JP2024085667A - Inkjet printer - Google Patents

Abstract

To make the quality of printing compatible with productivity in an inkjet printer that ejects a special ink and a color ink.SOLUTION: A control unit 20 of an inkjet printer 1 controls ejection of a special ink according to a first density characteristic line Q1 and controls ejection of a color ink according to a second density characteristic line Q2. In the first density characteristic line Q1, a special ink ejection allowing range in which the ejection of the special ink is allowed is set in a part on the upstream side or the downstream side of the first nozzle row Nzl; and the second density characteristic line Q2 partially overlaps the special ink ejection allowing range in a first direction. In the overlapping range S1, there is a range R2 in which the nozzle usage rate of the first nozzle row is higher than the nozzle usage rate of a second nozzle row Nzk (Nzc to Nzy).SELECTED DRAWING: Figure 6

Description

The present invention relates to inkjet printers, etc.

Patent document 1 shows an inkjet printer that simultaneously ejects clear ink and color ink to perform multi-pass printing (see, for example, [0054], Figures 2 and 5 of the specification).

Patent Document 2 describes a method of performing multi-pass (serial method) printing by simultaneously ejecting ink and a treatment liquid containing water, and applying a density characteristic line (in other words, a "density curve"), which is a characteristic line indicating the nozzle usage rate, to each of the nozzles ejecting the ink and the nozzles ejecting the treatment liquid, and individually controlling the ejection of the ink and the treatment liquid from each nozzle (for example, [0171] of the specification, Figures 4 to 9, etc.).
In the following description, the characteristic line indicating the nozzle usage rate will be referred to as the "density characteristic line."

Patent document 3 describes dividing the nozzles in a nozzle row that ejects clear ink into upstream nozzles and downstream nozzles, and applying different density characteristic lines to each of the upstream and downstream nozzles (for example, [0035] of the specification, Figures 3, 6, 7, etc.).

JP 2022-10609 A JP 2021-6390 A JP 2022-121833 A

The present inventors have investigated controlling the ejection of each of the special ink and color inks using density characteristic curves that are set independently for each ink, and as a result have come to the following findings.
As shown in Patent Document 2, if overlapping over the entire range of two density characteristic lines in a first direction (sub-scanning direction) is allowed, dots of special ink and dots of color ink will compete with each other in that overlapping range, and it is possible that the special ink may fail to land. Therefore, the wider the overlapping range, the more special ink will be wasted, and for example, the ejection of large amounts of special ink can be a cause of color unevenness.

Furthermore, as shown in Patent Document 3, if the multiple nozzles included in a nozzle row are divided into two in a first direction (sub-scanning direction) and density characteristic lines for each ink are set for the divided nozzle groups, there will be no overlap of the density characteristic lines, and competition between dots of each ink will be eliminated, thereby reducing the above-mentioned ink waste and color unevenness. However, on the other hand, the number of nozzles used to form a color image will be halved, which will lengthen the time it takes to complete printing of the image and reduce printing productivity (printing throughput).
Thus, the conventional techniques have room for improvement in terms of achieving both print quality and printing productivity.

One object of the present invention is to achieve both print quality and productivity in an inkjet printer that ejects special inks and color inks.

Other objects of the present invention will become apparent to those skilled in the art by reference to the following exemplary aspects and best modes, as well as the accompanying drawings.

In order to facilitate an understanding of the outline of the present invention, embodiments according to the present invention will be exemplified below.
In an aspect according to the present invention, an inkjet printer has a print head including a first nozzle row that ejects a special ink onto a medium and a second nozzle row that ejects a color ink onto the medium, a movement mechanism that moves the print head and the medium relatively in a first direction and a second direction intersecting the first direction, and a control unit that controls the print head and the movement mechanism to perform multi-pass printing on the medium, and the control unit controls the ejection of the special ink from each of a plurality of nozzles included in the first nozzle row in accordance with a first density characteristic line that indicates a nozzle usage rate for each nozzle. At the same time, the ejection of the color ink from each of the multiple nozzles included in the second nozzle row is controlled in accordance with a second density characteristic line that is set independently of the first density characteristic line and indicates the nozzle usage rate for each nozzle, and in the first density characteristic line, a special ink ejection permission range that permits the ejection of the special ink is set in a part of the first nozzle row, and the second density characteristic line partially overlaps with the special ink ejection permission range in the first direction, and within the overlapping range, there is a range in which the nozzle usage rate of the first nozzle row is higher than the nozzle usage rate of the second nozzle row.

In this embodiment, the first density characteristic line that controls the ejection of the special ink and the second density characteristic line that controls the ejection of the color ink are each designed to be independent and have a unique shape, making it possible to achieve both print quality and productivity.

When ejecting special ink, the number of nozzles used is reduced (preferably less than half of the nozzles in the nozzle row) to prevent unnecessary ejection of special ink and to prevent uneven application and color unevenness.

On the other hand, when it comes to ejecting color inks, there are no restrictions on the nozzles used, or the restrictions are lightened (preferably, more than half of the nozzles in the nozzle row are used, and even more preferably, all of the nozzles in the nozzle row are used), thereby ensuring the desired level of printing productivity.

In addition, although the number of nozzles that eject special ink is reduced, on the other hand, by setting the nozzle usage rate of the nozzles that eject special ink high (for example, to 100%), the special ink is made dominant in terms of nozzle usage rate in the overlapping range of the first and second density characteristic lines.

As a result, when dots of special ink and dots of color ink conflict with each other, even if the special ink fails to land on all of the conflicting dots, the special ink will still land successfully in the range where there is no dot conflict.

If the number of pixels on which this special ink lands successfully is large enough, the adhesion between the color ink and the media in that area, or the gloss of the color ink, can be ensured, and extreme deterioration of print quality can be reliably prevented, ensuring the desired level of print quality.

In this embodiment, the first and second density characteristic lines can be designed independently with a much higher degree of freedom than in the past. Therefore, the nozzle usage rates for the nozzles ejecting the special ink and the color ink can be precisely designed according to various conditions such as the purpose of the printed matter and the functionality required for printing.

This makes it possible to achieve both the required print quality and productivity, for example in multi-pass printing, which allows for the simultaneous ejection of special ink and color ink.

Those skilled in the art will readily appreciate that the exemplified embodiments of the present invention may be further modified without departing from the spirit of the present invention.

FIG. 1 is a diagram showing an example of the configuration of an inkjet printer. FIG. 2 is a perspective plan view showing an example of the configuration and arrangement of the UV lamps and the first and second sub-heads when the carriage is viewed from above. FIG. 3 is a diagram showing an example of a system configuration of a main part of a printer. FIG. 4 shows an example of setting a density characteristic line indicating nozzle usage rate when performing multi-pass printing by controlling the image density in the second direction (main scanning direction), and an example of ink ejection control based on that density characteristic line. FIG. 5A is a diagram showing a preferred example of a concentration characteristic line (triangular or trapezoidal), and FIG. 5B is a diagram showing another example of a concentration characteristic line. FIG. 6 is a diagram showing an example of density characteristic lines set for each of color ink and special ink in the same pass in multi-pass printing. FIG. 7 is a diagram showing an example of multi-pass printing to which the present invention is applied (an example in which primer ink is used as the special ink). 8A and 8B are diagrams showing other examples (modified examples) of density characteristic lines set for color ink and special ink in the same pass in multi-pass printing. 9(A) and 9(B) are diagrams showing further examples (other modified examples) of density characteristic lines set for color ink and special ink in the same pass in multi-pass printing. FIG. 10 is a diagram showing another example of multi-pass printing to which the present invention is applied (an example in which gloss ink is used as the special ink).

The best mode described below is used to easily understand the present invention. Therefore, those skilled in the art should note that the present invention is not unduly limited by the mode described below.

