hit (swell).
In this case, the waviness of the paper can be alleviated by applying an anti-curl agent around the area where a large amount of ink is applied. Also in this case, the anti-curl agent tends to wet and spread on the surface of the paper more than the colored ink, so that the undulation of the paper S can be alleviated by applying a smaller amount of the anti-curl agent to the periphery than the colored ink. it can.

<About liquid ejection device>
When applying colored liquid to the unit area on the printing surface of the medium, the control unit applies less colorless liquid to the area corresponding to the unit area on the surface opposite to the printing surface than the colored liquid. When the controller 10 of the printer 1 plays the role, the printer 1 alone corresponds to the liquid discharge device, and when the computer 60 plays the role of the control unit, the system connected to the printer 1 and the computer 60 is the liquid discharge device. It corresponds to a device.
In the above-described embodiment, the ink jet printer is exemplified as the liquid ejecting apparatus that performs the liquid ejecting method, but the present invention is not limited thereto. If it is a liquid ejection device, it can be applied to various industrial devices, not a printer (printing device). For example, a textile printing device for patterning a fabric, a display manufacturing device such as a color filter manufacturing device or an organic EL display, a DNA chip manufacturing device for manufacturing a DNA chip by applying a solution in which DNA is dissolved in a chip, a circuit board manufacturing The present invention can be applied even to an apparatus or the like.
In the printer of the above-described embodiment, the liquid is ejected by applying a voltage to the driving element (piezo element) to expand and contract the ink chamber, but the invention is not limited thereto. For example, a printer that generates bubbles in the nozzles using a heating element and discharges liquid by the bubbles may be used.

<About serial printers>
In the above-described embodiment, a line head printer is taken as an example, but the present invention is not limited to this. For example, a serial printer that forms an image by alternately repeating a transport operation that moves paper in the transport direction and an operation (pass) that forms dots while one head moves in a movement direction that intersects the transport direction But you can.

1 is an overall configuration block diagram of a printer according to an embodiment. FIG. 2A is a cross-sectional view of the printer, and FIG. 2B is a diagram illustrating how the printer transports printing paper. It is a figure which shows the mode of the ink discharged with respect to the paper from a nozzle. It is a figure which shows the curl of the paper in the case of single-sided printing. FIG. 5A is a cross-sectional view of a sheet on which a curl prevention measure is taken, and FIG. 5B is a view showing a surface opposite to the printing surface of the sheet on which a curl prevention measure is taken. It is a figure which shows the arrangement | sequence of the head in the lower surface of an upstream head unit and a downstream head unit. FIG. 7A is a diagram showing a nozzle arrangement on the lower surface of the upstream head, and FIG. 7B is a diagram showing an arrangement of nozzles on the lower surface of the downstream head. FIG. 8A is a diagram illustrating a state in which the colored ink and the anti-curl agent of the comparative example are discharged onto the paper, and FIG. 8B is a diagram illustrating an application example of the anti-curl agent of the comparative example. It is a figure which shows a mode that colored ink and the curl prevention agent of this embodiment are discharged on a paper. FIG. 10A is a diagram illustrating an application example of the anti-curl agent of the present embodiment, and FIG. 10B is an image diagram of a method of applying the anti-curl agent of the present embodiment. FIG. 11A is a diagram showing an application example of an anti-curl agent when four color inks are overprinted on one colored ink pixel, and FIG. 11B is an application of the anti-curl agent when colored inks are overprinted. It is an image figure of a method. FIG. 12A is a diagram showing an example of black ink and an anti-curl agent of this embodiment, and FIG. 12B is a diagram showing the relationship between surface tension and liquid wetting. It is an image figure which shows the mode of the curl prevention of a coated paper.

Explanation of symbols

1 printer,
10 controller, 11 interface unit, 12 CPU, 13 memory,
14 unit control circuit,
20 transport unit, 21A transport roller, 21B transport roller, 22 transport belt,
23 paper feed unit, 24 paper discharge unit,
30 head units, 31 heads,
40 paper reversing unit, 41A switching guide, 41B switching guide, 42 reversing section,
43 reverse roller 50 detector group,
60 computers,
70 coated paper

Claims (10)

Applying a colored liquid to a unit area on one side of the medium;
Corresponding to the unit area on the other surface is a colorless liquid that spreads more easily in the surface direction of the medium when applied on the other surface than the colored liquid applied on the one surface. Applying less than the colored liquid to the area to be
A liquid ejection method comprising: A liquid discharging method according to claim 1,
The colorless liquid is easier to spread in the surface direction on the surface of the medium than the colored liquid.
Liquid ejection method. The liquid discharge method according to claim 2,
The surface tension of the colorless liquid is smaller than the surface tension of the colored liquid.
Liquid ejection method. A liquid ejection method according to any one of claims 1 to 3,
The colored liquid and the colorless liquid are more likely to spread in the surface direction on the other surface than on the one surface.
Liquid ejection method. A liquid discharge method according to any one of claims 1 to 4,
The area in which the colored liquid spreads in the plane direction in the unit area is equal to the area in which the colorless liquid spreads in the plane direction in the corresponding area.
Liquid ejection method. A liquid discharge method according to any one of claims 1 to 5,
The number of colorless liquid droplets discharged toward the corresponding region is smaller than the number of colored liquid droplets discharged toward the unit region.
Liquid ejection method. A liquid discharge method according to any one of claims 1 to 5,
Colorless liquid droplets ejected into the corresponding area,
Smaller than colored liquid droplets discharged toward the unit area,
Liquid ejection method. A liquid discharge method according to any one of claims 1 to 7,
The colored nozzles that discharge the colored liquid are arranged at predetermined intervals in a predetermined direction,
The colorless nozzle that discharges the colorless liquid is disposed in the predetermined direction at an interval wider than the predetermined interval.
Liquid ejection method. The liquid discharge method according to claim 8,
A transport mechanism for transporting the medium in a direction intersecting the predetermined direction with respect to the colored nozzle and the colorless nozzle;
Liquid ejection method. A colored nozzle that discharges a colored liquid;
A colorless nozzle that discharges colorless liquid;
When a colored liquid is applied to a unit area on one side of the medium, the colored liquid applied on the one side is more in the surface direction of the medium when applied on the other side than the colored liquid applied on the one side. A control unit that applies a colorless liquid that easily spreads to an area corresponding to the unit area on the other surface, less than the colored liquid;
Having
Liquid ejection device.

Images