In this specification, the term "inkjet printer" can include printers that use printing methods using conventional inkjet technology, such as continuous methods such as the binary deflection method or the continuous deflection method, or various on-demand methods such as the thermal method or the piezoelectric element method.

In addition, "printers (printing devices)" can include 2D printers that print two-dimensional images and 3D printers (three-dimensional modeling devices) that create three-dimensional objects.

The term "ink" can also be interpreted broadly. For example, it can also be expressed as "liquid." For example, the term "inkjet printer" can also be expressed as "liquid ejection device."

In multi-pass printing, one scan (one drive) of the print head in a second direction (main scanning direction) that intersects (preferably perpendicular to) the first direction (sub-scanning direction) is called a "pass." In multi-pass printing, multiple passes are used to complete printing in a specified printing area. When a pass is updated, for example, the media is moved a specified number of pixels downstream in the first direction (sub-scanning direction).

Furthermore, assuming that the medium is moved (transported) along a first direction, the direction from which the medium originates can be defined as "upstream" and the direction to which the medium is transported can be defined as "downstream."
In other words, when the media is moved relative to the print head along a first direction by the movement mechanism, the direction from which the media is "moved" may be the "upstream side" or "one side", and the direction to which the media is "moved" may be the "downstream side" or "other side".
Also, for example, when the print head is moved relative to the media along a first direction by a moving mechanism, the direction of the "destination" of the print head may be the "upstream side" or "one side", and the direction of the "source" of the print head may be the "downstream side" or "other side".

Below, a preferred embodiment of the present invention will be described with reference to the drawings.

First Embodiment
Please refer to Fig. 1. Fig. 1 is a diagram showing an example of the configuration of an inkjet printer. A printer (printing device) 1 in Fig. 1 is a printer that supports multi-pass printing. Multi-pass printing will be described later.

Printer 1 is a 2D printer. In the following description, left, right, top, and bottom refer to the left, right, top, and bottom, respectively, as seen from the perspective of a user (the user of printer 1) standing in front of printer 1, with the side of printer 1 approaching the user being the front and the side moving away being the rear.

The symbols F, Rr, L, R, U, and D in the drawings represent front, rear, left, right, top, and bottom, respectively. The rear Rr of the printer 1 corresponds to the upstream side when the media 2 and carriage 10 move relatively in the sub-scanning direction, and is therefore indicated as "Rr (upstream)" and "F (downstream)" in FIG. 1.

The symbol X in the figure represents a first direction (sub-scanning direction or front-to-back direction), and the symbol Y represents a second direction (main scanning direction or left-to-right direction) that intersects (preferably perpendicular to) the first direction. In the following description, it may be referred to as "first direction (sub-scanning direction) X" or "first direction X", or it may be referred to as "second direction (main scanning direction) Y" or "second direction Y".

The symbol Z represents the up-down direction. The up-down direction can also be said to be the thickness direction of the medium (recording medium) 2 and the image formed on the medium 2.

Note that the media 2 and carriage 10 shown below move relative to one another in the first direction (sub-scanning direction) X. In other words, the media 2 may be transported from the upstream side to the downstream side along the first direction X, or the media 2 may not move and the carriage 10 may move along the first direction X.

The following explanation will be given of an example in which the media 2 is transported along the first direction (sub-scanning direction) X.

The printer 1 shown in A-1 and A-2 of Figure 1 has a platen 3, a guide rail 4, a casing 9, a carriage 10, a carriage movement mechanism 11, a print head 12, a UV lamp 17, and a control unit 20.

The casing 9 is the housing of the printer 1. The casing 9 extends in the second direction (main scanning direction Y). An operation panel 9A is provided at the right end of the casing 9. The operation panel 9A is provided with a display unit that displays the operation status, etc., and input keys that are operated by the user. By operating the operation panel 9A, the user can set various conditions required for multi-pass printing, for example.

The media 2 is placed on the platen 3. A pinch roller 5A is provided above the platen 3 to press down on the media 2. A grid roller 5B is provided at a position on the platen 3 opposite the pinch roller 5A. The grid roller 5B is connected to a feed motor (not shown in FIG. 1, reference symbol 5C in FIG. 3). The feed motor 5C is electrically connected to the control unit 20, and its operation is controlled by the control unit 20.

The grid roller 5B is configured to be rotatable by the driving force of the feed motor 5C. When the grid roller 5B rotates with the media 2 sandwiched between the pinch roller 5A and the grid roller 5B, the media 2 is transported in the first direction (sub-scanning direction X).

In this embodiment, the pinch roller 5A, the grid roller 5B, and the feed motor 5C constitute a transport mechanism that moves the media 2 in the first direction (sub-scanning direction) X.

The guide rail 4 is provided in the casing 9 and extends in the second direction (main scanning direction Y). A carriage 10 is slidably engaged with the guide rail 4.

The carriage 10 is equipped with a print head 12 and a UV lamp 17 as a light irradiation device. The carriage 10 can be moved along the second direction (main scanning direction Y) by a carriage movement mechanism 11.

The carriage movement mechanism 11 includes pulleys 6L and 6R arranged on the left and right sides of the guide rail 4, an endless belt 7 wound around the pulleys 6L and 6R, and a carriage motor 8 connected to the pulley 6R.

The carriage 10 is fixed to the belt 7. The carriage motor 8 is electrically connected to and controlled by the control unit 20. When the carriage motor 8 is driven, the pulley 6R rotates and the belt 7 runs. As a result, the carriage 10, the print head 12 mounted on the carriage 10, and the UV lamp 17 move together in the second direction (main scanning direction) Y along the guide rail 4.

The print head 12 has a first sub-head 121 that ejects colored light-curable ink (hereinafter, sometimes simply referred to as "color ink"), and a second sub-head 122 that ejects light-curable special ink (hereinafter, sometimes simply referred to as "special ink"). The special ink may include clear ink. The first and second sub-heads 121, 122 are arranged side by side along the second direction (main scanning direction) Y.

In this embodiment, the first and second sub-heads 121 and 122 are mounted on the carriage 10. However, each of the sub-heads 121 and 122 may be mounted on a separate carriage.

Please refer to Figure 2. Figure 2 is a perspective plan view showing an example of the configuration and arrangement of the UV lamp and the first and second sub-heads when the carriage is viewed from above.

The print head 12 is arranged between two UV lamps 17, 17 on the left and right along the second direction (main scanning direction) Y. However, this configuration is an example and is not limited to this configuration.

The first sub-head 121 includes a first head portion 12K that ejects process color (K) ink (e.g., black ink), a second head portion 12C that ejects cyan (C) ink, a third head portion 12M that ejects magenta (M) ink, and a fourth head portion 12Y that ejects yellow (Y) ink. The first sub-head 121 may also include a head portion that ejects white ink.

The second sub-head 122 has a fifth head section 12CL that ejects special (CL) ink.

Specialty inks can be classified, for example, into base-application type special inks intended to be applied underneath colored inks, and coating type special inks intended to be applied on top of colored inks or substrates (media).

Examples of special inks that are applied to the base include "primer ink" that is applied to the base of color inks in advance to ensure adhesion between the color inks and the base material (e.g., media), and "white ink" that is used to form an image that serves as the base for color inks. Primer inks may be colored or colorless. An example of multi-pass printing using an inkjet printer with primer ink will be described later with reference to Figures 6 to 9.

Examples of coating-type special inks include "gloss ink" that is applied to color inks or substrates (media) to ensure surface gloss, and "white ink" that is applied to color inks to form images. Gloss ink is preferably colorless. An example of multi-pass printing using an inkjet printer with "gloss ink" will be described later with reference to Figure 10.

The first head portion 12K is provided with a plurality of ink ejection nozzles (hereinafter simply referred to as "nozzles") NK1 to NKm (m can be set to, for example, approximately 300) arranged along the first direction X.
Similarly, the second head portion 12C includes nozzles NC1 to NCm, the third head portion 12M includes nozzles NM1 to NMm, the fourth head portion 12Y includes nozzles NY1 to NYm, and the fifth head portion 12CL also includes nozzles NL1 to NLm.

Note that the above configuration is one example and is not limited to this, and various configurations can be adopted for the number and arrangement of nozzles, etc. In FIG. 2, the first sub-head 121 and the second sub-head 122 are arranged in a position where they completely overlap in the first direction X, but the first sub-head 121 and the second sub-head 122 may be arranged in a position where they are offset in the first direction X. The number of color inks and special inks used can also be increased or decreased as appropriate.

Next, refer to FIG. 3. FIG. 3 is a diagram showing an example of the system configuration of the main parts of the printer. The control unit (print control device) 20 includes a print signal receiving unit 21, a feed control unit 22 that controls the transport of the media 2, a scan control unit 23 that controls the scanning of the carriage 10, an ejection control unit 24 that can individually control the ejection of color ink from each nozzle of the first sub-head 121 and the ejection of special ink from each nozzle of the second sub-head 122, an irradiation control unit 25 that controls the irradiation operation of UV light from the UV lamp (light irradiation device) 17, and a storage unit (memory) 26 in which a program (not shown) that controls the printing operation of the multi-pass method in the printer 1 is stored.

The above-mentioned ejection control unit 24 has a first ejection control unit 241 that can control the ejection of color ink from each nozzle in each of the first to fourth head units 12K, 12C, 12M, and 12Y, preferably individually for each nozzle, and a second ejection control unit 242 that can control the ejection of special ink from the nozzles in the fifth head unit 12CL, preferably individually for each nozzle.

The control unit 20 is also communicatively connected to the feed motor 5C, the carriage motor 8 which is a component of the carriage movement mechanism 11, the actuator 16 of the print head 12, and the UV lamp 17.

The transport operation of the media 2 in the first direction (sub-scanning direction) X by the feed motor 5C can be controlled by the feed control unit 22 of the control unit 20.

In addition, scanning of the print head 12 in the second direction (main scanning direction) Y by the carriage motor 8 can be controlled by the scan control unit 23 of the control unit 20.

In addition, the ink ejection operation in the print head 12 by the actuator 16 can be controlled by the ejection control unit 24 of the control unit 20.

In addition, the UV light irradiation operation of the UV lamp (light irradiation device) 17 can be controlled by the irradiation control unit 25 of the control unit 20.

Next, let us refer to Figure 4. Figure 4 shows an example of setting a density characteristic line when performing multi-pass printing by controlling the density of an image in the second direction (main scanning direction) using a density characteristic line indicating nozzle usage rate, and an example of ink ejection control based on that density characteristic line. Note that in Figure 4, the nozzle row and the range in which ink can be ejected from the nozzles are shown in a perspective plan view seen from above.

A-1 in Figure 4 shows, as an example, a nozzle row Nzk including nine nozzles (here, labeled with the reference numbers NK1 to NK9 for ease of explanation) in the first head unit 12K that ejects process color (K) ink (here, black ink) as shown in Figure 2 above. Note that "Nz" in the reference number Nzk represents the nozzle row, and "k" represents the nozzle row for K color ink (hereinafter, may be described as black).

To print using the multi-pass method, it is necessary to design a pass mask of a specified size for each pass. Each pass mask has a mask pattern, and this mask pattern is determined by the two-dimensional arrangement of ejection permission pixels/ejection non-permission pixels (neither shown), which determine whether or not ink can be ejected.

In designing a pass mask, a space for designing the pass mask is prepared, where a given number of nozzles are assigned to one pass mask, and a density characteristic line (characteristic line showing nozzle usage rate, in other words, a density curve) showing the nozzle usage rate of each nozzle is set. Each of the given number of nozzles is associated with a nozzle in an actual nozzle row.

In A-1 of FIG. 4, for convenience, the nozzle row Nzk is shown as including nine nozzles NK1 to NK9.

This shows that in designing the pass mask for the process color (K) ink, nine nozzles are assigned to one pass mask, and each nozzle corresponds to one of the actual nozzles NK1 to NK9 located upstream in the first head unit 12K shown in Figure 2.

However, this is just one example and is not limiting. The number of nozzles included in one nozzle row can be changed as appropriate depending on the conditions of multi-pass printing, the configuration of the print head used, etc.

In addition, in A-1 of FIG. 4, as an example, nozzle row Nzk that ejects process color (K) ink is shown, but the nozzle row may be nozzle rows Nzc, Nzm, and Nzy that eject color inks of C (cyan), M (magenta), and Y (yellow), or may be nozzle row Nzl that ejects special ink.

In addition, in A-1 of Figure 4, nine nozzles are labeled NK1 to NK9, but this is an example for ease of explanation, and it is also possible to arbitrarily extract, for example, nine consecutive nozzles from the nozzles NK1 to NKm shown in Figure 2 and assign these as the nozzles to be used in designing the mask pattern.

Also, in A-1 of FIG. 4, a band-shaped region 200 extending along the second direction (main scanning direction) Y is shown for nozzle NK1. This region 200 indicates the range in which ink can be ejected from nozzle NK1 when nozzle row Nzk moves once relative to the medium 2.

A-2 in FIG. 4 shows the area 202 onto which ink is actually ejected in the area 200 (ink ejectable range) in A-1 in FIG. 4. How the areas 202 are distributed on the area 200 can be determined randomly, for example, using random numbers. In A-2 in FIG. 4 and A-3 in FIG. 4 described later, for the sake of convenience, the areas 202 have a predetermined length, but in reality, minute areas 202 are distributed on the area 200.

The ratio of the total length of the area 202 where ink is ejected to the total length of the area 200 can be shown by a density characteristic line (a characteristic line showing the nozzle usage rate). Here, the nozzle usage rate means, for example, "the ratio (percentage) of the amount of ink ejected during printing when the maximum amount of ink ejected from one nozzle in one pass under specified printing conditions is taken as 100%."

For example, if the total length of area 200 is 100 and the total length of area 202 from which ink is ejected is 40, the nozzle usage rate is 40%.

A-3 in Figure 4 shows an example of a density characteristic line Q20 that indicates the nozzle usage rate for each of the nine nozzles NK1 to NK9 included in the nozzle Nzk.

The shape of this density characteristic line (characteristic line showing nozzle usage rate) Q20 resembles the shape of a triangular wave of an electrical signal, so in the following explanation it may be referred to as a "triangular shape." Note that using a triangular-shaped density characteristic line (and a trapezoidal-shaped density characteristic line) has the effect of reducing banding (streaky color unevenness) (this point will be explained in Figure 5).

The vertical axis of density characteristic line Q20 indicates the position (in other words, the nozzle number) of each of the nine nozzles NK1 to NK9 that are arranged at regular intervals along the first direction (sub-scanning direction). The horizontal axis indicates the density that varies between 0% and 100%.

As shown on the right side of A-3 in Figure 4, the area 202 into which ink is actually ejected can be determined for each of the nine nozzles NK1 to NK9 based on the density characteristic line Q20.

In the above explanation, the nozzle usage rate is shown as the ratio of the area 202 onto which ink is actually ejected to the area 200 indicating the range in which ink can be ejected, but the nozzle usage rate can also be expressed by the number of pixels onto which ink is actually ejected to a given number of pixels.

In A-4 of Figure 4, the nozzle usage rate is represented by the number of pixels (indicated by patterned circles in the figure) onto which ink is ejected among multiple (here, 10) pixels (dots) arranged along the second direction (main scanning direction) Y.

In A-4 of Figure 4, the concentration characteristic line Q40 is used. For ease of explanation, the upper limit of the concentration in this concentration characteristic line Q40 is set to 50%.

In A-4 of FIG. 4, for example, the nozzle usage rate of nozzle NK1 is 10%, so of the 10 pixels (dots) lined up in the second direction (main scanning direction) Y, one pixel is the pixel from which ink is ejected. Also, for example, the nozzle usage rate of nozzle NK2 is 20%, so of the 10 pixels (dots), two pixels are the pixels from which ink is ejected. For the other nozzles as well, the number of pixels from which ink is ejected is determined in accordance with density characteristic line Q40.

Note that in Figures 6 to 10 described below, we will use as an example the method A-4 in Figure 4, that is, a method that appropriately controls the number of pixels onto which ink is actually ejected based on the density characteristic line.

Next, refer to FIG. 5. FIG. 5(A) shows a preferred example of a concentration characteristic line (triangular or trapezoidal), and FIG. 5(B) shows another example of a concentration characteristic line.

In A-1 of Figure 5(A), two triangular density characteristic lines Q0 and Q0' are shown. Here, for example, the upstream density characteristic line Q0 indicates the nozzle usage rate for the first pass in multi-pass printing, and the downstream density characteristic line Q0' indicates the nozzle usage rate for the second pass.

At point U1 on the upstream density characteristic line Q0, the nozzle usage rate is at its minimum, 0%. At point U2, which is a distance D/2 away from point U1 along the first direction (sub-scanning direction) X, the nozzle usage rate reaches its maximum value of 100%. At point U3, which is a further distance D/2 away from point U2, the nozzle usage rate returns to 0%.

The downstream concentration characteristic line Q0' is the upstream concentration characteristic line Q0 shifted downstream by D/2.

The concentration characteristic lines Q0 and Q0' overlap in the range from point U2 to point U3. In other words, the contour shape of the overlapping portion of each concentration characteristic line is triangular. However, since there is a triangular non-overlapping portion of the same size as the overlapping portion, combining the overlapping portion and the non-overlapping portion essentially forms a trapezoidal concentration characteristic line Q0'' as shown in A-2 of Figure 5.

In the range between points U2 and U3 on this trapezoidal density characteristic line Q0'', the density (nozzle usage rate) is at its highest (100% here), and in this range, an image with a substantially uniform density distribution is formed. This makes it possible to suppress the occurrence of banding (streaky color unevenness).

For example, in FIG. 5B, the shape of the density characteristic line Q0 is a triangle in which the nozzle usage rate changes like a broken line, rather than a straight line. Such modifications can be made as appropriate.

The shape of the concentration characteristic line may be a straight line, a curved line, or a combination of straight lines and curved lines.

Next, let us refer to FIG. 6. FIG. 6 is a diagram showing an example of density characteristic lines set for each of color ink and special ink in the same pass in multi-pass printing. Note that in FIG. 6, the nozzle row is shown in a perspective plan view seen from above.

In A-1 of FIG. 6, as an example, a nozzle row Nzl that ejects special ink and nozzle rows Nzk, Nzc, Nzm, and Nzy that eject color inks of K (process color: black in this case), C (cyan), M (magenta), and Y (yellow) are arranged at predetermined intervals along the second direction (main scanning direction) Y from left (L) to right (R).

In A-1 of FIG. 6, as an example, the number of nozzles in each nozzle row is nine. However, this is just an example and is not limited to this.

A-2 in Figure 6 shows an example of the setting of density characteristic lines (characteristic lines indicating nozzle usage rates) for each of the nozzle row Nzl that ejects special ink and the nozzle row Nzk that ejects K (black) ink (however, this is an example of a nozzle row that ejects color ink, and may be a nozzle row that ejects ink of another color).

As shown on the left side of A-2 in FIG. 6, the nozzle row Nzl includes nine nozzles NL1 to NL9. Of these nozzles, the nozzle NL1 located most upstream is defined as the first nozzle in the nozzle row Nzl, and the nozzle NL9 located most downstream is defined as the ninth nozzle.

The distance between the first nozzle NL1 and the ninth nozzle NL9 is L. The distance between the first and ninth nozzles NL1 and NL9 and the fifth nozzle NL5 located in the center is L1/2.

On the left side of A-2 in Figure 6, an example of a first density characteristic line (characteristic line showing nozzle usage rate) Q1 is shown, which indicates the nozzle usage rate for each of the nine nozzles NL1 to NL9 included in the nozzle row Nzl that ejects the special ink.

The shape of this first concentration characteristic line Q1 resembles the shape of a square wave (quadrature wave) of an electrical signal, so in the following description it may be referred to as a "quadrature" or "quadrature concentration characteristic line." However, the shape of the concentration characteristic line Q1 may also be a triangular shape as shown in A-2 of FIG. 9, or a trapezoidal shape as shown in FIG. 5.

The first concentration characteristic line Q1 has a stepped shape in which the nozzle usage rate is maximum (here, 100%) in the range from point J1 to point J2 and is minimum (here, 0%) in other ranges.

Here, the range from point J1 to point J2 (the range indicated by the symbol S1) is the range in which the nozzle usage rate is not 0%, in other words, the range in which the special ink is permitted to be ejected.

In addition, in the range from point J3 to point J4, the nozzle usage rate is 0%, and therefore the range from point J3 to point J4 is a range in which special ink is not ejected (a range in which ejection of special ink is not permitted).

In the first density characteristic line Q1, the range S1 (range from point J1 to point J2) in which ink is ejected is set to a range of L1/2 upstream of the central fifth nozzle NL5 (excluding the fifth nozzle NL5).

In this way, in the first density characteristic line Q1, the special ink ejection permitted range S1, in which the ejection of special ink is permitted, is set in a portion of the upstream side of the first nozzle row Nzl.

Also, on the right side of A-2 in Figure 6, an example of a second density characteristic line (characteristic line indicating nozzle usage rate) Q2 is shown, which indicates the nozzle usage rate for each of the nine nozzles NK1 to NK9 included in the nozzle row Nzk.

This second concentration characteristic line Q2 has the triangular shape shown above.

That is, the second density characteristic line Q2 has a nozzle usage rate of 0% at point J5, and as it moves downstream in the second direction (sub-scanning direction) X, the nozzle usage rate gradually increases in a linear manner, reaching the maximum nozzle usage rate (here, for convenience of explanation, 50%) at point J6. Furthermore, as it moves downstream in the second direction (sub-scanning direction) X, the nozzle usage rate gradually decreases in a linear manner, returning to 0% at point J6.

In the following description, the portion 50 of the second density characteristic line Q2 where the nozzle usage rate gradually increases, indicated by the straight line connecting points J5 and J6, may be referred to as the "first portion." Also, the portion 60 where the nozzle usage rate gradually decreases, indicated by the straight line connecting points J6 and J7, may be referred to as the "second portion."

The first portion 50 of the second density characteristic line Q2 partially overlaps with the special ink ejection permitted range S1 in the first direction (sub-scanning direction) X.

If we imagine the first and second concentration characteristic lines Q1 and Q2 overlapping in a plan view, we can see that there are ranges (areas) R1 and R2 indicated by diagonal lines in the lower right of A-2 in Figure 6.

Range R1 is the range in which the nozzle usage rate of the first nozzle row Nzl can be considered to be the same as the nozzle usage rate of the second nozzle row Nzk (Nzc to Nzy).

On the other hand, range R2 is the range in which the nozzle usage rate of the first nozzle row Nzl is higher than the nozzle usage rate of the second nozzle row Nzk (Nzc to Nzy).

In range R1, if special ink and color ink were to be ejected at the same time, the special ink dots and color ink dots would compete with each other, and in the worst case scenario, the special ink would fail to land on all pixels (dots).

For example, if the special ink should land on the underlying media 2, but the color ink lands on the underlying media 2, the landing of the special ink at that pixel will fail, and it may even be the case that the landing of the special ink will fail at all pixels with competing dots.

However, in range R2, there is no competition between the special ink dots and the color ink dots, and the ejected special ink is guaranteed to land successfully. If the number of pixels where the special ink lands successfully is large enough, adhesion between the color ink and the media in that area can be ensured, extreme deterioration of print quality can be reliably prevented, and the desired level of print quality can be ensured.

In the example of A-2 in Figure 6, the first density characteristic line Q1 that controls the ejection of the special ink and the second density characteristic line Q2 that controls the ejection of the color ink are each designed to be independent and have a unique shape, making it possible to achieve both print quality and productivity.

When ejecting special ink, the number of nozzles used is reduced (preferably less than half of the nozzles in the nozzle row) to prevent unnecessary ejection of special ink and to prevent uneven application and color unevenness.

On the other hand, when ejecting color inks, there are no restrictions on the nozzles used, or the restrictions are lightened (preferably, more than half of the nozzles in the nozzle row are used, and even more preferably, all of the nozzles in the nozzle row are used), thereby ensuring the desired level of printing productivity.

In addition, although the number of nozzles that eject special ink is reduced, on the other hand, by setting the nozzle usage rate of the nozzles that eject special ink high (for example, to 100%), the special ink is made dominant in terms of nozzle usage rate in the overlapping range of the first and second density characteristic lines.

As a result, even if the special ink fails to land on all of the competing dots in the range where dots of special ink and color ink compete (range R1 in the figure), the special ink will still land successfully in the range where dots do not compete (range R2 in the figure).

If the number of pixels on which this special ink lands successfully is large enough, the adhesion between the color ink and the media in that area, or the gloss of the color ink, can be ensured, and extreme deterioration of print quality can be reliably prevented, ensuring the desired level of print quality.

In A-2 of Figure 6, the first and second density characteristic lines can be designed independently with a much higher degree of freedom than before. Therefore, the nozzle usage rates for the nozzles ejecting the special ink and color ink can be designed in detail according to various conditions such as the purpose of the printed matter and the functionality required for printing.

This makes it possible to achieve both the required print quality and productivity, for example in multi-pass printing, which allows for the simultaneous ejection of special ink and color ink.

In this way, in the example of Figure 6, it is possible to achieve both print quality and productivity when printing by ejecting color ink and special ink upstream.

Furthermore, the following three modes (1) to (3) can be assumed for the ejection of the special ink and the color ink.
(1) A first ejection mode in which, when a special ink is ejected from a plurality of nozzles, color inks are ejected simultaneously from each of the color ink nozzles corresponding to each of the plurality of special ink nozzles.
(2) A second ejection mode in which color ink is not ejected simultaneously from some of the nozzles among a plurality of nozzles of the special ink. For example, in the initial period, simultaneous ejection of color ink is not performed from some of the nozzles, and after the initial period has elapsed, color ink is ejected simultaneously from those nozzles as well.
(3) A third ejection mode in which the special ink and the color ink are not ejected simultaneously. For example, there may be cases in which the color ink is ejected after the ejection of all the special inks has been completed. In other words, this corresponds to a case in which the layer printing technology is also applied to multi-pass printing.

In the case of the above-mentioned form (3), in the conventional simultaneous printing (layer printing), for example, the number of nozzles used for ejecting the special ink and the color ink was the same (for example, half the number of all nozzles included in the nozzle row), so there was a limit to the freedom of printing.
According to the present invention, the number of nozzles to be used for each of the special ink and the color ink can be set independently, preferably on a nozzle-by-nozzle basis, providing a high degree of freedom in printing.
Which of the above ejection modes (1) to (3) is used is determined in consideration of the balance between print quality and print productivity.

Next, refer to FIG. 7. FIG. 7 is a diagram showing an example of multi-pass printing to which the present invention is applied (an example in which primer ink is used as the special ink). Note that in FIG. 7, the nozzle row and the application example are shown in a perspective plan view seen from above.

A-1 in Figure 7 is a repeat of A-2 in Figure 6. In A-1 in Figure 7 as well, the density characteristic lines Q1 and Q2 described above are used as the density characteristic lines that control the nozzle usage rates for the special ink and color ink, respectively.

A-2 and A-3 in Figure 7 show examples of ink application in the first and second passes in multi-pass printing.

In A-2 and A-3 of FIG. 7, a special ink (here, a primer ink intended to be applied to the base) and a color ink are applied onto the base (media 2) according to the density characteristic lines Q1 and Q2.

The right side of A-2 in Figure 7 shows an example of ink application in the first pass of multi-pass printing.

In the diagram, dots where no ink has landed are shown as open circles. Dots where color ink has landed in the first pass are shown as patterned circles of the same diameter as the open dots. Dots of special ink (primer ink) that have landed on the base (media 2) are shown as open triangles.

In the figure, the symbols A to I are assigned along the first direction (sub-scanning direction) X, and the symbols 1 to 10 are assigned along the second direction (main scanning direction) Y. This makes it possible to identify the position of the dots in the dot matrix.

For example, in the area PT1 enclosed by the dashed ellipse, a dot of color ink is formed in the third column of row A, and this dot can be represented as dot A3.

For example, two color ink dots B1 and B8 are formed on row B. Three color ink dots C2, C5, and C10 are formed on row C.

Now, let us assume that all six dots of color ink, A3, B1, B8, C2, C5, and C10, in area PT1 land on the base (media 2). In this case, application of the special ink (primer ink) has failed for these dot positions.

However, as explained above, the nozzle usage rate for the special ink is set high within this area PT1, so of the 30 dots, all 24 dots other than the above 6 dots are dots of special ink that have landed on the base (media 2) (shown as white triangles in the figure). Therefore, the application of special ink to the base (media 2) (ink landing) is successful in this area.

Next, refer to A-3 in Figure 7. On the right side of A-3 in Figure 7, an example of ink application in the second pass in multi-pass printing is shown. Note that in the figure, the color ink dots in the second pass are shown as patterned circles with a smaller diameter than the white dots.

The diameter of the circles representing the color ink dots in the second pass is smaller as a convenience to distinguish them from the color ink dots in the first pass, and the actual dot diameter is the same as the diameter of the dots in the first pass.

In A-3 of FIG. 7, the base medium 2 is moved downstream in the first direction (sub-scanning direction) X by a distance of, for example, four pixels. However, this is just one example, and the amount of movement can be set arbitrarily.

In area PT1 enclosed by the dashed ellipse, a total of 12 small diameter patterned circles are drawn over the 24 white triangles shown in A-2 of Figure 7. These circles represent the color ink of the second pass that has landed on the special ink (primer ink) applied to the base (media 2). Because the special ink exists underneath these color inks, extreme deterioration in adhesion between the color ink and the base (media 2) is suppressed. This ensures the desired level of adhesion.

In addition, in the area PT2 enclosed by the dashed rectangle in the figure, the nozzle usage rate for the special ink is set high, just like in the area PT1 in A-2 of Figure 7 described above, so of the 30 dots, all 24 dots other than the six color ink dots in the second pass are dots of special ink that have landed on the base (media 2) (shown as white triangles in the figure). Therefore, the special ink has been successfully applied to the base (media 2) in this area.

In this way, by limiting the range in which the special ink is ejected, unnecessary use of special ink can be reduced.

In addition, even if the special ink fails to land on the base (media 2) in areas where it competes with the color ink, the density (nozzle usage rate) of the special ink is dominant, so in areas where the inks do not compete with each other, the special ink will definitely land (be applied) successfully.

Therefore, in the successful areas, it is possible to reliably and effectively improve the adhesion between the color ink and the base (media 2).

Therefore, even if the amount of special ink ejected is small, it is possible to reliably prevent extreme deterioration in adhesion and suppress extreme deterioration in print quality, thereby achieving the effect of ensuring the desired level of adhesion (i.e., print quality).

In addition, as described above, the nozzles that eject color ink are not limited to half of the total nozzles as in Patent Document 3, but more than half of the total nozzles can be used, and preferably all of the nozzles can be used, so that high productivity can be maintained in printing color images.

In this way, in this embodiment, it is possible to achieve both print quality and productivity when printing by ejecting color ink and special ink upstream.

Second Embodiment
Next, reference is made to Fig. 8. Fig. 8(A) and Fig. 8(B) are diagrams showing other examples (variations) of density characteristic lines set for color ink and special ink in the same pass in multi-pass printing. Note that in Fig. 8, the nozzle row is shown in a perspective plan view seen from above.

In A-2 of Figure 6 (A-1 of Figure 7) described above, the first density characteristic line Q1 for the special ink and the second density characteristic line Q3 for the color ink have an overlapping range S1 in the first direction (sub-scanning direction) X, and in this overlapping range S1, the second density characteristic line Q2 does not include the 0% range.

In contrast, in FIG. 8(A), in the overlap range S1, the first concentration characteristic line Q1 overlaps with the range 51 of the second concentration characteristic line Q3 where the nozzle usage rate is zero, and with part of the first portion 50' where the nozzle usage rate gradually increases.

In the range 51 where the nozzle usage rate of the second density characteristic line Q3 is zero, color ink is not ejected. Therefore, in the special ink range 51, there is no competition between color ink and special ink.

Therefore, in FIG. 8(A), the substantial overlap range between the first concentration characteristic line Q1 and the second concentration characteristic line Q3 is S2 (<S1).

In other words, in range 51, the ejected special ink (primer ink) reliably lands on the base (media 2). As a result, in FIG. 8A, the range over which the special ink is applied to the base (media 2) is increased compared to A-2 in FIG. 6 (A-1 in FIG. 7), and this improves the adhesion between the color ink and the base (media 2) (i.e., print quality).

Next, refer to FIG. 8(B). In FIG. 8(B), in the overlap range S1, the first density characteristic line Q1 overlaps only with the range 51' of the second density characteristic line Q4 where the nozzle usage rate is zero. In other words, in FIG. 8(B), the first and second density characteristic lines Q1 and Q4 can be considered to have substantially no overlapping range.

In range 51', color ink is not ejected. Therefore, in special ink range 51', there is no competition between color ink and special ink, and the ejected special ink (primer ink) lands reliably on the base (media 2).

In FIG. 8(B), the area over which the special ink is applied onto the base (media 2) is further increased compared to FIG. 8(A), and this further improves the adhesion between the color ink and the base (media 2) (i.e., the print quality).

Third Embodiment
Next, reference is made to Fig. 9. Fig. 9(A) and Fig. 9(B) are diagrams showing further examples (other modified examples) of density characteristic lines set for color ink and special ink in the same pass in multi-pass printing. Note that in Fig. 9, the nozzle row is shown in a perspective plan view seen from above.

First, let us explain Figure 9 (A). In Figure 6 (A-2) and Figure 7 (A-1) shown above, a triangular concentration characteristic line Q2 was used as the second concentration characteristic line. In contrast, Figure 9 (A) uses a trapezoidal concentration characteristic line Q5.

As explained above in A-2 of Figure 5, the trapezoidal density characteristic line has a wide range of maximum density (highest nozzle usage rate), and in this range, an image with a substantially uniform density distribution is formed, making it possible to suppress the occurrence of banding (streaky color unevenness). Therefore, as shown in Figure 9 (A), a trapezoidal density characteristic line may be used instead of a triangular one.

When using this trapezoidal density distribution Q5, it is preferable to set each density characteristic line so that the range S1 of maximum nozzle usage rate of the special ink density characteristic line (square density characteristic line) Q1 does not overlap with the range S4 of maximum nozzle usage rate of the color ink density characteristic line (trapezoidal density characteristic line) Q5, as shown in Figure 9 (A). In other words, if the ranges of maximum nozzle usage rate of each density characteristic line overlap, when the inks are ejected simultaneously, competition between the inks increases, increasing waste of the special ink, and the application may become uneven, affecting the appearance, so it is preferable to avoid such overlap.

Next, FIG. 9B will be described.
In the previously shown A-2 in Fig. 6 and A-1 in Fig. 7, a rectangular density characteristic line Q1 was used as the first density characteristic line. In contrast, in Fig. 9(B), a triangular density characteristic line Q6, in which the peak value of the nozzle usage rate is 100%, is used instead of the rectangular density characteristic line Q1.

The same effect can be obtained by using a trapezoidal concentration characteristic line with the same peak value instead of this triangular concentration characteristic line Q6.

Fourth Embodiment
Next, reference is made to Fig. 10. Fig. 10 is a diagram showing another example of multi-pass printing to which the present invention is applied (an example in which gloss ink is used as the special ink). Note that in Fig. 10, the nozzle row and the application example are shown in a perspective plan view.

In the example of Figure 10, gloss ink is used as the special ink. Gloss ink is a coating type special ink that is intended to be applied on top of color ink. By applying gloss ink on top of color ink, it is possible to give a glossy appearance to the printed matter, for example.

In A-1 of FIG. 10, the density characteristic line Q7 of the special ink (gloss ink) is a rectangular density characteristic line, similar to A-2 of FIG. 6 and A-1 of FIG. 7 described above. However, this is just one example and is not limiting. The density characteristic line Q7 of the special ink may also be triangular, as shown in FIG. 9 (B).

However, since the special ink needs to be applied over the color ink, in A-1 of Figure 10, the permitted ejection range of the density characteristic line Q7 that permits the ejection of the special ink is set downstream.

In other words, the permitted range of the special ink on the density characteristic line Q7 overlaps with the second portion 60 (excluding the portion where the maximum nozzle usage rate is reached) of the color ink density characteristic line Q2, which is the portion where the nozzle usage rate gradually decreases.

For color inks, the triangular density characteristic line Q2 described above in A-2 of Figure 6 and A-1 of Figure 7 is used.

However, this is just one example. The shape of the color ink density characteristic line of A-1 in Figure 10 may be the same as that of (A) and (B) in Figure 8 described above (a shape in which the overlapping range includes a range where the nozzle usage rate is zero, or a shape in which the overlapping range is only a range where the density is zero), or a shape similar to the trapezoidal density characteristic line shown in (A) in Figure 9 may be used. In this case, it is possible to obtain the same effect as in the example described above.

A-2 and A-3 in Figure 10 show examples of ink application in the first and second passes in multi-pass printing. The dot notation is the same as A-2 and A-3 in Figure 7 described above.

However, in A-3 of Figure 10, the special ink dots in the second pass are represented by smaller triangles to distinguish them from the special ink dots in the first pass.

In area PT10 in A-2 of Figure 10, let's assume that all six color ink dots G3, G5, G7, H6, H8, and I10 land on the special ink. In this case, application of the special ink (gloss ink) has failed for these dot positions.

However, as explained above, the nozzle usage rate for color ink is set low within this area PT10, so out of the 30 dots, only the six pixels mentioned above fail to receive the special ink (gloss ink), and this does not pose any particular problem.

Next, refer to A-3 in Figure 10. On the right side of A-3 in Figure 10, an example of ink application in the second pass in multi-pass printing is shown.

In the diagram, the color ink dots in the second pass are shown as patterned circles with a smaller diameter than the white dots, and as mentioned above, the special ink dots in the second pass are shown as smaller triangles compared to the first pass. These are just convenient notations to distinguish them from the color ink dots in the first pass, and the actual dots are the same as the dots in the first pass.

In A-3 of FIG. 10, the base medium 2 is moved downstream in the first direction (sub-scanning direction) X by a distance of, for example, 4 dots. However, this is just one example, and the relative amount of movement can be set as desired.

In the area PT20 enclosed by the dashed rectangle, six second pass color ink dots (indicated by small patterned circles) are formed, just as in the first pass. Even if application of the special ink (gloss ink) fails on all six dots, special ink (gloss ink) will be applied to the other 24 pixels, and if there are dots of first pass color ink within this range, special ink (gloss ink) will be applied reliably on those dots. In the figure, the small triangle drawn to overlap the large diameter patterned circle (dots of first pass color ink) indicates the special ink of the second pass.

In area PT20 in A-3 of Figure 10, the special ink (gloss ink) formed in the second pass is present on top of the color ink dots from the first pass, so the glossiness of the color image is maintained in this area.

In other words, even if only a small amount of special ink (gloss ink) is applied, the color ink can be efficiently coated with the special ink, thereby preventing an extreme decrease in glossiness of the color image.

This ensures the desired level of gloss (i.e., image quality) of the color image.

In addition, as described above, the nozzles that eject color ink are not limited to half of the total nozzles as in Patent Document 3, but more than half of the total nozzles can be used, and preferably all of the nozzles can be used, so that high productivity can be maintained in printing color images.

In this way, in this embodiment, it is possible to achieve both print quality and productivity when printing by ejecting color ink and special ink downstream.

As described above, the present embodiment includes the following aspects.
In a first aspect of this embodiment, a printing head including a first nozzle row that ejects a special ink onto a medium and a second nozzle row that ejects a color ink onto the medium, a movement mechanism that moves the printing head and the medium relatively in a first direction and a second direction intersecting the first direction, and a control unit that controls the printing head and the movement mechanism to perform multi-pass printing on the media, wherein the control unit controls the ejection of the special ink from each of a plurality of nozzles included in the first nozzle row in accordance with a first density characteristic line that indicates the nozzle usage rate for each nozzle, and The ejection of color ink from each of a plurality of nozzles included in a second nozzle row is controlled in accordance with a second density characteristic line that is set independently of the first density characteristic line and indicates the nozzle usage rate for each nozzle, and in the first density characteristic line, a special ink ejection permitted range that permits the ejection of special ink is set in a part of the first nozzle row, and the second density characteristic line partially overlaps with the special ink ejection permitted range in a first direction, and within the overlapping range, there is a range in which the nozzle usage rate of the first nozzle row is higher than the nozzle usage rate of the second nozzle row.

In this embodiment, the first density characteristic line that controls the ejection of the special ink and the second density characteristic line that controls the ejection of the color ink are each designed independently and with a unique shape, making it possible to achieve both print quality and productivity.
When ejecting special ink, the number of nozzles used is reduced (preferably to less than half of the nozzles included in the nozzle row), thereby preventing unnecessary ejection of special ink and preventing uneven application and color unevenness.
On the other hand, when it comes to ejecting color inks, there are no restrictions on the nozzles used, or the restrictions are lightened (preferably, more than half of the nozzles in the nozzle row are used, and even more preferably, all of the nozzles in the nozzle row are used), thereby ensuring the desired level of printing productivity.
Furthermore, while the number of nozzles that eject special ink is reduced, on the other hand, by setting the nozzle usage rate of the nozzles that eject special ink high (for example, to 100%), the special ink is made dominant in terms of nozzle usage rate in the overlapping range of the first and second density characteristic lines.
As a result, when dots of special ink and dots of color ink compete with each other, even if the special ink fails to land on all of the competing dots, the special ink will be sure to land successfully within a range where dots do not compete with each other.
If the number of pixels on which the special ink lands successfully is large enough, the adhesion between the color ink and the media in that area, or the gloss of the color ink, can be ensured, and extreme deterioration of print quality can be reliably prevented, ensuring the desired level of print quality.
In this way, in the first aspect, the first and second density characteristic curves can be designed independently with a much higher degree of freedom than in the past, and therefore the nozzle usage rates for the nozzles ejecting the special ink and the color ink can be precisely designed according to various conditions such as the purpose of the printed matter and the functionality required for printing.
This makes it possible to achieve both the required print quality and productivity, for example, in multi-pass printing that allows simultaneous ejection of special ink and color ink.
Another advantage is that extreme mixing of special ink and color ink can be suppressed.

In a second aspect dependent on the first aspect, the first concentration characteristic line may have a rectangular shape with a portion in which the nozzle usage rate changes stepwise from one side to the other side in the first direction, or a triangular shape or a trapezoidal shape with a first portion on one side in which the nozzle usage rate changes so as to gradually increase from one side to the other side in the first direction, and a second portion on the other side in which the nozzle usage rate changes so as to gradually decrease from one side to the other side in the first direction.

In the second aspect, an example of the shape of the "first density characteristic line" suitable for suppressing banding (striped color unevenness) is shown. By using a triangular shape, for example, one pass and the next pass can be overlapped at the ? portion, and banding can be suppressed by appropriately setting the overlapping portion.
Furthermore, when a trapezoidal density characteristic line is used, the range of maximum density (highest nozzle usage rate) is wide, and within this range, an image with a substantially uniform density distribution is formed, making it possible to suppress the occurrence of banding.
In addition, in the second aspect, the expression "from one side to the other side in the first direction" is used. A supplementary explanation will be given on this point.
When a virtual line segment of finite length is assumed in a first direction, two ends (end points) can be assumed for the line segment. If one of the two ends (two end points) is defined as "one end" and the other as "the other end," for example, when a medium moves along the first direction, the movement can be defined as, for example, movement from the side of one end to the side of the other end.
Therefore, "the side of either one of the ends" can be regarded as the above-mentioned "one side", and "the side of the other of the ends" can be regarded as the above-mentioned "other side".
Furthermore, the above "one side" may be rephrased as, for example, the "upstream side," and the above "other side" may be rephrased as, for example, the "downstream side." Here, when, for example, a medium or a print head moves, "the side from which the movement originates" can be referred to as the upstream side, and "the side to which the movement destination occurs" can be referred to as the downstream side. However, this is merely an example, and it is preferable to flexibly interpret the above "one side" and "other side," or "upstream side" and "downstream side," in accordance with the circumstances.
The above interpretation can be similarly applied to the third, fourth, and other aspects.

In a third aspect dependent on the first aspect, the second concentration characteristic line may have a triangular or trapezoidal shape including a third portion on one side where the nozzle usage rate gradually increases from one side to the other side in the first direction, and a fourth portion on the other side where the nozzle usage rate gradually decreases from one side to the other side in the first direction.

The third aspect shows an example of the shape of the "second density characteristic line" that is suitable for suppressing banding. The explanation of the second aspect above can be applied to this aspect as well.

In a fourth aspect dependent on the first aspect, when the moving mechanism moves the medium relative to the print head along the first direction, the direction from which the medium moves is one side and the direction to which the medium moves is the other side; when the moving mechanism moves the print head relative to the medium along the first direction, the direction to which the print head moves is one side and the direction from which the print head moves is the other side; when the special ink is a base-coating type special ink intended to be applied to a medium that is a base for color inks, the special ink discharge permission range may be set to partially overlap on one side of the second density characteristic line; and when the special ink is a coating type special ink intended to be applied on top of color inks, the special ink discharge permission range may be set to partially overlap on the other side of the second density characteristic line.

This makes it possible to perform multi-pass printing with an inkjet printer whether using a base-coating type special ink or a coating type special ink.

In a fifth aspect dependent on any one of the first to fourth aspects, in the overlapping range in which the special ink ejection permitted range and the second density characteristic line overlap, the second density characteristic line may include a range in which the nozzle usage rate is 0%.

In a fifth aspect, the second density characteristic line is allowed to include a portion of a range in which the nozzle usage rate is 0%.
In the range where the nozzle usage rate of the second density characteristic line is zero, the color ink is not ejected, so even if the color ink is ejected simultaneously with the special ink, there is no competition between the color ink and the special ink in that range.
In other words, within that range, the ejected special ink (here, for example, primer ink) will land reliably on the base (media). This increases the area over which the special ink is applied to the base (media), improving the adhesion between the color ink and the base (media) (i.e., print quality).

In a sixth aspect which is dependent on any one of the first to fifth aspects, the special ink and the color ink may be photocurable inks, and a light irradiation device may be provided which irradiates the ejected special ink and color ink with light.

According to the sixth aspect, the photocurable ink can be quickly cured by light (ultraviolet light, etc.). This eliminates the need for drying, as is the case with water-based inks and solvent-based inks.

In a seventh aspect which is dependent on any one of the first to sixth aspects, the control unit may be capable of controlling the ejection of the special ink and color ink in each of the first and second nozzle rows on a nozzle-by-nozzle basis using the first and second density characteristic lines.

In the conventional simultaneous printing (layer printing) technology, for example, the number of nozzles used to eject the special ink and the color ink were the same, which limited the degree of freedom in printing. However, according to the seventh aspect, the number of nozzles to be used for each of the special ink and the color ink can be set independently, on a nozzle-by-nozzle basis, thereby significantly improving the degree of freedom in printing.

As described above, the present invention eliminates the conventional restriction of dividing multiple nozzles in a nozzle row into two, upstream and downstream, to prevent overlapping of color ink and special ink, making it possible to perform multi-pass printing with greater flexibility.

In other words, it will be possible to freely adjust the ejection of each ink, preferably on a nozzle-by-nozzle basis, improving the freedom of designing masks for multi-pass printing.

When applying color ink, for example, it is possible to eject color ink using all the nozzles in the nozzle row, in which case the productivity of color image printing can be achieved at the same level as when special ink is not used.

On the other hand, when applying special ink, the special ink is ejected from the upstream or downstream nozzles (excluding the nozzles with the highest nozzle usage rate), which reduces the amount of special ink used and cuts down on waste.

In addition, the density characteristic line that controls the ejection of the special ink overlaps in the first direction (sub-scanning direction) with, for example, the density portion (first portion or second portion) of the density characteristic line that controls the ejection of the color ink, where the nozzle usage rate gradually changes. In the overlapping range, the special ink is dominant in terms of the nozzle usage rate. Therefore, even if the application of the special ink fails at a pixel position where the special inks compete with each other when the special ink and the color ink are ejected simultaneously, the application of the special ink can be reliably successful at other pixel positions, and therefore extreme deterioration in adhesion and glossiness can be reliably suppressed.

In this way, the present invention makes it possible to achieve both print quality and productivity in multi-pass printing that uses both special inks and color inks.

The present invention is not limited to the exemplary embodiments described above, and a person skilled in the art could easily modify the exemplary embodiments described above to the extent that they fall within the scope of the claims.

1: Inkjet printer (printer, printing device), 3: Platen, 4: Guide rail, 5A: Pinch roller, 5B: Grid roller, 5C: Feed motor, 6L, 6R: Pulley, 7: Belt, 8: Carriage motor, 9: Casing, 9A: Operation panel (operation unit), 10: Carriage, 11: Carriage movement mechanism, 12: Print head (ink head), 12K, 12C, 12M, 12Y, 12CL: First, second, third, fourth, fifth head units, 16: Actuator, 17: UV lamp (light irradiation device), 20: Control unit, 21: Print signal receiving unit, 22: Feed control unit, 23: Scan control unit, 24: Discharge control unit, 25: Irradiation control unit, 26: Memory unit (memory), 50: A first nozzle on the upstream side, in which the nozzle usage rate gradually increases from the upstream side to the downstream side in the first direction Part 60: A second downstream part in which the nozzle usage rate gradually decreases from the upstream side to the downstream side in the first direction; Q1, Q6: First density characteristic line (characteristic line showing the nozzle usage rate of nozzles ejecting special ink); Q2, Q4, Q5: Second density characteristic line (characteristic line showing the nozzle usage rate of nozzles ejecting color ink); 121, 122: First and second sub-heads; 241, 242: First and second ejection control units; Nzl: Nozzle row ejecting special ink; Nzk: Nozzle row ejecting process color (e.g. black) ink; Nzm: Nozzle row ejecting magenta ink; Nzy: Nozzle row ejecting yellow ink; NL1-NLm: Nozzles ejecting special ink; NC1-NCm: Nozzles ejecting cyan ink; NM1-NMm: Nozzles ejecting magenta ink; NY1-NYm: Nozzles ejecting yellow ink.

Claims (7)

a print head including a first nozzle row that ejects a special ink onto a medium and a second nozzle row that ejects a color ink onto the medium;
a moving mechanism that moves the print head and the medium relative to one another in a first direction and a second direction that intersects with the first direction;
a control unit that controls the print head and the movement mechanism to perform multi-pass printing on the medium;
having
The control unit is
controlling the ejection of the special ink from each of a plurality of nozzles included in the first nozzle row in accordance with a first density characteristic line indicating a nozzle usage rate for each nozzle;
controlling the ejection of the color ink from each of a plurality of nozzles included in the second nozzle row in accordance with a second density characteristic line that indicates a nozzle usage rate for each nozzle and is set independently of the first density characteristic line;
and,
In the first concentration characteristic curve,
a special ink ejection permitted range in which ejection of the special ink is permitted is set in a portion of the first nozzle row,
The second concentration characteristic curve is
a special ink ejection permitted range that partially overlaps with the special ink ejection permitted range in the first direction;
In that overlapping range,
a range exists in which the nozzle usage rate of the first nozzle row is higher than the nozzle usage rate of the second nozzle row;
Inkjet printer. The first concentration characteristic curve is
a rectangular shape including a portion in which the nozzle usage rate changes stepwise from one side to the other side in the first direction;
Or,
a first portion on one side, the nozzle usage rate gradually increasing from one side to the other side in the first direction;
a second portion on the other side in which the nozzle usage rate changes so as to gradually decrease from one side to the other side in the first direction;
A triangular or trapezoidal shape,
having
2. The inkjet printer according to claim 1. The second concentration characteristic curve is
a third portion on one side, the nozzle usage rate gradually increasing from one side to the other side in the first direction;
a fourth portion on the other side in which the nozzle usage rate changes so as to gradually decrease from one side to the other side in the first direction;
having a triangular or trapezoidal shape;
2. The inkjet printer according to claim 1. When the medium is moved relative to the print head by the movement mechanism along a first direction, the direction from which the medium is moved is defined as one side, and the direction to which the medium is moved is defined as the other side;
When the print head is moved relative to the medium in a first direction by the movement mechanism, a direction to which the print head is moved is defined as one side, and a direction from which the print head is moved is defined as the other side,
In the case where the special ink is a base-coated special ink intended to be applied to the medium that is a base for the color ink,
the special ink ejection permitted range is set so as to overlap partially on one side of the second density characteristic line,
In the case where the special ink is a coating type special ink intended to be applied on the color ink,
the special ink ejection permitted range is set so as to partially overlap with the other side of the second density characteristic line;
2. The inkjet printer according to claim 1. In the overlapping range in which the special ink ejection permitted range and the second density characteristic line overlap,
the second density characteristic line includes a range in which the nozzle usage rate is 0%;
2. The inkjet printer according to claim 1. the special ink and the color ink are photocurable inks,
a light irradiation device is provided that irradiates the special ink and the color ink that have already been ejected with light;
2. The inkjet printer according to claim 1. The control unit is
Using the first and second density characteristic curves, ejection of the special ink and the color ink in each of the first and second nozzle rows can be controlled on a nozzle-by-nozzle basis.
7. The inkjet printer according to claim 1.

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